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  • Artikel  (250)
  • Berkeley Electronic Press (now: De Gruyter)
  • Elektrotechnik, Elektronik, Nachrichtentechnik  (147)
  • Medizin  (90)
  • Sociologie  (13)
  • 1
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2008, 1, art12 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: The treatment-enhancement distinction is difficult to make, and defenders of enhancement often base their case on that. Critics of enhancement, however, often have prototypical cases of enhancement-oriented interventions in mind, and the ethics of these can be evaluated on a case by case basis. Things like intelligence enhancement may have adverse effects on equality and utility. If the equality and utility effects of such enhancements were sufficiently severe, then restrictions would be called for. We need to think more about how to make tradeoffs between liberty, equality, and utility--and we need to know more about the extent to which each of these is at stake--before reaching conclusions about the ethics of, and appropriate social policy regarding, human enhancement.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2008, 1, art11 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: Aubrey de Grey's enthusiasm may or may not be infectious, but it is certainly palpable. And it adds a dimension to the discussion the priority that should be given to life-extension/anti-ageing research of which he seems to be unaware. For on the cusp of developments in emerging technologies we find ourselves button-holed by enthusiasts whose ``transhumanist" visions importunately press upon us the most radical understanding of their implications. My suspicion is that the transhumanist mini-insurgency is partly responsible for the general failure of the policy establishment to summon up the courage and vision to address the implications of emerging technologies at all. The insurgents' effort at ``branding" these technologies as transhumanist (like that of the Raelian flying-saucer cult, a decade ago, to claim cloning as their own) does no favors to the technology. The irony is that de Grey and his fellow-visionaries, far from generating consensus enthusiasm for emerging technology applications, are making them too hot to handle.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2008, 1, art9 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: Liberal eugenics according to one version is distinguished from authoritarian eugenics on the basis that the choice of enhancement is devolved to parents. The argument for liberal eugenics combines a commitment to the right of parents to autonomy - in reproductive decisions and in the upbringing of children - and a parity claim that there is no morally significant difference between ante-natal and post-natal alterations of a child. The article reviews the putative constraints on parental choice, and assesses some criticisms of the parity claim. It concludes that a liberal commitment to social justice is in tension with a liberal commitment to parental choice, but judges that the former commitment does not entail the authoritarian eugenics which is represented as the alternative to liberal eugenics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2008, 1, art13 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: This article examines Aubrey de Grey's case for allocating substantial funding to interventive biogerontological research immediately. The conclusion is that the case is inconclusive and that scientific analyses of costs and probabilities would be needed to defend it properly.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 4 (2008), S. 1 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: The commonly used two-sample tests of equal area-under-the-curve (AUC), where AUC is based on the linear trapezoidal rule, may have poor properties when observations are missing, even if they are missing completely at random (MCAR). We propose two tests: one that has good properties when data are MCAR and another that has good properties when the data are missing at random (MAR), provided that the pattern of missingness is monotonic. In addition, we discuss other non-parametric tests of hypotheses that are similar, but not identical, to the hypothesis of equal AUCs, but that often have better statistical properties than do AUC tests and may be more scientifically appropriate for many settings.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2008, 1, art10 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: This short comment presents arguments in support of human enhancement.What is enhancement? Surely it is a procedure that improves our functioning: any intervention which increases our general capabilities for human flourishing. We exclude from consideration those procedures often termed ``enhancements" that are of dubious overall benefit (for example breast or penis augmentation, or the taking of anabolic steroids to increase muscle mass). Equally we are not talking of ``designer" modifications which are more akin to aesthetic or fashion preferences than to improvements: hair colour, eye colour, or physique. An enhancement (as we are using the term) is something of benefit to the individual.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 1, art1 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Brushless doubly-fed machines (BDFMs) allow the use of a partially rated inverter and therefore offer reliable, maintenance-free operation at low cost, especially in large power variable speed applications with limited speed ranges such as off-shore wind turbines, pumps etc. However, with a special cage rotor design, the machine has substantial rotor losses, poor efficiency and complicated control being difficult to implement.The BDFM reluctance type, the brushless doubly-fed reluctance machine (BDFRM), can overcome most of the above BDFM deficiencies while retaining all its merits. It has a "cold" reluctance rotor, which makes it more efficient and much easier to model/control than the BDFM.A theoretical study of the BDFRM is very important to gain proper understanding of its unusual operation, the main control features and compromises between optimal performance and the size of the inverter and machine required. This paper will attempt to develop, and provide a comprehensive comparative analysis of, different control strategies for the machine that are suitable for digital implementation.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 3, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Very Fast Transient Overvoltages (VFTO) and the associated Very Fast Transient Currents (VFTC) generated during switching operations in a Gas Insulated Substation (GIS) couple conductively and inductively to the secondary equipment connected to the GIS. The frequency spectrum of the VFTC gives the dominant frequencies present but cannot provide the time varying current amplitude w.r.t. any particular frequency. Since the transient response of the control circuits is a function of the frequency content of the VFTC, it becomes necessary to segregate the VFTC waveform both in time and frequency scale simultaneously. This has been achieved by employing the GABOR wavelet function and the time-frequency spectrum of the VFTC waveform has been calculated at various locations for a 245 kV GIS during a switching event. The validity of the wavelet model is confirmed by reconstructing the VFTC signal at the GIS-cable termination as well as at the switching point using the time varying current waveforms obtained for different frequencies. Finally, the transient current vs frequency as well as the current vs distance charts are developed for the 245 kV GIS under study during various switching operations.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 3, art6 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: During the last two decades, renewable wind energy has become increasingly popular as a consequence of strong ecological concerns and appealing advantages with regard to economical energy solutions in remote communities. Furthermore, with very large wind farms emerging, the dispersed renewable wind energy is required to be fully connected to the electrical distribution networks. However, the integration of dispersed renewable wind energy will pose a great challenge to the power quality in the distribution networks when the weak nature of the grid in remote areas and the uncertainty of wind are taken into consideration.This paper presents a novel Modulated Power Filter Compensator (MPFC) for the distribution networks with dispersed renewable wind energy interfaced. A tri-loop error driven controller is used to adjust the PWM switching of the modulated power filter compensator. Full power factor correction and power quality improvement is validated under different operation conditions, like load switching and wind velocity excursions. The MPFC device is a member of novel FACTS based compensators developed by the first author.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 4, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents an approach for identifying the faulted line section and fault location on transmission systems using support vector machines (SVMs) for diagnosis/post-fault analysis purpose. Power system disturbances are often caused by faults on transmission lines. When fault occurs on a transmission system, the protective relay detects the fault and initiates the tripping operation, which isolates the affected part from the rest of the power system. Based on the fault section identified, rapid and corrective restoration procedures can thus be taken to minimize the power interruption and limit the impact of outage on the system. The approach is particularly important for post-fault diagnosis of any mal-operation of relays following a disturbance in the neighboring line connected to the same substation. This may help in improving the fault monitoring/diagnosis process, thus assuring secure operation of the power systems. In this paper we compare SVMs with radial basis function neural networks (RBFNN) in data sets corresponding to different faults on a transmission system. Classification and regression accuracy is reported for both strategies. Studies on a practical 24-Bus equivalent EHV transmission system of the Indian Southern region is presented for indicating the improved generalization with the large margin classifiers in enhancing the efficacy of the chosen model.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 4, art6 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents a novel concept of Static Var Compensator (SVC) damping control using a weighted sum of bus voltage angles of remote generators that are responsible for causing inter-area oscillations in power systems. These remote bus voltage angle signals are acquired through Phasor Measurement Units (PMUs). A time domain simulation study on a 39-bus New England multi-machine system is utilized to show that an SVC auxiliary damping control, based on the derivative of these remote bus voltage angles, is superior to the conventionally employed local signals in damping inter-area oscillations. The effect of transmission delay in the acquisition of remote signals is also presented and a simple mechanism to compensate this delay is proposed and validated. The robustness of the delay compensator is finally shown for a wide range of signal transmission delays. The designed SVC controller shows a superior performance in damping the inter-area oscillations despite the signal transmission delays.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 6, art1 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Series compensation at the midpoint of a transmission line creates problems to conventional protection approaches. A new fault classification technique has been developed for a transmission line with a series capacitor at the midpoint, having different percentages of compensation varying from 25% to 75%. The proposed technique requires three line currents and voltages at each end and computes fundamental phasors of these quantities using a modified version of Full Cycle Discrete Fourier Transform. Using these phasors, the absolute values of three phase impedances are calculated for faulted phase identification. Moreover, the involvement of the ground in the fault is identified using a zero sequence component of the fault current. Using a PSCAD/EMTDC software package, a large test data (28,800) set has been generated with different types of faults and system variables, which includes fault resistances, fault inception angles, fault positions (before and after series capacitor) and variable loading conditions along with wide variations in the source impedances at both ends of a transmission line. The proposed scheme is tested on the said data set and the results are found to be promising. The results indicate that the proposed technique is fast, accurate and robust for a wide variation in system and fault conditions.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 5, art7 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The proposed voltage source converter is composed of a series double bridge converter with an auxiliary circuit. The auxiliary circuit injects DC voltage via the mid point of the double bridge converter. The injection ratio and frequency are chosen to convert the standard 12-pulse into 60-pulse configuration without PWM or increasing the number of bridges, thus the voltage and current harmonic can fulfill the THD limit without a conventional filter. The converter is operated under fundamental frequency for the main bridges, thus its switching lose is low. The converter can be widely used in the STATCOM and HVDC system. The paper describes the principles and control strategies of the proposed converter. The operational feasibility of the proposed converter is verified by computer simulation using the PSCAD/EMTDC package.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 5, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In this paper a comprehensive dynamical assessment of a high order synchronous generator plant is carried out using the Individual Channel Analysis and Design (ICAD) framework -a multivariable control engineering tool that allows robustness and system performance evaluations. The great benefits of ICAD are elucidated and contrasted to those provided by the long-time honored block diagram representations. Several models used for the small signal stability analysis of synchronous generators are evaluated under the framework of ICAD. The study, which builds on pioneering work, reveals the great advantages of carrying out control system analysis and design with higher order generator models. Moreover, careful analysis of the ICAD's Multivariable Structure Function (MSF) helps to explain, formally, why some operating conditions of the control system are more critical than others. Furthermore, correct interpretations of MSFs are amenable to robust and stable control system designs. Two kinds of studies are considered in the paper; one assesses operation under various power factor conditions and the other under a varying tie-line reactance. The control system design and stability and structural robustness assessment of the system are presented in the second part of this paper. Moreover, results obtained under the ICAD framework are compared with those arising from conventional controllers.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 6, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: For high-frequency (HF) interference in an HVDC converter station, the modeling of the noise source which causes interference with the power line carrier (PLC) remains a problem. Based on the profound analysis of the basic principles on which HF noise in PLC band is produced during the commutation process, the equivalent model of the HVDC valve with a snubber circuit is applied to the simulation of the GUI-GUANG HVDC project in PSCAD/EMTDC. Then spectrum plots of the noise source in the frequency domain are obtained by FFT analysis of the voltage waveforms gained from the simulation. Through analyzing the spectrum characteristics of the noise source in various operating modes, the main factors influencing the level of HF noise are found. Furthermore, a modified empirical model used to calculate the level of the noise source is introduced, with particular explanation of the physical quantities used in the model. The spectra of the noise source gained from the modified empirical model and from the simulation are compared with an actual spectrum based on the GUI-GUANG HVDC project. The results show that the modified empirical model can meet the requirement of HF interference calculation.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 10 (2007), S. 1 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: The impact of aging on healthcare expenditure (HCE) has been at the center of a prolonged debate. This paper purports to shed light on several issues of this debate by presenting new evidence on the "red herring" hypothesis advanced by Zweifel, Felder and Meier (1999). This hypothesis amounts to distinguishing a mortality from a morbidity component in healthcare expenditure (HCE) and claiming that failure to make this distinction results in excessive estimates of future growth of HCE. A re-estimation based on a much larger data set is performed, using the refined econometric methodology. The main contribution is consistency, however. Rather than treating the mortality component as a residual in forecasting, its dynamics are analyzed in the same detail as that of the morbidity component when predicting the impact of population aging on the future growth of HCE. For the case of Switzerland, it finds this impact to be relatively small regardless of whether or not the mortality component is accounted for, thus qualifying the "red herring" hypothesis.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2007, 1, art3 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: This paper's account of the core issues at stake in relation to genetic enhancement is presented as an alternative to mainstream liberal defenses of enhancement. The mainstream arguments are identified as being associated with reproductive autonomy, individual choice, and a `neutral', passive interpretation of technology. The alternative account is associated with the perspective of `woman' or child-bearer, with a fundamental concern for social justice, and an understanding of society in both a global and a contextual sense. This paper adopts a theoretical framework informed by feminist ethics, particularly a feminist ethic of care. The paper begins by outlining some of the key points of the care perspective, highlighting how this contrasts with a mainstream `justice' perspective, and illustrating how this is reflected in arguments relating to genetic enhancement. The paper then turns to a consideration of how a care perspective might be applied to questions of genetic enhancement, and how this may bring forward new issues. This includes in particular a consideration of IVF technologies and how applying understandings from research into this area brings forward usually unaddressed concerns in considering genetic enhancement. The final section of the paper covers some of the questions that there is space to ask once the narrow focus on individual rights is overcome.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2007, 1, art5 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: The pace of a given strand of scientific research, whether purely curiosity-driven or motivated by a particular technological goal, is strongly influenced by public attitudes towards its value. In the case of research directed to the radical postponement of aging and the consequent extension of healthy and total lifespans, public opinion is entrenched in a "pro-aging trance" - a state of resolute irrationality. This arises from the entirely rational attitude to a grisly, inevitable and relatively far-off fate: putting it out of one's mind allows one to make the most of what time one has, free of preoccupation with one's demise, and it is immaterial how irrational the arguments that one uses to achieve this are, e.g. by persuading oneself that aging is not such a bad thing after all. As biotechnology increasingly nears the point where aging will no longer be inevitable, however, this studied fatalism has become a core part of the problem, making people reluctant to join the crusade to hasten that technology's arrival. An effective way to address this hesitation is to promote debate about the reasons people give for fearing the defeat of aging, most of which are sociological. Such debate exposes people to the glaring flaws in their own logic. Thus, the more the debate is sustained and promoted, the harder it is for those flaws to be ignored.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 7 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: The objective of this work is to introduce a new method called the Survivorship Instantaneous Log-odds Ratios (SILOR); to illustrate the creation of SILOR from empirical bivariate survival functions; to also derive standard errors of estimation; to compare results with those derived from logistic regression. Hip fracture, AGE and BMI from the Third National Health and Nutritional Examination Survey (NHANES III) were used to calculate empirical survival functions for the adverse health outcome (AHO) and non-AHO. A stable copula was used to create a parametric bivariate survival function, that was fitted to the empirical bivariate survival function. The bivariate survival function had SILOR contours which are not constant. The proposed method has better advantages than logistic regression by following two reasons. The comparison deals with (i) the shapes of the survival surfaces, S(X1, X2), and (ii) the isobols of the log-odds ratios. When using logistic regression the survival surface is either a hyper plane or at most a conic section. Our approach preserves the shape of the survival surface in two dimensions, and the isobols are observed in every detail instead of being overly smoothed by a regression with no more than a second degree polynomial. The present method is straightforward, and it captures all but random variability of the data.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 3 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Marginal structural models (MSM) are an important class of models in causal inference. Given a longitudinal data structure observed on a sample of n independent and identically distributed experimental units, MSM model the counterfactual outcome distribution corresponding with a static treatment intervention, conditional on user-supplied baseline covariates. Identification of a static treatment regimen-specific outcome distribution based on observational data requires, beyond the standard sequential randomization assumption, the assumption that each experimental unit has positive probability of following the static treatment regimen. The latter assumption is called the experimental treatment assignment (ETA) assumption, and is parameter-specific. In many studies the ETA is violated because some of the static treatment interventions to be compared cannot be followed by all experimental units, due either to baseline characteristics or to the occurrence of certain events over time. For example, the development of adverse effects or contraindications can force a subject to stop an assigned treatment regimen.In this article we propose causal effect models for a user-supplied set of realistic individualized treatment rules. Realistic individualized treatment rules are defined as treatment rules which always map into the set of possible treatment options. Thus, causal effect models for realistic treatment rules do not rely on the ETA assumption and are fully identifiable from the data. Further, these models can be chosen to generalize marginal structural models for static treatment interventions. The estimating function methodology of Robins and Rotnitzky (1992) (analogue to its application in Murphy, et. al. (2001) for a single treatment rule) provides us with the corresponding locally efficient double robust inverse probability of treatment weighted estimator. In addition, we define causal effect models for "intention-to-treat" regimens. The proposed intention-to-treat interventions enforce a static intervention until the time point at which the next treatment does not belong to the set of possible treatment options, at which point the intervention is stopped. We provide locally efficient estimators of such intention-to-treat causal effects.
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 6 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Consider a longitudinal observational or controlled study in which one collects chronological data over time on a random sample of subjects. The time-dependent process one observes on each subject contains time-dependent covariates, time-dependent treatment actions, and an outcome process or single final outcome of interest. A statically optimal individualized treatment rule (as introduced in van der Laan et. al. (2005), Petersen et. al. (2007)) is a treatment rule which at any point in time conditions on a user-supplied subset of the past, computes the future static treatment regimen that maximizes a (conditional) mean future outcome of interest, and applies the first treatment action of the latter regimen. In particular, Petersen et. al. (2007) clarified that, in order to be statically optimal, an individualized treatment rule should not depend on the observed treatment mechanism. Petersen et. al. (2007) further developed estimators of statically optimal individualized treatment rules based on a past capturing all confounding of past treatment history on outcome. In practice, however, one typically wishes to find individualized treatment rules responding to a user-supplied subset of the complete observed history, which may not be sufficient to capture all confounding. The current article provides an important advance on Petersen et. al. (2007) by developing locally efficient double robust estimators of statically optimal individualized treatment rules responding to such a user-supplied subset of the past. However, failure to capture all confounding comes at a price; the static optimality of the resulting rules becomes origin-specific. We explain origin-specific static optimality, and discuss the practical importance of the proposed methodology. We further present the results of a data analysis in which we estimate a statically optimal rule for switching antiretroviral therapy among patients infected with resistant HIV virus.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 8 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: In individuals infected with human immunodeficiency virus (HIV), distributions of quantitative HIV RNA measurements may be highly left-censored due to values falling below assay detection limits (DL). It is of the interest to find the relationship between plasma and semen viral loads. To address this type of problem, we developed an empirical goodness-of-fit test to check the Clayton model assumption for bivariate truncated data. We also used truncated tau to estimate the dependence parameter in the Clayton model for this type of data. It turns out that the proposed methodology works for both truncated and fixed left censored bivariate data. The proposed test procedure is demonstrated using an HIV data set, and statistical inference is drawn based on corresponding test result.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 4 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: We consider random design nonparametric regression when the response variable is subject to right censoring. Following the work of Fan and Gijbels (1994), a common approach to this problem is to apply what has been termed a censoring unbiased transformation to the data to obtain surrogate responses, and then enter these surrogate responses with covariate data into standard smoothing algorithms. Existing censoring unbiased transformations generally depend on either the conditional survival function of the response of interest, or that of the censoring variable. We show that a mapping introduced in another statistical context is in fact a censoring unbiased transformation with a beneficial double robustness property, in that it can be used for nonparametric regression if either of these two conditional distributions are estimated accurately. Advantages of using this transformation for smoothing are illustrated in simulations and on the Stanford heart transplant data.
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 13 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Mortality rate ratios and the associated proportional hazards models have been used to summarize the effect of Alzheimer's disease on longevity. However, the mortality rate ratios vary by age and therefore do not provide a simple parsimonious summary of the effect of the disease on lifespan. Instead, we propose a new parameter that is defined by an additive multistate model. The proposed multistate model accounts for different stages of disease progression. The underlying assumption of the model is that the effect of disease on mortality is to add a constant amount to death rates once the disease progresses from an early to late stage. We explored the properties of the proposed model; in particular the behavior of the mortality rate ratio and median survival that is induced by the model. We combined information from several data sources to estimate the parameter in our model. We found that the effect of Alzheimer's disease on longevity is to increase the absolute annual risk of death by about 8% once a person progressed to late stage disease. Most importantly, we find that this additive effect is the same regardless of the patients' age or gender. Thus, the proposed additive multi-state model provides a parsimonious and clinically interpretable description of the effects of Alzheimer's disease on mortality.
    Materialart: Digitale Medien
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  • 25
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 2, art1 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In recent years, renewable energy generation has been coming up for effective use of natural energy, such as wind energy. Induction generators consisting squirrel-cage rotors are widely used as wind generators because of their salient features like robust rotor design, simplicity in the construction, maintenance free operation, etc. In this paper, it is derived that the transient current, electromechanical torque, and active power taking into account rotor speed change of induction generators at three-phase fault conditions. The output equations of the induction generator has nonlinearity, and the speed-time characteristic in a fault period is also expressed by the nonlinear equation. The approximation to derive analytical formulas for transient conditions is proposed, and the transient behavior of the induction generator is analyzed by the developed equations. The simulation block diagram in MATLAB/SIMULINK is constituted using the system equation in consideration of the nonlinearity of the induction generator. The simulation results obtained from each theoretical analysis are in close agreement with that of results obtained using MATLAB/SIMULINK simulation. Furthermore, theoretical discussion also developed to determine the fault phase angle and the time at which maximum transient currents flow in the system.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 1, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper investigates the use of trajectory sensitivity analysis (TSA) technique for assessing the transient stability of a power system at various operating conditions. The effect of placement of a thyristor controlled series compensator (TCSC) as well as the influence of the change in firing angle is also discussed. The TCSC is modeled by a variable capacitor, the value of which changes with the firing angle. The systems studied are the WSCC 3-machine, 9-bus system and IEEE 16 machine 68 bus system. The results using TSA are validated by PSCAD/EMTDC simulation.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 3, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The present paper reports the results of a study of dielectric ageing of Ethylene Propylene Diene Monomer (EPDM) by gamma radiation. EPDM flat specimens were aged under gamma radiation with three different doses. Samples were irradiated in air up to 300 kRad with a dose rate of 51 kRad/h using a 60Co gamma source. The resistance to tracking on applying DC and AC voltage was examined. We found that the DC resistance to tracking is lower than the AC resistance. The tracking resistance under -ve DC voltages are lower than +ve DC values. With the increase in radiation dose, the DC and AC tracking resistances change in a non-linear way. The erosion depth and contact angle affected by radiation have been studied. In addition, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) analyses were done, to analyze the morphological changes.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 2, art7 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A range of techniques has been proposed to define the optimal locations and capacities of distributed generation (DG) as a means of ensuring that the maximum amount of DG can be connected to existing and future networks. However, there are limitations inherent in these methods, not least in finding the best combination of sites for connecting a predefined number of DGs. Here, a method combining optimal power flow and genetic algorithms aims to meet this requirement. Its use would be in enabling Distribution Network Operators to search a network for the best sites and capacities available to strategically connect a defined number of DGs among a large number of potential combinations. Some applications of the proposed methodology confirmed its effectiveness in sitting and sizing an assigned number of DG units.
    Materialart: Digitale Medien
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  • 29
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 3, art7 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper addresses the problem of curtailing the number of control actions using fuzzy expert approach for voltage/reactive power dispatch. It presents an approach using fuzzy set theory for reactive power control with the purpose of improving the voltage profile of a power system. To minimize the voltage deviations from pre-desired values of all the load buses, using the sensitivities with respect to reactive power control variables form the basis of the proposed Fuzzy Logic Control (FLC). Control variables considered are switchable VAR compensators, On Load Tap Changing (OLTC) transformers and generator excitations. Voltage deviations and controlling variables are translated into fuzzy set notations to formulate the relation between voltage deviations and controlling ability of controlling devices. The developed fuzzy system is tested on a few simulated practical Indian power systems and modified IEEE-30 bus system. The performance of the fuzzy system is compared with conventional optimization technique and results obtained are encouraging. Results obtained for a modified IEEE-30 bus test system and a 205-node equivalent EHV system a part of Indian southern grid are presented for illustration purposes. The proposed fuzzy-expert technique is found suitable for on-line applications in energy control centre as the solution is obtained fast with significant speedups with few number of controllers.
    Materialart: Digitale Medien
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  • 30
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 4, art7 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents a new decision tree (DT) based approach for fast voltage contingency screening and ranking for on-line applications in energy management systems. The hybrid decision tree model is developed to learn all the selected contingencies simultaneously, therefore fewer DTs are required. To reduce the size and improve the accuracy of the decision tree, the K-class problem is converted into the set of K two-class problems, and separate decision tree modules are trained for each of the two class problems. All the selected contingencies are presented to the filter module, which is trained to separate them in critical and non-critical contingency classes, which reduces the burden on ranking modular DT. The critical contingencies screened out by the filter module are presented to the ranking modular decision tree for their further ranking. To measure the severity of contingencies, bus voltage violation based scalar performance index is used. Full AC load flow is performed to generate the training and testing patterns for the proposed hybrid decision tree, under each contingency. The effectiveness of the proposed approach is tested on IEEE test systems. Once trained, a hybrid decision tree method gives fast and accurate screening and ranking of contingencies for unknown load patterns.
    Materialart: Digitale Medien
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  • 31
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 5, art1 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In this paper, a novel control algorithm is proposed to compensate the unbalanced and non-linear loads in a three-phase four-wire system using active power filters. The algorithm results in balanced and sinusoidal source currents under unbalanced and distorted three-phase supply voltages. The algorithm makes use of the positive sequence extraction of the supply voltage and the theory of instantaneous symmetrical components. To illustrate the concept, a three-phase four-wire system with unbalanced and non-linear load is considered for compensation. The detailed simulation and experimental results are presented to validate the proposed method.
    Materialart: Digitale Medien
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  • 32
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 5, art6 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The necessity of dynamic equivalents for power system analysis has been well known since the expansion of large interconnected power networks, and has been discussed during the last decades. The present paper proposes a new method for constructing dynamic equivalents of power systems. In this method, at the first step the ``study system" is modeled completely via a single machine-infinite bus modeling procedure. Then the ``external system" is identified as a MIMO feedback block of this model in such a manner that can include dynamic effects of the latter on the behavior of the former. The method is successfully experimented on a part of the Iranian southern network.
    Materialart: Digitale Medien
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  • 33
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 6, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper describes a new iterative method to locate fault on a single transmission line. The method uses synchronized voltage and current measurements from both line terminals. Using the positive sequence components of the pre-fault and the post-fault phasors, positive sequence source impedances at both terminals are first estimated. Using these source impedances and the line data, the positive sequence bus impedance matrix (Zbus) is formed. Using the properties of Zbus, an iterative algorithm is proposed to locate the fault. This algorithm is tested extensively with data obtained from the EMTP simulation of a long transmission line simulated with distributed parameters in the presence of fault resistance and CT saturation. The simulation results show that the method is very accurate and robust.
    Materialart: Digitale Medien
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  • 34
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 10 (2007), S. 5 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: This paper studies the impact of antiretroviral therapies (ARVs) on HIV testing and risky sexual behavior. I use data collected in San Francisco among a high-risk population from 1994 to 2002. The evidence supports the hypothesis of a causal link between the introduction of ARVs in late 1996 and the sharp increase in risky sexual behavior that ensued. Further, following ARVs, testers take more risks while non-testers take fewer risks. The proportion of testers remains stable, which was ambiguous a priori. To the extent that ARVs may induce changes in the composition of the testing and non-testing groups, such effects do not seem to affect the results.
    Materialart: Digitale Medien
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  • 35
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 10 (2007), S. 2 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: In an attempt to improve the nation's health, many U.S. policy makers have or are considering imposing taxes on the fat in food. Dairy products constitute a large portion of at home fat consumption of particularly harmful types of fat, and nearly all U.S. households consume these products. We estimate a demand system for dairy products, which we use to simulate substitution effects among dairy products and the welfare impacts of fat taxes on various consumer groups. We find that even a 10 percent ad valorem tax on the percentage of fat would reduce fat consumption by less than a percentage point. Given that the demand for most dairy products is inelastic, a fat tax is an effective means to raise revenue. However, these fat taxes are unattractive because they are extremely regressive, and the elderly and poor suffer much greater welfare losses from the taxes than do younger and richer consumers.
    Materialart: Digitale Medien
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  • 36
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 10 (2007), S. 3 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: In an effort to balance their budgets many states are considering reducing eligibility for Medicaid. Using variation in state policies, this paper models the effect of more stringent eligibility criteria for Medicaid on the insurance status and the use of antiretroviral therapy (HAART) for people living with HIV, a group heavily dependent on Medicaid. Using nationally representative data from the mid-1990's, we find that stricter eligibility thresholds for Medicaid raise uninsurance rates and reduce the use of antiretroviral therapy among HIV+ patients, especially for those who are disabled. These stricter eligibility thresholds in turn adversely affect the survival prospects of HIV+ patients by lowering the rate of HAART use. Our estimates suggest approximately 13,000 lives could have been saved if all states had adopted the eligibility thresholds of California. We do not find any evidence of a "crowding out" effect of public insurance on private coverage among these patients.
    Materialart: Digitale Medien
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  • 37
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 10 (2007), S. 4 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: Many U.S. employers have recently adopted less generous prescription drug benefits. In addition, in 2006 the U.S. began to offer prescription drug insurance to approximately 42 million Medicare beneficiaries. We used data on individual health insurance claims and benefit data from 1997 to 2003 to study how changes in consumers' co-payments for prescription drugs affect use of and expenditure on prescription drugs, inpatient care, and outpatient care. We analyzed the effects both in the year of the co-payment change and in the year following the change. Our results show that increases in prescription drug prices reduce both use of and spending on prescription drugs. They also show that consumers substitute the use of outpatient care for prescription drug use and that about 35% of the expenditure reductions on prescription drugs are offset by increases in other spending.
    Materialart: Digitale Medien
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  • 38
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2007, 1, art6 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: Biogerontologist Aubrey de Grey has suggested that one of the reasons we as a society invest so little in research on combating aging is because we are in an intellectual trance. We think the effort will be futile: aging is immutable, so why try? A healthy skepticism can be a good thing but it is a major mistake to bet against the irresistible force of inexorable technological progress. Over the next few decades, nanotechnology will come to play a pivotal role in the solution to the problem of human aging. Medical nanorobotics, if it can be made to work, can unquestionably offer convenient solutions to all known causes of age-related damage and most likely can also successfully address any new causes of senescence that remain undiscovered today.
    Materialart: Digitale Medien
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  • 39
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2007, 1, art4 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: In this paper I argue that the virtue ethics tradition can enhance the moral discourse on the ethics of prenatal genetic enhancements in distinctive and valuable ways. Virtue ethics prescribes we adopt a much more provisional stance on the issue of the moral permissibility of prenatal genetic enhancements. A stance that places great care on differentiating between the different stakes involved with developing different phenotypes in our children and the different possible means (environmental vs. genetic manipulation) available to parents for pursuing legitimate concerns of parental love and virtue. Key components of the virtue ethics account of morality, such as the Aristotelian account of happiness, love and the doctrine of the mean, provide an adequate basis for rejecting the claim that it is morally impermissible for parents to pursue (safe and effective) prenatal enhancements. Furthermore, there is good reason to believe that a virtue ethics account of morality could actually support the stronger claim that utilising such interventions can (in certain contexts) be morally required.
    Materialart: Digitale Medien
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  • 40
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 2 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Characterizing the genetic correlates to complex diseases requires consideration of a large number of potentially informative biological markers. In addition, attention to alignment of alleles within or across chromosomal pairs, commonly referred to as phase, may be essential for uncovering true biological associations. In the context of population based association studies, phase is generally unobservable. Preservation of type-1 error in a setting with multiple testing presents a further analytical challenge. This manuscript combines a likelihood-based approach to handling missing-ness in phase with a resampling method to adjust for multiple testing. Through simulations we demonstrate preservation of the family-wise error rate and reasonable power for detecting associations. The method is applied to a cohort of 626 HIV-1 infected individuals receiving highly active anti-retroviral therapies, to ascertain potential genetic contributions to abnormalities in lipid profiles. The haplotypic effects of 2 genes, hepatic lipase (HL) and endothelial lipase (EL), on high-density lipoprotein cholesterol (HDL-C) are tested.
    Materialart: Digitale Medien
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  • 41
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 12 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Understanding the genetic underpinnings to complex diseases requires consideration of sophisticated analytical methods designed to uncover intricate associations across multiple predictor variables. At the same time, knowledge of whether single nucleotide polymorphisms within a gene are on the same (in cis) or on different (in trans) chromosomal copies, may provide crucial information about measures of disease progression. In association studies of unrelated individuals, allelic phase is generally unobservable, generating an additional analytical challenge. In this manuscript, we describe a novel approach that combines multiple imputation and random forests for this high-dimensional, unobservable data setting. An application to a cohort of HIV-1 infected individuals receiving anti-retroviral therapies is presented. A simulation study is also presented to characterize method performance.
    Materialart: Digitale Medien
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  • 42
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 1 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Under the setting of a case-cohort design, covariate values are ascertained for a smaller subgroup of the original study cohort which typically is a representative sample from a population. Individuals with a specific event outcome are selected to the second stage study group as cases and an additional subsample is selected to act as a control group. We carry out analysis of such a design using conditional likelihood where the likelihood expression is conditioned on the ascertainment to the second stage study group. Such likelihood expression involves the probability of ascertainment which need to be expressed in terms of the model parameters. We present examples of conditional likelihoods for models for categorical response and time-to-event response. We show that the conditional likelihood inference leads to valid estimation of population parameters. Our application considers joint estimation of haplotype-event association parameters and population haplotype frequencies based on SNP genotype data collected under a case-cohort design.
    Materialart: Digitale Medien
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  • 43
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 5 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: As a generalization of the accelerated failure time models, we consider parametric models of lifetime Y, where the conditional mean E(Y|X;beta) can depend nonlinearly on the covariates X and some parameters beta. The error distribution can be heteroscedastic and dependent on X. With observed data subject to right censoring, we propose regression analysis for beta based on Kaplan-Meier estimates of the means over several regions of X. Consistency and asymptotic distributional properties of the estimators are established under general conditions. A resulting estimator of beta is shown to be the sum of two possibly dependent asymptotic normal quantities, based on which conservative confidence intervals and tests are derived. Simulation studies are conducted to investigate the performance of the proposed estimator and to compare it with Buckley-Jame's method. To illustrate the methodology, we study an example with kidney transplant data, where a nonlinear relationship called "mixtures-of-experts", proposed in the neural networks literature, is used to model the relationship between the survival time and the age of the patients.
    Materialart: Digitale Medien
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  • 44
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 11 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: We present a reformulation of the Benjamini-Hochberg method that is useful in 'large-scale' multiple testing problems based on discrete test statistics and derive its basic asymptotic (as the number of hypotheses tends to infinity) properties, subsuming earlier results. A set of gene expression data is used to illustrate the workings of the method in a multiple testing problem based on Kolmogorov-Smirnov and Mann-Whitney statistics.
    Materialart: Digitale Medien
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  • 45
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 4, art1 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Dynamic economic emission dispatch is an extension of the conventional economic emission dispatch problem that takes into consideration the ramp rate limits of the generators. Evolutionary programming based fuzzy satisfying method has been proposed to determine the optimal noninferior generation schedule. This paper treats economy and emission as competing objectives for optimal dispatch, which requires some form of conflict resolution to arrive at a solution. The multi-objective problem is configured as a minimax problem under the assumption that the decision-maker has fuzzy goals for each of the objective functions. The present algorithm employs evolutionary programming technique in solving this problem. The solution methodology can offer a global or near-global noninferior solution for the decision-maker. Numerical results of a sample test system have been presented to demonstrate the performance and applicability of the proposed method. Results obtained from the proposed method are compared to those obtained by fuzzy satisfying method based on simulated annealing technique.
    Materialart: Digitale Medien
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  • 46
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 5, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The tariff is the best incentive factor for the industrial customer today to reduce the peak load. This paper describes different methods of pricing electricity. It is important to study the influence of the tariff on the industrial loads and the costs of electricity before ILM can be implemented. This paper is interested in studying the economic aspects of fixed and operating cost, other factors affecting the generation economy, distribution of power, etc. Costs of supplying electricity to consumers are also considered. A utility can influence its customers' load by providing financial incentives through the prices charged for electricity at different times of use. By designing discriminatory time of use tariffs in which the prices of electricity corresponds to the marginal cost of supply, a utility provides appropriate signals to the customer to increase consumption of electricity at off peak periods. The proposed algorithm is implemented to a real system in operation.
    Materialart: Digitale Medien
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  • 47
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 2, art6 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents a Digital Signal Processor (DSP) based implementation of Hybrid of Fuzzy Logic Controller (FLC) and Proportional-Integral (PI) speed controller for Direct Torque Controlled (DTC) Permanent Magnet Synchronous Motor (PMSM) drive. The fuzzy membership function is used for hybrid control of these two FLC and PI speed controllers in such a way that at the time of dynamic conditions such as starting, the degree of belonging for FLC speed controller is higher than the PI speed controller and near set point the degree of belonging of PI controller is having higher weightage. The simulation model of the drive system is developed in MATLAB environment with simulink, PSB and FLC toolboxes to analyze the performance of the PMSM drive system. This hybrid speed controller is found suitable for DTC based PMSM drive to maintain the high level of performance while maintaining the excellent response at the time of starting, speed reversal, load perturbation and steady-state operating condition of the drive.
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  • 48
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 1, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The operating cost of a radial distribution system may be minimized by reducing the amount of real power and reactive power drawn from the transmission system. Presently, real power is being priced through a market clearing scheme all over North America. Reactive power is an ancillary service and its supply would be priced appropriately in the near future through a clearing market structure. A recent US Federal Energy Regulatory Commission staff report [1] has initiated a discussion on the formulation of a reactive power market. When such a market is designed and operated, large customers (distribution corporations) will have to purchase reactive power along with real power from the transmission corporation through an independent system operator. Envisaging such a prospect, this paper proposes a new method of reconfiguring radial systems considering costs of real and reactive power while maintaining an appropriate voltage profile and level of reliable power supply. The proposed method is tested on sample test systems and reported.
    Materialart: Digitale Medien
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  • 49
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 2, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The benefit to end-users of electricity, mainly in terms of low prices, is strictly related to the interaction among the consumers themselves and retailers. The literature on retail competition has highlighted possible distortions in market outcomes due to unresponsive demand and boundedly rational consumers. Hence, a model appropriate to represent this aspect of the market is needed. The paper proposes a general model of the interaction among retailers and consumers in the electricity market based on the theory of multi-agent systems. The model incorporates different assumptions concerning the behavior of the players that corresponds to different levels of interaction in determining the market outcomes. The model is validated interpretively by the results provided in terms of Game Theory equilibrium. The results of an extensive set of simulations on a population of 1,000 consumers is presented and discussed.
    Materialart: Digitale Medien
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  • 50
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 1, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Deregulation of the power industry, increases in consumer demand of electricity and mandates to reduce greenhouse gases has significantly heightened the interest in distributed generation (DG). Typical DG sources include wind turbines, fuel cells, micro gas/diesel turbines, small hydro generators and photovoltaics. Currently most of these generation sources are optimized for local operation and thus the potential of DG that is both dispatchable and cost-effective has yet to be fully realized. One key technical challenge is the development of low-cost communications for remote telemetry and control of individual DG sources. Along with cost, other key communication system requirements are modularity, range and reliability. This paper presents a distributed generation communication system (DGCS) that is based on a wide area network (WAN) and local area network (LAN) topology and utilizes two variants of low-cost radio modems (RM) to satisfy the desired connectivity between the DG sites and a centralized control center. For the LAN, low-cost RMs operating in the industrial, scientific, and medical (ISM) frequency band offers point-to-multipoint scalability to multiple DG sites within a limited range. Integration of the ISM RMs with a cellular RM provides connectivity to a WAN or Internet thus providing long-range access to DG sites from any facility that has internet-access. Given the LAN scalability requirement, an ISM field programmable gate array (FPGA) channel simulator was developed to assess DGCS performance using channel impairments such as free-space path loss, multipath reflections, additive white Gaussian noise (AWGN), multiple access interference, and narrowband interference. This study provides the evaluation of two commercially available ISM radio modems and recommendations are made based on LAN requirements such as cost and performance given difficult channel conditions.
    Materialart: Digitale Medien
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  • 51
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 1, art7 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A stochastic multi-objective line security constrained problem is formulated to minimize non-commensurable objectives viz. operating cost, polluting gaseous emission and variance of active power generation and reactive power generation, with explicit recognition of statistical uncertainties in the thermal power generation cost coefficients, gaseous emission coefficients, power demands and hence power generations and bus voltages, which are considered random variables. Specific technique is put forth to convert the stochastic models into their respective deterministic equivalents. Fuzzy set theory has been exploited to evaluate the different objectives that are quantified by defining their membership functions. Security of transmission lines with respect to expected active power flow is considered in the form of fuzzy objective function. The solution set of such formulated problems is non-inferior due to contradictions among the objectives undertaken. The weighting method is used to simulate the trade-off relationship between the conflicting objectives in the non-inferior domain. Generally, the weights are either simulated or searched in the non-inferior domain. In the paper Evolutionary search technique is implemented to search the 'preferred' weightage pattern in the non-inferior domain, which corresponds to the 'best' compromised solution. Among the non-inferior solutions, the system operator selects the 'preferred' optimal operating point that provides maximum satisfaction level of the most under achieved objective in terms of membership function and is termed as fitness function. The validity of the proposed method has been demonstrated on an IEEE system comprising of 11-nodes, 17-lines and 5-generators.
    Materialart: Digitale Medien
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  • 52
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 1, art6 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The security of the transmission system is dependent on the relays' performance after various disturbances. Undesirable relay operation will trip the lines and lead to cascading events. In this paper the operation margin of mho relays is equivalently redefined as function of bus voltages instead of line impedance. The sensitivities of the operation margin to bus voltage and bus power is applied to quantify the vulnerability of transmission system. The contribution of the shunt compensation by SVC is analyzed based on the sensitivities (control factors) of the operation margin to the shunt susceptance. It is found that the control effect of SVC is approximately linear when the mho relay has relative smaller operation margin. In this range the linear model based on the control factors is accurate enough to simulate the control effect. It is also found that the shunt compensations at different locations may yield opposite effect to the operation margin of the mho relays, which can be easily judged by the value of the control factors.
    Materialart: Digitale Medien
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  • 53
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 5, art5 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents the design and analysis of a multi-phase ac-dc converter system for harmonic reduction at the point of common coupling (PCC) in vector controlled induction motor drives (VCIMD's). The design of the proposed 3-phase to 15-phase autotransformer is presented along with the VCIMD. The proposed 15-phase ac-dc converter is found capable of suppressing up to the 29th harmonic in the supply current, along with the power factor improvement close to unity in the wide operating range of the drive. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. A set of power quality indices on input ac mains and on dc bus for a VCIMD fed from existing 6-pulse and proposed 15-phase ac-dc converters are also given to compare their performance.
    Materialart: Digitale Medien
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  • 54
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 2, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The importance and conduct of necessary studies on grid reliability evaluation have become increasingly important in recent years due to the number of blackout events occurring throughout the world. Additionally, quantitative evaluation of transmission system reliability is very important in a competitive electricity environment. The reason is that successful operation of an electric power under a deregulated electricity market depends on transmission system reliability management. This paper suggests that the important input parameters of a probabilistic reliability evaluation tool for the KEPCO-system by sensitivity analysis of high reliability level operation. Simultaneously, it also presents sensitivity analysis probabilistic reliability evaluation of practical KEPCO-system long-term transmission system expansion planning (2006-2010). The tool utilized a Transmission Reliability Evaluation for Large-Scale Systems (TRELSS) which was developed by EPRI and Southern Company Services Inc.
    Materialart: Digitale Medien
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  • 55
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 1, art5 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The electric power industry in the United States and in other countries is undergoing profound regulatory and operational changes. The underlying rationale behind these transformations is to move once highly monopolized vertically-integrated industry from a centralized operation approach to a competitive one. The emerging competitive markets and an increase in the number of market participants have, in turn, fundamentally changed not only electricity trading patterns but also the structure of the electric power supply chains. This new framework requires new mathematical and engineering models and associated algorithmic tools. Moreover, the availability of fuels for electric power generation is a topic of both economic importance and national security. This paper uses the model developed by Nagurney and Matsypura (2004, 2006) as the foundation for the introduction of explicit fuel suppliers, in the case of nonrenewable and/or renewable fuels, and their optimizing behavior, into a general electric power supply chain network model along with "direct-supply" generation. We derive the optimality conditions for the various decision-makers, including fuel suppliers, power generators, suppliers, as well as the transmission service providers and the consumers at the demand markets. We establish that the governing equilibrium conditions satisfy a finite-dimensional variational inequality problem. We provide qualitative properties of the equilibrium flow pattern; in particular, existence of a solution and uniqueness under suitable assumptions. Finally, we discuss how the equilibrium fuel supply and electric power flow pattern can be computed.
    Materialart: Digitale Medien
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  • 56
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 4, art5 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper proposes a new approach for solving the state estimation problem. The approach is aimed at producing a robust estimator that rejects bad data, even if they are associated with leverage-point measurements. This is achieved by solving a sequence of Linear Programming (LP) problems. Optimization is carried via a new algorithm which is a combination of ``upper bound optimization technique" and ``an improved algorithm for discrete linear approximation". In this formulation of the LP problem, in addition to the constraints corresponding to the measurement set, constraints corresponding to bounds of state variables are also involved, which enables the LP problem more efficient in rejecting bad data, even if they are associated with leverage-point measurements. Results of the proposed estimator on IEEE 39-bus system and a 24-bus EHV equivalent system of the southern Indian grid are presented for illustrative purpose.
    Materialart: Digitale Medien
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  • 57
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 5, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Large power systems are highly complex systems that defy predictions with any degree of certainty. In this paper, an analytical framework for the assessment of small signal stability under operating uncertainty is presented. A rigorous analysis framework for the description of uncertainty in operating conditions is suggested. Using structured singular value theory and optimization tools, techniques for robust stability analysis of complex power systems are then derived and a method to quantify the effect of parametric uncertainties on the stability of critical inter-area modes is presented. A computationally-efficient method for modeling parametric uncertainty based on linear fractional transformation (LFT) theory is investigated and tested. With this approach, it becomes possible to estimate the effects of variations in the parameters of major transmission resources on the nominal stability of critical inter-area modes.The use of the analysis methods is demonstrated on two systems: i) a two-machine test system, and ii) a two-area, 11-bus, 4-machine test system.
    Materialart: Digitale Medien
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  • 58
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 6, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents an assessment of the vulnerability of the power grid to blackout using graph topological indexes. Based on a FERC 715 report and the outage reports, the cascading faults of summer WSCC 1996 are reconstructed, and the graphical property of the grid is compared between two cases: when the blackout triggering lines are removed simulating the actual sequence of cascading outages and when the same number of randomly selected lines are removed. The investigation finds that the critical path lengths of the triggering events of the July and August outages of 1996 WSCC blackout are higher than those of no-outage and arbitrary events. In addition, the small world-ness index for each of the outage triggering events is much smaller than that of normal or any no-outage scenario, indicating that events of shifting a network from small world to a random network would be more likely cascaded to wide area outage.
    Materialart: Digitale Medien
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  • 59
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 10 (2007), S. 8 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: While the fraction of obese people is not as large in Europe as in the United States, obesity is becoming an important issue in Europe as well. Using comparable data from the Survey of Health, Aging and Retirement in Europe (SHARE) and the Health and Retirement Study in the U.S. (HRS), we analyze the correlates of obesity in the population ages 50 and above, focusing on measures of energy intake and expenditure as well as socio-economic status. We find that obesity rates differ substantially on both sides of the Atlantic and across European countries, with most of the difference coming from the right tail of the weight distribution. The well-known SES gradient in the prevalence of obesity differs across countries and cannot be fully explained by the variation in food expenditure or physical activity. Obesity is associated with lack of physical activity, calorie intake, time spent on cooking, and time and money spent on eating at home and away from home, but some of these associations vary across countries. More research is needed to analyze why this is the case.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 10 (2007), S. 6 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: This study examines past patterns and projects future prevalence rates of obesity and severe obesity among US adults. Trends in body mass index (BMI), overweight (BMI?25), obesity (BMI?30), class 2 obesity (BMI?35), class 3 obesity (BMI?40) and class 4 obesity (BMI?45) of 20-74 year olds are obtained using data from the first National Health Examination Survey and the National Health and Nutrition Examination Surveys. Quantile regression methods are then used to forecast future prevalence rates through 2020. By that year, 77.6% of men are predicted to be overweight and 40.2% obese, with class 2, 3 and 4 obesity prevalence rates projected at 16.4%, 6.3% and 3.1%. The corresponding forecasts for women are 71.1%, 43.3%, 25.3%, 12.8% and 5.6%. The large growth predicted for severe obesity represents a major public health challenge, given the accompanying high medical expenditures and elevated risk of mortality and morbidity. Combating severe obesity is likely to require strategies targeting the particularly large weight gains of the heaviest individuals.
    Materialart: Digitale Medien
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  • 61
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2007, 1, art7 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: This is a reply to the discussion piece Life Span Extension Research and Public Debate: Societal Considerations, Studies in Ethics, Law, and Technology by Audrey de Grey. Having read the article there seem to be four messages. The first being, that longevity/immortality research faces rejection, resistance and neglect from `classic anti-aging' researchers, policy makers, the funding system and the public. The second being that the `pro-aging' trance is illogical; the third being that not pushing for longevity and immortality research is immoral; and the fourth being that so far no valid reason for opposing longevity and immortality has been generated and that we will deal with potential problems if and when they appear. My message in this invited comment is 1) that de Grey is right with his first point; 2) that his second point is debatable and depends on certain assumptions; 3) that his third point is even on weaker feet and debatable (Morals and ethics are social and cultural constructions and depending on ones frame of reference something can be seen as moral and ethical or not. This is a whole different paper as to who decides which morals and ethics are right and wrong and can't be covered here.) and 4) that the longevity and immortality research exhibits the same discourse problems as the other new and emerging technology discourses, namely that its makes light of potential and real social risks that it tailors to a minority of the world and ignores the marginalized majority of the world.
    Materialart: Digitale Medien
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  • 62
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2007, 1, art2 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: Sport is one of the first areas in which enhancement has become commonplace. It is also one of the first areas in which the use of enhancement technologies has been heavily regulated. Some have thus seen sport as a testing ground for arguments about whether to permit enhancement. However, I argue that there are fairness-based objections to enhancement in sport that do not apply as strongly in some other areas of human activity. Thus, I claim that there will often be a stronger case for permitting enhancement outside of sport than for permitting enhancement in sport. I end by considering some methodological implications of this conclusion.
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  • 63
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2007, 1, art1 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: Bioethics has paid little attention to the issues raised by health in athletic competition, with the single exception of the use of prohibited performance enhancements. However, in competitive athletics, the treatment and prevention of athletic injury and the development of training programs designed to maximize athletic achievement share many characteristics with medical innovation and clinical research, and should be understood to constitute enhancement research.Athletes should, in at least some circumstances, be viewed as vulnerable research subjects, akin to desperate patients. Competitive athletes are often encouraged to sacrifice long-term health benefits for short-term gains; cultural mythology about sports and high-stakes financial investments at the organizational level in team sports exercise great influence on individual athletes' range of choices. Technological advances in training, equipment, and injury treatment serve to raise the bar in competitive athletics, in turn increasing not only the risks of harm but the level of expectation with regard to performance, injury, and recovery. It is common for athletes to seek, and teams to offer, intensive and innovative training regimens from which data are gathered, thus transforming innovation into research.As technology continues to enhance the prospects for athletic enhancement, it is time for bioethics to take a closer look at the way competitive athletics highlights the troubling questions posed by enhancement research.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 9 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Child growth is characterised by increases in height, and increases in maturational status. Functional data analysis provides a tool to separate these two sources of variation (registration) and differentiates between the variation in maturational tempo (temporal, or "phase" variation) and the variation in height (amplitude variation). We extended this concept by combining Principal Component Analysis (PCA) and the Maximum Likelihood Principle. Longitudinal data on height were obtained from two large growth studies from Lublin, Poland, and Zurich, Switzerland, with altogether 361 children. Variation in amplitude monotonically rises with age; variation in phase peaks during puberty. During mid-puberty, phase variation is large and explains up to 40 percent of total height variance in girls, and up to 50 percent in boys. Eight amplitude and 4 phase components appeared biologically significant. The largest amplitude component explained 91% of the amplitude variance and is characterised by an almost horizontal pattern. The largest phase component explained 66% (boys) and 63% (girls) of phase variance, rises throughout childhood and reaches up to 0.85 years in adolescent boys, and up to 0.75 years in adolescent girls. Phase components significantly correlated with the clinical signs of puberty. The combination of PCA and the Maximum Likelihood Principle provides a new, powerful and automatic tool for growth modelling that includes estimates of future growth, adult stature and developmental tempo. Preliminary results indicate that this approach can be used for automatised screening purposes.
    Materialart: Digitale Medien
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  • 65
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 10 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Analyses of individual disease-exposure data within a population are useful when exposure of interest varies sufficiently within the population. When the within-population variance of exposure is limited, however, power of the individual-data analysis is reduced. In such situations, aggregated-data analyses of disease data across populations, with a sample of individual exposure data from each population, can be powerful in estimating the exposure effect if between-population variation of exposure is large. In this paper, we consider a new analytical framework that is a combination of the individual- and aggregated-data analyses, based on an estimating equation approach. The proposed analysis utilizes strengths from individual data and aggregated data in the estimation of the exposure effect of interest, depending on which of the exposure variations (within- versus between-population) dominates. Simulation studies under various different scenarios were performed to show the strengths of the proposed approach in the estimation of the exposure effects of interest.
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 3 (2007), S. 14 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: Observational studies of prescription medications and other medical interventions based on administrative data are increasingly used to inform regulatory and clinical decision making. The validity of such studies is often questioned, however, because the available data may not contain measurements of important prognostic variables that guide treatment decisions. Recently, approaches to this problem have been proposed that use instrumental variables (IV) defined at the level of an individual health care provider or aggregation of providers. Implicitly, these approaches attempt to estimate causal effects by using differences in medical practice patterns as a quasi-experiment. Although preference-based IV methods may usefully complement standard statistical approaches, they make assumptions that are unfamiliar to most biomedical researchers and therefore the validity of such an analysis can be hard to evaluate. Here, we describe a simple framework based on a single unobserved dichotomous variable that can be used to explore how violations of IV assumptions and treatment effect heterogeneity may bias the standard IV estimator with respect to the average treatment effect in the population. This framework suggests various ways to anticipate the likely direction of bias using both empirical data and commonly available subject matter knowledge, such as whether medications or medical procedures tend to be overused, underused, or often misused. This approach is described in the context of a study comparing the gastrointestinal bleeding risk attributable to different non-steroidal anti-inflammatory drugs.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 3, art1 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper focuses on dispatching of mixed generation portfolio of renewable energy (RE) and non-RE (firm) units. A genetic algorithm (GA) based rolling window approach is developed for solving economic dispatch (ED) problem. Profit maximisation ED problem is formulated and solved which also considers New Electricity Trading Arrangements for England and Wales (NETA) market features. In this problem, a penalty approach is used in order to consider intermittency problem of RE generation output. A single GA technique is also applied for solving the formulated problem. Of these, GA based rolling window approach achieved promising results for a Generator Company, which holds both renewable and fossil fuel units and participates in the short-term market trading. It is also shown that a Generator Company can get more profit by using the possibility of increase in generation output of RE sources from their forecast positions by combining both RE and non-RE units and participating in a NETA-like market trading. This approach allows to some extent the management of uncertainty problem of RE generation output, which also accounts risk associated with power non-delivery.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 2, art5 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Accurate electricity load and pool-price forecasting can provide a set of vital predicted information that helps generation, transmission and retailer participating companies to bid strategically into a deregulated electricity market in order to maximize their profits and increase returns to their stakeholders. Although a number of forecasting methods have been proposed to solve the short-term and long-term electricity load forecast, pool-price forecasting is a relatively new research area. In this article, we propose an autoregressive approach, based on a wavelet multiscale decomposition, for the prediction of one-hour ahead load and pool price based respectively on historical electricity load, and pool-price data. This approach is based on a multiple resolution decomposition of the signal using the redundant Haar à trous wavelet transform whose advantage is taking into account the asymmetric nature of the time-varying data. There is an additional computational advantage in that there is no need to re-compute the wavelet transform (wavelet coefficients) of the full signal if the electricity and pool price data (time series) is regularly updated. We assess results produced by this multiscale autoregressive method, in both linear and nonlinear variants, with single resolution autoregressive, multilayer perceptron, Elman recurrent neural network and the general regression neural network models. The input data consists of historical load and pool price data, which is collected over a period of 3 years (1999-2001), used for training, and 1 year (2002) used for testing. Experimental results are based on the New South Wales (Australia) electricity load and pool price data that is provided by the National Electricity Market Management Company.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 69
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 3, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Unit commitment (UC), originally employed to minimize the generating cost of a vertically integrated utility, has become a basic tool for revenue adequacy evaluation by GENeration COmpanies (GENCOs). The strategic role of UC is apparent in those market environments where GENCOs are asked to internalize all costs and the relevant UC decisions within their day-ahead market bids. In this paper, a parametric UC method is presented to assess the convenience of making energy bids for marginal or nearly marginal generation units. The convenience is gauged by the basis of revenue adequacy that is on each unit's ability to cover all expenses and generate profits. Beside UC choices, the parametric UC procedure provides a market price behavior that would make it profitable to commit a certain unit for generation. A Monte Carlo simulation program is employed to find the probability that actual market prices will fulfill the revenue adequacy requirements. Market prices are handled as random variables with multivariate normal distribution, taking into account the correlation between prices at successive time periods. The parametric UC procedure and the Monte Carlo simulation are carried out by using reasonable data of generation units available to some Italian GENCOs.
    Materialart: Digitale Medien
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  • 70
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 2, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In recent developments wind power has been gaining rapid usage as an alternative source of electrical power and there is need to formulate optimized control schemes for power generation. This paper presents a sensorless maximum power point tracking control methodology for a wind power generation system. For the sensorless vector control a sliding mode observer is utilized in the estimation of the rotor speed while the rotor position is estimated based on the flux linkage. The Powell method is introduced to improve the efficiency of the permanent magnet synchronous generator (PMSG) d-axis current optimization. To ensure robustness of the proposed paradigm to parameter variations, the windmill loss coefficients determining the optimal rotor speed are identified online. Results of simulations confirm the effectiveness of the proposed method.
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  • 71
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 3, art5 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents the steady-state and transient behavior of a single-phase self-excited induction generator (SEIG) using a three-phase machine with one shunt and one series excitation capacitors for resistive and inductive loads. The generation scheme consists of one three-phase delta connected induction machine and two capacitors - one connected in parallel with one winding and the other in series with a single-phase load. The dynamic model of the system has been developed as a hybrid model considering the stator phase currents in abc reference frame and the rotor currents in stationary d-q axes reference frame as state variables. The simulated and experimental results are presented for different dynamic conditions such as initiation of self-excitation, load perturbation and short-circuit. The simulated results of the steady-state analysis have been compared with the transient and experimental results and a close agreement between them indicates the accuracy and effectiveness of the approach.
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  • 72
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 4, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The present work proposes an extended model representing part of a huge aluminum industry load for short-term voltage stability investigations in time domain. The efforts were concentrated in the expansion of the industrial power distribution system model including explicit representation of the main transformers, capacitors, feeders and induction motors. The extended model is validated through a comparison between computer simulation results and the industry/power system utility recordings. A real sequence of events which took place in the Brazilian North Power System in the year of 2002 causing a complete industry breakdown (loss of bulk supply) was considered here for this purpose.
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  • 73
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 8.2007, 4, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The steady state thermal rating of overhead transmission lines is limited by the conductor`s maximum design temperature, which is related to the maximum sag and the loss of tensile strength of the conductors. Traditionally, this overhead transmission lines rating is computed using a deterministic approach, with reference to severe weather conditions. Thus, the application of this method leads to conservative results resulting in under-utilization of conductors. In this paper, a new method based on an hourly probabilistic index is proposed to predict the line thermal rating for each hour of the day; this index is evaluated using the conductor current limit probability density function (pdf). The method uses Bayesian time series models for the weather parameters (ambient temperature, wind speed and wind direction) and calculates the conductor current limit pdf using a Monte Carlo simulation. The probabilistic index is applied by considering measured weather data of both hot and cold seasons; the corresponding lines ratings are reported and analyzed.
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  • 74
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 10 (2007), S. 7 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: With falling prices of antiretroviral drugs in countries like India, there has been an increasing awareness that antiretroviral therapy can be made available and accessible to a large number of HIV-positive individuals. Prices, however, still remain high enough to keep ART out of reach of a majority of affected individuals in India. This study analyses the demand for antiretroviral therapy (ART) using a contingent valuation approach, by estimating the willingness to pay for ART among a sample of HIV positive individuals in India. The study finds a very high willingness to be on ART, but substantially lower willingness to pay for it. To cover 70 percent of patients would require the price to be around Rs. 500 per month. Economic status generally and of females in particular have a positive relationship with the willingness to pay for drugs, whereas being a female exerts a downward pressure on the demand for ART.
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  • 75
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Studies in ethics, law and technology 1.2007, 1, art8 
    ISSN: 1941-6008
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Sociologie , Technik allgemein
    Notizen: Genomics and the technologies arising out of the science are often heralded as a means of securing cures for diseases which have proved resistant to the progress of medicine. These, generally hereditary diseases, with advances in genomic science are becoming more understood, but as of yet the possibilities of effective cures, whether through for example somatic or germ-line gene therapy, remain elusive. This has not stopped despite speculation and debate on potential future applications such as the use of genetic technologies in enhancing humans. Curative applications and enhancement applications are inextricably linked however both through the social contexts in which these technologies are to be deployed and the discourses which inform and frame the debates on their use. This article seeks to explore these links and in doing so aims to investigate some of the wider dimensions of the enhancement debate.
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  • 76
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 5.2006, 1, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Security assessment of a power system is very important function to detect any violation in the system and to ensure secure operation of the system in deregulated environment. Contingency ranking is the process of indexing the possible contingencies of system on the basis of their severity. The contingencies of higher ranking are further analyzed for detailed analysis. The contingencies based on the real power flow and the voltage deviations should be dealt simultaneously for better ranking. The paper presents fuzzy approach to combine ranking based on MW and Mvar losses and a new rank list is prepared. The proposed approach is tested on IEEE-30 bus test system.
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  • 77
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 7.2006, 2, art1 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The increases in power flows and environmental constraints are forcing electricity utilities to install new equipment to enhance network operation. Some application of Flexible AC Transmission System (FACTS) technologies to existing high-voltage power systems has proved the use of FACTS technology may be a cost-effective option for power delivery system enhancements. Amongst various power electronic devices, the unified power flow controller (UPFC) device has captured the interest of researchers for its capability of regulating the power flow and minimizing the power losses simultaneously. Since for a cost-effective application of FACTS technology a proper selection of the number and placement of these devices is required, the scope of this paper is to propose a methodology, based on a genetic algorithm, able to identify the optimal number and location of UPFC devices in an assigned power system network for maximizing system capabilities, social welfare and to satisfy contractual requirements in an open market power.In order to validate the usefulness of the approach suggested herein, a case study using a IEEE 30-bus power system is presented and discussed.
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  • 78
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 5.2006, 2, art7 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The flexible AC transmission system (FACTS) in a power system improves the stability, reduces the losses, reduces the cost of generation and also improves the loadability of the system. In the proposed work, a non-traditional optimization technique, a Genetic Algorithm (GA) is conjunction with Fuzzy logic (FL) is used to optimize the various process parameters involved in introduction of FACTS devices in a power system. The various parameters taken into consideration were the location of the device, their type, and their rated value of the devices. The simulation was performed on a 30-bus power system with various types of FACTS controllers, modeled for steady state studies. The optimization results are compared to the solution given by another search method. This comparison confirms the efficiency of the proposed method which makes it promising to solve combinorial problem of FACTS device location in a power system network.
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  • 79
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 5.2006, 1, art5 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper introduces some field analyses of the wooden pole fire reports and online condition monitoring recorded data for line insulators of 33kV and 132kV overhead power lines of Petroleum Development Oman (PDO). From the statistical analysis of PDO pole fire reports, it was found that PDO southern directorates had higher number of pole fires during May-September 2004. Pole fires mostly occur for single poles of 33kV distribution lines close to graded roads, where the most common burning locations are at crossarm fixation and at ground foundation. Pollution monitoring systems provide very useful information which can be used to predict the pole fire events.
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  • 80
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 6.2006, 2, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Based on a damping control strategy for oscillation energy descent, an adaptive UPFC fuzzy-logic damping control scheme is proposed. Using the UPFC line power as the input signal, the controller can adaptively adjust the control parameters according to the magnitude of power oscillation in the UPFC line using fuzzy rules to effectively damp the power oscillation. One of advantages of the controller is that the detailed model and parameters of systems is not needed in the controller design. Case studies on the 10-generator New England test system show that the controller can effectively enhance dynamic stability of systems with good robustness.
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  • 81
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 7.2006, 2, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Presently, there is still a critical shortage of experts to interpret and diagnose problems associated with power system harmonics. Thus, the use of a rule based expert system is proposed for the identification of harmonic sources originating from various single phase nonlinear loads such as uninterruptible power supply, personal computer, fluorescent lamp with magnetic and electronic ballasts, PC monitor and oscilloscope. Identification of harmonics originating from single phase nonlinear loads is implemented by first analyzing the harmonic current waveforms using fractal and fast Fourier transform analyses so as to characterize the harmonic signatures of the different types of nonlinear loads. Then, a rule-based expert system is developed in which the system identifies and classifies the different types of nonlinear loads from the input current waveforms. The expert system with its user interface has been developed in MATLAB and it has been verified with real current measurements. The results obtained prove that the system enables accurate identification of nonlinear loads.
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  • 82
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 6.2006, 2, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In this paper, a new approach based on µ-synthesis technique is presented for the robust decentralized load frequency controller design of a restructured multi area power under the possible contracts. In each control area, the connections between this area and the rest of the system and the effects of possible contracts are treated as a set of new disturbance signals to achieve decentralization. It is shown that, subject to a condition based on the structured singular values and H infinity norm, each local area load frequency controller can be designed independently. The stability condition for the overall system can be stated as to achieve a sufficient interaction margin and a sufficient gain and phase margin defined in classical feedback theory during each independent design. The proposed method is tested on a four-area power system with the possible contracts and compared with the PI controller for a wide range of operating conditions and load changes. The resulting controllers are shown to minimize the effects of load disturbances and maintain robust performance in the presence of specified uncertainties and system nonlinearities.
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  • 83
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 6.2006, 1, art6 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents the design and implementation of a learning controller for the Automatic Generation Control (AGC) in power systems based on a reinforcement learning (RL) framework. In contrast to the recent RL scheme for AGC proposed by us, the present method permits handling of power system variables such as Area Control Error (ACE) and deviations from scheduled frequency and tie-line flows as continuous variables. (In the earlier scheme, these variables have to be quantized into finitely many levels). The optimal control law is arrived at in the RL framework by making use of Q-learning strategy. Since the state variables are continuous, we propose the use of Radial Basis Function (RBF) neural networks to compute the Q-values for a given input state. Since, in this application we cannot provide training data appropriate for the standard supervised learning framework, a reinforcement learning algorithm is employed to train the RBF network. We also employ a novel exploration strategy, based on a Learning Automata algorithm, for generating training samples during Q-learning. The proposed scheme, in addition to being simple to implement, inherits all the attractive features of an RL scheme such as model independent design, flexibility in control objective specification, robustness etc. Two implementations of the proposed approach are presented. Through simulation studies the attractiveness of this approach is demonstrated.
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  • 84
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 6.2006, 2, art5 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents a study of market design issues for the future Electricity Supply Industry of countries in transition from monopolistic to more competitive structures. An approach is developed to apply a standard measurement of market concentration, such as Herfindahl Hirschman Index (HHI) within the market design context. Typically, HHI is used to study market power issues in established electricity markets. The approach presented in this paper indicates that HHI can also be used as a primary method to study market design ahead of implementation. A dynamic simulation of the Thai market is used to confirm the applicability of the approach presented in this paper.
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  • 85
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 7.2006, 2, art6 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: It is well known to electricity authority worldwide of difficulty in meeting an ever increasing demand of a rural load center tens to hundred kilometers away from the interconnected grid. In many cases, upgrading sub-transmission system seemed appropriate in technical, economic and environmental aspects. Nevertheless, there are cases where addition of local generation is the only means to meet the increasing demand. For more than ten years, Thailand's Provincial Electricity Authority has been tackling complications of adding more and more local generations until exceeding the local off peak demand. These generations consist of four small hydro, one geothermal and one fuel oil power plants. Unfortunately, the unplanned attempts made to resolve problem concerning provision of electricity supply to meet the demand without conducting any pre-engineering study had proved ineffective and sustainable solution could not be attained. This paper described, analyzed and discussed in details the development of PEA's distribution system planning to supply quality and reliable electricity to a small rural and remote community in the country Northern province. Extensive field surveys and technical analyses were carried out to investigate impacts of distributed generation on the performance of the network. Finally, recommendations were given as guideline for further study in search of feasible and sustainable solutions.
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  • 86
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 7.2006, 1, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Dynamic behaviour analysis of electric power system has always played a vital role in operation and planning of power systems. This analysis relies on computer simulation which are usually based on simplifying assumptions which aim at rendering system modelling more amenable to numerical solution. However, it is well known that uncertainties and unmodelled dynamics could in some cases lead to unexpected results. In the paper a simplified dynamic model of transmission network is employed to evaluate the influence of network transients on dynamic behaviour of power systems. Although simplified, this model can easily capture usually neglected dynamics. Applications of this modelling is proposed with respect to two test systems, highlighting the effects of usually unmodelled dynamics.
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  • 87
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 7.2006, 1, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Japan imports almost all of the energy resources with 40% of them used for electricity generation. Electricity is generated mainly by five types of power plants (LNG-fired, LNG-CC, oil-fired, coal-fired, and nuclear), which have various environmental impacts, for example, fossil fuel depletion, global warming, acid rain, etc. The purpose of this paper is to make a life cycle assessment (LCA) of the electricity generating processes of power plants in Japan and to suggest some concrete measures to reduce the environmental impacts.Our study proceeds as follows. We focus on the fuel procuring process reflecting Japan's import of fuel resources and then the whole electricity generating process of the different types of power plants. Firstly, we quantify the environmental loads resulting from each type of plant by Life Cycle Inventory (LCI) analysis. Secondly, Life Cycle Impact Assessment (LCIA) method is applied to evaluate the total impacts of each type of plant. Thirdly, we make some concluding remarks on reduction of the environmental impacts. LCI analysis and LCIA evaluation are done with use of the 'LCA-NETS' scheme we have developed. Our LCIA evaluation shows that in the fuel procuring process nuclear plants rank top, coal-fired plants second, oil-fired plants third, and LNG-fired plants bottom in the ascending (better) order of the `NETS/MJ' values, and that in the whole electricity generating process LNG-CC plants rank top, LNG-fired and coal-fired plants second, oil-fired plants third and nuclear plants last in the ascending (better) order of the `NETS/kWh' values.Our findings about the fuel procuring process imply that if LNG-fired plants can find an effective usage of their byproduct of cold energy or import natural gas without liquefaction directly from nearby countries, they will rank up next to nuclear plants and that if any legal regulations of desulfurization are imposed on sea transportation the impacts of crude oil and coal will be reduced a great deal.It follows from the total evaluation of the whole electricity generating process that if coal-fired plants can reduce the total impacts by 20% by introducing a technology of coal gasification they will be superior to LNG-CC plants and that if nuclear plants can adopt a technology of recycling uranium to reduce the total impacts by 50% they will be as good as LNG-CC plants.
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  • 88
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 5.2006, 2, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A transmission system based on voltage-source three-level flying capacitor (FC) multilevel converters with selective harmonic elimination pulse-width modulation (SHE-PWM) control is presented in this paper. The generation of the switching patterns for each power device is described taking into account the natural balancing of the FC voltages. A new and simple control method for balancing the FC voltages of the FC converter when using SHE-PWM is proposed which is based on the small change of the firing angle according to the load current polarity. Implementation of the SHE-PWM with capacitor voltage balancing is provided. Simulation studies for a 300MW/+-150kV transmission system are presented to confirm the satisfactory performance of the proposed system.
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  • 89
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 5.2006, 2, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Mitigation of voltage-sag effects on loads due to the starting of an induction motor is considered. If a series compensator is connected upstream of the motor, the large transient current caused by the switching event could damage the compensator or deplete the energy stored in it. Maximum motor-starting current and the required energy during the starting process are derived from which the ratings of the compensator can be determined. Simulation verifies the analysis is effective and the compensator is shown to be able to maintain good supply quality during the motor- start event.
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  • 90
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 6.2006, 1, art7 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: There are IEC 60060-1 requirements on three impulse current waveforms. For the damped-oscillating waves, margins of the front time T1 and the time to half the peak T2 are 10 per cent whilst any value after the polarity reversal has to be less than 20 per cent of the peak value. Authors have tried to construct impulse current calibrator for reference measuring system, which would generate a waveform having the time parameters quite close to ideals. After numerous simulations in selecting values for circuit composing components, authors came to an impression that a damped-oscillating current generator whose output waveform has parameter values close to standard, cannot be realised. In the paper, authors' "impression" is theoretically proved and mathematically possible margins for the parameters are to be presented in detail.
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  • 91
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 7.2006, 3, art2 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The aging of insulators often results in corona discharge, and the measurement of the ultraviolet light (UV-light) can be used to detect insulator defects. This paper introduces a new tester, the ultraviolet detector, which can detect defective insulators by measuring the UV-light from the discharging insulators. Some tests were carried out. The results indicated that the detector can identify the existence of corona discharge with good performance. And it can be used for discharge detection of power system and transformer substation.
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  • 92
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 7.2006, 3, art3 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Electrostatic and electrodynamic field analyses of 33kV line insulators were introduced to compare the electric-field and the current density profiles of commonly used line insulators in Oman; namely, silicone rubber (SiR) and porcelain line post insulators, and porcelain cap and pin insulator string. SLIM software package was used for such simulation, which is a fully integrated collection of software modules that provides facilities for the generation and solution of electromagnetic finite element models. The simulation results reveal that for the electrostatic simulation under pollution conditions, SiR and porcelain line-post insulators give maximum values of the electric field of 360kV/m and 1700kV/m, respectively. The latter value exceeds the recommended electric field level of 500kV/m. For the electrodynamic simulation under pollution conditions, the electric field and the current density are much higher for porcelain insulator compared to those of SiR insulator. The simulation of four cap-pin standard insulator string reveals that there is high electric field (1250kV/m) at the cap-insulator gap which can cause high current density for polluted case. Finally, the trend of the simulation results has been verified by experimental tests, which has been conducted on different 33kV line insulators having different designs and materials.
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  • 93
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 7.2006, 4, art4 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper presents an approach for short-term electricity price and load forecasting using the artificial neural network (ANN) computing technique. The described approach uses the three-layered ANN paradigm with back-propagation. The publicly available data, acquired from the deregulated Victorian power system, was used for training and testing the ANN. The ANN approach based on similarity technique has been proposed according to which the load and price curves are forecasted by using the information of the days being similar to that of the forecast day. A Euclidean norm with weighted factors is used for the selection of similar days. Two different ANN models, one for load forecasting and another for price forecasting, have been proposed. Test results show that average price and load MAPEs for the year 2003 by using the ANN approach are obtained as 14.29% and 0.95%, respectively. MAPE values obtained from the price and load forecasting results confirm considerable value of the ANN based approach in forecasting short-term electricity prices and loads.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 9 (2006), S. 2 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: This paper uses data from physician group practice to examine the relationship between malpractice premium levels and physician net incomes for the years 1994, 1998, and 2002, a period in which malpractice premiums rose rapidly. We find, as did work covering earlier periods of premium growth, that physician net incomes were not reduced by high or rising premiums, and that gross practice revenues were higher when premiums were higher. There is evidence that this forward shifting of costs was associated more with higher quantities of services than with higher unit fees.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 9 (2006), S. 5 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: Health accounts document changes over time in the level and composition of health spending. There has been a continued evolution in the ability to track such outlays. Less rapid has been the ability to interpret changes in spending. In this paper we apply quality adjusted price indexes for several major mental disorders to national mental health expenditure account estimates to assess changes in real "output". We show that using the new price indexes reveals large gains in real output relative to the application of the U.S. Bureau of Labor Statistics' indexes.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    Forum for health economics & policy 9 (2006), S. 4 
    ISSN: 1558-9544
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Medizin , Wirtschaftswissenschaften
    Notizen: We used claims data from a large U.S. employer that introduced changes in its medical and drug coverage offerings in 2002 for non-Medicare eligible retirees. In addition to the existing plans, the employer introduced two new plans in 2002 that were less generous both in terms of medical and drug coverage. Further, one of the new plans had an annual benefit limit of $2,500 on prescription drugs, similar to the "doughnut hole" in the standard Medicare Part D benefit. We examined beneficiaries switching behavior in response to the new choice set and estimated the independent effects of medical and drug benefits on plan selection. We found that beneficiaries in better health were more likely to switch to the new, less generous plans. While the generosity of the medical benefit played a more important role in choosing a plan, choices did not vary significantly by health status. In contrast, sicker individuals were more likely to enroll in plans with generous drug benefits. This suggests that drug coverage may be more susceptible to adverse selection than medical insurance.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 2 (2006), S. 1 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: A natural choice of time scale for analyzing recurrent event data is the ``gap" (or soujourn) time between successive events. In many situations it is reasonable to assume correlation exists between the successive events experienced by a given subject. This paper looks at the problem of extending the accelerated failure time (AFT) model to the case of dependent recurrent event data via intensity modeling. Specifically, the accelerated gap times model of Strawderman (2005), a semiparametric intensity model for independent gap time data, is extended to the case of multiplicative gamma frailty. As argued in Aalen & Husebye (1991), incorporating frailty captures the heterogeneity between subjects and the ``hazard" portion of the intensity model captures gap time variation within a subject. Estimators are motivated using semiparametric efficiency theory and lead to useful generalizations of the rank statistics considered in Strawderman (2005). Several interesting distinctions arise in comparison to the Cox-Andersen-Gill frailty model (e.g., Nielsen et al, 1992; Klein, 1992). The proposed methodology is illustrated by simulation and data analysis.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    The @international journal of biostatistics 2 (2006), S. 4 
    ISSN: 1557-4679
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Biologie , Mathematik , Medizin
    Notizen: In the case of incomplete data we give general relationships between the first and second derivatives of the loglikelihood relative to the full and the incomplete observation set-ups. In the case where these quantities are easy to compute for the full observation set-up we propose to compute their analogue for the incomplete observation set-up using the above mentioned relationships: this involves numerical integrations. Once we are able to compute these quantities, Newton-Raphson type algorithms can be applied to find the maximum likelihood estimators, together with estimates of their variances. We detail the application of this approach to parametric multiplicative frailty models and we show that the method works well in practice using both a real data and a simulated example. The proposed algorithm outperforms a Newton-Raphson type algorithm using numerical derivatives.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 99
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 5.2006, 1, art6 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper proposes a new method of optimal number and location of TCSC using mixed integer non-linear programming approach in the deregulated electricity markets. Optimal number and location of TCSC controller can effectively enhance system loadability and their placement is a crucial issue due to their high cost. Since, in the competitive electricity environment more and more transactions are negotiated, which can compromise the system security. Therefore, it has become essential to determine secure transactions occurring in the new environment for better planning and management. The system loadability has been determined in a hybrid market model utilizing the secure transaction matrix. The proposed technique has been tested on IEEE 24-bus reliability test system (RTS).
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 100
    Digitale Medien
    Digitale Medien
    Berkeley, Calif. : Berkeley Electronic Press (now: De Gruyter)
    International journal of emerging electric power systems 6.2006, 2, art1 
    ISSN: 1553-779X
    Quelle: Berkeley Electronic Press Academic Journals
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: At present the Indian Power Sector is seriously considering the optimization of their existing inter-regional transmission links, and also planning to form new inter-regional links. As one of the options, Thyristors Controlled Series Compensation (TCSC) scheme has been implemented recently in the Uttar Pradesh State, in the 400 kV links between Anpara and Unnao, and further efforts have not been made yet. At this stage, as a helping hand to the Power Sector in its decision-making, this paper explores the need for further transmission system upgrading, and based on a prototype transmission system study, it identifies a few more inter-regional transmission links for TCSC implementation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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