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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 1444-1446 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel technique was developed to grow high-purity polycrystalline diamond films at 850 °C and 50 mTorr with 10% CH4, 2% O2, and balance H2 using a filament-assisted chemical vapor deposition technique in combination with an electron cyclotron resonance (ECR) plasma. Using Raman spectroscopy and in situ plasma diagnostics, we have shown that the hydrogen plasma selectively etched nondiamond components during deposition. Experiments with ECR plasma and the filament-assisted technique from 10−6 Torr to 50 mTorr and 500–1000 °C indicated that low-energy electrons are a key factor in growth of diamond thin films.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1311-1313 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Etching of SiO2 with low-energy Ar ions has been studied in an electron cyclotron resonance (ECR) based etching system. Ion energies were controlled by a capacitively coupled 13.56 MHz bias of the substrate. Etch rates of over 100 A(ring)/min have been achieved at ion energies below 100 V. The variation in etch rate has been studied as a function of ECR power, self-induced bias, and position of the wafer relative to the ECR source. This low-energy process can be utilized for cleaning of semiconductor surfaces prior to chemical vapor deposition or metallization processes.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reactive ion etching is important for III-V device fabrication. Commonly encountered applications include the need to remove an epitaxial layer selectively from underlying layers and the need for definition of mesas and other structures with carefully controlled dimensions. We present results showing the use of very thin Al0.9Ga0.1As and In0.2Ga0.8As stop-etch layers, which when used in conjunction with a particular etch chemistry can provide highly selective removal of epitaxial layers in GaAs-based III-V compound semiconductors. In addition, we report the selective removal of an Al0.3Ga0.7As layer from underlying GaAs by the use of a thin In0.2Ga0.8As interlayer.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The generation of slip dislocations in BF2 ion-implanted, 100-mm-diam silicon wafers during rapid thermal annealing is investigated. Whole wafer x-ray topography shows that annealing at 1150 °C causes slip to initiate randomly at positions of maximum resolved stress at the wafer edges and over scribe marks made on the back surface prior to annealing. Lowering the annealing temperature by 20 °C, which corresponds to decreasing the silicon yield stress by less than 106 dyn cm−2, prevents slip from occurring and allows sufficient removal of implantation-induced defects from which junction diodes with good current-voltage characteristics are fabricated.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1083-1085 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of a reactive ion etch process with high selectivity for etching GaAs layers and stopping on underlying AlGaAs layers is reported. A key feature is the high degree of control that can be maintained over the GaAs-to-AlGaAs selectivity by changing the SF6/SiCl4 ratio while keeping other etch parameters such as pressure, dc bias, or power constant. Values of the GaAs-to-AlGaAs selectivity can be varied from 1 to 500. Diluent gases such as helium can be added to reduce the etch rate, which is important to avoid damage to sensitive device structures and to the overhang profile of resist materials used for liftoff metallization. The application of this etch process for high electron mobility transistor fabrication is discussed.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2019-07-13
    Description: The use of the column V-trialkyls trimethylarsenic (TMAs) and trimethylantimony (TMSb) for the organometallic vapor phase epitaxy (OM-VPE) of III-V compound semiconductors is reviewed. A general discussion of the interaction chemistry of common Group III and Group V reactants is presented. The practical application of TMSb and TMAs for OM-VPE is demonstrated using the growth of GaSb, GaAs(1-y)Sb(y), Al(x)Ga(1-x)Sb, and Ga(1-x)In(x)As as examples.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Semiconductor growth technology;; January 26-27, 1982; Los Angeles, CA
    Format: text
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  • 8
    Publication Date: 2019-07-13
    Description: INTRODUCTION: Sudden cardiac death is the leading cause of line of duty death among firefighters, accounting for approximately 45% of fatalities annually. Firefighters perform strenuous muscular work while wearing heavy, encapsulating personal protective equipment in high ambient temperatures, under chaotic and emotionally stressful conditions. These factors can precipitate sudden cardiac events like myocardial infarction, serious dysrhythmias, or cerebrovascular accidents in firefighters with underlying cardiovascular disease. PURPOSE: The purpose of this study was to deploy and then evaluate the contribution of resting advanced ECG (A-ECG) in addition to other screening tools (family history, lipid profiles, and cardiopulmonary exercise tests, XT) in assessment of an individual fs cardiac risk profile. METHODS: Forty-four career firefighters were recruited to perform comprehensive baseline assessments including tests of aerobic performance, fasting lipids and glucose. Five-min resting 12-lead A-ECGs were obtained in a subset of firefighters (n=21) and transmitted over a secure networked system to a NASA physician collaborator. Using myocardial perfusion and other imaging as the gold standard, A-ECG scoring has been proven useful in accurately identifying a number of cardiac pathologies including coronary artery disease (CAD), left ventricular hypertrophy, hypertrophic cardiomyopathy, and non-ischemic and ischemic cardiomyopathy. RESULTS: Subjects f mean (SD) age was 43 (8) years, weight 91 (13) kg, and BMI 28 (3) kg/m2. Fifty-one percent of subjects had .3 cardiovascular risk factors. One subject had ST depression on XT ECG, at least one positive A-ECG score for CAD, and documented CAD based on cardiology referral. While all other subjects, including those with fewer risk factors, higher aerobic fitness, and normal exercise ECGs, were classified as healthy by A-ECG, there was no trend for association between risk factors and any of 20 A-ECG parameters in the grouped data.
    Keywords: Life Sciences (General)
    Type: JSC-CN-25097 , 59th American College of Sports Medicine Annual meeting; 29 May - 2 Jun. 2012; San Francisco, CA; United States
    Format: application/pdf
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  • 9
    Publication Date: 2019-07-19
    Description: INTRODUCTION Sudden cardiac death is the leading cause of line of duty death among firefighters, accounting for approximately 45% of fatalities annually. Firefighters perform strenuous muscular work while wearing heavy, encapsulating personal protective equipment in high ambient temperatures, under chaotic and emotionally stressful conditions. These factors can precipitate sudden cardiac events like myocardial infarction, serious dysrhythmias, or cerebrovascular accidents in firefighters with underlying cardiovascular disease. Screening for cardiovascular risk factors is recommended but not always followed in this population. PHASER is a project charged with identifying and prioritizing risk factors in emergency responders. We have deployed an advanced ECG (A-ECG) system developed at NASA for improved sensitivity and specificity in the detection of cardiac risk. METHODS Forty-four professional firefighters were recruited to perform comprehensive baseline assessments including tests of aerobic performance and laboratory tests for fasting lipid profiles and glucose. Heart rate and conventional 12-lead ECG were obtained at rest and during incremental treadmill exercise testing (XT). In addition, a 5-min resting 12-lead A-ECG was obtained in a subset of firefighters (n=18) and transmitted over a secure networked system to a physician collaborator at NASA for advanced-ECG analysis. This A-ECG system has been proven, using myocardial perfusion and other imaging, to accurately identify a number of cardiac pathologies including coronary artery disease (CAD), left ventricular hypertrophy, hypertrophic cardiomyopathy, non-ischemic cardiomyopathy, and ischemic cardiomyopathy. RESULTS Subjects mean (SD) age was 43 (8) years, weight 91 (13) kg, and BMI of 28 (3) kg/square meter. Maximum oxygen uptake (VO2max) was 39 (9) ml/kg/min. This compares with the 45th %ile in healthy reference values and a recommended standard of 42 ml/kg/min for firefighters. The metabolic threshold (VO2Theta) above which lactate accumulates was 23 (8) ml/kg/min. The chronotropic index, a measure of cardiovascular strain during XT was 35 (8) /L compared with reference values for men of 40 /L. Total cholesterol, LDL-C and HDL-C were 202 (34),126 (29), and 55 (15) mg/dl, respectively. Fifty-one percent of subjects had .3 cardiovascular risk factors, 2 subjects had resting hypertension (BP.140/90), and 23 had pre-hypertension (.120/80 but 〈140/90). Seven had exaggerated exercise induced hypertension but only one had ST depression on XT ECG, at least one positive A-ECG score for CAD, and documented CAD based on cardiology referral. While all other subjects, including those with fewer risk factors, higher aerobic fitness, and normal exercise ECGs, were classified as healthy by A-ECG, there was no trend for association between risk factors and any of 20 A-ECG parameters in the grouped data. CONCLUSIONS A-ECG screening correctly identified the individual with CAD although there was no trend for A-ECG parameters to distinguish those with elevated BP or multiple risk factors but normal XT ECG. We have demonstrated that a new technology, advanced-ECG, can be introduced for remote firefighter risk assessment. This simple, time and cost-effective approach to risk identification that can be acquired remotely and transmitted securely can detect individuals potentially at risk for line-of-duty death. Additional research is needed to further document its value.
    Keywords: Aerospace Medicine
    Type: JSC-CN-24585 , UCLA''s Department of Medicine Research Conference; 20 Sep. 2011; Los Angeles, CA; United States
    Format: application/pdf
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  • 10
    Publication Date: 2019
    Description: 〈p〉Tough, biological materials (e.g., collagen or titin) protect tissues from irreversible damage caused by external loads. Mimicking these protective properties is important in packaging and in emerging applications such as durable electronic skins and soft robotics. This paper reports the formation of tough, metamaterial-like core-shell fibers that maintain stress at the fracture strength of a metal throughout the strain of an elastomer. The shell experiences localized strain enhancements that cause the higher modulus core to fracture repeatedly, increasing the energy dissipated during extension. Normally, fractures are catastrophic. However, in this architecture, the fractures are localized to the core. In addition to dissipating energy, the metallic core provides electrical conductivity and enables repair of the fractured core for repeated use. The fibers are 2.5 times tougher than titin and hold more than 15,000 times their own weight for a period 100 times longer than a hollow elastomeric fiber.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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