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  • Institute of Physics  (114)
  • American Institute of Physics (AIP)  (31)
  • Oxford University Press  (3)
  • American Association for the Advancement of Science (AAAS)  (2)
  • 1
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    Perpendicular diffusion of energetic particles: Numerical test of the theorem on reduced dimensionality (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-01-15
    Description: A fundamental statement in diffusion theory is provided by the so-called theorem on reduced dimensionality . The latter theorem is saying that if the dimensionality of the turbulence is reduced, charged particles are tied to a single magnetic field line. If there is pitch-angle scattering and therewith parallel diffusion, this usually means that perpendicular transport is subdiffusive. Subdiffusive transport was found in numerous simulations for slab turbulence. However, it was unclear whether the theorem is valid for other models with reduced dimensionality such as the two-dimensional model. In the current paper, we simultaneously trace magnetic field lines and energetic particles and we compute the distance between the particle and the initial field line. We confirm the aforementioned theorem for slab turbulence but we cannot confirm it for two-dimensional turbulence. We also show that particles are not tied to field lines for two-component turbulence.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    A technique for measuring dynamic friction coefficient under impact loading (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-09-06
    Description: We develop a novel setup based on the split Hopkinson pressure bar technique to test the dynamic friction coefficient under impact loading. In the setup, the major improvement is that the end of the incident bar near the specimen is wedge-shaped, which results in a combined compressive and shear loading applied to the specimen. In fact, the shear loading is caused by the interfacial friction between specimen and bars. Therefore, when the two loading force histories are measured, the friction coefficient histories can be calculated without any assumptions and theoretical derivations. The geometry of the friction pairs is simple, and can be either cuboid or cylindrical. Regarding the measurements, two quartz transducers are used to directly record the force histories, and an optical apparatus is designed to test the interfacial slip movement. By using the setup, the dynamic friction coefficient of PTFE/aluminum 7075 friction pairs was tested. The time resolved dynamic friction coefficient and slip movement histories were achieved. The results show that the friction coefficient changes during the loading process, the average data of the relatively stable flat plateau section of the friction coefficient curves is 0.137, the maximum normal pressure is 52 MPa, the maximum relative slip velocity is 1.5 m/s, and the acceleration is 8400 m 2 /s. Furthermore, the friction test was simulated using an explicit FEM code LS-DYNA. The simulation results showed that the constant pressure and slip velocity can both be obtained with a wide flat plateau incident pulse. For some special friction pairs, normal pressure up to a few hundred MPa, interfacial slip velocities up to 10 m/s, and slip movement up to centimeter-level can be expected.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Genetic evidence for high-altitude adaptation in Tibet (2010)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2010-05-15
    Description: Tibetans have lived at very high altitudes for thousands of years, and they have a distinctive suite of physiological traits that enable them to tolerate environmental hypoxia. These phenotypes are clearly the result of adaptation to this environment, but their genetic basis remains unknown. We report genome-wide scans that reveal positive selection in several regions that contain genes whose products are likely involved in high-altitude adaptation. Positively selected haplotypes of EGLN1 and PPARA were significantly associated with the decreased hemoglobin phenotype that is unique to this highland population. Identification of these genes provides support for previously hypothesized mechanisms of high-altitude adaptation and illuminates the complexity of hypoxia-response pathways in humans.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Simonson, Tatum S -- Yang, Yingzhong -- Huff, Chad D -- Yun, Haixia -- Qin, Ga -- Witherspoon, David J -- Bai, Zhenzhong -- Lorenzo, Felipe R -- Xing, Jinchuan -- Jorde, Lynn B -- Prchal, Josef T -- Ge, RiLi -- 1P01CA108671-01A2/CA/NCI NIH HHS/ -- DK069513/DK/NIDDK NIH HHS/ -- GM059290/GM/NIGMS NIH HHS/ -- HL50077/HL/NHLBI NIH HHS/ -- R00 HG005846/HG/NHGRI NIH HHS/ -- New York, N.Y. -- Science. 2010 Jul 2;329(5987):72-5. doi: 10.1126/science.1189406. Epub 2010 May 13.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Eccles Institute of Human Genetics, University of Utah School of Medicine, Salt Lake City, UT 84112, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20466884" target="_blank"〉PubMed〈/a〉
    Keywords: *Acclimatization ; *Altitude ; Asian Continental Ancestry Group/genetics ; Ethnic Groups/genetics ; Female ; Genetic Association Studies ; Genetic Variation ; Genome, Human ; Haplotypes ; Hemoglobins/*analysis ; Humans ; Hypoxia-Inducible Factor 1/metabolism ; Hypoxia-Inducible Factor-Proline Dioxygenases ; Linear Models ; Male ; *Oxygen ; PPAR alpha/*genetics ; Phenotype ; Polymorphism, Single Nucleotide ; Procollagen-Proline Dioxygenase/*genetics ; *Selection, Genetic ; Signal Transduction ; Tibet
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Nonparametric maximum likelihood estimation for the multisample Wicksell corpuscle problem (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-25
    Description: We study nonparametric maximum likelihood estimation for the distribution of spherical radii using samples containing a mixture of one-dimensional, two-dimensional biased and three-dimensional unbiased observations. Since direct maximization of the likelihood function is intractable, we propose an expectation-maximization algorithm for implementing the estimator, which handles an indirect measurement problem and a sampling bias problem separately in the E- and M-steps, and circumvents the need to solve an Abel-type integral equation, which creates numerical instability in the one-sample problem. Extensions to ellipsoids are studied and connections to multiplicative censoring are discussed.
    Print ISSN: 0006-3444
    Electronic ISSN: 1464-3510
    Topics: Biology , Mathematics , Medicine
    Published by Oxford University Press
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  • 5
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    Gene integrated set profile analysis: a context-based approach for inferring biological endpoints (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-21
    Description: The identification of genes with specific patterns of change (e.g. down-regulated and methylated) as phenotype drivers or samples with similar profiles for a given gene set as drivers of clinical outcome, requires the integration of several genomic data types for which an ‘integrate by intersection’ (IBI) approach is often applied. In this approach, results from separate analyses of each data type are intersected, which has the limitation of a smaller intersection with more data types. We introduce a new method, GISPA (Gene Integrated Set Profile Analysis) for integrated genomic analysis and its variation, SISPA (Sample Integrated Set Profile Analysis) for defining respective genes and samples with the context of similar, a priori specified molecular profiles. With GISPA, the user defines a molecular profile that is compared among several classes and obtains ranked gene sets that satisfy the profile as drivers of each class. With SISPA, the user defines a gene set that satisfies a profile and obtains sample groups of profile activity. Our results from applying GISPA to human multiple myeloma (MM) cell lines contained genes of known profiles and importance, along with several novel targets, and their further SISPA application to MM coMMpass trial data showed clinical relevance.
    Keywords: Computational Methods, Genomics
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 6
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    Stripe order in the underdoped region of the two-dimensional Hubbard model (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-12-01
    Description: Competing inhomogeneous orders are a central feature of correlated electron materials, including the high-temperature superconductors. The two-dimensional Hubbard model serves as the canonical microscopic physical model for such systems. Multiple orders have been proposed in the underdoped part of the phase diagram, which corresponds to a regime of maximum numerical difficulty. By combining the latest numerical methods in exhaustive simulations, we uncover the ordering in the underdoped ground state. We find a stripe order that has a highly compressible wavelength on an energy scale of a few kelvin, with wavelength fluctuations coupled to pairing order. The favored filled stripe order is different from that seen in real materials. Our results demonstrate the power of modern numerical methods to solve microscopic models, even in challenging settings.
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Electroluminescence from an Au - extra-thin silicon oxynitride film - Si structure (1996)
    Institute of Physics
    Details
    Publication Date: 1996-04-01
    Print ISSN: 0953-8984
    Electronic ISSN: 1361-648X
    Topics: Physics
    Published by Institute of Physics
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  • 8
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    Electroluminescence from Au/(SiO2/Si/SiO2) nanometer double barrier/p-Si structures and its mechanism (2001)
    Institute of Physics
    Details
    Publication Date: 2001-11-30
    Print ISSN: 0953-8984
    Electronic ISSN: 1361-648X
    Topics: Physics
    Published by Institute of Physics
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  • 9
    Electronic Resource
    Electronic Resource
    Characterization of stain etched porous Si with photoluminescence, electron paramagnetic resonance, and infrared absorption spectroscopy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7615-7617 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Porous Si (PS) layers are prepared by stain etching in a HF/NaNO2 solution on both p- and n-type crystal Si substrates, and are characterized by photoluminescence (PL), electron paramagnetic resonance (EPR), and infrared absorption (IR) spectroscopy. The PL spectra under 488 nm laser excitation exhibit a strong peak at 680–720 nm for various samples of different substrate parameters and remain stable upon aging in air or γ irradiation; as-etched (∼20 min in air before measurement) and aged (for up to six months) samples show no detectable EPR signal but the γ-irradiated samples show an isotropic g=2.006 signal of peak-to-peak linewidth of 1.1 mT supporting an amorphous Si structure; the IR spectra show both hydrogen and oxygen related IR modes in the as-etched samples and the former decreases with aging time in air while the latter increases. Comparing our results with those of anodically etched PS samples we conclude that: (1) the PL peak position of the stain PS seems to be unique and stable as compared with that of the anodic PS varying in 620–830 nm; (2) the isotropic EPR signal of the stain PS reflects no crystallinity, in contrast with the anisotropic signal of the anodic PS; and (3) obvious oxidation in the as-etched stain PS is also in contrast with the nonobservation of oxygen-related IR modes in the as-etched anodic PS. We discuss the results in terms of structural properties and PL mechanism of PS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354940
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  • 10
    Electronic Resource
    Electronic Resource
    Deep levels in γ-ray irradiated n- and p-type hydrogen-grown float-zoned silicon (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1182-1188 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The generation rates and annealing behavior of the irradiation defects in n- and p-type hydrogen-grown float-zoned silicon (irradiated with γ rays from 60Co) have been studied by the deep-level transient spectroscopy technique and compared with those of irradiated argon-grown float-zoned silicon. Assuming the generation rate of the irradiation defects created by γ rays in argon-grown float-zoned silicon is 1, then the generation rates of the A center, divacancy, and phosphorus vacancy in n-type hydrogen-grown float-zoned silicon are 0.23, 0.78, and 0.19, respectively, while the generation rates of the divacancy and H(0.37 eV) in p-type hydrogen-grown silicon are 0.79 and 0.10, respectively. Due to the existence of hydrogen, the generation rate reduction of the major irradiation defects in γ-ray irradiated silicon is more pronounced than that in 1-MeV electron irradiated silicon. Three hydrogen-related defects, H(0.10 eV), H(0.29 eV), and H(0.56 eV), were seen in γ-ray irradiated hydrogen-grown float-zoned silicon, among which H(0.10 eV) and H(0.56 eV) were reported by us to exist in electron irradiated hydrogen-grown float-zoned silicon, while H(0.29 eV) is reported for the first time. The convergence effect of annealing temperatures for the irradiation defects was observed. That is, the annealing temperatures at which the irradiation defects diminish are almost the same for most irradiation defects, similar to that in the case of electron irradiation, was observed, showing that this effect is characteristic of the hydrogen behavior in silicon, and irrelevent to the type of irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351285
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