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  • 11
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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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  • 12
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    Ghrelin and hepatic lipogenesis [Medical Sciences] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-09-10
    Description: Although ghrelin has been demonstrated to stimulate energy intake and storage through a central mechanism, its effect on hepatic lipid metabolism remains largely uncharacterized. Ghrelin receptor antagonism or gene deletion significantly decreased obesity-associated hepatic steatosis by suppression of de novo lipogenesis, whereas exogenous ghrelin stimulated lipogenesis, leading to hepatic lipid...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 13
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    CXCR4:CXCL12 complex stoichiometry and geometry [Biophysics and Computational Biology] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-12-17
    Description: Chemokines and their receptors regulate cell migration during development, immune system function, and in inflammatory diseases, making them important therapeutic targets. Nevertheless, the structural basis of receptor:chemokine interaction is poorly understood. Adding to the complexity of the problem is the persistently dimeric behavior of receptors observed in cell-based studies, which...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 14
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    Modulation of galactic cosmic rays during the unusual solar minimum between cycles 23 and 24 (2014)
    Wiley
    Details
    Publication Date: 2014-03-12
    Description: During the recent solar minimum between cycles 23 and 24 (solar minimum P 23/24 ) the intensity of Galactic Cosmic Rays (GCRs) measured at the Earth was the highest ever recorded since space age. It is the purpose of this paper to resolve the most plausible mechanism for this unusually high intensity. A GCR transport model in three-dimensional heliosphere based on a simulation of Markov stochastic process is used to find the relation of cosmic ray modulation to various transport parameters, including solar wind (SW) speed, distance of heliospheric boundary, magnitude of interplanetary magnetic field (IMF) at the Earth, tilt angle of heliospheric current sheet (HCS), values of parallel and perpendicular diffusion coefficients. We calculate GCR proton energy spectra at the Earth for the last three solar minima P 21/22 , P 22/23 , and P 23/24 , with the transport parameters obtained from observations. Besides weak IMF magnitude and slow SW speed, we find that a possible low magnetic turbulence, which increases the parallel diffusion and reduces the perpendicular diffusion in the polar direction, might be an additional possible mechanism for the high GCR intensity in the solar minimum P 23/24 .
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 15
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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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  • 16
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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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  • 17
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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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  • 18
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    An observation-based GCR model of heavy nuclei: measurements from CRIS onboard ACE spacecraft (2013)
    Wiley
    Details
    Publication Date: 2013-03-19
    Description: [1]  We present an observation-based elemental Galactic Cosmic Ray (GCR) heavy nuclei spectra model, based on ACE/CRIS measurements. Then we extrapolate the spectra model to the lower energy range of ACE/SIS instrument. In addition, we compare the modeling results with both the CRIS and SIS measurements. The flux of lower energetic particles measured by SIS are despiked since there are Solar Energetic Particle (SEP) events. The good agreement between the modeling and the observation results, especially for the solar minimum, indicates the validity of our model in the energy range 30 MeV/nuc–500 MeV/nuc. Compared with two GCR radiation environment models, CRÈME96/Nymmik model and Badhwar & O'Neill model, our model can provide an improved fit to the GCRs spectra measured by ACE. Furthermore, our model is a phenomenological one, without consideration of the physical process during GCRs' propagating through the heliosphere. Therefore, it is more straight-forward and applicable in practice. Finally, the model can reproduce and predict the GCR spectra in the past and future, respectively, based on the strong correlation between the model parameters and solar activity indicated by sunspot number.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 19
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    A study of cosmic ray flux based on the noise in raw CCD data from solar images (2016)
    Wiley
    Details
    Publication Date: 2016-10-29
    Description: Raw solar images from CCDs are often contaminated with single-pixel noise which is thought to be made by cosmic ray hits. The cosmic ray affected pixels are usually outstanding when compared with the perimeter zone. In this work, we use a method based on the median filtering algorithm to identify and count the cosmic ray traces from SOHO/EIT solar images to estimate the cosmic ray (CR) flux. With such cosmic ray flux, we study the transient variations associated with the violent solar activities, such as the Solar Particle Events (SPEs), which show good similarity with the observations of GOES 11 P6 channel with an energy interval 80 − 165 MeV. Further, using SPE list observed by SOHO/ERNE proton channels with more narrow energy intervals, it is found that CRs in the energy range 118 − 140 MeV affect the SOHO/EIT images the most. In addition, by using a robust automatic despiking method we get the background of the cosmic ray flux from solar images, which is considered to be the galactic cosmic ray (GCR) flux. The GCR flux from solar images shows an 11-year period due to the solar modulation, similar to the SOHO/ERNE GCR flux and Newark neutron monitor count rates. Furthermore, GCRs from solar images have a 27-day period and show good anti-correlation with the changes of solar wind velocity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 20
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    Numerical analysis of flow in a centrifugal compressor with circumferential grooves: influence of groove location and number on flow instability (2017)
    Institute of Physics (IOP)
    Details
    Publication Date: 2017-09-07
    Description: As an effective and economic method for flow range enhancement, circumferential groove casing treatment (CGCT) is widely used to increase the stall margin of compressors. Different from traditional grooved casing treatments, in which the grooves are always located over the rotor in both axial and radial compressors, one or several circumferential grooves are located along the shroud side of the diffuser passage in this paper. Numerical investigations were conducted to predict the performance of a low flow rate centrifugal compressor with CGCT in diffuser. Computational fluid dynamics (CFD) analysis is performed under stage environment in order to find the optimum location of the circumferential casing groove in consideration of stall margin enhancement and efficiency gain at design point, and the impact of groove number to the effect of this grooved casing treatment configuration in enhancing the stall margin of the compressor stage is studied. The results indicate that the cent...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics (IOP)
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