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Yang, H.

Publications and source records attributed to Yang, H..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

BICEP2/Keck Array XI: Beam Characterization and Temperature-to-Polarization Leakage in the BK15 Data Set

Precision measurements of cosmic microwave background (CMB) polarization require extreme control of instrumental systematics. In a companion paper we have presented cosmological constraints from observations with the BICEP2 and Keck Array experiments up to and including the 2015 observing season (BK15), resulting in the deepest CMB polarization maps to date and a statistical sensitivity to the tensor-to-scalar ratio of σ ( r ) = 0.020. In this work we characterize the beams and constrain potential systematic contamination from main beam shape mismatch at the three BK15 frequencies (95, 150, and 220 GHz). Herein far-field maps of 7360 distinct beam patterns taken from 2010–2015 are used to measure differential beam parameters and predict the contribution of temperature-to-polarization leakage to the BK15 B -mode maps. In the multifrequency, multicomponent likelihood analysis that uses BK15, Planck , and Wilkinson Microwave Anisotropy Probe maps to separate sky components, we find that adding this predicted leakage to simulations induces a bias of Δ r = 0.0027 ± 0.0019. Future results using higher-quality beam maps and improved techniques to detect such leakage in CMB data will substantially reduce this uncertainty, enabling the levels of systematics control needed for BICEP Array and other experiments that plan to definitively probe large-field inflation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Carbon isotopic signatures of super-deep diamonds mediated by iron redox chemistry

Among redox sensitive elements, carbon is specifically important because it may have been a driver rather than a passive recorder of Earth’s redox evolution. The extent to which the isotopic composition of carbon records the redox processes that shaped the Earth is still debated. In particular, the highly reduced deep mantle may be metal-saturated, yet, it is still unclear how the presence of metallic phases influences the carbon isotopic compositions of super-deep diamonds. Here we report ab initio results for the vibrational properties of carbon in carbonates, diamond, and Fe 3 C under pressure and temperature conditions relevant to super-deep diamond formation. Previous work on this question neglected the effect of pressure on the equilibrium carbon isotopic fractionation between diamond and Fe 3 C but our calculations show that this assumption overestimates the fractionation by a factor of ~1.3. Our calculated probability density functions for the carbon isotopic compositions of super-deep diamonds derived from metallic melt can readily explain the very light carbon isotopic compositions observed in some super-deep diamonds. Our results therefore support the view that metallic phases are present during the formation of super-deep diamonds in the mantle below ~250 km.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Muon-Computed Tomography using POCA Trajectory for Imaging Spent Nuclear Fuel in Dry Storage Casks

Cosmic ray muon-computed tomography (μCT) is a new imaging modality with unique characteristics that can be particularly important for applications in nuclear proliferation detection and international treaty verification. Using cosmic ray muons for nuclear security presents several potential advantages. Among others, muons are generated naturally in the atmosphere, can penetrate high-density materials, and are freely available. No radiological sources are required and consequently there is no associated radiological dose. Recently, the feasibility of using muons for imaging spent nuclear fuel stored in shielded casks has been explored and has been proved beneficial. However, challenges in μCT imaging include low muon flux of ~10,000 muons/m2/min, the effects of multiple Coulomb scattering (MCS) blurring the image, and inefficiency in being able to use all recorded muons for imaging. In this paper, we argue that the use of muon tracing should produce tomographic muon images with improved quality – or more quickly for the same image quality – compared to the case where conventional methods are used. In our paper, we report on the development and assessment of a novel muon tracing method for μCT. The proposed method back projects the muon’s scattering angle into each pixel crossed by its PoCA trajectory then forward projects the variance of the scattering angle in each pixel to detector bins along the muon’s incident horizontal direction. Two scenarios were simulated to assess the expected detection capability of this proposed method. GEANT4 was used to model the main characteristics of 1-60 GeV muons through matter. The simulated images showed an expected improvement in resolution and a reduced the reliance on the muon momentum information compared to a more conventional muon tomography method.

Liu, Zhengzhi↗
DOE OSTI2018

A sub-sampled approach to extremely low-dose STEM

The inpainting of deliberately and randomly sub-sampled images offers a potential means to image specimens at a high resolution and under extremely low-dose conditions (≤1 e - /Å 2 ) using a scanning transmission electron microscope. We show that deliberate sub-sampling acquires images at least an order of magnitude faster than conventional low-dose methods for an equivalent electron dose. More importantly, when adaptive sub-sampling is implemented to acquire the images, there is a significant increase in the resolution and sensitivity which accompanies the increase in imaging speed. Lastly, we demonstrate the potential of this method for beam sensitive materials and in-situ observations by experimentally imaging the node distribution in a metal-organic framework.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Neutrophil CD16b crosslinking induces lipid raft-mediated activation of SHP-2 and affects cytokine expression and retarded neutrophil apoptosis

Highlights: • FcγRIIIb receptor is GPI anchored to the cell membrane and its signal transduction is still ambiguous. • Several groups have established surprisingly that it can transduce signals by itself. In contrast, others have stated that FcγRIIIB must cooperate with one or several neighboring transmembrane partners. • SHP-2 is activated by FcγRIIIB cross-linking in neutrophil as a component of the raft-mediated signaling pathway. Two different types of FcRs for IgG are constitutively expressed on the surface of human neutrophils, namely, FcγRIIA (CD32a) and FcγRIIIB (CD16b). Unlike FcγRIIA, FcγRIIIb is GPI anchored to the cell membrane and its signal transduction is still ambiguous. To further understand the signal transduction of CD16b, we compared neutrophil cytokine expression and apoptosis by the cross-linking of CD32a and CD16b respectively. We found that both CD32a and CD16b crosslinking can activate neutrophils, but did not exactly share cytokine expression profiles. On the other hand, CD16b cross-linking retarded neutrophil apoptosis while CD32a promoted it. By interrupting the lipid raft with methyl-β-cyclodextrin (MβCD) and inhibiting the ITAM-SYK pathway with an SYK inhibitor (piceatannol), we found reduced apoptosis was at least partially mediated by lipid raft structure, but not the ITAM-SYK pathway. Additionally, CD16b but not CD32a cross-linking triggered SHP-2 phosphorylation and led to its translocation into lipid rafts. SHP-2 phosphorylation and translocation were inhibited by MβCD. Moreover, pre-inhibition of SHP-2 by a specific inhibitor (SHP099) converted IL-10 and SOCS3 expression level and promoted neutrophil apoptosis after CD16b crosslinking. In conclusion, these results, for the first time, collectively indicate that SHP-2 is activated by CD16b crosslinking in neutrophils and functions as a component of the raft-mediated signaling pathway.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Effects of haemodilution on the optical properties of blood during coagulation studied by optical coherence tomography

We report an investigation of the effects of blood dilution with hypertonic (7.5 %) and normal (0.9 %) saline on its optical properties during coagulation in vitro using optical coherence tomography. The light penetration depth and attenuation coefficient are obtained from the dependences of reflectance on the depth. Normal whole blood has served as the control group. The average coagulation time is equal to 420±16,418±16 and 358±14 s with blood volume replacement of 2 %, 11 %, and 20 % by 0.9 % normal saline, respectively. With 2 %, 11% and 20% blood volume replacement with 7.5 % hypertonic saline, the average coagulation time is 422±17,1160±45 and 1730±69 s, respectively. For normal whole blood, the average coagulation time amounts to 425±19 s. it is shown that dilution with normal saline has a procoagulant effect when it replaces 20 % of blood volume, and hypertonic saline has an anticoagulant effect if it replaces 11 % or more of blood volume. It is concluded that optical coherence tomography is a potential technique to quantify and monitor the liquid – gel transition during the coagulation process of blood diluted by normal and hypertonic saline. (biophotonics)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

First restults from the Faint Infrared Grism Survey (FIGS): first simultaneous detection of Lyα emission and Lyman break from a galaxy at z = 7.51

Galaxies at high redshifts are a valuable tool for studying cosmic dawn, therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyα emission and the Lyman break from a z=7.512 ± 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with the G102 grism on the Hubble Space Telescope (HST), show a significant emission line detection (6σ) in two observational position angles (PAs), with Lyα line flux of 1.06±0.19×10{sup −17} erg s{sup −1} cm{sup −2}. The line flux is nearly a factor of four higher than that in the archival MOSFIRE spectroscopic observations. This is consistent with other recent observations, implying that ground-based near-infrared spectroscopy underestimates the total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyα measurements. A 4σ detection of the NV line in one PA also suggests a weak active galactic nucleus (AGN), and if confirmed, would make this source the highest-redshift AGN yet found. These observations from HST thus clearly demonstrate the sensitivity of the FIGS survey, and the capability of grism spectroscopy for studying the epoch of reionization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The thickness design of unintentionally doped GaN interlayer matched with background doping level for InGaN-based laser diodes

In order to reduce the internal optical loss of InGaN laser diodes, an unintentionally doped GaN (u-GaN) interlayer is inserted between InGaN/GaN multiple quantum well active region and Al{sub 0.2}Ga{sub 0.8}N electron blocking layer. The thickness design of u-GaN interlayer matching up with background doping level for improving laser performance is studied. It is found that a suitably chosen u-GaN interlayer can well modulate the optical absorption loss and optical confinement factor. However, if the value of background doping concentration of u-GaN interlayer is too large, the output light power may decrease. The analysis of energy band diagram of a LD structure with 100 nm u-GaN interlayer shows that the width of n-side depletion region decreases when the background concentration increases, and may become even too small to cover whole MQW, resulting in a serious decrease of the output light power. It means that a suitable interlayer thickness design matching with the background doping level of u-GaN interlayer is significant for InGaN-based laser diodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effects of atmospheric pressure cold plasma on human hepatocarcinoma cell and its 5-fluorouracil resistant cell line

Atmospheric pressure cold plasma showed selective killing efficiency on cancer cells in vitro and in vivo, which makes plasma a potential option for cancer therapy. However, the plasma effects on chemotherapeutic drugs-resistant cells are rarely to be found. In this paper, the effects of plasma on human hepatocellular carcinoma Bel7402 cells and 5-fluorouracil (5-FU) resistant Bel7402/5FU cells were intensively investigated. The results showed that plasma induced superior toxicity to Bel7402 cells compared with Bel7402/5FU cells. Incubation with plasma-treated medium for 20 s induced more than 85% death rate in Bel7402 cells, while the same death ratio was achieved when Bel7402/5FU cells were treated for as long as 300 s. The hydrogen peroxide in the medium played a leading role in the cytotoxicity effects. Further studies implicated that when the treatment time was shorter than 60 s, the depolarization of mitochondrial membrane potential and apoptosis occurred through the intracellular reactive oxygen species accumulation in Bel7402 cells. Molecular analysis showed an increase in the transcription factor activity for AP-1, NF-kB, and p53 in Bel7402 cells. No obvious damage could be detected in plasma-treated Bel7402/5FU cells due to the strong intracellular reactive oxygen stress scavenger system.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Protecting nickel with graphene spin-filtering membranes: A single layer is enough

We report on the demonstration of ferromagnetic spin injectors for spintronics which are protected against oxidation through passivation by a single layer of graphene. The graphene monolayer is directly grown by catalytic chemical vapor deposition on pre-patterned nickel electrodes. X-ray photoelectron spectroscopy reveals that even with its monoatomic thickness, monolayer graphene still efficiently protects spin sources against oxidation in ambient air. The resulting single layer passivated electrodes are integrated into spin valves and demonstrated to act as spin polarizers. Strikingly, the atom-thick graphene layer is shown to be sufficient to induce a characteristic spin filtering effect evidenced through the sign reversal of the measured magnetoresistance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Investigation of scanning tunneling spectra on iron-based superconductor FeSe 0.5 Te 0.5

FeSe 0.5 Te 0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) measureflents in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73± 0.03 Å which is consistent with the lattice constant 3.78 Å. The Se and Te atoms with a height difference of about 0.35 Å are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconducting state. According to the positions of coherence peaks, we determine the superconducting gap 2Δ = 5.5 meV, and the reduced gap 2Δ/kBTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy Ω of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature Ω/kBTc ≈ 4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Optical and structural characteristics of high indium content InGaN/GaN multi-quantum wells with varying GaN cap layer thickness

The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) with different thicknesses of low temperature grown GaN cap layers are investigated. It is found that the MQW emission energy red-shifts and the peak intensity decreases with increasing GaN cap layer thickness, which may be partly caused by increased floating indium atoms accumulated at quantum well (QW) surface. They will result in the increased interface roughness, higher defect density, and even lead to a thermal degradation of QW layers. An extra growth interruption introduced before the growth of GaN cap layer can help with evaporating the floating indium atoms, and therefore is an effective method to improve the optical properties of high indium content InGaN/GaN MQWs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

The significant effect of the thickness of Ni film on the performance of the Ni/Au Ohmic contact to p-GaN

The significant effect of the thickness of Ni film on the performance of the Ohmic contact of Ni/Au to p-GaN is studied. The Ni/Au metal films with thickness of 15/50 nm on p-GaN led to better electrical characteristics, showing a lower specific contact resistivity after annealing in the presence of oxygen. Both the formation of a NiO layer and the evolution of metal structure on the sample surface and at the interface with p-GaN were checked by transmission electron microscopy and energy-dispersive x-ray spectroscopy. The experimental results indicate that a too thin Ni film cannot form enough NiO to decrease the barrier height and get Ohmic contact to p-GaN, while a too thick Ni film will transform into too thick NiO cover on the sample surface and thus will also deteriorate the electrical conductivity of sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗