In situ characterization of tensile behavior of laser rapid solidified Al–Si heterogeneous microstructures

Heterogeneous Al–Si microstructure comprising of sub-micron-scale Al dendrites and nanoscale Al–Si fibrous eutectic was fabricated by processing as-cast Al-20wt.%Si alloy using laser rapid solidification. In situ tension tests explored high tensile strength ( ∼ 600 MPa) and ductility ( ∼ 10%) and high strain hardening rate ( ∼ 7 GPa). Microstructural characterization revealed the plastic co[1]deformation mechanisms between soft Al dendrites and hard nanoscale Al–Si eutectic. The progression of plasticity in nanoscale Al–Si eutectic with increasing applied strain is accommodated by dislocation plasticity in the nano-Al channels and cracking Si nanofibers. The propagation of nano-cracks is suppressed by surrounding Al, retaining good ductility of the sample

Characterization of Dopaminergic System in the Striatum of Young Adult Park2(-/-) Knockout Rats

Mutations in parkin gene (Park2) are linked to early-onset autosomal recessive Parkinson's disease (PD) and young-onset sporadic PD. Park2 knockout (PKO) rodents;however, do not display neurodegeneration of the nigrostriatal pathway, suggesting age-dependent compensatory changes. Our goal was to examine dopaminergic (DAergic) system in the striatum of 2 month-old PKO rats in order to characterize compensatory mechanisms that may have occurred within the system. The striata form wild type (WT) and PKO Long Evans male rats were assessed for the levels of DAergic markers, for monoamine oxidase (MAO) A and B activities and levels, and for the levels of their respective preferred substrates, serotonin (5-HT) and beta-phenylethylamine (beta-PEA). The PKO rats displayed lower activities of MAOs and higher levels of beta-PEA in the striatum than their WT counterparts. Decreased levels of beta-PEA receptor, trace amine-associated receptor 1 (TAAR-1), and postsynaptic DA D2 (D2L) receptor accompanied these alterations. Drug-naive PKO rats displayed normal locomotor activity;however, they displayed decreased locomotor response to a low dose of psychostimulant methamphetamine, suggesting altered DAergic neurotransmission in the striatum when challenged with an indirect agonist. Altogether, our findings suggest that 2 month-old PKO male rats have altered DAergic and trace aminergic signaling

9R phase enabled superior radiation stability of nanotwinned Cu alloys via in situ radiation at elevated temperature

Nanotwinned metals exhibit outstanding radiation tolerance as twin boundaries effectively engage, transport and eliminate radiation-induced defects. However, radiation-induced detwinning may reduce the radiation tolerance associated with twin boundaries, especially at elevated temperatures. Here we show, via in-situ Kr ion irradiation inside a transmission electron microscope, that 3 at. % Fe in epitaxial nanotwinned Cu (Cu97Fe3) significantly improves the thermal and radiation stability of nanotwins during radiation up to 5 displacements-per-atom at 200 °C. Such enhanced stability of nanotwins is attributed to a diffuse 9R phase resulted from the dissociation of incoherent twin boundaries in nanotwinned Cu97Fe3. The mechanisms for the enhanced stability of twin boundaries in irradiated nanotwinned alloys are discussed. The stabilization of nano-twins opens up opportunity for the application of nanotwinned alloys for aggressive radiation environments. Includes supplemental Appendix. Video files are attached below

Improvement of current crowding effect in VCSEL arrays with non-uniform oxidation aperture design

A compact electro-opto-thermal model of 2-D vertical cavity surface emitting laser (VCSEL) arrays considering the current crowding effect in each array cell is established to study the impact of oxidation aperture on the device performance. Simulated results shows that increasing oxidation aperture of array cell is helpful to improve the uniformity of current density distribution. With careful design of non-uniform oxidation aperture layout, both the uniformity of the temperature distribution and the current distribution is improved by 36.52% and 42.08%, respectively. Furthermore, 3×3 VCSEL arrays with uniform oxidation aperture (array-1) and non-uniform oxidation aperture (array-2) are fabricated and the L-I-V curves of two types of VCSEL arrays at different biases are also measured. The peak output optical power of array-2 is enhanced to 1.83mW with an improvement of 8.91% when compared with that of array-1. Moreover, the total optical output power of array-2 is always superior to that of array-1 over a wide bias current range

Improvement of thermally induced current bifurcation in VCSEL arrays with non-uniform series resistance design

Non-uniform series resistance design of VCSEL arrays is studied to improve thermally induced current bifurcation based on an electro-opto-thermal model of VCSEL arrays. Taking an 850nm VCSEL array with 4×4 cells for example, the impact of series resistance on current bifurcation is investigated. Increasmg series resistance is helpful to enhance the critical current values of current bifurcation point (Irc) and hence delay the current bifurcation phenomenon. For VCSEL array with non-uniform series resistance, Irc is increased by 28.6% and the total output optical power is enhanced by 14.3% when compared with that of VCSEL array with uniform series resistance. Therefore, non-uniform series resistance design is a better method for delaying the current bifurcation phenomenon and enhancuig the output optical power of VCSEL arrays

Enhanced Electron Correlation and Significantly Suppressed Thermal Conductivity in Dirac Nodal-Line Metal Nanowires by Chemical Doping

Enhancing electron correlation in a weakly interacting topological system has great potential to promote correlated topological states of matter with extraordinary quantum properties. Here, the enhancement of electron correlation in a prototypical topological metal, namely iridium dioxide (IrO2), via doping with 3d transition metal vanadium is demonstrated. Single-crystalline vanadium-doped IrO2 nanowires are synthesized through chemical vapor deposition where the nanowire yield and morphology are improved by creating rough surfaces on substrates. Vanadium doping leads to a dramatic decrease in Raman intensity without notable peak broadening, signifying the enhancement of electron correlation. The enhanced electron correlation is further evidenced by transport studies where the electrical resistivity is greatly increased and follows an unusual √ T dependence on the temperature (T). The lattice thermal conductivity is suppressed by an order of magnitude via doping even at room temperature where phonon-impurity scattering becomes less important. Density functional theory calculations suggest that the remarkable reduction of thermal conductivity arises from the complex phonon dispersion and reduced energy gap between phonon branches, which greatly enhances phase space for phonon–phonon Umklapp scattering. This work demonstrates a unique system combining 3d and 5d transition metals in isostructural materials to enrich the system with various types of interactions

Empirical Bayes Methods for Count Data

High-throughput sequencing (HTS) techniques such as RNA-seq, ChIP-seq and ATAC-seq have enabled researchers to investigate complex biological processes in unprecedented detail. One common feature of HTS data is that they often consist of counts. For example, in RNA-seq, the counts typically represent the number of times a RNA molecule has been sequenced and are a proxy for the expression level. Recently, the advent of single-cell sequencing techniques such as scRNA-seq and scATAC-seq has unveiled the transcriptome at cell-level resolution. However, the single-cell count data are sparse and come with high levels of technical noise. With the emergence of large, sparse and noisy sequencing data, there is a need for rigorous statistical methods that can accurately model these counts. On the other hand, due to the complex structure of the sequencing data exhibited, the statistical methods developed for the data should be flexible enough to incorporate different assumptions and structural information. For instance, matrix factorization has been extensively employed to uncover the latent structure of gene expression across a variety of cell types. The incorporation of sparsity assumptions into these latent structures has been shown to yield a more parsimonious representation and enhance the interpretability of results. Consequently, it would be beneficial to integrate sparsity assumptions when modeling the structure of sequencing data. In this thesis, we focus on developing flexible empirical Bayes (EB) methods for statistical modeling and inference in the field of genomics. We first explore EB Poisson mean models as a fundamental component for developing sophisticated models and as a simple problem for evaluating different approaches. Then we study EB smoothing methods that can account for extra variation or over-dispersion in sequencing data, and apply the methods to visualize gene expression patterns along the genome. We further introduce a general variational inference method for non-Gaussian data, and develop an EB Poisson matrix factorization method, with applications to single cell RNA sequencing data. Finally, we extend Poisson non-negative matrix factorization methodologies to accommodate spatially-structured or sparse factors and loadings

Crystallographic Orientation Dependence [email protected] Mechanical Responses of FeCrAl Micropillars

Iron-chromium-aluminum (FeCrAl) alloys are used in automobile exhaust gas purifying systems and nuclear reactors due to its superior high-temperature oxidation and excellent corrosion resistance. Single-phase FeCrAl alloys with a body centered cubic structure plastically deform through dislocation slips at room temperature. Here, we investigated the orientation dependence of mechanical responses of FeCrAl alloy through testing single-crystal and bi-crystal micropillars in a scanning electron microscopy at room temperature. Single-crystal micropillars were fabricated with specific orientations which favor the activity of single slip system or two slip systems or multiple slip systems. The strain hardening rate and flow strength increase with increasing the number of activated slip system in micropillars. Bi-crystal with respect to the continuity of slip systems across grain boundary the effect of grain boundary on slip transmission. The high geometrical compatibility factor corresponds to a high flow strength and strain hardening rate. Experimental results provide insight into understanding mechanical response of FeCrAl alloy and developing the mechanisms-based constitutive laws for FeCrAl polycrystalline aggregates

A new sequence logo plot to highlight enrichment and depletion

Abstract Background Sequence logo plots have become a standard graphical tool for visualizing sequence motifs in DNA, RNA or protein sequences. However standard logo plots primarily highlight enrichment of symbols, and may fail to highlight interesting depletions. Current alternatives that try to highlight depletion often produce visually cluttered logos. Results We introduce a new sequence logo plot, the EDLogo plot, that highlights both enrichment and depletion, while minimizing visual clutter. We provide an easy-to-use and highly customizable R package Logolas to produce a range of logo plots, including EDLogo plots. This software also allows elements in the logo plot to be strings of characters, rather than a single character, extending the range of applications beyond the usual DNA, RNA or protein sequences. And the software includes new Empirical Bayes methods to stabilize estimates of enrichment and depletion, and thus better highlight the most significant patterns in data. We illustrate our methods and software on applications to transcription factor binding site motifs, protein sequence alignments and cancer mutation signature profiles. Conclusions Our new EDLogo plots and flexible software implementation can help data analysts visualize both enrichment and depletion of characters (DNA sequence bases, amino acids, etc.) across a wide range of applications