316 research outputs found
Slow and fast micro-field components in warm and dense hydrogen plasmas
The aim of this work is the investigation of the statistical properties of
local electric fields in an ion-electron two component plasmas for coupled
conditions. The stochastic fields at a charged or at a neutral point in plasmas
involve both slow and fast fluctuation characteristics. The statistical study
of these local fields based on a direct time average is done for the first
time. For warm and dense plasma conditions, typically , , well controlled molecular dynamics (MD)
simulations of neutral hydrogen, protons and electrons have been carried out.
Relying on these \textit{ab initio} MD calculations this work focuses on an
analysis of the concepts of statistically independent slow and fast local field
components, based on the consideration of a time averaged electric field. Large
differences are found between the results of these MD simulations and
corresponding standard results based on static screened fields. The effects
discussed are of importance for physical phenomena connected with stochastic
electric field fluctuations, e.g., for spectral line broadening in dense
plasmas.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
LÓPEZ, FERNANDA [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201
Enhanced inverse bremsstrahlung heating rates in a strong laser field
Test particle studies of electron scattering on ions, in an oscillatory
electromagnetic field have shown that standard theoretical assumptions of small
angle collisions and phase independent orbits are incorrect for electron
trajectories with drift velocities smaller than quiver velocity amplitude. This
leads to significant enhancement of the electron energy gain and the inverse
bremsstrahlung heating rate in strong laser fields. Nonlinear processes such as
Coulomb focusing and correlated collisions of electrons being brought back to
the same ion by the oscillatory field are responsible for large angle, head-on
scattering processes. The statistical importance of these trajectories has been
examined for mono-energetic beam-like, Maxwellian and highly anisotropic
electron distribution functions. A new scaling of the inverse bremsstrahlung
heating rate with drift velocity and laser intensity is discussed.Comment: 12 pages, 12 figure
How metal films de-wet substrates - identifying the kinetic pathways and energetic driving forces
We study how single-crystal chromium films of uniform thickness on W(110)
substrates are converted to arrays of three-dimensional (3D) Cr islands during
annealing. We use low-energy electron microscopy (LEEM) to directly observe a
kinetic pathway that produces trenches that expose the wetting layer. Adjacent
film steps move simultaneously uphill and downhill relative to the staircase of
atomic steps on the substrate. This step motion thickens the film regions where
steps advance. Where film steps retract, the film thins, eventually exposing
the stable wetting layer. Since our analysis shows that thick Cr films have a
lattice constant close to bulk Cr, we propose that surface and interface stress
provide a possible driving force for the observed morphological instability.
Atomistic simulations and analytic elastic models show that surface and
interface stress can cause a dependence of film energy on thickness that leads
to an instability to simultaneous thinning and thickening. We observe that
de-wetting is also initiated at bunches of substrate steps in two other
systems, Ag/W(110) and Ag/Ru(0001). We additionally describe how Cr films are
converted into patterns of unidirectional stripes as the trenches that expose
the wetting layer lengthen along the W[001] direction. Finally, we observe how
3D Cr islands form directly during film growth at elevated temperature. The Cr
mesas (wedges) form as Cr film steps advance down the staircase of substrate
steps, another example of the critical role that substrate steps play in 3D
island formation
Unusually strong space-charge-limited current in thin wires
The current-voltage characteristics of thin wires are often observed to be
nonlinear, and this behavior has been ascribed to Schottky barriers at the
contacts. We present electronic transport measurements on GaN nanorods and
demonstrate that the nonlinear behavior originates instead from
space-charge-limited current. A theory of space-charge-limited current in thin
wires corroborates the experiments, and shows that poor screening in high
aspect ratio materials leads to a dramatic enhancement of space-charge limited
current, resulting in new scaling in terms of the aspect ratio.Comment: 4 pages, 3 figures, to appear in Physical Review Letter
Hubungan antara Pembangunan Penerapan Nilai dalam Pendidikan Abad Ke-21 dengan Pembentukan Sahsiah Murid Sekolah Kurang Murid (SKM) Luar Bandar di Sabah
Penerapan nilai dalam pendidikan abad ke-21 amat penting bagi membentuk sahsiah murid yang mapan dalam pelbagai aspek seperti yang digariskan dalam Falsafah pendidikan Kebangsaan (FPK). Kajian korelasi ini dijalankan bagi mengkaji hubungan pembangunan penerapan nilai dalam pendidikan abad ke-21 dengan pembentukan sahsiah murid Sekolah Kurang Murid (SKM) luar bandar di Sabah. Kajian ini menggunakan reka bentuk bukan eksperimen dan kaedah kuantitatif. Seramai 209 orang guru SKM dijadikan sampel dalam kajian ini yang dipilih menggunakan kaedah pensamplean rawak mudah. Instrumen soal selidik pula digunakan bagi mengukur variabel-variabel kajian. Data mentah dianalisis menggunakan perisian Statistical Package for Social Sciences (SPSS) dengan menggunakan analisis statistik inferensi yang melibatkan ujian Korelasi Pearson. Hasil analisis menunjukkan terdapat hubungan positif signifikan yang kuat antara pembangunan penerapan nilai dalam pendidikan abad ke-21 dengan pembentukan sahsiah murid Sekolah Kurang Murid (SKM) luar bandar di Sabah (r=0.88, P<0.05). Dapatan kajian ini memberi maklumat berguna berkaitan dengan penerapan nilai dalam pendidikan abad ke-21 dan pembentukan sahsiah murid yang diharap dapat memberikan sumbangan ke arah memperkasakan sistem pendidikan kebangsaan
Methods of photoelectrode characterization with high spatial and temporal resolution
Materials and photoelectrode architectures that are highly efficient, extremely stable, and made from low cost materials are required for commercially viable photoelectrochemical (PEC) water-splitting technology. A key challenge is the heterogeneous nature of real-world materials, which often possess spatial variation in their crystal structure, morphology, and/or composition at the nano-, micro-, or macro-scale. Different structures and compositions can have vastly different properties and can therefore strongly influence the overall performance of the photoelectrode through complex structure–property relationships. A complete understanding of photoelectrode materials would also involve elucidation of processes such as carrier collection and electrochemical charge transfer that occur at very fast time scales. We present herein an overview of a broad suite of experimental and computational tools that can be used to define the structure–property relationships of photoelectrode materials at small dimensions and on fast time scales. A major focus is on in situ scanning-probe measurement (SPM) techniques that possess the ability to measure differences in optical, electronic, catalytic, and physical properties with nano- or micro-scale spatial resolution. In situ ultrafast spectroscopic techniques, used to probe carrier dynamics involved with processes such as carrier generation, recombination, and interfacial charge transport, are also discussed. Complementing all of these experimental techniques are computational atomistic modeling tools, which can be invaluable for interpreting experimental results, aiding in materials discovery, and interrogating PEC processes at length and time scales not currently accessible by experiment. In addition to reviewing the basic capabilities of these experimental and computational techniques, we highlight key opportunities and limitations of applying these tools for the development of PEC materials
SOLORZANO, ÁNGELES Y ROSARIO [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201
LRRK2 but not ATG16L1 is associated with Paneth cell defect in Japanese Crohn\u27s disease patients
BACKGROUND. Morphological patterns of Paneth cells are a prognostic biomarker in Western Crohn’s disease (CD) patients, and are associated with autophagy-associated ATG16L1 and NOD2 variants. We hypothesized that genetic determinants of Paneth cell phenotype in other ethnic CD cohorts are distinct but also involved in autophagy. METHODS. We performed a hypothesis-driven analysis of 56 single nucleotide polymorphisms (SNPs) associated with CD susceptibility or known to affect Paneth cell function in 110 Japanese CD patients who underwent ileal resection. We subsequently performed a genome-wide association analysis. Paneth cell phenotype was determined by defensin-5 immunofluorescence. Selected genotype–Paneth cell defect correlations were compared to a Western CD cohort (n = 164). RESULTS. The average percentage of abnormal Paneth cells in Japanese CD was similar to Western CD (P = 0.87), and abnormal Paneth cell phenotype was also associated with early recurrence (P = 0.013). In contrast to Western CD, ATG16L1 T300A was not associated with Paneth cell defect in Japanese CD (P = 0.20). Among the 56 selected SNPs, only LRRK2 M2397T showed significant association with Paneth cell defect (P = 3.62 × 10(–4)), whereas in the Western CD cohort it was not (P = 0.76). Pathway analysis of LRRK2 and other candidate genes with P less than 5 × 10(–4) showed connections with known CD susceptibility genes and links to autophagy and TNF-α networks. CONCLUSIONS. We found dichotomous effects of ATG16L1 and LRRK2 on Paneth cell defect between Japanese and Western CD. Genes affecting Paneth cell phenotype in Japanese CD were also associated with autophagy. Paneth cell phenotype also predicted prognosis in Japanese CD. FUNDING. Helmsley Charitable Trust, Doris Duke Foundation (grant 2014103), Japan Society for the Promotion of Science (KAKENHI grants JP15H04805 and JP15K15284), Crohn’s and Colitis Foundation grant 274415, NIH (grants 1R56DK095820, K01DK109081, and UL1 TR000448)
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