347 research outputs found
Junior Recital:Dakota M. Pawlicki, Tuba
Kemp Recital Hall Tuesday Evening April 17, 2007 8:00p.m
Primary microRNA transcript retention at sites of transcription leads to enhanced microRNA production
MicroRNAs (miRNAs) are noncoding RNAs with important roles in regulating gene expression. In studying the earliest nuclear steps of miRNA biogenesis, we observe that primary miRNA (pri-miRNA) transcripts retained at transcription sites due to the deletion of 3′-end processing signals are converted more efficiently into precursor miRNAs (pre-miRNAs) than pri-miRNAs that are cleaved, polyadenylated, and released. Flanking exons, which also increase retention at transcription sites, likewise contribute to increased levels of intronic pri-miRNAs. Consistently, efficiently processed endogenous pri-miRNAs are enriched in chromatin-associated nuclear fractions. In contrast, pri-miRNAs that accumulate to high nuclear levels after cleavage and polyadenylation because of the presence of a viral RNA element (the ENE of the Kaposi's sarcoma–associated herpes virus polyadenylated nuclear RNA) are not efficiently processed to precursor or mature miRNAs. Exogenous pri-miRNAs unexpectedly localize to nuclear foci containing splicing factor SC35; yet these foci are unlikely to represent sites of miRNA transcription or processing. Together, our results suggest that pri-miRNA processing is enhanced by coupling to transcription
Exact relations between damage spreading and thermodynamic functions for the N-color Ashkin-Teller model
Exact results are derived relating quantities computable by the so-called
damage spreading method and thermodynamic functions for the N-color
Ashkin-Teller model. The results are valid for any ergodic dynamics. Since we
restrict our analysis to the ferromagnetic case the results are also valid for
any translational invariant lattice. The derived relations should be used in
order to determine numerically the N-color Ashkin-Teller critical exponents
with better accuracy and less computational efforts than standard Monte Carlo
simulations.Comment: 6 pages, to be published in JSTAT (Journal of Statistical Mechanics:
Theory and Experiment). The results of a computer simulation were included
for N=3 as an example on how to use the analytical relations derived in the
paper as a guide to obtain the critical temperature and critical exponent
Correlated Electrical and Chemical Nanoscale Properties in Potassium-Passivated, Triple-Cation Perovskite Solar Cells
Perovskite semiconductors are an exciting class of materials due to their promising performance outputs in photovoltaic devices. To boost their efficiency further, researchers introduce additives during sample synthesis, such as KI. However, it is not well understood how KI changes the material and, often, leaves precipitants. To fully resolve the role of KI, multiple microscopy techniques are applied and the electrical and chemical behavior of a Reference (untreated) and a KI‐treated perovskite are compared. Upon correlation between electrical and chemical nanoimaging techniques, it is discovered that these local properties are linked to the macroscopic voltage enhancement of the KI‐treated perovskite. The heterogeneity revealed in both the local electrical and chemical responses indicates that the additive partially migrates to the surface, yet surprisingly does not deteriorate the performance locally, rather, the voltage response homogeneously increases. The research presented within provides a diagnostic methodology, which connects the nanoscale electrical and chemical properties of materials, relevant to other perovskites, including multication and Pb‐free alternatives
Correlated Electrical and Chemical Nanoscale Properties in Potassium-Passivated, Triple-Cation Perovskite Solar Cells
Perovskite semiconductors are an exciting class of materials due to their
promising performance outputs in optoelectronic devices. To boost their
efficiency further, researchers introduce additives during sample synthesis, such as KI. However, it is not well understood how KI changes the material
and, often, leaves precipitants. To fully resolve the role of KI, a multiple
microscopy techniques is applied and the electrical and chemical behavior of a Reference (untreated) and a KI-treated perovskite are compared. Upon correlation between electrical and chemical nanoimaging techniques, it is discovered that these local properties are linked to the macroscopic voltage enhancement of the KI-treated perovskite. The heterogeneity revealed in both the local electrical and chemical responses indicates that the additive partially migrates to the surface, yet surprisingly; does not deteriorate the performance locally, rather, the voltage response homogeneously increases. The research presented within provides a diagnostic methodology, which connects the nanoscale electrical and chemical properties of materials, relevant to other perovskites, including multication and Pb-free alternatives.University of Maryland All-S.T.A.R. Fellowship
Hulka Energy Research Fellowship
National Science Foundation
US Department of Energy
The Royal Society
Office of Naval Researc
A Study in Depth of f0(1370)
Claims have been made that f0(1370) does not exist. The five primary sets of
data requiring its existence are refitted. Major dispersive effects due to the
opening of the 4pi threshold are included for the first time; the sigma -> 4pi
amplitude plays a strong role. Crystal Barrel data on pbar-p -> 3pizero at rest
require f0(1370) signals of at least 32 and 33 standard deviations in 1S0 and
3P1 annihilation respectively. Furthermore, they agree within 5 MeV for mass
and width. Data on pbar-p -> eta-eta-pizero agree and require at least a 19
standard deviation contribution. This alone is sufficient to demonstrate the
existence of f0(1370). BES II data for J/Psi -> phi-pi-pi contain a visible
f0(1370) signal > 8 standard devations. In all cases, a resonant phase
variation is required. The possibility of a second pole in the sigma amplitude
due to the opening of the 4pi channel is excluded. Cern-Munich data for pi-pi
elastic scattering are fitted well with the inclusion of some mixing between
sigma, f0(1370) and f0(1500). The pi-pi widths for f2(1565), rho3(1690),
rho3(1990) and f4(2040) are determined.Comment: 25 pages, 22 figures. Typos corrected in Eqs 2 and 7. Introduction
rewritten. Conclusions unchange
Scalar meson production in nucleon-nucleon collisions near threshold
We establish the model-independent spin structure of the matrix elements for
the near-threshold scalar meson production in and -collisions, when
the final particles are emitted in S-state. Polarization phenomena are derived
in a general form. The properties of the channel dynamics, which is based
on different meson exchanges, are studied in terms of the channel
parametrization of the matrix element. The prediction of a 'realistic' model,
based on -exchanges are also presented.Comment: 16 pages 6 figure
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