5,449 research outputs found
The Effect of Spectral Composition on the Photochemical Production of Hydrogen Peroxide in Lake Water
Hydrogen peroxide was produced when samples of lake water were exposed to direct or filtered sunlight in which UV or UV(B+C) light was selectively removed. In all cases, the concentration of hydrogen peroxide increased linearly with time-integrated irradiance. While both visible and UV light can induce the formation of hydrogen peroxide, the contribution from the latter was disproportionately large as it was responsible for about two-thirds of the formation of hydrogen peroxide. Among the UV lights, the contributions from UV-A and UV-(B+C) light were 70% and 30% respectively. The contribution from UV-A light was equivalent to about one half of the total production of hydrogen peroxide. Thus, relative to its contribution to the total irradiance in the solar spectrum, UV-A light is the most efficient type of light for the formation of hydrogen peroxide in lake waters
ASYMPTOTIC PROPERTIES OF THE GENERALIZED SEMI-PARAMETRIC MLE IN LINEAR REGRESSION
Abstract: Consider the semi-parametric linear regression model, Y = β X + , with sample size n, where has an unknown cdf Fo. The semi-parametric MLE (SMLE) βn of β under this set-up, called the generalized SMLE or GSMLE, has neither been studied in the literature nor an algorithm for it. We begin with an algorithm for the GSMLE. It is then shown that if Fo has a discontinuity point, P{βn = β if n is large} = 1. Simulation suggests that under some discontinuous distributions, βn = β even for n = 50. In contrast the least squares estimator (LSE),βn, satisfies P{βn = β i.o.} = 1. We demonstrate via a real discontinuous data example that the GSMLE can be better than the LSE in applications. Properties of the GSMLE in the continuous case are also mentioned
Viscosity and the Soft Ridge at RHIC
Correlation studies exhibit a ridge-like feature in rapidity and azimuthal
angle, with and without a jet trigger. We ask whether the feature in
untriggered correlations can be a consequence of transverse flow and viscous
diffusion.Comment: Proc. Quark Matter 2008, Jaipur, Indi
Series Expansion Calculation of Persistence Exponents
We consider an arbitrary Gaussian Stationary Process X(T) with known
correlator C(T), sampled at discrete times T_n = n \Delta T. The probability
that (n+1) consecutive values of X have the same sign decays as P_n \sim
\exp(-\theta_D T_n). We calculate the discrete persistence exponent \theta_D as
a series expansion in the correlator C(\Delta T) up to 14th order, and
extrapolate to \Delta T = 0 using constrained Pad\'e approximants to obtain the
continuum persistence exponent \theta. For the diffusion equation our results
are in exceptionally good agreement with recent numerical estimates.Comment: 5 pages; 5 page appendix containing series coefficient
Cosmological Lepton Asymmetry, Primordial Nucleosynthesis, and Sterile Neutrinos
We study post weak decoupling coherent active-sterile and active-active
matter-enhanced neutrino flavor transformation in the early universe. We show
that flavor conversion efficiency at Mikheyev-Smirnov-Wolfenstein resonances is
likely to be high (adiabatic evolution) for relevant neutrino parameters and
energies. However, we point out that these resonances cannot sweep smoothly and
continuously with the expansion of the universe. We show how neutrino flavor
conversion in this way can leave both the active and sterile neutrinos with
non-thermal energy spectra, and how, in turn, these distorted energy spectra
can affect the neutron-to-proton ratio, primordial nucleosynthesis, and
cosmological mass/closure constraints on sterile neutrinos. We demonstrate that
the existence of a light sterile neutrino which mixes with active neutrinos can
change fundamentally the relationship between the cosmological lepton numbers
and the primordial nucleosynthesis He-4 yield.Comment: 24 pages, 11 figures; v3: matches PRD versio
Three routes to the exact asymptotics for the one-dimensional quantum walk
We demonstrate an alternative method for calculating the asymptotic behaviour
of the discrete one-coin quantum walk on the infinite line, via the Jacobi
polynomials that arise in the path integral representation. This is
significantly easier to use than the Darboux method. It also provides a single
integral representation for the wavefunction that works over the full range of
positions, including throughout the transitional range where the behaviour
changes from oscillatory to exponential. Previous analyses of this system have
run into difficulties in the transitional range, because the approximations on
which they were based break down here. The fact that there are two different
kinds of approach to this problem (Path Integral vs. Schr\"{o}dinger wave
mechanics) is ultimately a manifestation of the equivalence between the
path-integral formulation of quantum mechanics and the original formulation
developed in the 1920s. We discuss how and why our approach is related to the
two methods that have already been used to analyse these systems.Comment: 25 pages, AMS preprint format, 4 figures as encapsulated postscript.
Replaced because there were sign errors in equations (80) & (85) and Lemma 2
of the journal version (v3
p150 ADAR1 isoform involved in maintenance of HeLa cell proliferation
BACKGROUND: RNA-specific adenosine deaminase ADAR1 is ubiquitously expressed in a variety of mammalian cells and tissues. Although its physiological importance in non-nervous tissues has been confirmed by analysis of null mutation phenotypes, few endogenous editing substrates have been identified in numerous peripheral tissues and biological function of ADAR1 has not been fully understood. METHODS: A conditional site-specific, ribozyme-based gene knock-down strategy was utilized to study the function of full-length isoform of ADAR1 (p150 protein) in HeLa cell. Double-stable HeLa cell lines were developed by transfecting HeLa Tet-On cells with a pTRE-derived plasmid that can express a hammerhead ribozyme against mRNA of p150 ADAR1 isoform under induction condition. Semi-quantitative RT-PCR and Western blotting were performed to measure the expression of p150 in selected cell clones. Cell proliferation was evaluated by means of MTT assay and growth curve analysis. Cellular morphological changes were observed under light microscope. Flow Cytometry was used for cell cycle analysis. Growth rate of cell transplants in BALB/c nude mice was also investigated. RESULTS: Both HeLa cell proliferation in vitro and the growth rate of transplanted HeLa cell-derived tumors in nude mice in vivo were significantly inhibited due to reduced expression of ADAR1 p150. Additionally, cell cycle analysis showed that cell progression from G1 phase to S phase was retarded in the ADAR1 p150 suppressed cells. CONCLUSION: Our results suggest that normal expression and functioning of p150 ADAR1 is essential for the maintenance of proper cell growth. The mechanisms underlying ADAR1's action might include both editing of currently unknown double-stranded RNAs and interacting with other cellular dsRNA-related processes
Phase-ordering dynamics of the Gay-Berne nematic liquid crystal
Phase-ordering dynamics in nematic liquid crystals has been the subject of
much active investigation in recent years in theory, experiments and
simulations. With a rapid quench from the isotropic to nematic phase a large
number of topological defects are formed and dominate the subsequent
equilibration process. We present here the results of a molecular dynamics
simulation of the Gay-Berne model of liquid crystals after such a quench in a
system with 65536 molecules. Twist disclination lines as well as type-1 lines
and monopoles were observed. Evidence of dynamical scaling was found in the
behavior of the spatial correlation function and the density of disclination
lines. However, the behavior of the structure factor provides a more sensitive
measure of scaling, and we observed a crossover from a defect dominated regime
at small values of the wavevector to a thermal fluctuation dominated regime at
large wavevector.Comment: 18 pages, 16 figures, animations available at
http://www.physics.brown.edu/Users/faculty/pelcovits/lc/coarsening.htm
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