3,898 research outputs found
Humidity contribution to C_n^2 over a 600m pathlength in a tropical marine environment
We present new optical turbulence structure parameter measurements, C_n^2,
over sea water between La Parguera and Magueyes Island (17.6N 67W) on the
southwest coast of Puerto Rico. The 600 meter horizontal paths were located
approximately 1.5 m and 10 m above sea level. No data of this type has ever
been made available in the literature. Based on the data, we show that the
C_n^2 measurements are about 7 times less compared to equivalent land data.
This strong evidence reinforces our previous argument that humidity must be
accounted for to better ascertain the near surface atmospheric turbulence
effects, which current visible / near infrared C_n^2 bulk models fail to do. We
also explore the generalised fractal dimension of this littoral data and
compare it to our reference land data. We find cases that exhibit monofractal
characteristics, that is to say, the effect of rising temperatures during the
daylight hours upon turbulence are counterbalanced by humidity, leading to a
single characteristic scale for the measurements. In other words, significant
moisture changes in the measurement volume cancels optical turbulence increases
due to temperature rises. Figures available as JPG only.Comment: 7 pages, 4 figures, 1 table, SPIE Photonics West 2007, paper 6457B-2
Applying the Hilbert--Huang Decomposition to Horizontal Light Propagation C_n^2 data
The Hilbert Huang Transform is a new technique for the analysis of
non--stationary signals. It comprises two distinct parts: Empirical Mode
Decomposition (EMD) and the Hilbert Transform of each of the modes found from
the first step to produce a Hilbert Spectrum. The EMD is an adaptive
decomposition of the data, which results in the extraction of Intrinsic Mode
Functions (IMFs). We discuss the application of the EMD to the calibration of
two optical scintillometers that have been used to measure C_n^2 over
horizontal paths on a building rooftop, and discuss the advantage of using the
Marginal Hilbert Spectrum over the traditional Fourier Power Spectrum.Comment: 9 pages, 11 figures, proc. SPIE 626
Vibrational Excitations in Weakly Coupled Single-Molecule Junctions: A Computational Analysis
In bulk systems, molecules are routinely identified by their vibrational
spectrum using Raman or infrared spectroscopy. In recent years, vibrational
excitation lines have been observed in low-temperature conductance measurements
on single molecule junctions and they can provide a similar means of
identification. We present a method to efficiently calculate these excitation
lines in weakly coupled, gateable single-molecule junctions, using a
combination of ab initio density functional theory and rate equations. Our
method takes transitions from excited to excited vibrational state into account
by evaluating the Franck-Condon factors for an arbitrary number of vibrational
quanta, and is therefore able to predict qualitatively different behaviour from
calculations limited to transitions from ground state to excited vibrational
state. We find that the vibrational spectrum is sensitive to the molecular
contact geometry and the charge state, and that it is generally necessary to
take more than one vibrational quantum into account. Quantitative comparison to
previously reported measurements on pi-conjugated molecules reveals that our
method is able to characterize the vibrational excitations and can be used to
identify single molecules in a junction. The method is computationally feasible
on commodity hardware.Comment: 9 pages, 7 figure
A Characterization of Scale Invariant Responses in Enzymatic Networks
An ubiquitous property of biological sensory systems is adaptation: a step
increase in stimulus triggers an initial change in a biochemical or
physiological response, followed by a more gradual relaxation toward a basal,
pre-stimulus level. Adaptation helps maintain essential variables within
acceptable bounds and allows organisms to readjust themselves to an optimum and
non-saturating sensitivity range when faced with a prolonged change in their
environment. Recently, it was shown theoretically and experimentally that many
adapting systems, both at the organism and single-cell level, enjoy a
remarkable additional feature: scale invariance, meaning that the initial,
transient behavior remains (approximately) the same even when the background
signal level is scaled. In this work, we set out to investigate under what
conditions a broadly used model of biochemical enzymatic networks will exhibit
scale-invariant behavior. An exhaustive computational study led us to discover
a new property of surprising simplicity and generality, uniform linearizations
with fast output (ULFO), whose validity we show is both necessary and
sufficient for scale invariance of enzymatic networks. Based on this study, we
go on to develop a mathematical explanation of how ULFO results in scale
invariance. Our work provides a surprisingly consistent, simple, and general
framework for understanding this phenomenon, and results in concrete
experimental predictions
Determinants of whistleblowing intention : evidence from the South Korean government
In 2001, the South Korean government passed the Anti-Corruption Act, which provides whistleblower protection in the public sector. The system of protections and rewards was strengthened in 2011 by the Act on the Protection of Public Interest Whistleblowers. Although these laws ensure immunity—and even financial incentives—for whistleblowers, whistleblowing is still not a straightforward task. Based on a survey of 5706 public officials in central government, this study examines how a range of factors influence whistleblowing intention: attitude; knowledge; colleague support; organizational support; and protection against retaliation. A number of demographic variables, relating to gender; marital status; length of tenure; duty; and position type are used as controls. The results of the ordered probit regression analysis show all of the independent variables to have a significant positive effect on whistleblowing intention. However, colleague support and organizational support have the biggest effects, while perceived protection against retaliation has the smallest. This suggests that there is a need for future government efforts to build upon the available legal protections by focusing on creating a supportive culture among colleagues and in the organization more generally
Two-pion correlations in Au+Au collisions at 10.8 GeV/c per nucleon
Two-particle correlation functions for positive and negative pions have been
measured in Au+Au collisions at 10.8~GeV/c per nucleon. The data were analyzed
using one- and three-dimensional correlation functions. From the results of the
three-dimensional fit the phase space density of pions was calculated. It is
consistent with local thermal equilibrium.Comment: 5 pages RevTeX (including 3 Figures
Directed flow of antiprotons in Au+Au collisions at AGS
Directed flow of antiprotons is studied in Au+Au collisions at a beam
momentum of 11.5A GeV/c. It is shown that antiproton directed flow is
anti-correlated to proton flow. The measured transverse momentum dependence of
the antiproton flow is compared with predictions of the RQMD event generator.Comment: 16 pages, 6 figure
Proton and Pion Production in Au+Au Collisions at 10.8A GeV/c
We present proton and pion tranverse momentum spectra and rapidity
distributions for Au+Au collisions at 10.8A GeV/c. The proton spectra exhibit
collective transverse flow effects. Evidence of the influence of the Coulomb
interaction from the fireball is found in the pion transverse momentum spectra.
The data are compared with the predictions of the RQMD event generator.Comment: plain tex (revtex), 24 pages Submitted to Phys. Rev.
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