5,519 research outputs found
The Rise of a Middle Class and the Changing Concept of Equity in Indonesia: An Interpretation
Page range: 71-9
Carbon monoxide pollution experiment
The experiment is designed to obtain data for the investigation of mechanisms by which CO is removed from the earth's atmosphere. The approach uses an orbiting platform to remotely map global CO concentrations and determine vertical CO profiles using a correlation interferometer measurement technique. The instrument is capable of measuring CO over the range of expected atmospheric burdens and of measuring trace atmospheric constituents
Development of a breadboard model correlation interferometer for the carbon monoxide pollution experiment
The breadboard model of the correlation interferometer for the Carbon Monoxide Pollution Experiment has been designed, fabricated, and tested. Laboratory, long-path, and atmospheric tests which were performed show the technique to be a feasible method for obtaining a global carbon monoxide map and a vertical carbon monoxide profile and similar information is readily obtainable for methane as well. In addition, the technique is readily applicable to other trace gases by minor instrumental changes. As shown by the results and the conclusions, it has been determined that CO and CH4 data can be obtained with an accuracy of 10% using this technique on the spectral region around 2.3 microns
A systematic review of associations between environmental exposures and development of asthma in children aged up to 9 years
Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.Peer reviewedPublisher PD
Application of quasi-Monte Carlo methods to PDEs with random coefficients -- an overview and tutorial
This article provides a high-level overview of some recent works on the
application of quasi-Monte Carlo (QMC) methods to PDEs with random
coefficients. It is based on an in-depth survey of a similar title by the same
authors, with an accompanying software package which is also briefly discussed
here. Embedded in this article is a step-by-step tutorial of the required
analysis for the setting known as the uniform case with first order QMC rules.
The aim of this article is to provide an easy entry point for QMC experts
wanting to start research in this direction and for PDE analysts and
practitioners wanting to tap into contemporary QMC theory and methods.Comment: arXiv admin note: text overlap with arXiv:1606.0661
Do individual differences in need strength moderate the relations between basic psychological need satisfaction and organizational citizenship behavior?
An important theoretical debate in the literature on psychological needs concerns the potential moderating role of individuals’ need strength in the effects of basic psychological need satisfaction. The present study adds to the relatively small literature with inconsistent findings by examining whether the relations between work-related basic psychological need satisfaction (autonomy, competence, and relatedness) and organizational citizenship behavior (i.e., constructive voluntary job performance) are enhanced when employees’ work-specific explicit need strength increases. Survey data from two samples of employees in the United States (N = 353; MAge = 38.13) and in the Netherlands (N = 298; MAge = 44.57) consistently showed that across the need domains, need satisfaction was positively associated with organizational citizenship behavior through work engagement. However, we only found minor evidence for a moderating role of need strength. These findings largely endorse core self-determination theory assertions, as they underscore the relevance of employees’ psychological need satisfaction rather than fit between high psychological need satisfaction and high need strength in the workplace
Laser frequency stabilization to a single ion
A fundamental limit to the stability of a single-ion optical frequency
standard is set by quantum noise in the measurement of the internal state of
the ion. We discuss how the interrogation sequence and the processing of the
atomic resonance signal can be optimized in order to obtain the highest
possible stability under realistic experimental conditions. A servo algorithm
is presented that stabilizes a laser frequency to the single-ion signal and
that eliminates errors due to laser frequency drift. Numerical simulations of
the servo characteristics are compared to experimental data from a frequency
comparison of two single-ion standards based on a transition at 688 THz in
171Yb+. Experimentally, an instability sigma_y(100 s)=9*10^{-16} is obtained in
the frequency difference between both standards.Comment: 15 pages, 5 figures, submitted to J. Phys.
Kinetic Characterization and X-ray Structure of a Mutant of Haloalkane Dehalogenase with Higher Catalytic Activity and Modified Substrate Range
Conversion of halogenated aliphatics by haloalkane dehalogenase proceeds via the formation of a covalent alkyl-enzyme intermediate which is subsequently hydrolyzed by water. In the wild type enzyme, the slowest step for both 1,2-dichloroethane and 1,2-dibromoethane conversion is a unimolecular enzyme isomerization preceding rapid halide dissociation. Phenylalanine 172 is located in a helix-loop-helix structure that covers the active site cavity of the enzyme, interacts with the Clβ of 1,2-dichloroethane during catalysis, and could be involved in stabilization of this helix-loop-helix region of the cap domain of the enzyme. To obtain more information about the role of this residue in dehalogenase function, we performed a mutational analysis of position 172 and studied the kinetics and X-ray structure of the Phe172Trp enzyme. The Phe172Trp mutant had a 10-fold higher kcat/Km for 1-chlorohexane and a 2-fold higher kcat for 1,2-dibromoethane than the wild-type enzyme. The X-ray structure of the Phe172Trp enzyme showed a local conformational change in the helix-loop-helix region that covers the active site. This could explain the elevated activity for 1-chlorohexane of the Phe172Trp enzyme, since it allows this large substrate to bind more easily in the active site cavity. Pre-steady-state kinetic analysis showed that the increase in kcat found for 1,2-dibromoethane conversion could be attributed to an increase in the rate of an enzyme isomerization step that preceeds halide release. The observed conformational difference between the helix-loop-helix structures of the wild-type enzyme and the faster mutant suggests that the isomerization required for halide release could be a conformational change that takes place in this region of the cap domain of the dehalogenase. It is proposed that Phe172 is involved in stabilization of the helix-loop-helix structure that covers the active site of the enzyme and creates a rigid hydrophobic cavity for small apolar halogenated alkanes.
Hyper-Ramsey Spectroscopy of Optical Clock Transitions
We present non-standard optical Ramsey schemes that use pulses individually
tailored in duration, phase, and frequency to cancel spurious frequency shifts
related to the excitation itself. In particular, the field shifts and their
uncertainties of Ramsey fringes can be radically suppressed (by 2-4 orders of
magnitude) in comparison with the usual Ramsey method (using two equal pulses)
as well as with single-pulse Rabi spectroscopy. Atom interferometers and
optical clocks based on two-photon transitions, heavily forbidden transitions,
or magnetically induced spectroscopy could significantly benefit from this
method. In the latter case these frequency shifts can be suppressed
considerably below a fractional level of 10^{-17}. Moreover, our approach opens
the door for the high-precision optical clocks based on direct frequency comb
spectroscopy.Comment: 5 pages, 4 figure
Versatile compact atomic source for high resolution dual atom interferometry
We present a compact Rb atomic source for high precision dual atom
interferometers. The source is based on a double-stage magneto-optical trap
(MOT) design, consisting of a 2-dimensional (2D)-MOT for efficient loading of a
3D-MOT. The accumulated atoms are precisely launched in a horizontal moving
molasses. Our setup generates a high atomic flux ( atoms/s) with
precise and flexibly tunable atomic trajectories as required for high
resolution Sagnac atom interferometry. We characterize the performance of the
source with respect to the relevant parameters of the launched atoms, i.e.
temperature, absolute velocity and pointing, by utilizing time-of-flight
techniques and velocity selective Raman transitions.Comment: uses revtex4, 9 pages, 12 figures, submitted to Phys. Rev.
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