701 research outputs found
Heat transfer in a plane incompressible laminar jet
Partial differential equation for heat transfer in plane incompressible laminar jet is reduced by similarity transformation to ordinary differential equatio
Estimation of PM Machine Efficiency Maps from Limited Data
This article investigates the accuracy of the estimation of efficiency maps for permanent magnet (PM) machines using the stator resistance, d- and q-axis flux-linkages versus the corresponding axis current and the iron loss versus the speed characteristic. The ultimate goal is to apply this approach to the experimental measurements, but this article performs initial investigation using only the finite-element (FE) data. Detailed FE data for 50-kW surface PM (SPM) and interior PM (IPM) machines are used to determine the 'actual' or exact efficiency map and, hence, the accuracy of using approximations. This article examines the effect on the torque-speed capability curve when ignoring cross-saturation effects. It also examines the modeling of the variation of iron losses as a function of load in the constant torque and power regions. A novel approach based on scaling the no-load (NL) losses as a function of load is proposed and shown to give promising results. FE results from two other machines are also provided, which show good correspondence
The role of microarthropods in emerging models of soil organic matter
A new understanding of soil organic matter (SOM) formation and stabilization has emerged over the past decade, highlighting the importance of microbial activity, mineral association of organic matter and aggregate occlusion of organic matter to SOM persistence. To date, the contribution of microarthropods to litter decomposition and SOM formation processes has not received due consideration and theoretical and empirical models should be modified to include how these organisms impact SOM protection. Here, we highlight the biological, chemical and physical mechanisms by which microarthropods influence SOM formation both directly and indirectly. Although more data is needed to quantify the impacts of different microarthropods on SOM dynamics, we highlight areas where inclusion of microarthropods in emerging models of SOM formation could reduce model uncertainties
Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest
Measuring in situ soil fluxes of carbon dioxide (CO2), methane
(CH4), and nitrous oxide (N2O) continuously at high
frequency requires appropriate technology. We tested the combination of a
commercial automated soil CO2 flux chamber system (LI-8100A) with a
CH4 and N2O analyzer (Picarro G2308) in a tropical
rainforest for 4 months. A chamber closure time of 2 min was sufficient for
a reliable estimation of CO2 and CH4 fluxes (100 %
and 98.5 % of fluxes were above minimum detectable flux – MDF,
respectively). This closure time was generally not suitable for a reliable
estimation of the low N2O fluxes in this ecosystem but was
sufficient for detecting rare major peak events. A closure time of 25 min
was more appropriate for reliable estimation of most N2O fluxes
(85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1). Our study highlights the importance of
adjusted closure time for each gas.</p
Relativistic effects and two-body currents in using out-of-plane detection
Measurements of the reaction were performed
using an 800-MeV polarized electron beam at the MIT-Bates Linear Accelerator
and with the out-of-plane magnetic spectrometers (OOPS). The
longitudinal-transverse, and , and the
transverse-transverse, , interference responses at a missing momentum
of 210 MeV/c were simultaneously extracted in the dip region at Q=0.15
(GeV/c). On comparison to models of deuteron electrodisintegration, the
data clearly reveal strong effects of relativity and final-state interactions,
and the importance of the two-body meson-exchange currents and isobar
configurations. We demonstrate that these effects can be disentangled and
studied by extracting the interference response functions using the novel
out-of-plane technique.Comment: 4 pages, 4 figures, and submitted to PRL for publicatio
Measurement of the Transverse-Longitudinal Cross Sections in the p (e,e'p)pi0 Reaction in the Delta Region
Accurate measurements of the p(e,e?p)pi0 reaction were performed at
Q^2=0.127(GeV/c)^2 in the Delta resonance energy region. The experiments at the
MIT-Bates Linear Accelerator used an 820 MeV polarized electron beam with the
out of plane magnetic spectrometer system (OOPS). In this paper we report the
first simultaneous determination of both the TL and TL? (``fifth" or polarized)
cross sections at low Q^{2} where the pion cloud contribution dominates the
quadrupole amplitudes (E2 and C2). The real and imaginary parts of the
transverse-longitudinal cross section provide both a sensitive determination of
the Coulomb quadrupole amplitude and a test of reaction calculations.
Comparisons with model calculations are presented. The empirical MAID
calculation gives the best overall agreement with this accurate data. The
parameters of this model for the values of the resonant multipoles are
|M_{1+}(I=3/2)|= (40.9 \pm 0.3)10^{-3}/m_pi, CMR= C2/M1= -6.5 \pm 0.3%,
EMR=E2/M1=-2.2 \pm 0.9%, where the errors are due to the experimental
uncertainties.Comment: 10 pages, 3 figures, minor corrections and addition
Childhood socioeconomic position and objectively measured physical capability levels in adulthood: a systematic review and meta-analysis
<p><b>Background:</b> Grip strength, walking speed, chair rising and standing balance time are objective measures of physical capability that characterise current health and predict survival in older populations. Socioeconomic position (SEP) in childhood may influence the peak level of physical capability achieved in early adulthood, thereby affecting levels in later adulthood. We have undertaken a systematic review with meta-analyses to test the hypothesis that adverse childhood SEP is associated with lower levels of objectively measured physical capability in adulthood.</p>
<p><b>Methods and Findings:</b> Relevant studies published by May 2010 were identified through literature searches using EMBASE and MEDLINE. Unpublished results were obtained from study investigators. Results were provided by all study investigators in a standard format and pooled using random-effects meta-analyses. 19 studies were included in the review. Total sample sizes in meta-analyses ranged from N = 17,215 for chair rise time to N = 1,061,855 for grip strength. Although heterogeneity was detected, there was consistent evidence in age adjusted models that lower childhood SEP was associated with modest reductions in physical capability levels in adulthood: comparing the lowest with the highest childhood SEP there was a reduction in grip strength of 0.13 standard deviations (95% CI: 0.06, 0.21), a reduction in mean walking speed of 0.07 m/s (0.05, 0.10), an increase in mean chair rise time of 6% (4%, 8%) and an odds ratio of an inability to balance for 5s of 1.26 (1.02, 1.55). Adjustment for the potential mediating factors, adult SEP and body size attenuated associations greatly. However, despite this attenuation, for walking speed and chair rise time, there was still evidence of moderate associations.</p>
<p><b>Conclusions:</b> Policies targeting socioeconomic inequalities in childhood may have additional benefits in promoting the maintenance of independence in later life.</p>
Single-molecule experiments in biological physics: methods and applications
I review single-molecule experiments (SME) in biological physics. Recent
technological developments have provided the tools to design and build
scientific instruments of high enough sensitivity and precision to manipulate
and visualize individual molecules and measure microscopic forces. Using SME it
is possible to: manipulate molecules one at a time and measure distributions
describing molecular properties; characterize the kinetics of biomolecular
reactions and; detect molecular intermediates. SME provide the additional
information about thermodynamics and kinetics of biomolecular processes. This
complements information obtained in traditional bulk assays. In SME it is also
possible to measure small energies and detect large Brownian deviations in
biomolecular reactions, thereby offering new methods and systems to scrutinize
the basic foundations of statistical mechanics. This review is written at a
very introductory level emphasizing the importance of SME to scientists
interested in knowing the common playground of ideas and the interdisciplinary
topics accessible by these techniques. The review discusses SME from an
experimental perspective, first exposing the most common experimental
methodologies and later presenting various molecular systems where such
techniques have been applied. I briefly discuss experimental techniques such as
atomic-force microscopy (AFM), laser optical tweezers (LOT), magnetic tweezers
(MT), biomembrane force probe (BFP) and single-molecule fluorescence (SMF). I
then present several applications of SME to the study of nucleic acids (DNA,
RNA and DNA condensation), proteins (protein-protein interactions, protein
folding and molecular motors). Finally, I discuss applications of SME to the
study of the nonequilibrium thermodynamics of small systems and the
experimental verification of fluctuation theorems. I conclude with a discussion
of open questions and future perspectives.Comment: Latex, 60 pages, 12 figures, Topical Review for J. Phys. C (Cond.
Matt
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