3,430 research outputs found
Tornadoes in a Microchannel
In non-dilute colloidal suspensions, gradients in particle volume fraction
result in gradients in electrical conductivity and permittivity. An externally
applied electric field couples with gradients in electrical conductivity and
permittivity and, under some conditions, can result in electric body forces
that drive the flow unstable forming vortices. The experiments are conducted in
square 200 micron PDMS microfluidic channels. Colloidal suspensions consisted
of 0.01 volume fraction of 2 or 3 micron diameter polystyrene particles in 0.1
mM Phosphate buffer and 409 mM sucrose to match particle-solution density. AC
electric fields at 20 Hz and strength of 430 to 600 V/cm were used. We present
a fluid dynamics video that shows the evolution of the particle aggregation and
formation of vortical flow. Upon application of the field particles aggregate
forming particle chains and three dimensional structures. These particles form
rotating bands where the axis of rotation varies with time and can collide with
other rotating bands forming increasingly larger bands. Some groups become
vortices with a stable axis of rotation. Other phenomena showed include counter
rotating vortices, colliding vortices, and non-rotating particle bands with
internal waves
Gapless Hamiltonians for the toric code using the PEPS formalism
We study Hamiltonians which have Kitaev's toric code as a ground state, and
show how to construct a Hamiltonian which shares the ground space of the toric
code, but which has gapless excitations with a continuous spectrum in the
thermodynamic limit. Our construction is based on the framework of Projected
Entangled Pair States (PEPS), and can be applied to a large class of
two-dimensional systems to obtain gapless "uncle Hamiltonians".Comment: 8 pages, 2 figure
Role of cross helicity in magnetohydrodynamic turbulence
Strong incompressible three-dimensional magnetohydrodynamic turbulence is
investigated by means of high resolution direct numerical simulations. The
simulations show that the configuration space is characterized by regions of
positive and negative cross-helicity, corresponding to highly aligned or
anti-aligned velocity and magnetic field fluctuations, even when the average
cross-helicity is zero. To elucidate the role of cross-helicity, the spectra
and structure of turbulence are obtained in imbalanced regions where
cross-helicity is non-zero. When averaged over regions of positive and negative
cross-helicity, the result is consistent with the simulations of balanced
turbulence. An analytical explanation for the obtained results is proposed.Comment: 4 pages, 4 figure
Chemical Abundances in Field Red Giants from High-Resolution H-Band Spectra using the APOGEE Spectral Linelist
High-resolution H-band spectra of five bright field K, M, and MS giants,
obtained from the archives of the Kitt Peak National Observatory (KPNO) Fourier
Transform Spectrometer (FTS), are analyzed to determine chemical abundances of
16 elements. The abundances were derived via spectrum synthesis using the
detailed linelist prepared for the SDSS III Apache Point Galactic Evolution
Experiment (APOGEE), which is a high-resolution near-infrared spectroscopic
survey to derive detailed chemical abundance distributions and precise radial
velocities for 100,000 red giants sampling all Galactic stellar populations.
Measured chemical abundances include the cosmochemically important isotopes
12C, 13C, 14N, and 16O, along with Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co,
Ni, and Cu. A comparison of the abundances derived here with published values
for these stars reveals consistent results to ~0.1 dex. The APOGEE spectral
region and linelist is, thus, well-suited for probing both Galactic chemical
evolution, as well as internal nucleosynthesis and mixing in populations of red
giants using high-resolution spectroscopy.Comment: Accepted for publication in The Astrophysical Journal. 42 pages, 12
figure
the SDSS-III APOGEE Spectral Line List for H-Band Spectroscopy
We present the H-band spectral line lists adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The APOGEE line lists comprise astrophysical, theoretical, and laboratory sources from the literature, as well as newly evaluated astrophysical oscillator strengths and damping parameters. We discuss the construction of the APOGEE line list, which is one of the critical inputs for the APOGEE Stellar Parameters and Chemical Abundances Pipeline, and present three different versions that have been used at various stages of the project. The methodology for the newly calculated astrophysical line lists is reviewed. The largest of these three line lists contains 134,457 molecular and atomic transitions. In addition to the format adopted to store the data, the line lists are available in MOOG, Synspec, and Turbospectrum formats. The limitations of the line lists along with guidance for its use on different spectral types are discussed. We also present a list of H-band spectral features that are either poorly represented or completely missing in our line list. This list is based on the average of a large number of spectral fit residuals for APOGEE observations spanning a wide range of stellar parameters.Alfred P. Sloan FoundationNational Science FoundationU.S. Department of Energy Office of ScienceJanos Bolyai Research Scholarship of the Hungarian Academy of SciencesSpanish Ministry of Economy and Competitiveness AYA-2011-27754, AYA-2014-58082-PRSF 14-50-00043McDonald Observator
Occupational Health and Safety Prevention Plan in Water Treatment Plant
The research was carried out at the "El Guarumo" drinking water plant located in Santa Ana, province of ManabĂ, Ecuador. The objective of the investigation was the proposal of a plan of prevention of occupational risks that allows the management of the labor risks in said plant. The main tools used were: survey, interview, checklist, LEST questionnaire for the diagnosis of the current situation in terms of working conditions, the risk identification matrix and the binary method of risk assessment. The main results obtained were the identification of the risks in their different categories, observing that the critical risk factors are related to the physical overexertion, the uncomfortable postures and the manual lifting of the load. Among the important risks are falling objects, skin contact with toxic substances and mental overwork, closely related to work pressures and job security? It was possible to carry out the proposal of preventive and corrective measures in order to properly manage the risks and contribute to the safety and health of the workers
Background
Placenta-derived exosomes continuously increase in maternal circulation over the first trimester of pregnanc
Automated Quantitative Analysis of a Mouse Model of Chronic Pulmonary Inflammation using Micro X-ray Computed Tomography
Micro-CT has emerged as an excellent tool for in-vivo imaging
of the lungs of small laboratory animals. Several studies have shown
that it can be used to assess the evolution of pulmonary lung diseases in
longitudinal studies. However, most of them rely on non-automatic tools
for image analysis, or are merely qualitative. In this article, we present
a longitudinal, quantitative study of a mouse model of silica-induced
pulmonary inflammation. To automatically assess disease progression,
we have devised and validated a lung segmentation method that combines
threshold-based segmentation, atlas-based segmentation and level
sets. Our volume measurements, based on the automatic segmentations,
point at a compensation mechanism which leads to an increase of the
healthy lung volume in response to the loss of functional tissue caused
by inflammation
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