24,640 research outputs found
High frequency ultrasonic characterization of sintered SiC
High frequency (60 to 160 MHz) ultrasonic nondestructive evaluation was used to characterize variations in density and microstructural constituents of sintered SiC bars. Ultrasonic characterization methods included longitudinal velocity, reflection coefficient, and precise attenuation measurements. The SiC bars were tailored to provide bulk densities ranging from 90 to 98 percent of theoretical, average grain sizes ranging from 3.0 to 12.0 microns, and average pore sizes ranging from 1.5 to 4.0 microns. Velocity correlated with specimen bulk density irrespective of specimen average grain size, average pore size, and average pore orientation. Attenuation coefficient was found to be sensitive to both density and average pore size variations, but was not affected by large differences in average grain size
Trajectory computational techniques emphasizing existence, uniqueness, and construction of solutions to boundary problems for ordinary differential equations Final report
Trajectory computational techniques emphasizing existence, uniqueness, and construction of solutions to boundary problems for ordinary differential equation
Quantum theory of electric polarization nonlinearity in metal nanofilms
We develop a quantum theory of electron confinement in metal nanofilms. The
theory is used to compute the nonlinear response of the film to a static or
low-frequency external electric field and to investigate the role of boundary
conditions imposed on the metal surface. We find that the sign and magnitude of
the nonlinear polarizability depends dramatically on the type of boundary
condition used.Comment: Accepted to PRB in this for
Heat exchange mediated by a quantum system
We consider heat transfer between two thermal reservoirs mediated by a
quantum system using the generalized quantum Langevin equation. The thermal
reservoirs are treated as ensembles of oscillators within the framework of the
Drude-Ullersma model. General expressions for the heat current and thermal
conductance are obtained for arbitrary coupling strength between the reservoirs
and the mediator and for different temperature regimes. As an application of
these results we discuss the origin of Fourier's law in a chain of large, but
finite subsystems coupled to each other by the quantum mediators. We also
address a question of anomalously large heat current between the STM tip and
substrate found in a recent experiment. The question of minimum thermal
conductivity is revisited in the framework of scaling theory as a potential
application of the developed approach.Comment: 16 pages, 6 figure
Bose-Einstein Condensation in the Relativistic Ideal Bose Gas
The Bose-Einstein condensation (BEC) critical temperature in a relativistic
ideal Bose gas of identical bosons, with and without the antibosons expected to
be pair-produced abundantly at sufficiently hot temperatures, is exactly
calculated for all boson number-densities, all boson point rest masses, and all
temperatures. The Helmholtz free energy at the critical BEC temperature is
found to be lower, thus implying that the omission of antibosons always leads
to the computation of a metastable state.Comment: 10 pages, 4 figure
Bond-Propagation Algorithm for Thermodynamic Functions in General 2D Ising Models
Recently, we developed and implemented the bond propagation algorithm for
calculating the partition function and correlation functions of random bond
Ising models in two dimensions. The algorithm is the fastest available for
calculating these quantities near the percolation threshold. In this paper, we
show how to extend the bond propagation algorithm to directly calculate
thermodynamic functions by applying the algorithm to derivatives of the
partition function, and we derive explicit expressions for this transformation.
We also discuss variations of the original bond propagation procedure within
the larger context of Y-Delta-Y-reducibility and discuss the relation of this
class of algorithm to other algorithms developed for Ising systems. We conclude
with a discussion on the outlook for applying similar algorithms to other
models.Comment: 12 pages, 10 figures; submitte
The lack of variability of the iron line in MCG-6-30-15: general relativistic effects
The spectrum and variability of the Seyfert galaxy MCG-6-30-15 can be
decomposed into two apparently disconnected components: a highly variable power
law and an almost constant component which contains a broad and strong iron
line. We explore a possible explanation of the puzzling lack of variability of
the iron line, by assuming that the variations of the power law component are
due to changes in the height of the primary source in the near vicinity of a
rotating black hole. Due to the bending of light in the strong field of the
central black hole, the apparent brightness of the power-law component can vary
by about a factor 4 according to its position, while the total iron line flux
variability is less than 20 percent. This behaviour is obtained if the primary
source is located within 3-4 gravitational radii () from the
rotation axis with a variable height of between 3 and 8 .
These results revive the possibility that future X-ray observations of
MCG-6-30-15 can map out the strong gravity regime of accreting black holes.Comment: accepted for publication in MNRAS Letter
A multi-color fast-switching microfluidic droplet dye laser
We describe a multi-color microfluidic dye laser operating in whispering gallery mode based on a train of alternating droplets containing solutions of different dyes; this laser is capable of switching the wavelength of its emission between 580 nm and 680 nm at frequencies up to 3.6 kHz -— the fastest among all dye lasers reported; it has potential applications in on-chip spectroscopy and flow cytometry
Working And Musculoskeletal Disorders Posture On Concrete Workers Of Production Division At PT. X Bali
Introduction: Musculoskeletal disorders are injuries that Affect the musculoskeletal systemthat can be the caused or aggravated by the working environment. Factors that can causemusculoskeletal disorders are exertion of force, repetition, and awkward posture. Awkwardposture held too long in the same position will cause injuries and complaints , which in turnwill Decrease the productivity for the workers and the company. Purpose: The aim of the study is to examine the correlation between working posture andmusculoskeletal disorders on concrete workers of the production division in PT. X Bali. Method: This study is an observational analytical study with cross-sectional design,participated by 43 concrete workers of production division using consecutive samplingtechnique. The study was held at PT X's concrete plant on Jl. Prof. Dr. Ida Bagus Mantra No.2461, Gianyar, Bali from 15th July to 17th July. Working posture was measured with RapidEntire Body Assessment (REBA) and the level of musculoskeletal disorder was measured with Nordic Body Map (NBM). Both variables were Analyzed using Kendall's Tau-C to Determine the correlation between working posture and musculoskeletal disorders. Results: Most workers had moderate risk of working posture measured with REBA (46.5%).Using the NBM method, most workers had moderate levels of musculoskeletal disorders.(46.5%). The distribution of MSDs on the body part are mostly located on the shoulder andhip. Analysis of correlation between working posture and musculoskeletal disorder results in(p < 0.001) and (r = 0.769). Conclusion: that there is a significant correlation between work posture with musculoskeletalcomplaints in concrete factory workers of the production unit at PT. X Bali
Studying the X-ray hysteresis in GX 339-4: the disc and iron line over one decade
We report on a comprehensive and consistent investigation into the X-ray
emission from GX 339-4. All public observations in the 11 year RXTE archive
were analysed. Three different types of model - single powerlaw, broken
powerlaw and a disc + powerlaw - were fitted to investigate the evolution of
the disc, along with a fixed gaussian component at 6.4 keV to investigate any
iron line in the spectrum. We show that the relative variation in flux and
X-ray colour between the two best sampled outbursts are very similar. The decay
of the disc temperature during the outburst is clearly seen in the soft state.
The expected decay is S_Disc \propto T^4; we measure T^4.75\pm0.23. This
implies that the inner disc radius is approximately constant in the soft state.
We also show a significant anti-correlation between the iron line significant
width and the X-ray flux in the soft state while in the hard state the EW is
independent of the flux. This results in hysteresis in the relation between
X-ray flux and both line flux and EW. To compare the X-ray binary outburst to
the behaviour seen in AGN, we construct a Disc Fraction Luminosity Diagram for
GX 339-4, the first for an X-ray binary. The shape qualitatively matches that
produced for AGN. Linking this with the radio emission from GX 339-4 the change
in radio spectrum between the disc and power-law dominated states is clearly
visible.Comment: Accepted for publication in MNRAS, 20 pages, 17 figures. For high-res
version see http://www.astro.soton.ac.uk/~r.j.dunn/publications.htm
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