161,828 research outputs found
The Al Gamma-ray Line from Massive-Star Regions
The measurement of gamma rays from the diffuse afterglow of radioactivity
originating in massive-star nucleosynthesis is considered a laboratory for
testing models, when specific stellar groups are investigated, at known
distance and with well-constrained stellar population. Regions which have been
exploited for such studies include Cygnus, Carina, Orion, and
Scorpius-Centaurus. The Orion region hosts the Orion OB1 association and its
subgroups at about 450~pc distance. We report the detection of Al gamma
rays from this region with INTEGRAL/SPI.Comment: Contribution to Symposium "Nuclei in the Cosmos XIV", Niigata, Japan,
Jun 2016; 3 pages, 2 figures; accepted for publication in JPS (Japan Physical
Society) Conference Proceedings http://jpscp.jps.jp
Exploring Lifetime Effects in Femtoscopy
We investigate the role of lifetime effects from resonances and emission
duration tails in femtoscopy at RHIC in two Blast-Wave models. We find the
non-Gaussian components compare well with published source imaged data, but the
value of R_out obtained from Gaussian fits is not insensitive to the
non-Gaussian contributions when realistic acceptance cuts are applied to
models.Comment: 5 pages, 2 figure
Thermal-capillary model for Czochralski growth of semiconductor materials
The success of efficiently calculating the temperature field, crystal radius, melt mensicus, and melt/solid interface in the Czochralski crystal growth system by full finite-element solution of the government thermal-capillary model is demonstrated. The model predicts realistic response to changes in pull rate, melt volume, and the thermal field. The experimentally observed phenomena of interface flipping, bumping, and the difficulty maintaining steady-state growth as the melt depth decreases are explained by model results. These calculations will form the basis for the first quantitative picture of Cz crystal growth. The accurate depiction of the melt meniscus is important in calculating the crystal radius and solidification interface. The sensitivity of the results to the equilibrium growth angle place doubt on less sophisticated attempts to model the process without inclusion of the meniscus. Quantitative comparison with experiments should be possible once more representation of the radiation and view factors in the thermal system and the crucible are included. Extensions of the model in these directions are underway
Boundary States and Black Hole Entropy
Black hole entropy is derived from a sum over boundary states. The boundary
states are labeled by energy and momentum surface densities, and parametrized
by the boundary metric. The sum over state labels is expressed as a functional
integral with measure determined by the density of states. The sum over metrics
is expressed as a functional integral with measure determined by the universal
expression for the inverse temperature gradient at the horizon. The analysis
applies to any stationary, nonextreme black hole in any theory of gravitational
and matter fields.Comment: 4 pages, Revte
Coaxial Atomic Force Microscope Tweezers
We demonstrate coaxial atomic force microscope (AFM) tweezers that can trap
and place small objects using dielectrophoresis (DEP). An attractive force is
generated at the tip of a coaxial AFM probe by applying a radio frequency
voltage between the center conductor and a grounded shield; the origin of the
force is found to be DEP by measuring the pull-off force vs. applied voltage.
We show that the coaxial AFM tweezers (CAT) can perform three dimensional
assembly by picking up a specified silica microsphere, imaging with the
microsphere at the end of the tip, and placing it at a target destination.Comment: 9 pages, 3 figures, in review at Applied Physics Letter
Radial segregation induced by natural convection and melt/solid interface shape in vertical Bridgman growth
The roles of natural convection in the melt and the shape of the melt/solid interface on radial dopant segregation are analyzed for a prototype of vertical Bridgman crystal growth system by finite element methods that solve simultaneously for the velocity field in the melt, the shape of the solidification isotherm, and the temperature distribution in both phases. Results are presented for crystal and melt with thermophysical properties similar to those of gallium-doped germanium in Bridgman configurations with melt below (thermally destabilizing) and above (stabilizing) the crystal. Steady axisymmetric flow are classified according to Rayleigh number as either being nearly the growth velocity, having a weak cellular structure or having large amplitude cellular convention. The flows in the two Bridgman configurations are driven by different temperature gradients and are in opposite directions. Finite element calculations for the transport of a dilute dopant by these flow fields reveal radial segregation levels as large as sixty percent of the mean concentration. Segregation is found most severe at an intermediate value of Rayleigh number above which the dopant distribution along the interface levels as the intensity of the flow increases
Hierarchical approach to 'atomistic' 3-D MOSFET simulation
We present a hierarchical approach to the 'atomistic' simulation of aggressively scaled sub-0.1-μm MOSFETs. These devices are so small that their characteristics depend on the precise location of dopant atoms within them, not just on their average density. A full-scale three-dimensional drift-diffusion atomistic simulation approach is first described and used to verify more economical, but restricted, options. To reduce processor time and memory requirements at high drain voltage, we have developed a self-consistent option based on a solution of the current continuity equation restricted to a thin slab of the channel. This is coupled to the solution of the Poisson equation in the whole simulation domain in the Gummel iteration cycles. The accuracy of this approach is investigated in comparison to the full self-consistent solution. At low drain voltage, a single solution of the nonlinear Poisson equation is sufficient to extract the current with satisfactory accuracy. In this case, the current is calculated by solving the current continuity equation in a drift approximation only, also in a thin slab containing the MOSFET channel. The regions of applicability for the different components of this hierarchical approach are illustrated in example simulations covering the random dopant-induced threshold voltage fluctuations, threshold voltage lowering, threshold voltage asymmetry, and drain current fluctuations
Dipole and Quadrupole electroexcitations of the isovector T=1 particle-hole states in C-12
Electroexcitations of the dominantly T=1 particle-hole states of C-12 are
studied in the framework of the harmonic oscillator shell model. All possible
T=1 single-particle-hole states of all allowed angular momenta are considered
in a basis including single-particle states up to the 1f-2p shell. The
Hamiltonian is diagnoalized in this space in the presence of the modified
surface delta interaction. Correlation in the ground state wave functions by
mixing more than one configuration is considered and shows a major contribution
that leads to enhance the calculations of the form factors. A comparison with
the experiment shows that this model is able to fit the location of states and
a simple scaling of the results give a good fit to the experimental form
factors.Comment: 5 pages, 4 figures, 5 tables, Late
Relationship between Allan variances and Kalman Filter parameters
A relationship was constructed between the Allan variance parameters (H sub z, H sub 1, H sub 0, H sub -1 and H sub -2) and a Kalman Filter model that would be used to estimate and predict clock phase, frequency and frequency drift. To start with the meaning of those Allan Variance parameters and how they are arrived at for a given frequency source is reviewed. Although a subset of these parameters is arrived at by measuring phase as a function of time rather than as a spectral density, they all represent phase noise spectral density coefficients, though not necessarily that of a rational spectral density. The phase noise spectral density is then transformed into a time domain covariance model which can then be used to derive the Kalman Filter model parameters. Simulation results of that covariance model are presented and compared to clock uncertainties predicted by Allan variance parameters. A two state Kalman Filter model is then derived and the significance of each state is explained
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