10,809 research outputs found
Interactive cutting path analysis programs
The operation of numerically controlled machine tools is interactively simulated. Four programs were developed to graphically display the cutting paths for a Monarch lathe, Cintimatic mill, Strippit sheet metal punch, and the wiring path for a Standard wire wrap machine. These programs are run on a IMLAC PDS-ID graphic display system under the DOS-3 disk operating system. The cutting path analysis programs accept input via both paper tape and disk file
Transform-limited pulses are not optimal for resonant multiphoton transitions
Maximizing nonlinear light-matter interactions is a primary motive for
compressing laser pulses to achieve ultrashort transform limited pulses. Here
we show how, by appropriately shaping the pulses, resonant multiphoton
transitions can be enhanced significantly beyond the level achieved by
maximizing the pulse's peak intensity. We demonstrate the counterintuitive
nature of this effect with an experiment in a resonant two-photon absorption,
in which, by selectively removing certain spectral bands, the peak intensity of
the pulse is reduced by a factor of 40, yet the absorption rate is doubled.
Furthermore, by suitably designing the spectral phase of the pulse, we increase
the absorption rate by a factor of 7.Comment: 4 pages, 3 figure
Long-term material compatibility testing system
System includes procedure for hermetically sealing solid materials and fluids in glass ampoule and use of temperature-controlled facility containing sample holder, which permits sample containers to be retrieved safely and conveniently. Solid material and fluid are sealed within chemically-clean glass ampoule according to highly detailed procedure
A mean field description of jamming in non-cohesive frictionless particulate systems
A theory for kinetic arrest in isotropic systems of repulsive,
radially-interacting particles is presented that predicts exponents for the
scaling of various macroscopic quantities near the rigidity transition that are
in agreement with simulations, including the non-trivial shear exponent. Both
statics and dynamics are treated in a simplified, one-particle level
description, and coupled via the assumption that kinetic arrest occurs on the
boundary between mechanically stable and unstable regions of the static
parameter diagram. This suggests the arrested states observed in simulations
are at (or near) an elastic buckling transition. Some additional numerical
evidence to confirm the scaling of microscopic quantities is also provided.Comment: 9 pages, 3 figs; additional clarification of different elastic moduli
exponents, plus typo fix. To appear in PR
Second order equation of motion for electromagnetic radiation back-reaction
We take the viewpoint that the physically acceptable solutions of the
Lorentz--Dirac equation for radiation back-reaction are actually determined by
a second order equation of motion, the self-force being given as a function of
spacetime location and velocity. We propose three different methods to obtain
this self-force function. For two example systems, we determine the second
order equation of motion exactly in the nonrelativistic regime via each of
these three methods, the three methods leading to the same result. We reveal
that, for both systems considered, back-reaction induces a damping proportional
to velocity and, in addition, it decreases the effect of the external force.Comment: 13 page
Characterizing Circumgalactic Gas around Massive Ellipticals at z~0.4 - II. Physical Properties and Elemental Abundances
We present a systematic investigation of the circumgalactic medium (CGM)
within projected distances d<160 kpc of luminous red galaxies (LRGs). The
sample comprises 16 intermediate-redshift (z=0.21-0.55) LRGs of stellar mass
M_star>1e11 M_sun. Combining far-ultraviolet Cosmic Origin Spectrograph spectra
from the Hubble Space Telescope and optical echelle spectra from the ground
enables a detailed ionization analysis based on resolved component structures
of a suite of absorption transitions, including the full HI Lyman series and
various ionic metal transitions. By comparing the relative abundances of
different ions in individually-matched components, we show that cool gas (T~1e4
K) density and metallicity can vary by more than a factor of ten in in an LRG
halo. Specifically, metal-poor absorbing components with <1/10 solar
metallicity are seen in 50% of the LRG halos, while gas with solar and
super-solar metallicity is also common. These results indicate a complex
multiphase structure and poor chemical mixing in these quiescent halos. We
calculate the total surface mass density of cool gas, \Sigma_cool, by applying
the estimated ionization fraction corrections to the observed HI column
densities. The radial profile of \Sigma_cool is best-described by a projected
Einasto profile of slope \alpha=1 and scale radius r_s=48 kpc. We find that
typical LRGs at z~0.4 contain cool gas mass of M_cool= (1-2) x1e10 M_sun at
d<160 kpc (or as much as 4x1e10 M_sun at d<500 kpc), comparable to the cool CGM
mass of star-forming galaxies. Furthermore, we show that high-ionization OVI
and low-ionization absorption species exhibit distinct velocity profiles,
highlighting their different physical origins. We discuss the implications of
our findings for the origin and fate of cool gas in LRG halos.Comment: Accepted for publication in MNRAS after a minor revision. 23 pages,
14 figures, and a 29-page Appendix with 27 additional figure
Controlled biomineralization of magnetite (Fe<sub>3</sub>O<sub>4</sub>) by <i>Magnetospirillum gryphiswaldense</i>
Results from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as well as chain character and length. The analysed crystals showed a narrow size range (∼14-67 nm) with an average diameter of 46±6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range
Sublattice identification in noncontact atomic force microscopy of the NaCl(001) surface
We compare the three-dimensional force field obtained from frequency-distance measurements above the NaCl(001) surface to atomistic calculations using various tip models. In the experiments, long-range forces cause a total attractive force even on the similarly charged site. Taking force differences between two sites minimizes the influence of such long-range forces. The magnitude of the measured force differences are by a factor of 6.5–10 smaller than the calculated forces. This is an indication that for the particular tip used in this experiment several atoms of the tip interact with the surface atoms at close tip-sample distances. The interaction of these additional atoms with the surface is small at the imaging distance, because symmetric images are obtained. The force distance characteristics resemble those of a negative tip apex ion which could be explained, e.g., by a neutral Si tip.Peer reviewe
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