42,144 research outputs found
Optical Lenses for Atomic Beams
Superpositions of paraxial laser beam modes to generate atom-optical lenses
based on the optical dipole force are investigated theoretically. Thin, wide,
parabolic, cylindrical and circular atom lenses with numerical apertures much
greater than those reported in the literature to date can be synthesized. This
superposition approach promises to make high quality atom beam imaging and
nano-deposition feasible.Comment: 10 figure
Holographic photography of high velocity particles
Fourier transform hologram camera increases the velocity range for holography by a factor of 10 to 1000. Two different optical systems, using a triangular arrangement of beam splitters and a mirror to illuminate the object from two directions, are investigated
W49A North - Global or Local or No Collapse?
We attempt to fit observations with 5" resolution of the J=2-1 transition of
CS in the directions of H II regions A, B, and G of W49A North as well as
observations with 20" resolution of the J=2-1, 3-2, 5-4, and 7-6 transitions in
the directions of H II regions A and G by using radiative transfer
calculations. These calculations predict the intensity profiles resulting from
several spherical clouds along the line of sight. We consider three models:
global collapse of a very large (5 pc radius) cloud, localized collapse from
smaller (1 pc) clouds around individual H II regions, and multiple, static
clouds. For all three models we can find combinations of parameters that
reproduce the CS profiles reasonably well provided that the component clouds
have a core-envelope structure with a temperature gradient. Cores with high
temperature and high molecular hydrogen density are needed to match the higher
transitions (e.g. J=7-6) observed towards A and G. The lower temperature, low
density gas needed to create the inverse P-Cygni profile seen in the CS J=2-1
line (with 5" beam) towards H II region G arises from different components in
the 3 models. The infalling envelope of cloud G plus cloud B creates the
absorption in global collapse, cloud B is responsible in local collapse, and a
separate cloud, G', is needed in the case of many static clouds. The exact
nature of the velocity field in the envelopes for the case of local collapse is
not important as long as it is in the range of 1 to 5 km/s for a turbulent
velocity of about 6 km/s. High resolution observations of the J=1-0 and 5-4
transitions of CS and C34S may distinguish between these three models. Modeling
existing observations of HCO+ and C18O does not allow one to distinguish
between the three models but does indicate the existence of a bipolar outflow.Comment: 42 pages, 27 figures, accepted for publication in the ApJS August
2004, v153 issu
Feasibility Study of Velocity Synchronized Fourier Transform Hologram Camera System
Velocity synchronized Fourier transform hologram camera syste
Solutions of the Generic Non-Compact Weyl Equation
In this paper, solutions of the generic non-compact Weyl equation are
obtained. In particular, by identifying a suitable similarity transformation
and introducing a non-trivial change of variables we are able to implement
azimuthal dependence on the solutions of the diagonal non-compact Weyl
equation. We also discuss some open questions related to the construction of
infinite BPS monopole configurations.Comment: 12 pages, Latex. Few extra comments and a reference adde
Solute location in a nanoconfined liquid depends on charge distribution
Nanostructured materials that can confine liquids have attracted increasing attention for their diverse properties and potential applications. Yet, significant gaps remain in our fundamental understanding of such nanoconfined liquids. Using replica exchange molecular dynamics simulations of a nanoscale, hydroxyl-terminated silica pore system, we determine how the locations explored by a coumarin 153 (C153) solute in ethanol depend on its charge distribution, which can be changed through a charge transfer electronic excitation. The solute position change is driven by the internal energy, which favors C153 at the pore surface compared to the pore interior, but less so for the more polar, excited-state molecule. This is attributed to more favorable non-specific solvation of the large dipole moment excited-state C153 by ethanol at the expense of hydrogen-bonding with the pore. It is shown that a change in molecule location resulting from shifts in the charge distribution is a general result, though how the solute position changes will depend upon the specific system. This has important implications for interpreting measurements and designing applications of mesoporous materials
Threshold Corrections in Precision LHC Physics: QED otimes QCD
With an eye toward LHC processes in which theoretical precisions of 1 percent
are desired, we introduce the theory of the simultaneous YFS resummation of QED
and QCD to compute the size of the expected resummed soft radiative threshold
effects in precision studies of heavy particle production at the LHC. Our
results show that both QED and QCD soft threshold effects must be controlled to
be on the conservative side to achieve such precision goals.Comment: 4 pages, no figures; presented by B.F.L. Ward in DPF200
Ammonia Inhibition in Thermophilic Anaerobic Digestion of Dairy Cattle Manure
This study investigated the effect of five different concentrations of total ammonia nitrogen (TAN)and free ammonia (FA) on the methane yield and digester performance under thermophilic conditions(50°C). Five identical continuously fed digesters were used. The experiment was run for four timeshydraulic retention time (HRT). Data were statitically analysed using the data Analysis Tool Packavailable with the Microsoft Excel program. Different ammonia levels were obtained by pulsing urea toobtain the target level of TAN and FA, and to subsequently maintaining the concentration of ammonialevels by daily urea additions. The result showed a strong negative correlation between both TAN andFA concentrations and methane yield. The methane yield was reduced by 24, 30, 52 and 66% indigesters that had TAN levels of 2.9, 3.6, 4.4 and 5.1 g/L, respectively, corresponding to 0.7, 1.1,1.5 and1.8 g/L FA. Total volatile fatty acid and especially isovaleric and isobutyric acid concentrations wereelevated during ammonia inhibition. Concentration of TAN in the biogas digester exceeding 3 g/Lindicating that very often the full biogas potential is not achieved due to ammonia inhibition and thatlonger HRT should be used to compensate or a lower process temperature should be chosen
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