7,765 research outputs found
Thomson scattering in a low-pressure neon mercury positive column
The electron density and the electron temperature in a low-pressure neon mercury positive column are determined using Thomson scattering. Special attention has been given to the stray light reduction in the Thomson scattering setup. The results are obtained in a discharge tube with a 26 mm diam, 10 mbar of neon, a mercury pressure inbetween 0.14 and 0.85 Pa, and an electric current ranging from 100 to 400 mA. The systematic error in the electron density is 15%–45%, the statistical error is 25%–35%. The total error in the electron temperature is 15%–35%. ©2001 American Institute of Physics
Nambu monopoles in lattice Electroweak theory
We considered the lattice electroweak theory at realistic values of
and and for large values of the Higgs mass. We investigated
numerically the properties of topological objects that are identified with
quantum Nambu monopoles. We have found that the action density near the Nambu
monopole worldlines exceeds the density averaged over the lattice in the
physical region of the phase diagram. Moreover, their percolation probability
is found to be an order parameter for the transition between the symmetric and
the broken phases. Therefore, these monopoles indeed appear as real physical
objects. However, we have found that their density on the lattice increases
with increasing ultraviolet cutoff. Thus we conclude, that the conventional
lattice electroweak theory is not able to predict the density of Nambu
monopoles. This means that the description of Nambu monopole physics based on
the lattice Weinberg - Salam model with finite ultraviolet cutoff is
incomplete. We expect that the correct description may be obtained only within
the lattice theory that involves the description of TeV - scale physics.Comment: LATE
The canonical structure of Podolsky's generalized electrodynamics on the Null-Plane
In this work we will develop the canonical structure of Podolsky's
generalized electrodynamics on the null-plane. This theory has second-order
derivatives in the Lagrangian function and requires a closer study for the
definition of the momenta and canonical Hamiltonian of the system. On the
null-plane the field equations also demand a different analysis of the
initial-boundary value problem and proper conditions must be chosen on the
null-planes. We will show that the constraint structure, based on Dirac
formalism, presents a set of second-class constraints, which are exclusive of
the analysis on the null-plane, and an expected set of first-class constraints
that are generators of a U(1) group of gauge transformations. An inspection on
the field equations will lead us to the generalized radiation gauge on the
null-plane, and Dirac Brackets will be introduced considering the problem of
uniqueness of these brackets under the chosen initial-boundary condition of the
theory
Compact polymer components for an integrated add-drop multiplexer
A phasar and a digital thermo optic switch have been designed and processed in a high index contrast polymer technology. Both devices are small enough to fabricate two integrated add-drop multiplexers on one 4 inch wafe
Binderless zeolite LTA beads with hierarchical porosity for selective CO<sub>2</sub> adsorption in biogas upgrading
In the context of CO2 removal from biogas, a series of binderless zeolite LTA adsorbents with a macroscopic bead format (0.5–1.0 mm) and with hierarchical porosity (i.e. with the zeolitic micropores being accessible through meso- and macropores mainly in the 10–100 nm range) was synthesized with a variety of Si/Al ratios (1.2–3.9) using Amberlite IRA-900 anion-exchange resin beads as a hard template. The CO2 and CH4 adsorption capacity of the beads in Na-form with different Si/Al ratios were measured, reaching higher CO2/CH4 selectivity and similar, yet slightly higher CO2 adsorption compared to commercial zeolite LTA pellets containing a binder. Subsequently, one the zeolitic beads was subjected to different degrees of ion-exchange (0–96%) with KCl and then tested in the adsorption of CO2 and CH4. The best performance among all the ion-exchanged beads was achieved with Na58K42-LTA beads, which gave very high CO2/CH4 selectivity (1540). Although essentially no CH4 was adsorbed on these beads, the CO2 adsorption capacity was still substantial (1.9 mmol g−1 at 0.4 bar CO2, i.e. the partial pressure of CO2 in biogas)
Stability limits of n-nonane calculated from molecular dynamics interface simulations
Based on molecular dynamics simulation of the vapor-liquid interface the classical thermodynamic spinodal for n-nonane is estimated using an earlier developed method. The choice of n-nonane as investigated molecule originates from the question whether a deviation from the spherical symmetry of a molecule affects the prediction of the stability limit data. As a result we find that the estimated stability limit data for n-nonane are consistent within the experimental data available for the homologous series of the n-alkanes. It turns out that the slight alignment of the molecules parallel to the interface reported in the literature does not affect the method of transferring interface properties to the bulk phase stability limit
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