8,321 research outputs found
Macrofaunal community inside and outside of the Darwin Mounds Special Area of Conservation, NE Atlantic
Peer reviewedPublisher PD
Gas ion laser construction for electrically isolating the pressure gauge thereof
The valve and the pressure gauge of a gas ion laser were electrically insulated from the laser discharge path by connecting them in series with the cathode of the laser. The laser cathode can be grounded and preferably is a cold cathode although a hot cathode may be used instead. The cold cathode was provided with a central aperture to which was connected both the pressure gauge and the gas pressure reservoir through the valve. This will effectively prevent electric discharges from passing either to the pressure gauge or the valve which would otherwise destroy the pressure gauge
Discriminants and Functional Equations for Polynomials Orthogonal on the Unit Circle
We derive raising and lowering operators for orthogonal polynomials on the
unit circle and find second order differential and -difference equations for
these polynomials. A general functional equation is found which allows one to
relate the zeros of the orthogonal polynomials to the stationary values of an
explicit quasi-energy and implies recurrences on the orthogonal polynomial
coefficients. We also evaluate the discriminants and quantized discriminants of
polynomials orthogonal on the unit circle.Comment: 27 pages, Latex2e plus AMS packages Fix to Eqs. (2.72) and (2.74
A Ulysses Detection of Secondary Helium Neutrals
The Interstellar Boundary EXplorer (IBEX) mission has recently studied the
flow of interstellar neutral He atoms through the solar system, and discovered
the existence of a secondary He flow likely originating in the outer
heliosheath. We find evidence for this secondary component in Ulysses data. By
coadding hundreds of Ulysses He beam maps together to maximize signal-to-noise,
we identify a weak signal that is credibly associated with the secondary
component. Assuming a laminar flow from infinity, we infer the following He
flow parameters: V=12.8+/-1.9 km/s, lambda=74.4+/-1.8 deg, beta=-10.5+/-4.1
deg, and T=3000+/-1100 K; where lambda and beta are the ecliptic longitude and
latitude direction in J2000 coordinates. The secondary component has a density
that is 4.9+/-0.9% that of the primary component. These measurements are
reasonably consistent with measurements from IBEX, with the exception of
temperature, where our temperature is much lower than IBEX's T=9500 K. Even the
higher IBEX temperature is suspiciously low compared to expectactions for the
outer heliosheath source region. The implausibly low temperatures are due to
the incorrect assumption of a laminar flow instead of a diverging one, given
that the flow in the outer heliosheath source region will be deflecting around
the heliopause. As for why the IBEX and Ulysses T values are different,
difficulties with background subtraction in the Ulysses data are a potential
source of concern, but the discrepancy may also be another effect of the
improper laminar flow assumption, which could affect the IBEX and Ulysses
analyses differently.Comment: 9 pages, 4 figures, to appear in The Astrophysical Journa
High-Precision Spectroscopy with Counter-Propagating Femtosecond Pulses
An experimental realization of high-precision direct frequency comb
spectroscopy using counter-propagating femtosecond pulses on two-photon atomic
transitions is presented. Doppler broadened background signal, hampering
precision spectroscopy with ultrashort pulses, is effectively eliminated with a
simple pulse shaping method. As a result, all four 5S-7S two-photon transitions
in a rubidium vapor are determined with both statistical and systematic
uncertainties below 10, which is an order of magnitude better than
previous experiments on these transitions.Comment: 5 pages, 4 figures. Accepted to PR
Revisiting Ulysses Observations of Interstellar Helium
We report the results of a comprehensive reanalysis of Ulysses observations
of interstellar He atoms flowing through the solar system, the goal being to
reassess the interstellar He flow vector and to search for evidence of
variability in this vector. We find no evidence that the He beam seen by
Ulysses changes at all from 1994-2007. The direction of flow changes by no more
than ~0.3 deg and the speed by no more than ~0.3 km/s. A global fit to all
acceptable He beam maps from 1994-2007 yields the following He flow parameters:
V_ISM=26.08+/-0.21 km/s, lambda=75.54+/-0.19 deg, beta=-5.44+/-0.24 deg, and
T=7260+/-270 K; where lambda and beta are the ecliptic longitude and latitude
direction in J2000 coordinates. The flow vector is consistent with the original
analysis of the Ulysses team, but our temperature is significantly higher. The
higher temperature somewhat mitigates a discrepancy that exists in the He flow
parameters measured by Ulysses and the Interstellar Boundary Explorer, but does
not resolve it entirely. Using a novel technique to infer photoionization loss
rates directly from Ulysses data, we estimate a density of n_He=0.0196+/-0.0033
cm^-3 in the interstellar medium.Comment: to appear in The Astrophysical Journa
- …