3,718 research outputs found
The 8-14-μ Appearance of Venus Before the 1964 Conjunction
In an earlier paper (Murray, Wildey, and Westphal 1963) we have described the detailed
mapping of the 8-14-μ radiation from Venus using the 200-inch Hale telescope.
This paper extends that work over a period of about 7 months from December 15, 1963,
to June 6, 1964. Detailed maps for 6 days are presented that show the morphology of
the upper-atmosphere brightness temperature and illustrate a number of anomalous
features near the cusps. The problem of atmospheric extinction and the derived brightness
temperature is discussed
Lifetime of Stringy de Sitter Vacua
In this note we perform a synopsis of the life-times from vacuum decay of
several de Sitter vacuum constructions in string/M-theory which have a single
dS minimum arising from lifting a pre-existing AdS extremum and no other local
minima existent after lifting. For these vacua the decay proceeds via a
Coleman--De Luccia instanton towards the universal Minkowski minimum at
infinite volume. This can be calculated using the thin--wall approximation,
provided the cosmological constant of the local dS minimum is tuned
sufficiently small. We compare the estimates for the different model classes
and find them all stable in the sense of exponentially long life times as long
as they have a very small cosmological constant and a scale of supersymmetry
breaking > TeV.Comment: 1+16 pages, 2 figures, LaTeX, uses JHEP3 class, v2: references added,
inclusion of an additional subclass of de Sitter vacu
Sco X-1: The Evolution and Nature of the Twin Compact Radio Lobes
The radio components associated with the LMXB Sco X-1 have been monitored
with extensive VLBI imaging at 1.7 and 5.0 GHz over four years, including a
56-hour continuous VLBI observation in 1999 June. We often detected one strong
and one weak compact radio component, moving in opposite directions from the
radio core. We suggest that the moving components are radio lobes generated by
the disruption of energy flow in a twin-beam from the binary system. The
average lifetime of a lobe-pair, the space motion of the lobes and the measured
energy flow in the beam are discussed in arXiv:astro-ph/0104325. The lobe has a
flux density that is variable over a time-scale of one hour, a measured minimum
size of 1 mas (2.8 au), and is extended perpendicular to its motion. This short
electron radiative lifetime may be caused by synchrotron losses if the lobe
magnetic field is 300 G, or by adiabatic expansion of the electrons as soon as
they are produced at the working surface. The lobes also show periods of slow
expansion and a steepening radio spectrum, perhaps related to the
characteristics of the beam energy flow. The radio morphology for Sco X-1 is
more simple than for most other Galactic jet sources. The lobes of Sco X-1 are
similar to hot-spots found in many extragalactic double sources. Scaling the
phenomena observed in Sco X-1 to extragalactic sources implies hot-spot
variability time-scales of 10^4 yr and hot-spot lifetimes of 10^5 yr. The
recurrent formation of lobes in Sco X-1 probably does not occur for
extragalactic radio sources.Comment: 22 pages of text + 16 figures. ApJ, in pres
Infrared and Optical Measurements of the Crab Pulsar NP 0532
Observations of the pulsating component of NP 0532 at 2.2 and 1.65 μ are given. The energy density per pulse at 2.2 μ is (3.2 ± 0.4) X 10^(-31) J m^(-2) Hz^(-1) and forms a smooth continuation of the visual data
On the aerodynamic and aeroacoustic characteristics of a NACA 65-410 airfoil at moderate Reynolds number
Dynamics of relaxor ferroelectrics
We study a dynamic model of relaxor ferroelectrics based on the spherical
random-bond---random-field model and the Langevin equations of motion. The
solution to these equations is obtained in the long-time limit where the system
reaches an equilibrium state in the presence of random local electric fields.
The complex dynamic linear and third-order nonlinear susceptibilities
and , respectively, are calculated as
functions of frequency and temperature. In analogy with the static case, the
dynamic model predicts a narrow frequency dependent peak in ,
which mimics a transition into a glass-like state.Comment: 15 pages, Revtex plus 5 eps figure
Fractional Operators, Dirichlet Averages, and Splines
Fractional differential and integral operators, Dirichlet averages, and
splines of complex order are three seemingly distinct mathematical subject
areas addressing different questions and employing different methodologies. It
is the purpose of this paper to show that there are deep and interesting
relationships between these three areas. First a brief introduction to
fractional differential and integral operators defined on Lizorkin spaces is
presented and some of their main properties exhibited. This particular approach
has the advantage that several definitions of fractional derivatives and
integrals coincide. We then introduce Dirichlet averages and extend their
definition to an infinite-dimensional setting that is needed to exhibit the
relationships to splines of complex order. Finally, we focus on splines of
complex order and, in particular, on cardinal B-splines of complex order. The
fundamental connections to fractional derivatives and integrals as well as
Dirichlet averages are presented
Laser interferometry with translucent and absorbing mechanical oscillators
The sensitivity of laser interferometers can be pushed into regimes that
enable the direct observation of quantum behaviour of mechanical oscillators.
In the past, membranes with subwavelength thickness (thin films) have been
proposed as high-mechanical-quality, low-thermal-noise oscillators. Thin films
from a homogenous material, however, generally show considerable light
transmission accompanied by heating due to light absorption, which typically
reduces the mechanical quality and limits quantum opto-mechanical experiments
in particular at low temperatures. In this work, we experimentally analyze a
Michelson-Sagnac interferometer including a translucent silicon nitride (SiN)
membrane with subwavelength thickness. We find that such an interferometer
provides an operational point being optimally suited for quantum
opto-mechanical experiments with translucent oscillators. In case of a balanced
beam splitter of the interferometer, the membrane can be placed at a node of
the electro-magnetic field, which simultaneously provides lowest absorption and
optimum laser noise rejection at the signal port. We compare the optical and
mechanical model of our interferometer with experimental data and confirm that
the SiN membrane can be coupled to a laser power of the order of one Watt at
1064 nm without significantly degrading the membrane's quality factor of the
order 10^6, at room temperature
- …