2,164 research outputs found
A search for electron cyclotron maser emission from compact binaries
Unipolar induction (UI) is a fundamental physical process, which occurs when
a conducting body transverses a magnetic field. It has been suggested that UI
is operating in RX J0806+15 and RX J1914+24, which are believed to be
ultra-compact binaries with orbital periods of 5.4 min and 9.6 min
respectively. The UI model predicts that those two sources may be electron
cyclotron maser sources at radio wavelengths. Other systems in which UI has
been predicted to occur are short period extra-solar terrestrial planets with
conducting cores. If UI is present, circularly polarised radio emission is
predicted to be emitted. We have searched for this predicted radio emission
from short period binaries using the VLA and ATCA. In one epoch we find
evidence for a radio source, coincident in position with the optical position
of RX J0806+15. Although we cannot completely exclude that this is a chance
alignment between the position of RX J0806+15 and an artifact in the data
reduction process, the fact that it was detected at a significance level of 5.8
sigma and found to be transient, suggests that it is more likely that RX
J0806+15 is a transient radio source. We find an upper limit on the degree of
circular polarisation to be ~50%. The inferred brightness temperature exceeds
10^18 K, which is too high for any known incoherent process, but is consistent
with maser emission and UI being the driving mechanism. We did not detect radio
emission from ES Cet, RX J1914+24 or Gliese 876.Comment: Accepted for publication MNRA
Oxygen isotopes implanted in the LDEF spacecraft
Secondary ion mass spectrometry was used to study oxygen implanted in the surface of copper from the Long Duration Exposure Facility (LDEF). Oxidation that occurred in orbit shows a characteristic oxygen isotope composition, depleted in O-18. The measured depletion is comparable to the predicted depletion (45 percent) based on a model of the gravitational separation of the oxygen isotopes. The anomalous oxygen was contained within 10nm of the surface. Tray E10 was calculated to have received 5.14 x 10(exp 21) atoms of oxygen cm(sup -2) during the LDEF mission and so there is sufficient anomalous implanted oxygen present in the surface to obtain a reliable isotopic profile
Adhesives for laminating polyimide insulated flat conductor cable
Polymer adhesive laminates polyimide-film flat conductor cable. It is obtained by reacting an appropriate diamine with a dianhydride. The adhesive has also been used in the lamination of copper to copper for the preparation of multilayer circuit boards
Accretion in dipole magnetic fields: flow structure and X-ray emission of accreting white dwarfs
Field-channelled accretion flows occur in a variety of astrophysical objects,
including T Tauri stars,magnetic cataclysmic variables and X-ray pulsars. We
consider a curvilinear coordinate system and derive a general hydrodynamic
formulation for accretion onto stellar objects confined by a stellar dipole
magnetic field. The hydrodynamic equations are solved to determine the
velocity, density and temperature profiles of the flow. We use accreting
magnetic white-dwarf stars as an illustrative example of astrophysical
applications. Our calculations show that the compressional heating due to the
field geometry is as important as radiative cooling and gravity in determining
the structure of the post-shock flow in accreting white-dwarf stars. The
generalisation of the formulation to accretion flows channelled by higher-order
fields and the applications to other astrophysical systems are discussed.Comment: Accepted A&
Use of soil moisture information in yield models
There are no author-identified significant results in this report
Unusual Response to a Localized Perturbation in a Generalized Elastic Model
The generalized elastic model encompasses several physical systems such as
polymers, membranes, single file systems, fluctuating surfaces and rough
interfaces. We consider the case of an applied localized potential, namely an
external force acting only on a single (tagged) probe, leaving the rest of the
system unaffected. We derive the fractional Langevin equation for the tagged
probe, as well as for a generic (untagged) probe, where the force is not
directly applied. Within the framework of the fluctuation-dissipation
relations, we discuss the unexpected physical scenarios arising when the force
is constant and time periodic, whether or not the hydrodynamic interactions are
included in the model. For short times, in case of the constant force, we show
that the average drift is linear in time for long range hydrodynamic
interactions and behaves ballistically or exponentially for local hydrodynamic
interactions. Moreover, it can be opposite to the direction of external
disturbance for some values of the model's parameters. When the force is time
periodic, the effects are macroscopic: the system splits into two distinct
spatial regions whose size is proportional to the value of the applied
frequency. These two regions are characterized by different amplitudes and
phase shifts in the response dynamics
The Dynamics of Radiative Shock Waves: Linear and Nonlinear Evolution
The stability properties of one-dimensional radiative shocks with a power-law
cooling function of the form are the main
subject of this work. The linear analysis originally presented by Chevalier &
Imamura, is thoroughfully reviewed for several values of the cooling index
and higher overtone modes. Consistently with previous results, it is
shown that the spectrum of the linear operator consists in a series of modes
with increasing oscillation frequency. For each mode a critical value of the
cooling index, , can be defined so that modes with are unstable, while modes with
are stable. The perturbative analysis is complemented by several numerical
simulations to follow the time-dependent evolution of the system for different
values of . Particular attention is given to the comparison between
numerical and analytical results (during the early phases of the evolution) and
to the role played by different boundary conditions. It is shown that an
appropriate treatment of the lower boundary yields results that closely follow
the predicted linear behavior. During the nonlinear regime, the shock
oscillations saturate at a finite amplitude and tend to a quasi-periodic cycle.
The modes of oscillations during this phase do not necessarily coincide with
those predicted by linear theory, but may be accounted for by mode-mode
coupling.Comment: 33 pages, 12 figures, accepted for publication on the Astrophysical
Journa
Changes in women’s facial skin color over the ovulatory cycle are not detectable by the human visual system
Human ovulation is not advertised, as it is in several primate species, by conspicuous sexual swellings. However, there is increasing evidence that the attractiveness of women’s body odor, voice, and facial appearance peak during the fertile phase of their ovulatory cycle. Cycle effects on facial attractiveness may be underpinned by changes in facial skin color, but it is not clear if skin color varies cyclically in humans or if any changes are detectable. To test these questions we photographed women daily for at least one cycle. Changes in facial skin redness and luminance were then quantified by mapping the digital images to human long, medium, and shortwave visual receptors. We find cyclic variation in skin redness, but not luminance. Redness decreases rapidly after menstrual onset, increases in the days before ovulation, and remains high through the luteal phase. However, we also show that this variation is unlikely to be detectable by the human visual system. We conclude that changes in skin color are not responsible for the effects of the ovulatory cycle on women’s attractiveness
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