53 research outputs found
Adsorbate vibrational modes enhancement of radiative heat transfer and van der Waals friction
We study the dependence of the heat transfer and the van der Waals friction
between two semi-infinite solids on the dielectric properties of the bodies. We
show that the heat transfer and van der Waals friction at short separation
between the solids may increase by many orders of magnitude when the surfaces
are covered by adsorbates, or can support low-frequency surface plasmons. In
this case the heat transfer and van der Waals friction are determined by
resonant photon tunneling between adsorbate vibrational modes, or surface
plasmon modes. The enhancement of the van der Waals friction is especially
large when in the adsorbed layer there is an acoustic branch for the vibrations
parallel to the surface like in the case of Cs adsorption on Cu(100) surface.
In this case we show that even for separation nm, the van der Waals
friction induced by adsorbates can be so large that it can be measured with the
present state-of-art equipment. The van an der Waals friction is characterized
by a strong distance dependence (), and at the small distances it
can be much larger than \textit{the electrostatic} friction observed in
\cite{Stipe}. \vskip 0.3cm \textit{Keywords}: non-contact friction, van der
Waals friction, radiative heat transfer, atomic force microscope, adsorbate
vibrational modeComment: published in Surface Scienc
Heat to Electricity Conversion by a Graphene Stripe with Heavy Chiral Fermions
A conversion of thermal energy into electricity is considered in the
electrically polarized graphene stripes with zigzag edges where the heavy
chiral fermion (HCF) states are formed. The stripes are characterized by a high
electric conductance Ge and by a significant Seebeck coefficient S. The
electric current in the stripes is induced due to a non-equilibrium thermal
injection of "hot" electrons. This thermoelectric generation process might be
utilized for building of thermoelectric generators with an exceptionally high
figure of merit Z{\delta}T \simeq 100 >> 1 and with an appreciable electric
power densities \sim 1 MW/cm2.Comment: 8 pages, 3 figure
Effective Hamiltonian and unitarity of the S matrix
The properties of open quantum systems are described well by an effective
Hamiltonian that consists of two parts: the Hamiltonian of the
closed system with discrete eigenstates and the coupling matrix between
discrete states and continuum. The eigenvalues of determine the
poles of the matrix. The coupling matrix elements
between the eigenstates of and the continuum may be very
different from the coupling matrix elements between the eigenstates
of and the continuum. Due to the unitarity of the matrix, the
\TW_k^{cc'} depend on energy in a non-trivial manner, that conflicts with the
assumptions of some approaches to reactions in the overlapping regime. Explicit
expressions for the wave functions of the resonance states and for their phases
in the neighbourhood of, respectively, avoided level crossings in the complex
plane and double poles of the matrix are given.Comment: 17 pages, 7 figure
The colour magnitude relation for galaxies in the Coma cluster
We present a new photometric catalogue of the Coma galaxy cluster in the
Johnson U- and V- bands. We cover an area of 3360arcmin2 of sky, to a depth of
V=20 mag in a 13 arcsec diameter aperture, and produce magnitudes for ~1400
extended objects in metric apertures from 8.8 to 26arcsec diameters. The mean
internal RMS scatter in the photometry is 0.014 mag in V, and 0.026 mag in U,
for V13 < 17 mag.
We place new limits on the levels of scatter in the colour--magnitude
relation (CMR) in the Coma cluster, and investigate how the slope and scatter
of the CMR depends on galaxy morphology, luminosity and position within the
cluster. As expected, the lowest levels of scatter are found in the elliptical
galaxies, while the late type galaxies have the highest numbers of galaxies
bluewards of the CMR. We investigate whether the slope of the CMR is an
artifact of colour gradients within galaxies and, show that it persists when
the colours are measured within a diameter that scales with galaxy size.
Looking at the environmental dependence of the CMR, we find a trend of
systematically bluer galaxy colours with increasing projected cluster-centric
radius which we associate with a gradient in the mean galactic ages.Comment: 18 pages, 13 Figures. For associated data file, see
ftp://ftp.sr.bham.ac.uk/pub/ale/ComaPhot
Radiative Corrections to One-Photon Decays of Hydrogenic Ions
Radiative corrections to the decay rate of n=2 states of hydrogenic ions are
calculated. The transitions considered are the M1 decay of the 2s state to the
ground state and the E1(M2) decays of the and states to
the ground state. The radiative corrections start in order , but the method used sums all orders of . The leading
correction for the E1 decays is calculated and compared
with the exact result. The extension of the calculational method to parity
nonconserving transitions in neutral atoms is discussed.Comment: 22 pages, 2 figure
QCD Corrections to QED Vacuum Polarization
We compute QCD corrections to QED calculations for vacuum polarization in
background magnetic fields. Formally, the diagram for virtual loops
is identical to the one for virtual loops. However due to
confinement, or to the growth of as decreases, a direct
calculation of the diagram is not allowed. At large we consider the
virtual diagram, in the intermediate region we discuss the role of
the contribution of quark condensates \left and at the
low-energy limit we consider the , as well as charged pion
loops. Although these effects seem to be out of the measurement accuracy of
photon-photon laboratory experiments they may be relevant for -ray
burst propagation. In particular, for emissions from the center of the galaxy
(8.5 kpc), we show that the mixing between the neutral pseudo-scalar pion
and photons renders a deviation from the power-law spectrum in the
range. As for scalar quark condensates \left and
virtual loops are relevant only for very high radiation density
and very strong magnetic fields of order .Comment: 15 pages, 4 figures; Final versio
EBIC-guidelines for management of severe head injury in adults
Guidelines for the management of severe head injury in adults as evolved by the European Brain Injury Consortium are presented and discussed. The importance of preventing and treating secondary insults is emphasized and the principles on which treatment is based are reviewed. Guidelines presented are of a pragmatic nature, based on consensus and expert opinion, covering the treatment from accident site to intensive care unit. Specific aspects pertaining to the conduct of clinical trials in head injury are highlighted. The adopted approach is further discussed in relation to other approaches to the development of guidelines, such as evidence based analysis
The composition of the protosolar disk and the formation conditions for comets
Conditions in the protosolar nebula have left their mark in the composition
of cometary volatiles, thought to be some of the most pristine material in the
solar system. Cometary compositions represent the end point of processing that
began in the parent molecular cloud core and continued through the collapse of
that core to form the protosun and the solar nebula, and finally during the
evolution of the solar nebula itself as the cometary bodies were accreting.
Disentangling the effects of the various epochs on the final composition of a
comet is complicated. But comets are not the only source of information about
the solar nebula. Protostellar disks around young stars similar to the protosun
provide a way of investigating the evolution of disks similar to the solar
nebula while they are in the process of evolving to form their own solar
systems. In this way we can learn about the physical and chemical conditions
under which comets formed, and about the types of dynamical processing that
shaped the solar system we see today.
This paper summarizes some recent contributions to our understanding of both
cometary volatiles and the composition, structure and evolution of protostellar
disks.Comment: To appear in Space Science Reviews. The final publication is
available at Springer via http://dx.doi.org/10.1007/s11214-015-0167-
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