1,137 research outputs found
Nature of fault planes in solid neutron star matter
The properties of tectonic earthquake sources are compared with those deduced
here for fault planes in solid neutron-star matter. The conclusion that
neutron-star matter cannot exhibit brittle fracture at any temperature or
magnetic field is significant for current theories of pulsar glitches, and of
the anomalous X-ray pulsars and soft-gamma repeaters.Comment: 5 AAS LaTeX pages 1 eps figur
Liquid n-hexane condensed in silica nanochannels: A combined optical birefringence and vapor sorption isotherm study
The optical birefringence of liquid n-hexane condensed in an array of
parallel silica channels of 7nm diameter and 400 micrometer length is studied
as a function of filling of the channels via the vapor phase. By an analysis
with the generalized Bruggeman effective medium equation we demonstrate that
such measurements are insensitive to the detailed geometrical (positional)
arrangement of the adsorbed liquid inside the channels. However, this technique
is particularly suitable to search for any optical anisotropies and thus
collective orientational order as a function of channel filling. Nevertheless,
no hints for such anisotropies are found in liquid n-hexane. The n-hexane
molecules in the silica nanochannels are totally orientationally disordered in
all condensation regimes, in particular in the film growth as well as in the
the capillary condensed regime. Thus, the peculiar molecular arrangement found
upon freezing of liquid n-hexane in nanochannel-confinement, where the
molecules are collectively aligned perpendicularly to the channels' long axes,
does not originate in any pre-alignment effects in the nanoconfined liquid due
to capillary nematization.Comment: 7 pages, 5 figure
Preferred orientation of n-hexane crystallized in silicon nanochannels: A combined x-ray diffraction and sorption isotherm study
We present an x-ray diffraction study on n-hexane in tubular silicon channels
of approximately 10 nm diameter both as a function of the filling fraction f of
the channels and as a function of temperature. Upon cooling, confined n-hexane
crystallizes in a triclinic phase typical of the bulk crystalline state.
However, the anisotropic spatial confinement leads to a preferred orientation
of the confined crystallites, where the crystallographic direction
coincides with the long axis of the channels. The magnitude of this preferred
orientation increases with the filling fraction, which corroborates the
assumption of a Bridgman-type crystallization process being responsible for the
peculiar crystalline texture. This growth process predicts for a channel-like
confinement an alignment of the fastest crystallization direction parallel to
the long channel axis. It is expected to be increasingly effective with the
length of solidifying liquid parcels and thus with increasing f. In fact, the
fastest solidification front is expected to sweep over the full silicon
nanochannel for f=1, in agreement with our observation of a practically perfect
texture for entirely filled nanochannels
Tricritical Phenomena at the Cerium Transition
The isostructural transition in the
CeLaTh system is measured as a function of La alloying
using specific heat, magnetic susceptibility, resistivity, thermal
expansivity/striction measurements. A line of discontinuous transitions, as
indicated by the change in volume, decreases exponentially from 118 K to close
to zero with increasing La doping and the transition changes from being
first-order to continuous at a critical concentration . At the tricritical point, the coefficient of the linear term in the
specific heat and the magnetic susceptibility start to increase
rapidly near = 0.14 and gradually approaches large values at =0.35
signifying that a heavy Fermi-liquid state evolves at large doping. Near ,
the Wilson ratio, , has a value of 3.0, signifying the presence of
magnetic fluctuations. Also, the low-temperature resistivity shows that the
character of the low-temperature Fermi-liquid is changing
Pressure-induced phase transition in the electronic structure of palladium nitride
We present a combined theoretical and experimental study of the electronic
structure and equation of state (EOS) of crystalline PdN2. The compound forms
above 58 GPa in the pyrite structure and is metastable down to 11 GPa. We show
that the EOS cannot be accurately described within either the local density or
generalized gradient approximations. The Heyd-Scuseria-Ernzerhof
exchange-correlation functional (HSE06), however, provides very good agreement
with experimental data. We explain the strong pressure dependence of the Raman
intensities in terms of a similar dependence of the calculated band gap, which
closes just below 11 GPa. At this pressure, the HSE06 functional predicts a
first-order isostructural transition accompanied by a pronounced elastic
instability of the longitudinal-acoustic branches that provides the mechanism
for the experimentally observed decomposition. Using an extensive Wannier
function analysis, we show that the structural transformation is driven by a
phase transition of the electronic structure, which is manifested by a
discontinuous change in the hybridization between Pd-d and N-p electrons as
well as a conversion from single to triple bonded nitrogen dimers. We argue for
the possible existence of a critical point for the isostructural transition, at
which massive fluctuations in both the electronic as well as the structural
degrees of freedom are expected.Comment: 9 pages, 12 figures. Revised version corrects minor typographical
error
Complete pressure dependent phase diagrams for SrFe2As2 and BaFe2As2
The temperature dependent electrical resistivity of single crystalline
SrFe2As2 and BaFe2As2 has been measured in a liquid medium, modified Bridgman
anvil cell for pressures in excess of 75 kbar. These data allow for the
determination of the pressure dependence of the higher temperature, structural
/ antiferromagnetic phase transitions as well as the lower temperature
superconducting phase transition. For both compounds the ambient pressure,
higher temperature structural / antiferromagnetic phase transition can be fully
suppressed with a dome-like region of zero resistivity found to be centered
about its critical pressure. Indeed, qualitatively, the temperature dependence
of the resistivity curves closest to the critical pressures are the closest to
linear, consistent with possible quantum criticality. For pressures
significantly higher than the critical pressure the zero resistivity state is
suppressed and the low temperature resistivity curves asymptotically approach a
universal, low temperature manifold. These results are consistent with the
hypothesis that correlations / fluctuations associated with the
ambient-pressure, high-temperature, tetragonal phase have to be brought to low
enough temperature to allow superconductivity, but if too fully suppressed can
lead to the loss of the superconducting state
Three Questions on Lorentz Violation
We review the basics of the two most widely used approaches to Lorentz
violation - the Stardard Model Extension and Noncommutative Field Theory - and
discuss in some detail the example of the modified spectrum of the synchrotron
radiation. Motivated by touching upon such a fundamental issue as Lorentz
symmetry, we ask three questions: What is behind the search for Lorentz
violation? Is String Theory a physical theory? Is there an alternative to
Supersymmetry?Comment: 16 pages; invited luecture at DICE2006 - Piombino, Italy - September
200
Mathematical structure of unit systems
We investigate the mathematical structure of unit systems and the relations
between them. Looking over the entire set of unit systems, we can find a
mathematical structure that is called preorder (or quasi-order). For some pair
of unit systems, there exists a relation of preorder such that one unit system
is transferable to the other unit system. The transfer (or conversion) is
possible only when all of the quantities distinguishable in the latter system
are always distinguishable in the former system. By utilizing this structure,
we can systematically compare the representations in different unit systems.
Especially, the equivalence class of unit systems (EUS) plays an important role
because the representations of physical quantities and equations are of the
same form in unit systems belonging to an EUS. The dimension of quantities is
uniquely defined in each EUS. The EUS's form a partially ordered set. Using
these mathematical structures, unit systems and EUS's are systematically
classified and organized as a hierarchical tree.Comment: 27 pages, 3 figure
Positive-Operator-Valued Time Observable in Quantum Mechanics
We examine the longstanding problem of introducing a time observable in
Quantum Mechanics; using the formalism of positive-operator-valued measures we
show how to define such an observable in a natural way and we discuss some
consequences.Comment: 13 pages, LaTeX, no figures. Some minor changes, expanded the
bibliography (now it is bigger than the one in the published version),
changed the title and the style for publication on the International Journal
of Theoretical Physic
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