765 research outputs found
Investigation of stratiform sulphide mineralisation at Meall Mor, South Knapdale, Argyll
A co-ordinated geochemical-geophysical-geological investigation of copper
mineralisation in the Meal1 ?46r area, South Knapdale, Argyll was carried 0th
in 1976 and followed by a drilling programme of 3 shallow holes in early 1977.
The mineralisation occursin a zone of weak stratiform sulphide mineralisation
(the pyrite zone) with a strike length of 1Okm in the Upper &ins Quartz&e
of the Middle Dalradian.
The geochemical drainage survey showed the existence of a strongly anomalous
distribution of Cu and Sb in the Abhainn Srathain draining south from .
Meal1 M&- and detailed soil sampling over the pyrite zone outlined a broad
area enriched in copper. Deeper soil sampling confirmed the anomalously
high copper values and a coincident IP anomaly was found stretching from
Meal1 M& south to the old mine workings on Abhainn Srathain, and is probably
caused by a local enrichment of pyrite and chalcopyrite within the pyrite
zone.
Three boreholes were drilled; two on coincident geochemical and geophysical
anomalies, and the third beneath the old mines at Abhainn Srathain. Copper
values in the first two holes range up to 0.24% Cu over 4.27m, but up to
1.06% Cu over 2.67m in the third and this enrichment may be related to a
later remobilisation of the disseminated chalcopyrite. The results of subsequent
drilling at two other sites are given in Appendix III
Relation between Tunneling and Particle Production in Vacuum Decay
The field-theoretical description of quantum fluctuations on the background
of a tunneling field is revisited in the case of a functional
Schrodinger approach. We apply this method in the case when quantum
fluctuations are coupled to the field through a mass-squared term,
which is 'time-dependent' since we include the dynamics of . The
resulting mode functions of the fluctuation field, which determine the quantum
state after tunneling, display a previously unseen resonance effect when their
mode number is comparable to the curvature scale of the bubble. A detailed
analysis of the relation between the excitations of the field about the true
vacuum (interpreted as particle creation) and the phase shift coming from
tunneling is presented.Comment: 20 pages, 4 figures, submitted to PR
Qualitative Properties of Magnetic Fields in Scalar Field Cosmology
We study the qualitative properties of the class of spatially homogeneous
Bianchi VI_o cosmological models containing a perfect fluid with a linear
equation of state, a scalar field with an exponential potential and a uniform
cosmic magnetic field, using dynamical systems techniques. We find that all
models evolve away from an expanding massless scalar field model in which the
matter and the magnetic field are negligible dynamically. We also find that for
a particular range of parameter values the models evolve towards the usual
power-law inflationary model (with no magnetic field) and, furthermore, we
conclude that inflation is not fundamentally affected by the presence of a
uniform primordial magnetic field. We investigate the physical properties of
the Bianchi I magnetic field models in some detail.Comment: 12 pages, 2 figures in REVTeX format. to appear in Phys. Rev.
Coupled oscillators as models of phantom and scalar field cosmologies
We study a toy model for phantom cosmology recently introduced in the
literature and consisting of two oscillators, one of which carries negative
kinetic energy. The results are compared with the exact phase space picture
obtained for similar dynamical systems describing, respectively, a massive
canonical scalar field conformally coupled to the spacetime curvature, and a
conformally coupled massive phantom. Finally, the dynamical system describing
exactly a minimally coupled phantom is studied and compared with the toy model.Comment: 18 pages, LaTeX, to appear in Physical Review
Magnetohydrodynamics and Plasma Cosmology
We study the linear magnetohydrodynamic (MHD) equations, both in the
Newtonian and the general-relativistic limit, as regards a viscous magnetized
fluid of finite conductivity and discuss instability criteria. In addition, we
explore the excitation of cosmological perturbations in anisotropic spacetimes,
in the presence of an ambient magnetic field. Acoustic, electromagnetic (e/m)
and fast-magnetosonic modes, propagating normal to the magnetic field, can be
excited, resulting in several implications of cosmological significance.Comment: 9 pages, RevTeX, To appear in the Proceedings of the Peyresq X
Meeting, IJTP Conference Serie
Effective Theoretical Approach to Back Reaction of the Dynamical Casimir Effect in 1+1 Dimensions
We present an approach to studying the Casimir effects by means of the
effective theory. An essential point of our approach is replacing the mirror
separation into the size of space S^1 in the adiabatic approximation. It is
natural to identify the size of space S^1 with the scale factor of the
Robertson-Walker-type metric. This replacement simplifies the construction of a
class of effective models to study the Casimir effects. To check the validity
of this replacement we construct a model for a scalar field coupling to the
two-dimensional gravity and calculate the Casimir effects by the effective
action for the variable scale factor. Our effective action consists of the
classical kinetic term of the mirror separation and the quantum correction
derived by the path-integral method. The quantum correction naturally contains
both the Casimir energy term and the back-reaction term of the dynamical
Casimir effect, the latter of which is expressed by the conformal anomaly. The
resultant effective action describes the dynamical vacuum pressure, i.e., the
dynamical Casimir force. We confirm that the force depends on the relative
velocity of the mirrors, and that it is always attractive and stronger than the
static Casimir force within the adiabatic approximation.Comment: Published Version, 16 pages, LaTeX2e with graphics package, 1 figur
Superinflation, quintessence, and nonsingular cosmologies
The dynamics of a universe dominated by a self-interacting nonminimally
coupled scalar field are considered. The structure of the phase space and
complete phase portraits are given. New dynamical behaviors include
superinflation (), avoidance of big bang singularities through
classical birth of the universe, and spontaneous entry into and exit from
inflation. This model is promising for describing quintessence as a
nonminimally coupled scalar field.Comment: 4 pages, 2 figure
Subtyping sub-Saharan esophageal squamous cell carcinoma by comprehensive molecular analysis
Esophageal squamous cell carcinoma (ESCC) is endemic in regions of sub-Saharan Africa (SSA), where it is the third most common cancer. Here, we describe whole-exome tumor/normal sequencing and RNA transcriptomic analysis of 59 patients with ESCC in Malawi. We observed similar genetic aberrations as reported in Asian and North American cohorts, including mutations of TP53, CDKN2A, NFE2L2, CHEK2, NOTCH1, FAT1, and FBXW7. Analyses for nonhuman sequences did not reveal evidence for infection with HPV or other occult pathogens. Mutational signature analysis revealed common signatures associated with aging, cytidine deaminase activity (APOBEC), and a third signature of unknown origin, but signatures of inhaled tobacco use, aflatoxin and mismatch repair were notably absent. Based on RNA expression analysis, ESCC could be divided into 3 distinct subtypes, which were distinguished by their expression of cell cycle and neural transcripts. This study demonstrates discrete subtypes of ESCC in SSA, and suggests that the endemic nature of this disease reflects exposure to a carcinogen other than tobacco and oncogenic viruses
Molecular dynamics simulation of the order-disorder phase transition in solid NaNO
We present molecular dynamics simulations of solid NaNO using pair
potentials with the rigid-ion model. The crystal potential surface is
calculated by using an \emph{a priori} method which integrates the \emph{ab
initio} calculations with the Gordon-Kim electron gas theory. This approach is
carefully examined by using different population analysis methods and comparing
the intermolecular interactions resulting from this approach with those from
the \emph{ab initio} Hartree-Fock calculations. Our numerics shows that the
ferroelectric-paraelectric phase transition in solid NaNO is triggered by
rotation of the nitrite ions around the crystallographical c axis, in agreement
with recent X-ray experiments [Gohda \textit{et al.}, Phys. Rev. B \textbf{63},
14101 (2000)]. The crystal-field effects on the nitrite ion are also addressed.
Remarkable internal charge-transfer effect is found.Comment: RevTeX 4.0, 11 figure
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