150 research outputs found
Lithostratigraphical subdivision of the Sherwood Sandstone Group (Triassic) of the north-eastern part of the Carlisle Basin, Cumbria, and adjacent parts of Dumfries and Galloway, UK.
This report presents a review of the history of the lithostratigraphical subdivision of the Triassic
Sherwood Sandstone Group of the north-eastern part of the Carlisle Basin, Cumbria, and
adjacent parts of Dumfries and Galloway, UK. Two formations, the St Bees Sandstone and
Kirklinton Sandstone, have been mapped in the past. However, previous workers have found
considerable difficulty in consistently identifying, defining and mapping the Kirklinton
Sandstone Formation. Moreover, previous accounts of the sandstones in the Carlisle area appear
to suggest that the succession there differs in several key aspects from its correlatives in other
parts of Cumbria and, in particular, the adjacent offshore area. As a result of a short period of
field work in the area, it is concluded that the principal lithological change is between mainly
fine-grained sandstones, that are generally or commonly micaceous and contain common or
numerous mudstone interbeds, in the lower and middle parts of the group, and fine- to coarsegrained
sandstones with rare or no mica and mudstone partings at the top of the group. This
change occurs within the Kirklinton Sandstone Formation as previously mapped, and it is
suggested that this unit is now invalid. Several options are considered as to how the group should
be subdivided and the nomenclature to be adopted. All options presently have some associated
problems, but the adoption of the same terminology as in the continuous offshore is suggested,
i.e. St Bees Sandstone Formation below (subdivided where possible into Rottington Sandstone
and Calder Sandstone Members) and Ormskirk Sandstone Formation above
A GIS of the extent of historical mining activities in Scotland: explanatory notes
As part of the secondment of BGS staff to SEPA to help implement the Water Framework
Directive (WFD) in Scotland, BGS have been asked to provide an approximate outline of the
extent of historical mining in Scotland. This will be used to help characterize pressures on
Scottish groundwater as part of the initial characterization of groundwater bodies for the WFD.
Initial characterization has to be completed by December 2004; for bodies deemed to be at risk
there will be further characterization after 2004. A team of BGS geologists carried out the work
during September 2003.
The aim of the study was:
“To delineate the extent of known and inferred historical and current shallow and dee
Minigap in a long disordered SNS junction: analytical results
We review and refine analytical results on the density of states in a long
disordered superconductor - normal-metal - superconductor junction with
transparent interfaces. Our analysis includes the behavior of the minigap near
phase differences zero and PI across the junction, as well as the density of
states at energies much larger than the minigap but much smaller than the
superconducting gap.Comment: 4 page
Partial credit in mathematics exams - a comparison of traditional and CAA exams
With the growing trend in many subjects to deliver at least some part of examinations by computer, it is important to know whether there are any differences in the results obtained by candidates sitting examinations taken by computer compared to those obtained by candidates sitting conventional examinations using pen and paper. The purpose of this paper is to describe a pilot project to compare the traditional type of assessment with assessment done by computer in mathematics examinations and in particular to investigate the role of partial credit in these examinations. In paper based examinations full marks are awarded for a completely correct answer. If, however, a student obtains an incorrect answer but gets some parts of the working correct then in mathematics examinations partial credit is normally awarded. In a computer examination an incorrect answer to a question is normally awarded no marks with no consideration of any partial credit. The mechanism for giving partial credit in the computer examinations of this project was to break the question down into Steps. The project compared results of students taking computer tests in three different formats (either no Steps, compulsory Steps or optional Steps) and the partial credit they would have obtained by taking the corresponding examinations on paper. The tests were at the level of Scottish Higher school examinations and were taken by school students who were about to sit their Higher examinations. This level was chosen as it was high enough to test the students on strategy and mathematical working, while the questions were not too long so that a clearer analysis of the results was possible
Effect of magnetic and non-magnetic impurities on highly anisotropic superconductivity
We generalize Abrikosov-Gor'kov solution of the problem of weakly coupled
superconductor with impurities on the case of a multiband superconductor with
arbitrary interband order parameter anisotropy, including interband sign
reversal of the order parameter. The solution is given in terms of the
effective (renormalized) coupling matrix and describes not only
suppression but also renormalization of the superconducting gap basically at
all temperatures. In many limiting cases we find analytical solutions for the
critical temperature suppression. We illustrate our results by numerical
calculations for two-band model systems.Comment: 18 pages (12pt) RevTeX, 4 postscript figure
Low Energy Excitations in Spin Glasses from Exact Ground States
We investigate the nature of the low-energy, large-scale excitations in the
three-dimensional Edwards-Anderson Ising spin glass with Gaussian couplings and
free boundary conditions, by studying the response of the ground state to a
coupling-dependent perturbation introduced previously. The ground states are
determined exactly for system sizes up to 12^3 spins using a branch and cut
algorithm. The data are consistent with a picture where the surface of the
excitations is not space-filling, such as the droplet or the ``TNT'' picture,
with only minimal corrections to scaling. When allowing for very large
corrections to scaling, the data are also consistent with a picture with
space-filling surfaces, such as replica symmetry breaking. The energy of the
excitations scales with their size with a small exponent \theta', which is
compatible with zero if we allow moderate corrections to scaling. We compare
the results with data for periodic boundary conditions obtained with a genetic
algorithm, and discuss the effects of different boundary conditions on
corrections to scaling. Finally, we analyze the performance of our branch and
cut algorithm, finding that it is correlated with the existence of
large-scale,low-energy excitations.Comment: 18 Revtex pages, 16 eps figures. Text significantly expanded with
more discussion of the numerical data. Fig.11 adde
Role of the E2g phonon in the superconductivity of MgB2: a Raman scattering study
Temperature dependent Raman scattering studies in polycrystalline
MgB2(10<T<300 K)reveal that the E2g phonon does not experience any self energy
renormalization effect across the superconducting critical temperature Tc ~ 40
K. In contrast, most of the current theoretical models rely on the role of the
E2g phonon in the electron-phonon coupling mechanism of superconductivity in
MgB2. According to these models, a hardening of 12% is expected below Tc at the
Gamma point of the Brillouim zone. In the presence of our results, those models
must be reviewed. The analysis of the temperature dependence of the E2g phonon
frequency yields to a isobaric Gruneisen parameter of -1.2< gama(E2g)< 0.2,
smaller than the value of 3.9 obtained from isothermal Raman experiments under
pressure. It is suggested that this apparent disagreement can be explained in
terms of pressure induced changes of the topology of the Fermi surface. Finally
we notice that the phonon linewidth presents the expected two-phonon anharmonic
decay as a function of T and no anomalous temperature dependence of the
linewidth is observed near Tc.Comment: Published in Solid State Comm. 125, 499 (2003
Theory of asymmetric non-additive binary hard-sphere mixtures
We show that the formal procedure of integrating out the degrees of freedom
of the small spheres in a binary hard-sphere mixture works equally well for
non-additive as it does for additive mixtures. For highly asymmetric mixtures
(small size ratios) the resulting effective Hamiltonian of the one-component
fluid of big spheres, which consists of an infinite number of many-body
interactions, should be accurately approximated by truncating after the term
describing the effective pair interaction. Using a density functional treatment
developed originally for additive hard-sphere mixtures we determine the zero,
one, and two-body contribution to the effective Hamiltonian. We demonstrate
that even small degrees of positive or negative non-additivity have significant
effect on the shape of the depletion potential. The second virial coefficient
, corresponding to the effective pair interaction between two big spheres,
is found to be a sensitive measure of the effects of non-additivity. The
variation of with the density of the small spheres shows significantly
different behavior for additive, slightly positive and slightly negative
non-additive mixtures. We discuss the possible repercussions of these results
for the phase behavior of binary hard-sphere mixtures and suggest that
measurements of might provide a means of determining the degree of
non-additivity in real colloidal mixtures
The three-dimensional random field Ising magnet: interfaces, scaling, and the nature of states
The nature of the zero temperature ordering transition in the 3D Gaussian
random field Ising magnet is studied numerically, aided by scaling analyses. In
the ferromagnetic phase the scaling of the roughness of the domain walls,
, is consistent with the theoretical prediction .
As the randomness is increased through the transition, the probability
distribution of the interfacial tension of domain walls scales as for a single
second order transition. At the critical point, the fractal dimensions of
domain walls and the fractal dimension of the outer surface of spin clusters
are investigated: there are at least two distinct physically important fractal
dimensions. These dimensions are argued to be related to combinations of the
energy scaling exponent, , which determines the violation of
hyperscaling, the correlation length exponent , and the magnetization
exponent . The value is derived from the
magnetization: this estimate is supported by the study of the spin cluster size
distribution at criticality. The variation of configurations in the interior of
a sample with boundary conditions is consistent with the hypothesis that there
is a single transition separating the disordered phase with one ground state
from the ordered phase with two ground states. The array of results are shown
to be consistent with a scaling picture and a geometric description of the
influence of boundary conditions on the spins. The details of the algorithm
used and its implementation are also described.Comment: 32 pp., 2 columns, 32 figure
Superconducting proximity effect in clean ferromagnetic layers
We investigate superconducting proximity effect in clean ferromagnetic layers
with rough boundaries. The subgap density of states is formed by Andreev bound
states at energies which depend on trajectory length and the ferromagnetic
exchange field. At energies above the gap, the spectrum is governed by resonant
scattering states. The resulting density of states, measurable by tunneling
spectroscopy, exhibits a rich structure, which allows to connect the
theoretical parameters from experiments.Comment: 11 pages, 5 figures (included
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