850 research outputs found
Marine Platform of Probable Sangamon Age, and Associated Terrace Deposits, Cape Thompson Area, Northwestern Alaska
Reports geomorphic studies, as part of the US Atomic Energy Commission's investigations in this area 1958-1962. A coastal terrace, observed and measured along a 20-mi section crossing Ogotoruk Creek, is described and its origin, age, and morphology discussed. The feature is complex, consisting of a marine platform planed across bedrock, overlying marine and beach deposits, and a depositional upper surface of nonmarine sediments which coincides in area and configuration with the platform, possibly as a result of factors unique to polar areas. The marine platform and gravels record the last high stand of sea level, 28-40 ft above the present, which occurred about 38,000 yr ago. Other evidence in the area indicates still higher seas in earlier times
Gauge Coupling Instability and Dynamical Mass Generation in N=1 Supersymmetric QED(3)
Using superfield Dyson-Schwinger equations, we compute the infrared dynamics
of the semi-amputated full vertex, corresponding to the effective running gauge
coupling, in N-flavour {\mathcal N}=1 supersymmetric QED(3). It is shown that
the presence of a supersymmetry-preserving mass for the matter multiplet
stabilizes the infrared gauge coupling against oscillations present in the
massless case, and we therefore infer that the massive vacuum is thus selected
at the level of the (quantum) effective action. We further demonstrate that
such a mass can indeed be generated dynamically in a self-consistent way by
appealing to the superfield Dyson-Schwinger gap equation for the full matter
propagator.Comment: 14 pages ReVTeX; four axodraw figures incorporate
Automatic structures for semigroup constructions
We survey results concerning automatic structures for semigroup
constructions, providing references and describing the corresponding automatic
structures. The constructions we consider are: free products, direct products,
Rees matrix semigroups, Bruck-Reilly extensions and wreath products.Comment: 22 page
Constraining the variation of the coupling constants with big bang nucleosynthesis
We consider the possibility of the coupling constants of the gauge interactions at the time of big bang nucleosynthesis
having taken different values from what we measure at present, and investigate
the allowed difference requiring the shift in the coupling constants not
violate the successful calculation of the primordial abundances of the light
elements. We vary gauge couplings and Yukawa couplings (fermion masses) using a
model in which their relative variations are governed by a single scalar field,
dilaton, as found in string theory. The results include a limit on the fine
structure constant
, which is
two orders stricter than the limit obtained by considering the variation of
alone.Comment: 7 page
Law, politics and the governance of English and Scottish joint-stock companies 1600-1850
This article examines the impact of law on corporate governance by means of a case study of joint-stock enterprise in England and Scotland before 1850. Based on a dataset of over 450 company constitutions together with qualitative information on governance practice, it finds little evidence to support the hypothesis that common-law regimes such as England were more supportive of economic growth than civil-law jurisdictions such as Scotland: indeed, levels of shareholder protection were slightly stronger in the civil-law zone. Other factors, such as local political institutions, played a bigger role in shaping organisational forms and business practice
Space-time evolution of electron cascades in diamond
Here we describe model calculations to follow the spatio-temporal evolution
of secondary electron cascades in diamond. The band structure of the insulator
has been explicitly incorporated into the calculations as it affects
ionizations from the valence band. A Monte-Carlo model was constructed to
describe the path of electrons following the impact of a single electron of
energy E 250 eV. The results show the evolution of the secondary electron
cascades in terms of the number of electrons liberated, the spatial
distribution of these electrons, and the energy distribution among the
electrons as a function of time. The predicted ionization rates (5-13 electrons
in 100 fs) lie within the limits given by experiments and phenomenological
models. Calculation of the local electron density and the corresponding Debye
length shows that the latter is systematically larger than the radius of the
electron cloud. This means that the electron gas generated does not represent a
plasma in a single impact cascade triggered by an electron of E 250 eV energy.
This is important as it justifies the independent-electron approximation used
in the model. At 1 fs, the (average) spatial distribution of secondary
electrons is anisotropic with the electron cloud elongated in the direction of
the primary impact. The maximal radius of the cascade is about 50 A at this
time. As the system cools, energy is distributed more equally, and the spatial
distribution of the electron cloud becomes isotropic. At 90 fs maximal radius
is about 150 A. The Monte-Carlo model described here could be adopted for the
investigation of radiation damage in other insulators and has implications for
planned experiments with intense femtosecond X-ray sources.Comment: 26 pages, latex, 13 figure
Universality of Frequency and Field Scaling of the Conductivity Measured by Ac-Susceptibility of a Ybco-Film
Utilizing a novel and exact inversion scheme, we determine the complex linear
conductivity from the linear magnetic ac-susceptibility
which has been measured from 3\,mHz to 50\,MHz in fields between 0.4\,T and
4\,T applied parallel to the c-axis of a 250\,nm thin disk. The frequency
derivative of the phase and the dynamical scaling of
above and below provide clear evidence for a
continuous phase transition at to a generic superconducting state. Based
on the vortex-glass scaling model, the resulting critical exponents and
are close to those frequently obtained on films by other means and
associated with an 'isotropic' vortex glass. The field effect on
can be related to the increase of the glass coherence length,
.Comment: 8 pages (5 figures upon request), revtex 3.0, APK.94.01.0
Retrieval of 3D polygonal objects based on multiresolution signatures
In this paper we present a method for retrieving 3D polygonal objects by using two sets of multiresolution signatures. Both sets are based on the progressive elimination of object's details by iterative processing of the 3D meshes. The first set, with five parameters, is based on mesh smoothing. This mainly affects an object's surface. The second set, with three parameters, is based on difference volumes after successive mesh erosions and dilations. Characteristic feature vectors are constructed by combining the features at three mesh resolutions of each object. In addition to being invariant to mesh resolution, the feature vectors are invariant to translation, rotation and size of the objects. The method was tested on a set of 40 complex objects with mesh resolutions different from those used in constructing the feature vectors. By using all eight features, the average ranking rate obtained was 1.075: 37 objects were ranked first and only 3 objects were ranked second. Additional tests were carried out to determine the significance of individual features and all combinations. The same ranking rate of 1.075 can be obtained by using some combinations of only three features. © 2011 Springer-Verlag
Non-linear Dynamics in QED_3 and Non-trivial Infrared Structure
In this work we consider a coupled system of Schwinger-Dyson equations for
self-energy and vertex functions in QED_3. Using the concept of a
semi-amputated vertex function, we manage to decouple the vertex equation and
transform it in the infrared into a non-linear differential equation of
Emden-Fowler type. Its solution suggests the following picture: in the absence
of infrared cut-offs there is only a trivial infrared fixed-point structure in
the theory. However, the presence of masses, for either fermions or photons,
changes the situation drastically, leading to a mass-dependent non-trivial
infrared fixed point. In this picture a dynamical mass for the fermions is
found to be generated consistently. The non-linearity of the equations gives
rise to highly non-trivial constraints among the mass and effective (`running')
gauge coupling, which impose lower and upper bounds on the latter for dynamical
mass generation to occur. Possible implications of this to the theory of
high-temperature superconductivity are briefly discussed.Comment: 29 pages LATEX, 7 eps figures incorporated, uses axodraw style.
Discussion on the massless case (section 2) modified; no effect on
conclusions, typos correcte
General Relativity as an Attractor in Scalar-Tensor Stochastic Inflation
Quantum fluctuations of scalar fields during inflation could determine the
very large-scale structure of the universe. In the case of general
scalar-tensor gravity theories these fluctuations lead to the diffusion of
fundamental constants like the Planck mass and the effective Brans--Dicke
parameter, . In the particular case of Brans--Dicke gravity, where
is constant, this leads to runaway solutions with infinitely large
values of the Planck mass. However, in a theory with variable we find
stationary probability distributions with a finite value of the Planck mass
peaked at exponentially large values of after inflation. We conclude
that general relativity is an attractor during the quantum diffusion of the
fields.Comment: LaTeX (with RevTex) 11 pages, 2 uuencoded figures appended, also
available on WWW via http://star.maps.susx.ac.uk/index.htm
- …