25,359 research outputs found
Transport in the Trans-Pennine Corridor: Present Conditions and Future Options. Interregional Study Working Paper 3.
This paper reports on a desk study carried out by the Institute for Transport Studies as part of a wider study of opportunities for inter-regional working in the trans-Pennine corridor, considering economic, environmental and transport issues. It draws together available information on transport and movement flows in the trans-Pennine corridor. These patterns of movement are examined from a broad perspective which considers intra-regional, inter- regional and international movements within and across the study area. The report proposes a regional package approach to transport, based on demand management and modal transfer
The solar wind structures associated with cosmic ray decreases and particle acceleration in 1978-1982
The time histories of particles in the energy range 1 MeV to 1 GeV at times of all greater than 3 percent cosmic ray decreases in the years 1978 to 1982 are studied. Essentially all 59 of the decreases commenced at or before the passages of interplanetary shocks, the majority of which accelerated energetic particles. We use the intensity-time profiles of the energetic particles to separate the cosmic ray decreases into four classes which we subsequently associate with four types of solar wind structures. Decreases in class 1 (15 events) and class 2 (26 events) can be associated with shocks which are driven by energetic coronal mass ejections. For class 1 events the ejecta is detected at 1 AU whereas this is not the case for class 2 events. The shock must therefore play a dominant role in producing the depression of cosmic rays in class 2 events. In all class 1 and 2 events (which comprise 69 percent of the total) the departure time of the ejection from the sun (and hence the location) can be determined from the rapid onset of energetic particles several days before the shock passage at Earth. The class 1 events originate from within 50 deg of central meridian. Class 3 events (10 decreases) can be attributed to less energetic ejections which are directed towards the Earth. In these events the ejecta is more important than the shock in causing a depression in the cosmic ray intensity. The remaining events (14 percent of the total) can be attributed to corotating streams which have ejecta material embedded in them
Fast nonadiabatic dynamics of many-body quantum systems
Modeling many-body quantum systems with strong interactions is one of the core challenges of modern physics. A range of methods has been developed to approach this task, each with its own idiosyncrasies, approximations, and realm of applicability. However, there remain many problems that are intractable for existing methods. In particular, many approaches face a huge computational barrier when modeling large numbers of coupled electrons and ions at finite temperature. Here, we address this shortfall with a new approach to modeling many-body quantum systems. On the basis of the Bohmian trajectory formalism, our new method treats the full particle dynamics with a considerable increase in computational speed. As a result, we are able to perform large-scale simulations of coupled electron-ion systems without using the adiabatic Born-Oppenheimer approximation
Commercial air transport hazard warning and avoidance system. Volume 2 - Requirements studies Final report
Operational requirements and cost effectiveness of commercial air transport hazard warning and avoidance syste
Instability of the salinity profile during the evaporation of saline groundwater
We investigate salt transport during the evaporation and upflow of saline groundwater. We describe a model in which a sharp evaporation-precipitation front separates regions of soil saturated with an air-vapour mixture and with saline water. We then consider two idealised problems. We first investigate equilibrium configurations of the fresh-water system when the depth of the soil layer is finite, obtaining results for the location of the front and for the upflow of water induced by the evaporation. Motivated by these results, we develop a solution for a propagating front in a soil layer of infinite depth, and we investigate the gravitational stability of the salinity profile which develops below the front, obtaining marginal linear stability conditions in terms of a Rayleigh number and a dimensionless salt saturation parameter. Applying our findings to realistic parameter regimes, we predict that salt fingering is unlikely to occur in low-permeability soils, but is likely in high-permeability (sandy) soils under conditions of relatively low evaporative upflow
On spherical twisted conjugacy classes
Let G be a simple algebraic group over an algebraically closed field of good
odd characteristic, and let theta be an automorphism of G arising from an
involution of its Dynkin diagram. We show that the spherical theta-twisted
conjugacy classes are precisely those intersecting only Bruhat cells
corresponding to twisted involutions in the Weyl group. We show how the
analogue of this statement fails in the triality case. We generalize to good
odd characteristic J-H. Lu's dimension formula for spherical twisted conjugacy
classes.Comment: proof of Lemma 6.4 polished. The journal version is available at
http://www.springerlink.com/content/k573l88256753640
Belief propagation algorithm for computing correlation functions in finite-temperature quantum many-body systems on loopy graphs
Belief propagation -- a powerful heuristic method to solve inference problems
involving a large number of random variables -- was recently generalized to
quantum theory. Like its classical counterpart, this algorithm is exact on
trees when the appropriate independence conditions are met and is expected to
provide reliable approximations when operated on loopy graphs. In this paper,
we benchmark the performances of loopy quantum belief propagation (QBP) in the
context of finite-tempereture quantum many-body physics. Our results indicate
that QBP provides reliable estimates of the high-temperature correlation
function when the typical loop size in the graph is large. As such, it is
suitable e.g. for the study of quantum spin glasses on Bethe lattices and the
decoding of sparse quantum error correction codes.Comment: 5 pages, 4 figure
A model for the operation of perovskite based hybrid solar cells:formation, analysis and comparison to experiment
This work is concerned with the modeling of perovskite based hybrid solar cells formed by sandwiching a slab of organic lead halide perovskite (CH3NH3PbI3?xClx) photo-absorber between (n-type) acceptor and (p-type) donor materials—typically titanium dioxide and spiro. A model for the electrical behavior of these cells is formulated based on drift-diffusion equations for the motion of the charge carriers and Poisson’s equation for the electric potential. It is closed by (i) internal interface conditions accounting for charge recombination/generation and jumps in charge carrier densities arising from differences in the electron affinity/ionization potential between the materials and (ii) ohmic boundary conditions on the contacts. The model is analyzed by using a combination of asymptotic and numerical techniques. This leads to an approximate—yet highly accurate—expression for the current-voltage relationship as a function of the solar induced photo- current. In addition, we show that this approximate current-voltage relation can be interpreted as an equivalent circuit model consisting of three diodes, a resistor, and a current source. For sufficiently small biases the device’s behavior is diodic and the current is limited by the recombination at the internal interfaces, whereas for sufficiently large biases the device acts like a resistor and the current is dictated by the ohmic dissipation in the acceptor and donor. The results of the model are also compared to experimental current-voltage curves, and good agreement is shown
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