3,458 research outputs found
Collisions with ice-volatile objects: Geological implications
The collision of the Earth with extra-terrestrial ice-volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record. These bodies would be analogs of the ice satellites found for the Jovian planets and suspected for comets and certain low density bodies in the Asteroid belt. Five generic end-members are postulated: (1) water ice; (2) dry ice: carbon-carbon dioxide rich, (3) oceanic (chloride) ice; (4) sulfur-rich ice; (5) ammonia hydrate-rich ice; and (6) clathrate: methane-rich ice. Due to the volatile nature of these bodies, evidence for their impact with the Earth would be subtle and probably best reflected geochemically or in the fossil record. Actual boloids impacting the Earth may have a variable composition, generally some admixture with water ice. However for discussion purposes, only the effects of a dominant component will be treated. The general geological effects of such collisions, as a function of the dominant component would be: (1) rapid sea level rise unrelated to deglaciation, (2) decreased oceanic pH and rapid climatic warming or deglaciation; (3) increased paleosalinities; (4) increased acid rain; (5) increased oceanic pH and rapid carbonate deposition; and (6) rapid climatic warming or deglaciation
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A Galerkin boundary element method for high frequency scattering by convex polygons
In this paper we consider the problem of time-harmonic acoustic scattering in two dimensions by convex polygons. Standard boundary or finite element methods for acoustic scattering problems have a computational cost that grows at least linearly as a function of the frequency of the incident wave. Here we present a novel Galerkin boundary element method, which uses an approximation space consisting of the products of plane waves with piecewise polynomials supported on a graded mesh, with smaller elements closer to the corners of the polygon. We prove that the best approximation from the approximation space requires a number of degrees of freedom to achieve a prescribed level of accuracy that grows only logarithmically as a function of the frequency. Numerical results demonstrate the same logarithmic dependence on the frequency for the Galerkin method solution. Our boundary element method is a discretization of a well-known second kind combined-layer-potential integral equation. We provide a proof that this equation and its adjoint are well-posed and equivalent to the boundary value problem in a Sobolev space setting for general Lipschitz domains
Development of integrated thermionic circuits for high-temperature applications
Integrated thermionic circuits (ITC) capable of extended operation in ambient temperatures up to 500 C are studied. A set of practical design and performance equations is demonstrated. Experimental results are discussed in which both devices and simple circuits were successfully operated in 5000 C environments for extended periods. It is suggested that ITC's may become an important technology for high temperature instrumentation and control systems in geothermal and other high temperature environments
Electron Correlations in a Quantum Dot with Bychkov-Rashba Coupling
We report on a theoretical approach developed to investigate the influence of
Bychkov-Rashba interaction on a few interacting electrons confined in a quantum
dot. We note that the spin-orbit coupling profoundly influences the energy
spectrum of interacting electrons in a quantum dot. Inter-electron interaction
causes level crossings in the ground state and a jump in magnetization. As the
coupling strength is increased, that jump is shifted to lower magnetic fields.
Low-field magnetization will therefore provide a direct probe of the spin-orbit
coupling strength in a quantum dot
Extreme rejuvenation of a bulk metallic glass at the nanoscale by swift heavy ion irradiation
Swift heavy ions can be used as a tool to tune material properties by generating high aspect ratio, nanometric
trails of defects, or new disordered phases. This work explores different aspects of using this tool for rejuvenating
and enhancing plasticity in bulk metallic glasses. An amorphous alloy with a nominal composition of Pd40Ni40P20
was irradiated with GeV-accelerated Au ions. Irradiation-induced out-of-plane swelling steps up to approxi-
mately 100 nm in height are measured at the boundary between irradiated and non-irradiated areas. Changes of
the relaxation enthalpy have been investigated using differential scanning calorimetry. Low-temperature heat
capacity measurements substantiate an irradiation-induced increase of the boson peak height with increasing
fluences. Accompanying transport measurements using radioactive Ag atoms as tracer also revealed increased
diffusion rates in the irradiated samples dependent on the total fluence. Nano-indentation measurements show
enhanced plasticity in the ion-irradiated glass which can be correlated with an increased heterogeneity as
indicated by variable resolution fluctuation electron microscopy. The whole volume of the derived data sub-
stantiates a prominent enhancement of the excess volume in the solidified ion tracks and the irradiation-induced
modifications are discussed and analyzed in the framework of strong glass rejuvenation within the nanometric
ion tracks
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Efficient calculation of two-dimensional periodic and waveguide acoustic Green’s functions
New representations and efficient calculation methods are derived for the problem of propagation from an infinite regularly spaced array of coherent line sources above a homogeneous impedance plane, and for the Green's function for sound propagation in the canyon formed by two infinitely high, parallel rigid or sound soft walls and an impedance ground surface. The infinite sum of source contributions is replaced by a finite sum and the remainder is expressed as a Laplace-type integral. A pole subtraction technique is used to remove poles in the integrand which lie near the path of integration, obtaining a smooth integrand, more suitable for numerical integration, and a specific numerical integration method is proposed. Numerical experiments show highly accurate results across the frequency spectrum for a range of ground surface types. It is expected that the methods proposed will prove useful in boundary element modeling of noise propagation in canyon streets and in ducts, and for problems of scattering by periodic surfaces
Mindfulness Training in UK Secondary Schools: a Multiple Case Study Approach to Identification of Cornerstones of Implementation
This is the final version. Available from Springer Verlag via the DOI in this record.This paper examined the facilitators and barriers to implementation of mindfulness training (MT) across seven secondary/high schools using a qualitative case study design. Schools varied in level of implementation. Within schools, head teachers, members of school senior leadership teams, and staff members involved in the implementation of MT were interviewed individually. In addition, focus groups were conducted with other members of school staff to capture a broad range of views and perspectives. Across the case studies, several key themes emerged, which suggested four cornerstones to successful implementation of MT in schools. These were: people, specifically the need for committed individuals to champion the approach within their schools, with the support of members of the senior leadership teams; resources, both time and financial resources required for training and delivery of MT; journey, reflecting the fact that implementation takes time, and may be a non-linear process with stops and starts; and finally perceptions, highlighting the importance of members of the school community sharing an understanding what MT is and why it is being introduced in each school context. Similarities and differences between the current findings and those of research on implementation of other forms of school mental health promotion programs, and implementation of MT in healthcare settings, are discussed.Wellcome Trus
Information trade-offs for optical quantum communication
Recent work has precisely characterized the achievable trade-offs between
three key information processing tasks---classical communication (generation or
consumption), quantum communication (generation or consumption), and shared
entanglement (distribution or consumption), measured in bits, qubits, and ebits
per channel use, respectively. Slices and corner points of this
three-dimensional region reduce to well-known protocols for quantum channels. A
trade-off coding technique can attain any point in the region and can
outperform time-sharing between the best-known protocols for accomplishing each
information processing task by itself. Previously, the benefits of trade-off
coding that had been found were too small to be of practical value (viz., for
the dephasing and the universal cloning machine channels). In this letter, we
demonstrate that the associated performance gains are in fact remarkably high
for several physically relevant bosonic channels that model free-space /
fiber-optic links, thermal-noise channels, and amplifiers. We show that
significant performance gains from trade-off coding also apply when trading
photon-number resources between transmitting public and private classical
information simultaneously over secret-key-assisted bosonic channels.Comment: 6 pages, 2 figures, see related, longer article at arXiv:1105.011
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