635 research outputs found
Representations of solutions of the wave equation based on relativistic wavelets
A representation of solutions of the wave equation with two spatial
coordinates in terms of localized elementary ones is presented. Elementary
solutions are constructed from four solutions with the help of transformations
of the affine Poincar\'e group, i.e., with the help of translations, dilations
in space and time and Lorentz transformations. The representation can be
interpreted in terms of the initial-boundary value problem for the wave
equation in a half-plane. It gives the solution as an integral representation
of two types of solutions: propagating localized solutions running away from
the boundary under different angles and packet-like surface waves running along
the boundary and exponentially decreasing away from the boundary. Properties of
elementary solutions are discussed. A numerical investigation of coefficients
of the decomposition is carried out. An example of the field created by sources
moving along a line with different speeds is considered, and the dependence of
coefficients on speeds of sources is discussed.Comment: submitted to J. Phys. A: Math. Theor., 20 pages, 6 figure
Why and when the Minkowski's stress tensor can be used in the problem of Casimir force acting on bodies embedded in media
It is shown that the criticism by Raabe and Welsch of the
Dzyaloshinskii-Lifshitz-Pitaevskii theory of the van der Waals-Casimir forces
inside a medium is based on misunderstandings. It is explained why and at which
conditions one can use the ''Minkowski-like '' stress tensor for calculations
of the forces. The reason, why approach of Raabe and Welsch is incorrect, is
discussed.Comment: Comment, 2 pages. 2 misprints were correcte
Tunneling spin-galvanic effect
It has been shown that tunneling of spin-polarized electrons through a
semiconductor barrier is accompanied by generation of an electric current in
the plane of the interfaces. The direction of this interface current is
determined by the spin orientation of the electrons, in particular the current
changes its direction if the spin orientation changes the sign. Microscopic
origin of such a 'tunneling spin-galvanic' effect is the spin-orbit
coupling-induced dependence of the barrier transparency on the spin orientation
and the wavevector of electrons.Comment: 3 pages, 2 figure
Implementing Fixed Dose Combination Medications for the Prevention and Control of Cardiovascular Diseases.
Highlights:Â - Despite clinical evidence of its effectiveness in secondary prevention of cardiovascular disease, uptake of fixed dose combination therapy (FDCs) for CVD has been poor.- A symposium was held bringing together stakeholders on this issue, including from academia, government and NGOs.- The conclusion made was that what is now needed to improve implementation of FDCs is country-specific health systems analyses to design appropriate implementation strategies.- Implementation strategies must look beyond listing on the WHO Essential Medicines List to consider approaches to improving FDC availability, accessibility, affordability, and adherence.- Strategies might include incorporation of FDCs into the WHO HEARTS technical package, simplified treatment and monitoring algorithms, decentralisation of medicine dispensing and task-sharing for treatment management
Spatial structure of an individual Mn acceptor in GaAs
The wave function of a hole bound to an individual Mn acceptor in GaAs is
spatially mapped by scanning tunneling microscopy at room temperature and an
anisotropic, cross-like shape is observed. The spatial structure is compared
with that from an envelope-function, effective mass model, and from a
tight-binding model. This demonstrates that anisotropy arising from the cubic
symmetry of the GaAs crystal produces the cross-like shape for the hole
wave-function. Thus the coupling between Mn dopants in GaMnAs mediated by such
holes will be highly anisotropic.Comment: 3 figures, submitted to PR
Characterization of deep impurities in semiconductors by terahertz tunneling ionization
Tunneling ionization in high frequency fields as well as in static fields is suggested as a method for the characterization of deep impurities in semiconductors. It is shown that an analysis of the field and temperature dependences of the ionization probability allows to obtain defect parameters like the charge of the impurity, tunneling times, the Huang–Rhys parameter, the difference between optical and thermal binding energy, and the basic structure of the defect adiabatic potentials. Compared to static fields, high frequency electric fields in the terahertz-range offer various advantages, as they can be applied contactlessly and homogeneously even to bulk samples using the intense radiation of a high power pulsed far-infrared laser. Furthermore, impurity ionization with terahertz radiation can be detected as photoconductive signal with a very high sensitivity in a wide range of electric field strengths
Collective and static properties of model two-component plasmas
Classical MD data on the charge-charge dynamic structure factor of
two-component plasmas (TCP) modeled in Phys. Rev. A 23, 2041 (1981) are
analyzed using the sum rules and other exact relations. The convergent power
moments of the imaginary part of the model system dielectric function are
expressed in terms of its partial static structure factors, which are computed
by the method of hypernetted chains using the Deutsch effective potential.
High-frequency asymptotic behavior of the dielectric function is specified to
include the effects of inverse bremsstrahlung. The agreement with the MD data
is improved, and important statistical characteristics of the model TCP, such
as the probability to find both electron and ion at one point, are determined.Comment: 25 pages, 6 figures, 5 tables. Published in Physical Review E
http://link.aps.org/abstract/PRE/v76/e02640
Strong Attraction between Charged Spheres due to Metastable Ionized States
We report a mechanism which can lead to long range attractions between
like-charged spherical macroions, stemming from the existence of metastable
ionized states. We show that the ground state of a single highly charged
colloid plus a few excess counterions is overcharged. For the case of two
highly charged macroions in their neutralizing divalent counterion solution we
demonstrate that, in the regime of strong Coulomb coupling, the counterion
clouds are very likely to be unevenly distributed, leading to one overcharged
and one undercharged macroion. This long-living metastable configuration in
turn leads to a long range Coulomb attraction.Comment: REVTEX-published versio
The Irrigation Efficiency Trap: Rational Farm-Scale Decisions Can Lead to Poor Hydrologic Outcomes at the Basin Scale
Agricultural irrigation practices have changed through time as technology has enabled more efficient conveyance and application. In some agricultural regions, irrigation can contribute to incidental aquifer recharge important for groundwater return flows to streams. The Henrys Fork Snake River, Idaho (United States) overlies a portion of the Eastern Snake Plain Aquifer, where irrigated agriculture has occurred for over a century. Using irrigator interviews, aerial and satellite imagery, and statistical streamflow analysis, we document the impact of farm-scale decisions on basin-scale hydrology. Motivated to improve economic efficiency, irrigators began converting from surface to center-pivot sprinkler irrigation in the 1950s, with rapid adoption of center-pivot sprinklers through 2000. Between 1978–2000 and 2001–2022, annual surface-water diversion decreased by 311 Mm3 (23%) and annual return flow to the river decreased by 299 Mm3 over the same period. Some reaches that gained water during 1978–2000 lost water to the aquifer during the later period. We use an interdisciplinary approach to demonstrate how individual farm-scale improvements in irrigation efficiency can cumulatively affect hydrology at the landscape scale and alter groundwater-surface water relationships. Return flows are an important part of basin hydrology in irrigated landscapes and we discuss how managed and incidental aquifer recharge can be implemented to recover return flows to rivers
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