Non-relativistic limit of multidimensional gravity: exact solutions and applications

It is found the exact solution of the Poisson equation for the multidimensional space with topology $M_{3+d}=\mathbb{R}^3\times T^d$. This solution describes smooth transition from the newtonian behavior $1/r_3$ for distances bigger than periods of tori (the extra dimension sizes) to multidimensional behavior $1/r^{1+d}_{3+d}$ in opposite limit. In the case of one extra dimension $d=1$, the gravitational potential is expressed via compact and elegant formula. These exact solutions are applied to some practical problems to get the gravitational potentials for considered configurations. Found potentials are used to calculate the acceleration for point masses and gravitational self-energy.It is proposed models where the test masses are smeared over some (or all) extra dimensions. In 10-dimensional spacetime with 3 smeared extra dimensions, it is shown that the size of 3 rest extra dimensions can be enlarged up to submillimeter for the case of 1TeV fundamental Planck scale $M_{Pl(10)}$. In the models where all extra dimensions are smeared, the gravitational potential exactly coincides with the newtonian one regardless of size of the extra dimensions. Nevertheless, the hierarchy problem can be solved in these models.Comment: LaTex file, 18 pages, 4 figure

Electrostatic traps for dipolar excitons

We consider the design of two-dimensional electrostatic traps for dipolar indirect excitons. We show that the excitons dipole-dipole interaction, combined with the in-plane electric fields that arise due to the trap geometry, constrain the maximal density and lifetime of trapped excitons. We derive an analytic estimate of these values and determine their dependence on the trap geometry, thus suggesting the optimal design for high density trapping as a route for observing excitonic Bose-Einstein condensation.Comment: 5 pages, 3 figures. This 2nd version contains a revised Fig.3 + minor revisions to the discussion and abstrac

Terahertz imaging of sub-wavelength particles with Zenneck surface waves

Impact of sub-wavelength-size dielectric particles on Zenneck surface waves on planar metallic antennas is investigated at terahertz (THz) frequencies with THz near-field probe microscopy. Perturbations of the surface waves show the particle presence, despite its sub-wavelength size. The experimental configuration, which utilizes excitation of surface waves at metallic edges, is suitable for THz imaging of dielectric sub-wavelength size objects. As a proof of concept, the effects of a small strontium titanate rectangular particle and a titanium dioxide sphere on the surface field of a bow-tie antenna are experimentally detected and verified using full-wave simulations

Terahertz near-field microscopy using the self-mixing effect in a quantum cascade laser

We demonstrate terahertz (THz) apertureless near-field microscopy exploiting the self-mixing effect in a quantum cascade laser (QCL). A THz wave is scattered by a sharp needle positioned above an object and coupled back into the QCL cavity resulting in detection of the THz near-field signal through the self-mixing effect. Using this technique we demonstrate two-dimensional imaging at 2.53 THz with a spatial resolution of 1 μm - the highest image resolution achieved with a THz frequency QCL to date. This method offers an experimentally simple approach to coherent, high-resolution THz imaging

Fast Ray Tracing of Lunar Digital Elevation Models

Ray-tracing (RT) of Lunar Digital Elevation Models (DEM)'s is performed to virtually derive the degree of radiation incident to terrain as a function of time, orbital and ephemeris constraints [I- 4]. This process is an integral modeling process in lunar polar research and exploration due to the present paucity of terrain information at the poles and mission planning activities for the anticipated spring 2009 launch of the Lunar Reconnaissance Orbiter (LRO). As part of the Lunar Exploration Neutron Detector (LEND) and Lunar Crater Observation and Sensing Satellite (LCROSS) preparations RI methods are used to estimate the critical conditions presented by the combined effects of high latitude, terrain and the moons low obliquity [5-7]. These factors yield low incident solar illumination and subsequently extreme thermal, and radiation conditions. The presented research uses RT methods both for radiation transport modeling in space and regolith related research as well as to derive permanently shadowed regions (PSR)'s in high latitude topographic minima, e.g craters. These regions are of scientific and human exploration interest due to the near constant low temperatures in PSRs, inferred to be < 100 K. Hydrogen is thought to have accumulated in PSR's through the combined effects of periodic cometary bombardment and/or solar wind processes, and the extreme cold which minimizes hydrogen sublimation [8-9]. RT methods are also of use in surface position optimization for future illumination dependent on surface resources e.g. power and communications equipment

Terahertz near-field microscopy using the self-mixing effect in a quantum cascade laser

We demonstrate terahertz (THz) apertureless nearfield microscopy exploiting the self-mixing effect in a quantum cascade laser (QCL). A THz wave is scattered by a sharp needle positioned above an object and coupled back into the QCL cavity resulting in detection of the THz near-field signal through the self-mixing effect. Using this technique we demonstrate twodimensional imaging at 2.53 THz with a spatial resolution of ︎ 1 µm – the highest image resolution achieved with a THz frequency QCL to date. This method offers an experimentally simple approach to coherent, high-resolution THz imaging

Origin of resistivity contrast in interfacial phase-change memory: The crucial role of Ge/Sb intermixing

Phase-change memories based on reversible amorphous-crystal transformations in pseudobinary GeTe-Sb2Te3 alloys are one of the most promising nonvolatile memory technologies. The recently proposed superlattice-based memory, or interfacial phase-change memory (iPCM), is characterized by significantly faster switching, lower energy consumption, and better endurance. The switching mechanism in iPCM, where both the SET and RESET states are crystalline, is still contentious. Here, using the ab initio density functional theory simulations, a conceptually new switching mechanism for iPCM is derived, which is based on the change in the potential landscape of the bandgap, associated with local deviations from the pseudobinary stoichiometry across the van der Waals gaps and the associated shift of the Fermi level. The crucial role in this process belongs to Ge/Sb intermixing on the cation planes of iPCM. These findings offer a comprehensive understanding of the switching mechanisms in iPCM and are an essential step forward to the insightful development of phase-change memory technology.</jats:p