Potential markets for a satellite-based mobile communications system

The objective of the study was to define the market needs for improved land mobile communications systems. Within the context of this objective, the following goals were set: (1) characterize the present mobile communications industry; (2) determine the market for an improved system for mobile communications; and (3) define the system requirements as seen from the potential customer's viewpoint. The scope of the study was defined by the following parameters: (1) markets were confined to U.S. and Canada; (2) range of operation generally exceeded 20 miles, but this was not restrictive; (3) the classes of potential users considered included all private sector users, and non-military public sector users; (4) the time span examined was 1975 to 1985; and (5) highly localized users were generally excluded - e.g., taxicabs, and local paging

Black holes in asymptotically Lifshitz spacetimes with arbitrary critical exponent

Recently, a class of gravitational backgrounds in 3+1 dimensions have been proposed as holographic duals to a Lifshitz theory describing critical phenomena in 2+1 dimensions with critical exponent $z\geq 1$. We numerically explore black holes in these backgrounds for a range of values of $z$. We find drastically different behavior for $z>2$ and $z2$ ($z<2$) the Lifshitz fixed point is repulsive (attractive) when going to larger radial parameter $r$. For the repulsive $z>2$ backgrounds, we find a continuous family of black holes satisfying a finite energy condition. However, for $z<2$ we find that the finite energy condition is more restrictive, and we expect only a discrete set of black hole solutions, unless some unexpected cancellations occur. For all black holes, we plot temperature $T$ as a function of horizon radius $r_0$. For $z\lessapprox 1.761$ we find that this curve develops a negative slope for certain values of $r_0$ possibly indicating a thermodynamic instability.Comment: 23 pages, 6 figures, references corrected, graphs made readable in greyscal

A test of the performance of portable electric mixers for household use

At the time this study was initiated, the small electrical food mixer was a common appliance in the home, serving in many ways to facilitate and hasten the tasks of whipping, beating and mixing during food preparation. Then, as now, the homemaker with a small food mixer wanted to use it for all her mixing and beating operations. Advertising claims indicated that it was adequate for such purposes. Many mixers, however, would not perform all the tasks required. The beater speed was too fast; the bowl turned too rapidly or did not turn at all; portions of the food remained unmixed and had to be mixed by hand. The most serious fault was a failure of the motor to function at low speed with a heavy load, sometimes even with a medium load

Thermodynamics of black branes in asymptotically Lifshitz spacetimes

Recently, a class of gravitational backgrounds in 3+1 dimensions have been proposed as holographic duals to a Lifshitz theory describing critical phenomena in 2+1 dimensions with critical exponent $z\geq 1$. We continue our earlier work \cite{Bertoldi:2009vn}, exploring the thermodynamic properties of the "black brane" solutions with horizon topology $\mathbb{R}^2$. We find that the black branes satisfy the relation $\mathcal{E}=\frac{2}{2+z}Ts$ where $\mathcal{E}$ is the energy density, $T$ is the temperature, and $s$ is the entropy density. This matches the expected behavior for a 2+1 dimensional theory with a scaling symmetry $(x_1,x_2)\to \lambda (x_1,x_2)$, $t\to \lambda^z t$.Comment: 8 pages, references added and regroupe

Verteerbaarheid en voederwaarde van eiwitrijke grondstoffen bij biologische biggen

Op Varkensproefbedrijf Raalte is onderzocht wat de nutriëntensamenstelling, verteerbaarheid en EW is van raapzaadeiwit concentraat, erwteneiwit concentraat, tarweglutenmeel en veldboneneiwitconcentraat bij biologisch gehouden gespeende biggen. De resultaten van het onderzoek zijn in dit rapport beschreven

Properties of the ionised plasma in the vicinity of the neutron-star X-ray binary EXO 0748-676

Aims. We present the spectral analysis of a large set of XMM-Newton observations of EXO 0748-676, a bright dipping low-mass X-ray binary. In particular, we focus on the dipping phenomenon as a result of changes in the properties of the ionised gas close to the source.Methods. We analysed the high-resolution spectra collected with the reflection grating spectrometer on board XMM-Newton. We studied dipping and persistent spectra separately. We used the Epic data to constrain the broad-band continuum. We explored two simple geometrical scenarios for which we derived physical quantities of the absorbing material like the density, size, and mass.Results. We find that the continuum is absorbed by a neutral gas, and by both a collisionally (temperature T similar to 70 eV) and photoionised (ionisation parameter log xi similar to 2.5) absorbers. Emission lines from OVII and OVIII are also detected. This is the first time that evidence of a collisionally ionised absorber has been found in a low-mass X-ray binary. The collisionally ionised absorber may be in the form of dense (n &gt; 10(14) cm(-3)) filaments, located at a distance r greater than or similar to 10(11) cm. During dips, the photoionised absorber significantly increases its column density (factor 2-4) while becoming less ionised. This strengthens the idea that the colder material of the accretion stream impinging the disc is passing on our line of sight during dips. In this scenario, we find that the distance from the neutron star to the impact region (similar to 5 x 10(10) cm) is similar to the size of the neutron star's Roche lobe. The gas observed during the persistent state may have a flattened geometry. Finally, we explore the possibility of the existence of material forming an initial, hotter portion of a circumbinary disc.</p

Hard Scattering and Gauge/String Duality

We consider high-energy fixed-angle scattering of glueballs in confining gauge theories that have supergravity duals. Although the effective description is in terms of the scattering of strings, we find that the amplitudes are hard (power law). This is a consequence of the warped geometry of the dual theory, which has the effect that in an inertial frame the string process is never in the soft regime. At small angle we find hard and Regge behaviors in different kinematic regions.Comment: 4 page

On solvable models of type IIB superstring in NS-NS and R-R plane wave backgrounds

We consider type IIB string in the two plane-wave backgrounds which may be interpreted as special limits of the AdS_3 x S^3 metric supported by either the NS-NS or R-R 3-form field. The NS-NS plane-wave string model is equivalent to a direct generalization of the Nappi-Witten model, with its spectrum being similar to that of strings in constant magnetic field. The R-R model can be solved in the light-cone gauge, where the Green-Schwarz action describes 4 massive and 4 massless copies of free bosons and fermions. We find the spectra of the two string models and study the asymptotic density of states. We also discuss a more general class of exactly solvable plane-wave models with reduced supersymmetry which is obtained by adding twists in two spatial 2-planes.Comment: 36 pages, harvmac. v2: discussion of equivalence of the supergravity parts of the spectra of the NS-NS and R-R models added in sect.5.3; v3: added remark on periodicity of the NS-NS spectrum; v4: minor correction in sect.6.

Black Holes and Five-brane Thermodynamics

The phase diagram for Dp-branes in M-theory compactified on $T^4$, $T^4/Z_2$, $T^5$, and $T^6$ is constructed. As for the lower-dimensional tori considered in our previous work (hep-th/9810224), the black brane phase at high entropy connects onto matrix theory at low entropy; we thus recover all known instances of matrix theory as consequences of the Maldacena conjecture. The difficulties that arise for $T^6$ are reviewed. We also analyze the D1-D5 system on $T^5$; we exhibit its relation to matrix models of M5-branes, and use spectral flow as a tool to investigate the dependence of the phase structure on angular momentum.Comment: 57 pages, 6 eps figures, latex. v2: DLCQ limit of 5-brane corrected; typos corrected, references added. v3: reference added, typos corrected v4: comments on DLCQ limit of 5-brane corrected one last time. Final version, to appear in Phys. Rev.