A feasibility study of a hypersonic real-gas facility

A four month feasibility study of a hypersonic real-gas free flight test facility for NASA Langley Research Center (LARC) was performed. The feasibility of using a high-energy electromagnetic launcher (EML) to accelerate complex models (lifting and nonlifting) in the hypersonic, real-gas facility was examined. Issues addressed include: design and performance of the accelerator; design and performance of the power supply; design and operation of the sabot and payload during acceleration and separation; effects of high current, magnetic fields, temperature, and stress on the sabot and payload; and survivability of payload instrumentation during acceleration, flight, and soft catch

On the Role of Chaos in the AdS/CFT Connection

The question of how infalling matter in a pure state forms a Schwarzschild black hole that appears to be at non-zero temperature is discussed in the context of the AdS/CFT connection. It is argued that the phenomenon of self-thermalization in non-linear (chaotic) systems can be invoked to explain how the boundary theory, initially at zero temperature self thermalizes and acquires a finite temperature. Yang-Mills theory is known to be chaotic (classically) and the imaginary part of the gluon self-energy (damping rate of the gluon plasma) is expected to give the Lyapunov exponent. We explain how the imaginary part would arise in the corresponding supergravity calculation due to absorption at the horizon of the black hole.Comment: 18 pages. Latex file. Minor changes. Final version to appear in Modern Physics Letters

Suppression of Bremsstrahlung at Non-Zero Temperature

The first-order bremsstrahlung emission spectrum is $\alpha d\omega/\omega$ at zero temperature. If the radiation is emitted into a region that contains a thermal distribution of photons, then the rate is increased by a factor $1+N(\omega)$ where $N(\omega)$ is the Bose-Einstein function. The stimulated emission changes the spectrum to $\alpha Td\omega/\omega^{2}$ for $\omega\ll T$. If this were correct, an infinite amount of energy would be radiated in the low frequency modes. This unphysical result indicates a breakdown of perturbation theory. The paper computes the bremsstrahlung rate to all orders of perturbation theory, neglecting the recoil of the charged particle. When the perturbation series is summed, it has a different low-energy behavior. For $\omega\ll\alpha T$, the spectrum is independent of $\omega$ and has a value proportional to $d\omega/\alpha T$ .Comment: 16 pages (plain TeX), figures available on reques

Modification of Z Boson Properties in Quark-Gluon Plasma

We calculate the change in the effective mass and width of a Z boson in the environment of a quark-gluon plasma under the conditions expected in Pb-Pb collisions at the LHC. The change in width is predicted to be only about 1 MeV at a temperature of 1 GeV, compared to the natural width of 2490$\pm$7 MeV. The mass shift is even smaller. Hence no observable effects are to be expected.Comment: 7 pages latex file with 6 embedded PS figure

Light-front Schwinger Model at Finite Temperature

We study the light-front Schwinger model at finite temperature following the recent proposal in \cite{alves}. We show that the calculations are carried out efficiently by working with the full propagator for the fermion, which also avoids subtleties that arise with light-front regularizations. We demonstrate this with the calculation of the zero temperature anomaly. We show that temperature dependent corrections to the anomaly vanish, consistent with the results from the calculations in the conventional quantization. The gauge self-energy is seen to have the expected non-analytic behavior at finite temperature, but does not quite coincide with the conventional results. However, the two structures are exactly the same on-shell. We show that temperature does not modify the bound state equations and that the fermion condensate has the same behavior at finite temperature as that obtained in the conventional quantization.Comment: 10 pages, one figure, version to be published in Phys. Rev.

The Boltzmann Equation in Scalar Field Theory

We derive the classical transport equation, in scalar field theory with a V(phi) interaction, from the equation of motion for the quantum field. We obtain a very simple, but iterative, expression for the effective action which generates all the n-point Green functions in the high-temperature limit. An explicit closed form is given in the static case.Comment: 10 pages, using RevTeX (corrected TeX misprints

The graviton self-energy in thermal quantum gravity

We show generally that in thermal gravity, the one-particle irreducible 2-point function depends on the choice of the basic graviton fields. We derive the relevant properties of a physical graviton self-energy, which is independent of the parametrization of the graviton field. An explicit expression for the graviton self-energy at high-temperature is given to one-loop order.Comment: 13 pages, 2 figure

Energy and pressure densities of a hot quark-gluon plasma

We calculate the energy and hydrostatic pressure densities of a hot quark-gluon plasma in thermal equilibrium through diagrammatic analyses of the statistical average, $\langle \Theta_{\mu \nu} \rangle$, of the energy-momentum-tensor operator $\Theta_{\mu \nu}$. To leading order at high temperature, the energy density of the long wave length modes is consistently extracted by applying the hard-thermal-loop resummation scheme to the operator-inserted no-leg thermal amplitudes $\langle \Theta_{\mu \nu} \rangle$. We find that, for the long wave length gluons, the energy density, being positive, is tremendously enhanced as compared to the noninteracting case, while, for the quarks, no noticeable deviation from the noninteracting case is found.Comment: 33 pages. Figures are not include

Spontaneous discrimination of urine odours in wild African lions (Panthera leo)

Olfactory communication is the primary mode of communication for many mammals, yet research on this form of signalling is still largely descriptive in most species. Thus, despite the apparent importance of scent-marking in the social lives of wild felids, experimental studies directly investigating the function of olfactory communication are lacking. We conducted scent presentation experiments to investigate whether wild African lions can discriminate another lion's social group and sex from a sample of its urine. Our results indicated that lion urine has the potential to signal depositor sex and social group, and that lions can use urine to discriminate males from females and residents from non-residents. The response of lions to urine was also dependent on both the sex and age of the subject receiving the presentation. Female lions responded less frequently to urine from resident females than to either non-resident females or resident males. Males responded more strongly to urine from resident males than resident females, but did not appear to differentiate urine from non-resident and resident females. Observations of flehmen and further scent-marking responses from lions provide additional evidence that lion urine functions in scent-marking. These results establish that urine scent-marks contain sufficient information for receivers to discriminate the sex and social affiliation of the signaller, and are the first to experimentally demonstrate the functional relevance of scent-marking in African lions

Relation of Root Distribution to Organic Matter in Prairie Soil

Although the root distribution of the chief grasses and forbs of tall-grass prairie has been known for 15 years (18), no studies on the relation of root distribution to the organic matter in the soil have been made. In fact, so far as the writers are aware, few studies of this type have been undertaken in America. SPRAGUE (15), working in New Jersey, has attempted to correlate root occupation of the several soil layers with their specific soil properties. The grasses, chiefly Kentucky bluegrass and Colonial bent grass, were grown on a formerly cultivated soil of the gray-brown forest soil group of the humid eastern states. Practically all of the roots were found in the upper 9 inches of soil, the abundance decreasing rapidly with depth. He found no correlation between root distribution and organic carbon content of the soil