Rolling tachyon solution of two-dimensional string theory

We consider a classical (string) field theory of $c=1$ matrix model which was developed earlier in hep-th/9207011 and subsequent papers. This is a noncommutative field theory where the noncommutativity parameter is the string coupling $g_s$. We construct a classical solution of this field theory and show that it describes the complete time history of the recently found rolling tachyon on an unstable D0 brane.Comment: 19 pages, 2 figures, minor changes in text and additional references, correction of decay time (version to appear in JHEP.

Seismic stability of reinforced-soil wall by pseudo-dynamic method

Determination of the internal stability of reinforced soil walls under earthquake conditions is an important part of seismic design. The horizontal method of slices is used for determining internal stability or for tieback analysis of the reinforced soil wall. A pseudo-dynamic method is adopted in the present analysis, which considers the effect of phase difference in both the shear and primary waves travelling through the backfill due to seismic excitation. Reinforced soil walls with cohesionless backfill material have been considered in the analysis. Results are presented in graphical and tabular form to show the required tensile force and length of geosynthetic reinforcement to maintain the stability of the reinforced soil wall under seismic conditions. The effects of variation of parameters such as soil friction angle and horizontal and vertical seismic accelerations on the stability of the reinforced soil wall have been studied. With an increase of seismic accelerations in both the horizontal and vertical directions the stability of the reinforced soil wall decreases significantly, and thus greater strength and length of the geosynthetic reinforcement are required to maintain stability of the wall. The seismic vertical acceleration in an upward direction gives higher values of the required geosynthetic tensile strength, and the seismic vertical acceleration in the downward direction yields higher values of the length of geosynthetic reinforcement. Comparisons of the present results with available pseudo-static results are shown, and the limitations of the pseudo-static results are highlighted

HIV and respiratory illness in the antiretroviral therapy era

Respiratory illness is a common manifestation of HIV infection. The availability of effective antiretroviral therapy (ART) has changed the pattern of respiratory ill-health experienced by people living with HIV (PLWH). Among populations with good access to ART, opportunistic respiratory infections such as Pneumocystis jirovecii pneumonia (PCP) are becoming less frequent. However, there is evidence to suggest that these populations may be at greater risk of serious non-AIDS illness including chronic respiratory disease. Although there is remaining uncertainty about the extent to which HIV represents an independent risk-factor for respiratory illness in individuals with a suppressed HIV viral load and immune reconstitution, in many settings PLWH have greater exposure to risk factors for respiratory illness (in particular tobacco smoking), which contribute to this burden of disease. As HIV-positive populations age, management of these conditions will therefore become increasingly important. Healthcare services need to manage this growing burden of chronic respiratory illness and provide access to preventative measures including smoking cessation and immunisation against vaccine-preventable respiratory infections in a way that is appropriate to the populations served

Seismic Design of Geosynthetic Reinforced Soil Walls

In this paper, the design geogrid/geotextile reinforced retaining walls are summarized. Design of geosynthetics reinforced walls includes internal and external stability analyses. Seismic analyses also considered for design of geosynthetics reinforced walls. Many designers do not have all of the tools required to complete all of the components of the stability analysis for site conditions. Most current geosynthetics reinforced soil retaining wall design software products do not address all of the components of the stability analysis. This paper is directed towards researchers, practitioners, and regulators, and gives guidance for future research and development of codes for reinforced soil walls

Photon & Axion Oscillation In a Magnetized Medium: A Covariant Treatment

Pseudoscalar particles, with almost zero mass and very weak coupling to the visible matter, arise in many extensions of the standard model of particle physics. Their mixing with photons in the presence of an external magnetic field leads to many interesting astrophysical and cosmological consequences. This mixing depends on the medium properties, the momentum of the photon and the background magnetic field. Here we give a general treatment of pseudoscalar-photon oscillations in a background magnetic field, taking the Faraday term into account. We give predictions valid in all regimes, under the assumption that the frequency of the wave is much higher than the plasma frequency of the medium. At sufficiently high frequencies, the Faraday effect is negligible and we reproduce the standard pseudoscalar-photon mixing phenomenon. However at low frequencies, where Faraday effect is important, the mixing formulae are considerably modified. We explicitly compute the contribution due to the longitudinal mode of the photon and show that it is negligible.Comment: 16 pages, no figure

Extended Jaynes-Cummings models and (quasi)-exact solvability

The original Jaynes-Cummings model is described by a Hamiltonian which is exactly solvable. Here we extend this model by several types of interactions leading to a nonhermitian operator which doesn't satisfy the physical condition of space-time reflection symmetry (PT symmetry). However the new Hamiltonians are either exactly solvable admitting an entirely real spectrum or quasi exactly solvable with a real algebraic part of their spectrum.Comment: 16 pages, 3 figures, discussion extended, one section adde

BLACK HOLES IN THREE-DIMENSIONAL DILATON GRAVITY THEORIES

Three dimensional black holes in a generalized dilaton gravity action theory are analysed. The theory is specified by two fields, the dilaton and the graviton, and two parameters, the cosmological constant and the Brans-Dicke parameter. It contains seven different cases, of which one distinguishes as special cases, string theory, general relativity and a theory equivalent to four dimensional general relativity with one Killing vector. We study the causal structure and geodesic motion of null and timelike particles in the black hole geometries and find the ADM masses of the different solutions.Comment: 19 pages, latex, 4 figures as uuencoded postscript file

Strong Coupling Phenomena on the Noncommutative Plane

We study strong coupling phenomena in U(1) gauge theory on the non-commutative plane. To do so, we make use of a T-dual description in terms of an $N\to\infty$ limit of U(N) gauge theory on a commutative torus. The magnetic flux on this torus is taken to be $m=N-1$, while the area scales like 1/N, keeping $\Lambda_{QCD}$ fixed. With a few assumptions, we argue that the speed of high frequency light in pure non-commutative QED is modified in the non-commutative directions by the factor $1 + \Lambda_{QCD}^4 \theta^2$, where $\theta$ is the non-commutative parameter. If charged flavours are included, there is an upper bound on the momentum of a photon propagating in the non-commutative directions, beyond which it is unstable against production of charged pairs. We also discuss a particular $\theta\to\infty$ limit of pure non-commutative QED which is T-dual to a more conventional $N\to\infty$ limit with $m/N$ fixed. In the non-commutative description, this limit gives rise to an exotic theory of open strings.Comment: 24 pages, latex, 2 figures, corrected typo in eqn 6.

Giants and loops in beta-deformed theories

We study extended objects in the gravity dual of the N=1 beta-deformation of N=4 Super Yang-Mills theory. We identify probe brane configurations corresponding to giant gravitons and Wilson loops. In particular we identify a new class of objects, given by D5-branes wrapped on a two-torus with a world-volume gauge field strength turned on along the torus. These appear when the deformation parameter assumes a rational value and the gauge theory spectrum has additional branches of vacua. We give an interpretation of the new D5-brane dual giant gravitons in terms of rotating vacuum expectation values in these additional branches.Comment: 26 pages; typos corrected, published versio