The influence of radiation shielding on reusable nuclear shuttle design

Alternate reusable nuclear shuttle configurations were synthesized and evaluated. Particular attention was given to design factors which reduced tank exposure to direct and scattered radiation, increased payload-engine separation, and improved self-shielding by the LH2 propellant. The most attractive RNS concept in terms of cost effectiveness consists of a single conical aft bulkhead tank with a high fineness ratio. Launch is accomplished by the INT-21 with the tank positioned in the inverted attitude. The NERVA engine is delivered to orbit separately where final stage assembly and checkout are accomplished. This approach is consistent with NERVA definition criteria and required operating procedures to support an economically viable nuclear shuttle transportation program in the post-1980 period

Vortex macroscopic superpositions in ultracold bosons in a double-well potential

We study macroscopic superpositions in the orbital rather than the spatial degrees of freedom, in a three-dimensional double-well system. We show that the ensuing dynamics of $N$ interacting excited ultracold bosons, which in general requires at least eight single-particle modes and ${N+7 \choose N}$ Fock vectors, is described by a surprisingly small set of many-body states. An initial state with half the atoms in each well, and purposely excited in one of them, gives rise to the tunneling of axisymmetric and transverse vortex structures. We show that transverse vortices tunnel orders of magnitude faster than axisymmetric ones and are therefore more experimentally accessible. The tunneling process generates macroscopic superpositions only distinguishable by their orbital properties and within experimentally realistic times.Comment: 9 pages, 6 figure

Symplectic gauge fields and dark matter

The dynamics of symplectic gauge fields provides a consistent framework for fundamental interactions based on spin three gauge fields. One remarkable property is that symplectic gauge fields only have minimal couplings with gravitational fields and not with any other field of the Standard Model. Interactions with ordinary matter and radiation can only arise from radiative corrections. In spite of the gauge nature of symplectic fields they acquire a mass by the Coleman-Weinberg mechanism which generates Higgs-like mass terms where the gravitational field is playing the role of a Higgs field. Massive symplectic gauge fields weakly interacting with ordinary matter are natural candidates for the dark matter component of the Universe.Comment: 16 page

Casimir Effect and Global Theory of Boundary Conditions

The consistency of quantum field theories defined on domains with external borders imposes very restrictive constraints on the type of boundary conditions that the fields can satisfy. We analyse the global geometrical and topological properties of the space of all possible boundary conditions for scalar quantum field theories. The variation of the Casimir energy under the change of boundary conditions reveals the existence of singularities generically associated to boundary conditions which either involve topology changes of the underlying physical space or edge states with unbounded below classical energy. The effect can be understood in terms of a new type of Maslov index associated to the non-trivial topology of the space of boundary conditions. We also analyze the global aspects of the renormalization group flow, T-duality and the conformal invariance of the corresponding fixed points.Comment: 11 page

Quasi-Periodic Oscillations and energy spectra from the two brightest Ultra-Luminous X-ray sources in M82

Ultra-Luminous X-ray sources are thought to be accreting black holes that might host Intermediate Mass Black Holes (IMBH), proposed to exist by theoretical studies, even though a firm detection (as a class) is still missing. The brightest ULX in M82 (M82 X-1) is probably one of the best candidates to host an IMBH. In this work we analyzed the data of the recent release of observations obtained from M82 X-1 taken by XMM-Newton. We performed a study of the timing and spectral properties of the source. We report on the detection of (46+-2) mHz Quasi-Periodic Oscillations (QPOs) in the power density spectra of two observations. A comparison of the frequency of these high-frequency QPOs with previous detections supports the 1:2:3 frequency distribution as suggested in other studies. We discuss the implications if the (46+-2) mHz QPO detected in M82 X-1 is the fundamental harmonic, in analogy with the High-Frequency QPOs observed in black hole binaries. For one of the observations we have detected for the first time a QPO at 8 mHz (albeit at a low significance), that coincides with a hardening of the spectrum. We suggest that the QPO is a milli-hertz QPO originating from the close-by transient ULX M82 X-2, with analogies to the Low-Frequency QPOs observed in black hole binaries.Comment: 9 pages (with 4 figures and 4 tables). Accepted for publication in MNRAS (26/09/13

Ultraluminous X-ray sources with flat-topped noise and QPO

We analyzed the X-ray power density spectra of five ultraluminous X-ray sources (ULXs) NGC5408 X-1, NGC6946 X-1, M82 X-1, NGC1313 X-1 and IC342 X-1 that are the only ULXs which display both flat-topped noise (FTN) and quasi-periodic oscillations (QPO). We studied the QPO frequencies, fractional root-mean-square (rms) variability, X-ray luminosity and spectral hardness. We found that the level of FTN is anti-correlated with the QPO frequency. As the frequency of the QPO and brightness of the sources increase, their fractional variability decreases. We propose a simple interpretation using the spherizarion radius, viscosity time and $\alpha$-parameter as basic properties of these systems. The main physical driver of the observed variability is the mass accretion rate which varies >3 between different observations of the same source. As the accretion rate decreases the spherization radius reduces and the FTN plus the QPO move toward higher frequencies resulting in a decrease of the fractional rms variability. We also propose that in all ULXs when the accretion rate is low enough (but still super-Eddington) the QPO and FTN disappear. Assuming that the maximum X-ray luminosity depends only on the black hole (BH) mass and not on the accretion rate (not considering the effects of either the inclination of the super-Eddington disc nor geometrical beaming of radiation) we estimate that all the ULXs have about similar BH masses, with the exception of M82 X-1, which might be 10 times more massive.Comment: 15 pages, 7 figures, accepted for publication in MNRA

Comparative analysis of Bacillus weihenstephanensis KBAB4 spores obtained at different temperatures

The impact of Bacillus weihenstephanensis KBAB4 sporulation temperature history was assessed on spore heat resistance, germination and outgrowth capacity at a temperature range from 7 to 30 °C. Sporulation rate and efficiency decreased at low temperature, as cells sporulated at 12, 20 and 30 °C with approximately 99% efficiency, whereas at 7 °C and 10 °C, a maximum 15% of sporulation was reached. Spores formed at 30 °C showed the highest wet heat resistance at 95 °C, with spores formed at 7 and 10 °C displaying only survival of 15 min exposure at 70 °C, indicating their low level heat resistance. RT-PCR analysis revealed expression of sporulation sigma factor sigG, and germinant receptor operons gerI, gerK, gerL, gerR, gerS, and (plasmid-located) gerS2 to be activated in all sporulation conditions tested. Subsequent germination assays revealed a combination of inosine and L-Alanine to be very efficient, triggering over 99% of the spores to germinate, with spores obtained at 30 °C showing the highest germination rates (99%). Notably, spores obtained at 12, 20 and 30 °C, germinated at all tested temperatures, showing > 70% spore germination even at temperatures as low as 5 °C. Less than 5% of spores obtained at 7 and 10 °C showed a germination response. Furthermore, spores produced at 12, 20 and 30 °C showed similar outgrowth effiency at these temperatures, indicating that low temperature sporulation history does not improve low temperature outgrowth performance. Insights obtained in sporulation and germination behaviour of B. weihenstephanensis KBAB4, in combination with the availability of its genome sequence, may contribute to our understanding of the behaviour of psychrotolerant spoilage and pathogenic Bacill