Generic features of Einstein-Aether black holes

We reconsider spherically symmetric black hole solutions in Einstein-Aether theory with the condition that this theory has identical PPN parameters as those for general relativity, which is the main difference from the previous research. In contrast with previous study, we allow superluminal propagation of a spin-0 Aether-gravity wave mode. As a result, we obtain black holes having a spin-0 "horizon" inside an event horizon. We allow a singularity at a spin-0 "horizon" since it is concealed by the event horizon. If we allow such a configuration, the kinetic term of the Aether field can be large enough for black holes to be significantly different from Schwarzschild black holes with respect to ADM mass, innermost stable circular orbit, Hawking temperature, and so on. We also discuss whether or not the above features can be seen in more generic vector-tensor theories.Comment: 9 pages, 9 figures, basic equations and their analytic arguments are adde

Disordered Carbon nanotube alloys in the Effect Medium Super Cell Approximation

We investigate a disordered single-walled carbon nanotube (SWCNT) in an effective medium super cell approximation (EMSCA). First type of disorder that we consider is the presence of vacancies. Our results show that the vacancies induce some bound states on their neighbor host sites, leading to the creation of a band around the Fermi energy in the SWCNT average density of states.Second type of disorder considered is a substitutional $B_{cb}N_{cn}C_{1-cb-cn}$ alloy due to it's applications in hetrojunctions. We found that for a fixed boron (nitrogen) concentration, by increasing the nitrogen (boron) concentration the averaged semiconducting gap, $E_{g}$, decreases and at a critical concentration it disappears. A consequence of our results for nano electronic devices is that by changing the boron(nitrogen) concentration, one can make a semiconductor SWCNT with a pre-determined energy gap.Comment: 4 page

Mechanically-Induced Transport Switching Effect in Graphene-based Nanojunctions

We report a theoretical study suggesting a novel type of electronic switching effect, driven by the geometrical reconstruction of nanoscale graphene-based junctions. We considered junction struc- tures which have alternative metastable configurations transformed by rotations of local carbon dimers. The use of external mechanical strain allows a control of the energy barrier heights of the potential profiles and also changes the reaction character from endothermic to exothermic or vice-versa. The reshaping of the atomic details of the junction encode binary electronic ON or OFF states, with ON/OFF transmission ratio that can reach up to 10^4-10^5. Our results suggest the possibility to design modern logical switching devices or mechanophore sensors, monitored by mechanical strain and structural rearrangements.Comment: 10 pages, 4 figure

Residue codes of extremal Type II Z_4-codes and the moonshine vertex operator algebra

In this paper, we study the residue codes of extremal Type II Z_4-codes of length 24 and their relations to the famous moonshine vertex operator algebra. The main result is a complete classification of all residue codes of extremal Type II Z_4-codes of length 24. Some corresponding results associated to the moonshine vertex operator algebra are also discussed.Comment: 21 pages, shortened from v

Decoupled and inhomogeneous gas flows in S0 galaxies

A recent analysis of the "Einstein" sample of early-type galaxies has revealed that at any fixed optical luminosity Lb S0 galaxies have lower mean X-ray luminosity Lx per unit Lb than ellipticals. Following a previous analytical investigation of this problem (Ciotti & Pellegrini 1996), we have performed 2D numerical simulations of the gas flows inside S0 galaxies in order to ascertain the effectiveness of rotation and/or galaxy flattening in reducing the Lx/Lb ratio. The flow in models without SNIa heating is considerably ordered, and essentially all the gas lost by the stars is cooled and accumulated in the galaxy center. If rotation is present, the cold material settles in a disk on the galactic equatorial plane. Models with a time decreasing SNIa heating host gas flows that can be much more complex. After an initial wind phase, gas flows in energetically strongly bound galaxies tend to reverse to inflows. This occurs in the polar regions, while the disk is still in the outflow phase. In this phase of strong decoupling, cold filaments are created at the interface between inflowing and outflowing gas. Models with more realistic values of the dynamical quantities are preferentially found in the wind phase with respect to their spherical counterparts of equal Lb. The resulting Lx of this class of models is lower than in spherical models with the same Lb and SNIa heating. At variance with cooling flow models, rotation is shown to have only a marginal effect in this reduction, while the flattening is one of the driving parameters for such underluminosity, in accordance with the analytical investigation.Comment: 32 pages LaTex file, plus 5 .ps figures and macro aasms4.sty -- Accepted on Ap

History Memorized and Recalled upon Glass Transition

The memory effect upon glassification is studied in the glass to rubber transition of vulcanized rubber with the strain as a controlling parameter. A phenomenological model is proposed taking the history of the temperature and the strain into account, by which the experimental results are interpreted. The data and the model demonstrate that the glassy state memorizes the time-course of strain upon glassification, not as a single parameter but as the history itself. The data also show that the effect of irreversible deformation in the glassy state is beyond the scope of the present model. Authors' remark: The title of the paper in the accepted version is above. The title appeared in PRL is the one changed by a Senior Assistant Editor after acceptance of the paper. The recovery of the title was rejected in the correction process.Comment: 4 pages, 4 figure

Thermal Stability of Metallic Single-Walled Carbon Nanotubes: An O(N) Tight-Binding Molecular Dynamics Simulation Study

Order(N) Tight-Binding Molecular Dynamics (TBMD) simulations are performed to investigate the thermal stability of (10,10) metallic Single-Walled Carbon Nanotubes (SWCNT). Periodic boundary conditions (PBC) are applied in axial direction. Velocity Verlet algorithm along with the canonical ensemble molecular dynamics (NVT) is used to simulate the tubes at the targeted temperatures. The effects of slow and rapid temperature increases on the physical characteristics, structural stability and the energetics of the tube are investigated and compared. Simulations are carried out starting from room temperature and the temperature is raised in steps of 300K. Stability of the simulated metallic SWCNT is examined at each step before it is heated to higher temperatures. First indication of structural deformation is observed at 600K. For higher heat treatments the deformations are more pronounced and the bond breaking temperature is reached around 2500K. Gradual (slow) heating and thermal equilibrium (fast heating) methods give the value of radial thermal expansion coefficient in the temperature range between 300K-600K as 0.31x10^{-5}(1/K) and 0.089x10^{-5}(1/K), respectively. After 600K, both methods give the same value of 0.089x10^{-5}(1/K). The ratio of the total energy per atom with respect to temperature is found to be 3x10^{-4} eV/K

Dynamical Evolution of Globular Clusters in Hierarchical Cosmology

We probe the evolution of globular clusters that could form in giant molecular clouds within high-redshift galaxies. Numerical simulations demonstrate that the large and dense enough gas clouds assemble naturally in current hierarchical models of galaxy formation. These clouds are enriched with heavy elements from earlier stars and could produce star clusters in a similar way to nearby molecular clouds. The masses and sizes of the model clusters are in excellent agreement with the observations of young massive clusters. Do these model clusters evolve into globular clusters that we see in our and external galaxies? In order to study their dynamical evolution, we calculate the orbits of model clusters using the outputs of the cosmological simulation of a Milky Way-sized galaxy. We find that at present the orbits are isotropic in the inner 50 kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10 kpc from the center formed in the now-disrupted satellite galaxies. The spatial distribution of model clusters is spheroidal, with a power-law density profile consistent with observations. The combination of two-body scattering, tidal shocks, and stellar evolution results in the evolution of the cluster mass function from an initial power law to the observed log-normal distribution.Comment: 5 pages, proceedings of IAU 246 "Dynamical Evolution of Dense Stellar Systems", eds. Vesperini, Giersz, Sill

Spectral evolution of magnetic flares and time lags in accreting black hole sources

We present a model for the short timescale spectral variability of accreting black holes. It describes well the time-averaged spectra as well as temporal characteristics such as power-density spectrum, time/phase lags, and coherence function of Cygnus X-1. We assume that X/gamma-rays are produced in compact magnetic flares at radii < 100GM/c^2 from the central black hole. The tendency for magnetic loops to inflate and detach from the underlying accretion disc causes the spectrum of a flare to evolve from soft to hard due to the decrease of the feedback from the cold disc, so causing time delays between hard and soft photons. We identify the observed time lags with the evolution timescales of the flares, which are of the order of the Keplerian timescale. We model the overall temporal variability using a pulse avalanche model in which each flare has a certain probability to trigger a neighbouring flare, thus occasionally producing long avalanches. The duration of the avalanches determines the Fourier frequencies where most of the power emerges.Comment: 6 pages, 3 figures, version accepted to MNRA