Some comments on spacelike minimal surfaces with null polygonal boundaries in AdSmAdS_m

We discuss some geometrical issues related to spacelike minimal surfaces in $AdS_m$ with null polygonal boundaries at conformal infinity. In particular for $AdS_4$, two holomorphic input functions for the Pohlmeyer reduced system are identified. This system contains two coupled differential equations for two functions $\alpha (z,\bar z)$ and $\beta (z,\bar z)$, related to curvature and torsion of the surface. Furthermore, we conjecture that, for a polynomial choice of the two holomorphic functions, the relative positions of their zeros encode the conformal invariant data of the boundary null $2n$-gon.Comment: 13 pages, a note and references added, version to appear in JHE

A note on string solutions in AdS_3

We systematically search for classical open string solutions in AdS_3 within the general class expressed by elliptic functions (i.e., the genus-one finite-gap solutions). By explicitly solving the reality and Virasoro conditions, we give a classification of the allowed solutions. When the elliptic modulus degenerates, we find a class of solutions with six null boundaries, among which two pairs are collinear. By adding the S^1 sector, we also find four-cusp solutions with null boundaries expressed by the elliptic functions.Comment: 17 pages, 1 figure; (v2) added 1 figure and discussion on solutions with 6 null boundaries; (v3) corrected equation numbers; (v4) added comment

A New Galactic Extinction Map of the Cygnus Region

We have made a Galactic extinction map of the Cygnus region with 5' spatial resolution. The selected area is 80^\circ to 90^\circ in the Galactic longitude and -4^\circ to 8^\circ in the Galactic latitude. The intensity at 140 \mum is derived from the intensities at 60 and 100 \mum of the IRAS data using the tight correlation between 60, 100, and 140 \mum found in the Galactic plane. The dust temperature and optical depth are calculated with 5' resolution from the 140 and 100 \mum intensity, and Av is calculated from the optical depth. In the selected area, the mean dust temperature is 17 K, the minimum is 16 K, and the maximum is 30 K. The mean Av is 6.5 mag, the minimum is 0.5 mag, and the maximum is 11 mag. The dust temperature distribution shows significant spatial variation on smaller scales down to 5'. Because the present study can trace the 5'-scale spatial variation of the extinction, it has an advantage over the previous studies, such as the one by Schlegel, Finkbeiner, & Davis, who used the COBE/DIRBE data to derive the dust temperature distribution with a spatial resolution of 1^\circ. The difference of Av between our map and Schlegel et al.'s is \pm 3 mag. A new extinction map of the entire sky can be produced by applying the present method.Comment: 27 pages, 14 figures, accepted for publication in Ap

Existence of Dynamical Scaling in the Temporal Signal of Time Projection Chamber

The temporal signals from a large gas detector may show dynamical scaling due to many correlated space points created by the charged particles while passing through the tracking medium. This has been demonstrated through simulation using realistic parameters of a Time Projection Chamber (TPC) being fabricated to be used in ALICE collider experiment at CERN. An interesting aspect of this dynamical behavior is the existence of an universal scaling which does not depend on the multiplicity of the collision. This aspect can be utilised further to study physics at the device level and also for the online monitoring of certain physical observables including electronics noise which are a few crucial parameters for the optimal TPC performance.Comment: 5 pages, 6 figure

A radiation driven implosion model for the enhanced luminosity of protostars near HII regions

Context. Molecular clouds near the H II regions tend to harbor more luminous protostars. Aims. Our aim in this paper is to investigate whether or not radiation-driven implosion mechanism enhances luminosity of protostars near regions of high-ionizing fluxes. Methods. We performed numerical simulations to model collapse of cores exposed to UV radiation from O stars. We investigated dependence of mass loss rates on the initial density profiles of cores and variation of UV fluxes. We derived simple analytic estimates of accretion rates and final masses of protostars. Results. Radiation-driven implosion mechanism can increase accretion rates of protostars by 1-2 orders of magnitude. On the other hand, mass loss due to photo-evaporation is not large enough to have a significant impact on the luminosity. The increase of accretion rate makes luminosity 1-2 orders higher than those of protostars that form without external triggering. Conclusions. Radiation-driven implosion can help explain the observed higher luminosity of protostars in molecular clouds near H II regions.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and Astrophysic

Moduli Dynamics of AdS_3 Strings

We construct a general class of solutions for a classical string in AdS_3 spacetime. The construction is based on a Pohlmeyer type reduction, with the sinh-Gordon model providing the general N-soliton solutions. The corresponding exact spiky string configurations are then reconstructed through the inverse scattering method. It is shown that the string moduli are determined entirely by those of the solitons.Comment: 22 pages, no figures; references adde

Polarized triplet production by circularly polarized photons

A process of the pair production by a circularly polarized photon in the field of unpolarized atomic electron has been considered in the Weizaecker-Williams approximation. The degree of longitudinal polarization of positron and electron has been calculated. An exclusive cross-section as well as a spectral distribution are obtained. We estimate the accuracy of our calculations at the level of a few percent. We show the identity of the positron polarization for considered process and for process of pair production in the screened Coulomb field of nucleus.Comment: 9 pages, 3 picture

Spitzer-MIPS survey of the young stellar content in the Vela Molecular Cloud-D

A new, unbiased Spitzer-MIPS imaging survey (~1.8 square degs) of the young stellar content of the Vela Molecular Cloud-D is presented. The survey is complete down to 5mJy and 250mJy at 24micron (mu) and 70mu, respectively. 849 sources are detected at 24mu and 52 of them also have a 70mu counterpart. The VMR-D region is one that we have already partially mapped in dust and gas millimeter emission, and we discuss the correlation between the Spitzer compact sources and the mm contours. About half of the 24mu sources are located inside the region delimited by the 12CO(1-0) contours (corresponding to only one third of the full area mapped with MIPS) with a consequent density increase of about 100% of the 24mu sources [four times for 70mu ones] moving from outside to inside the CO contours. About 400 sources have a 2MASS counterpart. So we have constructed a Ks vs. Ks-[24] diagram and identified the protostellar population. We find an excess of Class I sources in VMR-D in comparison with other star forming regions. This result is reasonably biased by the sensitivity limits, or, alternatively, may reflect a very short lifetime (<=10^6yr) of the protostellar content in this cloud. The MIPS images have identified embedded cool objects in most of the previously identified starless cores; in addition, there are 6 very young, possibly Class 0 objects identified. Finally we report finding of the driving sources for a set of five out of six very compact protostellar jets previously discovered in near-infrared images.Comment: 29 pages, 14 figures. To appear in Ap.