Hypernatural Numbers as Ultrafilters

In this paper we present a use of nonstandard methods in the theory of ultrafilters and in related applications to combinatorics of numbers

Perioperative Hypothermia (33°C) Does Not Increase theOccurrence of Cardiovascular Events in PatientsUndergoing Cerebral Aneurysm SurgeryFindings from the Intraoperative Hypothermia for AneurysmSurgery Trial

The IHAST Trial randomized patients undergoing cerebral aneurysm surgery to intraoperative hypothermia or normothermia. Cardiovascular events were prospectively followed until 3-month follow-up and were compared in hypothermic and normothermic patients. Conclusion: In patients undergoing cerebral aneurysm surgery, perioperative hypothermia was not associated with an increased occurrence of cardiovascular events

The effect of activity-related meridional flow modulation on the strength of the solar polar magnetic field

We studied the effect of the perturbation of the meridional flow in the activity belts detected by local helioseismology on the development and strength of the surface magnetic field at the polar caps. We carried out simulations of synthetic solar cycles with a flux transport model, which follows the cyclic evolution of the surface field determined by flux emergence and advective transport by near-surface flows. In each hemisphere, an axisymmetric band of latitudinal flows converging towards the central latitude of the activity belt was superposed onto the background poleward meridional flow. The overall effect of the flow perturbation is to reduce the latitude separation of the magnetic polarities of a bipolar magnetic region and thus diminish its contribution to the polar field. As a result, the polar field maximum reached around cycle activity minimum is weakened by the presence of the meridional flow perturbation. For a flow perturbation consistent with helioseismic observations, the polar field is reduced by about 18% compared to the case without inflows. If the amplitude of the flow perturbation depends on the cycle strength, its effect on the polar field provides a nonlinearity that could contribute to limiting the amplitude of a Babcock-Leighton type dynamo.Comment: 16 pages, 5 figures, accepted by Ap

Detection of Cold Atomic Clouds in the Magellanic Bridge

We report a detection of cold atomic hydrogen in the Magellanic Bridge using 21-cm absorption spectroscopy toward the radio source B0312-770. With a column density of N_HI=1.2E20 cm^-2, a maximum absorption optical depth of tau=0.10 and a maximum 21-cm emission brightness temperature of 1.4 K, this line of sight yields a spin temperature, T_s, between 20 K and 40 K. H I 21-cm absorption and emission spectroscopy toward 7 other low column density sightlines on the periphery of the LMC and SMC reveal absorption toward one additional background radio source behind the SMC with tau=0.03. The data have typical sensitivities of sigma_tau=0.005 to 0.070 in absorption and sigma_{T_B}=0.03 K in emission. These data demonstrate the presence of a cold atomic phase which is probably accompanied by molecular condensations in the tenuous interstellar medium of the Bridge region. Young OB stars observed in the Magellanic Bridge could form "in situ" from these cold condensations rather than migrate from regions of active star formation in the main body of the SMC. The existence of cold condensations and star formation in the Magellanic Bridge might be understood as a small scale version of the mechanism that produces star formation in the tidal tails of interacting galaxies.Comment: 25 pages, uses AASTeX and psfig; Accepted for Publication in the Astronomical Journa

Acoustic Power Absorption and its Relation with Vector Magnetic Field of a Sunspot

The distribution of acoustic power over sunspots shows an enhanced absorption near the umbra--penumbra boundary. Earlier studies revealed that the region of enhanced absorption coincides with the region of strongest transverse potential field. The aim of this paper is to (i) utilize the high-resolution vector magnetograms derived using Hinode SOT/SP observations and study the relationship between the vector magnetic field and power absorption and (ii) study the variation of power absorption in sunspot penumbrae due to the presence of spine-like radial structures. It is found that (i) both potential and observed transverse fields peak at a similar radial distance from the center of the sunspot, and (ii) the magnitude of the transverse field, derived from Hinode observations, is much larger than the potential transverse field derived from SOHO/MDI longitudinal field observations. In the penumbra, the radial structures called spines (intra-spines) have stronger (weaker) field strength and are more vertical (horizontal). The absorption of acoustic power in the spine and intra-spine shows different behaviour with the absorption being larger in the spine as compared to the intra-spine.Comment: 18 pages, 7 figures, In Press Solar Physics, Topical Issue on Helio-and-Astroseismolog

Fundamental-mode Oscillations of Two Coronal Loops within a Solar Magnetic Arcade

We analyze intensity variations, as measured by the Atmospheric Imaging Assembly in the 171 Å passband, in two coronal loops embedded within a single coronal magnetic arcade. We detect oscillations in the fundamental mode with periods of roughly 2 minutes and decay times of 5 minutes. The oscillations were initiated by interaction of the arcade with a large wavefront issuing from a flare site. Further, the power spectra of the oscillations evince signatures consistent with oblique propagation to the field lines and for the existence of a two-dimensional waveguide instead of a one-dimensional one

Herbig Ae/Be Stars in the Magellanic Bridge

We have found Herbig Ae/Be star candidates in the western region of the Magellanic Bridge. Using the near infrared camera SIRIUS and the 1.4 m telescope IRSF, we surveyed about 3.0 deg x 1.3 deg (24 deg < RA < 36 deg, -75 deg < Dec. < -73.7 deg) in the J, H, and Ks bands. On the basis of colors and magnitudes, about 200 Herbig Ae/Be star candidates are selected. Considering the contaminations by miscellaneous sources such as foreground stars and early-type dwarfs in the Magellanic Bridge, we estimate that about 80 (about 40%) of the candidates are likely to be Herbig Ae/Be stars. We also found one concentration of the candidates at the young star cluster NGC 796, strongly suggesting the existence of pre-main-sequence (PMS) stars in the Magellanic Bridge. This is the first detection of PMS star candidates in the Magellanic Bridge, and if they are genuine PMS stars, this could be direct evidence of recent star formation. However, the estimate of the number of Herbig Ae/Be stars depends on the fraction of classical Be stars, and thus a more precise determination of the Be star fraction or observations to differentiate between the Herbig Ae/Be stars and classical Be stars are required.Comment: 22 pages, 6 figures. Accepted for publication in Ap

Dark Matter and the Chemical Evolution of Irregular Galaxies

We present three types of chemical evolution models for irregular galaxies: closed-box with continuous star formation rates (SFRs), closed-box with bursting SFRs, and O-rich outflow with continuous SFRs. We discuss the chemical evolution of the irregular galaxies NGC 1560 and II Zw 33, and a ``typical'' irregular galaxy. The fraction of low-mass stars needed by our models is larger than that derived for the solar vicinity, but similar to that found in globular clusters. For our typical irregular galaxy we need a mass fraction of about 40% in the form of substellar objects plus non baryonic dark matter inside the Holmberg radius, in good agreement with the results derived for NGC 1560 and II Zw 33 where we do have an independent estimate of the mass fraction in non baryonic dark matter. Closed-box models are better than O-rich outflow models in explaining the C/O and Z/O observed values for our typical irregular galaxy.Comment: 14 pages, 2 figure, uses emulateapj.sty package. ApJ in press. New models were added. The order of Tables has been correcte

Time-dependent suppression of oscillatory power in evolving solar magnetic fields

Oscillation amplitudes are generally smaller within magnetically active regions like sunspots and plage when compared to their surroundings. Such magnetic features, when viewed in spatially resolved power maps, appear as regions of suppressed power due to reductions in the oscillation amplitudes. Employing high spatial- and temporal-resolution observations from the Dunn Solar Telescope (DST) in New Mexico, we study the power suppression in a region of evolving magnetic fields adjacent to a pore. By utilizing wavelet analysis, we study for the first time how the oscillatory properties in this region change as the magnetic field evolves with time. Image sequences taken in the blue continuum, G-band, Ca ii K, and Hα filters were used in this study. It is observed that the suppression found in the chromosphere occupies a relatively larger area, confirming previous findings. Also, the suppression is extended to structures directly connected to the magnetic region, and is found to get enhanced as the magnetic field strength increased with time. The dependence of the suppression on the magnetic field strength is greater at longer periods and higher formation heights. Furthermore, the dominant periodicity in the chromosphere was found to be anti-correlated with increases in the magnetic field strength

Newly identified properties of surface acoustic power

The cause of enhanced acoustic power surrounding active regions, the acoustic halo, is not as yet understood. We explore the properties of the enhanced acoustic power observed near disk center from 21 to 27 January 2002, including AR 9787. We find that (i) there exists a strong correlation of the enhanced high frequency power with magnetic-field inclination, with greater power in more horizontal fields, (ii) the frequency of the maximum enhancement increases along with magnetic field strength, and (iii) the oscillations contributing to the halos show modal ridges which are shifted to higher wavenumber at constant frequency in comparison to the ridges of modes in the quiet-Sun.Comment: 16 pages, 10 figures, submitted to solar physic