On classical string configurations

Equations which define classical configurations of strings in $R^3$ are presented in a simple form. General properties as well as particular classes of solutions of these equations are considered.Comment: 10 pages, Latex, no figures, trivial corrections, submitted to Modern Physics Letters

Incidence and public health burden of sunburn among beachgoers in the United States.

The beach environment creates many barriers to effective sun protection, putting beachgoers at risk for sunburn, a well-established risk factor for skin cancer. Our objective was to estimate incidence of sunburn among beachgoers and evaluate the relationship between sunburn incidence and sun-protective behaviors. A secondary analysis, of prospective cohorts at 12 locations within the U.S. from 2003 to 2009 (n = 75,614), were pooled to evaluate sunburn incidence 10-12 days after the beach visit. Behavioral and environmental conditions were cross-tabulated with sunburn incidence. Multivariable logistic regression was used to estimate the association between new sunburn and sun-protective behaviors. Overall, 13.1% of beachgoers reported sunburn. Those aged 13-18 years (16.5%), whites (16.0%), and those at beach locations along the Eastern Seaboard (16.1%), had the highest incidence of sunburn. For those spending ≥5 h in the sun, the use of multiple types of sun protection reduced odds of sunburn by 55% relative to those who used no sun protection (Odds Ratio = 0.45 (95% Confidence Interval:0.27-0.77)) after adjusting for skin type, age, and race. Acute health effects of sunburn tend to be mild and self-limiting, but potential long-term health consequences are more serious and costly. Efforts to encourage and support proper sun-protective behaviors, and increase access to shade, protective clothing, and sunscreen, can help prevent sunburn and reduce skin cancer risk among beachgoers

Analysis of hydrogen-rich magnetic white dwarfs detected in the Sloan Digital Sky Survey

We model the structure of the surface magnetic fields of the hydrogen-rich white dwarfs in the SDSS. We have calculated a grid of state-of-the-art theoretical optical spectra of hydrogen-rich magnetic white dwarfs with magnetic field strengths between 1 MG and 1200 MG for different angles, and for effective temperatures between 7000 K and 50000 K. We used a least-squares minimization scheme with an evolutionary algorithm in order to find the magnetic field geometry best fitting the observed data. We used simple centered dipoles or dipoles which were shifted along the dipole axis to model the coadded SDSS fiber spectrum of each object. We have analysed the spectra of all known magnetic DAs from the SDSS (97 previously published plus 44 newly discovered) and also investigated the statistical properties of magnetic field geometries of this sample. The total number of known magnetic white dwarfs already more than tripled by the SDSS and more objects are expected from a more systematic search. The magnetic fields span a range between ~1 and 900 MG. Our results further support the claim that Ap/Bp population is insufficient in generating the numbers and field strength distributions of the observed MWDs, and either another source of progenitor types or binary evolution is needed. Moreover clear indications for non-centered dipoles exist in about ~50% of the objects which is consistent with the magnetic field distribution observed in Ap/Bp stars.Comment: 15 pages, accepted for publication in A&A. For online version with full appendix figures, see http://www.ari.uni-heidelberg.de/mitarbeiter/bkulebi/papers/12570_online.pd

VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic Imager

In this paper we describe in detail the implementation and main properties of a new inversion code for the polarized radiative transfer equation (VFISV: Very Fast inversion of the Stokes vector). VFISV will routinely analyze pipeline data from the Helioseismic and Magnetic Imager (HMI) on-board of the Solar Dynamics Observatory (SDO). It will provide full-disk maps (4096$\times$4096 pixels) of the magnetic field vector on the Solar Photosphere every 10 minutes. For this reason VFISV is optimized to achieve an inversion speed that will allow it to invert 16 million pixels every 10 minutes with a modest number (approx. 50) of CPUs. Here we focus on describing a number of important details, simplifications and tweaks that have allowed us to significantly speed up the inversion process. We also give details on tests performed with data from the spectropolarimeter on-board of the Hinode spacecraft.Comment: 23 pages, 9 figures (2 color). Submitted for publication to Solar Physic

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

Magnetic Field Structures in a Facular Region Observed by THEMIS and Hinode

The main objective of this paper is to build and compare vector magnetic maps obtained by two spectral polarimeters, i.e. THEMIS/MTR and Hinode SOT/SP, using two inversion codes (UNNOFIT and MELANIE) based on the Milne-Eddington solar atmosphere model. To this end, we used observations of a facular region within active region NOAA 10996 on 23 May 2008, and found consistent results concerning the field strength, azimuth and inclination distributions. Because SOT/SP is free from the seeing effect and has better spatial resolution, we were able to resolve small magnetic polarities with sizes of 1" to 2", and we could detect strong horizontal magnetic fields, which converge or diverge in negative or positive facular polarities. These findings support models which suggest the existence of small vertical flux tube bundles in faculae. A new method is proposed to get the relative formation heights of the multi-lines observed by MTR assuming the validity of a flux tube model for the faculae. We found that the Fe 1 6302.5 \AA line forms at a greater atmospheric height than the Fe 1 5250.2 \AA line.Comment: 20 pages, 9 figures, 3 tables, accepted for publication in Solar Physic

Surfaces immersed in su(N+1) Lie algebras obtained from the CP^N sigma models

We study some geometrical aspects of two dimensional orientable surfaces arrising from the study of CP^N sigma models. To this aim we employ an identification of R^(N(N+2)) with the Lie algebra su(N+1) by means of which we construct a generalized Weierstrass formula for immersion of such surfaces. The structural elements of the surface like its moving frame, the Gauss-Weingarten and the Gauss-Codazzi-Ricci equations are expressed in terms of the solution of the CP^N model defining it. Further, the first and second fundamental forms, the Gaussian curvature, the mean curvature vector, the Willmore functional and the topological charge of surfaces are expressed in terms of this solution. We present detailed implementation of these results for surfaces immersed in su(2) and su(3) Lie algebras.Comment: 32 pages, 1 figure; changes: major revision of presentation, clarifications adde

Magnetic Field Measurement with Ground State Alignment

Observational studies of magnetic fields are crucial. We introduce a process "ground state alignment" as a new way to determine the magnetic field direction in diffuse medium. The alignment is due to anisotropic radiation impinging on the atom/ion. The consequence of the process is the polarization of spectral lines resulting from scattering and absorption from aligned atomic/ionic species with fine or hyperfine structure. The magnetic field induces precession and realign the atom/ion and therefore the polarization of the emitted or absorbed radiation reflects the direction of the magnetic field. The atoms get aligned at their low levels and, as the life-time of the atoms/ions we deal with is long, the alignment induced by anisotropic radiation is susceptible to extremely weak magnetic fields ($1{\rm G}\gtrsim B\gtrsim 10^{-15}$G). In fact, the effects of atomic/ionic alignment were studied in the laboratory decades ago, mostly in relation to the maser research. Recently, the atomic effect has been already detected in observations from circumstellar medium and this is a harbinger of future extensive magnetic field studies. A unique feature of the atomic realignment is that they can reveal the 3D orientation of magnetic field. In this article, we shall review the basic physical processes involved in atomic realignment. We shall also discuss its applications to interplanetary, circumstellar and interstellar magnetic fields. In addition, our research reveals that the polarization of the radiation arising from the transitions between fine and hyperfine states of the ground level can provide a unique diagnostics of magnetic fields in the Epoch of Reionization.Comment: 30 pages, 12 figures, chapter in Lecture Notes in Physics "Magnetic Fields in Diffuse Media". arXiv admin note: substantial text overlap with arXiv:1203.557