Analysis of spiral arms using anisotropic wavelets: gas, dust and magnetic fields in M51

We have developed a technique of isolating elongated structures in galactic images, such as spiral arms, using anisotropic wavelets and apply this to maps of the CO, infrared and radio continuum emission of the grand-design spiral galaxy M51. Systematic shifts between the ridges of CO, infrared and radio continuum emission that are several \kpc long are identified, as well as large variations in pitch angle along spiral arms, of a few tens of degrees. We find two types of arms of polarized radio emission: one has a ridge close to the ridge of CO, with similar pitch angles for the CO and polarization spirals and the regular magnetic field; the other does not always coincide with the CO arm and its pitch angle differs from the orientation of its regular magnetic field. The offsets between ridges of regular magnetic field, dense gas and warm dust are compatible with the sequence expected from spiral density wave triggered star formation, with a delay of a few tens of millions of years between gas entering the shock and the formation of giant molecular clouds and a similar interval between the formation of the clouds and the emergence of young star clusters. At the position of the CO arms the orientation of the regular magnetic field is the same as the pitch angle of the spiral arm, but away from the gaseous arms the orientation of the regular field varies significantly. Spiral shock compression can explain the generation of one type of arm of strong polarized radio emission but a different mechanism is probably responsible for a second type of polarization arm. (Shortened abstract.

Magnetic fields in galaxies: I. Radio disks in local late-type galaxies

We develop an analytical model to follow the cosmological evolution of magnetic fields in disk galaxies. Our assumption is that fields are amplified from a small seed field via magnetohydrodynamical (MHD) turbulence. We further assume that this process is fast compared to other relevant timescales, and occurs principally in the cold disk gas. We follow the turbulent energy density using the Shabala & Alexander (2009) galaxy formation and evolution model. Three processes are important to the turbulent energy budget: infall of cool gas onto the disk and supernova feedback increase the turbulence; while star formation removes gas and hence turbulent energy from the cold gas. Finally, we assume that field energy is continuously transferred from the incoherent random field into an ordered field by differential galactic rotation. Model predictions are compared with observations of local late type galaxies by Fitt & Alexander (1993) and Shabala et al. (2008). The model reproduces observed magnetic field strengths and luminosities in low and intermediate-mass galaxies. These quantities are overpredicted in the most massive hosts, suggesting that inclusion of gas ejection by powerful AGNs is necessary in order to quench gas cooling and reconcile the predicted and observed magnetic field strengths.Comment: 10 pages, 8 figures; MNRAS in pres

The spatial distribution of star and cluster formation in M51

Aims. We study the connection between spatially resolved star formation and young star clusters across the disc of M51. Methods. We combine star cluster data based on B, V, and I-band Hubble Space Telescope ACS imaging, together with new WFPC2 U-band photometry to derive ages, masses, and extinctions of 1580 resolved star clusters using SSP models. This data is combined with data on the spatially resolved star formation rates and gas surface densities, as well as Halpha and 20cm radio-continuum (RC) emission, which allows us to study the spatial correlations between star formation and star clusters. Two-point autocorrelation functions are used to study the clustering of star clusters as a function of spatial scale and age. Results. We find that the clustering of star clusters among themselves decreases both with spatial scale and age, consistent with hierarchical star formation. The slope of the autocorrelation functions are consistent with projected fractal dimensions in the range of 1.2-1.6, which is similar to other galaxies, therefore suggesting that the fractal dimension of hierarchical star formation is universal. Both star and cluster formation peak at a galactocentric radius of 2.5 and 5 kpc, which we tentatively attribute to the presence of the 4:1 resonance and the co-rotation radius. The positions of the youngest (<10 Myr) star clusters show the strongest correlation with the spiral arms, Halpha, and the RC emission, and these correlations decrease with age. The azimuthal distribution of clusters in terms of kinematic age away from the spiral arms indicates that the majority of the clusters formed 5-20 Myr before their parental gas cloud reached the centre of the spiral arm.Comment: 14 pages, 21 figures, accepted for publication in A&

Simulations of the grand design galaxy M51: a case study for analysing tidally induced spiral structure

We present hydrodynamical models of the grand design spiral M51 (NGC 5194), and its interaction with its companion NGC 5195. Despite the simplicity of our models, our simulations capture the present day spiral structure of M51 remarkably well, and even reproduce details such as a kink along one spiral arm, and spiral arm bifurcations. We investigate the offset between the stellar and gaseous spiral arms, and find at most times (including the present day) there is no offset between the stars and gas to within our error bars. We also compare our simulations with recent observational analysis of M51. We compute the pattern speed versus radius, and like the observations, find no single global pattern speed. We also show that the spiral arms cannot be fitted well by logarithmic spirals. We interpret these findings as evidence that M51 does not exhibit a quasi-steady density wave, as would be predicted by density wave theory. The internal structure of M51 derives from the complicated and dynamical interaction with its companion, resulting in spiral arms showing considerable structure in the form of short-lived kinks and bifurcations. Rather than trying to model such galaxies in terms of global spiral modes with fixed pattern speeds, it is more realistic to start from a picture in which the spiral arms, while not being simple material arms, are the result of tidally induced kinematic density `waves' or density patterns, which wind up slowly over time.Comment: 23 pages, 20 figures, accepted for publication in MNRA

Quantitative assessment of microbicide-induced injury in the ovine vaginal epithelium using confocal microendoscopy

<p>Abstract</p> <p>Background</p> <p>The development of safe topical microbicides that can preserve the integrity of cervicovaginal tract epithelial barrier is of great interest as this may minimize the potential for increased susceptibility to STI infections. High resolution imaging to assess epithelial integrity in a noninvasive manner could be a valuable tool for preclinical testing of candidate topical agents.</p> <p>Methods</p> <p>A quantitative approach using confocal fluorescence microendoscopy (CFM) for assessment of microbicide-induced injury to the vaginal epithelium was developed. Sheep were treated intravaginally with one of five agents in solution (PBS; 0.02% benzalkonium chloride (BZK); 0.2% BZK) or gel formulation (hydroxyethyl cellulose (HEC); Gynol II nonoxynol-9 gel (N-9)). After 24 hours the vaginal tract was removed, labeled with propidium iodide (PI), imaged, then fixed for histology. An automated image scoring algorithm was developed for quantitative assessment of injury and applied to the data set. Image-based findings were validated with histological visual gradings that describe degree of injury and measurement of epithelial thickness.</p> <p>Results</p> <p>Distinct differences in PI staining were detected following BZK and N-9 treatment. Images from controls had uniformly distributed nuclei with defined borders, while those after BZK or N-9 showed heavily stained and disrupted nuclei, which increased in proportion to injury detected on histology. The confocal scoring system revealed statistically significant scores for each agent versus PBS controls with the exception of HEC and were consistent with histology scores of injury.</p> <p>Conclusions</p> <p>Confocal microendoscopy provides a sensitive, objective, and quantitative approach for non-invasive assessment of vaginal epithelial integrity and could serve as a tool for real-time safety evaluation of emerging intravaginal topical agents.</p

ЛЕТНАЯ ОТРАБОТКА РАCПРЕДЕЛЕННОЙ CИCТЕМЫ ИНЕРЦИАЛЬНО-CПУТНИКОВОЙ МИКРОНАВИГАЦИИ ДЛЯ РАДИОЛОКАТОРА C CИНТЕЗИРОВАННОЙ АПЕРТУРОЙ

The current state of the onboard systems is characterized by the integration of aviation and radio-electronic equipment systems for solving problems of navigation and control. These problems include micro-navigation of the anten- na phase center (APC) of the radar during the review of the Earth's surface from aboard the aircraft. Increasing of the reso- lution of the radar station (RLS) by hardware increasing the antenna size is not always possible due to restrictions on the aircraft onboard equipment weight and dimensions. Therefore the implementation of analytic extension of the radiation pattern by "gluing" the images, obtained by RLS on the aircraft motion trajectory is embodied. The estimations are con- verted into amendments to the signals of RLS with synthetic aperture RSA to compensate instabilities. The purpose of the research is building a theoretical basis and a practical implementation of procedures for evaluating the trajectory APS in- stabilities using a distributed system of inertial-satellite micro-navigation (DSMN) taking into account the RSA flight oper- ations actual conditions. The technology of evaluation and compensation of RSA trajectory instabilities via DSMN is con- sidered. The implementation of this technology is based on the mutual support of inertial, satellite and radar systems. Syn- chronization procedures of inertial and satellite measurements in the evaluation of DSMN errors are proposed. The given results of DSMN flight testing justify the possibility and expediency to apply the proposed technology in order to improve the resolution of RSA. The compensation of aircraft trajectory instabilities in RSA signals can be provided by inertial- satellite micro-navigation system, taking into account the actual conditions of the RSA flight operations. The researches show that in order to achieve the required resolution of RSA it seems to be appropriate to define the rational balance be- tween accuracy DSMN characteristics and RSA wavelength range.Современное состояние бортовых комплексов характеризуется интеграцией систем авиационного и радио- электронного оборудования при решении задач навигации и управления. К таким задачам относится микронавига- ция фазового центра антенны (ФЦА) радиолокатора при обзоре земной поверхности с борта летательного аппарата (ЛА). Повышение разрешающей способности радиолокационной станции (РЛС) путем аппаратурного увеличения размера антенны не всегда представляется возможным из-за ограничений на массу и габариты бортового оборудо- вания ЛА. Поэтому реализуют аналитическое расширение диаграммы направленности путем «склейки» изображе- ний, получаемых бортовой РЛС на траектории движения ЛА. Для компенсации нестабильностей оценки преобра- зуются в поправки к сигналам РЛС радиолокатора с синтезированной апертурой (РСА). Цель работы - теоретиче- ское обоснование и практическая реализация процедур оценки траекторных нестабильностей ФЦА с помощью распределенной системы инерциально-спутниковой микронавигации (РСМН) с учетом реальных условий летной эксплуатации РСА. Рассматривается технология оценки и компенсации траекторных нестабильностей РСА с по- мощью РСМН. Реализация такой технологии опирается на взаимную поддержку инерциальной, спутниковой и радиолокационной систем. Предлагаются процедуры синхронизации инерциальных и спутниковых измерений при оценке ошибок РСМН. Приводятся результаты летной отработки РСМН, подтверждающие возможность и целесо- образность применения предлагаемой технологии для повышения разрешающей способности РСА. Компенсация траекторных нестабильностей ЛА в сигналах РСА может быть обеспечена с помощью инерциально-спутниковой системы микронавигации с учетом реальных условий летной эксплуатации РСА. Проведенные исследования пока- зали, что для обеспечения требуемого разрешения РСА целесообразным представляется определение рационально- го соотношения между точностными характеристиками РСМН и диапазоном длин волн РСА

New polymer-graphene nanocomposite electrodes with platinum-palladium nanoparticles for chemical power sources

In the present experimental work new polymer-reduced graphene oxide (rGO) nanocomposites with bimetallic platinum-palladium nanoparticles as functional electrodes for chemical power sources were prepared. The size and shape of nanoparticles in the composites have been studied by use of atomic force and high-resolution transmission electron microscopy techniques, X-ray phase analysis and small-angle X-ray scattering. Model tests on the basis of chemically-obtained composite electrodes under operating conditions of fuel elements with formic acid oxidation were carried out