Electron-Electron scattering and resistivity of ballistic multimode channels

We show that electron--electron scattering gives a positive contribution to the resistivity of ballistic multimode wires whose width is much smaller than their length. This contribution is not exponentially small at low temperatures and therefore may be experimentally observable. It scales with temperature as $T^2$ for three-dimensional channels and as $T^{5/2}$ for two-dimensional ones.Comment: 4 pages, 3 figures; published versio

Aromaticity in a Surface Deposited Cluster: Pd4_4 on TiO2_2 (110)

We report the presence of \sigma-aromaticity in a surface deposited cluster, Pd$_4$ on TiO$_2$ (110). In the gas phase, Pd$_4$ adopts a tetrahedral structure. However, surface binding promotes a flat, \sigma-aromatic cluster. This is the first time aromaticity is found in surface deposited clusters. Systems of this type emerge as a promising class of catalyst, and so realization of aromaticity in them may help to rationalize their reactivity and catalytic properties, as a function of cluster size and composition.Comment: 4 pages, 3 figure

Mexametric Assessment of Melanin Level in Children's Skin

Background. High predisposition to sunburn in childhood and associated increased risk of malignant skin tumors development, decrease with age. There is a likelihood of a relationship between the described trends and dynamic age related changes in functional state of melanocytes and melanin.Aim: to evaluate the level of melanin in the skin in children of different age. Materials and methods. The study involved 78 children aged from 7 to 17 years, without any disorders of skin pigmentation. Three groups of observations were formed: Group 1 - 28 children from 7 to 9 years, Group 2 - 25 children from 10 to 12 years, Group 3 - 25 children from 16 to 17years. The melanin level was evaluated in the skin of face, body and extremities using mexametry.Results. The highest level of skin melanin was observed in forearms and lower legs in all age groups (up to 28.3 ± 10.8, 23.3 ± 8.6 and 26.7 ± 10.6 c.u. in Group 1, 2 and 3 respectively), the lowest - in cheeks and chest (up to 8.0 ± 4.7, 4.4 ± 3.4 and 9.5 ± 4.1 c.u. in Group 1, 2 and 3 respectively). There were relationships between skin site and level of melanin, but no relationships between level of melanin and gender or age.Findings. The level of melanin in the skin in children aged from 7 to 17 years is individual and depends on the location of the skin area, but does not depend on gender or age. The distribution of melanin in the skin is stable and does not change over time

Identification of particles with Lorentz factor up to 10410^{4} with Transition Radiation Detectors based on micro-strip silicon detectors

This work is dedicated to the study of a technique for hadron identification in the TeV momentum range, based on the simultaneous measurement of the energies and of the emission angles of the Transition Radiation (TR) X-rays with respect to the radiating particles. A detector setup has been built and tested with particles in a wide range of Lorentz factors (from about $10^3$ to about $4 \times 10^4$ crossing different types of radiators. The measured double-differential (in energy and angle) spectra of the TR photons are in a reasonably good agreement with TR simulation predictions.Comment: 31 pages, 12 figures, paper published on Nuclear Instruments & Methods

Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XV. Long-Term Optical Monitoring of NGC 5548

We present the results of three years of ground-based observations of the Seyfert 1 galaxy NGC 5548, which combined with previously reported data, yield optical continuum and broad-line H-beta light curves for a total of eight years. The light curves consist of over 800 points, with a typical spacing of a few days between observations. During this eight-year period, the nuclear continuum has varied by more than a factor of seven, and the H-beta emission line has varied by a factor of nearly six. The H-beta emission line responds to continuum variations with a time delay or lag of 10-20 days, the precise value varying somewhat from year to year. We find some indications that the lag varies with continuum flux in the sense that the lag is larger when the source is brighter.Comment: 29 pages, 6 figures. Accepted for publication in ApJ (1999 Jan 10

Maximal Spontaneous Photon Emission and Energy Loss from Free Electrons

Free electron radiation such as Cerenkov, Smith--Purcell, and transition radiation can be greatly affected by structured optical environments, as has been demonstrated in a variety of polaritonic, photonic-crystal, and metamaterial systems. However, the amount of radiation that can ultimately be extracted from free electrons near an arbitrary material structure has remained elusive. Here we derive a fundamental upper limit to the spontaneous photon emission and energy loss of free electrons, regardless of geometry, which illuminates the effects of material properties and electron velocities. We obtain experimental evidence for our theory with quantitative measurements of Smith--Purcell radiation. Our framework allows us to make two predictions. One is a new regime of radiation operation---at subwavelength separations, slower (nonrelativistic) electrons can achieve stronger radiation than fast (relativistic) electrons. The second is a divergence of the emission probability in the limit of lossless materials. We further reveal that such divergences can be approached by coupling free electrons to photonic bound states in the continuum (BICs). Our findings suggest that compact and efficient free-electron radiation sources from microwaves to the soft X-ray regime may be achievable without requiring ultrahigh accelerating voltages.Comment: 7 pages, 4 figure

Preventive Screening of Young People from the Perspective of Vascular Aging Phenotypes: the Role of Body Weight

Aim. To study the cardiovascular stiffness index CAVI in relation to main risk factors (RF) in young people from the point of their vascular aging phenotype and gender.Material and methods. 264 young people (93 boys and 171 girls) at age of 18 to 25 years were examined. Vascular screening was performed with evaluating of CAVI. All subjects were divided into tertile groups for this indicator, taking into account gender. Such interval analysis of gender- and age- homogeneous sample allows to identify carriers of the phenotypes of premature (upper CAVI-tercile), normal (middle CAVI-tercile), and favorable or healthy (low CAVI-tercile) vascular aging. The first of them is also called EVA (early vascular aging) syndrome. In these groups, the incidence of carriers of insufficient, normal body mass (BM) and overweight were estimated. In three groups formed by BM indicator, the parameters of CAVI, hemodynamic and metabolic status in response to changes in BM were determined.Results. Among of the presented RF, the correlation was significant for CAVI with a weight -0.428 (p<0.001) for R-CAVI, -0.453 (p<0.001) for L- CAVI, and even more significant with the BM index - at the level of -0.410 (p<0.001) for R-CAVI and -0.462 (p<0.001) for L-CAVI. This connection is found in boys. Among boys and girls with excessive BM, the most favorable vascular aging phenotype is observed 2.7 and 2.2 times more often than the EVA syndrome. In contrast, among girls with insufficient BM, a favorable vascular phenotype is detected almost twice rarely as compared with EVA syndrome. In similar group of boys, a healthy vascular phenotype is not observed at all. Among normal-weight boys and girls, the occurrence of the two extreme vascular phenotypes is almost identical. The arterial rigidity decrease on the background of BM increase occurs despite the сhanges of hemo- dynamic and metabolic indicators. This changes are especially pronounced in girls. The difference between the extreme weight categories in terms of R- CAVI and L-CAVI for boys was 1.4, while for girls it was only 0.3 for R-CAVI and 0.4 for L-CAVI.Conclusion. When carrying out preventive measures among young people, one should not limit oneself to evaluating only traditional RF. Based on the concept of vascular aging, angiological screening should be more widely implemented. It will allow for more individualized preventive interventions among young people in the future

The unprecedented optical outburst of the quasar 3C 454.3. The WEBT campaign of 2004-2005

The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. The maximum brightness detected was R = 12.0, which represents the most luminous quasar state thus far observed (M_B ~ -31.4). In order to follow the emission behaviour of the source in detail, a large multiwavelength campaign was organized by the Whole Earth Blazar Telescope (WEBT). Continuous optical, near-IR and radio monitoring was performed in several bands. ToO pointings by the Chandra and INTEGRAL satellites provided additional information at high energies in May 2005. The historical radio and optical light curves show different behaviours. Until about 2001.0 only moderate variability was present in the optical regime, while prominent and long-lasting radio outbursts were visible at the various radio frequencies, with higher-frequency variations preceding the lower-frequency ones. After that date, the optical activity increased and the radio flux is less variable. This suggests that the optical and radio emissions come from two separate and misaligned jet regions, with the inner optical one acquiring a smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index behaviour (generally redder-when-brighter) during the outburst suggests the presence of a luminous accretion disc. A huge mm outburst followed the optical one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux started to increase in early 2005 and reached a maximum at the end of our observing period (end of September 2005). VLBA observations at 43 GHz during the summer confirm theComment: 7 pages, 4 figures, to be published in A&