Optical-thermal mathematical model for endovenous laser ablation of varicose veins

Endovenous laser ablation (EVLA) is successfully used to treat varicose veins. However, the exact working mechanism is still not fully identified and the clinical procedure is not yet standardized. Mathematical modeling of EVLA could strongly improve our understanding of the influence of the various EVLA processes. The aim of this study is to combine Mordon's optical-thermal model with the presence of a strongly absorbing carbonized blood layer on the fiber tip. The model anatomy includes a cylindrically symmetric blood vessel surrounded by an infinite homogenous perivenous tissue. The optical fiber is located in the center of the vessel and is withdrawn with a pullback velocity. The fiber tip includes a small layer of strongly absorbing material, representing the layer of carbonized blood, which absorbs 45 % of the emitted laser power. Heat transfer due to boiling bubbles is taken into account by increasing the heat conduction coefficient by a factor of 200 for temperatures above 95°C. The temperature distribution in the blood, vessel wall, and surrounding medium is calculated from a numerical solution of the bioheat equation. The simulations were performed in MATLAB™ and validated with the aid of an analytical solution. The simulations showed, first, that laser wavelength did virtually not influence the simulated temperature profiles in blood and vessel wall, and, second, that temperatures of the carbonized blood layer varied slightly, from 952 to 1,104°C. Our improved mathematical optical-thermal EVLA model confirmed previous predictions and experimental outcomes that laser wavelength is not an important EVLA parameter and that the fiber tip reaches exceedingly high temperatures

Conductance through strongly interacting rings in a magnetic field

We study the conductance through finite Aharonov-Bohm rings of interacting electrons weakly coupled to non-interacting leads at two arbitrary sites. This model can describe an array of quantum dots with a large charging energy compared to the interdot overlap. As a consequence of the spin-charge separation, which occurs in these highly correlated systems, the transmittance is shown to present pronounced dips for particular values of the magnetic flux piercing the ring. We analyze this effect by numerical and analytical means and show that the zero-temperature equilibrium conductance in fact presents these striking features which could be observed experimentally.Comment: 4 pages, 3 figures. FCM 2008 proceeding

Трансформация социально-политических ценностей в Европейском Союзе. Материалы "Круглого стола" сотрудников, студентов и аспирантов Российского университета дружбы народов

Round table debate “Transformation of political values in the EU: pros and cons” was held on February 13 2017 on the Faculty of the humanities and social sciences of Peoples’ Friendship University of Russia (RUDN University). The “Round-table” debate has been realized in the frame of the project “Transformation of the social and political values: the EU practice” (project number: 575361-EPP-1-2016-1-RU-EPPJMO-MODULE), Erasmus+ Jean Monnet Actions. Jean Monnet Module “Transformation of the social and political values: the EU practice”.13 февраля 2017 г. на факультете гуманитарных и социальных наук в рамках Дня науки в РУДН и в рамках проекта «Трансформация социально-политических ценностей: практика ЕС», Эразмус+, Жан Монне модуль прошел круглый стол студентов, аспирантов и молодых ученых на тему «Трансформация социально-политических ценностей в Европейском союзе

Endovenous laser ablation (EVLA): a review of mechanisms, modeling outcomes, and issues for debate

Endovenous laser ablation (EVLA) is a commonly used and very effective minimally invasive therapy to manage leg varicosities. Yet, and despite a clinical history of 16 years, no international consensus on a best treatment protocol has been reached so far. Evidence presented in this paper supports the opinion that insufficient knowledge of the underlying physics amongst frequent users could explain this shortcoming. In this review, we will examine the possible modes of action of EVLA, hoping that better understanding of EVLA-related physics stimulates critical appraisal of claims made concerning the efficacy of EVLA devices, and may advance identifying a best possible treatment protocol. Finally, physical arguments are presented to debate on long-standing, but often unfounded, clinical opinions and habits. This includes issues such as (1) the importance of laser power versus the lack of clinical relevance of laser energy (Joule) as used in Joule per centimeter vein length, i.e., in linear endovenous energy density (LEED), and Joule per square centimeter vein wall area, (2) the predicted effectiveness of a higher power and faster pullback velocity, (3) the irrelevance of whether laser light is absorbed by hemoglobin or water, and (4) the effectiveness of reducing the vein diameter during EVLA therapy

Scattering theory and ground-state energy of Dirac fermions in graphene with two Coulomb impurities

We study the physics of Dirac fermions in a gapped graphene monolayer containing two Coulomb impurities. For the case of equal impurity charges, we discuss the ground-state energy using the linear combination of atomic orbitals (LCAO) approach. For opposite charges of the Coulomb centers, an electric dipole potential results at large distances. We provide a nonperturbative analysis of the corresponding low-energy scattering problem

Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory

Data from the Pierre Auger Observatory are analyzed to search for anisotropies near the direction of the Galactic Centre at EeV energies. The exposure of the surface array in this part of the sky is already significantly larger than that of the fore-runner experiments. Our results do not support previous findings of localized excesses in the AGASA and SUGAR data. We set an upper bound on a point-like flux of cosmic rays arriving from the Galactic Centre which excludes several scenarios predicting sources of EeV neutrons from Sagittarius $A$. Also the events detected simultaneously by the surface and fluorescence detectors (the `hybrid' data set), which have better pointing accuracy but are less numerous than those of the surface array alone, do not show any significant localized excess from this direction.Comment: Matches published versio

The exposure of the hybrid detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays. It consists of a surface array to measure secondary particles at ground level and a fluorescence detector to measure the development of air showers in the atmosphere above the array. The "hybrid" detection mode combines the information from the two subsystems. We describe the determination of the hybrid exposure for events observed by the fluorescence telescopes in coincidence with at least one water-Cherenkov detector of the surface array. A detailed knowledge of the time dependence of the detection operations is crucial for an accurate evaluation of the exposure. We discuss the relevance of monitoring data collected during operations, such as the status of the fluorescence detector, background light and atmospheric conditions, that are used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic

Age at menopause in Latin America

OBJECTIVE: To assess the age at menopause (AM) in Latin America urban areas. DESIGN: A total of 17,150 healthy women, aged 40 to 59 years, accompanying patients to healthcare centers in 47 cities of 15 Latin American countries, were surveyed regarding their age, educational level, healthcare coverage, history of gynecological surgery, smoking habit, presence of menses, and the use of contraception or hormone therapy at menopause. The AM was calculated using logit analysis. RESULTS: The mean age of the entire sample was 49.4 ± 5.5 years. Mean educational level was 9.9 ± 4.5 years, and the use of hormone therapy and oral contraception was 22.1% and 7.9%, respectively. The median AM of women in all centers was 48.6 years, ranging from 43.8 years in Asuncion (Paraguay) to 53 years in Cartagena de Indias (Colombia). Logistic regression analysis determined that women aged 49 living in cities at 2,000 meters or more above sea level (OR = 2.0, 95% CI: 1.4-2.9, P less than 0.001) and those with lower educational level (OR = 1.9, 95% CI: 1.3-2.8, P less than 0.001) or living in countries with low gross national product (OR = 2.1, 95% CI: 1.5-2.9, P less than 0.001) were more prone to an earlier onset of menopause. CONCLUSIONS: The AM varies widely in Latin America. Lower income and related poverty conditions influence the onset of menopause. © 2006 by The North American Menopause Society