Resonance-Induced Effects in Photonic Crystals

For the case of a simple face-centered-cubic photonic crystal of homogeneous dielectric spheres, we examine to what extent single-sphere Mie resonance frequencies are related to band gaps and whether the width of a gap can be enlarged due to nearby resonances. Contrary to some suggestions, no spectacular effects may be expected. When the dielectric constant of the spheres $\epsilon_s$ is greater than the dielectric constant $\epsilon_b$ of the background medium, then for any filling fraction $f$ there exists a critical $\epsilon_c$ above which the lowest lying Mie resonance frequency falls inside the lowest stop gap in the (111) crystal direction, close to its midgap frequency. If $\epsilon_s <\epsilon_b$, the correspondence between Mie resonances and both the (111) stop gap and a full gap does not follow such a regular pattern. If the Mie resonance frequency is close to a gap edge, one can observe a resonance-induced widening of a relative gap width by $\approx 5$.Comment: 14 pages, 3 figs., RevTex. For more info look at http://www.amolf.nl/external/wwwlab/atoms/theory/index.htm

Photonic Band Gaps of Three-Dimensional Face-Centered Cubic Lattices

We show that the photonic analogue of the Korringa-Kohn-Rostocker method is a viable alternative to the plane-wave method to analyze the spectrum of electromagnetic waves in a three-dimensional periodic dielectric lattice. Firstly, in the case of an fcc lattice of homogeneous dielectric spheres, we reproduce the main features of the spectrum obtained by the plane wave method, namely that for a sufficiently high dielectric contrast a full gap opens in the spectrum between the eights and ninth bands if the dielectric constant $\epsilon_s$ of spheres is lower than the dielectric constant $\epsilon_b$ of the background medium. If $\epsilon_s> \epsilon_b$, no gap is found in the spectrum. The maximal value of the relative band-gap width approaches 14% in the close-packed case and decreases monotonically as the filling fraction decreases. The lowest dielectric contrast $\epsilon_b/\epsilon_s$ for which a full gap opens in the spectrum is determined to be 8.13. Eventually, in the case of an fcc lattice of coated spheres, we demonstrate that a suitable coating can enhance gap widths by as much as 50%.Comment: 19 pages, 6 figs., plain latex - a section on coated spheres, two figures, and a few references adde

A simple formula for the L-gap width of a face-centered-cubic photonic crystal

The width $\triangle_L$ of the first Bragg's scattering peak in the (111) direction of a face-centered-cubic lattice of air spheres can be well approximated by a simple formula which only involves the volume averaged $\epsilon$ and $\epsilon^2$ over the lattice unit cell, $\epsilon$ being the (position dependent) dielectric constant of the medium, and the effective dielectric constant $\epsilon_{eff}$ in the long-wavelength limit approximated by Maxwell-Garnett's formula. Apparently, our formula describes the asymptotic behaviour of the absolute gap width $\triangle_L$ for high dielectric contrast $\delta$ exactly. The standard deviation $\sigma$ steadily decreases well below 1% as $\delta$ increases. For example $\sigma< 0.1$ for the sphere filling fraction $f=0.2$ and $\delta\geq 20$. On the interval $\delta\in(1,100)$, our formula still approximates the absolute gap width $\triangle_L$ (the relative gap width $\triangle_L^r$) with a reasonable precision, namely with a standard deviation 3% (4.2%) for low filling fractions up to 6.5% (8%) for the close-packed case. Differences between the case of air spheres in a dielectric and dielectric spheres in air are briefly discussed.Comment: 13 pages, 4 figs., RevTex, two references added. For more info see http://www.amolf.nl/external/wwwlab/atoms/theory/index.htm

ITPA gene variant may protect against anemia induced during pegylated interferon alfa and ribavirin combination treatment in Ukrainian patients with chronic hepatitis C

The aim of this study was to clarify the association between the inosine triphosphate pyrophosphatase (ITPA) gene variants and PEG-IFNα/RBV combination treatment induced anemia in chronic hepatitis C (CHC) Ukrainian patients. The data were collected from 80 CHC patients with HCV genotype 1 infection. All study participants received standard doses of PEG-IFNα and RBV. According to the Hb level changes patients were distributed into: case group—42 patients with combination treatment induced anemia, and control group—38 patients with no signs of anemia. Genotyping for ITPA gene rs1127354 and rs7270101 variants was performed using PCR followed by RFLP assay. Fisher’s exact test was used to estimate the difference in genotype and allelic distribution. Distribution of rs7270101 genotypes was not significantly different between groups of CHC patients with RBV-induced anemia and without it. The frequency of rs1127354 A allele carriers was significantly higher (P < 0.05) in group of CHC patients without anemia (23.7%) comparing to the group of patients with anemia (7.3%). The respective allele frequency in control group (13.2%) was almost 3-fold higher (P < 0.05) comparing to the case group (4.9%). Significant association of ITPA gene rs1127354 with protection against RBV-induced hemolytic anemia was found in Ukrainian patients with CHC infection. Rs1127354 variant may assist as a pharmacogenetic marker in HCV antiviral therapy correction for side effect avoidance.Целью настоящего исследования было изучить ассоциацию аллельных вариантов гена инозин трифосфат пирофосфатазы (ITPA) с анемией, индуцированной комбинированной терапией пегилированным интерфероном (PEG-IFNα) и рибавирином (RBV) у пациентов из Украины с хроническим гепатитом С (ХГС). Данные собраны у 80 пациентов с ХГС, которые имели первый генотип вируса. Все участники исследования получали стандартные дозы PEG – IFNα и RBV. В соответствии с изменениями уровня гемоглобина пациенты были разделены на исследуемую группу (42 пациента с анемией) и контрольную (38 пациентов без признаков анемии). Ге-нотипирование полиморфных вариантов rs1127354 и rs7270101 гена ITPA проводили с помощью ПЦР с последующим ПДРФ анализом. Распределение генотипов по полиморфному варианту rs7270101 достоверно не отличалось в группе ХГС пациентов с RBV-индуцированной анемией и без нее. Частота носителей аллеля rs1127354 A была выше в группе пациентов c ХГС без анемии (23,7 %) по сравнению с группой пациентов с анемией. Частота соответствующего аллеля в контрольной группе (13,2 %) была выше, чем в группе пациентов с анемией (4,9 %)почти втрое. Найдена достоверная ассоциация полиморфного варианта rs1127354 гена ITPA с протекцией против рибавирин-индуцированной гемолитической анемии у пациентов из Украины с ХГС. Полиморфный вариант rs1127354 может служить фармакогенетическим маркером для коррекции противовирусной терапии гепатита С во избежание побочных эффектов.Метою даного дослідження було вивчити асоціацію алельних варіантів гена інозин трифосфат пірофосфатази (ITPA) з анемією, індукованою комбінованою терапією пегильованим інтерфероном (PEG-IFNα) і рибавірином (RBV) у пацієнтів з України з хронічним гепатитом С (ХГС). Дані були зібрані у 80 пацієнтів з ХГС, які мали 1-ий генотип вірусу. Всі учасники дослідження отримували стандартні дози PEG-IFNα та RBV. Відповідно до змін рівня гемоглобіну, пацієнти були розподілені на: групу дослідження – 42 пацієнти з анемією, індукованою комбінованою терапією, та контрольну групу – 38 пацієнтів без ознак анемії. Генотипування поліморфних варіантів rs1127354 та rs7270101 гена ITPA проводили за допомогою ПЛР з наступним ПДРФ аналізом. З метою оцінки достовірності відмінностей в розподілі генотипів та алелів використовували точний тест Фішера. Розподіл генотипів за поліморфним варіантом rs7270101 достовірно не відрізнявся в групі ХГС пацієнтів з RBV-індукованою анемією та без неї. Частота носіїв алеля rs1127354 A була достовірно вище (P<0,05) в групі ХГС пацієнтів без анемії (23,7%), порівняно з групою пацієнтів з анемією. Частота відповідного алеля в контрольній групі була також достовірно вищою (P<0,05) та перевищувала таку в групі пацієнтів з анемією(4,9%) майже втричі. Було знайдено достовірну асоціацію поліморного варіанта rs1127354 гена ITPA із захистом проти рибавірин-індукованої гемолітичної анемії у пацієнтів з хронічним гепатитом С з України. Поліморфний варіант rs1127354 може слугувати фармакогенетичних маркером для корекції противірусної терапії гепатиту С з метою уникнення побічних ефектів

Bifurcations and instabilities in rotating, two-layer fluids: II. ?-plane

International audienceIn this paper, we show that the behavior of weakly nonlinear waves in a 2-layer model of baroclinic instability on a b-plane with varying viscosity is determined by a single, degenerate codimension three bifurcation. In the process, we show how previous studies, using the method of multiple scales to derive evolution equations for the slowly varying amplitude of the growing wave, arise as special limits of the general evolution description

A superconvergent representation of the Gersten-Nitzan and Ford-Webber nonradiative rates

An alternative representation of the quasistatic nonradiative rates of Gersten and Nitzan [J. Chem. Phys. 1981, 75, 1139] and Ford and Weber [Phys. Rep. 1984, 113, 195] is derived for the respective parallel and perpendicular dipole orientations. Given the distance d of a dipole from a sphere surface of radius a, the representations comprise four elementary analytic functions and a modified multipole series taking into account residual multipole contributions. The analytic functions could be arranged hierarchically according to decreasing singularity at the short distance limit d ---> 0, ranging from d^{-3} over d^{-1} to ln (d/a). The alternative representations exhibit drastically improved convergence properties. On keeping mere residual dipole contribution of the modified multipole series, the representations agree with the converged rates on at least 99.9% for all distances, arbitrary particle sizes and emission wavelengths, and for a broad range of dielectric constants. The analytic terms of the representations reveal a complex distance dependence and could be used to interpolate between the familiar d^{-3} short-distance and d^{-6} long-distance behaviors with an unprecedented accuracy. Therefore, the representations could be especially useful for the qualitative and quantitative understanding of the distance behavior of nonradiative rates of fluorophores and semiconductor quantum dots involving nanometal surface energy transfer in the presence of metallic nanoparticles or nanoantennas. As a byproduct, a complete short-distance asymptotic of the quasistatic nonradiative rates is derived. The above results for the nonradiative rates translate straightforwardly to the so-called image enhancement factors Delta, which are of relevance for the surface-enhanced Raman scattering.Comment: 30 pages including 6 figure

Rashba effect in 2D mesoscopic systems with transverse magnetic field

We present semiclassical and quantum mechanical results for the effects of a strong magnetic field in Quantum Wires in the presence of Rashba Spin Orbit coupling. Analytical and numerical results show how the perturbation acts in the presence of a transverse magnetic field in the ballistic regime and we assume a strong reduction of the backward scattering interaction which could have some consequences for the Tomonaga-Luttinger transport. We analyze the spin texture due to the action of Spin Orbit coupling and magnetic field often referring to the semiclassical solutions that magnify the singular spin polarization: results are obtained for free electrons in a twodimensional electron gas and for electrons in a Quantum Wire. We propose the systems as possible devices for the spin filtering at various regimes.Comment: 12 pages, 12 figures, to appear in Phys. Rev.

Comparison of the diagnostic efficiency of various noninvasive methods for diagnosing liver fibrosis in patients with chronic viral hepatitis C

Summary: the article presents the results of the examination of patients with chronic viral hepatitis C namely the study of the informativeness of instrumental (fibroelastography) and serological (the content of hyaluronic acid in serum) of markers of fibrosis by assessing their predictive value by ROC- analysis. The purpose of the study: to find out the possibility of non-invasive methods for diagnosing liver fibrosis in patients with chronic viral hepatitis C (CHC). Materials and methods 66 patients with CHC with the 1-st genotype of the virus were examined, which were at the dispensary observation and ambulatory treatment at DCC CCH №1 in Vinnitsa and in the clinical department of viral hepatitis at the Institute of Epidemiology and Infectious Diseases named after L.V. Gromashevsky NAMS of Ukraine. All patients received fibroelastography (FEG) with a METAVIR score. All patients with CHC and group of control determined the content of hyaluronic acid (GA) in blood serum (ELISA using the Hyaluronic Acid (Corgenix, Inc., USA)). Research results Sensitivity of determination of GA in blood serum of patients with CHC with degree of fibrosis of liver F0-F2 was 91.23%, and specificity - 90.46%. For the FEG method, respectively: 74.33% and 77.25%. In the group of patients with degree of fibrosis F3 sensitivity of the definition of GA in blood serum was 72.21%, and specificity - 74.71%. The corresponding qualitative characteristics for FEG were: 98.32% and 91.45% respectively. The sensitivity of the determination of the content of GA in serum of patients with CHC with the degree of liver fibrosis F4 was 88.23%, and the specificity was 92.12%. For these patients the sensitivity and specificity of determining the degree of fibrosis by the FEG method were 87.78% and 91.45% respectively. Conclusions High diagnostic efficiency of determination of the content of GA in serum was established for assessing the degree of liver fibrosis in patients with CSF (AUC = 0,720-0,917, p˂0,01). Relatively higher sensitivity and specificity of the diagnosis of liver fibrosis was observed in determining the content of GA in serum compared with the FEG method (AUC = 0.914 vs. AUC = 0.817 (p˂0.05)) in the group with a lack or initial signs of liver fibrosis (F0-F2)

On the equivalence of the Langevin and auxiliary field quantization methods for absorbing dielectrics

Recently two methods have been developed for the quantization of the electromagnetic field in general dispersing and absorbing linear dielectrics. The first is based upon the introduction of a quantum Langevin current in Maxwell's equations [T. Gruner and D.-G. Welsch, Phys. Rev. A 53, 1818 (1996); Ho Trung Dung, L. Kn\"{o}ll, and D.-G. Welsch, Phys. Rev. A 57, 3931 (1998); S. Scheel, L. Kn\"{o}ll, and D.-G. Welsch, Phys. Rev. A 58, 700 (1998)], whereas the second makes use of a set of auxiliary fields, followed by a canonical quantization procedure [A. Tip, Phys. Rev. A 57, 4818 (1998)]. We show that both approaches are equivalent.Comment: 7 pages, RevTeX, no figure