On the lowest energy excitations of one-dimensional strongly correlated electrons

It is proven that the lowest excitations $E_{low}(k)$ of one-dimensional half-integer spin generalized Heisenberg models and half-filled extended Hubbard models are $\pi$-periodic functions. For Hubbard models at fractional fillings $E_{low}{(k+ 2 k_f)} = E_{low}(k)$, where $2 k_f= \pi n$, and $n$ is the number of electrons per unit cell. Moreover, if one of the ground states of the system is magnetic in the thermodynamic limit, then $E_{low}(k) = 0$ for any $k$, so the spectrum is gapless at any wave vector. The last statement is true for any integer or half-integer value of the spin.Comment: 6 Pages, Revtex, final versio

Microstructural and morphological properties of homoepitaxial (001)ZnTe layers investigated by x-ray diffuse scattering

The microstructural and morphological properties of homoepitaxial (001)ZnTe layers are investigated by x-ray diffuse scattering. High resolution reciprocal space maps recorded close to the ZnTe (004) Bragg peak show different diffuse scattering features. One kind of cross-shaped diffuse scattering streaks along directions can be attributed to stacking faults within the epilayers. Another kind of cross-shaped streaks inclined at an angle of about 80deg with respect to the in-plane direction arises from the morphology of the epilayers. (abridged version

Correlation between Crystallographic Alignment of Self-induced GaN Nanowires and Features of Si(111) Nitridation

Formation and spatial ordering of self-induced GaN nanowires grown by molecular beam epitaxy on a spatially pre-nitridazed Si(111) substrate have been studied. It was found the close correlation between Si substrate nitridation parameters and crystallographic alignment of NWs. Conditions for NWs nucleation and in- plane orientation are predefined by a structural anisotropy of silicon nitride nanolayer. Mechanism of NWs orderly emergence suggested. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3540

Incremental expansions for Hubbard-Peierls systems

The ground state energies of infinite half-filled Hubbard-Peierls chains are investigated combining incremental expansion with exact diagonalization of finite chain segments. The ground state energy of equidistant infinite Hubbard (Heisenberg) chains is calculated with a relative error of less than $3 \cdot 10^{-3}$ for all values of $U$ using diagonalizations of 12-site (20-site) chain segm ents. For dimerized chains the dimerization order parameter $d$ as a function of the onsite repulsion interaction $U$ has a maximum at nonzero values of $U$, if the electron-phonon coupling $g$ is lower than a critical value $g_c$. The critical value $g_c$ is found with high accuracy to be $g_c=0.69$. For smaller values of $g$ the position of the maximum of $d(U)$ is approximately $3t$, and rapidly tends to zero as $g$ approaches $g_c$ from below. We show how our method can be applied to calculate breathers for the problem of phonon dynamics in Hubbard-Peierls systems.Comment: 4 Pages, 3 Figures, REVTE

The weak password problem: chaos, criticality, and encrypted p-CAPTCHAs

Vulnerabilities related to weak passwords are a pressing global economic and security issue. We report a novel, simple, and effective approach to address the weak password problem. Building upon chaotic dynamics, criticality at phase transitions, CAPTCHA recognition, and computational round-off errors we design an algorithm that strengthens security of passwords. The core idea of our method is to split a long and secure password into two components. The first component is memorized by the user. The second component is transformed into a CAPTCHA image and then protected using evolution of a two-dimensional dynamical system close to a phase transition, in such a way that standard brute-force attacks become ineffective. We expect our approach to have wide applications for authentication and encryption technologies.Comment: 5 pages, 6 figer

Correlation between luminescent characteristics and phase composition of ZnS:Cu powder prepared by self-propagating high temperature synthesis

a b s t r a c t The powder-like ZnS:Cu grown by self-propagating high temperature synthesis from the mixture of Zn, S and CuCl is investigated before and after annealing at 800 1C by photoluminescence (PL) and X-ray diffraction (XRD) techniques. It is found that after synthesis the ZnS:Cu powder consists of a mixture of cubic and hexagonal ZnS phases as well as crystalline Cu x Zn 1 À x solid solution. PL spectrum shows a wide PL band which is the superposition of green and blue Cu-related bands as well as self-activated one. It is shown that annealing at 800 1C gives rise to three processes, controlled by the heating time to annealing temperature: (i) phase transformation of ZnS hexagonal phase to cubic one; (ii) oxidation processes resulting in ZnO formation; (iii) the non-monotonic changes of Cu x Zn 1 À x phase composition and decrease of its content. These changes are accompanied by the non-monotonic variation of the blue to green Cu-related PL band intensities ratio which correlates with the variation of Cu x Zn 1 À x phase composition. The model that explains the changes of ZnS:Cu PL characteristics by indiffusion of Zn and Cu from Cu x Zn 1 À x phase is proposed. The anisotropic character of ZnS phase transformation and oxidation process is found

МЕТОД ХИРУРГИЧЕСКОГО ЛЕЧЕНИЯ ПАЦИЕНТОВ С РЕФРАКТЕРНЫМ ТЕЧЕНИЕМ ГЛАУКОМЫ С ПРИМЕНЕНИЕМ ДРЕНАЖА ИЗ ЛЕЙКОСАПФИРА

PURPOSE: To increase the efficiency of refractory glaucoma surgical treatment.METHODS: A retrospective study of 29 patients (29 eyes) with refractory glaucoma, who underwent the original leucosapphire drainage implantation («VIM», SaintPetersburg). Most patients (25 eyes — 86.2%) had primary open-angle glaucoma and have been repeatedly operated previously. 2 patients (6.9%) had traumatic glaucoma, and 2 patients (6.9%) had neovascular glaucoma. The average IOP before surgery was 32.4Ѓ}0.7 mm Hg. All IOP measurements were conducted by means of Maklakov tonometry with 10 g weights. Follow up period varied from 1 to 8 years.RESULTS: After the implantation of leucosapphire drainage, IOP level significantly decreased from 32.4Ѓ}0.7 mm Hg to 14.8Ѓ}1.0 mm Hg. In 1 month after drainage implantation mean IOP was 19.3Ѓ}1.0 mm Hg, after 3 months it equaled 19.8Ѓ}0.9 mm Hg, after 6 months — 20.0Ѓ}0.9 mm Hg, one year after surgery — 20.5Ѓ}0.9 mm Hg. IOP was below 26.0 in 89.6% cases, in 37.9% of which no additional medication had been administered. Compensation at the IOP level of ≤22.0 mm Hg was noted in 75.9% of cases. Visual field test was stable in 69.0% of patients. The following postoperative complications were registered in our study: a shallow anterior chamber (17.2%), hypertension episode (20.7%), hyphema (17.2%), ciliochoroidal detachment (17.2%), external filtration (10.3%), uveal reaction (6.9%).CONCLUSION: Leucosapphire drainage device implantation may be considered an alternative method of effective surgical treatment of patients with refractory forms of glaucoma.ЦЕЛЬ. Повышение эффективности хирургического лечения пациентов с рефрактерным течением глаукомы.МЕТОДЫ. Проведен анализ результатов хирургического лечения 29 пациентов (29 глаз) с рефрактерным течением глаукомы, которым был имплантирован оригинальный дренаж из кристалла лейкосапфира (ЗАО «ВИМ», г. Санкт-Петербург). Средний возраст пациентов на момент операции составил 67,4Ѓ}2,5 года. У большинства пациентов отмечалась первичная открытоугольная некомпенсированная ранее неоднократно оперированная глаукома — 25 (86,2%) глаз. У 2 (6,9%) больных была отмечена вторичная посттравматическая глаукома, еще у 2 (6,9%) — вторичная неоваскулярная глаукома (с хотя бы частично открытым к моменту операции радужнороговичным углом и достаточно глубокой передней камерой). Средний уровень ВГД до операции составил 32,4Ѓ}0,7 мм рт.ст. (по Маклакову, груз 10 г). Срок наблюдения от 1 года до 8 лет.РЕЗУЛЬТАТЫ. Средний уровень ВГД после имплантации лейкосапфирового дренажа снизился у всех пациентов и в первые дни после операции составил в среднем 14,8Ѓ}1,0 мм рт.ст., спустя 1 месяц после имплантации дренажа — 19,3Ѓ}1,0 мм рт.ст., через 3 месяца — 19,8Ѓ} 0,9 мм рт.ст., через 6 месяцев — 20,0Ѓ}0,9 мм рт.ст. Спустя 1 год после операции средний уровень ВГД у прооперированных пациентов был 20,5Ѓ}0,9 мм рт.ст. ВГД ниже 26,0 мм рт.ст. к этому сроку отмечалось у 89,6% больных, причем у 37,9% — без дополнительной медикаментозной терапии. Компенсация ВГД на уровне 22,0 мм рт.ст. и ниже зафиксирована в 75,9% случаев. Периметрические показатели удалось стабилизировать у 69,0% пациентов. Среди послеоперационных осложнений отмечены: синдром мелкой передней камеры (17,2%); краткосрочный эпизод гипертензии (20,7%); гифема (17,2%); развитие цилиохориоидальной отслойки, потребовавшей у части больных (17,2%) ревизии или выполнения задней трепанации склеры; наружная фильтрация (10,3%); увеальные реакции (6,9%).ЗАКЛЮЧЕНИЕ. По результатам проведенного исследования имплантация лейкосапфирового дренажа зарекомендовала себя как эффективный метод хирургического лечения пациентов, страдающих рефрактерными формами глаукомы

On the correllation effect in Peierls-Hubbard chains

We reexamine the dimerization, the charge and the spin gaps of a half-filled Peierls-Hubbard chain by means of the incremental expansion technique. Our numerical findings are in significant quantitative conflict with recently obtained results by M. Sugiura and Y. Suzumura [J. Phys. Soc. Jpn. v. 71 (2002) 697] based on a bosonization and a renormalization group method, especially with respect to the charge gap. Their approach seems to be valid only in the weakly correlated case.Comment: 7pages,4figures(6eps-files