Hardening mechanism of commercially pure Mg processed by high pressure torsion at room temperature

Coarse-grained Mg in the as-cast condition and fine-grained Mg in the extruded condition were processed by high pressure torsion (HPT) at room temperature for up to 16 turns. Microstructure observation and texture analysis indicate that to fulfil the Von Mises criterion, the non-basal slip is activated in the as-cast Mg and tension twinning is activated in the as-extruded Mg. Although the deformation mechanism is different in the as-cast Mg and the as-extruded Mg during HPT, their hardening evolutions are similar, i.e. after 1/8 turn of HPT, microhardness of the as-cast Mg and the extruded Mg both show a significant increase and further HPT processing does not significantly further increase the microhardness. Texture strengthening can explain the rapid hardening. Hardness anisotropy and texture data results suggest that texture strengthening plays an important role for both types of samples. Texture strengthening weakens with decreasing grain size

Aspisol inhibits tumor growth and induces apoptosis in breast cancer

Nonsteroidal anti-inflammatory drugs inhibit cell proliferation and induce apoptosis in various cancer cell lines, which is considered to be an important mechanism for their anti-tumor activity and cancer prevention. However, the molecular mechanisms through which these compounds induce apoptosis are not well understood. Aim: to determine the effects of nonselective cyclooxygenase-2 (COX-2) inhibitor, aspisol on breast cancer cells in vitro and in vivo. Methods: The cytotoxic activity of aspisol was evaluated by MTT assay. The apoptosis index of cells was measured by flow cytometry. Immunohistochemical staining was used to detect expressions of COX-2 and caspase-3 in MDA-MB-231 cells. The expression of bcl-2 and bax was analyzed by Western blot analysis. The content of prostaglandin E2 (PGE2) in MDA-MB-231 cells was estimated by ELISA. In vivo apoptosis of the tumor cells was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). Results: Our results showed that aspisol reduced viability of MDA-MB-231 cells in time- and dose- dependent fashions and induced apoptosis by increase of caspase-3 and bax expressions while decrease of COX-2 and bcl-2 expression in vitro. In addition, exposure to aspisol decreased the basal release of PGE2. In vivo, aspisol also inhibited the proliferation of breast cancer cells and induced their apoptosis. Conclusions: Our in vitro and in vivo data indicated that the antitumor effects of aspisol on breast cancer cells was probably mediated by the induction of apoptosis, and it could be linked to the downregulation of the COX-2 or bcl-2 expression and up-regulation of caspase-3 or bax expression.Нестероидные противовоспалительные препараты ингибируют пролиферацию клеток и вызывают апоптоз во многих опухолевых клеточных линиях, что считается важным механизмом их противоопухолевой активности и профилактики развития рака. Тем не менее молекулярные механизмы апоптотического действия этих препаратов изучены недостаточно. Цель: изучить действие неспецифического ингибитора циклогексиназы-2 (COX-2) — аспизола — на злокачественные клетки рака молочной железы in vitro и in vivo. Методы: выживаемоть клеток MDA-MB-231 определяли с помощью MTT-теста. Апоптотический индекс измеряли с помощью проточной цитометрии и иммуногистохимическим окрашиванием с антителами против COX-2 и каспазы-3. Экспрессию bcl-2 и bax изучали с помощью Вестерн-блот-анализа. Содержание простагландина E2 (PGE2 ) в клетках MDA-MB-231 оценивали методом ELISA. In vivo апоптоз опухолевых клеток определяли путем выявления разрывов ДНК с помощью концевой дезоксинуклеот-идилтранферазы (метод TUNEL). Результаты: показано, что в зависимости от времени инкубации и дозы аспизол угнетал рост клеток MDA-MB-231 in vitro и вызывал их апоптоз на фоне повышения экспрессии каспазы-3 и bax, а также снижения экспрессии COX-2 и bcl-2. В условиях in vivo аспизол также ингибировал пролиферацию злокачественных клеток рака молочной железы и вызывал их апоптоз. Выводы: данные, полученные in vitro и in vivo, свидетельствуют о противоопухолевом эффекте аспизола на клетки рака молочной железы, что скорее всего опосредовано его проапоптотическим действием и может быть связано со снижением экспрессии COX-2 и bcl-2, а также повышением экспрессии каспазы-3 и bax

Universal structure of the edge states of the fractional quantum Hall states

We present an effective theory for the bulk fractional quantum Hall states on the Jain sequences on closed surfaces and show that it has a universal form whose structure does not change from fraction to fraction. The structure of this effective theory follows from the condition of global consistency of the flux attachment transformation on closed surfaces. We derive the theory of the edge states on a disk that follows naturally from this globally consistent theory on a torus. We find that, for a fully polarized two-dimensional electron gas, the edge states for all the Jain filling fractions $\nu=p/(2np+1)$ have only one propagating edge field that carries both energy and charge, and two non-propagating edge fields of topological origin that are responsible for the statistics of the excitations. Explicit results are derived for the electron and quasiparticle operators and for their propagators at the edge. We show that these operators create states with the correct charge and statistics. It is found that the tunneling density of states for all the Jain states scales with frequency as $|\omega|^{(1-\nu)/\nu}$.Comment: 10 page

Quantum Hall Fluids

We review the effective field theory treatment of topological quantum fluids, focussing on the Hall fluids.Comment: 82 pages, TeX, Preprint ITP (This version comes with ALL the MACROS appended at the end of the file)

Size Dependence of Residual Thermal Stresses in Micro Multilayer Ceramic Capacitors by Using Finite Element Unit Cell Model Including Strain Gradient Effect

The residual thermal stresses induced by the high-temperature sintering process in multilayer ceramic capacitors (MLCCs) are investigated by using a finite element unit cell model, in which the strain gradient effect is considered. The numerical results show that the residual thermal stresses depend on the lateral margin length, the thickness ratio of the dielectrics layer to the electrode layer, and the MLCC size. At a given thickness ratio, as the MLCC size is scaled down, the peak shear stress reduces significantly and the normal stresses along the length and thickness directions change slightly with the decrease in the ceramic layer thickness td as td >1 μm, but as td <1 μm, the normal stress components increase sharply with the increase in td. Thus, the residual thermal stresses induced by the sintering process exhibit strong size effects and, therefore, the strain gradient effect should be taken into account in the design and evaluation of MLCC devices.Розглянуто задачу про залишкові температурні напруження в багатошарових керамічних конденсаторах, викликані високотемпературним процесом спікання. Застосовано модель одиничної чарунки в методі скінченних елементів, де враховано вплив градієнта деформацій. Отримані числові результати показують, що залишкові температурні напруження залежать від довжини поздовжнього краю, відношення товщини діелектричних шарів до товщини електродних шарів і розміру конденсатора. При заданому відношенні товщин, коли розмір конденсатора зменшується, то найвищі зсувні напруження зменшуються суттєво і нормальні напруження вздовж довжини та в напрямку зміни товщини змінюються незначно зі зменшенням товщини керамічного шару до величини, меншої 1 мікрона. Коли ця величина є більшою 1 мікрона, то нормальні напруження зростають різко зі збільшенням товщини керамічного шару. Таким чином, залишкові температурні напруження, викликані високотемпературним процесом спікання, виявляють сильний вплив розміру конденсатора і тому вплив градієнта деформації повинен братися до уваги в процесі створення і оцінювання роботи багатошарових керамічних конденсаторів

Skyrmions in the Fractional Quantum Hall Effect

It is verified that, at small Zeeman energies, the charged excitations in the vicinity of 1/3 filled Landau level are skyrmions of composite fermions, analogous to the skyrmions of electrons near filling factor unity. These are found to be relevant, however, only at very low magnetic fields.Comment: 13 pages including 2 postscript figures; accepted for publication in Solid State Communications (1996

Skyrmion Excitations in Quantum Hall Systems

Using finite size calculations on the surface of a sphere we study the topological (skyrmion) excitation in quantum Hall system with spin degree of freedom at filling factors around $\nu=1$. In the absence of Zeeman energy, we find, in systems with one quasi-particle or one quasi-hole, the lowest energy band consists of states with $L=S$, where $L$ and $S$ are the total orbital and spin angular momentum. These different spin states are almost degenerate in the thermodynamic limit and their symmetry-breaking ground state is the state with one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman energy and electron-electron interaction and the skyrmion shrinks to a spin texture of finite size. We have calculated the energy gap of the system at infinite wave vector limit as a function of the Zeeman energy and find there are kinks in the energy gap associated with the shrinking of the size of the skyrmion. breaking ground state is the state with one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman energy and electron-electronComment: 4 pages, 5 postscript figures available upon reques

Mott Transition in An Anyon Gas

We introduce and analyze a lattice model of anyons in a periodic potential and an external magnetic field which exhibits a transition from a Mott insulator to a quantum Hall fluid. The transition is characterized by the anyon statistics, $\alpha$, which can vary between Fermions, $\alpha=0$, and Bosons, $\alpha=1$. For bosons the transition is in the universality class of the classical three-dimensional XY model. Near the Fermion limit, the transition is described by a massless $2+1$ Dirac theory coupled to a Chern-Simons gauge field. Analytic calculations perturbative in $\alpha$, and also a large N-expansion, show that due to gauge fluctuations, the critical properties of the transition are dependent on the anyon statistics. Comparison with previous calcualations at and near the Boson limit, strongly suggest that our lattice model exhibits a fixed line of critical points, with universal critical properties which vary continuosly and monotonically as one passes from Fermions to Bosons. Possible relevance to experiments on the transitions between plateaus in the fractional quantum Hall effect and the magnetic field-tuned superconductor-insulator transition are briefly discussed.Comment: text and figures in Latex, 41 pages, UBCTP-92-28, CTP\#215

Haldane's Fractional Exclusion Statistics for Multicomponent Systems

The idea of fractional exclusion statistics proposed by Haldane is applied to systems with internal degrees of freedom, and its thermodynamics is examined. In case of one dimension, various bulk quantities calculated show that the critical behavior of such systems can be described by $c=1$ conformal field theories and conformal weights are completely characterized by statistical interactions. It is also found that statistical interactions have intimate relationship with a topological order matrix in Chern-Simons theory for the fractional quantum Hall effect.Comment: 12 pages, Revtex, preprint YITP/K-107

Mixed States of Composite Fermions Carrying Two and Four Vortices

There now exists preliminary experimental evidence for some fractions, such as $\nu$ = 4/11 and 5/13, that do not belong to any of the sequences $\nu=n/(2pn\pm 1)$, $p$ and $n$ being integers. We propose that these states are mixed states of composite fermions of different flavors, for example, composite fermions carrying two and four vortices. We also obtain an estimate of the lowest-excitation dispersion curve as well as the transport gap; the gaps for 4/11 are smaller than those for 1/3 by approximately a factor of 50.Comment: Accepted for PRB rapid communication (scheduled to appear in Nov 15, 2000 issue