Impurity scattering and Friedel oscillations in mono-layer black phosphorus

We study the effect of impurity scattering effect in black phosphorurene (BP) in this work. For single impurity, we calculate impurity induced local density of states (LDOS) in momentum space numerically based on tight-binding Hamiltonian. In real space, we calculate LDOS and Friedel oscillation analytically. LDOS shows strong anisotropy in BP. Many impurities in BP are investigated using $T$-matrix approximation when the density is low. Midgap states appear in band gap with peaks in DOS. The peaks of midgap states are dependent on impurity potential. For finite positive potential, the impurity tends to bind negative charge carriers and vise versa. The infinite impurity potential problem is related to chiral symmetry in BP

Fiber Based Multiple-Access Optical Frequency Dissemination

We demonstrate a fiber based multiple-access optical frequency dissemination scheme. Without using any additional laser sources, we reproduce the stable disseminated frequency at an arbitrary point of fiber link. Relative frequency stability of 3E10^{-16}/s and 4E10^{-18}/10^4s is obtained. A branching fiber network for highly-precision synchronization of optical frequency is made possible by this method and its applications are discussed.Comment: 5 pages, 3 figure

Dual-mode mechanical resonance of individual ZnO nanobelts

©2003 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/82/4806/1DOI:10.1063/1.1587878The mechanical resonance of a single ZnO nanobelt, induced by an alternative electric field, was studied by in situ transmission electron microscopy. Due to the rectangular cross section of the nanobelt, two fundamental resonance modes have been observed corresponding to two orthogonal transverse vibration directions, showing the versatile applications of nanobelts as nanocantilevers and nanoresonators. The bending modulus of the ZnO nanobelts was measured to be ~52 GPa and the damping time constant of the resonance in a vacuum of 5×10–8 Torr was ~1.2 ms and quality factor Q = 500

Existence problem of proton semi-bubble structure in the 21+2_1^+ state of 34^{34}Si

The fully self-consistent Hartree-Fock (HF) plus random phase approximation (RPA) based on Skyrme-type interaction is used to study the existence problem of proton semi-bubble structure in the $2_1^+$ state of $^{34}$Si. The experimental excitation energy and the B(E2) strength of the $2_1^+$ state in $^{34}$Si can be reproduced quite well. The tensor effect is also studied. It is shown that the tensor interaction has a notable impact on the excitation energy of the $2_1^+$ state and a small effect on the B(E2) value. Besides, its effect on the density distributions in the ground and $2_1^+$ state of $^{34}$Si is negligible. Our present results with T36 and T44 show that the $2_1^+$ state of $^{34}$Si is mainly caused by proton transiton from $\pi 1d_{5/2}$ orbit to $\pi 2s_{1/2}$ orbit, and the existence of a proton semi-bubble structure in this state is very unlikely.Comment: 6 pages, 3 figures, 3 table

Celecoxib inhibits tumor growth and angiogenesis in an orthotopic implantation tumor model of human colon cancer

Aim: To examine the effect of celecoxib on tumor growth and angiogenesis in an orthotopic implantation tumor model of colon cancer. Methods: Human colorectal adenocarcinoma HT-29 cells were implanted subcutaneously in nude mice. Four groups of animals received different doses of celecoxib after tumor implantation. After 42 days, all animals were evaluated for changes in body weight, the volume and weight of colorectal tumors, and tumor growth inhibition. The content of prostaglandin E2 (PGE2) in the tumor tissue homogenate was estimated by radioimmunoassay (RIA). Cyclooxygenase-2 (COX-2) and CD34 expression in tumor tissue was assessed by immunohistochemistry, and the microvessel density (MVD) of tumor tissue was determined. Apoptosis of the tumor cells was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). The expression of vascular endothelial growth factor (VEGF) mRNA and matrix metalloproteinase-2 (MMP-2) mRNA extracted from the tumor tissue was analyzed by reverse transcriptase polymerase chain reaction (RT-PCR). Results: There was no statistically significant change in the animals’ body weight between the treatment groups. However, with increasing doses of celecoxib, the volume and weight of the tumor decreased. The rates of tumor growth inhibition for the L (low), M (medium) and H (high) groups were 25.30%, 38.80%, and 76.92%, respectively, which were significant compared to the C (control) group. There were significant differences in COX-2 expression in the tumor tissue between all groups, except between the L and M groups. Celecoxib exposure also reduced PGE2 levels in the tumor tissue homogenates. The level of PGE2 correlated to the weight of tumor (r = 0.8814, P < 0.05) and to COX-2 expression (r = 0.8249, P < 0.05). Compared to the control group, the tumor cells from celecoxib-treated mice had a significantly higher apoptotic index. Celecoxib also decreased CD34+ expression in tumors from treated mice. There were significant differences in the MVD between all groups except between groups H and M. Celecoxib significantly reduced the expression of VEGF and MMP-2 mRNA in the group H but not in L and M groups. The MVD in tumor tissue was closely related to the PGE2 levels, as well as the expression of VEGF and MMP-2 mRNA (r = 0.9006, r = 0.8573 and r = 0.6427, respectively; P < 0.05). Conclusions: By inhibiting COX-2, PGE2 synthesis, and VEGF and MMP-2 mRNA expression in tumor tissue, celecoxib enhances tumor cell apoptosis, thereby inhibiting the growth and angiogenesis of orthotopically implanted tumors in a mouse model of human colorectal cancer.Цель: изучить влияние целекоксиба на рост опухоли и ангиогенез в модели ортопической имплантации опухоли толстой кишки человека. Методы: клетки колоректальной аденокарциномы человека НT-29 подкожно имплантировали бестимусным мышам. После имплантации опухоли четыре группы животных получали разные дозы целекоксиба. Через 42 дня изучали изменения веса животных, объем опухолей, эффект ингибирования роста опухоли. С помощью радиоиммунного анализа (RIA) в гомо- RIA) в гомо ) в гомогенате опухолей определяли содержание простогландина E2 (PGE2 ). В опухолевой ткани иммуногистохимическим методом выявляли экспрессию циклооксигеназы-2 (COX-2) и CD34 и оценивали плотность микрососудов (MVD). Апоптотические клетки выявляли методом TUNEL. Экспрессия мРНК фактора роста эндотелия сосудов (VEGF) и металлопротеиназы-2 (MMP-2) в опухолях проанализирована методом обратной транскриптазной реакции (RT-PCR). Результаты: статистически достоверных различий в весе животных между разными группами обнаружено не было. Вто же время, с увеличением дозы целекоксиба объем и вес опухоли уменьшался. По сравнению с контрольной группой (C), рост опухоли статистически достоверно ингибировался в L (низкая доза), M (средняя доза) и H (высокая доза) группах животных на 25,30%, 38,80% и 76,92% соответственно. Были обнаружены значительные отличия в экспрессии COX-2 в опухолевых тканях между всеми группами животных, кроме групп L и M. Было показано целекоксиб-зависимое уменьшение уровня PGE2 в гомогенатах опухолей. Уровень PGE2 коррелировал с весом опухоли (r = 0,8814, P < 0,05) и экспрессией COX-2 (r = 0,8249, P < 0,05). По сравнению с контрольной группой опухолевые клетки мышей, получавших целекоксиб, имели значительно более высокий апоптотический индекс. Целекоксиб также снижал экспрессию CD34+ на поверхности опухолевых клеток. Были обнаружены статистически достоверные различия в MVD между всеми исследованными группами, кроме H и M. Целекоксиб способствовал уменьшению экспрессии мРНК VEGF и MMP-2 в группе Н, но не в группах L и M. MVD в опухолевой ткани кореллировал с уровнем PGE2 , а также с экспрессией мРНК VEGF и MMP-2 (r = 0,9006, r = 0,8573 и r = 0,6427 соответственно; P < 0,05). Выводы: целекоксиб способствует апоптозу опухолевых клеток, ингибирует рост опухоли и ангиогенез при ортотопической имплантации мышам колоректальной аденокарциномы человека. Такой эффект целекоксиба связан с угнетением синтеза COX-2, PGE2 и экспрессии мРНК VEGF и MMP-2 в опухолевой ткани

Characterization of the mesostructural organization of cement particles in fresh cement paste

Comparative study on the mesostructures of fresh cement paste (FCP) in different dispersion mediums was carried out aiming at characterizing the structural organization of cement particles in FCP at a mesoscopic scale and establishing the correlation of mesostructure with rheological properties. For the first time, Morphologi G3 was adopted to in-situ characterize the mesostructure of FCP. Several dispersion mediums including air, deionized water, ethanol and an aqueous solution of ethanol were chosen to study the dispersion of cement particles in the selected mediums. Superplasticizers, as dispersing aids for cement particles, were added to change the dispersion of cement particles. Results show that Morphologi G3 with the high sensitivity and the high resolution is a powerful tool for in-situ characterization of the mesostructure of FCP by providing high-quality images associated with structural parameters. The structural parameters including particle size, circularity and fractal dimension of particle spatial distribution (Dpd) allow to quantitatively characterize the organization of cement particles in FCP at a mesoscopic scale, through which the relationship between the mesostructure and the rheological behavior of FCP was established. Higher fluidity signifies larger Dpd and circularity but a lower mean particle size. Moreover, the mean particle size and Dpd are more sensitive to indicate the fluidity change

Air pollution forecasts: An overview

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Air pollution is defined as a phenomenon harmful to the ecological system and the normal conditions of human existence and development when some substances in the atmosphere exceed a certain concentration. In the face of increasingly serious environmental pollution problems, scholars have conducted a significant quantity of related research, and in those studies, the forecasting of air pollution has been of paramount importance. As a precaution, the air pollution forecast is the basis for taking effective pollution control measures, and accurate forecasting of air pollution has become an important task. Extensive research indicates that the methods of air pollution forecasting can be broadly divided into three classical categories: statistical forecasting methods, artificial intelligence methods, and numerical forecasting methods. More recently, some hybrid models have been proposed, which can improve the forecast accuracy. To provide a clear perspective on air pollution forecasting, this study reviews the theory and application of those forecasting models. In addition, based on a comparison of different forecasting methods, the advantages and disadvantages of some methods of forecasting are also provided. This study aims to provide an overview of air pollution forecasting methods for easy access and reference by researchers, which will be helpful in further studies