10,313 research outputs found
Prediction of higher thermoelectric performance in BiCuSeO by weakening electron-polar optical phonon scattering
BiCuSeO is a promising thermoelectric material, but its applications are hindered by low carrier mobility. We use first-principles calculations to analyse electronâphonon scattering mechanisms and evaluate their contributions to the thermoelectric figure of merit ZT. The combined scattering of carriers by polar optical (PO) and longitudinal acoustic (LA) phonons yields an intrinsic hole mobility of 32 cm^{2} V^{â1} s^{â1} at room temperature and a temperature power law of T^{â1.5} between 100â875 K, which agree well with experiments. We demonstrate that electronâphonon scattering in the CuâSe layer dominates at low T (< 500 K), while contributions from the BiâO layer become increasingly significant at higher T. At room temperature, ZT is calculated to be 0.48 and can be improved by 30% through weakening PO phonon scattering in the CuâSe layer. This finding agrees with the experimental observation that weakening the electronâphonon interaction by Te substitution in the CuâSe layer improves mobility and ZT. At high T, the figure of merit is improved by weakening the electronâPO phonon scattering in the BiâO layer instead. The theoretical ZT limit of BiCuSeO is calculated to be 2.5 at 875 K
Effects of Octahedral Tilting on Band Structure and Thermoelectric Power Factor of Titanate Perovskites: A First-Principles Study on SrTiOâ
Doped SrTiO_{3} and other perovskite structured titanates are attracting interest as n-type thermoelectric materials due to their relatively high thermoelectric power factor, low toxicity, and modest cost. Taking SrTiO_{3} as an example, the effects of octahedral tilting on the electronic band structure and thermoelectric power factor of titanate perovskites have been studied from first-principles calculations. By utilizing Glazerâs notation, six representative tilt systems, including three out-of-phase (a^{0}a^{0}c^{â}, a^{0}b^{-}b^{â}, and a^{â}a^{â}a^{â}) and three in-phase tilt systems (a^{0}a^{0}c^{+}, a^{0}b^{+}b^{+}, and a^{+}a^{+}a^{+}), were investigated. It is found that out-of-phase tilting improves the optimum power factor as compared to the cubic aristotype, while in-phase tilting marginally lowers the optimum power factor. The largest increase in power factor (âŒ100%) is obtained in the one-tilt system a^{0}a^{0}c^{â} at a tilt angle of 15°, which can be achieved with an energy cost of only 44 kJ mol^{â1} per formula unit. These findings agree with the experimental evidence that increased power factors are found in a^{0}a^{0}c^{â} and a^{â}a^{â}a^{â} tilt systems of titanate perovskites. The predicted increase of Seebeck coefficient as a function of tilt angle in the a^{â}a^{â}a^{â} tilt system of SrTiO_{3} is also consistent with the experimental increase of Seebeck coefficient in a^{â}a^{â}a^{â} titanates of La_{0.55}K_{0.45}TiO_{3} and La_{0.5}Na_{0.5}Ti_{0.9}Nb_{0.1}O_{3}. Our simulations provide valuable insights into tuning the thermoelectric power factor of titanate perovskites by controlling octahedral tilting
Light cigarette smoking increases risk of all-cause and cause-specific mortality: Findings from the NHIS Cohort Study
Very few studies have examined the association between light cigarette smoking (i.e., â€5 cigarettes per day) and mortality. The aim of this study was to examine the association of light cigarette smoking with all-cause and cause-specific mortality among adults in the United States. Data were from 13 waves of the National Health Interview Survey (1997 to 2009) that were linked to the National Death Index records through December 31, 2011. A total of 329,035 participants aged â„18 years in the United States were included. Deaths were from all cause, cancer, cardiovascular disease (CVD) and respiratory disease and were confirmed by death certification. During a median follow-up of 8.2 years, 34,862 participants died, of which 8415 were from cancer, 9031 from CVD, and 2040 from respiratory disease. Compared with never-smokers, participants who smoked 1-2 (hazard ratios (HR) = 1.94, 95%CI = 1.73-2.16) and 3-5 cigarettes (HR = 1.99, 1.83-2.17) per day were at higher risk of all-cause mortality after adjustment for demographic variables, lifestyle factors and physician-diagnosis of chronic disease. The associations were stronger for respiratory disease-specific mortality, followed by cancer-specific mortality and CVD-specific mortality. For example, the HRs (95% CIs) of smoking 1-2 cigarettes per day were 9.75 (6.15-15.46), 2.28 (1.84-2.84) and 1.93 (1.58-2.36), respectively, for these three cause-specific mortalities. This study indicates that light cigarette smoking increases risk of all-cause and cause-specific mortality in US adults
Soliton interaction in a fiber ring laser
Author name used in this publication: H. Y. Tam2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Pulse-train nonuniformity in a fiber soliton ring laser mode-locked by using the nonlinear polarization rotation technique
Author name used in this publication: P. ShumAuthor name used in this publication: H. Y. Tam2003-2004 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Efficient and long-lived quantum memory with cold atoms inside a ring cavity
Quantum memories are regarded as one of the fundamental building blocks of
linear-optical quantum computation and long-distance quantum communication. A
long standing goal to realize scalable quantum information processing is to
build a long-lived and efficient quantum memory. There have been significant
efforts distributed towards this goal. However, either efficient but
short-lived or long-lived but inefficient quantum memories have been
demonstrated so far. Here we report a high-performance quantum memory in which
long lifetime and high retrieval efficiency meet for the first time. By placing
a ring cavity around an atomic ensemble, employing a pair of clock states,
creating a long-wavelength spin wave, and arranging the setup in the
gravitational direction, we realize a quantum memory with an intrinsic spin
wave to photon conversion efficiency of 73(2)% together with a storage lifetime
of 3.2(1) ms. This realization provides an essential tool towards scalable
linear-optical quantum information processing.Comment: 6 pages, 4 figure
Live-cell imaging to detect phosphatidylserine externalization in brain endothelial cells exposed to ionizing radiation: Implications for the treatment of brain arteriovenous malformations
© 2016 AANS. Objective Stereotactic radiosurgery (SRS) is an established intervention for brain arteriovenous malformations (AVMs). The processes of AVM vessel occlusion after SRS are poorly understood. To improve SRS efficacy, it is important to understand the cellular response of blood vessels to radiation. The molecular changes on the surface of AVM endothelial cells after irradiation may also be used for vascular targeting. This study investigates radiation-induced externalization of phosphatidylserine (PS) on endothelial cells using live-cell imaging. methods An immortalized cell line generated from mouse brain endothelium, bEnd.3 cells, was cultured and irradiated at different radiation doses using a linear accelerator. PS externalization in the cells was subsequently visualized using polarity-sensitive indicator of viability and apoptosis (pSIVA)-IANBD, a polarity-sensitive probe. Live-cell imaging was used to monitor PS externalization in real time. The effects of radiation on the cell cycle of bEnd.3 cells were also examined by flow cytometry. results Ionizing radiation effects are dose dependent. Reduction in the cell proliferation rate was observed after exposure to 5 Gy radiation, whereas higher radiation doses (15 Gy and 25 Gy) totally inhibited proliferation. In comparison with cells treated with sham radiation, the irradiated cells showed distinct pseudopodial elongation with little or no spreading of the cell body. The percentages of pSIVA-positive cells were significantly higher (p = 0.04) 24 hours after treatment in the cultures that received 25-and 15-Gy doses of radiation. This effect was sustained until the end of the experiment (3 days). Radiation at 5 Gy did not induce significant PS externalization compared with the sham-radiation controls at any time points (p > 0.15). Flow cytometric analysis data indicate that irradiation induced growth arrest of bEnd.3 cells, with cells accumulating in the G2 phase of the cell cycle. coNclusioNs Ionizing radiation causes remarkable cellular changes in endothelial cells. Significant PS externalization is induced by radiation at doses of 15 Gy or higher, concomitant with a block in the cell cycle. Radiation-induced markers/targets may have high discriminating power to be harnessed in vascular targeting for AVM treatment
Gain-guided solitons in dispersion-managed fiber lasers with large net cavity dispersion
Author name used in this publication: C. Lu2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Pulse breaking recovery in fiber lasers
Author name used in this publication: H. Y. TamAuthor name used in this publication: C. Lu2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Induced solitons formed by cross-polarization coupling in a birefringent cavity fiber laser
Author name used in this publication: H. Y. TamVersion of RecordPublishe
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