Precise measurement of the top-quark mass from lepton + jets events

We measure the mass of the top quark using top-quark pair candidate events in the lepton+jets channel from data corresponding to 1 fb;{-1} of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron collider. We use a likelihood technique that reduces the jet energy scale uncertainty by combining an in situ jet energy calibration with the independent constraint on the jet energy scale (JES) from the calibration derived using photon+jets and dijet samples. We find the mass of the top quark to be 171.5+/-1.8(stat.+JES)+/-1.1(syst.) GeV.     

Observation of time correlation function of multimode two-photon pairs on a rubidium D2 line

We report on the generation of a type-I multimode two-photon state on a rubidium D(2) line (780 nm) using periodically poled KTiOPO(4) crystals. With a degenerate optical parametric oscillator far below threshold, we observe an oscillatory correlation function; the cross correlation between two photons shows a cavity bandwidth of about 7.8 MHz. We also use a Fabry-Perot etalon to filter its most longitudinal modes and observe its time correlation function. The experimental data are well fitted to theoretical curves. This system could be utilized for demonstrating storage and retrieval of narrow-band photons in Rb atomic ensembles, which is important for long-distance quantum communication.     

MRI assessment of drug-induced fluid accumulation in humans: validation of the technology

PURPOSE: The purpose of this study was to evaluate the feasibility of using proton and sodium magnetic resonance imaging (MRI) to detect fluid accumulation produced by fludrocortisone and nifedipine - two drugs known to cause salt/water retention by different mechanisms. MATERIALS AND METHODS: Twelve young healthy male subjects were randomly assigned to one of two groups and treated with either fludrocortisone or nifedipine for 14 or 25 days, respectively. The change in sodium MRI, as well as in proton T(2) value and T(1)-weighted signal intensity in the calf following postural change [referred to here as 'postural delta signal'(PDS)], was evaluated before, during and after drug administration. The changes in MRI PDS were compared to conventional physiological parameters, including body weight, calf volume and pitting edema. RESULTS: When compared to the baseline pretreatment values, the subjects treated with fludrocortisone showed a 5.5% increase in sodium MRI PDS (P=.01), a 2-ms increase in proton T(2) PDS of the gastrocnemius muscle (P=.06) and a body weight gain of 2.3% (P=.001) within 1 week. In the nifedipine-treated subjects, the sodium MRI PDS increased by 6% versus baseline (P=.03), while the proton T(2) PDS of the gastrocnemius muscle increased by 3.7 ms (P=.01), associated with a 0.5% weight gain (P=.55), within 3 weeks. No significant changes were noted in the T(1)-weighed images following postural change. Measurements of calf circumference, volume and pitting edema did not show consistent changes associated with the drug administration. CONCLUSION: The postural change in sodium MRI and proton T(2) signals provides a sensitive method for detecting the fluid accumulation produced by fludrocortisone and nifedipine. The MRI results are consistent with treatment-induced increases in extracellular fluid volume and correlate well with the observed weight gain. These findings support the potential utility of MRI for the evaluation of medication-induced fluid retention.     

Measurement of the tt[over] production cross section in pp[over] collisions at sqrt(s)=1.96 TeV

We measure the tt[over] production cross section in pp[over] collisions at sqrt(s)=1.96 TeV in the lepton + jets channel. Two complementary methods discriminate between signal and background: b tagging and a kinematic likelihood discriminant. Based on 0.9 fb(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure sigma(tt[over])=7.62+/-0.85 pb, assuming the current world average m(t)=172.6 GeV. We compare our cross section measurement with theory predictions to determine a value for the top-quark mass of 170+/-7 GeV.     

太赫兹波段石墨烯等离子体的增益特性

基于麦克斯韦方程组和物质本构方程对石墨烯表面等离子体进行了研究.从理论上探索了石墨烯表面等离子体激元在太赫兹波段的增益特性曲线,并且讨论了石墨烯表面等离子体增益与石墨烯中载流子浓度、石墨烯所处温度以及载流子动量弛豫时间的关系.研究结果表明:在太赫兹波段增益峰值随着石墨烯载流子浓度的增加而发生蓝移,并且在所讨论的温度范围内,由于增益峰所对应的频率都大于1 THz,因此温度的变化对增益峰值以及相应频率的影响不大,即在不同的温度下,相同载流子浓度所对应的增益曲线上峰值的位置和强度几乎相同;增益与石墨烯载流子动量弛豫时间相关,随着载流子动量弛豫时间的增加,使得激发态激励的电子增加,从而导致石墨烯表面等离子体增益变得更大,但这种动量弛豫时间的增加却因弛豫时间对受激辐射频率影响较小而并未对增益峰值位置产生影响.     

从微观角度再看理想气体的绝热过程

在“ 从微观角度看理想气体的绝热过程”一文中提到了一种从微观角度来计算理想气体绝热公式的推 导, 这一推导中的物理本质为气体分子对活塞壁做功的集体效应, 即气体压强的微观解释. 基于这一思考, 从气体 分子对外做功的角度给出了相应的推导, 同时发现该文结论在其给定模型下的一个更为直观的解, 与热力学第一 定律中的做功项可以更直接地对应, 从而更直接地联系起微观过程和宏观的理想气体状态方程     

新工科视域下地方高校化材类应用型人才培养新模式的创建与成效

论述了地方高校化材类应用型人才培养探索与实践的必要性和紧迫性。重点阐述了在人才培养模式更新、特色课程设置、校企合作协同育人机制的创新等多方面的改革。更新了“接地气、近产业”新工科应用型人才培养定位,探索实践了“双四六”应用型人才培养模式,重构了与应用型人才培养相配套的课程体系,实施了“三三制”产学研协同育人机制。最后以丰硕的成果给创建的新模式做了诠释。     

南方籼稻米胶稠度近红外光谱分析数学模型的构建与验证

培育优质高产水稻品种是当前水稻育种的重要任务之一;胶稠度是稻米蒸煮食味品质最重要的指标之一.传统的化学法测定稻米胶稠度,前处理复杂、过程繁琐、试剂消耗多,难以满足大批量水稻品种(组合)胶稠度快速无损检测的需求.近红外光谱分析能快速、无损、无污染地分析检测.以137份南方稻区主栽或新育成的籼稻品种(组合)为供试材料,用传...     

基于宽范围粒径谱仪的气溶胶探测方法

通过改变基于宽范围粒径谱仪的温度控制方法,研究温度变化对气溶胶浓度的影响和作用.本文首先对宽范围粒径谱仪进样系统温度控制方法进行改进,即采用钽管加热器及不加热切换的温度控制方法来改变宽范围粒径谱仪进样部分温度,使用改进后的系统测量室内外大气气溶胶,对不同温度下大气气溶胶的浓度分布情况进行讨论与分析.结果表明室外粒子数浓度分布的峰值与室内粒子浓度分布的峰值相比,室内空气中粒子数浓度峰值明显要小,即室外大气中的粒径大的粒子更多.证实了宽范围粒径谱仪适用于大气气溶胶的检测,在环境检测中有广泛的应用前景.     

高效液相色谱法测定啤酒花及其制品中的α-酸、β-酸和异α-酸

1引言a-酸、B-酸及异a-酸是啤酒苦味酸的主要成分，它们的分析是啤酒花及其制品质量评价及控制的主要内容，国内主要使用光度法和电导滴定法分析，这两种方法因存在许多问题而影响测定结果，因此，国外近年已逐渐用高效液相色谱法（HPIn）分析啤酒、啤酒花及各种啤酒花制品的a一酸、卢一酸及异o一酸。我们在研究啤酒花制品时需要同时分析a一酸、卢·酸及异a一酸，但是已有的HPIn法仅可以同时测定a·酸和公酸，而异a一酸是单独分析的，只有在梯度洗脱和较高的柱温时可以同时测定三者，这就限制了它的推广应用。本文建立了室温下同时测定它…