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1.
增加光子奇偶q相干态的高阶压缩效应 总被引:8,自引:3,他引:5
通过数值计算研究了增加光子奇q相干态aq+m|α>qo和增加光子偶q相干态aq+m|α>qe的高阶压缩效应.结果表明:当q较小时,态aq+m|α>qo和aq+m|α>qe都能呈现出强烈的奇次方阶压缩效应,但无偶次方阶压缩效应,而且奇次方阶压缩随m的增大而增强.当m=0时aq+m|α>qo和aq+m|α>qe为光场振幅偶次幂的最小测不准态,但当m≠0时它们不是光场振幅偶次幂的最小测不准态. 相似文献
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利用Spitzer的广义欧姆定律分析等离子体中由垂直于磁场的压强梯度所引起的宏观瞬变性质。在垂直于磁场方向的初始流动速度为零的条件下,得出在恒稳磁场中的瞬时扩散系数(当ωceτ?1)为 D= (2kmec2)/e2 T/(B2τ)+(kc)/eT/Be-me/(miτ)tsinωcit,式中τ为电子离子的平均碰撞时间间隔。 相似文献
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利用Monte-Carlo模拟研究了全局耦合网络上扩散限制的不可逆聚集-湮没过程的动力学行为. 在系统中, 同种类集团相遇, 将发生聚集反应; 不同种类的集团相遇, 则发生部分湮没反应. 模拟结果表明:1) 当两种粒子初始浓度相等时, 系统长时间演化后, 集团浓度c(t)和粒子浓度g(t)呈现幂律形式, c(t)~t- α和g(t)~t-β, 其中幂指数α 和β 满足α=2β 的关系, 且α=2/(2 + q); 集团大小分布随时间的演化满足标度律, akt)=k-τt-ω\varPhi (k/t^z), 其中τ≈-1.27q, ω≈(3 + 1.27q)/(2 + q), z=α/2=1/(2 + q); 2) 当两种粒子初始浓度不相等时, 系统经长时间演化后, 初始浓度较小的种类完全湮没, 而初始浓度较大的那个种类的集团浓度cA(t)仍具有幂律形式, cA(t)~t-α, 其中α=1/(1+q), 其集团大小分布随时间的演化也满足标度律, 标度指数为τ≈-1.27q, ω≈(2 + 1.27q)/(1 + q)和z=α=1/(1 + q). 模拟结果与已报道的理论分析结果相符得很好. 相似文献
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采用基于密度泛函理论中的广义梯度近似的第一性原理研究, 优化了纤锌矿结构化合物CrX(X=As、Sb、O、Se和Te)的几何结构, 并详细计算了它们的磁电性能. 结果表明, 这些磷族或硫族化合物在费米面处的自旋极化率均为100%, 分子磁矩分别为整数3.00和4.00 μB; 分子磁矩主要来自于Cr离子; 磷族和硫族化合物中存在亚铁磁性耦合; 它们的居里温度均较高; 磷族和硫族化合物中Cr离子的电子结构分别为a21g↑↓t41u↑↓t11u↑e2g↑和a21g↑↓t41u↑↓t11u↑t32g↑. 相似文献
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本文报导了对以Ni3Al为基的r′单晶体所做的蠕变及持久试验的结果。结果表明,r′晶体的稳态蠕变速εs遵从 εs=Cσmexp(-Qc′/RT) 的关系。指数m仅和温度有关。m(850℃)=3.95,m(950℃)=3.62。对Ni3Al,Qc′=88kcal/g-at。合金元素Ti,Nb,W都使Qc′升高,其中Nb的作用最大,然而W在提高蠕变强度上最有效。晶体取向对εs有显著影响。<111>取向的Ni3Al晶体εs最低,持久寿命tr最长。在1050℃,σ=5kg/mm2时,tr可≥100小时,Ni3Al单晶体也同样符合Monkman-Grant关系tr(εs)p=常数,其中p=0.82。r′晶体蠕变中的滑移系统是{111}<211>。 相似文献
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制备了Er3+和Yb3+共掺的碲钨酸盐玻璃样品65TeO2-25 WO3-10RmOn(RmOn=PbO,BaO),(65+x)TeO2-(25-x)WO 3-10La2O3 (x=0,5,10), (60+x)TeO2-(30 -x)WO3-10Bi2O3 (x=0,5,10).测试了玻璃样品的吸收光谱、荧光光谱、能级寿命及热稳定性能.结果表明除含Bi 2O3的碲钨酸盐玻璃外,其余玻璃样品均没出现析晶开始温度(Tx),说明碲钨酸盐 是一种适合于光纤拉制的玻璃基质材料.应用Judd-Ofelt理论计算了强度参数Ωt(t=2, 4,6),研究表明Ω2在碲钨酸盐玻璃中主要受到Er-O键的共价性的影响,而Er3 + 离子周围配位场的非对称性影响可以忽略.测得了Er3+在15 μm发射谱的荧光 半高宽 (FWHM=71—77nm)和Er3+的4I13/2能级寿命 (τm=3—34 ms).应用McCumber理论计算了Er3+在15 μm处的受激发射截面(σpeak=068—103×10-20 cm2).比较了Er3+在不同玻璃基质里 的15 μm荧光带宽和发射截面,研究结果表明碲钨酸盐玻璃是一种制备宽带光纤放大器的理想基质材料. 相似文献
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以时序t为自变量,可给出自由质点空间测地线的参数方程组{Xi(t)},借助于仿射参量R(t)变换实现测地线微分方程的齐次化, 推导出仿射参量R满足的一阶微分方程、获得以有理数Cu为标志的序列解析解R.基于R定义平直四维坐标系{t,r,θ,φ}的空间距离单位,建立自由质点测地线仿射参量时空坐标系{t,ξ,θ,φ}.研究{t,ξ,θ,φ}中狭义相对论时空间隔模型度规张量g的对角化过程, 发现与对角化度规对应的特征量t1(t,ξ), τ1(τ,ξ),tt(t,τ,ξ),ττ1(t,τ,ξ); 从而推出时空坐标系{t,ξ,θ,φ}维数小于4. 相似文献
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香蕉叶片Chla荧光动力学参量对激发光强的反应 总被引:5,自引:4,他引:1
在蓝色激发光(λm=660nm)作用下,香蕉叶片的叶绿素a(Chla)发出波长为720~740nm的荧光信号,荧光强度随时间呈现有规律的变化.随着激发光强的增加,荧光动力学参量F0和FVI/FV呈上升趋势,FV/F0与FV/FM逐渐达到饱和,而CA和T1/2呈下降趋势.研究结果表明,保证香蕉叶片光合机构高速有序运转的适宜光强在20~60μmol·m-2·s-1之间,过量的光强将造成叶片光合机构的损伤.讨论了香蕉叶片诸荧光动力学参量的生物学意义及其随激发光强度增加而变化的原因. 相似文献
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CHARLIE BENDER 《Molecular physics》2013,111(3):335-336
The effects of molecular motions on spin-echo signals (2n + 1)90°y—τ—90°x:—Acq(t) in nuclear spin systems with dipolar interactions have been investigated. It was found that in the case of a rigid lattice (M2τ2 c: >> 1) and a motionally narrowed NMR line (M2τ2 c,<< 1) a maximum of echo signals is observed at te = 2τ + t2—t1/2, where t1 and t2 are the widths of the RF pulses. It also was found that in the slow motion region (M2τ2 c ? 1) an amplitude of the dipolar echo signal is reduced and the maximum of the echo signal is shifted to the end of the second pulse. The theory developed is confirmed by the experimental results obtained for C6H6. 相似文献
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Optimal regimes for electrode conditioning in a vacuum by applying voltage pulses with different waveforms are considered. For nanosecond pulses with a constant duration (t p = const), the impulse dielectric strength for an oblique voltage wave is shown to be more than four times higher than for a rectangular pulse with an infinitely short leading-edge duration. The dependences of the dielectric strength on the conditioning pulse duration in the range 10?10 < t p < 10?3 s for pulses with different rise rates are obtained. The dielectric strength increases from 2 × 107 V/m for microsecond pulses to 1010 V/m for subnanosecond pulses. 相似文献
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利用非线性汤姆孙散射的理论,从理论和数值模拟上研究了单电子在横向穿越高斯激光束束 腰时所辐射的x射线阿秒脉冲列的性质. 主要分析了电子以初始能量γ0=1M eV—100M eV横向穿越激光振幅参数为a0=1—10的高斯光束束腰获得的阿秒辐射脉冲的 时间 和空间性质. 计算表明,辐射呈现脉冲列的形式. 脉冲列的包络宽度取决于激光强度、束腰 的宽度以及入射电子能量. 电子的初始能量比激光强度对电子辐射脉冲的影响更大. 辐射脉 宽、脉冲间隔和脉冲包络宽度都正比于1/γ20,辐射功率正比于 γ60,辐射能 量正比于γ40. 当改变激光振幅a0时,辐射功率正比 于a20、辐射包络中单 个脉冲脉宽正比于1/a0、脉冲之间的间隔正比于a0. 当保持激光强 度不变,而改变光束 束腰半径w0时,辐射的脉冲数量、包络和辐射能量正比于w0. 当 激光功率保 持不变时而改变激光强度和束腰半径时,脉冲包络宽度和最大辐射能量都基本不变. 当激光 振幅参数a0=1,电子初始能量为10MeV时,激光束腰为两个激光波长时,电子 辐 射脉冲包络宽度只有14×10-3τ0(τ0为入 射激光周期),达到几个阿秒的量级.
关键词:
阿秒脉冲
非线性汤姆孙散射
高斯激光光束 相似文献
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J.A.J. Hermans G.A.P. Engelbertink L.P. Ekström H.H. Eggenhuisen M.A. Van Driel 《Nuclear Physics A》1977,284(2):307-328
Mean lives in the range 1–20 ps of low-lying states of 13C, 16N, 20O and 36Cl have been measured with the Doppler-shift attenuation method by heavy-ion bombardment of 2H and 3H targets. The recoils are slowed down in Mg, Al, Cu, Ag and Au. The γ-ray patterns are observed with a large Ge(Li) detector at 0° in coincidence with protons; for 13C the patterns are measured in singles with a Compton-suppression spectrometer. Analysis of the γ-ray patterns with 4He-scaled stopping power data of Northcliffe and Schilling yields the following results: 13C, τm(3.85 MeV) = 12.6 ± 0.3ps; 16N, τm(0.40 MeV) = 5.1 ± 0.3 ps; 20O, τm(1.67 MeV) = 9.8 ± 0.7 ps; 36Cl, τm(0.79 MeV) = 19.9 ± 1.7 ps, τm(1.16 MeV) = 9.2 ± 0.6 ps and τm(1.60 MeV) = 0.94 ± 0.06 ps. A comparison with results obtained with the recoil-distance method shows agreement to about 10 %, with a slight tendency to somewhat longer lifetimes for the recoil-distance technique. The above stopping power is also used to reanalyze our previously published measurements. The new mean lives differ less than 4.5 % from the previous results. 相似文献
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B.F. Armaly T.T. Lam A.L. Crosbie 《Journal of Quantitative Spectroscopy & Radiative Transfer》1973,13(8):813-819
The functions B1(τ), D2(τ), and D3(τ), which arise in the study of radiative transfer through a planar medium with a relative refractive index different from unity, have been investigated. These functions reduce to exponential integrals when the refractive index of the medium is equal to that of the surroundings. Their behavior has been examined and is presented graphically and in tabular form for various ratios of the interface refractive index. When the interface refractive index ratio is larger than 1.2, these functions can be accurately approximated by an exponential of the form a e?bτ. 相似文献
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The mean path l of freshly introduced dislocations in NaCl crystals under the effect of triangular loading pulses τ(t) is shown to depend only on the pulse amplitude τm and be insensitive to the rate of stress growth. The replacement of triangular pulses with trapezoidal ones with a constant-load plateau (τ=const) extension of up to 60 min only insignificantly changes the l(τm) dependence. The data obtained are interpreted on the basis of the concept of quasi-static relaxation in a nonequilibrium system of dislocations subject to a combined effect of time-dependent applied stresses τ(t), coordinate-dependent internal stresses τi(x), and “dry friction” τp due to the pinning of dislocations by point defects. In such a model, the l(τm) dependence should saturate at τm<2τp; this is in fact observed in the range of 0.2τm<τm<0.3τy (here, τy is the yield stress), which gives an estimate for the pinning stress τp≈0.1τy. Based on the model suggested, a series of experimentally confirmed predictions were obtained, e.g., a recipe of “switching-off” of anomalies. Thus, a preliminary treatment of the samples by a series of stress pulses or holding in a magnetic field, which transforms the system of fresh dislocations into a more equilibrium state, sharply decreases the density of mobile dislocations quasi-statically responding to a pulsed load. It is shown that the discussed anomalies of dislocation mobility should be observed only in sufficiently pure crystals, where , and should be absent in contaminated crystals, where τp ~ τy. 相似文献
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Decay modes and lifetimes of low-lying levels in 30S and 34Ar were investigated by the Doppler-shift attenuation method using the 28Si(3He, n)30S and 32S(3He, n)34Ar reactions. The lifetimes measured in 30S were (in fs): τm(2210) = 310 ± 75, τm(3402) = 160 ± 45 and τm(3664) > 1400; and in 34Ar: τm(2090) = 150 ± 50, τm(3286) = 120 ± 65 and τm(4513) = 300 ± 80, also in fs. These results are compared with theoretical calculations. A comparison of the E2 decay strengths in masses 30 and 34 is also made to test the isospin dependence of electro-magnetic transitions. 相似文献
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S. Balk J. G. Körner D. Pirjol 《The European Physical Journal C - Particles and Fields》1998,1(1-2):221-233
We employ OPE techniques within HQET to calculate the inclusive semileptonic decays of polarized Λb baryons. Lepton mass effects are included which enables us to also discuss rates into polarized τ-leptons. We present explicit results for the longitudinal polarization of the τ in the Λb rest frame as well as in the (τ?, vτ) c.m. frame. In both the Λb rest frame and in the (τ?, vτ) c.m. frame we make use of novel calculational techniques which considerably simplify the calculations. The transverse polarization components of the τ are calculated in the (τ?, vτ) c.m. frame. We delineate how to measure the full set of 14 polarized and unpolarized structure functions of the decay process by angular correlation measurements. A set of observables are identified that allow one to isolate the contributions of the twoO(1/m t 2) nonperturbative matrix elementsK b and εb. 相似文献
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本文讨论用ps光脉冲简并四波混频测量非线性介质弛豫率和在适度或强的相位调制情况下测量激光脉冲宽度的方法,通过用计算机模拟及与实验结果比较,得出结论:对tp>>τr和tp<<τr两种极限情况,该方法是足够精确的.对τr/tp的中间情况,该方法只能给出一个估计. 相似文献