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151.
过去几十年中差分吸收光谱技术(differential optical absorption spectroscopy,DOAS)在大气污染物监测方面取得了成功应用.文章提出了根据差分吸光度最大值(OD'm)设定阈值的思想,将传统DOAS算法与基于卡尔曼滤波的DOAS算法相结合,利用两种算法在相同信噪比下具有不同反演精度的特点,在保证测量精度的前提下提高了DOAS系统的检测极限,较好地解决了短光程下低浓度气体的测量精度问题.在常温常压和流动状态下,对烟气中的SO2浓度测量进行了理论和实验研究.研究结果表明,改进的DOAS算法在OD'm<0.048 1时,SO2浓度测量精度较高,测量下限可低于28.6 mg·m-3,零点漂移低于2.9 mg·m-3传统DOAS算法在0.048 1<OD'm<0.927 2时,SO2浓度测量精度较高;两种算法对OD'm>0.927 2时的SO2浓度测量都存在较大的误差,必须进行线性度校正. 相似文献
152.
Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scaling with the laser amplitude within a large range is also discussed. 相似文献
153.
154.
V. Garzó 《The European physical journal. E, Soft matter》2009,29(3):261-274
A theory based on a solution of the inelastic Enskog equation that goes beyond the weak dissipation limit is used to determine
the thermal diffusion factor of a binary granular mixture under gravity. The Enskog equation that aims to describe moderate
densities neglects velocity correlations but retains spatial correlations arising from volume exclusion effects. As expected,
the thermal diffusion factor provides a segregation criterion that shows the transition between the Brazil-nut effect (BNE)
and the reverse Brazil-nut effect (RBNE) by varying the parameters of the system (masses, sizes, composition, density and
coefficients of restitution). The form of the phase diagrams for the BNE/RBNE transition is illustrated in detail in the tracer
limit case, showing that the phase diagrams depend sensitively on the value of gravity relative to the thermal gradient. Two
specific situations are considered: i) absence of gravity, and ii) homogeneous temperature. In the latter case, after some
approximations, our results are consistent with previous theoretical results derived from the Enskog equation. Our results
also indicate that the influence of dissipation on thermal diffusion is more important in the absence of gravity than in the
opposite limit. The present analysis, which is based on a preliminary short report of the author (Phys. Rev. E 78, 020301(R) (2008)), extends previous theoretical results derived in the dilute limit case. 相似文献
155.
G. Kaniadakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(1):3-13
In ordinary statistical mechanics the Boltzmann-Shannon
entropy is related to the Maxwell-Bolzmann distribution
pi by means of a twofold link. The first link is differential and
is offered by the Jaynes Maximum Entropy Principle. Indeed, the
Maxwell-Boltzmann distribution is obtained by maximizing the Boltzmann-Shannon entropy under
proper constraints. The second link is algebraic and imposes that
both the entropy and the distribution must be expressed in
terms of the same function in direct and inverse form. Indeed, the
Maxwell-Boltzmann distribution pi is expressed in terms of the exponential
function, while the Boltzmann-Shannon entropy is defined as the mean value of
-ln (pi).
In generalized statistical mechanics the second link is customarily
relaxed. Of course, the generalized exponential function defining
the probability distribution function after inversion, produces a
generalized logarithm Λ(pi). But, in general, the mean value
of -Λ(pi) is not the entropy of the system. Here we
reconsider the question first posed in [Phys. Rev. E 66,
056125 (2002) and 72, 036108 (2005)], if and how is it
possible to select generalized statistical theories in which the
above mentioned twofold link between entropy and the distribution
function continues to hold, such as in the case of ordinary
statistical mechanics.
Within this scenario, apart from the standard
logarithmic-exponential functions that define ordinary statistical
mechanics, there emerge other new couples of direct-inverse
functions, i.e. generalized logarithms Λ(x) and generalized
exponentials Λ-1(x), defining coherent and
self-consistent generalized statistical theories. Interestingly, all
these theories preserve the main features of ordinary statistical
mechanics, and predict distribution functions presenting power-law
tails. Furthermore, the obtained generalized entropies are both
thermodynamically and Lesche stable. 相似文献
156.
The evolution of a granular gas of viscoelastic particles in the homogeneous cooling state is studied. The velocity distribution function of granular particles and the time dependence of the mean kinetic energy of particles (granular temperature) are found. The noticeable deviation of the distribution function from the Maxwell distribution and its non-monotonous evolution are established. The perturbation theory with respect to the small dispersion parameter is elaborated and the analytical expressions for the asymptotic time dependence of the velocity distribution function and the granular gas temperature are derived. 相似文献
157.
We discuss the zero temperature phase diagram of a dilute gas with three fermionic species. We make use of solvable limits to conjecture the behavior of the system in the “unitary” regions. The physics of the Thomas-Efimov effect plays a role in these considerations. We find a rich phase diagram with superfluid, gapless superfluid and inhomogeneous phases with different symmetry breaking patterns. We then discuss one particular possible experimental implementation in a system of 6Li atoms and the possible phases arising in this system as an external magnetic field is varied across three overlapping Feshbach resonances. We also suggest how to experimentally distinguish the different phases. 相似文献
158.
以硝酸改变氯化镁基体为硝酸镁 ,减轻基体对铬的干扰。选取优化的条件 ,在硝酸镁介质中 ,使用原子吸收光谱法测定铬 ,线性范围 0— 80 ng/ m L,回收率 87.5 %— 10 9.7% ,相对标准偏差小于 10 %。方法简便 ,结果令人满意。 相似文献
159.
XRF法测定铁矿石中TFe、SiO2和P 总被引:2,自引:0,他引:2
四硼酸锂为熔剂 ,钴为内标 ,高温熔融法对铁矿石进行均一处理 ,X射线荧光光谱法测定铁矿石中TFe、Si O2 和 P,取得满意结果。 相似文献
160.
麦克斯韦-玻耳兹曼统计分布律的相对论修正 总被引:3,自引:0,他引:3
为了避免光速极限带来的复杂性,首先给出了理想气体分子动量的分布律公式.在此基础上,进一步讨论了麦克斯韦一玻耳兹曼统计分布律的相对论修正.解析和数值计算均表明,这一修正几乎没有可观测的物理效应.这说明,大学物理教学中介绍的麦克斯韦一玻耳兹曼速度分布律公式对实际应用已经足够精确.当然,我们决不可据此近似公式断言气体分子有一定的概率可以超光速运动. 相似文献