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91.
Mathematical apparatus, which makes it possible to perform calculations of the current-voltage characteristics of cathodes of fuel cells with a solid polymer electrolyte in conditions where there are present extraneous diffusion restrictions is proposed. In so doing, the partial pressure of oxygen and the absolute pressure of gas in the gas chamber may assume any values. First of all presented are the results of calculations of the current-voltage characteristics intrinsic to active layers of the air and oxygen cathodes, which are performed under the assumption that the extraneous diffusion restrictions are absent altogether. Thereafter, in the same conditions (at the same parameters that characterize the active layer of a cathode), obtained are results of a calculation of the current-voltage characteristics inherent in the air and oxygen cathodes in the presence of extraneous diffusion restrictions. Afterward there is performed an analysis of the way a gas-diffusion layer restricts the process of generation of current in a cathode and of what measures should be taken in order for the extraneous diffusion restrictions to become less significant. 相似文献
92.
Earlier studies of electric field assisted LC (EF-LC) have shown that the effect on charged analytes of the application of an electric field over a capillary LC column is relatively small. Charged analytes can only be affected by the electric field while present in the mobile phase, which makes the effective time for influence of the electric field t(0) independent of retention time. Because the charged analytes only can be affected for a short time the electric field strength ought to be high in order to increase the impact of the electric field on the separation. We have, however, found that only a relatively low electric field strength can be used in EF-LC when pressure is used as main driving force. The useful field strength was limited by a dramatic increase in the current. This increase in current was found to origin from an increased concentration of buffer ions that have an electrophoretic mobility towards the pumped flow. 相似文献
93.
Influence
of heating rate on kinetic quantities of solid phase thermal decomposition 总被引:1,自引:0,他引:1
Thermogravimetric
analyses of thermal decomposition (pyrolysis, thermal dissociation and combustion)
of 9 different samples were carried out in dynamic conditions at different
heating rates. The kinetic parameters (E, A and km)
of thermal decomposition were determined and interrelations between the parameters
and heating rate q were analyzed. There
were also relations between Arrhenius and Eyring equations analyzed for thermal
decomposition of solid phase. It was concluded that Eyring theory is an element,
which interconnects used thermokinetic equations containing Arrhenius law
and suggests considering kinetic quantities in way relative to 3 kinetic constants
(E, A
and km). Analysis
of quantities other than km (i.e. E, A, Δ+H, Δ+S) in relation to heating rate is an incomplete method
and does not lead to unambiguous conclusions. It was ascertained that in ideal
case, assuming constant values of kinetic parameters (E
and A) towards heating rate and satisfying
both Kissinger equations, reaction rate constant km
should take on values intermediate between constants (km)1
and (km)2
determined from these equations. Whereas behavior of parameters E and A towards q were not subjected to any rule, then plotting relation km vs. q in the background of (km)1
and (km)2
made possible classification of differences between thermal decomposition
processes taking place in oxidizing and oxygen-free atmosphere. 相似文献
94.
Vapor-liquid equilibria have been investigated experimentally for the nitrogen-isobutane system at temperatures from 120 K
to 220 K and at pressures up to 150 bar. Below 126.5 K, two liquid phases were observed as pressure was increased to near
the vapor pressure of pure nitrogen. The equilibrium ratio of nitrogen in the binary system and the Henry’s law constants
for nitrogen in isobutane were determined from experimental data. The experimental phase equilibrium data were correlated
by means of the Peng-Robinson equation of state. 相似文献
95.
Ward Whitt 《Queueing Systems》1991,9(3):235-268
A fundamental principle of queueing theory isL=W (Little's law), which states that the time-average or expected time-stationary number of customers in a system is equal to the product of the arrival rate and the customer-average or expected customer-stationary time each customer spends in the system. This principle is now well known and frequently applied. However, in recent years there have been extensions, such as H=G and the continuous, distributional, ordinal and central-limit-theorem versions, which show that theL=W relation, when viewed properly, has much more power than was previously realized. Moreover, connections have been established between H=G and other fundamental relations, such as the rate conservation law and PASTA (Poisson arrivals see time averages), which show that there is a much greater unity in the overall theory than was previously realized. This paper provides a review.This paper is dedicated to the memory of our colleague Professor Peter Franken (1937–1989), who contributed greatly to the subject of this paper and to queueing theory more generally. 相似文献
96.
Groshev gave a characterization of the union of domains of partial attraction of all Poisson laws in 1941. His classical condition is expressed by the underlying distribution function and disguises the role of the mean of the attracting distribution. In the present paper we start out from results of the recent probabilistic approach and derive characterizations for any fixed >0 in terms of the underlying quantile function. The approach identifies the portion of the sample that contributes the limiting Poisson behavior of the sum, delineates the effect of extreme values, and leads to necessary and sufficient conditions all involving . It turns out that the limiting Poisson distributions arise in two qualitatively different ways depending upon whether >1 or <1. A concrete construction, illustrating all the results, also shows that in the boundary case when =1 both possibilities may occur. 相似文献
97.
Hideki Takayasu Misako Takayasu Astero Provata Greg Huber 《Journal of statistical physics》1991,65(3-4):725-745
We study a generalized aggregation process in which charged particles diffuse and coalesce randomly on a lattice. For one-dimensional and mean-field models, we show that there exists a statistically-invariant steady state when randomly charged particles are continuously injected. The steady-state charge distribution obeys a power law with the exponent depending both on the type of the injection and on the spatial dimension. The response of the system to a perturbation (i.e., relaxation) is characterized by either a power law decay (t
–
,1) or a compressed exponential decay [exp(–t
),>1]. 相似文献
98.
Norman O. Smith 《Journal of solution chemistry》1994,23(4):521-539
A method of finding the activity coefficients of salts, anhydrous or hydrated, in binary solid solutions, described in an earlier paper as it applies to continuous series, has been applied to discontinuous series. The salts must differ with respect to only one ion. The method requires isothermal distribution data for equilibria between liquid (aqueous) and solid solutions in the ternary system consisting of the two salts and water. The following salt pairs were used for illustration: K(I/Br) at 0, 15, 25, 35, and 50°C., (NH4/K)SCN at 0, 30, 60, and 90°C., (K/Tl)C103 at 10°C., and (NH4/K)SO3NH2, (NH4/K)Br, (Mg/Co)SO4-7H2O, and (Mn/Cu) SO4.n H2O-all at 25°C. Two kinds of behavior were noted and treated differently: systems in which the two series have the same, and those in which they have different crystal lattices. For two salts, A and B, which have the same lattice, and whose rational activity coefficients, f
A
and f
B
, can be described by 2-suffix Margules equations (regular solutions), lnf
A
=Bsx
B
2
and lnf
B
=Bsx
A
2
to be partially miscible, Bs>2, but this requirement does not apply if the lattices are different. In each series, distribution constants for the equilibria were also determined. Where possible, the calculated activities of the salts or the Gibbs excess energies of the solid solutions were compared with values reported by others who determined them by other methods. All the salt pairs studied show slight or strong positive deviations from ideality. 相似文献
99.
100.
The third law of thermodynamics, in the sense that the entropy per unit volume goes to zero as the temperature goes to zero, is investigated within the framework of statistical mechanics for quantum and classical lattice models. We present two main results: (i) For all models the question of whether the third law is satisfied can be decided completely in terms of ground-state degeneracies alone, provided these are computed for all possible boundary conditions. In principle, there is no need to investigate possible entropy contributions from low-lying excited states, (ii) The third law is shown to hold for ferromagnetic models by an analysis of the ground states.Dedicated to Pierre Résibois. Work supported in part by NSF grant PHY-7825390 A01. 相似文献