Configurational effects of templating on the adsorption isotherms of templated porous materials

The porosity and pore geometry of disordered materials can be influenced by employing a removable template during synthesis. A theoretical and simulation study is reported of the configurational effects of template size and density on the adsorption isotherms of templated porous materials. To isolate the configurational (entropic) contributions, the adsorbate, matrix and template components are modelled as hard spheres. The replica Ornstein-Zernike equations proposed by Zhang, L. and Van Tassel, P. R. (2000) J. chem Phys., 112, 3006 are used within the Percus-Yevick approximation to calculate adsorption isotherms for differently sized adsorbate and template components. These theoretical results are compared with results from Monte Carlo simulation. It is found that adsorption is most enhanced whenever the size of the template is equal to or slightly larger than that of the adsorbate. Also, for systems of constant matrix density or constant matrix plus template density, increasing the density of template enhances the adsorption.     

基于延迟抖动的流媒体传输QoS机制

着眼于流媒体的传输服务质量问题,研究给定网络条件下流媒体的自适应传输策略,提出了一种基于延迟抖动的流媒体传输QoS(Quality of Service)方法。仿真实验表明该方法能够迅速判断网络状态,使流媒体的数据传输与网络当前状态及时吻合,能够获得较低丢包率的同时获得较大数据传输     

Predictor-Corrector Methods for Periodic Second-Order Initial-Value Problems

Predictor-corrector methods are constructed for the accuraterepresentation of the eigenmodes in the solution of second-orderdifferential equations without first derivatives. These methodshave (algebraic) order 4 and 6, and phase errors of orders upto 10. For linear and weakly nonlinear problems where homogeneoussolution components dominate, the methods proposed in this paperare considerably more accurate than conventional methods.     

Improving the Stability of Predictor-Corrector Methods by Residue Smoothing

Residue smoothing is usually applied in order to acceleratethe convergence of iteration processes. Here, we show that residuesmoothing can also be used in order to increase the stabilityregion of predictor-corrector methods. We shall concentrateon increasing the real stability boundary. The iteration parametersand the smoothing operators are chosen such that the stabilityboundary becomes as large as c(m, q)m²4^g where m is the numberof right-hand side evaluations per step, q the number of smoothingoperations applied to each right-hand side evaluation, and c(m,q) a slowly varying function of m and q, of magnitude 1.3 ina typical case. Numerical results show that, for a variety oflinear and nonlinear parabolic equations in one and two spatialdimensions, these smoothed predictor-corrector methods are atleast competitive with conventional implicit methods.     

Maintenance optimization on parallel production units

The optimal preventive-maintenance schedule for a productionsystem consisting of N identical parallel production units isinvestigated. The lifetimes of the units are IFR-distributed,i.e. with an increasing failure rate, and are supposed to bestatistically independent. The relevant costs are due to productionlosses, which are increasing and convex in the number of unitsthat are out of operation simultaneously. Actual maintenancecosts (either preventive or corrective) are supposed to be negligibleas compared to the costs due to these production losses. First we consider the apparently trivial case of geometric (discrete-time)or exponential (continuous-time) lifetime distributions forthe units. In this situation, preventive maintenance cannotimprove the condition of a unit. Hence, apparently the onlyrelevant policy is to do corrective maintenance on failed units.However, the analysis reveals that this conclusion is not correct.It turns out that taking non-failed units out of operation deliberatelycan be better than restricting to corrective maintenance only. We first show that, in the case of geometrically distributedlifetimes and unit repair times, the optimal preventive–maintenancepolicy is characterized by a single control limit K. Wheneverthe number of working units is less than or equal to K, no unitsare taken out of operation, while i – K units are setapart whenever i ( > K) units are operational. Next we consider the case with exponentially distributed lifetimesand repair times. Moreover, we assume that the repair capacityis limited, in the sense that only s ( N) units can be underrepair simultaneously. We show that, also in this case, it canbe optimal to take a working unit out of operation until thenext decision epoch (which is either a failure epoch or a repaircompletion epoch). It is shown that the optimal policy has aweak monotonicity property: the number of units which remainin operation increases with the number of available units. However,it is not necessarily true that, under the optimal policy, thenumber of units in standby position increases with the numberof available units. Numerical examples are presented which illustrate that, fora wide range of parameter values, the easiest policy (only performcorrective maintenance on failed units) performs rather wellas compared to the overall optimal policy. Finally we consider the possible extension to the practicallymore interesting case of non-exponential lifetime distributions.In particular, we assume that the lifetimes are composed oftwo non-identical exponential phases. A unit in its first lifephaseis called ‘good’, while a unit in its second phaseis called "doubtful". In this situation, one has the optionto put a good or doubtful unit in standby position until thenext decision epoch or to perform preventive maintenance ona doubtful unit. The latter brings a unit back from the doubtfulinto the good state. An indication is given of the problemsthat arise in generalizing the results obtained for the exponentialcase.     

THE PRIMARY REACTION IN THE PHOTOREDUCTION OF PROTOCHLOROPHYLLIDE MONITORED BY NANOSECOND FLUORESCENCE MEASUREMENTS

Abstract— Time resolved fluorescence measurements, carried out on protochlorophyllide reductase enriched membranes from oat ( Avena sativa ), are described. A fast (1 ns at 293 K) decaying fluorescence component is assigned to the photoactive NADPH-protochlorophyllide-enzyme complex, while a slower (5 ns) component is ascribed to non-photoactive protochlorophyllide. The results are interpreted in terms of a new fast primary step in the light requiring step of chlorophyll synthesis. The temperature dependence of the rate of this reaction has been studied by measuring the decay time of the fast fluorescence component at various temperatures from 77 to 293 K. Complete spectra of the kinetic fluorescence components have been measured at 293, 160 and 77 K.     

A procedure of determining potential energy surfaces of triatomic molecules from inversion of spectroscopic data

In this paper,we have suggested an iterative procedure of optimization of the linearparameters in an analytic potential energy function for a triatomic molecule,by combining both variational and second order perturbation methods.The most important feature of this procedure is that the objective function is an analytical expression which can be optimized easily.The application to the water molecule is presented.     

SPECTROSCOPY AND PHOTOCHEMISTRY OF 8-SUBSTITUTED 5-DEAZAFLAVINS

Abstract— Absorption, fluorescence and phosphorescence spectra as well as fluorescence and phosphorescence quantum yields of 8-X-5-deazaflavins (X = C1, NO₂, p -NO₂-C₆H₄, N(CH₃)₂, NH₂, p -NH₂-C₆H₄, p -N(CH₃)₂-C₆H₄-N=N) were determined. It was found that all these data are highly influenced by the substituent at position 8 of the 5-deazaisoalloxazine skeleton. Also the photoreduction of 8-X-5-deazaflavins in the presence of electron donors was studied. It was established that the photoreduction leads to the formation of a 5,5'-dimer and/or a 6,7-dihydro compound. Reduction of the C(6)-C(7) bond is promoted by strong electron-donating substituents and bulky electron donors. 5-Deazaftavins with a reducible substituent at position 8 exhibit reduction of the substituent prior to the reduction of the 5-deazaisoalloxazine skeleton.     

Application of a Direct Stiffness Method to Wave Propagation in Multiphase Poroelastic Media

In this paper, it is demonstrated how a direct stiffness method for wavepropagation in multilayered saturated poroelastic media, based on integraltransform techniques, can be modified to account for a small amount of gasin the pores. Unsaturated media with small gas fractions can be treatedusing Smeulders extension of Biots poroelastic theory. The effect of thepresence of gas bubbles on the fluid bulk modulus and the dispersioncharacteristics of a water-saturated sand of Mol is demonstrated. Thedirect stiffness method is illustrated with a numerical example wheretransient wave propagation in a dry, saturated and unsaturated halfspaceis considered.