A preemptive discrete-time priority buffer system with partial buffer sharing

This paper considers a Geo/Geo/1 discrete-time queue with preemptive priority. Both the arrival and service processes are Bernoulli processes. There are two kinds of customers: low-priority and high-priority customers. The high-priority customers have a preemptive priority over low-priority customers. If the total number of customers is equal or more than the threshold (k), the arrival of low-priority customers will be ignored. Hence the system buffer size is finite only for the low-priority customers. A recursive numerical procedure is developed to find the steady-state probabilities. With the aid of recursive equations, we transform the infinite steady-state departure-epoch equations set to a set of (k + 1) × (k + 2)/2 linear equations set based on the embedded Markov Chain technique. Then, this reduced linear equations set is used to compute the steady-state departure-epoch probabilities. The important performance measures of the system are calculated. Finally, the applicability of the solution procedure is shown by a numerical example and the sensitivity of the performance measures to the changes in system parameters is analyzed.     

On optimal service capacity allocation policy in an advance selling environment in continuous time

Based on some general reasonable assumptions, this paper employs the techniques of calculus of variations and optimal control theory to derive 10 main propositions associated with a service provider who aims at maximizing the present value of revenues/profits over a planning horizon in continuous time. Employing an aggregate pricing-response function that is dependent on excess capacity and a convex service cost formulation, the results show that (i) for a zero discount rate and unanticipated competitive entry, units of service capacity are allocated evenly over time, (ii) for a zero discount rate and anticipated competitive entry, units of allocated service capacity are increasing over time, (iii) for a positive discount rate and unanticipated competitive entry, units of allocated service capacity are decreasing over time, and (iv) for a positive discount rate and anticipated competitive entry, units of allocated service capacity are increasing over time, or are decreasing at first then increasing later. In addition, the questions of how deep a service firm should advance sell, whether advance selling is optimal in continuous time, and whether excess capacity could be an optimal strategy have been addressed. Furthermore, related sensitivity analyses are performed and endpoint constraints together with alternative shapes of the service-cost function are discussed. The managerial implications of the study’s results have been demonstrated.     

On the upper semicontinuity of Choquet capacities

The Choquet capacity T of a random closed set X on a metric space E is regarded as or related to a non-additive measure, an upper probability, a belief function, and in particular a counterpart of the distribution functions of ordinary random vectors. While the upper semicontinuity of T on the space of all closed subsets of E (hit-or-miss topology) is highly desired, T is not necessarily u.s.c. if E is not compact, e.g. E=Rⁿ. For any locally compact separable metric space E, this controversial situation can be resolved in the probabilistic context by stereographically projecting X into the Alexandroff compactification E_∞ of E with the “north pole” added to the projection. This leads to a random compact set that is defined on the same probability space, takes values in a space homeomorphic to the space of X, and possesses an equivalent probability law. Particularly, the Choquet capacity of is u.s.c. on the space of all closed subsets of E_∞. Further, consequences of the upper semicontinuity of are explored, and a proof of the equivalence between the upper semicontinuity of T and continuity from above on F(E) is provided.     

非等距时序灰色预测模型及其在岩石锚碇承载力分析中的应用

在许多桥梁工程中,锚碇岩石边坡的承载力和稳定性对整个桥梁工程的稳定和正常运营起着至关重要的作用.利用推广的非等间距灰色预测理论模拟了虎门大桥锚碇隧洞拉拔力试验中拉拔力与相应山体位移间的关系,并用所得到的非等距灰色预测模型预测了山体位移,结果表明,非等间距灰色预测模型的预测精度令人满意.研究结果对桥梁工程安全施工和岩石工程预测预报有重要理论意义和工程价值.     

西部地区高技术产业自主创新能力组合评价研究

为了提高综合评价的全面性、科学性和合理性,分别运用模糊综合评价法和灰色关联投影法对西部7省(区)1市高技术产业自主创新能力进行评价,在此基础上,利用模糊Borda法对两种单一方法的评价结果进行组合,得出组合评价结果.与单一方法相比,组合评价结果具有较高的可信度,可作为全面提升西部地区高技术产业自主创新能力的决策依据.     

Crystal structure and physical properties of the novel ternary intermetallics URuSi3−x and U3Ru2Si7

Two novel ternary intermediate phases, namely URuSi_3−x (x=0.11) and U₃Ru₂Si₇ were found in the Si-rich part of the U-Ru-Si phase diagram. Single crystal X-ray diffraction measurements, carried out at room temperature, indicated that URuSi_3−x crystallizes in its own tetragonal type structure (space group P4/nmm, no. 129; unit cell parameters: a=12.108(1) Å and c=9.810(1) Å), being a derivative of the BaNiSn₃-type structure. U₃Ru₂Si₇ adopts in turn a disordered orthorhombic La₃Co₂Sn₇-type structure (space group Cmmm, no. 65; unit cell parameters: a=4.063(1) Å, b=24.972(2) Å and c=4.072(1) Å). As revealed by magnetization, electrical resistivity and specific heat measurements, both compounds order magnetically at low temperatures. Namely URuSi_3−x is a ferromagnet with T_C=45 K, and U₃Ru₂Si₇ shows ferrimagnetic behavior below T_C=29 K.     

Dextran-grafted cation exchanger based on superporous agarose gel: Adsorption isotherms,uptake kinetics and dynamic protein adsorption performance

A novel chromatographic medium for high-capacity protein adsorption was fabricated by grafting dextran (40 kDa) onto the pore surfaces of superporous agarose (SA) beads. The bead was denoted as D-SA. D-SA, SA and homogeneous agarose (HA) beads were modified with sulfopropyl (SP) group to prepare cation exchangers, and the adsorption and uptake of lysozyme on all three cation-exchange chromatographic beads (SP-HA, SP-SA and SP-D-SA) were investigated at salt concentrations of 6–50 mmol/L. Static adsorption experiments showed that the adsorption capacity of SP-D-SA (2.24 mmol/g) was 78% higher than that of SP-SA (1.26 mmol/g) and 54% higher than that of SP-HA (1.45 mmol/g) at a salt concentration of 6 mmol/L. Moreover, salt concentration had less influence on the adsorption capacity and dissociation constant of SP-D-SA than it did on SP-HA, suggesting that dextran-grafted superporous bead is a more potent architecture for chromatographic beads. In the dynamic uptake of lysozyme to the three cation-exchange beads, the D_e/D₀ (the ratio of effective pore diffusivity to free solution diffusivity) values of 1.6–2.0 were obtained in SA-D-SA, indicating that effective pore diffusivities of SP-D-SA were about two times higher than free solution diffusivity for lysozyme. At 6 mmol/L NaCl, the D_e value in SA-D-SA (22.0 × 10⁻¹¹ m²/s) was 14.4-fold greater than that in SP-HA. Due to the superior uptake kinetics in SA-D-SA, the highest dynamic binding capacity (DBC) and adsorption efficiency (the ratio of DBC to static adsorption capacity) was likewise found in SP-D-SA. It is thus confirmed that SP-D-SA has combined the advantages of superporous matrix structure and drafted ligand chemistry in mass transport and offers a new opportunity for the development of high-performance protein chromatography.     

聚砜阴离子交换膜的制备及结构与性能研究

以1,4-二氯甲氧基丁烷(BCMB)为氯甲基化试剂,使聚砜(PSF)发生氯甲基化反应,制得了氯甲基化聚砜(CMPSF),考察了主要因素对聚砜氯甲基化反应的影响,并使用FTIR及1H-NMR等法对CMPSF的化学结构进行了表征.采用三乙胺(TEA)、三丙胺(TPA)及三丁胺(TBA)等3种叔胺对CMPSF进行了季铵化反应,并以4,4′-联吡啶为交联剂实施了交联反应,制备了聚砜阴离子交换膜(PSFAEM).测定了交换膜PSFAEM的主要性能,包括离子交换容量(IEC)、含水量(WC)及膜电阻(Rm).实验结果表明,使用BCMB,聚砜的氯甲基化反应可顺利进行,以氯仿为溶剂,以SnCl4为Lewis酸催化剂,可制得氯甲基化程度为1.75mmol/g的CMPSF.交换膜PSFAEM的IEC、WC及Rm与季铵化反应时间及叔胺的种类密切相关.季铵化反应时间相同时,采用烷基中碳原子数少的叔胺TEA所制备的交换膜具有高的IEC与WC,低的Rm;使用同一种叔胺时,随季铵化反应时间的增长,交换膜的IEC与WC增大,Rm减小.     

强碱性阴离子交换纤维结构和性能的关系

制备了不同紧密程度结构的强碱性阴离子交换纤维。研究了他们在水、乙醇中的膨胀性,用含水量、乙醇吸附量来表征。测定了吸附动力学曲线。结果表明,含水量52～68%,乙醇吸附量和含水量相近,结构紧密的纤维含水量、乙醇吸附量低于结构松散的纤维,前者的吸附平衡时间大于400s后者小于200s。     

Crystal Structure, Phase Transition, and Thermodynamic Properties of Bis-dodecylammonium Tetrachlorozincate (C12H25NH3)2ZnCl4(s)

The crystal structure and composition of (C₁₂H₂₅NH₃)₂ZnCl₄(s) were characterized by chemical and elemental analysis, X‐ray powder diffraction technique and X‐ray crystallography. The lattice energy of the title compound was calculated to be U_POT=888.82 kJ·mol^?1. Low temperature heat capacities of the title compound have been measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 403 K. An obvious solid to solid phase transition occurred in the heat capacity curve, and the peak temperature, molar enthalpy and molar entropy of the phase transition of the compound were determined to be T_trs= (364.02±0.03) K, (_trsH_m= (77.567±0.341) kJ·mol^?1, and (_trsS_m= (213.77±1.17) J·K^?1·mol^?1, respectively. Experimental molar heat capacities before and after the phase transition were respectively fitted to two polynomial equations. The smoothed molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were calculated and tabulated at an interval of 5 K.