On the irregularity strength of trees

For any graph G, let n_i be the number of vertices of degree i, and . This is a general lower bound on the irregularity strength of graph G. All known facts suggest that for connected graphs, this is the actual irregularity strength up to an additive constant. In fact, this was conjectured to be the truth for regular graphs and for trees. Here we find an infinite sequence of trees with λ(T) = n₁ but strength converging to . © 2004 Wiley Periodicals, Inc. J Graph Theory 45: 241–254, 2004     

Delayed breakdown diode and its optimal design for solid state picosecond closing switch

We study a Si-based diode with a p⁺nn⁺ structure for picosecond semiconductor closing switch and discuss the physical process, which underlies the operation principle of high-power closing switch based on a delayed breakdown diode (DBD). From the results of numerical simulations and theoretical analysis, single device has demonstrated reliable operation at 2.3 kV, 89 ps risetime, and high output dV/dt(30 kV/ns). As a contribution to the optimal design, some conclusions about trade-off are drawn by changing structure parameters and physical parameters.     

Production systems with interruptions, arbitrary topology and finite buffers

We consider a production system with finite buffers and arbitrary topology where service time is subject to interruptions in one of three ways, viz. machine breakdown, machine vacations or Npolicy. We develop a unified approximation (analytical) methodology to calculate the throughput of the system using queueing networks together with decomposition, isolation and expansion techniques. The methodology is rigorously tested covering a large experimental region. Orthogonal arrays are used to design the experiments in order to keep the number of experiments manageable. The results obtained using the approximation methodology are compared to the simulation results. The ttests carried out to investigate the differences between the two results show that they are statistically insignificant. Finally, we test the methodology by applying it to several arbitrary topology networks. The results show that the performance of the approximation methodology is consistent, robust and produces excellent results in a variety of experimental conditions.     

Mn22+离子1s22s-1s2np的偶极跃迁能和振子强度

用全实加关联方法计算了类锂Mn22 离子1s22s-1s2np(2≤n≤9)的偶极跃迁能和振子强度.1s2np(2≤n≤9)态的精细结构通过计算自旋-轨道与自旋-其他轨道相互作用算符的期待值确定.依据单通道量子亏损理论,确定了Rydberg系列1s2np的量子数亏损.从而可以用这些作为能量的缓变函数的量子亏损,实现对任意高激发态(n≥10)的能量的可靠预言.将这些分立态振子强度与单通道量子亏损理论相结合,得到在电离阈附近束缚态-束缚态跃迁振子强度以及束缚态-连续态跃迁的振子强度密度,从而将Mn22 离子的这一重要光谱特性的理论预言外推到整个能域.     

Ultrasonic characterization of heavy metal TeO2–WO3–PbO glasses below room temperature

The longitudinal ultrasonic attenuation measurements have been made using pulse echo method at fundamental frequencies of 2, 4, 6 and 8 MHz in 20WO₃–(80−x) TeO₂–xPbO ternary tellurite glasses (x=10, 12.5, 15, 17.5 and 20 mol%) in the temperature range 160–280 K. The results showed the presence of a broad peak which shifts to higher temperature with increasing frequency. The ultrasonic attenuation peaks suggest that the experimental behavior is controlled by thermally activated structural relaxations. The internal friction, acoustic activation energy, deformation potential, relaxation strength, number of loss centers and density of state have been calculated both as a function of temperature and PbO content. The acoustic activation energy was found to decrease from 0.156 to 0.135 eV with the increase of PbO content. The results showed that both the number of loss centers and their activation energy decrease with the atomic ring size. An increase in the density of state is observed with addition of PbO content at the same frequency in the whole range of temperature which is associated with structural units formed when PbO is added.     

ICF靶用空心玻璃微球耐压性能测试

 利用自行研制的空心微球耐外压装置和充气装置，测试了目前激光惯性约束聚变实验打靶使用的空心玻璃微球耐内压能力和耐外压能力。空心玻璃微球采用液滴法制备，直径为180～250 mm、壁厚为0.8~4.0 mm。理论计算表明，当微球纵横比超过90时，耐外压能力与球壳材料的杨氏模量有关，由此测量得到的空心玻璃微球杨氏模量为55~75 GPa。玻璃微球的耐内压能力主要与球壳材料的抗拉强度有关，实验测量得到的玻璃微球抗拉强度为90~140 MPa。     

Numerical calculation of domains of analyticity for perturbation theories in the presence of small divisors

We study numerically the complex domains of validity for KAM theory in generalized standard mappings. We compare methods based on Padé approximants and methods based on the study of periodic orbits.     

Second Dissociation Constant of Bis-[(2-hydroxyethyl)amino]acetic Acid (BICINE) and pH of Its Buffer Solutions from 5 to 55 °C

The values of the second dissociation constant, K ₂, and related thermodynamic quantities of the ampholyte bis[(2-hydroxyethyl)amino]acetic acid (BICINE) have been determined at temperatures from 5 to 55 ^∘C. The pH values of six equimolal buffer solutions, and four buffer solutions having ionic strengths (I = 0.16 mol⋅kg⁻¹) similar to those in blood plasma, have been evaluated at 12 temperatures from 5 to 55 ^∘C using the Bates–Guggenheim convention. The liquid junction potentials (E _j ) between the buffer solutions of BICINE and saturated KCl solution of the calomel electrode at 25 and 37 ^∘C have been estimated by measurement with a flowing junction cell. These values of E _j have been used to ascertain the operational pH values at 25 and 37 ^∘C. The pK ₂ values at 25 and 37 ^∘C are 8.333 and 8.156, respectively. The thermodynamic quantities associated with the second acid dissociation have been calculated from the values of pK ₂ as a function of temperature. The zwitterionic buffer BICINE was shown to be useful as a pH standard in the region close to that of blood serum.     

An AlGaN/GaN HEMT with reduced surface electric field and improved breakdown voltage

A reduced surface electric field in AlGaN/GaN high electron mobility transistor (HEMT) is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas (2-DEG) channel as an electric field shaping layer. The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions. Compared with the HEMTs with conventional source-connected field plate and double field plate, the HEMT with Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge. By optimizing both the length of Mg-doped layer, L_m, and the doping concentration, a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure, respectively. In a device with V_GS=-5 V, L_m=1.5 μm, a peak Mg doping concentration of 8× 10¹⁷ cm^-3 and a drift region length of 10 μm, the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.     

Interfacial interaction in carbon fiber/thermoplastic composites

This work was undertaken in order to increase the understanding of the mechanism responsible for fiber/matrix interaction in carbon fiber/thermoplastic composite. From results of previous study on carbon fiber/PEEK composite, which suggested that the formation of the fiber/ matrix interaction was primarily related to a chemisorption mechanism, a study was done of the conditions required to obtain efficient fiber/matrix interaction in PA-12 and PP/carbon fiber composites. The interest in studying carbon fiber composite based on PP and PA-12 was that these two matrices are very different in terms of reactivity, polyamide having many more reactive groups than polypropylene. As expected, due to the non-reactive chemical structure of the polypropylene, fiber/matrix interaction in carbon fiber/PP composite occurred only when the matrix was thermally degraded, i.e. when the composite was molded at high temperature or under long residence time at the melt temperature. For the carbon fiber/PA-12 composite, strong fiber/matrix interaction occurred readily at relatively low molding temperature, i.e. well before thermal degradation of the matrix. It was also found that the short beam shear strength in these composites seems to evolve with molding temperature, and a maximum interfacial strength was observed at a molding temperature corresponding to the thermal degradation of the matrix. This indicates that although matrix degradation often results in strong reduction in the composite performance, some matrix degradation can be beneficial in terms of interfacial mechanical properties. Finally, this work demonstrated that while the formation of fiber/matrix interaction seems to be primarily related to a chemisorption mechanism, the contribution of interphase crystallinity to the interfacial strength is not negligible. In fact, interfacial crystallinity was found to be essential to ensure optimum interfacial strength.