Intermolecular interactions of methyl acetate, β-propiolactone,ethyl acetate,and γ-butyrolactone: An AM1 semiempirical study

Closely related structures, like esters and lactones, have vastly different physical properties. This is apparently due to differences in the intermolecular interactions. The intermolecular interactions of methyl acetate, β-propiolactone, ethyl acetate, and γ-butyrolactone have been studied using the AM1 semiempirical method. Some of the “arranged clusters” were also compared to possible covalently bound trimers and tetramers of β-propiolactone and γ-butyrolactone. © 1992 John Wiley & Sons, Inc.     

Efficient Group-Based Multimedia-on-Demand Service Delivery in Wireless Networks

Recently, an upsurge of interest has been observed in providing multimedia on-demand (MoD) services to mobile users over wireless networks. Nevertheless, due to the rapidly varying nature of mobile networks and the scarcity of radio resources, the commercial implementation is still limited. This paper presents an efficient group-based multimedia-on-demand (GMoD) service model over multicast-enabled wireless infrastructures, where users requesting the same content are grouped and served simultaneously with a single multicast stream. The grouping is fulfilled through a process named "batching". An analytical model is derived to analyse a timeout-based batching scheme with respect to the tradeoff between user blocking probability and reneging probability. Based on the deduced analytical model, an optimal timeout-based batching scheme is proposed to dynamically identify the optimal tradeoff point that maximizes the system satisfaction ratio given a particular system status. The proposed scheme is evaluated by means of simulation and compared with two basic batching schemes (timeout-based, size-based), and two hybrid ones (combined-for-profit, combined-for-loss). The simulation results demonstrate the proposed approach can ensure significant gains in terms of user satisfaction ratio, with low reneging and blocking probabilities     

Morphology of intermetallic compounds formed between lead-free Sn-Zn based solders and Cu substrates

The morphologies of intermetallic compounds formed between Sn-Zn based solders and Cu substrates were investigated in this study. The investigated solders were Sn-9Zn, Sn-8.55Zn-0.45Al, and Sn-8.55Zn-0.45Al-0.5Ag. The experimental results indicated that the Sn-9Zn solder formed Cu₅Zn₈ and CuZn₅ compounds on the Cu substrate, while the Al-containing solders formed the Al_4.2Cu_3.2Zn_0.7 compound. The addition of Ag to the Sn-8.55Zn-0.45Al solder resulted in the formation of the AgZn₃ compound at the interface between the Al_4.2Cu_3.2Zn_0.7 compound and the solder. Furthermore, it was found that the cooling rate of the specimen after soldering had an effect on the quantity of AgZn₃ compound formed at the interface. The AgZn₃ compound formed with an air-cooling condition exhibited a rougher surface and larger size than with a water-quenched condition. It was believed that the formation of the AgZn₃ compound at the interface occurs through heterogenous nucleation during solidification.     

One convenient synthesis route to boron nitride nanotube

We describe one convenient synthesis route to boron nitride (BN) nanotube by the reaction of boron powder, iron oxide, and ammonium chloride at 600 °C for 12 h. Characterized by XRD, FTIR, XPS, TEM and SAED, the composition and morphology of the products are confirmed. The possible reaction mechanism is also discussed.     

MMSE-optimal approximation of continuous-phase modulated signal as superposition of linearly modulated pulses

The optimal linear modulation approximation of any M-ary continuous-phase modulated (CPM) signal under the minimum mean-square error (MMSE) criterion is presented in this paper. With the introduction of the MMSE signal component, an M-ary CPM signal is exactly represented as the superposition of a finite number of MMSE incremental pulses, resulting in the novel switched linear modulation CPM signal models. Then, the MMSE incremental pulse is further decomposed into a finite number of MMSE pulse-amplitude modulated (PAM) pulses, so that an M-ary CPM signal is alternatively expressed as the superposition of a finite number of MMSE PAM components, similar to the Laurent representation. Advantageously, these MMSE PAM components are mutually independent for any modulation index. The optimal CPM signal approximation using lower order MMSE incremental pulses, or alternatively, using a small number of MMSE PAM pulses, is also made possible, since the approximation error is minimized in the MMSE sense. Finally, examples of the MMSE-optimal CPM signal approximation and its comparison with the Laurent approximation approach are given using raised-cosine frequency-pulse CPM schemes.     

The Fundamental Experiments of Red Tide Chemical Forecast

Many food algae and red tide algae were cultivated in the f/2 medium, and the nitric oxide (NO) concentration of the medium and the cell density were determined. The experiments on algae were conducted when different concentrations of NO were added into the medium using two methods. The results show that low concentrations of NO were self-produced by marine algae during the exponential growth period and were about nmol/L level. But at the end of the period, i.e., 2 or 3 days before the cell density reaches the maximum, an NO peak appeared, with the NO concentration reaching 10 nmol/L. The NO threshold concentration exists according to the influence of exogenous NO on the marine phytoplankton growth. One type is the threshold concentration that can promote algae growth, and its value is between 10 and 1 nmol level, or even lower. The other type can inhibit the phytoplankton growth, which is about μmol level or higher. The results indicate that red tide algae are far more sensitive to NO than are food algae. The fundamental experimental outcome above may provide a new clue for red tide chemical forecast by inspecting the NO change.     

Nanomechanical analyses of porous SiO2 low-dielectric-constant films for evaluation of interconnect structure reliability

Porous SiO₂ low-dielectric-constant films containing different porosities and sizes of uniformly distributed pores were prepared in this study. Their nanomechanical properties including true flow stress and fracture toughness were analyzed by a nanoindentation test. The hardness and elastic modulus of the films prepared with an ethanol molar ratio of 3 and an aging time of 16 h reached maximum values of 2.4 and 40 GPa, respectively. With increasing ethanol molar ratio, the porosity increased, and the mechanical properties consequently decreased. With increasing aging time, the mechanical properties increased and then dropped due to enlarged pore sizes. From converted true flow stress, the porous SiO₂ films were found to yield at an ultimate stress of 3.1 GPa, and the maximum fracture energy release rate was calculated as 3.4 J/m². The plastic deformation and fracture behavior of the porous films was observed through crack initiation and propagation along the large amount of pores.     

"受迫振动共振"演示实验的改进

高一物理新教材第九章第七节受迫振动共振中出现了三种频率：物体受迫振动的频率、驱动力的频率和物体的固有频率，对三种频率的理解学生感到困难；其次，对共振曲线的理解也感到很抽象。为此，对本节演示实验进行了较科学的改进，收到了很好的效果。     

Self-Organization of Microlens Arrays Caused by the Spin-Coating-Assisted Hydrophobic Effect

A simple, low-cost, low-temperature, and shape-controllable approach has been demonstrated to fabricate polymer microlens arrays (MLAs). By using microcontact printing of the self-assembled monolayers and then spin coating, the microlenses were able to organize themselves on the patterned glass substrate. High-quality MLAs made of NOA65 prepolymer with lens-diameters of 50, 75, and 100 mum have been fabricated by this method. Lens shapes can be controlled by changing the spin rates of the prepolymer coating. Optical measurements have revealed an excellent light-collecting capability from the fabricated MLAs. It is anticipated that the technique will be ideally suited to low-cost and high-volume production     

浅谈集成电路的废气处理

集成电路的工业废气有含氟化物、硫酸雾的酸性废气,含氨的碱性废气,含异丙醇、光刻胶的有机废气,含SiO_2的含尘废气,以及含硅烷、磷烷的工艺尾气等,这些工业废气中大部分成分是有毒有害的,必须进行有效的处理才能排入大气中。主要讨论上述工业废气的分类、处理方式、应用范围及应用实例等。