Diffusion soldering using a Gallium metallic paste as solder alloy: study of the phase formation systematics

In this work preliminary results are reported on the characterization of Pb-free joints produced by using a diffusion soldering method at a process temperature of 700 °C during 20 min. The solder alloy is a metallic paste involving Ga and Al and Ni powder, and the substrates are Cu and Ni. The dissolution and diffusion-reaction processes, which take place at the interfaces of the interconnection zone, have been investigated by means of SEM and EPMA. A solid solution and intermetallic compounds (IMCs) with high melting point form as layers almost free from defect, allowing service temperatures about 500 °C higher than the process temperature. The phase stability sequence starting from the Ni to the Cu interface is the following: α′-Ni₃Ga, γ-Cu₉Ga₄, β-Cu₃Ga and (Cu) solid solution of the Ga–Cu system. The relative reaction front displacement of the layers and the implications of the present findings for the applicability of the diffusion-soldering method are also discussed.     

A new look at the long-term performance of general solar thermal systems

This work addresses the problem of evaluating the long-term performance of solar thermal systems, which is quantified through the monthly or seasonal/annual solar fraction. It is shown that for a general solar system it may be expressed as a function of monthly utilizabilities, calculated for two different temperature (radiation) levels, which correspond to minimum and maximum operating temperatures. Both systems without storage and with storage are considered. Examples for solar cooling and solar cogeneration systems are shown.     

Effects of labor contractions on catecholamine release and breathing frequency in newborn rats.

Plasma catecholamines in newborn rats (0-2 hr old) were analyzed following vaginal birth, cesarean section with simulated labor contractions, or cesarean section without labor contractions. Upon delivery, pups were exposed to key elements of the rat's natural birth process, that is, umbilical cord occlusion, tactile stimulation, and cooling. Only pups exposed to actual or simulated labor showed an immediate rise in norepinephrine and epinephrine. Initial postpartum respiratory frequencies were higher in vaginal than in cesarean delivered pups and, in all groups, inversely correlated with catecholamine titers, suggesting respiratory distress or transient tachypnea at lower catecholamine levels. These findings establish a rat model for analyzing effects of labor on neonatal adaptive response during the transition from prenatal to postnatal life. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recovery from control plane failures in GMPLS‐controlled optical networks

The health status of the control plane and the data plane of a GMPLS‐controlled optical network is independent in the physically separated control network implementation. In most control plane designs, besides the topology information, the entities of the routing protocol only record the number of available wavelengths on each link. However, the status of each wavelength is maintained by the entities of the signalling protocol. Without recovery ability of the signalling protocol CR‐LDP, a failure in the control plane will result in the permanent loss of the status information of wavelengths. A mechanism to recover the status information of the wavelengths is proposed. A downstream node maintains a label information database (LID) about assignable (free) labels in each incoming link. A copy of LID is redundantly stored in the upstream node as a label information mirror (LIM). A systematic procedure is proposed to synchronize the contents of a LIM and the corresponding LID. The initialization of a new LDP session with the enhanced recovery mechanism will guarantee the revival of the status information of wavelengths. It can recover multiple control channel failures, but it only applies to single node failure among any pair of adjacent nodes. © Crown copyright 2002. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

能产生模拟输出信号的微处理器

无刷直流电动机需要多种电压电平来控制转速：OV使电动机停转．5V使电动机以最大转速运转．而在OV和5V之间的电压则使电动机以较低的转速运转。当你在受徽处理器监控的系统中使用这种电动机时．微控制器应该产生所有这些电压。但     

Low birth weight and interactions between traditional risk factors

The effects of traditional risk factors on low birth weight were examined, using logistic regression analyses and adjusting for interactions between multiple factors. Data for 11,936 births were obtained from a state birth cohort file. The effect for maternal ethnicity was dependent on education and marital status; the effect of marital status was dependent on ethnicity, medical risk, and level of prenatal care; and the effect of prenatal care was dependent on marital status. Results suggest that examining only main effects and ignoring interactions can produce overgeneralized conclusions about the influence of individual risk factors on low birth weight.     

2,6-Dibromo-3,5-dimethyl-4-hydroxybenzyl ether and epoxy systems

Summary Meta-halogenated phenols are generally known to be more chemically and thermally stable than their ortho-or para-halogenated counterparts. A novel compound, 2,6-dibromo-3,5-dimethyl-4-hydroxybenzyl ether, is synthesized and is being used to incorporate this stable meta-bromo-phenol moiety into epoxy resins. In electronic encapsulation applications, epoxy derivatives of novolacs containing meta-bromo-phenol have exhibited exceptional hydrolytic and thermal stability compared to the conventional tetrabromobisphenol-A epoxies which are ortho-brominated phenolics. The meta-bromo-phenol moiety contributes to the extended device reliability life while providing fire retardency property.     

A Direct Solver for 2D Non-Stationary Boltzmann-Poisson Systems for Semiconductor Devices: A MESFET Simulation by WENO-Boltzmann Schemes

We present preliminary results of a high order WENO scheme applied to deterministic computations for two dimensional formulation of the transients for the Boltzmann-Poisson system describing electron transport in semiconductor devices. The collisional term models optical-phonon interactions which become dominant under strong energetic conditions corresponding to nanoscale active regions under applied bias. We treat the Boltzmann Transport equation in a spherical coordinate system for the wave-vector space. The problem is three dimensional in the wave-vector space and two dimensional in the physical space, plus the time variable driving to steady states. The new formulation avoids the singularity due to the spherical coordinate system.     

Dielectric relaxation behaviour of poly(cyclobutyl methacrylate)s

Dielectric behaviour of two poly(methacrylate)s with cyclobutyl groups in the side‐chains has been studied. This investigation was performed by determining the dielectric permittivity and loss in terms of frequency and temperature for poly(cyclobutyl methacrylate) (PCBuM) and poly(cyclobutylmethyl methacrylate) (PCBuMM). Dynamic dielectric measurements show sub‐glass relaxations, probably due to motions in the lateral chain, including the cyclobutyl ring. The effect of the insertion of a flexible spacer group into the side‐chain is also analyzed. The α relaxations were analyzed in terms of the Havriliak–Negami equation and the free volume theory tested according to the Vogel–Fulcher–Tamman–Hesse equation. The conductive and interfacial phenomena were studied by hopping and MacDonald–Coelho models. © 2002 Society of Chemical Industry     

Dynamic mechanical and dielectric relaxation behaviour of poly(methacrylate)s containing saturated rings with seven and eight members in the side‐chains

Dynamic mechanical and dielectric behaviour of poly(cycloheptyl methacrylate), poly(cycloheptylmethyl methacrylate) and poly(cyclooctyl methacrylate) have been investigated. The study was performed by determining the components of the complex relaxation modulus E* and the complex dielectric permittivity ?*. Results are discussed in terms of the effect of the size and structure of the side ring. The saturated ring group shows mechanical and dielectric activity at low temperature that is analyzed in terms of the Fuoss–Kirkwood equation. The free volume for the three polymers was determined. The conductive and interfacial phenomena were studied by MacDonald and Coelho models, where the dipolar contribution was introduced. © 2002 Society of Chemical Industry