Dual-mode control of tri-state boost converter for improved performance

A tri-state boost converter with an additional boost-inductor free-wheeling interval was proposed earlier to eliminate the right-half-plane (RHP) zero that occurs in the control-to-output transfer function of a classical boost converter under continuous-conduction mode of operation. A "constant-D/sub o/" control scheme, in which the "capacitor-charging" interval of the converter was kept constant, was employed. This resulted in a relatively large inductor current, especially under high line and load conditions, thereby causing high circuit losses. This paper proposes two variations of a novel dual-mode control (DMC) scheme that vary both the "boost" and the "capacitor-charging" intervals. Control analysis, design, and limitations of the proposed DMC schemes are presented. Through computer simulations and hardware experiments the performance of the tri-state boost converter with DMC schemes are compared with those of the tri-state boost converter with "constant-D/sub o/" control scheme, and the classical PI-controlled boost converter. The DMC schemes achieve a significant (about 10%) improvement in converter's efficiency for a wide load range over the "constant-D/sub o/" control scheme.     

Evolution of multiprotocol label switching

Multiprotocol label switching (MPLS) is rapidly emerging as an Internet Engineering Task Force (IETF) standard intended to enhance the speed, scalability, and service provisioning capabilities in the Internet. MPLS uses the technique of packet forwarding based on labels, to enable the implementation of a simpler high-performance packet forwarding engine. This also decouples packet forwarding from routing, facilitating the provision of varied routing services independent of the packet forwarding paradigm. The authors track the evolution of this technology in relation to other existing technologies. Then an overview of the MPLS architecture and design is provided. In addition, some of the work that was a precursor to MPLS is discussed, as well as related issues and debates     

Effects of humidity and temperature on in vitro dissolution of carbamazepine tablets

The rate and extent of dissolution of various approved marketed carbamazepine (CBZ) tablets exposed to 33, 52, 75, and 97% relative humidities at both room temperature and 40 degrees C, and saturated water vapor at room temperature were compared to fresh unstressed tablets. The dissolution data indicate that exposure of CBZ tablets to high humidity and temperature can have a profound effect on tablet disintegration and dissolution. The dissolution rates of some batches of CBZ products exposed to 97% humidity at 40 degrees C or saturated water vapor at room temperature were drastically reduced in only 6-7 days.     

Effect of Sb, P, Sn and B on the microstructure and creep properties of normalized and tempered 1.25 Cr-0.5 Mo steels

A program to study the effect of Sb, P, Sn and B on creep properties of four normalized and tempered 1.25 Cr-0.5 Mo steels at 538°C (1000°F) has been completed. Results show that even a combined addition of large amounts of Sb, P and Sn does not affect short time creep strength or ductility of the steel at 538°C (1000°F). Addition of B resulted in an increase or decrease of creep strength depending on the nature of the impurity species present, presumably due to B-impurity interactions. Regardless of the effect on creep strength, B additions caused sharp reductions in rupture ductility in all cases. Comparison of the present results on the four laboratory steels (100 pct bainite) with results of a previous study on a commercial steel (60 pct bainite + 40 pct ferrite) show that the effect of microstructure becomes negligible and rupture strength values of the various steels at 538°C (1000°F) approach each other at rupture times in excess of 10⁴ h.     

Modeling the tensile properties in β-processed α/β Ti alloys

The development of a set of computational tools that permit microstructurally based predictions for the tensile properties of commercially important titanium alloys, such as Ti-6Al-4V, is a valuable step toward the accelerated maturation of materials. This paper will discuss the development of neural network models based on a Bayesian framework to predict the yield and ultimate tensile strengths of Ti-6Al-4V at room temperature. The development of such rules-based model requires the population of extensive databases, which in the present case are microstructurally based. The steps involved in database development include producing controlled variations of the microstructure using novel approaches to heat treatments, the use of standardized stereology protocols to characterize and quantify microstructural features rapidly, and mechanical testing of the heat-treated specimens. These databases have been used to train and test neural network models for prediction of tensile properties. In addition, these models have been used to identify the influence of individual microstructural features on the tensile properties, consequently guiding the efforts toward development of more robust mechanistically based models. Based on the neural network model, it is possible to investigate the influence of individual microstructural features on the tensile properties, and in certain cases these dependencies can point toward unrecognized phenomena. For example, the apparently unexpected trend of increase in tensile strength with increasing prior β-grain size has led to the determination of the pronounced role of the basketweave microstructure in strengthening these alloys, especially in case of larger prior β grains. This article is based on a presentation made in the symposium “Computational Aspects of Mechanical Properties of Materials,” which occurred at the 2005 TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA, under the auspices of the MPMD-Computational Materials Science & Engineering (Jt. ASM-MSCTS) Committee.     

Childhood thyroid cancer. Characteristics and long-term outcome in children irradiated for benign conditions of the head and neck

OBJECTIVE: To determine the characteristics and long-term outcome of radiation-induced thyroid cancer in children. DESIGN: Retrospective review of a cohort of 4296 irradiated patients who received childhood radiation treatment to the head and neck area at the same hospital. PATIENTS: Forty-one children who were younger than 20 years when thyroid cancer developed in them and 77 adults in whom thyroid cancer developed. All 118 cases were diagnosed before 1974 and were followed up for a median of 19.4 years. RESULTS: Children presented with clinically palpable lymph nodes more often than adults (30.7% vs 15.1%, P = .05) and had more recurrences (39% vs 16%, P = .05). Despite these frequent recurrences, only one patient (an adult) died of thyroid cancer. Seventy percent of the recurrences occurred during the first 10 years of follow-up, but recurrences continued after 20 years. The adults had previously identified factors that predicted the risk of recurrences, but none could be identified in the children. CONCLUSION: The presentation and relatively good outcome of radiation-induced thyroid cancer in children is similar to that in nonirradiated children. Frequent and late recurrences call for lifelong follow-up.     

Microstructural effects on the tensile properties and deformation behavior of a Ti-48Al gamma titanium aluminide

The effects of microstructure on the tensile properties and deformation behavior of a binary Ti-48Al gamma titanium aluminide were studied. Tensile-mechanical properties of samples with microstructures ranging from near γ to duplex to fine grained, near- and fully-lamellar were determined at a range of temperatures, and the deformation structures in these characterized by transmission electron microscopy (TEM). Microstructure was observed to exert a strong influence on the tensile properties, with the grain size and lamellar volume fraction playing connected, but complex, roles. Acoustic emission response monitored during the tensile test revealed spikes whose amplitude and frequency increased with an increase in the volume fraction of lamellar grains in the microstructure. Analysis of failed samples suggested that microcracking was the main factor responsible for the spikes, with twinning providing a minor contribution in the near-lamellar materials. The most important factor that controls ductility of these alloys is grain size. The ductility, yield stress, and work-hardening rate of the binary Ti-48Al alloy exhibit maximum values between 0.50 and 0.60 volume fraction of the lamellar constituent. The high work-hardening rate, which is associated with the low mobility of dislocations, is the likely cause of low ductility of these alloys. In the near-γ and duplex structures, slip by motion of 1/2<110] unit dislocations and twinning are the prevalent deformation modes at room temperature (RT), whereas twinning is more common in the near- and fully-lamellar structures. The occurrence of twinning is largely dictated by the Schmid factor. The 1/2<110] unit dislocations are prevalent even for grain orientations for which the Schmid factor is higher for <101] superdislocations, though the latter are observed in favorably oriented grains. The activity of both of these systems is responsible for the higher ductility at ambient temperatures compared with Al-rich single-phase γ alloys. A higher twin density is observed in lamellar grains, but their propagation depends on the orientation and geometry of the individual γ lamellae. The increase in ductility at high temperatures correlates with increased activity of 1/2<110] dislocations (including their climb motion) and twin thickening. The role of microstructural variables on strength, ductility, and fracture are discussed. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

Analysis of the mechanism of die soldering in aluminum die casting

A mechanism of soldering of an aluminum alloy die casting to a steel die is proposed. A soldering critical temperature is postulated, at which iron begins to react with aluminum to form an aluminum-rich liquid phase and solid intermetallic compounds. The liquid joins the die with the casting upon solidification. The critical temperature is determined by the elements in both the casting alloy and the die material and is equal to the solidus temperature of the resulting alloy. The critical temperature is used to predict the onset of die soldering, and the local liquid fraction is related to the soldering tendency. Experiments have been carried out to validate the concept and to determine the critical temperature for die soldering in an iron-aluminum system. Thermodynamic calculations are used to determine the critical temperature and soldering tendency for the cases of pure aluminum and a 380 alloy in a steel mold. Factors affecting the soldering tendency are discussed, and methods for reducing die soldering are suggested.     

蓝牙模块的测试方案

测试项目在蓝牙环境中，哪些方面需要测试？蓝牙模块包括连接到主机设备的无线电 (硬件)和堆栈 (软件)。协议是构成堆栈的一套代码，在生产车间中将不会测试协议。修订系统软件可能会改变硬件性能，但必须在设计集成阶段对其进行粼选。需要使用的一些重要参数，如误码率(BER)、功率电平等对功能进行测试。选择测试必需理解由于无线电的设计方式哪些内容可能会改变，并根据测试的项目查看其发挥的作用。它是否提供了独特的功能？没有提供哪些功能？如打印机使用的蓝牙链路。在技术得到验证前，打印机可能仍会通过电缆提供打印功能，因此测…     

Supplementation of squalene attenuates experimentally induced myocardial infarction in rats

We have investigated the preventive effects of squalene against isoprenaline-induced myocardial infarction in male albino rats. Supplementation with squalene significantly prevented the isoprenaline-induced adverse changes in the levels of protein and glycoprotein components in plasma and heart tissue of experimental groups of rats. It exerted an antioxidant effect by inhibiting the isoprenaline-induced lipid peroxidation and by maintaining the level of non-enzymatic free radical-scavenger, reduced glutathione at near normalcy. Histopathological observations also confirmed the possible cardioprotective action of squalene by maintaining the normal architecture of the heart tissue. The results of the present investigation demonstrate that supplementation with squalene offers cardioprotection in experimental rats by its antioxidant and membrane- stabilizing properties.