Experimental investigation of the influence of the FSW plunge processing parameters on the maximum generated force and torque

A statistical design of experiments (DOE) approach was used to determine if specific build orientation parameters impacted mechanical strength of stereolithography (SL) fabricated parts. A single platform (25.4 × 25.4-cm cross-section) on the 3D Systems Viper si2 SL machine was designed to hold 18 ASTM D-638 type I samples manufactured in different orientations. The DOE tested three factors: axis, layout, and position. Samples were fabricated parallel with the x-axis or y-axis, or 45° to both axes (called axes 1, 2, and 3, respectively). For each axis, samples were fabricated either flat or on an edge relative to the x–y plane (called layouts 1 and 2, respectively). Three samples were manufactured for each layout and axis combination, and the samples were labeled as positions 1, 2, or 3 depending on the distance from the center of the platform with position 1 being the closest to the center. The results from the statistical analyses showed that axis and position had no significant effect on ultimate tensile stress (UTS) or modulus of elasticity in tension (E). However, layout (or whether a sample was built flat or on an edge) was shown to have a statistically significant effect on UTS and E (at a 95% level of confidence). The differences between average UTS and E for each of the samples built flat and on an edge were ~3.53% (43.2 versus 44.8 MPa) and ~4.59% (763.9 versus 800.7 MPa), respectively. Because of the relatively small differences in means for UTS and E, the statistical differences between layout most likely would not have been identified without performing the multifactor analysis of variance. Furthermore, layout was the only factor that tested different orientations of build layers (or layer-to-layer interfaces) with respect to the sample part, and thus, it appears that the orientation of the build layer (layer-to-layer interfaces) with respect to the fabricated part has a significant effect on the resulting mechanical properties. This study represents one of many to follow that is using statistical analyses to identify and classify important fabrication parameters on mechanical properties for layer-manufactured parts. Although SL is the focus of this work, the techniques developed and presented here can be applied to any layered manufacturing technology producing any ASTM-type specimen with any particular material.     

弥漫性轴索损伤实验装置的研制和应用

为研究弥漫性轴索损伤(DAI)问题,研制了一套稳定性高、重复性好且能比较真实地模拟DAI临床损伤机制的实验装置。详细阐述了实验装置的设计过程,包括驱动力的选择、联动结构设计、限位固定块的设计和传感器的选择等。最后通过大鼠实验验证了实验装置的可行性和优越性。     

Study of the Transit-Time Limitations of the Impulse Response in Mid-Wave Infrared HgCdTe Avalanche Photodiodes

The impulse response in frontside-illuminated mid-wave infrared HgCdTe electron avalanche photodiodes (APDs) has been measured with localized photoexcitation at varying positions in the depletion layer. Gain measurements have shown an exponential gain, with a maximum value of M = 5000 for the diffusion current at a reverse bias of V _b = 12 V. When the light was injected in the depletion layer, the gain was reduced as the injection approached the N+ edge of the junction. The impulse response was limited by the diode series resistance–capacitance product, RC, due to the large capacitance of the diode metallization. Hence, the fall time is given by the RC constant, estimated as RC = 270 ps, and the rise time is due to the charging of the diode capacitance via the transit and multiplication of carriers in the depletion layer. The latter varies between t _10–90 = 20 ps (at intermediate gains M < 500) and t _10–90 = 70 ps (at M = 3500). The corresponding RC-limited bandwidth is BW = 600 MHz, which yields a new absolute record in gain–bandwidth product of GBW = 2.1 THz. The increase in rise time at high gains indicates the existence of a limit in the transit-time-limited gain–bandwidth product, GBW = 19 THz. The impulse response was modeled using a one-dimensional deterministic model, which allowed a quantitative analysis of the data in terms of the average velocity of electrons and holes. The fitting of the data yielded a saturation of the electron and hole velocity of v _e = 2.3 × 10⁷ cm/s and v _h = 1.0 × 10⁷ cm/s at electric fields E > 1.5 kV/cm. The increase in rise time at high bias is consistent with the results of Monte Carlo simulations and can be partly explained by a reduction of the electron saturation velocity due to frequent impact ionization. Finally, the model was used to predict the bandwidth in diodes with shorter RC = 5 ps, giving BW = 16 GHz and BW = 21 GHz for x _j = 4 μm and x _j = 2 μm, respectively, for a gain of M = 100.     

如何实现真实世界下的PC“绿色”能效

计算机原设备制造商（OEM）正面对商业、环保和法规等多方面的压力,需要体现他们产品的能效,提供更“绿色”的台式个人电脑（PC）和服务器。这使设计这些产品的工程师需要设计出符合诸如美国80 PLUS、“能源之星”（ENERGYSTAR）和计算产业拯救气候行动计划（CSCI）等能效标准的PC电源。     

A Cross-Layer Approach to Enhance QoS for Multimedia Applications Over Satellite

The need for on-demand QoS support for communications over satellite is of primary importance for distributed multimedia applications. This is particularly true for the return link which is often a bottleneck due to the large set of end-users accessing a very limited uplink resource. Facing this need, Demand Assignment Multiple Access (DAMA) is a classical technique that allows satellite operators to offer various types of services, while managing the resources of the satellite system efficiently. Tackling the quality degradation and delay accumulation issues that can result from the use of these techniques, this paper proposes an instantiation of the Application Layer Framing (ALF) approach, using a cross-layer interpreter (xQoS-Interpreter). The information provided by this interpreter is used to manage the resource provided to a terminal by the satellite system in order to improve the quality of multimedia presentations from the end user’s point of view. Several experiments are carried out for different loads on the return link. Their impact on QoS is measured through different application as well as network level metrics.

Efficient Access Control for Wireless Sensor Data

Although very developed in many sectors (databases, filesystems), access control schemes are still somewhat elusive when it comes to wireless sensor networks. However, it is clear that many WSN systems—such as healthcare and automotive ones—need a controlled access to data that sensor nodes produce, given its high sensitivity. Enforcing access control in wireless sensor networks is a particularly difficult task due to the limited computational capacity of wireless sensor nodes. In this paper we present a full-fledged access control scheme for wireless sensor data. We enforce access control through data encryption, thus embedding access control in sensor data units. We also propose a lightweight key generation mechanism, based on cryptographic hash functions, that allows for hierarchical key derivation. The suggested protocol only relies on simple operations, does not require interactions between nodes and data consumers and has minimal storage requirements.

Rigid PVC/(layered silicate) nanocomposites produced through a novel melt‐blending approach

On the basis of the fusion behavior of poly(vinyl chloride) (PVC), the influence of compounding route on the properties of PVC/(layered silicate) nanocomposites was studied. Four different compounding addition sequences were examined during the melt compounding of PVC with montmorillonite (MMT) clay, including (a) a direct dry mixing of PVC and nanoclay, (b) an addition of nanoclay at compaction, (c) an addition of nanoclay at the onset of fusion, and (d) an addition of nanoclay at equilibrium torque. Both unmodified sodium montmorillonite (Na⁺‐MMT) and organically modified montmorillonite (Org.‐MMT) clays were used, and the effect of the addition sequence of the clay during compounding on its dispersion in the matrix was evaluated by X‐ray diffraction and transmission electron miscroscopy. The surface color change, dynamic mechanical analysis, and flexural and tensile properties of PVC/clay nanocomposites were also studied. The experimental results indicated that both the extent of property improvement and the dispersion of nanoparticles in PVC/(layered silicate) nanocomposites are strongly influenced by the degree of gelation achieved in PVC compounds during processing. The addition of nanoclay to PVC must be accomplished at the onset of fusion, when PVC particles are reduced in size, in order to produce nanocomposites with better nanodispersion and enhanced mechanical properties. Overall, rigid PVC nanocomposites with unmodified clay (Na⁺‐MMT) were more thermally stable and exhibited better mechanical properties than their counterparts with organically modified clay (Org.‐MMT). J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Influence of mixing characteristics for water encapsulation by self-assembling hydrophobic silica nanoparticles

Water encapsulation using silica nanoparticles was assessed using two different types of single step mixing processes. The influential mixing characteristics have been determined. Direct mixing at high rotational speed requires high shear and vigorous stirring properties. Progressive water atomisation using gentle mixing process requires high atomisation pressure and rapid surface refreshing of the mixed material. Mechanisms of powder formation were also proposed. Encapsulation of micrometric water droplets in shell-like structure is respectively obtained by either progressive size reduction of macroscopic particulates or direct coating of pre-formed microscopic droplets. These mechanisms resulting from the interactions between a solid particle and a liquid highly depend on parameters such as particle's hydrophobicity, surface tension or kinetic energy.     

Preparation of TiO2-pillared montmorillonite as photocatalyst Part I. Microwave calcination, characterisation, and adsorption of a textile azo dye

Two photocatalysts based on TiO₂-pillared intercalated montmorillonite have been prepared by microwave for 10 min at 700 W or by furnace heating at 673 K. Montmorillonite pillaring with TiO₂ increased the basal spacing to 14.7 Å (conventional heating) and 17.6 Å (microwave heating). XRD patterns of both materials showed the presence of 100% anatase with a slightly higher rate of crystallinity obtained through microwave calcination than by conventional heating at 673 K. The BET specific surface area of the microwave prepared photocatalyst (151 m² g^− 1) was 3 fold higher than those of the Degussa TiO₂ P25. At pH = 5.8, the maximum adsorption capacity of Solophenyl red 3BL (a textile azo dye) on the TiO₂-pillared montmorillonite calcined by microwave was 185 mg g^− 1, whereas it was 1.4 and 3 fold lower on the TiO₂-pillared montmorillonite calcined at 673 K, and on the Degussa TiO₂ P25 respectively. The influence of pH on the adsorption of the dye depended on the pH_ZPC of the pillared montmorillonites.     

减少供热系统失水是节能的重要措施

节约能源是我国的一项长期战略方针,建筑节能包括围护结构节能和供热采暖系统节能两个方面,而在采暖系统节能中。系统的失水能耗损失占很大比重,本文经过计算,每失1t热水需要多消耗16．38kgce。堵住失水的漏洞是供热企业应该关心的首要问题。不偷放热水,提高公民的法律意识,也是热力企业需要大力宣传的一个主题。