基于MATLAB对Wi-MAX与其他技术的比较和可适性分析(英文)

目前全球电信系统的宽带技术已经影响巨大.如果没有宽带接入技术,就不可能有效和迅速进入信息超级高速公路.而目前的蜂窝技术或现有的宽带网络,只能满足部分要求.因为,这些技术的速度较低而成本较高.因此,人们需要更快捷和成本更低的宽带接入技术.WiMAX(微波接入全球互联)技术能够满足目前的需求.最近,WiMAX系统已引入全球宽带接入技术领域.本文研究表明:与其他现存技术相比,WiMAX系统提供的技术不属于通常的Wi-Fi、2.5cellular系统和其他现有技术,该技术可以对现有网络娱乐服务技术进行有效的补充,同时,WiMAX技术还能够提供更高的速度,且成本更低.由于WiMAX技术的发展和在世界上被普遍采用,它将给宽带服务领域带来革命性的变化,将成为现代娱乐生活的组成部分.     

Propagation of a cylindrical shock wave in a mixture of a non-ideal gas and small solid particles under the action of monochromatic radiation

A cylindrical shock wave in a dusty gas under the action of monochromatic radiation into the stellar atmosphere with a constant intensity per unit area is discussed. The gas is assumed to be grey and opaque, and the shock is assumed to be transparent. The dusty gas is considered as a mixture of a non-ideal gas and small solid particles. To obtain some essential features of shock propagation, small solid particles are considered as a pseudo-fluid, and it is assumed that the equilibrium flow condition is maintained in the entire flowfield. The effects of the parameters of the gas non-idealness, the mass concentration of solid particles in the mixture, the ratio of the density of solid particles to the initial density of the gas, and the radiation parameter on flow variables are investigated. It is shown that an increase in the gas non-idealness and the radiation parameter has a decaying effect on the shock waves, whereas the shock strength increases with an increase in the ratio of the density of solid particles to the initial density of the gas. It is found that an increase in the gas non-idealness and the ratio of the density of solid particles to the initial density of the gas has the opposite effects on the fluid velocity, pressure, and shock strength. It is also shown that an increase in the radiation parameter has a trend to decrease the flow variables and the shock strength.     

Effect of protein fusion on the transition temperature of an environmentally responsive elastin-like polypeptide: a role for surface hydrophobicity?

The limited throughput, scalability and high cost of protein purification by chromatography provide motivation for the development of non-chromatographic protein purification technologies that are cheaper and easier to implement in a high-throughput format for proteomics applications and to scale up for industrial bioprocessing. We have shown that genetic fusion of a recombinant protein to an elastin-like polypeptide (ELP) imparts the environmentally sensitive solubility property of the ELP to the fusion protein, and thereby allows selective separation of the fusion protein from Escherichia coli lysate by aggregation above a critical temperature (T(t)). Further development of ELP fusion proteins as widely applicable purification tools necessitates a quantitative understanding of how fused proteins perturb the ELP T(t) such that purification conditions (T(t)) may be predicted a priori for new recombinant proteins. We report here the effect that fusing six different proteins has on the T(t) of an ELP. A negative correlation between T(t) and the fraction hydrophobic surface area on the fused proteins was observed, which was determined from computer modeling of the available three-dimensional structure. The thermally triggered aggregation behavior of ELP-coated, functionalized gold colloids as well as ligand binding to the tendamistat-ELP fusion protein support the hypothesis that hydrophobic surfaces in molecular proximity to ELPs depress the ELP T(t) by a mechanism analogous to hydrophobic residue substitution in the ELP repeat, Val-Pro-Gly-Xaa-Gly.     

Rheological studies on cordierite honeycomb extrusion

The rheological parameters for a cordierite honeycomb extrusion were investigated using the Benbow–Bridgwater model. The extrusion pastes were formulated using typical binders, plasticizers, lubricants and pore-forming agents normally used for such extrusions. Pastes were found to have good pseudo-plasticity, low bulk yield and very low die-land shear stress, compared with the velocity dependent components of the respective pressure drops. In some formulation, reduced velocity contribution to the extrusion pressure with increased binder content found useful for better honeycomb extrusion. These characteristics of the honeycomb extrusion batches were analyzed by using dynamic bulk and shear stress components derived from the Benbow–Bridgwater six-parameter model and compared with the results of honeycomb extrusion trials. Plasticizing agents like polyethylenglycol (PEG) and glycerin were found to decrease the die entry pressure but showed no external lubricating effect leading to higher die-land pressure. Pore-forming agent, graphite was found to reduce both die entry and die land pressures, whereas, carbon increases the die entry pressure.     

Dual Activity of Some Modified Thiocarbamyl Sulfenamides in the Vulcanization of NR Accelerated by Dibenzothiazyl Disulfide

The retarding and the accelerating activities of some modified thiocarbamyl sulfenamides—namely, N-cyclopentamethylene thiocarbamyl-N′-(cyclohexyl, thiocyclohexyl) sulfenamide (CPCTS), N-cyclopenta-methylenethiocarbamyl-N′-(cyclohexyl, N-cyclopentamethylene thio) sulfenamide (CPCCS), and N-cyclopentamethylenethiocarbamyl-N′-(cyclohexyl, N-oxydiethylene thio) sulfenamide (CPCOS)—have been studied in dibenzothiazyl disulfide (MBTS)-accelerated vulcanization of natural rubber (NR). It is found that CPCTS, CPCOS, and CPCCS delay the onset of cure and generate active accelerators during vulcanization. In addition to this, the accelerator systems are quite capable of producing age-resistant vulcanizates. The results indicate that thiocarbamyl sulfenamides modified chemically at the >NH functionality retain their accelerating property. Thus CPCTS, CPCOS, and CPCCS play the dual role of an accelerator and a retarder in the vulcanization of NR accelerated by MBTS.     

Redox Signaling Is an Early Event in the Pathogenesis of Renovascular Hypertension

Activation of the renin-angiotensin-aldosterone system plays a critical role in the development of chronic renal damage in patients with renovascular hypertension. Although angiotensin II (Ang II) promotes oxidative stress, inflammation, and fibrosis, it is not known how these pathways intersect to produce chronic renal damage. We tested the hypothesis that renal parenchymal cells are subjected to oxidant stress early in the development of RVH and produce signals that promote influx of inflammatory cells, which may then propagate chronic renal injury. We established a reproducible murine model of RVH by placing a tetrafluoroethhylene cuff on the right renal artery. Three days after cuff placement, renal tissue demonstrates no histologic abnormalities despite up regulation of both pro- and anti-oxidant genes. Mild renal atrophy was observed after seven days and was associated with induction of Tnfα and influx of CD3+ T cells and F4/80+ macrophages. By 28 days, kidneys developed severe renal atrophy with interstitial inflammation and fibrosis, despite normalization of plasma renin activity. Based on these considerations, we propose that renal parenchymal cells initiate a progressive cascade of events leading to oxidative stress, interstitial inflammation, renal fibrosis, and atrophy.     

Effect of Divalent Cation Additives on the γ-Al2O3-to-α-Al2O3 Phase Transition

The effect on the γ-Al₂O₃-to-α-Al₂O₃ phase transition of adding divalent cations was investigated by differential thermal analysis, X-ray diffractometry, and surface-area measurements. The cations, Cu²⁺, Mn²⁺, Co²⁺, Ni²⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, were added by impregnation, using the appropriate nitrate solution. These additives were classified into three groups, according to their effect: (1) those with an accelerating effect (Cu²⁺ and Mn²⁺), (2) those with little or no effect (Co²⁺, Ni²⁺, and Mg²⁺), and (3) those with a retarding effect (Ca²⁺, Sr²⁺, and Ba²⁺). The crystalline phase formed by reaction of the additive with γ-Al₂O₃ at high temperature was a spinel-type structure in groups (1) and (2) and a magnetoplumbite-type structure in group (3). In groups (2) and (3), a clear relationship was found between the transition temperature and the difference in ionic radius of Al³⁺ and the additive (Δ r ): The transition temperature increased as Δ r increased. This result indicates that additives with larger ionic radii are more effective in suppressing the diffusion of Al³⁺ and O²⁻ in γ-Al₂O₃, suppressing the grain growth of γ-Al₂O₃, and retarding the transformation into α-Al₂O₃.     

Synthesis,PASS-Predication and in Vitro Antimicrobial Activity of Benzyl 4-O-benzoyl-α-l-rhamnopyranoside Derivatives

Benzyl α-l-rhamnopyranoside 4, obtained by both conventional and microwave assisted glycosidation techniques, was subjected to 2,3-O-isopropylidene protection to yield compound 5 which on benzoylation and subsequent deprotection of isopropylidene group gave the desired 4-O-benzoylrhamnopyranoside 7 in reasonable yield. Di-O-acetyl derivative of benzoate 7 was prepared to get newer rhamnopyranoside. The structure activity relationship (SAR) of the designed compounds was performed along with the prediction of activity spectra for substances (PASS) training set. Experimental studies based on antimicrobial activities verified the predictions obtained by the PASS software. Protected rhamnopyranosides 5 and 6 exhibited slight distortion from regular ¹C₄ conformation, probably due to the fusion of pyranose and isopropylidene ring. Synthesized rhamnopyranosides 4–8 were employed as test chemicals for in vitro antimicrobial evaluation against eight human pathogenic bacteria and two fungi. Antimicrobial and SAR study showed that the rhamnopyranosides were prone against fungal organisms as compared to that of the bacterial pathogens. Interestingly, PASS prediction of the rhamnopyranoside derivatives 4–8 were 0.49 < P_a < 0.60 (where P_a is probability ‘to be active’) as antibacterial and 0.65 < P_a < 0.73 as antifungal activities, which showed significant agreement with experimental data, suggesting rhamnopyranoside derivatives 4–8 were more active against pathogenic fungi as compared to human pathogenic bacteria thus, there is a more than 50% chance that the rhamnopyranoside derivative structures 4–8 have not been reported with antimicrobial activity, making it a possible valuable lead compound.     

Microstructure,mechanical and tribological properties of microwave sintered calcia-doped zirconia for biomedical applications

Among the available ceramics materials for load bearing bio-implant applications, Y-TZP is superior (fracture toughness: ∼10 MPa m^0.5) for its better mechanical properties. However, due to concerns related to property degradation of Y-TZP during long exposure in body fluid, the current work is taken up to study the feasibility of developing stabilised zirconia ceramics in CaO–ZrO₂ system, using microwave sintering (MW) technique. The present paper reports the processing, microstructure and tribological properties of microwave sintered Ca-doped ZrO₂ based ceramics. An important experimental result is that MW sintering to greater than 90% theoretical density can be achieved in Ca-PSZ (8 mol% CaO) and Ca-FSZ (16 mol% CaO) ceramics by sintering at 1585 °C for 1 h. The sintered materials exhibit Vickers hardness ∼8–10 GPa, which would allow them to be used as load bearing implants. Also, a modest fracture toughness (∼6 MPa m^0.5) was measured for Ca-PSZ, which is better than commercial grade alumina. So, it is possible to synthesize a material which has better combination of hardness and toughness than other commercially available bioceramics like alumina, hydroxyapatite, TCP, etc. Considering its specific application for THR (total hip replacement), tribological experiments using fretting wear tester serve to provide data about the wear behaviour of the proposed materials. The fretting experiments were conducted against a bearing-steel counterbody in air as well as in a SBF (simulated body fluid) environment. The wear behaviour of the investigated tribocouple is dominated by the formation of Fe oxide/chloride layer at the worn surface.