工作频率为2GHz的低成本可编程振荡器

各种无线通讯系统都需要本机振荡器。图1示出了一种带宽为2GHz的低成本锁相环(PLL)电路,可用于这样一些场合,如工业、科技、医疗、卫星用的个人通讯系统(CS-PCS)。该电路的核心IC芯片为LMX2325(美国国家半导体公司产品,www.national.com)频率综合器,其特点是射频工作可达2.5GHz。这种IC芯片包括了一个可编程的(N-     

Electrochemical preparation and properties of polypyrrole and its blend with poly(vinyl sulfonate) doped with perchlorate anions

In this article, we report polypyrrole (PPy)/poly(vinyl sulfonate) (PVS) and PPy/perchlorate (ClO) composite films generated by the electrochemical oxidation of pyrrole on a glassy carbon electrode (GCE) in an aqueous solution. The response of the produced films to an applied potential at 0.7 V was obtained by a cyclic voltammetry study in acetonitrile media. The films were significantly similar in their electrochemical behavior when ClO ions doped during the redox process. We concluded that with an increasing number of cycles, the anodic current increased because the number of the electroactive participants transported in the copolymer matrix was increased. Theoretical studies based on the Nernst and Butler–Volmer equations indicated that the ClO ion was transported during the oxidation/reduction process of the PPY/PVS and PPY/ClO films. The produced films were characterized further by means of IR spectroscopy, electrochemical impedance spectroscopy, and scanning electron microscopy to verify that the anion of ClO was doped into the copolymer matrix as well. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Correlation of tunnel convergence with TBM operational parameters and chip size in the Ghomroud tunnel, Iran

Evaluating the impact of rock mass properties on a tunneling operation is crucial, especially when using a tunnel boring machine (TBM). It is an integral part of machine selection and performance prediction in the design and bidding stage. Monitoring and analysis of ground conditions during the construction is also essential to allow the operator to take precautionary measures in adverse geological conditions. This involves adjusting TBM operational parameters such as machine thrust and penetration to avoid potential problems caused by face collapse or excessive convergence and subsequent machine seizure that can cause long delays. Tunnel wall convergence is a function of rock mass characteristics, in situ stresses, size of excavation, and rate of penetration (ROP). It is one of the main factors in determining the use of shielded machines in deep rock tunnel projects. The case study of the Ghomroud water conveyance tunnel project, under construction by a double shield TBM, is used to examine the effect of rock mass parameters on tunnel convergence and hence on the need for over excavation and shield lubrication to avoid problems such as shield seizure. Results of a preliminary analysis of field observations show that the amount of the tunnel convergence can have a direct relationship with the percentage of powder and large rock fragments in the muck. In addition, tunnel convergence has shown a strong relationship with the TBM thrust/torque and rate of penetration (ROP). These relationships have been examined and the results of the analysis as well as the resulting formulas will be explained in this paper.     

A semi-analytical solution for forced vibrations response of rectangular orthotropic plates with various boundary conditions

Orthotropic plates form an essential part of many marine, aerospace, and automobile structures. The recent increase in the use of composite materials for plate-type structures intensified the need for solutions utilizing orthotropic plates. These structural components, in many instances, are subjected to vibration. The main purpose of this paper is to present a semi-analytical analysis of the response of orthotropic plates to forced vibrations with different combinations of boundary conditions subjected to a general distributed excitation. The solution of the partial differential equation was reduced to an iterative sequential solution of ordinary differential equations using extended Kantorovich method. The efficiency and accuracy of the proposed method were examined through comparison with available literature and was in good agreement with them.     

A Hall Microscope for Visualizing the Magnetic States of Objects

A three-dimensional microscope with a sensitivity of 2.5 G/Hz^1/2 has been developed on the basis of two Hall probes. The magnetic field dynamic range of the microscope at a frequency of 19 Hz is 2.5 G–80 kG. The maximum observed area of the objects under study is 7.5 × 7.5 mm² with a resolution of 50 × 50 m². The minimum scanning step along the X and Y axes is 5 m. The maximum displacement along the Z axis is 25 mm with a minimum scanning step of 1 m. An arbitrarily shaped instrument function can be created in the magnetic complex by combining the temperature, the stationary and alternating magnetic fields, and the transport current. The microscope was used for the spatial and temporal visualization of the structure and properties of the critical state, as well as for diagnosing superconductors at temperatures of 4.2–300 K in magnetic fields of 0–80 kG.     

Study of macroinitiator efficiency and microstructure–thermal properties in the atom transfer radical polymerization of methyl methacrylate

The atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with poly vinylacetate macroinitiator (PVAc-CCl₃) and CuCl/PMDETA as catalyst was successfully carried out in bulk and solution. The apparent propagation rate constant () and concentration of active species ([P°]) were higher in the bulk. In solution they increased with polarity of solvent. Two different molecular weights of macroinitiators were used in ATRP of MMA. The linear relation of Ln[M]₀/[M] versus time was only confirmed for the low molecular weight macroinitiator. The ratio of was calculated in the bulk reaction with the low molecular weight macroinitiator, this ratio was 1.77 × 10¹⁴ M⁻¹ s⁻¹ for larger macroinitiator in solution. The MWD of block copolymers were sharper with lower molecular weight macroinitiator in the solution, but it appeared broader in the bulk polymerization. Our results indicated that smaller molecular weight macroinitiator was more efficient and formed a block copolymer with lower PDI. Thermal analysis and microstructure of the block copolymers are investigated by ¹H NMR, FT-IR, TGA and DSC. The chain tacticity of the MMA units is found not to be sensitive to the kinetic of the reactions with two different molecular weights of macroinitiator. DSC measurement shows two different transitions at 39 and 108 °C assigned to PVAc and PMMA blocks. The TGA profile shows a three-step degradation. The initial small weight loss that occurs around 220 °C and two large weight loss around 238 and 310 °C are attributed to dechlorination step and decomposition of the PMMA and PVAc blocks.     

Role of Carboxylic Acid-Functionalized MWCNTs in Potentially Biodegradable Poly(Amide–Imide) Nanocomposites Based on N,N′-(Pyromellitoyl)-bis-S-valine: Preparation,Thermal and Morphological Properties

A simple solution-blending process was used to efficiently disperse of carboxyl-modified multiwalled carbon nanotubes into a potentially biodegradable poly(amide–imide) to obtain poly(amide–imide)/carboxyl-modified multiwalled carbon nanotubes bionanocomposites. Carboxyl-modified multiwalled carbon nanotubes were utilized to better dispersion of multiwalled carbon nanotubes into the polymer matrix. The poly(amide–imide)/carboxyl-modified multiwalled carbon nanotube bionanocomposites were prepared with different carboxyl-modified multiwalled carbon nanotube contents (5–15 wt%). The resulting bionanocomposites are characterized by several techniques, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Adding carboxyl-modified multiwalled carbon nanotube into polymer matrix significantly increased the thermal stability of bionanocomposites due to the increased interfacial interaction between the poly(amide–imide) matrix and carboxyl-modified multiwalled carbon nanotube.     

The Role of BDNF in Experimental and Clinical Traumatic Brain Injury

Traumatic brain injury is one of the leading causes of mortality and morbidity in the world with no current pharmacological treatment. The role of BDNF in neural repair and regeneration is well established and has also been the focus of TBI research. Here, we review experimental animal models assessing BDNF expression following injury as well as clinical studies in humans including the role of BDNF polymorphism in TBI. There is a large heterogeneity in experimental setups and hence the results with different regional and temporal changes in BDNF expression. Several studies have also assessed different interventions to affect the BDNF expression following injury. Clinical studies highlight the importance of BDNF polymorphism in the outcome and indicate a protective role of BDNF polymorphism following injury. Considering the possibility of affecting the BDNF pathway with available substances, we discuss future studies using transgenic mice as well as iPSC in order to understand the underlying mechanism of BDNF polymorphism in TBI and develop a possible pharmacological treatment.     

Second modification of a polyamide membrane surface

The aim of this study was to develop the water flux and antifouling properties of a polyamide (PA) nanofiltration membrane. A nascent PA membrane was prepared with an interfacial polymerization technique and modified with 2,5‐diaminobenzene sulfonic acid (2,5‐DABSA) as a second modification. The effects of the 2,5‐DABSA monomer concentration and the modification time on the membrane performance were investigated. The chemical structure, morphology, roughness, hydrophilicity, molecular weight cutoff, and antifouling properties of the membranes were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force spectroscopy, contact angle measurement, poly(ethylene glycol) tracers, and cetyl trimethyl ammonium bromide filtration, respectively. The PA membrane with optimized performance was shown to have a greater than 44% higher water permeate flux with a change in the salt rejection in the order RNa₂SO₄ > RCaCl₂ > RNaCl to RNa₂SO₄ > RNaCl > RCaCl₂. The improvement of the hydrophilicity led to excellent antifouling properties in the new PA membranes and illustrated a promising and simple method for the fabrication of high‐performance PA membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43583.