Poly(N-alkylmethacrylate)S: characterization,good and poor solvents,densities and intrisic viscosities

Samples of three different poly (n-alkylmethacrylate)s, namely poly(methylmethacrylate), poly(n-butylmethacrylate), and poly(n-decylmethacrylate), of narrow molecular weight distribution were characterized by means of light-scattering and gel permeation chromatography. For the following measurements, each of the polymers was investigated in one good and in one poor solvent. The demixing behaviour of the solutions was determined visually by means of cloud-points. In the case of poly(n-butylmethacrylate), additional viscosimetric measurements were made to obtain information on the gelation, this system exhibits. The densities of the solutions were measured up to the highest experimentally useable concentration (20 wt-%). Analytical expressions are given for the dependence of the densities on temperature and concentration; excess volumes, derived from these data, are discussed. Capillary viscosimetric measurements yielded intrinsic viscosities and Huggins constants for a large temperature range. These results demonstrate that all solutions are endothermal and that the chain stiffness increases as the n-alkyl side groups become larger. The hydrodynamic coil expansion factor is discussed with respect to coil collapse phenomena.     

Inflammation as a cause of malnutrition, atherosclerotic cardiovascular disease, and poor outcome in hemodialysis patients

Cardiovascular disease (CVD) remains the major cause of morbidity and mortality in end‐stage renal disease (ESRD) patients treated by hemodialysis (HD). Although traditional risk factors are common in dialysis patients, they may not alone be sufficient to account for the unacceptable high prevalence of CVD in this patient group. Recent evidence demonstrates that chronic inflammation, a nontraditional risk factor that is commonly observed in HD patients, may cause malnutrition and progressive atherosclerotic CVD by several pathogenetic mechanisms. The cause(s) of inflammation in HD patients is multifactorial and includes both dialysis‐related (such as graft and fistula infections, bioincompatibility, impure dialysate, and back‐filtration) and dialysis‐unrelated factors. Although inflammation may reflect underlying CVD, an acute‐phase reaction may also be a direct cause of vascular injury. Available data suggest that proinflammatory cytokines play a central role in the genesis of both malnutrition and CVD in ESRD. Thus, it could be speculated that suppression of the vicious cycle of malnutrition, inflammation, and atherosclerosis (MIA syndrome) would improve survival in dialysis patients. As there is not yet any recognized, or even proposed, targeted treatment for ESRD patients with chronic inflammation; it would be of considerable interest to study the long‐term effect of various anti‐inflammatory treatment strategies on nutritional and cardiovascular status as well as outcome in these patients.     

Empirically modeling polymer collapse in a poor solvent via a non-equilibrium,granular chain experiment

We present a new empirical method for investigating the collapse of a semi-flexible, homogeneous polymer-like structure in a poor solvent. A stainless steel chain in a thin film of water that is vertically oscillated plays the role of the polymer in our model system. As the system is shaken, the chain collapses into a steady-state compact configuration. Collapse is largely dominated by the surface tension of the water; however other factors also contribute in a one-to-one correspondence with real homopolymers. This system may be tailored to investigate the physics of polymer folding in a fundamental manner. We use the normalized radius of gyration to compare collapse dynamics between experiments of different chain lengths. Free energy minimizing behavior is observed as the polymer passes through both “on-pathway” and “off-pathway” intermediate states. At all chain lengths, nucleation (formation of pearls) dominates the early stage of collapse dynamics. If the ends of the chain remain within the radius of gyration, collapse occurs quickly. However, when the ends of the chain stray far outside the radius of gyration, nucleation is impeded and collapse progresses more slowly.     

Capacitance-voltage measurements on Schottky diodes with poor ohmiccontacts

The frequency-dependent admittance of Al-GaAs Schottky diodes with nonideal ohmic contacts is tested, using a simple three-component small-signal equivalent circuit model. Both the ohmic and the rectifying contacts of this diode are produced during one process step. This simplifies the formation procedure and saves testing time and costs. However, the nonalloyed ohmic contacts lead to a high series resistance, minority carrier injection, and deep level influence. All of these effects give a frequency-dependent diode admittance. Frequency-dependent admittance analysis in a certain frequency range using the three-component equivalent circuit model leads to the space-charge capacitance of the diode reflecting only the free majority carriers. The method is highly suitable for the automatic routine control of semiconductor material properties, diode, or gate capacitances     

改善劣质实时图像预处理效果的优选法研究

针对某次实际飞行实验条件下所采集的有较严重问题的CCD实时景像图预处理算法研究问题，提出一种优选法。该方法先利用已有的Photoshop图形处理软件与人工手动调节相结合对原始图像进行处理，得到期望图像，再根据原图像的具体问题和已有的先验知识选择几种可能的预处理方法对原图像进行仿真，将所得图像与期望图像进行对比选出最适合处理此种劣质图像数据的优化预处理算法。将该算法应用于本次飞行实验数据上，飞行航线的匹配概率由5．41％提高到了86．48％，结果表明本文提出的优选法具有可行性和实用性。     

水平井地质导向技术在薄差油层中的应用

水平井随钻测量数据滞后于钻头的实际位置,在薄差油层中设计水平井时,精准的地质导向是提高砂体钻遇率的关键。     

The poor bending response of the four-node plane stress quadrilateral

Many plane stress finite elements which can exactly represent rigid-body and constant-strain modes are too stiff in their response to the simple flexural action of a beam. This problem has received considerable interest. In this paper we explore a new interpretation of the problem and show that the poor bending response of the original 4-node plane stress quadrilateral can be quantitatively predicted by an error model.     

Pulse method for determining thermal diffusivity of poor heat conductors

Conclusions The above pulse method serves to obtain a simple design solution without the use of complicated systems. By using two specimens a good thermal contact with a required surface is obtained. This method is essential for nonmetallic materials (ceramics, glass, polymers, etc.). We used specimens in the form of plates, since this shape can be easily provided for the majority of substances, and at the same time it is suitable for measuring precisely the distance between the heated surface and the point of contact between the measuring thermocouple and the tested material. The heating of specimens with a bad heat conduction lasts longer than those with a good one. However, adequate adiabatic conditions at the instant of measurement were obtained for the former materials without special automatic control or regulation circuits.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 33–34, October, 1969.     

导电性较差样品的扫描电镜优化观测条件

为解决扫描电镜测试中样品的荷电问题,采用场发射扫描电镜(FESEM),以导电性较差样品如介孔硅SBA-15粉末、介孔SiO2纳米球、聚苯乙烯球及SBA-15/W等为研究对象,比较不同测试条件下的FESEM图片。结果表明,影响FESEM图像质量的因素较多,其中工作距离和加速电压是影响图片质量的主要因素;较小的工作距离、较低的加速电压、一定量背散射电子信号的加入、下探测器的选用(放大倍数小于5万倍)、减速观察模式及线平均扫描模式,是导电性较差样品FESEM图片的优化观测条件。     

Physics-based approach to color image enhancement in poor visibility conditions

Degradation of images by the atmosphere is a familiar problem. For example, when terrain is imaged from a forward-looking airborne camera, the atmosphere degradation causes a loss in both contrast and color information. Enhancement of such images is a difficult task because of the complexity in restoring both the luminance and the chrominance while maintaining good color fidelity. One particular problem is the fact that the level of contrast loss depends strongly on wavelength. A novel method is presented for the enhancement of color images. This method is based on the underlying physics of the degradation process, and the parameters required for enhancement are estimated from the image itself.     

Exploitation of poor Greek kaolins: Durability of metakaolin concrete

In this paper the effect of metakaolin on concrete durability is investigated. A Greek kaolin of low kaolinite content was thermally treated at defined conditions and the produced metakaolin was finely ground. In addition, a commercial metakaolin of high purity was used. Eight mixture proportions were used to produce high performance concrete, where metakaolin replaced either cement or sand in percentages 10% or 20% by weight of the control cement content. Durability of metakaolin concrete was evaluated by means of resistance to chloride penetration, air permeability, sorptivity, porosity and pore size distribution. Metakaolin concrete exhibits significantly lower chloride permeability, gas permeability and sorptivity. The addition of metakaolin refines the pore system of concrete, leading to a decreased mean pore size and improved uniformity of the pore size distribution. The produced metakaolin, derived from the poor Greek kaolin, imparts similar behavior to that of the commercial metakaolin, with respect to the concrete durability.     

Performance of the titanium sublimation trap in relatively poor vacuum systems

The properties of small sublimation traps designed for use in general vacuum systems, as an alternative to the conventional liquid nitrogen trap, are described in this paper. Particular attention is paid to traps suitable for interposing between sensitive electronic measuring equipment and manifolds where pressures are in the range 10⁻³–10⁻⁴ mbar. It is shown that simple systems can be built and operated where the active titanium surface is maintained by slow but continuous sublimation onto a stainless steel substrate from a titanium molybdenum alloy wire. Provided care is taken to outgas all internal surfaces effective operation can be maintained at trap temperatures above 200°C. This is a particularly valuable feature for systems where neither liquid nitrogen nor cooling water is available. Applications are in conventional leak detection systems where the feature of trapping gases such as oxygen and water vapour in combination with being completely inert to helium and argon is particularly attractive. It is shown that the background pressure in a small mass spectrometer can be kept below 10⁻⁶ mbar even with pressures in the main manifold of the order of 10⁻³ mbar.     

Assessment of granulation technologies for an API with poor physical properties

Granulation technologies are widely used in solid oral dosage forms to improve the physical properties during manufacture. Wet, dry, and melt granulation techniques were assessed for Compound A, a BCS class II compound. Characterization techniques were used to quantify physical property limitations inherent for Compound A including hygroscopicity, low solubility and bulk density, and poor powder flowability. High shear aqueous wet granulation induced an undesirable water mediated phase transition of the solid form. A formulation and process for dry granulation by roller compaction was developed and scaled to 10 kg batch size. Roll force, and roll gap parameters were assessed. Porosity of compacted ribbons was analyzed by mercury intrusion porosimetry, and particle size distributions of milled ribbons by sieve analysis. A roll force of 15 kN/cm produced granules with higher density and improved flow properties compared to the pre-blend. Fines content (<75 µm) decreased from approximately 90% pre-granulation to 26% post-granulation. Cohesive properties of Compound A limited drug loading (API:excipient ratio) in roller compaction to 0.6:1 or less. Hot melt granulation by extrusion assessed with four polymers. A vast improvement in drug loading of 4:1 was achieved via melt processes using low molecular weight thermo-binders (glyceryl behenate and Polyethylene glycol 4000). Granules produced by melt processing contained less fines compared to wet and dry granulation. Both roller compaction and melt extrusion are viable granulation process alternatives for scale up to overcome the physical property limitations of Compound A.     

Esco to sell microfiltration and separations businesses because of poor performance

Esco Technologies Inc is planning to sell its microfiltration and separations businesses.This is a short news story only. Visit www.filtsep.com for the latest filtration industry news     

Metakaolin as a main cement constituent. Exploitation of poor Greek kaolins

In this work, the properties and the hydration procedure of cements containing metakaolin were monitored for periods up to 180 days. Four metakaolins, derived from poor Greek kaolins, as well as a commercial metakaolin of high purity were used. Cement mortars and pastes, with 0%, 10% and 20% replacement of cement with the above metakaolins, were examined. Strength development, water demand and setting time were determined in all samples. In addition, XRD and TGA were applied in order to study the hydration products and the hydration rate in the cement–metakaolin pastes. It is concluded that metakaolin has a very positive effect on the cement strength after 2 days and specifically at 28 and 180 days. The blended cements demand significantly more water than the relatively pure cement and the water demand increase is higher, the higher the metakaolin content. The produced metakaolins as well as the commercial one give similar hydration products after 28 days and the pozzolanic reaction is accelerated between 7 and 28 days, accompanied by a steep decrease of Ca(OH)₂ content. Finally, it is concluded that a 10% metakaolin content seems to be, generally, more favorable than 20%. The produced metakaolins, derived from poor Greek kaolins, as well as the commercial one impart similar properties with respect to the cement strength development, the setting and the hydration.     

Challenges of providing maintenance hemodialysis in a resource poor country: Experience from a single teaching hospital in Lagos,Southwest Nigeria

Providing maintenance hemodialysis is associated with high costs and poor outcomes. In Nigeria, more than 90% of the population lives below the poverty line, and patients with end‐stage renal disease (ESRD) pay out‐of‐pocket for maintenance hemodialysis. To highlight the challenges of providing maintenance hemodialysis for patients with ESRD in Nigeria, we reviewed records of all patients who joined the maintenance hemodialysis program of our dialysis unit over a 21‐month period. Information regarding frequency of hemodialysis, types of vascular access for dialysis, mode of anemia treatment and frequency of blood transfusion received were retrieved. One hundred and twenty patients joined the maintenance hemodialysis program of our unit during the period under review. Seventy‐two (60%) were males and the mean age of the study population was 47 + 14 years. The mean hemoglobin concentration at commencement of dialysis was 7.3 g/dL + 1.6 g/dL. The initial vascular access was femoral vein cannulation in all the patients. A total of 73.5% of the patients required blood transfusion at some point with 33% receiving five or more pints of blood. Only 3.3% of the patients had thrice weekly dialysis, 21.7% dialyzed twice weekly, 23.3% once weekly, 16.7% once in two weeks, 2.5% once in three weeks and 11.7% once monthly. At the time of review, 8.3% of the patients had died while 38.3% were lost to follow‐up. Majority of patients with ESRD on maintenance hemodialysis in our unit were poorly prepared for dialysis, were under‐dialyzed, and were frequently transfused with blood with resultant poor outcomes.     

Squeezing out ultrafine hydrophobic and poor water-soluble drug particles with water vapour

This short communication describes a scalable new method to produce ultrafine hydrophobic or poorly soluble drug particles. Ultrafine Vitamin D3, Aspirin and Ibuprofen particles in the submicron range were produced. The method is an extension of the antisolvent vapour precipitation technique which exposes a droplet to an antisolvent vapour with reference to the dissolved materials within the droplet. In this work, the drug material was dissolved in ethanol droplets and then exposed to a convective stream of water vapour. Absorption of the water vapour into the droplet resulted in the precipitation of the particles. The precipitated submicron particles showed good dispersion behaviour in water droplets. This work will form the basis for using spray dryers as high-throughput scalable micro-precipitators.     

Development of optoelectronic-based pulsed current sensor to detect the poor laser discharge condition

A current transformer (CT)-based sensor has been developed to detect poor discharge conditions in copper vapour laser. The optoelectronic-based pulsed current sensor architecture involves the optical transmitter–receiver HFBR, high-frequency current transformer, and fiber optic link. The CT has been designed and calibrated to ensure generation of an optical signal at the current threshold crossover. Bandwidth analysis of the CT is carried out using the bode plot. The optoelectronic inter-conversion of the pulsed voltage of the CT and transmission via fiber optic link provides the non-contact current sensing and remote signal processing of the signal. This study discusses the details of the sensor.     

Flowability measurements of pharmaceutical powder mixtures with poor flow using five different techniques

Four different tablet formulations for direct compression with poor flow properties were tested regarding flowability using five different techniques: Hausner ratio, avalanching behavior, powder rheometer, uniaxial tester, and Jenike tester. In addition, the behavior of three of the formulations during emptying of the mixer and tableting was observed and compared to the results of the flowability measurements. The rank order correlation of the formulations was generally the same with all techniques. The flow properties measured by the different techniques reflected the behavior during processing of the powder mixtures.