Low Pressure Applications Research Articles

Biocatalytic polyester acrylation—process optimization and enzyme stability

An OH-functional polyester has been acrylated via transesterification of ethyl acrylate, catalyzed by Candida antarctica lipase B (CalB) in two different preparations: Novozym 435 and immobilized on Accurel MP1000. The batch process resulted in incomplete acrylation as well as severe degradation of the polyester. A high degree of acrylation was achieved by optimization through the application of low pressure (15 kPa), continuous inflow of ethyl acrylate and continuous distillation to evaporate the by-product, ethanol. The enzyme preparations displayed good stability with half-lives of 180 and 324 h for Novozym 435 and CalB/MP1000, respectively. This translates into product yields of 3600 and 6200 times the weight of the catalyst, indicating that the enzyme will have a marginal impact on the total process cost.

Application of selective right or left hepatic arterial regional blockade and low central venous pressure during hepatic resection

目的 观察选择性肝左、右动脉阻断联合控制性低中心静脉压术中出血量的影响.方法 择期全麻下行肝叶切除术患者24例.分为2组:低中心静脉压组(LCVP组)和选择性肝左、右动脉阻断联合控制性低中心静脉压组(S组).二组病人均为12人.二组在肝实质完全离断过程中CVP控制在0～0.49kPa水平.测量两组病人术中出血量.结果 选择性肝左,右动脉阻断联合控制性低中心静脉压组和LCVP组术中出血量分别为(313±167)ml和(474±222)ml(P<0.05).结论 选择性肝左、右动脉阻断联合控制性低中心静脉压较单存低中心静脉压可减少肝叶切除手术术中出血量。

Studies To Evaluate Chemicals and Conditions with Low-Pressure Applications for Reducing Microbial Counts on Cattle Hides

Studies were conducted to identify effective antimicrobials and application parameters that could be used as decontamination interventions to reduce microbial loads on cattle hides before removal from carcasses. In study I, hide swatches inoculated with Escherichia coli O157:H7 were sprayed with 10% acetic acid (at 23 and 55°C), 10% lactic acid (at 23 and 55°C), 3% sodium hydroxide (at 23°C) or 4 and 5% sodium metasilicate (at 23°C). All antimicrobials were evaluated independently after being applied alone, being applied after a water rinse, or being followed by a water rinse. Antimicrobial treatments followed by a water rinse lowered E. coli O157:H7 populations by 0.6 to 2.4 log CFU/cm2 and resulted in hides with a surface pH of 6.3 to 9.2. Treatments in which a water rinse was followed by antimicrobial application lowered E. coli O157:H7 populations by 1.5 to 5.1 log CFU/cm2 but resulted in hides with a surface pH of 3.9 to 10.5. In study II, whole hides were treated with one of four antimicrobials (acetic acid, lactic acid, sodium hydroxide, or sodium metasilicate) followed by a water rinse. Hides were evaluated for aerobic bacterial counts, total coliform counts, and E. coli counts. Generally, all antimicrobials resulted in greater reductions (P < 0.05) of E. coli counts when compared with the control; however, only acetic and lactic acids resulted in greater reductions (P < 0.05) of aerobic bacterial counts and total coliform counts compared with the controls. These antimicrobials could be used to reduce microbial contamination on hides, potentially reducing micro-biological contamination transferred to carcasses or to the plant environment.

Countercurrent de-acidification of vegetable oils using supercritical CO 2: Holdup and RTD experiments

The separation efficiency of packed columns is strongly influenced by hydrodynamics. It is therefore of importance in the design of packed columns the estimation of parameters such as liquid holdup (both dynamic and static), pressure drop and flooding point. In this field, there is a large number of experimental results published for low pressure applications. However, data for high-pressure systems is relatively scarce. In this work, hydrodynamic data was experimentally obtained in a 7.5-m tall, 40 mm i.d. column. In the experiments, the separation of free fatty acids from vegetable oils was studied. Separation efficiency, and static and dynamic holdup were determined for various packing materials (random and structured) at several operating conditions. Through experiments with a carotene tracer, the residence time distribution was measured. Several known correlations, which take into account the buoyancy effect of dense gases, were applied to the experimental data, and good agreement with the results of other authors was observed.

Wet gas measurement model for low pressure applications in horizontal orientated Venturi tube

Wet gas measurement model for low pressure applications in horizontal orientated Venturi tube

Distillation Trays that Operate Beyond the Limits of Gravity by Using Centrifugal Separation

The interest of industry in super-high capacity fractionation trays has significantly increased in the last few years (Bravo and Kusters, 2000). This paper focuses on a comparison of these technologies, using available data from open literature. In addition new research data for the ConSep tray will be presented using state of the art gamma-scanning capabilities. Four tray technologies fall in this category — The shell swirltube tray, Jaeger COFLO tray, Koch-Glitsch ULTRA-FRAC tray and the shell ConSep tray. Publications on these trays have focused on a broad spectrum of applications—low liquid load operations such as glycol contractors (Weiland and Griesel, 2004) and low-pressure applications such as a hydrocracker main fractionator (Groenendaal et al., 2001) to high-pressure systems such as refinery superfractionators (De Villiers et al., 2005; Mosca et al., 2004a, b), debutanizers (De Villiers et al., 2004, 2005) and depropanizers (Wilkinson et al., 2006).

Temporally and spatially integrated elemental analysis algorithm for low-pressure micro-LIBS measurements

Microscopic laser-induced breakdown spectroscopy (micro-LIBS) is a promising measurement technique for determining the relative elemental abundances of microscopic spots. Currently, the predominant source of measurement accuracy errors for micro-LIBS is shown to be based on a constant plasma temperature assumption. To reduce these measurement errors particularly in low-pressure applications (i.e., extraterrestrial environments), a mathematical data analysis algorithm is presented that utilizes the many linear independent emission lines per element to estimate the time-integrated state of the plasma in the form of a plasma state matrix coupled with a vector of relative elemental abundances in the observed emission.

Synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 by successive freeze-drying and self-ignition of a hydroxypropylmethyl cellulose solution

The present paper reports the synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 perovskite powders by a method combining freeze-drying and self-ignition of an aqueous solution of metallic nitrates containing hydroxypropylmethyl cellulose. The precursor powder obtained after self-ignition was submitted to various thermal treatments and the resulting powders were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption–desorption isotherm analysis, mercury porosimetry and laser granulometry. It turns out that this synthesis method yields single-phase powders with good homogeneity and sinterability properties. The precursor powder treated at 1200 °C presents a coral-like structure which collapses under application of low uniaxial pressure, resulting in a narrow grain size distribution suitable for sintering (98.8% relative density for a pellet sintered at 1400 °C during 1 h). The fact that no milling step is necessary is an additional advantage of this method, which shows promising prospects for the synthesis of other multicationic oxides.

Tracing of Gastric Reflux Into the Middle Ear in a Mongolian Gerbil Model

The purpose of this study was to trace induced gastric reflux and to examine whether it reaches the middle ear in a Mongolian gerbil model. Otitis media with effusion is the most frequent middle ear disease in childhood. Gastroesophageal reflux is suspected to be a possible factor in its pathogenesis. Seventeen Mongolian gerbils were assigned to three groups: the control (phosphate-buffered saline application to the lower esophageal sphincter) and two experimental groups (Aquo-Trinitrosan [Merck, Darmstadt, Germany] application to the lower esophageal sphincter, low gastric pressure and Aquo-Trinitrosan application, higher gastric pressure). We injected Chinese ink into the stomach to trace the path of a potential gastroesophageal reflux in all three groups. The traces of ink were investigated by ear and larynx endoscopy and histology. There were no signs of gastroesophageal reflux based on the data obtained from the control group. In animals with traceable laryngeal reflux, the ink was also shown to advance through the eustachian tube and reach the middle ear. In addition, we found that when reflux reaches the middle ear on one side, it also reaches the contralateral middle ear in most cases. Gastroesophageal reflux induced by relaxation of the lower esophageal sphincter was shown to reach the middle ear in our Mongolian gerbil model. These results support recent hypotheses linking gastroesophageal reflux to the development of otitis media with effusion.

X-ray transmission properties of intelligent anvils in diamond anvil cells

High-pressure and/or high-temperature analysis of geo- and material science samples routinely employs diamond anvil cells (DACs) as a research instrument. In particular, DACs allow for various in situ characterizations (e.g. Raman and Fourier transform infra red spectroscopies, X-ray diffraction (XRD), X-ray spectroscopy including fluorescence (XRF) and absorption (XAS)) at elevated pressure and temperature. The measurement of pressure (P) and/or temperature (T) in the sample chamber is crucial, but not always accurate, more specifically in the case of low-pressure applications (a few GPa). The development of modified diamonds (intelligent anvils ‘i-anvils’) adapted to a new generation of DACs (intelligent diamond anvil cells: iDAC) can contribute to solve this problem, as the diamond itself serves as the PT sensor, being prepared, for example, by high-energy ion implantation [H. Bureau, M. Burchard, S. Kubsky et al., This volume (2006).] on a micrometric scale. Several most interesting measurement methods used with DACs are based on X-ray techniques (e.g. XRF, XRD, XAS). We present the first results of X-ray transmission measurements with iDACs, performed at the hard-X-ray microfocus beamline ID22 at the ESRF (European Synchrotron Radiation Facility), Grenoble, France. Sensor response to intense irradiation as a function of X-ray energy (E ph∈10;18.1 keV) was investigated. The values of the sensor were found to be independent of the irradiation in the investigated energy range and thus validate the use of these sensors for precise and reliable measurements on a wide range of applications with high-energy synchrotron radiation. No influence of the sensor on the X-ray transmission properties of the anvil has been found.

Design optimization of a high performance silicon MEMS piezoresistive pressure sensor for biomedical applications

In this paper the design optimization of high performance conventional silicon-based pressure sensors on flat diaphragms for low-pressure biomedical applications has been achieved by optimizing the doping concentration and the geometry of the piezoresistors. A new figure of merit called the performance factor (PF) is defined as the ratio of the product of sensor sensitivity (S) and sensor signal-to-noise ratio (SNR) to the temperature coefficient of piezoresistance (TCPR). PF has been introduced as a quantitative index of the overall performance of the pressure sensor for low-range biomedical applications. A comprehensive analysis considering the impact of doping concentration, length of the piezoresistor and thickness of the diaphragm indicates that for achieving the highest figure of merit an optimum concentration of 1018 atoms cc−1 and geometry of 100 µm long piezoresistor and 10 µm thick membrane for the specified biomedical application are required.

Immobilized Hyperbranched Glycoacrylate Films as Bioactive Supports

[Image: see text] We report on the low-pressure plasma immobilization, characterization and application of thin films of hyperbranched glycoacrylates, poly(3-O-acryloyl-alpha,beta-D-glucopyranoside) (AGlc), on PTFE-like fluorocarbon surfaces. This method is an efficient and versatile way to immobilize sugar-carrying branched acrylates as thin films of approximately 5 nm thickness on polymeric substrates while the functional groups and properties of the immobilized molecules are largely retained. The extent of poly(AGlc) degradation during plasma immobilization was investigated using FTIR-ATR spectroscopy and XPS. The thickness and topography of the immobilized films were characterized using spectroscopic ellipsometry and SFM, respectively. Studies of protein adsorption, as well as cell adhesion and proliferation on the poly(AGlc) surfaces, showed that these materials are suitable for the control of biointerfacial phenomena. Fluorescence images of fibronectin adsorbed on to the branched glycoacrylate with a mask.

Regulation of gene expression in intervertebral disc cells by low and high hydrostatic pressure

Intervertebral disc structures are exposed to wide ranges of intradiscal hydrostatic pressure during different loading exercises and are at their minimum during lying or relaxed sitting and at maximum during lifting weights with a round back. We hypothesize that these different loading magnitudes influence the intervertebral disc (IVD) by alteration of disc matrix turnover depending on their magnitudes. Therefore the aim of this study was to assess changes in gene expression of human nucleus cells after the application of low hydrostatic pressure (0.25 MPa) and high hydrostatic pressure (2.5 MPa). IVD cells isolated from the nucleus of human (n = 18) and bovine (n = 24 from four animals) disc biopsies were seeded into three-dimensional collagen type-I matrices and exposed to the different loading magnitudes by specially developed pressure chambers. The lower pressure range (0.25 MPa, 30 min, 0.1 Hz) was applied with a recently published device by using an external compression cylinder. For the application of higher loads (2.5 MPa, 30 min, 0.1 Hz) the cell-loaded collagen gels were sealed into sterile bags with culture medium and stimulated in a newly developed water-filled compression cylinder by using a loading frame. These methods allowed the comparison of loading regimes in a wide physiological range under an equal three-dimensional culture conditions. Cells were harvested 24 h after the end of stimulation and changes in the expression of genes known to influence IVD matrix turnover (collagen-I, collagen-II, aggrecan, MMP1, MMP2, MMP3, MMP13) were analyzed by real-time RT-PCR. A Wilcoxon signed-rank test(1) and a Wilcoxon 2-sample test(2) were performed to detect differences between the stimulated and control samples(1) and differences between low and high hydrostatic pressure(2). Multiple testing was considered by adjusting the p value appropriately. Both regimes of hydrostatic pressure influenced gene expression in nucleus cells with opposite tendencies for the matrix forming proteins aggrecan and collagen type-I in response to the two different pressure magnitudes: Low hydrostatic-pressure (0.25 MPa) tended to increase collagen-I and aggrecan expression of human nucleus cells (P < 0.05) but only to a small degree. High hydrostatic pressure (2.5 MPa) tended to decrease gene expression of all anabolic proteins with significant effects on aggrecan expression of nucleus cells (P = 0.004). Low hydrostatic pressure had no influence on the expression of matrix metalloproteinases (MMP1, MMP2, MMP3 and MMP13). In contrast, high hydrostatic pressure tended to increase the expression of MMP1, MMP3 and MMP13 of human nucleus cells with high individual-individual variations. The decreased expression of aggrecan (P = 0.008) and collagen type II (P = 0.023) and the increased MMP3 expression (P = 0.008) in response to high hydrostatic pressure could be confirmed in additional experiments with bovine nucleus cells. These results suggest that hydrostatic pressure as one of the physiological stimuli of the IVD may influence matrix turnover in a magnitude dependent way. Low hydrostatic pressure (0.25 MPa) has quite small influences with a tendency to anabolic effects, whereas high hydrostatic pressure (2.5 MPa) tends to decrease the matrix protein expression with a tendency to increase some matrix-turnover enzymes. Therefore, hydrostatic pressure may regulate disc matrix turnover in a dose-dependent way.

Dynamic Test and Real-time Control Platform of Anode Recirculation for PEM Fuel Cell Systems

Anode recirculation is essential to the pure-hydrogen proton exchange membrane fuel cell system. Keeping the pressure difference between the anode and the cathode is also important to the membrane health. In this paper, a dynamic platform was designed for the recirculation test of injection pump and real-time control of the anode pressure tracking. The test bench can work in a wide range of conditions for high- and low-pressure application. Based on the MATLAB/xPC Target environment, some S functions were written to drive the PC board for the hardware-in-loop application. Then an analytical full-order and a reduced-order model were built with good accuracy. By linearization of the nonlinear dynamic model, a linear quadratic Gaussian algorithm based on state feedback was used for set-point tracking. Moreover, an adaptive fuzzy neural network with an on-line neural network identifier was also designed to improve the control robustness. The foundation of the test bench and realization of the real-time control algorithms are meaningful to the future application in fuel cell systems.

Characteristics of an arc column in a hollow cathode arc

The hollow cathode arc (HCA) was developed as a plasma source for low-pressure applications in the 1960s, since when it has been variously researched to clarify its underlying mechanism.1, 2 When arranged to incorporate a relatively high arc current, HCA can also be used as a welding heat source.3–5 Through being a plasma source in low-pressure environments, HCA has further attracted attention as a welding heat source for use in space.6, 7 Through providing a degree of base metal fusion incommensurably greater than that obtainable with a conventional GTA (gas tungsten arc) heat source at atmospheric pressure, HCA is also regarded as being effective for industrial applications in low-pressure terrestrial environments.8

Enhancement of tissue engineered bone formation by a low pressure system improving cell seeding and medium perfusion into a porous scaffold

To obtain more extensive bone formation in composites of porous ceramics and bone marrow stromal cells (BMSCs), we hypothesized that a low-pressure system would serve to facilitate the perfusion of larger number of BMSCs into the porous scaffold, enhancing bone formation within the composites. After culturing BMSCs in osteogenic medium, porous blocks of β-tricalcium phosphate (β-TCP) were soaked in the cell suspension. Composites of the block and BMSCs were put immediately into a vacuum desiccator. Low pressure was applied to the low pressure group, while controls were left at atmospheric pressure. Composites were incubated in vitro or subcutaneously implanted into syngeneic rats, then analyzed biologically and histologically. In the in vitro group, cell suspension volume, cell seeding efficiency, alkaline phosphatase (ALP) activity, and DNA content in the β-TCP blocks were significantly higher in low pressure group than in the controls. Scanning electron microscopy (SEM) demonstrated that a greater number of cells covered the central parts of the composites in the low pressure group. ALP activity in the composites was increased at 3 and 6 weeks after implantation into rats. Histomorphometric analysis revealed more uniform and extensive bone formation in the low pressure group than in the controls. The application of low pressure during the seeding of BMSCs in perfusing medium into a porous scaffold is useful for tissue-engineered bone formation.

Kinetic investigations on methanol steam reforming on PdZn catalysts in microchannel reactors and model transfer into the pressure gap region

In the present study, a microchannel reactor was used in an integral mode of reactor operation to investigate parameter influences on the steam reforming of methanol on PdZn catalysts prepared by washcoating the microchannels with ZnO nanoparticles. Different models derived from significant concentration parameters were evaluated concerning their suitability to describe the kinetics of the methanol reforming reaction in the examined parameter range. Water gas shift reaction was found to be negligible in the reaction network. Methanol decomposition, even though it was influenced by the reactor material, was neglected for the modelling since CO was present only at a minor extent at the reactor outlet. Superior isothermal behaviour of the microchannel reactor is supposed to be responsible for good correlations of the derived models with experimental results. One of the models, the “global model”, was transferred to results from experiments in the pressure gap region obtained in a similar microchannel reactor suitable for low-pressure application. Although this was a model extrapolation, model and experiment were in good accordance for a wide range of absolute and methanol partial pressures, molar ratios of water to methanol and temperatures.

The high-pressure behaviour of Ba-dopedNa1/2Bi1/2TiO3 investigated by Raman spectroscopy

We report high-pressure Raman measurements up to 20.2 GPa on the perovskite-type oxide(Na1/2Bi1/2)0.89Ba0.11TiO3 (NBT–BT0.11), which is of interest as a potential lead-free piezoelectric material. Distinctchanges of the Raman spectra with increasing pressure illustrate thatNBT–BT0.11 shows at least two phase transitions. First, the application oflow pressure progressively reduces the tetragonal signature inNBT–BT0.11 and leads at around 1.8 GPa to a Raman spectrum reminiscent of rhombohedral NBT.Second, with further increase of pressure, the pressure-dependent behaviour ofNBT–BT0.11 resembles that of NBT and transforms to a non-cubic high-pressure structureat around 9 GPa. These observations suggest that a progressive substitution ofNa+/Bi3+ by Ba2+ pushes the pressure-induced structural instabilities of NBT towards higher pressure, corresponding toa Ba2+-induced negative (tensile) pressure within the structure.

Application of low central venous pressure in liver resection

目的 研究低中心静脉压技术是否能降低肝叶切除术中的出血量,并评价这一技术对肾功能的影响.方法 60例择期行肝叶切除术的病人.随机均分为对照组和低中心静脉压(LCVP)组.均采用静吸复合气管插管全麻.LCVP组通过吸入异氟醚,静注芬太尼,切肝前控制输液量,必要时微泵静注硝酸甘油,将CVP控制在4 mmHg左右.观察两组病人术中出血量、输血量、切肝前输液量和收缩压、以及术后24h肾功能变化.结果 LCVP组术中出血量、输血量、切肝前输液量和收缩压均低于对照组(P 0.05).结论低中心静脉压技术可减少肝叶切除术中的出血量及输血量,且对肾功能无明显影响。

Mortality of Life Stages of Cowpea Weevil (Coleoptera: Bruchidae) Exposed to Low Pressure at Different Temperatures

Previous studies have shown that low pressure creates a low oxygen controlled atmosphere that can kill stored-product insects. The current study was conducted to determine the mortality of life stages of the cowpea weevil, Callosbruchus maculatus (F.) (Coleoptera: Bruchidae), exposed to different low pressures and temperatures for various exposure periods. The adults were the most susceptible life stage to low pressure; 99% mortality was achieved within 0.8 h at 32.5 mmHg, 30 degrees C. The pupae were the most tolerant life stage to low pressure, requiring exposure periods between 28.98 and 153.20 h at temperatures of 20-35 degrees C to achieve 99% mortality. Mortality increased with exposure time and also with increasing temperature in all life stages. Early stage eggs (3 h old) and late stage eggs (48 h old) experienced higher mortality (values for LT99 of 42.331 and 46.652 h, respectively) compared with intermediate aged eggs (24 h old; LT99 of 74.735 h) under the same conditions of low pressure and temperature. Dried beans, including cowpea, Vigna unguiculata (Walp.), are currently protected with fumigants. Application of low pressure as a pest management tool represents a potential nonchemical alternative to fumigants such as methyl bromide and phosphine for controlling the cowpea weevil and related bruchids.