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At least 1,171 records · Page 65Linked to original sources
PubMed2000

Centrifugal precipitation chromatography: principle, apparatus, and optimization of key parameters for protein fractionation by ammonium sulfate precipitation.

A novel chromatographic system introduced here internally generates a concentration gradient of ammonium sulfate (AS) through a long separation channel under a centrifugal force field. Protein samples are exposed to a gradually increasing AS concentration and precipitated along the channel. Then, chromatographic elution is initiated by gradually decreasing the AS concentration in the gradient which causes the proteins to repeat dissolution and precipitation through the channel. Consequently, they are eluted out in the order of their solubility in the AS solution. The separation column consists of a pair of disks equipped with mutually mirror-imaged spiral grooves. A dialysis membrane is sandwiched between the disks to form two identical channels partitioned by the membrane. The disk assembly is mounted on the sealless continuous-flow centrifuge. When a concentrated AS solution is eluted through one channel and water through the other channel in an opposite direction, an exponential AS gradient is formed through the water channel. A series of basic experiments was performed to study the rates of AS transfer and osmosis through the membrane, and the operational parameters including elution time, revolution speed, inclination of gradient, and sample size were optimized using stable protein samples. Preliminary applications were successful in purification of monoclonal antibody from cell culture supernatant and an affinity separation of recombinant ketosteroid isomerase from a crude Escherichia coli lysate.

Ammonium Sulfate↗
PubMed1999

Optimal configuration of multiple-focused ultrasound transducers for external hyperthermia.

External ultrasound hyperthermia is considered to be a very flexible modality for heating deep-seated tumors owing to its penetration and focusing ability. However, using this flexibility requires that many complicated, interacting decisions be made to obtain optimal treatment. This paper presents the feasibility of arranging multiple-focused ultrasound transducers to produce an appropriate heating pattern for a specific treatment, based on the optimal scan parameters obtained from an optimization algorithm. The variable scan parameters of the heating system optimized are the transducer tilt and rotation angles, focal depth, scan radius, and output acoustical power. After obtaining the optimal scan parameters, multiple transducers are systematically arranged according to these scan parameters. Three-dimensional ultrasound power deposition and temperature distribution for a specific treatment are calculated for this multiple ultrasound transducer system. A more uniform temperature distribution in the treatment region for a large, highly perfused tumor can be achieved by scanning the system with respect to the central scan axis and/or swinging the transducers inwards and outwards. The maximum heating depth of focused ultrasound transducers used in this heating system is also studied. Simulation results demonstrate that the optimal arrangement of this multiple-focused ultrasound transducer system is highly promising for heating deep, large, and highly perfused tumors.

Algorithms↗
PubMed2001

Using experimental design to optimize the process parameters in fluidized bed granulation on a semi-full scale.

A face-centered central composite design was applied in order to optimize the granulation process on a semi-full scale (30-kg batch) for the geometric mean granule size. The granulation process variables investigated were: inlet air temperature, inlet airflow rate, spray rate and inlet air humidity. Based on the process variables, the theoretical powder bed moisture content after the spraying process and a measure for the droplet size were determined. Multiple regression modeling was used to develop two models for the granule size: an empirical model, based on the four process parameters, and a fundamental model, based on the balance between the granule growth affected by the theoretical powder bed moisture content and the droplet size and the breakage effect of the airflow rate. These regression models were used to optimize the granulation process to obtain a granule size between 300 and 500 microm. Additional experiments confirmed that these models were valid. Other granule properties, namely the geometric standard deviation, the Hausner index, the angle of repose and the moisture content, were evaluated at the optimal operation conditions.

Research Design↗
PubMed2006

[Cardiac MR tagging: optimization of sequence parameters and comparison at 1.5 T and 3.0 T in a volunteer study].

PURPOSE: The aim of this study was the optimization of a gradient echo (GRE) MR tagging sequence at 3.0 T in comparison to 1.5 T in order to obtain the best image contrast between the myocardium, tag lines and blood signal. Theoretically expected improvements of signal-to-noise (SNR) and contrast-to-noise ratios (CNR) were also calculated. MATERIALS AND METHODS: 14 healthy volunteers (8 male, 6 female; mean age 43.4 +/- 10.3 years) were scanned using a 3.0 T as well as a 1.5 T whole-body system. A GRE flash-2 D tagging sequence was evaluated (midventricular short axis view) by varying the flip angle (8 - 16 degrees ), slice thickness (4 - 8 mm; fixed flip angle 1.5/3.0 T: 12 degrees /8 degrees , tag size 8 mm) and tag size (4 - 8 mm, fixed flip angle 1.5/3.0 T: 12 degrees /8 degrees , slice thickness 6 mm). The field of view, acquisition time and temporal resolution (45 ms) were kept constant. Qualitative and quantitative image analysis was performed by calculating the SNR, CNR (tag) as well as the relative contrast between the myocardium and tag lines (RCMT). RESULTS: Based on individual comparison, the best imaging protocol was found at a slice thickness of 6 mm, tag size of 8 mm, optimized flip angle of 8 degrees (3.0 T) and 12 degrees (1.5 T), respectively. Compared to 1.5 T, a significantly higher overall image score was determined (mean +/- sd; 3.2 +/- 0.2 vs. 2.7 +/- 0.4) and a strong correlation between the CNR (tag) and RCMT for flip angle alpha and the slice thickness was found. A higher field strength resulted in an 80 % increase in the CNR (tag) compared to 1.5 T (mean 10.7/6.1). Furthermore, the SNR was improved by 35 % (mean 20.6/15.3) and the RCMT by 35 % (mean 0.47/0.35). CONCLUSION: Myocardial tagging at 3.0 T has shown superior image quality in comparison to 1.5 T due to a higher baseline SNR and an improved CNR as well as RCMT. The suppressed fading of the tags enables the accessibility to the diastolic phase of the cardiac cycle.

Adult↗
PubMedDate not supplied

Optimization of pacing parameters for conditioned latissimus dorsi muscle in cardiomyoplasty.

Synchronous paced contractions of latissimus dorsi muscle pedicle (LDM) around the heart improve ventricular function in dynamic cardiomyoplasty. To optimize assistance and prolong pacemaker battery life, the LDM should be stimulated with the lowest energy pacing parameters (PP) that will produce maximal muscle contraction. Muscle fractional shortening (FS) and duration of contraction (CT) were studied in conditioned, fatigue-resistant LDM of six goats. Fractional shortening and CT were determined at increasing amplitude, (A, 1-6v); pulse width, (PW, 60-450 musec); and frequency, (F, 5-130 Hz). Maximal rate of contraction was determined by pacing at higher rates. Maximal FS plateaued after V, 2.4 +/- .6v; PW, 125 +/- 47 musec; and F, 36 +/- 9 Hz. Mean CT for all PP was significantly longer (p less than or equal to 0.001) than the burst length (185 msec). Increasing F resulted in CT, which peaked at 460 +/- 59 msec. Increasing rate of contraction demonstrated that over 87 beats per minute the muscle fails to achieve complete relaxation, and, therefore, maximal FS.

Animals↗
PubMed1991

Estimation of the optimal tissue oxygenation parameters in adult respiratory distress syndrome (ARDS).

We hypothesised earlier that the simultaneous examination of the basic tissue oxygenation parameters (O2 delivery-DO2, O2 extraction ratio-O2ER, O2 consumption-VO2) results in a more adequate relationship to characterize the oxidative metabolism of tissues than a separate evaluation. The aim of present study was to prove this hypothesis. That is for while the results of these oxygenation measurements were examined simultaneously in a 3-dimensional analysis in 30 patients with ARDS. It was found that all measured values distributed on a 3-dimensional space net. An optimal range on the tissue oxygenation surface could be separated where 64% of the data of survivors were inside this range, while 77% of the data of "late stage" nonsurvivors--patients, where the measurement were done on the last 5 days of their life--were outside this range. The therapeutic goal in the treatment of ARDS patients is to change the oxygenation parameters to be inside this optimal range.

Adolescent↗
PubMed2006

Computer code for the optimization of performance parameters of mixed explosive formulations.

LOTUSES is a novel computer code, which has been developed for the prediction of various thermodynamic properties such as heat of formation, heat of explosion, volume of explosion gaseous products and other related performance parameters. In this paper, we report LOTUSES (Version 1.4) code which has been utilized for the optimization of various high explosives in different combinations to obtain maximum possible velocity of detonation. LOTUSES (Version 1.4) code will vary the composition of mixed explosives automatically in the range of 1-100% and computes the oxygen balance as well as the velocity of detonation for various compositions in preset steps. Further, the code suggests the compositions for which least oxygen balance and the higher velocity of detonation could be achieved. Presently, the code can be applied for two component explosive compositions. The code has been validated with well-known explosives like, TNT, HNS, HNF, TATB, RDX, HMX, AN, DNA, CL-20 and TNAZ in different combinations. The new algorithm incorporated in LOTUSES (Version 1.4) enhances the efficiency and makes it a more powerful tool for the scientists/researches working in the field of high energy materials/hazardous materials.

Algorithms↗
PubMed2004

Optimization of formulation parameters for the preparation of flutamide liposomes by 3(3) factorial 26-term logit model.

This study deals with the study of the optimization of the volume of organic phase (X1), the volume of aqueous phase (X2), and the drug:phosphotidylcholine (PC): cholesterol (Chol) molar ratio (X3) using 3(3) factorial 26-term logit model to maximize the Flutamide absorption at the target site in the treatment of prostatic cancer by maximizing the entrapment of Flutamide (FLT) in the preparation of FLT liposomes. FLT liposomes are expected to be an excellent carrier for FLT to the prostatic cancer site based on the use of liposomes with other drugs. A 3(3) factorial 26-term logit model for coded factors X1, X2, and X3 is used to develop a second-order response surface regression equation for predicting percent entrapment efficiency (%EE) for FLT. In turn, the regression equation is used to develop contour plots that show the %EE is maximized at the level of 1:15:2 of the drug: PC: Chol molar ratio with the volume of organic phase (chloroform: methanol) (1:2) at 5 mL and the volume of distilled water at 1.5 mL.

Chemistry, Pharmaceutical↗
PubMed2004

On-resin head-to-tail cyclization of cyclotetrapeptides: optimization of crucial parameters.

Cyclotetrapeptides are constrained cyclic peptides whose synthesis is considered a difficult task. A methodology based on on-resin head-to-tail cyclization by anchoring the side chain of a trifunctional amino acid was investigated. A series of model cyclotetrapeptides containing the RGD sequence cyclo(Xaa-Arg-Gly-Asp) (Xaa = Ala, Phe, Phg, D-Ala, D-Phe, D-Phg) was synthesized with no cyclodimerization by-products. An evaluation and optimization study of all of the parameters directly involved in the ring closure was performed.

Cyclization↗
PubMed1997

Parameter selection to optimize speech recognition with the Nucleus implant.

Speech coding strategy, frequency boundary assignment table, and speech processor program minimum and maximum stimulation levels are parameters of the Nucleus Cochlear Implant System whose selection affects speech recognition performance in adults and children. Research studies show that speech recognition is significantly better with (1) the Spectral Peak than with the Multipeak speech coding strategy and (2) frequency boundary assignment Table 7 than with Table 9 in an individual's speech processor program (MAP). Minimum and maximum stimulation levels in this MAP are based on psychophysical measurements on each electrode but often need to be modified for optimum use in everyday life. Many children and adults have increases, decreases, or fluctuations in electrical hearing that require changes in the MAP minimum and maximum levels to maintain their ability to recognize speech and other sounds.

Adult↗
PubMed2005

Contribution of Geographic Information Systems and location models to planning of wastewater systems.

This paper presents the contributions of Geographic Information Systems (GIS) and location models towards planning regional wastewater systems (sewers and wastewater treatment plants) serving small agglomerations, i.e. agglomerations with less than 2,000 inhabitants. The main goal was to develop a decision support tool for tracing and locating regional wastewater systems. The main results of the model are expressed in terms of number, capacity and location of Wastewater Treatment Plants (WWTP) and the length of main sewers. The decision process concerning the location and capacity of wastewater systems has a number of parameters that can be optimized. These parameters include the total sewer length and number, capacity and location of WWTP. The optimization of parameters should lead to the minimization of construction and operation costs of the integrated system. Location models have been considered as tools for decision support, mainly when a geo-referenced database can be used. In these cases, the GIS may represent an important role for the analysis of data and results especially in the preliminary stage of planning and design. After selecting the spatial location model and the heuristics, two greedy algorithms were implemented in Visual Basic for Applications on the ArcGIS software environment. To illustrate the application of these algorithms a case study was developed, in a rural area located in the central part of Portugal.

Algorithms↗
PubMed2003

Optimization of electroporation parameters for the intramuscular delivery of plasmids in pigs.

Increased transgene expression after plasmid transfer to the skeletal muscle is obtained with electroporation in many species, but optimum conditions are not well defined. Using a plasmid with a muscle-specific secreted embryonic alkaline phosphatase (SEAP) gene, we have optimized the electroporation conditions in a large mammal (pig). Parameters tested included electric field intensity, number of pulses, lag time between plasmid injection and electroporation, and plasmid delivery volume. Electric pulses, between 0.4 and 0.6 Amp constant current, applied 80 sec after the injection of 0.5 mg SEAP-expressing plasmid in a total volume of 2 mL produced the highest levels of expression. Further testing demonstrated that electroporation of a nondelineated injection site reduces the levels of SEAP expression. These results demonstrate that electroporation parameters such as amperage, lag time, and the number of pulses are able to regulate the levels of reporter gene expression in pigs.

Alkaline Phosphatase↗
PubMed2000

Optimization of processing parameters for the analysis and detection of embolic signals.

The fast Fourier transform (FFT), which is employed by all commercially available ultrasonic systems, provides a time-frequency representation of Doppler ultrasonic signals obtained from blood flow. The FFT assumes that the signal is stationary within the analysis window. However, the presence of short duration embolic signals invalidates this assumption. For optimal detection of embolic signals if FFT is used for signal processing, it is important that the FFT parameters such as window size, window type, and required overlap ratio should be optimized. The effect of varying window type, window size and window overlap ratio were investigated for both simulated embolic signals, and recorded from patients with carotid artery stenosis. An optimal compromise is the use of a Hamming or Hanning window with a FFT size of 64 (8.9 ms) or 128 (17.9 ms). A high overlap ratio should also be employed in order not to miss embolic events occurring at the edges of analysis windows. The degree of overlap required will depend on the FFT size. The minimum overlap should be 65% for a 64-point window and 80% for a 128-point window.

Blood Flow Velocity↗
PubMed2005

Use of a zona laser treatment system in assisted hatching: optimal laser utilization parameters.

OBJECTIVE: This study aimed to establish the benefit of laser micromanipulation of the zona pellucida as a method of assisted hatching and to determine the optimal technical settings. DESIGN: Prospective pilot study. SETTING: University teaching hospital. ANIMAL(S): Six- to 8-week-old F1 female mice. INTERVENTION(S): Mouse embryos were treated with a laser (Hamilton Thorne Research) using both research and preset clinical settings. The research option allows the user to alter pulse duration, number of pulses, and beam intensity. In this study, laser intensity and duration, as well as the depth and number of disruptions, were altered. MAIN OUTCOME MEASURE(S): Embryos were scored after treatment as either arrested blastocysts, arrested during hatching, hatched, or degenerate. RESULT(S): The treatment where the laser intensity was halved but the number of laser pulses used was doubled was the most beneficial treatment. Zona thinning was not effective. CONCLUSION(S): The study showed that laser-assisted hatching can safely and significantly increase the percentage of embryos reaching the hatched blastocyst stage. A proportionately sized hole in a human embryo may have the same beneficial effect as has been shown in this study.

Animals↗
PubMed1998

Calibration of STUD+ parameters to achieve optimally efficient broadband adiabatic decoupling in a single transient

To provide the most efficient conditions for spin decoupling with least RF power, master calibration curves are provided for the maximum centerband amplitude, and the minimum amplitude for the largest cycling sideband, resulting from STUD+ adiabatic decoupling applied during a single free induction decay. The principal curve is defined as a function of the four most critical experimental input parameters: the maximum amplitude of the RF field, RFmax, the length of the sech/tanh pulse, Tp, the extent of the frequency sweep, bwdth, and the coupling constant, Jo. Less critical parameters, the effective (or actual) decoupled bandwidth, bweff, and the sech/tanh truncation factor, beta, which become more important as bwdth is decreased, are calibrated in separate curves. The relative importance of nine additional factors in determining optimal decoupling performance in a single transient are considered. Specific parameters for efficient adiabatic decoupling can be determined via a set of four equations which will be most useful for 13C decoupling, covering the range of one-bond 13C1H coupling constants from 125 to 225 Hz, and decoupled bandwidths of 7 to 100 kHz, with a bandwidth of 100 kHz being the requirement for a 2 GHz spectrometer. The four equations are derived from a recent vector model of adiabatic decoupling, and experiment, supported by computer simulations. The vector model predicts an inverse linear relation between the centerband and maximum sideband amplitudes, and it predicts a simple parabolic relationship between maximum sideband amplitude and the product JoTp. The ratio bwdth/(RFmax)2 can be viewed as a characteristic time scale, tauc, affecting sideband levels, with tauc approximately Tp giving the most efficient STUD+ decoupling, as suggested by the adiabatic condition. Functional relationships between bwdth and less critical parameters, bweff and beta, for efficient decoupling can be derived from Bloch-equation calculations of the inversion profile for a single sech/tanh pulse. Residual splitting of the centerband, normally associated with incomplete or inefficient decoupling, is not seen in sech/tanh decoupling and therefore cannot be used as a measure of adiabatic decoupling efficiency. The calibrated experimental performance levels achieved in this study are within 20% of theoretical performance levels derived previously for ideal sech/tanh decoupling at high power, indicating a small scope for further improvement at practical RF power levels. The optimization procedures employed here will be generally applicable to any good combination of adiabatic inversion pulse and phase cycle. Copyright 1998 Academic Press.

Journal Article↗
PubMed2004

Vesical pacing: pacing parameters required for normalization of vesical electric activity in patients with overactive bladder.

There are several modalities for the treatment of the overactive bladder (OAB), but the results may not be satisfactory. A recent study has demonstrated that the OAB has a dysrhythmic electric activity that seems to result from a disordered vesical pacemaker. We hypothesized that vesical pacing may correct the irregularities of the vesical electric waves and consequently normalize the vesical contractility. In this communication, we primarily defined the adequate pacing parameters required for correction of the vesical dysrhythmia. 36 patients with OAB were divided into a study group (22; 13 women; mean age 40.2 years) and a control group (14; 8 women; mean age 41.8 years). Ten healthy volunteers (6 women; mean age 39.8 years) were included in the study. Three 28-gauge cardiac pacing electrodes were hooked to the vesical mucosa: one (pacing) to the vault, and two (recording) to the lateral wall. Electric activity at rest and during stimulation of the pacing electrode was recorded in the study group and the healthy volunteers. In the control group, recording was done without pacing. Reproducible regular triphasic SWs were recorded from the 2 electrodes of the healthy volunteers with a similar pattern from the 2 electrodes of each individual subject. The optimal pacing parameters we determined were: an amplitude of 5 mA, a pulse width of 200 ms and a frequency of 20% higher than the frequency of the basal vesical waves. Vesical pacing effected a significant increase of waves' variables. The OAB patients exhibited a "dysrhythmic" wave pattern which was normalized during vesical pacing using the aforementioned pacing parameters. The optimal parameters required for vesical pacing of the dysrhythmic waves of the OAB were determined and succeeded in normalization of the vesical electric activity. Vesical pacing is suggested to be used as a therapeutic tool for the treatment of the OAB.

Adult↗
PubMed2004

Sex pheromone of the citrus mealybug Planococcus citri: synthesis and optimization of trap parameters.

A simple synthesis of the pheromone of the citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae), has been developed. Various factors affecting capture of males have been assessed to optimize the trap design and to develop a lure with high efficacy and longevity. Male capture was the same with the racemic and chiral pheromone; technical pheromone (85% purity) was statistically as attractive as pure pheromone (97%). A special formulation was used to determine the actual release rate of the pheromone under field conditions as related to male capture. Generally, plate traps caught more males than delta traps, and large traps caught more than small ones. The effects of aging on the performance of three types of rubber dispensers were evaluated. It was found that the American dispenser displayed the most consistent trapping performance and could be used for monitoring for at least 16 wk with a load of 200 microg of pheromone. The dose-response of the males to sex pheromone was tested within the range of 25-1,600 microg.

Animals↗