Optimal Conditions For Use Research Articles

Effect of the ζ-potential on the micro/ultra-filtration of yeast suspensions using ceramic membranes

The influence of the zeta-potentials ( ζ-potentials) of membranes and particles in the micro/ultra-filtration of yeast suspensions is investigated. Cylindrical ceramic micro-filtration (MF) and ultra-filtration (UF) membranes were used in this study; alumina and zirconia membranes being used for MF and UF, respectively. The ζ-potentials of particles and membranes were determined and the results used to select the test conditions for the filtration experiments. Choice of appropriate test conditions allows assessment of the importance of changed electrokinetic properties of the membranes and particles in the filtration process. The electrokinetic properties of membranes and particles were altered by changing the pH and electrolyte concentration. The ζ-potentials of ceramic membranes depend on the pH, the ionic strength of the electrolyte seems of lesser importance. The ζ-potential of yeast particles seems to depend on the concentration of electrolyte aluminium sulphate (Al 2(SO 4) 3) and to a much lesser extent on pH. Changes in the size distribution of suspensions of yeast particles suggest that they are flocculated in the presence of Al 2(SO 4) 3. In MF, the best permeate flux is found when Al 2(SO 4) 3 is used and this seems independent of pH. In contrast, in UF the control of pH is the significant factor and the aluminium concentration has a lesser effect. Generally, the best permeate fluxes are found when the yeast is flocculated. The interactions between particles and membranes are important in filtration and the choice of membrane material can influence the optimal conditions for use. Thus, electrokinetic measurements can play an important role in membrane characterisation.

MAXIMUM HEAT TRANSFER RATE DENSITY IN TWO-DIMENSIONAL MINICHANNELS AND MICROCHANNELS

The objective of the present article is to compare previous experimental data of Gao et al. [20] to the predictions of Bejan and Sciubba's analysis [7] on the optimal spacing for maximum heat transfer from a package of parallel plates. Experimental investigations of the flow and the associated heat transfer were conducted in two-dimensional microchannels in order to test possible size effects on the laws of hydrodynamics and heat transfer and to infer optimal conditions of use from the measurements. The test section was designed to modify easily the channel height e between 1 mm and 0.1 mm. Measurements of the overall friction factor and local Nusselt numbers show that the classical laws of hydrodynamics and heat transfer are verified for e > 0.4 mm. For lower values of e, a significant decrease of the Nusselt number is observed, whereas the Poiseuille number continues to have the conventional value of laminar developed flow. The transition to turbulence is not affected by the channel size. The experimental data were processed by using the dimensionless parameters of Bejan and Sciubba's analysis [7]. For fixed pressure drop across the channel, a maximum of heat transfer rate density is found for a particular value of e. The corresponding dimensionless optimal spacing and heat transfer rate density are in very good agreement with the predictions of Bejan and Sciubba. This article reports the first time that the optimal spacing between parallel plates is determined experimentally.

Banking of Urine Sediments as DNA Source in Epidemiologic Studies

The Authors Respond: Thank you for the opportunity to respond to the concerns of Dr. van Noord 1 about our article in Epidemiology. 2 We agree that urine sediment may provide a source of nucleated cells that can be easily and noninvasively obtained from adults and that may prove to be a useful source of DNA for epidemiologic studies. Dr. van Noord cites at least seven published reports of studies in which urine sediment is used as a source of DNA for genotyping. 3–9 Of the studies cited, five systematically assessed the suitability of urine sediment as a source of DNA for genetic studies, 3–5,8,9 and two are epidemiologic studies that used urine specimens as a DNA source but did not systematically assess the suitability of these specimens. 6,7 We found an additional study that evaluated urine sediment as a source of DNA for genotyping, 10 and two studies that found urine to be a satisfactory source of DNA from animals in the wild. 11,12 However, when we compared evidence in the literature for the utility of two noninvasive DNA sources—buccal cells and cells from urine sediment—we found much less methodologic evidence available to validate the reliability or to document the optimal conditions for use of urine specimens. 2,9 Although DNA yield is quite variable for both types of specimen, we chose to discuss buccal cells and not urine sediment cells in our review because more information was available for buccal cell specimens. Two of the reports cited by Dr. van Noord state that urine may be a useful specimen in large epidemiologic studies “when blood samples cannot be obtained or have not been stored.”8,9 These reports show genotyping success rates of 89% for one locus 8 and 78% for six loci. 9 Additionally, we suspect that obtaining urine specimens suitable for DNA banking from infants is more difficult than obtaining buccal cells, but we could find no published comparison of these specimens to confirm our suspicion. In summary, we believe that urine specimens may prove to be suitable sources of DNA for large epidemiologic studies but that systematic studies should be done to compare urine specimens with specimens that have been more thoroughly evaluated. We appreciate Dr. van Noord’s raising this issue, and we hope that simple alternatives to blood specimens will continue to be explored and validated. Karen K. Steinberg Deborah Nickerson Michele Caggana Margaret Gallagher

Development and application of parallel-plate avalanche counter for in-beam Mössbauer spectroscopy

For Mossbauer γ-rays in the “in-beam” Mossbauer experiments using various beams such as heavy ion, secondary short-lived isotope, and neutron beams, it is important to develop a detector. A parallel-plate avalanche counter (PPAC) is the most suitable gas counter for on-line measurements, because PPAC collects the internal conversion electrons emitted by the Mossbauer effect even under high γ-background. We evaluated the influences of the pressure and flow rate of the counter gas against the counting efficiency of PPAC, and determined the optimum conditions for use in the in-beam Mossbauer experiments.

Sorption Properties of Thermally Expanded Graphite from Different Oxidation Stages

The effect of the oxidation stage on the sorption properties of thermally expanded graphite in absorption of liquid hydrocarbons is investigated. The structural characteristics of the sorbents are reported, and their effect on the sorption capacity of powders is demonstrated. The mechanism of sorption of liquids by a bed of sorbent is examined. The optimum conditions of use of the sorbent with consideration of the costs of its production and consumption for eliminating spills are determined.

Rapid relaxation times measurements by MRI: an in vivo application to contrast agent modeling for muscle fiber types characterization

This paper is a description of a simulation method to evaluate the contrast in NMR imaging and its aim is to help to optimize the use of contrast media in clinical imaging. Indeed, there is a need to define objective criteria in order to choose among several contrast media the ones that are the most effective and to define their optimal conditions of use, such as: the dose to be injected, the required time after injection to obtain the best enhancement and the optimal imaging sequence parameter values. The method is based on NMR signal simulation in the presence of contrast media and requires the fast measurement of the T 1 and T 2 relaxation times to obtain the dynamic relaxometry variation of tissues after contrast injection. In this work the fast imaging techniques that are to be described enable the measurement of T 1 and T 2 with a 30sec temporal resolution on 128∗256 matrix images. The accuracy of the method was assessed in rabbit muscles after the injection of two gadolinium chelates (Gd-DTPA and Gd-DOTA) with the aim of improving the in vivo characterization of fast-twitch and slow-twitch muscle fiber types. The simulation results were in close agreement with contrast image analysis and showed, for relevant clinical doses, a small efficacy for both chelates. The interest of the proposed simulation method lies in the fact that it enables to objectively compare the efficacy of different contrast agents, to forecast the efficacy of a given contrast reagent and to define the optimal dose and the optimal imaging sequence parameters that give the best contrast. This simulation method obviates numerous prior experiments to evaluate the benefit expected from different contrast media. The method, which has been evaluated here for muscle investigations is applicable to any tissue analysis and can help to guide the best condition of use of contrast agents in MR imaging.

Influence of heat flowmeters on thermal measurements

The measurement of heat flows in the engineering field is relevant to thermophysical characteristics of materials in the study of the behaviour of a wall or the achievement of an energy balance in a building. Nevertheless, the utilisation of heat flowmeters in a thermal circuit has to be accompanied by some precautions, notably for materials which are slightly heat conducting. The perturbation induced by the presence of the heat flowmeter is in fact often difficult to evaluate. An analysis method is proposed that allows the definition of optimum conditions of use of two sensor types in the case of conductive exchanges. This analysis is based on a simplified model considering the heat flowmeter as a resistive and capacitive thermal layer placed in series in the studied system. The modelling of these perturbations demonstrates three influential factors: the type of heat flowmeter, the ratio of the temperature of the surface of the studied system to the outgoing heat flow, and the time scale characterising the studied phenomena. An example of the use of heat flowmeters to measure the thermal effusivity of building materials and the measurement of the heat flow inside walls of building is presented.

Behaviour of Au/Pd thermocouple in various gases

Thermoelectric properties of Au/Pd thermocouple in various atmospheres are investigated at the Ag, Al and Zn fixed points in order to find the optimum conditions of use. Gas compositions are selected as pure argon, argon oxygen, pure nitrogen and nitrogen oxygen. In pure argon and nitrogen atmospheres, Au/Pd thermocouple shows smaller fixed point EMFs and poorer reproducibilities and immersion characteristics than in oxygen mixture. When thermocouples in pure argon and nitrogen are exposed to air, their properties become the same as those of oxygen-containing thermocouples. It is confirmed that any oxygen existing in oxide form on the palladium wire surface is sufficient to stabilize the Au/Pd thermocouple. It is believed that oxidized palladium has a more negative Seebeck coefficient than oxide-free palladium. Based on the experimental results, it is recommended to oxidize the palladium wire during the preparatory heat treatment stage before use in order to obtain a stable and reproducible thermal EMF. The use of the Au/Pd thermocouple in air can also be recommended.

Drying of gas?Air mixtures with Vion KN-1 chemisorption fibre

The use of Vion KN-1 chemisorption fibre in hydrogen form as a selective drying agent for a gas—air mixture containing sulfur dioxide, carbon monoxide, hydrogen sulfide, and nitrogen dioxide was substantiated. The optimum conditions of use and regeneration of the drying agent were determined.

On the performance of a discriminant function

In two-class discriminant problems, objects are allocated to one of the two classes by means of threshold rules based on discriminant functions. In this paper we propose to examine the quality of a discriminant functiong in terms of its performance curve. This curve is the plot of the two misclassification probabilities as the thresholdt assumes various real values. The role of such performance curves in evaluating and ordering discriminant functions and solving discriminant problems is presented. In particular, it is shown that: (i) the convexity of such a curve is a sufficient condition for optimal use of the information contained in the data reduced byg, and (ii)g with non-convex performance curve should be corrected by an explicitly obtained transformation.

Plasma waves observed in the near vicinity of the space shuttle

The OSS 1 and Spacelab 2 missions found intense broadband waves in the near vicinity of the space shuttle. This paper contains a detailed observational characterization and theoretical investigation of the plasma waves observed within about 10 m of the space shuttle during the XPOP roll period of the Spacelab 2 mission. High wave levels are found from 31 Hz to 10 kHz (near the lower hybrid frequency). Above 10 kHz the wave levels decrease with frequency, reaching the background level near 56 kHz. The frequency distribution of wave electric fields is best interpreted in terms of three components below about 10 kHz and a high‐frequency tail. The primary component is a fairly uniform, high level of waves covering the frequency range from 31 Hz to 10 kHz. The two superposed components in this frequency range have electric fields of order twice the uniform level. The second component corresponds to a low‐frequency peak in the range 100–178 Hz. The third component is found near, and follows the trend of, the lower hybrid frequency. No evidence is found for a high‐frequency component localized above about 10 kHz. The waves show a pronounced amplitude and frequency variation with the quantity V∥/VT which measures the angle between the ionospheric magnetic field and the shuttle's velocity vector. Very low wave levels and small frequency extents are observed when V∥/VT ∼ 1 and the shuttle is moving primarily along the magnetic field. This implies that the waves are probably driven by water pickup ions. Observations of the waves below about 20 kHz during the free‐flight mission imply that the near‐zone waves have wave vectors oriented perpendicular to the magnetic field. The nulls observed in the wave data as the PDP spacecraft moves through the orbiter's wake imply that wavenumber increases with wave frequency. Hwang et al.'s theory for the near‐zone waves is shown to be inconsistent with the frequency distribution and wave vector orientations of the observed waves. A new theory involving Doppler‐shifted lower hybrid waves driven by beamlike distributions of water ions near the space shuttle is developed using linear theory. This linear theory can explain generation of waves with (1) frequencies ranging from near zero frequency to the lower hybrid frequency, (2) wave vectors essentially perpendicular to the magnetic field, (3) wavenumbers increasing with wave frequency, and (4) wavelengths observable by the PDP antenna. These characteristics are all consistent with the observed properties of the waves, thereby providing strong support for the theory. In addition, the theory permits two qualitative explanations for the V∥/VT effect. However, the linear theory cannot explain the details of the observed frequency spectrum of the waves. Strong, qualitative arguments that the effects of spatial inhomogeneity and nonlinear effects should modify the predicted linear spectrum are presented. In particular, the observed ratio of wave energy to thermal plasma energy is of order 10−5, sufficient for nonlinear and strong turbulence effects to be potentially important. Lastly, the observed V∥/VT effect implies optimum conditions for use of the space shuttle as a base for observing plasma waves generated by active experiments or natural ionospheric waves. Ideally, the shuttle's orbit should be designed so that V∥/VT exceeds about 0.7, thereby favoring polar orbits and arguing against equatorial orbits. Alternatively, free‐flying experiments should be used.

Tungsten electrode for urea

Tungsten electrodes for urea were prepared via covalent linking of urease on oxidized metal surfaces in different ways. The most stable electrodes were obtained when tungsten was silanized and activated by glutaraldehyde or hexamethylene diisocyanate. The electrode with urease coupled via glutaraldehyde was tested for optimum conditions of use. The nature of the buffer and its concentration and ionic strength are particularly important.

Optimized production of the acylium diagnostic ions in the chemical ionization NO+ mass spectra of long‐chain monoolefins

AbstractA recent reinvestigation of the reactivity of NO+ towards straight‐chain monoolefinic compounds revealed that the characteristic acylium ions, previously reported for alkenyl acetates and related compounds, could also be obtained from alkenes and alkenoic acids (or esters). In this study, the influence of the sample pressure and that of NO on the production of the acylium ions was investigated, leading to disappearance graphs indicative of a strong dependence on these experimental factors. This gives a further explanation for previous apparent discrepancies in the literature and the optimum conditions of use for double‐bond location in a variety of substituted or unsubstituted monoolefins.

Analyse critique d'une methode d'estimation de la conductivite thermique d'un sol in situ

A numerical method for determining the thermal conductivity of a soil in situ is proposed. It requires the measure of the temperature at three levels in the soil. From the knowledge of the boundary conditions (temperatures at the top and the bottom of the soil layer) and an estimation of the initial the mal profile, the temperature at the intermediate level can be calculated by integration of the monodimensional heat conduction equation with a numerical method (finite elements method). The boundary conditions are interpolated by the FOURIER series. The heat capacity is calculated according to the model of DE VRIES. The thermal conductivity is estimated by minimizing the residual sum of squares between calculated and measured temperatures at the intermediate level. The soil layer can be considered either homogeneous or stratified in two sub-layers. Using simulated temperature data, the optimal conditions of use of the method are defined and the sensitivity of the method to errors made on the measure of the temperature and on the position of the temperature probes is studied. In the case of an homogeneous soil layer, the method yields a good estimation of the thermal conductivity (error ≤1%) with a 4 hours period of estimation, whatever the position of the intermediate probe. The more precise estimation is obtained with an intermediate probe placed at the middle of the layer and with a high thermal amplitude. The method is not sensitive to errors made on temperature measures (biased or truncated measures) if the estimation is made on a period of 24 hours. It is highly sensitive to errors made on the position of the temperature probes. In the case of a stratified layer, the method allows to estimate the thermal conductivity of each sub-layer whatever the position of the intermediate probe if the period of estimation is at least 12 hours. The method is very sensitive to errors made on temperature measures (whatever the duration of the estimation period), on the position of the temperature probes and on the position of the limit between the two sub-layers. Therefore, its use for a stratified soil layer seems delicate.

Optimal use of the cytocentrifuge for recovery and diagnosis of Pneumocystis carinii in bronchoalveolar lavage and sputum specimens

To facilitate the diagnosis of Pneumocystis carinii from bronchoalveolar lavage and sputum specimens, we have defined conditions for optimal use of the cytocentrifuge for this purpose. Centrifugation in the cytocentrifuge at 1,200 rpm for 10 min yielded the best recovery of P. carinii. To reliably ensure complete absorption of the fluid specimen from the cytocentrifuge chamber, it was necessary to use two absorption filters simultaneously. Different methods of treating induced sputum with mucolytic agents to process sputum with the cytocentrifuge were tried. Results of these studies and our current method for treating sputa are discussed. Comparisons of slides prepared by traditional centrifugation and by cytocentrifuge processing showed the latter to be equally effective for detecting P. carinii. The most prominent advantage of the cytocentrifuge was the much smaller area to review and consequently the shortened time required to read the slides.

A study of the chemiluminescence of some acidic triphenylmethane dyes

Chemiluminescence was observed when some acidic triphenylmethane dyes were oxidized with hydrogen peroxide in alkaline solution. Trace amounts of Co(II) catalysed this chemiluminescent reaction strongly, especially in the presence of the cationic surfactant cetyltrimethylammonium bromide. The chemiluminescence spectra of some compounds and the absorption spectra of some products of the chemiluminescent reactions were investigated, and some acidic triphenylmethane dyes were studied by the Hückel molecular orbital method. On the basis of these investigations, a possible mechanism for this chemiluminescent reaction, and an initial explanation for the relationship between the structure of the reagents and their chemiluminescent behaviour were proposed. The optimum conditions for use of some of the chemiluminescent reaction systems were selected by means of the modified simplex method, and a chemiluminescent analytical method for determination of ultratrace amounts of cobalt was established, with a detection limit of 5 pg/ml. It was used for analysis of natural water samples, and good results were obtained.

A HP Ge-Telescope as Compton Suppression Spectrometer

A Ge-telescope, consisting of a planar and two large volume coaxial detectors has been built and tested. Close packing and minimum material for detector support and cryostat yield optimum conditions for use of the telescope in a Compton-suppression spectrometer. Three detectors are mounted in one cryostat without affecting the resolutions. No cross-talk has been observed. The performance of this telescope, in combination with a cylindrical NaI + BGO shield has been tested with a 137Cs and a 60Co source. Excellent Compton suppression has been achieved, also at the backscatter- and Compton-edges.

Photolysis of polymers using the medium pressure mercury lamp: Part 1—Photolysis and product analysis apparatus and the effect of some experimental variables

A photolysis cell, designed for irradiation of a polymer film deposited on a stainless steel support under closely controlled temperature conditions, is described. Using an evacuated system, detection and estimation of small amounts of volatile products may be carried out by subambient thermal volatilisation analysis (SATVA). Illustrative SATVA results are presented for the photolyses of poly(methyl acrylate) and poly(2-ethylhexyl acrylate). Each product appears as a peak on the SATVA trace, which is a record of rate of transfer of volatile material as a function of time, as products are allowed to warm up slowly from −196°C to ambient temperature. The area under a given SATVA peak measures the amount of substance volatilised. Calibration data are given, relating peak area to moles of material for each of the various products. The effect of lamp to sample distance, film thickness and irradiation time on the yield of condensable volatile products has been tested for poly(methyl acrylate) in order to establish optimum conditions for use of the apparatus.

Visible light-cured composites and activating units

In summary, visible light-activated composites offer better regulation of working time. Their composition differs from chemically activated composites only in the initiators and activators. The physical and mechanical properties of adequately polymerized photoactivated composites are similar to chemically activated composites. Depth of cure evaluations of the photoactivated composites are dependent on many factors, both experimental and inherent. There is currently no consensus on depth of cure values and evaluation methods. It is suggested that, if necessary, visible light-activated composites should be placed and polymerized in about 2-mm increments. It is prudent to use a longer exposure time. Exposure of visible light composites to dental operatory lights or strong ambient lighting (or both) during restorative procedures should be minimized to avoid premature polymerization. There are differences in design, spectral distribution, and radiation intensity of photoactivating light units. No definitive information is currently available on the effectiveness and optimal conditions for use of different light/composite combinations. Little information is currently available on the bioeffect of visible light radiation on human optical systems and oral tissue. At the present time there are reports of afterimages but no long-lasting bioeffects. It is strongly recommended that precautions should be taken in the care, use, and operation of photoactivating light units. Protective filter glasses should be used.

Monte Carlo Simulation of the Sequential Probability Ratio Test for Radiation Monitoring

A computer program simulates the Sequential Probability Ratio Test (SPRT) using Monte Carlo techniques. The program, SEQTEST, performs random number sampling of either a Poisson or normal distribution to simulate radiation monitoring data. The results are in terms of the detection probabilities and the average time required for a trial. The computed SPRT results can be compared with tabulated single interval test (SIT) values to determine the better statistical test for particular monitoring applications. Use of the SPRT in a hand-and-foot alpha monitor shows that the SPRT provides better detection probabilities while generally requiring less counting time. Calculations are also performed for a monitor where the SPRT is not permitted to the take longer than the single interval test. Although the performance of the SPRT is degraded by this restriction, the detection probabilities are still similar to the SIT values, and average counting times are always less than 75% of the SIT time. Some optimal conditions for use of the SPRT are described. The SPRT should be the test of choice in many radiation monitoring situations.