Ideal Factors Research Articles

Electric and Dielectric Properties of Barium Titanate Schottky Barrier Diodes

The electrode properties of yttrium‐doped barium titanate ceramics were studied. The current–oltage (I–V) and capacitance‐voltage (C–V) characteristics of fritted‐Pt‐paste electrodes, nonfritted‐Pt‐paste electrodes, vacuum‐deposited‐Pt electrodes, and vacuum‐deposited‐Au electrodes were measured. In general, the I–V data indicated that the diodes are metal–interface–semiconductor type junctions with the depletion–layer dielectric properties described by the Devonshire theory of barium titanate. The observed I–V and C–V data have unusual characteristics which could be related to the ferroelectric properties of barium titanate. The large diode ideal factors observed in the I–V data were attributed to the effect of the high dielectric constant of barium titanate. For fritted‐Pt‐paste electrodes, the forward and reverse bias had the same value for the diode factor near the zero‐bias region, and the interface layer thickness is estimated to be δ/ɛir= 1.60 Å. At the high–bias region, the fritted electrodes gave a positive‐temperature‐coefficient effect of the diode factor n, which was explained as an effect of the nonlinear dielectric properties of the barium titanate. The nonfritted and deposited types of electrode had different values of diode ideal factor n for forward bias and reverse bias. This difference of barrier‐height lowering effect between the forward and reverse bias was explained by the relative motion between the electrode and the semiconductor surface caused by the piezoelectric effect of the depletion layer on the loosely bonded elecrodes. The spontaneous polarizations of barium titanate were found to have two different effects on the electrode flat‐band barrier height, depending on the thickness of the interface layer. When a thick interface layer was involved in the case of nonfritted electrodes, the spontaneous polarizations would bend the band at the electrode surface, have the charges compensated for by the density states at the top of the valence band, and give a barrier height as high as the band gap. In the case of intimate‐contact electrodes, the charge compensation could be accomplished by the metal‐induced gap states (MIGS) of the electrode and yield a low barrier height, which, regardless of the electrode materials, could give an ohmic‐type electrode behavior due to the low electron mobility of barium titanate.

Novel rolltruded films: 4. Gas separation characteristics of rolltruded isotactic polypropylene

Abstract The gas separation characteristics of isotactic polypropylene (iPP) thin films produced via the rolltrusion solid-state processing technique have been studied in order to establish some principles underlying permeation/separation behaviour in relation to membrane texture. Ideal and actual separation factors have been determined for various processing temperatures and draw ratios to assess the impact of the unique triaxial morphology produced during rolltrusion. Previously, we have shown that this unique morphological texture can improve the gas permeability of iPP by reducing the diffusive pathway tortuosity and by increasing the microvoid content in the polymer. In this study we show that the separation factors generally improve in iPP as a result of rolltrusion processing. However, the actual separation factors for a mixture of CO 2 and N 2 are less than the ideal values for all processing conditions studied, although this difference decreases with increasing draw ratio and decreasing processing temperature. This discrepancy between the actual and ideal separation factors is attributed to a depression in the permeability of CO 2 in the mixture compared to the pure gas because of the presence of N 2 .

低温プラズマ処理ポリ（１‐トリメチルシリル‐１‐プロピン）膜の処理層の気体透過性と分離性

A poly (1-trimethylsilyl-1-propyne) membrane, which has extremely high gas permeability coefficients, was modified with low temperature argon-plasma treatments. Siloxane bonds, carbonyl and hydroxyl groups were produced on the treated surface, which were determined from the ESCA and ATR-FT-IR analyses. The polymer chains in the treated layer were cross-linked, and its layer's depth was estimated at about 200 Å. For permeability coefficients for various gases in the treated membranes, the series resistance model, which composed of the treated layer and the bulk, could beused because the theoretical curves fitted the experimental data of the ideal separation factors for various gas pairs. The ideal separation factors in the treated layer could be theoretically estimated, and the factors for oxygen/nitrogen, ethylene/ethane and propylene/propane were 4.2, 1.5 and 3.5, respectively. The permeability coefficients for various gases in the treated layer could be also calculated, and the values were 10-10-10-12 (cm3 (STP) cm/ (cm2. sec. cmHg)), which were 105-fold smaller than those of the non-treated PMSP membrane. With increasing penetrant diameter, a difference in the permeability coefficients berween in the treated layer and in the bulk increased.

A simple model for a water gas shift membrane reactor

A simplified process model was developed to simulate a catalytic membrane water gas shift (WGS) reactor. A number of computer simulations were conducted to determine the potential of increased carbon monoxide (CO) conversion in WGS reaction due to simultaneous separation of product hydrogen (H2) from the reactant mixture. Gas separation factors based on Knudsen diffusion were used in these simulations to assess the feasibility of inorganic and ceramic membranes in a high-temperature, high-pressure (HTHP) coal gasification environment. The simulations indicated that although the increase in CO conversion and hydrogen concentration in a single membrane reactor stage was significant, a multistage membrane separation system would be needed to increase the hydrogen product concentration above 90%. As expected, increasing the feed pressure to permeate pressure ratio was found to increase the CO conversion and the product hydrogen concentration. At low feed to permeate pressure ratios, the model predicted a much better membrane reactor performance with a countercurrent feed and permeate flow scheme when compared with a concurrent flow scheme. The membrane performance, of course, depends strongly on the gas separation factors. With gas separation factors lower than the ideal Knudsen diffusion separation factors (e.g. H2 to CO2 separation factor of 2 instead of the ideal Knudsen value of 4.7), the model simulation predicted a much smaller increase in CO conversion and product hydrogen concentration.

Gas transport properties of poly(2,2,4,4‐tetramethyl cyclobutane carbonate)

AbstractGas transport properties of semicrystalline films of poly(2,2,4,4‐tetramethyl cyclobutane carbonate) (TMCBPC) were studied. Permeability coefficients for He, O2, N2, CH4, and CO2 at 35°C for pressures between 1 and 20 atm are reported as well as sorption isotherms for N2, CH4, and CO2 at the same conditions. The permeability coefficients for TMCBPC are larger than corresponding values for the aromatic bisphenol‐A polycarbonate (PC) and tetramethyl bisphenol‐A polycarbonate (TMPC), even though the TMCBPC films are semicrystalline. These results are explained on the basis of the larger free volume available for permeation in this polymer. Significant TMCBPC plasticization by CO2 was also observed and this causes typical time‐dependent behavior. The plasticization process starts at very low pressures compared with the behavior of aromatic polycarbonates PC and TMPC. This early onset of plasticization seems to be related also to the larger free volume in the amorphous phase of TMCBPC which favors high gas sorption. The diffusion coefficients for TMCBPC are also larger than those reported for the aromatic polycarbonates PC and TMPC. Ideal gas separation factors were found to follow the usual trend; that is, as permeability increases, the ideal separation factor decreases. © 1993 John Wiley & Sons, Inc.

Optimal Spinal Strength Normalization Factors Among Male Railroad Workers

In spite of increasing interest in techniques and devices for quantifying trunk strength and lifting capacity, relatively little research has been done to determine optimal normalizing factors for strength. The isolation of the ideal factors is a critical prerequisite for comparison of patient data to expected physical capacities in the uninjured population. In the present study, 160 incumbent railroad workers from four heavy laboring jobs were tested for isokinetic trunk strength and lumbar/cervical isokinetic lifting capacity as part of a study to establish normative data (Union Pacific RR, Omaha, NE). Three variables relating height and weight were studied to determine optimal normalization: actual body weight (BW), ideal weight (IW) and adjusted weight (AW). "IW" is actually a height/weight variable based on a weight control chart specifying ideal weights for given heights and genders. "AW" represents the lesser of BW or IW. Subjects were tested for isokinetic trunk extension/flexion for lumbar (floor-to-knuckle) and cervical (knuckle-to-shoulder) lifts. Results demonstrated that the isolated trunk strength tests showed the best correlation coefficients with BW for flexion-extension work at 60 and 150 per sec. Moreover, the correlation coefficients between the lumbar isokinetic lifting peak force measures and BW were high (ranging 0.49-0.67, P < 0.001), with much lower correlations for AW or IW. By contrast, cervical correlations between Liftask peak force and the height/weight variables were all lower, and were also better for AW than for BW or IW (ranging 0.37-0.50). It appears that body weight is the best normalizing factor for isokinetic trunk flexor/extensor strength and lumbar (floor-to-knuckle) lifting.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of coating procedure on composite gas separation membrane performance

The influence of different coating procedures on the transport and separation properties of composite gas separation membranes was studied. The composite membrane (CM) comprises a coating material (silicone rubber) in occluding contact with an asymmetric polysulfone flat membrane (AM). Permeabilities, ideal separation factors and structure of the CM were found to depend strongly on the evaporation time, volume and concentration of the coating solutions. Gas permeation experiments (H 2 , N 2 , CO 2 , CH 4 ) indicated that gas permeabilities decreased rapidly with an increasing amount of coating. A maximum in the H 2 /N 2 , H 2 /CH 4 ideal separation factor was reached as the amount of coating was increased. Scanning electron microscopy (SEM) studies revealed the presence of a dense isotropic layer of coating material above an anisotropic layer comprised of a mixture of polysulfone nodules and silicone material. The results showed that the CM prepared with a concentration of 6% silicone solution and contact time of 1 min has the best gas separation performance.

Modernization and Postmodernization: Whither India?

We hear much talk these days about the emergence of a new order, an order (presumably) ushering in an era of peace and prosperity, terminating the arms race among superpowers and the nuclear balance of terror. Seen as an antidote to anarchy, this vision of order surely has an appealing ring: feuds among states are to give way to a unified structure of humankind, narrow national self-interest to shared concern for our global village.1 Unfortunately, on closer inspection, the brightness of the vision quickly begins to dim especially when attention is drawn to the motivating forces behind unity. In large measure, unification seems to be propelled by the dictates of the market or world economy, a market that is governed, in turn, by the interests of leading industrial or postindustrial nations. On a more general (and more theoretical) plane, one may ask in which language or idiom the vision tends to be articulated. Unsurprisingly, this language is typically of Western origin, reflecting specifically the aspirations of Western modernity with its bent toward rational universalism.2 From its inception, modern Western thought carried a teleological imprint marked by a dialectical twist: the opposition between advancement and regression, between development and nonor underdevelopment. Confronted with the Western model, non-Western countries or cultures were expected to catch up sooner or later with the postulated telos or else to suffer defeat and obsolescence. In this developmental schema, material and ideal factors were inextricably linked: disparities of material or economic progress were matched with asymmetries of culture, language, and human worth. In this essay, I shall explore the issue of development and modernization in a particular context although, I believe, broader

Permeation of oxygen, argon and nitrogen through polymer membranes

In order to screen polymer materials suitable for the separation of O2/Ar mixtures, gas permeability coefficients of O2, Ar and N2 through a total of 19 polymers were measured at 25°C and atmospheric pressure. Diffusion coefficients and solubility coefficients were calculated from time-lag data. The gas permeabilities and diffusivities in all polymers tested are in the order of O2>Ar>N2, while the gas solubilities are in the order of Ar>O2>N2. Higher permselectivities are observed in glassy polymers than in rubbery polymers. Permeability ratios, which denote the ideal separation factors, for O2/Ar in glassy polymers are strongly affected by the contribution of the diffusivity ratios. The absolute diffusivities and the diffusivity ratios are correlated rather well using the free volume theory of polymers which employs the group contribution method based on the chemical structure of polymers. Slight deviations from the expected values are discussed by introducing a factor of polymer chain fluctuation speed. Poly (2,6-dimethyl-1,4-phenylene oxide) and tetramethyl bisphenol-A polycarbonate exhibit a relatively high permeability of O2 and a high permeability ratio of O2/Ar. Temperature and pressure dependencies of gas permeabilities are examined with these two polymers.

Hollow Fiber Inorganic Membranes for Gas Separations

Abstract Pure gas permeabilities of He, H2, CO2, N2, and CO were measured for microporous silica hollow fiber membranes as a function of temperature. The transport mechanism for gas permeation is clearly non-Knudsen since several heavier gases permeate faster than lighter gases. An excellent correlation is obtained between permeability and kinetic diameter of the penetrant. The proposed mass transfer mechanism is a combination of surface diffusion and molecular sieving. High ideal separation factors (permeability ratios) are observed at 343 K for H2/N2 and H2/CO of 163 and 62.4, respectively, which compare very favorably with polymeric and molecular sieve gas separation membranes.

An Exploratory Study of Role Adaptation of Newly Employed Nurses.

The purpose of this study was to investigate factors influencing role adaptation in newly employed nurses and the consistency between role expectations before employment and after one year of employment. The results of this study may contribute to strategy development towards positive role adaptation in newly employed nurses. The data used in this study were collected from 111 nurses, the sample was drawn from all newly employed professional nurses working at Y Medical Center in 1987. The data were collected longitudinally in the 2nd-3rd weeks, the 3rd month and the 12th month after employment. The results of this study were as follows: 1. The degree of change the importance of factors influencing role adaptation and the length of time after employment were investigated. The result showed that the degree of change was the greatest within the first 3 months after employment. Important factors related to role adaptation were working conditions, the environment of the assigned ward and the work load. These factors always displayed high scores without any great change over time. New employees put more importance on practical factors which were obtained through experience in their jobs rather than on ideal factors which they had considered more important while in school. 2. Consistency between role expectation before employment and after 12 month of employment was investigated. The highest consistency item was the expectation about the variety of patients, and the highest inconsistency was the expectation about their own welfare. An average score of 69.07 points was achieved from a maximum of 125 points for the 25 items, showing that expectations for role development before employment were not fully satisfied. In conclusion the administrator should assess the initial expectation at the time of employment of new nurses and she/he should make clear to the new nurses that these expectations may not be realistic. In this way the administrator can provide more satisfactory conditions towards the expectations of the new nurses and help them towards positive role adaptation and reduction of role conflict. Newly employed nurses have high and unrealistic expectations about socialization to the profession from their nursing educational program. It is suggested that a transitional training program should be planned and carried out for newly employed nurses.

Polymeric membranes based on bisphenol-A for gas separations

Abstract Pure gas sorption and transport data for five, commercially available, bisphenol-A-based polymers were used to examine the effect of the connecting group between bisphenol-A units on the gas separation characteristics of membranes formed from these polymers. An unusually high He/CH4 selectivity was noted for one of the members in the series of polymers. This property was explained in terms of the low free volume present in this material as compared to the other polymers derived from bisphenol-A monomers. Permeability coefficients for a mixture of carbon dioxide and methane were measured and compared to predicted values using an extension of the dual mode/partial immobilization model for mixed gases. Measured mixed gas separation factors were compared to predicted values and to ideal separation factors obtained from pure gas permeability coefficients.

Gas permeation in miscible homopolymer‐copolymer blends: II. Tetramethyl bisphenol‐A polycarbonate and a styrene/acrylonitrile copolymer

AbstractGas sorption and transport properties for He, H2, O2, N2, Ar, CH4, and CO2 at 35°C near atmospheric pressure have been obtained for miscible blends of tetramethyl bisphenol‐A polycarbonate (TMPC) and a random copolymer of styrene with acrylonitrile (SAN) containing 9.5% by weight of acrylonitrile. All gas permeability, diffusion, and solubility coefficients obtained are lower than that calculated from the semilogarithmic additivity rule. These results are qualitatively interpreted by ternary solution theory and activated state theory which have been proposed to describe gas sorption and diffusion in miscible blends. The negative deviation of gas permeabilities for the blends from this rule can be explained semiquantitatively by free volume theory which takes volume contraction on mixing into account. The negative deviation increases with gas molecular size which results in larger ideal gas separation factors than that calculated from the additivity rule. For He/CH4 and H2/CH4 pairs, the permselectivities for the blends are higher than that for either pure TMPC or SAN. The deviation from additivity for gas transport properties of TMPC/SAN blends is the opposite of that observed in the first paper of this series for PMMA/SAN blends. This can be attributed to the stronger interactions in TMPC/SAN blends than in PMMA/SAN blends.

Gas permeation in miscible homopolymer–copolymer blends. I. Poly(methyl methacrylate) and styrene/acrylonitrile copolymers

AbstractGas transport properties in homogeneous blends of PMMA with each of two SAN random copolymers, containing 13.5 and 28% by weight of acrylonitrile respectively, have been measured at 35°C for He, H2, O2, N2, Ar, CH4, and CO2. For all cases, the permeability and diffusion coefficients are higher than that expected from the semilogarthmic additivity rule. On the other hand, the solubility coefficients and the ideal gas separation factors follow this rule well. These results for PMMA/SAN blends differ from those observed recently for other miscible blend systems; however, they agree well with recent theories proposed to describe gas sorption and permeation behavior in polymer mixtures. The composition dependence of gas transport properties observed in PMMA/SAN blends is attributed to the very weak net interactions between PMMA and SAN produced by repulsions between styrene and acrylonitrile units in the SAN random copolymers. Gas transport properties in phase‐separated PMMA/SAN blends have also been studied. The phase‐separated blends show sorption and permeation properties very similar to the corresponding homogeneous blends which can be explained by an isotropic, interconnected, two‐phase model proposed by Kraus and Rollmann. Gas permeabilities for the solution cast PMMA films used here are compared with melt‐extruded specimens used previously, and the differences are attributed to molecular orientation.

Gas permeation in miscible blends of poly(methyl methacrylate) with bisphenol chloral polycarbonate

The miscibility of poly(methyl methacrylate) (PMMA) with bisphenol chloral polycarbonate (BCPC) has been studied using differential scanning calorimetry (DSC), optical indication of phase separation on heating (i.e., lower critical solution temperature (LCST) behavior), density measurement, and gas permeation. All evidence indicates that PMMA is miscible with BCPC over the whole blend composition range. Single composition-dependent glass transition temperature and LCST behavior have been observed for each blend. The specific volumes of the blends follow closely the simple additivity rule indicating the interaction between PMMA and BCPC is weak. Gas permeability coefficients for He, H2, O2, Ar, N2, CH4, and CO2 measured at 35°C under 1 to 2 atm upstream pressure are lower than those calculated from the semilogarithmic additivity rule. The difference between this calculated permeability and the measured one increases with gas molecular size. As a result, the ideal gas separation factors for He/CH4, CO2/CH4, and O2/N2 gas pairs estimated from the ratio of pure gas permeabilities are higher than predicted from the semilogarithmic additivity rule. These permeation results were interpreted in terms of the free volume theory and the activated state theory, which have been proposed to describe gas transport behavior in polymer mixtures.

Nonequilibrium boron doping effects in low-temperature epitaxial silicon films

We report the first preparation of in situ boron-doped epilayers by a low-temperature chemical vapor deposition process (T=550 °C). Boron incorporation is approximately linear in source gas concentration, and active levels of boron incorporation exceeding 1×1020 B/cm3 have been achieved in as-deposited 550 °C epilayers. This value exceeds solid solubility limits for boron in silicon at these temperatures by two orders of magnitude, and highlights the nonequilibrium nature of this process. High resolution transmission electron microscopy lattice imaging of this material shows it to be free of boron precipitates, while both plane view transmission electron microscopy and x-ray topography fail to reveal extended defects. Utilizing low-temperature processing throughout, p/n junctions have been fabricated in several of the in situ doped layers, with essentially ideal junction quality factors (n=1.0 –1.05) found for junctions of 1×106 μm2.

"Ethos." Its Relationship to Reail and Ideal Sociological Factors in Max Scheler's Philosophy of Culture

"Ethos." Its Relationship to Reail and Ideal Sociological Factors in Max Scheler's Philosophy of Culture

The Body Politic: Normal Female Adolescent Development and the Development of Eating Disorders

The Body Politic: Normal Female Adolescent Development and the Development of Eating Disorders

Series solutions for a gas permeator with countercurrent and cocurrent flow

The difficulties in the numerical solution of differential equations for countercurrent binary gas permeators are discussed. For a permeator with countercurrent or cocurrent flow of a binary gas mixture without axial pressure drops, a series solution technique is introduced to express each product composition as a power series in terms of a dimensionless membrane area. For countercurrent flow over a wide range of parameters, compute product compositions and fractions of the feed mixture permeating the membranes compare very well with those from a numerical solution of the governing equations for small to moderate permeate fractions in the range considered practical. For ideal separation factors of 2, 5, 10, 25, and 80, significant deviations occur at fractions larger than 0.7, 0.5, 0.33, 0.25, and 0.15, respectively, at a pressure ratio of around 0.1 and a more-permeable-component feed mole fraction around 0.2. Cocurrent flow predictions are excellent at somewhat lower permeate fractions. Preliminary countercurrent permeator design or rating problems will require solution of only one o two cubic equations.

Estimation of Series Resistance Losses and Ideal Fill Factors for Photoelectrochemical Cells

A simple method is presented for estimating series resistance losses and ideal fill factors for a given photoelectrochemical device from current‐voltage measurements at varying light intensity. This method is demonstrated on a model PEC device comprising the Pyridinium Chloride, Ferrocene/ Ferricenium ion couple |C system. The extent to which the photovoltaic output is degraded by high series resistance losses can be directly estimated using the present approach.