Model-dependent Parameters Research Articles

Finite size effect on critical transition temperature of superconductive nanosolids

A simple and unified model is developed for finite size effect on the critical transition temperature of superconductive nanosolids, which is based on the size-dependent Debye temperature of crystals within the McMillan expression. In the model, two material and structure dependent parameters of D 0 and α are used, which, respectively, are the critical size at which all atoms of a low-dimensional material are located on its surface, and the ratio of the mean square vibrational amplitude between surface atoms and interior atoms, In light of this model, the critical transition temperatures of superconductive nanosolids can decrease or increase with the dropping size of nanosolids depending on the bond strength changes of interfacial atoms. The predicated results are consistent with the available experimental results for superconductors MgB 2 and Nb thin films, Bi and Pb granular thin films and nanoparticles, Al thin films and nanoparticles.

Estimation of pharmacokinetic parameters from non-compartmental variables using Microsoft Excel®

This study was conducted to develop a method, termed 'back analysis (BA)', for converting non-compartmental variables to compartment model dependent pharmacokinetic parameters for both one- and two-compartment models. A Microsoft Excel spreadsheet was implemented with the use of Solver and visual basic functions. The performance of the BA method in estimating pharmacokinetic parameter values was evaluated by comparing the parameter values obtained to a standard modelling software program, NONMEM, using simulated data. The results show that the BA method was reasonably precise and provided low bias in estimating fixed and random effect parameters for both one- and two-compartment models. The pharmacokinetic parameters estimated from the BA method were similar to those of NONMEM estimation.

The value of the equation of state of dark energy

From recent CMB and Large Scale Structure observations the value of the equation of state of dark energy, assuming it to be constant in time, is constrained to be −1.3< w<−0.7 at the 95% confidence level: consistent with dark energy being a classical vacuum term. Here, we describe two novel and independent methods, sensitive to different systematics, that give the same value for w and similar confidence regions. This suggests that systematics are not an issue in current determinations of w. The first method yields a measurement of w that relies on the minimum number of model-dependent parameters; the second method is a non-parametric measurement of the time dependence of w( z). We also present a method to statistically determine the edge of a distribution.

Spectrum and tunneling in self-assembled quantum dots

We present analytical results for the tunneling escape rate for nanoscale quantum dots (QD's). It is shown that tunneling from excited states with nonzero angular momentum is suppressed. The tunneling from the states with zero angular momentum is described by a universal expression where only the preexponential factor is dependent of a particular model for a QD. The result is used to calculate the photocurrent spectrum in QD arrays. The expression for the photocurrent is reduced to a simple formula with few model-dependent parameters. The results are in quantitative agreement with experimental data. Average electron ground-state energy of a QD at the flatband condition is extracted from the best fit.

The effect of enzyme inhibitor and absorption site following [D-ala2, D-leu5]enkephalin oral administration in rats.

The effects of enzyme inhibitor, amastatin, and absorption site following intravenous (i.v.) oral (p.o.), jejunal and ileal administration of [D-ala(2), D-leu(5)]enkephalin (YdAGFdL) were investigated in rats. Model dependent and independent pharmacokinetic parameters were obtained and compared. Linear pharmacokinetics of YdAGFdL were evaluated at 0.28 and 500 microg doses for i.v. and at 1, 500, and 1000 microg for p.o. and ileal routes. Plasma samples were collected and assayed for intact YdAGFdL using a radiometric thin layer chromatography. The clearance (CL) and half lives of the distribution and elimination phases following the 0.28 microg (n=6) i.v. dose were 42.7+/-26.2 (S.D.) ml/min, 0.48+/-0.17 min, and 3.98+/-0.92 min, while those of the 500 microg dose (n=6) were 48.0+/-23.3 ml/min, 0.59+/-0.25, and 6.81+/-3.12 min, respectively, suggesting apparent linear kinetics. The CL values were close to the cardiac output of rats (50 ml/min) indicating very rapid elimination from the body. Mean bioavailability (F) values following p.o. (n=15), jejunal (n=4), and ileal (n=16) administration were 0.40+/-0.24% (S.E.), 1.25+/-0.39, and 1.78+/-0.40, respectively, and were not significantly different (p<0.05) among three doses (1, 1000, 5000 microg). The F value of YdAGFdL following ileal administration in the presence of amastatin was 8.76+/-4.47% (n=6), a 22 fold increase over po administration and a five fold increase over ileal administration without an inhibitor. These results indicate that 'effective' oral delivery of small peptides may be achievable.

On the estimation of galaxy structural parameters: the Sersic model

This paper addresses some questions which have arisen from the use of the S\'ersic r^{1/n} law in modelling the luminosity profiles of early type galaxies. The first issue deals with the trend between the half-light radius and the structural parameter n. We show that the correlation between these two parameters is not only real, but is a natural consequence from the previous relations found to exist between the model-independent parameters: total luminosity, effective radius and effective surface brightness. We also define a new galaxy concentration index which is largely independent of the image exposure depth, and monotonically related with n. The second question concerns the curious coincidence between the form of the Fundamental Plane and the coupling between _e and r_e when modelling a light profile. We explain, through a mathematical analysis of the S\'ersic law, why the quantity r_e_e^{0.7} appears almost constant for an individual galaxy, regardless of the value of n (over a large range) adopted in the fit to the light profile. Consequently, Fundamental Planes of the form r_e_e^{0.7} propto sigma_0^x (for any x, and where sigma_0 is the central galaxy velocity dispersion) are insensitive to galaxy structure. Finally, we address the problematic issue of the use of model-dependent galaxy light profile parameters versus model-independent quantities for the half-light radii, mean surface brightness and total galaxy magnitude. The former implicitly assume that the light profile model can be extrapolated to infinity, while the latter quantities, in general, are derived from a signal-to-noise truncated profile. We quantify (mathematically) how these parameters change as one reduces the outer radius of an r^{1/n} profile, and reveal how these can vary substantially when n>4.

Updated analysis ofɛ′/ɛin the standard model with hadronic matrix elements from the chiral quark model

We discuss the theoretical and experimental status of the CP violating ratio eps'/eps. We revise our 1997 standard-model estimate-based on hadronic matrix elements computed in the chiral quark model up to O(p^4) in the chiral expansion-by including an improved statistical analysis of the uncertainties and updated determination of the Cabibbo-Kobayashi-Maskawa elements and other short-distance parameters. Using normal distributions for the experimental input data we find Re eps'/eps = (2.2 \pm 0.8) x 10^{-3}, whereas a flat scanning gives 0.9 x 10^{-3} < Re eps'/eps < 4.8 x 10^{-3}. Both results are in agreement with the current experimental data. The key element in our estimate is, as before, the fit of the Delta I=1/2 rule, which allows us to absorb most of the theoretical uncertainties in the determination of the model-dependent parameters in the hadronic matrix elements. Our semi-phenomenological approach leads to numerical stability against variations of the renormalization scale and scheme dependence of the short- and long-distance components. The same dynamical mechanism at work in the selection rule also explains the larger value obtained for \ratio with respect to other estimates. A coherent picture of K -> pi pi decays is thus provided.

Melting studies of short DNA hairpins: influence of loop sequence and adjoining base pair identity on hairpin thermodynamic stability.

Spectroscopic and calorimetric melting studies of 28 DNA hairpins were performed. These hairpins form by intramolecular folding of 16 base self-complementary DNA oligomer sequences. Sequence design dictated that the hairpin structures have a six base pair duplex linked by a four base loop and that the first five base pairs in the stem are the same in every molecule. Only loop sequence and identity of the duplex base pair closing the loop vary for the set of hairpins. For these DNA samples, melting studies were carried out to investigate effects of the variables on hairpin stability. Stability of the 28 oligomers was ascertained from their temperature-induced melting transitions in buffered 115 mM Na(+) solvent, monitored by ultraviolet absorbance and differential scanning calorimetry (DSC). Experiments revealed the melting temperatures of these molecules range from 32.4 to 60.5 degrees C and are concentration independent over strand concentrations of 0.5 to 260 microM; thus, as expected for hairpins, the melting transitions are apparently unimolecular. Model independent thermodynamic transition parameters, DeltaH(cal), DeltaS(cal), and DeltaG(cal), were determined from DSC measurements. Model dependent transition parameters, DeltaH(vH), DeltaS(vH), and DeltaG(vH) were estimated from a van't Hoff (two-state) analysis of optical melting transitions. Results of these studies reveal a significant sequence dependence to DNA hairpin stability. Thermodynamic parameters evaluated by either procedure reveal the transition enthalpy, DeltaH(cal) (DeltaH(vH)) can differ by as much as 20 kcal/mol depending on sequence. Similarly, values of the transition entropy DeltaS(cal) (DeltaS(vH)) can differ by as much as 60 cal/Kmol (eu) for different molecules. Differences in free energies DeltaG(cal) (DeltaG(vH)) are as large as 4 kcal/mol for hairpins with different sequences. Comparisons between the model independent calorimetric values and the thermodynamic parameters evaluated assuming a two-state model reveal that 10 of the 28 hairpins display non-two-state melting behavior. The database of sequence-dependent melting free energies obtained for the hairpins was employed to extract a set of n-n (nearest-neighbor) sequence dependent loop parameters that were able to reproduce the input data within error (with only two exceptions). Surprisingly, this suggests that the thermodynamic stability of the DNA hairpins can in large part be reasonably represented in terms of sums of appropriate nearest-neighbor loop sequence parameters.

Temperature and Composition Dependence of Exciton Peak Positions and Band Gap Energies of Zn1?xMgx(?0.19Se Epitaxial Films

The temperature dependence of the 1s exciton energy has been measured in Zn1—xMgxSe epitaxial films at compositions x = 0, 0.07, 0.12, and 0.19 from 2 K up to 280 K. Detailed numerical fits of the individual temperature dependences are provided on the basis of an analytical four-parameter representation developed recently by one of the authors. These are compared with previously used three-parameter models of Viña et al. and Varshni. The x-dependence of the exciton energy, E1s(T, x), and of the fundamental band gap energy, Eg(T, x), is given to very good approximation by linear functions of the composition x for any T from absolute zero up to room temperature. A comparison with recent room temperature band gap energy data by Jobst et al. shows that this linear dependence holds up to x ≈︂ 0.7. The magnitudes of the model-dependent empirical parameters, which control the temperature dependence of the band gap energy in different compounds, are found to change significantly with increasing magnesium content. From the magnitude of the effective phonon temperature, particularly in the case of ZnSe, we conclude that the main contributions to the band gap shrinkage effect are due to acoustic phonons.

Effect of fasting on the uptake of bilirubin and sulfobromophthalein by the isolated perfused rat liver

BACKGROUND & AIMS: Occurrence of hyperbilirubinemia after fasting has been recognized for many years. The pathogenesis of this syndrome is unclear. Although recent studies suggest that increased intestinal deconjugation and reabsorption of bilirubin may play a major role in establishment of hyperbilirubinemia during fasting, other studies have suggested that fasting down-regulates intrinsic hepatocyte transport of bilirubin. The present study was designed to examine this possibility in the isolated perfused rat liver.METHODS: Transport of 3H-bilirubin and 35S-sulfobromophthalein (BSP) was examined in isolated perfused livers from 48-hour fasted or control rats using a multiple indicator dilution technique. Data were analyzed to quantify single-pass extraction (model-independent analysis) and were also fit by computer to the model of Goresky to quantify unidirectional fluxes.RESULTS: Fasting for 48 hours resulted in an approximately 40% reduction in liver weight but had no effect on model-dependent or model-independent parameters of transport. Despite the fact that the liver was smaller, single-pass extraction of bilirubin and BSP by livers from fasted animals did not differ from control, indicating a greater efficiency at uptake of bilirubin and BSP.CONCLUSIONS: Enhanced enterohepatic circulation of bilirubin, not altered hepatic transport, is a major factor in the pathogenesis of fasting-induced hyperbilirubinemia.(Gastroenterology 1997 Nov;113(5):1707-13)

The absorption and first-pass metabolism of [14C]-1,3-dinitrobenzene in the isolated vascularly perfused rat small intestine.

We tested the hypothesis that the small intestine is capable of the first-pass, reductive metabolism of xenobiotics. A simplified version of the isolated vascularly perfused rat small intestine was developed to test this hypothesis with 1,3-dinitrobenzene (1,3-DNB) as a model xenobiotic. Both 3-nitroaniline (3-NA) and 3-nitroacetanilide (3-NAA) were formed and absorbed following intralumenal doses of 1,3-DNB (1.8 or 4.2 mumol) to isolated vascularly perfused rat small intestine. Dose, fasting, or antibiotic pretreatment had no effect on the absorption and metabolism of 1,3-DNB in this model system. The failure of antibiotic pretreatment to alter the metabolism of 1,3-DNA indicated that 1,3-DNB metabolism was mammalian rather than microfloral in origin. All data from experiments initiated with lumenal 1,3-DNB were fit to a pharmacokinetic model (model A). ANOVA analysis revealed that dose, fasting, or antibiotic pretreatment had no statistically significant effect on the model-dependent parameters. 3-NA (1.5 mumol) was administered to the lumen of isolated vascularly perfused rat small intestine to evaluate model A predictions for the absorption and metabolism of this metabolite. All data from experiments initiated with 3-NA were fit to a pharmacokinetic model (model B). Comparison of corresponding model-dependent pharmacokinetic parameters (i.e. those parameters which describe the same processes in models A and B) revealed quantitative differences. Evidence for significant quantitative differences in the pharmacokinetics or metabolism of formed versus preformed 3-NA in rat small intestine may require better definition of the rate constants used to describe tissue and lumenal processes or identification and incorporation of the remaining unidentified metabolites into the models.

THE ABSORPTION AND FIRST‐PASS METABOLISM OF [14C]-1, 3-DINITROBENZENE IN THE ISOLATED VASCULARLY PERFUSED RAT SMALL INTESTINE

We tested the hypothesis that the small intestine is capable of the first-pass, reductive metabolism of xenobiotics. A simplified version of the isolated vascularly perfused rat small intestine was developed to test this hypothesis with 1, 3-dinitrobenzene (1, 3-DNB) as a model xenobiotic. Both 3-nitroaniline (3-NA) and 3-nitroacetanilide (3-NAA) were formed and absorbed following intralumenal doses of 1, 3-DNB (1·8 or 4·2 μmol) to isolated vascularly perfused rat small intestine. Dose, fasting, or antibiotic pretreatment had no effect on the absorption and metabolism of 1, 3-DNB in this model system. The failure of antibiotic pretreatment to alter the metabolism of 1, 3-DNB indicated that 1, 3-DNB metabolism was mammalian rather than microfloral in origin. All data from experiments initiated with lumenal 1, 3-DNB were fit to a pharmacokinetic model (model A). ANOVA analysis revealed that dose, fasting, or antibiotic pretreatment had no statistically significant effect on the model-dependent parameters. 3-NA (1·5 μmol) was administered to the lumen of isolated vascularly perfused rat small intestine to evaluate model A predictions for the absorption and metabolism of this metabolite. All data from experiments initiated with 3-NA were fit to a pharmacokinetic model (model B). Comparison of corresponding model-dependent pharmacokinetic parameters (i.e. those parameters which describe the same processes in models A and B) revealed quantitative differences. Evidence for significant quantitative differences in the pharmacokinetics or metabolism of formed versus preformed 3-NA in rat small intestine may require better definition of the rate constants used to describe tissue and lumenal processes or identification and incorporation of the remaining unidentified metabolites into the models.

Antibiotic activity in serum following single and repeated oral administration of sodium fusidate in volunteers.

The pharmacokinetics of antibiotic activity were investigated in 10 healthy, female volunteers receiving a single oral dose of sodium fusidate (500 mg) followed after 48 h by repeated oral dosing of 250 mg b.i.d. for 5 consecutive days. By use of turbidimetry, drug-related antibiotic activity in serum was determined and expressed as fusidic acid equivalents. After a single dose and repeated dosing, the peak concentrations were (mean +/- SE): 30 +/- 3 micrograms/ml and 27 +/- 3 micrograms/ml, respectively (NS), and the trough concentration at steady state was 8.4 +/- 1.8 micrograms/ml. The experimental and predicted accumulation ratios were 2.1 +/- 0.1 versus 1.6 +/- 0.2, respectively (P < 0.16). By use of a model independent method, the terminal elimination half-lives were estimated to be 11 +/- 1 h and 13 +/- 2 h after a single dose and repeated doses, respectively (NS). The total clearances of antibiotic activity were 2.0 +/- 0.4 l/h after a single dose and 1.6 +/- 0.2 l/h after repeated doses (P < 0.11). Model dependent pharmacokinetic parameters were also obtained by fitting a two-compartment open model to the median serum concentrations which, with respect to half-life and clearance, gave values close to those observed by use of the model independent approach. Safety-wise, biochemical parameters were within the normal range. However, a statistically significant increase in ASAT and a decrease in leucocytes were observed. The tolerability of the drug was good and only minor adverse events were reported.

Electrochemical characterization of a hemodialysis membrane

Transport parameters characterizing a commercial hemodialysis membrane (AN69, Hospal), with and without pretreatment with an adsorbed albumin layer, were determined as a function of the external sodium chloride equilibrium concentration. Measurements included membrane potential, streaming potential, and electroosmosis data. Transference numbers of cations and water were directly calculated from these data and were characteristic of high permselectivity at low ionic strength. Model-dependent parameters of the charged membrane, such as ξ potential and fixed charge density, were also calculated

Amplitude universality for driven interfaces and directed polymers in random media.

We present accurate estimates for the prefactors of the second and third moments of the height and free-energy fluctuations, as well as the leading correction to the growth rate and free energy per unit length, obtained from extensive simulations of a wide range of one-dimensional models of growing interfaces and directed polymers in a random environment. When scaled by the appropriate model-dependent parameters the amplitudes reduce to universal numbers which characterize the strong-coupling fixed point of the equation of Kardar, Parisi, and Zhang [Phys. Rev. Lett. 56, 889 (1986)]. To check the expected scaling we use models for which the model parameters can be computed analytically. For other systems, such as ballistic deposition, the restricted solid-on-solid model, and the finite-temperature directed polymer, the parameters are determined numerically from steady-state properties. Apart from the standard transient simulation which starts from a flat interface, we also report results for time-dependent correlations in the steady state, which give rise to different universal amplitudes. We compare our results with recent predictions arising from replica calculations and dynamic renormalization-group treatments, finding agreement in the latter but severe discrepancies in the former case. We speculate that the failure of replica theory may be indicative of replica symmetry breaking.

The pharmacokinetics of recombinant double-chain t-PA (duteplase): Effects of bolus injection, infusions, and administration by weight in patients with myocardial infarction

The current mode of administration of recombinant tissue-type plasminogen activator (rt-PA) in acute myocardial infarction is rather complex, although the rationale for the different components of this scheme is not clearly established. We compared pharmacokinetics of a continuous infusion of 38.5 MU of Burroughs Wellcome t-PA (duteplase) over 90 minutes in nine patients (phase I) with a scheme including a 0.04 MU/kg bolus, a 60-minute 0.36 MU/kg lytic infusion and a 180-minute 0.21 MU/kg maintenance infusion in 15 patients with acute myocardial infarction (Phase II). t-PA activity and antigen were fitted in a one-compartment model from which model-dependent and model-independent parameters were derived. Clearance of t-PA activity was 1020 +/- 465 (mean +/- SD) ml/min in phase I and 1359 +/- 590 ml/min in phase II. Clearance of t-PA antigen was 666 +/- 230 ml/min in phase I and 704 +/- 199 ml/min in phase II. Clearance of activity was significantly (p less than 0.01) higher than of antigen. Clearance and steady-state plasma levels showed a large interindividual variability (coefficient of variation, 56.4%), but this was significantly reduced by dosing by weight (coefficient of variation, 28.9%; p = 0.031). A 10% bolus in phase II shortened the time to reach 75% and 90% of the steady-state plasma level by 4 and 5 minutes, respectively, not significantly different from phase I. A simulation study showed that a bolus should be approximately 15% of the lytic dose to achieve a maximal level in the shortest period.

A simple parameterization of ozone infrared absorption for atmospheric heating rate calculations

A simple parameterization of ozone absorption in the 9.6‐μm region which is suitable for two‐ and three‐dimensional stratospheric and tropospheric models is presented. The band is divided into two parts, a band center region and a band wing region, grouping together regions for which the temperature dependence of absorption is similar. Each of the two regions is modeled with a function having the form of the Goody random model, with pressure and temperature dependent band parameters chosen by empirically fitting line‐by‐line equivalent widths for pressures between 0.25 and 1000 mbar and ozone absorber amounts between 1.0×10−7 and 1.0 cm atm. The model has been applied to calculations of atmospheric heating rates using an absorber amount weighted mean pressure and temperature along the inhomogeneous paths necessary for flux computations. In the stratosphere, maximum errors in the heating rates relative to line‐by‐line calculations are 0.1 K/d, or 5% of the peak cooling at the stratopause. In the troposphere the errors are at most 0.005 K/d.

Modulation of metarhodopsin formation by cholesterol-induced ordering of bilayer lipids

The effect of lipid ordering on the kinetics and extent of metarhodopsin II (meta II) formation was evaluated in bovine rhodopsin which had been reconstituted into phosphatidylcholine vesicles containing 0, 15, and 30 mol% cholesterol. The rate of establishment of the dynamic equilibrium between metarhodopsin I (meta I) and the two kinetically distinguished forms of meta II in the branched meta II model [meta IIfast and meta IIslow; Straume, M., Mitchell, D. C., Miller, J. L., & Litman, B. J. (1990) Biochemistry (preceding paper in this issue)] is derived from kinetic measurements of rhodopsin photolysis in these vesicle systems at several temperatures. Values of the meta I in equilibrium with meta IItotal equilibrium constant, Keq, are calculated from the derived model-dependent rate constants, and are shown to be equivalent to those derived from rapidly acquired absorbance spectra. The presence of 30 mol% cholesterol reduces Keq by approximately 50% between 10 and 37 degrees C. Analysis of the model-dependent parameters in terms of delta H and delta S reveals that cholesterol raises the free energy of meta IIslow, relative to meta I, by increasing delta H whereas it raises the relative free energy of meta IIfast by making delta S meta IIfast relative to meta I less positive. The reduction in Keq by both temperature and cholesterol is found to be directly correlated with a parameter that reflects the free volume available for molecular motion in the hydrophobic core of the bilayer [Straume, M., & Litman, B. J. (1988) Biochemistry 27, 7723-7733].(ABSTRACT TRUNCATED AT 250 WORDS)

Chaos and incoherence in a classical rotation-vibration model of infrared multiple-photon excitation.

By including rotations in a previously developed generic vibrational model of ir multiple-photon excitation (MPE) [Phys. Rev. Lett. 51, 1259 (1983) and Phys. Rev. A 34, 1211 (1986)] it is found that the combination of chaotic dynamics and rotational averaging leads to fluence-dependent absorption and removes the sensitivity of the results to model-dependent parameters. Therefore, a complete propagation calculation through a molecular medium of this type would show a Beer's law absorption of photons consistent with the vast majority of MPE experiments performed to date, a result which previously was attributed to rate-equation dynamics in the molecular quasicontinuum. In addition, the classical rotation-vibration dynamics observed in this model correlate very well with one's quantum intuition based on a molecule's P-, Q-, and R-branch structure and on the red shift of the vibrational absorption feature with excitation.

Single-dose pharmacokinetics of oral cibenzoline in man.

The pharmacokinetics of cibenzoline, a new antiarrhythmic drug, were examined in healthy male volunteers. In a Latin Square, three-way crossover design, six subjects in three groups of two were given single 100-, 150-, or 200-mg oral doses of cibenzoline succinate in a fasting state. The plasma and urinary concentrations of cibenzoline and its dehydro metabolite were determined by high performance liquid chromatography. Cibenzoline plasma concentrations declined in a biexponential manner after reaching the maximum plasma concentrations. The mean±standard deviation maximum plasma concentrations of 201±39, 311±43, and 478±120 ng/ml were attained from 1 to 2 hours after doses of 100, 150, and 200 mg, respectively. The elimination half-life was dose-independent and averaged 5.47±0.59 hours. The maximum plasma concentration and the area under the plasma concentration-time curve increased in proportion to the dose. The maximum plasma concentrations of dehydro metabolite were very low and were about 1/20 times or less than those of cibenzoline. The average of 58.9±11.2 % of the given dose was excreted as cibenzoline dose-independently in the urine and only 1.13±0.55 % as dehydro metabolite. Besides the above model-independent pharmacokinetic parameters, model-dependent parameters were also obtained by curve-fitting the plasma data to a two-compartment model with zero-order absorption. Cibenzoline was well tolerated by all subjects. Clinically significant adverse effects were not observed.