A Randomized Controlled Trial of R-Form Verapamil Added to Ongoing Metformin Therapy in Patients with Type 2 Diabetes

CONTEXT

There is a medical need for effective insulin-independent antidiabetic drugs that can promote pancreatic β-cell function and have a low risk of hypoglycemia in type 2 diabetes mellitus (T2DM) patients. R-form verapamil (R-Vera), which is able to enhance the survival of β-cells and has higher cardiovascular safety margin compared with racemic verapamil, was developed as a novel approach for T2DM treatment.

OBJECTIVE

This randomized, double-blind, placebo-controlled clinical trial was designed to evaluate the efficacy and safety of 3 dosages of R-Vera added to ongoing metformin therapy in T2DM patients who had inadequate glycemic control on metformin alone.

METHODS

Participants were randomly assigned in an equal ratio to receive R-Vera 450, 300, or 150 mg per day, or matching placebo, in combination with metformin. The primary endpoint was change in hemoglobin A1c (HbA1c) after 12 weeks of treatment.

RESULTS

A total of 184 eligible participants were randomized to receive either R-Vera or placebo plus metformin. At week 12, significant reductions in HbA1c were observed for R-Vera 300 mg/day (-0.36, P = 0.0373) and 450 mg/day (-0.45, P = 0.0098) compared with placebo. The reduction in HbA1c correlated with decreasing fasting plasma glucose levels and improved HOMA2-β score. Treatment with R-Vera was well tolerated with no hypoglycemic episodes occurring during the trial.

CONCLUSION

Addition of R-Vera twice daily to ongoing metformin therapy significantly improved glycemic control in T2DM patients. The favorable efficacy and safety profile of R-Vera 300 mg/day can be considered as the appropriate dose for clinical practice.

Effect of Household Preparation on Levels of Pesticide Residues in Produce

In 1993, the National Academy of Sciences released a report on the effects of pesticides in the diets of infants and children, indicating that current tolerances do not take into account the eating habits and metabolism of young children. In response to that report, a study was undertaken to determine pesticide residues in raw agricultural commodities at levels below the tolerances established by the Environmental Protection Agency. The objective of the study was to determine whether normal household washing, peeling, and cooking procedures had any effect on pesticide residue levels. Low levels of pesticide residues were detected in 97 (40%) of the 243 samples analyzed. The number of samples containing detectable residues dropped to 47 (19%) after household preparation. Results indicate that residue levels in most commodities are substantially reduced after household preparation.

Comparison of neutralizing antibody and cell-mediated immune responses to pandemic H1N1 2009 influenza virus before and after H1N1 2009 influenza vaccination of elderly subjects and healthcare workers

BACKGROUND

The recent H1N1 pandemic virus that emerged in 2009 resulted in high morbidity rates mainly in younger individuals, albeit with relatively low mortality. We investigated both humoral and cellular immune responses against the pandemic H1N1 2009 virus before and after immunization with inactivated H1N1 2009 vaccine.

METHODS

We obtained paired blood specimens from a cohort of participants from nursing homes (n=108) and a public hospital (n=60) in Singapore. Serum samples were tested for neutralizing antibodies against H1N1 2009 using microneutralization assays, while peripheral blood mononuclear cells were subjected to interferon-γ enzyme-linked immunosorbent spot (ELISPOT) assays for whole virus-specific T-cell responses.

RESULTS

We observed significant increases in geometric mean titers of neutralizing antibodies after H1N1 2009 vaccination (from 23.6 pre-vaccination to 94.7 post-vaccination). Approximately 77% and 54% of the cohort exhibited ≥2-fold and ≥4-fold increases in neutralizing antibody titers following vaccination; 89.9% of the cohort had a post-vaccination antibody titer of ≥32. Adjusted for gender, participants aged ≥60 years were less likely to have a ≥4-fold increase in antibody titers after vaccination than those aged <60 years (0.48; 95% confidence interval (95% CI) 0.32-0.71, p=0.007). There was a 1.4-fold elevation in H1N1 2009-specific T-cell responses after vaccination (p<0.05). Adjusted for gender, age ≥60 years was positively associated with a greater increase in T-cell response (β=4.9, 95% CI 1.58-8.29, p=0.018). No significant correlation was observed between humoral and cellular immune responses.

CONCLUSIONS

Influenza vaccination elicits significant neutralizing antibody and T-cell responses to pandemic H1N1 2009 influenza virus. However, in response to vaccination, increases in neutralizing antibody titers were comparatively lower but T-cell responses were higher in older participants. Therefore, our study suggests that memory T-cells may play a crucial role in protecting older individuals against pandemic H1N1 2009 infection.

A parallel fuzzy inference model with distributed prediction scheme for reinforcement learning

This paper proposes a three-layered parallel fuzzy inference model called reinforcement fuzzy neural network with distributed prediction scheme (RFNN-DPS), which performs reinforcement learning with a novel distributed prediction scheme. In RFNN-DPS, an additional predictor for predicting the external reinforcement signal is not necessary, and the internal reinforcement information is distributed into fuzzy rules (rule nodes). Therefore, using RFNN-DPS, only one network is needed to construct a fuzzy logic system with the abilities of parallel inference and reinforcement learning. Basically, the information for prediction in RFNN-DPS is composed of credit values stored in fuzzy rule nodes, where each node holds a credit vector to represent the reliability of the corresponding fuzzy rule. The credit values are not only accessed for predicting external reinforcement signals, but also provide a more profitable internal reinforcement signal to each fuzzy rule itself. RFNN-DPS performs a credit-based exploratory algorithm to adjust its internal status according to the internal reinforcement signal. During learning, the RFNN-DPS network is constructed by a single-step or multistep reinforcement learning algorithm based on the ART concept. According to our experimental results, RFNN-DPS shows the advantages of simple network structure, fast learning speed, and explicit representation of rule reliability.

Micromechanics of wastewater sludge floc: Force–deformation relationship at cyclic freezing and thawing

This study examined shape changes in two typical wastewater flocs subjected to cyclic freezing and thawing and the associated force exerted by the ice front. While freezing, the engulfing ice front gradually pulled the floc apart. Subsequent thawing only partially restored the floc's shape. By the Maxwell model, used to interpret gross shape deformations, both flocs were visco-elastic objects exhibiting time-varying rheological characteristics which were more viscous than elastic. Detailed observations of floc 1 deformation demonstrated a two-stage force-displacement relationship. Following 1 cycle of freezing and thawing, the interior structure of the floc deteriorated and the force required to elongating a unit length of floc decreased by 60%. The original floc 2 had a dense "core" and loose "tail"; the core was more resistant to deformation under normal stress than the loose tail. Although both flocs had similar shapes and sizes and were acquired from the same activated sludge stream at a wastewater treatment plant, their rheological behaviors differed substantially. A comprehensive theoretical model for freezing and thawing processes should incorporate these rheological characteristics as they corresponded to observed structural changes and reduction in bound water content in sludge following a cyclic treatment of freezing and thawing.

Electrophoretic mobility of a particle covered with an ion-penetrable membrane

The electrophoretic behavior of a planar particle covered by an ion-penetrable membrane, which simulates a biological entity, is investigated. We show that, in general, a point charge model will overestimate the electrophoretic mobility of a particle and the deviation increases with the increase in the concentration of fixed charge and with the decrease in the thickness of membrane layer. As in the case of a point charge model, the present model also predicts a local maximum in the absolute mobility as the thickness of membrane layer varies. If the sizes of counterions of various valences are the same, then the lower the valence of counterions, the larger the mobility, and the larger the counterions, the greater the mobility. The latter is consistent with the experimental observations in the literature. For the level of the concentration of fixed charge examined, the effect of coions on the mobility is negligible.

The role of cell density in the survival of cultured cerebellar granule neurons

The dependence for survival of cerebellar granule neurons on the cell density was examined both experimentally and theoretically. The results of batch experiments revealed that the cell survival index (CSI) was inappreciable, if cell density was below a critical level. If cell density exceeded this critical value, CSI increased with the increase in cell density. In addition, CSI was significantly increased by using a conditioned medium from the dense cultures. This suggests that not only cell density promotes survival of neurons, but also an increased concentration of growth factors produced by neurons has a direct effect on the survival of the neurons. A quantitative model describing the distribution of the growth factor at different cell densities was proposed to investigate the role of cell density in the survival of the neurons. We showed the existence of a critical level for cell density, and good agreement in the improvement of CSI was found between the theoretical prediction and the experimental result. Finally, the average concentration of growth factor necessary for cell survival based on our model was in a reasonable range compared to the practice of the addition of neurotrophic factors to the medium of cultured cerebellar granule neurons.

Electrokinetic flow in a planar slit covered by an ion-penetrable charged membrane

The electrokinetic flow of an electrolyte solution in a planar slit covered by an ion-penetrable charged membrane layer is analyzed theoretically. An approximate analytical expression for the spatial variation in the electrical potential is derived, and the electroosmotic velocity, the total electric current, and the streaming potential of the system under consideration are evaluated. The effects of epsilon' (relative permittivity of liquid phase/relative permittivity of membrane layer), eta' (viscosity of liquid phase/viscosity of membrane layer) and the valence of anions (coions) on the volumetric flow rate and total current are examined. We show that the effect of the valence of cations (counterions) on the volumetric flow rate is less significant than that of epsilon' and that of eta'. However, the effect of epsilon' on the total current is less significant than that of the valence of cations and that of eta'. The variation of total current as a function of ionic strength is found to have a local minimum, regardless of whether a pressure gradient is applied or not. The absolute streaming potential has a local maximum as the concentration of fixed charge varies, which was not found in previous studies.

Electroosmotic Flow of a General Electrolyte Solution through a Fibrous Medium

The electroosmotic flow of a general electrolyte solution through a fibrous medium is modeled theoretically taking the effect of double-layer polarization into account. The result obtained is applicable to an arbitrary level of electrical potential. We show that if the effect of double-layer polarization is neglected using the linearized Poisson-Boltzmann equation will underestimate electroosmotic velocity. The deviation becomes inappreciable, however, if kappaa is either very large or very small, kappa and a being, respectively, the reciprocal Debye length and the radius of a fiber. If the surface potential is high, the variation of electroosmotic velocity as a function of kappaa may exhibit a local maximum and a local minimum, and the larger the porosity of the fibrous medium the lower the level of surface potential for the local extremals to occur. If kappaa is small, the effect of surface potential on the electroosmotic velocity is more significant than that of double-layer polarization, and the reverse is true if kappaa is large. Copyright 2000 Academic Press.

Electrophoretic mobility of concentrated spheres with a charge-regulated surface

The electrophoretic behavior of a concentrated spherical colloidal particle is modeled theoretically under the Debye-Hückel condition. The surface of a particle contains dissociable functional groups, the dissociation of which yields negative fixed charges. The model derived is applicable to an arbitrarily thick double layer. We show that the absolute surface potential decreases with the increase in kappa(a); kappa and a are the reciprocal Debye length and the radius of a particle, respectively. Moreover, the variation of the absolute electrophoretic mobility as a function of kappa(a) has a maximum.

Electrical Interaction Energy between Two Charged Entities in an Electrolyte Solution

The electrical interaction energy between two charged entities in an electrolyte solution plays a significant role in various phenomena in colloid and interface science. Available methods for the estimation of this energy under the Debye-Huckel condition are discussed briefly, and a systematic approach based on a boundary integral method, which has the potential to yield an approximate analytical expression for various types of surfaces under a general surface condition, is introduced. The linear sizes of the interacting entities can be comparable or one is much larger than the other. A typical example for the former includes, for instance, the interaction between two colloidal particles. The stability behavior of a colloidal dispersion belongs to this category. That for the latter includes the interaction between a particle and a wall. The adsorption of particles to surfaces and the electrophoretic motion of particles near a boundary, for example, belong to this category. Extensions to more complicated cases, for example, multiple particles and arbitrary surfaces, are also discussed. Copyright 1999 Academic Press.

Electrophoretic Mobility of a Concentrated Suspension of Spherical Particles

The electrophoretic behavior of concentrated spherical colloidal particles is analyzed theoretically for all levels of scaled surface potential &phi;a, taking the effect of double-layer polarization (DLP) into account. The result of numerical simulation reveals that for a very small kappaa (<0.01), kappa and a being, respectively, the reciprocal Debye length and the particle radius, or a very large kappaa (>100), using a linearized Poisson-Boltzmann equation (PBE) and neglecting the effect of DLP is reasonable; for an intermediate kappaa, appreciable deviation may result. The deviation is negative if kappaa is small, and positive if kappaa is large. The mobility against kappaa curve may have a local minimum and a local maximum. If &phi;a is low, the mobility increases with the porosity of the system under consideration, and for a fixed porosity, the mobility increases with kappaa. If &phi;a is high and kappaa is small, the effect of &phi;a (i.e., solving a nonlinear PBE) on the mobility of a particle is more significant than that of double-layer polarization, and the reverse is true if kappaa is large. For an intermediate kappaa, the effect of DLP is more significant than that of &phi;a when the porosity is high, and the reverse is true if it is low. Copyright 1999 Academic Press.

Electrophoretic Mobility of a Sphere in a Spherical Cavity

The electrophoretic behavior of a spherical particle in a spherical cavity is analyzed theoretically, taking the effect of double layer polarization into account. We show that for the case where the particle is positively charged and the cavity uncharged if the surface potential of particle is high, the variation of the mobility of the particle as a function of kappaa has a minimum, kappa and a being respectively the reciprocal Debye length and particle radius. This minimum does not appear if the effect of double layer polarization is neglected. The variation of the mobility as a function of kappaa has a minimum for a medium value of lambda (= particle radius/cavity radius); it becomes negligible if lambda is either small or large. In the case where the particle is uncharged and the cavity positively charged, if the surface potential is high, the variation of mobility as a function of kappaa has a maximum; if it is low, the mobility increases monotonically with kappaa. Here, the mobility is mainly determined by the drag force, rather than by the electric force, acting on the particle as in the case where the particle is positively charged and the cavity uncharged. If both the particle and the cavity are charged, the electrophoretic behavior of the particle can be deduced from the results of the above two cases. Copyright 1998 Academic Press.

Electrophoretic Mobility of a Spherical Particle in a Spherical Cavity

The electrophoretic mobility U of a spherical particle in a spherical cavity for the case of low electric field is estimated for an arbitrary thick electrical double layer. We show that if the particle is uncharged and the cavity negatively charged, the deviation in the mobility based on the linearized Poisson-Boltzmann equation, UL, can be serious even at a low electrical potential. In this case, the variation of the absolute deviation, |U - UL| as a function of kappaa, kappa and a being, respectively, the reciprocal Debye length and particle radius, has a maximum. The kappaa at which the maximal absolute deviation occurs increases with lambda (particle size/cavity size), and the maximal absolute deviation decreases with lambda. The latter increases with the absolute surface potential of cavity. If the particle is positively charged and the cavity uncharged, UL is sufficiently accurate if the electrical potential is low. Copyright 1997 Academic Press.

Dynamic Interactions of Two Electrical Double Layers

The unsteady-state electrical potential and the concentrations of ions between two identical, negatively-charged particles immersed in an a:b electrolyte solution are investigated. In particular, the effects of ionic strength, I, the geometric mean of the diffusivities of counterions Dcon and coions Dco, D, the separation distance between two particles, H, and the surface charge density, sigma0, on these distributions are examined. We conclude that under the following conditions a system needs a longer time for ions to reach equilibrium distributions: (a) small I, (b) small D, (c) large H, and (d) large sigma0. The rate of approach of two particles is faster if both surfaces are maintained at constant potential than if both surfaces are at constant charge density. The dynamic behavior of the relaxation of ions in the double layers has the effect of retarding the motion of particles. The deviation in the contact time between two particles predicted by an equilibrium model, which assumes that the distributions of ions in a double layer reach the Boltzmann distribution instantly, from that estimated by the corresponding dynamic model is on the order of 10%. Copyright 1997 Academic Press. Copyright 1997Academic Press

Electrostatic Potential Distribution for Spheroidal Surfaces in Symmetric Electrolyte Solutions

The electrostatic potential distribution for a charged spheroidal surface immersed in a symmetric electrolyte solution is derived. Such surfaces simulate a wide class of dispersed entities. Two types of boundary condition at the solid surface are considered, constant surface potential and constant amount of surface charges; both conductive and nonconductive surfaces are examined for the latter. The present analysis extends the conventional one-dimensional treatment on simple geometries to a two-dimensional space. A perturbation method is adopted to solve the governing Poisson-Boltzmann equation for the case of thin to moderately thick double layers. The classic results for planar and spherical surfaces can be recovered as special cases of the present analysis. The basic thermodynamic properties of the system under consideration, such as Helmholtz free energy, entropy, and surface excess, are derived. We show that using an equivalent sphere to approximate a spheroid can lead to an appreciable deviation in the prediction of the Helmholtz free energy. For a thin double layer, assuming a planar geometry will underestimate the Helmholtz free energy. Copyright 1997Academic Press

Electrostatic Interaction between Two Ion-Penetrable Charged Spheroids

The electrostatic interaction between two ion-penetrable, charged spheroidal particles is examined theoretically. These particles can assume different sizes and an arbitrary spatial orientation. The electrical potential distribution is derived analytically under the Debye-Huckle condition. The results for two interaction spheres, one spheroidal particle and a planar surface, and rigid particles covered by an ion-penetrable membrane can be recovered as the special cases of the present general problem. We show that, for a fixed center-to-center distance between two particles, regardless of their relative sizes, the interaction free energy is the greatest if their major axes lie on the same line (head-to-head), and the smallest if their major axes are perpendicular to each other but not on the same plane (perpendicular).

The Critical Coagulation Concentration of Counterions: Spherical Particles in Asymmetric Electrolyte Solutions

The ratio of the critical coagulation concentration (CCC) of counterions is evaluated for spherical particles and asymmetric electrolytes. A perturbation method is adopted to solve the Poisson-Boltzmann equation governing the electrical potential distribution of the system under consideration. On the basis of the result obtained, an approximate expression for the CCC is derived. Another approach based on the Derjaguin approximation is also used to estimate the CCC. We show that the CCC ratio of counterions is a complicated function of the valences of the ion species in the liquid phase and the sizes of particles. Depending upon the thickness of the Debye length, the CCC ratio of counterions for various combinations of electrolytes can be estimated. The classic Schulze-Hardy rule for planar particles in a symmetric electrolyte solution can be recovered as a limiting case of the present model. If the surface potential is low, the effect of curvature on the CCC ratio of counterions is negligible.

Electrical Potential Distribution for Multiple Charged Surfaces under a General Boundary Condition

The electrical potential distribution of a system containing multiple charged surfaces with a general boundary condition is investigated theoretically. Here, a surface can assume a constant potential/charge density, or an arbitrary combination of the two, i.e., a mixed boundary condition; the latter is of particular significance in practice. Typical example includes surfaces containing various ionizable functional groups, charge-regulated surfaces, dynamic surface conditions, and patchwise charged surfaces. A systematic iterative method is proposed for the resolution of the linearized Poisson-Boltzmann equation governing the electrical potential distribution of the system under consideration. The sufficient and necessary condition under which the method proposed is applicable is discussed. Since the coefficients in the expression for the boundary condition at surface can be an arbitrary function, the present problem is a generalized Robin problem. The conventional constant potential (Dirichlet) problem and constant surface charge (Neumann) problem can be recovered as special cases of the present model. A criterion is proposed to decide whether the separation distances between particles is appropriate for various approximate procedures, e.g., pairwise addition and linear superposition. We show that a system containing a large number of surfaces can be simulated by one which has relatively few surfaces.

Effect of household preparation on levels of pesticide residues in produce

In 1993, the National Academy of Sciences released a report on the effects of pesticides in the diets of infants and children, indicating that current tolerances do not take into account the eating habits and metabolism of young children. In response to that report, a study was undertaken to determine pesticide residues in raw agricultural commodities at levels below the tolerances established by the Environmental Protection Agency. The objective of the study was to determine whether normal household washing, peeling, and cooking procedures had any effect on pesticide residue levels. Low levels of pesticide residues were detected in 97 (40%) of the 243 samples analyzed. The number of samples containing detectable residues dropped to 47 (19%) after household preparation. Results indicate that residue levels in most commodities are substantially reduced after household preparation.

Electrophoretic mobility of biological cells in asymmetric electrolyte solutions

The electrophoretic mobility of a particle covered by a membrane in an a:b electrolyte solution is modeled theoretically. The membrane, which simulates the surface of a biological cell, is ion-penetrable, and carries homogeneously distributed negative fixed charges. An approximate expression for the electrophoretic mobility is derived. Based on the results of numerical simulation, we conclude the following: (1) The absolute Donnan potential increases with the concentration of the fixed charges C0, but decreases with the ionic strength I. (2) The greater the valence of cation alpha, the lower the absolute potential distribution. (3) The greater the C0, the greater the absolute mobility of a particle, magnitude of mu, and the greater the friction coefficient of the membrane phase gamma, the smaller the magnitude of mu. (4) A large I or a large a leads to a small magnitude of mu. (5) The greater the ratio (permittivity of solution/permittivity of membrane phase), the smaller the magnitude of mu. (6) For a large gamma, magnitude of mu decreases with the thickness of membrane d under the condition of constant amount of fixed charges. However, if gamma is sufficiently small, the variation of magnitude of mu as a function of d exhibits a maximum. The classic result of Smoluchowski for the electrophoretic mobility of a rigid particle can be recovered as a limiting case of the present model.

Estimation and hypothesis testing of treatment effects in animal reproductive toxicology studies

Healy (1) and Dempster et al. (8) proposed statistical methods to evaluate the treatment effects in animal reproductive toxicology research. Both methods assume homogeneous variance for the dams and the pups, respectively, in all the treatment groups. In this paper, via mixed effect modeling, we propose a method to estimate the treatment effects allowing heterogeneous variances for the dams and the pups, respectively, in different treatment groups. Covariates will also be included in the model. A procedure to test the fixed effects is also discussed. An example from an animal reproductive toxicological study is used to illustrate the procedures.

A theoretical analysis of a new drug delivery system: a cylindrical device with a vertical opening on its surface

A theoretical analysis of a proposed drug delivery device is presented. The device is of cylindrical shape with an opening on its side surface. Analytical expressions for the temporal variations in the amount of drug released and the size of the unreleased portion of the device are derived. The result of numerical simulation reveals that an approximately zero-order mechanism can be obtained, provided that the device is designed appropriately. The applicability of the analytical expressions derived is justified by examining the release of sodium salicylate embedded in polyethylene. The present work is a generalization of analyses suggested previously for some similar devices.

Fast turnaround multiresidue screen for pesticides in produce

A rapid multiresidue screen for 110 pesticides was applied to 5628 produce samples. Samples were extracted, analyzed, and evaluated within 6 1/2 h of receipt. Analyses were confirmed within a 24 h period on those samples in which a potential residue was found above the U.S. Environmental Protection Agency's tolerance level. A thorough yet quick chromatographic interpretation program is also described.

Modeling the repair of radiation-induced DNA double-strand breaks

A problem often overlooked in the study of the repair of radiation-induced DNA double-strand breads (DSBs) is the question of what the status of a regular site is in the DNA duplex immediately after a radiation treatment. Here, we suggest a mixed repair mechanism which consists of a gradual process and an instantaneous process. A comparison of the present kinetic model with those which have appeared in the literature shows that the former is a generalization of the latter. We have shown that different repair mechanisms may lead to equivalent mathematical representations. Therefore, care must be taken in interpreting the repair mechanism on the basis of the experimentally observed transient number of DSBs.

The effect of multivalent cations on adhesion time for cellular adhesion to solid surfaces

The dynamic behavior of the adhesion of a charge-regulated cell to a solid surface of constant potential is investigated. In particular, the effect of the presence of multivalent cations in the suspension medium on adhesion time is discussed. By neglecting the effect of hydrodynamic retardation and assuming that the bulk liquid phase is stagnant, we show that the presence of multivalent cations has the effect of retarding cell adhesion. At a fixed level of ionic strength, the adhesion time increases with the increase of the concentration of multivalent cations in the suspension medium, and decreases with the increase in magnitude of the Hamaker constant. For a fixed concentration of cations, the adhesion time decreases with the increase of ionic strength. The effect of the magnitude of Hamaker constant on adhesion time is appreciable if both the ionic strength and the concentration of cations are high.

A comparison of the parameter estimating procedures for the Michaelis-Menten model

The performance of four parameter estimating procedures for the estimation of the adjustable parameters in the Michaelis-Menten model, the maximum initial rate Vmax, and the Michaelis-Menten constant Km, including Lineweaver & Burk transformation (L-B), Eadie & Hofstee transformation (E-H), Eisenthal & Cornish-Bowden transformation (ECB), and Hsu & Tseng random search (H-T) is compared. The analysis of the simulated data reveals the followings: (i) Vmax can be estimated more precisely than Km. (ii) The sum of square errors, from the smallest to the largest, follows the sequence H-T, E-H, ECB, L-B. (iii) Considering the sum of square errors, relative error, and computing time, the overall performance follows the sequence H-T, L-B, E-H, ECB, from the best to the worst. (iv) The performance of E-H and ECB are on the same level. (v) L-B and E-H are appropriate for pricesly measured data. H-T should be adopted for data whose error level are high. (vi) Increasing the number of data points has a positive effect on the performance of H-T, and a negative effect on the performance of L-B, E-H, and ECB.

A kinetic analysis of the repair of radiation-induced DNA double-strand breaks

The repair of radiation-induced DNA double-strand breaks (DSBs) is analyzed kinetically. It is assumed that a fraction of the damaged sites in the DNA duplex are irreparable. The kinetic model takes the effect of radiation dose into account. The analysis of the available experimental data reveals that, although the number of irreparable DSBs is a quadratic function of radiation dose, the normalized number of irreparable DSBs correlates linearly with this variable.

A stochastic analysis of the repair of radiation-induced DNA double-strand breaks

A three-state stochastic model is described for the repair of radiation-induced double-strand breaks (DSBs) in DNA. If irradiated, a site or region in DNA is assumed to be in a potentially damaged state; this site may either become permanently damaged or be repaired after a certain period of time. The result of the analysis of the available experimental data reveals that the present two-parameter model is capable of interpreting the rapid decrease in the number of DSBs in the initial period, which cannot be predicted by previously proposed models. The stochastic analysis yields not only the temporal variation of the mean of the number of DSBs but also its variance, and therefore is a generalization of the conventional deterministic models.

A stochastic simulation of tumor growth

The growth of a tumor is described by a nonlinear stochastic representation. A systematic approach based on Taylor series expansion is adopted to solve the nonlinear master equation governing the variation of tumor weight as a function of time. The analysis of the available experimental data reveals that the growth rate of a tumor has a power law dependence on its weight.

Analytical methods for detection of nonoccupational exposure to pesticides

An analytical protocol is developed to analyze for 33 compounds in ambient air around the household, drinking water, and from dermal contact while applying pesticides. Soxhlet extraction is used on both the polyurethane foam plugs, which were used as air sample trapping media, and the gloves reflecting dermal contact. The extraction procedure of U.S. Environmental Protection Agency (EPA) Method 608 is used for water samples. A stringent gas chromatography/electron capture detection (GC/ECD) and gas chromatography/mass spectroscopy/multiple ion detection (GC/MS/MID) analytical approach parallel to the procedures of the current EPA contract laboratory program is used for analysis.

Measurement of atmospheric concentrations of common household pesticides: A pilot study

Air concentrations of 28 of the most commonly used household pesticides were measured inside nine homes in Jacksonville, Florida, and compared with corresponding outdoor levels. The households selected were sorted into three categories according to the degree of pesticide indoor usage. Personal air monitoring was also performed on one resident of each household by means of a portable sampler, which was kept with the person at all times. Five of the pesticides were found in the air inside of the majority of the homes at concentrations as high as 15 μgm(-3) (average concentrations, 12 ngm(-3) to 2.4 μgm(-3)). Indoor levels were generally one to two ordrrs of magnitude higher than surrounding outdoor air levels and personal air measurements were within ± 50% of corresponding indoor values. All samples were collected over 24-hr periods on polyurethane foam and analyzed by capillary colum gas chromatography with mass spectrometric and/or electron capture detection.

Bacterial adhesion onto particulate substrates

The adhesion of anaerobic saccharolytic bacteria onto cellulose powder and raw starch granules through scanning electron microscope were observed. The adhering bacteria had a tendency to penetrate the granule surface; colonization was observed to occur on both the surface and inside the starch granule. The inner material of the starch granules was first digested, resulting in a shell type of structure at this stage. This implied that the surface of starch granules might have a different structure from its inner material. Bacterial adhesion and substrate digestion were found to be affected by operating temperature.

Stochastic modeling of bacterial adhesion: a two-step mechanism with linear adhesion rate

Stochastic analysis of bacterial adhesion onto the surface of solid substrate is presented. Bacterial adhesion is assumed to occur in two steps: (i) a reversible adhesion between bacteria and solid surface; bacteria on the surface are weakly bound during this period, followed by (ii) an irreversible surface reaction which results in a strong binding force between bacteria and the surface; bacteria are considered to be in adhered form at this stage. The stochastic representation provides both the macroscopic and fluctuating information about the transient behavior of the phenomenon under consideration.

Kinetics of bacterial adhesion--a stochastic analysis

In a previous work (Hsu & Wang, 1986), a birth-death type of stochastic model was proposed to analyze bacterial adhesion onto the substrate surface. The model is based upon the assumption that the number of available active sites on the substrate surface is relatively large compared to that of the cells in the system. This assumption is relaxed in the present study, and thus, the problem is considered in a more rigorous manner. The transient behavior of bacterial adhesion is examined through simulation studies. It is found that the present stochastic model should be employed when the number of available active sites is less than or on the same order of magnitude as that of the cells.

Ulcerogenicity of piroxicam: an analysis of spontaneously reported data

Previous reports have suggested that piroxicam may be more ulcerogenic than other non-steroidal anti-inflammatory drugs (NSAIDs) in use. Critics have attributed this putative relation to flawed comparisons of spontaneously reported data. In this study cases of upper gastrointestinal bleeding, perforation, and ulcer reported to the Food and Drug Administration's spontaneous reporting system over 12 years were examined. Reporting rates for eight NSAIDs were compared over identical periods of their marketing life cycles. After adjustments were made for the heterogeneity in the underlying reporting rates the difference in rates between piroxicam and the other drugs was considerably reduced but piroxicam retained its top ranking among the drugs; however, large and clinically important differences in the frequency of cases of upper gastrointestinal bleeding, perforation, and ulcer between piroxicam and the rest of the NSAIDs compared probably do not exist.

The impact of the addition of naloxone on the use and abuse of pentazocine

An epidemic of abuse with "T's and blues" began in the late 1970's in which pentazocine-Talwin tablets ("T")--and the antihistamine tripelennamine (known as blues) were crushed, dissolved together, filtered, and injected intravenously. The resulting high was reported to be similar to that of heroin. In 1981, the manufacturer and the Food and Drug Administration met to discuss a possible solution. As a result, 0.5 mg of naloxone hydrochloride, a narcotic antagonist that is pharmacologically inactive at that dose orally but active if administered parenterally, was added to the tablet formulation. The reformulated product, Talwin Nx, was approved for marketing in late 1982 and introduced in the second quarter of 1983. Distribution of Talwin tablets in the United States was discontinued. The Drug Abuse Warning Network (DAWN) of the National Institute of Drug Abuse and IMS America's National Prescription Audit were used to review the use and abuse patterns of pentazocine before and after the naloxone intervention. The number of prescriptions dispensed quarterly for pentazocine products remained fairly stable from 1981 through the first quarter of 1983 and increased after the introduction of Talwin Nx. In contrast, DAWN emergency room and medical examiner mentions decreased after the product reformulation. The rates of both emergency room and medical examiner mentions per million prescriptions were substantially lower in the 2 years following the introduction of Talwin Nx (decreases of 70 percent by emergency rooms and 71 percent by medical examiners), indicating that the product reformulation successfully reduced pentazocine abuse.

Solid state fermentation of swine manures

A kinetic model for the solid state fermentation of swine manures under both aerobic and anaerobic conditions have been proposed. The rate of CO2 production is used as an indicator of the degree of stabilization of swine manures. Analysis of available experimental data suggests that the initial rate of stabilization, as measured by the product of the reaction constant and the initial activity of bacteria, increases with temperature and correlates with the initial moisture content of swine manures. The rate of deactivation of bacteria, as reflected by the deactivation rate constant, is relatively constant for low and medium temperatures (25-35 degrees C) and is fast for higher temperature (45 degrees C). The optimum operating scheme should adopt a medium high temperature (35 degrees C) and an appropriate amount of initial moisture.