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PubMed2004

Imperfect DNA lesion repair in the semiconservative quasispecies model: derivation of the Hamming class equations and solution of the single-fitness peak landscape.

This paper develops a Hamming class formalism for the semiconservative quasispecies equations with imperfect lesion repair, first presented and analytically solved in Y. Brumer and E.I. Shakhnovich (q-bio.GN/0403018, 2004). Starting from the quasispecies dynamics over the space of genomes, we derive an equivalent dynamics over the space of ordered sequence pairs. From this set of equations, we are able to derive the infinite sequence length form of the dynamics for a class of fitness landscapes defined by a master genome. We use these equations to solve for a generalized single-fitness-peak landscape, where the master genome can sustain a maximum number of lesions and remain viable. We determine the mean equilibrium fitness and error threshold for this class of landscapes, and show that when lesion repair is imperfect, semiconservative replication displays characteristics from both conservative replication and semiconservative replication with perfect lesion repair. The work presented here provides a formulation of the model which greatly facilitates the analysis of a relatively broad class of fitness landscapes, and thus serves as a convenient springboard into biological applications of imperfect lesion repair.

Animals↗
PubMed2002

A new technique for tear film fluorophotometry.

AIM: To develop a reliable and objective non-touch technique for determination of tear volume and tear secretion by means of tear film fluorophotometry. METHODS: 10 defined concentrations of sodium fluorescein were given in an artificial chamber and measured by the Fluorotron Master (Coherent Radiation Inc). A calibration line was established and the calibration equation was programmed into the Fluorotron Master computer software. In 28 patients (56 eyes) with dry eye symptoms and 15 volunteers (30 eyes) tear volume and tear secretion were then measured directly without taking a tear sample, using the new technique. RESULTS: The values obtained by the Fluorotron Master measuring 10 defined fluorescein concentrations within an artificial chamber are approximately 100 times lower than the actual concentrations. The calibration line led to a calibration equation: y = 36 + 0.01 x X. The mean tear secretion in 56 eyes of patients with dry eye symptoms was 2.48 microl/min, compared to 3.4 microl/min in healthy volunteers. The difference was statistically significant. Average tear volume was 7.0 microl in patients and 7.2 microl in healthy volunteers with no statistically significant difference. CONCLUSION: The method developed is a simple and reliable non-touch technique without the need for taking a tear sample, which makes the examination faster and more comfortable for the patient.

Adult↗
PubMed2005

Activation energy-activation volume master plots for ion transport behavior in polymer electrolytes and supercooled molten salts.

We demonstrate the use of activation energy versus activation volume "master plots" to explore ion transport in typical fragile glass forming systems exhibiting non-Arrhenius behavior. These systems include solvent-free salt complexes in poly(ethylene oxide) (PEO) and low molecular weight poly(propylene oxide) (PPO) and molten 2Ca(NO3)2.3KNO3 (CKN). Plots showing variations in apparent activation energy EA versus apparent activation volume VA are straight lines with slopes given by M = DeltaEA/DeltaVA. A simple ion transport mechanism is described where the rate determining step involves a dilatation (expressed as VA) around microscopic cavities and a corresponding work of expansion (EA). The slopes of the master plots M are equated to internal elastic moduli, which vary from 1.1 GPa for liquid PPO to 5.0 GPa for molten CKN on account of differing intermolecular forces in these materials.

Journal Article↗
PubMed1993

[Significance of psychological stress, absence of stress and resources for health promotion at the workplace].

Stress is defined as a lasting, averse situation, the avoidance of which appears to be subjectively important and where the individual is not sure of having enough ability to control it. Eustress, contrary to this, is characterized by the individual's confidence of being able to master given demands successfully. Therefore eustress can not equated with stress. One may assume that the repeated experience of mastering given demands constitutes a resource in coping with stressors. Empirical findings have shown psychic stressors to be systematically linked with individual discomfort preceding clinical symptoms. Therefore alterations to psychic stressors may be a mean of prophylaxis. Data from surveys on blue-collar workers moreover have suggested that two working conditions themselves may provide resources for coping with stressors: decision latitude and social support. Hence enlarging decision latitude and enhancing social support may be possibilities for prevention, especially in such cases, where stressors cannot (yet) be directly changed.

Adaptation, Psychological↗
PubMed2000

Evaluating porcelain color match of different porcelain shade-matching systems.

PURPOSE: This in vitro study was designed to evaluate the new ShadeEye-EX Chroma Meter and a new visual porcelain shade-matching system (Vitapan 3-D Master, Omega 900) in comparison to the traditionally used visual porcelain shade-matching system (Vita Lumin Vacuum, VMK 68). MATERIALS AND METHODS: Shade matches and porcelain fabrications on individualized shade tabs were carried out. The fabricated porcelain tabs were evaluated against the respective natural tooth using the United States Public Health Service (USPHS) criteria to determine clinically acceptable match. The tabs also were ranked according to the final-color match to the corresponding natural tooth. RESULTS: The percentage of clinically acceptable color matches were as follows: Vita Lumin Vacuum (46.67%), ShadeEye-EX (40%), and Vitapan 3-D Master (56.67%). The generalized estimating equation (alpha = 0.5) showed no statistically significant difference between systems in obtaining a clinically acceptable match (p = .5729). The chi-squared test (alpha = 0.5) showed no statistically significant difference between systems in terms of rank order (p = .5017). The two new systems do not produce color match that is better than the conventional visual porcelain shade-matching system.

Chi-Square Distribution↗
PubMed1976

Successive discrimination training with equated reinforcement frequencies: failure to obtain behavioral contrast.

In two experiments, pigeons were trained on two-component multiple schedules in which responding in one component (S(1)) was always maintained by a variable-interval schedule. In Experiment I, low response rates were reinforced in the second (S(2)) component for six master subjects. This schedule was adjusted to equate reinforcement frequencies in the two components. These subjects were compared to yoked partners, for which reinforcement in the S(2) component was made available on a variable-interval schedule whose value was determined by the master subjects. A similar procedure was used in Experiment II, where the S(2) schedule for master subjects made reinforcers contingent on the absence of responding. No evidence was found in either experiment for a behavioral contrast effect in the S(1) component attributable to response reduction in the S(2) component. A reliable contrast effect was obtained from a group of pigeons given extinction conditions in the S(2) component, which was compared to a group maintained throughout on a multiple variable-interval schedule. The results suggest that previous indications of behavioral contrast in similar situations were probably caused by uneven reinforcement distributions or reflect uncontrolled fluctuations in response rates.

Journal Article↗
PubMed2005

The mediating role of self-efficacy in the development of entrepreneurial intentions.

The purpose of this study was to investigate the mediating role of self-efficacy in the development of students' intentions to become entrepreneurs. The authors used structural equation modeling with a sample of 265 master of business administration students across 5 universities to test their hypotheses. The results showed that the effects of perceived learning from entrepreneurship-related courses, previous entrepreneurial experience, and risk propensity on entrepreneurial intentions were fully mediated by entrepreneurial self-efficacy. Contrary to expectations, gender was not mediated by self-efficacy but had a direct effect such that women reported lower entrepreneurial career intentions. The authors discuss practical implications and directions for future research.

Adult↗
PubMed1987

Biogeochemical Conditions Favoring Magnetite Formation during Anaerobic Iron Reduction.

Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environment, produced magnetite when cultured in combinations but not when cultured alone in synthetic iron oxyhydroxide medium. When glucose was added as a carbon source, the pH of the medium decreased (to 5.5) and no magnetite was formed. When the same growth medium without glucose was used, the pH increased (to 8.5) and magnetite was formed. In both cases, Fe was released into the growth medium. Geochemical equilibrium equations with E(h) and pH as master variables were solved for the concentrations of iron and inorganic carbon that were observed in the system. Magnetite was predicted to be the dominant iron oxide formed at high pHs, while free Fe or siderite were the dominant forms of iron expected at low pHs. Thus, magnetite formation occurs because of microbial alteration of the local E(h) and pH conditions, along with concurrent reduction of ferric iron (direct biological reduction or abiological oxidation-reduction reactions).

Journal Article↗
PubMed2004

Extension of equations for predicting viscosity parameters with whole body bioelectrical impedance to a sedentary population.

In a previous paper we determined predictive equations for predicting viscosity parameters with whole body Bioelectrical impedance (BIA) in athletes. We have tried to extend this analysis to a sedentary population. 36 sedentary obese or insulin resistant patients (40.36+/-2.30 years; 85.77+/-3.54 kg; 165.93+/-1.56 cm) were enrolled into this study. Body composition was assessed with a multifrequency bioelectrical impedancemeter Dietosystem Human IM Scan that uses low intensity at the following frequencies: 1, 5, 10, 50 and 100 kHz. Analysis was performed with the software Master 1.0 that gives the choice among 25 published equations for body composition calculation. Viscometric measurements were done at 1000 s(-1) with a falling ball viscosimeter (MT 90 Medicatest). Hematocrit was measured with microcentrifuge. Two hemorheological parameters were independently correlated with impedance (Z) measurements at 50 kHz: whole blood viscosity (WBV) (r=0.541, p=0.01) and hematocrit (Hct) (r=-0.686, p=0.01). New equations slightly different from those we report in the previous paper were found. These findings confirm our previous reports of relationships between whole body electric properties and factors of blood viscosity in athletes and allow the use of BIA to a sedentary population. Obviously, extension of this study will be needed to determine if BIA can be used to generalize predictive equations in both sedentary and trained individuals.

Adult↗
PubMed1999

Differences in whole body measurements by DXA-scanning using two Lunar DPX-L machines.

OBJECTIVE: To compare bone mineral and body composition results of two dual-energy X-ray absorptiometry (DXA) instruments from the same manufacturer. SETTINGS: The Medical departments of Sahlgrenska University Hospital, Göteborg and University Hospital, Uppsala, Sweden. DESIGN: Unique aluminium spine phantoms (Phant A and B) delivered with each DXA machine (DXA-A and DXA-B) were cross-checked on the other machine by using the 'AP spine mode'. Eight adolescents were examined on both instruments within 5 h to ascertain total body variables by using standard, as well as extended, modes of analysis. All these double-examinations were undertaken on two occasions, before and after exchange of a detector on the DXA-B. SUBJECTS: Four males and four females aged 15.4-19.2 y with normal body weights, were examined on both occasions. On each occasion, the first examination was performed in Göteborg on four individuals and in Uppsala on four individuals. RESULTS: On the first occasion the phantom measurements resulted in much lower bone mineral density (BMD) values on the DXA-B than on the DXA-A. Later it was detected that a so-called R-value and the corresponding '%-fat' value were out of range on the DXA-B. After exchange of detector, the difference in phantom BMD-values between the two machines had diminished. On the first occasion in vivo BMD values were lowest on the DXA-B (P < 0.01), while on the second occasion they were significantly lower on the DXA-A (P < 0.05). Soft tissue differences were greater after detector exchange and as compared to DXA-A, DXA-B underestimated body fat by 3.5 kg (13.2 vs 9.7 kg, P < 0.001) and overestimated lean tissue mass by 3.8 kg (47.1 vs 50.9 kg, P < 0.001) on the second occasion. CONCLUSIONS: The differences in results between two apparently identical Lunar DPX-L machines were not acceptable. In multicenter studies, it may be necessary to standardise results of participating machines into results of one machine by means of regression equations obtained by examining subsamples of individuals on one master machine and other participating instruments.

Absorptiometry, Photon↗
PubMed2004

New approaches to shock and trauma research: learning from multidisciplinary exchange.

BACKGROUND: Our understanding of the complex network of pathophysiology after multiple injury is limited. It is proposed to overcome the limitations of the traditional linear reductionism approach by merging the expertise of biology and medicine with other disciplines such as mathematics, physics and computer science. METHODS: We organized a two-days-workshop, where surgeons and surgical scientists explained the problem from the medical (pathophysiological) perspective to a well selected group of German applied mathematicians and computer scientists. Vice versa they presented and discussed their approaches to complex system analysis. RESULTS AND CONCLUSIONS: Physicians found it difficult to develop questions and concepts that go beyond the classic mechanistic thinking. Well formulated questions are the most important prerequisites for successful application of mathematical tools. The possibilities and borders of Artificial Neural Networks (ANN), Hidden Markow Models (HMM), Agent Based Models (ABM), differential equations for problem solving were discussed. There is no master model for all aspects of pathophysiology, however, application of the models to specific problems is mandatory. CONCLUSIONS: Future breakthroughs can only be expected if we overcome language problems between disciplines. This cross talk was considered by all participants as a most important step.

Communication↗
PubMed2002

Synchronization: stability and duration time.

We consider the problem of stability and duration of the synchronization process between self-excited oscillators, both in their regular and chaotic states. Making use of the properties of Hill equation describing the deviation between the slave and the master, we derive the stability conditions and expressions of the synchronization time. A fairly good agreement is obtained between the analytical and numerical results.

Journal Article↗
PubMed2003

General stability analysis of synchronized dynamics in coupled systems.

We consider the stability of synchronized states (including equilibrium point, periodic orbit, or chaotic attractor) in arbitrarily coupled dynamical systems (maps or ordinary differential equations). We develop a general approach, based on the master stability function and Gershgörin disk theory, to yield constraints on the coupling strengths to ensure the stability of synchronized dynamics. Systems with specific coupling schemes are used as examples to illustrate our general method.

Journal Article↗
PubMed2005

Interconversion of mechanical and dielectrical relaxation measurements for dicyclohexylmethyl-2-methyl succinate.

A comparison between results of dielectrical relaxation and dynamic mechanical spectroscopies is carried out for the alpha-relaxation of the ester dicyclohexyl methyl-2-methyl succinate (DCMMS). The results for the dielectric permittivity and the shear modulus measurements are presented according to the empirical Havriliak-Negami (HN) equation. By using the time-temperature principle a master curve in each case was obtained for several temperatures. The comparative analysis presented here is based on the assumption of a relationship between rotational and shear viscosities. The former one is associated to the dielectrical relaxation, whereas the latter is associated to mechanical relaxation. Both viscosities are not necessarily equal in general, and we assume that the difference between them is an important factor to appropriately compare the dielectrical and mechanical results.

Journal Article↗
PubMed2004

Master curves for gas amplification in low vacuum and environmental scanning electron microscopy.

The concept of universal amplification profiles for gas cascade amplification of signals in low vacuum and environmental scanning electron microscopes is demonstrated both experimentally and theoretically using water vapor. For a given gas, cascade amplification gain profiles can be plotted onto a single master curve where the independent reduced parameter is the ratio of pressure to amplification field strength. When plotted in this fashion, both desired secondary electron and spurious background signal components fall onto respective master curves, with the amplitude being a function of anode bias only. These master curves can be described by simple Townsend Gas Capacitor equations using only two gas-specific parameters. As long as single scattering conditions apply, this approach allows for simplified, direct comparison of the gain characteristics of different gases and allows more intelligent selection of imaging conditions. The utility of treating signal amplification in this manner is demonstrated through a series of images collected under a variety of conditions, but with the ratio of pressure to amplification field strength kept constant. In practice, the range of operational parameter space in which this description can be applied to imaging is limited, as images typically have a mixture of secondary and backscattered contributions.

Journal Article↗
PubMedDate not supplied

Multielemental analysis of food and agricultural matrixes by inductively coupled plasma-mass spectrometry.

The suitability of quadrupole inductively coupled plasma-mass spectrometry (ICP-MS) for multielemental analysis of food following microwave closed vessel digestion of samples was evaluated in relation to analytical challenges presented by some major food and agricultural matrixes. Fifteen key analytes (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, Sn, V, Zn) were determined in 9 reference materials representative of 3 major groups of staple foods (cereals, seafood, and meat). For all measurements, the method of external calibration was used and Rh was selected as internal standard. Matrix-induced interferences were evaluated for each material, and suitable methods to overcome them were applied. Spectral interferences caused by C, Cl, and Ca content of digestates were quantitated and corrected by entering a simple system of mathematical correction equations into the instrument software before each analytical run. Full mastering of interferences together with adoption of a series of measures to control the reliability of analytical measurements produced accurate results for all the analytes. A standard analytical protocol is outlined for the benefit of both research and routine high-throughput laboratories that perform ICP-MS analyses of food.

Animals↗
PubMedDate not supplied

Personality characteristics, body image and social attitudes of organ transplant donors versus nondonors.

Thirty adults willing their body at death to medical science were compared on a number of personality variables with 30 nondonors, both groups equated for age, education, and socioeconomic status. Donors are internally directed, masters of their fate; nondonors rely on chance or luck to explain outcome. A more definite body image characterizes donors while nondonors are more concerned about body integrity. Donors accept their mortality while nondonors worry more about death. At the fantasy level donors display more hostility, depression, and guilt, and the prospective act of donation may represent an attempt at atonement. Donation represents a convenient and socially acceptable outlet for expression of humanitarian needs by donors.

Adult↗
PubMed2002

Synchronization of chaotic systems with different order.

The chaotic synchronization of third-order systems and second-order driven oscillator is studied in this paper. Such a problem is related to synchronization of strictly different chaotic systems. We show that dynamical evolution of second-order driven oscillators can be synchronized with the canonical projection of a third-order chaotic system. In this sense, it is said that synchronization is achieved in reduced order. Duffing equation is chosen as slave system whereas Chua oscillator is defined as master system. The synchronization scheme has nonlinear feedback structure. The reduced-order synchronization is attained in a practical sense, i.e., the difference e=x(3)-x(1)(') is close to zero for all time t> or =t(0)> or =0, where t(0) denotes the time of the control activation.

Journal Article↗