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Search Results: 1 - 10 of 149760 matches for " Igor B. Mekjavic "
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New Onset of Constipation during Long-Term Physical Inactivity: A Proof-of-Concept Study on the Immobility-Induced Bowel Changes
Paola Iovino, Giuseppe Chiarioni, Giancarlo Bilancio, Massimo Cirillo, Igor B. Mekjavic, Rado Pisot, Carolina Ciacci
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0072608
Abstract: Background The pathophysiological mechanisms underlining constipation are incompletely understood, but prolonged bed rest is commonly considered a relevant determinant. Aims Our primary aim was to study the effect of long-term physical inactivity on determining a new onset of constipation. Secondary aim were the evaluation of changes in stool frequency, bowel function and symptoms induced by this prolonged physical inactivity. Methods Ten healthy men underwent a 7-day run-in followed by 35-day study of experimentally-controlled bed rest. The study was sponsored by the Italian Space Agency. The onset of constipation was evaluated according to Rome III criteria for functional constipation. Abdominal bloating, flatulence, pain and urgency were assessed by a 100mm Visual Analog Scales and bowel function by adjectival scales (Bristol Stool Form Scale, ease of passage of stool and sense of incomplete evacuation). Daily measurements of bowel movements was summarized on a weekly score. Pre and post bed rest Quality of Life (SF-36), general health (Goldberg’s General Health) and depression mood (Zung scale) questionnaires were administered. Results New onset of functional constipation fulfilling Rome III criteria was found in 60% (6/10) of participants (p=0.03). The score of flatulence significantly increased whilst the stool frequency significantly decreased during the week-by-week comparisons period (repeated-measures ANOVA, p=0.02 and p=0.001, respectively). Stool consistency and bowel symptoms were not influenced by prolonged physical inactivity. In addition, no significant changes were observed in general health, in mood state and in quality of life at the end of bed rest Conclusions Our results provide evidence that prolonged physical inactivity is relevant etiology in functional constipation in healthy individuals. The common clinical suggestion of early mobilization in bedridden patients is supported as well.
Exercise Training during Normobaric Hypoxic Confinement Does Not Alter Hormonal Appetite Regulation
Tadej Debevec, Elizabeth J. Simpson, Ian A. Macdonald, Ola Eiken, Igor B. Mekjavic
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0098874
Abstract: Background Both exposure to hypoxia and exercise training have the potential to modulate appetite and induce beneficial metabolic adaptations. The purpose of this study was to determine whether daily moderate exercise training performed during a 10-day exposure to normobaric hypoxia alters hormonal appetite regulation and augments metabolic health. Methods Fourteen healthy, male participants underwent a 10-day hypoxic confinement at ~4000 m simulated altitude (FIO2 = 0.139±0.003%) either combined with daily moderate intensity exercise (Exercise group; N = 8, Age = 25.8±2.4 yrs, BMI = 22.9±1.2 kg·m?2) or without any exercise (Sedentary group; N = 6 Age = 24.8±3.1 yrs, BMI = 22.3±2.5 kg·m?2). A meal tolerance test was performed before (Pre) and after the confinement (Post) to quantify fasting and postprandial concentrations of selected appetite-related hormones and metabolic risk markers. 13C-Glucose was dissolved in the test meal and 13CO2 determined in breath samples. Perceived appetite ratings were obtained throughout the meal tolerance tests. Results While body mass decreased in both groups (?1.4 kg; p = 0.01) following the confinement, whole body fat mass was only reduced in the Exercise group (?1.5 kg; p = 0.01). At Post, postprandial serum insulin was reduced in the Sedentary group (?49%; p = 0.01) and postprandial plasma glucose in the Exercise group (?19%; p = 0.03). Fasting serum total cholesterol levels were reduced (?12%; p = 0.01) at Post in the Exercise group only, secondary to low-density lipoprotein cholesterol reduction (?16%; p = 0.01). No differences between groups or testing periods were noted in fasting and/or postprandial concentrations of total ghrelin, peptide YY, and glucagon-like peptide-1, leptin, adiponectin, expired 13CO2 as well as perceived appetite ratings (p>0.05). Conclusion These findings suggest that performing daily moderate intensity exercise training during continuous hypoxic exposure does not alter hormonal appetite regulation but can improve the lipid profile in healthy young males.
Impulse Spatial-Temporal Domains in Semiconductor Laser with Feedback  [PDF]
Igor B. Krasnyuk
Journal of Applied Mathematics and Physics (JAMP) , 2016, DOI: 10.4236/jamp.2016.49180
Abstract: An initial value boundary problem for system of diffusion equations with delay arguments and dynamic nonlinear boundary conditions is considered. The problem describes evolution of the carrier density and the radiation density in the semiconductor laser or laser diodes with “memory” and with feedback. It is shown that the boundary problem can be reduced to a system of difference equations with continuous time. For large times, solutions of these equations tend to piecewise constant asymptotic periodic wave functions which represent chain of shock waves with finite or infinite points of discontinuities on a period. Applications to the optical systems with linear media and nonlinear surface optical properties with feedback have been done. The results are compared with the experiment.
Organizing the Vertebrate Embryo—A Balance of Induction and Competence
Igor B. Dawid
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.0020127
Abstract:
Protein sequence alignment with family-specific amino acid similarity matrices
Igor B Kuznetsov
BMC Research Notes , 2011, DOI: 10.1186/1756-0500-4-296
Abstract: I utilize a comprehensive set of reference alignments obtained from structural superposition of homologous and analogous proteins to design a quantitative statistical framework for evaluating the performance of alignment scoring functions in global pairwise sequence alignment. This framework is applied to study how existing general-purpose amino acid similarity matrices perform on individual protein families and structural folds, and to compare them to family-specific and fold-specific matrices derived in this work. I describe an adaptive alignment procedure that automatically selects an appropriate similarity matrix and optimized gap penalties based on the properties of the sequences being aligned.The results of this work indicate that using family-specific similarity matrices significantly improves the quality of the alignment of homologous sequences over the traditional sequence alignment based on a single general-purpose similarity matrix. However, using fold-specific similarity matrices can only marginally improve sequence alignment of proteins that share the same structural fold but do not share a common evolutionary origin. The family-specific matrices derived in this work and the optimized gap penalties are available at http://taurus.crc.albany.edu/fsm webcite.Pairwise alignment of amino acid sequences is a cornerstone sequence comparison method used in a variety of computational applications [1-4]. A mathematically rigorous and computationally efficient way of finding optimal global [5] and local [6] alignments for a given pair of sequences is provided by dynamic programming. The outcome of a dynamic programming procedure applied to align amino acid sequences critically depends on the alignment scoring function used by this procedure [7,8]. Therefore, for a specific alignment problem one needs a way of selecting the best performing scoring function [7-9]. The traditional alignment scoring function most commonly used in dynamic programming consists of an ami
Organizing the Vertebrate Embryo—A Balance of Induction and Competence
Igor B Dawid
PLOS Biology , 2004, DOI: 10.1371/journal.pbio.0020127
Abstract:
Mechanisms of geometrical seismic attenuation
Igor B. Morozov
Annals of Geophysics , 2011, DOI: 10.4401/ag-4780
Abstract: In several recent reports, we have explained the frequency dependence of the apparent seismic quality-factor (Q) observed in many studies according to the effects of geometrical attenuation, which was defined as the zero-frequency limit of the temporal attenuation coefficient. In particular, geometrical attenuation was found to be positive for most waves traveling within the lithosphere. Here, we present three theoretical models that illustrate the origin of this geometrical attenuation, and we investigate the causes of its preferential positive values. In addition, we discuss the physical basis and limitations of both the conventional and new attenuation models. For waves in media with slowly varying properties, geometrical attenuation is caused by variations in the wavefront curvature, which can be both positive (for defocusing) and negative (for focusing). In media with velocity/density contrasts, incoherent reflectivity leads to geometrical-attenuation coefficients which are proportional to the mean squared reflectivity and are always positive. For coherent reflectivity, the geometrical attenuation is approximately zero, and the attenuation process can be described according to the concept of scattering Q . However, the true meaning of this parameter is in describing the mean reflectivity within the medium, and not that of the traditional resonator quality factor known in mechanics. The general conclusion from these models is that non-zero and often positive levels of geometrical attenuation are common in realistic, heterogeneous media, both observationally and theoretically. When transformed into the conventional Q-factor form, this positive geometrical attenuation leads to Q values that quickly increase with frequency. These predictions show that the positive frequency-dependent Q observed in many datasets might represent artifacts of the transformations of the attenuation coefficients into Q.
Quantum Non-Demolition Detection of Polar Molecule Complexes: Dimers, Trimers, Tetramers
Igor B. Mekhov
Physics , 2011, DOI: 10.1088/1054-660X/23/1/015501
Abstract: The optical nondestructive method for in situ detection of the bound states of ultracold polar molecules is developed. It promises a minimally destructive measurement scheme up to a physically exciting quantum non-demolition (QND) level. The detection of molecular complexes beyond simple pairs of quantum particles (dimers, known, e.g., from the BEC-BCS theory) is suggested, including three-body (trimers) and four-body (tertramers) complexes trapped by one-dimensional tubes. The intensity of scattered light is sensitive to the molecule number fluctuations beyond the mean-density approximation. Such fluctuations are very different for various complexes, which leads to radically different light scattering. This type of research extends "quantum optics of quantum gases" to the field of ultracold molecules. Merging the quantum optical and ultracold gas problems will advance the experimental efforts towards the study of the light-matter interaction at its ultimate quantum level, where the quantizations of both light and matter are equally important.
Nonlinear relationships between atmospheric aerosol and its gaseous precursors: Analysis of long-term air quality monitoring data by means of neural networks
Igor B. Konovalov
Physics , 2002,
Abstract: The nonlinear features of the relationships between concentrations of aerosol and volatile organic compounds (VOC) and oxides of nitrogen (NOx) in urban environments are derived directly from data of long-term routine measurements of NOx, VOC, and total suspended particulate matter (PM). The main idea of the method used for the analysis is creation of special empirical models based on artificial neural networks. These models which are in essence the nonlinear extension of commonly used linear statistical models are believed to provide the best fit for the real (nonlinear) PM-NOx-VOC relationships under different atmospheric conditions. It is believed that such models may be useful in context of various scientific and practical problems concerning atmospheric aerosols. The method is demonstrated by the example of two empirical models created with independent data-sets collected at two air quality monitoring stations at South Coast Air Basin, California. It is shown that in spite of considerable distance between the monitoring stations (more than 50 km) and thus substantially different environmental conditions, the empirical models manifest several common qualitative features. Specifically, it is found that, under definite conditions, the decrease of the level of NOx or VOC may lead to the increase of mass concentration of aerosol. It is argued that these features are caused by the nonlinear dependence of hydroxyl radical on VOC and NOx.
On ramification theory in the imperfect residue field case
Igor B. Zhukov
Mathematics , 2002, DOI: 10.1070/SM2003v194n12ABEH000785
Abstract: We consider the class of complete discretely valued fields such that the residue field is of prime characteristic p and the cardinality of a $p$-base is 1. This class includes two-dimensional local and local-global fields. A new definition of ramification filtration for such fields is given. It appears that a Hasse-Herbrand type functions can be defined with all the usual properties. Therefore, a theory of upper ramification groups, as well as the ramification theory of infinite extensions, can be developed. Next, we consider an equal characteristic two-dimensional local field $K$. We introduce some filtration on the second K-group of a given field. This filtration is other than the filtration induced by the valuation. We prove that the reciprocity map of two-dimensional local class field theory identifies this filtration with the ramification filtration.
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