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Search Results: 1 - 10 of 7578 matches for " Tomá? Albrecht "
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Variation in Apical Hook Length Reflects the Intensity of Sperm Competition in Murine Rodents
Martin ?andera, Tomá? Albrecht, Pavel Stopka
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0068427
Abstract: Background Post-copulatory sexual selection has been shown to shape morphology of male gametes. Both directional and stabilizing selection on sperm phenotype have been documented in vertebrates in response to sexual promiscuity. Methodology Here we investigated the degree of variance in apical hook length and tail length in six taxa of murine rodents. Conclusions Tail sperm length and apical hook length were positively associated with relative testis mass, our proxy for levels of sperm competition, thus indicating directional post-copulatory selection on sperm phenotypes. Moreover, our study shows that increased levels of sperm competition lead to the reduction of variance in the hook length, indicating stabilizing selection. Hence, the higher risk of sperm competition affects increasing hook length together with decreasing variance in the hook length. Species-specific post-copulatory sexual selection likely optimizes sperm morphology.
The Dominant Role of the Chemical Potential for Driving Currents in Oceans and Air  [PDF]
Albrecht Elsner
Journal of Geoscience and Environment Protection (GEP) , 2014, DOI: 10.4236/gep.2014.23016
Abstract:

Applying the thermodynamic zeros of the entropy  and internal energy  of the gas mass  in the volume

Thermodynamic Fit Functions of the Two-Phase Fluid and Critical Exponents  [PDF]
Albrecht Elsner
Engineering (ENG) , 2014, DOI: 10.4236/eng.2014.612076
Abstract: Two-phase fluid properties such as entropy, internal energy, and heat capacity are given by thermodynamically defined fit functions. Each fit function is expressed as a temperature function in terms of a power series expansion about the critical point. The leading term with the critical exponent dominates the temperature variation between the critical and triple points. With β being introduced as the critical exponent for the difference between liquid and vapor densities, it is shown that the critical exponent of each fit function depends (if at all) on β. In particular, the critical exponent of the reciprocal heat capacity c﹣1 is α=1-2β and those of the entropy s and internal energy u are 2β, while that of the reciprocal isothermal compressibility κ﹣1T is γ=1. It is thus found that in the case of the two-phase fluid the Rushbrooke equation conjectured α + 2β + γ=2 combines the scaling laws resulting from the two relations c=du/dT and κT=dlnρ/dp. In the context with c, the second temperature derivatives of the chemical potential μ and vapor pressure p are investigated. As the critical point is approached, ﹣d2μ/dT2 diverges as c, while d2p/dT2 converges to a finite limit. This is explicitly pointed out for the two-phase fluid, water (with β=0.3155). The positive and almost vanishing internal energy of the one-phase fluid at temperatures above and close to the critical point causes conditions for large long-wavelength density fluctuations, which are observed as critical opalescence. For negative values of the internal energy, i.e. the two-phase fluid below the critical point, there are only microscopic density fluctuations. Similar critical phenomena occur when cooling a dilute gas to its Bose-Einstein condensate.
Thermodynamic Equilibrium of the Saturated Fluid with a Free Surface Area and the Internal Energy as a Function of the Phase-Specific Volumes and Vapor Pressure  [PDF]
Albrecht Elsner
Engineering (ENG) , 2015, DOI: 10.4236/eng.2015.79053
Abstract: This study is concerned with describing the thermodynamic equilibrium of the saturated fluid with and without a free surface area A. Discussion of the role of A as system variable of the interface phase and an estimate of the ratio of the respective free energies of systems with and without A show that the system variables\"\" given by Gibbs suffice to describe the volumetric properties of the fluid. The well-known Gibbsian expressions for the internal energies of the two-phase fluid, namely \"\" for the vapor\"\" and for the condensate (liquid or solid), only differ with respect to the phase-specific volumes\"\" and \"\". The saturation temperature T, vapor presssure p, and chemical potential\"\" are intensive parameters, each of which has the same value everywhere within the fluid, and hence are phase-independent quantities. If one succeeds in representing \"\" as a function of \"\" and \"\" , then the internal energies can also be described by expressions that only differ from one another with respect to their dependence on\"\" and \"\". Here it is shown that \"\" can be uniquely expressed by the volume function\"\" . Therefore, the internal energies can be represented explicitly as functions of the vapor pressure and volumes of the saturated vapor and condensate and are absolutely determined. The hitherto existing problem of applied thermodynamics, calculating the internal energy from the measurable quantities T, p,\"\" , and \"\" , is thus solved. The same method applies to the calculation of the entropy,
Absolute Internal Energy of the Real Gas  [PDF]
Albrecht Elsner
Engineering (ENG) , 2017, DOI: 10.4236/eng.2017.94020
Abstract: The internal energy U of the real, neutral-gas particles of total mass M in the volume V can have positive and negative values, whose regions are identified in the state chart of the gas. Depending on the relations among gas temperature T, pressure p and mass-specific volume v=V/M, the mass exists as a uniform gas of freely-moving particles having positive values U or as more or less structured matter with negative values U. In the regions U>0?above the critical point [Tc , pc , vc] it holds that p(T,v)>pc and v>vc, and below the critical point it holds that p(T,v)c and v>vv , where vv is the mass-specific volume of saturated vapor. In the adjacent regions with negative internal energy values U<0 the mean distances between particles are short enough to yield negative energy contributions to U?due to interparticle attraction that exceeds the thermal, positive energy contributions due to particle motion. The critical isochor vc is the line of equal positive and negative energy contributions and thus represents a line of vanishing internal energy ?U=0. At this level along the critical isochor the ever present microscopic fluctuations in energy and density become macroscopic fluctuations as the pressure decreases on approaching the critical point; these are to be observed in experiments on the critical opalescence. Crossing the isochor vc from U>0 to U<0, the change in energy ΔU>0 happens without any discontinuity. The saturation line vv also separates the regions between U>0 and U<0 , but does not represent a line U=0. The internal-energy values of saturated vapor Uv and condensate Ui can be determined absolutely as functions of vapor pressure p and densities (M/V)v and (M/V)i , repectively,
Absolute Reference Values of the Real Gas  [PDF]
Albrecht Elsner
Engineering (ENG) , 2018, DOI: 10.4236/eng.2018.105019
Abstract: With his publication in 1873 [1] J. W. Gibbs formulated the thermodynamic theory. It describes almost all macroscopically observed properties of matter and could also describe all phenomena if only the free energy U - ST were explicitly known numerically. The thermodynamic uniqueness of the free energy obviously depends on that of the internal energy U and the entropy S, which in both cases Gibbs had been unable to specify. This uncertainty, lasting more than 100 years, was not eliminated either by Nernst’s hypothesis S = 0 at T = 0. This was not achieved till the advent of additional proof of the thermodynamic relation U = 0 at T = Tc. It is noteworthy that from purely thermodynamic consideration of intensive and extensive quantities it is possible to derive both Gibbs’s formulations of entropy and internal energy and their now established absolute reference values. Further proofs of the vanishing value of the internal energy at the critical point emanate from the fact that in the case of the saturated fluid both the internal energy and its phase-specific components can be represented as functions of the evaporation energy. Combining the differential expressions in Gibbs’s equation for the internal energy, d(μ/T)/d(1/T) and d(p/T)/d(1/T), to a new variable d(μ/T)/d(p/T) leads to a volume equation with the lower limit vc as boundary condition. By means of a variable transformation one obtains a functional equation for the sum of two dimensionless variables, each of them being related to an identical form of local interaction forces between fluid particles, but the different particle densities in the vapor and liquid spaces produce different interaction effects. The same functional equation also appears in another context relating to the internal energy. The solution of this equation can be given in analytic form and has been published [2] [3]. Using the solutions emerging in different sets of problems, one can calculate absolutely the internal energy as a function of temperature-dependent, phase-specific volumes and vapor pressure.
An Alternative Theoretical Approach to Escape Decision-Making: The Role of Visual Cues
Veronika Jav?rková, Arno?t Leo? ?izling, Jakub Kreisinger, Tomá? Albrecht
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032522
Abstract: Escape enables prey to avoid an approaching predator. The escape decision-making process has traditionally been interpreted using theoretical models that consider ultimate explanations based on the cost/benefit paradigm. Ultimate approaches, however, suffer from inseparable extra-assumptions due to an inability to accurately parameterize the model's variables and their interactive relationships. In this study, we propose a mathematical model that uses intensity of predator-mediated visual stimuli as a basic cue for the escape response. We consider looming stimuli (i.e. expanding retinal image of the moving predator) as a cue to flight initiation distance (FID; distance at which escape begins) of incubating Mallards (Anas platyrhynchos). We then examine the relationship between FID, vegetation cover and directness of predator trajectory, and fit the resultant model to experimental data. As predicted by the model, vegetation concealment and directness of predator trajectory interact, with FID decreasing with increased concealment during a direct approach toward prey, but not during a tangential approach. Thus, we show that a simple proximate expectation, which involves only visual processing of a moving predator, may explain interactive effects of environmental and predator-induced variables on an escape response. We assume that our proximate approach, which offers a plausible and parsimonious explanation for variation in FID, may serve as an evolutionary background for traditional, ultimate explanations and should be incorporated into interpretation of escape behavior.
MHC Class IIB Exon 2 Polymorphism in the Grey Partridge (Perdix perdix) Is Shaped by Selection, Recombination and Gene Conversion
Marta Promerová, Tereza Králová, Anna Bryjová, Tomá? Albrecht, Josef Bryja
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0069135
Abstract: Among bird species, the most studied major histocompatibility complex (MHC) is the chicken MHC. Although the number of studies on MHC in free-ranging species is increasing, the knowledge on MHC variation in species closely related to chicken is required to understand the peculiarities of bird MHC evolution. Here we describe the variation of MHC class IIB (MHCIIB) exon 2 in a population of the Grey partridge (Perdix perdix), a species of high conservation concern throughout Europe and an emerging galliform model in studies of sexual selection. We found 12 alleles in 108 individuals, but in comparison to other birds surprisingly many sites show signatures of historical positive selection. Individuals displayed between two to four alleles both on genomic and complementary DNA, suggesting the presence of two functional MHCIIB loci. Recombination and gene conversion appear to be involved in generating MHCIIB diversity in the Grey partridge; two recombination breakpoints and several gene conversion events were detected. In phylogenetic analysis of galliform MHCIIB, the Grey partridge alleles do not cluster together, but are scattered through the tree instead. Thus, our results indicate that the Grey partridge MHCIIB is comparable to most other galliforms in terms of copy number and population polymorphism.
Study of electromagnetic backgrounds in the 25-300 MHz frequency band at the South Pole
Jan Auffenberg,Dave Besson,Tom Gaisser,Klaus Helbing,Timo Karg,Albrecht Karle,Ilya Kravchenko
Physics , 2010,
Abstract: Extensive air showers are detectable by radio signals with a radio surface detector. A promising theory of the dominant emission process is the coherent synchrotron radiation emitted by e+ e- shower particles in the Earth's magnetic field (geosynchrotron effect). A radio air shower detector can extend IceTop, the air shower detector on top of IceCube. This could increase the sensitivity of IceTop to higher shower energies and for inclined showers significantly. Muons from air showers are a major part of the background of the neutrino telescope IceCube. Thus a surface radio air shower detector could act as a veto detector for this muonic background. Initial radio background measurements with a single antenna in 2007 revealed a continuous electromagnetic background promising a low energy threshold of radio air shower detection. However, short pulsed radio interferences can mimic real signals and have to be identified in the frequency range of interest. These properties of the electromagnetic background was being measured at the South Pole during the Antarctic winter 2009 with two different types of surface antennas. In total four antennas are placed at distances ranging up to 400m from each other. In 2010 a small eight channel surface detector will test an amplitude threshold self trigger strategy with large dipole antennas on the South Pole snow ground. The installation will be described.
Cerebrospinal Fluid Magnesium Level in Different Neurological Disorders  [PDF]
Carl-Albrecht Haensch
Neuroscience & Medicine (NM) , 2010, DOI: 10.4236/nm.2010.12009
Abstract: Magnesium (Mg) is an essential cofactor for many enzymatic reactions, especially those involved in energy metabolism. The aim of the present study was to determine the CSF concentration of Mg in various neurological disorders (n = 72) and in healthy subjects (n = 75). The control group included 35 males and 40 females, aged 16-89 years (mean age 53 years) who were subjected to a lumbar puncture for diagnostic reasons. The CSF examination was normal mainly as concerns the macroscopically examination, the leukocyte count and the protein level. The determination of Mg was performed with xylidyl-blue photometry. Our normal CSF Mg mean value was 0.97 ± 0.08 mmol/l (range 0.6-1.4 mmol/l). In the group of patients (n = 11) with convulsive seizures a slightly but significantly lower Mg were revealed (0.92 ± 0.03 mmol/l; p = 0.001; paired two-tailed Student’s t-tests). No statistically significant change of CSF Mg levels was noted in patients suffering from alcohol withdrawal syndrome, multiple sclerosis or Bell’s palsy. Our results indi-cate that magnesium deficiency may play a role for seizure manifestation even in patients with a moderate low Mg without neurological signs. Low CSF magnesium is associated with epilepsy, further studies may determine the influ-ence of anti-epileptic drug therapy on CSF magnesium levels.
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