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Search Results: 1 - 10 of 326080 matches for " S. Albrecht "
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OBSERVATIONS OF THE B[E] STAR MWC 349 WITH MID-INFRARED INTERFEROMETRY
A. Quirrenbach,S. Albrecht
Revista mexicana de astronomía y astrofísica , 2010,
Abstract: MWC349A es probablemente una estrella masiva joven rodeada por un disco y un fuerte viento ionizado desde la super cie del disco. Las caracter sticas m s espectaculares del disco de MWC349A son l neas m ser y l ser de recombinaci n del hidr geno en longitudes de onda milim trica, sub-milim trica y de IR-medio. Hemos conducido observaciones de MWC349A con el instrumento MIDI del VLTI a 10 um. Las visibilidades en el continuo muestran la rma caracter stica esperada en un disco de polvo. Adem s, las rmas de por lo menos una docena de l neas de emisi n han sido identi cadas en los datos interferom tricos.
Convergence of switching diffusions
S?ren Christensen,Albrecht Irle
Mathematics , 2014, DOI: 10.1016/j.spa.2015.03.010
Abstract: This paper studies the asymptotic behavior of processes with switching. More precisely, the stability under fast switching for diffusion processes and discrete state space Markovian processes is considered. The proofs are based on semimartingale techniques, so that no Markovian assumption for the modulating process is needed.
Efficient Management of Short-Lived Data
Albrecht Schmidt,Christian S. Jensen
Computer Science , 2005,
Abstract: Motivated by the increasing prominence of loosely-coupled systems, such as mobile and sensor networks, which are characterised by intermittent connectivity and volatile data, we study the tagging of data with so-called expiration times. More specifically, when data are inserted into a database, they may be tagged with time values indicating when they expire, i.e., when they are regarded as stale or invalid and thus are no longer considered part of the database. In a number of applications, expiration times are known and can be assigned at insertion time. We present data structures and algorithms for online management of data tagged with expiration times. The algorithms are based on fully functional, persistent treaps, which are a combination of binary search trees with respect to a primary attribute and heaps with respect to a secondary attribute. The primary attribute implements primary keys, and the secondary attribute stores expiration times in a minimum heap, thus keeping a priority queue of tuples to expire. A detailed and comprehensive experimental study demonstrates the well-behavedness and scalability of the approach as well as its efficiency with respect to a number of competitors.
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.
Why Do At-Risk Mothers Fail To Reach Referral Level? Barriers Beyond Distance and Cost
Marga Kowalewski, Albrecht Jahn, Suleiman S. Kimatta
African Journal of Reproductive Health , 2000,
Abstract: In southern Tanzania, few high-risk pregnancies are channeled through antenatal care to the referral level. We studied the influences that make pregnant women heed or reject referral advice. Semi-structured interviews with sixty mothers-to-be, twenty-six health workers and six key-informants to identify barriers to use of referral level were conducted. Expert-defined risk-status was found to have little influence on a woman's decision to seek hospital care. Besides well known geographical and financial barriers, we found that pregnant women have different perceptions and interpretations of danger signs. Furthermore, rural women avoid the hospital because they fear discrimination. We conclude that a more individualised antenatal consultation could be provided by taking into account women's perception of risk and their explanatory models. Hospital services should be reorganised to address rural women's feelings of fear and insecurity. (Afr J Reprod Health 2000; 4 [1]: 100-109) Key Words: Antenatal care, risk concept, community perception, health seeking behaviour, Tanzania
The torsion-freeness of ext
U. Albrecht,S. Friedenberg,L. Strungmann
International Journal of Algebra , 2012,
Abstract:
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