123 research outputs found
On the exploitability of thermo-charged capacitors
Recently [Physics Letters A, 374, (2010) 1801] the concept of vacuum
capacitor spontaneously charged harnessing the heat from a single thermal
reservoir at room temperature has been introduced, along with a mathematical
description of its functioning and a discussion on the main paradoxical feature
that seems to violate the Second Law of Thermodynamics. In the present paper we
investigate the theoretical and practical possibility of exploiting a such
thermo-charged capacitor as voltage/current generator: we show that if very
weak provisos on the physical characteristics of the capacitor are fulfilled,
then a non-zero current should flow across the device, allowing the generation
of potentially usable voltage, current and electric power out of a single
thermal source at room temperature. Preliminary results show that the power
output is tiny but non-zero.Comment: 23 Pages, 10 Figures. Physica A 390/6 (2011) 482 + Addendum (2013
The Peculiar Status of the Second Law of Thermodynamics and the Quest for its Violation
Even though the second law of thermodynamics holds the supreme position among
the laws of nature, as stated by many distinguished scientists, notably
Eddington and Einstein, its position appears to be also quite peculiar. Given
the atomic nature of matter, whose behaviour is well described by statistical
physics, the second law could not hold unconditionally, but only statistically.
It is not an absolute law. As a result of this, in the present paper we try to
argue that we have not yet any truly cogent argument (known fundamental
physical laws) to exclude its possible macroscopic violation. Even Landauer's
information-theoretic principle seems to fall short of the initial expectations
of being the fundamental `physical' reason of all Maxwell's demons failure.
Here we propose a modified Szilard engine which operates without any steps in
the process resembling the creation or destruction of information. We argue
that the information-based exorcisms must be wrong, or at the very least
superfluous, and that the real physical reason why such engines cannot work
lies in the ubiquity of thermal fluctuations (and friction).
We see in the above peculiar features the main motivation and rationale for
pursuing exploratory research to challenge the second law, which is still
ongoing and probably richer than ever. A quite thorough (and critical)
description of some of these challenges is also given.Comment: 25 pages, 8 figures; Studies in History and Philosophy of Modern
Physics, to appear. arXiv admin note: text overlap with arXiv:1011.395
Exciton scattering in light-harvesting systems of purple bacteria
Using the reduced density matrix formalism the exciton scattering in
light-harvesting systems of purple bacteria is calculated. The static disorder
(fluctuations of the site energies) as well as the dynamic disorder
(dissipation) is taken into account in this work. Circular aggregates with 18
pigments are studied to model the B850 ring of bacteriochlorophylls with LH2
complexes. It can be shown that the influence of dissipation may not be
neglected in the simulation of the time-dependent anisotropy of fluorescence.
Also an elliptical deformation of the ring could be essential
Influence of Static and Dynamic Disorder on the Anisotropy of Emission in the Ring Antenna Subunits of Purple Bacteria Photosynthetic Systems
Using the reduced density matrix formalism the time dependence of the exciton
scattering in light-harvesting ring systems of purple bacteria is calculated.
In contrast to the work of Kumble and Hochstrasser (J. Chem. Phys. 109 (1998)
855) static disorder (fluctuations of the site energies) as well as dynamic
disorder (dissipation) is taken into account. For the description of
dissipation we use Redfield theory in exciton eigenstates without secular
approximation. This is shown to be equivalent to the Markovian limit of Capek's
theory in local states. Circular aggregates with 18 pigments are studied to
model the B850 ring of bacteriochlorophyls within LH2 complexes. It can be
demonstrated that the dissipation is important for the time-dependent
anisotropy of the fluorescence. Smaller values of static disorder are
sufficient to produce the same decay rates in the anisotropy in comparison with
the results by Kumble and Hochstrasser
Thermalisation by a boson bath in a pure state
We consider a quantum system weakly coupled to a large heat bath of harmonic
oscillators. It is well known that such a boson bath initially at thermal
equilibrium thermalises the system. We show that assuming a priori an
equilibrium state is not necessary to obtain the thermalisation of the system.
We determine the complete Schr\"odinger time evolution of the subsystem of
interest for an initial pure product state of the composite system consisting
of the considered system and the bath. We find that the system relaxes into
canonical equilibrium for almost all initial pure bath states of
macroscopically well-defined energy. The temperature of the system asymptotic
thermal state is determined by the energy of the initial bath state as the
corresponding microcanonical temperature. Moreover, the time evolution of the
system is identical to the one obtained assuming that the boson bath is
initially at thermal equilibrium with this temperature. A significant part of
our approach is applicable to other baths and we identify the bath features
which are requisite for the thermalisation studied
The issue of groin injuries and risk factors affecting this type of injuries among football players.
Název práce Problematika poranění třísel a ovlivnění rizikových faktorů tohoto zranění u fotbalistů. Cíl práce Hlavní cíl této diplomové práce je shrnutí teoretických poznatků týkající se poranění v oblasti třísla u fotbalistů a ověření účinnosti preventivního programu pro snížení výskytu zranění v oblasti třísel u těchto hráčů fotbalu. Metody řešení Teoretická část se zabývá danou problematikou na úrovni literární rešerše české a zejména zahraniční literatury. Poznatky teoretické části byly čerpány zejména ze zahraničních odborných periodik, monografií a elektronických databází, převážně PubMed a PEDro. V druhé experimentální části byl aplikován preventivní program. Experimentu se zúčastnili hráči fotbalu (n=42) věkové kategorie U16 (n=20) a U17 (n=22). Vybraná skupina probandů prováděla preventivní intervenci 1x týdně po dobu 6 měsíců. Následně byly výsledky sledovaného zranění porovnány se stejným obdobím v předchozím roce, kdy se hráči nevěnovali žádným preventivním opatřením. Informace o předchozích zraněních byly získány nestandardizovaným dotazníkovým šetřením. Výsledky Na základě literární rešerše je předchozí zranění považováno za nejvýznamnější rizikový faktor pro vznik nového zranění v oblasti třísla. Mezi další významné rizikové faktory patří předčasný návrat do tréninkového procesu či...Title The issue of groin injuries and risk factors affecting this type of injuries among football players. Objectives The main objective of this thesis is to summarize theoretical findings regarding the groin injuries among soccer players and to prove efficiency of preventive training program aimed at reduction of groin injuries incidence in soccer players. Methods The theoretical part deals with the given issue as a research and theoretical overview of the current findings, based on Czech and especially foreign literature. Findings of theoretical part were obtained by foreign periodicals, monographies and electronic database, mostly PubMed and PEDro. In the second part of thesis a preventive training program was applied at a specific group of soccer players (n=42) in age U16 (n=20) and U17 (n=22). Selected group of probands performed preventive intervention training once a week for 6 months. After that results were compared with the same time of season in the previous year, when no preventive measures had been taken. Information about previous injury has been obtained by non-standardized questionnaire. Results Based on the literature review previous injury is considered to be the most significant risk factor for new injury in groin. Other significant risk factors include untimely return to...FyzioterapieFakulta tělesné výchovy a sportuFaculty of Physical Education and Spor
The issue of groin injuries and risk factors affecting this type of injuries among football players.
Název práce . Cíl práce Hlavní cíl této diplomové práce je shrnutí týkající se v vního programu pro snížení výsky fotbalu. Metod slouží jako podklad k v . monografií a elektronických databází, PubMed a PEDro. V druhé . Experimentu se fotbalu (n=42) (n=20) a U17 (n=22). y výsledky porovnány se stejným obdobím v , kdy získány nestandardizo . Výsledky nejvýznamn v . Mezi další rehabilitace. zaznamenáno na . byl faul. dvaceti v oblast celkového bylo hlášeno dvacet á 20 %. :Title The issue of groin injuries and risk factors affecting this type of injuries among football players. Objectives The main objective of this thesis is to summarize theoretical findings regarding the groin injuries among soccer players and to prove efficiency of preventive training program aimed at reduction of groin injuries incidence in soccer players. Methods The theoretical part deals with the given issue as a research and theoretical overview of the current findings, based on Czech and especially foreign literature. Findings of theoretical part were obtained by foreign periodicals, monographies and electronic database, mostly PubMed and PEDro. In the second part of thesis a preventive training program was applied at a specific group of soccer players (n=42) in age U16 (n=20) and U17 (n=22). Selected group of probands performed preventive intervention training once a week for 6 months. After that results were compared with the same time of season in the previous year, when no preventive measures had been taken. Information about previous injury has been obtained by non-standardized questionnaire. Results Based on the theoretical overview previous injury is considered to be the most significant risk factor for new injury in groin. Other significant risk factors include untimely return to...FyzioterapieFakulta tělesné výchovy a sportuFaculty of Physical Education and Spor
A Note on Solid-State Maxwell Demon
Starting from 2002, at least two kinds of laboratory-testable, solid-state
Maxwell demons have been proposed that utilize the electric field energy of an
open-gap n-p junction and that seem to challenge the validity of the Second Law
of Thermodynamics. In the present paper we present some arguments against the
alleged functioning of such devices.Comment: 9 pages, 4 figures. Foundations of Physics, forthcoming. arXiv admin
note: substantial text overlap with arXiv:1101.505
Global and local relaxation of a spin-chain under exact Schroedinger and master-equation dynamics
We solve the Schroedinger equation for an interacting spin-chain locally
coupled to a quantum environment with a specific degeneracy structure. The
reduced dynamics of the whole spin-chain as well as of single spins is
analyzed. We show, that the total spin-chain relaxes to a thermal equilibrium
state independently of the internal interaction strength. In contrast, the
asymptotic states of each individual spin are thermal for weak but non-thermal
for stronger spin-spin coupling. The transition between both scenarios is found
for couplings of the order of , with denoting
the Zeeman-splitting. We compare these results with a master equation
treatment; when time averaged, both approaches lead to the same asymptotic
state and finally with analytical results.Comment: RevTeX, 8 pages, 14 figures, added DOI and forgotten reference
Electronic Coherence Dephasing in Excitonic Molecular Complexes: Role of Markov and Secular Approximations
We compare four different types of equations of motion for reduced density
matrix of a system of molecular excitons interacting with thermodynamic bath.
All four equations are of second order in the linear system-bath interaction
Hamiltonian, with different approximations applied in their derivation. In
particular we compare time-nonlocal equations obtained from so-called
Nakajima-Zwanzig identity and the time-local equations resulting from the
partial ordering prescription of the cummulant expansion. In each of these
equations we alternatively apply secular approximation to decouple population
and coherence dynamics from each other. We focus on the dynamics of intraband
electronic coherences of the excitonic system which can be traced by coherent
two-dimensional spectroscopy. We discuss the applicability of the four
relaxation theories to simulations of population and coherence dynamics, and
identify features of the two-dimensional coherent spectrum that allow us to
distinguish time-nonlocal effects.Comment: 14 pages, 8 figure
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