7,632 research outputs found
A Relativistic Version of the Two-Level Atom in the Rest-Frame Instant Form of Dynamics
We define a relativistic version of the two-level atom, in which an extended
atom is replaced by a point particle carrying suitable Grassmann variables for
the description of the two-level structure and of the electric dipole. After
studying the isolated system "atom plus the electro-magnetic field" in the
electric-dipole representation as a parametrized Minkowski theory, we give its
restriction to the inertial rest frame and the explicit form of the Poincar\'e
generators. After quantization we get a two-level atom with a spin 1/2 electric
dipole and the relativistic generalization of the Hamiltonians of the Rabi and
Jaynes-Cummings models.Comment: 23 page
Flavor-dependent eigenvolume interactions in a hadron resonance gas
Eigenvolume effects in the hadron resonance gas (HRG) model are studied for
experimental hadronic yields in nucleus-nucleus collisions. If particle
eigenvolumes are different for different hadron species, the excluded volume
HRG (EV-HRG) improves fits to multiplicity data. In particular, using different
mass~-~volume relations for strange and non-strange hadrons we observe a
remarkable improvement in the quality of the fits. This effect appears to be
rather insensitive to other details in the schemes employed in the EV-HRG. We
show that the parameters found from fitting the data of the ALICE Collaboration
in central Pb+Pb collisions at the collision energy ~TeV entail the same improvement for all centralities at the same
collision energy, and for the RHIC and SPS data at lower collision energies.
Our findings are put in the context of recent fits of lattice QCD results.Comment: 4 figure
Lattice QCD-based equations of state at vanishing net-baryon density
We present realistic equations of state for QCD matter at vanishing
net-baryon density which embed recent lattice QCD results at high temperatures
combined with a hadron resonance gas model in the low-temperature, confined
phase. In the latter, we allow an implementation of partial chemical
equilibrium, in which particle ratios are fixed at the chemical freeze-out, so
that a description closer to the experimental situation is possible. Given the
present uncertainty in the determination of the chemical freeze-out temperature
from first-principle lattice QCD calculations, we consider different values
within the expected range. The corresponding equations of state can be applied
in the hydrodynamic modeling of relativistic heavy-ion collisions at the LHC
and at the highest RHIC beam energies. Suitable parametrizations of our results
as functions of the energy density are also provided.Comment: Updated journal version with refined EoS-parametrization. July 2014.
8 pp. 4 figs. 3 parametrization-tables and weblink Ref. [45
Generating and verifying graph states for fault-tolerant topological measurement-based quantum computing in 2D optical lattices
We propose two schemes for implementing graph states useful for
fault-tolerant topological measurement-based quantum computation in 2D optical
lattices. We show that bilayer cluster and surface code states can be created
by global single-row and controlled-Z operations. The schemes benefit from the
accessibility of atom addressing on 2D optical lattices and the existence of an
efficient verification protocol which allows us to ensure the experimental
feasibility of measuring the fidelity of the system against the ideal graph
state. The simulation results show potential for a physical realization toward
fault-tolerant measurement-based quantum computation against dephasing and
unitary phase errors in optical lattices.Comment: 6 pages and 4 figures (minor changed
The effect of insect herbivory on the growth and fitness of introduced Verbascum thapsus L.
A majority of the plant species that are introduced into new ranges either do not become established, or become naturalized yet do not attain high densities and are thus considered ecologically and economically unproblematic. The factors that limit these relatively “benign” species are not well studied. The biotic resistance hypothesis predicts that herbivores, pathogens and competition reduce growth and reproduction of individual plants and so suppress population growth of non-native species. We explored the effect of insect herbivory and surrounding vegetation on growth and fitness of the non-native biennial plant Verbascum thapsus (common mullein) in Colorado, USA. Mullein is widespread in its introduced North American range, yet is infrequently considered a management concern because populations are often ephemeral and restricted to disturbed sites. To evaluate the impact of insect herbivores on mullein performance, we reduced herbivory using an insecticide treatment and compared sprayed plants to those exposed to ambient levels of herbivory. Reducing herbivory increased survival from rosette to reproduction by 7%, from 70–77%. Of plants that survived, reducing herbivory increased plant area in the first year and plant height, the length of the reproductive spike, and seed set during the second year. Reducing herbivory also had a marked effect on plant fitness, increasing seed set by 50%, from about 48,000 seeds per plant under ambient herbivory to about 98,000 per plant under reduced herbivory. Our findings also highlight that the relationship between herbivory and performance is complex. Among plants exposed to ambient herbivory, we observed a positive relationship between damage and performance, suggesting that, as predicted by the plant vigor hypothesis, insect herbivores choose the largest plants for feeding when their choice is not restricted by insecticide treatment. In contrast to the strong effects of experimentally reduced herbivory, we found that cover of other plants surrounding our focal plants explained relatively little variation in performance outcomes. Overall, we found that herbivore-induced impacts on individual plant performance and seed set are substantial, and thus may help prevent this naturalized species from becoming dominant in undisturbed recipient communities
Aging phenomena in spin glass and ferromagnetic phases: domain growth and wall dynamics
We compare aging in a disordered ferromagnet and in a spin glass, by studying
the different phases of a reentrant system. We have measured the relaxation of
the low-frequency ac susceptibility, in both the ferromagnetic and spin-glass
phases of a CdCr_{1.9}In_{0.1}S_4 sample. A restart of aging processes when the
temperature is lowered (`chaos-like' effect) is observed in both phases. The
memory of previous aging at a higher temperature can be retrieved upon
re-heating, but in the ferromagnetic phase it can rapidly be erased by the
growth of ferromagnetic domains. We interpret the behaviour observed in the
ferromagnetic phase in terms of a combination of domain growth and pinned wall
reconformations, and suggest that aging in spin glasses is dominated by such
wall reconformation processes.Comment: SPEC, CEA Saclay, 91191 Gif sur Yvette Cedex, France, to appear in
Europhys. Lett. (2000
Application of Robust Model Predictive Control to a Renewable Hydrogen-based Microgrid
In order to cope with uncertainties present in the renewable energy generation, as well as in the demand consumer, we propose in this paper the formulation and comparison of three robust model predictive control techniques, i. i. e., multi-scenario, tree-based, and chance-constrained model predictive control, which are applied to a nonlinear plant-replacement model that corresponds to a real laboratory-scale plant located in the facilities of the University of Seville. Results show the effectiveness of these three techniques considering the stochastic nature, proper of these systems
Holographic quenches and anomalous transport
We study the response of the chiral magnetic effect due to continuous
quenches induced by time dependent electric fields within holography.
Concretely, we consider a holographic model with dual chiral anomaly and
compute the electric current parallel to a constant, homogeneous magnetic field
and a time dependent electric field in the probe approximation. We explicitly
solve the PDEs by means of pseudospectral methods in spatial and time
directions and study the transition to an universal "fast" quench response.
Moreover, we compute the amplitudes, i.e.,~residues of the quasi normal modes,
by solving the (ODE) Laplace transformed equations. We investigate the
possibility of considering the asymptotic growth rate of the amplitudes as a
well defined notion of initial time scale for linearized systems. Finally, we
highlight the existence of Landau level resonances in the electrical
conductivity parallel to a magnetic field at finite frequency and show
explicitly that these only appear in presence of the anomaly. We show that the
existence of these resonances induces, among others, a long-lived AC electric
current once the electric field is switched off.Comment: 34 pages, 10 figure
Desigualdades en los sistemas educativos en la EducaciĂłn Infantil
Treball Final de Grau en Mestre o Mestra d'Educació Infantil. Codi: MI1040. Curs acadèmic: 2016/2017Este trabajo tiene como objetivo realizar un estudio sobre las desigualdades en los
sistemas educativos europeos en la etapa de infantil.
Su metodologĂa se basa en bĂşsquedas bibliográficas relacionadas con el tema de las
desigualdades en los sistemas educativos de los paĂses a comparar (España, Grecia, Alemania y
Finlandia). Con estas búsquedas se pretende comparar los elementos más destacados dentro de
cada sistema educativo. Para llevar a cabo estas bĂşsquedas se han utilizado diversas fuentes,
como libros, artĂculos de revistas de educaciĂłn y materiales extraĂdos de la red.
La parte principal de este trabajo corresponde a la descripciĂłn de la educaciĂłn infantil en España y otros paĂses de Europa como Grecia, Alemania y Finlandia, para observar las desigualdades que presentan y asĂ, poder compararlas. A continuaciĂłn, se resumen las desigualdades observadas en los distintos sistemas educativos, centrándonos en el inicio de la educaciĂłn infantil, la obligatoriedad de esta, la escolarizaciĂłn y la financiaciĂłn. Finalmente, se presentan las conclusiones.
Ningún modelo educativo por sà solo puede ser más o menos efectivo sobre otro sistema.
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