682 research outputs found
Hadron masses in QCD with one quark flavour
One-flavour QCD - a gauge theory with SU(3) colour gauge group and a fermion
in the fundamental representation - is studied by Monte Carlo simulations. The
mass spectrum of hadronic bound states is investigated in a volume with
extensions of L ~ 4.4r_0 (~2.2fm) at two different lattice spacings: a ~
0.37r_0 (~0.19fm) and a ~ 0.27r_0 (~0.13fm). The lattice action is Symanzik
tree-level-improved Wilson action for the gauge field and (unimproved) Wilson
action for the fermion.Comment: 21 pages, 4 figures; further references adde
Hot electroweak matter near to the endpoint of the phase transition
The electroweak phase transition is investigated near to its endpoint in the
framework of an effective three-dimensional model. We measure the very weak
interface tension with the tunneling correlation length method. First results
for the mass spectrum and the corresponding wave functions in the symmetric
phase are presented.Comment: 3 pages, 5 figures, uses espcrc2.sty, contribution to LATTICE9
Perturbation theory for the two-dimensional abelian Higgs model in the unitary gauge
In the unitary gauge the unphysical degrees of freedom of spontaneously
broken gauge theories are eliminated. The Feynman rules are simpler than in
other gauges, but it is non-renormalizable by the rules of power counting. On
the other hand, it is formally equal to the limit of the
renormalizable R-gauge. We consider perturbation theory to one-loop
order in the R-gauge and in the unitary gauge for the case of the
two-dimensional abelian Higgs model. An apparent conflict between the unitary
gauge and the limit of the R-gauge is resolved, and it is
demonstrated that results for physical quantities can be obtained in the
unitary gauge.Comment: 15 pages, LaTeX2e, uses the feynmf package, formulations correcte
Chiral perturbation theory for partially quenched twisted mass lattice QCD
Partially quenched Quantum Chromodynamics with Wilson fermions on a lattice
is considered in the framework of chiral perturbation theory. Two degenerate
quark flavours are associated with a chirally twisted mass term. The pion
masses and decay constants are calculated in next-to-leading order including
terms linear in the lattice spacing .Comment: 7 pages, LaTeX2e, final published versio
The microcanonical thermodynamics of finite systems: The microscopic origin of condensation and phase separations; and the conditions for heat flow from lower to higher temperatures
Microcanonical thermodynamics allows the application of statistical mechanics
both to finite and even small systems and also to the largest, self-gravitating
ones. However, one must reconsider the fundamental principles of statistical
mechanics especially its key quantity, entropy. Whereas in conventional
thermostatistics, the homogeneity and extensivity of the system and the
concavity of its entropy are central conditions, these fail for the systems
considered here. For example, at phase separation, the entropy, S(E), is
necessarily convex to make exp[S(E)-E/T] bimodal in E. Particularly, as
inhomogeneities and surface effects cannot be scaled away, one must be careful
with the standard arguments of splitting a system into two subsystems, or
bringing two systems into thermal contact with energy or particle exchange. Not
only the volume part of the entropy must be considered. As will be shown here,
when removing constraints in regions of a negative heat capacity, the system
may even relax under a flow of heat (energy) against a temperature slope. Thus
the Clausius formulation of the second law: ``Heat always flows from hot to
cold'', can be violated. Temperature is not a necessary or fundamental control
parameter of thermostatistics. However, the second law is still satisfied and
the total Boltzmann entropy increases. In the final sections of this paper, the
general microscopic mechanism leading to condensation and to the convexity of
the microcanonical entropy at phase separation is sketched. Also the
microscopic conditions for the existence (or non-existence) of a critical
end-point of the phase-separation are discussed. This is explained for the
liquid-gas and the solid-liquid transition.Comment: 23 pages, 2 figures, Accepted for publication in the Journal of
Chemical Physic
New approach for a comprehensive method for urban vehicle concepts with electric powertrain and their necessary vehicle structures
By the strict discussions regarding energy saving and the goal to reduce CO2 emissions to 95g CO2/km, which is specified for the year 2020, [1] there is a keen demand for lighter and lightweight designed automotive structures to support the energy saving targets. In view of a holistic approach and also to prospectively meet the requirements of the automotive sector, beside the previously mentioned challenges, economic and production-orientated aspects, as well as joining technologies, within the scope of multi-material design, have to be considered to realize a great leap forward medium to large-scale productions.
To achieve these goals, a comprehensive method for urban vehicle concepts with electric powertrain and their necessary vehicle structures is presented. The dimensions and packaging of the presented vehicle is based on demands of a future urban vehicle with space for four occupants including baggage, steerable front system wheels and a rear axle including an electric powertrain.
At the beginning of the method the relevant user requirements, e.g. space for persons and baggage, range for the urban vehicle are defined. In addition, input variables are discharged through the state of the art of electric vehicles. It is also an important point in this step to look on further requirements such as crash requirements or requirements for electrical components in the vehicle design.
With the defined requirements the package of the urban car has to be defined. Two paths are determined to a geometrically and a simulative way. The simulative consideration is limited to the vehicle longitudinal dynamics, thus a rough dimensioning of the drive components is derived. The outputs of the simulation are the performance measures which are then converted into components for the overall model for dimensioning for example electric motor or battery.
The geometric design phase begins with the positioning of the occupants in the passenger compartment and ergonomic layout. Based on this conception of the complete vehicle, various FEM optimizations (topology, topography, size) are carried out for the body in white in order to construct structures towards individual (functional) components/modules. This top-down approach raises the opportunity to extract constructive innovations, which must be integrated within this early concept phase, also to reduce costs when aiming to development of a series product.
With this holistic approach a load-specific optimized structural design is virtually generated and evaluated, and also an outlook on dynamic loads (crash behavior) is given. The focus here is on the potential in innovations by the definition of novel package alignments in combination with the useful application of multi-material-design method, resulting in a light modular vehicle structure
Correlations around an interface
We compute one-loop correlation functions for the fluctuations of an
interface using a field theory model. We obtain them from Feynman diagrams
drawn with a propagator which is the inverse of the Hamiltonian of a
Poschl-Teller problem. We derive an expression for the propagator in terms of
elementary functions, show that it corresponds to the usual spectral sum, and
use it to calculate quantities such as the surface tension and interface
profile in two and three spatial dimensions. The three-dimensional quantities
are rederived in a simple, unified manner, whereas those in two dimensions
extend the existing literature, and are applicable to thin films. In addition,
we compute the one-loop self-energy, which may be extracted from experiment, or
from Monte Carlo simulations. Our results may be applied in various scenarios,
which include fluctuations around topological defects in cosmology,
supersymmetric domain walls, Z(N) bubbles in QCD, domain walls in magnetic
systems, interfaces separating Bose-Einstein condensates, and interfaces in
binary liquid mixtures.Comment: RevTeX, 13 pages, 6 figure
Ultra-high–strength Bainitic Steels
Novel bainitic microstructures, consisting of slender ferrite plates (tens of nm) in a matrix of retained austenite, have reported maximum yield strength of 1.4 GPa, ultimate tensile strength of 2.2 GPa, 30% ductility and respectable levels of fracture toughness (∼51 MPa m0.5). The unusual combination of properties is attributed to the fine bainitic plates and the presence of retained austenite in the microstructure.The authors acknowledge financial support from the
Spanish Ministerio de Educación y Ciencia for the financial
support in the form of Ramón y Cajal contracts (RyC 2002
and 2004 respectively). Some of this work was carried out
under the auspices of an EPSRC/MOD sponsored project
on bainitic steels at the University of Cambridge; we are
extremely grateful for this support over a period of three
years. The authors are extremely grateful to Prof. H. K. D.Peer reviewe
Non-analytic microscopic phase transitions and temperature oscillations in the microcanonical ensemble: An exactly solvable 1d-model for evaporation
We calculate exactly both the microcanonical and canonical thermodynamic
functions (TDFs) for a one-dimensional model system with piecewise constant
Lennard-Jones type pair interactions. In the case of an isolated -particle
system, the microcanonical TDFs exhibit (N-1) singular (non-analytic)
microscopic phase transitions of the formal order N/2, separating N
energetically different evaporation (dissociation) states. In a suitably
designed evaporation experiment, these types of phase transitions should
manifest themselves in the form of pressure and temperature oscillations,
indicating cooling by evaporation. In the presence of a heat bath (thermostat),
such oscillations are absent, but the canonical heat capacity shows a
characteristic peak, indicating the temperature-induced dissociation of the
one-dimensional chain. The distribution of complex zeros (DOZ) of the canonical
partition may be used to identify different degrees of dissociation in the
canonical ensemble.Comment: version accepted for publication in PRE, minor additions in the text,
references adde
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