564 research outputs found
Phase-field-crystal models for condensed matter dynamics on atomic length and diffusive time scales: an overview
Here, we review the basic concepts and applications of the
phase-field-crystal (PFC) method, which is one of the latest simulation
methodologies in materials science for problems, where atomic- and microscales
are tightly coupled. The PFC method operates on atomic length and diffusive
time scales, and thus constitutes a computationally efficient alternative to
molecular simulation methods. Its intense development in materials science
started fairly recently following the work by Elder et al. [Phys. Rev. Lett. 88
(2002), p. 245701]. Since these initial studies, dynamical density functional
theory and thermodynamic concepts have been linked to the PFC approach to serve
as further theoretical fundaments for the latter. In this review, we summarize
these methodological development steps as well as the most important
applications of the PFC method with a special focus on the interaction of
development steps taken in hard and soft matter physics, respectively. Doing
so, we hope to present today's state of the art in PFC modelling as well as the
potential, which might still arise from this method in physics and materials
science in the nearby future.Comment: 95 pages, 48 figure
Excitations of attractive 1-D bosons: Binding vs. fermionization
The stationary states of few bosons in a one-dimensional harmonic trap are
investigated throughout the crossover from weak to strongly attractive
interactions. For sufficient attraction, three different classes of states
emerge: (i) N-body bound states, (ii) bound states of smaller fragments, and
(iii) gas-like states that fermionize, that is, map to ideal fermions in the
limit of infinite attraction. The two-body correlations and momentum spectra
characteristic of the three classes are discussed, and the results are
illustrated using the soluble two-particle model.Comment: 7 pages, 5 figure
The reaction 2H(p,pp)n in three kinematical configurations at E_p = 16 MeV
We measured the cross sections of the H(p,pp)n breakup reaction at
E=16 MeV in three kinematical configurations: the np final-state
interaction (FSI), the co-planar star (CST), and an intermediate-star (IST)
geometry. The cross sections are compared with theoretical predictions based on
the CD Bonn potential alone and combined with the updated 2-exchange
Tucson-Melbourne three-nucleon force (TM99'), calculated without inclusion of
the Coulomb interaction. The resulting excellent agreement between data and
pure CD Bonn predictions in the FSI testifies to the smallness of three-nucleon
force (3NF) effects as well as the insignificance of the Coulomb force for this
particular configuration and energy. The CST also agrees well whereas the IST
results show small deviations between measurements and theory seen before in
the pd breakup space-star geometries which point to possible Coulomb effects.
An additional comparison with EFT predictions (without 3NF) up to order NLO
shows excellent agreement in the FSI case and a rather similar agreement as for
CD Bonn in the CST and IST situations.Comment: 20 pages, 11 figure
Binding between two-component bosons in one dimension
We investigate the ground state of one-dimensional few-atom Bose-Bose
mixtures under harmonic confinement throughout the crossover from weak to
strong inter-species attraction. The calculations are based on the numerically
exact multi-configurational time-dependent Hartree method. For repulsive
components we detail the condition for the formation of a molecular
Tonks-Girardeau gas in the regime of intermediate inter-species interactions,
and the formation of a molecular condensate for stronger coupling. Beyond a
critical inter-species attraction, the system collapses to an overall bound
state. Different pathways emerge for unequal particle numbers and intra-species
interactions. In particular, for mixtures with one attractive component, this
species can be viewed as an effective potential dimple in the trap center for
the other, repulsive component.Comment: 10 pages, 10 figure
Complex networks embedded in space: Dimension and scaling relations between mass, topological distance and Euclidean distance
Many real networks are embedded in space, where in some of them the links
length decay as a power law distribution with distance. Indications that such
systems can be characterized by the concept of dimension were found recently.
Here, we present further support for this claim, based on extensive numerical
simulations for model networks embedded on lattices of dimensions and
.
We evaluate the dimension from the power law scaling of (a) the mass of
the network with the Euclidean radius and (b) the probability of return to
the origin with the distance travelled by the random walker. Both
approaches yield the same dimension. For networks with , is
infinity, while for , obtains the value of the embedding
dimension . In the intermediate regime of interest , our numerical results suggest that decreases continously from to , with for close to
. Finally, we discuss the scaling of the mass and the Euclidean
distance with the topological distance . Our results suggest that in
the intermediate regime , and do
not increase with as a power law but with a stretched exponential,
and , where . The parameters
and are related to by , such that . For , increases exponentially with , as
known for , while is constant and independent of . For
, we find power law scaling, and
, with .Comment: 17 pages, 11 figure
An Exactly Solvable Two-Way Traffic Model With Ordered Sequential Update
Within the formalism of matrix product ansatz, we study a two-species
asymmetric exclusion process with backward and forward site-ordered sequential
update. This model, which was originally introduced with the random sequential
update, describes a two-way traffic flow with a dynamic impurity and shows a
phase transition between the free flow and traffic jam. We investigate the
characteristics of this jamming and examine similarities and differences
between our results and those with random sequential update.Comment: 25 pages, Revtex, 7 ps file
Cross sections and tensor analyzing powers Ayy of the reaction 1H(→d,pp)n in “symmetric constant relative energy” geometries at Ed=19 MeV
We measured the cross sections and tensor analyzing powers of the 1H(→d, pp)n breakup reaction at Ed=19 MeV in four symmetric constant relative energy (SCRE) configurations. The data are compared with theoretical predictions from four different approaches: the first based on high-precision (semi)phenomenological potentials alone or, the second, combined with model three-nucleon forces, and the third based on chiral forces up to next-to-next-to-leading order (NNLO) in the chiral expansion. In these cases the Coulomb interaction is not included. In addition, a fourth approach consists in a comparison with predictions based on CD Bonn including the Δ excitation and the Coulomb force. In all cases the measured cross sections are significantly below the theoretical values, whereas the magnitudes of the tensor analyzing powers agree within the error bars in three of the four cases. The apparent discrepancies in the breakup cross sections are similar to the known differences for the space-star breakup. This adds to the data base of unsolved low-energy discrepancies (puzzles)
Falsification Of The Atmospheric CO2 Greenhouse Effects Within The Frame Of Physics
The atmospheric greenhouse effect, an idea that many authors trace back to
the traditional works of Fourier (1824), Tyndall (1861), and Arrhenius (1896),
and which is still supported in global climatology, essentially describes a
fictitious mechanism, in which a planetary atmosphere acts as a heat pump
driven by an environment that is radiatively interacting with but radiatively
equilibrated to the atmospheric system. According to the second law of
thermodynamics such a planetary machine can never exist. Nevertheless, in
almost all texts of global climatology and in a widespread secondary literature
it is taken for granted that such mechanism is real and stands on a firm
scientific foundation. In this paper the popular conjecture is analyzed and the
underlying physical principles are clarified. By showing that (a) there are no
common physical laws between the warming phenomenon in glass houses and the
fictitious atmospheric greenhouse effects, (b) there are no calculations to
determine an average surface temperature of a planet, (c) the frequently
mentioned difference of 33 degrees Celsius is a meaningless number calculated
wrongly, (d) the formulas of cavity radiation are used inappropriately, (e) the
assumption of a radiative balance is unphysical, (f) thermal conductivity and
friction must not be set to zero, the atmospheric greenhouse conjecture is
falsified.Comment: 115 pages, 32 figures, 13 tables (some typos corrected
A Professional Ethics for Researchers?
Historical research has shown that, at its inception, research ethics was conceived as distinct from existing discourses of professional ethics. Subsequently, this distinction has been maintained and, as a result, the discourse of research ethics appears to be an external to and independent of the practices it normatively analyses and comments upon. This chapter challenges these founding preconceptions and considers if research ethics can be understood as a professional ethics. Therefore, this chapter examines the criteria sociological research identifies as constitutive of a profession, and while one might conclude that research is obviously not formally instantiated as a profession, some of the sociological criteria have significant relevance. In this light it is argued that we might rethink the notion of research ethics in terms of a professional ethics. To do so would be to more clearly embed ethical discourse in the practice(s) of research, something that is consistent with the current turn to integrity
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