357 research outputs found
Are the notions of past, present and future compatible with the General Theory of Relativity?
The notions of time and causality are revisited, as well as the A- and
B-theory of time, in order to determine which theory of time is most compatible
with relativistic spacetimes. By considering orientable spacetimes and defining
a time-orientation, we formalize the concepts of a time-series in relativistic
spacetimes; A-theory and B-theory are given mathematical descriptions within
the formalism of General Relativity. As a result, in time-orientable
spacetimes, the notions of events being in the future and in the past, which
are notions of A-theory, are found to be more fundamental than the notions of
events being earlier than or later than other events, which are notions of
B-theory. Furthermore, we find that B-theory notions are incompatible with some
structures encountered in globally hyperbolic spacetimes, namely past and
future inextendible curves. Hence, GR is favorable to A-theory and the notions
of past, present and future.Comment: 19 pages, 2 figure
Analysis of transport properties of iron pnictides: spin-fluctuation scenario
We present a phenomenological theory of quasiparticle scattering and
transport relaxation in the normal state of iron pnictides based on the
simplified two-band model coupled via spin fluctuations. In analogy with
anomalous properties of cuprates it is shown that a large and anomalous
normal-state resistivity and thermopower can be interpreted as the consequence
of strong coupling to spin fluctuations. The generalization to the
superconducting phase is also discussed.Comment: Revised version, 6 pages, 11 references adde
The generalized identification of truly interfacial molecules (ITIM) algorithm for nonplanar interfaces
We present a generalized version of the ITIM algorithm for the identification of interfacial molecules, which is able to treat arbitrarily shaped interfaces. The algorithm exploits the similarities between the concept of probe sphere used in ITIM and the circumsphere criterion used in the α-shapes approach, and can be regarded either as a reference-frame independent version of the former, or as an extended version of the latter that includes the atomic excluded volume. The new algorithm is applied to compute the intrinsic orientational order parameters of water around a dodecylphosphocholine and a cholic acid micelle in aqueous environment, and to the identification of solvent-reachable sites in four model structures for soot. The additional algorithm introduced for the calculation of intrinsic density profiles in arbitrary geometries proved to be extremely useful also for planar interfaces, as it allows to solve the paradox of smeared intrinsic profiles far from the interface. © 2013 American Institute of Physics
Are the notions of past, present and future compatible with the General Theory of Relativity?
The notions of time and causality are revisited, as well as the A- and B-theory of time, in order to determine which theory of time is most compatible with relativistic spacetimes. By considering orientable spacetimes and defining a time-orientation, we formalize the concepts of a time-series in relativistic spacetimes; A-theory and B-theory are given mathematical descriptions within the formalism of General Relativity. As a result, in time-orientable spacetimes, the notions of events being in the future and in the past, which are notions of A-theory, are found to be more fundamental than the notions of events being earlier than or later than other events, which are notions of B-theory. Furthermore, we find that B-theory notions are incompatible with some structures encountered in globally hyperbolic spacetimes, namely past and future inextendible curves. Hence, GR is favorable to A-theory and the notions of past, present and future
Electron Spin Resonance of SrCu2(BO3)2 at High Magnetic Field
We calculate the electron spin resonance (ESR) spectra of the
quasi-two-dimensional dimer spin liquid SrCu2(BO3)2 as a function of magnetic
field B. Using the standard Lanczos method, we solve a Shastry-Sutherland
Hamiltonian with additional Dzyaloshinsky-Moriya (DM) terms which are crucial
to explain different qualitative aspects of the ESR spectra. In particular, a
nearest-neighbor DM interaction with a non-zero D_z component is required to
explain the low frequency ESR lines for B || c. This suggests that crystal
symmetry is lowered at low temperatures due to a structural phase transition.Comment: 4 pages, 4 b&w figure
FePO(4)NPs Are an Efficient Nutritional Source for Plants: Combination of Nano-Material Properties and Metabolic Responses to Nutritional Deficiencies
Phosphorous and iron are a macro- and micronutrient, respectively, whose low bioavailability can negatively affect crop productivity. There is ample evidence that the use of conventional P and Fe fertilizers has several environmental and economical disadvantages, but even though great expectations surround nanotechnology and its applications in the field of plant nutrition, little is known about the mechanisms underlying the uptake and use of these sub-micron particles (nanoparticles, NPs) by crop species. This work shows that cucumber and maize plants both use the nutrients borne by FePO(4)NPs more efficiently than those supplied as bulk. However, morpho-physiological parameters and nutrient content analyses reveal that while cucumber plants (aStrategy Ispecies with regard to Fe acquisition) mainly use these NPs as a source of P, maize (aStrategy IIspecies) uses them preferentially for Fe. TEM analyses of cucumber root specimens revealed no cell internalization of the NPs. On the other hand, electron-dense nanometric structures were evident in proximity of the root epidermal cell walls of the NP-treated plants, which after ESEM/EDAX analyses can be reasonably identified as iron-oxyhydroxide. It appears that the nutritional interaction between roots and NPs is strongly influenced by species-specific metabolic responses
Mesoscopic simulations of the counterion-induced electroosmotic flow - a comparative study
We present mesoscopic simulations of the counterion-induced electroosmotic
flow in different electrostatic coupling regimes. Two simulation methods are
compared, Dissipative Particle Dynamics (DPD) and coupled
Lattice-Boltzmann/Molecular Dynamics (LB/MD). A general mapping scheme to match
DPD to LB/MD is developed. For the weak-coupling regime, analytic expressions
for the flow profiles in the presence of partial-slip as well as no-slip
boundary conditions are derived from the Poisson-Boltzmann and Stokes
equations, which are in good agreement with the numerical results. The
influence of electrofriction and partial slip on the flow profiles is
discussed.Comment: 10 pages, 8 figures, 3 tables, additional references and minor
changes in the tex
Correlation of test results and influence of a mass balance constraint on risks in conformity assessment of a substance or material
When components of a substance or material are subject to a mass balance constraint, test results of the
components’ contents are intrinsically correlated because of the constraint. This so-called ‘spurious’ correlation
is observed in addition to possible metrologically-related correlation of test results, and natural
and/or technological correlation of the components’ contents. Such correlations may influence understanding
of test results and evaluation of risks of false decisions, due to measurement uncertainty, in conformity
assessment of the substance or material. The objective of the present paper is the development of
a technique for appropriate evaluation of the risks. A Bayesian multivariate approach to evaluate the conformance
probability of materials or objects and relevant risks is discussed for different scenarios of the
data modelling, taking into account all observed correlations. A Monte Carlo method, including the mass
balance constraint, written in the R programming environment, is provided for the necessary
calculations
Optical conductivity of the Hubbard model at finite temperature
The optical conductivity, , of the two dimensional one-band
Hubbard model is calculated at finite temperature using exact diagonalization
techniques on finite clusters. The in-plane d.c. resistivity, , is
also evaluated. We find that at large U/t and temperature T, is
approximately linear with temperature, in reasonable agreement with experiments
on high-T superconductors. Moreover, we note that displays
charge excitations, a mid-infrared (MIR) band and a Drude peak, also as
observed experimentally. The combination of the Drude peak and the MIR
oscillator strengths leads to a conductivity that decays slower than
at energies smaller than the insulator gap near half-filling.Comment: 12 pages, 3 figures appended, Revtex version 2.0, preprin
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