8,938 research outputs found
Ground State Spin Structure of Strongly Interacting Disordered 1D Hubbard Model
We study the influence of on-site disorder on the magnetic properties of the
ground state of the infinite U 1D Hubbard model. We find that the ground state
is not ferromagnetic. This is analyzed in terms of the algebraic structure of
the spin dependence of the Hamiltonian. A simple explanation is derived for the
1/N periodicity in the persistent current for this model.Comment: 3 pages, no figure
Mpemba effect and phase transitions in the adiabatic cooling of water before freezing
An accurate experimental investigation on the Mpemba effect (that is, the
freezing of initially hot water before cold one) is carried out, showing that
in the adiabatic cooling of water a relevant role is played by supercooling as
well as by phase transitions taking place at 6 +/- 1 oC, 3.5 +/- 0.5 oC and 1.3
+/- 0.6 oC, respectively. The last transition, occurring with a non negligible
probability of 0.21, has not been detected earlier. Supported by the
experimental results achieved, a thorough theoretical analysis of supercooling
and such phase transitions, which are interpreted in terms of different
ordering of clusters of molecules in water, is given.Comment: revtex, 4 pages, 2 figure
Assortative human pair-bonding for partner ancestry and allelic variation of the dopamine receptor D4 (DRD4) gene
The 7R allele of the dopamine receptor D4 gene has been associated with attention-deficit hyperactivity disorder and risk taking. On the cross-population scale, 7R allele frequencies have been shown to be higher in populations with more of a history of long-term migrations. It has also been shown that the 7R allele is associated with individuals having multiple-ancestries. Here we conduct a replication of this latter finding with two independent samples. Measures of subjects’ ancestry are used to examine past reproductive bonds. The individuals’ history of inter-racial/ancestral dating and their feelings about this are also assessed. Tentative support for an association between multiple ancestries and the 7R allele were found. These results are dependent upon the method of questioning subjects about their ancestries. Inter-racial dating and feelings about inter-racial pairing were not related to the presence of the 7R allele. This might be accounted for by secular trends that might have substantively altered the decision-making process employed when considering relationships with individuals from different groups. This study provides continued support for the 7R allele playing a role in migration and/or mate choice patterns. However, replications and extensions of this study are needed and must carefully consider how ancestry/race is assessed
Inhibition by small-molecule ligands of formation of amyloid fibrils of an immunoglobulin light chain variable domain.
Overproduction of immunoglobulin light chains leads to systemic amyloidosis, a lethal disease characterized by the formation of amyloid fibrils in patients' tissues. Excess light chains are in equilibrium between dimers and less stable monomers which can undergo irreversible aggregation to the amyloid state. The dimers therefore must disassociate into monomers prior to forming amyloid fibrils. Here we identify ligands that inhibit amyloid formation by stabilizing the Mcg light chain variable domain dimer and shifting the equilibrium away from the amyloid-prone monomer
Representation of Quantum Mechanical Resonances in the Lax-Phillips Hilbert Space
We discuss the quantum Lax-Phillips theory of scattering and unstable
systems. In this framework, the decay of an unstable system is described by a
semigroup. The spectrum of the generator of the semigroup corresponds to the
singularities of the Lax-Phillips -matrix. In the case of discrete (complex)
spectrum of the generator of the semigroup, associated with resonances, the
decay law is exactly exponential. The states corresponding to these resonances
(eigenfunctions of the generator of the semigroup) lie in the Lax-Phillips
Hilbert space, and therefore all physical properties of the resonant states can
be computed.
We show that the Lax-Phillips -matrix is unitarily related to the
-matrix of standard scattering theory by a unitary transformation
parametrized by the spectral variable of the Lax-Phillips theory.
Analytic continuation in has some of the properties of a method
developed some time ago for application to dilation analytic potentials.
We work out an illustrative example using a Lee-Friedrichs model for the
underlying dynamical system.Comment: Plain TeX, 26 pages. Minor revision
The extinct, giant giraffid Sivatherium giganteum: skeletal reconstruction and body mass estimation
Sivatherium giganteum is an extinct giraffid from the Plio–Pleistocene boundary of the Himalayan foothills. To date, there has been no rigorous skeletal reconstruction of this unusual mammal. Historical and contemporary accounts anecdotally state that Sivatherium rivalled the African elephant in terms of its body mass, but this statement has never been tested. Here, we present a three-dimensional composite skeletal reconstruction and calculate a representative body mass estimate for this species using a volumetric method. We find that the estimated adult body mass of 1246 kg (857—1812 kg range) does not approach that of an African elephant, but confirms that Sivatherium was certainly a large giraffid, and may have been the largest ruminant mammal that has ever existed. We contrast this volumetric estimate with a bivariate scaling estimate derived from Sivatherium's humeral circumference and find that there is a discrepancy between the two. The difference implies that the humeral circumference of Sivatherium is greater than expected for an animal of this size, and we speculate this may be linked to a cranial shift in centre of mass
Phase diagram for a Cubic Consistent-Q Interacting Boson Model Hamiltonian: signs of triaxiality
An extension of the Consistent-Q formalism for the Interacting Boson Model
that includes the cubic QxQxQ term is proposed. The potential energy surface
for the cubic quadrupole interaction is explicitly calculated within the
coherent state formalism using the complete chi-dependent expression for the
quadrupole operator. The Q-cubic term is found to depend on the asymmetry
deformation parameter gamma as a linear combination of cos(3gamma) and
cos^2(3\gamma) terms, thereby allowing for triaxiality. The phase diagram of
the model in the large N limit is explored, it is described the order of the
phase transition surfaces that define the phase diagram, and moreover, the
possible nuclear equilibrium shapes are established. It is found that, contrary
to expectations, there is only a very tiny region of triaxiality in the model,
and that the transition from prolate to oblate shapes is so fast that, in most
cases, the onset of triaxiality might go unnoticed.Comment: 18 pages, 19 figure
The wall shear rate distribution for flow in random sphere packings
The wall shear rate distribution P(gamma) is investigated for pressure-driven
Stokes flow through random arrangements of spheres at packing fractions 0.1 <=
phi <= 0.64. For dense packings, P(gamma) is monotonic and approximately
exponential. As phi --> 0.1, P(gamma) picks up additional structure which
corresponds to the flow around isolated spheres, for which an exact result can
be obtained. A simple expression for the mean wall shear rate is presented,
based on a force-balance argument.Comment: 4 pages, 3 figures, 1 table, RevTeX 4; significantly revised with
significantly extended scop
- …