30 research outputs found
Quantum sticking, scattering and transmission of 4He atoms from superfluid 4He surfaces
We develop a microscopic theory of the scattering, transmission, and sticking
of 4He atoms impinging on a superfluid 4He slab at near normal incidence, and
inelastic neutron scattering from the slab. The theory includes coupling
between different modes and allows for inelastic processes. We find a number of
essential aspects that must be observed in a physically meaningful and reliable
theory of atom transmission and scattering; all are connected with
multiparticle scattering, particularly the possibility of energy loss. These
processes are (a) the coupling to low-lying (surface) excitations
(ripplons/third sound) which is manifested in a finite imaginary part of the
self energy, and (b) the reduction of the strength of the excitation in the
maxon/roton region
Scattering of He-3 Atoms from He-4 Surfaces
We develop a first principles, microscopic theory of impurity atom scattering
from inhomogeneous quantum liquids such as adsorbed films, slabs, or clusters
of He-4. The theory is built upon a quantitative, microscopic description of
the ground state of both the host liquid as well as the impurity atom. Dynamic
effects are treated by allowing all ground-state correlation functions to be
time-dependent.
Our description includes both the elastic and inelastic coupling of impurity
motion to the excitations of the host liquid. As a specific example, we study
the scattering of He-3 atoms from adsorbed He-4 films. We examine the
dependence of ``quantum reflection'' on the substrate, and the consequences of
impurity bound states, resonances, and background excitations for scattering
properties.
A thorough analysis of the theoretical approach and the physical
circumstances point towards the essential role played by inelastic processes
which determine almost exclusively the reflection probabilities. The coupling
to impurity resonances within the film leads to a visible dependence of the
reflection coefficient on the direction of the impinging particle.Comment: 36 pages, 16 figure
Holographic studies of quasi-topological gravity
Quasi-topological gravity is a new gravitational theory including
curvature-cubed interactions and for which exact black hole solutions were
constructed. In a holographic framework, classical quasi-topological gravity
can be thought to be dual to the large limit of some non-supersymmetric
but conformal gauge theory. We establish various elements of the AdS/CFT
dictionary for this duality. This allows us to infer physical constraints on
the couplings in the gravitational theory. Further we use holography to
investigate hydrodynamic aspects of the dual gauge theory. In particular, we
find that the minimum value of the shear-viscosity-to-entropy-density ratio for
this model is .Comment: 45 pages, 6 figures. v2: References adde
Density-functional Study of Small Molecules within the Krieger-Li-Iafrate Approximation
We report density-functional studies of several small molecules (, and ) within the Krieger-Li-Iafrate (KLI)
approximation to the exact Kohn-Sham local exchange potential, using a
three-dimensional real-space finite-difference pseudopotential method. It is
found that exchange-only KLI leads to markedly improved eigenvalue spectra
compared to those obtained within the standard local-density approximation
(LDA), the generalized gradient approximation (GGA), and the Hartree-Fock (HF)
method. For structural properties, exchange-only KLI results are close to the
corresponding HF values. We find that the addition of LDA or GGA correlation
energy functionals to the KLI exact exchange energy functional does not lead to
systematic improvements.Comment: 16 pages including 1 fugure, to be published in Phys. Rev. A Nov. 1
'9
Pairing in nuclear systems: from neutron stars to finite nuclei
We discuss several pairing-related phenomena in nuclear systems, ranging from
superfluidity in neutron stars to the gradual breaking of pairs in finite
nuclei. We focus on the links between many-body pairing as it evolves from the
underlying nucleon-nucleon interaction and the eventual experimental and
theoretical manifestations of superfluidity in infinite nuclear matter and of
pairing in finite nuclei. We analyse the nature of pair correlations in nuclei
and their potential impact on nuclear structure experiments. We also describe
recent experimental evidence that points to a relation between pairing and
phase transitions (or transformations) in finite nuclear systems. Finally, we
discuss recent investigations of ground-state properties of random two-body
interactions where pairing plays little role although the interactions yield
interesting nuclear properties such as 0+ ground states in even-even nuclei.Comment: 74 pages, 33 figs, uses revtex4. Submitted to Reviews of Modern
Physic
Inherited liver shunts in dogs elucidate pathways regulating embryonic development and clinical disorders of the portal vein
Congenital disorders of the hepatic portal vasculature are rare in man but occur frequently in certain dog breeds. In dogs, there are two main subtypes: intrahepatic portosystemic shunts, which are considered to stem from defective closure of the embryonic ductus venosus, and extrahepatic shunts, which connect the splanchnic vascular system with the vena cava or vena azygos. Both subtypes result in nearly complete bypass of the liver by the portal blood flow. In both subtypes the development of the smaller branches of the portal vein tree in the liver is impaired and terminal branches delivering portal blood to the liver lobules are often lacking. The clinical signs are due to poor liver growth, development, and function. Patency of the ductus venosus seems to be a digenic trait in Irish wolfhounds, whereas Cairn terriers with extrahepatic portosystemic shunts display a more complex inheritance. The genes involved in these disorders cannot be identified with the sporadic human cases, but in dogs, the genome-wide study of the extrahepatic form is at an advanced stage. The canine disease may lead to the identification of novel genes and pathways cooperating in growth and development of the hepatic portal vein tree. The same pathways likely regulate the development of the vascular system of regenerating livers during liver diseases such as hepatitis and cirrhosis. Therefore, the identification of these molecular pathways may provide a basis for future proregenerative intervention
A rapidly resorbable hemostatic biomaterial based on dihydroxyacetone
We have developed a rapid acting, rapidly resorbable, non-toxic, topical hemostatic agent comprised of a PEGylated, polymerized sequence of dihydroxyacetone (MPEG-pDHA) that is highly effective in vivo. Twenty-eight Sprague-Dawley rats underwent left lateral hepatectomy. To the cut edge of the liver, rats received MPEG-pDHA (50 mg), normal saline (0.5 mL), or Instat (50 mg), a commercially available hemostatic compound. Bleeding time and total blood loss were quantified. Coagulation studies and scanning electron microscopy were performed on phlebotomized blood combined with MPEG-pDHA. Rats treated with MPEG-pDHA had significantly decreased bleeding time (97 s) and total blood loss (1.35 g) compared to normal saline (464 s and 3.83 g, p <0.05 for each), and a significantly shorter bleeding time compared to Instat (165 s, p <0.05). Histology confirmed that all MPEG-pDHA was metabolized within 3 weeks. The addition of MPEG-pDHA to whole blood did not significantly affect prothrombin time (12.0 s vs. 13.2 s, p = 0.130), partial thromboplastin time (27.0 s vs. 21.8 s, p = 0.118), or thrombin clotting time. MPEG-pDHA is an effective and rapidly resorbable hemostatic agent that may find broad hemostatic application in a wide range of surgical procedure