337 research outputs found
Precision benchmark calculations for four particles at unitarity
The unitarity limit describes interacting particles where the range of the
interaction is zero and the scattering length is infinite. We present precision
benchmark calculations for two-component fermions at unitarity using three
different ab initio methods: Hamiltonian lattice formalism using iterated
eigenvector methods, Euclidean lattice formalism with auxiliary-field
projection Monte Carlo, and continuum diffusion Monte Carlo with fixed and
released nodes. We have calculated the ground state energy of the unpolarized
four-particle system in a periodic cube as a dimensionless fraction of the
ground state energy for the non-interacting system. We obtain values 0.211(2)
and 0.210(2) using two different Hamiltonian lattice representations, 0.206(9)
using Euclidean lattice, and an upper bound of 0.212(2) from fixed-node
diffusion Monte Carlo. Released-node calculations starting from the fixed-node
result yield a decrease of less than 0.002 over a propagation of 0.4/E_F in
Euclidean time, where E_F is the Fermi energy. We find good agreement among all
three ab initio methods.Comment: 23 pages, 7 figures, final version to appear in Phys. Rev.
Cubic Twistorial String Field Theory
Witten has recently proposed a string theory in twistor space whose
D-instanton contributions are conjectured to compute N=4 super-Yang-Mills
scattering amplitudes. An alternative string theory in twistor space was then
proposed whose open string tree amplitudes reproduce the D-instanton
computations of maximal degree in Witten's model.
In this paper, a cubic open string field theory action is constructed for
this alternative string in twistor space, and is shown to be invariant under
parity transformations which exchange MHV and googly amplitudes. Since the
string field theory action is gauge-invariant and reproduces the correct cubic
super-Yang-Mills interactions, it provides strong support for the conjecture
that the string theory correctly computes N-point super-Yang-Mills tree
amplitudes.Comment: 19+1 pages, 4+1 EPS figures, JHEP3 LaTeX; v2: minor corrections,
references added; v3: the final version published in JHEP with a new footnote
on the d=0 on-shell contributio
Approximate and exact nodes of fermionic wavefunctions: coordinate transformations and topologies
A study of fermion nodes for spin-polarized states of a few-electron ions and
molecules with one-particle orbitals is presented. We find exact nodes
for some cases of two electron atomic and molecular states and also the first
exact node for the three-electron atomic system in state using
appropriate coordinate maps and wavefunction symmetries. We analyze the cases
of nodes for larger number of electrons in the Hartree-Fock approximation and
for some cases we find transformations for projecting the high-dimensional node
manifolds into 3D space. The node topologies and other properties are studied
using these projections. We also propose a general coordinate transformation as
an extension of Feynman-Cohen backflow coordinates to both simplify the nodal
description and as a new variational freedom for quantum Monte Carlo trial
wavefunctions.Comment: 7 pages, 7 figure
Inventory of Epiphytic Moss Flora in the Montane Forest of Mt. Kasiling Dako, Tarragona, Davao Oriental
Mosses have been found to be good indicators of environmental conditions. Their significant in the environment helps to evaluate and assess the effect of environmental changes on the ecosystem. This study aims to determine the record status of the collected species of mosses found in Mt. Kasiling Dako, Tomoaong, Tarragona, Davao Oriental, Philippines. The said station has an approximate elevation of 392.6 meters or 1,388.0 feet above mean sea level (masl). The inventory of the moss floral species was done through a transect walk (Alpha Taxonomy) which covers 200 meters following the trail of the forest. The choice of the area conducted through a purposive sampling method in which all mosses was examined and investigated. Twenty – one species of mosses was identified, classified, and described based on their life forms and habitat. Of the 21 specimens collected, eleven locally assessed as abundant while ten found rare. Based on the habitat preference of the mosses, nine preferred tree trunk, five preferred rocks, three for tree base, and two for both tree log and clay. Thus, these protected areas need to be preserved in order to ensure mosses’ growth and abundance. This furtherly recommend the conduct of morphological examination and find a standardized method of measuring status record of the moss floral species.  
Electron correlation in C_(4N+2) carbon rings: aromatic vs. dimerized structures
The electronic structure of C_(4N+2) carbon rings exhibits competing
many-body effects of Huckel aromaticity, second-order Jahn-Teller and Peierls
instability at large sizes. This leads to possible ground state structures with
aromatic, bond angle or bond length alternated geometry. Highly accurate
quantum Monte Carlo results indicate the existence of a crossover between C_10
and C_14 from bond angle to bond length alternation. The aromatic isomer is
always a transition state. The driving mechanism is the second-order
Jahn-Teller effect which keeps the gap open at all sizes.Comment: Submitted for publication: 4 pages, 3 figures. Corrected figure
Parallel symbolic state-space exploration is difficult, but what is the alternative?
State-space exploration is an essential step in many modeling and analysis
problems. Its goal is to find the states reachable from the initial state of a
discrete-state model described. The state space can used to answer important
questions, e.g., "Is there a dead state?" and "Can N become negative?", or as a
starting point for sophisticated investigations expressed in temporal logic.
Unfortunately, the state space is often so large that ordinary explicit data
structures and sequential algorithms cannot cope, prompting the exploration of
(1) parallel approaches using multiple processors, from simple workstation
networks to shared-memory supercomputers, to satisfy large memory and runtime
requirements and (2) symbolic approaches using decision diagrams to encode the
large structured sets and relations manipulated during state-space generation.
Both approaches have merits and limitations. Parallel explicit state-space
generation is challenging, but almost linear speedup can be achieved; however,
the analysis is ultimately limited by the memory and processors available.
Symbolic methods are a heuristic that can efficiently encode many, but not all,
functions over a structured and exponentially large domain; here the pitfalls
are subtler: their performance varies widely depending on the class of decision
diagram chosen, the state variable order, and obscure algorithmic parameters.
As symbolic approaches are often much more efficient than explicit ones for
many practical models, we argue for the need to parallelize symbolic
state-space generation algorithms, so that we can realize the advantage of both
approaches. This is a challenging endeavor, as the most efficient symbolic
algorithm, Saturation, is inherently sequential. We conclude by discussing
challenges, efforts, and promising directions toward this goal
Half-lives of Sr-73 and Y-76 and the consequences for the proton dripline
The half-lives of seven nuclei have been determined in the neutron-deficient mass-70 region following their production via fragmentation of a 345 MeV/nucleon Xe-124 primary beam on a 740 mg/cm(2) Be-9 target at the RI Beam Factory, RIKEN. The results include two new (Sr-73 and Y-76) half-lives and a more precise measurement for the ground-state half-life of Sr-74. The new results are discussed with reference to previously published calculations that predict the location of the proton dripline in the light Sr and Y region of the nuclear chart. In addition, differences in the ground-state structure of Rb-72 and Y-76 are discussed with the aid of density functional theory calculations. These provide a possible explanation for why Rb-72 undergoes proton decay while the alpha-conjugate nucleus Y-76 predominantly undergoes beta(+) decay.Peer reviewe
Borna disease virus (BDV) circulating immunocomplex positivity in addicted patients in the Czech Republic: a prospective cohort analysis
<p>Abstract</p> <p>Background</p> <p>Borna disease virus (BDV) is an RNA virus belonging to the family Bornaviridae. Borna disease virus is a neurotropic virus that causes changes in mood, behaviour and cognition. BDV causes persistent infection of the central nervous system. Immune changes lead to activation of infection. Alcohol and drug dependence are associated with immune impairment.</p> <p>Methods</p> <p>We examined the seropositivity of BDV circulating immunocomplexes (CIC) in patients with alcohol and drug dependence and healthy individuals (blood donors). We examined 41 addicted patients for the presence of BDV CIC in the serum by ELISA at the beginning of detoxification, and after eight weeks of abstinence. This is the first such study performed in patients with alcohol and drug dependence.</p> <p>Results</p> <p>BDV CIC positivity was detected in 36.59% of addicted patients on day 0 and in 42.86% on day 56. The control group was 37.3% positive. However, we did not detect higher BDV CIC positivity in addicted patients in comparison with blood donors (p = 0.179). The significantly higher level of BDV CIC was associated with lower levels of GGT (gamma glutamyl transferase) (p = 0.027) and approached statistical significance with the lower age of addicted patients (p = 0.064). We did not find any association between BDV CIC positivity and other anamnestic and demographic characteristics.</p> <p>Conclusions</p> <p>In our study addicted patients did not have significantly higher levels of BDV CIC than the control group. The highest levels of BDV CIC were detected in patients with lower levels of GGT and a lower age.</p> <p>Trial registration</p> <p>This study was approved by the ethical committee of the University Hospital Medical Faculty of Charles University in Pilsen, Czech Republic (registration number 303/2001).</p
Beta decay of the Tz=-2 nucleus 64Se and its descendants
International audience; The beta decay of the Tz=-2 nucleus 64Se has been studied in a fragmentation reaction at RIKEN-Nishina Center. 64Se is the heavies Tz=-2 nucleus that decays to bound states in the daughter nucleus and the heaviest case where the mirror reaction 64Zn(3He,t)64Ga on the Tz=+2 64Zn stable target exists and can be compared. Beta-delayed gamma and proton radiation is reported for the 64Se and 64As cases. New levels have been observed in 64As, 64Ge (N=Z), 63Ge and 63Ga. The associated T1/2 values have been obtained
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