20,180 research outputs found
Pairing in the Framework of the Unitary Correlation Operator Method (UCOM): Hartree-Fock-Bogoliubov Calculations
In this first in a series of articles, we apply effective interactions
derived by the Unitary Correlation Operator Method (UCOM) to the description of
open-shell nuclei, using a self-consistent Hartree-Fock-Bogoliubov framework to
account for pairing correlations. To disentangle the particle-hole and
particle-particle channels and assess the pairing properties of \VUCOM, we
consider hybrid calculations using the phenomenological Gogny D1S interaction
to derive the particle-hole mean field. In the main part of this article, we
perform calculations of the tin isotopic chain using \VUCOM in both the
particle-hole and particle-particle channels. We study the interplay of both
channels, and discuss the impact of non-central and non-local terms in
realistic interactions as well as the frequently used restriction of pairing
interactions to the partial wave. The treatment of the center-of-mass
motion and its effect on theoretical pairing gaps is assessed independently of
the used interactions.Comment: 14 pages, 10 figures, to appear in Phys. Rev. C, title modified
accordingl
Depletion potentials near geometrically structured substrates
Using the recently developed so-called White Bear version of Rosenfeld's
Fundamental Measure Theory we calculate the depletion potentials between a
hard-sphere colloidal particle in a solvent of small hard spheres and simple
models of geometrically structured substrates: a right-angled wedge or edge. In
the wedge geometry, there is a strong attraction beyond the corresponding one
near a planar wall that significantly influences the structure of colloidal
suspensions in wedges. In accordance with an experimental study, for the edge
geometry we find a free energy barrier of the order of several which
repels a big colloidal particle from the edge.Comment: 7 pages, 7 figure
Science Verification Results from PMAS
PMAS, the Potsdam Multi-Aperture Spectrophotometer, is a new integral field
instrument which was commissioned at the Calar Alto 3.5m Telescope in May 2001.
We report on results obtained from a science verification run in October 2001.
We present observations of the low-metallicity blue compact dwarf galaxy
SBS0335-052, the ultra-luminous X-ray Source X-1 in the Holmberg II galaxy, the
quadruple gravitational lens system Q2237+0305 (the "Einstein Cross"), the
Galactic planetary nebula NGC7027, and extragalactic planetary nebulae in M31.
PMAS is now available as a common user instrument at Calar Alto Observatory.Comment: 4 pages, 9 figures (attached in JPEG format), Euro3D Science Workshop
Proceedings, held in Cambridge May 21-23, 2003, to appear in AN (accepted
Stable marriage and roommates problems with restricted edges: complexity and approximability
In the Stable Marriage and Roommates problems, a set of agents is given, each of them having a strictly ordered preference list over some or all of the other agents. A matching is a set of disjoint pairs of mutually acceptable agents. If any two agents mutually prefer each other to their partner, then they block the matching, otherwise, the matching is said to be stable. We investigate the complexity of finding a solution satisfying additional constraints on restricted pairs of agents. Restricted pairs can be either forced or forbidden. A stable solution must contain all of the forced pairs, while it must contain none of the forbidden pairs.
Dias et al. (2003) gave a polynomial-time algorithm to decide whether such a solution exists in the presence of restricted edges. If the answer is no, one might look for a solution close to optimal. Since optimality in this context means that the matching is stable and satisfies all constraints on restricted pairs, there are two ways of relaxing the constraints by permitting a solution to: (1) be blocked by as few as possible pairs, or (2) violate as few as possible constraints n restricted pairs.
Our main theorems prove that for the (bipartite) Stable Marriage problem, case (1) leads to View the MathML source-hardness and inapproximability results, whilst case (2) can be solved in polynomial time. For non-bipartite Stable Roommates instances, case (2) yields an View the MathML source-hard but (under some cardinality assumptions) 2-approximable problem. In the case of View the MathML source-hard problems, we also discuss polynomially solvable special cases, arising from restrictions on the lengths of the preference lists, or upper bounds on the numbers of restricted pairs
Integer programming methods for special college admissions problems
We develop Integer Programming (IP) solutions for some special college
admission problems arising from the Hungarian higher education admission
scheme. We focus on four special features, namely the solution concept of
stable score-limits, the presence of lower and common quotas, and paired
applications. We note that each of the latter three special feature makes the
college admissions problem NP-hard to solve. Currently, a heuristic based on
the Gale-Shapley algorithm is being used in the application. The IP methods
that we propose are not only interesting theoretically, but may also serve as
an alternative solution concept for this practical application, and also for
other ones
p3d: a general data-reduction tool for fiber-fed integral-field spectrographs
The reduction of integral-field spectrograph (IFS) data is demanding work.
Many repetitive operations are required in order to convert raw data into,
typically a large number of, spectra. This effort can be markedly simplified
through the use of a tool or pipeline, which is designed to complete many of
the repetitive operations without human interaction. Here we present our
semi-automatic data-reduction tool p3d that is designed to be used with
fiber-fed IFSs. Important components of p3d include a novel algorithm for
automatic finding and tracing of spectra on the detector, and two methods of
optimal spectrum extraction in addition to standard aperture extraction. p3d
also provides tools to combine several images, perform wavelength calibration
and flat field data. p3d is at the moment configured for four IFSs. In order to
evaluate its performance we have tested the different components of the tool.
For these tests we used both simulated and observational data. We demonstrate
that for three of the IFSs a correction for so-called cross-talk due to
overlapping spectra on the detector is required. Without such a correction
spectra will be inaccurate, in particular if there is a significant intensity
gradient across the object. Our tests showed that p3d is able to produce
accurate results. p3d is a highly general and freely available tool. It is
easily extended to include improved algorithms, new visualization tools and
support for additional instruments. The program code can be downloaded from the
p3d-project web site http://p3d.sourceforge.netComment: 18 pages, 15 figures, 3 tables, accepted for publication in A&
Matrix Elements and Few-Body Calculations within the Unitary Correlation Operator Method
We employ the Unitary Correlation Operator Method (UCOM) to construct
correlated, low-momentum matrix elements of realistic nucleon-nucleon
interactions. The dominant short-range central and tensor correlations induced
by the interaction are included explicitly by an unitary transformation. Using
correlated momentum-space matrix elements of the Argonne V18 potential, we show
that the unitary transformation eliminates the strong off-diagonal
contributions caused by the short-range repulsion and the tensor interaction,
and leaves a correlated interaction dominated by low-momentum contributions. We
use correlated harmonic oscillator matrix elements as input for no-core shell
model calculations for few-nucleon systems. Compared to the bare interaction,
the convergence properties are dramatically improved. The bulk of the binding
energy can already be obtained in very small model spaces or even with a single
Slater determinant. Residual long-range correlations, not treated explicitly by
the unitary transformation, can easily be described in model spaces of moderate
size allowing for fast convergence. By varying the range of the tensor
correlator we are able to map out the Tjon line and can in turn constrain the
optimal correlator ranges.Comment: 16 pages, 9 figures, using REVTEX
Deficiency of RgpG causes major defects in cell division and biofilm formation, and deficiency of LytR-CpsAPsr family proteins leads to accumulation of cell wall antigens in culture medium by Streptococcus mutans
ABSTRACT
Streptococcus mutans
is known to possess rhamnose-glucose polysaccharide (RGP), a major cell wall antigen.
S. mutans
strains deficient in
rgpG
, encoding the first enzyme of the RGP biosynthesis pathway, were constructed by allelic exchange. The
rgpG
deficiency had no effect on growth rate but caused major defects in cell division and altered cell morphology. Unlike the coccoid wild type, the
rgpG
mutant existed primarily in chains of swollen, âsquarishâ dividing cells. Deficiency of
rgpG
also causes significant reduction in biofilm formation (
P
< 0.01). Double and triple mutants with deficiency in
brpA
and/or
psr
, genes coding for the LytR-CpsA-Psr family proteins BrpA and Psr, which were previously shown to play important roles in cell envelope biogenesis, were constructed using the
rgpG
mutant. There were no major differences in growth rates between the wild-type strain and the
rgpG brpA
and
rgpG psr
double mutants, but the growth rate of the
rgpG brpA psr
triple mutant was reduced drastically (
P
< 0.001). Under transmission electron microscopy, both double mutants resembled the
rgpG
mutant, while the triple mutant existed as giant cells with multiple asymmetric septa. When analyzed by immunoblotting, the
rgpG
mutant displayed major reductions in cell wall antigens compared to the wild type, while little or no signal was detected with the double and triple mutants and the
brpA
and
psr
single mutants. These results suggest that RgpG in
S. mutans
plays a critical role in cell division and biofilm formation and that BrpA and Psr may be responsible for attachment of cell wall antigens to the cell envelope.
IMPORTANCE
Streptococcus mutans
, a major etiological agent of human dental caries, produces rhamnose-glucose polysaccharide (RGP) as the major cell wall antigen. This study provides direct evidence that deficiency of RgpG, the first enzyme of the RGP biosynthesis pathway, caused major defects in cell division and morphology and reduced biofilm formation by
S. mutans
, indicative of a significant role of RGP in cell division and biofilm formation in
S. mutans
. These results are novel not only in
S. mutans
, but also other streptococci that produce RGP. This study also shows that the LytR-CpsA-Psr family proteins BrpA and Psr in
S. mutans
are involved in attachment of RGP and probably other cell wall glycopolymers to the peptidoglycan. In addition, the results also suggest that BrpA and Psr may play a direct role in cell division and biofilm formation in
S. mutans
. This study reveals new potential targets to develop anticaries therapeutics.
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Magnetic properties of single-crystalline CeCuGa3
The magnetic behavior of single-crystalline CeCuGa3 has been investigated.
The compound forms in a tetragonal BaAl4-type structure consisting of
rare-earth planes separated by Cu-Ga layers. If the Cu-Ga site disorder is
reduced, CeCuGa3 adopts the related, likewise tetragonal BaNiSn3-type
structure, in which the Ce ion are surrounded by different Cu and Ga layers and
the inversion symmetry is lost. In the literature conflicting reports about the
magnetic order of CeCuGa3 have been published. Single crystals with the
centrosymmetric structure variant exhibit ferromagnetic order below approx. 4 K
with a strong planar anisotropy. The magnetic behavior above the transition
temperature can be well understood by the crystal-field splitting of the 4f
Hund's rule ground-state multiplet of the Ce ions
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Dynamic interpersonal therapy for moderate to severe depression: A pilot randomized controlled and feasibility trial
Background: Improving Access to Psychological Therapies (IAPT) services treat most patients in England who present to primary care with major depression. Psychodynamic psychotherapy is one of the psychotherapies offered. Dynamic Interpersonal Therapy (DIT) is a psychodynamic and mentalization-based treatment for depression. 16 sessions are delivered over approximately 5 months. Neither DIT's effectiveness relative to low-intensity treatment (LIT), nor the feasibility of randomizing patients to psychodynamic or cognitive-behavioural treatments (CBT) in an IAPT setting has been demonstrated.
Methods: 147 patients were randomized in a 3:2:1 ratio to DIT (n = 73), LIT (control intervention; n = 54) or CBT (n = 20) in four IAPT treatment services in a combined superiority and feasibility design. Patients meeting criteria for major depressive disorder were assessed at baseline, mid-treatment (3 months) and post-treatment (6 months) using the Hamilton Rating Scale for Depression (HRSD-17), Beck Depression Inventory-II (BDI-II) and other self-rated questionnaire measures. Patients receiving DIT were also followed up 6 months post-completion.
Results: The DIT arm showed significantly lower HRSD-17 scores at the 6-month primary end-point compared with LIT (d = 0.70). Significantly more DIT patients (51%) showed clinically significant change on the HRSD-17 compared with LIT (9%). The DIT and CBT arms showed equivalence on most outcomes. Results were similar with the BDI-II. DIT showed benefit across a range of secondary outcomes.ConclusionsDIT delivered in a primary care setting is superior to LIT and can be appropriately compared with CBT in future RCTs
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