170 research outputs found
Q Rings
We show the existence of new stable ring-like localized scalar field
configurations whose stability is due to a combination of topological and
nontopological charges. In that sense these defects may be called
semitopological. These rings are Noether charged and also carry Noether current
(they are superconducting). They are local minima of the energy in scalar field
theories with an unbroken U(1) global symmetry. We obtain numerical solutions
of the field configuration corresponding to large rings and derive virial
theorems demonstrating their stability. We also derive the minimum energy field
configurations in 3D and simulate the evolution of a finite size Q ring on a
three dimensional lattice thus generalizing our demonstration of stability.Comment: 4 double column pages including 2 figure
wormholes and topological charge
I investigate solutions to the Euclidean Einstein-matter field equations with
topology in a theory with a massless periodic scalar
field and electromagnetism. These solutions carry winding number of the
periodic scalar as well as magnetic flux. They induce violations of a
quasi-topological conservation law which conserves the product of magnetic flux
and winding number on the background spacetime. I extend these solutions to a
model with stable loops of superconducting cosmic string, and interpret them as
contributing to the decay of such loops.Comment: 18 pages (includes 6 figs.), harvmac and epsf, CU-TP-62
Interaction between vortices in models with two order parameters
The interaction energy and force between widely separated strings is analyzed
in a field theory having applications to superconducting cosmic strings, the
SO(5) model of high-temperature superconductivity, and solitons in nonlinear
optics. The field theory has two order parameters, one of which is broken in
the vacuum (giving rise to strings), the other of which is unbroken in the
vacuum but which could nonetheless be broken in the core of the string. If this
does occur, there is an effect on the energetics of widely separated strings.
This effect is important if the length scale of this second order parameter is
longer than that of the other fields in the problem.Comment: 11 pages, 3 figures. Minor changes in the text. Accepted for
publication in Phys. Rev.
Off-Shell Rho-Omega Mixing Through Quark Loops With Non-Perturbative Meson Vertex And Quark Mass Functions
The momemtum dependence of the off-shell - mixing amplitude is
calculated through a two-quark loop diagram, using non-perturbative meson-quark
vertex functions for the and mesons, as well as
non-perturbative quark propagators. Both these quantities are generated
self-consistently through an interlinked BSE-cum-SDE approach with a 3D support
for the BSE kernel with two basic constants which are pre- checked against a
wide cross section of both meson and baryon spectra within a common structural
framework for their respective 3D BSE's. With this pre-calibration, the
on-shell strength works out at -2.434 in units of the change in
"constituent mass squared", which is consistent with the to
data for a u-d mass difference of ~4 MeV ,while the relative
off-shell strength (0.99 0.01) lies midway between quark-loop and QCD-SR
results. We also calculate the photon-mediated - propagator whose
off-shell structure has an additional pole at =0. The implications of
these results vis-a-vis related investigations are discussed.Comment: 12 Pages, latex file, NTUTH-94-0
Phases of dual superconductivity and confinement in softly broken N=2 supersymmetric Yang-Mills theories
We study the electric flux tubes that undertake color confinement in N=2
supersymmetric Yang-Mills theories softly broken down to N=1 by perturbing with
the first two Casimir operators. The relevant Abelian Higgs model is not the
standard one due to the presence of an off-diagonal coupling among different
magnetic U(1) factors. We perform a preliminary study of this model at a
qualitative level. BPS vortices are explicitely obtained for particular values
of the soft breaking parameters. Generically however, even in the ultrastrong
scaling limit, vortices are not critical but live in a "hybrid" type II phase.
Also, ratios among string tensions are seen to follow no simple pattern. We
examine the situation at the half Higgsed vacua and find evidence for solutions
with the behaviour of superconducting strings. In some cases they are solutions
to BPS equations.Comment: 15 pages, 1 figure, revtex; v2: typos corrected, final versio
Plant-Symbiotic Fungi as Chemical Engineers: Multi-Genome Analysis of the Clavicipitaceae Reveals Dynamics of Alkaloid Loci
The fungal family Clavicipitaceae includes plant symbionts and parasites that produce several psychoactive and bioprotective alkaloids. The family includes grass symbionts in the epichloae clade (EpichloΓ« and Neotyphodium species), which are extraordinarily diverse both in their host interactions and in their alkaloid profiles. Epichloae produce alkaloids of four distinct classes, all of which deter insects, and someβincluding the infamous ergot alkaloidsβhave potent effects on mammals. The exceptional chemotypic diversity of the epichloae may relate to their broad range of host interactions, whereby some are pathogenic and contagious, others are mutualistic and vertically transmitted (seed-borne), and still others vary in pathogenic or mutualistic behavior. We profiled the alkaloids and sequenced the genomes of 10 epichloae, three ergot fungi (Claviceps species), a morning-glory symbiont (Periglandula ipomoeae), and a bamboo pathogen (Aciculosporium take), and compared the gene clusters for four classes of alkaloids. Results indicated a strong tendency for alkaloid loci to have conserved cores that specify the skeleton structures and peripheral genes that determine chemical variations that are known to affect their pharmacological specificities. Generally, gene locations in cluster peripheries positioned them near to transposon-derived, AT-rich repeat blocks, which were probably involved in gene losses, duplications, and neofunctionalizations. The alkaloid loci in the epichloae had unusual structures riddled with large, complex, and dynamic repeat blocks. This feature was not reflective of overall differences in repeat contents in the genomes, nor was it characteristic of most other specialized metabolism loci. The organization and dynamics of alkaloid loci and abundant repeat blocks in the epichloae suggested that these fungi are under selection for alkaloid diversification. We suggest that such selection is related to the variable life histories of the epichloae, their protective roles as symbionts, and their associations with the highly speciose and ecologically diverse cool-season grasses
Improving Newborn Survival in Low-Income Countries: Community-Based Approaches and Lessons from South Asia
David Osrin and colleagues discuss the critical importance of reducing global neonatal mortality in developing countries and how community-based approaches can help
The use of antenatal and postnatal care: perspectives and experiences of women and health care providers in rural southern Tanzania
BACKGROUND\ud
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Although antenatal care coverage in Tanzania is high, worrying gaps exist in terms of its quality and ability to prevent, diagnose or treat complications. Moreover, much less is known about the utilisation of postnatal care, by which we mean the care of mother and baby that begins one hour after the delivery until six weeks after childbirth. We describe the perspectives and experiences of women and health care providers on the use of antenatal and postnatal services.\ud
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METHODS\ud
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From March 2007 to January 2008, we conducted in-depth interviews with health care providers and village based informants in 8 villages of Lindi Rural and Tandahimba districts in southern Tanzania. Eight focus group discussions were also conducted with women who had babies younger than one year and pregnant women. The discussion guide included information about timing of antenatal and postnatal services, perceptions of the rationale and importance of antenatal and postnatal care, barriers to utilisation and suggestions for improvement.\ud
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RESULTS\ud
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Women were generally positive about both antenatal and postnatal care. Among common reasons mentioned for late initiation of antenatal care was to avoid having to make several visits to the clinic. Other concerns included fear of encountering wild animals on the way to the clinic as well as lack of money. Fear of caesarean section was reported as a factor hindering intrapartum care-seeking from hospitals. Despite the perceived benefits of postnatal care for children, there was a total lack of postnatal care for the mothers. Shortages of staff, equipment and supplies were common complaints in the community.\ud
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CONCLUSION\ud
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Efforts to improve antenatal and postnatal care should focus on addressing geographical and economic access while striving to make services more culturally sensitive. Antenatal and postnatal care can offer important opportunities for linking the health system and the community by encouraging women to deliver with a skilled attendant. Addressing staff shortages through expanding training opportunities and incentives to health care providers and developing postnatal care guidelines are key steps to improve maternal and newborn health
Abortion experiences among Zanzibari women: a chain-referral sampling study
Abstract Background In Zanzibar, a semi-autonomous region of Tanzania, induced abortion is illegal but common, and fewer than 12Β % of married reproductive-aged women use modern contraception. As part of a multi-method study about contraception and consequences of unwanted pregnancies, the objective of this study was to understand the experiences of Zanzibari women who terminated pregnancies. Methods The cross-sectional study was set in Zanzibar, Tanzania. Participants were a community-based sample of women who had terminated pregnancies. We carried out semi-structured interviews with 45 women recruited via chain-referral sampling. We report the characteristics of women who have had abortions, the reasons they had abortions, and the methods used to terminate their pregnancies. Results Women in Zanzibar terminate pregnancies that are unwanted for a range of reasons, at various points in their reproductive lives, and using multiple methods. While clinical methods were most effective, nearly half of our participants successfully terminated a pregnancy using non-clinical methods and very few had complications requiring post abortion care (PAC). Conclusions Even in settings where abortion is illegal, some women experience illegal abortions without adverse health consequences, what we might call βsaferβ unsafe abortions; these kinds of abortion experiences can be missed in studies about abortion conducted among women seeking PAC in hospitals
Therapeutic approach to FSGS in children
Therapy of primary focal segmental glomerulosclerosis (FSGS) in children incorporates conservative management and immunosuppression regimens to control proteinuria and preserve kidney function. In long-term cohort studies in adults and children with primary FSGS, renal survival has been directly associated with degree of proteinuria control. This educational article reviews the current therapeutic approach toward children with primary FSGS
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