747 research outputs found
Fluctuation Effects in High Sheet Resistance Superconducting Films
As the normal state sheet resistance, , of a thin film superconductor
increases, its superconducting properties degrade. For
superconductivity disappears and a transition to a nonsuperconducting state
occurs. We present electron tunneling and transport measurements on ultrathin,
homogeneously disordered superconducting films in the vicinity of this
transition. The data provide strong evidence that fluctuations in the amplitude
of the superconducting order parameter dominate the tunneling density of states
and the resistive transitions in this regime. We briefly discuss possible
sources of these amplitude fluctuation effects. We also describe how the data
suggest a novel picture of the superconductor to nonsuperconductor transition
in homogeneous 2D systems.Comment: 11 pages, 5 figure
Periocular Myxoma in a Child
Myxomas are locally invasive, benign mesenchymal neoplasms with odontogenic, osteogenic, or soft tissue origin. Facial myxomas probably account for less than 0.5% of all paranasal sinus and nasal tumors. We report a case of a left painless periocular mass in a 11-month-old girl. The lesion was resected with a clinical diagnosis of lacrimal sac tumor. Histopathology and immunohistochemistry proved the tumor to be a myxoma. There has been no recurrence after 4 years of followup. Midfacial myxomas should be differentiated from other benign and malignant tumors such as dermoid, hamartoma, neurofibroma, nasolacrimal duct cyst, and sarcomas in particular embryonal rhabdomyosarcoma. Because of the infiltrative nature of these tumors, a wide surgery is required to achieve clear resection margins and avoid recurrence
The Upper Critical Field in Disordered Two-Dimensional Superconductors
We present calculations of the upper critical field in superconducting films
as a function of increasing disorder (as measured by the normal state
resistance per square). In contradiction to previous work, we find that there
is no anomalous low-temperature positive curvature in the upper critical field
as disorder is increased. We show that the previous prediction of this effect
is due to an unjustified analytical approximation of sums occuring in the
perturbative calculation. Our treatment includes both a careful analysis of
first-order perturbation theory, and a non-perturbative resummation technique.
No anomalous curvature is found in either case. We present our results in
graphical form.Comment: 11 pages, 8 figure
Effect of Magnetic Impurities on Suppression of the Transition Temperature in Disordered Superconductors
We calculate the first-order perturbative correction to the transition
temperature in a superconductor with both non-magnetic and magnetic
impurities. We do this by first evaluating the correction to the effective
potential, , and then obtain the first-order correction to the
order parameter, , by finding the minimum of . Setting
finally allows to be evaluated. is now a function of
both the resistance per square, , a measure of the non-magnetic
disorder, and the spin-flip scattering rate, , a measure of the
magnetic disorder. We find that the effective pair-breaking rate per magnetic
impurity is virtually independent of the resistance per square of the film, in
agreement with an experiment of Chervenak and Valles. This conclusion is
supported by both the perturbative calculation, and by a non-perturbative
re-summation technique.Comment: 29 pages, 9 figure
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Insertion of a self-splicing intron into the mtDNA of atriploblastic animal
Nephtys longosetosa is a carnivorous polychaete worm that lives in the intertidal and subtidal zones with worldwide distribution (pleijel&rouse2001). Its mitochondrial genome has the characteristics typical of most metazoans: 37 genes; circular molecule; almost no intergenic sequence; and no significant gene rearrangements when compared to other annelid mtDNAs (booremoritz19981995). Ubiquitous features as small intergenic regions and lack of introns suggested that metazoan mtDNAs are under strong selective pressures to reduce their genome size allowing for faster replication requirements (booremoritz19981995Lynch2005). Yet, in 1996 two type I introns were found in the mtDNA of the basal metazoan Metridium senile (FigureX). Breaking a long-standing rule (absence of introns in metazoan mtDNA), this finding was later supported by the further presence of group I introns in other cnidarians. Interestingly, only the class Anthozoa within cnidarians seems to harbor such introns. Although several hundreds of triploblastic metazoan mtDNAs have been sequenced, this study is the first evidence of mitochondrial introns in triploblastic metazoans. The cox1 gene of N. longosetosa has an intron of almost 2 kbs in length. This finding represents as well the first instance of a group II intron (anthozoans harbor group I introns) in all metazoan lineages. Opposite trends are observed within plants, fungi and protist mtDNAs, where introns (both group I and II) and other non-coding sequences are widespread. Plant, fungal and protist mtDNA structure and organization differ enormously from that of metazoan mtDNA. Both, plant and fungal mtDNA are dynamic molecules that undergo high rates of recombination, contain long intergenic spacer regions and harbor both group I and group II introns. However, as metazoans they have a conserved gene content. Protists, on the other hand have a striking variation of gene content and introns that account for the genome size variation. In contrast to this mtDNA structure and organization diversity, current genome level studies point to a monophyletic origin of the mitochondria (REFS), raising questions such as: what are the pressures at work shaping the evolution of the mitochondrial genome at 'higher' levels? What drives the absence of introns and other non-coding spacers in metazoan mtDNA? What characteristics must have an intron to be maintained in an environment where 'extra chromosomes' are usually selected against
Weak Localization Effect in Superconductors
We study the effect of weak localization on the transition temperatures of
superconductors using time-reversed scattered state pairs, and find that the
weak localization effect weakens electron-phonon interactions. With solving the
BCS equation, the calculated values for are in good agreement
with experimental data for various two- and three-dimensional disordered
superconductors. We also find that the critical sheet resistance for the
suppression of superconductivity in thin films does not satisfy the universal
behavior but depends on sample, in good agreement with experiments. but depends
on sample, in good agreement with experiments.Comment: 14 pages, Revtex, 5 ps figure
Metatranscriptomics and Pyrosequencing Facilitate Discovery of Potential Viral Natural Enemies of the Invasive Caribbean Crazy Ant, Nylanderia pubens
BACKGROUND: Nylanderia pubens (Forel) is an invasive ant species that in recent years has developed into a serious nuisance problem in the Caribbean and United States. A rapidly expanding range, explosive localized population growth, and control difficulties have elevated this ant to pest status. Professional entomologists and the pest control industry in the United States are urgently trying to understand its biology and develop effective control methods. Currently, no known biological-based control agents are available for use in controlling N. pubens. METHODOLOGY AND PRINCIPAL FINDINGS: Metagenomics and pyrosequencing techniques were employed to examine the transcriptome of field-collected N. pubens colonies in an effort to identify virus infections with potential to serve as control agents against this pest ant. Pyrosequencing (454-platform) of a non-normalized N. pubens expression library generated 1,306,177 raw sequence reads comprising 450 Mbp. Assembly resulted in generation of 59,017 non-redundant sequences, including 27,348 contigs and 31,669 singlets. BLAST analysis of these non-redundant sequences identified 51 of potential viral origin. Additional analyses winnowed this list of potential viruses to three that appear to replicate in N. pubens. CONCLUSIONS: Pyrosequencing the transcriptome of field-collected samples of N. pubens has identified at least three sequences that are likely of viral origin and, in which, N. pubens serves as host. In addition, the N. pubens transcriptome provides a genetic resource for the scientific community which is especially important at this early stage of developing a knowledgebase for this new pest
In processu Lic. Iosephi Aymeric, Rectoris Ecclesiae Parochialis Loci de Peñalba : super apprehensione de las primicias pertenecientes a dicha Iglesia: en satisfaccion a las dudas que ha participado el Consejo por dicho lugar de Peñalba
Precede al texto en p.1, viñeta con la inscripción "Jesus, Maria, Joseph"Copia digital : Diputación Provincial de Zaragoza. Servicio de Archivos y Bibliotecas, 2010Datos de tít. tomados de p.1, y mención de responsabilidad del final del textoTexto fechado al final del mismo en Zaragoza ... 1704Sign.: A-Z\p2\s, 2A-2K\p2\sInic. grab. xil. en p.
Plan de emergencia elaborado por la Corporación Autónoma Regional de la Sabana de Bogotá y de los valles de Ubaté y Chiquinquira, CAR, con el objeto de minimizar el riesgo de inundaciones del río Bogotá en la zona urbana del distrito especial de Bogotá
Plan de emergencia que integra actividades desarrolladas año 197
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