Fluctuation Effects in High Sheet Resistance Superconducting Films

As the normal state sheet resistance, $R_n$, of a thin film superconductor increases, its superconducting properties degrade. For $R_n\simeq h/4e^2$ 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 $T_c$ in a superconductor with both non-magnetic and magnetic impurities. We do this by first evaluating the correction to the effective potential, $\Omega(\Delta)$, and then obtain the first-order correction to the order parameter, $\Delta$, by finding the minimum of $\Omega(\Delta)$. Setting $\Delta=0$ finally allows $T_c$ to be evaluated. $T_c$ is now a function of both the resistance per square, $R_\square$, a measure of the non-magnetic disorder, and the spin-flip scattering rate, $1/\tau_s$, 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

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 $T_{c}$ equation, the calculated values for $T_c$ 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

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Evidence of Vortices on the Insulating Side of the Superconductor-Insulator Transition

The magnetoresistance of ultrathin insulating films of Bi has been studied with magnetic fields applied parallel and perpendicular to the plane of the sample. Deep in the strongly localized regime, the magnetoresistance is negative and independent of field orientation. As film thicknesses increase, the magnetoresistance becomes positive, and a difference between values measured in perpendicular and parallel fields appears, which is a linear function of the magnetic field and is positive. This is not consistent with the quantum interference picture. We suggest that it is due to vortices present on the insulating side of the superconductor-insulator transition.Comment: 4 pages, 3 figure