Disorder effects in pnictides: a tunneling spectroscopy study.

We present the synthesis and the tunneling spectroscopy study of superconducting FeSe(0.5)Te(0.5) (T(c) = 14 K), SmFeAsO(0.85) (T(c) = 54 K) and SmFeAsO(0.9)F(0.1) (T(c) = 45 K). The samples were characterized by Rietveld refinement of x-ray diffraction patterns and transport as well as temperature-dependent magnetic measurements. Tunneling experiments on FeSe(0.5)Te(0.5) revealed a single superconducting gap ∼ 1 meV in BCS-like tunneling conductance spectra. In SmFeAsO(0.85) and SmFeAsO(0.9)F(0.1), however, more complex spectra were observed, characterized by two gap-like structures at ∼ 4 and ∼ 10 meV. These spectra are qualitatively understood assuming a two-band superconductor with a 's ±' order parameter. We show that, depending on the sign relation between the pairing amplitudes in the two bands, the interband quasiparticle scattering has a crucial effect on the shape of the tunneling spectra. On the other hand, single-gap spectra found in FeSe(0.5)Te(0.5) are more compatible with a disorder-induced 's '-wave gap, due to the Se-Te substitution.

Scanning tunneling spectroscopy on the novel superconductor CaC6.

We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC6. The tunneling conductance spectra, measured between 3 and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with Delta0=1.6+/-0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows us to deduce a coherence length in the ab plane xiab approximately 33 nm.

Probing the superfluid velocity with a superconducting tip: the Doppler shift effect.

We address the question of probing the supercurrents in superconducting (SC) samples on a local scale by performing scanning tunneling spectroscopy (STS) experiments with a SC tip. In this configuration, we show that the tunneling conductance is highly sensitive to the Doppler shift term in the SC quasiparticle (QP) spectrum of the sample, thus allowing the local study of the superfluid velocity. Intrinsic screening currents, such as those surrounding the vortex cores in a type II SC in a magnetic field, are directly probed. With Nb tips, the STS mapping of the vortices, in single crystal 2H-NbSe(2), reveals both the vortex cores, on the scale of the SC coherence length xi, and the supercurrents, on the scale of the London penetration length lambda. A subtle interplay between the SC pair potential and the supercurrents at the vortex edge is observed. Our results open interesting prospects for the study of screening currents in any superconductor.

Two-gap state density in MgB(2): a true bulk property or a proximity effect?

We report on the temperature dependence of the quasiparticle density of states in the simple binary compound MgB(2) directly measured using scanning tunneling microscope (STM). To achieve high quality tunneling conditions, a small crystal of MgB(2) is used as a tip in the STM experiment. The "sample" is chosen to be a 2H- NbSe(2) single crystal presenting an atomically flat surface. At low temperature the tunneling conductance spectra show a gap at the Fermi energy followed by two well-pronounced conductance peaks on each side. They appear at voltages V(S) approximately +/-3.8 mV and V(L) approximately +/-7.8 mV. With rising temperature both peaks disappear at the T(C) of the bulk MgB(2), a behavior consistent with the model of two-gap superconductivity. The possibility of a particular proximity effect is also discussed.

Influence of disorder on the local density of states in high- T(c) superconducting thin films

Using a low temperature scanning tunneling microscope in the spectroscopic mode, we find that the disorder in a Bi(2)Sr(2)CaCu(2)O(8+delta) thin film modifies dramatically the quasiparticle local density of states. Small, but well-defined superconducting regions, coexisting with dominating semiconducting areas, show well-pronounced gap structures, similar to those observed previously in high-quality single crystals. Surprisingly, between these two regions, the detailed shape of the quasiparticle spectrum is virtually identical to the pseudogap previously observed at temperatures T>T(c), or in the vortex core, at 4.2 K. Thus, the role of the disorder in destroying the superconducting phase is comparable to that of the magnetic field or thermal fluctuations.

Study design in the evaluation of breast cancer imaging technologies.

RATIONALE AND OBJECTIVES: Bringing a new imaging technology to market is a complex process. Beyond conceptualization and proof of concept, obtaining U.S. Food and Drug Administration (FDA) approval for clinical use depends on the documented experimental establishment of safety and efficacy. In turn, safety and efficacy are evaluated in the context of the intended use of the technology. The purpose of this study was to examine a conceptual framework for technology development and evaluation, focusing on new breast imaging technologies as a highly visible and current case in point. MATERIALS AND METHODS: The FDA views technology development in terms of a preclinical and four clinical phases of assessment. With a concept of research and development as a learning model, this phased-assessment concept of regulatory review against intended use was integrated with a five-level version of a hierarchy-of-efficacy framework for evaluating imaging technologies. Study design and analysis issues are presented in this context, as are approaches to supporting expanded clinical indications and new intended uses after a new technology is marketed. CONCLUSION: Breast imaging technologies may be intended for use as replacements for standard-of-care technologies, as adjuncts, or as complementary technologies. Study designs must be appropriate to establish claims of superiority or equivalence to the standard for the intended use. Screening technologies are ultimately judged on their demonstrated effectiveness in decreasing cause-specific mortality through early detection, but they may be brought to market for other uses on the basis of lesser standards of efficacy (eg, sensitivity, specificity, positive and negative predictive value, and stage of disease detected).

Variations in sedating uncooperative, stable children for post-traumatic head CT.

OBJECTIVE: To characterize variations among pediatric emergency physicians and their hospital facilities regarding sedation of the uncooperative, stable child for head CT following closed head injury. DESIGN: Mail survey with two follow-up mailings. PARTICIPANTS: Surveys were sent to all members of the Emergency Medicine Section of the American Academy of Pediatrics (AAP). RESULTS: Of 596 surveys sent, 431 (72%) were returned, with 304 (51%) usable responses. Respondents annually sedate over 17,500 children for post-traumatic head CT. Formal training to sedate children for head CT was noted by 73%. Published guidelines for sedation are followed by 74%; 10% were unaware of the existence of published guidelines for sedation. Twenty-six percent of the respondents were very or somewhat dissatisfied with their sedation-related practices. In response to three clinical scenarios involving sedation of 8-month-old, 3-year-old, and 6-year-old children for head CT, midazolam was the most commonly chosen drug. Over 20 different sedation strategies were selected for each scenario. CONCLUSIONS: Sedation practices for post-traumatic pediatric head CT vary widely, among both physicians and individual practitioners. Institutional and individual sedation-relation policies vary widely as well. Variation and dissatisfaction with sedation practices may reflect uncertainty regarding optimal sedation strategies. Further cost-effectiveness research is necessary.

Oligopeptide elicitor-mediated defense gene activation in cultured parsley cells.

We have used suspension-cultured parsley cells (Petroselinum crispum) and an oligopeptide elicitor derived from a surface glycoprotein of the phytopathogenic fungus Phytophthora megasperma f.sp. glycinea to study the signaling pathway from elicitor recognition to defense gene activation. Immediately after specific binding of the elicitor by a receptor in the plasma membrane, large and transient increases in several inorganic ion fluxes (Ca2+, H+, K+, Cl-) and H2O2 formation are the first detectable plant cell responses. These are rapidly followed by transient changes in the phosphorylation status of various proteins and by the activation of numerous defense-related genes, concomitant with the inactivation of several other, non-defense-related genes. A great diversity of cis-acting elements and trans-acting factors appears to be involved in elicitor-mediated gene regulation, similar to the apparently complex nature of the signal transduced intracellularly. With few exceptions, all individual defense responses analyzed in fungus-infected parsley leaves have been found to be closely mimicked in elicitor-treated, cultured parsley cells, thus validating the use of the elicitor/cell culture system as a valuable model system for these types of study.

Molecular characterization of nucleotide sequences encoding the extracellular glycoprotein elicitor from Phytophthora megasperma.

cDNA sequences encoding the 42 kDa glycoprotein elicitor from the oomycete, Phytophthora megasperma, that induces the defense response in parsley have been cloned and sequenced. The 5' end of the mRNA matches a consensus derived from sequences surrounding the transcription initiation sites of seven other oomycete genes. The major transcript of 1802 nucleotides contains a 529-codon open reading frame, which was predicted to encode a 57 kDa precursor protein. On the basis of peptide sequencing, the N-terminus of the mature protein is at position 163, suggesting that proteolytic processing events, in addition to signal peptide cleavage, generate the protein purified from the fungal culture filtrate. Expression studies in Escherichia coli with the cDNA as well as smaller subfragments demonstrated that a region of 47 amino acids located in the C-terminal third of the protein was sufficient to confer elicitor activity. The gene encoding the elicitor was found to be a member of a multigene family in P. megasperma. Homologous families of differing sizes were found in all eight other Phytophthora species tested, but not in other filamentous fungi including other Oomycetes. No significant similarity of the elicitor preprotein to sequences present in the databases has yet been detected.

High affinity binding of a fungal oligopeptide elicitor to parsley plasma membranes triggers multiple defense responses.

An oligopeptide of 13 amino acids (Pep-13) identified within a 42 kDa glycoprotein elicitor from P. mega-sperma was shown to be necessary and sufficient to stimulate a complex defense response in parsley cells comprising H+/Ca2+ influxes, K+/Cl- effluxes, an oxidative burst, defense-related gene activation, and phytoalexin formation. Binding of radiolabeled Pep-13 to parsley microsomes and protoplasts was specific, reversible, and saturable. Identical structural features of Pep-13 were found to be responsible for specific binding and initiation of all plant responses analyzed. The high affinity binding site recognizing the peptide ligand (KD = 2.4 nM) may therefore represent a novel class of receptors in plants, and the rapidly induced ion fluxes may constitute elements of the signal transduction cascade triggering pathogen defense in plants.

Perception and transduction of an elicitor signal in cultured parsley cells.

Treatment of cultured parsley cells or protoplasts with a purified extracellular glycoprotein from Phytophthora megasperma f.sp. glycinea induces the transcription of the same set of defence-related genes as is activated in parsley leaves upon infection. Elicitor activity was shown to reside in a specific portion of the protein moiety which was isolated, sequenced and synthesized. Partial cDNAs encoding the entire mature protein as well as other related proteins have been isolated, indicating the presence of a small gene family. The elicitor-active oligopeptide is located in the C-terminal portion of the deduced amino acid sequence. Binding of the elicitor to target sites on the parsley plasma membrane appears to be the initial event in defence gene activation. The subsequent intracellular transduction of the elicitor signal was shown to involve rapid and transient influxes of Ca2+ and H+, as well as effluxes of K+ and Cl-. Inhibition of elicitor-induced ion fluxes by channel blockers also inhibited phytoalexin synthesis, while stimulation of similar ion fluxes by treatment of cells or protoplasts with the polyene antibiotic, amphotericin B, induced the production of phytoalexins and activated the complete set of defence-related genes in the absence of elicitor.

Inhibition of pyruvate dehydrogenase complex (PDHC) by antipsychotic drugs.

The effects of 11 antipsychotic drugs on the pyruvate dehydrogenase complex (PDHC) prepared from bovine heart and rat brain were investigated. All inhibited PDHC to varying extents. With clinically equivalent doses, chlorpromazine and thioridazine inhibited the most and fluphenazine and thiothixene the least. The relationship of degree of inhibition of PDHC by neuroleptics to clinical improvement of 32 outpatients treated with acetazolamide and thiamine (A + T) ancillary therapy for chronic mental illness suggests that patients treated with psychoactive drugs that inhibit PDHC the least are most likely to have a favorable response with A + T treatment.

Design of a 13C (1H) RF probe for monitoring the in vivo metabolism of [1-13C]glucose in primate brain.

The design of an RF probe suitable for obtaining proton-decoupled 13C spectra from a subhuman primate brain is described. Two orthogonal saddle coils, one tuned to the resonant frequency of 13C and the other to the resonant frequency of 1H, were used to monitor the in vivo metabolism of [1-13C]glucose in rhesus monkey brain at 2.1 T. Difference spectra showed the appearance of 13C-enriched glutamate and glutamine 30 to 40 min after a bolus injection of [1-13C]glucose.

Acetazolamide and thiamine: an ancillary therapy for chronic mental illness.

Twenty-four chronic schizophrenic patients were treated successfully with the addition of acetazolamide and thiamine (A + T) to their unchanged existing therapies in a double-blind, placebo-controlled crossover study. Therapeutic effects were measured by the Scale for the Assessment of Positive Symptoms and the Scale for the Assessment of Negative Symptoms. Overall, 50% of the patients showed improvement on all assessment scales. No untoward effects occurred in these patients or in patients in previous studies who have been treated continuously with A + T therapy for as long as 3 years.