Spectroscopy of magnetic excitations in magnetic superconductors using vortex motion.

In magnetic superconductors a moving vortex lattice is accompanied by an ac magnetic field which leads to the generation of spin waves. At resonance conditions the dynamics of vortices in magnetic superconductors changes drastically, resulting in strong peaks in the dc I-V characteristics at voltages at which the washboard frequency of the vortex lattice matches the spin wave frequency omegaS(g), where g are the reciprocal vortex lattice vectors. We show that if the washboard frequency lies above the magnetic gap, measurement of the I-V characteristics provides a new method to obtain information on the spectrum of magnetic excitations in borocarbides and cuprate layered magnetic superconductors.

Strongly enhanced current densities in superconducting coated conductors of YBa2Cu3O7-x + BaZrO3.

There are numerous potential applications for superconducting tapes based on YBa(2)Cu(3)O(7-x) (YBCO) films coated onto metallic substrates. A long-established goal of more than 15 years has been to understand the magnetic-flux pinning mechanisms that allow films to maintain high current densities out to high magnetic fields. In fact, films carry one to two orders of magnitude higher current densities than any other form of the material. For this reason, the idea of further improving pinning has received little attention. Now that commercialization of YBCO-tape conductors is much closer, an important goal for both better performance and lower fabrication costs is to achieve enhanced pinning in a practical way. In this work, we demonstrate a simple and industrially scaleable route that yields a 1.5-5-fold improvement in the in-magnetic-field current densities of conductors that are already of high quality.

Reflectivity and microwave absorption in crystals with alternating intrinsic Josephson junctions.

We compute the frequency and magnetic field dependencies of the reflectivity R(omega) in layered superconductors with two alternating intrinsic Josephson junctions with different critical current densities and quasiparticle conductivities for the electric field polarized along the c axis. The parameter alpha describing the electronic compressibility of the layers and the charge coupling of neighboring junctions was extracted for the SmLa1-xSr xCuO (4-delta) superconductor from two independent optical measurements, the fit of the loss function L(omega) at zero magnetic field and the magnetic field dependence of the peak positions in L(omega). The experiments are consistent with a free electron value for alpha.

Closing the pseudogap by Zeeman splitting in Bi2Sr2CaCu2O8+y at high magnetic fields.

Interlayer tunneling resistivity is used to probe the low-energy density-of-states (DOS) depletion due to the pseudogap in the normal state of Bi2Sr2CaCu2O8+y. Measurements up to 60 T reveal that a field that restores DOS to its ungapped state shows strikingly different temperature and doping dependencies from the characteristic fields of the superconducting state. The pseudogap closing field and the pseudogap temperature T small star, filled evaluated independently are related through a simple Zeeman energy scaling. These findings indicate a predominant role of spins over the orbital effects in the formation of the pseudogap.

C-axis Josephson plasma resonance observed in Tl(2)Ba(2)CaCu(2)O(8) superconducting thin films by use of terahertz time-domain spectroscopy.

We have unambiguously observed the c -axis Josephson plasma resonance (JPR) in high-critical-temperature (T(c)) cuprate (Tl(2)Ba(2)CaCu(2)O(8)) superconducting thin films, employing terahertz time-domain spectroscopy in transmission as a function of temperature in zero magnetic field. These are believed to be the first measurements of the JPR temperature dependence of a high-T(c) material in transmission. With increasing temperature, the JPR shifts from 705 GHz at 10 K to ~170 GHz at 98 K, corresponding to an increase in c-axis penetration depth from 22.4+/-0.6mum to 94+/-9mum . The linewidth of the JPR peak increases with temperature, which indicates an increase in the quasi-particle scattering rate. We have probed the onset of the c -axis phase coherence to ~0.95T(c) . The JPR vanishes above T(c) as expected.

Survival of enterococci and staphylococci on hospital fabrics and plastic.

The transfer of gram-positive bacteria, particularly multiresistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE), among patients is a growing concern. One critical aspect of bacterial transfer is the ability of the microorganism to survive on various common hospital surfaces. The purpose of this study was to determine the survival of 22 gram-positive bacteria (vancomycin-sensitive and -resistant enterococci and methicillin-sensitive and -resistant staphylococci) on five common hospital materials: smooth 100% cotton (clothing), 100% cotton terry (towels), 60% cotton-40% polyester blend (scrub suits and lab coats), 100% polyester (privacy drapes), and 100% polypropylene plastic (splash aprons). Swatches were inoculated with 10(4) to 10(5) CFU of a microorganism, assayed daily by placing the swatches in nutritive media, and examining for growth after 48 h. All isolates survived for at least 1 day, and some survived for more than 90 days on the various materials. Smaller inocula (10(2)) survived for shorter times but still generally for days. Antibiotic sensitivity had no consistent effect on survival. The long survival of these bacteria, including MRSA and VRE, on commonly used hospital fabrics, such as scrub suits, lab coats, and hospital privacy drapes, underscores the need for meticulous contact control procedures and careful disinfection to limit the spread of these bacteria.

The 1999 Lindberg award. 3% hydrogen peroxide for the gram-positive disinfection of fabrics.

Because of growing concern about the spread of antibiotic-resistant gram-positive bacteria in burn and trauma units, an inexpensive, safe, effective means of spot-disinfecting fabrics (such as privacy curtains) that remain in clinic or patient rooms as various patients use the rooms was sought. From comparisons of cost and safety data, 3% hydrogen peroxide was chosen to be tested for its efficacy in the control of these bacteria. Systematic laboratory testing used 30 antibiotic-resistant and sensitive staphylococci and enterococci and 4 common hospital fabrics: cotton (clothing), terry cloth (towels), cotton-polyester blend (scrub suits), and polyester (curtains). Without disinfection, bacteria survived for many hours to several days. After a single spraying with 3% hydrogen peroxide, all bacteria on all fabrics were dead within 5 to 120 minutes. On-site testing targeted privacy curtains in patients' rooms. Curtain edges that tended to be grabbed when moving the curtain showed a mixture of gram-positive and gram-negative bacteria (median, 22 bacteria/24 cm2). After these areas were sprayed with 3% hydrogen peroxide, no bacteria were found. It was concluded that spraying with 3% hydrogen peroxide is a safe, inexpensive, effective means of spot-disinfecting fabrics in patients' rooms; this simple procedure may limit the spread of potentially pathogenic antibiotic-resistant bacteria.

Causes of colonization of autografted burn wounds.

The progression of autograft colonization to infection presents significant problems in the care of grafted burn wounds. To determine whether graft colonization arises from self-contamination or from some exogenous source, we characterized pregraft and graft Candida albicans isolates through serotyping and biotyping (Leicester system) and Pseudomonas aeruginosa isolates through serotyping (Japan Pseudomonas aeruginosa Society system). In 21 of 24 patients, the serotype/biotype of the graft isolate was the same as the serotype/biotype of a C. albicans strain previously isolated from the same patient. Fifteen of 16 P. aeruginosa graft contaminants also showed the same serotype as that in a pregraft isolate. Therefore, whereas it has long been surmised that the grafts of patients with burns are self-colonized, this study provides definite data showing that most C. albicans and P. aeruginosa autograft isolates are indeed self-contaminants.

Use of nonsterile gloves for routine noninvasive procedures in thermally injured patients.

A total of 26 boxes of gloves were analyzed to determine if using nonsterile gloves for routine noninvasive procedures was sufficient for thermally injured patients and if the risk of infection increased. All of the study boxes had some organism present on or in the used box; the most common type found was Staphylococcus aureus. Eleven of the 13 subjects (85%) had specific antibiotic-resistant strains of S. aureus present on cultures obtained from open wounds. Seven (64%) of these corresponded to the glove boxes assigned to that patient. The remaining four boxes of gloves had no S. aureus present. In all of the boxes of gloves that had positive S. aureus cultures, 100% of the resistant strains occurred after it was first cultured from the patient. As a result, nonsterile gloves can be used safely for routine non-invasive procedures in the thermally injured patient. It is imperative to avoid using a common box of gloves for two or more patients to prevent the transfer of organisms between patients.

The value of culturing central-line catheter tips in burn patients.

Fifty burn patients who had central venous cannulations performed were randomly assigned to one of two groups. In group 1, the skin around the catheter insertion site was cleaned with 70% isopropyl alcohol prior to catheter removal. In group 2, the skin around the catheter insertion site was not cleaned prior to catheter removal. Twenty (40%) of the patients had negative cultures. The remaining 30 patients had positive cultures, 11 (37%) of which were positive for both skin and catheter tip specimens. All 11 of these cultures matched for the same organism. Six (55%) were from group 1 and five (45%) from group 2. Of the 14 patients with cultures positive for the catheter tips but not the skin, eight (57%) did not have the skin cleaned prior to catheter removal. Five skin cultures were positive, with no organism growth on the corresponding catheter tip; four (80%) of these were from group 2. Data from blood and intravenous (IV) catheter tip cultures performed from November 1982 through December 1985 demonstrated that of the 441 blood cultures obtained, 91 (21%) were positive. Twenty-seven (6%) were positive blood and IV catheter tip cultures; only ten (37%) of these matched for the same organism, accounting for only 2% of the total number of cultures obtained.