The miniaturization and integration of frequency-agile microwave circuits--relevant to electronically tunable filters, antennas, resonators and phase shifters--with microelectronics offers tantalizing device possibilities, yet requires thin films whose dielectric constant at gigahertz frequencies can be tuned by applying a quasi-static electric field. Appropriate systems such as BaxSr1-xTiO3 have a paraelectric-ferroelectric transition just below ambient temperature, providing high tunability. Unfortunately, such films suffer significant losses arising from defects. Recognizing that progress is stymied by dielectric loss, we start with a system with exceptionally low loss--Srn+1TinO3n+1 phases--in which (SrO)2 crystallographic shear planes provide an alternative to the formation of point defects for accommodating non-stoichiometry. Here we report the experimental realization of a highly tunable ground state arising from the emergence of a local ferroelectric instability in biaxially strained Srn+1TinO3n+1 phases with n ≥ 3 at frequencies up to 125 GHz. In contrast to traditional methods of modifying ferroelectrics-doping or strain-in this unique system an increase in the separation between the (SrO)2 planes, which can be achieved by changing n, bolsters the local ferroelectric instability. This new control parameter, n, can be exploited to achieve a figure of merit at room temperature that rivals all known tunable microwave dielectrics.
Two hundred and twelve urine specimens, from several clinical groups, were examined for BK virus (BKV) using the polymerase chain reaction (PCR) to detect the VP1 region of BKV DNA. Positive results were obtained on 14 specimens from 44 post-transplant patients (31.8%), 10 specimens from 39 pregnant women (25.6%), and 5 specimens from 100 children (5%) but not on any specimens from 29 laboratory staff. Twenty-eight of the amplified BKV genomes, 19 from urine specimens, eight from culture fluid of inoculated tissue, and also one from a throat washing were directly sequenced from single-stranded templates immobilized via a biotinylated primer; it was possible to assign all to one of the four subtypes of BKV which had previously been identified on the basis of variation in nucleotide sequence of the VP1 region. Serological subgroup classification correlated with the genomic subtyping results in 21 of the isolates. The distribution of the BKV subtypes and the clinical status of the infected individuals are discussed.
We present a new technique to measure the complex surface impedance of the mixed state of superconducting thin films over the broad frequency range 45 MHz-20 GHz. The surface impedance is extracted from measurements of the complex reflection coefficient made on the film using a vector network analyzer. The technique takes advantage of a special geometry in which the self-fields from currents flowing in the film are everywhere parallel to the film surface, making it an ideal configuration in which to study vortex dynamics in superconductors. The broadband nature of the measurement system allows us to explore a region of magnetic field-temperature-frequency parameter space of superconductors previously inaccessible with other measurement techniques. The power of the technique is illustrated by measurements on thin films of the high temperature superconductor YBa,Cu,07 _ 8
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.