Observation of Antiferromagnetic Magnon Pseudospin Dynamics and the Hanle Effect.

We report on experiments demonstrating coherent control of magnon spin transport and pseudospin dynamics in a thin film of the antiferromagnetic insulator hematite utilizing two Pt strips for all-electrical magnon injection and detection. The measured magnon spin signal at the detector reveals an oscillation of its polarity as a function of the externally applied magnetic field. We quantitatively explain our experiments in terms of diffusive magnon transport and a coherent precession of the magnon pseudospin caused by the easy-plane anisotropy and the Dzyaloshinskii-Moriya interaction. This experimental observation can be viewed as the magnonic analog of the electronic Hanle effect and the Datta-Das transistor, unlocking the high potential of antiferromagnetic magnonics toward the realization of rich electronics-inspired phenomena.

Improving the modelling of susceptibility-induced spatial distortions in MRI-guided extra-cranial radiotherapy.

Magnetic-resonance linear-accelerator (MR-LINAC) systems integrating in-room magnetic-resonance-imaging (MRI) guidance are a currently emerging technology. Such systems address the need to provide frequent imaging at optimal soft-tissue contrast for treatment guidance. However, the use of MRI-guidance in radiotherapy should address imaging-related spatial distortions, which may hinder accurate geometrical characterization of the treatment site. Since spatial encoding relies on well-defined magnetic fields, accurate modeling of the magnetic field alterations due to [Formula: see text]-inhomogeneities, gradient nonlinearities, and susceptibilities is needed. In this work, the modeling of susceptibility induced distortions is considered. Dedicated susceptibility measurements are reported, aiming at extending the characterization of different tissues for MRI-guided extra-cranial radiotherapy applications. A digital 4D anthropomorphic phantom, providing time-resolved anatomical changes due to breathing, is exploited as reference anatomy to quantify spatial distortions due to variations in tissue susceptibility. Sub-millimeter values can be attributed to susceptibility-induced distortions, with maximum values up to 2.3 mm at a gradient strength of 5 mT m-1. Improvements in susceptibility simulation for extra-cranial sites are shown when including specifically the contributions from lung, liver and muscular tissues.

Spin Hall magnetoresistance induced by a nonequilibrium proximity effect.

We report anisotropic magnetoresistance in Pt|Y(3)Fe(5)O(12) bilayers. In spite of Y(3)Fe(5)O(12) being a very good electrical insulator, the resistance of the Pt layer reflects its magnetization direction. The effect persists even when a Cu layer is inserted between Pt and Y(3)Fe(5)O(12), excluding the contribution of induced equilibrium magnetization at the interface. Instead, we show that the effect originates from concerted actions of the direct and inverse spin Hall effects and therefore call it "spin Hall magnetoresistance."

Observation of an unconventional metal-insulator transition in overdoped CuO2 compounds.

The electron dynamics in the normal state of Bi(2)Sr(2)CaCu(2)O(8+delta) is studied by inelastic light scattering over a wide range of doping. A strong anisotropy of the electron relaxation is found which cannot be explained by single-particle properties alone. The results strongly indicate the presence of an unconventional quantum-critical metal-insulator transition where "hot" (antinodal) quasiparticles become insulating while "cold" (nodal) quasiparticles remain metallic. A phenomenology is developed which allows a quantitative understanding of the Raman results and provides a scenario which links single- and many-particle properties.

Activation and repression of transcription initiation by a distant DNA structural transition.

Negative superhelical tension can drive local transitions to alternative DNA structures. Long regions of DNA may contain several sites that are susceptible to forming alternative structures. Their relative propensities to undergo transition are ordered according to the energies required for their formation. These energies have two components - the energy needed to drive the transition and the energy relieved by the partial relaxation of superhelicity that the transition provides. This coupling can cause a complex competition among the possible transitions, in which the formation of one energetically favourable alternative structure may inhibit the formation of another within the same domain. In principle, DNA structural competitions can affect the structural and energetic requirements for the initiation of transcription at distant promoter sites. We have tested this possibility by examining the effects of structural transitions on transcription initiation from promoter sites in the same superhelical domain. Specifically, we describe the effects of the presence of a Z-DNA-forming DNA sequence on the basal levels of expression of two supercoiling-sensitive promoters of Escherichia coli, ilvPG and gyrA. We demonstrate transcriptional repression of the ilvPG promoter and activation of the gyrA promoter. We present evidence that this regulation is effected by the superhelically induced B- to Z-DNA transition in a manner that is both orientation and distance independent. We discuss the mechanism of topological coupling between left-handed Z-DNA and the regulation of promoter activity. We also discuss the possibility that the coupling of DNA structural transitions and transcriptional activity might be used as a general regulatory mechanism for gene expression.

The effects of DNA supercoiling on the expression of operons of the ilv regulon of Escherichia coli suggest a physiological rationale for divergently transcribed operons.

Transcriptional activities of closely spaced divergent promoters are affected by the accumulation of local negative superhelicity in the region between transcribing RNA polymerase molecules (transcriptional coupling). The effect of this transcription-induced DNA supercoiling on these promoters depends on their intrinsic properties. As the global superhelical density of the chromosome is controlled by the energy charge of the cell, which is affected by environmental stresses and transitions from one growth state to another, the transcriptional coupling that occurs between divergently transcribed promoters is likely to serve a physiological purpose. Here, we suggest that transcriptional coupling between the divergent promoters of the ilvYC operon of Escherichia coli serves to co-ordinate the expression of this operon with other operons of the ilv regulon during metabolic adjustments associated with growth state transitions. As DNA supercoiling-dependent transcriptional coupling between the promoters of other divergently transcribed operons is investigated, additional global gene regulatory mechanisms and physiological roles are sure to emerge.

DNA supercoiling-dependent transcriptional coupling between the divergently transcribed promoters of the ilvYC operon of Escherichia coli is proportional to promoter strengths and transcript lengths.

The twin-domain model of Liu and Wang suggested that high levels of DNA supercoiling generated in the region between closely spaced divergently transcribed promoters could serve to couple the activities of these promoters transcriptionally. In this report, we use topoisomer sets of defined superhelical densities as DNA templates in a purified in vitro transcription system to demonstrate transcriptional coupling between the divergently transcribed ilvY and ilvC promoters of the ilvYC operon of Escherichia coli. Current evidence for this type of DNA supercoiling-dependent transcriptional coupling, based largely on the in vivo activities of promoters contained in engineered DNA constructs, suggests that the transcription complex must be physically hindered to generate DNA supercoils and to prevent their diffusion throughout the DNA duplex. However, the in vitro results presented here demonstrate that (i) transcriptional coupling is observed between the divergent promoters of the ilvYC operon in the absence of transcript anchoring; (ii) the magnitude of the negative DNA supercoiling generated in the divergent promoter region is proportional to the sum of the global and transcription-induced superhelicity; and (iii) the magnitude of this transcription-induced superhelicity is proportional to promoter strengths and transcript lengths.

Transcriptional coupling between the divergent promoters of a prototypic LysR-type regulatory system, the ilvYC operon of Escherichia coli.

The twin-domain model [Liu, L. F. & Wang, J. C. (1987) Proc. Natl. Acad. Sci. USA 84, 7024-7027] suggests that closely spaced, divergent, superhelically sensitive promoters can affect the transcriptional activity of one another by transcriptionally induced negative DNA supercoiling generated in the divergent promoter region. This gene arrangement is observed for many LysR-type-regulated operons in bacteria. We have examined the effects of divergent transcription in the prototypic LysR-type system, the ilvYC operon of Escherichia coli. Double-reporter constructs with the lacZ gene under transcriptional control of the ilvC promoter and the galK gene under control of the divergent ilvY promoter were used to demonstrate that a down-promoter mutation in the ilvY promoter severely decreases in vivo transcription from the ilvC promoter. However, a down-promoter mutation in the ilvC promoter only slightly affects transcription from the ilvY promoter. In vitro transcription assays with DNA topoisomers showed that transcription from the ilvC promoter increases over the entire range of physiological superhelical densities, whereas transcription initiation from the ilvY promoter exhibits a broad optimum at a midphysiological superhelical density. Evidence that this promoter coupling is DNA supercoiling-dependent is provided by the observation that a novobiocin-induced decrease in global negative superhelicity results in an increase in ilvY promoter activity and a decrease in ilvC promoter activity predicted by the in vitro data. We suggest that this transcriptional coupling is important for coordinating basal level expression of the ilvYC operon with the nutritional and environmental conditions of cell growth.

An automated patient registration and treatment randomization system for multicenter clinical trials.

This article describes an automated patient registration/treatment randomization system for multicenter clinical trials. Registrations take place centrally using telephone keypads (tone-dial) for data entry and synthesized speech (at the coordinating center) for confirmation. The system permits a wide variety of protocol designs and treatment assignment schemes and presently supports more than 85 protocols of the Pediatric Oncology Group. It is developed in modules to permit easy addition/deletion of studies and treating sites. The system permits uninterrupted, unattended operation at the coordinating center 7 days a week, 24 hours a day.

Fatigue effects on intelligence test performance in the elderly.

The purpose of the study was to investigate effects of fatigue on intelligence test performance in the elderly. Dependent variables were Verbal Comprehension, Numerical Facility, Perceptual Speed, and Word Fluency tests. Fatigue effects were investigated by varying the number of previous tests administered, by introducing breaks between tests in some conditions, and by using a pre-test fatigue-producing condition, a modified form of the Finding A's test. Subjects' ages were between 57 to 91-years. It was hypothesized that the Finding A's test would be more fatiguing than a long battery of tests and that introducing a break condition between the Finding A's test and the main battery would alleviate fatigue effects. Analyses of Variance resulted in a main effect due to a pre-test condition for the Perceptual Speed test only, and only when the main battery was preceded by the Finding A's task (p less than .001). It appears that the elderly are not as susceptible to test fatigue as previous results seemed to suggest.