Spin-seebeck effect: a phonon driven spin distribution

Here we report on measurements of the spin-Seebeck effect in GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.

Early clinical experience of the safety and effectiveness of Hemospray in achieving hemostasis in patients with acute peptic ulcer bleeding

BACKGROUND AND STUDY AIMS

Endoscopic therapy of upper gastrointestinal bleeding remains challenging with conventional endoscopic devices. Use of Hemospray, where a nanopowder with clotting abilities is sprayed onto the bleeding site, had been highly effective for management of arterial bleeding in a heparizined animal model. The safety and effectiveness of Hemospray for hemostasis of active peptic ulcer bleeding in humans was evaluated.

PATIENTS AND METHODS

In a prospective, single-arm, pilot clinical study, consecutive adults with confirmed peptic ulcer bleeding (Forrest score Ia or Ib), who had all given informed consent to participation, underwent upper gastrointestinal endoscopy and application of Hemospray within 24 hours of hospital admission once hemodynamically stable. Up to two applications of Hemospray, not exceeding a total of 150 g were allowed. Bleeding recurrence was monitored post procedurally, by second-look endoscopy (72 hours post treatment), and by phone at 30 days. Rate of hemostasis, recurrent bleeding, mortality, need for surgical intervention, and treatment-related complications were assessed.

RESULTS

20 patients were recruited (18 men, 2 women; mean age 60.2 years). Acute hemostasis was achieved in 95 % (19 / 20) of patients; 1 patient had a pseudoaneurysm requiring arterial embolization. Bleeding recurred in 2 patients within 72 hours (shown by hemoglobin drop); neither had active bleeding identified at the 72-hour endoscopy. No mortality, major adverse events, or treatment- or procedure-related serious adverse events were reported during 30-day follow-up.

CONCLUSION

These pilot results indicate that Hemospray is safe in humans. Hemospray was effective in achieving acute hemostasis in active peptic ulcer bleeding.

Morphology of femtosecond laser modification of bulk dielectrics

Using 3D Finite-Difference-Time-Domain simulations, we study the morphology of the laser-created damage inside fused silica. Among the competing effects limiting the intensity in the dielectric, we find the most important is the pulse defocusing by the plasma lens, partially balanced by the Kerr effect. Less important are collisional energy dissipation and laser depletion by multi-photon absorption. We also found that the profile of generated plasma is asymmetrical in the transverse cross-section, with the plasma extended along the direction perpendicular to the laser polarization.

Observation of the spin-Seebeck effect in a ferromagnetic semiconductor

Reducing the heat generated in traditional electronics is a chief motivation for the development of spin-based electronics, called spintronics. Spin-based transistors that do not strictly rely on the raising or lowering of electrostatic barriers can overcome scaling limits in charge-based transistors. Spin transport in semiconductors might also lead to dissipation-less information transfer with pure spin currents. Despite these thermodynamic advantages, little experimental literature exists on the thermal aspects of spin transport in solids. A recent and surprising exception was the discovery of the spin-Seebeck effect, reported as a measurement of a redistribution of spins along the length of a sample of permalloy (NiFe) induced by a temperature gradient. This macroscopic spatial distribution of spins is, surprisingly, many orders of magnitude larger than the spin diffusion length, which has generated strong interest in the thermal aspects of spin transport. Here, the spin-Seebeck effect is observed in a ferromagnetic semiconductor, GaMnAs, which allows flexible design of the magnetization directions, a larger spin polarization, and measurements across the magnetic phase transition. This effect is observed even in the absence of longitudinal charge transport. The spatial distribution of spin currents is maintained across electrical breaks, highlighting the local nature of this thermally driven effect.

Oscillatory spin polarization and magneto-optical Kerr effect in Fe₃O₄ thin films on GaAs(001)

The spin dependent properties of epitaxial Fe₃O₄ thin films on GaAs(001) are studied by the ferromagnetic proximity polarization (FPP) effect and magneto-optical Kerr effect (MOKE). Both FPP and MOKE show oscillations with respect to Fe₃O₄ film thickness, and the oscillations are large enough to induce repeated sign reversals. We attribute the oscillatory behavior to spin-polarized quantum well states forming in the Fe₃O₄ film. Quantum confinement of the t(2g) states near the Fermi level provides an explanation for the similar thickness dependences of the FPP and MOKE oscillations.

Spin control of drifting electrons using local nuclear polarization in ferromagnet-semiconductor heterostructures

We demonstrate methods to locally control the spin rotation of moving electrons in a GaAs channel. The Larmor frequency of optically injected spins is modulated when the spins are dragged through a region of spin-polarized nuclei created at a MnAs/GaAs interface. The effective field created by the nuclei is controlled either optically or electrically using the ferromagnetic proximity polarization effect. Spin rotation is also tuned by controlling the carrier traverse time through the polarized region. We demonstrate coherent spin rotations of 5π   rad during transport.

[Demographic distribution and prevalence of overactive bladder in Venezuela]

OBJECTIVE

There is a lack of information regarding overactive bladder (OAB) in South America. Our aim in this study was to estimate the prevalence of overactive bladder (OAB) in Venezuela based on the 2002 International Continence Society (ICS) consensus criteria and also to verify its demographic distribution in this country.

SUBJECTS AND METHODS

We performed a multicentric prospective evaluation of patients from 2003 to 2007 in different cities in Venezuela. A number 3.407 adults (M:38%, F:62%) between 18 and 75 years of age (mean age 54 years) completed a physician guided questionnaire (V8) of urinary symptoms, bladder function, diet, general habits and general medical condition. Statistical procedures were carried out using software based on R programming for computational statistics.

RESULTS

The overall prevalence of OAB in Venezuela was determined as 21%. Female were more affected as compared to male (25.6% vs. 13.7% in men, p < 0.005) OAB was detected at early age (18 yrs) maintaining higher prevalence in women (M: 9%, F: 14%). In the studied cohort OAB shows its highest prevalence between the subgroup of 65 to 69 years of age. In all statistical tests the level of significance was defined as p < 0.005, with a confidence interval of 95%.

CONCLUSION

The OAB-V8 questionnaire aids to clearly identify patients with OAB symptoms. The overall prevalence of OAB in Venezuela is 21%. It is present in both genders, predominantly women and can be detected at early age.

Emergence of the persistent spin helix in semiconductor quantum wells

According to Noether's theorem, for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electron's spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin-orbit coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be achieved in a two-dimensional electron gas, despite the presence of spin-orbit coupling. The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the 'persistent spin helix'. SU(2) is realized, in principle, when the strengths of two dominant spin-orbit interactions, the Rashba (strength parameterized by alpha) and linear Dresselhaus (beta(1)) interactions, are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron-electron interactions, but is broken by the cubic Dresselhaus term (beta(3)) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as alpha approaches beta(1). Here we report experimental observation of the emergence of the persistent spin helix in GaAs quantum wells by independently tuning alpha and beta(1). Using transient spin-grating spectroscopy, we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant spin-orbit terms, identifying beta(3) as the main SU(2)-violating term in our samples. The tunable suppression of spin relaxation demonstrated in this work is well suited for application to spintronics.

A comprehensive view of the structure and expression of the ependymoma genome at presentation and relapse

2073

Background: Although pediatric and adult ependymomas are associated with significant mortality and morbidity, little is known about the biology of these tumors. To identify underlying genetic alterations and cellular pathways that drive this disease, we conducted a genomic study of 200 adult and pediatric ependymomas. Methods: Using 500k single nucleotide polymorphism arrays, U133 Affymetrix gene and microRNA (miRNA) expression microarrays, and appropriate bioinformatics, we characterized 56 supratentorial (ST), 104 posterior fossa (PF), and 40 spinal (SP) ependymomas. Real-Time polymerase chain reaction and fluorescence in situ hybridization validated observed genetic events. Results: Gene expression profiles segregated tumors by site and identified disease subgroups within each anatomical region (4 ST, 4 PF, 1 SP). miRNA expression profiles identified these same subgroups, indicating that they are biologically distinct. Subgroup-specific gene expression profiles were dictated partly by developmental regulatory genes and partly by large chromosomal gains (eg. 1q, 5p, 16p) and losses (eg. 9p, 22q). Integrated genetic and expression mapping revealed key candidate tumor suppressor (TSG) and onco- genes, likely drivers of these large alterations. While large chromosomal changes occurred more frequently in SP tumors (p < 0.0001), ST tumors averaged more focal changes (n = 13.2) than PF (n = 6.2) or SP tumors (n = 3.0) (p < 0.0001). A total of 29 and 33 non-random focal amplifications and deletions, respectively, encompassing 402 known genes and miRNA clusters, were validated, of which 80 displayed copy number driven expression. These genetic alterations targeted specific cellular functions (e.g., cell adhesion, cell-cycle, neuronal development) and pathways (e.g., NOTCH, EPHRIN, TP53). Our cohort also included five sample sets consisting of primary tumor and at least two corresponding relapses. Genomic analysis of these tumors identified large chromosomal alterations as well as focal gains and losses associated with disease relapse. Conclusions: We present a highly comprehensive view of the ependymoma genome, including 80 previously unrecognized candidate TSG and oncogenes that may afford diagnostic and therapeutic targets.

No significant financial relationships to disclose.

Inversion of ferromagnetic proximity polarization by MgO interlayers

We investigate the spin-dependent reflection properties in Fe/MgO/GaAs heterostructures by optical pump-probe measurement of the ferromagnetic proximity polarization (FPP). As a function of MgO thickness, the FPP is initially enhanced (<2.0 A) and then exhibits an unexpected sign reversal at approximately 5.0 A. The identification of two competing thresholds in the intensity dependence of FPP and the observation of FPP sign reversal in Fe/Mg/GaAs suggest that the inversion of FPP is related to an interfacial bonding effect.