Electronic transport in single-molecule magnets on metallic surfaces

An electron transport is studied in the system that consists of a scanning tunneling microscopy, single-molecule magnet metal. Because of quantum tunneling of magnetization in a single-molecule magnet, linear response conductance exhibits stepwise behavior with increasing longitudinal field, and each step is maximized at a certain value of field sweeping speed. The conductance at each step oscillates as a function of the additional transverse magnetic field along the hard axis. A rigorous theory is presented that combines the exchange model with the Landau-Zener model.     

Feasibility of proton chemical shift imaging with a stereotactic headframe

To prove feasibility of proton chemical shift imaging ((1)H CSI) during stereotactic procedure, authors performed (1)H CSI in combination with a stereotactic headframe and selected targets according to local metabolic information, evaluated the pathologic results. The (1)H CSI directed stereotactic biopsy was performed in four patients. (1)H CSI and conventional Gd-enhancement stereotactic MRI were performed simultaneously after the fitting of a stereotactic headframe. Focal areas of increased phosphocholine(Cho)/phosphocreatine(Cr) and Lactate/Cr ratios were selected as target sites in the stereotactic MR images. (1)H CSI is possible with the stereotactic headframe in place. Pathologic samples taken from areas of increased Cho/Cr ratios and decreased NAA/Cr ratios provided information upon increased cellularity, mitoses and cellular atypism, and facilitated diagnosis. Pathologic samples taken from areas of increased Lac/Cr ratio showed predominant feature of necrosis. (1)H CSI was feasible with the stereotactic headframe in place. The final pathologic results obtained were concordant with the local metabolic information from (1)H CSI. We believe that (1)H CSI-directed stereotactic biopsy has the potential to significantly improve the accuracy of stereotactic biopsy targeting.     

Kondo effect in magnetic tunnel junctions

Tunneling magnetoresistance was found to be suppressed with decreasing temperature for magnetic tunnel junctions (MTJs) oxidized under high plasma power. A strong temperature dependence of the junction resistance was observed, along with zero-bias anomalies of dynamic resistance at low temperatures. Resistance shows a logarithmic dependence on temperature, and resistance versus temperature exhibits a scaling behavior. Our experimental data can be explained in a consistent way by the Kondo effect in the MTJs with the Kondo temperature TK=20-30 K.     

Comparison of noise power spectrum methodologies in measurements by using megavoltage X-ray energies

The noise power spectrum (NPS) is one of the most general methods for measuring the noise amplitude and the quality of an image acquired from a uniform radiation field. The purpose of this study was to compare different NPS methodologies by using megavoltage X-ray energies. The NPS evaluation methods in diagnostic radiation were applied to therapy using the International Electrotechnical Commission standard (IEC 62220-1). In order to measure the region of interest (ROI) of the NPS, we used the following five factors: the overlapping impact, the non-overlapping impact, the penumbra, the flatness and different ROI sizes. We used NPS from four different types of detectors, the CR-IP (computed radiography image plate: photo-stimulable phosphor screen), the CR-IP-lead (hexalon lead screen), the CR-IP-back [lanex TM fast back screen: {terbium-doped gadolinium oxysulfide granular phosphor screen (Gd₂O₂S:Tb,133 mg/cm²)} + 1-mm-thick copper plate and the CR-IP-front (lanex TM fast front screen). A Kodak 2000 RT photo-stimulable phosphor-based computed radiographic (CR) system showed that the normalized noise power spectrum (NNPS) curve gradually decreased, in compliance with increasing spatial resolution. In addition, each detector showed a different reactivity of the NPS to megavoltage. The results of multivariate analysis of variance (MANOVA) test (methods × detectors) revealed significant main effects of the methods [F(1, 4) = 53.543, P = 0.001 and of the detectors [F(1, 4) = 17.556, P = 0.001]. The present study revealed that various factors could be employed to produce megavoltage imaging (MVI) of the NPS and as a baseline standard for NPS control in MVI.

     

Thermopower of an Aharonov-Bohm interferometer: theoretical studies of quantum dots in the Kondo regime

We report on the thermopower of an Aharonov-Bohm (AB) interferometer with a quantum dot in the Kondo regime. The thermopower is anomalously enhanced due to the Kondo effect as in heavy fermion systems. In contrast to bulk systems, the sign of the thermopower can be changed by adjusting the energy level scheme or the particle-hole asymmetry of a dot with the gate voltage. Further the magnitude and even the sign of the thermopower in the AB ring can be changed at will with varying either magnetic fields or the gate voltages.     

Repeated-Binge Ethanol Intoxication Leads to Lower Choline-Containing Compound Signals in Adult Rats: An In Vivo Marker of Ethanol-Induced Neurochemical Abnormalities

Ethanol is the most commonly abused intoxicating substance among young and middle-aged adults, and ranks highly as a cause of disability and mortality. A pattern of heavy consumption, called binge drinking, leads to various psychiatric disorders. However, to the best of our knowledge, assessments of the influence of short-term binge ethanol (SBE) intoxication on cerebral metabolite changes in human and rat models are scarce. We used in vivo ¹H magnetic resonance spectroscopy (¹H-MRS) to quantitatively assess neurochemical responses in hippocampus in a rat model of SBE intoxication. Seven SBE-exposed rats received an initial dose of 5.0-g/kg ethanol (30 %-w/v solution) through gavage and additional doses of 2.0-g/kg ethanol (25 %-w/v solution), every 8 hour for 4 days. Six rats in sham control group (CNTL) received an equivalent volume of distilled water at comparable times. Sixty minutes after last gavage session, in vivo ¹H-MRS scans were obtained from all rats using a 4.7 Tesla animal scanner. For neurochemical analysis, a single voxel was positioned in the hippocampal region and spectra were fitted for the quantification of 17 cerebral neurochemical signals. In hippocampus, the concentration of total choline-containing compound signals (tCho: [glycerophosphocholine] + [phosphocholine]) was significantly lower in SBE-exposed rats than in CNTL rats. Moreover, gamma-aminobutyric acid (GABA)/total creatine (tCr: creatine + phosphocreatine), tCho/tCr, and tCho/total N-acetyl-aspartate (tNAA: N-acetyl-aspartate + N-acetyl-aspartyl-glutamate) ratios were significantly lower in SBE-exposed rats than CNTL rats. We determined that tCho, GABA, and tNAA signals were highly sensitive to short-term binge ethanol intoxication, which provides insights into neurochemical alterations associated with ethanol abuse.