Extraordinary Magnetoresistance in Hybrid Semiconductor-Metal Systems

We show that extraordinary magnetoresistance (EMR) arises in systems consisting of two components; a semiconducting ring with a metallic inclusion embedded. The im- portant aspect of this discovery is that the system must have a quasi-two-dimensional character. Using the same materials and geometries for the samples as in experiments by Solin et al.[1;2], we show that such systems indeed exhibit a huge magnetoresistance. The magnetoresistance arises due to the switching of electrical current paths passing through the metallic inclusion. Diagrams illustrating the flow of the current density within the samples are utilised in discussion of the mechanism responsible for the magnetoresistance effect. Extensions are then suggested which may be applicable to the silver chalcogenides. Our theory offers an excellent description and explanation of experiments where a huge magnetoresistance has been discovered[2;3].Comment: 12 Pages, 5 Figure

Room temperature ballistic transport in InSb quantum well nanodevices

We report the room temperature observation of significant ballistic electron transport in shallow etched four-terminal mesoscopic devices fabricated on an InSb/AlInSb quantum well (QW) heterostructure with a crucial partitioned growth-buffer scheme. Ballistic electron transport is evidenced by a negative bend resistance signature which is quite clearly observed at 295 K and at current densities in excess of 10$^{6}$ A/cm$^{2}$. This demonstrates unequivocally that by using effective growth and processing strategies, room temperature ballistic effects can be exploited in InSb/AlInSb QWs at practical device dimensions

Multifunctional semiconductor micro-Hall devices for magnetic, electric, and photo-detection

We report the real-space voltage response of InSb/AlInSb micro-Hall devices to local photo-excitation, electric, and magnetic fields at room temperature using scanning probe microscopy. We show that the ultrafast generation of localised photocarriers results in conductance perturbations analogous to those produced by local electric fields. Experimental results are in good agreement with tight-binding transport calculations in the diffusive regime. The magnetic, photo, and charge sensitivity of a 2 μm wide probe are evaluated at a 10 μA bias current in the Johnson noise limit (valid at measurement frequencies > 10 kHz) to be, respectively, 500 nT/√Hz; 20 pW/√Hz (λ = 635 nm) comparable to commercial photoconductive detectors; and 0.05 e/√Hz comparable to that of single electron transistors. These results demonstrate the remarkably versatile sensing attributes of simple semiconductor micro-Hall devices that can be applied to a host of imaging and sensing applications

Subjective mental well-being among higher education students in Finland during the first wave of COVID-19

Aims: Increased mental health problems during the COVID-19 pandemic have become a major concern among young adults. Our aim was to understand which COVID-19-related questions predicted mental well-being during the outbreak. Methods: Two cross-sectional datasets were used. The primary dataset was collected in May 2020 (n = 1001), during the initial COVID-19 outbreak, and the secondary in April 2019 (n = 10866), before the pandemic. Mental well-being was assessed with the Short Warwick-Edinburgh Mental Well-Being Scale. Relationships between mental well-being and COVID-19-related questions were investigated with lasso regression. As an exploratory analysis, two-way ANOVAs were used to compare mental well-being before and during the outbreak. Results: Higher levels of mental well-being were associated with lower levels of academic stress and COVID-19-related worry, along with a higher satisfaction with the procedures and information provided by the higher education institutions and the government. COVID-19-related symptoms and infections did not have an impact on students' mental well-being during the outbreak. Small to moderate effect sizes across the time points were detected, indicating an overall decrease in mental well-being across age and gender during the outbreak. Conclusions: COVID-19 had an impact on higher education students' mental well-being. Higher education institutes may play a crucial role in protecting their students' well-being during uncertain times.Peer reviewe

Cessation of anti-VLA-4 therapy in a focal rat model of multiple sclerosis causes an increase in neuroinflammation

BackgroundPositron emission tomography (PET) can be used for in vivo evaluation of the pathology associated with multiple sclerosis. We investigated the use of longitudinal PET imaging and the 18-kDa translocator protein (TSPO) binding radioligand [F-18]GE-180 to detect changes in a chronic multiple sclerosis-like focal delayed-type hypersensitivity experimental autoimmune encephalomyelitis (fDTH-EAE) rat model during and after anti-VLA-4 monoclonal antibody (mAb) treatment. Thirty days after lesion activation, fDTH-EAE rats were treated with the anti-VLA-4 mAb (n=4) or a control mAb (n=4; 5mg/kg, every third day, subcutaneously) for 31days. Animals were imaged with [F-18]GE-180 on days 30, 44, 65, 86 and 142. Another group of animals (n=4) was used for visualisation the microglia with Iba-1 at day 44 after a 2-week treatment period.ResultsAfter a 2-week treatment period on day 44, there was a declining trend (p=0.067) in [F-18]GE-180-binding in the anti-VLA-4 mAb-treated animals versus controls. However, cessation of treatment for 4days after a 31-day treatment period increased [F-18]GE-180 binding in animals treated with anti-VLA-4 mAb compared to the control group (p=0.0003). There was no difference between the groups in TSPO binding by day 142.ConclusionsThese results demonstrated that cessation of anti-VLA-4 mAb treatment for 4days caused a transient rebound increase in neuroinflammation. This highlights the usefulness of serial TSPO imaging in the fDTH-EAE model to better understand the rebound phenomenon

Refined estimates of local recurrence risks by DCIS score adjusting for clinicopathological features: a combined analysis of ECOG-ACRIN E5194 and Ontario DCIS cohort studies

Purpose Better tools are needed to estimate local recurrence (LR) risk after breast-conserving surgery (BCS) for DCIS. The DCIS score (DS) was validated as a predictor of LR in E5194 and Ontario DCIS cohort (ODC) after BCS. We combined data from E5194 and ODC adjusting for clinicopathological factors to provide refined estimates of the 10-year risk of LR after treatment by BCS alone. Methods Data from E5194 and ODC were combined. Patients with positive margins or multifocality were excluded. Identical Cox regression models were fit for each study. Patient-specific meta-analysis was used to calculate precision-weighted estimates of 10-year LR risk by DS, age, tumor size and year of diagnosis. Results The combined cohort includes 773 patients. The DS and age at diagnosis, tumor size and year of diagnosis provided independent prognostic information on the 10-year LR risk (p ≤ 0.009). Hazard ratios from E5194 and ODC cohorts were similar for the DS (2.48, 1.95 per 50 units), tumor size ≤ 1 versus > 1–2.5 cm (1.45, 1.47), age ≥ 50 versus 15%) 10-year LR risk after BCS alone compared to utilization of DS alone or clinicopathological factors alone. Conclusions The combined analysis provides refined estimates of 10-year LR risk after BCS for DCIS. Adding information on tumor size and age at diagnosis to the DS adjusting for year of diagnosis provides improved LR risk estimates to guide treatment decision making

Renormalization-group study of Anderson and Kondo impurities in gapless Fermi systems

Thermodynamic properties are presented for four magnetic impurity models describing delocalized fermions scattering from a localized orbital at an energy-dependent rate $\Gamma(\epsilon)$ which vanishes precisely at the Fermi level, $\epsilon = 0$. Specifically, it is assumed that for small $|\epsilon|$, $\Gamma(\epsilon)\propto|\epsilon|^r$ with $r>0$. The cases $r=1$ and $r=2$ describe dilute magnetic impurities in unconventional superconductors, ``flux phases'' of the two-dimensional electron gas, and zero-gap semiconductors. For the nondegenerate Anderson model, the depression of the low-energy scattering rate suppresses mixed valence in favor of local-moment behavior, and leads to a marked reduction in the exchange coupling on entry to the local-moment regime, with a consequent narrowing of the range of parameters within which the impurity spin becomes Kondo-screened. The relationship between the Anderson model and the exactly screened Kondo model with power-law exchange is examined. The intermediate-coupling fixed point identified in the latter model by Withoff and Fradkin (WF) has clear signatures in the thermodynamic properties and in the local magnetic response of the impurity. The underscreened, impurity-spin-one Kondo model and the overscreened, two-channel Kondo model both exhibit a conditionally stable intermediate-coupling fixed point in addition to unstable fixed points of the WF type. In all four models, the presence or absence of particle-hole symmetry plays a crucial role.Comment: 44 two-column REVTex pages, 31 epsf-embedded EPS figures. MINOR formatting changes. To appear in Phys. Rev.

Increased Brain Fatty Acid Uptake in Metabolic Syndrome

OBJECTIVE: To test whether brain fatty acid uptake is enhanced in obese subjects with metabolic syndrome (MS) and whether weight reduction modifies it. RESEARCH DESIGN AND METHODS: We measured brain fatty acid uptake in a group of 23 patients with MS and 7 age-matched healthy control subjects during fasting conditions using positron emission tomography (PET) with [(11)C]-palmitate and [(18)F]fluoro-6-thia-heptadecanoic acid ([(18)F]-FTHA). Sixteen MS subjects were restudied after 6 weeks of very low calorie diet intervention. RESULTS: At baseline, brain global fatty acid uptake derived from [(18)F]-FTHA was 50% higher in patients with MS compared with control subjects. The mean percentage increment was 130% in the white matter, 47% in the gray matter, and uniform across brain regions. In the MS group, the nonoxidized fraction measured using [(11)C]-palmitate was 86% higher. Brain fatty acid uptake measured with [(18)F]-FTHA-PET was associated with age, fasting serum insulin, and homeostasis model assessment (HOMA) index. Both total and nonoxidized fractions of fatty acid uptake were associated with BMI. Rapid weight reduction decreased brain fatty acid uptake by 17%. CONCLUSIONS: To our knowledge, this is the first study on humans to observe enhanced brain fatty acid uptake in patients with MS. Both fatty acid uptake and accumulation appear to be increased in MS patients and reversed by weight reduction

Probing Mechanical Properties of Graphene with Raman Spectroscopy

The use of Raman scattering techniques to study the mechanical properties of graphene films is reviewed here. The determination of Gruneisen parameters of suspended graphene sheets under uni- and bi-axial strain is discussed and the values are compared to theoretical predictions. The effects of the graphene-substrate interaction on strain and to the temperature evolution of the graphene Raman spectra are discussed. Finally, the relation between mechanical and thermal properties is presented along with the characterization of thermal properties of graphene with Raman spectroscopy.Comment: To appear in the Journal of Materials Scienc