Valley spin polarization by using the extraordinary Rashba effect on silicon

The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. So far, however, such devices have not been realized due to the difficulty to polarize the valleys, which is an indispensable step to activate this degree of freedom. Here we show the formation of 100% spin-polarized valleys by a simple and easy way using the Rashba effect on a system with C-3 symmetry. This polarization, which is much higher than those in ordinary Rashba systems, results in the valleys acting as filters that can suppress the backscattering of spin-charge. The present system is formed on a silicon substrate, and therefore opens a new avenue towards the realization of silicon spintronic devices with high efficiency.X114334Nsciescopu

Ferromagnetic Kondo-Lattice Model

We present a many-body approach to the electronic and magnetic properties of the (multiband) Kondo-lattice model with ferromagnetic interband exchange. The coupling between itinerant conduction electrons and localized magnetic moments leads, on the one hand, to a distinct temperature-dependence of the electronic quasiparticle spectrum and, on the other hand, to magnetic properties, as e.~g.the Curie temperature T_C or the magnon dispersion, which are strongly influenced by the band electron selfenergy and therewith in particular by the carrier density. We present results for the single-band Kondo-lattice model in terms of quasiparticle densities of states and quasiparticle band structures and demonstrate the density-dependence of the self-consistently derived Curie temperature. The transition from weak-coupling (RKKY) to strong-coupling (double exchange) behaviour is worked out. The multiband model is combined with a tight-binding-LMTO bandstructure calculation to describe real magnetic materials. As an example we present results for the archetypal ferromagnetic local-moment systems EuO and EuS. The proposed method avoids the double counting of relevant interactions and takes into account the correct symmetry of atomic orbitals.Comment: 15 pages, 10 figure

Magnetocaloric effect and magnetic cooling near a field-induced quantum-critical point

The presence of a quantum critical point (QCP) can significantly affect the thermodynamic properties of a material at finite temperatures T. This is reflected, e.g., in the entropy landscape S(T, r) in the vicinity of a QCP, yielding particularly strong variations for varying the tuning parameter r such as pressure or magnetic field B. Here we report on the determination of the critical enhancement of $\delta S / \delta B$ near a B-induced QCP via absolute measurements of the magnetocaloric effect (MCE), $(\delta T / \delta B)_S$, and demonstrate that the accumulation of entropy around the QCP can be used for efficient low-temperature magnetic cooling. Our proof of principle is based on measurements and theoretical calculations of the MCE and the cooling performance for a Cu$^{2+}$-containing coordination polymer, which is a very good realization of a spin-1/2 antiferromagnetic Heisenberg chain - one of the simplest quantum-critical systems.Comment: 21 pages, 4 figure

In Vitro Proliferation of Adult Human Beta-Cells

A decrease in functional beta-cell mass is a key feature of type 2 diabetes. Glucagon-like peptide 1 (GLP-1) analogues induce proliferation of rodent beta-cells. However, the proliferative capacity of human beta-cells and its modulation by GLP-1 analogues remain to be fully investigated. We therefore sought to quantify adult human beta-cell proliferation in vitro and whether this is affected by the GLP-1 analogue liraglutide

Bimodal Effect on Pancreatic β-Cells of Secretory Products From Normal or Insulin-Resistant Human Skeletal Muscle

OBJECTIVE: Type 2 diabetes is characterized by insulin resistance with a relative deficiency in insulin secretion. This study explored the potential communication between insulin-resistant human skeletal muscle and primary (human and rat) beta-cells. RESEARCH DESIGN AND METHODS: Human skeletal muscle cells were cultured for up to 24 h with tumor necrosis factor (TNF)-alpha to induce insulin resistance, and mRNA expression for cytokines was analyzed and compared with controls (without TNF-alpha). Conditioned media were collected and candidate cytokines were measured by antibody array. Human and rat primary beta-cells were used to explore the impact of exposure to conditioned media for 24 h on apoptosis, proliferation, short-term insulin secretion, and key signaling protein phosphorylation and expression. RESULTS: Human myotubes express and release a different panel of myokines depending on their insulin sensitivity, with each panel exerting differential effects on beta-cells. Conditioned medium from control myotubes increased proliferation and glucose-stimulated insulin secretion (GSIS) from primary beta-cells, whereas conditioned medium from TNF-alpha-treated insulin-resistant myotubes (TMs) exerted detrimental effects that were either independent (increased apoptosis and decreased proliferation) or dependent on the presence of TNF-alpha in TM (blunted GSIS). Knockdown of beta-cell mitogen-activated protein 4 kinase 4 prevented these effects. Glucagon-like peptide 1 protected beta-cells against decreased proliferation and apoptosis evoked by TMs, while interleukin-1 receptor antagonist only prevented the latter. CONCLUSIONS: Taken together, these data suggest a possible new route of communication between skeletal muscle and beta-cells that is modulated by insulin resistance and could contribute to normal beta-cell functional mass in healthy subjects, as well as the decrease seen in type 2 diabetes

Spin dynamics in the diluted ferromagnetic Kondo lattice model

The interplay of disorder and competing interactions is investigated in the carrier-induced ferromagnetic state of the Kondo lattice model within a numerical finite-size study in which disorder is treated exactly. Competition between impurity spin couplings, stability of the ferromagnetic state, and magnetic transition temperature are quantitatively investigated in terms of magnon properties for different models including dilution, disorder, and weakly-coupled spins. A strong optimization is obtained for T_c at hole doping p << x, highlighting the importance of compensation in diluted magnetic semiconductors. The estimated T_c is in good agreement with experimental results for Ga_{1-x}Mn_x As for corresponding impurity concentration, hole bandwidth, and compensation. Finite-temperature spin dynamics is quantitatively studied within a locally self-consistent magnon renormalization scheme, which yields a substantial enhancement in T_c due to spin clustering, and highlights the nearly-paramagnetic spin dynamics of weakly-coupled spins. The large enhancement in density of low-energy magnetic excitations due to disorder and competing interactions results in a strong thermal decay of magnetization, which fits well with the Bloch form M_0(1-BT^{3/2}) at low temperature, with B of same order of magnitude as obtained in recent squid magnetization measurements on Ga_{1-x}Mn_x As samples.Comment: 13 pages, 14 figure

Sustained Effects of Interleukin-1 Receptor Antagonist Treatment in Type 2 Diabetes

Objective: Interleukin (IL)-1 impairs insulin secretion and induces beta-cell apoptosis. Pancreatic beta-cell IL-1 expression is increased and interleukin-1-receptor antagonist (IL-1Ra) expression reduced in patients with type 2 diabetes mellitus. Treatment with recombinant IL-1Ra improves glycemia and beta-cell function and reduces inflammatory markers in patients with type 2 diabetes mellitus. Here we investigated the durability of these responses. Research Design and Methods: Among 70 ambulatory patients with type 2 diabetes and A1C and body mass index higher than 7.5% and 27, respectively, randomly assigned to receive 13 weeks of anakinra, a recombinant human IL-1Ra, or placebo, 67 completed treatment and were included in this double-blinded 39 week follow-up study. Primary outcome was change in betacell function following anakinra withdrawal. Analysis was done by intention-to-treat. Results: Thirty-nine weeks following anakinra withdrawal the proinsulin to insulin (PI/I) ratio but not stimulated C-peptide remained improved by -0.07 (95% CI -0.14 to -0.02, P=0.011) compared to placebo treated patients. Interestingly, a subgroup characterized by genetically determined low baseline IL-1Ra serum levels, maintained the improved stimulated C-peptide obtained by 13 weeks of IL-1Ra treatment. Reductions of C-reactive protein (-3.2 mg/l [95% CI -6.2 to -1.1, P=0.014]) and of IL-6 (-1.4 ng/l [95% CI -2.6 to -0.3, P=0.036]) were maintained until end of study. Conclusions: IL-1 blockade with anakinra induces improvement of the PI/I ratio and in markers of systemic inflammation lasting 39 weeks following treatment withdrawal

Gutzwiller-Correlated Wave Functions: Application to Ferromagnetic Nickel

Ferromagnetic Nickel is the most celebrated iron group metal with pronounced discrepancies between the experimental electronic properties and predictions of density functional theories. In this work, we show in detail that the recently developed multi-band Gutzwiller theory provides a very good description of the quasi-particle band structure of nickel. We obtain the correct exchange splittings and we reproduce the experimental Fermi-surface topology. The correct (111)-direction of the magnetic easy axis and the right order of magnitude of the magnetic anisotropy are found. Our theory also reproduces the experimentally observed change of the Fermi-surface topology when the magnetic moment is oriented along the (001)-axis. In addition to the numerical study, we give an analytical derivation for a much larger class of variational wave-functions than in previous investigations. In particular, we cover cases of superconductivity in multi-band lattice systems.Comment: 35 pages, 3 figure

Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons

The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions