Adiabatic transport in nanostructures

A confined system of non-interacting electrons, subject to the combined effect of a time-dependent potential and different external chemical-potentials, is considered. The current flowing through such a system is obtained for arbitrary strengths of the modulating potential, using the adiabatic approximation in an iterative manner. A new formula is derived for the charge pumped through an un-biased system (all external chemical potentials are kept at the same value); It reproduces the Brouwer formula for a two-terminal nanostructure. The formalism presented yields the effect of the chemical potential bias on the pumped charge on one hand, and the modification of the Landauer formula (which gives the current in response to a constant chemical-potential difference) brought about by the modulating potential on the other. Corrections to the adiabatic approximation are derived and discussed.Comment: 8 pages, 2 figure

Kondo screening cloud effects in mesoscopic devices

We study how finite size effects may appear when a quantum dot in the Kondo Coulomb blockade regime is embedded into a mesoscopic device with finite wires. These finite size effects appear when the size of the mesoscopic device containing the quantum dot is of the order of the size of Kondo cloud and affect all thermodynamic and transport properties of the Kondo quantum dot. We also generalize our results to the experimentally relevant case where the wires contain several transverse modes/channels. Our results are based on perturbation theory, Fermi liquid theory and slave boson mean field theory.Comment: 19 pages, 9 figure

Ternary Imidazolium-Pyrrolidinium-Based Ionic Liquid Electrolytes for Rechargeable Li-O 2 Batteries

The conductivity and anodic stability of ternary mixed ionic liquid (IL) electrolytes consisting of pyrrolidinium [N-butyl-Nmethylpyrrolidinium + (PYR 14 + )] and imidazolium [1-butyl-3-methylimidazolium + (BMIM + )] based bis(trifluoromethylsulfonyl) imide (TFSI − ) with 0.5 M LiTFSI salt were investigated. PYR 14 TFSI ionic liquid has been reported to be stable under an oxidative environment, while BMIMTFSI provides good ionic conductivity. A conductivity study of IL electrolytes revealed a linear correlation of conductivity as a function of IL -Li salt concentration and IL volume fraction. As a result, improved battery cycling in a mixture of 4:1 (80/20 v/v%) BMIM + : PYR 14 + was observed with a specific capacity of 330 mAh.g −1 over 50 cycles at a current density of 0.1 mA.cm −2 . Also, an EIS study revealed decreasing cathode polarization by demonstrating lower impedance values for ternary mixed electrolyte than that of the pure electrolytes upon cycling. The commercial potential of Li-O 2 rechargeable batteries is tremendous due to their extremely high theoretical energy density of 12 kWh.kg −1 (excluding oxygen), which is comparable to that of gasoline. 1 For automotive applications, Li-O 2 battery technology may be viable if it can provide 1.7 kWh.kg −1 of energy to the wheels after losses from the battery chemistry. However, this technology is suffering with several issues related to electrodes and electrolyte such as lithium metal corrosion, electrolyte decomposition, wettability, cathode structure retention, catalyst selection, among others, which result in a large irreversibility and poor cycle life. 1,2 Previous reports on electrolytes 3-5 suggest that conventional carbonate based electrolyte decomposes during the discharge process to produce irreversible byproducts such as alkyl carbonates and lithium carboxylates; and during the charging process, the oxidative decomposition of these byproducts 6 lead to CO 2 , CO, and other gases instead of O 2 . It has been found that this decomposition process is favored by the highly reactive superoxide radical anion (O 2 •− ) formed through single-electron reduction of oxygen (O 2 + e − → O 2 •− ). 9-11 Another polar solvent, dimethyl sulfoxide (DMSO), is not stable against a Li anode as it can absorb moisture from the air. 20 Although PYR 14 TFSI is stable, its high viscosity (100 centipoise) and low conductivity (1.4 × 10 −3 S cm −1 ) 21 limit the diffusion rate of lithium ions in the electrolyte. On the other hand, various imidazolium based molten salts have demonstrated better cyclability compared to pyrrolidinium in lithium batteries 22 because of the higher ionic conductivity and lower viscosity. Hence, a mixed imidazolium and pyrrolidinium based IL electrolyte could provide the stability and conductivity needed for both Liair and high power Li-ion batteries (LIB). For instance, a ternary ionic liquid: 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide, N-cyanoethyl-N,N,N-trimethylammonium bis(trifluoromethanesulfonyl)imide, and LiTFSI, exhibited a discharge capacity close z E-mail: [email protected] to the theoretical value with good compatibility with a LiCoO 2 cathode. 23 For Li-O 2 batteries, Cecchetto et al. investigated a mixture of PYR 14 TFSI: TEGDME-LiCF 3 SO 3 (1:1) and observed a lower overvoltage with higher conductivity for the electrolyte mixture than TEGDME alone. The present study aims to investigate ternary mixtures (IL 1 -IL 2 -Li-salt) of imidazolium and pyrrolidinium based ILs for Li-O 2 applications. BMIMTFSI was chosen as the imidazolium based IL as it has high ionic conductivity (4 mS.cm −1 ) and lower viscosity (32 centipoise), whereas, PYR 14 TFSI as a pyrrolidinium based IL as a stable solvent. Herein, different ternary mixtures of BMIMTFSI + PYR 14 TFSI + 0.5 M LiTFSI were prepared to study the effect of IL composition on ionic conductivity, electrochemical stability, lithium transference number, and Li-O 2 battery performance. It was found that 4:1 (BMIMTFSI:PYR 14 TFSI) mixed electrolyte enhanced both cyclic performance and columbic efficiency compared to BMIMTFSI or PYR 14 TFSI used alone. Experimental Ternary mixtures of electrolyte preparation.-1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl imide) (BMIMTFSI) (Sigma-Aldrich), and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR 14 TFSI) (TCI America) were used as room-temperature ionic liquids. The chemical structures are shown in Conductivity measurement.-Conductivity of all pure and mixtures of ILs were determined using a digital conductivity meter (VWR International, LLC, model 2052). All tests were measured at room temperature inside the glove box. Electrochemical stability measurement.-The electrochemical stability window of the LiTFSI-IL solutions was determined by linear sweep voltammetry (LSV) using a Gamry Reference 3000 Potentiosta

Temperature and Field Dependence of the Energy Gap of MgB2/Pb planar junction

We have constructed MgB2/Pb planar junctions for both temperature and field dependence studies. Our results show that the small gap is a true bulk property of MgB2 superconductor, not due to surface effects. The temperature dependence of the energy gap manifests a nearly BCS-like behavior. Analysis of the effect of magnetic field on junctions suggests that the energy gap of MgB2 depends non-linearly on the magnetic field. Moreover, MgB2 has an upper critical field of 15 T, in agreement with some reported Hc2 from transport measurements.Comment: 5 pages, 5 figures. Submitted to Phys. Rev.

Mesoscopic Fluctuations in Quantum Dots in the Kondo Regime

Properties of the Kondo effect in quantum dots depend sensitively on the coupling parameters and so on the realization of the quantum dot -- the Kondo temperature itself becomes a mesoscopic quantity. Assuming chaotic dynamics in the dot, we use random matrix theory to calculate the distribution of both the Kondo temperature and the conductance in the Coulomb blockade regime. We study two experimentally relevant cases: leads with single channels and leads with many channels. In the single-channel case, the distribution of the conductance is very wide as $T_K$ fluctuates on a logarithmic scale. As the number of channels increases, there is a slow crossover to a self-averaging regime.Comment: 4 pages, 3 figure

Siglec-7 represents a glyco-immune checkpoint for non-exhausted effector memory CD8+ T cells with high functional and metabolic capacities

While inhibitory Siglec receptors are known to regulate myeloid cells, less is known about their expression and function in lymphocytes subsets. Here we identified Siglec-7 as a glyco-immune checkpoint expressed on non-exhausted effector memory CD8+ T cells that exhibit high functional and metabolic capacities. Seahorse analysis revealed higher basal respiration and glycolysis levels of Siglec-7+ CD8+ T cells in steady state, and particularly upon activation. Siglec-7 polarization into the T cell immune synapse was dependent on sialoglycan interactions in trans and prevented actin polarization and effective T cell responses. Siglec-7 ligands were found to be expressed on both leukemic stem cells and acute myeloid leukemia (AML) cells suggesting the occurrence of glyco-immune checkpoints for Siglec-7+ CD8+ T cells, which were found in patients' peripheral blood and bone marrow. Our findings project Siglec-7 as a glyco-immune checkpoint and therapeutic target for T cell-driven disorders and cancer. Keywords: CD8+ T cells; Siglec-7; acute myeloid leukemia; hypersialylation; immune checkpoint; sialoglycans; tumor immunity and immunotherap

Siglec-7 represents a glyco-immune checkpoint for non-exhausted effector memory CD8+ T cells with high functional and metabolic capacities.

While inhibitory Siglec receptors are known to regulate myeloid cells, less is known about their expression and function in lymphocytes subsets. Here we identified Siglec-7 as a glyco-immune checkpoint expressed on non-exhausted effector memory CD8+ T cells that exhibit high functional and metabolic capacities. Seahorse analysis revealed higher basal respiration and glycolysis levels of Siglec-7+ CD8+ T cells in steady state, and particularly upon activation. Siglec-7 polarization into the T cell immune synapse was dependent on sialoglycan interactions in trans and prevented actin polarization and effective T cell responses. Siglec-7 ligands were found to be expressed on both leukemic stem cells and acute myeloid leukemia (AML) cells suggesting the occurrence of glyco-immune checkpoints for Siglec-7+ CD8+ T cells, which were found in patients' peripheral blood and bone marrow. Our findings project Siglec-7 as a glyco-immune checkpoint and therapeutic target for T cell-driven disorders and cancer

First Observation of Radiative B^0 -> \phi K^0 \gamma Decays and Measurements of Their Time-Dependent CP Violation

We report the first observation of the radiative decay B^0 -> \phi K^0 \gamma using a data sample of 772 x 10^6 B B-bar pairs collected at the \Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We observe a signal of 37+/-8 events with a significance of 5.4 standard deviations including systematic uncertainties. The measured branching fraction is ${\cal B}(B^0 -> \phi K^0 \gamma) = (2.74\pm 0.60 \pm 0.32) \times 10^{-6}$, where the uncertainties are statistical and systematic, respectively. We also report the first measurements of time-dependent CP violation parameters: ${\mathcal S}_{\phi K_S^0 \gamma} = +0.74^{+0.72}_{-1.05} (stat)^{+0.10}_{-0.24} (syst)$ and ${\mathcal A}_{\phi K_S^0 \gamma} = +0.35 +/- 0.58 (stat)^{+0.23}_{-0.10} (syst)$. Furthermore, we measure ${\mathcal B}(B^+ -> \phi K^+ \gamma) = (2.48 +/- 0.30 +/- 0.24) x 10^{-6}$, ${\mathcal A}_{CP} = -0.03 +/- 0.11 +/- 0.08$ and find that the signal is concentrated in the M_{\phi K} mass region near threshold.Comment: 6 pages, 3 figures, Modified version is to be published in PRD(RC