250 research outputs found
Negative tunnel magnetoresistance and differential conductance in transport through double quantum dots
Spin-dependent transport through two coupled single-level quantum dots weakly
connected to ferromagnetic leads with collinear magnetizations is considered
theoretically. Transport characteristics, including the current, linear and
nonlinear conductance, and tunnel magnetoresistance are calculated using the
real-time diagrammatic technique in the parallel, serial, and intermediate
geometries. The effects due to virtual tunneling processes between the two dots
via the leads, associated with off-diagonal coupling matrix elements, are also
considered. Negative differential conductance and negative tunnel
magnetoresistance have been found in the case of serial and intermediate
geometries, while no such behavior has been observed for double quantum dots
coupled in parallel. It is also shown that transport characteristics strongly
depend on the magnitude of the off-diagonal coupling matrix elements.Comment: 12 pages, 13 figure
HLA-Associated viral mutations are common in human immunodeficiency virus type 1 elite controllers
Elite controllers (EC) of human immunodeficiency virus type 1 (HTV-1) maintain viremia below the limit of detection without antiretroviral treatment. Virus-specific cytotoxic CD8+ T lymphocytes are believed to play a crucial role in viral containment, but the degree of immune imprinting and compensatory mutations in EC is unclear. We obtained plasma gag, pol, and nef sequences from HLA-diverse subjects and found that 30 to 40% of the predefined HLA-associated polymorphic sites show evidence of immune selection pressure in EC., compared to approximately 50% of the sites in chronic progressors. These data indicate ongoing viral replication and escape from cytotoxic T lymphocytes are present even in strictly controlled HTV-1 infection
HLA-Cw*0102-restricted HIV-1 p24 epitope variants can modulate the binding of the inhibitory KIR2DL2 receptor and primary NK cell function
The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads
We analyze numerically the spin-dependent transport through coherent chains
of three coupled quantum dots weakly connected to external magnetic leads. In
particular, using the diagrammatic technique on the Keldysh contour, we
calculate the conductance, shot noise and tunnel magnetoresistance (TMR) in the
sequential and cotunneling regimes. We show that transport characteristics
greatly depend on the strength of the interdot Coulomb correlations, which
determines the spacial distribution of electron wave function in the chain.
When the correlations are relatively strong, depending on the transport regime,
we find both negative TMR as well as TMR enhanced above the Julliere value,
accompanied with negative differential conductance (NDC) and super-Poissonian
shot noise. This nontrivial behavior of tunnel magnetoresistance is associated
with selection rules that govern tunneling processes and various high-spin
states of the chain that are relevant for transport. For weak interdot
correlations, on the other hand, the TMR is always positive and not larger than
the Julliere TMR, although super-Poissonian shot noise and NDC can still be
observed
50 Tbit/s Massively ParallelWDMTransmission in C and L Band Using Interleaved Cavity-Soliton Kerr Combs
Interleaving two soliton Kerr combs we generate 179 carriers for WDM transmission and demonstrate transmission of a data stream of 50 Tbit/s over 75 km. This is the highest data rate achieved with a chip-scale comb source
Searching for Exoplanets Using a Microresonator Astrocomb
Detection of weak radial velocity shifts of host stars induced by orbiting
planets is an important technique for discovering and characterizing planets
beyond our solar system. Optical frequency combs enable calibration of stellar
radial velocity shifts at levels required for detection of Earth analogs. A new
chip-based device, the Kerr soliton microcomb, has properties ideal for
ubiquitous application outside the lab and even in future space-borne
instruments. Moreover, microcomb spectra are ideally suited for astronomical
spectrograph calibration and eliminate filtering steps required by conventional
mode-locked-laser frequency combs. Here, for the calibration of astronomical
spectrographs, we demonstrate an atomic/molecular line-referenced,
near-infrared soliton microcomb. Efforts to search for the known exoplanet HD
187123b were conducted at the Keck-II telescope as a first in-the-field
demonstration of microcombs
Coherent WDM transmission using quantum-dash mode-locked laser diodes as multi-wavelength source and local oscillator
Quantum-dash (QD) mode-locked laser diodes (MLLD) lend themselves as
chip-scale frequency comb generators for highly scalable wavelength-division
multiplexing (WDM) links in future data-center, campus-area, or metropolitan
networks. Driven by a simple DC current, the devices generate flat broadband
frequency combs, containing tens of equidistant optical tones with line
spacings of tens of GHz. Here we show that QD-MLLDs can not only be used as
multi-wavelength light sources at a WDM transmitter, but also as
multi-wavelength local oscillators (LO) for parallel coherent reception. In our
experiments, we demonstrate transmission of an aggregate data rate of 4.1
Tbit/s (23x45 GBd PDM-QPSK) over 75 km standard single-mode fiber (SSMF). To
the best of our knowledge, this represents the first demonstration of a
coherent WDM link that relies on QD-MLLD both at the transmitter and the
receiver
Functionally Inert HIV-Specific Cytotoxic T Lymphocytes Do Not Play a Major Role in Chronically Infected Adults and Children
The highly sensitive quantitation of virus-specific CD8+ T cells using major histocompatibility complex–peptide tetramer assays has revealed higher levels of cytotoxic T lymphocytes (CTLs) in acute and chronic virus infections than were recognized previously. However, studies in lymphocytic choriomeningitis virus infection have shown that tetramer assays may include measurement of a substantial number of tetramer-binding cells that are functionally inert. Such phenotypically silent CTLs, which lack cytolytic function and do not produce interferon (IFN)-γ, have been hypothesized to explain the persistence of virus in the face of a quantitatively large immune response, particularly when CD4 help is impaired. In this study, we examined the role of functionally inert CTLs in chronic HIV infection. Subjects studied included children and adults (n = 42) whose viral loads ranged from <50 to >100,000 RNA copies/ml plasma. Tetramer assays were compared with three functional assays: enzyme-linked immunospot (Elispot), intracellular cytokine staining, and precursor frequency (limiting dilution assay [LDA]) cytotoxicity assays. Strong positive associations were observed between cell numbers derived by the Elispot and the tetramer assay (r = 0.90). An even stronger association between tetramer-derived numbers and intracellular cytokine staining for IFN-γ was present (r = 0.97). The majority (median 76%) of tetramer-binding cells were consistently detectable via intracellular IFN-γ cytokine staining. Furthermore, modifications to the LDA, using a low input cell number into each well, enabled LDAs to reach equivalence with the other methods of CTL enumeration. These data together show that functionally inert CTLs do not play a significant role in chronic pediatric or adult HIV infection
Silicon-organic hybrid (SOH) devices and their use in comb-based communication systems
Advanced wavelength-division multiplex-ing (WDM) requires both efficient multi-wavelength light sources to generate optical carriers and highly scalable photonic-electronic interfaces to encode data on these carriers. In this paper, we give an overview on our recent progress regarding silicon-organic hy-brid (SOH) integration and comb-based WDM transmission
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