442 research outputs found
Impact of Excess Lead Iodide on the Recombination Kinetics in Metal Halide Perovskites
Fundmental
comprehension of light-induced processes in perovskites
are still scarce. One active debate surrounds the influence of excess
lead iodide (PbI2) on device performance, as well as optoelectronic
properties, where both beneficial and detrimental traits have been
reported. Here, we study its impact on charge carrier recombination
kinetics by simultaneously acquiring the photoluminescence quantum
yield and time-resolved photoluminescence as a function of excitation
wavelength (450–780 nm). The presence of PbI2 in
the perovskite film is identified via a unique spectroscopic signature
in the PLQY spectrum. Probing the recombination in the presence and
absence of this signature, we detect a radiative bimolecular recombination
mechanism induced by PbI2. Spatially resolving the photoluminescence,
we determine that this radiative process occurs in a small volume
at the PbI2/perovskite interface, which is only active
when charge carriers are generated in PbI2, and therefore
provide deeper insight into how excess PbI2 may improve
the properties of perovskite-based devices
Atomic Dark Matter
We propose that dark matter is dominantly comprised of atomic bound states.
We build a simple model and map the parameter space that results in the early
universe formation of hydrogen-like dark atoms. We find that atomic dark matter
has interesting implications for cosmology as well as direct detection:
Protohalo formation can be suppressed below for weak scale dark matter due to Ion-Radiation interactions in the
dark sector. Moreover, weak-scale dark atoms can accommodate hyperfine
splittings of order 100 \kev, consistent with the inelastic dark matter
interpretation of the DAMA data while naturally evading direct detection
bounds.Comment: 17 pages, 3 figure
Direct Probing of Gap States and Their Passivation in Halide Perovskites by High-Sensitivity, Variable Energy Ultraviolet Photoelectron Spectroscopy
Direct detection of intrinsic defects in halide perovskites (HaPs) by standard methods utilizing optical excitation is quite challenging, due to the low density of defects in most samples of this family of materials (≤10^{15} cm^{–3} in polycrystalline thin films and ≤10^{11} cm^{–3} in single crystals, except melt-grown ones). While several electrical methods can detect defect densities 2 eV) HaPs. By measuring HaP layers on both hole- and electron-contact layers, as well as single crystals without contacts, we conclude that the observed deep defects are intrinsic to the Br-based HaP, and we propose a passivation route via the incorporation of a 2D-forming ligand into the precursor solution
Hitting sbottom in natural SUSY
We compare the experimental prospects of direct stop and sbottom pair
production searches at the LHC. Such searches for stops are of great interest
as they directly probe for states that are motivated by the SUSY solution to
the hierarchy problem of the Higgs mass parameter - leading to a "Natural" SUSY
spectrum. Noting that sbottom searches are less experimentally challenging and
scale up in reach directly with the improvement on b-tagging algorithms, we
discuss the interplay of small TeV scale custodial symmetry violation with
sbottom direct pair production searches as a path to obtaining strong sub-TeV
constraints on stops in a natural SUSY scenario. We argue that if a weak scale
natural SUSY spectrum does not exist within the reach of LHC, then hopes for
such a spectrum for large regions of parameter space should sbottom out.
Conversely, the same arguments make clear that a discovery of such a spectrum
is likely to proceed in a sbottom up manner.Comment: 18 pages, 8 figures,v2 refs added, JHEP versio
Jet Dipolarity: Top Tagging with Color Flow
A new jet observable, dipolarity, is introduced that can distinguish whether
a pair of subjets arises from a color singlet source. This observable is
incorporated into the HEPTopTagger and is shown to improve discrimination
between top jets and QCD jets for moderate to high pT.Comment: 8 pages, 6 figures (updated to JHEP version
Diboson-Jets and the Search for Resonant Zh Production
New particles at the TeV-scale may have sizeable decay rates into boosted
Higgs bosons or other heavy scalars. Here, we investigate the possibility of
identifying such processes when the Higgs/scalar subsequently decays into a
pair of W bosons, constituting a highly distinctive "diboson-jet." These can
appear as a simple dilepton (plus MET) configuration, as a two-prong jet with
an embedded lepton, or as a four-prong jet. We study jet substructure methods
to discriminate these objects from their dominant backgrounds. We then
demonstrate the use of these techniques in the search for a heavy spin-one Z'
boson, such as may arise from strong dynamics or an extended gauge sector,
utilizing the decay chain Z' -> Zh -> Z(WW^(*)). We find that modes with
multiple boosted hadronic Zs and Ws tend to offer the best prospects for the
highest accessible masses. For 100/fb luminosity at the 14 TeV LHC, Z' decays
into a standard 125 GeV Higgs can be observed with 5-sigma significance for
masses of 1.5-2.5 TeV for a range of models. For a 200 GeV Higgs (requiring
nonstandard couplings, such as fermiophobic), the reach may improve to up to
2.5-3.0 TeV.Comment: 23 pages plus appendices, 9 figure
Dual Function of the NK Cell Receptor 2B4 (CD244) in the Regulation of HCV-Specific CD8+ T Cells
The outcome of viral infections is dependent on the function of CD8+ T cells
which are tightly regulated by costimulatory molecules. The NK cell receptor 2B4
(CD244) is a transmembrane protein belonging to the Ig superfamily which can
also be expressed by CD8+ T cells. The aim of this study was to analyze the
role of 2B4 as an additional costimulatory receptor regulating CD8+ T cell
function and in particular to investigate its implication for exhaustion of
hepatitis C virus (HCV)-specific CD8+ T cells during persistent infection.
We demonstrate that (i) 2B4 is expressed on virus-specific CD8+ T cells
during acute and chronic hepatitis C, (ii) that 2B4 cross-linking can lead to
both inhibition and activation of HCV-specific CD8+ T cell function,
depending on expression levels of 2B4 and the intracellular adaptor molecule SAP
and (iii) that 2B4 stimulation may counteract enhanced proliferation of
HCV-specific CD8+ T cells induced by PD1 blockade. We suggest that 2B4 is
another important molecule within the network of costimulatory/inhibitory
receptors regulating CD8+ T cell function in acute and chronic hepatitis C
and that 2B4 expression levels could also be a marker of CD8+ T cell
dysfunction. Understanding in more detail how 2B4 exerts its differential
effects could have implications for the development of novel immunotherapies of
HCV infection aiming to achieve immune control
Characterization of antigenic variants of hepatitis C virus in immune evasion
<p>Abstract</p> <p>Background</p> <p>Antigenic variation is an effective way by which viruses evade host immune defense leading to viral persistence. Little is known about the inhibitory mechanisms of viral variants on CD4 T cell functions.</p> <p>Results</p> <p>Using sythetic peptides of a HLA-DRB1*15-restricted CD4 epitope derived from the non-structural (NS) 3 protein of hepatitis C virus (HCV) and its antigenic variants and the peripheral blood mononuclear cells (PBMC) from six HLA-DRB1*15-positive patients chronically infected with HCV and 3 healthy subjects, the <it>in vitro </it>immune responses and the phenotypes of CD4<sup>+</sup>CD25<sup>+ </sup>cells of chronic HCV infection were investigated. The variants resulting from single or double amino acid substitutions at the center of the core region of the Th1 peptide not only induce failed T cell activation but also simultaneously up-regulate inhibitory IL-10, CD25<sup>-</sup>TGF-β<sup>+ </sup>Th3 and CD4<sup>+</sup>IL-10<sup>+ </sup>Tr1 cells. In contrast, other variants promote differentiation of CD25<sup>+</sup>TGF-β<sup>+ </sup>Th3 suppressors that attenuate T cell proliferation.</p> <p>Conclusions</p> <p>Naturally occuring HCV antigenic mutants of a CD4 epitope can shift a protective peripheral Th1 immune response into an inhibitory Th3 and/or Tr1 response. The modulation of antigenic variants on CD4 response is efficient and extensive, and is likely critical in viral persistence in HCV infection.</p
Structure of Fat Jets at the Tevatron and Beyond
Boosted resonances is a highly probable and enthusiastic scenario in any
process probing the electroweak scale. Such objects when decaying into jets can
easily blend with the cornucopia of jets from hard relative light QCD states.
We review jet observables and algorithms that can contribute to the
identification of highly boosted heavy jets and the possible searches that can
make use of such substructure information. We also review previous studies by
CDF on boosted jets and its measurements on specific jet shapes.Comment: invited review for a special "Top and flavour physics in the LHC era"
issue of The European Physical Journal C, we invite comments regarding
contents of the review; v2 added references and institutional preprint
number
Hepatitis C Virus (HCV)-Specific Immune Responses of Long‐Term Injection Drug Users Frequently Exposed to HCV
BACKGROUND: Injection drug users (IDUs) who successfully clear hepatitis C virus (HCV) have a reduced risk of developing chronic reinfection, despite their continuing exposure to the virus. To identify immunological correlates for this apparent protection, we studied HCV-specific immune responses in long-term IDUs (duration, >10 years). METHODS: HCV-specific T cell responses were assessed in proliferation, enzyme-linked immunospot (ELISPOT), interferon (IFN)–γ secretion, and cytotoxicity assays, whereas HCV-specific antibodies were assessed in enzyme immunoassays (EIAs), chemiluminescent assays, and in vitro neutralization assays. RESULTS: HCV-specific T cell proliferation and IFN-γ production were more common in nonviremic EIA-positive IDUs (16 [94%] of 17 IDUs) than in viremic EIA-positive IDUs (9 [45%] of 20 IDUs) (P = .003). They were also noted in 16 (62%) of 26 nonviremic EIA-negative IDUs. In contrast, 19 (90%) of 21 viremic IDUs displayed neutralizing antibodies (nAbs), compared with 9 (56%) of 16 nonviremic EIA-positive IDUs (P = .04) and 0 of 24 nonviremic EIA-negative IDUs. Nonviremic IDUs with nAbs were older (P = .0115) than those without nAbs, but these groups did not differ in terms of either injection drug use duration or HCV-specific T cell responses. CONCLUSION: The reduced risk of HCV persistence in IDUs previously recovered from HCV infection correlated with T cell responses, and prolonged antigenic stimulation appears to be required to maintain humoral responses
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