358 research outputs found
Influence of molecular structure on the antimicrobial function of phenylenevinylene conjugated oligoelectrolytes.
Conjugated oligoelectrolytes (COEs) with phenylenevinylene (PV) repeat units are known to spontaneously intercalate into cell membranes. Twelve COEs, including seven structures reported here for the first time, were investigated for the relationship between their membrane disrupting properties and structural modifications, including the length of the PV backbone and the presence of either a tetraalkylammonium or a pyridinium ionic pendant group. Optical characteristics and interactions with cell membranes were determined using UV-Vis absorption and photoluminescence spectroscopies, and confocal microscopy. Toxicity tests on representative Gram-positive (Enterococcus faecalis) and Gram-negative (Escherichia coli) bacteria reveal generally greater toxicity to E. faecalis than to E. coli and indicate that shorter molecules have superior antimicrobial activity. Increased antimicrobial potency was observed in three-ring COEs appended with pyridinium ionic groups but not with COEs with four or five PV repeat units. Studies with mutants having cell envelope modifications indicate a possible charge based interaction with pyridinium-appended compounds. Fluorine substitutions on COE backbones result in structures that are less toxic to E. coli, while the addition of benzothiadiazole to COE backbones has no effect on increasing antimicrobial function. A weakly membrane-intercalating COE with only two PV repeat units allowed us to determine the synthetic limitations as a result of competition between solubility in aqueous media and association with cell membranes. We describe, for the first time, the most membrane disrupting structure achievable within two homologous series of COEs and that around a critical three-ring backbone length, structural modifications have the most effect on antimicrobial activity
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
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
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
Finally, inkjet printed metal halide perovskite LEDs utilizing seed crystal templating of salty PEDOT PSS
Solution processable metal halide perovskites are increasingly implemented in perovskite based light emitting diodes PeLEDs . Especially green PeLEDs based on methylammonium lead bromide MAPbBr3 composites exhibit impressive optoelectronic properties, while allowing processing by low cost and upscalable printing methods. In this study, we have investigated the influence of potassium chloride KCl blended into the common hole injection material poly 3,4 ethylenedioxythiophene polystyrene sulfonate PEDOT PSS to boost PeLED device performance. The inclusion of KCl firstly results in a change in morphology of the PEDOT PSS layer, which then acts as a template during deposition of the perovskite layer. A MAPbBr3 polyethylene glycol PEG composite was used, which does not require the deposition of an anti solvent droplet to induce preferential perovskite crystallization and is therefore suitable for spin coating and scalable inkjet printing processes. PeLEDs utilizing the KCl induced templating effect on a planar PEDOT PSS MAPbBr3 PEG architecture show improved performance, predominantly due to improved crystallization. PeLEDs incorporating spin coated perovskite layers yield a 40 fold increase in luminance 8000 cd m 2 while the turn on voltage decreases to 2.5 V. KCl modified PEDOT PSS contact layers enabled the realization of inkjet printed PeLEDs with luminance increased by a factor of 20 at a maximum of 4000 cd m 2 and a turn on voltage of 2.5 V. This work paves the way for inkjet printed perovskite light emitting devices for a wide variety of low cost and customizable application
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
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
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
Gas flow assisted vacuum drying Identification of a novel process for attaining high quality perovskite films
Controlling the nucleation and crystal growth in solution processed metal halide perovskite MHP thin films is the pivotal point in fabricating homogenous and pinhole free films. Using scalable coating and printing techniques, vacuum and gas flow assisted drying processes turn out to be the most promising methods to induce nucleation and crystallization. Yet, the exact interplay and nature of these processes are unclear. In our work, we optically monitor these processes in situ. For the first time, we can show that a controlled venting of the vacuum chamber and the use of a subsequent gas flow are key to achieve homogenous nucleation. Utilizing this gas flow assisted vacuum drying process, we find that regular, optically dense and pinhole free MHP layers can be fabricated via inkjet printing, which yield solar cells with a power conversion efficiency of 16 , as compared to 4.5 for vacuum dryin
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
- …