37 research outputs found
Erratum: Search for Resonant and Nonresonant Higgs Boson Pair Production in the bb[over ¯]τ^{+}τ^{-} Decay Channel in pp Collisions at sqrt[s]=13 TeV with the ATLAS Detector [Phys. Rev. Lett. 121, 191801 (2018)]
Operation and performance of the ATLAS Tile Calorimeter in Run 1
The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter’s performance during the years 2008–2012 using cosmic-ray muon events and proton–proton collision data at centre-of-mass energies of 7 and 8TeV with a total integrated luminosity of nearly 30 fb−1. The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Finally, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton–proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report
Microfluidic Examination of the “Hard” Biomolecular Corona Formed on Engineered Particles in Different Biological Milieu
The formation of
a biomolecular corona around engineered particles
determines, in large part, their biological behavior in vitro and
in vivo. To gain a fundamental understanding of how particle design
and the biological milieu influence the formation of the “hard”
biomolecular corona, we conduct a series of in vitro studies using
microfluidics. This setup allows the generation of a dynamic incubation
environment with precise control over the applied flow rate, stream
orientation, and channel dimensions, thus allowing accurate control
of the fluid flow and the shear applied to the proteins and particles.
We used mesoporous silica particles, poly(2-methacryloyloxyethylphosphorylcholine)
(PMPC)-coated silica hybrid particles, and PMPC replica particles
(obtained by removal of the silica particle templates), representing
high-, intermediate-, and low-fouling particle systems, respectively.
The protein source used in the experiments was either human serum
or human full blood. The effects of flow, particle surface properties,
incubation medium, and incubation time on the formation of the biomolecular
corona formation are examined. Our data show that protein adhesion
on particles is enhanced after incubation in human blood compared
to human serum and that dynamic incubation leads to a more complex
corona. By varying the incubation time from 2 s to 15 min, we demonstrate
that the “hard” biomolecular corona is kinetically subdivided
into two phases comprising a tightly bound layer of proteins interacting
directly with the particle surface and a loosely associated protein
layer. Understanding the influence of particle design parameters and
biological factors on the corona composition, as well as its dynamic
assembly, may facilitate more accurate prediction of corona formation
and therefore assist in the design of advanced drug delivery vehicles
Base-Free Methanol Dehydrogenation Using a Pincer-Supported Iron Compound and Lewis Acid Co-catalyst
Hydrogen is an attractive alternative
energy vector to fossil fuels
if effective methods for its storage and release can be developed.
In particular, methanol, with a gravimetric hydrogen content of 12.6%,
is a promising target for chemical hydrogen storage. To date, there
are relatively few homogeneous transition metal compounds that catalyze
the aqueous phase dehydrogenation of methanol to release hydrogen
and carbon dioxide. In general, these catalysts utilize expensive
precious metals and require a strong base. This paper shows that a
pincer-supported Fe compound and a co-catalytic amount of a Lewis
acid are capable of catalyzing base-free aqueous phase methanol dehydrogenation
with turnover numbers up to 51 000. This is the highest turnover
number reported for either a first-row transition metal or a base-free
system. Additionally, this paper describes preliminary mechanistic
experiments to understand the reaction pathway and propose a stepwise
process, which requires metal–ligand cooperativity. This pathway
is supported by DFT calculations and explains the role of the Lewis
acid co-catalyst
Highly Active Iron Catalyst for Ammonia Borane Dehydrocoupling at Room Temperature
The iron complex [FeH(CO) (PNP)]
(PNP = N(CH<sub>2</sub>CH<sub>2</sub>P<i>i</i>Pr<sub>2</sub>)<sub>2</sub>) is a highly
active catalyst for ammonia borane dehydrocoupling at room temperature.
Mainly linear polyaminoborane is obtained upon release of 1 equiv
of H<sub>2</sub>. Mechanistic studies suggest that both hydrogen release
and B–N coupling are metal-catalyzed and proceed via free aminoborane.
Catalyst deactivation results from reaction with free BH<sub>3</sub> that is formed by aminoborane rearrangement. Importantly, borane
trapping with a simple amine allows for the observation of a TON that
is unprecedented for a well-defined base metal catalyst
Well-Defined Iron Catalysts for the Acceptorless Reversible Dehydrogenation-Hydrogenation of Alcohols and Ketones
Acceptorless
dehydrogenation of alcohols, an important organic transformation,
was accomplished with well-defined and inexpensive iron-based catalysts
supported by a cooperating PNP pincer ligand. Benzylic and aliphatic
secondary alcohols were dehydrogenated to the corresponding ketones
in good isolated yields upon release of dihydrogen. Primary alcohols
were dehydrogenated to esters and lactones, respectively. Mixed primary/secondary
diols were oxidized at the secondary alcohol moiety with good chemoselectivity.
The mechanism of the reaction was investigated using both experiment
and DFT calculations, and the crucial role of metal–ligand
cooperativity in the reaction was elucidated. The iron complexes are
also excellent catalysts for the hydrogenation of challenging ketone
substrates at ambient temperature under mild H<sub>2</sub> pressure,
the reverse of secondary alcohol dehydrogenation
Interrupted Energy Transfer: Highly Selective Detection of Cyclic Ketones in the Vapor Phase
We detail our efforts toward the selective detection of cyclic ketones, e.g. cyclohexanone, a component of plasticized explosives. Thin films comprised of a conjugated polymer are used to amplify the emission of an emissive receptor via energy transfer. We propose that the energy transfer is dominated by an electron-exchange mechanism to an upper excited state of the fluorophore followed by relaxation and emission to account for the efficient energy transfer in the absence of appreciable spectral overlap. Exposure to cyclic ketones results in a ratiometric fluorescence response. The thin films show orthogonal responses when exposed to cyclic ketones versus acyclic ketones. We demonstrate that the exquisite selectivity is the result of a subtle balance between receptor design and the partition coefficient of molecules into the polymer matrix.United States. Army Research OfficeMassachusetts Institute of Technology. Institute for Soldier NanotechnologiesNational Science Foundation (U.S.) (Grant CHE-0946721
Contrasting Transport and Electrostatic Properties of Selectively Fluorinated Alkanethiol Monolayers with Embedded Dipoles
Surface
dipoles are a powerful tool in interfacial modification
for improving device output via energy level matching. Fluorinated
alkanethiols show a strong promise for these applications as they
can generate large and tunable dipoles based on fluorine location
and chain length. Furthermore, these chains can be designed to possess
fluorocarbons solely along the backbone, enabling an “embedded”
configuration that generates a significant dipole effect from the
fluorines while maintaining surface chemistry to prevent deleterious
side effects from altered surface interactions. However, fluorine
substitution can modify other molecular electronic properties, and
it is important to consider the transport properties of these interfacial
modifiers so that knowledge can be used to tailor the optimal device
performance. In this paper, we report the transport properties of
self-assembled monolayers derived from a series of fluorinated alkanethiols,
both with and without the embedded dipole structure. Photoelectron
spectroscopy and Kelvin probe force microscopy show significant work
function modification from all fluorine-containing molecules compared
to purely hydrocarbon thiols. However, although embedded fluorocarbons
generate a smaller electrostatic effect than terminal fluorocarbons,
they yield higher tunneling currents across Au/monolayer/eutectic
gallium–indium junctions compared to both terminal fluorocarbon
and purely hydrocarbon alkanethiols. Computational studies show that
the location of the fluorine constituents modifies not only dipoles
and energy levels but also molecular orbitals, enabling the presence
of delocalized lowest unoccupied molecular orbital levels within the
alkanethiol backbone and, thereby, the appearance of larger tunneling
currents compared to other alkanethiols. Ultimately, we show that
fluorinated alkanethiols and the embedded dipole architecture are
both powerful tools, but they must be thoroughly analyzed for proper
utilization in a device setting
Effect of Aggregation on the Photophysical Properties of Three Fluorene–Phenylene-Based Cationic Conjugated Polyelectrolytes
Quantification of Trichothecene-Producing Fusarium Species in Harvested Grain by Competitive PCR To Determine Efficacies of Fungicides against Fusarium Head Blight of Winter Wheat
We developed a PCR-based assay to quantify trichothecene-producing Fusarium based on primers derived from the trichodiene synthase gene (Tri5). The primers were tested against a range of fusarium head blight (FHB) (also known as scab) pathogens and found to amplify specifically a 260-bp product from 25 isolates belonging to six trichothecene-producing Fusarium species. Amounts of the trichothecene-producing Fusarium and the trichothecene mycotoxin deoxynivalenol (DON) in harvested grain from a field trial designed to test the efficacies of the fungicides metconazole, azoxystrobin, and tebuconazole to control FHB were quantified. No correlation was found between FHB severity and DON in harvested grain, but a good correlation existed between the amount of trichothecene-producing Fusarium and DON present within grain. Azoxystrobin did not affect levels of trichothecene-producing Fusarium compared with those of untreated controls. Metconazole and tebuconazole significantly reduced the amount of trichothecene-producing Fusarium in harvested grain. We hypothesize that the fungicides affected the relationship between FHB severity and the amount of DON in harvested grain by altering the proportion of trichothecene-producing Fusarium within the FHB disease complex and not by altering the rate of DON production. The Tri5 quantitative PCR assay will aid research directed towards reducing amounts of trichothecene mycotoxins in food and animal feed