311 research outputs found
Low Catalyst Loadings in Olefin Metathesis: Synthesis of Nitrogen Heterocycles by Ring-Closing Metathesis
A series of ruthenium catalysts have been screened under ring-closing metathesis (RCM) conditions to produce five-, six-, and seven-membered carbamate-protected cyclic amines. Many of these catalysts demonstrated excellent RCM activity and yields with as low as 500 ppm catalyst loadings. RCM of the five-membered carbamate series could be run neat, the six-membered carbamate series could be run at 1.0 M, and the seven-membered carbamate series worked best at 0.2−0.05 M
Monolithic Polarizing Circular Dielectric Gratings on Bulk Substrates for Improved Photon Collection from InAs Quantum Dots
III-V semiconductor quantum dots (QDs) are near-ideal and versatile
single-photon sources. Because of the capacity for monolithic integration with
photonic structures as well as optoelectronic and optomechanical systems, they
are proving useful in an increasingly broad application space. Here, we develop
monolithic circular dielectric gratings on bulk substrates -- as opposed to
suspended or wafer-bonded substrates -- for greatly improved photon collection
from InAs quantum dots. The structures utilize a unique two-tiered distributed
Bragg reflector (DBR) structure for vertical electric field confinement over a
broad angular range. Opposing ``openings" in the cavities induce strongly
polarized QD luminescence without harming collection efficiencies. We describe
how measured enhancements depend critically on the choice of collection optics.
This is important to consider when evaluating the performance of any photonic
structure that concentrates farfield emission intensity. Our cavity designs are
useful for integrating QDs with other quantum systems that require bulk
substrates, such as surface acoustic wave phonons
Strong transient magnetic fields induced by THz-driven plasmons in graphene disks
Strong circularly polarized excitation opens up the possibility to generate
and control effective magnetic fields in solid state systems, e.g., via the
optical inverse Faraday effect or the phonon inverse Faraday effect. While
these effects rely on material properties that can be tailored only to a
limited degree, plasmonic resonances can be fully controlled by choosing proper
dimensions and carrier concentrations. Plasmon resonances provide new degrees
of freedom that can be used to tune or enhance the light-induced magnetic field
in engineered metamaterials. Here we employ graphene disks to demonstrate
light-induced transient magnetic fields from a plasmonic circular current with
extremely high efficiency. The effective magnetic field at the plasmon
resonance frequency of the graphene disks (3.5 THz) is evidenced by a strong
(~1{\deg}) ultrafast Faraday rotation (~ 20 ps). In accordance with reference
measurements and simulations, we estimated the strength of the induced magnetic
field to be on the order of 0.7 T under a moderate pump fluence of about 440 nJ
cm-2
Alopecia areata is associated with increased expression of heart disease biomarker cardiac troponin I
YesThe development of androgenetic alopecia is associated
with a risk of developing cardiovascular diseases,
but the association of alopecia areata with cardiovascular
diseases in humans is largely unexplored. We
measured the plasma level of two common cardiovascular
disease markers, cardiac troponin I and Creactive
protein, in alopecia areata and androgenetic
alopecia-affected subjects. Also, we investigated the
possible presence of pro-apoptotic factors in the plasma
of hair loss subjects. The mean plasma cardiac troponin
I level was highest in alopecia areata subjects,
moderately higher in androgenetic alopecia subjects,
and lowest in subjects without hair loss (p < 0.05).
Alopecia areata subjects not receiving treatments had
highest levels of cardiac troponin I (p < 0.05). Alopecia
areata plasma samples with high cardiac troponin I
levels also induced significantly higher rates of cardiomyocyte
apoptosis in cell culture assays. The results
suggest the potential for increased heart remodelling.
Close monitoring of cardiovascular health in alopecia
areata subjects, as well as subsets of androgenetic
alopecia patients, may be appropriate.Canadian Institutes of Health Research (CIHR; MOP-82927). EW is the recipient of a Banting Postdoctoral Fellowship (SAC-92845)
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Design and implementation of the START (STem cells for ARDS Treatment) trial, a phase 1/2 trial of human mesenchymal stem/stromal cells for the treatment of moderate-severe acute respiratory distress syndrome
Background: Despite advances in supportive care, moderate-severe acute respiratory distress syndrome (ARDS) is associated with high mortality rates, and novel therapies to treat this condition are needed. Compelling pre-clinical data from mouse, rat, sheep and ex vivo perfused human lung models support the use of human mesenchymal stem (stromal) cells (MSCs) as a novel intravenous therapy for the early treatment of ARDS. Methods: This article describes the study design and challenges encountered during the implementation and phase 1 component of the START (STem cells for ARDS Treatment) trial, a phase 1/2 trial of bone marrow-derived human MSCs for moderate-severe ARDS. A trial enrolling 69 subjects is planned (9 subjects in phase 1, 60 subjects in phase 2 treated with MSCs or placebo in a 2:1 ratio). Results: This report describes study design features that are unique to a phase 1 trial in critically ill subjects and the specific challenges of implementation of a cell-based therapy trial in the ICU. Conclusions: Experience gained during the design and implementation of the START study will be useful to investigators planning future phase 1 clinical trials based in the ICU, as well as trials of cell-based therapy for other acute illnesses. Trial registration Clinical Trials Registration: NCT01775774 and NCT02097641
UltraSail - Ultra-Lightweight Solar Sail Concept
UltraSail is a next-generation high-risk, high-payoff sail system for the launch, deployment, stabilization and control of very large (sq km class) solar sails enabling high payload mass fractions for high (Delta)V. Ultrasail is an innovative, non-traditional approach to propulsion technology achieved by combining propulsion and control systems developed for formation-flying micro-satellites with an innovative solar sail architecture to achieve controllable sail areas approaching 1 sq km, sail subsystem area densities approaching 1 g/sq m, and thrust levels many times those of ion thrusters used for comparable deep space missions. Ultrasail can achieve outer planetary rendezvous, a deep space capability now reserved for high-mass nuclear and chemical systems. One of the primary innovations is the near-elimination of sail supporting structures by attaching each blade tip to a formation-flying micro-satellite which deploys the sail, and then articulates the sail to provide attitude control, including spin stabilization and precession of the spin axis. These tip micro-satellites are controlled by 3-axis micro-thruster propulsion and an on-board metrology system. It is shown that an optimum spin rate exists which maximizes payload mass
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Photofission-Based, Nuclear Material Detection: Technology Demonstration
The Idaho National Engineering and Environmental Laboratory (INEEL), the Los Alamos National Laboratory (LANL), and the Advanced Research and Applications Corporation (ARACOR) [Sunnyvale, California] performed a photonuclear technology demonstration for shielded nuclear material detection during August 21–22, 2002, at the LANL TA-18 facility. The demonstration used the Pulsed Photonuclear Assessment Technique (PPAT) that focused on the application of a photofission-based, nuclear material detection method as a viable complement to the ARACOR Eagle inspection platform. The Eagle is a mobile and fully operational truck and cargo inspection system that uses a 6-MeV electron accelerator to perform real-time radiography. This imaging is performed using an approved “radiation-safe” or “cabinet safe” operation relative to the operators, inspectors, and any stowaways within the inspected vehicles. While the PPAT has been primarily developed for active interrogation, its neutron detection system also maintains a complete and effective passive detection capability
UBVRI Light Curves of 44 Type Ia Supernovae
We present UBVRI photometry of 44 type-Ia supernovae (SN Ia) observed from
1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence
Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The
data set comprises 2190 observations and is the largest homogeneously observed
and reduced sample of SN Ia to date, nearly doubling the number of
well-observed, nearby SN Ia with published multicolor CCD light curves. The
large sample of U-band photometry is a unique addition, with important
connections to SN Ia observed at high redshift. The decline rate of SN Ia
U-band light curves correlates well with the decline rate in other bands, as
does the U-B color at maximum light. However, the U-band peak magnitudes show
an increased dispersion relative to other bands even after accounting for
extinction and decline rate, amounting to an additional ~40% intrinsic scatter
compared to B-band.Comment: 84 authors, 71 pages, 51 tables, 10 figures. Accepted for publication
in the Astronomical Journal. Version with high-res figures and electronic
data at http://astron.berkeley.edu/~saurabh/cfa2snIa
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