A major challenge to increasing bandwidth in optical telecommunications is to encode electronic signals onto a lightwave carrier by modulating the light up to very fast rates. Polymer electro-optic ...materials have the necessary properties to function in photonic devices beyond the 40-GHz bandwidth currently available. An appropriate choice of polymers is shown to effectively eliminate the factors contributing to an optical modulator's decay in the high-frequency response. The resulting device modulates light with a bandwidth of 150 to 200 GHz and produces detectable modulation signal at 1.6 THz. These rates are faster than anticipated bandwidth requirements for the foreseeable future.
Heptapeptides containing residues with terminal olefin-derivatized side chains (3 and 4) have been treated with ruthenium alkylidene 1 and undergone facile ring-closing olefin metathesis (RCM) to ...give 21- and 23-membered macrocyclic peptides (5 and 6). The primary structures of peptides 3 and 4 were based upon a previously studied heptapeptide (2), which was shown to adopt a predominantly 310-helical conformation in CDCl3 solution and an α-helical conformation in the solid state. Circular dichroism, IR, and solution-phase 1H NMR studies strongly suggested that acyclic precursors 3 and 4 and the fully saturated macrocyclic products 7 and 8 also adopted helical conformations in apolar organic solvents. Single-crystal X-ray diffraction of cyclic peptide 8 showed it to exist as a right-handed 310-helix up to the fifth residue. Solution-phase NMR structures of both acyclic peptide 4 and cyclic peptide 8 in CD2Cl2 indicated that the acyclic diene assumes a loosely 310-helical conformation, which is considerably rigidified upon macrocyclization. The relative ease of introducing carbon−carbon bonds into peptide secondary structures by RCM and the predicted metabolic stability of these bonds renders olefin metathesis an exceptional methodology for the synthesis of rigidified peptide architectures.
We report the properties of all the 841 coronal mass ejections (CMEs) observed by the Solar and Heliospheric Observatory (SOHO) Large Angle Spectroscopic Coronagraph (LASCO) C2 and C3 white‐light ...coronagraphs from January 1996 through June 1998, and we compare those properties to previous observations by other similar instruments. Both the CME rate and the distribution of apparent locations of CMEs varied during this period as expected based on previous solar cycles. The distribution of apparent speeds and the fraction of CMEs showing acceleration were also in agreement with earlier reports. The pointing stability provided by an L‐1 orbit and the use of CCD detectors have resulted in superior brightness sensitivity for LASCO over earlier coronagraphs; however, we have not detected a significant population of fainter (i.e., low mass) CMEs. The general shape of the distribution of apparent sizes for LASCO CMEs is similar to those of earlier reports, but the average (median) apparent size of 72° (50°) is significantly larger. The larger average apparent size is predominantly the result of the detection of a population of partial and complete halo CMEs, at least some of which appear to be events with a significant longitudinal component directed along the Sun‐Earth line, either toward or away from the Earth. Using full disk solar images obtained by the Extreme ultraviolet Imaging Telescope (EIT) on SOHO, we found that 40 out of 92 of these events might have been directed toward the Earth, and we compared the timing of those with the Kp geomagnetic storm index in the days following the CME. Although the “false alarm” rate was high, we found that 15 out of 21 (71%) of the Kp ≥ 6 storms could be accounted for as SOHO LASCO/EIT frontside halo CMEs. If we eliminate three Kp storms that occurred following LASCO/EIT data gaps, then the possible association rate was 15 out of 18 (83%).
The incidence of acute renal failure, defined by the risk, injury, or failure criteria of the RIFLE criteria (risk, injury, failure, loss, and end-stage kidney disease), in 66 patients who received ...colistimethate sodium was 45%, and 21% of patients stopped therapy because of nephrotoxicity. The RIFLE criteria should be used in the future to allow for comparison of nephrotoxicity among studies.
We report the discovery of a Neptune-like planet (LP 714-47 b,
P
= 4.05204 d,
m
b
= 30.8 ± 1.5
M
⊕
,
R
b
= 4.7 ± 0.3
R
⊕
) located in the “hot Neptune desert”. Confirmation of the TESS Object of ...Interest (TOI 442.01) was achieved with radial-velocity follow-up using CARMENES, ESPRESSO, HIRES, iSHELL, and PFS, as well as from photometric data using TESS,
Spitzer
, and ground-based photometry from MuSCAT2, TRAPPIST-South, MONET-South, the George Mason University telescope, the Las Cumbres Observatory Global Telescope network, the El Sauce telescope, the TÜBİTAK National Observatory, the University of Louisville Manner Telescope, and WASP-South. We also present high-spatial resolution adaptive optics imaging with the Gemini Near-Infrared Imager. The low uncertainties in the mass and radius determination place LP 714-47 b among physically well-characterised planets, allowing for a meaningful comparison with planet structure models. The host star LP 714-47 is a slowly rotating early M dwarf (
T
eff
= 3950 ± 51 K) with a mass of 0.59 ± 0.02
M
⊙
and a radius of 0.58 ± 0.02
R
⊙
. From long-term photometric monitoring and spectroscopic activity indicators, we determine a stellar rotation period of about 33 d. The stellar activity is also manifested as correlated noise in the radial-velocity data. In the power spectrum of the radial-velocity data, we detect a second signal with a period of 16 days in addition to the four-day signal of the planet. This could be shown to be a harmonic of the stellar rotation period or the signal of a second planet. It may be possible to tell the difference once more TESS data and radial-velocity data are obtained.
•We have generated the first, complete geomorphologic map of Titan's polar regions.•Most of Titan's lake depressions can be found with a single plains unit, suggesting that the unit is conducive to ...the formation of such features.•Uplands materials are not uniform in composition, where mountains and dissected uplands have different radar backscattering behaviors.•The observed landscape appears as an underlying bedrock material that was mantled by vast sedimentary deposits. Superposed on these sedimentary deposits are steep-sided depressions, canyons and seas.•We offer a conceptual model that is able to explain the distribution and superposition relationships among our map units, where in Titan's distant past the poles were submerged under larger liquid bodies.
We present a geomorphologic map of Titan's polar terrains. The map was generated from a combination of Cassini Synthetic Aperture Radar (SAR) and Imaging Science Subsystem imaging products, as well as altimetry, SARTopo and radargrammetry topographic datasets. In combining imagery with topographic data, our geomorphologic map reveals a stratigraphic sequence from which we infer process interactions between units. In mapping both polar regions with the same geomorphologic units, we conclude that processes that formed the terrains of the north polar region also acted to form the landscape we observe at the south. Uniform, SAR-dark plains are interpreted as sedimentary deposits, and are bounded by moderately dissected uplands. These plains contain the highest density of filled and empty lake depressions, and canyons. These units unconformably overlay a basement rock that outcrops as mountains and SAR-bright dissected terrains at various elevations across both poles. All these units are then superposed by surficial units that slope towards the seas, suggestive of subsequent overland transport of sediment. From estimates of the depths of the embedded empty depressions and canyons that drain into the seas, the SAR-dark plains must be >600m thick in places, though the thickness may vary across the poles. At the lowest elevations of each polar region, there are large seas, which are currently liquid methane/ethane filled at the north and empty at the south. The large plains deposits and the surrounding hillslopes may represent remnant landforms that are a result of previously vast polar oceans, where larger liquid bodies may have allowed for a sustained accumulation of soluble and insoluble sediments, potentially forming layered sedimentary deposits. Coupled with vertical crustal movements, the resulting layers would be of varying solubilities and erosional resistances, allowing formation of the complex landscape that we observe today.
The availability of future fusion devices, such as a fusion nuclear science facility or demonstration fusion power station, greatly depends on long operating lifetimes of plasma facing components in ...their divertors. ORNL is designing the Material Plasma Exposure eXperiment (MPEX), a superconducting magnet, steady-state device to address the plasma material interactions of fusion reactors. MPEX will utilize a new highintensity plasma source concept based on RF technology. This source concept will allow the experiment to cover the entire expected plasma conditions in the divertor of a future fusion reactor. It will be able to study erosion and redeposition for relevant geometries with relevant electric and magnetic fields in-front of the target. MPEX is being designed to allow for the exposure of a priori neutron-irradiated samples. The target exchange chamber has been designed to undock from the linear plasma generator such that it can be transferred to diagnostics stations for more detailed surface analysis. MPEX is being developed in a staged approach with successively increased capabilities. After the initial development step of the helicon source and electron cyclotron heating system, the source concept is being tested in the Proto-MPEX device. Proto-MPEX has achieved electron densities of more than 4×10 19 m -3 with a large diameter (13 cm) helicon antenna at 100 kW power. First heating with microwaves resulted in a higher ionization represented by higher electron densities on axis, when compared with the helicon plasma only without microwave heating.
Interventions that improve cognitive function in Alzheimer's disease are urgently required.
To assess whether a novel cognitive training paradigm based on 'chunking' improves working memory and ...general cognitive function, and is associated with reorganisation of functional activity in prefrontal and parietal cortices (trial registration: ISRCTN43007027).
Thirty patients with mild Alzheimer's disease were randomly allocated to receive 18 sessions of 30 min of either adaptive chunking training or an active control intervention over approximately 8 weeks. Pre- and post-intervention functional magnetic resonance imaging (fMRI) scans were also conducted.
Adaptive chunking training led to significant improvements in verbal working memory and untrained clinical measures of general cognitive function. Further, fMRI revealed a bilateral reduction in task-related lateral prefrontal and parietal cortex activation in the training group compared with controls.
Chunking-based cognitive training is a simple and potentially scalable intervention to improve cognitive function in early Alzheimer's disease.
We present the discovery and characterization of two transiting planets observed by TESS in the light curves of the young and bright (V = 9.67) star HD73583 (TOI-560). We perform an intensive ...spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterize the system. We found that HD73583 is a young (similar to 500 Myr) active star with a rotational period of 12.08 +/- 0.11 d, and a mass and radius of 0.73 +/- 0.02 M-circle dot and 0.65 +/- 0.02 R-circle dot, respectively. HD 73583 b (P-b = 6.3980420(-0.0000062)(+0.0000067 )d) has a mass and radius of 10.2(-3.1)(+3.4) M-circle plus and 2.79 +/- 0.10 R-circle plus, respectively, which gives a density of 2.58(-0.81)(+0.95) g cm(-3). HD 73583 c (P-c = 18.87974(-0.00074)(+0.00086) d) has a mass and radius of 9.7(-1.7)(+1.8) M-circle plus and 2.39(-0.09)(+0.10) R-circle plus, respectively, which translates to a density of 3.88(-0.80)(+0.91) g cm(-3). Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments.
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