1,384 research outputs found
Macropolyhedral boron-containing cluster chemistry. Ligand-induced two-electron variations of intercluster bonding intimacy. Structures of nineteen-vertex[(eta(5)-C5Me5) HIrB18H19(PMe2Ph)] and the related carbene complex [(eta(5)-C5Me5)HIrB18H19{C(NHMe)(2)}]
Addition of PMe2Ph to fused-cluster syn-[(η5-C5Me5)IrB18H20] 1 to give [(η5-C5Me5)HIrB18H19(PMe2Ph)] 3 entails a diminution in the degree of intimacy of the intercluster fusion, rather than retention of inter-subcluster binding intimacy and a nido → arachno conversion of the character of either of the subclusters. Reaction with MeNC gives [(η5-C5Me5)HIrB18H19{C(NHMe)2}] 4 which has a similar structure, but with the ligand now being the carbene {:C(NHMe)2}, resulting from a reductive assembly reaction involving two MeNC residues and the loss of a carbon atom
Optimal Planar Electric Dipole Antenna
Considerable time is often spent optimizing antennas to meet specific design
metrics. Rarely, however, are the resulting antenna designs compared to
rigorous physical bounds on those metrics. Here we study the performance of
optimized planar meander line antennas with respect to such bounds. Results
show that these simple structures meet the lower bound on radiation Q-factor
(maximizing single resonance fractional bandwidth), but are far from reaching
the associated physical bounds on efficiency. The relative performance of other
canonical antenna designs is compared in similar ways, and the quantitative
results are connected to intuitions from small antenna design, physical bounds,
and matching network design.Comment: 10 pages, 15 figures, 2 tables, 4 boxe
Retinal Vessel Segmentation Using the 2-D Morlet Wavelet and Supervised Classification
We present a method for automated segmentation of the vasculature in retinal
images. The method produces segmentations by classifying each image pixel as
vessel or non-vessel, based on the pixel's feature vector. Feature vectors are
composed of the pixel's intensity and continuous two-dimensional Morlet wavelet
transform responses taken at multiple scales. The Morlet wavelet is capable of
tuning to specific frequencies, thus allowing noise filtering and vessel
enhancement in a single step. We use a Bayesian classifier with
class-conditional probability density functions (likelihoods) described as
Gaussian mixtures, yielding a fast classification, while being able to model
complex decision surfaces and compare its performance with the linear minimum
squared error classifier. The probability distributions are estimated based on
a training set of labeled pixels obtained from manual segmentations. The
method's performance is evaluated on publicly available DRIVE and STARE
databases of manually labeled non-mydriatic images. On the DRIVE database, it
achieves an area under the receiver operating characteristic (ROC) curve of
0.9598, being slightly superior than that presented by the method of Staal et
al.Comment: 9 pages, 7 figures and 1 table. Accepted for publication in IEEE
Trans Med Imag; added copyright notic
Epidemiological and clinical features of travel-associated cryptosporidiosis
ABSTRACTData concerning the clinical and epidemiological features of travel-associated cryptosporidiosis are lacking. In order to investigate the impact of this disease on travellers' health, a retrospective study was conducted at the Institute of Tropical Medicine, Berlin. In total, 57 cryptosporidial infections were identified between 2000 and 2004, resulting in a prevalence of 2.9% in patients with travel-associated diarrhoea. Travel to south-central Asia, especially India, was associated with a higher prevalence of infection than was travel to other destinations. Clinically, the disease resembled giardiasis, but fever and arthralgias seemed to occur more frequently
Modified embedded-atom method interatomic potentials for the Mg-Al alloy system
We developed new modified embedded-atom method (MEAM) interatomic potentials
for the Mg-Al alloy system using a first-principles method based on density
functional theory (DFT). The materials parameters, such as the cohesive energy,
equilibrium atomic volume, and bulk modulus, were used to determine the MEAM
parameters. Face-centered cubic, hexagonal close packed, and cubic rock salt
structures were used as the reference structures for Al, Mg, and MgAl,
respectively. The applicability of the new MEAM potentials to atomistic
simulations for investigating Mg-Al alloys was demonstrated by performing
simulations on Mg and Al atoms in a variety of geometries. The new MEAM
potentials were used to calculate the adsorption energies of Al and Mg atoms on
Al (111) and Mg (0001) surfaces. The formation energies and geometries of
various point defects, such as vacancies, interstitial defects and
substitutional defects, were also calculated. We found that the new MEAM
potentials give a better overall agreement with DFT calculations and
experiments when compared against the previously published MEAM potentials.Comment: Fixed a referenc
Virtual Affinity Fingerprints for Target Fishing: A New Application of Drug Profile Matching
We recently introduced Drug Profile Matching (DPM), a novel virtual affinity fingerprinting bioactivity prediction method. DPM is based on the docking profiles of ca. 1200 FDA-approved small-molecule drugs against a set of nontarget proteins and creates bioactivity predictions based on this pattern. The effectiveness of this approach was previously demonstrated for therapeutic effect prediction of drug molecules. In the current work, we investigated the applicability of DPM for target fishing, i.e. for the prediction of biological targets for compounds. Predictions were made for 77 targets, and their accuracy was measured by Receiver Operating Characteristic (ROC) analysis. Robustness was tested by a rigorous 10-fold cross-validation procedure. This procedure identified targets (N = 45) with high reliability based on DPM performance. These 45 categories were used in a subsequent study which aimed at predicting the off-target profiles of currently approved FDA drugs. In this data set, 79% of the known drug-target interactions were correctly predicted by DPM, and additionally 1074 new drug-target interactions were suggested. We focused our further investigation on the suggested interactions of antipsychotic molecules and confirmed several interactions by a review of the literature
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