Stretched Exponential Dynamics in Online Article Views

Article view statistics offers a measure to quantify scientific and public impact of online published articles. Popularity of a paper in online community changes with time. To understand popularity dynamics of article views, we propose a decay dynamics based on a stretched exponential model. We find that a stretched exponent gradually decreases with time after online publication following a power-law scaling. Compared with a simple exponential or biexponential model, a stretched exponential model with a time-dependent exponent well describes long-tailed popularity dynamics of online articles. This result gives a useful insight into how popularity diminishes with time in online community.

Accuracies and Contrasts of Models of the Diffusion-weighted-dependent Attenuation of the Mri Signal at Intermediate B-values

The diffusion-weighted-dependent attenuation of the MRI signal E( b) is extremely sensitive to microstructural features. The aim of this study was to determine which mathematical model of the E( b) signal most accurately describes it in the brain. The models compared were the monoexponential model, the stretched exponential model, the truncated cumulant expansion (TCE) model, the biexponential model, and the triexponential model. Acquisition was performed with nine b-values up to 2500 s/mm2 in 12 healthy volunteers. The goodness-of-fit was studied with F-tests and with the Akaike information criterion. Tissue contrasts were differentiated with a multiple comparison corrected nonparametric analysis of variance. F-test showed that the TCE model was better than the biexponential model in gray and white matter. Corrected Akaike information criterion showed that the TCE model has the best accuracy and produced the most reliable contrasts in white matter among all models studied. In conclusion, the TCE model was found to be the best model to infer the microstructural properties of brain tissue.

Measuring Biexponential Transverse Relaxation of the ASL Signal at 9.4 T to Estimate Arterial Oxygen Saturation and the Time of Exchange of Labeled Blood Water into Cortical Brain Tissue

The transverse decay of the arterial spin labeling (ASL) signal was measured at four inflow times in the rat brain cortex at 9.4 T. Biexponential T2 decay was observed that appears to derive from different T2 values associated with labeled water in the intravasculature (IV) and extravascular (EV) compartments. A two compartment biexponential model was used to assess the relative contribution of the IV and EV compartments to the ASL signal, without assuming a value for T2 of labeled blood water in the vessels. This novel methodology was applied to estimate the exchange time of blood water into EV tissue space and the oxygen saturation of blood on the arterial side of the vasculature. The mean exchange time of labeled blood water was estimated to be 370 ± 40 ms. The oxygen saturation of the arterial side of the vasculature was significantly less than 100% (~85%), which may have implications for quantitative functional magnetic resonance imaging studies where the arterial oxygen saturation is frequently assumed to be 100%.

Development of cephalexin-loaded poly(ethyl cyanoacrylate) colloidal nanospheres

This article considers the preparation and physicochemical characterization of a novel colloidal formulation of the β-lactam antibiotic cephalexin, loaded in poly(ethyl cyanoacrylate) colloidal nanospheres. The drug was loaded by means of drug incorporation in the interior of poly(ethyl cyanoacrylate) particles during the polymerization of the respective monomer in aqueous medium. The obtained colloids were characterized by scanning electron microscopy, dynamic and electrophoretic light scattering, Fourier transform infrared and nuclear magnetic resonance spectroscopy. It was found that the drug loading efficiency depends on the initial concentration of monomer and cephalexin in the polymerization medium. The average size of cephalexin-loaded particles was around 400 nm and did not depend significantly on the concentrations of drug and monomer. Drug-loaded particles with drug content as high as 21% (w/w) were prepared. The drug release kinetics was studied in physiological phosphate-buffered saline. It was found that a biexponential model could describe well the experimental release kinetics.

Sugammadex and Neostigmine Dose-finding Study for Reversal of Shallow Residual Neuromuscular Block

Introduction Sugammadex effectively and rapidly reverses deep to moderate rocuronium-induced neuromuscular block. However, the required dose of sugammadex for smaller degrees of residual block is unknown. Therefore we investigated the efficacy of sugammadex and neostigmine at a train-of-four (TOF) ratio of 0.5. Methods After ethics committee (Munich, Germany) approval and written informed consent were obtained, 99 patients were anesthetized with propofol, remifentanil, and rocuronium. Neuromuscular monitoring was performed by calibrated electromyography. At recovery of the TOF ratio to 0.5, patients randomly received sugammadex (0.0625, 0.125, 0.25, 0.5, or 1.0 mg/kg), neostigmine (5, 8, 15, 25, or 40 μg/kg), or saline. The time between study drug injection, at TOF ratio of 0.5, and postoperative TOF ratio of 0.9 was measured. The dose-response relationship was analyzed with a biexponential model using the dose as the independent variable and the logarithm of the recovery time as the dependent variable. Effective doses were interpolated from regression models. Results Sugammadex, 0.22 mg/kg, is able to reverse a TOF ratio of 0.5 to 0.9 or higher in an average time of 2 min. Within 5 min, 95% of patients reach this TOF ratio. Neostigmine, 34 μg/kg, is able to reverse a TOF ratio of 0.5 to 0.9 or higher within 5 min. No recurarization was observed. Conclusions Sugammadex, 0.22 mg/kg, and neostigmine, 34 μg/kg, effectively and comparably reverse a rocuronium-induced shallow residual neuromuscular block at a TOF ratio of 0.5.