Auditory vertical localization in the median plane with conflicting dynamic interaural time difference and other elevation cues.

Both dynamic variation of interaural time difference (ITD) and static spectral cues provide information for front-back discrimination and vertical localization. However, the contributions of the two cues are still unclear. The static spectral cue has conventionally been regarded as the dominant one. In the present work, psychoacoustic experiments were conducted to examine the contribution of dynamic ITD and static spectral cues to vertical localization in the median plane. By modifying the head-related transfer functions used in a dynamic virtual auditory display, binaural signals with conflicting dynamic ITD and spectral cues that were either static or dynamically modified according to instantaneous head position were created. The results indicated that the dynamic ITD and static spectral cues contribute to vertical localization at low and high frequencies, respectively. For full a bandwidth stimulus, conflicting dynamic ITD and static spectral cues usually result in two separated virtual sources at different elevations corresponding to the spatial information conveyed by the low- and high-frequency bands, respectively. In most cases, no fused localization occurs in the high-level cognition system. Therefore, dynamic ITD and static spectral cues contribute to vertical localization at different frequency ranges, and neither of them dominates vertical localization in the case of wideband stimuli.

Biomimetic Engineering Preparation of High Mechanical and Flame Retardant Elastomers by Introducing Sacrificial Bonds in Covalently Cross-Linked Chloroprene Rubber.

Designing and preparing chloroprene rubber (CR) with robust mechanical and excellent flame retardancy performance are challenging. In this work, a biomimetic design for high mechanical and flame-retardant CR by synchronous introducing of sacrificial bond (disulfide) crosslinked networks into the chemically crosslinked network is developed based on two new types of vulcanization reactions. Under the catalysis of Mg(OH)2, the dynamic bond cross-linked network is formed by the reaction between the amino group of cystamine dihydrochloride (CA) and the allylic chlorine group of CR, while the covalently crosslinked network is synchronously formed by two types of nucleophilic substitution reactions in series between Mg(OH)2 and CR. The disulfide bonds serve as sacrificial bonds that preferentially rupture prior to the covalent network, dissipating energy and facilitating rubber chain orientation, so a CA-0.5 sample (CR/CA(0.5 wt%)/Mg(OH)2 (10 wt%) with dual crosslinked networks exhibits excellent mechanical performance, and the tensile strength and elongation at the break of CA-0.5 are 1.41 times and 1.17 times greater than those of the CR-0 sample with covalently crosslinked networks, respectively. Moreover, the addition of Mg(OH)2 significantly improves the flame retardancy of CR.

Flame retardant chloroprene rubbers with high tensile strength and elongation at break via dual cross-linked networks.

The tensile strength and elongation at break of rubbers are mutually restrictive factors. Design and preparation of chloroprene rubber (CR) with high tensile strength, high elongation at break and excellent flame retardancy at the same time is challenging. Melamine cyanurate (MCA) is for the first time discovered to be a reactive flame retardant for CR. The tensile strength of C-M36 (with 3 wt% ZnO and 36 wt% MCA) vulcanizate is 2.5 times that of C-M0 (only with 3 wt% ZnO) vulcanizate, while the elongation at break of C-M36 vulcanizate is 1.3 times that of ZnO cross-linked C-M0 vulcanizate. At the same time, the limiting oxygen index of C-M36 (39%) is 1.22 times that of C-M0 (32%). FTIR and the vulcanization tests confirm that the reaction between CR and cyanuric acid occurs under the catalysis of a base (melamine), and the cyanuric acid molecules are grafted onto the molecular chain of CR. Two types of crosslinking networks are formed in CR vulcanizate, namely the traditional covalent bond crosslinks and the triple hydrogen crosslinks formed between cyanuric acid and melamine. Thus, the flame-retardant CR/MCA vulcanizate with high strength and high elongation at break is obtained. This research will strongly promote the industrial application of CR.

Necessity of heparin for maintaining peripheral venous catheters: A systematic review and meta-analysis.

Heparin has typically been used as a flushing or infusion solution for vascular lines in daily practice. However, several clinical trials have yielded controversial results about the benefits of heparin in maintaining peripheral venous catheters. The present meta-analysis was conducted to evaluate the efficacy of heparin on the patency profiles and complications in peripheral intravenous catheters. PubMed, Embase and Cochrane Central Register of Controlled Trials were searched up to February 2016 for randomized controlled trials comparing heparin with placebo in maintaining peripheral intravenous catheters. Additional studies were retrieved from the reference lists of identified articles. In total 32 eligible studies were included, from which the pooled standard mean difference (SMD), relative risk (RR) and corresponding 95% confidence interval (CI) were calculated. The use of heparin as a continuous infusion significantly prolonged the duration of patency (SMD, 0.90; 95% CI, 0.48-1.32; P<0.001), reduced rates of infusion failure (RR, 0.83; 95% CI, 0.76-0.92; P<0.001) and occlusion (RR, 0.82; 95% CI, 0.69-0.98; P<0.05) in a peripheral intravenous catheter. However, there were no significant changes in the duration of patency and infusion failure when heparin was used intermittently as a flushing solution, although a significantly decreased risk of occlusion was observed in this setting (RR, 0.80; 95% CI, 0.66-0.98; P<0.05). Furthermore, the risk of phlebitis was significantly decreased by both continuous infusion (RR, 0.66; 95% CI, 0.58-0.75; P<0.01) and intermittent flushing (RR, 0.70; 95% CI, 0.56-0.86; P<0.01) of heparin in peripheral venous catheters. In conclusion, the use of heparin as continuous infusion in peripheral intravenous catheters improved the duration of patency, reduced infusion failure and phlebitis, whereas heparin as intermittent flushing showed more benefits in ameliorating phlebitis rather than in patency profiles.