Structural principles for the propeller assembly of beta-sheets: the preference for seven-fold symmetry.

Twisted beta-sheets, packed face to face, may be arranged in circular formation like blades of a propeller or turbine. This beta-propeller fold has been found in three proteins: that in neuraminidase consists of six beta-sheets while those in methylamine dehydrogenase and galactose oxidase are composed of seven beta-sheets. A model for multisheet packing in the beta-propeller fold is proposed. This model gives both geometrical parameters of the beta-propellers composed of different numbers of sheets and patterns of residue packing at their sheet-to-sheet interfaces. All the known beta-propeller structures have been analyzed, and the observed geometries and residue packing are found to be in good agreement with those predicted by models. It is shown that unusual seven-fold symmetry is preferable to six- or eight-fold symmetry for propeller-like multi-sheet assembly. According to the model, a six-beta-sheet propeller has to have predominantly small residues in the beta-strands closed to its six-fold axis, but no strong sequence constraints are necessary for a seven-fold beta-propeller.     

The results of a close follow-up of trainees to gain a good blood collection practice

BackgroundPhlebotomy is one of the most important steps in the preanalytical phase of a clinical laboratory process. In order to decrease phlebotomy errors, this specific procedure should be taught in detail by laboratory organizations. Our study aims to practice the training program on venous blood sampling and observe the close follow-up results.MethodsIn this observational study, 127 students who started their summer internship in Antalya Education and Research Hospital were given a one-day theoretical phlebotomy training in accordance with the Venous Blood Sampling Guidelines. After the theoretical training, phlebotomy applications of 10 students who were working in the field of out-patient blood sampling were observed both with and without their knowledge. A comprehensive checklist related to phlebotomy was created by the trainers in Antalya Education and Research Hospital and the observers answered each question as yes or no. For the statistical analysis, IBM SPSS Statistics 21.0 was used.ResultsAfter the theoretical education, the trainees were observed but no significant difference was found between the first and the second informed observations (p = 0.125). The students were observed three times more in the following week without their knowledge. There was a statistically significant difference between the first and the third unannounced observations (p=0.001).ConclusionsIn order to perform phlebotomy correctly, apart from theoretical education, a close follow-up is necessary too.     

The Force-Biased Algorithm for the Irregular Close Packing of Equal Hard Spheres

Abstract

We present a “force-biased” algorithm for generating the irregular close packing of hard spheres. The algorithm is partly based on Jodrey and Tory's ideas [9] and incorporates methods from Molecular Dynamics. Packings generated by means of the two algorithms are consistent up to final packing fraction of 0.65, which seems to be the limit density of Jodrey and Tory's method. Significantly higher densities (up to 0.71) can be achieved for small numbers of spheres by the force-biased algorithm. However the shape of the radial and angle distribution functions implies that a partial short-range ordering occurs in packings of those densities.     

Social monitoring via close calls in meerkats

Social monitoring of the actions of group members is thought to be a key development associated with group living. Humans constantly monitor the behaviour of others and respond to them in a flexible way depending on past interactions and the current social context. While other primates have also been reported to change their behaviour towards other group members flexibly based on the current state of their relationship, empirical evidence is typically linked to contextually specific events such as aggressive or reproductive interactions. In the cooperatively breeding meerkat (Suricata suricatta), we investigated whether subordinate females use frequently emitted, non-agonistic close calls to monitor the location of the dominant female and whether they subsequently adjust their response based on recent social interactions during conflict and non-conflict periods. Subjects discriminated between the close calls of the dominant female and control playbacks, responding by approaching the loudspeaker and displaying submissive behaviour only if they were currently threatened by eviction. Our results suggest that meerkats assess the risk for aggressive interactions with close associates depending on social circumstances, and respond accordingly. We argue that social monitoring based on non-agonistic cues is probably a common mechanism in group-living species that allows the adjustment of behaviour depending on variation in relationships.     

不同土壤水分含量下高寒草地CH4释放的比较研究

2003年6月30日～9月4日,利用密闭箱-气相色谱法,对发育于不同水分状况下的灌丛草甸(GC)、矮嵩草草甸(AC)、藏嵩草草甸(ZC)和季节性湿地(SD)的CH4释放速率进行了比较研究.结果表明,观测期间,季节性湿地处于淹水状态,其它三种土壤平均水分含量分别为39.6%(GC)、38.4%(AC)、65.9%(ZC),而CH4平均释放速率分别为-0.031±0.030(GC)、-0.026±0.018(AC)、1.103±0.240(ZC)和6.922±4.598 mg·m-2·h-1(SD),随着土壤水分含量的增加,高寒草地土壤CH4释放由吸收转为排放,表现出与土壤湿度很好的一致性.矮嵩草草甸不同处理CH4吸收强度AC＜AJ＜AL,它们之间的差异除与土壤水分有关,还可能与处理引起的CH4传输途径不同有关.实验期间,矮嵩草草甸和灌丛草甸土壤-植物系统分别吸收CH438.69和46.13 mg·m-2,是大气温室气体CH4的弱汇,藏嵩草草甸和季节性湿地则是大气温室气体CH4的源,分别排放CH4 1.641和10.30 g·m-2.     

Individuals in foraging groups may use vocal cues when assessing their need for anti-predator vigilance

Many studies of social species have reported variation in the anti-predator vigilance behaviour of foraging individuals depending on the presence and relative position of other group members. However, little attention has focused on how foragers assess these variables. It is commonly assumed that they do so visually, but many social species produce frequent calls while foraging, and these 'close' calls might provide valuable spatial information. Here, we show that foraging pied babblers (Turdoides bicolor) are less vigilant when in larger groups, in the centre of a group and in closer proximity to another group member. We then show that foragers are less vigilant during playbacks of close calling by more individuals and individuals on either side of them when compared with calls of fewer individuals and calls on one side of them. These results suggest that foragers can use vocal cues to gain information on group size and their spatial position within a group. Future studies of anti-predator vigilance should consider the relative importance of both visual and vocal monitoring of group members.     

海南橡胶林植物多样性特征

为探讨人工林物种多样性维持机制及人为干扰后人工林群落的多样性恢复机制, 作者依据自然林的核心理论建立了一个1 ha的橡胶(Hevea brasiliensis)林固定样地, 通过研究近自然管理后样地内植物物种组成与分布来探讨近自然管理后橡胶林生物多样性的特征。结果表明: 近自然管理后橡胶林群落物种多样性较高, 1 ha样地内共有植物69科155属183种。在面积为4,000 m²、3,000 m²和2,000 m²时分别包含了样地内大约90%的种、属和科; 逻辑斯蒂模型拟合拟合种-面积曲线效果较好(R²=0.997), 证明了1 ha取样尺度可以满足橡胶林群落物种多样性研究的需要。多度-面积曲线和丰富度-面积曲线与随机分布模型有明显的差异, 表明橡胶林群落内个体数及物种分布呈非随机性。(4)对数级数模型和对数正态模型拟合橡胶林群落的种-多度分布都不理想, 相比而言后者拟合效果稍好。     

Balancing Light Absorption and Charge Transport in Vertical SnS2 Nanoflake Photoanodes with Stepped Layers and Large Intrinsic Mobility

Significant optical absorption in the blue–green spectral range, high intralayer carrier mobility, and band alignment suitable for water splitting suggest tin disulfide (SnS₂) as a candidate material for photo‐electrochemical applications. In this work, vertically aligned SnS₂ nanoflakes are synthesized directly on transparent conductive substrates using a scalable close space sublimation (CSS) method. Detailed characterization by time‐resolved terahertz and time‐resolved photoluminescence spectroscopies reveals a high intrinsic carrier mobility of 330 cm² V^?1 s^?1 and photoexcited carrier lifetimes of 1.3 ns in these nanoflakes, resulting in a long vertical diffusion length of ≈1 µm. The highest photo‐electrochemical performance is achieved by growing SnS₂ nanoflakes with heights that are between this diffusion length and the optical absorption depth of ≈2 µm, which balances the competing requirements of charge transport and light absorption. Moreover, the unique stepped morphology of these CSS‐grown nanoflakes improves photocurrent by exposing multiple edge sites in every nanoflake. The optimized vertical SnS₂ nanoflake photoanodes produce record photocurrents of 4.5 mA cm^?2 for oxidation of a sulfite hole scavenger and 2.6 mA cm^?2 for water oxidation without any hole scavenger, both at 1.23 V_RHE in neutral electrolyte under simulated AM1.5G sunlight, and stable photocurrents for iodide oxidation in acidic electrolyte.     

Evaluation of an Allosteric BACE Inhibitor Peptide to Identify Mimetics that Can Interact with the Loop F Region of the Enzyme and Prevent APP Cleavage

The aspartyl protease BACE1 (BACE) has emerged as an appealing target for reduction of amyloid-β in Alzheimer's disease. The clinical fate of active-site BACE inhibitors may depend on potential side effects related to enzyme and substrate selectivity. One strategy to reduce this risk is through development of allosteric inhibitors that interact with and modulate the Loop F region unique to BACE1. Previously, a BACE-inhibiting antibody (Ab) was shown by co-crystallization to bind and induce conformational changes of Loop F, resulting in backbone perturbations at the distal S6 and S7 subsites, preventing proper binding of a long APP-like substrate to BACE and inhibiting its cleavage. In an effort to discover small Loop F-interacting molecules that mimic the Ab inhibition, we evaluated a peptide series with a YPYF(I/L)P(L/Y) motif that was reported to bind a BACE exosite. Our studies show that the most potent inhibitor from this series, peptide 65007, has a similar substrate cleavage profile to the Ab and reduces sAPPβ levels in cell models and primary neurons. As our modeling indicates, it interacts with the Loop F region causing a conformational shift of the BACE protein backbone near the distal subsites. The peptide-bound enzyme adopts a conformation that closely overlays with the crystal structure (PDB: 3R1G) from Ab binding. Importantly, peptide 65007 appears to be BACE substrate and enzyme selective, showing little inhibition of NRG1, PSGL1, CHL1, or Cat D. Thus, peptide 65007 is a promising lead for discovery of Loop F-interacting small-molecule mimetics as allosteric inhibitors of BACE.     

Oriented Grains with Preferred Low‐Angle Grain Boundaries in Halide Perovskite Films by Pressure‐Induced Crystallization

A general methodology is reported to create organic–inorganic hybrid metal halide perovskite films with enlarged and preferred‐orientation grains. Simply pressing polyurethane stamps with hexagonal nanodot arrays on partially dried perovskite intermediate films can cause pressure‐induced perovskite crystallization. This pressure‐induced crystallization allows to prepare highly efficient perovskite solar cells (PSCs) because the preferred‐orientation and enlarged grains with low‐angle grain boundaries in the perovskite films exhibit suppressed nonradiative recombination. Consequently, the photovoltaic response is dramatically improved by the uniaxial compression in both inverted‐planar PSCs and normal PSCs, leading to power conversion efficiencies of 19.16%.