Unveiling the temperature-dependent thermoelectric properties of the undoped and Na-doped monolayer SnSe allotropes: a comparative study

Motivated by the excellent thermoelectric (TE) performance of bulk SnSe, extensive attention has been drawn to the TE properties of the monolayer SnSe. To uncover the fundamental mechanism of manipulating the TE performance of the SnSe monolayer, we perform a systematic study on the TE properties of five monolayer SnSe allotropes such asα-,β-,γ-,δ-, andε-SnSe based on the density functional theory and the non-equilibrium Green's functions. By comparing the TE properties of the Na-doped SnSe allotropes with the undoped ones, the influences of the Na doping and the temperature on the TE properties are deeply investigated. It is shown that the figure of meritZTwill increase as the temperature increases, which is the same for almost all the Na-doped and undoped cases. The Na doping can enhance or suppress theZTin different SnSe allotropes at different temperatures, implying the presence of the anomalous suppression of theZT. The Na doping inducedZTsuppression may be caused basically by the sharp decrease of the power factor and the weak decrease of the electronic thermal conductance, rather than by the decrease of the phononic thermal conductance. We hope this work will be able to enrich the understanding of the manipulation of TE properties by means of dimensions, structurization, doping, and temperature.

Electronic structures, transport properties, and optical absorption of bilayer blue phosphorene nanoribbons

Based on first-principles density functional theory and nonequilibrium Green's function, we study the electronic band structures, the electronic transport properties, and the optical absorption of bilayer blue phosphorene nanoribbons (BPNRs). Both bilayer armchair BPNRs (a-BPNRs) and zigzag BPNRs (z-BPNRs) behave as semiconductors in the narrow nanoribbon case and metals in the wide nanoribbon case, sharply different from their monolayer counterparts where the monolayer a-BPNRs (z-BPNRs) are always semiconducting (metallic). This indicates that interlayer couplings or the increasing layer number may induce the switching of the conductivity of the monolayer BPNRs, which is absent in graphene and phosphorene nanoribbons. Furthermore, we explore the edge states of the energy bands near Fermi energy, and find that there are almost no pure edge-state band branches in the bilayer BPNRs, which can be attributed to the interlayer couplings between the edge-states in one layer and the bulk-states in the other. Consequently, the resulting complex band structures cannot be directly analyzed any more in the framework of the two-body coupling picture just according to the simple band structures of the monolayer BPNRs. Finally, we present the current-voltage characteristics and the optical absorption of the bilayer a-BPNRs and z-BPNRs. The influences of the nanoribbon width and the interlayer couplings on the current and the anisotropic optical absorption can be understood based on the complex energy band structures. This research should be an important reference of extending the field of BPNRs from the monolayer to the bilayer case, and deepen the understanding of the difference between the monolayer and bilayer nanoribbons in different materials.

[Incidence of blood stream infections of 1265 patients with hematopoietic stem cell transplantation and analysis of pathogenic bacteria]

目的

分析造血干细胞移植（HSCT）患者血流感染的发生率、病原菌分布及药敏情况，为临床血流感染的经验性治疗提供依据。

方法

对2013–2015年在苏州大学附属第一医院行HSCT的1 265例患者进行血流感染发生率、血培养阳性率、病原菌种类和耐药情况分析。

结果

1 265例HSCT患者中，有784例（61.98%）共发生1 422例次血流感染，464例（59.2%）患者处于粒细胞缺乏期（ANC<0.5×10⁹/L）。2013–2015年病原菌检出率逐年上升，总体为20.07%。检出的401株病原菌中，革兰阴性菌221株（55.1%），革兰阳性菌165株（41.2%），真菌15株（3.7%）。排名前三位为大肠埃希菌（16.0%）、表皮葡萄球菌（15.5%）和肺炎克雷伯菌（11.2%）；细菌耐药情况严峻，多重耐药的鲍曼不动杆菌和嗜麦芽窄食单胞菌比例分别为64.70%与63.64%，耐甲氧西林金黄色葡萄球菌（MRSA）比例为57.14%，均超过50.0%。耐万古霉素肠球菌（VRE）与耐碳青霉烯类抗生素肠杆菌科细菌（CRE）比例分别为14.29%、6.78%。革兰阴性菌中肠杆菌科细菌对三、四代头孢类药物耐药率较高，对碳青霉烯类抗生素耐药率较低（6.4%）。非发酵菌对抗菌药物耐药情况差别较大，对碳青霉烯类抗生素耐药率较高（47.8%）；葡萄球菌属菌株对万古霉素、替考拉宁和利奈唑胺的敏感率均为100.0%。

结论

HSCT患者血流感染发生率较高，病原菌仍以革兰阴性菌为主，非发酵菌的占比也较高，未检测到对万古霉素、替考拉宁和利奈唑胺耐药的葡萄球菌。