The thermal and electrical properties of the promising semiconductor MXene Hf2CO2

In this work, we investigate the thermal and electrical properties of oxygen-functionalized M2CO2 (M = Ti, Zr, Hf) MXenes using first-principles calculations. Hf2CO2 is found to exhibit a thermal conductivity better than MoS2 and phosphorene. The room temperature thermal conductivity along the armchair direction is determined to be 86.25-131.2 Wm-1K-1 with a flake length of 5-100 um, and the corresponding value in the zigzag direction is approximately 42% of that in the armchair direction. Other important thermal properties of M2CO2 are also considered, including their specific heat and thermal expansion coefficients. The theoretical room temperature thermal expansion coefficient of Hf2CO2 is 6.094x10-6 K-1, which is lower than that of most metals. Moreover, Hf2CO2 is determined to be a semiconductor with a band gap of 1.657 eV and to have high and anisotropic carrier mobility. At room temperature, the Hf2CO2 hole mobility in the armchair direction (in the zigzag direction) is determined to be as high as 13.5x103 cm2V-1s-1 (17.6x103 cm2V-1s-1), which is comparable to that of phosphorene. Broader utilization of Hf2CO2 as a material for nanoelectronics is likely because of its moderate band gap, satisfactory thermal conductivity, low thermal expansion coefficient, and excellent carrier mobility. The corresponding thermal and electrical properties of Ti2CO2 and Zr2CO2 are also provided here for comparison. Notably, Ti2CO2 presents relatively low thermal conductivity and much higher carrier mobility than Hf2CO2, which is an indication that Ti2CO2 may be used as an efficient thermoelectric material.Comment: 26 pages, 5 figures, 2 table

Bank lending and CEO turnover: Evidence from China

To maintain bank relationship, borrowers have motives to discipline themselves by forcing out underperforming CEOs. In this paper, we show that the state ownership in emerging markets renders this disciplinary mechanism ineffective. Using the contract information of bank loans for Chinese listed firms, we find that higher bank loan intensity overall does not affect the probability of forcing out an underperforming CEO. The absence of disciplinary effect is driven by the bank-firm pairs in which either the borrower or the lender is state-owned. However, the disciplinary effect is significant if a firm’s bank loans mostly consist of secured and short-term bank loans. Bank loans increase the likelihood of a forced CEO turnover, especially when joint-equity banks serve as the main lender. Overall, we propose that state ownership is an important factor driving the inefficiency of credit market in emerging countries

Minimum energy as the general form of critical flow and maximum flow efficiency and for explaining variations in river channel pattern

Although the Bélanger-Böss theorem of critical flow has been widely applied in open channel hydraulics, it was derived from the laws governing ideal frictionless flow. This study explores a more general expression of this theorem and examines its applicability to flow with friction and sediment transport. It demonstrates that the theorem can be more generally presented as the principle of minimum energy (PME), with maximum efficiency of energy use and minimum friction or minimum energy dissipation as its equivalents. Critical flow depth under frictionless conditions, the best hydraulic section where friction is introduced, and the most efficient alluvial channel geometry where both friction and sediment transport apply are all shown to be the products of PME. Because PME in liquids characterizes the stationary state of motion in solid materials, flow tends to rapidly expend excess energy when more than minimally demanded energy is available. This leads to the formation of relatively stable but dynamic energy-consuming meandering and braided channel planforms and explains the existence of various extremal hypotheses

Aqua[N-(2,5-dihydroxybenzyl)imino­diacetato]copper(II)

The title complex, [Cu(C11H11NO6)(H2O)], contains a CuII atom in a distorted square-pyramidal geometry. The metal centre is coordinated in the basal sites by one water mol­ecule and two carboxyl­ate O atoms and one N atom of the tetra­dentate ligand [Cu—O range, 1.9376 (11)–1.9541 (12), Cu—N, 1.9929 (12) Å] while the apical site is occupied by a hydro­quinone O donor atom [Cu—O, 2.3746 (12) Å]. Inter­molecular hydrogen bonding inter­actions involving both hydro­quinone hydr­oxy groups and the coordinated water as donors give a three-dimensional framework structure

Wearable low back trainer combined with massage in the treatment of chronic nonspecific low back pain

Objective: To observe the clinical effect of wearable low back trainer combined with massage in the treatment of chronic non-specific low back pain. Methods: A total of 56 chronic nonspecific low back pain patients were randomly assigned to three groups. The ob group (n=19) was treated with wearable device treatments based on massage for two weeks, once a day, eight minutes each time, five times a week, while the control group (n=19) received massage only for two weeks, once a day, 20 minutes each time, and the blank group (n=18) rest only with closely observation. The therapeutic effect of three groups were evaluated by VAS and ODI scores before the treatment, one week after treatment and two weeks after treatment respectively. Results: There was no significant difference in the VAS score between the observation group and the control group before treatment (P>0.05) while the VAS score difference between the three groups after one week and two weeks of treatment were statistically significant (P<0.05). The VAS scores of the observation group and the control group showed a downward trend with time. After 2 weeks of treatment, the VAS value of the observation group decreased significantly more than the control group, and the difference was statistically significant (P<0.05). The decrease of VAS value in the group was significantly greater than that in the blank group, and the difference was statistically significant (P<0.05). There was no significant difference in the ODI score between the observation group and the control group before treatment and after 1 week of treatment (P>0.05). However, there was a statistically significant difference in the ODI score between the three groups after 2 weeks of treatment (P<0.05). The changing trends of ODI values in the three groups were different and both the observation group and the control group showed a downward trend. After two weeks of treatment, the ODI values of the observation group decreased significantly more than the control group with statistically significant differences (P<0.05). However, the ODI value of the blank group decreased after 1 week of treatment and increased again after two weeks of treatment. Conclusion: The use of the wearable low back trainer combined with massage therapy has a better therapeutic effect on chronic non-specific low back pain and can relieve pain more effectively than just simple massage therapy alone