基于氮掺杂石墨烯/泡沫铁的三维复合阳极

利用浸渍和高温还原法制备了一种由氮掺杂石墨烯包覆泡沫铁(N-rGO/IF)复合阳极,该阳极为大比表面积的三维结构且亲水性良好,可实现高密度微生物负载(1534μg/cm^(2))。利用N-rGO/IF阳极将原电池集成在微生物燃料电池装置中以增加新的产电方式,从而组成了混合微生物燃料电池。电化学测试结果显示,在原电池(功率密度0.3585 mW/cm^(2))的增强作用下,以N-rGO/IF为复合阳极的混合微生物燃料电池实现了0.6019 mW/cm^(2)的最大功率密度。结果表明,N-rGO/IF复合阳极可用于设计和制造大功率混合微生物燃料电池。

制定数据中心功率密度规范的指导原则

制定数据中心功率密度规范的传统方法不仅含糊不清,而且容易误导用户。使用W/ft2或W/m2来描述数据中心的功率密度不足以确定数据中心的供电或制冷能力是否满足高密度计算负载(例如,刀片式服务器)的要求。在以前,没有一种明确而标准的方法可用来指定数据中心在高密度负载条件下实现可预期的行为。一个适当的数据中心功率密度规范应该能够确保数据中心符合预期的高密度负载的要求,能够为设计、安装供电和制冷设备提供明确的指示,能够防止过度规划,并能够使用电效率最大化。本文就制定数据中心供电和制冷基础设施规范的改进方法在科研领域和实际生产中的应用进行了说明。

数据中心风墙气流组织的CFD模拟研究

为研究空调箱机组的布置、送风距离对于风墙气流组织的影响,建立了采用卧式空调箱机组冷却的数据机房模型。以6SigmaRoom仿真软件分别对4+1、5+1及6+1的风墙空调箱机组配置方案在送风距离15 m及16.8 m时,按照机组全开热备份、中间备机不开、侧边备机不开3种不同运行模式进行气流组织模拟。通过分析模拟得出的温度场发现,在空调箱机组全开热备份运行模式下,3种机组布局方案差异不大,冷通道的温升都在1℃左右;备机不开,则温度场存在明显差异,不同方案温升相差近5℃,机组数量越多,冷通道的最高温度越低,温升越小。模拟得到的流场显示,相同运行模式下,机组数量越多,流线更均匀。就样本数据机房的7+1风墙空调箱机组配置方案分别假设送风距离为9.6 m(单柜发热量20 kW)、12 m(单柜发热量15 kW)、15 m(单柜发热量12 kW)、19.8 m(单柜发热量8 kW)及25.2 m(单柜发热量5 kW)进行气流组织模拟。模拟结果显示,在确保最大送风温升不超过2℃的前提下,送风距离为9.6 m时,风墙的气流组织可以支撑高达20 kW的单机柜发热量;单机柜发热量为8 kW时,风墙的气流组织最远送风距离可达到19.8 m。

Activity and selectivity of propane oxidative dehydrogenation over VO_3/CeO_2(111) catalysts: A density functional theory study

The oxidative dehydrogenation（ODH） of propane on monomeric VO3 supported by CeO2（111）（VO3/CeO 2（111）） is studied by periodic density functional theory calculations. Detailed energetic, structural, and electronic properties of these reactions are determined. The calculated activation energies of the breaking of the first and second C–H bonds of propane on the VO3/CeO2（111） catalyst are compared, and it is found that both the unique structural and electronic effects of the VO3/CeO2（111） catalyst contribute to the relatively easy rupture of the first C–H bond of the propane molecule during the ODH reaction. In particular, the so-called new empty localized states that are mainly constituted of O2 porbitals of the ceria-supported VO3 species are determined to be crucial for assisting the cleavage of the first C–H bond of the propane molecule. Following this they become occupied and the remaining C–H bonds become increasingly difficult to break owing to the increasing repulsion between the localized 4 felectrons at the Cecations, resulting in the adsorption of more H and other moieties. This work illustrates that CeO2-supported monomeric vanadium oxides can exhibit unique activity and selectivity for the catalytic ODH of alkanes to alkenes.

Ru surface density effect on ammonia synthesis activity and hydrogen poisoning of ceria-supported Ru catalysts

Evaluating the effect of metal surface density on catalytic performance is critical for designing high-activity metal-based catalysts.In this study,a series of ceria(CeCO_(2))-supported Ru catalysts(Ru/CeCO_(2))were prepared to analyze the effect of Ru surface density on the catalytic performance of Ru/CeCO_(2) for ammonia synthesis.For the Ru/CeCO_(2) catalysts with Ru surface densities lower than 0.68 Ru nm^(-2),the Ru layers were in close contact with CeCO_(2),and electrons were transferred directly from the CeCO_(2) defect sites to the Ru species.In such cases,the adsorption of hydrogen species on the Ru sites in the vicinity of 0 atoms was high,leading to a high ammonia synthesis activity and strong hydrogen poisoning.In contrast,the preferential aggregation of Ru species into large particles on top of the Ru overlayer resulted in the coexistence of Ru clusters and particles,for catalysts with a Ru surface density higher than 1.4 Ru nm^(-2),for which Ru particles were isolated from the direct electronic influence of CeCO_(2).Consequently,the Ru-Ceth interactions were weak,and hydrogen poisoning can be significantly alleviated.Overall,electron transfer and hydrogen adsorption synergistically affected the synthesis of ammonia over Ru/CeCO_(2) catalysts,and catalyst samples with a Ru surface density lower than 0.31 Ru nm^(-2) or exactly 2.1 Ru nm^(-2) exhibited high catalytic activity for ammonia synthesis.

Freights loading optimization with balanced and unconcentrated loading constraints

The optimization of high density and concentrated-weight freights loading requires an even distribution of the freight's weight and unconcentrated loading on the floor of the car.Based on the characteristics of concentrated-weight category freights,an improvement method is put forward to build freight towers and a greedy-construction algorithm is utilized based on heuristic information for the initial layout.Then a feasibility analysis is performed to judge if the balanced and unconcentrated loading constrains are reached.Through introducing optimization or adjustment methods,an overall optimal solution can be obtained.Experiments are conducted using data generated from real cases showing the effectiveness of our approach: volume utility ratio of 90.4% and load capacity utility ratio of 86.7% which is comparably even to the packing of the general freights.

High loading cotton cellulose-based aerogel self-standing electrode for Li-S batteries

Lithium-sulfur(Li-S) batteries have attracted considerable attention due to their high energy density(2600 Wh kg-1). However, its commercialization is hindered seriously by the low loading and utilization rate of sulfur cathodes. Herein, we designed the cellulose-based graphene carbon composite aerogel(CCA) self-standing electrode to enhance the performance of Li-S batteries. The CCA contributes to the mass loading and utilization efficiency of sulfur, because of its unique physical structure: low density(0.018 g cm-3), large specific surface area(657.85 m2 g-1), high porosity(96%), and remarkable electrolyte adsorption(42.25 times). Compared to Al(about 49%), the CCA displayed excellent sulfur use efficiency(86%) and could reach to high area capacity of 8.60 mAh cm-2 with 9.11 mgS loading. Meanwhile,the CCA exhibits the excellent potential for pulse sensing applications due to its flexibility and superior sensitivity to electrical response signals.

HEART RATE VARIABILITY DURING HIGH-INTENSITY EXERCISE

The aim of this paper is to describe and analyse the behaviour of heart rate variability(HRV)during constant-load,high-intensity exercise using a time frequency analysis(Wavelet Transform).Eleven elite cyclists took part in the study(age:18.6±3.0 years;VO_(2max):4.88±0.61 litres·min^(-1)).Initially,all subjects performed an incremental cycloergometer test to determine load power in a constant load-test(379.55±36.02 W;89.0%).HRV declined dramatically from the start of testing(p<0.05).The behaviour of power spectral density within the LF band mirrored that of total energy,recording a significant decrease from the outset LF peaks fell rapidly thereafter,remaining stable until the end of the test.HF-VHF fell sharply in the first 20 to 30 seconds.The relative weighting(%) of HF-VHF was inverted with the onset of fatigue,[1.6%at the start,7.1(p<0.05) at the end of the first phase,and 43.1%(p<0.05) at the end of the test].HF-VHF_(peak) displayed three phases:a moderate initial increase,followed by a slight fall,thereafter increasing to the end of the test.The LF/HF-VHF ratio increased at the start,later falling progressively until the end of the first phase and remaining around minimal values until the end of the test.