Temporal Variation in Sap-Flux-Scaled Transpiration and Cooling Effect of a Subtropical Schima superba Plantation in the Urban Area of Guangzhou

Agriculture could suffer the water stress induced by climate change. Because climate warming affects global hydrological cycles, it is vital to explore the effect of tree transpiration, as an important component of terrestrial evapotranspiration, on the environment. Thermal dissipation probes were used to measure xylem sap flux density of a Schima superba plantation in the urban area of Guangzhou City, South China. Stand transpiration was calculated by mean sap flux density times total sapwood area. The occurrence of the maximum sap flux density on the daily scale was later in wet season than in dry season. The peak of daily sap flux density was the highest of 59 g m-2 s^-1 in July and August, and the lowest of 28 g m-2 s-1 in December. In the two periods （November 2007-October 2008 and November 2008-October 2009）, the stand transpiration reached 263.2 and 291.6 ram, respectively. During our study period, stand transpiration in wet season （from April to September） could account for about 58.5 and 53.8% of the annual transpiration, respectively. Heat energy absorbed by tree transpiration averaged 1.4×10s and 1.6×10s kJ per month in this Schima superba plantation with the area of 2 885 m2, and temperature was reduced by 4.3 and 4.7℃ s^-1 per 10 m3 air.

THERMAL EFFECTS OF BUILDING′S EXTERNAL SURFACES IN CITY——Characteristics of Heat Flux into and out of External Wall Surfaces

This study examined the thermal effects of building′s external wall surfaces, using observational data of spatial-temporal distribution of surface temperature, air temperature, and heat flux into and out of external surface. Results indicate that external wall surface temperature and nearby air temperature vary with the change of orientation, height and season. In general, the external wall surface temperature is lower near the ground, and is higher near the roof, than nearby air temperature. But north wall surface temperature is mostly lower than nearby air temperature at the same height; south wall surface temperature during the daytime in December, and west wall surface temperature all day in August, is respectively higher than nearby air temperature. The heat fluxes into and out of external wall surfaces show the differences that exist in the various orientations, heights and seasons. In December, south wall surface at the lower sites emits heat and north wall surface at the higher sites absorbs heat. In April, all external wall surfaces, emit heat near the ground and absorb heat near the roof. In August, west wall surface all day emits heat, and other wall surfaces just show the commensurate behavior with that in April.

A Re-examination of Density Effects in Eddy Covariance Measurements of CO_2 Fluxes

Corrections of density effects resulting from air-parcel expansion/compression are important in interpreting eddy covariance fluxes of water vapor and CO2 when open-path systems are used. To account for these effects, mean vertical velocity and perturbation of the density of dry air are two critical parameters in treating those physical processes responsible for density variations. Based on various underlying assumptions, different studies have obtained different formulas for the mean vertical velocity and perturbation of the density of dry air, leading to a number of approaches to correct density effects. In this study, we re-examine physical processes related to different assumptions that are made to formulate the density effects. Specifically, we re-examine the assumptions of a zero dry air flux and a zero moist air flux in the surface layer, used for treating density variations, and their implications for correcting density effects. It is found that physical processes in relation to the assumption of a zero dry air flux account for the influence of dry air expansion/compression on density variations. Meanwhile, physical processes in relation to the assumption of a zero moist air flux account for the influence of moist air expansion/compression on density variations. In this study, we also re-examine mixing ratio issues. Our results indicate that the assumption of a zero dry air flux favors the use of the mixing ratio relative to dry air, while the assumption of a zero moist air flux favors the use of the mixing ratio relative to the total moist air. Additionally, we compare different formula for the mean vertical velocity, generated by air-parcel expansion/compression, and for density effect corrections using eddy covariance data measured over three boreal ecosystems.

Analysis of cooling effectiveness for heat flux based on reference enthalpy

In order to quickly and accurately compute the wall temperature distribution along the combustor axial line, a method to compute the temperature field of combustion chamber with active regeneratively cooling was presented. On the condition of nonstationary wall temperature, the one-dimensional cooling model based on reference enthalpy was established, and the distribution of the wall heat flux and the wall temperature along the combustor axial line were obtained at different mach numbers by using the heat transfer empirical equation. For the existing two types of cooling system structure, the cooling effectiveness of which was investigated through the presented method. And the satisfactory results obtained show the validity of the method.

Investigation of flux dependent sensitivity on single event effect in memory devices

Heavy-ion flux is an important experimental parameter in the ground based single event tests. The flux impact on a single event effect in different memory devices is analyzed by using GEANT4 and TCAD simulation methods. The transient radial track profile depends not only on the linear energy transfer （LET） of the incident ion, but also on the mass and energy of the ion. For the ions with the energies at the Bragg peaks, the radial charge distribution is wider when the ion LET is larger. The results extracted from the GEANT4 and TCAD simulations, together with detailed analysis of the device structure, are presented to demonstrate phenomena observed in the flux related experiment. The analysis shows that the flux effect conclusions drawn from the experiment are intrinsically connected and all indicate the mechanism that the flux effect stems from multiple ion-induced pulses functioning together and relies exquisitely on the specific response of the device.

Effect of Counter-Gradient in the Computation of Turbulent Fluxes of Heat and Moisture in a Regional Model

The counter-gradient terms in the computations of turbulent fluxes of heat and moisture have been included in the PBL parameterization of a regional model for monsoon prediction. Results show that inclusion of counter-gradient terms has a marginal impact in the prediction of large scale monsoon circulation and rainfall rates.

Effect of slip velocity on Casson thin film flow and heat transfer due to unsteady stretching sheet in presence of variable heat flux and viscous dissipation

The aim of the present paper is to study flow and heat transfer charac- teristics of a viscous Casson thin film flow over an unsteady stretching sheet subject to variable heat flux in the presence of slip velocity condition and viscous dissipation. The governing equations are partial differential equations. They are reduced to a set of highly nonlinear ordinary differential equations by suitable similarity transformations. The re- sulting similarity equations are solved numerically with a shooting method. Comparisons with previous works are macle, and the results are found to be in excellent agreement. In the present work, the effects of the unsteadiness parameter, the Casson parameter, the Eckert number, the slip velocity parameter, and the Prandtl number on flow and heat transfer characteristics are discussed. Also, the local skin-friction coefficient and the local Nusselt number at the stretching sheet are computed and discussed.

基于热电堆的微型热流传感器制备及性能研究

航空发动机内部温度和热辐射的不均匀分布可能导致叶片表面出现热点,引起叶尖等区域的材料损坏。因此,监测单位时间内通过叶片表面的热量十分重要。热电堆型热流传感器以其测量范围广、稳定性好、精度高等优点,成为监测高温环境热流参数的常用方法。本文采用丝网印刷和高温烧结工艺,在10 mm×10 mm×1 mm的99%Al_(2)O_(3)陶瓷基片上制备了Pt-Rh10/Pt热电堆型热流传感器,并搭建了热流实验平台对传感器进行测试。结果表明,该热流传感器在1 019.4℃的高温环境下,所测热流密度为179.67 kW/m^(2),输出电压为0.462 3 mV。经过3次热循环测试可知,该热流传感器的重复性偏差小于5%,具有较好的重复性。

贵州省碳吸收/碳排放时空变化特征及其与经济的脱钩效应

贵州省是我国喀斯特生态系统的典型分布区,生态敏感且脆弱,同时其也曾是我国的连片特困区,经济发展愿望迫切。对区域环境-经济发展状况及相互作用关系进行研究具有重要意义。研究从植被净生态系统生产力、土壤碳储量、岩溶碳通量三方面计算了贵州省陆地生态系统碳吸收,以能源燃烧排放的CO_(2)表征碳排放量,对区域碳吸收和碳排放的时空变化特征进行剖析,在此基础上构建环境碳负荷指数和脱钩弹性系数,用于解析贵州省碳收支状况及环境碳负荷与经济发展之间的脱钩关系。结果显示:(1)贵州省植被净生态系统生产力均值为257.72 g C/m^(2),呈逐步增强趋势,空间上呈现西高东低、南高北低的分布格局;岩溶碳通量的均值为6.71 t C/km^(2),年际波动较大,集中分布在研究区东北和西南部;土壤碳储量的均值为8.38 t/hm^(2),其高值区主要位于研究区南部和东部边缘;(2)区域碳排放呈现出了逐年增长的特征,表明了能源消耗的增强,形成了以城市高值区为中心向外辐射递减,各点之间以道路连通为特征的分布格局;(3)环境碳负荷指数呈逐年增长趋势,表征区域面临的环境压力越来越大,特别是在贵州省主城区出现了明显的收支不平衡,能源结构优化亟待加强;(4)综合脱钩状态整体以弱脱钩和扩张连接为主,且随时间推移脱钩状态由弱脱钩向扩张连接转变,说明环境保护滞后于经济发展,也就意味着贵州省经济的发展一定程度上牺牲了环境保护。未来应进一步强化生态修复工程的可持续性,同时发展绿色经济以促进区域生态-经济可持续发展。

尿毒症患者行高通量血透治疗的效果分析

目的分析高通量血透治疗尿毒症的临床疗效。方法选取2022年1—12月青岛市胶州中心医院血液透析科收治的90例尿毒症患者为研究对象,以奇偶数形式分为两组,各45例,常规组采取中通量血液透析治疗,观察组采取高通量血透治疗,比较两组肾功能水平、并发症发生率、治疗有效率。结果治疗后,观察组肾功能水平优于常规组,差异有统计学意义(P<0.05);观察组并发症发生率为4.44%,低于常规组的20.00%,差异有统计学意义(χ^(2)=5.075,P=0.024);观察组治疗有效率高于常规组,差异有统计学意义(P<0.05)。结论尿毒症患者以高通量血透方式治疗,能够有效改善患者肾功能,降低并发症发生率,有较高的疾病治疗有效率。

磁-热-弹多物理场耦合波的反射和透射

应用麦克斯韦电磁学理论引入洛伦兹力,反映外磁场对弹性波传播的影响.通过应用广义热弹性GN(Ⅱ)模型,反映热力耦合效应对弹性波传播的影响.通过色散方程和相速度,分析了外磁场和热力耦合效应对波动模式和色散特性的影响.应用连续性边界条件,计算出各种反射波和透射波与入射波的能流比,通过法向能量守恒验证了数值计算结果的可靠性.

基于PYTHON的城市人为热通量与温度关系分析及风险评估

针对全球城市热岛效应日趋严重而复杂形势,提出了一种运用SUEWS模型和Python进行数据分析的方法,探讨人为热通量影响城市热岛效应的重要性与形成机理,重点分析温度变化对制冷度日和人为热通量的影响程度。通过对城市气候大数据的分析研究,发现制冷度日和人为热通量之间存在一定相关性,人为热通量与温度变化之间有敏感响应关系;最后提出相应建议和措施。

高焓流场球头外形气动热试验研究

再入地球大气层时,飞行器的再入速度极高,面临严重的气动加热问题。为了研究高焓流动导致的热化学非平衡现象,在高焓膨胀风洞FD-14X中开展了球头外形的热流测量试验以及CFD仿真模拟。FD-14X为中国空气动力研究与发展中心新建成的高焓膨胀风洞,速度模拟能力达到第二宇宙速度,总温模拟能力超过10000 K,能够产生总焓70 MJ/kg的试验气体。试验来流总焓16.9~63.5 MJ/kg,球头直径20~50 mm,流场采用自发光拍照,同时CFD仿真采用Park双温非平衡模型计算球头绕流流场。试验与仿真结果表明:来流总焓大于5 MJ/kg时,球头绕流场存在显著的热化学非平衡现象;304钢模型壁面在来流总焓小于20 MJ/kg时表现为非催化壁面特性,在来流总焓大于30 MJ/kg时表现为催化壁面特性;当球头表面镀氧化锆膜、来流总焓49.5 MJ/kg时,球头壁面表现为非催化壁面特性。

Effect of pyroxenite and olivine minerals as source of MgO in hematite pellet on improvement of metallurgical properties

Pelletization of hematite ore requires high fineness and very high induration temperature(~1325 °C) owing to its poor diffusion bonding unlike magnetite ore. Further, high-alumina hematite pellets show very high reduction degradation index(RDI) during low temperature(500-650 °C) reduction due to their volume expansion and lattice distortion. Noamundi(India) hematite ore contains very high Al2O3(2.3%) with adverse ratio of alumina to silica(~2) for which, it shows very high RDI. In this work, the acid pellets prepared from Noamundi ore fines of optimum Blaine fineness show good cold crushing strength(CCS). However, it shows very high RDI(77%). In order to reduce RDI, Mg O in form of two different gangue-containing fluxes, such as pyroxenite and olivine in varying quantities has been added. The optimum requirement and performance of these fluxes has been examined and compared. Both pyroxenite and olivine fluxed pellets show significant lowering of RDI(26% and 23%, respectively) and improvement of other properties, viz CCS, swelling indices etc with good reducibility(70%-77%). Finally, a good quality acidic hematite pellet was developed from high-alumina ore without using any lime which is very important charge material in combination of basic sinter in blast furnace.

Quantum transport through two series Aharonov-Bohm interferometers with zero total magnetic flux

With the help of nonequilibrium Green＇s function technique, the electronic transport through series Aharonov-Bohm （AB） interferometers is investigated. We obtain the AB interference pattern of the transition probability characterized by the Mgebraic sum φ and the difference θ of two magnetic fluxes, and particularly a general rule of AB oscillation period depending on the ratio of integer quantum numbers of the fluxes. A parity effect is observed, showing the asymmetric AB oscillations with respect to the even and odd quantum numbers of the total flux in antiparallel AB interferometers. It is also shown that the AB flux can shift the Fano resonance peaks of the transmission spectrum.

Anisotropic Magnetocaloric Effect and Magnetic Order in Antiferromagnetic Gd₂InGe₂

We investigated the transport, thermal and magnetic properties of antiferromagnetic (TN = 45 K) Gd2InGe2. Magnetization measurements under applied magnetic field, oriented along different crystallographic directions, were used to extract the anisotropic magnetocaloric effect. We also measured magnetization under pulsed field up to 45 T. From the analysis of the electrical transport and magnetization, conduction band electrons were weakly coupled to Gd f-electron local moments. Differential scanning calorimeter data confirmed a second order phase of the antiferromagnetic to paramagnetic transition. The anisotropic magnetocaloric effect points to a model of magnetic ordering whereby Gd local moments couple ferromagnetically and antiferromagnetically perpendicular and parallel, respectively, to the c-axis.

Propagation effects of low frequency electromagnetic waves in production well

The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well logging has a strong shielding effect on the electromagnetic waves, thus bringing some difficulties to the application of the frequency domain electromagnetic method in production well logging. According to the relation of the field source geometry to the ring around the mandrel, the general expressions of frequency domain electromagnetic responses in axially symmetrical layered conductive medium are deduced. The propagation effects caused by the low-frequency electromagnetic waves in cased hole are also analyzed. The distribution curves of eddy current density and magnetic flux density along the radial direction in the mandrel indicate that the eddy loss within the mandrel is proportional to the transmission signal frequency and the mandrel conductivity. The secondary field responses of different casing materials show that the transmission frequency has an important effect on the ability of electromagnetic waves penetrating the metal casing. The transmission frequency should be ultra-low in order to enable the electromagnetic signal to penetrate the casing easily. The numerical results of frequency responses for different casing physical parameters show that the casing thickness has a significant impact on the choice of the transmission frequency. It is also found that the effect of the casing radius on the transmission frequency can be neglected.

Matching effect in superconducting NbN thin film with a square lattice of holes

A square hole array is fabricated over a micro-bridge of NbN thin film by electron beam lithography and reactive ion milling. Magneto-resistance is measured across the micro-bridge filled with a hole array near the superconducting transition temperature. It is found that magneto-resistance minima occur when the number of vortices is an integer multiple or a fractional multiple of the number of holes. The temperature and the current dependences of the matching effect are studied.

考虑边缘磁通的LCT新型六电容频域解析模型

基于有限元的松耦合变压器(LCT)设计往往只能考虑电场或磁场效应,存在计算复杂、耗时,不能得到参数间较为直观的物理关系,以及不能进行频域设计等问题;为此以相邻式磁罐变压器为例,在考虑气隙边缘磁通效应的基础上,提出了一种新型六电容频域解析模型。采用磁路法和静电能量等效法分别计算了互感、漏感和分布电容参数,采用回路电流法建立了频域模型,然后采用频域分析法,对比研究了不同分布参数模型的传输特性。最后,通过有限元方法验证了考虑边缘磁通效应的电感模型的准确性,仿真和实验结果表明了本文松耦合变压器分布电容模型解析计算的正确性,同时相较于其他现有模型,提出了从频域角度分析的LCT六电容模型,并获得了比现有方法准确性更高的计算模型。

成都热岛效应研究在公园城市建设中的应用

随着成都城市化进程的加快,热岛效应逐渐加剧,而公园城市建设是缓解热岛效应的有效手段。基于Landsat8影像,利用劈窗算法反演得到地表温度,进而得到研究区净辐射通量和土壤热通量的热辐射分布特征,并根据成都热岛效应分布特征提出了公园城市建设的措施。结果表明,成都热岛效应冬季更明显;主城区地表温度高、热通量大,郊县热通量小,热岛效应较低。由回归分析可知,成都热岛效应与植被覆盖度呈线性负相关,净辐射通量与地表温度呈线性正相关,环境空气质量与热岛效应呈线性正相关。