Analytical models for evaluating buoyancy-driven ventilation due to stack effect in a shaft considering heat transfer from shaft interior boundaries

Stack effect is a dominant driving force for building natural ventilation.Analytical models were developed for the evaluation of stack effect in a shaft,accounting for the heat transfer from shaft interior boundaries.Both the conditions with constant heat flux from boundaries to the airflow and the ones with constant boundary temperature were considered.The prediction capabilities of these analytical models were evaluated by using large eddy simulation(LES) for a hypothetical shaft.The results show that there are fairly good agreements between the predictions of the analytical models and the LES predictions in mass flow rate,vertical temperatures profile and pressure difference as well.Both the results of analytical models and LES show that the neutral plane could locate higher than one half of the shaft height when the upper opening area is identical with the lower opening area.Further,it is also shown that the analytical models perform better than KLOTE's model does in the mass flow rate prediction.

A simple plume model induced by stack effect in a vertical shaft

After comparing the mechanism of tilted plume under stack effect with that of spill plume,the tilted plume model induced by stack effect in a vertical shaft is developed simply based on the theoretical results and a series of full-scale tests. It is shown that the two sides of plume are symmetrical and have an accordant regulation that the plume radius has a linear relation to the height z. The profile of fire plume under stack effect is similar to the windblown flame in wind tunnel,and the range of flame deflection angle is about from 50 to 60 degree.

Study on Stack Effect of Stairwell by Numerical Model of Leakage Flow through Gap of Door

Since stack effect that occurs in high-rise buildings has an effect on the indoor environment of the buildings, energy loss and smoke control in case of a fire, there is a need to conduct research on this. For an analysis of the stack effect, analysis methods on the leakage flow through gap of interior door shall be formulated. Until now, studies related to the gap leakage flow in buildings have mainly analyzed flow field and pressure in the buildings one-dimensionally using pressure difference-leakage flowrate relations of Orifice Equation and a network numerical analysis algorithm that as- sumes each compartment in the buildings as a single point. In this study, the Momentum Loss Model which enables pressure drop to be proportional to the flow velocity through the gap of door in computational domain of 3-dimensional numerical analysis was proposed to reflect the gap flow phenomenon effectively in 3-dimensional numerical analysis. Using the proposed model, 3-dimensional numerical analysis of the stack effect on the stairs in buildings was performed, and the effects of separation door and lobby between stair and accommodation on the stack effect were investigated.

Leakage Current Estimation of CMOS Circuit with Stack Effect

Leakage current of CMOS circuit increases dramatically with the technologyscaling down and has become a critical issue of high performance system. Subthreshold, gate andreverse biased junction band-to-band tunneling (BTBT) leakages are considered three maindeterminants of total leakage current. Up to now, how to accurately estimate leakage current oflarge-scale circuits within endurable time remains unsolved, even though accurate leakage modelshave been widely discussed. In this paper, the authors first dip into the stack effect of CMOStechnology and propose a new simple gate-level leakage current model. Then, a table-lookup basedtotal leakage current simulator is built up according to the model. To validate the simulator,accurate leakage current is simulated at circuit level using popular simulator HSPICE forcomparison. Some further studies such as maximum leakage current estimation, minimum leakage currentgeneration and a high-level average leakage current macromodel are introduced in detail.Experiments on ISCAS85 and ISCAS89 benchmarks demonstrate that the two proposed leakage currentestimation methods are very accurate and efficient.

STUDY ON THE STABILITY AND STACKING INTERACTION EFFECT OF THE TERNARY M(Ⅱ)(ATP)AND PYRIDINE-LIKE LIGANDS

The stabilities of the complexes of three pyridine-like ligands with M(II)(ATP)^(2-) and M(II)(M=Ni,Co)were studied by spectrophotometry and by comparing the stability constants of the ternary complexes with these of the binary complexes.A stacking interaction between the pyridine ring and the purine ring of ATP is indicated.The general existence of the stacking interaction encourages us to interpret the antitumor mechanism of a new class of antitumor drugs.

Oxygen Scavenging Effect of LaLuO_3/TiN Gate Stack in High-Mobility Si/SiGe/SOI Quantum-Well Transistors

Higher-s dielectric LaLuO3, deposited by molecular beam deposition, with TiN as gate stack is integrated into high-mobility Si/SiGe/SOI quantum-well p-type metal-oxide-semiconduetor field effect transistors. Threshold voltage shift and capacitance equivalent thickness shrink are observed, resulting from oxygen scavenging effect in LaLuO3 with ti-rich TiN after high temperature annealing. The mechanism of oxygen scavenging and its potential for resistive memory applications are analyzed and discussed.

Stacked lateral double-diffused metal–oxide–semiconductor field effect transistor with enhanced depletion effect by surface substrate

A stacked lateral double-diffused metal–oxide–semiconductor field-effect transistor(LDMOS) with enhanced depletion effect by surface substrate is proposed(ST-LDMOS), which is compatible with the traditional CMOS processes. The new stacked structure is characterized by double substrates and surface dielectric trenches(SDT). The drift region is separated by the P-buried layer to form two vertically parallel devices. The doping concentration of the drift region is increased benefiting from the enhanced auxiliary depletion effect of the double substrates, leading to a lower specific on-resistance(Ron,sp). Multiple electric field peaks appear at the corners of the SDT, which improves the lateral electric field distribution and the breakdown voltage(BV). Compared to a conventional LDMOS(C-LDMOS), the BV in the ST-LDMOS increases from 259 V to 459 V, an improvement of 77.22%. The Ron,sp decreases from 39.62 m?·cm^2 to 23.24 m?·cm^2 and the Baliga's figure of merit(FOM) of is 9.07 MW/cm^2.

Predicting air pressure in drainage stack of high-rise building

It is necessary to understand the features of air pressure in a drainage stack of a high-rise building for properly designing and operating a drainage system. This paper presents a mathematical model for predicting the stack performance. A step function is used to describe the effect of the air entrainment caused by the water discharged from branch pipes. An additional source term is introduced to reflect the gas-liquid interphase interaction （GLII） and stack base effect. The drainage stack is divided into upper and base parts. The air pressure in the upper part is predicted by a total variation diminishing （TVD） scheme, while in the base part, it is predicted by a characteristic line method （CLM）. The predicted results are compared with the data measured in a real-scale high- rise test building. It is found that the additional source term in the present model is effective. It intensively influences the air pressure distribution in the stack. The air pressure is also sensitive to the velocity-adjusting parameter （VAP）, the branch pipe air entrainment, and the conditions on the stack bottom.

An Improved SOI CMOS Technology Based Circuit Technique for Effective Reduction of Standby Subthreshold Leakage

Silicon-on-insulator (SOI) CMOS technology is a very attractive option for implementing digital integrated circuits for low power applications. This paper presents migration of standby subthreshold leakage control technique from a bulk CMOS to SOI CMOS technology. An improved SOI CMOS technology based circuit technique for effective reduction of standby subthreshold leakage power dissipation is proposed in this paper. The proposed technique is validated through design and simulation of a one-bit full adder circuit at a temperature of 27℃, supply voltage, VDD of 0.90 V in 120 nm SOI CMOS technology. Existing standby subthreshold leakage control techniques in CMOS bulk technology are compared with the proposed technique in SOI CMOS technology. Both the proposed and existing techniques are also implemented in SOI CMOS technology and compared. Reduction in standby subthreshold leakage power dissipation by reduction factors of 54x and 45x foraone-bit full adder circuit was achieved using our proposed SOI CMOS technology based circuit technique in comparison with existing techniques such as MTCMOS technique and SCCMOS technique respectively in CMOS bulk technology. Dynamic power dissipation was also reduced significantly by using this proposed SOI CMOS technology based circuit technique. Standby subthreshold leakage power dissipation and dynamic power dissipation were also reduced significantly using the proposed circuit technique in comparison with other existing techniques, when all circuit techniques were implemented in SOI CMOS technology. All simulations were performed using Microwindver 3.1 EDA tool.

Mechanism of floating body effect mitigation via cutting off source injection in a fully-depleted silicon-on-insulator technology

In this paper, the effect of floating body effect （FBE） on a single event transient generation mechanism in fully depleted （FD） silicon-on-insulator （SOI） technology is investigated using three-dimensional technology computer-aided design （3D- TCAD） numerical simulation. The results indicate that the main SET generation mechanism is not carder drift/diffusion but floating body effect （FBE） whether for positive or negative channel metal oxide semiconductor （PMOS or NMOS）. Two stacking layout designs mitigating FBE are investigated as well, and the results indicate that the in-line stacking （IS） layout can mitigate FBE completely and is area penalty saving compared with the conventional stacking layout.

基于红外焦平面读出电路应用的多层stack电容设计及SPICE模型研究

基于0.5μm CMOS工艺设计并制备了一种应用于红外焦平面读出电路的多层堆叠(stack)电容结构,测试结果表明,相比单一形式电容,stack电容的单位面积值增大两倍以上,因而能够有效地提升红外焦平面读出电路的电荷存储能力。此外,本文还为设计的多层stack电容建立了一套描述其电学特性的SPICE模型,模型均方根误差在2%以内,因此可以准确描述stack电容的电学特性,满足了红外焦平面读出电路的仿真设计要求。

基于改进Stacking集成学习方法的武器装备体系作战效能预测

作战效能预测对武器装备体系从建设、生产到实战的全过程都具有重要意义。在Stacking集成学习模型的基础上,优化模型对数据的交叉验证方式,针对原有模型次级学习器输入向量较为稀疏的问题,为次级学习层的输入增加多项式特征和经主成分分析法降维后的各项作战仿真数据指标(原始数据),形成一种改进Stacking集成学习模型的装备体系作战效能预测方法。以合成营攻占某一阵地的作战效能预测为例,验证该方法的有效性。

Study on two-dimensional analytical models for symmetrical gate stack dual gate strained silicon MOSFETs

Based on the exact resultant solution of two-dimensional Poisson＇s equation, the novel two-dimensional models, which include surface potential, threshold voltage, subthreshold current and subthreshold swing, have been developed for gate stack symmetrical double-gate strained-Si MOSFETs. The models are verified by numerical simulation. Besides offering the physical insight into device physics, the model provides the basic designing guidance of further immunity of short channel effect of complementary metal-oxide-semiconductor （CMOS）-based device in a nanoscale regime.

A two-dimensional analytical modeling for channel potential and threshold voltage of short channel triple material symmetrical gate Stack(TMGS) DG-MOSFET

In the present work, a two-dimensional（2D） analytical framework of triple material symmetrical gate stack（TMGS）DG-MOSFET is presented in order to subdue the short channel effects. A lightly doped channel along with triple material gate having different work functions and symmetrical gate stack structure, showcases substantial betterment in quashing short channel effects to a good extent. The device functioning amends in terms of improved exemption to threshold voltage roll-off, thereby suppressing the short channel effects. The encroachments of respective device arguments on the threshold voltage of the proposed structure are examined in detail. The significant outcomes are compared with the numerical simulation data obtained by using 2D ATLAS;device simulator to affirm and formalize the proposed device structure.

THE FAILURE MECHANISM OF REVERSE SHAPE MEMORYEFFECT IN A Cu-BASE ALLOY

The interior structural evolution accompanying reverse shape memory effect (RSMEin a Cu-Zn-Al alloy was studied by means of transmission electron microscopy. It was found that RSME is closely related to bainitic transformation in this alloy during the isothermal reaction at moderate temperatures. At a given temperature and a certain external constraint stress, the shape memory effect depends mainly on the aging time.During the early stage, the shape memory effect enhances with the increase of reactiotn time. Then it will decrease gradually apon further aging. If the alloy is overaged, the stacking faults of bainite will disappear gradually by the motion of partial dislocations through which long range diffusion of solute atoms takes place, giving rise to the deterioration of RSME. When all the bainite transforms to α phase, RSME will lose completely.

半U形隧道火灾补气速度和最高烟气温升的机器学习预测

半U形隧道是考虑火灾发生在水下隧道变坡点前而简化得到的隧道结构,通过理论推导很难建立有关烟气运动参数预测模型。因此,借助于FDS数值模拟和机器学习对320组火灾工况进行模拟分析和机器学习预测。结果表明:纵向风速的增大对于空气补充速度会有一定的抑制效果,BP神经网络在测试集和训练集上的预测效果较其他机器学习模型更为精确,决定系数R~2能够达到0.99;通过Shap值对影响隧道内空气补充速度的特征因素按重要性从高到低排序依次为高度效应、热效应、风效应;最高烟气温升受风速影响,坡高小则温升随风速减小剧烈,坡高大时风速影响不显著,并且相较于其他机器学习方法,BP神经网络和理论计算均能准确预测烟气最高温升,R~2均大于0.9。研究结合数值模拟与机器学习,为高效预测隧道火灾动力学行为及通风排烟系统优化设计提供了新方法。

箱内马铃薯码放形式对贮藏效果影响的数值模拟研究

随着马铃薯逐步使用包装箱进行贮藏,为研究其在包装箱内不同摆放方式下对贮藏效果产生的影响,采用直接计算流体力学数值方法对模型进行模拟计算。通过对比分析各种码放形式下的气体流速和温度分布均匀性情况,对贮藏效果的影响进行了分析,得出了最佳的码放方式。结果表明,包装箱内中间层气流速度较高,马铃薯的温度相对较低;其他平面的气流速度较低,马铃薯的温度高于中间层的温度且分布较均匀。在通风300 min后,包装箱内马铃薯的温度均降低为3~5℃,符合预期要求,具有较好的通风效果。针对不同码放形式,错位间隔排列时上下两平面气流速度的最大值与最小值之比为2.5,温度的最大值与最小值相差0.2℃;中间平面气流速度最大值与最小值之比为4.8、相差约2.85 m/s,且箱内气流速度均匀,降温效果较好。对于箱装马铃薯的贮藏,应当优先选择错位间隔排列码放方式,以得到较好的贮藏效果。

单坡度V字形隧道火灾中等效纵向风速及温度场研究

火灾发生在水下隧道的变坡点附近时,隧道结构可简化为单坡度V形隧道。在单坡度V形隧道发生火灾时,烟气运动会受到一侧倾斜隧道烟囱效应的影响。采用FDS数值模拟研究方法,对自然通风状态下单坡度V形隧道火灾中的等效纵向风速以及隧道温度场进行研究,并建立了预测模型。结果表明,火灾产生的等效纵向风速与隧道坡高和热释放速率有关,其数值大小与热释放速率的1/3次幂和无量纲坡高成正比;单坡度V形隧道顶板下烟气的最大温升随着坡度的增加而线性递减,整个火灾下游的烟气温度分布呈指数衰减,且坡度越大,纵向烟气温度在火源周围的衰减越明显,衰减曲线也更陡峭。

倾斜隧道火灾烟气分层稳定性研究

隧道内的烟气分层特征对分析疏散和救援的难度以及制定有效的应急策略具有至关重要的作用。倾斜隧道中的烟气流动受到浮力和烟囱效应的共同影响,导致烟气的分布和运动规律与水平隧道存在显著差异。在倾斜隧道中,烟气分层稳定性受到多种因素的影响,且相关研究较少。本文采用数值模拟方法对倾斜角度为1%~15%的两端开口的倾斜隧道火灾烟气分布特性及其影响因素进行了研究。研究表明:Newman提出的判定烟气分层状态的临界无量纲温差在倾斜隧道火灾中仍然适用(坡度在1%~15%范围内)。倾斜隧道火灾发生后,火源与低端入口之间的烟气层始终能够保持稳定的烟气分层。而火源与下游出口之间的烟气层则随着烟囱效应的增强,稳定分层被破坏的区域不断扩大,并逐渐扩展至整个下游区域。火源功率和火源与下游出口之间的高差可直接影响隧道内的烟囱效应和烟气自身浮力,进而影响烟气分层状态。在此基础上,提出了用于预测倾斜隧道火灾烟气分层特性的计算模型,并确定了烟气分层区域1和区域2之间的临界Froude数为0.9。本文研究可为隧道火灾排烟及疏散设计提供指导。

温室效应和烟囱效应在双层呼吸式玻璃幕墙中实际效果验证及定性分析

温室效应对双层呼吸式玻璃幕墙热工性能存在负面影响,烟囱效应的实际效果也没有直观感受。本文对某双层呼吸式玻璃幕墙进行了一次简易热工性能实测,目的是对存在的温室效应和烟囱效应实际效果进行验证,进一步对夏季高温环境下双层呼吸式玻璃幕墙的隔热效果和原理进行定性分析。