Climatic implications in earlywood and latewood width indices of Chinese pine in north central China

Latewood width(LWW)indices of trees are considered a reliable proxy of summer precipitation in the Northern Hemisphere.However,the strong coupling and high correlation between earlywood width(EWW)and LWW indices often prevent registration of climate signals of the LWW index.In this study,328-year-long earlywood width and latewood width chronologies were developed from Chinese pine at two sites in the Hasi Mountains,north central China.The climate responses of these chronologies were analyzed and the LWW index used to derive sum-mer precipitation signals.Correlation analyses showed that LWW was particularly influenced by earlywood growth and recorded stronger climate signals of the previous year as EWW,rather than those of the current year with infrequent summer climate signals.However,after removing the effect of earlywood growth using a simple regression model,the adjusted LWW chronology(LWW_(adj))showed a strong relationship with July precipitation in dry years.This suggests that the LWW_(adj) chronology has the potential to be used to investigate long-term variability in summer precipitation in drought-limited regions.

EFFECTIVE FLANGE WIDTH OF SIMPLY SUPPORTED BOX GIRDER UNDER UNIFORM LOAD

A new method for the determination of effective flange width under uniform load on simply supported box girder bridges considering shear lag effect is proposed in this paper. Based on the Symplectic Elasticity method, the flange slab of the box girder is simplified into a plane stress plate. Using equilibrium conditions of the plates, the Hamilton dual equations for top plate element is established. The analytical formulas of each plate element considering shear lag effect are derived. The closed polynomial effective width expression of flange slab under uniform load on the whole span length has been obtained. Through examples using the finite element method, the results obtained by the proposed method are examined and the accuracy of the proposed method is verified.

Effects of microwave pulse-width damage on a bipolar transistor

This paper presents a theoretical study of the pulse-width effects on the damage process of a typical bipolar transistor caused by high power microwaves（HPMs） through the injection approach.The dependences of the microwave damage power,P,and the absorbed energy,E,required to cause the device failure on the pulse width τ are obtained in the nanosecond region by utilizing the curve fitting method.A comparison of the microwave pulse damage data and the existing dc pulse damage data for the same transistor is carried out.By means of a two-dimensional simulator,ISE-TCAD,the internal damage processes of the device caused by microwave voltage signals and dc pulse voltage signals are analyzed comparatively.The simulation results suggest that the temperature-rising positions of the device induced by the microwaves in the negative and positive half periods are different,while only one hot spot exists under the injection of dc pulses.The results demonstrate that the microwave damage power threshold and the absorbed energy must exceed the dc pulse power threshold and the absorbed energy,respectively.The dc pulse damage data may be useful as a lower bound for microwave pulse damage data.

Required width of exit to avoid the faster-is-slower effect in highly competitive evacuation

A group of competitive people escaping through an exit could lead to the formation of a deadlock, which significantly increases the evacuation time. Such a phenomenon is called the faster-is-slower effect（FIS） and it has been experimentally verified in different systems of particles flowing through an opening. In this paper, the numerical simulation based on discrete element method（DEM） is adopted to study a group of highly competitive people through an exit of varying widths. The FIS effect is observed for a narrow exit whilst it is not observed for the exit wide enough to accommodate two people through it side-by-side. Experimental validation of such a phenomenon with humans is difficult due to ethical issues. The mouse is a kind of self-driven and soft-body creature and it exhibits selfish behaviour under stressed conditions.Particles flowing through an opening in different systems, such as pedestrian flow, animal flow, silo flow, etc. have similar characteristics. Therefore, experimental study is conducted by driving mice to escape through an exit of different widths at varying levels of stimulus. The escape time through a narrow exit（i.e., 2 cm） increases obviously with the increase of stimulus level but it is quite opposite to a wider exit（i.e., 4 cm）. The FIS effect is avoided for an exit wide enough to accommodate two mice passing through it side-by-side. The study illustrates that FIF effect could be effectively prevented for an exit when its width is twice the size of particles.

Guiding of 150 keV O^(6+) ions through nanocapillaries in an uncoated Al_2O_3 membrane:special time dependence of the transmission profile width

This paper reports that the transmission of O6＋ ions with energy of 150keV through capillaries in an uncoated Al2O3 membrane was measured, and agreements with previously reported results in general angular distribution of the transmitted ions and the transmission fractions as a function of the tilt angle well fitted to Gaussian-like functions were observed. Due tousing an uncoated capillary membrane, our φc is larger than that using a gold-coated one with a smaller value of Ep/q, which suggests a larger equilibrium charge Q∞ in our experiment. The observed special width variation with time and a larger width than that using a smaller Ep/q were qualitatively explained by using mean-field classical transport theory based on a classical-trajectory Monte Carlo simulation.

Effect of Valence Band Tail Width on the Open Circuit Voltage of P3HT:PCBM Bulk Heterojunction Solar Cell:AMPS-1D Simulation Study

The effect of the valence band tail width on the open circuit voltage of P3HT：PCBM bulk heterojunction solar cell is investigated by using the AMPS-1D computer program. An effective medium model with exponential valence and conduction band tail states is used to simulate the photovoltaic cell. The simulation result shows that the open circuit voltage depends Iinearly on the logarithm of the generation rate and the slope depends on the width of the valence band tail. The open circuit voltage decreases with the increasing width of the band tail. The dark and light ideality factors increase with the width of the valence band tail.

Temporal characteristic analysis of single event effects in pulse width modulator

In this paper,the nature and origin of single event effects(SEE) are studied by injecting laser pulses into different circuit blocks,combining with analysis to map pulse width modulators circuitry in the microchip die.A time-domain error-identification method is used in the temporal characteristic analysis of SEE.SEE signatures of different injection times are compared.More serious SEE are observed when the laser shot occurs on a rising edge of the device output for blocks of the error amplifier,current sense comparator,and T and SR latches.

Impact of Channel Length and Width for Charge Transportation of Graphene Field Effect Transistor

The effect of channel length and width on the large and small-signal parameters of the graphene field effect transistor have been explored using an analytical approach.In the case of faster saturation as well as extremely high transit frequency,the graphene field effect transistor shows outstanding performance.From the transfer curve,it is observed that there is a positive shift of Dirac point from the voltage of 0.15 V to 0.35 V because of reducing channel length from 440 nm to 20 nm and this curve depicts that graphene shows ambipolar behavior.Besides,it is found that because of widening channel the drain current increases and the maximum current is found approximately 2.4 mA and 6 mA for channel width 2μm and 5μm respectively.Furthermore,an approximate symmetrical capacitance-voltage(C-V)characteristic of the graphene field effect transistor is obtained and the capacitance reduces when the channel length decreases but the capacitance can be increased by raising the channel width.In addition,a high transconductance,that demands high-speed radio frequency(RF)applications,of 6.4 mS at channel length 20 nm and 4.45 mS at channel width 5μm along with a high transit frequency of 3.95 THz have been found that demands high-speed radio frequency applications.

Effect of Overlap Stress as Well as Tie Beam Length and Width on Settlement of Isolated Footings Using Finite Element

Effects of tie beam length, width and overlap stress on settlement of foundations have been investigated. In this investigation square concrete footings have been used with dimensions (B × B × d) where (d) is footing depth and (B) is footing width (1, 1.5,2 m). Width of tie beam (b) has been taken equal to 0.25, 0.30, 0.40, 0.50 and 0.75 (m). Tie beam length (L) has been taken varying from B till 3B with same footing depth = 0.50 m. Effect of overlap stress on settlement as well as effect of tie beam width and length on settlement has been determined. Also, the efficiency of tie beam length and width has been obtained. An equation is presented to compute the overlap stress zone in case of existing tie beam. It is found that the settlement increases with increasing the length of tie beam which is clear after the effect of the overlap stresses zone. The width of overlap stress zone case of existing tie beam has been found to be equal to (1.6 -1.75) B. The settlement of footings decreases with increasing tie beam width. It is found that the settlement after the effect of the overlap stress zone increases with increasing the length of tie beam.

超薄层稠油油藏有效开发方式研究

大庆WE区块萨尔图稠油油藏属于低丰度超薄层稠油油藏,此前仅开展过小规模蒸汽吞吐现场试验,开发程度较低,经济效益不过关,未形成有效的开发技术体系,不同砂体规模布井模式及有效动用方式不明确。为此,基于储层流体渗流特征,通过岩心驱油实验和数值模拟、经济评价研究,对比分析弹性开发、热水驱、蒸汽吞吐、弹性开发转蒸汽吞吐、蒸汽驱的开发效果,建立超薄层稠油油藏开发方式及布井模式优化设计方法,评价不同河道砂体规模下直井和水平井的井控储量,计算不同开发方式技术经济井距。结果表明:弹性开发有效期为240~300d,弹性开发转蒸汽吞吐采收率较高、内部收益率最高。将研究成果用于指导区块分四期编制开发布井方案,设计开发井493口(水平井155口),设计产能32.59×10^(4)t,河道宽度大于250m、有效厚度大于2.3m的区域部署水平井,河道宽度小于250m、有效厚度大于2.7m的区域部署直井,采用140m井距,采取前期弹性开发后期转蒸汽吞吐开发方式。截至目前已完钻并投产292口井,累积产油量32.7×10^(4)t,实现了当年增储、当年建产、当年拿油。

“两宽两高”地震勘探技术及应用成效

宽方位、宽频带、高密度(简称“两宽一高”)地震采集技术在解决低信噪比地区勘探、复杂地质体成像等难题方面具有明显的技术优势。随着复杂地层岩性和非常规油气藏等隐蔽性油气藏勘探的不断深入,地震资料的保真度要求大幅度提高。提高保真度需要野外地震采集采用宽频超高灵敏度传感器,提高弱信号记录能力,消除激发和接收的组合效应以及解决从近地表至目标层的地层吸收衰减问题。为此,提出了宽方位、宽频带、高密度、高保真(简称“两宽两高”)的地震采集理念,经过多年实践与发展,形成了“两宽两高”单点三维地震勘探技术。高保真的核心是野外采用高灵敏度的检波器,提高数据记录动态范围,单点接收消除组合效应,既提高弱信号记录能力,又消除组合带来的检波器时差问题,降低近地表起伏和速度差异带来的静校正、速度拾取等影响保真度的问题。“两宽两高”地震勘探技术提出后,率先在长庆油田、辽河油田、四川油田等探区进行了试验,均取得了良好的应用效果。随着节点地震采集系统和“双高”地震处理、真地表地震成像等技术的全面推广应用,目前“两宽两高”地震勘探技术已成为中国石油陆上油气勘探开发的主要技术。

超宽组合梁剪力滞效应分析

超宽组合梁宽高比很大,在弯矩作用下超宽组合梁的力学特性与普通梁较为不同,目前相关技术规范尚缺乏关于超宽梁有效宽度的系统化公式。为了深入分析在弯矩作用下超宽组合梁剪力滞效应引起的正应力分布不均的特征,以深汕大桥为工程背景,利用ABAQUS有限元软件建立跨中15道中横梁梁段52.5m空间壳单元有限元简支梁体系模型和采用Midas civil建立空间杆系单元全桥模型,分析在自重、车道荷载、人群荷载和吊杆杆力作用下跨中截面顶、底板和1/4跨截面顶板的正应力和剪力滞系数的分布规律。分析结果表明,超宽组合梁在荷载作用下,结构受力存在明显的剪力滞效应,目前相关技术规范关于翼缘有效宽度计算公式的安全系数比实际高1.21~1.63倍。

置信区间宽度等高线图在线性混合效应模型样本量规划中的应用

线性混合效应模型在分析具有嵌套结构的心理学实验数据时具有明显优势。本文提出了置信区间宽度等高线图用于该模型的样本量规划。通过等高线图,确定同时符合检验力、效应量准确性以及置信区间宽度要求的被试量和试次数。结合关注被试内实验效应和被试变量调节效应的两类典型模型,通过两个模拟研究,采用基于蒙特卡洛模拟方法,探索效应量、随机效应大小和被试变量类型对置信区间宽度等高线图及样本量规划结果的影响。

A Kind of PWM Pneumatic Servo Control System——Modulation Methods and Dynamic Responses

Vibrations or dither's are features of the PWM servo control system in their steady outputs. On the grounds of analyses and experiments of a PWM pneumatic servo control system, the paper puts forward four varieties of PWM modulation methods, and concludes on the relationship between dithers and the different methods, and then discusses the influence of friction to the dithers. Results from experiments regarding the dynamic and static responses on the given system support the theories presented.

基于混合效应的杉木人工林冠幅模型

构建杉木(Cunninghamia lanceolata)人工林单木冠幅模型,可以提高杉木冠幅的预测精度,并为杉木人工林的科学经营提供参考依据。以杉木为研究对象,基于江西省崇义县杉木人工林57个样地的7198株单木数据,对基础模型进行扩展,并构建含林分因子和单木因子的冠幅非线性混合效应模型;采用十折交叉验证方法,以调整后的决定系数(R_(adj)^(2))、均方根误差(E_(RMS))和平均绝对误差(E_(MA))模型评价指标对各模型的预测效果进行评价。结果表明:(1)备选模型中,Logistic模型的预测效果最佳。(2)除胸径以外,有6个指标对冠幅有显著影响(P<0.05)。6个指标分别是地位指数、林龄、基尼系数(Gini系数)、林分密度指数、枝下高和大于对象木的断面积之和。添加协变量构建的广义模型较基础模型更优,R_(adj)^(2)增加了28.53%,E_(RMS)和E_(MA)分别下降了17.80%和15.72%。(3)考虑样地水平随机效应的混合效应模型优于广义模型,R_(adj)^(2)增加了27.86%,E_(RMS)和E_(MA)分别降低了35.73%和51.87%。协变量和随机效应的加入能有效提高冠幅模型的预测精度,且反映林木大小多样性的Gini系数在冠幅模拟中表现较好,值得进一步探讨该类指标在其他类型人工林模拟中的应用。

BCD工艺中大电流下纵向双极晶体管的电流集边效应研究

在大电流条件下,随着电流密度的增加,发射区结电流集边效应、基区电导调制效应、基区展宽效应会随之出现。基于研究单位的BCD工艺,在集成CMOS和DMOS的基础上集成功率纵向NPN双极晶体管用于输出。设计了75μm×4μm、50μm×6μm、30μm×10μm三种不同尺寸的发射极并进行TCAD仿真研究。在发射极面积相同的情况下,发射极长宽比越小,TCAD可观察到的电流集边效应越严重,最终流片并进行测试验证,得出75μm×4μm的细长结构尺寸能够提升晶体管在大电流下的放大能力,较30μm×10μm的结构提升约11.4%。

混凝土深受弯构件力学性能分析与裂缝宽度检测

为保证混凝土深受弯构件的服役寿命,分析了其在载荷作用下的力学性能,并检测其裂缝宽度。在制备4种不同剪跨比的混凝土深受弯构件后,制定加载方案。然后基于有限元模型分析构件在载荷下的应力分布情况,并通过构件受剪分析模型计算混凝土深受弯构件的受剪承载力,同时利用拉压杆模型检测裂缝宽度。试验结果显示:剪跨比能够直接影响构件的力学性能。剪跨比为0.26、载荷达到600 kN左右时,跨中位移最高值为8.6 mm;剪跨比为1.04、载荷为300 kN左右时,跨中位移达到12.5 mm,构件从剪切破坏状态变化成剪弯破坏;根据构件裂缝之间的受力情况,可以准确获取裂缝最大宽度值;剪跨比较大时,构件裂缝较宽位置,大部分均位于支座附近。

不同长径比的具有固定宽度金纳米棒的合成

金纳米棒在光学、电学、信息学和生物医学等领域具有广泛的应用。然而,一些具有特殊要求的金纳米棒还不能通过常规的方法制备。在本研究中,我们创新地将十二醇(LA)分子引入到传统种子生长方法中,成功实现了具有固定宽度的不同长径比(AR)金纳米棒(FW-Au NR)的按需制备。此外,通过合理地选择相应的反应条件(如氯金酸和硝酸银的浓度),可以在130–38.4,109–26.4和16–46 nm范围之间分别调节FW^(23)-Au NRs,FW^(14)-Au NRs和FW^(6.5)-Au NRs (右上角的标注数字表示金纳米棒的宽度)的长度。即,可在一个较大的长度范围内调节具有固定宽度的金纳米棒的长径比。并且,在合适浓度的十二醇,0.24–0.30 mmol·L^(-1)范围内调节硝酸银浓度,可以使这些金纳米棒的宽度固定在6.5–23 nm之间。另外,实现FW-Au NRs制备的关键是银离子和十二醇分子对分布在金种子晶面上的CTA-Br-Ag^(+)化合物的密度的协同影响。

关节间隙宽度测量对内侧膝关节单髁置换效果及预后的影响

背景:与全膝关节置换相比,膝关节单髁置换具有康复快、成本低、本体感觉好等优点,但其术后高翻修率也是不容忽视的问题。目前对于导致膝关节单髁置换后高翻修率的原因尚不完全明确,因此术前严格把握手术指征对改善膝关节单髁置换后疗效和降低翻修率至关重要。作为常用的影像学测量手段,关节间隙宽度的评估可能对膝关节单髁置换手术指征的选择具有重要的临床参考价值。目的:综述关节间隙宽度的测量方法及对判定内侧膝关节单髁置换疗效和预后的影响。方法:通过万方和PubMed数据库检索1950-01-01/2023-06-01发表关于膝关节单髁置换疗效评价因素和关节间隙宽度对膝关节单髁置换疗效影响的相关文献,通过将文献汇总、分析,对关节间隙宽度的测量方法、术前内侧间室关节间隙宽度对内侧膝关节单髁置换疗效的影响、内侧膝关节单髁置换后外侧间室关节间隙宽度变化对预后的影响做以综述。结果与结论:①尽管目前用于研究和测量膝关节关节间隙宽度的方法很多,但负重位下X射线片测量关节间隙宽度仍是日常骨科实践中评估骨关节炎进展的常用方法,其可适度反映软骨厚度。②术前膝关节内侧间室关节间隙宽度会影响内侧活动平台膝关节单髁置换后的疗效,内侧关节间隙宽度/外侧关节间隙宽度<40%或内侧关节间隙宽度≤2mm的膝骨关节炎患者,可能更适合行内侧活动平台膝关节单髁置换。③内侧膝关节单髁置换后外侧间室关节间隙宽度变化对预后产生一定影响,术后通过改善外侧间室的关节匹配度,可延缓外侧间室关节退变的进展、降低假体翻修率,但尚欠缺相关的临床研究。总之,关节间隙宽度的影像学测量对判定内侧膝关节单髁置换的术后疗效和预后具有重要的临床参考价值。

基于竞争与立地效应的湖南栎类天然林冠幅模型

【目的】分析立地因子和竞争因子对冠幅生长的影响,构建含立地因子和竞争因子的混合效应湖南栎类天然林冠幅预测模型,为栎类天然林科学经营决策提供理论依据。【方法】以51块湖南栎类天然林样地的1 429株栎类林木为研究对象,筛选对冠幅影响显著的因子,将显著性因子按照标准分级、组合,构成竞争类型和立地类型;从10个基础模型中筛选出最优模型;应用k-means聚类方法将初始竞争类型聚类成竞争类型组;将立地类型和竞争类型组作为随机效应加入最优模型,构建含竞争和立地效应的湖南栎类天然林冠幅模型。【结果】对冠幅影响显著的因子包括海拔、坡度、坡位、坡向、土壤类型、相对断面积(R_(S))、简单竞争指数(C_(LH))和大于对象木断面积之和(B_(AL)),立地因子显著性顺序为海拔>坡度>坡向>坡位>土壤类型,竞争因子中R_(S)与冠幅呈正相关,而C_(LH)、B_(AL)与冠幅呈负相关;最优基础模型为异速生长模型(有截距),R^(2)为0.534 8;将筛选的3个竞争因子按照标准分级、组合构成竞争类型,加入基础模型构建含竞争类型的混合效应模型,R^(2)升至0.583 5;应用k-means聚类将初始竞争类型聚类成17个竞争类型组,作为随机效应加入基础模型,R^(2)升至0.749 2;将立地类型作为随机效应再加入模型,构建基于竞争和立地混合效应的冠幅模型,R^(2)升至0.841 6,相对基础模型提升了57.36%。【结论】含竞争因子和立地因子的湖南栎类天然林冠幅模型具有较好的拟合效果及预测精度。因此,本研究所构建的冠幅模型可以很好地预测湖南栎类天然林的冠幅,可为研究栎类天然林生长、经营管理以及更新森林资源调查数据库提供支持。