煤粒径对煤堆蓄热环境的影响分析

为了探求煤粒径对煤堆内部蓄热环境的影响,借助采空区"自燃三带"理论论述了煤堆的"三带"模型,并进行了不同粒径下的漏风规律模拟实验。结果表明:大颗粒煤样对风速的影响占主导作用,合理且分粒径堆积煤堆将有效解决其内部环境的升温自燃现象。     

甲流时期如何选购口罩

戴口罩是预防甲型H1N1流感的一项有效措施,尤其是出入人员密集、空气不畅的场所或医院,戴上口罩可有效降低患病的风险。然而不同类型口罩过滤效果存在很大差异,因此,选购恰当的口罩能更好地预防甲型H1N1流感。     

玉米发酵液中食用乳酸钙结晶的研究

以玉米发酵液为原料,研究了不同的结晶器温度和不同的发酵液在结晶器内的停留时间对乳酸钙结晶颗粒粒径和产率的影响。通过实验得出:发酵液在某一温度下乳酸钙结晶时,当最大颗粒粒径较大时,出现最小颗粒粒径较小的现象;当最大颗粒粒径较小时,会出现最小颗粒粒径较大的现象。停留时间和结晶器温度对颗粒的粒径分布范围及体积分数产生影响。同时,结果表明随着结晶器温度的升高,乳酸钙收率降低;随着发酵液在结晶器内停留时间的增加,乳酸钙收率升高。     

基于双超声波接收头的防撞小车系统

本文提出了一种基于单片机控制的超声波定位前方物体的监测控制系统。通过一左一右的双超声波接收头检测信号,送单片机进行数据计算处理,能够精确计算与障碍物的距离,同时判断该障碍物是否位于车辆行径的路线上。从而能保证车辆行驶中能准确避障。实验测试系统表明,该系统有效距离可达8m,测量精度可达0.05m,小车能自由避开前方障碍物,或遇到障碍物时紧急刹车停下。     

直接空冷机组空冷岛地下进风技术分析

针对当前空冷机组运行过程中所存在的问题,指出了通过空冷岛地下进风的方式。并对这种进风方式下的冷凝汽器传热性能与汽轮机背压两个方面所表现出的优势进行了分析,通过相应的理论计算可以得出散热器在不同迎风速率作用下的传热系数,对于与环境的风速与风温,凝汽器表现出不同的蒸汽压力。实践的结果表明,环境风的风温宜选取为25~28℃之间,环境风的风速宜选取在2~4m/s之间,此时可以有效的保证地下冷凝系统的最优状态,为此进一步证实了直接空冷机组空冷岛地下进风技术有着明显的优越性。     

蚊子会传播艾滋病病毒吗？

不会。蚊子叮咬时，把一个人的血液吸入其胃里的一个部分，然后又把从胃里分泌出的唾液注入人体肌肤，导致皮肤搔痒。蚊子的唾液会传播疟疾，疟疾是由一种微生物引起的，可以存在于人体内和蚊子体内。如果人们能从蚊子身上感染艾滋病病毒的话，那么，各种年龄层次的人感染的机率就更趋一致。事实上不是这样，艾滋病病毒的感染主要发生在年轻人身上，他们处于性活跃期，还主要发生在注射毒品的人身上，以及一些从母亲那里直接感染的婴儿。     

XH固沙剂在青海湖沙漠地区的试验研究

本文主要对XH固沙材料在沙漠地区中选择沙丘较高,风速较大的迎风坡流沙面进行每平方米喷播不同用量的XH固沙材料,来研究它的渗透性,耐水性,保水性,耐老化性,抗冻融稳定性和耐风蚀能力等进行不定期的观测研究来选择最佳XH用量的固沙效果,便于在今后推广应用时为治理沙漠工程提供有力保障。     

新冠病毒康复者能获得免疫吗?现实情况更为复杂

随着世界每天新增的新冠肺炎病例数量开始减少,各国开始考虑减少社会隔离措施,但一个巨大的未知数依然存在--哪些人对这个病毒产生了免疫,以及免疫期能持续多久?当人体的免疫系统遇到病毒时就会产生抗体,从而识别特定的病毒并攻击它。人们通常认为,一旦一个人感染了某种病毒,免疫力就会使人不可能再染上同样的病毒。但具体情况更加复杂。免疫力好比光谱,有些病毒抗体能终生保护,比如水痘和麻疹,而另一端则相反,比如HIV感染者所产生的抗体通常不能提供任何保护作用。     

室内温度和风速周期波动对人体热舒适影响研究

长时间处于稳态空调环境会降低人体的热适应，且容易造成能源浪费。本研究以家用柜式空调器为对象，通过模拟住宅客厅空调环境，设置不同的温度和风速波动周期营造动态热环境，研究了温度、风速动态变化下的人体热响应及热舒适。实验招募24名受试者，并让其暴露在7个工况（设定温度范围：24～28℃；设定风速档范围：低～高风速；温差：2℃/0.5h、2℃/1h；风速差：低风速-高风速/0.5h），连续监测并收集受试者主观反应和生理参数。出于满足室内人员热舒适与节能需求的考虑，推荐工况：28～26℃（2℃/1h）和28℃（低-高风速/0.5h），得出动态空调环境下中性温度Tn为27.2℃，对应的中性平均皮肤温度为35.1℃。本研究为提出合理的室内空气温度和风速动态控制设计参数、保障室内热环境健康、舒适及节能提供一定参考。     

汽车前向防撞报警系统的开发与应用

为防止汽车在视线不佳的工况下,易发生追尾事故且造成严重死伤。为此,文章开发了一种基于毫米波雷达的汽车前向防撞报警装置系统。利用车载毫米波雷达探测车辆与前方目标之间的距离等信息,综合车间距离、相对速度、车速、驾驶员反应时间、制动性能及气候环境等因素,在自车和前方行驶的车辆间存在的撞击事故时,发出提醒驾驶员的警报信息,防止因为追尾碰撞而引起的交通事故和人身伤亡。     

Screening strategies to inhibit the spread of AIDS

In this paper we explore the costs and benefits of screening programs for the human immunodeficiency virus (H1V). Because of the low prevalence rate of the virus among the general population, the cost per detected case of a program to screen the population at large is very high. We show how this cost changes with the prevalence rate, and how screening high risk groups reduces the cost per detected case. Screening has little point, however, unless there are follow-up activities to reduce the continued spread of the virus. To this end, we present a modeling framework for determination of optimal policy alternatives after screening.     

风力送丝系统参数与烟丝物理指标关系的研究

通过在线试验,重点分析比较不同风送速度和距离对烟丝物理指标的影响程度。结果表明:在试验范围内,随着风送速度和距离的增加,风送后烟丝含水率、整丝率、填充值和弹性指标下降程度整体呈递增趋势。在满足生产的条件下,适当降低风送速度和距离,可减少烟丝物理指标改变程度。     

一位痊愈返岗医生的7天

"很多人问我怎么不休息一下?医护力量这么紧张,我到一线,医治一个是一个,得对得起自己的良心。"赵智刚医生说接通电话时,赵智刚医生刚下夜班。那是2月8日早上,从7日下午5:30到8日早上8点,他工作了整整14.5个小时。这对一个刚刚痊愈3天的新冠肺炎患者来说,无疑是体力和精力上的巨大考验。     

企业财务诊断视角下的企业应收账款管理分析——以KN公司为例

财务是企业发展的命脉.随着企业竞争环境的日益复杂,财务链完整、有序地运营已经成为企业竞争中的重要环节.其中,应收账款管理正被越来越多的企业所重视.企业的应收账款能够直接反映企业的资金周转情况,直接决定了企业是否能够顺利开展日常业务.文章选取KN公司为研究对象,通过走访调查以及搜集相关二手资料,分析KN公司应收账款的管理现状,并结合KN公司的经营特点,发现KN公司应收账款管理中存在应收账款增长速度快、占总周转资金收入高等问题;同时,还明确了KN公司的经营风险和财务风险,分析了应收账款对KN公司经营发展存在的影响,并针对性地提出了一些建议,以期能够帮助KN公司实施更好的应收账款管理.     

探讨中微子超光速的现象

如果中微子属于中性轻子的话,其速度是不可能超过光速的,为什么欧洲核子研究中心的实验测量上出现中微子超光速现象呢?只能有一种合理解释:宇宙中的确存在反时空。也就是说甲乙两地距离除了视界的正空间,还应存在着反空间,在极端高能条件下中微子在反空间中通过甲乙两地,因甲乙两地距离的反空间小于正空间,所以中微子通过反空间所用的时间比正空间所用的时间短,即使中微子的速度小于等于光速,而实际测量时从正空间看来会出现中微子超光速的假象。所以欧洲核子研究中心发现的中微子超光速现象暗示人们宇宙中有可能存在着反时空。     

Short‐Term Wind Speed Forecasting for Power System Operations

The emphasis on renewable energy and concerns about the environment have led to large‐scale wind energy penetration worldwide. However, there are also significant challenges associated with the use of wind energy due to the intermittent and unstable nature of wind. High‐quality short‐term wind speed forecasting is critical to reliable and secure power system operations. This article begins with an overview of the current status of worldwide wind power developments and future trends. It then reviews some statistical short‐term wind speed forecasting models, including traditional time series approaches and more advanced space–time statistical models. It also discusses the evaluation of forecast accuracy, in particular, the need for realistic loss functions. New challenges in wind speed forecasting regarding ramp events and offshore wind farms are also presented.     

Covid-19 attacks the body of purchasing and supply management: A medical check of the immune system

Much like the immune system of the body, the ‘immune system’ of purchasing and supply management (PSM) is also affected by the Covid-19 virus. Medicine must hinder the spread of the virus and outbreak of disease, just as PSM must prevent risk events and handle supply disruptions. The existing debate on supply resilience and robustness can be demonstrated using this medical analogy. The purpose of this article was to perform a medical check of the ‘PSM immune system’ to identify lessons and research gaps when confronted with a low-frequency-high-impact event such as the pandemic. As a provocative note, this article identifies research gaps in elements of the immune system of PSM (e.g., helper cells – consultancy support or memory cells – feedback loops). The results call for a more holistic debate on the immune system of PSM. Two approaches for research on ‘conventional’ or ‘alternative’ risk management schools of thought are presented as a basis for future discourse on how to improve the PSM immune system.     

Spatiotemporal wind forecasting by learning a hierarchically sparse inverse covariance matrix using wind directions

Given the advances in online data acquisition systems, statistical learning models are increasingly used to forecast wind speed. In electricity markets, wind farm production forecasts are needed for the day-ahead, intra-day, and real-time markets. In this work, we use a spatiotemporal model that leverages wind dynamics to forecast wind speed. Using a priori knowledge of the wind direction, we propose a maximum likelihood estimate of the inverse covariance matrix regularized with a hierarchical sparsity-inducing penalty. The resulting inverse covariance estimate not only exhibits the benefits of a sparse estimator, but also enables meaningful sparse structures by considering wind direction. A proximal method is used to solve the underlying optimization problem. The proposed methodology is used to forecast six-hour-ahead wind speeds in 20-minute time intervals for a case study in Texas. We compare our method with a number of other statistical methods. Prediction performance measures and the Diebold–Mariano test show the potential of the proposed method, specifically when reasonably accurate estimates of the wind directions are available.     

Valuing spread options with counterparty risk and jump risk

In this paper, we investigate spread options with counterparty risk in a jump-diffusion model. Due to the fact that there is no closed-form formula of spread options with counterparty risk, we obtain analytical expressions of lower and upper bounds by employing the measure-change technique. Finally, we numerically check the accuracy of the bounds and analyze the impacts of counterparty risk and jump risk on spread option prices.