Transient changes in milk production efficiency and bacterial community composition resulting from near-total exchange of ruminal contents between high- and low-efficiency Holstein cows

The objectives of this study were to determine if milk production efficiency (MPE) is altered by near-total exchange of ruminal contents between high- (HE) and low-MPE (LE) cows and to characterize ruminal bacterial community composition (BCC) before exchange and over time postexchange. Three pairs of ruminally cannulated, third-lactation cows were selected whose MPE (energy-corrected milk per unit of dry matter intake) differed over their first 2 lactations. Approximately 95% of ruminal contents were exchanged between cows within each pair. Ruminal pH and volatile fatty acid (VFA) profiles, along with BCC (characterized by sequencing of the variable 4 region of 16S rRNA genes), were assessed just before feeding on d ?8, ?7, ?5, ?4, ?1, 1, 2, 3, 7, 10, 14, 21, 28, 35, 42, and 56, relative to the exchange date. High-MPE cows had higher total ruminal VFA concentrations, higher molar percentages of propionate and valerate, and lower molar percentages of acetate and butyrate than did LE cows, and re-established these differences 1 d after contents exchange. Across all LE cows, MPE increased during 7 d postexchange but declined thereafter. Two of the 3 HE cows displayed decreases in MPE following introduction of the ruminal contents from the corresponding LE cow, but MPE increased in the third HE cow, which was determined to be an outlier. For all 6 cows, both liquid- and solids-associated BCC differed between individuals within a pair before contents exchange. Upon exchange, BCC of both phases in all 3 pairs was more similar to that of the donor inoculum than to preexchange host BCC. For 5 of 6 cows, the solids-associated community returned within 10 d to more resemble the preexchange community of that host than that of the donor community. Individual variability before the exchange was greater in liquids than in solids, as was the variability in response of bacterial communities to the exchange. Individual cows varied in their response, but generally moved toward re-establishment of their preexchange communities by 10 d after contents exchange. By contrast, ruminal pH and VFA profiles returned to preexchange levels within 1 d. Despite the small number of cows studied, the data suggest an apparent role for the ruminal bacterial community as a determinant of MPE.     

高校机械类专业《机械工程材料》课程实验教学改革探讨

对机械类专业基础课程《机械工程材料》的实验教学内容、教学方法及手段等的改革进行了探讨,旨在改进机械类专业基础课程实验教学质量,着力培养学生工程意识和实践创新能力,巩固和强化学生专业基础知识,进而提高其独立思考、自主创新能力。     

土木工程材料课程教学改革和效果评价

文章分析了土木工程材料课程教学中存在的主要问题,从教材编写、授课内容编排、课时分配等教学内容,理论教学、实验教学、实践教学等教学模式,以及视频播放与课堂讨论、网络辅助教学、考核方法等教学方法三个方面,阐述了南昌大学土木工程材料课程的教学改革,并对其教学改革效果进行评价。     

国内外雨水花园研究综述

系统归纳国内外雨水花园的研究现状,明确了国内的研究内容主要涉及雨水花园的起源与发展、国外优秀案例介绍、雨水花园的营造技术、雨水花园场地试验及模型构建等;国外的研究内容主要涉及雨水花园的水文模拟研究、土壤渗透力研究、污染物滞留能力研究、不同植物应用对水文的影响、建造及应用等,为今后的雨水花园研究工作奠定基础和提供借鉴。     

含石粉机制砂在商品混凝土中的研究应用

针对碎石生产过程中产生大量石灰石粉的可持续发展,通过在商品混凝土中的研究应用,实现石粉的附加值利用,缓解原材料资源匮乏提供了新途径。本文在水灰比一定的情况下,机制砂取代天然砂的不同掺量对商品混凝土性能各方面的影响,结果表明含石粉机制砂取代部分天然砂在工程应用中是可行的,并能有效地改善和提高了混凝土性能。     

Fe_2O_3含量对MnZn铁氧体中Fe~(2+)量、磁性能及导电机制的影响

通过测量MnZn铁氧体的磁性能及Fe2+、Mn3+含量,考察了MnZn铁氧体中的Fe2+含量与配方中Fe2O3、MnO含量的关系及其对MnZn铁氧体磁性能的影响,并探究了MnZn铁氧体的导电机制。结果表明:随着(Fe2O3)a(MnO)b(ZnO)c主组成配方中a值递增(52.55≤a≤53.35)、b值递减(38.33≥b≥37.52),呈现出Fe2+、Mn3+含量均增加的趋势。随着Fe2+含量增加,Pcv谷底温度向低温方向移动,Pcv(min)先减后增,Pcv(20/70/100℃)均先减后增,均在Fe2+含量=1.55%附近达到最小值;起始磁导率μi(20/70/100℃)均先增后减。根据Pcv-Fe2+含量和μi-Fe2+含量两个关系图在Fe2O3=53.15mol%附近出现极值点这一现象,初步推测铁氧体Znα2+Mnβ-x2+Mnx3+Fey2+Feχ-y3+O4+σ(0.1794≥α≥0.1786,0.754≥β≥0.734,0.0031≤x≤0.0040,0.051≤y≤0.070)的导电机制为:y0.064时小极化子间的束缚能主导,y0.064时电子跃迁主导。     

Effect of Cu contents on aging precipitation behaviors of Cu-rich phase in Fe-Cr-Ni alloy

 Abstract: The precipitation characteristics and effect on strengthening mechanism of Cu-rich phases during short-time and long-time aging in the Super 304H steels with different Cu contents were investigated by the use of X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results show that the size of Cu-rich phase particles increases, the distance of Cu-rich phase particles decreases and the density of Cu-rich phases increases with the increase of Cu content during short-time aging (~ 800 h) at 650℃ in the Super 304H steels. During long-time aging (>2000 h) at 650℃, Cu-rich phases precipitate sufficiently and the strengthening effect of Cu-rich phases is preferable in the Super 304H steel with 4% Cu. The strengthening effect of Cu-rich phases in the Super 304H steels with 2.2 % Cu or 5 % Cu is weaker than that with 4% Cu during long-time aging (>2000 h).     

Stochastic model for BOD and DO in streams when the velocity is random and distance‐dependent

The stochastic model studied in this paper is a random differential equation of the form X(t) = A(t) X(t) = Y(t), t ≥ 0, with initial conditions X₀ = X(0). X(t) is a vector with biochemical oxygen demand (BOD) and dissolved oxygen (DO) at a distance t downstream from the pollution source for components. The velocity of the stream is incorporated into the vector A(t) and is random and distance dependent. The inhomogeneous term Y(t) and the initial conditions are random vectors. Therefore, this model contains random initial conditions, random coefficients and random inhomogeneous terms. Simulated trajectories of the BOD and DO are computed.     

C语言实验教学考核评价指标及其观测内容分析

针对C程序设计语言实验教学考核的需要，阐述了制定实验考核评价指标的基本原则，确立了各项考核评价指标，比较详细地说明了各项指标的观测内容。该指标体系能够帮助教师对C语言的实验教学考核作出整体评价。     

建筑工程预结算审核的体会

建筑工程预结算的审核是合理确定工程造价的必要程序及重要手段,高素质的从业人员,齐全的工程造价资料,正确的审核方法,全面的审核内容是合理确定工程造价的条件,提高工程预结算审核的水平能达到有效控制工程造价的目的。