Direct demonstration of an adaptive constraint

The role of constraint in adaptive evolution is an open question. Directed evolution of an engineered beta-isopropylmalate dehydrogenase (IMDH), with coenzyme specificity switched from nicotinamide adenine dinucleotide (NAD) to nicotinamide adenine dinucleotide phosphate (NADP), always produces mutants with lower affinities for NADP. This result is the correlated response to selection for relief from inhibition by NADPH (the reduced form of NADP) expected of an adaptive landscape subject to three enzymatic constraints: an upper limit to the rate of maximum turnover (kcat), a correlation in NADP and NADPH affinities, and a trade-off between NAD and NADP usage. Two additional constraints, high intracellular NADPH abundance and the cost of compensatory protein synthesis, have ensured the conserved use of NAD by IMDH throughout evolution. Our results show that selective mechanisms and evolutionary constraints are to be understood in terms of underlying adaptive landscapes.     

Direct demonstration of macula densa-mediated renin secretion

An in vitro method has been used to examine whether secretion of renin from the juxtaglomerular apparatus is affected by changes in the sodium chloride concentration of the tubular fluid at the macula densa. Single juxtaglomerular apparatuses were microdissected from rabbits and the tubule segment containing the macula densa was perfused, while simultaneously the entire juxtaglomerular apparatus was superfused, and the fluid was collected for renin measurement. In this preparation, in which influences from renal nerves and local hemodynamic effects are eliminated, a decrease in the tubular sodium chloride concentration at the macula densa results in a prompt stimulation of the renin release rate.     

Direct demonstration of impaired functionality of a purified desensitized beta-adrenergic receptor in a reconstituted system

Long-term exposure of various cell types to beta-adrenergic agonists such as isoproterenol leads to an attenuated responsiveness ("desensitization") of the adenylate cyclase system to further challenge with these agonists. The turkey erythrocyte model system was used earlier to show that a covalent modification of the receptor (phosphorylation) is associated with this process. The functionality of the "desensitized" beta-adrenergic receptor was assessed by implanting purified beta-adrenergic receptor preparations from control and desensitized turkey erythrocytes into phospholipid mixtures and then fusing them with receptor-deficient cells (Xenopus laevis erythrocytes). Desensitized beta-adrenergic receptors showed a 40 to 50 percent reduction in their ability to couple to the heterologous adenylate cyclase system, comparable to the reduction in their functionality observed in their original membrane environment. These results demonstrate the utility of recently developed receptor reconstitution techniques for assessing the functionality of purified receptors and show a direct link between a covalent modification of a membrane-bound receptor and its impaired functionality in a reconstituted system.     

Morphogenesis of syncytiotrophoblast in vivo: an autoradiographic demonstration

In an in vivo autoradiographic study of immature primate trophoblast, tritiated thymidine was first found only in nuclei of cytotrophoblast but after 22 hours, labeled nuclei appeared in syncytiotrophoblast as well. Hence syncytiotrophoblast of the monkey appears to originate by differentiation of cytotrophoblast.     

欠发达地区生态建设与新农村建设的探索：以贵州毕节试验区为例

毕节试验区是典型的喀斯特岩溶山区,是全国石漠化最严重的地区.通过实施喀斯特山区植被恢复与生态林业建设工程、加强水土保持与水资源高效利用建设、提高粮食综合生产能力,形成了经济与社会、人与自然和谐发展的新观念.对其生态建设的方法及成效进行分析,提出了欠发达地区生态建设对新农村建设的几点启示.     

乳酶作为奶牛隐性乳房炎诊断指标的研究

【目的】定量实时检测奶牛牛乳中的乳酶活性,通过分析其变化规律为奶牛隐性乳房炎的诊断提供理论依据。【方法】随机选择220头荷斯坦泌乳奶牛,采集乳汁测定体细胞数(Somatic cell counts,SCC)和5种乳酶活性,研究乳酶活性在健康和患隐性乳房炎奶牛乳汁中的变化规律及与SCC的相关性。【结果】以乳汁体细胞数50×104mL-1作为判定乳房炎的标准,患隐性乳房炎奶牛乳汁中N-乙酰基-1-β-D-氨基葡萄糖苷酶(NAG)、乳酸脱氢酶(LDH)、乳过氧化物酶(LP)、碱性磷酸酶(ALP)和髓过氧化物酶(MPO)活性均显著高于健康奶牛(P<0.05),乳酶活性与SCC(lgSCC)呈正相关,其中NAG活性与SCC(lgSCC)的相关性系数R2=0.98,NAG与LDH活性之间的相关性系数R2=0.95。【结论】奶牛隐性乳房炎对LDH、NAG、LP、ALP和MPO活性有显著影响(P<0.05),乳酶NAG和LDH可联合应用作为早期奶牛隐性乳房炎的诊断指标。     

Direct high-temperature ohmic heating of metals as liquid pipes

When a sufficiently high electric current is passed through a liquid metal, the electromagnetic pressure pinches off the liquid metal and interrupts the flow of current. For the first time the pinch effect has been overcome by use of centrifugal acceleration. By rotation of a pipe of liquid metal, tin or bismuth or their alloys, at sufficiently high speed, it can be heated electrically without intermission of the electric current. One may now heat liquid metallic substances, by resistive (ohmic) heating, to 5000 degrees K and perhaps higher temperatures.     

天优华占作烟后稻轻简栽培示范总结

2012年在建宁县溪源乡水稻高产创建“五新”展示片,对天优华占作烟后稻开展机械插秧、标秧等轻简栽培示范,总结其示范效果及栽培技术要点。     

Paleogeographic reconstructions of coastal aegean archaeological sites

Many studies have been made of ancient Greek topography, some of the more recent ones based on modern techniques. However, most still ignore the subsurface dimension of coastal and other environments and hence fail to fully explain coastal and alluvial-colluvial processes, rates of change of geomorphology, and the effects of coastal change on humans. In this article subsurface geological analyses have been used to elucidate paleogeographic coastal settings of major archaeological sites around the Aegean Sea. Similar approaches could be applied in the Middle and Far East and elsewhere in the Mediterranean.     

Silicon: an essential element for the chick

Silicon is required for normal growth and development in the chick when a low silicon diet is fed in a trace element controlled environment. Day-old deutectomized cockerels fed a purified amino acid diet showed significantly retarded growth and development within 2 to 3 weeks. Chicks fed the same diet plus a silicon supplement showed 50 percent higher growth and normal development. Silicon meets the criteria for an essential trace element.     

农旅融合与城乡收入差距 ——以全国休闲农业与乡村旅游示范县创建为例

统筹城乡融合发展是推进乡村振兴的重要抓手之一。本研究基于全国休闲农业与乡村旅游示范县的创建这一准自然实验,利用2006—2021年全国253个地级市的面板数据,采用渐进双重差分模型实证检验了农旅融合政策对城乡收入差距的影响,并运用中介效应模型与调节效应模型探讨了其内在机制及作用的区域异质性。研究结论表明：农旅融合政策显著促进地级市城乡收入差距的缩小,且在运用合成控制双重差分法（SDID）等对模型进行有效性检验和工具变量法处理内生性问题后结论依然稳健。机制分析显示,农旅融合政策通过完善交通基础设施建设和促进城乡人员流动来弥合城乡收入差距。进一步,通过调节效应模型发现,因地区间经济发展水平不同,农旅融合政策对城乡收入差距的缩小作用呈现出区域异质性。因此,为有效缩小城乡收入差距,建议持续发挥示范县的带动引领作用,明确非示范县“农业+旅游业”的整体定位和核心竞争力;加大对交通基础设施建设的财政性投入,推动城乡间人员的畅通流动;实施精准的差异化措施,更好发挥农旅融合对城乡收入差距的异质性效应,为推进农业现代化发展与乡村振兴提供新思路。     

Hurler's syndrome: demonstration of an inherited disorder of connective tissue in cell culture

Skin fibroblasts from three patients with Hurler's syndrome were grown in tissue culture and shown to contain metachromatic granules when stained for mucopolysaccharides with toluidine blue O. Similar inclusions were observed in cultures of fibroblasts from other members of the families, who appeared to be clinically normal but who were, judged from studies of pedigree, heterozygous or hemizygous for the abnormal gene.     

基于三维激光扫描技术的果园景观可视化方法——以贵州关岭火龙果标准示范园为例

基于数字示范果园与高效农业产业园区建设与管理的需要,利用Riegl VZ-400三维激光扫描仪对贵州关岭县火龙果标准示范园进行实景扫描,并结合RISAN PRO系统配套软件对扫描点云数据、影像数据进行拼接处理,从而实现火龙果园的三维可视化,为虚拟果园管理和园区规划提供直观参考和布局。     

农业信息化与区域经济的发展

农业信息化建设对于社会主义新农村建设有着深远的影响,农业信息化对于区域经济发展的作用也是巨大的.农业信息化能够推动区域经济发展,为区域经济可持续发展奠定坚实的基础.     

分布式直接数据输入多处理机数控系统

本研究分析了分布式直接数据输入多处理机数控系统,包括:硬件结构、软件模块、插补算法、刀具轨迹、刀具控制、数据通信、对话式处理和显示控制等.     

检测牛奶中结合珠蛋白的电流型免疫传感器的研制

为构建可定量检测牛奶中结合珠蛋白(Hp)含量的电流型免疫传感器,以三电极系统中的金电极为工作电极,采用层层自组装技术将L-半胱氨酸、纳米金颗粒和抗牛Hp抗体依次组装在工作电极上,制成免疫传感器。制成的免疫传感器对Hp的线性检测范围为15～100 mg.L-1,最低检测限为0.63 mg.L-1,并具有较好的重现性和稳定性。分别采用该传感器和ELISA检测试剂盒对隐性乳房炎患牛乳样中的Hp含量进行检测的结果表明,两种检测结果间无显著差异(P>0.05)。结论:制备的免疫传感器可定量检测牛奶中的结合珠蛋白(Hp)。     

论鲜活农产品直配模式的形成机理及交易效率——以河北省为例

随着我国农业产业化程度的提高和农产品流通体制的健全,鲜活农产品在其生产和流通领域正在发生一些变化。通过对河北各地的实地考察,文章对河北省鲜活农产品配送模式中两种典型的直配模式进行了分析和比较,认为"合作经济组织+超市"模式具有较高的组织化程度和交易效率,但由于其市场目标一般为高端市场,其规模不宜太大;"生产基地+终端消费市场"模式计划性很强,是目前组织化程度最高的配送模式之一,但其外生交易费用较高。     

喀斯特风景区园林造景的植物配置特点与效果——贵州省松柏山生态保护示范基地实例分析

对贵州松柏山生态保护示范基地9个不同景区的植物配置原理、植物的利用、植物配置遵循原则、植物配置类型、树丛配置方法、植物配置艺术手法等多方面进行了分析,以期对营造喀斯特地貌绿色旅游地提供参考。     

农业高职院校在“一带一路”国家境外办学的探索——以北京农业职业学院泰国分院办学为例

高等学校境外办学是新时代中国高等职业教育 “走出去”、推进中外人文交流、共建 “一带一路”、服务党和国家工作大局的重要途径。近几年农业高职院校积极开展境外办学,取得了一定的效果。以北京农业职业学院境外办学为例,该校尝试多主体协同创立海外分院,通过构建“泰国需求导向 +北京都市农业特色”的国际化教学标准和课程体系、培训与外派并举建设师资队伍等方式保障了泰国分院境外办学的教学质量。同时 ,境外办学中存在的瓶颈问题如国际化发展意识、中泰农业和职业教育办学的差异、国际化师资队伍建设等方面深入思考了并提出了建议,以期为国内其他院校提供参考和借鉴。