设计参数对平面凸轮机构压力角的影响

凸轮机构的压力角是凸轮机构设计的一个重要参数,决定了凸轮大小和机构强度等诸元素,同时压力角又受其他设计参数的影响。文章以减小凸轮机构压力角为目的。从平面凸轮机构结构型式、基本尺寸、从动件运动规律曲线、凸轮副材料、摩擦状态等设计参量对压力角的影响入手进行分析。运用数值计算和分析类比的方法。得出在合理设计凸轮参数的情况下减小凸轮机构压力角的相应措施。图2表1参10     

滚子凸轮机构基本尺寸的综合

凸轮基圆半径是决定凸轮机构基本尺寸的一个重要参数。文章从机构最小压力角及高副接触应力等2个方面分析讨论了基圆半径及滚子半径与它们的关系,并提出了凸轮机构最小基本尺寸的选择原则方法。     

内啮合弧面凸轮机构压力角的计算方法

弧面凸轮机构现有的外啮合形式结构尺寸较大,分度数有限,为此提出内啮合弧面凸轮机构.通过空间曲面啮合原理,结合回转变换张量得到了内啮合弧面凸轮机构压力角的计算方法,并通过分析计算寻找压力角的影响因素.结果表明中心距、凸轮基圆半径、从动件运动规律对机构压力角影响较大,从动盘回转半径、滚子形状和尺寸、啮合点位置变化对压力角影...     

确定形封闭凸轮机构基本尺寸的解析法

本文结合S-dS/dΦ曲线,通过求解凸轮压力角限制线与结构位置线的交点和划分轴心区间,讨论了按许用压力角设计形封闭直动式盘形凸轮机构的12种方案,直接推导了确定最小基圆半径和偏距的计算公式,从而为凸轮机构的CAD提供了理论依据和数学模型。     

直动从动杆盘形凸轮基圆半径的确定

凸轮机构的压力角和机构尺寸之间的关系,在机械原理中已做了详细的叙述。设计时为了减少凸轮尺寸、重量和高速转动的不平衡,应取尽可能小的基圆半径。本文用拉格朗日乘数法或非线性规划法可以确定凸轮基圆半径的最小值和凸轮回转中心的相应位置,可以获得良好效果。     

中投梭机构改进设计的探讨

由空间几何分析导出中投梭机构的空间凸轮机构压力角计算式,并为改善投梭机构的动力性能,运用优化设计方法改进确定凸轮机构的有关结构尺寸,并举例说明。     

直线往复运动的固定凸轮连杆机构的优化设计

本文对直线往复运动的固定凸轮连杆机构的特点进行了分析与讨论,提出了以机构纵向尺寸为目标函数,平均效率为传动质量指标,适当限制压力角的优化设计方法,并对它进行设计。本文还对机构的传动质量指标进行了探讨,得到了能适用于一般基本机构的传动质量指标公式。     

大行程凸轮排线机构设计的理论与实践

为适应针布大卷装而加宽料盘,相应地对排线机构的凸轮进行了重新设计与计算。计算所得的凸轮压力角超过了书上推荐的许用压力角。为此,对自锁压力角进行核算并在结构上采取措施。实践证明:选用比许用压力角大的压力角在某种情况下是可行的,是凸轮机构改造的一个成功例子。     

内廓接触直动从动件盘型凸轮机构的设计条件

详细分析了内廓接触直动从动件盘型凸轮机构转角、从动件运动规律及机构基本尺寸之间的关系，推导出该类机构运动学尺寸设计的通用公式和基本条件，具有较强的应用价值。     

摆动从动杆盘状凸轮机构的运动设计——同时考虑压力角和最小曲率半径的优化设计

本文对摆动从动杆盘状凸轮机构的最大压力角和最小曲率半径问题进行了详细的讨论。根据优化原理,同时考虑许用压力角和最小曲率半径,对摆动从动杆盘状凸轮机构进行了最优化设计。在仅给出摆杆运动规律、摆杆最大摆角和相应凸轮转角的情况下,直接确定凸轮的最小基圆半径、摆杆长度和摆杆初始位置角。     

Reliable identification of grapevine rootstock varieties using RAPD PCR on woody samples

Since grapevine ( Vitis spp .) rootstock material is being traded increasingly as disbudded woody material a lack of distinctive morphological features on such material necessitates an alternative and reliable means of identification. Methods described here were developed for rapid and efficient extraction of DNA from woody samples rich in phenolic compounds and polysaccharides, and for subsequent identification of varieties by RAPD PCR. Using these methods, and with the application of only one selected RAPD primer, we were able to differentiate sixteen rootstock varieties, including the seven varieties most commonly used in Germany. Problems commonly encountered with reproducibility of RAPD patterns were avoided by choosing primers with a dinucleotide sequence and a high G/C content that allowed a rather high annealing temperature of 45°C. Methods described here should also be useful for other horticultural crops, especially those with woody tissues rich in phenolic compounds and polysaccharides.     

An internet compendium of analytical methods and spectroscopic information for monomers and additives used in food packaging plastics

An internet website (http://cpf.jrc.it/smt/) has been produced as a means of dissemination of methods of analysis and supporting spectroscopic information on monomers and additives used for food contact materials (principally packaging). The site which is aimed primarily at assisting food control laboratories in the European Union contains analytical information on monomers, starting substances and additives used in the manufacture of plastics materials. A searchable index is provided giving PM and CAS numbers for each of 255 substances. For each substance a data sheet gives regulatory information, chemical structures, physico-chemical information and background information on the use of the substance in particular plastics, and the food packaging applications. For monomers and starting substances (155 compounds) the infra-red and mass spectra are provided, and for additives (100 compounds); additionally proton NMR are available for about 50% of the entries. Where analytical methods have been developed for determining these substances as residual amounts in plastics or as trace amounts in food simulants these methods are also on the website. All information is provided in portable document file (PDF) format which means that high quality copies can be readily printed, using freely available Adobe Acrobat Reader software. The website will in future be maintained and up-dated by the European Commission's Joint Research Centre (JRC) as new substances are authorized for use by the European Commission (DG-ENTR formerly DGIII). Where analytical laboratories (food control or other) require reference substances these can be obtained free-ofcharge from a reference collection housed at the JRC and maintained in conjunction with this website compendium.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 μm-thick oriented PP) into the food simulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.     

Analysis of benzo[a]pyrene in spiked fatty foods by second derivative synchronous spectrofluorimetry after microwave-assisted treatment of samples

A simple, rapid and inexpensive method has been developed for the determination of benzo[a     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. II: Certification study

This paper describes the second part of a project undertaken to develop certified mussel reference materials for paralytic shellfish poisoning toxins. In the first part two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin and decarbamoyl-saxitoxin in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the certification exercise. Fifteen laboratories participated in this certification study and were asked to measure saxitoxin and decarbamoyl-saxitoxin in rehydrated lyophilized mussel material and in a saxitoxin-enriched mussel material. The participants were allowed to use a method of their choice but with an extraction procedure to be strictly followed. The study included extra experiments to verify the detection limits for both saxitoxin and decarbamoyl-saxitoxin. Most participants (13 of 15) were able to meet all the criteria set for the certification study. Results for saxitoxin.2HCl yielded a certified mass fraction of <0.07 mg/kg in the rehydrated lyophilized mussels. Results obtained for decarbamoyl-saxitoxin.2HCl yielded a certified mass fraction of 1.59+/-0.20 mg/kg. The results for saxitoxin.2HCl in enriched blank mussel yielded a certified mass fraction of 0.48 +/- 0.06 mg/kg. These certified reference materials for paralytic shellfish poisoning toxins in lyophilized mussel material are the first available for laboratories to test their method for accuracy and performance.     

Detection of adulteration of locust bean gum with guar gum by capillary electrophoresis and polarized light microscopy

Capillary electrophoresis (CE) and polarized light microscopy (PLM) were utilized in the detection of the adulteration of locust bean gum with guar gum. For CE analyses, standards of locust bean and guar gums were extracted with 30% CH₃CN, removing the residual proteins from the gum matrix. A 8.75 mM NaH₂PO₄-20.6 mM Na₂B₄O₇ buffer, pH 9, was used to separate these proteins and to identify marker proteins that were present in the guar gum. These markers did not co-migrate with components in the extracts of mechanically processed locust bean gum, and are used as indicators of adulteration. Using PLM with toluidine blue and iodine staining techniques, unadulterated locust bean gum samples were distinguished from mixed samples through the differential staining of components in locust bean versus guar and tara gums. These experiments in the use of CE and PLM provide orthogonal and complementary methods for the verification of 'true' positives and the elimination of 'false' positives.     

Announcing a new international peer-reviewed journal:Food Science and Human Wellness now accepting manuscript submission in English

<正>We are pleased to announce the launch of a new international peer-reviewed journal-Food Science and Human Wellness,ISSN 2213-4530,which is an open access journal,produced and hosted by Elsevier B.V.on behalf of Beijing Academy of Food Sciences.Food Science and Human Wellness is an international peer-reviewed English journal that provides a forum for the dissemination of the     

Chinese CTP Market

According to Printing and Printing Equipment Industries Association of China（PEIAC）＇s statistics to the plate manufucturer in China, in 2013, the actual offset plate production has reached 346 million square meters in China. Among them, the CTP production volume was 245 million square meters, up by 11% than that of last year; the total sales of the CTP plate was 239 million square meters, up by 13%.