Limitations of pH-potentiometric titration for the determination of the degree of deacetylation of chitosan

The degree of deacetylation (DDA) of chitosan determines the biopolymer's physico-chemical properties and technological applications. pH-Potentiometric titration seems to offer a simple and convenient means of determining DDA. However, to obtain accurate pH-potentiometric DDA values, several factors have to be taken into consideration. We found that the moisture content of the air-dry chitosan samples can be as high as 15%, and a reasonable fraction of this humidity cannot be removed by ordinary drying. Corrections have to be made for the ash content, as in some samples it can be as high as 1% by weight. The method of equivalence point determination was also found to cause systematic variations in the results and in some samples extra acid as high as 1 mol% of the free amino content was also identified. To compensate for the latter effect, the second equivalence point of the titration has to be determined separately and the analytical concentration of the acid be corrected for it. All the corrections listed here are necessary to obtain DDA values that are in reasonable agreement with those obtained from (1)H NMR and IR spectroscopic measurements. The need for these corrections severely limits the usefulness of pH-metry for determining accurate DDA values and thus potentiometry is hardly able to compete with other standard spectroscopic procedures, that is, (1)H NMR spectroscopy.     

Comparative anatomy of the heart of mammals

Hearts from 20 mammalian orders were examined according to a fixed protocol to determine if the gross differences of shape and internal anatomy could be explained. Three generalizations can be made: firstly differences are most closely related to taxonomic position, secondly some features, such as the prominence of the conus of the right ventricle in animals that leap, dig or sprint regularly as part of their defence mechanism and a long, narrow left ventricle in endurance performers may be more closely related to activity than ancestry, and lastly some characteristics may be pleiotropic effects of thoracic morphogenesis.     

具重复Kringle结构分子的缺失体和嵌合体的构建方法

确定肝细胞生长因子(HGF)和巨噬细胞刺激蛋白(MSP)各4个Kringle结构的共有序列并设计公用引物,此公用引物配合HGF和MSP上、下游引物,利用DNA聚合酶链式反应(PCR)技术,可在一次PCR反应中扩增出多条片段,以不同的组合方式将这些片段两两连接,得到了缺失不同Kringle的缺失体和两种分子间不同区域的缺失型嵌合体,从而为HGF和MSP结构与功能的研究奠定了基础。此方法可普遍适用于含有两个或两个以上Kringle分子的缺失体与嵌合体的构建。克隆过程中对存在引物酶切位点的cDNA片段的克隆方法的建立,为同类问题的解决提供了可靠的方法。     

Control and prevention of tuberculosis in Britain: an updated code of practice. Subcommittee of the Joint Tuberculosis Committee of the British Thoracic Society.

A subcommitte was appointed by the Joint Tuberculosis Committee of the British Thoracic Society to review and bring up to date guidelines on control measures for tuberculosis. The updated code of practice emphasises that all cases of tuberculosis must be notified. A minority of patients need admission, and those with positive sputum smears should be regarded as infectious until they have received two weeks of chemotherapy. NHS staff at risk should be protected, and evidence of infectious tuberculosis should be sought as routine among certain prospective NHS employees, schoolteachers, and others. Contact tracing should be vigorously pursued, and all entrants to Britain from countries where tuberculosis is common should be screened. BCG vaccination should be offered in selected instances, and local organisation of tuberculosis services should be extended.     

Assessment of the potential germ cell mutagenicity of industrial and plant protection chemicals as part of an integrated study of genotoxicity in vitro and in vivo

An approach is described that enables the germ cell mutagenicity of chemicals to be assessed as part of an integrated assessment of genotoxic potential. It is recommended, first, that the genotoxicity of a chemical be defined by appropriate studies in vitro. This should involve use of the Salmonella mutation assay and an assay for the induction of chromosomal aberrations, but supplementary assays may be indicated in specific instances. If negative results are obtained from these 2 tests there is no need for the conduct of additional tests. Agents considered to be genotoxic in vitro should then be assessed for genotoxicity to rodents. This will usually involve the conduct of a bone marrow cytogenetic assay, and in the case of negative results, a genotoxicity test in an independent tissue. Agents found to be non-genotoxic in vivo are regarded as having no potential for germ cell mutagenicity. Agents found to be genotoxic in vivo may either be assumed to have potential as germ cell mutagens, or their status in this respect may be defined by appropriate germ cell mutagenicity studies. The basis of the approach, which is supported by the available experimental data, is that germ cell mutagens will be evident as somatic cell genotoxins in vivo, and that these will be detected as genotoxins in vitro given appropriate experimentation. The conduct of appropriate and adequate studies is suggested to be of more value than the conduct of a rigid set of prescribed tests.     

高压蒸汽灭菌柜性能验证方法的研究

高压蒸汽灭菌柜在使用之前和运行一定时间后,必须进行性能验证,采用热分布,热穿透和微生物挑战试验法对GE,GEV型脉冲式蒸汽灭菌柜的性能进行验证,多孔物质及流体物质灭菌循环中,灭菌腔内不存在冷点,具备有效的热穿透力,嗜热脂肪芽孢杆菌（ATCC7953）在规定灭菌时间内被完全杀死。因而确认高压灭菌柜的各项性能均达到生产要求,由此建立的一套验证方案及试验方法和结果得到了国家GMP认证中心的认可。     

Virus-induced fusion of human erythrocyte ghosts I. Effects of macromolecules on the final stages of the fusion reaction

Human erythrocyte ghosts prepared by hypotonic hemolysis can be fused by Sendai virus, provided that certain macromolecules (bovine serum albumin, dextran and others) are sequestered in the ghosts. Since fusion of the ghosts is dependent on intactness of the F(fusion)-glycoprotein of the virion, and since the other requirements for this reaction are also similar to those for the Sendai virus-induced fusion of intact erythrocytes, this system can be used as a model for the Sendai virus-induced cell fusion reaction. Sequestered macromolecules seem to be required for rounding of locally fused ghosts. Under low osmotic swelling conditions, such as use of ghosts sealed without macromolecules or using bovine serum albumin-loaded ghosts sealed in the presence of external macromolecules, no apparently complete cell fusion (large spherical polyghost formation) could be observed. Even under these conditions, however, occurence of local cell fusion could be demonstrated either by transfer of fluorescent-labeled albumin from one ghost to an other, or by observation of polyghost formation after osmotic swelling in the cold. Thus, final stages of the fusion reaction can be divided into local cell-cell fusion which could not be observed by phase-contrast microscopy, and rounding (i.e. formation of spherical polyghost). For the observation of fusion of ghosts, the last step seems to be important.     

Biorisk assessment of natural science laboratories of Bicol University College of Science,Philippines

A biorisk assessment of natural science laboratories in Bicol University was conducted as an initial step towards improvement of laboratories and contributing to a culture of safety in the university. Survey among laboratory workers and ocular inspection of natural science labs was done. Results showed that gaps exist in the safety knowledge and practices of laboratory workers. Microbial assets pose the lowest risk, while equipment and the use of chemicals in biological assays pose the highest risk. The likelihood that such events will occur ranges from low to moderate while consequences range from moderate to high. The research recommends that a policy on biological safety be formulated and be integrated in the overall safety guidelines of the university, that existing guidelines and SOPs be improved and that their implementation be monitored, to introduce a course for undergraduates that will tackle the basics of safety and security in the laboratory, and that the equipment and physical design be improved to reduce the risks to acceptable levels.     

Evaluation of the Biological Activity of Several Analogs of the Dopaminergic Neurotoxin 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine

Several analogs of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were synthesized and screened for their capacity to be oxidized by monoamine oxidase (MAO-A or MAO-B) and their capacity to produce nigrostriatal dopaminergic neurotoxicity in mice. All of the compounds were relatively weak substrates for MAO-A but many of the compounds were found to be good substrates for MAO-B. Only three of the compounds, in addition to MPTP itself, were found to be neurotoxic. These were 1-methyl-4-cyclohexyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine and 1-methyl-4-(3'-methoxyphenyl)-1,2,3,6-tetrahydropyridine. All three of these neurotoxic compounds were found to be substrates for MAO-B; in contrast no compound was found to be neurotoxic that was not oxidized by MAO-B. The capacity of the compounds studied to be oxidized by MAO-B appears to be an important aspect of the neurotoxic process.     

试论城市化进程中的生态建设

城市化对于发展经济和控制人口自然增长率有积极意义。人是城市生态系统的主体,城市生态必须满足人的生活的基本需要:方便、健康和舒适,特别是健康的需要。强化生态建设才能适应城市化的发展。消除环境“四害”是城市生态建设的重点。城市规划必须超前,规划中的生态建设必须与其他城市建设同步实施,优先完成。     

石片研究

石片是石制品的重要组成部分, 其分类须遵循逻辑划分, 研究应规范化、系统化和简单化。按照台面和背面特征划分石片类型越来越趋向共识。石片台面由其背面缘和破裂面缘构成,是由直线、折线和弧线相互组成的几何图形, 它的形状反映剥片思维的逻辑构想。依据单疤、双疤、多疤组合和单向、双向、多向组合观察石片背面有助于剥片流程的分析。从背面观测石片的长度和划分左右较为合理, 参照人的手掌和手指判定石片大小和依据黄金分割律确认石片的形态应该是较有理的选择。石片除了制作食物外, 更多功效的猜想也值得考虑, 如敬奉首领、示爱异性、切割头发胡须、挠痒痒和清理排泄物等。     

Stability properties of 2-species models of mutualism: Simulation studies

Summary Most previous analyses of the stability properties of models of mutualism have emphasized the destabilizing effects of mutualism. However, these analyses can be shown to be based upon inappropriate assumptions, or to be applicable only for special cases of mutualism. In this paper three basic 2-species models of mutualism are presented and their six combinations are analyzed by computer simulation for their return time stability and persistence stability. Four out of six models show greater return time stability than an appropriate model without mutualism, and all models show higher persistence stability than the model without mutualism. It is argued that real biological systems can be related to the qualitative structure of each of the basic models of mutualism, and that therefore none of the basic models or their stability properties can be eliminated a priori as being inappropriate. The conclusion follows that while some kinds of mutualistic interactions may be relatively unstable, other mutualisms, probably representing the majority of cases, can be considered to be relatively stable. The limitations of these models and analyses are considered.     

Aspects of the distribution of HbS in the United States

Frequencies of HbS obtained by several screening clinics are analyzed for age, sex, and location effects. All seem to be present in some form, though age and sex effects may be conditional on location. An attempt is made to elaborate the common observation of increasing frequency with age. This is shown to be the result of differences in fertility favoring the normal. A simulation which íncludes 25% admixture was done. The results indicate a genetically relevant New World experience for the population to be about 9–12 generations with the heterozygote having fitness of 0.96–0.99.     

Measurement of soil macropore geometry by image analysis of sections through impregnated soil

The geometry of the soil pore space affects root growth directly by providing pathways for root extension and indirectly through its effects on soil aeration and on water infiltration, redistribution and drainage. Image analysis of sections through impregnated blocks of undisturbed soil allows quantitative assessment of the pore space. Samples are dehydrated and impregnated with resin containing a fluorescent dye. Once the resin has hardened, the blocks can be cut to reveal a section through the structure. An image of the pore space, which is now filled with resin, can be obtained using ultra-violet light either photographically or digitally. Digital images are segmented into pore space and solid. Image analysis techniques can be used to classify the pore space into channels, fissures and packing pores. This allows appropriate measurements to be made on each class so that stereology can be used to estimate 3-D parameters from the measurements made on the image. Various indices can also be derived to quantify the pore structure.     

An elemental analysis of archaeological bone from Sicily as a test of predictability of diagenetic change

Cortical human bone samples from three tightly dated components of a single Sicilian site were chemically analyzed employing the highly sensitive technique of inductively coupled plasma emission spectroscopy. Although the skeletons appeared to be excellently preserved, significant diagenesis was detected. Moreover, a majority of the elements tested showed no constant or linear variation over time, implying that diagenetic change tends not to be a predictable function of duration of interment. Variation among major long bones of a single skeleton was quite high, as was variation across the cortex. The latter may reflect chemical inhomogeneity in bone tissue or may be an artifact of postmortem change. The results demonstrate the hazards of unsuspected and unpredictable diagenesis, which must be controlled before reliable dietary inferences can be drawn.     

Analytical solutions of a minimal model of species migration in a bounded domain

 A minimal model of species migration is presented which takes the form of a parabolic equation with boundary conditions and initial data. Solutions to the differential problem are obtained that can be used to describe the small- and large-time evolution of a species distribution within a bounded domain. These expressions are compared with the results of numerical simulations and are found to be satisfactory within appropriate temporal regimes. The solutions presented can be used to describe existing observations of nematode distributions, can be used as the basis for further work on nematode migration, and may also be interpreted more generally. Received: 15 August 1999     

The Genetic Improvement of Entomopathogenic Nematodes and Their Symbiont Bacteria: Phenotypic Targets, Genetic Limitations and an Assessment of Possible Hazards

The methodologies of classical genetics and genetic engineering can be used for the genetic improvement of entomopathogenic nematodes (EPNs) and their symbiont bacteria. Many of the complex behavioural and physiological traits which are targets for genetic improvement are likely to be controlled polygenically, thus selective breeding for improvements to these traits would be appropriate. Much basic research needs to be carried out before researchers will be able to effect improvements to EPNs and their symbionts by genetic engineering. There is a lack of basic information on the genetics and biochemistry of the characteristics that might be altered by transgenic methods in EPNs, and their bacteria, and existing transformation protocols need to be made more effective.     

温州蜜柑萎缩病毒和柑桔衰退病毒在苗木各部位分布的全年分析

１９９１年９月至１９９２年８月逐月采样,采用ＤＡＳ－ＥＬＩＳＡ法对温州蜜柑萎缩病毒（ＳＤＶ）在温州蜜柑苗木各部位及对柑桔衰退病毒（ＣＴＶ）在甜橙苗木各部位的分布进行了全年分析。结果表明ＳＤＶ在老叶、老枝皮中全年均检测不到;在根中仅在７、８月份可检出有少显病毒存在;在嫩叶中３、４、５、６、９、１０月均可检出且浓度较高,而７、８月在嫩叶中检测不出,在嫩枝皮中４、５、６、７、１０月均可检出而７月份浓度有较大幅度降低。这说明冷凉温度下的嫩组织适立于ＳＤＶ的繁殖,最佳检测时期为春梢和秋梢的嫩梢期,最佳检测部位为幼嫩的叶和嫩枝皮。对ＣＴＶ在甜橙苗木各部位分布检测结果表明各部位全年均可检测出带毒且含量均较高,总的变幅不大,冬季和夏季含量有所下降,在老叶中变幅稍大些,这说明甜橙苗木各个部位均适宜于采样且全年均可进行分析。     

西部干旱区生态需水的规律及特点——以塔里木河下游绿色走廊为例

天然植被蒸散耗水量小,水分有效利用程度高,生态需水可塑性及水质变幅较大等是生态需水的主要特点．保护塔里木河下游绿色走廊的生态需水量,主要是指大西海子以下自然植被的需水量．即地下水位恢复总水量和全河段生态总维持水量,前者主要包括水位恢复水量、侧向排泄量及河道蒸发水量．2005年泄水目标为阿尔干,生态总需水量为恢复大西海于至阿尔干地下水的总水量,该水量为13．20×10^8m^3,年均需水量为2．64×10^8m^3．2010年泄水目标及植被保护目标都是台特玛湖,生态总需水量包括恢复阿尔干至台特玛湖段地下水位的水量以及维持大西海子至台特玛湖段生态的维持水量,该水量为18．32×10^8m^3,年均需水量为3．66×10^8m^3．2010—2030年的生态总需水量包括每年维持大西海子至台特玛湖段生态的总维持水量,同时也包括增加植被18．67×10^4hm^2所需要的水量,20年生态总需水量为139．00×10^8m^3,年均需水量为6．95×10^8m^3．通过一系列措施保证生态用水,是干旱区生态建设的关键．     

Isolation of Phages for Phage Therapy: A Comparison of Spot Tests and Efficiency of Plating Analyses for Determination of Host Range and Efficacy

Phage therapy, treating bacterial infections with bacteriophages, could be a future alternative to antibiotic treatment of bacterial infections. There are, however, several problems to be solved, mainly associated to the biology of phages, the interaction between phages and their bacterial hosts, but also to the vast variation of pathogenic bacteria which implies that large numbers of different phages are going to be needed. All of these phages must under present regulation of medical products undergo extensive clinical testing before they can be applied. It will consequently be of great economic importance that effective and versatile phages are selected and collected into phage libraries, i.e., the selection must be carried out in a way that it results in highly virulent phages with broad host ranges. We have isolated phages using the Escherichia coli reference (ECOR) collection and compared two methods, spot testing and efficiency of plating (EOP), which are frequently used to identify phages suitable for phage therapy. The analyses of the differences between the two methods show that spot tests often overestimate both the overall virulence and the host range and that the results are not correlated to the results of EOP assays. The conclusion is that single dilution spot tests cannot be used for identification and selection of phages to a phage library and should be replaced by EOP assays. The difference between the two methods can be caused by many factors. We have analysed if the differences and lack of correlation could be caused by lysis from without, bacteriocins in the phage lysate, or by the presence of prophages harbouring genes coding for phage resistance systems in the genomes of the bacteria in the ECOR collection.