太阳紫外辐射增加对材料的作用

合成高分子,天然生物高分子以及其它一些商品材料都要受到太阳紫外辐射(UV)的有害作用。这些材料,特别是塑料在需要经常曝露于日光的环境下的应用,只有利用光稳定剂和(或)表面处理对它们进行保护才有可能。因此,由于部分臭氧减少引起的日光UV含量的任何增高都将增加这些材料的光降解速率,减少它们在户外的应用寿命。这种由日光中UV辐射增加引起的破坏的性质和程度可用作用光谱(action spectra)进行定量表征。虽然在文献上报道了几个高分子的作用光谱,现有资料常不足以对增加的破坏进行可靠的估计。高分子材料的配方,所使用的破坏判据乃至解释数据的方式都常常能影响结果。然而,从已有的资料可清楚看出,短波UV-B过程是引起曝露于日光下的高分子的光破坏的主要原因,这些破坏包括从变色直到整体机械性能的丧失。在许多情况下这些变化仍未有清楚的分子水平的解释。可以用在高分子配方中加入更多量常用光稳定剂的方法来减轻日光中增加的UV含量的作用。但是,这个方法包含了以下假设:a)在日光光谱改变了的情况下这些光稳定剂仍继续有效;b)这些稳定剂曝露于富UV的日光下自身是光稳定的;c)在足够低的深度下它们仍足够有效以达到经济的目的。尚缺乏有关这方面的实验资料。正在进行的研究,特别是有关高分子在极端环境条件下曝露的研究,可能会使这些问题变得更加清晰。用光稳定性更好的塑料和其它材料来代替原来的材料也是一个引人注意的解决方法。上述两种解决方法都将增加应用的塑料产品的价格。随着塑料大量取代传统的材料在许多方面的应用,这是需要考虑的重要问题,尤其在发展中国家更是如此。

An approach to incorporate linkage disequilibrium structure into genomic association analysis

In this study, we propose to use the principal component analysis （PCA） and regression model to incorporate linkage disequilibrium （LD） in genomic association data analysis. To accommodate LD in genomic data and reduce multiple testing, we suggest performing PCA and extracting the PCA score to capture the variation of genomic data, after which regression analysis is used to assess the association of the disease with the principal component score. An empirical analysis result shows that both genotype-based correlation matrix and haplotype-based LD matrix can produce similar results for PCA. Principal component score seems to be more powerful in detecting genetic association because the principal component score is quantitatively measured and may be able to capture the effect of multiple loci.

MUTATIONAL SPECTRA OF INDUCED MUTATIONS IN THE ad-3 REGION OF Neurospora crassa:EVIDENCE FOR MUTAGEN SPECIFICITY

Specific-locus mutations induced in the ad-3region of two-component heterokaryons ofNeurospora have been compared by means ofMutational Spectra.Genetic characterization ofad-3 mutations has revealed that there are majorclasses:gene/point mutations,multilocus deletionmutations and unknowns (mutants that grow toorapidly alone on minimal medium to be classified).

Value of multi-quadrants biopsy:Pooled analysis of 11 population-based cervical cancer screening studies

Objective:The accuracy of colposcopy-guided biopsy is key to the success of colposcopic triage in cervical cancer screening programs.However,there is no widely adopted biopsy guideline up to date.Our study aimed to determine whether multi-quadrants biopsy improves the yield of cervical lesions.Methods:Eleven population-based cervical cancer screening studies were conducted in China.Cytology,highrisk human papillomavirus(hrHPV)testing and visual inspection were performed for primary screening.Females positive on one or more tests were referred for colposcopy and biopsy.The proportion of detected cervical intraepithelial neoplasia(CIN)2+and yields by quadrant lesion-targeted biopsy or 4-quadrant random biopsy were compared.Results:Among 4,923 females included,1,606 had quadrant lesion-targeted biopsy,and 3,317 had 4-quadrant random biopsy.The cumulative CIN2+yield increased from 0.10 for only one quadrant-targeted biopsy to 0.21,0.34,and 0.58 for at most two,three and four quadrants targeted biopsies.Among hrHPV positive females with high-grade squamous intraepithelial lesion(HSIL)+cytology,the cumulative CIN2+yield of a second targeted biopsy in another quadrant was significantly increased(P<0.05).Among hrHPV-negative females,the yield of 4-quadrant random biopsies was 0.005,and the yield by lesion-targeted biopsies was 0.017.For hrHPV positive females who had 4-quadrant random biopsy,the additional CIN2+yield for HSIL+,low-grade squamous intraepithelial lesion(LSIL)cytology,or abnormal visual inspection via acetic acid and Lugol’s iodine(VIA/VILI)were 0.46,0.11,0.14.Conclusions:A 4-quadrant random biopsy is recommended only for hrHPV positive females with HSIL cytology,and is acceptable if hrHPV positive with LSIL cytology or with abnormal VIA/VILI.Our findings add evidences for an objective and practical biopsy standard to guide colposcopy in cervical cancer screening programs in low-and middle-income countries.

IDENTIFICATION OF ENVIRONMENTAL MUTAGENS/CARCINOGENS:SPECIFICLOCUS ASSAYS IN NEUROSPORA

The measurement of specific-locus mutations in various eukaryotic organismshas been used as a mechanism to estimate the genetic consequences of humanexposure to environmental mutagens.Specific-iocus assays are usually confined tosingle genes and measure various types of genetic damage ranging from single base-pair substitutions to multilocus deletions.Not all such assays measure the samerange of genetic damage.Thus.different specific-locus assays may provide differentdata,both quantitative and qualitative.as a result of exposure to the sameenvironmental mutagen.The specific-locus assay in the ad-3 region of Neurosporacrassa measures genetic damage at 2 closely linked loci as well as other loci in thegenome.As a result.this assay permits a comprehensive evaluation of the types ofgenetic damage produced by different environmental mutagens.In this paper.thespectrum of genetic damage that can be detected in Neurospora is reviewed andcompared with other eukaryotic systems.

System-level Pareto frontiers for on-chip thermoelectric coolers

The continuous rise in heat dissipation of integrated circuits necessitates advanced thermal solutions to ensure system reliability and efficiency. Thermoelectric coolers are among the most promising techniques for dealing with localized on-chip hot spots. This study focuses on establishing a holistic optimization methodol- ogy for such thermoelectric coolers, in which a thermo- electric element＇s thickness and the electrical current are optimized to minimize source temperature with respect to ambient, when the thermal and electrical parasitic effects are considered. It is found that when element thickness and electrical current are optimized for a given system architecture, a ＂heat flux vs. temperature difference＂ Pareto frontier curve is obtained, indicating that there is an optimum thickness and a corresponding optimum current that maximize the achievable temperature reduc- tion while removing a particular heat flux. This methodol- ogy also provides the possible system level AT＇s that can be achieved for a range of heat fluxes, defining the upper limits of thermoelectric cooling for that architecture. In this study, use was made of an extensive analytical model, which was verified using commercially available finite element analysis software. Through the optimization process, 3 pairs of master curves were generated, which were then used to compose the Pareto frontier for any given system architecture. Finally, a case study wasperformed to provide an in-depth demonstration of the optimization procedure for an example application.