如何在WWW万维网上查寻地球科学资料

指数倍快速增长的国际互联网 ,对发展能够在WWW万维网上找到有用信息的工具提出了新的要求 ,“模拟图书馆 (VirtualLibraries)”和“搜索器 (SearchEngines)”就是两种已有的工具 ,可被用于搜寻地球科学信息资料。由于各种数据库中的信息在质与量上有很大的差异 ,为了收集到与某一特定题目有关的大量信息 ,就得采用有效的互联网搜索技术。此外 ,对所收集的信息的质量必须进行严格的评估     

BIOCHEMICAL RESPONSES OF CHESTNUT OAK TO A GALLING CYNIPID

We characterized the distribution of nutritional and defensive biochemical traits in galls elicited on chestnut oak (Quercus prinus L.) by the gall wasp Andricus petiolicolus Basse (Cynipidae) in comparison with gypsy moth-wounded and unwounded leaves. Gall cortex and epidermis exhibited elevated soluble peroxidase (POX) and soluble invertase activities, and greater condensed tannin concentrations than did nutritive tissues or leaves. Nutritive tissue, on which the insect feeds, contained few polyphenols, and lower POX and invertase activities compared with other gall tissues and leaves. Elevated total POX activity arose from a complex pattern of enhanced and suppressed isoform activities in galls. Invertase enzyme activity decreased in all tissues over the course of the 7-d study, although gypsy moth wounding suppressed this decline slightly in ungalled leaves. Our results indicate that the distribution of biochemical defenses in this typical cynipid gall differs significantly from the leaf tissue from which it is formed and support a role for invertases in establishing the gall as a sink. A. petiolicolus larvae do not induce, and may suppress, plant defense responses in nutritive tissue, while enzymatic activity and phenolic accumulation are enhanced in gall tissues surrounding feeding sites. These patterns suggest that the gall is manipulated by the insect to enhance its food and protective value.     

Technological Extinctions of Industrial Firms: An Inquiry into their Nature and Causes

After a buildup in the number of firms, new industries commonlyexperience a ‘shakeout’ in which the number of firmsdeclines sharply. Three theoretical perspectives on how technologicalchange contributes to industry shakeouts are analyzed. The theoriesare used to synthesize predictions concerning technologicalchange and industry evolution. The predictions inform an analysisof four US industries that experienced sharp shakeouts: automobiles,tires, televisions and penicillin. Using data on firm participationand innovation from the commercial inception of the four productsthrough their formative eras, we uncover regularities in howthe products evolved. The regularities suggest that shakeoutsare not triggered by particular technological innovations norby dominant designs, but by an evolutionary process in whichtechnological innovation contributes to a mounting dominanceby some early-entering firms.     

INHIBITION OF SALMONELLA SEROVARS, ESCHERICHIA COLI O157:H7 AND LISTERIA MONOCYTOGENES DURING DRY-CURING AND DRYING OF MEAT: A CASE STUDY WITH BASTURMA

Basturma, a spiced beef product intended to be cooked before consumption, was prepared in three trials by dry‐curing intact surface‐inoculated (6 log cfu per piece with Salmonella serovars, Escherichia coli O157:H7 and Listeria monocytogenes) beef eye of round subprimals for 21 days at 6.7C, and then rinsing, pressing and drying for 6–8 days at 21–27C. The finished products had percentage water‐phase salt concentrations of 8.3–18.0 and water activity of 0.84–0.95. In the finished product, no surviving Salmonella serovars and E. coli O157:H7 were detected (<1.0 log cfu) in two trials; in the third trial the reductions were 4.5 and 5.0 log cfu, respectively. L. monocytogenes populations decreased 4.0–4.9 log cfu. Basturma prepared by dry‐curing, rinsing, pressing and drying appears to present little risk of foodborne infection because this process reduces populations of Salmonella serovars, E. coli O157:H7 and L. monocytogenes. Dry‐curing and drying are potentially very important pathogen‐reduction steps.     

CUTTING RESISTANCE OF A RESTRUCTURED FRUIT BAR AS INFLUENCED BY WATER ACTIVITY

The cutting resistance, of thin rectangular strips of a restructured dehydrated fruit bar was measured over a range of water activity, 0.30-0.97. There was a 100-fold increase in cutting force as the product was dried from an initial cutting resistance of 4.4 N at a_w, = 0.86 to a maximum of 452 N at a_w= 0.33. Below a water activity of 0.33, samples became brittle and showed lower cutting resistances; for example, 68 N at a_w= 0.30. The major ingredients in the fruit product affecting cutting resistance were the level of apple puree and maltodextrin.