868 resultados para History of chemistry
Resumo:
The aim of this short article is to trace the history of limnology in Sicily, from the end of the last century up to the present, and pay a little homage to a scientist to whom limnology is deeply indebted: G.E. Hutchinson. Due to its insular and climatic conditions, Sicily is characterised by a drainage network formed by numerous short, torrent-like rivers, and by a few small, natural lakes. The geological characteristics of the island strongly condition the quality of these small waterbodies which generally have surface areas of less than 0.2 km super(2). The earliest observations on Sicilian lentic waters go back more than a century; in particular, at the end of the 19th century, some of the issues regarding the natural lakes had already been brought into focus. Subsequent studies on natural waterbodies concentrated on the geomorphology of landslide lakes or lakes created by the dissolution of the gypsum tableland. However, many of the waterbodies no longer exist because of land reclamation which took place up to the first half of the 1950s. During the last 35 years, there has been a notable increase in limnological publications. In addition, these studies show a more careful and integrated approach to the limnological aspects of waterbodies, compared with the early studies.
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An account is given of a study of African tropical waters, drawing on the personal experiences of the author. Reviewing developments since 1900, the author examines the way in which research has developed and the influence the changes in the policitcal map of Africa, in particular the change from colonial rule, has had on research.
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During late - and post-glacial times lakes played a leading role in the development of the landscape of the North-west European part of USSR. A variety of geographic circumstances created great variegation of natural conditions in lakes and determined the composition of their diatoms. The basic stages of the development of the diatom flora of lakes are linked with general climatic changes. The deepwater regions of large periglacial lakes of the North-west USSR are inhabited by plankton diatoms of the genera Melosira and Cyclotella. Diatom analysis is further applied for the study of the history of the lakes of north-west USSR.
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O objetivo da presente pesquisa é o de discutir a reescrita da história da Irlanda, mais especificamente aspectos relacionados à construção da identidade nacional e de marcas da tradição, a partir da leitura do romance Tipperary, de Frank Delaney. Publicada em 2007, essa obra aborda de forma singular as querelas sobre identidade nacional, nacionalismo, passado, memória, e seus personagens principais e a trama estão significativamente ligados ao contexto político-social da história da Irlanda. Nessa reconstrução da história, o passado é revisitado através de diferentes pontos de vista. Nossa atenção estará voltada para a seleção de elementos/momentos da história do país que ganham foco na narrativa, e as possíveis repercussões deste processo. Além disso, nos concentraremos na questão das tênues fronteiras entre história e ficção, ou seja, as fronteiras pouco delimitadas entre o discurso histórico e o discurso ficcional. Na escrita da história em Tipperary, Delaney aborda questões relativas a mitos, lendas e tradições como importantes fatores de identidade nacional em uma Irlanda que emerge como uma nação independente. No romance em questão, podemos observar como história e memória se unem na jornada do protagonista, em sua empreitada de narrar a história de sua vida e de seu país
Resumo:
To achieve the apparently simple Periodic Table of the Elements has implied tremendous efforts over thousands of years. In this paper we present a brief history of the discovery of the chemical elements from prehistory to the present day, revealing the controversies that arose on the way and claiming the important work performed by alchemists in the advancement of knowledge. This is especially important if we consider that alchemy had a period of existence of many thousands of years, while the "Chemistry", officially established as a science in the eighteenth century, has operated as such for only a few hundred years. Even so, if we consider the progress of discovery and isolation of chemical elements throughout history, it can be observed that the number of elements identified is achieved mainly in the nineteenth and twentieth centuries, reflecting the development of instrumental techniques, that facilitated this task.
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Citharichthys cornutus and C. gymnorhinus, diminutive flatfishes inhabiting continental shelves in the western Atlantic Ocean, are infrequently reported and poorly known. We identified 594 C. cornutus in 56 different field collections (68–287 m; most between 101–200 m) off the eastern United States, Bahamas, and eastern Caribbean Sea. Historical records and recently captured specimens document the northern geographic range of adults on the shelf off New Jersey (40°N, 70°W). Citharichthys cornutus measured 17.2–81.3 mm standard length (SL); males (20.0–79.1 mm SL) and females (28.0–81.3 mm SL) attain similar sizes (sex could not be determined for fish <20 mm SL). Males reach nearly 100% maturity at ≥60 mm SL. The smallest mature females are 41.5 mm SL, and by 55.1 mm SL virtually all are mature. Juveniles are found with adults on the outer shelf. Only 214 C. gymnorhinus were located in 42 different field collections (35–201 m, with 90% between 61 and 120 m) off the east coast of the United States, Bahamas, and eastern Caribbean Sea. Adults are found as far north as the shelf off Cape Hatteras, NC (35°N, 75°W). This diminutive species (to 52.4 mm SL) is among the smallest flatfishes but males (n=131; 20.3–52.4 mm SL) attain a slightly larger maximum size than that of females (n=58; 26.2–48.0 mm SL). Males begin to mature between 29 and 35 mm SL and reach 100% maturity by 35–40 mm SL. Some females are mature at 29 mm SL, and all females >35.1 mm SL are mature. Overlooked specimens in museum collections and literature enabled us to correct long-standing inaccuracies in northern distributional limits that appear in contemporary literature and electronic data bases for these species. Associated locality-data for these specimens allow for proper evaluation of distributional information for these species in relation to hypotheses regarding shifts in species ranges due to climate change effects.
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Fishing with explosives is still being practiced aroung Hong Kong. The first legislation against blast fishing was passed in Hong Kong in 1903. Since then, successive legislation has increased the penalties and fines on blast fishing and fishing with poisons. However, the problem has not been eliminated as enforcement puts pressure on the resources of the marine police. It would be more effective to educate the local communities on the destructive effects of these practices and make them more vigilant and responsible in controlling them.
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The Argentine sandperch Pseudopercis semifasciata (Pinguipedidae) sustains an important commercial and recreational fishery in the northern Patagonian gulfs of Argentina. We describe the morphological features of larvae and posttransition juveniles of P. semifasciata and analyze the abundance and distribution of early life-history stages obtained from 19 research cruises conducted on the Argentine shelf between 1978 and 2001. Pseudopercis semifasciata larvae were distinguished from other larvae by the modal number of myomeres (between 36 and 38), their elongated body, the size of their gut, and by osteological features of the neuro- and branchiocranium. Pseudopercis semifasciata and Pinguipes brasilianus (the other sympatric species of pinguipedid fishes) posttransition juveniles were distinguished by their head shape, pigmentation pattern, and by the number of spines of the dorsal fin (five in P. semifasciata and seven in P. brasilianus). The abundance and distribution of P. semifasciata at early stages indicate the existence of at least three offshore reproductive grounds between 42−43°S, 43−44°S, and 44−45°S, and a delayed spawning pulse in the southern stocks.
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Oysters, Crassostrea virginica, and softshell clams, Mya arenaria, along the Massachusetts coast were harvested by European colonists beginning in the 1600’s. By the 1700’s, official Commonwealth rules were established to regulate their harvests. In the final quarter of the 1800’s, commercial fishermen began harvesting northern quahogs, Mercenaria mercenaria, and northern bay scallops, Argopecten irradians irradians, and regulations established by the Massachusetts Legislature were applied to their harvests also. Constables (also termed wardens), whose salaries were paid by the local towns, enforced the regulations, which centered on restricting harvests to certain seasons, preventing seed from being taken, and personal daily limits on harvests. In 1933, the Massachusetts Legislature turned over shellfisheries management to individual towns. Local constables (wardens) enforced the rules. In the 1970’s, the Massachusetts Shellfish Officers Association was formed, and was officially incorporated in 2000, to help the constables deal with increasing environmental problems in estuaries where fishermen harvest mollusks. The constables’ stewardship of the molluscan resources and the estuarine environments and promotion of the fisheries has become increasingly complex.
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Thirteen bottom trawl surveys conducted in Alaska waters for red king crab, Paralithodes camtschaticus, during 1940–61 are largely forgotten today even though they helped define our current knowledge of this resource. Government publications on six exploratory surveys (1940–49, 1957) included sample locations and some catch composition data, but these documents are rarely referenced. Only brief summaries of the other seven annual (1955–61) grid-patterned trawl surveys from the eastern Bering Sea were published. Although there have been interruptions in sampling and some changes in the trawl survey methods, a version of this grid-patterned survey continues through the present day, making it one of the oldest bottom-trawl surveys in U.S. waters. Unfortunately, many of the specific findings made during these early efforts have been lost to the research community. Here, we report on the methods, results, and significance of these early surveys, which were collated from published reports and the unpublished original data sheets so that researchers might begin incorporating this information into stock assessments, ecosystem trend analyses, and perhaps even revise the baseline population distribution and abundance estimates.
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This is a broad historical overview of the bay scallop, Argopecten irradians, fishery on the East and Gulf Coasts of North America (Fig. 1). For a little over a century, from about the mid 1870’s to the mid 1980’s, bay scallops supported large commercial fisheries mainly in the U.S. states of Massachusetts, New York, and North Carolina and on smaller scales in the states in between and in western Florida. In these states, the annual harvests and dollar value of bay scallops were far smaller than those of the other important commercial mollusks, the eastern oysters, Crassostrea virginica, and northern quahogs, Mercenaria mercenaria, but they were higher than those of softshell clams, Mya arenaria (Table 1). The fishery had considerable economic importance in the states’ coastal towns, because bay scallops are a high-value product and the fishery was active during the winter months when the economies in most towns were otherwise slow. The scallops also had cultural importance as a special food, an ornament owing to its pretty shell design, and an interesting biological component of
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This article covers the biology and the history of the bay scallop habitats and fishery from Massachusetts to North Carolina. The scallop species that ranges from Massachusetts to New York is Argopecten irradians irradians. In New Jersey, this species grades into A. i. concentricus, which then ranges from Maryland though North Carolina. Bay scallops inhabit broad, shallow bays usually containing eelgrass meadows, an important component in their habitat. Eelgrass appears to be a factor in the production of scallop larvae and also the protection of juveniles, especially, from predation. Bay scallops spawn during the warm months and live for 18–30 months. Only two generations of scallops are present at any time. The abundances of each vary widely among bays and years. Scallops were harvested along with other mollusks on a small scale by Native Americans. During most of the 1800’s, people of European descent gathered them at wading depths or from beaches where storms had washed them ashore. Scallop shells were also and continue to be commonly used in ornaments. Some fishing for bay scallops began in the 1850’s and 1860’s, when the A-frame dredge became available and markets were being developed for the large, white, tasty scallop adductor muscles, and by the 1870’s commercial-scale fishing was underway. This has always been a cold-season fishery: scallops achieve full size by late fall, and the eyes or hearts (adductor muscles) remain preserved in the cold weather while enroute by trains and trucks to city markets. The first boats used were sailing catboats and sloops in New England and New York. To a lesser extent, scallops probably were also harvested by using push nets, picking them up with scoop nets, and anchor-roading. In the 1910’s and 1920’s, the sails on catboats were replaced with gasoline engines. By the mid 1940’s, outboard motors became more available and with them the numbers of fishermen increased. The increases consisted of parttimers who took leaves of 2–4 weeks from their regular jobs to earn extra money. In the years when scallops were abundant on local beds, the fishery employed as many as 10–50% of the towns’ workforces for a month or two. As scallops are a higher-priced commodity, the fishery could bring a substantial amount of money into the local economies. Massachusetts was the leading state in scallop landings. In the early 1980’s, its annual landings averaged about 190,000 bu/yr, while New York and North Carolina each landed about 45,000 bu/yr. Landings in the other states in earlier years were much smaller than in these three states. Bay scallop landings from Massachusetts to New York have fallen sharply since 1985, when a picoplankton, termed “brown tide,” bloomed densely and killed most scallops as well as extensive meadows of eelgrass. The landings have remained low, large meadows of eelgrass have declined in size, apparently the species of phytoplankton the scallops use as food has changed in composition and in seasonal abundance, and the abundances of predators have increased. The North Carolina landings have fallen since cownose rays, Rhinoptera bonsais, became abundant and consumed most scallops every year before the fishermen could harvest them. The only areas where the scallop fishery remains consistently viable, though smaller by 60–70%, are Martha’s Vineyard, Nantucket, Mass., and inside the coastal inlets in southwestern Long Island, N.Y.