首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
An unusual silver celestial planisphere is held in the collection of the Whipple Museum of the History of Science (Wh.1762); little information about this object is recorded in the museum’s documentation. A comparison of this silver example with celestial planispheres printed on paper, coupled with the consideration of other aspects of the lives and work of the cartographers and instrument-makers involved in producing such objects, suggests some possibilities regarding its production. Through this individual case study, I aim to demonstrate that the careful examination of an individual instrument, coupled with an understanding of the class of instruments to which it belongs and the milieu in which it was produced, can result in a deeper understanding of any given artefact, its circumstances of design and manufacture, and its intended use and users.  相似文献   

2.
Summary Chymomyza amoena larvae in apples in summer were found to be either potentially freeze tolerant or to supercool. By late September only potentially freeze tolerant larvae were recovered from apples. Larvae from walnut husks in winter supercooled to avoid freezing. However, freeze tolerance could be induced in laboratory grown larvae by placing them in apples around the seed area and maintaining them at chilling temperatures for several weeks. Overwintering mechanisms employed byC. amoena larvae in Michigan appear to depend upon larval feeding site.Prof. Davis at Michigan Agricultural College placed 9C. amoena emerging from apples in August and Sept. 1891 along with codling moth in the MAC (=MSU) Entomological Museum collection.  相似文献   

3.
Summary Larvae ofNyctemera annulata Boisduval ingest pyrrolizidine alkaloids fromSenecio spathulatus A. Rich. which subsequently appear in the adult months and their eggs; the acquisition of the alkaloids by a parasite of theN. annulata larvae provides a further illustration of their ability to persist in insects.Acknowledgments. We thank Dr R. Yamdagni of the Chemistry Department, University of Calgary, Canada, and Dr O. Madsen of the Organic Chemistry Department, The Technical University of Denmark, Lyngby, Denmark, for much help with the MS data collection. We are also very grateful to Dr C.C.J. Culvenor, CSIRO Animal Health Lab., Parkville, Victoria, Australia, who most generously provided us with authentic reference specimens of pyrrolizidine alkaloids.  相似文献   

4.
Summary Lactate dehydrogenase zymograms of mature testes ofHymenochirus boettgeri show in addition to the five isozymes composed of LDH-A and LDH-B subunits, a second 5-band system which is due to isozymes formed between LDH-A and a third subunit, LDH-C. These testis-specific LDH-C isozymes appear around 6 months after metamorphosis indicating that their expression is correlated with sexual maturity as is generally the case in mammals. This is the first report of a testis-specific LDH isozyme in a lower tetrapod; such isozymes have hitherto only been reported in mammals and in the pigeon.This study was supported by a grant from the Fond National Suisse de la Recherche Scientifique to H.R.K. We thank M. Sateur and F. Bourquin for their technical help.  相似文献   

5.
Bonaventura Cavalieri has been the subject of numerous scholarly publications. Recent students of Cavalieri have placed his geometry of indivisibles in the context of early modern mathematics, emphasizing the role of new geometrical objects, such as, for example, linear and plane indivisibles. In this paper, I will complement this recent trend by focusing on how Cavalieri manipulates geometrical objects. In particular, I will investigate one fundamental activity, namely, superposition of geometrical objects. In Cavalieri’s practice, superposition is a means of both manipulating geometrical objects and drawing inferences. Finally, I will suggest that an integrated approach, namely, one which strives to understand both objects and activities, can illuminate the history of mathematics.  相似文献   

6.
Summary The solubilities and other properties of compounds made by combination of optically active components, e.g. the solubilities of the salts made from the dextro-form of an acid and the dextro- or the laevo-form of a base are in some instancesextremely different. It is a consequence of these differences that in a living organism, containing optically active substance,the degree of optical purity of these substances is of outmost importance. The presence of undesired antipodes of any kind might fundamentally disturb the metabolism. It is also known that living organisms at least partly and continuously produce the optically active substances needed bysynthesis from optically inactive material.A kinetical and thermodynamical study of the conditions under which optically active substances can, with use of optically active catalysers, be synthetized from inactive material, shows that the degree of optical purity of the material synthetized is, even under the most favorable conditions, maximum in the beginning of the synthesis andis bound to decay when the synthesis is, chemically speaking,completed and if the synthetized material is left in contact with the catalyzer. Thus a racemization of the synthetized active material occurs in which the catalyzer which has originally produced this active substance actively accelerates the deterioration of its state of optical purity.The means are discussed by which the organism is able to delay this loss of optical purity; and it is shown that all poosible means to do so are indeed used by the organism. As these means can delay but never completely avoid the decay of optical purity, this decay, even if it be slow, i.e.an ageing of optical purity, is a necessity in the course of the life of a living organism. As a loss of optical purity must disturb the normal metabolism, this must, even if no other events occur, limit the individual life.Experimental evidence which would check the prediction of decay of optical purity with age is incomplete; in several instances, however, the experimental technique permits us to detect and to follow the occurrence of finite small amounts of undesired antipodes, e.g. of some amino acids in the proteins of living organisms.

Vortrag, gehalten vor der Schweizerischen Gerontologischen Gesellschaft in Basel am 11. Dezember 1954.  相似文献   

7.
The concept of a technical frontier in branches of experimental measurement, such as the resolution of the microscope, angular measure and time telling, has been around for more than 60 years. The purpose of this brief paper is to identify the technical frontier operating on the achromatic astronomical telescope, where a limiting factor of the resolution of fine detail was the quality of the optical glass available. The achromatically corrected objective is formed from two kinds of glass, the common crown glass and the heavy clear flint glass or lead glass. This last was difficult to make homogeneous, that is without regions of different density, and therefore different refraction and dispersion. Unusually, optical glass had to pass a second frontier, this time placed on the whole glass industry by the English Government in the form of excise duty, administered with a bureaucratic efficiency that effectively stopped, in around 1800, the making of optical glass suitable for the serious astronomical telescopes. The result of the tax imposition was to delay the English production of improved optical glass for more than 80 years.  相似文献   

8.
ABSTRACT

During the sixteenth and seventeenth centuries, the Inquisition was the institution most invested in the censorship of printed books in the Portuguese empire. Besides publishing the Indices of Forbidden Books, the Holy Office was also responsible for overseeing their implementation and ensuring their efficacy in preventing the importation, reading, and circulation of banned books. Overall, the sixteenth-century Indices condemned 785 authors and 1081 titles, including 52 authors and 85 titles of medicine, natural history, natural philosophy, astronomy, chronology, cosmography, astrology, and divinatory arts. By looking at the largest collection of early modern scientific books in Portugal, I will argue that a closer inspection of marginalia and ownership, and the establishment of a typology of expurgations is essential for the comprehension of the actual practices and the mechanisms of censorship. By examining the material evidence of censorship, in order to reconstruct expurgation practices, this paper reveals the processes and effectiveness of ecclesiastical control in the Portuguese Inquisition and highlights the differences between what inquisitors wrote in the Indices and what others put into practice.  相似文献   

9.
Summary A new diterpenoid named jungermanool was isolated fromJungermannia torticalyx and the structure was found to be labda-8 (17), 14-dien-9, 13-diol by chemical and spectroscopical methods.Chemical constituents fromHepaticae, Part XXIV: Part XXIII,A. Matsuo, H. Nozaki, M. Nakayama, Y. Kushi, S. Hayashi andN. Kamijo, Tetrahedron Lett.1975, 241.The authors wish to express their gratitude to Dr.T. Seki, Department of Botany, Hiroshima University, for the collection and identification of the liverwort.  相似文献   

10.
This paper is a contribution to our understanding of the constructive nature of Greek geometry. By studying the role of constructive processes in Theodoius’s Spherics, we uncover a difference in the function of constructions and problems in the deductive framework of Greek mathematics. In particular, we show that geometric problems originated in the practical issues involved in actually making diagrams, whereas constructions are abstractions of these processes that are used to introduce objects not given at the outset, so that their properties can be used in the argument. We conclude by discussing, more generally, ancient Greek interests in the practical methods of producing diagrams.  相似文献   

11.
Summary A glass filtration-apparatus provided with an exchangeable nylon-tissue filter permits collection, fixation, dehydration, staining and preembedding of small biological objects in a simple and rapid way.This work was supported by grant No 3.218.-077 of the Swiss National Science Foundation.  相似文献   

12.
It is shown in this article that the two sides of an equation in the medieval Arabic algebra are aggregations of the algebraic “numbers” (powers) with no operations present. Unlike an expression such as our 3x + 4, the Arabic polynomial “three things and four dirhams” is merely a collection of seven objects of two different types. Ideally, the two sides of an equation were polynomials so the Arabic algebraists preferred to work out all operations of the enunciation to a problem before stating an equation. Some difficult problems which involve square roots and divisions cannot be handled nicely by this basic method, so we do find square roots of polynomials and expressions of the form “A divided by B” in some equations. But rather than initiate a reconsideration of the notion of equation, these developments were used only for particularly complex problems. Also, the algebraic notation practiced in the Maghreb in the later middle ages was developed with the “aggregations” interpretation in mind, so it had no noticeable impact on the concept of polynomial. Arabic algebraists continued to solve problems by working operations before setting up an equation to the end of the medieval period. I thank Mahdi Abdeljaouad, who provided comments on an earlier version of this paper, and Haitham Alkhateeb, for his help with some of the translations. Notes on references: When page numbers are separated by a “ / ”, the first number is to the Arabic text, and the second to the translation. Also, a semicolon separates page number from line number. Example: [Al-Khwārizmī, 1831, 31;6/43] refers to page 31 line 6 of the Arabic text, and page 43 of the translation.  相似文献   

13.
In this article we model the log of the US inflation rate by means of fractionally integrated processes. We use the tests of Robinson (1994) for testing this type of hypothesis, which include, as particular cases, the I(0) and I(1) specifications, and which also, unusually, have standard null and local limit distributions. A model selection criterion is established to determine which may be the best model specification of the series, and the forecasting properties of the selected models are also examined. The results vary substantially depending on how we specify the disturbances. Thus, if they are white noise, the series is I(d) with d fluctuating around 0.25; however, imposing autoregressive disturbances, the log of the US inflation rate seems to be anti‐persistent, with an order of integration smaller than zero. Looking at the forecasting properties, those models based on autocorrelated disturbances (with d < 0) predict better over a short horizon, while those based on white noise disturbances (with d > 0) seem to predict better over longer periods of time. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

14.
Summary The spectral sensitivity of 3 species of planktonic Rotatoria (Asplanchna priodonta, Polyarthra remata, Filinia longiseta) were measured by means of the positive phototactic reaction.Asplanchna andPolyarthra both have a broad maximum sensitivity range around 540 nm and a near maximum at 440 nm. In the UV direction (to 360 nm) the spectral sensitivity increases. In contrast,Filinia has only a maximum of 460 nm in the visible spectrum, but behaves similarly to the other species in the UV region. The ecological significance of these results is discussed, as well as their bearing on a possible dermal light sense.  相似文献   

15.
Summary During the crushing of hard objects, the adductor muscles ofTrachydosaurus are activated in an unfused tetanus with the tetanic pulses of the several motor units occurring in synchrony.  相似文献   

16.
It has not been sufficiently emphasized that there existed two kinds of modification theory of colours, Aristotle's modification theory and Descartes-Hook's modification theory. This seems to have caused some confusion in the interpretation of the optical controversy between Newton and Hooke in 1672. The aim of the present paper is to prove that these two kinds of modification theory really coexisted, and on that basis to present a new interpretation of the optical controversy of 1672. The characteristics and the historical role of each of these theories will be described. Newton's colour theory was formed under the influence of Aristotle's modification theory, which had been disseminated through the work of an English Gassendist, Walter Charleton. Newton's optical theories were created not only under the influence of Descartes, as we have been often told, but also under the conspicuous influence of corpuscular philosophers.  相似文献   

17.
Summary To test whether mole-ratsCryptomys hottentotus were able to use the magnetic field for orientation, laboratory experiments were conducted which were based on the animals' spontaneous tendency to build their nests at the same position in a circular arena. In the local geomagnetic field, the animals preferred the SE-sector. When magnetic north was turned by 120o or by 180o, the mole-rats changed their nest position accordingly. This clearly shows that they can use the magnetic field for direction finding.  相似文献   

18.
Part of the distinction between artefacts, objects made by humans for particular purposes, and natural objects is that artefacts are subject to normative judgements. A drill, say, can be a good drill or a poor drill, it can function well or correctly or it can malfunction. In this paper I investigate how such judgements fit into the domain of the normative in general and what the grounds for their normativity are. Taking as a starting point a general characterization of normativity proposed by Dancy, I argue how statements such as ‘this is a good drill’ or ‘this drill is malfunctioning’ can be seen to express normative facts, or the content of normative statements. What they say is that a user who has a desire to achieve a particular relevant outcome has a reason to use, or not to use, the artefact in question. Next this analysis is extended to show that not just statements that say that an artefact performs its function well or poorly, but all statements that ascribe a function to an artefact can be seen as expressing a normative fact. On this approach the normativity of artefacts is analyzed in terms of reasons on grounds of practical, and to a lesser extent theoretical, rationality. I close by investigating briefly to what extent reasons on moral grounds are, in the analysis adopted here, involved in the normativity of artefacts.  相似文献   

19.
Two classes of sponges (animal phylum Porifera) possess a siliceous skeleton which is composed of spicules. Studying the optical fiber-mechanical properties of large spicules from hexactinellid sponges (> 5 cm) it was demonstrated that they are effective light-collecting optical fibers. Here, we report that the demosponge Suberites domuncula is provided with a biosensor system composed of the (organic) light producing luciferase and the (inorganic) light transducing silica spicules. The light transmission feature of these smaller spicules (200 μm) has been demonstrated and the ability of sponge tissue to generate light has been proven. Screening for a luciferase gene in S. domuncula was successful; the recombinant luciferase was prepared and shown to be bioactive. The luciferase protein is abundantly present in the close neighborhood of the spicules. The expression of the luciferase gene is under the control of light. Received 14 August 2008; received after revision 09 November 2008; accepted 26 November 2008  相似文献   

20.
Summary Goldfinches (Carduelis carduelis) consume the feces of their nestlings until the digestive efficiency of nestlings and adults is nearly equal. With increasing nestling age from the first day onwards, the energy content of the nestlings' feces decreases. The percentage of fecal pellets swallowed by the adults during the course of the nestling period is negatively correlated with their energy content. It may be concluded that adults use the feces of their young as an energy source.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号