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  • General Chemistry  (12)
  • Analytical Chemistry and Spectroscopy  (4)
  • Elasmobranchii  (3)
  • Wiley-Blackwell  (16)
  • Springer  (3)
  • Blackwell Publishing Ltd
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  • Wiley-Blackwell  (16)
  • Springer  (3)
  • Blackwell Publishing Ltd
  • 1
    ISSN: 1573-5133
    Keywords: Batoidea ; Chondrichthyes ; Elasmobranchii ; Amazon ; Magdalena ; Maracaibo ; Orinoco ; Paraná-Paraguay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis The number of venomous caudal spines and their length and position relative to one another were determined in seven species of South American freshwater rays (Potamotrygonidae) and eight marine or euryhaline species of four families from the Caribbean Coast of South and Central America. Most species have two visible spines at certain stages in the shedding-replacement cycle and only one visible spine at other stages (following shedding). If we include the embryological beginnings of the spines before they erupt and become visible, the spine counts of most rays are actually 2 rather than 1 or 2. Since most species apparently follow this pattern, spine counts are of little use in distinguishing between species except in the relatively few that may have only one, or no spines. Eight captive Potamotrygon specimens maintained in simulated tropical temperature conditions over 12 months showed periodic shedding and replacement of spines. The molts were biannual for a given ray but annual for a given spine. They alternated between two spine loci and their cycles were approximately six months out of phase with each other. Recent studies on Dasyatis sabina by others report only one molt per year, with replacement spines forming always posterior to the primary spine rather than alternating between posterior and anterior. Supernumerary spines (counts of more than two, up to five) are also discussed, as are counts of one and zero.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5133
    Keywords: Amazonia ; Batoidea ; Brazil ; Captive breeding ; Chondrichthyes ; Colombia ; Elasmobranchii ; Freshwater adaptation ; Growth rate ; Potamotrygonidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Observations of reproductive features and body measurements were made on wild-caught, freshwater stingrays, Potamotrygon circularis and P. motoro, from the Amazon drainage of western Brazil and southern Colombia. Further observations were made in Detroit's Belle Isle Aquarium on a captive pair of P. motoro and their descendants, which constitute the first known captive breeding colony of potamotrygonids. The gross structure and function of female and male reproductive systems are described. There is no obvious difference between those of the two species. They are aplacentally viviparous, the young being nourished in advanced stages by uterine milk secreted by trophonemata. Size at onset and completion of sexual maturation, breeding season and behavior, gestation period, litter size and sex ratios are discussed. Up to 21 proportional measurements were made on several fetal and postnatal stages of both species. Several proportional changes occur in very early fetal life, but most body proportions undergo only minor changes from advanced fetal through adult stages. A growth curve is proposed for P. motoro based on observations of the captive colony.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5133
    Keywords: Elasmobranchii ; Euryhalinity ; Freshwater adaptation ; Dam lake ; Osmoregulation ; Central America
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis The Río Bayano in eastern Panama is one of many tropical rivers in which bull sharks (Carcharhinus leucas) and largetooth sawfish (Pristis perotteti) have been known to occur. Since both species can osmoregulate in fresh water throughout life, theoretically, both could survive in landlocked situations for many years.P. perotteti reproduces in fresh water, butC. leucas ordinarily does not, so only the former would appear to have the potential for establishing a breeding stock in such a landlocked freshwater body. The damming of the Rio Bayano and the creation of a large impoundment in 1976 provides a test of the ability of members of both species trapped there to survive and to establish breeding stocks. In 1980 and 1981 three mature femaleC. leucas were found dead in Lake Bayano and three sub-adult femaleP. perotteti were taken by trammel net. These events confirm the ability of both to survive in fresh water for long periods, but the establishment of breeding stocks appears doubtful and the question may not be answered for many years.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 8 (1994), S. 391-407 
    ISSN: 0886-9383
    Keywords: Neural networks ; Non-linear multivariate regression ; Pattern classification ; Kalman filter ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Finding methods for the optimization of weights in feedforward neural networks has become an ongoing developmental process in connectionist research. The current focus on finding new methods for the optimization of weights is mostly the result of the slow and unreliable convergence properties of the gradient descent optimization used in the original back-propagation algorithm. More accurate and computationally expensive second-order gradient methods have displaced earlier first-order gradient optimization of the network connection weights. The global, extended Kalman filter is among the most accurate and computationally expensive of these second-order weight optimization methods. The iterative, second-order nature of the filter results in a large number of calculations for each sweep of the training set. This can increase the training time dramatically when training is conducted with data sets that contain large numbers of training patterns. In this paper an adaptive variant of the global, extended Kalman filter that exhibits substantially improved convergence properties is presented and discussed. The adaptive mechanism permits more rapid convergence of network training by identifying data that contain redundant information and avoiding calculations based on this redundant information.
    Additional Material: 9 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 9 (1986), S. 281-284 
    ISSN: 0935-6304
    Keywords: Liquid chromatography, HPLC ; Time-switched detectors ; UV detection ; Fluorimetric detection ; Vitamin A ; Vitamin E ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An HPLC method utilizing a UV and a fluorimetric detector linked in series is described. By use of a simple integrator-controlled time-switched relay, analysis of serum vitamin A and E is accomplished on the same chromatogram and at optimum sensitivity for each detector. A single internal standard (retinyl acetate) monitored only by the UV detector permits measurement of both vitamins over a wide linear range. Precision of the assays is satisfactory, both on a within-day and on a day-to-day basis. Recoveries of both vitamins are virtually 100% whilst sensitivity is 2 μg/L (retinol) and 0.05 mg/L (α-tocopherol).
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 3 (1980), S. 241-247 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; Quantitative analysis at 10-10g level ; Steroids in urine ; Amino acid fluorobutyrates (19 in 35 min) ; Installation of glass capillaries ; Connection to FM-ECD ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glass capillary columns are ideal for analysis of urinary steroid profiles (i.e. the total steroid neutral fraction without prior separation into sub-groups).In this paper performance of both SCOT and wide-bore WCOT columns has been compared, resulting in no significant quantitative difference on urine extracts run as trimethylsilyl ether derivatives. However, because of increased efficiency the WB-WCOT column exhibited more sensitivity in measurement of small amounts of 11-ox-aetiocholanolone. Sensitivity of other steroids was greatly enhanced by use of either SCOT or WB-WCOT, leading to an almost tenfold increase over conventional packed columns (e.g. androsterone and aetiocholanolone 〈 40 μg per 24 h urine sample). A simple splitless injection system (based on a design of Dr. W. Greenaway, Oxford University) is presented.Experiments were also carried out using a SCOT column in conjunction with an FM-electron capture detector. Whilst efficiency was impaired due to the design of the detector, use of He (carrier) and N2 (make up gas) showed that several steroid derivatives could be easily measured at well below the 10-10 g level with much more rapid retention times than with a 1½m packed column. Highly successful separation of 19 amino acids (as fluoro-acyl derivatives) was achieved in 35 minutes using a SCOT (30 m) SP2100 column.
    Additional Material: 12 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 76 (1964), S. 249-258 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In dieser Arbeit werden verbesserte Wege zur Darstellung von 19-nor-Steroiden beschrieben. Sie beruhen auf neuen Totalsynthesen des Östrons und auf der intramolekularen Funktionalisierung und Eliminierung der Methylgruppe C-19 in Androstan-Derivaten.
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  • 8
    ISSN: 0044-8249
    Keywords: Oxidoreduktasen ; Redoxchemie ; Rhenium ; Schwefel ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 9
    ISSN: 0044-8249
    Keywords: Halbleiter ; Polymere ; Schwefelverbindungen ; Thione ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 97 (1985), S. 745-760 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Es ist schon sehr lange bekannt, daß sich manche Übergangsmetallsulfide in wäßrigem Ammoniumpolysulfid lösen. Obwohl anzunehmen war, daß sich dabei Metallpolysulfide bilden, hat man sich diesem Verbindungstyp erst in den letzten Jahren intensiver zugewandt. Dabei konnte eine Fülle neuer Komplexe mit Polysulfido-Chelatliganden Sn2- (n=2,3,4…) isoliert und charakterisiert werden. Die Komplexe interessieren bezüglich ihrer Struktur und Reaktivität, aber auch im Hinblick auf mögliche Anwendungen; mit ihnen können Schwefelringe definierter Größe gezielt hergestellt werden, und es deutet sich an, daß sie auch in der Katalyse Verwendung finden könnten.
    Additional Material: 26 Ill.
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