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  • 1995-1999  (313)
  • 1970-1974  (14)
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  • 21
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 571-573 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of fixed volume phase holograms in lithium niobate is studied. The new measurement method is able to distinguish between electronic compensation and true erasure. It is found that at temperatures in the range of 70–120 °C both electronic thermal detrapping and ionic movement are active effects. The actual lifetime of fixed holograms is determined in this temperature range. From these measurements, we extrapolate a lifetime for the fixed hologram refractive index change of 3.7 years at room temperature. © 1997 American Institute of Physics.
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  • 22
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3263-3265 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: SiNx:H films with a wide composition range and, some of them, with low oxygen content are deposited at room temperature. The defects observed in the films are attributed to Si-dangling bonds, with a structure depending on film composition. For the N-rich films they are of the form ⋅Si≡(N3), whereas for the films with similar [N]/[Si] ratio but containing oxygen, the predominant defect is proposed to be ⋅Si≡(Si2O), despite of the high N content and the low O content of these films. The spin density of the films has been related to the bonds that hydrogen establishes (either Si–H or N–H), with the maximum value corresponding to the minimum hydrogen content. Both maximum and minimum values, respectively, are obtained at the silicon percolation limit of the Si–Si bonds into the SiNx:H network, x∼1.10. © 1995 American Institute of Physics.
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  • 23
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Available deformation data for superplastic yttria-stabilized zirconia polycrystals with grain size 〈1 µm have been analyzed at temperatures between 1250° and 1450°C as a function of stress, grain size, and impurity content. The apparent stress exponent nfor the higher-purity materials (residual impurity content 〈0.10 wt%) varies from 2 (region II) to greaterthan equal to3 (region I), and then toward 1 when the stress is decreased. The stress for transition between region II and region I decreases when the temperature and/or grain size is increased. The activation energy Qfor flow in region II is 460 kJ/mol, which is approximately that for cation lattice diffusion. The grain-size exponent pdecreases continuously and Qincreases continuously with decreasing stress in region I. The constitutive equation for superplastic flow in region II is identical to that for metallic systems when lattice diffusion is the rate-controlling mechanism. The experimental results have been correlated with a single deformation process that incorporates a threshold stress, below which grain-boundary sliding does not contribute to strain. The threshold stress may result from yttrium segregation at grain boundaries and its interaction with grain-boundary dislocations. A single deformation regime with n= 2 exists for low-purity materials (impurity content 〉0.10 wt%) over the entire stress range. The strain-rate enhancement with respect to high-purity materials is related to the grain-boundary amorphous phase present in such materials.
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  • 24
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 106 (1999), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Barley (Hordeum vulgare L.) exposed to low temperature increases its freezing tolerance. This increase has been associated with several metabolic changes caused by low temperature, including expression of dehydrins (DHN), a family of proteins induced by dehydration and cold acclimation. DHNs play an undetermined role in dehydration responses during freezing. We have studied the accumulation of an 80-kDa DHN-like protein (P-80) in barley under cold acclimation 6/4°C (day/night), postulating that it is localized in tissues where primary ice nucleation occurs. P-80 was absent in nonacclimated plants and was detectable after 48 h of cold acclimation, reaching a stable level after 6 days. P-80 decreased when plants were returned to 20–25°C. Drought, ABA and high temperature did not increase the levels of P-80, suggesting that its expression could be specifically regulated by cold. Immunolocalization by tissue printing and fresh cross sections of leaves showed the protein to be associated with vascular tissues and epidermis. The localization of P-80 is consistent with our hypothesis because vascular tissue and the epidermis are preferential ice nucleation zones during the onset of freezing. The differential accumulation of P-80 may have an adaptive value by participating in tolerance mechanisms during freeze-induced dehydration.
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  • 25
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 103 (1998), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The role of ABA in freezing resistance in nonacclimated and cold-acclimated barley (Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT50, ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT50 and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT50 of leaves of cold-acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT50 decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.
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  • 26
    ISSN: 1439-0426
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The main objective of this study was to analyse differences and similarities in morphometric characteristics among specimens of the same year class of Acipenser naccarii (Bonaparte, 1836), comparing fish raised either in Italy or Spain. All specimens were Fl of captive broodstock in Italy.Fifteen biometric variables were measured, and three derived indices were calculated, on 30 individuals of 3+ year class from Lombardy (Italy) and 90 individuals of 1+, 2+ and 3+ year class from Riofrio (Granada, Spain). A stepwise discriminate analysis (SDA) was carried out, and the results were contrasted using a non-hierarchical cluster analysis. The two groups proved to be similar, so a principal component analysis and a simple regression analysis were performed on all individuals, taking total length (Tl) as the independent variable and all the biometric variables as dependent.The study revealed that although the Soljan index (i.e. ratio of mouth width to snout length) is related to Tl, and is a valid taxonomic characteristic, the CA index (i.e. relative position of the barbels) and FB index (i.e. ratio of snout length to width) are also valid characteristics for individuals longer than 57 cm, being independent of Tl.
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  • 27
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 785 (1996), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
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  • 28
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 783 (1996), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
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  • 29
    ISSN: 1748-7692
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 30
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: φ29 DNA replication starts at both DNA ends by a protein priming mechanism. The formation of the terminal protein-dAMP initiation complex is directed by the second nucleotide from the 3′ end of the template. The transition from protein-primed initiation to normal DNA elongation has been proposed to occur by a sliding-back mechanism that is necessary for maintaining the sequences at the φ29 DNA ends. Structure—function studies have been carried out in the φ29 DNA polymerase. By site-directed mutagenesis of amino acids conserved among distantly related DNA polymerases we have shown that the N-terminal domain of φ29 DNA polymerase contains the 3′–5′ exonuclease activity and the strand-displacement capacity, whereas the C-terminal domain contains the synthetic activities (protein-primed initiation and DNA polymerization). Viral protein p6 stimulates the initiation of φ29 DNA replication. The structure of the protein p6—DNA complex has been determined, as well as the main signals at the φ29 DNA ends recognized by protein p6. The DNA binding domain of protein p6 has been studied. The results indicate that an α-helical structure located in the N-terminal region of protein p6 is involved in DNA binding through the minor groove. The φ29 protein p5 is the single-stranded DNA binding (SSB) protein involved in φ29 DNA replication, by binding to the displaced single-stranded DNA (ssDNA) in the replication intermediates. In addition, protein p5 is able to unwind duplex DNA. The properties of the φ29 SSB—ssDNA complex are described. Using the four viral proteins, terminal protein, DNA polymerase, protein p6 and the SSB protein, it was possible to amplify the 19285-bp φ29 DNA molecule by a factor of 4000 after 1 h of incubation at 30°C. The infectivity of the in vitro amplified DNA was identical to that of φ29 DNA obtained from virions.
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