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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 237 (1972), S. 82-88 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] By characterization of fragments, isolated from a nuclease digest of MS2 RNA, the entire nucleotide sequence of the coat gene was established. A “flower”-like model is proposed for the secondary structure. The genetic code makes use of 49 different codons to specify the sequence of the ...
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The nucleotide sequence of the A-protein gene of bacteriophage MS2 has been determined and a model for its secondary structure is proposed. Also the amino acid sequence of the A-protein has been almost completely ...
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  • 3
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2016-06-19
    Description: Emulation of biological synapses is an important step toward construction of large-scale brain-inspired electronics. Despite remarkable progress in emulating synaptic functions, current synaptic devices still consume energy that is orders of magnitude greater than do biological synapses (~10 fJ per synaptic event). Reduction of energy consumption of artificial synapses remains a difficult challenge. We report organic nanowire (ONW) synaptic transistors (STs) that emulate the important working principles of a biological synapse. The ONWs emulate the morphology of nerve fibers. With a core-sheath–structured ONW active channel and a well-confined 300-nm channel length obtained using ONW lithography, ~1.23 fJ per synaptic event for individual ONW was attained, which rivals that of biological synapses. The ONW STs provide a significant step toward realizing low-energy–consuming artificial intelligent electronics and open new approaches to assembling soft neuromorphic systems with nanometer feature size.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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  • 4
    Publication Date: 2013-06-11
    Description: To enhance the feasibility of seismic full waveform inversion (FWI) for various types of geological structures, the model parameters should be updated along directions such that both long- and short-wavelength structures can be properly resolved. These long- and short-wavelength structures are primarily influenced by the low- and high-frequency components of the gradients, respectively. In some cases, however, the gradients are not flexible to reconstruct both the long- and the short-wavelength structures. This problem can be related to the scaling method using the Hessian matrix and the effect of the source spectrum. In this study, we analyse the problems of conventional scaling methods in frequency-domain FWI and propose a weighting method to compensate for these problems. The weighting method is applied to the conventional elastic FWI, where the gradient is scaled by the diagonal of the pseudo-Hessian matrix inside the frequency loop so that the effect of the source spectrum can be removed through cancellation. The weighting factors are designed using the backpropagated wavefields incited by the deconvolved residuals, which play a role in making the descent directions appropriately reflect the spectral differences between the observed data and the initial (or the inverted) modelling responses. We analyse the characteristics of the Jacobians and residuals and compare the descent directions of the two conventional waveform inversion methods with descent directions of the weighting method for thick rectangular-shaped and thin-layers models. The results indicate that the descent directions computed using the conventional inversion methods do not reflect the characteristics of deconvolved residuals and that particular frequency components are always emphasized regardless of geological models, while the spatial resolution of the descent direction calculated using the weighting method is flexibly determined depending on the differences between the true and the assumed models. Inversion results for the Marmousi-2 model show that the weighting method is not sensitive to the initial guess even though we do not apply the frequency marching strategy. Numerical examples for the SEG/EAGE salt model show that the weighting method can properly recover the high velocities of the salt body and the low velocities below the salt body. Our numerical examples are based on the assumption that low frequencies are available. Further study is needed to apply the weighting method to real field data that are noisy and do not have low-frequency components.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 5
    Publication Date: 2013-04-11
    Description: To enhance the robustness of the l 2 -norm elastic full-waveform inversion (FWI), we propose a denoise function that is incorporated into single-frequency gradients. Because field data are noisy and modelled data are noise-free, the denoise function is designed based on the ratio of modelled data to field data summed over shots and receivers. We first take the sums of the modelled data and field data over shots, then take the sums of the absolute values of the resultant modelled data and field data over the receivers. Due to the monochromatic property of wavefields at each frequency, signals in both modelled and field data tend to be cancelled out or maintained, whereas certain types of noise, particularly random noise, can be amplified in field data. As a result, the spectral distribution of the denoise function is inversely proportional to the ratio of noise to signal at each frequency, which helps prevent the noise-dominant gradients from contributing to model parameter updates. Numerical examples show that the spectral distribution of the denoise function resembles a frequency filter that is determined by the spectrum of the signal-to-noise (S/N) ratio during the inversion process, with little human intervention. The denoise function is applied to the elastic FWI of synthetic data, with three types of random noise generated by the modified version of the Marmousi-2 model: white, low-frequency and high-frequency random noises. Based on the spectrum of S/N ratios at each frequency, the denoise function mainly suppresses noise-dominant single-frequency gradients, which improves the inversion results at the cost of spatial resolution.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
    Publication Date: 2016-04-09
    Description: A flux dropout is a sudden and sizable decrease in the energetic electron population of the outer radiation belt on the timescale of a few hours. We simulated a flux dropout of highly relativistic 〉 2.5 MeV electrons using the Radiation Belt Environment (RBE) model, incorporating the pitch-angle diffusion coefficients caused by EMIC waves for the geomagnetic storm event of 23 – 26 October 2002. This simulation showed a remarkable decrease in the 〉 2.5 MeV electron flux during main phase of the storm, compared to those without EMIC waves. This decrease was independent of magnetopause shadowing or drift loss to the magnetopause. We suggest that the flux decrease was likely to be primarily due to pitch-angle scattering to the loss cone by EMIC waves. Furthermore, the 〉 2.5 MeV electron flux calculated with EMIC waves correspond very well with that observed from SAMPEX spacecraft. EMIC wave scattering is therefore likely one of the key mechanisms to understand flux dropouts. We modeled EMIC wave intensities by the Kp index. However, the calculated dropout is a several hours earlier than the observed one. We propose that Kp is not the best parameter to predict EMIC waves.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2011-06-08
    Description: We fit the size distribution of liquid-ordered (Lo) domains measured from fluorescence images of model cytoplasmic myelin monolayers with an equilibrium thermodynamic expression that includes the competing effects of line tension, λ, dipole density difference, Δm, and the mixing entropy. From these fits, we extract the line tension, λ, and dipole density difference, Δm, between the Lo and liquid-disordered (Ld) phases. Both λ and Δm decrease with increasing surface pressure, , although λ/Δm2 remains roughly constant as the monolayer approaches the miscibility surface pressure. As a result, the mean domain size changed little with surface pressure, although the polydispersity increased significantly. The most probable domain radius was significantly smaller than that predicted by the energy alone, showing that the mixing entropy promotes a greater number of smaller domains. Our results also explain why domain shapes are stable; at equilibrium, only a small fraction of the domains are large enough to undergo theoretically predicted shape fluctuations. Monolayers based on the composition of myelin from animals with experimental allergic encephalomyelitis had slightly lower values of λ and Δm, and a higher area fraction of domains, than control monolayers at all . While it is premature to generalize these results to myelin bilayers, our results show that the domain distribution in myelin may be an equilibrium effect and that subtle changes in surface pressure and composition can alter the distribution of material in the monolayer, which will likely also alter the interactions between monolayers important to the adhesion of the myelin sheath.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 8
    Publication Date: 2015-06-30
    Description: The diffusion of electrons via a linearly polarized, growing electromagnetic (EM) wave propagating along a uniform magnetic field is investigated. The diffusion of electrons that interact with the growing EM wave is investigated through the autocorrelation function of the parallel electron acceleration in several tens of electron gyration timescales, which is a relatively short time compared with the bounce time of electrons between two mirror points in Earth's radiation belts. Furthermore, the pitch-angle diffusion coefficient is derived for the resonant and non-resonant electrons, and the effect of the wave growth on the electron diffusion is discussed. The results can be applied to other problems related to local acceleration or the heating of electrons in space plasmas, such as in the radiation belts.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 9
    Publication Date: 2011-10-20
    Description: We present the results of simultaneous high resolution observations of far ultraviolet (FUV) spectra/images and precipitating electrons made for the polar region during a period of slightly disturbed geomagnetic conditions. The polar region was divided into five subregions: the dayside subauroral region, dayside auroral zone, polar cap, nightside auroral zone, and nightside subauroral region. Precipitation in the dayside subauroral region was dominated by soft electrons, and the intensity of the OI 135.6 nm line relative to the NI 149.3 nm line was significantly enhanced, while electrons of a few keV energies also existed. On the other hand, the nightside subauroral region showed the hardest electron spectrum among the five subregions, and the FUV intensity was the brightest there, with substantial increase in the long Lyman-Birge-Hopfield (LBH) band. The auroral zones showed series of inverted-V events with more energetic electrons in the nightside than in the dayside, and the corresponding FUV auroral features were also brighter and broader in the nightside. In the polar cap region, discrete polar arcs were seen, with corresponding electron beams of ∼keV, embedded in the diffuse low-intensity FUV background caused by polar rain. The relative intensity of OI 135.6 nm to the NI 149.3 nm line was evaluated for the five subregions and it was found to decrease with increasing electron characteristic energy when energy was smaller than ∼2 keV, and remained more or less the same above ∼2 keV, which was confirmed by simulations. On the other hand, the relative intensity of the long LBH band to the short LBH band increased with increasing characteristic energy over the entire energy range up to ∼4 keV. The OI 135.6 nm line and long LBH band intensities were compared with the energy flux of precipitating electrons, and they were found to have good correlations. When the energy flux was fitted as a function of the long LBH intensity by a power law, the power index was found to be 1.37 for the entire polar region with ∼75 km spatial bins, similar to the value obtained previously for inverted-V events with similar spatial averages.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2013-10-16
    Description: Protein methyltransferase (PMT)-mediated posttranslational modification of histone and nonhistone substrates modulates stability, localization, and interacting partners of target proteins in diverse cellular contexts. These events play critical roles in normal biological processes and are frequently deregulated in human diseases. In the course of identifying substrates of individual PMTs, bioorthogonal profiling...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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