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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4995-5001 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The detonation velocity following type II deflagration-to-detonation transitions (DDT) has been observed to be markedly different to that which would be expected were the charges directly initiated. In charges of pentaerythritol tetranitrate (PETN) velocities as high as 5.6 mm μs−1 have been observed compared to 3.7 mm μs−1 which is both predicted and measured for the charge were it to be directly initiated. Experiments have also been carried out that attempt to measure the temperature within columns of PETN prior to a type II DDT event. Other experiments and hydrocode simulations have been carried out that attempt to isolate the possible causes of the anomalous detonation velocity and as a result determine what the critical factors that determine the velocity are. These studies have led to a greater understanding not only of the reasons behind the change in detonation velocity, but also of the stages that occur in the build up to type II DDT. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 65-69 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Charges of pentaerythritol tetranitrate (PETN) were impacted by laser-driven flyer plates launched from substrate backed aluminum films. The flyers were produced by single pulses from a Q-switched Nd:YAG laser. The aluminum flyers were between 3 and 5 μm thick, had diameters of 1 mm, and achieved velocities up to 8 km s−1. The stresses were intense but of only nanosecond duration. This falls into an interesting regime since the shock thickness of a few microns is of the order of typical hot-spot sizes and less than the grain size of conventional explosive powders. Ultrafine PETN (∼1 μm grain size) was readily initiated, whereas conventional, 135 sieve PETN with a grain size of 106 μm was not, although limited reaction was observed in some cases. Environmental scanning electron microscopy was carried out to help elucidate the differences in behavior. © 2000 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1749-1753 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation has been carried out into the differences between the deflagration-to-detonation (DDT) process as it occurs in low density [∼30% theoretical maximum density (TMD)] columns of conventional grain size (∼180 μm) pentaerythritol tetranitrate (PETN) and in ultrafine PETN with a grain size ∼1 μm. The principle technique for observing the process utilized charges confined within a steel housing fitted with a polycarbonate slit window. This allowed direct recording of the transition using high speed streak photography. The explosive was thermally ignited using a pyrotechnic mixture with low gaseous emission to minimize any prepressurization of the charge. In addition to the photographic records of the events, the outputs of photodiodes along the length of the column were monitored in order to determine the rate at which the reaction proceeds. The results obtained show that the DDT process in the larger grain PETN at low density was similar in structure to the DDT process at higher densities. In contrast a different mechanism leads to detonation in columns composed of the smaller grain size PETN when packed to densities less than 50% TMD. After ignition hot gases propagate along the column both compacting and igniting material as they pass. After the gases have reached the downstream end of the column, the column continues to burn and the pressure and temperature increase. Some time later initiation takes place at a point along the burning column, and detonation waves propagate in both directions from this point. The detonation waves propagate from the initiation point at speeds that would normally be associated with material compacted to around 60% TMD. The process appears to be in effect a deflagration-to-localized thermal explosion detonation transition. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2012-10-31
    Description: In early stages of various pulmonary diseases, such as emphysema and fibrosis, the change in X-ray attenuation is not detectable with absorption-based radiography. To monitor the morphological changes that the alveoli network undergoes in the progression of these diseases, we propose using the dark-field signal, which is related to small-angle...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 5
    Publication Date: 2014-09-25
    Description: Motivation: There are a number of algorithms to infer causal regulatory networks from time series (gene expression) data. Here we analyse the phenomena of regulator interference, where regulators with similar dynamics mutually suppress both the probability of regulating a target and the associated link strength; for instance, interference between two identical strong regulators reduces link probabilities by ~50%. Results: We construct a robust method to define an interference-corrected causal network based on an analysis of the conditional link probabilities that recovers links lost through interference. On a large real network ( Streptomyces coelicolor , phosphate depletion), we demonstrate that significant interference can occur between regulators with a correlation as low as 0.865, losing an estimated 34% of links by interference. However, levels of interference cannot be predicted from the correlation between regulators alone and are data specific. Validating against known networks, we show that high numbers of functional links are lost by regulator interference. Performance against other methods on DREAM4 data is excellent. Availability and implementation : The method is implemented in R and is publicly available as the NIACS package at http://www2.warwick.ac.uk/fac/sci/systemsbiology/research/software . Contact: N.J.Burroughs@warwick.ac.uk Supplementary information: Supplementary materials are available at Bioinformatics online.
    Print ISSN: 1367-4803
    Electronic ISSN: 1460-2059
    Topics: Biology , Computer Science , Medicine
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  • 6
    Publication Date: 2013-09-11
    Description: Phenotypic plasticity is presumed to be involved in adaptive change toward species diversification. We thus examined how candidate genes underlying natural variation across populations might also mediate plasticity within an individual. Our implementation of an integrative “plasticity space” approach revealed that the root plasticity of a single Arabidopsis accession exposed...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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