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  • Springer  (27)
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  • 1995-1999  (27)
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  • Physics  (27)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Earth, moon and planets 82-83 (1998), S. 149-166 
    ISSN: 1573-0794
    Keywords: Comet ; comet ejection ; Leonids ; meteor ; meteor shower ; meteoroid ; model predictions ; orbital dynamics ; radiation pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A simple model is described that predicts the time of occurrences and peak activity of Leonid shower outbursts. It is assumed that the ejection speeds of escaping particles at each return of the parent comet near perihelion are very small, but solar radiation pressure acting differently on different particles causing a spread of particles into different period orbits. Earlier papers predicted the position of the resulting dust trails. This paper sets forth to better predict the strength of the expected outbursts by considering the role of non-isotropic effects in the interaction with the solar radiation on the dispersion of particles away from the dust trail center. This paper determines the approximate magnitude of the relevant effects. Predictions for the next few years are presented that include such considerations, for reasonable assumptions of particle properties. For example, earlier predictions for the 1999 storm of ZHR = 6,000−7,000 are now reduced by a factor of two, which is in better agreement with the observed ZHR ∼ 4,000. The success of the technique, when applied to historic meteor storms and outbursts without need of additional free parameters, lends confidence to the soundness of the underlying model and to its application for future predictions. We predict that the best encounters of this return of the parent-comet will occur in the years 2001 and 2002.
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  • 2
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    Earth, moon and planets 82-83 (1998), S. 325-350 
    ISSN: 1573-0794
    Keywords: Asteroid ; bolide ; chemistry ; comet ; cosmic dust ; fireball ; interplanetary dust particle (IDP) ; meteorite ; meteor ; mineralogy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The bulk density and bulk porosity of IDPs and various meteorite classes show that protoplanet accretion and evolution were arrested at different stages as a function of parent body modification. The collected IDPs, micrometeorites and meteorites are aggregates of different structural entities that were inherited from the earliest times of solar system evolution. These structural entities and the extent of parent body lithification will determine the material strength of the meteoroids entering the Earth's atmosphere. There is a need for measurements of the material strength of collected extraterrestrial materials because they will in part determine the nature of the chemical interactions of descending meteors and fireballs in the atmosphere. High—precision determinations of meteor and fireball compositions are required to search for anhydrous, carbon-rich proto-CI material that has survived in the boulders of comet nuclei.
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  • 3
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    Earth, moon and planets 82-83 (1998), S. 391-398 
    ISSN: 1573-0794
    Keywords: Leonids 1999 ; meteor ; meteor physics ; photon counting imager ; ultraviolet
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract During the 1999 Leonid meteor storm, a camera with a UV sensitive image intensifier and CCD readout (ICCD), was operated at the Wise Observatory in Mitzpe Ramon, Israel. The photocathode spectral response, together with the transmittance of the atmosphere, limited the sensitivity to a narrow band around 320 nm. The aim was to obtain quantitative information on emitted radiance in this band, for comparison with recordings of the same tracks in other wavelengths. The field of view of 7°.2 × 5°.7 was pointed to the East at about 60° elevation and the video recorded from 21 until 03 UT, Nov. 18, 1999. At least five clear images of meteor tracks were recorded, and compared with the signals from known stars. It was concluded that the brightest track gave an estimated monochromatic magnitude at 320 nm peaking at ∼ −4. Some of the peculiarities of astronomical observation with a photon-counting imager are discussed.
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  • 4
    ISSN: 1573-0794
    Keywords: Comet dust trial ; dispersion ; Leonids 1999 ; meteor ; meteor orbit ; meteor trajectory ; orbital dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Photographic multi-station observations of 47 Leonid meteors are presented that were obtained from two ground locations in Spain during the 1999 meteor storm. We find an unresolved compact cluster of radiants at α = 153.67 ± 0.05 and δ = 21.70 ± 0.05 for a mean solar longitude of 235.282 (J2000). The position is identical to that of the Nov. 17/18 outburst of 1998, which implies that both are due to comet 55P/Tempel-Tuttle's ejecta from 1899. We also find a halo which contains about 28% of all meteors. The spatial distribution of radiant positions appears to be Lorentzian, with a similar fraction of meteors in the profile wings as the meteor storm activity curve.
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  • 5
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    Earth, moon and planets 82-83 (1998), S. 457-470 
    ISSN: 1573-0794
    Keywords: Fireball ; leonids 1999 ; lower thermosphere ; mesosphere ; meteor ; persistent train ; winds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The atmospheric trajectory is calculated of a particularly well studied fireball and train during the 1999 Leonid Multi-Instrument Aircraft Campaign. Less than a minute after the meteor's first appearance, the train curves into a "2"-shape, which persisted until at least 13 minutes after the fireball. We conclude that the shape results because of horizontal winds from gravity waves with a scale height of 8.3 km at 79–91 km altitude, as well as a westerly wind gradient with altitude. In addition, there is downward drift that affects the formation of loops in the train early on.
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  • 6
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    Earth, moon and planets 82-83 (1998), S. 471-488 
    ISSN: 1573-0794
    Keywords: Airglow ; chemistry ; dynamics ; Leonids 1998 ; lower thermosphere ; mesosphere ; meteor ; persistent train
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The dynamical evolution of the persistent train of a bright Leonid meteor was examined for evidence of the source of the luminosity and the physical conditions in the meteor path. The train consisted of two parallel somewhat diffuse luminous tracks, interpreted as the walls of a tube. A general lack of wind shear along the trail allowed these structures to remain intact for nearly 200 s, from which it was possible to determine that the tubular structure expanded at a near constant 10.5 ms−1, independent of altitude between 86 and 97 km. An initial fast decrease of train intensity below 90 km was followed by an increase in intensity and then a gradual decrease at longer times, whereas at high altitudes the integrated intensity was nearly constant with time. These results are compared to a model that describes the dynamical evolution of the train by diffusion, following an initial rapid expansion of the hot gaseous trail behind the meteoroid. The train luminosity is produced by O (1S) emission at 557 nm, driven by elevated atomic O levels produced by the meteor impact, as well as chemiluminescent reactions of the ablated metals Na and Fe with O3. Ozone is rapidly removed within the train, both by thermal decomposition and catalytic destruction by the metallic species. Hence, the brightest emission occurs at the edge of the train between outwardly diffusing metallic species and inwardly diffusing O3. Although the model is able to account plausibly for a number of characteristic features of the train evolution, significant discrepancies remain that cannot casily be resolved.
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  • 7
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    Earth, moon and planets 82-83 (1998), S. 47-56 
    ISSN: 1573-0794
    Keywords: Ground-based observations ; Leonids 1999 ; meteor ; meteor shower ; meteor storm ; Multi-instrument Aircraft Campaign
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Ground-based meteor observations from Israel were coordinated with the 1999 Leonid Multi-Instrument Aircraft Campaign. For the first time, a large concentration of observational means for meteor astronomy was gathered in a small country. Many observations were specifically keyed to the peak of the Leonid activity, when the predictions indicated a possibly strong storm component that would be ideally observable from the Middle East. This unique opportunity allowed us to forge collaborations with the amateur astronomers community and with high-technology industries, who contributed unique observational means. The elaborate preparations led to an unprecedented success, yielding unique observational results. Some of these are included in these proceedings, but their interpretation and incorporation in a coherent picture of the Leonid meteors is still to come.
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  • 8
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    Journal of superconductivity 11 (1998), S. 641-648 
    ISSN: 1572-9605
    Keywords: Superconductivity ; Ag composites ; percolation ; granularity ; weak-link resistivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Temperature-dependent electrical resistivity in a set of YBa2Cu3O7−x /Ag composites, all prepared under an identical sintering schedule, is analyzed to extract granularity information. The weak-link resistivity ρ wl across the grain boundaries and the percolation factor α arising due to current frustration caused by misalignment of anisotropic grains and sample defects such as voids and cracks are estimated from the residual resistivity ρ0 and the temperature coefficient of resistivity dρ/dT. Variation of these parameters with Ag vol.% quantifying the extent of granularity indicates that granularity in the composites decreases and their electrical characteristics tend to be identical to that of Ag-free YBa2Cu3O7−x single crystals and epitaxial thin films as Ag vol.% approaches a value where onset of current percolation occurs through Ag channels. The increased α and decreased ρ wl observed at higher Ag vol.% explains the larger grains in the composites with narrow size distribution.
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  • 9
    ISSN: 1572-9605
    Keywords: Superconductivity ; La2.5Y0.5CaBa3(Cu0.88Fe0.12)7O z ; compensated oxide ; magnetic pair breaking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The structural and superconducting properties of single-phase La2.5−y Y0.5Ca1+y Ba3 (Cu0.88Fe0.12)7O z (LYCaBCuFe) (y= 0.0−1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T c R=0 shows a marginal increase from 31 K to 37 K for y = 0.0−0.21 and thereafter it decreases with increasing y leading to zero T c R=0 at y ≥ 0.84. This shows that the suppression of T c from 80 K to 31 K by Fe doping at x = 0.12 La2.5Y0.5CaBa3(Cu1−x Fe x )7O z cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.
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  • 10
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    Journal of superconductivity 11 (1998), S. 707-712 
    ISSN: 1572-9605
    Keywords: Superconductivity ; antiferromagnetic order ; ErNi2Bi2C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Upper critical field and penetration depth of superconducting ErNi2B2C borocarbide thin films have been investigated and compared with the same properties of SmRh4B4 films. The coexistence of superconductivity and antiferromagnetic order is described through Machida's theory. A fairly satisfactory description of the experimental results is obtained.
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  • 11
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    Journal of statistical physics 93 (1998), S. 943-964 
    ISSN: 1572-9613
    Keywords: Superconductivity ; macroscopic quantum phenomena ; mesoscopic systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider the problem of two capacitively coupled Josephson junction arrays made of ultrasmall junctions. Each one of the arrays can be in the semiclassical or quantum regimes, depending on its physical parameter values. The former case is dominated by a Cooper-pair superfluid, while the quantum case is dominated by dynamic vortices leading to an insulating behavior. We first consider the limit when both arrays are in the semiclassical limit, and next the case when one array is quantum and the other semiclassical. We present WKB and mean-field theory results for the critical temperature of each array when both are in the semiclassical limit. When one array is in the semiclassical regime and the other one is in the quantum-fluctuations-dominated regime, we derive a duality transformation between the charge and vortex-dominated arrays that involves a gauge vector field which is proportional to the site coupling capacitance between the arrays. The system considered here has been fabricated and we make some predictions as to possible experimentally measurable quantities that could be compared with theory.
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  • 12
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    Earth, moon and planets 82-83 (1998), S. 209-220 
    ISSN: 1573-0794
    Keywords: Leonid MAC ; meteor ; meteor flux ; Zenithal Hourly Rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We operated identical Low-Light level TV cameras to observe the Leonid 1999 meteor storm, both from a ground-based station in Southern Spain and from the ARIA airplane of the Leonid Multi-Aircraft Campaign. The ground-based camera was pointed to a fixed position about 50° from the zenith, the airborne camera was pointed through a window at 75° from the zenith. During the peak of the Leonid storm, the two cameras were located between 10° and 20° apart in geographical longitude. The recorded meteor numbers differed by a factor 5.3 ± 0.4, the airborne camera recording the higher rates. This is much more than what could be expected from the geographical separation of the cameras. The different elevation angles and altitudes of the cameras can explain this. Pointing the camera low to the horizon results in a much larger volume in the atmosphere which is observed, resulting in higher meteor count rates. However, the meteors are on average much further away than when observing high above the horizon. The atmospheric extinction reduces the brightness of the meteors, effectively reducing the count rates. For two ground-based cameras, these two effects are expected to compensate. Due to the high altitude of the airborne camera, the increasing effect of the count rate dominates. We set up an atmospheric extinction model taking into account Rayleigh scattering that quantitatively explains the number difference. Using the same model, we predict number differences for cameras observing from the same location, but pointed at different elevation angles. For typical observing conditions, neglecting this effect can result in differences up to a factor of 10 in the derived meteor numbers.
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  • 13
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    Earth, moon and planets 82-83 (1998), S. 249-256 
    ISSN: 1573-0794
    Keywords: Flux ; Leonids 1999 ; Liquid Mirror Telescope ; meteor ; meteor shower ; satellite impact hazard
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The November 1999 Leonid meteor shower was videotaped with a low light level camera from the grounds of the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) in Houston, Texas. Additionally, observations of the Leonids were recorded both digitally with the Liquid Mirror Telescope (LMT) and with a low light level camera at the JSC Observatory near Cloudcroft, New Mexico. The tapes were analyzed using a computer-automated meteor analysis system developed at JSC. These results were used to form estimates of the Leonid mass-distribution. These estimates were compared to a Leonid mass distribution model used by NASA in risk assessment calculations associated with Space Shuttle missions. The observed data agrees favorably with the NASA model in the 0.002 to 0.02 milligram range (based upon the LMT observations) and in the 0.02 to 0.2 gram range (based upon the low light level camera observations). This comparison supports the continued use of this model.
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  • 14
    ISSN: 1573-0794
    Keywords: Comet ; comet: 55P/Tempel-Tuttle ; dust trail ; flux ; Leonids 1999 ; Lorentz profile ; meteor ; meteor storm ; predictions ; satellite impact hazard ; observing techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A new hybrid technique of visual and video meteor observations was developed to provide high precision near real-time flux measurements for satellite operators from airborne platforms. A total of 33,000 Leonids, recorded on video during the 1999 Leonid storm, were watched by a team of visual observers using a video head display and an automatic counting tool. The counts reveal that the activity profile of the Leonid storm is a Lorentz profile. By assuming a radial profile for the dust trail that is also a Lorentzian, we make predictions for future encounters. If that assumption is correct, we passed 0.0003 AU deeper into the 1899 trailet than expected during the storm of 1999 and future encounters with the 1866 trailet will be less intense than predicted elsewhere.
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  • 15
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    Earth, moon and planets 82-83 (1998), S. 221-247 
    ISSN: 1573-0794
    Keywords: Clustering ; flux ; fragmentation ; Leonids 1999 ; meteor ; meteoroid ; optimal video pointing ; satellite impact hazard ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A detailed meteor flux analysis is presented of a seventeen-minute portion of one videotape, collected on November 18, 1999, during the Leonid Multi-instrument Aircraft Campaign. The data was recorded around the peak of the Leonid meteor storm using an intensified CCD camera pointed towards the low southern horizon. Positions of meteors on the sky were measured. These measured meteor distributions were compared to a Monte Carlo simulation, which is a new approach to parameter estimation for mass ratio and flux. Comparison of simulated flux versus observed flux levels, seen between 1:50:00 and 2:06:41 UT, indicate a magnitude population index of r = 1.8 ± 0.1 and mass ratio of s = 1.64 ± 0.06. The average spatial density of the material contributing to the Leonid storm peak is measured at 0.82 ± 0.19 particles per square kilometer per hour for particles of at least absolute visual magnitude +6.5. Clustering analysis of the arrival times of Leonids impacting the earth's atmosphere over the total observing interval shows no enhancement or clumping down to time scales of the video frame rate. This indicates a uniformly random temporal distribution of particles in the stream encountered during the 1999 epoch. Based on the observed distribution of meteors on the sky and the model distribution, recommendations are made for the optimal pointing directions for video camera meteor counts during future ground and airborne missions.
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  • 16
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    Earth, moon and planets 82-83 (1998), S. 399-428 
    ISSN: 1573-0794
    Keywords: Afterglow ; debris ; dust ; H ; meteor ; persistent train ; spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two video spectra of a meteoric afterglow were obtained for the first time during the 1999 Leonid aircraft campaign. The train was produced by a −13 magnitude Leonid fireball at a relatively low height between 91-75 km. The meteor spectrum has a strong hydrogen emission, proportional to 10–20 II atoms per one Fe atom The train spectrum consisted of a red continuum, yellow continuum, and about 50 atomic lines between 3700–9000 Å. The yellow continuum, possibly due to NO2, was also detected in the persistent train. The red continuum is interpreted as a thermal radiation of dust from meteoric debris at about 1400 K. Evidence for secondary ablation is found in the afterglow. The atomic lines decayed within seconds of the meteor. The lines of Fe I, Mg I, Na I, Ca I, Ca II, Cr I, Mn I, K I, and possibly Al I were present in the glow together with the 5577 Å forbidden O I line. The gas temperature in the train was close to 5000 K at the beginning and decayed to 1200 K within two seconds. However, thermal equilibrium was not satisfied for all populated levels.
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  • 17
    ISSN: 1573-0794
    Keywords: Ablation ; airglow ; Leonids 1999 ; lower thermosphere ; O2 ; OH ; mesosphere ; meteor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract As part of the 1999 Leonid MAC Campaign an extensive set of infrared (1.00 – 1.65 µm) airglow spectra and imaging data were collected from onboard the USAF FISTA aircraft. These data will permit a detailed study of the upper atmospheric conditions over a several day period centered on the Leonid meteor storm of 17/18 November, 1999 as well as during the meteor storm itself. We describe initial results of a spectral analysis that indicates a small but significant enhancement in the OH airglow emission during the peak of the storm but we cannot yet be certain of a cause and effect relationship. No similar systematic enhancement was observed in the O2 (1.27 µm) airglow emission recorded with the same instrument.
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  • 18
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    Earth, moon and planets 82-83 (1998), S. 265-276 
    ISSN: 1573-0794
    Keywords: Flux ; Leonids 1999 ; meteor ; meteor shower ; radar ; radio forward ; meteor scatter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Results of joint campaigns of the Leonid meteoroid stream performed throughout the 1995–1999 years by the BLM (Bologna-Lecce-Modra) forward scatter (FS) radar, are shown and compared with visual observations. In 1998 and 1999 at both the stations of Lecce and Modra, the total reflection time is shown to give a better indication of the Leonid activity. For the two years the trends of the reflection time and of the overdense echoes (T 〉 8 sec duration) exhibit multiple peaks just at the maximum of the shower activity. In 1999, strong evidence of a short and extremely intense activity at the nodal longitude of the parent comet (November 18, 02h UT), is deduced from the radio data. The Leonid display is shown to follow a Gaussian activity profile and the particle density/stream width relationship is found to match observations of IRAS dust trails of comparable short-period comets. The mass distribution exponent shows a representation of an extended component of larger particles (brighter Leonids) in 1996 and especially in 1998. Average mass and population indices of radio and visual data show a similar trend in the 1995–1999 period.
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  • 19
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    Earth, moon and planets 82-83 (1998), S. 295-304 
    ISSN: 1573-0794
    Keywords: Leonids 1998 ; meteor ; meteor shower ; meteoroid ; orbits ; video
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Double-station video observations of the 1998 Leonid shower from China resulted in 55 trajectories and orbits of meteoroids in the visual magnitude range from +0 to +6 magn. The 1998 Leonid outburst consisted of a relatively long duration shower that was rich in large meteoroids and peaked in the night of November 16/17, and an outburst of shorter duration that was rich in smaller meteoroids and peaked in the next night. The average orbit obtained during the first night agrees well with that from photographic observations. During the second night, the combined set of video and photographic observations shows temporal variation in the radiant distribution. This adds to the earlier discovery of an unusual asymmetric flux profile. In addition, the radiant distribution is shown to be mass dependent. The data suggest the presence of at least two merged dust components or a single dust component perturbed by planetary encounters.
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  • 20
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    Journal of superconductivity 11 (1998), S. 615-639 
    ISSN: 1572-9605
    Keywords: Superconductivity ; rare-earths
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Using only two principles: (i) high-temperature superconductivity requires hypercharged oxygen, and (ii) the superconducting condensates are located in those parts of the crystal structures where they are unaffected by magnetic pair breaking, we are able to explain why certain rare-earth ions R are compatible with superconductivity and others are not, in the compounds RBa2Cu3O7, RBa2Cu4O8, RBa2Cu2NbO8, R2 − z Ce z CuO4, and R2 − z Ce z Sr2Cu2NbO10. Various defects are proposed as having central roles in the superconductivity or the suppression of superconductivity in these compounds. Many experiments for testing this physical picture are suggested.
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  • 21
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    Journal of superconductivity 11 (1998), S. 1-4 
    ISSN: 1572-9605
    Keywords: Superconductivity ; magnets ; cryogenics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A review of U.S. Navy efforts in superconducting technology is given. Programs include development of superconducting magnets for motors in ship propulsion systems and to generate magnetic moments in mine sweeping systems. A program to develop superconducting quantum interference devices (SQUIDs) for detection of mines and buried ordnance has successfully been demonstrated. In electronic applications, superconducting filters, resonators, and antennae are being developed for radar, communication, and space systems. Concurrent with these superconductivity programs are efforts to improve the efficiency, reliability, and affordability of refrigeration systems.
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  • 22
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    Journal of superconductivity 11 (1998), S. 339-345 
    ISSN: 1572-9605
    Keywords: Superconductivity ; non-Fermi liquid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The critical temperature of a superconductor with a non-Fermi liquid ground state has been calculated. The density of states has two different forms and is energy dependent. The critical values of the coupling factor λ were calculated. The constant density of states results are obtained as particular cases. These results are an extension of the work done by Grosu et al. [Phys. Rev. B 56, 8298 (1997)].
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  • 23
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    Journal of superconductivity 11 (1998), S. 123-124 
    ISSN: 1572-9605
    Keywords: Superconductivity ; Nitrates ; Oxycarbonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have synthesised a series of compounds in both the (PbTl)Sr4Cu2O7(CO3)1−y(NO3)y (0.1≤y≤0.5) and TlSr2Ba2Cu2O7(CO3)1−y(NO3)y (0.1≤y≤0.2) systems. We report the synthesis conditions of these materials, an X-ray diffraction analysis of their structure and the changes induced in superconducting behaviour produced by the introduction of nitrate groups into the starting composition.
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  • 24
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    Journal of superconductivity 11 (1998), S. 129-132 
    ISSN: 1572-9605
    Keywords: Superconductivity ; TIPbSrCaCuO ; thin films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Thin films of (Tl,Pb)Sr2Ca0.8Y0.2Cu2O7, and (Tl,Pb)Sr2CuO5 can be grown in a single step process which involves sputter deposition from a mixed oxide target and simultaneous thermal evaporation of Tl2O. The use of a radiant heater has allowed extension of this in situ deposition process to full LaAlO3 and NdGaO3 wafers. Variations in the composition of the deposited film is 〈 4% across a 50 mm wafer while the thickness uniformity is ≍ 8%. The highest transition temperature for a (Tl,Pb)Sr2Ca0.8Y0.2 Cu2O7 film thus far is 83 K. The RMS surface roughness of (Tl,Pb)Sr2CuO5 films is uniform across the wafer and approximately 1% of the film thickness for films 20 to 100 nm thick.
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  • 25
    ISSN: 1572-9605
    Keywords: Superconductivity ; mercury ; chromium ; synthesis ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report preliminary results concerning the synthesis and structural characterisation of the chromium stabilised 1201 phases: Hg1−xCrxSr2CuO4+δ. A systematic study of the formation of phases in this system has been undertaken, together with a combined powder neutron and synchrotron x-ray diffraction study, to address the issue of chromium clustering and ordering in this system.
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  • 26
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    Journal of superconductivity 11 (1998), S. 169-171 
    ISSN: 1572-9605
    Keywords: Superconductivity ; Alkali-doping ; Hg-based Cuprates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The effect of Na- and Li-doping in Hg-based cuprates has been studied. It has been found that superconductivity can be achieved in samples containing small amount of Na or Li. While little change is found in the crystalline structure, the formed superconducting phase have the onset Tc typically above 140 K and zero-resistance Tc up to 136K. More interestingly, the processing temperature for the doped Hg-1223 can be reduced significantly to near 700 °C which is promising for thin films growth on many technologically compatible substrates.
    Type of Medium: Electronic Resource
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  • 27
    ISSN: 1572-9605
    Keywords: Superconductivity ; thin film ; columnar defect ; pinning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The mixed state Hall effect has been studied in high quality HgBa2CaCu2O6+δ thin films while the pinning strength is modified by the irraddition of columnar defects. It has been shown that the pinning strength can be significantly improved by columnar defects. The sign reversal in Hall resistivity is found to be nearly independent of pinning while the scaling behavior between Hall resistivity (ρxy) and longitudinal resistivity (ρxx) is influenced by pinning. The exponent β in the scaling law β xy ∼ β xy β decrease from 1.8 ± 0.1 to 1.5 ± 0.1 as pinning is enhanced. This results suggest that the sign reversal and the scaling are unrelated, and pinning is not the mechanism of the sign reversal.
    Type of Medium: Electronic Resource
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