266 research outputs found
Characteristics of anomalously high multiplicity cosmic ray interactions
Six events with the number of secondaries ranging from 250 to several thousands were registered by an installation consisting of a thin graphite target, above and under which are placed photolayers followed by the usual lead X-ray film and emulsion chambers. Data concerning the number of secondaries and their angular distribution are given. The variance of the angular distribution is compared with data obtained at accelerator energies
Roughness of moving elastic lines - crack and wetting fronts
We investigate propagating fronts in disordered media that belong to the
universality class of wetting contact lines and planar tensile crack fronts. We
derive from first principles their nonlinear equations of motion, using the
generalized Griffith criterion for crack fronts and three standard mobility
laws for contact lines. Then we study their roughness using the self-consistent
expansion. When neglecting the irreversibility of fracture and wetting
processes, we find a possible dynamic rough phase with a roughness exponent of
and a dynamic exponent of z=2. When including the irreversibility,
we conclude that the front propagation can become history dependent, and thus
we consider the value as a lower bound for the roughness exponent.
Interestingly, for propagating contact line in wetting, where irreversibility
is weaker than in fracture, the experimental results are close to 0.5, while
for fracture the reported values of 0.55--0.65 are higher.Comment: 15 pages, 6 figure
Hydrodynamic theory of de-wetting
A prototypical problem in the study of wetting phenomena is that of a solid
plunging into or being withdrawn from a liquid bath. In the latter, de-wetting
case, a critical speed exists above which a stationary contact line is no
longer sustainable and a liquid film is being deposited on the solid.
Demonstrating this behavior to be a hydrodynamic instability close to the
contact line, we provide the first theoretical explanation of a classical
prediction due to Derjaguin and Levi: instability occurs when the outer, static
meniscus approaches the shape corresponding to a perfectly wetting fluid
Asymptotic theory for a moving droplet driven by a wettability gradient
An asymptotic theory is developed for a moving drop driven by a wettability
gradient. We distinguish the mesoscale where an exact solution is known for the
properly simplified problem. This solution is matched at both -- the advancing
and the receding side -- to respective solutions of the problem on the
microscale. On the microscale the velocity of movement is used as the small
parameter of an asymptotic expansion. Matching gives the droplet shape,
velocity of movement as a function of the imposed wettability gradient and
droplet volume.Comment: 8 fig
Quasicontinuum -decay of Zr: benchmarking indirect () cross section measurements for the -process
Nuclear level densities (NLDs) and -ray strength functions
(SFs) have been extracted from particle- coincidences of the
Zr()Zr and Zr()Zr
reactions using the Oslo method. The new Zr SF data, combined
with photonuclear cross sections, cover the whole energy range from ~MeV up to the giant dipole resonance at ~MeV. The wide-range SF data display structures at ~MeV, compatible with a superposition of the spin-flip
resonance and a pygmy resonance. Furthermore, the SF shows a
minimum at ~MeV and an increase at lower -ray
energies. The experimentally constrained NLDs and SFs are shown to
reproduce known () and Maxwellian-averaged cross sections for
Zr using the {\sf TALYS} reaction code, thus serving as a benchmark
for this indirect method of estimating () cross sections for Zr
isotopes.Comment: 10 pages and 9 figure
Partial level density of the n-quasiparticle excitations in the nuclei of the 39< A <201 region
Level density and radiative strength functions are obtained from the analysis
of two-step cascades intensities following the thermal neutrons capture. The
data on level density are approximated by the sum of the partial level
densities corresponding to n quasiparticles excitation. The most probable
values of the collective enhancement factor of the level density are found
together with the thresholds of the next Cooper nucleons pair breaking. These
data allow one to calculate the level density of practically any nucleus in
given spin window in the framework of model concepts, taking into account all
known nuclear excitation types. The presence of an approximation results
discrepancy with theoretical statements specifies the necessity of rather
essentially developing the level density models. It also indicates the
possibilities to obtain the essentially new information on nucleon correlation
functions of the excited nucleus from the experiment.Comment: 29 pages, 8 figures, 2 table
Level density of Fe and low-energy enhancement of -strength function
The MnFe differential cross section is measured at
MeV\@. The Fe level density obtained from neutron evaporation spectra is
compared to the level density extracted from the
FeHe,Fe reaction by the Oslo-type technique.
Good agreement is found between the level densities determined by the two
methods. With the level density function obtained from the neutron evaporation
spectra, the Fe -strength function is also determined from the
first-generation matrix of the Oslo experiment. The good agreement
between the past and present results for the -strength function
supports the validity of both methods and is consistent with the low-energy
enhancement of the strength below MeV first discovered by the
Oslo method in iron and molybdenum isotopes.Comment: 7 pages, 5 figure
Understanding Human and Ecosystem Dynamics in the Kola Arctic : A Participatory Integrated Study
The Lake Imandra watershed is located in one of the most developed regions in the Arctic - the Kola Peninsula of Russia. Approximately 300 000 people live on the roughly 27 000 km² watershed, making it one of the most densely populated areas of the Arctic. Most of the people are involved in large-scale mineral extraction and processing and the infrastructure needed to support this industry. This paper reports the results of a pilot project staged for the Lake Imandra watershed that has put human dynamics within the framework of ecosystem change to integrate available information and formulate conceptual models of likely future scenarios. The observation period is one of both rapid economic growth and human expansion, with an overall economic decline in the past decade. We are applying the Participatory Integrated Assessment (PIA) approach to integrate information, identify information gaps, generate likely future scenarios, and link scientific findings to the decision-making process. We found an increasingly vulnerable human population in varying states of awareness about their local environment and fully cognizant of their economic troubles, with many determined to attempt maintenance of relatively high population densities in the near future even as many residents of northern Russia migrate south. A series of workshops have involved the citizens and local decision makers in an attempt to tap their knowledge of the region and to increase their awareness about the linkages between the socioeconomic and ecological components.Le bassin hydrographique du lac Imandra est situé dans l'une des régions les plus développées de l'Arctique, soit la presqu'île de Kola, en Russie. Près de 300 000 personnes vivent dans la zone du bassin qui couvre environ 27 000 km², ce qui en fait l'une des régions les plus peuplées de l'Arctique. La plupart des habitants travaillent dans l'extraction et le traitement miniers à grande échelle ainsi que dans l'infrastructure qui soutient cette industrie. Le présent article rapporte les résultats d'un projet pilote mis sur pied pour le bassin du lac Imandra, projet qui a placé la dynamique humaine dans le cadre du changement des écosystèmes, afin d'intégrer l'information disponible et de formuler des modèles conceptuels de scénarios probables dans l'avenir. La période d'observation en est une à la fois de croissance économique et d'expansion démographique rapides, suivie d'un déclin général au cours de la dernière décennie. On a recours à la méthode d'évaluation participative intégrée (EPI) pour intégrer l'information, y dégager des lacunes, générer des scénarios probables dans l'avenir et établir un lien entre résultats de la recherche et processus décisionnel. On a trouvé qu'il y avait une population humaine de plus en plus vulnérable qui était sensibilisée à divers degrés aux problèmes locaux de l'environnement et pleinement consciente des difficultés économiques, population dont une bonne part était fermement décidée à tenter de maintenir à brève échéance des densités de population relativement élevées, alors même que les résidents du nord de la Russie migrent en grand nombre vers le Sud. On a tenu une série d'ateliers avec citoyens et décideurs locaux pour chercher à capter leurs connaissances de la région et à accroître leur sensibilisation aux liens existant entre les composantes socio-économiques et écologiques
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