202 research outputs found
Noble Gas Clusters and Nanoplasmas in High Harmonic Generation
We report a study of high harmonic generation from noble gas clusters of
xenon atoms in a gas jet. Harmonic spectra were investigated as a function of
backing pressure, showing spectral shifts due to the nanoplasma electrons in
the clusters. At certain value of laser intensity this process may oppose the
effect of the well-known ionization-induced blueshift. In addition, these
cluster-induced harmonic redshifts may give the possibility to estimate cluster
density and cluster size in the laser-gas jet interaction range.Comment: 5 pages, 4 figure
Computer Tomograph Measurements in Shear and Gravity Particle Flows
The paper reports the recent results obtained on the applicability of cross-sectional digital
imaging method to study particle flow characteristics in 3D particle beds forced to move by
gravity or shear. X-ray CT imaging technique is widely used in medical diagnostics and, during
the last decades, its spatial and temporal resolution has been improved significantly. In this study,
an attempt was made to use this technique for engineering purposes. Two experimental set-ups
with different types of particle flows were investigated using Siemens Somatom Plus type CT
equipment. A series of trials were carried out in a small model hopper with flat bottom and
almost cylindrical side wall slightly deviating from verticality. Non steady-state flow was studied
during the outflow of particulate material from this vessel, through a central hole at the bottom.
Further investigation was fulfilled in a modified Cuette-type shearing device to study steady-state
shear flow. This equipment consisted of an almost cylindrical vessel identical to that used for
gravity flow measurements, and a smaller inner cylinder rotating within this vessel concentrically,
around its vertical axis. The surface of the inner cylinder was notched vertically, i.e.
perpendicularly to the direction of rotation to increase wall friction between the particles and the
cylinder. Almost spherical sucrose granules, also used for gravity flow measurements, were filled
into the gap between the rotating cylinder and the outer wall of the equipment. Movement of
particles took place due to shear, generated within the particle bed. By using X-ray CT technique,
cross-sectional digital images were obtained in every two seconds for both types of particle flows.
For this, the cross-sectional variation of the local Hounsfield density values were measured in a
matrix of 0.1x0.1x2.0 mm space elements. It was proved that the applied non-invasive crosssectional
imaging technique was suitable to distinguish the stationary and moving particle
regions, and by this, to estimate the location of the boundary zone between them
Convergence to a steady state for asymptotically autonomous semilinear heat equations on RN
AbstractWe consider parabolic equations of the formut=Îu+f(u)+h(x,t),(x,t)âRNĂ(0,â), where f is a C1 function with f(0)=0, fâČ(0)<0, and h is a suitable function on RNĂ[0,â) which decays to zero as tââ (hence the equation is asymptotically autonomous). We show that, as tââ, each bounded localized solution uâ©Ÿ0 approaches a set of steady states of the limit autonomous equation ut=Îu+f(u). Moreover, if the decay of h is exponential, then u converges to a single steady state. We also prove a convergence result for abstract asymptotically autonomous parabolic equations
Hospitality, Culture and Regeneration: Urban decay, entrepreneurship and the "ruin" bars of Budapest
This paper considers the relationships between hospitality, culture and urban regeneration through an examination of rom (ruin) venues, which operate in dilapidated buildings in Budapest, Hungary. The paper reviews previous work on culture and urban regeneration in order to locate the role of hospitality within emerging debates. It subsequently interrogates the evolution of the rom phenomenon and demonstrates how, in this context, hospitality thrives because of social and physical decay in urban locations, how operators and entrepreneurs exploit conflicts among various actors involved in regeneration, and how hospitality may be mobilised purposefully in the regeneration process. The paper demonstrates how networked entrepreneurship maintains these operations and how various forms of cultural production are entangled and mobilised in the venuesâ hospitality propositions
Mono- and double carbonylation of aryl iodides with amine nucleophiles in the presence of recyclable palladium catalysts immobilised on a supported dicationic ionic liquid phase
Silica modified with organic dicationic moieties proved to be an excellent support for palladium catalysts used in the aminocarbonylation of aryl iodides. By an appropriate choice of the reaction conditions, the same catalyst could be used for selective mono- or double carbonylations leading to amide and [small alpha]-ketoamide products, respectively. The best catalyst could be recycled for at least 10 consecutive runs with a loss of palladium below the detection limit. By the application of the new support, efficient catalyst recycling could be achieved under mild reaction conditions (under low pressure and in a short reaction time). Palladium-leaching data support a mechanism with dissolution-re-precipitation of the active palladium species
Pre-Excitation Studies for Rubidium-Plasma Generation
The key element in the Proton-Driven-Plasma-Wake-Field-Accelerator (AWAKE)
project is the generation of highly uniform plasma from Rubidium vapor. The
standard way to achieve full ionization is to use high power laser which can
assure the over-barrier-ionization (OBI) along the 10 meters long active
region. The Wigner-team in Budapest is investigating an alternative way of
uniform plasma generation. The proposed Resonance Enhanced Multi Photon
Ionization (REMPI) scheme probably can be realized by much less laser power. In
the following the resonant pre-excitations of the Rb atoms are investigated,
theoretically and the status report about the preparatory work on the
experiment are presented.Comment: 8 pages, 6 figures, submitted to Nucl. Inst. and Meth. in Phys. Res.
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