5,804 research outputs found
Maximum occupation number for composite boson states
One of the major differences between fermions and bosons is that fermionic
states have a maximum occupation number of one, whereas the occupation number
for bosonic states is in principle unlimited. For bosons that are made up of
fermions, one could ask the question to what extent the Pauli principle for the
constituent fermions would limit the boson occupation number. Intuitively one
can expect the maximum occupation number to be proportional to the available
volume for the bosons divided by the volume occupied by the fermions inside one
boson, though a rigorous derivation of this result has not been given before.
In this letter we show how the maximum occupation number can be calculated from
the ground-state energy of a fermionic generalized pairing problem. A very
accurate analytical estimate of this eigenvalue is derived. From that a general
expression is obtained for the maximum occupation number of a composite boson
state, based solely on the intrinsic fermionic structure of the bosons. The
consequences for Bose-Einstein condensates of excitons in semiconductors and
ultra cold trapped atoms are discussed.Comment: 4 pages, Revte
Design of a Microstructured System for Homogenization of Dairy Products with High Fat Content
High pressure homogenization of dairy products is today state of the art but limited by the fat content (max 17 vol.-%). This article describes the development of a novel simultaneous homogenization and mixing (SHM) valve which allows homogenization of dairy products with a fat content of up to 42 vol.-%. The challenging task of homogenizing dairy products with high fat content is to stabilize disrupted fat droplets especially against extensive aggregation. Aggregation and coalescence rates could be significantly reduced by a new microstructured valve allowing the emulsifier-containing phase to be injected directly into the zone of droplet disruption
Hydrodynamic object recognition using pressure sensing
Hydrodynamic sensing is instrumental to fish and some amphibians. It also represents, for underwater vehicles, an alternative way of sensing the fluid environment when visual and acoustic sensing are limited. To assess the effectiveness of hydrodynamic sensing and gain insight into its capabilities and limitations, we investigated the forward and inverse problem of detection and identification, using the hydrodynamic pressure in the neighbourhood, of a stationary obstacle described using a general shape representation. Based on conformal mapping and a general normalization procedure, our obstacle representation accounts for all specific features of progressive perceptual hydrodynamic imaging reported experimentally. Size, location and shape are encoded separately. The shape representation rests upon an asymptotic series which embodies the progressive character of hydrodynamic imaging through pressure sensing. A dynamic filtering method is used to invert noisy nonlinear pressure signals for the shape parameters. The results highlight the dependence of the sensitivity of hydrodynamic sensing not only on the relative distance to the disturbance but also its bearing
Progress of the Felsenkeller shallow-underground accelerator for nuclear astrophysics
Low-background experiments with stable ion beams are an important tool for
putting the model of stellar hydrogen, helium, and carbon burning on a solid
experimental foundation. The pioneering work in this regard has been done by
the LUNA collaboration at Gran Sasso, using a 0.4 MV accelerator. In the
present contribution, the status of the project for a higher-energy underground
accelerator is reviewed. Two tunnels of the Felsenkeller underground site in
Dresden, Germany, are currently being refurbished for the installation of a 5
MV high-current Pelletron accelerator. Construction work is on schedule and
expected to complete in August 2017. The accelerator will provide intense, 50
uA, beams of 1H+, 4He+, and 12C+ ions, enabling research on astrophysically
relevant nuclear reactions with unprecedented sensitivity.Comment: Submitted to the Proceedings of Nuclei in the Cosmos XIV, 19-24 June
2016, Niigata/Japa
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Roll-to-roll manufacturing of micropatterned adhesives by template compression
For the next generation of handling systems, reversible adhesion enabled by micropatterned dry adhesives exhibits high potential. The versatility of polymeric micropatterns in handling objects made from various materials has been demonstrated by several groups. However, specimens reported in most studies have been restricted to the laboratory scale. Upscaling the size and quantity of micropatterned adhesives is the next step to enable successful technology transfer. Towards this aim, we introduce a continuous roll-to-roll replication process for fabrication of high-performance, mushroom-shaped micropatterned dry adhesives. The micropatterns were made from UV-curable polyurethane acrylates. To ensure the integrity of the complex structure during the fabrication process, flexible templates were used. The compression between the template and the wet prepolymer coating was investigated to optimize replication results without structural failures, and hence, to improve adhesion. As a result, we obtained micropatterned adhesive tapes, 10 cm in width and several meters in length, with adhesion strength about 250 kPa to glass, suitable for a wide range of applications. © 2018 by the authors
Slow dynamics near glass transitions in thin polymer films
The -process (segmental motion) of thin polystyrene films supported
on glass substrate has been investigated in a wider frequency range from
10 Hz to 10 Hz using dielectric relaxation spectroscopy and thermal
expansion spectroscopy. The relaxation rate of the -process increases
with decreasing film thickness at a given temperature above the glass
transition. This increase in the relaxation rate with decreasing film thickness
is much more enhanced near the glass transition temperature. The glass
transition temperature determined as the temperature at which the relaxation
time of the -process becomes a macroscopic time scale shows a distinct
molecular weight dependence. It is also found that the Vogel temperature has
the thickness dependence, i.e., the Vogel temperature decreases with decreasing
film thickness. The expansion coefficient of the free volume is
extracted from the temperature dependence of the relaxation time within the
free volume theory. The fragility index is also evaluated as a function of
thickness. Both and are found to decrease with decreasing film
thickness.Comment: 9 pages, 7 figures, and 2 table
Obesity: A Biobehavioral Point of View
Excerpt: If you ask an overweight person, “Why are you fat?’, you will, almost invariably, get the answer, “Because 1 eat too much.” You will get this answer in spite of the fact that of thirteen studies, six find no significant differences in the caloric intake of obese versus nonobese subjects, five report that the obese eat significantly less than the nonobese, and only two report that they eat significantly more
High Pressure Insulator-Metal Transition in Molecular Fluid Oxygen
We report the first experimental evidence for a metallic phase in fluid
molecular oxygen. Our electrical conductivity measurements of fluid oxygen
under dynamic quasi-isentropic compression show that a non-metal/metal
transition occurs at 3.4 fold compression, 4500 K and 1.2 Mbar. We discuss the
main features of the electrical conductivity dependence on density and
temperature and give an interpretation of the nature of the electrical
transport mechanisms in fluid oxygen at these extreme conditions.Comment: RevTeX, 4 figure
Seroprevalence of anti-Yersinia antibodies in meat juice samples of pigs
This investigation was intended to provide actual data on the seroprevalence of Yersinia antibodies in German slaughtering pigs. The recomB lot western blot assay based on five recombinantly produced Yersinia Outer Proteins (Yap) is well evaluated for human Yersiniosis and proved to be also valuable for the detection of porcine anti-Yap antibodies. 970 out of 1014 meat juice samples collected in 145 Bavarian pig farms contained anti-Yap antibodies. As other animal pathogens like Salmonella express the proteins of secretion apparatus III as well, we propose that only blots with three and more detectable signals should be considered as positive. This means that at least 45.2% of the pigs and 82% of the pig farms respectively had a previous history of Yersinia infection. Yersinia infection in pigs is still a severe hygienical problem. Furtheron, pigs may not only be asymptomatic carriers but may also suffer from disease leading to economical losses
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