245 research outputs found
Characterizing ~submanifolds by -integrability of global curvatures
We give sufficient and necessary geometric conditions, guaranteeing that an
immersed compact closed manifold of class and of
arbitrary dimension and codimension (or, more generally, an Ahlfors-regular
compact set satisfying a mild general condition relating the size of
holes in to the flatness of measured in terms of beta
numbers) is in fact an embedded manifold of class ,
where and . The results are based on a careful analysis of
Morrey estimates for integral curvature--like energies, with integrands
expressed geometrically, in terms of functions that are designed to measure
either (a) the shape of simplices with vertices on or (b) the size of
spheres tangent to at one point and passing through another point of
.
Appropriately defined \emph{maximal functions} of such integrands turn out to
be of class for if and only if the local graph
representations of have second order derivatives in and
is embedded. There are two ingredients behind this result. One of them is an
equivalent definition of Sobolev spaces, widely used nowadays in analysis on
metric spaces. The second one is a careful analysis of local Reifenberg
flatness (and of the decay of functions measuring that flatness) for sets with
finite curvature energies. In addition, for the geometric curvature energy
involving tangent spheres we provide a nontrivial lower bound that is attained
if and only if the admissible set is a round sphere.Comment: 44 pages, 2 figures; several minor correction
Recent Labour Market Trends in the Visegrad Group Countries
The large declines in the Slovak and Czech employment appeared because the countries' GDPs grew smaller while real wages grew bigger. Shorter working hours and limitations on labour productivity that the two countries introduced could not reverse the unfavourable employment trends that occurred during economic downturn.Duże spadki zatrudnienia w Słowacji i Czechach były związane ze słabym wzrostem PKB i silnym wzrostem płac realnych. Redukcje czasu pracy i wydajności pracy nie były w stanie odwrócić niekorzystnych tendencji w zatrudnieniu
Featured Snippets Results in Google Web Search: An Exploratory Study
In this paper authors analyzed 163412 keywords and results with featured
snippets collected from localized Polish Google search engine. A method-ology
for retrieving data from Google search engine was proposed in terms of
obtaining necessary data to study featured snippets. It was observed that
almost half of featured snippets (48%) is taken from result on first ranking
position. Furthermore, some correlations between prepositions and the most
often appearing content words in keywords was discovered. Results show that
featured snippets are often taken from trustworthy websites like e.g.,
Wikipedia and are mainly presented in form of a paragraph. Paragraph can be
read by Google Assistant or Home Assistant with voice search. We conclude our
findings with discussion and research limitations.Comment: 10 pages, 6 tables, accepted to conference ICMarktech'1
Structural and optical properties of as-grown and annealed Alq3 thin films
International audienc
Improved Unsteady RANS Models Applied to Jet Transverse to a Pipe Flow
An unsteady RANS model is developed in order to simulate the complex situations involving both free and bounded flows. This model tuned to catch coherent flow structures is developed both in the k-ε and k-l approaches. The full 3D geometry of a round jet exiting from a reservoir into a pipe has been computed. Periodic conditions are applied in order to compare with an experiments consisting of eight jets exiting in a cross pipe flow. Improvement has been obtained with this URANS turbulence model compared to RANS and good agreement compared with experiments has been obtained. Unsteady phenomena are reproduced by the model and provide more insight into the physical properties of the flow and of the transport of a passive scalar
Topological effects in the thermal properties of knotted polymer rings
The topological effects on the thermal properties of several knot
configurations are investigated using Monte Carlo simulations. In order to
check if the topology of the knots is preserved during the thermal fluctuations
we propose a method that allows very fast calculations and can be easily
applied to arbitrarily complex knots. As an application, the specific energy
and heat capacity of the trefoil, the figure-eight and the knots are
calculated at different temperatures and for different lengths. Short-range
repulsive interactions between the monomers are assumed. The knots
configurations are generated on a three-dimensional cubic lattice and sampled
by means of the Wang-Landau algorithm and of the pivot method. The obtained
results show that the topological effects play a key role for short-length
polymers. Three temperature regimes of the growth rate of the internal energy
of the system are distinguished.Comment: 7 pages, 12 figures, LaTeX + RevTeX. With respect to the first
version, in the second version the text has been improved and all figures are
now in black and whit
Studies of unicellular micro-organisms Saccharomyces cerevisiae by means of Positron Annihilation Lifetime Spectroscopy
Results of Positron Annihilation Lifetime Spectroscopy (PALS) and microscopic
studies on simple microorganisms: brewing yeasts are presented. Lifetime of
ortho - positronium (o-Ps) were found to change from 2.4 to 2.9 ns (longer
lived component) for lyophilised and aqueous yeasts, respectively. Also
hygroscopicity of yeasts in time was examined, allowing to check how water -
the main component of the cell - affects PALS parameters, thus lifetime of o-Ps
were found to change from 1.2 to 1.4 ns (shorter lived component) for the dried
yeasts. The time sufficient to hydrate the cells was found below 10 hours. In
the presence of liquid water an indication of reorganization of yeast in the
molecular scale was observed.
Microscopic images of the lyophilised, dried and wet yeasts with best
possible resolution were obtained using Inverted Microscopy (IM) and
Environmental Scanning Electron Microscopy (ESEM) methods. As a result visible
changes to the surface of the cell membrane were observed in ESEM images.Comment: Nukleonika (2015
Compressive Sensing of Signals Generated in Plastic Scintillators in a Novel J-PET Instrument
The J-PET scanner, which allows for single bed imaging of the whole human
body, is currently under development at the Jagiellonian University. The dis-
cussed detector offers improvement of the Time of Flight (TOF) resolution due
to the use of fast plastic scintillators and dedicated electronics allowing for
sam- pling in the voltage domain of signals with durations of few nanoseconds.
In this paper we show that recovery of the whole signal, based on only a few
samples, is possible. In order to do that, we incorporate the training signals
into the Tikhonov regularization framework and we perform the Principal
Component Analysis decomposition, which is well known for its compaction
properties. The method yields a simple closed form analytical solution that
does not require iter- ative processing. Moreover, from the Bayes theory the
properties of regularized solution, especially its covariance matrix, may be
easily derived. This is the key to introduce and prove the formula for
calculations of the signal recovery error. In this paper we show that an
average recovery error is approximately inversely proportional to the number of
acquired samples
Transparent amorphous zinc oxide thin films for NLO applications
This review focuses on the growth and optical properties of amorphous zinc oxide (ZnO) thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz and glass substrates at temperature equal to 350 K. The amorphous nature of the films was verified by X-ray diffraction. Atomic Force Microscopy was used to evaluate the surface morphology of the films. The optical characteristics of amorphous thin films have been investigated in the spectral range 190–1100 nm. Measurement of the polarized optical properties was shows a high transmissivity (80–99%) and low absorptivity (<5%) in the visible and near infrared regions at different angles of incidence. Linear optical properties were investigated by classic and Time-Resolved Photoluminescence (TRPL) measurements. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. An innovative TRPL technique has enabled the measurement of the photoluminescence decay time as a function of temperature. TRPL measurements reveal a multiexponential decay behavior typical for amorphous thin films. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064 nm in picosecond regime for investigations of the nonlinear optical properties. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications in the optical switching devices based on refractive index changes. Presented spectra confirm high structural and optical quality of the investigated zinc oxide thin films
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