Length Scale of Free Stream Turbulence and Its Impact on Bypass Transition in a Boundary Layer

An experimental investigation was carried out to study the turbulent flow over a flat plate in a subsonic wind tunnel. The enhanced level of turbulence was generated by five wicker grids with square meshes, and different parameters (diameter of the grid rod d = 0.3 to 3 mm and the grid mesh size M = 1 to 30 mm). The velocity of the flow was measured by means of a 1D hot-wire probe, suitable for measurements in a boundary layer. The main aim of the investigation was to explore the influence of the free stream turbulence length scale on the onset of laminar-turbulent bypass transition in a boundary layer on a flat plate. For this purpose, several transition correlations were presented, including intensity and length scales of turbulence, both at the leading edge of a plate and at the onset of transition. The paper ends with an attempt to create a correlation, which takes into account a simultaneous impact of turbulence intensity and turbulence scale on the boundary layer transition. To assess the isotropy of turbulence, the skewness factor of the flow velocity distribution was determined. Also several longitudinal scales of turbulence were determined and compared (integral scale, dissipation scale, Taylor microscale and Kolmogorov scale) for different grids and different velocities of the mean flow U = 4, 6, 10, 15, 20 m/s

POLISH TOWNS AND THE CHANGES IN THEIR AREAS AND POPULATION DENSITIES

DOI: 10.2478 Available on-line at: http://www.bulletinofgeography.umk.pl http://versita.com/bgssThis article presents the spatial and population density changes in Polish towns in the years 1960–2003. The assumed time frame allowed identifying area changes for a complete set of towns in different socio-economic conditions: the period of intense industrialisation, the economic crisis of the 1980s, the period of economic transition and finally in the years of a market economy. The investigation revealed that the trend shown by changes and the size of a town as measured by the number of its population are distinctly interrelated. It also demonstrated a much stronger dynamics of changes in the first subperiod, i.e. years 1960–1985, followed by a phase of relative stabilization (compared with the previous period) after the year 1980 (mainly of the spatial changes). Moreover, change intensity and change trends observed for the urban areas and population densities vary considerably in terms of space

The influence of diol chain extender on morphology and properties of thermally-triggered UV-stable self-healing polyurethane coatings

Two sets of waterborne polyurethane dispersions were synthesised from polycarbonate polyol with molecular mass of 500 Da and hexamethylene diisocyanate or isophorone diisocyanate. Formulations were prepared without a chain extender, with aliphatic diol with two to five carbon atoms or with diethylene glycol. Coatings were prepared on cellulose triacetate sheets, damaged by a steel-wool scratch instrument and left to heal at room temperature and at 60˚C. Self-healing efficiency was examined by comparison of haze before damage and at intervals after damage. Samples were analysed using Differential Scanning Calorimetry, Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy. The tests were repeated after 12 weeks to investigate ageing of the polymers. Samples were also tested for their stability to weathering. Optimally designed coatings obtained up to 100% recovery within 10 minutes at 60˚C and partial recovery at room temperature. The self-healing properties of coatings were found to be linked to macro-organisation of polymer chains caused by interactions between hard segments and soft segments of the polyurethane moiety, leading to phase-mixing, promoted by bulky, non-symmetrical isophorone diisocyanate, or phase-separation, promoted by linear, symmetrical hexamethylene diisocyanate. The length of chain extender was found to have large influence on formulations prepared with hexamethylene diisocyanate, increasing phase-separation and haze with the increase of chain length. Diethylene glycol was found to improve phase-mixing and self-healing properties of hexamethylene diisocyanate based materials. The influence of chain extenders was found to be minimal for isophorone diisocyanate based materials

The Optical Alignment System of the ZEUS MicroVertex Detector

The laser alignment system of the ZEUS microvertex detector is described. The detector was installed in 2001 as part of an upgrade programme in preparation for the second phase of electron-proton physics at the HERA collider. The alignment system monitors the position of the vertex detector support structure with respect to the central tracking detector using semi-transparent amorphous-silicon sensors and diode lasers. The system is fully integrated into the general environmental monitoring of the ZEUS detector and data has been collected over a period of 5 years. The primary aim of defining periods of stability for track-based alignment has been achieved and the system is able to measure movements of the support structure to a precision around $10 \mu$m.Comment: 38 pages; 17 figure

An improved measurement of muon antineutrino disappearance in MINOS

We report an improved measurement of muon anti-neutrino disappearance over a distance of 735km using the MINOS detectors and the Fermilab Main Injector neutrino beam in a muon anti-neutrino enhanced configuration. From a total exposure of 2.95e20 protons on target, of which 42% have not been previously analyzed, we make the most precise measurement of the anti-neutrino "atmospheric" delta-m squared = 2.62 +0.31/-0.28 (stat.) +/- 0.09 (syst.) and constrain the anti-neutrino atmospheric mixing angle >0.75 (90%CL). These values are in agreement with those measured for muon neutrinos, removing the tension reported previously.Comment: 5 pages, 4 figures. In submission to Phys.Rev.Let

Improved Search for Muon-Neutrino to Electron-Neutrino Oscillations in MINOS

We report the results of a search for ν_e appearance in a ν_μ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of 8.2×10^(20) protons on the NuMI target at Fermilab, we find 2sin^2(θ_(23))sin^2(2θ_(13))<0.12(0.20) at 90% confidence level for δ=0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin^2(θ_(23))sin^2(2θ_(13))=0.041^(+0.047)_(-0.031)(0.079^(+0.071)_(-0.053). The θ_(13)= 0 hypothesis is disfavored by the MINOS data at the 89% confidence level

Search for the disappearance of muon antineutrinos in the NuMI neutrino beam

We report constraints on antineutrino oscillation parameters that were obtained by using the two MINOS detectors to measure the 7% muon antineutrino component of the NuMI neutrino beam. In the Far Detector, we select 130 events in the charged-current muon antineutrino sample, compared to a prediction of 136.4 ± 11.7(stat)^(+10.2)_(-8.9)(syst) events under the assumption │Δm^2│ = 2.32 X 10^(-3) eV^2, sin^2(2θ) = 1.0

Active to Sterile Neutrino Mixing Limits from Neutral-Current Interactions in MINOS

Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of 7.07×10^(20) protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of 754±28(stat)±37(syst) for oscillations among three active flavors. The fraction f_s of disappearing ν_μ that may transition to ν_s is found to be less than 22% at the 90% C.L