223 research outputs found
Properties of pedestrians walking in line - Fundamental diagrams
We present experimental results obtained for a one-dimensional flow using
high precision motion capture. The full pedestrians' trajectories are obtained.
In this paper, we focus on the fundamental diagram, and on the relation between
the instantaneous velocity and spatial headway (distance to the predecessor).
While the latter was found to be linear in previous experiments, we show that
it is rather a piecewise linear behavior which is found if larger density
ranges are covered. Indeed, our data clearly exhibits three distinct regimes in
the behavior of pedestrians that follow each other. The transitions between
these regimes occur at spatial headways of about 1.1 and 3 m, respectively.
This finding could be useful for future modeling.Comment: 9 figures, 3 table
Optimizacija vremena zamjene vatrostalne obloge na segmentnim pećima
The goal of the study is to establish the influence of temporal wearing of refractory lining on energy losses of the furnaces by conducting heat through the furnaces walls. Object of the study were sectional furnaces, type SELAS, situated in the seam tubes production line in Željezara Sisak, Croatia. In order to reduce production costs, it was attempted to define the timely replacement of refractory lining by the criteria of comparing the costs resulted by heat loss through the furnace lining with the costs of refractory lining replacement. Data for the calculation of heat losses was obtained by use of the infrared camera.Rad je izrađen s ciljem da se utvrdi utjecaj vremenskog trošenja vatrostalne obloge na energetske gubitke provođenjem topline kroz ziđe peći. Kao objekt istraživanja odabrane su segmentne peći tipa SELAS, koje se nalaze u valjaonici šavnih cijevi Željezare Sisak. U cilju smanjenja proizvodnih troškova pokušala se odrediti pravovremena zamjena vatrostalne obloge pojedinog segmenta prema kriteriju usporedbe povećanih proizvodnih troškova, nastalih povećanjem energetskih gubitaka provođenjem topline kroz ziđe peći, s troškovima zamjene vatrostalne obloge. Za proračun gubitaka topline koristili su se podaci dobiveni snimanjem infracrvenom kamerom
Properties of pedestrians walking in line: Stepping behavior
In human crowds, interactions among individuals give rise to a variety of
self-organized collective motions that help the group to effectively solve the
problem of coordination. However, it is still not known exactly how humans
adjust their behavior locally, nor what are the direct consequences on the
emergent organization. One of the underlying mechanisms of adjusting individual
motions is the stepping dynamics. In this paper, we present first quantitative
analysis on the stepping behavior in a one-dimensional pedestrian flow studied
under controlled laboratory conditions. We find that the step length is
proportional to the velocity of the pedestrian, and is directly related to the
space available in front of him, while the variations of the step duration are
much smaller. This is in contrast with locomotion studies performed on isolated
pedestrians and shows that the local density has a direct influence on the
stepping characteristics. Furthermore, we study the phenomena of
synchronization -walking in lockstep- and show its dependence on flow
densities. We show that the synchronization of steps is particularly important
at high densities, which has direct impact on the studies of optimizing
pedestrians flow in congested situations. However, small synchronization and
antisynchronization effects are found also at very low densities, for which no
steric constraints exist between successive pedestrians, showing the natural
tendency to synchronize according to perceived visual signals.Comment: 8 pages, 5 figure
Galactic interstellar filaments as probed by LOFAR and Planck
Recent Low Frequency Array (LOFAR) observations at 115-175 MHz of a field at
medium Galactic latitudes (centered at the bright quasar 3C196) have shown
striking filamentary structures in polarization that extend over more than 4
degrees across the sky. In addition, the Planck satellite has released full sky
maps of the dust emission in polarization at 353GHz. The LOFAR data resolve
Faraday structures along the line of sight, whereas the Planck dust
polarization maps probe the orientation of the sky projected magnetic field
component. Hence, no apparent correlation between the two is expected. Here we
report a surprising, yet clear, correlation between the filamentary structures,
detected with LOFAR, and the magnetic field orientation, probed by the Planck
satellite. This finding points to a common, yet unclear, physical origin of the
two measurements in this specific area in the sky. A number of follow-up multi-
frequency studies are proposed to shed light on this unexpected finding.Comment: 6 pages, 4 figures, accepted for publication in MNRAS Letter
Foregrounds for observations of the cosmological 21 cm line: II. Westerbork observations of the fields around 3C196 and the North Celestial Pole
In the coming years a new insight into galaxy formation and the thermal
history of the Universe is expected to come from the detection of the highly
redshifted cosmological 21 cm line. The cosmological 21 cm line signal is
buried under Galactic and extragalactic foregrounds which are likely to be a
few orders of magnitude brighter. Strategies and techniques for effective
subtraction of these foreground sources require a detailed knowledge of their
structure in both intensity and polarization on the relevant angular scales of
1-30 arcmin. We present results from observations conducted with the Westerbork
telescope in the 140-160 MHz range with 2 arcmin resolution in two fields
located at intermediate Galactic latitude, centred around the bright quasar
3C196 and the North Celestial Pole. They were observed with the purpose of
characterizing the foreground properties in sky areas where actual observations
of the cosmological 21 cm line could be carried out. The polarization data were
analysed through the rotation measure synthesis technique. We have computed
total intensity and polarization angular power spectra. Total intensity maps
were carefully calibrated, reaching a high dynamic range, 150000:1 in the case
of the 3C196 field. [abridged]Comment: 20 pages, 22 figures, accepted for publication in A&A. A version with
full resolution figures is available at
http://www.astro.rug.nl/~bernardi/NCP_3C196/bernardi.pd
Systematic Effects of Foreground Removal in 21cm Surveys of Reionization
It is well-known that foreground subtraction in 21cm surveys removes large
scale power. We investigate associated systematic biases. We show that removing
line-of-sight fluctuations on large scales aliases into suppression of the 3D
power spectrum across a broad range of scales. This bias can be eliminated by
marginalizing over small k in the 1D power spectrum; however, the unbiased
estimator will have unavoidably larger variance. We also show that Gaussian
realizations of the power spectrum permit accurate and extremely rapid
Monte-Carlo simulations for error analysis; repeated realizations of the fully
non-Gaussian field are unnecessary. We perform Monte-Carlo maximum-likelihood
simulations of foreground removal which yield unbiased, minimum variance
estimates of the power spectrum in agreement with Fisher matrix estimates.
Foreground removal also distorts the 21cm PDF, reducing the contrast between
neutral and ionized regions. We show that it is the subtraction of large-scales
modes which is responsible for this distortion, and that it is less severe in
the earlier stages of reionization. It can be reduced by using larger
bandwidths for foreground removal. In the late stages of reionization, the
largest ionized regions (which consist of foreground emission only) provides
calibration points which potentially allow recovery of large-scale modes.
Finally, we also show that: (i) the broad frequency response of synchrotron and
free-free emission will smear out any features in the electron momentum
distribution and ensure spectrally smooth foregrounds; (ii) extragalactic radio
recombination lines should be negligible foregrounds.Comment: Minor editorial changes (including title) to match published version;
conclusions unchanged. 20 pages, 18 figure
Simple and Low-cost Fiber-optic Sensors for Detection of UV Radiation
In this paper two simple and low-cost fiberoptic sensors for detection of UV radiation are presented. A U-shaped sensor covered with an UV marker for UV radiation detection and a fiber-optic sensor with one end covered with powder from a mercury lamp are produced and described in details. Both sensors are made of large-core PMMA plastic optical fibers. As UV sources, a solar simulator and four different UV lamps are used. The light spectrum on the fiber output is measured by using an USB spectrometer. Dependence of output light intensity on the distance of end-type sensor with powder from a mercury lamp from UV lamp is investigated as well. On the output of the sensor covered with powder from a mercury lamp are obtained peaks of fluorescent emission at approximately 616 nm and 620 nm wavelengths
Distribution and forms of iron in the vertisols of Serbia
Soil of arable land and meadows from the Ap horizon, taken from ten different localities, were investigated for different forms of Fe, including total (HF), pseudo-total (HNO3), 0.1 M HCl extractable and DTPA (diethylenetriaminepentaacetic acid)-extractable. A sequential fractional procedure was employed to separate the Fe into fractions: water soluble and exchangeable Fe (I), Fe specifically adsorbed with carbonates (II), reducibly releasable Fe in oxides (III), Fe bonded with organic matter (IV) and Fe structurally bonded in silicates (residual fraction) (V). The soil pH, cation exchange capacity, and size fractions (clay and silt) had a strongest influence on the distribution of the different forms of Fe. The different extraction methods showed similar patterns of the Fe content in arable and meadow soils. However, the DTPA iron did not correspond with the total iron, which confirms the widespread incidence of iron-deficiency in vertisols is independent of the total iron in soils. The amount of exchangeable (fraction I) and specifically adsorbed (II) iron showed no dependence on its content in the other fractions, indicating low mobility of iron in vertisols. The strong positive correlation (r = 0.812 and 0.956) between the content of iron in HNO3 and HF and its contents in the primary and secondary minerals (fraction – V) indicate a low content of plant accessible iron in the vertisol. The sequential fractional procedure was confirmed as suitable for accessing the content and availability of iron in the vertisols of Serbia
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