802 research outputs found
The LeRC rail accelerators: Test designs and diagnostic techniques
The feasibility of using rail accelerators for various in-space and to-space propulsion applications was investigated. A 1 meter, 24 sq mm bore accelerator was designed with the goal of demonstrating projectile velocities of 15 km/sec using a peak current of 200 kA. A second rail accelerator, 1 meter long with a 156.25 sq mm bore, was designed with clear polycarbonate sidewalls to permit visual observation of the plasma arc. A study of available diagnostic techniques and their application to the rail accelerator is presented. Specific topics of discussion include the use of interferometry and spectroscopy to examine the plasma armature as well as the use of optical sensors to measure rail displacement during acceleration. Standard diagnostics such as current and voltage measurements are also discussed
Scaling and Universality in the Counterion-Condensation Transition at Charged Cylinders
We address the critical and universal aspects of counterion-condensation
transition at a single charged cylinder in both two and three spatial
dimensions using numerical and analytical methods. By introducing a novel
Monte-Carlo sampling method in logarithmic radial scale, we are able to
numerically simulate the critical limit of infinite system size (corresponding
to infinite-dilution limit) within tractable equilibration times. The critical
exponents are determined for the inverse moments of the counterionic density
profile (which play the role of the order parameters and represent the inverse
localization length of counterions) both within mean-field theory and within
Monte-Carlo simulations. In three dimensions (3D), correlation effects
(neglected within mean-field theory) lead to an excessive accumulation of
counterions near the charged cylinder below the critical temperature
(condensation phase), while surprisingly, the critical region exhibits
universal critical exponents in accord with the mean-field theory. In two
dimensions (2D), we demonstrate, using both numerical and analytical
approaches, that the mean-field theory becomes exact at all temperatures
(Manning parameters), when number of counterions tends to infinity. For finite
particle number, however, the 2D problem displays a series of peculiar singular
points (with diverging heat capacity), which reflect successive de-localization
events of individual counterions from the central cylinder. In both 2D and 3D,
the heat capacity shows a universal jump at the critical point, and the energy
develops a pronounced peak. The asymptotic behavior of the energy peak location
is used to locate the critical temperature, which is also found to be universal
and in accordance with the mean-field prediction.Comment: 31 pages, 16 figure
Diritto Privato
Lo scritto ha ad oggetto i capitoli su modi di estinzione dell'obbligazione diversi dall'adempimento, singoli contratti, possesso, famiglia e trascrizione dei tomi secondo e terzo del manuale Diritto Privato (Utet) in adozione presso alcune UniversitĂ Italiane e diffuso anche allâestero.
I menzionati capitoli si segnalano per una trattazione non meramente istituzionale, ma particolarmente attenta al dato applicativo e giurisprudenziale, che rende il manuale stesso utilizzato largamente per la preparazione allâesame per avvocato e ai concorsi pubblici di secondo livello (magistratura ordinaria e amministrativa.
Retinal blood vessels extraction using probabilistic modelling
© 2014 Kaba et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article has been made available through the Brunel Open Access Publishing Fund.The analysis of retinal blood vessels plays an important role in detecting and treating retinal diseases. In this review, we present an automated method to segment blood vessels of fundus retinal image. The proposed method could be used to support a non-intrusive diagnosis in modern ophthalmology for early detection of retinal diseases, treatment evaluation or clinical study. This study combines the bias correction and an adaptive histogram equalisation to enhance the appearance of the blood vessels. Then the blood vessels are extracted using probabilistic modelling that is optimised by the expectation maximisation algorithm. The method is evaluated on fundus retinal images of STARE and DRIVE datasets. The experimental results are compared with some recently published methods of retinal blood vessels segmentation. The experimental results show that our method achieved the best overall performance and it is comparable to the performance of human experts.The Department of Information Systems, Computing and Mathematics, Brunel University
Self-similar shear-thickening behavior in CTAB/NaSal surfactant solutions
The effect of salt concentration Cs on the critical shear rate required for
the onset of shear thickening and apparent relaxation time of the
shear-thickened phase, has been investigated systematically for dilute
CTAB/NaSal solutions. Experimental data suggest a self-similar behavior of the
critical shear rate and relaxation time as functions of Cs. Specifically, the
former ~ Cs^(-6) whereas the latter ~ Cs^(6) such that an effective Weissenberg
number for the onset of the shear thickened phase is only weakly dependent on
Cs. A procedure has been developed to collapse the apparent shear viscosity
versus shear rate data obtained for various values of Cs into a single master
curve. The effect of Cs on the elastic modulus and mesh size of the
shear-induced gel phase for different surfactant concentrations is discussed.
Experiments performed using different flow cells (Couette and cone-and-plate)
show that the critical shear rate, relaxation time and the maximum viscosity
attained are geometry-independent. The elastic modulus of the gel phase
inferred indirectly by employing simplified hydrodynamic instability analysis
of a sheared gel-fluid interface is in qualitative agreement with that
predicted for an entangled phase of living polymers. A qualitative mechanism
that combines the effect of Cs on average micelle length and Debye parameter
with shear-induced configurational changes of rod-like micelles is proposed to
rationalize the self-similarity of SIS formation.Comment: 27 pages, 17 figure
Anomalous codeposition of cobalt and ruthenium from chloride-sulfate baths
Codeposition of Ru and Co was studied at room temperature and at 50oC with various Ru3+ and Co2+ concentrations in the electrolyte. The codeposition of Co and Ru proved to be anomalous since no pure Ru could be obtained in the presence of Co2+ in the electrolyte, but a significant Co incorporation into the deposit was detected at potentials where the deposition of pure Co was not possible. The composition of the deposits varied monotonously with the change of the concentration ratio of Co2+ and Ru3+. The deposition of Ru was much hindered and the current efficiency was a few percent only when the molar fraction of Co in the deposit was low. Continuous deposits could be obtained only when the molar fraction of Co in the deposit was at least 40 at.%. The deposit morphology was related to the molar fraction of Co in the deposit. The X-ray diffractograms are in conformity with a hexagonal close-packed alloy and indicate the formation of nanocrystalline deposits. Two-pulse plating did not lead to a multilayer but to a Co-rich alloy. Magnetoresistance of the samples decreased with increasing Ru content
Dynamics of orientational ordering in fluid membranes
We study the dynamics of orientational phase ordering in fluid membranes.
Through numerical simulation we find an unusually slow coarsening of
topological texture, which is limited by subdiffusive propagation of membrane
curvature. The growth of the orientational correlation length obeys a
power law with in the late stage. We also discuss
defect profiles and correlation patterns in terms of long-range interaction
mediated by curvature elasticity.Comment: 5 pages, 3 figures (1 in color); Eq.(9) correcte
Effect of vessel wettability on the foamability of "ideal" surfactants and "real-world" beer heads
The ability to tailor the foaming properties of a solution by controlling its chemical composition is highly desirable and has been the subject of extensive research driven by a range of applications. However, the control of foams by varying the wettability of the foaming vessel has been less widely reported. This work investigates the effect of the wettability of the side walls of vessels used for the in situ generation of foam by shaking aqueous solutions of three different types of model surfactant systems (non-ionic, anionic and cationic surfactants) along with four different beers (Guinness Original, Banksâs Bitter, Bass No 1 and Harvest Pale). We found that hydrophilic vials increased the foamability only for the three model systems but increased foam stability for all foams except the model cationic system. We then compared stability of beer foams produced by shaking and pouring and demonstrated weak qualitative agreement between both foam methods. We also showed how wettability of the glass controls bubble nucleation for beers and champagne and used this effect to control exactly where bubbles form using simple wettability patterns
The black hole and host galaxy growth in an isolated QSO observed with ALMA
The outstanding mass growth of supermassive black holes (SMBHs) at the
Reionisation Epoch and how it is related to the concurrent growth of their host
galaxies, poses challenges to theoretical models aimed at explaining how these
systems formed in short timescales (<1 Gyr). To trace the average evolutionary
paths of quasi-stellar objects (QSOs) and their host galaxies in the BH
mass-host mass () plane, we compare the star formation rate (SFR),
derived from the accurate estimate of the dust temperature and the dust mass
(), with the BH accretion rate. To this aim, we
analysed a deep, pc resolution ALMA observation of the sub-mm continuum,
[CII] and HO of the QSO J2310+1855, enabling a detailed study of
dust properties and cold gas kinematics. We performed an accurate SED analysis
obtaining a dust temperature of K and a dust mass of
. The implied AGN-corrected SFR
is , a factor of 2 smaller than previously
reported for this QSO. We derived the best estimate of the dynamical mass
within kpc, based on
a dynamical model of the system. We found that , suggesting that AGN feedback might be efficiently
acting to slow down the SMBH accretion, while the stellar mass assembly is
still vigorously taking place in the host galaxy. In addition, we were also
able to detect high-velocity emission on the red and blue sides of the [CII]
emission line, that traces a gaseous outflow, and for the first time, we mapped
a spatially-resolved water vapour disk through the HO v=0
emission line detected at GHz,
whose kinematic properties and size are broadly consistent with those of the
[CII] disk.Comment: 15 pages, 10 figures, 4 tables. Accepted in A&
Black hole and host galaxy growth in an isolated z 6 QSO observed with ALMA
The outstanding mass growth of supermassive black holes (SMBHs) at the epoch of reionisation and its relation to the concurrent growth of their host galaxies poses challenges to theoretical models aimed at explaining how these systems formed on short timescales (< 1 Gyr). To trace the average evolutionary paths of quasi-stellar objects (QSOs) and their host galaxies in the plane of BH mass to host mass (Mdyn), we compare the star formation rate (SFR), derived from the accurate estimate of the dust temperature and the dust mass (Tdust,âMdust) based on infrared and sub-millimeter (sub-mm) spectral energy distribution (SED), with the BH accretion rate, derived from Lbol based on X-ray and optical and ultraviolet SED. To this aim, we analysed a deep ALMA observation of the sub-mm continuum, [CII], and H2O of the zââŒâ6 QSO J2310+1855 with a resolution of 900 pc, which enabled a detailed study of dust properties and cold gas kinematics. We performed an accurate SED analysis obtaining a dust temperature of Tdustâ=â71â
屉
4 K, dust mass Mdustâ=â(4.4â
屉
0.7)Ă108âMâ, and total far-infrared luminosity of LTIR = 2.5â0.5+0.6 Ă 1013 Lâ. The implied active galactic nuclei (AGN) â corrected SFR = 1240â260+310 Mâ yrâ1 is a factor of 2 lower than previously reported for this QSO. We measured a gas-to-dust ratio of GDRâ=â101â
屉
20. The dust continuum and [CII] surface brightness profiles are spatially extended out to rââŒâ6.7 kpc and rââŒâ5 kpc, respectively, with half-light radii of 0.9 and 1.1 kpc for the dust and gas, respectively. The derived gas surface density, ÎŁgas, and star formation rate density, ÎŁSFR, place the J2310+1855 host galaxy above the Kennicutt-Schmidt relation. We derived a best estimate of the dynamical mass Mdynâ=â5.2â
Ăâ
1010âMâ within râ=â1.7 kpc based on a dynamical model of the system with a rotating disk inclined at iâ=â25 deg. The Toomre parameter profile across the disk is QgasââŒâ3 and implies that the disk is unstable. We found that SFR/Mdyn > áčBH/MBH, suggesting that AGN feedback might be efficiently acting to slow down the SMBH accretion, while stellar mass assembly is still vigorously taking place in the host galaxy. In addition, we were also able to detect high-velocity emission on the red and blue sides of the [CII] emission line that is not consistent with disk rotation and traces a gaseous outflow. We derived an outflow mass Moutâ=â3.5â
Ăâ
108âMâ, and a mass outflow rate in the range áčout = 1800 â 4500 Mâ yrâ1. The implied Äout ⌠0.0005 â 0.001 Lbol is in agreement with the values observed for ionised winds. For the first time, we mapped a spatially resolved water vapour disk through the H2O vâ=â0 3(2,â2)â
ââ
3(1,â3) emission line detected at Îœobsâ=â274.074 GHz, whose kinematic properties and size are broadly consistent with those of the [CII] disk. The luminosity ratio LH2O/LTIRâ=â1.4â
Ăâ
10â5 is consistent with line excitation by dust-reprocessed star formation in the interstellar medium of the host galaxy
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