126 research outputs found
Particle motion and stain removal during simulated abrasive tooth cleaning
Stain removal from teeth is important both to prevent decay and for appearance. This is usually achieved using a filament-based toothbrush with a toothpaste consisting of abrasive particles in a carrier fluid. This work has been carried out to examine how these abrasive particles interact with the filaments and cause material removal from a stain layer on the surface of a tooth. It is important to understand this mechanism as while maximum cleaning efficiency is required, this must not be accompanied by damage to the enamel or dentine substrate. In this work simple abrasive scratch tests were used to investigate stain removal mechanism of two abrasive particles commonly used in tooth cleaning, silica and perlite. Silica particles are granular in shape and very different to perlite particles, which are flat and have thicknesses many times smaller than their width. Initially visualisation studies were carried out with perlite particles to study how they are entrained into a filament/counterface contact. Results were compared with previous studies using silica. Reciprocating scratch tests were then run to study how many filaments have a particle trapped at one moment and are involved in the cleaning process. Stain removal tests were then carried out in a similar manner to establish cleaning rates with the two particle types. Perlite particles were found to be less abrasive than silica. This was because of their shape and how they were entrained into the filament contacts and loaded against a counterface. With both particles subsurface damage during stain removal was found to be minimal. A simple model was built to predict stain removal rates with silica particles, which gave results that correlated well with the experimental data
Interaction between toothbrushes and toothpaste abrasive particles in simulated tooth cleaning
There are currently many toothbrush designs on the market incorporating different
filament configurations such as filaments at various angles and different lengths and
made from several different materials. In order to understand how the tooth cleaning
process occurs there is a need to investigate in detail how the abrasive particles in a
toothpaste interact with the filaments in a teeth cleaning contact and cause material
removal from a plaque or stain layer.
The following describes the development of optical apparatus to enable the
visualisation of simulated teeth cleaning contacts. Studies have been carried out using
the apparatus to investigate particle entrainment into the contact and how it differs
with varying bristle configurations. The effects of filament stiffness and tip shape
were also investigated. Various types of electric toothbrushes were also tested.
The studies have shown how particles are trapped at the tips of toothbrush filaments.
Particles, suspended in fluid, approach the filament tips, as they pass through they
may become trapped. Greater particle entrainment into the filament tip contact occurs
with a reciprocating action at low filament loads and deflections than with a sliding
motion. Large particles are less likely to enter tip contacts and are trapped between
tips or under the filament bend at higher loads.
Whether the particles are likely to be trapped and how long they remain so depends
on the filament stiffness and degree of splay on loading and the filament
configuration. The direction the filaments point in, the number of filaments in a tuft,
the spacing of the tufts and the way the filaments splay when deflected all have an
influence on entrainment of particles. Tufts with tightly packed stiff filaments which
deflected together on loading were more effective at trapping particles than more flexible filaments that splayed out on loading as they present more of a barrier to
particle entry and exit from the tip region
Analysis of anisotropic flow with Lee-Yang zeroes
We present a new method to extract anisotropic flow in heavy ion collisions
from the genuine correlation among a large number of particles. Anisotropic
flow is obtained from the zeroes in the complex plane of a generating function
of azimuthal correlations, in close analogy with the theory of phase
transitions by Lee and Yang. Flow is first estimated globally, i.e., averaged
over the phase space covered by the detector, and then differentially, as a
function of transverse momentum and rapidity for identified particles. The
corresponding estimates are less biased by nonflow correlations than with any
other method. The practical implementation of the method is rather
straightforward. Furthermore, it automatically takes into account most
corrections due to azimuthal anisotropies in the detector acceptance. The main
limitation of the method is statistical errors, which can be significantly
larger than with the ``standard'' method of flow analysis if the flow and/or
the event multiplicities are too small. In practice, we expect this to be the
most accurate method to analyze directed and elliptic flow in fixed-target
heavy-ion collisions between 100 MeV and 10 GeV per nucleon (at the Darmstadt
SIS synchrotron and the Brookhaven Alternating Gradient Synchrotron), and
elliptic flow at ultrarelativistic energies (at the Brookhaven Relativistic
Heavy Ion Collider, and the forthcoming Large Hadron Collider at CERN).Comment: 32 pages, 7 eps figures, RevTe
Global Observations from PHOBOS
Particle production in Au+Au collisions has been measured in the PHOBOS
experiment at RHIC for a range of collision energies. Three empirical
observations have emerged from this dataset which require theoretical
examination. First, there is clear evidence of limiting fragmentation. Namely,
particle production in central Au+Au collisions, when expressed as
(), becomes energy independent at high energy for a
broad region of around . This energy-independent region grows
with energy, allowing only a limited region (if any) of longitudinal
boost-invariance. Second, there is a striking similarity between particle
production in e+e- and Au+Au collisions (scaled by the number of participating
nucleon pairs). Both the total number of produced particles and the
longitudinal distribution of produced particles are approximately the same in
e+e- and in scaled Au+Au. This observation was not predicted and has not been
explained. Finally, particle production has been found to scale approximately
with the number of participating nucleon pairs for . This scaling
occurs both for the total multiplicity and for high \pT particles (3 <\pT<
4.5 GeV/c).Comment: QM2002 plenary talk, 10 pages, 11 figure
Evidence of Final-State Suppression of High-p_T Hadrons in Au + Au Collisions Using d + Au Measurements at RHIC
Transverse momentum spectra of charged hadrons with 6 GeV/c have
been measured near mid-rapidity (0.2 1.4) by the PHOBOS experiment
at RHIC in Au + Au and d + Au collisions at . The spectra for different collision centralities are compared to collisions at the same energy. The resulting nuclear modification
factor for central Au + Au collisions shows evidence of strong suppression of
charged hadrons in the high- region ( GeV/c). In contrast, the d +
Au nuclear modification factor exhibits no suppression of the high-
yields. These measurements suggest a large energy loss of the high-
particles in the highly interacting medium created in the central Au + Au
collisions. The lack of suppression in d + Au collisions suggests that it is
unlikely that initial state effects can explain the suppression in the central
Au + Au collisions.Comment: 3 pages, 4 figures, International Europhysics Conference on High
Energy Physics EPS (July 17th-23rd 2003) in Aachen, German
Identified particles in Au+Au collisions at sqrt{s_NN} = 200 GeV
The yields of identified particles have been measured at RHIC for Au+Au
collisions at sqrt{s_NN} = 200 GeV using the PHOBOS spectrometer. The ratios of
antiparticle to particle yields near mid-rapidity are presented. The first
measurements of the invariant yields of charged pions, kaons and protons at
very low transverse momenta are also shown.Comment: 4 pages, 4 figures, Contribution to Quark Matter 2002, Nantes,
France, July 200
Universal Behavior of Charged Particle Production in Heavy Ion Collisions
The PHOBOS experiment at RHIC has measured the multiplicity of primary
charged particles as a function of centrality and pseudorapidity in Au+Au
collisions at sqrt(s_NN) = 19.6, 130 and 200 GeV. Two kinds of universal
behavior are observed in charged particle production in heavy ion collisions.
The first is that forward particle production, over a range of energies,
follows a universal limiting curve with a non-trivial centrality dependence.
The second arises from comparisons with pp/pbar-p and e+e- data.
N_tot/(N_part/2) in nuclear collisions at high energy scales with sqrt(s) in a
similar way as N_tot in e+e- collisions and has a very weak centrality
dependence. This feature may be related to a reduction in the leading particle
effect due to the multiple collisions suffered per participant in heavy ion
collisions.Comment: 4 Pages, 5 Figures, contributed to the Proceedings of Quark Matter
2002, Nantes, France, 18-24 July 200
Recent Results from PHOBOS at RHIC
The PHOBOS experiment at RHIC has recorded measurements for Au-Au collisions
spanning nucleon-nucleon center-of-mass energies from 19.6 GeV to 200 GeV.
Global observables such as elliptic flow and charged particle multiplicity
provide important constraints on model predictions that characterize the state
of matter produced in these collisions. The nearly 4 pi acceptance of the
PHOBOS experiment provides excellent coverage for complete flow and
multiplicity measurements. Results including beam energy and centrality
dependencies are presented and compared to elementary systems.Comment: 4 pages, 4 figures, proceedings from PANIC02 in Osaka, Japa
Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays
Average charged multiplicities have been measured separately in , and
light quark () events from decays measured in the SLD experiment.
Impact parameters of charged tracks were used to select enriched samples of
and light quark events, and reconstructed charmed mesons were used to select
quark events. We measured the charged multiplicities:
,
, from
which we derived the differences between the total average charged
multiplicities of or quark events and light quark events: and . We compared
these measurements with those at lower center-of-mass energies and with
perturbative QCD predictions. These combined results are in agreement with the
QCD expectations and disfavor the hypothesis of flavor-independent
fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters
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