922 research outputs found
Microbial risk assessment of drinking water based on hydrodynamic modelling of pathogen concentrations in source water
Norovirus contamination of drinking water sources is an important cause of waterborne disease outbreaks. Knowledge on pathogen concentrations in source water is needed to assess the ability of a drinking water treatment plant (DWTP) to provide safe drinking water. However, pathogen enumeration in source water samples is often not sufficient to describe the source water quality. In this study, the norovirus concentrations were characterised at the contamination source, i.e. in sewage discharges. Then, the transport of norovirus within the water source (the river Gota alv in Sweden) under different loading conditions was simulated using a hydrodynamic model. Based on the estimated concentrations in source water, the required reduction of norovirus at the DWTP was calculated using quantitative microbial risk assessment (QMRA). The required reduction was compared with the estimated treatment performance at the DWTP. The average estimated concentration in source water varied between 4.8 x 10(2) and 7.5 x 10(3) genome equivalents L-1; and the average required reduction by treatment was between 7.6 and 8.8 Log(10). The treatment performance at the DWTP was estimated to be adequate to deal with all tested loading conditions, but was heavily dependent on chlorine disinfection, with the risk of poor reduction by conventional treatment and slow sand filtration. To our knowledge, this is the first article to employ discharge-based QMRA, combined with hydrodynamic modelling, in the context of drinking water. (C) 2015 Elsevier B.V. All rights reserved
Perturbations on steady spherical accretion in Schwarzschild geometry
The stationary background flow in the spherically symmetric infall of a
compressible fluid, coupled to the space-time defined by the static
Schwarzschild metric, has been subjected to linearized perturbations. The
perturbative procedure is based on the continuity condition and it shows that
the coupling of the flow with the geometry of space-time brings about greater
stability for the flow, to the extent that the amplitude of the perturbation,
treated as a standing wave, decays in time, as opposed to the amplitude
remaining constant in the Newtonian limit. In qualitative terms this situation
simulates the effect of a dissipative mechanism in the classical Bondi
accretion flow, defined in the Newtonian construct of space and time. As a
result of this approach it becomes impossible to define an acoustic metric for
a conserved spherically symmetric flow, described within the framework of
Schwarzschild geometry. In keeping with this view, the perturbation, considered
separately as a high-frequency travelling wave, also has its amplitude reduced.Comment: 8 pages, no figur
Implications of nonlinearity for spherically symmetric accretion
We subject the steady solutions of a spherically symmetric accretion flow to
a time-dependent radial perturbation. The equation of the perturbation includes
nonlinearity up to any arbitrary order, and bears a form that is very similar
to the metric equation of an analogue acoustic black hole. Casting the
perturbation as a standing wave on subsonic solutions, and maintaining
nonlinearity in it up to the second order, we get the time-dependence of the
perturbation in the form of a Li\'enard system. A dynamical systems analysis of
the Li\'enard system reveals a saddle point in real time, with the implication
that instabilities will develop in the accreting system when the perturbation
is extended into the nonlinear regime. The instability of initial subsonic
states also adversely affects the temporal evolution of the flow towards a
final and stable transonic state.Comment: 14 pages, ReVTeX. Substantially revised with respect to the previous
version. Three figures and a new section (Sec. VI) adde
Secular instability in quasi-viscous disc accretion
A first-order correction in the -viscosity parameter of Shakura and
Sunyaev has been introduced in the standard inviscid and thin accretion disc. A
linearised time-dependent perturbative study of the stationary solutions of
this "quasi-viscous" disc leads to the development of a secular instability on
large spatial scales. This qualitative feature is equally manifest for two
different types of perturbative treatment -- a standing wave on subsonic
scales, as well as a radially propagating wave. Stability of the flow is
restored when viscosity disappears.Comment: 15 pages, 2 figures, AASTeX. Added some new material and upgraded the
reference lis
A Toy Model for Blandford-Znajek Mechanism
A toy model for the Blandford-Znajek mechanism is investigated: a Kerr black
hole with a toroidal electric current residing in a thin disk around the black
hole. The toroidal electric current generates a poloidal magnetic field
threading the black hole and disk. Due to the interaction of the magnetic field
with remote charged particles, the rotation of the black hole and disk induces
an electromotive force, which can power an astrophysical load at remote
distance. The power of the black hole and disk is calculated. It is found that,
for a wide range of parameters specifying the rotation of the black hole and
the distribution of the electric current in the disk, the power of the disk
exceeds the power of the black hole. The torque provided by the black hole and
disk is also calculated. The torque of the disk is comparable to the torque of
the black hole. As the disk loses its angular momentum, the mass of the disk
gradually drifts towards the black hole and gets accreted. Ultimately the power
comes from the gravitational binding energy between the disk and the black
hole, as in the standard theory of accretion disk, instead of the rotational
energy of the black hole. This suggests that the Blandford-Znajek mechanism may
be less efficient in extracting energy from a rotating black hole with a thin
disk. The limitations of our simple model and possible improvements deserved
for future work are also discussed.Comment: 16 pages, 4 figures. Accepted for publication in Physical Review
Characteristics and quality of life of patients presenting to cancer support centres: Patient rated outcomes and use of complementary therapies
Background: In order to effectively target and provide individualised patient support strategies it is crucial to have a comprehensive picture of those presenting for services. The purpose of this study was to determine the characteristics and patient rated outcomes of individuals presenting to SolarisCare cancer support centres and their choices regarding complementary and integrated therapies (CIT).Methods: A cohort with a current or previous cancer diagnosis aged 18 - 87 years presenting to a SolarisCare centre during a 5-day period completed a questionnaire. Four SolarisCare centres participated in the trial including regional and metropolitan locations. Outcomes included medical and demographic characteristics, CIT variables and patient rated outcomes (PROs) including quality of life (QoL).Results: Of the 95 participants (70.3%) who completed the survey, the mean age was 60.5 years with 62% currently receiving treatment. Eighty percent of the sample had at least one other comorbid condition, with the most popular CIT being relaxation massage. Of the PROs, QoL was significantly lower than norms for the Australian population and other mixed cancer populations. No notable differences were seen between genders, however significantly poorer outcomes were found for the younger age group. Fifty percent of the population did not meet physical activity recommendations, and musculoskeletal symptoms explained between 25-27% of variance in QoL.Conclusions: A greater understanding of the health profiles of patients presenting to supportive care centres and their use of CIT, provides Western Australian health professionals with key information to ensure the safety of supportive care practices, as well as fosters optimal patient outcomes and enhances the integration of supportive care strategies within mainstream medical care
Positive patient experiences in an Australian integrative oncology centre
Background: The purpose of this study was to explore the experiences of cancer patients\u27 utilising complementary and integrative therapies (CIT) within integrative oncology centres across Western Australia.Methods: Across four locations 135 patients accessed CIT services whilst undergoing outpatient medical treatment for cancer. Of the 135 patients, 66 (61 ± 12 y; female n = 45; male n = 21) agreed to complete a personal accounts questionnaire consisting of open-ended questions designed to explore patients\u27 perceptions of CIT. All results were transcribed into nVivo (v9) and using thematic analysis, key themes were identified.Results: Of the 66 participants, 100% indicated they would recommend complementary therapies to other patients and 92% stated CIT would play a significant role in their future lifestyle . A mean score of 8 ± 1 indicated an improvement in participants\u27 perception of wellbeing following a CIT session. Three central themes were identified: empowerment, support and relaxation. Fourteen sub-themes were identified, with all themes clustered into a framework of multifaceted views held by cancer patients in relation to wellbeing, role of significant others and control.Conclusions: Exploration of patients\u27 experiences reveals uniformly positive results. One of the key merits of the environment created within the centres is patients are able to work through their cancer journey with an increased sense of empowerment, without placing them in opposition to conventional medical treatment. In order to effectively target integrative support services it is crucial to explore the experiences of patients in their own words and use those forms of expression to drive service delivery
Evolution of transonicity in an accretion disc
For inviscid, rotational accretion flows driven by a general pseudo-Newtonian
potential on to a Schwarzschild black hole, the only possible fixed points are
saddle points and centre-type points. For the specific choice of the Newtonian
potential, the flow has only two critical points, of which the outer one is a
saddle point while the inner one is a centre-type point. A restrictive upper
bound is imposed on the admissible range of values of the angular momentum of
sub-Keplerian flows through a saddle point. These flows are very unstable to
any deviation from a necessarily precise boundary condition. The difficulties
against the physical realisability of a solution passing through the saddle
point have been addressed through a temporal evolution of the flow, which gives
a non-perturbative mechanism for selecting a transonic solution passing through
the saddle point. An equation of motion for a real-time perturbation about the
stationary flows reveals a very close correspondence with the metric of an
acoustic black hole, which is also an indication of the primacy of
transonicity.Comment: 18 page
Improving the Prospects for Detecting Extrasolar Planets in Gravitational Microlensing in 2002
Gravitational microlensing events of high magnification have been shown to be
promising targets for detecting extrasolar planets. However, only a few events
of high magnification have been found using conventional survey techniques.
Here we demonstrate that high magnification events can be readily found in
microlensing surveys using a strategy that combines high frequency sampling of
target fields with online difference imaging analysis. We present 10
microlensing events with peak magnifications greater than 40 that were detected
in real-time towards the Galactic Bulge during 2001 by MOA. We show that Earth
mass planets can be detected in future events such as these through intensive
follow-up observations around the event peaks. We report this result with
urgency as a similar number of such events are expected in 2002.Comment: 11 pages, 3 embedded ps figures including 2 colour, revised version
accepted by MNRA
Microlensing optical depth towards the Galactic bulge from MOA observations during 2000 with Difference Image Analysis
We analyze the data of the gravitational microlensing survey carried out by
by the MOA group during 2000 towards the Galactic Bulge (GB). Our observations
are designed to detect efficiently high magnification events with faint source
stars and short timescale events, by increasing the the sampling rate up to 6
times per night and using Difference Image Analysis (DIA). We detect 28
microlensing candidates in 12 GB fields corresponding to 16 deg^2. We use Monte
Carlo simulations to estimate our microlensing event detection efficiency,
where we construct the I-band extinction map of our GB fields in order to find
dereddened magnitudes. We find a systematic bias and large uncertainty in the
measured value of the timescale in our simulations. They are
associated with blending and unresolved sources, and are allowed for in our
measurements. We compute an optical depth tau = 2.59_{-0.64}^{+0.84} \times
10^{-6} towards the GB for events with timescales 0.3<t_E<200 days. We consider
disk-disk lensing, and obtain an optical depth tau_{bulge} =
3.36_{-0.81}^{+1.11} \times 10^{-6}[0.77/(1-f_{disk})] for the bulge component
assuming a 23% stellar contribution from disk stars. These observed optical
depths are consistent with previous measurements by the MACHO and OGLE groups,
and still higher than those predicted by existing Galactic models. We present
the timescale distribution of the observed events, and find there are no
significant short events of a few days, in spite of our high detection
efficiency for short timescale events down to t_E = 0.3 days. We find that half
of all our detected events have high magnification (>10). These events are
useful for studies of extra-solar planets.Comment: 65 pages and 30 figures, accepted for publication in ApJ. A
systematic bias and uncertainty in the optical depth measurement has been
quantified by simulation
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