7,320 research outputs found
Continuous-flow laboratory simulation of stream water quality changes downstream of an untreated wastewater discharge.
In regions of the world with poor provision of wastewater treatment, raw sewage
is often discharged directly into surface waters. This paper describes an
experimental evaluation of the fate of two organic chemicals under these
conditions using an artificial channel cascade fed with a mix of settled sewage
and river water at its upstream end and operated under continuous steady-state
conditions. The experiments underpin an environmental risk assessment
methodology based on the idea of an “impact zone” (IZ) – the zone downstream of
wastewater emission in which water quality is severely impaired by high
concentrations of unionised ammonia, nitrite and biochemical oxygen demand
(BOD). Radiolabelled dodecane-6-benzene sulphonate (DOBS) and aniline
hydrochloride were used as the model chemical and reference compound
respectively. Rapid changes in 14C counts were observed with flow-time for both
these materials. These changes were most likely to be due to complete
mineralisation. A dissipation half-life of approximately 7.1 h was observed for
the 14C label with DOBS. The end of the IZ was defined as the point at which the
concentration of both unionised ammonia and nitrite fell below their respective
predicted no-effect concentrations for salmonids. At these points in the
cascade, approximately 83 and 90% of the initial concentration of 14C had been
removed from the water column, respectively. A simple model of mineral nitrogen
transformations based on Michaelis–Menten kinetics was fitted to observed
concentrations of NH4, NO2 and NO3. The cascade is intended to provide a
confirmatory methodology for assessing the ecological risks of chemicals under
direct discharge co
Accretion-ejection connection in the young brown dwarf candidate ISO-Cha1 217
As the number of observed brown dwarf outflows is growing it is important to
investigate how these outflows compare to the well studied jets from young
stellar objects. A key point of comparison is the relationship between outflow
and accretion activity and in particular the ratio between the mass outflow and
accretion rates (/). The brown dwarf candidate
ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric
study of brown dwarfs, to be driving an asymmetric outflow with the
blue-shifted lobe having a position angle of 20. The aim here
is to further investigate the properties of ISO-ChaI 217, the morphology and
kinematics of its outflow, and to better constrain
(/). The outflow is spatially resolved in the
lines and is detected out to 1\farcs6
in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry
between the two lobes is confirmed although the velocity asymmetry is less
pronounced with respect to our previous study. Using thirteen different
accretion tracers we measure log() [M/yr]= -10.6
0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI
217 outflow was derived for a range of values of A, up to
a value of A = 2.5 mag estimated for the source extinction. The logarithm
of the mass outflow () was estimated in the range -11.7 to -11.1
for both jets combined. Thus / [\Msun/yr] lies
below the maximum value predicted by magneto-centrifugal jet launching models.
Finally, both model fitting of the Balmer decrements and spectro-astrometric
analysis of the H line show that the bulk of the H I emission comes
from the accretion flow.Comment: accepted by Astronomy & Astrophysic
Development and application of a catchment scale pesticide fate and transport model for use in drinking water risk assessment
This paper describes the development and application of IMPT (Integrated Model for Pesticide Transport), a parameter-efficient tool for predicting diffuse-source pesticide concentrations in surface waters used for drinking water supply. The model was applied to a small UK headwater catchment with high frequency (8 h) pesticide monitoring data and to five larger catchments (479–1653 km2) with sampling approximately every 14 days. Model performance was good for predictions of both flow (Nash Sutcliffe Efficiency generally > 0.59 and PBIAS < 10%) and pesticide concentrations, although low sampling frequency in the larger catchments is likely to mask the true episodic nature of exposure. The computational efficiency of the model, along with the fact that most of its parameters can be derived from existing national soil property data mean that it can be used to rapidly predict pesticide exposure in multiple surface water resources to support operational and strategic risk assessments
XMM-Newton observation of SNR J0533-7202 in the Large Magellanic Cloud
Aims. We present an X-ray study of the supernova remnant SNR J0533-7202 in
the Large Magellanic Cloud (LMC) and determine its physical characteristics
based on its X-ray emission. Methods. We observed SNR J0533-7202 with
XMM-Newton (flare-filtered exposure times of 18 ks EPIC-pn and 31 ks
EPIC-MOS1/MOS2). We produced X-ray images of the SNR, performed an X-ray
spectral analysis, and compared the results to multi-wavelength studies.
Results. The distribution of X-ray emission is highly non-uniform, with the
south-west region brighter than the north-east. The X-ray emission is
correlated with the radio emission from the remnant. We determine that this
morphology is likely due to the SNR expanding into a non-uniform ambient medium
and not an absorption effect. We estimate the size to be 53.9 (\pm 3.4) x 43.6
(\pm 3.4) pc, with the major axis rotated ~64 degrees east of north. We find no
spectral signatures of ejecta and infer that the X-ray plasma is dominated by
swept-up interstellar medium. Using the spectral fit results and the Sedov
self-similar solution, we estimate an age of ~17-27 kyr, with an initial
explosion energy of (0.09-0.83) x 10^51 erg. We detected an X-ray source
located near the centre of the remnant, namely XMMU J053348.2-720233. The
source type could not be conclusively determined due to the lack of a
multi-wavelength counterpart and low X-ray counts. We find that it is likely
either a background active galactic nucleus or a low-mass X-ray binary in the
LMC. Conclusions. We detected bright thermal X-ray emission from SNR J0533-7202
and determined that the remnant is in the Sedov phase of its evolution. The
lack of ejecta emission prohibits us from typing the remnant with the X-ray
data. Therefore, the likely Type Ia classification based on the local stellar
population and star formation history reported in the literature cannot be
improved upon.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
A Population of Short-Period Variable Quasars from PTF as Supermassive Black Hole Binary Candidates
Supermassive black hole binaries (SMBHBs) at sub-parsec separations should be
common in galactic nuclei, as a result of frequent galaxy mergers.
Hydrodynamical simulations of circumbinary discs predict strong periodic
modulation of the mass accretion rate on time-scales comparable to the orbital
period of the binary. As a result, SMBHBs may be recognized by the periodic
modulation of their brightness. We conducted a statistical search for periodic
variability in a sample of 35,383 spectroscopically confirmed quasars in the
photometric database of the Palomar Transient Factory (PTF). We analysed
Lomb-Scargle periodograms and assessed the significance of our findings by
modeling each individual quasar's variability as a damped random walk (DRW). We
identified 50 quasars with significant periodicity beyond the DRW model,
typically with short periods of a few hundred days. We find 33 of these to
remain significant after a re-analysis of their periodograms including
additional optical data from the intermediate-PTF and the Catalina Real-Time
Transient Survey (CRTS). Assuming that the observed periods correspond to the
redshifted orbital periods of SMBHBs, we conclude that our findings are
consistent with a population of unequal-mass SMBHBs, with a typical mass ratio
as low as q = M2/M1 ~ 0.01.Comment: MNRAS (accepted), new section 4.
Sensitivity of predicted bioaerosol exposure from open windrow composting facilities to ADMS dispersion model parameters
Bioaerosols are released in elevated quantities from composting facilities and are associated with negative health effects, although dose-response relationships are not well understood, and require improved exposure classification. Dispersion modelling has great potential to improve exposure classification, but has not yet been extensively used or validated in this context. We present a sensitivity analysis of the ADMS dispersion model specific to input parameter ranges relevant to bioaerosol emissions from open windrow composting. This analysis provides an aid for model calibration by prioritising parameter adjustment and targeting independent parameter estimation. Results showed that predicted exposure was most sensitive to the wet and dry deposition modules and the majority of parameters relating to emission source characteristics, including pollutant emission velocity, source geometry and source height. This research improves understanding of the accuracy of model input data required to provide more reliable exposure predictions
A fast stroboscopic spectral method for rotating systems in numerical relativity
We present a numerical technique for solving evolution equations, as the wave
equation, in the description of rotating astrophysical compact objects in
comoving coordinates, which avoids the problems associated with the light
cylinder. The technique implements a fast spectral matching between two domains
in relative rotation: an inner spherical domain, comoving with the sources and
lying strictly inside the light cylinder, and an outer inertial spherical
shell. Even though the emphasis is placed on spectral techniques, the matching
is independent of the specific manner in which equations are solved inside each
domain, and can be adapted to different schemes. We illustrate the strategy
with some simple but representative examples.Comment: 16 pages, 15 figure
Models of helically symmetric binary systems
Results from helically symmetric scalar field models and first results from a
convergent helically symmetric binary neutron star code are reported here;
these are models stationary in the rotating frame of a source with constant
angular velocity omega. In the scalar field models and the neutron star code,
helical symmetry leads to a system of mixed elliptic-hyperbolic character. The
scalar field models involve nonlinear terms that mimic nonlinear terms of the
Einstein equation. Convergence is strikingly different for different signs of
each nonlinear term; it is typically insensitive to the iterative method used;
and it improves with an outer boundary in the near zone. In the neutron star
code, one has no control on the sign of the source, and convergence has been
achieved only for an outer boundary less than approximately 1 wavelength from
the source or for a code that imposes helical symmetry only inside a near zone
of that size. The inaccuracy of helically symmetric solutions with appropriate
boundary conditions should be comparable to the inaccuracy of a waveless
formalism that neglects gravitational waves; and the (near zone) solutions we
obtain for waveless and helically symmetric BNS codes with the same boundary
conditions nearly coincide.Comment: 19 pages, 7 figures. Expanded version of article to be published in
Class. Quantum Grav. special issue on Numerical Relativit
PENGARUH KINERJA KEUANGAN DAN UKURAN PERUSAHAAN TERHADAP HARGA SAHAM (Studi pada Perusahaan Perbankan yang Terdaftar di Bursa Efek Indonesia Tahun 2012-2014)
Penelitian ini dilakukan untuk menguji pengaruh Kinerja Keuangan dan Ukuran Perusahaan terhadap Harga Saham pada Perusahaan Perbankan yang terdaftar di Bursa Efek Indonesia tahun 2012 sampai 2014. Variabel yang digunakan adalah Capital Adequacy Ratio (CAR), Non Performing Loan (NPL), Return On Asset (ROA), Loan to Deposit Ratio (LDR), Firm Size (Ukuran Perusahaan). Teknik sampling yang digunakan adalah purposive sampling selama kurun waktu penelitian tahun 2012 sampai 2014. Data diperoleh berdasarkan publikasi Indonesian Capital Market Directory (ICMD 2015). Dan diperoleh jumlah sampel sebanyak 18 perusahaan. Teknik analisis yang digunakan adalah regresi berganda dengan persamaan kuadrat terkecil dan uji hipotesis menggunakan t-statistik untuk menguji koefisien regresi parsial serta f-statistik untuk menguji keberartian pengaruh secara bersama-sama dengan level of significance 5%. Selain itu juga dilakukan uji asumsi klasik yang meliputi uji normalitas, uji multikolinearitas, uji heteroskedastisitas, dan uji autokolerasi. Berdasarkan karakteristik keseluruhan data, tidak terjadi penyimpangan asumsi klasik, hal ini menunjukkan bahwa data yang tersedia telah memenuhi syarat untuk menggunakan model persamaan regresi linier berganda. Dari hasil penelitian menunjukkan bahwa variabel independen yang terdiri dari CAR, NPL, ROA, LDR, dan FIRM SIZE tahun 2012-2014 secara simultan mempunyai pengaruh signifikan terhadap harga saham. Adapun secara parsial, variabel ROA berpengaruh signifikan positif. Sedangkan variabel CAR, NPL, LDR dan FIRM SIZE berpengaruh signifikan negatif terhadap harga saham. Hasil uji R square pada penelitian ini menunjukkan bahwa variabel CAR, NPL, ROA, LDR, dan FIRM SIZE memiliki pengaruh 20,7% terhadap harga saham. Kata Kunci : CAR, NPL, ROA, LDR, Firm Size, Harga Saham
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