5,561 research outputs found
Low Cost Dewatering of Waste Slurries
The U.S. Bureau of Mines has developed a technique for dewatering mineral waste slurries which utilizes polymer and a static screen. A variety of waste slurries from placer gold mines and crushed stone operations have been successfully treated using the system. Depending on the waste, a number of polymers have been used successfully with polymer costs ranging from 0.15 per 1,000 gal treated. The dewatering is accomplished using screens made from either ordinary window screen or wedge wire. The screens used are 8 ft wide and 8 ft long. The capacity of the screens varies from 3 to 7 gpm/sq. ft. The water produced is acceptable for recycling to the plant or for discharge to the environment. For example, a fine grain dolomite waste slurry produced from a crushed stone operation was dewatered from a nominal 2.5 pct solids to greater than 50 pct solids using 0.15 worth of polymer per 1,000 gal of slurry. The resulting waste water had a turbidity of less than 50 NTU and could be discharged or recycled. The paper describes field tests conducted using the polymer-screen dewatering system
Chandra HRC Localization of the Low Mass X-ray Binaries X1624-490 and X1702-429: The Infrared Counterparts
We report on the precise localization of the low mass X-ray binaries
X1624-490 and X1702-429 with the Chandra HRC-I. We determine the best positions
to be 16:28:02.825 -49:11:54.61 (J2000) and 17:06:15.314 -43:02:08.69 (J2000)
for X1624-490 and X1702-429, respectively, with the nominal Chandra positional
uncertainty of 0.6". We also obtained deep IR observations of the fields of
these sources in an effort to identify the IR counterparts. A single, faint
(Ks=18.3 +/- 0.1) source is visible inside the Chandra error circle of
X1624-490, and we propose this source as its IR counterpart. For X1702-429, a
Ks=16.5 +/- 0.07 source is visible at the edge of the Chandra error circle. The
brightness of both counterpart candidates is comparable to that of other low
mass X-ray binary IR counterparts when corrected for extinction and distance.Comment: 5 pages, 2 figures, accepted for publication in Ap
Simple Photoelectric Absorption during Dipping in the ASCA Observation of XB1916-053
We report results of analysis of the ASCA observation of the Low Mass X-ray
Binary dipping source XB1916-053 made on 1993, May 2nd. We have shown that the
spectra can be well fitted by the same two-component model previously used to
give good explanations of the very different dip sources X1755-338 and
X1624-490, consisting of point-source blackbody emission from the neutron star
plus extended Comptonised emission from the accretion disk corona. In
XB1916-053, all levels of dipping can be fitted using kT_bb= 2.14+/-0.28 keV
and power law photon index = 2.42 +/-0.21. Dipping is shown to be due to large
increases of column density for the point-like blackbody, combined with the
extended power law component being progressively covered by absorber until in
the deepest parts of dips, the partial covering fraction approaches unity. This
approach differs radically from the ``absorbed plus unabsorbed'' approach
previously used in spectral modelling of XB1916-053 and similar sources, in
which the normalisation of the unabsorbed component is allowed to decrease
markedly in dipping, behavior generally attributed to the effects of electron
scattering. Thus we have shown that spectral evolution in XB1916-053 can be
explained simply in terms of photoelectric absorption without the need for
substantial electron scattering. This explanation is supported by calculation
of the relative importance of photoelectric absorption and electron scattering
in the absorbing region which shows that little electron scattering is expected
in the ASCA energy band.Comment: 9 pages, Latex, 5 eps figure
The temporal relationship between the neural and vascular actions of kallidin within the nose
The time course of effect of the B2-receptor agonist kallidin (K) on induced changes of nasal airflow, rhinorrhoea, nasal pain, sneezing and nasal microvascular leakage has been examined and compared with its B2 metabolite agonist bradykinin (B) and the B1-agonist [des-arg9]-bradykinin (D). When administered as a single dose K and B induced an immediate sensation of pain, rhinorrhoea, elevations in lavage albumin and protein levels and a sustained increase in nasal airways resistance (NAR) for 5–40 min post-challenge. [des-arg9]-Bradykinin and vehicle placebo (V) were without effect on any of these indices. These studies identify the action of K and B within the nose and differentiate the neural and vascular effects of these kinins in addition to suggesting the potential that nasal blockage and nasal microvascular leakage represent alterations in differing vascular compartments. These findings have implications for the understanding and therapeutic manipulation of rhinitis
New XMM-Newton analysis of three bright X-ray sources in M31 globular clusters, including a new black hole candidate
We present detailed analysis of three globular cluster X-ray sources in the
XMM-Newton extended survey of M31. The X-ray counterpart to the M31 globular
cluster Bo 45 (XBo 45) was observed with XMM-Newton on 2006 December 26. Its
combined pn+MOS 0.3--10 keV lightcurve exhibited a r.m.s variability of ~10%,
and its 0.3--7.0 keV emission spectrum was well described by an absorbed power
law with photon index 1.440.12. Its variability and emission is
characteristic of low mass X-ray binaries (LMXBs) in the low-hard state,
whether the accretor is a neutron star or black hole. Such behaviour is
typically observed at luminosities \la10% Eddington. However, XBo 45
exhibited this behaviour at an unabsorbed, 0.3--10 keV luminosity of
2.5 erg s, or{~140%} Eddington for a 1.4
neutron star accreting hydrogen. Hence, we identify XBo 45 as a new
candidate black hole LMXB. XBo 45 appears to have been consistently bright for
~30 years, consistent with theoretical prediction for a globular cluster black
hole binary formed via tidal capture. Bo 375 was observed in the 2007, January
2 XMM-Newton observation, and has a two-component spectrum that is typical for
a bright neutron star LMXB. Bo 135 was observed in the same field as Bo 45, and
could contain either a black hole or neutron star.Comment: Accepted by ApJ, 16 pages, 5 figures. This version includes the final
changes made at the request of the refere
Distributed top-k aggregation queries at large
Top-k query processing is a fundamental building block for efficient ranking in a large number of applications. Efficiency is a central issue, especially for distributed settings, when the data is spread across different nodes in a network. This paper introduces novel optimization methods for top-k aggregation queries in such distributed environments. The optimizations can be applied to all algorithms that fall into the frameworks of the prior TPUT and KLEE methods. The optimizations address three degrees of freedom: 1) hierarchically grouping input lists into top-k operator trees and optimizing the tree structure, 2) computing data-adaptive scan depths for different input sources, and 3) data-adaptive sampling of a small subset of input sources in scenarios with hundreds or thousands of query-relevant network nodes. All optimizations are based on a statistical cost model that utilizes local synopses, e.g., in the form of histograms, efficiently computed convolutions, and estimators based on order statistics. The paper presents comprehensive experiments, with three different real-life datasets and using the ns-2 network simulator for a packet-level simulation of a large Internet-style network
Measurements of Sunyaev-Zel'dovich Effect Scaling Relations for Clusters of Galaxies
We present new measurements of the Sunyaev-Zel'dovich (SZ) effect from
clusters of galaxies using the Sunyaev-Zel'dovich Infrared Experiment (SuZIE
II). We combine these new measurements with previous cluster observations with
the SuZIE instrument to form a sample of 15 clusters of galaxies. For this
sample we calculate the central Comptonization, y, and the integrated SZ flux
decrement, S, for each of our clusters. We find that the integrated SZ flux is
a more robust observable derived from our measurements than the central
Comptonization due to inadequacies in the spatial modelling of the
intra-cluster gas with a standard Beta model. This is highlighted by comparing
our central Comptonization results with values calculated from measurements
using the BIMA and OVRO interferometers. On average, the SuZIE calculated
central Comptonizations are approximately 60% higher in the cooling flow
clusters than the interferometric values, compared to only approximately 12%
higher in the non-cooling flow clusters. We believe this discrepancy to be in
large part due to the spatial modelling of the intra-cluster gas. From our
cluster sample we construct y-T and S-T scaling relations. The y-T scaling
relation is inconsistent with what we would expect for self-similar clusters;
however this result is questionable because of the large systematic uncertainty
in the central Comptonization. The S-T scaling relation has a slope and
redshift evolution consistent with what we expect for self-similar clusters
with a characteristic density that scales with the mean density of the
universe. We rule out zero redshift evolution of the S-T relation at 90%
confidence.Comment: Accepted to Astrophysical Journal. 52 pages, 14 tables, 7 figures
;replaced to match ApJ accepted versio
The Cessation of Flickering during Dips in Cygnus X-1
We report the discovery of the cessation of flickering in dips in the black
hole candidate Cygnus X-1, detected for the first time in the ASCA observation
of May 9th., 1995. During this observation, particularly deep dipping took
place resulting in strong changes in hardness ratio corresponding to absorption
of the power law spectral component. The deadtime corrected light curve with
high time resolution clearly shows a dramatic decrease in the extent of
flickering in the band 0.7 - 4.0 keV during dipping, but in the band 4.0 - 10.0
keV, there is relatively little change. We show that the rms flickering
amplitude in the band 0.7 - 4.0 keV is proportional to the X-ray intensity in
this band which changes by a factor of almost three. This is direct evidence
that the strong Low State flickering is intrinsic to the power law emission; ie
takes place as part of the emission process. The rms amplitude is proportional
to the intensity in the low energy band, except for a possible deviation from
linearity at the lower intensities. If confirmed, this non-linearity could
imply a process such as electron scattering of radiation which will tend to
smear out the fluctuations, or a process of fluctuation generation which
depends on radial position in the source. Thus timing observations during
absorption dips can give information about the source region and may place
constraints on its size.Comment: 6 pages including 4 figures, accepted for publication in
Astrophysical Journal Letter
Exploring the Feasibility of Service Integration in a Low-Income Setting: A Mixed Methods Investigation into Different Models of Reproductive Health and HIV Care in Swaziland.
Integrating reproductive health (RH) with HIV care is a policy priority in high HIV prevalence settings, despite doubts surrounding its feasibility and varying evidence of effects on health outcomes. The process and outcomes of integrated RH-HIV care were investigated in Swaziland, through a comparative case study of four service models, ranging from fully integrated to fully stand-alone HIV services, selected purposively within one town. A client exit survey (n=602) measured integrated care received and unmet family planning (FP) needs. Descriptive statistics were used to assess the degree of integration per clinic and client demand for services. Logistic regression modelling was used to test the hypothesis that clients at more integrated sites had lower unmet FP needs than clients in a stand-alone site. Qualitative methods included in-depth interviews with clients and providers to explore contextual factors influencing the feasibility of integrated RH-HIV care delivery; data were analysed thematically, combining deductive and inductive approaches. Results demonstrated that clinic models were not as integrated in practice as had been claimed. Fragmentation of HIV care was common. Services accessed per provider were no higher at the more integrated clinics compared to stand-alone models (p>0.05), despite reported demand. While women at more integrated sites received more FP and pregnancy counselling than stand-alone models, they received condoms (a method of choice) less often, and there was no statistical evidence of difference in unmet FP needs by model of care. Multiple contextual factors influenced integration practices, including provider de-skilling within sub-specialist roles; norms of task-oriented routinised HIV care; perceptions of heavy client loads; imbalanced client-provider interactions hindering articulation of RH needs; and provider motivation challenges. Thus, despite institutional support, factors related to the social context of care inhibited provision of fully integrated RH-HIV services in these clinics. Programmes should move beyond simplistic training and equipment provision if integrated care interventions are to be sustained
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