11,144 research outputs found
Influence of pH and Temperature on Basaluminite Dissolution Rates
This is the author accepted manuscript. The final version is available from the American Chemical Society via the DOI in this record.The processes, rates, and controlling factors of basaluminite (Al4(SO4)(OH)10·4H2O) dissolution
were assessed using batch dissolution experiments in both H2SO4 and HCl at pHs of 2.4, 2.9-3.1,
3.5-3.6 and 4.0-4.1, and temperatures of c. 279, 293, 303 and 312 K. Basaluminite dissolution is
incongruent over most of the studied pH range, giving generally a lower Al/S ratio in solution than
in the pristine basaluminite sample. The lower Al/S ratio may be at least partially explained by the
preferential release of sulfate compared to Al from the dissolving basaluminite. The dissolution
rates range between 10â7.6 and 10â9.1 mol·mâ2
·s
â1
. At 291-293K, the slowest rates were observed
at pH 4.1 in H2SO4 solutions, while at pH 3.0, the slowest rates were observed at 279 K in HCl
solutions. Decreases in pH and increases in temperature increase dissolution rates. The influence
of pH and temperature on the basaluminite dissolution rate, expressed as Al release, can be described
by the following expression:
= 107.3±0.5+
0.64±0.04
â78±3â
Where rateAl is the basaluminite dissolution rate, based on the rate of Al release from dissolving
basaluminite (in mol·mâ2
·sâ1
); aH+ is the activity of hydrogen ions in solution; R is the Universal
gas constant (in kJ·molâ1
·Kâ1
) and T is temperature (in K). In light of the calculated value for the
activation energy (78±3 kJ·molâ1
), basaluminite dissolution appears to be surface-controlled. The
reaction for basaluminite dissolution under the experimental conditions is proposed to be
Al4(SO4)(OH)10·4H2O + 10 H
+â 4 Al3+ + SO4
2- + 14 H2O.We acknowledge funding for this study provided by the EC Marie Curie Intra-European Fellowship
program (Project entitled âReactivity of Aluminum Sulfate Minerals in Mine Wastesâ;
RASMIM) through a fellowship to P.A. We thank Gareth Tarbuck (UCL, London, UK) for help
with the geochemical analyses and mineralogical determinations and their interpretation. We also
thank the reviewers whose comments significantly improved the manuscript
Constraints on Association of Single-pulse Gamma-ray Bursts and Supernovae
We explore the hypothesis, similar to one recently suggested by Bloom and
colleagues, that some nearby supernovae are associated with smooth,
single-pulse gamma-ray bursts, possibly having no emission above ~ 300 keV. We
examine BATSE bursts with durations longer than 2 s, fitting those which can be
visually characterized as single-pulse events with a lognormal pulse model. The
fraction of events that can be reliably ascertained to be temporally and
spectrally similar to the exemplar, GRB 980425 - possibly associated with SN
1998bw - is 4/1573 or 0.25%. This fraction could be as high as 8/1573 (0.5%) if
the dimmest bursts are included. Approximately 2% of bursts are morphologically
similar to GRB 980425 but have emission above ~ 300 keV. A search of supernova
catalogs containing 630 detections during BATSE's lifetime reveals only one
burst (GRB 980425) within a 3-month time window and within the total 3-sigma
BATSE error radius that could be associated with a type Ib/c supernova. There
is no tendency for any subset of single-pulse GRBs to fall near the
Supergalactic Plane, whereas SNe of type Ib/c do show this tendency. Economy of
hypotheses leads us to conclude that nearby supernovae generally are not
related to smooth, single-pulse gamma-ray bursts.Comment: 25 pages, 5 figure
Mitoxantrone is superior to doxorubicin in a multiagent weekly regimen for patients older than 60 with high-grade lymphoma: results of a BNLI randomized trial of PAdriaCEBO versus PMitCEBO
A prospective, multicenter, randomized trial was undertaken to compare the efficacy and toxicity of adriamycin with mitoxantrone within a 6-drug combination chemotherapy regimen for elderly patients (older than 60 years) with high-grade non-Hodgkin lymphoma (HGL) given for a minimum of 8 weeks. A total of 516 previously untreated patients aged older than 60 years were randomized to receive 1 of 2 anthracycline-containing regimens: adriamycin, 35 mg/m2 intravenously (IV) on day 1 (n = 259), or mitoxantrone, 7 mg/m2 IV on day 1 (n = 257); with prednisolone, 50 mg orally on days 1 to 14; cyclophosphamide, 300 mg/m2 IV on day 1; etoposide, 150 mg/m2 IV on day 1; vincristine, 1.4 mg/m2 IV on day 8; and bleomycin, 10 mg/m2 IV on day 8. Each 2-week cycle was administered for a minimum of 8 weeks in the absence of progression. Forty-three patients were ineligible for analysis. The overall and complete remission rates were 78% and 60% for patients receiving PMitCEBO and 69% and 52% for patients receiving PAdriaCEBO (P = .05, P = .12, respectively). Overall survival was significantly better with PMitCEBO than PAdriaCEBO (P = .0067). However, relapse-free survival was not significantly different (P = .16). At 4 years, 28% of PAdriaCEBO patients and 50% of PMitCEBO patients were alive (P = .0001). Ann Arbor stage III/IV, World Health Organization performance status 2-4, and elevated lactate dehydrogenase negatively influenced overall survival from diagnosis. In conclusion, the PMitCEBO 8-week combination chemotherapy regimen offers high response rates, durable remissions, and acceptable toxicity in elderly patients with HGL
Cold Molecule Spectroscopy for Constraining the Evolution of the Fine Structure Constant
We report precise measurements of ground-state, -doublet microwave
transitions in the hydroxyl radical molecule (OH). Utilizing slow, cold
molecules produced by a Stark decelerator we have improved over the precision
of the previous best measurement by twenty-five-fold for the F' = 2 F = 2
transition, yielding (1 667 358 996 4) Hz, and by ten-fold for the F' = 1
F = 1 transition, yielding (1 665 401 803 12) Hz. Comparing these
laboratory frequencies to those from OH megamasers in interstellar space will
allow a sensitivity of 1 ppm for over
years.Comment: This version corrects minor typos in the Zeeman shift discussio
The effect of topology on the structure and free energy landscape of DNA kissing complexes
We use a recently developed coarse-grained model for DNA to study kissing
complexes formed by hybridization of complementary hairpin loops. The binding
of the loops is topologically constrained because their linking number must
remain constant. By studying systems with linking numbers -1, 0 or 1 we show
that the average number of interstrand base pairs is larger when the topology
is more favourable for the right-handed wrapping of strands around each other.
The thermodynamic stability of the kissing complex also decreases when the
linking number changes from -1 to 0 to 1. The structures of the kissing
complexes typically involve two intermolecular helices that coaxially stack
with the hairpin stems at a parallel four-way junction
Current status and developing recommendations of tailings dam failure
This is the final version of the article. Available from Hindawi Publishing Corporation via the DOI in this record.Tailings dam failure accidents with limited emergency response time and huge potential threats, can often lead to heavy
casualties and serious financial losses. In recent years, the decreasing trend of tailings dam failure accidents evidences the development
of modern technology and safety management. However, the frequency of major tailings dam failure accidents has increased, rather than
decreased. The 2015 Samarco Accident in Brazil and the 2014 Mount Polley Accident in Canada, along with their disastrous
consequences, once again sounded the alarm for the tailings ponds safety. China is now facing a complicated safety situation, with 8869
tailings ponds all over the country, including 1425 âOverhead Tailings Pondsâ which represents the tailings ponds that located within 1
km upstream of residential area, workshops, schools or other important facilities. Based on a large amount of relevant research literatures, focusing on three main aspects of accident prevention and control which include safety monitoring, early-warning and emergency
preparation, safety management codes and standards, the current status and frontier progress were reviewed in this paper. Furthermore,
the relevant problems in China were discussed and several improvement recommendations were put forward, which could provide a
reference for the tailings pond accident prevention theoretical research and technological innovation. The result shows: (1) the safety
monitoring standards in China are relatively strict. However, the monitoring instruments are lack of the stability, reliability and
practicability. Thus the development of specific devices and new technologies is urgently needed. (2) The current early-warning method
is lack of diversity and reliability. And further interdisciplinary application of information technology is becoming the developing trend.
(3) The emergency management and decision-making should be based on sufficient scientific proof. However the relevant research is
limited by test methods and simulating algorithms. (4) China now has built a complete system of safety management codes and standards.
But with shortcomings of safety level classification, life-cycle management, change management process, accident investigation and so
on, there is still a long way to go
First limits on the 3-200 keV X-ray spectrum of the quiet Sun using RHESSI
We present the first results using the Reuven Ramaty High-Energy Solar
Spectroscopic Imager, RHESSI, to observe solar X-ray emission not associated
with active regions, sunspots or flares (the quiet Sun). Using a newly
developed chopping technique (fan-beam modulation) during seven periods of
offpointing between June 2005 to October 2006, we obtained upper limits over
3-200 keV for the quietest times when the GOES12 1-8A flux fell below
Wm. These values are smaller than previous limits in the 17-120 keV
range and extend them to both lower and higher energies. The limit in 3-6 keV
is consistent with a coronal temperature MK. For quiet Sun periods
when the GOES12 1-8A background flux was between Wm and
Wm, the RHESSI 3-6 keV flux correlates to this as a power-law,
with an index of . The power-law correlation for microflares has
a steeper index of . We also discuss the possibility of
observing quiet Sun X-rays due to solar axions and use the RHESSI quiet Sun
limits to estimate the axion-to-photon coupling constant for two different
axion emission scenarios.Comment: 4 pages, 3 figures, Accepted by ApJ letter
Gene-history correlation and population structure
Correlation of gene histories in the human genome determines the patterns of
genetic variation (haplotype structure) and is crucial to understanding genetic
factors in common diseases. We derive closed analytical expressions for the
correlation of gene histories in established demographic models for genetic
evolution and show how to extend the analysis to more realistic (but more
complicated) models of demographic structure. We identify two contributions to
the correlation of gene histories in divergent populations: linkage
disequilibrium, and differences in the demographic history of individuals in
the sample. These two factors contribute to correlations at different length
scales: the former at small, and the latter at large scales. We show that
recent mixing events in divergent populations limit the range of correlations
and compare our findings to empirical results on the correlation of gene
histories in the human genome.Comment: Revised and extended version: 26 pages, 5 figures, 1 tabl
Galaxy Distances in the Nearby Universe: Corrections For Peculiar Motions
By correcting the redshift--dependent distances for peculiar motions through
a number of peculiar velocity field models, we recover the true distances of a
wide, all-sky sample of nearby galaxies (~ 6400 galaxies with velocities
cz<5500 km/s), which is complete up to the blue magnitude B=14 mag. Relying on
catalogs of galaxy groups, we treat ~2700 objects as members of galaxy groups
and the remaining objects as field galaxies.
We model the peculiar velocity field using: i) a cluster dipole
reconstruction scheme; ii) a multi--attractor model fitted to the Mark II and
Mark III catalogs of galaxy peculiar velocities. According to Mark III data the
Great Attractor has a smaller influence on local dynamics than previously
believed, whereas the Perseus-Pisces and Shapley superclusters acquire a
specific dynamical role. Remarkably, the Shapley structure, which is found to
account for nearly half the peculiar motion of the Local Group, is placed by
Mark III data closer to the zone of avoidance with respect to its optical
position.
Our multi--attractor model based on Mark III data favors a cosmological
density parameter Omega ~ 0.5 (irrespective of a biasing factor of order
unity). Differences among distance estimates are less pronounced in the ~ 2000
- 4000 km/s distance range than at larger or smaller distances. In the last
regions these differences have a serious impact on the 3D maps of the galaxy
distribution and on the local galaxy density --- on small scales.Comment: 24 pages including (9 eps figures and 7 tables). Figures 1,2,3,4 are
available only upon request. Accepted by Ap
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