416 research outputs found
C*-algebras associated with endomorphisms and polymorphisms of compact abelian groups
A surjective endomorphism or, more generally, a polymorphism in the sense of
\cite{SV}, of a compact abelian group induces a transformation of .
We study the C*-algebra generated by this operator together with the algebra of
continuous functions which acts as multiplication operators on .
Under a natural condition on the endo- or polymorphism, this algebra is simple
and can be described by generators and relations. In the case of an
endomorphism it is always purely infinite, while for a polymorphism in the
class we consider, it is either purely infinite or has a unique trace. We prove
a formula allowing to determine the -theory of these algebras and use it to
compute the -groups in a number of interesting examples.Comment: 25 page
Telephone follow-up to identify incident lung cancer symptoms in COPD patients
Background: COPD patients are at very high risk of lung cancer, yet new respiratory symptoms of lung cancer may be particularly hard to identify. Aim: We sought to assess the feasibility of actively seeking lung cancer symptoms to improve the timeliness of diagnosis in this group. Design and setting: Observational study to evaluate the feasibility and practicability of the intervention. Patients were recruited from a primary care COPD register and were contacted by telephone 4-monthly over 12 months. Chest X-ray rates were assessed over the 20 months before, during the intervention and for 20 months following it, in both the study group and in patients on the register who did not volunteer for the intervention. Results: Most symptoms were identified at the first call, with 13 (17%) subjects admitting to a new persistent cough and 7 (9%) to a change in their cough. As a result of symptoms identified on the first call, 21 (27%) of the participating patients were referred for a chest X-ray and 4 (5%) were referred urgently to secondary care. Incident symptoms continued frequently to be identified at all subsequent calls, with an overall total of 49% of patients qualifying for and receiving a chest X-ray. Interestingly, the chest X-ray rate remained significantly elevated for the 20 months following the intervention, whilst there appeared to be little change in the non-study COPD patients. Conclusion: The intervention was readily practicable and lung cancer symptoms were frequently identified. The intervention may have resulted in a behavior change leading to a persistently higher chest X-ray rate, although the comparator group was not a formal control group and further assessment in a randomized control trial appears justified
Hoop conjecture for colliding black holes : non-time-symmetric initial data
The hoop conjecture is well confirmed in momentarily static spaces, but it
has not been investigated systematically for the system with relativistic
motion. To confirm the hoop conjecture for non-time-symmetric initial data, we
consider the initial data of two colliding black holes with momentum and search
an apparent horizon that encloses two black holes. In testing the hoop
conjecture, we use two definitions of gravitational mass : one is the ADM mass
and the other is the quasi-local mass defined by Hawking. Although both
definitions of gravitational mass give fairly consistent picture of the hoop
conjecture, the hoop conjecture with the Hawking mass can judge the existence
of an apparent horizon for wider range of parameters of the initial data
compared to the ADM mass.Comment: 15pages, 4 figure
Entanglement required in achieving entanglement-assisted channel capacities
Entanglement shared between the two ends of a quantum communication channel
has been shown to be a useful resource in increasing both the quantum and
classical capacities for these channels. The entanglement-assisted capacities
were derived assuming an unlimited amount of shared entanglement per channel
use. In this paper, bounds are derived on the minimum amount of entanglement
required per use of a channel, in order to asymptotically achieve the capacity.
This is achieved by introducing a class of entanglement-assisted quantum codes.
Codes for classes of qubit channels are shown to achieve the quantum
entanglement-assisted channel capacity when an amount of shared entanglement
per channel given by, E = 1 - Q_E, is provided. It is also shown that for very
noisy channels, as the capacities become small, the amount of required
entanglement converges for the classical and quantum capacities.Comment: 9 pages, 2 figures, RevTex
Impacts of Multiple Environmental Changes on LongâTerm Nitrogen Loading From the Chesapeake Bay Watershed
Excessive nutrient inputs from land, particularly nitrogen (N), have been found to increase the occurrence of hypoxia and harmful algal blooms in coastal ecosystems. To identify the main contributors of increased N loading and evaluate the efficacy of water pollution control policies, it is essential to quantify and attribute the longâterm changes in riverine N export. Here, we use a stateâofâtheâart terrestrialâaquatic interface model to examine how multiple environmental factors may have affected N export from the Chesapeake Bay watershed since 1900. These factors include changes in climate, carbon dioxide, land use, and N inputs (i.e., atmospheric N deposition, animal manure, synthetic N fertilizer use, and wastewater discharge). Our results estimated that ammonium (NH4+) and nitrate (NO3â) export increased substantially (66% for NH4+ and 123% for NO3â) from the 1900s to the 1990s and then declined (32% for NH4+ and 14% for NO3â) since 2000. The temporal trend of dissolved organic nitrogen (DON) export paralleled that of dissolved inorganic N, while particulate organic nitrogen export was relatively constant during 1900â2015. Precipitation was the primary driver of interannual variability in N export to the Bay. Wastewater discharge explained most of the longâterm change in riverine NH4+ and DON fluxes from 1900 to 2015. The changes in atmospheric deposition, wastewater, and synthetic fertilizer were responsible for the trend of riverine NO3â. In light of our modelâbased attribution analysis, terrestrial nonâpoint source nutrient management will play an important role in achieving water quality goals
The role of parent, classmate, and teacher support in student engagement: Evidence from Ghana
The literature is unequivocal about the importance of improving academic engagement in addressing challenges such as school drop out or increasing student motivation. What is less certain, particularly in the literature from developing countries, is how social support systems (parents, teachers, and classmates) influence studentsâ emotional and behavioral engagement. Drawing from the ecological perspective, this study analyzes data from Ghana using structural equation modeling to examine mediated and unmediated pathways through which parent, teacher, and classmate support affect studentsâ emotional and behavioral engagement. Findings suggest classmate support has the strongest association with student engagement, followed by parental support. Teacher support is neither a mediator nor a direct predictor of student engagement. These findings have implications for teacher training and professional development, especially training on how to actively involve parents in motivating their children to be engaged scholars
Impacts of Multiple Environmental Changes on LongâTerm Nitrogen Loading From the Chesapeake Bay Watershed
Excessive nutrient inputs from land, particularly nitrogen (N), have been found to increase the occurrence of hypoxia and harmful algal blooms in coastal ecosystems. To identify the main contributors of increased N loading and evaluate the efficacy of water pollution control policies, it is essential to quantify and attribute the longâterm changes in riverine N export. Here, we use a stateâofâtheâart terrestrialâaquatic interface model to examine how multiple environmental factors may have affected N export from the Chesapeake Bay watershed since 1900. These factors include changes in climate, carbon dioxide, land use, and N inputs (i.e., atmospheric N deposition, animal manure, synthetic N fertilizer use, and wastewater discharge). Our results estimated that ammonium (NH4+) and nitrate (NO3â) export increased substantially (66% for NH4+ and 123% for NO3â) from the 1900s to the 1990s and then declined (32% for NH4+ and 14% for NO3â) since 2000. The temporal trend of dissolved organic nitrogen (DON) export paralleled that of dissolved inorganic N, while particulate organic nitrogen export was relatively constant during 1900â2015. Precipitation was the primary driver of interannual variability in N export to the Bay. Wastewater discharge explained most of the longâterm change in riverine NH4+ and DON fluxes from 1900 to 2015. The changes in atmospheric deposition, wastewater, and synthetic fertilizer were responsible for the trend of riverine NO3â. In light of our modelâbased attribution analysis, terrestrial nonâpoint source nutrient management will play an important role in achieving water quality goals
Anomalous synchronization threshold in coupled logistic maps
We consider regular lattices of coupled chaotic maps. Depending on lattice
size, there may exist a window in parameter space where complete
synchronization is eventually attained after a transient regime. Close outside
this window, an intermittent transition to synchronization occurs. While
asymptotic transversal Lyapunov exponents allow to determine the
synchronization threshold, the distribution of finite-time Lyapunov exponents,
in the vicinity of the critical frontier, is expected to provide relevant
information on phenomena such as intermittency. In this work we scrutinize the
distribution of finite-time exponents when the local dynamics is ruled by the
logistic map . We obtain a theoretical estimate for the
distribution of finite-time exponents, that is markedly non-Gaussian. The
existence of correlations, that spoil the central limit approximation, is shown
to modify the typical intermittent bursting behavior. The present scenario
could apply to a wider class of systems with different local dynamics and
coupling schemes.Comment: 6 pages, 6 figure
Nanofiltration separation of polyvalent and monovalent anions in desalination brines
This work, as part of a global membrane process for the recovery of alkali and acids from reverse osmosis (RO) desalination brines, focuses on the nanofiltration (NF) separation of polyvalent and monovalent anions, more specifically sulfate and chloride. This pretreatment stage plays a key role in the whole recovery process. Working with model brines simulating the concentration of RO concentrates, 0.2â1.2 M chloride concentration and 0.1 M sulfate concentration, the experimental performance and modeling of the NF separation is reported. The study has been carried out with the NF270 (Dow Filmtec) membrane. The effect of operating pressure (500â2000 kPa), ionic strength (0.4â1.3 M) and chloride initial concentration (0.2â1.2 M) on the membrane separation capacity has been investigated. Finally, the Donnan Steric Pore Model (DSPM) together with experimentally determined parameters, effective pore radius (rp), thickness of the membrane effective layer (d) and effective membrane charge density (Xd), was proved accurate enough to satisfactorily describe the experimental results. In this work we provide for the first time the analysis of partitioning effects and transport mechanism in the NF separation of sulfate and chloride anions in concentrations that simulate those found in RO desalination brines.This work has been financially supported by projects CTQ2008-0690, ENE2010-15585 and CTM2011-23912 (co-financed by ERDF Funds).The authors would like to acknowledge SADYT, S.A. for providing assistance for this work
The role of point-like topological excitations at criticality: from vortices to global monopoles
We determine the detailed thermodynamic behavior of vortices in the O(2)
scalar model in 2D and of global monopoles in the O(3) model in 3D. We
construct new numerical techniques, based on cluster decomposition algorithms,
to analyze the point defect configurations. We find that these criteria produce
results for the Kosterlitz-Thouless temperature in agreement with a topological
transition between a polarizable insulator and a conductor, at which free
topological charges appear in the system. For global monopoles we find no pair
unbinding transition. Instead a transition to a dense state where pairs are no
longer distinguishable occurs at T<Tc, without leading to long range disorder.
We produce both extensive numerical evidence of this behavior as well as a
semi-analytic treatment of the partition function for defects. General
expectations for N=D>3 are drawn, based on the observed behavior.Comment: 14 pages, REVTEX, 13 eps figure
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