376 research outputs found
SYN -1,4-addition of carboxylate salts to cyclic allylic epoxides mediated by cuprous chloride
A mild method for the 1,4- opening of certain cyclic allylic epoxides has been found, using sodium carboxylates in the presence of cuprous chloride.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25416/1/0000865.pd
Tracking Turbulent Coherent Structures by Means of Neural Networks
[EN] The behaviours of individual flow structures have become a relevant matter of study in turbulent flows as the computational power to allow their study feasible has become available. Especially, high instantaneous Reynolds Stress events have been found to dominate the behaviour of the logarithmic layer. In this work, we present a viability study where two machine learning solutions are proposed to reduce the computational cost of tracking such structures in large domains. The first one is a Multi-Layer Perceptron. The second one uses Long Short-Term Memory (LSTM). Both of the methods are developed with the objective of taking the the structures' geometrical features as inputs from which to predict the structures' geometrical features in future time steps. Some of the tested Multi-Layer Perceptron architectures proved to perform better and achieve higher accuracy than the LSTM architectures tested, providing lower errors on the predictions and achieving higher accuracy in relating the structures in the consecutive time steps.This work was supported by RTI2018-102256-B-I00 of MINECO/FEDER. The computations of the new simulations were made possible by a generous grant of computing time from the Barcelona Supercomputing Centre, reference AECT-2020-2-0005.Aguilar-Fuertes, JJ.; Noguero-Rodríguez, F.; Jaen Ruiz, JC.; García-Raffi, LM.; Hoyas, S. (2021). Tracking Turbulent Coherent Structures by Means of Neural Networks. Energies. 14(4):1-15. https://doi.org/10.3390/en1404098411514
Long-term trends of midlatitude horizontal mesosphere/lower thermosphere winds over four decades
We analyse 43 years of mesosphere/lower thermosphere (MLT) horizontal winds obtained from a joint analysis of low frequency (LF) spaced receiver lower ionospheric drift measurements from late 1978 through 2008 and VHF meteor radar wind observations since summer 2004 at Collm (51.3∘ N, 13.0∘ E). Due to limitations of the earlier LF measurements, we restrict ourselves to the analysis of monthly mean winds near 90 km, which represents the meteor peak height as well as mean LF reflection heights in the MLT. We observe mainly positive trends of the zonal prevailing wind throughout the year, while the meridional winds tend to decrease in magnitude in both summer and winter. Furthermore, there is a change in long-term trends around the late 1990s, which is most clearly visible in summer MLT winds. We compare these measurements with long-term partial reflection radar observations of winds at 81–85 km over Juliusruh (54.6∘ N, 13.4∘ E) since 1990, and find general qualitative agreement of trends except for summer. The latter can be explained by the different altitudes considered, and by the latitude dependence of the summer mesospheric jet.</p
Get screened: a pragmatic randomized controlled trial to increase mammography and colorectal cancer screening in a large, safety net practice
Abstract Background Most randomized controlled trials of interventions designed to promote cancer screening, particularly those targeting poor and minority patients, enroll selected patients. Relatively little is known about the benefits of these interventions among unselected patients. Methods/Design "Get Screened" is an American Cancer Society-sponsored randomized controlled trial designed to promote mammography and colorectal cancer screening in a primary care practice serving low-income patients. Eligible patients who are past due for mammography or colorectal cancer screening are entered into a tracking registry and randomly assigned to early or delayed intervention. This 6-month intervention is multimodal, involving patient prompts, clinician prompts, and outreach. At the time of the patient visit, eligible patients receive a low-literacy patient education tool. At the same time, clinicians receive a prompt to remind them to order the test and, when appropriate, a tool designed to simplify colorectal cancer screening decision-making. Patient outreach consists of personalized letters, automated telephone reminders, assistance with scheduling, and linkage of uninsured patients to the local National Breast and Cervical Cancer Early Detection program. Interventions are repeated for patients who fail to respond to early interventions. We will compare rates of screening between randomized groups, as well as planned secondary analyses of minority patients and uninsured patients. Data from the pilot phase show that this multimodal intervention triples rates of cancer screening (adjusted odds ratio 3.63; 95% CI 2.35 - 5.61). Discussion This study protocol is designed to assess a multimodal approach to promotion of breast and colorectal cancer screening among underserved patients. We hypothesize that a multimodal approach will significantly improve cancer screening rates. The trial was registered at Clinical Trials.gov NCT00818857http://deepblue.lib.umich.edu/bitstream/2027.42/78264/1/1472-6963-10-280.xmlhttp://deepblue.lib.umich.edu/bitstream/2027.42/78264/2/1472-6963-10-280.pdfPeer Reviewe
Gravity as Backreaction
Quadratic theory of gravity is a complicated constraint system. We
investigate some consequences of treating quadratic terms perturbatively
(higher derivative version of backreaction effects). This approach is shown to
overcome some well known problems associated with higher derivative theories,
i.e., the physical gravitational degree of freedom remains unchanged from those
of Einstein gravity.
Using such an interpretation of gravity, we investigate a
classical and Wheeler DeWitt evolution of gravity for a
particular sign of , corresponding to non- tachyon case. Matter is
described by a phenomenological . It is concluded that
both the Friedmann potential () and the
Wheeler DeWitt potential () develop repulsive barriers near for
(i.e., ). The interpretations is clear. Repulsive
barrier in implies that a contracting FRW universe ()
will bounce to an expansion phase without a total gravitational collapse.
Repulsive barrier in means that is a classically forbidden
region. Therefore, probability of finding a universe with the big bang
singularity ( ) is exponentially suppressed.Comment: Accepted for publication in Phy. Rev. D.,18 pages, 6 figures, Latex
fil
Hamiltonian formulation for the classical EM radiation-reaction problem: application to the kinetic theory for relativistic collisionless plasmas
A notorious difficulty in the covariant dynamics of classical charged
particles subject to non-local electromagnetic (EM) interactions arising in the
EM radiation-reaction (RR) phenomena is due to the definition of the related
non-local Lagrangian and Hamiltonian systems. The lack of a standard
Lagrangian/Hamiltonian formulation in the customary asymptotic approximation
for the RR equation may inhibit the construction of consistent kinetic and
fluid theories. In this paper the issue is investigated in the framework of
Special Relativity. It is shown that, for finite-size spherically-symmetric
classical charged particles, non-perturbative Lagrangian and Hamiltonian
formulations in standard form can be obtained, which describe particle dynamics
in the presence of the exact EM RR self-force. As a remarkable consequence,
based on axiomatic formulation of classical statistical mechanics, the
covariant kinetic theory for systems of charged particles subject to the EM RR
self-force is formulated in Hamiltonian form. A fundamental feature is that the
non-local effects enter the kinetic equation only through the retarded particle
4-position, which permits the construction of the related non-local fluid
equations. In particular, the moment equations obtained in this way do not
contain higher-order moments, allowing as a consequence the adoption of
standard closure conditions. A remarkable aspect of the theory concerns the
short delay-time asymptotic expansions. Here it is shown that two possible
expansions are permitted. Both can be implemented for the single-particle
dynamics as well as for the corresponding kinetic and fluid treatments. In the
last case, they are performed a posteriori on the relevant moment equations
obtained after integration of the kinetic equation over the velocity space.
Comparisons with literature are pointed out
Occupational exposure to nano-TiO2 in the life cycle steps of new depollutant mortars used in construction
The present work is focused on the measurement of workers exposure to nano-TiO2
in the life cycle steps of depollutant mortars. It has been done in the framework of the
SCAFFOLD project, which aims at the management of potential risks arising from the use of
manufactured nanomaterials in construction. Main findings can be summarized as follows: (1)
The occupational exposure to nano- TiO2 is below 0.3 mg/m3 for all measured scenarios. The
highest concentrations were measured during the cleaning task (in the nano- TiO2
manufacturing process) and during the application (spraying) of depollutant coatings on a wall.
(2) It was found a high release of particles above the background in several tasks as expected
due to the nature of the activities performed. The maximum concentration was measured
during drilling and during adding powder materials (mean total particle concentration up to
5.591E+04 particles/cm3 and 5.69E+04 particles/cm3). However, considering data on total
particle concentration released, no striking differences have been observed when tasks have
been performed using conventional materials in the sector (control) and when using materials
doped with nano-objects.European Commission's FP
On the energy of charged black holes in generalized dilaton-axion gravity
In this paper we calculate the energy distribution of some charged black
holes in generalized dilaton-axion gravity. The solutions correspond to charged
black holes arising in a Kalb-Ramond-dilaton background and some existing
non-rotating black hole solutions are recovered in special cases. We focus our
study to asymptotically flat and asymptotically non-flat types of solutions and
resort for this purpose to the M{\o}ller prescription. Various aspects of
energy are also analyzed.Comment: LaTe
- …