1,276 research outputs found
Una aproximación al trabajo con niños especialmente dotados en matemáticas
Este estudio se centra en el diseño e implementación de tareas que permitan a los futuros profesores identificar el talento matemático de los alumnos, al mismo tiempo que potencian en ellos su desarrollo. El trabajo fue realizado con estudiantes de entre 7 y 11 años, que participaron en cursos extraordinarios de matemática. La tarea se basó en la teoría de situaciones de Brosseau, con algunos conceptos de combinatoria y con movimientos en el espacio. En su desarrollo se utilizó material concreto como medio facilitador hacia la abstracción. Los futuros profesores debían observar la actividad de los alumnos y registrar todos los acontencimientos que, bajo su perspectiva, intervenían el la resolución de la tarea. En los resultados mostramos la potencialidad del trabajo desarrollado, cuáles fueron las características más destacadas que se potenciaron en los alumnos y cuáles fueron las identificadas por los futuros profesores
Effect of electric field on the photoluminescence of polymer-inorganic nanoparticles composites
We report on the effect of electric field on the photoluminescence, PL, from
a composite consisting of a conjugated polymer mixed with zinc oxide
nanoparticles. We have found that in the absence of electric field PL emission
from the composite film has two maxima in the blue and green-yellow regions.
Application of a voltage bias to planar gold electrodes suppresses the
green-yellow emission and shifts the only PL emission maximum towards the blue
region. Current-voltage characteristics of the polymer-nanoparticles composite
exhibit the non-linear behavior typical of non-homogeneous polymer-inorganic
structures. Generation of excited states in the composite structure implies the
presence of several radiative recombination mechanisms including formation of
polymer-nanoparticle complexes including exciplex states and charge transfer
between the polymer and nanoparticle that can be controlled by an electric
field.Comment: 5 pages, 5 figures. accepted for publication in Solid State
Communication
Two-phonon 1- state in 112Sn observed in resonant photon scattering
Results of a photon scattering experiment on 112Sn using bremsstrahlung with
an endpoint energy of E_0 = 3.8 MeV are reported. A J = 1 state at E_x =
3434(1) keV has been excited. Its decay width into the ground state amounts to
Gamma_0 = 151(17) meV, making it a candidate for a [2+ x 3-]1- two-phonon
state. The results for 112Sn are compared with quasiparticle-phonon model
calculations as well as the systematics of the lowest-lying 1- states
established in other even-mass tin isotopes. Contrary to findings in the
heavier stable even-mass Sn isotopes, no 2+ states between 2 and 3.5 MeV
excitation energy have been detected in the present experiment.Comment: 10 pages, including 2 figures, Phys. Rev. C, in pres
Viking Age garden plants from southern Scandinavia: diversity, taphonomy and cultural aspects
Plant finds recovered from archaeological sites in southern Scandinavia dated to the Viking Age reflect the diversity of useful plants that were cultivated and collected. This review presents the results of 14 investigations of deposits that are dated between AD 775 and 1050. The site types are categorized as agrarian, urban, military and burials. Garden plants are unevenly distributed, as the greatest diversity is recorded in features from urban contexts. We argue that taphonomic processes played an important role in the picture displayed. Archaeobotanical research results from neighbouring regions suggest that Viking Age horticulture has its roots in older traditions, and that the spectrum of garden plants is influenced by central and north-western European horticultural customs, which were to a great extent shaped by Roman occupation
Optical coherent feedback control of a mechanical oscillator
Feedback is a powerful and ubiquitous technique both in classical and quantum
system control. Its standard implementation relies on measuring the state of a
system, processing the classical signal, and feeding it back to the system. In
quantum physics, however, measurements not only read out the state of the
system but also modify it irreversibly. Coherent feedback is a different kind
of feedback that coherently processes and feeds back quantum signals without
actually measuring the system. Here, we report on the experimental realization
and the theoretical analysis of an optical coherent feedback platform to
control the motional state of a nanomechanical membrane in an optical cavity.
The coherent feedback loop consists of a light field interacting twice with the
same mechanical mode through different cavity modes, without {performing any}
measurement. Tuning the optical phase and delay of the feedback loop allows us
to control the motional state of the mechanical oscillator, its resonance
frequency and also its damping rate, which we use to cool the membrane close to
the quantum ground state. Our theoretical analysis provides the optimal cooling
conditions, showing that this new technique enables ground-state cooling.
Experimentally, we show that we can cool the membrane to a state with
phonons () in a
environment. This lies below the theoretical limit of cavity
dynamical backaction cooling in the unresolved sideband regime and is achieved
with only 1 of the optical power required for cavity cooling. Our feedback
scheme is very versatile, offering new opportunities for quantum control in a
variety of optomechanical systems.Comment: 17 pages, 7 figure
Tensile Properties and Microstructures of Laser-Formed Ti-6Al-4V
The room temperature tensile properties of Ti-6Al-4V alloy prepared under two different processing routes were evaluated and compared. One group of samples was prepared by conventional casting-forging-rolling into flat plates. The other group was prepared by using Triton\u27s Laser Free-Form Fabrication (LF3)(TM) processes, i.e., a laser was used to melt pre-alloyed powders of the required metallic composition as they were dropped onto a moveable substrate programmed to move in such a manner as to form a solid alloy plate. Five populations of Ti-6Al-4V were evaluated: a standard wrought form, an as-deposited form, a machined as-deposited form, a heat-treated as-deposited form, and a machined as-deposited and heat-treated form. The poorest mechanical properties occurred with the rough surfaces, likely due to existing microcracks and stress concentrations. The LF3 (TM) as-deposited material had mechanical properties comparable to, if not higher than, the mechanical properties of the wrought material. Further evaluations of the laser-formed material for complex spacecraft piece parts were warranted, specifically in regards to improving the surface finish of the materials
Exposure to ultrafine carbon particles at levels below detectable pulmonary inflammation affects cardiovascular performance in spontaneously hypertensive rats
<p>Abstract</p> <p>Background</p> <p>Exposure to particulate matter is a risk factor for cardiopulmonary disease but the underlying molecular mechanisms remain poorly understood. In the present study we sought to investigate the cardiopulmonary responses on spontaneously hypertensive rats (SHRs) following inhalation of UfCPs (24 h, 172 μg·m<sup>-3</sup>), to assess whether compromised animals (SHR) exhibit a different response pattern compared to the previously studied healthy rats (WKY).</p> <p>Methods</p> <p>Cardiophysiological response in SHRs was analyzed using radiotelemetry. Blood pressure (BP) and its biomarkers plasma renin-angiotensin system were also assessed. Lung and cardiac mRNA expressions for markers of oxidative stress (hemeoxygenase-1), blood coagulation (tissue factor, plasminogen activator inhibitor-1), and endothelial function (endothelin-1, and endothelin receptors A and B) were analyzed following UfCPs exposure in SHRs. UfCPs-mediated inflammatory responses were assessed from broncho-alveolar-lavage fluid (BALF).</p> <p>Results</p> <p>Increased BP and heart rate (HR) by about 5% with a lag of 1–3 days were detected in UfCPs exposed SHRs. Inflammatory markers of BALF, lung (pulmonary) and blood (systemic) were not affected. However, mRNA expression of hemeoxygenase-1, endothelin-1, endothelin receptors A and B, tissue factor, and plasminogen activator inhibitor showed a significant induction (~2.5-fold; p < 0.05) with endothelin 1 being the maximally induced factor (6-fold; p < 0.05) on the third recovery day in the lungs of UfCPs exposed SHRs; while all of these factors – except hemeoxygenase-1 – were not affected in cardiac tissues. Strikingly, the UfCPs-mediated altered BP is paralleled by the induction of renin-angiotensin system in plasma.</p> <p>Conclusion</p> <p>Our finding shows that UfCPs exposure at levels which does not induce detectable pulmonary neutrophilic inflammation, triggers distinct effects in the lung and also at the systemic level in compromised SHRs. These effects are characterized by increased activity of plasma renin-angiotensin system and circulating white blood cells together with moderate increases in the BP, HR and decreases in heart rate variability. This systemic effect is associated with pulmonary, but not cardiac, mRNA induction of biomarkers reflective of oxidative stress; activation of vasoconstriction, stimulation of blood coagulation factors, and inhibition of fibrinolysis. Thus, UfCPs may cause cardiovascular and pulmonary impairment, in the absence of detectable pulmonary inflammation, in individuals suffering from preexisting cardiovascular diseases.</p
The SM and NLO multileg working group: Summary report
This report summarizes the activities of the SM and NLO Multileg Working
Group of the Workshop "Physics at TeV Colliders", Les Houches, France 8-26
June, 2009.Comment: 169 pages, Report of the SM and NLO Multileg Working Group for the
Workshop "Physics at TeV Colliders", Les Houches, France 8-26 June, 200
The ANTARES Optical Beacon System
ANTARES is a neutrino telescope being deployed in the Mediterranean Sea. It
consists of a three dimensional array of photomultiplier tubes that can detect
the Cherenkov light induced by charged particles produced in the interactions
of neutrinos with the surrounding medium. High angular resolution can be
achieved, in particular when a muon is produced, provided that the Cherenkov
photons are detected with sufficient timing precision. Considerations of the
intrinsic time uncertainties stemming from the transit time spread in the
photomultiplier tubes and the mechanism of transmission of light in sea water
lead to the conclusion that a relative time accuracy of the order of 0.5 ns is
desirable. Accordingly, different time calibration systems have been developed
for the ANTARES telescope. In this article, a system based on Optical Beacons,
a set of external and well-controlled pulsed light sources located throughout
the detector, is described. This calibration system takes into account the
optical properties of sea water, which is used as the detection volume of the
ANTARES telescope. The design, tests, construction and first results of the two
types of beacons, LED and laser-based, are presented.Comment: 21 pages, 18 figures, submitted to Nucl. Instr. and Meth. Phys. Res.
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