803 research outputs found
On the semiclassical theory for universal transmission fluctuations in chaotic systems: the importance of unitarity
The standard semiclassical calculation of transmission correlation functions
for chaotic systems is severely influenced by unitarity problems. We show that
unitarity alone imposes a set of relationships between cross sections
correlation functions which go beyond the diagonal approximation. When these
relationships are properly used to supplement the semiclassical scheme we
obtain transmission correlation functions in full agreement with the exact
statistical theory and the experiment. Our approach also provides a novel
prediction for the transmission correlations in the case where time reversal
symmetry is present
Semiclassical Description of Wavepacket Revival
We test the ability of semiclassical theory to describe quantitatively the
revival of quantum wavepackets --a long time phenomena-- in the one dimensional
quartic oscillator (a Kerr type Hamiltonian). Two semiclassical theories are
considered: time-dependent WKB and Van Vleck propagation. We show that both
approaches describe with impressive accuracy the autocorrelation function and
wavefunction up to times longer than the revival time. Moreover, in the Van
Vleck approach, we can show analytically that the range of agreement extends to
arbitrary long times.Comment: 10 pages, 6 figure
Semiclassical approach to fidelity amplitude
The fidelity amplitude is a quantity of paramount importance in echo type
experiments. We use semiclassical theory to study the average fidelity
amplitude for quantum chaotic systems under external perturbation. We explain
analytically two extreme cases: the random dynamics limit --attained
approximately by strongly chaotic systems-- and the random perturbation limit,
which shows a Lyapunov decay. Numerical simulations help us bridge the gap
between both extreme cases.Comment: 10 pages, 9 figures. Version closest to published versio
Measuring the Lyapunov exponent using quantum mechanics
We study the time evolution of two wave packets prepared at the same initial
state, but evolving under slightly different Hamiltonians. For chaotic systems,
we determine the circumstances that lead to an exponential decay with time of
the wave packet overlap function. We show that for sufficiently weak
perturbations, the exponential decay follows a Fermi golden rule, while by
making the difference between the two Hamiltonians larger, the characteristic
exponential decay time becomes the Lyapunov exponent of the classical system.
We illustrate our theoretical findings by investigating numerically the overlap
decay function of a two-dimensional dynamical system.Comment: 9 pages, 6 figure
Pulping and pretreatment affect the characteristics of bagasse inks for 3D printing
Bagasse is an underutilized agro-industrial residue with great potential as raw material for the production of cellulose nanofibrils (CNF) for a range of applications. In this study, we have assessed the suitability of bagasse for production of CNF for three-dimensional (3D) printing. First, pulp fibers were obtained from the bagasse raw material using two fractionation methods, i.e. soda and hydrothermal treatment combined with soda. Second, the pulp fibers were pretreated by TEMPO-mediated oxidation using two levels of oxidation for comparison purposes. Finally, the CNF were characterized in detail and assessed as inks for 3D printing. The results show that CNF produced from fibers obtained by hydrothermal and soda pulping were less nanofibrillated than the corresponding material produced by soda pulping. However, the CNF sample obtained from soda pulp was cytotoxic, apparently due to a larger content of silica particles. All the CNF materials were 3D printable. We conclude that the noncytotoxic CNF produced from hydrothermally and soda treated pulp can potentially be used as inks for 3D printing of biomedical devices.Fil: Chinga Carrasco, Gary. RISE PFI; NoruegaFil: Ehman, Nanci Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Pettersson, Jennifer. RISE Bioscience and Materials; SueciaFil: Vallejos, María Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Felissia, Fernando Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Hakansson, Joakim. RISE Bioscience and Materials; SueciaFil: Area, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentin
Orthogonality Catastrophe in Parametric Random Matrices
We study the orthogonality catastrophe due to a parametric change of the
single-particle (mean field) Hamiltonian of an ergodic system. The Hamiltonian
is modeled by a suitable random matrix ensemble. We show that the overlap
between the original and the parametrically modified many-body ground states,
, taken as Slater determinants, decreases like , where is
the number of electrons in the systems, is a numerical constant of the
order of one, and is the deformation measured in units of the typical
distance between anticrossings. We show that the statistical fluctuations of
are largely due to properties of the levels near the Fermi energy.Comment: 12 pages, 8 figure
EVALUACIÓN DE LA PRECIPITACIÓN DISTRIBUIDA EN LA CUENCA KATARI BASADO EN TECNOLOGÍA SATELITAL Y PRODUCTOS DERIVADOS
La medición de la precipitación espacial, en alta resolución, es una variable crucial en la modelación hidrológica de cuencas, pero debido a las limitantes con respecto a la cantidad y distribución de pluviómetros, se hace necesario la generación de datos utilizando productos satelitales de precipitación. Para este estudio se usaron los productos: GSMaP, CHIRPS y GMET, cada uno con una resolución espacial y temporal diferente. El área de estudio es la cuenca Katari, al noreste de la ciudad del Alto y presenta alturas entre los 3 800 a 5 200 m.s.n.m. El periodo temporal seleccionado fue 2000 – 2016 y pare ello se realizó un análisis comparativo divido en subcuencas, donde se emplearon dos niveles comparativos: una comparación entre productos de precipitación base (GSMaP, CHIRPS y SENAMHI) y una comparación entre “GS-Katari”, un producto combinado por el método de ajuste iterativo entre GSMaP y SENAMHI, y “GMET”, un producto combinado a través de métodos estocásticos entre SENAMHI y CHIRPS. Inicialmente se demostró que, tanto GSMaP como CHIRPS presentan una sobrestimación de sus intensidades de precipitación con respecto a los datos de tierra, sin embargo, aparentemente presentan una excepción al acercarse al Lago Titicaca. Posteriormente, se realizó 5 iteraciones de ajuste para obtener el producto combinado GS-Katari, este producto ajustado presenta intensidades de precipitación que tienden a la subestimación con rangos menores al 10% del valor medido en tierra. Posterior a la generación del producto, se analizó los datos de precipitación entre GMET y el producto combinado y se comprobó que GMET presenta una sobrestimación con respecto a SENAMHI, pero en el área cercana al Lago Titicaca, se observa que GMET presenta una subestimación similar a CHIRPS y GSMaP con respecto a las intensidades de SENAMHI. Los resultados del presente artículo buscan proporcionar datos con una mayor resolución espacial e intensidades de precipitación más procesadas con el fin de generar modelos hidrológicos con menos incertidumbres, con el fin de gestionar de mejor manera los recursos hídricos para la zona
Aerosol-Assisted CVD-Grown PdO Nanoparticle-Decorated Tungsten Oxide Nanoneedles Extremely Sensitive and Selective to Hydrogen
We report for the first time the successful synthesis of palladium (Pd) nanoparticle (NP)-decorated tungsten trioxide (WO3) nanoneedles (NNs) via a two-step aerosol-assisted chemical vapor deposition approach. Morphological, structural, and elemental composition analysis revealed that a Pd(acac)2 precursor was very suitable to decorate WO3 NNs with uniform and well-dispersed PdO NPs. Gas-sensing results revealed that decoration with PdO NPs led to an ultrasensitive and selective hydrogen (H2) gas sensor (sensor response peaks at 1670 at 500 ppm of H2) with low operating temperature (150 °C). The response of decorated NNs is 755 times higher than that of bare WO3 NNs. Additionally, at a temperature near that of the ambient temperature (50 °C), the response of this sensor toward the same concentration of H2 was 23, which is higher than that of some promising sensors reported in the literature. Finally, humidity measurements showed that PdO/WO3 sensors displayed low-cross-sensitivity toward water vapor, compared to bare WO3 sensors. The addition of PdO NPs helps to minimize the effect of ambient humidity on the sensor response
Coulomb blockade conductance peak fluctuations in quantum dots and the independent particle model
We study the combined effect of finite temperature, underlying classical
dynamics, and deformations on the statistical properties of Coulomb blockade
conductance peaks in quantum dots. These effects are considered in the context
of the single-particle plus constant-interaction theory of the Coulomb
blockade. We present numerical studies of two chaotic models, representative of
different mean-field potentials: a parametric random Hamiltonian and the smooth
stadium. In addition, we study conductance fluctuations for different
integrable confining potentials. For temperatures smaller than the mean level
spacing, our results indicate that the peak height distribution is nearly
always in good agreement with the available experimental data, irrespective of
the confining potential (integrable or chaotic). We find that the peak bunching
effect seen in the experiments is reproduced in the theoretical models under
certain special conditions. Although the independent particle model fails, in
general, to explain quantitatively the short-range part of the peak height
correlations observed experimentally, we argue that it allows for an
understanding of the long-range part.Comment: RevTex 3.1, 34 pages (including 13 EPS and PS figures), submitted to
Phys. Rev.
Development and evaluation of an online education tool on attention deficit hyperactivity disorder for general practitioners: the important contribution of co-production
BackgroundAttention deficit hyperactivity disorder (ADHD) is underdiagnosed in the UK and the assessment and diagnosis pathway often involves a general practitioner (GP) referral to secondary care services. GPs’ levels of knowledge and understanding about ADHD is often a significant barrier in patients accessing care. The development of an online education resource could improve GPs knowledge of ADHD and optimise appropriate referrals. Involving end-users in co-creating interventions may enhance their clinical utility and impact routine clinical practice. However, there is limited published evidence describing how to meaningfully involve stakeholders in both the design and development components of co-production.MethodWe report a step wise, co-production approach towards developing an online ADHD education intervention for GPs. Preparatory work highlighted the relevant topics to be included in the intervention, from which educational videos were then developed. Workshops were then conducted with GPs, leading to further refinement of the video content and subsequently the final intervention. A pilot usability study (n = 10 GPs) was then conducted to assess the intervention’s acceptability, feasibility and accessibility.ResultsThe development of the online intervention was greatly facilitated by the involvement of GPs. Having a co-production development process ensured the consistent adaptation of the intervention to meet GPs’ needs. The usability study showed that the content of the intervention was suitable, easily accessible, engaging and delivered at an acceptable level of intensity, validating the development approach taken.ConclusionWhile further studies are needed to evaluate the efficacy of the developed intervention, preliminary findings demonstrated that it was acceptable and well received. The importance of co-development was highlighted in developing an intervention that addresses specific needs for GPs. This development approach may be useful for other researchers and developers of clinical interventions
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