14,797 research outputs found
The quantum Arnold transformation
By a quantum version of the Arnold transformation of classical mechanics, all
quantum dynamical systems whose classical equations of motion are
non-homogeneous linear second-order ordinary differential equations, including
systems with friction linear in velocity, can be related to the quantum
free-particle dynamical system. This transformation provides a basic
(Heisenberg-Weyl) algebra of quantum operators, along with well-defined
Hermitian operators which can be chosen as evolution-like observables and
complete the entire Schr\"odinger algebra. It also proves to be very helpful in
performing certain computations quickly, to obtain, for example, wave functions
and closed analytic expressions for time-evolution operators.Comment: 19 pages, minor changes, references update
Implementación de un sistema de control para el sistema nacional de contratación publica
The project seeks that all preferential processes comply 100% with the purpose for which they were created, which
is promoting the micro and small entrepreneurs originally from where it is to make the purchase, delivery or
performance of service the work. We will be able to confirm address information, financial statements, the volume
of assets in a truthful and provide us the Internal Revenue Service which is responsible for checking the veracity of
them. For these processes of engagement which are very attractive to providers as an opportunity to be awarded is
very high, overlooking the fact that manipulate their information by making false information is grounds for
suspension of the National Register of Suppliers. In this way our system of control that will optimize the savings
and especially the participation of micro and small entrepreneurs and artisans, because processes and contribution
minor there is a marked preference for this group of suppliers. The initial investment of this project is 8840 because
we only have to equip the space you already have the National Institute of Public Procurement within its
administrative offices in the city of Quito
Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers
Quantum nanomagnets can show a field dependence of the relaxation time very
different from their classical counterparts, due to resonant tunneling via
excited states (near the anisotropy barrier top). The relaxation time then
shows minima at the resonant fields H_{n}=n D at which the levels at both sides
of the barrier become degenerate (D is the anisotropy constant). We showed that
in Mn12, near zero field, this yields a contribution to the nonlinear
susceptibility that makes it qualitatively different from the classical curves
[Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to
finite dc fields showing how the bias can trigger the system to display those
quantum nonlinear responses, near the resonant fields, while recovering an
classical-like behaviour for fields between them. The analysis of the
experiments is done with heuristic expressions derived from simple balance
equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report
Smartphone-based simultaneous pH and nitrite colorimetric determination for paper microfluidic devices
In this work, an Android application for measurement of nitrite concentration and pH determination in
combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed imageprocessing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L−1 of resolution and 0.52 mg L−1 as the limit of detection was achieved
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