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71.
In the present work, a method was developed and optimized aiming at the determination of anatoxin-a in environmental water samples. The method is based on the direct derivatization of the analyte by adding hexylchloroformate in the alkalinized sample (pH = 9.0). The derivatized anatoxin-a was extracted by a solid-phase microextraction (SPME) procedure, submersing a PDMS fiber in an amber vial for 20 min under magnetic stirring. GC-MS was used to identify and quantify the analyte in the SIM mode. Norcocaine was used as internal standard. The following ions were chosen for SIM analyses (quantification ions in italics): anatoxin-a: 191, 164, 293 and norcocaine: 195, 136, 168. The calibration curve showed linearity in the range of 2.5-200 ng/mL and the LOD was 2 ng/mL. This method of SPME and GC-MS analysis can be readily utilized to monitor anatoxin-a for water quality control. 相似文献
72.
A quantum model of option pricing: When Black-Scholes meets Schrödinger and its semi-classical limit
The Black-Scholes equation can be interpreted from the point of view of quantum mechanics, as the imaginary time Schrödinger equation of a free particle. When deviations of this state of equilibrium are considered, as a product of some market imperfection, such as: Transaction cost, asymmetric information issues, short-term volatility, extreme discontinuities, or serial correlations; the classical non-arbitrage assumption of the Black-Scholes model is violated, implying a non-risk-free portfolio. From Haven (2002) [1] we know that an arbitrage environment is a necessary condition to embedding the Black-Scholes option pricing model in a more general quantum physics setting. The aim of this paper is to propose a new Black-Scholes-Schrödinger model based on the endogenous arbitrage option pricing formulation introduced by Contreras et al. (2010) [2]. Hence, we derive a more general quantum model of option pricing, that incorporates arbitrage as an external time dependent force, which has an associated potential related to the random dynamic of the underlying asset price. This new resultant model can be interpreted as a Schrödinger equation in imaginary time for a particle of mass 1/σ2 with a wave function in an external field force generated by the arbitrage potential. As pointed out above, this new model can be seen as a more general formulation, where the perfect market equilibrium state postulated by the Black-Scholes model represent a particular case. Finally, since the Schrödinger equation is in place, we can apply semiclassical methods, of common use in theoretical physics, to find an approximate analytical solution of the Black-Scholes equation in the presence of market imperfections, as it is the case of an arbitrage bubble. Here, as a numerical illustration of the potential of this Schrödinger equation analogy, the semiclassical approximation is performed for different arbitrage bubble forms (step, linear and parabolic) and compare with the exact solution of our general quantum model of option pricing. 相似文献
73.
Ernesto G. Birgin Erico M. Gozzi Mauricio G. C. Resende Ricardo M. A. Silva 《Journal of Global Optimization》2010,48(2):289-310
Global optimization seeks a minimum or maximum of a multimodal function over a discrete or continuous domain. In this paper,
we propose a hybrid heuristic—based on the CGRASP and GENCAN methods—for finding approximate solutions for continuous global
optimization problems subject to box constraints. Experimental results illustrate the relative effectiveness of CGRASP–GENCAN
on a set of benchmark multimodal test functions. 相似文献
74.
75.
Luciana S. Buriol Michael J. Hirsch Panos M. Pardalos Tania Querido Mauricio G. C. Resende Marcus Ritt 《Optimization Letters》2010,4(4):619-633
One of the main goals in transportation planning is to achieve solutions for two classical problems, the traffic assignment
and toll pricing problems. The traffic assignment problem aims to minimize total travel delay among all travelers. Based on
data derived from the first problem, the toll pricing problem determines the set of tolls and corresponding tariffs that would
collectively benefit all travelers and would lead to a user equilibrium solution. Obtaining high-quality solutions for this
framework is a challenge for large networks. In this paper, we propose an approach to solve the two problems jointly, making
use of a biased random-key genetic algorithm for the optimization of transportation network performance by strategically allocating
tolls on some of the links of the road network. Since a transportation network may have thousands of intersections and hundreds
of road segments, our algorithm takes advantage of mechanisms for speeding up shortest-path algorithms. 相似文献
76.
Richard C. Semelka Mateus de A. HernandesClifton G. Stallings Mauricio Castillo 《Magnetic resonance imaging》2013
Purpose
The purpose was to objectively evaluate a recently FDA-approved gadolinium-based contrast agent (GBCA) in comparison to our standard GBCA for acute adverse events and image quality by blinded evaluation.Methods
Evaluation was made of a recently FDA-approved GBCA, gadobutrol (Gadavist; Bayer), in comparison to our standard GBCA, gadobenate dimeglumine (MultiHance; Bracco), in an IRB- and HIPAA-compliant study. Both the imaging technologist and patient were not aware of the brand of the GBCA used. A total of 59 magnetic resonance studies were evaluated (59 patients, 31 men, 28 women, age range of 5–85 years, mean age of 52 years). Twenty-nine studies were performed with gadobutrol (22 abdominal and 7 brain studies), and 30 studies were performed with gadobenate dimeglumine (22 abdominal and 8 brain studies). Assessment was made of acute adverse events focusing on objective observations of vomiting, hives, and moderate and severe reactions. Adequacy of enhancement was rated as poor, fair and good by one of two experienced radiologists who were blinded to the type of agent evaluated.Results
No patient experienced acute adverse events with either agent. The target minor adverse events of vomiting or hives, and moderate and severe reactions were not observed in any patient. Adequacy of enhancement was rated as good for both agents in all patients.Conclusions
Objective, blinded evaluation is feasible and readily performable for the evaluation of GBCAs. This proof-of-concept study showed that both GBCAs evaluated exhibited consistent good image quality and no noteworthy adverse events. 相似文献77.
We consider the pseudo-euclidean space ${(\mathbb{R}^n, g)}$ , with n ≥ 3 and ${g_{ij} = \delta_{ij} \varepsilon_i, \varepsilon_i = \pm 1}$ and tensors of the form ${T = \sum \nolimits_i \varepsilon_i f_i (x) dx_i^2}$ . In this paper, we obtain necessary and sufficient conditions for a diagonal tensor to admit a metric ${\bar{g}}$ , conformal to g, so that ${A_{\bar g}=T}$ , where ${A_{\bar g}}$ is the Schouten Tensor of the metric ${\bar g}$ . The solution to this problem is given explicitly for special cases for the tensor T, including a case where the metric ${\bar g}$ is complete on ${\mathbb{R}^n}$ . Similar problems are considered for locally conformally flat manifolds. As an application of these results we consider the problem of finding metrics ${\bar g}$ , conformal to g, such that ${\sigma_2 ({\bar g })}$ or ${\frac{\sigma_2 ({\bar g })}{\sigma_1 ({\bar g })}}$ is equal to a given function. We prove that for some functions, f 1 and f 2, there exist complete metrics ${\bar{g} = g/{\varphi^2}}$ , such that ${\sigma_2 ({\bar g }) = f_1}$ or ${\frac{\sigma_2 ({\bar g })}{\sigma_1 ({\bar g })} = f_2}$ . 相似文献
78.
Mario Ahues Sara Arancibia Mauricio Telias 《Numerical Functional Analysis & Optimization》2013,34(9-10):839-850
We prove a posteriori error bounds and convergence of Rayleigh-Schrödinger Series for bases of maximal invariant subspaces of compact operators in Banach spaces. These results generalize those for eigenvectors associated with simple eigenvalues. Recursive formulae are given for the numerical computation of the series' coefficients.
This work has been partially supported by Grant 89–0879 Fondecyt Chile. 相似文献
79.
Aline B. de P. Abrantes Gustavo C. Dias Nadja C. Souza‐Pinto Mauricio S. Baptista 《Photochemistry and photobiology》2019,95(1):355-363
The p53 protein exerts fundamental roles in cell responses to a variety of stress stimuli. It has clear roles in controlling cell cycle, triggering apoptosis, activating autophagy and modulating DNA damage response. Little is known about the role of p53 in autophagy‐associated cell death, which can be induced by photoactivation of photosensitizers within cells. The photosensitizer 1,9‐dimethyl methylene blue (DMMB) within nanomolar concentration regimes has specific intracellular targets (mitochondria and lysosomes), photoinducing a typical scenario of cell death with autophagy. Importantly, in consequence of its subcellular localization, photoactive DMMB induces selective damage to mitochondrial DNA, saving nuclear DNA. By challenging cells having different p53 protein levels, we investigated whether p53 modulates DMMB/light‐induced phototoxicity and cell cycle dynamics. Cells lacking p53 activity were slightly more resistant to photoactivated DMMB, which was correlated with a smaller sub‐G1 population, indicative of a lower level of apoptosis. DMMB photosensitization seems to induce mostly autophagy‐associated cell death and S‐phase cell cycle arrest with replication stress. Remarkably, these responses were independent on the p53 status, indicating that p53 is not involved in either process. Despite describing some p53‐related responses in cells challenged by photosensitization, our results also provide novel information on the consequences of DMMB phototoxicity. 相似文献
80.
We calculate the medium dilepton yield from a quark-gluon plasma which has a time-dependent local momentum-space anisotropy. A phenomenological model for the hard momentum scale, p(hard)(tau), and plasma anisotropy parameter, xi(tau), is constructed which interpolates between longitudinal free streaming at early times (tautau(iso)). We show that high-energy dilepton production is sensitive to the plasma isotropization time, tau(iso), and can therefore be used to experimentally determine the time of onset for hydrodynamic expansion of a quark-gluon plasma and the magnitude of expected early-time momentum-space anisotropies. 相似文献