198,832 research outputs found
Semilinear problems in unbounded domains
No full textAbstractAs formulated by Silva [E.A. de B.e. Silva, Linking theorems and applications to semilinear elliptic problems at resonance, Nonlinear Anal. 16 (1991) 455–477] and Schechter [M. Schechter, A generalization of the saddle point method with applications, Ann. Polon. Math. 57 (3) (1992) 269–281; M. Schechter, New saddle point theorems, in: Generalized Functions and Their Applications, Varanasi, 1991, Plenum, New York, 1993, pp. 213–219], the sandwich theorem has become a very useful tool in finding critical points of functionals leading to solutions of partial differential equations. In the present paper, this theorem is strengthened to apply to more general situations. We present some applications
On the meromorphic and schechter-shapiro operational calculi
No full textThe well-known Dunford-Taylor operational calculus for closed linear operators in Banach spaces has been generalized in two different ways: First, by H. A. Gindler (Nagoya Math. J. 26 (1966), 31–38) and B. Nagy (Acta Math. Acad. Sci. Hungar. 33 (1979), 379–390), to include meromorphic functions with poles in the extended spectrum which are not eigenvalues. Second, by M. Schechter and J. Shapiro (Trans. Amer. Math. Soc. 175 (1973), 439–467), to include functions analytic on a neighborhood of the Fredholm spectrum. In this paper we give several results about the meromorphic calculus, in particular, spectral mapping theorems for essential spectra; and we apply our results to the study of the solutions of some integro-differential equations. Moreover, for functions admissible in both calculi, we verify that with suitable choice of quasi-resolvent and contour of integration, the Schechter-Shapiro calculus yields an extension of the operator provided by the meromorphic calculus
Involvement of 5-HT1A serotonergic receptor on Δ9-Tetrahydrocannabinol (Δ9-THC)-induced emotional response in rats
No full textThe major psychoactive constituent of cannabis, Δ9-THC, affects emotional reactivity in humans (Porter and Felder, 2001) and laboratory animals by activating brain cannabinoid receptors (Onaivi et al. 1990; Berrendero and Maldonado 2002). The 5HT system plays a key modulatory role in CNS processes that appear to be dysregulated in psychiatric disorders such as anxiety, fear, depression or aggression (Griebel, 1995). The role of 5HT1A serotonergic receptor, located in serotonergic patways projecting from mid-brain raphe nuclei to limbic areas, in the modulation of anxious states has been particularly well studied (Handley, 1995; Barnes and Sharp, 1999). To date, there is only one report on the involvement of 5HT1A serotonergic receptor in anxiogenic-like response induced by CP 55,940 (Marco et al., 2004). The aim of the present work was to further elucidate the role of 5-HT1A serotonergic receptor on emotional reactivity induced by cannabinoids in rats using the elevated plus-maze (EPM) and forced swimming test (FST). D9–THC (0.015-3 mg/kg), was studied in a EPM apparatus according to Pellow et al. (1985). The test length was 5 min, the total time spent in each arm and the number of arm entries were scored by trained observers in male Sprague-Dawley rats, 30 min after treatment. The FST, evaluated according to Porsolt et al., (1977), consisted in two swimming sessions where the time of immobility during the 2nd 5-min session was an indicator of antidepressant activity. D9–THC showed a biphasic effect being anxiolytic at a low (0.75 mg/kg) and anxiogenic at a high (3 mg/kg) dose. Lower doses as 0.015 and 0.075 mg/kg significantly reduced the immobility time in the FST, showing an antidepressant activity. Pre-treatment with the 5-HT1A serotonergic receptor antagonist, WAY 100635 (0.3 mg/kg) given s.c. 1h before D9–THC, significantly reversed its anxiolytic effect. A synergistic action on anxiolytic effect, when the 5-HT1A serotonergic receptor agonist 8-OH-DPAT (0.0075 mg/kg) was given in combination with D9–THC, was observed. These findings support a key role of 5-HT1A serotonergic receptor in the regulation of D9–THC-induced emotional states
AM 404 leads to neuroprotection against ischemia-induced neuronal injury
No full textAnandamide and 2-AG, the most endocannabinoids studied, are produced “on demand” after cerebral ischemia from membrane associated precursors (Baker et al., 2003). As soon as anandamide is released, the diffusion process is accelerated by a rapid and selective carrier system (Piomelli 2003). The development of a series of anandamide transport inhibitors, to slow its elimination and to magnify its beneficial effects, such as AM404, can provide a new tool to investigate the role of endocannabinoids (Piomelli, 2003). Since it is well known the protective role of anandamide in processes occurring during cerebral ischemia (van der Stelt et al., 2001; Berger et al, 2004), the aim of the present work was to investigate the effect of AM404 against neuronal injury in vivo. The animal model we used was the transient global cerebral ischemia induced by Bilateral Carotid Arteries Occlusion (BCAO) in mongolian gerbils. The compound was given i.p. 5 min after BCAO in a range of doses between 0.01 and 1 mg/kg. To quantify the ischemic damage we measured from 1 hour to 7 days after recirculation, electroencephalographic (EEG) mean total spectral power, spontaneous motor activity, cognitive function, rectal temperature and hippocampal neuronal count, all parameters known to be hardly influenced by BCAO (Peruche et al., 1995). AM404 antagonized hyperlocomotion, evaluated in an “activity cage” on Day 1 and the EEG flattening, on Day 7. AM 404 also induced a significant decrease of rectal temperature, within the first hour, and reversed ischemia-induced cognitive deficit, evaluated through the passive avoidance test, on Day 3. Finally, histological examination, carried out on Day 7 with cresyl violet staining, showed that AM404 protected against neuronal loss in CA1 hippocampal subfield. These results, taken together, demonstrate the anti-ischemic effect of AM 404 suggesting a protective role of endocannabinoids in events occurring during cerebral injury. Since it’s well documented an affinity for vanilloid receptors, experiments are in progress to clarify the mechanism by which AM404 shows its protective effect
Development of a 2-D black-oil reservoir simulator using a unique grid-block system
No full textThe grid orientation effect is a long-standing problem plaguing reservoir simulators that employ finite difference schemes. A rotation of the computational grids yields a substantially different solution under certain circumstances. For example, in a five-spot pattern, the predicted recovery, water cut performance and the locations of the fronts depend on the type of grid system used. A Cartesian grid with one axis parallel to the line joining an injector and producer gives a solution significantly different from a grid that has the axes oriented at 45���� to this line.
This study develops a unique grid-block assignment where rectangular grid blocks are interspersed with octagonal grid blocks. This grid block system is called the Hybrid Grid Block (HGB) system. The objective of this study is to evaluate the grid orientation effect of the HGB grid to see whether it is an improvement over the conventional Cartesian grid system.
In HGB, flow can progress in four directions in the octagonal grid blocks and two in the square grid blocks. The increase in the number of flow directions in the octagonal grid blocks is expected to reduce the grid orientation effect in the model. Hence, this study also evaluates the grid orientation effect of the HGB and compares it with the Cartesian grid system.
To test the viability of HGB, a general purpose finite difference IMPES-formulated two-dimensional black oil simulator was developed in this study, while retaining the familiar finite-difference discretization of the flow equations. Several simulation cases were conducted to compare HGB and conventional grid block systems. Comparisons with commercial simulator are also made. Despite the fact that the reservoir is isotropic and homogeneous, grid orientation effect was still observed when rectangular Cartesian grid models are run at mobility ratio, M = 1.0. Grid refinement can help to reduce the grid orientation effect in rectangular Cartesian grid models when there are favorable mobility ratios, i.e. M = 1.0 or less. However, at an unfavorable mobility ratio of M = 10.0, it is found that neither parallel nor diagonal orientation can be used reliably for the displacement problems run in this study. This is because as the number of grid blocks is increased, the performance of diagonal and parallel models actually diverges for the grid spacings investigated here. On the other hand, HGB grid is able to reduce the grid orientation effect even for unfavorable mobility ratio displacement problems (up to M = 50.0), with maximum relative difference in pore volume recovered of 6% between parallel and diagonal HGB grid models for all the cases run in this study. Comparisons between the conventional Cartesian and HGB grid show that the HGB grid is more effective in reducing the grid orientation effect than the Cartesian grid. The HGB grid performs better by consistently giving a smaller relative difference between HGB parallel grid and HGB diagonal grid in pore volume recovered (6.0, 4.5, 3.3, and 2.2%) compared to the relative difference between Cartesian parallel grid and Cartesian diagonal grid in pore volume recovered (17.0, 13.0, 9.3, 7.9%) at similar averaged area per grid block for all the four comparison cases studied
Evaluating different approaches to estimating vulnerability
No full textA number of researchers have recently proposed a variety of different `vulnerability'measures designed to capture the welfare consequences of risk for poor households, and also proposed a variety of different approaches to estimating these various measures of household vulnerability. However, it's possible to `mix-and-match'estimators and measures. Here we conduct Monte Carlo experiments designed to explore the performance of different estimators with different measures, under different assumptions regarding the underlying economic environment. We find that when the environment is stationary, and consumption expenditures are measured without error, that the best estimator is one proposed by Chaudhuri (2001), regardless of what measure of vulnerability is employed. If the vulnerability measure is risk-sensitive, but consumption is measured with error, a simple estimator proposed by the authors(2003) generally performs best. However, when the distribution of consumption is non-stationary, a modification of an estimator proposed by Pritchett et al. (2000) performs best. Future research should focus on combining the efficiency of the Chauduri estimator with the good properties of the authors (in environments with measurement error), and Pritchett (in non-stationary environments) estimators. However, even with present technology estimating vulnerability is simple, and much more informative, and useful than are static poverty measures, provided one has at least two rounds of panel data.Environmental Economics&Policies,Economic Theory&Research,Inequality,Poverty Lines,Consumption
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