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101.
Viterbo VC Braga JP Braga AP de Almeida MB 《Journal of chemical information and computer sciences》2001,41(2):309-313
Inversion of positron annihilation lifetime spectroscopy, based on a neural network Hopfield model, is presented in this paper. From a previous reported density function for lysozyme in water a simulated spectrum, without the superposition of statistical fluctuation and spectrometer resolution effects, was generated. These results were taken as the exact results from which the neural network was trained. The precision of the inverted density function was analyzed taking into account the number of neurons and the learning time of the neural network. A fair agreement was obtained when comparing the neural network results with the exact results. For example, the maximum of the density function, with a precision of 0.4% for the percentual relative error, was obtained for 64 neurons. 相似文献
102.
By means of a transfer matrix method, we show that the residual entropy S of the two dimensional square lattice Blume-Emery-Griffiths model on the antiquadrupolar-disordered and ferromagnetic-antiquadrupolar-disordered
phase boundaries satisfies the inequalities (ln λ
1,n
)/(n+1)≤S≤(ln λ
1,n
)/n, where λ
1,n
is the largest eigenvalue of a transfer matrix F
n
on a strip of width n. These bounds imply the existence of a O(1/n) correction in the approximation of S by (ln λ
1,n
)/n. Using these bounds, we calculate numerically the value of S, with precise estimates on the errors. 相似文献
103.
D. Braga S. L. Giaffreda M. Curzi Lucia Maini M. Polito Fabrizia Grepioni 《Journal of Thermal Analysis and Calorimetry》2007,90(1):115-123
Supramolecular reactions between crystalline materials can be exploited to prepare both hydrogen bonded co-crystals and coordination
networks. Mechanical mixing of molecular crystals as well as kneading provide an alternative, solvent-free, route to novel
materials hence these methods represent a green route to supramolecular solid-state chemistry. 相似文献
104.
105.
The splitting of the 2Πg state of BeF2+ into the 2B2 and 2A2 components has been investigated theoretically by ab initio UHF calculations. The 2A2 component is found to be linear, and the 2B2 state is calculated to have minima at bond angles of 180° and ≈100°, with the bent conformation lying lower. Analysis of a possible interaction between two states of 2B2 symmetry is made. Electron binding energies and symmetric bending force constants are reported. For comparison, a parallel investigation is reported on the analogous states of the isoelectronic CO2+. 相似文献
106.
The reaction of N-tosyltryptamines with thioortho esters, leading to 1-thiosubstituted tetrahydro-beta-carbolines under modified Pictet-Spengler conditions, is described. The 1-heterosubstituted beta-carbolines furnished 1-substituted beta-carbolines upon reaction with Grignard reagents and silyl derivatives under Lewis acid promotion. [reaction: see text] 相似文献
107.
We propose two new thermostats which can be employed in computer simulations to ensure that two different variants of the configurational temperature fluctuate around their equilibrium values. These new thermostats differ from one previously introduced by Delhommelle and Evans [Mol. Phys. 99, 1825 (2001)] in several important ways. First, our thermostats are derived in the same spirit as the Nosé-Hoover thermostat and therefore generate the canonical phase-space distribution. Second, our thermostats involve simpler equations of motion, which do not involve spatial gradients of the configurational temperature. They do not suffer from problems stemming from stiff equations of motion and furthermore, in large temperature perturbation simulations, the measured temperature follows the set-point temperature without any overshoot, and with good damping of oscillations. We show that both of our configurational thermostats are special cases of a more general set of Nosé-Hoover equations proposed by Kusnezov et al. [Ann. Phys. 204, 155 (1990)]. The new thermostats are expected to be highly useful in nonequilibrium simulations, particularly those characterized by spatial inhomogeneities. They should also find applicability in simulations involving large changes in temperature over small time scales, such as temperature quench molecular dynamics and radiation damage modeling. 相似文献
108.
A. Abras M. M. Braga J. C. Machado 《Journal of Radioanalytical and Nuclear Chemistry》1984,86(2):111-122
The products of the thermal decomposition in air of iron/III/benzoate [Fe3/C6H5COO/6/OH/2]OH.H2O have been studied using conventional thermal analysis, X-ray diffraction measurements and mainly Mössbauer spectroscopy. The decomposition occurs in the temperature range 200–350°C. It was possible to identify benzoic acid and ferric oxide as final products. Above 300°C, the observed ferric oxide showed a particle size distribution, which depends on the heating temperature and the heating time interval, as evidenced by the following detected phases: superparamagnetic -Fe2O3 and magnetically ordered state with crystal structure of the phases -Fe2O3 and -Fe2O3. Also, two iron/III/ benzoate complexes having four and three ligands within the coordination sphere are suggested as intermediate products. 相似文献
109.
Braga GU Flint SD Messias CL Anderson AJ Roberts DW 《Photochemistry and photobiology》2001,73(2):140-146
We tested the effects of irradiances of 920 and 1200 mW m-2 (weighted irradiance) on the conidia and germinants of the entomopathogenic Hyphomycete Metarhizium anisopliae. The conidia were exposed to the two irradiances for 1, 2, 4, 6, 7 or 8 h. Increased exposure decreased relative percent culturability. The inactivation provoked by the irradiance of 1200 mW m-2 was higher than for the 920 mW m-2, with a reduction in the 50% lethal time (LT50) from 6 h 40 min to 4 h 26 min. Reciprocity was not observed when conidia in water suspension and germinants in different stages of the germinative process were exposed to a 17.3 kJ m-2 total dose at both irradiance levels. Although nonreciprocity was observed in all situations, its magnitude varied as a function of metabolic state and/or cell-cycle phase in which the conidia were at the exposure time. The least difference between the effects of the two irradiance levels was observed when nongerminating conidia in suspension were exposed, and the greatest was observed when conidia were exposed during an advanced germination phase. Doses of 6.6 and 17.3 kJ m-2 supplied through the two irradiance levels delayed the germination of the surviving conidia. At both doses, delay was greater during exposure to the higher irradiance. Nonreciprocity was higher for the 17.3 kJ m-2 dose. Nonreciprocity magnitude, in addition to depending on the conidial physiological state, also depended on dose. The results demonstrate the importance of evaluating the impact of the increase in irradiance during the different stages of the fungal life cycle, especially during the stages which are more sensitive to UV, and not simply in dormant conidia. 相似文献
110.
Gilson Zeni Cristina W. NogueiraDagoberto O. Silva Paulo H. MenezesAntonio L. Braga Hélio A. StefaniJoão B.T. Rocha 《Tetrahedron letters》2003,44(7):1387-1390
Palladium(II) chloride catalyzed the cross-coupling reaction of 2,5-bis-(butyltelluro) furan and terminal alkynes yielding both symmetrically and unsymmetrically substituted 2,5-bis-acetylenic furan derivatives. The methodology represents a general and efficient protocol for carrying out the synthesis of furan derivatives with potential biological activities. 相似文献