23,626 research outputs found
Adubação de pimenta-do-reino em Porto Velho-RO.
No full textAs informações sobre dosagens de adubos minerais e orgânicos para cultivares de pimenta-do-reino, ainda são muito incipientes. Visando a obtenção de uma fórmula de adubação química para a região de Porto velho, estão sendo testadas três cultivares e cinco dosagens de N, P2O5 e K2O
A Comparison Between Frequency and Time Domain Approaches for Determining a Structural Damage Using the Adjoint Method
No full textThe present investigation is focused on the solution of a dynamic inverse problem which is concerned with the
assessment of damage in structures by means of measured vibration data. Considerable research and effort over
the last few decades has taken place in the field of damage detection and damage classification in structures,
generating a variety of experimental, numerical and analytical techniques [1, 2].
The inverse problem solution is generally unstable, therefore small perturbations in the input data, like random
errors inherent to the measurements used in the analysis, can cause large oscillations on the solution. In order
to overcame this difficulty a sort of methods have been propose by using regularization techniques coupled with
both deterministic and stochastic approaches. An example of deterministic approach is the conjugate gradient
method with the use of the adjoint equation whereas the genetic algorithm method belongs to the class of the
stochastic approaches. Both techniques have already been used successfully in inverse heat conduction problems
[3].
In this work the inverse vibration problem, i.e. the ill-posed problem, is presented as a well-posed functional
form, whose solution is obtained through the use of a hybrid approach which employs the genetic algorithm
method coupled with the conjugate gradient method with the adjoint equation, also called variational approach.
In addition, two different methodologies have been compared, the one based on frequency domain approach and
the other one based on time domain approach. In the first case it has been assumed that the experimental data
available are the eigenfrequencies and eigenmodes of the structure, whereas in the second one measurements
of displacements of the structure have been assumed as the data available for the analysis. In both cases the
damage estimation has been evaluated using noiseless and noisy synthetic experimental data. The idea of this
work is to analyze and compare the results obtained with the two formulations (i.e. the time-domain and the
frequency-domain formulation) making it possible a better understanding of the inverse method here adopted
and its ability to find, locate and quantify a damage in a structure
Electron and positron scattering from 1,1-C₂H₂F₂
No full text1,1-difluoroethylene (1,1-C₂H₂F₂) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90 degrees and 120 degrees for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (ν₂ and ν₉) stretching and the combined C-F (ν₃) stretching and CH₂ (ν₁₁) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B₂, B₁, and A₁ symmetries, respectively. The pi* resonance peak at 1.8 eV in C₂H₄ is observed shifted to 2.3 eV in 1,1-C₂H₂F₂ and to 2.5 eV in C₂F₄; a phenomenon attributed to the decreasing C=C bond length from C₂H₄ to C₂F₄. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV.The work was supported in part by a Grant-in-Aid, the
Ministry of Education, Science, Technology, Sport and Culture,
Japan, the Japan Society for the Promotion of Science
JSPS, and the Japan Atomic Energy Research Institute
JAERI. One of the authors C.M. is also grateful to the
JSPS for financial support under Grant No. P04064. Another
author H.T. acknowledges Dr. T. Ozeki of the JAERI for
his encouragement and support during this work. This work
was also done under the International Atomic Energy Agency
IAEA project for three of the authors C.M., M.H., and
H.T.. Two of the authors M.H.F.B. and M.A.P.L. acknowledge
support from the Brazilian agency Conselho Nacional
de Desenvolvimento Científico e Tecnológico CNPq.
MHFB also acknowledges support from the Paraná state
agency Fundação Araucária and from FINEP ( under Project
No. CT-Infra 1)
Silver-Mediated Direct sp(3) C-H Bond Functionalization
No full textDirect sp(3) C-H bond functionalization is an efficient, straightforward, and powerful method to construct new C-X (X = C, N, F, S) bonds from nonfunctionalized aliphatic motif of organic molecules, which has been used in late-stage modification of complex molecules. In this chapter, the recent developments of silver-mediated direct sp(3) C-H functionalizations are reviewed, categorized by C-C bond formation (C-H insertion), C-N bond formation (intramolecular and intermolecular amination/amidation), C-F bond formation, and C-S bond formation.SCI(E)[email protected]
A two-level procedure based on Genetic Algorithms to optimize an aeronautical composite structure
No full textOptimal design of complex engineering systems, such as aircraft composite structures, can often be accomplished only by applying decomposition techniques. In this paper, the optimal design of a composite wing-box is addressed by using a two-level scheme based on the Genetic Algorithm meta-heuristic. The two-level optimization strategy was evaluated for variations both in the angular step of the composite layers and in the strength of material
A COMPUTATIONAL INVESTIGATION OF c-CH...HX(X = F, Cl, Br) H-BONDED COMPLEXES
No full textAuthor Institution: Centre for Research in Molecular Modeling \& Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, CanadaCyclopropenylidene (c-CH) is of significant importance in interstellar chemistry and synthetic chemistry (e.g., transition metal and organic catalysis). Because of its peculiar structure, c-CH can act as a hydrogen-bond donor or acceptor. In order to gain insight into this feature, the ground-state potential energy surfaces of singlet c-CH complexed with hydrogen halides HX (X = F, Cl, Br) have been explored extensively by density-functional theory (B3LYP) and {\it{ab initio}} quantum chemistry (MP2) with a variety of basis sets, cc-pVxZ and aug-cc-pVxZ (x = D, T). The complexes characterized have the carbenic end of c-CH H-bonded to HX, with some proton transfer occurring, the extent of which follows the order HF < HCl < HBr. Accompanying the complex formation are the dipole moment enhancement, the charge transfer, red shifts of the HX vibrational stretching frequencies together with the significant enhancement of band intensity and concomitant HX bond elongation. The nature of H-bonding in these complexes has been explored, based on energy decomposition schemes and the Bader's quantum theory of atoms-in-molecules, with the conclusion that c-CH is a strong H-bond acceptor with respect to the hydrogen halides
C--H... and C--F...H--C INTERACTIONS IN THE ACETYLENE--FLUOROFORM DIMER
No full textAuthor Institution: Department of Chemistry, Eastern Illinois University, 600 Lincoln Ave.,; Charleston, IL 61920 USARotational spectra for four isotopomers of the HCCH--HCF complex have been identified by Fourier-transform microwave spectroscopy. The spectra exhibit considerable fine splittings, presumably arising from the internal motion of one or both subunits; both first- and second-order Stark effects have been observed. A fit of selected =0 and 1 components for the normal isotopomer (assigned using second-order Stark effect data) gave an rms of around 4 kHz and provided rotational constants MHz, MHz, MHz. These rotational constants and the planar moments are consistent with a structure of symmetry exhibiting C--H... and C--F...H--C interactions and are in excellent agreement with a structure obtained from optimizations at the MP2/6-311++G(2d,2p) level
Reis e rainhas no Desterro: um estudo de caso /
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas
ANALYSIS OF MICROWAVE SPECTRUM, INTERNAL ROTATION AND C--HF INTERACTIONS OF THE CHFCHF WEAKLY BOUND COMPLEX
No full textAuthor Institution: Department of Chemistry, Eastern Illinois University, 600 Lincoln; Ave., Charleston, IL 61920C--HX hydrogen bonds with systematic variation of halogens (X = F, Cl, Br) have been examined using Fourier-Transform Microwave (FTMW) spectroscopy. Rotational constants for trifluoromethane--vinyl fluoride (TFMVF) were consistent with a symmetry structure that exhibited both bifurcated and single C--HF interactions between the TFM and VF. This near prolate asymmetric top exhibited three-fold internal rotation of the CF group causing characteristic doubling in its spectra. Initial assignments were completed using chirped-pulse FTMW spectroscopy with additional measurements made using a resonant-cavity FTMW spectrometer. Rotational constants from ab initio calculations at the MP2/6-311++G(2d,2p) level were in agreement with preliminary experimental values ( MHz, MHz, MHz). XIAM, nderline{\textbf {51a}}, (1996), 923-932.} was used to provide the barrier to internal rotation ( cm) and other spectral information. Spectroscopic parameters for the normal isotopic species as well as preliminary structural results on the C--HF interactions in this complex will be presented
- …
