Search results for " density"
showing 10 items of 2709 documents
Solving fully randomized higher-order linear control differential equations: Application to study the dynamics of an oscillator
2021
[EN] In this work, we consider control problems represented by a linear differential equation assuming that all the coefficients are random variables and with an additive control that is a stochastic process. Specifically, we will work with controllable problems in which the initial condition and the final target are random variables. The probability density function of the solution and the control has been calculated. The theoretical results have been applied to study, from a probabilistic standpoint, a damped oscillator.
A New Software Tool for Design, Optimization, and Complete Analysis of Rotating Electrical Machines Windings
2015
In this paper, a new software tool developed by the authors for ac winding design, optimization, and complete analysis is presented. In particular, this software can be used as a valid aid in design and analysis for a wide variety of motor and generator windings with generic number of phases (including the case of those machines in which some slots are left empty), pole pairs, slot number, and so on. The calculation of winding factors and the evaluation of their harmonic distribution is also accomplished. The software is implemented in the MATLAB programming environment. By means of some examples, covering the most relevant winding types, the capabilities of this software will be shown. In …
Polarized Fourier transform infrared microscopy as a tool for structural analysis of adsorbates in molecular sieves
1992
Using FTIR microscopy with polarized IR radiation on silicalite I single crystals fully loaded with p-xylene, the existence of an ordered adsorbate could be proven for the first time by IR spectroscopy. By analyzing the polarized absorption bands the orientation of the p-xylene molecules relative to the host structure could be determined. The results agree well with structural data obtained from X-ray diffraction experiments. These first results suggest that polarized IR microscopy could develop into a powerful tool for the analysis of adsorbate structures, assisting in complete structure resolution by diffraction techniques
Time multiplexing super-resolved imaging without a priori knowledge of the spatial distribution of the encoding structured illumination
2021
Time multiplexing is a super-resolution technique that sacrifices time to overcome the resolution reduction obtained because of diffraction. There are many super resolution methods based on time multiplexing, but all of them require a priori knowledge of the time changing encoding mask, which is projected on the object and used to encode and decode the high-resolution information. In this paper, we present a time multiplexing technique that does not require the a priori knowledge on the projected encoding mask. First, the theoretical concept of the technique is demonstrated; then, numerical simulations and experimental results are presented.
Charge density waves in NbSe3: The models and the experimental evidence
2010
a b s t r a c t Charge density wave (CDW) ordering in the prototypical low-dimensional compound NbSe3 is reconsidered. It is shown that the model with two incommensurate modulations, q1 = (0, 0.241, 0) and q2 = (0.5, 0.260, 0.5), localized on type-III and type-I bi-capped trigonal prismatic columns, does not explain details, revealed by various microscopic methods. An alternative explanation, based on the existence of modulated layered nano-domains below both CDW onset temperatures, is suggested. It accounts for the presence of the q2 modulation in the STM images recorded above the T2 CDW transition and for the absence of q2 satellites in the corresponding diffraction patterns. The long per…
Revisiting the charge density analysis of 2,5-dichloro-1,4-benzoquinone at 20 K
2017
A high-resolution X-ray diffraction measurement of 2,5-dichloro-1,4-benzoquinone (DCBQ) at 20 K was carried out. The experimental charge density was modeled using the Hansen–Coppens multipolar expansion and the topology of the electron density was analyzed in terms of the quantum theory of atoms in molecules (QTAIM). Two different multipole models, predominantly differentiated by the treatment of the chlorine atom, were obtained. The experimental results have been compared to theoretical results in the form of a multipolar refinement against theoretical structure factors and through direct topological analysis of the electron density obtained from the optimized periodic wavefunction. The si…
Maximum entropy method : an unconventional approach to explore observables related to the electron density in phengites
2009
The maximum entropy method (MEM) is used here to get an insight into the electron density [rho(r)] of phengites 2M (1) and 3T, paying special attention to the M1-formally empty site and charge distribution. Room temperature single crystal X-ray diffraction data have been used as experimental input for MEM. The results obtained by MEM have been compared with those from conventional structure refinement which, in turn, has provided the prior-electron density to start the entropy maximization process. MEM reveals a comparatively non-committal approach, able to produce information related to the M1-site fractional occupancy, and yields results consistent with those from the difference Fourier s…
Electric properties of KTiOPO4and NaTiOPO4from temperature-dependent X-ray diffraction
1999
Single crystals of KTiOPO4(KTP) and NaTiOPO4(NaTP) show pronounced pyroelectric behaviour. In order to determine the origin of this property on an atomic scale, X-ray diffraction measurements have been carried out at several temperatures between 100 and 600 K. Modelling of the electron density and the evolution of the structure as a function of temperature has enabled the determination of values for the spontaneous polarization of the compounds and the pyroelectric coefficient of KTP, principally due to the alkaline-ion displacements with a value of 2.0 nC cm−2 K−1. Structure modifications, compared with NaTiOPO4, and the calculation of the electrostatic potential explain the anisotropic be…
Synchrotron X-ray Diffraction and Reflection Studies of a Polymacromonomer Monolayer at the Air−Water Interface: Transition from Aligned Single Mole…
2004
Monolayers of polymacromonomers with poly(vinyl)pyridine side chains of different lengths, polyPVP20.8 and polyPVP46.7, are studied at the air/water interface. Combination of reflection data and diffraction peaks allows the establishment of a structural model. In the expanded phase at pressures below approximately 15 mN/m, the side chains are adsorbed to the air/water interface, causing polymer backbone stretching and alignment of the single molecules. The in-plane peaks are due to the lateral electron density variation above and below the adsorption layer. The diameter of the flattened cylindrical molecules corresponds to twice the contour length of the side chains (25 and 12.5 nm, respect…
On the application of an experimental multipolar pseudo-atom library for accurate refinement of small-molecule and protein crystal structures
2007
International audience; With an increasing number of biomacromolecular crystal structures being measured to ultra-high resolution, it has become possible to extend to large systems experimental charge-density methods that are usually applied to small molecules. A library has been built of average multipole populations describing the electron density of chemical groups in all 20 amino acids found in proteins. The library uses the Hansen & Coppens multipolar pseudo-atom model to derive molecular electron density and electrostatic potential distributions. The library values are obtained from several small peptide or amino acid crystal structures refined against ultra-high-resolution X-ray diff…