Starting from a model study of the collinear (H, H
2
) exchange reaction in 1959, the time-dependent quantum mechanical wave packet (TDQMWP) method has come a long way in dealing with systems as ...large as Cl + CH
4
. The fast Fourier transform method for evaluating the second order spatial derivative of the wave function and split-operator method or Chebyshev polynomial expansion for determining the time evolution of the wave function for the system have made the approach highly accurate from a practical point of view. The TDQMWP methodology has been able to predict state-to-state differential and integral reaction cross sections accurately, in agreement with available experimental results for three dimensional (H, H
2
) collisions, and identify reactive scattering resonances too. It has become a practical computational tool in predicting the observables for many A + BC exchange reactions in three dimensions and a number of larger systems. It is equally amenable to determining the bound and quasi-bound states for a variety of molecular systems. Just as it is able to deal with dissociative processes (without involving basis set expansion), it is able to deal with multi-mode nonadiabatic dynamics in multiple electronic states with equal ease. We present an overview of the method and its strength and limitations, citing examples largely from our own research groups.
Starting from a model study of the collinear (H, H
2
) exchange reaction in 1959, the time-dependent quantum mechanical wave packet (TDQMWP) method has come a long way in dealing with systems as large as Cl + CH
4
.
Mechanical fatigue under strain controlled tension/tension (T/T) of rectangular un‐notched and notched specimens of high density polyethylene and polyamide 6 was performed. Under large amplitude ...oscillatory elongation, the stress response is nonlinear asymmetric due to a different stress response during loading and unloading and was analyzed via discrete Fourier transform. Dynamic strain (ε0) sweep tests revealed odd (I3/1 α ε02) and even (I2/1 α ε01) harmonics in the stress, well described by the Neo‐Hooke's law. Before crack onset for the Nc specimens, the storage and loss moduli and I2/1 are constant, but I3/1 increases with fatigue. The first derivative of I3/1 (dI3/1/dN) and the cumulative nonlinearity Qf parameter (integral of I3/1/ε02) were found to be strong criteria predicting fatigue. To break the unnotched specimens in the low and high cycle fatigue regime, large strain amplitudes were applied, resulting for both materials in initial plastic deformation followed by buckling when a critical compression force is exceeded. This results in a different time evolution of the linear and nonlinear parameters, especially as a minimum in the I2/1 curve. Finally, a model is proposed to describe the nonlinear viscoelastic specimen response under T/T and the effect of buckling.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
ABSTRACT Astronomical radio signals are subjected to phase dispersion while traveling through the interstellar medium. To optimally detect a short-duration signal within a frequency band, we have to ...precisely compensate for the unknown pulse dispersion, which is a computationally demanding task. We present the "fast dispersion measure transform" algorithm for optimal detection of such signals. Our algorithm has a low theoretical complexity of , where Nf, Nt, and NΔ are the numbers of frequency bins, time bins, and dispersion measure bins, respectively. Unlike previously suggested fast algorithms, our algorithm conserves the sensitivity of brute-force dedispersion. Our tests indicate that this algorithm, running on a standard desktop computer and implemented in a high-level programming language, is already faster than the state-of-the-art dedispersion codes running on graphical processing units (GPUs). We also present a variant of the algorithm that can be efficiently implemented on GPUs. The latter algorithm's computation and data-transport requirements are similar to those of a two-dimensional fast Fourier transform, indicating that incoherent dedispersion can now be considered a nonissue while planning future surveys. We further present a fast algorithm for sensitive detection of pulses shorter than the dispersive smearing limits of incoherent dedispersion. In typical cases, this algorithm is orders of magnitude faster than enumerating dispersion measures and coherently dedispersing by convolution. We analyze the computational complexity of pulsed signal searches by radio interferometers. We conclude that, using our suggested algorithms, maximally sensitive blind searches for dispersed pulses are feasible using existing facilities. We provide an implementation of these algorithms in Python and MATLAB.
•Obtaining the simulated Moiré pattern by calculating the sub-pixel transmittance matrix.•Analyzing the simulated Moiré pattern on metal mesh touch screen in spatial spectrum domain.•Introducing the ...characteristic spatial frequency to represent the visibility of Moiré.
This paper presents a novel algorithm to analyze and judge the visibility of Moiré appearing on metal mesh touch screen whose resolution is 2 K from spatial frequency domain by using Fourier transformation. In this method, we utilize the characteristic spatial frequency to represent the visibility of Moiré, and two-dimensional Fourier transformation is performed on the simulation image obtained by calculating the pixel transmittance. The characteristic frequency is obtained by frequency filtering, and the Moiré visibility is evaluated according to it. In this paper, three different displays are used for experiments, 1.89 lp/mm, 1.94 lp/mm and 1.85 lp/mm are taken respectively as the dividing line to classify the performance of Moiré. The matching ratios of the three displays are 84.47%, 82.30% and 80.12% respectively, showing pretty high accuracy with the practical matching result. This new method may be quite useful for guiding the manufacture of metal mesh touch panel.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Advances in high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) enable molecular-level characterization of ultracomplex asphaltene samples. Such analyses most ...often reveal compounds that are highly aromatic but alkyl-deficient in nature and, thus, support the classical “island” model of asphaltene architecture. However, recent works that combine chromatographic separations with mass spectrometry for the analysis of crude oils have shown that differences in ionization may greatly affect the analysis of complex mixtures (known as the matrix effect). Simply, compounds that ionize with greater efficiency are preferentially observed and mask the detection of poorly ionized compounds. Asphaltenes are not immune to this phenomenon. In the first of this series (10.1021/acs.energyfuels.7b02873), it was demonstrated that asphaltenes generated by different precipitants showed greatly varied monomer ion yields (ionization efficiencies). This work focuses on the development of an extrography fractionation method that selectively targets the removal of asphaltene species that exhibit high monomer ion yields and, thus, restrict mass spectral characterization of less efficiently ionized species. Silica gel was used as the stationary phase, and a unique solvent series separated asphaltenes based on their interaction with the silica surface, which was later determined to depend heavily upon the structure as well as monomer ion yield. The first two solvents (acetone and acetonitrile) isolated compounds that most efficiently produce monomeric asphaltene ions and, thus, cause bias in mass spectrometric analyses of whole asphaltenes. A solvent polarity gradient was then used, with n-heptane, toluene, tetrahydrofuran, and methanol, to separate remnant asphaltene compounds on the basis of polarity and structure. Our results demonstrate that mass spectrometry of whole asphaltenes does not reveal the complete molecular composition but rather preferentially exposes highly aromatic, alkyl-deficient, island-type structures. Early eluting fractions are shown to resemble the composition of the whole asphaltene and are enriched in island structures, whereas the analysis of later-eluting fractions reveals archipelago structural motifs as well as species with atypical asphaltene molecular compositions. We also demonstrate that, as molecular weight increases, the asphaltenes exhibit increased contributions of archipelago structural motifs. Higher mass ions (m/z > 550), even from asphaltene fractions enriched in island structures, exhibit fragmentation pathways that originate from archipelago structures. Thus, positive-ion atmospheric pressure photoionization (APPI) FT-ICR MS provides molecular-level data that suggest that the island model is not the dominant structure of asphaltenes. It coexists with abundant archipelago structures, and the ratios of each are sample-dependent.
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Abstract
This research aimed to study the feature of noise signal from various exhausts in motorcycles by the Fast Fourier Transform (FFT). The noise signal was examined into three different ...features; energy, entropy, and zero-crossing rate. The energy and entropy defined the noise came from an exhaust or non-exhaust, while the zero-crossing rate distinguished normal and racing-exhaust. The results showed that the energy of an exhaust noise was always in the range of 2.4 to 2.8 joule. The entropy of exhausts racing was observed in the range of 0.00 to 0.05 joule. When the acceleration pedal was on, the entropy was become higher. The zero-crossing rate of racing exhaust was in the range of 0.00 to 0.05, the non-racing exhaust was in the range 0.05 to 0.1.
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•Graphene oxide-chitosan hydrogel: an easily operated macroscopic adsorbent.•High adsorption capacity for U(VI) over a wide pH range.•Adsorption mechanism 1: at pH 3.5 and 5.0, ...surface complexation by –COO−, –OH, and –NH2.•Adsorption mechanism 2: at pH 8.3, UO2(hydrogel–NH2, C3–OH)(CO3)(H2O) proposed.
Aiming at the efficient and convenient treatment of radioactive wastewater, a graphene oxide-chitosan aerogel (GO-CS) was fabricated and utilized for uranium(VI) elimination. The adsorption of U(VI) on the aerogel was evaluated as a function of contact time, solution pH, ionic strength, initial uranium concentration, and competing metal ions. High adsorption capacity for the uranium could be achieved over a wide pH range, e.g., 200, 319.9, and 384.6mg/g at pH 3.5, 5.0, and 8.3, respectively. The interaction mechanism of U(VI) with GO-CS was systematically clarified by using Fourier transformation infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure spectroscopy (EXAFS). It was found that the U(VI) adsorption was mainly ascribed to the inner-sphere surface complexation by –COO−, –OH, and –NH2 groups anchored on the GO-CS and the involvement of these functional groups toward the coordination sphere was largely relevant to solution pH. At mild alkaline pH, –NH2 groups play a more important role, therefore leading to an extraordinarily high extraction of uranium from simulated seawater.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•MCC was prepared from tea waste by chemical and hydrolysis treatments.•The effects of hydrolysis conditions on the DP and yield of MCC were studied.•Hydrolysis conditions were optimized by ...orthogonal experiment.•Tea waste MCC maintained the cellulosic structure and had good thermal stability.
Microcrystalline cellulose (MCC) was prepared from Oolong tea waste by acid hydrolysis in the present study. Based on the single factor experiment results, the hydrolysis conditions were optimized by an orthogonal L9(3)4 experiment. Results showed that the degree of polymerization (DP) and yield of MCC were strongly influenced by the time and temperature of hydrolysis, the concentration of HCl and the ratio of acid to material. Under optimal conditions (acid to materials ratio 1:20, HCl concentration 1.5 mol/L, 65 °C, 90 min), the yield and DP of the tea waste MCC were 86.7% and 145, respectively. Fourier transform-infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis indicated that tea waste MCC had cellulosic structure and was cellulose I type. Scanning electron microscopy (SEM) showed that MCC had shorter fibers with some holes on the rough surface. The MCC prepared from tea waste had good thermal stability.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Success or failure of an IC product hinges on the quality of molding process which protects chips from the harm done by external force and moisture. Defects such as cracks, dilapidations or voids may ...be embedding on the molding surface while a chip was being molded. Human inspection often neglects a very tiny crack or a low-contrast void. Hence an automatic optical inspection system for the integrated circuit (IC) molding surface cannot be over emphasized. The proposed system is composed of a charged coupled device, a coaxial light, a back light and a motion control unit. Based on the characteristics of statistical textures of the molding surface, a series of digital image processing is carried out, including normalization, shrinking, segmenting and Fourier based image restoration and defect identification. Training of the parameter associated with defect inspection algorithm is also discussed. Results of the experiment suggest that the inspection system works effectively with high accuracy rate of 94.2 %, contributing to the inspection quality of IC molding surface.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A two-dimensional tandem mass spectrometry (2D MS/MS) scan has been developed for the linear quadrupole ion trap. Precursor ions are mass-selectively excited using a nonlinear ac frequency sweep at ...constant rf voltage, while simultaneously, all product ions of the excited precursor ions are ejected from the ion trap using a broad-band waveform. The fragmentation time of the precursor ions correlates with the precursor m/z value (the first mass dimension) and also with the ejection time of the product ions, allowing the correlation between precursor and product ions. Additionally, the second mass dimension (product ions’ m/z values) is recovered through fast Fourier transform of each mass spectral peak, revealing either intentionally introduced “frequency tags” or the product ion micropacket frequencies, both of which can be converted to product ion m/z through the classical Mathieu parameters, thereby revealing a product ion mass spectrum for every precursor ion without prior isolation. We demonstrate the utility of this method for analyzing a broad range of structurally related precursor ions, including chemical warfare agent simulants, fentanyls and other opioids, amphetamines, cathinones, antihistamines, and tetracyclic antidepressants.
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