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171.
Discrete dislocations in graphene 总被引:1,自引:0,他引:1
In this work, we present an application of the theory of discrete dislocations of Ariza and Ortiz (2005) to the analysis of dislocations in graphene. Specifically, we discuss the specialization of the theory to graphene and its further specialization to the force-constant model of Aizawa et al. (1990). The ability of the discrete-dislocation theory to predict dislocation core structures and energies is critically assessed for periodic arrangements of dislocation dipoles and quadrupoles. We show that, with the aid of the discrete Fourier transform, those problems are amenable to exact solution within the discrete-dislocation theory, which confers the theory a distinct advantage over conventional atomistic models. The discrete dislocations exhibit 5-7 ring core structures that are consistent with observation and result in dislocation energies that fall within the range of prediction of other models. The asymptotic behavior of dilute distributions of dislocations is characterized analytically in terms of a discrete prelogarithmic energy tensor. Explicit expressions for this discrete prelogarithmic energy tensor are provided up to quadratures. 相似文献
172.
T. Galeano Diaz A. Guiberteau J. M. Ortiz M. D. López F. Salinas 《Chromatographia》2001,53(1-2):40-46
Summary We have used an artificial neural network to optimize the composition of the mobile phase for an isocratic HPLC method for
the analysis of nitrophenol pesticides and related compounds, on the basic of different response functions, and have compared
the results with those obtained by application of response-surface methodology. These studies resulted in the selection the
mobile phase 10:30:15:45 methanol-acetonitrile-tetrahydrofuran-buffer solution (0.1m acetic acid and 0.1m sodium perchlorate); the flow-rate was 1 mL min−1. Under these conditions a chromatogram showing twelve well-resolved peaks was obtained in 14 min. Although the peaks corresponding
to ethylparathion and medinoterb acetate overlapped severely, it was possible, by use, of a diode-array spectrophotometer
for detection, and by combining the absorbance measured at different wavelengths as the signal, to separate the peaks corresponding
to one or other of the compounds. Calibration plots were constructed for the concentration range 2–10 ppm. Detection limits,
calculated by the method of Clayton et al., were approximately 0.32–0.69 ppm. The method has been applied to the analysis
of these compounds in fortified river water samples, after previous preliminary preconcentration by solid-liquid extraction
on a C18 cartridge. 相似文献
173.
A novel Arbitrary Lagrangian-Eulerian (ALE) finite element formulation for standard dissipative media at finite strains is presented. In contrast to previously published ALE approaches accounting for dissipative phenomena, the proposed scheme is fully variational. Consequently, no error estimates are necessary and thus, linearity of the problem and the corresponding Hilbert-space are not required. Hence, the resulting Variational Arbitrary Lagrangian-Eulerian (VALE) finite element method can be applied to highly nonlinear phenomena as well. In case of standard dissipative solids, so-called variational constitutive updates provide a variational principle. Based on these updates, the deformation mapping follows from minimizing an incrementally defined (pseudo) potential, i.e., energy minimization is the overriding criterion that governs every aspect of the system. Therefore, it is natural to allow the variational principle to drive mesh adaption as well. Thus, in the present paper, the discretizations of the deformed as well as the undeformed configuration are optimized jointly by minimizing the respective incremental energy of the considered mechanical system. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
174.
Jheyne N. Ortiz Robson R. de Araujo Diego F. Aranha Sueli I. R. Costa Ricardo Dahab 《Entropy (Basel, Switzerland)》2021,23(9)
Several works have characterized weak instances of the Ring-LWE problem by exploring vulnerabilities arising from the use of algebraic structures. Although these weak instances are not addressed by worst-case hardness theorems, enabling other ring instantiations enlarges the scope of possible applications and favors the diversification of security assumptions. In this work, we extend the Ring-LWE problem in lattice-based cryptography to include algebraic lattices, realized through twisted embeddings. We define the class of problems Twisted Ring-LWE, which replaces the canonical embedding by an extended form. By doing so, we allow the Ring-LWE problem to be used over maximal real subfields of cyclotomic number fields. We prove that Twisted Ring-LWE is secure by providing a security reduction from Ring-LWE to Twisted Ring-LWE in both search and decision forms. It is also shown that the twist factor does not affect the asymptotic approximation factors in the worst-case to average-case reductions. Thus, Twisted Ring-LWE maintains the consolidated hardness guarantee of Ring-LWE and increases the existing scope of algebraic lattices that can be considered for cryptographic applications. Additionally, we expand on the results of Ducas and Durmus (Public-Key Cryptography, 2012) on spherical Gaussian distributions to the proposed class of lattices under certain restrictions. As a result, sampling from a spherical Gaussian distribution can be done directly in the respective number field while maintaining its format and standard deviation when seen in via twisted embeddings. 相似文献
175.
The aim of this work was to analyze the possible use of differential scanning calorimetry (DSC) as a method to study the process
of protein modifications during enzymatic hydrolysis. Results of the enzymatic hydrolysis of soy protein showed significant
differences in the values of maximum deflection temperature (T
p), heat of reaction (ΔH), and width at half peak height (ΔT
1/2), between DSC curves corresponding to the substrate, or zerotime of hydrolysis, and those of the hydrolysates obtained by
the action of cucurbita and pomiferin enzymes. DSC curve changes mentioned were explained by the use of gel-filtration chromatography, denaturing electrophoresis
and surface hydrophobicity of the hydrolysis products obtained at 30 min of reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
176.
Rubén A. Toscano Simón Hernández-Ortega Benjamín Ortiz Rubén Sánchez-Obregón Fernando Walls Francisco Yuste 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(11):1313-1315
The thermal Diels–Alder cycloadditon reaction of diethyl 2-[cyano(toluene-4-sulfinyl)methylene]propanedioate, C16H17NO5S, with cyclopentadiene gave the pure racemates of two of the four possible diastereomers, with a complete π-facial selectivity and a high (80:20) endo/exo-sulfinyl selectivity. X-ray diffraction studies of diethyl 2-[cyano(toluene-4-sulfinyl)methylene]propanedioate and the major isomer of the cycloaddition product, namely diethyl 3-cyano-3-(toluene-4-sulfinyl)bicyclo[2.2.1]hepta-5-ene-2,2-dicarboxylate, C21H23NO5S, reveal that the conformation of the substituents on the acrylonitrile moiety produces both steric and electronic effects, which affect the stereoselectivity of the reaction. 相似文献
177.
Marian Poterasu Martín Ortiz Morales Joel Azpeitia 《Optics and Lasers in Engineering》2001,36(6):545-550
A simple, high accuracy small gap measurement system for rough industrial environments was designed and constructed. The system could detect apertures as small as 60 μm with less than 6 μm error in metallic parts with finite (cm range) depth. The principle is based in the transient analysis of transmitted laser intensity which is focused and swept along the region of the gap. The system is composed of a low power visible laser (semiconductor or He–Ne), focusing system, rotating mirror scanner, detection optics and amplifier, control unit for signal processing, speed control and data delivery to the process control unit. 相似文献
178.
Meng Yao Zhang Hyunjun Yang Gloria Ortiz Michael J. Trnka Nektaria Petronikolou Alma L. Burlingame William F. DeGrado Danica Galoni Fujimori 《Chemical science》2022,13(22):6599
Chemical probes for chromatin reader proteins are valuable tools for investigating epigenetic regulatory mechanisms and evaluating whether the target of interest holds therapeutic potential. Developing potent inhibitors for the plant homeodomain (PHD) family of methylation readers remains a difficult task due to the charged, shallow and extended nature of the histone binding site that precludes effective engagement of conventional small molecules. Herein, we describe the development of novel proximity-reactive cyclopeptide inhibitors for PHD3—a trimethyllysine reader domain of histone demethylase KDM5A. Guided by the PHD3–histone co-crystal structure, we designed a sidechain-to-sidechain linking strategy to improve peptide proteolytic stability whilst maintaining binding affinity. We have developed an operationally simple solid-phase macrocyclization pathway, capitalizing on the inherent reactivity of the dimethyllysine ε-amino group to generate scaffolds bearing charged tetraalkylammonium functionalities that effectively engage the shallow aromatic ‘groove’ of PHD3. Leveraging a surface-exposed lysine residue on PHD3 adjacent to the ligand binding site, cyclic peptides were rendered covalent through installation of an arylsulfonyl fluoride warhead. The resulting lysine-reactive cyclic peptides demonstrated rapid and efficient labeling of the PHD3 domain in HEK293T lysates, showcasing the feasibility of employing proximity-induced reactivity for covalent labeling of this challenging family of reader domains.We describe the development of covalent cyclic peptide ligands which target a chromatin methylation reader domain using a proximity-reactive sulfonyl fluoride moiety. 相似文献
179.
N. G. Semaltianos A. De Rossi B. Vinter V. Berger M. Calligaro V. Ortiz 《Optics & Laser Technology》2004,36(8):669-676
AlGaAs-based quantum well laser structures with third-order waveguide mode emission at 775 nm are a promising route toward compact twin-photon sources at 1.55 μm based on the principle of modal phase matching between the pumping frequency and fundamental modes at half frequency in III–V semiconductor waveguides. Following the demonstration and characterization of an optically pumped third-order mode semiconductor laser, in this paper we present data of the corresponding structure under conditions of electrical pumping. By pumping electrically and optically the same sample made for current injection, identical transverse far-field angular laser mode profiles are measured and with very low parasitic losses. Although they do not follow the third-order mode emission pattern as it is expected, however this means that the different way of pumping, that of the electrical one as compared to optical pumping is not responsible for the absence of third-order mode emission. Furthermore, since the undoped optically pumped laser sample correctly emits on the third-order mode, it is concluded that the cladding layers of the structure still need to be optimized in doping and thickness, in order to reduce the internal losses for the third-order mode. 相似文献
180.
The non-rigid group (NRG) for the wagging and torsion motions in methylamine is deduced in terms of rotation and inversion operations. The group is compared to that of LonguetHiggins for the same molecule expressed in terms of permutations and permutations-inversion. It is seen that the NRG is isomorphic to that of Longuet-Higgins and the C6
v symmetry point group. The character table is deduced, as well as the symmetry eigenvectors in terms of products of trigonometric functions. Selection rules for the infrared torsional-wagging transitions are given, and the band profiles of the spectrum discussed. 相似文献