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81.
The deformation process in copper and aluminium single crystals under shock loading is investigated using a multiscale model of plasticity that couples discrete dislocation dynamics and finite element analyses. Computer simulations are carried out to mimic loading condition of high strain rates ranging from 105 to 107?s?1, and short pulse durations of few nanoseconds involved in recent laser based experiments. The effects of strain rate, shock pulse duration and the nonlinear elastic properties are investigated. Relaxed configurations using dislocation dynamics show formation of dislocation micro bands and weak dislocation cells. Statistical analyses of the dislocation microstructures are preformed to study the characteristics of the local dislocation densities and the distribution of the instantaneous dislocations velocities. 相似文献
82.
Abstract Eisenbud et al. proved a number of results regarding Gröbner bases and initial ideals of those ideals J in the free associative algebra K ?X 1,…, X n ? which contain the commutator ideal. We prove similar results for ideals which contains the anti-commutator ideal (the defining ideal of the exterior algebra). We define one weak notion of generic initial ideals in K ?X 1,…, X n ?, and show that generic initial ideals of ideals containing the anti-commutator ideal, or the commutator ideal, are finitely generated. 相似文献
83.
Aleksandra Holownia Chieh‐Hung Tien Diego B. Diaz Reed T. Larson Andrei K. Yudin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(42):15292-15297
The synthesis and applications of carboxy‐MIDA‐boronate, a novel C1 building block, are described. This molecule is accessible via a ruthenium tetraoxide‐mediated cleavage of commercially available ethynyl‐MIDA‐boronate. In the course of this study, carboxy‐MIDA‐boronate was found to possess ambident reactivity towards nucleophiles. Carboxylic acid derivatization produces a broad range of previously unknown carbamoyl‐, oxycarbo‐ and thiocarboboronates. Carboxy‐MIDA‐boronate and its derivatives undergo condensations to access borylated heterocycles with boron at positions that are difficult to access using alternate methods. The resulting heterocycles participate in the Suzuki–Miyaura cross‐coupling reaction, enabling entry into diverse bis(heteroaryl) motifs. The carbon monoxide‐releasing capacity of carboxy‐MIDA‐boronate was also examined and applied in palladium‐catalyzed carbonylation. 相似文献
84.
Alice E. Dearle Daniel J. Cutler Hector W. L. Fraser Sergio Sanz Edward Lee Sourav Dey Ismael F. Diaz‐Ortega Gary S. Nichol Hiroyuki Nojiri Marco Evangelisti Gopalan Rajaraman Jürgen Schnack Leroy Cronin Euan K. Brechin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(47):17059-17062
The dissolution of anhydrous iron bromide in a mixture of pyridine and acetonitrile, in the presence of an organic amine, results in the formation of an [Fe34] metal oxide molecule, structurally characterised by alternate layers of tetrahedral and octahedral FeIII ions connected by oxide and hydroxide ions. The outer shell of the complex is capped by a combination of pyridine molecules and bromide ions. Magnetic data, measured at temperatures as low as 0.4 K and fields up to 35 T, reveal competing antiferromagnetic exchange interactions; DFT calculations showing that the magnitudes of the coupling constants are highly dependent on both the Fe‐O‐Fe angles and Fe?O distances. The simplicity of the synthetic methodology, and the structural similarity between [Fe34], bulk iron oxides, previous FeIII–oxo cages, and polyoxometalates (POMs), hints that much larger molecular FeIII oxides can be made. 相似文献
85.
With a proper perturbation, even a single-mode semiconductor laser can exhibit highly complex dynamical characteristics ranging from stable, narrow-linewidth oscillation to broadband chaos. In recent years, three approaches to invoke complex nonlinear dynamical states in a single-mode semiconductor laser have been thoroughly studied: optical injection, optical feedback, and optoelectronic feedback. In each case, the nonlinear dynamics of the semiconductor laser depends on five intrinsic laser parameters and three operational parameters. The dynamical state of a given laser can be precisely controlled by properly adjusting the three operational parameters. This ability to control the dynamical behavior of a laser, combined with the understanding of its characteristics, opens up the opportunity for a wide range of novel applications. This paper illustrates the utilization of the rich nonlinear dynamics of single-mode semiconductor lasers by focusing on the period-one oscillation for its applications in tunable photonic microwave generation, AM-to-FM conversion, and dual-frequency precision Doppler lidar. 相似文献
86.
The kinetics of noble metal nanoparticle formation in bottom-up syntheses are important for controlling and optimizing these methods. Hence, experimental probes that are easily accessible to most laboratories are also of interest. We collected kinetic curves for the formation of silver nanoparticles in a modified Turkevich method with citrate acting as the reducing and stabilizing agent by (i) measuring the change in silver nanoparticle surface plasmon resonance by UV-visible spectroscopy, a somewhat indirect method, and then also by (ii) measuring the change in silver ion concentration by ion-selective electrode potentiometry and/or atomic absorption spectroscopy, two more direct methods. The resulting sigmoidal kinetic curves were curvefitted with the Finke-Watzky two-step kinetic model of slow, continuous nucleation and fast autocatalytic growth to extract average rate constants. We found that the kinetic curves obtained by following the change in silver ion concentration were apparent mirror images of those constructed by following the change in nanoparticle surface plasmon resonance, and that their respective curvefits displayed the same sigmoidal characteristics. The resultant values of the rate constants for nucleation and growth overlapped within experimental error between the methods and showed similar trends over the range of citrate concentrations studied. The use of multiple probes in this work to follow the kinetics of nanoparticle formation helps fill a need for the comparison and evaluation of different methods available to scientists, particularly those considered easily accessible. 相似文献
87.
Facetti Masulli J. F. Kump Peter de Diaz Zulma V. de González Virginia R. 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(2):861-868
Journal of Radioanalytical and Nuclear Chemistry - Sediments play an important role in the distribution of trace elements in the aquatic system and act as a sink for metals. Incompatible elements... 相似文献
88.
A. Castiñeiras Gladys Diaz F. Florencio S. Garcia-Blanco S. Martinez-Carrera 《Journal of chemical crystallography》1988,18(4):395-401
Summary The X-ray crystal structure of the title compound, [Hg2(C16H20N2S2)I4], has been determined. The crystals are monoclinic (space groupP21/c), with cell dimensionsa=15.016(2),b=6.201(3),c=15.273(2) Å,=115.18(1)°;V
o
=1287.0(7) Å3,M
r
=1213.266,Z=4,D
x
=6.26mg m–3, MoK radiation (graphite crystal monochromator,
),(MoK)=336 cm–1,F(000)=4272, andT=290°K. The final conventionalR factor=0.054, andR
w
=0.062 for 2799 observed reflections. The structure was solved by Patterson and Fourier methods and refined by block-diagonal least-squares methods. The coordination around the mercury atoms is approximately tetrahedral, although with considerable distortion, with two iodine atoms and the N and S atoms of one-half of the ligand molecule. 相似文献
89.
Giuseppe Chirico Prof. Maddalena Collini Prof. Laura D'Alfonso Prof. Franck Denat Prof. Yuri A. Diaz‐Fernandez Dr. Luca Pasotti Dr. Yoann Rousselin Dr. Nicolas Sok Dr. Piersandro Pallavicini Prof. 《Chemphyschem》2008,9(12):1729-1737
Potentiometric titrations, fluorescence versus pH titrations, dynamic light scattering and fluorescence polarization anisotropy studies demonstrate that inside the nanodimensioned Triton X‐100 micelles, 1‐pyrenecarboxylic acid, PCOO?, forms an apical complex with the Zn2+ cation encircled by a lipophilic cyclen ligand and hugely increasing its fluorescence. The ability of the Zn2+‐cyclen‐PCOO? complex plus its micellar container to act as a fluorescent sensor to evaluate the lipophilicity of molecular species is demonstrated on the fatty acid series CH3(CH2)xCOOH (x=0–16). At pH 7.4 a decrease in fluorescence is observed on the addition of fatty acids that is directly related to their chain length, that is, to their tendency to enter the micellar containers, where they dislocate PCOO? from the Zn2+ centre. The independent determination of fatty acid pKa values in the presence of Triton X‐100 micelles confirms that our fluorescent micellar device is capable of sensing their lipophilicity. 相似文献
90.
Griffin TP Diaz JA Arkin CR Soto C Curley CH Gomez O 《Journal of the American Society for Mass Spectrometry》2008,19(10):1411-1418
The visualization of hazardous gaseous emissions at volcanoes using in-situ mass spectrometry (MS) is a key step towards a
better comprehension of the geophysical phenomena surrounding eruptive activity. In-situ data consisting of helium, carbon
dioxide, sulfur dioxide, and other gas species, were acquired with a quadrupole based MS system. Global position systems (GPS)
and MS data were plotted on ground imagery, topography, and remote sensing data collected by a host of instruments during
the second Costa Rica Airborne Research and Technology Applications (CARTA) mission. This combination of gas and imaging data
allowed three-dimensional (3D) visualization of the volcanic plume and the mapping of gas concentration at several volcanic
structures and urban areas. This combined set of data has demonstrated a better tool to assess hazardous conditions by visualizing
and modeling of possible scenarios of volcanic activity. The MS system is used for in-situ measurement of 3D gas concentrations
at different volcanic locations with three different transportation platforms: aircraft, auto, and hand-carried. The demonstration
for urban contamination mapping is also presented as another possible use for the MS system. 相似文献