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231.
Aditya Tatu François Lauze Stefan Sommer Mads Nielsen 《Journal of Mathematical Imaging and Vision》2010,38(3):226-240
This paper deals with restricting curve evolution to a finite and not necessarily flat space of curves, obtained as a subspace
of the infinite dimensional space of planar curves endowed with the usual but weak parametrization invariant curve L
2-metric. 相似文献
232.
233.
Patrick Juilland Aditya Kumar Emmanuel Gallucci Robert J. Flatt Karen L. Scrivener 《Cement and Concrete Research》2012,42(9):1175-1188
The kinetics of hydration of cementitious materials is sensitive to the mixing procedure. High shear mixing conditions lead to an increase in the kinetics of hydration at early age compared to low shearing conditions such as hand mixing. In this study the effect of mixing speed and procedure was studied on alite and Portland cement in the presence or not of aggregates. The kinetics of hydration was monitored using isothermal calorimetry at 20 °C. The early reactivity was enhanced both with an increase in the speed of mixing and the shearing conditions. The principal features are a shortening of the induction period; a higher rate of hydrate precipitation during the acceleration period as well as an increase in the height of the main heat evolution peak. Analysis of the results in terms of dissolution theory, coupled with quantitative simulation with the μic modelling platform indicate different effects of mixing prior to and after the end of the induction period. Before the end of the induction period mixing has an impact on the rate of dissolution in the fast dissolution regime and high undersaturation, which appears to be (at least partially) controlled by the rate of transport of ions away from the alite surface. After the end of the induction period the main effect of mixing appears to be the production of more C-S-H nuclei, due to the possible detachment of the primary C-S-H (metastable) by mechanical action. This higher nucleation density leads to a denser microstructure for systems mixed at high intensities. 相似文献
234.
The modelling platform μic [1] has been used to investigate the mechanisms occurring during the hydration of alite. It is shown that it is possible to obtain a good simulation of the hydration kinetics through the implementation of two mechanisms: a dissolution mechanism combined with nucleation and growth of products. The dissolution rate is varied according to the ratio β, between the ion activity product and the equilibrium solubility product according the theory published by Juilland et al. [2]. The solution concentrations are computed directly from the amount of alite dissolved taking into account the amount of water present and the amount of products formed, with activities and complex ion formation calculated according to standard methods. Saturation index calculations are implemented to compute the time of precipitation of C–S–H and portlandite (CH) individually. For the main heat evolution peak, the rate controlling mechanism switches to a modified form of boundary nucleation and growth. C–S–H grows in a diffuse manner in which the density of packing of the C–S–H phase increases with hydration [3]. The rate of heat evolution obtained from the simulations is compared with isothermal calorimetry data and good agreement is found. 相似文献
235.
In order to attain near-single user performance in uplink multicarrier code- division multiple-access (MC-CDMA) systems, multiuser
detection (MUD) methods may be employed which rely on simultaneous estimation of the channel frequency responses of multiple
users. Pilot symbol assisted (PSA) channel estimation is needed in fast fading channels and it can be performed either by
applying maximum likelihood (ML) criterion or minimum mean-squared error (MMSE) criterion. The performance of ML estimation
technique degrades significantly in the case of fractionally spaced (FS) multipath channels where dominant paths are closely
spaced with respect to the time resolution of the system. In such situation, the number of effective paths (which contribute
more towards signal power) becomes considerably less than the actual number of multipaths at low and moderate SNR values.
We propose an improved ML estimation method which considers only effective paths during the estimation process. The proposed
method performs nearly identical to the MMSE estimation method and it can also provide significant reduction in the computational
complexity when a large number of users are accommodated in the system. 相似文献
236.
Török B Sood A Bag S Kulkarni A Borkin D Lawler E Dasgupta S Landge S Abid M Zhou W Foster M LeVine H Török M 《ChemMedChem》2012,7(5):910-919
A broad group of structurally diverse small organofluorine compounds were synthesized and evaluated as inhibitors of β-amyloid (Aβ) self-assembly. The main goal was to generate a diverse library of compounds with the same functional group and to observe general structural features that characterize inhibitors of Aβ oligomer and fibril formation, ultimately identifying structures for further focused inhibitor design. The common structural motifs in these compounds are CF(3) -C-OH and CF(3) -C-NH groups that were proposed to be binding units in our previous studies. A broad range of potential small-molecule inhibitors were synthesized by combining various carbocyclic and heteroaromatic rings with an array of substituents, generating a total of 106 molecules. The compounds were tested by standard methods such as thioflavin-T fluorescence spectroscopy for monitoring fibril formation, biotinyl Aβ(1-42) single-site streptavidin-based assays for observing oligomer formation, and atomic force microscopy for morphological studies. These assays revealed a number of structures that show significant inhibition against either Aβ fibril or oligomer formation. A detailed analysis of the structure-activity relationship of anti-fibril and -oligomer properties is provided. These data present further experimental evidence for the distinct nature of fibril versus oligomer formation and indicate that the interaction of the Aβ peptide with chiral small molecules is not stereospecific in nature. 相似文献
237.
In order to achieve higher pulse energy in a passively mode-locked fiber ring laser, a long cavity length is commonly implemented. However, a long cavity operating in the anomalous dispersion regime also leads to pulse broadening, which reduces the average pulse power. In this paper, the trade-off between cavity length and average pulse power is investigated with the aim of optimizing the cavity length to achieve maximum pulse energy. Numerical simulation results, presented here, indicate that there exists an optimum cavity length for which the pulse energy is maximum and the optimum length shifts as the pump power changes. The simulation results for a pump power of 500 mW are verified by measurements carried out on a long cavity nonlinear polarization rotation mode-locked all-fiber ring laser operating in the anomalous dispersion regime. With a repetition rate of 266 kHz for the dissipative solitons, we achieve a pulse energy of 139.1 nJ for a cavity length of 700 m. Higher pulse energy can be expected by using a pump laser diode with higher pump power. 相似文献
238.
Alternative efforts to describe water quality by an aggregate index consisting of subindices of the constituent quality variables are examined. Ambiguity problems exist where all the subindices are acceptable and yet the overall index is not. Eclipsing problems exist where the overall index is insensitive to a single variable; such insensitivity is unacceptable. A mathematical formulation is developed that avoids these problems of ambiguity and eclipsing. Furthermore, the recommended index form is open to increasing the number of variables included within the index. 相似文献
239.
A theoretical investigation on the screening dependence of the superconducting state parameters (SSPs) viz. the electron-phonon coupling strength λ, the Coulomb pseudopotential μ∗, the transition temperature TC, the isotope effect exponent α and the effective interaction strength N0V of some ternary metallic glasses such as Ti50Be34Zr10, (Mo0.6Ru0.4)78B22, (Mo0.6Ru0.4)80B20, (Mo0.4Ru0.6)80P20, (Mo0.6Ru0.4)70Si30, (Mo0.6Ru0.4)84B16, (Mo0.6Ru0.4)72Si28, (Mo0.6Ru0.4)86B14, (Mo0.6Ru0.4)76Si24, (Mo0.6Ru0.4)78Si22, (Mo0.6Ru0.4)80Si20, (Mo0.6Ru0.4)82Si18 and (Mo0.6Ru0.4)80P20 is reported for the first time using Ashcroft''s empty core (EMC) model potential. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al (F) and Sarkar et al (S) are used in the present investigation to study the effect of screening on the aforesaid properties. It is observed that λ and TC are reasonably sensitive to the selection of the local field correction functions, whereas μ∗, α and N0V show weak dependences on the local field correction functions. The transition temperature TC obtained from the H-local field correction function is found to be in excellent agreement with available experimental data. Also, the present results are found to be in qualitative agreement with other earlier reported data, which confirms the existence of the superconducting phase in the above ternary metallic glasses. 相似文献
240.
The design of a language for model transformations 总被引:1,自引:0,他引:1
Aditya Agrawal Gabor Karsai Sandeep Neema Feng Shi Attila Vizhanyo 《Software and Systems Modeling》2006,5(3):261-288
Model-driven development of software systems envisions transformations applied in various stages of the development process. Similarly, the use of domain-specific languages also necessitates transformations that map domain-specific constructs into the constructs of an underlying programming language. Thus, in these cases, the writing of transformation tools becomes a first-class activity of the software engineer. This paper introduces a language that was designed to support implementing highly efficient transformation programs that perform model-to-model or model-to-code translations. The language uses the concepts of graph transformations and metamodeling, and is supported by a suite of tools that allow the rapid prototyping and realization of transformation tools. 相似文献