102,459 research outputs found
Accelerated superposition state molecular dynamics for condensed phase systems
No full textAn extension of superposition state molecular dynamics (SSMD) [Venkatnathan and Voth J. Chem. Theory Comput. 2005, 1, 36] is presented with the goal to accelerate timescales and enable the study of "long-time" phenomena for condensed phase systems. It does not require any a priori knowledge about final and transition state configurations, or specific topologies. The system is induced to explore new configurations by virtue of a fictitious (free-particle-like) accelerating potential. The acceleration method can be applied to all degrees of freedom in the system and can be applied to condensed phases and fluids
Diffusion mechanisms in smectic ionic liquid crystals: Insights from coarse-grained MD simulations
No full textWe present the results of MD simulations, using a coarse grained force field, concerning the mechanism of diffusion in ionic liquid crystals. The dynamical properties of the recently characterized (G. Saielli, Soft Matter, 2012, 8, 10279) model system of 1-hexadecyl-3-methylimidazolium nitrate in the smectic A phase are analysed in detail. Comparison is made with the dynamical behaviour of thermotropic non-ionic smectic liquid crystals (LCs) and with that of lamellar phases of surfactant-water mixtures. The self-diffusion anisotropy, that is the ratio between the parallel and perpendicular diffusion coefficients, is consistent with that of non-ionic smectic LCs, though a significant contribution to the parallel diffusion is given by "pore" defects, similarly to what was observed in lamellar phases. © 2013 The Royal Society of Chemistry
Potential Energy Surfaces for Chemical Reactions: An Analytical Representation from Coarse Grianed Data with an Application to Proton Transfer in Water
No full textIn this paper we address the issue of how to represent the potential energy surfaces that arise in chemical reactions from coarse grained electronic structure calculations. Using a reductionistic method based on the reaction surface model, we develop a computational protocol which combines tensor product spline fitting with bivariate interpolation. This approach is particularly useful when one wishes to retain a high degree of accuracy for a few special degrees of freedom. An application of the procedure has been developed for the transfer of a proton between two water molecules. Starting from MP2/6-311G** calculations on H5O2+ dimer, we construct the global potential energy surface governing the proton transfer as well as the pattern of charge distributions. In order to study large reactive systems embedded in an external medium, we show how a less demanding procedure can be implemented. It rests on a minimum coupling approach of second-order Taylor expansions of the potential about quasi-stationary points. The resulting potential energy surface is termed a “minimum coupling potential
The Computation of Electron Transfer Rates: The Non Adiabatic Instanton Solution
No full textA computational theory for determining electron transfer rate constants is formulated based on an instanton expression for the quantum rate and the self‐consistent solution of the imaginary time nonadiabatic steepest descent approximation. The theory obtains the correct asymptotic behavior for the electron transfer rate constant in the nonadiabatic and adiabatic cases, and it smoothly bridges between those two limits for intermediate couplings. Furthermore, no assumptions regarding the form of the diabatic potentials are invoked (e.g., harmonic) and more than two diabatic states can be included in the calculations. The method thereby holds considerable promise for computing electron transfer rate constants in realistic condensed phase system
An Overview of International Development Perspectives in History: Focus on Agricultural and Rural Development
No full textThis essay has developed gradually over the approximately 20 years, until 2000, that I taught what was then listed as AGEC 5163 and RSOC 5163, International Agricultural and Rural Development. The first draft was written during the "New Directions" mandate period, while the Green Revolution and its Agricultural Fundamentalism dominated and the Washington Consensus strategy was just emerging. Project funding was still common in international agricultural development, at least in USDA. A dramatic shift from the biological science research of the Green Revolution to Farming Systems Research was underway. The UoA Division of Agriculture had just obtained $5.0 million "Strengthening" grant from USAID, and had successfully competed for several large agricultural development contracts; in Egypt, Haiti, Rwanda, and Burundi. Major updates were prepared in 2000, and again in the summer of 2004.Community/Rural/Urban Development, International Development,
Mearuring the orientation and roation rate of 3D printed particles in turbulence
No full textThe orientation distribution and rotations of anisotropic particles in turbulent flows play a key role in many applications ranging from icy clouds to papermaking and drag reduction in pipe flow. However, experimental access to time-resolved orientations of anisotropic particles has not been easy to achieve. The use of 3D printing opens up the possibility to fabricate a wide range of particle shapes with smallest dimension down to 300 μm. So far, we have printed rods, crosses, jacks, triads, tetrads and helical particle shapes. We extract particle orientations from stereoscopic video images using a method of least squares optimization in Euler angle space. We find that in turbulence, the orientation and rotation-rate of many particles can be understood using a simple picture of alignment of both the vorticity and a long axis of the particle with the Lagrangian stretching direction of the flow
Factor prices and productivity growth during the British Industrial Revolution
No full textThis paper presents new estimates of total factor productivity growth in Britain for the period 1770–1860. We use the dual technique and argue that the estimates we derive from factor prices are of similar quality to quantity-based calculations. Our results provide further evidence, calculated on the basis of an independent set of sources, that productivity growth during the British Industrial Revolution was relatively slow. The Crafts–Harley view of the Industrial Revolution is thus reinforced. Our preferred estimates suggest a modest acceleration after 1800.British industrial revolution, productivity growth, dual measurement of productivity
Lagrangian acceleration measurements at large Reynolds numbers
No full textWe report experimental measurements of Lagrangian accelerations in a turbulent water flow between counter-rotating disks for Taylor-Reynolds numbers 900 < R-lambda < 2000. Particle tracks were recorded by imaging tracer particles onto a position sensitive photodiode, and Lagrangian information was obtained from fits to the position versus lime data. Several challenges associated with extracting Lagrangian statistical quantities from particle tracks are addressed. The acceleration variance is obtained as a function of Reynolds number and shows good agreement with Kolmogorov (1941) scaling. The Kolmogorov constant for the acceleration variance is found to be a(0) = 7 +/- 3. (C) 1998 American institute of Physics
Systematic coarse-graining of nanoparticle interactions in molecular dynamics simulation
No full textabstractA recently developed multiscale coarse-graining procedure [Izvekov, S.; Voth, G. A. J. Phys. Chem. B 2005, 109, 2469] is extended to derive coarse-grained models for nanoparticles. The methodology is applied to C60 and to carbonaceous nanoparticles produced in combustion environments. The coarse-graining of the interparticle force field is accomplished applying a force-matching procedure to data obtained from trajectories and forces from all-atom MD simulations. The CG models are shown to reproduce accurately the structural properties of the nanoparticle systems studied, while allowing for MD simulations of much larger self-assembled nanoparticle systems
The sustainable debts of Philip II: A reconstruction of Castile's fiscal position, 1566-1596
No full textThe defaults of Philip II have attained mythical status as the origin of sovereign debt crises. We reassess the fiscal position of Habsburg Castile, deriving comprehensive estimates of revenue, debt, and expenditure from new archival data. The king’s debts were sustainable. Primary surpluses were large and rising. Debt-to-revenue ratios remained broadly unchanged during Philip’s reign. Castilian finances in the sixteenth century compare favorably with those of other early modern fiscal states at the height of their imperial ambitions, including Britain. The defaults of Philip II therefore reflected short-term liquidity crises, and were not a sign of unsustainable debts.Debt sustainability, Early modern economic history, Philip II, State borrowing, Debt overhang, tax reform
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