Free energy of formation of clusters of sulphuric acid and water molecules determined by guided disassembly

We evaluate the grand potential of a cluster of two molecular species, equivalent to its free energy of formation from a binary vapour phase, using a nonequilibrium molecular dynamics technique where guide particles, each tethered to a molecule by a harmonic force, move apart to disassemble a cluster into its components. The mechanical work performed in an ensemble of trajectories is analysed using the Jarzynski equality to obtain a free energy of disassembly, a contribution to the cluster grand potential. We study clusters of sulphuric acid and water at 300 K, using a classical interaction scheme, and contrast two modes of guided disassembly. In one, the cluster is broken apart through simple pulling by the guide particles, but we find the trajectories tend to be mechanically irreversible. In the second approach, the guide motion and strength of tethering are modified in a way that prises the cluster apart, a procedure that seems more reversible. We construct a surface representing the cluster grand potential, and identify a critical cluster for droplet nucleation under given vapour conditions. We compare the equilibrium populations of clusters with calculations reported by Henschel et al. [J. Phys. Chem. A 118, 2599 (2014)] based on optimised quantum chemical structures

Toxic level hypergolic vapor detection sensor development

Development of an electrochemical sensor technology capable of PPB level hypergolic vapor sensing is reported. A portable instrument capable of meeting the design goals is described

Evaluation of present thermal barrier coatings for potential service in electric utility gas turbines

The resistance of present-day thermal barrier coatings to combustion gases found in electric utility turbines was assessed. The plasma sprayed coatings, both duplex and graded types, were primarily zirconia-based, although a calcium silicate was also evaluated. Both atmospheric burner rig tests and high pressure tests (135 psig) showed that several present-day thermal barrier coatings have a high potential for service in gas turbines burning the relatively clean GT No. 2 fuel. However, coating improvements are needed for use in turbines burning lower grade fuel such as residual oil. The duplex ZrO2.8Y2O3/NiCrA1Y coating was ranked highest and selected for near-term field testing, with Ca2SiO4/NiCrA1Y ranked second. Graded coatings show potential for corrosive turbine operating conditions and warrant further development. The coating degradation mechanisms for each coating system subjected to the various environmental conditions are also described

Kinetic Alfvén mode and kinetic magnetosonic mode from a fluid description

The dispersion relations for the classical electromagnetic modes in a uniform, magnetized, monoenergetic plasma, are reconstructed from a fluid approach. Under study are the Alfvén waves (parallel propagation) and the magnetosonic waves (perpendicular propagation). This fluid theory accounts for finite Larmor radius effects to all order, and is shown to yield identical results from the Vlasov formulation. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70334/2/PHPAEN-2-5-1367-1.pd

Sequence of phase formation in planar metal-Si reaction couples

A correlation is found between the sequence of phase formation in thin-film metal-Si interactions and the bulk equilibrium phase diagram. After formation of the first silicide phase, which generally follows the rule proposed by Walser and Bené, the next phase formed at the interface between the first phase and the remaining element (Si or metal) is the nearest congruently melting compound richer in the unreacted element. If the compounds between the first phase and the remaining element are all noncongruently melting compounds (such as peritectic or peritectoid phases), the next phase formed is that with the smallest temperature difference between the liquidus curve and the peritectic (or peritectoid) point

Transition to turbulence in a crossed‐field gap

The transition from laminar to turbulent behavior of the electron sheath in a cross‐field gap is examined for the regime B≳BH, where B is the external magnetic field and BH is the Hull cutoff value. An analytic expression is presented for the critical emitted current beyond which laminar solutions cease to exist. A one‐dimensional particle code is used to corroborate the analytic theory. This code shows several interesting properties when the emitted current exceeds the critical value. Chief among them is the presence of a turbulent microsheath near the cathode surface. The electrostatic potential in the gap’s vacuum region is found to oscillate at a frequency that is quite insensitive to the emitted current and to the electrons’ emission velocity. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71334/2/PHPAEN-1-12-3725-1.pd

Erratum: ‘‘Transition to turbulence in a crossed‐field gap’’ [Phys. Plasmas 1, 3725 (1994)]

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70343/2/PHPAEN-3-11-4293-1.pd

On modular signs

We consider some questions related to the signs of Hecke eigenvalues or Fourier coefficients of classical modular forms. One problem is to determine to what extent those signs, for suitable sets of primes, determine uniquely the modular form, and we give both individual and statistical results. The second problem, which has been considered by a number of authors, is to determine the size, in terms of the conductor and weight, of the first sign-change of Hecke eigenvalues. Here we improve significantly the recent estimate of Iwaniec, Kohnen and Sengupta.Comment: 23 pages, 1 figure; new version with new coauthor and strong improvements of two of the two main results

Credit's effect on productivity in Chinese agriculture : a microeconomic model of disequilibrium

Many government programs want to provide more credit to the farm sector to increase agricultural productivity. If the marginal effect on productivity is small, those resources might be put to better use elsewhere. The authors conducted an econometric analysis of the effect of credit on output supply which recognizies that credit markets are not necessarily at equilibrium - so that credit rationing and nonborrowing are both possible. Only about 37 percent of the farmers in the study area were constrained by inadequate formal credit. Informal credit sources provided funds for specific non-agricultural activities that were not fungible. The results indicate that one additional yuan of liquidity yielded 0.235 yuan of additional gross value of output. These results suggest that for the area of China covered in the study, a good part of the short-term credit may actually be used for consumption and investment. Two conclusions are suggested for evaluating the probable effect of expanding agricultural credit. First, not all farmers, and sometimes only a minority, are constrained in their farming operations by inadequate credit. And second, greater supplies of formal credit will be diverted in part to consumption, so the likely effect on output will be smaller than what one might expect if all funds are assumed to be used productively.Banks&Banking Reform,Financial Intermediation,International Terrorism&Counterterrorism,Economic Theory&Research,Environmental Economics&Policies