Total Chiral Symmetry Breaking during Crystallization: Who needs a "Mother Crystal"?

Processes that can produce states of broken chiral symmetry are of particular interest to physics, chemistry and biology. Chiral symmetry breaking during crystallization of sodium chlorate occurs via the production of secondary crystals of the same handedness from a single "mother crystal" that seeds the solution. Here we report that a large and "symmetric" population of D- and L-crystals moves into complete chiral purity disappearing one of the enantiomers. This result shows: (i) a new symmetry breaking process incompatible with the hypothesis of a single "mother crystal"; (ii) that complete symmetry breaking and chiral purity can be achieved from an initial system with both enantiomers. These findings demand a new explanation to the process of total symmetry breaking in crystallization without the intervention of a "mother crystal" and open the debate on this fascinating phenomenon. We present arguments to show that our experimental data can been explained with a new model of "complete chiral purity induced by nonlinear autocatalysis and recycling".Comment: 5 pages, 4 figures, Added reference

Aircraft energy efficiency laminar flow control wing design study

An engineering design study was performed in which laminar flow control (LFC) was integrated into the wing of a commercial passenger transport aircraft. A baseline aircraft configuration was selected and the wing geometry was defined. The LFC system, with suction slots, ducting, and suction pumps was integrated with the wing structure. The use of standard aluminum technology and advanced superplastic formed diffusion bonded titanium technology was evaluated. The results of the design study show that the LFC system can be integrated with the wing structure to provide a structurally and aerodynamically efficient wing for a commercial transport aircraft

The impact of space and space-related activities on a local economy. a case study of boulder, colorado. part ii- the income-product accounts

Total impact of space and space related activities on local economy of Boulder, Colorado - income-product account

A Reanalysis of the Hydrodynamic Theory of Fluid, Polar-Ordered Flocks

I reanalyze the hydrodynamic theory of fluid, polar ordered flocks. I find new linear terms in the hydrodynamic equations which slightly modify the anisotropy, but not the scaling, of the damping of sound modes. I also find that the nonlinearities allowed {\it in equilibrium} do not stabilize long ranged order in spatial dimensions $d=2$; in accord with the Mermin-Wagner theorem. Nonequilibrium nonlinearities {\it do} stabilize long ranged order in $d=2$, as argued by earlier work. Some of these were missed by earlier work; it is unclear whether or not they change the scaling exponents in $d=2$.Comment: 6 pages, no figures. arXiv admin note: text overlap with arXiv:0909.195

Diffusion Enhances Chirality Selection

Diffusion effect on chirality selection in a two-dimensional reaction-diffusion model is studied by the Monte Carlo simulation. The model consists of achiral reactants A which turn into either of the chiral products, R or S, in a solvent of chemically inactive vacancies V. The reaction contains the nonlinear autocatalysis as well as recycling process, and the chiral symmetry breaking is monitored by an enantiomeric excess $\phi$. Without dilution a strong nonlinear autocatalysis ensures chiral symmetry breaking. By dilution, the chiral order $\phi$ decreases, and the racemic state is recovered below the critical concentration $c_c$. Diffusion effectively enhances the concentration of chiral species, and $c_c$ decreases as the diffusion coefficient $D$ increases. The relation between $\phi$ and $c$ for a system with a finite $D$ fits rather well to an interpolation formula between the diffusionless(D=0) and homogeneous ($D=\infty$) limits.Comment: 7 pages, 6 figure

Crystal Structure and Magnetism of the Linear-Chain Copper Oxides Sr5Pb3-xBixCuO12

The title quasi-1D copper oxides (0=< x =<0.4) were investigated by neutron diffraction and magnetic susceptibility studies. Polyhedral CuO4 units in the compounds were found to comprise linear-chains at inter-chain distance of approximately 10 A. The parent chain compound (x = 0), however, shows less anisotropic magnetic behavior above 2 K, although it is of substantially antiferromagnetic (mu_{eff}= 1.85 mu_{B} and Theta_{W} = -46.4 K) spin-chain system. A magnetic cusp gradually appears at about 100 K in T vs chi with the Bi substitution. The cusp (x = 0.4) is fairly characterized by and therefore suggests the spin gap nature at Delta/k_{B} ~ 80 K. The chain compounds hold electrically insulating in the composition range.Comment: To be published in PR

Comparison of spin anisotropy and exchange alternation

Quasi‐1‐D magnetic systems with on the one hand an Ising‐Heisenberg type spin anisotropy and on the other hand an alternating (dimerized) character have many interesting features in common and a few interesting differences in their phase behavior and general magnetic properties. This report reviews results rather scattered in the literature in addition to presenting new results. These rather complex quantum models present a theoretical challenge. It is also hoped that this work will be helpful to magnetochemists interested in identifying the underlying magnetic character of their systems, and to experimentalists in general

Proportion Regulation in Globally Coupled Nonlinear Systems

As a model of proportion regulation in differentiation process of biological system, globally coupled activator-inhibitor systems are studied. Formation and destabilization of one and two cluster state are predicted analytically. Numerical simulations show that the proportion of units of clusters is chosen within a finite range and it is selected depend on the initial condition.Comment: 11 pages (revtex format) and 5 figures (PostScript)

The susceptibility and excitation spectrum of (VO)2_2P2_2O7_7 in ladder and dimer chain models

We present numerical results for the magnetic susceptibility of a Heisenberg antiferromagnetic spin ladder, as a function of temperature and the spin-spin interaction strengths $J_\perp$ and $J_{||}$. These are contrasted with new bulk limit results for the dimer chain. A fit to the experimental susceptibility of the candidate spin-ladder compound vanadyl pyrophosphate, (VO)$_2$P$_2$O$_7$, gives the parameters $J_\perp = 7.82$ meV and $J_{||} = 7.76$ meV. With these values we predict a singlet-triplet energy gap of $E_{gap} = 3.9$ meV, and give a numerical estimate of the ladder triplet dispersion relation $\omega(k)$. In contrast, a fit to the dimer chain model leads to $J_1=11.11$ meV and $J_2=8.02$ meV, which predicts a gap of $E_{gap} = 4.9$ meV.Comment: 16 pages, 6 figures available upon request, RevTex 3.0, preprint ORNL-CCIP-94-04 / RAL-94-02