3-D orbital evolution model of outer asteroid belt

The evolution of minor planets in the outer part of the asteroid belt is considered. In the framework of the semi-averaged elliptic restricted three-dimensional three-body model, the boundary of regions of the Hill's stability is found. As was shown in our work, the Jacobian integral exists

The Lyapunov Spectrum of a Continuous Product of Random Matrices

We expose a functional integration method for the averaging of continuous products $\hat{P}_t$ of $N\times N$ random matrices. As an application, we compute exactly the statistics of the Lyapunov spectrum of $\hat{P}_t$. This problem is relevant to the study of the statistical properties of various disordered physical systems, and specifically to the computation of the multipoint correlators of a passive scalar advected by a random velocity field. Apart from these applications, our method provides a general setting for computing statistical properties of linear evolutionary systems subjected to a white noise force field.Comment: Latex, 9 page

The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts

The acid–base neutralization reaction of commercially available disodium 2,6-naphthalenedisulfonate (NDS, 2 equivalents) and the tetrahydrochloride salt of tetrakis(4-aminophenyl)methane (TAPM, 1 equivalent) in water gave a novel three-dimensional charge-assisted hydrogen-bonded framework (CAHOF, F-1). The framework F-1 was characterized by X-ray diffraction, TGA, elemental analysis, and 1H NMR spectroscopy. The framework was supported by hydrogen bonds between the sulfonate anions and the ammonium cations of NDS and protonated TAPM moieties, respectively. The CAHOF material functioned as a new type of catalytically active Brønsted acid in a series of reactions, including the ring opening of epoxides by water and alcohols. A Diels–Alder reaction between cyclopentadiene and methyl vinyl ketone was also catalyzed by F-1 in heptane. Depending on the polarity of the solvent mixture, the CAHOF F-1 could function as a purely heterogeneous catalyst or partly dissociate, providing some dissolved F-1 as the real catalyst. In all cases, the catalyst could easily be recovered and recycled

Updated resonance photo-decay amplitudes to 2 GeV

We present the results of an energy-dependent and set of single-energy partial-wave analyses of single-pion photoproduction data. These analyses extend from threshold to 2 GeV in the laboratory photon energy, and update our previous analyses to 1.8 GeV. Photo-decay amplitudes are extracted for the baryon resonances within this energy range. We consider two photoproduction sum rules and the contributions of two additional resonance candidates found in our most recent analysis of $\pi N$ elastic scattering data. Comparisons are made with previous analyses.Comment: Revtex, 26 pages, 3 figures. Postscript figures available from ftp://clsaid.phys.vt.edu/pub/pr or indirectly from http://clsaid.phys.vt.edu/~CAPS

D-brane Decay in Two-Dimensional String Theory

We consider unstable D0-branes of two dimensional string theory, described by the boundary state of Zamolodchikov and Zamolodchikov [hep-th/0101152] multiplied by the Neumann boundary state for the time coordinate $t$. In the dual description in terms of the $c=1$ matrix model, this D0-brane is described by a matrix eigenvalue on top of the upside down harmonic oscillator potential. As suggested by McGreevy and Verlinde [hep-th/0304224], an eigenvalue rolling down the potential describes D-brane decay. As the eigenvalue moves down the potential to the asymptotic region it can be described as a free relativistic fermion. Bosonizing this fermion we get a description of the state in terms of a coherent state of the tachyon field in the asymptotic region, up to a non-local linear field redefinition by an energy-dependent phase. This coherent state agrees with the exponential of the closed string one-point function on a disk with Sen's marginal boundary interaction for $t$ which describes D0-brane decay.Comment: 19 pages, harvmac, minor change

Nanoscale engineering of hybrid magnetite–carbon nanofibre materials for magnetic resonance imaging contrast agents

Magnetic nanomaterials show significant promise as contrast agents for magnetic resonance imaging (MRI). We have developed a new highly efficient one-step procedure for the synthesis of magnetically- functionalised hollow carbon nanofibres, where (i) the carbon nanofibres act as both a template and a support for the nucleation and growth of magnetite nanoparticles and (ii) the structural (size, dispersity and morphology) and functional (magnetisation and coercivity) properties of the magnetic nanoparticles formed on nanofibres are strictly controlled by the mass ratio of the magnetite precursor to the nanofibres and the solvent employed during synthesis. We have shown that our magnetite-nanofibre materials are effectively solubilised in water resulting in a stable suspension that has been employed as a ‘‘negative’’ MRI contrast agent with an excellent transverse relaxivity (r2) of (268 13) mM s 1, surpassing current commercial materials and state-of-the-art magnetic nanoscale platforms in performance for MRI contrast at high magnetic fields. The preparation and evaluation of this unique hybrid nanomaterial represents a critical step towards the realisation of a highly efficient ‘‘smart’’ MRI theranostic agent – a material that allows for the combined diagnosis (with MRI), treatment (with magnetic targeting) and follow-up of a disease (with MRI) – currently in high demand for various clinical applications, including stratified nanomedicine

Interaction between Fe66Cr10Nb5B19 metallic glass and aluminum during spark plasma sintering

In the area of metal matrix composites, novel reinforcing options are currently being evaluated. Particles of amorphous alloys present an interesting possibility to reinforce soft metals. In the present work, the interaction between Fe66Cr10Nb5B19 metallic glass and aluminum during spark plasma sintering (SPS) was studied for the first time. In order to trace the phase and microstructural changes upon sintering, mixtures containing 20 vol% and 50 vol% of metallic glass were subjected to SPS at 500–570 °C. After SPS at 500 °C, no reaction layer between the metallic glass particles and aluminum was observed. After SPS at 570 °C, a reaction layer containing Fe2Al5 and FeAl3 formed around the Fe-based cores. The Vickers hardness of composites obtained from mixtures containing 20 vol% Fe66Cr10Nb5B19 at 540 °C was 75 HV and increased to 280 HV after sintering at 570 °C due to the formation of thicker reaction layers at the interface. The hardness of the composite sintered from the mixture containing 20 vol% Fe66Cr10Nb5B19 at 570 °C was between the values predicted by Reuss and Voigt models. Comparison of results of SPS of the powder mixtures with those of SPS of a pre-compacted pellet and electric current-free annealing suggests that local heating at the interface caused by interfacial resistance may be an important factor influencing the reaction advancement at the interface and the formation of Al-containing intermetallic