Corrosion and wear in moulding boxes

We assess the potential causes of damage to mould box ends and find that both HOT corrosion, due to burning of emitted volatiles, and COLD corrosion, due to the presence of high humidity (and possibly high chloride ion concentration), are likely to contribute to the damage. We suggest strategies to minimise the damage, including venting of the volatiles, ventilation of the pallet grooves during cooling and minimisation of brushing effects during cleaning. Some calculations are described in an attempt to quantify the various effects discussed, but we are unable to accurately estimate their significance

A first principles study of sub-monolayer Ge on Si(001)

Experimental observations of heteroepitaxial growth of Ge on Si(001) show a (2xn) reconstruction for sub-monolayer coverages, with dimer rows crossed by missing-dimer trenches. We present first-principles density-functional calculations designed to elucidate the energetics and relaxed geometries associated with this reconstruction. We also address the problem of how the formation energies of reconstructions having different stoichiometries should be compared. The calculations reveal a strong dependence of the formation energy of the missing-dimer trenches on spacing n, and demonstrate that this dependence stems almost entirely from elastic relaxation. The results provide a natural explanation for the experimentally observed spacings in the region of n \~ 8.Comment: 13 pages, 4 figures, submitted to Surface Scienc

Baryonium, tetra-quark state and glue-ball in large N_c QCD

From the large-N_c QCD point of view, baryonia, tetra-quark states, hybrids, and glueballs are studied. The existence of these states is argued for. They are constructed from baryons. In N_f=1 large N_c QCD, a baryonium is always identical to a glueball with N_c valence gluons. The ground state 0^{-+} glueball has a mass about 2450 MeV. f_0(1710) is identified as the lowest 0^{++} glueball. The lowest four-quark nonet should be f_0(1370), a_0(1450), K^*_0(1430) and f_0(1500). Combining with the heavy quark effective theory, spectra of heavy baryonia and heavy tetra-quark states are predicted. 1/N_c corrections are discussed.Comment: 16 pages, 3 figure

First normal stress difference and crystallization in a dense sheared granular fluid

The first normal stress difference (${\mathcal N}_1$) and the microstructure in a dense sheared granular fluid of smooth inelastic hard-disks are probed using event-driven simulations. While the anisotropy in the second moment of fluctuation velocity, which is a Burnett-order effect, is known to be the progenitor of normal stress differences in {\it dilute} granular fluids, we show here that the collisional anisotropies are responsible for the normal stress behaviour in the {\it dense} limit. As in the elastic hard-sphere fluids, ${\mathcal N}_1$ remains {\it positive} (if the stress is defined in the {\it compressive} sense) for dilute and moderately dense flows, but becomes {\it negative} above a critical density, depending on the restitution coefficient. This sign-reversal of ${\mathcal N}_1$ occurs due to the {\it microstructural} reorganization of the particles, which can be correlated with a preferred value of the {\it average} collision angle $\theta_{av}=\pi/4 \pm \pi/2$ in the direction opposing the shear. We also report on the shear-induced {\it crystal}-formation, signalling the onset of fluid-solid coexistence in dense granular fluids. Different approaches to take into account the normal stress differences are discussed in the framework of the relaxation-type rheological models.Comment: 21 pages, 13 figure

Double-slit interference pattern from single-slit screen and its gravitational analogues

The double slit experiment (DSE) is known as an important cornerstone in the foundations of physical theories such as Quantum Mechanics and Special Relativity. A large number of different variants of it were designed and performed over the years. We perform and discuss here a new verion with the somewhat unexpected results of obtaining interference pattern from single-slit screen. This outcome, which shows that the routes of the photons through the array were changed, leads one to discuss it, using the equivalence principle, in terms of geodesics mechanics. We show using either the Brill's version of the canonical formulation of general relativity or the linearized version of it that one may find corresponding and analogous situations in the framework of general relativity.Comment: 51 pages, 12 Figures five of them contain two subfigures and thus the number of figures is 17, 1 Table. Some minor changes introduced, especially, in the reference

Compton Scattering on the Deuteron in Baryon Chiral Perturbation Theory

Compton scattering on the deuteron is studied in the framework of baryon chiral perturbation theory to third order in small momenta, for photon energies of order the pion mass. The scattering amplitude is a sum of one- and two-nucleon mechanisms with no undetermined parameters. Our results are in good agreement with existing experimental data, and a prediction is made for higher-energy data being analyzed at SAL.Comment: 39 pages LaTeX, 19 figures (uses epsf

Effective theory of the Delta(1232) in Compton scattering off the nucleon

We formulate a new power-counting scheme for a chiral effective field theory of nucleons, pions, and Deltas. This extends chiral perturbation theory into the Delta-resonance region. We calculate nucleon Compton scattering up to next-to-leading order in this theory. The resultant description of existing $\gamma$p cross section data is very good for photon energies up to about 300 MeV. We also find reasonable numbers for the spin-independent polarizabilities $\alpha_p$ and $\beta_p$.Comment: 29 pp, 9 figs. Minor revisions. To be published in PR

Compton scattering on the proton, neutron, and deuteron in chiral perturbation theory to O(Q^4)

We study Compton scattering in systems with A=1 and 2 using chiral perturbation theory up to fourth order. For the proton we fit the two undetermined parameters in the O(Q^4) $\gamma$p amplitude of McGovern to experimental data in the region $\omega,\sqrt{|t|} \leq 180$ MeV, obtaining a chi^2/d.o.f. of 133/113. This yields a model-independent extraction of proton polarizabilities based solely on low-energy data: alpha_p=12.1 +/- 1.1 (stat.) +/- 0.5 (theory) and beta_p=3.4 +/- 1.1 (stat.) +/- 0.1 (theory), both in units of 10^{-4} fm^3. We also compute Compton scattering on deuterium to O(Q^4). The $\gamma$d amplitude is a sum of one- and two-nucleon mechanisms, and contains two undetermined parameters, which are related to the isoscalar nucleon polarizabilities. We fit data points from three recent $\gamma$d scattering experiments with a chi^2/d.o.f.=26.6/20, and find alpha_N=13.0 +/- 1.9 (stat.) +3.9/-1.5 (theory) and a beta_N that is consistent with zero within sizeable error bars.Comment: 57 pages, 16 figures. Substantial changes. Correction of errors in deuteron calculation results in different values for isoscalar polarizabilities. Results for the proton are unaffected. Text modified to reflect this change, and also to clarify various point

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging

We present a measurement of the top quark pair ($t\bar{t}$) production cross section ($\sigma_{t\bar{t}}$) in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using 230 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the $t\bar{t}$ purity of the selected sample. For a top quark mass of 175 GeV, we measure $\sigma_{t\bar{t}}=8.6^{+1.6}_{-1.5}(stat.+syst.)\pm 0.6(lumi.)$ pb, in agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let