Characterisation of porous solids using small-angle scattering and NMR cryoporometry

The characteristics of several porous systems have been studied by the use of small-angle neutron scattering [SANS] and nuclear magnetic resonance [NMR] techniques. The measurements reveal different characteristics for sol-gel silicas, activated carbons and ordered mesoporous silicas of the MCM and SBA type. Good agreement is obtained between gas adsorption measurements and the NMR and SANS results for pore sizes above 10 nm. Recent measurements of the water/ice phase transformation in SBA silicas by neutron diffraction are also presented and indicate a complex relationship that will require more detailed treatment in terms of the possible effects of microporosity in the silica substrate. The complementarity of the different methods is emphasised and there is brief discussion of issues related to possible future developments

Nuclear magnetic resonance cryoporometry

Nuclear Magnetic Resonance (NMR) cryoporometry is a technique for non-destructively determining pore size distributions in porous media through the observation of the depressed melting point of a confined liquid. It is suitable for measuring pore diameters in the range 2 nm-1 mu m, depending on the absorbate. Whilst NMR cryoporometry is a perturbative measurement, the results are independent of spin interactions at the pore surface and so can offer direct measurements of pore volume as a function of pore diameter. Pore size distributions obtained with NMR cryoporometry have been shown to compare favourably with those from other methods such as gas adsorption, DSC thermoporosimetry, and SANS. The applications of NMR cryoporometry include studies of silica gels, bones, cements, rocks and many other porous materials. It is also possible to adapt the basic experiment to provide structural resolution in spatially-dependent pore size distributions, or behavioural information about the confined liquid

Infrared Renormalons and Power Suppressed Effects in e+e−e^+e^- Jet Events

We study the effect of infrared renormalons upon shape variables that are commonly used to determine the strong coupling constant in $e^+e^-$ annihilation into hadronic jets. We consider the model of QCD in the limit of large $n_f$. We find a wide variety of different behaviours of shape variables with respect to power suppressed effects induced by infrared renormalons. In particular, we find that oblateness is affected by $1/Q$ non--perturbative effects even away from the two jet region, and the energy--energy correlation is affected by $1/Q$ non--perturbative effects for all values of the angle. On the contrary, variables like thrust, the $c$ parameter, the heavy jet mass, and others, do not develop any $1/Q$ correction away from the two jet region at the leading $n_f$ level. We argue that $1/Q$ corrections will eventually arise at subleading $n_f$ level, but that they could maintain an extra \as(Q) suppression. We conjecture therefore that the leading power correction to shape variables will have in general the form $\alpha^n_{\rm S}(Q)/Q$, and it may therefore be possible to classify shape variables according to the value of $n$.Comment: 20 pages, Latex, epsfig, 3 tar-gzip-uuencoded figures. Also available from http://surya11.cern.ch/users/nason/misc

EVALUATION OF MARKET ADVISORY SERVICE PERFORMANCE IN HOGS

The purpose of this paper is to investigate the pricing performance of agricultural market advisory services in hogs. Pricing recommendations are available for all quarters from the beginning of 1995 through the end of 2001. The results show that average differences between advisory programs and market benchmarks are small in nominal terms for all three benchmarks, -$0.41/bu.,$O.OO/cwt. and $-0.27/cwt. versus the cash, index and empirical benchmarks, respectively, and none of the average differences are significantly different from zero. Hence, advisory programs as a group do not outperform the market benchmarks in terms of average price. Advisory programs also do not outperform the market benchmarks in terms of average price and risk. Finally, there is little evidence that advisory programs with superior performance can be usefully selected based on past performance in the hog market.Marketing,

Polynomials, Riemann surfaces, and reconstructing missing-energy events

We consider the problem of reconstructing energies, momenta, and masses in collider events with missing energy, along with the complications introduced by combinatorial ambiguities and measurement errors. Typically, one reconstructs more than one value and we show how the wrong values may be correlated with the right ones. The problem has a natural formulation in terms of the theory of Riemann surfaces. We discuss examples including top quark decays in the Standard Model (relevant for top quark mass measurements and tests of spin correlation), cascade decays in models of new physics containing dark matter candidates, decays of third-generation leptoquarks in composite models of electroweak symmetry breaking, and Higgs boson decay into two tau leptons.Comment: 28 pages, 6 figures; version accepted for publication, with discussion of Higgs to tau tau deca

Reconstructing particle masses from pairs of decay chains

A method is proposed for determining the masses of the new particles N,X,Y,Z in collider events containing a pair of effectively identical decay chains Z to Y+jet, Y to X+l_1, X to N+l_2, where l_1, l_2 are opposite-sign same-flavour charged leptons and N is invisible. By first determining the upper edge of the dilepton invariant mass spectrum, we reduce the problem to a curve for each event in the 3-dimensional space of mass-squared differences. The region through which most curves pass then determines the unknown masses. A statistical approach is applied to take account of mismeasurement of jet and missing momenta. The method is easily visualized and rather robust against combinatorial ambiguities and finite detector resolution. It can be successful even for small event samples, since it makes full use of the kinematical information from every event.Comment: 12 pages, 5 figure

Clathrate formation and dissociation in vapor/water/ice/hydrate systems in SBA-15, sol-gel and CPG porous media, as probed by NMR relaxation, novel protocol NMR cryoporometry, neutron scattering and ab initio quantum-mechanical molecular dynamics simulation

The Gibbs-Thomson effect modifies the pressure and temperature at which clathrates occur, hence altering the depth at which they occur in the seabed. Nuclear magnetic resonance (NMR) measurements as a function of temperature are being conducted for water/ice/ hydrate systems in a range of pore geometries, including templated SBA-15 silicas, controlled pore glasses and sol-gel silicas. Rotator-phase plastic ice is shown to be present in confined geometry, and bulk tetrahydrofuran hydrate is also shown to probably have a rotator phase. A novel NMR cryoporometry protocol, which probes both melting and freezing events while avoiding the usual problem of supercooling for the freezing event, has been developed. This enables a detailed probing of the system for a given pore size and geometry and the exploration of differences between hydrate formation and dissociation processes inside pores. These process differences have an important effect on the environment, as they impact on the ability of a marine hydrate system to re-form once warmed above a critical temperature. Ab initio quantum-mechanical molecular dynamics calculations are also being employed to probe the dynamics of liquids in pores at nanometric dimensions

Jovian protons and electrons: Pioneer 11

A preliminary account of the Pioneer 11 passage through the Jovian magnetosphere as viewed by particle detector systems is presented. Emphasis is placed on the region well within the Jovian magnetosphere using data from the LET-II telescope, which measured the proton flux from 0.2 to 21.2 MeV in seven energy intervals and electrons from 0.1 to 2 MeV in four energy intervals. The relative trajectories of Pioneer 10 and 11 are discussed and indicate that Pioneer 11 was exposed to a much lower total radiation dose than Pioneer 10, largely as a result of the retrograde trajectory which approached and exited the inner region of the magnetosphere at high latitudes. Angular distributions, calculations from Pioneer 11 magnetic field data, and the low-energy nucleon component are included in the discussion

Herwig++ 2.0 Release Note

A new release of the Monte Carlo program Herwig++ (version 2.0) is now available. This is the first version of the program which can be used for hadron-hadron physics and includes the full simulation of both initial- and final-state QCD radiation.Comment: Source code and additional information available at http://hepforge.cedar.ac.uk/herwig