Difficulties in probing density dependent symmetry potential with the HBT interferometry

Based on the updated UrQMD transport model, the effect of the symmetry potential energy on the two-nucleon HBT correlation is investigated with the help of the coalescence program for constructing clusters, and the CRAB analyzing program of the two-particle HBT correlation. An obvious non-linear dependence of the neutron-proton (or neutron-neutron) HBT correlation function ($C_{np,nn}$) at small relative momenta on the stiffness factor $\gamma$ of the symmetry potential energy is found: when $\gamma \lesssim 0.8$, the $C_{np,nn}$ increases rapidly with increasing $\gamma$, while it starts to saturate if $\gamma \gtrsim 0.8$. It is also found that both the symmetry potential energy at low densities and the conditions of constructing clusters at the late stage of the whole process influence the two-nucleon HBT correlation with the same power.Comment: 11 pages, 4 figure

Exporting, R&D and Absorptive Capacity in UK Establishments: Evidence from the 2001 Community Innovation Survey

This paper models the determinants of exporting (both export propensity and export intensity), with a particular emphasis on the importance of absorptive capacity and the endogenous link between exporting and R&D. Based on a merged dataset of the 2001 Community Innovation Survey and the 2000 Annual Respondents Database for the UK, our results suggest that alongside other factors, undertaking R&D activities and having greater absorptive capacity (for scientific knowledge, co-operation with international organisations, and organisational structure and HRM practices) significantly reduce entry barriers into export markets, having controlled for selfselectivity into exporting and the endogenous link between exporting and R&D. Nevertheless, conditional on entry, only greater absorptive capacity (for scientific knowledge) seems to further boost export performance in international markets, whereas spending on R&D no longer has an impact on exporting behaviour once we have taken into account its endogenous nature.exports; R&D; absorptive capacity; sample selection

A model comparison of resonance lifetime modifications, a soft equation of state and non-Gaussian effects on π−π\pi-\pi correlations at FAIR/AGS energies

HBT correlations of $\pi^--\pi^-$ pairs at FAIR/AGS energies are investigated by using the UrQMD transport model and the CRAB analyzing program. Three different possible sources (treatment of resonance lifetimes, a soft equation of state and non-Gaussian effects) to understand the HBT $R_O/R_S$ puzzle are investigated. Firstly, we find that different treatments of the resonance decay time can not resolve the HBT time-related puzzle, however it can modify the HBT radii at low transverse momenta to some extent to explain the data slightly. Secondly, with a soft equation of state with momentum dependence, the measured transverse momentum dependent HBT radii and $R_O/R_S$ ratio can be described fairly well. Thirdly, non-Gaussian effects are visible in the calculated correlation function. Using the Edgeworth expansion, one finds that the non-Gaussian effect is strongest in the longitudinal direction and weakest in the sideward direction.Comment: 18 pages, 6 figures. To be published in J.Phys.

The Behaviour of Finely Ground Bottom Ash in Portland Cement

The aim of this project was to assess the effects of finely ground MSWI bottom ash in Portland cement. Mortar mixes were prepared with 10% and 40% replacement of cement by ground IBA and then tested with regards to their material composition and engineering behaviour. IBA was found not to be inert, but showed some degree of reactivity. Replacement of cement with IBA was found to have no detrimental effects at low concentrations. This was not the case for 40% replacement, where cement replacement greatly affected strength, creep and drying shrinkage

The Productivity Impact of Skills in English Manufacturing, 2001: Evidence from Plant-Level Matched Data

Microeconomic analyses of productivity for the UK have generally not been able to control for the quality of the labour input, primarily due to data availability, and yet the supply of suitably skilled labour is thought to be a major contributing factor to productivity levels. This paper combines the Annual Respondents Database with the Employers’ Skills Survey for 2001, which allows for a more detailed analysis of the role of skills in determining plant level productivity. Using an augmented Cobb-Douglas production function, the analysis shows that plants experiencing skills shortages were generally less productive than those who did not perceive a skills gap, having controlled for industry and regional effects. In more detail, the analysis reveals some interesting results: the impact that skills gaps have on productivity vary by industry, and higher qualifications do not always result in higher productivity, although innovative plants are seen to be on average 5 per cent more productive, as a result of their more qualified workforce.

Joint Symbol-Level Precoding and Reflecting Designs for IRS-Enhanced MU-MISO Systems

Intelligent reflecting surfaces (IRSs) have emerged as a revolutionary solution to enhance wireless communications by changing propagation environment in a cost-effective and hardware-efficient fashion. In addition, symbol-level precoding (SLP) has attracted considerable attention recently due to its advantages in converting multiuser interference (MUI) into useful signal energy. Therefore, it is of interest to investigate the employment of IRS in symbol-level precoding systems to exploit MUI in a more effective way by manipulating the multiuser channels. In this article, we focus on joint symbol-level precoding and reflecting designs in IRS-enhanced multiuser multiple-input single-output (MU-MISO) systems. Both power minimization and quality-of-service (QoS) balancing problems are considered. In order to solve the joint optimization problems, we develop an efficient iterative algorithm to decompose them into separate symbol-level precoding and block-level reflecting design problems. An efficient gradient-projection-based algorithm is utilized to design the symbol-level precoding and a Riemannian conjugate gradient (RCG)-based algorithm is employed to solve the reflecting design problem. Simulation results demonstrate the significant performance improvement introduced by the IRS and illustrate the effectiveness of our proposed algorithms

Microscopic Calculation of in-Medium Proton-Proton Cross Sections

We derive in-medium PROTON-PROTON cross sections in a microscopic model based upon the Bonn nucleon-nucleon potential and the Dirac-Brueckner approach for nuclear matter. We demonstrate the difference between proton-proton and neutron-proton cross sections and point out the need to distinguish carefully between the two cases. We also find substantial differences between our in-medium cross sections and phenomenological parametrizations that are commonly used in heavy-ion reactions.Comment: 9 pages of RevTex and 4 figures (postscript in separate uuencoded file), UI-NTH-930

Non-scale-invariant inverse curvature flows in Euclidean space

We consider the inverse curvature flows $\dot x=F^{-p}\nu$ of closed star-shaped hypersurfaces in Euclidean space in case $0<p\not=1$ and prove that the flow exists for all time and converges to infinity, if $0<p<1$, while in case $p>1$, the flow blows up in finite time, and where we assume the initial hypersurface to be strictly convex. In both cases the properly rescaled flows converge to the unit sphere.Comment: 21 pages, this is the published versio