Stopping and Radial Flow in Central 58Ni + 58Ni Collisions between 1 and 2 AGeV

The production of charged pions, protons and deuterons has been studied in central collisions of 58Ni on 58Ni at incident beam energies of 1.06, 1.45 and 1.93 AGeV. The dependence of transverse-momentum and rapidity spectra on the beam energy and on the centrality of the collison is presented. It is shown that the scaling of the mean rapidity shift of protons established for AGS and SPS energies is valid down to 1 AGeV. The degree of nuclear stopping is discussed; the IQMD transport model reproduces the measured proton rapidity spectra for the most central events reasonably well, but does not show any sensitivity between the soft and the hard equation of state (EoS). A radial flow analysis, using the midrapidity transverse-momentum spectra, delivers freeze-out temperatures T and radial flow velocities beta_r which increase with beam energy up to 2 AGeV; in comparison to existing data of Au on Au over a large range of energies only beta_r shows a system size dependence

K^+ production in the reaction 58Ni+58Ni^{58}Ni+^{58}Ni at incident energies from 1 to 2 AGeV

Semi-inclusive triple differential multiplicity distributions of positively charged kaons have been measured over a wide range in rapidity and transverse mass for central collisions of $^{58}$Ni with $^{58}$Ni nuclei. The transverse mass ($m_t$) spectra have been studied as a function of rapidity at a beam energy 1.93 AGeV. The $m_t$ distributions of K^+ mesons are well described by a single Boltzmann-type function. The spectral slopes are similar to that of the protons indicating that rescattering plays a significant role in the propagation of the kaon. Multiplicity densities have been obtained as a function of rapidity by extrapolating the Boltzmann-type fits to the measured distributions over the remaining phase space. The total K^+ meson yield has been determined at beam energies of 1.06, 1.45, and 1.93 AGeV, and is presented in comparison to existing data. The low total yield indicates that the K^+ meson can not be explained within a hadro-chemical equilibrium scenario, therefore indicating that the yield does remain sensitive to effects related to its production processes such as the equation of state of nuclear matter and/or modifications to the K^+ dispersion relation.Comment: 24 pages Latex (elsart) 7 PS figures to be submitted to Nucl. Phys

Central Collisions of Au on Au at 150, 250 and 400 A MeV

Collisions of Au on Au at incident energies of 150, 250 and 400 A MeV were studied with the FOPI-facility at GSI Darmstadt. Nuclear charge (Z < 16) and velocity of the products were detected with full azimuthal acceptance at laboratory angles of 1-30 degrees. Isotope separated light charged particles were measured with movable multiple telescopes in an angular range of 6-90 degrees. Central collisions representing about 1 % of the reaction cross section were selected by requiring high total transverse energy, but vanishing sideflow. The velocity space distributions and yields of the emitted fragments are reported. The data are analysed in terms of a thermal model including radial flow. A comparison with predictions of the Quantum Molecular Model is presented.Comment: LateX text 62 pages, plus six Postscript files with a total of 34 figures, accepted by Nucl.Phys.

Carbon Dioxide Emissions in a Methane Economy

Increasing reliance on natural gas (methane) to meet global energy demands holds implications for atmospheric CO2 concentrations. Analysis of these implications is presented, based on a logistic substitution model viewing energy technologies like biological species invading an econiche and substituting in case of superiority for existing species. This model suggests gas will become the dominant energy source and remain so for 50 years, peaking near 70 percent of world supply. Two scenarios of energy demand are explored, one holding per capita consumption at current levels, the second raising the global average in the year 2100 to the current U.S. level. In the first ("efficiency") scenario concentrations peak about 450 ppm, while in the second ("long wave") they near 600 ppm. Although projected CO2 concentrations in a "methane economy" are low in relation to other scenarios, the projections confirm that global climate warming is likely to be a major planetary concern throughout the twenty-first century. A second finding is that data on past growth of world per capita energy consumption group neatly into two pulses consistent with long-wave theories in economics

Fusion-Fission Hybrid Reactors

to the design of hybrid reactors and to inform the new generation of hybrid reactor researchers of the hybrid reactor data base developed in the seventies and early eighties

Repetitive control of MIMO systems using H∞ design

In many engineering problems, periodic signals which should either betracked preference signals) or rejected (disturbances) occur. A successful way of solving such problems is repetitive control, a well-known technique based on the internal model principle. Here, we extend repetitive control theory to plants with several outputs, of which only some have to track reference signals. The other outputs are used to supply additional information to the controller. We analyze stability, robustness and give estimates of the size of the error in such a feedback system. Our approach to this analysis is new, based on the recent theory of regular linear systems. We introduce a correction to the amount of delay used in the internal model and this idea leads to a significant improvement in performance (i.e. to a smaller error)

The development of technologies designed to increase energy efficiency

In recent years there has been a growing concern for more efficient use of energy in view of its increasing world consumption and the realization that fossil fuel resources, particularly the premium fuels — oil and gas — are being depleted rapidly. This concern appears quite justified if one looks at the growth of world consumption of energy over the last one hundred years (Figure 1). With the exception of some crisis periods, the consumption of primary energy in the world has been increasing exponentially at an average growth rate of about 5 % per year. Most of the growth so far may be attributed to the increasing energy demand by the present developed regions in the process of their industrialization and relatively fast economic growth. In 1975 world consumption of primary energy was about 8 Tirawatts (TW or 1012 Watts) of which the share of the developing regions (comprising about 70 % of the world population) was only about 16 %. Now as the developing regions undergo a process of industrialization they too will require a rapid increase in their energy consumption, much faster than the rate of their population growth, while the industrialized regions will also need more energy just to sustain their economic growth or even to avoid stagnation and depression. Will such a growth continue in the foreseeable future or can it be arrested through techno­logical developments and conservation measures at a level not much higher than the current level without serious repercussions on economic development and human welfare? To answer these questions one needs to understand the nature of energy demand, the potential of technological developments for improving the efficiency of energy use and the possible impact of conservation measures in different regions of the world