Strangeness production in pA and AA collisions at 158 A GeV

LUCIAE, a hadronic and string cascade model and its corresponding event generator are used to analyse strangeness production singly and multiply in p-Pb and Pb-Pb collisions at 158 A GeV. Spectra of multiplicity and transverse mass for single (Λ, Λ) and multiple (Ξ-, Ξ-, Ω-, Ω-) strangeness are given. In LUCIAE model it suggests a physical mechanism, i.e. the dependence of the strange quark suppression factor on incident energy, projectile mass and centrality of colliding system might result in increase of yield of strange particles with increasing the above three parameters. Calculations from the model reconstruct well the WA97 experimental data: increase of yield of strange particles with increasing centrality and increase of strangeness enhancement with increasing number of strange quarks, in relativistic nucleus-nucleus collisions.     

Characteristics ofπ −-nucleon collisions at a primary energy of 4·4 GeV

Eight hundred and sixteen nuclear interactions produced by 4·4 GeVπ ^?-mesons in nuclear emulsion have been obtained by “along the track” scanning procedure. Favourable secondary particles from a selected 290π ^?-N (pion-nucleon) collisions have been identified by blob-density and multiple scattering measurements. It is found that the pion often persists in theseπ ^?-N collisions, the average persistence is estimated to be 0·24 per collision. It is estimated thatπ-N andπ-π collisions account for 60% and 28% respectively of the secondary particles. The average number of charged shower particles is 〈n _s〉=2·09±0·12, the average number of created charged particles is 〈n _e±〉=1·94±0·12, the average number of protons with energy greater than 300 MeV is 〈n _p〉=0·15±0·05 and the average number of charged kaons is found to be 〈n _k±〉=0·11±0·06. The integral energy spectra of pions in C-system as well as in L-system are well represented by exponential forms. The average inelasticity of the proton in C-system is found to be 0·52±0·10. The charge retention probability for protons inπ ^?-p collisions is 0·45±0·07.     

Enhancement of φ meson production in p-p and Pb-Pb collisions at SPS energy

The φ meson yield, rapidity and transverse mass distributions in p-p and Pb-Pb collisions at 158 A GeV were studied by the hadron-string cascade model, LUCIAE. By adjusting the width parameter in q-q Gaussian like transverse momentum distribution in string fragmentation to fit the NA49 data ofφ meson transverse mass distribution in p-p collisions, the obtained φ meson rapidity distribution in p-p collisions, the rapidity and transverse mass distributions in Pb-Pb collisions, and theφ meson enhancement factor in Pb-Pb relative to p-p collisions were compatible with corresponding NA49 data, which might be attributed to the collective effect in gluon emission of string and the reduction of strange quark suppression mechanisms involved in the LUCIAE model.     

Coherent production of pions 17·2 GeV pion-nucleus interactions in emulsion nuclei

The coherent production of pions at 17·2 GeV in pion interactions with nuclei has been studied using Nuclear Emulsion Technique. The kinematical selection of such events was made out of three prong events in which all the prongs were identified as pions. The mean free path of coherent events was 65 meters. It was found that diffraction dissociation takes place with lighter nuclei, whereas the Coulomb dissociation plays a major role in the case of heavier emulsion nuclei.     

A parameterisation of impact laws in perfect multi-contact collisions

Impacts in rigid multibody systems cause instantaneous jumps in the generalised velocities. Naturally, the velocity after impact depends on the chosen impact law. An impact law should fulfil kinematic, kinetic as well as energy restrictions. In this paper, we study the domain of possible post-impact velocities for arbitrary impact laws. For single-contact collisions, this domain is at most one-dimensional but the domain becomes higher dimensional in the multi-contact case. The domain of possible post-impact velocities is a compact convex subset of the tangent space to the configuration manifold. Using a complete canonical parameterisation, the post-impact velocity of all impact laws can be addressed. For instance, the impact law corresponding to maximal dissipation as well as Newtons (extended) impact law are examples of incomplete canonical parameterisations. These impact laws are not complete as non-local impact effects are not addressed. Here, we try to find a complete canonical parameterisation which covers non-local impact effects. Moreover, the relationship between symmetries and conservation laws in this context will be elucidated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The influence of isobar production on charge ratio and transverse momentum of secondary particles in high energy collisions

An isobar model in which collision between two particles leads to the creation of only two bodies which by subsequent decay give rise to the observed secondaries has been considered. On the basis of such a model, the charge ratios of pions, kaons andΣ-hyperons inp?p andπ?p collisions have been computed and compared with the available experimental data. Some features of transverse momentum of pions and protons in 24 GeV/cp?p collisions have also been studied. The main conclusions can be summarised as follows:

1. (1)
   The observed positive excess among pions produced in high energyp?p collisions leading toπ ⁺/π ^? andπ ⁺/π ⁰ ratios of ～3 and 1·6 respectively for high momentum pions can be explained on the basis of the isobar model. Further, the fast increase of K⁺/K^? ratio as the kaon momentum increases, the high ratio (～4) ofΣ ⁺/Σ ^? in 24 GeV/cp?p collisions and the existence of a strong positive (negative) excess amongΣ-hyperons produced inπ ⁺?p(π ^??p) collisions at various primary energies result, in a natural way, from such a model. The agreement results mainly from the restriction of only two bodies in the final states and does not critically depend on the isospins of produced isobars.     
   
   

Observations on the nuclear interactions of cosmic ray pions and nucleons at energies ≳ 20 GeV

Detailed features of extremely collimated nuclear interactions induced by cosmic ray particles in carbon and brass (belonging to group I as classified in Part I of this series of papers) are presented. These extremely collimated nuclear interactions seem to be preferentially induced by pions rather than by nucleons; also the relative frequency of these seems to be less when brass is used as target compared to the case with carbon as target. The distribution of multiplicities of secondary particles emitted in the forward direction show certain regularities in the case of interactions induced by charged primaries. Observations on the γ-rays associated with these events give support to the interpretation that in these inelastic collisions pions are produced in pairs in the forward direction with low transverse momentum. It is suggested that such a low energy di-pion system could be the same as found in the so-called ABC effect.     

Levy stable law of intermittency and multifractal spectrum in Si–AgBr collisions at 14.6 AGeV

The scaled factorial moments F_q are studied for ²⁸Si–AgBr collisions at 14.6 AGeV. These moments follow the generalized power law F_q(M)∝[g(M)]^_q. The values of _q/₂ obtained from the linear fits of ln F_q versus ln F₂ graphs are found to obey the Brax–Peschanski formula with Levy index μ = 1.635 ± 0.012 for η space and μ = 1.801 ± 0.003 for space. These values lie within the Levy stable region 0  μ  2. An analytical continuation of the Brax–Peschanski formula has been used to obtain the multifractal spectra f(_q) in negative q region.     

A possible cosmic ray primary particle energy spectrum above 104 GeV and its astrophysical implications

A primary cosmic ray particle energy specturm of Galactic origin with a sharp cut-off at an energy per nucleon of 3 × 10⁴ GeV for protons and 5 × 10⁴ GeV for heavier particles and extending only upto energies ～ 10¹⁵ eV is deduced in part from the observed cosmic ray phenomena at the highest energies. It appears that the cut off is not due to the magnetic rigidity of the particles in the Galaxy but due to a cut off in or near the sources themselves. In particular, it is pointed out that Fermi type of acceleration is unlikely to be important in the production of energetic cosmic ray particles in the Galaxy. A pedestal in the energy spectrum from an extra Galactic component upto a maximum energy per nucleon ～ 10⁷ GeV with an upper limit of total energies ～ 10¹⁸ eV has been added.     

HOP: A software tool for production scheduling at Bridgestone/Firestone off-the-road

We describe the development of the Heater Optimization Program (HOP), a software tool for scheduling the curing operation at Bridgestone/Firestone Off-The-Road (BFOR). The company produces large tires for heavy off-the-road machines such as trucks, tractors and earthmoving equipment used in the construction, lumber and mining industries. The huge tires, having different priorities, are built in molds and put into heaters for the curing process. The problem is to find a feasible assignment of tires to molds and molds to heaters to achieve a maximum total priority. HOP produces about 7% more tires per shift compared to the previous manual way of developing schedules and moves the company towards its goal of quick response manufacturing with low inventories. A user-friendly Windows interface, written around our custom made optimization routines, allows for easy retrieval of the data from the company's data bases and provides for a graphical representation of the optimization results.     

A possible model for a singularity without collisions in the five body problem

A heuristic solution is described for the five body problem in the plane in which all five bodies escape to infinity in a finite time.     

A solution approach for optimizing long- and short-term production scheduling at LKAB’s Kiruna mine

We present a mixed-integer program to schedule long- and short-term production at LKAB’s Kiruna mine, an underground sublevel caving mine located in northern Sweden. The model minimizes deviations from monthly preplanned production quantities while adhering to operational constraints. Because of the mathematical structure of the model and its moderately large size, instances spanning a time horizon of more than a year or two tend to be intractable. We develop an optimization-based decomposition heuristic that, on average, obtains better solutions faster than solving the model directly. We show that for realistic data sets, we can generate solutions with deviations that comprise about 3-6% of total demand in about a third of an hour.     

A discrete-time Geo/G/1 retrial queue with preemptive resume and collisions

We consider a discrete-time Geo/G/1 retrial queue with preemptive resume, collisions of customers and general retrial times. We analyze the Markov chain underlying the considered queueing system and derive its ergodicity condition. Using generating function technique, the system state distribution as well as the orbit size and the system size distributions are studied. Some interesting and important performance measures are obtained. Besides, the stochastic decomposition property is investigated. Finally, some numerical examples are provided.     

A multi-item newsvendor problem with preseason production and capacitated reactive production

Given items with short life cycles or seasonal demands, one can potentially improve profits by producing during the selling season, especially when its production capacity is substantial. We develop a two-stage, multi-item model incorporating reactive production that employs a firm’s internal capacity. Production occurs in an uncapacitated preseason stage and a capacitated reactive stage. Demands occur in the reactive stage. Reactive capacities are pre-allocated to each item in the preseason stage and cannot be changed during the reactive stage. Reactive production occurs during the selling season with full knowledge of demands. The objective is expected profit maximization. Unsatisfied demand is lost. The revenue, salvage value, and production and lost sales costs are proportional. Assuming no fixed costs, we present a simple algorithm for computing optimal policies. For a model with fixed costs for allocating preseason stage production and reactive stage capacity to product families, we characterize optimal policies and develop optimal and heuristic algorithms.     

A production planning problem in FMS

We present in this work a hierarchical approach for generating alternatives for production planning in a generic floor shop problem within the environment of Flexible Manufacturing Systems (hereafter, FMS). Briefly, the problem can be stated as follows: Given the resources of a FMS and the characteristics of the parts to be produced along a planning horizon, obtain the loading ordering of the parts in the FMS, the execution ordering of the operations and the processing route of each part (i.e., the working stations where each operation is to be executed), such that the production and transport costs are minimized and the modules workload is levelized. The problem is decomposed into three subproblems which are arranged in a hierarchy; a variety of models is presented, as well as the input/output relations that allow to integrate them; we also propose some algorithmic ideas to exploit the special structure of the problem. Computational experience is reported.     

A tabu search experience in production scheduling

During the last four years, tabu search has been shown to be a remarkably effective method in solving difficult combinatorial optimization problems. Nowhere has this success been more marked than in the timely and very important area of production scheduling. In this paper, we review some of the research that has contributed to that success. We also give a synthesis of the various tabu search mechanisms that have been employed, giving special attention to advances that have led to major improvements. In the final section of the paper, we suggest directions for future research.     

A production lot size inventory model for deteriorating items and arbitrary production and demand rates

In this paper, we present a method for finding the optimal replenishment schedule for the production lot size model with deteriorating items, where demand and production are allowed to vary with time in an arbitrary way and in which shortages are allowed. The method is illustrated by a numerical example.     

Machine scheduling in production: A content analysis

This paper presents the results of a content analysis on a comprehensive and systematically generated sample of 132 literature surveys on machine scheduling problems in production (MSPP). The paper identifies the main attributes of MSPP by analyzing these surveys and proposes a classification scheme for MSPP consisting of seven main groups with several subgroups. The reliability of the results of the content analysis is examined in a sensitivity analysis. A close analysis of the results unveils several research gaps in the literature and enables us to propose promising avenues for future research.     

A large mixed integer production and distribution program

A decomposition algorithm for a production and distribution problem allows finding a very good suboptimal solution for an 85 000 variable model with 2600 0–1 variables. A global reoptimization process of the continuous part improves the final solution. Annual savings over 3.7% of variable costs and a reasonable CPU time are obtained. A user-oriented program (generation, solution and report) is developed.