A Bus Driver Scheduling Problem: a?new mathematical model and a GRASP approximate solution

This paper addresses the problem of determining the best scheduling for Bus Drivers, a $\mathcal{NP}$ -hard problem consisting of finding the minimum number of drivers to cover a set of Pieces-Of-Work (POWs) subject to a variety of rules and regulations that must be enforced such as spreadover and working time. This problem is known in literature as Crew Scheduling Problem and, in particular in public transportation, it is designated as Bus Driver Scheduling Problem. We propose a new mathematical formulation of a Bus Driver Scheduling Problem under special constraints imposed by Italian transportation rules. Unfortunately, this model can only be usefully applied to small or medium size problem instances. For large instances, a Greedy Randomized Adaptive Search Procedure (GRASP) is proposed. Results are reported for a set of real-word problems and comparison is made with an exact method. Moreover, we report a comparison of the computational results obtained with our GRASP procedure with the results obtained by Huisman et al. (Transp. Sci. 39(4):491?C502, 2005).     

Some Novel Cobalt Diphenylphosphine Complexes: Synthesis,Characterization, and Behavior in the Polymerization of 1,3-Butadiene

Some novel cobalt diphenylphosphine complexes were synthesized by reacting cobalt(II) chloride with (2-methoxyethyl)diphenylphosphine, (2-methoxyphenyl)diphenylphosphine, and 2-(1,1-dimethylpropyl)-6-(diphenylphosphino)pyridine. Single crystals suitable for X-ray diffraction studies were obtained for the first two complexes, and their crystal structure was determined. The novel compounds were then used in association with methylaluminoxane (MAO) for the polymerization of 1,3-butadiene, and their behavior was compared with that exhibited in the polymerization of the same monomer by the systems CoCl₂(PⁿPrPh₂)₂/MAO and CoCl₂(PPh₃)₂/MAO. Some significant differences were observed depending on the MAO/Co ratio used, and a plausible interpretation for such a different behavior is proposed.     

Strong-field multiphoton ionization of hydrogen. TheS-matrix treatment of the elementary process

Summary A theoretical model is presented to treat the elementary act of strong-field multiphoton ionization of atoms when the electron continuum final-state distribution is important. It is based on theS-matrix formalism and treats the final-state electron-radiation interaction in an essentially nonperturbative way. Selected numerical calculations concern the ionization of hydrogen atoms and include differential and total cross-sections of several multiphoton channels as a function of the laser intensity. Good, qualitative agreement with the experimental observations is found for values of the field intensity which are not critical with respect to the simplifications adopted in constructing the theoretical model. It applies particularly to the use of an ideal model for the laser field. Significant departure from observations is instead found when the implications of the ideal laser model play a critical role, as occurs at channel inversion and suppression. It is concluded that the theoretical treatment to be completely satisfactory needs essentially to incorporate a more realistic laser model such as a multimode one.

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Riassunto Si presenta un modello teorico per il processo elementare della ionizzazione multifotonica di atomi da parte di un forte campo laser quando diventa importante la distribuzione degli stati finali del continuo dell'elettrone. Il modello si fonda sul formalismo della matriceS e tratta l'interazione elettrone-radiazione nello stato finale in modo non perturbativo. I calcoli numerici qui riportati si riferiscono alla ionizzazione di atomi d'idrogeno e includono sezioni d'urto totali e differenziali per diversi canali multifotonici in funzione dell'intensità del laser. Si trova un accordo qualitativo con i dati sperimentali per valori dell'intensità del campo che non sono critici rispetto alle semplificazioni adottate nella costruzione del modello teorico. Un significativo distacco dai dati sperimentali si ha quando le implicazioni del modello di laser ideale giocano un ruolo critico, come si ha per l'inversione e la scomparsa dei canali. Si conclude che il trattamento teorico per essere completamente soddisfacente necessita dell'introduzione di un modello di laser piú realistico, quale, ad esempio, quello a molti modi.

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Резюме Предлагается теоретическая модель для рассмотрения элементарного акта многофотонной ионизации атомов в сильном поле, когда распределение электронных непрерывных конечных состояний является существенным. Подход базируется на формализмеS-матрицы и взаимодействие электронов в конечном состоянии с полем излучения рассматривается непертурбационным образом. Численные вычисления касаются ионизации атомов водорода и включают дифференциальные и полные поперечные сечения для некоторых многофотонных каналов, как функции интенсивности лазерного излучения. Получено хорошее качественное согласие с экспериментальными результатами для значений интенсивности поля, которые не являются критическими по отношению к упрощениям, используемым при конструировании теоретической модели. Используется идеальная модель для лазерного поля. Обнаружено существенное отклонение от экспериментальных результатов в тех случаях, когда имеет место инверсия и подавление каналов. Делается вывод, что теоретический подход становится удовлетворительным, если используется более реалистическая модель лазера, как например, многомодовая модель.

     

Near-barrier transfer and fusion of the systems33S +90,91,92Zr

Double differential cross sections of all prominent transfer channels have been measured in the systems³³S +^99,91,92Zr at two energies close to the nominal Coulomb barrier. In addition the fusion excitation functions of these systems have been measured below and around the barrier. The angular- andQ-distributions of the most important transfer reactions have been analysed in the framework of a simple semiclassical formalism. Particularly the two-nucleon transfer angular distributions exhibit strong multi step coupling effects which manifest themselves in reduced cross sections at large angles corresponding to close distances. From the angular distributions at forward angles, where a single step character of the transfer reaction can be assumed, approximate form factors have been extracted employing a first order perturbation theory. Within the uncertainties of a schematic coupled channels calculation the isotopic differences of the sub-barrier fusion enhancement can be understood on the basis of the isotopic differences of the transfer form factors andQ-values.     

Quantum mechanics for space applications

This paper is an introduction to the following articles in the scope of quantum mechanics for space study initiated by ESA and lead by ONERA. The context of quantum mechanics for space is summarised, and the fields under development are briefly introduced. Technological applications of quantum mechanics in space are explored and some tests of quantum mechanics are outlined. We also give a brief presentation of the opto-electronic section of the European Space Agency, and the technology development activities it carries out, with particular emphasis on those activities related to the topics of interest of the quantum mechanics in space workshop. As an example, a summary of two ESA studies on gravity gradiometry and their relevance to the field of atomic interferometry is given. In view of the scientific requirements, derived for both Earth observation and planetology for future space missions, atom interferometry shows promise and may provide an advantage over currently available accelerometer and inertial sensor systems. PACS 04.25.Nx; 04.80.Cc; 07.60.Ly; 95.30.Sf     

Copolymerization of Ethene and Carbon Monoxide with (Diphosphine)nickel Catalysts

This work presents the results of the ethene–CO copolymerization with in situ generated catalysts based on atropisomeric 1,4‐diphosphines and nickel(II). The influence of the reaction conditions and the NMR characterization of the copolymers are described.     

Fragmentation of the two-phonon γ-vibration in166Er

Two-phonon γ-vibrational states in¹⁶⁶Er have been populated using Coulomb excitation. The K^π=4⁺ component of the vibration appears to be fragmented over several states, whereas only one K^π=0⁺ state is observed.     

Parallel gradient projection successive overrelaxation for symmetric linear complementarity problems and linear programs

A gradient projection successive overrelaxation (GP-SOR) algorithm is proposed for the solution of symmetric linear complementary problems and linear programs. A key distinguishing feature of this algorithm is that when appropriately parallelized, the relaxation factor interval (0, 2) isnot reduced. In a previously proposed parallel SOR scheme, the substantially reduced relaxation interval mandated by the coupling terms of the problem often led to slow convergence. The proposed parallel algorithm solves a general linear program by finding its least 2-norm solution. Efficiency of the algorithm is in the 50 to 100 percent range as demonstrated by computational results on the CRYSTAL token-ring multicomputer and the Sequent Balance 21000 multiprocessor.This material is based on research supported by National Science Foundation Grants DCR-8420963 and DCR-8521228 and Air Force Office of Scientific Research Grants AFOSR-86-0172 and AFOSR-86-0255.