A hybrid particle swarm optimisation for scheduling just-in-time single machine with preemption,machine idle time and unequal release times

This paper addresses preemption in just-in-time (JIT) single–machine-scheduling problem with unequal release times and allowable unforced machine idle time as realistic assumptions occur in the manufacturing environments aiming to minimise the total weighted earliness and tardiness costs. Delay in production systems is a vital item to be focussed to counteract lost sale and back order. Thus, JIT concept is targeted including the elements required such as machine preemption, machine idle time and unequal release times. We proposed a new mathematical model and as the problem is proven to be NP-hard, three meta-heuristic approaches namely hybrid particle swarm optimisation (HPSO), genetic algorithm and imperialist competitive algorithm are employed to solve the problem in larger sizes. In HPSO, cloud theory-based simulated annealing is employed with a certain probability to avoid being trapped in a local optimum. Taguchi method is applied to calibrate the parameters of the proposed algorithms. A number of numerical examples are solved to demonstrate the effectiveness of the proposed approach. The performance of the proposed algorithms is evaluated in terms of relative percent deviation and computational time where the computational results clarify better performance of HPSO than other algorithms in quality of solutions and computational time.     

Deformation and life assessment of high temperature materials under creep fatigue loading

The knowledge of mechanical long term behaviour under static and cyclic loading for high temperature components requires methodologies for life assessment in order to employ the full potential of materials. A phenomenological life time prediction concept which was developed for multi‐stage creep fatigue loading demonstrates the applicability of rules for synthesis of stress strain path and relaxation including an internal stress concept, as well as mean stress effects. Further, a creep fatigue interaction concept which was also developed covers a wide range of creep dominant loading as well as fatigue dominant loading. Service‐type experiments conducted at different strain rates and hold times for verification purposes demonstrate the acceptability of life prediction method for variation of conventional 1 %Cr‐steels as well as modern high chromium 9‐10 %Cr‐steels. Generally, the service life of components is influenced by multi‐axial behaviour. Multi‐axial experiments with e.g. notched specimens and with cruciform specimens accompanied by advanced methods for calculation of stress strain path and life time prediction stress conditions are of future interest.     

Self‐Formed Electronic/Ionic Conductive Fe3S4 @ S @ 0.9Na3SbS4⋅0.1NaI Composite for High‐Performance Room‐Temperature All‐Solid‐State Sodium–Sulfur Battery

Fe₃S₄ @ S @ 0.9Na₃SbS₄?0.1NaI composite cathode is prepared through one‐step wet‐mechanochemical milling procedure. During milling process, ionic conduction pathway is self‐formed in the composite due to the formation of 0.9Na₃SbS₄?0.1NaI electrolyte without further annealing treatment. Meanwhile, the introduction of Fe₃S₄ can increase the electronic conductivity of the composite cathode by one order of magnitude and nearly double enhance the ionic conductivities. Besides, the aggregation of sulfur is effectively suppressed in the obtained Fe₃S₄ @ S @ 0.9Na₃SbS₄?0.1NaI composite, which will enhance the contact between sulfur and 0.9Na₃SbS₄?0.1NaI electrolyte, leading to a decreased interfacial resistance and improving the electrochemical kinetics of sulfur. Therefore, the resultant all‐solid‐state sodium–sulfur battery employing Fe₃S₄ @ S @ 0.9Na₃SbS₄?0.1NaI composite cathode shows discharge capacity of 808.7 mAh g^?1 based on Fe₃S₄@S and a normalized discharge capacity of 1040.5 mAh g^?1 for element S at 100 mA g^?1 for 30 cycles at room temperature. Moreover, the battery also exhibits excellent cycling stability with a reversible capacity of 410 mAh g^?1 at 500 mA g^?1 for 50 cycles, and superior rate capability with capacities of 952.4, 796.7, 513.7, and 445.6 mAh g^?1 at 50, 100, 200, and 500 mA g^?1, respectively. This facile strategy for sulfur‐based composite cathode is attractive for achieving room‐temperature sodium–sulfur batteries with superior electrochemical performance.     

Energy transfer phenomena of keV fullerenes during grazing scattering from an Al(0 0 1) surface

Angular distributions for grazing scattering of fullerenes with energies of up to some 10 keV from an atomically clean and flat Al(0 0 1) surface are studied. Scattering proceeds in the regime of surface channeling where the motions of projectiles parallel and normal to the surface are widely decoupled. At low energies for the motion with respect to the surface normal, the clusters are scattered nearly elastically, whereas for larger energies a substantial amount of normal energy is lost. The results are compared to trajectory simulations using the Tersoff potential for the cluster and 3D- as well as 1D-rigid-wall representations for the surface. We find that, despite the large mass of C₆₀, the surface can be considered as a 1D- rigid wall and that the exact form of the interaction potential with the surface does not influence the normal energy loss. Therefore, properties of the fullerene and its interaction with the surface can be studied under well-defined conditions. The energy loss is transferred to internal excitations of the fullerenes.     

Investigations of ferritic/martensitic super heat resistant 11‐12 %Cr steels for 650 °C power plants

The investigations of advanced ferritic/martensitic 11–12 %Cr steels for 650 °C power plant components focus on the improvement of high‐temperature creep properties with respect to chemical composition. The claim of the DFG research work was the development of new heat‐resistant 12 %Cr ferritic‐martensitic steels with sufficient creep and oxidation resistance for a 650 °C application by using basic principles and concepts of physical metallurgy on the basis of the state of art and to overcome the usual trial and error industrial alloy development. Efforts are focussed on a 100,000h creep strength of 100MPa at 650 °C in combination with a sufficient corrosion resistance by a Cr content of 12 % with contents 4‐5 %W, 3.4‐5,5 %Co, V, B and 1 %Cu as well as the choice of Ta or Ti instead of Nb. The results demonstrate that the aim is not to realize with the used alloying concept. In the long term range all 12 %Cr melts have a lower creep rupture strength than the advanced 9 %Cr piping steel P92. A high creep strength could be reached with a 0.06 % Ta alloyed 11 %Cr melt, which is in addition alloyed with a higher C and B content and as well as with lower W and Co portions. The results indicate in accordance with the finding of other steel researcher that a lower Cr content allows more effectiveness for the alloying partners respectively for the generation of more stable precipitates.     

Dual‐grid‐based tree/cotree decomposition of higher‐order interpolatory H(∇∧, Ω) basis

This work extends the zeroth‐order tree/cotree (TC) decomposition method into higher order (HO) interpolatory elements and develops the constraints operator required for the elimination of spurious solutions for general HO spectral basis. Earlier methods explicitly enforce the divergence condition that requires a mixed finite element (FE) formulation with both H¹ and H(?∧) expansions and involves repeated solutions of the Poisson equation. A recent approach, which avoids the mixed formulation and the Poisson problem, uses TC decomposition of edge DoF over the primal graph and construction of integration and gradient matrices. The approach is easily applied to HO hierarchical elements but becomes quite complex for HO spectral elements. In the presence of internal DoF, it is difficult to utilize the primal graph for an explicit decomposition of the spectral DoF. In contrast, this work utilizes the dual grid, resulting in an explicit decomposition of DoF and construction of constraint equations from a fixed element matrix. Thus, mixed formulation and the Poisson problems are avoided while eliminating the need for evaluation of integration and gradient matrices. The proposed constraints matrix is element‐geometry independent and possesses an explicit sparsity formulation reducing the need for dynamic memory allocation. Numerical examples are included for verification. Copyright © 2010 John Wiley & Sons, Ltd.     

Solar flares monitor with Fermi-LAT

Fermi-LAT is performing an all-sky γ-ray survey from 20 MeV to with unprecedented sensitivity and angular resolution. Fermi is the only mission able to detect high energy () emission from the Sun during the new solar cycle 24. Fermi was launched in June 2008, and since then the high energy emission from the Sun was continuously monitored searching for flare events. Upper limits were derived for all the solar flares detected by other missions and experiments (RHESSI, Fermi-GBM, GOES). We present the analysis techniques used for this study and the preliminary results obtained in the first months of this search.     

A bivariate optimal replacement policy for a multistate repairable system

In this paper, a deteriorating simple repairable system with k+1 states, including k failure states and one working state, is studied. It is assumed that the system after repair is not “as good as new” and the deterioration of the system is stochastic. We consider a bivariate replacement policy, denoted by (T,N), in which the system is replaced when its working age has reached T or the number of failures it has experienced has reached N, whichever occurs first. The objective is to determine the optimal replacement policy (T,N)^* such that the long-run expected profit per unit time is maximized. The explicit expression of the long-run expected profit per unit time is derived and the corresponding optimal replacement policy can be determined analytically or numerically. We prove that the optimal policy (T,N)^* is better than the optimal policy N^* for a multistate simple repairable system. We also show that a general monotone process model for a multistate simple repairable system is equivalent to a geometric process model for a two-state simple repairable system in the sense that they have the same structure for the long-run expected profit (or cost) per unit time and the same optimal policy. Finally, a numerical example is given to illustrate the theoretical results.     

A GEANT4 Monte-Carlo simulation code for precision spectroscopy

The measurement of the β asymmetry parameter in nuclear β decay is a potentially very sensitive tool to search for non V–A components in the charge-changing weak interaction. To reach the required precision (percent level) all effects that modify the emission pattern of the β radiation, i.e. the geometry of the setup, the effect of the magnetic field on the trajectories of β particles as well as (back)scattering in the source, on the sample holder and on the detector, have to be correctly taken into account in the analysis of the data. A thorough study of these effects and a new method based on detailed GEANT4 Monte-Carlo simulations that was developed for this purpose is presented here. The code was developed for β asymmetry measurements by means of the Low Temperature Nuclear Orientation (LTNO) method, but can in principle be generalized to other experimental setups using other polarization techniques.     

Field induced magnetic phase transition as a magnon Bose Einstein condensation

We report specific heat, magnetocaloric effect and magnetization measurements on single crystals of the frustrated quasi-2D spin antiferromagnet Cs₂CuCl₄ in the external magnetic field along a-axis and in the temperature range . Decreasing the applied magnetic field B from high fields leads to the closure of the field induced gap in the magnon spectrum at a critical field and a long-range incommensurate state below B_c. In the vicinity of B_c, the phase transition boundary is well described by the power law T_N∼(B_c-B)^1/φ with the measured critical exponent φ?1.5. These findings provide experimental evidence that the scaling law of the transition temperature T_N can be described by the universality class of 3D Bose-Einstein condensation (BEC) of magnons.     

An approximate method for linear signal decomposition in -ray tracking detectors

An approximate method for signal decomposition in γ-ray tracking detectors is presented, based on Singular Value Decomposition (SVD). With this algorithm, the CPU time scales linearly with the number of possible interaction sites for any number of interactions per γ ray. The method is also robust to uncertainty in the signal start time and is applicable to any γ-ray detectors with highly segmented crystals as well as any inverse problem that can be reduced to a search among a countable set of precalculated forward solutions.     

Low-energy neutron propagation in MCNPX and GEANT4

Simulations of neutron background from rock for underground experiments are presented. Neutron propagation through two types of rock, lead and hydrocarbon material, is discussed. The results show a reasonably good agreement between GEANT4, MCNPX and GEANT3 in transporting low-energy neutrons.     

A complementary note on Gegenbauer polynomial approximation for random response problem of stochastic structure

Recently, Gegenbauer polynomial approximation was proposed for solving the evolutionary random response problem of a random structure with bounded random parameters under evolutionary random excitations. The bounded random parameters used there are supposed to be proportional to a random variable with λ-PDF (probability density function). For this kind of random parameter, the Gegenbauer polynomial approximation is the unique correct choice for transforming a random structure into its deterministic equivalent system, which plays a central role in solving the response problem. Actually, the Gegenbauer polynomial approximation bridges the gap between the random structural response problem and the conventional methods. Just through its deterministic equivalent system, the random response problem of a random structure can be solved by any available, analytical and numerical method developed for deterministic systems. But the simple assumption on proportionality to λ-PDF may bring some unnecessary limitation on symmetry. Since λ-PDF is symmetrical about its center axis, so are these random parameters. However, not all random parameters have this kind of symmetry. Then, what can we do to lessen the limitation, if random parameters are non-symmetric per se? Besides, the graph of λ-PDF (see Fig. 1 in the text) shows its features’ dependence on λ, that is, the smaller the λ, the more dispersive the PDF. Then, what is the influence of different values of λ on the evolutionary random responses of the stochastic system? Moreover, is there any qualitative information about the dispersion in response with respect to every individual random parameter? This note is devoted to answering the above two questions and giving a supplementary note on Gegenbauer polynomial approximation. Our study shows that the symmetric limitation can be partly lessened by putting the random parameter into a polynomial function, even a quadratic one, of a random variable with λ-PDF. On the other hand, the second-order moment of the random responses of the stochastic structure relative to that of a nominal one can be used to describe qualitatively their relative dispersion with respect to each individual random parameter.     

BL Lacs bright in rays

In this preview we consider implications from the recent AGILE γ-ray detection of the BL Lac 0716+714 in September–October 2007, marked by two intense flaring episodes reaching peak fluxes of 200×10⁻⁸ photons cm⁻² s⁻¹ in the energy range 0.1–10 GeV. The source shows no evidence of emission lines or disk radiation, related to any surrounding gas; its pure non-thermal radiation is effectively represented in terms of the synchrotron-self Compton radiation in the Thomson regime, also supported by the observed quadratic relation of the γ-ray to the X-ray flux variations. With source parameters so derived, we find a total jet power of about 4×10⁴⁵ erg s⁻¹, that makes 0716+714 one of the brightest gas-poor BL Lacs so far detected at γ-ray energies. Thus it provides an ideal benchmark to compare its intrinsic luminosity with the top power extractable from a maximally rotating black-hole via the Blandford–Znajek mechanism. With a mass close to 5×10⁸M for the associated BH, we find the source to remain close to the Blandford–Znajek threshold during the flare. Other gas-poor but weaker BL Lacs remain well below the threshold. These findings and those expected from FERMI will provide a powerful test of GR at work.     

A radiation tolerant phototube power supply for the electromagnetic calorimeter of the HERA- experiment

The design of the phototube power supply for the HERA-B  Electromagnetic Calorimeter is presented. A choice of the solution on the basis of the Cockcroft–Walton voltage multiplier is validated. Schematics developed are discussed. A special section describes the behaviour of the crucial components under irradiation since radiation tolerance becomes one of the most important items in the severe HERA-B  radiation environment. Finally, performance achieved is presented.     

The observation of gamma ray bursts and terrestrial gamma-ray flashes with AGILE

Since its early phases of operation, the AGILE mission is successfully observing Gamma Ray Bursts (GRBs) in the hard X-ray band with the SuperAGILE imager and in the MeV range with the Mini-Calorimeter. Up to now, three firm GRB detections were obtained above 25 MeV and some bursts were detected with lower statistical confidence in the same energy band. When a GRB is localized, either by SuperAGILE or Swift/BAT or INTEGRAL/IBIS or Fermi/GBM or IPN, inside the field of view of the Gamma Ray Imager of AGILE, a detection is searched for in the gamma ray band or an upper limit is provided. A promising result of AGILE is the detection of very short gamma ray transients, a few ms in duration and possibly identified with Terrestrial Gamma-ray Flashes. In this paper we show the current status of the observation of Gamma Ray Bursts and Terrestrial Gamma-ray Flashes with AGILE.