Neutron measurements in the Vandellòs II nuclear power plant with a Bonner sphere system

In some Spanish nuclear power plants of pressurised water reactor (PWR) type, albedo thermoluminescence dosemeters are used for personal dosimetry while survey meters, based on a thermal-neutron detector inside a cylindrical or spherical moderator, are used for dose rate assessment in routine monitoring. The response of both systems is highly dependent on the energy of the existing neutron fields. They are usually calibrated by means of ISO neutron sources with energy distributions quite different from those encountered at these installations. Spectrometric measurements with a Bonner sphere system (BSS) allow us to determine the reference dosimetric values. The UAB group, under request from the National Coordinated Research Action, was in charge of characterising the neutron fields and evaluating the response of personal dosemeters at several measurement points inside the containment building of the Catalan Nuclear Power Plant Vandellòs II. The neutron fields were characterised at five places using the UAB-BSS and a home made unfolding code called MITOM. The results obtained confirm the presence of low-energy components in the neutron field in most of the selected points. Moreover, we have found no influence of the nuclear fuel burning on the shape of the spectrum.     

Vortex Dynamics in a Superconducting Film with a Kagome and?a?Honeycomb Pinning Landscape

The vortex dynamics in a superconducting thin Al film with a periodic Honeycomb or Kagome array of antidots has been investigated by electrical transport measurements. The large values of the superconducting coherence length and penetration depth of the Al films guarantee a maximum of one flux quantum trapped per pinning site. This allows us to directly compare the experimental results with previous theoretical investigations based on molecular dynamics simulations. For the Kagome lattice, two submatching features not anticipated theoretically at H/H ₁=1/3 and 2/3, where H ₁ is the field at which the number of vortices coincides with the number of pinning sites, are observed. Possible corresponding stable vortex patterns are suggested. For the Honeycomb pinning landscape, the commensurability effects are in agreement with the theoretical expectations. A preliminary analysis of the vortex mobility in this lattice shows the presence of a weak vortex guidance.     

Dynamics analysis of LFR model for a single‐stage high power factor correction diagonal half‐bridge flyback ac/dc converter

Abstract

By means of a graft scheme, a buck‐boost cell and a wide range diagonal half‐bridge flyback cell are combined to create a novel single‐stage high power factor correction (HPFC) diagonal half‐bridge flyback ac/dc converter in this paper. When both of the two cells operate in discontinuous conduction mode, the proposed converter exhibits high power factor and low bulk capacitor voltage stress independent of the load variations. Based on the Loss‐Free Resistor (LFR) model, a new technique, referred to as ac‐dc balancing method, is also proposed. It is useful to determine the dc values, voltage ripples, and phase angle shifts of the bulk capacitor and output voltage of the converter. Moreover, the component values are well designed according to the operation conditions and design specifications of the converter. Finally, a prototype of the proposed converter with output voltage 48 V and power 100 W is built to test the theoretical analysis. It is successfully validated by IsSpice simulations and experimental results.     

Optimal age replacement scheduling for a random work system with random lead time

System maintenance and spare parts are two closely related logistics activities since maintenance generates the demand for spare parts. Most studies on integrated models of preventive replacement and inventory of spare parts have focused on age replacement scheduling, while random replacement policy, which is sensible and necessary in practice, is rarely discussed and applied. The purpose of this paper is to present a generalised age replacement policy for a system which works at random time and considers random lead time for replacement delivery. To model an imperfect maintenance action, we consider that the system undergoes minimal repairs at minor failures and corrective replacements at catastrophic failures. Before catastrophic failures, the system is replaced preventively at age T or at the completion of a working time, whichever occurs first. The main objective is to determine an optimal schedule of age replacement that minimises the mean cost rate function of the system in a finite time horizon. The existence and uniqueness of optimal replacement policy are derived analytically and computed numerically. It can be seen that the proposed model is a generalisation of the previous works in maintenance theory.     

Optimal control of a stochastic production–inventory system under deteriorating items and environmental constraints

In this paper, we present an optimal control model of a stochastic production–inventory with deteriorating items, emission tax and pollution abatement investment. In our model, the emission tax is levied on the firm’s environmental obsolescence rate of technology rather than the total amount of the environmental externality. Our objective is to apply Hamilton–Jacobi–Bellman (HJB) equation to solve the stochastic production–inventory system with deteriorating items, emission tax and pollution abatement investment; and derive the optimal production rate and pollution abatement investment rate that maximise the objective function value. The results are discussed with some illustrative examples for different demand rate functions, and sensitivity analysis is conducted to study the effect of changing the parameters and coefficients on the objective function value.     

Set-up and production planning in hybrid manufacturing–remanufacturing systems with large returns

Hybrid systems that use both raw materials and returned products in the production process are considered. The system contains one facility, and undergoes set-ups each time it switches between two production modes. In particular, we address systems engaged mainly in remanufacturing and having a large percentage of return. This situation is encountered in companies with mature remanufacturing channels. The targeted application area is comprised of hybrid systems that uses leasing as a business model with manufacturing serving to attenuate return uncertainty. To evaluate the system performance, we take into account manufacturing and remanufacturing costs, holding costs in serviceable and return inventories, backlog and set-up costs. Our analysis of hybrid systems with high return levels reveals features that are peculiar to such systems and that differentiate them from systems with lower return rates. We first present analytical solutions for optimal production and set-up schedule, and determine the possible cycle shapes for reliable systems. Optimal policies contain intervals of manufacturing and remanufacturing at maximal rate, and intervals of on-demand and on-return remanufacturing. Failure-prone systems are studied next, using the formalism of stochastic dynamic programming. Optimal policies give rise to the trajectories converging to the patterns similar to the analytically calculated cycles.     

Population transfer in a Λ-type five-level system with equally populated initial and empty final doublet states

We investigate the selective and efficient population transfer in a Λ-type five-level system with equally populated initial and empty final doublet states by time-separated chirped pump and Stokes pulses. We show that it is possible to achieve selective, efficient, and robust population transfer from either of the equally populated initial doublet states to either of the final ground doublet levels by merging stimulated Raman adiabatic passage and chirped adiabatic passage techniques. Moreover, the maximal coherent superpositions between either of the initial doublet states and either of the final doublet states, between the intermediate level and either of the final doublet states, or between the final doublet levels can be achieved by varying the chirp rates and single-photon detuning of the pump and Stokes pulses. This method may have potential applications in quantum coherent control of population dynamics in realistic atomic or molecular systems with equally populated initial and empty final manifolds.     

Possibilities and sustainability of “biomass for power” solutions in the case of a coal-based power utility

This paper investigates the possibilities and the sustainability of “biomass for power” solutions on a real power system. The case example is JP Elektroprivreda BiH d.d.—Sarajevo (EPBiH), a typical conventional coal-based power utility operating in the region of South East Europe. Biomass use is one of the solutions considered in EPBiH as a means of increasing shares of renewable energy sources (RES) in final energy production and reducing CO₂ emissions. This ultimately is a requirement for all conventional coal-based power utilities on track to meet their greenhouse gas (GHG) cut targets by 2050. The paper offers a discussion of possible options as a function of sustainability principles, considering environmental, economic and social aspects of biomass use. In the case of EPBiH, the most beneficial would be waste woody biomass and energy crop co-firing on existing coal-based power plants, as suggested by biomass market analyses and associated technological studies. To assess the sustainability of the different biomass co-firing options, a multicriteria sustainability assessment (MSA) and single criteria analysis (SCA) were used. Four different options were considered, based on different ratios of biomass for co-firing: 0 wt%-reference case, and 5, 7 and 10 wt% of biomass. Both the MSA and the SCA confirmed that the option with the highest share of biomass is the most preferable one for the considered case. In addition to that, the CO₂ parameter proved to be a key sustainability indicator, effecting the most decision making with regard to preference of options from the point of sustainability. Following up on the results of the analyses, the long-term projection of biomass use in EPBiH has shown an increase in biomass utilization of up to 450,000 t/y in 2030 and beyond, with associated CO₂ cuts of up to 395,000 t/y. This resulted in a 4 % CO₂ cut achieved with biomass co-firing, compared to the 1990 CO₂ emission level. It should be noted that the proposed assessment model for biomass use may be applied to any conventional coal-based power utility as an option in contributing to meeting specific CO₂ cut targets, provided that the set of input data is available and reliable.     

A simplified time-domain design and implementation of cascaded PI-sliding mode controller for dc–dc converters used in off-grid photovoltaic applications with field test results

A time-domain design methodology for voltage regulation control of dc–dc boost and buck-boost converters based on a multi-loop controller with PI regulator for the outer loop and an inner loop with sliding mode current controller has been developed for renewable energy applications such as photovoltaic (PV)-fed dc–dc converters. This paper proposes a new method for the design of PI regulators in such multi-loop control scheme. The proposed design presents a simple analytical method for selecting controller gains and has been validated by simulation as well as hardware implementation. Also, this paper presents an illustrative example based on the proposed design for the voltage regulation control of PV-fed boost converters for off-grid applications. The simulation results for varying irradiation, temperature and load along with stability analysis have been presented in this paper. The proposed controller is implemented in hardware for a 1.1 kW PV-array-fed boost converter. Performance analysis based on field test results using real-time weather data validates the proposed design. Therefore the proposed controller could be considered as an attractive solution for off-grid renewable energy applications like PV- or fuel-cell-fed dc–dc converter, where the variations are stochastic in nature.     

Positive and negative dispersion in a three-level Λ system driven by a single pump

We extend our previous study of a nearly degenerate Λ three-level system that exhibits population trapping when driven by a single pump and produces an absorption or gain doublet in the probe absorption spectrum. In particular, we show that the probe dispersion is positive or negative between the doublet lines, and can survive Doppler broadening. For certain values of the pump Rabi frequency, the sign of the dispersion can be changed by altering the ratio of the splitting between the lower levels to the Doppler width.     

P, ρ, T-properties and phase equilibria in the water-n-hexane system with a low content of water

Using a piezometer of constant volume, we determined experimentally the P, ρ, and T properties and the phase equilibria for the binary water-n-hexane mixtures with 0.04, 0.05, 0.06, and 0.0673 mass fraction of H₂O over the density range of 0.067–0.607 g/cm³, temperature range of 380–680 K, at pressures up to 60 MPa. The equilibrium lines of the liquid-liquid and liquid-gas transition have been determined. The three-phase line, the line of the azeotrope, and the lower branch of the critical line (all lines are joined at the upper finite critical point) have been plotted in the work.     

Optimal collection and remanufacturing decisions in reverse supply chains with collector’s imperfect sorting

We consider a reverse supply chain comprising two independent companies: the collector and the remanufacturer. The collector is responsible for sorting the collected used products and then transporting the ‘remanufacturable’ items to the remanufacturer. As sorting is not perfectly accurate, the misclassification errors affect the optimal decisions in the reverse supply chain. We focus on the optimal collection quantity for the collector and the optimal order quantity for the remanufacturer using game theory under both deterministic and uncertain demand. We characterise the optimal solution and show that under certain conditions, the remanufacturer should allow the collector to transport more ‘remanufacturables’ than the order quantity. We then examine the case where both the collector and the remanufacturer belong to a single company with centralised decision-making and compare the optimal collection quantities under both structures of the reverse supply chain.     

Stabilization of a system modeling temperature and porosity fields in a Kelvin�CVoigt-type mixture

In this paper, we investigate the asymptotic behavior of solutions to the initial boundary value problem for the interaction between the temperature field and the porosity fields in a homogeneous and isotropic mixture from the linear theory of porous Kelvin?CVoigt materials. Our main result is to establish conditions which insure the analyticity and the exponential stability of the corresponding semigroup. We show that under certain conditions for the coefficients we obtain a lack of exponential stability. A numerical scheme is given.     

Optimal 1 → 3 economical phase-covariant quantum cloning with superconducting quantum interference devices in a cavity

We propose a scheme to implement the optimal 1 → 3 economical phase-covariant quantum cloning with superconducting quantum interference devices (SQUIDs) in a cavity. During the process, no transfer of quantum information between the SQUIDs and cavity is required. The cavity field is only virtually excited. The scheme is insensitive to cavity decay. Therefore, the scheme can be experimentally realized in the range of current cavity QED techniques.     

Imaging of porosity in fiber-reinforced composites with a fiber-optic pump–probe laser-ultrasound system

Assessing material porosity in composites is critical because pores can greatly affect material strength and lifetime. Ultrasound (US) is one of the primarily methods to quantify porosity, usually based on the relationship between US speed/attenuation and void content. However, most US approaches require a sample with plane parallel and relatively smooth surfaces to correctly measure the attenuation and speed, but such conditions cannot always be fulfilled in practice. In addition, conventional US cannot directly image porosity as X-rays can. Here we present a non-contact US method to directly image porosity that can be easily integrated with US speed/attenuation measurements. The overall approach uses ultra wideband acoustic signals generated at the surface of a composite material with a laser pulse (i.e., pump), and non-contact, point-like detection of backscattered transients (i.e., probe) with spatial resolution better than 1 ply. US-assessed porosity is compared with that measured gravimetrically.     

Design and construction of a position-sensitive rotating implantation target system with β–γ discrimination capabilities

A rotating implantation target system has been designed for use at the RIKEN projectile fragment separator. While the original design is for the study of short β-decay lifetimes, the versatility of the device is also noted. The ability of the position-sensitive detector system to distinguish β and γ rays is studied, and the correlation of implantation position to beam position for purposes of particle identification is also described. Future improvements and experiments are planned and described briefly. The target detector system represents a simple, inexpensive, yet efficient way of conducting online implantation experiments where particle identification and rapid measurements are desired.     

Degradative and mechanical properties of a novel resorbable plating system during a 3-year follow-up in vivo and in vitro

We tested the tissue reactions and mechanical strength of a novel biodegradable craniomaxillofacial plating system, Inion CPS™, in the course of degradation. Plates and screws composed of l-lactide, d-lactide and trimethylene carbonate were implanted to the mandible and dorsal subcutis of 12 sheep. The animals were sacrificed at 6–156 weeks. Histological evaluation was done using paraffin and methylmetacrylate techniques. Degradative and mechanical properties during the follow-up were measured both of in vivo and in vitro implants. In light microscopy, the in vivo implant material began to fragment at 52 weeks and could not be detected at 104 weeks. No significant foreign body reactions were seen in the mandibles. The dorsal subcutis disclosed mild reactions, which were, however, not of clinical significance. The implants in vitro maintained their entire mass for 26 weeks and lost 63–80% of the mass by week 104. The inherent viscosity of the implants in vitro and in vivo diminished uniformly. The screws retained their shear strength for 12–16 weeks. The plates maintained their tensile strength for at least 6 weeks. The maximum capacity of the plates in 3-point bending tests diminished gradually by 87% in 26 weeks. In conclusion, the plates and screws examined maintain adequate strength for the healing period of a bone fracture or osteotomy, producing no harmful foreign body reactions. Dr Nieminen is a consultant for Inion Ltd., while the other co-authors do not have any conflicts of interest. Inion Ltd. has financed the costs related to the study sheep, including their housing.