Analysis of the photon–photon resonance influence on the direct modulation bandwidth of dual-longitudinal-mode distributed feedback lasers

The paper explores the possibilities to extend the direct modulation bandwidth in dual-longitudinal-mode distributed feedback lasers by exploiting the photon–photon resonance induced by the interaction of the two modes in the laser cavity. The effects on the direct amplitude modulation and on the direct modulation of the difference frequency between the two modes are analyzed using simulation and experimental results. When the photon–photon resonance, which occurs at the difference frequency between the two modes, is properly placed at a higher frequency than the carrier-photon resonance, the small-signal amplitude modulation (AM) bandwidth of the laser can be significantly increased. However, both simulations and experiments point out that a high small-signal AM bandwidth does not lead to a high large-signal AM bandwidth if the small-signal modulation response has significant variations across the modulation bandwidth. The paper shows that a high large-signal AM bandwidth is obtained when the two modes are significantly unbalanced, whereas a high-bandwidth difference frequency modulation can be best detected when the two modes are balanced and the DC bias is properly chosen.     

A Multi-Period Renewal equipment problem

This paper looks at a Multi-Period Renewal equipment problem (MPR). It is inspired by a specific real-life situation where a set of hardware items is to be managed and their replacement dates determined, given a budget over a time horizon comprising a set of periods. The particular characteristic of this problem is the possibility of carrying forward any unused budget from one period to the next, which corresponds to the multi-periodicity aspect in the model. We begin with the industrial context and deduce the corresponding knapsack model that is the subject of this paper. Links to certain variants of the knapsack problem are next examined. We provide a study of complexity of the problem, for some of its special cases, and for its continuous relaxation. In particular, it is established that its continuous relaxation and a special case can be solved in (strongly) polynomial time, that three other special cases can be solved in pseudo-polynomial time, while the problem itself is strongly NP-hard when the number of periods is unbounded. Next, two heuristics are proposed for solving the MPR problem. Experimental results and comparisons with the Martello&Toth and Dantzig heuristics, adapted to our problem, are provided.     

39K NMR study of the low temperature phase transitions in KLiSO4

The³⁹K NMR spectra, spin-spin (T ₂) and spin-lattice (T ₁) relaxation times of KLiSO₄ have been measured in the temperature range from 300 K to 90 K. The temperature dependence of the³⁹K (I=3/2) NMR spectra demonstrates the occurrence of a first order phase transition atT _c1=217 K which occurs without a change in the K⁺ site symmetry and another first order transition atT _c2=190 K which is connected with a lowering of the K⁺ site symmetry and the formation of three kinds of ferroelastic domains. From the angular dependence of the second order quadrupole shifts of the³⁹K NMR 1/2–1/2 transitions the electric-field gradient (EFG) tensors at the potassium sites were determined at 290 K, 204 K and 180 K. The symmetry of the ferroelastic phase is monoclinic and not orthorhombic as the K⁺ EFG tensors are tilted away from thec-axis belowT _c2. TheT ₁ data further show the freezing in of the slow reorientational motion 10^–8 s with decreasing temperature from 300 to 90 K.On leave from: J. Stefan Institute, E. Kardelj University of Ljubljana, Ljubljana, Yugoslavia     

Novel pressure and displacement sensors based on carbon nanotubes

We report newly designed pressure and displacement capacitive sensors based on a flexible paper–CNT structure.The carbon nanotube(CNT)powder was deposited on a thin paper substrate and was pressed at an elevated temperature.The sheet resistance of the paper–CNT films was in the range of 2–4 kΩ/cm2.The paper–CNT films were used to fabricate pressure and displacement sensors.The sensitivities of the pressure and the displacement sensors were found to be17.3 p F·m2/k N and 0.93 10-3p F/μm,respectively.The experimental results were compared with the simulated data and they found good agreement with each other.     

Counterion influence on the N–I–N halogen bond

A detailed investigation of the influence of counterions on the [N–I–N]⁺ halogen bond in solution, in the solid state and in silico is presented. Translational diffusion coefficients indicate close attachment of counterions to the cationic, three-center halogen bond in dichloromethane solution. Isotopic perturbation of equilibrium NMR studies performed on isotopologue mixtures of regioselectively deuterated and nondeuterated analogues of the model system showed that the counterion is incapable of altering the symmetry of the [N–I–N]⁺ halogen bond. This symmetry remains even in the presence of an unfavorable geometric restraint. A high preference for the symmetric geometry was found also in the solid state by single crystal X-ray crystallography. Molecular systems encompassing weakly coordinating counterions behave similarly to the corresponding silver(i) centered coordination complexes. In contrast, systems possessing moderately or strongly coordinating anions show a distinctly different behavior. Such silver(i) complexes are converted into multi-coordinate geometries with strong Ag–O bonds, whereas the iodine centered systems remain linear and lack direct charge transfer interaction with the counterion, as verified by ¹⁵N NMR and DFT computation. This suggests that the [N–I–N]⁺ halogen bond may not be satisfactorily described in terms of a pure coordination bond typical of transition metal complexes, but as a secondary bond with a substantial charge-transfer character.     

A robust approach to the chance-constrained knapsack problem

In this paper, the chance-constrained knapsack problem (CKP) is addressed. Relying on robust optimization, a tractable combinatorial algorithm is proposed to solve approximately CKP. For two specific classes of uncertain knapsack problems, it is proved to solve CKP at optimality.     

The robust binomial approach to chance-constrained optimization problems with application to stochastic partitioning of large process networks

In this paper, we study an interpretation of the sample-based approach to chance-constrained programming problems grounded in statistical testing theory. On top of being simple and pragmatic, this approach is theoretically well founded, non parametric and leads to a general method for leveraging existing heuristic algorithms for the deterministic case to their chance-constrained counterparts. Throughout this paper, this algorithm design approach is illustrated on a real world graph partitioning problem which crops up in the field of compilation for parallel systems. Extensive computational results illustrate the practical relevance of the approach, as well as the robustness of the obtained solutions.     

Timetabling of sorting slots in a logistic warehouse

We study a problem that occurs at the end of a logistic stream in a warehouse and which concerns the timetabling of the sorting slots that are used to accommodate the prepared orders before they are dispatched. We consider a set of orders to be prepared in a certain number of preparation shops over a given time horizon. Each order is associated with the truck that will transport it to the customer. A sorting slot is an accumulation area where processed orders wait to be loaded onto a truck. For a given truck a known number of sorting slots is needed from the time the first order for this truck begins to be prepared, right up until the truck’s scheduled departure time. Since several orders destined for different trucks are processed simultaneously, and since the number of sorting slots is limited, the timetabling of these resources is necessary to ensure that all orders can be processed over the considered time horizon. In this paper we describe the general industrial context of the problem and we formalize it. We state that some particular cases of the problem are polynomially solvable while the general problem is NP-complete. We then propose optimization methods for solving the problem.     

van der Waals interactions are critical in Car–Parrinello molecular dynamics simulations of porphyrin–fullerene dyads

The interplay between electrostatic and van der Waals (vdW) interactions in porphyrin‐C₆₀ dyads is still under debate despite its importance in influencing the structural characteristics of such complexes considered for various applications in molecular photovoltaics. In this article, we sample the conformational space of a porphyrin‐C₆₀ dyad using Car–Parrinello molecular dynamics simulations with and without empirical vdW corrections. Long‐range vdW interactions, which are poorly described by the commonly used density functional theory functionals, prove to be essential for a proper dynamics of the dyad moieties. Inclusion of vdW corrections brings porphyrin and C₆₀ close together in an orientation that is in agreement with experimental observations. The structural differences arising from the vdW corrections are shown to be significant for several properties and potentially less important for others. Additionally, our Mulliken population analysis reveals that contrary to the common belief, porphyrin is not the primary electron donating moiety for C₆₀. In the considered dyad, fullerene's affinity for electrons is primarily satisfied by charge transfer from the amide group of the linker. However, we show that in the absence of another suitable bound donor, C₆₀ can withdraw electrons from porphyrin if it is sufficiently close. © 2015 Wiley Periodicals, Inc.     

Templated synthesis of a large and flexible covalent porphyrinic cage bearing orthogonal recognition sites

A large covalent cage incorporating two porphyrins attached by four long and flexible polyether chains each bearing two 3-pyridyl ligands was synthesized from a DABCO-templated olefin metathesis reaction. The X-ray structure of the cage with the DABCO coordinated inside the cavity to the two zinc(II) porphyrins reveals a highly symmetric structure.