Dynamic resource allocation: A flexible and tractable modeling framework

This paper presents a binary optimization framework for modeling dynamic resource allocation problems. The framework (a) allows modeling flexibility by incorporating different objective functions, alternative sets of resources and fairness controls; (b) is widely applicable in a variety of problems in transportation, services and engineering; and (c) is tractable, i.e., provides near optimal solutions fast for large-scale instances. To justify these assertions, we model and report encouraging computational results on three widely studied problems – the Air Traffic Flow Management, the Aircraft Maintenance Problems and Job Shop Scheduling. Finally, we provide several polyhedral results that offer insights on its effectiveness.     

Structural discrimination of isomeric tetrahydrofuran lignan glucosides by tandem mass spectrometry

Due to the possible role in human health, the number of analytical studies on lignans aimed at their quali‐ and quantitative analysis in plant extracts, biological fluids and foods is continuously increasing. However, helpful systematic mass spectrometric investigations on these compounds are few and rather limited to specific lignan sub‐classes. To increase the comprehension of the previously outlined picture of the gas‐phase properties of furofuran lignans, we extended the study to tetrahydrofuran lignans and here we reported the collision‐activated dissociation (CAD) fragmentation patterns of the alkali metal cation adducts, [M+Alk]⁺, and [M–H]^? ions of three isomeric tetrahydrofuran lignans, (+)‐8′‐hydroxylariciresinol 4′‐O‐β‐D ‐glucopyranoside (1), (+)‐7′‐hydroxylariciresinol 7′‐O‐β‐D ‐glucopyranoside (2) and 4‐O‐β‐D ‐glucopyranosyloxy‐3,3′‐dimethoxy‐7,9′‐epoxylignan‐5′,8′,9‐triol (3) investigated by electrospray ionization triple quadrupole mass spectrometry (ESI‐TQMS). Hydrogen/deuterium (H/D) solution exchange experiments, allowing the selective H/D exchange of all the acidic hydrogen atoms, proved to be a very effective tool to obtain information on the nature of fragments generated during TQ/CAD processes. The [M+Na]⁺ CAD mass spectra of the three isomeric tetrahydrofurans revealed four different pathways involving the loss of the glucose moiety, which allowed the assignment of the glycosylation site. In the negative ion mode, the main fragmentation channel of the [M–H]^? ions of O‐glucosylated lignans at the phenolic oxygen atoms is represented by the loss of 162 Da. When the sugar is bound to a benzylic OH group the loss of the sugar as a 180 Da unit occurs eventually following the loss of a water molecule involving both the C(9)H₂OH chain and the sugar. Copyright © 2010 John Wiley & Sons, Ltd.     

Evidence of electron wave function delocalization in CdSe/CdS asymmetric nanocrystals

We studied the delocalization of electron wave function in asymmetric CdSe/CdS nanocrystals, consisting of a spherical CdSe dot embedded in an elongated CdS shell, by means of a pump–probe technique. By comparing the transient spectra obtained upon pumping the band edge transition of the CdSe in CdSe/CdS heterostructure and in a bare CdSe dot, we observed the delocalization of electron wave function at the CdSe/CdS interface.     

Designing ring-current patterns: [10,5]-coronene, a circulene with inverted rim and hub currents

In an axial magnetic field, coronene, corannulene and kekulene support disjoint paratropic-hub and diatropic-rim ring currents. Bond-order and orbital arguments suggest [10,5]-coronene, C30H10, comprising 10 fused pentagons around a central decagon, as a system that should support an inverted diatropic-hub/paratropic-rim pattern of induced currents. The proposal is verified by ipsocentric ab initio mapping of currents, reproduced with the economical pseudo-pi method, thus validating a powerful toolkit for design of (induced) molecular magnets.     

Initial and Final Backward and Forward Discrete Time Non-homogeneous Semi-Markov Credit Risk Models

In this paper we show how it is possible to construct an efficient Migration models in the study of credit risk problems presented in Jarrow et al. (Rev Financ Stud 10:481–523, 1997) with Markov environment. Recently it was introduced the semi-Markov process in the migration models (D’Amico et al. Decis Econ Finan 28:79–93, 2005a). The introduction of semi-Markov processes permits to overtake some of the Markov constraints given by the dependence of transition probabilities on the duration into a rating category. In this paper, it is shown how it is possible to take into account simultaneously backward and forward processes at beginning and at the end of the time in which the credit risk model is observed. With such a generalization, it is possible to consider what happens inside the time after the first transition and before the last transition where the problem is studied. This paper generalizes other papers presented before. The model is presented in a discrete time environment.     

Bioactive clerodane diterpenes from roots of Carex distachya

Two new clerodane diterpenes were isolated from roots of Carex distachya Desf., a perennial plant widely distributed in the coastal area of the Mediterranean basin. Chemical characterization of the metabolites was carried out mainly by 1D and 2D NMR spectroscopy. The isolated compounds influenced either positively or negatively the plant growth (root and shoot elongation) of three coexisting herbaceous species.     

Poly(4-methylpentene-1)/hydrogenated oligo (cyclopentadiene) blends: Miscibility,tensile stress–strain,and dynamic mechanical behaviors

This article discusses the influence of the oligomeric resin, hydrogenated oligo(cyclopentadiene) (HOCP), on the morphology, and thermal and tensile mechanical properties of its blends with isotactic poly(4-methylpentene-1) (P4MP1). The P4MP1 and HOCP are found not miscible in the melt state. P4MP1/HOCP blends after solidification contain three phases: the crystalline phase of P4MP1, an amorphous phase of P4MP1, and an amorphous phase of HOCP. From optical micrographs obtained at 150°C, it is found that the solidified blends show a morphology constituted by P4MP1 microspherulites and small HOCP domains homogeneously distributed in intraspherulitic regions. DSC and DMTA results show that the blends present two glass transition temperatures (T_g) equal to the T_gs of the pure components. The tensile mechanical properties have been investigated at 20, 60, and 120°C. At 20°C both the HOCP oligomer and the amorphous P4MP1 are glassy, and it is found that all the blends are brittle and the stress–strain curves have equal trends. At 60°C the HOCP oligomer is glassy, whereas the amorphous P4MP1 is rubbery. The tensile mechanical properties at 60°C are found to depend on blend composition. It is found that the Young's modulus, the stresses at yielding and break points slightly decrease with HOCP content in the blends and these results are related to the decrease of blend crystallinity. The decrease of the elongation at break is accounted for by the presence of glassy HOCP domains that act as defects in the P4MP1 matrix, hampering the drawing. At 120°C both the amorphous phases are rubbery. It is found decreases of Young's modulus, stresses at yielding and break points. These results have been related to the decrease of blend crystallinity and to the increase of the total rubbery amorphous phase. Moreover, it is found that the blends present elongations at break equal to that of pure P4MP1. This constancy is attributed to: (a) at 120°C the HOCP domains are rubbery and their presence seems not to disturb the drawing of the samples; (b) a sufficient number of the tie-molecules and entanglements of P4MP1 present in the blends. In fact, although the numbers of tie-molecules and entanglements decrease in the blends, increasing the HOCP oligomer, they seem to be enough to keep the material interlaced and avoid earlier rupture. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1269–1277, 1997