Additional microstructural analysis on the samples examined in the paper ‘Are high resolution resistometric methods really useful for the early detection of electromigration damage?’

In a previous paper (A. Scorzoni, S. Franceschini, R. Balboni, M. Impronta, I. De Munari, and F. Fantini, Are high resolution resistometric methods really useful for the early detection of electromigration damage? Microelectr. Reliab. 1997;37(10/11):1479–1482), we reported largely different electromigration lifetimes and different high resolution early resistance changes measured on two nominally identical lots of 4 μm wide lines tested at moderately accelerated stress conditions. A microstructural analysis on unstressed samples was performed in order to detect the reason which induced these differences. The analysis confirmed a major defectivity of the lot with shorter lifetime: we detected the presence of TiAl₃ precipitates at the interface between the Al–Cu and the Ti-based metal barrier. This was not easily detectable by means of simple visual inspection. These additional findings confirm that a quick electrical detection of the metallization quality could be feasible by means of high resolution resistance measurements without the need of time-consuming direct examination of production lots.     

Preparation and thermal behavior of random poly(butylene terephthalate/azelate) copolyesters

Poly(butylene terephthalate), poly(butylene azelate), and poly(butylene terephthalate/butylene azelate) random copolymers of various compositions were synthesized in bulk using the well‐known two‐stage polycondensation procedure, and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. As far as the thermal stability is concerned, it was found to be rather similar for all copolymers and homopolymers investigated. All the copolymers were found to be partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. Flory's equation was found to describe the T_m–composition data and permitted to calculate the melting temperatures (T^°_m ) and the heats of fusion (ΔH_u) of both the completely crystalline homopolymers. Owing to the high crystallization rate, the glass transition was observable only for the copolymers containing from 30 to 70 mol % of the terephthalate units; even though the samples cannot be frozen in a completely amorphous state, the data obtained confirmed that the introduction of the aromatic units gave rise to an increase of T_g, due to a chain stiffening. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2694–2702, 1999     

Macromolecular design of novel sulfur‐containing copolyesters with promising mechanical properties

The miscibility of poly(butylene succinate) (PBS)/poly(butylene thiodiglycolate) (PBTDG) blends was investigated by DSC technique. PBS and PBTDG were completely immiscible in as blended‐state, as evidenced by the presence of two T_gs at ?34 and ?48°C, respectively. The miscibility changes upon mixing at elevated temperature: the original two phases merged into a single one because of transesterification reactions. Poly(butylene succinate/thiodiglycolate) block copolymers, prepared by reactive blending of the parent homopolymers, were studied to investigate the effects of transesterification reactions on the molecular structure and solid‐state properties. ¹³C‐NMR analysis evidenced the formation of copolymers whose degree of randomness increased with mixing time. Thermal characterization results showed that all the samples were semicrystalline, with a soft rubbery amorphous phase and a rigid crystal phase whose amount decreased by introducing BTDG units into the PBS chain (20 ≤ χ_c ≤ 41). Lastly, the mechanical properties were found strictly related to crystallinity degree (χ_c), the random copolymer, exhibiting the lowest elastic modulus (E = 61 MPa) and the highest deformation at break (ε_b (%) = 713). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Evaluation of the thermal resistance of Al---Cu electromigration test structures

The knowledge of the actual temperature of a metal line is fundamental in electromigration tests. It depends on the feasibility of thermal resistance measurements on the test structures. This work deals with the typical problems associated with the evaluation of the thermal resistance of Al---Cu test structures. As a consequence of significant copper-precipitation-induced resistance drops during high temperature electrical and thermal characterisation of the lines, it is shown that the derived thermal resistance value is a decreasing function of the measurement elapsed time. Thermal characterisations performed at temperatures lower than those typically used] allowed us to overcome this kind of problem.     

Melting behavior and crystallization kinetics of poly(butylene terephthalate‐co‐diethylene terephthalate) and poly(butylene terephthalate‐co‐triethylene terephthalate) copolyesters

The melting behavior of poly(butylene terephthalate‐co‐diethylene terephthalate) and poly(butylene terephthalate‐co‐triethylene terephthalate) copolymers was investigated by differential scanning calorimetry after isothermal crystallization from the melt. Multiple endotherms were found for all the samples, and attributed to the melting and recrystallization processes. By applying the Hoffman‐Weeks' method, the equilibrium melting temperatures of the copolymers under investigation were obtained. Two distinct peaks in the crystallization exothermic curve were observed for all the samples. Both of them appeared at higher times than that of PBT, indicating that the introduction of a comonomer decreased the crystallization rate. The observed dependence of this latter on composition was explained on the basis of the content of ether–oxygen atoms in diethylene and triethylene terephthalate units, and of the different sizes of these units. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3545–3551, 2001     

Iterated local search and simulated annealing algorithms for the inventory routing problem

This paper addresses the inventory routing problem (IRP), which consists in defining the customer visit schedule, the delivery quantities, and the vehicle routing plan to meet the demands of a set of customers over a given time horizon. We consider the variant with a single item, a single supplier, multiple vehicles, and a finite multiperiod planning horizon, minimizing the sum of inventory and travel costs. In addition, we address an alternative objective function that minimizes the logistic ratio, defined as the total travel cost divided by the total quantity delivered to customers. This second objective function, while more realistic in some logistics settings, poses a challenge for integer programming models and exact methods because of its nonlinearity. To our knowledge, no heuristic method has been proposed to address this objective in the IRP variant addressed in this paper. To solve this problem with each of these objective functions, we propose effective metaheuristic algorithms based on iterated local search and simulated annealing. Computational experiments show that these algorithms provide reasonably high‐quality solutions in relatively short running times for both objective functions when compared to other methods for well‐known instances from the literature. Moreover, the algorithms produce new best solutions for some of these instances.     

Environmentally friendly PBS-based copolyesters containing PEG-like subunit: Effect of block length on solid-state properties and enzymatic degradation

The use of biodegradable polymers could contribute to mitigate the huge environmental problems caused by the massive use of conventional non-biodegradable plastics, especially in the case of time-limited applications. In this framework, in the present study we propose a new class of multiblock eco-friendly copolyesters containing butylene succinate (BS) and triethylene succinate (TES) sequences. In particular, four copolyesters with the same chemical composition but different block lengths – P(BS₁₀TES₁₀), P(BS₅TES₅), P(BS₃TES₃), and P(BS₂TES₂) – were synthesized by reactive blending. For sake of comparison, homopolymer PBS was also considered. Physicochemical characterization (DSC, WAXS, tensile tests, WCA) of the copolymers synthesized demonstrated that it is possible to control polymer crystallinity, thermal and mechanical properties and wettability of the final product by simply varying block length. As a matter of fact, melting point, crystallinity degree, elastic modulus and surface wettability decreased with the block length; on the contrary, elongation to break significantly increased. Enzymatic hydrolysis performed with lipase from Candida cylindracea ([E] = 50 U/mL, T = 30 °C and pH = 7.0), showed that copolymers biodegradation is much higher than that of PBS homopolymer. Moreover, copolymers displayed a tunable range of degradation rates, related to their crystallinity degree and hydrophilic/hydrophobic ratio, which render them promising for different time-span applications, ranging from long-term (P(BS₁₀TES₁₀) to very short-term (P(BS₂TES₂)).     

Influence of branching on the thermal behavior of poly(butylene isophthalate)

The thermal behavior of linear and randomly branched poly(butylene isophthalate) samples was investigated by thermogravimetric analysis and differential scanning calorimetry. As to the thermal stability, it was found to be good and similar for all the samples. The thermal analysis carried out using DSC technique showed that the melting temperature of the polymers decreased with increasing branching unit content, although the glass‐transition temperature was practically not affected by ramifications. The multiple endotherms typical of linear PBI were also observed in branched samples and were found to be influenced both by temperature and degree of branching. By applying the Hoffman‐Weeks' method, the equilibrium melting temperatures of the polymers were obtained. The presence of a crystal‐amorphous interphase was evidenced only for the branched samples and the interphase amount was found to increase as the branching unit content was increased. Isothermal melt crystallization kinetics was analyzed according to Avrami's treatment. The introduction of branching points was found to decrease the overall crystallization rate of poly(butylene isophthalate). Values of Avrami's exponent n close to 3 were obtained for all the samples, in agreement with a crystallization process originating from predetermined nuclei and characterized by three dimensional spherulitic growth. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2001–2010, 2002; DOI 10.1002/app.10517     

Auditory and somatosensory evoked potentials in coma following spontaneous cerebral hemorrhage: early prognosis and outcome

Hereditary hemorrhagic telangiectasia (HHT), or Rendu-Osler-Weber disease, is an autosomal dominant disorder of localized angiodysplasia, although it is sometimes mistakenly identified as a hemostatic disorder due to its associated characteristic bleeding. The vascular lesions that develop consist of direct arteriovenous connections without an intervening capillary bed. Germline mutations in one of two different genes, endoglin or ALK-1, can cause HHT. Both are members of the transforming growth factor (TGF)-beta receptor family of proteins, and are expressed primarily on the surface of endothelial cells. They are associated together in a receptor complex on the cell surface. Biochemical studies suggest that endoglin modulates TGF-beta signaling through ALK-1 and the type I TGF-beta receptor. Most mutations identified in endoglin and ALK-1 create null alleles, which lead to reduced message or protein levels. A model of haploinsufficiency is proposed, in which inheritance of a mutation predisposes an individual to develop HHT-associated vascular lesions. The factors that initiate lesion formation are unknown, but disruption of these genes in mice should provide animal models to address these and other important questions about the pathogenesis of HHT.