Numerical study of 2024 T3 aluminum plates subjected to impact and perforation

The paper describes a work focused on the process of perforation of aluminum sheet. A numerical investigation has been carried out to analyze in details the perforation process subjected to normal impact by different nose shapes of projectiles. The perforation process has been simulated by the application of 3D analysis using IMPACT dynamic FE program suite. The comparison on failure modes depending on the projectile nose shape have been studied and evaluated. An appropriate constitutive relation was applied to describe the material behavior of the aluminum sheet. The study covered different failure modes including petalling, plug ejection and circumference necking of perforated aluminum sheet according to different level of impact velocity ranging from 100 m/s to 600 m/s. In this investigation, a special attention will be given on the deformation and failure.     

Branching-Depth Hierarchies

We study the distinguishing and expressive power of branching temporal logics with bounded nesting depth of path quantifiers. We define the fragments CTL^*_i and CTL_i of CTL^* and CTL, where at most i nestings of path quantifiers are allowed. We show that for all i ≥ 1, the logic CTL^*_i+1 has more distinguishing and expressive power than CTL^*_i; thus the branching-depth hierarchy is strict. We describe equivalence relations H_i that capture CTL^*_i: two states in a Kripke structure are H_i-equivalent iff they agree on exactly all CTL^*_i formulas. While H₁ corresponds to trace equivalence, the limit of the sequence H₁, H₂,… is Milner's bisimulation. These results are not surprising, but they give rise to several interesting observations and problems. In particular, while CTL^* and CTL have the same distinguishing power, this is not the case for CTL^*_i and CTL_i. We define the branching depth of a structure as the minimal index i for which H_i+1=H_i. The branching depth indicates on the possibility of using bisimulation instead of trace equivalence (and similarly for simulation and trace containment). We show that the problem of finding the branching depth is PSPACE-complete.     

Therapeutic Advances in Gut Microbiome Modulation in Patients with Inflammatory Bowel Disease from Pediatrics to Adulthood

There is mounting evidence that the gut microbiota plays an important role in the pathogenesis of inflammatory bowel disease (IBD). For the past decade, high throughput sequencing-based gut microbiome research has identified characteristic shifts in the composition of the intestinal microbiota in patients with IBD, suggesting that IBD results from alterations in the interactions between intestinal microbes and the host’s mucosal immune system. These studies have been the impetus for the development of new therapeutic approaches targeting the gut microbiome, such as nutritional therapies, probiotics, fecal microbiota transplant and beneficial metabolic derivatives. Innovative technologies can further our understanding of the role the microbiome plays as well as help to evaluate how the different approaches in microbiome modulation impact clinical responses in adult and pediatric patients. In this review, we highlight important microbiome studies in patients with IBD and their response to different microbiome modulation therapies, and describe the differences in therapeutic response between pediatric and adult patient cohorts.     

Thermal properties and enthalpy relaxation of tyrosine-derived polyarylates

Sixteen degradable, tyrosine-derived polyarylates with well-defined chemical structures were used to study the effect of polymer structure on the glass transition temperature and enthalpy relaxation kinetics (physical aging). These polyarylates compose a model system where the number of methylene groups present in either the pendent chain or the polymer backbone can be altered independently and in a systematic fashion. Quantitative differential scanning calorimetry was employed to measure the glass transition temperature and the enthalpy relaxation kinetics. Correlations between these material properties and the polymer structure were established. The glass transition temperature of this family of polymers ranged from 13 to 78°C. The addition of methylene groups to either the pendent chain or the polymer backbone made a fairly constant contribution to lowering the glass transition temperature. The rate of enthalpy relaxation increased with an increasing number of methylene groups in the polymer backbone, but was independent of the number of methylene groups in the pendent chain. This observation indicated that the rate of enthalpy relaxation in these polymers was limited by the mobility of the polymer backbone. The enthalpy relaxation data was fitted to the Cowie-Ferguson model and the relaxation times obtained ranged from 44 min to about 100 min. Although these structure-property correlations facilitate the design of new materials with predictable thermal properties, they are rarely investigated for biomedical polymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1441–1448, 1997     

Effect of humic acid on pyrene removal from water by polycation-clay mineral composites and activated carbon

Pyrene removal by polycation-montmorillonite (MMT) composites and granulated activated carbon (GAC) in the presence of humic acid (HA) was examined. Pyrene, HA, and sorbent interactions were characterized by FTIR, fluorescence and zeta measurements, adsorption, and column filtration experiments. Pyrene binding coefficients to the macromolecules were in the order of PVPcoS (poly-4-vinylpiridine-co-styrene) > HA > PDADMAC (poly diallyl-dimethyl-ammonium-chloride), correlating to pyrene-macromolecules compatibility. Electrostatic interactions explained the high adsorption of HA to both composites (～100%), whereas HA adsorption by GAC was low. Pyrene removal by the composites, unlike GAC, was enhanced in the presence of HA; removal by PDADMAC-MMT increased from ～50 (k(d) = 2.2 × 10(3) kg/L) to ～70% (k(d) = 2.4 × 10(3) kg/L) in the presence of HA. This improvement was attributed to the adsorption of pyrene-HA complexes. PVPcoS-MMT was most efficient in removing pyrene (k(d) = 1.1 × 10(4) kg/L, >95% removal) which was explained in terms of specific π donor-π acceptor interactions. Pyrene uptake by column filters of GAC reached ～50% and decreased to ～30% in the presence of HA. Pyrene removal by the PVPcoS-MMT filter was significantly higher (100-85% removal), exhibiting only a small decrease in the presence of HA. The utilization of HA as an enhancing agent in pollutant removal is novel and of major importance in water treatment.     

Long-term amorphisation of C and N2 implanted layers on a uranium surface

Ion implantation of C⁺ or N₂⁺ on uranium surfaces produces crystalline compounds (uranium carbides or nitrides, respectively), which have been shown to provide excellent protection against ambient corrosion. Some long-term changes of these implanted layers were detected that even though not affecting the protection ability, still are of fundamental interest. The most prominent change is the amorphisation of the carbide or nitride layers, which takes place after a few years of air exposure. This amorphisation did not result from the oxidation of the layer (the formed oxides are much thinner than the thickness of the implanted layers), but is still assisted by air exposure (i.e., the amorphisation rates of samples kept under vacuum are much lower than those exposed to the ambient atmosphere). Some additional long-term changes in the layer compositions (transitions of UN₂ to U₂N₃) and distributions (inward diffusion of the implanted ions) were also apparent. It is suggested that the presence of hydrogen in the implanted layer, originating from the dissociation of water molecules on the surface, may accelerate the amorphisation and the UN₂ to U₂N₃ transition due to the possible increase in the diffusion constant.     

Self-assembly of amphiphilic di and triblock copolymers of styrene and quaternized 5-(N,N-diethylamino) isoprene in selective solvents

Self-association of highly asymmetric block copolymers of styrene and quaternized 5-(N,N-diethylamino)isoprene was studied. After quaternization with dimethyl sulfate, the di and triblock copolymers consisted of a long block of polystyrene (PS) with a short poly[5-(N,N,N-diethylmethylammonium)isoprene][methyl sulfate](PAI) block at one or both chain ends, respectively. The aggregates were prepared by first dissolving the copolymers in an organic solvent and then adding water to induce the segregation of the PS chains. Pure DMF, THF or dioxane was used as the organic solvent, as well as DMF/THF mixtures. The critical water content (cwc) and the morphologies were studied as a function of the common solvent, initial copolymer concentration and architecture (di or triblock) by static light scattering and by Transmission Electron Microscopy (TEM), respectively. It was found that both, the cwc and the morphologies of the aggregates are most strongly affected by the nature of the common solvent. Some unexpected behaviors were found for the triblock copolymer. Morphologies of a triblock copolymer in various mixtures of DMF and THF, quenched at determined water contents, were investigated in order to study the degree of morphological control that can be achieved solely as function of the organic solvent composition. Multiple morphologies have been found including equilibrium morphologies and kinetically trapped ones. Finally, the stability of primary micelles prepared in DMF was studied by DLS, upon dilution with DMF and water, and a possible mechanism for the destabilization of the aggregates is proposed.     

The application of fuzzy logic to the precautionary principle

One of the major problems in the implementation of the precautionary principle in environmental cases is the estimation of the weight of evidence. In this paper we propose a formal method that determines the weight of evidence based on the specific parameters of a given case. The proposed method is based on an artificial intelligence approach called fuzzy logic, which is commonly used as an interface between logic and human perception, and often applied to computer-based complex decision making. We use one fuzzy expert system that provides a quantification of the estimated environmental damage, and a second fuzzy expert system that computes the weight of evidence in a given case. The proposed expert system can be easily defined and adjusted by regulators and environmental science and policy experts.