Implementation and validation of a strain rate dependent anisotropic continuum model for masonry

A newly developed strain rate dependent anisotropic continuum model is proposed for impact and blast applications in masonry. The present model adopted the usual approach of considering different yield criteria in tension and compression. The analysis of unreinforced block work masonry walls subjected to impact is carried out to validate the capability of the model. Comparison of the numerical predictions and test data revealed good agreement. Next, a parametric study is conducted to evaluate the influence of the tensile strengths along the three orthogonal directions and of the wall thickness on the global behavior of masonry walls.

Age-Dependent Properties of Acid & Alkaline DNases in Chick Brain

Acid and alkaline DNase activities in partially purified preparations from young and old chick brain were measured. The specific activity of acid DNase from old brain was lower by about 50% than that of enzyme from young brain , whereas alkaline DNase exhibited only marginal difference in activity of the two preparations . Study of various properties, viz. heat-stability and effect of exogenous compounds like Mg=', Hgl', Zn=', PHM B , on these enzymes revealed that while acid DNase in old brain is more susceptible to heat and heavy metal ion inhibition , alkaline DNase is devoid of any age-dependent variation in its properties.

Rate-dependent fracture toughness of polycrystalline ice

A series of three-point bend tests using single edge notched testpieces of pure polycrystalline ice have been performed at three different temperatures (–20°C, –30°C and –40°C). The displacement rate was varied from 1 mm/min to 100 mm/min, producing the crack tip strain rates from about 10–3 to 10–1 s–1. The results show that (a) the fracture toughness of pure polycrystalline ice given by the critical stress intensity factor (K IC) is much lower than that measured from the J—integral under identical conditions; (b) from the determination of K IC, the fracture toughness of pure polycrystalline ice decreases with increasing strain rate and there is good power law relationship between them; (c) from the measurement of the J—integral, a different tendency was appeared: when the crack tip strain rate exceeds a critical value of 6 × 10–3 s–1, the fracture toughness is almost constant but when the crack tip strain rate is less than this value, the fracture toughness increases with decreasing crack tip strain rate. Re-examination of the mechanisms of rate-dependent fracture toughness of pure polycrystalline ice shows that the effect of strain rate is related not only to the blunting of crack tips due to plasticity, creep and stress relaxation but also to the nucleation and growth of microcracks in the specimen.

Effect of cooling rate on properties of plasma nitrided AISI 1010 steel

In this work, AISI 1010 steel samples were plasma nitrided into 20% N 2 100 Pa and 400 Pa for N 2 and H 2 , respectively), temperatures of 500 and 580 °C, during 2 h. Three different procedures for cooling were accomplished after nitriding. In the first procedure the cooling occurred naturally, that is, the sample was kept on substrate holder. In the second one the sample was pulled off and cooling in a cold surface. Finally, in the third cooling process the sample was pulled off the substrate holder down into special reservoir filled with oil held at ambient temperature. The properties of the AISI 1010 steel samples were characterized by optical and electron microscopy, X-ray diffraction, Mössbauer spectroscopy and microhardness tests. Thermal gradient inside the sample kept on substrate holder during cooling process was measured by three inserted thermocouples at different depths. When samples were cooled rapidly the transformation of ϵ-Fe 2 − 3 N to γ′-Fe 4 N was inhibited. Such effect is indicated by the high concentration of ϵ-Fe compound zone. To get solid state solution of nitrogen in the diffusion zone, instead of precipitates of nitride phases, the cooling rate should be higher than a critical value of about 0.95 °C/s. When this value is reached at any depth of the diffusion zone, two distinct diffusion zones will appear. Temperature gradients were measured inside the samples as a consequence of the plasma treatment. It's suggested the need for standardization of the term “treatment temperature” for plasma treatment because different nitrided layer properties could be reported for the same “treatment temperature”.

Time-dependent properties in two-dimensional and Hamiltonian mappings

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Temperature- and strain-rate-dependent microfabric evolution in monomineralic mylonite: evidence from in situ deformation of norcamphor

Norcamphor (C7H10O) was subjected to plane strain simple shear in a see-through deformation rig at four different strain rate and temperature conditions. Two transient stages in the microfabric evolution to steady state are distinguished. The grain scale mechanisms associated with the microstructural and textural evolution vary with the applied temperature, strain rate and strain. In high-temperature-low-strain-rate experiments, computer integrated polarization microscopy reveals that the texture evolution is closely related to the crystallographic rotation paths and rotation rates of individual grains. High c-axis rotation rates at low to intermediate shear strains are related to the development of a symmetrical c-axis cross girdle by the end of the first transient stage (γ = 1.5 to 2). During the second transient stage (γ = 1.5 to 6), the cross girdle yields to an oblique c-axis single girdle as c-axis rotation rates decrease and the relative activity of grain boundary migration recrystallization increases. Steady state (γ > 8) is characterized by a stable end orientation of the sample texture and the cyclic growth, rotation and consumption of individual grains within the aggregate.

Host factor I, Hfq, binds to Escherichia coli ompA mRNA in a growth rate-dependent fashion and regulates its stability

The stability of the ompA mRNA depends on the bacterial growth rate. The 5′ untranslated region is the stability determinant of this transcript and the target of the endoribonuclease, RNase E, the key player of mRNA degradation. An RNA-binding protein with affinity for the 5′ untranslated region ompA was purified and identified as Hfq, a host factor initially recognized for its function in phage Qβ replication. The ompA RNA-binding activity parallels the amount of Hfq, which is elevated in bacteria cultured at slow growth rate, a condition leading to facilitated degradation of the ompA mRNA. In hfq mutant cells with a deficient Hfq gene product, the RNA-binding activity is missing, and analysis of the ompA mRNA showed that the growth-rate dependence of degradation is lost. Furthermore, the half-life of the ompA mRNA is prolonged in the mutant cells, irrespective of growth rate. Hfq has no affinity for the lpp transcript whose degradation, like that of bulk mRNA, is not affected by bacterial growth rate. Compatible with our results, we found that the intracellular concentration of RNase E and its associated degradosome components is independent of bacterial growth rate. Thus our results suggest a regulatory role for Hfq that specifically facilitates the ompA mRNA degradation in a growth rate-dependent manner.

Effect of cooling rate on properties of plasma nitrided AISI 1010 steel

In this work, AISI 1010 steel samples were plasma nitrided into 20% N 2 100 Pa and 400 Pa for N 2 and H 2 , respectively), temperatures of 500 and 580 °C, during 2 h. Three different procedures for cooling were accomplished after nitriding. In the first procedure the cooling occurred naturally, that is, the sample was kept on substrate holder. In the second one the sample was pulled off and cooling in a cold surface. Finally, in the third cooling process the sample was pulled off the substrate holder down into special reservoir filled with oil held at ambient temperature. The properties of the AISI 1010 steel samples were characterized by optical and electron microscopy, X-ray diffraction, Mössbauer spectroscopy and microhardness tests. Thermal gradient inside the sample kept on substrate holder during cooling process was measured by three inserted thermocouples at different depths. When samples were cooled rapidly the transformation of ϵ-Fe 2 − 3 N to γ′-Fe 4 N was inhibited. Such effect is indicated by the high concentration of ϵ-Fe compound zone. To get solid state solution of nitrogen in the diffusion zone, instead of precipitates of nitride phases, the cooling rate should be higher than a critical value of about 0.95 °C/s. When this value is reached at any depth of the diffusion zone, two distinct diffusion zones will appear. Temperature gradients were measured inside the samples as a consequence of the plasma treatment. It's suggested the need for standardization of the term “treatment temperature” for plasma treatment because different nitrided layer properties could be reported for the same “treatment temperature”.

Effect of cooling rate on properties of plasma nitrided AISI 1010 steel

In this work, AISI 1010 steel samples were plasma nitrided into 20% N 2 100 Pa and 400 Pa for N 2 and H 2 , respectively), temperatures of 500 and 580 °C, during 2 h. Three different procedures for cooling were accomplished after nitriding. In the first procedure the cooling occurred naturally, that is, the sample was kept on substrate holder. In the second one the sample was pulled off and cooling in a cold surface. Finally, in the third cooling process the sample was pulled off the substrate holder down into special reservoir filled with oil held at ambient temperature. The properties of the AISI 1010 steel samples were characterized by optical and electron microscopy, X-ray diffraction, Mössbauer spectroscopy and microhardness tests. Thermal gradient inside the sample kept on substrate holder during cooling process was measured by three inserted thermocouples at different depths. When samples were cooled rapidly the transformation of ϵ-Fe 2 − 3 N to γ′-Fe 4 N was inhibited. Such effect is indicated by the high concentration of ϵ-Fe compound zone. To get solid state solution of nitrogen in the diffusion zone, instead of precipitates of nitride phases, the cooling rate should be higher than a critical value of about 0.95 °C/s. When this value is reached at any depth of the diffusion zone, two distinct diffusion zones will appear. Temperature gradients were measured inside the samples as a consequence of the plasma treatment. It's suggested the need for standardization of the term “treatment temperature” for plasma treatment because different nitrided layer properties could be reported for the same “treatment temperature”.

Caractéristiques et origine fonctionnelle des propriétés fréquentielles du noeud auriculoventriculaire

Le nœud auriculoventriculaire (AV) joue un rôle vital dans le cœur normal et pathologique. Il connecte les oreillettes aux ventricules et, grâce à sa conduction lente, génère un délai entre les contractions auriculaire et ventriculaire permettant d’optimiser le pompage sanguin. Sa conduction lente et sa longue période réfractaire font du nœud AV un filtre d’impulsions auriculaires lors de tachyarythmies assurant ainsi une fréquence ventriculaire plus lente favorable au débit cardiaque. L’optimisation de ce filtrage est une cible dans le traitement de ces arythmies. Malgré ce rôle vital et de nombreuses études, le nœud AV demeure l’objet de plusieurs controverses qui en rendent la compréhension laborieuse. Nos études expérimentales sur des préparations isolées de cœurs de lapin visent à apporter des solutions à certains des problèmes qui limitent la compréhension des propriétés fréquentielles du nœud AV. Le premier problème concerne la définition de la propriété de récupération nodale. On s’accorde généralement sur la dépendance du temps de conduction nodale (intervalle auriculo-Hissien, AH) du temps de récupération qui le précède mais un débat presque centenaire persiste sur la façon de mesurer ce temps de récupération. Selon que l’on utilise à cette fin la longueur du cycle auriculaire (AA) ou l’intervalle His-auriculaire précédent (HA), la même réponse nodale montre des caractéristiques différentes, un paradoxe à ce jour inexpliqué. Le temps de conduction nodale augmente aussi avec le degré et la durée d'une fréquence rapide, un phénomène appelé fatigue. Or, les caractéristiques de la fatigue mesurée varient avec l’indice de récupération utilisé (AA vs. HA). De plus, une troisième propriété appelée facilitation qui entraîne un raccourcissement du temps de conduction diffère aussi avec l’indice de récupération utilisé. Pour établir l’origine de ce problème, nous avons déterminé les différences entre les courbes de récupération (AH compilé en fonction du AA ou HA) pour 30 états fonctionnels nodaux différents. Ces conditions étaient obtenues à l’aide de protocoles permettant la variation du cycle de base (BCL) et du cycle prétest (PTCL), deux paramètres connus pour altérer la fonction nodale. Nous avons pu établir que pour chaque état fonctionnel, la forme de la courbe de récupération et le niveau de fatigue étaient les mêmes pour les deux indices de récupération. Ceci s’applique aussi aux données obtenues à des BCL et PTCL égaux comme dans les protocoles de stimulation prématurée conventionnels couramment utilisés. Nos résultats ont établi pour la première fois que les propriétés nodales de récupération et de fatigue sont indépendantes de l’indice de récupération utilisé. Nos données montrent aussi que les différences entre les courbes de récupération en fonction de l’indice utilisé proviennent d’effets associés aux variations du PTCL. Notre deuxième étude établit à partir des mêmes données pourquoi les variations du PTCL altèrent différemment les courbes de récupération selon l’indice utilisé. Nous avons démontré que ces différences augmentaient en proportion directe avec l’augmentation du temps de conduction au battement prétest. Cette augmentation cause un déplacement systématique de la courbe construite avec l’intervalle AA vers la droite et de celle construite avec l’intervalle HA vers la gauche. Ce résultat met en évidence l’importance de tenir compte des changements du temps de conduction prétest dans l’évaluation de la fonction nodale, un paramètre négligé dans la plupart des études. Ce résultat montre aussi que chacun des deux indices a des limites dans sa capacité d’évaluer le temps de récupération nodale réel lorsque le temps de conduction prétest varie. Lorsque ces limites sont ignorées, comme c’est habituellement le cas, elles entraînent un biais dans l’évaluation des effets de fatigue et de facilitation. Une autre grande difficulté dans l’évaluation des propriétés fréquentielles du nœud AV concerne son état réfractaire. Deux indices sont utilisés pour évaluer la durée de la période réfractaire nodale. Le premier est la période réfractaire efficace (ERPN) définie comme l’intervalle AA le plus long qui n’est pas conduit par le nœud. Le deuxième est la période réfractaire fonctionnelle (FRPN) qui correspond à l’intervalle minimum entre deux activations mesurées à la sortie du nœud. Paradoxalement et pour des raisons obscures, l’ERPN augmente alors que la FRPN diminue avec l’augmentation de la fréquence cardiaque. De plus, ces effets varient grandement avec les sujets, les espèces et l’âge. À partir des mêmes données que pour les deux autres études, nous avons cherché dans la troisième étude l’origine des variations fréquentielles de l’ERPN et de la FRPN. Le raccourcissement du BCL prolonge l’ERPN mais n’affecte pas la FRPN. L’allongement de l’ERPN provient principalement d’un allongement du temps de conduction prétest. Un PTCL court en comparaison avec un BCL court allonge encore plus substantiellement le temps de conduction prétest mais raccourcit en même temps l’intervalle His-auriculaire, ces deux effets opposés s’additionnent pour produire un allongement net de l’ERPN. Le raccourcissement de l’intervalle His-auriculaire par le PTCL court est aussi entièrement responsable pour le raccourcissement de la FRPN. Nous avons aussi établi que, lorsque la composante du temps de conduction prétest est retirée de l’ERPN, un lien linéaire existe entre la FRPN et l’ERPN à cause de leur dépendance commune de l’intervalle His-auriculaire. Le raccourcissement combiné du BCL et du PTCL produit des effets nets prévisibles à partir de leurs effets individuels. Ces effets reproduisent ceux obtenus lors de protocoles prématurés conventionnels. Ces observations supportent un nouveau schème fonctionnel des variations fréquentielles de l’ERPN et de la FRPN à partir des effets distincts du BCL et du PTCL. Elles établissent aussi un nouveau lien entre les variations fréquentielles de l’ERPN et de la FRPN. En conclusion, la modulation fréquentielle de la fonction du nœud AV provient de la combinaison d’effets concurrents cumulatifs liés au cycle de base et non-cumulatifs liés au cycle prétest. Ces effets peuvent être interprétés de façon consistante indépendamment de l’indice de récupération en tenant compte des changements du temps de conduction au battement prétest. Les effets fréquentiels disparates sur l’ERPN et la FRPN sont aussi grandement liés aux changements du temps de conduction prétest. Lorsque l’analyse tient compte de ce facteur, l’ERPN et la FRPN montrent des variations parallèles fortement liées à celles de l’intervalle His-auriculaire. Le nouveau schème fonctionnel des propriétés fréquentielles du nœud AV supporté par nos données aidera à mieux cibler les études sur les mécanismes cellulaires contrôlant la modulation fréquentielle nodale. Nos données pourraient aider à l’interprétation et au contrôle des réponses nodales diverses associées aux tachyarythmies supraventriculaires et à leur traitement pharmacologique. En bref, nos travaux supportent une compréhension factuelle améliorée du comportement fréquentiel du nœud AV, un domaine aux applications multiples en rythmologie cardiaque.

The importance of wet-powder dynamic mechanical properties in understanding granulation

Granule impact deformation has long been recognised as important in determining whether or not two colliding granules will coalesce. Work in the last 10 years has highlighted the fact that viscous effects are significant in granulation. The relative strengths of different formulations can vary with strain rate. Therefore, traditional strength measurements made at pseudo-static conditions give no indication, even qualitatively, of how materials will behave at high strain rates, and hence are actually misleading when used to model granule coalescence. This means that new standard methods need to be developed for determining the strain rates encountered by granules inside industrial equipment and also for measuring the mechanical properties of granules at these strain rates. The constitutive equations used in theoretical models of granule coalescence also need to be extended to include strain-rate dependent components.

High strain rate constitutive modeling forhistorical structures subjected to blast loading

Doctoral Thesis Civil Engineering

An undergraduate level experiment on the synthesis of Au nanoparticles and their size-dependent optical and catalytic properties

The synthesis of gold nanoparticles (Au NPs) 15, 26, and 34 nm in diameter, followed by the investigation of their size-dependent optical and catalytic properties, is described herein as an undergraduate level experiment. The proposed experiment covers concepts on the synthesis, stabilization, and characterization of Au NPs, their size-dependent optical and catalytic properties at the nanoscale, chemical kinetics, and the role of a catalyst. The experiment should be performed by groups of two or three students in three lab sessions of 3 h each and organized as follows: i) synthesis of Au NPs of different sizes and investigation of their optical properties; ii) evaluation of their catalytic activity; and iii) data analysis and discussion. We believe that this activity enables students to integrate these multidisciplinary concepts in a single experiment as well as to become introduced/familiarized with an active research field and current literature in the areas of nanoparticle synthesis and catalysis.