An analytical insight into the buckling paradox for circular cylindrical shells under axial and lateral loading

A large number of authors in the past have concluded that the flow theory of plasticity tends to overestimate significantly the buckling load for many problems of plates and shells in the plastic range, while the deformation theory generally provides much more accurate predictions and is consequently used in practical applications. Following previous numerical studies by the same authors focused on axially compressed cylinders, the present work presents an analytical investigation which comprises the broader and different case of nonproportional loading. The analytical results are discussed and compared with experimental and numerical findings and the reason for the apparent discrepancy on the basis of the so-called “buckling paradox” appears once again to lay in the overconstrained kinematics on the basis of the analytical and numerical approaches present in the literature

Le sfide della teoria: una conversazione con Fiorenzo Iuliano

Fiorenzo Iuliano è ricercatore di Lingue e letterature angloamericane presso l'Università di Cagliari. I suoi ambiti di ricerca comprendono la letteratura americana contemporanea (romanzo, graphic novel, rapporti tra letteratura e musica, Studi Culturali negli USA), gli studi di genere e gli studi sulla corporeità e la teoria letteraria. Al momento sta lavorando a uno studio sulla costruzione del mito culturale della città di Seattle negli anni Novanta

Epidemiología de la infección hospitalaria por Pseudomonas aeruginosa multirresistente en niños quemados críticos

El aumento de la prevalencia de Pseudomonas aeruginosa multirresistente ocasiona un desafío terapéutico constante en las Unidades de Cuidados Intensivos en general y de Quemados en particular. El presente trabajo epidemiológico reveló una tasa de infecciones hospitalarias de 18,91/1000 pacientes/día, con un total de 63 episodios. La tasa de bacteriemia asociada a vía venosa central (VVC) fue de 13,48/1000 días de uso de VVC, con una tasa de utilización del 80,6% y 19 episodios de bacteriemia. Los gérmenes más frecuentemente hallados en la infecciones hospitalarias fueron Pseudomonas aeruginosa, Fusarium spp y Acinetobacter spp (37,5%, 8,3% y 6,9%, respectivamente). Pseudomonas aeruginosa estuvo presente como microorganismo causal de infección hospitalaria en 27 casos, siendo multirresistente en todos y con sensibilidad exclusiva al colistin.Increasing prevalence of multiresistant Pseudomonas aeruginosa is a constant challenge in the Intensive Care Units in general and particularly those treating burned patients. This epidemiological research showed a rate of hospital infections of 18.91 for every 1000 day-patients (63 episodes). The average rate of bacteriemia associated with central venous route (VCV) was 13.48 per 1000 days using VCV. The use rate of VCV was 80.6% with a resulting 19 episodes of bacteriemia. The most frequently encountered germs of nosocomial infections were Pseudomonas aeruginosa, Acinetobacter spp and Fusarium spp (37.5%, 8.3% y 6.9%, respectively). Pseudomonas aeruginosa was found in 27 episodes as the etiology of infection being multidrugresistant in all cases with exclusive sensitivity to colistin

Heart rate reduction with esmolol is associated with improved arterial elastance in patients with septic shock: a prospective observational study

PURPOSE: Ventricular–arterial (V–A) decoupling decreases myocardial efficiency and is exacerbated by tachycardia that increases static arterial elastance (Ea). We thus investigated the effects of heart rate (HR) reduction on Ea in septic shock patients using the beta-blocker esmolol. We hypothesized that esmolol improves Ea by positively affecting the tone of arterial vessels and their responsiveness to HR-related changes in stroke volume (SV). METHODS: After at least 24 h of hemodynamic optimization, 45 septic shock patients, with an HR ≥95 bpm and requiring norepinephrine to maintain mean arterial pressure (MAP) ≥65 mmHg, received a titrated esmolol infusion to maintain HR between 80 and 94 bpm. Ea was calculated as MAP/SV. All measurements, including data from right heart catheterization, echocardiography, arterial waveform analysis, and norepinephrine requirements, were obtained at baseline and at 4 h after commencing esmolol. RESULTS: Esmolol reduced HR in all patients and this was associated with a decrease in Ea (2.19 ± 0.77 vs. 1.72 ± 0.52 mmHg l−1), arterial dP/dtmax (1.08 ± 0.32 vs. 0.89 ± 0.29 mmHg ms−1), and a parallel increase in SV (48 ± 14 vs. 59 ± 18 ml), all p < 0.05. Cardiac output and ejection fraction remained unchanged, whereas norepinephrine requirements were reduced (0.7 ± 0.7 to 0.58 ± 0.5 µg kg−1 min−1, p < 0.05). CONCLUSIONS: HR reduction with esmolol effectively improved Ea while allowing adequate systemic perfusion in patients with severe septic shock who remained tachycardic despite standard volume resuscitation. As Ea is a major determinant of V–A coupling, its reduction may contribute to improving cardiovascular efficiency in septic shock

Natural ventilation in urban areas : results of the European Project URBVENT Part 1: urban environment

The application of natural ventilation is more difficult in urban than in rural environment, especially in street canyons due to reduced wind velocity, urban heat island, noise and pollution, which are considered to be important barriers to the application of natural ventilation. The wind, temperature, noise attenuation and outdoor-indoor pollution transfer were measured in a large range of variation and various types of urban configuration. The models obtained can be used in the initial stages of building design in order to assess the viability of natural ventilation in urban environment, especially in street canyons

Numerical And Analytical Analyses Of High-Strength Steel Cellular Beams: A Discerning Approach

The behaviour of cellular beams made from normal and high strength steel with various geometries is investigated through a large number of finite element analyses and a simple mechanical model for the Web-Post Buckling (WPB) failure is developed and analysed in order to highlight the factors which influence its occurrence and development for both normal and High-Strength (HS) steels. The performed FE analyses and the proposed modelling, once calibrated, allow to shed some light on the characteristics of the phenomenon and to provide the basis of a reliable design method to predict shear buckling of web-post of cellular beams made both of mild and HS steel

A coupled optical-thermal-electrical model to predict the performance of hybrid PV/T-CCPC roof-top systems

A crossed compound parabolic concentrator (CCPC) is applied into a photovoltaic/thermal (PV/T) hybrid solar collector, i.e. concentrating PV/T (CPV/T) collector, to develop new hybrid roof-top CPV/T systems. However, to optimise the system configuration and operational parameters as well as to predict their performances, a coupled optical, thermal and electrical model is essential. We establish this model by integrating a number of submodels sourced from literature as well as from our recent work on incidence-dependent optical efficiency, six-parameter electrical model and scaling law for outdoor conditions. With the model, electrical performance and cell temperature are predicted on specific days for the roof-top systems installed in Glasgow, Penryn and Jaen. Results obtained by the proposed model reasonably agree with monitored data and it is also clarified that the systems operate under off-optimal operating condition. Long-term electric performance of the CPV/T systems is estimated as well. In addition, effects of transient terms in heat transfer and diffuse solar irradiance on electric energy are identified and discussed

A numerical investigation into the plastic buckling paradox for circular cylindrical shells under axial compression

It is widely accepted that for many buckling problems of plates and shells in the plastic range the flow theory of plasticity leads to a significant overestimation of the buckling stress while the deformation theory provides much more accurate predictions and is therefore generally recommended for use in practical applications. The present work aims to contribute to further understanding of the seeming differences between these two theories with particular regards to circular cylindrical shells subjected to axial compression. A clearer understanding of the two theories is established using accurate numerical examples and comparisons with some widely cited accurate physical test results. It is found that, contrary to common perception, by using a geometrically nonlinear finite element formulation with carefully determined and validated constitutive laws very good agreement between numerical and test results can be obtained in the case of the physically more sound flow theory of plasticity. The reasons underlying the apparent buckling paradox found in the literature regarding the application of deformation and flow theories and the different conclusions reached in this work are investigated and discussed in detail. © 2014 Elsevier Ltd

Truncated and Helix-Constrained Peptides with High Affinity and Specificity for the cFos Coiled-Coil of AP-1

Protein-based therapeutics feature large interacting surfaces. Protein folding endows structural stability to localised surface epitopes, imparting high affinity and target specificity upon interactions with binding partners. However, short synthetic peptides with sequences corresponding to such protein epitopes are unstructured in water and promiscuously bind to proteins with low affinity and specificity. Here we combine structural stability and target specificity of proteins, with low cost and rapid synthesis of small molecules, towards meeting the significant challenge of binding coiled coil proteins in transcriptional regulation. By iteratively truncating a Jun-based peptide from 37 to 22 residues, strategically incorporating i-->i+4 helix-inducing constraints, and positioning unnatural amino acids, we have produced short, water-stable, alpha-helical peptides that bind cFos. A three-dimensional NMR-derived structure for one peptide (24) confirmed a highly stable alpha-helix which was resistant to proteolytic degradation in serum. These short structured peptides are entropically pre-organized for binding with high affinity and specificity to cFos, a key component of the oncogenic transcriptional regulator Activator Protein-1 (AP-1). They competitively antagonized the cJun–cFos coiled-coil interaction. Truncating a Jun-based peptide from 37 to 22 residues decreased the binding enthalpy for cJun by ~9 kcal/mol, but this was compensated by increased conformational entropy (TDS ≤ 7.5 kcal/mol). This study demonstrates that rational design of short peptides constrained by alpha-helical cyclic pentapeptide modules is able to retain parental high helicity, as well as high affinity and specificity for cFos. These are important steps towards small antagonists of the cJun-cFos interaction that mediates gene transcription in cancer and inflammatory diseases