868 research outputs found
A Dynamic Matrix for the Study of Free Vibrations of Thin Circular Cylindrical Shells under Different Boundary Conditions
Although free vibrations of thin-walled cylinders have been extensively addressed in the
relevant literature, finding a good balance between accuracy and simplicity of the procedures used for
natural frequency assessment is still an open issue. This paper proposes a novel approach with a high
potential for practical application for rapid esteem of natural frequencies of thin-walled cylinders
under different boundary conditions. Starting from Donnell–Mushtari’s shell theory, the differential
problem is simplified by using the principle of virtual work and introducing the flexural waveforms
of a beam as constrained as the cylinder. Hence, the formulation is reduced to the eigenvalue problem
of an equivalent 3 3 dynamic matrix, which depends on the cylinder geometry, material, and
boundary conditions. Several comparisons with experimental, numerical, and analytical approaches
are presented to prove model reliability and practical interest. An excellent balance between fast
usability and accuracy is achieved. The user-friendliness of the model makes it suitable to be
implemented during the design stage without requiring any deep knowledge of the topic
Power Losses Minimization for Optimal Operating Maps in Power-Split HEVs: A Case Study on the Chevrolet Volt
The power-split architecture is the most promising hybrid electric powertrain. However, a
real advantage in energy saving while maintaining high performance can be achieved only by the
implementation of a proper energy management strategy. This requires an optimized functional
design before and a comprehensive analysis of the powertrain losses after, which could be rather
challenging owing to the constructive complexity of the power-split transmission, especially for multimode
architecture with multiple planetary gearing. This difficulty was overcome by a dimensionless
model, already available in the literature, that enables the analysis of any power-split transmission,
even in full electric operation. This paper relies on this approach to find the operating points of the
internal combustion engine and both electric machines which minimize the total power losses. This
optimization is carried out for given vehicle speed and demanded torque, by supposing different
scenarios in respect of the battery capability of providing or gathering power. The efficiency of the
thermal engine and the electric machines is considered, as well as the transmission mechanical power
losses. The aim is to provide a global efficiency map that can be exploited to extract data for the
implementation of the most suitable real-time control strategy. As a case study, the procedure is
applied to the multi-mode power-split system of the Chevrolet Volt
Generic features of the fluctuation dissipation relation in coarsening systems
The integrated response function in phase-ordering systems with scalar,
vector, conserved and non conserved order parameter is studied at various space
dimensionalities. Assuming scaling of the aging contribution we obtain, by numerical simulations
and analytical arguments, the phenomenological formula describing the
dimensionality dependence of in all cases considered. The primary
result is that vanishes continuously as approaches the lower
critical dimensionality . This implies that i) the existence of a non
trivial fluctuation dissipation relation and ii) the failure of the connection
between statics and dynamics are generic features of phase ordering at .Comment: 6 pages, 5 figure
The Epoch of Reionization in Warm Dark Matter Scenarios
In this paper we investigate how the Reionization process is affected by early galaxy formation in different cosmological scenarios. We use a semi-analytic model with suppressed initial power spectra to obtain the UV Luminosity Function in thermal Warm Dark Matter and sterile neutrino cosmologies. We retrace the ionization history of intergalactic medium with hot stellar emission only, exploiting fixed and variable photons escape fraction models (fesc). For each cosmology, we find an upper limit to fixed fesc, which guarantees the completion of the process at z<6.7. The analysis is tested with two limit hypothesis on high-z ionized hydrogen volume fraction, comparing our predictions with observational results
A Survey on the Distribution of Ovothiol and ovoA Gene Expression in Different Tissues and Cells: A Comparative Analysis in Sea Urchins and Mussels
Ovothiols are histidine-derived thiols produced by a variety of marine invertebrates, protists and bacteria. These compounds, which are among the strongest natural antioxidants, are involved in controlling the cellular redox balance due to their redox exchange with glutathione. Although ovothiols were initially reported as protective agents against environmental stressors, new evidence suggests that they can also act as pheromones and participate in fundamental biological processes such as embryogenesis. To get further insight into the biological roles of ovothiols, we compared ovothiol biosynthesis in the sea urchin Paracentrotus lividus and in the mussel Mytilus galloprovincialis, the two species that represent the richest sources of these compounds among marine invertebrates. Ovothiol content was measured in different tissues and in the immune cells from both species and the expression levels of ovoA, the gene responsible for ovothiol biosynthesis, was inferred from publicly available transcriptomes. A comparative analysis of ovothiol biosynthesis in the two species allowed the identification of the tissues and cells synthesizing the metabolite and highlighted analogies and differences between sea urchins and mussels. By improving our knowledge on the biological roles of ovothiols and pointing out the existence of sustainable natural sources for their isolation, this study provides the basis for future biotechnological investigations on these valuable compounds
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