1,721,048 research outputs found
Methods to quantify biological contaminants in microalgae cultures
No full textMicroalgae cultivation processes are becoming increasingly used for food and feed production and for wastewaters treatment. Large part of laboratory experiments and industrial processes are carried out with microalgae cultivated in non-aseptic environments containing biological contaminants as bacteria, fungi, viruses and grazers. Such contaminants can significantly influence microalgae growth through interactions such as competition, parasitism, predation and mutualism. Accurate and selective quantification of contaminants and microalgae in terms of cell and biomass concentration and of elemental composition is fundamental to understand how and how much such interactions affect microalgae growth and the quality of the produced biomass. In this work a review is made about the main analytical methods that have been employed, and that might be potentially used in the future, to quantify microalgae and their biological contaminants in heterogeneous samples. Large part of data available about biological contaminants in microalgae cultures come from cell concentration analysis or from qualitative methods. Bacteria and grazers have been the mostly investigated contaminants, while less attention has been given to viruses and fungi. Flow cytometry and DNA analysis are two of the most powerful and promising techniques for cell concentration measurement, however relevant work is still required for protocols optimization, in particular to attain quantitative and reproducible methods. Biomass concentration and elemental composition of contaminants inside microalgae cultures has been scarcely investigated. For this aim, different innovative techniques for single cell mass and elemental composition analysis have been described, focusing on their potential application for microalgae samples
A fattening factor to quantify the accumulation ability of microorganisms under N-starvation
Full text linkMany microorganisms can accumulate biomass in the form of lipids and polysaccharides, which can be used for biofuels, bioplastics, food and feed. Some innovative bioprocesses exploit the competitive advantage provided by such accumulation ability, mainly under N-starvation, to select high-accumulating strains against biological contaminants, by using uncoupled nutrient feeding. However, there is no general and easily comparable parameter available to compare biomass accumulation ability among different microbial strains, which could measure the competitive advantage. Here, a parameter termed “fattening factor” (ηx) is described to quantify such strain-specific biomass accumulation ability in bacteria, yeasts and microalgae. This parameter measures how many fold a microbial population can increase its biomass just as the result of accumulation. It is derived from considerations about the main metabolic aspects of cells’ response to N-starvation, which induces variations in cell cycle, biomass production and biochemical composition. The fattening factor described here should be easily estimatable in N-starvation for every culturable microbial strain, by measuring the amount of accumulated biomass
Investigation on the Crashworthiness of a Composite Fuselage Barrel with Double–Double Designed Frames
No full textDouble–double (DD) laminates approach enables the design of mass-minimized composite structures with number and orientation of plies tailored on the acting loads. Thus, the investigation of the crashworthiness capabilities is crucial in assessing the airworthiness of DD designed structures. In this work, two composite fuselage barrel configurations with conventional and DD designed frames have been compared to study their crashworthiness performance during an impact event. Numerical results highlight that configurations with DD optimized frames exhibit performance in terms of crashworthiness and passive safety for passengers comparable to the one with conventional designed frames while reducing the structure's total mass by up to 13%
A Novel Approach for the Damage Tolerance Determination of Delaminated Stiffined Composite Panels
No full textUltrasound-assisted extraction of carbohydrates from microalgae
Full text linkMicroalgae are a promising new source of carbohydrates usable for several industrial applications in the food and biomaterial sector. Previous works on carbohydrate extraction from microalgae were mainly carried out by using destructive chemical hydrolysis, aiming at the extraction of simple sugars. Here in this work, a physical ultrasonication method was investigated to develop a process to extract microalgal carbohydrates in their polysaccharide form, as starch. To this end, different operative parameters were investigated: biomass concentration (3-6 g L-1), microalgae strain (Tetradesmus obliquus and Chlorella sp.), extraction time, amplitude (21-90 μm) and the configuration of the ultrasonication system (cyclic treatment, pulsed and continuous). The highest extractions were attained with higher amplitude (90 μm). The pulsed ultrasonication (ton/toff = 0.2) worked remarkably better than the continuous one, allowing to attain about 3 folds more carbohydrate extraction yield and consuming 6 folds less kWh per kg of extracted carbohydrates. The higher yield achieved with pulsed ultrasonication was related with a lower drop in the applied power during the ultrasonication treatment, which was -65 % with the continuous system and only -31 % with the pulsed one. The ultrasonication treatment induced a temperature increase up to 70 °C, that caused starch gelatinization and its solubilization in the recovered aqueous solution. Future studies should investigate better the effect of the ton/toff ratio, to limit the dead times (toff) of the process. The specific energy consumption was still too high for many practical applications; however, future optimizations on biomass concentration and operative temperature are expected to reduce remarkably the energy demand of the process
Numerical-Experimental Correlation of Interlaminar Damage Growth in Composite Structures: Setting Cohesive Zone Model Parameters
Full text linkComposite laminates are characterized by high mechanical in-plane properties while experiencing, on the contrary, a poor out-of-plane response. The composite laminates, indeed, are often highly vulnerable to interlaminar damages, also called "delaminations." One of the main techniques used for the numerical prediction of interlaminar damage onset and growth is the cohesive zone model (CZM). However, this approach is characterised by uncertainties in the definition of the parameters needed for the implementation of the cohesive behaviour in the numerical software. To overcome this issue, in the present paper, a numerical-experimental procedure for the calibration of material parameters governing the mechanical behaviour of CZM based on cohesive surface and cohesive element approaches is presented. Indeed, by comparing the results obtained from the double cantilever beam (DCB) and end-notched flexure (ENF) experimental tests with the corresponding numerical results, it has been possible to accurately calibrate the parameters of the numerical models needed to simulate the delamination growth phenomenon at coupon level
Integrated microalgae biomass production and olive mill wastewater biodegradation: optimization of the wastewater supply strategy
No full textOlive mill wastewater (OMW) was supplied to Scenedesmus sp. cultures to simultaneously achieve biomass production and wastewater biodegradation. Two OMW supply strategies were implemented to prevent the reduced growth performances that are attained, compared to photoautotrophic cultivation, when OMW is supplied at the beginning of cultivation (batch strategy). A fed-batch strategy including the gradual OMW supply yielded a biomass production equal to 0.86 g/L, while 1.4 g/L was attained by a two-stage strategy including OMW addition during nitrogen-starvation. OMW enhanced the carbohydrate accumulation (up to 44%) through the removal of OMW sugars (60–70%). About 55% OMW phenol removal was achieved by the fed-batch strategy when the phenol concentration was lower than 100 mg/L, and by the two-stage strategy when the heterotrophic stage lasted longer than 8–10 days. The illustrated results indicate that the OMW supply strategy can be purposefully tailored to regulate biomass production and OMW biodegradation
Use of PFA to determine design methods for composite stiffened panels with discrete damages
No full textNumerical, Experimental and Analytical Correlation for Predicting the Structural Behavior of Composite Structures under Impact
No full textIn the present work, numerical, experimental and analytical results regarding impact events on composite structure are presented. The test case consists in a classic 24 plies CAI specimen (100×150 mm) subjected to 10 J impact. The work can be divided into two phases. The first phase is finalized to the definition of a procedure able to provide a robust numerical model, which can simulate accurately the structural response of composite plates subjected to impact events. At this phase, the numerical results are compared with analytical ones. In the second phase, both inter- and intra-lamina failure are considered. Regarding the inter-laminar failure, an experimental-numerical procedure is defined in order to set the right parameters related to cohesive behaviour. For both phases, trade-off analyses on the main numerical parameters are performed. All numerical results are compared with experimental ones in terms of both energy balance and damaged area. © 2016 The Authors
Assessment of Progressive Failure Analysis Capabilities of Commercial FE Codes
No full textPurpose – The main objective of this work is to assess the current capabilities of different commercial finite element (FE) codes in simulating the progressive damage of composite structures under quasi-static loading condition in post-buckling regime.
Design/methodology/approach – Progressive failure analysis (PFA) methodologies, available in the investigated FE codes, were applied to a simple test case extracted from literature consisting in a holed composite plate loaded in compression.
Findings – Results of the simulations are significantly affected by the characteristic parameters needed to feed the degradation models implemented in each code. Such parameters, which often do not have a physical meaning, have to be necessarily set upon fitting activity with an experimental database at coupon level. Concerning the test case, all the codes were found able to capture the buckling load and the failure load with a good accuracy.
Originality/value – This paper would to give an insight into the PFA capabilities of different FE codes, providing the guidelines for setting the degradation model parameters which are of major interest
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