Experimental Investigation on Microstructure and Mechanical Properties of Direct Squeeze Cast Al–13%Si Alloy

Для литья под давлением характерно приложение давления к заготовке при ее затвердевании, вследствие чего активизируются различные физические процессы, которые влияютна металлургические свойства литых сплавов. Выполненное экспериментальное исследование свидетельствует о влиянии уровня давления на микроструктуру и механические характеристики сплава Al–13%Si. Показано, что давление при литье в интервале 0,1...100 МПа приводит к уменьшению зерен, улучшению прочностных свойств и повышению твердости по Виккерсу в центральной части образцов. При давлении 100...150 МПа наблюдаются высокие предварительные деформации при высокой температуре литья и укрупнение зерен, в результате чего ухудшаются прочностные свойства и уменьшается твердость. Анализ микрофотографий на электронном микроскопе показывает, что при давлении до 100 МПа механизм разрушения является более вязким, чем при повышенном давлении. Это позволяет оптимизировать уровень давления с целью предотвращения ухудшения свойств и ликвации материала в процессе литья под давлением.Для лиття під тиском характерно прикладення тиску до заготовки при її твердінні, в результаті чого активізуються різні физичні процеси, що впливають на металургійні властивості литих сплавів. Експериментальне дослідження свідчить про вплив рівня тиску намікроструктуру і механічні характеристики сплаву Al–13%Si. Показано, що тиск при литті в інтервалі 0,1...100 МПа призводить до зменшення зерен, покращанню міцнісних властивостей і підвищенню твердості по Віккерсу в центральній частині зразка. При дії тиску 100...150 МПа мають місце високі попередні деформації за високої температури лиття і збільшення зерен. У результаті цього погіршуються міцнісні властивості і зменшується твердість. Аналіз мікрофотографій на електронному мікроскопі показує, що при дії тиску до 100 МПа механізм руйнування є більш в’язким, ніж при підвищеному тиску. Це дозволяє оптимізувати рівень тиску з метою запобігання погіршення властивостей і ліквації матеріалу в процесі лиття під тиском

The effect of the process on mechanical properties of polylactic acid - date palm leaf fibers composite films produced by extrusion blowing

Biocomposite films prepared with melt compounding and film blowing have become a new trend in plastic research to deliver more eco-friendly packages. Polylactic acid (PLA) was melt compounded with minimally processed date palm leaf fiber (DPLF) and converted into films by blown film extrusion. The compounding was done in order to enhance the film mechanical properties in one hand, and to decrease the film production cost in the other hand. In this present study, a reference PLA film and films with 1%, 2%, and 5% of DPLF (weight %) were produced with different process parameters. The spatial variations in films thickness and lay flat width indicate that the addition of DPLF up to 2% enhances the bubble stability for the tested process parameters. However, the composite with 5% DPLF shows nearly the same processability window as the neat PLA. The structural and mechanical characterizations of films suggest a reinforcing effect of the PLA matrix up to 2% of fiber (with an optimum at 1%). Larger DPLF loading leads to depressed and more anisotropic mechanical properties, related to an increased density of defects at the fiber-PLA fragile interface and to a DPLF-induced enhanced PLA thermal degradation and amorphous phase orientatio

Modelling, control design, and analysis of the inner control's loops intended for single‐phase voltage‐controlled inverter‐based microgrid

In voltage-controlled voltage source inverters (VSIs)-based microgrids (MGs), the inner control is of prime interest task for guaranteeing safe and stable operation. In this paper, an in-depth investigation of the modelling, control design, and analysis of the voltage and current inner control loops intended for single-phase voltage-controlled VSIs is established. The main objective of this work is to provide a comprehensive study of the mathematical modelling, control design, and performance evaluation of the inner control's loops considering different proportional-integral (PI) controller types with and without compensation, and to determine the optimal scheme that can offer better performance in terms of implementation simplicity, robustness, and transient and steady-state responses. Thus, the mathematical closed-loop models of designed outer voltage and inner current control schemes based on PI, P, and feedforward controllers with and without compensation are, first, derived. Following this, a systematic and effective control design for tuning the different PI controllers’ parameters is proposed. Furthermore, an analysis revealing the performance of the designed voltage and current control schemes is provided. This analysis enables us to choose a P controller and PI feedforward controller for the current control loop and the voltage control loop, respectively. The chosen P and PI controllers should be simple; meanwhile, they should offer a wide bandwidth. A simulation study is carried out in MATLAB/Simulink software to assess the performance of the adopted inner control scheme for both linear and non-linear loads. In addition, an experimental setup, based on a TMS320F2837xD μC, of a single-phase VSI supplying linear and non-linear loads is built to verify the effectiveness and the robustness of the adopted inner controller. The results demonstrated: (1) the necessity of introducing the compensation term, which is responsible for offering control improvement against voltage perturbation, (2) the high tracking performance of the chosen controller in terms of dynamic and steady-state responses as well as its simplicity of implementation

An investigation by EXAFS of local atomic structure in an Mg-Nd alloy after processing by high-pressure torsion and ageing.

The local atomic structure of an Mg-1.44Nd (wt.%) alloy was investigated after solution annealing, high-pressure torsion (HPT) processing up to 1 and 10 turns and ageing at 250 °C for 5 h using X-ray absorption fine structure (XAFS) measurements at the Nd LIII-edge. The results show that HPT processing has no effect on the atomic structure around Nd atoms compared to the unprocessed state, whereas ageing at 250 °C for 5 h induces a significant modification in the coordination number and interatomic distances around the Nd atoms. These variations are analyzed based on the correlations between precipitation, defects and atomic mobility of the chemical species

Nonlinear characterization of a bistable energy harvester dynamical system

International audienceThis chapter explores the nonlinear dynamics of a piezo-magneto-elastic bistable energy device system regards the influence of external forcing parameters influence on system response. Time series, Poincaré maps, phase space trajectories, and bifurcation diagrams are employed in order to reveals system dynamics complexity and nonlinear effects, such as chaos incidence and hysteresis

MEDLEM database, a data collection on large elasmobranchs in the Mediterranean and Black Seas

The Mediterranean Large Elasmobranchs Monitoring (MEDLEM) database contains more than 3,000 records (with more than 4,000 individuals) of large elasmobranch species from 21 different countries around the Mediterranean and Black seas, observed from 1666 to 2017. The principal species included in the archive are the devil ray (1,868 individuals), the basking shark (935 individuals), the blue shark (622 individuals), and the great white shark (342 individuals). In the last decades, other species such as the thresher shark (187 individuals), the shortfin mako (180 individuals), and the spiny butterfly ray (138) were reported with increasing frequency. This was possibly due to increased public awareness on the conservation status of sharks, and the consequent development of new monitoring programs. MEDLEM does not have homogeneous reporting coverage throughout the Mediterranean and Black seas and it should be considered as a database of observed species presence. Scientific monitoring efforts in the south-eastern Mediterranean and Black seas are generally lower than in the northern sectors and the absence of some species in our database does not imply their actual absence in these regions. However, the available data allowed us to analyse the frequency and spatial distribution of records, the size frequencies for a few selected the available data allowed us to analyse the frequency and spatial distribution of records, the size frequencies for a few selected species, the overall area coverage, and which species are involved as bycatch by different fishing gears

Beta-thalassemia

Beta-thalassemias are a group of hereditary blood disorders characterized by anomalies in the synthesis of the beta chains of hemoglobin resulting in variable phenotypes ranging from severe anemia to clinically asymptomatic individuals. The total annual incidence of symptomatic individuals is estimated at 1 in 100,000 throughout the world and 1 in 10,000 people in the European Union. Three main forms have been described: thalassemia major, thalassemia intermedia and thalassemia minor. Individuals with thalassemia major usually present within the first two years of life with severe anemia, requiring regular red blood cell (RBC) transfusions. Findings in untreated or poorly transfused individuals with thalassemia major, as seen in some developing countries, are growth retardation, pallor, jaundice, poor musculature, hepatosplenomegaly, leg ulcers, development of masses from extramedullary hematopoiesis, and skeletal changes that result from expansion of the bone marrow. Regular transfusion therapy leads to iron overload-related complications including endocrine complication (growth retardation, failure of sexual maturation, diabetes mellitus, and insufficiency of the parathyroid, thyroid, pituitary, and less commonly, adrenal glands), dilated myocardiopathy, liver fibrosis and cirrhosis). Patients with thalassemia intermedia present later in life with moderate anemia and do not require regular transfusions. Main clinical features in these patients are hypertrophy of erythroid marrow with medullary and extramedullary hematopoiesis and its complications (osteoporosis, masses of erythropoietic tissue that primarily affect the spleen, liver, lymph nodes, chest and spine, and bone deformities and typical facial changes), gallstones, painful leg ulcers and increased predisposition to thrombosis. Thalassemia minor is clinically asymptomatic but some subjects may have moderate anemia. Beta-thalassemias are caused by point mutations or, more rarely, deletions in the beta globin gene on chromosome 11, leading to reduced (beta+) or absent (beta0) synthesis of the beta chains of hemoglobin (Hb). Transmission is autosomal recessive; however, dominant mutations have also been reported. Diagnosis of thalassemia is based on hematologic and molecular genetic testing. Differential diagnosis is usually straightforward but may include genetic sideroblastic anemias, congenital dyserythropoietic anemias, and other conditions with high levels of HbF (such as juvenile myelomonocytic leukemia and aplastic anemia). Genetic counseling is recommended and prenatal diagnosis may be offered. Treatment of thalassemia major includes regular RBC transfusions, iron chelation and management of secondary complications of iron overload. In some circumstances, spleen removal may be required. Bone marrow transplantation remains the only definitive cure currently available. Individuals with thalassemia intermedia may require splenectomy, folic acid supplementation, treatment of extramedullary erythropoietic masses and leg ulcers, prevention and therapy of thromboembolic events. Prognosis for individuals with beta-thalassemia has improved substantially in the last 20 years following recent medical advances in transfusion, iron chelation and bone marrow transplantation therapy. However, cardiac disease remains the main cause of death in patients with iron overload

Tracking Signals of Change in Mediterranean Fish Diversity Based on Local Ecological Knowledge

One of the expected effects of global change is increased variability in the abundance and distribution of living organisms, but information at the appropriate temporal and geographical scales is often lacking to observe these patterns. Here we use local knowledge as an alternative information source to study some emerging changes in Mediterranean fish diversity. A pilot study of thirty-two fishermen was conducted in 2009 from four Mediterranean locations along a south-north gradient. Semi-quantitative survey information on changes in species abundance was recorded by year and suggests that 59 fish species belonging to 35 families have experienced changes in their abundance. We distinguished species that increased from species that decreased or fluctuated. Multivariate analysis revealed significant differences between these three groups of species, as well as significant variation between the study locations. A trend for thermophilic taxa to increase was recorded at all the study locations. The Carangidae and the Sphyraenidae families typically were found to increase over time, while Scombridae and Clupeidae were generally identified as decreasing and Fistularidae and Scaridae appeared to fluctuate in abundance. Our initial findings strongly suggest the northward expansion of termophilic species whose occurrence in the northern Mediterranean has only been noted previously by occasional records in the scientific literature