1,354,784 research outputs found
Fatigue limit evaluation of a stainless steel using thermal data analysis
No full textFatigue is an irreversible process, accompanied by microstructural changes, localized plastic strains and energy dissipation. The temperature increase of a metallic material undergoing a fatigue test is a manifestation of the thermal energy dissipation and it was experimentally observed that the higher the applied stress amplitude the more pronounced the temperature increase of the material. Moreover, the trend of the observed temperature increase versus the applied stress amplitude presents a more or less abrupt positive change at a certain stress level. This characteristic stress amplitude was associated to the material fatigue limit [1-7]. Since the load-increasing tests are fast and a single specimens can be used to estimate the material fatigue limit, Risitano and co-workers set-up a rapid experimental methodology to determine the fatigue limit based on load-increasing tests monitored with an infrared camera, according to the so-called Risitano method [5].
It is known that due to plasticity, the stress amplitude and the material temperature waves present a phase shift. Therefore, taking advantage of the lock-in thermography, temperature oscillations due to dissipated energy, T2, can be obtained as the component having double frequency of the load signal sine wave by using the classical Fourier analysis, as suggest by Krapez et al [8]. They proposed to use T2, instead of the stabilized material temperature measured during a fatigue test in order to estimate the material fatigue limit. However, they noticed that the applicability of the method depends on the material under analysis. In particular, satisfactory results were found in the case of AISI 1050 steel and AISI 316L stainless steel, while the approach was useless while investigating the fatigue behavior of 7010 aluminum alloy, since temperature signal associated with the dissipated energy was very weak in relation to the available experimental equipment.
Aaki et al [9] proposed to use the dissipated energy, evaluated by using the lock-in thermography, to assess the material fatigue limit. They pointed out that satisfactory results were found in the case of AISI 316L, while in the case of AISI 304 the fatigue limit estimated by dissipated energy measurements provided a conservative value as compared to that evaluated by means of conventional fatigue test.
The phase shift angle was proposed as a suitable damage index for the rapid determination of material fatigue limit by Shiozawa et al [10]. They validated the approach against experimental results obtained from AISI 306L stainless steel specimens and noticed a satisfactory agreement with the fatigue limit determined by the conventional stair-case tests. Recently, Shiozawa et al [11] proposed a new experimental technique for fatigue limit estimation based on the phase 2f lock-in infrared method, where a single fatigue test was performed on AISI 316 steel specimens by increasing the applied stress amplitude, a, and by measuring the in-creasing rate of the dissipated energy, dq/da. By plotting dq/da versus a, an abrupt increase is seen when a exceeds the material fatigue limit.
Meneghetti [12] proposed an experimental technique for the direct evaluation of the heat energy density per cycle dissipated by a material undergoing a fatigue tests (the Q parameter). Q can be easily evaluated by stopping the fatigue test at t = t* after thermal equilibrium has been reached and by measuring the cooling gradient immediately after t*. Originally adopted to rationalise the notch effect in finite-life fatigue of stainless steel specimens [13], it is envisaged that the specific heat loss Q may be used also to estimate the fatigue limit.
This paper analyses all previous thermal methods for the rapid experimental estimation of the fatigue limit. In particular, the rapid engineering techniques proposed by La Rosa and Risitano [5], by Shiozawa et al [10] as well as by using the Q parameter [12] will be applied to estimate the fatigue limit of cold-drawn AISI 304L stainless steel bars and critical issues in practical applications of the analysed techniques will be singled out
Comparison of Experimental Thermal Methods for the Fatigue Limit Evaluation of a Stainless Steel
Get PDFThis paper regards the rapid determination of fatigue limit by using thermal data analysis.
Dierent approaches available in the literature to estimate the fatigue limit of cold-drawn AISI
304L bars are analyzed and compared, namely, temperature- and energy-based methods. Among
the temperature-based approaches, the Risitano Method (RM) and the method based on material
temperature evolution recorded during a static tensile test were analyzed. Regarding the energy-based
approaches, the input mechanical energy density stored in the material per cycle (i.e., the area of the
hysteresis loop), the heat energy dissipated by the material to the surroundings per cycle, and the
“2nd-harmonic-based” methods were considered. It was found that for the material analyzed, all the
considered energy-based approaches provided a very good engineering estimation of the material
fatigue limit compared to a staircase test
Determination of fatigue limit by static thermographic method and classic thermographic method on notched specimens
Get PDFThe aim of the present work is to investigate the possibility to evaluate the fatigue limit of such a component through the so-called Static Thermographic Method (STM). This new approach has been proposed in 2013 by Risitano and Risitano to determinate the fatigue limit of metallic materials through static tensile tests. Investigating the trend of the surface temperature of the material during static tensile test, the method proposes to correlate the first deviation from linearity of the surface temperature to a damage limit that has been proven to have relation with the fatigue limit. Static tensile tests at different stress rate have been carried out on V-notched specimens. Stepwise fatigue tests have been carried out in order to apply the classic Thermographic Method that has been hugely validated to determinate the fatigue limit of metallic components. Static tests at different stress rate showed that the method is dependent on this parameter; anyway, this dependence does not affect the results achieved in terms of fatigue limit. The experimental results showed a good agreement with the energetic methods considered in the present work
Paroxysmal nocturnal hemoglobinuria: pathophysiology, natural history and treatment options in the era of biological agents
No full textAntonio M Risitano, Bruno RotoliHematology, Department of Biochemistry and Medical Biotechnologies, Federico II University of Naples, ItalyAbstract: Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal non-malignant hematological disease characterized by the expansion of hematopoietic stem cells (HSCs) and progeny mature cells, whose surfaces lack all the proteins linked through the glycosyl-phosphatidyl inositol anchor. This defect arises from an acquired somatic mutation in the X-linked phosphatidyl-inositol glycan class A gene, with subsequent clonal expansion of the mutated HSCs as a result of a concomitant, likely immune-mediated, selective pressure. The disease is characterized by complement-mediated chronic intravascular hemolysis, resulting in hemolytic anemia and hemosiderinuria; capricious exacerbations lead to recurrent gross hemoglobinuria. Additional cardinal manifestations of PNH are a variable degree of bone marrow failure and an intrinsic propensity to thromboembolic events. The disease is markedly invalidating, with chronic symptoms requiring supportive therapy − usually including periodical transfusions; possible life-threatening complications may also ensue. The biology of PNH has been progressively elucidated in the past few years, but therapeutic strategies remained unsatisfactory for decades, the only exception being stem cell transplantation, which is restricted to selected patients and retains significant morbidity and mortality. Recently, a biological agent to treat PNH has been developed − the terminal complement inhibitor eculizumab − which has been tested in a number of clinical trials, with exciting results. All the data from worldwide clinical trials confirm that eculizumab radically modifies the symptoms, the biology, and the natural history of PNH, strongly improving the quality of life of PNH patients.Keywords: paroxysmal nocturnal hemoglobinuria, GPI-AP, PIG-A, complement, eculizuma
Stability of intramolecular DNA quadruplexes: comparison with DNA duplexes
No full textWe have determined the stability of intramolecular quadruplexes that are formed by a variety of G-rich sequences, using oligonucleotides containing appropriately placed fluorophores and quenchers. The stability of these quadruplexes is compared with that of the DNA duplexes that are formed on addition of complementary C-rich oligonucleotides. We find that the linkers joining the G-tracts are not essential for folding and can be replaced with nonnucleosidic moieties, though their sequence composition profoundly affects quadruplex stability. Although the human telomere repeat sequence d[G(3)(TTAG(3))(3)] folds into a quadruplex structure, this forms a duplex in the presence of the complementary C-rich strand at physiological conditions. The Tetrahymena sequence d[G(4)(T(2)G(4))(3)], the sequence d[G(3)(T(2)G(3))(3)], and sequences related to regions of the c-myc promoter d(G(4)AG(4)T)(2) and d(G(4)AG(3)T)(2) preferentially adopt the quadruplex form in potassium-containing buffers, even in the presence of a 50-fold excess of their complementary C-rich strands, though the duplex predominates in the presence of sodium. The HIV integrase inhibitor d[G(3)(TG(3))(3)] forms an extremely stable quadruplex which is not affected by addition of a 50-fold excess of the complementary C-rich strand in both potassium- and sodium-containing buffers. Replacing the TTA loops of the human telomeric repeat with AAA causes a large decrease in quadruplex stability, though a sequence with AAA in the first loop and TTT in the second and third loops is slightly more stable
Influence of loop size on the stability of intramolecular DNA quadruplexes
No full textWe have determined the stability of intramolecular DNA quadruplexes in which the four G(3)-tracts are connected by non-nucleosidic linkers containing propanediol, octanediol or hexaethylene glycol, replacing the TTA loops in the human telomeric repeat sequence. We find that these sequences all fold to form intramolecular complexes, which are stabilized by lithium < sodium < potassium. Quadruplex stability increases in the order propanediol < hexaethylene glycol < octanediol. The shallower shape of the melting profile with propanediol linkers and its lower dependency on potassium concentration suggests that this complex contains fewer stacks of G-quartets. The sequence with octanediol linkers displays a biphasic melting profile, suggesting that it can adopt more than one stable structure. All these complexes display melting temperatures above 310 K in the presence of 10 mM lithium, without added potassium, in contrast to the telomeric repeat sequence. These complexes also fold much faster than the telomeric repeat and there is little or no hysteresis between their melting and annealing profiles. In contrast, the human telomeric repeat sequence and a complex containing two hexaethylene glycol groups in each loop, are less stable and fold more slowly. The melting and annealing profiles for the latter sequence show significant differences, even when heated at 0.2degreesC min(-1). CD spectra for the oligonucleotides containing non-nucleosidic linkers show positive maxima at 264 nm, with negative minima similar to244 nm, which are characteristic of parallel quadruplex structures. These results show that the structure and stability of intramolecular quadruplexes is profoundly influenced by the length and composition of the loops. <br/
Inosine substitutions demonstrate that intramolecular DNA quadruplexes adopt different conformations in the presence of sodium and potassium
No full textWe have examined the stability of fluorescently-labelled oligonucleotides that are based on the human telomeric repeat [(GGGTTA)3GGG], in which one of the guanines in turn is substituted with inosine. We show that the relative stability of the substitutions is different in the presence of sodium and potassium. The data for potassium suggest a parallel arrangement of the strands, while the sodium form is mixed parallel and antiparallel.Graphical abstract
The relative stability of intramolecular quadruplexes containing inosine substitutions is different in sodium and potassium
T-PLL: Harmonizing criteria for research
No full textIn this issue of Blood, Staber et al report the initial activities of the newly created T-cell prolymphocytic leukemia (T-PLL) International Study Group (TPLL-ISG), which established consensus criteria for diagnosis, staging, and treatment response assessment of T-PLL.1
How do firms process info? Monitoring brand equity drivers in Food and Beverage Sector
No full textThe main purpose of this chapter is to show how to set a quantitative analysis of consumer behavior in the food and beverage industry and how the results from such analysis could be entered into producers’ decision making. The goal is to bridge the gap between theoretical research and practical needs of companies to improve their performance. The theoretical framework is the analysis of the relations among key brand equity drivers (brand experience and brand trust) and consumers’ behavior intentions (intent to buy, intent to use word-of-mouth, willingness to accept brand extensions). The empirical research proposes a structural equation model for analyzing such relations. The case study concerns the consumption of two product categories: coffee (nonalcoholic drink) and beer (alcoholic drink). Particular attention is paid to the interpretation of results and their use for managerial implications
Infectious Agents and Bone Marrow Failure: A Causal or a Casual Connection?
No full textAcquired bone marrow failure (BMF) syndromes are considered immune-mediated disorders because hematological recovery after immunosuppressive therapies is the strongest indirect evidence of the involvement of immune cells in marrow failure development. Among pathophysiology hypotheses, immune derangement after chronic antigen exposure or cross-reactivity between viral particles and cellular components are the most accepted; however, epitopes against whom these lymphocytes are directed to remain unknown. In this study, we showed that BMF-associated immunodominant clones, namely the most represented T cells carrying an antigen-specific T-cell receptor (TCR) sequence in a random pool, were frequently associated with those described in various infectious diseases, such as cytomegalovirus (CMV) and Mycobacterium tuberculosis infection. We hypothesize that these pathogens might elicit an autoimmune response triggered by cross-reactivity between pathogen-related components and proteins or might be expanded as an unspecific response to a global immune dysregulation during BMF. However, those frequent intracellular pathogens might not only be passengers in marrow failure development, while playing a central role in starting the autoimmune response against hematopoietic stem cells
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