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41.
Exfoliation and related microstructures in 2024 aluminum body skins on aging aircraft 总被引:3,自引:0,他引:3
Maria Posada L. E. Murr C. -S. Niou D. Roberson D. Little Roy Arrowood Debra George 《Materials Characterization》1997,38(4-5):259-272
Exfoliation, a directional attack along elongated grain boundaries, has been examined in some detail in rolled 2024 aluminum sheet and plate for KC-135 aging aircraft body skin samples utilizing optical (light) metallography, scanning electron microscopy, and transmission electron microscopy. A detailed analysis and comparison of precipitates within the grains and in the grain boundaries were performed, as well as an examination of elemental depletion profiles across grain boundaries. These observations suggest that corrosion-related anodic sites play a far less significant role in the propagation of exfoliation than do the hard corrosion products creating wedging stresses within the elongated grain boundaries, which seem to demonstrate unique and unusual structural or energetic features or both. 相似文献
42.
Burke M 《Environmental science & technology》1996,30(10):436A
Government. 相似文献
43.
Anna Sztaniszlav Magdolna Balla Maria Farkas-Jahnke Csaba Novák 《Journal of Materials Science》1990,25(5):2353-2358
The kinetics of solid-state reactions of powdered reactants were investigated by X-ray and by differential thermogravimetry in a magnetic field. Measurements revealed mutual diffusion of the Fe3+ and In3+ ions in the Fe2O3-In2O3 system heat treated for 3 h at 700 to 1400° C. Diffusion of indium into the Fe2O3 lattice caused a shift of the Curie temperature of the antiferromagnetic iron oxide towards lower temperatures. Only Caln2O4 was found between CaCO3 and In2O3 up to 1400° C. Also, in the Fe2O3-CaCO3-In2O3in system, the reaction started with the mutual diffusion of iron and indium and the forming of CaFe2O4. End-products were the magnetic -Ca4Fe14O25 and CaFe4O7, and the non-magnetic CaFe5O7, depending on the In3+ concentration. Indium stabilized the magnetic calcium-iron oxide structures, shifting their Curie temperatures towards lower values. 相似文献
44.
Maria da Graça Marcos J.A. Tenreiro MachadoT.-P. Azevedo-Perdicoúlis 《Applied Soft Computing》2012,12(2):589-599
Kinematic redundancy occurs when a manipulator possesses more degrees of freedom than those required to execute a given task. Several kinematic techniques for redundant manipulators control the gripper through the pseudo-inverse of the Jacobian, but lead to a kind of chaotic inner motion with unpredictable arm configurations. Such algorithms are not easy to adapt to optimization schemes and, moreover, often there are multiple optimization objectives that can conflict between them. Unlike single optimization, where one attempts to find the best solution, in multi-objective optimization there is no single solution that is optimum with respect to all indices. Therefore, trajectory planning of redundant robots remains an important area of research and more efficient optimization algorithms are needed. This paper presents a new technique to solve the inverse kinematics of redundant manipulators, using a multi-objective genetic algorithm. This scheme combines the closed-loop pseudo-inverse method with a multi-objective genetic algorithm to control the joint positions. Simulations for manipulators with three or four rotational joints, considering the optimization of two objectives in a workspace without and with obstacles are developed. The results reveal that it is possible to choose several solutions from the Pareto optimal front according to the importance of each individual objective. 相似文献
45.
Maria Bercea Silvia Ioan Bogdan C. Simionescu Cristofor I. Simionescu 《Polymer Bulletin》1992,27(5):571-575
Summary Systematic studies on solution properties of ultrahigh molecular weight polymers showed the existence of some special features as compared to usual length polymers. The paper discusses the possible appearance of branched structures in the polymerization process, structures able to influence the mentioned features. From experimental data on poly(methyl methacrylate), poly(butyl methacrylate) and polyacrylonitrile it appears that branching can be excluded, and the very high molecular weight domain considered may be responsible for the modifications observed in the molecular weight dependences on 2>, A2 or []. 相似文献
46.
López-Castejón Maria Luisa Hurtado Maria del Carmen de la Fuente Julia Mena Baltasar Bengoechea Carlos 《Iranian Polymer Journal》2021,30(7):723-735
Iranian Polymer Journal - The present work focuses on the assessment of the ability of porcine plasma protein (PPP) to be electrospun satisfactorily to form fibre mats, and their rheological and... 相似文献
47.
Kinga Ciechanowska Maria Pokornowska Anna Kurzyska-Kokorniak 《International journal of molecular sciences》2021,22(2)
Ribonuclease Dicer belongs to the family of RNase III endoribonucleases, the enzymes that specifically hydrolyze phosphodiester bonds found in double-stranded regions of RNAs. Dicer enzymes are mostly known for their essential role in the biogenesis of small regulatory RNAs. A typical Dicer-type RNase consists of a helicase domain, a domain of unknown function (DUF283), a PAZ (Piwi-Argonaute-Zwille) domain, two RNase III domains, and a double-stranded RNA binding domain; however, the domain composition of Dicers varies among species. Dicer and its homologues developed only in eukaryotes; nevertheless, the two enzymatic domains of Dicer, helicase and RNase III, display high sequence similarity to their prokaryotic orthologs. Evolutionary studies indicate that a combination of the helicase and RNase III domains in a single protein is a eukaryotic signature and is supposed to be one of the critical events that triggered the consolidation of the eukaryotic RNA interference. In this review, we provide the genetic insight into the domain organization and structure of Dicer proteins found in vertebrate and invertebrate animals, plants and fungi. We also discuss, in the context of the individual domains, domain deletion variants and partner proteins, a variety of Dicers’ functions not only related to small RNA biogenesis pathways. 相似文献
48.
Irina G. Bryndina Maria N. Shalagina Vladimir A. Protopopov Alexey V. Sekunov Andrey L. Zefirov Guzalia F. Zakirjanova Alexey M. Petrov 《International journal of molecular sciences》2021,22(5)
Muscle disuse and denervation leads to muscle atrophy, but underlying mechanisms can be different. Previously, we have found ceramide (Cer) accumulation and lipid raft disruption after acute hindlimb suspension (HS), a model of muscle disuse. Herein, using biochemical and fluorescent approaches the influence of unilateral denervation itself and in combination with short-term HS on membrane-related parameters of rat soleus muscle was studied. Denervation increased immunoexpression of sphingomyelinase and Cer in plasmalemmal regions, but decreased Cer content in the raft fraction and enhanced lipid raft integrity. Preliminary denervation suppressed (1) HS-induced Cer accumulation in plasmalemmal regions, shown for both nonraft and raft-fractions; (2) HS-mediated decrease in lipid raft integrity. Similar to denervation, inhibition of the sciatic nerve afferents with capsaicin itself increased Cer plasmalemmal immunoexpression, but attenuated the membrane-related effects of HS. Finally, both denervation and capsaicin treatment increased immunoexpression of proapoptotic protein Bax and inhibited HS-driven increase in antiapoptotic protein Bcl-2. Thus, denervation can increase lipid raft formation and attenuate HS-induced alterations probably due to decrease of Cer levels in the raft fraction. The effects of denervation could be at least partially caused by the loss of afferentation. The study points to the importance of motor and afferent inputs in control of Cer distribution and thereby stability of lipid rafts in the junctional and extrajunctional membranes of the muscle. 相似文献
49.
Asher Ornoy Maria Becker Liza Weinstein-Fudim Zivanit Ergaz 《International journal of molecular sciences》2021,22(6)
In spite of the huge progress in the treatment of diabetes mellitus, we are still in the situation that both pregestational (PGDM) and gestational diabetes (GDM) impose an additional risk to the embryo, fetus, and course of pregnancy. PGDM may increase the rate of congenital malformations, especially cardiac, nervous system, musculoskeletal system, and limbs. PGDM may interfere with fetal growth, often causing macrosomia, but in the presence of severe maternal complications, especially nephropathy, it may inhibit fetal growth. PGDM may also induce a variety of perinatal complications such as stillbirth and perinatal death, cardiomyopathy, respiratory morbidity, and perinatal asphyxia. GDM that generally develops in the second half of pregnancy induces similar but generally less severe complications. Their severity is higher with earlier onset of GDM and inversely correlated with the degree of glycemic control. Early initiation of GDM might even cause some increase in the rate of congenital malformations. Both PGDM and GDM may cause various motor and behavioral neurodevelopmental problems, including an increased incidence of attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Most complications are reduced in incidence and severity with the improvement in diabetic control. Mechanisms of diabetic-induced damage in pregnancy are related to maternal and fetal hyperglycemia, enhanced oxidative stress, epigenetic changes, and other, less defined, pathogenic mechanisms. 相似文献
50.
Prof. Alessia Carocci Dr. Mariagrazia Roselli Prof. Roberta Budriesi Dr. Matteo Micucci Prof. Jean-François Desaphy Dr. Concetta Altamura Dr. Maria Maddalena Cavalluzzi Dr. Maddalena Toma Dr. Giovanna Ilaria Passeri Dr. Gualtiero Milani Dr. Angelo Lovece Prof. Alessia Catalano Dr. Claudio Bruno Dr. Annalisa De Palma Prof. Filomena Corbo Prof. Carlo Franchini Prof. Solomon Habtemariam Prof. Giovanni Lentini 《ChemMedChem》2021,16(3):578-588
Under the hypothesis that cardioprotective agents might benefit from synergism between antiarrhythmic activity and antioxidant properties, a small series of mexiletine analogues were coupled with the 2,2,5,5-tetramethylpyrroline moiety, known for its antioxidant effect, in order to obtain dual-acting drugs potentially useful in the protection of the heart against post-ischemic reperfusion injury. The pyrroline derivatives reported herein were found to be more potent as antiarrhythmic agents than mexiletine and displayed antioxidant activity. The most interesting tetramethylpyrroline congener, a tert-butyl-substituted analogue, was at least 100 times more active as an antiarrhythmic than mexiletine. 相似文献