Desarrollo de un dispositivo de liberación para la industria aeroespacial basado en una aleación con memoria de forma de NiTi.

Los dispositivos liberadores son utilizados en los satélites para desplegar los paneles solares, antenas y otros apéndices en las etapas iniciales de su puesta en órbita. En la actualidad, muchos de estos dispositivos tienen actuadores activados con cargas pirotécnicas. Esto trae algunas desventajas: niveles de shock elevados sobre los componentes cercanos, no son reutilizables y no son seguros de manipular. Por ello, es que desde hace unos años se están realizando importantes esfuerzos para desarrollar dispositivos no-pirotécnicos. En este trabajo se realiza el desarrollo de un dispositivo liberador que utiliza como actuador un cilindro tubular de una Aleación de Memoria de Forma (SMA, del inglés Shape Memory Alloys) de NiTi. Las SMAs tienen la posibilidad de deformarse por debajo de determinada temperatura y luego al calentarse, recuperar su forma original. Al restringir mecánicamente la trayectoria de recuperación, la aleación genera un esfuerzo mecánico. En el presente trabajo se caracteriza esta aleación, recurriendo a diversos tratamientos térmicos para obtener las propiedades deseadas. La liberación del conjunto se produce cuando el elemento de unión entre las piezas, el cual consiste en un bulón con una entalla circunferencial, se fractura debido al estiramiento de un actuador de NiTi previamente comprimido. Dada la importancia del bulón, se estudiaron diversos materiales para el mismo. Además se analizó el efecto de la geometría de la entalla y la profundidad de la misma. Finalmente, se realizaron pruebas de integración entre el actuador de SMA, el bulón y otros elementos auxiliares. Se pudo probar el funcionamiento del conjunto con éxito.

Desarrollo de un dispositivo de liberación para la industria aeroespacial basado en una aleación con memoria de forma de NiTi.

Los dispositivos liberadores son utilizados en los satélites para desplegar los paneles solares, antenas y otros apéndices en las etapas iniciales de su puesta en órbita. En la actualidad, muchos de estos dispositivos tienen actuadores activados con cargas pirotécnicas. Esto trae algunas desventajas: niveles de shock elevados sobre los componentes cercanos, no son reutilizables y no son seguros de manipular. Por ello, es que desde hace unos años se están realizando importantes esfuerzos para desarrollar dispositivos no-pirotécnicos. En este trabajo se realiza el desarrollo de un dispositivo liberador que utiliza como actuador un cilindro tubular de una Aleación de Memoria de Forma (SMA, del inglés Shape Memory Alloys) de NiTi. Las SMAs tienen la posibilidad de deformarse por debajo de determinada temperatura y luego al calentarse, recuperar su forma original. Al restringir mecánicamente la trayectoria de recuperación, la aleación genera un esfuerzo mecánico. En el presente trabajo se caracteriza esta aleación, recurriendo a diversos tratamientos térmicos para obtener las propiedades deseadas. La liberación del conjunto se produce cuando el elemento de unión entre las piezas, el cual consiste en un bulón con una entalla circunferencial, se fractura debido al estiramiento de un actuador de NiTi previamente comprimido. Dada la importancia del bulón, se estudiaron diversos materiales para el mismo. Además se analizó el efecto de la geometría de la entalla y la profundidad de la misma. Finalmente, se realizaron pruebas de integración entre el actuador de SMA, el bulón y otros elementos auxiliares. Se pudo probar el funcionamiento del conjunto con éxito.

Effect of the time-of-day of training on explicit memory

Studies have shown a time-of-day of training effect on long-term explicit memory with a greater effect being shown in the afternoon than in the morning. However, these studies did not control the chronotype variable. Therefore, the purpose of this study was to assess if the time-of-day effect on explicit memory would continue if this variable were controlled, in addition to identifying the occurrence of a possible synchronic effect. A total of 68 undergraduates were classified as morning, intermediate, or afternoon types. The subjects listened to a list of 10 words during the training phase and immediately performed a recognition task, a procedure which they repeated twice. One week later, they underwent an unannounced recognition test. The target list and the distractor words were the same in all series. The subjects were allocated to two groups according to acquisition time: a morning group (N = 32), and an afternoon group (N = 36). One week later, some of the subjects in each of these groups were subjected to a test in the morning (N = 35) or in the afternoon (N = 33). The groups had similar chronotypes. Long-term explicit memory performance was not affected by test time-of-day or by chronotype. However, there was a training time-of-day effect [F (1,56) = 53.667; P = 0.009] with better performance for those who trained in the afternoon. Our data indicated that the advantage of training in the afternoon for long-term memory performance does not depend on chronotype and also that this performance is not affected by the synchronic effect.

Effect of temperature and strain rate on the compressive behaviour of supramolecular polyurethane

Supramolecular polyurethanes (SPUs) possess thermoresponsive and thermoreversible properties, and those characteristics are highly desirable in both bulk commodity and value-added applications such as adhesives, shape-memory materials, healable coatings and lightweight, impact-resistant structures (e.g. protection for mobile electronics). A better understanding of the mechanical properties, especially the rate and temperature sensitivity, of these materials are required to assess their suitability for different applications. In this paper, a newly developed SPU with tuneable thermal properties was studied, and the response of this SPU to compressive loading over strain rates from 10−3 to 104 s−1 was presented. Furthermore, the effect of temperature on the mechanical response was also demonstrated. The sample was tested using an Instron mechanical testing machine for quasi-static loading, a home-made hydraulic system for moderate rates and a traditional split Hopkinson pressure bars (SHPBs) for high strain rates. Results showed that the compression stress-strain behaviour was affected significantly by the thermoresponsive nature of SPU, but that, as expected for polymeric materials, the general trends of the temperature and the rate dependence mirror each other. However, this behaviour is more complicated than observed for many other polymeric materials, as a result of the richer range of transitions that influence the behaviour over the range of temperatures and strain rates tested.

Effect of Ag addition on the martensitic phase of the Cu-10 wt.% Al alloy

Thermal analysis and compression tests at room temperature have been carried out for Cu-10 wt.% Al and Cu-10 wt.% Al-10 wt.% Ag alloys samples. The results indicate that the decomposition reaction of the (beta(1)) parent phase is decreased suppressed and a martensite stabilization effect can be induced by Ag addition. The Cu-Al-Ag alloy shows some degree of shape memory capacity. (C) 2007 Elsevier B.V. All rights reserved.

Write-erase and read paper memory transistor

Applied Physics Letters, Vol.93, issue 20

Liquid crystal mobility and PDLC memory effects

Dissertation presented at Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa to obtain the Degree of Master in Chemical and Biochemical Engineering

Otimização da análise isotópica de UF6 utilizando-se a técnica de espectrometria de massas por quadrupolo

A procedure for determining of the isotope ratio 235U/238U in UF6 samples was established using a quadrupole mass spectrometer with ionization by electron impact. The following items were optimized in the spectrometer: the parameters in the ion source that provided the most intense peak, with good shape, for the most abundant isotope; the resolution that reduced the non linear effects and the number of analytical cycles that reduced the uncertainty in the results. The measurement process was characterized with respect to the effects of mass discrimination, linearity and memory effect.

Effect of inhibitory avoidance training on [3H]-glutamate binding in the hippocampus and parietal cortex of rats

Glutamate receptors have been implicated in memory formation. The aim of the present study was to determine the effect of inhibitory avoidance training on specific [3H]-glutamate binding to membranes obtained from the hippocampus or parietal cortex of rats. Adult male Wistar rats were trained (0.5-mA footshock) in a step-down inhibitory avoidance task and were sacrificed 0, 5, 15 or 60 min after training. Hippocampus and parietal cortex were dissected and membranes were prepared and incubated with 350 nM [3H]-glutamate (N = 4-6 per group). Inhibitory avoidance training induced a 29% increase in glutamate binding in hippocampal membranes obtained from rats sacrificed at 5 min (P<0.01), but not at 0, 15, or 60 min after training, and did not affect glutamate binding in membranes obtained from the parietal cortex. These results are consistent with previous evidence for the involvement of glutamatergic synaptic modification in the hippocampus in the early steps of memory formation.

Synthesis of nanoporous materials for preconcentration and determination of trace elements by ICP-AES ; Investigation and elimination of the memory effects of mercury, gold, silver and boron in ICP-AES

Nanoporous materials with large surface area and well-ordered pore structure have been synthesized. Thiol groups were grafted on the materials' surface to make heavy metal ion pre-concentration media. The adsorption properties ofthe materials were explored. Mercury, gold and silver can be strongly adsorbed by these materials, even in the presence of alkaline earth metal ion. Though the materials can adsorb other heavy metal ions such as lead and copper, they show differential adsorption ability when several ions are present in solution. The adsorption sequence is: mercury> == silver> copper » lead and cadmium. In the second part of this work, the memory effects of mercury, gold, silver and boron were investigated. The addition of 2% L-cysteine and 1% thiourea eliminates the problems of the three metal ions completely. The wash-out time for mercury dropped from more than 20 minutes to 18 seconds, and the wash-out time for gold decreased from more than 30 minutes to 49 seconds. The memory effect of boron can be reduced by the use of mannitol.

Magnetic field induced entropy change and magnetoelasticity in Ni-Mn-Ga alloys

The magnetocaloric effect that originates from the martensitic transition in the ferromagnetic Ni-Mn-Ga shape-memory alloy is studied. We show that this effect is controlled by the magnetostructural coupling at both the martensitic variant and magnetic domain length scales. A large entropy change induced by moderate magnetic fields is obtained for alloys in which the magnetic moment of the two structural phases is not very different. We also show that this entropy change is not associated with the entropy difference between the martensitic and the parent phase arising from the change in the crystallographic structure which has been found to be independent of the magnetic field within this range of fields.

Memory effects in liquid crystal elastomers

Free-standing monodomain liquid crystal elastomer samples are shown to have a complete memory of the orientational configuration at the time of cross-linking. This memory is demonstrated through samples in which the parent polymer system is first aligned in a magnetic field prior to cross-linking. These films show reversible nematic-isotropic phase transitions and x-ray scattering patterns characteristic of nematic phases. The liquid crystal elastomer films exhibit a remarkable memory effect, in that the sample may be held at temperatures well above the nematic-isotropic transition for extended periods ( > 2 weeks), but on cooling into the liquid crystal phase region, both the original director alignment and the degree of preferred orientation are recovered. It is demonstrated that these novel memory effects are equilibrium in nature. The origins of this phenomena in terms of coupling between the mesogenic side-chains and the polymer network are discussed.

Memory and burstiness in dynamic networks

A discrete-time random process is described, which can generate bursty sequences of events. A Bernoulli process, where the probability of an event occurring at time t is given by a fixed probability x, is modified to include a memory effect where the event probability is increased proportionally to the number of events that occurred within a given amount of time preceding t. For small values of x the interevent time distribution follows a power law with exponent −2−x. We consider a dynamic network where each node forms, and breaks connections according to this process. The value of x for each node depends on the fitness distribution, \rho(x), from which it is drawn; we find exact solutions for the expectation of the degree distribution for a variety of possible fitness distributions, and for both cases where the memory effect either is, or is not present. This work can potentially lead to methods to uncover hidden fitness distributions from fast changing, temporal network data, such as online social communications and fMRI scans.

Nanoscopic photoluminescence memory as a fingerprint of complexity in self-assembled alkyl/siloxane hybrids

A thermally activated photoluminescence memory effect, induced by a reversible order-disorder phase transition of the alkyl chains, is reported for highly organized bilayer alkyl/siloxane hybrids (see figure; left at room temperature, right at 120 degrees C). The emission energy is sensitive to the annihilation/formation of the hydrogen-bonded amide-amide array displaying a unique nanoscopic sensitivity (ca. 150 nm).

An investigations on local and global behavior of a (SMA) oscillator of 3 - DOF driven by a limited power supply

SMART material systems offer great possibilities in terms of providing novel and economical solutions to engineering problems. The technological advantages of these materials over traditional ones are due to their unique microstructure and molecular properties. Smart materials such as shape memory alloys (SMA), has been used in such diverse areas of engineering science, nowadays. In this paper, we present a numerical investigation of the dynamics interaction of a nonideal structure (NIS). We analyze the phenomenon of the passage through resonance region in the steady state processes. We remarked that this kind of problem can lead to the so-called Sommerfeld effect: steady state frequencies of the DC motor will usually increase as more power (voltage) is given to it in a step-by-step fashion. When a resonance condition with the structure it is reached, the better part of this energy it is consumed to generate large amplitude vibrations of the foundation without sensible change of the motor frequency as before. The results obtained by using numerical simulations are discussed in details. Copyright © 2009 by ASME.