Finite Element Analysis of Shape Memory Alloy Adaptive Trusses with Geometrical Nonlinearities

This contribution deals with the nonlinear analysis of shape memory alloy (SMA) adaptive trusses employing the finite element method. Geometrical nonlinearities are incorporated into the formulation together with a constitutive model that describes different thermomechanical behaviors of SMA. It has four macroscopic phases (three variants of martensite and an austenitic phase), and considers different material properties for austenitic and martensitic phases together with thermal expansion. An iterative numerical procedure based on the operator split technique is proposed in order to deal with the nonlinearities in the constitutive formulation. This procedure is introduced into ABAQUS as a user material routine. Numerical simulations are carried out illustrating the ability of the developed model to capture the general behavior of shape memory bars. After that, it is analyzed the behavior of some adaptive trusses built with SMA actuators subjected to different thermomechanical loadings.     

Synthesis and Study of the Photophysical Properties of a New Eu<Superscript>3+</Superscript> Complex with 3-Hydroxypicolinamide

This work reports on the synthesis and characterization of a new complex of Eu³⁺ with the 3-hydroxypicolinamide ligand (Hhpa). Here we present an approach for obtaining bis[2-carbamoyl(κO)pyridin-3-olato(κO’)] lanthanide complexes, which were characterized through elemental analysis, thermal analysis, infrared and photoluminescence spectroscopies (emission, excitation, luminescence lifetimes, quantum efficiencies, Judd-Ofelt parameters and quantum yields). Although hpa can act as a bidentate ligand in different conformations, the results attest for the occurrence of a unique coordination site of low symmetry for the Eu³⁺ ions, in which two anionic hpa ligands coordinate the cations through an O/O chelating system. The phosphorescence of the synthesized gadolinium complex provides the energy of the triplet state, which is determined to be at 20,830 cm^-1 over the ground state. This makes the Hhpa ligand very adequate for sensitizing the Eu³⁺ luminescence, which leads to a very efficient antenna effect and opens a wide range of applications for the complex in light emitting organic-inorganic devices.     

Autoresonant excitation of antiproton plasmas

We demonstrate controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense, and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination.     

Struggle for space: viral extinction through competition for cells

The design of protocols to suppress the propagation of viral infections is an enduring enterprise, especially hindered by limited knowledge of the mechanisms leading to viral extinction. Here we report on infection extinction due to intraspecific competition to infect susceptible hosts. Beneficial mutations increase the production of viral progeny, while the host cell may develop defenses against infection. For an unlimited number of host cells, a feedback runaway coevolution between host resistance and progeny production occurs. However, physical space limits the advantage that the virus obtains from increasing offspring numbers; thus, infection clearance may result from an increase in host defenses beyond a finite threshold. Our results might be relevant to devise improved control strategies in environments with mobility constraints or different geometrical properties.     

High average power large-pitch fiber amplifier with robust single-mode operation

Ytterbium-doped large-pitch fibers with very large mode areas are investigated in a high-power fiber amplifier configuration. An average output power of 294?W is demonstrated, while maintaining robust single-mode operation with a mode field diameter of 62?μm. Compared to previous active large-mode area designs, the threshold of mode instabilities is increased by a factor of about 3.     

High-speed modal decomposition of mode instabilities in high-power fiber lasers

A high-speed mode analysis technique is required to gain fundamental understanding of mode instabilities in high-power fiber laser systems. In this work a technique, purely based on the intensity profile of the beam, is demonstrated to be ideally suited to analyze fiber laser dynamics. This technique, together with a high-speed camera, has been applied to the study of the temporal dynamics of mode instabilities at high average powers with up to 20,000 frames per second. These measurements confirm that energy transfer between the fluctuating transversal modes takes place in millisecond-time-scale.     

Structure Determination of Hydroxytrypargine: A New Tetrahydro‐β‐Carboline Toxin from the Venom of the Spider Parawixia bistriata

A new, highly active tetrahydro‐β‐carboline toxin from the spider Parawixia bistriata, the most‐common species of social spider occurring in Brazil, was isolated. The new toxin was identified as 1,2,3,4‐tetrahydro‐6‐hydroxy‐β‐carboline (=N‐[3‐(2,3,4,9‐tetrahydro‐6‐hydroxy‐1H‐pyrido[3,4‐b]indol‐1‐yl)propyl]guanidine; 3 ). This type of alkaloid, not common among spider toxins, was found to be the most‐potent constituent of the spider's chemical weaponry to kill prey. When P. bistriata catch arthropods in their web, they apparently attack their prey in groups of many individuals injecting their venoms. In vivo toxicity assays with 3 demonstrated a potent lethal effect to honeybees, giving rise to clear neurotoxic effects (paralysis) before death. The compound's toxicity (LD₅₀ value) was determined to be ca. 8 ng/g of honeybee. The investigation of the pharmacological properties and neurotoxic actions of 3 may be used in the future for the development of new drugs to be applied for pest control in agriculture.     

Hermite pseudospectral approximations. An error estimate

We find an error bound for the pseudospectral approximation of a function in terms of Hermite functions, hn(x)=e−x²Hn(x), in certain weighted Sobolev spaces. We use properties of Hermite polynomials, as well as an asymptotic expression for their largest zeroes to achieve the mentioned estimate.     

Mössbauer effect study of the diagenesis on the southern brazilian triassic paleoherpetofauna

Mössbauer spectroscopy is applied to identify the iron contents of bony elements of southern Brazilian Triassic reptile remains, and the question of the paragenetic mineral assemblage is discussed.     

Techniques of fringe interpolation in moiré patterns

The objective of this paper is to report further developments on the application of the displacement-light-intensity law to fractional-fringe-order determination. The structure of moiré-fringe patterns is analyzed when the moiré fringes are recorded together with the lines producing them. A device used to record the information stored in the film is described. The influence of the combined effect of the film and the reading device is discussed. Departures from the ideal behavior of the whole process are analyzed together with the introduced errors. The mechanics of processing continuous moiré-fringe information is outlined together with the means utilized to reduce the influence of errors. Data are provided to show the degree of effectiveness achieved with the described process.