Effect of long-term exposure to Low Earth Orbit (LEO) space environment

Data obtained from components and materials from the Solar Maximum Mission satellite are presented and compared to data for similar materials obtained from the Advanced Composite Materials Exposure to Space Experiment (ACOMEX) flown on Shuttle mission STS-41G. In addition to evaluation of surface erosion and mass loss that may be of importance to very long-term missions, comparisons of solar absorptance and thermal emittance measurements for both long and short term exposures were made. Although the ratio of absorptance over emittance can be altered by proper choice of materials to ensure a proper operating environment for the spacecraft, once the thermal design is established, it is important that the material properties not change in order to maintain the operating environment for many payload and bus items such as electronics, batteries, fuel, etc. However, data presented show significant changes after short exposure in low Earth environment. Moreover, the measured changes are shown to differ according to the manner of exposure, i.e., normal or oblique, which also affects the resultant eroded surface morphology. These results identify constraints to be considered in development of flight experiments or laboratory testing

Research of an Active Tunable Vibration Absorber for Helicopter Vibration Control

Abstract Significant structural vibration is an undesirable characteristic in helicopter flight that leads to structural fatigue, poor ride quality for passengers and high acoustic signature. Previous Individual Blade Control (IBC) techniques to reduce these effects have been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an active tunable vibration absorber using IBC approach to adaptively alter the "structural impedance" at the blade root. In this paper, a mathematical model was developed to predict the response under harmonic excitations. An adaptive notch algorithm was designed and implemented on a TMS320c40 DSP platform. Reference signal synthesis techniques were used to automatically track the shifts in the fundamental vibratory frequency due to variations in flight conditions. Closed-loop tests performed on the proof-of-concept hardware achieved significant vibration suppression at harmonic peaks as well as the broadband reduction in vibration. The investigation verified the capability of the Smart Spring to suppress multiple harmonic components in blade vibration through active impedance control

Space environmental effects on polymer matrix composites as a function of sample location on LDEF

This paper presents results on the effect of circumferential location on the variation in solar absorptance (alpha(sub S)) and infrared emittance (epsilon) for five different polymer matrix composites (PMC), and variations in erosion depth due to atomic oxygen (AO) for fourteen different PMC materials. In addition, a chemical content design parameter (gamma) has been found that correlates well with the erosion yield obtained from space flight data and hyperthermal AO tests for hydrocarbon polymeric materials. This parameter defines the ratio of the total number of atoms in a repeat monomer unit to the difference between the total carbon content and the total number of intermolecular oxygen atoms in the same repeat unit

Proposed test program and data base for LDEF polymer matrix composites

A survey of the polymer matrix composite materials that were flown on Long Duration Exposure Facility (LDEF) is presented with particular attention to the effect of circumferential location (alpha) on the measured degradation and property changes. Specifically, it is known that atomic oxygen fluence (AO), VUV radiation dose, and number of impacts by micrometeoroids/debris vary with alpha. Thus, it is possible to assess material degradation and property damage changes with alpha for those materials that are common to three or more locations. Once the alpha-dependence functions were defined, other material samples will provide data that can readily be used to predict damage and property changes as a function of alpha as well. What data can be realistically obtained from these materials, how this data can be obtained, and the scientific/design value of the data to the user community is summarized. Finally, a proposed test plan is presented with recommended characterization methodologies that should be employed by all investigators to ensure consistency in the data base that will result from this exercise

Metal‐Cation Recognition in Water by a Tetrapyrazinoporphyrazine‐Based Tweezer Receptor

A series of zinc azaphthalocyanines with two azacrowns in a rigid tweezer arrangement were prepared and the fluorescence sensing properties were investigated. The size‐driven recognition of alkali and alkaline earth metal cations was significantly enhanced by the close cooperation of the two azacrown units, in which both donor nitrogen atoms need to be involved in analyte binding to switch the sensor on. The mono‐ or biphasic character of the binding isotherms, together with the binding stoichiometry and magnitude of association constants (KA), indicated specific complexation of particular analytes. Water solvation was shown to play an important role and resulted in a strong quenching of sensor fluorescence in the ON state. The lead compound was embedded into silica nanoparticles and advantageous sensing properties towards K+ were demonstrated in water (λF=671 nm, apparent KA=82 m−1, increase of 17×), even in the presence of (supra)physiological concentrations of Na+ and Ca2+.In a pinch: Close cooperation of azacrowns in fluorescence sensors derived from tetrapyrazinoporphyrazines is responsible for high sensitivity and selectivity towards particular cations. Water solvation, however, quenches the fluorescence strongly. Interestingly, embedding the sensor into silica nanoparticles overcomes this problem and result in an excellent red‐emitting fluorescence sensor (see figure).Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137532/1/chem201504268.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137532/2/chem201504268-sup-0001-misc_information.pd

Peripherally crowded cationic phthalocyanines as efficient photosensitizers for photodynamic therapy

Photodynamic therapy is a treatment modality of cancer based on the production of cytotoxic species upon the light activation of photosensitizers. Zinc phthalocyanine photosensitizers bearing four or eight bulky 2,6-di(pyridin-3-yl)phenoxy substituents were synthesized, and pyridyl moieties were methylated. The quaternized derivatives did not aggregate at all in water and retained their good photophysical properties. High photodynamic activity of these phthalocyanines was demonstrated on HeLa, MCF-7, and EA.hy926 cells with a very low EC50 of 50 nM (for the MCF-7 cell line) upon light activation while maintaining low toxicity in the dark (TC50 ≈ 600 μM), giving thus good phototherapeutic indexes (TC50/EC50) above 1400. The compounds localized primarily in the lysosomes, leading to their rupture after light activation. This induced an apoptotic cell death pathway with secondary necrosis because of extensive and swift damage to the cells. This work demonstrates the importance of a bulky and rigid arrangement of peripheral substituents in the development of photosensitizersThe work was supported by the Czech Science Foundation (19-14758Y), Charles University (PRIMUS/20/SCI/013, GAUK 1620219, SVV 260 550), and by the project EFSACDN (No. CZ.02.1.01/0.0/0.0/16_019/0000841) cofunded by the ERDF. For affiliations ‡, ∥, and ⊥, the work was supported by MINECO-Feder funds (CTQ2017-85393-P (T.T.), CTQ-2014-53673-P and CTQ-2017-89539-P (A.d.l.E.), PCIN-2017-042/EuroNanoMed2017-191, TEMPEAT (T.T.)). Affiliation ⊥ (IMDEA Nanociencia) also acknowledges support from the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (MINECO, Grant SEV2016-0686

Review of existing numerical methods and validation procedure available for bird strike modelling

Summary This paper reviews numerical methods that are currently available to simulate bird strike as well as the theory of the event. It also summarizes important parameters and provides guidelines as to how to set up the analysis and how to evaluate a model. The information provided is based on physical properties and available results regarding a bird and its behaviour upon impact. The simulations have been performed with LS-DYNA 970 but can be done in similar dynamic finite elements analysis codes

Actively Controlling Buffet-Induced Excitations

High performance aircraft, especially those with twin vertical tails, encounter unsteady buffet loads when flying at high angles of attack. These loads result in significant random stresses, which may cause fatigue damage leading to restricted capabilities and availability of the aircraft. An international collaborative research activity among Australia, Canada and the United States, conducted under the auspices of The Technical Cooperation Program (TTCP) contributed resources toward a program that coalesced a broad range of technical knowledge and expertise into a single investigation to demonstrate the enhanced performance and capability of the advanced active BLA control system in preparation for a flight test demonstration. The research team investigated the use of active structural control to alleviate the damaging structural response to these loads by applying advanced directional piezoelectric actuators, the aircraft rudder, switch mode amplifiers, and advanced control strategies on an F/A-18 aircraft empennage. Some results of the full-scale investigation are presented herein

Controlling Buffeting Loads by Rudder and Piezo-Actuation

High performance aircraft, especially those with twin vertical tails, encounter unsteady buffet loads when flying at high angles of attack. These stochastic loads result in significant stresses, which may cause fatigue damage leading to restricted capabilities and availability of the aircraft. An international collaborative research activity among Australia, Canada and the United States, conducted under the auspices of The Technical Cooperation Program (TTCP) contributed resources toward a program that coalesced a broad range of technical knowledge and expertise into a single investigation to demonstrate the enhanced performance and capability of the advanced active Buffet Load Alleviation ( ) control system in preparation for a flight test demonstration. The research team investigated the use of active structural control to alleviate the damaging structural response to these loads by applying advanced directional piezoelectric actuators, the aircraft rudder, switch mode amplifiers, and advanced control strategies on an F/A-18 aircraft empennage. Some results of the full-scale investigation are presented herein