Monotonic, Creep-Rupture, and Fatigue Behavior of Carbon Fiber Reinforced Silicon Carbide (C/SiC) at an Elevated Temperature

The main objective of this research effort was to examine the impact that cyclic loading frequency has on the life of a C/SiC composite at an elevated temperature of 550°C. Cyclic loading of C/SiC was investigated at frequencies of 375 Hz, 10 Hz, 1 Hz, and 0.1 Hz. Creep-Rupture tests and tests that were combinations of creep-rupture and fatigue were also accomplished. A monotonic tensile test was performed at 550°C and compared to a room temperature monotonic test. This study showed that an elevated temperature of 550°C has very little effect on the Ultimate Tensile Strength (UTS) of C/SiC. The UTS of C/SiC at 550°C was 487 MPa, while the room temperature UTS is 493 MPa. The three creep-rupture tests in this study performed at 350 MPa, 175 MPa and 105 MPa had lives of less than 11 hours despite the fact that the UTS of C/SiC is 487 MPa at 550°C. The short life of the specimens is due to the oxidation of the carbon fibers within the C/SiC composite. S-N curves developed from the fatigue tests indicate that there is an increase in cycles to failure as the frequency is increased. Another important discovery in this study was the fact that oxidation of the carbon fibers within C/SiC is reduced when frequency of fatigue is increased. At high frequency fatigue (10Hz to 375 Hz), C/SiC composites have longer cycle lives and time lives than at low cycle fatigue. Microscopic and SEM analysis verified that oxidation of carbon within C/SiC is slowed as frequency of fatigue is increased

Algebras of Measurements: the logical structure of Quantum Mechanics

In Quantum Physics, a measurement is represented by a projection on some closed subspace of a Hilbert space. We study algebras of operators that abstract from the algebra of projections on closed subspaces of a Hilbert space. The properties of such operators are justified on epistemological grounds. Commutation of measurements is a central topic of interest. Classical logical systems may be viewed as measurement algebras in which all measurements commute. Keywords: Quantum measurements, Measurement algebras, Quantum Logic. PACS: 02.10.-v.Comment: Submitted, 30 page

A red/far-red light-responsive bi-stable toggle switch to control gene expression in mammalian cells

Growth and differentiation of multicellular systems is orchestrated by spatially restricted gene expression programs in specialized subpopulations. The targeted manipulation of such processes by synthetic tools with high-spatiotemporal resolution could, therefore, enable a deepened understanding of developmental processes and open new opportunities in tissue engineering. Here, we describe the first red/far-red light-triggered gene switch for mammalian cells for achieving gene expression control in time and space. We show that the system can reversibly be toggled between stable on- and off-states using short light pulses at 660 or 740 nm. Red light-induced gene expression was shown to correlate with the applied photon number and was compatible with different mammalian cell lines, including human primary cells. The light-induced expression kinetics were quantitatively analyzed by a mathematical model. We apply the system for the spatially controlled engineering of angiogenesis in chicken embryos. The system's performance combined with cell- and tissue-compatible regulating red light will enable unprecedented spatiotemporally controlled molecular interventions in mammalian cells, tissues and organisms

Effect of ligand methylation on the spin-switching properties of surface-supported spin-crossover molecules

X-ray absorption spectroscopy investigations of the spin-state switching of spin-crossover (SCO) complexes adsorbed on a highly-oriented pyrolytic graphite (HOPG) surface have shown so far that HOPG is a promising candidate to realize applications such as spintronic devices because of the stability of SCO complexes on HOPG and the possibility of highly efficient thermal and light-induced spin-state switching. Herein, we present the spin switching of several Fe(II) SCO complexes adsorbed on an HOPG surface with particular emphasis on the thermally induced spin transition behaviour with respect to different structural modifications. The complexes of the type [Fe(bpz)2(L)] (bpz  =  dihydrobis(pyrazolyl)borate, L  =  1,10-phenanthroline, 2,2'-bipyridine) and their methylated derivatives exhibit SCO in the solid state with some differences regarding cooperative effects. However, in the vacuum-deposited thick films on quartz, complete and more gradual spin transition behavior is observable via UV/vis spectroscopy. In contrast to that, all complexes show large differences upon direct contact with HOPG. Whereas the unmodified complexes show thermal and light-induced SCO, the addition of e.g. two or four methyl groups leads to a partial or a complete loss of the SCO on the surface. The angle-dependent measurement of the N K-edge compared to calculations indicates that the complete SCO and HS-locked molecules on the surface exhibit a similar preferential orientation, whereas complexes undergoing an incomplete SCO exhibit a random orientation on the surface. These results are discussed in the light of molecule-substrate interactions

Micromechanical finite element parametric study of polyamide 6 based single polymer composites reinforced by woven textile structures

This study presents a finite element-based micromechanical analysis of woven single polymer composites (WSPC), prepared by compression molding from polyamide 6 (PA6) woven fabrics powder-coated with PA6 microparticles. Initially, the PA6 microparticles (MP) were synthesized by solution/precipitation activated anionic ring-opening polymerization of ε-caprolactam. After the powder coating, the MP fraction upon each textile ply was transformed into the continuous PA6 matrix by hot pressing at a temperature lower than the melting of the PA6 textile reinforcements. Plain and satin PA6 woven fabrics were selected as reinforcements that were stretched and annealed prior to molding so as to enhance their mechanical performance. The tensile and Izod impact properties of WSPC were characterized in relation to the reinforcement architecture, fiber content and ply orientation. Finite element analysis was used for a parametric study of woven reinforcements and to correlate the deformation and stress distribution of the structures with the tensile failure of the composites. Moreover, to assess the interfacial matrix-reinforcements bonding state, a study of the surfaces fracture, obtained by SEM topography, using image processing was performed.This work was partially financed by FEDER funds through the COMPETE program and by national funds through FCT – Foundation for Science and Technology within the project POCI-01-0145-FEDER007136. SDT thanks FCT for his PhD Grant SFRH/BD/94759/2013. NVD thanks for the financial support of FCT through the strategic project UID/CTM/50025/2013. ZZD is thankful to FCT for the SFRH/BSAB/130271/2017 personal research grant. All authors acknowledge the support of the project TSSiPRO-NORTE-01-0145-FEDER-000015 funded by the regional operational program NORTE 2020, under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund

Torsional-flexural buckling of unevenly battened columns under eccentrical compressive loading

In this paper, an analytical model is developed to determine the torsional-flexural buckling load of a channel column braced by unevenly distributed batten plates. Solutions of the critical-buckling loads were derived for three boundary cases using the energy method in which the rotating angle between the adjacent battens was presented in the form of a piecewise cubic Hermite interpolation (PCHI) for unequally spaced battens. The validity of the PCHI method was numerically verified by the classic analytical approach for evenly battened columns and a finite-element analysis for unevenly battened ones, respectively. Parameter studies were then performed to examine the effects of loading eccentricities on the torsional-flexural buckling capacity of both evenly and unevenly battened columns. Design parameters taken into account were the ratios of pure torsional buckling load to pure flexural–buckling load, the number and position of battens, and the ratio of the relative extent of the eccentricity. Numerical results were summarized into a series of relative curves indicating the combination of the buckling load and corresponding moments for various buckling ratios.National Natural Science Foundation of China (NSFC) under grant number (No.) 51175442 and Sichuan International Cooperation Research Project under grant No. 2014HH002

Experimental evidence for phonemic contrasts in a nonhuman vocal system

The ability to generate new meaning by rearranging combinations of meaningless sounds is a fundamental component of language. Although animal vocalizations often comprise combinations of meaningless acoustic elements, evidence that rearranging such combinations generates functionally distinct meaning is lacking. Here, we provide evidence for this basic ability in calls of the chestnut-crowned babbler (Pomatostomus ruficeps), a highly cooperative bird of the Australian arid zone. Using acoustic analyses, natural observations, and a series of controlled playback experiments, we demonstrate that this species uses the same acoustic elements (A and B) in different arrangements (AB or BAB) to create two functionally distinct vocalizations. Specifically, the addition or omission of a contextually meaningless acoustic element at a single position generates a phoneme-like contrast that is sufficient to distinguish the meaning between the two calls. Our results indicate that the capacity to rearrange meaningless sounds in order to create new signals occurs outside of humans. We suggest that phonemic contrasts represent a rudimentary form of phoneme structure and a potential early step towards the generative phonemic system of human language

A red/far-red light-responsive bi-stable toggle switch to control gene expression in mammalian cells

Growth and differentiation of multicellular systems is orchestrated by spatially restricted gene expression programs in specialized subpopulations. The targeted manipulation of such processes by synthetic tools with high-spatiotemporal resolution could, therefore, enable a deepened understanding of developmental processes and open new opportunities in tissue engineering. Here, we describe the first red/far-red light-triggered gene switch for mammalian cells for achieving gene expression control in time and space. We show that the system can reversibly be toggled between stable on- and off-states using short light pulses at 660 or 740 nm. Red light-induced gene expression was shown to correlate with the applied photon number and was compatible with different mammalian cell lines, including human primary cells. The light-induced expression kinetics were quantitatively analyzed by a mathematical model. We apply the system for the spatially controlled engineering of angiogenesis in chicken embryos. The system's performance combined with cell- and tissue-compatible regulating red light will enable unprecedented spatiotemporally controlled molecular interventions in mammalian cells, tissues and organism

A new Late Agenian (MN2a, Early Miocene) fossil assemblage from Wallenried (Molasse Basin, Canton Fribourg, Switzerland)

Excavations of two fossiliferous layers in the Wallenried sand- and marl pit produced a very diversified vertebrate fauna. New material allows the reassessment of the taxonomic position of the ruminant taxa Andegameryx andegaviensis and endemic Friburgomeryx wallenriedensis. An emended diagnosis for the second species is provided and additional material of large and small mammals, as well as ectothermic vertebrates, is described. The recorded Lagomorpha show interesting morphological deviations from other Central European material, and probably represent a unique transitional assemblage with a co-occurrence of Titanomys, Lagopsis and Prolagus. Rodentia and Eulipotyphla belong to typical and well-known species of the Agenian of the Swiss Molasse Basin. Abundant small mammal teeth have allowed us to pinpoint the biostratigraphic age of Wallenried to late MN2a. The biostratigraphic age conforms to data derived from the charophyte assemblages and confirms the oldest occurrence of venomous snake fangs. The palaeoenvironmental context is quite complex. Sedimentary structures and fauna (fishes, frogs, salamanders, ostracods) are characteristic for a humid, lacustrine environment within a flood plain system

Phytochrome-Based Extracellular Matrix with Reversibly Tunable mechanical Properties

Interrogation and control of cellular fate and function using optogenetics is providing revolutionary insights into biology. Optogenetic control of cells is achieved by coupling genetically encoded photoreceptors to cellular effectors and enables unprecedented spatiotemporal control of signaling processes. Here, a fast and reversibly switchable photoreceptor is used to tune the mechanical properties of polymer materials in a fully reversible, wavelength‐specific, and dose‐ and space‐controlled manner. By integrating engineered cyanobacterial phytochrome 1 into a poly(ethylene glycol) matrix, hydrogel materials responsive to light in the cell‐compatible red/far‐red spectrum are synthesized. These materials are applied to study in human mesenchymal stem cells how different mechanosignaling pathways respond to changing mechanical environments and to control the migration of primary immune cells in 3D. This optogenetics‐inspired matrix allows fundamental questions of how cells react to dynamic mechanical environments to be addressed. Further, remote control of such matrices can create new opportunities for tissue engineering or provide a basis for optically stimulated drug depots