2,584 research outputs found
Study of Hydrophobic Domains in Humic Acids
Fyzikálně-chemická povaha hydrofobních domén huminových kyselin byla studována z několika hledisek. K objasnění významu fluorescenčních spekter byly vzorky podrobeny sekvenční frakcionaci, která pomohla k částečnému objasnění vlivu vodorozpustných složek, volných a vázaných lipidů na optické vlastnosti huminových kyselin. Výsledky naznačily, že fluorescenční píky tradičně přiřazované superpozici jednotlivých struktur jsou spíše důsledkem agregačních vlastností huminových molekul tvořících vlivem hydrofobního efektu zdánlivě vysoce aromatické struktury. Dále pak bylo zjištěno, že na optických vlastnostech huminových kyselin mají podíl i molekuly, které nemají primárně fluoroforní nebo chromoforní vlastnosti. Tento pohled je v souladu s teorií supramolekulárního uspořádání huminových kyselin. Dále byly studovány agregace, konformační chování a termodynamická stabilita huminových kyselin pomocí metody vysoce rozlišovací ultrazvukové spektroskopie. Bylo prokázáno, že huminové kyseliny mají schopnost agregovat už od velmi nízkých koncentrací (The nature of hydrophobic domains in humic acids was studied from different points of view. To shed light on the meaning of fluorescent spectra, the measured samples underwent the sequential extraction which partially revealed the role of water-soluble components, free and bond lipids in optical properties of humic acids. The results indicated that the fluorescence peaks traditionally attributed to the superposition of individual chemical structures are rather a result of aggregation properties of humic molecules and hydrophobic effect driving aromatic molecules together forming aggregates apparently large molecular weight. Further, it seems that there is a significant influence of non-fluorophores and non-chromophores on the optical properties of humic acids. Results are consistent with the theory on supramolecular structure of humic acids. Next, the aggregation, conformational behaviour and thermodynamic stability of humic acids were studied by high resolution ultrasonic spectroscopy. It was demonstrated that humic molecules are able to interact and form aggregates at very low concentration (
BSP Functional Programming: Examples of a Cost Based Methodology
Abstract. Bulk-Synchronous Parallel ML (BSML) is a functional data-parallel language for the implementation of Bulk-Synchronous Parallel (BSP) algorithms. It makes an estimation of the execution time (cost) possible. This paper presents some general examples of BSML programs and a comparison of their predicted costs with the measured execution time on a parallel machine
Refined Tectonic Evolution of the Betic-Rif Orogen Through Integrated 3-D Microstructural Analysis and Sm-Nd Dating of Garnet Porphyroblasts
Acknowledgments
The authors would like to thank Ángel Perandrés-Villegas for preparing the thin sections used for this study, Fátima Linares Ordóñez for X-ray computed micro-tomography scanning, Mike Tappa for assistance with thermal ionization mass spectrometry analysis, Francisco Alonso-Chaves and Fernando Simancas for sending structural data, Whitney Behr, Johannes Glodny, Sean Mulcahy, and an anonymous reviewer for providing helpful reports, and editors Laurent Jolivet and Federico Rossetti for additional comments that helped improve two earlier manuscript versions. EFB gratefully acknowledges support from the NSF Grants EAR-1250497 and PIRE-1545903 as well as start up funds from the Boston College. DA and ARF gratefully acknowledge financial support through Spanish project “DAMAGE” (CGL2016-80687-R AEI/FEDER), and Junta de Andalucía project RNM148, both directed by Jesús Galindo Zaldivar. ARF acknowledges an PhD Grant (FPU) from the Spanish government. Open access fees have been funded by Universidad de Granada /CBUA.High-resolution microstructural analysis of porphyroblast inclusion trails integrated with Sm-Nd
garnet geochronology has provided new insight into the tectonic history of the Betic-Rif orogen. Three principal
age groups of porphyroblasts are demonstrated with distinctly oriented inclusion-trails. Inclusion-trail curvature
axes or “FIA” (Foliation Inflexion/Intersection Axes) are shown to represent “fossilized” crenulation axes
from which a succession of different crustal shortening directions can be deduced. The regional consistency
of microstructural orientations and their geometric relationship with multiple sets of macroscopic folds
reveal the composite character of the Gibraltar Arc formed by a superposition of different folding directions
and associated lineations. Bulk-garnet ages of 35–22 Ma obtained from five micaschist samples of the
Alpujarride-Sebtide complex (ASC) and of 35–13 Ma from four micaschists of the Nevado-Filabride complex
(NFC) allow to deduce NNE-SSW directed shortening in the Late Eocene changing to NW-SE shortening in
the early Oligocene, alternating with suborthogonal NE-SW shortening during the Miocene. These directions
can be related to a major swing in the direction of relative Africa-Iberia plate-motion known from kinematic
modeling of magnetic seafloor anomalies, and subsequent dynamic interference between plate convergence and
suborthogonal “tectonic escape” of the Alboran Domain. Coupled to previously established P-T-t paths, the
new garnet ages support a common tectono-metamorphic evolution of the ASC and NFC as laterally equivalent
orogenic domains until, in the Miocene, the second became re-buried under the first.NSF Grant EAR-1250497PIRE-1545903Spanish project “DAMAGE” (CGL2016-80687-R AEI/FEDER)Junta de Andalucía project RNM148PhD Grant (FPU) from the Spanish governmentOpen access fees have been funded by Universidad de Granada /CBU
Floquet stability analysis of a two-layer oscillatory flow near a flexible wall
We investigate the linear Floquet stability of two fluid layers undergoing
oscillations in the direction parallel to the flexible wall that separates
them. This canonical configuration is inspired by the cerebrospinal fluid flow
in the spinal canal of subjects with hydro-/syringomyelia.The analysis focuses
on the marginal conditions for the onset of instability, and how these depend
on the spatial wavelength of the perturbation, and on the values of the control
parameters, which are the two channel widths, the Reynolds number, and the wall
stiffness. Unstable perturbations are found to oscillate synchronous with the
base flow. The wavelength of the most unstable perturbation, of the order of
the stroke length of the basic oscillatory motion, depends strongly on the wall
stiffness, but is only weakly influenced by the channel widths and the Reynolds
number. In general, around criticality, it was found that increasing the
Reynolds number has a destabilizing effect, and that decreasing the canal
widths stabilizes the instability. The wall stiffness on the other hand has a
non-monotonic effect, exhibiting an intermediate value for which the
instability is maximally amplified. The present analysis is a first step
towards a better understanding of the physical mechanisms that govern many
(bio)fluid mechanical problems that involve oscillatory flows near compliant
walls
Radiation and temperature effects on the time-dependent response of T300/934 graphite/epoxy
A time-dependent characterization study was performed on T300/934 graphite/epoxy in a simulated space environment. Creep tests on irradiated and nonirradiated graphite/epoxy and bulk resin specimens were carried out at temperatures of 72 and 250 F. Irradiated specimens were exposed to dosages of penetrating electron radiation equal to 30 years exposure at GEO-synchronous orbit. Radiation was shown to have little effect on the creep response of both the composite and bulk resin specimens at 72 F while radiation had a significant effect at 250 F. A healing process was shown to be present in the irradiated specimens where broken bonds in the epoxy due to radiation recombined over time to form cross-links in the 934 resin structure. An analytical micromechanical model was also developed to predict the viscoelastic response of fiber reinforced composite materials. The model was shown to correlate well with experimental results for linearly viscoelastic materials with relatively small creep strains
Coherent spin dynamics of electrons and holes in CsPbBr perovskite crystals
The lead halide perovskites demonstrate huge potential for optoelectronic
applications, high energy radiation detectors, light emitting devices and solar
energy harvesting. Those materials exhibit strong spin-orbit coupling enabling
efficient optical orientation of carrier spins in perovskite-based devices with
performance controlled by a magnetic field. Perovskites are promising for
spintronics due to substantial bulk and structure inversion asymmetry, however,
their spin properties are not studied in detail. Here we show that elaborated
time-resolved spectroscopy involving strong magnetic fields can be successfully
used for perovskites. We perform a comprehensive study of high-quality
CsPbBr crystals by measuring the exciton and charge carrier -factors,
spin relaxation times and hyperfine interaction of carrier and nuclear spins by
means of coherent spin dynamics. Owing to their "inverted" band structure,
perovskites represent appealing model systems for semiconductor spintronics
exploiting the valence band hole spins, while in conventional semiconductors
the conduction band electrons are considered for spin functionality.Comment: 8 pages, 3 figures + supplementary informatio
Magnetotactic bacteria in a droplet self-assemble into a rotary motor
From intracellular protein trafficking to large scale motion of animal
groups, the physical concepts driving the self-organization of living systems
are still largely unraveled. Selforganization of active entities, leading to
novel phases and emergent macroscopic properties, recently shed new lights on
these complex dynamical processes. Here we show that, under the application of
a constant magnetic field, motile magnetotactic bacteria confined in
water-in-oil droplets self-assemble into a rotary motor exerting a torque on
the external oil phase. A collective motion in the form of a large-scale
vortex, reversable by inverting the field direction, builds-up in the droplet
with a vorticity perpendicular to the magnetic field. We study this collective
organization at different concentrations, magnetic fields and droplets radii
and reveal the formation of two torque-generating areas close to the droplet
interface. We characterize quantitatively the mechanical energy extractable
from this new biological and self-assembled motor
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