6,200 research outputs found
Low-velocity collisions of centimeter-sized dust aggregates
Collisions between centimeter- to decimeter-sized dusty bodies are important
to understand the mechanisms leading to the formation of planetesimals. We thus
performed laboratory experiments to study the collisional behavior of dust
aggregates in this size range at velocities below and around the fragmentation
threshold. We developed two independent experimental setups with the same goal
to study the effects of bouncing, fragmentation, and mass transfer in free
particle-particle collisions. The first setup is an evacuated drop tower with a
free-fall height of 1.5 m, providing us with 0.56 s of microgravity time so
that we observed collisions with velocities between 8 mm/s and 2 m/s. The
second setup is designed to study the effect of partial fragmentation (when
only one of the two aggregates is destroyed) and mass transfer in more detail.
It allows for the measurement of the accretion efficiency as the samples are
safely recovered after the encounter. Our results are that for very low
velocities we found bouncing as could be expected while the fragmentation
velocity of 20 cm/s was significantly lower than expected. We present the
critical energy for disruptive collisions Q*, which showed up to be at least
two orders of magnitude lower than previous experiments in the literature. In
the wide range between bouncing and disruptive collisions, only one of the
samples fragmented in the encounter while the other gained mass. The accretion
efficiency in the order of a few percent of the particle's mass is depending on
the impact velocity and the sample porosity. Our results will have consequences
for dust evolution models in protoplanetary disks as well as for the strength
of large, porous planetesimal bodies
Gas/particle partitioning and global distribution of polycyclic aromatic hydrocarbons â A modelling approach
The global atmospheric distribution and long-range transport (LRT) potential of three polycyclic aromatic hydrocarbons (PAH) - anthracene, fluoranthene and benzo[a]pyrene - are studied. The model used is a global aerosol-chemistry-transport-model, which is based on an atmospheric general circulation model. The model includes an in-built dynamic aerosol model coupled to two-dimensional surface compartments. Several parameterisations of gas/particle partitioning and different assumptions of degradation in the aerosol particulate phase were tested. PAHs are mostly distributed in the source regions but reach the Arctic and the Antarctic. The Canadian Arctic is predicted to be significantly less affected by mid-latitude PAH emissions than the European Arctic. Re-volatilisation is significant for semivolatile PAHs. Accumulation of semivolatile PAHs in polar regions, however, is not indicated. The model study suggests that gas/particle partitioning in air drastically influences the atmospheric cycling, the total environmental fate (e.g. compartmental distributions) and the LRT potential of the substances studied. A parameterisation which calculates the gas/particle partitioning assuming absorption into organic matter and adsorption to black carbon (soot) agrees best with the observations at remote sites. The study provides evidence that the degradation in the particulate phase must be slower than that in the gas-phase. The predicted concentrations of the semivolatile PAHs anthracene and fluoranthene in near-ground air at remote sites in mid and high northern latitudes are in line with measured concentrations, if adsorption of the substances to soot combined with absorption in particulate organic matter is assumed to determine gas/particle partitioning, but cannot be explained by adsorption alone (Junge-Pankow parameterisation of gas/particle partitioning). The results suggest that PAHs absorbed in the organic matrix of particulate matter is shielded from the gas-phase. (C) 2009 Elsevier Ltd. All rights reserved. [References: 42
Electrical detectability of magnon-mediated spin current shot noise
A magnonic spin current crossing a ferromagnet-metal interface is accompanied
by spin current shot noise arising from the discrete quanta of spin carried by
magnons. In thin films, e.g., the spin of so-called squeezed magnons have been
shown to deviate from the common value , with corresponding changes in
the spin noise. In experiments, spin currents are typically converted to charge
currents via the inverse spin Hall effect. We here analyze the magnitude of the
spin current shot noise in the charge channel for a typical electrically
detected spin pumping experiment, and find that the voltage noise originating
from the spin current shot noise is much smaller than the inevitable
Johnson-Nyquist noise. Furthermore, we find that due to the local nature of the
spin-charge conversion, the ratio of spin current shot noise and
Johnson-Nyquist noise cannot be systematically enhanced by tuning the sample
geometry, in contrast to the linear increase in dc spin pumping voltage with
sample length. Instead, the ratio depends sensitively on material-specific
transport properties. Our analysis thus provides guidance for the experimental
detection of squeezed magnons through spin pumping shot noise.Comment: Revised manuscript title, added paragraph of interpretation of the
shot noise enhancement with temperature, added brief discussion of the low
temperature limit, references adde
Root colonization by arbuscular mycorrhizal fungi is reduced in tomato plants sprayed with fungicides
Arbuscular mycorrhizal fungi (AMF) form symbioses with many agricultural crops and can improve plant biomass and health. The performance of the AM symbiosis is context dependent, for example, usually the inoculation of the AMF Rhizophagus irregularis benefits plant biomass, but benefits can be suppressed by high soil fertility levels. Nevertheless, the importance of many other agricultural management practices on AMF, such as fungicides application, is poorly understood. Also, pesticide regulations usually neglect a comprehensive safety testing of fungicides on AMF and lawmakers require empirical support to improve such laws. The objective of this study was to evaluate the effects of spraying fungicides on tomato plants and the subsequent root colonization of plants grown in natural soil containing AMF and inoculated with R. irregularis. We detected that the inoculation of R. irregularis increased the total root colonization of the control plants that did not receive fungicides and that spraying the plants with the fungicides SignumÂź and TopasÂź reduced total root colonization. The effect on specific AM fungal structures was variable according to the product. SignumÂź reduced the occurrence of arbuscules, while TopasÂź reduced the occurrence of AM hyphae in the colonized roots. CuprozinÂź did not reduce total root colonization but reduced the occurrence of AM vesicles. Sampling time was also relevant. Effects were detected at 90 days, but not at 35 days. Our results show that fungicides safety should be evaluated for their effects on root colonization of crops in non-sterilized soils and at adequate sampling time
Control of nonlocal magnon spin transport via magnon drift currents
Spin transport via magnon diffusion in magnetic insulators is important for a
broad range of spin-based phenomena and devices. However, the absence of the
magnon equivalent of an electric force is a bottleneck. In this work, we
demonstrate the controlled generation of magnon drift currents in yttrium iron
garnet/platinum heterostructures. By performing electrical injection and
detection of incoherent magnons, we find magnon drift currents that stem from
the interfacial Dzyaloshinskii-Moriya interaction. We can further control the
magnon drift by the orientation of the magnetic field. The drift current
changes the magnon propagation length by up to 6 % relative to diffusion.
We generalize the magnonic spin transport theory to include a finite drift
velocity resulting from any inversion asymmetric interaction, and obtain
results consistent with our experiments.Comment: 6 pages, 3 figure
All Electrical Access to Topological Transport Features in MnPtSn Films
The presence of non-trivial magnetic topology can give rise to non-vanishing
scalar spin chirality and consequently a topological Hall or Nernst effect. In
turn, topological transport signals can serve as indicators for topological
spin structures. This is particularly important in thin films or nanopatterned
materials where the spin structure is not readily accessible. Conventionally,
the topological response is determined by combining magnetotransport data with
an independent magnetometry experiment. This approach is prone to introduce
measurement artifacts. In this study, we report the observation of large
topological Hall and Nernst effects in micropatterned thin films of
MnPtSn below the spin reorientation temperature K. The magnitude of the topological Hall effect
nm is close to the value reported in
bulk MnPtSn, and the topological Nernst effect nV K measured in the same microstructure has a similar magnitude as
reported for bulk MnGe ( nV K), the
only other material where a topological Nernst was reported. We use our data as
a model system to introduce a topological quantity, which allows to detect the
presence of topological transport effects without the need for independent
magnetometry data. Our approach thus enables the study of topological transport
also in nano-patterned materials without detrimental magnetization related
limitations.Comment: 8 pages, 3 figure
Lipids From Trypanosoma cruzi Amastigotes of RA and K98 Strains Generate a Pro-inflammatory Response via TLR2/6
Lipids from microorganisms are ligands of Toll like receptors (TLRs) and modulate the innate immune response. Herein, we analyze in vitro the effect of total lipid extracts from Trypanosoma cruzi amastigotes of RA and K98 strains (with polar biological behavior) on the induction of the inflammatory response and the involvement of TLRs in this process. We demonstrated that total lipid extracts from both strains induced lipid body formation, cyclooxygenase-2 expression and TNF-a and nitric oxide release in macrophages, as well as NF-ÎșB activation and IL-8 release in HEK cells specifically through a TLR2/6 dependent pathway. We also evaluated the inflammatory response induced by total lipid extracts obtained from lysed parasites that were overnight incubated to allow the action of parasite hydrolytic enzymes, such as Phospholipase A1, over endogenous phospholipids. After incubation, these total lipid extracts showed a significantly reduced pro-inflammatory response, which could be attributed to the changes in the content of known bioactive lipid molecules like lysophospholipids and fatty acids, here reported. Moreover, analyses of total fatty acids in each lipid extract were performed by gas chromatography-mass spectrometry. Our results indicate a relevant role of T. cruzi lipids in the induction of a pro-inflammatory response through the TLR2/6 pathway that could contribute to the modulation of the immune response and host survival.Fil: Bott, Emanuel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica; ArgentinaFil: Carneiro, Alan B.. Instituto Oswaldo Cruz; BrasilFil: Gimenez, Guadalupe. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica; ArgentinaFil: LĂłpez, MarĂa Gabriela. Instituto Nacional de TecnologĂa Agropecuaria; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Lammel, Estela MarĂa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica; ArgentinaFil: Atella, Georgia C.. Universidade Federal do Rio de Janeiro; BrasilFil: Bozza, Patricia T.. Instituto Oswaldo Cruz; BrasilFil: BelaunzarĂĄn, MarĂa Laura. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica; Argentin
Spin-Hall-Active Platinum Thin Films Grown Via Atomic Layer Deposition
We study the magnetoresistance of yttrium iron garnet/Pt heterostructures in
which the Pt layer was grown via atomic layer deposition (ALD).
Magnetotransport experiments in three orthogonal rotation planes reveal the
hallmark features of spin Hall magnetoresistance. We estimate the spin
transport parameters by comparing the magnitude of the magnetoresistance in
samples with different Pt thicknesses. We compare the spin Hall angle and the
spin diffusion length of the ALD Pt layers to the values reported for
high-quality sputter-deposited Pt films. The spin diffusion length of 1.5nm
agrees well with platinum thin films reported in the literature, whereas the
spin Hall magnetoresistance is
approximately a factor of 20 smaller compared to that of our sputter-deposited
films. Our results demonstrate that ALD allows fabricating spin-Hall-active Pt
films of suitable quality for use in spin transport structures. This work
provides the basis to establish conformal ALD coatings for arbitrary surface
geometries with spin-Hall-active metals and could lead to 3D spintronic devices
in the future.Comment: 11 pages, 3 figure
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