9,289 research outputs found
Tunneling Splittings in Mn12-Acetate Single Crystals
A Landau-Zener multi-crossing method has been used to investigate the tunnel
splittings in high quality Mn-acetate single crystals in the pure
quantum relaxation regime and for fields applied parallel to the magnetic easy
axis. With this method several individual tunneling resonances have been
studied over a broad range of time scales. The relaxation is found to be
non-exponential and a distribution of tunnel splittings is inferred from the
data. The distributions suggest that the inhomogeneity in the tunneling rates
is due to disorder that produces a non-zero mean value of the average
transverse anisotropy, such as in a solvent disorder model. Further, the effect
of intermolecular dipolar interaction on the magnetic relaxation has been
studied.Comment: Europhysics Letters (in press). 7 pages, including 3 figure
Anomalous Hall conductivity control in MnNiN antiperovskite by epitaxial strain along the kagome plane
Antiferromagnetic manganese-based nitride antiperovskites, such as MnNiN,
hold a triangular frustrated magnetic ordering over their kagome lattice formed
by the Mn atoms along the (111)-plane. As such, frustration imposes a
non-trivial interplay between the symmetric and asymmetric magnetic
interactions, which can only reach equilibrium in a noncollinear magnetic
configuration. Consequently, the associated electronic interactions and their
possible tuning by external constraints, such as applied epitaxial strain, play
a crucial role in defining the microscopic and macroscopic properties of such
topological condensed matter systems. Thus, in the present work, we explored
and explained the effect of the epitaxial strain imposed within the
(111)-plane, in which the magnetic and crystallographic symmetry operations are
kept fixed, and only the magnitude of the ionic and electronic interactions are
tuned. We found a linear shifting in the energy of the band structure and a
linear increase/decrease of the available states near the Fermi level with the
applied strain. Concretely, the compression strain reduces the Mn-Mn distances
in the (111) kagome plane but linearly increases the separation between the
stacked kagome lattices and the available states near the Fermi level. Despite
the linear controlling of the available states across the Fermi energy, the
anomalous Hall conductivity shows a non-linear behavior where the
conductivity nearly vanishes for tensile strain. On the other
hand, fetches a maximum increase of 26\% about the unstrained
structure for a compression value close to 1.5\%.This behavior found an
explanation in the non-divergent Berry curvature within the kagome plane, which
is increased for constraining but significantly reduced for expansion strain
values..
A cosmological dust model with extended f(chi) gravity
Introducing a fundamental constant of nature with dimensions of acceleration
into the theory of gravity makes it possible to extend gravity in a very
consistent manner. At the non-relativistic level a MOND-like theory with a
modification in the force sector is obtained, which is the limit of a very
general metric relativistic theory of gravity. Since the mass and length scales
involved in the dynamics of the whole universe require small accelerations of
the order of Milgrom's acceleration constant a_0, it turns out that the
relativistic theory of gravity can be used to explain the expansion of the
universe. In this work it is explained how to use that relativistic theory of
gravity in such a way that the overall large-scale dynamics of the universe can
be treated in a pure metric approach without the need to introduce dark matter
and/or dark energy components.Comment: 7 pages, 1 figure. Accepted for publication in the European Physical
Journal
A first--order irreversible thermodynamic approach to a simple energy converter
Several authors have shown that dissipative thermal cycle models based on
Finite-Time Thermodynamics exhibit loop-shaped curves of power output versus
efficiency, such as it occurs with actual dissipative thermal engines. Within
the context of First-Order Irreversible Thermodynamics (FOIT), in this work we
show that for an energy converter consisting of two coupled fluxes it is also
possible to find loop-shaped curves of both power output and the so-called
ecological function against efficiency. In a previous work Stucki [J.W. Stucki,
Eur. J. Biochem. vol. 109, 269 (1980)] used a FOIT-approach to describe the
modes of thermodynamic performance of oxidative phosphorylation involved in
ATP-synthesis within mithochondrias. In that work the author did not use the
mentioned loop-shaped curves and he proposed that oxidative phosphorylation
operates in a steady state simultaneously at minimum entropy production and
maximum efficiency, by means of a conductance matching condition between
extreme states of zero and infinite conductances respectively. In the present
work we show that all Stucki's results about the oxidative phosphorylation
energetics can be obtained without the so-called conductance matching
condition. On the other hand, we also show that the minimum entropy production
state implies both null power output and efficiency and therefore this state is
not fulfilled by the oxidative phosphorylation performance. Our results suggest
that actual efficiency values of oxidative phosphorylation performance are
better described by a mode of operation consisting in the simultaneous
maximization of the so-called ecological function and the efficiency.Comment: 20 pages, 7 figures, submitted to Phys. Rev.
Theoretical study of incoherent phi photoproduction on a deuteron target
We study the photoproduction of phi mesons in deuteron, paying attention to
the modification of the cross section from bound protons to the free ones with
the aim of comparing with recent results at LEPS. For this purpose we take into
account Fermi motion in single scattering and rescattering of the phi to
account for phi absorption on a second nucleon as well as the rescattering of
the proton. We find that the contribution of the double scattering is much
smaller than the typical cross section of gamma p to phi p in free space, which
implies a very small screening of the phi production in deuteron. The
contribution from the proton rescattering, on the other hand, is found to be
not negligible compared to the cross section of gamma p to phi p in free space,
and leads to a moderate reduction of the phi photoproduction cross section on a
deuteron at forward angles if LEPS set up is taken into account. The Fermi
motion allows contribution of the single scattering in regions forbidden by
phase space in the free case. In particular, we find that for momentum
transferred squared close to the maximum value, the Fermi motion changes
drastically the shape of d sigma / dt, to the point that the ratio of this
cross section to the free one becomes very sensitive to the precise value of t
chosen, or the size of the bin used in an experimental analysis. Hence, this
particular region of t does not seem the most indicated to find effects of a
possible phi absorption in the deuteron. This reaction is studied theoretically
as a function of t and the effect of the experimental angular cuts at LEPS is
also discussed, providing guidelines for future experimental analyses of the
reaction.Comment: 17 pages, 16 figure
Degradation of seventeen contaminants of emerging concern in municipal wastewater effluents by sonochemical advanced oxidation processes
The simultaneous degradation of seventeen emerging concern pollutants in effluent
from the municipal wastewater treatment plant (MWTP) of Bogotá-Colombia was
studied using high frequency ultrasound (375 kHz). The considered compounds in the
effluent corresponded to pharmaceuticals (diclofenac, carbamazepine, venlafaxine,
ciprofloxacin, norfloxacin, valsartan, losartan, irbesartan, sulfamethoxazole,
clarithromycin, azithromycin, erythromycin, metronidazole, trimethoprim and the high potentiality of the sono-photo-Fenton/oxalic acid system for the pollutants
elimination in real-world wastewater matrices.
clindamycin); cocaine and its major metabolite benzoylecgonine. Due to limitation of the
MWTP for the pollutants elimination, ultrasound was applied to remove these
compounds. Interestingly, ultrasonic physical action led to releasing of ciprofloxacin,
norfloxacin, diclofenac and sulfamethoxazole from suspended solids, whereas the
chemical effects induced degradation of the rest of compounds. For the latter ones, an
interesting correlation between the sonodegradation and arithmetic multiplication
between hydrophobicity and concentration of pollutants was established. Afterwards,
the sonochemical process was complemented with ferrous ions (sono-Fenton), ferrous
ions plus light (sono-photo-Fenton) or ferrous ions plus light in presence of oxalic acid
(sono-photo-Fenton/oxalic acid). Additionally, to clarify fundamental aspects of the
different systems, individual treatments in distilled water of a model pollutant (valsartan)
were performed. The complemented processes significantly enhanced all compounds
degradation, following the order: sono-photo-Fenton/oxalic acid > sono-photo-Fenton ~
sono-Fenton > sonochemistry. The Fe2+ addition improved the pollutants elimination by
generation of more hydroxyl radicals in the solution bulk. Meanwhile, oxalic acid
avoided Fe3+ precipitation favoring the iron catalytic cycle. Thus, the work demonstrate
TLR9 ligation in pancreatic stellate cells promotes tumorigenesis
Modulation of Toll-like receptor (TLR) signaling can have protective or protumorigenic effects on oncogenesis depending on the cancer subtype and on specific inflammatory elements within the tumor milieu. We found that TLR9 is widely expressed early during the course of pancreatic transformation and that TLR9 ligands are ubiquitous within the tumor microenvironment. TLR9 ligation markedly accelerates oncogenesis, whereas TLR9 deletion is protective. We show that TLR9 activation has distinct effects on the epithelial, inflammatory, and fibrogenic cellular subsets in pancreatic carcinoma and plays a central role in cross talk between these compartments. Specifically, TLR9 activation can induce proinflammatory signaling in transformed epithelial cells, but does not elicit oncogene expression or cancer cell proliferation. Conversely, TLR9 ligation induces pancreatic stellate cells (PSCs) to become fibrogenic and secrete chemokines that promote epithelial cell proliferation. TLR9-activated PSCs mediate their protumorigenic effects on the epithelial compartment via CCL11. Additionally, TLR9 has immune-suppressive effects in the tumor microenvironment (TME) via induction of regulatory T cell recruitment and myeloid-derived suppressor cell proliferation. Collectively, our work shows that TLR9 has protumorigenic effects in pancreatic carcinoma which are distinct from its influence in extrapancreatic malignancies and from the mechanistic effects of other TLRs on pancreatic oncogenesis
Um Jogo Educativo na Web no Contexto do Ensino Fundamental
Este artigo tem como objetivo apresentar o Sim Investigador, um jogo que busca motivar o estudante através do lúdico com a construção e resolução de casos (histórias) envolvendo o conteúdo de uma disciplina, e desenvolvido para estudantes do ensino fundamental e médio. No Sim Investigador o estudante receberá o papel de um investigador no qual deverá solucionar casos utilizando seus conhecimentos aprendidos na escola ou colégio, como também poderá construir suas próprias histórias no contexto de um conteúdo programático proposto por um professor, se aprofundando no conteúdo estudado. Um estudo de caso foi realizado com 49 estudantes de três escolas. Os resultados obtidos no estudo de caso mostra que 69,38% dos estudantes informaram se sentir ainda mais motivados ao estudo com o uso do jogo Sim Investigador
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