153 research outputs found
Elucidation of role of graphene in catalytic designs for electroreduction of oxygen
Graphene is, in principle, a promising material for consideration as
component (support, active site) of electrocatalytic materials, particularly
with respect to reduction of oxygen, an electrode reaction of importance to
low-temperature fuel cell technology. Different concepts of utilization,
including nanostructuring, doping, admixing, preconditioning, modification or
functionalization of various graphene-based systems for catalytic
electroreduction of oxygen are elucidated, as well as important strategies to
enhance the systems' overall activity and stability are discussed
Fractional Hamiltonian Monodromy from a Gauss-Manin Monodromy
Fractional Hamiltonian Monodromy is a generalization of the notion of
Hamiltonian Monodromy, recently introduced by N. N. Nekhoroshev, D. A.
Sadovskii and B. I. Zhilinskii for energy-momentum maps whose image has a
particular type of non-isolated singularities. In this paper, we analyze the
notion of Fractional Hamiltonian Monodromy in terms of the Gauss-Manin
Monodromy of a Riemann surface constructed from the energy-momentum map and
associated to a loop in complex space which bypasses the line of singularities.
We also prove some propositions on Fractional Hamiltonian Monodromy for 1:-n
and m:-n resonant systems.Comment: 39 pages, 24 figures. submitted to J. Math. Phy
Evaluation of Reduced-Graphene-Oxide Aligned with WO3-Nanorods as Support for Pt Nanoparticles during Oxygen Electroreduction in Acid Medium
Hybrid supports composed of chemically-reduced graphene-oxide-aligned with
tungsten oxide nanowires are considered here as active carriers for dispersed
platinum with an ultimate goal of producing improved catalysts for
electroreduction of oxygen in acid medium. Here WO3 nanostructures are expected
to be attached mainly to the edges of graphene thus making the hybrid structure
not only highly porous but also capable of preventing graphene stacking and
creating numerous sites for the deposition of Pt nanoparticles. Comparison has
been made to the analogous systems utilizing neither reduced graphene oxide nor
tungsten oxide component. By over-coating the reduced-graphene-oxide support
with WO3 nanorods, the electrocatalytic activity of the system toward the
reduction of oxygen in acid medium has been enhanced even at the low Pt loading
of 30 microg cm-2. The RRDE data are consistent with decreased formation of
hydrogen peroxide in the presence of WO3. Among important issues are such
features of the oxide as porosity, large population of hydroxyl groups, high
Broensted acidity, as well as fast electron transfers coupled to unimpeded
proton displacements. The conclusions are supported with mechanistic and
kinetic studies involving double-potential-step chronocoulometry as an
alternative diagnostic tool to rotating ring-disk voltammetry.Comment: arXiv admin note: text overlap with arXiv:1805.0315
PF191012 Myszyniec - highest Orionid meteor ever recorded
On the night of Oct 18/19, 2012 at 00:23 UT a -14.7 mag Orionid fireball
occurred over northeastern Poland. The precise orbit and atmospheric trajectory
of the event is presented, based on the data collected by five video and one
photographic Polish Fireball Network (PFN) stations. The beginning height of
the meteor is 168.4 +\- 0.6 km which makes the PF191012 Myszyniec fireball the
highest ever observed, well documented meteor not belonging to the Leonid
shower. The ablation became the dominant source of light of the meteor at a
height of around 115 km. The thermalization of sputtered particles is suggested
to be the source of radiation above that value. The transition height of 115 km
is 10-15 km below the transition heights derived for Leonids and it might
suggest that the material of Leonids should be more fragile and have probably
smaller bulk density than in case of Orionids.Comment: 5 pages, 5 figures, accpeted for publication in Astronomy &
Astrophysic
Amino acid substitution equivalent to human chorea-acanthocytosis I2771R in yeast Vps13 protein affects its binding to phosphatidylinositol 3-phosphate
The rare human disorder chorea-acanthocytosis (ChAc) is caused by mutations in hVPS13A gene. The hVps13A protein interacts
with actin and regulates the level of phosphatidylinositol 4-phosphate (PI4P) in the membranes of neuronal cells. Yeast
Vps13 is involved in vacuolar protein transport and, like hVps13A, participates in PI4P metabolism. Vps13 proteins are conserved
in eukaryotes, but their molecular function remains unknown. One of the mutations found in ChAc patients causes
amino acids substitution I2771R which affects the localization of hVps13A in skeletal muscles. To dissect the mechanism of
pathogenesis of I2771R, we created and analyzed a yeast strain carrying the equivalent mutation. Here we show that in yeast,
substitution I2749R causes dysfunction of Vps13 protein in endocytosis and vacuolar transport, although the level of the protein
is not affected, suggesting loss of function. We also show that Vps13, like hVps13A, influences actin cytoskeleton organization
and binds actin in immunoprecipitation experiments. Vps13-I2749R binds actin, but does not function in the actin
cytoskeleton organization. Moreover, we show that Vps13 binds phospholipids, especially phosphatidylinositol 3-phosphate
(PI3P), via its SHR_BD and APT1 domains. Substitution I2749R attenuates this ability. Finally, the localization of Vps13-GFP is
altered when cellular levels of PI3P are decreased indicating its trafficking within the endosomal membrane system. These results
suggest that PI3P regulates the functioning of Vps13, both in protein trafficking and actin cytoskeleton organization.
Attenuation of PI3P-binding ability in the mutant hVps13A protein may be one of the reasons for its mislocalization and disrupted
function in cells of patients suffering from ChAc
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