935 research outputs found
Programming the assembly of carboxylic acid-functionalised hybrid polyoxometalates
We report here the straightforward synthesis and characterisation of a series Anderson-type hybrid
polyoxometalates in high yield, functionalised with carboxylic acid following the reaction of anhydride
precursors with the starting hybrid cluster ([n-N(C4H9)4]3[MnMo6O18((OCH2)3CNH2)2]). Seven new
structures have been obtained, five of which have acid-terminated ligands. Six of these structures have
been isolated with a yield higher than 80% with high purity. This reaction is limited by the bulkiness of the
anhydride used; this effect can be employed to selectively synthesise one isomer out of three other
possibilities. The acid groups and aromatic platforms attached to the clusters can act as building tools to
bridge several length scales and engineer molecular packing within the crystal structure. The presence of
acids should also change the hydrophilicity of the clusters, and therefore the way they interact with
hydrophilic surfaces. We also show a potential relationship between the acid group interaction in the
packing diagram and the cluster’s tendency to interact with a hydrophilic surface. In addition to reporting
a derived synthetic path to new acid-terminated Mn-Anderson-type hybrids, we describe here a new way
to program self-assembly motifs of these compounds in the crystal structure and at interfaces
Characterizing top gated bilayer graphene interaction with its environment by Raman spectroscopy
In this work we study the behavior of the optical phonon modes in bilayer
graphene devices by applying top gate voltage, using Raman scattering. We
observe the splitting of the Raman G band as we tune the Fermi level of the
sample, which is explained in terms of mixing of the Raman (Eg) and infrared
(Eu) phonon modes, due to different doping in the two layers. We theoretically
analyze our data in terms of the bilayer graphene phonon self-energy which
includes non-homogeneous charge carrier doping between the graphene layers. We
show that the comparison between the experiment and theoretical model not only
gives information about the total charge concentration in the bilayer graphene
device, but also allows to separately quantify the amount of unintentional
charge coming from the top and the bottom of the system, and therefore to
characterize the interaction of bilayer graphene with its surrounding
environment
On the inner Double-Resonance Raman scattering process in bilayer graphene
The dispersion of phonons and the electronic structure of graphene systems
can be obtained experimentally from the double-resonance (DR) Raman features by
varying the excitation laser energy. In a previous resonance Raman
investigation of graphene, the electronic structure was analyzed in the
framework of the Slonczewski-Weiss-McClure (SWM) model, considering the outer
DR process. In this work we analyze the data considering the inner DR process,
and obtain SWM parameters that are in better agreement with those obtained from
other experimental techniques. This result possibly shows that there is still a
fundamental open question concerning the double resonance process in graphene
systems.Comment: 5 pages, 3 figure
Dysregulation of mannose-6-phosphate–dependent cholesterol homeostasis in acinar cells mediates pancreatitis
Theory of excited state absorptions in phenylene-based -conjugated polymers
Within a rigid-band correlated electron model for oligomers of
poly-(paraphenylene) (PPP) and poly-(paraphenylenevinylene) (PPV), we show that
there exist two fundamentally different classes of two-photon A states in
these systems to which photoinduced absorption (PA) can occur. At relatively
lower energies there occur A states which are superpositions of one
electron - one hole (1e--1h) and two electron -- two hole (2e--2h) excitations,
that are both comprised of the highest delocalized valence band and the lowest
delocalized conduction band states only. The dominant PA is to one specific
member of this class of states (the mA). In addition to the above class of
A states, PA can also occur to a higher energy kA state whose 2e--2h
component is {\em different} and has significant contributions from excitations
involving both delocalized and localized bands. Our calculated scaled energies
of the mA and the kA agree reasonably well to the experimentally
observed low and high energy PAs in PPV. The calculated relative intensities of
the two PAs are also in qualitative agreement with experiment. In the case of
ladder-type PPP and its oligomers, we predict from our theoretical work a new
intense PA at an energy considerably lower than the region where PA have been
observed currently. Based on earlier work that showed that efficient
charge--carrier generation occurs upon excitation to odd--parity states that
involve both delocalized and localized bands, we speculate that it is the
characteristic electronic nature of the kA that leads to charge generation
subsequent to excitation to this state, as found experimentally.Comment: Revtex4 style, 2 figures inserted in the text, three tables, 10 page
Spatial variability of apparent electrical conductivity and soil properties in a coffee production field
Advancement in the pressureless sintering of CP titanium using high-frequency induction heating
High-frequency induction heating is applied as an alternative heating source for pressureless sintering of commercially pure Ti powders, aiming to intensify the sintering process. The effects of the process parameters on the properties of the sintered material are systematically studied. The initial powder compact density is the most influential parameter permitting sintered structures with highly porous to almost fully dense appearance. Short heating time combined with sintering to temperatures just above the β-transus resulted in a strong diffusion bonding between the Ti powder particles, and grain growth is observed at the former boundaries of the neighboring powder particles. The dimpled appearance of the fracture surface at those regions confirmed the strong metallic interparticle bonding. Tensile properties comparable to those of Ti-Grade 3 and Ti-Grade 4 are achieved, which also demonstrates the efficiency of the induction sintering process. A mechanism explaining the fast and efficient sintering is proposed. The process has the added advantage of minimizing the oxygen pickup
Synthesis and crystallographic analysis of short pyridine-based oligoamides as DNA-targeting supramolecular binders
Partial Wave Analysis of
BES data on are presented. The
contribution peaks strongly near threshold. It is fitted with a
broad resonance with mass MeV, width MeV. A broad resonance peaking at 2020 MeV is also required
with width MeV. There is further evidence for a component
peaking at 2.55 GeV. The non- contribution is close to phase
space; it peaks at 2.6 GeV and is very different from .Comment: 15 pages, 6 figures, 1 table, Submitted to PL
Measurements of the Mass and Full-Width of the Meson
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five different decay
channels: , , (with ), (with
) and . From a combined fit of all five
channels, we determine the mass and full-width of to be
MeV/ and
MeV/.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.
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