320 research outputs found
Correlation effects in the density of states of annealed GaMnAs
We report on an experimental study of low temperature tunnelling in hybrid
NbTiN/GaMnAs structures. The conductance measurements display a root mean
square V dependence, consistent with the opening of a correlation gap in the
density of states of GaMnAs. Our experiment shows that low temperature
annealing is a direct empirical tool that modifies the correlation gap and thus
the electron-electron interaction. Consistent with previous results on
boron-doped silicon we find, as a function of voltage, a transition across the
phase boundary delimiting the direct and exchange correlation regime.Comment: Replaced with revised version. To appear in Phys. Rev.
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Aryl-viologen pentapeptide self-assembled conductive nanofibers.
A pentapeptide sequence was functionalized with an asymmetric arylated methyl-viologen (AVI3D2) and through controllable β-sheet self-assembly, conductive nanofibers were formed. Using a combination of spectroscopic techniques and conductive atomic force microscopy, we investigated the molecular conformation of the resultant AVI3D2 fibers and how their conductivity is affected by β-sheet self-assembly. These conductive nanofibers have potential for future exploration as molecular wires in optoelectronic applications.ERC (‘ASPiRe’, 240629)
Marie Curie (FP7 ‘SASSYPOL’ ITN, 607602
Surface versus bulk characterization of the electronic inhomogeneity in a VO_{2} film
We investigated the inhomogeneous electronic properties at the surface and
interior of VO_{2} thin films that exhibit a strong first-order metal-insulator
transition (MIT). Using the crystal structural change that accompanies a VO_{2}
MIT, we used bulk-sensitive X-ray diffraction (XRD) measurements to estimate
the fraction of metallic volume p^{XRD} in our VO_{2} film. The temperature
dependence of the p was very closely correlated with the dc
conductivity near the MIT temperature, and fit the percolation theory
predictions quite well: (p - p_{c})^{t} with t = 2.00.1
and p_{c} = 0.160.01. This agreement demonstrates that in our VO
thin film, the MIT should occur during the percolation process. We also used
surface-sensitive scanning tunneling spectroscopy (STS) to investigate the
microscopic evolution of the MIT near the surface. Similar to the XRD results,
STS maps revealed a systematic decrease in the metallic phase as temperature
decreased. However, this rate of change was much slower than the rate observed
with XRD, indicating that the electronic inhomogeneity near the surface differs
greatly from that inside the film. We investigated several possible origins of
this discrepancy, and postulated that the variety in the strain states near the
surface plays an important role in the broad MIT observed using STS. We also
explored the possible involvement of such strain effects in other correlated
electron oxide systems with strong electron-lattice interactions.Comment: 27 pages and 7 figure
Energy-resolved electron-spin dynamics at surfaces of p-doped GaAs
Electron-spin relaxation at different surfaces of p-doped GaAs is
investigated by means of spin, time and energy resolved 2-photon photoemission.
These results are contrasted with bulk results obtained by time-resolved
Faraday rotation measurements as well as calculations of the Bir-Aronov-Pikus
spin-flip mechanism. Due to the reduced hole density in the band bending region
at the (100) surface the spin-relaxation time increases over two orders of
magnitude towards lower energies. At the flat-band (011) surface a constant
spin relaxation time in agreement with our measurements and calculations for
bulk GaAs is obtained.Comment: 6 pages, 4 figure
Стабилизация движения робота по показаниям электронного компаса
Laser-induced breakdown spectroscopy has been applied to polymer samples in order to investigate the possibility of using this method for the identification of different materials. The plasma emission spectra of high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyvinyl chloride (PVC), polyethylene terephthylene (PET), and polypropylene (PP) have been studied. Spectral features have been measured - for example, the 725.7 nm chlorine line, the 486.13 mm H(?) line, and the 247.86 nm carbon line - whose evaluation with neural networks permits identification accuracies between 90 and 1 00 per cent, depending on polymer type
Формирование алмазоподобных кремний-углеродных покрытий
Выпускная квалификационная работа 111 с., 23 рис., 29 табл., 39 источников, 1 прил.
Ключевые слова: алмазоподообные углеродные, кремний, ПФМС, несамостоятельный дуговой разряд, твердость, тонкие пленки.
Объектом исследования являются алмазоподобные кремний-углеродные покрытия, полученные из плазмы несамостоятельного дугового разряда с накаленным катодом.
Цель работы – изучение процесса формирования алмазоподобных кремний-углеродных покрытий и исследование их свойств
В процессе работы проводилась оптимизация процесса осаждения и экспериментальные исследования полученных пленок.
В результате исследования были получены твердые покрытия с низкой степенью износа и низким коэффициентом трения.
Область применения: повышение срока службы промышленных механизмов, медицинских инструментов и др.Final qualifying work of 111 p., 23 Fig., 29 tables, 39 source, 1 app.
Keywords: diamond-like carbon, silicon, PFMS, dependent arc discharge, hardness, thin films.
The object of the study is silicon-doped diamond-like carbon films prepared from the plasma of the dependent arc discharge with hot cathode.
The work objective was the optimization of the process of deposition of silicon-doped diamond-like carbon films, synthesis of coatings and their research.
In the process of the work it was carried out, that the optimization of the deposition process and experimental investigations of the received films.
The study was received the solid films with a high wear resistance and a low friction coefficient.
Scope: improving the lifetime of industrial machinery, medical tools, and other
The novel benzimidazole derivative BRP-7 inhibits leukotriene biosynthesis in vitro and in vivo by targeting 5-lipoxygenase-activating protein (FLAP).
BACKGROUND AND PURPOSE:
Leukotrienes (LTs) are inflammatory mediators produced via the 5-lipoxygenase (5-LOX) pathway and are linked to diverse disorders, including asthma, allergic rhinitis and cardiovascular diseases. We recently identified the benzimidazole derivative BRP-7 as chemotype for anti-LT agents by virtual screening targeting 5-LOX-activating protein (FLAP). Here, we aimed to reveal the in vitro and in vivo pharmacology of BRP-7 as an inhibitor of LT biosynthesis.
EXPERIMENTAL APPROACH:
We analysed LT formation and performed mechanistic studies in human neutrophils and monocytes, in human whole blood (HWB) and in cell-free assays. The effectiveness of BRP-7 in vivo was evaluated in rat carrageenan-induced pleurisy and mouse zymosan-induced peritonitis.
KEY RESULTS:
BRP-7 potently suppressed LT formation in neutrophils and monocytes and this was accompanied by impaired 5-LOX co-localization with FLAP. Neither the cellular viability nor the activity of 5-LOX in cell-free assays was affected by BRP-7, indicating that a functional FLAP is needed for BRP-7 to inhibit LTs, and FLAP bound to BRP-7 linked to a solid matrix. Compared with the FLAP inhibitor MK-886, BRP-7 did not significantly inhibit COX-1 or microsomal prostaglandin E2 synthase-1, implying the selectivity of BRP-7 for FLAP. Finally, BRP-7 was effective in HWB and impaired inflammation in vivo, in rat pleurisy and mouse peritonitis, along with reducing LT levels.
CONCLUSIONS AND IMPLICATIONS:
BRP-7 potently suppresses LT biosynthesis by interacting with FLAP and exhibits anti-inflammatory effectiveness in vivo, with promising potential for further development
Charge density waves and surface Mott insulators for adlayer structures on semiconductors: extended Hubbard modeling
Motivated by the recent experimental evidence of commensurate surface charge
density waves (CDW) in Pb/Ge(111) and Sn/Ge(111) sqrt{3}-adlayer structures, as
well as by the insulating states found on K/Si(111):B and SiC(0001), we have
investigated the role of electron-electron interactions, and also of
electron-phonon coupling, on the narrow surface state band originating from the
outer dangling bond orbitals of the surface. We model the sqrt{3} dangling bond
lattice by an extended two-dimensional Hubbard model at half-filling on a
triangular lattice. We include an on-site Hubbard repulsion U and a
nearest-neighbor Coulomb interaction V, plus a long-ranged Coulomb tail. The
electron-phonon interaction is treated in the deformation potential
approximation. We have explored the phase diagram of this model including the
possibility of commensurate 3x3 phases, using mainly the Hartree-Fock
approximation. For U larger than the bandwidth we find a non-collinear
antiferromagnetic SDW insulator, possibly corresponding to the situation on the
SiC and K/Si surfaces. For U comparable or smaller, a rich phase diagram
arises, with several phases involving combinations of charge and
spin-density-waves (SDW), with or without a net magnetization. We find that
insulating, or partly metallic 3x3 CDW phases can be stabilized by two
different physical mechanisms. One is the inter-site repulsion V, that together
with electron-phonon coupling can lower the energy of a charge modulation. The
other is a novel magnetically-induced Fermi surface nesting, stabilizing a net
cell magnetization of 1/3, plus a collinear SDW, plus an associated weak CDW.
Comparison with available experimental evidence, and also with first-principle
calculations is made.Comment: 11 pages, 9 figure
Nonlinear intensity dependence of ratchet currents induced by terahertz laser radiation in bilayer graphene with asymmetric periodic grating gates
We report on the observation of a nonlinear intensity dependence of the
terahertz radiation induced ratchet effects in bilayer graphene with asymmetric
dual grating gate lateral lattices. These nonlinear ratchet currents are
studied in structures of two designs with dual grating gate fabricated on top
of encapsulated bilayer graphene and beneath it. The strength and sign of the
photocurrent can be controllably varied by changing the bias voltages applied
to individual dual grating subgates and the back gate. The current consists of
contributions insensitive to the radiation's polarization state, defined by the
orientation of the radiation electric field vector with respect to the dual
grating gate metal stripes, and the circular ratchet sensitive to the radiation
helicity. We show that intense terahertz radiation results in a nonlinear
intensity dependence caused by electron gas heating. At room temperature the
ratchet current saturates at high intensities of the order of hundreds to
several hundreds of kWcm. At , the nonlinearity manifests
itself at intensities that are one or two orders of magnitude lower, moreover,
the photoresponse exhibits a complex dependence on the intensity, including a
saturation and even a change of sign with increasing intensity. This complexity
is attributed to the interplay of the Seebeck ratchet and the dynamic carrier
density redistribution, which feature different intensity dependencies and a
nonlinear behavior of the sample's conductivity induced by electron gas
heating. Our study demonstrates that graphene-based asymmetric dual grating
gate devices can be used as terahertz detectors at room temperature over a wide
dynamic range, spanning many orders of magnitude of terahertz radiation power.
Therefore, their integration together with current-driven read-out electronics
is attractive for the operation with high-power pulsed sources.Comment: 11 pages, 13 figure
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