1,441 research outputs found
Impact of Many-Body Effects on Landau Levels in Graphene
We present magneto-Raman spectroscopy measurements on suspended graphene to
investigate the charge carrier density-dependent electron-electron interaction
in the presence of Landau levels. Utilizing gate-tunable magneto-phonon
resonances, we extract the charge carrier density dependence of the Landau
level transition energies and the associated effective Fermi velocity
. In contrast to the logarithmic divergence of at
zero magnetic field, we find a piecewise linear scaling of as a
function of charge carrier density, due to a magnetic field-induced suppression
of the long-range Coulomb interaction. We quantitatively confirm our
experimental findings by performing tight-binding calculations on the level of
the Hartree-Fock approximation, which also allow us to estimate an excitonic
binding energy of 6 meV contained in the experimentally extracted
Landau level transitions energies.Comment: 10 pages, 6 figure
Band structures of rare gas solids within the GW approximation
Band structures for solid rare gases (Ne, Ar) have been calculated using the
GW approximation. All electron and pseudopotential ab initio calculations were
performed using Gaussian orbital basis sets and the dependence of particle-hole
gaps and electron affinities on basis set and treatment of core electrons is
investigated. All electron GW calculations have a smaller particle-hole gap
than pseudopotential GW calculations by up to 0.2 eV. Quasiparticle electron
and hole excitation energies, valence band widths and electron affinities are
generally in very good agreement with those derived from optical absorption and
photoemission measurements.Comment: 7 pages 1 figur
Ab initio many-body calculation of excitons in solid Ne and Ar
Absorption spectra, exciton energy levels and wave functions for solid Ne and
Ar have been calculated from first principles using many-body techniques.
Electronic band structures of Ne and Ar were calculated using the GW
approximation. Exciton states were calculated by diagonalizing an exciton
Hamiltonian derived from the particle-hole Green function, whose equation of
motion is the Bethe-Salpeter equation. Singlet and triplet exciton series up to
n=5 for Ne and n=3 for Ar were obtained. Binding energies and
longitudinal-transverse splittings of n=1 excitons are in excellent agreement
with experiment. Plots of correlated electron-hole wave functions show that the
electron-hole complex is delocalised over roughly 7 a.u. in solid Ar.Comment: 6 page
Integrated impedance bridge for absolute capacitance measurements at cryogenic temperatures and finite magnetic fields
We developed an impedance bridge that operates at cryogenic temperatures
(down to 60 mK) and in perpendicular magnetic fields up to at least 12 T. This
is achieved by mounting a GaAs HEMT amplifier perpendicular to a printed
circuit board containing the device under test and thereby parallel to the
magnetic field. The measured amplitude and phase of the output signal allows
for the separation of the total impedance into an absolute capacitance and a
resistance. Through a detailed noise characterization, we find that the best
resolution is obtained when operating the HEMT amplifier at the highest gain.
We obtained a resolution in the absolute capacitance of
6.4~aF at 77 K on a comb-drive actuator, while maintaining
a small excitation amplitude of 15~. We show the magnetic field
functionality of our impedance bridge by measuring the quantum Hall plateaus of
a top-gated hBN/graphene/hBN heterostructure at 60~mK with a probe signal of
12.8~.Comment: 7 pages, 5 figure
Fluorescent Nanozeolite Receptors for the Highly Selective and Sensitive Detection of Neurotransmitters in Water and Biofluids
The design and preparation of synthetic binders (SBs) applicable for small biomolecule sensing in aqueous media remains very challenging. SBs designed by the lock-and-key principle can be selective for their target analyte but usually show an insufficient binding strength in water. In contrast, SBs based on symmetric macrocycles with a hydrophobic cavity can display high binding affinities but generally suffer from indiscriminate binding of many analytes. Herein, a completely new and modular receptor design strategy based on microporous hybrid materials is presented yielding zeolite-based artificial receptors (ZARs) which reversibly bind the neurotransmitters serotonin and dopamine with unprecedented affinity and selectivity even in saline biofluids. ZARs are thought to uniquely exploit both the non-classical hydrophobic effect and direct non-covalent recognition motifs, which is supported by in-depth photophysical, and calorimetric experiments combined with full atomistic modeling. ZARs are thermally and chemically robust and can be readily prepared at gram scales. Their applicability for the label-free monitoring of important enzymatic reactions, for (two-photon) fluorescence imaging, and for high-throughput diagnostics in biofluids is demonstrated. This study showcases that artificial receptor based on microporous hybrid materials can overcome standing limitations of synthetic chemosensors, paving the way towards personalized diagnostics and metabolomics
A Distinct Pool of Nav1.5 Channels at the Lateral Membrane of Murine Ventricular Cardiomyocytes.
Background: In cardiac ventricular muscle cells, the presence of voltage-gated sodium channels Na <sub>v</sub> 1.5 at the lateral membrane depends in part on the interaction between the dystrophin-syntrophin complex and the Na <sub>v</sub> 1.5 C-terminal PDZ-domain-binding sequence Ser-Ile-Val (SIV motif). α1-Syntrophin, a PDZ-domain adaptor protein, mediates the interaction between Na <sub>v</sub> 1.5 and dystrophin at the lateral membrane of cardiac cells. Using the cell-attached patch-clamp approach on cardiomyocytes expressing Na <sub>v</sub> 1.5 in which the SIV motif is deleted (ΔSIV), sodium current (I <sub>Na</sub> ) recordings from the lateral membrane revealed a SIV-motif-independent I <sub>Na</sub> . Since immunostaining has suggested that Na <sub>v</sub> 1.5 is expressed in transverse (T-) tubules, this remaining I <sub>Na</sub> might be carried by channels in the T-tubules. Of note, a recent study using heterologous expression systems showed that α1-syntrophin also interacts with the Na <sub>v</sub> 1.5 N-terminus, which may explain the SIV-motif independent I <sub>Na</sub> at the lateral membrane of cardiomyocytes. Aim: To address the role of α1-syntrophin in regulating the I <sub>Na</sub> at the lateral membrane of cardiac cells. Methods and Results: Patch-clamp experiments in cell-attached configuration were performed on the lateral membranes of wild-type, α1-syntrophin knockdown, and ΔSIV ventricular mouse cardiomyocytes. Compared to wild-type, a reduction of the lateral I <sub>Na</sub> was observed in myocytes from α1-syntrophin knockdown hearts. Similar to ΔSIV myocytes, a remaining I <sub>Na</sub> was still recorded. In addition, cell-attached I <sub>Na</sub> recordings from lateral membrane did not differ significantly between non-detubulated and detubulated ΔSIV cardiomyocytes. Lastly, we obtained evidence suggesting that cell-attached patch-clamp experiments on the lateral membrane cannot record currents carried by channels in T-tubules such as calcium channels. Conclusion: Altogether, these results suggest the presence of a sub-pool of sodium channels at the lateral membrane of cardiomyocytes that is independent of α1-syntrophin and the PDZ-binding motif of Na <sub>v</sub> 1.5, located in membrane domains outside of T-tubules. The question of a T-tubular pool of Na <sub>v</sub> 1.5 channels, however, remains open
Airborne Topographic Mapper Calibration Procedures and Accuracy Assessment
Description of NASA Airborn Topographic Mapper (ATM) lidar calibration procedures including analysis of the accuracy and consistancy of various ATM instrument parameters and the resulting influence on topographic elevation measurements. The ATM elevations measurements from a nominal operating altitude 500 to 750 m above the ice surface was found to be: Horizontal Accuracy 74 cm, Horizontal Precision 14 cm, Vertical Accuracy 6.6 cm, Vertical Precision 3 cm
Label-free and fluorescence biosensing platform using one dimensional photonic crystal chips
The increasing demand for early detection of diseases drives the efforts to develop more and more sensitive techniques to detect biomarkers in extremely low concentrations. Electromagnetic modes at the surface of one dimensional photonic crystals, usually called Bloch surface waves, were demonstrated to enhance the resolution and constitute an attractive alternative to surface plasmon polariton optical biosensors. We report on the development of Bloch surface wave biochips operating in both label-free and fluorescence modes and demonstrate their use in ovalbumin recognition assays
On reminder effects, drop-outs and dominance: evidence from an online experiment on charitable giving
We present the results of an experiment that (a) shows the usefulness of screening out drop-outs and (b) tests whether different methods of payment and reminder intervals affect charitable giving. Following a lab session, participants could make online donations to charity for a total duration of three months. Our procedure justifying the exclusion of drop-outs consists in requiring participants to collect payments in person flexibly and as known in advance and as highlighted to them later. Our interpretation is that participants who failed to collect their positive payments under these circumstances are likely not to satisfy dominance. If we restrict the sample to subjects who did not drop out, but not otherwise, reminders significantly increase the overall amount of charitable giving. We also find that weekly reminders are no more effective than monthly reminders in increasing charitable giving, and that, in our three months duration experiment, standing orders do not increase giving relative to one-off donations
On the stability of 2 \sqrt{2} x 2 \sqrt{2} oxygen ordered superstructures in YBa2Cu3O6+x
We have compared the ground-state energy of several observed or proposed " 2
\sqrt{2} x 2 \sqrt{2} oxygen (O) ordered superstructures " (from now on HS),
with those of "chain superstructures" (CS) (in which the O atoms of the basal
plane are ordered in chains), for different compositions x in YBa2Cu3O6+x. The
model Hamiltonian contains i) the Madelung energy, ii) a term linear in the
difference between Cu and O hole occupancies which controls charge transfer,
and iii) covalency effects based on known results for models in one and
two dimensions. The optimum distribution of charge is determined minimizing the
total energy, and depends on two parameters which are determined from known
results for x=1 and x=0.5. We obtain that on the O lean side, only CS are
stable, while for x=7/8, a HS with regularly spaced O vacancies added to the
x=1 structure is more stable than the corresponding CS for the same x. We find
that the detailed positions of the atoms in the structure, and long-range
Coulomb interactions, are crucial for the electronic structure, the mechanism
of charge transfer, the stability of the different phases, and the possibility
of phase separation.Comment: 24 text pages, Latex, one fig. included as ps file, to be publisheb
in Phys. Rev.
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