38 research outputs found
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Iron redox pathway revealed in ferritin via electron transfer analysis.
Ferritin protein is involved in biological tissues in the storage and management of iron - an essential micro-nutrient in the majority of living systems. While there are extensive studies on iron-loaded ferritin, its functionality in iron delivery is not completely clear. Here, for the first time, differential pulse voltammetry (DPV) has been successfully adapted to address the challenge of resolving a cascade of fast and co-occurring redox steps in enzymatic systems such as ferritin. Using DPV, comparative analysis of ferritins from two evolutionary-distant organisms has allowed us to propose a stepwise resolution for the complex mix of concurrent redox steps that is inherent to ferritins and to fine-tune the structure-function relationship of each redox step. Indeed, the cyclic conversion between Fe3+ and Fe2+ as well as the different oxidative steps of the various ferroxidase centers already known in ferritins were successfully discriminated, bringing new evidence that both the 3-fold and 4-fold channels can be functional in ferritin
Characteristic nanoscale deformations on large area coherent graphite moir\'e
Highly oriented pyrolytic graphite (HoPG) may be the only known monatomic
crystal with the ability to host naturally formed moire patterns on its cleaved
surfaces, which are coherent over micrometer scales and with discrete sets of
twist angles of fixed periodicity. Such an aspect is in marked contrast to
twisted bilayer graphene (TBG) and other multilayered systems, where the long
range coherence of the moire is not easily maintained due to twist angle
disorder. We investigate the electronic and mechanical response of coherent
graphite moire patterns through inducing external strain from STM tip-induced
deformation. Consequently, unique anisotropic mechanical characteristics are
revealed. For example, a lateral widening of one-dimensional (1D) domain walls
(DWs) bridging Bernal (ABA) and rhombohedral (ABC) stacking domains (A, B and C
refer to the atomic layer positioning), was indicated. Further, in situ
tunneling spectroscopy as a function of the deformation indicated a tendency
towards increased electrical conductance, which may be associated with a higher
density of electronic states, and the consequent flattening of the electronic
energy band dispersion. Such features were probed across the DWs, with
implications for strain-induced electronic modulation of the moire
characteristics
Pinching and Probing of Polygonal Grain Boundaries
In this study, sub-angstrom spatial resolution is achieved in mapping and
spectroscopy of atoms and bonds within polygonal grain boundaries (GBs) of
graphite using Scanning Tunneling Microscopy (STM). Robust van Hove
singularities (VHS) are observed in addition to edge states under ambient
conditions. The bias-dependent nature of these states reveals metallic traits
of GB, through the charge accumulation and dissipation of localized electronic
states. Utilizing a surface elastic deformation technique induced by STM tip
allows pico-pinching of the GB, providing insights into its mechanical strength
as well as in-situ strain-induced modification of their unique spectroscopy,
revealing a tendency toward flattening of the electronic energy band
dispersion. An initial atomic-level experimental technique of probing
spin-polarized magnetic states is demonstrated, suggesting different densities
for spin-up and spin-down states within a spin-degenerate band structure
potentially applicable in spin transport or quantum spin sensing.Comment: Submitte
A single photoelectron transistor for quantum optical communications
A single photoelectron can be trapped and its photoelectric charge detected
by a source/drain channel in a transistor. Such a transistor photodetector can
be useful for flagging the safe arrival of a photon in a quantum repeater. The
electron trap can be photo-ionized and repeatedly reset for the arrival of
successive individual photons. This single photoelectron transistor (SPT)
operating at the lambda = 1.3 mu m tele-communication band, was demonstrated by
using a windowed-gate double-quantum-well InGaAs/InAlAs/InP heterostructure
that was designed to provide near-zero electron g-factor. The g-factor
engineering allows selection rules that would convert a photon's polarization
to an electron spin polarization. The safe arrival of the photo-electric charge
would trigger the commencement of the teleportation algorithm
On-chip unidirectional waveguiding for surface acoustic waves along a defect line in a triangular lattice
The latest advances in topological physics have yielded a rich toolset to
design highly robust wave transfer systems, for overcoming issues like beam
steering and lateral diffraction in surface acoustic waves (SAWs). However,
presently used designs for topologically protected SAWs have been largely
limited to spin or valley-polarized phases, which rely on non-zero Berry
curvature effects. Here we propose and experimentally demonstrate a highly
robust SAW waveguide on lithium niobate (LiNbO3), based on a line defect within
a true triangular phononic lattice, which instead employs an intrinsic
chirality of phase vortices and maintains a zero Berry curvature. The guided
SAW mode spans a wide bandwidth and shows confinement in the lateral direction
with 3 dB attenuation within half of the unit-cell length. SAW routing around
sharp bends has been demonstrated in such waveguide, with less than ~4%
reflection per bend. The waveguide has also been found robust for defect lines
with different configurations. The fully on-chip system permits unidirectional
SAW modes that are tightly bound to the waveguide, which provides a compact
footprint ideal for miniaturization of practical applications and offers
insight into the possibility of manipulating highly focused SAW propagation
Photoconductance Quantization in a Single-Photon Detector
We have made a single-photon detector that relies on photoconductive gain in
a narrow electron channel in an AlGaAs/GaAs 2-dimensional electron gas. Given
that the electron channel is 1-dimensional, the photo-induced conductance has
plateaus at multiples of the quantum conductance 2e/h. Super-imposed on
these broad conductance plateaus are many sharp, small, conductance steps
associated with single-photon absorption events that produce individual
photo-carriers. This type of photoconductive detector could measure a single
photon, while safely storing and protecting the spin degree of freedom of its
photo-carrier. This function is valuable for a quantum repeater that would
allow very long distance teleportation of quantum information.Comment: 4 pages, 4 figure
Computational study of flow-induced vibration of a reed in a channel and effect on convective heat transfer
Turbulence and skin friction modification in channel flow with streamwise-aligned superhydrophobic surface texture Phys. An analytical methodology to characterizing the effects of heat transport in internal laminar flows over ridged patterns, mimicking superhydrophobic surfaces, is indicated. The finite slip velocity on such surfaces and the thermal conductivity characteristics of the constituent material are both shown to modify the convective heat transport in the fluid. We use an effective medium approach to model the lowered thermal conductivity caused by the presence of air in the ridge interstices. The proposed analytical solutions for fully developed flow were verified through comparison with numerical simulations for a periodically ridged geometry in laminar flow. While the convective heat transport and the Nusselt Number (Nu) increase due to the modified fluid velocity profile on superhydrophobic surfaces, the decrease in the thermal conductivity of the substrate may play a larger role in determining the overall heat transfer in the channel. C 2015 AIP Publishing LLC