144 research outputs found
Andreev Bound states as a phase sensitive probe of the pairing symmetry of the iron pnictide superconductors
A leading contender for the pairing symmetry in the Fe-pnictide high
temperature superconductors is extended s-wave , a nodeless state in
which the pairing changes sign between Fermi surfaces. Verifying such a pairing
symmetry requires a special phase sensitive probe that is also momentum
selective. We show that the sign structure of pairing leads to surface
Andreev bound states at the sample edge. In the clean limit they only occur
when the edge is along the nearest neighbor Fe-Fe bond, but not for a diagonal
edge or a surface orthogonal to the c-axis. In contrast to d-wave Andreev bound
states, they are not at zero energy and, in general, do not produce a zero bias
tunneling peak. Consequences for tunneling measurements are derived, within a
simplified two band model and also for a more realistic five band model.Comment: 5 pages, 5 figure
High-Order Multipole Radiation from Quantum Hall States in Dirac Materials
We investigate the optical response of strongly disordered quantum Hall
states in two-dimensional Dirac materials and find qualitatively different
effects in the radiation properties of the bulk versus the edge. We show that
the far-field radiation from the edge is characterized by large multipole
moments (> 50) due to the efficient transfer of angular momentum from the
electrons into the scattered light. The maximum multipole transition moment is
a direct measure of the coherence length of the edge states. Accessing these
multipole transitions would provide new tools for optical spectroscopy and
control of quantum Hall edge states. On the other hand, the far-field radiation
from the bulk appears as random dipole emission with spectral properties that
vary with the local disorder potential. We determine the conditions under which
this bulk radiation can be used to image the disorder landscape. Such optical
measurements can probe sub-micron length scales over large areas and provide
complementary information to scanning probe techniques. Spatially resolving
this bulk radiation would serve as a novel probe of the percolation transition
near half-filling.Comment: v2: 8 pages, 4 figure
Near-Zero Modes in Superconducting Graphene
Vortices in the simplest superconducting state of graphene contain very low
energy excitations, whose existence is connected to an index theorem that
applies strictly to an approximate form of the relevant Bogoliubov-deGennes
equations. When Zeeman interactions are taken into account, the zero modes
required by the index theorem are (slightly) displaced. Thus the vortices
acquire internal structure, that plausibly supports interesting dynamical
phenomena.Comment: 9 pages, to appear in Proceedings of the Nobel Symposium on Graphene
and Quantum Matte
Shadow surface states in topological Kondo insulators
The surface states of 3D topological insulators in general have negligible quantum oscillations (QOs) when the chemical potential is tuned to the Dirac points. In contrast, we find that topological Kondo insulators (TKIs) can support surface states with an arbitrarily large Fermi surface (FS) when the chemical potential is pinned to the Dirac point. We illustrate that these FSs give rise to finite-frequency QOs, which can become comparable to the extremal area of the unhybridized bulk bands. We show that this occurs when the crystal symmetry is lowered from cubic to tetragonal in a minimal two-orbital model. We label such surface modes as 'shadow surface states'. Moreover, we show that the sufficient next-nearest neighbor out-of-plane hybridization leading to shadow surface states can be self-consistently stabilized for tetragonal TKIs. Consequently, shadow surface states provide an important example of high-frequency QOs beyond the context of cubic TKIs
One to one comparison of cell-free synthesized erythropoietin conjugates modified with linear polyglycerol and polyethylene glycol
With more than 20 Food and Drug Administration (FDA)-approved poly (ethylene glycol) (PEG) modified drugs on the market, PEG is the gold standard polymer in bioconjugation. The coupling improves stability, efficiency and can prolong blood circulation time of therapeutic proteins. Even though PEGylation is described as non-toxic and non-immunogenic, reports accumulate with data showing allergic reactions to PEG. Since PEG is not only applied in therapeutics, but can also be found in foods and cosmetics, anti-PEG-antibodies can occur even without a medical treatment. Hypersensitivity to PEG thereby can lead to a reduced drug efficiency, fast blood clearance and in rare cases anaphylactic reactions. Therefore, finding alternatives for PEG is crucial. In this study, we present linear polyglycerol (LPG) for bioconjugation as an alternative polymer to PEG. We report the conjugation of LPG and PEG by click-chemistry to the glycoprotein erythropoietin (EPO), synthesized in a eukaryotic cell-free protein synthesis system. Furthermore, the influence of the polymers on EPOs stability and activity on a growth hormone dependent cell-line was evaluated. The similar characteristics of both bioconjugates show that LPGylation can be a promising alternative to PEGylation
Neel order, quantum spin liquids and quantum criticality in two dimensions
This paper is concerned with the possibility of a direct second order
transition out of a collinear Neel phase to a paramagnetic spin liquid in two
dimensional quantum antiferromagnets. Contrary to conventional wisdom, we show
that such second order quantum transitions can potentially occur to certain
spin liquid states popular in theories of the cuprates. We provide a theory of
this transition and study its universal properties in an expansion.
The existence of such a transition has a number of interesting implications for
spin liquid based approaches to the underdoped cuprates. In particular it
considerably clarifies existing ideas for incorporating antiferromagnetic long
range order into such a spin liquid based approach.Comment: 18 pages, 17 figure
System identification and closed-loop control of laser hot-wire directed energy deposition using the parameter-signature-property modeling scheme
Hot-wire directed energy deposition using a laser beam (DED-LB/w) is a method
of metal additive manufacturing (AM) that has benefits of high material
utilization and deposition rate, but parts manufactured by DED-LB/w suffer from
a substantial heat input and undesired surface finish. Hence, monitoring and
controlling the process parameters and signatures during the deposition is
crucial to ensure the quality of final part properties and geometries. This
paper explores the dynamic modeling of the DED-LB/w process and introduces a
parameter-signature-property modeling and control approach to enhance the
quality of modeling and control of part properties that cannot be measured in
situ. The study investigates different process parameters that influence the
melt pool width (signature) and bead width (property) in single and multi-layer
beads. The proposed modeling approach utilizes a parameter-signature model as
F_1 and a signature-property model as F_2. Linear and nonlinear modeling
approaches are compared to describe a dynamic relationship between process
parameters and a process signature, the melt pool width (F_1). A fully
connected artificial neural network is employed to model and predict the final
part property, i.e., bead width, based on melt pool signatures (F_2). Finally,
the effectiveness and usefulness of the proposed parameter-signature-property
modeling is tested and verified by integrating the parameter-signature (F_1)
and signature-property (F_2) models in the closed-loop control of the width of
the part. Compared with the control loop with only F_1, the proposed method
shows clear advantages and bears potential to be applied to control other part
properties that cannot be directly measured or monitored in situ.Comment: 28 pages, 14 figures, 4 tables
Online Two-stage Thermal History Prediction Method for Metal Additive Manufacturing of Thin Walls
This paper aims to propose an online two-stage thermal history prediction
method, which could be integrated into a metal AM process for performance
control. Based on the similarity of temperature curves (curve segments of a
temperature profile of one point) between any two successive layers, the first
stage of the proposed method designs a layer-to-layer prediction model to
estimate the temperature curves of the yet-to-print layer from measured
temperatures of certain points on the previously printed layer. With
measured/predicted temperature profiles of several points on the same layer,
the second stage proposes a reduced order model (ROM) (intra-layer prediction
model) to decompose and construct the temperature profiles of all points on the
same layer, which could be used to build the temperature field of the entire
layer. The training of ROM is performed with an extreme learning machine (ELM)
for computational efficiency. Fifteen wire arc AM experiments and nine
simulations are designed for thin walls with a fixed length and unidirectional
printing of each layer. The test results indicate that the proposed prediction
method could construct the thermal history of a yet-to-print layer within 0.1
seconds on a low-cost desktop computer. Meanwhile, the method has acceptable
generalization capability in most cases from lower layers to higher layers in
the same simulation, as well as from one simulation to a new simulation on
different AM process parameters. More importantly, after fine-tuning the
proposed method with limited experimental data, the relative errors of all
predicted temperature profiles on a new experiment are smaller than 0.09, which
demonstrates the applicability and generalization of the proposed two-stage
thermal history prediction method in online applications for metal AM.Comment: 30 pages, 21 figures, 2 table
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