13,812 research outputs found
Classical Analogue of Electromagnetically Induced Transparency with a Metal-Superconductor Hybrid Metamaterial
Metamaterials are engineered materials composed of small electrical circuits
producing novel interactions with electromagnetic waves. Recently, a new class
of metamaterials has been created to mimic the behavior of media displaying
electromagnetically induced transparency (EIT). Here we introduce a planar EIT
metamaterial that creates a very large loss contrast between the dark and
radiative resonators by employing a superconducting Nb film in the dark element
and a normal-metal Au film in the radiative element. Below the critical
temperature of Nb, the resistance contrast opens up a transparency window along
with a large enhancement in group delay, enabling a significant slowdown of
waves. We further demonstrate precise control of the EIT response through
changes in the superfluid density. Such tunable metamaterials may be useful for
telecommunication because of their large delay-bandwidth products.Comment: 4 pages, 4 figure
Single-breath-hold photoacoustic computed tomography of the breast
We have developed a single-breath-hold photoacoustic computed tomography (SBH-PACT) system to reveal detailed angiographic structures in human breasts. SBH-PACT features a deep penetration depth (4 cm in vivo) with high spatial and temporal resolutions (255 µm in-plane resolution and a 10 Hz 2D frame rate). By scanning the entire breast within a single breath hold (~15 s), a volumetric image can be acquired and subsequently reconstructed utilizing 3D back-projection with negligible breathing-induced motion artifacts. SBH-PACT clearly reveals tumors by observing higher blood vessel densities associated with tumors at high spatial resolution, showing early promise for high sensitivity in radiographically dense breasts. In addition to blood vessel imaging, the high imaging speed enables dynamic studies, such as photoacoustic elastography, which identifies tumors by showing less compliance. We imaged breast cancer patients with breast sizes ranging from B cup to DD cup, and skin pigmentations ranging from light to dark. SBH-PACT identified all the tumors without resorting to ionizing radiation or exogenous contrast, posing no health risks
Liquid drop splashing on smooth, rough and textured surfaces
Splashing occurs when a liquid drop hits a dry solid surface at high
velocity. This paper reports experimental studies of how the splash depends on
the roughness and the texture of the surfaces as well as the viscosity of the
liquid. For smooth surfaces, there is a "corona" splash caused by the presence
of air surrounding the drop. There are several regimes that occur as the
velocity and liquid viscosity are varied. There is also a "prompt" splash that
depends on the roughness and texture of the surfaces. A measurement of the size
distribution of the ejected droplets is sensitive to the surface roughness. For
a textured surface in which pillars are arranged in a square lattice,
experiment shows that the splashing has a four-fold symmetry. The splash occurs
predominantly along the diagonal directions. In this geometry, two factors
affect splashing the most: the pillar height and spacing between pillars.Comment: 9 pages, 11 figure
Generalization of Wigner time delay to subunitary scattering systems
We introduce a complex generalization of Wigner time delay for
sub-unitary scattering systems. Theoretical expressions for complex time delay
as a function of excitation energy, uniform and non-uniform loss, and coupling,
are given. We find very good agreement between theory and experimental data
taken on microwave graphs containing an electronically variable lumped-loss
element. We find that time delay and the determinant of the scattering matrix
share a common feature in that the resonant behavior in and
serves as a reliable indicator of the condition for Coherent
Perfect Absorption (CPA). This work opens a new window on time delay in lossy
systems and provides a means to identify the poles and zeros of the scattering
matrix from experimental data. The results also enable a new approach to
achieving CPA at an arbitrary energy/frequency in complex scattering systems.Comment: 8 pages, 2 figures. Supplementary material adde
Mice lacking sialyltransferase ST3Gal-II develop late-onset obesity and insulin resistance
Sialyltransferases are a family of 20 gene products in mice and humans that transfer sialic acid from its activated precursor, CMP-sialic acid, to the terminus of glycoprotein and glycolipid acceptors. ST3Gal-II (coded by the St3gal2 gene) transfers sialic acid preferentially to the three positions of galactose on the Galβ1-3GalNAc terminus of gangliosides GM1 and GD1b to synthesize GD1a and GT1b, respectively. Mice with a targeted disruption of St3gal2 unexpectedly displayed lateonset obesity and insulin resistance. At 3 months of age, St3gal2-null mice were the same weight as their wild type (WT) counterparts, but by 13 months on standard chow they were visibly obese, 22% heavier and with 37% greater fat/lean ratio than WT mice. St3gal2-null mice became hyperglycemic and displayed impaired glucose tolerance by 9 months of age. They had sharply reduced insulin responsiveness despite equivalent pancreatic islet morphology. Analyses of insulin receptor (IR) tyrosine kinase substrate IRS-1 and downstream target Akt revealed decreased insulininduced phosphorylation in adipose tissue but not liver or skeletal muscle of St3gal2-null mice. Thin-layer chromatography and mass spectrometry revealed altered ganglioside profiles in the adipose tissue of St3gal2-null mice compared to WT littermates. Metabolically, St3gal2-null mice display a reduced respiratory exchange ratio compared to WT mice, indicating a preference for lipid oxidation as an energy source. Despite their altered metabolism, St3gal2-null mice were hyperactive. We conclude that altered ganglioside expression in adipose tissue results in diminished IR sensitivity and late-onset obesity.Fil: Lopez, Pablo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y MartÃn Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y MartÃn Ferreyra; Argentina. Johns Hopkins University School of Medicine; Estados UnidosFil: Aja, Susan. Johns Hopkins University School of Medicine; Estados UnidosFil: Aoki, Kazuhiro. University of Georgia; GreciaFil: Seldin, Marcus M.. Johns Hopkins University School of Medicine; Estados UnidosFil: Lei, Xia. Johns Hopkins University School of Medicine; Estados UnidosFil: Ronnett, Gabriele V. Johns Hopkins University School of Medicine; Estados UnidosFil: Wong, G. William. Johns Hopkins University School of Medicine; Estados UnidosFil: Schnaar, Ronald L.. Johns Hopkins University School of Medicine; Estados Unido
The vanishing ideal of a finite set of points with multiplicity structures
Given a finite set of arbitrarily distributed points in affine space with
arbitrary multiplicity structures, we present an algorithm to compute the
reduced Groebner basis of the vanishing ideal under the lexicographic ordering.
Our method discloses the essential geometric connection between the relative
position of the points with multiplicity structures and the quotient basis of
the vanishing ideal, so we will explicitly know the set of leading terms of
elements of I. We split the problem into several smaller ones which can be
solved by induction over variables and then use our new algorithm for
intersection of ideals to compute the result of the original problem. The new
algorithm for intersection of ideals is mainly based on the Extended Euclidean
Algorithm.Comment: 12 pages,12 figures,ASCM 201
Q-PAC: Automated Detection of Quantum Bug-Fix Patterns
Context: Bug-fix pattern detection has been investigated in the past in the
context of classical software. However, while quantum software is developing
rapidly, the literature still lacks automated methods and tools to identify,
analyze, and detect bug-fix patterns. To the best of our knowledge, our work
previously published in SEKE'23 was the first to leverage classical techniques
to detect bug-fix patterns in quantum code.
Objective: To extend our previous effort, we present a research agenda
(Q-Repair), including a series of testing and debugging methodologies, to
improve the quality of quantum software. The ultimate goal is to utilize
machine learning techniques to automatically predict fix patterns for existing
quantum bugs.
Method: As part of the first stage of the agenda, we extend our initial study
and propose a more comprehensive automated framework, called Q-PAC, for
detecting bug-fix patterns in IBM Qiskit quantum code. In the framework, we
develop seven bug-fix pattern detectors using abstract syntax trees, syntactic
filters, and semantic checks.
Results: To demonstrate our method, we run Q-PAC on a variety of quantum
bug-fix patterns using both real-world and handcrafted examples of bugs and
fixes. The experimental results show that Q-PAC can effectively identify
bug-fix patterns in IBM Qiskit.
Conclusion: We hope our initial study on quantum bug-fix detection can bring
awareness of quantum software engineering to both researchers and
practitioners. Thus, we also publish Q-PAC as an open-source software on
GitHub. We would like to encourage other researchers to work on research
directions (such as Q-Repair) to improve the quality of the quantum
programming.Comment: 16 pages, 2 figure
Switchable collective pinning of flux quanta using magnetic vortex arrays
We constructed a superconducting/ferromagnetic hybrid system in which the
ordering of the pinning potential landscape for flux quanta can be manipulated.
Flux pinning is induced by an array of magnetic nanodots in the magnetic vortex
state, and controlled by the magnetic history. This allows switching on and off
the collective pinning of the flux-lattice. In addition, we observed
field-induced superconductivity that originates from the annihilation of flux
quanta induced by the stray fields from the magnetic vortices.Comment: PDF file 18 pages including 5 figures, accepted for publication in
Phys. Rev.
Radiation induced oscillations of the Hall resistivity in two-dimensional electron systems
We consider the effect of microwave radiation on the Hall resistivity in
two-dimension electron systems. It is shown that the photon-assisted impurity
scattering of electrons can result in oscillatory dependences of both
dissipative and Hall components of the conductivity and resistivity tensors on
the ratio of radiation frequency to cyclotron frequency. The Hall resistivity
can include a component induced by microwave radiation which is an even
function of the magnetic field. The phase of the dissipative resistivity
oscillations and the polarization dependence of their amplitude are compared
with those of the Hall resistivity oscillations. The developed model can
clarify the results of recent experimental observations of the radiation
induced Hall effect.Comment: 4 pages, 1 figur
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