598 research outputs found
A numerical study on the excitation of guided waves in rectangular plates using multiple point sources
Ultrasonic guided waves are widely used to inspect and monitor the structural integrity of plates and plate-like structures, such as ship hulls and large storage-tank ïŹoors. Recently, ultrasonic guided waves have also been used to remove ice and fouling from ship hulls, wind-turbine blades and aeroplane wings. In these applications, the strength of the sound source must be high for scanning a large area, or to break the bond between ice, fouling and plate substrate. More than one transducer may be used to achieve maximum sound power output. However, multiple sources can interact with each other, and form a sound ïŹeld in the structure with local constructive and destructive regions. Destructive regions are weak regions and shall be avoided. When multiple transducers are used it is important that they are arranged in a particular way so that the desired wave modes can be excited to cover the whole structure. The objective of this paper is to provide a theoretical basis for generating particular wave mode patterns in ïŹnite-width rectangular plates whose length is assumed to be inïŹnitely long with respect to its width and thickness. The wave modes have displacements in both width and thickness directions, and are thus different from the classical Lamb-type wave modes. A two-dimensional semi-analytical ïŹnite element (SAFE) method was used to study dispersion characteristics and mode shapes in the plate up to ultrasonic frequencies. The modal analysis provided information on the generation of modes suitable for a particular application. The number of point sources and direction of loading for the excitation of a few representative modes was investigated. Based on the SAFE analysis, a standard ïŹnite element modelling package, Abaqus, was used to excite the designed modes in a three-dimensional plate. The generated wave patterns in Abaqus were then compared with mode shapes predicted in the SAFE model. Good agreement was observed between the intended modes calculated in SAFE and the actual, excited modes in Abaqus
Scaling Separability Criterion: Application To Gaussian States
We introduce examples of three- and four-mode entangled Gaussian mixed states
that are not detected by the scaling and Peres-Horodecki separability criteria.
The presented modification of the scaling criterion resolves this problem. Also
it is shown that the new criterion reproduces the main features of the scaling
pictures for different cases of entangled states, while the previous versions
lead to completely different outcomes. This property of the presented scheme is
evidence of its higher generality.Comment: 7 pages, 4 figure
An Elementary Quantum Network of Single Atoms in Optical Cavities
Quantum networks are distributed quantum many-body systems with tailored
topology and controlled information exchange. They are the backbone of
distributed quantum computing architectures and quantum communication. Here we
present a prototype of such a quantum network based on single atoms embedded in
optical cavities. We show that atom-cavity systems form universal nodes capable
of sending, receiving, storing and releasing photonic quantum information.
Quantum connectivity between nodes is achieved in the conceptually most
fundamental way: by the coherent exchange of a single photon. We demonstrate
the faithful transfer of an atomic quantum state and the creation of
entanglement between two identical nodes in independent laboratories. The
created nonlocal state is manipulated by local qubit rotation. This efficient
cavity-based approach to quantum networking is particularly promising as it
offers a clear perspective for scalability, thus paving the way towards
large-scale quantum networks and their applications.Comment: 8 pages, 5 figure
Efficient and long-lived quantum memory with cold atoms inside a ring cavity
Quantum memories are regarded as one of the fundamental building blocks of
linear-optical quantum computation and long-distance quantum communication. A
long standing goal to realize scalable quantum information processing is to
build a long-lived and efficient quantum memory. There have been significant
efforts distributed towards this goal. However, either efficient but
short-lived or long-lived but inefficient quantum memories have been
demonstrated so far. Here we report a high-performance quantum memory in which
long lifetime and high retrieval efficiency meet for the first time. By placing
a ring cavity around an atomic ensemble, employing a pair of clock states,
creating a long-wavelength spin wave, and arranging the setup in the
gravitational direction, we realize a quantum memory with an intrinsic spin
wave to photon conversion efficiency of 73(2)% together with a storage lifetime
of 3.2(1) ms. This realization provides an essential tool towards scalable
linear-optical quantum information processing.Comment: 6 pages, 4 figure
Topologically Protected Quantum State Transfer in a Chiral Spin Liquid
Topology plays a central role in ensuring the robustness of a wide variety of
physical phenomena. Notable examples range from the robust current carrying
edge states associated with the quantum Hall and the quantum spin Hall effects
to proposals involving topologically protected quantum memory and quantum logic
operations. Here, we propose and analyze a topologically protected channel for
the transfer of quantum states between remote quantum nodes. In our approach,
state transfer is mediated by the edge mode of a chiral spin liquid. We
demonstrate that the proposed method is intrinsically robust to realistic
imperfections associated with disorder and decoherence. Possible experimental
implementations and applications to the detection and characterization of spin
liquid phases are discussed.Comment: 14 pages, 7 figure
Quantum Simulation of Antiferromagnetic Spin Chains in an Optical Lattice
Understanding exotic forms of magnetism in quantum mechanical systems is a
central goal of modern condensed matter physics, with implications from high
temperature superconductors to spintronic devices. Simulating magnetic
materials in the vicinity of a quantum phase transition is computationally
intractable on classical computers due to the extreme complexity arising from
quantum entanglement between the constituent magnetic spins. Here we employ a
degenerate Bose gas confined in an optical lattice to simulate a chain of
interacting quantum Ising spins as they undergo a phase transition. Strong spin
interactions are achieved through a site-occupation to pseudo-spin mapping. As
we vary an applied field, quantum fluctuations drive a phase transition from a
paramagnetic phase into an antiferromagnetic phase. In the paramagnetic phase
the interaction between the spins is overwhelmed by the applied field which
aligns the spins. In the antiferromagnetic phase the interaction dominates and
produces staggered magnetic ordering. Magnetic domain formation is observed
through both in-situ site-resolved imaging and noise correlation measurements.
By demonstrating a route to quantum magnetism in an optical lattice, this work
should facilitate further investigations of magnetic models using ultracold
atoms, improving our understanding of real magnetic materials.Comment: 12 pages, 9 figure
Phase-locked indistinguishable photons with synthesized waveforms from a solid-state source
Resonance fluorescence in the Heitler regime provides access to single
photons with coherence well beyond the Fourier transform limit of the
transition, and holds the promise to circumvent environment-induced dephasing
common to all solid-state systems. Here we demonstrate that the coherently
generated single photons from a single self-assembled InAs quantum dot display
mutual coherence with the excitation laser on a timescale exceeding 3 seconds.
Exploiting this degree of mutual coherence we synthesize near-arbitrary
coherent photon waveforms by shaping the excitation laser field. In contrast to
post-emission filtering, our technique avoids both photon loss and degradation
of the single photon nature for all synthesized waveforms. By engineering
pulsed waveforms of single photons, we further demonstrate that separate
photons generated coherently by the same laser field are fundamentally
indistinguishable, lending themselves to creation of distant entanglement
through quantum interference.Comment: Additional data and analysis in PDF format is available for download
at the publications section of our website:
http://www.amop.phy.cam.ac.uk/amop-ma
Perk-dependent repression of miR-106b-25 cluster is required for ER stress-induced apoptosis
Activation of the unfolded protein response sensor PKR-like endoplasmic reticulum kinase (Perk) attenuates endoplasmic reticulum (ER) stress levels. Conversantly, if the damage is too severe and ER function cannot be restored, this signaling branch triggers apoptosis. Bcl-2 homology 3-only family member Bim is essential for ER stress-induced apoptosis. However, the regulatory mechanisms controlling Bim activation under ER stress conditions are not well understood. Here, we show that downregulation of the miR-106b-25 cluster contributes to ER stress-induced apoptosis and the upregulation of Bim. Hypericin-mediated photo-oxidative ER damage induced Perk-dependent cell death and led to a significant decrease in the levels of miRNAs belonging to miR-106b-25 cluster in wild-type (WT) but not in Perkâ/â MEFs. Further, we show that expression of miR-106b-25 and Mcm-7 (host gene of miR-106b-25) is co-regulated through the transcription factors Atf4 (activating transcription factor 4) and Nrf2 (nuclear factor-erythroid-2-related factor 2). ER stress increased the activity of WT Bim 3âČUTR (untranslated region) construct but not the miR-106b-25 recognition site-mutated Bim 3âČUTR construct. Overexpression of miR-106b-25 cluster inhibits ER stress-induced cell death in WT but did not confer any further protection in Bim-knockdown cells. Further, we show downregulation in the levels of miR-106b-25 cluster in the symptomatic SOD1G86R transgenic mice. Our results suggest a molecular mechanism whereby repression of miR-106b-25 cluster has an important role in ER stress-mediated increase in Bim and apoptosis
Current Methods for Hyperpolarized [1-13C]pyruvate MRI Human Studies
MRI with hyperpolarized (HP) 13C agents, also known as HP 13C MRI, can
measure processes such as localized metabolism that is altered in numerous
cancers, liver, heart, kidney diseases, and more. It has been translated into
human studies during the past 10 years, with recent rapid growth in studies
largely based on increasing availability of hyperpolarized agent preparation
methods suitable for use in humans. This paper aims to capture the current
successful practices for HP MRI human studies with [1-13C]pyruvate - by far the
most commonly used agent, which sits at a key metabolic junction in glycolysis.
The paper is divided into four major topic areas: (1) HP 13C-pyruvate
preparation, (2) MRI system setup and calibrations, (3) data acquisition and
image reconstruction, and (4) data analysis and quantification. In each area,
we identified the key components for a successful study, summarized both
published studies and current practices, and discuss evidence gaps, strengths,
and limitations. This paper is the output of the HP 13C MRI Consensus Group as
well as the ISMRM Hyperpolarized Media MR and Hyperpolarized Methods &
Equipment study groups. It further aims to provide a comprehensive reference
for future consensus building as the field continues to advance human studies
with this metabolic imaging modality
SNPs in the FCER1A Gene Region Show No Association with Allergic Rhinitis in a Han Chinese Population
Background: Immunoglobulin E (IgE) is a central player in the allergic response, and raised total IgE levels are considered as an indicator of atopy or potential development of atopy. A recent genome-wide scan in a German population-based cohort of adults identified the gene encoding the alpha chain of the high affinity receptor for IgE (FCER1A) as a susceptibility locus influencing total serum IgE levels. The aim of this study was to investigate whether the polymorphisms in the FCER1A gene are associated with allergic rhinitis (AR) in a Han Chinese population. Methodology/Principal Findings: A population of 378 patients with AR and 288 healthy controls was studied. Precise phenotyping of patients was accomplished by means of a questionnaire and clinical examination. Blood was drawn for DNA extraction and total serum immunoglobulin E (IgE) measurement. A total of 16 single nucleotide polymorphisms (SNPs) in FCER1A were selected and individually genotyped. None of the SNPs in the FCER1A showed an association with AR. Similarly, the lack of association was also evident in subgroup analysis for the presence of different allergen sensitivities. None of the selected SNPs in FCER1A was associated with total IgE level. Conclusions: Although FCER1A presents itself as a good candidate for contributing to total serum IgE, this study failed t
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