73 research outputs found
How does an interacting many-body system tunnel through a potential barrier to open space?
The tunneling process in a many-body system is a phenomenon which lies at the
very heart of quantum mechanics. It appears in nature in the form of
alpha-decay, fusion and fission in nuclear physics, photoassociation and
photodissociation in biology and chemistry. A detailed theoretical description
of the decay process in these systems is a very cumbersome problem, either
because of very complicated or even unknown interparticle interactions or due
to a large number of constitutent particles. In this work, we theoretically
study the phenomenon of quantum many-body tunneling in a more transparent and
controllable physical system, in an ultracold atomic gas. We analyze a full,
numerically exact many-body solution of the Schr\"odinger equation of a
one-dimensional system with repulsive interactions tunneling to open space. We
show how the emitted particles dissociate or fragment from the trapped and
coherent source of bosons: the overall many-particle decay process is a quantum
interference of single-particle tunneling processes emerging from sources with
different particle numbers taking place simultaneously. The close relation to
atom lasers and ionization processes allows us to unveil the great relevance of
many-body correlations between the emitted and trapped fractions of the
wavefunction in the respective processes.Comment: 18 pages, 4 figures (7 pages, 2 figures supplementary information
Resolving photon number states in a superconducting circuit
Electromagnetic signals are always composed of photons, though in the circuit
domain those signals are carried as voltages and currents on wires, and the
discreteness of the photon's energy is usually not evident. However, by
coupling a superconducting qubit to signals on a microwave transmission line,
it is possible to construct an integrated circuit where the presence or absence
of even a single photon can have a dramatic effect. This system is called
circuit quantum electrodynamics (QED) because it is the circuit equivalent of
the atom-photon interaction in cavity QED. Previously, circuit QED devices were
shown to reach the resonant strong coupling regime, where a single qubit can
absorb and re-emit a single photon many times. Here, we report a circuit QED
experiment which achieves the strong dispersive limit, a new regime of cavity
QED in which a single photon has a large effect on the qubit or atom without
ever being absorbed. The hallmark of this strong dispersive regime is that the
qubit transition can be resolved into a separate spectral line for each photon
number state of the microwave field. The strength of each line is a measure of
the probability to find the corresponding photon number in the cavity. This
effect has been used to distinguish between coherent and thermal fields and
could be used to create a photon statistics analyzer. Since no photons are
absorbed by this process, one should be able to generate non-classical states
of light by measurement and perform qubit-photon conditional logic, the basis
of a logic bus for a quantum computer.Comment: 6 pages, 4 figures, hi-res version at
http://www.eng.yale.edu/rslab/papers/numbersplitting_hires.pd
Emotion and themes recognition in music utilising convolutional and recurrent neural networks
Emotion is an inherent aspect of music, and associations to music can be made via both life experience and specific musical techniques applied by the composer. Computational approaches for music recognition have been well-established in the research community; however, deep approaches have been limited and not yet comparable to conventional approaches. In this study, we present our fusion system of end-to-end convolutional recurrent neural networks (CRNN) and pre-trained convolutional feature extractors for music emotion and theme recognition1. We train 9 models and conduct various late fusion experiments. Our best performing model (team name: AugLi) achieves 74.2 % ROC-AUC on the test partition which is 1.6 percentage points over the baseline system of the MediaEval 2019 Emotion & Themes in Music task
An extremely top-heavy initial mass function in the galactic center stellar disks
Composite armors, having two or more different materials, contain a ceramic layer in the front face and a metallic or polymer matrix composite as support on the back side backing. The function of the ceramic layer is to erode and break up the projectile and to increase the contact surface of the metallic plate by forming a hard cone. The role of the metallic backing layer is to absorb the kinetic energy of the projectile and support the fragmented ceramic. The most impportant advantage of these materials over monolithic metallic armors is to reduce the thickness by using the ceramic layer in front of the metallic layer. This provides reducing the weight of armor. In this study, experiments have been conducted to describe ballistic performance of polymer matrix composites having different geometrical shapes. To do these experiments, aramid and polyethilen composite specimens were first fabricated as laminates in different geometrical shapes. Then, these composite plates at charpy harms were investigeted in varios speed bullet to cover the impact damageKompozit zırhlar iki veya daha fazla farklı malzemeden oluşan, yüzeyde seramik katman ile arkada metal veya polimer matrisli kompozit destek içeren malzemelerdir. Seramik katmanın işlevi mermiyi aşındırma ve parçalamanın yanısıra sert koni oluşturarak metal katmanın temas yüzeyini artırmaktır. Metal destek katmanının görevi ise merminin kinetik enerjisini emmek ve darbe sonrası oluşacak seramik parçaları tutmaktır. Bu malzemelerin, tamamen metalik olan zırhlara göre en önemli avantajı, metalik katmandan önce seramik katmanın kullanılması yoluyla zırh kalınlığının, dolayısı ile zırhın ağırlığının azalmasını sağlamaktadır. Bu çalışmada değişik geometriye sahip, polimer matrisli kompozitlerin, balistik performansını ölçmek için deneyler yapılmıştır. Bunun için önce Aramid ve polietilen numuneler düz, iki değişik çapta silindirik ve küre plakalar halinde üretilmiştir. Bu kompozit plakalara atış poligonunda atışlar yapılmış ve oluşan darbe hasarları incelenmiştir
Direct Visualization of Protease Action on Collagen Triple Helical Structure
Enzymatic processing of extracellular matrix (ECM) macromolecules by matrix metalloproteases (MMPs) is crucial in mediating physiological and pathological cell processes. However, the molecular mechanisms leading to effective physiological enzyme-ECM interactions remain elusive. Only scant information is available on the mode by which matrix proteases degrade ECM substrates. An example is the enzymatic degradation of triple helical collagen II fragments, generated by the collagenase MMP-8 cleavage, during the course of acute inflammatory conditions by gelatinase B/MMP-9. As is the case for many other matrix proteases, it is not clear how MMP-9 recognizes, binds and digests collagen in this important physiological process. We used single molecule imaging to directly visualize this protease during its interaction with collagen fragments. We show that the initial binding is mediated by the diffusion of the protease along the ordered helix on the collagen ¾ fragment, with preferential binding of the collagen tail. As the reaction progressed and prior to collagen degradation, gelatin-like morphologies resulting from the denaturation of the triple helical collagen were observed. Remarkably, this activity was independent of enzyme proteolysis and was accompanied by significant conformational changes of the working protease. Here we provide the first direct visualization of highly complex mechanisms of macromolecular interactions governing the enzymatic processing of ECM substrates by physiological protease
Scopazzi del melo. Stato attuale della ricerca/Apfeltriebsucht. Aktueller stand der forschung
Heterotrimeric Collagen Peptides as Fluorogenic Collagenase Substrates: Synthesis, Conformational Properties, and Enzymatic Digestion
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