29,941 research outputs found
Quantum phase slip interference device based on superconducting nanowire
We propose a transistor-like circuit including two serially connected
segments of a narrow superconducting nanowire joint by a wider segment with a
capacitively coupled gate in between. This circuit is made of amorphous NbSi
film and embedded in a network of on-chip Cr microresistors ensuring a
sufficiently high external electromagnetic impedance. Assuming a virtual regime
of quantum phase slips (QPS)in two narrow segments of the wire, leading to
quantum interference of voltages on these segments, this circuit is dual to the
dc SQUID. Our samples demonstrated appreciable Coulomb blockade voltage (analog
of critical current of the SQUIDs) and periodic modulation of this blockade by
an electrostatic gate (analog of flux modulation in the SQUIDs). The model of
this QPS transistor is discussed.Comment: 5 pages including 3 figures; in v2 the title was updated, typos were
fixed and 4 references adde
The role of proton precipitation in Jovian aurora: Theory and observation
It was proposed that the Jovian auroral emissions observed by Voyager spacecraft could be explained by energetic protons precipitating into the upper atmosphere of Jupiter. Such precipitation of energetic protons results in Doppler-shifted Lyman alpha emission that can be quantitatively analyzed to determine the energy flux and energy distribution of the incoming particle beam. Modeling of the expected emission from a reasonably chosen Voyager energetic proton spectrum can be used in conjunction with International Ultraviolet Explorer (IUE) observations, which show a relative lack of red-shifted Lyman alpha emission, to set upper limits on the amount of proton precipitation taking place in the Jovian aurora. Such calculations indicate that less than 10 percent of the ultraviolet auroral emissions at Jupiter can be explained by proton precipitation
The controllable pi - SQUID
We have fabricated and studied a new kind of DC SQUID in which the magnitude
and sign of the critical current of the individual Josephson junctions can be
controlled by additional voltage probes connected to the junctions. We show
that the amplitude of the voltage oscillations of the SQUID as a function of
the applied magnetic field can be tuned and that the phase of the oscillations
can be switched between 0 and in the temperature range of 0.1 - 4.2 K
using a suitable control voltage. This is equivalent to the external
application of (n+1/2) flux quantum.Comment: 3 Figures, submitted to Applied Physics Letter
Entangling flux qubits with a bipolar dynamic inductance
We propose a scheme to implement variable coupling between two flux qubits
using the screening current response of a dc Superconducting QUantum
Interference Device (SQUID). The coupling strength is adjusted by the current
bias applied to the SQUID and can be varied continuously from positive to
negative values, allowing cancellation of the direct mutual inductance between
the qubits. We show that this variable coupling scheme permits efficient
realization of universal quantum logic. The same SQUID can be used to determine
the flux states of the qubits.Comment: 4 pages, 4 figure
Life long learning in rural areas: a report to the Countryside Agency
Lifelong Learning is a broad umbrella term which includes many different kinds of provision and different forms of learning. At its heart is formal learning, often classroom based, or involving paper and electronic media, undertaken within educational institutions such as colleges and universities. It may or may not lead to an award and it includes learning undertaken for vocational reasons as well as for general interest. It encompasses what are sometimes also known as adult education, continuing education, continuing professional development (cpd), vocational training and the acquisition of basic skills. It may also include work-based learning, and may overlap with post compulsory (post 16) education, i.e. with further education and higher education, but normally applies to all ‘adult learning’ i.e. by people over the age of 19, in particular those who are returning to study after completing their initial education.
From the perspective of the individual learner, however, non-formal learning (organised, systematic study carried on outside the framework of the formal system) is also important. This forms a continuum with informal learning that occurs frequently in the process of daily living, sometimes coincidentally for example through information media or through interpretive provision (such as at museums or heritage sites ).
This report focuses on those aspects of adult learning which are directly affected by government policies, and thus of prime concern for rural proofing
Active galactic nucleus feedback in clusters of galaxies
Observations made during the last ten years with the Chandra X-ray
Observatory have shed much light on the cooling gas in the centers of clusters
of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of
the hot intracluster medium in cluster centers can feed the supermassive black
holes found in the nuclei of the dominant cluster galaxies leading to AGN
outbursts which can reheat the gas, suppressing cooling and large amounts of
star formation. AGN heating can come in the form of shocks, buoyantly rising
bubbles that have been inflated by radio lobes, and the dissipation of sound
waves.Comment: Refereed review article published in Chandra's First Decade of
Discovery Special Feature edition of the Proceedings of the National Academy
of Science
Flux Qubits and Readout Device with Two Independent Flux Lines
We report measurements on two superconducting flux qubits coupled to a
readout Superconducting QUantum Interference Device (SQUID). Two on-chip flux
bias lines allow independent flux control of any two of the three elements, as
illustrated by a two-dimensional qubit flux map. The application of microwaves
yields a frequency-flux dispersion curve for 1- and 2-photon driving of the
single-qubit excited state, and coherent manipulation of the single-qubit state
results in Rabi oscillations and Ramsey fringes. This architecture should be
scalable to many qubits and SQUIDs on a single chip.Comment: 5 pages, 4 figures, higher quality figures available upon request.
Submitted to PR
Using Flow Specifications of Parameterized Cache Coherence Protocols for Verifying Deadlock Freedom
We consider the problem of verifying deadlock freedom for symmetric cache
coherence protocols. In particular, we focus on a specific form of deadlock
which is useful for the cache coherence protocol domain and consistent with the
internal definition of deadlock in the Murphi model checker: we refer to this
deadlock as a system- wide deadlock (s-deadlock). In s-deadlock, the entire
system gets blocked and is unable to make any transition. Cache coherence
protocols consist of N symmetric cache agents, where N is an unbounded
parameter; thus the verification of s-deadlock freedom is naturally a
parameterized verification problem. Parametrized verification techniques work
by using sound abstractions to reduce the unbounded model to a bounded model.
Efficient abstractions which work well for industrial scale protocols typically
bound the model by replacing the state of most of the agents by an abstract
environment, while keeping just one or two agents as is. However, leveraging
such efficient abstractions becomes a challenge for s-deadlock: a violation of
s-deadlock is a state in which the transitions of all of the unbounded number
of agents cannot occur and so a simple abstraction like the one above will not
preserve this violation. In this work we address this challenge by presenting a
technique which leverages high-level information about the protocols, in the
form of message sequence dia- grams referred to as flows, for constructing
invariants that are collectively stronger than s-deadlock. Efficient
abstractions can be constructed to verify these invariants. We successfully
verify the German and Flash protocols using our technique
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