2,937 research outputs found
Advanced Concepts in Josephson Junction Reflection Amplifiers
Low-noise amplification atmicrowave frequencies has become increasingly
important for the research related to superconducting qubits and
nanoelectromechanical systems. The fundamental limit of added noise by a
phase-preserving amplifier is the standard quantum limit, often expressed as
noise temperature . Towards the goal of the
quantum limit, we have developed an amplifier based on intrinsic negative
resistance of a selectively damped Josephson junction. Here we present
measurement results on previously proposed wide-band microwave amplification
and discuss the challenges for improvements on the existing designs. We have
also studied flux-pumped metamaterial-based parametric amplifiers, whose
operating frequency can be widely tuned by external DC-flux, and demonstrate
operation at pumping, in contrast to the typical metamaterial
amplifiers pumped via signal lines at .Comment: 9 pages, 6 figure
Cosmic Neutrino Last Scattering Surface
Neutrinos decoupled from the rest of the cosmic plasma when the Universe was
less than one second old, far earlier than the photons which decoupled at
t=380,000 years. Surprisingly, though, the last scattering surface of the
neutrinos is much closer to us than that of the photons. Here we calculate the
properties of the last scattering surfaces of the three species of neutrinos.Comment: Important reference to earlier work of Bisnovatyi-Kogan and Seidov
added, and mis-spelling of Opher reference correcte
Optimisation of variables for studying dilepton transverse momentum distributions at hadron colliders
In future measurements of the dilepton () transverse momentum,
\Qt, at both the Tevatron and LHC, the achievable bin widths and the ultimate
precision of the measurements will be limited by experimental resolution rather
than by the available event statistics. In a recent paper the variable \at,
which corresponds to the component of \Qt\ that is transverse to the dilepton
thrust axis, has been studied in this regard. In the region, \Qt\ 30 GeV,
\at\ has been shown to be less susceptible to experimental resolution and
efficiency effects than the \Qt. Extending over all \Qt, we now demonstrate
that dividing \at\ (or \Qt) by the measured dilepton invariant mass further
improves the resolution. In addition, we propose a new variable, \phistarEta,
that is determined exclusively from the measured lepton directions; this is
even more precisely determined experimentally than the above variables and is
similarly sensitive to the \Qt. The greater precision achievable using such
variables will enable more stringent tests of QCD and tighter constraints on
Monte Carlo event generator tunes.Comment: 8 pages, 5 figures, 2 table
Z boson transverse momentum spectrum from the lepton angular distributions
In view of recent discussions concerning the possibly limiting energy
resolution systematics on the measurement of the Z boson transverse momentum
distribution at hadron colliders, we propose a novel measurement method based
on the angular distributions of the decay leptons. We also introduce a
phenomenological parametrization of the transverse momentum distribution that
adapts well to all currently available predictions, a useful tool to quantify
their differences.Comment: 12 pages, 6 figure
Imprints of latitude, host taxon, and decay stage on fungus-associated arthropod communities
Interactions among fungi and insects involve hundreds of thousands of species. While insect communities on plants have formed some of the classic model systems in ecology, fungus-based communities and the forces structuring them remain poorly studied by comparison. We characterize the arthropod communities associated with fruiting bodies of eight mycorrhizal basidiomycete fungus species from three different orders along a 1200-km latitudinal gradient in northern Europe. We hypothesized that, matching the pattern seen for most insect taxa on plants, we would observe a general decrease in fungal-associated species with latitude. Against this backdrop, we expected local communities to be structured by host identity and phylogeny, with more closely related fungal species sharing more similar communities of associated organisms. As a more unique dimension added by the ephemeral nature of fungal fruiting bodies, we expected further imprints generated by successional change, with younger fruiting bodies harboring communities different from older ones. Using DNA metabarcoding to identify arthropod communities from fungal fruiting bodies, we found that latitude left a clear imprint on fungus-associated arthropod community composition, with host phylogeny and decay stage of fruiting bodies leaving lesser but still-detectable effects. The main latitudinal imprint was on a high arthropod species turnover, with no detectable pattern in overall species richness. Overall, these findings paint a new picture of the drivers of fungus-associated arthropod communities, suggesting that latitude will not affect how many arthropod species inhabit a fruiting body but, rather, what species will occur in it and at what relative abundances (as measured by sequence read counts). These patterns upset simplistic predictions regarding latitudinal gradients in species richness and in the strength of biotic interactions.Peer reviewe
Two Years Later: Journals Are Not Yet Enforcing the ARRIVE Guidelines on Reporting Standards for Pre-Clinical Animal Studies
There is growing concern that poor experimental design and lack of transparent reporting contribute to the frequent failure of pre-clinical animal studies to translate into treatments for human disease. In 2010, the Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines were introduced to help improve reporting standards. They were published in PLOS Biology and endorsed by funding agencies and publishers and their journals, including PLOS, Nature research journals, and other top-tier journals. Yet our analysis of papers published in PLOS and Nature journals indicates that there has been very little improvement in reporting standards since then. This suggests that authors, referees, and editors generally are ignoring guidelines, and the editorial endorsement is yet to be effectively implemented
Detecting bit-flip errors in a logical qubit using stabilizer measurements
Quantum data is susceptible to decoherence induced by the environment and to
errors in the hardware processing it. A future fault-tolerant quantum computer
will use quantum error correction (QEC) to actively protect against both. In
the smallest QEC codes, the information in one logical qubit is encoded in a
two-dimensional subspace of a larger Hilbert space of multiple physical qubits.
For each code, a set of non-demolition multi-qubit measurements, termed
stabilizers, can discretize and signal physical qubit errors without collapsing
the encoded information. Experimental demonstrations of QEC to date, using
nuclear magnetic resonance, trapped ions, photons, superconducting qubits, and
NV centers in diamond, have circumvented stabilizers at the cost of decoding at
the end of a QEC cycle. This decoding leaves the quantum information vulnerable
to physical qubit errors until re-encoding, violating a basic requirement for
fault tolerance. Using a five-qubit superconducting processor, we realize the
two parity measurements comprising the stabilizers of the three-qubit
repetition code protecting one logical qubit from physical bit-flip errors. We
construct these stabilizers as parallelized indirect measurements using
ancillary qubits, and evidence their non-demolition character by generating
three-qubit entanglement from superposition states. We demonstrate
stabilizer-based quantum error detection (QED) by subjecting a logical qubit to
coherent and incoherent bit-flip errors on its constituent physical qubits.
While increased physical qubit coherence times and shorter QED blocks are
required to actively safeguard quantum information, this demonstration is a
critical step toward larger codes based on multiple parity measurements.Comment: 6 pages, 4 figures, 10 supplementary figure
Systematic review and meta-analysis of temozolomide in animal models of glioma:was clinical efficacy predicted?
Background:Malignant glioma is an aggressive tumour commonly associated with a dismal outcome despite optimal surgical and radio-chemotherapy. Since 2005 temozolomide has been established as first-line chemotherapy. We investigate the role of in vivo glioma models in predicting clinical efficacy.Methods:We searched three online databases to systematically identify publications testing temozolomide in animal models of glioma. Median survival and number of animals treated were extracted and quality was assessed using a 12-point scale; random effects meta-analysis was used to estimate efficacy. We analysed the impact of study design and quality and looked for evidence of publication bias.Results:We identified 60 publications using temozolomide in models of glioma, comprising 2443 animals. Temozolomide prolonged survival by a factor of 1.88 (95% CI 1.74-2.03) and reduced tumour volume by 50.4% (41.8-58.9) compared with untreated controls. Study design characteristics accounted for a significant proportion of between-study heterogeneity, and there was evidence of a significant publication bias.Conclusion:These data reflect those from clinical trials in that temozolomide improves survival and reduces tumour volume, even after accounting for publication bias. Experimental in vivo glioma studies of temozolomide differ from those of other glioma therapies in their consistent efficacy and successful translation into clinical medicine
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