3,542 research outputs found
Universal scaling relation in high-temperature superconductors
Scaling laws express a systematic and universal simplicity among complex
systems in nature. For example, such laws are of enormous significance in
biology. Scaling relations are also important in the physical sciences. The
seminal 1986 discovery of high transition-temperature (high-T_c)
superconductivity in cuprate materials has sparked an intensive investigation
of these and related complex oxides, yet the mechanism for superconductivity is
still not agreed upon. In addition, no universal scaling law involving such
fundamental properties as T_c and the superfluid density \rho_s, a quantity
indicative of the number of charge carriers in the superconducting state, has
been discovered. Here we demonstrate that the scaling relation \rho_s \propto
\sigma_{dc} T_c, where the conductivity \sigma_{dc} characterizes the
unidirectional, constant flow of electric charge carriers just above T_c,
universally holds for a wide variety of materials and doping levels. This
surprising unifying observation is likely to have important consequences for
theories of high-T_c superconductivity.Comment: 11 pages, 2 figures, 2 table
GANDALF: Generative Adversarial Networks with Discriminator-Adaptive Loss Fine-tuning for Alzheimer's Disease Diagnosis from MRI
Positron Emission Tomography (PET) is now regarded as the gold standard for
the diagnosis of Alzheimer's Disease (AD). However, PET imaging can be
prohibitive in terms of cost and planning, and is also among the imaging
techniques with the highest dosage of radiation. Magnetic Resonance Imaging
(MRI), in contrast, is more widely available and provides more flexibility when
setting the desired image resolution. Unfortunately, the diagnosis of AD using
MRI is difficult due to the very subtle physiological differences between
healthy and AD subjects visible on MRI. As a result, many attempts have been
made to synthesize PET images from MR images using generative adversarial
networks (GANs) in the interest of enabling the diagnosis of AD from MR.
Existing work on PET synthesis from MRI has largely focused on Conditional
GANs, where MR images are used to generate PET images and subsequently used for
AD diagnosis. There is no end-to-end training goal. This paper proposes an
alternative approach to the aforementioned, where AD diagnosis is incorporated
in the GAN training objective to achieve the best AD classification
performance. Different GAN lossesare fine-tuned based on the discriminator
performance, and the overall training is stabilized. The proposed network
architecture and training regime show state-of-the-art performance for three-
and four- class AD classification tasks.Comment: Accepted for publication at the MICCAI 2020 conferenc
Memory-built-in quantum teleportation with photonic and atomic qubits
The combination of quantum teleportation and quantum memory of photonic
qubits is essential for future implementations of large-scale quantum
communication and measurement-based quantum computation. Both steps have been
achieved separately in many proof-of-principle experiments, but the
demonstration of memory-built-in teleportation of photonic qubits remains an
experimental challenge. Here, we demonstrate teleportation between photonic
(flying) and atomic (stationary) qubits. In our experiment, an unknown
polarization state of a single photon is teleported over 7 m onto a remote
atomic qubit that also serves as a quantum memory. The teleported state can be
stored and successfully read out for up to 8 micro-second. Besides being of
fundamental interest, teleportation between photonic and atomic qubits with the
direct inclusion of a readable quantum memory represents a step towards an
efficient and scalable quantum network.Comment: 19 pages 3 figures 1 tabl
Polymorphisms of SP110 are associated with both pulmonary and extra-pulmonary tuberculosis among the Vietnamese
Background: Tuberculosis (TB) is an infectious disease that remains a major cause of morbidity and mortality worldwide, yet the reasons why only 10% of people infected with Mycobacterium tuberculosis go on to develop clinical disease are poorly understood. Genetically determined variation in the host immune response is one factor influencing the response to M. tuberculosis. SP110 is an interferon-responsive nuclear body protein with critical roles in cell cycling, apoptosis and immunity to infection. However association studies of the gene with clinical TB in different populations have produced conflicting results. Methods: To examine the importance of the SP110 gene in immunity to TB in the Vietnamese we conducted a case-control genetic association study of 24 SP110 variants, in 663 patients with microbiologically proven TB and 566 unaffected control subjects from three tertiary hospitals in northern Vietnam. Results: Five SNPs within SP110 were associated with all forms of TB, including four SNPs at the C terminus (rs10208770, rs10498244, rs16826860, rs11678451) under a dominant model and one SNP under a recessive model, rs7601176. Two of these SNPs were associated with pulmonary TB (rs10208770 and rs16826860) and one with extra-pulmonary TB (rs10498244). Conclusion: SP110 variants were associated with increased susceptibility to both pulmonary and extra-pulmonary TB in the Vietnamese. Genetic variants in SP110 may influence macrophage signaling responses and apoptosis during M. tuberculosis infection, however further research is required to establish the mechanism by which SP110 influences immunity to tuberculosis infection. © 2014 Fox et al
Cosmic Hydrogen Was Significantly Neutral a Billion Years After the Big Bang
The ionization fraction of cosmic hydrogen, left over from the big bang,
provides crucial fossil evidence for when the first stars and quasar black
holes formed in the infant universe. Spectra of the two most distant quasars
known show nearly complete absorption of photons with wavelengths shorter than
the Ly-alpha transition of neutral hydrogen, indicating that hydrogen in the
intergalactic medium (IGM) had not been completely ionized at a redshift z~6.3,
about a billion years after the big bang. Here we show that the radii of
influence of ionizing radiation from these quasars imply that the surrounding
IGM had a neutral hydrogen fraction of tens of percent prior to the quasar
activity, much higher than previous lower limits of ~0.1%. When combined with
the recent inference of a large cumulative optical depth to electron scattering
after cosmological recombination from the WMAP data, our result suggests the
existence of a second peak in the mean ionization history, potentially due to
an early formation episode of the first stars.Comment: 14 Pages, 2 Figures. Accepted for publication in Nature. Press
embargo until publishe
The Optimal Exponent Base for emPAI Is 6.5
Exponentially Modified Protein Abundance Index (emPAI) is an established method of estimating protein abundances from peptide counts in a single LC-MS/MS experiment. EmPAI is defined as 10PAI minus one, where PAI (Protein Abundance Index) denotes the ratio of observed to observable peptides. EmPAI was first proposed by Ishihama et al [1] who found that PAI is approximately proportional to the logarithm of absolute protein concentration. I define emPAI65 = 6.5PAI-1 and show that it performs significantly better than emPAI, while it is equally easy to compute. The higher accuracy of emPAI65 is demonstrated by analyzing three data sets, including the one used in the original study [1]. I conclude that emPAI65 ought to be used instead of the original emPAI for protein quantitation
Climate changes reconstructed from a glacial lake in High Central Asiaover the past two millennia
Climatic changes in Arid Central Asia (ACA) over the past two millennia have been widely concerned. However, less attention has been paid to those in the High Central Asia (HCA), where the Asian water tower nurtures the numerous oases by glacier and/or snow melt. Here, we present a new reconstruction of the temperature and precipitation change over the past two millennia based on grain size of a well-dated glacial lake sediment core in the central of southern Tianshan Mountains. The results show that the glacial lake catchment has experienced cold-wet climate conditions during the Dark Age Cold Period (∼300–600 AD; DACP) and the Little Ice Age (∼1300–1870 AD; LIA), whereas warm-dry conditions during the Medieval Warm Period (∼700–1270 AD; MWP). Integration of our results with those of previously published lake sediment records, stalagmite δ18O records, ice core net accumulation rates, tree-ring based temperature reconstructions, and mountain glacier activities suggest that there has a broadly similar hydroclimatic pattern over the HCA areas on centennial time scale during the past two millennia. Comparison between hydroclimatic pattern of the HCA and that of the ACA areas suggests a prevailing 'warm-dry and cold-wet' hydroclimatic pattern over the whole westerlies-dominated central Asia areas during the past two millennia. We argue that the position and intensity of the westerlies, which are closely related to the phase of the North Atlantic Oscillation (NAO), and the strength of the Siberian High pressure (SH), could have jointly modulated the late Holocene central Asia hydroclimatic changes.<br /
Ionic high-pressure form of elemental boron
Boron is an element of fascinating chemical complexity. Controversies have
shrouded this element since its discovery was announced in 1808: the new
'element' turned out to be a compound containing less than 60-70 percent of
boron, and it was not until 1909 that 99-percent pure boron was obtained. And
although we now know of at least 16 polymorphs, the stable phase of boron is
not yet experimentally established even at ambient conditions. Boron's
complexities arise from frustration: situated between metals and insulators in
the periodic table, boron has only three valence electrons, which would favour
metallicity, but they are sufficiently localized that insulating states emerge.
However, this subtle balance between metallic and insulating states is easily
shifted by pressure, temperature and impurities. Here we report the results of
high-pressure experiments and ab initio evolutionary crystal structure
predictions that explore the structural stability of boron under pressure and,
strikingly, reveal a partially ionic high-pressure boron phase. This new phase
is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has
a hitherto unknown structure (space group Pnnm, 28 atoms in the unit cell)
consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement.
We find that the ionicity of the phase affects its electronic bandgap, infrared
adsorption and dielectric constants, and that it arises from the different
electronic properties of the B2 pairs and B12 clusters and the resultant charge
transfer between them.Comment: Published in Nature 453, 863-867 (2009
Experimental demonstration of a BDCZ quantum repeater node
Quantum communication is a method that offers efficient and secure ways for
the exchange of information in a network. Large-scale quantum communication (of
the order of 100 km) has been achieved; however, serious problems occur beyond
this distance scale, mainly due to inevitable photon loss in the transmission
channel. Quantum communication eventually fails when the probability of a dark
count in the photon detectors becomes comparable to the probability that a
photon is correctly detected. To overcome this problem, Briegel, D\"{u}r, Cirac
and Zoller (BDCZ) introduced the concept of quantum repeaters, combining
entanglement swapping and quantum memory to efficiently extend the achievable
distances. Although entanglement swapping has been experimentally demonstrated,
the implementation of BDCZ quantum repeaters has proved challenging owing to
the difficulty of integrating a quantum memory. Here we realize entanglement
swapping with storage and retrieval of light, a building block of the BDCZ
quantum repeater. We follow a scheme that incorporates the strategy of BDCZ
with atomic quantum memories. Two atomic ensembles, each originally entangled
with a single emitted photon, are projected into an entangled state by
performing a joint Bell state measurement on the two single photons after they
have passed through a 300-m fibre-based communication channel. The entanglement
is stored in the atomic ensembles and later verified by converting the atomic
excitations into photons. Our method is intrinsically phase insensitive and
establishes the essential element needed to realize quantum repeaters with
stationary atomic qubits as quantum memories and flying photonic qubits as
quantum messengers.Comment: 5 pages, 4 figure
Can spacetime curvature induced corrections to Lamb shift be observable?
The Lamb shift results from the coupling of an atom to vacuum fluctuations of
quantum fields, so corrections are expected to arise when the spacetime is
curved since the vacuum fluctuations are modified by the presence of spacetime
curvature. Here, we calculate the curvature-induced correction to the Lamb
shift outside a spherically symmetric object and demonstrate that this
correction can be remarkably significant outside a compact massive
astrophysical body. For instance, for a neutron star or a stellar mass black
hole, the correction is 25% at a radial distance of ,
16% at and as large as 1.6% even at , where is
the mass of the object, the Newtonian constant, and the speed of light.
In principle, we can look at the spectra from a distant compact super-massive
body to find such corrections. Therefore, our results suggest a possible way of
detecting fundamental quantum effects in astronomical observations.Comment: 13 pages, 3 figures, slight title change, clarifications and more
discussions added, version to be published in JHE
- …