78 research outputs found
The de Haas-van Alphen effect across the metamagnetic transition in SrRuO
We report a study of the de Haas-van Alphen (dHvA) effect on the itinerant
metamagnet SrRuO. Extremely high sample purity allows the
observation of dHvA oscillations both above and below the metamagnetic
transition field of 7.9 T. The quasiparticle masses are fairly large away from
the transition, and are enhanced by up to an extra factor of three as the
transition is approached, but the Fermi surface topography change is quite
small. The results are qualitatively consistent with a field-induced Stoner
transition in which the mass enhancement is the result of critical
fluctuations.Comment: 4 pages, 3 figure
Variable Step Random Walks and Self-Similar Distributions
We study a scenario under which variable step random walks give anomalous
statistics. We begin by analyzing the Martingale Central Limit Theorem to find
a sufficient condition for the limit distribution to be non-Gaussian. We note
that the theorem implies that the scaling index is 1/2. For
corresponding continuous time processes, it is shown that the probability
density function satisfies the Fokker-Planck equation. Possible forms
for the diffusion coefficient are given, and related to . Finally, we
show how a time-series can be used to distinguish between these variable
diffusion processes and L\'evy dynamics.Comment: 13pages, 2 figure
First Observation of Quantum Oscillations in the Ferromagnetic Superconductor UCoGe
We succeeded in growing high quality single crystals of the ferromagnetic
superconductor UCoGe and measured the magnetoresistance at fields up to 34T.
The Shubnikov-de Haas signal was observed for the first time in a U-111 system
(UTGe, UTSi, T: transition metal). A small pocket Fermi surface (F~1kT) with
large cyclotron effective mass 25m0 was detected at high fields above 22T,
implying that UCoGe is a low carrier system accompanyed with heavy
quasi-particles. The observed frequency decreases with increasing fields,
indicating that the volume of detected Fermi surface changes nonlinearly with
field. The cyclotron mass also decreases, which is consistent with the decrease
of the A coefficient of resistivity.Comment: 5 pages, 5 figures, accepted for publication in J. Phys. Soc. Jp
High-field magnetization of the 3d heavy-fermion system LiVO (d = 0, 0.08)
Metamagnetic behavior has been observed in LiV2O4 powder sample around 38 T
at 4.2 K. On the other hand, magnetization for oxygen deficient LiV2O3.92 shows
no indication of metamagnetism up to 40 T, and shows substantially reduced
magnetic moment compared to that of LiV2O4. These results suggest that
ferromagnetic interaction is strongly enhanced by magnetic fields in LiV2O4,
whereas antiferromagnetic interaction is dominant in LiV2O3.92.Comment: 9 pages, 3 figures, to be published in J. Phys.: Condens. Matte
Global update on the susceptibility of humam influenza viruses to neuraminidase inhibitors 2012-2013
Emergence of influenza viruses with reduced susceptibility to neuraminidase inhibitors (NAIs) is sporadic, often follows exposure to NAIs, but occasionally occurs in the absence of NAI pressure. The emergence and global spread in 2007/2008 of A(H1N1) influenza viruses showing clinical resistance to oseltamivir due to neuraminidase (NA) H275Y substitution, in the absence of drug pressure, warrants continued vigilance and monitoring for similar viruses. Four World Health Organization (WHO) Collaborating Centres for Reference and Research on Influenza and one WHO Collaborating Centre for the Surveillance, Epidemiology and Control of Influenza (WHO CCs) tested 11,387 viruses collected by WHO-recognized National Influenza Centres (NIC) between May 2012 and May 2013 to determine 50% inhibitory concentration (IC50) data for oseltamivir, zanamivir, peramivir and laninamivir. The data were evaluated using normalized IC50 fold-changes rather than raw IC50 data. Nearly 90% of the 11,387 viruses were from three WHO regions: Western Pacific, the Americas and Europe. Only 0.2% (n=27) showed highly reduced inhibition (HRI) against at least one of the four NAIs, usually oseltamivir, while 0.3% (n=39) showed reduced inhibition (RI). NA sequence data, available from the WHO CCs and from sequence databases (n=3661), were screened for amino acid substitutions associated with reduced NAI susceptibility. Those showing HRI were A(H1N1)pdm09 with NA H275Y (n=18), A(H3N2) with NA E119V (n=3) or NA R292K (n=1) and B/Victoria-lineage with NA H273Y (n=2); amino acid position numbering is A subtype and B type specific. Overall, approximately 99% of circulating viruses tested during the 2012-2013 period were sensitive to all four NAIs. Consequently, these drugs remain an appropriate choice for the treatment and prophylaxis of influenza virus infections
High-Field Fermi Surface Properties in the Low Carrier Heavy Fermion Compound URu2Si2
We performed the Shubnikov-de Haas (SdH) experiments of the low carrier heavy
fermion compound URu2Si2 at high fields up to 34T and at low temperatures down
to 30mK. All main SdH branches named alpha, beta and gamma were observed for
all the measured field-directions (H // [001] -> [100], [100] -> [110] and
[001] -> [110]), indicating that these are attributed to the closed Fermi
surfaces with nearly spherical shapes. Anomalous split of branch alpha was
detected for the field along the basal plane, and the split immediately
disappears by tilting the field to [001] direction, implying a fingerprint of
the hidden order state. High field experiments reveal the complicated
field-dependence of the SdH frequencies and the cyclotron masses due to the
Zeeman spin-splitting associated with the Fermi surface reconstruction in the
hidden order state with small carrier numbers. A new SdH branch named omega
with large cyclotron mass of 25m0 was detected at high fields above 23T close
to the hidden order instabilities.Comment: 6 pages, 7 figures, accepted for publication in J. Phys. Soc. Jp
Standardizing the influenza neuraminidase inhibition assay among United States public health laboratories conducting virological surveillance
Oseltamivir-resistant influenza A(H1N1)pdm2009 strains found in Brazil are endowed with permissive mutations, which compensate the loss of fitness imposed by antiviral resistance
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