1,408 research outputs found
Irreducible characters of GSp(4, q) and dimensions of spaces of fixed vectors
In this paper, we compute the conjugacy classes and the list of irreducible
characters of GSp(4,q), where q is odd. We also determine precisely which
irreducible characters are non-cuspidal and which are generic. These characters
are then used to compute dimensions of certain subspaces of fixed vectors of
smooth admissible non-supercuspidal representations of GSp(4,F), where F is a
non-archimedean local field of characteristic zero with residue field of order
q.Comment: 48 pages, 21 tables. Corrected an error in Table 16 for type V*
representations (theta_11 and theta_12 were switched
Ocean temperature and salinity components of the Madden-Julian oscillation observed by Argo floats
New diagnostics of the Madden-Julian Oscillation (MJO) cycle in ocean temperature and, for the first time, salinity are presented. The MJO composites are based on 4 years of gridded Argo float data from 2003 to 2006, and extend from the surface to 1,400 m depth in the tropical Indian and Pacific Oceans. The MJO surface salinity anomalies are consistent with precipitation minus evaporation fluxes in the Indian Ocean, and with anomalous zonal advection in the Pacific. The Argo sea surface temperature and thermocline depth anomalies are consistent with previous studies using other data sets. The near-surface density changes due to salinity are comparable to, and partially offset, those due to temperature, emphasising the importance of including salinity as well as temperature changes in mixed-layer modelling of tropical intraseasonal processes. The MJO-forced equatorial Kelvin wave that propagates along the thermocline in the Pacific extends down into the deep ocean, to at least 1,400 m. Coherent, statistically significant, MJO temperature and salinity anomalies are also present in the deep Indian Ocean
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Engineered MATE multidrug transporters reveal two functionally distinct ion-coupling pathways in NorM from Vibrio cholerae.
Multidrug and toxic compound extrusion (MATE) transport proteins confer multidrug resistance on pathogenic microorganisms and affect pharmacokinetics in mammals. Our understanding of how MATE transporters work, has mostly relied on protein structures and MD simulations. However, the energetics of drug transport has not been studied in detail. Many MATE transporters utilise the electrochemical H+ or Na+ gradient to drive substrate efflux, but NorM-VC from Vibrio cholerae can utilise both forms of metabolic energy. To dissect the localisation and organisation of H+ and Na+ translocation pathways in NorM-VC we engineered chimaeric proteins in which the N-lobe of H+-coupled NorM-PS from Pseudomonas stutzeri is fused to the C-lobe of NorM-VC, and vice versa. Our findings in drug binding and transport experiments with chimaeric, mutant and wildtype transporters highlight the versatile nature of energy coupling in NorM-VC, which enables adaptation to fluctuating salinity levels in the natural habitat of V. cholerae
Measurement of forward photon production cross-section in proton-proton collisions at = 13 TeV with the LHCf detector
In this paper, we report the production cross-section of forward photons in
the pseudorapidity regions of and ,
measured by the LHCf experiment with proton--proton collisions at =
13 TeV. The results from the analysis of 0.191 of data
obtained in June 2015 are compared to the predictions of several hadronic
interaction models that are used in air-shower simulations for
ultra-high-energy cosmic rays. Although none of the models agree perfectly with
the data, EPOS-LHC shows the best agreement with the experimental data among
the models.Comment: 21 pages, 4 figure
Quasi periodic oscillations in XTE J0111.2--7317, highest frequency among the HMXB pulsars
We report here discovery of Quasi Periodic Oscillations (QPOs) in the High
Mass X-ray Binary (HMXB) Pulsar XTE J0111.20-7317 during a transient outburst
in this source in December 1998. Using observations made with the proportional
counter array of the Rossi X-ray Timing Explorer during the second peak and the
declining phase of this outburst we have discovered a QPO feature at a
frequency of 1.27 Hz. We have ruled out the possibility that the observed QPOs
can instead be from the neighbouring bright X-ray pulsar SMC X-1. This is the
highest frequency QPO feature ever detected in any HMXB pulsar. In the absence
of a cyclotron absorption feature in the X-ray spectrum, the QPO feature, along
with the pulse period and X-ray flux measurement measurement helps us to
constrain the magnetic field strength of the neutron star.Comment: Accepted for publication in The Astrophysical Journa
Measurement of the cosmic-ray antiproton spectrum at solar minimum with a long-duration balloon flight over Antarctica
The energy spectrum of cosmic-ray antiprotons from 0.17 to 3.5 GeV has been
measured using 7886 antiprotons detected by BESS-Polar II during a
long-duration flight over Antarctica near solar minimum in December 2007 and
January 2008. This shows good consistency with secondary antiproton
calculations. Cosmologically primary antiprotons have been investigated by
comparing measured and calculated antiproton spectra. BESS-Polar II data show
no evidence of primary antiprotons from evaporation of primordial black holes.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
Sidebands Due to Quasi-periodic Oscillations in 4U 1626-67
The low-mass X-ray binary pulsar 4U 1626-67 shows 0.048 Hz quasi-periodic
oscillations (QPOs) and red noise variability as well as coherent pulsations at
the 0.130 Hz neutron star spin frequency. Power density spectra of observations
made with the Rossi X-ray Timing Explorer show significant sidebands separated
from the pulsar spin frequency (and its harmonics) by the QPO frequency. These
show that the instantaneous amplitude of the coherent pulsations is modulated
by the amplitude of the QPOs. This phenomenon is expected in models such as the
magnetospheric beat frequency model where the QPOs originate near the polar
caps of the neutron star. In the 4--8 keV energy range, however, the
lower-frequency sidebands are significantly stronger than their
higher-frequency complements; this is inconsistent with the magnetospheric beat
frequency model. We suggest that the 0.048 Hz QPOs are instead produced by a
structure orbiting the neutron star at the QPO frequency. This structure
crosses the line of sight once per orbit and attenuates the pulsar beam,
producing the symmetric (amplitude modulation) sidebands. It also reprocesses
the pulsar beam at the beat frequencies between the neutron star spin frequency
and the QPOs, producing the excess variability observed in the lower-frequency
sidebands. Quite independently, we find no evidence that the red noise
variability modulates the amplitude of the coherent pulsations. This is also in
contrast to the expectations of the magnetospheric beat frequency model and
differs from the behavior in some high-mass X-ray binary pulsars.Comment: 8 pages, 3 figures, AAS macros v4.0. To appear in ApJ Letter
Magnetic Fields of Accreting X-Ray Pulsars with the Rossi X-Ray Timing Explorer
Using a consistent set of models, we parameterized the X-ray spectra of all
accreting pulsars in the Rossi X-ray Timing Explorer database which exhibit
Cyclotron Resonance Scattering Features (CRSFs, or cyclotron lines). These
sources in our sample are Her X-1, 4U 0115+63, Cen X-3, 4U 1626-67, XTE
J1946-274, Vela X-1, 4U 1907+09, 4U 1538-52, GX 301-2, and 4U 0352+309 (X Per).
We searched for correlations among the spectral parameters, concentrating on
how the cyclotron line energy relates to the continuum and therefore how the
neutron star B-field influences the X-Ray emission. As expected, we found a
correlation between the CRSF energy and the spectral cutoff energy. However,
with our consistent set of fits we found that the relationship is more complex
than what has been reported previously. Also, we found that not only does the
width of the cyclotron line correlate with the energy (as suggested by theory),
but that the width scaled by the energy correlates with the depth of the
feature. We discuss the implications of these results, including the
possibility that accretion directly affects the relative alignment of the
neutron star spin and dipole axes. Lastly, we comment on the current state of
fitting phenomenological models to spectra in the RXTE/BeppoSAX era and the
need for better theoretical models of the X-Ray continua of accreting pulsars.Comment: 36 Pages, 9 Figures, 9 Tables, ApJ in pres
Residual properties of the modular group and other free products
AbstractUsing a probabilistic approach we establish new residual properties of the modular group PSL2(Z), and of more general free products. We prove that the modular group is residually in any infinite collection of finite simple groups not containing a Suzuki group Sz(q) or a 4-dimensional symplectic group PSp4(q) with q a power of 2 or 3. This result is best possible, since the groups excluded are not quotients of the modular group. We also show that if S is a collection of classical groups of unbounded rank, then an arbitrary free product A∗B of nontrivial finite groups, not both 2-groups, is residually S, and prove results about free products A∗Z
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