2,794 research outputs found
Follow-up of vestibular function in bilateral vestibulopathy
Objective: Bilateral vestibulopathy (BV) leads to a bilateral deficit of the vestibulo-ocular reflex and has various aetiologies. The main goal of this study was to determine the frequency and degree of recovery or worsening of vestibular function over time.Methods: 82 patients (59 males, 23 females; mean age at the time of diagnosis 56.3 (SD 17.6) years) were re-examined 51 (36) months after the first examination. All patients underwent a standardised neuro-ophthalmological and neuro-otological examination. Electronystagmography with bithermal caloric irrigation was analysed by measurement of the mean peak slow phase velocity (SPV) of the induced nystagmus. Patients evaluated the course of their disease in terms of balance, gait unsteadiness and health related quality of life.Results: Statistical analysis of the mean peak SPV of caloric induced nystagmus revealed a non-significant worsening over time (initial mean peak SPV 3.0 (3.5)°/s vs 2.1 (2.8)°/s). With respect to subgroups of aetiology, only patients with BV due to meningitis exhibited an increasing, but non-significant SPV (1.0 (1.4)°/s vs 1.9 (1.6)°/s). Vestibular outcome was independent of age, gender, time course of manifestation and severity of BV. Single analysis of all patients showed that a substantial improvement ⩾5°/s occurred in two patients on both sides (idiopathic n = 1, Sjögren's syndrome n = 1) and in eight patients on one side (idiopathic n = 6, meningitis n = 1, Menière's disease n = 1). In 84% of patients there was impairment of their health related quality of life (42% slight, 24% moderate, 18% severe). Forty-three per cent of patients rated the course of their disease as stable, 28% as worsened and 29% as improved.Conclusions: Our data support the view that more than 80% of patients with BV do not improve. Thus the prognosis of BV is less favourable than assumed
Spinon excitations in the XX chain: spectra, transition rates, observability
The exact one-to-one mapping between (spinless) Jordan-Wigner lattice
fermions and (spin-1/2) spinons is established for all eigenstates of the
one-dimensional s = 1=2 XX model on a lattice with an even or odd number N of
lattice sites and periodic boundary conditions. Exact product formulas for the
transition rates derived via Bethe ansatz are used to calculate asymptotic
expressions of the 2-spinon and 4-spinon parts (for large even N) as well as of
the 1-spinon and 3-spinon parts (for large odd N) of the dynamic spin structure
factors. The observability of these spectral contributions is assessed for
finite and infinite N.Comment: 19 pages, 10 figure
Insulating phases of the infinite-dimensional Hubbard model
A theory is developed for the T=0 Mott-Hubbard insulating phases of the
infinite-dimensional Hubbard model at half-filling, including both the
antiferromagnetic (AF) and paramagnetic (P) insulators. Local moments are
introduced explicitly from the outset, enabling ready identification of the
dominant low energy scales for insulating spin- flip excitations. Dynamical
coupling of single-particle processes to the spin-flip excitations leads to a
renormalized self-consistent description of the single-particle propagators
that is shown to be asymptotically exact in strong coupling, for both the AF
and P phases. For the AF case, the resultant theory is applicable over the
entire U-range, and is discussed in some detail. For the P phase, we consider
in particular the destruction of the Mott insulator, the resultant critical
behaviour of which is found to stem inherently from proper inclusion of the
spin-flip excitations.Comment: 13 pages Revtex, 12 postscript figure
The Sloan Digital Sky Survey Reverberation Mapping Project: Post-Starburst Signatures in Quasar Host Galaxies at z < 1
Quasar host galaxies are key for understanding the relation between galaxies
and the supermassive black holes (SMBHs) at their centers. We present a study
of 191 broad-line quasars and their host galaxies at z < 1, using high
signal-to-noise ratio (SNR) spectra produced by the Sloan Digital Sky Survey
Reverberation Mapping project. Clear detection of stellar absorption lines
allows a reliable decomposition of the observed spectra into nuclear and host
components, using spectral models of quasar and stellar radiations as well as
emission lines from the interstellar medium. We estimate age, mass (M*), and
velocity dispersion (sigma*) of the host stars, the star formation rate (SFR),
quasar luminosity, and SMBH mass (Mbh), for each object. The quasars are
preferentially hosted by massive galaxies with M* ~ 10^{11} Msun characterized
by stellar ages around a billion years, which coincides with the transition
phase of normal galaxies from the blue cloud to the red sequence. The host
galaxies have relatively low SFRs and fall below the main sequence of
star-forming galaxies at similar redshifts. These facts suggest that the hosts
have experienced an episode of major star formation sometime in the past
billion years, which was subsequently quenched or suppressed. The derived Mbh -
sigma* and Mbh - M* relations agree with our past measurements and are
consistent with no evolution from the local Universe. The present analysis
demonstrates that reliable measurements of stellar properties of quasar host
galaxies are possible with high-SNR fiber spectra, which will be acquired in
large numbers with future powerful instruments such as the Subaru Prime Focus
Spectrograph.Comment: ApJ in pres
Bipolar polaron pair recombination in P3HT/PCBM solar cells
The unique properties of organic semiconductors make them versatile base
materials for many applications ranging from light emitting diodes to
transistors. The low spin-orbit coupling typical for carbon-based materials and
the resulting long spin lifetimes give rise to a large influence of the
electron spin on charge transport which can be exploited in spintronic devices
or to improve solar cell efficiencies. Magnetic resonance techniques are
particularly helpful to elucidate the microscopic structure of paramagnetic
states in semiconductors as well as the transport processes they are involved
in. However, in organic devices the nature of the dominant spin-dependent
processes is still subject to considerable debate. Using multi-frequency pulsed
electrically detected magnetic resonance (pEDMR), we show that the
spin-dependent response of P3HT/PCBM solar cells at low temperatures is
governed by bipolar polaron pair recombination involving the positive and
negative polarons in P3HT and PCBM, respectively, thus excluding a unipolar
bipolaron formation as the main contribution to the spin-dependent charge
transfer in this temperature regime. Moreover the polaron-polaron coupling
strength and the recombination times of polaron pairs with parallel and
antiparallel spins are determined. Our results demonstrate that the pEDMR pulse
sequences recently developed for inorganic semiconductor devices can very
successfully be transferred to the study of spin and charge transport in
organic semiconductors, in particular when the different polarons can be
distinguished spectrally
Conceptual Design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) for the Subaru Telescope
Recent developments in high-contrast imaging techniques now make possible
both imaging and spectroscopy of planets around nearby stars. We present the
conceptual design of the Coronagraphic High Angular Resolution Imaging
Spectrograph (CHARIS), a lenslet-based, cryogenic integral field spectrograph
(IFS) for imaging exoplanets on the Subaru telescope. The IFS will provide
spectral information for 140x140 spatial elements over a 1.75 arcsecs x 1.75
arcsecs field of view (FOV). CHARIS will operate in the near infrared (lambda =
0.9 - 2.5 microns) and provide a spectral resolution of R = 14, 33, and 65 in
three separate observing modes. Taking advantage of the adaptive optics systems
and advanced coronagraphs (AO188 and SCExAO) on the Subaru telescope, CHARIS
will provide sufficient contrast to obtain spectra of young self-luminous
Jupiter-mass exoplanets. CHARIS is in the early design phases and is projected
to have first light by the end of 2015. We report here on the current
conceptual design of CHARIS and the design challenges
Electric Field Modulation of Galvanomagnetic Properties of Mesoscopic Graphite
Electric field effect devices based on mesoscopic graphite are fabricated for
galvanomagnetic measurements. Strong modulation of magneto-resistance and Hall
resistance as a function of gate voltage is observed as sample thickness
approaches the screening length. Electric field dependent Landau level
formation is detected from Shubnikov de Haas oscillations in
magneto-resistance. The effective mass of electron and hole carriers has been
measured from the temperature dependant behavior of these oscillations.Comment: 4 pages, 4 figures included, submitted to Phys. Rev. Let
Optical and X-ray Spectroscopy of 1E 0449.4-1823: Demise of the original type 2 QSO
New optical spectra of the original narrow-line quasar 1E 0449.4-1823 show
that it now has broad emission lines of considerable strength, eliminating it
as a "type 2 QSO" candidate. We suggest that the behavior of 1E 0449.4-1823 is
the same as that of some Seyfert 1.8 and 1.9 galaxies, in which Goodrich
attributed long-term variations of their broad Balmer lines to dynamical
motions of obscuring material located in or around the broad-line region. The
optical continuum and broad emission-line regions of 1E 0449.4-1823 may still
be partly covered in our line of sight, which would explain its large
forbidden-line equivalent widths and flat alpha_ox relative to other
low-redshift QSOs. Also present are apparent absorption features in the broad
Balmer lines and in Mg II, which may be related to the past obscuration and
current emergence of the broad-line region. However, it is difficult to
distinguish absorption from broad emission-line peaks that are displaced in
velocity; we consider the latter a plausible competing interpretation of these
peculiar line profiles. An ASCA X-ray spectrum of 1E 0449.4-1823 can be fitted
with a power-law of Gamma = 1.63, intrinsic N_H < 9 x 10^20 cm-2, and no Fe
Kalpha line emission. Its 2-10 keV luminosity is 6.7 x 10^44 ergs/s. With
regard to the still hypothetical type 2 QSOs, we argue that there is little
evidence for the existence of any among X-ray selected samples.Comment: to appear in ApJ July 1, 1998 (vol. 501). 23 pages including figures.
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