1,867 research outputs found
Cross-Generational Reproductive Fitness Enforced by Microchimeric Maternal Cells
SummaryExposure to maternal tissue during in utero development imprints tolerance to immunologically foreign non-inherited maternal antigens (NIMA) that persists into adulthood. The biological advantage of this tolerance, conserved across mammalian species, remains unclear. Here, we show maternal cells that establish microchimerism in female offspring during development promote systemic accumulation of immune suppressive regulatory TÂ cells (Tregs) with NIMA specificity. NIMA-specific Tregs expand during pregnancies sired by males expressing alloantigens with overlapping NIMA specificity, thereby averting fetal wastage triggered by prenatal infection and non-infectious disruptions of fetal tolerance. Therefore, exposure to NIMA selectively enhances reproductive success in second-generation females carrying embryos with overlapping paternally inherited antigens. These findings demonstrate that genetic fitness, canonically thought to be restricted to Mendelian inheritance, is enhanced in female placental mammals through vertically transferred maternal cells that promote conservation of NIMA and enforce cross-generational reproductive benefits
A biometrical study of the relationship between sodium-lithium countertransport and triglycerides
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66400/1/j.1469-1809.1997.6120121.x.pd
Two-Spinon and Orbital Excitations of the Spin-Peierls System TiOCl
We combine high-resolution resonant inelastic x-ray scattering with cluster
calculations utilizing a recently derived effective magnetic scattering
operator to analyze the polarization, excitation energy, and momentum dependent
excitation spectrum of the low-dimensional quantum magnet TiOCl in the range
expected for orbital and magnetic excitations (0 - 2.5 eV). Ti 3d orbital
excitations yield complete information on the temperature-dependent
crystal-field splitting. In the spin-Peierls phase we observe a dispersive
two-spinon excitation and estimate the inter- and intra-dimer magnetic exchange
coupling from a comparison to cluster calculations
Muon-spin relaxation measurements on the dimerized spin-1/2 chains NaTiSi2O6 and TiOCl
We report muon spin relaxation (muSR) and magnetic susceptibility
investigations of two Ti3+ chain compounds which each exhibit a spin gap at low
temperature, NaTiSi2O6 and TiOCl. From these we conclude that the spin gap in
NaTiSi2O6 is temperature independent, with a value of 2*Delta=660(50)K, arising
from orbital ordering at Too = 210K; the associated structural fluctuations
activate the muon spin relaxation rate up to temperatures above 270K. In TiOCl
we find thermally activated spin fluctuations corresponding to a spin gap
2*Delta=420(40)K below Tc1=67K. We also compare the methods used to extract the
spin gap and the concentration of free spins within the samples from muSR and
magnetic susceptibility data.Comment: 4 pages, 3 figure
Hubble Space Telescope Transmission Spectroscopy of the Exoplanet HD 189733b: High-altitude atmospheric haze in the optical and near-UV with STIS
We present Hubble Space Telescope optical and near-ultraviolet transmission
spectra of the transiting hot-Jupiter HD189733b, taken with the repaired Space
Telescope Imaging Spectrograph (STIS) instrument. The resulting spectra cover
the range 2900-5700 Ang and reach per-exposure signal-to-noise levels greater
than 11,000 within a 500 Ang bandwidth. We used time series spectra obtained
during two transit events to determine the wavelength dependance of the
planetary radius and measure the exoplanet's atmospheric transmission spectrum
for the first time over this wavelength range. Our measurements, in conjunction
with existing HST spectra, now provide a broadband transmission spectrum
covering the full optical regime. The STIS data also shows unambiguous evidence
of a large occulted stellar spot during one of our transit events, which we use
to place constraints on the characteristics of the K dwarf's stellar spots,
estimating spot temperatures around Teff~4250 K. With contemporaneous
ground-based photometric monitoring of the stellar variability, we also measure
the correlation between the stellar activity level and transit-measured
planet-to-star radius contrast, which is in good agreement with predictions. We
find a planetary transmission spectrum in good agreement with that of Rayleigh
scattering from a high-altitude atmospheric haze as previously found from HST
ACS camera. The high-altitude haze is now found to cover the entire optical
regime and is well characterised by Rayleigh scattering. These findings suggest
that haze may be a globally dominant atmospheric feature of the planet which
would result in a high optical albedo at shorter optical wavelengths.Comment: 14 pages, 14 figures, 4 tables, accepted to MNRAS, revised version
has minor change
Terahertz Conductivity at the Verwey Transition in Magnetite
The complex conductivity at the (Verwey) metal-insulator transition in
Fe_3O_4 has been investigated at THz and infrared frequencies. In the
insulating state, both the dynamic conductivity and the dielectric constant
reveal a power-law frequency dependence, the characteristic feature of hopping
conduction of localized charge carriers. The hopping process is limited to low
frequencies only, and a cutoff frequency nu_1 ~ 8 meV must be introduced for a
self-consistent description. On heating through the Verwey transition the
low-frequency dielectric constant abruptly decreases and becomes negative.
Together with the conductivity spectra this indicates a formation of a narrow
Drude-peak with a characteristic scattering rate of about 5 meV containing only
a small fraction of the available charge carriers. The spectra can be explained
assuming the transformation of the spectral weight from the hopping process to
the free-carrier conductivity. These results support an interpretation of
Verwey transition in magnetite as an insulator-semiconductor transition with
structure-induced changes in activation energy.Comment: 6 Pages, 3 Figure
Electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ
We study the electronic structure of the quasi-one-dimensional organic
conductor TTF-TCNQ by means of density-functional band theory, Hubbard model
calculations, and angle-resolved photoelectron spectroscopy (ARPES). The
experimental spectra reveal significant quantitative and qualitative
discrepancies to band theory. We demonstrate that the dispersive behavior as
well as the temperature-dependence of the spectra can be consistently explained
by the finite-energy physics of the one-dimensional Hubbard model at metallic
doping. The model description can even be made quantitative, if one accounts
for an enhanced hopping integral at the surface, most likely caused by a
relaxation of the topmost molecular layer. Within this interpretation the ARPES
data provide spectroscopic evidence for the existence of spin-charge separation
on an energy scale of the conduction band width. The failure of the
one-dimensional Hubbard model for the {\it low-energy} spectral behavior is
attributed to interchain coupling and the additional effect of electron-phonon
interaction.Comment: 18 pages, 9 figure
High-energy photoemission on Fe3O4: Small polaron physics and the Verwey transition
We have studied the electronic structure and charge ordering (Verwey)
transition of magnetite (Fe3O4) by soft x-ray photoemission. Due to the
enhanced probing depth and the use of different surface preparations we are
able to distinguish surface and volume effects in the spectra. The pseudogap
behavior of the intrinsic spectra and its temperature dependence give evidence
for the existence of strongly bound small polarons consistent with both dc and
optical conductivity. Together with other recent structural and theoretical
results our findings support a picture in which the Verwey transition contains
elements of a cooperative Jahn-Teller effect, stabilized by local Coulomb
interaction
Possible detection of phase changes from the non-transiting planet HD 46375b by CoRoT
The present work deals with the detection of phase changes in an exoplanetary
system. HD 46375 is a solar analog known to host a non-transiting Saturn-mass
exoplanet with a 3.0236 day period. It was observed by the CoRoT satellite for
34 days during the fall of 2008. We attempt to identify at optical wavelengths,
the changing phases of the planet as it orbits its star. We then try to improve
the star model by means of a seismic analysis of the same light curve and the
use of ground-based spectropolarimetric observations. The data analysis relies
on the Fourier spectrum and the folding of the time series. We find evidence of
a sinusoidal signal compatible in terms of both amplitude and phase with light
reflected by the planet. Its relative amplitude is Delta Fp/F* = [13.0, 26.8]
ppm, implying an albedo A=[0.16, 0.33] or a dayside visible brightness
temperature Tb ~ [1880,2030] K by assuming a radius R=1.1 R_Jup and an
inclination i=45 deg. Its orbital phase differs from that of the
radial-velocity signal by at most 2 sigma_RV. However, the tiny planetary
signal is strongly blended by another signal, which we attribute to a telluric
signal with a 1 day period. We show that this signal is suppressed, but not
eliminated, when using the time series for HD 46179 from the same CoRoT run as
a reference. This detection of reflected light from a non-transiting planet
should be confirmable with a longer CoRoT observation of the same field. In any
case, it demonstrates that non-transiting planets can be characterized using
ultra-precise photometric lightcurves with present-day observations by CoRoT
and Kepler. The combined detection of solar-type oscillations on the same
targets (Gaulme et al. 2010a) highlights the overlap between exoplanetary
science and asteroseismology and shows the high potential of a mission such as
Plato.Comment: 4 pages, 6 figure
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