12,277 research outputs found
Solar Irradiance Observed from PVO and Inferred Solar Rotation
Solar irradiance in the extreme ultraviolet flux (EUV) has been monitored for 11 years by the Pioneer Venus Orbiter (PVO). Since the experiment moves around the Sun with the orbital rate of Venus rather than that of Earth, the measurement gives us a second viewing location from which to begin unravelling which irradiance variations are intrinsic to the Sun, and which are merely rotational modulations whose periods depend on the motion of the observer. Researchers confirm an earlier detection, made with only 8.6 years of data, that the EUV irradiance is modulated by rotation rates of two families of global oscillation modes. One family is assumed to be r-modes occupying the convective envelope and sharing its rotation, while the other family (g-modes) lies in the radiative interior which as a slower rotation. Measured power in r-modes of low angular harmonic number indicates that the Sun's envelope rotated about 0.7 percent faster near the last solar maximum (1979 thru 1982) than it did during the next rise to maximum (1986 to 1989). No change was seen in the g-mode family of lines, as would be expected from the much greater rotational inertia of the radiative interior
Determinants of anemia and hemoglobin concentration in haitian school-aged children
Anemia diminishes oxygen transport in the body, resulting in potentially irreversible growth and developmental consequences for children. Limited evidence for determinants of anemia exists for school-aged children. We conducted a cluster randomized controlled trial in Haiti from 2012 to 2013 to test the efficacy of a fortified school snack. Children (N = 1,047) aged 3–13 years were followed longitudinally at three time points for hemoglobin (Hb) concentrations, anthropometry, and bioelectrical impedance measures. Dietary intakes, infectious disease morbidities, and socioeconomic and demographic factors were collected at baseline and endline. Longitudinal regression modeling with generalized least squares and logit models with random effects identified anemia risk factors beyond the intervention effect. At baseline, 70.6% of children were anemic and 2.6% were severely anemic. Stunting increased the odds of developing anemia (adjusted odds ratio [OR]: 1.48, 95% confidence interval [CI]: 1.05–2.08) and severe anemia (adjusted OR: 2.47, 95% CI: 1.30–4.71). Parent-reported vitamin A supplementation and deworming were positively associated with Hb concentrations, whereas fever and poultry ownership showed a negative relationship with Hb concentration and increased odds of severe anemia, respectively. Further research should explore the full spectrum of anemia etiologies in school children, including genetic causes
New Ultraviolet Extinction Curves for Interstellar Dust in M31
New low-resolution UV spectra of a sample of reddened OB stars in M31 were
obtained with HST/STIS to study the wavelength dependence of interstellar
extinction and the nature of the underlying dust grain populations. Extinction
curves were constructed for four reddened sightlines in M31 paired with closely
matching stellar atmosphere models. The new curves have a much higher S/N than
previous studies. Direct measurements of N(H I) were made using the Ly
absorption lines enabling gas-to-dust ratios to be calculated. The sightlines
have a range in galactocentric distance of 5 to 14 kpc and represent dust from
regions of different metallicities and gas-to-dust ratios. The metallicities
sampled range from Solar to 1.5 Solar. The measured curves show similarity to
those seen in the Milky Way and the Large Magellanic Cloud. The Maximum Entropy
Method was used to investigate the dust composition and size distribution for
the sightlines observed in this program finding that the extinction curves can
be produced with the available carbon and silicon abundances if the metallicity
is super-Solar.Comment: ApJ, in press, 9 pages, 5 figure
Spin-orbit coupled particle in a spin bath
We consider a spin-orbit coupled particle confined in a quantum dot in a bath
of impurity spins. We investigate the consequences of spin-orbit coupling on
the interactions that the particle mediates in the spin bath. We show that in
the presence of spin-orbit coupling, the impurity-impurity interactions are no
longer spin-conserving. We quantify the degree of this symmetry breaking and
show how it relates to the spin-orbit coupling strength. We identify several
ways how the impurity ensemble can in this way relax its spin by coupling to
phonons. A typical resulting relaxation rate for a self-assembled Mn-doped ZnTe
quantum dot populated by a hole is 1 s. We also show that decoherence
arising from nuclear spins in lateral quantum dots is still removable by a spin
echo protocol, even if the confined electron is spin-orbit coupled.Comment: 18 pages, 1 figur
The Ionization of the Local Interstellar Medium, as Revealed by FUSE Observations of N, O and Ar toward White Dwarf Stars
FUSE spectra of the white dwarf stars G191-B2B, GD 394, WD 2211-495 and WD
2331-475 cover the absorption features out of the ground electronic states of N
I, N II, N III, O I and Ar I in the far ultraviolet, providing new insights on
the origin of the partial ionization of the Local Interstellar Medium (LISM),
and for the case of G191-B2B, the interstellar cloud that immediately surrounds
the solar system. Toward these targets the interstellar abundances of Ar I, and
sometimes N I, are significantly below their cosmic abundances relative to H I.
In the diffuse interstellar medium, these elements are not likely to be
depleted onto dust grains. Generally, we expect that Ar should be more strongly
ionized than H (and also O and N whose ionizations are coupled to that of H via
charge exchange reactions) because the cross section for the photoionization of
Ar I is very high. Our finding that Ar I/H I is low may help to explain the
surprisingly high ionization of He in the LISM found by other investigators.
Our result favors the interpretation that the ionization of the local medium is
maintained by a strong EUV flux from nearby stars and hot gases, rather than an
incomplete recovery from a past, more highly ionized condition.Comment: 13 pages, 2 figures. To appear in a special issue of the
Astrophysical Journal Letters devoted to the first scientific results from
the FUSE missio
Multi-mode mediated exchange coupling in cavity QED
Microwave cavities with high quality factors enable coherent coupling of
distant quantum systems. Virtual photons lead to a transverse exchange
interaction between qubits, when they are non-resonant with the cavity but
resonant with each other. We experimentally probe the inverse scaling of the
inter-qubit coupling with the detuning from a cavity mode and its
proportionality to the qubit-cavity interaction strength. We demonstrate that
the enhanced coupling at higher frequencies is mediated by multiple
higher-harmonic cavity modes. Moreover, in the case of resonant qubits, the
symmetry properties of the system lead to an allowed two-photon transition to
the doubly excited qubit state and the formation of a dark state.Comment: 9 pages, 6 figure
Comments on Sweeny and Gliozzi dynamics for simulations of Potts models in the Fortuin-Kasteleyn representation
We compare the correlation times of the Sweeny and Gliozzi dynamics for
two-dimensional Ising and three-state Potts models, and the three-dimensional
Ising model for the simulations in the percolation prepresentation. The results
are also compared with Swendsen-Wang and Wolff cluster dynamics. It is found
that Sweeny and Gliozzi dynamics have essentially the same dynamical critical
behavior. Contrary to Gliozzi's claim (cond-mat/0201285), the Gliozzi dynamics
has critical slowing down comparable to that of other cluster methods. For the
two-dimensional Ising model, both Sweeny and Gliozzi dynamics give good fits to
logarithmic size dependences; for two-dimensional three-state Potts model,
their dynamical critical exponent z is 0.49(1); the three-dimensional Ising
model has z = 0.37(2).Comment: RevTeX, 4 pages, 5 figure
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