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Integrating the inputs that shape pancreatic islet hormone release.
The pancreatic islet is a complex mini organ composed of a variety of endocrine cells and their support cells, which together tightly control blood glucose homeostasis. Changes in glucose concentration are commonly regarded as the chief signal controlling insulin-secreting beta cells, glucagon-secreting alpha cells and somatostatin-secreting delta cells. However, each of these cell types is highly responsive to a multitude of endocrine, paracrine, nutritional and neural inputs, which collectively shape the final endocrine output of the islet. Here, we review the principal inputs for each islet-cell type and the physiological circumstances in which these signals arise, through the prism of the insights generated by the transcriptomes of each of the major endocrine-cell types. A comprehensive integration of the factors that influence blood glucose homeostasis is essential to successfully improve therapeutic strategies for better diabetes management
Dissociating task difficulty from incongruence in face-voice emotion integration
In the everyday environment, affective information is conveyed by both the face and the voice. Studies have demonstrated that a concurrently presented voice can alter the way that an emotional face expression is perceived, and vice versa, leading to emotional conflict if the information in the two modalities is mismatched. Additionally, evidence suggests that incongruence of emotional valence activates cerebral networks involved in conflict monitoring and resolution. However, it is currently unclear whether this is due to task difficulty—that incongruent stimuli are harder to categorize—or simply to the detection of mismatching information in the two modalities. The aim of the present fMRI study was to examine the neurophysiological correlates of processing incongruent emotional information, independent of task difficulty. Subjects were scanned while judging the emotion of face-voice affective stimuli. Both the face and voice were parametrically morphed between anger and happiness and then paired in all audiovisual combinations, resulting in stimuli each defined by two separate values: the degree of incongruence between the face and voice, and the degree of clarity of the combined face-voice information. Due to the specific morphing procedure utilized, we hypothesized that the clarity value, rather than incongruence value, would better reflect task difficulty. Behavioral data revealed that participants integrated face and voice affective information, and that the clarity, as opposed to incongruence value correlated with categorization difficulty. Cerebrally, incongruence was more associated with activity in the superior temporal region, which emerged after task difficulty had been accounted for. Overall, our results suggest that activation in the superior temporal region in response to incongruent information cannot be explained simply by task difficulty, and may rather be due to detection of mismatching information between the two modalities
On the viability of the shearing box approximation for numerical studies of MHD turbulence in accretion disks
Most of our knowledge on the nonlinear development of the magneto-rotational
instability (MRI) relies on the results of numerical simulations employing the
shearing box (SB) approximation. A number of difficulties arising from this
approach have recently been pointed out in the literature. We thoroughly
examine the effects of the assumptions made and numerical techniques employed
in SB simulations. This is done in order to clarify and gain better
understanding of those difficulties as well as of a number of additional
serious problems, raised here for the first time, and of their impact on the
results. Analytical derivations and estimates as well as comparative analysis
to methods used in the numerical study of turbulence are used. Numerical
experiments are performed to support some of our claims and conjectures. The
following problems, arising from the (virtually exclusive) use of the SB
simulations as a tool for the understanding and quantification of the nonlinear
MRI development in disks, are analyzed and discussed: (i) inconsistencies in
the application of the SB approximation itself; (ii) the limited spatial scale
of the SB; (iii) the lack of convergence of most ideal MHD simulations; (iv)
side-effects of the SB symmetry and the non-trivial nature of the linear MRI;
(v) physical artifacts arising on the too small box scale due to periodic
boundary conditions. The computational and theoretical challenge posed by the
MHD turbulence problem in accretion disks cannot be met by the SB
approximation, as it has been used to date. A new strategy to confront this
challenge is proposed, based on techniques widely used in numerical studies of
turbulent flows - developing (e.g., with the help of local numerical studies) a
sub-grid turbulence model and implementing it in global calculations.Comment: Accepted for publication in Astronomy and Astrophysic
Dynamical Evolution of Elliptical Galaxies with Central Singularities
We study the effect of a massive central singularity on the structure of a
triaxial galaxy using N-body simulations. Starting from a single initial model,
we grow black holes with various final masses Mh and at various rates, ranging
from impulsive to adiabatic. In all cases, the galaxy achieves a final shape
that is nearly spherical at the center and close to axisymmetric throughout.
However, the rate of change of the galaxy's shape depends strongly on the ratio
Mh/Mg of black hole mass to galaxy mass. When Mh/Mg < 0.3%, the galaxy evolves
in shape on a timescale that exceeds 100 orbital periods, or roughly a galaxy
lifetime. When Mh/Mg > 2%, the galaxy becomes axisymmetric in little more than
a crossing time. We propose that the rapid evolution toward axisymmetric shapes
that occurs when Mh/Mg > 2% provides a negative feedback mechanism which limits
the mass of central black holes by cutting off their supply of fuel.Comment: 27 Latex pages, 9 Postscript figures, uses aastex.sty. Accepted for
Publication in The Astrophysical Journal, Nov. 26, 199
Lattice Distortion and Resonant X-Ray Scattering in DyB2C2
We study the resonant x-ray scattering (RXS) spectra at the Dy
absorption edge in the quadrupole ordering phase of DyBC. Analyzing the
buckling of sheets of B and C atoms, we construct an effective model that the
crystal field is acting on the and states with the principal axes
different for different sublattices. Treating the states as a band and the
states as localized states, we calculate the spectra within the dipole
transition. We take account of processes that (1) the lattice distortion
directly modulates the states and (2) the charge anisotropy of the
quadrupole ordering states modulates the states through the -
Coulomb interaction. Both processes give rise to the RXS intensities on
and spots. Both give similar
photon-energy dependences and the same azimuthal-angle dependences for the main
peak, in agreement with the experiment. The first process is found to give the
intensities much larger than the second one in a wide parameter range of
crystal field. This suggests that the main-peak of the RXS spectra is not a
direct reflection of the quadrupole order but mainly controlled by the lattice
distortion.Comment: 8 pages, 8 figures, Latex, To be published in J. Phys. Soc. Jp
Multi-Particle Collision Dynamics -- a Particle-Based Mesoscale Simulation Approach to the Hydrodynamics of Complex Fluids
In this review, we describe and analyze a mesoscale simulation method for
fluid flow, which was introduced by Malevanets and Kapral in 1999, and is now
called multi-particle collision dynamics (MPC) or stochastic rotation dynamics
(SRD). The method consists of alternating streaming and collision steps in an
ensemble of point particles. The multi-particle collisions are performed by
grouping particles in collision cells, and mass, momentum, and energy are
locally conserved. This simulation technique captures both full hydrodynamic
interactions and thermal fluctuations. The first part of the review begins with
a description of several widely used MPC algorithms and then discusses
important features of the original SRD algorithm and frequently used
variations. Two complementary approaches for deriving the hydrodynamic
equations and evaluating the transport coefficients are reviewed. It is then
shown how MPC algorithms can be generalized to model non-ideal fluids, and
binary mixtures with a consolute point. The importance of angular-momentum
conservation for systems like phase-separated liquids with different
viscosities is discussed. The second part of the review describes a number of
recent applications of MPC algorithms to study colloid and polymer dynamics,
the behavior of vesicles and cells in hydrodynamic flows, and the dynamics of
viscoelastic fluids
Magnetic Ordering and Superconductivity in the REIrGe (RE = Y, La-Tm, Lu) System
We find that the compounds for RE = Y, La-Dy, crystallize in the tetragonal
Ibam (UCoSi type) structure whereas the compounds for RE = Er-Lu,
crystallize in a new orthorhombic structure with a space group Pmmn. Samples of
HoIrGe were always found to be multiphase. The compounds for RE = Y
to Dy which adopt the Ibam type structure show a metallic resistivity whereas
the compounds with RE = Er, Tm and Lu show an anomalous behavior in the
resistivity with a semiconducting increase in as we go down in
temperature from 300K. Interestingly we had earlier found a positive
temperature coefficient of resistivity for the Yb sample in the same
temperature range. We will compare this behavior with similar observations in
the compounds RERuGe and REBiPt. LaIrGe and
YIrGe show bulk superconductivity below 1.8K and 2.5K respectively.
Our results confirm that CeIrGe shows a Kondo lattice behavior and
undergoes antiferromagnetic ordering below 8.5K. Most of the other compounds
containing magnetic rare-earth elements undergo a single antiferromagnetic
transition at low temperatures (T12K) while GdIrGe,
DyIrGe and NdIrGe show multiple transitions. The
T's for most of the compounds roughly scale with the de Gennes factor.
which suggests that the chief mechanism of interaction leading to the magnetic
ordering of the magnetic moments may be the RKKY interaction.Comment: 25 pages, 16 figure
Identification of a novel type of spacer element required for imprinting in fission yeast
Asymmetrical segregation of differentiated sister chromatids is thought to be important for cellular differentiation in higher
eukaryotes. Similarly, in fission yeast, cellular differentiation involves the asymmetrical segregation of a chromosomal
imprint. This imprint has been shown to consist of two ribonucleotides that are incorporated into the DNA during laggingstrand
synthesis in response to a replication pause, but the underlying mechanism remains unknown. Here we present key
novel discoveries important for unravelling this process. Our data show that cis-acting sequences within the mat1 cassette
mediate pausing of replication forks at the proximity of the imprinting site, and the results suggest that this pause dictates
specific priming at the position of imprinting in a sequence-independent manner. Also, we identify a novel type of cis-acting
spacer region important for the imprinting process that affects where subsequent primers are put down after the
replication fork is released from the pause. Thus, our data suggest that the imprint is formed by ligation of a not-fullyprocessed
Okazaki fragment to the subsequent fragment. The presented work addresses how differentiated sister
chromatids are established during DNA replication through the involvement of replication barriers
The N2K Consortium. II. A Transiting Hot Saturn Around HD 149026 With a Large Dense Core
Doppler measurements from Subaru and Keck have revealed radial velocity
variations in the V=8.15, G0IV star HD 149026 consistent with a Saturn-Mass
planet in a 2.8766 day orbit. Photometric observations at Fairborn Observatory
have detected three complete transit events with depths of 0.003 mag at the
predicted times of conjunction. HD 149026 is now the second brightest star with
a transiting extrasolar planet. The mass of the star, based on interpolation of
stellar evolutionary models, is 1.3 +/- 0.1 solar masses; together with the
Doppler amplitude, K=43.3 m s^-1, we derive a planet mass Msin(i)=0.36 Mjup,
and orbital radius of 0.042 AU. HD 149026 is chromospherically inactive and
metal-rich with spectroscopically derived [Fe/H]=+0.36, Teff=6147 K, log g=4.26
and vsin(i)=6.0 km s^-1. Based on Teff and the stellar luminosity of 2.72 Lsun,
we derive a stellar radius of 1.45 Rsun. Modeling of the three photometric
transits provides an orbital inclination of 85.3 +/- 1.0 degrees and (including
the uncertainty in the stellar radius) a planet radius of 0.725 +/- 0.05 Rjup.
Models for this planet mass and radius suggest the presence of a ~67 Mearth
core composed of elements heavier than hydrogen and helium. This substantial
planet core would be difficult to construct by gravitational instability.Comment: 25 pages, 5 figures, accepted by the Astrophysical Journa
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