9,029 research outputs found
The molecular setup of the avian head mesoderm and its implication for craniofacial myogenesis
Magnetization of multicomponent ferrofluids
The solution of the mean spherical approximation (MSA) integral equation for
isotropic multicomponent dipolar hard sphere fluids without external fields is
used to construct a density functional theory (DFT), which includes external
fields, in order to obtain an analytical expression for the external field
dependence of the magnetization of ferrofluidic mixtures. This DFT is based on
a second-order Taylor series expansion of the free energy density functional of
the anisotropic system around the corresponding isotropic MSA reference system.
The ensuing results for the magnetic properties are in quantitative agreement
with our canonical ensemble Monte Carlo simulation data presented here.Comment: 12 pages including 4 figure
Theory of capillary-induced interactions beyond the superposition approximation
Within a general theoretical framework we study the effective,
deformation-induced interaction between two colloidal particles trapped at a
fluid interface in the regime of small deformations. In many studies, this
interaction has been computed with the ansatz that the actual interface
configuration for the pair is given by the linear superposition of the
interface deformations around the single particles. Here we assess the validity
of this approach and compute the leading term of the effective interaction for
large interparticle separation beyond this so-called superposition
approximation. As an application, we consider the experimentally relevant case
of interface deformations owing to the electrostatic field emanating from
charged colloidal particles. In mechanical isolation, i.e., if the net force
acting on the total system consisting of the particles plus the interface
vanishes, the superposition approximation is actually invalid. The effective
capillary interaction is governed by contributions beyond this approximation
and turns out to be attractive. For sufficiently small surface charges on the
colloids, such that linearization is strictly valid, and at asymptotically
large separations, the effective interaction does not overcome the direct
electrostatic repulsion between the colloidal particles.Comment: Minor typos correcte
On the stability and growth of single myelin figures
Myelin figures are long thin cylindrical structures that typically grow as a
dense tangle when water is added to the concentrated lamellar phase of certain
surfactants. We show that, starting from a well-ordered initial state, single
myelin figures can be produced in isolation thus allowing a detailed study of
their growth and stability. These structures grow with their base at the
exposed edges of bilayer stacks from which material is transported into the
myelin. Myelins only form and grow in the presence of a driving stress; when
the stress is removed, the myelins retract.Comment: 4 pages, 8 figures. Revised version, 1 new figure, additional
reference
RGMa and RGMb expression pattern during chicken development suggest unexpected roles for these repulsive guidance molecules in notochord formation, somitogenesis, and myogenesis
Background: Repulsive guidance molecules (RGM) are high-affinity ligands for the Netrin receptor Neogenin, and they are crucial for nervous system development including neural tube closure; neuronal and neural crest cell differentiation and axon guidance. Recent studies implicated RGM molecules in bone morphogenetic protein signaling, which regulates a variety of developmental processes. Moreover, a role for RGMc in iron metabolism has been established. This suggests that RGM molecules may play important roles in non-neural tissues. Results: To explore which tissues and processed may be regulated by RGM molecules, we systematically investigated the expression of RGMa and RGMb, the only RGM molecules currently known for avians, in the chicken embryo. Conclusions: Our study suggests so far unknown roles of RGM molecules in notochord, somite and skeletal muscle development. Developmental Dynamics, 2012. (C) 2012 Wiley Periodicals, Inc.AFMAFMCNPqCNPqFAPESPFAPES
High Redshift Quasars and Star Formation in the Early Universe
In order to derive information on the star formation history in the early
universe we observed 6 high-redshift (z=3.4) quasars in the near-infrared to
measure the relative iron and \mgii emission strengths. A detailed comparison
of the resulting spectra with those of low-redshift quasars show essentially
the same FeII/MgII emission ratios and very similar continuum and line spectral
properties, indicating a lack of evolution of the relative iron to magnesium
abundance of the gas since z=3.4 in bright quasars. On the basis of current
chemical evolution scenarios of galaxies, where magnesium is produced in
massive stars ending in type II SNe, while iron is formed predominantly in SNe
of type Ia with a delay of ~1 Gyr and assuming as cosmological parameters H_o =
72 km/s Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7$, we conclude that major
star formation activity in the host galaxies of our z=3.4 quasars must have
started already at an epoch corresponding to z_f ~= 10, when the age of the
universe was less than 0.5 Gyrs.Comment: 29 pages, 5 figures, ApJ in pres
Risk of Tooth Loss After Cigarette Smoking Cessation
INTRODUCTION. Little is known about the effect of cigarette smoking cessation on risk of tooth loss. We examined how risk of tooth loss changed with longer periods of smoking abstinence in a prospective study of oral health in men. METHODS. Research subjects were 789 men who participated in the Veterans Administration Dental Longitudinal Study from 1968 to 2004. Tooth status and smoking status were determined at examinations performed every 3 years, for a maximum follow-up time of 35 years. Risk of tooth loss subsequent to smoking cessation was assessed sequentially at 1-year intervals with multivariate proportional hazards regression models. Men who never smoked cigarettes, cigars, or pipes formed the reference group. Hazard ratios were adjusted for age, education, total pack-years of cigarette exposure, frequency of brushing, and use of floss. RESULTS. The hazard ratio for tooth loss was 2.1 (95% confidence interval [CI], 1.5-3.1) among men who smoked cigarettes during all or part of follow-up. Risk of tooth loss among men who quit smoking declined as time after smoking cessation increased, from 2.0 (95% CI, 1.4-2.9) after 1 year of abstinence to 1.0 (95% CI, 0.5-2.2) after 15 years of abstinence. The risk remained significantly elevated for the first 9 years of abstinence but eventually dropped to the level of men who never smoked after 13 or more years. CONCLUSION. These results indicate that smoking cessation is beneficial for tooth retention, but long-term abstinence is required to reduce the risk to the level of people who have never smoked.U.S. Department of Veterans Affairs Epidemiology (Merit Review grant); Massachusetts Veterans Epidemiology Research and Information Center; National Institutes of Health (R01 DA10073, R03 DE016357, R15 DE12644, K24 DE00419
Biocompatibility of a Novel Microfistula Implant in Nonprimate Mammals for the Surgical Treatment of Glaucoma
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