Cues from neuroepithelium and surface ectoderm maintain neural crest-free regions within cranial mesenchyme of the developing chick

Within the developing vertebrate head, neural crest cells (NCCs) migrate from the dorsal surface of the hindbrain into the mesenchyme adjacent to rhombomeres (r)1 plus r2, r4 and r6 in three segregated streams. NCCs do not enter the intervening mesenchyme adjacent to r3 or r5, suggesting that these regions contain a NCC-repulsive activity. We have used surgical manipulations in the chick to demonstrate that r3 neuroepithelium and its overlying surface ectoderm independently help maintain the NCC-free zone within r3 mesenchyme. In the absence of r3, subpopulations of NCCs enter r3 mesenchyme in a dorsolateral stream and an ectopic cranial nerve forms between the trigeminal and facial ganglia. The NCC-repulsive activity dissipates/degrades within 5-10 hours of r3 removal. Initially, r4 NCCs more readily enter the altered mesenchyme than r2 NCCs, irrespective of their maturational stage. Following surface ectoderm removal, mainly r4 NCCs enter r3 mesenchyme within 5 hours, but after 20 hours the proportions of r2 NCCs and r4 NCCs ectopically within r3 mesenchyme appear similar

Specific Heat of Quantum Elastic Systems Pinned by Disorder

We present the detailed study of the thermodynamics of vibrational modes in disordered elastic systems such as the Bragg glass phase of lattices pinned by quenched impurities. Our study and our results are valid within the (mean field) replica Gaussian variational method. We obtain an expression for the internal energy in the quantum regime as a function of the saddle point solution, which is then expanded in powers of $\hbar$ at low temperature $T$. In the calculation of the specific heat $C_v$ a non trivial cancellation of the term linear in $T$ occurs, explicitly checked to second order in $\hbar$. The final result is $C_v \propto T^3$ at low temperatures in dimension three and two. The prefactor is controlled by the pinning length. This result is discussed in connection with other analytical or numerical studies.Comment: 14 page

Radiative Models of Sgr A* from GRMHD Simulations

Using flow models based on axisymmetric general relativistic magnetohydrodynamics (GRMHD) simulations, we construct radiative models for sgr A*. Spectral energy distributions that include the effects of thermal synchrotron emission and absorption, and Compton scattering, are calculated using a Monte Carlo technique. Images are calculated using a ray-tracing scheme. All models are scaled so that the 230 GHz flux density is 3.4 Jy. The key model parameters are the dimensionless black hole spin a*, the inclination i, and the ion-to-electron temperature ratio Ti/Te. We find that: (1) models with Ti/Te=1 are inconsistent with the observed submillimeter spectral slope; (2) the X-ray flux is a strongly increasing function of a*; (3) the X-ray flux is a strongly increasing function of i; (4) 230 GHz image size is a complicated function of i, a*, and Ti/Te, but the Ti/Te = 10 models are generally large and at most marginally consistent with the 230 GHz VLBI data; (5) for models with Ti/Te=10 and i=85 deg the event horizon is cloaked behind a synchrotron photosphere at 230 GHz and will not be seen by VLBI, but these models overproduce NIR and X-ray flux; (6) in all models whose SEDs are consistent with observations the event horizon is uncloaked at 230 GHz; (7) the models that are most consistent with the observations have a* \sim 0.9. We finish with a discussion of the limitations of our model and prospects for future improvements.Comment: 25 pages, 5 figures, ApJ accepte

Going Beyond the Kantian Philosophy: On McDowell's Hegelian Critique of Kant

The Kant-Hegel relation has a continuing fascination for commentators on Hegel, and understandbly so: for, taking this route into the Hegelian jungle can promise many advantages. First, it can set Hegel's thought against a background with which we are fairly familiar, and in a way that makes its relevance clearly apparent; second, it can help us locate Hegel in the broader philisophical tradition, making us see that the traditional "analytic jump from Kant to Frege leaves out a crucial period in post-Kantian thought, third, it can show Hegel in a progressive light, as attempting to take that tradition further forward; fourth, it can help us locate familiar philisophical issues in Hegelian thought that other-wise can appear whooly sui generis; and finally, and perhaps most importantly of all, focusing on this relation can help raise and crystalise some of the fascinating ambiguties concerning Hegel's outlook, regarding whether Hegel's response to Kant shows him to have been a reactionary, Romantic, pre-critical thinker, who sought to turn the philosophical clock back to a time before Kant had written, or a modernist, Enlightented and essentially critical one, who remained true to the spirit if not the letter of Kant's philosophy

Synthetic prions generated in vitro are similar to a newly identified subpopulation of PrPSc from sporadic Creutzfeldt-Jakob disease

In recent studies, the amyloid form of recombinant prion protein (PrP) encompassing residues 89–230 (rPrP 89-230) produced in vitro induced transmissible prion disease in mice. These studies showed that unlike “classical” PrPSc produced in vivo, the amyloid fibrils generated in vitro were more proteinase-K sensitive. Here we demonstrate that the amyloid form contains a proteinase K-resistant core composed only of residues 152/153–230 and 162–230. The PK-resistant fragments of the amyloid form are similar to those observed upon PK digestion of a minor subpopulation of PrPSc recently identified in patients with sporadic Creutzfeldt-Jakob disease (CJD). Remarkably, this core is sufficient for self-propagating activity in vitro and preserves a β-sheet-rich fibrillar structure. Full-length recombinant PrP 23-230, however, generates two subpopulations of amyloid in vitro: One is similar to the minor subpopulation of PrPSc, and the other to classical PrPSc. Since no cellular factors or templates were used for generation of the amyloid fibrils in vitro, we speculate that formation of the subpopulation of PrPSc with a short PK-resistant C-terminal region reflects an intrinsic property of PrP rather than the influence of cellular environments and/or cofactors. Our work significantly increases our understanding of the biochemical nature of prion infectious agents and provides a fundamental insight into the mechanisms of prions biogenesis

Нормативно-правові засади розвитку туристичної діяльності в малих містах Рівненщини

Розглянуто нормативно-правові засади розвитку туристичної сфери в малих містах на прикладі Рівненської області. Особливу увагу приділено визначенню регіональних нормативних актів, що сприяють розвитку різних видів туризму в област

Investigation of f/2 and f/4 Waves in Granular Beds Subject to Vertical, Sinusoidal Oscillations

When a deep bed of granular material is subject to vertical, sinusoidal oscillations, a number of phenomena appear including two regimes of standing surface waves that form at one-half and one-quarter of the oscillation forcing frequency. These waves are referred to as f/2 and f/4 waves where f is the oscillation frequency. This paper presents the results from experiments and computer simulations designed to study the wavelength and wave amplitude dependence of the surface waves on the vibration parameters, collision coefficient of restriction, and the particle bed depth

Submarine groundwater discharge: an unseen yet potentially important coastal phenomenon

In collaboration with researchers from Florida State University, Florida Sea Grant introduces an important but poorly known topic: submarine groundwater discharge. Although nearly invisible, submarine groundwater discharge influences coastal systems. This brochure helps explain this important phenomenon. (8pp.