12,139 research outputs found
Buckling without bending: a new paradigm in morphogenesis
A curious feature of organ and organoid morphogenesis is that in certain
cases, spatial oscillations in the thickness of the growing "film" are
out-of-phase with the deformation of the slower-growing "substrate," while in
other cases, the oscillations are in-phase. The former cannot be explained by
elastic bilayer instability, and contradict the notion that there is a
universal mechanism by which brains, intestines, teeth, and other organs
develop surface wrinkles and folds. Inspired by the microstructure of the
embryonic cerebellum, we develop a new model of 2d morphogenesis in which
system-spanning elastic fibers endow the organ with a preferred radius, while a
separate fiber network resides in the otherwise fluid-like film at the outer
edge of the organ and resists thickness gradients thereof. The tendency of the
film to uniformly thicken or thin is described via a "growth potential".
Several features of cerebellum, +blebbistatin organoid, and retinal fovea
morphogenesis, including out-of-phase behavior and a film thickness amplitude
that is comparable to the radius amplitude, are readily explained by our simple
analytical model, as may be an observed scale-invariance in the number of folds
in the cerebellum. We also study a nonlinear variant of the model, propose
further biological and bio-inspired applications, and address how our model is
and is not unique to the developing nervous system.Comment: version accepted by Physical Review
Functional consequence of a novel Y129C mutation in a patient with two contradictory melanocortin-2-receptor mutations
L F C and T-T C are supported by M R C Clinical Research Training
Fellowships (grant numbers G0600408, G0700581) and L A M by the
Wellcome Trust (grant number 076430/Z/05/7)
Where do They Head for University Studies? The University Destinations of Chinese IBDP Graduates: A Study of the International Baccalaureate Diploma Program in China
Paper PresentationConference theme: Educational Reform and Social Change: East-West DialogueOver the last decade, the number of IB programs adopted by schools around the world has
dramatically increased by almost 400% (IB, 2009; Lee et al., in-press). In recent years China has also
evidenced an impressive gain in the number of schools adopting IB programs in general and the DP in
particular. Specifically, as of 2011, there were 50 IB schools authorized for the implementation of the
DP in China. Of these, 43 schools have been authorized since 2003 (IB, 2012), illustrating the fast
growth of IBDP schools in China in recent years. Despite such fast growth (and by implication,
popularity) of the IBDP schools in China, empirical studies exploring the impact of Chinese IBDP
studentsâ learning outcomes in terms of their university matriculation to foreign universities seems to
be almost nonexistent. With this in mind, the primary goal of this proposal is to document the patterns
of university destination of IBDP graduates in China over time. To this end, our analysis centers on
the following overarching question: Where have Chinese students who previously graduated from the
50 IB schools been educated? Alongside the focus of the main question, we seek answers to more
specific questions: Are there any trends in their university destinations in terms of geographical region
or university prestige (by ranking)? Are there any significant differences in studentsâ enrolment in
foreign universities before or after the 50 IB schoolsâ adoption of the DP (in the case that the 50 IB
schools implemented different international programs other than the DP before they adopted the IB)?
Does the adoption of the DP contribute to the growth (rate) of DP graduates enrolled in foreign
universities? To investigate these questions, we adopt a theoretical framework from research of
international student mobility. Specifically, we focus on internal and external forces (Altbach,
Reisberg & Rumbley, 2009; Li & Bray, 2007) that influence IB graduatesâ international flow in terms
of university destination. We employ a sequential explanatory design (Creswell, Plano, Gutmann, &
Hanson, 2003). As part of the mixed-methods research project, we plan to collect longitudinal data on
DP graduatesâ destinations for university study since the adoption of the DP. A series of quantitative
analysis (e.g., descriptive trend analysis, pre/post comparison âbefore and afterâ the 50 IB schoolsâ
adoption of the DP, and longitudinal analysis using piecewise modeling) will be employed to
determine trends and patterns in terms of university matriculation of the 50 schools over time. As first
of its kind, this study will evidence the impact of the DP on student preparation for university studies
abroad. In addition, the dataset may be employed for broader purposes (e.g., program development or
evaluation) within the IB and the community of schools in China or East Asian countries.published_or_final_versio
The location of an active nucleus and a shadow of a tidal tail in the ULIRG Mrk 273
Analysis of data from the Chandra X-ray Observatory for the double nucleus ULIRG Mrk 273 reveals an absorbed hard X-ray source coincident with the southwest nucleus, implying that this unresolved, near-infrared source is where an active nucleus resides, while the northern nuclear region contains a powerful starburst that dominates the far infrared luminosity. There is evidence of a slight image extension in the 6â7 keV band, where an Fe K line is present, towards the northern nucleus. A large-scale, diffuse emission nebula detected in soft X-rays contains a dark lane that spatially coincides with a high surface-brightness tidal tail extending ~50 arcsec (40 kpc) to the south. The soft X-ray source is likely located behind the tidal tail, which absorbs X-ray photons along the line of sight. The estimated column density of cold gas in the tidal tail responsible for shadowing the soft X-rays is N_H â„ 6 Ă 10^(21) cm^(-2), consistent with the tidal tail having an edge-on orientation
Design of 12.5 kA current leads for the Large Hadron Collider using high temperature superconductor material
The Large Hadron Collider will be equipped with about 8000 superconducting magnets. Some 2600 current leads will feed the currents ranging from 25 to 12500 A. CERN aims to reduce the consumption of liquid helium, using high temperature superconductors in these leads. A development of leads for 12.5 kA is being conducted in collaboration with Oxford Instruments. The design options for these leads are described. A test rig and prototype lead have been made according to one of the options. Electrical contact tests are in progress on BSCCO-2212 and YBCO-123 samples. In the first run, the prototype carried 13000 A
Detecting and Characterizing Small Dense Bipartite-like Subgraphs by the Bipartiteness Ratio Measure
We study the problem of finding and characterizing subgraphs with small
\textit{bipartiteness ratio}. We give a bicriteria approximation algorithm
\verb|SwpDB| such that if there exists a subset of volume at most and
bipartiteness ratio , then for any , it finds a set
of volume at most and bipartiteness ratio at most
. By combining a truncation operation, we give a local
algorithm \verb|LocDB|, which has asymptotically the same approximation
guarantee as the algorithm \verb|SwpDB| on both the volume and bipartiteness
ratio of the output set, and runs in time
, independent of the size of the
graph. Finally, we give a spectral characterization of the small dense
bipartite-like subgraphs by using the th \textit{largest} eigenvalue of the
Laplacian of the graph.Comment: 17 pages; ISAAC 201
Reactivity of Gold Hydrides: O2 Insertion into the AuâH Bond
Dioxygen reacts with the gold(I) hydride (IPr)AuH under insertion to give the hydroperoxide, (IPr)AuOOH, a long-postulated reaction in gold catalysis and the first demonstration of O2 activation by Au-H in a well-defined system. Subsequent condensation gave the peroxide (IPr)Au-OO-Au(IPr) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). The reaction kinetics are reported, as well as the reactivity of Au(I) hydrides with radical scavengers
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