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

Unified cyclic stress-strain model for normal and high strength concrete confined with FRP

Fiber reinforced polymer (FRP) has become increasingly popular as a confining material for concrete, both in the strengthening of existing columns where FRP wraps with fibers oriented completely or predominantly in the hoop direction are typically used, and in new construction where filament-wound FRP tubes with fibers oriented at desired angles to the longitudinal axis are typically used. For both types of applications, the stress-strain behavior of FRP-confined concrete under cyclic axial compression needs to be properly understood and modeled for the accurate simulation of such columns under seismic loading. This paper presents an improved cyclic stress-strain model for FRP-confined concrete on the basis of a critical assessment of an earlier model proposed by Lam and Teng in 2009 by making use of a database containing new test results of both concrete-filled FRP tubes (CFFTs) and concrete cylinders confined with an FRP wrap. The assessment reveals several deficiencies of Lam and Teng\u27s model due to the limited test results available to them. The proposed model corrects these deficiencies and is shown to provide reasonably accurate predictions for both concrete in CFFTs and concrete confined with an FRP wrap and for both normal strength concrete (NSC) and high strength concrete (HSC)

Density dependence of spin relaxation in GaAs quantum well at room temperature

Carrier density dependence of electron spin relaxation in an intrinsic GaAs quantum well is investigated at room temperature using time-resolved circularly polarized pump-probe spectroscopy. It is revealed that the spin relaxation time first increases with density in the relatively low density regime where the linear D'yakonov-Perel' spin-orbit coupling terms are dominant, and then tends to decrease when the density is large and the cubic D'yakonov-Perel' spin-orbit coupling terms become important. These features are in good agreement with theoritical predictions by L\"u {\em et al.} [Phys. Rev. B {\bf 73}, 125314 (2006)]. A fully microscopic calculation based on numerically solving the kinetic spin Bloch equations with both the D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms included, reproduces the density dependence of spin relaxation very well.Comment: 4 pages, 2 figures, Europhys. Lett., in pres

Axial compression tests on hybrid double-skin tubular columns filled with high strength concrete

Author name used in this publication: T. YuAuthor name used in this publication: J. G. TengRefereed conference paper2011-2012 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

Efficient and Accurate Linear Algebraic Methods for Large-scale Electronic Structure Calculations with Non-orthogonal Atomic Orbitals

The need for large-scale electronic structure calculations arises recently in the field of material physics and efficient and accurate algebraic methods for large simultaneous linear equations become greatly important. We investigate the generalized shifted conjugate orthogonal conjugate gradient method, the generalized Lanczos method and the generalized Arnoldi method. They are the solver methods of large simultaneous linear equations of one-electron Schr\"odinger equation and maps the whole Hilbert space to a small subspace called the Krylov subspace. These methods are applied to systems of fcc Au with the NRL tight-binding Hamiltonian (Phys. Rev. B {\bf 63}, 195101 (2001)). We compare results by these methods and the exact calculation and show them equally accurate. The system size dependence of the CPU time is also discussed. The generalized Lanczos method and the generalized Arnoldi method are the most suitable for the large-scale molecular dynamics simulations from the view point of CPU time and memory size.Comment: 13pages, 7figure

Unified cyclic stress–strain model for normal and high strength concrete confined with FRP

Fiber reinforced polymer (FRP) has become increasingly popular as a confining material for concrete, both in the strengthening of existing columns where FRP wraps with fibers oriented completely or predominantly in the hoop direction are typically used, and in new construction where filament-wound FRP tubes with fibers oriented at desired angles to the longitudinal axis are typically used. For both types of applications, the stress-strain behavior of FRP-confined concrete under cyclic axial compression needs to be properly understood and modeled for the accurate simulation of such columns under seismic loading. This paper presents an improved cyclic stress-strain model for FRP-confined concrete on the basis of a critical assessment of an earlier model proposed by Lam and Teng in 2009 by making use of a database containing new test results of both concrete-filled FRP tubes (CFFTs) and concrete cylinders confined with an FRP wrap. The assessment reveals several deficiencies of Lam and Teng\u27s model due to the limited test results available to them. The proposed model corrects these deficiencies and is shown to provide reasonably accurate predictions for both concrete in CFFTs and concrete confined with an FRP wrap and for both normal strength concrete (NSC) and high strength concrete (HSC)

Efficacy and acceptability of psychological interventions for social anxiety disorder in children and adolescents:a meta-analysis of randomized controlled trials

Social anxiety disorder (SAD) is highly prevalent and persistent in children and adolescents. However, evidence for the efficacy and acceptability of psychological interventions for SAD in children and adolescents remains unclear. Seven electronic databases (PubMed, CENTRAL, Embase, Web of Science, PsycINFO, CINAHL, and ProQuest) were searched. Randomized controlled trials (RCTs) that compared psychological interventions for SAD with control conditions in children and adolescents were included. Primary outcomes were the efficacy (mean change in anxiety symptom scores) and acceptability (dropouts for all reasons). Secondary outcomes were remission, quality of life/functional improvement, and depressive symptoms measures. Seventeen RCTs were included in this meta-analysis. Psychological interventions (including cognitive behavioral therapy and behavioral therapy) were significantly more effective than control conditions, with a standardized mean difference (SMD) of − 1.13, and remission with a risk ratio (RR) of 8.99, the number needed to treat was 3.3. There was no statistically significant difference between psychological interventions and control conditions for all-cause dropouts (RR = 1.00). Psychological interventions were superior to control conditions in improving quality of life/functioning (SMD = 0.79) and reducing depressive symptoms (SMD = − 0.39). Given considerable heterogeneity of primary efficacy outcome, a series of subgroup analyses of different variables were conducted. Psychological interventions are probably efficacious in the treatment of SAD among children and adolescents, and may markedly improve quality of life and functioning in this population. However, this finding should be interpreted with caution because of the high heterogeneity of trials and low literature quality. Keywords Child · Adolescent · Psychological intervention · Meta-analysis · Social anxiety disorde