Microheated substrates for patterning cells and controlling development

Here, we seek to control cellular development by devising a means through which cells can be subjected to a microheated environment in standard culture conditions. Numerous techniques have been devised for controlling cellular function and development via manipulation of surface environmental cues at the micro- and nanoscale. It is well understood that temperature plays a significant role in the rate of cellular activities, migratory behavior (thermotaxis), and in some cases, protein expression. Yet, the effects and possible utilization of micrometer-scale temperature fields in cell cultures have not been explored. Toward this end, two types of thermally isolated microheated substrates were designed and fabricated, one with standard backside etching beneath a dielectric film and another with a combination of surface and bulk micromachining and backside etching. The substrates were characterized with infrared microscopy, finite element modeling, scanning electron microscopy, stylus profilometry, and electrothermal calibrations. Neuron culture studies were conducted on these substrates to 1) examine the feasibility of using a microheated environment to achieve patterned cell growth and 2) selectively accelerate neural development on regions less than 100$mu m$wide. Results show that attached neurons, grown on microheated regions set at 37$~^circ C$, extended processes substantially faster than those incubated at 25$~^circ C$on the same substrate. Further, unattached neurons were positioned precisely along the length of the heater filament (operating at 45$~^circ C$) using free convection currents. These preliminary findings indicate that microheated substrates may be used to direct cellular development spatially in a practical manner.$hfillhbox[1414]

Perverse incentives and invisible tradeoffs in subway construction in China: a case study of Hangzhou subway collapse

Abstract—Hangzhou subway collapse is the most serious subway construction disaster to date in China. In this article, the management and regulatory questions the collapse raised are focused and a case study of Hangzhou subway collapse is given. By regarding the contractual arrangement as an outcome of a power game of principal-agent, the social causes and the perverse incentives to strategic behaviors of the key players are investigated to explain the particular project outcomes. In the end, some policy suggestions are given for improving the safety performance of subway construction

A_4 Symmetry and Lepton Masses and Mixing

Stimulated by Ma's idea which explains the tribimaximal neutrino mixing by assuming an A_4 flavor symmetry, a lepton mass matrix model is investigated. A Frogatt-Nielsen type model is assumed, and the flavor structures of the masses and mixing are caused by the VEVs of SU(2)_L-singlet scalars \phi_i^u and \phi_i^d (i=1,2,3), which are assigned to {\bf 3} and ({\bf 1}, {\bf 1}',{\bf 1}'') of A_4, respectively.Comment: 13 pages including 1 table, errors in Sec.7 correcte

Microstructures and intrinsic lubricity of in situ Ti3SiC2–TiSi2–TiC MAX phase composite fabricated by reactive spark plasma sintering (SPS)

MAX phase composite Ti3SiC2–TiSi2–TiC based on the Tin+1SiCn system was synthesized by spark plasma sintering (SPS) under vacuum sintering conditions. The microstructural evolution upon synthesis and Vickers indentation contact damaged were characterized using scanning electron microscopy (SEM) and optical microscopy (OM). Tribological behaviour of the SPSed MAX phase composite was investigated under dry sliding ambient conditions for evidence of intrinsic lubricity as well as to understand the influence of second phase TiC particles on the wear behaviour of this composite system. Further, the underlying wear mechanisms was elucidated via detailed analyses of the worn surfaces using Raman spectroscopy, SEM-EDS and transmission electron microscopy (TEM). Exhaustive analyses of the worn surface revealed evidence of solid lubrication. Transition in friction and wear is attributed to change in wear mechanism from tribo-oxidative to deformation-induced wear due to the disruption of the tribofilm architecture

Ramification of thermal expansion mismatch and phase transformation in TiC-particulate/SiC-matrix ceramic composite

This article presents a microstructural study on the role of incipient residual stress relaxation in TiC-particulate/SiC-matrix ceramic composite toughened by thermal expansion mismatch and phase transformation toughening. Exhaustive microstructural studies was undertaken using scanning electron microscopy and transmission electron microscopy following a wear test. It was found that the superposition of hydrostatic tensile stress induced at the surface following the sliding contact on the inherent residual stresses locked in the composite led to a relaxation and/or reduction in the residual stresses. Stress relaxation presented a wider implication for the tribological properties of this ceramic matrix composite (CMC) in the form of a grain-scale rippling microstructural phenomena

A nondiagrammatic calculation of the Rho parameter from heavy fermions

A simple nondiagrammatic evaluation of the nondecoupling effect of heavy fermions on the Veltman's Rho parameter is presented in detail. This calculation is based on the path integral approach, the electroweak chiral Lagrangian formalism, and the Schwinger proper time method.Comment: 11 page

Synthesis and microstructural evolution in ternary metalloceramic Ti3SiC2 consolidated via the Maxthal 312 powder route

A bulk specimen containing Ti3SiC2, TiSi2 and TiC was prepared through an in situ spark plasma sintering/solid-liquid reaction powder metallurgy method using the Maxthal 312 (nominally-Ti3SiC2) powder as a starting material. The reaction mechanism, phase constituents and evolution of the microstructure were systematically investigated by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) system, transmission electron microscopy (TEM), Raman spectroscopy, differential scanning calorimetry (DSC) and Vickers microhardness testing. Phase analysis and microstructural characterization revealed that the bulk sample contained binary ancillary phases, possibly due to Si evaporation and/or carburization. The deformed microstructure around the indents revealed evidence of plasticity, intrinsic lubricity and toughening. The Microstructural and orientation relationships between the phases contained in the bulk sample are reported

Universal and non-universal features of glassy relaxation in propylene carbonate

It is demonstrated that the susceptibility spectra of supercooled propylene carbonate as measured by depolarized-light-scattering, dielectric-loss, and incoherent quasi-elastic neutron-scattering spectroscopy within the GHz window are simultaneously described by the solutions of a two-component schematic model of the mode-coupling theory (MCT) for the evolution of glassy dynamics. It is shown that the universal beta-relaxation-scaling laws, dealing with the asymptotic behavior of the MCT solutions, describe the qualitative features of the calculated spectra. But the non-universal corrections to the scaling laws render it impossible to achieve a complete quantitative description using only the leading-order-asymptotic results.Comment: 37 pages, 16 figures, to be published in Phys. Rev.

Exploring the mechanism of “Rare Earth” texture evolution in a lean Mg–Zn–Ca alloy

The entire recrystallisation sequence and associated crystallographic texture evolution of Mg-0.8Zn-0.2Ca (wt.%) alloy was tracked using a quasi-in-situ electron backscatter diffraction (EBSD) method. Characteristic “Rare Earth” (RE) texture was formed, originating mainly from double twins and twinning-related shear bands consisting of compression and double twins. The RE textures appeared during the nucleation stage and were preserved during the relative uniform grain growth period because of solute segregation and concurrent precipitation although the alloying element content was very low. Ca and Zn co-segregated along grain boundaries with no evidence that segregation was preferred along special types of grain boundaries. The interactions between deformation microstructures, concurrent precipitation, solute drag, grain growth and texture evolution are discussed in detail. All the results indicate that Ca performs a similar role to that of RE elements in forming RE texture