144 research outputs found
Characterization of Epoxy Resin (SU-8) Film Using Thickness-Shear Mode (TSM) Resonator under Various Conditions
Characterization of an epoxy resin film, commonly known as SU-8, is presented using thickness shear mode (TSM) quartz resonator. The impedance-admittance characteristics of the equivalent circuit models of the unperturbed and coated resonators are analyzed to extract the storage modulus and loss modulus (G\u27 and G\u27\u27). Those parameters are needed to establish SU-8 film as an effective wave-guiding layer in the implementation of guided shear-horizontal surface acoustic wave (SH-SAW) sensor platforms. Both cured and uncured polymer films are studied at the fundamental and third harmonic frequencies of the TSM resonators. The storage modulus (G\u27) and loss modulus (G\u27\u27) of the SU-8 film approach constant values of 1.66 × 1010 dyne/cm2 and 6.0 × 108 dyne/cm2, respectively, for relatively thicker films (\u3e20 μm) at a relatively low frequency of 9 MHz. The most accurate values for the extracted shear moduli G (G = G\u27 + jG\u27\u27) are obtained at high thickness where the viscoelastic contribution to the TSM response is substantial. The effect of temperature on the storage and loss moduli is determined for the range of −75 to 40 °C. It is found that the polymer approaches a totally glassy state below −60 °C. Exposure to water appears to follow Fickian diffusion behavior at short times and this exposure also results in changes to both G\u27 and G\u27\u27. However, stability is rapidly reached with exposure to water, indicating relatively lower water absorption, consistent with the extracted diffusion coefficient
Influence of friction variability on isolation performance of a rolling-damper isolation system
Previously, many isolation systems with friction action are designed ignoring the variability of friction coefficient. By taking a rolling-damper isolation system as the study object, this paper analyzed the effects of non-uniform distribution of rolling friction coefficient on its isolation performance through a compiled computer program. The results show that the errors associated with the maximum structural relative displacement, acceleration and residual displacement due to ignoring the friction variability are sequentially growing, and this rule is weakened by the damper. Under the condition of large friction variability and little damper action, the calculation of the maximum structural relative displacement and acceleration should consider the friction variability. When the structural residual displacement is concerned, the variability of rolling friction coefficient should be fully considered regardless of friction variability degree
Metabolic engineering of yeast for increased production of cyclopropane fatty acids
Biological production of chemicals and fuels using whole cells is an important and growing segment of manufacturing and among the various forms, microorganisms are the most successfully utilized. In particular, yeasts such as Saccharomyces cerevisiae are both widely used production organisms and metabolic models for oleaginous yeasts. Fatty acid-containing lipids are one example of moderate value, highly versatile chemicals produced by yeasts that are used in a broad range of industries for lubrication, cosmetics, fuels and polymers. Production levels of standard fatty acids by yeasts has increased enormously over the past 10 years through the application of metabolic pathway engineering, flux analysis, computational approaches and to a lesser extent, bioprocessing improvements. Combined, these advances have brought yeast-based fatty acid production close to commercial reality. Functionalized fatty acids such as those containing hydroxyl or cyclopropyl groups are more valuable as chemical feedstocks and are an attractive target for yeast production as commercial supply is limited. Cyclopropane fatty acids, possessing a strained 3-membered ring and having a saturated chain, are especially attractive as they have application in cosmetics and specialty lubrication. However, cyclopropyl fatty acids present greater challenges for metabolic engineering as they are not produced naturally by yeast.
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GW26-e4567 The role of Hippo signal transduction pathway in the development of hypertrophic cardiomyopathy
Dynamical Effects of Magnetic Opacity in Neutron Star Accretion Columns
We present relativistic, radiation magnetohydrodynamic simulations of
supercritical neutron star accretion columns in Cartesian geometry, including
temperature-dependent, polarization-averaged Rosseland mean opacities
accounting for classical electron scattering in a magnetic field. Just as in
our previous pure Thomson scattering simulations, vertical oscillations of the
accretion shock and horizontally propagating entropy waves (photon bubbles) are
present in all our simulations. However, at high magnetic fields
~G, the magnetic opacities produce significant differences in
the overall structure and dynamics of the column. At fixed accretion rate,
increasing the magnetic field strength results in a shorter accretion column,
despite the fact that the overall opacity within the column is larger.
Moreover, the vertical oscillation amplitude of the column is reduced.
Increasing the accretion rate at high magnetic fields restores the height of
the column. However, a new, slower instability takes place at these field
strengths because they are in a regime where the opacity increases with
temperature. This instability causes both the average height of the column and
the oscillation amplitude to substantially increase on a time scale of
~ms. We provide physical explanations for these results, and discuss
their implications for the observed properties of these columns, including
mixed fan-beam/pencil-beam emission patterns caused by the oscillations.Comment: Accepted for publication in MNRA
Influence of friction variability on isolation performance of a rolling-damper isolation system
Previously, many isolation systems with friction action are designed ignoring the variability of friction coefficient. By taking a rolling-damper isolation system as the study object, this paper analyzed the effects of non-uniform distribution of rolling friction coefficient on its isolation performance through a compiled computer program. The results show that the errors associated with the maximum structural relative displacement, acceleration and residual displacement due to ignoring the friction variability are sequentially growing, and this rule is weakened by the damper. Under the condition of large friction variability and little damper action, the calculation of the maximum structural relative displacement and acceleration should consider the friction variability. When the structural residual displacement is concerned, the variability of rolling friction coefficient should be fully considered regardless of friction variability degree
In-plane ferroelectric tunnel junctions based on 2D α-In\u3csub\u3e2\u3c/sub\u3eSe\u3csub\u3e3\u3c/sub\u3e/ semiconductor heterostructures
Ferroelectric tunnel junctions (FTJs) have great potential for application in high-density non-volatile memories. Recently, α-In2Se3 was found to exhibit robust in-plane and out-of-plane ferroelectric polarizations at a monolayer thickness, which is ideal to serve as a ferroelectric component in miniaturized electronic devices. In this work, we design two-dimensional van der Waals heterostructures composed of an α-In2Se3 ferroelectric and a hexagonal IV–VI semiconductor and propose an in-plane FTJ based on these heterostructures. Our first-principles calculations show that the electronic band structure of the designed heterostructures can be switched between insulating and metallic states by ferroelectric polarization. We demonstrate that the in-plane FTJ exhibits two distinct transport regimes, tunneling and metallic, for OFF and ON states, respectively, leading to a giant tunneling electroresistance effect with the OFF/ON resistance ratio exceeding 1 × 104. Our results provide a promising approach for the highdensity ferroelectric memory based on the 2D ferroelectric/semiconductor heterostructures
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