Thin film stress studies using microcantilevers and microcantilever sensors

Microcantilever-based sensors have attracted much attention due to their potential as a platform for the development of myriad physical, chemical, and biological sensorsStudies have shown that thin bi-material microcantilevers undergo bending (deflection) due to differential stresses caused by exposure to such environments. Because of their very small spring constants (less than 0.01 N/m), microcantilevers are sensitive to stress differentials between the substrate and coating layer. Taking advantage of the ultra-high stress sensitivity of micrometer-sized microcantilevers, vapor adsorption on solid surfaces and adsorption-induced stress in thin metal films were investigated. Experimental results show that experimental systems can detect ppb (part-per-billion) or ppt (part-per-trillion) levels of hydrogen or mercury, respectively. Thin, coated cantilevers undergo bending if they are exposed to various biological, chemical and physical environments. This bending is due to a differential surface stress caused by stress changes that are induced during the adsorption process. Depending on the nature of analyte-substrate interactions (adsorption or absorption) the adsorption-induced stress in the thin film can be expressed as either a surface stress (N/m) or a bulk stress (N/m) Such stress effects can be used to create extremely sensitive sensors and can be much larger than mass-induced frequency shifts of the fundamental resonance. During the experiments, thin metal films were coated on one side of silicon or silicon-nitride based microcantilevers. Both optical and electrical cantilever deflection detection methods were employed. The two systems were selected to study two different interaction mechanisms: 1. Palladium-coated microcantilevers were employed to investigate the bulk-like absorption of hydrogen that diffuses into palladium and causes volume expansion. 2. Gold-coated microcantilevers were employed to study surface-like adsorption when mercury atoms adsorb onto the gold surface, thus changing the film stress. Adsorption-induced stress on bi-material microcantilevers can produce bending, which can be related to gas or vapor concentration. The sensitivity of microcantilevers (Si or SiN based) is in the pico-newton range. Bi-material cantilevers can be used to measure thin film stress or as a chemical sensor platform using selected coatings. For bulk-like absorption, vapors do not stop at the gas/solid interface on the film but actually penetrate the entire thickness of the film. An example is hydrogen adsorption in palladium that induces a volume expansion of the palladium film. The sensitivity of coated cantilevers is adjustable in a certain range by controlling the coating layer thickness: For surface-like adsorption, both stress and resistance changes depend only upon the number of adsorbate atoms adsorbed on the adsorbent surface. Film thickness has little effect on the sensitivity of coated cantilevers. An example is mercury adsorption onto a gold surface that causes a stress decrease. Novel simultaneous cantilever bending and electrical resistance measurements indicate that adsorption onto or absorption into thin metal films can induce stress changes and resistance changes at different rates. These differences may or may not vary with gas or vapor concentration depending on the interaction mechanisms; and they imply more complex chemical reactions during the adsorption process than were known before this study. Additional investigations will be required to ascertain such details. The investigation of mercury adsorption-induced stress on thin gold film described is believed to be the first complete work in this area. A surface adsorption model is proposed and shows excellent agreement with experimental data as well as that reported outside this dissertationThe model may serve as a guide for future studies in surface adsorption. Bi-material microcantilevers have shown ultra-high stress sensitivity that may be utilized to study thin film stress or employed as a sensor platform. Investigations of the two-adsorption mechanisms help to provide a clear understanding of gas (or vapor) adsorption onto solid surfaces as well as the associated stress. Both theoretical models and experimental results could be used to design and improve the performance of microcantilever-based sensors. Effects of environmental influences, such as relative humidity and temperature, were also investigated

Design of a large dynamic range readout unit for the PSD detector of DAMPE

A large dynamic range is required by the Plastic Scintillator Detector (PSD) of DArk Matter Paricle Explorer (DAMPE), and a double-dynode readout has been developed. To verify this design, a prototype detector module has been constructed and tested with cosmic rays and heavy ion beams. The results match with the estimation and the readout unit could easily cover the required dynamic range

Adaptive fault-tolerant attitude tracking control for hypersonic vehicle with unknown inertial matrix and states constraints

This paper proposes an adaptive fault-tolerant control (FTC) method for hypersonic vehicle (HSV) with unexpected centroid shift, actuator fault, time-varying full state constraints, and input saturation. The occurrence of unexpected centroid shift has three main effects on the HSV system, which are system uncertainties, eccentric moments, and variation of input matrix. In order to ensure the time-varying state constraints, a novel attitude state constraint control strategy, to keep the safe flight of HSV, is technically proposed by a time-varying state constraint function (TVSCF). A unified controller is designed to handle the time-varying state constraints according to the proposed TVSCF. Then, the constrained HSV system can be transformed into a novel free-constrained system based on the TVSCF. For the variation of system input matrix, input saturation and actuator fault, a special Nussbaum-type function is designed to compensate for those time-varying nonlinear terms. Additionally, the auxiliary systems is designed to compensate the constraint of system control inputs. Then, it is proved that the proposed control scheme can guarantee the boundedness of all closed-loop signals based on the Lyapunov stability theory. At last, the simulation results are provided to demonstrate the effectiveness of the proposed fault-tolerant control scheme.</p

Effects of Onshore and Offshore Environmental Parameters on the Leading Edge Erosion of Wind Turbine Blades : A Comparative Study

Author's accepted manuscript.Available from 13/01/2022.The presence of rain-induced leading edge erosion of wind turbine blades necessitates the development of erosion models. One of the essential parameters for erosion modelling is the relative impact velocity between rain droplets and the rotating blade. Based on this parameter, the erosion damage rate of a wind turbine blade is calculated to estimate the expected leading edge lifetime. The environmental conditions that govern this parameter have site-specific variations, and thus, rain and wind loading on a turbine differ for onshore and offshore locations. In addition, there are wave loads present in the offshore environment. The present paper tries to provide guidelines for erosion modelling and investigates whether there are differences in erosion of blades due to (1) varying rainfall conditions modelled using different droplet size distributions for onshore and offshore locations in combination with (2) winds of varying turbulence intensities and (3) wave-induced loads. Aero-hydro-servo-elastic simulations are carried out for an onshore wind turbine and a monopile-supported offshore wind turbine. Furthermore, erosion variables such as the relative impact velocities and the associated erosion damage rate of a blade are analysed for various blade azimuth angles. The study shows that the rainfall intensity and turbulence intensity minorly influence the impact velocity and pressure but have a substantial effect on the overall erosion damage rate. Additionally, a significantly higher erosion damage rate is found for blades exposed to offshore rainfall conditions than for blades under onshore rainfall conditions. Furthermore, no substantial influence on erosion is found because of wave-induced loads.acceptedVersio

A peculiar lens-shaped structure observed in the South China Sea

Lens-shaped structures within thermocline potentially play a significant role in subsurface transport of mass, heat, and salt in the global ocean. Whilst such structures have been documented in many oceanic regions, none has been observed in the China Seas. This study reports on observations of a lens-shaped structure within thermocline in the southwestern South China Sea in September 2007. This structure had a maximum thickness of approximately 60 m and a horizontal extent exceeding 220 km. This lens was peculiar in that its size is larger than most similar structures documented in the literature. The lens core was characterized by well-mixed water with higher temperature (~28.8 °C), lower salinity (~33.3) and lower potential vorticity (PV) compared to the surrounding waters. Based on an ocean reanalysis, possible generation mechanism of the lens is explored by examining the evolution of surface and subsurface thermohaline properties, and an analysis of vertical PV flux. The lens was likely generated by a mixture of the local mixed-layer water and the water from the coastal jet separation site

Complete genome of Phenylobacterium zucineum – a novel facultative intracellular bacterium isolated from human erythroleukemia cell line K562

<p>Abstract</p> <p>Background</p> <p><it>Phenylobacterium zucineum </it>is a recently identified facultative intracellular species isolated from the human leukemia cell line K562. Unlike the known intracellular pathogens, <it>P. zucineum </it>maintains a stable association with its host cell without affecting the growth and morphology of the latter.</p> <p>Results</p> <p>Here, we report the whole genome sequence of the type strain HLK1^T. The genome consists of a circular chromosome (3,996,255 bp) and a circular plasmid (382,976 bp). It encodes 3,861 putative proteins, 42 tRNAs, and a 16S-23S-5S rRNA operon. Comparative genomic analysis revealed that it is phylogenetically closest to <it>Caulobacter crescentus</it>, a model species for cell cycle research. Notably, <it>P. zucineum </it>has a gene that is strikingly similar, both structurally and functionally, to the cell cycle master regulator CtrA of <it>C. crescentus</it>, and most of the genes directly regulated by CtrA in the latter have orthologs in the former.</p> <p>Conclusion</p> <p>This work presents the first complete bacterial genome in the genus <it>Phenylobacterium</it>. Comparative genomic analysis indicated that the CtrA regulon is well conserved between <it>C. crescentus </it>and <it>P. zucineum</it>.</p

Optical Microscopy and Atomic Force Microscopy Imaging of 2,4,6-Trinitrotoluene Droplets and Clusters on Mica

Optical and atomic force microscopy (AFM) were used to image 2,4,6-trinitrotoluene (TNT) on a cleaved mica (001) surface. The vapor deposition of TNT resulted in ellipsoidal drop formation on the mica surface. The growth rate of the drop diameter was found to be linear with vapor dosing time while the drop density followed a 1/r2 dependence, where r is the length of the major axis of the ellipsoid, for increasing dosing times. TNT platelets surrounded by a region depleted of drops were observed after 8 hours of dosing. The depleted region is attributed to a 10% shrinkage for liquid-solid transition for TNT and also from the enthalpy of fusion which causes the vaporization of small drops and clusters of TNT. Residues of TNT located in the depleted regions were characterized by AFM lift-off forces and were attributed to different morphologies of TNT that nucleated at different sites on the mica surface or dinitro- and trinitro-benzene derivatives which are common impurities in 2,4,6-trinitrotoluene