344 research outputs found
A High Stability Optical Shadow Sensor with Applications for Precision Accelerometers
Gravimeters are devices which measure changes in the value of the
gravitational acceleration, \textit{g}. This information is used to infer
changes in density under the ground allowing the detection of subsurface voids;
mineral, oil and gas reserves; and even the detection of the precursors of
volcanic eruptions. A micro-electro mechanical system (MEMS) gravimeter has
been fabricated completely in silicon allowing the possibility of cost
e-effective, lightweight and small gravimeters. To obtain a measurement of
gravity, a highly stable displacement measurement of the MEMS is required. This
requires the development of a portable electronics system that has a
displacement sensitivity of nm over a period of a day or more. The
portable electronics system presented here has a displacement sensitivity nm ( nm at s). The battery power
system used a modulated LED for measurements and required temperature control
of the system to 2 mK, monitoring of the tilt to 2 radians,
the storage of measured data and the transmission of the data to an external
server.Comment: 8 Pages, 12 figures, 5 equations, currently submitted and under
review at IEEE Sensors SIE
Field tests of a portable MEMS gravimeter
Gravimeters are used to measure density anomalies under the ground. They are applied in
many different fields from volcanology to oil and gas exploration, but present commercial systems
are costly and massive. A new type of gravity sensor has been developed that utilises the same
fabrication methods as those used to make mobile phone accelerometers. In this study, we describe
the first results of a field-portable microelectromechanical system (MEMS) gravimeter. The stability
of the gravimeter is demonstrated through undertaking a multi-day measurement with a standard
deviation of 5.58 × 10−6 ms−2
. It is then demonstrated that a change in gravitational acceleration of
4.5 × 10−5 ms−2
can be measured as the device is moved between the top and the bottom of a 20.7 m
lift shaft with a signal-to-noise ratio (SNR) of 14.25. Finally, the device is demonstrated to be stable in
a more harsh environment: a 4.5 × 10−4 ms−2 gravity variation is measured between the top and
bottom of a 275-m hill with an SNR of 15.88. These initial field-tests are an important step towards
a chip-sized gravity senso
Finite Element Modelling of Tensile Reinforcement Laps in Steel Fibre Reinforced Concrete
For being able to design tensile reinforcement laps with confidence, a good understanding of the mechanical performance and failure process is required. In this study, the response of laps subjected to tension in plain and steel fibre reinforced concrete was investigated by nonlinear finite element analyses. For analysing reinforced concrete, the individual phases of the composite, namely concrete, steel and bond between steel and concrete, were modelled. For concrete, a damage-plasticity constitutive model was used. The stress-crack opening curve of concrete was calibrated to describe the influence of steel fibres on the cracking response. The results show that a small volume fraction of fibres improves the mechanical performance of tensile reinforcement laps significantly
Microelectromechanical system gravimeters as a new tool for gravity imaging
A microelectromechanical system (MEMS) gravimeter has been manufactured with a sensitivity of 40 ppb in an integration time of 1 s. This sensor has been used to measure the Earth tides: the elastic deformation of the globe due to tidal forces. No such measurement has been demonstrated before now with a MEMS gravimeter. Since this measurement, the gravimeter has been miniaturized and tested in the field. Measurements of the free-air and Bouguer effects have been demonstrated by monitoring the change in gravitational acceleration measured while going up and down a lift shaft of 20.7 m, and up and down a local hill of 275 m. These tests demonstrate that the device has the potential to be a useful field-portable instrument. The development of an even smaller device is underway, with a total package size similar to that of a smartphone
Power scalable TEM(oo) CW Nd: YAG laser with thermal lens compensation
We present finite-element analyzes and experimental results to validate our approach for building high-power single-mode Nd:YAG lasers. We show that the thermooptical and thermomechanical properties of a slab laser can be controlled. This is essential for the use of the proposed unstable resonator. We include demonstration of an efficient subscale laser operating at 20 W TEM00.D. Mudge, M. Ostermeyer, P. J. Veitch, J. Munch, B. Middlemiss, D. J. Ottaway and M. W. Hamilto
Contested Subjectivities in a UK Housing Cooperative: Old Hippies and Thatcher’s Children negotiating the commons
How can a long-standing cooperative respond to changes in society over time, and how do these changes affect the management of the cooperative? We looked at the visions, daily life and policies in a housing cooperative in the UK established in the 1970s and found a messy process that required constant negotiation and involved diverse subjectivities. We identified different visions of the commons: a minimalist vision focusing on housing alone, and a maximalist one, diffusing boundaries between the personal and the collective and involving many aspects of members’ lives. These visions have always existed in the cooperative, but the general trend was towards minimalism. Behind the changes are members’ changing subjectivities, reflecting changing processes of subject formation in relation to state and market. We found that difference in subjectivities was often displayed along generational lines, and affected commoners’ visions of the commons. Although the cooperative changed some of its practices to fit the more minimalist vision, it still endured as a form of commons that is resilient to challenge
Joint Experimental and Computational 17O and 1H Solid State NMR Study of Ba2In2O4(OH)2 Structure and Dynamics.
A structural characterization of the hydrated form of the brownmillerite-type phase Ba2In2O5, Ba2In2O4(OH)2, is reported using experimental multinuclear NMR spectroscopy and density functional theory (DFT) energy and GIPAW NMR calculations. When the oxygen ions from H2O fill the inherent O vacancies of the brownmillerite structure, one of the water protons remains in the same layer (O3) while the second proton is located in the neighboring layer (O2) in sites with partial occupancies, as previously demonstrated by Jayaraman et al. (Solid State Ionics2004, 170, 25-32) using X-ray and neutron studies. Calculations of possible proton arrangements within the partially occupied layer of Ba2In2O4(OH)2 yield a set of low energy structures; GIPAW NMR calculations on these configurations yield 1H and 17O chemical shifts and peak intensity ratios, which are then used to help assign the experimental MAS NMR spectra. Three distinct 1H resonances in a 2:1:1 ratio are obtained experimentally, the most intense resonance being assigned to the proton in the O3 layer. The two weaker signals are due to O2 layer protons, one set hydrogen bonding to the O3 layer and the other hydrogen bonding alternately toward the O3 and O1 layers. 1H magnetization exchange experiments reveal that all three resonances originate from protons in the same crystallographic phase, the protons exchanging with each other above approximately 150 °C. Three distinct types of oxygen atoms are evident from the DFT GIPAW calculations bare oxygens (O), oxygens directly bonded to a proton (H-donor O), and oxygen ions that are hydrogen bonded to a proton (H-acceptor O). The 17O calculated shifts and quadrupolar parameters are used to assign the experimental spectra, the assignments being confirmed by 1H-17O double resonance experiments.This work was supported in part by Grants DMR050612 and CHE0714183 from the National Science Foundation and Grant DESC0001284 from the Department of Energy (supporting Y.- L.L. and D.M.), by an Advanced Fellowship from the EU-ERC (C.P.G.), and by the EPSRC (D.S.M.). F.B. thanks the EU Marie Curie actions FP7 for an International Incoming fellowship (Grant No. 275212) and Clare Hall, University of Cambridge, for a Research Fellowship.This is the final version of the article. It first appeared from ACS Publications via http://dx.doi.org/10.1021/acs.chemmater.5b0032
Joint Experimental and Computational O-17 and H-1 Solid State NMR Study of Ba2In2O4(OH)(2) Structure and Dynamics
This is the final version of the article. It first appeared from ACS Publications via http://dx.doi.org/10.1021/acs.chemmater.5b00328A structural characterization of the hydrated form of the brownmillerite-type phase Ba2In2O5, Ba2In2O4(OH)2, is reported using experimental multinuclear NMR spectroscopy and density functional theory (DFT) energy and GIPAW NMR calculations. When the oxygen ions from H2O fill the inherent O vacancies of the brownmillerite structure, one of the water protons remains in the same layer (O3) while the second proton is located in the neighboring layer (O2) in sites with partial occupancies, as previously demonstrated by Jayaraman et al. ( Solid State Ionics 2004, 170, 25?32) using X-ray and neutron studies. Calculations of possible proton arrangements within the partially occupied layer of Ba2In2O4(OH)2 yield a set of low energy structures; GIPAW NMR calculations on these configurations yield 1H and 17O chemical shifts and peak intensity ratios, which are then used to help assign the experimental MAS NMR spectra. Three distinct 1H resonances in a 2:1:1 ratio are obtained experimentally, the most intense resonance being assigned to the proton in the O3 layer. The two weaker signals are due to O2 layer protons, one set hydrogen bonding to the O3 layer and the other hydrogen bonding alternately toward the O3 and O1 layers. 1H magnetization exchange experiments reveal that all three resonances originate from protons in the same crystallographic phase, the protons exchanging with each other above approximately 150 ?C. Three distinct types of oxygen atoms are evident from the DFT GIPAW calculations bare oxygens (O), oxygens directly bonded to a proton (H-donor O), and oxygen ions that are hydrogen bonded to a proton (H-acceptor O). The 17O calculated shifts and quadrupolar parameters are used to assign the experimental spectra, the assignments being confirmed by 1H?17O double resonance experiments.This work was supported in part by Grants DMR050612 and CHE0714183 from the National Science Foundation and Grant DESC0001284 from the Department of Energy (supporting Y.- L.L. and D.M.), by an Advanced Fellowship from the EU-ERC (C.P.G.), and by the EPSRC (D.S.M.). F.B. thanks the EU Marie Curie actions FP7 for an International Incoming fellowship (Grant No. 275212) and Clare Hall, University of Cambridge, for a Research Fellowship
2H and 27Al Solid-State NMR Study of the Local Environments in Al-Doped 2-Line Ferrihydrite, Goethite, and Lepidocrocite.
Although substitution of aluminum into iron oxides and oxyhydroxides has been extensively studied, it is difficult to obtain accurate incorporation levels. Assessing the distribution of dopants within these materials has proven especially challenging because bulk analytical techniques cannot typically determine whether dopants are substituted directly into the bulk iron oxide or oxyhydroxide phase or if they form separate, minor phase impurities. These differences have important implications for the chemistry of these iron-containing materials, which are ubiquitous in the environment. In this work, 27Al and 2H NMR experiments are performed on series of Al-substituted goethite, lepidocrocite, and 2-line ferrihydrite in order to develop an NMR method to track Al substitution. The extent of Al substitution into the structural frameworks of each compound is quantified by comparing quantitative 27Al MAS NMR results with those from elemental analysis. Magnetic measurements are performed for the goethite series to compare with NMR measurements. Static 27Al spin-echo mapping experiments are used to probe the local environments around the Al substituents, providing clear evidence that they are incorporated into the bulk iron phases. Predictions of the 2H and 27Al NMR hyperfine contact shifts in Al-doped goethite and lepidocrocite, obtained from a combined first-principles and empirical magnetic scaling approach, give further insight into the distribution of the dopants within these phases.J.K., A.J.I., D.M. and N.P. were supported by an NSF grant collaborative research grant in chemistry CHE0714183. An allocation of time upon the NANO computer cluster at the Center for Functional Nanomaterials, Brookhaven National Laboratory, U.S.A., which is supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886 is also acknowledged. D.S.M. and C.P.G. thank the EPSRC and the EU-ERC for support.This is the final version of the article. It first appeared from the American Chemical Society via http://dx.doi.org/10.1021/acs.chemmater.5b0085
Is Carbon Black a Suitable Model Colloidal Substrate for Diesel Soot?
Soot formation in diesel engines is known to cause premature engine wear. Unfortunately, genuine diesel soot is expensive to generate, so carbon blacks are often used as diesel soot mimics. Herein, the suitability of a commercial carbon black (Regal 250R) as a surrogate for diesel soot dispersed in engine base oil is examined in the presence of two commonly used polymeric lubricant additives. The particle size, morphology, and surface composition of both substrates are assessed using BET surface area analysis, TEM, and XPS. The extent of adsorption of a poly(ethylene-co-propylene) (dOCP) statistical copolymer or a polystyrene-block-poly(ethylene-co-propylene) (PS–PEP) diblock copolymer onto carbon black or diesel soot from n-dodecane is compared indirectly using a supernatant depletion assay technique via UV spectroscopy. Thermogravimetric analysis is also used to directly determine the extent of copolymer adsorption. Degrees of dispersion are examined using optical microscopy, TEM, and analytical centrifugation. SAXS studies reveal some structural differences between carbon black and diesel soot particles. The mean radius of gyration determined for the latter is significantly smaller than that calculated for the former, and in the absence of any copolymer, diesel soot suspended in n-dodecane forms relatively loose mass fractals compared to carbon black. SAXS provides evidence for copolymer adsorption and indicates that addition of either copolymer transforms the initially compact agglomerates into relatively loose aggregates. Addition of dOCP or PS–PEP does not significantly affect the structure of the carbon black primary particles, with similar results being observed for diesel soot. In favorable cases, remarkably similar data can be obtained for carbon black and diesel soot when using dOCP and PS–PEP as copolymer dispersants. However, it is not difficult to identify simple copolymer–particle–solvent combinations for which substantial differences can be observed. Such observations are most likely the result of dissimilar surface chemistries, which can profoundly affect the colloidal stability
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