4,894 research outputs found
Sedimentary facies and unconformity analysis of some Paleocene-Eocene sections, Marlborough and Campbell Island, New Zealand
No full textThroughout the Late Cretaceous to Eocene, sedimentation in gradually subsiding basins on the passive eastern margin of the micro-continent of Zealandia recorded climatic and paleoceanographic changes in a greenhouse world. One such fundamental change in Southern Ocean circulation is hypothesised to be recorded in a regionally extensive unconformity surface and short-lived lithofacies changes contained within Late Paleocene to Early Eocene sedimentary successions at key sections throughout New Zealand, and investigated here on Campbell Island and in southeastern Marlborough.
On Campbell Island, this oceanographic event is represented by an unconformity between the Late Cretaceous to Late Paleocene Garden Cove Formation and the Early Eocene to Oligocene Tucker Cove Limestone. This unconformity signifies a major lithofacies change from Garden Cove Formation which consists of siliceous mudstone containing fine sand to coarse silt sized siliciclastic grains, pelletal glaucony grains and rare quartz pebbles, to a nannofossil and foraminiferal limestone containing little to no siliciclastic grains comprising the Tucker Cove Limestone. Geochemically this lithofacies change is characterised by a dramatic decrease in terrigenous supply and a shift from siliceous to calcareous productivity, along with a significant concentration of Zr and rare earth elements. Lithofacies at this site are inferred to record possible episodes of ice rafting and eventual unconformity formation by invigorated intermediate depth ocean currents which resulted in winnowing of seafloor sediments and concentration of heavy minerals.
At the distal Mead Stream site in southeastern Marlborough, deposition of bio-siliceous sediments of the Mead Hill Formation and Amuri Limestone was locally disrupted by deposition of the Waipawa Formation, the lateral equivalent of an important hydrocarbon source rock identified in several of New Zealand‟s sedimentary basins. In outcrop, the Waipawa Formation at Mead Stream is characterised by a very distinctive rusty‟ brown fissile appearance, while in thin section, though radiolarians and sponge spicules are common, the overall fine grained nature of the unit makes identification of other components difficult. Geochemical proxies show a significant increase in terrigenous supply in the Waipawa Formation, along with an increase in siliceous productivity concomitant with a decrease in oxygenation at the site. Lithofacies changes through the Late Paleocene at Mead Stream suggest the site lay under a zone of upwelling which resulted in an increase in siliceous productivity during the Late Paleocene.
At the more proximal sites of Muzzle Stream and Kaikoura wharf in southeastern Marlborough, Mead Hill Formation and Amuri Limestone are separated by an unconformity, overlain by Teredo Limestone. The Teredo Limestone is considered to be a lateral equivalent of the Waipawa Formation, but both the base and top of the Teredo Limestone are timetransgressive. This means that at Muzzle Stream the unit is contemporaneous with the Waipawa Formation (Late Paleocene), while at Kaikoura wharf the unit is entirely Early Eocene in age. At these sites, the Teredo Limestone Member of the Amuri Limestone is a calcareous greensand sometimes containing phosphatised limestone clasts and sharks teeth. In thin sections, the unit consists of well sorted, fine to very fine sand sized siliciclastic grains and fine sand sized pelletal and vermicular glaucony set in a calcareous matrix that shows evidence of secondary silicification. Unconformity formation and the subsequent deposition of the overlying Teredo Limestone record a period of invigorated intermediate depth ocean currents that resulted in the transport of siliciclastic grains and glaucony to these bathyal sites. This interpretation is supported by a palinspastic map of the Teredo Limestone that suggests the unit was deposited under different conditions than those responsible for the deposition of the bounding Mead Hill Formation and Amuri Limestone. This map also suggests the Teredo Limestone was deposited as a skin drift‟, here named the Clarence Drift, possibly under the influence of contour currents.
Based on similarities between unconformities and lithofacies changes in Late Paleocene to Early Eocene sedimentary sections and an earlier, well documented event at the Cretaceous/Tertiary boundary in southeastern Marlborough, evidence for a period of enhanced siliceous productivity, invigorated ocean currents and possible episodes of ice rafting is suggested to be consistent with a brief period of Antarctic ice sheet growth during a phase of global cooling in the Late Paleocene.
The possible identification of Antarctic ice sheets, ephemeral though they may have been, not only challenges long held beliefs that the Antarctic continent remained ice free during the early Paleogene greenhouse world but also questions the suggested mechanisms responsible for Antarctic ice sheet growth. The lack of ocean gateways in the Southern Ocean during this time effectively rules out thermal isolation of the Antarctic continent as a driver. Given that this period of ice sheet growth is contemporaneous with a documented period of enhanced global ocean productivity and terrestrial carbon accumulation and related draw down in atmospheric CO2, it is suggested this may represent the driver responsible for brief Antarctic glaciation during this period, though the postulated link requires further investigation
Modelling delay and noise in arbitrarily coupled RC trees.
No full textClosed-form equations for second-order transfer functions of general arbitrarily coupled resistance-capacitance (RC) trees with multiple drivers are reported. The models allow precise delay and noise calculations for systems of coupled interconnects with guaranteed stability and represent the minimum complexity associated with this class of circuits. Their accuracy is extensively compared against other relevant models and is found to be better or comparable to more expensive models. All results are derived from a theoretical approach, and their physical basis is examined. The simplicity, accuracy, and generality of the models make them suitable for use in early signal integrity analyses of complex systems and incremental physical optimization
Practical Filters Using Distributed RC Structures
No full textTitle: Practical Filters Using Distributed RC Structures, Author: Edmund J. Wragg, Location: ThodeTheoretical and experimental studies into practical filters using distributed RC structures are described. Various techniques to surmount the transcendental nature of the circuit parameters of such structures are considered and shown to be mostly too clumsy or restricted for practical use. The use of computer-aided analysis together with a sound physical understanding is suggested as an alternative. Application of the structures to active filters is considered and the experimental development of lowpass and bandpass amplifiers using them described. This leads to the presentation of a general design procedure for bandpass amplifiers using distributed RC null circuits. It is concluded that distributed RC filters suffer from a number of limitation but have a part to play as a circuit element and are now ready to advance to the stage of practical implementation.ThesisMaster of Engineering (ME
A Compact 10-MHz RC Frequency Reference With a Versatile Temperature Compensation Scheme
No full textThis article presents the design and implementation of a compact CMOS RC frequency reference. It consists of a frequency-locked loop (FLL) that locks the period of a voltage-controlled oscillator (VCO) to the time an RC network takes to charge to a reference voltage. Conventionally, an RC time constant with a near-zero temperature coefficient (TC) is realized by using a trimmed network of resistors with different TCs. In this work, such a network is used to realize a temperature-dependent reference voltage whose TC cancels that of a single-resistor RC time constant. Compared with the conventional approach, which requires resistors with TCs of opposite polarity, the proposed approach can be implemented with resistors with TCs of similar polarity, and so it can be implemented in most CMOS processes. To compensate for RC spread, a trimmed capacitor is used to adjust the nominal frequency. Two prototype chips were made, one based on p- /n-polysilicon resistors and other based on silicided/p-diffusion resistors. Fabricated in a standard 180-nm CMOS technology, the polysilicon-based prototype has an active area of 0.01 mm2 and an absolute inaccuracy of ±2800 ppm from -45 °C to 125 °C with a fixed TC-trim and a one-point frequency trim. After one week of accelerated aging at 150 °C, however, significant drift (5000 ppm) was observed. The diffusion-based prototype exhibits greater inaccuracy (±14 400 ppm) but much less drift (600 ppm).Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
Regulation of IL-4 mediated signalling in primary human bronchial fibroblasts by IL-13Rα2
No full textFibroblasts are key effector cells involved in airway inflammation and remodelling in asthma. Interleukin (IL)-4 and IL-13 are important cytokines in the asthma phenotype which act on fibroblasts and other cell types. These cytokines exhibit overlapping functions through use of a common receptor, IL-4Rα:IL-13Rα1. Another receptor, IL 13 Receptor α2 (IL-13Rα2), originally thought to be a decoy receptor for IL-13, has recently been shown to attenuate responses to IL-4 as well as IL-13, by an unknown mechanism. In this thesis, I tested the hypothesis that IL-13Rα2 is responsible for the regulation of IL-4 mediated signalling in bronchial fibroblasts and that regulation by IL-13Rα2 is altered in asthma. The expression of IL-4 and IL-13 receptors on human bronchial fibroblasts (HBFs) was highly dynamic. IL-13Rα2 expression was significantly increased in response to both IL-4 and IL-13 over 24 hours, requiring de novo protein synthesis. A significant rapid reduction in IL-4Rα expression was also observed in response to either ligand, although levels rapidly returned to normal after removal of the stimulus. Use of a neutralizing antibody showed that induction of IL 13Rα2 suppressed STAT-6 activation and the pro-inflammatory effects of IL-4 and IL-13. No difference was observed in receptor expression levels or the regulatory effects of IL-13Rα2 between healthy and asthmatic subjects. IL-13Rα2 was also up-regulated by a range of Th1 stimuli including IFNγ and IFNβ, as well as double stranded RNA (dsRNA), with no disease-related differences. The up-regulation of IL 13Rα2 in response to dsRNA hampered attempts to knock down surface expression of IL-13Rα2 using siRNA, but revealed a potential role for IL-13Rα2 in the anti-viral response due to its ability to down-regulate responses to IL-4 and IL-13. An over expression model of IL-13Rα2 identified the potential for IL-4 to cause activation of STAT3 mediated by IL-13Rα2. In HBFs naturally expressing high levels of IL-13Rα2, addition of IL-4, but not IL-13, significantly increased activation of STAT3, a transcription factor associated with cell survival. Whilst IL-13Rα2 may have beneficial anti-inflammatory effects by suppressing STAT-6 mediated responses, further work is required to determine potential pro-fibrotic consequences of IL-4/IL-13Rα2 mediated STAT3 activation in HBFs. Since no difference was observed in IL-13Rα2 expression or in its anti-inflammatory efficacy in HBFs from normal or asthmatic donors, these data suggest that the atopic environment is more important than intrinsic differences in the ability of asthma-derived fibroblasts to respond to IL-4 and IL-13
A CMOS Dual-RC frequency reference with ±250ppm inaccuracy from -45°C to 85°C
No full textTo comply with wired communication standards such as USB, SATA and PCI/PCI-E, systems-on-chip require frequency references with better than 300ppm accuracy. LC-based references achieve 100ppm accuracy [1], but suffer from high power consumption (∼20mW). Thermal diffusivity (TD) references require less power (∼2mW), at the expense of less accuracy (1000ppm) [2]. RC-based references offer the lowest power consumption, but their accuracy is typically limited to ∼0.1% [3]. In RC relaxation oscillators, comparator offset and delay are the major sources of inaccuracy [4,5]. References based on frequency-locked loops (FLLs) circumvent these by locking an oscillator's frequency to the time-constant of an RC filter, but their accuracy is then limited by the nonlinear temperature dependency of on-chip resistors [3,6].Session 3.3 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Instrumentation(OLD)Applied Quantum ArchitecturesMicroelectronic
Evaporated Thin Film Distributed RC Networks
No full textThin film uniform and exponential distributed RC networks were fabricated and the network responses were investigated. It was necessary to take dielectric loss into consideration in the theoretical analysis before a close agreement could be obtained between the theoretical and experimental network responses.ThesisMaster of Engineering (ME
Optimal Shape of a Distributed RC Notch Filter - A Computer-Aided Design
No full text An improvement on the synthesis of a distributed RC notch filter, by computer-aided design techniques, is appraised. A brief presentation of the synthesis of thin-film RC tapered networks is made, along with applied uses of computer-aided design to RC distributed networks, particularly in the realizability of certain RC transfer functions. The preparation of the problem, accompanied by different methods of approach, is explained. Included are criticisms made, leading to the reasons for abandoning the more tasking ones. The Adjoint Network method of determining, gradients, with respect to circuit adjustable parameters, is evaluated fully, and the important use which it lends to the optimization problem is demonstrated. The outcome of the design approaches are given in tables, with theoretical responses compared in graphs. Actual circuit responses are indicated in photographs, and comparisons with theoretical responses are shown in graphs.ThesisMaster of Engineering (MEngr
Experimental and theoretical investigation of crack width calculation methods for RC ties
No full textThis paper theoretically and experimentally investigates the semi-empirical formulas recommended by Eurocode 2 (EC2), fib Model Code 2010 (MC2010), and Eurocode 2 with the German National Annex (DIN) for calculating crack widths in reinforced concrete. It is shown that the formulas can be derived from the principles for the idealized behavior of RC ties. However, instead of explicitly solving the resulting differential equations, the use of simplifications leads to inconsistent formulas. An experimental study was carried out involving the testing of eight RC ties to discover the modeling uncertainty of the formulas. It was found that EC2 substantially overestimated the crack widths for the RC ties. MC2010 and DIN seemed to predict the crack widths better, but gave rather a large number of nonconservative crack width predictions. These experimental results, combined with the theoretical study, suggest that a more consistent calculation model should be formulated by explicitly solving the resulting differential equation.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Mechanic
RC SMOOTHING OF SPECTRA
No full textAuthor Institution: Department of Physics, Michigan State University East LansingBy convoluting an exponential function with calculated spectra consisting of single and multiple sets of lines of various widths and line shapes, we have determined the effects that time constant (RC) has on recorded spectra. For equivalent experiments, in which the scanning rates d/dt are equal, we have concluded that the optimum value of RC is essentially independent of whether the spectrum is to be digitized or not, and independent of the sampling rate if digitization is used. A trade-off among the desirable and undesirable effects of RC leads us to recommend a value of RC about one-tenth of the full width at half height of the sharpest individual lines in the observed spectrum. This research was supported by a grant from the National Science Foundation
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