5,535 research outputs found
K2MOO3S, PREPARATION OF A PURE MONOTHIOMOLYBDATE
No full textMüller A, DORNFELD H, SCHULZE H, SHARMA RC. K2MOO3S, PREPARATION OF A PURE MONOTHIOMOLYBDATE. ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE. 1980;468(1):193-196
Modelling delay and noise in arbitrarily coupled RC trees.
Full text linkClosed-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
A3S1u <- X1Ug+ Laser Photoacoustic Spectroscopy of Br2 Vapor in the Extreme Red Wavelength Region 665-720 nm
No full textPOLYCHALCOGENOANIONS OF THE TRANSITION-METALS .4. NOVEL REDOX CONDENSATION-REACTIONS OF MOO2S22- IN H2O AND PREPARATION OF DU-MU-SULFIDO COMPLEXES OF MOV
No full textMüller A, RITTNER W, NEUMANN A, SHARMA RC. POLYCHALCOGENOANIONS OF THE TRANSITION-METALS .4. NOVEL REDOX CONDENSATION-REACTIONS OF MOO2S22- IN H2O AND PREPARATION OF DU-MU-SULFIDO COMPLEXES OF MOV. ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE. 1981;472(1):69-74
GENERATION OF THE TRIANGULO-GROUP MOV-ETA-S2 IN THE CONDENSATION OF [MOVIO2S2]2 TO [MO2VO2S2(S2)2]2
No full textRITTNER W, Müller A, NEUMANN A, BATHER W, SHARMA RC. GENERATION OF THE TRIANGULO-GROUP MOV-ETA-S2 IN THE CONDENSATION OF [MOVIO2S2]2 TO [MO2VO2S2(S2)2]2. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH. 1979;18(7):530-531
Experimental investigation of 3d RC exterior joint retrofitted with fully-fastened-haunch-retrofit-solution
Full text linkIn recent years, the use of post-installed anchors to connect the haunch elements with the structural members has been investigated proficiently. It represents a promising alternative for strengthening of joints of existing reinforce concrete (RC) structures (moment resisting frames) with low invasion. The efficacy of the fully-fastened-haunch-retrofit (FFHR) solution has been proven by past works for two-dimensional RC beam-to-column joints, subjected to cyclic loading, without transverse beam and slab. In these cases, the presence of the haunch, providing a suitable design of the anchoring system, modifies the strength hierarchy shifting the mode of failure from joint's shear breakout to the formation of the plastic hinge in the beam. However, due to the presence of the slab and transverse beam, as the authors discussed elsewhere, an increase both (i) in the joint resistance and (ii) in the beam flexural resistance must be expected, but particular care must be taken to the non-symmetric behavior. In this regard, results obtained for two RC beam-to-column sub-assemblies with transverse beam and slab retrofitted using FFHR are presented. The structural behavior under cyclic load is compared with the as-built identical specimen. The applicability of the FFHR to existing RC structures, is confirmed but, at high level of ductility demand, both anchorage break-down and reduced displacement capacity are observed
Ultrasonic Guided Wave and Acoustic Emission Techniques for monitoring corrosion in Reinforced Concrete Structures
Full text linkCorrosion of reinforcement is one of the principal causes of premature failure of Reinforced Concrete (RC) structures. In India, the annual loss due to corrosion has been estimated about 4% of the country’s gross domestic product (GDP) i.e., about USD 40 billion in a year in both infrastructure and industry segments. Exposure to extreme environments and the continuous ingress of chlorides in concrete from various sources neutralises the protective passive layer of concrete which is alkaline with a pH ranging from 12 to 13. The presence of moisture and oxygen leads to the formation of oxides and the initiation of reinforcement corrosion takes place. Corrosion of reinforcement in concrete affects the durability of the RC structures in two ways: the formation of rust products with larger volume than steel leads to spalling and the cracking of the concrete cover; and the area of cross-section of the steel bars reduces drastically due to dissolution of the steel leading to pit formation and hence, loss in the tensile strength and load carrying capacity of the structure. Therefore, an early prognosis and diagnosis of corrosion-induced damage in RC structures could facilitate the engineers to adopt correct repair measures.
A large variety of non-destructive techniques have been reported by researchers worldwide for detecting corrosion-induced damage in RC structures like visual inspection, electrochemical, Optical methods, PZT and piezo ceramic patches etc. but they suffer from practical applications owing to large civil infrastructure. Recently, the advent of wave propagation technologies for damage detection in RC structures have given a new dimension to damage monitoring capabilities. In this work, an integrated approach using active Ultrasonic Guided Wave (UGW) and passive Acoustic Emission (AE) technique for corrosion monitoring in RC structures has been attempted. Active UGW monitors the deterioration of reinforcing bar while corrosion takes place in RC structure whereas the AE technique listens to the cracks and records the damage in the surrounding concrete.
Initiation of corrosion in RC structures before it can be observed visually is done using the two techniques. For this, AE sensors were mounted on the concrete surface and typical guided wave modes were propagated through the embedded rebar. The NDT results were co-related with the already established electrochemical techniques. Active monitoring using UGW was found to have limited significance for tracking the initiation of corrosion when only the outer surface of the reinforcing bar is affected. Surface modifications on the embedded rebar during the initial stages of corrosion is clearly indicated by the L(0,1) mode. On the other hand, passive monitoring using AE clearly identified the onset and the initiation of corrosion during the early stages. The origin and the location of micro-cracks were well identified with the help of AE event maps.
Further, the techniques were used to investigate the progression of corrosion-induced damage in RC structures. It was found that UGW clearly differentiated the surface corrosion from the pitting corrosion with the help of specific guided wave modes. On the other hand, AE parameters like AE hits and cumulative signal strength (CSS) successfully picked up the regions of initiation of steel depassivation and progression of corrosion in the form of micro- and macro-cracking in the surrounding concrete. From the AE event maps, the entire damage progression from initiation of corrosion damage to damage progression in the later stages could be clearly observed.
Further, the effect of varying rates and different corrosion environments were investigated using the two wave propagation techniques. It was confirmed that corrosion mechanism is unaltered by varying rates of accelerated corrosion though the damage progression is delayed and picked up by both UGW and AE. In case of RC beams subjected to accelerated corrosion in the absence of chlorides simulating slow corrosion, UGW confirmed that pitting is insignificant due to slow steel-concrete bond deterioration, by picking up only delamination. On the other hand, AE clearly indicated the corrosion initiation as well as progression stages by cumulative AE hits.
The efficacy of UGW and AE techniques was also investigated to monitor the corrosion impediment offered using Fiber Reinforced Polymer (FRP) wraps on corroding RC cylinders. UGW monitoring with surface-seeking and core-seeking modes established that pulse-echo method is suitable to assess corrosion delay in FRP wrapped samples. The recorded AE hits exhibited significant decrease after the wrapping was done indicating success in corrosion impediment. This was confirmed by drop in the values of amplitude of AE hits from 100 dB to 65 dB after wrapping. No peak/knee was observed in the CSS curve, indicating that FRP wraps effectively delayed the corrosion progression.
It is observed that corrosion-induced damage in RC structures can effectively be tracked right from initiation to progression to concrete cracking using an integrated health monitoring approach involving wave propagation technologies of active ultrasonic guided wave and passive acoustic emission techniques along with benchmark electrochemical measurements. This would go a long way in non-destructive evaluation of residual capacities of reinforcements, which would help a great deal in devising a post-corrosion maintenance strategy of RC structures
Seismic Response of RC Frames with Haunch Retrofit Solution
No full textHaunch retrofit solution (HRS) has been investigated as a viable alternative for retrofitting of beam-column joints of reinforced concrete (RC) frame structures. For connecting the haunch elements to the frame members, partially prestressed rods were used. This solution, however, makes it difficult for implementation in practice due to the requirement of drilling holes through the slab. A more practical solution is to connect the haunch elements using post-installed anchors, resulting in fully fastened HRS (FFHRS). The solution has been tested at the subassembly level, and encouraging results were obtained. To verify the performance of the FFHRS to retrofit the frame structures subjected to real-life seismic loads, shake-table tests were performed on non-seismically detailed two-dimensional (2-D) RC frame structures. This paper presents the results of the experiments with the detailed discussion of the performance of the FFHRS under earthquake ground motions. © 2014, American Concrete Institute
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
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
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