83 research outputs found
Experimental and Numerical Simulation of the Microcrack Coalescence Mechanism in Rock-Like Material
No full textСкальные породы и скалоподобные материалы часто разрушаются при сжатии вследствие инициирования, распространения и слияния ранее возникших микротрещин. Выполнены экспериментальные и численные исследования механизма процесса слияния микротрещин в материалах типа скальных пород. Экспериментальные исследования включают в себя испытания на одноосное сжатие образцов, изготовленных из смеси цемента марки портланд пуццолан, слюды и воды..Скельні породи і скелеподібні матеріали часто руйнуються при стисненні внаслідок ініціювання, поширення і злиття мікротріщин, що з’явилися раніше. Виконано експериментальні і числові дослідження механізму процесу злиття мікротріщин у матеріалах типу скельних порід. Експериментальні дослідження включають випробування на одновісний стиск зразків, виготовлених із суміші цементу марки портланд пуцолан, слюди і води
Deployment of contact-based ultrasonic thickness measurements using over-actuated UAVs
Get PDFUnmanned Aerial Vehicles (UAVs) are increasingly being utilized for the structural health assessment of on and off-shore structures. Visual inspection is the usual methodology for acquiring data from these structures, but there is often a need for contact based structural measurements, for example to assess local thickness on corroding structures. Conventional UAV platform dynamics have not traditionally allowed for such contact measurements. The limited dynamic control afforded by fixed plane rotor UAVs means that forward thrust (to apply contact forces for surface transduction) is only possible by tilting the whole platform, thus taking the UAV into a non-stationary state and limiting positional accuracy. An over-actuated UAV platform (with fully vectored thrust capability) may provide the required contact force for such thickness measurements whilst maintaining stable hovering next to the structure. The authors herein present a contact based ultrasonic thickness measurement technique, whereby an ultrasonic wheel probe deployed from a UAV was used to make single point and scanned measurements across a surface to provide a set of local thickness measurements. A 5 MHz, dry-coupled, dual-element, ultrasonic wheel probe is used to measure the thickness of an aluminum sample plate with thicknesses of 8.2 mm, 4.5 mm and 3.2 mm, and a precision stepped calibration block with size from 31.5 mm to 17.5 mm in steps of 1 mm, then steps of 0.1 mm down to 16.5 mm over a total length of 500 mm. The thickness resolution obtainable from the ultrasonic wheel probe was typically 0.1 mm, and the positional accuracy attained from the over-actuated deployment platform was 16.6 mm when performing single point measurements
Transverse load distribution of skew cast-in-place concrete multicell box - girder bridges subjected to traffic condition
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Capacity of unreinforced rammed earth walls subject to lateral wind force: elastic analysis versus ultimate strength analysis
Full text linkAntimicrobial de-escalation in the critically ill patient and assessment of clinical cure: the DIANA study
Get PDFPurpose: The DIANA study aimed to evaluate how often antimicrobial de-escalation (ADE) of empirical treatment is performed in the intensive care unit (ICU) and to estimate the effect of ADE on clinical cure on day 7 following treatment initiation. Methods: Adult ICU patients receiving empirical antimicrobial therapy for bacterial infection were studied in a prospective observational study from October 2016 until May 2018. ADE was defined as (1) discontinuation of an antimicrobial in case of empirical combination therapy or (2) replacement of an antimicrobial with the intention to narrow the antimicrobial spectrum, within the first 3 days of therapy. Inverse probability (IP) weighting was used to account for time-varying confounding when estimating the effect of ADE on clinical cure. Results: Overall, 1495 patients from 152 ICUs in 28 countries were studied. Combination therapy was prescribed in 50%, and carbapenems were prescribed in 26% of patients. Empirical therapy underwent ADE, no change and change other than ADE within the first 3 days in 16%, 63% and 22%, respectively. Unadjusted mortality at day 28 was 15.8% in the ADE cohort and 19.4% in patients with no change [p = 0.27; RR 0.83 (95% CI 0.60\u20131.14)]. The IP-weighted relative risk estimate for clinical cure comparing ADE with no-ADE patients (no change or change other than ADE) was 1.37 (95% CI 1.14\u20131.64). Conclusion: ADE was infrequently applied in critically ill-infected patients. The observational effect estimate on clinical cure suggested no deleterious impact of ADE compared to no-ADE. However, residual confounding is likely
Electrode modification using nanocomposites of electropolymerised cobalt phthalocyanines supported on multiwalled carbon nanotubes
Get PDFA polymer of tetra(4)-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninatocobalt(II) (CoPyPc) has been deposited over a multiwalled carbon nanotube (MWCNT) platform and its electrocatalytic properties investigated side by side with polymerized cobalt tetraamino phthalocyanine (CoTAPc). X-ray photoelectron spectroscopy, scanning electron microscopy and cyclic voltammetry studies were used for characterization of the prepared polymers of cobalt phthalocyanine derivatives and their nanocomposites. L-Cysteine was used as a test analyte for the electrocatalytic activity of the nanocomposites of polymerized cobalt phthalocyanines and multiwalled carbon nanotubes. The electrocatalytic activity of both polymerized cobalt phthalocyanines was found to be superior when polymerization was done on top of MWCNTs compared to bare glassy carbon electrode. A higher sensitivity for L-cysteine detection was obtained on CoTAPc compared to CoPyPc
Simultaneous quantification of Bi(III) and U(VI) in environmental water samples with a complicated matrix containing organic compounds
Full text linkبررسی آزمایشگاهی تأثیر مقدار و آرایش میلگردهای طولی و عرضی در تیرهای بتنی پیش تنیده تحت خمش
No full textThe recent changes in urban communities and consequently the need for thinner
strong concrete structures has caught researchers' attention. Structural
performance characteristics such as ultimate loads, maximum loads, and
ductility along with formation and propagation of cracks in prestressed concrete beams have been studied by many researchers. In this paper, an experimental study was carried out to investigate the effect of amount and arrangement of non-prestressed longitudinal and transvers bars on improving the performance of six prestressed concrete beams with identical geometry and concrete properties under static loads. Cracking strength, formation and propagation, ultimate load carrying capacity and ductility of beams were determined. Unbonded post-tensioning is applied to 7-wire strand tendons with Grade 270 and diameter of 0.5in that are positioned with constant eccentricity within the beam. The test results indicate that adding non-prestressed reinforcement to concrete beams generally has a significant effect on properties of prestressed concrete beams such as ultimate load, maximum load, ductility and pattern of crack formation and propagation and also have a significant reduction in brittleness and showed better ductility. The response of beams significantly depends on the method of confinement by transverse reinforcement and also the distribution of longitudinal reinforcement
Contribution of water-soluble ions in the corrosion of reinforced concrete cooling towers using the response surface method
No full textEvery year, a significant number of reinforced concrete structures suffer from corrosion attributed to aggressive ions, posing a critical issue on durability and strength loss of structures. Therefore, identifying the contribution of each ion to concrete deterioration is crucial. This study employed the Response Surface Method (RSM) to investigate the coupling effects of different ions and PH values and their respective contributions to the corrosion degree of concrete structure of a cooling tower with severe corrosions induced by ion attacks. The deterioration growth of concrete volume in the corroded zones of the cooling tower was measured and monitored according to the amount of dissolved ions in several times. The results of each measurement were considered as a laboratory sample for the required experiments of the RSM. The results of the study revealed that chloride and sulfate ions were the most influential ions in deteriorating the concrete, causing the most significant negative impact on reinforced concrete deterioration. In contrast, magnesium and calcium ions had the least contribution to reinforced concrete corrosion
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