4,206 research outputs found
Pirate stealth or inattentional blindness?:the effects of target relevance and sustained attention on security monitoring for experienced and naïve operators
No full textClosed Circuit Television (CCTV) operators are responsible for maintaining security in various applied settings. However, research has largely ignored human factors that may contribute to CCTV operator error. One important source of error is inattentional blindness--the failure to detect unexpected but clearly visible stimuli when attending to a scene. We compared inattentional blindness rates for experienced (84 infantry personnel) and naïve (87 civilians) operators in a CCTV monitoring task. The task-relevance of the unexpected stimulus and the length of the monitoring period were manipulated between participants. Inattentional blindness rates were measured using typical post-event questionnaires, and participants' real-time descriptions of the monitored event. Based on the post-event measure, 66% of the participants failed to detect salient, ongoing stimuli appearing in the spatial field of their attentional focus. The unexpected task-irrelevant stimulus was significantly more likely to go undetected (79%) than the unexpected task-relevant stimulus (55%). Prior task experience did not inoculate operators against inattentional blindness effects. Participants' real-time descriptions revealed similar patterns, ruling out inattentional amnesia accounts
The influence of fiber-matrix adhesion on the linear viscoelastic creep behavior of CF/PPS composites
No full textThe influence of fiber-matrix adhesion on the linear viscoelastic creep behavior of as received and surface modified carbon fiber (AR-CF and SM-CF, respectively) reinforced polyphenylene sulfide (PPS) composite materials was investigated. Short-term tensile creep tests were performed on ±45° specimens under four different isothermal condition; 70, 80, 90 and 100°C. As a preliminary step to obtain the time-temperature master curve, as well as to characterize the changes in matrix dominated properties over storage time, physical aging effects were evaluated on both systems using the short-term test method established by Struik. The results showed that the surface treatment carried out in the SM-CF improved fiber-matrix adhesion, enhancing the mechanical performance of CF/PPS composites but with minor effects on the creep response. Increasing retardation times with physical aging was observed in all test conditions. Compared to temperature effects, physical aging showed to have a small contribution on the creep behavior of CF/PPS composites.Aerospace Structures & MaterialsAerospace Engineerin
On the post-impact fatigue behavior and theoretical life prediction of CF/PEEK-titanium hybrid laminates using an energy dissipation approach
No full textThis paper aims to illustrate the effect of the impact damage on fatigue behavior of CF/PEEK-titanium hybrid laminates. To achieve this end, a fatigue life model was proposed to predict the S–N curves of the laminates at various initial impact energy levels and stress ratios based on the energy dissipation approach. The energy dissipation behavior of the laminates during fatigue loading under different experimental conditions was analyzed through a large amount of post-impact fatigue tests, and the correlation between the initial impact damage and the total fatigue dissipation energy was determined. The full-field axial strain distribution of the titanium layer on the impacted side of the laminate was characterized in terms of initial impact energy level and maximum stress using digital image correlation, and then the post-impact fatigue failure mechanism of CF/PEEK-Ti hybrid laminates was summarized. Finally, the validity of the proposed model was verified by fatigue tests under other conditions of stress ratio and impact energy level. It is worth mentioning that the proposed model is also applicable to other types of FMLs, and can accurately predict the residual fatigue life of laminates after impact with only one set of S–N curve data.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.Structural Integrity & Composite
Novel thermomechanical characterization for shrinkage evolution of unidirectional semi-crystalline thermoplastic prepregs (PPS/CF) in melt, rubbery and glassy states
No full textShrinkages, distortions and high residual stresses in the thermoplastic composite parts are induced due to high processing temperature, anisotropy, and fiber–matrix shrinkage mismatch. In this paper the shrinkages have been investigated experimentally and modeled by thermo-mechanical constitutive equations for PolyPhenylene Sulfide (PPS) and the unidirectional Carbon Fiber (PPS/CF) composite prepreg. The thermal shrinkage and the crystallization shrinkage were retrieved from Thermal Mechanical Analysis and compared to a Pressure specific volume Temperature diagram. To describe the crystallization shrinkage in the cooling process accurately, the crystallization kinetics of PPS was evaluated using Differential Scanning Calorimetry. The temperature-dependent elastic modulus was measured by a shear rheometer to formulate a new constitutive model. The mathematical model for shrinkage was validated by a press consolidated [0]12 laminate and unbalanced laminates in four lay-ups. The thermo-mechanical model results presented here provide significant rules for the thermomechanical and shrinkage predictions for the industrial applications of thermoplastic composite.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.Aerospace Manufacturing Technologie
Facilitation and delay sensitivity of auditory cortex neurons in CF-FM bats, Rhinolopus rouxi and Pteronotus p. parnellii
No full textQuatification of carrageenan in gracilaria cf. Manilensis (Rhodophyta) exposed to different salinities and PH using attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR)
No full textCarrageenan is a gel-forming and viscosifying polysaccharides that is commonly found in red algae (Rhodophyta). Previous studies indicate that carrageenan content in the seaweed can be influenced by different environmental conditions. Therefore, in this study, Graciliaria cf. manilensis, a red algae, was exposed at 500 lux under different salinities (15, 20, 25 and 30 psu) and pH (7.6, 7.8 and 8.0) in laboratory condition and carrageenan was determined qualitatively and quantitatively using Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR). Qualitatively, kappa carrageenan was found in most of the Gracilaria samples. Quantitatively, kappa carrageenan was detected ranging from 29.74 ± 7.24 to 56.97 ± 4.03 % (w/w) with the highest carrageenan content was determined at low salinity and slightly neutral pH (15 psu and pH 7.6). . However, G. cf. manilaensis collected from farm and used as a control did not showed the presence of carrageenan. This suggests that different environmental conditions play an important role in determining the carrageenan type and content. This is important as carrageenan is widely used in food, medicinal, pharmaceutical and industrial applications. Furthermore, G. cf. manilensis can be an alternative source of carrageenan besides available sources which is quite limited, to fulfill the high demand of carrageenan
MICROWAVE SPECTRA AND STRUCTURE OF CFICO
No full textAuthor Institution: School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.KA Chirped Pulse Fourier transform Microwave spectrometer has been used to measure the pure rotational spectrum of CFICO. This complex is generated by supersonic expansion of a gas sample containing a small percentage of CFI, and CO in argon. The rotational constant , centrifugal distortion constants, \Delta_\it{J} and \Delta_\it{JK}, and nuclear quadrupole coupling constant for iodine, (I), have been determined for each of CFICO, CFICO and CFI CO allowing determination of the distance between the two sub-units. The complex is a prolate symmetric top with symmetry
Effects of SiC content on the mechanical and thermophysical properties of 3D C<sub>f</sub>/SiC–Al composites
No full text3D Cf/SiC–Al composites were achieved through the pressure infiltration of liquid Al–Si alloy into porous 3D Cf/SiC preform, which was produced by different cycles of precursor infiltration and pyrolysis. The effect of silicon carbide volume fraction on the microstructure, anisotropic mechanical response, and thermophysical characteristics of the 3D Cf/SiC–Al composites was investigated. The results demonstrated that the initial microstructure of 3D Cf/SiC can be retained, and the obtained Cf/SiC–Al composites presented remarkable anisotropy characteristics. As the silicon carbide ceramics content increased from 12.5 vol% to 41.8 vol%, the thermal conductivity and thermal expansion coefficient of 3D Cf/SiC–Al composites decreased, whereas the bending strength initially increased and then decreased in the Z-direction. The bending strength perpendicular (Z) to the carbon cloth layer of 3D Cf/SiC–Al composites was higher than that of parallel (X–Y) to the carbon cloth layer. However, a significant anisotropy in the thermal conductivity values was the opposite. The 3D Cf/SiC–Al composite with 1ow ceramic content (17 vol%) had a higher thermal conductivity in the X–Y direction (64 W m−1 K−1) than in the Z-direction (34 W m−1 K−1). The thermal expansion coefficient of all the 3D Cf/SiC–Al composites along the X–Y direction also decreased initially and then increased in the range of 100–450 °C, which presents low expansion characteristics.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.QN/Groeblacher La
High-temperature hybrid welding of thermoplastic (CF/Peek) to thermoset (CF/Epoxy) composites
No full textThermoset composites are widely used for the manufacturing of modern composite aircrafts. The use of thermoplastic composites (TPC) in aerospace applications is, however, gradually increasing owing to their cost-effectiveness in manufacturing and improved damage tolerance. An example of the use of thermoplastic composites in aircraft is the thousands of clips and cleats that connect structural elements in the fuselage of new composite passenger aircrafts, which are press formed from preconsolidated laminates in only a few minutes. Thermoplastic composite and thermoset composite parts are currently joined through mechanical fastening, which is known not to be an optimal joining technique for composites. Nevertheless, the ability of TPC to be welded with little surface preparation and short assembly times poses the question of whether thermoplastic and thermoset composites can be welded together. Hybrid thermoplastic to thermoset composite welding poses two main challenges: firstly, adhesion between the thermoplastic and thermoset resins; secondly, degradation of the thermoset resin when exposed to the welding temperatures. This paper presents a procedure to successfully prevent any negative thermal effects on the thermoset resin during high-temperature welding of thermoplastic to thermoset composites. The procedure is based on reducing the heating time to fractions of a second during the welding process. In order to achieve such short heating times, which are much too short for commercial welding techniques such as resistance or induction welding, ultrasonic welding is used. A particularly challenging scenario is analysed by considering welding of carbon-fibre reinforced poly-ether-ether-ketone (CF/PEEK), with a melting temperature of 340°C, to carbon-fibre reinforced epoxy (CF/epoxy) with a glass transition temperature of 157°C.Aerospace Structures & MaterialsAerospace Engineerin
Traffic flow on pedestrianized streets
No full textGreen 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.Transport and Plannin
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