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  • Author: Jiří Militký x
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Roman Republican coins in the collection of the Palacký University in Olomouc

Abstract

The collection of ancient coins of the Palacký University in Olomouc is recently preserved in the department of history there. It is very likely that the collection was founded sometimes between the second half of the 19th century and the beginning of the 20th century – no details are known about it and the collection became the university property evidently after 1946. The core of the Olomouc collection is represented by denarii dating back to 154–74 BC (cat. nos. 3–69). Only individual pieces of the earlier issues (cat. nos. 1–2) and the later issues (cat. nos. 70–72) are present here. Publication of this collection could be accepted as a small contribution to documentation of the physically verified material of the mentioned period. Parallelly, it is an interesting testimony of the collecting activities in Olomouc at the break of the 19th and 20th centuries.

Open access
Multicriteria Decision-Making in Complex Quality Evaluation of Ladies Dress Material

Abstract

Quality is the essence of any product for consumer satisfaction. However, different people have different perception of quality. Eventually the definition of quality varies from product to product and thus it is much more complex in textile clothing material evaluation. The end use application of a specific clothing material determines what should be the parameters of quality evaluation. Thus, the evaluation based on subjective assessment becomes unpredictable and unquantifiable. Quality for dress materials is not simply a physical parameter but something called as psycho-physical parameter. In recent times, many objective evaluation systems have been developed to evaluate the apparel grade textile materials with regard to their quality parameters. However, the evaluation does not involve enough statistical treatment of data so as to obtain a parametric weighted characterization of complex quality. The current work deals with parametric approach to complex quality evaluation based on multicriteria decision-making approach for ladies dress materials. The ladies dress materials are of numerous varieties and choices across the globe. The selection and marketing of these kinds of textile materials need to be given proper emphasis as it depends not only on physical parameters but also on climate, geography, ethnic group, market trend, age group, gender, and many such complex parameters, which are not quantifiable in absolute terms. In this study, woven fabrics used for ladies dress materials are collected from the market and they were evaluated for the consumer-oriented property parameters. A parametric approach is adopted to quantify the overall quality of these dress materials. Various objective techniques were used to evaluate the comfort and esthetic parameters. A complex quality index (CQI) was estimated with weighted combination of all the contributing parameters and total quality index was calculated. Selected consumers with different education level, age, and gender were interviewed to get a statistic of their opinion about quality parameters preferred by them. This complex quality index/degree of satisfaction shows very high correlation with subjective judgment. A CQI can be evaluated for each kind of clothing material looking into their applications.

Open access
Flex Fatigue Behavior Of Plastic Optical Fibers With Low Bending Cycles

Abstract

Flex fatigue behaviour of plastic optical fibres (POFs) with the diameters of 0.2 and 0.3 mm under different pretensions is measured with fatigue life curve by flexometer. The fatigue sensitivity coefficient is calculated by the linear fitting curve of normalised stress versus logarithm of bending cycles. The residual modulus is investigated during the flex fatigue processes. The results exhibit the exponential relationship between applied pretension and numbers of bending cycles at break. It is indicated that the flex fatigue of POFs might be sensitive with high swing angle or swing speed. There is an evident loss of modulus for two POFs with pretensions of 4 and 10% of ultimate tensile strength during 10-times bending cycles. The values of residual modulus of two POFs almost keep constant after 10-times bending cycles.

Open access
Ozone Effect On the Properties of Aramid Fabric

Abstract

The limitation of aramid fiber is its surface property, which results in its very poor interfacial adhesion to most of commercial resins. In order to improve the surface property of the aramid fiber, ozone treatment was carried out in this work. The aramid fabrics were evaluated in terms of surface morphology, wicking effect, tensile property, and ball bursting test. The results showed that the surface morphology of aramid fabrics did not undergo an obvious change; the wicking effect increased slightly with an increase in ozone treatment time; the tenacity and elongation of aramid fibers and fabrics did not significant change after ozone treatment, but the tenacity and elongation of aramid yarns showed significant improvement after ozone treatment, and increased with the increase of ozone treatment time; the ball bursting load and penetration displacement had a slight increase as well after ozone treatment. Therefore, ozone treatment could be one method to improve the surface property of the aramid fiber.

Open access
Evaluation of Illumination Intensity of Plastic Optical Fibres with Tio2 Particles by Laser Treatment

Abstract

CO2 laser treatment can increase the surface roughness of plastic optical fibres (POFs) with the diameter of 0.5 mm and enhance the input intensity and attenuation coefficient accordingly, which is supposed to weaken the side emission of POFs in long distance above 375 mm. TiO2 particles were applied to improve the increasing optical loss of POFs by laser treatment. POFs were first modified with fine TiO2 particles and then treated by CO2 laser with the pixel time from 30 to 120 ìs. The surface morphology was observed by scanning electron microscopy to investigate the changes of micro-structure before and after laser treatment and the distribution of TiO2 particles. The illumination intensity and attenuation coefficient were calculated and compared in two methods. It is visible that the evaluation by model LLF2 with two parts is more suitable for the fitting of experimental data and shows higher input intensity and lower attenuation than that by standard power function. Both the evaluation methods exhibit that the utilization of TiO2 particles could play an active role in the enhancement of side emission of POFs treated by CO2 laser.

Open access
3D Numerical Simulation of Laminar Flow and Conjugate Heat Transfer through Fabric

Abstract

The air flow and conjugate heat transfer through the fabric was investigated numerically. The objective of this paper is to study the thermal insulation of fabrics under heat convection or the heat loss of human body under different conditions (fabric structure and contact conditions between the human skin and the fabric). The numerical simulations were performed in laminar flow regime at constant skin temperature (310 K) and constant air flow temperature (273 K) at a speed of 5 m/s. Some important parameters such as heat flux through the fabrics, heat transfer coefficient, and Nusselt number were evaluated. The results showed that the heat loss from human body (the heat transfer coefficient) was smallest or the thermal insulation of fabric was highest when the fabric had no pores and no contact with the human skin, the heat loss from human body (the heat transfer coefficient) was highest when the fabric had pores and the air flow penetrated through the fabric.

Open access
Air permeability of polyester nonwoven fabrics

Abstract

Air permeability is one of the most important properties of non-woven fabrics in many applications. This paper aims to investigate the effects of thickness, porosity and density on the air permeability of needle-punched non-woven fabrics and compare the experimental values with two models which are based on hydraulic radius theory and drag theory, respectively. The air permeability of the samples was measured by an air permeability tester FX3300. The results showed that the air permeability of non-woven fabrics decreased with the increase in thickness and density of samples, increased with the increase of porosity, and the air permeability was not directly proportional to the pressure gradient. Meanwhile, the prediction model based on hydraulic radius theory had a better agreement with experimental values than the model based on drag theory, but the values were much higher than the experimental results, especially for higher porosity and higher pressure gradient.

Open access
An analysis of effective thermal conductivity of heterogeneous materials

Abstract

Effective thermal conductivity (ETC) is a very important index for evaluating the thermal property of heterogeneous materials, which include more than two different kinds of materials. Several analytical models were proposed for predicting the ETC of heterogeneous materials, but in some cases, these models cannot provide very accurate predictions. In this work, several analytical models and numerical simulations were studied in order to investigate the differences among them. In addition, some factors which would influence the ETC of heterogeneous materials were investigated by numerical simulation. The results demonstrated that the numerical simulation can provide very accurate prediction, indicated that different analytical models should be selected to predict specific problems based on their assumptions, and suggested that more variables need to be considered in order to improve these analytical models, such as inclusion shape, inclusion size, distribution of inclusions and contact area. Besides, numerical method could be an effective and reliable way to obtain the ETC of heterogeneous materials with any kind of complicated structures.

Open access
Investigation Of Sound Absorption Properties Of Bark Cloth Nonwoven Fabric And Composites

Abstract

The quest for sound-absorbing materials that are not only environmentally friendly, but also sustainable is the foremost reason for natural fibre-acoustic materials. Bark cloth is a natural non-woven fabric that is largely produced from Ficus trees. An exploratory investigation of bark cloth a non-woven material and its reinforcement in epoxy polymer composites has been fabricated and investigated for the sound absorption properties so as to find the most suitable applications and also to see whether bark cloth can be used in some applications in place of man-made fibres. Three types of material species were investigated with their respective composites. The fibre morphology showed bark cloth to be a porous fabric that showed promising sound absorption properties at higher frequencies. The sound absorption results of four-layer material selections of Ficus natalensis, Ficus brachypoda and Antiaris toxicaria bark cloth showed sound absorption coefficient of 0.7; 0.71 and 0.91 at f > 6400 Hz, respectively. The bark cloth reinforced laminar epoxy composites had reduced sound absorption coefficients, which ranged from 0.1 to 0.35, which was attributed to decreased porosity and vibration in the bark cloth fibre network.

Open access
Performance of Electrospun Polyvinylidene Fluoride Nanofibrous Membrane in Air Filtration

Abstract

Polyvinylidene fluoride (PVDF) fibrous membranes with fiber diameter from nanoscale to microscale were prepared by electrospinning. The structural parameters of PVDF fibrous membrane in terms of fiber diameter, pore size and its distribution, porosity or packing density, thickness, and areal weight were tested. The relationship between solution concentration and structural parameters of fibrous membrane was analyzed. The filtration performance of PVDF fibrous membrane in terms of air permeability and filtration efficiency was evaluated. The results demonstrated that the higher solution concentration led to a larger fiber diameter and higher areal weight of fibrous membrane. However, no regular change was found in thickness, porosity, or pore size of fibrous membrane under different solution concentrations. The air permeability and filtration efficiency of fibrous membrane had positive correlations with pore size. The experimental results of filtration efficiency were compared with the predicted values from current theoretical models based on single fiber filtration efficiency. However, the predicted values did not have a good agreement with experimental results since the fiber diameter was in nanoscale and the ratio of particle size to fiber diameter was much larger than the value that the theoretical model requires.

Open access