Essential oil of Citrus hystrix DC.: A mini-review on chemical composition, extraction method, bioactivities, and potential applications in food and pharmaceuticals

Citrus hystrix DC. is a common herb in tropical regions. Its essential oils are now widely researched and applied because of their high economic value and safety for humans and are interesting materials for future trends. This review provides an extensive overview of the biological activities of C. hystrix essential oil, characterized predominantly by citronellal, ?-Pinene, sabinene, limonene, and terpinene-4-ol, which are deciding factors in antimicrobial, antioxidant, insect repellent, anti-tumor, and anti-inflammatory properties. Therefore, it is applied in the fields of food preservation and pharmaceuticals. However, these applications should consider the ratio of these components in the essential oil, which is variable when using materials from different parts of the plant and depending on the original location of the plant, growth stages, traditional or modern extraction methods, and pre-treatment methods

Fractal properties and characterization of road profiles

International audienceA major problem in road engineering is to understand the mechanisms of friction between rubber and the road. We study road profiles obtained using tactile and laser captors. these profiles belong to different category characterized by different friction coefficients. We find that all our profiles indeed display strong fractal behaviour in terms of both correlation exponents and regularization dimension over a large range of scales. However, neither of these fractal parameters seem to be related to friction. We then use a local fractal parameter, namely the pointwise Holder exponent. We show that this exponent does discriminate profiles which have different friction properties

Effect of particles' characteristics and road surface's texture on the tire/road friction

This paper presents a laboratory study to investigate the lubrication induced by particles deposited on road surfaces which is responsible for the increase of accidents at the first rain after a long dry period. Particles are extracted from sediments collected at a catchment area and characterized by their chemical composition and size distribution. Protocol to simulate the particle deposit on the road surface and their compaction by the traffic is described. The test program includes variables such as particle concentrations, particles' size fractions and surface textures. Dry friction tests are conducted using the Skid Resistance Tester which simulates the sliding friction between a rubber slider and the test surface. Friction is lowered when the surface is covered by particles, compared with a clean surface. Repeated passages of the slider induce an increase of friction coefficient until reaching a stable value. Particles' flows during a friction run are separated into those ejected from the sample, those stored by the surface macrotexture and those that stay on the test surface; this study demonstrated that the friction coefficient is closely related to the quantity of particles available on the test surface. SEM analysis shows on the other hand that these particles are mainly trapped by the surface microtexture. Similar behavior between fine particles and powder in terms of lubrication mechanisms is observed

A Novel Wideband Bandpass Filter using H-shaped DGS

This paper presents a novel compact wide-band bandpass filter (BPF) having good selectivity. It is designed using a dual-plane structure which consists of a parallel-coupled microstrip line on the upper surface and three H-shape defected ground structures (DGS) on the ground plane. By adding three H-shape DGS units on the ground plane, then properly adjusting their dimensions and position, the bandwidth and selectivity of the designed filter can be significantly improved. A compact prototype of wide-band microstrip bandpass filter has been designed, fabricated and measured for the wireless systems applications. The filter exhibits a center frequency at 4.8 GHz, passband from 2.8 GHz to 6.8 GHz with best insertion loss and return loss of 0.8 dB and 40 dB, respectively. The measured results agrees well with the theoretical expectations validating the proposed design

Observations of dry particles behaviour at the tyre/road interface

Previous studies highlighted that friction value measured on real road surface textures covered by particles depends on particle sizes. This paper focuses on identification of particles behaviours at the tyre/road interface in the presence of particles. Identification is made by visual observations through high-speed camera, focus-variation microscopy and Scanning Electron Microscopy on the contaminated surface as scratch analysis on the surface. Two particle types were collected into samples picked next to roads. They are composed of clay and quartz which have different behaviours at the interface and affect the friction. Clay has a lasting effect due to its adhesive behaviour. Quartz has a scratching and rolling behaviour and is quickly ejected to the contact area due to a pinching effect

Fractal properties and characterization of road profiles

International audienceA major problem in road engineering is to understand the mechanisms of friction between rubber and the road. We study road profiles obtained using tactile and laser captors. these profiles belong to different category characterized by different friction coefficients. We find that all our profiles indeed display strong fractal behaviour in terms of both correlation exponents and regularization dimension over a large range of scales. However, neither of these fractal parameters seem to be related to friction. We then use a local fractal parameter, namely the pointwise Holder exponent. We show that this exponent does discriminate profiles which have different friction properties

Multi-layer moving plate method for dynamic analysis of pavement structures subjected to moving loads

This paper presents a new approach, namely multi-layer moving plate method (MMPM), for the dynamic analysis of pavement structures subjected to moving load. The pavement resting on multi-layer foundation is modeled as a two-layer plate connected by a spring-damper system resting on a viscoelastic foundation. This model gives a accurately pavement structure model so that the dynamic responses of the surface slab and the base can be obtained. The governing equations as well as the plate element mass, damping and stiffness matrices are formulated in a convected coordinate with the idea of attaching its origin to the applied point of the moving load. The proposed method simply treats the moving load as ‘stationary’ at the node of the plate to avoid the updating of the location of moving load due to change of contact points on the plate. Numerical examples related to the dynamic analysis of the pavement structure subjected to a moving load are conducted to investigate the effects of various parameters such as concrete slab thickness, base thickness, foundation stiffness and the load’s velocity on dynamic responses of the pavement structure

Lubrication of the tire/road interface by fine particles : Tribological approach

Accidents increase during the first rain after a long dry period. This trend is due to the accumulation of fine particles originated from different sources such as atmosphere, road and tires debris, fuel emissions, etc. These particles accumulate on the road surface during a long dry period and induce a friction loss between the tire and the road surface. In the road field, the tire/road skid resistance on dry conditions is considered satisfactory (considering the road surface as clean) and the loss of skid resistance is attributed to the sole action of water. Thus, there is an unexplored field concerning the particles' effect, alone in dry period and mixed with water in wet period, on the skid resistance. In this paper, we investigate the action of the particles during a dry period using two approaches developed in tribology: the third body approach, particularly the mass analysis inspired from Fillot et al. [1], to understand the particles flows at the tire/road interface; and the dry lubrication theories developed for powders (as molybdenum disulfide MoS2 ) [2] [3] to understand and model the friction.  Experiments are conducted in laboratory to understand and model this phenomenon. Particles are collected, by drying and sieving, from sediments sampled from a catchment area which collects runoff water. Analyses are performed to determine the particles' chemical composition and size distribution. Experimental protocol allows simulating the particles' build up process on the road surface. The specimen surface, representative of a road surface, includes a microtexture scale, representing the asperities of the aggregates, and a macrotexture scale, representing the space between the aggregates. Friction measurements are realized by means of the so-called Skid Resistance Tester Pendulum, widely used in the road field, which simulates the friction between a rubber pad sliding at 3 m/s on the specimen surface. On a surface initially covered with particles, successive friction runs are performed, without resupplying particles between two consecutive runs. Specimen's weight is recorded before and after each friction run. Results show that friction drops significantly, compared to a clean state, when the surface is covered by particles. Successive runs induce an increase of friction coefficient until reaching a stable value which is below that of a clean surface. Three particles' flows are calculated: particles ejected from the contact area between the friction slider and the test surface; particles trapped by the surface microtexture; particles stored by the surface macrotexture. Close relationship was found between the friction coefficient and the flow of particles trapped by the microtexture. Similarities are found, in terms of lubrication mechanisms, between the behavior of studied particles and powder [3].  Discussions allow understanding the relationship between particles' characteristics and Stribeck curves' parameters such as viscosity, lubricant film thickness and pressure. A first attempt of modeling allows to calculate the friction coefficient from the fraction of surface covered by particles. This study has allowed to see the contribution of tribology to the understanding of complex phenomena in the road field such as skid resistance on contaminated road surfaces. Perspectives, especially in terms of study of water and particles mixing, are presented.   [1] Fillot, N., Iordanoff, I., and Berthier, Y. Wear modeling and the third body concept. Wear, 262, 949-957, 2007. [2] Higgs, C.F., Wornyoh, E.Y.A. An in situ mechanism for self-replenishing powder transfer films: Experiments and modeling. Wear, 2008, 264, 131-138. [3] Heshmat, H. Wear reduction systems for coal-fueled diesel engines ? Experimental results and hydrodynamic model of powder lubrication. Wear, 1993, 162-164, 518-528