On the crescentic shape of barchan dune

Aeolian sand dunes originate from wind flow and sand bed interactions. According to wind properties and sand availability, they can adopt different shapes, ranging from huge motion-less star dunes to small and mobile barchan dunes. The latter are crescentic and emerge under a unidirectional wind, with a low sand supply. Here, a 3d model for barchan based on existing 2d model is proposed. After describing the intrinsic issues of 3d modeling, we show that the deflection of reptating particules due to the shape of the dune leads to a lateral sand flux deflection, which takes the mathematical form of a non-linear diffusive process. This simple and physically meaningful coupling method is used to understand the shape of barchan dunes.Comment: 8 pages, 9 figures, submitted to Eur. Phys. J. B v2 : major changes in grammar and in presentatio

Barchan dune corridors: field characterization and investigation of control parameters

The structure of the barchan field located between Tarfaya and Laayoune (Atlantic Sahara, Morocco) is quantitatively investigated and compared to that in La Pampa de la Joya (Arequipa, Peru). On the basis of field measurements, we show how the volume, the velocity and the output sand flux of a dune can be computed from the value of its body and horn widths. The dune size distribution is obtained from the analysis of aerial photographs. It shows that these fields are in a statistically homogeneous state along the wind direction and present a `corridor' structure in the transverse direction, in which the dunes have a rather well selected size. Investigating the possible external parameters controlling these corridors, we demonstrate that none among topography, granulometry, wind and sand flux is relevant. We finally discuss the dynamical processes at work in these fields (collisions and wind fluctuations), and investigate the way they could regulate the size of the dunes. Furthermore we show that the overall sand flux transported by a dune field is smaller than the maximum transport that could be reached in the absence of dunes, i.e. in saltation over the solid ground.Comment: revised version for JGR-ES, 36 pages, 21 figure

Metode Total Physical Response (TPR) Terhadap Pemahaman Kosakata Anak Tunarungu Kelas Persiapan di TKLB-B

ABSTRACTHearing disturbance caused hearing impairment children had limitedness in speech skill especially in vocabulary. Hearing impairment children functionally and in intelligence cognitive were very less however they were potentially the same as the normal. It meant that vocabulary ability to hearing impairment children could still be developed by guiding as early as possible so that it did not prevent their education and social interaction. The hearing impairment children’s ability in understanding and using the vocabulary could be trained through intervention as early as possible.The problems of hearing impairment children were: poor vocabulary, difficult to understand abstract words, difficult to interpret the implicit words and speech disturbance. The problems caused the language development to hearing impairment children slower compared to the normal. In this way, in developing understanding vocabulary it was more effective to train by teaching language method of Total Physical Response which was special for enhancing understanding vocabulary ability. There for, it required applying Total Physical Response method and the learning steps. The purpose of this research was to know the influence of Total Physical Response method toward understanding vocabulary to preparation class of hearing impairment children in TKLB-B Dharma Wanita Sidoarjo.This research used quantitative and pre experiment kind using “One Group, pretest – posttest design” arrangement. The data collection method used test and the technique of data analysis used statistic non parametric with sign test. The research result indicated that there was score enhancement of understanding vocabulary ability in pretest it was 45,16 to be 78,16 in posttest. Based on the data analysis it indicated that ZH = 2,05 > Z table = 1,96 to 5% significant level (two sides test). So it could be concluded that there was significant influence of Total Physical Response method toward understanding vocabulary to preparation class of hearing impairment children in TKLB-B Dharma Wanita Sidoarjo.Keywords: Total Physical Response method, understanding vocabular

When dunes move together, structure of deserts emerges

Crescent shaped barchan dunes are highly mobile dunes that are usually presented as a prototypical model of sand dunes. Although they have been theoretically shown to be unstable when considered separately, it is well known that they form large assemblies in desert. Collisions of dunes have been proposed as a mechanism to redistribute sand between dunes and prevent the formation of heavily large dunes, resulting in a stabilizing effect in the context of a dense barchan field. Yet, no models are able to explain the spatial structures of dunes observed in deserts. Here, we use an agent-based model with elementary rules of sand redistribution during collisions to access the full dynamics of very large barchan dune fields. Consequently, stationnary, out of equilibrium states emerge. Trigging the dune field density by a sand load/lost ratio, we show that large dune fields exhibit two assymtotic regimes: a dilute regime, where sand dune nucleation is needed to maintain a dune field, and a dense regime, where dune collisions allow to stabilize the whole dune field. In this dense regime, spatial structures form: the dune field is structured in narrow corridors of dunes extending in the wind direction, as observed in dense barchan deserts

A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples

The linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength $\lambda$ at which the bed destabilises to form dunes should scale with the drag length $L_{\rm drag} = \frac{\rho_s}{\rho_f} d$. This scaling law is tested using existing and new measurements performed in water (subaqueous ripples), in air (aeolian dunes and fresh snow dunes), in a high pressure CO$_2$ wind tunnel reproducing conditions close to the Venus atmosphere and in the low pressure CO$_2$ martian atmosphere (martian dunes). A difficulty is to determine the diameter of saltating grains on Mars. A first estimate comes from photographs of aeolian ripples taken by the rovers Opportunity and Spirit, showing grains whose diameters are smaller than on Earth dunes. In addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds. It confirms that the small grains visualised by the rovers should be grains experiencing saltation. Finally, we show that, within error bars, the scaling of $\lambda$ with $L_{\rm drag}$ holds over almost five decades. We conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on Mars.Comment: 27 pages, 10 figures, resubmitted to `Earth and Planetary Science Letters' with addition data and enlarged discussio

Polygons on a Rotating Fluid Surface

We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat. We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate. The slight asymmetry induces a tendency for mode-locking between the plate and the polygon, where the polygon rotates by one corner for each complete rotation of the plate

Decomposition of labor earnings: an analysis between metropolitan regions and non-metropolitan regions in Brazil

This paper aim at examining the dispersion of intra and inter-regional of principal labor earnings of the Metropolitan Regions (MR) and Non-Metropolitan Regions (NMR) of the States of Bahia, Ceará, Minas Gerais, Pará, Paraná, Pernambuco, Rio de Janeiro, Rio Grande do Sul and São Paulo, Brazil. It were applied the Chow structural test and decomposition of Oaxaca, and Heckman procedure. It was used data from the National Research by House Sample at 2006. The theoric approach was based on the Theory of Human Capital and Theory of Segmentation Labor Market. The results indicated that regional aspects and personal attributes of workers contributed for explaining the gap between labor earnings but were not homogeneous among States. Finally in the States that have highest Gross Domestic Product the regional effects were more important factors for explaining the differences for labor earnings among of MR and NMR

3D Dune Skeleton Model as a Coupled Dynamical System of 2D Cross-Sections

To analyze theoretically the stability of the shape and the migration process of transverse dunes and barchans, we propose a {\it skeleton model} of 3D dunes described with coupled dynamics of 2D cross-sections. First, 2D cross-sections of a 3D dune parallel to the wind direction are extracted as elements of a skeleton of the 3D dune, hence, the dynamics of each and interaction between them is considered. This model simply describes the essential dynamics of 3D dunes as a system of coupled ordinary differential equations. Using the model we study the stability of the shape of 3D transversal dunes and their deformation to barchans depending on the amount of available sand in the dune field, sand flow in parallel and perpendicular to wind direction.Comment: 6 pages, 6 figures, lette

Metode Total Physical Response (TPR) Terhadap Pemahaman Kosakata Anak Tunarungu Kelas Persiapan di TKLB-B

ABSTRACTHearing disturbance caused hearing impairment children had limitedness in speech skill especially in vocabulary. Hearing impairment children functionally and in intelligence cognitive were very less however they were potentially the same as the normal. It meant that vocabulary ability to hearing impairment children could still be developed by guiding as early as possible so that it did not prevent their education and social interaction. The hearing impairment children’s ability in understanding and using the vocabulary could be trained through intervention as early as possible.The problems of hearing impairment children were: poor vocabulary, difficult to understand abstract words, difficult to interpret the implicit words and speech disturbance. The problems caused the language development to hearing impairment children slower compared to the normal. In this way, in developing understanding vocabulary it was more effective to train by teaching language method of Total Physical Response which was special for enhancing understanding vocabulary ability. There for, it required applying Total Physical Response method and the learning steps. The purpose of this research was to know the influence of Total Physical Response method toward understanding vocabulary to preparation class of hearing impairment children in TKLB-B Dharma Wanita Sidoarjo.This research used quantitative and pre experiment kind using “One Group, pretest – posttest design” arrangement. The data collection method used test and the technique of data analysis used statistic non parametric with sign test. The research result indicated that there was score enhancement of understanding vocabulary ability in pretest it was 45,16 to be 78,16 in posttest. Based on the data analysis it indicated that ZH = 2,05 > Z table = 1,96 to 5% significant level (two sides test). So it could be concluded that there was significant influence of Total Physical Response method toward understanding vocabulary to preparation class of hearing impairment children in TKLB-B Dharma Wanita Sidoarjo.Keywords: Total Physical Response method, understanding vocabular