Spatial and inter-annual variability of specific sediment yield: case of hillside reservoirs in Central Tunisia

Water erosion is the major process responsible for soil loss in Central Tunisia. It represents a main risk of sedimentation which threatens the lifetime of water and soil conservation works in the region, such as hillside reservoirs. This paper focuses on the study of spatial and inter-annual variability of specific sediment yield (SSY) estimated from sediment yield (SY) of 23 small watersheds of hill reservoirs located in the Tunisian Dorsal and the Cap Bon regions. The calculated values of mean inter-annual specific sediment yield varied from 180 to 3298 t/km²/year, over a period of 12 years (from 1994 to 2006). The selected catchments were classified into three groups according to their SSY data. The SSY map, elaborated with a geographical information system (GIS), showed an important spatial variability between watersheds of the same group. Moreover, analyses of the coefficient of variation (CV) showed that 70% of the considered sites demonstrate a tendency to moderate and high inter-annual variability of SSY. In order to identify the principal factors governing variability of erosion and sedimentation, a multiple regression analysis was carried out using nine parameters characterizing morphology, topography, land cover, climate and protection works of the 23 considered sites. The generated model revealed that 85% of SSY variability is correlated to seven principal factors, which are drainage area (A), rainfall intensity recorded in 30 min (I ₃₀), percentage of water and soil conservation works, percentage of clay and carbonate in soils, vegetation land cover, overall slope index (I _G) and rainfall amount (R _a). The obtained SSY results were compared to others cited in a large bibliographical synthesis of studies carried out at the planet scale. We deduced that the SSY values obtained in this study are among the relatively high series in the world. The high variability of specific erosion rates in Central Tunisia is believed to be related to the semi-arid climate, characterized by the irregularity and the severity of storms and the spatial and temporal variability of other multiple factors affecting erosion processes.     

Mechanical characterization of glass/polyimide microjoints fabricated using cw fiber and diode lasers

This paper discusses the laser-irradiated microjoints between glass and polyimide for applications in neural implants. To facilitate bonding between them, a thin titanium film with a thickness of approximately 0.2 μm was deposited on glass wafers using the physical vapor deposition (PVD) process. Two sets of samples were fabricated where the bonds were created using diode and fiber lasers. The samples were subjected to tension using a microtester for bond strength measurements. The failure strengths of the bonds generated using fiber laser are quite consistent, while a wide variation of failure strengths are observed for the bonds generated with diode laser. Few untested samples were sectioned and the microstructures near the bond areas were studied using an optical microscope. The images revealed the presence of a sharp crack in the glass substrate near the bond generated with the diode laser. However, no such crack was observed in the samples made using fiber laser. To investigate the reasons behind such discrepancy in bond quality further, uncoupled three-dimensional finite element analyses (FEA) were conducted only for the samples created using diode laser. First, the transient heat diffusion-based FEA was conducted by using the laser power intensity distribution as a time dependent heat source. This model calculates the temperature distribution within the substrates as a function of time. Next, the structural model predicts the amount of residual stresses developed in the joint system as it is cooled down to room temperature. The out-of-plane normal component of residual stresses was within the failure strength range of glass that may have caused fracture initiation in the substrate.     

Silicon field effect transistors as dual-use sensor-heater hybrids

We demonstrate the temperature mediated applications of a previously proposed novel localized dielectric heating method on the surface of dual purpose silicon field effect transistor (FET) sensor-heaters and perform modeling and characterization of the underlying mechanisms. The FETs are first shown to operate as electrical sensors via sensitivity to changes in pH in ionic fluids. The same devices are then demonstrated as highly localized heaters via investigation of experimental heating profiles and comparison to simulation results. These results offer further insight into the heating mechanism and help determine the spatial resolution of the technique. Two important biosensor platform applications spanning different temperature ranges are then demonstrated: a localized heat-mediated DNA exchange reaction and a method for dense selective functionalization of probe molecules via the heat catalyzed complete desorption and reattachment of chemical functionalization to the transistor surfaces. Our results show that the use of silicon transistors can be extended beyond electrical switching and field-effect sensing to performing localized temperature controlled chemical reactions on the transistor itself.     

Single wire radial junction photovoltaic devices fabricated using aluminum catalyzed silicon nanowires

Single nanowire radial junction solar cell devices were fabricated using Si nanowires synthesized by Al-catalyzed vapor-liquid-solid growth of the p(+) core (Al auto-doping) and thin film deposition of the n(+)-shell at temperatures below 650 °C. Short circuit current densities of 11.7 mA cm(-2) were measured under 1-sun AM1.5G illumination, showing enhanced optical absorption. The power conversion efficiencies were limited to < 1% by the low open circuit voltage and fill factor of the devices, which was attributed to junction shunt leakage promoted by the high p(+)/n(+) doping. This demonstration of a radial junction device represents an important advance in the use of Al-catalyzed Si nanowire growth for low cost photovoltaics.     

橡胶木屑基活性炭—聚氨酯复合材料的制备及其微波吸收性能（英文）

采用ZnCl2对橡胶木屑进行化学活化制备出活性炭。ZnCl2与橡胶木屑的浸渍质量比为1.0-2.0,活化温度为500℃,时间为60min。通过扫描电镜、X射线衍射和BET比表面分析仪探讨浸渍比例对活性炭孔结构的影响。结果表明,当浸渍比为1.5∶1时,样品的比表面积和孔径分别为1301m2/g和0.37cm3/g。通过化学发泡工艺将不同质量分数(1%,2%,3%,5%,8%)的活性炭填充至聚氨酯中制备出聚氨酯复合材料。在1-5GHz频率范围内,复合材料吸收微波。随着活性炭含量增加,在1-3GHz范围内,介电常数(ε’)和回波损耗增加。活性炭含量为8%时复合材料的介电常数达到最大值3.0。在1.8GHz时,复合材料的回波损耗为10dB。在-2.5GHz,电磁屏蔽效率大于3dB。与传统聚合物材料如填加金属的聚氨酯和聚酯相比,所制复合材料呈微波段吸收,可作为电磁屏蔽材料。     

Wireless Body Area Sensor Network Authentication Using Voronoi Diagram of Retinal Vascular Pattern

This paper focuses on the problem of human authentication in Body Area Sensor Network using retina. In this proposed method, Voronoi Diagram (VD), a well known technique in computational geometry, is generated from the topological structure of the bifurcation points, considered as vertices, obtained from the blood vessels found in the retina which can further be used in the process of identification and verification. Since the structure formed by bifurcation points is unique in every retina, hence the calculated VD is also unique and provides the foundation of developing the system of retina based identification. The approach presented in this paper rejects any non-similar retina instantly while maintaining excellent accuracy and performance. Another advantage of using this approach is that it does not require the localization of Optic Disc and the Fovea, which most of the existing algorithms have required, and, experimental results proved that VD is efficient in template matching and storage requirements. Additionally, our proposed algorithm is invariant against any geometric transformation (i.e. scaling, translation and rotation).     

Discrete Element Modeling (DEM) of the Vertically Vibrated Particle Bed

Discreet element modeling (DEM) is a computational tool used for detailed exploration of dynamic particle bed behaviors. One such application is the analysis of finely sized particle mixtures under the influence of external forces such as vertical vibration, which is difficult, if barely at all accessible for detailed experimental analysis. Here, we examined the differential density dynamic particle bed behaviors, by the application of a modified two dimensional DEM-fluid model that incorporates the gravity and fluid effects, to replicate some of the important experimental based observations of segregation, heaping, tilting, high density particles on top and bottom, and partition cell separation. The simulation results compared favorably with the reported literature on the density segregation attributes such as high density particles on top at vertical vibration frequency of 6.3 and 7 Hz with corresponding dimensionless acceleration magnitude of 1.6 and 2, convection currents at vertical vibration frequency of 30, 40, and 30 with corresponding dimensionless acceleration magnitude of 3.5, 4, and 3, layer separation at vertical vibration frequency of 7 Hz with corresponding dimensionless acceleration magnitude 2 and partition cell separation at vertical vibration frequency of 45 Hz and corresponding dimensionless acceleration magnitude of 2.25 for simulated glass and bronze particle mixture properties.     

Architecture level optimization of 3-dimensional tree-based FPGA

We describe a methodology to design and optimize Three-dimensional (3D) Tree-based FPGA by introducing a break-point at particular tree level interconnect to optimize the speed, area, and power consumption. The ability of the design flow to decide a horizontal or vertical network break-point based on design specifications is a defining feature of our design methodology. The vertical partitioning is organized in such a way to balance the placement of logic blocks and switch blocks into multiple tiers while the horizontal partitioning optimizes the interconnect delay by segregating the logic blocks and programmable interconnect resources into multiple tiers to build a 3D stacked Tree-based FPGA. We finally evaluate the effect of Look-Up-Table (LUT) size, cluster size, speed, area and power consumption of the proposed 3D Tree-based FPGA using our home grown experimental flow and show that the horizontal partitioned 3D stacked Tree-based FPGA with LUT and cluster sizes equal to 4 has the best area-delay product to design and manufacture 3D Tree-based FPGA.     

Supporting multimedia applications through network redesign

Recent evolutions in high‐performance computing and high speed broadband Internet access have paved a way to enterprise‐wide multimedia applications, which require stern QoS from the underlying networks. In this paper, we have explored threefold studies on existing enterprise network, whereby we proposed an analytical approach to evaluate the performance of the existing network; we have examined the feasibility of existing enterprise networks to accommodate voice over Internet protocol (VoIP) services with acceptable QoS, and we have redesigned the enterprise network to accommodate VoIP services to comply with the user defined QoS. The network performance is evaluated by number of VoIP calls sustained by the network, bandwidth utilization, loss rate and latency through Network Simulation (NS‐2) tool. We have derived a cost model to show the cost‐effectiveness of VoIP services over telephonic network. For a medium‐size enterprise network of 200 clients and 9 servers, our simulation results show that the redesign improves the network performance by increasing the number of VoIP calls by 57% and decreasing bandwidth utilization and packet loss rate by 20% and 7%, respectively. Moreover, the proposed network redesign demonstrates that the network can be scalable and it can handle up to 4% increased voice calls in the future maintaining QoS standards. Copyright © 2012 John Wiley & Sons, Ltd.     

Miniaturized modified circular patch monopole antenna on ceramic-polytetrafluroethylene composite material substrate

A 0.22λ×0.29λ×0.03λ miniaturized modified circular patch monopole antenna on high permittivity ceramic-Polytetrafluoroethylene (PTFE) composite material substrate is presented. The proposed antenna is designed and investigated using 3D full wave high frequency electromagnetic simulator and fabricated using printed circuit board (PCB) prototyping machine. Impedance bandwidths (Reflection coefficient <?10 dB) of 26.76 % (5.0–6.3 GHz), 5.3 % (9.1–9.6 GHz) and 3.6 % (10.7–11 GHz) have measured. Average gains of 0.9 dBi, 3.68 dBi and 3.63 dBi measured at first, second and third band correspondingly. 87.3 %, 88.5 % and 93.1 % radiation efficiencies have achieved at three resonant frequencies 5.6 GHz, 9.5 GHz and 10.9 GHz respectively. The measured symmetric and nearly consistent radiation pattern makes the proposed antenna suitable for C band and X band applications. In this letter, the effects of dielectric properties of substrate material and design parameters have studied.