Runoff Estimation for an Ungauged Catchment Using Geomorphological Instantaneous Unit Hydrograph (GIUH) and Copulas

A methodology is proposed to apply Geomorphological Instantaneous Unit Hydrograph to ungauged basins using Monte Carlo Simulations and copulas. The effective rainfall, input of GIUH is assumed to be unknown; it is estimated with infiltration index method (?-index). Correlations are detected between this index and the characteristics of rainfall. They are modeled with copulas, and are used to derive effective rainfall hyetographs. The generated hydrographs from GIUH are analyzed and give statistically the same results: dispersion and variability for all studied characteristics (volume, peak discharge, peak time and base time). However, only these hydrographs derived from ? conditioned to maximum intensity distribution allow reconstituting the observed hydrographs. Moreover comparing the series of order statistics of interest output and observed series, leads to decide on the representative hydrograph of the catchment behavior.     

Dielectric characteristics of polyimide CP2

High-performance aerospace-grade polyimides such as CP2 fulfill many important roles in a wide range of applications. A thorough understanding of the polymer matrix’s physiochemical properties is an important consideration when developing polymer nanocomposite materials. In this work, we report the dielectric properties of polyimide CP2 including the primary and two secondary dipole relaxations, and their thermal characteristics by way of temperature variable impedance spectroscopy (10⁻² to 10⁶ Hz, −40 to 225 °C). Special emphasis has been placed on detailing the characteristic phenomena near CP2′s glass transition (199 °C). The consequences of residual DMAc solvent on CP2′s overall loss and relaxation characteristics are also discussed.     

In situ poling and imidization of amorphous piezoelectric polyimides

An amorphous piezoelectric polyimide containing polar functional groups has been developed using a combination of experimental and molecular modeling for potential use in high temperature applications. This amorphous polyimide, (β-CN)APB/ODPA, has exhibited good thermal stability and piezoelectric response at temperatures up to 150 °C. Density functional calculations predicted that a partially cured amic acid (open imide ring) possesses a dipole moment four times larger than the fully imidized closed ring. In situ poling and imidization of the partially cured (β-CN)APB/ODPA was studied in an attempt to maximize the degree of dipolar orientation and the resultant piezoelectric response. A positive corona poling was used to minimize localized arcing during poling and to allow use of higher poling fields without dielectric breakdown. The dielectric relaxation strength, remanent polarization, and piezoelectric response were evaluated as a function of the poling profile. The partially cured, corona poled polymers exhibited higher dielectric relaxation strength (Δε), remanent polarization (P_r) and piezoelectric strain coefficient (d₃₃) than the fully cured, conventionally poled ones.     

An ellipsometric study of polymer film curing: 2,6-Bis(3-aminophenoxy) benzonitrile/4,4′oxidiphthalic anhydride poly(amic acid)

The curing of 2,6-bis(3-aminophenoxy)benzonitrile/4,4′oxidiphthalic anhydride ((β-CN) APB/ODPA) has been investigated using spectroscopic ellipsometry on films with various degrees of imidization. Results indicate that much of the film imidization is accomplished at 200 °C and above. Three absorption peaks have been observed (4.1, 5, and 6 eV) which correspond to intra- and inter-molecular optical transitions. A comparison of the film optical constants for the pristine poly(amic acid) and the fully cured polyimide shows film densification upon imidization. A curing timeline has been obtained using in situ real-time spectroscopic ellipsometry, and ellipsometry is shown to serve as a general technique for studying organic film curing.     

Characterization of Solution‐Processed Double‐Walled Carbon Nanotube/Poly(vinylidene fluoride) Nanocomposites

Dispersion of CNTs in polymers can yield impressive property enhancements at low volume fractions, thus maintaining the inherent processability of the polymer. In particular, they can improve the electromechanical response of piezoelectric polymers by lowering the actuation voltage and increasing strain and stress response. In this work, piezoelectric PVDF and DWNTs are solution‐cast into films. SEM of fracture surfaces confirms good dispersion, and electrical conductivity measurements reveal a low percolation threshold (0.23 vol.‐%). The effect of CNTs on storage modulus, T_c, T_m and T_g of PVDF is studied. Electromechanical strain is observed at low actuation voltages, possibly due to enhanced local electric field in the presence of DWNTs.

     

Electrospinning of cellulose and SWNT-cellulose nano fibers for smart applications

Recently, electrospinning has attracted a great deal of attention as a means of producing non-woven membranes of nanofibers due to its simple methodology and the promise of nano applications. Despite its simplicity and relative low cost, there still remain a number of challenges associated with this process, such as low fiber production, presence of beads and repeatability issues due to the large number of experimental variables. In this paper, we investigated the use of the Design of Experiments (DOE) method and factorial testing as a means to identify the optimum electrospinning conditions and ensure repeatability of the process. We focused on two polymer solutions as the model systems, namely pure cellulose and cellulose with single wall carbon nanotubes (SWNTs). During the electrospinning experiment, we carefully monitored and adjusted the environmental conditions due to the highly sensitive nature of the solutions. We also adopted various ways of reducing surface tension to promote electrospinning, including convective heating of the solutions. As a first step, through initial screening using the DOE method, we eliminated the experimental variables that were less crucial to the electrospinning process, namely the distance from the needle to the grounded target and the needle size. Next, we demonstrated that three of the variables, i.e., flow rate, applied voltage and temperature, were essential to initiating the electrospinning process and were responsible for controlling the fiber diameter, dimension consistency, and abundance.     

Hybrid QoS based routing protocol for inter and intra wireless mesh infrastructure communications

Quality of service (QoS) in wireless mesh networks is an active area of research, which is driven by the increasing demand for real-time and multimedia applications, such as Voice over IP and Video on Demand. In this paper, we propose a novel QoS based routing protocol for wireless mesh infrastructure, called Hybrid QoS Mesh Routing (HQMR). It is composed of two QoS based routing sub-protocols: a reactive multi-metric routing protocol for intra-infrastructure communications and a proactive multi-tree based routing protocol for communications with external networks. The proposed routing protocol enables forwarding real-time and streaming applications with QoS guarantee in a mesh wireless environment, by assigning a specific routing path for each defined service class. To this end, three different QoS service classes are defined, depending on the applications requirements. We analyze in this paper the simulation results of different scenarios conducted on the network simulator ns-3 to demonstrate the effectiveness of the HQMR protocol and to compare it to other routing protocols while forwarding real-time applications with QoS guarantee.