Anode Distance Research Articles

Influence of terminal electron acceptor availability to the anodic oxidation on the electrogenic activity of microbial fuel cell (MFC)

The electrogenic activity of microbial fuel cell (MFC) with the function of anode placement from the terminal electron acceptor (TEA) was evaluated. Shorter anode distances from TEA showed higher electrogenesis due to the feasibility of higher electron acceptance as well as their discharge towards TEA. Substrate degradation was also higher at shorter anode placements from TEA due to the optimum substrate availability to the anodic biofilm. Bio-electro kinetics showed significant variation in the catalytic currents and exchange current densities with the function of anode placement indicating its role in electron acceptance and their transfer to the cathode. Anode placement of 3cm showed higher electrogenesis (406.38mW/m2) and substrate degradation (63.12%) along with significantly reduced polarization (6.72Ω) and charge transfer resistances compared to other anodic placements. The spacing between electrodes is crucial in accepting electrons as well as their discharge towards TEA which ultimately governs the power generation efficacy.

Groove Resistance Simulation Analysis and Fault Detection of Aluminum Reduction Cell

The power spectrum method of frequency domain is presented in this paper for analyzing the four states of aluminum reduction cell (that is the normal condition, the liquid aluminum fluctuation, the abnormally low polar distance or drop of an anode and the anodic long bud), the characteristics of frequency domain under circumstances of function and malfunction and pointing out that groove resistance simulation analysis provide reliable basis for fault detection of aluminum reduction cell.

Excessive Turbidity Removal from Textile Effluents Using Electrocoagulation Technique

The work was conducted for improving textile effluent quality via turbidity removal by electrocoagulation (EC) using aluminum sacrificial electrode. Effluents were treated at 30 minutes and 30 volts (30min-30V) and 60 minutes and 40 volts (60min-40V) condition in a 1000 ml reactor cell with anode distance of 4 cm. Prior to EC experiment, physico-chemical parameters of effluent were measured and turbidity level was found eight times higher than the Department of Environment (DoE) standard. Turbidity removal ranged from 53 to 96.2% and 58 to 97.5% for condition one and two, respectively. Dissolved oxygen (DO) increased satisfactorily for both conditions. Total operational cost ranged from 62.50 to 70.41 taka/m3 at 30min-30V and 159.57 to 187.7 taka/m3 at 60min-40V. Moreover, sludge formation ranged from 6.73×10-4 to 8.41×10-4 kg in first condition and 1.21×10-3 to 1.5431×10-3 kg in second one. So, EC treatment was very effective and capable of elevating quality of the textile wastewater effluent in terms of turbidity to discharge into inland surface water. During EC operation it was also possible to lessen the total cost in maximum removal by changing the operating condition and 30min-30V was enough to get environmental friendly solution. Results will encourage the industry-owner to treat polluted effluents by EC.Keywords: Textile industry; ETP; Electrocoagulation; Sacrificial Electrode; Turbidity; Operational cost.© 2011 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi:10.3329/jsr.v3i3.7533 J. Sci. Res. 3 (3), 567-578 (2011)

Fabrication of a nanoporous dual‐electrode system for electrochemical redox cycling

AbstractNanoporous electrodes are promising tools for highly sensitive electrochemical detection of molecules by redox cycling. In here, we report on a novel approach for the on‐chip fabrication of nanoporous dual‐electrode systems. The fabrication is based on template assisted dry etching into an electrode–insulator–electrode structure using a nanoporous alumina film as a mask. The mask itself is patterned by directly anodizing an aluminum layer on top of the chip. Homogeneous growth of the alumina nanopores on a wafer scale is achieved by adding a titanium intermediate film between the top electrode and the aluminum substrate as a stopping layer. The resulting electrodes are separated by approximately 100 nm and have pore diameters in the range of 30–50 nm. Thus they are ideally suited for redox cycling experiments based on fast diffusion of molecules between the electrodes. Integrating this process into microfabricated electrode structures promises to yield a stable and sensitive electrochemical sensor platform.magnified image Redox cycling scheme for a nanoporous dual‐electrode system. The close distance of anode and cathode provides a short diffusion path of oxidized and reduced molecules, as depicted by the arrows. The inlet shows a close‐up of the molecules within a pore. Different colours indicate different oxidation states.

Distance-based node activation for geographic transmissions in fading channels

In wireless multi-hop packet radio networks (MPRNs) that employ geographic transmissions, sleep schedules or node activation techniques may be used to power off some nodes to conserve energy. We consider the problem of selecting which nodes should power on to listen to a scheduled transmission when the channel suffers from random fading. We choose the objective of maximizing the expected value of the distance covered in a single transmission between a transmitter and the farthest receiver that successfully receives the packet, under a constraint on the expected number of receivers that turn on. Since there is a tradeoff between the distance of a node from the transmitter and the probability that the node receives the message correctly, we propose to use node-activation based on link-distance (NA-BOLD). We investigate optimal and sub-optimal NA-BOLD schemes and compare their performance with that of schemes that use a constant sleep schedule for every node within some radius of the transmitter. Our results show that the proposed NA-BOLD schemes achieve significantly larger transmission distances than conventional schemes.

Latency-aware and energy efficiency tradeoffs for wireless sensor networks

Latency and energy efficiency are two important parameters to evaluate the Wireless Sensor Networks (WSNs). To reduce delays in the WSN, the sensor node will send out redundant packets. Suppose the WSN has a cell-partitioned structure and the two-hop relay algorithm is adopted, the relay/destination nodes selection will determine the networks performance. The FLS is applied to the nodes selection. In contrast with the cases that only consider one descriptor, the FLS application can manage the delay/energy tradeoffs to meet the network performance requirements. Another work discussed is packets transmission in WSNs. We proposed FLS in the optimisation of SIR threshold selection. Average delay and distance of a node to the source node are selected as antecedents for the FLS. The output of FLS provided adjusting factors for the SIR threshold. Simulation results showed the fuzzy optimisation could achieve a better network efficiency, reduce the average delay and extend the network lifetime.

Efficient field emission from structured gold nanowire cathodes

Regular patch arrays of random gold nanostructures were fabricated by electrochemical deposition of nanowires in ion track-etched templates. During ion irradiation with GeV ions of fluence 10 6 , 10 7 , or 10 8 cm −2 , a shadow mask was used resulting in templates structured with square arrays of 50 μ m holes and 100 or 150 μ m pitch. The Au nanowires grown in the track-etched pores had a length of 7–28 μ m and a diameter of ~300 nm, and were either solitary or clustered after template dissolution. The structured wire ensembles were systematically investigated with scanning electron and field emission scanning microscopy. Field emission with about 90% efficiency was achieved for wide-spaced patch arrays with medium and high number of Au nanowires at 1500 V for 20 μ m anode distance. The current carrying capability of the patches strongly varied between 40 nA and 90 μ A. The corresponding processing effects are correlated to adsorbates and nanostructural changes of the wires which give suitable hints for the optimization of structured Au nanowire cathodes.

Empirical expression for the emission site density of nanotube film emitters

The influence of surface roughness on emission site density (ESD) is investigated fornanotube film emitters. An empirical expression for film emitters, , where B is the intercept in the modified Fowler–Nordheim (FN) plots,ACNT the emission areaof one site, and C related to the work function, is derived from the FN theory and experimentally proved.This expression effectively excludes the influence of electric field strength, being differentfrom the conventional method of counting site numbers from emission patterns. By usingthis equation and emission patterns, variation in ESD, induced by the change incathode–anode distance, is confirmed for film emitters with rough surfaces. This variationis ascribed to the change in screen-effect strength among emission sites. It is also foundthat the smaller gaps produce the higher emission uniformity and site densities forrough-surface film emitters.

Anode Distance Effect on Field Electron Emission from Carbon Nanotubes: A Molecular/Quantum Mechanical Simulation

Field electron emission from single-walled (5,5) carbon nanotubes was simulated with a quantum chemistry method, emphasizing the effect of distance between the anode and apex. The emission probability and the field enhancement factor were obtained for different anode-apex separations with two representative applied macroscopic fields. The quantum chemistry simulation was compared to the classical finite element calculation. It was found that the field enhancement factor was overestimated by about a factor 2 in the classical calculation (for the capped carbon nanotube). The effective work function lowering due to the field penetration into the apex has important contribution to the emission probability. A peculiar decrease of the effective work function with the anode-apex separation was found for the capped carbon nanotube, and its quantum mechanical origin is discussed.

Effect of Cathode–Anode Distance on Field Emission Properties for Carbon Nanotube Film Emitters

The influence of the cathode–anode distance (gap) on field emission (FE) properties is investigated for carbon nanotube film emitters. Any increase in the gap can cause a clear shift in the plot of emission current (I) against applied field (EA) (I–EA curve) to the low field regime, resulting from an increase in the corresponding field enhancement factor (βFN). However, normalization of these I–EA curves through the use of the local field (EL) concept shows that the emission sites are invariant during a change in the gap, although they attain stronger EL at larger gaps. When a modified Fowler–Nordheim plot [ln (I/EA2)–2ln βFN vs 1/EA] is employed, the plots obtained at various gaps provide a unique intercept with the vertical axis, consistent with the experimental data measured at differing gaps.

Field Emission from Modified P-Doped Diamond Surfaces with Different Barrier Heights

In this study, the field emission properties of P-doped diamond with various surface treatments were measured in order to understand the effects of surface treatments on the barrier height. The emission properties were acquired for diamond with C-reconstructed, oxidized, and H-plasma treated surfaces. The voltage drop across the vacuum was estimated for each surface, using threshold voltage–anode distance (V–d) measurement. The estimated electric fields near the diamond surface were 4.95, 26.6, and 54.1 V/µm for the C-reconstructed, oxidized, and H-plasma treated surfaces, respectively. The barrier height ratio of these surfaces derived from their electric fields was 1:3.1:4.9, which agrees with the result derived from Fowler–Nordheim (F–N) plots. Considering the electron affinities of all surfaces and the obtained results, positive electron affinities dominate the field emission properties of the C-reconstructed and oxidized surfaces. An internal barrier due to upward band bending on the H-plasma treated surface limits the field emission properties, even though it has a negative electron affinity. Our results suggest that the emission properties strongly depend on the barrier height, which is modified by surface treatment.

A distributed group mobility adaptive clustering algorithm for mobile ad hoc networks

This paper proposes a distributed group mobility adaptive (DGMA) clustering algorithm for mobile ad hoc networks (MANETs) on the basis of a revised group mobility metric, linear distance based spatial dependency ( LDSD), which is derived from the linear distance of a node’s movement instead of its instantaneous speed and direction. In particular, it is suitable for group mobility pattern where group partitions and mergence are prevalent behaviors of mobile groups. The proposed clustering scheme aims to form more stable clusters by prolonging cluster lifetime and reducing the clustering iterations even in highly dynamic environment. Simulation results show that the performance of the proposed framework is superior to two widely referenced clustering approaches, the Lowest-ID clustering scheme and the mobility based clustering algorithm MOBIC, in terms of average clusterhead lifetime, average resident time, average number of clusterhead changes, and average number of cluster reaffiliations.

Field emission from a selected multiwall carbon nanotube

The electron field emission characteristics of individual multiwalled carbon nanotubeswere investigated by a piezoelectric nanomanipulation system operating inside ascanning electron microscopy chamber. The experimental set-up ensures a preciseevaluation of the geometric parameters (multiwalled carbon nanotube lengthand diameter and anode–cathode separation) of the field emission system. Forseveral multiwalled carbon nanotubes, reproducible and quite stable emissioncurrent behaviour was obtained, with a dependence on the applied voltage welldescribed by a series resistance modified Fowler–Nordheim model. A turn-on field of∼30 V µm−1 and a field enhancement factor of around 100 at a cathode–anode distance of the order of1 µm were evaluated. Finally, the effect of selective electron beam irradiation on the nanotubefield emission capabilities was extensively investigated.

Specific features of wide-aperture glow discharge in helium

The characteristics of wide-aperture discharge in helium have been studied for a cathode diameter of 19.5 cm and a cathode-grid anode distance of 3 cm. It is established that the properties of discharge in this system are substantially different from those of a usual abnormal discharge. The difference is manifested in the bending of current-voltage characteristics, their pronounced dependence on the helium pressure, a nonmonotonic dependence of the electron beam generation efficiency η on the discharge voltage U, and an anomalously high efficiency (η ≈ 100%) in the range of U ≈ 350–1000 V.

Ground Chamber Measurements of the Electromagnetic Emissions from the Hayabusa Ion Engine

DOI: 10.2514/1.19473 Radiated electric field emissions from the prototype model of the ion engine system of the asteroid explorer Hayabusa (MUSES-C) were measured in approximate accordance to MIL-STD-461C. The typical noise level exceeded the narrowband specification at frequencies less than 5 MHz. The microwave discharge neutralizer generates broadband noise and narrowband oscillations that have a fundamental frequency of about 160 kHz and are accompanied by its harmonics up to the fifth. Leakage of 4.25 GHz microwaves for plasma production and its second harmonic were 65 dB and 35 dB above specifications, respectively. The X-band receiver onboard Hayabusa measured the noise from the ion engine system at the uplink frequency of 7.16 GHz through a horn antenna. This susceptibility test showed that the microwave discharge ion thruster is unlikely to interfere with deep space microwave communication. Nomenclature d = neutralizer orifice diameter ID = electron emission current of the neutralizer l = anode distance from the neutralizer _ m = xenon flow rate P� = microwave power for plasma discharge of the neutralizer VD = voltage between the neutralizer and the anode in diode mode operation

Efficient algorithms for computing the best subset regression models for large-scale problems

Several strategies for computing the best subset regression models are proposed. Some of the algorithms are modified versions of existing regression-tree methods, while others are new. The first algorithm selects the best subset models within a given size range. It uses a reduced search space and is found to outperform computationally the existing branch-and-bound algorithm. The properties and computational aspects of the proposed algorithm are discussed in detail. The second new algorithm preorders the variables inside the regression tree. A radius is defined in order to measure the distance of a node from the root of the tree. The algorithm applies the preordering to all nodes which have a smaller distance than a certain radius that is given a priori. An efficient method of preordering the variables is employed. The experimental results indicate that the algorithm performs best when preordering is employed on a radius of between one quarter and one third of the number of variables. The algorithm has been applied with such a radius to tackle large-scale subset-selection problems that are considered to be computationally infeasible by conventional exhaustive-selection methods. A class of new heuristic strategies is also proposed. The most important of these is one that assigns a different tolerance value to each subset model size. This strategy with different kind of tolerances is equivalent to all exhaustive and heuristic subset-selection strategies. In addition the strategy can be used to investigate submodels having noncontiguous size ranges. Its implementation provides a flexible tool for tackling large scale models.

ELECTRIC FIELD ENHANCEMENT FACTORS AROUND A METALLIC, END-CAPPED CYLINDER

We have calculated the electric field enhancement factor for a metallic cylinder with a hemispherical end-cap in a plane capacitor geometry paying particular attention to the dependence of the field enhancement factor on the anode distance. In addition, we have investigated the angular dependence of the local field at the end-cap. The numerical results, which cover a range of different ratios of cylinder lengths and anode distances, can be fitted with simple functional expressions which provide a useful scaling for calculations of field emission currents from closed cap carbon nanotubes or nanowires.

Factors affecting the characteristics and propagation of voltage gradient fields from electric fishing anodes

Abstract The relationship between applied anode voltage, ring anode diameter and distance to specific voltage gradient values was modelled from empirical measurements. The model allowed distance to specific voltage gradients to be predicted. Varying the anode to cathode resistance ratios had a significant effect on the electrical potential of the anode and thus the voltage gradient projected from it. The voltage gradient profile of twin anodes was reduced when they were held in close proximity (<5 m).

Low-temperature field emission system for development of ultracoherent electron beams

Here, we present the design and test-operation performance of a low-temperature field emission (FE) system which can be employed to image and characterize the FE beam from low-temperature tips. Three radiation shields cooled by liquid helium and liquid nitrogen cryostats surround the FE tips and anodes completely. Once the FE system is cooled down to 5 K, experiments can run for more than 15 h without interruption. The design allows not only for the exchange of tips and anodes by load-lock equipment but also for the adjustment of tip–anode distance using a piezo-tube. Test runs in projection microscopy mode have presented clear diffraction-fringe patterns near the shadows of nano objects at temperatures from room temperature to 5.5 K, indicating that the system is well suited for the investigation of the coherence of electron beam from FE tip.

An electromagnetically focused electron beam line source

A directly heated thermionic electron beam source was constructed. A tungsten wire of length 140 mm with diameter 0.9 mm was used as a cathode. An emission current of 5000 mA was achieved at an input heating power of 600 W. Cathode to anode distance of 6 mm with acceleration voltage of 10 kV was used. A uniform external magnetic field of 50 G was employed to obtain a well-focused electron beam at a deflection of 180°, with cathode to work site distance of 130 mm. Dimensions of the beam (1.25×120 mm) recorded at the work site were found to be in good agreement with the designed length of cathode. The deformation of the cathode was overcome by introducing a spring action mechanism, which gives uniform emission current density throughout the emission surface. We have achieved the saturation limit of the designed source resulting in smooth and swift operation of the gun for many hours (10–15 h continuously). The design of gun is so simple that it can accommodate longer cathodes for obtaining higher emission values. This gun has made it possible to coat large substrate surfaces at much faster evaporation rate at lower cost. It can also be useful in large-scale vacuum metallurgy plants for melting, welding and heat treatment.