Triboelectrification of wood with PTFE

Triboelectrification for a rolling contact between hardwood and softwood spheres and a polytetrafluoroethylene (PTFE) plane is studied. For a variety of experimental parameters, the saturation charge developed on the spheres was measured. The results are compared with those reported previously where PTFE spheres were rolled on wood planes. The observations suggest that different principles are involved in the two experimental situations; however, in both cases the saturation charge developed depends on the apparent area of contact.     

Triboelectrification of materials used in tape heads

Triboelectrification of tapes by read/write heads can result in either increased error rates or permanent damage to the heads through electrostatic discharge (ESD) or electrochemical processes. In order to understand these phenomena, we have studied triboelectrification between tapes and different tape head materials used in magnetic tape storage drives. The triboelectrification phenomenon can be modeled as a Thevenin equivalent battery or current source whose magnitude is highly dependent not only on materials, but also on physical parameters such as tape speed, wrap angle, the direction of tape over asymmetric multi-material substrates, and the complete electrical circuit. In this report, we will discuss the different physical parameters that affect the tribocharging of tape by different tape and head materials. We also show that tribocharging can cause ESD damage.     

Laser ablation of multilayers of ink from a paper substrate for tactile printing

This paper reports the effects of laser ablation upon multiple-layered coloured inks which have been printed on an ordinary white paper. The aim of this work is to examine the feasibility of generating a fully tactile three-coloured image by selectively removing ink layers to reveal underlying layers of a different colour. In this paper laser ablation has been carried out upon four layered ink samples consisting of white/cyan/white/black layers. Ablation was carried out using a Q-switched Nd : YAG laser. The results show that it is possible to selectively remove the inks to expose both the top white and the cyan layers, although charring occurs with deeper ablation. An evaporation/decomposition mechanism is proposed to describe process of ink ablation.     

Triboelectrification and razorbacks: geophysical patterns produced in dry grains

Electrostatic interactions between particles can dramatically affect granular flows, creating industrial safety and handling problems [K. N. Palmer, (Chapman and Hall, London, 1973), pp. 388-389]. We present experimental data demonstrating that charging of grains can also cause spontaneous self-assembly that may generate lasting geological patterns under arid conditions. Paradoxically, we find that grains that tribocharge enough to produce small explosions, ejecting grains meters into the air, leave little net charge on grains. Rather, grains charge into strongly heterogeneous polar clusters. These assemble into stereotyped residual structures that resemble geological features, for example, razorbacks observed on Mars ["The Razorback Mystery," July 16, 2004, http://www.jpl.nasa.gov/missions/mer/images.cfm?id=701].     

Enhancement of fMAX of InP-based HEMTs by double-recessed offset gate process

A double-recessed offset gate process technology for InP-based high electron mobility transistors (HEMTs) has been developed in this paper. Single-recessed and double-recessed HEMTs with different gate offsets have been fabricated and characterized. Compared with single-recessed devices, the maximum drain-source current (I_D,max) and maximum extrinsic transconductance (g_m,max) of double-recessed devices decreased due to the increase in series resistances. However, in terms of RF performance, double-recessed HEMTs achieved higher maximum oscillation frequency (f_MAX) by reducing drain output conductance (g_ds) and drain to gate capacitance (C_gd). In addition, further improvement of f_MAX was observed by adjusting the gate offset of double-recessed devices. This can be explained by suppressing the ratio of C_gd to source to gate capacitance (C_gs) by extending drain-side recess length (L_rd). Compared with the single-recessed HEMTs, the f_MAX of double-recessed offset gate HEMTs was increased by about 20%.     

TiO2-based superhydrophobic-superhydrophilic patterns: Fabrication via an ink-jet technique and application in offset printing

A superhydrophobic-superhydrophilic pattern was prepared on an anodized Al plate by a new fabrication process. The process consists of five key steps: (1) TiO₂ coating of the plate, (2) surface modification with self-assembled monolayers (SAMs), (3) formation of aqueous UV light-resistant ink patterns by an ink-jet technique, (4) photocatalytic decomposition of SAMs and surface conversion to the superhydrophilic state and (5) removal of the aqueous ink patterns by water washing. It is particularly noteworthy that the wettability pattern can be quickly formed on the plate, without the use of a photomask. The fabricated superhydrophobic-superhydrophilic pattern is shown to be applicable to offset printing.     

Triboelectrification of pharmaceutically relevant powders during low-shear tumble blending

A test apparatus and methods used to study the influence of physical properties of pharmaceutically relevant powders and powder mixtures on triboelectric behavior during low-shear blending is described. Samples were mixed using a stainless steel blender and dispensed directly into a Faraday pail to measure charge. Eight different materials commonly used in pharmaceutical solid dosage formulation were characterized. Particle size and known concentrations of discrete particle size distributions were shown to influence the measured surface charge densities consistent with previously reported results. Further, binary mixtures of the model compounds were studied and found to produce unanticipated trends in surface charge density. The effectiveness of process parameters, including hold time after processing, and formulation design in controlling the surface charge density in particulate systems is also discussed with supporting results obtained from the proposed apparatus.     

Temperature effect on an ultrasound-assisted paper de-inking process

The influence of temperature on an ultrasound-assisted ink removal process has been investigated. White copy paper was evenly soaked in black writing ink. After drying the paper to constant weight at 75 °C, ink removal was attempted under varying conditions. Results were assessed by monitoring the UV–vis absorbance of the aqueous phase and measuring the brightness of the paper. Sonication was observed to improve the brightness of the paper in the temperature range of 15–45 °C with an optimum effect at 35 °C. Monitoring UV–vis spectra of the aqueous phase provided evidence that modification of the chemical structure of the ink desorbed from the paper occured. Further investigation under the same conditions showed that ink, when not absorbed on paper, did not undergo the same chemical change. This supports the hypothesis that only the compound released from the ink absorbed onto the paper is sensitive to sonodegradation. One possible explanation is that the metal binding component of the ink stays absorbed on the paper, releasing the organic part, whose chemical structure can be altered by the effect of sonication. Inductively coupled plasma analysis was used to confirm that during the de-inking process of the paper, the metal binding component stays absorbed on the paper and only the organic part is released in the aqueous phase.     

Application of (super)cavitation for the recycling of process waters in paper producing industry

In paper production industry, microbial contaminations of process waters are common and can cause damage to paper products and equipment as well as the occurrence of pathogens in the end products. Chlorine omission has led to the usage of costly reagents and products of lower mechanical quality. In this study, we have tested a rotation generator equipped with two sets of rotor and stator assemblies to generate developed cavitation (unsteady cloud shedding with pressure pulsations) or supercavitation (a steady cavity in chocked cavitation conditions) for the destruction of a persistent bacteria Bacillus subtilis. Our results showed that only supercavitation was effective and was further employed for the treatment of waters isolated from an enclosed water recycle system in a paper producing plant. The water quality was monitored and assessed according to the chemical (COD, redox potential and dissolved oxygen), physical (settleable solids, insolubles and colour intensity) and biological methods (yeasts, aerobic and anaerobic bacteria, bacterial spores and moulds). After one hour of treatment, a strong 4 logs reduction was achieved for the anaerobic sulphate reducing bacteria and for the yeasts; a 3 logs reduction for the aerobic bacteria; and a 1.3 logs reduction for the heat resistant bacterial spores. A 22% reduction in COD and an increase in the redox potential (37%) were observed. Sediments were reduced by 50% and the insoluble particles by 67%. For bacterial destruction in real industrial process waters, the rotation generator of supercavitation spent 4 times less electrical energy in comparison to the previously published cavitation treatments inside the Venturi constriction design.     

Triboelectrification of houseflies (Musca domestica L.) walking on synthetic dielectric surfaces

Houseflies (Musca domestica L.) have been found to accumulate significant electrostatic charges when walking on uncharged dielectric surfaces. The number of steps taken was found to determine the amount of charge transferred whereas time, on its own, did not play a significant role. After walking only a short distance, typically 30 cm, flies reached saturation charge. The level of this varied according to the position of the surface in the triboelectric series relative to the fly. The rate of charging (pC/footstep) was directly proportional to the difference between the fly's charge and its saturation charge, hence the initial rate of charging for an uncharged fly was directly proportional to the saturation charge. A model has been fitted to the relationship between distance travelled (and hence the number of steps taken) with charge. The reciprocal charge left on the surface has been visualised using photocopier toner.     

Triboelectrification of granular insulating materials as affected by dielectric barrier discharge (DBD) treatment

The aim of this paper is to point out the influence of dielectric barrier discharge treatment on tribocharging of granular insulating materials. Particles of Polyvinyl Chloride (PVC) and Polypropylene (PP) were subjected to an AC dielectric barrier discharge (DBD) plasma treatment in ambient airprior to tribocharging in a vibratory device. The charge to mass ratio was measured for treated and untreated materials. Electrostatic separation of a mixture of granular materials (PVC and PP) to measure the effectiveness of DBD treatment was evaluated by processing treated and untreated PVC/PP granular mixtures in a free-fall electrostatic separator. The obtained results clearly indicate that DBD has the capability to influence surface charging proprieties of polymer granular materials. In case of short treatment time, typically less than 3 s, a marked increase in the charge to mass ratios was observed for both PVC (about 35%) and PP (roughly 45%). In the same way, the quantity of DBD-treated materials, recovered after electrostatic separation, was increased by about 104% and 30% for PVC and PP, respectively, as compared to untreated case. The DBD treatment time is a key factor to increase the tribo electric effect.     

Calculation of band offset in chalcopyrite system

A recently reformulated tight binding method is used to calculate valence band offset (VBO) at the CuInSe₂/CuGaSe₂ heterojunction. The hybrid energy is calculated in the s²p² configuration and a new model for the average hybrid energy is used. The theoretical VBO value of 0.05 eV is in good agreement with recent experimental value of 0.04 eV. The value of conduction band offset is 0.60 eV giving a type I alignment. The VBO varies linearly with bond length difference (l), as VBO=(0.24)l.     

Carrier-envelope offset dynamics of mode-locked lasers

We investigate coupling mechanisms between the amplitude and the carrier-envelope offset phase in mode-locked lasers. We find that nonlinear beam steering in combination with the intracavity prism compressor is the predominant mechanism that causes amplitude-to-phase conversion in our laser. A second mechanism, induced by self-steepening, is also identified. These mechanisms are important for stabilizing the carrier-envelope offset phase and also explain the extremely low pulse-to-pulse energy fluctuations observed in some lasers with carrier-envelope lock. The coupling mechanisms described have important implications for applications of few-cycle optical pulses.     

Optimization of offset frequency in the SORC pulse sequence using feedback.

The low signal-to-noise ratio (SNR) of nuclear quadrupolar resonance measurements has motivated research on signal enhancement methods, including multipulse sequences that facilitate signal averaging, the development of interlaced pulse sequences, and super-Q coils. More recently, it has been shown that feedback can be used to automatically optimize pulse sequence parameters, maximizing the SNR. This paper extends this work by using feedback to optimize the offset frequency in the strong off-resonant comb pulse sequence. Analysis and results are presented for a sample of sodium nitrite at both liquid nitrogen and room temperatures.     

Jet offset, harmonic content, and warble in the flute

The effects of jet offset in the flute, directing the jet above or below the edge, were explored by two distinct means-experiments with a Boehm flute sounded by an artificial blower, and time domain simulation. Very large changes in harmonic content and dynamics were observed, changing greatly with blowing pressure. Warble, a modulation of the tone at frequencies of the order of 20 Hz, was observed both in the experiment and in the simulation. The phenomenon is explained as a beat between the frequency of a second harmonic generated by nonlinearity in the jet current and a neighboring partial sustained by jet feedback near the second mode resonance. A second type of warble, in which amplitude modulation occurs in all partials but with different phases, is yet to be explained.     

Three-dimensional printing of conducting polymer microstructures into transparent polymer sheet: Relationship between process resolution and illumination conditions

Three-dimensional (3D) polypyrrole microstructures were successfully obtained in a transparent polymer sheet by 3D scanning of the laser focal point. The lateral process resolution of the microstructures was studied under different photofabrication conditions such as the repetition rate of the femtosecond pulse laser and the waiting time of the laser focal point scanning. As a result, a very small line width of the polypyrrole deposition of less than 500 nm was realized with good reproducibility.     

Passive signal enhancement in spatially offset Raman spectroscopy

We demonstrate experimentally, for the first time, the feasibility of enhancing signals in Spatially Offset Raman Spectroscopy (SORS) using a dielectric bandpass filter, building on our earlier experimental work on the enhancement of transmission Raman signals. The method is shown to lead to the enhancement of both the surface and subsurface Raman layer signal improving the signal‐to‐noise ratio of Raman spectra from the deep areas of samples, thus enhancing the technique's sensitivity and penetration depth. The filter is placed over the laser illumination zone, on the sample surface acting as a ‘unidirectional’ mirror transmitting the collimated laser beam on one side and reflecting photons escaping from the sample back into it. This enhances the degree of coupling of laser radiation into the medium and associated generated Raman signal. The feasibility study was performed on a two‐layer sample with the second layer located at the limit of the penetration depth of the method for this sample. The sample consisted of a 2.2‐mm over‐layer of a thinned paracetamol tablet followed by a 2‐mm layer of trans‐stilbene powder. The Raman signal was collected from a spatially offset region through a hole fabricated within the filter. The experiments demonstrate the presence of an enhancement of the Raman signal from both the layers by a factor of 4.4–4.5 and the improved signal‐to‐noise ratio of sublayer signal by a factor of 2.2, in agreement with photon shot noise dominated signal. Copyright © 2008 John Wiley & Sons, Ltd.     

Correlated dynamics in human printing behavior

Arrival times of requests to print in a student laboratory were analyzed. Inter-arrival times between subsequent requests follow a universal scaling law relating time intervals and the size of the request, indicating a scale invariant dynamics with respect to the size. The cumulative distribution of file sizes is well-described by a modified power-law often seen in non-equilibrium critical systems. For each user, waiting times between their individual requests show long range dependence and are broadly distributed from seconds to weeks. All results are incompatible with Poisson models, and may provide evidence of critical dynamics associated with voluntary thought processes in the brain.     

Bandwidth-independent linear method for detection of the carrier-envelope offset phase

We propose and demonstrate a novel linear procedure for measurement of the carrier-envelope offset (CEO) phase of femtosecond oscillators. The technique is based on a Mach-Zehnder interferometer, a ring resonator, and a spectrograph. In this scheme, interference between subsequent pulses from a pulse train may frustrate the interference between identical pulses in the Mach-Zehnder, resulting in a modification of interference contrast depending on the CEO phase. We suggest spectrally and spatially resolved interferometry for robust detection of the fringe visibility. It is shown by numerical simulations and experimentally demonstrated that the visibility of such fringes uniquely depends on the CEO phase of the pulse train. Since the method relies only on linear interactions and does not require any nonlinear conversion, it allows characterizing the CEO frequency of mode-locked oscillators with virtually arbitrarily low bandwidth and power levels.