Short Filter Research Articles

UV Enhanced Oxygen Response Resistance Ratio of ZnO Prepared by Thermally Oxidized Zn on Sapphire Substrate

ZnO thin film was fabricated by thermally oxidized Zn at 600°C for 1 h. A surface containing nanostructured dumbbell and lines was observed by scanning electron microscope (SEM). The ZnO resistor device was formed after the following Ti/Au metallization. The device resistance was characterized at different oxygen pressure environment in the dark and under ultraviolet (UV) light illumination coming from the mercury lamp with a short pass filter. The resistance increases with the increase of oxygen pressure. The resistance decreases and response increases with the increase of light intensity. Models considering the barrier height variation caused by the adsorbed oxygen related species were used to explain these results. The UV light illumination technology shows an effective method to enhance the detection response for this ZnO resistor oxygen sensor.

Low-cost multi-stage filtration enhanced by coagulation-flocculation in upflow gravel filtration

Abstract. This paper assesses the operational and design aspects of coagulation and flocculation in upflow gravel filters (CF-UGF) in a multi-stage filtration (MSF) plant. This study shows that CF-UGF units improve the performance of MSF considerably, when the system operates with turbidity above 30 NTU. It strongly reduces the load of particulate material before the water enters in the slow sand filters (SSF) and therewith avoids short filter runs and prevents early interruption in SSF operations. The removal efficiency of turbidity in the CF-UGF with coagulant was between 85 and 96%, whereas the average efficiency without coagulant dosing was 46% (range: 21–76%). Operating with coagulant also improves the removal efficiency for total coliforms, E-coli and HPC. No reduction was observed in the microbial activity of the SSF, no obstruction of the SSF bed was demonstrated and SSF runs were maintained between 50 and 70 days for a maximum head loss of 0.70 m. The most important advantage is the flexibility of the system to operate with and without coagulant according to the influent turbidity. It was only necessary for 20% of the time to operate with the coagulant. The CF-UGF unit represented 7% of total construction costs and the O&M cost for the use of coagulant represented only 0.3%.

Nonparametric Identification of Glucose-Insulin Process in IDDM Patient with Multi-meal Disturbance

Modern close loop control for blood glucose level in a diabetic patient necessarily uses an explicit model of the process. A fixed parameter full order or reduced order model does not characterize the inter-patient and intra-patient parameter variability. This paper deals with a frequency domain nonparametric identification of the nonlinear glucose-insulin process in an insulin dependent diabetes mellitus patient that captures the process dynamics in presence of uncertainties and parameter variations. An online frequency domain kernel estimation method has been proposed that uses the input–output data from the 19th order first principle model of the patient in intravenous route. Volterra equations up to second order kernels with extended input vector for a Hammerstein model are solved online by adaptive recursive least square (ARLS) algorithm. The frequency domain kernels are estimated using the harmonic excitation input data sequence from the virtual patient model. A short filter memory length of M = 2 was found sufficient to yield acceptable accuracy with lesser computation time. The nonparametric models are useful for closed loop control, where the frequency domain kernels can be directly used as the transfer function. The validation results show good fit both in frequency and time domain responses with nominal patient as well as with parameter variations.

Stereophonic hands-free communication system based on microphone array fixed beamforming: real-time implementation and evaluation

Abstract In this article, the authors propose an optimally designed fixed beamformer (BF) for stereophonic acoustic echo cancelation (SAEC) in real hands-free communication applications. Several contributions related to the combination of beamforming and echo cancelation have appeared in the literature so far, but, up to the authors’ knowledge, the idea of using optimal fixed BFs in a real-time SAEC system both for echo reduction and stereophonic audio rendering is first addressed in this contribution. The employment of such designed BFs allows positively addressing both issues, as the several simulated and real tests seem to confirm. In particular, the stereo-recording quality attainable through the proposed approach has been preliminarily evaluated by means of subjective listening tests. Moreover, the overall system robustness against microphone array imperfections and noise presence has been experimentally evaluated. This allowed the authors to implement a real hands-free communication system in which the usage of the proposed beamforming technique has proven its superiority with respect to the usual two-microphone one in terms of echo reduction, and guaranteeing a comparable spatial image. Moreover, the proposed framework requires a low computational cost increment with regard to the baseline approach, since only few extra filtering operations with short filters need to be executed. Nevertheless, according to the performed simulations, the BF-based SAEC configuration seems to not require the signal decorrelation module, resulting in an overall computational saving.

Identification of sparse impulse responses – design and implementation using the partial Haar block wavelet transform

This paper proposes an implementation for identifying sparse impulse responses. The new scheme follows the approach in which the location of the channel response peak is estimated in the wavelet domain. A short time-domain adaptive filter is then located about the estimated peak to identify the sparse response. The primary purpose of this paper is to present an efficient design of such a system. The use of a new block wavelet transform results in up to 70% less computational complexity and improved peak detection, as compared to previous solutions. A new robust time-domain adaptive filtering location and update scheme is also proposed that significantly reduces the occurrence of jitter problems and leads to improved residual mean-square error performance. The behavior of the transform-domain adaptive filter is analyzed, the Wiener solution is determined, and an accurate analytical model is obtained for the mean-square deviation of the adaptive coefficients. Monte Carlo simulations show excellent echo cancellation performance for typical ITU-T echo channels.

Reverse saturation current density imaging of highly doped regions in silicon: A photoluminescence approach

We present a camera-based technique for the local determination of reverse saturation current densities J0 of highly doped regions in silicon wafers utilizing photoconductance calibrated photoluminescence imaging (PC-PLI). We apply this approach to 12.5×12.5cm² float zone silicon samples with textured surfaces and a homogeneous phosphorous diffusion with sheet resistances between 24 and 230Ω/□. We find enhanced photoluminescence emission at metallized regions of a sample due to reflection of long-wavelength light at the rear side of the sample. Our measurement setup comprises an optical short pass filter in front of the camera effectively blocking wavelengths above 970nm and therefore ensuring a correct calibration of the PL signal in terms of excess charge carrier density Δn. We analyze two sets of samples comprising metal contacts to highly doped regions prepared by Laser Transfer Doping (LTD) as well as standard tube furnace phosphorus diffusion. We find a considerably smaller J0 value of 370fA/cm² for the LTD approach compared to a standard diffusion process resulting in J0=570fA/cm². On the basis of these results we demonstrate that J0 imaging is a powerful analysis technique for process optimization.

Iron removal using adsorptive filtration treatment for low iron concentration water from urban industrial region

Iron in urban runoff water from urban industrial regions is undesirable because of aesthetic and operational reasons. Generally iron is removed by chemical treatment processes. However, these systems have a limitation for water recycled as drinking water resources (∠0.3 mg/L). Conventionally, low iron concentration (0.3 mg/L–6 mg/L) in runoff is treated by the process of aeration followed by filtration in water treatment. The shortcomings of this process include short filter runs due to fouling by large volumes of sludge production and elevated headloss. Iron (II) is present in surface runoff in the urban industrial region and roadway, and can be removed by the adsorptive filtration or the conventional floc filtration process. The adsorptive filtration process has several potential advantages such as longer run, shorter ripening time, low sludge production and cost saving. In this study, the adsorptive filtration process shows better performance than the floc filtration. The use of the adsorptive filtration process is a feasible strategy to reduce the filter ripening time and sludge production with high iron (II) adsorption capacity. Also, this method can apply for treatment of discharging surface runoff and can be used as an alternative water resource through a decentralized system or best management practices (BMPs).

Pyramid Vector Quantization of Video Subband With Dithering

This paper describes the development of a low complexity and fixed–rate video compression scheme based on three–dimensional subband coding of video signals. The video codec first performs three–dimensional subband decomposition on a group of video frames, and then encode high frequency subbands with pyramid vector quantization and lowest tempo–spatial band with a DPCM coding in time and space. To improve the visual quality of reconstructed video, different types of subtractive and non–subtractive dithering of pyramid vector quantizers were experimented and its effectiveness was proved by a standard pair comparison subjective test. Coder complexity was reduced by using longer filters in the first level of spatial decomposition for better selectivity and coding gain and shorter filter in the second level of decomposition for lower complexity. Results at different low bit–rate (64, 128 and 384 Kbps) for several standard video sequences are reported and compared with ITU standard H.263.

OFDM/OQAM modulation for efficient dynamic spectrum access

The cognitive radio idea consists in the exploitation of spectral resources that are unused by a licensed user within a telecommunication standard. After having detected these available frequency bands by some sensing technique, our work takes a stand on the spectrum access problem. This issue requires some constraints on the modulation that must be taken into account. The flexibility in frequency offered by a multicarrier modulation (MCM) then represents a strong advantage which, in addition, can be fully exploited by the OFDM/OQAM modulation. Indeed, the fact that well localised frequency pulse shapes can be employed makes this modulation attractive for an optimised dynamic spectrum insertion. OFDM/OQAM and OFDM-based solutions are finally tested considering two different transmission scenarios. In both scenarios, it is shown that, for OFDM/OQAM, the time-frequency localisation criterion leads to a short prototype filter, satisfying a good compromise in terms of complexity/performance and also leads at the same time to a better peak-to-average power ratio (PAPR) distribution when compared to an analogue windowed OFDM scheme.

Roughing filtration as an effective pre-treatment system for high turbidity water

Effective water treatment is the prime goal of every water treatment facility. Chakwal Water Treatment Plant in Pakistan has been treating high-turbidity surface water through crude coagulation, sedimentation and slow sand filtration since the early 1980s. The process has always been tedious in terms of high coagulant dosage, large volumes of sludge and short filter runs especially after wet spells. A laboratory-scale study was conducted to see if roughing filtration, as the pre-treatment process, would help in reducing coagulant dose and sludge volume and improving effluent quality. Results indicated that up-flow rouging filtration with media grades decreasing in the direction of flow could reduce wet weather raw water turbidity (by more than 90%) and coagulant dose. Overall, the plant could save over US $54,000 annually in terms of coagulant cost only. Longer filter runs, improved product water quality leading to lower chlorine dose requirement, would be additional benefits.

Counting Ion and Water Molecules in a Streaming File through the Open-Filter Structure of the K Channel

The mechanisms underlying the selective permeation of ions through channel molecules are a fundamental issue related to understanding how neurons exert their functions. The "knock-on" mechanism, in which multiple ions in the selectivity filter are hit by an incoming ion, is one of the leading concepts. This mechanism has been supported by crystallographic studies that demonstrated ion distribution in the structure of the Streptomyces lividans (KcsA) potassium channel. These still pictures under equilibrium conditions, however, do not provide a snapshot of the actual, ongoing permeation processes. To understand the dynamics of permeation, we determined the ratio of the ion and water flow [the water-ion coupling ratio (CR(w-i))] through the KcsA channel by measuring the streaming potential (V(stream)) electrophysiologically. The V(stream) value was converted to the CR(w-i) value, which reveals how individual ion and water molecules are queued in the narrow and short filter during permeation. At high K(+) concentrations, the CR(w-i) value was 1.0, indicating that turnover between the alternating ion and water arrays occurs in a single-file manner. At low K(+), the CR(w-i) value was increased to a point over 2.2, suggesting that the filter contained mostly one ion at a time. These average behaviors of permeation were kinetically analyzed for a more detailed understanding of the permeation process. Here, we envisioned the permeation as queues of ion and water molecules and sequential transitions between different patterns of arrays. Under physiological conditions, we predicted that the knock-on mechanism may not be predominant.

Signal Codes: Convolutional Lattice Codes

The coded modulation scheme proposed in this paper has a simple construction: an integer sequence, representing the information, is convolved with a fixed, continuous-valued, finite impulse response (FIR) filter to generate the codeword - a lattice point. Due to power constraints, the code construction includes a shaping mechanism inspired by precoding techniques such as the Tomlinson-Harashima filter. We naturally term these codes “convolutional lattice codes” or alternatively “signal codes” due to the signal processing interpretation of the code construction. Surprisingly, properly chosen short FIR filters can generate good codes with large minimal distance. Decoding can be done efficiently by sequential decoding or for better performance by bidirectional sequential decoding. Error analysis and simulation results indicate that for the additive white Gaussian noise (AWGN) channel, convolutional lattice codes with computationally reasonable decoders can achieve low error rate close to the channel capacity.

A Two-Stage Method for the Design of Near-Field Broadband Beamformer

In this paper, the design of near-field broadband beamformer is considered. The idea is to design the beamformer filter coefficients such that the error between the actual response and the desired response is minimized. This problem can be formulated as a minimax optimization problem and can be transformed into a linear semi-definite programming problem. Interior point algorithm can then be applied after discretization. However, if the dimension of the problem is high, the number of discrete points of the specified region and consequently the dimension of the resultant constraint matrix is high. This high dimension provides a difficulty when directly employing interior point algorithm. Since it results in a large size problem, this problem is considered in this paper. To reduce the computational complexity and memory usage, a two-stage method has been proposed. In the first stage, by using an infinite length filter formulation, an infinite length limit for the original problem is obtained. Then, based on that limit, a reduced problem with a finite filter length is found. The computational complexity of this method is derived. It provides a significant reduction compared to a direct solution of the original problem. It is shown that as the filter length increases, the approximative problem comes close to the optimal infinite solution. Furthermore, we demonstrate with examples the close correspondence between proposed design and optimal design. Also the superiority of the suggested method is illustrated in a three-dimensional beamformer design, where the direct method can only design broadband beamformer of very short filter lengths.

Generic Feasibility of Perfect Reconstruction With Short FIR Filters in Multichannel Systems

We study the feasibility of short finite impulse response (FIR) synthesis for perfect reconstruction (PR) in generic FIR filter banks. Among all PR synthesis banks, we focus on the one with the minimum filter length. For filter banks with oversampling factors of at least two, we provide prescriptions for the shortest filter length of the synthesis bank that would guarantee PR almost surely. The prescribed length is as short or shorter than the analysis filters and has an approximate inverse relationship with the oversampling factor. Our results are in form of necessary and sufficient statements that hold generically, hence only fail for elaborately-designed nongeneric examples. We provide extensive numerical verification of the theoretical results and demonstrate that the gap between the derived filter length prescriptions and the true minimum is small. The results have potential applications in synthesis FB design problems, where the analysis bank is given, and for analysis of fundamental limitations in blind signals reconstruction from data collected by unknown subsampled multi-channel systems.

Effect of bias voltage on microstructure, mechanical and wear properties of Al–Si–N coatings deposited by cathodic arc evaporation

Al–Si–N coatings were deposited on tungsten carbide (WC–Co) and silicon wafer substrates using Cr and AlSi (12 at.% Si) alloy targets using a dual cathode source with short straight-duct filter in the cathode arc evaporation system. Al–Si–N coatings were synthesized under a constant flow of nitrogen, using various substrate bias voltages at a fixed AlSi cathode power. To enhance adhesive strength, the Cr/(Cr xAl ySi z)N graduated layer between the top coating and the substrate was deposited as a buffer interlayer. The effects of bias voltage on the microstructure, mechanical and wear properties of the Al–Si–N films were investigated. Experimental results reveal that the Al–Si–N coatings exhibited a nanocomposite structure of nano-crystalline h-AlN, amorphous Si 3N 4 and a small amount of free Si and oxides. It was also observed that the deposition rate of as-deposited films gradually decreased from about 25.1 to 18.8 nm/min when the substrate bias was changed from − 30 to − 150 V. The XRD results revealed that h-AlN preferred orientation changed from (002) to (100) as the bias voltage increased. The maximum hardness of approximately 35 GPa was obtained at the bias voltage of −90 V. Moreover, the grain size was inversely proportional to the hardness of the film. Wear test results reveal that the Al–Si–N film had a lower coefficient of friction, between 0.5 and 0.7, than that 0.7 of the AlN film.

Cooperative Filter-and-Forward Beamforming for Frequency-Selective Channels with Equalization

Most of the existing literature on cooperative relay networks has focused on frequency-nonselective channels or frequency-selective channels with multi-carrier transmission. However, several practical systems employ single-carrier transmission over frequency-selective channels and the design of corresponding relaying schemes is a largely under-explored topic. In this paper, we investigate filter-and-forward beamforming (FF-BF) for relay networks employing single-carrier transmission over frequency-selective channels. In contrast to prior work, we assume that the destination node is equipped with a simple linear or decision feedback equalizer. The FF-BF filters at the relays are optimized for maximization of the signal-to-noise ratio at the equalizer output under a joint relay power constraint. For infinite impulse response (IIR) FF-BF filters, we derive a unified expression for the filter frequency response valid for linear equalization, decision feedback equalization, and an idealized matched filter receiver. A numerical algorithm with guaranteed convergence is developed for optimization of the power allocation factor included in the expression for the IIR FF-BF filter frequency response. We also provide an efficient gradient algorithm for recursive calculation of near-optimal finite impulse response (FIR) FF-BF filters. Simulation results show that, in general, short FIR FF-BF filters are sufficient to closely approach the performance of IIR FF-BF filters even in severely frequency-selective channels and that the proposed FF-BF scheme with equalization at the destination achieves substantial performance gains compared to a previously proposed FF-BF scheme without equalization.

Phosphor Converted White LED with Improved Efficiency

Proposed short pass filter (SPF) employment to improve efficiency of phosphor converted white LED based on near UV LED dies and remote RGB phosphor architecture. SPF is transparent for near UV radiation in the 390-430 nm spectral range and possesses high reflectance for visual spectral range. SPF is placed between near UV LED and phosphor layer and redirects part of down warding white light to the outside of the package. Demonstrated 26 % average improvements for the conversion efficiency from 10.9 to 8.0 mW/Lm and 24 % average increase for luminous efficacy for 3000°K CCT and 85 CRI.

Groundwater parameter estimation using the ensemble Kalman filter with localization

The ensemble Kalman filter (EnKF), an efficient data assimilation method showing advantages in many numerical experiments, is deficient when used in approximating covariance from an ensemble of small size. Implicit localization is used to add distance-related weight to covariance and filter spurious correlations which weaken the EnKF’s capability to estimate uncertainty correctly. The effect of this kind of localization is studied in two-dimensional (2D) and three-dimensional (3D) synthetic cases. It is found that EnKF with localization can capture reliably both the mean and variance of the hydraulic conductivity field with higher efficiency; it can also greatly stabilize the assimilation process as a small-size ensemble is used. Sensitivity experiments are conducted to explore the effect of localization function format and filter lengths. It is suggested that too long or too short filter lengths will prevent implicit localization from modifying the covariance appropriately. Steep localization functions will greatly disturb local dynamics like the 0-1 function even if the function is continuous; four relatively gentle localization functions succeed in avoiding obvious disturbance to the system and improve estimation. As the degree of localization of the L function increases, the parameter sensitivity becomes weak, making parameter selection easier, but more information may be lost in the assimilation process.

Filters of wavelets on invariant sets for image denoising

Aiming at overcoming the shortcomings of existing wavelet denoising methods, we propose an image denoising algorithm based on wavelets on invariant sets. These wavelets, in comparison with classical wavelets, have the following features: they have vanishing moments of a high order and at the same time a short filter length. Moreover, boundary extension normally required for classical wavelets in wavelet transformations is not needed for wavelets on invariant sets. We identify a class of discrete orthogonal transforms, such as the discrete cosine transform of the second type, the Hadamard transform, the Slant transform and the Hartley transform with the filters of wavelets on invariant sets. This viewpoint gives us an insightful understanding of these transforms in the framework of the multiscale analysis. In turn, it leads to more efficient algorithms to image denoising. We demonstrate the performance of our algorithm on images with varying noise levels. The numerical results show that our proposed algorithm offers effective noise removal in noisy images.

Lamp‐based wavelength‐resolved fluorescence detection for protein capillary electrophoresis: Setup and detector performance

A lamp-based fluorescence detection (Flu) system for CE was extended with a wavelength-resolved (WR) detector to allow recording of full protein emission spectra. WRFlu was achieved using a fluorescence cell that employs optical fibres to lead excitation light from a Xe-Hg lamp to the capillary window and protein fluorescence emission to a spectrograph equipped with a CCD. A 280 nm band pass filter etc. together with a 300 nm short pass cut-off filter was used for excitation. A capillary cartridge was modified to hold the detection cell in a commercial CE instrument enabling WRFlu in routine CE. The performance of the WRFlu detection was evaluated and optimised using lysozyme as model protein. Based on reference spectral data, a signal-intensity adjustment was introduced to correct for transmission losses in the detector optics that occurred for lower protein emission wavelengths. CE-WRFlu of lysozyme was performed using BGEs of 50 mM sodium phosphate (pH 6.5 or 3.0) and a charged-polymer coated capillary. Using the 3-D data set, signal averaging over time and emission-wavelength intervals was carried out to improve the S/N of emission spectra and electropherograms. The detection limit for lysozyme was 21 nM, providing sufficient sensitivity to obtain spectral information on protein impurities.