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As a kind of geomagnetic data processing, downward continuation of potential field plays an important role in geologic interpretation and geomagnetic localization. The inherent instability of larger distance downward continuation restricts its practical applications. In this paper, we report a kind of one-step compensation downward continuation method free of iteration using the equivalent wave number domain continuation operator, which will speed downward continuation compared to iterative compensation, and prove theoretically the convergence of the downward continuation filtering factor about one-step immune-iterative compensation. The frequency responses of the low-pass filter factor are also discussed by different damping factors, iterative numbers and continuation depths. The regularity analysis of one-step compensation method is also discussed. We use the theoretical model of magnetic bodies and real data to test experimentally the immune-iterative compensation algorithm based on the equivalent wave number domain continuation factor, respectively. The results all show high accuracy and good stability of the one-step compensation downward continuation algorithm. The performances of downward continuation including three kinds of algorithms are demonstrated by three parameters, and comparisons prove the reported algorithm has less calculated error than the generalized inverse method, and less elapsed time than the iterative compensation method.

This paper presents the experiment results to identify the contamination control with hydraulic oil used over 250 tons of Hitachi hydraulic excavator works on coal mining operations. The nature of this topic is to analyze the effectiveness off-board filtering systems by using different sizes of micron rating filters in a specific time interval to reduce Particles Contaminant PC06 and PC14 in hydraulic oil. Based on the analysis results, conclusions can be drawn (1) The SNR value on the filter factor reaches optimal at level 2, a combination of Filter B (2 × 10 μm and 2 × 8 μm). At the time factor, it comes optimal at level 1 (1000 h) so that the combination of filter and time that can optimize (minimize) the PC06 content in the oil is to use filter B and 1000 h. (2) There is no significant effect of the filter, time, and interaction factors on PC14. The SNR value on the filter factor reaches optimal at level 2 using Filter B (2 × 10 μm and 2 × 8 μm). At the time factor, it comes optimal at level 1 (1000 h) so that the combination of filter and time that can optimize (minimize) is to use filter B and time 1000 h. (3) There is a significant effect of the factor filter on V100. There is a substantial effect of the time factor on V100. There is no influence on the interaction between factors on V100. The proportion of each factor’s contribution to the V100 response, filter factor has an effect of 14.926%, the time factor has an impact of 10.868%, and the filter interaction factor and time affect 0.17%.

The Schmidt–Kalman (or “consider” Kalman filter) has often been used to account for the uncertainty in so-called “nuisance” parameters when they are impactful to filter accuracy and consistency. Us...

It is commonly acknowledged that most of the output signals of digital receiver front-end are noisy and cannot be directly delivered to post-processing subject to the working condition and the limitations of devices. This study presents an improved singular value decomposition-based de-noising algorithm by the adoption of time-domain constrained optimisation. The improved algorithm contains a filter factor which plays a role in distributing information contributions of each retained singular value component to the de-noised signal, according to the relative contribution of noise in each singular value. The selection methods for several critical factors of the algorithm are discussed, including the noisy matrix, de-noising order, noise power and Lagrange multiplier. In particular, the effects of de-noising order and Lagrange multiplier on de-noising performance are studied. The results of the verification tests of extensive simulations and actual measurements from receiver front-end show that the proposed algorithm can significantly reduce the background noise and guarantee the integrity of the information contained in the de-noised signal.

not present; this is a Technical Note, only requiring an Introduction section

The objective of this work was to evaluate the efficiency of bidimensional array detectors (MatriXX® and QA BeamChecker Plus®) and a tridimensional array detector (ArcCHECK®) in the commissioning of dynamic wedge filters of clinical linear accelerators in order to discuss the convenience and limitation of these devices for such use. The efficiency of MatriXX was investigated in symmetry tests of the collimator jaws, dose linearity, dose rate, filter factor, dose profiles at different depths for 30°, 45°, and 60° dynamic wedge filters, and dose distribution. The efficiency of ArcCHECK was verified in a test of the influence of the gravitational force on the collimator simulating wedges filters. With QA BeamChecker Plus, the 6 MV megavoltage photon beam output constancy was analyzed. In all tests, the three detectors presented good results, indicating that this set of detectors is suitable for the commissioning of dynamic wedge filters.

When iterative methods are employed as regularizers of inverse problems, a main issue is the trade-off between smoothing effects and computation time, related to the convergence rate of iterations. Very often, faster methods obtain less accuracy. A new acceleration strategy is presented here, inspired by a choice of penalty terms formerly proposed in 2012 by Huckle and Sedlacek in the context of Tikhonov regularization by direct solvers. More precisely, we consider a special penalty term endowed with high regularization capabilities, and we apply it by using the opposite sign, that is negative, to its regularization parameter. This unprecedented choice leads to an “irregularization” phenomenon, which speeds up the underlying basic iterative method. The speeding up effects of the negative valued penalty term can be controlled through a sequence of decreasing coefficients as the iterations proceed in order to prevent noise amplification, tuning the weight of the correction term which generates the anti-regularization behavior. Filter factor expansion and convergence are analyzed in the simplified context of linear inverse problems in Hilbert spaces, by considering modified Landweber iterations as a first case study.

A new, efficient switching median–mean filter is proposed to remove high density impulse noise from digital images. The proposed method consists of detection and filtering stages. The pixels that are labeled noise-free in the detection stage remain unchanged and the noisy-pixels are replaced by the reference image based the proposed filter with 3 × 3 window. The simulation results show that the proposed filter outperforms some existing methods, both in vision and quantitative measurements. Moreover, our method is not only efficient to remove high density impulse noise and preserve the details in the image, but also possess a short processing time.

The purpose of bowtie filters in CT scanners is to homogenize the x-ray intensity measured by the detectors in order to improve the image quality and at the same time to reduce the dose to the patient because of the preferential filtering near the periphery of the fan beam. For CT dosimetry, especially for Monte Carlo calculations of organ and tissue absorbed doses to patients, it is important to take the effect of bowtie filters into account. However, material composition and dimensions of these filters are proprietary. Consequently, a method for bowtie filter simulation independent of access to proprietary data and/or to a specific scanner would be of interest to many researchers involved in CT dosimetry. This study presents such a method based on the weighted computer tomography dose index, CTDIw, defined in two cylindrical PMMA phantoms of 16 cm and 32 cm diameter. With an EGSnrc-based Monte Carlo (MC) code, ratios CTDIw/CTDI100,a were calculated for a specific CT scanner using PMMA bowtie filter models based on sigmoid Boltzmann functions combined with a scanner filter factor (SFF) which is modified during calculations until the calculated MC CTDIw/CTDI100,a matches ratios CTDIw/CTDI100,a, determined by measurements or found in publications for that specific scanner. Once the scanner-specific value for an SFF has been found, the bowtie filter algorithm can be used in any MC code to perform CT dosimetry for that specific scanner. The bowtie filter model proposed here was validated for CTDIw/CTDI100,a considering 11 different CT scanners and for CTDI100,c, CTDI100,p and their ratio considering 4 different CT scanners. Additionally, comparisons were made for lateral dose profiles free in air and using computational anthropomorphic phantoms. CTDIw/CTDI100,a determined with this new method agreed on average within 0.89% (max. 3.4%) and 1.64% (max. 4.5%) with corresponding data published by CTDosimetry (www.impactscan.org) for the CTDI HEAD and BODY phantoms, respectively. Comparison with results calculated using proprietary data for the PHILIPS Brilliance 64 scanner showed agreement on average within 2.5% (max. 5.8%) and with data measured for that scanner within 2.1% (max. 3.7%). Ratios of CTDI100,c/CTDI100, p for this study and corresponding data published by CTDosimetry (www.impactscan.org) agree on average within about 11% (max. 28.6%). Lateral dose profiles calculated with the proposed bowtie filter and with proprietary data agreed within 2% (max. 5.9%), and both calculated data agreed within 5.4% (max. 11.2%) with measured results. Application of the proposed bowtie filter and of the exactly modelled filter to human phantom Monte Carlo calculations show agreement on the average within less than 5% (max. 7.9%) for organ and tissue absorbed doses.

In this paper, we present a solution to the problem of reconstructing the input of a maximally decimated filter bank from the subband components using Wiener filtering. We present a generalized structure for applying Wiener filtering at the output of the analysis stage of a uniform filter bank (UFB). This structure can be used to model a situation where the desired signal is a filtered version of the input signal. Some interesting results for matrix inversion are derived and used to reduce the complexity of the Wiener filter expression. The resulting expression provides many insights into the properties of the Wiener synthesis filter designed. The Wiener synthesis filter turns out to be independent of the input spectral properties. The proposed Wiener synthesis filter bank exploits the pseudocirculant property. Thus all distortions are completely removed and the filter bank reduces to a linear time invariant (LTI) filter of interest. We later extend the analysis to non-uniform filter banks (NUFBs).

Acoustic imaging aims at localization and characterization of sound sources using microphone arrays. In this paper a new regularization method for acoustic imaging by inverse approach is proposed. The method first relies on the singular value decomposition of the plant matrix and on the projection of the measured data on the corresponding singular vectors. In place of regularization using classical methods such as truncated singular value decomposition and Tikhonov regularization, the proposed method involves the direct definition of the filter factors on the basis of a thresholding operation, defined from the estimated measurement noise. The thresholding operation is achieved using modified filter functions. The originality of the approach is to propose the definition of a filter factor which provides more damping to the singular components dominated by noise than that given by the Tikhonov filter. This has the advantage of potentially simplifying the selection of the best regularization amount in inverse problems. Theoretical results show that this method is comparatively more accurate than Tikhonov regularization and truncated singular value decomposition.

We have designed a photoelectric yarn signal acquisition system, which is based on the STM32 processor, having a sample rate up to 270kHz, and uploading data collection through synchronous parallel communication mode; Owing to the large noise of yarn signal and the unobviousness of yarn defect, we respectively adopting wiener filter and mean filter to filter this signal; The simulation result of matlab has manifested that both the wiener filter and mean filter can effectively decrease the noise level of the yarn signal and make the nep defects easier to identify, and that the wiener filter applies to application where the yarn speed is higher , while the mean filter is appropriate to the lower speed spinner.

Orthogonal pre-processing (orthogonal projection) of spectral data is a common approach to generate analyte-specific information for use in multivariate calibration. The goal of this pre-processing is to remove from each spectrum the respective sample interferent contributions (spectral interferences from overlap, scatter, noise, etc.). Two approaches to accomplish orthogonal pre-processing are net analyte signal (NAS) and generalized least squares (GLS). Developed in this paper is the mathematical relationship between NAS and GLS. It is also realized that orthogonal NAS pre-processing can remove too much analyte signal and that the degree of interferent correction can be regulated. Similar to GLS, the degree of correction is accomplished by using a regularization (tuning) parameter to form generalized NAS (GNAS). Also developed in this paper is an alternative to GNAS and GLS based on generalized Tikhonov regularization (GTR). The mathematical relationships between GTR, GNAS, and GLS are derived. A result is the ability to express the model vector as the sum of two contributions: the orthogonal NAS contribution and a non-NAS contribution from the interferent components. Thus, rather than the usual situation of sequentially pre-processing data by either GNAS or GLS followed by model building with the pre-processed data, the methods of GTR, GNAS, and GLS are expressed as direct computations of model vectors allowing concurrent pre-processing and model building to occur. Simultaneous pre-processing and model forming are shown to be natural to the GTR process. Two near-infrared spectroscopic data sets are studied to compare the theoretical relationships between GTR, GNAS, and GLS. One data set covers basic calibration, and the other data set is for calibration maintenance. Filter factor representation is key to developing the interprocess relationships. Copyright © 2013 John Wiley & Sons, Ltd.

Topology optimization is one of the most important methods of reducing the weight of structure. Optimality Criteria method (OC) as a heuristic way can be used to deal with this problem efficiently. Popular SIMP method implements micro-structural density as the design variable. During the process of optimization, numerical instabilities are always observed; Moreover, higher penalty factor is not better for decreasing intermediate density elements. In this paper a penalty factor is imposed in OC method, and a relation between the filtering area and elements is also obtained. Meanwhile, the nodal density is used as design variable for more smoothing boundary. The results show that numerical stability can be obtained, checkerboard patterns haven’t been observed, and the clear boundary of structure has been developed.

The filter factor is a type of wave fetch index for whole coastal areas used to describe the sheltering effect from islands. Apart from fetch, it also includes the cross-sectional areas between the studied area and the surroundings. Previously, the filter factor has shown correlation with, e.g., bottom dynamic conditions and deep water exchange, but has been difficult to calculate. In this paper, it is shown how to calculate the filter factor using modern Geographic Information System (GIS) software. Different aspects of the filter factor, such as the used number of lines, maximum line length, etc., were investigated using data from Swedish coastal areas. Possible improvements and simplifications were found that can both increase the correlation with bottom dynamic conditions and deep water exchange, but also substantially decrease the computation time. An alternative approach that calculates the proportion of islands in the outside region was also developed and tested with good results.

A hybrid silicon photonic integrated filter is proposed and demonstrated with a novel structure. This filter incorporates a ring resonator in one arm of a Mach-Zehnder interferometer making it possible to obtain a programmable filter response. The optical filter consists of a 5-mm-long delay loop made of low-loss silicon waveguides with integrated thermal modulators resulting in a 0.164-nm free spectral range with absolute phase tunability and gain elements that allow for the tuning of the filter factor. The microwave response of this integrated filter is measured and display tunability of 20 GHz.

Transport of Escherichia coli ATCC 11105 through porous media was investigated in this study using two sets of column experiments to quantify the attachment-related parameters (sticking efficiency, attachment rate coefficient and filter factor). The first set of experiments was performed in quartz sand under different ionic strength conditions (1, 20, 100, 200 mM) while the second experiments were carried out in quartz sand mixed with metal oxyhydroxide-coated sand (0, 5, 10, 25%). The breakthrough curves of bacteria were obtained by monitoring effluent, and then bacterial mass recovery and attachment-related parameters were quantified from these curves. The first experiments showed that the mass recoveries were in the range of 13.3 to 64.7%, decreasing with increasing ionic strength. In the second experiments, the mass recoveries were in the range of 15.0 to 43.4%, decreasing with increasing coated sand content. The analysis indicated that the sticking efficiency, attachment rate coefficient and filter factor increased with increasing ionic strength and coated sand content. The value of filter factor in the first experiments ranged from 1.45 e-2 to 6.72 e-2 1/cm while in the second experiments it ranged from 2.78 e-2 to 6.32 e-2 1/cm. Our filter factor values are one order of magnitude lower than those from other studies. This discrepancy can be attributed to the size of sand used in the experiment. The analysis demonstrated that the travel distance of bacteria estimated using the filter factor can be varied greatly depending on the solution chemistry and charge heterogeneity of porous media.

A Fourier transformation changes all the locations of an image to frequencies of gratings, and back again. This allows certain frequencies to be attenuated or amplified, for one purpose or another. The process for 8-bit images is described in Chap. 40. This Chapter shows examples of 1-bit images thus processed.

A bi-static range migration algorithm for 2-D multiple input multiple output imaging for single-frequency data processing is investigated in this paper. On the basis of considering the near field electromagnetic wave attenuation, the imaging algorithm formulae are deduced in detail by applying the Method of Stationary Phase strictly which leads to a key filter factor for 2-D single-frequency imaging algorithm as a consequence. Image can be focused or not depends on a Phase item of the filter factor while it is influenced by amplitude item slightly which can be ignored under certain conditions. In order to verify the performance of the algorithm, a simple 2-D sparse array is designed for the imaging experiments in a complex electromagnetic environment. The focusing results are excellent which shows that the MIMO imaging algorithm discussed in this paper can be used for short-range, high-resolution and real-time imaging system.

A PID controller is a second-order controller, and as such involves four parameters. However, many available tuning methods design only three parameters, and then use a default choice for the derivative filter factor. In this paper it is pointed out that for a PID controller of series form a default value for the derivative filter makes some sense, since it corresponds to a lead-lag controller. For PID controllers of ideal (or parallel) form default values are much less natural. The main purpose of the paper is to discuss the importance of model-based design methods, treating the derivative filter as an inherent part of the design. For example, it is illustrated how default choices for the derivative filter may lead to excessive control actions.

The main advantage of pseudoquadrature mirror filter cosine modulated filter banks with a spectral factor of a 2Mth band filter is that the optimization stage can be avoided when designing the prototype filter. However, these filter banks are constrained by the condition that the order of the prototype filter has to be an integer multiple of the M-number of channels in the bank. In this paper, we set the conditions that must be imposed to cosine-modulation phase factors so as to cancel the most significant terms of aliasing using a prototype filter of arbitrary length. An example is included to confirm the validity of the theory.

The role of forests in filtering airborne organic pollutants from the atmosphere and transferring them to soil was examined. A mathematical model was assembled to calculate the filter factor, defined as the quotient of the net deposition of a given compound to a forest and its net deposition to a bare soil. A simple equation was obtained that expressed the filter factor as a function of just two physical-chemical properties of the chemical: the octanol/air and air/water partition coefficients (KOA and KAW). The model was then applied to a spruce and to a beech/oak canopy close to Bayreuth for which measured deposition velocities were available. The model simulations indicated that there was little filter effect for volatile compounds with log KOA < 7 and for hydrophilic substances with log KAW < −6. Similarly, although forest canopies are thought to be effective filters of airborne particles, the filter factor for compounds that are primarily particle bound was also close to 1, since the dry particle bou...

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-12-05T16:28:50Z No. of bitstreams: 1 SUZANA ARAÚJO BARBOSA – DISSERTAÇÃO (PPGFísica) 2013.pdf: 4287089 bytes, checksum: ea83819f66b68fa4cae01975c1122a18 (MD5) Made available in DSpace on 2018-12-05T16:28:50Z (GMT). No. of bitstreams: 1 SUZANA ARAÚJO BARBOSA – DISSERTAÇÃO (PPGFísica) 2013.pdf: 4287089 bytes, checksum: ea83819f66b68fa4cae01975c1122a18 (MD5) Previous issue date: 2013 Capes Sabe-se que para garantir um melhor resultado no tratamento dos pacientes em Radioterapia é conveniente uma constância de parâmetros físicos como também a verifi cação do sistema de planejamento trabalhado. O trabalho que segue apresenta um estudo das propriedades físicas dos filtros dinâmicos do acelerador linear 6eX, da Varian Medical Systems, por meio de veri cações experimentais, comparando-as com cálculos desenvolvidos pelo sistema de planejamento Eclipse, sob as mesmas condições. Foram determinados os fatores fi ltro para campos simétricos e assimétricos para o eixo central e fora dele, veri cando a influência dos colimadores X e Y em diferentes aberturas; veri ficou-se também a dependência do fator filtro com a profundidade, com o aumento dos campos e com o aumento do ângulo empregado nos fi ltros, além dos per s dos campos para profundidade específi cas. A interpretação dos resultados dos fatores fi ltro, possibilita os cálculos do planejamento do tratamento em Radioterapia para uma eventual falta ou conferência do sistema de planejamento. It is known that to ensure a better outcome in the treatment of patients in Radiotherapy, there should be a constancy of the physical parameters as well as a verification of the worked planning system. The following work presents a study of the physical properties of the dynamic lters of the linear accelerator 6ex, from Varian Medical Systems, using experimental veri cation by comparing them with calculations made by the planning system Eclipse under the same conditions. The lter factors were determined for symmetrical and asymmetrical elds to the central axis and off of it, by checking the influence of collimators X and Y in di erent openings, there is also the dependence of the lter factor with the depth, with the increase of the elds and angles used in the lters, and the eld pro les for specifi c depths. The interpretation of the results of the lter factors, enables calculations in radiotherapy treatment planning, for a possible lack of planning system.

A typical way to compute a meaningful solution of a linear least squares problem involves the introduction of a filter factors array, whose aim is to avoid noise amplification due to the presence of small singular values. Beyond the classical direct regularization approaches, iterative gradient methods can be thought as filtering methods, due to their typical capability to recover the desired components of the true solution at the first iterations. For an iterative method, regularization is achieved by stopping the procedure before the noise introduces artifacts, making the iteration number playing the role of the regularization parameter. In this paper we want to investigate the filtering and regularizing effects of some first-order algorithms, showing in particular which benefits can be gained in recovering the filters of the true solution by means of a suitable scaling matrix.

A filter that is recommended to make fast trading. It must then be used only with assets possessing low transaction costs (Forex first).

International audience; Acoustic imaging aims at localization and characterization of sound sources using microphone arrays. In this paper a new regularization method for acoustic imaging by inverse approach is proposed. The method first relies on the singular value decomposition of the plant matrix and on the projection of the measured data on the corresponding singular vectors. In place of regularization using classical methods such as truncated singular value decomposition and Tikhonov regularization, the proposed method involves the direct definition of the filter factors on the basis of a thresholding operation, defined from the estimated measurement noise. The thresholding operation is achieved using modified filter functions. This has the advantage of symplifying the selection of the best regularization amount. Theoretical results show that this method is promising, in terms of ease of implementation and accuracy of results, in comparison with Tikhonov regularization and truncated singular value decomposition.

In this work, a novel way to adjust a bilateral filter is presented. The bilateral filter is a combination of domain and range filtering. The domain filter acts as a low-pass filter. The range filter stands for the nonlinear component and plays an important part in edge preserving. Both filtering components can be adjusted by according parameters. Pursuant to our experience and achieved results in terms of the image quality it is more effective to readjust the range filter to the noise level than to cope with the fine tuning of the spatial filter. In this work, we show how the adjustment parameter for the nonlinear range component can be derived from the standard deviation of noise, which allows automatic noise-adaptive adjustment of the filter.

A computational model of multi-scale population densities was developed based on the native population database of Shijiazhuang city. The model comprises four parts: data processing, down-scaling, data format conversion and up-scaling. Down-scaling was completed by apportioning village population to each street block. The vector dataset of block population was converted into 100m×100m grid dataset, which is the minimum grain population density. By changing the radius of circular filter factor, the up-scaling of population density was realized and the multi-scale population density was obtained. The results show that the long-term balance of human and nature environment can be clearly revealed on the maps of population densities at R = 0, R =3, R =12, R =29 and R =99. The model is helpful to observe the interaction of man-land relationship at different scales systematically, and to build a mathematical foundation for studying the MAUP (The Modifiable Area Unit Problem) of population density.

In this paper, the theory of uniform filter banks using all-pass tilters is further developed. A new structure of two stage filter banks using all-pass filter is proposed. The prestage is half-band filter with period, the post-stage is two sets of band-pass filter banks. The pre-stage filter stop-band just controls the don’t-care-band of the post-stage filter banks using all-pass polyphase, so as to realize a continuous stop-band property. Moreover, a method of synthesizing filter bank is derived, which eliminates aliasing and amplitude distortions of the analysis/synthesis system. Finally, an example is given.

Diagnostics are fundamental to multivariate calibration (MC). Two common diagnostics are leverages and spectral F-ratios and these have been formulated for many MC methods such as partial least square (PLS), principal component regression (PCR) and classical least squares (CLS). While these are some of the most common methods of calibration in analytical chemistry, ridge regression is also common place and yet spectral F-ratios have not been developed for it. Noting that ridge regression is a form of Tikhonov regularization (TR) and using the unifying filter factor representation for MC, this paper develops the filter factor form of leverages and spectral F-ratios. The approach is applied to a spectral data set to demonstrate computational speed-up advantages and ease of implementation for the filter factor representation. Copyright © 2010 John Wiley & Sons, Ltd.

The third-order Adams–Bashforth method is compared with the leapfrog scheme. Like the leapfrog scheme, the third-order Adams–Bashforth method is an explicit technique that requires just one function evaluation per time step. Yet the third-order Adams–Bashforth method is not subject to time splitting instability and it is more accurate than the leapfrog scheme. In particular, the O[(Δt)4] amplitude error of the third-order Adams–Bashforth method can be a marked improvement over the O[(Δt)2] amplitude error generated by the Asselin-filtered leapfrog scheme—even when the filter factor is very small. The O[(Δt)4] phase-speed errors associated with third-order Adams–Bashforth time differencing can also be significantly less than the O[(Δt)2] errors produced by the leapfrog method. The third-order Adams–Bashforth method does use more storage than the leapfrog method, but its storage requirements are not particularly burdensome. Several numerical examples are provided illustrating the superiority of thi...

WOS: 000254240200009, A flexible synthesis procedure for electronically tunable nth-order current-mode (CM) universal filter using state variable-method is given. The proposed configuration uses n+1 multi-output second generation current conveyors (MO-CCIIs), n capacitors and n resistors. These resistors can be removed by using multi-output second generation current controlled conveyors (MO-CCCIIs) instead of MO-CCIIs. It is straightforward to find the values of the passive elements from the coefficients of the transfer function to be realized. The validity of the proposed filter is verified through PSpice simulations.

The question addressed in this work is the determination of the practical capability of model-based methods to reconstruct a given acoustic source distribution from either pressure-based or velocity-based measurements at field points inside a cylindrical duct. An analytical model has first been implemented for the sound field due to elementary sources in a hard-walled duct of finite length. An interpretation is proposed of in-duct multi-modal propagation in terms of wavenumber-filtering. Due to the modal characteristic impedance terms, spatial low-pass filtering is associated to pressure-based field whereas this filter factor does not appear when considering velocity-based field. The inversion of the pressure-based frequency response functions involves a reciprocal factor which amplifies the high spatial frequency and increases the numerical instability of the inversion. It is found that, under non-ideal conditions, i.e. at low frequency and beyond the near-field zone, velocity-based field measurements are more favourable than pressure-based field measurements for acoustic source reconstruction in terms of both accuracy and spatial resolution.

By using a bit vector and a set of hash functions to represent data set, bloom filter can query a given data effectively. Bloom filter can be used to determine an element belongs to data set or not. Split bloom filter is amelioration to the bloom filter, which use a S times N bit matrix to represent data set. In distributed systems, if the number of the elements increases continually, the increasing error rate of bloom filter will make the representation nonsensically. Split bloom filter can only weaken this problem. In this paper, a new kind of bloom filter, named as K-divided bloom filter, is presented. Compared with split bloom filter, it can reduce space and time spending and has a resembling or better performance. K-divided bloom filter gets better tradeoff among error rate, space and time.

This paper proposes the new two-pole band-pass filter design principle for the all-pass filter and notch filter by applying the least square. The first step is to design notch filter by using pole-zero placement and then modify pole positions to control pass-band filter gain to ensure the symmetry with the maximum gain at the target level. After that, there is the design of all-pass filter with pole at the same positions as the notch filters to make the negative cascade with the designed notch filter to get the transfer function with band-pass filter magnitude response. The results from the experiments on MATLAB have shown the two-pole band-pass filter of the new design with the accurate and symmetric gain