Fast convolutional sparse coding using matrix inversion lemma

Convolutional sparse coding is an interesting alternative to standard sparse coding in modeling shift-invariant signals, giving impressive results for example in unsupervised learning of visual features. In state-of-the-art methods, the most time-consuming parts include inversion of a linear operator related to convolution. In this article we show how these inversions can be computed non-iteratively in the Fourier domain using the matrix inversion lemma. This greatly speeds up computation and makes convolutional sparse coding computationally feasible even for large problems. The algorithm is derived in three variants, one of them especially suitable for parallel implementation. We demonstrate algorithms on two-dimensional image data but all results hold for signals of arbitrary dimension.     

Bayesian sparse solutions to linear inverse problems with non-stationary noise with Student-t priors

Bayesian approach has become a commonly used method for inverse problems arising in signal and image processing. One of the main advantages of the Bayesian approach is the possibility to propose unsupervised methods where the likelihood and prior model parameters can be estimated jointly with the main unknowns. In this paper, we propose to consider linear inverse problems in which the noise may be non-stationary and where we are looking for a sparse solution. To consider both of these requirements, we propose to use Student-t prior model both for the noise of the forward model and the unknown signal or image. The main interest of the Student-t prior model is its Infinite Gaussian Scale Mixture (IGSM) property. Using the resulted hierarchical prior models we obtain a joint posterior probability distribution of the unknowns of interest (input signal or image) and their associated hidden variables. To be able to propose practical methods, we use either a Joint Maximum A Posteriori (JMAP) estimator or an appropriate Variational Bayesian Approximation (VBA) technique to compute the Posterior Mean (PM) values. The proposed method is applied in many inverse problems such as deconvolution, image restoration and computed tomography. In this paper, we show only some results in signal deconvolution and in periodic components estimation of some biological signals related to circadian clock dynamics for cancer studies.     

New technique revives direct deconvolution methods for Wellbore storage removal in pressure transient analysis

Eliminating wellbore storage (WBS) effects inherent in pressure transient data is one of the challenges in well test analysis. The available WBS-removal techniques are either direct or time-consuming approaches. The direct methods are mostly unstable and require accurate data with almost no noise. However, well test data often have noise in both rate and pressure measurements.This work discusses the development of a stable technique to overcome the shortcomings in the available WBS-removal methods. The technique presented here takes advantage of the recently developed stable deconvolution algorithms (e.g. von Schroeter algorithm) to achieve a stable WBS-removal process. The developed approach provides longer WBS-free reservoir response signal (extended over the entire test duration) than the previous methods. In addition, the approach introduced here can remove WBS-effects in noisy data and does not require sandface rate measurements.Different simulated and field examples were used to validate the proposed approach. The examples included data with different levels of rate and pressure measurement errors and covered wide variety of well/reservoir models. The available approaches were implemented to the same examples. A comparison of the results shows the superiority of the approach presented in this paper.     

Large-Eddy Simulation of double-row compound-angle film cooling: Setup and validation

Film cooling is an important technique allowing to increase the thermal efficiency of gas turbines. By blowing cool air through an array of small holes in the turbine blades a thin fluid film is set up shielding the blades from the hot gas arriving from the combustion chamber.This work presents a Large-Eddy Simulation of a particular film-cooling configuration known to provide a high level of effectiveness. It incorporates spanwise rows of holes which, by pairwise combination, generate a so-called anti-kidney-vortex. The simulation setup employs the Navier–Stokes code NSMB for compressible flow including the Approximate Deconvolution Model for subgrid turbulence modeling, the Synthetic-Eddy Method for turbulent inflow generation and reflection-reducing outflow boundary conditions. The setup is first validated by simulations of standard flat-plate turbulent boundary-layer flow without blowing. Results of the film-cooling simulation are then compared with related experimental data. They show reasonable agreement of the cooling effectiveness and temperature distribution, thus confirming the validity of the simulation approach which will be used in future studies of film cooling.     

Extraction of the first bolus passage in dynamic susceptibility contrast perfusion measurements

Object  The processing of dynamic susceptibility contrast perfusion measurements requires an extraction of the first bolus passage of the injected contrast agent. State-of-the-art methods employ the fit of a gamma variate function to the measured data. The use of a gamma variate function is motivated by its shape similarity to the expected relaxation rate time-course during the first bolus passage. However, the quality of this result is strongly influenced by the amount of overlap of the first and second bolus passage. In this work we present an alternative, data-driven method for the extraction of the first bolus passage from a measured relaxation time-course. Materials and methods  By using prior knowledge of the injection function, the measured time-courses can be transformed to time-courses that would occur at a shorter injection duration where the two bolus passages have less overlap. This time-course is found by Tikhonov regularized deconvolution of the measured time-courses with an injection function that bases on the measurement protocol. A minimum search yields the cut-off point at which the first bolus can be extrapolated to zero. The gamma variate fit is performed using Powells algorithm. The proposed approach is compared to the gamma variate fit approach using simulations and an exemplary dataset from one healthy volunteer. Results  The new method performs comparably stable as the gamma variate function fit approach in simulations. Both methods are superior to a simple exponential extrapolation approach. Applied to volunteer data, the new method performs much faster than the gamma variate fit approach. The results obtained from both methods correspond well. Conclusion  The new method offers a conceptual understanding of the first bolus passage and yields similar results to the gamma variate function fit approach but performs much faster.     

A New Rapidly Absorbed Paracetamol Tablet Containing Sodium Bicarbonate. II. Dissolution Studies and In Vitro/In Vivo Correlation

ABSTRACT

The objective of this study was to compare the in vitro dissolution profile of a new rapidly absorbed paracetamol tablet containing sodium bicarbonate (PS) with that of a conventional paracetamol tablet (P), and to relate these by deconvolution and mapping to in vivo release. The dissolution methods used include the standard procedure described in the USP monograph for paracetamol tablets, employing buffer at pH 5.8 or 0.05 M HCl at stirrer speeds between 10 and 50 rpm. The mapping process was developed and implemented in Microsoft Excel® worksheets that iteratively calculated the optimal values of scale and shape factors which linked in vivo time to in vitro time. The in vitro–in vivo correlation (IVIVC) was carried out simultaneously for both formulations to produce common mapping factors. The USP method, using buffer at pH 5.8, demonstrated no difference between the two products. However, using an acidic medium the rate of dissolution of P but not of PS decreased with decreasing stirrer speed. A significant correlation (r = 0.773; p<.00001) was established between in vivo release and in vitro dissolution using the profiles obtained with 0.05 M HCl and a stirrer speed of 30 rpm. The scale factor for optimal simultaneous IVIVC in the fasting state was 2.54 and the shape factor was 0.16; corresponding values for mapping in the fed state were 3.37 and 0.13 (implying a larger in vitro–in vivo time difference but reduced shape difference in the fed state). The current IVIVC explains, in part, the observed in vivo variability of the two products. The approach to mapping may also be extended to different batches of these products, to predict the impact of any changes of in vitro dissolution on in vivo release and plasma drug concentration–time profiles.     

Approximations to the Mean and Standard Deviation of Reciprocals of Observations

Instrument performance evaluation is generally based on accuracy and repeatability, with the test process consisting of observations of known or standard events. The data are then reduced by various manipulations. This paper will show how to simplify such manipulations when the observation is the reciprocal of the desired event. In addition, it will show that the error introduced is negligible under certain easily tested conditions.     

A method of PSF generation for 3D brightfield deconvolution

This paper addresses the problem of 3D deconvolution of through focus widefield microscope datasets (Z‐stacks). One of the most difficult stages in brightfield deconvolution is finding the point spread function. A theoretically calculated point spread function (called a ‘synthetic PSF’ in this paper) requires foreknowledge of many system parameters and still gives only approximate results. A point spread function measured from a sub‐resolution bead suffers from low signal‐to‐noise ratio, compounded in the brightfield setting (by contrast to fluorescence) by absorptive, refractive and dispersal effects. This paper describes a method of point spread function estimation based on measurements of a Z‐stack through a thin sample. This Z‐stack is deconvolved by an idealized point spread function derived from the same Z‐stack to yield a point spread function of high signal‐to‐noise ratio that is also inherently tailored to the imaging system. The theory is validated by a practical experiment comparing the non‐blind 3D deconvolution of the yeast Saccharomyces cerevisiae with the point spread function generated using the method presented in this paper (called the ‘extracted PSF’) to a synthetic point spread function. Restoration of both high‐ and low‐contrast brightfield structures is achieved with fewer artefacts using the extracted point spread function obtained with this method. Furthermore the deconvolution progresses further (more iterations are allowed before the error function reaches its nadir) with the extracted point spread function compared to the synthetic point spread function indicating that the extracted point spread function is a better fit to the brightfield deconvolution model than the synthetic point spread function.     

反射波法在某水电站预选厂址中的应用

反射波法作为工程物探的一种主要方法,勘探精度不仅受激发、接收等因素的影响,还与地震资料处理的精度密切相关。本文结合某水电站厂房选址工作,通过分析对比确定了反射波法资料处理的主要方法和基本流程,着重使用了反褶积技术,提高了分辨率,得到清晰的反射剖面,取得了良好的应用效果。     

Harshaw6600热释光监测系统测量技术

Ｈａｒｓｈａｗ６６００热释光量系统是当今比较先进和完善一套外照射个人剂量监测系统本文简单介绍了该系统组成，描述了系统的使用方法，根据多年的使用经验，着重总结分的了系统了刻度方法，剂量估算方法，热释光发曲线解仪器的日常维护与故障检测。