Biomedical subjects

Moe Razaz

Publications and source records attributed to Moe Razaz.

5 recordsLinked to original sources

PubMed2006

MLEM deconvolution of protein X-ray diffraction images based on a multiple-PSF model.

In this paper we analyze the degradation of protein X-ray diffraction images by diffuse light distortion (DLD). In order to correct the degradation, a new multiple point spread function (PSF) model is introduced and used to restore X-ray diffraction image data (XRD). Raw PSFs are collected from isolated spots in high-resolution areas on the diffraction patterns which represent the orientation of DLDs. An adaptive ridge regression (ARR) technique is used to remove noise from the raw PSF data. A target Gaussian function is used to model the raw PSFs. A maximum likelihood expectation maximization (MLEM) algorithm combined with a multi-PSF model is employed to restore high intensity, asymmetrical protein X-ray diffraction data. Experimental results using a single and multiple PSFs are presented and discussed. We show that using a multiple PSF model in the deconvolution algorithm improved the quality of the XRD and as a result the spot integration error (chi-squared) and corresponding electron density mapare improved.

Algorithms↗

PubMed2005

Stochastic modelling of individual cell growth using flow chamber microscopy images.

In this paper, we analysed individual cell growth images obtained by flow chamber microscopy system. We used replicate flow chamber experiment data as reported by [Elfwing, A., Le Marc, Y., Baranyi, J., Ballagi, A., 2004. Observing the growth and division of large number of individual bacteria using image analysis. Applied and Environmental Microbiology 70, 675-678] involving both unstressed and heat shocked Listeria innocua cells. After observing the kinetics of a large number of cells, we propose a new stochastic model for their individual growth. By comparing our model with other existing models in the literature, we demonstrate that ours can accurately describe the growth of both stressed and unstressed cells. Our results indicate that the lag period, in terms of cell division, coincides dominantly with a lag period in terms of cell size. We also reveal various connections between cell length, lag time and cell division models. Finally, we present the results of our investigation on the effect of the duration of sublethal heat shock on the found growth properties.

Biomass↗

PubMed2005

Connection between stochastic and deterministic modelling of microbial growth.

We present in this paper various links between individual and population cell growth. Deterministic models of the lag and subsequent growth of a bacterial population and their connection with stochastic models for the lag and subsequent generation times of individual cells are analysed. We derived the individual lag time distribution inherent in population growth models, which shows that the Baranyi model allows a wide range of shapes for individual lag time distribution. We demonstrate that individual cell lag time distributions cannot be retrieved from population growth data. We also present the results of our investigation on the effect of the mean and variance of the individual lag time and the initial cell number on the mean and variance of the population lag time. These relationships are analysed theoretically, and their consequence for predictive microbiology research is discussed.

Bacteria↗

PubMed2005

Adaptive penalty likelihood for reconstruction of multidimensional confocal microscopy images.

In this paper we devise a penalty likelihood with noise constraints method to restore 2D and 3D confocal microscope images. Regularization is a commonly used technique in image restoration to balance restored image quality and noise suppression, but despite this noise is usually amplified. Taking into account common confocal imaging system degradation, we develop an algorithm by using a gradient descent method (PLGDA) to approach the minimum solution of the penalty likelihood equation. A Lagrange parameter controls the balance between the penalty and likelihood terms and is estimated using an adaptive method. We show that the a priori information is key to the regularization and Lagrange parameter estimation. The convergence characteristics are analysed and discussed. PLGDA and a traditional maximum likelihood expectation maximization are used to restore 2D and 3D confocal images. The point spread function (PSF), used to restore the data is collected from an experiment and modelled by bi-cubic splines to give an accurate noise free representation. Our experimental results show that the restored images are significantly improved by PLGDA.

Algorithms↗

PubMed2003

The DynDom database of protein domain motions.

UNLABELLED: A relational database has been developed based on the results from the application of the DynDom program to a number of proteins for which multiple X-ray conformers are available. The database is populated via a web-based tool that allows visitors to the website to run the DynDom program server-side by selecting pairs of X-ray conformers by Protein Data Bank code and chain identifier. AVAILABILITY: The website can be found at: http://www.sys.uea.ac.uk/dyndom.

Crystallography↗