Independent sets of some graphs associated to commutative rings

Let $G=(V,E)$ be a simple graph. A set $S\subseteq V$ is independent set of $G$, if no two vertices of $S$ are adjacent. The independence number $\alpha(G)$ is the size of a maximum independent set in the graph. %An independent set with cardinality Let $R$ be a commutative ring with nonzero identity and $I$ an ideal of $R$. The zero-divisor graph of $R$, denoted by $\Gamma(R)$, is an undirected graph whose vertices are the nonzero zero-divisors of $R$ and two distinct vertices $x$ and $y$ are adjacent if and only if $xy = 0$. Also the ideal-based zero-divisor graph of $R$, denoted by $\Gamma_I(R)$, is the graph which vertices are the set {x\in R\backslash I | xy\in I \quad for some \quad y\in R\backslash I\} and two distinct vertices $x$ and $y$ are adjacent if and only if $xy \in I$. In this paper we study the independent sets and the independence number of $\Gamma(R)$ and $\Gamma_I(R)$.Comment: 27 pages. 22 figure

Chromatographic Purification of Recombinant Nucleocapsid Protein of Nipah Virus from Escherichia Coli Homogenate

The nucleocapsid protein (NCp) of Nipah virus (NiV) expressed in Escherichia coli (E. coli) is antigenic and immunogenic. NCp-NiV is a potential serological antigen that can be used in the diagnosis of NiV infections. The yield of NCp expressed in E. coli is low due to the proteolytic degradation by host endogenous proteases. Therefore, it is important to inhibit the endogenous proteolytic degradation activity and shorten the protein recovery process to avoid or reduce the action of protease on the recombinant NCp. A method to predict the type of potential protease that attacks the NCp-NiV and its potential cleavage sites in E. coli to enhance the recovery of NCp was developed. A bioinformatics tool, PeptideCutter was used to identify potential protease and its cleavage sites from the amino acid sequences deduced from the published DNA sequence of the NCp-NiV. The predicted proteases were serine proteases, hence, a range of serine protease inhibitors were tested to improve the yield of NCp. The yield of NCp was increased by 2-fold after the phenylmethylsulphonyl fluoride (PMSF) supplementation. The downstream processing of the NCp-NiV from clarified E. coli homogenate was investigated. Two types of preparative chromatographic purification in a packed bed column; immobilised metal affinity chromatography (IMAC) and hydrophobic interaction chromatography (HIC) were studied and compared. A direct recovery of recombinant NCp-NiV from unclarified E. coli homogenate based on EBA chromatography was then developed by using the type of chromatography that can obtain high yield of the NCp with high antigenicity. In the IMAC system, HisTrapTM 6 Fast Flow was applied to purify the recombinant histidine-tagged NCp. A histidine hexamer tag was placed at the C-terminus of the NCp and this enabled the purification of NCp by IMAC system. The optimal binding was achieved at pH 7.5 and superficial velocity of 75 cm/h. The bound NCp was successfully recovered by a stepwise elution with a range of imidazole concentration (50, 150, 300 and 500 mM). The NCp was captured and eluted from an inlet NCp concentration of 0.4 mg/ml in a scale-up IMAC packed bed column of Nickel SepharoseTM 6 Fast Flow with the optimized conditions obtained from the scouting method. The purification of histidine-tagged NCp using IMAC packed bed column has resulted a 68.3% yield and a purification factor of 7.94. In the HIC system, ammonium sulfate precipitation experiment was performed and it showed that 15% saturation of the salt was the most suitable concentration for the binding buffer. Batch binding of the NCp was performed using Sepharose™ 6 Fast Flow adsorbents coupling separately with four different types of ligand; phenyl low substitution, phenyl high substitution, butyl and octyl. The phenyl low substitution ligand was selected for subsequent optimization process due to its highest yield and purity of the NCp achieved from the batch binding experiment. The HIC for purification of the NCp was further scaled up using a 10 cm column packed with phenyl low substitution Sepharose™ adsorbent. A recovering yield of 81% of the NCp with a purification factor of 9.3 was achieved from this scaled-up HIC operation. Hence, the HIC adsorbent was used to capture the NCp in an EBA column due to its higher yield and purity obtained in the third chapter than the IMAC purification in the second chapter of this study. DNase was added to reduce the viscosity of feedstock and improve the axial mixing prior to the loading of the feedstock to the EBA column packed with the StreamlineTM HIC adsorbent charged with phenyl. The addition of glycerol to the washing buffer has reduced the volume of washing buffer applied, and thus reduced the loss of the NCp during washing stage. The dynamic binding capacity at 10% breakthrough of 3.2 mg/g adsorbent was achieved at a linear flow velocity of 178 cm/h, bed expansion of two and viscosity of 3.4 mPas. The adsorbed NCp was eluted with the buffer containing a step gradient of salt concentration. The purification of hydrophobic NCp using HIC-EBA column has resulted an 80% yield and a purification factor of 12.5

Proactive Traffic-Adaptive Tuning of Contention Window for Wireless Sensor Network Medium-Access Control Protocol

The ongoing advances in wireless networks have further expanded the boundaries to the new and challenging area of Wireless Sensor Networks (WSN). Unique properties of sensor nodes such as limited energy storage, constrained processing capabilities and the especially different environments they are usually deployed in have prompted the need of novel protocols in all the layers of the communication stack. A Medium Access Control (MAC) protocol is responsible to sufficiently provide access to a shared medium. Therefore effective techniques in order to reduce the probability of collisions while contending for the medium can be established in a MAC protocol for it organizes the specific time slot a node can have access to the channel. The need for further improving the current applied MAC protocols for WSN in order to reduce the probability of collisions while being energy aware has motivated this research. Sensor MAC as the very first MAC protocol for WSN has been designed on top of the IEEE 802.11 MAC protocol along with some added features to meet the special requirements of a WSN. However the Back-Off scheme of Sensor MAC (S-MAC) is based on a fixed Contention Window (CW) size. This is known as a significant trouble spot in S-MAC in the sense that the delay produced during collisions and idle listening can be so critical to the limited battery lifetime of a sensor node. IEEE 802.11 MAC protocol follows a static approach for obtaining the back-off time and resets the CW to its default minimum upon just one successful transmission and doubles it each time it faces a collision. While the back-off algorithm of IEEE 802.11 suffers from unfairness for its faulty behaviour in both high and low traffic loads the back-off mechanism in S-MAC suffers from a fixed CW size. Reducing the undesired idle listening time caused by unnecessary long back-off times when traffic is low and also decreasing the probability of collisions in situations with high traffic load due to the fixed CW size in S-MAC have motivated our research. We have tried to come up with a dynamic back-off algorithm for SMAC that can extract the current traffic information of the network and engage them in estimating the contention window from which the back-off time is chosen. Our approach is a proactive algorithm to get the CW of the neighbouring nodes ready before contending for the medium. The performance of our algorithm has been measured in terms of average delay, average throughput, delivery ratio, and average energy efficiency. It is shown that our back-off scheme has reduced the delay by 47% and has decreased the energy consumption up to above 15% over the current SMAC implementation. The delivery ratio and throughput have been improved up to 44% and 28% respectively

Time-sequential Pipelined Imaging with Wavefront Coding and Super Resolution

Wavefront coding has long offered the prospect of mitigating optical aberrations and extended depth of field, but image quality and noise performance are inevitably reduced. We report on progress in the use of agile encoding and pipelined fusion of image sequences to recover image quality

A deep-learning approach for high-speed Fourier ptychographic microscopy

We demonstrate a new convolutional neural network architecture to perform Fourier ptychographic Microscopy (FPM) reconstruction, which achieves high-resolution phase recovery with considerably less data than standard FPM.https://www.researchgate.net/profile/Thanh_Nguyen68/publication/325829575_A_deep-learning_approach_for_high-speed_Fourier_ptychographic_microscopy/links/5b2beec20f7e9b0df5ba4872/A-deep-learning-approach-for-high-speed-Fourier-ptychographic-microscopy.pdfhttps://www.researchgate.net/profile/Thanh_Nguyen68/publication/325829575_A_deep-learning_approach_for_high-speed_Fourier_ptychographic_microscopy/links/5b2beec20f7e9b0df5ba4872/A-deep-learning-approach-for-high-speed-Fourier-ptychographic-microscopy.pdfhttps://www.researchgate.net/profile/Thanh_Nguyen68/publication/325829575_A_deep-learning_approach_for_high-speed_Fourier_ptychographic_microscopy/links/5b2beec20f7e9b0df5ba4872/A-deep-learning-approach-for-high-speed-Fourier-ptychographic-microscopy.pdfhttps://www.researchgate.net/profile/Thanh_Nguyen68/publication/325829575_A_deep-learning_approach_for_high-speed_Fourier_ptychographic_microscopy/links/5b2beec20f7e9b0df5ba4872/A-deep-learning-approach-for-high-speed-Fourier-ptychographic-microscopy.pdfhttps://www.researchgate.net/profile/Thanh_Nguyen68/publication/325829575_A_deep-learning_approach_for_high-speed_Fourier_ptychographic_microscopy/links/5b2beec20f7e9b0df5ba4872/A-deep-learning-approach-for-high-speed-Fourier-ptychographic-microscopy.pdfhttps://www.researchgate.net/profile/Thanh_Nguyen68/publication/325829575_A_deep-learning_approach_for_high-speed_Fourier_ptychographic_microscopy/links/5b2beec20f7e9b0df5ba4872/A-deep-learning-approach-for-high-speed-Fourier-ptychographic-microscopy.pdfPublished versio

Sampling and processing for multiple scattering in inline compressive holography

Inline holography is approached from a computational perspective by incorporating a nonlinear forward model based on the iterative Born approximation (IBA). Sampling and its effects on multiple scattering computations are discussed.Published versio

Miniature Fourier Ptychography Microscope using Raspberry Pi Camera and Hardware

We report a Fourier ptychography setup using a raspberry pi camera sensor and its lens in reversed configuration. In this work data acquisition was performed by means of a raspberry pi board which eliminates the requirement of a computer for data acquisition thus allowing a miniaturized system for remote data acquisition costing around £100