Bipul Das - Academia.edu (original) (raw)

Papers by Bipul Das

Journal of Colloid and Interface Science, 2009

Among many ferromagnetic materials, CoPt alloy nanoparticles with high coercivity and small grain... more Among many ferromagnetic materials, CoPt alloy nanoparticles with high coercivity and small grain size are one of the potential candidates having its application in high-density storage media manufacturing. CoPt alloy nanoparticles of different compositions have been prepared in TX-100 micellar medium and capped with sodium oleate to prevent the agglomeration during annealing at high temperature. Their structural and magnetic properties were investigated before and after heat treatment. The particles with 50:50compositionsofCoandPtgivesL10phaseafterannealingat900°Cfor1handshowahighcoercivity(50:50 compositions of Co and Pt gives L1 0 phase after annealing at 900°C for 1 h and show a high coercivity (50:50compositionsofCoandPtgivesL10phaseafterannealingat900°Cfor1handshowahighcoercivity(4.4 kOe at room temperature) and remanence due to its highly anisotropic L1 0 structure.

Magnetic nanoparticles of high coercivity with small grain size are useful for high-density stora... more Magnetic nanoparticles of high coercivity with small grain size are useful for high-density storage media and CoPt alloys are one of the good candidates for this purpose. We have prepared CoPt alloy nanoparticles of different compositions and investigated their magnetic properties before and after annealing the samples. The micellar technique was used to synthesize the particles. The particles of 50:50 composition of Co and Pt in CoPt alloy shows very promising results in magnetic property among different batches.

Journal of Applied Physics, 2010

We have prepared nanoparticles in micellar medium by wet chemical technique and obtained very hig... more We have prepared nanoparticles in micellar medium by wet chemical technique and obtained very high coercivity value of 4.4 kOe at room temperature for particle size . A large coercivity is observed on cooling down to 2.5 K. We annealed the sample at different temperatures ...

Journal of Applied Physics, 2011

Cation vacancy-induced d0 room temperature ferromagnetism was observed in nonmagnetic potassium (... more Cation vacancy-induced d0 room temperature ferromagnetism was observed in nonmagnetic potassium (K) doped ZnO nanowires (NWs) synthesized within the pores of the anodic aluminum oxide template. The ferromagnetic signature was found to be significantly enhanced in the K-doped ZnO NWs with respect to the pristine ZnO NWs. The photoluminescence studies clearly indicated the presence of a large concentration of zinc vacancies in the K-doped ZnO NWs. An interesting correlation between the saturation magnetization and green luminescence intensity with the increase of K-doping has suggested that the magnetic moment originates due to Zn vacancy defects. It is expected that the incorporation of K-related defects at the Zn site might promote the formation of zinc vacancies in the system and introduce holes to stabilize the hole-mediated room-temperature ferromagnetism. For the doped ZnO NWs the ferromagnetic response was found to be a maximum at an optimum K-concentration of 4 at. %. This study demonstrates that the ferromagnetism in ZnO can be tuned by controlling the cation vacancy-defects with the proper dopant in the host semiconductors.

Atherosclerotic cerebrovascular disease leads to formation of lipid-laden plaques that can form e... more Atherosclerotic cerebrovascular disease leads to formation of lipid-laden plaques that can form emboli when ruptured causing blockage to cerebral vessels. The clinical manifestation of this event sequence is stroke; a leading cause of disability and death. In vivo MR imaging provides detailed image of vascular architecture for the carotid artery making it suitable for analysis of morphological features. Assessing the status of carotid arteries that supplies blood to the brain is of primary interest to such investigations. Reproducible quantification of carotid artery dimensions in MR images is essential for plaque analysis. Manual segmentation being the only method presently makes it time consuming and sensitive to inter and intra observer variability. This paper presents a deformable model for lumen and vessel wall segmentation of carotid artery from MR images. The major challenges of carotid artery segmentation are (a) low signal-to-noise ratio, (b) background intensity inhomogeneity and (c) indistinct inner and/or outer vessel wall. We propose a new, effective object-class uncertainty based deformable model with additional features tailored toward this specific application. Object-class uncertainty optimally utilizes MR intensity characteristics of various anatomic entities that enable the snake to avert leakage through fuzzy boundaries. To strengthen the deformable model for this application, some other properties are attributed to it in the form of (1) fully arc-based deformation using a Gaussian model to maximally exploit vessel wall smoothness, (2) construction of a forbidden region for outer-wall segmentation to reduce interferences by prominent lumen features and (3) arc-based landmark for efficient user interaction. The algorithm has been tested upon T1- and PD-weighted images. Measures of lumen area and vessel wall area are computed from segmented data of 10 patient MR images and their accuracy and reproducibility are examined. These results correspond exceptionally well with manual segmentation completed by radiology experts. Reproducibility of the proposed method is estimated for both intra- and inter-operator studies.

Atherosclerotic cerebrovascular disease leads to formation of lipid-laden plaques that can cause ... more Atherosclerotic cerebrovascular disease leads to formation of lipid-laden plaques that can cause symptoms when ruptured. Recent advances in high-resolution MR imaging now provide detailed images of vascular architecture. A key target of such investigations involves the carotid arteries that provide the blood supply to the brain. Reproducible quantification of plaque volume requires a robust computer-aided plaque segmentation system. Further, plaque

Pattern Recognition, 2007

Object segmentation is of paramount interest in many imaging applications, especially, those invo... more Object segmentation is of paramount interest in many imaging applications, especially, those involving numeric, symbolic, syntactic, or even high level cognitive knowledge perception. Among others, "snake"-an "active contour" model-is a popular boundary-based segmentation approach where a smooth curve is continuously deformed to lock onto an object boundary. The dynamics of a snake is governed by different internal and external forces. A major limitation of the present framework has been the difficulty of incorporating object-intensity driven features into snake dynamics so as to prevent uncontrolled expansion/contraction once the snake leaks through a weak boundary region. In this paper, a local-intensity-driven "adaptive force" is introduced into the model using object class-uncertainty theory. Given a priori knowledge of object/background intensity distributions, class-uncertainty theory yields object/background classification of every location and establishes its confidence level. It has been demonstrated earlier that confidence level is high inside homogeneous regions and low near boundaries. In the current paper, object class-uncertainty theory has been applied to control snake deformation leading to a new adaptive force acting outward (expanding) inside intensity-defined object regions and inward (squeezing) inside background regions. It has been demonstrated that the method possesses potential to resist uncontrolled expansion of a snake contour (for an expanding type) inside background after leaking through a weak boundary. Further, it has been shown that the adaptive force operates in a complementary fashion with the image intensity gradient by reducing its strength near boundaries using the confidence level of classification. Another major contribution of this paper is the formulation of a "hybrid snake" (HS)-a new model, where an initial contour is gradually deformed over a hybrid energy surface composed of some direct energies (e.g., internal energies) and other indirect energies contributed by local contour displacements over a force-field (e.g., image or userconstrained force-field). Applications of the proposed adaptive force-enabled HS on different phantom and real images have been presented and comparisons have been made with a conventional snake (CS). Finally, a quantitative comparison based on computer-generated phantoms at various levels of blur and noise has been provided.

Tree-like vessel structures are an information-rich source for many image analysis tasks. Hence t... more Tree-like vessel structures are an information-rich source for many image analysis tasks. Hence tracking algorithms extracting such structures have wide applicability. However, due to image artifacts and the minute nature of vessels, these algorithms face several challenges; two of the most common ones are 1) early termination, where tracking stops before the structure ends and 2) leaking, where tracking leaks into nearby closed organs or irrelevant structures. To address these issues, this paper makes two main contributions: a generic rebooting scheme that identifies early terminations and then restarts tracking to track objects in their entirety and a modelbased pruning algorithm that uses global optimization to identify and mitigate leaking. The performance of the proposed algorithm is demonstrated by tracking coronary arteries on 3D cardiac Computed Tomography Angiography (CTA) data from 28 human subjects. Our methods dramatically improve tracking results by detecting and recovering from early terminations and identifying and removing leaking in 98% (63 of 64) branches, with a single erroneously removed valid branch.

In this paper an array architecture for computation of Complex Discrete Wavelet Transform has bee... more In this paper an array architecture for computation of Complex Discrete Wavelet Transform has been proposed. The wavelet filter coefficients are realized u sing multiplier less pipelined CORDIC algorithm. The choice of pipelined CORDIC algorithm over the conventional one for realizing the filter coefficient of CDWT is hardware effective and also effects in high frequency operation. The controller unit clusters input samples into even and odd samples coming in proper sequence at each clock cycles. This clustering provides a good amount of parallelism for faster operation of the filter compared to direct filter realization. The 8-tap filter bank is implemented u sing array architecture, effecting in high throughput. The algorithm developed is implemented on FPGA using the Virtex XCV100 series.

Abstract-This paper proposes an automated diagnostic approach for a Doppler ultrasonography syste... more Abstract-This paper proposes an automated diagnostic approach for a Doppler ultrasonography system (DUS) us-ing the spectrogram features and image information. Vari-ous boundary and moment features of the spectrogram are fed to a supervised ANN to diagonise the ...

Summary form only given. An optimized memory organization has been designed for the hierarchical ... more Summary form only given. An optimized memory organization has been designed for the hierarchical coding of wavelet subbands. Changing the RAM access pattern and using multiple location access at each clock instant can accomplish a better economy in time and resources. The ...

In this paper a real-time 3-D discrete wavelet transform algorithm is proposed. The inter-frame d... more In this paper a real-time 3-D discrete wavelet transform algorithm is proposed. The inter-frame decomposition is achieved using the last two frames of the sequence. Reduced buffer and real-time applicability makes the algorithm usable for high-speed bi-directional interactive applications of multimedia and also HOTY. An efficient VLSI architecture which promises 100% hardware utilization low buffering and low hardware complexity is designed for the realization of the 3-D wavelet transform. DWT filters, designed by data-folding architecture and QMF lattice filters are arranged in pipeline to achieve the spatial decomposition with high through-put. A parallel array architecture is used for the decomposition in temporal direction which proves efficient to accomodate the huge amount of data.

Iee Proceedings-computers and Digital Techniques, 2002

Abstract: Frequency analysis using the DFT, the DHT, the DCT or the DST is an obvious choice for ... more Abstract: Frequency analysis using the DFT, the DHT, the DCT or the DST is an obvious choice for the entire image and signal processing domain. A chip has been designed to obtain a unified architecture for the DFT=DHT=DCT=DST called DXT. For the low-power budget of many ...

The aim of this paper is to develop an automated diagnosis system for arterial diseases from the ... more The aim of this paper is to develop an automated diagnosis system for arterial diseases from the Doppler ultrasonography spectrogram. A feature-based classification of Doppler spectrogram has been done for its clinical assessment. Development of the automated diagnostic tool for Doppler spectrogram involves three steps (a) feature extraction, (b) classification of spectrogram based on clinical symptoms and (c) diagnosis of arterial condition of the concerned region. Artificial Neural Network is used for classification of the spectrograms. Arterial condition of a specified region is evaluated from symptoms obtained from a number of spectrograms in the different nearby regions. Bayesian probabilistic method is used for diagnostic evaluation of the arterial status from the obtained spectrogram. The results satisfied 83% of the obtained cases.

This paper proposes a memory efficient real-time 3-D DWT algorithm and its architectural implemen... more This paper proposes a memory efficient real-time 3-D DWT algorithm and its architectural implementation. As the running 3D-DWT refreshes the wavelet coefficients with the arrival of every two new frames, the latency of the conventional 3D-DWT reduces by at least 1/4 times. For realization of the transform canonical signed digit multiplier has been used. Parallelism being an added advantage for fast processing has been used with three pipelined stages in this architecture. For coefficient mapping, correlation between LPF and HPF in orthogonal Daubechies wavelet filter has been used. In this design the memory requirement has been optimized to the order O(KN2 + (K - 2) × N). The proposed architecture has been implemented on Xilinx FPGA devices at an operating frequency of 75 MHz. This low complexity architecture ensures 100% hardware utilization.

Iee Proceedings-circuits Devices and Systems, 2005

A real-time 3-D sub-band coding (SBC) technique using a discrete wavelet transform is proposed. T... more A real-time 3-D sub-band coding (SBC) technique using a discrete wavelet transform is proposed. The main advantages of the proposed scheme lie in the reduction of wait time and diminution of buffer size in 3-D SBC. The major delay which is due to the group of frames (GOF) generation in the temporal direction is decreased by dynamic updating of the transform coefficients. The dynamic updating handles much a lower dimension of data compared to 3-D SBC, and thus facilitates better hardware utilisation with lower overhead. A data-folding architecture is used in unison with the CORDIC-based QMF lattice filters for realisation of 2-D DWTs using a 4-tap Daubechies filter. The data scanning pattern for the spatial domain signal results in a low-complexity control circuit. The multiplierless DWT architecture operating at 100 MHz is implemented on 0.25 mm BiCMOS technology and found to have much lower power dissipation compared to the multiplier-based structures for FIR realisation. The optimised design of the DWT filter using data-folding architecture resulted in an appreciable low memory budget of N 2 /4+2N for 2-D DWT and O(N 2 /M) time required for temporal direction decomposition. Hardware utilisation in the proposed architecture is 100%.

Iee Proceedings-vision Image and Signal Processing, 2004

Snakes, or active contour models are used extensively for image segmentation in varied fields. Ho... more Snakes, or active contour models are used extensively for image segmentation in varied fields. However, some major challenges restrict their use in many fields. The authors propose a new inertial snake model, that introduces an inertial effect of the control points into the snake framework. The proposed inertial force along with the first-and second-order continuity forces controls the spline motion through the concavities and also against weak edge forces. This smart force field, added to the inertial energy framework, posses the ability to adaptively reduce its effect near the true edges, so that the energy minimising spline converges into the edges. A greedy snake has been used for computation of the energy minimising spline. The algorithm has been tested on phantoms and ultrasound images as well. It is shown in the results that the proposed algorithm classifies the object from the background class in most of the images perfectly. Ultrasound images of a lower limb artery of an adult woman have been tested with this algorithm, and also extended for motion tracking.

In this paper a real-time 3-D DWT algorithm and its architecture realization is proposed. Reduced... more In this paper a real-time 3-D DWT algorithm and its architecture realization is proposed. Reduced buffer and low wait-time are the salient features which makes it fit for bidirectional videoconferencing applications mostly in real-time biomedical applications. The proposed algorithm updates the coefficients in the temporal direction with every two new frames. In the architectural implementation, the memory requirement is minimal due to low buffering requirement. The reduced hardware complexity and 100% hardware utilization is ensured in this design. Time area product for the spatial DWT is 1.5 at. This architecture implemented on 0.25 μ BiCMOS technology. At a operating frequency of 100 MHz the power consumption is appreciably lower compared to those reported.

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