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Search Results: 1 - 7 of 7 matches for " Budhachandra Khundrakpam "
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Scaling in topological properties of brain networks
Soibam Shyamchand Singh,Khundrakpam Budhachandra Singh,Romana Ishrat,B. Indrajit Sharma,R. K. Brojen Singh
Physics , 2015,
Abstract: The organization in brain networks shows highly modular features with weak inter-modular interaction. The topology of the networks involves emergence of modules and sub-modules at different levels of constitution governed by fractal laws. The modular organization, in terms of modular mass, inter-modular, and intra-modular interaction, also obeys fractal nature. The parameters which characterize topological properties of brain networks follow one parameter scaling theory in all levels of network structure which reveals the self-similar rules governing the network structure. The calculated fractal dimensions of brain networks of different species are found to decrease when one goes from lower to higher level species which implicates the more ordered and self-organized topography at higher level species. The sparsely distributed hubs in brain networks may be most influencing nodes but their absence may not cause network breakdown, and centrality parameters characterizing them also follow one parameter scaling law indicating self-similar roles of these hubs at different levels of organization in brain networks.
Anatomical Substrates of the Alerting, Orienting and Executive Control Components of Attention: Focus on the Posterior Parietal Lobe
Xuntao Yin, Lu Zhao, Junhai Xu, Alan C. Evans, Lingzhong Fan, Haitao Ge, Yuchun Tang, Budhachandra Khundrakpam, Jian Wang, Shuwei Liu
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0050590
Abstract: Both neuropsychological and functional neuroimaging studies have identified that the posterior parietal lobe (PPL) is critical for the attention function. However, the unique role of distinct parietal cortical subregions and their underlying white matter (WM) remains in question. In this study, we collected both magnetic resonance imaging and diffusion tensor imaging (DTI) data in normal participants, and evaluated their attention performance using attention network test (ANT), which could isolate three different attention components: alerting, orienting and executive control. Cortical thickness, surface area and DTI parameters were extracted from predefined PPL subregions and correlated with behavioural performance. Tract-based spatial statistics (TBSS) was used for the voxel-wise statistical analysis. Results indicated structure-behaviour relationships on multiple levels. First, a link between the cortical thickness and WM integrity of the right inferior parietal regions and orienting performance was observed. Specifically, probabilistic tractography demonstrated that the integrity of WM connectivity between the bilateral inferior parietal lobules mediated the orienting performance. Second, the scores of executive control were significantly associated with the WM diffusion metrics of the right supramarginal gyrus. Finally, TBSS analysis revealed that alerting performance was significant correlated with the fractional anisotropy of local WM connecting the right thalamus and supplementary motor area. We conclude that distinct areas and features within PPL are associated with different components of attention. These findings could yield a more complete understanding of the nature of the PPL contribution to visuospatial attention.
Effect of Perturbations in Coriolis and Centrifugal Forces on the Nonlinear Stability of Equilibrium Point in Robe's Restricted Circular Three-Body Problem
P. P. Hallan,Khundrakpam Binod Mangang
Advances in Astronomy , 2008, DOI: 10.1155/2008/425412
Abstract: The effect of perturbations in Coriolis and cetrifugal forces on the nonlinear stability of the equilibrium point of the Robe's (1977) restricted circular three-body problem has been studied when the density parameter K is zero. By applying Kolmogorov-Arnold-Moser (KAM) theory, it has been found that the equilibrium point is stable for all mass ratios μ in the range of linear stability 8/9
Band Structure, Reflection Properties and Abnormal Behaviour of One-Dimensional Plasma Photonic Crystals
Vipin Kumar;Khundrakpam Saratchandra Singh;Sant Prasad Ojha
PIER M , 2009, DOI: 10.2528/PIERM09101701
Abstract: In this paper, some studies on one-dimensional plasma photonic crystal (PPC) containing alternate layers of dielectric and micro-plasma have been presented. The band structures, reflectivity, group velocities and effective group index of such photonic crystals have been studied. For the purpose of computation, we have used transfer matrix method. In this study, we take two PPC structures named PPC1 and PPC2. In PPC1, we take SO as the material for the dielectric layers whereas in PPC2, we take TO as the material for the dielectric layers. It is found that the forbidden band gap(s) can be increased by increasing the thickness of plasma layers. The ranges of 100% reflection is found to be in the higher normalized frequency region in the case of PPC1 whereas in PPC2 the ranges of 100% reflection is found in the lower normalized frequency region. It is also found that for a certain normalized frequency, the group velocity becomes negative in both PPCs. However, the range of normalized frequency for which the group velocity is negative is larger in the case PPC1 than in PPC2. This abnormal behaviour of group velocities of both PPCs results in superluminal propagation (speed of EM wave in PPC greater than speed of light) of electromagnetic waves. Also, because of the abnormal behaviour of group velocity, effective group index becomes negative and possesses ultra high values. uch structures may be considered as a flip flop as there is positive and negative symmetry of effective group velocity. Also, PPC2 exhibits superluminal propagation for wider range of normalized frequency where there is superluminal propagation inside the structure as compared to that of PPC1.
Broadening of Omnidirectional Photonic Band Gap in Si-Based One Dimensional Photonic Crystals
Vipin Kumar;Khundrakpam Saratchandra Singh;Sudesh Kumar Singh;Sant Prasad Ojha
PIER M , 2010, DOI: 10.2528/PIERM10062807
Abstract: A simple design of one dimensional gradual stacked photonic crystal (GSPC) structure has been proposed. The proposed structure consists of a periodic array of alternate layers of SiO2 and Si as the materials of low and high refractive indices respectively. The structure considered here has three stacks of periodic structures with five layers each. The lattice period of successive stack is increased by a certain multiple (say gradual constant, γ) of the lattice period of the just preceding stack. For numerical computation, the method of transfer matrix method (TMM) has been employed. It is found that such a structure has wider reflection bands in comparison to a conventional dielectric PC structure, and the width of the omni-directional reflection (ODR) bands can be enlarged by increasing the value of the gradual constant. Hence, a GSPC structure can be used as a broadband omnidirectional reflector, and the bandwidth of omni-directional gaps can be tuned to a desired wavelength region by choosing appropriate value of γ.
Thermal Expansion of Photonic Band Gap for One Dimensional Photonic Crystal
Bhuvneshwer Suthar;Vipin Kumar;Arun Kumar;Khundrakpam Saratchandra Singh;Anami Bhargava
PIER Letters , 2012, DOI: 10.2528/PIERL12041906
Abstract: The effect of temperature on the photonic band gap has been investigated. One dimensional photonic crystal in the form of Si/air multilayer system has been studied in this communication. The refractive index of silicon layers is taken as a function of temperature and wavelength both. Therefore, this study may be considered to be physically more realistic. It may be useful for computing the optical properties for wider range of wavelength as well as temperature. We can use the proposed structure as temperature sensing device, narrow band optical filter and in many optical systems.
Tunable Wavelength Demultiplexer for Dwdm Application Using 1-D Photonic Crystal
Arun Kumar;Bhuvneshwer Suthar;Vipin Kumar;Khundrakpam Saratchandra Singh;Anami Bhargava
PIER Letters , 2012, DOI: 10.2528/PIERL12042009
Abstract: Transmission characteristics of 1-D photonic crystal (PC) structure with a defect have been studied. We consider a Si/ZnS multilayer system. We also consider the refractive index of both layers to be dependent on temperature and wavelength simultaneously. The refractive indices of Si and ZnS layers are functions of temperature as well in the wavelength of incident light. This property can be used while tuning defect modes at desired wavelength. As defect modes are function of temperature, one can tune the defect modes to desired wavelength. It is found that the average change in central wavelength of each defect mode is 0.07 nm/K. This property can be exploited in the design of a tunable wavelength demultiplexer for DWDM application in optical communication.
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