Suppressed weak antilocalization in the topological insulator Bi2Se3 proximity coupled to antiferromagnetic NiO

Bhowmick, T.,Jerng, S. K.,Jeon, J.,Roy, S.,Kim, Y.,Seo, J.,Kim, J.,Chun, S. H. Royal Society of Chemistry 2017 Nanoscale Vol.9 No.2

<P>Time-reversal symmetry (TRS) breaking of the topological insulators (TIs) is a prerequisite to observe the quantum anomalous Hall effect (QAHE) and topological magnetoelectric effect (TME). Although anti-ferromagnetism as well as ferromagnetism could break the TRS and generate massive Dirac surface states in the TIs, no attention has been paid to the antiferromagnet-TI heterostructures. Herein, we report the magnetotransport measurements of Bi2Se3 proximately coupled to antiferromagnetic NiO. Thin films of Bi2Se3 were successfully grown on the NiO (001) single crystalline substrates by molecular beam epitaxy. Unexpectedly, we observed a strong suppression of the weak antilocalization effect, which is similar to the case of TIs coupled to the ferromagnetic materials. For the 5 nm-thick Bi2Se3 sample on NiO, we even observed a crossover to weak localization at 2 K. These behaviors are attributed to the strong magnetic exchange field from the Ni 3d electrons. Our results show the effectiveness of the antiferromagnetic materials in breaking the TRS of TIs by the proximity effect and their possible applications for QAHE and TME observations.</P>

Fatigue and debris generation at indentation-induced cracks in silicon

Bhowmick, Sanjit,Cha, Hyunmin,Jung, Yeon-Gil,Lawn, Brian R. Elsevier 2009 ACTA MATERIALIA Vol.57 No.2

<P><B>Abstract</B></P><P>The nature of fatigue in bulk silicon subjected to cyclic loading is considered. Indentation tests with hard spheres of millimeter-scale radius are used to generate fractures principally in {100} silicon surfaces, but also in selected {111} silicon, polycrystalline silicon and {100} monocrystalline germanium surfaces. Pronounced damage accumulation is observed with progressive indenter cycling, as ejection of slabs and particles onto the specimen surfaces. It is argued that the fatigue arises from sliding at friction points within the crack interfaces, with consequent production of debris outside and (ultimately) within the contact. Section views through the indentation sites provide clues as to the material ejection process, involving coalescence of secondary cracks into a primary ring crack to create the slabs. Ejection is facilitated by linkage between adjacent ring cracks, leading ultimately to mass removal.</P>

Calculating Hermitian Forms: The Importance of Considering Singular Points

Somnath Bhowmick,Denis Hagebaum-Reignier,Gwang-Hi Jeung 대한화학회 2020 Bulletin of the Korean Chemical Society Vol.41 No.3

In this paper, we point out the importance of boundary conditions in the evaluation of expectation values of quantum mechanical operators involved in upper bound (i.e., variational principle) or lower bound (e.g., methods using ) calculations. The existence of singular points (or discontinuities) either in the trial function or in the operator itself needs to be carefully handled when calculating integrals, otherwise leads to non-physical (e.g., imaginary) expectation values or to false values. In this case, the use of generalized functions (e.g., Heaviside or Dirac functions) is necessary to cure the singularity problems. As examples to put a stress on this mathematical subtleties, we discuss the wrong and true solutions obtained for the calculation of the mean values of the and (and ) operators using two standard simple models: the one-dimensional harmonic oscillator and the three-dimensional hydrogen atom, along with Slater-type and Gaussian trial functions.

Curcuma longa extract ameliorates motor and cognitive deficits of 6-hydroxydopamine-infused Parkinson’s disease model rats

Sujan Bhowmick,Marzan Sarkar,Jakir Hussain,Mehedi Hassan,Mafroz Basunia,Taslima Nahar,Azizur Rahman,Borhan Uddin,Shahdat Hossain 경희대학교 융합한의과학연구소 2022 Oriental Pharmacy and Experimental Medicine Vol.22 No.4

Parkinson’s disease (PD) results mostly from the degeneration of dopaminergic neurons in the substantia nigra pars compacta. It is characterized by the manifestations of anxiety, tremor, muscle rigidity, bradykinesia and cognitive impairments. Oxidative stress is attributed to the neurodegeneration of PD. Curcuma longa is a commonly used spice and has high levels of anti-oxidative phyto-constituents. Here, we evaluated whether the chronic oral administration of C. longa extract affects the degree of anxiety, neuromotor and cognitive deficits of 6-hydroxydopamine (6-OHDA)-infused PD model rats. Following the surgery, animals were orally administered with C. longa extract for twelve weeks. The degree of anxiety/depression, motor and cognitive performances were determined with a variety of neurobehavioral experimental paradigms, including elevated plus, Morris water maze task, rotarod, open field, forced swim, sucrose preference and tail suspension tests. Brain levels of lipid peroxide (LPO) were measured by standard method. Tumor necrosis factor-α (TNFα), α-synuclein, synaptosomeassociated protein-25 (SNAP25) and brain-derived neurotrophic factor (BDNF) of the brain tissues were measured by ELISA. Oral administration of C. longa significantly (P < 0.05) protected the deterioration of the motor activity, learning-related memory cognitions and the degree of anxiety- and depression-like behaviors in PD model rats. The preventive effects were accompanied with decreased brain levels of LPO, TNFα, α-synuclein and increased levels of cognition-related proteins SNAP-25 and BDNF. The experimental results suggest that C. longa ameliorates PD-like symptoms by suppressing the oxidative/pro-inflammatory stress and levels of α-synuclein and increasing the levels of SNAP-25 and BDNF.

Epidemic Propagation With Polarized Opinions Over Signed Network

Sourav Bhowmick,N. Mohan Kumar,Surajit Panja 제어·로봇·시스템학회 2023 International Journal of Control, Automation, and Vol.21 No.11

This technical note deals with a coupled epidemic-opinion dynamical model over a multiplex network, where the interplay between polarized opinions over social interaction network regarding protective measures and disease spreading captured by susceptible-exposed-infected-vigilant (SEIV) epidemic model over transmission network is investigated. For this coupled model, sufficient condition of the disease free state is obtained for the network epidemic model, while the perceived disease severity drops to zero at this state through opinion sharing. The simulation results corroborate the findings.

Seismic response estimation of steel plate shear walls using nonlinear static methods

Anjan K. Bhowmick,Moon Moon Dhar 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.20 No.4

One of the major components for performance based seismic design is accurate estimation of critical seismic demand parameters. While nonlinear seismic analysis is the most appropriate analysis method for estimation of seismic demand parameters, this method is very time consuming and complex. Single mode pushover analysis method, N2 method and multi-mode pushover analysis method, modal pushover analysis (MPA) are two nonlinear static methods that have recently been used for seismic performance evaluation of few lateral load-resisting systems. This paper further investigates the applicability of N2 and MPA methods for estimating the seismic demands of ductile unstiffened steel plate shear walls (SPSWs). Three different unstiffened SPSWs (4-, 8-, and 15-storey) designed according to capacity design approach were analysed under artificial and real ground motions for Vancouver. A comparison of seismic response quantities such as, height-wise distribution of floor displacements, storey drifts estimated using N2 and MPA methods with more accurate nonlinear seismic analysis indicates that both N2 and MPA procedures can reasonably estimates the peak top displacements for low-rise SPSW buildings. In addition, MPA procedure provides better predictions of inter-storey drifts for taller SPSW. The MPA procedure has been extended to provide better estimate of base shear of SPSW.

Identification of tissue‑specific tumor biomarker using different optimization algorithms

Shib Sankar Bhowmick,Debotosh Bhattacharjee,Luis Rato 한국유전학회 2019 Genes & Genomics Vol.41 No.4

Background Identification of differentially expressed genes, i.e., genes whose transcript abundance level differs across different biological or physiological conditions, was indeed a challenging task. However, the inception of transcriptome sequencing (RNA-seq) technology revolutionized the simultaneous measurement of the transcript abundance levels for thousands of genes. Objective In this paper, such next-generation sequencing (NGS) data is used to identify biomarker signatures for several of the most common cancer types (bladder, colon, kidney, brain, liver, lung, prostate, skin, and thyroid) Methods Here, the problem is mapped into the comparison of optimization algorithms for selecting a set of genes that lead to the highest classification accuracy of a two-class classification task between healthy and tumor samples. As the optimization algorithms Artificial Bee Colony (ABC), Ant Colony Optimization, Differential Evolution, and Particle Swarm Optimization are chosen for this experiment. A standard statistical method called DESeq2 is used to select differentially expressed genes before being feed to the optimization algorithms. Classification of healthy and tumor samples is done by support vector machine Results Cancer-specific validation yields remarkably good results in terms of accuracy. Highest classification accuracy is achieved by the ABC algorithm for Brain lower grade glioma data is 99.10%. This validation is well supported by a statistical test, gene ontology enrichment analysis, and KEGG pathway enrichment analysis for each cancer biomarker signature Conclusion The current study identified robust genes as biomarker signatures and these identified biomarkers might be helpful to accurately identify tumors of unknown origin

In silico markers: an evolutionary and statistical approach to select informative genes of human breast cancer subtypes

Shib Sankar Bhowmick,Debotosh Bhattacharjee,Luis Rato 한국유전학회 2019 Genes & Genomics Vol.41 No.12

Background Recent advancement in bioinformatics offers the ability to identify informative genes from high dimensional gene expression data. Selection of informative genes from these large datasets has emerged as an issue of major concern among researchers. Objective Gene functionality and regulatory mechanisms can be understood through the analysis of these gene expression data. Here, we present a computational method to identify informative genes for breast cancer subtypes such as Basal, human epidermal growth factor receptor 2 (Her2), luminal A (LumA), and luminal B (LumB). Methods The proposed In Silico Markers method is a wrapper feature selection method based on Least Absolute Shrinkage and Selection Operator (LASSO), Covariance Matrix Adaptation Evolution Strategy (CMA-ES) and Support Vector Machine (SVM) as a classifier. Moreover, the composite measure consisting of relevance, redundancy, and rank score of frequently appeared genes are used to select informative genes. Results The informative genes are validated by statistical and biologically relevant criteria. For a comparative evaluation of the proposed approach, biological similarity score designed on semantic similarity measure of GO terms are investigated. Further, the proposed technique is evaluated with 7 existing gene selection techniques using two-class annotated breast cancer subtype datasets. Conclusion The utilization of this method can bring about the discovery of informative genes. Furthermore, under multiple criteria decision-making set-up, informative genes selected by the In Silico Markers are found to be admirable than the compared methods selected genes.

Green synthesis of fluorescent carbon nanoparticles from Lychee (Litchi chinensis) plant

Vidhi Chaudhary,Anil Kumar Bhowmick 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.8

Fluorescent carbon nanoparticles (CNPs) were prepared from waste lychee peel by hydrothermal process using green chemistry. These CNPs were characterized by UV-vis absorption, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. Their morphology was analyzed by field emission scanning electron microscopy. Spherical carbon nanoparticles with a particle size ranging from 40-70 nm were observed. FTIR data indicated that these CNPs were functionalized with hydroxyl and carboxylic or carbonyl group. The maximum fluorescence intensity for these CNPs was observed on the excitation wavelength at 365 nm with emission maxima centered at 450 nm. These particles exhibited excitation wavelength dependent fluorescence emission spectra. CNPs were found to be highly fluorescent and exhibited high water solubility. The band gap was estimated to be 3.8 eV. Therefore, as prepared CNPs would be useful in bioimaging, biolabeling and in the other applications of nanobiotechnology.

SEPARATION AXIOMS ON BI-GENERALIZED TOPOLOGICAL SPACES

Ray, A. Deb,Bhowmick, Rakesh Chungcheong Mathematical Society 2014 충청수학회지 Vol.27 No.3

In this paper, introducing various separation axioms on a bi-GTS, it has been observed that such separation axioms actually unify the well-known separation axioms on topological spaces. Several characterizations of such separation properties of a bi-GTS are established in terms of ${\gamma}_{{\mu}_i,{\mu}_j}$-closure operator, generalized cluster sets of functions and graph of functions.