Electron optics with dirac fermions: electron transport in monolayer and bilayer graphene through magnetic barrier and their superlattices

In this review article we discuss the recent progress in studying ballistic transport for charge carriers in graphene through highly inhomogenous magnetic field known as magnetic barrier in combination with gate voltage induced electrostatic potential. Starting with cases for a single or double magnetic barrier we also review the progress in understanding electron transport through the superlattices created out of such electromagnetic potential barriers and discuss the possibility of experimental realization of such systems. The emphasis is particularly on the analogy of such transport with propagation of light wave through medium with alternating dielectric constant. In that direction we discuss electron analogue of optical phenomena like fabry perot resonances, negative refraction, Goos-H\"anchen effect, beam collimation in such systems and explain how such analogy is going to be useful for device generation. The resulting modification of band structure of dirac fermions, the emergence of additional dirac points was also discussed accompanied by brief section on the interconvertibility of electric and magnetic field for relativistic dirac fermions. We also discuss the effect of such electromagnetic potential barrier on bilayer graphene in a similar framework.Comment: To be published as an invited review article in International Journal of Modern Physics

“Vitamins and Antioxidants Activity of Cassia Siamea Lam Seed’s Oil”

A medicinal plant from the family- Fabaceae, subfamily- Caesalpiniaceae called Cassia Siamea Lam has been chosen for study. In this study, we determined the Antioxidant activity, and Vitamins of Cassia Siamea Lam seed oil. The oil from the seeds of Cassia Siamea Lam was extracted with a Soxhlet extractor using petroleum ether as a solvent. Antioxidant activity was defined by a Spectrophotometer using 2, 2-diphenyl-1-picryl-hydrazyl (DPPH) solvent. Vitamins B1, B2, B3, and Vitamin C were determined by the HPLC technic. The Antioxidant activity of Cassia Siamea Lam seed oil is 7.5mg TE/100g. This oil contains Below Detection Limit of vitamins B1, B2, and B3, as well as 15.70 mg/kg of vitamin C. Vitamin C is essential for a number of body functions, including collagen formation, iron absorption, immune system function, wound healing, and the preservation of cartilage, bones, and teeth. The body needs Vitamins to boost the immune system and speed up wound healing. As an Antioxidant, it acts to shield your cells from free radicals, which have been linked to cancer, heart disease, and other illnesses. This study suggests that Cassia Siamea Lam seed oil is rich in Antioxidants and Vitamin C

A Green's function approach to transmission of massless Dirac fermions in graphene through an array of random scatterers

We consider the transmission of massless Dirac fermions through an array of short range scatterers which are modeled as randomly positioned $\delta$- function like potentials along the x-axis. We particularly discuss the interplay between disorder-induced localization that is the hallmark of a non-relativistic system and two important properties of such massless Dirac fermions, namely, complete transmission at normal incidence and periodic dependence of transmission coefficient on the strength of the barrier that leads to a periodic resonant transmission. This leads to two different types of conductance behavior as a function of the system size at the resonant and the off-resonance strengths of the delta function potential. We explain this behavior of the conductance in terms of the transmission through a pair of such barriers using a Green's function based approach. The method helps to understand such disordered transport in terms of well known optical phenomena such as Fabry Perot resonances.Comment: 22 double spaced single column pages. 15 .eps figure

Reversal of Klein reflection in bilayer graphene

Whereas massless Dirac fermions in monolayer graphene exhibit Klein tunneling when passing through a potential barrier upon normal incidence, such a barrier totally reflects massive Dirac fermions in bilayer graphene due to difference in chirality. We show that, in the presence of magnetic barriers, such massive Dirac fermions can have transmission through even at normal incidence. The general consequence of this behaviour for multilayer graphene consisting of massless and massive modes are mentioned. We also briefly discuss the effect of a bias voltage on such magnetotransport.Comment: 10 double space single column latexed pages, 15 eps files in four figure

Pharmacophore modeling and 3D-QSAR studies of 2,4-disubstituted pyrimidine derivatives as Janus kinase 3 inhibitors

A robust pharmacophore model was developed and the structure-activity relationship was analyzed using 71 pyrimidine derivatives reported for covalent Janus Kinase 3 (JAK3) inhibition. Pharmacophore modeling developed a five featured pharmacophore: one H-bond acceptor, two H-bond donors, one hydrophobic, and one aromatic ring features. The atom-based three-dimensional QSAR models with statistical significance were generated using the training set of 52 compounds. The excellent predictive correlation coefficients were obtained for 3D models determined using a test set of 19 molecules. The generated QSAR model implies that the hydrophobic character is important for the JAK3 inhibitory activity of these compounds. Additionally, electron-withdrawing and hydrogen bond donor groups at specific positions positively contribute to the JAK3 inhibition potency. These results provided essential three-dimensional structural requirements and the crucial binding features of 2,4-disubstituted pyrimidine derivatives, which may direct for the design and discovery of novel potent JAK3 inhibitors. </jats:p

Synthetic and therapeutic potential of 4-thiazolidinone and its analogs

Past researches on 4-thiazolidinone nucleus have revealed the prominent potential of derivatives containing this nucleus to be developed as a potent therapeutic agent. Because of these biological activities, their structure-activity relationship has created an interest for medicinal chemists leading to the discovery of a number of lead molecules. This review highlights the routes for its synthesis and summarizes the past and recent studies on its biological activities to guide the medicinal chemists working on this nucleus in the development of clinically viable drugs.</jats:p

A Comparative Study of UWB Micro-strip Antenna for Wireless Communication and RF Energy Harvesting

Abstract Ultra Wide Band (UWB) is first-class famous technology in recent wireless communication since it affords excessive data rates and excellent high-quality offerings. FCC (Federal Communications Commission) opens a 7.5 GHz spectrum (extending 3.1 GHz - 10.6 GHz) in 2002 for wireless ultra-wide band system [1]. With high data rates of wireless communication technology, UWB is increasingly advancing and the micro-strip antenna is also being developed with bandwidths of 1 to 5%. However, within the ultimate decade, UWB has additionally been proposed as a RF energy harvester. The strategies which enhance bandwidth are one of the popular research areas in patch antenna’s field. The bandwidth is generally described as just a percent of the width of the desired frequency range and the resonant antenna frequencies. Other constraint like return loss, efficient radiation and VSWR (voltage standing wave ratio) are also accustomed to describe the bandwidth of a micro-strip antenna. Several things need to be considered into account in choosing an ideal aerial for Ultra-Wide Band including physical structure, performance and frequency band, and radiation quality and emission pattern.The major issue in UWB antenna system is to achieve only the wide bandwidth with high levels of radiation efficiency and compact size. So several method have been extensively investigated for the wide bandwidth of patch antenna and to optimize the qualities of array antenna, as described in various published articles in this survey paper.</jats:p

Caustical patterns in circular magnetic dots in graphene

The scattered wavefunction of an incoming plane wave of electrons due to a circular symmetric step-like potential shows an interference pattern which resembles that of ‘cup caustics’. The high intensity maximum located around caustics can be calculated from Snell’s law with negative refractive index. This paper investigates the wavefunction for a plane wave incident on a circular magnetic dot where the magnetic field is nonzero only in a finite, circular disc-like region of space in the presence of a commensurate scalar potential barrier and vanishes outside that region. By formulating the optical analogy, the caustical curves are described inside the scattering region in terms of geometrical optics and analyse the effect of magnetic field on it. The caustical curves obtained in the presence of weak magnetic field are found to be rotated as compared to the case in the absence of magnetic field. This theoretical formulation using geometrical optics also captures the features developed due to bending of classical trajectories in the presence of magnetic field