Optical transitions in a quantum wire with spin-orbit interaction and its applications in terahertz electronics: Beyond zeroth-order theory

We calculate the terahertz absorption spectra associated with intersubband transitions in a semiconductor quantum wire in the presence of spin-orbit interaction and a transverse magnetic field. The frequencies and intensities of the absorption peaks are found to depend strongly on the spin-orbit coupling strength, which can be varied with an external electric field. This feature can be exploited to realize reconfigurable multispectral terahertz detectors and amplitude and/or frequency modulators. We also show that electric dipole transitions between spin-split levels in the same subband (which are normally deemed forbidden) become allowed because of spin texturing effects. The absorption associated with these transitions experience a redshift (blueshift) with increasing spin-orbit coupling strength for materials with negative (positive) g factor. The normally allowed transitions, on the other hand, experience the opposite shift, i.e., blue for materials with negative g factor and red for materials with positive g factor. The theory described here is universal and applies to all semiconductors

On the Stability of Coherent States for Pais-Uhlenbeck Oscillator

We have constructed coherent states for the higher derivative Pais-Uhlenbeck Oscillator. In the process we have suggested a novel way to construct coherent states for the oscillator having only negative energy levels. These coherent states have negative energies in general but their coordinate and momentum expectation values and dispersions behave in an identical manner as that of normal (positive energy) oscillator. The coherent states for the Pais-Uhlenbeck Oscillator have constant dispersions and a modified Heisenberg Uncertainty Relation. Moreover, under reasonable assumptions on parameters these coherent states can have positive energies.Comment: Title changed, modified version with no major change in results and conclusions, to appear in Mod.Phys.Lett.

Magnetic field effects on spin texturing in a quantum wire with Rashba spin-orbit interaction

A quantum wire with strong Rashba spin-orbit interaction is known to exhibit spatial modulation of spin density along its width owing to coupling between subbands caused by the Rashba interaction. This is known as spin texturing. Here, we show that a transverse external magnetic field introduces additional complex features in spin texturing, some of which reflect the intricate details of the underlying energy dispersion relations of the spin-split subbands. One particularly intriguing feature is a 90° phase shift between the spatial modulations of two orthogonal components of the spin density, which is observed at moderate field strengths and when only the lowest spin-split level is occupied by electrons. Its origin lies in the fact that the Rashba interaction acts as an effective magnetic field whose strength is proportional to the electron’s velocity

Magnetic-field-induced propulsion of jellyfish-inspired soft robotic swimmers

The multifaceted appearance of soft robots in the form of swimmers, catheters, surgical devices, and drug-carrier vehicles in biomedical and microfluidic applications is ubiquitous today. Jellyfish-inspired soft robotic swimmers (jellyfishbots) have been fabricated and experimentally characterized by several researchers that reported their swimming kinematics and multimodal locomotion. However, the underlying physical mechanisms that govern magnetic-field-induced propulsion are not yet fully understood. Here, we use a robust and efficient computational framework to study the jellyfishbot swimming kinematics and the induced flow field dynamics through numerical simulation. We consider a two-dimensional model jellyfishbot that has flexible lappets, which are symmetric about the jellyfishbot center. These lappets exhibit flexural deformation when subjected to external magnetic fields to displace the surrounding fluid, thereby generating the thrust required for propulsion. We perform a parametric sweep to explore the jellyfishbot kinematic performance for different system parameters—structural, fluidic, and magnetic. In jellyfishbots, the soft magnetic composite elastomeric lappets exhibit temporal and spatial asymmetries when subjected to unsteady external magnetic fields. The average speed is observed to be dependent on both these asymmetries, quantified by the glide magnitude and the net area swept by the lappet tips per swimming cycle, respectively. We observe that a judicious choice of the applied magnetic field and remnant magnetization profile in the jellyfishbot lappets enhances both these asymmetries. Furthermore, the dependence of the jellyfishbot swimming speed upon the net area swept (spatial asymmetry) is twice as high as the dependence of speed on the glide ratio (temporal asymmetry). Finally, functional relationships between the swimming speed and different kinematic parameters and nondimensional numbers are developed. Our results provide guidelines for the design of improved jellyfish-inspired magnetic soft robotic swimmers

Identification of novel single nucleotide polymorphism (SNP) in DPB1 gene in ethnic population from West Bengal

HLA-DP antigens present peptides to CD4+ T cells and play an important role in autoimmune diseases and parasitic infections. We have sequenced HLA-DPB1 exon-2 from the ethnic populations in West Bengal, India and report a novel single nucleotide polymorphism (SNP) - rs111221466. The rs111221466 SNP induced silent mutation from CGA (Arg) to TGA (Stop Codon) and showed a frequency of 83.24%. In conventional sense, the frequency of novel SNP is very high. We have sequenced HLA-DPB1 exon-2 from a Bengali Population in West Bengal, India. HLA-DP antigens present peptides to CD4+ T cells and play an important role in autoimmune diseases and parasitic infections. Here, we report a novel single nucleotide polymorphism of HLA-DPB1 gene in the population. rs111221466 showed a frequency of 83.24, which is important to note, in view of common polymorphisms involved in disease susceptibility