Nonlinear oscillations, chaotic dynamics, and stability analysis of bilayer graphene-like structures.

In this work, we have investigated the nonlinear oscillations and chaotic dynamics of perturbed bilayer graphene-like structures. The potential energy surface (PES) of bilayer graphene-like geometries is obtained by considering interactions of a co-aligned and counter-aligned arrangement of atoms. We studied the dynamics using the Poincaré surface of section for co-aligned hydrofluorinated graphene (HFG) and counter-aligned hexagonal boron nitride (h-BN) and generalized it for other systems using various choices of interaction parameters. The nature of the oscillations is understood via power spectra and the Lyapunov exponents. We found that the PES is very sensitive to the perturbation for all bilayer graphene-like systems. It is seen that the bilayer HFG system displays chaotic oscillations for strong perturbation, while for the h-BN system, the signature of chaos is found for weak perturbation. We have also generalized the work for perturbed bilayer graphene-like geometries, considering different interlayer interactions and the strength of perturbation. We found a signature of transition from regular to quasiperiodic and finally chaotic oscillations tuned via the strength of the perturbation for these geometries. The nature of the equilibrium points for bilayer graphene-like systems is analyzed via Jacobian stability conditions. We found three stable nodes for co-aligned HFG and counter-aligned h-BN systems for all interaction strengths. Though all other nodes are unstable saddle nodes, the signature of a local bifurcation is also found for weak perturbation.

Phenotypic variation of Chitala chitala (Hamilton, 1822) from Indian rivers using truss network and geometric morphometrics.

Chitala chitala (Hamilton, 1822) is an economically important food fish species occurring throughout Indian rivers, which also has ornamental value. This study focuses on morphological variations in C. chitala from seven river basins across India namely; Son, Tons, Ken, Brahmaputra, Ganga, Gomti and Gandak. A truss network was constructed by interconnecting nine landmarks to generate 36 morphometric variables extracted from digital images of specimens sampled from the study locations. Transformed truss measurements were subjected to principal component analysis (PCA), canonical discriminant function analysis (CDFA) and discriminant analyses of principal components (DAPC). DAPC function coefficients performed much better in capturing the variation pattern and discrimination between the rivers which was not achieved using CDFA. Eight truss variables were identified with significant and highest loading for truss variables on principal components and coefficients on discriminant function from DAPC contributing to maximum variation between the rivers. Performance graph and functional distribution of identified truss variables clearly indicated distinction between the rivers. Thin plate spline analysis and procrustes shape analysis further showed the variation in morphology between specimens across the rivers. The significant parameters differentiating specimens from different rivers were linked to dorsal fin origin, the base of the pectoral fin and the perpendicular point on the anal fin from the dorsal fin origin. Variation in the hydrodynamics of the rivers studied might be possibly affecting the fin kinematics and consequently leading to adaption seen as phenotypic variation in C. chitala. The results showcased in the present study shall help in better understanding of intra-specific diversity which is significant for management and conservation of a species.

Mitochondrial DNA markers reveal genetic connectivity among populations of Osteoglossiform fish Chitala chitala.

Genetic diversity and population structure in Indian featherback fish, Chitala chitala (Hamilton, 1822) was investigated by combined analyses of two full mitochondrial genes, ATPase 6/8 and Cytochrome b. A total of 403 individuals, collected from 14 rivers yielded 61 haplotypes. Hierarchical partitioning analysis identified 19.01% variance 'among' and 80.99% variance 'within groups and populations'. The mean coefficient of genetic differentiation (FST) was observed to be significant 0.26 (p < 0.05). Mantel tests rejected the hypothesis that genetic and geographic distances were correlated. The patterns of genetic differentiation, AMOVA and principal coordinate analyses indicated that natural populations were sub-structured and comprised of four genetic stocks of C. chitala in Indian rivers. The results also supported the higher resolution potential of concatenated gene sequences. The knowledge of genetic variation and divergence, from this study, can be utilized for its scientific conservation and management in the wild.

Microsatellite marker set for genetic diversity assessment of primitive Chitala chitala (Hamilton, 1822) derived through SMRT sequencing technology.

In present study, single molecule-real time sequencing technology was used to obtain a validated set of microsatellite markers for application in population genetics of the primitive fish, Chitala chitala. Assembly of circular consensus sequencing reads resulted into 1164 sequences which contained 2005 repetitive motifs. A total of 100 sequences were used for primer designing and amplification yielded a set of 28 validated polymorphic markers. These loci were used to genotype n = 72 samples from three distant riverine populations of India, namely Son, Satluj and Brahmaputra, for determining intraspecific genetic variation. The microsatellite loci exhibited high level of polymorphism with PIC values ranging from 0.281 to 0.901. The genetic parameters revealed that mean heterozygosity ranged from 0.6802 to 0.6826 and the populations were found to be genetically diverse (Fst 0.03-0.06). This indicated the potential application of these microsatellite marker set that can used for stock characterization of C. chitala, in the wild. These newly developed loci were assayed for cross transferability in another notopterid fish, Notopterus notopterus.

The complete mitochondrial genome of olive barb, Systomus sarana sarana (Hamilton, 1822) and its phylogenetic status.

Systomus sarana sarana, commonly known as olive barb, is an important food and ornamental fish species with wide distribution in South Asia. Here, the complete mitogenome was sequenced on HiSeq 2500. With 16,590 nucleotides, the base composition was 32.9% (A), 26% (C), 15.4% (G) and 25.7% (T), comparable with other carps. The clustering pattern depicted the monophyly of S. sarana sarana with sister cyprinids.