Re-enterant efficiency of phototaxis in Chlamydomonas reinhardtii cells

Phototaxis is one of the most fundamental stimulus-response behaviors in biology wherein motile micro-organisms sense light gradients to swim towards the light source. Apart from single cell survival and growth, it plays a major role at the global scale of aquatic ecosystem and bio-reactors. We study photoaxis of single celled algae Chalmydomonas reinhardtii as a function of cell number density and light stimulus using high spatio-temporal video microscopy. Surprisingly, the phototactic efficiency has a minimum at a well-defined number density, for a given light gradient, above which the phototaxis behaviour of collection of cells can even exceed the performance obtainable from single isolated cells. We show that the origin of enhancement of performance above the critical concentration lies in the slowing down of the cells which enables them to sense light more effectively. We also show that this steady state phenomenology is well captured by a modelling the phototactic response as a density dependent torque acting on an active Brownian particle

Design and Analysis of Dual Band Micro strip Patch Antenna

This thesis involves the design and analysis of Dual band Microstrip patch antenna which operates at lower and upper resonating frequency of 3.05 GHz and 7.24 GHz respectively. Basically transmission line modelling approach has been used to model the antenna. The proposed antenna has been fed with 50O microstrip feed line. In the first frequency band we have bandwidth of 310MHz (2.91-3.22 GHz) with gain and directivity 3.304dB and 4.393dBi respectively. The second frequency band has a bandwidth of 580MHz (6.69-8.27 GHz) with gain and directivity of 3.534dB and 5.516dBi. Radiation efficiency at the two bands of operations are 75.12% and 63.52% respectively. Design parameters for the proposed antenna have been calculated from the transmission line model equations considering the effects of introducing inset notch parallel to the radiating edge of the antenna. Ground plane dimensions have been optimized by analyzing the antenna characteristics through parametric study. The CST Microwave Studio software has been used to implement the desired design and various antenna parameters have been studied. Furthermore, an attempt has been taken to calculate the return loss vs frequency response through MATLAB coding. The proposed antenna covers a good portion of S-band and C-band. It can be embedded in mobile devices for the purposes of mobile WiMAX, Wi-Fi, Bluetooth and WLAN operations due to its very small size and weight. Also it can be used by weather radar, surface ship radar, and some communications satellites for various surveillance and communication purpose

Direct Observation of Unusual Interfacial Dzyaloshinskii-Moriya Interaction in Graphene/NiFe/Ta Heterostructure

Graphene/ferromagnet interface promises a plethora of new science and technology. The interfacial Dzyaloshinskii Moriya interaction (iDMI) is essential for stabilizing chiral spin textures, which are important for future spintronic devices. Here, we report direct observation of iDMI in graphene/Ni80Fe20/Ta heterostructure from non-reciprocity in spin-wave dispersion using Brillouin light scattering (BLS) technique. Linear scaling of iDMI with the inverse of Ni80Fe20 thicknesses suggests primarily interfacial origin of iDMI. Both iDMI and spin-mixing conductance increase with the increase in defect density of graphene obtained by varying argon pressure during sputter deposition of Ni80Fe20. This suggests that the observed iDMI originates from defect-induced extrinsic spin-orbit coupling at the interface. The direct observation of iDMI at graphene/ferromagnet interface without perpendicular magnetic anisotropy opens new route in designing thin film heterostructures based on 2-D materials for controlling chiral spin structure such as skyrmions and bubbles, and magnetic domain-wall-based storage and memory devices

Spin pumping and spin torque in interfacial tailored Co2FeAl/\b{eta}-Ta layers

The Heusler ferromagnetic (FM) compound Co2FeAl interfaced with a high-spin orbit coupling non-magnetic (NM) layer is a promising candidate for energy efficient spin logic circuits. The circuit potential depends on the strength of angular momentum transfer across the FM/NM interface; hence, requiring low spin memory loss and high spin-mixing conductance. To highlight this issue, spin pumping and spin-transfer torque ferromagnetic resonance measurements have been performed on Co_2FeAl/\beta-Ta heterostructures tailored with Cu interfacial layers. The interface tailored structure yields an enhancement of the effective spin-mixing conductance. The interface transparency and spin memory loss corrected values of the spin-mixing conductance, spin Hall angle and spin diffusion length are found to be 3.40 \pm 0.01 \times 10^{19} m^{-2}, 0.029 \pm 0.003, and 2.3 \pm 0.5 nm, respectively. Furthermore, a high current modulation of the effective damping of around 2.1 % has been achieved at an applied current density of 1 \times 10^9 A/m^2 , which clearly indicates the potential of using this heterostructure for energy efficient control in spin devicesComment: 12 Pages, 8 figures, 1 table, Magnetic heterostructures for spin-torque oscillator

Effect of in-situ electric field assisted growth on anti-phase boundaries in epitaxial Fe3O4 thin films on MgO

Anti-phase boundaries (APBs) normally form as a consequence of the initial growth conditions in all spinel ferrite thin films. The presence of APBs in epitaxial films of the inverse spinel Fe3O4 alters their electronic and magnetic properties due to strong antiferromagnetic (AF) interactions across these boundaries. The effect of using in-situ electric field assisted growth on the migration of APBs in hetero epitaxial Fe3O4(100)/MgO(100) thin films have been explored in the present work. The electric field assisted growth is found to reduce the AF interactions across APBs and as a consequence APBs free thin film like properties are obtained, which have been probed by electronic, magnetic and structural characterization. An increase in energy associated with the nucleation and/or early stage of the growth and, therefore, a corresponding increase in surface mobility of the ad-atoms play a critical role in controlling the density of APBs. This innovative technique can be employed to grow epitaxial spinel thin films with controlled AF interactions across APBs.Comment: 15 Pages, 7 Figures, 1 Table, Regular Articl

Roles of members of the conserved DedA/Tvp38 membrane protein family in Escherichia coli drug resistance and alkaline pH tolerance

The objective of this dissertation is to understand the functions of Escherichia coli YqjA and YghB, which are members of the conserved DedA/Tvp38 membrane protein family. YqjA and YghB are inner membrane (IM) proteins with multiple predicted membrane–spanning domain, sharing 62% amino acid identity and partly overlapping functions. Simultaneous in-frame deletions of these two genes in a strain named BC202 results in various phenotypes including cell division defects, temperature sensitivity, and sensitivity to drugs and alkaline pH. The cell division defect of BC202 is due to the inefficient secretion of periplasmic amidases by the twin arginine transport (Tat) pathway into the periplasm and drug sensitivity is due to the inefficient function of various drug efflux pumps. Both these phenotypes are related to the loss of proton motive force (PMF) in BC202. Overexpression of MdfA, a Na+-K+/H+ antiporter or growth in acidic media has the ability to rescue all the phenotypes of BC202. In addition, the ∆yqjA mutant (but not the ∆yghB mutant) is alkaline sensitive and overexpression of yqjA can restore growth at alkaline pH only when more than 100mM of sodium or potassium ions is present in the growth medium. Osmotic pressure augments the YqjA mediated growth at alkaline pH. Furthermore, charged amino acids are also essential for YqjA and YghB function that were previously shown important for various secondary transporters. Additionally, yqjA expression is higher at alkaline pH and increased expression of yqjA also required sodium/potassium salts above pH 9.0. The transcriptional regulator CpxR is required for the expression of yqjA at alkaline pH in the presence of Na+/K+. Based on these results, we suggest YqjA and YghB are osmosensing proton-dependent transporters required for E. coli drug resistance and alkaline pH tolerance

A case study of death and bereavement arising from political violence in Nepal

This thesis is about death and bereavement arising from political violence in Nepal. Throughout the thesis, an attempt is made to analyse death and bereavement in the context of a post-conflict situation with an emphasis on the people‘s engagement with death and their coping mechanisms for grief and loss. Chapter one, as the 'Introduction', outlines the background framework as well as the rationale for this thesis. A layout of the broader socio-economic and political picture of Nepal is presented so as to place the study of death and bereavement within a contemporary Nepali perspective. The second chapter, titled 'Death: Meanings and Perceptions', presents historical and theoretical perspectives in which death and bereavement in the post-conflict Nepal must be discussed. The third chapter 'Researching Politically Implicated Violent Death: Some Methodological Issues' provides the rationale for employing a qualitative methodology, particularly 'multi-sited' ethnography, which was used to collect data. The challenges and complications of being in the field are discussed in detail. Drawing upon analysis, the fourth chapter, 'Understanding of Death in Post-Conflict Nepali Society' discusses the meaning of death in detail. The analysis highlights the ways in which the meanings of death constructed in various cases are interconnected with one another in some visible or invisible form, concluding that death was not only a sense of acceptance or rejection but also seen as a transcendental approach and a means to self-actualisation. Furthermore, the meaning of death, appear to overlap within categories and to extend beyond the limits of categories to give a pragmatic outlook to life. Chapter five, discusses the way in which the deceased were commemorated under the heading 'Commemorating Violent Death: Ritual Perspectives and Practices', suggesting that death, when viewed through the lens of rituals, it presented a complicated case. Rituals appeared as important but challenging to incorporate, which had its implications and was recognised as a social issue as well as a political problem. Chapter six analyses grief and bereavement patterns under the title 'Understanding Grief and Bereavement following Violent Death'. It notes that handling grief and the ways of bereavement were significant when death was put to the test with the concept of living. The meaning for living was important, and was particularly envisaged within a 'dukkha' model of grief. It was the concept of everyday living that encouraged family members to recreate their own worldviews. Finally, chapter seven, titled 'Conclusion – towards a Framework for Understanding Political Death in Nepal' concludes the thesis, suggesting that it is necessary to understand death in its complexities, if life is to be lived in its totality, of which the understanding of death and grieving in a micro and macro perspective are an important part

Unconfined Compressive Strength of Bentonite - Lime-Phosphogypsum Mixture Reinforced with Sisal Fibers

This paper presents the effect of sisal fibers on the unconfined compressive strength of bentonite. The present study is aimed at determining the behavior of bentonite-lime-phosphogypsum reinforced with sisal fibers in a random manner. The sisal fiber content was varied from 0.5 to 2 %. The results indicated that the unconfined compressive strength of bentonite can be increased by the addition of lime, phosphogypsum and sisal fibers. The increase in unconfined compressive strength was highest with 8 % lime, 8 % phosphogypsum and 1 % sisal fibers. The reference mix reinforced with sisal fibers was able to bear higher strains at failure as compared to bentonite and bentonite- lime-phosphogypsum mixture. With the increase in sisal fiber content (0.5 to 2 %) in reference mix, there was an increase in the unconfined compressive strength. The bentonite - lime-phosphogypsum-sisal fiber mixture will boost the construction of temporary roads on such problematic soils. Further, its use will also provide environmental motivation for providing a means of consuming large quantities of phosphogypsum and natural fibers

LEARNING THEORIES: REFLECTION DURING ENGLISH CLASSES AT SENIOR SECONDARY LEVEL

This research paper observes the reflection of various learning theories during actual classroom teaching learning situations by using mixed method approach. The sample used in the study includes students studying in class xi and xii of both CBSE and RBSE affiliated schools and trained teachers teaching at senior secondary level of Jaipur district. The tool used in the study is self-constructed observation schedule.  Article visualizations