Engineering Physics

We explore correlations between dynamics of different microtubules in a bundle, via numerical simulations, using a one-dimensional stochastic model of a microtubule. The guanosine triphosphate (GTP)-bound tubulins undergo diffusion-limited binding to the tip. Random hydrolysis events take place along the microtubule and converts the bound GTP in tubulin to guanosine diphosphate (GDP). The microtubule starts depolymerising when the monomer at the tip becomes GDP-bound; in this case, detachment of GDP-tubulin ensues and continues until either GTP-bound tubulin is exposed or complete depolymerisation is achieved. In the latter case, the microtubule is defined to have undergone a “catastrophe”. Our results show that, in general, the dynamics of growth and catastrophe in different microtubules are coupled to each other; the closer the microtubules are, the stronger the coupling. In particular, all microtubules grow slower, on average, when brought closer together. The reduction in growth velocity also leads to more frequent catastrophes. More dramatically, catastrophe events in the different microtubules forming a bundle are found to be correlated; a catastrophe event in one microtubule is more likely to be followed by a similar event in the same microtubule. This propensity of bunching disappears when the microtubules move farther apart.

ABSTRACT We report our experimental observations of variation in on-off statistics and fluorescence intensity of single Rhodamine6G molecules in presence of resonantly driven surface plasmon of silver nanoparticle. Derived lifetimes from on-off statistics of fluorophore show that interaction between the fluorophore and the subwavelength metal nanoparticle improves photostability and enhances fluorescence intensity. This enhancement follows the trend predicted by the dipole-dipole interaction model. Key word list: Rhodamine 6G, SMF, ...

The existence of a real quadratic polynomial factor, given any polynomial with real coefficients, is proven using only elementary real analysis. The aim is to provide an approachable proof to anyone familiar with the least upper bound property for real numbers, continuity and growth property of polynomials. Complex numbers naturally arise as solutions to the general real quadratic divisors of any polynomial.

The resonance wavelength, where a fiber mode converter grating written using periodic external perturbations achieves phase matching, is both a critical design parameter and a device parameter. However, a method to precisely predict the resonance wavelength for any new fiber and grating writing apparatus has been missing so far. The missing link was the lack of direct experimental methods to estimate the modified intermodal phase after writing with external perturbations. The presented method can make this estimation from a single experiment, over a broad wavelength range, based on a novel mathematical connection between two-mode interference and mode conversion. Using the novel methods, experimentally measured resonance wavelengths for different pitch and irradiation conditions have been predicted within relative errors of 4×10-3.

Given any polynomial with real coefficients, the existence of a real quadratic polynomial factor is proven using only basic real analysis. The aim is to provide an approachable proof to anybody who is familiar with the least upper bound property for real numbers, continuity and growth property of polynomials, and unfamiliar with complex numbers, field extension or advanced topology.

Achieving large bandwidth at strong mode conversion strengths is a central problem in few-mode optical waveguides. Externally-written gratings for broadband operation have missed multiple points as yet: (a) use of a single phase shift in a standard grating, (b) requisite control of the critical phase shift value at resonance wavelength, and (c) deterministic method for placement of the phase shift(s) accommodating the change in waveguide properties during grating writing. From semi-analytical considerations, we show that our unique design of a single-phase-shifted grating increases the bandwidth at 99 \% conversion strength by more than 2.8 times, for which we also elucidate crucial parameter tolerances. The phase-shift placement is determinable on-the-go from the conversion spectra, thereby obviating any estimation of modified waveguide properties during grating-writing. This offers the longed on-demand in-fiber solution for dispersion control in fiber laser cavities and communicat...

Two-mode interference and fibre Bragg grating were used to characterize the strain and temperature sensitivity of a few-mode fibre around the group velocity equalization wavelength. The sensitivity increase near the group velocity equalisation wavelength was characterized.

Without resorting to complex numbers or any advanced topological arguments, we show that any real polynomial of degree greater than two always has a real quadratic polynomial factor, which is equivalent to the fundamental theorem of algebra. The proof uses interlacing of bivariate polynomials similar to Gauss’s first proof of the fundamental theorem of algebra using complex numbers, but in a different context of division residues of strictly real polynomials. This shows the sufficiency of basic real analysis as the minimal platform to prove the fundamental theorem of algebra.

Viruses and their hosts can undergo coevolutionary arms races where hosts evolve increased resistance and viruses evolve counter-resistance. Given these arms race dynamics (ARD), viruses and hosts are each predicted to evolve along a single trajectory as more recently evolved genotypes replace their predecessors. Here, by coupling phenotypic and genomic analyses of coevolving populations of bacteriophage λ and Escherichia coli, we find conflicting evidence for ARD. Virus-host infection phenotypes fit the ARD model, yet whole genome analyses did not. Rather than coevolution unfolding along a single trajectory, cryptic genetic variation emerges during initial virus-host coevolution. This variation is maintained across generations and eventually supplants dominant lineages. These observations constitute what we term 'leapfrog' coevolutionary dynamics, revealing weaknesses in the predictive power of standard coevolutionary models. The findings shed light on the mechanisms that s...

During the struggle for survival, populations occasionally evolve new functions that give them access to untapped ecological opportunities. Theory suggests that coevolution between species can promote the evolution of such innovations by deforming fitness landscapes in ways that open new adaptive pathways. We directly tested this idea by using high throughput gene editing-phenotyping technology (MAGE-Seq) to measure the fitness landscape of a virus, bacteriophage λ, as it coevolved with its host, the bacterium Escherichia coli. Through computer simulations of λ’s evolution on the empirical fitness landscape, we showed that λ was more likely to evolve to use a new receptor if it experienced a shift in its fitness landscape caused by coevolution. This result was further validated by additional laboratory experiments. This study provides direct evidence for the role of coevolution in driving evolutionary novelty and provides a quantitative framework for predicting evolution in coevolvi...

Field emission from hollow pillars of multi wall carbon nanotubes show lower screening effect and their turn on field can be tailored by tuning the annular width of the pillars. Simulations show that the energy variation in the extracted electrons can be decreased by lowering the ...

Field emission from hollow pillars of multi wall carbon nanotubes show lower screening effect and their turn on field can be tailored by tuning the annular width of the pillars. Simulations show that the energy variation in the extracted electrons can be decreased by lowering the annular width of the hollow pillars; for the hollow pillars of 10 μm annular width the energy width is ~0.5 eV, fourfold lower than the solid pillars. This can reduce further by reducing the annular width of the pillars paving the way forward for the monochromatic electron emission.

Students learn a particular concept when their prior misconceptions are conflicted (Duit & Treagust, 2003). Students’ misconceptions generally coincide with previous scientists’ wrong beliefs (Wandersee, 1985). Seker and Welsh (2006) showed significant differences in the change of perceptions of the nature of science due to the use of History of Science in teaching science. This research study is aimed at clearing students’ misconceptions by introducing them to research work done by previous scientists. The study also focuses on students’ misconceptions regarding how plants gain mass. Many students as well as adults think that plants gain a majority of their mass by absorbing water and/or contents from soil (Taber K, 2002).  Jan Helmont had similar beliefs which were corrected by Nicolas Theodor de Saussure in 19th century. A content flow was designed consisting of research work done by Jan Helmont, Priestley, Ingen-Housz and Nicolas Theodor. It also includes 2 open ended questions to probe students’ deeper understanding of the nature of science. Students were introduced to experiments performed by these 4 scientists and they had to note down their observations, infer from them and had to draw conclusions based on observations. Content effectiveness was tested on 84 students of class 7 and 8. Only 2 out of 84 students could answer correctly in the pre-test, while 44 out of 84 were able to answer correctly in the post-test after intervention. This study shows the potential of using History of Science as a tool in clarifying students' misconceptions in science.
Keywords – History of Science, misconceptions, gain in plant’s mass, photosynthesis, nature of science