Department of Bioscience & Bioengineering

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We consider a model dilute ferrofluid that is subjected to a strong, homogeneous magnetic field directed perpendicular to the surface of the ferrofluid, such that there is a chain formation in the direction perpendicular to the surface of the liquid. We study the propagation of impulses generated at high-frequency across finite times through the ferrofluid chains. Our numerical analysis shows that a very high-frequency sequence of non-linear acoustic pulses of appropriate magnitudes, initiated at the base of the container, can lead to the ejection of desired number of ferrofluid grains through the liquid-air interface. The proposed mechanism, if successfully realized in the laboratory, could help design a nozzle-free, ultrafast, ink-jet printer of unparalleled resolution.

World University root node

Journal of Magnetism and Magnetic Materials

Possibility of controlled ejection of ferrofluid grains from a magnetically ordered ferrofluid using high frequency non-linear acoustic pulses - a particle dynamical study

We present numerical simulations to demonstrate that it may be possible to eject ferrofluid grains from a ferrofluid using non-linear acoustic impulses. The study considers a container with some dilute ferrofluid that is placed in a strong, vertical, homogeneous magnetic field. The field induces the formation of magnetic dipoles into vertical chains that approximately span the region between the base and the surface of the container. We use particle dynamical simulations to show that an impulse generated at the base of any chain, will typically travel as a weakly dispersive bundle of energy. When the impulse magnitudes are appropriate (typically ∼60 m/s or more) the ferrofluid grain nearest to the surface of the liquid may be ejected by the impulse. Since all ferrofluid grains possess a coating of the liquid host, the ejected grain can be used as an ink-drop, with typical diameter of 15 or so nanometers. The velocities of the ejecting grains can be controlled and hence the method, if experimentally feasible, may have wide ranging applications. One of these applications is likely to be in designing special-purpose nozzle-free inkier printers of unprecedented resolution.

Materials Research Society Symposium - Proceedings

Impulse acoustics based ejection of ferrofluid grains from a ferrofluid: The blueprint of a concept for a nozzle-free inkjet printer

Objectives - Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by expansion of GAA repeats in the frataxin gene. We have carried out the first molecular analysis at the Friedreich's ataxia locus in the Indian population. Materials and methods - Three families clinically diagnosed for Friedreich's ataxia were analyzed for GAA expansion at the FRDA locus. The distribution of GAA repeats was also estimated in normal individuals of Indian origin. Results - All patients clinically diagnosed for Friedreich's ataxia were found to be homozygous for GAA repeat expansion. The GAA repeat in the normal population show a bimodal distribution with 94% of alleles ranging from 7-16 repeats. Conclusion - Indian patients with expansion at the FRDA locus showed typical clinical features of Friedreich's ataxia. The low frequency of large normal alleles (6%) could indicate that the prevalence of this disease in the Indian population is likely to be low.

Acta Neurologica Scandinavica

Molecular analysis of Friedreich's ataxia locus in the Indian population

Expansion of CTG/CAG trinucleotide repeats has been shown to cause a number of autosomal dominant cerebellar ataxias (ADCA) such as SCA1, SCA2, SCA3/ MJD, SCA6, SCA7, SCA8 and DRPLA. There is a wide variation in the clinical phenotype and prevalence of these ataxias in different populations. An analysis of ataxias in 42 Indian families indicates that SCA2 is the most frequent amongst all the ADCAs we have studied. In the SCA2 families, together with an intergenerational increase in repeat size, a horizontal increase with the birth order of the offspring was also observed, indicating an important role for parental age in repeat instability. This was strengthened by the detection of a pair of dizygotic twins with expanded alleles showing the same repeat number. Haplotype analysis indicates the presence of a common founder chromosome for the expanded allele in the Indian population. Polymorphism of CAG repeats in 135 normal individuals at the SCA loci studied showed similarity to the Caucasian population but was significantly different from the Japanese population.

Fulltext

Human Genetics

Molecular analysis of autosomal dominant hereditary ataxias in the Indian population: High frequency of SCA2 and evidence for a common founder mutation

The Ising model is known widely for studying equilibrium behavior. We show that the model is also useful for studying nonequilibrium behavior in some special situations. The method of recurrence relations has been applied to obtain the time evolution of a non-commuting spin operator. Also obtained are the structure functions and their time dependent behavior. It is shown that the transverse component of the static susceptibility can be obtained from the dynamic results.

Brazilian Journal of Physics

Time Dependent transverse correlations in the Ising model in D dimensions

Elastic beads repel in a highly nonlinear fashion, as described by Hertz law, when they are compressed against one another. Vertical stacking results in significant compressions of beads at finite distances from the surface of the stack due to gravity. Analytic studies that have been reported in the literature assume acoustic excitations upon weak perturbation [J. Hong et al., Phys. Rev. Lett. 82, 3058 (1999)] and soliton-like excitations upon strong perturbation [V. Nesterenko, J. Appl. Mech. Tech. Phys. 5, 733 (1983); S. Sen and M. Manciu, Physica A 268, 644 (1999)]. The present study probes the position, velocity and acceleration and selected two-point temporal correlations and their power spectra for individual beads for cases in which the system has been (i) weakly, (ii) strongly, and (iii) moderately perturbed at the surface in the sense specified in the text. Our studies reveal the existence of distinctly different dynamical behavior of the tagged beads, in contrast to conventional acoustic response, as the strength of the perturbation is varied at fixed gravitational loading. We also comment on the effects of polydispersity on system dynamics and probe the relaxation of isolated light and heavy beads in the chain. © 2000 American Institute of Physics.

Chaos

Dynamics of a gravitationally loaded chain of elastic beads

The study of sound propagation in granular beds at frequencies exceeding a MHz has been a subject of study for many years. Much remains to be learnt about sound propagation at lower frequencies, We shall present our studies on the problem of impulse propagation and briefly comment on low frequency acoustic propagation in model granular beds using particle dynamical simulations. The following results will be briefly discussed. (i) Impulses propagating as solitary waves in I-D granular chains with Hertz contacts in the absence of precompression. (ii) The effects of uniform precompression and gravitational loading on wave propagation. (iii) Impulse propagation in 3-D granular beds. The research presented shall highlight the intrinsically nonlinear nature of wave propagation in granular beds. © 2000 Materials Research Society.

Materials Research Society Symposium-Proceedings

Impulse and low frequency acoustic wave propagation in granular beds

The organization of neocortex in the short-tailed opossum (Monodelphis domestica) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.

Somatosensory and Motor Research

The organization of somatosensory cortex in the short-tailed opossum (Monodelphis domestica)

Nonlinear acoustic impulses travel as weakly dispersive bundles of energy through 3-D, dry, granular assemblies. Such impulses can therefore be exploited to probe for buried objects in 3-D granular assemblies. In this article, we shall discuss the details of propagation of an impulse generated at the surface of a granular bed. The role of polydispersity will be briefly addressed. The calculations suggest that backscattered data, as received at predetermined locations at the surface, may be helpful in reconstructing an approximate image of the buried inclusion, as viewed from above. © 2000 Materials Research Society.

Backscattering of nonlinear acoustic impulses from buried inclusions in granular beds

We present a detailed report [see S. Sen et al., Phys. Rev. Lett. 77, 4855 (1996)] of our numerical and analytical studies on the relaxation of a classical particle in the potentials [Formula Presented]. Both of the approaches confirm that at all temperatures, the relaxation functions (e.g., velocity relaxation function and position relaxation function) decay asymptotically in time t as [Formula Presented]. Numerically calculated power spectra of the relaxation functions show a gradual transition with increasing temperature from a single sharp peak located at the harmonic frequency [Formula Presented] to a broad continuous band. The [Formula Presented] relaxation is also found when [Formula Presented] is a polynomial in powers of [Formula Presented] with a nonvanishing coefficient accompanying the [Formula Presented] term in [Formula Presented]. Numerical calculations show that in the cases in which the leading term in [Formula Presented] behaves as [Formula Presented] with integer n, the asymptotic relaxation exhibits [Formula Presented] decay where [Formula Presented]. We briefly discuss the analytical approaches to relaxation studies in these strongly anharmonic systems using direct solution of the equation of motion and using the continued fraction formalism approach for relaxation studies. We show that the study of the dynamics of strongly anharmonic oscillators poses unique difficulties when studied via the continued fraction or any other time-series construction based approaches. We close with comments on the physical processes in which the insights presented in this work may be applicable. © 1999 The American Physical Society.