PubMed Health⌕ Search

Biomedical subjects

Akhlesh Lakhtakia

Publications and source records attributed to Akhlesh Lakhtakia.

9 recordsLinked to original sources
PubMed2006

Biological reduction of nanoengineered iron(III) oxide sculptured thin films.

Sculptured thin films (STFs) are assemblies of nominally identical, parallel nanowires with tailored shapes such as chevrons and spirals. A series of iron(lll) STFs were produced with varied crystallinity (from hematite toferrihydrite) and nanowire shapes (slanted columnar, clockwise helical, and counterclockwise helical). When the dissimilatory metal-reducing bacterium Shewanella putrefaciens CN32 was used to measure their bioreducibility, it was found that bioreduction was controlled primarily by oxide crystallinity. STFs were characterized by scanning electron microscopy, atomic force microscopy, and grazing incidence small-angle X-ray scattering. Postbioreduction characterizations determined that mineralogy of the film materials did not change, but surface roughness generally increased. Changes caused by bioreduction were assessed in terms of both transmittance and reflectance of light incident normal to the STFs. The greatest optical changes were obtained with crystalline hematite films. These results underscore the feasibility of an STF-based fiber optic iron(lll) reduction sensor for in situ subsurface deployment.

Ferric Compounds↗
PubMed2006

Classification of dispersion equations for homogeneous, dielectric-magnetic, uniaxial materials.

The geometric representation at a fixed frequency of the wave vector (or dispersion) surface omega(k) for lossless, homogeneous, dielectric-magnetic uniaxial materials is explored for the case when the elements of the relative permittivity and permeability tensors of the material can have any sign. Electromagnetic plane waves propagating inside the material can exhibit dispersion surfaces in the form of ellipsoids of revolution, hyperboloids of one sheet, or hyperboloids of two sheets. Furthermore, depending on the relative orientation of the optic axis, the intersections of these surfaces with fixed planes of propagation can be circles, ellipses, hyperbolas, or straight lines. The understanding obtained is used to study the reflection and refraction of electromagnetic plane waves due to a planar interface with an isotropic medium.

Journal Article↗
PubMed2005

Structurally perturbed chiral Bragg reflectors for elliptically polarized light.

The structure of an inorganic chiral medium represented as a stack of identical form-birefringent layers that twist steadily with increasing thickness is perturbed by realigning a fraction of each layer to a fixed direction. Experimental results show that the resulting chiral-birefringent composite medium exhibits Bragg resonance with elliptically polarized light, and simulations indicate that Bragg reflectors can be designed for any polarization including linear.

Journal Article↗
PubMed2004

Plane-wave diffraction at the periodically corrugated boundary of vacuum and a negative-phase-velocity material.

Considering the diffraction of a plane wave by a periodically corrugated half-space, we show that the transformation of the refracting medium from positive (negative) phase velocity to negative (positive) phase velocity type has an influence on the diffraction efficiencies. This effect increases with increasing corrugation depth, owing to the presence of evanescent waves in the troughs of the corrugated interface.

Journal Article↗
PubMed2004

Plane waves with negative phase velocity in Faraday chiral mediums.

The propagation of plane waves in a Faraday chiral medium is investigated. Conditions for the phase velocity to be directed opposite to the direction of power flow are derived for propagation in an arbitrary direction; simplified conditions which apply to propagation parallel to the distinguished axis are also established. These negative phase-velocity conditions are explored numerically using a representative Faraday chiral medium, arising from the homogenization of an isotropic chiral medium and a magnetically biased ferrite. It is demonstrated that the phase velocity may be directed opposite to power flow, provided that the gyrotropic parameter of the ferrite component medium is sufficiently large compared with the corresponding nongyrotropic permeability parameters.

Journal Article↗
PubMed2003

Supermodes of chiral photonic filters with combined twist and layer defects.

We consider the circularly polarized localized modes of chiral photonic structures with combined central twist and isotropic layer defects. The general filter is shown to suffer from anomalous remittance and saturation of linewidth as the thickness of the structure is increased. However, by choosing parameters that phase match the elements of the round-trip matrix of the isotropic layer defect, we demonstrate the existence of supermodes that maintain exceptional purity of polarization state and exponential decrease in linewidth as the thickness is increased.

Journal Article↗