33 research outputs found
A new model for magnetoreception
Certain migratory birds can sense the earth's magnetic field. The nature of
this process is not yet properly understood. Here we offer a simple explanation
according to which birds literally `see' the local magnetic field: Our model
relates the well-established radical pair hypothesis to the phenomenon of
Haidinger's brush, a capacity to see the polarisation of light. This new
picture explains recent surprising experimental data indicating long lifetimes
for the radical pair. Moreover there is a clear evolutionary path toward this
field sensing mechanism: it is an enhancement of a weak effect that may be
present in many species.Comment: 8 pages, 5 figures, version of final published pape
Power dependence of size of laser ablated colloidal silver nanoparticles
Silver nanoparticles have been produced by laser ablation of silver metal in
nanopure water without any chemical additives. It has been observed that
laser power has a control over the size of the nanoparticles. Increasing
laser power shows a clear blue shift in the absorption peak of fabricated
nanoparticles indicating that the average size of the particles decreases
with increasing laser power. Ablation for longer period reduces the average
size of nanoparticles which is attributed to the re-ablation of fabricated
nanoparticles. A good correlation has been observed between the peak of the
absorption spectrum measured by UV-VIS spectroscopy and the average particle
size measured by scanning electron microscope imaging method. The value of
the coefficient of correlation is determined to be 0.965
Laser Raman Spectroscopy with Different Excitation Sources and Extension to Surface Enhanced Raman Spectroscopy
A dispersive Raman spectrometer was used with three different excitation sources (Argon-ion, He-Ne, and Diode lasers operating at 514.5 nm, 633 nm, and 782 nm, resp.). The system was employed to a variety of Raman active compounds. Many of the compounds exhibit very strong fluorescence while being excited with a laser emitting at UV-VIS region, hereby imposing severe limitation to the detection efficiency of the particular Raman system. The Raman system with variable excitation laser sources provided us with a desired flexibility toward the suppression of unwanted fluorescence signal. With this Raman system, we could detect and specify the different vibrational modes of various hazardous organic compounds and some typical dyes (both fluorescent and nonfluorescent). We then compared those results with the ones reported in literature and found the deviation within the range of ±2 cm−1, which indicates reasonable accuracy and usability of the Raman system. Then, the surface enhancement technique of Raman spectrum was employed to the present system. To this end, we used chemically prepared colloidal suspension of silver nanoparticles as substrate and Rhodamine 6G as probe. We could observe significant enhancement of Raman signal from Rhodamine 6G using the colloidal solution of silver nanoparticles the average magnitude of which is estimated to be 103
Laser Raman Spectroscopy with Different Excitation Sources and Extension to Surface Enhanced Raman Spectroscopy
A dispersive Raman spectrometer was used with three different excitation sources (Argon-ion, He-Ne, and Diode lasers operating at 514.5 nm, 633 nm, and 782 nm, resp.). The system was employed to a variety of Raman active compounds. Many of the compounds exhibit very strong fluorescence while being excited with a laser emitting at UV-VIS region, hereby imposing severe limitation to the detection efficiency of the particular Raman system. The Raman system with variable excitation laser sources provided us with a desired flexibility toward the suppression of unwanted fluorescence signal. With this Raman system, we could detect and specify the different vibrational modes of various hazardous organic compounds and some typical dyes (both fluorescent and nonfluorescent). We then compared those results with the ones reported in literature and found the deviation within the range of ±2 cm −1 , which indicates reasonable accuracy and usability of the Raman system. Then, the surface enhancement technique of Raman spectrum was employed to the present system. To this end, we used chemically prepared colloidal suspension of silver nanoparticles as substrate and Rhodamine 6G as probe. We could observe significant enhancement of Raman signal from Rhodamine 6G using the colloidal solution of silver nanoparticles the average magnitude of which is estimated to be 10 3