116 research outputs found
Optimal anti-ferromagnets for light dark matter detection
We propose anti-ferromagnets as optimal targets to hunt for sub-MeV dark
matter with spin-dependent interactions. These materials allow for multi-magnon
emission even for very small momentum transfers, and are therefore sensitive to
dark matter particles as light as the keV. We use an effective theory to
compute the event rates in a simple way. Among the materials studied here, we
identify nickel oxide (a well-assessed anti-ferromagnet) as an ideal candidate
target. Indeed, the propagation speed of its gapless magnons is very close to
the typical dark matter velocity, allowing the absorption of all its kinetic
energy, even through the emission of just a single magnon
Tools for creating wide-field views of the human retina using Optical Coherence Tomography
Optical Coherence Tomography (OCT) has allowed in-vivo viewing of details of retinal layers like never before. With the development of spectral domain OCT (SD-OCT) details of nearly 2µm axial resolution and higher imaging speed have been reported. Nevertheless, a single volume scan of the retina is typically restricted to 6mm x 6mm in size. Having a larger field of view of the retina will definitely enhance the clinical utility of the OCT.
A tool was developed for creating wide-field thickness maps of the retina by combining the use of already available tools like i2k Retina (DualAlign, LLC, Clifton Park, NY) and the thickness maps from Cirrus HD-OCT research browser (Carl Zeiss Meditec, Dublin, California, USA). Normal subjects (n=20) were imaged on Zeiss Cirrus HD-OCT using 512x128 Macular Cube scanning protocol. Sixteen overlapping volumetric images were obtained by moving the internal fixation target around such that the final stitched maps were 12mm x 14mm in size. The thickness maps were corrected for inter-individual differences in axial lengths measured using Zeiss IOL Master and averaged to obtain a normative map.
An algorithm was also developed for montaging 3-D volume scans. Using this algorithm two OCT volume scans can be registered and stitched together to obtain a larger volume scan. The algorithm can be described as a two step process involving 3-D phase-correlation and 2-D Pseudo-polar Fourier transform (PPFT). In the first step, 3-D phase-correlation provides translation values in the x, y and z axis. The second step involves applying PPFT on each overlapping pair of B-scans to find rotation in the x-y plane. Subsequent volumes can be stitched to obtain a large field of view.
We developed a simple and robust method for creating wide-field views of the retina using existing SD-OCT hardware. As segmentation algorithms improve, this method could be expanded to produce wide-field maps of retinal sub-layers, such as the outer nuclear layer or retinal nerve fiber layer. These wide-field views of the retina may prove useful in evaluating retinal diseases involving the peripheral retina (e.g., retinitis pigmentosa and glaucoma)
Photoluminescence and photocatalytic degradation studies on some metallophthalocyanines
This paper deals with the up-conversion intrinsic photoluminescence by exciting the Metallo-Phthalocyanine (MPc) prepared by melt method. MPcs were further characterized using UV visible spectrophotometer, FT-IR, and thermal analysis. The magnetic susceptibility, optical absorption and photoluminescence behavior of these compounds were studied. Photocatalytic degradation of amido black 10B dye using different MPcs at varing pH was done to see the efficiency of these compounds. High emission intensity and easy preparation makes these systems potential candidates for application as luminescent material
Magnetic field measurement from the Davis-Chandrasekhar-Fermi method employed with Atomic Alignment
The Davis-Chandrasekhar-Fermi (DCF) method is widely employed to estimate the
mean magnetic field strength in astrophysical plasmas. In this study, we
present a numerical investigation using the DCF method in conjunction with a
promising new diagnostic tool for studying magnetic fields: the polarization of
spectral lines resulting from the atomic alignment effect. We obtain synthetic
spectro-polarimetry observations from 3D magnetohydrodynamic (MHD) turbulence
simulations and estimate the mean magnetic field projected onto the plane of
the sky using the DCF method with GSA polarization maps and a modification to
account for the driving scale of turbulence. We also compare the method to the
classical DCF approach using dust polarization observations. Our observations
indicate that the modified DCF method correctly estimates the plane-of-sky
projected magnetic field strengths for sub-Alfv\'enic turbulence using a newly
proposed correction factor of . We find that the field
strengths are accurately obtained for all magnetic field inclination and
azimuth angles. We also observe a minimum threshold for the mean magnetic field
inclination angle with respect to the line of sight, ,
for the method. The magnetic field dispersion traced by the polarization from
the spectral lines is comparable in accuracy to dust polarization, while
mitigating some of the uncertainties associated with dust observations. The
measurements of the DCF observables from the same atomic/ionic line targets
ensure the same origin for the magnetic field and velocity fluctuations and
offer a possibility of tracing the 3D direction of the magnetic field
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