Investigating viscous damping using a webcam

We describe an experiment involving a mass oscillating in a viscous fluid and analyze viscous damping of harmonic motion. The mechanical oscillator is tracked using a simple webcam and an image processing algorithm records the position of the geometrical center as a function of time. Interesting information can be extracted from the displacement-time graphs, in particular for the underdamped case. For example, we use these oscillations to determine the viscosity of the fluid. Our mean value of 1.08 \pm 0.07 mPa s for distilled water is in good agreement with the accepted value at 20\circC. This experiment has been successfully employed in the freshman lab setting.Comment: 13 pages, 5 figure

Experimental determination of heat capacities and their correlation with quantum predictions

This article demonstrates an undergraduate experiment for the determination of specific heat capacities of various solids based on a calorimetric approach, where the solid vaporizes a measurable mass of liquid nitrogen. We demonstrate our technique for the metals copper and aluminum, the semi-metal graphite and also present the data in relation with Einstein's model of independent harmonic oscillators and the more accurate Debye model based on vibrational modes of a continuous crystal. Furthermore, we elucidate an interesting material property, the Verwey transition in magnetite occurring around 120-140 K. We also demonstrate that the use of computer based data acquisition and subsequent statistical averaging helps reduce measurement uncertainties.Comment: 16 pages, 8 figures. Partially accepted in American Journal of Physics (2011

NMR quantum information processing with para-hydrogen

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Dielectric and magnetic investigations of mixed cubic spinel Co-ferrites with controlled Mg content

High temperature frequency dependent dielectric properties, and room temperature magnetic behavior of mixed ferrites with controlled content of Mg in Co₁₋ₓMgₓFe₂O₄ (x=0.0,0.1,0.3,0.5,0.7,0.9 and 1.0) compositions are studied. Single phase spinel structure with cubic symmetry, lattice parameters, crystallite size, magnetic and dielectric properties were substantiated with x-ray diffractometer, transmission electron microscope, vibrating sample magnetometer and impedance analysis, respectively. Due to interfacial polarization, dielectric behavior of all the compositions shows dispersion with increase in frequency. The dielectric data was investigated by comparing the tangent loss and electric modulus for assigning the type and mechanism of dielectric relaxation. Temperature dependent dielectric constant, tangent loss and AC conductivity increase due to thermal activation of charge carriers and drift mobility. Furthermore, room temperature weak ferromagnetic behavior is observed due to the incorporation of non-magnetic Mg ions.8 page(s

Polarisation insensitive multifunctional metasurfaces based on all-dielectric nanowaveguides

Metasurfaces, two dimensional (2D) metamaterials comprised of subwavelength features, can be used to tailor the amplitude, phase and polarisation of an incident electromagnetic wave propagating at an interface. Though many novel metasurfaces have been explored, the hunt for cost-effective, highly efficient, low-loss and polarisation insensitive applications is ongoing. In this work, we utilise an efficient and cost-effective dielectric material, hydrogenated amorphous silicon (a-Si:H), to create a ultra-thin transmissive surface that simultaneously controls phase. This material exhibits significantly lower absorption in the visible regime compared to standard amorphous silicon, making it an ideal candidate for various on-chip applications. Our proposed design, which works on the principle of index waveguiding, integrates two distinct phase profiles, that of a lens and of a helical beam, and is versatile due to its polarisation-insensitivity. We show how this metasurface can lead to highly concentrated optical vortices in the visible domain, whose focused ring-shaped profiles carry orbital angular momentum at the miniaturised scale.11Nsciescopu

Optical spin-symmetry breaking for high-efficiency directional helicity-multiplexed metaholograms

Holography: Metasurfaces based on asymmetrical spin-orbit interactions (SOIs) Metasurfaces are thin films composed of different elements that provide an efficient, miniaturized platform for nano-optics, and a metasurface based on asymmetrical SOIs has been developed that overcomes the limitations with metasurfaces using symmetrical SOIs. Owing to their ability to accommodate the wavefronts of light at the sub-wavelength scale, metasurfaces have found wide application in displays, communications, and data storage. However, metasurfaces based on symmetrical SOIs have limitations with holographic imaging. A team headed by Junsuk Rho at Pohang University of Science and Technology (POSTECH), South Korea has succeeded in designing a metasurface based on asymmetrical SOIs that operates in the visible light domain using low-loss dielectric materials. The team employed a simple, cost-effective fabrication method, and the design offers considerable potential for applications in such areas as asymmetric data inscription and smartphone displays. Helicity-multiplexed metasurfaces based on symmetric spin-orbit interactions (SOIs) have practical limits because they cannot provide central-symmetric holographic imaging. Asymmetric SOIs can effectively address such limitations, with several exciting applications in various fields ranging from asymmetric data inscription in communications to dual side displays in smart mobile devices. Low-loss dielectric materials provide an excellent platform for realizing such exotic phenomena efficiently. In this paper, we demonstrate an asymmetric SOI-dependent transmission-type metasurface in the visible domain using hydrogenated amorphous silicon (a-Si:H) nanoresonators. The proposed design approach is equipped with an additional degree of freedom in designing bi-directional helicity-multiplexed metasurfaces by breaking the conventional limit imposed by the symmetric SOI in half employment of metasurfaces for one circular handedness. Two on-axis, distinct wavefronts are produced with high transmission efficiencies, demonstrating the concept of asymmetric wavefront generation in two antiparallel directions. Additionally, the CMOS compatibility of a-Si:H makes it a cost-effective alternative to gallium nitride (GaN) and titanium dioxide (TiO2) for visible light. The cost-effective fabrication and simplicity of the proposed design technique provide an excellent candidate for high-efficiency, multifunctional, and chip-integrated demonstration of various phenomena.11Nsciescopu