Stability of higher order optical vortices produced by spatial light modulators

The stability of higher charge optical vortices generated with a spatial light modulator is investigated. It is observed that higher charge vortices split into an array of unit charge vortices with the tilting of a spatial light modulator. An interferometric method is used to show the exact location of split unit charge vortices. The rotation dynamics of generated unit charge vortices is visualized from the recorded images. A symmetric high charge vortex can be produced with a normal incidence of input laser beam to the spatial light modulator.     

Optimisation and performance analysis of vertical axis wind turbine with blade pitching at best position angle for different tip speed ratios

ABSTRACT

Best pitch position of each blade in the rotation of turbine at different azimuth angle has been calculated at different Tip Speed Ratios (TSRs) by using the aerodynamic analysis. This paper analyses and optimises the various design parameters and its influence on the starting turbine by itself, power coefficient and overall performance of the Vertical Axis Wind Turbine (VAWT). The results indicate that the best pitch position blade method improves the self-starting capacity and power coefficient. The best position blade pitching curve-1 gives maximum power coefficient at 45° pitch angles for TSRs of 0.5 and the best position blade pitching curve-5 with 15° pitch angle gives maximum coefficient of power about 0.49 for TSRs at 2.5. The results indicate that the variation of pitch angle from 45° to 10° with six best position blade pitching curves give the maximum power coefficient for TSRs from 0.5 to 3.     

A comprehensive review of the solar dryer

ABSTRACT

Drying of agricultural products is an energy-demanding process. High costs, scarcities in fossil fuels and environmental threats attract the use of solar energy as an alternate source, especially in developing countries. Increasing environmental concerns led to the use of clean and green energy resources in the field of drying agricultural products. A solar dryer integrated with a thermal energy storage system is reasonably efficient for continuous and uniform drying of agricultural produce in the temperature range of 40–75°C which is the requisite for drying most of the products. Such dryers have become a natural choice to replace drying systems based on fossil fuels. Many studies have been performed till date by a number of researchers for the last few decades for drying agriculture and food products by a solar dryer. This review paper primarily presents an appraisal of the significant contributions made so far in the field of solar drying systems, with the latest updates in drying technology. Solar dryers which offer drying during off-sunshine hours have been specially mentioned. Some novel ideas like use of phase change materials and desiccant materials which enhance the performance and effectiveness of the dryer have also been attempted.     

Pavement performance assessment using a cost‐effective wireless accelerometer system

Pavement condition monitoring is required to identify pavements in need of maintenance or rehabilitation. Early identification of reduction in pavement's structural resistance and improving the structural resistance by minor repairs can lead to significantly lower maintenance costs for transportation agencies. In this study, a cost‐effective wireless sensor that can be embedded in the road to measure the transient vibrations due to different applied loads was tested to determine its effectiveness in terms of pavement displacement measurements. Test results show that the vibration sensor, combined with the algorithms, can be embedded in new or existing pavements and used as an accurate wireless displacement sensor. The low cost of the sensor system allows the use of these sensors at high densities for monitoring the performance of an entire road network. Outputs from the developed system can be directly used to evaluate the condition and performance of pavement structure (increasing displacement over time indicating increasing pavement damage). In addition, displacement data from the system can be used to backcalculate pavement layer stiffnesses, which can be used to predict long‐term performance of the pavement structure. Reduction in pavement layer stiffness over time can be used to determine long‐term damage accumulation.     

Fluid filled scleral contact lens in pediatric patients: challenges and outcome

PurposeTo study the indications and the challenges while fitting scleral contact lens (ScCL) filled with fluid prior to lens insertion in pediatric patients.MethodsWe retrospectively reviewed charts of patients of 16 years or less who received ScCL (PROSE – Prosthetic Replacement of the Ocular Surface Ecosystem, Boston Foundation for Sight, Needham Heights, MA, USA) that were filled with fluid (Normal saline) before lens insertion during July 2006 to April 2010. The main goal of ScCL fitting was to improve vision in patients having keratoconus (KC) and improve the ocular microenvironment in ocular surface disease (OSD). Visual acuity before and after lens wear was noted.ResultsFluid-filled ScCL were dispensed to 15 patients (20 eyes). The indications for ScCL fitting were KC (n = 3 eyes), Stevens Johnson syndrome (SJS, n = 13 eyes), radiation keratopathy (n = 1 eye), combined KC and SJS (n = 1 eye) and KC and vernal keratoconjunctivitis (VKC, n = 2 eyes). Mean age of the patients was 12.85 years. The average daily lens wear was 9 h. The vision improved by 2 lines or more in 85% and dropped by 2 lines or more in 45% eyes after 4 h of lens wear due to tear debris collection. None of the patients had any complications. Patients were self sufficient inserting and removing ScCL. Two patients had broken lenses during the follow-up.ConclusionsScCL are useful for pediatric patients who have OSD, irregular astigmatism or the two coexisting; KC combined with VKC or SJS, helping to maintain the health of the ocular surface and improves vision in these patients.     

Experimental Study on Fluid Flow and Heat Transfer from a Rectangular Prism Approaching the Wall of a Wind Tunnel

Experimental investigations in fluid flow and heat transfer have been carried out to study the effect of wall proximity due to flow separation around rectangular prisms. Experiments have been carried out for the Reynolds number 2.6 × 10⁴, blockage ratios are 0.1, 0.2, 0.3, and 0.4, aspect ratios (d/c) are 1.5, 1.33, 0.667, and 0.333, with different height‐ratios and various angles of attack. The static pressure distribution has been measured on all faces of the rectangular prisms. The results have been presented in the form of pressure coefficient, drag coefficient for various height‐ratios and blockage ratios. The pressure distribution shows positive values on the front face whereas on the rear face negative values of the pressure coefficient have been observed. The drag coefficient decreases with the increase in angle of attack as the height‐ratio decreases. The heat transfer experiments have been carried out under constant heat flux conditions. Heat transfer coefficients are determined from the measured wall temperature and ambient temperature and presented in the form of a Nusselt number. Both local and average Nusselt numbers have been presented for various height‐ratios. The variation of the local Nusselt number has been shown with nondimensional distance for different angles of attack and blockage ratios. The variation of the average Nusselt number has also been shown with different angles of attack for blockage ratios. The local as well as average Nusselt number decreases as the height‐ratio decreases for all nondimensional distances and angles of attack, respectively, for rectangular prisms. Empirical correlations for the average Nusselt number have been presented for a rectangular prism as a function of the Reynolds number, Prandtl number and relevant nondimensional parameters.     

Microstructure,Mechanical Properties,and Corrosion Behavior of Co-Based Stellite 6 Multilayer Overlays Deposited on ASTM A36 Steel by Gas Metal Arc Welding Process

Hardfacing is an effective method for restoring the damaged part. Herein, cobalt-based superalloy Stellite-6 is deposited on A36 substrate using gas metal arc welding process. The mechanical properties, microstructure, and corrosion behavior of Stellite-6 overlays on A36 substrate are examined. Defect-free hard overlays are obtained, and a dilution ratio of 19.9% is achieved with weaving technique. X-ray diffraction analysis reveals the presence of M₇C₃, M₂₃C₆, M₆C, and martensite in the Stellite-6 hard overlays. The microstructure of the deposit contains martensite, carbides, and interdendritic precipitates while the mean hardness is 471 HV_0.5. Tensile testing with specimens extracted on the longitudinal (LD) and transverse (TD) orientation of the stellite-6 deposit shows a strength above 950 MPa along with the brittle nature of fracture. Grain growth is epitaxial and shows dendritic morphologies. The higher fraction of high-angle grain boundaries improves the tensile strength of the deposit and interface region. The localized corrosion behavior of stellite-6 hard overlays is found to be excellent, and the corrosion analysis exhibits a corrosion rate of 0.10 mils per year (mpy). The outcomes of the study highlight the feasibility of Stellite-6 hard overlays for extending the service life of A36 steel in chloride environments.     

Investigation of Quantum Confinement Effects on Molybdenum Disulfide (MoS2) Based Transistor Using Ritz Galerkin Finite Element Technique

Silicon - This paper presents the effect of quantum confinement on the potential of short channel mono-layer molybdenum disulfide (MoS2) based transistor using Ritz Galerkin finite element...