INVESTIGATION OF LIGHT INTENSITY OF LIGHT CURING UNITS AFTER DIFFERENT PERIODS OF USE

Quartz-tungsten halogen light curing units (LCUs) have been the main source of light for the polymerization of resin based composites (RBCs) for several decades. Since the beginning of the 20th century, however, their use has been reduced due to the invention and improvement of LED LCUs. Various factors can cause a decrease in the light intensity of LED LCUs, one of which is diode aging. The aim of the present paper is to study the change in light intensity of LCUs after different periods of intensive use. For this purpose, the light intensity of 94 regularly used LED LCUs aged between 1 and 10 years was measured with a digital radiometer. The devices were used in conventional mode with maximum light intensity. It was found that regardless of the type and model of LCU, there is a direct relationship between the time of use and light intensity - the longer the operation period of a device is and the more used it is, the lower its intensity is. The decrease in light intensity as devices age is different for different models, as well as for different devices of the same model. In the studied LCUs with a 10-year period of use, 77.5% have light intensity lower than the required minimum of 400 mW/cm2, which makes them unusable. It can be concluded that dentists should regularly monitor and measure the light intensity of their LCUs, especially as they age, to ensure the longevity of their restorative procedures.

A Survey of Novae in M83

The results of the first synoptic survey of novae in the barred spiral and starburst galaxy, M83 (NGC 5236), are presented. A total of 19 novae and one background supernova were discovered during the course of a nearly 7 year survey comprised of over 200 individual nights of observation between 2012 December 12 and 2019 March 14. After correcting for the limiting magnitude and the spatial and temporal coverage of the survey, the nova rate in M83 was found to be R = 19+5 −3 yr−1. This rate, when normalized to the K-band luminosity of the galaxy, yields a luminosity-specific nova rate, ν K = 3.0+0.9 −0.6 × 10−10 yr −1 L ⊙,K −1. The spatial distribution of the novae is found to be more extended than the overall galaxy light suggesting that the observed novae are likely dominated by a disk population. This result is consistent with the observed novae light curves, which reveals that the M83 novae are on average more luminous at maximum light and fade faster when compared with novae observed in M31. Generally, the more luminous M83 novae were observed to fade more rapidly, with the complete sample being broadly consistent with a linear maximum magnitude versus rate of decline relation.

Carnegie Supernova Project: The First Homogeneous Sample of Super-Chandrasekhar-mass/2003fg-like Type Ia Supernovae

We present a multiwavelength photometric and spectroscopic analysis of 13 super-Chandrasekhar-mass/2003fg-like Type Ia supernovae (SNe Ia). Nine of these objects were observed by the Carnegie Supernova Project. The 2003fg-like SNe have slowly declining light curves (Δm 15(B) < 1.3 mag), and peak absolute B-band magnitudes of −19 < M B < −21 mag. Many of the 2003fg-like SNe are located in the same part of the luminosity–width relation as normal SNe Ia. In the optical B and V bands, the 2003fg-like SNe look like normal SNe Ia, but at redder wavelengths they diverge. Unlike other luminous SNe Ia, the 2003fg-like SNe generally have only one i-band maximum, which peaks after the epoch of the B-band maximum, while their near-IR (NIR) light-curve rise times can be ≳40 days longer than those of normal SNe Ia. They are also at least 1 mag brighter in the NIR bands than normal SNe Ia, peaking above M H = −19 mag, and generally have negative Hubble residuals, which may be the cause of some systematics in dark-energy experiments. Spectroscopically, the 2003fg-like SNe exhibit peculiarities such as unburnt carbon well past maximum light, a large spread (8000–12,000 km s−1) in Si ii λ6355 velocities at maximum light with no rapid early velocity decline, and no clear H-band break at +10 days. We find that SNe with a larger pseudo-equivalent width of C ii at maximum light have lower Si ii λ6355 velocities and more slowly declining light curves. There are also multiple factors that contribute to the peak luminosity of 2003fg-like SNe. The explosion of a C–O degenerate core inside a carbon-rich envelope is consistent with these observations. Such a configuration may come from the core-degenerate scenario.

A STUDY OF THE SECULAR VARIATION OF THE HIGH-AMPLITUDE DELTA SCUTI STAR AD CMI

We determine the nature of the Delta Scuti star AD CMi and its physical parameters from newly determined times of maximum light and other times from the literature, as well as from uvby −β photoelectric photometry.

A STUDY OF THE SX PHE STAR BL CAM

We determined the physical parameters of the SX Phe star BL Cam from newly available times of maximum light and other times from the literature, as well as from uvby − β photoelectric photometry. From our analysis we found that this star is a binary system. The mass of the companion star was calculated in term of the mass of the primary star and the orbital angle. For this star we determined a metallicity [Fe/H] of −1.2 ± 0.3.

Effects of Par on Plant Spacing in Relation to Yield Efficiency in Peach

Effects of PAR in relation with plant spacing in peach cultivar ‘Shan-i-Punjab’ during the year 2013-14 and 2014-15 were evaluated. The trees were trained to 4 different training systems and each system consisted of 2 spacings viz., 5 × 3 m and 5 × 2 m. Daily PAR was recorded at morning, midday and evening and it was found that irrespective of planting distance maximum light interception was recorded at midday hours. Plants spaced at 5 × 3m received more light inside the canopy during full day which directly influenced number of fruits per tree, number of picking, fruiting density, yield efficiency, relative pattern of fruit maturity whereas, fruit yield per hectare was maximum in 5 × 2 m. Bangladesh J. Bot. 50(3): 701-707, 2021 (September)

Design and Development of a Single-Axis Solar Tracking System

With solar tracking, it will become possible to generate more energy since the solar panel can maintain a perpendicular profile to the rays of the sun. Even though the initial cost of setting up the tracking system is considerably high, there are cheaper options that have been proposed over time. This research discuss the design and construction of a prototype for a solar tracking system that has a single axis of freedom. Light Dependent Resistors (LDRs) are used for sunlight detection. The control circuit is based on an ATMega328P microcontroller. It was programmed to detect sunlight via the LDRs before actuating the servo to position the solar panel. The solar panel is positioned where it is able to receive maximum light. As compared to other motors, the servo motors are able to maintain their torque at high speed. They are also more efficient with efficiencies in the range of 80-90%. Servos can supply roughly twice their rated torque for short periods. Through tracking, there will be increased exposure of the panel to the sun, making it have increased power output. The trackers can either be dual or single axis trackers. As a single tracking system is cheaper, less complex, and still achieves the required efficiency, so it was used.

Investigation of the Kerr effect on polarised light

A constructed Kerr cell with brass electrodes and liquid nitrobenzene was used for studying the Kerr effect on polarised light. Laser light was plane polarised and passed through an energised Kerr cell. The plane polarised light after travelling a path length equal to the cell electrode length in a birefringent medium, suffered optical retardance before passing through an analyser which then transmitted light of certain intensity to a photodiode. Data used were generated from experiments and theoretical considerations using Kerr’s law and Malus’ law. With crossed Polaroids, the Kerr cell behaved as an electro-optic shutter and the maximum light intensity transmitted rose steadily with increased phase difference to about 0.82. With parallel Polaroids, the maximum light intensity transmitted was higher and found to be 0.89 at zero phase difference. This value indicates a large phase delay and decreased to a non-zero value. At maximum electric field intensity, a ‘climbing’ of the nitrobenzene on the Kerr cell walls and electrodes was observed with more nitrobenzene attracted to the anode. The effect suspected to be of electrostatic origin may have been driven by the predominant ions in the nitrobenzene. Furthermore, the higher level of the nitrobenzene meniscus at the anode probably suggests that while the cathode injected carriers of negative charge into the liquid the injection of carriers from the anode was weaker. For better results, attention should be given to Polaroid quality, the purity of the liquid nitrobenzene and the length of the electrodes used.

Solar Panel Automatic Positioning and Maximum Light Flux Direction Tracking

The paper analyzes the state and possible ways of development of alternative energy, describes the prospects for the development of solar power plants, their classification and areas of application. Within the research, we revealed the problems that arise when installing and operating solar panels and identified the reasons that reduce their efficiency. Consequently, we analyzed the ways to increase the efficiency of power generation by solar panels and suggested solar panel automatic positioning and maximum light flux direction tracking as a possible solution to the problem. The study introduces a new device for positioning solar panels, which is distinguished by the automatic deployment and positioning of solar panels according to the actual direction of the maximum light flux. The device provides possible automation of the installation and greater efficiency of solar panels. The novelty of the device is protected by a utility model patent no. 180765 RF. To confirm the efficiency and to obtain a quantitative value of the increase in power generation by solar panels due to the use of the developed device, we present the comparison methodology and a description of the experiment. The schematic diagram and external view of the developed device are also shown. The experimental results are processed and shown in a graph. The possibility of increasing power generation by solar panels by tracking the maximum light flux and reorienting the solar panel towards it during the day has been confirmed, and a quantitative value of the increase in power generation has been obtained. Based on the positive results of the experiment, the possibility of using the developed device for automating the process of deploying solar panels in an autonomous way and excluding human participation in this process is described. The operation of the developed device on a moving vehicle and other methods of its application are considered. The results are summed up, conclusions are drawn and possible further directions for the development and use of the proposed method for increasing the efficiency of solar panels and the developed device for improving the performance of solar panels are identified