Topic Review
Zeta Ursae Majoris
Mizar is a 2nd magnitude star in the handle of the Big Dipper asterism in the constellation of Ursa Major. It has the Bayer designation ζ Ursae Majoris (Latinised as Zeta Ursae Majoris). It forms a well-known naked eye double star with the fainter star Alcor, and is itself a quadruple star system. The whole system lies about 83 light-years away from the Sun, as measured by the Hipparcos astrometry satellite, and is part of the Ursa Major Moving Group.
  • 9
  • 29 Sep 2022
Biography
Yuri Raizer
Yuri Raizer was born in 1927 in Kharkov, Ukraine. He graduated from the Leningrad Polytechnic Institute in 1949, and became Doctor of Sciences (Physics and Mathematics) in 1959, full professor in 1968, and Honored Scientist of the Russian Federation in 2002. He was a chief researcher at the Institute for Problems in Mechanics of the Russian Academy of Sciences, and Honored Professor of the Mosco
  • 58
  • 29 Aug 2022
Topic Review
Wind Turbines Vibration Control
The larger wind turbines are facing higher loads, and the imperatives of mass reduction make them more flexible. Size increase of wind turbines results in higher structural vibrations that reduce the lifetime of the components (blades, main shaft, bearings, generator, gearbox, etc.) and might lead to failure or destruction. Different systems to control the vibration of wind turbines are available, acting either on the tower or directly on the blade.
  • 707
  • 06 Jun 2021
Topic Review
Wearable Body Sensors
The use of wearable body sensors for health monitoring is a quickly growing field with the potential of offering a reliable means for clinical and remote health management. This includes both real-time monitoring and health trend monitoring with the aim to detect/predict health deterioration and also to act as a prevention tool. The aim of this systematic review was to provide a qualitative synthesis of studies using wearable body sensors for health monitoring. The synthesis and analysis have pointed out a number of shortcomings in prior research. Major shortcomings are demonstrated by the majority of the studies adopting an observational research design, too small sample sizes, poorly presented, and/or non-representative participant demographics (i.e., age, gender, patient/healthy). These aspects need to be considered in future research work.
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  • 29 Oct 2020
Topic Review
Wearable Airbags
Fall-related injury is a common cause of mortality among the elderly. Hip fractures are especially dangerous and can even be fatal. In this study, a threshold-based preimpact fall detection algorithm was developed for wearable airbags that minimize the impact of falls on the user’s body. Acceleration sum vector magnitude (SVM), angular velocity SVM, and vertical angle, calculated using inertial data captured from an inertial measurement unit were used to develop the algorithm. To calculate the vertical angle accurately, a complementary filter with a proportional integral controller was used to minimize integration errors and the effect of external impacts. In total, 30 healthy young men were recruited to simulate 6 types of falls and 14 activities of daily life. The developed algorithm achieved 100% sensitivity, 97.54% specificity, 98.33% accuracy, and an average lead time (i.e., the time between the fall detection and the collision) of 280.25 ± 10.29 ms with our experimental data, whereas it achieved 96.1% sensitivity, 90.5% specificity, and 92.4% accuracy with the SisFall public dataset. This paper demonstrates that the algorithm achieved a high accuracy using our experimental data, which included some highly dynamic motions that had not been tested previously.
  • 461
  • 01 Nov 2020
Topic Review
Wavefront shaping concepts in OCT
Optical coherence tomography (OCT) enables three-dimensional imaging with resolution on the micrometer scale. The technique relies on the time-of-flight gated detection of light scattered from a sample and has received enormous interest in applications as versatile as non-destructive testing, metrology and non-invasive medical diagnostics. However, in strongly scattering media such as biological tissue, the penetration depth and imaging resolution are limited. Combining OCT imaging with wavefront shaping approaches significantly leverages the capabilities of the technique by controlling the scattered light field through manipulation of the field incident on the sample.
  • 277
  • 24 Dec 2020
Topic Review
Wave-particle Duality Relation
The Wave–particle duality relation, often loosely referred to as the Englert–Greenberger–Yasin duality relation, or the Englert–Greenberger relation, relates the visibility, [math]\displaystyle{ V }[/math], of interference fringes with the definiteness, or distinguishability, [math]\displaystyle{ D }[/math], of the photons' paths in quantum optics. As an inequality: Although it is treated as a single relation, it actually involves two separate relations, which mathematically look very similar. The first relation, derived by Greenberger and Yasin in 1988, is expressed as [math]\displaystyle{ P^2+ V^2\le 1 \, }[/math]. It was later extended by Jaeger, Shimony, and Vaidman in 1995. This relation involves correctly guessing which of the two paths the particle would have taken, based on the initial preparation. Here [math]\displaystyle{ P }[/math] can be called the predictability. An year later Englert, in 1996, derived a related relation which dealt with experimentally acquiring knowledge of the two paths using an apparatus, as opposed to predicting the path based on initial preparation This relation is [math]\displaystyle{ D^2+ V^2\le 1 \, }[/math]. Here [math]\displaystyle{ D }[/math] is called the distinguishability. The significance of the relations is that they express quantitatively the complementarity of wave and particle viewpoints in double slit experiments. The complementarity principle in quantum mechanics, formulated by Niels Bohr, says that the wave and particle aspects of quantum objects cannot be observed at the same time. The wave–particle duality relations makes Bohr's statement more quantitative – an experiment can yield partial information about the wave and particle aspects of a photon simultaneously, but the more information a particular experiment gives about one, the less it will give about the other. The predictability [math]\displaystyle{ P }[/math] which expresses the degree of probability with which path of the particle can be correctly guessed, and the distinguishability [math]\displaystyle{ D }[/math] which is the degree to which one can experimentally acquire information about the path of the particle, are measures of the particle information, while the visibility of the fringes [math]\displaystyle{ V }[/math] is a measure of the wave information. The relations shows that they are inversely related, as one goes up, the other goes down.
  • 16
  • 27 Sep 2022
Topic Review
Water Hammer Modelling
Water Hammer is a physical phenomenon that occurs due to sudden stopping of flow in a pipeline system which causes a sudden large pressure rise mimicking the hammering effect. It is considered one of the worst nightmare for hydraulic engineers due to its potential of causing widespread damage to property and lives. Therefore, numerical estimation of water hammer pressure is crucial for the design, operation, and risk analysis of pipeline systems. Generally, the traditional Method of Characteristics (MOC) is preferred by modellers worldwide due to its simplicity and usability. However, due to high shock generation during large water hammer event in pipeline, Finite Volume Method (FVM) has a clear advantage because of its desirable attribute of conserving mass, momentum compared to traditional MOC Schemes. Further, modelling of the water hammer phenomenon for dynamic characteristics within a turbine is impossible using the classical 1D MOC or 1D FVM schemes, and such applications require more extensive 3D grids and turbulence models. Several commercial pieces of software for turbulence modelling available today can be effectively used for this type of study. Some well-known and well-applied turbulence models currently in use are FLUENT and CFX (https://www.ansys.com(accessed on 1 June 2021)).
  • 199
  • 24 Jun 2021
Topic Review
Vibrational Spectroscopy
Vibrational spectroscopy, as a label-free, non-invasive and non-destructive analytical technique, is a valuable technique which can provide detailed biochemical fingerprint information, based on the structure of the molecular constituents, for analysis of cells, tissues, and body fluids.
  • 202
  • 05 Feb 2021
Topic Review
Vector Beam with Longitudinally Varying Polarization during Propagation
The vector optical beam with longitudinally varying polarization during propagation in free space has attracted significant attention in recent years. Compared with traditional vector optical beams with inhomogeneous distribution of polarization in the transverse plane, manipulating the longitudinal distribution of polarization provides a new dimension for the expansion of the applications of vector optical beams in volume laser machining, longitudinal detection, and in vivo micromanipulation. 
  • 164
  • 29 Nov 2021
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