We consider the problem of estimating the extrinsic parameters (pose) of a camera with respect to a reference 3D object without a direct view. Since the camera does not view the object directly, ...previous approaches have utilized reflections in a planar mirror to solve this problem. However, a planar mirror based approach requires a minimum of three reflections and has degenerate configurations where estimation fails. In this paper, we show that the pose can be obtained using a single reflection in a spherical mirror of known radius. This makes our approach simpler and easier in practice. In addition, unlike planar mirrors, the spherical mirror based approach does not have any degenerate configurations, leading to a robust algorithm. While a planar mirror reflection results in a virtual perspective camera, a spherical mirror reflection results in a non-perspective axial camera. The axial nature of rays allows us to compute the axis (direction of sphere center) and few pose parameters in a linear fashion. We then derive an analytical solution to obtain the distance to the sphere center and remaining pose parameters and show that it corresponds to solving a 16th degree equation. We present comparisons with a recent method that use planar mirrors and show that our approach recovers more accurate pose in the presence of noise. Extensive simulations and results on real data validate our algorithm.
Advances in ultrafast lasers, chirped pulse amplifiers, and frequency comb technology require fundamentally new pulse-modulation strategies capable of supporting unprecedentedly large bandwidth and ...high peak power while maintaining high spectral resolution. We demonstrate how dielectric metasurfaces can be leveraged to shape the temporal profile of a near-infrared femtosecond pulse. Finely tailored pulse-shaping operations, including splitting, compression, chirping, and higher-order distortion, are achieved using a Fourier-transform setup embedding metasurfaces able to manipulate, simultaneously and independently, the amplitude and phase of the constituent frequency components of the pulse. Exploiting metasurfaces to manipulate the temporal characteristics of light expands their impact and opens new vistas in the field of ultrafast science and technology.
Abstract
The coronavirus disease 2019 (COVID-19) crisis has greatly affected human lives across the world. Uncertainty and quarantine have been affecting people’s mental health. Estimations of mental ...health problems are needed immediately for the better planning and management of these concerns at a global level. A rapid scoping review was conducted to get the estimation of mental health problems in the COVID-19 pandemic during the first 7 months. Peer-reviewed, data-based journal articles published in the English language were searched in the PubMed, Medline, and Google Scholar electronic databases from December 2019 to June 2020. Papers that met the inclusion criteria were analyzed and discussed in this review. A total of 16 studies were included. Eleven studies were from China, two from India, and one from Spain, Italy, and Iran. Prevalence of all forms of depression was 20%, anxiety 35%, and stress 53% in the combined study population of 113,285 individuals. The prevalence rate of all forms of depression, anxiety, stress, sleep problems, and psychological distress in general population was found to be higher during COVID-19 pandemic.
Several small-scale flow networks involve low Peclet gaseous flows when subjected to heat transfer. Flow phenomena associated with these conditions are characterized by significant axial conduction. ...Although the available literature is replete with low Peclet flows for liquid metals, the studies for low Peclet gaseous flows are limited. Since gaseous flows also experience considerable changes in their properties during heat transfer, their separate and complete analysis becomes necessary. This work presents numerical solution of the complete forms of transport equations for mass, momentum and total energy. Peclet number (
Pe
) in the range 1–100 is considered with property variation retained. The solutions are obtained using the academic version of FLUENT-2020-R2 with SIMPLEC algorithm. Both the conditions of constant wall temperature (CWT) and constant wall heat flux (CHF) are used as the prescribed thermal boundaries. The influence of varying degrees of supplied heat at the wall is also analyzed. It is observed that both the CWT and CHF cases experience increasing backward penetration of heat with reduction in
Pe
and with an increase in the supplied heat. This represents an increase in Nusselt number for CWT cases where fully developed Nusselt number approaches
4.08
corresponding to
Pe
=
1
for the minimum wall temperature case. With increase in wall temperature, this value rises further to
4.17
for the highest heating rate, as against
3.65
for high
Pe
laminar flows without considering property variation. For CHF cases, the fully developed Nusselt number remains close to
4.34
for low
Pe
cases and it drops to
4.27
for the highest
Pe
of
100
. Notably, Nusselt number is found to drop to a minimum before attaining asymptotic value. The radial advection term of the energy equation manifests itself to be primarily responsible for minimum Nusselt number. Thus, the analysis of low
Pe
gaseous flows requires consideration of radial advection term and property variation. These unreported results are significant inasmuch as the design of small-scale heat exchangers need to be optimal under space constraints.
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