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Portable Instrument for Monitoring Environmental Toxins Using Immobilized Quantum Dots as the Sensing Material
摘要： A portable instrumental system was designed for the routine environmental monitoring of toxic volatile organic compounds (VOCs) in atmospheric conditions based on changes in the photoluminescence emission of semiconductor nanoparticles (quantum dots) entrapped in a sol-gel matrix as the solid sensing material. The sol-gel sensing material displayed a long-lived phosphorescent emission, which is quenched in the presence of trace levels of a volatile organic compound (acetone) in gaseous atmospheres. The developed instrument could measure and process the changes in the photoluminescence of the sensing material after exposure to gaseous acetone. The developed prototype device consists of a deep-ultraviolet light-emitting diode (UV LED), which excites the chemical sensing material; an optical filter to remove scattered light and other non-desirable wavelengths; a photomultiplier tube (PMT) to convert the phosphorescence emission of the sensor phase to an electrical signal; and a microcontroller to correlate the signal with the analyte concentration. The developed prototype was evaluated for its ability to measure low levels of gaseous acetone in contaminated atmospheres with high sensitivity (detection limit: 9 ppm). The obtained results show the feasibility of this type of instrument for environmental analytical control purposes.
关键词： quantum dots (QDs),photomultiplier,UV LED,instrumentation,nanoparticles,room temperature phosphorescence (RTP)
更新于2025-09-23 15:21:01
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Near-infrared scattered light properties of the HR?4796?A dust ring
摘要： Context. HR 4796 A is surrounded by a debris disc, observed in scattered light as an inclined ring with a high surface brightness. Past observations have raised several questions. First, a strong brightness asymmetry detected in polarised re?ected light has recently challenged our understanding of scattering by the dust particles in this system. Secondly, the morphology of the ring strongly suggests the presence of planets, although no planets have been detected to date. Aims. We aim here at measuring with high accuracy the morphology and photometry of the ring in scattered light, in order to derive the phase function of the dust and constrain its near-infrared spectral properties. We also want to constrain the presence of planets and set improved constraints on the origin of the observed ring morphology. Methods. We obtained high-angular resolution coronagraphic images of the circumstellar environment around HR 4796 A with VLT/SPHERE during the commissioning of the instrument in May 2014 and during guaranteed-time observations in February 2015. The observations reveal for the ?rst time the entire ring of dust, including the semi-minor axis that was previously hidden either behind the coronagraphic spot or in the speckle noise. Results. We determine empirically the scattering phase function of the dust in the H band from 13.6? to 166.6?. It shows a prominent peak of forward scattering, never detected before, for scattering angles below 30?. We analyse the re?ectance spectra of the disc from the 0.95 μm to 1.6 μm, con?rming the red colour of the dust, and derive detection limits on the presence of planetary mass objects. Conclusions. We con?rm which side of the disc is inclined towards the Earth. The analysis of the phase function, especially below 45?, suggests that the dust population is dominated by particles much larger than the observation wavelength, of about 20 μm. Compact Mie grains of this size are incompatible with the spectral energy distribution of the disc, however the observed rise in scattering e?ciency beyond 50? points towards aggregates which could reconcile both observables. We do not detect companions orbiting the star, but our high-contrast observations provide the most stringent constraints yet on the presence of planets responsible for the morphology of the dust.
关键词： planets and satellites: detection,planetary systems,scattering,instrumentation: high angular resolution,planet-disk interactions
更新于2025-09-23 15:21:01
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Timepix in LEO Orbit onboard the VZLUSAT-1 Nanosatellite: 1-year of Space Radiation Dosimetry Measurements
摘要： The VZLUSAT-1 satellite, the first Czech CubeSat, was successfully launched on June 23, 2017, to a 510 km Sun-synchronous low-Earth orbit. It carries several scientific payloads including a Timepix detector as focal plane imager for the X-Ray telescope onboard. The Timepix detector contributes significantly to the satellite data collection, with more than 25 000 sampling acquisitions in the first year of deployment. Despite limitations of the satellite attitude control system, necessary for capturing X-Ray images of the Sun, the Timepix detector allows measuring the space radiation environment along the satellite orbit. As of September 2018, we conducted 33 whole-Earth mappings, recording radiation doses around the planet. Further, we show data from scans of the South Atlantic Anomaly and polar radiation horns, where the location and acquisition time were tailored to minimize event pile-up and particle track overlap. Since October 2017, the optics segment of the onboard X-Ray telescope was deployed, which exposed the Timepix detector unshielded to free open space. This change produced entirely new observations namely of low energy charged particles and a significant increase of measured particle flux. We also registered the effects of exposing the sensor to direct intense sunlight. We will summarize on the actual performance of the custom readout interface, which exceeds expectations in the constrained environment of the low-cost and low-powered CubeSat nanosatellite.
关键词： Particle detectors,On-board space electronics,X-ray detectors and telescopes,Space instrumentation
更新于2025-09-23 15:21:01
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Development of a spectrometer for airborne measurement of droplet sizes in clouds
摘要： The objective of this article is to present the development and the validation in flight of an airborne probe that can measure in clouds the size of droplets whose diameters are in the range [20 μm; 200 μm].
关键词： Interferometric laser imaging laser for droplets sizing,airborne instrumentation,clouds,two-phase flows
更新于2025-09-23 15:21:01
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The EBEX Balloon-borne Experiment—Optics, Receiver, and Polarimetry
摘要： The E and B Experiment (EBEX) was a long-duration balloon-borne cosmic microwave background (CMB) polarimeter that flew over Antarctica in 2012. We describe the experiment’s optical system, receiver, and polarimetric approach and report on their in-flight performance. EBEX had three frequency bands centered on 150, 250, and 410 GHz. To make efficient use of limited mass and space, we designed a 115 cm2 sr high-throughput optical system that had two ambient temperature mirrors and four antireflection-coated polyethylene lenses per focal plane. All frequency bands shared the same optical train. Polarimetry was achieved with a continuously rotating achromatic half-wave plate (AHWP) that was levitated with a superconducting magnetic bearing (SMB). This is the first use of an SMB in astrophysics. Rotation stability was 0.45% over a period of 10 hr, and angular position accuracy was 0°.01. The measured modulation efficiency was above 90% for all bands. To our knowledge the 109% fractional bandwidth of the AHWP was the broadest implemented to date. The receiver, composed of one lens and the AHWP at a temperature of 4 K, the polarizing grid and other lenses at 1 K, and the two focal planes at 0.25 K, performed according to specifications, giving focal plane temperature stability with a fluctuation power spectrum that had a 1/f knee at 2 mHz. EBEX was the first balloon-borne instrument to implement technologies characteristic of modern CMB polarimeters, including high-throughput optical systems, and large arrays of transition edge sensor bolometric detectors with multiplexed readouts.
关键词： cosmology: observations,instrumentation: polarimeters,cosmic background radiation,polarization,balloons
更新于2025-09-23 15:21:01
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Assessment of anterior and posterior corneal indices using two Scheimpflug analyzers
摘要： Purpose: To assess the agreement between the elevation and curvature measurements of the anterior and posterior corneal surfaces obtained using the Galilei Dual Scheimpflug Analyzer and those obtained using the Pentacam single Scheimpflug system. Methods: This prospective, noninterventional, diagnostic study was conducted at the Department of Ophthalmology at the American University of Beirut (Medical Center) and included 60 eyes of 60 consecutive patients. Measurements were obtained using 2 different Scheimpflug analyzers (Galilei and Pentacam). The best-fit sphere was set at 8 mm in both machines. Pachymetry (CCT), anterior elevation (AE) and posterior elevation (PE), and curvature were assessed. Pearson’s correlation coefficients, comparison of means, and Bland-Altman plots were used to evaluate agreement between the 2 systems. Results: The average CCT (at the corneal apex) was 533 ± 35 μm and 532 ± 37 μm (p=0.980), the average central AE was 1.25 ± 3.95 μm and 2.29 ± 5.28 μm (p=0.964), and the average central PE was 4.19 ± 8.18 μm and 5.42 ± 14.05 (p=0.956) μm with the Galilei and Pentacam, respectively. Conclusion: The Scheimpflug analyzers correlated well in the assessment of pachymetry, elevation, and curvature.
关键词： Corneal pachymetry,Photography/instrumentation,Cornea/pathology,Cornea/anatomy & histology,Corneal topography
更新于2025-09-23 15:21:01
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A Wide-Field Camera and Fully Remote Operations at the Wyoming Infrared Observatory
摘要： Upgrades at the 2.3 meter Wyoming Infrared Observatory telescope have provided the capability for fully remote operations by a single operator from the University of Wyoming campus. A line-of-sight 300 Megabit s?1 11 GHz radio link provides high-speed internet for data transfer and remote operations that include several realtime video feeds. Uninterruptable power is ensured by a 10 kVA battery supply for critical systems and a 55 kW autostart diesel generator capable of running the entire observatory for up to a week. The construction of a new four-element prime-focus corrector with fused-silica elements allows imaging over a 40′ field of view with a new 40962 UV-sensitive prime-focus camera and filter wheel. A new telescope control system facilitates the remote operations model and provides 20″ rms pointing over the usable sky. Taken together, these improvements pave the way for a new generation of sky surveys supporting space-based missions and flexible-cadence observations advancing emerging astrophysical priorities such as planet detection, quasar variability, and long-term time-domain campaigns.
关键词： instrumentation: miscellaneous,telescopes,instrumentation: photometers
更新于2025-09-23 15:19:57
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Enhancement of optical penetration depth of LED-based NIRS systems by comparing different beam profiles
摘要： Near-Infrared Spectroscopy (NIRS) is a non-invasive brain imaging technique involving the quantification of oxy and deoxy-hemoglobin concentrations resolved from the measurement of Near-Infrared (NIR) light attenuation within the tissue. Previous studies have shown that NIR light is more influenced by the optical properties of the superficial layers than those of the deeper target layers such as cortex. NIR light produced by the Laser source penetrates deeper regions of the tissue rather than the LED source although Laser needs more expensive instrumentation. In this study, we investigate the effect of Uniform and Gaussian beam profiles on the enhancement of LED light penetration depth. The latter beam profiles were generated and compared using Flat and Aspherical lenses applied to the LED sources. In order to increase the signal to noise ratio, the lenses were also applied to the light detector. For performance analysis, two experiments were carried out by scanning the intra space of a liquid phantom by static and dynamic (pulsating) absorbers. Monte Carlo simulations were also carried out to be compared with the experiment. The results showed that Gaussian beam profile and in particular, Bi-Convex lenses applied to both source and detector leads to a greater light penetration depth in the liquid phantom close to that of a Laser source.
关键词： near infrared spectroscopy,optical sensors,biomedical optic,monte carlo simulation,instrumentation
更新于2025-09-23 15:19:57
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Stealth Design of the Quantum Radar Scattering Based on the Two Typical 2D Targets
摘要： We have developed a robust sensor for mounting on bridges over rivers and streams. These bridge-mounted river stage sensors (BMRSS) make periodic measurements of the distance from the sensor to the water level below. Properly interpreted, these measurements provide river-stage information, data of great importance to society and crucial to effective ?ood forecasting. The traditional approach to river stage measurement is the installation of pipes in rivers, digging stilling wells, and the construction of attendant brick-and-mortar infrastructure. The cost of this approach limits the deployment to larger rivers. In most instances, river-stage data from smaller tributaries are few, even though such data can greatly enhance the quality of ?ood-forecasting models’ outputs. In contrast, BMRSS units are an order of magnitude less expensive and allow for widespread deployment. BMRSS units incorporate an ultrasonic distance-measuring module, a solar panel/battery/charge controller, and a GPS receiver. In recent years, the Internet access through commercial cellular networks has become ubiquitous, even in most rural areas. BMRSS units incorporate cell modems and transmit data through the Internet to servers at the Iowa Flood Center. Here, the data are ingested into relational databases and made available to ?ood forecasting models and information systems. We have deployed and operated more than 220 BMRSS units across Iowa, many for several years continuously.
关键词： hazards,cellular networks,Sensor systems and applications,instrumentation and measurement
更新于2025-09-23 15:19:57
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50-GHz Repetition Gain Switching Using A Cavity-enhanced DFB Laser Assisted By Optical Injection Locking
摘要： This paper introduces the (cid:2) counter, a frequency counter—i.e., a frequency-to-digital converter—based on the linear regression (LR) algorithm on time stamps. We discuss the noise of the electronics. We derive the statistical properties of the (cid:2) counter on rigorous mathematical basis, including the weighted measure and the frequency response. We describe an implementation based on a system on chip, under test in our laboratory, and we compare the (cid:2) counter to the traditional (cid:3) and (cid:4) counters. The LR exhibits the optimum rejection of white phase noise, superior to that of the (cid:3) and (cid:4) counters. White noise is the major practical problem of wideband digital electronics, both in the instrument internal circuits and in the fast processes, which we may want to measure. With a measurement time τ , the variance is proportional to 1/τ 2 for the (cid:3) counter, and to 1/τ 3 for both the (cid:4) and (cid:2) counters. However, the (cid:2) counter has the smallest possible variance, 1.25 dB smaller than that of the (cid:4) counter. The (cid:2) counter ?nds a natural application in the measurement of the parabolic variance, described in the companion article in this Journal [vol. 63 no. 4 pp. 611–623, April 2016 (Special Issue on the 50th Anniversary of the Allan Variance), DOI 10.1109/TUFFC.2015.2499325].
关键词： noise,regression analysis,frequency measurement,instrumentation and measurement,time measurement,phase noise,Frequency estimation
更新于2025-09-23 15:19:57