On the Design of Rate Adaptation for Relay-Assisted Satellite Hybrid FSO/RF Systems

<p>This paper addresses the design of hybrid free-space optical/radio frequency (FSO/RF) systems for a high-altitude platform (HAP)-aided relaying satellite communication for mobile networks supported by unmanned aerial vehicle (UAV). While prior work primarily focused on fixed-rate design, which frequently switches between FSO and RF lead to reduce the system performance, we propose a rate adaptation design that gradually adjusts the data rate in each link when its channel state fluctuates. The proposed design's downlink performance is analyzed, taking into account many challenging issues, including beam spreading loss, cloud attenuation, statistical behaviors of the atmospheric turbulence in the dual-hop channel, and pointing misalignment due to the UAV hovering. Different performance metrics are analytically derived based on channel modelings, such as outage probability, average transmission rate, achievable spectrum efficiency, and average transmission rate. The numerical results quantitatively confirm the effectiveness of our proposed system under the impact of UAV hovering misalignment and atmospheric-related issues like clouds and turbulence. Finally, Monte-Carlo simulations validate the accuracy of theoretical results.</p>

CDFS-6664: A Candidate of Lyman-continuum Emission at z ∼ 3.8 Detected by the Hubble Deep UV Legacy Survey

We report the detection of Lyman continuum (LyC) emission from the galaxy, CDFS-6664, at z = 3.797 in a sample of Lyman break galaxies with detected [O iii] emission lines. The LyC emission is detected with a significance ∼5σ in the F336W band of the Hubble Deep UV Legacy Survey, corresponding to the 650–770 Å rest frame. The light centroid of the LyC emission is offset from the galaxy center by about 0.″2 (1.4 pkpc). The Hubble deep images at longer wavelengths show that the emission is unlikely provided by low-redshift interlopers. The photometric and spectroscopic data show that the possible contribution of an active galactic nucleus is quite low. Fitting the spectral energy distribution of this source to stellar population synthesis models, we find that the galaxy is young (∼50 Myr) and actively forming stars with a rate of 52.1 ± 4.9 M ⊙ yr−1. The significant star formation and the spatially offset LyC emission support a scenario where the ionizing photons escape from the low-density cavities in the ISM excavated by massive young stars. From the nebular model, we estimate the escape fraction of LyC photons to be 38% ± 7% and the corresponding intergalactic medium (IGM) transmission to be 60%, which deviates more than 3σ from the average transmission. The unusually high IGM transmission of LyC photons in CDFS-6664 may be related to a foreground type-2 quasar, CDF-202, at z = 3.7, with a projected separation of 1.′2 only. The quasar may have photoevaporated optically thick absorbers and enhance the transmission on the sightline of CDFS-6664.

Crucial Factors for Lyα Transmission in the Reionizing Intergalactic Medium: Infall Motion, H ii Bubble Size, and Self-shielded Systems

Using the CoDa II simulation, we study the Lyα transmissivity of the intergalactic medium (IGM) during reionization. At z > 6, a typical galaxy without an active galactic nucleus fails to form a proximity zone around itself due to the overdensity of the surrounding IGM. The gravitational infall motion in the IGM makes the resonance absorption extend to the red side of Lyα, suppressing the transmission up to roughly the circular velocity of the galaxy. In some sight lines, an optically thin blob generated by a supernova in a neighboring galaxy results in a peak feature, which can be mistaken for a blue peak. Redward of the resonance absorption, the damping-wing opacity correlates with the global IGM neutral fraction and the UV magnitude of the source galaxy. Brighter galaxies tend to suffer lower opacity because they tend to reside in larger H ii regions, and the surrounding IGM transmits redder photons, which are less susceptible to attenuation, owing to stronger infall velocity. The H ii regions are highly nonspherical, causing both sight-line-to-sight-line and galaxy-to-galaxy variation in opacity. Also, self-shielded systems within H ii regions strongly attenuate the emission for certain sight lines. All these factors add to the transmissivity variation, requiring a large sample size to constrain the average transmission. The variation is largest for fainter galaxies at higher redshift. The 68% range of the transmissivity is similar to or greater than the median for galaxies with M UV ≥ −21 at z ≥ 7, implying that more than a hundred galaxies would be needed to measure the transmission to 10% accuracy.

Blue-Light Transmittance In Sunglasses Over Long-Term Irradiation Within A Solar Simulator

Blue-light transmittance in sunglasses plays an important role for the consumer regarding eye health. Current standards do not have specific requirements for blue-light protection, as in the past. However, the literature has warned about the potential harms of blue light for the eye. The limits imposed in the past state that the average transmission in the 380 nm to 500 nm region should not exceed 1.2X the transmittance in the visible range (380 nm – 780 nm). This work investigates, besides the transmittance of blue light in sunglasses, whether those limits imposed aiming to eye health are respected. Additionally, this study examines the blue-light transmittances pre- and post-artificially aging the material in a solar simulator. Twelve samples of sunglasses were tested for compliance with a former standard and submitted to the aging process up to 2500 h within the solar simulator. The results showed relevant changes in the lenses over time, that is, they considerably lost their blue-light attenuation capabilities. The results suggest that the aging test should be carried out on sunglasses not only for ultraviolet radiation, as required by most standards, but also for blue light. Furthermore, the standards should comprise some constraints concerning the blue-light attenuation.

Multi-objective optimization of muffler for vehicle air-conditioning compressor pipeline

The noise reduction of air-conditioning systems has gradually become an urgent problem with the comfortable requirement of driving, and the muffler is a commonly used noise reduction equipment for air-conditioning pipeline. In this article, the transmission loss of prototype muffler is co-simulated at different speeds. For optimizing the muffler, a new method that combines orthogonal optimization and detailed optimization is proposed. In orthogonal optimization, the multi-objectives orthogonal test is used to analyze the effect of four structural parameters (the shoulder height, the length of the cavity, the diameter of cavity, and the length of intubation) on the average transmission loss, the transmission loss at 1120Hz, and the frequency band width below 4dB. The influence of different factors on the transmission loss is studied at different speeds, and it found that the length of intubation has a significant impact on the transmission loss. In detailed optimization, the method is characterized by rapidity in the design of air conditioning system of vehicle, and the final optimization model is determined. The results show that the optimized structure is better than the original structure. The maximum reduction of average noise can reach 11.99dB, and the maximum noise reduction at 1120Hz reach 8.58dB.

Analysis of Composite Scrubber with Built-In Silencer for Marine Engines

The International Maritime Organization (IMO) is strengthening regulations on reducing sulfur oxide emissions, and the demand for reducing exhaust noise affecting the environment of ships is also increasing. Various technologies have been developed to satisfy these needs. In this paper, a composite scrubber for ships that can simultaneously reduce sulfur oxide and noise was proposed, and the flow characteristics and noise characteristics were analyzed. For the silencer, vane type and resonate type were applied. In the case of the vane type, the effects of the direction, size, and location of the vane were analyzed, and in the case of the resonate type, the effects of the hole location and the number of holes were analyzed. The result shows that the length increase of the vane increased the average transmission loss and had a great effect, especially in the low frequency region. The transmission loss increased when the vane was installed outside, and the noise reduction effect was excellent when the vane was in the reverse direction. In the resonate type, increasing the number of holes is advantageous for noise reduction. The condition for maximally reducing noise in the range not exceeding 840 Pa, which is 70% of the allowable back pressure, is a vane length of 225 mm in the outer vane reverse type. The pressure drop under this condition was 777 Pa, and the average transmission losses in the low frequency region and the entire frequency region were 43.5 and 54.5 dB, respectively.

Mo/W/Al doped tin oxide thin films: Exploring optical and mechanical properties for transparent protective coating applications

For the last few years research has been intensified in exploring and improving mechanical properties of tin oxide thin films besides the optical and electrical ones that enhances the film’s functionality and broadens its application purview. The present investigation reports a comprehensive study on the effect of Mo, W, and Al doping on optoelectronic and mechanical properties of tin oxide thin films. The films exhibited an optical transparency over 350-400 nm with an average transmission of 85-98% at 550 nm and mechanical hardness spanning over 2-8 GPa, and electrically resistivity in the range 900-200 Ωm, based on the dopant used and its content. Compared to bare tin oxide film, the doped films exhibited a decrease in optical transparency with an improvement in the hardness. 10wt.% Mo doped tin oxide film exhibited good average optical transparency 72% at 550 nm, highest elastic recovery of 70%, highest hardness 8.0 ± 0.5 GPa and reduced-modulus of 89 ± 0.5 GPa of all the films. The investigation demonstrates a simple technique of producing mechanically hard tin oxide thin films useful as transparent protective coatings.

On the Design of Rate Adaptation for Relay-Assisted Satellite Hybrid FSO/RF Systems

<p>This paper addresses the design of hybrid free-space optical/radio frequency (FSO/RF) systems for a high-altitude platform (HAP)-aided relaying satellite communication for mobile networks supported by unmanned aerial vehicle (UAV). While prior work primarily focused on fixed-rate design, which frequently switches between FSO and RF lead to reduce the system performance, we propose a rate adaptation design that gradually adjusts the data rate in each link when its channel state fluctuates. The proposed design's downlink performance is analyzed, taking into account many challenging issues, including beam spreading loss, cloud attenuation, statistical behaviors of the atmospheric turbulence in the dual-hop channel, and pointing misalignment due to the UAV hovering. Different performance metrics are analytically derived based on channel modelings, such as outage probability, average transmission rate, achievable spectrum efficiency, and average transmission rate. The numerical results quantitatively confirm the effectiveness of our proposed system under the impact of UAV hovering misalignment and atmospheric-related issues like clouds and turbulence. Finally, Monte-Carlo simulations validate the accuracy of theoretical results.</p>