Free space optical (FSO) communication has gained significant popularity in recent years due to large bandwidth, license‐free spectrum, high data rates, less power consumption, and low mass ...requirements. However, system performance strongly depends on atmospheric conditions and ambient noise. In this letter, the duobinary modulation technique is applied and the system performance is investigated in the presence of ambient noise. The system is evaluated on the basis of Q‐factor, eye diagram, input power, transmission distance, and bit error rate. A significant improvement is observed in the presence of noise while using duobinary modulation. This study exploits extensive simulations to investigate the performance of the system. All simulations are performed for a single link of FSO communication network having a data rate of 40 Gbps in the Optisystem simulator and ambient noise is created using LEDs. After the exhaustive set of simulations, a significant improvement in transmission length is observed. It is also observed that at low input power, doubinary modulation provides better results when compared with on‐off keying (OOK) format. Scintillation effect has also be observed for doubinary modulation and compared with OOK modulation format. It is concluded that doubinary modulation provides better results in the presence of low and moderate scintillation.
Open clusters appear as simple objects in many respects, with a high degree of homogeneity in their (initial) chemical composition, and the typical solar-scaled abundance pattern that they exhibit ...for the majority of the chemical species. The striking singularity is represented by heavy elements produced from the slow process of the neutron-capture reactions. In particular, young open clusters (ages less than a few hundred Myr) give rise to the so-called barium puzzle: that is an extreme enhancement in their Be/Fe ratios, up to a factor of four of the solar value, which is not followed by other nearby s-process elements (e.g., lanthanum and cerium). The definite explanation for such a peculiar trend is still wanting, as many different solutions have been envisaged. We review the status of this field and present our new results on young open clusters and the pre-main sequence star RZ Piscium.
Recombination zone (RZ) confinement and charge balance are the most important factors for realizing the enhanced efficiency in phosphorescent organic light emitting devices (Ph-OLEDs). Here, we ...demonstrated the RZ movement and improved Ph-OLED efficiency by varying the electron transport layer 2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) thickness. The thickness increment of TPBi not only control the electron transport on to the emission layer but also shifting the RZ towards cathode. The RZ movement in Ph-OLED with different thick TPBi is extracted from the exciplex peak generated at exciton blocking layer/emission layer (EML) interface. The optimized electron to hole ratio at EML have occurred with 40 nm TPBi in which the Ph-OLED exhibits superior current efficiency of 80 cd A−1. The Ph-OLED efficiency roll-off is also very low in 40 nm TPBi based devices. This efficiency roll-off and RZ shift were simply estimated by interface exciplex peak in electroluminescence intensity without extra sensing layers. Further, the electron only devices made with various TPBi thickness also demonstrated the possible changes in the electron transport and supports the RZ and charge balance tactics.
We present design techniques for single-bit continuous-time delta-sigma modulators that attain high resolution (>16 bits) over a bandwidth (BW) that is more than ten times the audio range. We ...introduce the zapped, virtual-ground-switched dual return-to-open DAC which is immune to ISI and other transition-dependent errors. FIR feedback facilitates chopping, improves clock-jitter sensitivity and the loop filter's linearity. We show that the compensation FIR DAC, which is typically bulky, can be implemented in an extremely power- and area-efficient manner in a single-bit modulator using a capacitive DAC and passive summation. Thanks to these techniques, the fabricated prototype achieves 103.2-/104.3-dB signal to noise and distortion ratio (SNDR)/signal to noise ratio (SNR) in a 250-kHz bandwidth while operating at 48 MS/s. Consuming 17.7 mW from a 1.8-V supply, the modulator occupies 1.1 mm 2 in a 180-nm CMOS process. The Schreier (SNDR) figure of merit (FoM) is 174.7 dB.
Discrepancies between competing optical and near-infrared (NIR) spectral typing systems for L dwarfs have motivated us to search for a classification scheme that ties the optical and NIR schemes ...together, and addresses complexities in the spectral morphology. We use new and extant optical and NIR spectra to compile a sample of 171 L dwarfs, including 27 low-gravity β and γ objects, with spectral coverage from 0.6-2.4 m. We present 155 new low-resolution NIR spectra and 19 new optical spectra. We utilize a method for analyzing NIR spectra that partially removes the broad-band spectral slope and reveals similarities in the absorption features between objects of the same optical spectral type. Using the optical spectra as an anchor, we generate near-infrared spectral average templates for L0-L8, L0-L4γ, and L0-L1β type dwarfs. These templates reveal that NIR spectral morphologies are correlated with the optical types. They also show the range of spectral morphologies spanned by each spectral type. We compare low-gravity and field-gravity templates to provide recommendations on the minimum required observations for credibly classifying low-gravity spectra using low-resolution NIR data. We use the templates to evaluate the existing NIR spectral standards and propose new ones where appropriate. Finally, we build on the work of Kirkpatrick et al. to provide a spectral typing method that is tied to the optical and can be used when only H or K band data are available. The methods we present here provide resolutions to several long-standing issues with classifying L dwarf spectra and could also be the foundation for a spectral classification scheme for cloudy exoplanets.
We present the results of long-term monitoring of the X-ray emission from the ultraluminous X-ray source XMMU J122939.9+075333 in the extragalactic globular cluster RZ2109. The combination of the ...high X-ray luminosity, short-term X-ray variability, X-ray spectrum, and optical emission suggests that this system is likely an accreting black hole in a globular cluster. To study the long-term behavior of the X-ray emission from this source, we analyze both new and archival Chandra and XMM-Newton observations, covering 16 years from 2000 to 2016. For all of these observations, we fit extracted spectra of RZ2109 with xspec models. The spectra are all dominated by a soft component, which is very soft with typical fit temperatures of T 0.15 keV. The resulting X-ray fluxes show strong variability on short and long timescales. We also find that the X-ray spectrum often shows no significant change even with luminosity changes as large as a factor of five.
Gamma-ray astrophysics in the MeV range De Angelis, Alessandro; Tatischeff, Vincent; Argan, Andrea ...
Experimental astronomy,
06/2021, Volume:
51, Issue:
3
Journal Article
Peer reviewed
Open access
The energy range between about 100 keV and 1 GeV is of interest for a vast class of astrophysical topics. In particular, (1) it is the missing ingredient for understanding extreme processes in the ...multi-messenger era; (2) it allows localizing cosmic-ray interactions with background material and radiation in the Universe, and spotting the reprocessing of these particles; (3) last but not least, gamma-ray emission lines trace the formation of elements in the Galaxy and beyond. In addition, studying the still largely unexplored MeV domain of astronomy would provide for a rich observatory science, including the study of compact objects, solar- and Earth-science, as well as fundamental physics. The technological development of silicon microstrip detectors makes it possible now to detect MeV photons in space with high efficiency and low background. During the last decade, a concept of detector (“ASTROGAM”) has been proposed to fulfil these goals, based on a silicon hodoscope, a 3D position-sensitive calorimeter, and an anticoincidence detector. In this paper we stress the importance of a medium size (M-class) space mission, dubbed “ASTROMEV”, to fulfil these objectives.
This study has clarified the optical fiber systems performance signature based on the dispersion mitigation techniques in based on the dispersion compensated dense wavelength division multiplexing ...(WDM) systems in the presence of RZ/NRZ modulation code method. The high-transmission reach-based dense multiplexing channels through the WDM network by OptiSystem software. The long reach dense multiplexing system is modeled at 100 GHz for high bit rates through SMF with possible 200 km transmission. The Dense WDM technique is tested with the input signal variations. Three compensation techniques are employed that are namely symmetrical dispersion compensated fiber, fiber Bragg grating method and Chirped fiber Bragg grating method. The study has demonstrated the efficient compensation methods for upgrading the optical/electrical signal per noise ratio especially with the use of chirped fiber Bragg grating technique.
We discuss a revision of accretion activity and kinematics of the enigmatic isolated UX Ori type star RZ Psc. Previously, RZ Psc was known to possess only spectroscopic signatures of outflow in the ...low-excitation lines of alkali metals. The archival high-resolution spectra reveal a short-lived episode of magnetospheric accretion in the system observed via inverse P Cyg profiles at the Hα and Ca II 8542 Å lines. The simultaneous presence of accretion and outflow signatures at Ca II 8542 Å is suggestive of an accretion-driven origin of the RZ Psc wind. We argue that RZ Psc experiences matter ejection via the magnetic propeller mechanism but variable accretion episodes allow it to sometimes move in the magnetospheric accretion regime. The presence of the weak accretion in the system is also supported by the radiation of the hot accretion spot on the stellar surface observed spectroscopically at the deep photometric minimum of the star. The Galactic motion of RZ Psc calculated with new Gaia DR2 astrometric data suggests possible membership in Cas-Tau OB association with an age of t = 20−5+3 t = 20 − 5 + 3 $ t=20^{+3}_{-5} $ Myr.
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