Multiband Approaches Research Articles

Semi-automated bathymetry using Sentinel-2 for coastal monitoring in the Western Mediterranean

Nearshore bathymetry is one of the main parameters used in coastal studies. However, regular and continuous bathymetries are scarce due to the difficulty of continuous data collection using traditional surveys. Remote sensing offers an attractive alternative to conventional collection methods for acquiring freely available, reliable, and frequent high-resolution data from space missions, such as the European Union's Copernicus programme Sentinel-2A/B satellites, which are increasingly demonstrating their potential to derive bathymetric information. Consequently, satellite-derived bathymetry (SDB) is being used more regularly because of its low cost and high efficiency. In this study, we apply a log-transformed band ratio SDB model in the Western Mediterranean Sea (Mallorca Island, Spain). This model has been widely used in the Caribbean and along the U.S. coast, among other sites, with outstanding results in heterogeneous environments. The SDB model consists of an automatic multi-scene approach applied over several images corrected by a robust atmospheric correction model (ACOLITE), a switching model, and a procedure to remove pixels from optically deep waters. We retrieve depths up to 14 m with a mean bias of 0.02 m and a median absolute error of 0.71 m compared with multibeam echo-sounder (MBES) data. The outcomes of this study confirm the effectiveness of the multi-scene approach to automatically correct the imagery to derive accurate depths and characterize erosional and accretion patterns annually. Furthermore, it highlights the benefit of the switching model to take advantage of the spectral sensitivity of different multi-band ratio approaches. This study will provide the scientific community with substantial knowledge and improved SDB techniques to consolidate the understanding of nearshore processes in such a relevant ecosystem as the Mediterranean Sea.

Adaptive Multi-Band Negative-Group-Delay RF Circuits With Low Reflection

Two classes of frequency-reconfigurable multi-band negative-group-delay (NGD) circuit networks that feature low-input-power-reflection capabilities are reported. They consist of lossy-complementary-diplexer architectures, in which the NGD properties are obtained within the stopband regions of their lossy multi-band bandstop-filter (BSF) channel. Their complementary lossy multi-band bandpass-filter (BPF) branch absorbs in its terminating resistor the RF-input-signal energy that is not transmitted by the lossy multi-band BSF channel within its stopbands. In this manner, the input-reflectionless/absorptive behavior is realized. The theoretical foundations of the devised lossy-multi-band-BSF-based NGD structures using a coupling-routing-diagram formalism and single-to-multi-band admittance transformations are described. For the first-order case as illustration, guidelines for the synthesis in the bandpass frequency domain are provided. Furthermore, the extension of these multi-band NGD approaches to higher-order and in-series-cascade multi-stage realizations for more-general and wider-band NGD patterning, as well as to two-port/symmetrical designs, is shown. In addition, the conception of multi-functional passive components with NGD characteristics, such as wide-band BPFs and power directional couplers with embedded NGD regions, is also addressed. For experimental-demonstration purposes, an electronically-reconfigurable microstrip prototype of a two-stage-in-series-cascade dual-band NGD circuit is manufactured and measured.

M giants found in the First Byurakan Spectral Sky data base. V. Gaia DR2 data

In this paper we study bright M{type giants found in the First Byurakan Survey (FBS) low-resolution (lr) spectroscopic data base. Phase dependence light-curves from large sky area variability data bases such as Catalina Sky Survey (CSS) and All-Sky Automated Survey for Supernovae (ASAS-SN), and the second Gaia data release data (Gaia DR2) high-quality photometric data are analyzed to estimate some important physical parameters for 1096 M-type giants found at high Galactic latitudes. Their Gaia DR2 broad-band G magnitudes are in the range 8.0 < G < 16.0 mag. Gaia DR2 radial velocities (RV) are available for 134 and luminosities for 158 stars out of 1096. The Gaia DR2 color/absolute magnitude diagram (CaMD), their Galactic distribution, also some other diagrams based on Gaia DR2 photometric data are presented. Absolute magnitudes cover the range +1.0 > M(G) > -5.4 mag. They follow to the behaviors and occupy the same regions on the color-magnitude diagrams studied in many papers by different researches for long period variables (LPVs). Particularly, we consider the locations of the FBS giants on the new diagrams, using multi-band approaches in combination with Wesenheit functions, obtained recently by Lebzelter and colleagues (2018) for the oxygen-rich (O-rich) and carbon-rich (C-rich) LPVs in the Large Magellanic Cloud. Period-Luminosity (P-L) diagram was presented for 112 M Mira-variables. The upper limit of the initial stellar masses can be estimate near 5 Msun for M giants according to the new diagnostic tools. The kinematic properties, space distribution also more interesting cases among the sample were considered.

Superconductivity-induced phonon renormalization onNaFe1−xCoxAs

We report a study of the lattice dynamics in superconducting NaFeAs (Tc = 8 K) and doped NaFe0.97Co0.03As (Tc = 20 K) using Raman light scattering. Five of the six phonon modes expected from group theory are observed. In contrast with results obtained on iso-structural and iso-electronic LiFeAs, anomalous broadening of Eg(As) and A1g(Na) modes upon cooling is observed in both samples. In addition, in the Co-doped sample, a superconductivity-induced renormalization of the frequency and linewidth of the B1g(Fe) vibration is observed. This renormalization can not be understood within a single band and simple multi-band approaches. A theoretical model that includes the effects of SDW correlations along with sign-changing s-wave pairing state and interband scattering has been developed to explain the observed behavior of the B1g(Fe) mode.

Model Order Reduction for Quantum Transport Simulation of Band-To-Band Tunneling Devices

Simulations of nanoelectronic devices with nonequilibrium Green's function are computationally very intensive, in particular, when combined with multiband approaches, such as the k·p methods. To reduce the cost and make the simulation of realistic devices tractable, we have developed a model order reduction method for the simulation of hole transport in silicon nanowires using three- and six-band k·p models. It is shown in this paper that, with a spurious band elimination process, the method can be readily extended to the eight-band case that enables us to simulate band-to-band tunneling devices. The method is demonstrated via constructing reduced models for indium arsenide (InAs) nanowires and simulation of I-V characteristics of InAs tunneling field-effect transistors (TFETs). The results indicate that significant model reduction can be achieved with good accuracy retained. The method is then applied to study InAs TFETs with different channel orientations and source-pocket TFETs with n-p-i-p doping profiles.

Wideband and Multiband Antenna Design and Fabrication for Modern Wireless Communications Systems

One of the major challenges due to spectrum scarcity in modern wireless communication is on antenna design that can serve a non-contagious frequency spectrum. In this paper, wideband and multiband design approaches are proposed to produce antennas that can serve various wireless technologies using different frequencies from 2.3 to 6.0 GHz, covering WiFi frequencies at 2.4-2.48 GHz, 5,15-5,35 GHz and 5,725-5,825 GHz, as well as WiMax frequencies at 2.3-2.4 GHz, 2.495-2.695 GHz, 3.3-3.8 GHz, and 5.25-5.85 GHz. The wideband and multiband antenna were implemented on an 0.8 mm thick of FR4 epoxy dielectric substrate with permittivity er=4.3. The return loss of 10 dB can be achieved for 2.3 to 6 GHz in wideband antenna, and a tripe band of 2.3-2.8 GHz, 3.3-3.7 GHz, and above 4.6 GHz in multiband antenna. The gain of both antennas increases almost linearly from 0 dB at 2.3 GHz to around 4.5 dB at 6 GHz, except for the stop band at 2.8-3.3 GHz which has a significant drop of gain, corresponding to the stop frequency band. Antenna radiation pattern is bidirectional at x-y plane and nearly omnidirectional at y-z plane, and shows a similar patern for both wideband and multiband design approaches.

PERFORMANCE ANALYSIS OF ULTRA WIDEBAND MEDIA ACCESS CONTROL PROTOCOL PROVIDING TWO CLASS TRAFFIC

UWB (Ultra wideband) technology has a huge potential for revolutionizing the world of digital communications, particularly wireless communications that based primarily on the impulse radio paradigm. UWB technology was originally seen purely as a physical layer technology, with no or little protocol to control the communication. It is now clear that Media Access Control (MAC) features play a major role in UWB communication systems. In this paper, a communication system is considered with a small number of geographically separated nodes in UWB ad hoc networks. An active node can be in one of two possible classes (H,L); high priority or low priority class, depending on its nature and / or the type of information that it desires to transmit. Nodes in class-H are given some priority over those in class-L. The motivation comes from the observation that, in the absence of a sophisticated equalizer, the size of a slot for transmitting a UWB pulse is typically dictated by the Delay Spread of the channel which amounts to 60 ns in indoor environments. Therefore, using a wider frequency band to shorten the transmission time for each pulse may not increase the data rate in proportion to the available bandwidth. Thus, a multiband approach is considered to better utilize the available spectrum, where each transmitter sends longer pulses in one of many narrower frequency bands. Measures of system performance including throughput, average delay and bit error rate will be presented in single band and multiband approaches. Additionally, there is a comparison between numerical results and how they are achieved by simulation of the entire system providing two priority classes.

The Use of Overlapped Sub-Bands in Multi-Band, Multi-SNR, Multi-Path Recognition of Noisy Word Utterances

A solution to the problem of improving robustness to noise in automatic speech recognition is presented in the framework of multi-band, multi-SNR, and multi-path approaches. In our word recognizer, the whole frequency band is divided into seven-overlapped sub-bands, and then sub-band noisy phoneme HMMs are trained on speech data mixed with the filtered white Gaussian noise at multiple SNRs. The acoustic model of a word is built as a set of concatenations of clean and noisy sub-band phoneme HMMs arranged in parallel. A Viterbi decoder allows a search path to transit to another SNR condition at a phoneme boundary. The recognition scores of the sub-bands are then recombined to give the score for a word. Experiments show that the overlapped seven-band system yields the best performance under nonstationary ambient noises. It is also shown that the use of filtered white Gaussian noise is advantageous for training noisy phoneme HMMs.