Small Bandwidth Research Articles

Contextual variables of student math proficiency and their geographic variations in Missouri

This study examines variables of student math proficiency relevant to family, teacher, and school characteristics, and investigates how effects of significant variables vary by geographic areas in the State of Missouri, United States, using aggregated data at the school-district level. Ordinary Least Squares (OLS) regression analysis derives a statewide model of five significant predictor variables with an R square of 0.35, showing that school districts with higher family income, higher parent education levels, higher two-parent percentage, more teacher years of experience, and higher percentage of certified teaching assignments tend to have higher student math proficiency. Geographically Weighted Regression (GWR) local regression analysis using the five significant variables from OLS regression achieves R squares between 0.37 and 0.45 at different bandwidths, i.e., the spatial extent of local regression. Examining GWR local regression coefficients, we found that the variable effects can change considerably across different geographic areas, and some prominent variable effects can only be manifested at a small GWR bandwidth. The results of this study identified the most influential factors of math proficiency for local areas, which provide useful insights for policy makers to prioritize educational resources for improving student math proficiency.

Performance analysis of LT code-based HARQ error control in underwater acoustic sensor networks

Underwater acoustic sensor network (UASN) is an emerging technology meant for underwater explorations. In underwater communication, the acoustic signal travels a longer distance with smaller bandwidth. Characteristics of the acoustic channel and the distance between underwater sensor nodes vary with time due to the variations in the water current. This affects the channel quality as well as the topology of the network. Connectivity issues in UASN cause transmission reliability challenges, in transferring the data sensed by various sensor nodes to the other end. Thus, data reliability and energy efficiency are the two critical issues in the case of UASN. The robust signal attenuation leads to the reception of erroneous data or data loss. In this paper, Recursive Luby transform (RLT) code-based Hybrid Automatic Repeat reQuest is proposed to overcome the data reliability issues and to obtain transmission efficiency. RLT is a form of Luby transform code with small degree of distribution. The proposed rateless code-based Hybrid ARQ scheme combines the RLT code and selective retransmission ARQ (RLTCH). The RLT code is adopted for its minimal complexity in encoding and decoding processes. The performance of RLTCH is evaluated by considering the underwater-specific channel characteristics. Simulation results of RLTCH for multi-hop UASN reveal that the proposed technique increase the network throughput with reduced energy consumption and end-to-end delay. Comparative performance studies were conducted to confirm the superiority of RLTCH with other schemes based on parameters such as throughput, packet arrival ratio, delay and energy consumption.

HF Noise Measurement in the Western Part of Romania

Abstract Despite the extraordinary development of mobile communications, HF radio links have several advantages that make them unique in some application areas. Knowledge of HF noise is critical for the setup of a point to point HF communication. The paper presents HF noise measurements performed using a broadband antenna and Software Defined Radio equipment for signal acquisition, followed by offline signal processing. The recording has been split into several sub-bands of small bandwidth and for each sub-band the mean power has been computed, to find the sub-band with the lowest power. It might be assumed that the frequency band having the lowest power contains only noise. An analysis of the influence of sub-band size on the noise level hasalso been made. Measurements cover a large part of HF band and a large time interval to observe the noise behaviour.The paper analyses the noise level over short and long time periods, and over a large frequency band, and reports also simultaneous noise measurements in two locations in the western part of Romania, a dense urban one and a small town one, to highlight the differences caused by man-made noise of industrial type.

Deep-ocean inertial subrange small bandwidth coherence and Ozmidov-frequency separation

The inertial subrange of turbulence in a density stratified environment is the transition from internal waves to isotropic turbulence, but it is unclear how to interpret its extension to anisotropic “stratified” turbulence. Knowledge about stratified turbulence is relevant for the dispersal of suspended matter in geophysical flows, such as in most of the ocean. For studying internal-wave-induced ocean-turbulence, moored high-resolution temperature (T-)sensors are used. Spectra from observations on episodic quasiconvective internal wave breaking above a steep slope of large seamount Josephine in the Northeast-Atlantic demonstrate an inertial subrange that can be separated in two parts: A large-scale part with relatively coherent portions adjacent to less coherent portions and a small-scale part that is smoothly continuous (to within standard error). The separation is close to the Ozmidov frequency and coincides with the transition from anisotropic/quasideterministic stratified turbulence to isotropic/stochastic inertial convective motions as inferred from a comparison of vertical and horizontal cospectra. These observations contrast with T-sensor observations of shear-dominated internal wave breaking in an equally turbulent environment above the slope of a small Mid-Atlantic ridge-crest, which demonstrate a stochastic inertial subrange throughout.

Impact of distributed Bragg reflector on carrier and photon dynamics in GaN-based surface emitting diodes manifested by ultrafast transient absorption spectroscopy

Small signal modulation bandwidth characterized by relaxation oscillations (ROs) of GaN-based vertical cavity surface emitting laser diodes are of great importance in high-speed applications. In this work, we investigate the impact of distributed Bragg reflectors (DBRs) on ROs by developing a simulation framework, which can accommodate the reflected photons self-consistently in the rate equation model. Carrier and photon dynamics in the active region and at the transmitting end have been evaluated for a typical GaN/InGaN multiple quantum well heterostructure having a dielectric DBR. Temporal broadening in photon dynamics is observed due to the phase difference. Interestingly, an enhanced radiative recombination rate is also noticed due to the increased confinement, which leads to a reduced turn-on delay. Transient absorption spectroscopy has been performed to obtain the decay rates of captured carriers in the well and it turns out be in harmony with the simulation results. Photoluminescence spectroscopy also validates the increased radiative recombination.

On the Asymmetric Spectral Broadening of a Hydrodynamic Modulated Wave Train in the Optical Regime

Amplitude modulation of a propagating wave train has been observed in various media including hydrodynamics and optical fibers. The notable difference of the propagating wave trains in these media is the magnitude of the nonlinearity and the associated spectral bandwidth. The nonlinearity and dispersion parameters of optical fibers are two orders of magnitude smaller than the hydrodynamic counterparts, and therefore, considered to better assure the slowly varying envelope approximation (SVEA) of the nonlinear Schrödinger equations (NLSE). While most optics experiment demonstrate an NLSE-like symmetric solutions, experimental studies by Dudley et al. (Optics Express, 2009, 17, 21497–21508) show an asymmetric spectral evolution in the dynamics of unstable electromagnetic waves with high intensities. Motivated by this result, the hydrodynamic Euler equation is numerically solved to study the long-term evolution of a water-wave modulated wave train in the optical regime, i.e., at small steepness and spectral bandwidth. As the initial steepness is increased, retaining the initial spectral bandwidth thereby increasing the Benjamin–Feir Index, the modulation localizes, and the asymmetric and broad spectrum appears. While the deviation of the evolution from the NLSE solution is a result of broadband dynamics of free wave interaction, the resulting asymmetry of the spectrum is a consequence of the violation of the SVEA.

항공기 레이다에 있어 두 개의 주파수를 사용하였을 때저고도 표적 다중경로 각도 추정의 CRLB

If two signals with the same single-tone frequency and differing phases impinge simultaneously on an antenna at slightly differing angles, then a large error in the angle estimation might occur if the phase difference is either 0° or 180°. This phenomenon might arise with an airborne fire-control radar, which has a relatively small bandwidth, for a low-flying target over the sea or terrain surface. In this paper, we show that the Cramér-Rao lower bound for such a target can be significantly lowered with the use of two frequencies.

Hardware prototype demonstration of a cognitive sub‐Nyquist automotive radar

Automotive radar (AR) plays a key role in autonomous vehicles. A modern-day AR requires cognition to adapt to its dynamically changing environment. In an automotive environment, the number of ARs needed to operate simultaneously varies rapidly and these ARs should transceive without mutual interference. Most widely used AR systems use frequency-modulated continuous-wave radar due to their smaller bandwidth and cost compared with pulse Doppler radar (PDR). By using sub-Nyquist based techniques, such as Xampling, the authors show here that the targets could be estimated from low rate samples even with a PDR. In this study, they demonstrate a hardware prototype demonstrating the applicability of sub-Nyquist PDR as a cognitive AR. They consider a scenario where a number of ARs are mounted on a vehicle and need to look simultaneously into different directions without interfering with each other. The available bandwidth is divided into several non-overlapping subbands, which depend on the number of ARs required. Each AR is assigned a set of randomly spaced subbands for its transceiver to operate. Through simulations, they show that the ARs could detect targets simultaneously without interference. Furthermore, the noise robustness of their sub-Nyquist reconstruction method is better than the standard matched-filtering approach.

The Repair Problem for Reed–Solomon Codes: Optimal Repair of Single and Multiple Erasures With Almost Optimal Node Size

The repair problem in distributed storage addresses recovery of the data encoded using an erasure code, for instance, a Reed–Solomon (RS) code. We consider the problem of repairing a single node or multiple nodes in RS-coded storage systems using the smallest possible amount of inter-nodal communication. According to the cut-set bound, communication cost of repairing $h\geqslant 1$ failed nodes for an $(n,k=n-r)$ maximum distance separable (MDS) code using $d$ helper nodes is at least $dhl/(d+h-k)$ , where $l$ is the size of the node. Guruswami and Wootters (2016) initiated the study of efficient repair of RS codes, showing that they can be repaired using a smaller bandwidth than under the trivial approach. At the same time, their work as well as follow-up papers stopped short of constructing RS codes (or any scalar MDS codes) that meet the cut-set bound with equality. In this paper, we construct the families of RS codes that achieve the cut-set bound for repair of one or several nodes. In the single-node case, we present the RS codes of length $n$ over the field ${\mathbb F}_{q^{l}}, l=\exp ((1+o(1))n\log n)$ that meet the cut-set bound. We also prove an almost matching lower bound on $l$ , showing that super-exponential scaling is both necessary and sufficient for scalar MDS codes to achieve the cut-set bound using linear repair schemes. For the case of multiple nodes, we construct a family of RS codes that achieve the cut-set bound universally for the repair of any $h=1,2, {\dots },r$ failed nodes from any subset of $d$ helper nodes, $k\leqslant d\leqslant n-h$ . For a fixed number of parities $r$ , the node size of the constructed codes is close to the smallest possible node size for codes with such properties.

Effective Transmission Method With Adaptive Nonstationary Channel Equalization for Hypersonic Reentry Communications

The reentry plasma sheath propagation environment is nonstationary and has high-dynamic characteristics. The communication signal suffers serious parasitic modulation effect since the time-varying degree of the channel is on the same order as the telemetry symbol rate. This paper proposes an effective transmission scheme to cancel the plasma sheath channel (PSC) distortion by utilizing the short spreading and adaptive nonstationary channel equalization technology. The proposed scheme spreads the telemetry signal and inserts a small number of pilot signals to determine whether the nonstationary state of the channel is changed by the channel amplitude attention value of the pilot signals. A novel adaptive nonstationary stochastic gradient recursive minimum mean square error (NSGR–MMSE) algorithm is then proposed to estimate the other channel response values in each current state. Finally, the channel equalization is performed to mitigate the damage from the parasitic modulation effect. The proposed method can accommodate the nonstationary characteristics of the channel and the small-scale channel distortion simultaneously with small bandwidth efficiency scarification and minimal algorithm complexity cost. The simulation results show that the proposed transmission scheme can ensure reliable communication under two typical reentry PSC models. Furthermore, the performance of the proposed adaptive NSGR–MMSE algorithm is improved by at least 3 dB versus the classic MMSE algorithm under the effective transmission scheme.

LPWA Network Design and Implementation Strategy of Jakarta and Tangerang Area for Smart Meter Utilities

Internet of Things (IoT) is increasingly being implemented in major cities in the world, including in Indonesia. Currently, several cities in Indonesia have implemented smart city programs. Smart city implementation in Indonesia has not been supported by networks which are suitable for connectivity of equipment such as sensors. Sensors which are connected are still using cellular networks so they are not efficient in terms of power usage and bandwidth, where sensors only require small power and bandwidth. A network technology designed for the use of sensors is LPWA networks (Low Power Wide Area Networks) where, this network connects a large number of sensors with small power usage and narrow bandwidth. In this paper the authors try to design the LPWA network using LoRa technology for the purpose of using smart meters for electricity, water and gas in the DKI Jakarta and Tangerang areas with an approach to network performance parameters. The network parameters designed will be analyzed and adapted to the conditions of the region so that it has good network performance and capacity can meet the needs of smart meters in the region. The purpose of this paper is to produce a network design that fits the needs of smart meters which are expected to be a material consideration for operators in designing the LPWA network.

Lifetimes of Rogue Wave Events in Direct Numerical Simulations of Deep-Water Irregular Sea Waves

The issue of rogue wave lifetimes is addressed in this study, which helps to detail the general picture of this dangerous oceanic phenomenon. The direct numerical simulations of irregular wave ensembles are performed to obtain the complete accurate data on the rogue wave occurrence and evolution. Purely collinear wave systems, moderately crested, and short-crested sea states have been simulated by means of the high-order spectral method for the potential Euler equations. As rogue waves are transient and poorly reflect the physical effects, we join instant abnormally high waves in close locations and close time moments to new objects, rogue events, which helps to retrieve the abnormal occurrences more stably and more consistently from the physical point of view. The rogue event lifetime probability distributions are calculated based on the simulated wave data. They show the distinctive difference between rough sea states with small directional bandwidth on one part, and small-amplitude sea states and short-crested states on the other part. The former support long-living rogue wave patterns (the corresponding probability distributions have heavy tails), though the latter possess exponential probability distributions of rogue event lifetimes and generally produce much shorter rogue wave events.

A fast radio burst with frequency-dependent polarization detected during Breakthrough Listen observations

ABSTRACT Here, we report on the detection and verification of fast radio burst FRB 180301, which occurred on utc 2018 March 1 during the Breakthrough Listen observations with the Parkes telescope. Full-polarization voltage data of the detection were captured – a first for non-repeating FRBs – allowing for coherent de-dispersion and additional verification tests. The coherently de-dispersed dynamic spectrum of FRB 180301 shows complex, polarized frequency structure over a small fractional bandwidth. As FRB 180301 was detected close to the geosynchronous satellite band during a time of known 1–2 GHz satellite transmissions, we consider whether the burst was due to radio interference emitted or reflected from an orbiting object. Based on the pre-ponderance of our verification tests, we cannot conclusively determine FRB 180301 to be either astrophysical or anthropogenic in origin.

Irreversible Meta‐Magnetic Transition in Charge Ordered Nd0.5Ca0.5MnO3 Manganite

The investigation of charge ordering (CO) suppression and consequence effects in manganites are of interest to the scientific community as they help them to understand the interactions among the spin, charge and orbital degrees of freedom of conduction electrons. In this work, the suppression of CO in small bandwidth half‐doped manganite, Nd0.5Ca0.5MnO3 (NCMO) has been demonstrated by reducing the particle size. Bulk and nano forms of NCMO materials are prepared by sol‐gel technique and characterized by various physicochemical techniques. The magnetic and magnetotransport properties of bulk samples show the exciting features, viz., CO, training and irreversible metamagnetic effects, whereas these features are significantly suppressed in the nanoscale sample. The observed behavior in the present investigation is explained in terms of magnetic phase separation and spin memory effects. Our investigation establishes a combined effect of surface spin disorder and lattice strains for the suppression of CO behavior in NCMO manganite system.

Small-Signal Analysis of High-Performance VCSELs

In this paper, a comprehensive model to describe the small-signal modulation response of ultra-high performance single- and multi-mode vertical-cavity surface-emitting lasers (VCSELs), with modulation bandwidths exceeding 30 GHz, is presented. Traditionally, utmost simplified dynamic models are used to extract dynamic figures of merit from single-mode edge-emitting lasers. These methods are later on also applied to evaluate the dynamic performance of VCSELs, even though these devices have a very different geometrical layout and modal confinement. However, to understand the dynamic performance of high-speed VCSELs, a model supporting the transverse and longitudinal mode profile, and the driving current inhomogeneity in the active region, is needed. Therefore, multi-mode VCSEL rate equations are established here. Moreover, to access the dynamic figures of merit of these devices, a comprehensive analytical fitting function based on our carrier reservoir splitting approach is derived. Thus, because of the high carrier and photon densities inside these optimized VCSELs, the common carrier reservoir splits up as a result of numerous effects such as mode competition, carrier diffusion and spatial hole burning. These and other effects have a tremendous impact on the small signal modulation response shape and bandwidth, and also on the current distribution profile in the carrier reservoirs. Compared with our recently reported work, this novel model presented includes the effects of gain compression and inhomogeneous current injection between the different lasing modes. Consequently, it is found that the further tuning of our multi-mode VCSEL dynamic model, to include these effects, yields a more physical and consistent figures of merit of high-performance VCSELs.

A Comparison Study of HO-CFD and DSC-RSK with Small Computational Bandwidths for Solving Some Classes of Boundary-Value and Eigenvalue Problems

This paper conducts a comparison analysis of high order central finite difference (HO-CFD) method and discrete singular convolution-regularized Shannon kernel (DSC-RSK) scheme with small computational bandwidths for solving some classes of boundary-value and eigenvalue problems. Second-, fourth- and sixth-order partial differential equations are taken into account. New strategies to generate parameters [Formula: see text] in DSC-RSK are proposed to ensure minimum errors for each case, and the influence of parameters [Formula: see text] with more decimal places is analyzed. Apart from the existing matched interface and boundary (MIB) scheme, a new double-parameter MIB scheme is also proposed. The influence of small computational bandwidths is discussed in detail. Numerical results by using HO-CFD and DSC-RSK are presented and compared to illustrate the performance of both methods in small bandwidth limit. Some remarkable conclusions have been drawn at the end of this study.

Synchrotron based absorption edge tomography for the analysis of 3D printed polymer embedded MOF

Absorption edge tomography (AET), also known as differential tomography at absorption edges, is a method which exploits the sudden change of the attenuation coefficient, when the photon energy crosses the absorption edge of an element [1]. Synchrotron radiation is the best source for absorption edge tomography, because of its small bandwidth, high intensity and easily adjustable photon energy [2]. The synchrotron beamline BAMline at the synchrotron radiation facility BESSY II in Berlin, which is operated by the Bundesanstalt für Materialforschung und -prüfung (BAM), provides a monochromatized beam in a photon energy range from 5 keV up to 80 keV with a bandwidth of 2%, when the double multilayer monochromator is used [3]. Together with the microtomography setup, this enables differential tomography with submicron resolution at the K edge of the elements [4] from chromium up to the lanthanides, and up to uranium, when the L edges are used as well. In this work, mechanochemically synthesized metal-organic framework (MOF) material HKUST-1 in combination with acrylonitrile- butadiene styrene (ABS) polymer was used to form a polymer MOF composite material by a simple extruder. This composite filament was used for 3D printing. Absorption edge tomography facilitated the evaluation of the 3D distribution of the MOF material both in the filament and the resultant printed sample up to μm resolution. Our very first data indicate, that HKUST-1 is mainly homogeneously dispersed in both polymer bulk materials. In addition, a few clusters having significantly higher Cu concentration were found. AET in combination with data fusion also allows for the calculation of the MOF amount located on the external polymer surface.

Photon enhancement in a homogeneous axion dark matter background

We study the propagation of photons in a homogeneous axion dark matter background. When the axion decay into two photons is stimulated, the photon field exhibits a parametric instability in a small bandwidth centered on one half of the axion mass. We estimate analytically the enhancement for both coherent and non-coherent axion fields and we find that this effect could be relevant in the context of miniclusters and galactic halos.

Dechirping Compression Method for Nonlinear Frequency Modulation Waveforms

This letter proposes a novel dechirp processing method for wideband nonlinear frequency modulation (NLFM) waveform which enables low sampling rate of data. As we know, NLFM waveform can easily realize optimal shape of power spectral density which helps to achieve better pulse compression result with low range sidelobes without signal-to-noise ratio degradation caused by weighting as we usually do for LFM waveforms. In the approach, hamming window is adopted in the generation of the NLFM waveform for better balance on the low range sidelobes and a relative small bandwidth. In dechirp operation, the NLFM radar echoes are mixed with a local reference LFM signal, and thus narrowband signals are resulted and only low sampling rate is needed. The dechirped NLFM signals are then up-sampled and inverse dechirped by software and finally matched filtering is conducted to complete pulse compression. Both numerically simulated data and real radar data are processed to verify the effectiveness of the proposed method.

Fiber-optic multipoint laser-ultrasonic excitation transducer using coreless fibers.

Photoacoustic ultrasound excitation has great potential in structural nondestructive testing and applications for medical treatments as a promising alternative to electrical ultrasound. This study proposes and demonstrates a multipoint optical fiber laser-ultrasonic transducer system, wherein the fiber-optic ultrasonic transducer is fabricated by a coreless fiber segment's fusion with single-mode fibers at each end. Simulation and experiment results show that the transducer coupling ratio is dependent on the coreless fiber's length. The structure of such an ultrasonic transducer is easily manufactured. Thus, the structures of these optical fiber ultrasonic transducers with different coupling ratios are connected in the order of small to large coupling ratios. In this manner, multipoint ultrasonic excitation with equal intensities at each excitation point can be obtained using this simple and low-cost method. Using laser guidance through the optical fiber to generate ultrasound can efficiently solve some shortcomings of traditional ultrasonic transducers, such as large volume, small bandwidth, and electromagnetic interference. Moreover, this type of fiber-optic ultrasound transducer has higher mechanical strength than other fiber-optic ultrasound transducers and is expected to be useful in structural health-monitoring of buildings.