Frequency Spread Research Articles

Information Visualization Using Clustering and Predictive Model

This paper aims to reveal the impact of rainfall on tea export from India, an issue that remained unexplored in the existing literature. This study explores a new model to predict India's tea export more accurately that would be helpful for Indian tea planters and exporters to plan their production as well as the inventory holding for deriving maximum value from tea export. A two-stage modelling approach has been developed. Firstly, an artificial intelligence-based growing hierarchical self-organising map algorithm is employed on the monthly time series of monthly frequency spreading over April 2005 to December 2013 to segregate India's monthly tea export data series into visual clusters of recognized pattern. Further, a predictive model using support vector machine has been developed and applied to forecast the tea export and then the importance of the predictor variables of the tea export have been identified. Finally, using the appropriate measures of performance a comparative analysis has been performed for each of the model. The newness of the study pertains to the two facts revealed from the study: firstly, India's tea export is embedded of complexity and nonlinearity, which could receive a successful clustering through growing hierarchical self organizing map that would make a deeper analysis easier with a further application of rich statistical techniques. Secondly, the analysis of prediction errors and the relative importance of the predictor variables establish rainfall as one of the most significant variable in predicting India's tea export, insight that has never surfaced in the literature developed thus far.

In response: Motor blockade after iliopsoas plane (IPB) and pericapsular nerve group (PENG) blocks: A little may go a long way.

We would like to thank Endersby et al. for sharing their experience with the PENG block for pain related to hip surgery and the risk of associated motor blockade.1,2 The authors of the PENG block claim that it anaesthetizes the hip articular branches from both the femoral, obturator and accessory obturator nerves without motor blockade.3,4 Unfortunately, no high-quality prospective blinded randomized studies have been published to back this claim. The evidence base is a plethora of lower quality case reports and letters, trying to assess the clinical effect, spread of injectate and frequency of motor blockade of the PENG block.

Non-stationary historical trends in wave energy climate for coastal waters of the United States

The thirty-year non-stationary historical trends in the wave energy climate for United States coastal waters between 1980 and 2009 are investigated using spectral partitioned wave data generated from a WaveWatch III® (version 5.05) hindcast. In addition to historical trends in the omni-directional wave power, frequency and directionally resolved wave power, frequency and directional spreading, and seasonal variability, are examined for the first time, including their geographical distribution. These historical wave energy climate trends are linked to changes to the dominant wave systems and commensurate trends in the historical wind climate. Total wave power trends are consistent with other studies, but the present study identifies regions, and specific frequency and direction bands, where significant wave energy climate changes have occurred. For some regions, changes to wave climate parameters exceeded one-percent annually, more than thirty-percent over the study period. Non-stationary trends of this magnitude have significant implications for ocean and coastal engineering projects designed assuming wave climates are stationary and warrant their consideration in design practices.

Air-to-Ground Channel Characterization for Low-Height UAVs in Realistic Network Deployments

Due to the decrease in cost, size and weight, \acp{UAV} are becoming more and more popular for general-purpose civil and commercial applications. Provision of communication services to \acp{UAV} both for user data and control messaging by using off-the-shelf terrestrial cellular deployments introduces several technical challenges. In this paper, an approach to the air-to-ground channel characterization for low-height \acp{UAV} based on an extensive measurement campaign is proposed, giving special attention to the comparison of the results when a typical directional antenna for network deployments is used and when a quasi-omnidirectional one is considered. Channel characteristics like path loss, shadow fading, root mean square delay and Doppler frequency spreads and the K-factor are statistically characterized for different suburban scenarios.

Experimental investigation on flame spread over jet fuel with influence of external heat radiation

The development of liquid fires commonly accompanies with the external heat radiation. This subject concentrates on the laboratory-scale experiments (100 cm × 4.4 cm × 2.0 cm) on flame spread over jet fuel of RP-3 with radiant heat fluxes of 1.1, 1.69, 2.25, 2.8 and 3.6 kW/m2. The results show that the flame behaviors, subsurface flow and heat transfer mechanism depend strongly on the intensity of external heat flux. The measurements of flame pulsation frequency and flame spread rate verify that they increase significantly initially but augment slightly afterwards with the externally applied heat flux, indicating that the heat flux is principally used for raising the liquid’s temperature in the initial stage of flame spreading. The heat exchanges involving flame spread process, namely, external heat radiation, convective heat flux, conductive heat flux, flame radiation, and re-radiant heat losses are analyzed. The energy calculation model confirms that the total heat flux is approximately equal to the sum of heat fluxes from radiant panel and convective flow. The scaling analysis of velocity of subsurface flow proves that it should be linearly related to the externally applied heat flux in the correlation of us∼q˙er2/3.

Video Depth Inversion at a Microtidal Site Exposed to Prevailing Low-energy Short-period Waves and Episodic Severe Storms

Bouvier, C.; Balouin Y.; Castelle B., and Valentini N., 2020. Video depth inversion at a microtidal site exposed to prevailing low-energy short-period waves and episodic severe storms. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1021–1026. Coconut Creek (Florida), ISSN 0749-0208.Over the last decades, a wide range of depth inversion algorithms have been developed, which aim to infer local water depth from remotely-sensed wave parameters based on physical relations. Particularly, the depth inversion algorithm named cBathy (Holman, Plant, and Holland, 2013) showed good results for a range of wave conditions and environments but the method was only applied to beaches exposed to moderate or highly energetic wave climate, with wave peak period often larger than 8 s. This paper applies the cBathy algorithm for the very first time on a Mediterranean Sea beach, Sète, southeast France, a semidiurnal microtidal environment exposed to a moderate-energy modal wave climate and episodic severe storms. The objective of the paper is to assess the ability of the cBathy algorithm to estimate the nearshore bathymetry for waves with large energy spread in both direction and frequency. After a comparison between the remotely sensed bathymetry and a ground truth bathymetric survey, we use a non-linear, depth-averaged morphodynamic model, 2DBeach (Dubarbier et al., 2017), on remotely sensed bathymetries to determine the sensitivity of nearshore waves and horizontal circulations to the estimated morphology. The depth inversion technique estimates the nearshore bathymetry with good accuracy (RMSE = 0.39 m) for a beach area extending respectively 1600 m and 600 m in the longshore and cross-shore directions, respectively, suggesting the technical feasibility of coupling remotely-sensed bathymetry to 2DH numerical model, even at short-waves exposed Mediterranean beaches.

ROLE OF TRPV4 CHANNEL SIGNALING IN SHEAR STRESS RESPONSES

Shear stress along the vascular intima promotes blood flow and preserves vascular wall structure, providing vital protection against progressive cardiovascular disease. Indeed, obstructive cardiovascular disease states such as atherosclerosis are associated with early shear stress disruption that leads to endothelial dysfunction and vascular remodeling. A key feature of shear stress action is a rapid and sustained increase in dynamic (spatially and temporally) Ca2+ signals within the endothelium, which promotes vasodilation and opposes inflammation. Although specific mechanisms remain unclear, recent studies have implicated mechanosensitive TRPV4 cation channels in shear stress mediated Ca2+ entry. We hypothesize that shear stress‐induced endothelial Ca2+ signals arise from graded recruitment of TRPV4 Ca2+ transients. We performed Ca2+ imaging studies on arteries isolated from wild type and genetically altered TRPV4 knockout mice. Carotid arteries were isolated, opened, and mounted in specialized flow chambers. The chambers were connected to a peristaltic pump and placed on the stage of a microscope adapted for high‐speed confocal imaging (488 nm ex, 510 nm emission; 8 frames/s). Endothelial Ca2+ dynamics were recorded at increasing flow rates (shear stress 0, 12, 52, 75, and 102 dynes/cm2). Image analysis was performed using ImageJ and custom software (LC_Pro) designed to discern distinct profiles of signal frequency, amplitude, duration and spatial spread. Artery segments were also subjected to immunostaining to assess relative expression and distribution of TRPV4 channels. We found that the wild type and TRPV4 knockouts both responded to shear stress. The TRPV4 knockout exhibited a reduced Ca2+ event frequency and shorter event durations compared to wild type controls in response to physiologic elevations in shear stress. Future experiments will focus on expounding upon the flow response, particularly the importance of TRPV4 channels in the time‐course of Ca2+ signal patterning changes under chronic low flow conditions.Support or Funding InformationSponsored by Mark Taylor and David Weber, Ph.D., Department of Physiology/Cell Biology, University of South Alabama College of Medicine, Mobile, AL. Summer Medical Student Research Program

The Effect of Scale and Working Fluid on Sweeping Jet Frequency and Oscillation Angle

Abstract This study was conducted to quantify in a controlled manner the effect of oscillator scale and working fluid on oscillator performance. The performance parameters of interest include the oscillation frequency and oscillation spread angle. Three scale models were manufactured with model attributes identical except for scale with models at two times and three times a baseline scale. Four working fluids were tested including helium, ethylene, carbon dioxide, and propane to generate a range of densities and viscosities. The frequency and oscillation angle measurements were obtained using high-speed video recordings of visible schlieren imagery. Trends in frequency were observed and quantified for each oscillator scale and working gas as a function of mass flowrate. This paper shows that these values could all be nondimensionalized with the data collapsing to a single Strouhal number between 0.015 and 0.018 depending on surface roughness, independent of the Reynolds number. This result expands on the authors' previously published work and confirms the previous finding that reveals the geometry and fluid properties also scale and collapse.

Calibration of Motional Frequency Spread for Wide-Band FMCW Automotive Millimeter-Wave Radar

As a key module for self-driving cars and advanced driver assistant systems (ADAS), frequency modulation continuous wave (FMCW) automotive millimeter-wave (mmwave) radar has a good market prospect. Due to the relative motion of target and radar in the detection window, the motional frequency spread is inevitable especially for wide-band FMCW automotive mmwave radar systems with large bandwidth and possible high-speed motion. In this paper, for wide-band FMCW automotive mmwave radar systems, we first derive analytical expressions of the motional frequency interference term and phase interference term in the intermediate frequency (IF) signal. Then, the effect of frequency spread is comprehensively analyzed with the help of numerical results. Motivated by the mechanism and influence of frequency spread, we propose three schemes for motional frequency spread calibration with different performance-complexity tradeoff. Finally, simulations verify that the proposed schemes can effectively compensate the degradation of system resolution and parameter estimation accuracy due to frequency spread.

Mitigation of intensity limitation in the CERN SPS using a double RF system

The Super Proton Synchrotron (SPS) at CERN is the injector of the Large Hadron Collider (LHC). Multi-bunch instabilities limit the intensity of the beam that can be accelerated to 450 GeV in the SPS and transferred to the LHC. Without mitigation measures, the threshold of bunch intensity of the longitudinal instability is three times below the nominal bunch intensity of the LHC beam. The High Luminosity LHC project (HL-LHC), which requires a doubling of the nominal bunch intensity, relies on improvement of beam stability in the SPS. A fourth harmonic RF system allows, presently, to stabilize the beam up to nominal LHC intensity. It increases the synchrotron frequency spread inside the bunch, providing more efficient Landau damping of beam instability. However, nonlinearities of the synchrotron frequency distribution inside the bunch pose a limitation on bunch length. This paper explores possible intensity increase in the SPS by studying the effect on beam stability of the voltage ratio between two RF systems. The results are substantiated by beam measurements and particle-tracking simulations. An optimized voltage program of the second RF system during the cycle has been tested in operation and beam stability and the quality have been successfully improved.

Statistical analysis of low-latitude spread F observed over Puer, China, during 2015\u20132016

Statistical analysis of spread F (SF), recorded at Puer (PUR, 22.7° N, 101.05° E, Dip Latitude 12.9° N) during 2015–2016, was carried out to reveal its characteristics at the northern equatorial ionization anomaly. In our study, SF was categorized into four types, frequency spread F (FSF), range spread F (RSF), mix spread F (MSF) and strong range spread F (SSF). The statistical results presented that FSF and MSF were dominant over Puer. Most types of SF appeared mostly in summer months, except the maximum occurrence of SSF in equinox months. Moreover, observations of SF events also showed that the solar activity and magnetic activity dependence of SF varied with seasons. Compared with observations at other region, the present results suggest that medium-scale traveling ionospheric disturbances (MSTIDs) may play a key role in generation of SF in low-latitude region.

Doppler Characterization in Ultra Wideband BAN Channels During Breathing

Monitoring the physical parameters from devices inside the body, using ultra wideband (UWB) technology, enables the development of high bandwidth demanding applications in real time. The relative movement of the nodes deployed in the body, due to breathing, can give rise to a frequency shifting effect, increasing the fading level in the propagation channel during transmissions. In this article, therefore, we present a study of the frequency effects on the propagation channel derived from the relative movement between two nodes of a wireless body area network (WBAN), at least one of them placed inside the human body, caused by breathing. The study is performed on the basis of the Doppler spectrum characterization in terms of the shape fitting and frequency spread parameter derivation. Continuous wave (CW) signals have been used to cover the UWB range at four selected frequencies: 3.1, 4.8, 6, and 8.5 GHz, and a liquid phantom has been employed for emulating the dielectric properties of the high water content tissues at the considered UWB frequencies.

The role of frequency spread on swash dynamics

The swash zone is the most dynamic part of the upper beach. Here breaking waves interact with sediments, leading to beach morphodynamics, and eventually to coastal erosion and flooding. An understanding of swash characteristics such as the vertical excursion and mean swash period is of vital importance to identify and predict the possible impact of storms in coastal areas. The prediction of these swash parameters is commonly based on bulk offshore spectral wave parameters and the beach slope, the latter being expensive to monitor. In this study, a dataset from an intermediate beach on the south-west coast of Sylt, Germany was derived to analyze swash characteristics. Field observations show high variability in swash excursion even for similar incident wave conditions if expressed by bulk parameters. Here, the role of frequency spread was further investigated. An inverse relationship between swash frequency spread and swash characteristics (excursion and mean period) was identified. A parameterization for the swash frequency spread based on incident wave parameters is proposed, and a new approach to obtain total swash excursion and mean swash period is developed. The parameterization is validated using two independent swash datasets (Duck 1982 and Duck 1994) and compared to the predictive ability of other parameterizations. It is highlighted that common parameterizations based on peak period do not perform well in characterizing incident conditions when bi-modal spectra are present. The choice of the right descriptor for wave periods may have a more pronounced influence on the predictive skill than the inclusion of the beach slope.

“Jam Me If You Can:” Defeating Jammer With Deep Dueling Neural Network Architecture and Ambient Backscattering Augmented Communications

With conventional anti-jamming solutions like frequency hopping or spread spectrum, legitimate transceivers often tend to “escape” or “hide” themselves from jammers. These reactive anti-jamming approaches are constrained by the lack of timely knowledge of jamming attacks (especially from smart jammers). Bringing together the latest advances in neural network architectures and ambient backscattering communications, this work allows wireless nodes to effectively “face” the jammer (instead of escaping) by first learning its jamming strategy, then adapting the rate or transmitting information right on the jamming signals (i.e., backscattering modulated information on the jamming signals). Specifically, to deal with unknown jamming attacks (e.g., jamming strategies, jamming power levels, and jamming capability), existing work often relies on reinforcement learning algorithms, e.g., Q -learning. However, the Q -learning algorithm is notorious for its slow convergence to the optimal policy, especially when the system state and action spaces are large. This makes the Q -learning algorithm pragmatically inapplicable. To overcome this problem, we design a novel deep reinforcement learning algorithm using the recent dueling neural network architecture. Our proposed algorithm allows the transmitter to effectively learn about the jammer and attain the optimal countermeasures (e.g., adapt the transmission rate or backscatter or harvest energy or stay idle) thousand times faster than that of the conventional Q -learning algorithm. Through extensive simulation results, we show that our design (using ambient backscattering and the deep dueling neural network architecture) can improve the average throughput (under smart and reactive jamming attacks) by up to 426% and reduce the packet loss by 24%. By augmenting the ambient backscattering capability on devices and using our algorithm, it is interesting to observe that the (successful) transmission rate increases with the jamming power. Our proposed solution can find its applications in both civil (e.g., ultra-reliable and low-latency communications or URLLC) and military scenarios (to combat both inadvertent and deliberate jamming).

Resilient architecture; a design approach to counter terrorism in building for safety of occupants

The intensity of fear of insecurity has increased in 21st century due to the frequency and global spread of terrorism. Homes, public infrastructures and utilities have been damaged; physical and psychological injuries inflicted; economic fortunes wrecked in a minute; many rendered homeless and lives lost as a result of terrorism and threats to terrorism. Historically, bombs and explosives have been a favourite tactic of terrorists, this is because ingredients for homemade bombs are effortlessly obtained in the open market, as are the techniques for its construction and also are easy and quick to execute. However, one area counter terrorism strategy has been universally identical is in architecture and urban planning. The aim of this paper is to reveal the need for a change in ideological approach to design by architects and planners in Nigeria in order to safeguard the environment. It discusses architectural design approach to counter terrorism in building for occupant’s safety and draws analogy from the defensive architecture of ancient times. The paramount theme is on terrorist attack with regards to explosive and bomb, the focus is on an approach that limits damage or mitigates damage rather than a blast-resistant approach. The study employed the use of case study research method with extensive review of literature of the past and present approach to counter terrorism. The result highlights some practical security design strategy that will improve occupant’s safety within a structure if incorporated in architectural designs. This will also facilitate evacuation efforts and enhance rescue endeavour in an unlikely incidence of terror attack. It concludes and advocate for a proactive design strategy for buildings in Nigeria.

Runup uncertainty on planar beaches

Parameterization of wave runup is of paramount importance for an assessment of coastal hazards. Parametric models employ wave (e.g., Hs and Lp) and beach (i.e., β) parameters to estimate extreme runup (e.g., R2%). Thus, recent studies have been devoted to improving such parameterizations by including additional information regarding wave forcing or beach morphology features. However, the effects of intra-wave dynamics, related to the random nature of the wave transformation process, on runup statistics have not been incorporated. This work employs a phase- and depth- resolving model, based on the Reynolds-averaged Navier-Stokes equations, to investigate different sources of variability associated with runup on planar beaches. The numerical model is validated with laboratory runup data. Subsequently, the role of both aleatory uncertainty and other known sources of runup variability (i.e., frequency spreading and bed roughness) is investigated. Model results show that aleatory uncertainty can be more important than the contributions from other sources of variability such as the bed roughness and frequency spreading. Ensemble results are employed to develop a new parametric model which uses the Hunt (J Waterw Port Coastal Ocean Eng 85:123–152, 1959) scaling parameter $\beta \left (H_{s}L_{p}\right )^{1/2}$.

Experimental Study of the Precessing Vortex Core Impact on the Liquid Fuel Spray in a Gas Turbine Model Combustor

Abstract Despite being good candidates for the reduction of pollutant emissions from gas turbines, burners operating in lean premixed prevaporized regimes often face stability issues and can be sensitive to perturbations. The swirling flow used to aerodynamically stabilize the flame can also lead to the appearance of a large-scale coherent flow structure known as the precessing vortex core (PVC). In this study, a swirl-stabilized combustor fed with liquid dodecane is studied at a globally lean operating condition with the help of high-speed diagnostics and dynamic mode decomposition (DMD) as the main postprocessing method. It is shown that the trace of a PVC originating inside the injector is still present in the fuel spray at the entrance of the chamber even though the aerodynamical structure itself is not detectable anymore. The perturbation of the fuel spray is then transmitted to the flame through local equivalence ratio fluctuations. It is observed that the PVC trace on the spray and thus on the flame can be suppressed by air flow modulations generated by a siren device. The suppression of this trace is shown to come from a decay of the aerodynamical structure itself rather than by a change in fuel mixing or vaporization. Analysis of the characteristic frequency of the PVC shows a frequency spread indicating a loss of coherence of the structure with the high-amplitude air flow rate fluctuations.

Temporal Frequency Spread of Plane Wave Propagation through Moderate to Strong Turbulence

In this study, we derive new expressions for the atmospheric-brought on frequency unfold of plane waves propagating thru slight to strong turbulence in a horizontal direction based on the modified anisotropic non-Kolmogorov electricity spectrum as antagonistic to conventional Kolmogorov electricity spectrum. The energy regulation price varies from three to 4 instead of the traditional Kolmogorov power law price; the general amplitude price differs from the conventional Kolmogorov regular cost 0.033. these new expressions are based on slight to robust fluctuation vicinity and anisotropic non-Kolmogorov turbulence. The simulation results show that temporal frequency unfold will decrease even as the anisotropic component   2  is increasing

Numerical Assessment of Infragravity Swash Response to Offshore Wave Frequency Spread Variability

AbstractWe use a numerical model, already validated for this purpose, to simulate the effect of wave frequency spread on wave transformation and swash amplitudes. Simulations are performed for planar beach slope cases and for offshore wave spectra whose frequency spread changes over realistic values. Results indicate that frequency spread, under normally approaching waves, affects swash amplitudes. For moderately dissipative conditions, the significant infragravity swash increases for increasing values of the offshore frequency spread. The opposite occurs under extremely dissipative conditions. The numerical analysis suggests that this inverted pattern is driven by the effect that different distributions of incoming long‐wave energy have on low‐frequency wave propagation and dissipation. In fact, with large frequency spreads, wave groups force relatively short subharmonic waves that are strongly enhanced in the shoaling zone. This process leads to an infragravity swash increase for increasing frequency spread under moderately dissipative conditions in which low‐frequency energy dissipation in shallow water is negligible or small. However, under extremely dissipative conditions, the significant low‐frequency energy dissipation associated with large frequency spreads overturns the strong energy growth in the shoaling zone eventually yielding an infragravity swash decrease for increasing frequency spread.

Resistorless Frequency Locked On-Chip Oscillator with Proportional-to-Absolute Temperature References

A 36-kHz frequency locked on-chip oscillator is proposed, the proportional-to-absolute temperature (PTAT) current and voltage generator is presented to eliminate conventional temperature-compensated resistors. The resistorless approach reduces the process variation of frequency and the chip area. The oscillator is fabricated in 0.18-[Formula: see text]m standard CMOS process with an active area of 0.072[Formula: see text]mm2. The temperature coefficient of frequency is 48[Formula: see text]ppm/∘C at best and 82.5[Formula: see text]ppm/∘C on average over [Formula: see text]–70∘C and the frequency spread is 1.43% ([Formula: see text]/[Formula: see text] without calibration. The supply voltage sensitivity is 1.8%/V in the range from 0.65[Formula: see text]V to 1[Formula: see text]V and the power consumption is 95[Formula: see text]nW under the supply voltage of 0.65[Formula: see text]V.