Current Wave Research Articles

Conversion of 30 W laser light at 1064 nm to 20 W at 2128 nm and comparison of relative power noise

Abstract All current gravitational wave (GW) observatories operate with Nd:YAG lasers with a wavelength of 1064 nm. The sensitivity of future GW observatories could benefit significantly from changing the laser wavelength to approximately 2 μm combined with exchanging the current room temperature test mass mirrors with cryogenically cooled crystalline silicon test masses with mirror coatings from amorphous silicon and amorphous silicon nitride layers. Laser light of the order of ten watts with a low relative power noise would be required. Here we use a laboratory-built degenerate optical parametric oscillator (OPO) to convert the light from a high-power Nd:YAG laser to 2128 nm. With an input power of 30 W, we achieve an output power of 20 W, which corresponds to an external conversion efficiency of approximately 67%. We find that the relative power noise spectrum marginally increases during the wavelength conversion process. Our result is an important step in the development of low-noise light around 2 μm based on existing low-noise Nd:YAG lasers.

Electrodynamic analysis of a sinusoidal antenna for small wave sizes

Background. The work is aimed at developing and researching rigorous methods for calculating thin-wire structures with a complex generatrix shape, having small wave sizes, as well as studying the physical processes occurring in them. A special case of such structures is a sinusoidal antenna operating in a standing current wave mode. Aim. In progress the solution of internal and external problems of electrodynamics is carried out for a sinusoidal antenna of small wave sizes located above an infinitely extended ideal reflector. The currents on the elements of the structure are calculated, its input resistance and radiation characteristics are determined. Methods. The research is based on a strict electrodynamic approach, within the framework of which, for the specified structure in the thin-wire approximation, an integral representation of the electromagnetic field is formed, which, when considered on the surface of conductors together with boundary conditions, is reduced to a system of Fredholm integral equations of the second kind, written relative to unknown current distributions on conductors (internal task). Results. A mathematical model of the radiating structure is proposed, determined: the input resistance of the structure and the basic characteristics of its radiation. It is shown that the operating range of a sinusoidal antenna in the standing wave mode is determined by the quality factor of the input impedance resonances; An increase in the width of the sinusoidal conductor leads to a decrease in the resonant frequencies of the input resistance with a simultaneous increase in the quality factor of the resonances. Conclusion. From a practical point of view, the use of the considered structure allows significantly reduce the dimensions in comparison with a thin electric vibrator, however in this case, the operating range will be correspondingly narrowed, which is determined, due to the weak dependence of the radiation characteristics on frequency, by the quality factor of the resonances. The current distribution on the generatrix of the structure can be considered as a «projection» standing surface wave localized in the plane of a sinusoidal conductor, and resulting from the superposition of forward and backward surface (slow) waves propagating at a speed significantly lower than the speed of light. To further clarify the physics of the processes occurring in the structure, one should use spectral analysis of current functions and study the distributions of the electromagnetic field in the near zone of the structure.

Improve power quality and stability of grid - Connected PV system by using series filter

As the world increasingly focuses on renewable energy sources, grid-connected PV systems will continue to play a critical role in meeting our energy needs. This integration has brought many benefits, but has also created various problems related to power quality and stability at the connection points. Various techniques are used to improve the power quality, such as passive filters, tuned passive harmonic filters, and active filters. This paper presents the use of a series active filter on the DC side of grid-connected PV systems to improve their power quality, stability, and dynamic performance. The proposed filter consists of an inductor, two capacitors, and four transistor-diode pairs, the operation of which is controlled by a sinusoidal pulse width modulation (SPWM) scheme. The MATLAB/Simulink is used to build and validate a comprehensive mathematical model of the studied system. The transfer function of the system is identified and its transient response is studied under various test input signals. A Bode plot is also generated to assess the impact of the integration of this component on the stability of the system. The results showed that incorporating the filter resulted in a significant reduction in the total harmonic distortion factor (Thd%) for both the voltage and current waves at the inverter output. Moreover, it improved the transient response characteristics of the system by significantly reducing the maximum overshoot value of the system response with respect to the test input signals. The results indicate that the stability of the system is improved after the filter addition, as evidenced by the increased gain margin and phase margin in the system Bode plot.

Modelling the Sea Surface of Cardigan Bay

The aim of this project was to model the sea surface of Cardigan Bay, to be able to expand upon QinetiQ’s current wave models, used within their radar assurance activities. The sea surface can cause unwanted detections, which is referred to as clutter. The sea is not the only source of clutter such as litter and birds, have an impact on the returns detected by the radar. This project explored two different approaches, modelling the propagation of waves and modelling the distribution of energy across the sea surface. The first approach explored two open source models, WAVEWATCH III and SWAN, and after having technical errors, two real world, existing examples of where these models were implemented were researched. This research showed a lot of promise, and would be worth expanding upon. The second approach looked into two recognised equations for calculating the energy density of the waves, and then calculating the significant wave height. Overall, modelling the propagation of waves would produce more representative results, particularly SWAN which was a model designed for coastal waters, however to set up the wave models fell outside of the scope of this project.

Enhancing water management in Northern European lowland chalk streams: A parsimonious, high-resolution hydrological model using groundwater level as a proxy for baseflow

Study regionThe River Frome, a chalk stream in West Dorset, UK. Study focusHigh-resolution hydrological models are required to integrate with the current wave of high-frequency data and advance our understanding of pollutant sources, pathways, and sinks. This presents several challenges in chalk streams, as their high-permeability and unique hydrogeological characteristics often leads to complex models that are overparameterized and computationally burdensome. In this article, we develop a novel and parsimonious modelling approach to describe the surface hydrology for a chalk stream in high resolution (15-minute frequency, ≤ 100 m cross-section spacing), using groundwater levels as a proxy for spring discharges. New hydrological insights for the regionOur results show that chalk stream dry-weather flows can be simulated accurately and parsimoniously at high-resolution (Nash-Sutcliffe efficiency = 0.97, mean relative error = 2.86 %, for a five-year period). We also show that spring discharges are the dominant form of flow accretion in all seasons and are critical to dilute sewage treatment inputs during the ecological growing season, whilst runoff and quick-flow pathways in the river valley corridor contribute a small proportion to annual flow accretion (< 5.2 %). Due to its simplicity and few parameters to calibrate, this modelling approach has broad applicability in lowland permeable catchments. Management implications include expeditious investigations of high-resolution freshwater quality responses to pollution and informing abstraction limits to sustain robust ecological conditions.

Distribution and Controlling Factors of the Contourites on the Northern Continental Slope of the South China Sea

ABSTRACTThe northern continental margin of the South China Sea (SCS) is an important component of deep‐water circulation, providing excellent conditions for studying bottom currents in a marginal sea. Seismic data were employed to discern the sedimentary patterns prevalent in the deep‐water continental slope sediments on the northern continental margin of the SCS, encompassing gravity flow, contourite and mixed depositional systems. The contourite depositional system includes various types of deposits (such as separated mounded drifts, patch or channel‐related drifts, deformed sheeted drifts, composite drifts, bottom current sediment waves, plastered contourite drifts) and various morphologic erosional features eroded by the bottom current (such as moats, non‐depositional surfaces, troughs and scarps). These contourite features are related to the continental slope's morphology and its sources. The Dongsha slope exhibits distinctive characteristics marked by intense bottom current erosion and deposition, featuring separated mounded drifts and deformed sheeted drifts along its lower slope. The lower slope of the Pearl River showcases a spectrum of bottom current‐induced features, including sediment wave fields, erosion fields and contourite drifts. The southern flank of the Shenhu slope is characterised by a bottom current erosion field, a non‐depositional surface, a sediment wave field and isolated mounded drifts. On the Yingqiong slope, the contourite drifts are limited to its southern flank where gravity flow action is absent, and the complex geomorphology interacts with the bottom current, forming a complex contourite depositional system. The results of this study serve as a foundational framework for further global research on bottom current circulation and hydrodynamics.

Electromagnetic Model of K‐Changes

AbstractK‐changes are observed as step‐like increases in the thundercloud electric fields. The K‐changes occur in the late part of intra‐cloud lightning or during negative cloud‐to‐ground lightning between return strokes. It has been shown that the processes leading to K‐changes initiate in the decayed part of a positive leader channel and propagate toward the flash origin. They are often accompanied by microsecond‐scale electric field pulses. We introduce a new model to simulate processes leading to the K‐changes in cloud‐to‐ground lightning. Our method is based on the full solution of Maxwell's equations coupled to Poisson's equation for the thundercloud charge structure. To model the K‐changes, we gradually increase the decayed channel conductivity. The modeled current wavefront propagates due to the K‐processes downward along a vertical channel and completely attenuates before reaching the ground. We derive the evolution of the linear charge densities and the scalar electric potential along the channel leading to K‐changes. We model electrostatic step‐like changes in the measured electric field together with the approximate rates and amplitudes of the microsecond scale pulses. Step‐like changes increase their amplitudes with the length of the simulated channel and with a higher conductivity of the channel. The microsecond‐scale pulse waveshapes depend mainly on the propagation velocity of the current wave, and the time scale of the conductivity increase. We show that our modeled waveforms are in a good agreement with observations conducted in Florida.

Current summer heat waves impair rainbow trout (Oncorhynchus mykiss) spermatogenesis: Implications for future fish farming management practices in South Europe

Freshwater environments provide different ecosystem services for human well-being, and are one of the most important natural sources of healthy animal protein. Climate change and extreme temperature events, among other factors, represent a growing concern for their sustainable use. In contrast to the research effort to elucidate how global warming affects these aquatic environments, few studies pay attention to the potential effects of heat waves, a current phenomenon with direct effects on contemporaneous organisms. Here, the potential effects of a single heat wave event on rainbow trout (Oncorhynchus mykiss) males, mimicking a recorded environmental event, have been evaluated by means of biometric, redox and stress response, plasma testosterone, histopathology and transcriptomic analyses. Environmental monitoring showed how, during the last 4 years, mean water temperature increased (2–4 °C; from April to October), heat wave duration progressively increased (from 15 to 100 days), and mean intensities ranged 1.7–3.8 °C with a maximum of 8.0 °C. An experimentally recreated heat wave lasting only 16 days, with mean and maximum intensities of 2.7 and 6.7 °C, induced a decrease in body weight and total antioxidant status, but increased blood plasma cortisol levels and redox enzyme activity. The induced heat wave decreased testosterone plasma levels and sperm quality, arrested spermatocyte type I and II differentiation and increased spermatozoa apoptosis. These effects were correlated with a differential expression of 1156 genes (116 up- and 1040 down-regulated genes) in exposed fish when compared to Control fish, reflecting an alteration in cell apoptosis and spermatozoa maturation processes. These results not only increase concern about current heat wave events, recreating a real scenario, but also unveil for the first time the particular molecular mechanisms of subsequent spermatogenesis disruption, opening new avenues for designing urgent and necessary strategies to mitigate the effects of extreme climate change conditions on freshwater aquaculture.

Exposure to Multiple Natural Disasters and Externalising and Internalising Behavior: A Longitudinal Study of Adolescents

PurposeAs natural disasters become more frequent and more severe, there is a corresponding need to understand their relationship with child and adolescent mental health, and in particular, to understand exposure to multiple natural disasters. This study assesses the relationship between exposure to both single and multiple disasters and adolescent internalising and externalising behavior. MethodsThe study used five waves of a nationally representative longitudinal Australian dataset. Exposure to sudden-onset (fires, floods, storms) and slow-onset (drought) disasters was collected across five waves. Adolescent internalising and externalising behavior collected in the final three waves using the self-reported Strengths and Difficulties Questionnaire. Random effects regressions assessed sudden- and slow-onset disasters and multiple disaster exposure, controlling for geographic and socioeconomic variables. ResultsExposure to multiple disasters was associated with adverse adolescent outcomes. Two or more sudden- and slow-onset disaster exposures in the last 12 months was related to more conduct problems. Exposure to multiple sudden-onset disasters in the current and previous waves was related to increased problems with peers. A single exposure to either sudden- or slow-onset disasters was not associated with Strengths and Difficulties Questionnaire outcomes. DiscussionThe study findings suggest that multiple exposure to disasters has a negative association with adolescent wellbeing. These findings suggest that, rather than adapting to disasters, youth exposed to multiple disasters suffer more than their peers, including peers exposed to a single disaster.

Quasi-normal modes of loop quantum black holes formed from gravitational collapse

In this paper, we study the quasi-normal modes (QNMs) of a scalar field in the background of a large class of quantum black holes that can be formed from gravitational collapse of a dust fluid in the framework of effective loop quantum gravity. The loop quantum black holes (LQBHs) are characterized by three free parameters, one of which is the mass parameter, while the other two are purely due to quantum geometric effects. Among these two quantum parameters, one is completely fixed by black hole thermodynamics and its effects are negligible for macroscopic black holes, while the second parameter is completely free (in principle). In the studies of the QNMs of such LQBHs, we pay particular attention to the difference of the QNMs between LQBHs and classical ones, so that they can be observed for the current and forthcoming gravitational wave observations, whereby place the LQBH theory directly under the test of observations.

Gravitational Wave Ringdown Analysis Using the F -statistic

After the final stage of the merger of two black holes (BHs), the ringdown signal takes an important role in providing information about the gravitational dynamics in strong field. We introduce a novel time-domain (TD) approach, predicated on the F -statistic, for ringdown analysis. This method diverges from traditional TD techniques in that its parameter space remains constant irrespective of the number of modes incorporated. This feature is achieved by reconfiguring the likelihood and analytically maximizing over the extrinsic parameters that encompass the amplitudes and reference phases of all modes. Consequently, when performing the ringdown analysis under the assumption that the ringdown signal is detected by the Einstein Telescope, the parameter estimation computation time is shortened by at most 5 orders of magnitude compared to the traditional TD method. We further establish that traditional TD methods become difficult when including multiple overtone modes due to close oscillation frequencies and damping times across different overtone modes. Encouragingly, this issue is effectively addressed by our new TD technique. The accessibility of this new TD method extends to a broad spectrum of research and offers flexibility for various topics within BH spectroscopy applicable to both current and future gravitational wave detectors.

Gravitational wave background from primordial black holes in globular clusters

Primordial black holes still represent a viable candidate for a significant fraction, if not for the totality, of dark matter. If these compact objects have masses of order tens of solar masses, their coalescence can be observed by current and future ground-based gravitational wave detectors. Therefore, finding new gravitational wave signatures associated with this dark matter candidate can either lead to their detection or help constraining their abundance. In this work we consider the phenomenology of primordial black holes in dense environments, in particular globular clusters. We model the internal structure of globular clusters in a semi-analytical fashion, and we derive the expected merger rate. We show that, if primordial black holes are present in globular clusters, their contribution to the GW background can be comparable to other well-known channels, such as early- and late-time binaries, thus enhancing the detectability prospects of primordial black holes and demonstrating that this contribution needs to be taken into account.

Longitudinal wave propagation in FG rods under impact force

A well-known fact is that one-dimensional wave analysis is the theoretical basis of the famous Hopkinson bar dynamic testing technique. The current one-dimensional wave theory is mostly confined to the slender rods of isotropic materials. It is not easy to obtain an analytical solution to the wave equation of an anisotropic rod. In this work, rods with both elastic modulus and density graded in the length direction are presented and analyzed. The one-dimensional variable coefficient wave equation corresponding to the functionally graded rod is constructed and converted into a second-order variable coefficient partial differential equation using the Laplace approach. Then, the details of solving the partial differential equation of the second-order variable coefficients are given. It is worth noting that here we construct a variable coefficient equation that satisfies the form of Euler's equation. It is still difficult to obtain analytical solutions for other equations that do not satisfy this form. Subsequently, studies of the wave propagation characteristics of rods with different graded configurations are carried out. The theoretical results show that the wave propagation behavior and post-impact vibration of the rod are significantly influenced by the graded configuration. It is possible to adjust not only the impact response at the end but also the impact response in the middle of the rod by optimizing the design of the rod's graded configuration.

Topology design of variable speed drive systems for enhancing power quality in industrial grids

In the last two decades, a rapid increase in the utilization of non-linear loads within electrical grids has been observed. Consequently, elevated levels of harmonics are found in both voltage and current waves, and adverse effects on power quality are caused. In this context, the variable speed drive (VSD) systems are considered a significant non-linear contributor. To mitigate the harmonic content in VSD systems, various techniques are explored, such as electronic smoothing inductor incorporation in the DC-link, active filters utilization at the grid side, and passive filters integration. A technique centered on the reconfiguration of the DC-link in the VSD systems is proposed in this paper to improve the overall performance of the VSD systems. The configuration comprises two transistors and two diodes, along with smoothing inductors and a capacitor to enhance power quality in the VSD systems. The utilization of three-stage sine pulse width modulation (SPWM) control technology ensures accurate control of the switches, generating optimal control signals that enhance the power quality of the voltage and current waves at the grid side. The effectiveness of the proposed approach is tested via time-domain simulation in MATLAB/Simulink under both constant and variable loading conditions and is verified using a laboratory prototype. The obtained results demonstrate a notable improvement in power quality, showcasing reduced total harmonic distortion (THD) in AC voltage and current waveforms, as well as minimized ripple factor in the DC-link when compared to existing methods.

Global Observations of Geomagnetically Induced Currents Caused by an Extremely Intense Density Pulse During a Coronal Mass Ejection

AbstractA variety of magnetosphere‐ionosphere current systems and waves have been linked to geomagnetic disturbance (GMD) and geomagnetically induced currents (GIC). However, since many location‐specific factors control GMD and GIC intensity, it is often unclear what mechanisms generate the largest GMD and GIC in different locations. We address this challenge through analysis of multi‐satellite measurements and globally distributed magnetometer and GIC measurements. We find embedded within the magnetic cloud of the 23–24 April 2023 coronal mass ejection (CME) storm there was a global scale density pulse lasting for 10–20 min with compression ratio of . It caused substantial dayside displacements of the bow shock and magnetopause, changes of and , respectively, which in turn caused large amplitude GMD in the magnetosphere and on the ground across a wide local time range. At the time this global GMD was observed, GIC measured in New Zealand, Finland, Canada, and the United States were observed. The GIC were comparable (within factors of 2–2.5) to the largest ever recorded during 14 year monitoring intervals in New Zealand and Finland and represented 2‐year maxima in the United States during a period with several Kp7 geomagnetic storms. Additionally, the GIC measurements in the USA and other mid‐latitude locations exhibited wave‐like fluctuations with 1–2 min period. This work suggests that large density pulses in CME should be considered an important driver of large amplitude, global GMD and among the largest GIC at mid‐latitude locations, and that sampling intervals are required to capture these GMD/GIC.

Teacher’s Attitude towards the Use of Digital Technologies for Capturing Students’ Data in Secondary Schools in Imo State, Nigeria

In Imo State, the researchers observed that teachers still use inventory book, admission register and continuous assessment record booklets to capture students’ data in secondary schools. This is surprising given the current wave of digitalization. Thus, the study examined teachers' attitude towards the use of digital technologies for students’ data capturing in secondary schools in Orlu education zone of Imo State, Nigeria. One research question guided the study and two hypotheses were tested. Descriptive survey design was adopted. The population of this study comprised 1209 teachers in the 105 public secondary schools in Orlu education zone of Imo State. 240 public secondary school teachers were used as the sample for the study using multi stage sampling procedure. The instrument for data collection was a validated self-administered questionnaire. Cronbach alpha formula was used to determine the internal consistency of the questionnaire and co-efficient of 0.83 was obtained. Mean and standard deviation were used to answer the research question and determine the homogeneity or otherwise of the respondents while t-test was used for testing the null hypotheses at 0.05 level of significance. Findings revealed that teachers’ have a positive attitude towards the use of digital technologies for capturing students' data in secondary schools in Orlu education zone. There was no significant difference in the mean ratings of teachers on their positive attitude towards the use of digital technologies for capturing students’ data in secondary schools irrespective of their years of teaching experience and location. It was recommended among others that, management of secondary schools should be organizing ICT-related seminars for teachers to improve their ICT skills in order to increase their attitude towards the utilization of digital technologies for capturing students' data.

Experimental demonstration of frequency- downconverted arm-length stabilization for a future upgraded gravitational wave detector.

Ground-based laser interferometric gravitational wave detectors (GWDs) consist of multiple optical cavity systems whose lengths need to be interferometrically controlled. An arm-length stabilization (ALS) system has played an important role in bringing these interferometers into an operational state and enhancing their duty cycle. The sensitivity of these detectors can be improved if the thermal noise of their test mass mirror coatings is reduced. Crystalline AlGaAs coatings are a promising candidate for this. However, the current ALS system with a frequency-doubled 532 nm light is no longer an option with AlGaAs coatings because the 532 nm light is absorbed by AlGaAs coatings due to the narrow bandgap of GaAs. Therefore, alternative locking schemes must be developed. In this Letter, we describe an experimental demonstration of a novel ALS scheme, to the best of our knowledge, which is compatible with AlGaAs coatings. This ALS scheme will enable the use of AlGaAs coatings in current and future terrestrial gravitational wave detectors.

Synthetic rotational Doppler shift on transmission lines and it’s microwave applications

Rotational Doppler shift of a circularly polarized wave impinging normally on a rotating anisotropic surface, causes scattered waves with frequency shift equals twice the surface rotation frequency. We show that virtual rotational Doppler shift can be realized in transmission line platforms through a time-varying junction. In a system consisting of a pair of decoupled but identical transmission lines, voltage waves with a 90-degree phase difference between the two lines mimic a circularly polarized wave. A junction, comprising three time-varying capacitors and a static two-port network, connects the two lines and acts as a synthetically rotating anisotropic surface. As a result, the reflected and transmitted voltage (or current) waves undergo a frequency shift equal to twice the synthetic rotation frequency. Utilizing this effect, a full frequency converter is then proposed by augmenting the synthetically rotating capacitive junction with a dispersive phase shifter, followed by a short circuit. The system efficiently converts the incident tone into a single down- or up-converted tone, with amplification observed in the case of up-conversion. The frequency converter is subsequently employed to design a magnetic-free isolator. Circuit simulations with both ideal and switch-based time-varying capacitors match theoretical predictions.

Self-determination and secessionism in Nigeria: a contextual analysis through Edward Azar’s protracted social conflict theory

ABSTRACT This article examines the rising divergence but convergence of self-determination and secessionist campaigns in Nigeria. For a contextual analysis, it turns to Edward Azar's protracted social conflict (PSC) theory, exploring the connections between communal disgruntlement and self-determination. The analysis indicates a significant relationship between communal dissatisfaction and self-determination. Through purposive sampling, it selected 44 in-depth interview respondents to obtain complementary qualitative data that were content analysed. In contrast to the 1960s secessionism, which was largely restricted to Eastern Nigeria, combined with the legacies of colonial rule, popularity of ethno-religious politics, an increase in insecurity and violence, economic hardship, communal insecurity, and deeper perception of ethnic marginalisation, the current wave of self-determination is more contagious and politically attractive in three (South West (SW), South East (SE) and South (SS) –) of the existing six geopolitical zones in Nigeria. The article concludes, returning to the erstwhile regionalism will salvage Nigeria from territorial disintegration..

Numerical model of changes in current patterns due to reclamation around the Mireng River estuary, Gresik

Abstract The Mireng River is in Gresik Regency and empties into the Madura Strait. Around the mouth of the Mireng River, two industrial areas require construction facilities through reclamation. The consequences of reclamation will cause phenomena due to the interaction of marine and environmental dynamics, which can change current patterns, wave heights, and sedimentation processes, affecting the surrounding environment. This study explicitly discusses the changes in flow patterns that occur due to reclamation. The investigation was performed using numerical model simulations with Delft 3D software. The model results show the movement pattern and current speed during the highest and lowest low tides. There was a change in the average flow speed to 0.18 m/s around the reclamation area due to flow obstruction due to reclamation. This condition has the potential for sedimentation to occur in the area. Therefore, mitigation efforts are needed to reduce this impact.