Frequency Characteristics Research Articles

Non-Destructive Inspection Method Using Elastic Waves for Quality Management in the Bending Process Region of BFRTP

In order to establish a sustainable infrastructure, structures must maintain their minimum required performance for an extended period. Typically, existing concrete structures are reinforced with steel, but the susceptibility of steel reinforcements to corrosion, attributed to factors such as carbonation and chlorides, can lead to performance degradation, rendering the specified requirements unmet. As a remedy, there has been a growing interest in using lightweight and corrosion-resistant fiber-reinforced polymer (FRP) bars as an alternative to traditional steel reinforcement in concrete structures. Particularly noteworthy is the use of FRP bars manufactured with thermoplastic resins (FRTP) due to their ease of processing and convenient applicability on construction sites. This study delves into the mechanical behavior evaluation by examining the propagation characteristics of elastic waves in the curved section of basalt FRTP (BFRTP). Multiple BFRTP bars underwent a 180-degree bending process, subject to various conditions, including heat and twist variations. Subsequent measurements focused on the propagation characteristics of elastic waves in the curved sections, emphasizing wave attenuation, frequency features, and propagation velocity. Additionally, bending tensile tests were conducted on the curved bars, and a comparative analysis was performed between the tensile strength and the aforementioned elastic wave propagation characteristics. The results affirm a consistent correlation between the propagation characteristics of elastic waves (amplitude ratio, centroid frequency, velocity) during the traversal of the curved BFRTP section and its tensile strength. Notably, both centroid frequency and velocity exhibited correlation coefficients exceeding 0.7, suggesting their potential efficacy as reliable indicators for estimating tensile strength.

Transient Energy Dissipation Control of Energy Storage Devices in Wind Power Generation Systems

The transient stability of power systems with high penetration of wind power generation can be significantly improved through the utilization of variable virtual inertia if the energy source of rotational inertia can be expanded by energy storage devices (ESDs). This paper first establishes the relationship of energy conversion between ESD and mechanical kinetic energy inside a synchronous generator (SG). Then, the impact of the controllable inertia on system frequency characteristics and power angle oscillation is analyzed using the small-signal model corresponding to this system. Based on the analysis of the change of transient energy at different stages in the transient process, the control of transient energy dissipation is proposed employing ESDs for reliable inertia support. Finally, a typical simulation system with high penetration of wind power generation is carried out to demonstrate the viability of the proposed control scheme. The test results show that the fluctuation of SG’s power angle and system frequency can be reduced by regulating the variable inertia in transient events, significantly improving the reliability of the inertia support provided by the ESDs.

Effect of micro-/nano-porous thin film surfaces prepared by a hybrid method of etching and electrochemical deposition on pool boiling heat transfer performance

Surfaces created using efficient and inexpensive methods are highly demanded in industrial applications of extremely high temperatures. In this study, Composite Nano-particle Coated Over CuO Filmed (CNCCF) surface is prepared through two processes, first through chemical etching to produce a thin film of CuO over bare Cu surface, and secondly deposition of Ni-Al2O3 composite nano-particle over CuO thin filmed copper surface by electrochemical deposition process. The completed CNCCF surface exhibits favorable characteristics for improved boiling heat transmission, such as wettability, roughness, porosity, etc. An experiment on pool boiling is conducted on the CNCCF and bare Cu surface. DI water at atmospheric pressure is used as the boiling fluid. Findings show that the CNCCF surface exhibits enhanced Critical Heat Flux (CHF) and Boiling heat Transfer Coefficient (BHTC) than bare Cu surface. The increased porosity, roughness, and other properties of the CNCCF surface are the cause of this improvement in CHF and BHTC. A high-speed camera is also used to monitor and analyze bubble behavior during boiling on all surfaces, including the Bare Cu. Further evidence for the enhancement of boiling heat transfer on the CNCCF surface comes from the nucleation site density, departure diameter, and frequency characteristics of bubbles.

Viscoelastic characterization of coating layers by ultrasonic interference and critical attenuation

This study proposes a characterization technique for a viscoelastic coating layer on a metal substrate immersed in water based on ultrasonic interference and critical attenuation phenomena. Theoretical analysis shows that the reflection spectrum for the normal incidence wave has local minima at the resonance frequencies of the coating layer, which provide its elastic property if the layer thickness is given a priori. Furthermore, it is revealed that the lower envelope of the reflection spectrum takes a minimum, whose frequency can be related to the critical attenuation condition. This feature implies a possibility that the viscous property of the coating material can be estimated by similarly measuring a characteristic frequency to the estimation of the elastic property. Two bonded specimens consisting of polycarbonate (PC) sheets and metal substrates were prepared to validate the proposed method. The reflection spectra measured for the normal wave incidence showed multiple local minima and critical attenuation, which are predicted to appear by theoretical predictions. The wave velocities and loss factors of PC estimated from the two specimens are in fair agreement with the properties shown in the previous paper. This result demonstrates that the ultrasonic interference and critical attenuation behavior can be applied to the characterization of the viscoelastic coating layers.

Subject review: Human activity recognition based on depth images

Human activity recognition (HAR) has becomes a well-known area of study for researchers due to its multiple possible applications. HAR systems are applied in many areas including supervisory nursing care, medical supervision, surveillance, human- machine interaction, gaming and entertainment, etc. However, developing a robust HAR system that incorporates a comprehensive and scalable set of feature spaces is a challenging task. Much research has been done in this area to develop efficient HAR systems. In this article, a review of the developments in Human Activity Recognition (HAR) will be presented. Human activity recognition works on two basic principles; feature extraction from sensor data and classification of features into action classes. The review presented in this article is hence divided into two parts. The first part deals with feature representation in HAR systems such as Space-time Features, Frequency Features, Local Descriptors, Optical Flow Based, and Skeleton Joints. The second part deals with the classification approaches used in the literature such as Bayesian, and HMM.

Early postoperative complications in open heart surgery patients: A review

Over the past few decades, open heart surgery has undergone significant progress in terms of technologies used, operative techniques and resuscitation care. This has led to a significant increase in patient survival and quality of life after discharge. However, there are still a number of challenges to be addressed, one of which is reducing the incidence of early postoperative complications. They are directly and primarily determined by patients’ demographic and clinical characteristics, as well as by the characteristics of the surgical intervention itself and are a major factor in the outcome of the surgery performed. This review presents the most important and frequent early complications, their epidemiological and clinical features. Their good knowledge is the key to achieving an optimal treatment approach and seeking effective opportunities for their prediction and incidence reduction.

The Creation of Geotechnical Seismic Isolation from Materials with Damping Properties for the Protection of Architectural Monuments

This paper presents the results of a study on the relevance of seismic isolation systems for protecting architectural monuments from seismic and vibration impacts. This work aims to develop a method for protecting architectural monuments from seismic and vibration effects by installing geotechnical seismic isolation systems made of various geomaterials, such as a silicate soil mixture (SSM), a cement–soil mixture (CSM), a bitumen–soil mixture (BSM), and a rubber–soil mixture (RSM). The novelty of the work lies in the results of studying the wave processes in different models of geomaterials to assess their effectiveness in a seismic isolation system in the form of damping barrier screens to ensure the seismic resistance of architectural monuments. By comparing the amplitude–frequency characteristics of various geomaterials, it was found that the rubber–soil mixture (RSM), the cement–soil mixture (CSM), and the bitumen–soil mixture (BSM) have the most effective damping properties. A proposed method for protecting architectural monuments with geotechnical seismic isolation in the form of vertical screen barriers and technology for their installation ensures the integrity and safety of architectural monuments at all stages of construction and operation.

Simulated dynamical transitions in a heterogeneous marmoset pFC cluster

Network analysis of the marmoset cortical connectivity data indicates a significant 3D cluster in and around the pre-frontal cortex. A multi-node, heterogeneous neural mass model of this six-node cluster was constructed. Its parameters were informed by available experimental and simulation data so that each neural mass oscillated in a characteristic frequency band. Nodes were connected with directed, weighted links derived from the marmoset structural connectivity data. Heterogeneity arose from the different link weights and model parameters for each node. Stimulation of the cluster with an incident pulse train modulated in the standard frequency bands induced a variety of dynamical state transitions that lasted in the range of 5–10 s, suggestive of timescales relevant to short-term memory. A short gamma burst rapidly reset the beta-induced transition. The theta-induced transition state showed a spontaneous, delayed reset to the resting state. An additional, continuous gamma wave stimulus induced a new beating oscillatory state. Longer or repeated gamma bursts were phase-aligned with the beta oscillation, delivering increasing energy input and causing shorter transition times. The relevance of these results to working memory is yet to be established, but they suggest interesting opportunities.

EEG Emotion Recognition Network Based on Attention and Spatiotemporal Convolution

Human emotions are complex psychological and physiological responses to external stimuli. Correctly identifying and providing feedback on emotions is an important goal in human–computer interaction research. Compared to facial expressions, speech, or other physiological signals, using electroencephalogram (EEG) signals for the task of emotion recognition has advantages in terms of authenticity, objectivity, and high reliability; thus, it is attracting increasing attention from researchers. However, the current methods have significant room for improvement in terms of the combination of information exchange between different brain regions and time–frequency feature extraction. Therefore, this paper proposes an EEG emotion recognition network, namely, self-organized graph pesudo-3D convolution (SOGPCN), based on attention and spatiotemporal convolution. Unlike previous methods that directly construct graph structures for brain channels, the proposed SOGPCN method considers that the spatial relationships between electrodes in each frequency band differ. First, a self-organizing map is constructed for each channel in each frequency band to obtain the 10 most relevant channels to the current channel, and graph convolution is employed to capture the spatial relationships between all channels in the self-organizing map constructed for each channel in each frequency band. Then, pseudo-three-dimensional convolution combined with partial dot product attention is implemented to extract the temporal features of the EEG sequence. Finally, LSTM is employed to learn the contextual information between adjacent time-series data. Subject-dependent and subject-independent experiments are conducted on the SEED dataset to evaluate the performance of the proposed SOGPCN method, which achieves recognition accuracies of 95.26% and 94.22%, respectively, indicating that the proposed method outperforms several baseline methods.

Effective multispike learning in a spiking neural network with a new temporal feedback backpropagation for breast cancer detection

This paper presents an effective learning multi-spike deep spiking neural network with temporal feedback backpropagation for breast cancer detection using contrast-enhanced MRI images. The learning in the spiking network is a new universal temporal feedback called Temporal_Feedback_SpikeProp (TF_SpikeProp) and Temporal_Feedback_ReSuMe (TF_ReSuMe). Thus, it can be implemented on all kinds of algorithms such as MultiSpikeProp and MultiReSuMe algorithms and is compatible with all temporal codings. The presented spiking network is a functional network with high accuracy and convergence in low epochs. The new algorithm explores the influence of all presynaptic neurons on the output error and reduces the role of inactive neurons. Therefore, the error propagation of the spiking network is such that it affects not only the spike time of each neuron in the output spike time, but also the refractory time and the presynaptic spikes of the neuron during the spiking time of the output neuron. The spiking network can correct and adjust the weights, spike delay, spike threshold, and also the time constant of the spike collection kernel. In order to diagnose cancer tissue, time–frequency features such as STFT and packet wavelet transform (WPT) have been used along with texture recognition features such as co-occurrence matrix. The presented network achieved an accuracy of 98.3% in 23 epochs in SpikeProp algorithm, 97.4% in ReSuMe with Duke MRI dataset, 98.64% on MNIST, and 96.1% on Iris. The results have shown that the training algorithm used in this study can achieve high accuracy in low epochs compared to traditional algorithms, while solving the challenge of getting stuck in local minima and poor convergence, as well as reducing the problem of time confusion of output spikes to an acceptable level and providing a fully functional network in practice and reality.

Effects of fluid saturation and viscosity on seismic dispersion characteristics in Berea sandstone

Despite additional availability of laboratory data from water-saturated sandstone at seismic frequencies, measurements of rock samples saturated with high viscous fluids, particularly at partial saturation, are still rare. To quantify the effects of fluid viscosity and saturation levels on seismic dispersion and attenuation characteristics, we conducted two comparative forced-oscillation measurements in partially saturated sandstone with varying fluid viscosity (e.g., water, glycerin) at seismic frequencies (2-400 Hz). The results demonstrate that both fluid viscosity and saturation levels substantially influence the dispersion and attenuation characteristics at the measured frequencies. Significant dispersion and attenuation are observed in the presence of a relatively small amount of gas (∼6% - 8%) for both glycerin and water saturation cases but vary in their magnitudes and characteristic frequencies. Specifically, the maximum extensional attenuation (∼0.024) occurs at approximately 200 Hz for water-saturated rock at 94% saturation, while at around 30 Hz with a peak of 0.032 for glycerin-saturated rock at 92% saturation. Based on theoretical modeling analysis, we suggest that mesoscopic fluid flow might be a dominant mechanism accounting for the observed attenuation in partial water or glycerin saturation, while the microscopic (squirt) flow mechanism possibly dominates the fully saturated cases.

Surveillance and phylogenetic analysis of a pathogenic bacterium candidate in nasal discharge from children.

"The infectious organism lurking in human airways (IOLA)" is a candidate pathogenic bacterium detected in bronchoalveolar lavage fluid specimens derived from adult patients with chronic lower respiratory tract infections. Genomic analyses of IOLA have revealed that it possesses the smallest and most AT-rich genome among human-derived bacteria. However, its biological properties remain unclear because no culture method has been established for IOLA. Here, we conducted a large-scale IOLA surveillance study of nasal discharge specimens from children in Japan and investigated the correlation between IOLA detection frequency and patient characteristics. We detected IOLA in 5.4% (103 of 1,920) of pediatric nasal discharge samples. No significant differences were observed in the frequency of detection based on the patient's background. However, with respect to age, the frequency of detection tended to be significantly high at 2-3 and 6 years old. Phylogenetic analysis revealed five phylotypes in the IOLA 16S rRNA gene sequences, and the sequences detected in adult patients with respiratory infections in a previous study belonged to one of the five phylotypes. The involvement of IOLA in the symptoms is not clear, but IOLA is detected at a relatively high frequency in pediatric nasal discharge. Many subjects with detected IOLA were not always IOLA positive, and IOLA was detected transiently. Our findings suggest that IOLA is horizontally transmitted through groups in nursery and elementary schools, and there are differences in biological characteristics among the IOLA phylotypes.IMPORTANCE"The infectious organism lurking in human airways (IOLA)" is a candidate pathogenic bacterium strongly suspected to be infectious to the respiratory tracts of humans and animals. However, a culture method for IOLA has not been established yet, and its properties remain unclear. In this study, IOLA was detected at a relatively high frequency in the nasal discharge of children, and five phylotypes of IOLA were identified. One of these phylotypes was found in the bronchoalveolar lavage fluid from adult patients, suggesting lineage-specific differences in the pathogenicity of IOLA. Moreover, it was suggested that IOLA is horizontally transmitted when children gather in groups such as nursery and elementary schools. These findings strongly indicate that IOLAs have been clinically undetected so far but are spreading among children, with one lineage being involved in respiratory diseases in adults. Examining the presence of IOLA in clinical specimens may help to understand the etiology of respiratory diseases with unknown causes.

The Force–Frequency Characteristics of Quartz Wafers under a Cantilever Beam Structure

This study investigated the force–frequency characteristics of quartz wafers inside a cantilever beam frame. Firstly, the force–frequency coefficient formula of quartz wafers with fixed ends under axial force was analyzed. Firstly, the formula for the force–frequency coefficient of quartz wafers with fixed ends under axial force was analyzed. A force–frequency coefficient formula suitable for cantilever beam structures was derived by considering the changes in surface stress and stiffness of quartz wafers with fixed ends and one end under force on the other. Subsequently, the formula’s accuracy was verified by experiments, and the accuracy was more than 92%. In addition, strain simulation analysis was performed on three different shapes of quartz wafers, and experimental verification was carried out on two of them. The results revealed that trapezoidal quartz wafers and cantilever beam structures exhibited superior stress distribution to rectangular chips. Furthermore, by positioning electrodes at various locations on the surface of the quartz chip, it was observed that, as the electrodes moved closer to the fixed end, the force–frequency coefficient of the rectangular quartz chip increased, along with an increase in chip strain under the cantilever structure. In summary, this study provides a new approach for designing cantilever quartz resonator sensors in the future.

Early-Stage Fault Diagnosis of Motor Bearing Based on Kurtosis Weighting and Fusion of Current–Vibration Signals

To solve the problem of a low signal-to-noise ratio of fault signals and the difficulty in effectively and accurately identifying the fault state in the early stage of motor bearing fault occurrence, this paper proposes an early fault diagnosis method for bearings based on the Differential Local Mean Decomposition (DLMD) and fusion of current–vibration signals. This method uses DLMD to decompose the current signal and vibration signal, respectively, and weights the decomposed product function (PF) according to the kurtosis value to reconstruct the signal, and then fuses the reconstructed signals to obtain the current–vibration fusion signal after normalization, and then analyzes the fusion signal spectrally through the Hilbert envelope spectrum. Finally, the fusion signal is analyzed by the Hilbert envelope spectrum, and a clear fault characteristic frequency is obtained. The experimental results demonstrate that compared to traditional bearing fault diagnosis methods, the proposed method significantly improves the signal-to-noise ratio of fault signals, effectively enhances the sensitivity of early-stage fault detection in motor bearings, and improves the accuracy of fault identification.

Spin-charge-lattice couplings and Co doping effect in Ba(Fe 1−x Co x )2As2: an ab initio molecular dynamics study

As one of the typical iron-based superconductors, Ba(Fe 1−x Co x )2As2 exhibits a dome-like evolution of superconducting transition temperature T c with the Co doping (x), which provides an ideal platform to explore the mechanism of unconventional superconductivity. Through ab initio molecular dynamics (AIMD) studies, we find that the spin, charge, and lattice degrees of freedom in Ba(Fe 1−x Co x )2As2 are intimately coupled with a characteristic frequency around 5.5 THz, which originates from the A1g phonon mode of the As atoms. Compared with the undoped BaFe2As2, the spin dynamics in Ba(Fe 1−x Co x )2As2 (x = 0.0625, 0.1250, 0.1875) shows enhanced spatial inhomogeneities, though the features of the charge dynamics are rarely modified. Along with the increasing Co doping, the spatial inhomogeneities of Fe spin dynamics display nonmonotonic changes, meanwhile the lattice vibrational spectra first show peak broadening and then restore the main peak around 5.5 THz, being both consistent with the nonmonotonic behavior of superconducting T c. Our study provides a molecular dynamics approach to investigate the couplings of spin, charge, and lattice in doped BaFe2As2, which could also be applied to explore the dome-like evolution of superconductivity in other Fe-based superconductors.

#234 Clinical spectrum and genetic variants of Alport syndrome and thin basement membrane nephropathy—single center experience

Abstract Background and aims Alport syndrome (AS) and thin basement membrane nephropathy (TBMN) are genetically heterogeneous kidney diseases that manifest with kidney involvement, AS also with hearing and visual impairment. Electron microscopic examination shows characteristic ultrastructural changes in the glomerular basement membrane (GBM) in AS and TBMN, but cannot reliably distinguish between the two entities. Therefore, molecular genetic studies and the identification of individual pathogenic variants in the target genes are crucial to confirm the diagnosis. The aim of our study is to determine the significance of the genetic variants associated with the ultrastructural changes of GBM found in the renal biopsy. Method We retrospectively analyzed records of patients from the University Medical Centre Ljubljana in which ultrastructural GBM changes characteristic for AS and TBMN were found in the renal biopsy, including their clinical, laboratory and histological features. Molecular genetic investigations were made using the new generation sequencing method (NGS) to determine germline pathogenic variants in genes directly related to AS and TBMN (COL4A3, COL4A4 and COL4A5) and in genes that are important in syndromes with a related clinical picture (COL4A6, CD151, LMX1B, MYH9, FN1 and MYO1E). The pathogenicity of variants was determined according to the Clinical Molecular Genetic Society best practice guidelines. Results The study included 73 patients with ultrastructurally confirmed thin GBM. Indications for kidney biopsy were chronic nephritis syndrome in 33 patients (45%), acute worsening of renal function in 16 (22%), nephrotic syndrome in 9 (12%), nephrotic proteinuria and chronic kidney disease in 6 (8%), isolated proteinuria in 5 (7%) and suspected vasculitis in 4 patients (6%). At the time of kidney biopsy average age was 50 ± 16 years, average creatinine 112 ± 70 µmol/L and average estimated glomerular filtration rate (eGFR) 65 ± 24 ml/min/1.73 m2, 7 patients had eGFR below 30 ml/min/1.73 m2. Average daily proteinuria was 2.4 ± 3.3 gr and 88% of patients had hematuria. 38% of them have hearing impairment and 43% had positive familiar history of kidney disease. We recorded 33 patients (45%) with genetic variants associated with AS or TBMN: 22 patients (67%) with pathogenic variants, 2 patients (6%) with likely pathogenic and 9 patients (27%) with variants of uncertain significance. The presence of a positive genetic analysis was associated with a higher level of hematuria (p = 0.003), a lower level of proteinuria (p = 0.004) and a positive family history of kidney disease (p < 0.001). It was also associated with hearing loss, but the association was not statistically significant (p = 0.099). Patients with genetic variants had similar eGFR to those with negative genetics (63.9 ml/min/1.73 m2 (58.3-69.4) vs 66.2 ml/min/1.73 m2 (60.0-72.3)), p = 0.698. We also found no differences in GBM thickness in patients without compared to those with identified gene variants (213 nm (160-315) vs. 209 nm (140-410)), p = 0.761. 32 patients (44%) had only focal chronic changes and ultrastructural changes of thin GBM present on kidney biopsy and 41 patients (56%) had also been diagnosed with other renal pathology. When comparing these two groups, patients without associated pathology had lower daily proteinuria (p = 0.048), higher level of hematuria (p = 0.021), frequent hearing impairment (p = 0.008) and also positive genetics analysis (p = 0.016). Conclusion We have shown that in patients with proven ultrastructural alterations in GBM, the presence of so far recognized genetic variants associated with AS and TBMN is 45%, and corresponds to the frequency of other phenotypic characteristics of AS, including hearing impairment and positive family history. In the future, additional clinical tools will be required to accurately determine the role of coexistent thin GBM on the prognosis of patients with other relevant kidney pathology and other genetic tools beyond NGS should be employed to explore other pathologic genetic variants associated with the AS spectrum.

Chronic exercise effects on overall depression severity and distinct depressive symptoms in older adults: A protocol of a systematic and meta-analytic review.

There is high evidence that chronic exercise benefits overall depression severity in older adults. However, late-life depression is characterized by considerable heterogeneity in clinical manifestation emphasizing the need for more individualized exercise intervention programs. Therefore, the objective of the proposed review is to investigate the effects of chronic exercise on overall depression severity and on different symptoms of depression in randomized controlled trials (RCTs) including older adults with a mean age of at least 60 years, and by considering the moderating effects of intervention characteristics and individual characteristics. This protocol is guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols (PRISMA-P). We will use the Population-Intervention-Comparator-Outcomes-Study design (PICOS) criteria for study inclusion and will search the following database sources for relevant RCTs: Web of Science, Academic Search Complete, CINAHL, APA Psycinfo, SPORTDiscuss, Cochrane. Two independent reviewers will conduct the study selection, data extraction, and quality assessment. Disagreement will be solved by a third reviewer. Primary outcome will be changes in overall depression severity and secondary outcomes will encompass changes in symptoms of depression as defined by the DSM-5, such as sleep quality, fatigue, anxiety, mood, apathy, changes in weight, information processing speed, and executive functions, from baseline until the end of the intervention and to any available intermediary measurement or follow up. Meta-analysis will be undertaken to synthesize the effects of chronic exercise on primary and secondary outcomes. Subgroup analysis will investigate the moderating effects of intervention characteristics (frequency, intensity, duration, type of exercise, cognitive demand, social interactions, exercise supervision, behavioral change techniques, compliance, study design, dropout-rate, type of control group) and individual characteristics (age, sex, education, functional capacity, global cognition, population) on primary and secondary outcomes. Additionally, we plan to assess quality of evidence and publication bias, and to carry out sensitivity analysis. The results of the proposed review are anticipated to have a substantial impact on research and clinical practice. On the one hand, the review's conclusions could form the foundation for developing evidence-based recommendations for individualized exercise programs that alleviate depression in older adults. On the other hand, by revealing research gaps, the review results could encourage the formulation of research questions for further RCTs. This protocol has been published in the Prospero repository (PROSPERO 2022 CRD42022361418, available from: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022361418).

Space-Time Variability of Drought Characteristics in Pernambuco, Brazil

Drought is the most complex natural hazard that can occur over large spatial scales and during long time periods. It affects more people than any other natural hazard, particularly in areas with a dry climate, such as the semiarid region of the Brazilian Northeast (NEB), which is the world’s most populated dry area. In this work, we analyzed trends and the spatial distribution of drought characteristics (frequency, affected area, and intensity) based on the Standardized Precipitation Index (SPI) on annual (SPI-12) and seasonal (SPI-3) scales. The study used monthly precipitation data recorded between 1962 and 2012 at 133 meteorological stations in Pernambuco State, Brazil, which is located in the eastern part of the NEB and has more than 80% of its territory characterized by a semiarid climate. The regions of Sertão, Agreste, and Zona da Mata of Pernambuco were considered for comparison. The Mann–Kendall and Sen’s slope tests were used to detect the trend and determine its magnitude, respectively. The results indicated that annual droughts in the state of Pernambuco became more frequent from the 1990s onwards, with summer having the greatest spatial coverage, followed by winter, autumn, and spring. Sertão presented a greater number of stations with a significant positive trend in drought frequency. Regarding the drought-affected area, global events occurred in a greater number of years on an annual scale and during the summer. Trend analysis pointed to an increase in areas with drought events on both scales. As for the drought intensity, the entire state of Pernambuco experienced drought events with high intensity during the autumn. The relationship between drought characteristics indicated an increase in the affected area as the result of an increase in drought intensity.

An adaptive frequency-based C/N0-constrained multipath extraction and mitigation method for GNSS pseudorange measurements

Abstract The multipath effect poses an inevitable challenge for Global Navigation Satellite System
(GNSS) receivers, particularly pronounced in smart devices, which are nevertheless the most common means through which the general public accesses GNSS positioning. So we propose a novel adaptive method for extracting multipath errors, which fully exploits the multipath frequency characteristics, multipath repeatability, and the correlation between multipath errors and carrier to- -noise ratio (C/N0). This approach aims to enhance the susceptibility of smart devices to multipath influences. Specifically, this method uses the code minus carrier (CMC) method to calculate the noisy multipath error,multipath to constrain the frequency range,exploits the correlation between C/N0 andemploys the ensemble empirical modedecomposition (EEMD) method to decompose the error signal, and utilizes the Hilbert–Huangtransform (HHT) method to obtain the frequency information of the signal component.multipath Inrepeatability, the proposed method can effectively improve the correlation ofmultipath signals by up to 0.79. By applying the extraction method, the positioning
performance of smart devices can be improved by 13.9%. Therefore, the proposed method extracts multipath error more accurately and is highly usable in low-cost devices and real-time applications.

Effects of electroweak symmetry breaking on axionlike particles as dark matter

Axionlike particles (ALPs), the pseudo Nambu-Goldstone bosons associated to the spontaneous breaking of global symmetry, have emerged as promising dark matter candidates. Conventionally, in the context of misalignment mechanism, the nonthermally produced ALPs happen to stay frozen due to Hubble friction initially, and at a later stage, they begin to oscillate (before matter-radiation equality) at characteristic frequencies defined by their masses and behaving like cold dark matter. In this work, we study the influence of electroweak symmetry breaking (EWSB), through a higher order Higgs portal interaction, on the evolution of ALPs. Such an interaction is found to contribute partially to the ALP’s mass during EWSB, thereby modifying oscillation frequencies during EWSB as well as impacting upon the existing correlation between the scale of symmetry breaking and their masses. The novelty of the work lies in broadening the relic satisfied parameter space so as to probe it in near future via a wide range of experiments. Published by the American Physical Society 2024