Wavelet Power Spectrum Analysis Research Articles

Temporal Evolution, Oscillation and Coherence Characteristics Analysis of Global Solar Radiation Distribution in Major Cities in China’s Solar-Energy-Available Region Based on Continuous Wavelet Transform

The majority of the energy required for human survival is derived either directly or indirectly from solar radiation, thus it is important to investigate the periodic fluctuations in global solar radiation over time. In this study, six cities—Harbin, Shenyang, Beijing, Shanghai, Wuhan, and Guangzhou—located in the utilizable areas of solar energy in China, were selected, and the periodicity of the daily global solar radiation of these six cities with time were investigated by means of wavelet power spectrum analysis. Furthermore, Harbin, which has the lowest monthly average of global solar radiation in the cold of winter, was selected to explore the temporal evolution relationship between global solar radiation and other meteorological factors, and air quality factors by wavelet coherence analysis. Among the meteorological factors, the correlation between global solar radiation and sunshine duration exhibits the highest level of consistency. Global solar radiation demonstrates a positive association with atmospheric temperature/wind speed/precipitation over the annual cycle. Conversely, it displays a negative correlation with atmospheric pressure during this time frame. Additionally, on shorter timescales, global solar radiation is negatively correlated with air humidity and precipitation. Among air quality factors, the relationship between global solar radiation and CO/NO2/O3/PM2.5/PM10/SO2 primarily manifests in the broader annual cycle time scale. Within this context, global solar radiation shows a positive correlation with O3, while displaying negative associations with the other five air quality indicators. These findings contribute to urban environmental planning and the effective management and utilization of solar radiation, thereby providing valuable insights to guide the future development of cross-regional comprehensive energy utilization projects under diverse climatic and geographical conditions. Additionally, they serve as a reference for subsequent research aimed at enhancing the accuracy of global solar radiation prediction models.

Tracking states and transitions in semiarid rangelands: A spatiotemporal archetypal analysis of productivity dynamics using wavelets

Climate change poses challenges in classifying ecosystem dynamics, as they are influenced by shifting dynamics resulting from changes in climate forces and meteorological variables, including temperature and water availability. To address this, our study presents a novel approach using Continuous Wavelet Transform (CWT) and power spectrum analysis to classify vegetation dynamics, considering the time-dependent variability of ecosystem frequencies. We applied our method to centred and standardized MODIS NDVI time series for the period 2000–2021, using an experimental field station in northern Patagonia as a case study. By performing a continuous wavelet transform on the data for each pixel, we obtained instantaneous power spectra, capturing variability across different dates and pixels. These spectrums were then consolidated into a comprehensive database, and subsequently classified using archetypal analysis. We identified a convex combination of archetypal spectrums that best represented the entire power spectrum database. Mapping the resulting archetypes and their weights in both space and time allowed us to explore pixels' variations in archetype weights in relation to factors such as time, topography, and climate. In addition, to examine the potential relationship between the NDVI time series and climate drivers, we computed the Average Cross-Wavelet Power Spectrum (ACWPS) to different climatic indices. Three archetypes were sufficient to explain the majority of power spectrum variability in the study area. These archetypes exhibited distinctive characteristics: 1) medium-frequency variability (2–4 years), 2) low-frequency variability (>4 years), and 3) an annual (i.e. seasonal) cycle with low-frequency variability. Spatially, the first two archetypes were predominantly observed in highland steppes, while the third archetype prevailed in lowland areas associated with meadows. At the beginning of the studied period, Archetypes 1 and 3 dominated, but after the Puyehue-Cordón Caulle Volcanic Complex eruption in 2011 their prominence diminished, and Archetype 2 became more prevalent in the whole study area. Finally, all three NDVI series representative of archetypes showed a relative peak at approximately four years, which could be linked to the Indian Ocean Dipole variability. These results highlight an abrupt shift in the system's behaviour, primarily related to changes in variability distribution rather than mean values. This disturbance-induced transition aligns with the theory of state and transitions in ecological system dynamics. We propose that the states in this model are not fixed but represent alternative dynamic behaviours, akin to different types of limit cycles. Consequently, employing a wavelet analysis-based classification method provides a robust means of studying and understanding such variability and transitions, thereby offering clarity and comprehension of ecosystem states. Notably, this methodology proves particularly effective for large databases of detailed time series.

Revisiting the impact of geopolitical risk on Sukuk, stocks, oil and gold markets during the crises period: fresh evidence from wavelet-based approach

Purpose In this study, the authors analyze the impact of geopolitics risk on Sukuk, Islamic and composite stocks, oil and gold markets and portfolio diversification implications during the COVID-19 pandemic and Russia–Ukraine conflict period.Design/methodology/approachThe study used a mix of wavelet-based approaches, including continuous wavelet transformation and discrete wavelet transformation. The analysis used data from the Geopolitical Risk index (GP{R), Dow Jones Sukuk index (SUKUK), Dow Jones Islamic index (DJII), Dow Jones composite index (DJCI), one of the top crude oil benchmarks which is based on the Europe (BRENT) (oil fields in the North Sea between the Shetland Island and Norway), and Global Gold Price Index (gold) from May 31, 2012, to June 13, 2022.Findings The results of the study indicate that during the COVID-19 and Russia–Ukraine conflict period geopolitical risk (GPR) was in the leading position, where BRENT confirmed the lagging relationship. On the other hand, during the COVID-19 pandemic period, SUKUK, DJII and DJCI are in the leading position, where GPR confirms the lagging position.Originality/value The present study is unique in three respects. First, the authors revisit the influence of GPR on global asset markets such as Islamic stocks, Islamic bonds, conventional stocks, oil and gold. Second, the authors use the wavelet power spectrum and coherence analysis to determine the level of reliance based on time and frequency features. Third, the authors conduct an empirical study that includes recent endogenous shocks generated by health crises such as the COVID-19 epidemic, as well as shocks caused by the geopolitical danger of a war between Russia and Ukraine.Highlights We analyze the impact of geopolitics risk on Sukuk, Islamic and composite stocks, oil and gold markets and portfolio diversification implications during the COVID-19 pandemic and Russia–Ukraine conflict period.The results of the wavelet-based approach show that Dow Jones composite and Islamic indexes have observed the highest mean return during the study period.GPR and BRENT are estimated to have the highest amount of risk throughout the observation period.Dow Jones Sukuk, Islamic and composite stock show similar trend of volatility during the COVID-19 pandemic period and comparatively gold observes lower variance during the COVID-19 pandemic and Russia–Ukraine conflict.

Time-frequency analysis between Bloomberg Commodity Index (BCOM) and WTI crude oil prices

The price movement of commodities in general and crude oil, in particular, are critical for both commodity-consuming and producing countries. The prime objective of this study is to examine the characteristic behavior of commodity futures and commodity index and the dynamic relationships between commodity index and commodity futures. The study first investigates the evolution of volatility of Bloomberg commodity index (BCOM) and WTI crude oil (CRUDE) prices at different time scales using Wavelet Power Spectrum Analysis. Second, the correlation and causality between BCOM and CRUDE are investigated using Wavelet Coherency and Phase Difference methodology. The average level volatility of BCOM and CRUDE is different at different time scales. Wavelet Coherence shows that they are correlated in medium to long term periods and not in the short term. Further, during the period of changed correlation structure over the study period, the causality structure between BCOM and CRUDE is also changed at different time scales. Therefore, policy measures to control prices should be different in the short term than in the medium to long term when both the prices are not correlated.

An attempt to implement partially premixed combustion strategy in a multi-cylinder CRDI engine: A detailed experimental and wavelet transform analysis

The main objective of this research was to effectively employ the n-butanol fuel in advanced combustion strategy ‘partially premixed combustion (PPC)’ and provide the maximum possible replacement of diesel fuel. An experimental study was conducted on a multi-cylinder turbocharged intercooler CRDI engine to optimize the injection timings and diesel/n-butanol blended fuels based on performance, emissions, and combustion characteristics, including cyclic variability, in order to achieve the PPC strategy without compromising thermal efficiency significantly. The combustion characteristics analysis indicate that adding n-butanol fuel into diesel fuel combined with advanced injection (16° CA BTDC) timing leads to a drastic decrease in smoke emission as well as increases in NOX emission than diesel fuel. However, DB20 fuel at 8° CA BTDC injection timing achieved low-temperature PPC mode and reduced NOX (8.08%↓) and smoke (48%↓) emissions simultaneously compared to diesel fuel at 2 bar BMEP engine load. In addition, wavelet power spectrum (WPS) and global wavelet spectrum (GWS) analysis were utilized to investigate the temporal and spectral fluctuations in the partially premixed combustion parameter (indicated mean effective pressure) at optimum injection timing (8° CA BTDC). Results reveal that DB20 possesses lesser cyclic variations with higher frequency (at period 2–6 cycles) intermittent fluctuation in partially premixed combustion at 2 bar BMEP engine load than other tested fuels. A statistical analysis of IMEP variations was also performed to validate the temporal variation in the IMEP time-series signals of the WPS results. The results of WPS could be used to establish an efficient engine control method based on in-cylinder pressure feedback.

Study of nonlinear time series and wavelet power spectrum analysis using solar wind parameters and geomagnetic indices

ABSTRACT We investigate the time series of solar wind parameters (interplanetary magnetic field, Bz and solar wind speed, Vx) and geomagnetic indices (disturbance storm time, Dst and auroral electrojet, AE) using wavelet analysis and nonlinear dynamics time series techniques. The data were collected from the Flight Center Space Physics Data Facility (GSFC/SPDF) OMNIWEB interface between 2008 and 2017. Wavelet power spectrum (WPS) analysis assists in breaking down the time series of Bz, Vx, Dst and AE parameters into different scales. It was noted that there is a greater concentration of power between the 512 and 1024 months bands across the Bz, Vx, Dst and AE parameters. We also applied non-linear time series modelling methods to examine the Bz, Vx, Dst and AE parameters. We utilised both the time delay and embedded dimension in computing average mutual information (AMI) and false nearest neighbors (FNN), respectively. The Lyapunov exponent (LE) is used to express the complexity of the nonlinear dynamics based on embedding parameters. The Lyapunov exponents depict positive values which confirm that the complex solar wind parameters and the geomagnetic indices are deterministic chaotic systems. The results show noticeable chaotic characteristics in the Bz, Vx, Dst and AE parameters.

Features and Source Current of Long‐Period Induced Geoelectric Field During Magnetic Storms: A Case Study

AbstractWe present a case study on the long‐period ( s) induced geoelectric field disturbance during magnetic storms. A set of continuous 33‐day measurements of the geoelectric field, geomagnetic field, geomagnetic indices, and interplanetary magnetic field are analyzed. In the studied 33 days, two magnetic storms occurred after 10 geomagnetic quiet days. To exclude the effects from the different underground electrical structures, geomagnetic and geoelectric field measurements from the same ground observatory enrolled in Chinese Meridian Project are studied. Besides, Space Weather Modeling Framework is adopted to calculate the global geomagnetic field disturbances and the contribution from different current systems. The wavelet power spectra analysis reveals that the long‐period geoelectric field disturbance appears only during magnetic storms. Especially, stronger magnetic storm generates weaker geoelectric disturbances at the same observatory. The opposite‐direction eastward geomagnetic field disturbance, which is generated mainly by the field‐aligned current at different magnetic local time, significantly changes the magnitude and direction of the induced geoelectric field via the underground impedance tensor. Therefore, both the effects caused by ring current and field‐aligned current should be considered in analyzing the ground induced geoelectric field. Excluding the effect from the geospace current source, the more accurate electrical conductivity in the upper mantle would be obtained in future.

Ionospheric Response to the 2018 Sudden Stratospheric Warming Event at Middle‐ and Low‐Latitude Stations Over China Sector

AbstractThe total electron content (TEC) recorded at two middle‐latitude stations (Mohe and Beijing), and four low‐latitude stations (Xiamen, Guangzhou, Nanning, and Kunming) in the China sector are analyzed to study the response of the ionosphere during the sudden stratospheric warming (SSW) event in February 2018. The TEC and deviation of TEC (ΔTEC) present remarkable perturbation after the reversal of the zonal wind during the SSW period. The ΔTEC presents enhancement during the daytime and decreases after sunset, especially around the temperature peak. Results of wavelet power spectra analysis show that the ΔTEC shows intensive semidiurnal and diurnal oscillations during the SSW period. The percentage of dTEC exhibits moderate correlation with solar geophysical drivers (such as solar wind speed, F10.7, and Ap index) during the period of 11–26 February at low‐latitude stations. The significant correlation between equatorial electrojet and the percentage of dTEC monitored at low latitude indicates that the equatorial electrojet plays a key role in the anomaly perturbation and periodic oscillation of TEC, while it has a weak correlation at middle latitude.

Evaluation of engine combustion and exhaust emissions characteristics using diesel/butanol blended fuel

Depletion of non-renewable fuel sources accompanied with never-ending engine exhaust emissions pollution from internal combustion lead to renewed interests in alternative energy resources. Alcohol fuel had emerged as one of the viable candidates as a fuel substitute to reduce the use of fossil fuels in diesel engine. The aim of the experimental investigation is to study the effects of engine fuel properties characteristics towards engine combustion and exhaust emissions characteristics. In this experimental study, the diesel engine was tested at butanol/diesel percentage volume ratios of 5:95 (DBu5), 10:90 (DBu10) and 15:85 (DBu15) of butanol-to-diesel, respectively. Combustion analysis results showed that butanol/diesel blends have a lower in-cylinder pressure, rate of pressure rise and rate of heat release. Moreover, the mass fraction burned analysis shows longer ignition delay and burn duration. Apart from that, the wavelet power spectrum analysis suggested that DBu15 possesses high engine cyclic variations. The engine exhaust emissions show generally a reduction of nitrogen oxides, carbon monoxides and unburned hydrocarbon.

Seasonal Difference of the Deep Currents in the Luzon Strait during October 2008-January 2009 and July-August 2009

Based on direct current measurements from two separated cruises in October 2008-January 2009 and July-August 2009, we obtained a valuable deep current observation of the Luzon Strait (LS). Rectified wavelet power spectra analysis (RWPSA) and the geostrophic current calculation are used to study the deep current. We find that the deep current differs in different seasons. The current is strongest in autumn (October-November) and weaker in summer (July-August) and in winter (December-January). The cyclonic and anti-cyclonic meander with different subtidal current directions plays an important role in the seasonal difference of the deep current in the LS. The observed seasonal difference of the deep current in the LS is connected with the deep current observed at the western boundary of the northern Philippine Basin and is also linked with the overflow near the central Bashi Channel and Luzon Trough. The RWPSA of the long observation suggests the dominant periods of 8 d, 19 d in the deep current. The dynamical cause of the resulting velocity distribution at 1850 and 1760 m is the pressure field and bottom topography steering. The observed deep current agrees well with the geostrophic current calculation.

A multilayer approach and its application to model a local gravimetric quasi-geoid model over the North Sea: QGNSea V1.0

Abstract. A multilayer approach is set up for local gravity field recovery within the framework of multi-resolution representation, where the gravity field is parameterized as the superposition of multiple layers of Poisson wavelets located at different depths beneath the Earth's surface. The layers are designed to recover gravity signals at different scales, where the shallow and deep layers mainly capture the short- and long-wavelength signals, respectively. The depths of these layers are linked to the locations of different anomaly sources beneath the Earth's surface, which are estimated by wavelet decomposition and power spectrum analysis. For testing the performance of this approach, a gravimetric quasi-geoid model over the North Sea, QGNSea V1.0, is modeled and validated against independent control data. The results show that the multilayer approach fits the gravity data better than the traditional single-layer approach, particularly in regions with topographical variation. An Akaike information criterion (AIC) test shows that the multilayer model obtains a smaller AIC value and achieves a better balance between the goodness of fit of data and the simplicity of the model. Further, an evaluation using independent GPS/leveling data tests the ability of regional models computed from different approaches towards realistic extrapolation, which shows that the accuracies of the QGNSea V1.0 derived from the multilayer approach are better by 0.4, 0.9, and 1.1 cm in the Netherlands, Belgium, and parts of Germany, respectively, than that using the single-layer approach. Further validation with existing models shows that QGNSea V1.0 is superior with respect to performance and may be beneficial for studying ocean circulation between the North Sea and its neighboring waters.

Exploring the Impact of Climate Variability on Malaria Transmission Using a Dynamic Mosquito-Human Malaria Model.

Introduction:The reasons for malaria resurgence mostly in Africa are yet to be well understood. Although the causes are often linked to regional climate change, it is important to understand the impact of climate variability on the dynamics of the disease. However, this is almost impossible without adequate long-term malaria data over the study areas.Methods:In this study, we develop a climate-based mosquito-human malaria model to study malaria dynamics in the human population over KwaZulu-Natal, one of the epidemic provinces in South Africa, from 1970-2005. We compare the model output with available observed monthly malaria cases over the province from September 1999 to December 2003. We further use the model outputs to explore the relationship between the climate variables (rainfall and temperature) and malaria incidence over the province using principal component analysis, wavelet power spectrum and wavelet coherence analysis. The model produces a reasonable fit with the observed data and in particular, it captures all the spikes in malaria prevalence.Results:Our results highlight the importance of climate factors on malaria transmission and show the seasonality of malaria epidemics over the province. Results from the principal component analyses further suggest that, there are two principal factors associated with climates variables and the model outputs. One of the factors indicate high loadings on Susceptible, Exposed and Infected human, while the other is more correlated with Susceptible and Recovered humans. However, both factors reveal the inverse correlation between Susceptible-Infected and Susceptible-Recovered humans respectively. Through the spectrum analysis, we notice a strong annual cycle of malaria incidence over the province and ascertain a dominant of one year periodicity. Consequently, our findings indicate that an average of 0 to 120-day lag is generally noted over the study period, but the 120-day lag is more associated with temperature than rainfall. This is consistence with other results obtained from our analyses that malaria transmission is more tightly coupled with temperature than with rainfall in KwaZulu-Natal province.

Features of 3–7-day planetary-wave-type oscillations in F-layer vertical drift and equatorial spread F observed over two low-latitude stations in China

Abstract. Recent studies on the equatorial atmosphere–ionosphere coupling system have shown that planetary-wave-type oscillations, as an important seeding mechanism for equatorial spread F (ESF), play an important role in ESF irregularity development and its day-to-day variability in the equatorial latitudes. In this study, ionosonde virtual height and ESF measurements over Sanya (18.4° N, 109.6° E; 12.8° N dip latitude) and meteor radar neutral-wind measurements over Fuke (19.5° N, 109.1° E; 14° N dip latitude) during 2013 are used to investigate the features of planetary-wave-type oscillations in both the lower atmosphere and the ionosphere and their possible influences on ESF occurrence under the weak solar maximum year. The ∼ 3-day and ∼ 7-day planetary-wave-type oscillations have been observed in the neutral zonal winds and the time rate of change in F-layer virtual heights. According to the propagation characteristics, the 3-day and 7-day planetary-wave-type oscillations are basically recognized as ultrafast and fast Kelvin waves, respectively. With increasing heights, the 3-day wave oscillations are gradually amplified, while the 7-day wave oscillations are generally constant. By performing a cross-wavelet transform on the onsets of ESF and the vertical drifts of the F layer, we found that there are simultaneously occurring 7-day and 3-day common wave oscillations between them. The 7-day waves are mainly in the inversion phase, while the 3-day waves are mostly in an in-phase state, indicating that the 7-day waves may play a main role in ESF initiation. Approximate delays of 6 days for the 7-day waves and 5 days for the 3-day waves in their propagation upward from the lower atmosphere to the ionosphere are evaluated with wavelet power spectrum analysis. The estimated upward velocities from these time delays provide consistent evidence that the 7-day and 3-day waves propagate vertically upward with typical Kelvin wave characteristics. The results highlight the role of planetary-wave-type oscillations in the initiation and development of ESF in the Chinese low-latitude region.

Analysis of longer period variation of the Kuroshio Current intrusion into the Luzon Strait using rectified wavelet power spectra

Longer period variation of the Kuroshio into the Luzon Strait (LS) was identified using acoustic Doppler current profiler (ADCP) observations as well as pressure and temperature time series data recorded by two TDs (manufactured by the RBR Ltd.) at mooring station N2 (20°40.441′N, 120°38.324′E). The ADCP was deployed at depths of 50–300m between July 7, 2009 and April 10, 2011, and the TDs at around 340 and 365m between July 9, 2009 and July 9, 2011. Observations provide strong evidence of longer period variation of the Kuroshio into the LS using the Vector rotary spectra (VRS) and Rectified wavelet power spectra analysis (RWPSA). RWPSA of the observations allowed the identification of two types of dominant periods. The first type, with the strongest power spectral density (PSD), had a dominant period of 112d and was found throughout the upper 300m. For example, the maximum PSD for western and northern velocity components time series were 3800 and 3550 at 50m, respectively. The maximum power spectral density decrease with deeper depths, i.e., the depth dependence of maximum PSD. The 112d period was also identified in the pressure and temperature time series data, at 340m and 365m. Combined RWPSA with VRS and mechanism analysis, it is clear that the occurrence of the most dominant period of 112d in the upper 300m is related to the clockwise meandering of the Kuroshio into the LS, which is caused by westward propagating stronger anticyclonic eddies from the interior ocean due to the interaction of Rossby eddies with the Kuroshio. The second type of dominant period, for example a 40d period, is related to the anticlockwise meandering of the Kuroshio. The final dominant period of 14d coincides with the fortnightly spring-neap tidal period.

Condition monitoring and fault diagnosis of a small permanent magnet generator

Small wind turbines are often used in remote locations, making them difficult and expensive to repair. This suggests the need for remote condition monitoring and fault diagnosis which has not been used extensively for small turbines. In order to investigate small direct drive wind turbine generators working at variable speed and develop new condition monitoring and fault diagnosis techniques, a test facility based on a 500 W permanent magnet generator was built. The investigation concentrated on mechanical faults which include ball bearing outer race defect and a rotor imbalance. Electrical load imbalance was also investigated. Imbalance detection was performed through wavelet power spectrum analysis of vibration signals. Three time–frequency analysis techniques were performed on vibration signals and performances are compared. These were short time Fourier transforms, continuous wavelet transform, and order analysis. Order analysis proved to be a simple, intuitive, and reliable technique for vibration analysis under variable speed.

Google trends-enabled digital pharmacovigilance: Monitoring interest towards antidepressants and their usage patterns in Italy

Introduction The Internet is playing a major role in nowadays life and more often psychiatric patients are using it as a valuable source of information. Furthermore, the new media can be exploited for providing them with personalized psycho-educational interventions and counseling. On the other hand, a misuse of the new technologies can lead to cyber-addiction behaviors and to others psychopathologies. Objectives and aims In this contribution, we want to explore the Internet pattern of searching online for antidepressants in the Italian population. The prescriptions and usage of these drugs have been increasing in the last years, and therefore constitute an important economic burden for the National Health System (NHS). Methods We analyzed the hit-search volumes with Google Trends, an online tracking system of Internet hit-search volumes, and the wavelet power spectrum analysis (WPSA), a mathematical technique that decomposes a time series into time versus frequency space. The hist-search volume data were compared with the data provided by the Italian National Drug Agency. Pearson correlation was used and P -values less than 0.05 were considered to be statistically significant. Results We found a seasonality and cyclical pattern in searching online for antidepressants, as confirmed by the WPSA. Moreover, the pattern was increasing throughout the years, reflecting the usage pattern as recorded and monitored by the Italian Drug Agency. Pearson correlation yielded a value of 0.98 with a P -value of 1.4210 −5 . Conclusion Digital pharmacovigilance can be employed as a complementary approach together with the classical traditional methodology.

Comparison of the Effect of Different Alcohol Additives with Blended Fuel on Cyclic Variation in Diesel Engine

Blended biodiesel-diesel fuel approved as a commercial fuel for unmodified diesel engine in many countries up to 20% (B20). Biodiesel fuel properties have limited their application in diesel engines at high blending ratio therefore, chemical additives introduced as a vaible option to improve these properties. Hence, in the present study, the effect of alcohol additived with biodiesel-diesel blended fuel B30 on diesel engine cyclic variations was investigated with 6% of two alcohol additives (ethanol and butanol). The in-cylinder pressure analyses results reveal that the lowest coefficient of variation indicated for the blended fuel B30 without additives. Furthermore, the engine cyclic variability increases above that of diesel fuel when using alcohol additives with blended fuel B30 with higher engine cyclic variation for the blended fuel B30 with ethanol compared to butanol. The results of wavelet power spectra analysis reveal that the in-cylinder pressure variations exhibit different types of behavior varying from intermittent fluctuations for B30 without additive to strongly periodic oscillations for B30 with alcohol additives compare to that of diesel fuel. Furthermore, the global wavelet spectra show that the overall spectral power increases when using alcohol additives with the blended fuel B30, which is in agreement with the coefficient of variation results.

Googling Insects as a New Trend in Cultural Entomology: An Italian Perspective

Cultural entomology (CE) explores the interactions between the world of insects and mankind. Since the inter- net plays a major role in nowadays life, it would be of great interest to investigate the insects-related internet usage and activities. However, there are very few studies about this. For this reason, inspired by the seminal work carried out by the Japanese Takada, we decided to replicate his findings. We analyzed with Google Trends and with the wavelet power spec- trum analysis (WPSA) the hit-search volumes of the most common insects. We found that the five most commonly searched insects are bees, butterflies, mosquitoes, ants and spiders which are arachnids, but are commonly believed to be insects. We found a seasonality for some insects, as confirmed by the WPSA, and with peaks related to the seasonal pe- riod in which the insects are most visible, while we could not detect any regularity or trend for other insects, which are not clearly related to any particular season. In addition, we proved that, at least in some cases, hit-search volumes were influ- enced by the media and that the degree of seasonal regularity as measured by the WPSA was variable. Thus, we have proven the robustness of previous finding, extending their validity also in another culture and another context. Therefore, rather than being confined to a specific culture, googling insects could be a universal behavior and attitude, even though with some cross-cultural differences. Further systematic research is needed to shed light on this topic.

Equatorial ionization anomaly variability over the Brazilian region during boreal sudden stratospheric warming events

AbstractThis study refers to the connection between the stratosphere and ionosphere, investigating, specifically, the behavior of the equatorial ionization anomaly (EIA) and ionospheric effects over the Brazilian region during sudden stratospheric warming (SSW) events. We studied three major warmings that occurred in the Northern Hemisphere winter 2007–2008, 2008–2009, and 2009–2010 and a minor warming that occurred in 2010–2011. The solar activity was low for the first two cases and relatively moderate for the last two. In this study the EIA behavior was investigated using the ΔTEC (total electron content) parameter, which expresses the EIA relative intensity for the Brazilian sector. The results for the Brazilian region show, mainly after SSW temperature peak, an increase in the EIA intensity in the morning, followed by a decrease in the afternoon. As identified through ΔTEC signatures and consistently confirmed through wavelet power spectra analysis, this semidiurnal behavior is preserved for a number of days equal to the polar region thermal stabilization phase and it is very similar to the results obtained in pioneer studies in the Peruvian sector, in which TEC data was also used. In some cases the TEC negative variation is stronger than the positive, being noticeably more intense around the prereversal enhancement time, when the EIA is strongly suppressed in the Brazilian sector.

Study on Nonlinear Cutting Forces Phenomenon of Difficult-to-Machining Materials

To investigate the nonlinear phenomena of cutting forces when machining difficult-to-machining materials in the high-speed cutting process, system experiments by factorial design and Latin hypercube sampling design were conducted. The cutting force nonlinear characteristics were analyzed in time domain and frequency domain through wave-let analysis and power spectrum analysis. Experiments indicated that in the high-speed milling process, the characteristic curves of primary cutting forces could not strictly maintain their linearity with the variation of cutting parameters, the effect of one cutting parameter on primary cutting forces is sensitive to the combination of cutting parameters, and a lower frequency periodic signal appears when the cutting speed is above 471 m/min (spindle speed is 3000 r/min).