Frequency Variability Research Articles

The relationship between pesticide exposure and neuropathy in farmers in Wuluhan district

Farmers rely heavily on pesticides to protect crops from pests. Pesticides exposure will inhibit the acetylcholinesterase enzyme and will cause cholinergic symptoms which manifest as neuropathy. The research was conducted in March-April 2023 in Wuluhan District, Jember Regency. Pesticide exposure was evaluated through interviews using a pesticide exposure questionnaire, while neuropathy was evaluated through interviews and physical examination using the Diabetic Neuropathy Symptom Score-Indonesian version (DNS-Ina) and Diabetic Neuropathy Examination-Indonesian version (DNE-Ina) questionnaires. Univariate data analysis and bivariate analysis using the Chi-Square test. The results of this study showed that most of the study subjects had worked 10 years, the frequency of using pesticides ≤2 times per week, the duration of using pesticides ≤3 hours per day, the use of PPE is lacking. Bivariate analysis showed that neuropathy occurred in the farmer group, and there was a significant relationship between length of service and neuropathy, as well as the completeness of PPE use and neuropathy. However, there was no relationship between the frequency of pesticide use and neuropathy and the duration of pesticide use and neuropathy. The conclusion of this study is that the variable length of service and the completeness of the use of PPE have a relationship with the symptoms of neuropathy in farmers. While the variables of frequency and duration of use of pesticides are not related to neuropathy in farmers.

Enhancing efficiency and measuring sloshing in oscillating water column (OWC) systems: An experimental investigation of novel inlet geometry optimization and innovative measurement method

Sea wave characteristics could be the most crucial sloshing occurrence caused by OWCs. In this paper, an OWC with different inlet geometries has been investigated experimentally to optimize the performance and reduce sloshing. Eight wave gauges (WG) are applied to measure water free surface to determine the sloshing. The results showed that the converter performance decrease when sloshing occurs. To reduce sloshing, four inlet openings were installed at the inlet of OWC, and to achieve optimal efficiency in sloshing conditions, the geometry optimization done by genetic algorithm; then, the converter's performance with optimum inlet was experimentally investigated, sloshing phenomenon was observed in 4 frequencies in converter without opening; However, after installing the optimal opening, sloshing occurred in only one frequency, and also in this case, sloshing was 42 % reduced. The data correlation results showed a positive correlation between the frequency and the Top Free Surface of water inside the OWC (shown by a line called TFS) angle. At the same time, there is a negative correlation between the frequency and the flow rate, pressure difference, and power generated. The comparison of the converter results with opening and without opening shows that the correlation between frequency and other variables is always lower in the case with opening. Also, geometry optimization improved the sloshing frequency's 42.89 % performance.

EFL Students’ Self-Regulated Online Learning in Post-Pandemic Hybrid Education

This study measured self-regulated online learning skills of English language learners in post-pandemic hybrid education. A quantitative survey design was adopted and students majoring in English Language and Literature at a state university in Türkiye in 2021-2022 academic year constituted the population of the research. The Self-Regulated Online Learning Scale was administered to the students of three active grades in the department (preparatory, first and second grades). As a result of statistical analyses, the findings demonstrated that the students’ self-regulated online learning skills were at a moderate level both in general and with respect to self-regulation dimensions. Additionally, no significant difference was observed in students’ reported self-regulated learning across groups of gender, years of education and perceived foreign language levels whereas significant differences were revealed for the variable of frequency of attendance to online classes. The results are discussed and some recommendations are provided.

Investigations of the mechanical properties of dissimilar joint of GTD-111 superalloy and 316 stainless steel obtained by laser welding

The objective of this study is to improve the mechanical properties of dissimilar joint between 316 stainless steel and GTD-111 superalloy obtained by laser welding. Hence, the input variables of pulse frequency, welding speed and laser power were employed to optimize the output variables of weld penetration, hardness and tensile strength through the desirability function technique and response surface methodology. In order to study the changes of microstructure in the welded samples, the optical and scanning electron microscopies were applied. It was observed that an increase in the laser power from 1500 to 2500 W enhanced the penetration depth of weld, while it worsened the hardness and tensile strength owing to nucleation of solidification cracks and formation of Laves phase caused by segregation of Ta, Ti, Nb, W, and Mo elements. Moreover, the faster welding speed up to 1.5 mm/s resulted in a decrease in the penetration depth and an increase in the hardness and tensile strength, which is due to the nucleation of a small dendritic structure and the nucleation of fewer Laves phase owing to lesser heat input. When the variables of pulse frequency and laser power increased simultaneously, the liquation cracks were formed within HAZ of GTD-111 superalloy due to nucleation of γ′-γ eutectic phase, while the cracks and shrinkage voids were observed within HAZ of 316 stainless steel. The results of desirability function technique indicated that the optimum mechanical properties have been obtained at a pulse frequency of 15 Hz, welding speed of 0.8 mm/s and a laser power of 1550 W.

Longitudinal resting-state EEG in amyloid-positive patients along the Alzheimer’s disease continuum: considerations for clinical trials

BackgroundTo enable successful inclusion of electroencephalography (EEG) outcome measures in Alzheimer’s disease (AD) clinical trials, we retrospectively mapped the progression of resting-state EEG measures over time in amyloid-positive patients with mild cognitive impairment (MCI) or dementia due to AD.MethodsResting-state 21-channel EEG was recorded in 148 amyloid-positive AD patients (MCI, n = 88; dementia due to AD, n = 60). Two or more EEG recordings were available for all subjects. We computed whole-brain and regional relative power (i.e., theta (4-8 Hz), alpha1 (8-10 Hz), alpha2 (10-13 Hz), beta (13-30 Hz)), peak frequency, signal variability (i.e., theta permutation entropy), and functional connectivity values (i.e., alpha and beta corrected amplitude envelope correlation, theta phase lag index, weighted symbolic mutual information, inverted joint permutation entropy). Whole-group linear mixed effects models were used to model the development of EEG measures over time. Group-wise analysis was performed to investigate potential differences in change trajectories between the MCI and dementia subgroups. Finally, we estimated the minimum sample size required to detect different treatment effects (i.e., 50% less deterioration, stabilization, or 50% improvement) on the development of EEG measures over time, in hypothetical clinical trials of 1- or 2-year duration.ResultsWhole-group analysis revealed significant regional and global oscillatory slowing over time (i.e., increased relative theta power, decreased beta power), with strongest effects for temporal and parieto-occipital regions. Disease severity at baseline influenced the EEG measures’ rates of change, with fastest deterioration reported in MCI patients. Only AD dementia patients displayed a significant decrease of the parieto-occipital peak frequency and theta signal variability over time. We estimate that 2-year trials, focusing on amyloid-positive MCI patients, require 36 subjects per arm (2 arms, 1:1 randomization, 80% power) to detect a stabilizing treatment effect on temporal relative theta power.ConclusionsResting-state EEG measures could facilitate early detection of treatment effects on neuronal function in AD patients. Their sensitivity depends on the region-of-interest and disease severity of the study population. Conventional spectral measures, particularly recorded from temporal regions, present sensitive AD treatment monitoring markers.

GeneToCN: an alignment-free method for gene copy number estimation directly from next-generation sequencing reads

Genomes exhibit large regions with segmental copy number variation, many of which include entire genes and are multiallelic. We have developed a computational method GeneToCN that counts the frequencies of gene-specific k-mers in FASTQ files and uses this information to infer copy number of the gene. We validated the copy number predictions for amylase genes (AMY1, AMY2A, AMY2B) using experimental data from digital droplet PCR (ddPCR) on 39 individuals and observed a strong correlation (R = 0.99) between GeneToCN predictions and experimentally determined copy numbers. An additional validation on FCGR3 genes showed a higher concordance for FCGR3A compared to two other methods, but reduced accuracy for FCGR3B. We further tested the method on three different genomic regions (SMN, NPY4R, and LPA Kringle IV-2 domain). Predicted copy number distributions of these genes in a set of 500 individuals from the Estonian Biobank were in good agreement with the previously published studies. In addition, we investigated the possibility to use GeneToCN on sequencing data generated by different technologies by comparing copy number predictions from Illumina, PacBio, and Oxford Nanopore data of the same sample. Despite the differences in variability of k-mer frequencies, all three sequencing technologies give similar predictions with GeneToCN.

One year monitoring of an offshore wind turbine: Variability of modal parameters to ambient and operational conditions

This paper presents the variation of identified modal parameters of an offshore wind turbine (OWT) over one year of continuous monitoring. The considered OWT is a Haliade 150–6 MW GE turbine on a jacket substructure at the Block Island Wind Farm in Rhode Island, U.S. The turbine was instrumented with a monitoring system including accelerometers, strain gauges, inclinometers, and a data acquisition system with automatic data transfer to cloud storage. Continuous vibration measurements of the OWT have been collected over one year from April 2021 to April 2022. An automated output-only operational modal identification approach is developed to extract modal parameters of the OWT over this one-year period using windows of 10-min data. The identified modal parameters of the first few vibration modes show variability and correlation with several ambient and operational conditions. It is observed that the identified natural frequencies and damping ratios of the first side-to-side (SS) mode are stable over time and have very small variation, but those of the first fore-aft (FA) mode show significant variability. The second FA/SS modes can only be identified with reasonable accuracy when the turbine is in idle condition. Similar to the first FA/SS modes, the second FA mode has larger variability in frequencies and damping ratios than the second SS mode because of the aerodynamics effects. The system identification results over one full year verify the effectiveness and robustness of the proposed approach for long-term monitoring of this OWT and serve as the reference database.

Feasibility and Utility of a Smartphone Application-Based Longitudinal Cough Monitoring in Chronic Cough Patients in a Real-World Setting.

This study evaluated the feasibility and utility of longitudinal cough frequency monitoring with the Hyfe Cough Tracker, a mobile application equipped with cough-counting artificial intelligence algorithms, in real-world patients with chronic cough. Patients with chronic cough (> 8-week duration) were monitored continuously for cough frequency with the Hyfe app for at least one week. Cough was also evaluated using the Leicester Cough Questionnaire (LCQ) and daily cough severity scoring (0-10). The study analyzed adherence rate, the correlation between objective cough frequency and subjective scores, day-to-day variability, and patient experience. Of 65 subjects consecutively recruited, 43 completed the study. The median cough monitoring duration was 13.9days, with a median adherence of 91%. Study completion was associated with baseline cough severity, and the adherence rate was higher in younger subjects. Cross-sectional correlation analyses showed modest correlations between objective and subjective cough measures at the group level. However, in time series correlation analyses, correlations between objective and subjective measures widely varied across individuals. Cough frequency had greater day-to-day variability than daily cough severity scores in most subjects. A patient experience survey found that 70% of participants found the cough monitoring helpful, 86% considered it acceptable, and 84% felt it was easy to use. Monitoring cough frequency longitudinally for at least one week may be feasible. The substantial day-to-day variability in objective cough frequency highlights the need for continuous monitoring. Grasping the implications of daily cough variability is crucial in both clinical practice and clinical trials.

Examining Workflow for Simulated Pediatric Emergency Medical Services Care

Purpose: Workflow analysis is an important approach for understanding clinical care in complex systems. This is particularly true for low frequency events such as the care of children in the out-of-hospital setting. The purpose of this study was to characterize emergency medical service (EMS) workflow in the care of children during simulated emergency, prehospital encounters.
 Methods: This is a secondary analysis exploring high-fidelity videorecorded simulations, performed by emergency personnel. Two scenarios were used in 19 simulations which consisted of a 15-month and a 1-month old with respiratory decompensation and shock requiring intravenous fluid, respiratory support, and medication administration. One trained investigator performed review of the videos of teams EMS practitioners, quantifying the sequence and number of tasks performed and time to completion of the simulated intervention. The variance in sequence of tasks was quantified using the Levenshtein distance. We quantified the proportion of time with no activity (idle time) and temporal overlap (team multitasking time).
 Results: We identified 17 types of distinct tasks performed during the simulation. There was high variability across simulations in the sequences, types, and number of tasks performed. Team multitasking was noted in all scenarios, with a mean of 99% multitasking ratio (range: 52-202%). Mean proportion of idle time was 4% (range: 0-11%). Weight estimate, intravenous or intraosseous access, radio report, blood glucose level (BGL), medication administration, pulse check and respiration check were observed in all videos. Other tasks were observed in only a proportion of scenarios with varying frequencies. Median number of differences in sequence of tasks between scenarios was 15.
 Conclusions: Our analysis found a high percentage of team multitasking and significant variability in frequency and sequence of task completion. Further research is needed to assess the reasons and effect of this degree of variability on the efficiency and effectiveness of prehospital interventions.

Headaches treatment with EMG biofeedback: a focused systematic review and meta-analysis.

The aim of this paper was to present an up-to-date evaluation of the efficacy of EMG-biofeedback (EMG-BFB) for primary headaches and to address possible mediators of outcome. PubMed, Scopus, Embase and Pedro databases were searched from inception to May 1, 2023. All randomized controlled trials (RCT) studies using an EMG-BFB to treat headache have been included in this systematic review. The current systematic review was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations and was registered in the PROSPERO database (CRD42022312827). Methodological quality was assessed through the Risk of Bias tool 2 (RoB 2). The effect sizes and 95% confidence interval (CI) were calculated by random-effect models on frequency, intensity, and duration variables. Egger regression and the Begg-Mazumdar rank correlation test were used for publication bias. A total of 3059 articles were identified through the database searches. 29 articles, involving 1342 participants, met the inclusion criteria for the systematic review; of them, 4 were included in the meta-analysis. Ten studies reported a significant improvement in the EMG-BFB group with respect to the control group. Meta-analyses show a reduction in the intensity of attacks in patients subjected to EMG-BFB (ES 0.21 [(95% CI=-0.02; 0.44), P value=0.07] based on 293 patients). EMG-BFB represents a non-pharmacological approach to headache treatment as shown via qualitative synthesis, despite not impressive results, this technique can be particularly useful in paediatric or in adult patients who cannot undergo drug therapies. Quantitative synthesis revealed a promising effect in the intensity of headaches attacks. Moreover, no significant effect was found about the effectiveness of EMG-BFB in the reduction of frequency and durations of headache attacks. Future studies with new multimodal technologic assessment and following RCT guidelines can unmask the potentiality of EMG-BFB in the treatment of headache.

건설현장의 불안전상태·행동이 사고재해율의 빈도·강도에 미치는 영향

Although the government is strengthening safety inspections and reforming the system, the number of construction accident victims (work accident victims) and the accident rate has been increasing over the past five years (2018~2022). This requires analyzing which areas to focus on through construction disaster data.
 In this study, we intend to analyze construction accidents using the Risk Assessment theory. According to the Risk Assessment theory, Hazard was classified into the frequency and intensity of accident rates. The research problem is, First, how unstable state and unstable behavior at construction sites will effect the factors that cause frequent accidents (the frequency of accident rates). Second, unstable state and unstable behavior at construction sites will affect the type of disaster (intensity of accident rate) in which disaster occur strongly.
 A survey was conducted between June and July 2023 on 189 managers and workers working at domestic construction sites to find out the effect of unsafe state and unsafe behavior on frequency and intensity at construction sites. The questionnaire consisted of 4 general characteristics, 7 independent variables (unstable state, unstable behavior), and 7 dependent variables (frequency, intensity). The analysis method was found to be good as a result of the validity and reliability analysis of the survey item, and frequency analysis and correlation analysis were conducted using the Jamovi program, and hypothesis verification was conducted through regression analysis.
 As a result of the study, the hypothesis on the unstable state of the construction site was rejected by the significant probability p value, and all hypothesis on the unstable behavior were adopted. The research conclusions are as follows. First, controlling for anxiety behavior by major construction sites reduces the frequency of accidents rates. Second, controlling for anxiety behavior by major disaster type at construction sites reduces the intensity of accidents rate. Third, controlling unstable behavior at construction sites reduces the frequency and intensity of accident rates. This means that continued research into unstable behavior at construction sites is needed.

Qualification of the differential leukocyte count and immunophenotyping in cryopreserved ex vivo whole blood assay.

We developed a flow cytometry-based assay, termed Differential Leukocyte Counting and Immunophenotyping in Cryopreserved Ex vivo whole blood (DLC-ICE), that allows quantification of absolute counts and frequencies of leukocyte subsets and measures expression of activation, phenotypic and functional markers. We evaluated the performance of the DLC-ICE assay by determining inter-operator variability for processing fresh whole blood (WB) from healthy donors collected at multiple clinical sites. In addition, we assessed inter-operator variability for staining of fixed cells and robustness across different anticoagulants. Accuracy was evaluated by comparing DLC-ICE measurements to real-time cell enumeration using an accredited hematology analyzer. Finally, we developed and tested the performance of a 27-colour immunophenotyping panel on cryopreserved fixed WB and compared results to matched fresh WB. Overall, we observed <20% variability in absolute counts and frequencies of granulocytes, monocytes and lymphocytes (T, B and NK cells) when fresh WB was collected in different anti-coagulant tubes, processed or stained by independent operators. Absolute cell counts measured across operators and anti-coagulants using the DLC-ICE method exhibited excellent correlation with the reference method, complete blood count (CBC) with differential, measured using a hematology analyzer (r2 > 0.9 for majority of measurements). A comparison of leukocyte immunophenotyping on fresh WB versus DLC-ICE processed blood yielded equivalent and linear results over a wide dynamic range (r2 = 0.94 over 10-104 cells/μL). These results demonstrate low variability across trained operators, high robustness, linearity and accuracy, supporting utility of the DLC-ICE assay for large cohort studies involving multiple clinical research sites.

Cardioautonomic lability assessed by heart rate variability changes in Royal Canadian Mounted Police cadets during the cadet training program.

The current study examined variations in cardioautonomic lability during the Royal Canadian Mounted Police (RCMP) Cadet Training Program (CTP) between cadets starting their training who did or did not screen positive for one or more mental health disorders (i.e., posttraumatic stress disorder [PTSD], major depressive disorder [MDD], social anxiety disorder [SAD], generalized anxiety disorder [GAD], panic disorder [PD], alcohol use disorder [AUD]). Electrocardiogram (ECG) signals integrated into Hexoskin garments were used to record ECG and heart rate Over the 26-week CTP. There were 31 heart rate variability (HRV) parameters calculated using Kubios Premium HRV analysis software. Mann-Whitney U-tests were used to perform groupwise comparisons of participant raw values and HRV during the CTP. A total of 157 cadets (79% male) were screened for any mental disorder using self-report surveys and then grouped by positive and negative screening. Analyses indicated a statistically significant (p < 0.05) decrease in low frequency (LF): High Frequency (HF) variability during CTP, but only for cadets who endorsed clinically significant anxiety symptoms on the GAD-7 at the start of their training. There were no other statistically significant groupwise differences. The results indicate the participants have excellent cardiac health overall and suggest potentially important differences between groups, such that cadets who endorsed clinically significant anxiety symptoms on the GAD-7 showed less variability in the LF:HF ratio over the course of the CTP. The relatively lower variability suggests decreased parasympathetic tone in those without clinically significant anxiety symptoms. The results also have important implications for future investigations of cardioautonomic dysfunction and chronic hypothalamic pituitary adrenal (HPA) axis deviations in policing populations with anxiety disorders; specifically, cardioautonomic inflexibility related to cardiovascular morbidity and mortality. In any case, the current results provide an important baseline for future cardiac research with cadets and serving officers.

АКУСТИЧКЕ КАРАКТЕРИСТИКЕ ГЛАСА И ГОВОРА ОДРАСЛИХ ОСОБА СА АТАКСИЧНОМ ДИЗАРТРИЈОМ

The aim of this study was to determine the acoustic characteristics of voice and speech in adults with ataxic dysarthria, and to examine the extent to which they differ from those of typical speakers. The sample consisted of 30 patients with ataxic dysarthria, ages 21 through 82 (M = 56.07). Using the computer programme for multidimensional voice analysis (MDVP), the individual values of 10 acoustic voice parameters were determined for each sex. Additionally, the programme provided the frequency values of the first two formants for all five vowels of the Serbian language, based on the participants’ reading of the Balanced Text. The results of the analysis showed statistically significant differences in the values of the acoustic parameters between the participants with ataxic dysarthria and the reference values valid for typical speakers, which were generated by the MDVP. These differences were observed in parameters indicating voice frequency variability (F0, Fhi, Flo, STD, Jitt, vF0), voice intensity variability (Shim and vAm), and the presence of voice interruptions (DVB) and voiceless periods (DUV). Furthermore, a statistically significant difference was found between participants with ataxic dysarthria and typical speakers in the second formant (F2) of the vowels /E/ (p &lt;0.01), /I/ (p &lt;0.01), and /U/ (p &lt;0.05). The significant deviations from the norms applicable to typical speakers indicate the substantial changes present in the voice and speech of individuals with ataxic dysarthria.

Examining past and projecting future: an 800-year streamflow reconstruction of the Australian Murray river

Managing water security and sustaining ecosystem functions under future warming poses substantial challenges for semi-arid regions. The Murray–Darling Basin (MDB) is particularly vulnerable given the considerable demand for water that underpins Australia’s agricultural production and contribution to the national economy. Understanding future drought risk requires a robust assessment of natural variability in drought length, frequency, and magnitude. In the absence of long instrumental records, past drought characteristics can be inferred from paleo-records. We reconstruct over 800 years of Murray River streamflow using a suite of tree-ring chronologies from regions with strong climate teleconnections to the MDB. The reconstruction (1190–2000 CE) captures a broad spectrum of natural climate variability, not fully represented in instrumental records, contributing to an improved understanding of the occurrence rate of multi-year droughts. We found that the Millennium Drought, which occurred in the 2000s, was the most severe (joint duration, magnitude, and peak) during the 800-year reconstruction. The return period of this event is estimated to be ∼2500 years. However, droughts in the early-1200s were of a longer duration and similar magnitude to the Millennium Drought. We used climate models to assess how the occurrence probability of severe droughts might change in the future. Compared to the 800-year baseline, climate models project an increase in future drought severity. While the increase in drought occurrence is within the uncertainty range for most future projections, the driest forecast shows a significant increase in the likelihood of severe droughts compared to natural variability. Our results highlight the need for water management strategies not to rely solely on instrumental data as it may not fully represent current and future risks. Ensuring a resilient MDB under future warming will require a robust water security policy that captures a broader range of natural and anthropogenic variability than currently recognised.

EFFECTS OF PHYSICAL EXERCISE ON HEART RATE VARIABILITY IN POSTMENOPAUSAL WOMEN: A SYSTEMATIC REVIEW WITH META-ANALYSIS OF RANDOMIZED CONTROLLED TRIALS

Background: Heart rate variability is a marker of the cardiac autonomic system and is associated with the mortality of cardiovascular disease. Decreased physical exercise may induce a lower level of heart rate variability and poor cardiac function in postmenopausal women. This review aimed to address the relationships between physical exercise and heart rate variability and to provide clinical evidence for the formulation of exercise prescriptions for improving cardiovascular function in postmenopausal women. Method: Authors searched 5 databases including PubMed, Scopus, Embase, Cochrane Library, and Web of Science to identify eligible articles between database inception and May 13, 2023. All randomized controlled trials of exercise intervention for postmenopausal women were included, only English articles and without date restrictions. The standardized mean differences of heart rate variability time domain parameters and frequency domain parameters were calculated, comparing postmenopausal women who did and who did not exercise via random-effects meta-analyses. The quality of the evidence was assessed with the Cochrane risk of bias tool. This study was registered on PROSPERO, number CRD42020208037.

Influence of transcutaneous electrical nerve stimulation on the distance walked by older adults during the 6-min test of walking endurance

The purpose of our study was to compare the influence of two types of transcutaneous electrical nerve stimulation (TENS) on the performance of older adults on the 6-min test of walking endurance and on the ability to maintain balance during upright standing. Twenty-six healthy older adults (72 ± 5.4 yrs) performed tests of motor function while TENS was applied to the tibialis anterior and rectus femoris muscles of each leg. Linear mixed models were used to compare the influence of TENS on walking distance in a 6-min test of walking endurance and on sway-area rate in tests of standing balance. There was a significant decrease in the distances walked in each minute of the 6-min walk test for both the Continuous and Burst TENS modes compared with Baseline (p < 0.01 and p < 0.001, respectively). The influence of TENS on walking distance was associated with several significant effects on the mean and coefficient of variation for stride length and stride frequency between the first and last minute of the test and between the two TENS modes and the Baseline values. In contrast, there was no significant effect of TENS on sway-area rate in any balance test, which indicates that the supplementary sensory feedback compromised walking performance of older adults but not the ability to maintain balance during upright standing.

A 900-Year Isotopic Proxy Rainfall Record from Northeastern Botswana

A high-resolution climate archive was reconstructed based on carbon isotope analysis and radiocarbon dating of the Chapman baobab in northeastern Botswana. The Chapman baobab, which exhibited an open ring-shaped structure composed of six stems, collapsed in January 2016 during an intense El Niño event. Two samples belonging to the oldest stems were investigated in order to obtain a proxy rainfall record, which provides insight into the precipitation regime over the last millennium, evincing centennial and decadal scale variability. The results indicate that the Medieval Warm Period was marked by relatively stable precipitation, whereas rainfall variability and drought frequency increased during the Little Ice Age. The investigated area has experienced both wetter and drier conditions in the past. The wettest conditions of the last millennium were registered before 1450 while the driest period occurred in 1835. For southern Africa, inter-annual rainfall variability is mainly associated with sea surface temperatures in the Agulhas Current core region, which determine the east–west displacement of tropical temperate troughs. Previous studies suggested that positive sea surface temperature anomalies in the Mozambique Channel led to an eastward movement of the troughs but the Chapman record demonstrates a westward displacement in the past, causing drought in northeastern South Africa and wetter conditions in the central part of southern Africa. The positive rainfall correlation with SST anomalies reversed after 1900, causing a gradual decrease in precipitation and confirming the current aridity trend for Botswana. The results contribute to a better understanding of the past climate of southern Africa for which paleoclimate reconstructions remain scarce.

Visualization of the frequency effect of pulsed electric field on enzymatic browning of peel ground tissue

The enzymatic browning behavior of a model ground tissue, banana peel, influenced by the frequency variable of pulsed electric field (PEF), has been visualized and studied. The tissue was PEF-treated with 15 µs pulse at 3.3 kV/cm using trains of 5, 15, and 30 pulses, each varying from 0.1 Hz to 10 Hz; images and electrical conductivity were recorded intermittently throughout the incubation. The degree of browning was quantified with a browning index (BI) term, and the uniformity of browning was visually assessed by inspecting the pattern of pigment distribution. Moreover, the degree of tissue disintegration was calculated using a conductivity-based tissue disintegration index (DI) and compared to the BI and specific energy input. Browning uniformity was found to be significantly affected and increased with decreasing frequency. The effect was most noticeable up to disintegration degree of about 63, DI, or when the frequency of 5 or 15 pulses was reduced from 1 Hz to 0.1 Hz. Remarkably, the decrease at 5 pulses resulted in a significant increase in BI without a substantial increase in DI. The observed effect has been attributed to increased electrophoretic mobility of browning agents along the extracellular path during 0.1 Hz pulsation. Furthermore, lowering the frequency to 0.1 Hz reduced the energy required for a browning level close to saturation by about 57% compared to 10 Hz.

Genetic based density peak possibilistic fuzzy c-means algorithms to cluster analysis- a case study on customer segmentation

Finding the target consumers for a business depends heavily on its market segmentation approach. Applying clustering analysis to consumer segmentation is one of the most common methods. However, most clustering algorithms can easily fall into the local optimum solution. Besides, it can be challenging to handle noise and outliers and determine the optimal parameters. The initial cluster centers can also affect the clustering result. Thus, this study proposes a clustering algorithm that first employs density peak clustering to obtain the initial cluster centers. Then, the proposed method integrates genetic algorithm (GA) with possibilistic fuzzy c-means (PFCM) algorithm, where GA is used to optimize the cluster centers and the parameters of the PFCM algorithm to overcome the problems above. Using eleven benchmark datasets, the computational results demonstrate that the proposed algorithm can provide better and more robust results in terms of accuracy, adjusted rand index (ARI), and normalized mutual information (NMI) compared to previous clustering algorithms. Additionally, the proposed algorithm is used to segment customers of a retail company in a dataset containing recency, frequency, and monetary (RFM) variables. The clustering result for customer segmentation is also very promising.