Coefficient Values Research Articles

Comparison of piperine content, antimicrobial and antioxidant activity of Piper chaba root and stem

Piper chaba (locally known as “Choi Jhal”) is used traditionally as spices and folk medicine in different parts of Bangladesh. One of the most important bioactive compounds in this plant is piperine. In this study, the amount of piperine in P. chaba root and stem was investigated and the optimal solvent for piperine extraction at room temperature was also studied. High performance liquid chromatography (HPLC) was operated using a reverse phase column where methanol and water (70:30) were used as mobile phase. The detection was performed using photo diode array (PID) detector at a wavelength of 345 nm. The standard piperine showed linearity between 0.005 % and 0.04 % and the correlation co-efficient found for the linearity was 0.9933. The percentage of relative standard deviation (RSD) for both retention time and peak area were less than 2.0 %. The theoretical plate number (N) > 3000 and a tailing factor (T) < 1.5 were found in the acceptable range. The recovery percentage (%) of standard piperine was 99.16 %. Low value of co-efficient of variation and standard deviation are recognized for high precision of the method. The highest amount of piperine was found in root extracted with methanol (MR) amounting to 1.75 % in the root powder. The maximum amount of piperine in the stem was 1.59 % when extracted with methanol (MS). The piperine quantification in other extract like n-hexane root (HR), ethyl acetate root (ER), n-hexane stem (HS), ethyl acetate stem (ES) were 0.76 %, 1.69 %, 0.33 % and 1.46 % respectively. Methanol has given the highest yield of piperine compared to ethyl acetate and n-hexane for both root and stem. The developed method was simple, rapid, economic and validated in terms precision, accuracy and recovery. This selective method is found to be repeatable, accurate and successfully utilized for the Piper extract in marketed and pharmaceutical samples with well chromatographic conditions. The ethyl acetate extract of root and stem showed promising DPPH (1, 1-diphenyl-2-picrylhydrazyl) free radical scavenging activity with an IC50 value of 39.62 ± 0.95 μg/mL and 43.85 ± 1.50 μg/mL respectively. The study reports potential antibacterial activity and antifungal activity of P. chaba root and stem extracts. These outcomes revealed that different extracts of P. chaba may be used as natural preservatives.

The 3D-QSAR Study, Molecular Docking, and ADMET Analysis of Darunavir Derivatives of HIV-1 Protease Inhibitors

Background: Acquired Immunodeficiency Syndrome (AIDS) is one of most prevalent infectious diseases in the world , and HIV-1 protease (PR) is a vital target of drug design. Nowadays, three-dimensional quantitative structure-activity relationships (3D-QSAR) are applied to help design new protease inhibitions (PIs). Objective: The primary objective of this study is to apply the 3D-QSAR study to a series of 42 derivatives of Darunavir (DRV) and to design new molecules possessing high antivirus activity. Methods: Partial Least Squares (PLS) were used to cross-validate the dataset of compounds, and the optimal number of principal components (ONC), cross-validate coefficient (q²), standard error of estimate (SEE), non-cross-validated correlation coefficient (R²) and fisher test value (F) were calculated to assess model robustness. In this study, the CoMSIA-DAH model (q²=0.754, r²= 0.988, rpred2=0.57) possessed the highest predicted activity. Newly designed molecules were analyzed by docking studies with compound 25 taken as a template. Results: Within eight newly designed drugs, compound N02 possessed the highest antivirus activity (IC50=0.00461 nM) predicted by the CoMSIA-DAH model. The Surflex-Dock module of SYBYL-X 2.0 was used to affirm the predicted anti-PR activity of the newly designed compounds and the results of docking complex structure could be visualized. All newly designed molecules were in agreement with CSore above four and the docking study revealed that Asp29, Asp30, Ile50, Asp124, Asp128, Asp129 and Ile149 were critical residues in the process of inhibiting PR. Conclusion: One of the main aspects of this study is the successful design of a series of molecules with excellent investigatory values, which elucidates explicit quantitative structure-activity relationships of DRV derivatives and will provide significant suggestions for future pharmaceutical research.

Gender Differences in the Predictive Value of Obesity Indices for Insulin Resistance in Adult Mexican Individuals.

Obesity-linked insulin resistance (IR) is an important risk factor for metabolic diseases, and anthropometric indices are commonly used for risk assessment. The study aimed to assess possible differences between women and men in the predictive value and association of nine obesity indices with IR, as assessed by HOMA-IR, in a nondiabetic adult population. The cross-sectional study included individuals recruited from a hospital in Mexico City. Indices evaluated were waist circumference (WC), hip circumference (HC), body mass index (BMI), waist-to-hip ratio, waist-to-height ratio, visceral adiposity index, body adiposity index (BAI), relative fat mass (RFM), and conicity index (CI). Fasting plasma glucose and insulin were measured to calculate HOMA-IR. Correlation analysis was performed between obesity indices and HOMA-IR. Receiver operating characteristics curve analyses were performed to determine predictive accuracy and cut-off values of obesity indices for IR. A binary logistic regression (BLR) analysis with OR calculation was performed to determine the strength of association with HOMA-IR. We included 378 individuals (59% females, mean age 46.38 ±12.25 years). The highest Pearson coefficient value was observed for BMI among women, while among men, the highest values were found for BMI and BAI. WC among women, and BAI and RFM among men showed the highest sensitivity, while the highest specificity was observed for WHR among women and WC among men with respect to insulin prediction. In the adjusted BLR model, BMI, WC, and WHR among women and WC and RFM and BAI among men were independently associated with IR, showing the highest odds ratio (OR). In Mexican adults, WC, WHR, RFM and BAI could be complementary tools for BMI in screening for IR.

Digital-Based Learning and the Sustainability of Business Education Programmes among College of Education Lecturers in Cross River State

The study examined digital-based learning and the sustainability of business education programs among College of Education lecturers in Cross River State. Two research questions and two null hypotheses guided the study. The study adopted a descriptive survey research design. The study was carried out in Cross River State. The population of this study consisted of forty (40) students in business education from the Federal College of Education Obudu and the College of Education Akamkpe, all in Cross River State. There was no sampling since the population is manageable and accessible to the researchers. A self-developed questionnaire titled “Digital Based Learning and the Sustainability of Business Education Programmes Questionnaire (DBLSBEPQ). A 10-item self-developed questionnaire was validated by three experts. The reliability of the instrument was established using a pilot-testing approach, and the Cronbach's alpha calculation yielded an overall coefficient's value of.78. The mean and standard deviation were used to analyze the responses to the items in the questionnaire, while an independent t-test was used to test the hypotheses at the 0.05 level of significance. The decision level was based on a 2.50 cut-off point. Findings of the study showed that business education lecturers in colleges of education in Cross River State do not adopt nor utilize digital learning tools for the sustainability of business education programs in colleges of education in Cross River. Based on the findings of the study, the researcher concludes that business education lecturers should be able to develop digital skills to enhance their adaptation and the utilization of digital skills for the sustainability of business education programs in Nigerian colleges of education. It was recommended, among others, that the provost of colleges of education should make regular digital technology training programs compulsory for all college lecturers in Nigeria. Received: 19 June 2024 / Accepted: 24 June 2024 / Published: 8 July 2024

Comparative Analysis of Ventilatory Responses during Stress Tests in Patients with Chronic Pain: Implications for Therapeutic Interventions.

Understanding the differences in ventilatory responses during exercise between patients with fibromyalgia and those with other chronic pain disorders is crucial for developing effective therapeutic interventions, especially in exercise to identify the better physical therapy prescription. Both populations face unique challenges that impact their ability to engage in physical activity; yet, the underlying physiological responses can vary significantly. In this context, the methodology of this study entailed conducting a comparative analysis of the ventilatory response during exercise in patients with fibromyalgia and those with other chronic pain disorders. The experimental protocol included a total of 31 participants (n = 13 diagnosed with fibromyalgia and n = 18 diagnosed with other chronic pain conditions). All participants completed a stress test, where the ventilatory parameters were measured in three stages (i.e., resting, incremental exercise, and recovery). The results revealed significant differences (p<0.05) in ventilatory responses between both groups. Patients with fibromyalgia exhibited reduced time for the aerobic threshold and a higher respiratory frequency in the anaerobic threshold compared to those with other chronic pain disorders. Furthermore, fibromyalgia patients demonstrated higher values in the ventilatory coefficient during the test and in the recovery stage. In conclusion, these differences underscore the need for tailored exercise programs that specifically address the unique ventilatory challenges faced by fibromyalgia patients to improve their physical function and overall quality of life.

Application of Electrical Resistivity Sounding Method for Groundwater Exploration in Ugboshi-Afe, Akoko-Edo, Southwestern Nigeria

Schlumberger configuration of Vertical Electrical Sounding (VES) was deplored for groundwater exploration in Ugboshi-Afe study location. A total of nine (9) vertical electrical sounding (VES) locations, spread across the community were occupied to gain insights on the hydrogeological settings within the area. Quantitative computer interpretation of the data yielded three to six geoelectrical layers. The geoelectrical interpretation models were geologically interpreted as: clayey sand/sandy topsoil with resistivity values ranging from 54 Ohm-m to 424 Ohm-m, this is underlain by a relatively high resistivity layer (228-868 Ohm-m) interpreted as lateritic sand, and below this the low resistivity (21.38 Ohm-m – 42.4 Ohm-m) interpreted as clay, then the fractured/weathered geoelectric layer (95Ohm-m to 385Ohm-m), while the fresh basement has resistivity greater than 400 Ohm-m. Several maps such as fractured window thickness map, isoresistivity map of the fractured interval, overburden map were generated to investigate trends that may hold prospects for groundwater exploitation. Furthermore, hydro-resistivity parameters such as Total Transverse Resistance, Total Longitudinal Conductance, Resistivity Reflection Co-efficient and Resistivity Contrast values were calculated for further screening of the study site for groundwater development. The VES1, VES2, VES6 and VES7 locations were concluded as holding prospects for groundwater potentials in the study area.

Environmental Management Framework for Road Network Demolition Wastes for Construction Industry of Pakistan

Demolition waste from construction industry, especially from road networks, is one of the most voluminous and harmful categories of waste worldwide; therefore, its proper handling is essential for sustainable waste management for environmental, social, and economic benefits. Prolific and unregulated construction activities, conflicts, and defective works are major reasons. The current work aims to address the issue by presenting a framework for an enhanced understanding of sustainable demolition waste management (DWM). A critical analysis of the literature aided to identify major concerns related to different causes, their impacts, and challenges being faced by the construction industry in such management endeavors. The study adopted questionnaire-based methodology to understand the critical relation among the three variables. The Delphi technique supported by industry professionals and pilot study helped to formulate a realistic questionnaire tool. Using the concept of multivariate statistical analysis, structure equation modeling (SEM) helped to assess the structural relationships between the three variables. The research instrument met the reliability, validity and internal consistency criteria required. Each variable achieved a high effect size, f2, with a value of co-efficient of determination of more than the threshold value of 70%. Thus, this supported the fitness criterion of the SEM-based measurement model. Path coefficients yielded the acceptance of all alternate hypotheses, resulting in a strong positive relationship among the three constructs. Therefore, demolition waste impacts are deemed as an effective mediator when explaining the impact between the other two variables. The developed framework presents a coherent and systematic approach and identifies strategies that could be used to address these issues and lead to DWM, including options available for capacity building and implementation and evaluation for supporting sustainability.

Role of diffusion weighted imaging with background body signal suppression (DWIBS) in diagnosis of breast masses and correlation with histopathological findings

BackgroundDynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is the important tool in breast imaging. However, two major limitations are represented by its specificity and by the injection of contrast material. Diffusion weighted imaging (DWI) provides important functional information without the need for contrast material. A newly introduced diffusion weighted imaging with background suppression (DWIBS) sequence is an accurate and rapid tool for the identification and characterization of breast lesions, with its short examination time, high lesion-to-background contrast and lack of need for intravenous contrast agents.ObjectiveTo assess the role of DWIBS sequence in the evaluation of indeterminate and suspicious breast masses and to compare its accuracy with DCE-MRI in correlation with histopathological findings.MethodsThirty-five patients were included in the study, referred from sono-mammography clinic to MRI unit for further MRI assessment of probably benign, suspicious and malignant looking breast masses (BIRADS 3, BIRADS 4 & BIRADS 5) on sono-mammography imaging results. MRI breast protocol which included DCE-MRI and DWIBS sequences were obtained for characterization and were verified by core needle biopsy or excisional biopsy. The results were statistically analyzed. Sensitivity, specificity, diagnostic accuracy (DA), positive predictive value (PPV) and negative predictive value (NPV) were calculated for DCE-MRI and DWIBS. Apparent diffusion co-efficient (ADC) values were calculated with ADC ≤ 1.2 × 10−3 mm2/s was considered suspicious for malignancy. The results were then compared with the histological findings.ResultsThirty-five female patients had 39 breast masses included in our study. By DCE-MRI, 8 (20.5%) masses were categorized as benign and 31(79.5%) masses were categorized as malignant. By DWIBS sequence, 7 (17.9%) masses were categorized as benign and 32 (82.1%) masses were categorized as malignant. By histopathology, 14 (35.9%) masses were benign and 25 (64.1%) masses were malignant. DCE-MRI obtained accuracy, sensitivity, specificity, PPV and NPV values of 84.6, 100, 57.1, 80.6 and 100%, respectively. DWIBS sequences obtained accuracy, sensitivity, specificity, PPV and NPV values of 82.1, 100, 50, 78.1and 100%, respectively.ConclusionsDWIBS can be added to DCE-MRI, as complementary tool to make radiologist more confident about the diagnosis. It can also be used instead of DCE-MRI sequences in certain circumstances such as in cases of renal impairment.

Comparative Study of Groundwater Quality for Drinking and Irrigation Purposes in Selected Villages of Manipur, India

A comparative study was done to monitor the groundwater qualities, both for drinking as well as irrigation purposes in some villages of Imphal East district, Manipur, in the period of pre-monsoon and monsoon of 2021. Totally, fifteen (15) groundwater samples were collected and examined for some important parameters like temperature, pH, TDS, TH, TA, Mg2+, K+, HCO3-, Ca2+, CO32-, Na+, Cl-, NO3- and SO42-. The results revealed that all the groundwaters were slightly alkaline in nature and fall under freshwater category. In both the seasons, majority of the parameters for various groundwaters have found their values/ concentrations below its acceptable limits, as given by BIS and WHO. In pre-monsoon, 73.33% of groundwaters were found as ‘moderately hard water’ and 26.67% (hard water) whereas in monsoon, 60% (moderately hard water) and 40% (hard water). Dominant ions in both seasons were Na+ (sodium) and HCO3- (bicarbonate) for cations and anions respectively. In most of the samples of monsoon, values and concentrations of the studied parameters were observed to be greater/higher as compared to that of pre-monsoon. It was mainly due to the leaching out of the soluble salts in the earth’s crust by rainwaters and finally mingled with the groundwater bodies in the aquifers in monsoon season. WQI values showed that in pre-monsoon, 26.67% of groundwaters were found as excellent water, 66.67% (good) and 6.66% (poor) while in monsoon, 60% (good) and 40% (poor). For irrigation water qualities, the indices (RSC, SAR, %Na, PI and KR) were examined. In the overall, all the samples can be utilized for irrigation (agriculture) purposes in both seasons. Correlation co-efficient (r) values showed that in both the seasons, the TH of various groundwaters was mainly because of dissolved sulphates of Ca2+ along with Mg2+.

The Influence of Leadership and Motivation on Employee Work Discipline at Fave Hotel Olo Padang

The study was undertaken to explore how leadership and motivation impact employee work discipline at Fave Hotel Padang. The primary objective is the investigation of the correlation between leadership, motivation, and work discipline. The research methodology employed was quantitative in nature. The data utilized in the study comprised both primary and secondary sources. The study's target population encompassed the staff of Fave Hotel Padang. A sample size of 30 employees was selected using a non-probability sampling technique. Data collection was facilitated through a questionnaire designed with a Likert scale, which was pretested for validity and reliability. The collected data were subjected to analysis using SPSS 25.00 software.The findings of the study revealed that leadership was classified as moderately satisfactory (46.67%). Furthermore, the motivational aspect was rated positively (80%), while the variable of work discipline garnered an agreeable response (76.67%). The influence exerted by leadership (X1) and motivation (X2) on work discipline (Y) was determined to be 24.1% and 75.9% respectively, with other factors contributing to the remaining impact. Further analysis unveiled that the leadership variable (X1) displayed a Beta or Standardized Coefficient value of 0.086, surpassing the threshold of 0, accompanied by a T-count value of (0.400) with a significance level of 0.002, lower than 0.05. Hence, it can be deduced that the leadership variable (X1) exhibits a significant and favorable impact on work discipline (Y). Similarly, the hypothesis stemming from the motivation segment of the research displayed a Beta or Standardized Coefficient value of 0.110, surpassing the threshold of 0, coupled with a calculated T-value of (0.511) at a significance level of 0.013, also less than 0.05. This underscores the fact that the motivational (X2) significantly and positively affects work discipline (Y).

Influencing factors for the human development index in West Java using geographically and temporally weighted regression kernel functions

Human Development Index (HDI) is a competitive index that serves as one of the crucial metrics for evaluating the effectiveness of enhancing the quality of human resources. HDI values from different areas can be compared. This study aims to spatially and temporally explore the HDI data from districts or cities in West Java and examine the factors that influence HDI in each of these districts or cities using the GTWR Great Circle Distance Fixed Kernels model. In this study, we used a combination of cross-sectional data from districts or cities in West Java and time series data with seven annual periods from 2015-2021. The GTWR Great Circle Distance Fixed Kernels model was expected to display coefficient values at each location and time simultaneously, providing more in-depth information and analysis results at each location and time. The analysis results using the GTWR Great Circle Distance Fixed Kernels model show that HDI in West Java carries a positive influence on the location and time. This finding should be of particular concern to the relevant government, particularly the factors presenting a natural effect on HDI based on location and time. The positive influence obtained by an area at a particular time will also have a positive impact on other regions, and if there is a negative influence, it will undoubtedly affect other regions as well. Analysis of the HDI model in West Java using the GTWR Great Circle Distance Fixed Exponential Kernel model also presents better results in comparison to the Global OLS model and the GTWR model without the Great Circle Fixed Exponential Kernel. The final parameter estimator results are displayed in the form of a geographic map to facilitate ease of understanding.

The alterations of functional brain networks and its relationship with sport decision-making and training duration in soccer players across different skill levels

Studies have indicated that skilled soccer players possess superior decision-making abilities compared to their less-skilled counterparts. However, the underlying neural mechanism for this phenomenon remains incompletely understood. In our investigation, we explored distinctions in the topology of functional brain networks between skilled and less-skilled soccer players. Employing mediating analysis, we scrutinized the relationships among functional brain network parameters, training duration, and decision-making accuracy. Our findings revealed that skilled soccer players demonstrated significantly higher decision-making accuracy compared to their less-skilled counterparts. Skilled players also exhibited increased values in the cluster coefficient, characteristic path length and local efficiency but lower global efficiency. Moreover, we observed enhanced functional brain connectivity within the occipital and cingulo-opercular networks, as well as between the fronto-parietal and cingulo-opercular networks in skilled soccer players. Cluster coefficient and functional connectivity between fronto-parietal and cingulo-opercular networks had positive mediating effects on the association between training duration and sport decision-making accuracy. In conclusion, our study provides initial evidence for distinctions in functional brain network parameters between soccer players with varying skill levels and their relationship with sport decision-making accuracy.

The Role of Inflation and The Performance of Rural Banks on Indonesia’s Economic Growth

The Role of Inflation and The Performance of Rural Banks on Indonesia’s Economic Growth

Effects of management strategies on the performance of street food vending in urban areas of Western Kenya

Street food (SF) vending is a common livelihood activity in many urban areas globally. It generates income for the vendors and contributes to the urban economy. However, the trade performs poorly due to the strategies used by urban authorities to manage the sector. The purpose of this study was to analyze the effects of urban management strategies on the performance of SF vending in Kakamega, Bungoma and Busia urban areas of Western Kenya. A cross-sectional descriptive survey was adopted for the study. Proportionate sampling and simple random sampling were used to select respondents in each urban area. A total of two hundred and twenty-four respondents were interviewed. Data was collected through questionnaires, observation checklists and photography. The questionnaire had a reliability Coefficient value of 0.781. Findings show that SF vendors were hardly engaged in decisions that affected them neither did they participate in formulation of rules governing their trade. Failure to observe the rules often led to conflict with enforcement officers. Lighting and waste collection were the only services provided appreciably while support in training, credit and registration were largely lacking. Authorities also charged levies which reduced the SF vendors’ earnings considerably. The strategies, therefore, contributed to the loss of SF vendors’ livelihood assets including their customers, finances, physical facilities and food stuffs. Loss of these assets contributed to the poor performance of the trade. It is recommended that urban authorities embrace an inclusive approach whereby vendors are engaged in urban management issues and their views considered in decision making processes.

Investigation of combined parallel and triple-pass v-corrugated solar air heater: A numerical and experimental study

Renewable and safe energy sources have been used more in recent years because of rising energy needs and finite fossil fuel resources. A solar air heater (SAH) is a device that utilizes solar energy to warm air for diverse applications, including room heating, drying procedures, or ventilation. The major aim of the current study is investigating the performance of the combined utilization of grooved absorber and triple-flow air channel modification in a SAH using numerical modeling. Accordingly, CFD method has been used to model the heat and flow characteristics inside a parallel-flow v-grooved SAH (PFVSAH), a triple-flow v-grooved SAH (TFVSAH), and a combined-SAH. The experimental and numerical evaluation of PFVSAH was conducted under different climatic conditions and mass flow rates of 0.019 kg/s, 0.015 kg/s, and 0.012 kg/s. Additionally, a numerical comparison was made between PFVSAH, TFVSAH and combined-SAH. According to the numerical results, the calculated temperature differences in a TFVSAH are greater than those in a PFVSAH and less than in a combined-SAH. According to the experimental results, when the mass flow rate is 0.012 kg/s, the PFVSAH shows average thermal and exergy efficiencies of 59.51% and 29.09%, respectively. In PFVSAH, the highest temperature difference between the outlet and the inlet was 28 °C. The recorded values for the top heat loss coefficient (THLC) of the PFVSAH varied between 4.3 and 8.93 W/m2.

A Chiral B-N Adduct as a New Frontier in Ferroelectrics and Piezoelectric Energy Harvesting.

Within the burgeoning field of electronic materials, B-N Lewis acid-base pairs, distinguished by their partial charge distribution across boron and nitrogen centers, represent an underexplored class with significant potential. These materials exhibit inherent dipoles and are excellent candidates for ferroelectricity. However, the challenge lies in achieving the optimal combination of hard-soft acid-base pairs to yield B-N adducts with stable dipoles. Herein, we present an enantiomeric pair of B-N adducts [R/SC6H5CH(CH3)NH2BF3] (R/SMBA-BF3) crystallizing in the polar monoclinic P21 space group. The ferroelectric measurements on RMBA-BF3 gave a rectangular P-E hysteresis loop with a remnant polarization of 7.65 μC cm-2, a value that aligns with the polarization derived from the extensive density-functional theory computations. The PFM studies on the drop-casted film of RMBA-BF3 further corroborate the existence of ferroelectric domains, displaying characteristic amplitude-bias butterfly and phase-bias hysteresis loops. The piezoelectric nature of the RMBA-BF3 was confirmed by its direct piezoelectric coefficient (d33) value of 3.5 pC N-1 for its pellet. The piezoelectric energy harvesting applications on the sandwich devices fabricated from the as-made crystals of RMBA-BF3 gave an open circuit voltage (VPP) of 6.2 V. This work thus underscores the untapped potential of B-N adducts in the field of piezoelectric energy harvesting.

A low-profile high-isolation endfire MIMO antenna based on spoof surface plasmon polaritons for X-band applications

This work proposes a three-port, low-profile, coplanar endfire multiple-input-multiple-output (MIMO) antenna based on spoof surface plasmon polaritons (SSPPs). The proposed antenna comprises a coplanar waveguide (CPW)-fed SSPPs transmission line (TL). A transition to transform the CPW quasi-TEM mode to the SSPPs mode. The radiator section with asymmetric discontinuities converts the bounded SSPPs waves into radiating waves. The proposed MIMO antenna exploits the inherent feature of high isolation in the SSPPs TL due to its strong field confinement competency. Wider beamwidths for ample azimuth and elevation coverage with a stable pattern in the endfire direction are achieved in the 9.52–11.23 GHz operating band. In the operating band, the MIMO antenna has an average realized gain of 6 dBi. Mainly, it has high isolation below -35 dB (measured) in the operating range, a maximum envelope correlation coefficient (ECC) of 1.5 × 10−3, and a total active reflection coefficient (TARC) value below 0.3. The measured results are closely matched with the simulated ones in terms of S-parameters, radiation pattern, ECC, TARC, and CCL.

Study of the effect of macrogeometry of rubbing steel bodies at their point contact on the tribological characteristics of lubricants under boundary lubrication conditions

The effect of the shape of contacting nonconformal elements of friction units that form an initial point contact on the tribological characteristics of lubricants during friction in the boundary lubrication mode. Point contact of rubbing bodies is realized on four-ball friction machines when testing tribological characteristics of lubricants in accordance with Russian GOST 9490–75 and GOST 23.221–84 Standards.However, these tests are carried out with the friction of standard bearing balls and does not allow taking into account the impact of materials of rubbing bodies on the results of the experiment. Therefore, two alternative designs of mandrels were developed, which allow implementation of two friction schemes: «rotating ball clamped in the spindle of the machine – three roller face planes» and «rotating ball — three cylindrical rollers». The load on the friction unit for both friction schemes, as well as in parallel on the mandrel under testing, in which three balls are installed, is the same (108 N), the spindle rotation speed is equal to 1 rpm, duration of testing is 60 min. The diameter of balls used in these experiments was 12.7 mm, and diameters of rollers were 5 and 8 mm, respectively. The material of samples was ShKh-15 tool steel or its 100Cr6 analogue. The designs of mandrels and the dimensions of samples were chosen in such a way that in all cases the contact areas of the experimental samples with the wearing (upper) ball would lie on a circle with a diameter of 7.32 mm. The tests were carried out under dry friction, and in boundary lubricated conditions in a PAO-4 polyalphaolefin oil medium, as well as in the same oil medium with the additives of oleic acid and DF-11 (a solution of zinc dialkyldithiophosphate in a low-viscosity oil). It is shown that the composition of a lubricating medium has a decisive effect on the test results (i.e., on the values of the friction coefficients and on the values of the areas of wear scars), while the geometry of the rubbing bodies, as well as the maximum Hertz stresses in the tribological contact, had a little effect on the antifriction and anti-wear characteristics of oils.

Extension of the fixed point theory to tuned mass dampers with piezoelectric stack energy harvester

A tuned mass damper with a piezoelectric stack energy harvester (TMD-PSEH) is a passive vibration control device for the dual purpose of absorbing vibration and harvesting energy. This paper develops the fixed point theory for the optimal design of a TMD-PSEH attached to an undamped primary structure under harmonic external excitation. It has been proven that the existence of two fixed points of the amplitude-frequency curve doest not depend on the damping of the primary structure. Based on the requirements for suppressing the vibration of the primary structure and enlarging the harvested power, the analytical expressions for the optimal tuning, damping, and resistance ratios are determined. It is found that the minimum damping ratio occurs in the vicinity of the electrical resistance ratio α=1 for various values of the electromechanical coupling coefficient. Power flow analysis is carried out resulting in closed-form expressions of instantaneous and average powers. Numerical examinations of the system with the obtained optimal parameters are performed demonstrating a very good compatibility between theory and computation. In addition, the effect of damping in the primary structure is also investigated. It is shown that not only the vibration of the primary structure effectively reduces, but also a large amount of the harvested energy can be captured in the main resonance region.

Complexity in road freight transport outsourcing networks. TRANSOPE: An agent-based dynamic model

This paper proposes a dynamic agent-based model (TRANSOPE) to simulate outsourcing among transport companies where, for the first time, accumulated knowledge is included as a variable to select service providers. The model consists of two main procedures. Firstly, the model simulates the decision-making of the professionals that contract transport service providers and the formation of outsourcing chains. Secondly, the model simulates the direct learning of participating companies and the transfer of knowledge towards their environment. Imperfect competition is replicated in three different scenarios, which involve the demand for transport services, regional distances and the intensity of knowledge transfer. The model is based on expert consultations and a survey conducted in an environment with a high concentration of transport companies in the Basque Country, Spain. The results indicate significant imbalances in the distribution of outsourcing, particularly in situations of low transport service demand, where 30% of transport companies do not secure any contracts. However, such situations led to strong regional interdependence. The dynamics of outsourcing reveals that over 75% of the contracted companies participate in all simulated scenarios from the first day. A strong hierarchy is also observed in the network, where certain transport companies act as connector hubs (with z-score values higher than 2.5 and participation coefficient values between 0.3 and 0.75), indicating a greater capacity for interaction and leadership in the transfer of knowledge. This feature allows the collaboration network to be identified as a scale-free network. The model has a low computational cost since the distances between agents remain constant. Finally, the formalisation of outsourcing decision-making in the model underpins its validity in forecasting the conduct of a freight transport system under shifting scenarios.