Hellenic Mediterranean University
  • Irákleion, Crete, Greece
Recent publications
Selecting salt-tolerant crop species for cultivation might be a feasible option to maintain crop productivity in arable lands affected by salinity. In this context, here we examine the responses of the wild edible green golden thistle (Scolymus hispanicus L.) to moderate levels of salinity when grown in a soilless system for culinary use. Treatments were obtained by establishing four NaCl concentrations (0.5, 5.0, 10.0, and 15.0 mM) in a standard nutrient solution, resulting in initial solution electrical conductivities (EC) of 2.2, 2.8, 3.2, and 3.8 dS m ⁻ ¹, respectively. By the end of the experiment, 120 days after transplanting (DAT) drainage EC reached 2.65, 3.33, 3.96, and 4.51 dS m ⁻ ¹, respectively. At the first harvest, 90 DAT, the increase of the NaCl concentration had no significant impact on the number of leaves per plant, leaf fresh and dry weight [g plant⁻¹], and root dry weight [g plant⁻¹]. At the second harvest (120 DAT), 15.0 mM NaCl significantly decreased root and leaf fresh and dry weight without affecting the number of leaves per plant compared to 0.5 and 5.0 mM NaCl, while 10 mM NaCl had no impact on any of these parameters. The concentrations of K⁺, Ca²⁺, Mg²⁺, and P in the leaves were not influenced by the tested salinity levels, while those of organic-N and NO3⁻-N were significantly reduced by 10 and 15 mM NaCl, 90 DAT. Furthermore, 10 and 15 mM NaCl significantly increased the Cl⁻ and Na⁺ concentrations in leaves, but not in the roots. In the root tissues, only the K concentration was reduced by salinity while P increased at the highest salinity level (15 mM NaCl). Based on these results, we conclude that S. hispanicus L. is resilient to moderate salinity levels and can be considered a promising candidate plant for introduction to soilless cropping systems.
Stationarity of hedge ratios can be viewed as a first step for portfolio hedging since it represents that the sensitivity of spot and Future returns follow a process whose main characteristics do not depend on time. However, we provide evidence that the hedge ratios of the main European stock indices are better described as a combination of two different mean-reverting stationary processes, which depend on the state of the market. Also, when analysing the dynamics of hedge ratios at intraday level, results display a similar picture suggesting that intraday dynamics of the hedge between spot and Future are driven mainly by market participants with similar perspectives of the investment horizon.
Hydrothermal carbonization of wet biomasses has been known to produce added-value materials for a wide range of applications. From catalyst substrates, to biofuels and soil amendments, hydrochars have distinct advantages to offer compared to conventional materials. With respect to the agricultural application of hydrochars, both positive and negative results have been reported. The presence of N, P and K in certain hydrochars is appealing and may contribute to the reduction of chemical fertilizer application. However, regardless of biomass, hydrothermal carbonization results in the production of phytotoxic organic compounds. Additionally, hydrochars from sewage sludge often contain heavy metal concentrations which exceed the regulatory limits set for agricultural use. This review critically discusses the phytotoxic aspects of hydrochar and provides an account of the substances commonly responsible for these. Furthermore, phytotoxicity reduction approaches are proposed and compared with each other, in view of field-scale applications.
Although considerable knowledge exists on the impact of crop residues on soil N availability, information about their impact on nitrification specifically is lacking. The unique physiologies of ammonia oxidizing archaea (AOA) suggests their activities might respond differently to crop residue amendment compared to ammonia oxidizing bacteria (AOB). An incubation study was conducted on two widely distributed Oregon agricultural silt loam soils of the Walla Walla (WW) and Woodburn (CC) series, amended with a fertilizer rate of 70 μg N g⁻¹ soil in the form of (1) NH4⁺-N, (2) clover stems (C:N ~ 25), or (3) clover leaves (C:N ~ 13). NH4⁺ accumulation in the presence of acetylene, and the relative amounts of AOA and AOB activities, in the presence of the selective AOB inhibitor, 1-octyne, were examined over a 28-31d incubation. Nitrifying activity in the crop residue-amended WW soil matched the rate of ammonification and was predominately octyne-resistant suggesting that nitrifying activity was dominated by AOA. In CC soil, the relative contributions of AOA and AOB to emergent activities was influenced by the nature of the residue and in a soil specific manner. In leaf amended CC soil, AOB contributed the majority of initial nitrifying activity over 0-7d, with the contribution of AOA activity increasing post 7d to represent 100% of the total rate. In stem amended CC soil, emergence of nitrifying and ammonifying activities were delayed, but after 7d incubation AOA activity emerged at a rate greater than the accompanying rate of ammonification. In NH4⁺-N amended soils, AOB activity emerged quickly at rates greater than when N was supplied by residues. The response of AOA activity to NH4⁺-N was soil specific being immediate and at a greater rate than leaf residue supported activity in WW soil, whereas in CC soil, AOA activity was temporally delayed (as with residue treatment) and emerged at a rate similar to that supported by leaf residue. From a practical perspective, the findings of this study show that an application of 70 μg N g⁻¹ soil as crop residues can prevent AOB driven nitrifying activity from reaching its potential compared to an inorganic NH4⁺-N application, and also suggest the potential of AOA activity to be modified by residues in a soil specific manner.
This study investigates the mechanical response of antibacterial PA12/TiO2 nanocomposite 3D printed specimens by varying the TiO2 loading in the filament, raster deposition angle, and nozzle temperature. The prediction of the antibacterial and mechanical performance of such nanocomposites is a challenging field, especially nowadays with the covid-19 pandemic dilemma. The experimental work in this study utilizes a fully factorial design approach to analyze the effect of three parameters on the mechanical response of 3D printed components. Therefore, all combinations of these three parameters were tested, resulting in twenty-seven independent experiments, in which each combination was repeated three times (a total of eighty-one experiments). The antibacterial performance of the fabricated PA12/TiO2 nanocomposite materials was confirmed, and regression and arithmetic artificial neural network (ANN) models were developed and validated for mechanical response prediction. The analysis of the results showed that an increase in the TiO2% loading decreased the mechanical responses but increased the antibacterial performance of the nanocomposites. In addition, higher nozzle temperatures and zero deposition angles optimize the mechanical performance of all TiO2% nanocomposites. Independent experiments evaluated the proposed models with mean absolute percentage errors (MAPE) similar to the ANN models. These findings and the interaction charts show a strong interaction between the studied parameters. Therefore, the authors propose the improvement of predictions by utilizing artificial neural network models and genetic algorithms as future work and the spreading of the experimental area with extra variable parameters and levels.
The aim of this paper is the creation of an integrated and free-access web platform for parcel irrigation water management on a large spatial scale (Water District of Crete, in Greece) in order to: a) accurately determine the irrigation needs of the main crops for Crete such as olives, citrus, avocados and vineyards, b) design strategies, for optimal adaptation of the agricultural sector in the context of climate change, and c) incorporate the dynamic integration of the above information through the creation of a digital platform. In the proposed decision-making system, essential factors are taken into account, such as real-time meteorological data, information about the type and spatial distribution of the agricultural parcels in Crete, algorithms for calculation crop evapotranspiration per development stage and age of the crops, satellite remote sensing techniques in combination with field surveys to depict accurate soil texture map for the whole island of Crete as well as sustainable cultivation practices for saving water per crop and parcel geomorphology. Based on the proposed decision-making system, users will have the opportunity in any specific location/farm in Crete to know the irrigation needs of the crops in real-time and obtain information about proper climate-water adaptation practices. The main novelty points of the proposed platform include the derivation of parcel-level soil texture data from Sentinel-2 satellite imagery and field samples, the comprehensiveness of the irrigation management information, the relatively low data requirements and the application interface simplicity provided to the end-user.
In this work, material extrusion (MEX) 3D-printed polylactic acid (PLA) thin workpieces were joined via the friction stir welding (FSW) process to evaluate the feasibility and the key features of the process. To ensure the reliability of the process, a special fixture was designed and manufactured. Three critical parameters were investigated, i.e., the welding tool geometry, the travel speed, and the tool rotational speed. Two different tool geometries were manufactured and tested. Specimens were welded with various welding parameters values, to calibrate the experimental ranges of the subsequent full factorial course. The results were recorded and evaluated with an optical microscope, a stereoscope, and scanning electron microscopy (SEM). The thermal field and the mechanical performance of the joints were measured and evaluated. In the majority of the welding scenarios, the welded specimens’ mechanical performance was increased compared to the identical not welded 3D-printed samples. The travel speed proved to be the most critical parameter affecting the mechanical strength of the parts. The highest tensile strength is reported for a specimen welded with 6 mm/min travel speed, 1400 rpm rotational speed, and weld tool with the cylindrical pin. The results were analyzed and optimized with statistical modeling tools, to evaluate and document the impact of each parameter studied herein. Herewith, a cost-effective and efficient FSW joining process of MEX-made polymeric pieces enables a new possibility to permanently assemble 3D-printed parts of limited size to larger assemblies, with the aid of simple tools and a milling machine.
The present study examines: (a) the knowledge of healthcare students on cervical cancer (CC) issues and the use of related preventive services, as well as their association with the field of study and other sociodemographic characteristics; (b) the possible effect of social capital and its parameters. A cross-sectional study was conducted, using a convenience non-probability sampling technique. The final sample consisted of forty-nine social work and fifty-one nursing students. The two groups were similar regarding their sociodemographic characteristics and the knowledge and use of gynecological preventive services. However, the nursing students undertook a PAP smear check-up to a lesser extent (48.6%) compared to social work students (51.4%) (p = 0.026). The social capital scores were high for both groups, but social work students were significantly more ‘Tolerant to diversity’. For the total sample, only the ‘Family and friends connections’ subscale correlated with knowledge about the existing gynecological preventive services. Among the main reasons explaining university students’ avoidance of preventive testing were the feelings of fear and embarrassment associated with the PAP smear test. Given the significance of the future professional roles of healthcare students as information sources and leaders in women’s CC preventive behavior, understanding the individual factors contributing to their own adherence is essential. It is equally important to increase their scientific knowledge through the improvement of academic curricula regarding these issues.
The feasibility of joining material extrusion (MEX) 3D-printed acrylonitrile butadiene styrene (ABS) plates with the friction stir welding (FSW) process was investigated herein as a promising topic of hybrid additive manufacturing (HAM). The influence of three process parameters on the mechanical strength of the joints was thoroughly examined and analyzed with a full factorial experimental design and statistical modeling. Hereto, the welding tool pin geometry, travel speed, and rotational speed were investigated. The joint's efficiency and quality are evaluated through tensile tests and morphological characterization. More specifically, specimens' areas of particular interest were investigated with stereoscopic, optical, and scanning electron microscopy. Throughout the FSW experimental course, the welding temperature was monitored to evaluate the state of the ABS material during the process. The majority of the welded specimens exhibited increased mechanical strength compared with the respective ones of non-welded 3D printed specimens of the same geometry. Statistical modeling proved that all processing parameters were significant. The feasibility of the FSW process in 3D printed ABS workpieces was confirmed, making the FSW a cost-effective process for joining 3D printing parts, further expanding the industrial merit of the approach.
This work investigates the efficiency of the Box-Behnken design (BBD) in contrast with the full-factorial design (FFD) in ultimate tensile strength (UTS) of PA12 material extrusion 3D printing (ME-3DP) specimens. Three input parameters, i.e., the raster angle (A), layer thickness (B), and nozzle temperature (C) with three levels each, were employed to compare the BBD and FFD efficiency. The 81 full-factorial UTS initial experimental data used in this research have been produced in a previous work published by the authors. Fifteen (15) out of 81 experiments were selected for the BBD design with three repetitions on the central point (0,0,0). Main effect plots (MEP), interaction plots, surface plots, ANOVA analysis, normality plots, mean absolute percentage error (MAPE), and the root-mean-square error (RMSE) evaluate the BBD and FFD approaches. The BBD MAPE and RMSE indexes show that the Box-Behnken design is appropriate for parameter analysis and processing investigation resulting in a 5.3% MAPE and 2.75 RMSE, close to 5.2% and 2.44 of the full-factorial MAPE and RMSE indexes.
In the present work, a methodology for the low-cost crafting of an interactive layered dashboard is proposed. Our aim is that the tangible surface be constructed using domestic materials that are easily available in every household. Several tests were performed on different capacitive materials before the selection of the most suitable one for use as a capacitive touch sensor. Various calibration methods were evaluated so that the behavior of the constructed capacitive touch sensors is smooth and reliable. The layered approach is achieved by a menu of few touch buttons on the left side of the dashboard. Thus, various different layers of content can be projected over the same construction, offering extendibility and ease of use to the users. For demonstration purposes, we developed an entertaining plus an educational application of projection mapping for the pervasive and interactive projection of multimedia content to the users of the presented tangible interface. The whole design and implementation approach are thoroughly analyzed in the paper and are presented through the illustration and application of various multimedia layers over the dashboard. An evaluation of the final construction proves the feasibility of the proposed work.
As a vital step towards the industrialization of perovskite solar cells, outdoor field tests of large-scale perovskite modules and panels represent a mandatory step to be accomplished. Here we demonstrate the manufacturing of large-area (0.5 m²) perovskite solar panels, each containing 40 modules whose interfaces are engineered with two-dimensional materials (GRAphene-PErovskite (GRAPE) panels). We further integrate nine GRAPE panels for a total panel area of 4.5 m² in a stand-alone solar farm infrastructure with peak power exceeding 250 W, proving the scalability of this technology. We provide insights on the system operation by analysing the panel characteristics as a function of temperature and light intensity. The analysis, carried out over a months-long timescale, highlights the key role of the lamination process of the panels on the entire system degradation. A life-cycle assessment based on primary data indicates the high commercial potential of the GRAPE panel technology in terms of energy and environmental performances.
In recent years, demand for electric energy has steadily increased; therefore, the integration of renewable energy sources (RES) at a large scale into power systems is a major concern. Wind and solar energy are among the most widely used alternative sources of energy. However, there is intense variability both in solar irradiation and even more in windspeed, which causes solar and wind power generation to fluctuate highly. As a result, the penetration of RES technologies into electricity networks is a difficult task. Therefore, more accurate solar irradiation and windspeed one-day-ahead forecasting is crucial for safe and reliable operation of electrical systems, the management of RES power plants, and the supply of high-quality electric power at the lowest possible cost. Clouds’ influence on solar irradiation forecasting, data categorization per month for successive years due to the similarity of patterns of solar irradiation per month during the year, and relative seasonal similarity of windspeed patterns have not been taken into consideration in previous work. In this study, three deep learning techniques, i.e., multi-head CNN, multi-channel CNN, and encoder–decoder LSTM, were adopted for medium-term windspeed and solar irradiance forecasting based on a real-time measurement dataset and were compared with two well-known conventional methods, i.e., RegARMA and NARX. Utilization of a walk-forward validation forecast strategy was combined, firstly with a recursive multistep forecast strategy and secondly with a multiple-output forecast strategy, using a specific cloud index introduced for the first time. Moreover, the similarity of patterns of solar irradiation per month during the year and the relative seasonal similarity of windspeed patterns in a timeseries measurements dataset for several successive years demonstrates that they contribute to very high one-day-ahead windspeed and solar irradiation forecasting performance.
Introduction Increasing life expectancy has led to a higher incidence of cancer in the elderly, thus making them vulnerable and worsening their health-related quality of life (HRQoL) and their need for support. Objective The aim of this study was to examine the HRQoL and social support in elderly Greek lung and gastrointestinal cancer patients undergoing chemotherapy. Methods This was a descriptive, cross-sectional study of 104 elderly cancer patients, who were receiving chemotherapy in the outpatient department and inpatient ward of a General Hospital in Athens. The data were collected using purposive sampling between December 2019 and May 2020, and included demographic and clinical characteristics, the HRQoL questionnaire, Short Form 36 (SF36), and the Personal Resource Questionnaire (PRQ-2000). Results The participants' median age was 72 years; the majority were male (62.5%) and had lung cancer (57.7%). The SF36 data revealed a relatively moderate (42.7–62.61) HRQoL in most subscales. The “Pain” subscale recorded the highest score (75.0), and the “social function” subscale the lowest (42.79). The PQR-2000 indicated a satisfactory level of social support (81.65), with values ranging between 48 and 105; married patients with higher education scored more highly ( p < .05). Patients aged 65–75 years reported better HRQoL and greater social support than older patients. In addition, patients with their own family and a relatively high income reported better HRQoL and social support compared to single individuals, with low income, who were cared for by their children. Positive and statistically significant ( p < .05) correlations were found between the SF36 subscales of role functioning/physical, vitality, general health, emotional well-being and the PRQ-2000. Conclusion The HRQoL and social support of elderly cancer patients positively affect the course of their health. Healthcare systems and social services should address the multiplying needs of these patients with targeted interventions to support their well-being.
Objectives: To develop a prediction model that could risk stratify abdominal aortic aneurysms (AAAs) into high and low growth rate groups, using machine learning algorithms based on variables from different pathophysiological fields. Methods: A cohort of 40 patients with small AAAs (maximum diameter 32-53 mm) who had at least an initial and a follow-up CT scan (median follow-up 12 months, range 3-36 months) were included. 29 input variables from clinical, biological, morphometric, and biomechanical pathophysiological aspects extracted for predictive modeling. Collected data were used to build two supervised machine learning models. A gradient boosting (XGboost) and a support vector machines (SVM) algorithm were trained with 60% and tested with 40% of the data to predict which AAA would achieve a growth rate higher than the median of our study cohort. Receiver operating characteristics (ROC) curves and areas under the curve (AUC) were used for the evaluation of the developed algorithms. Results: XGboost achieved the highest AUC in predicting high compared to low AAA growth rate with an AUC of 81.2% (95% CI from 61.1 to 100%). SVM achieved the second highest performance with an AUC of 68.8% (95% CI from 46.5 to 91%). Based on the best performing algorithm, variable importance was estimated. Diameter-diameter ratio (maximum diameter/neck diameter), Tortuosity from Renal arteries to aortic bifurcation, and maximum thickness of the intraluminal thrombus were found to be the most important factors for model predictions. Other factors were also found to play a significant but less important role. Conclusions: A prediction model that can risk stratify AAAs into high and low growth rate groups could be developed by analyzing several factors implicated in the multifactorial pathophysiology of this disease, with the use of machine learning algorithms. Future studies including larger patient cohorts and implementing additional risk markers may aid in the establishment of such methodology during AAA rupture risk estimation.
Water quality is a fundamental issue for the survival of a city, especially on dry land. In ancient times, water availability determined the location and size of villages and cities. Water supply and treatment methods were developed and perfected along with the evolution of urbanization. In Europe, after the fall of the Roman Empire, water supply and sewage systems went through fundamental changes. However, in medieval times, the lack of proper sanitation and low water quality increased the spreading and effects of epidemics. The importance of potable water quality was established during modern times. In Greece, the significance of water filtration and disinfection was not understood until the beginning of the 20th century. Moreover, the beneficial effects of water quality and sanitation on human health and especially on life expectancy are considered. In Greece and other countries, a dramatic increase in life expectancy mainly after the 2nd World War is probably due to the improvement of potable water quality and hygiene conditions. However, since the mid-20th century, new water quality issues have emerged, such as eutrophication, the improvement of water treatment technologies, as well as chemical and microbiological water pollution problems. This study, in addition to the historical evolution of water quality, highlights and discusses the current issues and challenges with regard to the management and protection of water quality, including global changes in population and urbanization, lack of infrastructure, use of nonconventional water resources, spreading of emerging pollutants and contaminants (e.g., antibiotics and microplastics), and climatic variability impacts. Against these, a review of the main proposed strategies and measures is presented and discussed to protect water quality and maintain water supplies for the future. Understanding the practices and solutions of the past provides a lens with which to view the present and future.
In this work, we present an effective process easily adapted in industrial environments for the development of multifunctional nanocomposites for material extrusion (MEX) 3D printing (3DP). The literature is still very limited in this field, although the interest in such materials is constantly increasing. Nanocomposites with binary inclusions were prepared and investigated in this study. Polylactic acid (PLA) was used as the matrix material, and cuprous oxide (Cu2O) and cellulose nanofibers (CNF) were used as nanoadditives introduced in the matrix material to enhance the mechanical properties and induce antibacterial performance. Specimens were built according to international standards with a thermomechanical process. Tensile, flexural, impact, and microhardness tests were conducted. The effect on the thermal properties of the matrix material was investigated through thermogravimetric analysis, and Raman spectroscopic analysis was conducted. The morphological characteristics were evaluated with atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDS) analyses. The antibacterial performance of the prepared nanomaterials was studied against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria, with a screening agar well diffusion method. All nanocomposites prepared exhibited biocidal properties against the bacteria tested. The tested PLA/1.0 CNF/0.5 Cu2O material had 51.1% higher tensile strength and 35.9% higher flexural strength than the pure PLA material.
Covalent triazine frameworks (CTFs) are among the most valuable frameworks owing to many fantastic properties. However, molten salt-involved preparation of CTFs at 400 - 600°C causes debate on whether CTFs represent organic frameworks or carbon. Herein, new CTFs based on the 1,3-dicyanoazulene monomer (CTF-Azs) were synthesized using molten ZnCl2 at 400-600°C. Chemical structure analysis revealed that the CTF-Az prepared at low temperature (400°C) exhibits polymeric features, whereas those prepared at high temperatures (600°C) exhibit typical carbon features. Even after being treated at even higher temperatures, the CTF-Azs retained their rich porosity, but the polymeric features vanished. Although structural de-conformation is a widely accepted outcome in polymer-to-carbon rearrangement processes, our study evaluates such processes in the context of CTF systems. We performed a proof-of-concept study, observing that the as-synthesized CTF-Azs exhibited promising performance as cathodes for Li- and K-ion batteries. Moreover, the as-prepared NPCs exhibited excellent catalytic oxygen reduction reaction performance; hence, they can be used as air cathodes in Zn-air batteries. This study not only provides new building blocks for novel CTFs with controllable polymer/carbon features but also offers insights into the formation and structure transformation history of CTFs during thermal treatment. This article is protected by copyright. All rights reserved.
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1,371 members
Vassilis Saltas
  • Department of Electronics Engineering
Eleni Kokinou
  • School of Agricultural Technology
KLEIO Koutra
  • School of Health and Welfare Services
Christos F. Kleisiaris
  • School of Health and Welfare Services
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