Ruben Gatt | University of Malta (original) (raw)
Papers by Ruben Gatt
The geometry of a two-level hierarchical rotating square system may be described by the aperture ... more The geometry of a two-level hierarchical rotating square system may be described by the aperture between the Level 0 squares (θ0), the aperture between the Level 1 square-like units (θ1) and the number of Level 0 repeat units (N0). This means that the Level 1 building block is made up of N0×N0 Level 0 repeat units which corresponds to 2N0×2N0 squares. These parameters may be used to de ne the linear dimensions of the Level 1 square-like units, u1 and v1, as follows: u1 = 2N0l cos ( θ0 2 ) + 2(N0 − 1)l sin ( θ0 2 ) and v1 = 2N0l ( cos ( θ0 2 ) + sin ( θ0 2 )) , where l stands for the length of the sides of the Level 0 squares. These dimensions can in turn be used to de ne the overall on-axis dimensions of the system:
Using experimental data, it is shown that the Poisson’s ratios of conventional (untreated) foam v... more Using experimental data, it is shown that the Poisson’s ratios of conventional (untreated) foam vary when loading in different loading directions, since foam is inherently asymmetric and anisotropic. The loading direction which is in plane orthogonal to the rise direction of the foam constantly exhibited the most negative Poisson’s ratio across foam samples of different types. It was also shown that although the foam may become auxetic at very high values of compressive strain, it shows an incremental negative Poisson’s ratio at much lower compressive strains. The results are compared to previous publications and the effects of changing loading direction on the mechanical response of the foam are highlighted.
SUMMARY The identification and quantification of phenolic compounds and flavonoids in various nat... more SUMMARY The identification and quantification of phenolic compounds and flavonoids in various natural food products is typically conducted using HPLC analysis. Their analysis is particularly complex since most natural food products contain a large number of different phenolic compounds, many of which have similar chemical characteristics such as polarity, which makes complete separation of all eluents extremely difficult. In this work we present and validate a method for the quantitative determination of the concentration of two compounds with similar retention times, i.e. they show overlapping peaks in a mixed solution. Two pairs of phenolic compounds were investigated: caffeic and vanillic acids and ferulic and p-coumaric acids. This technique takes advantage of the different absorbances of the two phenolic compounds in the eluent at various wavelengths and can be used for the quantitative determination of the concentration of these compounds even if they are not separated in the ...
H2O ice is known to exist as a number of different polymorphs. One such polymorph is ice X, a sym... more H2O ice is known to exist as a number of different polymorphs. One such polymorph is ice X, a symmetrical phase of ice which is known to be stable at high pressures and low temperatures. In this work, the mechanical properties of ice X have been studied through DFT simulations, and it has been shown that ice X has the potential to exhibit auxetic behaviour (negative Poisson's ratio) at 45° off-axis in the (100), (010) and (001) planes. Studying the deformation of two orthogonally interconnected rhombi has shown that this predicted negative Poisson's ratio can be attributed to the interplay between distortion and hinging of these rhombi. Moreover, it has been shown that the auxetic potential of ice X increases with an increase in hydrostatic pressure, which behaviour is explained by the rhombi approaching quasi-perfect behaviour resulting in a decrease in the distortion of the rhombi and an increase in hinging mechanism.
Acta Scientific Orthopaedics
Acta Mechanica
Mechanical metamaterials are systems which derive their mechanical properties from their structur... more Mechanical metamaterials are systems which derive their mechanical properties from their structure rather than their intrinsic material composition. In this work, we investigate a class of highly anisotropic mechanical metamaterials designed by the introduction of diamond and elliptically shaped perforations which possess the ability to show auxetic behaviour. By the use of finite element simulations, we show how these highly tuneable systems have the potential to exhibit a large range of Poisson’s ratios, ranging from highly positive to giant negative values, simply by altering the geometric parameters and orientation of the perforations. The anomalous properties of these systems have also been shown to be retained over significant tensile strain ranges, highlighting the vast potential applicability and functionality of these mechanical metamaterials.
International Journal of Solids and Structures
Abstract In this work, through the use of Molecular Dynamics simulations, we show the capability ... more Abstract In this work, through the use of Molecular Dynamics simulations, we show the capability of different mechanical metamaterials to induce their own global rotational motion as a result of an internal deformation. We also show that one of the considered structures, i.e. the hexachiral system, may manifest a superior extent of the global rotation in comparison to other systems. In addition to that, we discuss that the self-induced global rotation can be observed for mechanical metamaterials with a discrete mass distribution which allows to prove that this phenomenon is not limited to macroscopic systems and applications involving the control of the rotational motion of objects such as satellites or wind turbines where the continuous mass distribution of structural elements is normally required. In fact, this study serves as a blueprint to show that a similar effect may also be expected for various systems at very different scales.
AIP Advances
In this work, we propose the concept that a device based on mechanical metamaterials can be used ... more In this work, we propose the concept that a device based on mechanical metamaterials can be used to induce and control its own rotational motion as a result of internal deformations due to the conversion of translational degrees of freedom into rotational ones. The application of a linear force on the structural units of the system may be fine-tuned in order to obtain a desired type of rotation. In particular, we show, how it is possible to maximise the extent of rotation of the system through the alteration of the geometry of the system. We also show how a device based on this concept can be connected to an external body in order to rotate it which result may potentially prove to be very important in the case of applications such as telescopes employed in space.
International Journal of Fruit Science, 2016
ABSTRACT In this article a detailed review of the fungal diseases that can affect pear fruit is p... more ABSTRACT In this article a detailed review of the fungal diseases that can affect pear fruit is provided. Each section comprises a complete description of the fungi responsible for the diseases and the symptoms they produce on the pears. The majority of pear fungal diseases, including blue mold, grey mold, bitter rot, black spot, brown rot, bull’s eye rot, Phytophthora rot, pink mold rot, powdery mildew, Rhizopus rot, scab, side rot, sooty blotch, and flyspeck, are presented. Sources of infection are comprehensively described in relation to harvesting or post-harvesting handling and intervention practices, respectively. As these diseases are dependent on a number of environmental parameters, the optimal temperature ranges for disease development are described and the causal agents are identified. Previous studies on the diagnostic indications are reviewed while information about the optimal environmental parameters of temperature, pressure, pH, water activity, and oxygen level for the fungal growth is comprehensively summarized.
Materials
In this work, we use computer simulations (Molecular Dynamics) to analyse the behaviour of a spec... more In this work, we use computer simulations (Molecular Dynamics) to analyse the behaviour of a specific auxetic hierarchical mechanical metamaterial composed of square-like elements. We show that, depending on the design of hinges connecting structural elements, the system can exhibit a controllable behaviour where different hierarchical levels can deform to the desired extent. We also show that the use of different hinges within the same structure can enhance the control over its deformation and mechanical properties, whose results can be applied to other mechanical metamaterials. In addition, we analyse the effect of the size of the system as well as the variation in the stiffness of its hinges on the range of the exhibited auxetic behaviour (negative Poisson’s ratio). Finally, it is discussed that the concept presented in this work can be used amongst others in the design of highly efficient protective devices capable of adjusting their response to a specific application.
Materials
In this work, through the use of a theoretical model, we analyse the potential of a specific thre... more In this work, through the use of a theoretical model, we analyse the potential of a specific three-dimensional mechanical metamaterial composed of arrowhead-like structural units to exhibit a negative Poisson’s ratio for an arbitrary loading direction. Said analysis allows us to assess its suitability for use in applications where materials must be able to respond in a desired manner to a stimulus applied in multiple directions. As a result of our studies, we show that the analysed system is capable of exhibiting auxetic behaviour for a broad range of loading directions, with isotropic behaviour being shown in some planes. In addition to that, we show that there are also certain loading directions in which the system manifests negative linear compressibility. This enhances its versatility and suitability for a number of applications where materials exhibiting auxetic behaviour or negative linear compressibility are normally implemented.
physica status solidi (b)
physica status solidi (b)
physica status solidi (b)
Although, high heels are known to affect the biomechanics of human movement, most notably by incr... more Although, high heels are known to affect the biomechanics of human movement, most notably by increasing forefoot plantar pressure it is commonly used worn due to the influence of fashion. To deal with resulting clinical issues some prescriptions include the use of cushioning pads to redistribute the plantar loads and increase comfort. This preliminary study has sought to investigate whether auxetic foam would be a good candidate for the redistribution of plantar loafing in the forefoot when compared to a more traditional material. From the results obtained, it was shown that auxetic foam demonstrated a decrease in forefoot peak plantar pressure while a commercial product, a material traditionally used for plantar cover paddings, increased pressure in the region of the 2 nd-4 th MPJ. This demonstrates the potential for auxetic materials to become a material of choice for such applications, especially since it can be further remodeled until its properties can produce a significant forefoot pressure reduction.
Materials & Design
The term "mechanical metamaterials" encompasses a wide range of systems whose anomalous mechanica... more The term "mechanical metamaterials" encompasses a wide range of systems whose anomalous mechanical properties arise primarily from their structure rather than composition. This unique characteristic gives them an edge over many conventional natural or readily available materials and makes them well-suited for a variety of applications where tailormade mechanical properties are required. In this study, we present a new class of mechanical metamaterials featuring various star-shaped perforations, which have the potential to exhibit auxetic or zero Poisson's ratio () properties. Using finite element modelling in conjunction with experimental measurements on 3D printed prototypes, we demonstrate that these starshaped porous systems possess the potential to retain their unusual mechanical properties up to tensile strains exceeding 15%. By virtue of these exceptional properties, the proposed concept could be applied for engineering numerous potential applications in a wide range of fields.
physica status solidi (b)
Journal of Food Processing and Preservation
Journal of food protection, 2018
Rapid assessment of fungal growth and screening antifungal compounds, such as nanoparticles (NPs)... more Rapid assessment of fungal growth and screening antifungal compounds, such as nanoparticles (NPs), for effectiveness is a challenging procedure because no primary standards exist as they do for yeasts and bacteria. Because fungi do not grow as single cells, but as hyphal filaments, they cannot be quantified by the usual enumeration techniques used in bacteriology. The growth of three postharvest fungal isolates ( Alternaria alternata, Rhizopus stolonifer, and Botrytis cinerea) was investigated at different inoculum concentrations and in three nutrient media (Sabouraud dextrose agar, potato dextrose agar, and yeast extract dextrose agar [YED]) with a turbidimetric assay. Sequential measurements were performed to generate optical density versus time plots, whereas the growth responses were expressed quantitatively as the generated trapezoidal area. YED medium showed the lowest variation among replicated experiments; potato dextrose agar showed the next lowest, but there was no signifi...
The geometry of a two-level hierarchical rotating square system may be described by the aperture ... more The geometry of a two-level hierarchical rotating square system may be described by the aperture between the Level 0 squares (θ0), the aperture between the Level 1 square-like units (θ1) and the number of Level 0 repeat units (N0). This means that the Level 1 building block is made up of N0×N0 Level 0 repeat units which corresponds to 2N0×2N0 squares. These parameters may be used to de ne the linear dimensions of the Level 1 square-like units, u1 and v1, as follows: u1 = 2N0l cos ( θ0 2 ) + 2(N0 − 1)l sin ( θ0 2 ) and v1 = 2N0l ( cos ( θ0 2 ) + sin ( θ0 2 )) , where l stands for the length of the sides of the Level 0 squares. These dimensions can in turn be used to de ne the overall on-axis dimensions of the system:
Using experimental data, it is shown that the Poisson’s ratios of conventional (untreated) foam v... more Using experimental data, it is shown that the Poisson’s ratios of conventional (untreated) foam vary when loading in different loading directions, since foam is inherently asymmetric and anisotropic. The loading direction which is in plane orthogonal to the rise direction of the foam constantly exhibited the most negative Poisson’s ratio across foam samples of different types. It was also shown that although the foam may become auxetic at very high values of compressive strain, it shows an incremental negative Poisson’s ratio at much lower compressive strains. The results are compared to previous publications and the effects of changing loading direction on the mechanical response of the foam are highlighted.
SUMMARY The identification and quantification of phenolic compounds and flavonoids in various nat... more SUMMARY The identification and quantification of phenolic compounds and flavonoids in various natural food products is typically conducted using HPLC analysis. Their analysis is particularly complex since most natural food products contain a large number of different phenolic compounds, many of which have similar chemical characteristics such as polarity, which makes complete separation of all eluents extremely difficult. In this work we present and validate a method for the quantitative determination of the concentration of two compounds with similar retention times, i.e. they show overlapping peaks in a mixed solution. Two pairs of phenolic compounds were investigated: caffeic and vanillic acids and ferulic and p-coumaric acids. This technique takes advantage of the different absorbances of the two phenolic compounds in the eluent at various wavelengths and can be used for the quantitative determination of the concentration of these compounds even if they are not separated in the ...
H2O ice is known to exist as a number of different polymorphs. One such polymorph is ice X, a sym... more H2O ice is known to exist as a number of different polymorphs. One such polymorph is ice X, a symmetrical phase of ice which is known to be stable at high pressures and low temperatures. In this work, the mechanical properties of ice X have been studied through DFT simulations, and it has been shown that ice X has the potential to exhibit auxetic behaviour (negative Poisson's ratio) at 45° off-axis in the (100), (010) and (001) planes. Studying the deformation of two orthogonally interconnected rhombi has shown that this predicted negative Poisson's ratio can be attributed to the interplay between distortion and hinging of these rhombi. Moreover, it has been shown that the auxetic potential of ice X increases with an increase in hydrostatic pressure, which behaviour is explained by the rhombi approaching quasi-perfect behaviour resulting in a decrease in the distortion of the rhombi and an increase in hinging mechanism.
Acta Scientific Orthopaedics
Acta Mechanica
Mechanical metamaterials are systems which derive their mechanical properties from their structur... more Mechanical metamaterials are systems which derive their mechanical properties from their structure rather than their intrinsic material composition. In this work, we investigate a class of highly anisotropic mechanical metamaterials designed by the introduction of diamond and elliptically shaped perforations which possess the ability to show auxetic behaviour. By the use of finite element simulations, we show how these highly tuneable systems have the potential to exhibit a large range of Poisson’s ratios, ranging from highly positive to giant negative values, simply by altering the geometric parameters and orientation of the perforations. The anomalous properties of these systems have also been shown to be retained over significant tensile strain ranges, highlighting the vast potential applicability and functionality of these mechanical metamaterials.
International Journal of Solids and Structures
Abstract In this work, through the use of Molecular Dynamics simulations, we show the capability ... more Abstract In this work, through the use of Molecular Dynamics simulations, we show the capability of different mechanical metamaterials to induce their own global rotational motion as a result of an internal deformation. We also show that one of the considered structures, i.e. the hexachiral system, may manifest a superior extent of the global rotation in comparison to other systems. In addition to that, we discuss that the self-induced global rotation can be observed for mechanical metamaterials with a discrete mass distribution which allows to prove that this phenomenon is not limited to macroscopic systems and applications involving the control of the rotational motion of objects such as satellites or wind turbines where the continuous mass distribution of structural elements is normally required. In fact, this study serves as a blueprint to show that a similar effect may also be expected for various systems at very different scales.
AIP Advances
In this work, we propose the concept that a device based on mechanical metamaterials can be used ... more In this work, we propose the concept that a device based on mechanical metamaterials can be used to induce and control its own rotational motion as a result of internal deformations due to the conversion of translational degrees of freedom into rotational ones. The application of a linear force on the structural units of the system may be fine-tuned in order to obtain a desired type of rotation. In particular, we show, how it is possible to maximise the extent of rotation of the system through the alteration of the geometry of the system. We also show how a device based on this concept can be connected to an external body in order to rotate it which result may potentially prove to be very important in the case of applications such as telescopes employed in space.
International Journal of Fruit Science, 2016
ABSTRACT In this article a detailed review of the fungal diseases that can affect pear fruit is p... more ABSTRACT In this article a detailed review of the fungal diseases that can affect pear fruit is provided. Each section comprises a complete description of the fungi responsible for the diseases and the symptoms they produce on the pears. The majority of pear fungal diseases, including blue mold, grey mold, bitter rot, black spot, brown rot, bull’s eye rot, Phytophthora rot, pink mold rot, powdery mildew, Rhizopus rot, scab, side rot, sooty blotch, and flyspeck, are presented. Sources of infection are comprehensively described in relation to harvesting or post-harvesting handling and intervention practices, respectively. As these diseases are dependent on a number of environmental parameters, the optimal temperature ranges for disease development are described and the causal agents are identified. Previous studies on the diagnostic indications are reviewed while information about the optimal environmental parameters of temperature, pressure, pH, water activity, and oxygen level for the fungal growth is comprehensively summarized.
Materials
In this work, we use computer simulations (Molecular Dynamics) to analyse the behaviour of a spec... more In this work, we use computer simulations (Molecular Dynamics) to analyse the behaviour of a specific auxetic hierarchical mechanical metamaterial composed of square-like elements. We show that, depending on the design of hinges connecting structural elements, the system can exhibit a controllable behaviour where different hierarchical levels can deform to the desired extent. We also show that the use of different hinges within the same structure can enhance the control over its deformation and mechanical properties, whose results can be applied to other mechanical metamaterials. In addition, we analyse the effect of the size of the system as well as the variation in the stiffness of its hinges on the range of the exhibited auxetic behaviour (negative Poisson’s ratio). Finally, it is discussed that the concept presented in this work can be used amongst others in the design of highly efficient protective devices capable of adjusting their response to a specific application.
Materials
In this work, through the use of a theoretical model, we analyse the potential of a specific thre... more In this work, through the use of a theoretical model, we analyse the potential of a specific three-dimensional mechanical metamaterial composed of arrowhead-like structural units to exhibit a negative Poisson’s ratio for an arbitrary loading direction. Said analysis allows us to assess its suitability for use in applications where materials must be able to respond in a desired manner to a stimulus applied in multiple directions. As a result of our studies, we show that the analysed system is capable of exhibiting auxetic behaviour for a broad range of loading directions, with isotropic behaviour being shown in some planes. In addition to that, we show that there are also certain loading directions in which the system manifests negative linear compressibility. This enhances its versatility and suitability for a number of applications where materials exhibiting auxetic behaviour or negative linear compressibility are normally implemented.
physica status solidi (b)
physica status solidi (b)
physica status solidi (b)
Although, high heels are known to affect the biomechanics of human movement, most notably by incr... more Although, high heels are known to affect the biomechanics of human movement, most notably by increasing forefoot plantar pressure it is commonly used worn due to the influence of fashion. To deal with resulting clinical issues some prescriptions include the use of cushioning pads to redistribute the plantar loads and increase comfort. This preliminary study has sought to investigate whether auxetic foam would be a good candidate for the redistribution of plantar loafing in the forefoot when compared to a more traditional material. From the results obtained, it was shown that auxetic foam demonstrated a decrease in forefoot peak plantar pressure while a commercial product, a material traditionally used for plantar cover paddings, increased pressure in the region of the 2 nd-4 th MPJ. This demonstrates the potential for auxetic materials to become a material of choice for such applications, especially since it can be further remodeled until its properties can produce a significant forefoot pressure reduction.
Materials & Design
The term "mechanical metamaterials" encompasses a wide range of systems whose anomalous mechanica... more The term "mechanical metamaterials" encompasses a wide range of systems whose anomalous mechanical properties arise primarily from their structure rather than composition. This unique characteristic gives them an edge over many conventional natural or readily available materials and makes them well-suited for a variety of applications where tailormade mechanical properties are required. In this study, we present a new class of mechanical metamaterials featuring various star-shaped perforations, which have the potential to exhibit auxetic or zero Poisson's ratio () properties. Using finite element modelling in conjunction with experimental measurements on 3D printed prototypes, we demonstrate that these starshaped porous systems possess the potential to retain their unusual mechanical properties up to tensile strains exceeding 15%. By virtue of these exceptional properties, the proposed concept could be applied for engineering numerous potential applications in a wide range of fields.
physica status solidi (b)
Journal of Food Processing and Preservation
Journal of food protection, 2018
Rapid assessment of fungal growth and screening antifungal compounds, such as nanoparticles (NPs)... more Rapid assessment of fungal growth and screening antifungal compounds, such as nanoparticles (NPs), for effectiveness is a challenging procedure because no primary standards exist as they do for yeasts and bacteria. Because fungi do not grow as single cells, but as hyphal filaments, they cannot be quantified by the usual enumeration techniques used in bacteriology. The growth of three postharvest fungal isolates ( Alternaria alternata, Rhizopus stolonifer, and Botrytis cinerea) was investigated at different inoculum concentrations and in three nutrient media (Sabouraud dextrose agar, potato dextrose agar, and yeast extract dextrose agar [YED]) with a turbidimetric assay. Sequential measurements were performed to generate optical density versus time plots, whereas the growth responses were expressed quantitatively as the generated trapezoidal area. YED medium showed the lowest variation among replicated experiments; potato dextrose agar showed the next lowest, but there was no signifi...