Michalis Velegrakis | Foundation for Research and Technology - Hellas (original) (raw)
Papers by Michalis Velegrakis
Food science and engineering, Dec 21, 2023
Analytical Letters, Oct 15, 2023
EVOO is widely considered a superior edible oil due to its unique taste and aroma. Its consumptio... more EVOO is widely considered a superior edible oil due to its unique taste and aroma. Its consumption is associated with several health benefits, many of which are attributed to its phenolic compounds. This work involved the analysis of 203 EVOO samples using the official method recommended by the IOC (COI/T.20/Doc. No 29/ Rev.1 2017) to determine their polyphenolic content. In addition, ultraviolet (UV) absorption spectroscopy has been applied to the same EVOO samples in combination with PLS regression to assess the polyphenolic content. This work demonstrates that ultraviolet absorption spectroscopy offers an efficient and cost-effective alternative.
Journal of the Science of Food and Agriculture, 2021
BACKGROUNDThe botanical origin of honey attracts both commercial and research interest. Consumers... more BACKGROUNDThe botanical origin of honey attracts both commercial and research interest. Consumers’ preferences and medicinal uses of particular honey types drive the demand for the determination of their authenticity with regard to their botanical origin. This study presents the discrimination of thyme, multi‐floral. and honeydew honeys by Fourier‐transform infrared (FTIR) and ultraviolet (UV) absorption spectroscopy combined with multivariate statistical analysis. UV absorption spectroscopy was applied without any dilution of the sample using a custom‐made cuvette. FTIR and UV absorption spectroscopic data were processed by means of the orthogonal partial least squares discriminant analysis.RESULTSThe optimal classification of floral and honeydew honeys was accomplished with UV spectroscopy with a successful estimation of 92.65% for floral honey and 91.30% for honeydew honey. The discrimination of thyme versus the multi‐floral honey was best achieved with FTIR, with a correct class...
Metal Ion Solvation and Metal-Ligand Interactions, 2001
Analytical Letters, 2016
The adulteration of extra virgin olive oil with low quality and inexpensive seed oil is a serious... more The adulteration of extra virgin olive oil with low quality and inexpensive seed oil is a serious problem in the industry. In recent years, the characterization of extra virgin olive oil adulteration with various techniques has been successfully implemented. In this work, a comparative study of Raman and visible spectroscopy is presented. These methods are rapid, non-invasive, and no sample pretreatment is required. We used both methods to study Cretan extra virgin olive oil adulterated with sunflower oil. Statistical analysis based on partial least squares regression was used to determine the detection limits of the methods. Raman spectroscopy was superior in comparison to visible spectroscopy with detection limits of 3.5 and 5.5%, respectively, for the same samples. These results indicate that both techniques are suitable for olive oil quality control.
physica status solidi (b), 2014
Applied Physics A, 2014
ABSTRACT Oxygen-rich niobium oxide clusters are formed by mixing laser-produced Nb plasma with pu... more ABSTRACT Oxygen-rich niobium oxide clusters are formed by mixing laser-produced Nb plasma with pure oxygen, and their stability is investigated by mass spectrometry and collision-induced dissociation. We use an experimental configuration recently developed by our group, where the cluster ions beam is crossed with a secondary beam of noble gas atoms, and the fragments are rejected by a retarding field energy analyzer. In this way, the relative collision cross sections of Nb x O y + (x = 1, 2, y = 2–12) clusters have been measured and information about their fragmentation channels has been obtained.
International Journal of Mass Spectrometry and Ion Processes, 1996
We present mass spectra obtained using a simple cluster source based on the mixing of the plasma ... more We present mass spectra obtained using a simple cluster source based on the mixing of the plasma produced from the laser ablation of a solid target with the supersonic expansion of a noble gas. Depending on the formatiou conditions, tills source produces several distinct types of cluster, such as the strongly bonded covalent C.;,. and the weakly bonded ('-/Si~/Ge ~-doped noble gas clusters. From the analysis of the observed time-of-flight spectra as a function of the source conditions, we are able to infer the possible microscopic mechanisms responsible for the !k~rmation of flmse clusters.
Physical Chemistry Chemical Physics, 1999
ABSTRACT The photofragmentation spectrum of the Sr+Ar2 duster has been recorded in a time of flig... more ABSTRACT The photofragmentation spectrum of the Sr+Ar2 duster has been recorded in a time of flight mass spectrometer and in the energy range 21 000-27 000 cm(-1). Three absorption bands are observed which are related to transitions from the ground electronic state, X (2)A(1), to the three states that correlate with 5p orbitals of Sr+. The first and third bands result from the production of pure Sr+, while the second band is associated with the production of Sr+ and Sr+Ar in almost equal amounts. Potential energy surfaces computed using a one electron perturbation theory and expression in analytical forms offer a framework for the interpretation of the photofragmentation spectra.
Materials Letters, 1999
Ž. A new configuration of the pulsed laser deposition PLD technique for improving the growth of t... more Ž. A new configuration of the pulsed laser deposition PLD technique for improving the growth of thin films in a gas ambient is described. A nozzle arrangement is used to create high pressure N and He pulses in the region above an ablated 2 carbon target for the formation of C:N and C thin films. Films deposited by both the standard and the new configuration are compared in terms of their mechanical properties, nitrogen concentration and microstructure. When the standard configuration is used, the maximum values attained for the nitrogen concentration and film microhardness are 32.25% and 13 GPa, Ž. respectively. When the pulsed N nozzle configuration is used, the nitrogen concentration 30.58% is almost equal to the 2 Ž. highest value attained with the standard configuration but the film microhardness is higher 15.8 GPa. When the He nozzle is used the film microhardness increases further, up to a value of 34 GPa. Interestingly, the elastic recovery of most films reaches relatively high values, between 60% and 70%. In all cases the films are amorphous and macroparticle inclusions are observed.
The Journal of Chemical Physics, 1998
Photoionization of iron pentacarbonyl/argon clusters with 30 ps, 266 nm laser pulses results in t... more Photoionization of iron pentacarbonyl/argon clusters with 30 ps, 266 nm laser pulses results in the ultimate detection of iron ions solvated with argon atoms. Clusters such as Fem+Arn (m=1,2; n=1–26) are readily observed following the laser-induced decarbonylation of the [Fe(CO)5]mArn species formed in the supersonic jet. An interesting intensity alternation of the Fe+Arn ions is observed up to a magic number at n=6, after which a monotonically decreasing intensity pattern is noted. The pattern is similar to a more extensive spectrum (with additional magic numbers) observed in separate experiments where metallic iron is laser ablated into a supersonic flow of argon, krypton, or xenon, and the resulting cluster ions are detected in a reflectron mass spectrometer. In another experiment in the latter apparatus, the sputtering of iron into a mixture of carbon monoxide and argon shows the relative reactivity of Fe+ to form Fe+Arn and Fe+(CO)n ions. Mechanisms for the energy disposal duri...
The Journal of Chemical Physics, 1998
The mass spectra of argon clusters doped with d9 transition metal ions, Ni+Arn and Pt+Arn, show p... more The mass spectra of argon clusters doped with d9 transition metal ions, Ni+Arn and Pt+Arn, show pronounced intensity at n=4 and n=6. Density functional theory geometry optimization calculations in Ni+Arn support a square planar geometry for Ni+Ar4 and an elongated octahedron for Ni+Ar6.
The Journal of Chemical Physics, 1996
The photofragmentation spectrum of the weakly bound Sr+Ar is measured over the 418–448 nm wavelen... more The photofragmentation spectrum of the weakly bound Sr+Ar is measured over the 418–448 nm wavelength region. Two vibrational progressions are observed and are attributed to transitions from the X2 Σ1/2 electronic ground state to vibrational levels of the excited A 2Π1/2 and A 2Π3/2 states. Isotope-resolved measurements of several of the observed transitions are performed to obtain the absolute vibrational numbering. From these, the spectroscopic constants of the involved states are deduced. We obtain ωe′=120.8 cm−1, ωeχe′=1.67 cm−1, and D0′=2303±232 cm−1 for the A 2Π1/2 state and ωe′=122 cm−1, ωeχe′=1.6 cm−1, and D0′=2575±256 cm−1 for the A 2Π3/2 state. For the ground X 2Σ1/2 state the observed hot bands yield ΔG1/2″=48 cm−1. Furthermore a value of 803±244 cm−1 is estimated for D0″. Finally the potential constants are compared with pseudopotential calculations from literature and the trends of binding energies for group II cation–argon complexes are discussed.
The Journal of Chemical Physics, 1998
We present the size distributions of metal ion-doped noble gas clusters of the form M+Xn (M=Mg, K... more We present the size distributions of metal ion-doped noble gas clusters of the form M+Xn (M=Mg, K and X=Ar, Kr, Xe) studied with time-of-flight mass spectrometry. All the recorded spectra exhibit magic number patterns, which change gradually from the familiar icosahedral sequence N=n+1=13,19,23,26,29,32 to another one that exhibits the magic numbers N=9,10,11,17,21,24,26,27,30, as the atomic size ratio of the metal ion to the noble gas atom decreases. Furthermore, as the cluster size N increases, the new sequence seems to convert again to the icosahedral one at some critical cluster size. Molecular dynamics simulations using pairwise additive Lennard-Jones potentials are performed in order to investigate the stability and the geometrical structure of these systems as a function of radii ratio, interaction energy, and cluster size. The results obtained are in very good agreement with the experimental ones and indicate that when the size of the dopant is comparable to that of the nobl...
The Journal of Chemical Physics, 1991
In K–C2H2 collisions at collision energies 0.4≲E≲1.3 eV and scattering angles 40°≲ϑ≲180° surprisi... more In K–C2H2 collisions at collision energies 0.4≲E≲1.3 eV and scattering angles 40°≲ϑ≲180° surprisingly little transfer of energy from translation into the internal degrees of freedom of the acetylene molecule is found. The observations are consistent with the assumptions of electronically covalent encounters, insignificant activation of the acetylene vibrations, and rotational excitation produced by spindle-shaped equipotentials, nearly spherical in a broad vicinity of the C 3/4 C bond.
International Journal of Mass Spectrometry, 1999
Time-of-flight mass spectra of ionic species produced by the laser ablation of a YBa2Cu3O7−x targ... more Time-of-flight mass spectra of ionic species produced by the laser ablation of a YBa2Cu3O7−x target have been measured. The experimental geometry and laser conditions used in this study are similar to those used for the deposition of thin films by laser ablation. A comparison of the mass spectra by using both an infrared laser and an ultraviolet laser as irradiation sources, provides valuable information regarding the identification of the species responsible for the growth of thin films. In the case of the infrared laser both light- and heavy-mass species are observed. In the case of the ultraviolet laser, only metal ions and their oxides are observed. Oxygen introduced with a pulsed nozzle near the plume enhances the formation of oxides. It is suggested that these oxides provide the means by which the oxygen is transported to the substrate.
Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1988
Chemical Physics Letters, 1990
We have measured an angular distribution and time of flight spectra of HCI scattered from Ar at a... more We have measured an angular distribution and time of flight spectra of HCI scattered from Ar at a collision energy of 85 meV. QCT simulations of the time of flight spectra based on the MS potential with Hutson and Howard's parameters deviate significantly from the data To remedy this discrepancy without deteriorating the properties of the M5 potential precisely known from spectroscopic data we had to revise those parameters which are responsible for the anisotropy of the well depth. We find a lower rotational barrier between the two collinear conformations and further indication for the existence of a secondary potential energy minimum.
Food science and engineering, Dec 21, 2023
Analytical Letters, Oct 15, 2023
EVOO is widely considered a superior edible oil due to its unique taste and aroma. Its consumptio... more EVOO is widely considered a superior edible oil due to its unique taste and aroma. Its consumption is associated with several health benefits, many of which are attributed to its phenolic compounds. This work involved the analysis of 203 EVOO samples using the official method recommended by the IOC (COI/T.20/Doc. No 29/ Rev.1 2017) to determine their polyphenolic content. In addition, ultraviolet (UV) absorption spectroscopy has been applied to the same EVOO samples in combination with PLS regression to assess the polyphenolic content. This work demonstrates that ultraviolet absorption spectroscopy offers an efficient and cost-effective alternative.
Journal of the Science of Food and Agriculture, 2021
BACKGROUNDThe botanical origin of honey attracts both commercial and research interest. Consumers... more BACKGROUNDThe botanical origin of honey attracts both commercial and research interest. Consumers’ preferences and medicinal uses of particular honey types drive the demand for the determination of their authenticity with regard to their botanical origin. This study presents the discrimination of thyme, multi‐floral. and honeydew honeys by Fourier‐transform infrared (FTIR) and ultraviolet (UV) absorption spectroscopy combined with multivariate statistical analysis. UV absorption spectroscopy was applied without any dilution of the sample using a custom‐made cuvette. FTIR and UV absorption spectroscopic data were processed by means of the orthogonal partial least squares discriminant analysis.RESULTSThe optimal classification of floral and honeydew honeys was accomplished with UV spectroscopy with a successful estimation of 92.65% for floral honey and 91.30% for honeydew honey. The discrimination of thyme versus the multi‐floral honey was best achieved with FTIR, with a correct class...
Metal Ion Solvation and Metal-Ligand Interactions, 2001
Analytical Letters, 2016
The adulteration of extra virgin olive oil with low quality and inexpensive seed oil is a serious... more The adulteration of extra virgin olive oil with low quality and inexpensive seed oil is a serious problem in the industry. In recent years, the characterization of extra virgin olive oil adulteration with various techniques has been successfully implemented. In this work, a comparative study of Raman and visible spectroscopy is presented. These methods are rapid, non-invasive, and no sample pretreatment is required. We used both methods to study Cretan extra virgin olive oil adulterated with sunflower oil. Statistical analysis based on partial least squares regression was used to determine the detection limits of the methods. Raman spectroscopy was superior in comparison to visible spectroscopy with detection limits of 3.5 and 5.5%, respectively, for the same samples. These results indicate that both techniques are suitable for olive oil quality control.
physica status solidi (b), 2014
Applied Physics A, 2014
ABSTRACT Oxygen-rich niobium oxide clusters are formed by mixing laser-produced Nb plasma with pu... more ABSTRACT Oxygen-rich niobium oxide clusters are formed by mixing laser-produced Nb plasma with pure oxygen, and their stability is investigated by mass spectrometry and collision-induced dissociation. We use an experimental configuration recently developed by our group, where the cluster ions beam is crossed with a secondary beam of noble gas atoms, and the fragments are rejected by a retarding field energy analyzer. In this way, the relative collision cross sections of Nb x O y + (x = 1, 2, y = 2–12) clusters have been measured and information about their fragmentation channels has been obtained.
International Journal of Mass Spectrometry and Ion Processes, 1996
We present mass spectra obtained using a simple cluster source based on the mixing of the plasma ... more We present mass spectra obtained using a simple cluster source based on the mixing of the plasma produced from the laser ablation of a solid target with the supersonic expansion of a noble gas. Depending on the formatiou conditions, tills source produces several distinct types of cluster, such as the strongly bonded covalent C.;,. and the weakly bonded ('-/Si~/Ge ~-doped noble gas clusters. From the analysis of the observed time-of-flight spectra as a function of the source conditions, we are able to infer the possible microscopic mechanisms responsible for the !k~rmation of flmse clusters.
Physical Chemistry Chemical Physics, 1999
ABSTRACT The photofragmentation spectrum of the Sr+Ar2 duster has been recorded in a time of flig... more ABSTRACT The photofragmentation spectrum of the Sr+Ar2 duster has been recorded in a time of flight mass spectrometer and in the energy range 21 000-27 000 cm(-1). Three absorption bands are observed which are related to transitions from the ground electronic state, X (2)A(1), to the three states that correlate with 5p orbitals of Sr+. The first and third bands result from the production of pure Sr+, while the second band is associated with the production of Sr+ and Sr+Ar in almost equal amounts. Potential energy surfaces computed using a one electron perturbation theory and expression in analytical forms offer a framework for the interpretation of the photofragmentation spectra.
Materials Letters, 1999
Ž. A new configuration of the pulsed laser deposition PLD technique for improving the growth of t... more Ž. A new configuration of the pulsed laser deposition PLD technique for improving the growth of thin films in a gas ambient is described. A nozzle arrangement is used to create high pressure N and He pulses in the region above an ablated 2 carbon target for the formation of C:N and C thin films. Films deposited by both the standard and the new configuration are compared in terms of their mechanical properties, nitrogen concentration and microstructure. When the standard configuration is used, the maximum values attained for the nitrogen concentration and film microhardness are 32.25% and 13 GPa, Ž. respectively. When the pulsed N nozzle configuration is used, the nitrogen concentration 30.58% is almost equal to the 2 Ž. highest value attained with the standard configuration but the film microhardness is higher 15.8 GPa. When the He nozzle is used the film microhardness increases further, up to a value of 34 GPa. Interestingly, the elastic recovery of most films reaches relatively high values, between 60% and 70%. In all cases the films are amorphous and macroparticle inclusions are observed.
The Journal of Chemical Physics, 1998
Photoionization of iron pentacarbonyl/argon clusters with 30 ps, 266 nm laser pulses results in t... more Photoionization of iron pentacarbonyl/argon clusters with 30 ps, 266 nm laser pulses results in the ultimate detection of iron ions solvated with argon atoms. Clusters such as Fem+Arn (m=1,2; n=1–26) are readily observed following the laser-induced decarbonylation of the [Fe(CO)5]mArn species formed in the supersonic jet. An interesting intensity alternation of the Fe+Arn ions is observed up to a magic number at n=6, after which a monotonically decreasing intensity pattern is noted. The pattern is similar to a more extensive spectrum (with additional magic numbers) observed in separate experiments where metallic iron is laser ablated into a supersonic flow of argon, krypton, or xenon, and the resulting cluster ions are detected in a reflectron mass spectrometer. In another experiment in the latter apparatus, the sputtering of iron into a mixture of carbon monoxide and argon shows the relative reactivity of Fe+ to form Fe+Arn and Fe+(CO)n ions. Mechanisms for the energy disposal duri...
The Journal of Chemical Physics, 1998
The mass spectra of argon clusters doped with d9 transition metal ions, Ni+Arn and Pt+Arn, show p... more The mass spectra of argon clusters doped with d9 transition metal ions, Ni+Arn and Pt+Arn, show pronounced intensity at n=4 and n=6. Density functional theory geometry optimization calculations in Ni+Arn support a square planar geometry for Ni+Ar4 and an elongated octahedron for Ni+Ar6.
The Journal of Chemical Physics, 1996
The photofragmentation spectrum of the weakly bound Sr+Ar is measured over the 418–448 nm wavelen... more The photofragmentation spectrum of the weakly bound Sr+Ar is measured over the 418–448 nm wavelength region. Two vibrational progressions are observed and are attributed to transitions from the X2 Σ1/2 electronic ground state to vibrational levels of the excited A 2Π1/2 and A 2Π3/2 states. Isotope-resolved measurements of several of the observed transitions are performed to obtain the absolute vibrational numbering. From these, the spectroscopic constants of the involved states are deduced. We obtain ωe′=120.8 cm−1, ωeχe′=1.67 cm−1, and D0′=2303±232 cm−1 for the A 2Π1/2 state and ωe′=122 cm−1, ωeχe′=1.6 cm−1, and D0′=2575±256 cm−1 for the A 2Π3/2 state. For the ground X 2Σ1/2 state the observed hot bands yield ΔG1/2″=48 cm−1. Furthermore a value of 803±244 cm−1 is estimated for D0″. Finally the potential constants are compared with pseudopotential calculations from literature and the trends of binding energies for group II cation–argon complexes are discussed.
The Journal of Chemical Physics, 1998
We present the size distributions of metal ion-doped noble gas clusters of the form M+Xn (M=Mg, K... more We present the size distributions of metal ion-doped noble gas clusters of the form M+Xn (M=Mg, K and X=Ar, Kr, Xe) studied with time-of-flight mass spectrometry. All the recorded spectra exhibit magic number patterns, which change gradually from the familiar icosahedral sequence N=n+1=13,19,23,26,29,32 to another one that exhibits the magic numbers N=9,10,11,17,21,24,26,27,30, as the atomic size ratio of the metal ion to the noble gas atom decreases. Furthermore, as the cluster size N increases, the new sequence seems to convert again to the icosahedral one at some critical cluster size. Molecular dynamics simulations using pairwise additive Lennard-Jones potentials are performed in order to investigate the stability and the geometrical structure of these systems as a function of radii ratio, interaction energy, and cluster size. The results obtained are in very good agreement with the experimental ones and indicate that when the size of the dopant is comparable to that of the nobl...
The Journal of Chemical Physics, 1991
In K–C2H2 collisions at collision energies 0.4≲E≲1.3 eV and scattering angles 40°≲ϑ≲180° surprisi... more In K–C2H2 collisions at collision energies 0.4≲E≲1.3 eV and scattering angles 40°≲ϑ≲180° surprisingly little transfer of energy from translation into the internal degrees of freedom of the acetylene molecule is found. The observations are consistent with the assumptions of electronically covalent encounters, insignificant activation of the acetylene vibrations, and rotational excitation produced by spindle-shaped equipotentials, nearly spherical in a broad vicinity of the C 3/4 C bond.
International Journal of Mass Spectrometry, 1999
Time-of-flight mass spectra of ionic species produced by the laser ablation of a YBa2Cu3O7−x targ... more Time-of-flight mass spectra of ionic species produced by the laser ablation of a YBa2Cu3O7−x target have been measured. The experimental geometry and laser conditions used in this study are similar to those used for the deposition of thin films by laser ablation. A comparison of the mass spectra by using both an infrared laser and an ultraviolet laser as irradiation sources, provides valuable information regarding the identification of the species responsible for the growth of thin films. In the case of the infrared laser both light- and heavy-mass species are observed. In the case of the ultraviolet laser, only metal ions and their oxides are observed. Oxygen introduced with a pulsed nozzle near the plume enhances the formation of oxides. It is suggested that these oxides provide the means by which the oxygen is transported to the substrate.
Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1988
Chemical Physics Letters, 1990
We have measured an angular distribution and time of flight spectra of HCI scattered from Ar at a... more We have measured an angular distribution and time of flight spectra of HCI scattered from Ar at a collision energy of 85 meV. QCT simulations of the time of flight spectra based on the MS potential with Hutson and Howard's parameters deviate significantly from the data To remedy this discrepancy without deteriorating the properties of the M5 potential precisely known from spectroscopic data we had to revise those parameters which are responsible for the anisotropy of the well depth. We find a lower rotational barrier between the two collinear conformations and further indication for the existence of a secondary potential energy minimum.