The occurrence of one specimen of Am-phiorchis solus (Simha & Chattopadhyaya, 1970) found in the ... more The occurrence of one specimen of Am-phiorchis solus (Simha & Chattopadhyaya, 1970) found in the heart of a green sea turtle Chelonia mydas Linnaeus, 1758 from Ceará state, Brazil, is reported. A comparison of the morphology of Amphorchis caborojoensis Fischthal & Acholonu, 1976 and A. solus also is presented. A new geographical distribution of A. solus is reported. The family Spirorchiidae Stunkard, 1921 includes 10 genera reported only from sea turtles (Platt, 2002). Only 4 spirorchiid species have been reported from turtles in Brazil: Learedius learedi Price, 1934 (Werneck et al., 2006) and Monticellius indicum Mehra, 1939 (Werneck et al., 2008a) in Chelonia mydas Linnaeus, 1758; and Carettacola stunkard Martin & Bamberger, 1952 and Amphiorchis cabor-ojoensis Fischthal & Acholonu, 1976 in Eretmo-chelys imbricata Linnaeus, 1758 (Werneck et al., 2008b). The present note reports the first occurrence of Amphiorchis solus (Simha & Chattopadhyaya, 1970) in Brazilian waters. In October ...
Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará co... more Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará coast in NE Brazil are reported. Concentrations varied from <0.34 to 856.6 ng.g(-1) d.w., and were highest (average of 154.8 ng.g(-1) d.w.) in juveniles (n = 22), whereas lowest concentrations (average of 2.5 ng.g(-1) d.w.) were observed in adult/sub-adult animals (n = 3). There was a significant negative correlation between animal size and Hg concentration probably due to different diets between juveniles and sub-adults/adults. Carapace fragments, which are non-invasive, non-lethal substrates, may be of importance for monitoring purposes of these generally endangered species.
... rates and behaviour. Through these research and conservation activities, TAMARis gaining a be... more ... rates and behaviour. Through these research and conservation activities, TAMARis gaining a better understandingof sea turtles at different life history stages and working to protect them as well as their habitats. All work is carried ...
The helminth fauna of 31 juvenile specimens of Eretmochelys imbricata from the Brazilian coast wa... more The helminth fauna of 31 juvenile specimens of Eretmochelys imbricata from the Brazilian coast was examined. Seventeen individuals were infected with helminths (54.8%). The heminths found were: Diaschistorchis pandus, Cricocephalus albus, Metacetabulum invaginatum, Pronocephalus obliquus (Pronocephalidae), Cymatocarpus solearis (Brachycoeliidae), Styphlotrema solitaria (Styphlotrematidae), Carettacola stunkardi, Amphiorchis caborojoensis (Spirorchiidae), Orchidasma amphiorchis (Telorchiidae) and Anisakis type I nematode larvae. Species richness, mean intensity, and abundance, were lower than in the other sea turtle species, mainly due to the life phase of analyzed individuals. This report is the first analysis of parasite communities in this host.
Polymer brushes can be used, e.g., to stabilize colloids, reduce friction between surfaces and to... more Polymer brushes can be used, e.g., to stabilize colloids, reduce friction between surfaces and to provide lubrication in artificial joints. In this talk, we will present results from the polymer density-functional theory calculations on the structure, phase behavior and colloidal forces at various solution conditions. The implication of theoretical predictions to relevant experiments, in particular, for fabrication of protein-resistant surfaces, will also be discussed.
Data from several sources and original data are presented regarding sightings, strandings and inc... more Data from several sources and original data are presented regarding sightings, strandings and incidental captures of leatherback sea turtles (Dermochelys coriacea) on the Brazilian coast in a 33 year period, from 1969 to 2001. Two of the turtles were small juveniles (curved carapace length¼40 cm and approximately 85 cm) and the remaining animals with known carapace size were large juveniles or adults. The origin of leatherbacks observed in Brazil is unknown. Several colonies in South America, including a Brazilian one, in the Caribbean, in western Africa and even in eastern South Africa could be the source of these turtles. The data presented here suggest that more e¡ort should be directed to the assessment of the impact of ¢shing gear and marine pollution on leatherbacks and that systematic surveys on beaches should be maintained in order to monitor long term £uctuations in stranding levels and spatial stranding patterns. Genetic studies and satellite telemetry would be helpful in clarifying the origin of leatherbacks stranded or incidentally captured on the Brazilian coast.
The Donnan potential can be observed in many biological systems due to the presence of polyelectr... more The Donnan potential can be observed in many biological systems due to the presence of polyelectrolytes as proteins and nucleic acids. The aim of this work was to present a useful tool to describe the fixed and charge-regulated volume charge density profile through the use of a smoothing function and to obtain the electrostatic potential profile as well as the Donnan potential of this system by solving Poisson-Boltzmann (PB) equation. When we use the smoothing function, the Donnan potential arises automatically from the solution of only one Poisson-Boltzmann equation and it is not necessary to impose this potential for treating charged system in the presence of a membrane. The electrostatic behavior across the Bacillus brevis wall considering the dependence on the ionization of the cell wall functional groups as a function of the solution pH was analyzed. An important issue was to show that potentiometric titration data could be used together with the Poisson-Boltzmann equation to predict the electrostatic behavior (e.g., zeta potential) of the bacterial cell surface.
The movements of 8 green turtles Chelonia mydas in Brazilian coastal waters were tracked using tr... more The movements of 8 green turtles Chelonia mydas in Brazilian coastal waters were tracked using transmitters linked to the Argos system for periods of between 1 and 197 d. These were the first tracking data gathered on juveniles of this species in this important foraging ground. Information was integrated with that collected over a decade using traditional flipper-tagging methods at the same site. Both satellite telemetry and flipper tagging suggested that turtles undertook 1 of 3 general patterns of behaviour: pronounced long range movements (>100 km), moderate range movements (<100 km) or extended residence very close to the capture/release site. There seemed to be a general tendency for the turtles recaptured/tracked further afield to have been among the larger turtles captured. Satellite tracking of 5 turtles which moved from the release site showed that they moved through coastal waters; a factor which is likely to predispose migrating turtles to incidental capture as a result of the prevailing fishing methods in the region. The movements of the 3 turtles who travelled less than 100 km from the release site challenge previous ideas relating to home range in green turtles feeding in sea grass pastures. We hypothesise that there may be a fundamental difference in the pattern of habitat utilisation by larger green turtles depending on whether they are feeding on seagrass or macroalgae. Extended tracking of 2 small turtles which stayed near the release point showed that small juvenile turtles, whilst in residence in a particular feeding ground, can also exhibit high levels of site-fidelity with home ranges of the order of several square kilometers.
In virtually all mammal cells, we can observe a much higher concentration of potassium ions insid... more In virtually all mammal cells, we can observe a much higher concentration of potassium ions inside the cell and vice versa for sodium ions. Classical theories ignore the specific ion effects and the difference in the thermodynamic reference states between intracellular and extracellular environments. Usually, this differential ion partitioning across a cell membrane is attributed exclusively to the active ion transport. Our aim is to investigate how much the dispersion forces contribute to active ion pumps in an erythrocyte (red blood cell) as well as the correction of chemical potential reference states between intracellular and extracellular environments. The ionic partition and the membrane potential in an erythrocyte are analyzed by the modified Poisson−Boltzmann equation, considering nonelectrostatic interactions between ions and macromolecules. Results show that the nonelectrostatic potential calculated by Lifshitz theory has only a small influence with respect to the high concentration of K + in the intracellular environment in comparison with Na + .
Testing theories of dispersal is challenging in highly migratory species. In sea turtles, populat... more Testing theories of dispersal is challenging in highly migratory species. In sea turtles, population size, geographic distance, natal homing, and ocean currents are hypothesized to affect dispersal. Little is known, however, about these mechanisms in sea turtles foraging along the South American coast. Green sea turtles feeding at Ubatuba (UB, n 5 114) and Almofala (AF, n 5 117), Brazil, were sequenced at the mitochondrial DNA (mtDNA) control region (486 bp) and genotyped at 7 microsatellite loci to test dispersal hypotheses. Fifteen mtDNA haplotypes were revealed, including a previously undescribed sequence, and the average observed heterozygosity (H o ) was 76.4%. Overall short-term temporal differences were not detected, and differentiation was less pronounced in microsatellite than in mtDNA analyses. Mitochondrial results reveal significant differentiation between the Brazilian feeding grounds and most other Atlantic groups, whereas microsatellites uncover similarities to some of the geographically closest populations. Ubatuba and Almofala are mixed stocks, drawn primarily from Ascension, with lesser contributions from Surinam/Aves and Trindade. Costa Rica is also a significant source of individuals feeding at AF. The results are consistent with a model of juvenile natal homing impacted by other factors. Effective protection of turtles foraging along the extensive Brazilian coast may enhance breeding populations thousands of kilometers away.
There is a considerable effort in the literature trying to calculate the mean force between globu... more There is a considerable effort in the literature trying to calculate the mean force between globular proteins (and colloidal particles). To this purpose, we used here the ion-specific Poisson-Boltzmann (PB) equation that presents good results of ionic concentration profiles around a macroion, especially for salt solutions containing monovalent ions. The ion-specific PB equation includes not only electrostatic interactions but also dispersion potentials, originated from polarizabilities of ions and proteins. This enables us to predict ion-specific properties of colloidal systems. Results are in agreement with the experimental observed Hofmeister series. The main contribution of this paper is the use of a differential approach to calculate the mean force between aqueous proteins and colloidal particles instead of the classical quadrature approach. The integral expressions needed to calculate the mean force, potential of mean force and second virial coefficients have been avoided using this new numerical procedure. These integrals were transformed in a set of first order partial differential equations solved simultaneously with the ion-specific PB equation. Resulted expressions were written in bispherical coordinates, and then numerically solved through finite volume method. This simultaneous approach presents more accuracy in the calculation of the mean force in comparison with the classical approach, where the potential profile is obtained by solving the PB equation, and mean force is calculated afterwards. Important thermodynamic properties are obtained from the mean force (and consequently, from the potential of mean force), e.g., osmotic second virial coefficients and phase diagrams. These thermodynamic properties are related to protein aggregation, essential in biotechnology and pharmaceutical industries.
A much-improved Poisson-Boltzmann equation for two globular proteins using bispherical coordinate... more A much-improved Poisson-Boltzmann equation for two globular proteins using bispherical coordinates is used to establish the potential of mean force (PMF) between two globular lysozyme particles. Calculations presented here include previously ignored ion-protein nonelectrostatic potentials. The lysozyme-lysozyme PMF is used to calculate osmotic second virial coeffiencients. The theoretical PMF curve as a function of sodium chloride concentration is successfully compared with that from experiment. Our theoretical PMF shows how the second virial coefficient and the phase diagram depends on salt concentration, pH and, most notably, on the choice of salt in the aquous solution. † Part of the "Keith E. Gubbins Festschrift".
Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará co... more Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará coast in NE Brazil are reported. Concentrations varied from <0.34 to 856.6 ng.g -1 d.w., and were highest (average of 154.8 ng.g -1 d.w.) in juveniles (n = 22), whereas lowest concentrations (average of 2.5 ng.g -1 d.w.) were observed in adult/sub-adult animals (n = 3). There was a significant negative correlation between animal size and Hg concentration probably due to different diets between juveniles and sub-adults/adults. Carapace fragments, which are non-invasive, non-lethal substrates, may be of importance for monitoring purposes of these generally endangered species.
In two-phase finite volume systems of electroneutral phospholipids, the electrolyte concentration... more In two-phase finite volume systems of electroneutral phospholipids, the electrolyte concentration is different in the two phases. The partitioning is highly anion-specific, a phenomenon not accounted for by classical electrolyte theories. It is explained if ionic dispersion forces that lead to specific ion binding are taken into account. The mechanism provides a contribution to active ion pumps not previously considered.
Mean-field theories that include nonelectrostatic interactions acting on ions near interfaces hav... more Mean-field theories that include nonelectrostatic interactions acting on ions near interfaces have been found to accommodate many experimentally observed ion specific effects. However, it is clear that this approach does not fully account for the liquid molecular structure and hydration effects. This is now improved by using parametrized ionic potentials deduced from recent nonprimitive model molecular dynamics (MD) simulations in a generalized Poisson-Boltzmann equation. We investigate how ion distributions and double layer forces depend on the choice of background salt. There is a strong ion specific double layer force set up due to unequal ion specific short-range potentials acting between ions and surfaces.
The interaction between surface patches of proteins with different surface properties has a vital... more The interaction between surface patches of proteins with different surface properties has a vital role to play driving conformational changes in proteins in different salt solutions. We demonstrate the existence of ion-specific attractive double-layer forces between neutral hydrophobic and hydrophilic surfaces in the presence of certain salt solutions. This is performed by solving a generalized Poisson-Boltzmann equation for two unequal surfaces. In the calculations, we utilize parametrized ion-surface potentials and dielectric-constant profiles deduced from recent non-primitive-model molecular dynamics simulations that partially account for molecular structure and hydration effects.
The double layer forces between spherical colloidal particles, according to the Poisson-Boltzmann... more The double layer forces between spherical colloidal particles, according to the Poisson-Boltzmann (PB) equation, have been accurately calculated in the literature. The classical PB equation takes into account only the electrostatic interactions, which play a significant role in colloid science. However, there are at, and above, biological salt concentrations other non-electrostatic ion specific forces acting that are ignored in such modelling. In this paper, the electrostatic potential profile and the concentration profile of co-ions and counterions near charged surfaces are calculated. These results are obtained by solving the classical PB equation and a modified PB equation in bispherical coordinates, taking into account the van der Waals dispersion interactions between the ions and both surfaces. Once the electrostatic potential is known we calculate the double layer force between two charged spheres. This is the first paper that solves the modified PB equation in bispherical coordinates. It is also the first time that the finite volume method is used to solve the PB equation in bispherical coordinates. This method divides the calculation domain into a certain number of sub-domains, where the physical law of conservation is valid, and can be readily implemented. The finite volume method is implemented for several geometries and when it is applied to solve PB equations presents low computational cost. The proposed method was validated by comparing the numerical results for the classical PB calculations with previous results reported in the literature. New numerical results using the modified PB equation successfully predicted the ion specificity commonly observed experimentally.
The occurrence of one specimen of Am-phiorchis solus (Simha & Chattopadhyaya, 1970) found in the ... more The occurrence of one specimen of Am-phiorchis solus (Simha & Chattopadhyaya, 1970) found in the heart of a green sea turtle Chelonia mydas Linnaeus, 1758 from Ceará state, Brazil, is reported. A comparison of the morphology of Amphorchis caborojoensis Fischthal & Acholonu, 1976 and A. solus also is presented. A new geographical distribution of A. solus is reported. The family Spirorchiidae Stunkard, 1921 includes 10 genera reported only from sea turtles (Platt, 2002). Only 4 spirorchiid species have been reported from turtles in Brazil: Learedius learedi Price, 1934 (Werneck et al., 2006) and Monticellius indicum Mehra, 1939 (Werneck et al., 2008a) in Chelonia mydas Linnaeus, 1758; and Carettacola stunkard Martin & Bamberger, 1952 and Amphiorchis cabor-ojoensis Fischthal & Acholonu, 1976 in Eretmo-chelys imbricata Linnaeus, 1758 (Werneck et al., 2008b). The present note reports the first occurrence of Amphiorchis solus (Simha & Chattopadhyaya, 1970) in Brazilian waters. In October ...
Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará co... more Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará coast in NE Brazil are reported. Concentrations varied from <0.34 to 856.6 ng.g(-1) d.w., and were highest (average of 154.8 ng.g(-1) d.w.) in juveniles (n = 22), whereas lowest concentrations (average of 2.5 ng.g(-1) d.w.) were observed in adult/sub-adult animals (n = 3). There was a significant negative correlation between animal size and Hg concentration probably due to different diets between juveniles and sub-adults/adults. Carapace fragments, which are non-invasive, non-lethal substrates, may be of importance for monitoring purposes of these generally endangered species.
... rates and behaviour. Through these research and conservation activities, TAMARis gaining a be... more ... rates and behaviour. Through these research and conservation activities, TAMARis gaining a better understandingof sea turtles at different life history stages and working to protect them as well as their habitats. All work is carried ...
The helminth fauna of 31 juvenile specimens of Eretmochelys imbricata from the Brazilian coast wa... more The helminth fauna of 31 juvenile specimens of Eretmochelys imbricata from the Brazilian coast was examined. Seventeen individuals were infected with helminths (54.8%). The heminths found were: Diaschistorchis pandus, Cricocephalus albus, Metacetabulum invaginatum, Pronocephalus obliquus (Pronocephalidae), Cymatocarpus solearis (Brachycoeliidae), Styphlotrema solitaria (Styphlotrematidae), Carettacola stunkardi, Amphiorchis caborojoensis (Spirorchiidae), Orchidasma amphiorchis (Telorchiidae) and Anisakis type I nematode larvae. Species richness, mean intensity, and abundance, were lower than in the other sea turtle species, mainly due to the life phase of analyzed individuals. This report is the first analysis of parasite communities in this host.
Polymer brushes can be used, e.g., to stabilize colloids, reduce friction between surfaces and to... more Polymer brushes can be used, e.g., to stabilize colloids, reduce friction between surfaces and to provide lubrication in artificial joints. In this talk, we will present results from the polymer density-functional theory calculations on the structure, phase behavior and colloidal forces at various solution conditions. The implication of theoretical predictions to relevant experiments, in particular, for fabrication of protein-resistant surfaces, will also be discussed.
Data from several sources and original data are presented regarding sightings, strandings and inc... more Data from several sources and original data are presented regarding sightings, strandings and incidental captures of leatherback sea turtles (Dermochelys coriacea) on the Brazilian coast in a 33 year period, from 1969 to 2001. Two of the turtles were small juveniles (curved carapace length¼40 cm and approximately 85 cm) and the remaining animals with known carapace size were large juveniles or adults. The origin of leatherbacks observed in Brazil is unknown. Several colonies in South America, including a Brazilian one, in the Caribbean, in western Africa and even in eastern South Africa could be the source of these turtles. The data presented here suggest that more e¡ort should be directed to the assessment of the impact of ¢shing gear and marine pollution on leatherbacks and that systematic surveys on beaches should be maintained in order to monitor long term £uctuations in stranding levels and spatial stranding patterns. Genetic studies and satellite telemetry would be helpful in clarifying the origin of leatherbacks stranded or incidentally captured on the Brazilian coast.
The Donnan potential can be observed in many biological systems due to the presence of polyelectr... more The Donnan potential can be observed in many biological systems due to the presence of polyelectrolytes as proteins and nucleic acids. The aim of this work was to present a useful tool to describe the fixed and charge-regulated volume charge density profile through the use of a smoothing function and to obtain the electrostatic potential profile as well as the Donnan potential of this system by solving Poisson-Boltzmann (PB) equation. When we use the smoothing function, the Donnan potential arises automatically from the solution of only one Poisson-Boltzmann equation and it is not necessary to impose this potential for treating charged system in the presence of a membrane. The electrostatic behavior across the Bacillus brevis wall considering the dependence on the ionization of the cell wall functional groups as a function of the solution pH was analyzed. An important issue was to show that potentiometric titration data could be used together with the Poisson-Boltzmann equation to predict the electrostatic behavior (e.g., zeta potential) of the bacterial cell surface.
The movements of 8 green turtles Chelonia mydas in Brazilian coastal waters were tracked using tr... more The movements of 8 green turtles Chelonia mydas in Brazilian coastal waters were tracked using transmitters linked to the Argos system for periods of between 1 and 197 d. These were the first tracking data gathered on juveniles of this species in this important foraging ground. Information was integrated with that collected over a decade using traditional flipper-tagging methods at the same site. Both satellite telemetry and flipper tagging suggested that turtles undertook 1 of 3 general patterns of behaviour: pronounced long range movements (>100 km), moderate range movements (<100 km) or extended residence very close to the capture/release site. There seemed to be a general tendency for the turtles recaptured/tracked further afield to have been among the larger turtles captured. Satellite tracking of 5 turtles which moved from the release site showed that they moved through coastal waters; a factor which is likely to predispose migrating turtles to incidental capture as a result of the prevailing fishing methods in the region. The movements of the 3 turtles who travelled less than 100 km from the release site challenge previous ideas relating to home range in green turtles feeding in sea grass pastures. We hypothesise that there may be a fundamental difference in the pattern of habitat utilisation by larger green turtles depending on whether they are feeding on seagrass or macroalgae. Extended tracking of 2 small turtles which stayed near the release point showed that small juvenile turtles, whilst in residence in a particular feeding ground, can also exhibit high levels of site-fidelity with home ranges of the order of several square kilometers.
In virtually all mammal cells, we can observe a much higher concentration of potassium ions insid... more In virtually all mammal cells, we can observe a much higher concentration of potassium ions inside the cell and vice versa for sodium ions. Classical theories ignore the specific ion effects and the difference in the thermodynamic reference states between intracellular and extracellular environments. Usually, this differential ion partitioning across a cell membrane is attributed exclusively to the active ion transport. Our aim is to investigate how much the dispersion forces contribute to active ion pumps in an erythrocyte (red blood cell) as well as the correction of chemical potential reference states between intracellular and extracellular environments. The ionic partition and the membrane potential in an erythrocyte are analyzed by the modified Poisson−Boltzmann equation, considering nonelectrostatic interactions between ions and macromolecules. Results show that the nonelectrostatic potential calculated by Lifshitz theory has only a small influence with respect to the high concentration of K + in the intracellular environment in comparison with Na + .
Testing theories of dispersal is challenging in highly migratory species. In sea turtles, populat... more Testing theories of dispersal is challenging in highly migratory species. In sea turtles, population size, geographic distance, natal homing, and ocean currents are hypothesized to affect dispersal. Little is known, however, about these mechanisms in sea turtles foraging along the South American coast. Green sea turtles feeding at Ubatuba (UB, n 5 114) and Almofala (AF, n 5 117), Brazil, were sequenced at the mitochondrial DNA (mtDNA) control region (486 bp) and genotyped at 7 microsatellite loci to test dispersal hypotheses. Fifteen mtDNA haplotypes were revealed, including a previously undescribed sequence, and the average observed heterozygosity (H o ) was 76.4%. Overall short-term temporal differences were not detected, and differentiation was less pronounced in microsatellite than in mtDNA analyses. Mitochondrial results reveal significant differentiation between the Brazilian feeding grounds and most other Atlantic groups, whereas microsatellites uncover similarities to some of the geographically closest populations. Ubatuba and Almofala are mixed stocks, drawn primarily from Ascension, with lesser contributions from Surinam/Aves and Trindade. Costa Rica is also a significant source of individuals feeding at AF. The results are consistent with a model of juvenile natal homing impacted by other factors. Effective protection of turtles foraging along the extensive Brazilian coast may enhance breeding populations thousands of kilometers away.
There is a considerable effort in the literature trying to calculate the mean force between globu... more There is a considerable effort in the literature trying to calculate the mean force between globular proteins (and colloidal particles). To this purpose, we used here the ion-specific Poisson-Boltzmann (PB) equation that presents good results of ionic concentration profiles around a macroion, especially for salt solutions containing monovalent ions. The ion-specific PB equation includes not only electrostatic interactions but also dispersion potentials, originated from polarizabilities of ions and proteins. This enables us to predict ion-specific properties of colloidal systems. Results are in agreement with the experimental observed Hofmeister series. The main contribution of this paper is the use of a differential approach to calculate the mean force between aqueous proteins and colloidal particles instead of the classical quadrature approach. The integral expressions needed to calculate the mean force, potential of mean force and second virial coefficients have been avoided using this new numerical procedure. These integrals were transformed in a set of first order partial differential equations solved simultaneously with the ion-specific PB equation. Resulted expressions were written in bispherical coordinates, and then numerically solved through finite volume method. This simultaneous approach presents more accuracy in the calculation of the mean force in comparison with the classical approach, where the potential profile is obtained by solving the PB equation, and mean force is calculated afterwards. Important thermodynamic properties are obtained from the mean force (and consequently, from the potential of mean force), e.g., osmotic second virial coefficients and phase diagrams. These thermodynamic properties are related to protein aggregation, essential in biotechnology and pharmaceutical industries.
A much-improved Poisson-Boltzmann equation for two globular proteins using bispherical coordinate... more A much-improved Poisson-Boltzmann equation for two globular proteins using bispherical coordinates is used to establish the potential of mean force (PMF) between two globular lysozyme particles. Calculations presented here include previously ignored ion-protein nonelectrostatic potentials. The lysozyme-lysozyme PMF is used to calculate osmotic second virial coeffiencients. The theoretical PMF curve as a function of sodium chloride concentration is successfully compared with that from experiment. Our theoretical PMF shows how the second virial coefficient and the phase diagram depends on salt concentration, pH and, most notably, on the choice of salt in the aquous solution. † Part of the "Keith E. Gubbins Festschrift".
Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará co... more Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará coast in NE Brazil are reported. Concentrations varied from <0.34 to 856.6 ng.g -1 d.w., and were highest (average of 154.8 ng.g -1 d.w.) in juveniles (n = 22), whereas lowest concentrations (average of 2.5 ng.g -1 d.w.) were observed in adult/sub-adult animals (n = 3). There was a significant negative correlation between animal size and Hg concentration probably due to different diets between juveniles and sub-adults/adults. Carapace fragments, which are non-invasive, non-lethal substrates, may be of importance for monitoring purposes of these generally endangered species.
In two-phase finite volume systems of electroneutral phospholipids, the electrolyte concentration... more In two-phase finite volume systems of electroneutral phospholipids, the electrolyte concentration is different in the two phases. The partitioning is highly anion-specific, a phenomenon not accounted for by classical electrolyte theories. It is explained if ionic dispersion forces that lead to specific ion binding are taken into account. The mechanism provides a contribution to active ion pumps not previously considered.
Mean-field theories that include nonelectrostatic interactions acting on ions near interfaces hav... more Mean-field theories that include nonelectrostatic interactions acting on ions near interfaces have been found to accommodate many experimentally observed ion specific effects. However, it is clear that this approach does not fully account for the liquid molecular structure and hydration effects. This is now improved by using parametrized ionic potentials deduced from recent nonprimitive model molecular dynamics (MD) simulations in a generalized Poisson-Boltzmann equation. We investigate how ion distributions and double layer forces depend on the choice of background salt. There is a strong ion specific double layer force set up due to unequal ion specific short-range potentials acting between ions and surfaces.
The interaction between surface patches of proteins with different surface properties has a vital... more The interaction between surface patches of proteins with different surface properties has a vital role to play driving conformational changes in proteins in different salt solutions. We demonstrate the existence of ion-specific attractive double-layer forces between neutral hydrophobic and hydrophilic surfaces in the presence of certain salt solutions. This is performed by solving a generalized Poisson-Boltzmann equation for two unequal surfaces. In the calculations, we utilize parametrized ion-surface potentials and dielectric-constant profiles deduced from recent non-primitive-model molecular dynamics simulations that partially account for molecular structure and hydration effects.
The double layer forces between spherical colloidal particles, according to the Poisson-Boltzmann... more The double layer forces between spherical colloidal particles, according to the Poisson-Boltzmann (PB) equation, have been accurately calculated in the literature. The classical PB equation takes into account only the electrostatic interactions, which play a significant role in colloid science. However, there are at, and above, biological salt concentrations other non-electrostatic ion specific forces acting that are ignored in such modelling. In this paper, the electrostatic potential profile and the concentration profile of co-ions and counterions near charged surfaces are calculated. These results are obtained by solving the classical PB equation and a modified PB equation in bispherical coordinates, taking into account the van der Waals dispersion interactions between the ions and both surfaces. Once the electrostatic potential is known we calculate the double layer force between two charged spheres. This is the first paper that solves the modified PB equation in bispherical coordinates. It is also the first time that the finite volume method is used to solve the PB equation in bispherical coordinates. This method divides the calculation domain into a certain number of sub-domains, where the physical law of conservation is valid, and can be readily implemented. The finite volume method is implemented for several geometries and when it is applied to solve PB equations presents low computational cost. The proposed method was validated by comparing the numerical results for the classical PB calculations with previous results reported in the literature. New numerical results using the modified PB equation successfully predicted the ion specificity commonly observed experimentally.
The design of a micromachined polyethylene lens for WiGig modules is described and its electromag... more The design of a micromachined polyethylene lens for WiGig modules is described and its electromagnetic characteristics are measured. The lens is electromagnetically fed by linearly polarized Tx and Rx patch antennas integrated in an existing ball-grid-array (BGA) organic module. Antennas are separated from each other by a distance of 4.45 mm (0.89lambda at 60 GHz). The goal of the lens is to increase the gain of each antenna while lowering the beam depointing effect due to their offset position regarding the focal point of the lens. A geometrical optics/physical optics (GO/PO) hybrid method is applied to the design and analysis of the lens shape for noncollimating purpose. Using a lens height of 30 mm for both Tx and Rx antennas, a 13-dBi minimum realized gain from 54 to 66 GHz is obtained. Compared to an elliptical lens providing an equivalent realized gain over the same bandwidth, the depointing angle from the boresight direction is reduced from 15° to 4°. Full-wave simulations are verified by measurements.
A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-b... more A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-band satellite and high altitude platform (HAP) providing broadband access services. The wide-angle elevation beam steering is achieved by in-plane translation of a thin offset flat lens in front of a stationary primary feed while full azimuth coverage is obtained by simple 360º rotation of the lens. A new strategy is also proposed to reduce the effective F/D of the focusing system and consequently the total antenna height without increasing beam distortion: a second small flat lens is added on top of the primary feed to create a virtual focus located well below the feed phase center. The challenge is to conciliate high gain both with wide beam scanning and reduced antenna height. Design rules are presented for this antenna concept along with a 27.3-dBi gain fabricated example for the up-link Ka-band (29.5–30 GHz), with circular polarization, 0◦ to 50◦ 20 elevation scan, better than 2.8-dB scan loss and an effective F/D of only 0.55. Both lenses are 3.35-mm thick, formed by a suitable assembly of phase shifting unit cells with less than 0.4 dB of transmission loss in simulation. The main lens dimensions are 195 mm × 145 mm and its weight is 215 g. Total antenna height, including the feed is 26 84 mm.
A simple low-cost mobile ground terminal antenna for Ka-band satellite communications is presente... more A simple low-cost mobile ground terminal antenna for Ka-band satellite communications is presented. The antenna is composed of a shaped dielectric lens which tilts and rotates in front of a feed to direct the beam. The wideband feed system is composed of a quad-ridged horn with a 45° slant aperture and a coaxial-to-quad-ridged circular waveguide transition. The lens allows simple mechanical beam steering from 0° to 65° in relation to the zenith and 360° in azimuth by rotating both the lens and the feed slanted aperture. Performance measurements of a manufactured prototype prove the beam tilting capabilities in elevation with a maximum gain of 22 dBi and scan loss below 3 dB at 20 GHz and 24 dBi gain with less than 4.5 dB scan loss at 30 GHz.
Starting from a challenge in the early 1990s to develop a highly shaped beam dielectric lens ante... more Starting from a challenge in the early 1990s to develop a highly shaped beam dielectric lens antenna for a pilot 150 Mb/s cellular mobile broadband system operating in the 60-GHz band, several new developments have been accomplished over more than 20 years at Instituto de Telecomunicações [1] in the areas of millimeter-wave shaped dielectric lens antennas and planar metamaterial lenses. We review here a few representative examples with numerical and experimental results, covering applications in mobile broadband communications, radiometry, satellite communications, multigigabit short-range communications, and sublambda near-field target detection.
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Papers by Eduardo Lima