The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Hakan F Oztop - One of the best experts on this subject based on the ideXlab platform.
-
Effects of a partially conductive partition in MHD conjugate convection and entropy generation for a horizontal annulus
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Fatih Selimefendigil, Hakan F Oztop, Omid MahianAbstract:Magnetohydrodynamic free convection in a horizontal annulus formed by two isothermal surfaces and partially partitioned with a conductive ring was numerically studied by using finite element method. The numerical investigation was performed for various values of Rayleigh numbers (between 104 and 106), Hartmann number (between 0 and 40), Magnetic Inclination angle (between 0° and 90°), thermal conductivity ratio (between 0.01 and 100) and various locations of the conductive partition. Average Nusselt number enhances as the value of Rayleigh number, Magnetic Inclination angle and thermal conductivity ratio increases and as the value of Hartmann number decreases. The location of the partial conductive partition on the average Nusselt number becomes more effective for higher values of Rayleigh number and lower values of Hartmann number. Heat transfer process is effective when the partition is located on the bottom part of the hot wall. Heat transfer enhancement with location of the partition depends on the Inclination angle of the Magnetic field. Second law analysis of the system with entropy generation was also performed. It was observed that for higher values of Magnetic field strength and lower values of Magnetic Inclination angle the entropy generation rate reduces, while the conductivity ratio increases the entropy generation rate.
-
mhd pulsating forced convection of nanofluid over parallel plates with blocks in a channel
International Journal of Mechanical Sciences, 2019Co-Authors: Fatih Selimefendigil, Hakan F OztopAbstract:Abstract Forced convection of pulsating nanofluid flow over corrugated parallel plate in the presence of inclined Magnetic field is numerically studied by using Galerkin weighted residual finite element method. Impacts of Reynolds number (between 100 and 500), Hartmann number (between 0 and 15), Magnetic Inclination angle (between 0 o and 90 o ), number (between 1 and 12) of corrugation wave, height (between 0.05h and 0.35h) of the corrugation wave, solid particle volume fraction (between 0% and 4%), pulsation amplitude (between 0 and 0.9) and frequency (Strouhal number between 0.25 and 2) on the convective heat transfer features are analyzed. It is observed that increasing the Reynolds number, Hartmann number, Magnetic Inclination angle and solid particle volume fraction of the nanoparticle results in heat transfer enhancement while corrugation wave parameters have reverse impact on heat transfer enhancement in steady flow case. Various blocks of the heated plate contribute differently to the overall heat transfer rate and influence of block height on the distribution of the contributed effects is remarkable. Magnetic field redistribute the vortices between heated blocks of the corrugated plate and enhance the heat transfer both in steady flow and pulsating flow. Values for the spatial average Nusselt number are higher in pulsating flow as compared to steady case. At pulsation amplitude of 0.9, 40.30% and 34% heat transfer enhancement are obtained as compared to steady case in the absence and presence of Magnetic field at Hartmann number of 15. Including nanoparticles in pulsating flow shifts the spatial average Nusselt number plots as compared to base fluid. The values at the highest particle volume fraction are higher 15–16% in pulsating flow as compared to base fluid and they are slightly different than the ones obtained in the steady flow.
-
fluid solid interaction of elastic step type corrugation effects on the mixed convection of nanofluid in a vented cavity with Magnetic field
International Journal of Mechanical Sciences, 2019Co-Authors: Fatih Selimefendigil, Hakan F OztopAbstract:Abstract In this study, numerical analysis of mixed convection of CuO-water nanofluid in a cavity with inlet and outlet ports is performed under the effects of inclined Magnetic field and step like corrugated elastic walls. The numerical simulation results are obtained by using finite element method. The Arbitrary-Lagrangian–Eulerian method is utilized for the description of the fluid motion with the elastic wall in the fluid-structure interaction model. In the current study, multiple step like corrugation of the wall is considered and it is made elastic which adds additional flexibility for the control of convective heat transfer features of the vented cavity. Effects of various pertinent parameters such as Reynolds number (between 100 and 500), Hartmann number (between 0 and 40), Magnetic Inclination angle (between 0° and 90°), elastic modulus of the flexible wall (between 5 × 104 and 108), number of step-like corrugation (between 1 and 8) and nanoparticle volume fraction (between 0 and 3%) on the fluid flow and heat transfer characteristics are numerically examined. It is observed that for higher value of Reynolds number, local Nusselt number both deteriorates and enhances in various locations along the hot wall whereas the changes in the local Nusselt number are marginal for lower value of Reynolds number. The multiple vortices in the vented cavity are influenced by the variation of Magnetic field parameters and number of step like corrugation of the wall while the effects are not significant for the change of Magnetic Inclination angle. When the value of Hartmann number augments, the average heat transfer reduces until Hartmann number of 30 and increases for the highest value of Hartmann number. The average Nusselt number increment are in the range of 9-9.5% with the nanoparticle addition at the highest volume fraction in the absence and presence of Magnetic field. Even though significant changes in the local Nusselt number are observed when the number of step like corrugation increases, it has a deterioration effect on the average heat transfer generally and 5.5% reduction in the average Nusselt number is obtained when the value is increased from 1 to 8.
-
Natural convection in a CuO–water nanofluid filled cavity under the effect of an inclined Magnetic field and phase change material (PCM) attached to its vertical wall
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Fatih Selimefendigil, Hakan F Oztop, Ali J ChamkhaAbstract:In this study, natural convection of CuO–water nanofluid in a square cavity with a conductive partition and a phase change material (PCM) attached to its vertical wall is numerically analyzed under the effect of an uniform inclined Magnetic field by using finite element method. Effects of various pertinent parameters such as Rayleigh number (between $$10^5$$ 10 5 and $$10^6$$ 10 6 ), Hartmann number (between 0 and 100), Magnetic Inclination angle (between $$0^{\circ}$$ 0 ∘ and $$90^{\circ}$$ 90 ∘ ), PCM height (between 0.2 H and 0.8 H ), PCM length (between 0.1 H and 0.8 H ), thermal conductivity ratio (between 0.1 and 100) and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were numerically analyzed. It was observed that when Magnetic field is imposed, more reduction in average Nusselt number for water is obtained as compared to nanofluid which is $$31.81\%$$ 31.81 % for the nanofluid at the highest particle volume fraction. The average heat transfer augments with Magnetic Inclination angle, but it is less than $$5\%$$ 5 % . When the height of the PCM is increased which is from 0.2 H to 0.8 H , local and average Nusselt number reduced which is $$42.14\%$$ 42.14 % . However, the length of the PCM is not significant on the heat transfer enhancement. When the conductivity ratio of the PCM to the base fluid within the cavity is increased from 0.1 to 10, $$29.5\%$$ 29.5 % of the average Nusselt number enhancement is achieved.
-
natural convection in a cuo water nanofluid filled cavity under the effect of an inclined Magnetic field and phase change material pcm attached to its vertical wall
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Fatih Selimefendigil, Hakan F Oztop, Ali J ChamkhaAbstract:In this study, natural convection of CuO–water nanofluid in a square cavity with a conductive partition and a phase change material (PCM) attached to its vertical wall is numerically analyzed under the effect of an uniform inclined Magnetic field by using finite element method. Effects of various pertinent parameters such as Rayleigh number (between \(10^5\) and \(10^6\)), Hartmann number (between 0 and 100), Magnetic Inclination angle (between \(0^{\circ}\) and \(90^{\circ}\)), PCM height (between 0.2H and 0.8H), PCM length (between 0.1H and 0.8H), thermal conductivity ratio (between 0.1 and 100) and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were numerically analyzed. It was observed that when Magnetic field is imposed, more reduction in average Nusselt number for water is obtained as compared to nanofluid which is \(31.81\%\) for the nanofluid at the highest particle volume fraction. The average heat transfer augments with Magnetic Inclination angle, but it is less than \(5\%\). When the height of the PCM is increased which is from 0.2H to 0.8H, local and average Nusselt number reduced which is \(42.14\%\) . However, the length of the PCM is not significant on the heat transfer enhancement. When the conductivity ratio of the PCM to the base fluid within the cavity is increased from 0.1 to 10, \(29.5\%\) of the average Nusselt number enhancement is achieved.
Fatih Selimefendigil - One of the best experts on this subject based on the ideXlab platform.
-
Effects of a partially conductive partition in MHD conjugate convection and entropy generation for a horizontal annulus
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Fatih Selimefendigil, Hakan F Oztop, Omid MahianAbstract:Magnetohydrodynamic free convection in a horizontal annulus formed by two isothermal surfaces and partially partitioned with a conductive ring was numerically studied by using finite element method. The numerical investigation was performed for various values of Rayleigh numbers (between 104 and 106), Hartmann number (between 0 and 40), Magnetic Inclination angle (between 0° and 90°), thermal conductivity ratio (between 0.01 and 100) and various locations of the conductive partition. Average Nusselt number enhances as the value of Rayleigh number, Magnetic Inclination angle and thermal conductivity ratio increases and as the value of Hartmann number decreases. The location of the partial conductive partition on the average Nusselt number becomes more effective for higher values of Rayleigh number and lower values of Hartmann number. Heat transfer process is effective when the partition is located on the bottom part of the hot wall. Heat transfer enhancement with location of the partition depends on the Inclination angle of the Magnetic field. Second law analysis of the system with entropy generation was also performed. It was observed that for higher values of Magnetic field strength and lower values of Magnetic Inclination angle the entropy generation rate reduces, while the conductivity ratio increases the entropy generation rate.
-
mhd pulsating forced convection of nanofluid over parallel plates with blocks in a channel
International Journal of Mechanical Sciences, 2019Co-Authors: Fatih Selimefendigil, Hakan F OztopAbstract:Abstract Forced convection of pulsating nanofluid flow over corrugated parallel plate in the presence of inclined Magnetic field is numerically studied by using Galerkin weighted residual finite element method. Impacts of Reynolds number (between 100 and 500), Hartmann number (between 0 and 15), Magnetic Inclination angle (between 0 o and 90 o ), number (between 1 and 12) of corrugation wave, height (between 0.05h and 0.35h) of the corrugation wave, solid particle volume fraction (between 0% and 4%), pulsation amplitude (between 0 and 0.9) and frequency (Strouhal number between 0.25 and 2) on the convective heat transfer features are analyzed. It is observed that increasing the Reynolds number, Hartmann number, Magnetic Inclination angle and solid particle volume fraction of the nanoparticle results in heat transfer enhancement while corrugation wave parameters have reverse impact on heat transfer enhancement in steady flow case. Various blocks of the heated plate contribute differently to the overall heat transfer rate and influence of block height on the distribution of the contributed effects is remarkable. Magnetic field redistribute the vortices between heated blocks of the corrugated plate and enhance the heat transfer both in steady flow and pulsating flow. Values for the spatial average Nusselt number are higher in pulsating flow as compared to steady case. At pulsation amplitude of 0.9, 40.30% and 34% heat transfer enhancement are obtained as compared to steady case in the absence and presence of Magnetic field at Hartmann number of 15. Including nanoparticles in pulsating flow shifts the spatial average Nusselt number plots as compared to base fluid. The values at the highest particle volume fraction are higher 15–16% in pulsating flow as compared to base fluid and they are slightly different than the ones obtained in the steady flow.
-
fluid solid interaction of elastic step type corrugation effects on the mixed convection of nanofluid in a vented cavity with Magnetic field
International Journal of Mechanical Sciences, 2019Co-Authors: Fatih Selimefendigil, Hakan F OztopAbstract:Abstract In this study, numerical analysis of mixed convection of CuO-water nanofluid in a cavity with inlet and outlet ports is performed under the effects of inclined Magnetic field and step like corrugated elastic walls. The numerical simulation results are obtained by using finite element method. The Arbitrary-Lagrangian–Eulerian method is utilized for the description of the fluid motion with the elastic wall in the fluid-structure interaction model. In the current study, multiple step like corrugation of the wall is considered and it is made elastic which adds additional flexibility for the control of convective heat transfer features of the vented cavity. Effects of various pertinent parameters such as Reynolds number (between 100 and 500), Hartmann number (between 0 and 40), Magnetic Inclination angle (between 0° and 90°), elastic modulus of the flexible wall (between 5 × 104 and 108), number of step-like corrugation (between 1 and 8) and nanoparticle volume fraction (between 0 and 3%) on the fluid flow and heat transfer characteristics are numerically examined. It is observed that for higher value of Reynolds number, local Nusselt number both deteriorates and enhances in various locations along the hot wall whereas the changes in the local Nusselt number are marginal for lower value of Reynolds number. The multiple vortices in the vented cavity are influenced by the variation of Magnetic field parameters and number of step like corrugation of the wall while the effects are not significant for the change of Magnetic Inclination angle. When the value of Hartmann number augments, the average heat transfer reduces until Hartmann number of 30 and increases for the highest value of Hartmann number. The average Nusselt number increment are in the range of 9-9.5% with the nanoparticle addition at the highest volume fraction in the absence and presence of Magnetic field. Even though significant changes in the local Nusselt number are observed when the number of step like corrugation increases, it has a deterioration effect on the average heat transfer generally and 5.5% reduction in the average Nusselt number is obtained when the value is increased from 1 to 8.
-
Natural convection in a CuO–water nanofluid filled cavity under the effect of an inclined Magnetic field and phase change material (PCM) attached to its vertical wall
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Fatih Selimefendigil, Hakan F Oztop, Ali J ChamkhaAbstract:In this study, natural convection of CuO–water nanofluid in a square cavity with a conductive partition and a phase change material (PCM) attached to its vertical wall is numerically analyzed under the effect of an uniform inclined Magnetic field by using finite element method. Effects of various pertinent parameters such as Rayleigh number (between $$10^5$$ 10 5 and $$10^6$$ 10 6 ), Hartmann number (between 0 and 100), Magnetic Inclination angle (between $$0^{\circ}$$ 0 ∘ and $$90^{\circ}$$ 90 ∘ ), PCM height (between 0.2 H and 0.8 H ), PCM length (between 0.1 H and 0.8 H ), thermal conductivity ratio (between 0.1 and 100) and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were numerically analyzed. It was observed that when Magnetic field is imposed, more reduction in average Nusselt number for water is obtained as compared to nanofluid which is $$31.81\%$$ 31.81 % for the nanofluid at the highest particle volume fraction. The average heat transfer augments with Magnetic Inclination angle, but it is less than $$5\%$$ 5 % . When the height of the PCM is increased which is from 0.2 H to 0.8 H , local and average Nusselt number reduced which is $$42.14\%$$ 42.14 % . However, the length of the PCM is not significant on the heat transfer enhancement. When the conductivity ratio of the PCM to the base fluid within the cavity is increased from 0.1 to 10, $$29.5\%$$ 29.5 % of the average Nusselt number enhancement is achieved.
-
natural convection in a cuo water nanofluid filled cavity under the effect of an inclined Magnetic field and phase change material pcm attached to its vertical wall
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Fatih Selimefendigil, Hakan F Oztop, Ali J ChamkhaAbstract:In this study, natural convection of CuO–water nanofluid in a square cavity with a conductive partition and a phase change material (PCM) attached to its vertical wall is numerically analyzed under the effect of an uniform inclined Magnetic field by using finite element method. Effects of various pertinent parameters such as Rayleigh number (between \(10^5\) and \(10^6\)), Hartmann number (between 0 and 100), Magnetic Inclination angle (between \(0^{\circ}\) and \(90^{\circ}\)), PCM height (between 0.2H and 0.8H), PCM length (between 0.1H and 0.8H), thermal conductivity ratio (between 0.1 and 100) and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were numerically analyzed. It was observed that when Magnetic field is imposed, more reduction in average Nusselt number for water is obtained as compared to nanofluid which is \(31.81\%\) for the nanofluid at the highest particle volume fraction. The average heat transfer augments with Magnetic Inclination angle, but it is less than \(5\%\). When the height of the PCM is increased which is from 0.2H to 0.8H, local and average Nusselt number reduced which is \(42.14\%\) . However, the length of the PCM is not significant on the heat transfer enhancement. When the conductivity ratio of the PCM to the base fluid within the cavity is increased from 0.1 to 10, \(29.5\%\) of the average Nusselt number enhancement is achieved.
Ali J Chamkha - One of the best experts on this subject based on the ideXlab platform.
-
Natural convection in a CuO–water nanofluid filled cavity under the effect of an inclined Magnetic field and phase change material (PCM) attached to its vertical wall
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Fatih Selimefendigil, Hakan F Oztop, Ali J ChamkhaAbstract:In this study, natural convection of CuO–water nanofluid in a square cavity with a conductive partition and a phase change material (PCM) attached to its vertical wall is numerically analyzed under the effect of an uniform inclined Magnetic field by using finite element method. Effects of various pertinent parameters such as Rayleigh number (between $$10^5$$ 10 5 and $$10^6$$ 10 6 ), Hartmann number (between 0 and 100), Magnetic Inclination angle (between $$0^{\circ}$$ 0 ∘ and $$90^{\circ}$$ 90 ∘ ), PCM height (between 0.2 H and 0.8 H ), PCM length (between 0.1 H and 0.8 H ), thermal conductivity ratio (between 0.1 and 100) and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were numerically analyzed. It was observed that when Magnetic field is imposed, more reduction in average Nusselt number for water is obtained as compared to nanofluid which is $$31.81\%$$ 31.81 % for the nanofluid at the highest particle volume fraction. The average heat transfer augments with Magnetic Inclination angle, but it is less than $$5\%$$ 5 % . When the height of the PCM is increased which is from 0.2 H to 0.8 H , local and average Nusselt number reduced which is $$42.14\%$$ 42.14 % . However, the length of the PCM is not significant on the heat transfer enhancement. When the conductivity ratio of the PCM to the base fluid within the cavity is increased from 0.1 to 10, $$29.5\%$$ 29.5 % of the average Nusselt number enhancement is achieved.
-
natural convection in a cuo water nanofluid filled cavity under the effect of an inclined Magnetic field and phase change material pcm attached to its vertical wall
Journal of Thermal Analysis and Calorimetry, 2019Co-Authors: Fatih Selimefendigil, Hakan F Oztop, Ali J ChamkhaAbstract:In this study, natural convection of CuO–water nanofluid in a square cavity with a conductive partition and a phase change material (PCM) attached to its vertical wall is numerically analyzed under the effect of an uniform inclined Magnetic field by using finite element method. Effects of various pertinent parameters such as Rayleigh number (between \(10^5\) and \(10^6\)), Hartmann number (between 0 and 100), Magnetic Inclination angle (between \(0^{\circ}\) and \(90^{\circ}\)), PCM height (between 0.2H and 0.8H), PCM length (between 0.1H and 0.8H), thermal conductivity ratio (between 0.1 and 100) and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were numerically analyzed. It was observed that when Magnetic field is imposed, more reduction in average Nusselt number for water is obtained as compared to nanofluid which is \(31.81\%\) for the nanofluid at the highest particle volume fraction. The average heat transfer augments with Magnetic Inclination angle, but it is less than \(5\%\). When the height of the PCM is increased which is from 0.2H to 0.8H, local and average Nusselt number reduced which is \(42.14\%\) . However, the length of the PCM is not significant on the heat transfer enhancement. When the conductivity ratio of the PCM to the base fluid within the cavity is increased from 0.1 to 10, \(29.5\%\) of the average Nusselt number enhancement is achieved.
Verner P. Bingman - One of the best experts on this subject based on the ideXlab platform.
-
Conditioned discrimination of Magnetic Inclination in a spatial-orientation arena task by homing pigeons (Columba livia)
Journal of Experimental Biology, 2014Co-Authors: Cordula V. Mora, Merissa L. Acerbi, Verner P. BingmanAbstract:It has been well established that homing pigeons are able to use the Earth’s Magnetic field to obtain directional information when returning to their loft and that their Magnetic compass is based, at least in part, on the perception of Magnetic Inclination. Magnetic Inclination has also been hypothesized in pigeons and other long-distance navigators, such as sea turtles, to play a role providing positional information as part of a map. Here we developed a behavioural paradigm which allows us to condition homing pigeons to discriminate Magnetic Inclination cues in a spatial-orientation arena task. Six homing pigeons were required to discriminate in a circular arena between feeders located either in a zone with a close to 0o Inclination cue or in a zone with a rapidly changing Inclination cue (-3o to +85o when approaching the feeder and +85o to -3o when moving away from the feeder) to obtain a food reward. The pigeons consistently performed this task above chance level. Control experiments, during which the coils were turned off or the current was running anti-parallel through the double-wound coils system, confirmed that no alternative cues were used by the birds in the discrimination task. The results show that homing pigeons can be conditioned to discriminate differences in Magnetic field Inclination, enabling investigation into the peripheral and central neural processing of geoMagnetic Inclination under controlled laboratory conditions.
-
Conditioned discrimination of Magnetic Inclination in a spatial-orientation arena task by homing pigeons (Columba livia).
The Journal of experimental biology, 2014Co-Authors: Cordula V. Mora, Merissa L. Acerbi, Verner P. BingmanAbstract:It has been well established that homing pigeons are able to use the Earth's Magnetic field to obtain directional information when returning to their loft and that their Magnetic compass is based, at least in part, on the perception of Magnetic Inclination. Magnetic Inclination has also been hypothesized in pigeons and other long-distance navigators, such as sea turtles, to play a role providing positional information as part of a map. Here we developed a behavioral paradigm which allows us to condition homing pigeons to discriminate Magnetic Inclination cues in a spatial-orientation arena task. Six homing pigeons were required to discriminate in a circular arena between feeders located either in a zone with a close to 0 deg Inclination cue or in a zone with a rapidly changing Inclination cue (-3 deg to +85 deg when approaching the feeder and +85 deg to -3 deg when moving away from the feeder) to obtain a food reward. The pigeons consistently performed this task above chance level. Control experiments, during which the coils were turned off or the current was running anti-parallel through the double-wound coil system, confirmed that no alternative cues were used by the birds in the discrimination task. The results show that homing pigeons can be conditioned to discriminate differences in Magnetic field Inclination, enabling investigation into the peripheral and central neural processing of geoMagnetic Inclination under controlled laboratory conditions.
Catherine M. F. Lohmann - One of the best experts on this subject based on the ideXlab platform.
-
Long-distance transequatorial navigation using sequential measurements of Magnetic Inclination angle.
Journal of the Royal Society Interface, 2021Co-Authors: Brian K. Taylor, Kenneth J. Lohmann, Luke T. Havens, Catherine M. F. Lohmann, Jesse GrangerAbstract:Diverse taxa use Earth's Magnetic field in combination with other sensory modalities to accomplish navigation tasks ranging from local homing to long-distance migration across continents and ocean basins. Several animals have the ability to use the Inclination or tilt of Magnetic field lines as a component of a Magnetic compass sense that can be used to maintain migratory headings. In addition, a few animals are able to distinguish among different Inclination angles and, in effect, exploit Inclination as a surrogate for latitude. Little is known, however, about the role that Magnetic Inclination plays in guiding long-distance migrations. In this paper, we use an agent-based modelling approach to investigate whether an artificial agent can successfully execute a series of transequatorial migrations by using sequential measurements of Magnetic Inclination. The agent was tested with multiple navigation strategies in both present-day and reversed Magnetic fields. The findings (i) demonstrate that sequential Inclination measurements can enable migrations between the northern and southern hemispheres, and (ii) demonstrate that an Inclination-based strategy can tolerate a reversed Magnetic field, which could be useful in the development of autonomous engineered systems that must be robust to Magnetic field changes. The findings also appear to be consistent with the results of some animal navigation experiments, although whether any animal exploits a strategy of using sequential measurements of Inclination remains unknown.
-
DETECTION OF Magnetic Inclination ANGLE BY SEA TURTLES: A POSSIBLE MECHANISM FOR DETERMINING LATITUDE
The Journal of experimental biology, 1994Co-Authors: Kenneth J. Lohmann, Catherine M. F. LohmannAbstract:For animals that migrate long distances, the Magnetic field of the earth provides not only a possible cue for compass orientation, but a potential source of world-wide positional information. At each location on the globe, the geoMagnetic field lines intersect the earth's surface at a specific angle of Inclination. Because Inclination angles vary with latitude, an animal able to distinguish between different field Inclinations might, in principle, determine its approximate latitude. Such an ability, however, has never been demonstrated in any animal. We studied the Magnetic orientation behavior of hatchling loggerhead sea turtles (Caretta caretta L.) exposed to earth-strength Magnetic fields of different Inclinations. Hatchlings exposed to the natural field of their natal beach swam eastward, as they normally do during their offshore migration. In contrast, those subjected to an Inclination angle found on the northern boundary of the North Atlantic gyre (their presumed migratory path) swam south-southwest. Hatchlings exposed to an Inclination angle found near the southern boundary of the gyre swam in a northeasterly direction, and those exposed to Inclination angles they do not normally encounter, or to a field Inclination found well within the northern and southern extremes of the gyre, were not significantly oriented. These results demonstrate that sea turtles can distinguish between different Magnetic Inclination angles and perhaps derive from them an approximation of latitude. Most sea turtles nest on coastlines that are aligned approximately northsouth, so that each region of nesting beach has a unique Inclination angle associated with it. We therefore hypothesize that the ability to recognize specific Inclination angles may largely explain how adult sea turtles can identify their natal beaches after years at sea.
