Testicular development in migrant and spawning bluefin tuna (Thunnus thynnus (L.)) from the eastern Atlantic and Mediterranean

Testis histological structure was studied in bluefin tuna (Thunnus thynnus) from the eastern Atlantic and Mediterranean during the reproductive season (from late April to early June). Testicular maturation was investigated by comparing samples from bluefin tuna caught on their eastward reproductive migration off Barbate (Strait of Gibraltar area) with samples of bluefin tuna fished in spawning grounds around the Balearic Islands. Histological evaluations of cross sections showed that the testis consists of two structurally different regions, an outer proliferative region where germ cells develop synchronously in cysts, and a central region made up of a well-developed system of ducts that convey the spermatozoa produced in the proliferative region to the main sperm duct. Ultrastructural features of the different stages of the male germ cell line are very similar to those described in other teleost species. The bluefin tuna testis is of the unrestricted spermatogonial testicular type, where primary spermatogonia are present all along the germinative portion of the lobules. All stages of spermatogenesis were present in the gonad tissue of migrant and spawning bluefin tuna, although spermatids were more abundant in spawning fish. The testis size was found to increase by a factor of four (on average) during migration to the Mediterranean spawning grounds, whereas the fat bodies (mesenteric lipid stores associated with the gonads) became reduced to half their weight, and the liver mass did not change significantly with sexual maturation. Linear regression analysis of the pooled data of migrant and spawning bluefin tuna revealed a significant negative correlation between the gonad index (IG) and the fat tissue index (IF), and a weaker positive correlation between the gonad index (IG) and the liver index (IL). Our analyses indicate that the liver does not play a significant role in the storage of lipids and that mesenteric lipid reserves constitute an important energy source for gametogenesis in bluefin tuna.

Extending the transmission distance of a directly modulated laser source using Bragg grating dispersion compensators

Comprehensive computer modelling has been used to investigate the dependence of dispersion penalty on transmission length in an optical communications system employing a directly modulated 2.5Gbit/s DFB laser source and an optimised fibre grating dispersion compensator. Two grating apodization schemes, tanh and Gaussian, have been compared. The 2dB dispersion penalty transmission distance is shown to be approximately 520km along standard monomode fibre after compensation with a 5cm tanh grating. This represents a great improvement over the 150km range expected for a similar uncompensated system.

A normal force distance regulation scheme for near-field optical microscopy

A near-field optical microscope (NFOM) has been developed that combines the features of a near-field optical microscope and an atomic force microscope. Improved control over tip-sample separation has led to improved optical imaging and independent surface topography information. The tip oscillation is normal to the sample plane thereby reducing lateral forces - important for nonperturbative imaging of soft samples. Both topographic images and reflection near-field optical images are presented which demonstrate the capability of the system. © 1996 American Institute of Physics.

Finite volume distance field solution applied to medial axis transform

Accurate and efficient computation of the nearest wall distance d (or level set) is important for many areas of computational science/engineering. Differential equation-based distance/ level set algorithms, such as the hyperbolic-natured Eikonal equation, have demonstrated valuable computational efficiency. Here, in the context, as an 'auxiliary' equation to the main flow equations, the Eikonal equation is solved efficiently with two different finite volume approaches (the cell vertex and cell-centered). Application of the distance solution is studied for various geometries. Moreover, a procedure using the differential field to obtain the medial axis transform (MAT) for different geometries is presented. The latter provides a skeleton representation of geometric models that has many useful analysis properties. As an alternative approach to the pure geometric methods (e.g. the Voronoi approach), the current d-MAT procedure bypasses many difficulties that are usually encountered by pure geometric methods, especially in three dimensional space. It is also shown that the d-MAT approach provides the potential to sculpt/control the MAT form for specialized solution purposes. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.