Studies of the sexual development and spawning of yellowfin tuna, Neothunnus macropterus, and skipjack, Katsuwonus pelamis, in three areas of the Eastern Pacific Ocean, by examination of gonads.

ENGLISH: Knowledge of the size and age at maturity, spawning seasons, and spawning areas of the tropical tunas supporting the fishery in the Eastern Pacific is an important part of the basic information required for understanding their life history, population structure, and fishery dynamics. Until a few years ago nothing was known of these matters. In 1947 the senior author and one of his colleagues (Schaefer and Marr 1948, Schaefer 1948) were able to demonstrate that both yellowfin tuna and skipjack spawn offshore from Central America at least during the late winter and spring months. During January to April many yellowfin tuna over about 70 cm. total length in commercial catches from that region were found to have gonads in advanced stages of maturity, and specimens caught during late June were found to be spent. Maturing skipjack were collected in late February, and spawned-out fish were observed in late March. Numerous very young juveniles of the yellowfin, down to 10 mm. in length, and two very young juvenile skipjack, were captured in this area between January and May. SPANISH: El conocimiento del tamaño y la edad que corresponden a la primera madurez sexual, así como de las estaciones y áreas de desove de los atunes tropicales que mantienen las pesquerías del Pacífico Oriental, constituyen parte importante de la información que es menester para comprender la historia natural, la estructura de la población y la dinámica de la pesquería. Hasta hace pocos años nada se sabía sobre el particular. En 1947 el autor principal y uno de sus colegas (Schaefer y Marr, 1948; Schaefer, 1948) pudieron demostrar que tanto el atún aleta amarilla como el barrilete desovan en el mar abierto, frente a América Central, por lo menos durante la última parte del invierno y en la primavera. De enero a abril encontraron que muchos de los atunes aleta amarilla de más de 70 cm. de longitud total, procedentes de las pescas comerciales de dicha región; tenían gónadas en avanzados estados de madurez, mientras que ejemplares pescados hacia fines de junio ya habían desovado. Se recolectaron barriletes en vías de maduración a fines de febrero, al paso que en los últimos días de marzo se encontraron especímenes que ya habían desovado. Numerosos ejemplares muy juveniles del atún aleta amarilla, tan pequeños como 10 mm., y dos barriletes también muy juveniles, fueron pescados en esta región entre enero y mayo. (PDF contains 65 pages.)

Structural Integrity of the Contralesional Hemisphere Predicts Cognitive Impairment in Ischemic Stroke at Three Months

After stroke, white matter integrity can be affected both locally and distally to the primary lesion location. It has been shown that tract disruption in mirror's regions of the contralateral hemisphere is associated with degree of functional impairment. Fourteen patients suffering right hemispheric focal stroke (S) and eighteen healthy controls (HC) underwent Diffusion Weighted Imaging (DWI) and neuropsychological assessment. The stroke patient group was divided into poor (SP; n = 8) and good (SG; n = 6) cognitive recovery groups according to their cognitive improvement from the acute phase (72 hours after stroke) to the subacute phase (3 months post-stroke). Whole-brain DWI data analysis was performed by computing Diffusion Tensor Imaging (DTI) followed by Tract Based Spatial Statistics (TBSS). Assessment of effects was obtained computing the correlation of the projections on TBSS skeleton of Fractional Anisotropy (FA) and Radial Diffusivity (RD) with cognitive test results. Significant decrease of FA was found only in right brain anatomical areas for the S group when compared to the HC group. Analyzed separately, stroke patients with poor cognitive recovery showed additional significant FA decrease in several left hemisphere regions; whereas SG patients showed significant decrease only in the left genu of corpus callosum when compared to the HC. For the SG group, whole brain analysis revealed significant correlation between the performance in the Semantic Fluency test and the FA in the right hemisphere as well as between the performance in the Grooved Pegboard Test (GPT) and theTrail Making Test-part A and the FA in the left hemisphere. For the SP group, correlation analysis revealed significant correlation between the performance in the GPT and the FA in the right hemisphere. Palabras clave

Three-dimensional growth as multicellular spheroid activates the proangiogenic phenotype of colorectal carcinoma cells via LFA-1-dependent VEGF: implications on hepatic micrometastasis

Background: The recruitment of vascular stromal and endothelial cells is an early event occurring during cancer cell growth at premetastatic niches, but how the microenvironment created by the initial three-dimensional (3D) growth of cancer cells affects their angiogenesis-stimulating potential is unclear. Methods: The proangiogenic profile of CT26 murine colorectal carcinoma cells was studied in seven-day cultured 3D-spheroids of <300 mu m in diameter, produced by the hanging-drop method to mimic the microenvironment of avascular micrometastases prior to hypoxia occurrence. Results: Spheroid-derived CT26 cells increased vascular endothelial growth factor (VEGF) secretion by 70%, which in turn increased the in vitro migration of primary cultured hepatic sinusoidal endothelium (HSE) cells by 2-fold. More importantly, spheroid-derived CT26 cells increased lymphocyte function associated antigen (LFA)-1-expressing cell fraction by 3-fold; and soluble intercellular adhesion molecule (ICAM)-1, given to spheroid-cultured CT26 cells, further increased VEGF secretion by 90%, via cyclooxygenase (COX)-2-dependent mechanism. Consistent with these findings, CT26 cancer cells significantly increased LFA-1 expression in non-hypoxic avascular micrometastases at their earliest inception within hepatic lobules in vivo; and angiogenesis also markedly increased in both subcutaneous tumors and hepatic metastases produced by spheroid-derived CT26 cells. Conclusion: 3D-growth per se enriched the proangiogenic phenotype of cancer cells growing as multicellular spheroids or as subclinical hepatic micrometastases. The contribution of integrin LFA-1 to VEGF secretion via COX-2 was a micro environmental-related mechanism leading to the pro-angiogenic activation of soluble ICAM-1-activated colorectal carcinoma cells. This mechanism may represent a new target for specific therapeutic strategies designed to block colorectal cancer cell growth at a subclinical micrometastatic stage within the liver.

On optimal message vector length for block single parallel partition algorithm in a three-dimensional ADI solver

It has long been recognized that many direct parallel tridiagonal solvers are only efficient for solving a single tridiagonal equation of large sizes, and they become inefficient when naively used in a three-dimensional ADI solver. In order to improve the parallel efficiency of an ADI solver using a direct parallel solver, we implement the single parallel partition (SPP) algorithm in conjunction with message vectorization, which aggregates several communication messages into one to reduce the communication costs. The measured performances show that the longest allowable message vector length (MVL) is not necessarily the best choice. To understand this observation and optimize the performance, we propose an improved model that takes the cache effect into consideration. The optimal MVL for achieving the best performance is shown to depend on number of processors and grid sizes. Similar dependence of the optimal MVL is also found for the popular block pipelined method.

Selectivity of three aquatic weeds as diet for Nile tilapia (Oreochromis niloticus)

A total of sixty juvenile Oreochromis niloticus (Nile tilapia) were fed three species of aquatic weed, namely Azolla filiculoides (water fern), Elodea sp. and Pistia stratiotes (water lettuce) to determine which of the weeds will be selectively consumed, and preferred of all. A control group of twenty Nile tilapia was fed compounded feed. The selectivity of the weeds was observed based on their utilization as food source, and Azolla filiculoides was found to be highly utilized, followed by Elodea sp. and the roots of Pistia stratiotes. The growth response of the fish to the diets was found to be highest for fish fed compounded feed followed by Azolla filiculoides and Elodea sp., while Pistia stratiotes produced a negative growth trend. It is therefore postulated that Azolla filiculoides and Pista sp. are good feedstuffs for O. niloticus especially when used together with other feedstuffs

Two mechanisms for population inversion via two-colour coherent excitation in three-level systems

We analyse the physical origin of population inversion via continuous wave two-colour coherent excitation in three-level systems by dressing the inverted transition. Two different mechanisms are identified as being responsible for the population inversion. For V-configured systems and cascade (E) configured systems with inversion on the lower transition, the responsible mechanism is the selective trapping of dressed states, and the population inversion approaches the ideal value of 1. For Lambda-configured systems and Xi-configured systems with inversion on the upper transition, population inversion is based on the selective excitation of dressed states, with the population inversion tending towards 0.5. As the essential difference between these two mechanisms, the selective trapping of dressed states occurs in systems with strong decay into dressed states while the selective excitation appears in systems with strong decay out of dressed states.

Three-photon-excited upconversion luminescence of YVO4 single crystal by infrared femtosecond laser irradiation

We report on the upconversion luminescence of a pure YVO4 single crystal excited by an infrared femtosecond laser. The luminescent spectra show that the upconversion luminescence comes from the transitions from the lowest excited states T-3(1), T-3(2) to the ground state (1)A(1) of the VO43-. The dependence of the fluorescence intensity on the pump power density of laser indicates that the conversion of infrared irradiation to visible emission is dominated by three-photon excitation process. We suggest that the simultaneous absorption of three infrared photons promotes the VO43- to excited states, which quickly cascade down to lowest excited states, and radiatively relax to ground states, resulting in the broad characteristic fluorescence of VO43-. (c) 2005 Optical Society of America.

Three-dimensional supercell simulation of novel semiconductor nanostructures

In this thesis we investigate atomic scale imperfections and fluctuations in the quantum transport properties of novel semiconductor nanostructures. For this purpose, we have developed a numerically efficient supercell model of quantum transport capable of representing potential variations in three dimensions. This flexibility allows us to examine new quantum device structures made possible through state-of-the-art semiconductor fabrication techniques such as molecular beam epitaxy and nanolithography. These structures, with characteristic dimensions on the order of a few nanometers, hold promise for much smaller, faster and more efficient devices than those in present operation, yet they are highly sensitive to structural and compositional variations such as defect impurities, interface roughness and alloy disorder. If these quantum structures are to serve as components of reliable, mass-produced devices, these issues must be addressed.

In Chapter 1 we discuss some of the important issues in resonant tunneling devices and mention some of thier applications. In Chapters 2 and 3, we describe our supercell model of quantum transport and an efficient numerical implementation. In the remaining chapters, we present applications.

In Chapter 4, we examine transport in single and double barrier tunneling structures with neutral impurities. We find that an isolated attractive impurity in a single barrier can produce a transmission resonance whose position and strength are sensitive to the location of the impurity within the barrier. Multiple impurities can lead to a complex resonance structure that fluctuates widely with impurity configuration. In addition, impurity resonances can give rise to negative differential resistance. In Chapter 5, we study interface roughness and alloy disorder in double barrier structures. We find that interface roughness and alloy disorder can shift and broaden the n = 1 transmission resonance and give rise to new resonance peaks, especially in the presence of clusters comparable in size to the electron deBroglie wavelength. In Chapter 6 we examine the effects of interface roughness and impurities on transmission in a quantum dot electron waveguide. We find that variation in the configuration and stoichiometry of the interface roughness leads to substantial fluctuations in the transmission properties. These fluctuations are reduced by an attractive impurity placed near the center of the dot.