Ignition conditions for inertial confinement fusion targets with a nuclear spin-polarized DT fuel

The nuclear fusion cross-section is modified when the spins of the interacting nuclei are polarized. In the case of deuterium?tritium it has been theoretically predicted that the nuclear fusion cross-section could be increased by a factor d = 1.5 if all the nuclei were polarized. In inertial confinement fusion this would result in a modification of the required ignition conditions. Using numerical simulations it is found that the required hot-spot temperature and areal density can both be reduced by about 15% for a fully polarized nuclear fuel. Moreover, numerical simulations of a directly driven capsule show that the required laser power and energy to achieve a high gain scale as d-0.6 and d-0.4 respectively, while the maximum achievable energy gain scales as d0.9.

Changes in nuclear phenotypes following cold shock in Panstrongylus megistus (Burmeister)

The nuclear phenotypes of Malpighian tubule epithelial cells of 5th instar male nymphs of the blood-sucking insect Panstrongylus megistus were studied immediately after a short (1 h) cold shock at 0ºC, and 10 and 30 days later. The objective was to compare the responses to a cold shock with those known to occur after hyperthermia in order to provide insight into the cellular effect of cold in this species. Nuclei which usually exhibited a conspicuous Y chromosome chromocenter were the most frequent phenotype in control and treated specimens. Phenotypes in which the heterochromatin was unravelled, or in which there was nuclear fusion or cell death were more abundant in the shocked specimens. Most of the changes detected have also been found in heat-shocked nymphs, except for nuclear fusion which generates giant nuclei and which appeared to be less effective or necessary than that elicited after heat shock. Since other studies showed that a short cold shock does not affect the survival of more than 14% of 5th instar nymphs of P. megistus with domestic habit and can induce tolerance to a prolonged cold shock, heat shock proteins proteins are probably the best candidates for effective protection of the cells and the insects from drastic damage caused by low temperature shocks.

Changes in nuclear phenotype frequencies following sequential cold shocks in Triatoma infestans (Hemiptera, Reduviidae)

The nuclear phenotypes of Malpighian tubule cells in fifth instar nymphs of Triatoma infestans, one of the most important vectors of Chagas disease, were studied following sequential shocks at 0ºC, separated by intervals of 8 h and 24 h at 30ºC, under conditions of moderate fasting and full nourishment. The insects pertained to colonies reared in the laboratory and originated from domestic specimens collected in the Brazilian states of São Paulo (north) and Minas Gerais (south). Since nuclear phenotypes in this species are affected by single cold shocks, it was expected that these phenotypes could also be changed by sequential shocks. Nuclear phenotypes indicative of mechanisms of cell survival (nuclear fusion and heterochromatin decondensation) and cell death (apoptosis and necrosis) were observed concomitantly in all the conditions tested. Nuclear fusion and heterochromatin decondensation were not found relevant for the presumed acquisition of the cold-hardening response in T. infestans. The decreased frequency of apoptosis and necrosis following sequential cold shocks including under fasting conditions, indicated that tolerance to sequential cold shocks occurred in T. infestans of the mentioned origin.

Effect of sequential heat and cold shocks on nuclear phenotypes of the blood-sucking insect, Panstrongylus megistus (Burmeister) (Hemiptera, Reduviidae)

Thermal shocks induce changes in the nuclear phenotypes that correspond to survival (heterochromatin decondensation, nuclear fusion) or death (apoptosis, necrosis) responses in the Malpighian tubules of Panstrongylus megistus. Since thermal tolerance increased survival and molting rate in this species following sequential shocks, we investigated whether changes in nuclear phenotypes accompanied the insect survival response to sequential thermal shocks. Fifth instar nymphs were subjected to a single heat (35 or 40°C, 1 h) or cold (5 or 0°C, 1 h) shock and then subjected to a second shock for 12 h at 40 or 0°C, respectively, after 8, 18, 24 and 72 h at 28°C (control temperature). As with specimen survival, sequential heat and cold shocks induced changes in frequency of the mentioned nuclear phenotypes although their patterns differed. The heat shock tolerance involved decrease in apoptosis simultaneous to increase in cell survival responses. Sequential cold shocks did not involve cell/nuclear fusion and even elicited increase in necrosis with advancing time after shocks. The temperatures of 40 and 0ºC were more effective than the temperatures of 35 and 5ºC in eliciting the heat and cold shock tolerances, respectively, as shown by cytological analysis of the nuclear phenotypes. It is concluded that different sequential thermal shocks can trigger different mechanisms of cellular protection against stress in P. megistus, favoring the insect to adapt to various ecotopes.

Garvey-Kelson relations for nuclear charge radii

The Garvey-Kelson relations (GKRs) are algebraic expressions originally developed to predict nuclear masses. In this letter we show that the GKRs provide a fruitful framework for the prediction of other physical observables that also display a slowly-varying dynamics. Based on this concept, we extend the GKRs to the study of nuclear charge radii. The GKRs are tested on 455 out of the approximately 800 nuclei whose charge radius is experimentally known. We find a rms deviation between the GK predictions and the experimental values of only 0.01 fm. This should be contrasted against some of the most successful microscopic models that yield rms deviations almost three times as large. Predictions -with reliable uncertainties- are provided for 116 nuclei whose charge radius is presently unknown.

Thermal release rate studies of nuclear reaction products from polycrystalline metal matrices

The thermal release rate of nuclear reaction products was investigated in offline annealing experiments. This work was motivated by the search for a high melting catcher material for recoiling products from heavy ion induced nuclear fusion reactions. Polycrystalline refractory metal foils of Ni, Y, Zr, Nb, Mo, Hf, W, and Re were investigated as catcher metals. Diffusion data for various tracer/host combinations were deduced from the measured release rates. This work focuses on the diffusion and the release rate of volatile p-elements from row 5 and 6 of the periodic table as lighter homologues of the superheavy elements with Z ≥ 113 to be studied in future experiments. A massive radiation damage enhancement of the diffusion velocity was observed. Diffusion trends have been established along the groups and rows of the periodic table based on the dependence of diffusion velocity on atomic sizes.

The role of spatial and temporal radiation deposition in inertial fusion chambers: the case of HiPER¿

The first wall armour for the reactor chamber of HiPER will have to face short energy pulses of 5 to 20 MJ mostly in the form of x-rays and charged particles at a repetition rate of 5–10 Hz. Armour material and chamber dimensions have to be chosen to avoid/minimize damage to the chamber, ensuring the proper functioning of the facility during its planned lifetime. The maximum energy fluence that the armour can withstand without risk of failure, is determined by temporal and spatial deposition of the radiation energy inside the material. In this paper, simulations on the thermal effect of the radiation–armour interaction are carried out with an increasing definition of the temporal and spatial deposition of energy to prove their influence on the final results. These calculations will lead us to present the first values of the thermo-mechanical behaviour of the tungsten armour designed for the HiPER project under a shock ignition target of 48 MJ. The results will show that only the crossing of the plasticity limit in the first few micrometres might be a threat after thousands of shots for the survivability of the armour.

Viabilidad técnica para la explotación y separación isotópica de Li y prospectiva en el mercado de baterías de ION-7Li y de 6Li como material base de diseño en reactores de fusión nuclear

En claro alineamiento con estrategias de sostenibilidad en el uso de recursos naturales en un escenario constante de aumento de la demanda energética mundial, el desarrollo de la tecnología energética en la Historia de la Especie Humana muestra un vector de evolución permanente desde su origen en el sentido del desarrollo y uso de nuevas fuentes energéticas con la explotación de recursos naturales de manera más eficiente: soluciones energéticas con aumento de la densidad energética (exoenergía de proceso por unidad de masa de recurso natural). Así el cambio de escala en la demanda de explotación del Litio como recurso natural se viene presentando en la última década ligada al desarrollo del mercado de las baterías "ion-Litio" y los requisitos de combustible (Deuterio y Litio) en el camino de la fusión nuclear como opción energética próxima. El análisis anticipado de las demandas sinérgicas a escala de ambos mercados aparece de enorme interés prospectivo en sus aspectos técnicos: (1) tecnologías de base para la extracción mineral y de agua marina y (2) su enriquecimiento isotópico (de interés sinérgico; 7Li para baterías eficientes ion-litio; 6Li como regenerador de tritio en ciclo de combustible en fusión nuclear) a la vez que en sus aspectos económicos. Este Proyecto realiza: (1) un ejercicio de análisis prospectivo de la demanda y de mercado para el enriquecimiento 6Li/7Li para las próximas décadas, (2) se califican los desarrollos tecnológicos específicos que van a poder permitir la producción a escala conforme a la demanda; (3) se selecciona y califica una técnica [de centrifugación / termo-difusión/ destilación combinada] como opción tecnológicamente viable para la producción a escala de formas litiadas; (4) se propone un diseño conceptual de planta de producción y finalmente (5) propone un estudio de viabilidad para la demostración de proceso y construcción de dicha planta de demostración de la nueva capacidad tecnológica. ABSTRACT Clearly aligned with sustainability strategies under growing world energy demand in the use of natural resources the development of energy technology in the history of the human species shows a vector of ongoing evolution from its origin in the sense of the development and use of new energy sources with the exploitation of natural resources in a more efficient manner. The change of scale in the demand for exploitation of Lithium as a natural resource appears during the last decade as bound to the deployment of "lithium-ion" batteries market and to the Nuclear Fusion fuels (deuterium and lithium) supply scaled demands. The prospective analysis of demands to scale in both markets appears in scene with huge prospective interest in its technical aspects: (1) base technologies for mineral and water marine extraction (2) its isotopic enrichment (synergistic interests; 7Li efficient battery Li-ion; 6Li as fusion nuclear fuel breeder (tritium) as well as in its economic aspects. This Project: (1) propose a prospective analysis exercise of the synergistic supply demand for coming decades for the enrichment of 6Li and 7Li, (2) qualifies specific technological developments ongoing to respond to supply demand; (3) select and qualifies an appropriate technique [combined centrifugation/thermo-diffusion/distillation] as technologically viable option for lithiated forms scaled-production; (4) proposes a conceptual design of production plant based on the technique and finally (5) proposes a feasibility study for the process demonstration and construction of this new technological capability Demonstration Plant.

The use of the ESS Bilbao installations for laser fusion studies

In this work the use of ESS-Bilbao fast neutron lines for irradiation of materials for nuclear fusion is studied. For the comparison of ESS-Bilbao with an inertial fusion facility a simplified model of HiPER chamber has been used. Several positions for irradiation at ESS-Bilbao have been also compared. The material chosen for the damage analysis is silica due to its importance on IFC optics. In this work a detailed comparison between the two facilities for silica irradiation is given. The comparison covers the neutron fluxes, doses, defect production and PKA spectra. This study is also intended as a methodological approach or guideline for future works on other materials.

Silica final lens performance in laser fusion facilities: HiPER and LIFE

Nowadays, the projects LIFE (Laser Inertial Fusion Energy) in USA and HiPER (High Power Laser Energy Research) in Europe are the most advanced ones to demonstrate laser fusion energy viability. One of the main points of concern to properly achieve ignition is the performance of the final optics (lenses) under the severe irradiation conditions that take place in fusion facilities. In this paper, we calculate the radiation fluxes and doses as well as the radiation-induced temperature enhancement and colour centre formation in final lenses assuming realistic geometrical configurations for HiPER and LIFE. On these bases, the mechanical stresses generated by the established temperature gradients are evaluated showing that from a mechanical point of view lenses only fulfil specifications if ions resulting from the imploding target are mitigated. The absorption coefficient of the lenses is calculated during reactor startup and steady-state operation. The obtained results reveal the necessity of new solutions to tackle ignition problems during the startup process for HiPER. Finally, we evaluate the effect of temperature gradients on focal length changes and lens surface deformations. In summary, we discuss the capabilities and weak points of silica lenses and propose alternatives to overcome predictable problems

Fabricación y caracterización de wolframio nanoestructurado como material de primera pared en reactores de fusión nuclear

El trabajo que se llevará a cabo se basa en el desarrollo de nuevos materiales que sean capaces de resistir las condiciones extremas a las que estarían expuestos en el interior de un reactor de fusión nuclear, como son los altos choques térmicos y los altos flujos iónicos. Actualmente se está investigando en el potencial del wolframio nanoestructurado como material de primera pared (en inglés PFM: Plasma Facing Material). La principal ventaja de éste frente al wolframio masivo radica en su gran densidad de fronteras de grano que hacen que el material sea más resistente a la irradiación. El objetivo de este trabajo será la búsqueda de las condiciones óptimas para la fabricación de recubrimientos de wolframio nanoestructurado mediante la técnica de pulverización catódica ("sputtering") en diferentes configuraciones, continuo ("Direct Current Magnetron Sputtering" o DCMS) y/o pulsado ("High Power Impulse Magnetron Sputtering" o HiPIMS) y caracterizar sus propiedades como PFM mediante perfilometría, microscopía óptica, microscopía electrónica de barrido ("Scanning Electron Microscope" o SEM) y difracción de rayos X ("X-Ray Diffraction" o XRD). A su vez, se realizará un ensayo de implantación con un plasma pulsado de He para analizar los efectos de la irradiación en uno de los recubrimientos. Abstract: The work that will be carried out is based on the development of new materials capable of withstanding the extreme conditions that they will have to face inside a nuclear fusion reactor, such as high thermal loads and high ion fluxes. Currently, nanostructured tungsten potential is being investigated as a plasma facing material (PFM). The main advantage over coarse grain tungsten is its high density of grain boundaries which make the material more resistant to irradiation. The project´s main objective will be the search of the optimal conditions that will allow us to fabricate nanostructured tungsten thin films by using the sputtering technique in different configurations, such as DCMS (Direct Current Magnetron Sputtering) and/or HiPIMS (High Power Impulse Magetron Sputtering) and characterize their properties as a PFM by perfilometry, optical microscopy, SEM (Scanning Electron Microcopy) and XRD (X-Ray Diffracion) analysis. Moreover, an implantation test with a He pulsed plasma will be carried out to analyze the effects of irradiation on one of the coatings.

Modelización y validación experimental del transporte de tritio en metal líquido y otros materiales para reactores de fusión nuclear magnética e inercial

La presente tesis se centra en el estudio de los fenómenos de transporte de los isótopos de hidrógeno, y más concretamente del tritio, en materiales de interés para los reactores de fusión nuclear. Los futuros reactores de fusión nuclear necesitarán una Planta de Tritio, con una envoltura regeneradora (breeding blanket) y unos sistemas auxiliares claves para su diseño. Por lo tanto su desarrollo y cualificación son cruciales para demostrar que los reactores de fusión son una opción viable como futura fuente de energía. Se han resaltado los diferentes retos de la difusión y retención de estas especies ligeras para cada sistema de la Planta de Tritio, y se han identificado las necesidades experimentales y paramétricas para abordar las simulaciones de difusión, como factores de transporte como la difusividad, absorción/desorción, solubilidad y atrapamiento. Se han estudiado los fenómenos de transporte y parámetros del T en el metal líquido LiPb, componente del breeding blanket tanto para una planta de fusión magnética como inercial. Para ello se han utilizado dos experimentos con características diversas, uno de ellos se ha llevado a cabo en un reactor de alto flujo, y por lo tanto, en condiciones de irradiación, y el otro sin irradiación. Los métodos de simulación numérica aplicados se han adaptado a los experimentos para las mediciones y para estudiar el régimen de transporte. En el estudio de estos experimentos se ha obtenido un valor para algunos de los parámetros claves en el transporte y gestión del tritio en el reactor. Finalmente se realiza un cálculo de la acumulación y difusión de tritio en una primera pared de tungsteno para un reactor de fusión inercial. En concreto para el proyecto de fusión por láser europeo, HiPER (para sus fases 4a y 4b). Se ha estudiado: la implantación de los isótopos de H y He en la pared de W tras una reacción de fusión por iluminación directa con un láser de 48MJ; el efecto en el transporte de T de los picos de temperatura en el W debido a la frecuencia de los eventos de fusión; el régimen de transporte en la primera pared. Se han identificado la naturaleza de las trampas más importantes para el T y se ha propuesto un modelo avanzado para la difusión con trampas. ABSTRACT The present thesis focuses into study the transport phenomenons of hydrogen isotopes, more specifically tritium, in materials of interest for nuclear fusion reactors. The future nuclear reactors will be provided of a Tritium Plant, with its breeding blanket and its auxiliary systems, all of them essential components for the plant. Therefore a reliable development and coalification are key issues to prove the viability of the nuclear fusion reactors as an energy source. The currently challenges for the diffusion and accumulation of these light species for each system of the TP has been studied. Experimental and theoretical needs have been identified and analyzed, specially from the viewpoint of the parameters. To achieve reliable simulations of tritium transport, parameters as diffusivity, absorption/desorption, solubility and trapping must be reliables. Transport phenomenon and parameters of T in liquid metal have been studied. Lead lithium is a key component of the breeding blanket, either in magnetic or inertial fusion confinement. Having this aim in mind, two experiments with different characteristics have been used; one of them has been realized in a high flux reactor, and hence, under irradiation conditions. The other one has been realized without radiation. The mathematical methods for the simulation have been adapted to the experiments, for the measures and also to study the transport behavior. A value for some key parameters for tritium management has been obtained in these studies. Finally, tritium accumulation and diffusion in a W first wall of an inertial nuclear fusion reactor has been assessed. A diffusion model of the implanted H, D, T and He species for the two initial phases of the proposed European laser fusion Project HiPER (namely, phase 4a and phase 4b) has been implemented using Tritium Migration Analysis Program, TMAP7. The effect of the prompt and working temperatures and the operational pulsing modes on the diffusion are studied. The nature of tritium traps in W and their performance has been analyzed and discussed.

Microstructural and mechanical characterization of tungsten based materials for fusion reactors

El wolframio (W) y sus aleaciones se consideran los mejores candidatos para la construcción del divertor en la nueva generación de reactores de fusión nuclear. Este componente va a recibir las cargas térmicas más elevadas durante el funcionamiento del reactor ya que estará en contacto directo con el plasma. En los últimos años, después de un profundo análisis y siguiendo una estrategia de reducción de costes, la Organización de ITER tomó la decisión de construir el divertor integramente de wolframio desde el principio. Por ello, el wolframio no sólo actuará como material en contacto con el plasma (PFM), sino que también tendría aplicaciones estructurales. El wolframio, debido a sus excelentes propiedades termo-físicas, cumple todos los requerimientos para ser utilizado como PFM, sin embargo, su inherente fragilidad pone en peligro su uso estructural. Por tanto, uno de los principales objetivos de esta tesis es encontrar una aleación de wolframio con menor fragilidad. Durante éste trabajo, se realizó la caracterización microstructural y mecánica de diferentes materiales basados en wolframio. Sin embargo, ésta tarea es un reto debido a la pequeña cantidad de material suministrado, su reducido tamaño de grano y fragilidad. Por ello, para una correcta medida de todas las propiedades físicas y mecánicas se utilizaron diversas técnicas experimentales. Algunas de ellas se emplean habitualmente como la nanoindentación o los ensayos de flexión en tres puntos (TPB). Sin embargo, otras fueron especificamente desarrolladas e implementadas durante el desarrollo de esta tesis como es el caso de la medida real de la tenacidad de fractura en los materiales masivos, o de las medidas in situ de la tenacidad de fractura en las láminas delgadas de wolframio. Diversas composiciones de aleaciones de wolframio masivas (W-1% Y2O3, W-2% V-0.5% Y2O3, W-4% V-0.5% Y2O3, W-2% Ti-1% La2O3 y W-4% Ti-1% La2O3) se han estudiado y comparado con un wolframio puro producido en las mismas condiciones. Estas aleaciones, producidas por ruta pulvimetalúrgica de aleado mecánico (MA) y compactación isostática en caliente (HIP), fueron microstructural y mecánicamente caracterizadas desde 77 hasta 1473 K en aire y en alto vacío. Entre otras propiedades físicas y mecánicas se midieron la dureza, el módulo elástico, la resistencia a flexión y la tenacidad de fractura para todas las aleaciones. Finalmente se analizaron las superficies de fractura después de los ensayos de TPB para relacionar los micromecanismos de fallo con el comportamiento macroscópico a rotura. Los resultados obtenidos mostraron un comportamiento mecánico frágil en casi todo el intervalo de temperaturas y para casi todas las aleaciones sin mejoría de la temperatura de transición dúctil-frágil (DBTT). Con el fin de encontrar un material base wolframio con una DBTT más baja se realizó también un estudio, aún preliminar, de láminas delgadas de wolframio puro y wolframio dopado con 0.005wt.% potasio (K). Éstas láminas fueron fabricadas industrialmente mediante sinterizado y laminación en caliente y en frío y se sometieron posteriormente a un tratamiento térmico de recocido desde 1073 hasta 2673 K. Se ha analizado la evolución de su microestructura y las propiedades mecánicas al aumentar la temperatura de recocido. Los resultados mostraron la estabilización de los granos de wolframio con el incremento de la temperatura de recocido en las láminas delgadas de wolframio dopado con potasio. Sin embargo, es necesario realizar estudios adicionales para entender mejor la microstructura y algunas propiedades mecánicas de estos materiales, como la tenacidad de fractura. Tungsten (W) and tungsten-based alloys are considered to be the best candidate materials for fabricating the divertor in the next-generation nuclear fusion reactors. This component will experience the highest thermal loads during the operation of a reactor since it directly faces the plasma. In recent years, after thorough analysis that followed a strategy of cost reduction, the ITER Organization decided to built a full-tunsgten divertor before the first nuclear campaigns. Therefore, tungsten will be used not only as a plasma-facing material (PFM) but also in structural applications. Tungsten, due to its the excellent thermo-physical properties fulfils the requirements of a PFM, however, its use in structural applications is compromised due to its inherent brittleness. One of the objectives of this phD thesis is therefore, to find a material with improved brittleness behaviour. The microstructural and mechanical characterisation of different tunsgten-based materials was performed. However, this is a challenging task because of the reduced laboratory-scale size of the specimens provided, their _ne microstructure and their brittleness. Consequently, many techniques are required to ensure an accurate measurement of all the mechanical and physical properties. Some of the applied methods have been widely used such as nanoindentation or three-point bending (TPB) tests. However, other methods were specifically developed and implemented during this work such as the measurement of the real fracture toughness of bulk-tunsgten alloys or the in situ fracture toughness measurements of very thin tungsten foils. Bulk-tunsgten materials with different compositions (W-1% Y2O3, W-2% V- 0.5% Y2O3, W-4% V-0.5% Y2O3, W-2% Ti-1% La2O3 and W-4% Ti-1% La2O3) were studied and compared with pure tungsten processed under the same conditions. These alloys, produced by a powder metallurgical route of mechanical alloying (MA) and hot isostatic pressing (HIP), were microstructural and mechanically characterised from 77 to 1473 K in air and under high vacuum conditions. Hardness, elastic modulus, flexural strength and fracture toughness for all of the alloys were measured in addition to other physical and mechanical properties. Finally, the fracture surfaces after the TPB tests were analysed to correlate the micromechanisms of failure with the macroscopic behaviour. The results reveal brittle mechanical behaviour in almost the entire temperature range for the alloys and micromechanisms of failure with no improvement in the ductile-brittle transition temperature (DBTT). To continue the search of a tungsten material with lowered DBTT, a preliminary study of pure tunsgten and 0.005 wt.% potassium (K)-doped tungsten foils was also performed. These foils were industrially produced by sintering and hot and cold rolling. After that, they were annealed from 1073 to 2673 K to analyse the evolution of the microstructural and mechanical properties with increasing annealing temperature. The results revealed the stabilisation of the tungsten grains with increasing annealing temperature in the potassium-doped tungsten foil. However, additional studies need to be performed to gain a better understanding of the microstructure and mechanical properties of these materials such as fracture toughness.

Saccharomyces cerevisiae Cells with Defective Spindle Pole Body Outer Plaques Accomplish Nuclear Migration via Half-Bridge–organized Microtubules

Cnm67p, a novel yeast protein, localizes to the microtubule organizing center, the spindle pole body (SPB). Deletion of CNM67 (YNL225c) frequently results in spindle misorientation and impaired nuclear migration, leading to the generation of bi- and multinucleated cells (40%). Electron microscopy indicated that CNM67 is required for proper formation of the SPB outer plaque, a structure that nucleates cytoplasmic (astral) microtubules. Interestingly, cytoplasmic microtubules that are essential for spindle orientation and nuclear migration are still present in cnm67Δ1 cells that lack a detectable outer plaque. These microtubules are attached to the SPB half- bridge throughout the cell cycle. This interaction presumably allows for low-efficiency nuclear migration and thus provides a rescue mechanism in the absence of a functional outer plaque. Although CNM67 is not strictly required for mitosis, it is essential for sporulation. Time-lapse microscopy of cnm67Δ1 cells with green fluorescent protein (GFP)-labeled nuclei indicated that CNM67 is dispensable for nuclear migration (congression) and nuclear fusion during conjugation. This is in agreement with previous data, indicating that cytoplasmic microtubules are organized by the half-bridge during mating.