Kinetics of color center formation in silica irradiated with swift heavy ions: Thresholding and formation efficiency

We have determined the cross-section σ for color center generation under single Br ion impacts on amorphous SiO2. The evolution of the cross-sections, σ(E) and σ(Se), show an initial flat stage that we associate to atomic collision mechanisms. Above a certain threshold value (Se > 2 keV/nm), roughly coinciding with that reported for the onset of macroscopic disorder (compaction), σ shows a marked increase due to electronic processes. In this regime, a energetic cost of around 7.5 keV is necessary to create a non bridging oxygen hole center-E′ (NBOHC/E′) pair, whatever the input energy. The data appear consistent with a non-radiative decay of self-trapped excitons.

Interstitial Ti for intermediate band formation in Ti-supersaturated silicon

We have analyzed by means of Rutherford backscattering spectrometry (RBS) the Ti lattice location and the degree of crystalline lattice recovery in heavily Ti implanted silicon layers subsequently pulsed laser melted (PLM). Theoretical studies have predicted that Ti should occupy interstitial sites in silicon for a metallic-intermediate band (IB) formation. The analysis of Ti lattice location after PLM processes is a crucial point to evaluate the IB formation that can be clarifyied by means of RBS measurements. After PLM, time-of-flight secondary ion mass spectrometry measurements show that the Ti concentration in the layers is well above the theoretical limit for IB formation. RBS measurements have shown a significant improvement of the lattice quality at the highest PLM energy density studied. The RBS channeling spectra reveals clearly that after PLM processes Ti impurities are mostly occupying interstitial lattice sites.

Estudios termodinámicos de los procesos de vitrificación en la crioconservación de germoplasma vegetal=Thermodynamic studies of vitrification processes in plant germplasm cryopreservation

En la actualidad, las técnicas de crioconservación poseen una importancia creciente para el almacenamiento a largo plazo de germoplasma vegetal. En las dos últimas décadas, estos métodos experimentaron un gran desarrollo y se han elaborado protocolos adecuados a diferentes sistemas vegetales, utilizando diversas estrategias como la vitrificación, la encapsulación-desecación con cuentas de alginato y el método de “droplet”-vitrificación. La presente tesis doctoral tiene como objetivo aumentar el conocimiento sobre los procesos implicados en los distintos pasos de un protocolo de crioconservación, en relación con el estado del agua presente en los tejidos y sus cambios, abordado mediante diversas técnicas biofísicas, principalmente calorimetría diferencial de barrido (DSC) y microscopía electrónica de barrido a baja temperatura (crio-SEM). En un primer estudio sobre estos métodos de crioconservación, se describen las fases de enfriamiento hasta la temperatura del nitrógeno líquido y de calentamiento hasta temperatura ambiente, al final del periodo de almacenamiento, que son críticas para la supervivencia del material crioconservado. Tanto enfriamiento como calentamiento deben ser realizados lo más rápidamente posible pues, aunque los bajos contenidos en agua logrados en etapas previas de los protocolos reducen significativamente las probabilidades de formación de hielo, éstas no son del todo nulas. En ese contexto, se analiza también la influencia de las velocidades de enfriamiento y calentamiento de las soluciones de crioconservación de plantas en sus parámetros termofísicos referente a la vitrificación, en relación su composición y concentración de compuestos. Estas soluciones son empleadas en la mayor parte de los protocolos actualmente utilizados para la crioconservación de material vegetal. Además, se estudia la influencia de otros factores que pueden determinar la estabilidad del material vitrificado, tales como en envejecimiento del vidrio. Se ha llevado a cabo una investigación experimental en el empleo del crio-SEM como una herramienta para visualizar el estado vítreo de las células y tejidos sometidos a los procesos de crioconservación. Se ha comparado con la más conocida técnica de calorimetría diferencial de barrido, obteniéndose resultados muy concordantes y complementarios. Se exploró también por estas técnicas el efecto sobre tejidos vegetales de la adaptación a bajas temperaturas y de la deshidratación inducida por los diferentes tratamientos utilizados en los protocolos. Este estudio permite observar la evolución biofísica de los sistemas en el proceso de crioconservación. Por último, se estudió la aplicación de películas de quitosano en las cuentas de alginato utilizadas en el protocolo de encapsulación. No se observaron cambios significativos en su comportamiento frente a la deshidratación, en sus parámetros calorimétricos y en la superficie de las cuentas. Su aplicación puede conferir propiedades adicionales prometedoras. ABSTRACT Currently, cryopreservation techniques have a growing importance for long term plant germplasm storage. These methods have undergone great progress during the last two decades, and adequate protocols for different plant systems have been developed, making use of diverse strategies, such as vitrification, encapsulation-dehydration with alginate beads and the dropletvitrification method. This PhD thesis has the goal of increasing the knowledge on the processes underlying the different steps of cryopreservation protocols, in relation with the state of water on tissues and its changes, approached through diverse biophysical techniques, especially differential scanning calorimetry (DSC) and low-temperature scanning electron microscopy (cryo-SEM). The processes of cooling to liquid nitrogen temperature and warming to room temperature, at the end of the storage period, critical for the survival of the cryopreserved material, are described in a first study on these cryopreservation methods. Both cooling and warming must be carried out as quickly as possible because, although the low water content achieved during previous protocol steps significantly reduces ice formation probability, it does not completely disappear. Within this context, the influence of plant vitrification solutions cooling and warming rate on their vitrification related thermophysical parameters is also analyzed, in relation to its composition and component concentration. These solutions are used in most of the currently employed plant material cryopreservation protocols. Additionally, the influence of other factors determining the stability of vitrified material is studied, such as glass aging. An experimental research work has been carried out on the use of cryo-SEM as a tool for visualizing the glassy state in cells and tissues, submitted to cryopreservation processes. It has been compared with the better known differential scanning calorimetry technique, and results in good agreement and complementary have been obtained. The effect on plant tissues of adaptation to low temperature and of the dehydration induced by the different treatments used in the protocols was explored also by these techniques. This study allows observation of the system biophysical evolution in the cryopreservation process. Lastly, the potential use of an additional chitosan film over the alginate beads used in encapsulation protocols was examined. No significant changes could be observed in its dehydration and calorimetric behavior, as well as in its surface aspect; its application for conferring additional properties to gel beads is promising.

Speech features of the domain of the word in heterosexual twins during the second yeard of life

Speech is the major function, emergence and which development radically changes all course of formation of the identity of the child already in the early childhood. If language and speech development in solitary born children is investigated today quite well, at twin children this process practically is not studied. Our research was carried out for the purpose of studying of an originality of mastering by speech by heterosexual children of pair of twins within communicative and pragmatist approach (T.N. Ushakov,G. V. Chirkina). Application of this approach to the analysis of process of communication at twin children allowed us to allocate those peculiar receptions and means of communication which they functionally develop in a situation of pair of twins, as allows them to show the phenomena of the speech which are not meeting at solitary born contemporaries. In this work results of supervision and research of pair of heterosexual twins of the second year of the life, carried out by a technique developed by us under the scientific guide of G. V. Chirkina

Laser Processes for Contact Optimization in c-Si Solar Cells

Solid State Lasers (SSL) have been used in microelectronic and photovoltaic (PV) industry for decades but, currently, laser technology appears as a key enabling technology to improve efficiency and to reduce production costs in high efficiency solar cells fabrication. Moreover, the fact that the interaction between the laser radiation and the device is normally localized and restricted to a controlled volume makes SSL a tool of choice for the implementation of low temperature concepts in PV industry. Specifically, SSL are ideally suited to improve the electrical performance of the contacts further improving the efficiency of these devices. Advanced concepts based on standard laser firing or advanced laser doping techniques are optimal solutions for the back contact of a significant number of structures of growing interest in the c-Si PV industry, and a number of solutions has been proposed as well for emitter formation, to reduce the metallization optical losses or even to remove completely the contacts from the front part of the cell. In this work we present our more recent results of SSL applications for contact optimization in c-Si solar cell technology, including applications on low temperature processes demanding devices, like heterojunction solar cells.

Characterization of the manufacturing processes to grow triple-junction solar cells

A number of important but little-investigated problems connected with III-V/Ge heterostructure in the GaInP/GaInAs/Ge multijunction solar cells grown by MOVPE are considered in the paper. The opportunity for successfully applying the combination of reflectance and reflectance anisotropy spectroscopy in situ methods for investigating III-V structure growth on a Ge substrate has been demonstrated. Photovoltaic properties of the III-V/Ge narrow-band subcell of the triple-junction solar cells have been investigated. It has been shown that there are excess currents in the Ge photovoltaic p-n junctions, and they have the tunneling or thermotunneling character. The values of the diode parameters for these current flow mechanisms have been determined. The potential barrier at the III-V/Ge interface was determined and the origin of this barrier formation during MOVPE heterogrowth was suggested.

Optimizing phosphorus diffusion for photovoltaic applications: peak doping, inactive phosphorus,gettering, and contact formation

The phosphosilicate glass (PSG), fabricated by tube furnace diffusion using a POCl3 source, is widely used as a dopant source in the manufacturing of crystalline silicon solar cells. Although it has been a widely addressed research topic for a long time, there is still lack of a comprehensive understanding of aspects such as the growth, the chemical composition, possible phosphorus depletion, the resulting in-diffused phosphorus profiles, the gettering behavior in silicon, and finally the metal-contact formation. This paper addresses these different aspects simultaneously to further optimize process conditions for photovoltaic applications. To do so, a wide range of experimental data is used and combined with device and process simulations, leading to a more comprehensive interpretation. The results show that slight changes in the PSG process conditions can produce high-quality emitters. It is predicted that PSG processes at 860 °C for 60 min in combination with an etch-back and laser doping from PSG layer results in high-quality emitters with a peak dopant density Npeak = 8.0 × 1018 cm−3 and a junction depth dj = 0.4 μm, resulting in a sheet resistivityρsh = 380 Ω/sq and a saturation current-density J0 below 10 fA/cm2. With these properties, the POCl3 process can compete with ion implantation or doped oxide approaches.

Network formation of lipid membranes: Triggering structural transitions by chain melting

Phospholipids when dispersed in excess water generally form vesicular membrane structures. Cryo-transmission and freeze-fracture electron microscopy are combined here with calorimetry and viscometry to demonstrate the reversible conversion of phosphatidylglycerol aqueous vesicle suspensions to a three-dimensional structure that consists of extended bilayer networks. Thermodynamic analysis indicates that the structural transitions arise from two effects: (i) the enhanced membrane elasticity accompanying the lipid state fluctuations on chain melting and (ii) solvent-associated interactions (including electrostatics) that favor a change in membrane curvature. The material properties of the hydrogels and their reversible formation offer the possibility of future applications, for example in drug delivery, the design of structural switches, or for understanding vesicle fusion or fission processes.

Duplicated genes evolve independently after polyploid formation in cotton

Of the many processes that generate gene duplications, polyploidy is unique in that entire genomes are duplicated. This process has been important in the evolution of many eukaryotic groups, and it occurs with high frequency in plants. Recent evidence suggests that polyploidization may be accompanied by rapid genomic changes, but the evolutionary fate of discrete loci recently doubled by polyploidy (homoeologues) has not been studied. Here we use locus-specific isolation techniques with comparative mapping to characterize the evolution of homoeologous loci in allopolyploid cotton (Gossypium hirsutum) and in species representing its diploid progenitors. We isolated and sequenced 16 loci from both genomes of the allopolyploid, from both progenitor diploid genomes and appropriate outgroups. Phylogenetic analysis of the resulting 73.5 kb of sequence data demonstrated that for all 16 loci (14.7 kb/genome), the topology expected from organismal history was recovered. In contrast to observations involving repetitive DNAs in cotton, there was no evidence of interaction among duplicated genes in the allopolyploid. Polyploidy was not accompanied by an obvious increase in mutations indicative of pseudogene formation. Additionally, differences in rates of divergence among homoeologues in polyploids and orthologues in diploids were indistinguishable across loci, with significant rate deviation restricted to two putative pseudogenes. Our results indicate that most duplicated genes in allopolyploid cotton evolve independently of each other and at the same rate as those of their diploid progenitors. These indications of genic stasis accompanying polyploidization provide a sharp contrast to recent examples of rapid genomic evolution in allopolyploids.

Rab5 Induces Rac-independent Lamellipodia Formation and Cell Migration

Rab5 is a regulatory GTPase of vesicle docking and fusion that is involved in receptor-mediated endocytosis and pinocytosis. Introduction of active Rab5 in cells stimulates the rate of endocytosis and vesicle fusion, resulting in the formation of large endocytic vesicles, whereas dominant negative Rab5 inhibits vesicle fusion. Here we show that introduction of active Rab5 in fibroblasts also induced reorganization of the actin cytoskeleton but not of microtubule filaments, resulting in prominent lamellipodia formation. The Rab5-induced lamellipodia formation did not require activation of PI3-K or the GTPases Ras, Rac, Cdc42, or Rho, which are all strongly implicated in cytoskeletal reorganization. Furthermore, lamellipodia formation by insulin, Ras, or Rac was not affected by expression of dominant negative Rab5. In addition, cells expressing active Rab5 displayed a dramatic stimulation of cell migration, with the lamellipodia serving as the leading edge. Both lamellipodia formation and cell migration were dependent on actin polymerization but not on microtubules. These results demonstrate that Rab5 induces lamellipodia formation and cell migration and that the Rab5-induced lamellipodia formation occurs by a novel mechanism independent of, and distinct from, PI3-K, Ras, or Rho-family GTPases. Thus, Rab5 can control not only endocytosis but also actin cytoskeleton reorganization and cell migration, which provides strong support for an intricate relationship between these processes.

Cell-Adhesive Responses to Tenascin-C Splice Variants Involve Formation of Fascin Microspikes

Tenascin-C is an adhesion-modulating matrix glycoprotein that has multiple effects on cell behavior. Tenascin-C transcripts are expressed in motile cells and at sites of tissue modeling during development, and alternative splicing generates variants that encode different numbers of fibronectin type III repeats. We have examined the in vivo expression and cell adhesive properties of two full-length recombinant tenascin-C proteins: TN-190, which contains the eight constant fibronectin type III repeats, and TN-ADC, which contains the additional AD2, AD1, and C repeats. In situ hybridization with probes specific for the AD2, AD1, and C repeats shows that these splice variants are expressed at sites of active tissue modeling and fibronectin expression in the developing avian feather bud and sternum. Transcripts incorporating the AD2, AD1, and C repeats are present in embryonic day 10 wing bud but not in embryonic day 10 lung. By using a panel of nine cell lines in attachment assays, we have found that C2C12, G8, and S27 myoblastic cells undergo concentration-dependent adhesion to both variants, organize actin microspikes that contain the actin-bundling protein fascin, and do not assemble focal contacts. On a molar basis, TN-ADC is more active than TN-190 in promoting cell attachment and irregular cell spreading. The addition of either TN-190 or TN-ADC in solution to C2C12, COS-7, or MG-63 cells adherent on fibronectin decreases cell attachment and results in decreased organization of actin microfilament bundles, with formation of cortical membrane ruffles and retention of residual points of substratum contact that contain filamentous actin and fascin. These data establish a biochemical similarity in the processes of cell adhesion to tenascin-C and thrombospondin-1, also an “antiadhesive” matrix component, and also demonstrate that both the adhesive and adhesion-modulating properties of tenascin-C involve similar biochemical events in the cortical cytoskeleton. In addition to these generic properties, TN-ADC is less active in adhesion modulation than TN-190. The coordinated expression of different tenascin-C transcripts during development may, therefore, provide appropriate microenvironments for regulated changes in cell shape, adhesion, and movement.

Calcium-dependent enzyme activation and vacuole formation in the apical granular region of pancreatic acinar cells

The pancreatic acinar cell produces powerful digestive enzymes packaged in zymogen granules in the apical pole. Ca2+ signals elicited by acetylcholine or cholecystokinin (CCK) initiate enzyme secretion by exocytosis through the apical membrane. Intracellular enzyme activation is normally kept to a minimum, but in the often-fatal human disease acute pancreatitis, autodigestion occurs. How the enzymes become inappropriately activated is unknown. We monitored the cytosolic Ca2+ concentration ([Ca2+]i), intracellular trypsin activation, and its localization in isolated living cells with specific fluorescent probes and studied intracellular vacuole formation by electron microscopy as well as quantitative image analysis (light microscopy). A physiological CCK level (10 pM) eliciting regular Ca2+ spiking did not evoke intracellular trypsin activation or vacuole formation. However, stimulation with 10 nM CCK, evoking a sustained rise in [Ca2+]i, induced pronounced trypsin activation and extensive vacuole formation, both localized in the apical pole. Both processes were abolished by preventing abnormal [Ca2+]i elevation, either by preincubation with the specific Ca2+ chelator 1,2-bis(O-aminophenoxy)ethane-N,N-N′,N′-tetraacetic acid (BAPTA) or by removal of external Ca2+. CCK hyperstimulation evokes intracellular trypsin activation and vacuole formation in the apical granular pole. Both of these processes are mediated by an abnormal sustained rise in [Ca2+]i.

Metabolism to a response pathway selective retinoid ligand during axial pattern formation

We report identification of 9-cis-4-oxo-retinoic acid (9-cis-4-oxo-RA) as an in vivo retinoid metabolite in Xenopus embryos. 9-Cis-4-oxo-RA bound receptors (RARs) α, β, and γ as well as retinoid X receptors (RXRs) α, β, and γ in vitro. However, this retinoid displayed differential RXR activation depending on the response pathway used. Although it failed to activate RXRs in RXR homodimers, it activated RXRs and RARs synergistically in RAR-RXR heterodimers. 9-Cis-4-oxo-RA thus acted as a dimer-specific agonist. Considering that RAR-RXR heterodimers are major functional units involved in transducing retinoid signals during embryogenesis and that 9-cis-4-oxo-RA displayed high potency for modulating axial pattern formation in Xenopus, metabolism to 9-cis-4-oxo-RA may provide a mechanism to target retinoid action to this and other RAR-RXR heterodimer-mediated processes.

Targeted expression of constitutively active receptors for parathyroid hormone and parathyroid hormone-related peptide delays endochondral bone formation and rescues mice that lack parathyroid hormone-related peptide

Mice in which the genes encoding the parathyroid hormone (PTH)-related peptide (PTHrP) or the PTH/PTHrP receptor have been ablated by homologous recombination show skeletal dysplasia due to accelerated endochondral bone formation, and die at birth or in utero, respectively. Skeletal abnormalities due to decelerated chondrocyte maturation are observed in transgenic mice where PTHrP expression is targeted to the growth plate, and in patients with Jansen metaphyseal chondrodysplasia, a rare genetic disorder caused by constitutively active PTH/PTHrP receptors. These and other findings thus indicate that PTHrP and its receptor are essential for chondrocyte differentiation. To further explore the role of the PTH/PTHrP receptor in this process, we generated transgenic mice in which expression of a constitutively active receptor, HKrk-H223R, was targeted to the growth plate by the rat α1 (II) collagen promoter. Two major goals were pursued: (i) to investigate how constitutively active PTH/PTHrP receptors affect the program of chondrocyte maturation; and (ii) to determine whether expression of the mutant receptor would correct the severe growth plate abnormalities of PTHrP-ablated mice (PTHrP−/−). The targeted expression of constitutively active PTH/PTHrP receptors led to delayed mineralization, decelerated conversion of proliferative chondrocytes into hypertrophic cells in skeletal segments that are formed by the endochondral process, and prolonged presence of hypertrophic chondrocytes with delay of vascular invasion. Furthermore, it corrected at birth the growth plate abnormalities of PTHrP−/− mice and allowed their prolonged survival. “Rescued” animals lacked tooth eruption and showed premature epiphyseal closure, indicating that both processes involve PTHrP. These findings suggest that rescued PTHrP−/− mice may gain considerable importance for studying the diverse, possibly tissue-specific role(s) of PTHrP in postnatal development.

Anatomy of word and sentence meaning

Reading and listening involve complex psychological processes that recruit many brain areas. The anatomy of processing English words has been studied by a variety of imaging methods. Although there is widespread agreement on the general anatomical areas involved in comprehending words, there are still disputes about the computations that go on in these areas. Examination of the time relations (circuitry) among these anatomical areas can aid in understanding their computations. In this paper, we concentrate on tasks that involve obtaining the meaning of a word in isolation or in relation to a sentence. Our current data support a finding in the literature that frontal semantic areas are active well before posterior areas. We use the subject’s attention to amplify relevant brain areas involved either in semantic classification or in judging the relation of the word to a sentence to test the hypothesis that frontal areas are concerned with lexical semantics and posterior areas are more involved in comprehension of propositions that involve several words.