Blobs versus bars:psychophysical evidence supports two types of orientation response in human color vision

The classic hypothesis of Livingstone and Hubel (1984, 1987) proposed two types of color pathways in primate visual cortex based on recordings from single cells: a segregated, modularpathway that signals color but provides little information about shape or form and a second pathway that signals color differences and so defines forms without the need to specify their colors. A major problem has been to reconcile this neurophysiological hypothesis with the behavioral data. A wealth of psychophysical studies has demonstrated that color vision has orientation-tuned responses and little impairment on form related tasks, but these have not revealed any direct evidence for nonoriented mechanisms. Here we use a psychophysical method of subthreshold summation across orthogonal orientations for isoluminant red-green gratings in monocular and dichoptic viewing conditions to differentiate between nonoriented and orientation-tuned responses to color contrast. We reveal nonoriented color responses at low spatial frequencies (0.25-0.375 c/deg) under monocular conditions changing to orientation-tuned responses at higher spatial frequencies (1.5 c/deg) and under binocular conditions. We suggest that two distinct pathways coexist in color vision at the behavioral level, revealed at different spatial scales: one is isotropic, monocular, and best equipped for the representation of surface color, and the other is orientation-tuned, binocular, and selective for shape and form. This advances our understanding of the organization of the neural pathways involved in human color vision and provides a strong link between neurophysiological and behavioral data

Biochemical characterization of the bi-lobe complex in Trypanosoma brucei

Ph.DDOCTOR OF PHILOSOPH

Dip coating of silica layer on melt-spun Finemet ribbons: surface morphology and electrical resistivity changes

In this study, melt-spun Finemet ribbons were coated by a thin layer of SiO2 using dip coating method. Amorphous ribbon prepared by melt spinning method and dip coating were done by using a solution of tetraethylen orthosilicate as a SiO2 precursor, ethanol as solvent and distilled water for hydrolysis. Different thicknesses of SiO2 layer, namely 304, 349, 451, 526 and 970 nm were obtained proportional to the number of dipping. Surface morphology and chemical composition of the coatings were analyzed by using Scanning Electron Microscope equipped with an energy dispersive spectroscope. The results clearly verified the presence of Si and O elements and confirmed the presence of silica layer on the surface of all coated ribbons. Microstructure and surface morphology of samples showed a smooth and brittle layer. Electrical resistivity of the samples was measured with a standard four-point probe device. The results confirmed an intense in increase of resistivity. Average value of electrical resistivity for coated samples was around 104 Ω-m compared to 10-6 Ω-m for Finemet ribbons. Capacity of the samples was evaluated by electronic parameter analyzer device in two different frequencies of 100 kHz and 1000 kHz. Impedance measurements of coated samples in 100 and 1000 kHz showed an increase about 70 and 10 times respectively

A Comparative Proteomic Analysis Reveals a New Bi-Lobe Protein Required for Bi-Lobe Duplication and Cell Division in Trypanosoma brucei

A Golgi-associated bi-lobed structure was previously found to be important for Golgi duplication and cell division in Trypanosoma brucei. To further understand its functions, comparative proteomics was performed on extracted flagellar complexes (including the flagellum and flagellum-associated structures such as the basal bodies and the bi-lobe) and purified flagella to identify new bi-lobe proteins. A leucine-rich repeats containing protein, TbLRRP1, was characterized as a new bi-lobe component. The anterior part of the TbLRRP1-labeled bi-lobe is adjacent to the single Golgi apparatus, and the posterior side is tightly associated with the flagellar pocket collar marked by TbBILBO1. Inducible depletion of TbLRRP1 by RNA interference inhibited duplication of the bi-lobe as well as the adjacent Golgi apparatus and flagellar pocket collar. Formation of a new flagellum attachment zone and subsequent cell division were also inhibited, suggesting a central role of bi-lobe in Golgi, flagellar pocket collar and flagellum attachment zone biogenesis

TAC102 is a novel component of the mitochondrial genome segregation machinery in trypanosomes

Trypanosomes show an intriguing organization of their mitochondrial DNA into a catenated network, the kinetoplast DNA (kDNA). While more than 30 proteins involved in kDNA replication have been described, only few components of kDNA segregation machinery are currently known. Electron microscopy studies identified a high-order structure, the tripartite attachment complex (TAC), linking the basal body of the flagellum via the mitochondrial membranes to the kDNA. Here we describe TAC102, a novel core component of the TAC, which is essential for proper kDNA segregation during cell division. Loss of TAC102 leads to mitochondrial genome missegregation but has no impact on proper organelle biogenesis and segregation. The protein is present throughout the cell cycle and is assembled into the newly developing TAC only after the pro-basal body has matured indicating a hierarchy in the assembly process. Furthermore, we provide evidence that the TAC is replicated de novo rather than using a semi-conservative mechanism. Lastly, we demonstrate that TAC102 lacks an N-terminal mitochondrial targeting sequence and requires sequences in the C-terminal part of the protein for its proper localization

Orientation tuning in human color vision at detection threshold: a psychophysical approach

Object processing is an essential task of the human visual system that is thought to beaccomplished through hierarchical processing of objects attributes in the ventral occipitotemporal cortex. An object can primarily be delineated by its shape and surface information,including its color and texture. A shape can initially be defined as a set of oriented elementsdefined in luminance or color contrast. It is now thought that red-green color vision can detectcolor-defined edges almost as well as luminance vision can detect luminance-defined edges. Thisis supported by evidence from both psychophysical experiments and single cell recordings.However, it is not yet well understood how color contrast is used by the visual system in formprocessing. Color vision can have an important additional role to luminance vision in objectperception, by processing the surface color of an object. Evidence from single cell recordings inprimates have shown the presence of a neurons population of about 10% in V1 that respondexclusively to full field color stimuli and are not tuned to spatial frequency or orientation,making them candidates for surface color processing. Psychophysical experiments, however,have not revealed any direct evidence for non-oriented color mechanisms.In this thesis I use the psychophysical method of subthreshold summation to determine theorientation tuning of the red-green color mechanisms in human vision, and for luminancecontrast under equivalent conditions. Psychophysical models, based on the presence of multipletuned detectors or a single, non-oriented mechanism, are used to determine tuning properties ofthe neural detectors underlying the psychophysical responses.The first set of experiments revealed evidence for two types of red-green color mechanism: 1)non-oriented revealed monocularly at low spatial frequencies (0.25-0.375 cycles/degree), and 2)oriented that appeared binocularly or at higher spatial frequencies (1.5 cycles/degree). Inluminance vision, evidence supported the presence of orientation tuning at all spatial scales andviewing conditions. Based on these findings, further experiments were done to measure the fullmonocular orientation tuning responses of color vision, in comparison to luminance vision, atdifferent spatial scales. At mid spatial frequencies, similar orientation tuning responses andneural detector bandwidth estimates were found for color and luminance vision (16 and 13 degsrespectively). At low spatial frequencies, tuning curves for color contrast were extremely broadand fitted reasonably by a model involving isotropic detectors. For luminance vision, orientationtuning is preserved with no change in detector bandwidth. Finally, binocular responses weremeasured using dichoptic chromatic stimuli that revealed orientation tuning at both low and midspatial frequencies. In summary, the results of this thesis have revealed the presence of twodistinct pathways in color vision at the behavioral level that are best equipped, respectively forthe representation of an object's surface-color and form, and have provided estimates of theorientation bandwidth of their underlying neural detectors.Le traitement des objets est une tache essentielle pour le système visuel humain que l'on penseêtre accomplie à travers un traitement hiérarchique des attributs de l'objet dans la régionoccipito-temporale ventrale du cerveau. Premièrement un objet peut être délimité par sesinformations de forme et de surface, ce qui inclut sa couleur et sa texture. La forme peut êtreinitialement définie comme un groupe d'éléments orientés définis par leur contraste enluminance ou couleur. On pense maintenant que la vision de la couleur rouge-verte est capablede détecter des arêtes définies par leur couleur presque aussi bien que la vision de la luminancepeut détecter des arêtes définies par leur luminances. Les preuves a l'appui proviennent à la foisd'expériences en psychophysique et d'enregistrements électrophysiologiques cellule simple.Cependant on ne comprend pas encore très bien comment le contraste en couleur est utilise par lesystème visuel pour le traitement de la forme. La vision de la couleur peut avoir un rôleadditionnel important pour la vision de la luminance dans la perception des objets, en traitant lacouleur de la surface de l'objet. Des preuves provenant d'enregistrements cellule simple ontmontré l'existence d'une population de neurones - représentant environ 10% des neurones de V1- qui répond exclusivement aux stimuli couleur plein champ et qui n'est sensible ni à lafréquence spatiale ni à l'orientation, ce qui rend ces neurones de bon candidats pour le traitementdes surfaces colorées. En revanche, aucune expérience en psychophysique n'a mise en évidenceun mécanisme couleur non-orienté.Dans cette thèse j'utilise la méthode psychophysique de sommation subliminaire pour déterminerla sélectivité aux orientations et la sensibilité au contraste de luminance des mécanismes de lacouleur rouge-verte dans la vision humaine avec des conditions comparables. Des modèlespsychophysiques basés sur l'existence, soit de multiples détecteurs sensibles à l'orientation, soitd'un unique mécanisme non-orienté, ont été utilisés pour déterminer les propriétés de sensibilitédes détecteurs neuraux qui sous-tendent les réponses psychophysiques.Un premier groupe d'expériences a révélé l'existence de deux types de mécanisme de la couleurrouge-verte: 1) un mécanisme non-orienté qui a été mis en évidence en vision monoculaire et ce,à basses fréquences spatiales (0.25-0.375 cycles/degré) et 2) un mécanisme sensible àl'orientation qui est apparue en vision binoculaire mais également à haute fréquence spatiale (1.5cycles/degré). Dans la vision de la luminance les preuves supportent l'existence de mécanismessensibles à l'orientation pour toutes les fréquences spatiales et pour toutes les conditions de vue.Au regard de ces résultats, les expériences suivantes ont été menées afin de mesurer le spectreentier de la sensibilité aux orientations de la vision de la couleur sous condition monoculaire, dele comparer à celui de la vision de la luminance et ce, à différentes échelles spatiales. Pour lesfréquences spatiales intermédiaires, la vision de la couleur et la vision de la luminanceprésentaient des réponses de sensibilité aux orientations semblables et des estimations de bandespassantessimilaires pour les détecteurs neuraux. Pour les basses fréquences spatiales, les courbesde sensibilité au contraste de couleur étaient très larges et s'expliquaient raisonnablement bien àl'aide d'un modèle impliquant des détecteurs isotropiques. Dans le cas de la vision de laluminance, la sensibilité aux orientations est préservée sans changement de bandes-passantes dudétecteur. Enfin les réponses binoculaires ont été mesurées à l'aide de stimuli chromatiquesprésentés de façon dichoptique pour révéler en même temps la sensibilité aux orientations dansles basses fréquences spatiales et dans les fréquences spatiales intermédiaires

An interplay between Centrin2 and Centrin4 on the bi-lobed structure in Trypanosoma brucei

10.1111/j.1365-2958.2012.07998.xMolecular Microbiology8361153-1161MOMI

Technical and Economic Evaluation of Hybrid wind/PV/Battery Systems for Off-Grid Areas using HOMER Software

Incremental consumption of electrical energy, reduction of fossil fuel resources and environmental pollution problems caused by them are the main reasons, which tend the managers and officials in countries energy sector to develop use of renewable systems. In the not-too-distant future the use of renewable energy such as wind and solar will be very important and will play predominant role in economic indices of power systems. In recent years, technological advances in renewable energy and increasing price of petroleum products promote system managers to use low-cost and low-emission energy resources in form of hybrid systems and widespread propagation of electricity generation have been developed in remote areas. In Hybrid systems two or more sources of renewable energy is typically adopted, which increases the reliability of these systems. In this paper, the technical and economical consideration of a wind and solar hybrid system to supply electrical energy for a number of remote users (aid and medical emergency Shelter in Yazd) is provided. In order to investigate optimization and economic analysis of the proposed hybrid system, the HOMER software is used.  The results of Simulation in HOMER software show that Solar cells and wind systems with average generation power of 896 kWh/yr. and 343 kWh/yr., consist proportion of 72 and 28 percent of the total generated energy respectively, which are dedicated to satisfy the load