Academic literature on the topic 'Exogenous and endogenous attention'

In everyday life, the allocation of spatial attention typically entails the interplay between voluntary (endogenous) and stimulus-driven (exogenous) attention. Furthermore, stimuli in different sensory modalities can jointly influence the direction of spatial attention, due to the existence of cross-sensory links in attentional control. Using fMRI, we examined the physiological basis of these interactions. We induced exogenous shifts of auditory spatial attention while participants engaged in an endogenous visuospatial cueing task. Participants discriminated visual targets in the left or right hemifield. A central visual cue preceded the visual targets, predicting the target location on 75% of the trials (endogenous visual attention). In the interval between the endogenous cue and the visual target, task-irrelevant nonpredictive auditory stimuli were briefly presented either in the left or right hemifield (exogenous auditory attention). Consistent with previous unisensory visual studies, activation of the ventral fronto-parietal attentional network was observed when the visual targets were presented at the uncued side (endogenous invalid trials, requiring visuospatial reorienting), as compared with validly cued targets. Critically, we found that the side of the task-irrelevant auditory stimulus modulated these activations, reducing spatial reorienting effects when the auditory stimulus was presented on the same side as the upcoming (invalid) visual target. These results demonstrate that multisensory mechanisms of attentional control can integrate endogenous and exogenous spatial information, jointly determining attentional orienting toward the most relevant spatial location.

Attention alters perception across the visual field. Typically, endogenous (voluntary) and exogenous (involuntary) attention similarly improve performance in many visual tasks, but they have differential effects in some tasks. Extant models of visual attention assume that the effects of these two types of attention are identical and consequently do not explain differences between them. Here, we develop a model of spatial resolution and attention that distinguishes between endogenous and exogenous attention. We focus on texture-based segmentation as a model system because it has revealed a clear dissociation between both attention types. For a texture for which performance peaks at parafoveal locations, endogenous attention improves performance across eccentricity, whereas exogenous attention improves performance where the resolution is low (peripheral locations) but impairs it where the resolution is high (foveal locations) for the scale of the texture. Our model emulates sensory encoding to segment figures from their background and predict behavioral performance. To explain attentional effects, endogenous and exogenous attention require separate operating regimes across visual detail (spatial frequency). Our model reproduces behavioral performance across several experiments and simultaneously resolves three unexplained phenomena: 1) the parafoveal advantage in segmentation, 2) the uniform improvements across eccentricity by endogenous attention, and 3) the peripheral improvements and foveal impairments by exogenous attention. Overall, we unveil a computational dissociation between each attention type and provide a generalizable framework for predicting their effects on perception across the visual field.

The studies presented in this thesis investigated the neural correlates of attention in touch. In particular, the electrophysiology of exogenous tactile processing and inhibition of return (IOR) - an area previously unexplored. In all studies a variation of the Posner cue-target paradigm was used. Typically, a cue was presented to the left or right hand. Following a stimulus onset asynchrony of 800 ms, a target would appear at the same or opposite hand. Behavioural results consistently demonstrated IOR when employing a simple target detection task, showing that IOR is a reliable phenomenon in touch. The concurrently recorded event related potentials (ERPs) demonstrated an early attention modulation of the N80 in all studies presented in this thesis, regardless of the presence or absence of IOR. This early component likely reflects processing of the exogenous lateralized cues. Following the N80, the attention modulations varied across studies. The conclusion to be drawn from this thesis is that not one particular ERP component is directly associated with IOR. Analysis of endogenous tactile attention (Chapter V) demonstrated modulations at the N140 and Nd components. Moreover, correlation analysis showed that larger ERP attention modulation was associated with a larger behavioural effect, demonstrating a novel relationship between ERP modulations and response time effects. Analysis of the cue-target interval has previously only been investigated during endogenous orienting. Here, and for the first time, an anterior directing attention negativity (ADAN) was demonstrated during exogenous orienting. This ADAN was unaffected by varying posture suggesting exogenous tactile attention and IOR are somatotopically coded. Indications of an external frame of reference were only demonstrated during shifts of endogenous attention, as indicated by the presence of a late directing attention positivity (LDAP) (endogenous counter-predictive task presented in Chapter V). The final study of this thesis (Chapter VI) demonstrated that varying visual perceptual load influenced tactile processing. Specifically, high perceptual load led to elimination of IOR. Moreover, the P100 for irrelevant tactile stimuli was significantly reduced in high versus low load condition. This suggests perceptual load may suppress irrelevant tactile stimuli relatively early (around 100 ms post stimuli onset) during tactile processing. Taken together, this thesis presents a series of experiments which map out effects of endogenous and exogenous attention and how these mechanisms interact, both through behaviour and underlying neural correlates.

The experiments in this thesis were designed to examine the consequences of endogenous and exogenous spatial cueing in a dual-task set-up. The first experiments, presented in Chapters 2 and 3, explored whether spatial attention generalises across dimensions in the same location. Chapters 4, 5, and 6 contain a second series of experiments using exogenous cues, in which cue properties were manipulated. A dual-task set-up was used in all studies in this thesis, with a display of four random dot kinematograms containing motion and colour features. In order to examine whether endogenous attention may be spatially oriented to only one feature dimension, a central cue was presented that was 70% valid for the location of only one task. Both tasks showed validity effects, but the task for which the cue was informative showed larger attentional modulation. This suggests that spatial attention is not a single 'spotlight' but can be biased in favour of expected features. There was also asymmetry in the tasks, whereby the validity effect was modulated for motion, but comparable for colour regardless of the task for which the cue was informative. This asymmetry was also evident when using uninformative exogenous cues preceding the same tasks. Peripheral luminance and colour cues affected the validity effects for the motion and colour tasks differently, suggesting that the relationship between cue properties and proceeding stimuli modulates attentional effects. The size of a frame cue leads to different attentional effects on tasks of different sizes. These experiments make a considerable contribution to the spatial attention literature, by showing that spatial attention may be biased either by cue properties or cue information, suggesting that spatial attention and feature-based attention may interact. They also provide further evidence that motion is better represented than colour in visual attention.

Converging evidences from neurophysiological, neuropsychological and functional neuroimaging literature suggested the involvement of a large-scale fronto-parietal network in the volitional and reflexive attentional control, which enables the biological systems to select relevant portions of the input stream for facilitating processing, in order to flexibly guide behavior on the basis of internal or external goals. This system acts in tight interplay with lateralized structures deputed to the achievement and maintenance of an adequate level of arousal, and with medial frontal structures responsible for the on-line modification of action and thought in response to an ever-changing external world. This project aims at clarifying the spatio-temporal dynamics of the recruitment of these three tightly related systems (alertness, orienting and executive control) and at a better explanation of integrative effects previously reported, by means of a series of high-density electrophysiological recording experiments combined with source localization methods. Experiment 1 combined a spatial cueing paradigm with a flanker task, showing early occipital and parietal activations in response to valid cues, and a lateralized pattern of sources for the responses of the phasic alertness system to both spatially valid and spatially neutral cues; additionally, we reported behavioral, electrophysiological and functional indexes of a modulation exerted by the orienting system upon the executive control one. Experiment 2 compared lateralized shifts of attention elicited by centrally and peripherally presented spatially valid and neutral cues, in a combined cueing and go/no-go task. The results again suggested an early involvement of the selective attention system in response to the task-relevant cues, as expressed in occipito-temporal enhanced responses to the valid cues as compared to the neutral ones; additionally, lateralized superior parietal and frontal activations were recorded, concurrently with attentional shifts. Again, a modulation of the conflict monitoring/response inhibition system was observed in case of validly cued stimuli, as indexed by anticipations of the fronto-central NoGoN2 in response to non-targets preceded by valid warning signals. Experiment 3 tested the hypothesis of bidirectional modulations between the attention and control systems, by means of an integrated stop-signal/flanker task. The results showed that the selective response inhibition, required in case of incompatible flankers in the primary stimuli, interfered with the attentional switch towards the relevant stop-signals, as reflected in dimmed auditory responses to the stop-tones. All in all, the present results point toward a complex interplay among the three systems, and suggest that any interpretation of the scientific results obtained in paradigms addressing the attentional networks should account also for alertness and executive control effects, which are indirectly manipulated when capitalizing on cueing/switching paradigms.

1. Introduction The multidisciplinary approach of using brain signals for directly controlling external devices, like computers or prosthesis, is named brain-computer interface (BCI). Farwell and Donchin (1988) showed that it is possible for humans to communicate using a BCI, by means of their event-related potentials (ERPs; e.g., P300), without the involvement of their voluntary muscle activity. The use of brain-wave-guided BCIs offered new perspectives regarding communication and control of devices for patients suffering from severe motor impairment or for patients who completely paralyzed, such as the patients affected by amyotrophic lateral sclerosis (ALS), in the latest stages of the illness. In the last two decades an important scientific and clinical challenge has been the development of efficient BCIs for ALS patients. Most of the progress in the field has been mainly concerned with algorithm improvement for better signal classification. In contrast, only few studies have addressed, to date, the role of cognitive mechanisms underlying the elicitation of brain-signals in BCIs. In the present study we investigated the possibility to modulate the brain signal and, by doing so, the performance of an ERP-guided BCI system, by designing and implementing three new interfaces in which participants were required to perform covert visuospatial attention orienting (Posner, 1980), in order to control the movement of a cursor on a monitor. 2. Experiment 1 The effects of covert visuospatial attention orienting within an ERP-guided BCI were tested on healthy participants. We compared the effectiveness of three visual interfaces, each of whom elicited different modalities of covert visuospatial attention orienting (exogenous vs. endogenous). Twelve adult participants performed 20 sessions, using the abovementioned ERP-guided BCI interfaces to control the movement of a cursor. Brain waves were recorded on each trial and were subsequently classified online, by means of an ad-hoc algorithm. Each time the target ERPs were correctly classified, the cursor moved towards the target position. The “endogenous” interface was associated with significantly higher performance than the other two interfaces during the testing sessions, but not in the follow-up sessions. Endogenous visuospatial attention orienting can be effectively implemented to increase the performance of ERP-guided BCIs. 3. Experiment 2 To investigate whether the findings reported in Experiment 1 depended on the used classification system, we performed an offline reclassification of the data of Experiment 1. The online analysis of the epochs was made via Independent Component Analysis (ICA), which, in turn, was followed by fixed features extraction and support vector machine (SVM) classification. The offline epochs analysis was performed by means of a genetic algorithm (GA), which permitted us to retrieve the relevant features of the signal to be classified, and then to categorise them with a logistic classifier. The offline analysis confirmed the advantages derived from the use of the “endogenous” interface. The performance-related findings were in line with those obtained in the neurophysiological data analysis. Nonetheless, epoch categorization was performed better with the GA algorithm than with the ICA: the higher mean and the smaller standard deviation of the classification performed with the GA seem to promise a possible improvement of the ERP-guided BCI also on online tests. 4. Experiment 3 On the basis of the results of Experiments 1 and 2, we tested the efficacy of two visual interfaces, each of whom elicited different modalities of covert visuospatial attention orienting (exogenous vs. endogenous), in ALS patients. Ten ALS patients performed 16 online sessions with each interface. Although the ALS patients had a performance of about 70% with both the interfaces, the endogenous interface elicited a larger difference on ERP potentials between target and non-target trials. These results supported the hypothesis that the use of the endogenous interface may offer a more efficient channel of communication for ALS patients with respect to the use of the exogenous interface. 5. Conclusions Neurological diseases that affect the motor system may impair communication abilities of patients, as in the case of amyotrophic lateral sclerosis. This pathology might evolve in the locked-in syndrome (LIS), a condition in which patients remain conscious but cannot move any of their muscles. For instance, they may become unable to express their opinions and decisions on important questions regarding their clinical treatment or their living and biological wills. The BCIs represent a potential solution to the communication problems of ALS-LIS patients. Despite the fact that more than 20 years have passed since the first published article on a P300-guided BCI, the effects of cognitive mechanisms (i.e., executive functions, attention, memory, etc.) involved in brain signal elicitation have not been investigated extensively. In the abovementioned experiments, we tested the effect of covert visuospatial attention orienting on an ERP-guided BCI, by comparing a number of visual interfaces, each of whom elicited a different modality of covert visuospatial attention orienting. Taken together, the results supported our main hypothesis: It is possible to modulate the performance of an ERP-guided BCI, by using endogenous or exogenous visuospatial attention orienting. Of particular relevance is the fact that our ALS patients were able to use endogenous visuospatial attention orienting and, by doing so, they could increase their performance in an ERP-guided BCI. We suggest that the study of covert visuospatial attention orienting is essential for developing efficient visual BCIs for patients who cannot control their eye movements. Implementing principles taken from cognitive psychology, may improve BCIs efficiency. This, in turn, can increase the benefits for patients with severe motor and communication disabilities. Finally, an efficient cognitive-based BCI may have the considerable ethical implication of “giving a voice” to CLIS-ALS patients<br>1. Introduzione Farwell e Donchin (1988) per primi hanno dimostrato la possibilità che l’uomo ha di comunicare usando i potenziali evento correlati (ERP; e.g., P300), senza bisogno di usare alcun muscolo per tale fine. Questa scoperta ha offerto nuove prospettive per la comunicazione ed il controllo di periferiche in pazienti affetti da gravi disabilità motorie o completamente paralizzati, come nel caso dei pazienti affetti da sclerosi laterale amiotrofica (SLA), negli stadi più avanzati di malattia. L’approccio multidisciplinare che consente di tradurre segnali cerebrali direttamente in comandi per controllare computer o protesi meccaniche è chiamato brain-computer interface (BCI). Negli ultimi vent’anni un’importante sfida scientifica è stata quella di sviluppare una BCI efficace, affinché potesse essere usata nella pratica clinica con i pazienti. I progressi più rilevanti fatti finora riguardano principalmente la registrazione e l’elaborazione dei segnali cerebrali, grazie ad algoritmi sempre più potenti ed efficaci nella categorizzazione dei biosegnali. Minore attenzione è stata posta, invece, nell’investigare il ruolo dei meccanismi cognitivi che sottendono l’uso di una BCI. Nel presente studio è stata indagata la potenzialità dei partecipanti di modulare specifiche onde cerebrali e, di conseguenza, l’efficacia di un sistema BCI guidato dagli ERP, attraverso l’uso di diversi processi di orientamento implicito dell’attenzione visuospaziale (Posner, 1980). A tale scopo sono state progettate e testate tre nuove interfacce visive per controllare il movimento di un cursore su un monitor. 2. Esperimento 1 Nel primo esperimento è stato testato l’effetto dell’orientamento implicito dell’attenzione visuospaziale in partecipanti sani, il cui scopo era di controllare il movimento di un cursore con una BCI guidata da ERP, per raggiungere specifici bersagli. È stato confrontato l’uso di tre interfacce, ciascuna delle quali prevedeva l’utilizzo di una specifica modalità dell’orientamento implicito dell’attenzione visuospaziale (esogeno vs. endogeno). Dodici partecipanti adulti hanno eseguito 20 sessioni, con ciascuna delle tre interfacce. Simultaneamente, gli ERP associati a ciascun trial di ogni interfaccia erano registrati e classificati da un algoritmo ad hoc. Ogni volta che gli ERP associati alla direzione della posizione bersaglio erano correttamente classificati, il cursore era mosso di un passo verso la posizione bersaglio. I partecipanti hanno ottenuto un’accuratezza migliore nel controllo del cursore con l’interfaccia che prevedeva l’orientamento endogeno dell’attenzione visuospaziale rispetto alle due interfacce che prevedevano l’orientamento esogeno. 3. Esperimento 2 Nel secondo studio è stata eseguita una classificazione offline degli ERP registrati nell’Esperimento 1, con lo scopo di verificare se gli effetti ottenuti nell’Esperimento 1 fossero indipendenti dal tipo di algoritmo di classificazione utilizzato. La classificazione online dei segnali cerebrali avveniva attraverso l’analisi delle componenti indipendenti (ICA), un’estrazione di 78 caratteristiche stabilite a priori del segnale, e la loro categorizzazione attraverso un algoritmo matematico di tipo lineare (support vector macchine: SVM). La riclassificazione offline è stata eseguita per mezzo di un algoritmo genetico (genetic algorithm: GA), che rilevava ad personam le caratteristiche significative del segnale, le quali, infine, venivano categorizzate attraverso un classificatore logistico. Il metodo di classificazione offline nell’Esperimento 2 ha confermato l’effetto ottenuto nell’Esperimento 1. Questi risultati sono stati confermati anche dalle analisi statistiche eseguite sui dati neurofisiologici. Inoltre, le medie di accuratezza più alte e la minore variabilità associate al sistema di classificazione offline sembrano offrire potenziali miglioramenti dell’efficacia dell’uso in tempo reale della nostra BCI. 4. Esperimento 3 Alla luce dei risultati riportati negli Esperimenti 1 e 2, è stata testata l’efficacia di un’interfaccia che prevedeva l’uso dell’orientamento esogeno dell’attenzione visuospaziale e di un’altra che prevedeva l’uso dell’orientamento endogeno, con pazienti affetti da SLA. Dieci pazienti con SLA hanno eseguito 16 sessioni con ciascuna delle due interfacce. Anche se i pazienti hanno ottenuto un’accuratezza di circa 70% con entrambe le interfacce, è stata registrata una maggior differenza tra gli ERP target e quelli non-target con l’uso dell’interfaccia “endogena”. Questi risultati supportano l’ipotesi che l’interfaccia che usa l’orientamento endogeno dell’attenzione visuospaziale consenta un miglior controllo del sistema BCI, con conseguenti vantaggi comunicativi per i pazienti affetti da SLA. 5. Conclusioni Le patologie neurologiche che colpiscono il sistema motorio possono intaccare i normali canali di comunicazione, come nel caso di pazienti affetti dal SLA. Questa malattia può sfociare nello stato denominato sindrome locked-in (LIS), una condizione clinica in cui i pazienti sono completamente paralizzati ma mantengono intatta la loro consapevolezza. Nella condizione di LIS, un paziente non può comunicare, non potendo così esprimere la propria opinione riguardo alle scelte etico-giuridiche legate alla sua condizione clinica. Le BCI rappresentano una potenziale soluzione ai problemi comunicativi dei pazienti nella LIS. Negli ultimi vent’anni di ricerca scientifica sulle BCI è stata rivolta grande attenzione alle componenti tecnologiche implicate nella registrazione del segnale cerebrale e nella sua classificazione in comandi per controllare specifiche periferiche. Viceversa, minor attenzione è stata posta alle caratteristiche dell’utente nell’utilizzo delle BCI, in particolar modo riguardo alle componenti cognitive coinvolte. Negli esperimenti riportati nella presente tesi, abbiamo testato l’efficacia di diverse interfacce, ciascuna delle quali utilizzava una specifica modalità dell’orientamento implicito dell’attenzione visuospaziale (endogena o esogena). I risultati di questi esperimenti supportano l’ipotesi che è possibile modulare l’efficacia di una BCI guidata da ERP attraverso l’implementazione di interfacce visive che utilizzano diversi principi dell’orientamento implicito dell’attenzione visuospaziale. Tale risultato è di particolare rilevanza dal punto di vista clinico per i pazienti affetti da SLA, negli stadi terminali di malattia, cioè quando entrano nella condizione clinica di LIS. In particolare nell’Esperimento 3 è riportato come l’ampiezza degli ERP sia diversamente modulata nelle due interfacce testate e questo fatto può giocare un ruolo rilevante nello sviluppo di un efficace sistema BCI che permetta la comunicazione a pazienti affetti da SLA nella condizione di completa LIS. I nostri risultati portano evidenze di come l’implementazione dei principi della psicologia cognitiva nello sviluppo di una BCI ne possano modulare l’efficacia, e questo a vantaggio dei pazienti affetti da gravi disabilità motorie. In conclusione, un’efficace applicazione dei principi cognitivi nello sviluppo delle BCI può avere l’effetto rilevante di “dare una voce” a pazienti in stato di completa LIS

Cette thèse portait sur l'attention visuelle sélective, dans le domaine non-spatial, c'est-à-dire la capacité à favoriser le traitement perceptif de certains objets de la scène visuelle au détriment des autres. En particulier, l'objectif était d'étudier, à l'aide de tâches de recherche visuelle, les différentes interactions possibles entre les processus endogènes (liés aux intentions et connaissances du sujet) et les processus exogènes (liés aux caractéristiques perceptives des objets). Une première série d'expériences démontrait que la saillance pouvait présenter des effets relativement durables. Cependant, ces effets de saillance pouvaient être favorisés ou contrecarrés par des processus endogènes (induits par indiçage portant sur la taille), et modulés par l'amorçage perceptif. Une seconde série d'expériences démontrait que la résistance à l'interférence induite par un distracteur saillant dépendait de ressources attentionnelles centrales, et était modulée par la charge perceptive. Enfin, la troisième série d'expériences validait l'hypothèse d'une intégration entre des signaux endogènes et exogènes compatibles mais strictement distincts. La falsification de l'inégalité de Miller (1982) précisait que cette intégration reposait sur une coactivation effective, non sur une simple facilitation statistique entre signaux strictement indépendants. Le locus cognitif de cette intégration semble être le système perceptif. L'ensemble des données présentées souligne la flexibilité du contrôle attentionnel, et invite à développer un modèle général de l'attention visuelle sélective basé sur l'hypothèse de compétition biaisée (Desimone &amp; Duncan, 1995)<br>This thesis was about visual selective attention, toward non-spatial features, that is, the ability to favour the perceptual processing of some objects in the visual scene, at the expense of others. In particular, the aim was to study, through visual search experiments, the various possible interactions between endogenous (linked with incentives and knowledge of subjects) and exogenous (linked with perceptual properties of the objects) processes. The first series of experiments showed long-lived salience effects. These salience effects could, hewever, be favoured or overriden by endogenous processes (induced by cueing the target size), and modulated by perceptual priming. The second series evidenced that resisting the interference induced by a salient distractor depended on central attentional resources, and was modulatted by perceptual load. Finally, the third series demonstrated that separate endogenous and exogenous signals could genuinely integrate. This integration could not be accounted for by a race between strictly independant signals, as evidenced by the falsification of the Miller's (1982) inequality. This integration might occur in the perceptual system. Theglobal set of data highlighted the flexibility of endogenous attentional control, and invited developping a general model of visual selective attention, on the basis of the biased competition hypothesis

The theoretical and practical foundations of engineering geology, the geological structure and origin of the Earth are described, the minerals of rocks and the rocks themselves of igneous, sedimentary and metamorphic origin are considered. Considerable attention is paid to the geomorphological, geodynamic, and hydrogeological conditions of the construction site with the allocation of three types of underground water: upper water, ground water, and inter-reservoir. The dynamics of the development of various forms of relief caused by endogenous and exogenous processes is given. The zonal elements of engineering and geological conditions of any construction site are given. Meets the requirements of the federal state educational standards of secondary vocational education of the latest generation. For students of secondary vocational education institutions studying engineering geology.

Abstract In this paper, the supercritical carbon dioxide power cycle used to recover the waste heat of gas turbine is investigated by means of conventional exergy analysis and advanced exergy analysis. Firstly, the thermodynamic parameters of carbon dioxide cycle in design stage are determined by single-objective optimization with net power output as objective function. Then, conventional exergy analysis is carried out on the partial heating cycle under real, unavoidable and ideal conditions. After that, advanced exergy analysis, in which the exergy destruction is divided into endogenous / exogenous part and avoidable / unavoidable part is adopted to reveal the improvement potential of the system and illustrate the interaction among the components. According to the calculation results, a total amount of 3.55MW (47.33%) exergy destruction could be reduced by the improvement of component efficiency. Endogenous exergy destruction is higher than exogenous exergy destruction in all components. Based on the results of conventional exergy analysis, the high-temperature heater should be paid attention in order to reduce exergy destruction. However, according to the results of advanced exergy analysis, the technical improvement of turbine should be emphasized due to its high endogenous-avoidable exergy destruction. Meanwhile, for the components with high unavoidable exergy destruction, external systems should be employed to exploit the underutilized energy and enhance the system performance.

This article is aimed at analysing the economic interrelation between actors in the tomato production chain in Uzbekistan and find ways to increase the smallholders’ income. We used a PROBIT model to determine the influence of exogenous and endogenous factors on the choice of a small trading partner. The customers that come to the smallholders’ house to purchase the product are regarded as an exogenous factor. More attention needs to be paid to increasing value-added in the food chain in Uzbekistan and improving economic relations between its actors. The factor obtained as an instrumental variable is assessed as having a positive and high impact on the choice of smallholder intermediate trade partner. In other words, an increase in the level of acquaintances of intermediaries with smallholders will increase economic cooperation by 1.2 times, an increase in family income from agriculture by 19% and an increase in smallholder activity in the mahalle by 15.7%. It is estimated that the increase in the number of respondents’ livestock per unit, foreign experience per year and the level of use of credits per unit will increase economic cooperation with direct consumers by 34.4, 13.4 and 28.5%, respectively. It also provides guidelines for tomato farmers to reduce transaction costs and risks and increase their profitability.

One of the roles of exergy analysis is to provide thermal system designers and operators with information useful for the system optimization. An exergy analysis identifies the sources of thermodynamic inefficiencies by evaluating the exergy destruction within each system component. However, care must be taken when using the total exergy destruction within a component to reach conclusions regarding the optimization of the overall energy system. The reason is that the total exergy destruction occurring in a component is not due exclusively to that component but is also caused by the inefficiencies within the remaining system components. The endogenous exergy destruction within a component is defined as that part of the component's exergy destruction that is independent of any change in the exergy destruction within the remaining components. The part of the component's exergy destruction which depends upon the changes of the exergy destruction within the other components is defined as the exogenous exergy destruction. It is apparent that the sum of endogenous and exogenous exergy destruction is equal to the total exergy destruction within the component being considered. Knowledge of the exogenous and endogenous exergy destruction for the most important components can further assist the engineer in deciding whether an adjustment in that component or in the structure of the system (i.e. in the remaining components) is required to improve the overall system. The paper presents the general concept of endogenous and exogenous exergy destruction. Using a graphical approach, the endogenous and exogenous exergy destruction of a simple gas turbine process and simple refrigeration machine are investigated.

It will be shown how light induced fluorescence is used for the localization of early cancer in the upper serodigestive tract, the tracheobronchial tree, the esophagus and the bladder. Both endogenous and exogenous dyes will be used. Early results with a two wavelengths observation procedure for image enhancements are reported using frequency domain imaging.

Modern macroeconomics focuses on the identification of the primitive exogenous forces generating business cycles. This is at odds with macroeconomic forecasts collected through surveys, which are about endogenous variables. To address this divorce, our paper uses a general equilibrium model as a multivariate filter to infer the shocks behind market analysts' forecasts and thus, unravel their implicit macroeconomic stories. By interpreting all analysts' forecasts through the same lenses, it is possible to understand the differences between projected endogenous variables as differences in the types and magnitudes of shocks. It also allows to explain market's uncertainty about the future in terms of analysts' disagreement about these shocks. The usefulness of the approach is illustrated by adapting the canonical SOE semi-structural model in Carabenciov et al. (2008a) to Colombia and then using it to filter forecasts of its Central Bank's Monthly Expectations Survey during the COVID-19 crisis.

This essay aims to utilize the concept of conviviality for connecting the coexistence of seemingly contradictory phenomena in Colombia. It argues that while conviviality implies a normative content – a society in which members do not slaughter each other is better than one in which members resort to violence – the meekness of that normative claim suggests that it is better used as an analytical tool that seeks to connect the contradictions that coexist in the real lifeworld. Colombia’s history of violence and democracy is such a contradictory case. Comparativists have situated Colombia’s deficits on the “extra-institutional playing field”, lamenting that it is a “besieged” or “threatened democracy”. Conviviality helps us to specify these “extra-institutional” defects by suggesting impediments exogenous and endogenous to the state-building logic of the Colombian nation-state.

Ethylene is a plant hormone that controls many plant responses, such as growth, senescence, ripening, abscission and seed germination. Recently, 1-methy- cyclopropene (1-MCP), was shown to bind to ethylene receptor for a certain period of time and prevent ethylene action. The objectives of this research were to synthesize analogues of 1-MCP and test their potency to block the ethylene receptor and inhibit ethylene action. During the course of this project, procedures for synthesis and shipment of the cyclopropene compounds were developed as well assay procedures for each compound were worked out. Thirteen new compounds were synthesized. All of them are structural analogues of 1-MCP, with substitution in the 1-position and a side chain containing 2 to 10 carbons. After preliminary studies, nine promising compounds were selected for in-depth study. The potency of the compounds to inhibit ethylene action was tested on a wide scope of systems like: climacteric fruits (banana, avocado and tomato), the triple response (etiolated peas), and leaf abscission (citrus). As the putative inhibitors are suspected to compete for the site of binding and a competitive type of inhibition could be considered, a high concentration of ethylene (300 m1.L-1) was used to induce ripening and other physiological processes. The tests were conducted under extreme conditions which hasten ripening like treatment and storage at 22 to 25oC. There were fluctuations in the responses as related to the concentrations of the inhibitors. Some required much higher concentration to exert the same effect, while some, when applied at the same concentration, blocked the receptor for a longer period of time than the others. Some fruits and other plant organs responded differently to the same inhibitor, indicating differences in characteristics and availability of the ethylene receptors in the various tissues. The potency of the putative inhibitors was found to be greatly affected by their molecular structural and size. In addition, it was found that treatment with the inhibitor should be given before the onset of ethylene action In the case of fruit, treatment should be carried out before the pre-climacteric stage. Simultaneous treatment with ethylene and the inhibitors reduced the inhibitors' effect. The relationship between ethylene and the inhibitors is of a non-competitive nature. All the fruits treated with the putative inhibitors resumed normal ripening after recovery from the inhibition. This fact is of great importance when considering the inhibitors for practical use. The advantage of using inhibitors of ethylene action over inhibitors of ethylene production lies in the ability of the inhibitors of ethylene action to protect the tissue against both endogenous and exogenous ethylene, thus providing better overall protection. Our findings indicate that 1-MCP and its structural analogues are potent inhibitors of ethylene action capable of providing good protection against endogenous and exogenous ethylene. The fact that the compounds are in a gas phase and are non-phytotoxic, odorless and effective at minute concentrations, renders them promising candidates for commercial use. However, the development of water-soluble inhibitors will expand the potential use of the inhibitors in agriculture.

Altering milk composition via transgenesis depends on three main factors. (1) The availability of an efficient regulatory sequences for targeting transgene(s) to the mammary gland; (2) a reliable in vitro model to test the expression of transgenes prior to their introduction to the animal genome; and (3) better understanding of the major factors which determine the rate of gene expression and protein synthesis. The current studies provide the necessary means and knowledge to alter milk protein composition via transgenesis. The following specific goals were achieved: a: Identifying regulatory regions in the b-lactoglobulin (BLG) gene and the cross-talk between elements which enabled us to construct an efficient vector for the expression of desirable cDNA's in the mammary gland. b: The establishment of a sheep mammary cell line that serves as a model for the analysis of endogenous and exogenous milk protein synthesis in the mammary gland of livestock. c: An accurate comparison of the potency of the 5' regulatory sequences from the BLG and whey acidic protein (WAP) promoters in directing the expression of human serum albumin (HSA) to the mammary gland in vitro and in vivo. In this study we have also shown that sequences within the coding region may determine a specific pattern of expression for the transgene, distinct from that of the native milk protein genes. d: Characterizing the dominant role of ECM in transgene expression in mammary epithelial cells. e: Further characterization of the BCE-1 enhancer element in the promoter of the b-casein gene as a binding site for the c/EBP-b and Stat5. Identifying its interaction with chromatin and its up regulation by inhibitors of histone deacetylation. f: Identifying a mechanism of translational control as a mediator for the synergistic effect of insulin and prolactin on protein synthesis in the mammary gland.

Fruit deterioration is a consequence of a genetically-determined fruit ripening and senescence programs, in which developmental factors lead to a climacteric rise of ethylene production in ethylene-sensitive fruits such as tomato and banana. Breeding of tomato with extended fruit shelf life involves the incorporation of a mutation in RIN, a MADS-box transcription factor participating in developmental control signalling of ripening. The RIN mode of action is not fully understood, and it may be predicted to interact with other MADS-box genes to execute its effects. The overall goal of this study was to demonstrate conservation of ripening control functions between banana and tomato and thus, the potential to genetically extend shelf-life in banana based on tools developed in tomato. The specific objectives were: 1. To increase the collection of potential RIN-like genes from banana; 2. To verify their action as developmental regulators; 3. To elucidate MADS-box gene mode of action in ripening control; 4. To create transgenic banana plants that express low levels of endogenous Le-RIN- like, MaMADS- gene(s). We have conducted experiments in banana as well as in tomato. In tomato we have carried out the transformation of the tomato rin mutant with the MaMADS1 and MaMADS2 banana genes. We have also developed a number of domain swap constructs to functionally examine the ripening-specific aspects of the RIN gene. Our results show the RIN-C terminal region is essential for the gene to function in the ripening signalling pathway. We have further explored the tomato genome databases and recovered an additional MADS-box gene necessary for fruit ripening. This gene has been previously termed TAGL1 but has not been functionally characterized in transgenic plants. TAGL1 is induced during ripening and we have shown via RNAi repression that it is necessary for both fleshy fruit expansion and subsequent ripening. In banana we have cloned the full length of six MaMADS box genes from banana and determined their spatial and temporal expression patterns. We have created antibodies to MaMADS2 and initiated ChI assay. We have created four types of transgenic banana plants designed to reduce the levels of two of the MaMADS box genes. Our results show that the MaMADS-box genes expression in banana is dynamically changing after harvest and most of them are induced at the onset of the climacteric peak. Most likely, different MaMADS box genes are active in the pulp and peel and they are differently affected by ethylene. Only the MaMADS2 box gene expression is not affected by ethylene indicating that this gene might act upstream to the ethylene response pathway. The complementation analysis in tomato revealed that neither MaMADS1 nor MaMADS2 complement the rin mutation suggesting that they have functionally diverged sufficiently to not be able to interact in the context of the tomato ripening regulatory machinery. The developmental signalling pathways controlling ripening in banana and tomato are not identical and/or have diverged through evolution. Nevertheless, at least the genes MaMADS1 and MaMADS2 constitute part of the developmental control of ripening in banana, since transgenic banana plants with reduced levels of these genes are delayed in ripening. The detailed effect on peel and pulp, of these transgenic plants is underway. So far, these transgenic bananas can respond to exogenous ethylene, and they seem to ripen normally. The response to ethylene suggest that in banana the developmental pathway of ripening is different than that in tomato, because rin tomatoes do not ripen in response to exogenous ethylene, although they harbor the ethylene response capability This study has a major contribution both in scientific and agricultural aspects. Scientifically, it establishes the role of MaMADS box genes in a different crop-the banana. The developmental ripening pathway in banana is similar, but yet different from that of the model plant tomato and one of the major differences is related to ethylene effect on this pathway in banana. In addition, we have shown that different components of the MaMADS-box genes are employed in peel and pulp. The transgenic banana plants created can help to further study the ripening control in banana. An important and practical outcome of this project is that we have created several banana transgenic plants with fruit of extended shelf life. These bananas clearly demonstrate the potential of MaMADS gene control for extending shelf-life, enhancing fruit quality, increasing yield in export systems and for improving food security in areas where Musaspecies are staple food crops.

The hypothalamic melanocortin system plays a central role in the regulation of food consumption and energy homeostasis in mammals. Accordingly, our working hypothesis in this project was that genetic editing of the mc4r gene, encoding Melanocortin Receptor 4 (MC4R), will enhance food consumption, feed efficiency and growth in fish. To test this hypothesis and to assess the utility of mc4r editing for the enhancement of feed efficiency and growth in fish, the following objectives were set: Test the effect of the mc4r-null allele on feeding behavior, growth, metabolism and survival in zebrafish. Generate mc4r-null alleles in tilapia and examine the consequences for growth and survival, feed efficiency and body composition. Generate and examine the effect of naturally-occurring mc4r alleles found in swordfish on feeding behavior, growth and survival in zebrafish. Define the MC4R-mediated and MC4R-independent effects of AgRP by crossing mc4r- null strains with fish lacking AgRP neurons or the agrpgene. Our results in zebrafish did not support our hypothesis. While knockout of the agrpgene or genetic ablation of hypothalamic AgRP neurons led to reduced food intake in zebrafish larvae, knockout (KO) of the mc4r gene not only did not increase the rate of food intake but even reduced it. Since Melanocortin Receptor 3 (MC3R) has also been proposed to be involved in hypothalamic control of food intake, we also tested the effectofmc3r gene KO. Again, contrary to our hypothesis, the rate of food intake decreased. The next step was to generate a double mutant lucking both functional MC3R and MC4R. Again, the double KO exhibited reduced food intake. Thus, the only manipulation within the melanocortin system that affected food intake in consistent with the expected role of the system was seen in zebrafish larvae upon agrpKO. Interestingly, despite the apparent reduced food intake in the larval stage, these fish grow to be of the same size as wildtype fish at the adult stage. Altogether, it seems that there is a compensatory mechanism that overrides the effect of genetic manipulations of the melanocortin system in zebrafish. Under Aim 3, we introduced the Xna1, XnB1l, and XnB2A mutations from the Xiphophorus MC4R alleles into the zebrafish MC4R gene. We hypothesized that these MC4R mutations would act as dominant negative alleles to increase growth by suppressing endogenous MC4R activity. When we examined the activity of the three mutant alleles, we were unable to document any inhibition of a co-transfected wild type MC4R allele, hence we did not introduce these alleles into zebrafish. Since teleost fish possess two agrpgenes we also tested the effect of KO of the agrp2 gene and ablation of the AgRP2 cells. We found that the AgRP2 system does not affect food consumption but may rather be involved in modulating the stress response. To try to apply genetic editing in farmed fish species we turned to tilapia. Injection of exogenous AgRP in adult tilapia induced significant changes in the expression of pituitary hormones. Genetic editing in tilapia is far more complicated than in zebrafish. Nevertheless, we managed to generate one mutant fish carrying a mutation in mc4r. That individual died before reaching sexual maturity. Thus, our attempt to generate an mc4r-mutant tilapia line was almost successful and indicate out non-obvious capability to generate mutant tilapia.