Low-rank optimization with trace norm penalty

The paper addresses the problem of low-rank trace norm minimization. We propose an algorithm that alternates between fixed-rank optimization and rank-one updates. The fixed-rank optimization is characterized by an efficient factorization that makes the trace norm differentiable in the search space and the computation of duality gap numerically tractable. The search space is nonlinear but is equipped with a Riemannian structure that leads to efficient computations. We present a second-order trust-region algorithm with a guaranteed quadratic rate of convergence. Overall, the proposed optimization scheme converges superlinearly to the global solution while maintaining complexity that is linear in the number of rows and columns of the matrix. To compute a set of solutions efficiently for a grid of regularization parameters we propose a predictor-corrector approach that outperforms the naive warm-restart approach on the fixed-rank quotient manifold. The performance of the proposed algorithm is illustrated on problems of low-rank matrix completion and multivariate linear regression. © 2013 Society for Industrial and Applied Mathematics.

Effectiveness of granular columns in containing settlement

Laboratory-based research studies and full-scale evaluations of the behaviour of ground improved with granular columns are ample regarding bearing capacity, but limited in respect to the settlement response. This paper presents a laboratory model study that considers the settlement performance of isolated pad footings bearing on reinforced sand deposits under the influence of a fluctuating groundwater table. This is a particularly onerous condition for loose sand deposits in coastal areas which may undergo significant collapse settlement over time. Loose and dense experimental sand beds were constructed and the performance of rigid footings under a maintained load and bearing on sand incorporating different column configurations were monitored under cycling of the water table over a period of 28 days, with one filling/empting cycle every 18 h. It was found that settlement, while greatly reduced compared with unreinforced footings, was ongoing and typically occurred at a much greater rate for loose sand than dense sand. Also, settlement rates were slightly higher for fully penetrating than partially penetrating columns and also for footings reinforced by a column group rather than a single column. This was attributed to the migration of sand grains into the larger column voids.

A study on the performance of flexible pavements on mature soil subgrades

The country has witnessed tremendous increase in the vehicle population and increased axle loading pattern during the last decade, leaving its road network overstressed and leading to premature failure. The type of deterioration present in the pavement should be considered for determining whether it has a functional or structural deficiency, so that appropriate overlay type and design can be developed. Structural failure arises from the conditions that adversely affect the load carrying capability of the pavement structure. Inadequate thickness, cracking, distortion and disintegration cause structural deficiency. Functional deficiency arises when the pavement does not provide a smooth riding surface and comfort to the user. This can be due to poor surface friction and texture, hydro planning and splash from wheel path, rutting and excess surface distortion such as potholes, corrugation, faulting, blow up, settlement, heaves etc. Functional condition determines the level of service provided by the facility to its users at a particular time and also the Vehicle Operating Costs (VOC), thus influencing the national economy. Prediction of the pavement deterioration is helpful to assess the remaining effective service life (RSL) of the pavement structure on the basis of reduction in performance levels, and apply various alternative designs and rehabilitation strategies with a long range funding requirement for pavement preservation. In addition, they can predict the impact of treatment on the condition of the sections. The infrastructure prediction models can thus be classified into four groups, namely primary response models, structural performance models, functional performance models and damage models. The factors affecting the deterioration of the roads are very complex in nature and vary from place to place. Hence there is need to have a thorough study of the deterioration mechanism under varied climatic zones and soil conditions before arriving at a definite strategy of road improvement. Realizing the need for a detailed study involving all types of roads in the state with varying traffic and soil conditions, the present study has been attempted. This study attempts to identify the parameters that affect the performance of roads and to develop performance models suitable to Kerala conditions. A critical review of the various factors that contribute to the pavement performance has been presented based on the data collected from selected road stretches and also from five corporations of Kerala. These roads represent the urban conditions as well as National Highways, State Highways and Major District Roads in the sub urban and rural conditions. This research work is a pursuit towards a study of the road condition of Kerala with respect to varying soil, traffic and climatic conditions, periodic performance evaluation of selected roads of representative types and development of distress prediction models for roads of Kerala. In order to achieve this aim, the study is focused into 2 parts. The first part deals with the study of the pavement condition and subgrade soil properties of urban roads distributed in 5 Corporations of Kerala; namely Thiruvananthapuram, Kollam, Kochi, Thrissur and Kozhikode. From selected 44 roads, 68 homogeneous sections were studied. The data collected on the functional and structural condition of the surface include pavement distress in terms of cracks, potholes, rutting, raveling and pothole patching. The structural strength of the pavement was measured as rebound deflection using Benkelman Beam deflection studies. In order to collect the details of the pavement layers and find out the subgrade soil properties, trial pits were dug and the in-situ field density was found using the Sand Replacement Method. Laboratory investigations were carried out to find out the subgrade soil properties, soil classification, Atterberg limits, Optimum Moisture Content, Field Moisture Content and 4 days soaked CBR. The relative compaction in the field was also determined. The traffic details were also collected by conducting traffic volume count survey and axle load survey. From the data thus collected, the strength of the pavement was calculated which is a function of the layer coefficient and thickness and is represented as Structural Number (SN). This was further related to the CBR value of the soil and the Modified Structural Number (MSN) was found out. The condition of the pavement was represented in terms of the Pavement Condition Index (PCI) which is a function of the distress of the surface at the time of the investigation and calculated in the present study using deduct value method developed by U S Army Corps of Engineers. The influence of subgrade soil type and pavement condition on the relationship between MSN and rebound deflection was studied using appropriate plots for predominant types of soil and for classified value of Pavement Condition Index. The relationship will be helpful for practicing engineers to design the overlay thickness required for the pavement, without conducting the BBD test. Regression analysis using SPSS was done with various trials to find out the best fit relationship between the rebound deflection and CBR, and other soil properties for Gravel, Sand, Silt & Clay fractions. The second part of the study deals with periodic performance evaluation of selected road stretches representing National Highway (NH), State Highway (SH) and Major District Road (MDR), located in different geographical conditions and with varying traffic. 8 road sections divided into 15 homogeneous sections were selected for the study and 6 sets of continuous periodic data were collected. The periodic data collected include the functional and structural condition in terms of distress (pothole, pothole patch, cracks, rutting and raveling), skid resistance using a portable skid resistance pendulum, surface unevenness using Bump Integrator, texture depth using sand patch method and rebound deflection using Benkelman Beam. Baseline data of the study stretches were collected as one time data. Pavement history was obtained as secondary data. Pavement drainage characteristics were collected in terms of camber or cross slope using camber board (slope meter) for the carriage way and shoulders, availability of longitudinal side drain, presence of valley, terrain condition, soil moisture content, water table data, High Flood Level, rainfall data, land use and cross slope of the adjoining land. These data were used for finding out the drainage condition of the study stretches. Traffic studies were conducted, including classified volume count and axle load studies. From the field data thus collected, the progression of each parameter was plotted for all the study roads; and validated for their accuracy. Structural Number (SN) and Modified Structural Number (MSN) were calculated for the study stretches. Progression of the deflection, distress, unevenness, skid resistance and macro texture of the study roads were evaluated. Since the deterioration of the pavement is a complex phenomena contributed by all the above factors, pavement deterioration models were developed as non linear regression models, using SPSS with the periodic data collected for all the above road stretches. General models were developed for cracking progression, raveling progression, pothole progression and roughness progression using SPSS. A model for construction quality was also developed. Calibration of HDM–4 pavement deterioration models for local conditions was done using the data for Cracking, Raveling, Pothole and Roughness. Validation was done using the data collected in 2013. The application of HDM-4 to compare different maintenance and rehabilitation options were studied considering the deterioration parameters like cracking, pothole and raveling. The alternatives considered for analysis were base alternative with crack sealing and patching, overlay with 40 mm BC using ordinary bitumen, overlay with 40 mm BC using Natural Rubber Modified Bitumen and an overlay of Ultra Thin White Topping. Economic analysis of these options was done considering the Life Cycle Cost (LCC). The average speed that can be obtained by applying these options were also compared. The results were in favour of Ultra Thin White Topping over flexible pavements. Hence, Design Charts were also plotted for estimation of maximum wheel load stresses for different slab thickness under different soil conditions. The design charts showed the maximum stress for a particular slab thickness and different soil conditions incorporating different k values. These charts can be handy for a design engineer. Fuzzy rule based models developed for site specific conditions were compared with regression models developed using SPSS. The Riding Comfort Index (RCI) was calculated and correlated with unevenness to develop a relationship. Relationships were developed between Skid Number and Macro Texture of the pavement. The effort made through this research work will be helpful to highway engineers in understanding the behaviour of flexible pavements in Kerala conditions and for arriving at suitable maintenance and rehabilitation strategies. Key Words: Flexible Pavements – Performance Evaluation – Urban Roads – NH – SH and other roads – Performance Models – Deflection – Riding Comfort Index – Skid Resistance – Texture Depth – Unevenness – Ultra Thin White Topping

Untersuchungen zu kumulativen psychischen und physiologischen Effekten des fliegenden Personals auf der Kurzstrecke

Die fliegerische Tätigkeit auf der Kurzstrecke in der zivilen Luftfahrt unterliegt arbeitsspezifischen Belastungsfaktoren, die sich in wesentlichen Punkten von denen auf der Langstrecke unterscheiden. Eine hohe Arbeitsbelastung auf der Kurzstrecke ist mit vielen Starts und Landungen am Tag verbunden. Neben der Anzahl der Flugabschnitte können auch lange Flugdienstzeiten und/oder unregelmäßige Arbeitszeiten sowie der Zeitdruck während der Einsätze auf der Kurzstrecke zur Belastung für Cockpitbesatzungsmitglieder werden und zu Ermüdungserscheinungen führen. Bisher wurden flugmedizinische und -psychologische Daten hauptsächlich auf der Langstrecke in Bezug auf die Auswirkungen der Jet-Leg Symptomatik und kaum auf der Kurzstrecke erhoben. Deshalb wurde im Rahmen des DLR- Projekts „Untersuchungen zu kumulativen psychischen und physiologischen Effekten des fliegenden Personals auf der Kurzstrecke“ eine Langzeituntersuchung zur Belastung/Beanspruchung, Ermüdung sowie Erholung des Cockpitpersonals auf der Kurzstrecke über jeweils 56 Tage durchgeführt. In Zusammenarbeit mit der Deutschen Lufthansa AG dauerte die Untersuchung zu den Auswirkungen arbeitsspezifischer Belastungsfaktoren auf die Cockpitbesatzungsmitglieder der Boeing 737-Flotte von 2003 bis 2006. ZIEL: Unter Berücksichtigung theoretisch fundierter arbeitspsychologischer Konzepte war das Ziel der Studie, kumulative und akute Effekte auf das Schlaf-Wach-Verhalten, auf die Belastung/Beanspruchung sowie auf die Müdigkeit zu identifizieren, die durch aufeinander folgende Einsätze auf der Kurzstrecke innerhalb eines Zeitraums von acht Wochen auftreten können. Hierfür wurden Daten von 29 Piloten (N=13 Kapitäne; N=16 Erste Offiziere) aufgezeichnet. Das Durchschnittsalter lag bei 33,8 ± 7,9 Jahren (Kapitäne: 42,0 ± 3,8 Jahre; Erste Offiziere: 27,4 ± 2,2 Jahre). METHODEN: Über ein Handheld PC konnten effizient Fragebögen bearbeitet und das Sleep Log sowie das Flight Log geführt werden. Die subjektive Ermüdung und Arbeitsbeanspruchung wurden durch standardisierte Fragebögen (z.B. Ermüdungsskala von Samn & Perelli (1982), NASA-TLX) operationalisiert. Im Sleep Log und im Flight Log wurden das Schlaf-Wach-Verhalten sowie flugspezifische Daten dokumentiert (z.B. Dienstbeginn, Dienstende, Flugabschnitte, Zielorte, etc.). Der Schlaf-Wach-Zyklus wurde mittels der Aktimetrie während des gesamten Messverlaufs aufgezeichnet. Die objektive Leistungsfähigkeit wurde täglich morgens und abends mit Hilfe einer computergestützten Psychomotor Vigilance Task (PVT) nach Dinges & Powell (1985) erfasst. Die Leistung in der PVT diente als Indikator für die Ermüdung eines Piloten. Zusätzliche Befragungen mit Paper-Pencil-Fragebögen sollten Aufschluss über relevante, psychosoziale Randbedingungen geben, die bei den täglichen Erhebungen nicht berücksichtigt wurden (z.B. Arbeitszufriedenheit; Essgewohnheiten; Kollegenbeziehungen). ERGEBNISSE: Unter Beachtung kumulativer Effekte wurde über die Studiendauer keine Veränderung in der Schlafqualität und im Schlafbedürfnis festgestellt. Die Müdigkeit nahm dagegen während der achtwöchigen Untersuchung zu. Die Reaktionszeit in der PVT zeigte an Flugdiensttagen eine Verschlechterung über die Zeit. Insgesamt wurden keine kritischen längerfristigen Effekte analysiert. Akute signifikante Effekte wurden bei der Ermüdung, der Gesamtbelastung und der Leistungsfähigkeit an Flugdiensttagen gefunden. Die Ermüdung als auch die Gesamtbelastung stiegen bei zunehmender Flugdienstdauer und Leganzahl und die Leistung nahm in der PVT ab. Der „time on task“ Effekt zeigte sich besonders in der Ermüdung durch die fliegerische Tätigkeit ab einer Flugdienstzeit von > 10 Stunden und > 4 Legs pro Tag. SCHLUSSFOLGERUNG: Mit diesen Ergebnissen konnte eine wissenschaftliche Datenbasis geschaffen werden aus der Empfehlungen resultieren, wie die Einsatzplanung für das Cockpitpersonal auf der Kurzstrecke unter flugmedizinischen und flugpsychologischen Gesichtspunkten optimiert werden kann. Zudem kann ein sachgerechter Beitrag im Rahmen der Diskussion zur Flugdienst- und Ruhezeitenregelung auf europäischer Ebene geleistet werden.

Fuzzy logic controller optimized by particle swarm optimization for DC motor speed control

In this paper, we presented an optimized fuzzy logic controller using particle swarm optimization for DC motor speed control. The controller model is simulated using MATLAB software and also experimentally tested on a laboratory DC motor. A comparison of the performance of different controllers such as PID controller, fuzzy logic controller and optimized fuzzy logic controller is presented as well. With reference to the results of digital simulations and experiment, the designed FLC-PSO speed controller obtains much better dynamic behavior compared to PID and the normal FLC designed. Moreover, it can acquire superior performance of the DC motor, and also perfect speed tracking with no overshoot. The optimized membership functions (MFs) are obviously proved to be able to provide a better performance and higher robustness in comparison with a regular fuzzy model, when the MFs were heuristically defined. Besides, experimental results verify the ability of proposed FLC under sudden change of the load torque which leads to speed variances.

Ensaios acelerados de pavimentos para avaliação de desempenho de recapeamentos asfálticos

Esta dissertação apresenta uma avaliação da eficiência de um recapeamento constituído por mistura de asfalto-borracha (processo via-úmida), no retardamento de reflexão de trincas, através da técnica de ensaios acelerados. Para a realização do estudo foi construído um pavimento experimental com camada final de terraplenagem de argila arenosa de comportamento laterítico (50 cm), base de brita graduada (30 cm), camada de concreto asfáltico trincado (4 cm) e camada de recapeamento em asfalto-borracha (5 cm). O simulador de tráfego DAER/UFRGS aplicou aproximadamente 513.000 ciclos de carga de eixo de 100 kN. Ao longo do experimento o desempenho do pavimento foi acompanhado, com ênfase no surgimento de trincas. A evolução da condição estrutural do pavimento foi monitorada através das medidas de deflexões e dados de instrumentação (tensões e deformações). O registro da evolução da condição funcional do pavimento foi feito através do levantamento de afundamento de trilha de roda, e macro e micro textura. Com a finalidade de comparar o desempenho do recapeamento em asfalto-borracha com os de outros recapeamentos convencionais previamente ensaiados, desenvolveu-se um procedimento para correção de temperaturas. Constatou-se que o emprego de asfalto-borracha retardou em cinco vezes o surgimento de trincas. Assim, o nível de severidade do trincamento igual a 100 cm/m2 ocorreu no recapeamento em asfalto-borracha após 340.000 solicitações (100 kN), enquanto no recapeamento em asfalto convencional tal nível de severidade foi registrado com somente 66.000 solicitações da mesma carga de eixo. Globalmente, o recapeamento em asfalto-borracha conferiu ao pavimento melhores condições funcionais e estruturais, se comparado com um recapeamento convencional da mesma espessura, executado sobre um pavimento com níveis de degradação similares.

Desenvolvimento de protótipo de coletor automático destinado à coleta de amostras de água em corpos aquáticos para análise em laboratório

The aim of this approach is to describe the design and construction of a low-cost automated water sampler prototype. In recent years, there is an increasing need on the use of automated equipments for hydro climatic variables to be use in urban and rural environments. Such devices are always used to provide measured information which is of crucial importance on the development of water resources strategies at watershed scale. Actually, many research and water public institutions have been using these kinds of equipments. In most of the cases, automated equipments are expensive and need to be imported, generating a situation of technologic dependency. The prototype is based on an electronic system which controls a peristaltic pump functioning, five solenoid valves and an ultrasonic sensor connected to a datalloger. An interface with the user allows communication with a PC, when the equipment functioning parameters can be provided. The equipment has a hydraulic module composed by a 12V peristaltic pump connected to a distribution circuit composed by five solenoid valves, one of them being used to clean the circuit before each sampling procedure. Samples are collected by four 1.95 polyethylene bottles. The sampler body was made of acrylic material, with a cylindrical shape, and dimensions 0.72 m and 0.38 m height and diameter, respectively. The weight of the equipment without samples is approximately 15 kg, which infers to its portability. The prototype development total cost budget was approximately US$ 1,560.00. Laboratory tests aimed to evaluate the equipment performance and functioning demonstrated satisfactory results

Influência da fadiga no comportamento neuromuscular do quadríceps femoral, após reconstrução do ligamento cruzado anterior

Muscle fatigue is a phenomenon that promotes physiological and biomechanical disorders and their changes in healthy subjects have been widely studied and have significant importance for care in preventing injuries, but we do not have many information about its effects in patients after ACL reconstruction. Thus, this study is to analyze the effects of fatigue on neuromuscular behavior of quadriceps after ACL reconstruction. To reach this objective, participants were forty men, twenty healthy (26,90 ± 6,29 years) and twenty after ACL reconstruction (29,75 ± 7,01 years) with a graft of semitendinosus and gracilis tendons, between four to six months after surgery. At first, there was an assessment of joint position sense (JPS) at the isokinetic dynamometer at a speed of 5°/s and target angle of 45° to analyze the absolute error of JPS. Next, we applied the a muscle fatigue protocol, running 100 repetitions of isokinetic knee flexion-extension at 90°/s. Concurrently with this protocol, there was the assessment of muscle performance, as the peak torque (PT) and fatigue index, and electromyographic activity (RMS and median frequency). Finally, we repeated the assessment of JPS. The statistical analysis showed that patients after ACL reconstruction have, even under normal conditions, the amended JPS compared with healthy subjects and that after fatigue, both have disturbances in the JPS, but this alteration is significantly exacerbated in patients after ACL reconstruction. About muscle performance, we could notice that these patients have a lower PT, although there are no differences between the dynamometric and EMG fatigue index. These findings show the necessity about the cares of pacients with ACL reconstruction in respect of the risks of articulate instability and overload in ligamentar graft

Análises bromatológicas e fitoquímicas de frutos de Licania tomentosa (Benth) FRITSCH

This study conducted chemical analyzes of the fruits of Licania tomentosa Benth belonging to the Chrysobalanaceae family, order and superorder Rosiflorae Rosales. Samples were collected in February 2011 in the city of Natal - RN. The fruits were separated into peel, pulp and seed, and the samples were analyzed on moisture and ash by thermogravimetric methods, reducing and total sugars, lipids by Soxhlet extraction, minerals by ICP / OES and other analyzes by physical measurements of the fruit. The fruits for the analysis of determination of flavonoids and phenolic compounds were dried at 40 ° C and ground. For the analyzes to determine the content of phenolics and flavonols was used spectroscopy in the visible region, and also performed the characterization of ethanol extracts by high performance liquid chromatography and test for antioxidant activity hydroethanolic extracts. The results obtained are about 83.9% of the fruits have a length between 4.0 to 6.0 cm with respect to the diameter of the fruit about 97.4% of the fruits have a diameter between 2.0 - 4, 0 cm, mean weight of 36.14 g (7.86), the bark showed 60.5 (1.5)% relative humidity, the flesh 72.3 (0.9) and 44.4 seeds (0.4 )%, the bark showed 0.22 (0.00)% ash, the pulp 1.41 (0.01)% and the seed 1.18 (0.01)%, the bark showed 3.73 (0, 09) mg lipids / 100 g sample of the pulp 0.40 (0.04) and the seed 0.05 (0.00). With respect to reducing sugars and total gave the results, 16.23 (0.23) g/100g and 20.70 (0.24) g/100g. The fruit is presented with a good source of nutrients especially carbohydrates and lipids. The analysis for determining the antioxidant activity tests were performed reducing power and antioxidant capacity, the antioxidant capacity of hydroethanolic extracts of peel and pulp showed similar results, with higher concentrations however hydroethanolic bark extract. Regarding the content of phenolics and flavonoids hidroetanílico bark extract showed higher concentration values. The characterization of the extracts by high performance liquid chromatography identified the following compounds by retention time indicated by the race of the standards: galic acid, kaempferol and kaempferol derivatives. Considering the results of the fruit Licania tomentosa Benth may be an alternative food by analysis of their nutritional content and has substances with antioxidant action

Properties advanced of the silicon nitride based ceramics and recent performance on automotive parts manufacture by machining process: Advanced Ceramics, demand Forecast

Automotive parts manufacture by machining process using silicon nitride-based ceramic tool development in Brazil already is a reality. Si 3N4-based ceramic cutting tools offer a high productivity due to their excellent hot hardness, which allows high cutting speeds. Under such conditions the cutting tool must be resistant to a combination of mechanical, thermal and chemical attacks. Silicon nitride based ceramic materials constitute a mature technology with a very broad base of current and potential applications. The best opportunities for Si3N 4-based ceramics include ballistic armor, composite automotive brakes, diesel particulate filters, joint replacement products and others. The goal of this work was to show latter advance in silicon nitride manufacture and its recent evolution on machining process of gray cast iron, compacted graphite iron and Ti-6Al-4V. Materials characterization and machining tests were analyzed by X-Ray Diffraction, Scanning Electron Microscopy, Vickers hardness and toughness fracture and technical norm. In recent works the authors has been proved to advance in microstructural, mechanical and physic properties control. These facts prove that silicon nitride-based ceramic has enough resistance to withstand the impacts inherent to the machining of gray cast iron (CI), compacted graphite iron (CGI) and Ti-6Al-4V (6-4). Copyright © 2008 SAE International.

Monitoring chronic physical stress using biomarkers, performance protocols and mathematical functions to identify physiological adaptations in rats

This study was undertaken to characterize the effects of monotonous training at lactate minimum (LM) intensity on aerobic and anaerobic performances; glycogen concentrationsin the soleus muscle, the gastrocnemius muscle and the liver; and creatine kinase (CK), free fatty acids and glucose concentrations in rats. The rats were separated into trained (n =10), baseline (n = 10) and sedentary (n=10) groups. The trained group was submitted to the following: 60 min/day, 6 day/week and intensity equivalent to LM during the 12-week training period. The training volume was reduced after four weeks according to a sigmoid function. The total CK (U/L) increased in the trained group after 12 weeks (742.0±158.5) in comparison with the baseline (319.6±40.2) and the sedentary (261.6+42.2) groups. Free fatty acids and glycogen stores (liver, soleus muscle and gastrocnemius muscle) increased after 12 weeks of monotonous training but aerobic and anaerobic performances were unchanged in relation to the sedentary group. The monotonous training at LM increased the level of energy substrates, unchanged aerobic performance, reduced anaerobic capacity and increased the serum CK concentration; however, the rats did not achieve the predicted training volume.

In situ real-time investigation of Organic Ultra-Thin-Film transistors: growth, electrical properties and biosensing applications

Organic electronics has grown enormously during the last decades driven by the encouraging results and the potentiality of these materials for allowing innovative applications, such as flexible-large-area displays, low-cost printable circuits, plastic solar cells and lab-on-a-chip devices. Moreover, their possible field of applications reaches from medicine, biotechnology, process control and environmental monitoring to defense and security requirements. However, a large number of questions regarding the mechanism of device operation remain unanswered. Along the most significant is the charge carrier transport in organic semiconductors, which is not yet well understood. Other example is the correlation between the morphology and the electrical response. Even if it is recognized that growth mode plays a crucial role into the performance of devices, it has not been exhaustively investigated. The main goal of this thesis was the finding of a correlation between growth modes, electrical properties and morphology in organic thin-film transistors (OTFTs). In order to study the thickness dependence of electrical performance in organic ultra-thin-film transistors, we have designed and developed a home-built experimental setup for performing real-time electrical monitoring and post-growth in situ electrical characterization techniques. We have grown pentacene TFTs under high vacuum conditions, varying systematically the deposition rate at a fixed room temperature. The drain source current IDS and the gate source current IGS were monitored in real-time; while a complete post-growth in situ electrical characterization was carried out. At the end, an ex situ morphological investigation was performed by using the atomic force microscope (AFM). In this work, we present the correlation for pentacene TFTs between growth conditions, Debye length and morphology (through the correlation length parameter). We have demonstrated that there is a layered charge carriers distribution, which is strongly dependent of the growth mode (i.e. rate deposition for a fixed temperature), leading to a variation of the conduction channel from 2 to 7 monolayers (MLs). We conciliate earlier reported results that were apparently contradictory. Our results made evident the necessity of reconsidering the concept of Debye length in a layered low-dimensional device. Additionally, we introduce by the first time a breakthrough technique. This technique makes evident the percolation of the first MLs on pentacene TFTs by monitoring the IGS in real-time, correlating morphological phenomena with the device electrical response. The present thesis is organized in the following five chapters. Chapter 1 makes an introduction to the organic electronics, illustrating the operation principle of TFTs. Chapter 2 presents the organic growth from theoretical and experimental points of view. The second part of this chapter presents the electrical characterization of OTFTs and the typical performance of pentacene devices is shown. In addition, we introduce a correcting technique for the reconstruction of measurements hampered by leakage current. In chapter 3, we describe in details the design and operation of our innovative home-built experimental setup for performing real-time and in situ electrical measurements. Some preliminary results and the breakthrough technique for correlating morphological and electrical changes are presented. Chapter 4 meets the most important results obtained in real-time and in situ conditions, which correlate growth conditions, electrical properties and morphology of pentacene TFTs. In chapter 5 we describe applicative experiments where the electrical performance of pentacene TFTs has been investigated in ambient conditions, in contact to water or aqueous solutions and, finally, in the detection of DNA concentration as label-free sensor, within the biosensing framework.

Synthetic polymers for ophthalmic applications

The contact lens represents a well-established important class of biomaterials. This thesis brings together the literature, mostly Japanese and American patents, concerned with an important group of polymers, `rigid gas permeable contact lens materials'. A comparison is made of similarities in the underlying chemical themes, centring on the use of variants of highly branched siloxy compounds with polymerizable methacrylate groups. There is a need for standard techniques to assess laboratory behaviour in relation to in vitro performance. A major part of the present work is dedicated to the establishment of such standardised techniques. It is apparent that property design requirements in this field (i.e. oxygen permeability, surface and mechanical properties) are to some extent conflicting. In principle, the structural approaches used to obtain high oxygen permeability lead to surface properties that are less than ideal in terms of compatibility with tears. PMMA is known to have uniquely good (but not perfect) surface properties in this respect; it has been used as a starting point in attempting to design new materials that possess a more acceptable compromise of transport and surface properties for ocular use. Initial examination of the oxygen permeabilities of relatively simple alkyl methacrylates, show that butyl methacrylate which has a permeability some fifty times greater than PMMA, represents an interesting and hitherto unexplored group of materials for ophthalmic applications. Consideration was similarly given to surface modification techniques that would produce materials having the ability to sustain coherent tear film in the eye without markedly impairing oxygen transport properties. Particular attention is paid to the use of oxygen plasma techniques in this respect. In conclusion, similar design considerations were applied to an extended wear hydrogel lens material in an attempt to overcome mechanical stability deficiencies which manifest themselves lq`in vivo' but not `in vitro'. A relatively simple structure modification, involving steric shielding of the amide substituent group, proved to be an effective solution to the problem.