Repository hosted by TU Delft Library

In our modern society, complex technological systems typically require people to perform several tasks in a limited period of time. In order to be able to optimize such technological systems, the present thesis aims at explicating some difficulties with regard to the fundamentals of multiple-task performance theory - especially in relation to aging- and at providing some basic theoretical improvements. First, the fundamental assumptions of the main recent theories concerning multiple-task performance. In brief, these theories are based on the notion that human performers possess one or a few 'pools' or supplies of central limited-capacity resources. A theoretical analysis shows that these current frameworks offer rather trivial explanations, lack neurobiological support, efficiently account for behavioral plasticity with training. The prevalent conception of attention as 'central supervisory control' does not provide an explanation for what has to be explained, i.e., the control process itself. In this connection, a cognitive neuroscience framework is invoked, which starts with current knowledge concern-ing the basic principles of brain function-ing in combination with the nature of capacity limitations in human performance. According to this framework, the problem of limited behavioral capacity is explained by the way biological systems satisfy two conflicting requirements: massive associative processing power and flexibility against coherent and goal-directed action control. This control conflict is not solved by a mysteri-ous supervisory attentional system. Behavior control basically emerges from elementary, self-regulating, characteris-tics of neuronal information processing. In addition, neurobiology and psychologicanervous system is well-suited for integrated information processing. Hence, atten-tional limitations generally occur when perceptual, cognitive, or motor opera-tions have to be segregated in task performance, whereas the potential efficien-cy of information processing and action increases with the degree to which dual-task elements are related or coherent, such that subtasks can be performed as a whole (skill integration). According to the cognitive neuroscience framework, presented in this thesis, aging-related neuronal de-cline may provide an appropriate, and a neurobio-logi-cally well-founded, basis for explanati-ons for aging-related functional problems. Decreased neuronal connectivity and plasticity may produce several phenomena, such as dealing with emerging task characteristics that affect the integration or segregation of skills (brain programs), to suppress the activation of irrelevant (dominant) routines or to modify these, or to process informa-tion quickly. The second, experimental part, of this thesis reports four experiments aimed at demonstrating that these mecha-nisms may explain dual-task deficits encountered in old age.

Background Activities of daily living (ADL) are often used as predictors of health and function in older persons. This systematic review is part of a series initiated by the European Network for Action on Ageing and Physical Activity (EUNAAPA). Aim To assess psychometric properties of ADL instruments for use in older populations. Methods Electronic databases (Medline, EMBASE, AMED, Psycinfo, CINAHL) were searched, using MeSH terms and relevant keywords. Studies, published in English, were included if they evaluated one or more psychometric properties of ADL instruments in community-dwelling older persons aged 60 years and older. Combination scales with IADL were excluded. This systematic review adhered to a pre-specified protocol regarding reliability, validity, and responsiveness. Results In total, 140 articles describing more than 50 different ADL instruments were included. Ten instruments which were applied in minimally three different articles of good quality (clear descriptions and adequate design according to the protocol), were evaluated for reliability, validity and responsiveness; each received a summary score. The four instruments with the highest scores were the Functional Autonomy Measurement System (SMAF), 5-items Katz list (although content and wording are often inconsistent across studies), Functional Independence and Difficulty Scale (FIDS) and the Barthel Index. Discussion Critical reflection is essential to avoid unnecessary modifications and use of instruments that have not been documented to be valid or reliable. Conclusion Based on this systematic review, we recommend the SMAF, 5-item Katz, FIDS and Barthel index as ADL measures for research and care practice in older populations.

In this article the importance of mineral suppletion for teeth and jawbone is explained in a step-wise manner. The steps discussed are the pre-eruptive phase of teeth and the growth, adult and ageing phase of the skeleton. Mineral suppletion should be seen as a measure to prevent dental caries (fluoride) and to ensure a maximal resistance against the spontaneous bone loss during ageing. Therefore, it seems not suitable for therapy of osteoporosis. If an enhanced bone loss occurs as a result of decreased production of sex hormones or immobility, mineral suppletion will probably have a minor effect. An optimal mineral intake will ensure a maximal peak bone mass built up during the growth phase of bone, a maintenance of this peak bone mass as much as possible during the phase of neutral bone balance and a minimal bone loss during the ageing period with negative bone balance.

Objective - To determine variations in biochemical characteristics of equine articular cartilage in relation to age and the degree of predisposition for osteochondral disease at a specific site. Sample Population - Articular cartilage specimens from 53 horses 4 to 30 years old. Procedure - Healthy specimens were obtained from 2 locations on the proximal articular surface of the first phalanx that had different disease prevalences (site 1 at the mediodorsal margin and site 2 at the center of the medial cavity). Water, total collagen, and hydroxylysine contents and enzymatic (hydroxylysylpyridinoline [HP]) and nonenzymatic (pentosidine) crosslinking were determined at both sites. Differences between sites were analyzed by ANOVA (factors, site, and age), and age correlation was tested by Pearson's product-moment correlation analysis. Significance was set at P < 0.01. Results - Correlation with age was not found for water, collagen, hydroxylysine contents, and enzymatic cross-linking. Nonenzymatic crosslinking was higher in older horses and was linearly related to age (r = 0.94). Water and collagen contents and HP and pentosidine crosslinks were significantly higher at site 1. Hydroxylysine content was significantly lower at site 1. Conclusions - Except for nonenzymatic glycation, the composition of articular cartilage collagen does not change significantly in adult horses. A significant topographic variation exists in biochemical characteristics of the articular cartilage collagen network in equine metacarpophalangeal joints. These differences may influence local biomechanical properties and, hence, susceptibility to osteochondral disease, as will greater pentosidine crosslinks in older horses that are likely to cause stiffer and more brittle cartilage.

The metabolism of glutamate, taken as an index of the metabolic state of the brain, was studied in brains of 3-, 12- and 30-month-old rats. Following the injection of a mixture of [3H]acetate and d-[2-14C]glucose, the brain levels of glutamate and aspartate were decreased in 30-month-old rats when compared with those of 3-month-old rats. No significant age-related differences were found in glutamine levels. Neither the protein levels nor the incorporation of the radioactivity in brain proteins differed among the three age groups, suggesting that there are no age-related differences in protein synthesis. The incorporation of d-[2-14C]glucose in aspartate and glutamine, expressed as the respective relative specific activities (RSA: specific activity of amino acid/specific activity of glutamate), did not change with age. Since glucose is the precursor of the large glutamate pool in brain, it can be concluded that no age-related changes occur in the metabolism of glutamate in the large compartment. The incorporation of [3H]acetate into aspartate, expressed as the RSA, did not differ among the age groups. The RSA of 3H-labelled glutamine, however, was significantly decreased 10 minutes after injection of the precursor mixture in brains of 30-month-old rats when compared with those of 3-month-old rats. This difference had disappeared 20 minutes after injection, suggesting a somewhat delayed metabolism of glutamate in the small compartment, for which acetate is a precursor. These results and all the other parameters measured indicate that no large age-related metabolic changes in rat brain occur. Chemicals/CAS: glutamic acid, 11070-68-1, 138-15-8, 56-86-0, 6899-05-4; Acetates; Aspartic Acid, 56-84-8; Glucose, 50-99-7; Glutamates; Glutamine, 56-85-9

Cartilaginous tissue in the heart of rat has been described in literature by some as an ageing phenomenon, while others have observed it in young animals. Hearts of rats of different ages were studied for the occurence and localization of cartilaginous tissue. A cartilaginous focus has been regularly found in rats as young as 1 week old. This focus was always localized in the wall of the aorta at the region of the base of the non-coronary semilunar valve. The occurence of cartilaginous tissue in the heart of rats must be regarded as physiological and is ascribed to mechanical forces at this site. Résumé Le tissu cartilagineux dans le coeur du rat a été décrit par d'aucuns comme phénomène de vieillissement, tandis que d'autres l'ont observé chez les jeunes animaux. Des coeurs de rats d'âges différents ont été étudiés dans le but d'y détecter et localiser le tissu cartilagineux. Un foyer cartilagineux était régulièrement présent chez des rats qui n'étainent âgés que d'une semaine. Ce foyer était toujours localisé dans la paraoi de l'aorte, dans la région de la base de la valvule sémilunaire non coronaire. La présence de tissu cartilagineux dans le coeur du rat doit être considérée comme physiologique et est attribuée à des forces mécaniques agissant à cet endroit. Zusammenfassung Knorpelgewebe im Rattenherz wurde in der Literatur als Altersphänomen gewertet. Andere Autoren fanden es auch bei jungen Tieren. Herzen von Ratten unterschiedlichen Alters wurden auf Vorkommen und Lokalisation von Knorpelgewebe untersucht. Schon bei Ratten im Alter von einer Woche fand sich regelmäβig ein Knorpelherd. Der Herd lag immer in der Aortenwand an der Basis der nichtkoronaren Semilunarklappe. Das Auftreten von Knorpelgewebe im Rattenherz muβ als physiologisch betrachtet werden. Es wird auf die an dieser Stelle einwirkenden mechanischen Kräfte zurückgeführt. Реферат Пpиcyтcтвиe чpяшeвoй ткaни в cepдцeкpыc тpaктyeтcя нeкoтopыми aвчopaми в литepaтype кaк явлeниe cтapeиня, тoтдa кaк дpyгиe нaблюдaли этo яблeниe y мoлoдыч зивoтныx. Пpoвoдилocь иccлeдoвaниe cepдeц oт кpыc paэличнoгo вoэpacтa нa пpиcy;тcтвиe и чoкaлизцию xpяшeвoй ткaчи. Фoкyc xpяшeвoй тк aни нaблюдaлcя пocтoяннo y кpыc дaзe тaкoгo paннeгo бoзpacтa кaк oднa нeдeля. Этo tcy; фoкyc вceгдa нaxoдилcя в cтeнкe aopты в oблacти ocнoвaния нe-кopoнapнoгo пoлyлyн y;oгo клaпaнa. Haxoздeниe xpышвoй тaни в cepдцe кpыc дoлзнo paccмaтpивтьcя ч aк физиoлoгичecкoe явлeниe, кoтopoe пpипиcывaeтcя мexaниcким cилaм в этoм мecт;e.

Abstract for the International Society for Aging and Physical activity's 6th World Congress on Aging and Physical Activity: From Research to Action for an Aging Society London, Ontario, Canada, August 3-7 2004

Abstract for the 7th World Congress on Aging and Physical Activity: Active aging: Focus on Longevity and Physical Activity Japan 26-29 July 2008.

Abstract for the 7th World Congress on Aging and Physical Activity: Active aging: Focus on Longevity and Physical Activity Japan 26-29 July 2008.

Abstract for the 7th World Congress on Aging and Physical Activity: Active aging: Focus on Longevity and Physical Activity Japan 26-29 July 2008.

Piezoelectric composites made from soft and hard lead zirconium titanate (PZT) particles as filler and an epoxy as the matrix were prepared by dielectrophoresis and studied for their piezoelectric properties. It was found that the dielectric constant of the piezoelectric filler plays a significant role in determining the final piezoelectric properties of the composites. Composites with lower dielectric constant for the PZT filler material showed better piezoelectric properties compared to the composites with high dielectric constant filler. This can be ascribed to a more efficient poling of the piezoelectric filler particles. The aging behaviour of these composites was compared to that reported for monolithic ceramics.

The effects of excessive non-toxic dietary Vitamin D3 supplementation on Ca homeostasis with specific effects on endochondral ossification and skeletal remodeling were investigated in a group of growing Great Dane dogs supplemented with cholecalciferol (Vitamin D3; HVitD) versus a control group (CVitD) (1350 μg versus 11.4 μg Vitamin D3 per kilogram diet) from 6 to 21 weeks of age. There were no differences between groups in plasma concentrations of total Ca, inorganic phosphate, growth hormone, and insulin-like growth factor I and no signs of Vitamin D3 intoxication in HVitD. For the duration of the study in HVitD compared to CVitD, plasma levels of parathyroid hormone (PTH) decreased, calcitonin (CT) increased, 25-hydroxycholecalciferol [25(OH)D3] increased 30- to 75-fold, 24,25-dihydroxycholecalciferol [24,25(OH)2D3] increased 12- to 16-fold, and 1,25-dihydroxycholecalciferol [1,25(OH)2D3] decreased by approximately 40%. The latter was attributed to the two-fold increased metabolic clearance rate in the HVitD versus CVitD accompanied by the absence of the anabolic effect of PTH on the production of 1,25(OH)2D3. Fractional Ca absorption (α) did not differ between groups at 8 and 14 weeks of age, whereas at 20 weeks of age α increased by only 16.4% in HViAtD compared to CVitD. Excessive non-toxic Vitamin D3 supplementation resulted in decreased bone remodeling and focal enlargement of the growth plate with morphology resembling those induced by administration of CT. Hypercalcitoninemia and the imbalanced relationship between 1,25(OH)2D3 and 24,25(OH)2D3 are potent candidates for the disturbed endochondral ossification. © 2003 Elsevier Science Inc. All rights reserved.

This article deals with the development of design rules for structural adhesive bonded joints. In daily practice engineers are confronted with the problem to verify the reliability of their designs. This can be done with use of an experimental programme, but for the marine, transport, building and civil engineering sectors this will not be an option, because it is too expensive and time consuming. The use of design rules might be an alternative, but current guidelines for structural adhesive bonded joints do not guarantee the reliability. To develop design rules that meet the required level of reliability, new approaches have to be used. Such a systematic approach is presented in this article. It is based on the current structural adhesive bonding technology and on structural reliability methods. Partial factors are used to take the required reliability level into account. Additional conversion factors are introduced to cover the effects of ageing. Methods are discussed how to calibrate these factors. To illustrate the developed approach, examples of calibrating design rules for metal overlap joints with epoxy and polyurethane adhesives are presented.

The 'disector' method was used to estimate number and size of simple non-perforated and complex 'perforated' synapses and their 'perforations' in the hippocampal CA3 area of 3, 12, 24 and 30 months old rats. A decrease with age from 3 to 24 months of age in the number of non-perforated synapses per neuron was found. Both non-perforated and perforated synapses increase in size with age. The perforations in the perforated synapses increase in size and number from 3 to 24 months. In all 4 age-groups, perforated synapses are larger and more complex (perforations) than non-perforated synapses. The increase in size (and complexity) of the synapses with age was considered as increased efficacy of the synapses. It was suggested that this enhanced efficacy of synaptic transmission may reflect a compensatory reaction of synapses proper in response to the observed loss of synapses. The latter, in itself, may lead to impairment of the synaptic circuitry.

Preliminary resuits on accelerated aging of lab-scale produced AP/HTPB propellant and propellants from dissectioned rocket motors are discussed, including aging logic, storage conditions, test techniques and resuits on mechanical, ballistic and safety testing. The mam aging effect observed was hardening of the propellant with time. The aging rate was found to be strongly dependent on the used storage conditions. Plasticizer depletion is identified as the main aging mechanism for the propellafits when stored under atmospheric condftions. The aging behaviour could well be described by the commonly used Layton’s model. Plasticizer from the propellant was found in the seals of test equipment, indicating a potential lifetime problem for rocket motors due to a possible interaction with rubbery motor components.

1. Two growth trials were performed to measure the effects of dietary methionine and cystine (SAA) on growth rate, food conversion efficiency and breast meat deposition in male broilers. 2. In experiment 1, broilers were grown on 6 experimental diets covering a range from 6.9 to 9.6 g SAA/kg. The diets were fed from 15 to 33 d of age. Similarly, in experiment 2, 6 diets containing 6.0 to 8.5 g SAA/kg were fed to finishing broilers 33 to 43 d of age. In each experiment 60 birds per treatment were processed, and carcase yield and breast meat percentage were determined. 3. Significant responses in weight gain, efficiency of food conversion and breast meat percentage were detected, which could be described well by exponential regression curves. Dietary SAA requirements to obtain maximum efficiency of food utilisation and maximum breast meat deposition were estimated to be about 9.0 g/kg from 15 to 33 d of age, and about 8.0 g/kg from 33 to 43 d of age. 4. Economic aspects were considered to calculate optimum SAA specifications from the results. In both trials, the dietary optimum of SAA was found to be higher for birds to be further processed than for birds to be marketed as whole carcases.