Visual coding for action violates fundamental psychophysical principles

According to Weber's law, a basic perceptual principle of psychological science, sensitivity to changes along a given physical dimension decreases when stimulus intensity increases [1]. In other words, the ‘just noticeable difference’ (JND) for weaker stimuli is smaller — hence resolution power is greater — than that for stronger stimuli on the same sensory continuum. Although Weber's law characterizes human perception for virtually all sensory dimensions, including visual length [2] and [3], there have been no attempts to test its validity for visually guided action. For this purpose, we asked participants to either grasp or make perceptual size estimations for real objects varying in length. A striking dissociation was found between grasping and perceptual estimations: in the perceptual conditions, JND increased with physical size in accord with Weber's law; but in the grasping condition, JND was unaffected by the same variation in size of the referent objects. Therefore, Weber's law was violated for visually guided action, but not for perceptual estimations. These findings document a fundamental difference in the way that object size is computed for action and for perception and suggest that the visual coding for action is based on absolute metrics even at a very basic level of processing.     

An experimental approach to the fundamental principles of hemodynamics

An experimental model has been developed to give students hands-on experience with the fundamental laws of hemodynamics. The proposed experimental setup is of simple construction but permits the precise measurements of physical variables involved in the experience. The model consists in a series of experiments where different basic phenomena are quantitatively investigated, such as the pressure drop in a long straight vessel and in an obstructed vessel, the transition from laminar to turbulent flow, the association of vessels in vascular networks, or the generation of a critical stenosis. Through these experiments, students acquire a direct appreciation of the importance of the parameters involved in the relationship between pressure and flow rate, thus facilitating the comprehension of more complex problems in hemodynamics.     

Molecular hydrogen and radiation protection

Molecular hydrogen (dihydrogen, H(2)) acts as a therapeutic antioxidant by selectively reducing hydroxyl radicals (?OH) and peroxynitrite (ONOO-). It has been well-known that ionising radiation (IR) causes oxidative damage and consequent apoptosis mainly due to the production of ?OH that follows radiolysis of H(2)O. Our department reported the protective effect of H(2) in irradiated cells and mice for the first time, and this effect is well repeated by us and another laboratory in different experimental animal models. A randomised, placebo-controlled investigation also showed consumption of H(2) can improve the quality of life of patients treated with radiotherapy for liver tumours. These encouraging results suggested that H(2) has a potential as a radioprotective agent with efficacy and non-toxicity.     

Optical coherence tomography: fundamental principles, instrumental designs and biomedical applications

The advances made in the last two decades in interference technologies, optical instrumentation, catheter technology, optical detectors, speed of data acquisition and processing as well as light sources have facilitated the transformation of optical coherence tomography from an optical method used mainly in research laboratories into a valuable tool applied in various areas of medicine and health sciences. This review paper highlights the place occupied by optical coherence tomography in relation to other imaging methods that are used in medical and life science areas such as ophthalmology, cardiology, dentistry and gastrointestinal endoscopy. Together with the basic principles that lay behind the imaging method itself, this review provides a summary of the functional differences between time-domain, spectral-domain and full-field optical coherence tomography, a presentation of specific methods for processing the data acquired by these systems, an introduction to the noise sources that plague the detected signal and the progress made in optical coherence tomography catheter technology over the last decade.     

Haemopoietic recovery during radiation disease: Comments on combined-injuries

Summary The regenerative ability of haemopoietic organs during combined radiation injuries has not been adequately investigated. Interactions among individual factors can critically influence the processes involved in haemopoietic recovery. An overview of radiation injuries is given, and a concept towards a hypothetical mode of action at the cellular level is presented. The influence which interacting factors can have on the concentration of pluripotential haemopoietic stem cells (HSC) is demonstrated by results from an initial experiment. The importance of synergistic and antagonistic reactions is emphasised and commented upon.Dedicated to Prof. Dr. med. Otfried Messerschmidt, München, on the occasion of his 60th birthday     

Radiation protection of the environment: anthropocentric and eco-centric principles

The second half of the XX century was dominated in the field of radiation protection of the environment by the anthropocentric concept stated by the International Commission on Radiological Protection (ICRP). According to this concept "if man is adequately protected by radiological standards then biota are also adequately protected". At the end of the XX--beginning of the XXI centuries in the area of area of radiation protection of nature an ecocentric strategy is beginning to develop where emphasis has swung to the protection of biota in their environment. Inadequacy of ICRP's anthroposentric concept is reported. Issues are discussed such as ecological dosimetry, nonequidosal irradiation of man and biota, criteria for estimating radiation induced changes in biota and man, as well as the need to harmonize permissible exposure doses to man and biota. An urgent need is stressed to develop a single (synthetic) concept of radiation protection which simultaneously ensures protection of human health and biota well-being in their environment. This concept is to be based on the recognition of the integrity of socio-natural ecosystems where man and biota are considered as a unity.     

The response of bone to mechanical loading and disuse: fundamental principles and influences on osteoblast/osteocyte homeostasis

Bone’s response to increased or reduced loading/disuse is a feature of many clinical circumstances, and our daily life, as habitual activities change. However, there are several misconceptions regarding what constitutes loading or disuse and why the skeleton gains or loses bone. The main purpose of this article is to discuss the fundamentals of the need for bone to experience the effects of loading and disuse, why bone loss due to disuse occurs, and how it is the target of skeletal physiology which drives pathological bone loss in conditions that may not be seen as being primarily due to disuse. Fundamentally, if we accept that hypertrophy of bone in response to increased loading is a desirable occurrence, then disuse is not a pathological process, but simply the corollary of adaptation to increased loads. If adaptive processes occur to increase bone mass in response to increased load, then the loss of bone in disuse is the only way that adaptation can fully tune the skeleton to prevailing functional demands when loading is reduced. The mechanisms by which loading and disuse cause bone formation or resorption are the same, although the direction of any changes is different. The osteocyte and osteoblast are the key cells involved in sensing and communicating the need for changes in mass or architecture as a result of changes in experienced loading. However, as those cells are affected by numerous other influences, the responses of bone to loading or disuse are not simple, and alter under different circumstances. Understanding the principles of disuse and loading and the mechanisms underlying them therefore represents an important feature of bone physiology and the search for targets for anabolic therapies for skeletal pathology.     

Neutron, proton, and photonuclear cross-sections for radiation therapy and radiation protection

I review recent work at Los Alamos undertaken to evaluate neutron, proton, and photonuclear cross-sections up to 150 MeV (to 250 MeV for protons), based on experimental data and nuclear model calculations. These data are represented in the ENDF format and can be used in computer codes to simulate radiation transport. They permit calculations of absorbed dose in the body from therapy beams, and through use of kerma coefficients allow absorbed dose to be estimated for a given neutron energy distribution. In radiation protection, these data can be used to determine shielding requirements in accelerator environments and to calculate neutron, proton, gamma-ray, and radionuclide production. Illustrative comparisons of the evaluated cross-section and kerma coefficient data with measurements are given.