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The important topic of proton transport through molecular wires is usually associated with the Grotthuss mechanism. In this paper we propose an alternative conductor based on chains of lone pairs. B3LYP/6-31+G** and PW91 DFT calculations on model compounds (1,2,3,4-tetrasubstituted benzenes) show that these compounds could play the role of proton conductors.
We have simulated CF scattering from Si(100) using the molecular dynamics method. Translational energy loss spectra are presented. The shape of the energy loss distribution as a result of internal energy release is analyzed. At the classical turning point, the internal energy of the molecule is mainly in the form of rotational energy. The strong rotational excitation results in additional molecule-surfaces interactions during the latter half of the collision. These additional collisions permit some molecules that initially gain internal energy exceeding the bond strength to ultimately survive the collision process via rotational de-excitation. The rotational motion exhibited by surviving molecules is determined by the combination of the molecular axis orientation and the local surface structure during the collision process. The rotation planes of the surviving molecules are preferentially aligned with the surface normal (cartwheel-like and propeller-like motions). In this study, propeller-like motion of the surviving molecules is predicted. The majority of surviving molecules exhibit a cartwheel-like motion. However, molecules that gain a propeller-like rotation exhibit a much better alignment of their planes-of-rotation compared with molecules exhibiting cartwheel-like motion.
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The presented model of controlled apoptosis has been based on the assumption that correct information exchange between an organism as a whole, and each of its cells is conditioned by mutual proportions of cAMP and cGMP concentrations (CcAMP, CcGMP), according to the formula CcAMP x CcGMP = 'a' (constant). The regulation of balance of these 'second messengers' in a cell and an extracellular space would depend on the mutual proportions of concentrations of Melatonin and monomers of Melanin. These indoloderived compounds could be the activators of the transcription factors i.e. RZR and NFkappa-B, regulating the expression of Prohormone Convertase (PC) gen and Nitric Oxide Synthase (NOS) gen, respectively. Additionally, maternal Melatonin and Nitric Oxide (NO), being able to pass through trophoblast or placenta freely, would play decisive role in the synchronization of embryogenesis and intrauterine development of the fetus. In case of an embryo or a fetus, the result of CcAMP and CcGMP multiplication, different from the proper constant 'a'-value, would mean occurrence of disorders in the structure and functioning of the cellular tensegrity system and, in consequence, disturbances in the intercellular information exchange. It would lead to deviation in cellular metabolism, oriented cell movement, uncontrolled apoptosis, and as a consequence, would lead to the development of fetal defects. In case of a child or an adult, a sudden occurrence and prolongation of such disturbances in CcAMP-CcGMP proportions would induce a process of apoptosis of normal cells and an initiation of a cancerogenesis. On the other hand, the recovery of equilibrium in the information exchange system would initiate apoptosis of neoplastic cells, and simultaneously, proliferation of connective tissue cells. According to the presented hypothesis, a decrease in CcAMP and destabilization of the CcAMP-CcGMP balance in an embryo or a fetus would result from relatively excessive amounts of maternal Melatonin (monomers) in fetal circulation, while a decrease of CcAMP and destabilization of the CcAMP-CcGMP balance in a child or an adult would be a consequence of relatively insufficient amounts of Melatonin (dimers) in an organism. It seems possible, that determination of both CcAMP and CcGMP would enable an early detection of high risk of developmental defects occurrence in an embryo or a fetus and neoplastic processes in a child or an adult. This method might also be considerably useful in monitoring a safe substitutional hormonotherapy.
We study a reaction-diffusion-advection model for the dynamics of populations under biological control. A control agent is assumed to be a predator species that has the ability to perceive the heterogeneity of pest distribution. The advection term represents the predator density movement according to a basic prey taxis assumption: acceleration of predators is proportional to the prey density gradient. The prey population reproduces logistically, and the local population interactions follow the Holling Type II trophic function. On the scale of the population, our spatially explicit approach subdivides the predation process into random movement represented by diffusion, directed movement described by prey taxis, local prey encounters, and consumption modeled by the trophic function. Thus, our model allows studying the effects of large-scale predator spatial activity on population dynamics. We show under which conditions spatial patterns are generated by prey taxis and how this affects the predator ability to maintain the pest population below some economic threshold. In particular, intermediate taxis activity can stabilize predator-pest populations at a very low level of pest density, ensuring successful biological control. However, very intensive prey taxis destroys the stability, leading to chaotic dynamics with pronounced outbreaks of pest density.
In consideration of the importance of film dosimetry for the dosimetric verification of IMRT treatment plans, the Schwarzschild effect or failure of the reciprocity law, i.e. the reduction of the net optical density under 'protraction' or 'fractionation' conditions at constant dose, has been experimentally studied for Kodak XOMAT-V (Martens et al 2002 Phys. Med. Biol. 47 2221-34) and EDR 2 dosimetry films (Djouguela et al 2005 Phys. Med. Biol. 50 N317-N321). It is known that this effect results from the competition between two solid-state physics reactions involved in the latent-image formation of the AgBr crystals, the aggregation of two Ag atoms freshly formed from Ag(+) ions near radiation-induced occupied electron traps and the spontaneous decomposition of the Ag atoms. In this paper, we are developing a mathematical model of this mechanism which shows that the interplay of the mean lifetime tau of the Ag atoms with the time pattern of the irradiation determines the magnitude of the observed effects of the temporal dose distribution on the net optical density. By comparing this theory with our previous protraction experiments and recent fractionation experiments in which the duration of the pause between fractions was varied, a value of the time constant tau of roughly 10 s at room temperature has been determined for EDR 2. The numerical magnitude of the Schwarzschild effect in dosimetry films under the conditions generally met in radiotherapy amounts to only a few per cent of the net optical density (net OD), so that it can frequently be neglected from the viewpoint of clinical applications. But knowledge of the solid-state physical mechanism and a description in terms of a mathematical model involving a typical time constant of about 10 s are now available to estimate the magnitude of the effect should the necessity arise, i.e. in cases of large fluctuations of the temporal pattern of film exposure.
This paper discusses the work of the EUHPID Project to develop a European Health Promotion Monitoring System based on a common set of health promotion indicators. The Project has established three working groups to progress this task--health promotion policy and practice-driven, data-driven and theory-driven. The work of the latter group is reviewed in particular. EUHPID has taken a systems theory approach in order to develop a model as a common frame of reference and a rational basis for the selection, organization and interpretation of health promotion indicators. After reviewing the strengths and weaknesses of those health promotion models currently proposed for indicator development, the paper proposes a general systems model of health development, and specific analytical, socio-ecological models related to public health and health promotion. These are described and discussed in detail. Taking the Ottawa Charter as the preferred framework for health promotion, the socio-ecological model for health promotion adopts its five action areas to form five types of systems. The structure and processes for each of these five systems are proposed to form the basis of a classification system for health promotion indicators. The paper goes on to illustrate such a system with reference to indicators in the workplace setting. The EUHPID Consortium suggest that their socio-ecological model could become a common reference point for the public health field generally, and offer an invitation to interested readers to contribute to this development.
A novel approach to solving microdosimetry problems using conditional probabilities and geometric concepts has been developed. This approach is valid for cases where a convex site is immersed in uniform or discontinuous distributions of heavy charged particle tracks and assumes no restrictions in site geometry or the kind of randomness. These conditions are relevant to the study of microdosimetry in applications such as neutron capture therapy (NCT), irradiation experiments using heavy ion particle beams, environmental radon, or occupational exposure to radioactive materials. Expressions applicable to the case of surface-distributed sources of tracks are presented that may represent situations such as NCT, where boron compounds are bound to the membranes of cellular nuclei. Microdosimetric spectra, specific energy averages, and mean number of 10B capture reactions for cell inactivation are calculated, showing their dependence on 10B localisation.
A comprehensive computer model of the cerebral circulation, based on both hydrodynamics and electrical network analysis, was used to investigate the influences of arteriovenous malformations (AVM) on regional cerebral hemodynamics. The basic model contained 114 normal compartments: 55 arteries, 37 veins, 20 microvessel groups (MVG), one compartment representing systemic and extracranial vascular resistance, and one representing the heart. Each microvessel group, which represented the arteriolar bed, consisted of 5000 microvessels. Cerebral blood flow autoregulation was simulated by a formula that determined the resistance and therefore the flow rate of the microvessel groups (arterioles) as a function of perfusion pressure. Elasticity was introduced to describe the compliance of each vessel. Flow rate was made a controlling factor for the positive regulation of the diameters of conductance vessels by calculation of shear stress on the vessel wall (vessel dilation). Models containing an AVM were constructed by adding an AVM compartment and its feeding arteries and draining veins. In addition to the basic model, AVM models were simulated with and without autoregulation and flow-induced conductance vessel dilation to evaluate the contributions of these factors on cerebral hemodynamics. Results for the model with vessel dilation were more similar to clinical observations than those without vessel dilation. Even in the presence of total vasoparalysis of the arteriolar bed equivalent, obliteration of a large (1000 mL/min) shunt flow AVM resulted in a near-field CBF increase from a baseline of 21 to a post-occlusion value of no more than 74 mL/100 g/min, casting doubt on a purely hemodynamic basis for severe hyperemia after treatment. The results of the simulations suggest that our model may be a useful tool to study hemodynamic problems of the cerebral circulation.
OBJECTIVE: The cerebrovascular bed and cerebrospinal fluid circulation have been modeled extensively except for the cerebral venous outflow, which is the object of this study. METHODS: A hydraulic experiment was designed for perfusion of a collapsible tube in a pressurized chamber to simulate the venous outflow from the cranial cavity. CONCEPT: The laboratory measurements demonstrate that the majority of change in venous flow can be attributed to either inflow pressure when the outflow is open, or the upstream transmural pressure when outflow is collapsed. On this basis, we propose a mathematical model for pressure distribution along the venous outflow pathway depending on cerebral blood flow and intracranial pressure. The model explains the physiological strong coupling between intracranial pressure and venous pressure in the bridging veins, and we discuss the limits of applicability of the Starling resistor formula to the venous flow rates. The model provides a complementary explanation for ventricular collapse and origin of subdural hematomas resulting from overshunting in hydrocephalus. The noncontinuous pressure flow characteristic of the venous outflow is pinpointed as a possible source of the spontaneous generation of intracranial slow waves. CONCLUSION: A new conceptual mathematical model can be used to explain the relationship between pressures and flow at the venous outflow from the cranium.
This study examines the role of social support, self-efficacy, outcome expectancy, and anxiety as predictors of medication management in persons with epilepsy. A model based on social cognitive theory was constructed to explain managing medications under conditions of scarcity. A survey instrument was sent to 450 individuals who participated in job training programs for persons with epilepsy. One hundred ninety-five completed questionnaires were returned and met the inclusion criteria. The proposed structural model was tested using structural equation modeling procedures. The assistance aspect of social support was positively related to regimen-specific support. The paths from self-efficacy to outcome expectancy and anxiety were significant and in the predicted directions, as was the path from anxiety to self-management.
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Cavity configuration factor (C-factor) is the ratio of the bonded surface area in a cavity to the unbonded surface area. In a box-like class I cavity, there may be five times more bonded surface area than the unbonded surface area. During polymerization, the volume of monomers is reduced, which creates sufficient shrinkage stresses to debond the material from dentin, thereby decreasing retention and increasing leakage. The important variables influencing bonding adhesive root-filling materials to canals was examined using a truncated inverted cone model. C-factors in bonded root canals exhibit a negative correlation with sealer thickness. For a 20 mm-long canal prepared with a size 25 file, calculated C-factors ranged from 46 to 23,461 with decreasing sealer thickness (500-1 microm), compared to a C-factor of 32 when the canal was filled only with sealer. As the thickness of the adhesive is reduced, the volummetric shrinkage is reduced, which results in a reduction in shrinkage stress (S-factor). C-factors above 954 calculated with sealer thickness smaller than 25 microm are partially compensated by increases in bonding area and decreases in shrinkage volume. However, the interaction of these two geometrically related factors (C- and S-factors) predicts that bonding of adhesive root-filling materials to root canals is highly unfavorable when compared with indirect intracoronal restorations with a similar resin film thickness.
In contrast to a previous report [Baertlein et al. (2000)], the transverse electomagnetic resonator used in magnetic resonance imaging is shown to be similar to the high-pass "birdcage" resonator in having an electric field minimum in correspondence with the maximum of the magnetic field. The noise performance of each resonator will, in consequence, be comparable, since at high frequencies patient conductive losses are predominant.
Five hospitalized patients in different stages of Alzheimer-type dementia were monitored by unstructured, direct observations during morning care. Orem's model of nursing as a compensation for the patient's lack of self-care capabilities was used as a frame of reference for an analysis of the behaviours of patients and nurses during morning care. A 12-step classification system was developed to be used as a guide to understand and determine abilities essential for performance of morning care for demented patients. The quantitative assessment showed that none of the patients was able to manage morning care independently, but there was a wide variation in their highest level of performance.
A new model which provides an explanation for pH-induced co-operativity of hysteretic enzymes is proposed. The essence of the model is that a region, or a domain, of the enzyme undergoes a spontaneous 'slow' conformational change which does not affect the geometry of the active site. The region which undergoes this spontaneous conformational transition bears an ionizable group. Kinetic co-operativity occurs if the pK of this ionizable group changes upon this conformational transition. Thus co-operativity does not arise from a distortion of the active site. An interesting prediction of the model is that at 'extreme' pH values co-operativity must be suppressed. Although the kinetic equation pertaining to the model is of the 2:2 type, co-operativity is not maximum or minimum at half-saturation of the enzyme by the substrate, as occurs with 2:2 binding isotherms. A new index of maximum or minimum kinetic co-operativity, whether this extreme occurs at half-saturation or not, has been proposed which allows the change of kinetic co-operativity to be followed as a function of pH. It is believed that this model will be useful in explaining the behaviour of enzymes attached to biological polyelectrolytes, such as membranes or cell envelopes.
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