Mathematical modeling of thermal and circulatory effects during hemodialysis.

Intradialytic hypotension (IDH) is one of the most common complications of hemodialysis (HD) treatment. The initiating factor of IDH is a decrease in blood volume which is related to an imbalance between ultrafiltration (UF) and refilling rate. Impaired reactivity of resistance and capacitance vessels in reaction to hypovolemia plays possibly a major role in the occurrence of IDH. These vessels also fulfill an important function in body temperature regulation. UF induced cutaneous vasoconstriction would result in a reduced surface heat loss and an increase in core temperature. To release body heat, skin blood flow (SBF) is increased at a later stage of the HD treatment, whereby possibly IDH can occur. Aim of the study is to develop a mathematical model which can provide insight into the impact of thermoregulatory processes on the cardiovascular system during HD treatment. The mathematical procedure has been created by coupling a thermo-physiological (TP) model with a cardiovascular (CV) model to study regulation mechanisms in the human body during HD+UF. Model simulations for isothermal vs. thermoneutral HD+UF were compared to measurement data of patients on chronic intermittent HD (n=13). Core temperature during simulated HD+UF sessions increased within the range of measurement data (0.23ºC vs. 0.32±0.41ºC). The model showed a decline in mean arterial pressure (MAP) of -7% for thermoneutral HD+UF versus -4% for isothermal HD+UF after 200 minutes during which relative blood volume (RBV) changed by -13%. In conclusion, simulation results of the combined model show possibilities for predicting circulatory and thermal responses during HD+UF

Validation of an individualised model of human thermoregulation for predicting responses to cold air

Most computer models of human thermoregulation are population based. Here, we individualised the Fiala model [Fiala et al. (2001) Int J Biometeorol 45:143–159] with respect to anthropometrics, body fat, and metabolic rate. The predictions of the adapted multisegmental thermoregulatory model were compared with measured skin temperatures of individuals. Data from two experiments, in which reclining subjects were suddenly exposed to mild to moderate cold environmental conditions, were used to study the effect on dynamic skin temperature responses. Body fat was measured by the three-compartment method combining underwater weighing and deuterium dilution. Metabolic rate was determined by indirect calorimetry. In experiment 1, the bias (mean difference) between predicted and measured mean skin temperature decreased from 1.8°C to -0.15°C during cold exposure. The standard deviation of the mean difference remained of the same magnitude (from 0.7°C to 0.9°C). In experiment 2 the bias of the skin temperature changed from 2.0±1.09°C using the standard model to 1.3±0.93°C using individual characteristics in the model. The inclusion of individual characteristics thus improved the predictions for an individual and led to a significantly smaller systematic error. However, a large part of the discrepancies in individual response to cold remained unexplained. Possible further improvements to the model accomplished by inclusion of more subject characteristics (i.e. body fat distribution, body shape) and model refinements on the level of (skin) blood perfusion, and control functions, are discussed

Measurement of model coefficients of skin sympathetic vasoconstriction

Many researchers have already attempted to model vasoconstriction responses, commonly using the mathematical representation proposed by Stolwijk (1971 NASA Contractor Report CR-1855 (Washington, DC: NASA)). Model makers based the parameter values in this formulation either on estimations or by attributing the difference between their passive models and measurement data fully to thermoregulation. These methods are very sensitive to errors. This study aims to present a reliable method for determining physiological values in the vasoconstriction formulation. An experimental protocol was developed that enabled us to derive the local proportional amplification coefficients of the toe, leg and arm and the transient vasoconstrictor tone. Ten subjects participated in a cooling experiment. During the experiment, core temperature, skin temperature, skin perfusion, forearm blood flow and heart rate variability were measured. The contributions to the normalized amplification coefficient for vasoconstriction of the toe, leg and arm were 84%, 11% and 5%, respectively. Comparison with relative values in the literature showed that the estimated values of Stolwijk and the values mentioned by Tanabe et al (2002 Energy Build. 34 637-46) were comparable with our measured values, but the values of Gordon (1974 The response of a human temperature regulatory system model in the cold PhD Thesis University of California, Santa Barbara) and Fiala et al (2001 Int. J. Biometeorol. 45 143159) differed significantly. With the help of regression analysis a relation was formulated between the error signal of the standardized core temperature and the vasoconstrictor tone. This relation was formulated in a general applicable way, which means that it can be used for situations where vasoconstriction thresholds are shifted, like under anesthesia or during motion sickness

Evaporative microchannel cooling:An atomistic approach

Heat generation and temperature rise in electronic devices is a technical problem with increasing importance, since the number of transistors per surface area on integrated circuitries is rapidly increasing. If the heat cannot effectively be carried away damage in the circuitry may occur. Therefore enhanced and integrated cooling is needed. A promising technique is evaporative microchannel cooling. However, a major problem in modeling such micro-device is that the continuum approach starts to fail in the vapor phase and more detailed modeling becomes necessary. Since on these small scales the boundary and interface conditions are very important for the overall performance of the device, we choose the approach in which we start with understanding the essential physical phenomena at a molecular level. In this paper a detailed particle-based model is derived for these interactions: local interactions between the three phases are studied by molecular dynamics (MD) simulations in a detailed way. In this way physically and thermodynamically correct interface and boundary conditions (e.g. slip velocities and temperature jumps) are ensured. Finally, the enhanced heat transfer in the evaporative zone (Argon on a Calcium surface) is simulated by our molecular model and is compared to the results obtained by the continuum microregion model developed by P. Stephan et al. (Int. J. Heat Mass Transfer, 35, pp.383-391, 1992).</p

Management tools for hydro energy interventions in water systems

[EN] There is significant potential for energy recovery through the use of micro-hydropower installations in water supply systems (WSS). To exploit the full potential of hydro energy in balance with the optimal hydraulic performance and water supply service, multi-objective management tools are needed. This paper presents the application of four management tools: (1) an energy audit to evaluate the potential hydro energy in the water pressurised systems of Alcoy; (2) multi-criteria decision-making methods for the selection of the preferred energy-efficient operation of a system with a pump-storage reservoir and hydro-turbines in the Algarve; (3) a numerical dynamic tool for optimal turbine operation in the water distribution of Langhirano; and (4) an urban water optioneering tool to estimate the hydropower potential of the external aqueduct network in Athens. These methods showed that through an integrated approach the WSS can be optimised for both hydraulic performance and hydro energy production.The research results presented have been executed within the framework of the TRUST project: Transitions to the Urban Water Services of Tomorrow. The TRUST project has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 265122.Frijns, J.; Cabrera Marcet, E.; Carrico, N.; Covas, D.; Monteiro, AJ.; Ramos, HM.; Bolognesi, A.... (2015). Management tools for hydro energy interventions in water systems. Water Practice & Technology. 10(2):214-227. https://doi.org/10.2166/wpt.2015.024S214227102Araujo, L. S., Ramos, H., & Coelho, S. T. (2006). Pressure Control for Leakage Minimisation in Water Distribution Systems Management. Water Resources Management, 20(1), 133-149. doi:10.1007/s11269-006-4635-3Cabrera, E., Pardo, M. A., Cobacho, R., & Cabrera, E. (2010). Energy Audit of Water Networks. Journal of Water Resources Planning and Management, 136(6), 669-677. doi:10.1061/(asce)wr.1943-5452.0000077Carravetta, A., Del Giudice, G., Fecarotta, O., & Ramos, H. M. (2012). Energy Production in Water Distribution Networks: A PAT Design Strategy. Water Resources Management, 26(13), 3947-3959. doi:10.1007/s11269-012-0114-1Frijns, J., Middleton, R., Uijterlinde, C., & Wheale, G. (2012). Energy efficiency in the European water industry: learning from best practices. Journal of Water and Climate Change, 3(1), 11-17. doi:10.2166/wcc.2012.068Frijns, J., Hofman, J., & Nederlof, M. (2013). The potential of (waste)water as energy carrier. Energy Conversion and Management, 65, 357-363. doi:10.1016/j.enconman.2012.08.023Gonçalves, F. V., Costa, L. H., & Ramos, H. M. (2011). Best economical hybrid energy solution: Model development and case study of a WDS in Portugal. Energy Policy, 39(6), 3361-3369. doi:10.1016/j.enpol.2011.03.031McNabola, A., Coughlan, P., Corcoran, L., Power, C., Prysor Williams, A., Harris, I., … Styles, D. (2013). Energy recovery in the water industry using micro-hydropower: an opportunity to improve sustainability. Water Policy, 16(1), 168-183. doi:10.2166/wp.2013.164Ramos, J. S., & Ramos, H. M. (2009). Sustainable application of renewable sources in water pumping systems: Optimized energy system configuration. Energy Policy, 37(2), 633-643. doi:10.1016/j.enpol.2008.10.006Ramos, H. M., Kenov, K. N., & Vieira, F. (2011). Environmentally friendly hybrid solutions to improve the energy and hydraulic efficiency in water supply systems. Energy for Sustainable Development, 15(4), 436-442. doi:10.1016/j.esd.2011.07.009Rogers, M., & Bruen, M. (2000). Using ELECTRE III to Choose Route for Dublin Port Motorway. Journal of Transportation Engineering, 126(4), 313-323. doi:10.1061/(asce)0733-947x(2000)126:4(313)Rozos, E., & Makropoulos, C. (2013). Source to tap urban water cycle modelling. Environmental Modelling & Software, 41, 139-150. doi:10.1016/j.envsoft.2012.11.015Rozos, E., Makropoulos, C., & Butler, D. (2010). Design Robustness of Local Water-Recycling Schemes. Journal of Water Resources Planning and Management, 136(5), 531-538. doi:10.1061/(asce)wr.1943-5452.0000067San Cristóbal Mateo, J. R. (2012). Multi Criteria Analysis in the Renewable Energy Industry. Green Energy and Technology. doi:10.1007/978-1-4471-2346-0Tzeng, G.-H., & Huang, J.-J. (2011). Multiple Attribute Decision Making. doi:10.1201/b11032Nogueira Vilanova, M. R., & Perrella Balestieri, J. A. (2014). Energy and hydraulic efficiency in conventional water supply systems. Renewable and Sustainable Energy Reviews, 30, 701-714. doi:10.1016/j.rser.2013.11.024Vilanova, M. R. N., & Balestieri, J. A. P. (2014). Hydropower recovery in water supply systems: Models and case study. Energy Conversion and Management, 84, 414-426. doi:10.1016/j.enconman.2014.04.05

Mathematical modeling of thermal and circulatory effects during hemodialysis.

Intradialytic hypotension (IDH) is one of the most common complications of hemodialysis (HD) treatment. The initiating factor of IDH is a decrease in blood volume, which is related to an imbalance between ultrafiltration (UF) and refilling rate. Impaired reactivity of resistance and capacitance vessels in reaction to hypovolemia plays possibly a major role in the occurrence of IDH. These vessels also fulfill an important function in body temperature regulation. UF-induced cutaneous vasoconstriction would result in a reduced surface heat loss and an increase in core temperature. To release body heat, skin blood flow is increased at a later stage of the HD treatment, whereby possibly IDH can occur. The aim of the study is to develop a mathematical model that can provide insight into the impact of thermoregulatory processes on the cardiovascular (CV) system during HD treatment. The mathematical procedure has been created by coupling a thermo-physiological model with a CV model to study regulation mechanisms in the human body during HD + UF. Model simulations for isothermal versus thermoneutral HD + UF were compared with measurement data of patients on chronic intermittent HD (n = 13). Core temperature during simulated HD + UF sessions increased within the range of measurement data (0.23 degrees C vs. 0.32 +/- 0.41 degrees C). The model showed a decline in mean arterial pressure of -7% for thermoneutral HD + UF versus -4% for isothermal HD + UF after 200 min during which relative blood volume changed by -13%. In conclusion, simulation results of the combined model show possibilities for predicting circulatory and thermal responses during HD + UF

Large-scale production of polypropylenimine dendrimers

Th synthesis and characterization of a new series of polypropylenimine (I) dendrimers is reported. Using a repetition of the sequence of a Michael addn. to a primary amine, followed by a heterogeneously catalyzed hydrogenation, ultra-pure polypropylenimine macromols. with mol. wts. £6912 are synthesized. The reaction sequence allows the prepn. of these dendrimers at very large scales, while the availability of a simple purifn. in the sequence affords ultra-pure samples. The I dendrimers are fully characterized; apart from the first 0.5 generation they are all oils, possess a glass transition temp. of -90° to -40°, and are unexpectedly stable. Their intrinsic viscosity drops after generation 4

Large-scale production of polypropylenimine dendrimers

Th synthesis and characterization of a new series of polypropylenimine (I) dendrimers is reported. Using a repetition of the sequence of a Michael addn. to a primary amine, followed by a heterogeneously catalyzed hydrogenation, ultra-pure polypropylenimine macromols. with mol. wts. £6912 are synthesized. The reaction sequence allows the prepn. of these dendrimers at very large scales, while the availability of a simple purifn. in the sequence affords ultra-pure samples. The I dendrimers are fully characterized; apart from the first 0.5 generation they are all oils, possess a glass transition temp. of -90° to -40°, and are unexpectedly stable. Their intrinsic viscosity drops after generation 4

Non-Standard Errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in sample estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty: non-standard errors. To study them, we let 164 teams test six hypotheses on the same sample. We find that non-standard errors are sizeable, on par with standard errors. Their size (i) co-varies only weakly with team merits, reproducibility, or peer rating, (ii) declines significantly after peer-feedback, and (iii) is underestimated by participants