The Influence of Heart and Lung Dynamics on the Impedance Cardiogram — A Simulative Analysis

Impedance cardiography (ICG) is a simple and cheap method for acquiring hemodynamic parameters. Unfortunately, not all physiological influences on the ICG signal have yet been identified. In this work, the influence of heart and lung dynamics is analyzed using a simplified model of the human thorax with high temporal resolution. Simulations are conducted using the finite integration technique (FIT) with temporal resolution of 103 Hz. It is shown that changes in heart volume as well as conductivity changes of the lung have a high impact on the ICG signal, if analyzed separately. Considering the sum signal of both physiological sources, it can be shown that they compensate each other and thus do not contribute to the signal. This finding supports Kubicek’s model

Water and Carbon Dioxide Adsorption on CaO(001) Studied via Single Crystal Adsorption Calorimetry

A new method to analyze microcalorimetry data was employed to study the adsorption energies and sticking probabilities of D2O and CO2 on CaO(001) at several temperatures. This method deconvolutes the line shapes of the heat detector response into an instrument response function and exponential decay functions, which correspond to the desorption of distinct surface species. This allows for a thorough analysis of the adsorption, dissociation, and desorption processes that occur during our microcalorimetry experiments. Our microcalorimetry results, show that D2O adsorbs initially with an adsorption energy of 85–90 kJ/mol at temperatures ranging from 120 to 300 K, consistent with prior spectroscopic studies that indicate dissociation. This adsorption energy decreases with increasing coverage until either D2O multilayers are formed at low temperatures (120 K) or the surface is saturated (150 K). Artificially producing defects on the surface by sputtering prior to dosing D2O sharply increases this adsorption energy, but these defects may be healed after annealing the surface to 1300 K. CO2 adsorbs on CaO(001) with an initial adsorption energy of ~ 125 kJ/mol, and decreases until the saturation coverage is reached, which is a function of surface temperature. The results showed that pre-adsorbed water blocks adsorption sites, lowers the saturation coverage, and lowers the measured adsorption energy of CO2. The calorimetry data further adds to our understanding of D2O and CO2 adsorption on oxide surfaces

Adsorption energetics of CO on supported Pd nanoparticles as a function of particle size by single crystal microcalorimetry

The heat of adsorption and sticking probability of CO on well-defined Pd nanoparticles were measured as a function of particle size using single crystal adsorption microcalorimetry. Pd particles of different average sizes ranging from 120 to 4900 atoms per particle (or from 1.8 to 8 nm) and Pd(111) were used that were supported on a model in situ grown Fe3O4/Pt(111) oxide film. To precisely quantify the adsorption energies, the reflectivities of the investigated model surfaces were measured as a function of the thickness of the Fe3O4 oxide layer and the amount of deposited Pd. A substantial decrease of the binding energy of CO was found with decreasing particle size. Initial heat of adsorption obtained on the virtually adsorbate-free surface was observed to be reduced by about 20–40 kJ mol-1 on the smallest 1.8 nm sized Pd particles as compared to the larger Pd clusters and the extended Pd(111) single crystal surface. This effect is discussed in terms of the size-dependent properties of the Pd nanoparticles. The CO adsorption kinetics indicates a strong enhancement of the adsorbate flux onto the metal particles due to a capture zone effect, which involves trapping of adsorbates on the support and diffusion to metal clusters. The CO adsorption rate was found to be enhanced by a factor of 8 for the smallest 1.8 nm sized particles and by 1.4 for the particles of 7–8 nm size

Selective Partial Hydrogenation of Acrolein on Pd: a Mechanistic Study

Identifying the surface processes governing the selectivity in hydrogenation of α,β-unsaturated carbonyl compounds on late transition metals is crucial for the rational design of catalytic materials with the desired selectivity toward C=C or C=O bond hydrogenation. The partial selective hydrogenation of acrolein on a Pd(111) single crystal and Fe₃O₄- supported Pd nanoparticles under well-de fined UHV conditions was investigated in the present study as a prototypical reaction. Molecular beam techniques were combined with infrared reflection − absorption spectroscopy (IRAS) and quadrupole mass spectrometry (QMS) in order to simultaneously monitor the evolution of surface species and the formation of the final gas-phase products under isothermal reaction conditions as a function of surface temperature. Over a Pd(111) single crystal, acrolein is hydrogenated at the C=O bond to form the desired reaction product propenol with nearly 100% selectivity in the temperature range between 250 and 300 K, while over Pd/Fe₃O₄, selective hydrogenation of the C=C bond to form propanal occurs. We found that the high selectivity toward C=O bond hydrogenation over Pd(111) is connected to the initial modification of the catalytic surface with a dense monolayer of an oxopropyl surface species. This strongly bound oxopropyl layer is formed on the pristine Pd crystal in the induction period from half-hydrogenation of the C=C bond in acrolein. Subsequently deposited acrolein molecules adsorb via the C=O bond and form a half-hydrogenated reaction intermediate propenoxy species, which is attached to Pd via a C-O single bond. The evolution of the surface concentration of the propenoxy intermediate monitored spectroscopically was found to closely follow the propenol formation rate detected in the gas phase. At temperatures higher than 300 K on Pd(111) and on Pd nanoparticles supported on Fe₃O₄, decarbonylation of acrolein occurs, leading to accumulation of CO and strongly dehydrogenated carbonaceous species on the surface. This process prevents formation of well-ordered overlayers of oxopropyl species required for selective C=O bond hydrogenation, resulting in only minor nonselective hydrogenation of acrolein. At temperatures below 250 K on Pd(111), only a small fraction of the initially adsorbed acrolein is converted into the oxopropyl species, yielding a partially modified surface and thus rather unselective formation of both propanal and propenol products