The optimum performance of absorption cycles with external and internal Irreversibilities

A new model is presented to describe an irreversible absorption refrigerator, in which not only the irreversibilities of heat conduction but also the irreversibilities resulting from the friction, eddy and other irreversible effects inside the working fluid are considered. The influence of these irreversible effects on the performance of an absorption refrigerator with continuous flow is investigated. The analytical expressions of the optimal refrigeration coefficient and the cooling rate of the refrigerator are derived. The predictions of the model are compared with semi-empirical cycle model of single-stage absorption refrigeration machines. The results obtained here can describe the optimal performance of a four-temperature-level absorption refrigeration affected simultaneously by the internal and external irreversibilities and provide the theoretical base s for the optimal design and operation of real absorption refrigerators operating between four temperature level.A new model is presented to describe an irreversible absorption refrigerator, in which not only the irreversibilities of heat conduction but also the irreversibilities resulting from the friction, eddy and other irreversible effects inside the working fluid are considered. The influence of these irreversible effects on the performance of an absorption refrigerator with continuous flow is investigated. The analytical expressions of the optimal refrigeration coefficient and the cooling rate of the refrigerator are derived. The predictions of the model are compared with semi-empirical cycle model of single-stage absorption refrigeration machines. The results obtained here can describe the optimal performance of a four-temperature-level absorption refrigeration affected simultaneously by the internal and external irreversibilities and provide the theoretical base s for the optimal design and operation of real absorption refrigerators operating between four temperature level

On- and Off-ramps Generating 1/f Noise in Traffic Flow

A simple model of a motorway junction consisting of two connected periodic roads is presented; each of them is connected to the other by on- and off-ramps. This constitutes a detailed structure for the region of on- and off-ramps, which is a new aspect of this paper and a useful step towards a more realistic modelling of the vehicular dynamics near the ramps. The traffic flow through the ramps has an effect on the capacity of the main roads. This effect is identified by the formation of the so-called ”plateau” in the fundamental diagram. The value increase of one of the probabilities pin and pout decreases the value of the indicated plateau. Here pin is the probability to enter the main road through the on-ramp and pout denotes the probability to exit the main road through the off-ramp. The first important feature in the simulated system is the symmetry between the connected main roads. This symmetry does not depend on the variation of the difference between the probabilities pin and pout. The other most outstanding feature is the existence of correlations between the connected main roads, which can be traced back to the lane change of vehicles in the ramp regions. These correlations are characterized by the occurrence of 1/fα fluctuations in the global traffic flow of a chosen main road of the simulated system.A simple model of a motorway junction consisting of two connected periodic roads is presented; each of them is connected to the other by on- and off-ramps. This constitutes a detailed structure for the region of on- and off-ramps, which is a new aspect of this paper and a useful step towards a more realistic modelling of the vehicular dynamics near the ramps. The traffic flow through the ramps has an effect on the capacity of the main roads. This effect is identified by the formation of the so-called ”plateau” in the fundamental diagram. The value increase of one of the probabilities pin and pout decreases the value of the indicated plateau. Here pin is the probability to enter the main road through the on-ramp and pout denotes the probability to exit the main road through the off-ramp. The first important feature in the simulated system is the symmetry between the connected main roads. This symmetry does not depend on the variation of the difference between the probabilities pin and pout. The other most outstanding feature is the existence of correlations between the connected main roads, which can be traced back to the lane change of vehicles in the ramp regions. These correlations are characterized by the occurrence of 1/fα fluctuations in the global traffic flow of a chosen main road of the simulated system

Atomistic insights into the mixed-alkali effect in phosphosilicate glasses

Oxide glasses have proven useful as bioactive materials, owing to their fast degradation kinetics and tunable properties. Hence, in recent years tailoring the properties of bioactive glasses through compositional design have become the subject of widespread interest for their use in medical application, e.g., tissue regeneration. Understanding the mixed alkali effect (MAE) in oxide glasses is of fundamental importance for tailoring the glass compositions to control the mobility of ions and, therefore, the glass properties that depend on it, such as ion release, glass transition temperature, and ionic conductivity. However, most of the previously designed bioactive glasses were based on trial-and-error, which is due to the complex glass structure that is nontrivial to analyze and, thus, the lack of a clear picture of the glass structure at short- and medium-range order. Accordingly, we use molecular dynamics simulations to study whether using the MAE can control the bioactivity and properties of 45S5 glass and its structural origins. We showed that the network connectivity, a structural parameter often used to access the bioactivity of silicate glasses, does not change with Na substitution with Li or K. On the contrary, the elastic moduli showed a strong dependence on the type of the modifier as they increased with increasing mean field strength. Similarly, the mobility of the glass elements was significantly affected by the type of modifier used to substitute Na. The change of the properties is further discussed and explained using changes at the short- and medium-range structure by giving evidence of previous experimental findings. Finally, we highlight the origin of the nonexistence of the MAE, the effect of the modifier on the bioactivity of the glasses, the importance of dynamical descriptors in predicting the bioactivity of oxide glasses, and we provide the necessary insights, at the atomic scale, needed for further development of bioactive glasses

Dynamic model of fracture

We study the failure properties of heterogeneous materials within the framework of the fiber bundle model subject to the global load-sharing rule in which the load failing elements is shared equally among all surviving elements. We develop a simulation technique by using the Langevin equation in order to investigate some characteristics of our model. It is found that the behavior of time to failure tf decreases with an exponential law and the avalanche size distribution present a power law.We study the failure properties of heterogeneous materials within the framework of the fiber bundle model subject to the global load-sharing rule in which the load failing elements is shared equally among all surviving elements. We develop a simulation technique by using the Langevin equation in order to investigate some characteristics of our model. It is found that the behavior of time to failure tf decreases with an exponential law and the avalanche size distribution present a power law

Electron-loss and target ionization cross sections for water vapor by 20-150 keV neutral atomic hydrogen impact

A complete set of cross sections is reported for the ionization of water molecules by neutral atomic hydrogen impact at velocities of the order of the Bragg peak. The measured relative cross sections are normalized by comparison with proton impact results for the same target conditions and previous absolute data. Event by event coincidence analysis of the product ions and the projectile enables partial cross sections for target ionization and target plus projectile ionization to be determined, as well as total cross sections for electron loss reactions.Comment: To be published in Chemical Physics Letter

IONIC HYDROGEN CLUSTERS: STRUCTURE AND EVAPORATION

Abstract We report the first account of a hydrogen cluster evaporation study in which we compare three constant rate evaporation models with the experimental cross section of unimolecular dissociation obtained after the collisional reaction between H e and accelerated hydrogen cluster + n H (n=3 to 21, odd) with incident energy equal to 60kev/amu. The calculations performed in the framework of these three models reproduce remarkably well experimental data

Absolute partial cross sections for the destruction of H₂ and H3⁺ in collisions with helium atoms at 50 and 60 keV/amu

The first partial cross-section measurements are presented for the various channels of H3+ and H2 dissociation in collisions with helium atoms at 50 and 60 keV/amu. The experimental technique includes the use of a removable grid in front of a surface barrier detector to enable neutrals of mass 2 amu to be separated into H2 and 2H channels