National Technical University of Athens

About: National Technical University of Athens is a education organization based out in Athens, Attiki, Greece. It is known for research contribution in the topics: Large Hadron Collider & Nonlinear system. The organization has 13445 authors who have published 31259 publications receiving 723504 citations. The organization is also known as: Athens Polytechnic & NTUA.

Supercritical fluid extraction of celery seed oil

Abstract: The supercritical fluid extraction of oil from milled celery seeds, using CO2 as a solvent, is presented in this study. The effect of the process parameters — pressure and temperature of extraction, particle size of celery seeds and flow rate of CO2 — on the extraction rate was examined in a series of experiments. The results indicated a significant increase in extraction rate with increase of pressure or decrease of the particle size of celery seed. A similar effect was observed with the increase of the solvent flow rate and decrease of temperature. The experimental data were described by an empirical model and two mass balance models: (1) a simplified model, which takes into account only the time dependence of the extract concentration in the two phases and is coupled with various equilibrium relationships, and (2) an extended Lack's model. The correlation results were satisfactory especially for the mass balance models, which account for the double regime — solubility and diffusion controlled regimes — of the extraction.

Pilot-Plant Investigation of the Leaching Process for the Recovery of Scandium from Red Mud

Abstract: A pilot-plant process has been developed based on an innovative laboratory-scale method for the recovery of scandium that exists in economically interesting concentrations in red mud, the main byproduct of alumina production. This method includes acid leaching of the red mud pulp, ion-exchange separation of scandium and lanthanides from the co-leached main elements such as iron, and subsequent liquid−liquid extraction of the eluate for further scandium purification and enrichment. In this work, experimental and theoretical investigation of the pilot-scale leaching process was performed. The following parameters were tested: mode of agitation, solid-to-liquid ratio, acidity of the leachate, number of stages in the process, and pretreatment of red mud with concentrated acids in order to achieve optimum scandium recovery combined with low iron dissolution. Furthermore, by theoretical interpretation of the experimental data, a predictive correlation for the scandium leaching efficiency was developed.

On the Stability of the Passive Dynamics of Quadrupedal Running with a Bounding Gait

Abstract: This paper examines the passive dynamics of quadrupedal bounding. First, an unexpected difference between local and global behavior of the forward speed versus touchdown angle in the self-stabilized Spring Loaded Inverted Pendulum (SLIP) model is exposed and discussed. Next, the stability properties of a simplified sagittal plane model of our Scout II quadrupedal robot are investigated. Despite its simplicity, this model captures the targeted steady state behavior of Scout II without dependence on the fine details of the robot structure. Two variations of the bounding gait, which are observed experimentally in Scout II, are considered. Surprisingly, numerical return map studies reveal that passive generation of a large variety of cyclic bounding motion is possible. Most strikingly, local stability analysis shows that the dynamics of the open loop passive system alone can confer stability to the motion! These results can be used in developing a general control methodology for legged robots, resulting from the synthesis of feedforward and feedback models that take advantage of the mechanical system, and might explain the success of simple, open loop bounding controllers on our experimental robot.

New Facets of Urban Segregation in Southern Europe: Gender, Migration and Social Class Change in Athens

Abstract: This article explores how primary features of occupational restructuring, such as the feminization of employment and migration, and changes in patterns of residential mobility of Greek and migrant women since the 1990s have contributed to shaping new forms of sociospatial segregation in Athens. We examine changes in the occupational structure and in segregation indices from 1991 to 2001. Findings suggest that new gender and ethnic divisions in the occupational structure combine with residential mobility and introduce strong tendencies towards spatial fragmentation. Intra-urban and migratory flows reflect diversified occupational trajectories among women and contribute to shaping the socioeconomic profile of the destination areas: (a) migrant domestic and unskilled service workers locate to central city and suburban areas; (b) Greek managers and professionals, move to ‘upper-class suburbs’; (c) small Greek entrepreneurs and independent workers sprawl to peri-urban areas; (d) salespersons and clerks move to...