An orbital-free molecular dynamics study of melting in K_20, K_55, K_92, K_142, Rb_55 and Cs_55 clusters

The melting-like transition in potasium clusters K_N, with N=20, 55, 92 and 142, is studied by using an orbital-free density-functional constant-energy molecular dynamics simulation method, and compared to previous theoretical results on the melting-like transition in sodium clusters of the same sizes. Melting in potasium and sodium clusters proceeds in a similar way: a surface melting stage develops upon heating before the homogeneous melting temperature is reached. Premelting effects are nevertheless more important and more easily established in potasium clusters, and the transition regions spread over temperature intervals which are wider than in the case of sodium. For all the sizes considered, the percentage melting temperature reduction when passing from Na to K clusters is substantially larger than in the bulk. Once those two materials have been compared for a number of different cluster sizes, we study the melting-like transition in Rb_55 and Cs_55 clusters and make a comparison with the melting behavior of Na_55 and K_55. As the atomic number increases, the height of the specific heat peaks decreases, their width increases, and the melting temperature decreases as in bulk melting, but in a more pronounced way.Comment: LaTeX file. 6 pages with 17 pictures. Final version with minor change

Robust vehicle steering control design based on the disturbance observer

A robust steering controller is introduced for improving the yaw dynamics of a passenger car. A specific two degree of freedom control architecture known as the disturbance observer is adapted to the vehicle yaw dynamics control problem and shown to robustly improve performance. The relevant design specifications are formulated in terms of eigenvalues (T-stability) and in frequency domain as bounds on weighted sensitivity and complementary sensitivity functions (B-stability). The parameter space method is used to map the specifications for controller design. A Popov criterion based nonlinear stability analysis is also carried out to prove absolute stability in the presence of actuator rate limitation. Simulations are used to demonstrate the effectiveness of the final design

Robust two degree of freedom vehicle steering control satisfying mixed sensitivity constraint

Robust steering control is used here for improving the yaw dynamics of a passenger car. A specific two degree of freedom control structure is adapted to the vehicle yaw dynamics problem and shown to robustly improve performance. The design study is based on six operating conditions for vehicle speed and the coefficient of friction between the tires and the road representing the operating domain of the vehicle. The relevant design specifications are formulated as attaining Hurwitz stability and a mixed sensitivity frequency domain bound. Simple, and therefore, easily implementable controller transfer functions with two design parameters are chosen for the two steering controller degrees of freedom. Using the parameter space method, the design specifications are mapped into the plane of controller parameters. The effectiveness of the final design is demonstrated using simulations

Robust Two Degree-of-Freedom Vehicle Steering Controller Design

Robust steering control based on a specific two degree of freedom control structure is used here for improving the yaw dynamics of a passenger car. The usage of an auxiliary steering actuation system for imparting the corrective action of the steering controller is assumed. The design study is based on six operating conditions for vehicle speed and the coefficient of friction between the tires and the road representing the boundary of the operating domain of the vehicle. The design is carried out by finding the region in controller parameter plane where Hurwitz stability and a mixed sensitivity frequency domain constraint are simultaneously satisfied. A velocity based gain scheduling type implementation is used. Moreover, the steering controller has a fading effect that leaves the low frequency driving task to the driver, intervening only when necessary. The effectiveness of the final design is demonstrated using linear and nonlinear simulations

Robust two degree of freedom vehicle steering controller design

Robust steering control based on a specific two degree of freedom control structure is used here for improving the yaw dynamics of a passenger car. The usage of an auxiliary steering actuation system for imparting the corrective action of the steering controller is assumed. The design study is based on six operating conditions for vehicle speed and the coefficient of friction between the tires and the road representing the boundary of the operating domain of the vehicle. The design is carried out by finding the region in controller parameter plane where Hurwitz stability and a mixed sensitivity frequency domain constraint are simultaneously satisfied. A velocity based gain scheduling type implementation is used. Moreover, the steering controller has a fading effect that leaves the low frequency driving task to the driver, intervening only when necessary. The effectiveness of the final design is demonstrated using linear and nonlinear simulations

In vitro effect of trimetazine on K-Cl cotransport and superoxide dismutase activity in Hemoglobin SS erythrocytes

Background and Purpose: Trimetazidine (TMZ) (1-2,3,4 trimethoxybenzyl piperazine dihydrochloride) is a cyto-productive agent which is used as an anti-anginal drug. Sickle Cell Anemia (SCA) is characterized by increased K-Cl cotransport (KCC) activity and self-generated free radicals. The aim of study was to investigate the effect of TMZ on KCC activity and free radicals in SCA patients. Material and Method: The blood samples were drawn by 20 patients with SCA. After the washing procedure the samples were encubated with TMZ for 20 min. Superoxide dismutase (SOD) and KCC activity were measured before and after incubation. Results and Conclusion: It was observed that treatment with TMZ for 20 min has a negative effect on SOD activity in linear relation with the doses used as 50, 100, 150, 200 mM, in vitro (respectively 2494.95±102.73, 2253±99.51, 1497.25±111.14 U/g Hb). However; TMZ had no effect on neither volume dependent nor chloride dependent KCC activity. In conclusion further in vivo studies with TMZ should be conducted

The effect of antiepileptic drugs on vitamin B12 metabolism

PubMedID: 18190464The effects of antiepileptic drugs (AED) on the serum concentration of vitamin B12, folic acid and homocysteine (HMC), and erythrocyte folic acid levels were determined in 45 epileptic patients (30 women, 15 men; mean age 31.7 years) and 23 healthy volunteers (control group; 18 women, five men; mean age 33.4 years). All patients were either on carbamazepine (CMZ), oxcarbazepine (OXZ), or valporate (VP) monotherapy. Serum vitamin B12 levels were low in 17.8% of patients and 8.7% of the controls (P = 0.299). Serum homocysteine levels were high in 17.8% of the patients (P = 0.008). Fifty percent of the patients who had hyperhomocysteinemia, and 75% of the patients who had low serum vitamin B12 level were on CMZ monotherapy. Peripheral blood smears showed hypersegmented neutrophils and macrocytosis in 13.3%, hypochromia and microcytosis in 26.7%, acanthocytes in 2.2%, and thrombocytosis in 2.2% of all patients. The control group had normal peripheral blood smears, except in four cases that showed hypocromia and microcytosis. Long-term administration of AED may cause elevation of homocysteine and development of subnormal serum vitamin B12 levels. Peripheral blood smear abnormalities were frequently seen in patients receiving antiepileptic treatment (P = 0.022), particularly in patients on CMZ monotherapy (P = 0.281). However, homocysteine, vitamin B12, folic acid levels and peripheral blood smear findings did not correlate with the drugs used (P = 0.665, 0.336, 0.249 for CMZ, OXZ, VP, respectively). © 2007 The Authors

The unusually stable B \u3c inf\u3e 100 Fullerene, structural transitions in boron nanostructures, and a comparative study of α- and γ-boron and sheets

Solid α-B12 rhombohedral and γ-B28 orthorhombic boron as well as boron nanostructures in the form of spheres, sheets, and multirings beside a ring consisting of icosahedral B12 units were investigated using ab initio quantum chemical and density functional methods. The structure of the B100 fullerene exhibits unusual stability among all noninteracting free-standing clusters, and is more stable than the B120 cluster fragment of the γ-B28 solid, recently predicted and observed by Oganov et al. (Nature 2009, 457, 863). In addition, we compared the stability of the multirings and reported the structural transition from double-ring to triple-ring systems. This structural transition occurs between B52 and B54 clusters. We confirm that the noninteracting free-standing triangular buckled-sheet is more stable than the γ-sheet, assembled in this work, and than the α-sheet, proposed by Tang and Ismail-Beigi (Phys. Rev. Lett. 2007, 99, 115501). In contrast, however, when these sheets are considered as infinite periodic systems, then the α-sheet remains the most stable one.©2010 American Chemical Society.