Steep central islands after myopic photorefractive keratectomy

The nitric oxide synthase inhibitor 7-nitroindazole (7-NI) dose-dependently (3.0-30.0 mg/kg) displayed anxiolytic activity, as measured by an increase in open arm exploration time in the elevated plus-maze (EPM), following intraperitoneal (i.p.) administration in rats. Acute administration of 7-NI at 30.0 mg/kg significantly (P < 0.05) increased open arm exploration time by 176% compared to vehicle control, similar to the benzodiazepine diazepam at 1.0 and 3.0 mg/kg (+ 191 and + 200%, respectively). However, 39 h following subchronic 5-day administration of diazepam twice daily (bid) at 3.0 mg/kg, diazepam was devoid of anxiolytic activity at 1.0 mg/kg, as measured by no difference in open arm exploration time compared to vehicle control, while the 3.0 mg/kg dose still produced a significant (P < 0.05) 175% increase in open arm exploration time. In contrast, following subchronic administration of 7-NI (30.0 mg/kg, bid), a significant (P < 0.01) enhancement in open arm exploration time was observed at 30.0 mg/kg (+ 665% compared to control). Therefore, inhibition of nitric oxide synthase by 7-NI resulted in anxiolysis similar to diazepam following acute administration in the EPM. However, following subchronic administration, unlike diazepam which showed an attenuation of anxiolytic activity, 7-NI displayed enhanced anxiolytic efficacy and was devoid of tolerance.     

Influence of CAD-CAM milling on the flexural strength of Y-TZP dental ceramics

In this work, the influence of milling strategy and cutter wear on the flexural strength of sintered Y-TZP ceramics machined in a CAD-CAM system, was investigated. Pre-sintered Y-TZP blocks were machined with tungsten carbide (WC) milling cutters and divided into three groups: a) samples machined with New Cutting Tools (NCT); b) samples machined with End-of-life cutting tools (ELCT); and c) samples machined and subsequently polished. The samples were machined parallel and perpendicularly to the diameter of pre-sintered Y-TZP blocks aiming to evaluate the effect of the machining orientation on roughness. After cutting, the specimens were sintered at 1530?°C for 2?h and characterized. After sintering, dense Y-TZP samples presenting grain size average of 0.81?±?0.23?μm, hardness of 1205?±?12 HV, K_C of 7.7?±?0.4 MPam^1/2 and flexural strength of 1207?±?199?MPa were obtained. Furthermore, the control roughness (polished surfaces) presented R_a?=?0.058?±?0.011?μm. The surface roughness of the samples was influenced by the machining methodology using NCT mills, with R_a?=?0.386?±?0.149?μm and R_a?=?0.292?±?0.105?μm for samples machined parallel and perpendicularly to the pre-sintered Y-TZP blocks, respectively. The use of ELCT led to a roughness increasing (R_a?=?0.582?±?0.183?μm for samples milled perpendicularly, and R_a?=?0.919?±?0.164?μm for samples cut parallel to the pre-sintered blocks. The flexural strength of the sintered Y-TZP decreases with use of ELCT as consequence of surface roughness increasing, resulting from wear of WC mills, which presented chippings with sizes ranging from 30 to 340?μm in the cutting edge.     

Synthesis, mesomorphic properties and light scattering of polyacrylates liquid crystals

Summary The synthesis and phase behavior of three homopolymers with liquid crystalline side-chains is described. These new homopolymers show a dependence of the phase transition temperatures on the molecular weight. The synthesized material exhibits typical mesomorphism-nematic, smectic A and C. We compare the mesomorphic behavior of the homopolymers of the different liquid crystals polyacrylates. In addition, a dynamic and static light scattering study in different solvents has been undertaken. The hydrodynamic radius as well as the diffusion coefficient of the single polymer molecules could be determined. Moreover, the experimental results suggest the formation of aggregates or clusters in the THF dilute regime. Received: 29 November 1998/Revised version: 2 April 1999/Accepted: 5 April 1999     

Optimal meter placement for maintaining observability during singlebranch outages

This paper presents a method for designing measurement systems, that will not only make the systems observable, but also will maintain observability against loss of network branches. A linear programming based solution is proposed for choosing a measurement configuration that will make the system fully observable. Subsequently, a systematic method of appending a minimum number of additional measurements to ensure full observability against branch outages, is described. Contingencies considered in this paper relate to the loss of any single branch. However, the method can be extended to the case of multiple contingencies, provided the cost of adding more meters is financially justifiable. Numerical examples illustrating the proposed method, are given in the paper     

A unified approach to robust meter placement against loss ofmeasurements and branch outages

This paper presents a systematic procedure by which measurement systems can be optimally upgraded. The proposed procedure yields a measurement configuration that can withstand any single branch outage or loss of single measurement, without losing network observability. It is a numerical method based on the measurement Jacobian and sparse triangular factorization, making its implementation easy in existing state estimators. It can be used off-line in planning and meter placement studies or it can be implemented as part of the on-line observability analysis function. Details of the procedure are presented using numerical examples     

Elimination of leverage measurements via matrix stretching

Some of the measurements of a power system may have a much stronger influence on the state estimate than others due to their location, the local measurement redundancy, the network topology, and parameters. Such measurements, referred to as leverage measurements, will distort the solution of the least absolute value estimation, when they carry bad data. This paper presents a matrix stretching method by which leveraging effects of injection measurements can be eliminated. Simulation results are included to show the effectiveness of the method on typical power systems.