A note on the value function for constrained control problems

We consider the Mayer optimal control problem with dynamics given by a nonconvex differential inclusion, whose trajectories are constrained to a given set and we obtain a relation between the costate function that appears in the maximum principle and the value function. This relation extends the known conditions existing in the literature for unconstrained problems to those for problems under state constraints.     

Ba(Ti1−xSnx)O3 (x=0.13) Dielectric Ceramics Prepared by Coprecipitation

Fine-grain BaTi_0.87Sn_0.13O₃ (BTS₁₃) powder was synthesized from an oxalate precursor and used to prepare sintered ferroelectric BTS₁₃ ceramics. The evolution of the morphology and structure of a BTS₁₃ precipitate precursor as a function of temperature was analyzed. We compare the sintering behavior as well as the dielectric properties of the BTS₁₃ ceramics obtained using uniaxial and cold isostatic pressing.     

The surgical approach to invasive orbital tumors

The orbital exenteration is less and less practiced today, because of the reduced pathology which may impose such a radical intervention, but also because it has been transferred, in the lest two decades, to the maxillofacial plastic surgery. The paper presents three orbital exenterations, accomplished in the spinous-cell carcinoma of the inferior eye lid invading in the orbit, basal-cell epithelioma of internal angle recidivated during repeated interventions and conjunctival malignant melanoma invading the orbit. It is shown that orbital exenteration must not to abandoned by the ophthalmologists, which are the first doctors contracted by these patients and the only ones which can decide when the ocular globe may be sacrificed, with a recovery of the region as aesthetic as can be.     

Dielectric Ba(Ti1?xSnx)O3 (x?=?0.13) ceramics, sintered by spark plasma and conventional methods

A two-step sintering approach composed of spark-plasma-sintering (SPS) technique at 1000 °C for 1 min and under a uniaxial pressure of 63 MPa followed by conventional sintering at 1400 °C for 3 h is proposed for synthesis of dense Ba(Ti_0.87Sn_0.13)O₃ ceramics. Starting powders had grain size of about 90 nm and were obtained by co-precipitation. The SPS pellets consist of submicron (300–500 nm) grains. X-ray diffraction analysis of as-prepared Ba(Ti_0.87Sn_0.13)O₃ ceramic shows the occurrence of cubic and tetragonal phase coexistence for the pellets obtained after SPS processing and the presence of only tetragonal phase in the samples after the second (conventional) sintering. Grain uniformity in the final product is high, with average size of ~2 μm. The apparent densities of the sintered pellets at temperature of 1400 °C were ~92% of the theoretical value of Ba(Ti_0.87Sn_0.13)O₃. The ceramics exhibit a high relative dielectric constant of 6,550 and a dielectric loss (tan δ) = 0.078 at Curie temperature of 63 °C and 10 Hz.     

La2O3-doped BaTiO3 thin films obtained by pulsed laser deposition

Abstract

La²O³-doped barium titanate (BaTiO³) thin films have been obtained by pulsed laser deposition. The structure and quality of deposited films were characterized by X-ray diffraction and scanning electron microscopy. A smooth surface was obtained when the films were deposited in 30 Pa ambient oxygen. The composition (elements and oxides) of the thin films were close to those of the target. The layer obtained by pulsed laser deposition from a target of BaTiO³ doped with 0.5 at.% La exhibits good dielectric characteristics: capacitance 88 pF, Curie temperature 59°C and dielectrics loss, tanδ, 0.084.     

Preparation by sol–gel and solid state reaction methods and properties investigation of double perovskite Sr2FeMoO6

Double perovskite Sr₂FeMoO₆ was prepared by two ways consisting in sol–gel technique and solid-state reaction method. The resulting powders from gel and mixed oxides precursors showed microstructures consisting of very fine grains (0.5–0.8 μm) and a crystalline perovskite structure. The structural and microstructural properties of the double perovskite Sr₂FeMoO₆ powders as-prepared and ceramics were compared. Tetragonal Sr₂FeMoO₆ pellets were prepared from the two powders by spark plasma sintering at: 1000, 1100 and 1200 °C and then annealing at 1200 °C, 2 h in 5%H₂/Ar. The pellets presented different magnetic characteristics. The saturation magnetization of the samples prepared by sol–gel is close to those prepared by conventional synthesis method.     

Scalable Joint Source and Channel Coding of Meshes

This paper proposes a new approach for joint source and channel coding (JSCC) of meshes, simultaneously providing scalability and optimized resilience against transmission errors. An unequal error protection approach is followed, to cope with the different error-sensitivity levels characterizing the various resolution and quality layers produced by the input scalable source codec. The number of layers and the protection levels to be employed for each layer are determined by solving a joint source and channel coding problem. In this context, a novel fast algorithm for solving the optimization problem is conceived, enabling a real-time implementation of the JSCC rate-allocation. An instantiation of the proposed JSCC approach is demonstrated for MeshGrid, which is a scalable 3-D object representation method, part of MPEG-4 AFX. In this context, the L-inflnite distortion metric is employed, which is to our knowledge a unique feature in mesh coding. Numerical results show the superiority of the L-inflnite norm over the classical L-2 norm in a JSCC setting. One concludes that the proposed joint source and channel coding approach offers resilience against transmission errors, provides graceful degradation, enables a fast real-time implementation, and preserves all the scalability features and animation capabilities of the employed scalable mesh codec.     

Preparation and characterization of Ce-doped BaTiO3 thin films by r.f. sputtering

Ce-doped BaTiO₃ thin films prepared on silicon-platinium by r.f. sputtering has been investigated. BaTiO₃ doped with 5.5 mol%CeO₂ thin film was deposited at 550°C substrate temperature in an Ar atmosfere. The crystal structure and shape were examined by X-ray diffraction and scanning electron microscopy with EDAX. Analysis by X-ray diffraction patterns show that the crystalline film with a cubic structure of BaTiO₃, was obtained. The surface morphology (roughness, the grain size and the droplet size) of the thin film surface was examined by atomic force microscopy (AFM). The grain size is about 160 nm, the droplet size is about 0.675 m and the roughness is 36.88 nm. EDAX analysis established a composition of the film to be identical with that of the target (BaTiO₃ doped with 5.5 mol%CeO₂). The broad peak in the capacitance versus temperature curve at the Curie point indicate that the r.f. sputtered Ce-doped BaTiO₃ film is ferroelectric. The values of the capacitance of the thin film at 1 KHz were found to be 86 pF and the loss dielectric was tan = 0.0875. The film exibits a dielectric anomaly peak at 23°C showing ferroelectric to paraelectric phase transition.     

Piezoelectric BNT-BT<Subscript>0.11</Subscript> thin films processed by sol–gel technique

0.89(Na_0.5Bi_0.5)TiO₃–0.11BaTiO₃, (BNT-BT_0.11) thin film was fabricated by sol–gel/spin coating process, on platinized silicon wafer. Perovskite structure with random orientation of crystallites has been obtained at 700 °C. Piezoelectric activity of BNT-BT_0.11 thin film was detected using piezoresponse force microscopy (PFM). Effective piezoelectric coefficient d _33eff of such film, recorded at 5 V applied dc voltage, was ~29 pm/V, which is similar to other BNT-BT _x thin films. The complex refractive index and dielectric function of BNT-BT_0.11 thin films were also investigated. The high leakage current density significantly influences the dielectric, ferroelectric, and piezoelectric properties of the BNT-BT_0.11 films.     

Characterization of fine grain Ba0.995Y0.005TiO3 ceramics obtained from gel-precursor nanopowder

Using an acetate-alkoxide sol-gel route in which the precursors are barium acetate, yttrium isopropoxide and titanium diisopropoxide bis-acetylacetonate, we prepared a ferroelectric material with the formula: Ba1-xYxTiO3, x = 0.005. SEM analysis showed a polymeric microstructure of the gel due to the chelated titanium alkoxide precursor used as starting materials. The evolution of the structure and microstructure of the precursor gel heated at temperatures up to 1000 degrees C was studied by various techniques. The powder obtained by heating the gel at 1100 degrees C presented a homogeneous structure consisting of submicronic particles (approximately 200 nm). XRD and SAED analyses revealed that Ba0.995Y0.005TiO3 nanocrystals of about 5-10 nm appeared at 600 degrees C, together with BaCO3. The presence of barium carbonate was identified also by IR spectroscopy and thermal analyses. The ceramics obtained from the as-prepared powder presented good dielectric properties (capacitance = 840 pF/dielectric constant = 3860 and dielectric loss (tandelta) = 0.078 at Curie temperatures of 120-121 degrees C).