Finite element modeling on the effect of intra-granular porosity on the dielectric properties of BaTiO 3 MLCCs

The effect of porosity on the electrical properties of BaTiO3-based MultilayerCeramic Capacitors (MLCCs) is studied. A dense ceramic prepared via powderfrom a solid-state processing route is compared against a ceramic that containsintra-granular pores from powder prepared via hydrothermal processing. Finiteelement models are created to contain intra-granular pores, solved and analyzed toshow an increase in the electric field and current density surrounding the pores.For single-pore and two intra-pore arrangements, the electric field is enhanced bya factor of~1.5 and 2.5, respectively, when compared to a fully dense (pore-free)material. For ceramics with equivalent density, the number of pores dramaticallyalters the electrical response. For a system containing 100 pores, the electric fieldcan increase at least fourfold, therefore facilitating a possible starting route forelectrical breakdown of the grain. These results are compared to the Gerson-Mar-shall model, typically used in the literature for the calculation of the breakdownstrength due to porosity. The results highlight the need to include the effect ofadjacent pore interactions. Although studied here for BaTiO3-based MLCC’s theresults are applicable to other devices based on ceramics containing porosity

Utilizing UV and Visible Sensors on Micro Satellites to Demonstrate Target Acquisition and Tracking

The Distributed Sensing Experiment (DSE) program is a technology demonstration of target acquisition, tracking, and three-dimensional track development using a constellation of three micro satellites. DSE will demonstrate how micro satellites, working singly and as a group, can observe test-missile boost and ballistic-flight events. The overarching program objective is to demonstrate a means of fusing measurements from multiple sensors into a composite track. To perform this demonstration, each DSE micro satellite will acquire and track a target, determine a two-dimensional direction and movement rate for each, communicate observations to other DSE satellites, determine a three-dimensional target position and velocity, and relay this information to ground systems. A key design parameter of the program is incorporating commercial off-the-shelf (COTS) hardware and software to reduce risk and control costs, while maintaining performance. Having completed a successful Critical Design Review, the program is currently in fabrication, integration, and test phase. The constellation of satellites is scheduled for launch in CY2009. This paper describes the status and capabilities of the UV and visible sensor payloads, as well as the algorithms and software being developed to achieve the DSE mission

ORS Responsive Manufacturing 6U Spacecraft

The Operationally Responsive Space Office is developing a small satellite capability and small satellite design specifically for advanced manufacturing and assembly methods for a semi-automated assembly and test facility. Designing a small satellite to be assembled and tested with this novel and innovative approach enables reduced costs, schedule, and risk. This presentation will discuss the implementation, unique design features, lessons learned, and challenges associated with developing for this new rapid-assembly capability as well as the unique benefits and challenges of assembly and test using automated, robotic systems. The presentation will also include discussions of the role that design-for-manufacturing, modular open system architecture, componentized subsystems, and standardized interfaces each play in developing the spacecraft. Assembly processes, ground support interfaces, and other assembly, integration and test needs will also be discussed

The Density Matrix Renormalization Group for finite Fermi systems

The Density Matrix Renormalization Group (DMRG) was introduced by Steven White in 1992 as a method for accurately describing the properties of one-dimensional quantum lattices. The method, as originally introduced, was based on the iterative inclusion of sites on a real-space lattice. Based on its enormous success in that domain, it was subsequently proposed that the DMRG could be modified for use on finite Fermi systems, through the replacement of real-space lattice sites by an appropriately ordered set of single-particle levels. Since then, there has been an enormous amount of work on the subject, ranging from efforts to clarify the optimal means of implementing the algorithm to extensive applications in a variety of fields. In this article, we review these recent developments. Following a description of the real-space DMRG method, we discuss the key steps that were undertaken to modify it for use on finite Fermi systems and then describe its applications to Quantum Chemistry, ultrasmall superconducting grains, finite nuclei and two-dimensional electron systems. We also describe a recent development which permits symmetries to be taken into account consistently throughout the DMRG algorithm. We close with an outlook for future applications of the method.Comment: 48 pages, 17 figures Corrections made to equation 19 and table

RBCS1A and RBCS3B, two major members within the Arabidopsis RBCS multigene family, function to yield sufficient Rubisco content for leaf photosynthetic capacity

Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit (RBCS) is encoded by a nuclear RBCS multigene family in many plant species. The contribution of the RBCS multigenes to accumulation of Rubisco holoenzyme and photosynthetic characteristics remains unclear. T-DNA insertion mutants of RBCS1A (rbcs1a-1) and RBCS3B (rbcs3b-1) were isolated among the four Arabidopsis RBCS genes, and a double mutant (rbcs1a3b-1) was generated. RBCS1A mRNA was not detected in rbcs1a-1 and rbcs1a3b-1, while the RBCS3B mRNA level was suppressed to ∼20% of the wild-type level in rbcs3b-1 and rbcs1a3b-1 leaves. As a result, total RBCS mRNA levels declined to 52, 79, and 23% of the wild-type level in rbcs1a-1, rbcs3b-1, and rbcs1a3b-1, respectively. Rubisco contents showed declines similar to total RBCS mRNA levels, and the ratio of Rubisco-nitrogen to total nitrogen was 62, 78, and 40% of the wild-type level in rbcs1a-1, rbcs3b-1, and rbcs1a3b-1, respectively. The effects of RBCS1A and RBCS3B mutations in rbcs1a3b-1 were clearly additive. The rates of CO2 assimilation at ambient CO2 of 40 Pa were reduced with decreased Rubisco contents in the respective mutant leaves. Although the RBCS composition in the Rubisco holoenzyme changed, the CO2 assimilation rates per unit of Rubisco content were the same irrespective of the genotype. These results clearly indicate that RBCS1A and RBCS3B contribute to accumulation of Rubisco in Arabidopsis leaves and that these genes work additively to yield sufficient Rubisco for photosynthetic capacity. It is also suggested that the RBCS composition in the Rubisco holoenzyme does not affect photosynthesis under the present ambient [CO2] conditions

Organization of chromosome ends in the rice blast fungus, Magnaporthe oryzae

Eukaryotic pathogens of humans often evade the immune system by switching the expression of surface proteins encoded by subtelomeric gene families. To determine if plant pathogenic fungi use a similar mechanism to avoid host defenses, we sequenced the 14 chromosome ends of the rice blast pathogen, Magnaporthe oryzae. One telomere is directly joined to ribosomal RNA-encoding genes, at the end of the ∼2 Mb rDNA array. Two are attached to chromosome-unique sequences, and the remainder adjoin a distinct subtelomere region, consisting of a telomere-linked RecQ-helicase (TLH) gene flanked by several blocks of tandem repeats. Unlike other microbes, M.oryzae exhibits very little gene amplification in the subtelomere regions—out of 261 predicted genes found within 100 kb of the telomeres, only four were present at more than one chromosome end. Therefore, it seems unlikely that M.oryzae uses switching mechanisms to evade host defenses. Instead, the M.oryzae telomeres have undergone frequent terminal truncation, and there is evidence of extensive ectopic recombination among transposons in these regions. We propose that the M.oryzae chromosome termini play more subtle roles in host adaptation by promoting the loss of terminally-positioned genes that tend to trigger host defenses

Open Ceramics

The thermal stability, elemental/phase composition evolution and crystallization behaviour of Si–B–C–N ceramics obtained by the pyrolysis of a series of poly (vinylmethyl-co-methyl)silazanes displaying various boron contents were investigated through annealing in the temperature range 1000–1800 ​°C under nitrogen atmosphere. The increase of the boron content in the early stage of the process involved the nucleation of β-SiC, inhibited the crystallization of α-Si3N4 and modified the activity of the sp2-hybridised carbon phase in the derived ceramics obtained at 1000 and 1400 ​°C. At 1800 °C, low boron content Si–B–C–N ceramics gradually evolved toward a major SiC phase mainly formed via the carbothermal reaction of amorphous Si3N4 whereas high boron content Si–B–C–N ceramics led to highly stable materials with a complex microstructure made of SiC, Si3N4 and a BN-rich B(C)N phase that inhibited the activity of sp2-hybridised carbon toward the carbothermal reaction of amorphous Si3N4 and significantly reduced the SiC crystallization process