A 15-GHz monolithic two-modulus prescaler

A high-speed two-modulus prescaler for divide-by-4/5 select was successfully realized adopting a new circuit design that reduces the effective fan-out of each D-flip-flop (D-FF) to one. To assure stable and high-speed operation, a low-voltage signal amplitude of 250 mV in the D-FF was adopted for both true-and-complementary and single-phase signals. Using a 70-GHz-f_T GaAs/AlGaAs HBT technology, the D-FF operated stably up to 18.6 Gb/s at designed bias voltages of 9 V with power dissipation of 0.55 W, and the prescaler operated up to 15.5 GHz with power dissipation of 1.5 W     

Analysis of discontinuities in a grounded slab waveguide by combination of finite-element and boundary-element methods

A combined approach of the finite-element and boundary-element methods is formulated for the analysis of arbitrarily shaped discontinuities in a grounded slab waveguide. In this approach, the discontinuity region is divided into two regions. One is a finite region with arbitrary inhomogeneities; the other is a semi-infinite and homogeneous region. The finite-element and the boundary-element methods are applied to the former and the latter regions, respectively, Also, analytical solutions in which both the guided and the radiation modes are taken into account are used for uniform waveguide regions connected to the discontinuity region. To show the validity and usefulness of this approach, computed results are given for several kinds of discontinuities, and some of them are compared with theoretical results previously published. © 1992 John Wiley & Sons, Inc.     

Properties of rapidly deposited amorphous hydrogenated carbon films

The properties of hydrogenated amorphous carbon films prepared by the rapid and low-temperature decomposition of toluene in an r.f. glow discharge have been investigated. The films are composed of a mixture of sp² and sp³ bonded carbons. Measurements of the optical gap show that the optical gap decreases with an increase of the r.f. power and increases with increasing pressure. The room-temperature dielectric constant decreases with increasing pressure with a dielectric loss tangent of 1%.     

Measurement and analysis of induced activities in concrete irradiated using high-energy neutrons at KENS Neutron Spallation Source Facility

Precise estimation of induced activities in concrete shields for high-energy accelerator facilities is one of the most important issues that need to be solved, not only for the reduction of exposure for workers, but also for the reduction of radioactive wastes. Irradiation experiments have been performed by using the 500 MeV Neutron Spallation Source Facility in KEK. The large concrete assembly was placed in the direction of 0 degrees to the beamline. Two kinds of samples were placed at several positions in the assembly. The irradiation period was about 1 week and induced activities in the samples were measured until approximately 1.5 y after irradiation. From the comparison between the experiment and the available Monte Carlo calculation code system, good agreement was obtained for 24Na, 47Sc, 47Ca and 54Mn within a factor 2; however, large discrepancies were observed for some other nuclides.     

Atom inlays performed at room temperature using atomic force microscopy

The ability to manipulate single atoms and molecules laterally for creating artificial structures on surfaces is driving us closer to the ultimate limit of two-dimensional nanoengineering. However, experiments involving this level of manipulation have been performed only at cryogenic temperatures. Scanning tunnelling microscopy has proved, so far, to be a unique tool with all the necessary capabilities for laterally pushing, pulling or sliding single atoms and molecules, and arranging them on a surface at will. Here we demonstrate, for the first time, that it is possible to perform well-controlled lateral manipulations of single atoms using near-contact atomic force microscopy even at room temperature. We report the creation of 'atom inlays', that is, artificial atomic patterns formed from a few embedded atoms in the plane of a surface. At room temperature, such atomic structures remain stable on the surface for relatively long periods of time.     

A new method for preparing plan-view TEM specimen of multilayered films using focused ion beam

A new method is proposed for preparing plan-view specimens of a CeO(2)/Gd(2)Zr(2)O(7) multilayer on a metal substrate using focused ion beam milling. In the plan-view specimen, a membrane from the surface region of the CeO(2) to the Gd(2)Zr(2)O(7) layer was thinned to electron transparence so that the entire span of the multilayer can be observed in a single sample. The in-plane alignments of the CeO(2) layer and the Gd(2)Zr(2)O(7) layer were analysed using selected-area diffraction patterns (SADPs). The boundaries between the CeO(2) grains were also examined using SADPs.     

Improvement of thermal stability of Streptomyces cholesterol oxidase by random mutagenesis and a structural interpretation

Random mutagenesis was used to enhance the thermal stability of Streptomyces cholesterol oxidase. Four thermostable mutants were isolated and the following amino acid substitutions were identified: Ser103 to Thr (mutant S103T), Val121 to Ala (mutant V121A), Arg135 to His (mutant R135H) and Val145 to Glu (mutant V145E). The wild-type and mutant enzymes were purified and characterized. The properties of mutants S103T, V121A and R135H were similar to those of the wild type but they showed improved thermal stability. When the V145E mutation was introduced, the thermal stability of the enzyme was markedly increased and the optimum pH was desirably changed to encompass a broad range from acid to alkali. Analysis of multiple mutants constructed by site- directed mutagenesis showed that all the mutations except that of R135H had an additive influence on the other mutations. These mutational effects are discussed in terms of a three-dimensional structural model of the enzyme constructed on the basis of homology modelling.      

Systemic atherosclerosis in dogs: histopathological and immunohistochemical studies of atherosclerotic lesions

Cytosolic phospholipase A2 (cPLA2) catalyzes the selective release of arachidonic acid from the sn-2 position of phospholipids and is believed to play a key cellular role in the generation of arachidonic acid. When assaying the human recombinant cPLA2 using membranes isolated from [3H]arachidonate-labeled U937 cells as substrate, 3,3-Dimethyl-6-(3-lauroylureido)-7-oxo-4-thia-1-azabicyclo[3,2,0] heptane-2-carboxylic acid (1) was found to inhibit the enzyme in a dose-dependent manner (IC50 = 72 microM). This beta-lactam did not inhibit other phospholipases, including the human nonpancreatic secreted phospholipase A2. The inhibition of cPLA2 was found not to be time-dependent. This, along with the observation that the degradation of the inhibitor was not catalyzed by the enzyme, demonstrates that the inhibition does not result from the formation of an acyl-enzyme intermediate with the active site serine residue. Moreover, the ring-opened form of 1 is also able to inhibit cPLA2 with near-equal potency. To further characterize the mechanism of inhibition, an assay in which the enzyme is bound to vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphomethanol containing 6-10 mole percent of 1-palmitoyl-2-[1-14C]-arachidonoyl-sn-glycero-3-phosphocholine was employed. With this substrate system, the dose-dependent inhibition was defined by kinetic equations describing competitive inhibition at the lipid/water interface. The apparent dissociation constant for the inhibitor bound to the enzyme at the interface (KI*app) was determined to be 0.5 +/- 0.1 mole% versus an apparent dissociation constant for the arachidonate-containing phospholipid of 0.4 +/- 0.1 mole%. Thus, 1 represents a novel structural class of inhibitors of cPLA2 which partitions into the phospholipid bilayer and competes with the phospholipid substrate for the active site.     

Optimization of growth of peptide chain by ribosomes on messenger RNA

To elucidate the integrated functional properties and organization strategy of the peptide elongation process of ribosomes on messenger RNA, we took a theoretical approach by applying a linear system analysis and optimal hypothesis. The basic theoretical model published by Gerst in 1965 was founded on reported experimental data. We have simplified the mechanism of the peptide elongation process by making the following assumptions. (1) When the left-most site (the 5′ terminal) on the messenger RNA is empty, the newly arrived amino-acyl-transfer-RNA (AT) links to the 5′ terminal even though other sites are empty. (2) When all other sites on the ribosomes except the 5′ terminal are empty and the first ribosome is not yet filled, ATs which arrive subsequently continue to bind to the 5′ terminal site of the first ribosome until the first ribosome has been filled. (3) When a given ribosome has been filled by an amount of product equivalent to the product ofp (amino acid residues) andq ribosomes, the filled ribosome advances to the next ribosomal region (q+1). There, the amino acid attainspq+1. After this transition, theqth ribosomal region becomes empty. (4) When the sites on the ribosomes are not all filled, newly arrived AT binds from the right of the total sequence. By applying the mass action law, the elongation process was expressed by 23 rate equations. The rate constants for the binding ribosome, turn over, peptide bond formation and transitional movement of ribosomes were utilized from reported experimental data. The optimal state was defined when the square of the concentration of all the transitional states and control input were minimized. This means that the elongation process is in the most economical state when there are no excessive changes at any steps of the elongation process and the least energy consumption. Linear system analysis showed that system was stable and controllable. The singular value was depressed by system optimization. The impulse response terminated earlier by a smaller peak amplitude in the optimized system than in those without optimization. The present model under optimal control is available to evaluate the functions of peptide synthesis on a messenger RNA, and to produce artificial protein from the standpoint of system optimization.