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  • Induction plasma  (2)
  • Complexity  (1)
  • CoupledWell MODFET  (1)
  • Erwinia herbicola  (1)
  • Springer  (5)
  • Wiley-Blackwell
  • BMJ Publishing
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  • Springer  (5)
  • Wiley-Blackwell
  • BMJ Publishing
Years
  • 1
    ISSN: 1572-9559
    Keywords: Submillimeter MODFET ; Quantum Wire MODFET ; InGaAs MODFET ; CoupledWell MODFET
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A coupled-well InAlAs/InGaAs quantum wire MODFET structure is proposed, for which simulations predict improved frequency performance (〉500 GHz), over a wider range of Vg, as compared to well/wire devices with a standard MODFET heterointerface. A comparison of several transverse potential well profiles, obtained by varying the placement of a thin barrier within a 100 Å finite well, is presented. In all cases, the quantum wires consist of a 0.1 μm long channel and a 150 Å finite-square-well lateral profile. It has been found that the peak of the electron distribution for the first confined state, as measured from the heterointerface, changes dramatically depending on the location of the thin barrier. For quantum wire structures, realized in the lattice matched system of In0.52Al0.48As/In0.53Ga0.47As/InP, a change in the barrier location of 25 Å is accompanied by a shift in the carrier peak of more than 40 Å (~20 Å closer to or farther from the spacer-well interface than in the standard MODFET profile). Implications of this are reflected in the current-voltage characteristics (Id-Vd) and frequency responses (fT-Vg) of the proposed structures.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-8986
    Keywords: Induction plasma ; modeling ; chemical equilibrium ; silicon nitride synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A mathematical model is presented for the numerical simulation of the flow, temperature, and concentration fields in an rf plasma chemical reactor. The simulation is performed assuming chemical equilibrium. The extent of validity of this assumption is discussed. The system considered is the reaction of SiCl4 and NH3 for the production of Si3N4.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-8986
    Keywords: Induction plasma ; modeling ; chemical kinetics ; dissociation of silicon tetrachloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A kinetic model has been developed for the prediction of the concentration gelds in an rf plasma reactor. A sample calculation for a SiCl4/H2 system is then performed. The model considers the mixing processes along with the kinetics of seven reactions involving the decomposition of these reactants. The results obtained are compared to those assuming chemical equilibrium. The predictions indicate that an equilibrium assumption will result in lower predicted temperature fields in the reactor. Furthermore, for the chemical system considered here, while differences exist between the concentration fields obtained by the two models, the differences are not substantial.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1432
    Keywords: phe operon ; tyr operon ; Attenuation ; Secondary structure ; Nucleotide sequence ; Erwinia herbicola ; Chorismate mutase ; Prephenate dehydatase ; Prephenate dehydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Extensive knowledge exists inEscherichia coli about the contiguouspheA andaroF-tyrA operons which have opposite transcription orientations and are separated by a bidirectional transcription terminator. The corresponding structural genes and individual components of the terminator and attenuator fromErwinia herbicola have been analyzed from an evolutionary vantage point. A 7.5-kb DNA fragment fromE. herbicola carrying the linkedpheA, tyrA, andaroF genes was cloned by functional complementation ofE. coli auxotrophic requirements. A 3,433-bp segment of DNA consisting of more than half ofaroF, all oftyrA, and the entire phenylalanine operon (promoter, leader region encoding the leader peptide and containing thephe attenuator, andpheA) was sequenced. A bidirectional transcription terminator was positioned between the divergently transcribedpheA andtyrA. The adjacentaroF andtyrA genes share a common transcription orientation, consistent with their probable coexistence within an operon. However,tyrA can be expressed efficiently from an internal promoter which appears to lie within the 3′ portion ofaroF. The gene order ispheA tyrA aroF inE. herbicola, with the same tail-to-tail arrangement of transcription known to exist inE. coli. ThepheL coding region of the phe operon was dominated by phenylalanine codons, seven of the 15 amino acid residues of the leader peptide beingl-phenylalanine. TheE. herbicola pheA andtyrA genes were 1,161 by and 1,119 by in length, respectively, and corresponded to deduced gene products having subunit molecular weights of 43,182 and 41,847. The deduced amino acid sequences ofPheA andTyrA were homologous at their N-termini, consistent with a common evolutionary origin of the chorismate mutase domains present at the amino terminus of bothPheA andTyrA. A detailed comparison of theE. coli andE. herbicola sequences was made. ThepheA, tyrA, andaroF genes ofE. herbicola exhibited high overall identity with the counterpartE. coli genes. Within the leader region of thephe operon, the leader peptide coding region was highly conserved. Although the 1:2 and 2′:3′ stems defining the pause structure and the antiterminator, respectively, were also highly conserved, RNA segment 4 of the attenuator terminator exhibited considerable divergence, as did the distal portion of the attenuator region. Within the span of attenuator region encoding the three stern-loop structures of mRNA secondary configuration, hot spots of base-residue divergence were localized to looped-out regions. No changes occurred which would simultaneously disrupt alternative pairing relationships of secondary configuration. The bidirectional terminator betweenpheA andtyrA has diverged very substantially. Much of the promoter region and the untranslated region between the promoter and thepheL coding region also differed considerably between the two organisms.
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  • 5
    ISSN: 1432-0606
    Keywords: Complexity ; Estimates by integrals ; Analytic centers ; Path-following method ; Interior-point method ; Linear programs ; 90C60 ; 90C05 ; 49M35 ; 68Q25
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we study a particular class of primal-dual path-following methods which try to follow a trajectory of interior feasible solutions in primal-dual space toward an optimal solution to the primal and dual problem. The methods investigated are so-called first-order methods: each iteration consists of a “long” step along the tangent of the trajectory, followed by explicit recentering steps to get close to the trajectory again. It is shown that the complexity of these methods, which can be measured by the number of points close to the trajectory which have to be computed in order to achieve a desired gain in accuracy, is bounded by an integral along the trajectory. The integrand is a suitably weighted measure of the second derivative of the trajectory with respect to a distinguished path parameter, so the integral may be loosely called a curvature integral.
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