The completable digraphs for the totally nonnegative completion problem

In this paper, we study the totally nonnegative completion problem when the partial totally nonnegative matrix is non-combinatorially symmetric. In general, this type of partial matrix does not have a totally nonnegative completion. Here, we give necessary and sufficient conditions for completion of a partial totally nonnegative matrix to a totally nonnegative matrix in the cases where the digraph of the off-diagonal specified entries takes certain forms as path, cycles, alternate paths, block graphs, etc., distinguishing between the monotonically and non-monotonically labeled case.     

Minimally k-Edge-Connected Directed Graphs of Maximal Size

Let D=(V,E) be a minimally k-edge-connected simple directed graph. We prove that there is a function f(k) such that |V|f(k) implies |E|2k(|V|–k). We also determine the extremal graphs whose size attains this upper bound.Basic Research in Computer Science, funded by the Danish National Research Foundation.Supported by the MTA-ELTE Egerváry Research Group on Combinatorial Optimization, and the Hungarian Scientific Research Fund grant No. F034930, T037547, and FKFP grant No. 0143/2001. Part of this research was done when the second author visited BRICS, University of Aarhus, Denmark.     

Self-immobilization of poly(methyloctylsiloxane) on high-performance liquid chromatographic silica

Poly(methyloctylsiloxane) (PMOS) was deposited on HPLC silica by a solvent evaporation procedure and this material was then extracted, using a good solvent for the PMOS, after different time periods, to remove unretained liquid polymer. Solvent extraction data reveal changes which occur at ambient temperature as a function of the time interval between particle loading and extraction. The quantity of PMOS remaining on the silica after extraction, as determined by elemental analysis for carbon, is attributed to strongly adsorbed polymer. This phenomenon is termed self-immobilization. Solid-state 29Si NMR spectra indicate the formation of a silicon species with a different chemical shift than the original PMOS. These new signals are attributed to a combination of different adsorbed and chemically bonded groups.     

Numerical stability analysis and control of umbilical–ROV systems in one-degree-of-freedom taut–slack condition

In this paper, the stability of an umbilical–ROV system under nonlinear oscillations in heave motion is analyzed using numerical methods for the uncontrolled and controlled cases comparatively. Mainly the appearance of the so-called taut–slack phenomenon on the umbilical cable produced by interactions of monochromatic waves and an operated ROV is specially focused. Nonlinear elements were considered as nonlinear drag damping, bilinear restoring force and saturation of the actuators. Free-of-taut/slack stability regions are investigated in a space of physical bifurcation parameters involving a set of both operation and design parameters. They indicate a wide diversity in qualitative behaviors, both in the periodicity and possible routes to chaos from the stability regions to outside. For detection of periodicity of the nonlinear oscillations inside and outside the stability regions, a method based on Cauchy series is developed. The first part of the results is dedicated to the stability of the uncontrolled dynamics. These results suggest the design of a control system that is able to counteract hefty hauls of the cable during the sinking/lifting operation under perturbation. A combination of a force and cinematic controller based on nonlinear model–reference control is proposed. Through a comparative study of the stability regions for uncontrolled and controlled dynamics, it is shown that the control system can extend considerably these regions without appearance of the taut–slack phenomenon despite the presence of wave perturbations. The limits between the taut and taut–slack zones are defined by the wave steepness and the available energy of the actuators.     

From Ynamides to Highly Substituted Benzo[b]furans: Gold(I)‐Catalyzed 5‐endo‐dig‐Cyclization/Rearrangement of Alkylic Oxonium Intermediates

A series of arylynamides with alkyloxy groups at the ortho position of the aryl group was prepared through a short alkylation/cross‐coupling/amidation sequence. The gold‐catalyzed conversion of these substrates combined both C? O and C? C formation steps, thus providing benzofurans with amine functionalities at the 2‐position and alkyl groups at the 3‐position. Cross‐over experiments showed that the alkyl‐migration step was an intermolecular process. X‐ray crystal‐structure analysis of two of the products supported our structural assignment. In some cases, the corresponding benzofurans without the alkyl group at the 3‐position were obtained as side‐products, which were formed through a competing protodeauration process.     

催化:古老却富有挑战性的石墨烯基材料(英文)

An assessment is offered regarding the progress made, and the remaining challenges, in the field of carbocatalysis. The fundamental principles that govern the preparation and performance of sp2-hybridized carbon materials in heterogeneous catalysis have been known for decades, and the level of understanding of key issues – especially the importance of textural and ion-exchange properties (i.e., surface area, pore size distribution, and proton transfer) – remains quite satisfactory. The opportunities for novel catalytic materials – especially graphene nanosheets and carbon nanotubes– are tremendous, especially when it comes to taking advantage of their structural order, such that electron transfer can be both better understood and controlled to enhance catalytic activity and selectivity.