Large Scale Linear Programs and Heuristics for the Design of Survivable Telecommunication Networks

We consider the problem of providing a minimum cost multi-service network subject to one link failure scenarios. We assume our network is fully meshed and demand is satisfied by using direct or two hop-paths. We provide a large scale linear programming formulation and propose and test two effective heuristics.     

On the Congruences of Some Combinatorial Numbers

In this paper, we apply Lucas' theorem to evaluate the congruences of several combinatorial numbers, including the central Delannoy numbers and a class of Apéry-like numbers, the numbers of noncrossing connected graphs, the numbers of total edges of all noncrossing connected graphs on n vertices, etc. One of these results verifies a conjecture given by Deutsch and Sagan recently. In the end, we use an automaton to explain the idea of our approach.     

电抗管调频电路中影响频偏之因素

在电抗管调频电路中,频偏与载波频率之比值,乃随调频器之诸变相常数,及振荡电路中L_f/C_f之比率而变更。本文即就两种基本调频电路,作理论之推引,得出两个基本方程式,表明其间之关系,并佐以实验之证明。     

A Traveling Wave Ion Mobility Spectrometry (TWIMS) Study of the Robo1-Heparan Sulfate Interaction

Roundabout 1 (Robo1) interacts with its receptor Slit to regulate axon guidance, axon branching, and dendritic development in the nervous system and to regulate morphogenesis and many cell functions in the nonneuronal tissues. This interaction is known to be critically regulated by heparan sulfate (HS). Previous studies suggest that HS is required to promote the binding of Robo1 to Slit to form the minimal signaling complex, but the molecular details and the structural requirements of HS for this interaction are still unclear. Here, we describe the application of traveling wave ion mobility spectrometry (TWIMS) to study the conformational details of the Robo1-HS interaction. The results suggest that Robo1 exists in two conformations that differ by their compactness and capability to interact with HS. The results also suggest that the highly flexible interdomain hinge region connecting the Ig1 and Ig2 domains of Robo1 plays an important functional role in promoting the Robo1-Slit interaction. Moreover, variations in the sulfation pattern and size of HS were found to affect its binding affinity and selectivity to interact with different conformations of Robo1. Both MS measurements and CIU experiments show that the Robo1-HS interaction requires the presence of a specific size and pattern of modification of HS. Furthermore, the effect of N-glycosylation on the conformation of Robo1 and its binding modes with HS is reported.

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Facile and efficient synthesis of 1-[2-(6,7-dimethyl-3,4-dihydronaphthalen-2-yl)ethyl]pyrrolidine hydrochloride

An efficient and facile procedure for the preparation of 1-[2-(6,7-dimethyl-3,4-dihydronaphthalen-2-yl)ethyl]pyrrolidine hydrochloride from 6,7-dimethyl-1,2,3,4-tetrahydronaphtalen-1-one in four steps is proposed. It includes one-step synthesis of 1-(6,7-dimethyl-1,2,3,4-tetrahydronaphthalen-2-yl)acetic acid as key intermediate and subsequent transformations of functional groups therein. Published in Russian in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 3, pp. 449–453. The text was submitted by the authors in English.     

Preparation and properties of amino-terminated anionic waterborne-polyurethane-silica hybrid materials through a sol-gel process in the absence of an external catalyst

A series of polymer-silica hybrid materials consisting of amino-terminated anionic waterborne-polyurethane (WPU) and inorganic silica particles have been prepared through a sol-gel process in the absence of an external catalyst. Typically, amino-terminated anionic WPU was first synthesized from polycaprolactone, dimethylol propionic acid, and 4,4′-methylenebis(cyclohexyl isocyanate) with specific molar ratios, followed by further reaction with triethylamine and triethylene tetramine to give as-prepared WPU. The WPU obtained was characterized by FTIR spectroscopy and gel permeation chromatography. Subsequently, a series of hybrid materials with different silica contents were prepared by performing sol-gel reactions with tetraethyl orthosilicate (TEOS) in an amino-terminated WPU matrix without the addition of an external catalyst. This was followed by examination by transmission electron microscopy and ²⁹Si solid-state NMR. The terminated primary amine groups attached to the as-prepared WPU chains functioned as an internal base catalyst for the sol-gel process of TEOS. The effect of composition on the thermal stability, mechanical strength, surface wettability, and optical clarity of the hybrid materials was evaluated by the thermogravimetric analysis, dynamic mechanical analysis, contact angle measurement, and UV-visible transmission spectroscopy, respectively.     

Synthesis, structure, and cation complexation of a novel crown ether porphyrin

A new porphyrin appended with four crown ether units at meso-positions via an acetylene bridge was synthesized and structurally characterized, and its complexation with a variety of metal and diammonium cations was investigated.     

Nafion/PTFE and zirconium phosphate modified Nafion/PTFE composite membranes for direct methanol fuel cells

We prepared Nafion/PTFE (NF) and zirconium phosphate (ZrP) hybridized Nafion/PTFE composite membranes (NF–ZrP). NF–ZrP composite membranes were prepared via two processes. One is impregnating sub-μm porous PTFE membrane directly in a Nafion/ZrOCl₂ solution (NF–Zr–d). The other is impregnating sub-μm porous PTFE membrane in a Nafion solution to prepare NF composite membrane, and then the NF membrane was impregnated in a ZrOCl₂ aqueous solution via in situ precipitation method (NF–Zr–I). The ZrOCl₂ inserted in NF composite membranes was then reacted with phosphoric acid to form ZrP and thus NF–ZrP–d and NF–ZrP–I composite membranes were obtained. The direct methanol fuel cell (DMFC) performances of membrane electrode assemblies prepared from Nafion-117, NF, NF–ZrP–d, and NF–ZrP–I composite membranes were investigated. The effects of introducing sub-μm porous PTFE film and ZrP particles into Nafion membranes on the DMFC performance were investigated. The influence of ZrP hybridizing process into NF membranes (the process of preparing NF–ZrP–I is inserting ZrOCl₂ into NF membranes after Nafion is annealed and the process of preparing NF–ZrP–d is mixing ZrOCl₂ into a Nafion solution before Nafion is annealed) on the morphology of NF–ZrP composite membranes and thus on the DMFC performance was also discussed.     

C3′‐Deoxygenation of Paromamine Catalyzed by a Radical S‐Adenosylmethionine Enzyme: Characterization of the Enzyme AprD4 and Its Reductase Partner AprD3

C3′‐deoxygenation of aminoglycosides results in their decreased susceptibility to phosphorylation thereby increasing their efficacy as antibiotics. However, the biosynthetic mechanism of C3′‐deoxygenation is unknown. To address this issue, aprD4 and aprD3 genes from the apramycin gene cluster in Streptomyces tenebrarius were expressed in E. coli and the resulting gene products were characterized in vitro. AprD4 is shown to be a radical S‐adenosylmethionine (SAM) enzyme, catalyzing homolysis of SAM to 5′‐deoxyadenosine (5′‐dAdo) in the presence of paromamine. [4′‐²H]‐Paromamine was prepared and used to show that its C4′‐H is transferred to 5′‐dAdo by AprD4, during which the substrate is dehydrated to a product consistent with 4′‐oxolividamine. In contrast, paromamine is reduced to a deoxy product when incubated with AprD4/AprD3/NADPH. These results show that AprD4 is the first radical SAM diol‐dehydratase and, along with AprD3, is responsible for 3′‐deoxygenation in aminoglycoside biosynthesis.