Influence of mass moment of inertia on the normal modes of a preloaded solar array mast

Earth-orbiting spacecraft often contain solar arrays or antennas supported by a preloaded mast. Due to weight and cost considerations, the supporting structures of the spacecraft appendages are made extremely light and flexible. Therefore, it is essential to investigate the influence of all physical and structural parameters on the dynamic behavior of the overall structure. The governing equation of motion and its general solution for the preloaded mast are developed. Furthermore, the mass moment of inertia of the mast subjected to bending vibrations is included in the governing equation of motion to investigate its influence on determining the circular frequencies. To verify the developed formulations, a finite element technique was implemented. The accuracy and limitation of the technique on calculating the circular frequencies are discussed. Although the study described in this paper primarily focuses on the mast for the space station solar arrays, the developed formulations and techniques can be applied to any large and flexible beam in zero gravity.     

On the behavior of ECN/RED gateways under a large number of TCP flows: Limit theorems

We consider a discrete-time stochastic model of an ECN/RED gateway where competing TCP sources share the link capacity. As the number of competing flows becomes large, the asymptotic queue behavior (normalized by the number of flows) at the gateway can be described by a simple recursion and the throughput behavior of individual TCP flows becomes asymptotically independent. A Central Limit Theorem complement is also presented, yielding a more accurate characterization of the asymptotic queue size. These results suggest a scalable yet accurate model of this complex large-scale stochastic feedback system, and crisply reveal the sources of queue fluctuations. This work was prepared through collaborative participation in the Communications and Networks Consortium sponsored by the U.S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011. This work was also supported by the Space and Naval Warfare Systems Center—San Diego under Contract No: N66001-00-C-8063. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government.     

NMR of Terminal Oxygen. Part 14. Kinetically stabilized simple enols containing methylated uracil groups: Application of a 17O-NMR test of H-bonding

In the crystalline N,N′-dimethylated uracil derivatives 2a , b , the kinetically stabilized enol group forms an H-bond with O? C(4), as demonstrated by increased shielding of specifically labelled 2a and 2b in the ¹⁷O-NMR spectra (Δδ(¹⁷O)(C(4)—O) ? ?30 ppm); absence of dilution and solvent effects show that the H-bridge is intra-molecular, forming an eight-membered chelate ring. The (apparent) shielding effect Δδ(¹⁷O) in 2a, b is larger than that in salicylamide. The strong H-bond explains why the enols 2 , in spite of the absence of steric hindrance, are kinetically stabilized.     

Etude par spectrométrie de masse de la fragmentation des cyclopentane-triols-1,2,3, des cyclopentane-tétrols et des cyclopentane-pentols

The mass spectra of the three cyclopentane-1,2,3-triols, six cyclopentane-tetrols and four cyclopentane-pentols stereoisomers have been studied. Complex processes, especially regarding the H₂O eliminations, were detected by extensive deuterium labelling.     

Polysulfonylamine. CLX [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 10 [2] Die dreidimensionalen Koordinationspolymere M[(CH3SO2)2N] mit M = Kalium,Rubidium, Caesium (isotype Strukturen für M = K,Rb)

Polysulfonylamines. CLX. Crystal Structures of Metal Di(methanesulfonyl)amides. 10. The Three‐Dimensional Coordination Polymers M[(CH₃SO₂)₂N], where M is Potassium, Rubidium, Cesium (Isotypic Structures for M = K, Rb) Low‐temperature X‐ray crystal structures are reported for KA (monoclinic, space group P2₁/c, Z′ = 1), RbA (isotypic and isostructural with KA), and CsA (monoclinic, P2₁/n, Z′ = 1), where A^— denotes the anion obtained by deprotonation of the strong nitrogen acid (MeSO₂)₂NH. In KA and RbA, the anion is distorted into a rare C₁ conformation, whereas the standard C₂ conformation is retained in the cesium complex. The structures consist of three‐dimensional coordination networks, in which each cation adopts an irregular (O₆N)‐heptacoordination by forming close contacts to one (O, N)‐chelating, one (O, O)‐chelating and three κ¹O‐bonding ligands; however, the coordination number for Cs⁺ is effectively increased to 8 by a very short Cs···Cs contact distance of 422.5 pm. The crystal packings of the isotypic compounds KA and RbA display lamellar layer substructures that involve six independent ligand‐metal bonds and comprise an internal cation lamella and peripheral regions built up from anion monolayers; the 3D framework is completed by one independent M—O bond cross‐linking the layer substructures. In contrast, CsA features anion monolayers that intercalate planar zigzag chains of cations (Cs···Cs alternatingly 422.5 and 487.5 pm, Cs···Cs···Cs 135.7°), whereby each chain is surrounded and coordinated by four anion stacks and each anion stack connects two cation chains. All structures exhibit close C—H···A interanion contacts consistent with weak hydrogen bonding.     

ETUDE DE LA FRAGMENTATION DE N-ARYL ET DE N-ALKYL AMINOCETONES EN SPECTROMETRIE DE MASSE

A Comparison of the chemical ionisation and elctron-impact mass spectra of alkyl and aryl aminoketones has bee carried out. This has revealed the particular stabilization of the N-aryl grops in all cases.     

Photosensitized Oxygenation of Abieta-7,9(11)-dien-13β-ol

Dehydration of abiet-8-ene-7β, 13β-diol (ibozol, 1 ) leads to abieta-7,9(11)-dien-13β-ol ( 2 ) which aromatizes slowly to the known abieta-8,11,13-triene ( 3 ). Photosensitized oxygenation of the heteroannular diene 2 yields a mixture from which three compounds were identified; abiet-7-ene-9α, 11α, 13β-triol ( 4 ), abieta-8,11,13-trien-7-one ( 5 ), and abieta-8,11,13-trien-7α-ol ( 6 ).     

Pyridazino[3,4-b]quinoxalines and their reduced derivatives. Preparation and structure

The reaction of o-phenylenediamine with a β-ketoacid, leads in most cases to quinoxalinones. Their structure has been determined as well as that of their corresponding hydrazones. The reaction of hydrazine with these quinoxalinones gives dihydropyridazino[3,4-b]quinoxalines, the structure of which has been ascertained. It has been shown that among the six possible formulas, the only 1,2-dihydro structure fits with the spectroscopic data. On the contrary, N-substituted o-phenylenediamines lead to 2,10-dihydro derivatives. The electrochemical behavior of the 2,10-dihydro-10-methyl-3-phenylpyridazino[3,4-b]quinoxaline has been investigated. It has also been shown that the 3,4,6-trichloropyridazine reacts with o-phenylenediamines to give 5,10-dihydropyridazino[3,4-b]quinoxalines. These compounds can be oxidized to give the new heterocycle pyridazino[3,4-b]quinoxaline.