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Cluster Shows (cluster + shows)
Selected AbstractsSynchronization patterns in spaghetti-like nanoclustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008Acep Purqon Abstract Spaghetti-like nanoclusters concern disordered shapes and irregular shape fluctuations in few correlated biological lipids. We evaluate the shape fluctuations by introducing Symmetry- S as a physical parameter for measuring symmetry degrees and detecting shape transitions. From numerical simulation of few correlated lipids of POPC and POPE at 300 K and 340 K by using molecular dynamics, we investigate the symmetry dynamics for each individual cluster by analyzing both spatiotemporal and frequency. From spatiotemporal analysis, we find several jump motions in S -dynamics and non-Gaussian distributions in S -distribution. Interestingly, the jump motions likely contribute on the existence of transitions in the non-Gaussian distributions. Additionally, even number of lipids show more symmetric than the odd number of lipids and the symmetry distributions shift at higher temperature, while, from three dimension of actual position of symmetry dynamics, they are not easy to configure high symmetry as well as showing certain patterns. From power spectra density analysis, each individual cluster shows nearly random fluctuation. Besides individual clusters, we also investigate mutual clusters. Surprisingly, although individual clusters show fluctuations randomly, mutual clusters show certain direction correlations. Moreover, they show certain patterns in delayed time analysis such as mutual fluctuations periodically occur for same number of lipids. It indicates that an existence of synchronization patterns occur in shape fluctuations of spaghetti-like nanoclusters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Long-lived disc accretion in the , Chamaeleontis pre-main sequence star clusterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004Warrick A. Lawson ABSTRACT High-resolution spectroscopic study of late-type members of the ,9-Myr-old , Chamaeleontis star cluster shows that four stars, RECX 5, 9, 11 and ECHA J0843.3,7905, have broad H, profiles indicative of ballistic accretion of material from circumstellar discs first identified by virtue of their infrared (IR) excess emission. Quantitative analysis of the profiles finds accretion in , Cha stars at rates comparable to that derived by Muzerolle et al. for members of the similarly aged TW Hydrae Association (TWA); rates 1,3 orders of magnitude lower than in younger classical T Tauri (CTT) stars. Together these studies indicate that the fraction of long-lived inner discs can be significantly higher than that inferred from study of younger pre-main sequence (PMS) populations, which suggest a disc lifetime of <6 Myr. The detection of long-lived discs may have implications for the formation of planetary systems. If slow accretion processes are the dominant formation mechanism for Jovian planets then long-lived discs may be ideal sites to search for evidence for protoplanets. [source] Structure solution of the basic decagonal Al,Co,Ni phase by the atomic surfaces modelling methodACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2002Antonio Cervellino The atomic surfaces modelling technique has been used to solve the structure of the basic Ni-rich Al,Co,Ni decagonal phase. Formula Al70.6Co6.7Ni22.7, space group , five-dimensional unit-cell parameters: d1 = d4 = 4.752,(3),Å, d2 = d3 = 3.360,(2),Å, d5 = 8.1710,(2),Å; ,12 = ,34 = 69.295°, ,13 = ,24 = 45°, ,14 = 41.410°, ,23 = ,i5 = 90° (i = 1,4), V = 291.2,(7),Å5; Dx = 3.887,Mg,m,3. Refinement based on |F|; 2767 unique reflections (|F| > 0), 749 parameters, R = 0.17, wR = 0.06. Describing the structure of quasicrystals embedded in n -dimensional superspace in principle takes advantage of n -dimensional periodicity to select the minimal set of degrees of freedom for the structure. The method of modelling of the atomic surfaces yielded the first fully detailed structure solution of this phase. Comparison with numerous former, less accurate models confirms several features already derived, but adds a new essential insight of the structure and its complexity. The atoms fill the space forming recurrent structure motifs, which we will (generically) refer to as clusters. However, no unique cluster exists, although differences are small. Each cluster shows a high degree of structural disorder. This gives rise to a large configurational entropy, as much as expected in a phase which is stable at high temperature. On the other side, the cluster spatial arrangement is perfectly quasiperiodic. These considerations, corroborated by analysis of the structural relationship with neighbouring periodic phases, strongly suggest the existence of a non-local, long-range interaction term in the total energy which may be essential to the stability. [source] Synthesis and Characterisation of ,3 -Octahedral [Ni36Pd8(CO)48]6, and [Ni35Pt9(CO)48]6, Clusters Displaying Unexpected Surface Segregation of Pt Atoms and Molecular and/or Crystal Substitutional Ni/Pd and Ni/Pt DisorderCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2004Cristina Femoni Dr. Abstract The synthesis and structure, as well as the chemical and electrochemical characterisation of two new ,3 -octahedral bimetallic clusters with the general [Ni44,xMx(CO)48]6, (M = Pd, x = 8; M = Pt, x = 9) formula is reported. The [Ni35Pt9(CO)48]6, cluster was obtained in reasonable yields (56,% based on Pt) by reaction of [Ni6(CO)12]2, with 1.1 equivalents of PtII complexes, in ethyl acetate or THF as the solvent. The [Ni36Pd8(CO)48]6, cluster was obtained from the related reaction with PdII salts in THF, and was isolated only in low yields (5,10,% based on Pd), mainly because of insufficient differential solubility of its salts. The unit cell of the [NBu4]6[Ni35Pt9(CO)48] salt contains a substitutionally Ni,Pt disordered [Ni24(Ni14,xPtx)Pt6(CO)48]6, (x = 3) hexaanion. A combination of crystal and molecular disorder is necessary to explain the disordering observed for the Ni/Pt sites. The unit cell of the corresponding [Ni36Pd8(CO)48]6, salt contains two independent [Ni30(Ni8,xPdx)Pd6(CO)48]6, (x = 2) hexaanions. The two display similar substitutional Ni,Pd disorder, which probably arises only from crystal disorder. The structure of [Ni36Pd8(CO)48]6, establishes the first similarity between the chemistry of Ni-Pd and Ni-Pt carbonyl clusters. A comparison of the chemical and electrochemical properties of [Ni35Pt9(CO)48]6, with those of the related [Ni38Pt6(CO)48]6, cluster shows that surface colouring of the latter with Pt atoms decreases redox as well as protonation propensity of the cluster. In contrast, substitution of all internal Pt and two surface Ni with Pd atoms preserves the protonation behaviour and is only detrimental with respect to its redox aptitude. A qualitative rationalisation of the different surface-site selectivity of Pt and Pd, based on distinctive interplays of MM and MCO bond energies, is suggested. [source] Cluster correlations in redshift spaceMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002N.D. Padilla We test an analytic model for the two-point correlations of galaxy clusters in redshift space using the Hubble volume N -body simulations. The correlation function of clusters shows no enhancement along the line of sight, owing to the lack of any virialized structures in the cluster distribution. However, the distortion of the clustering pattern arising from coherent bulk motions is clearly visible. The distribution of cluster peculiar motions is well described by a Gaussian, except in the extreme high-velocity tails. The simulations produce a small but significant number of clusters with large peculiar motions. The form of the redshift-space power spectrum is strongly influenced by errors in measured cluster redshifts in extant surveys. When these errors are taken into account, the model reproduces the power spectrum recovered from the simulation to an accuracy of 15 per cent or better over a decade in wavenumber. We compare our analytic predictions with the power spectrum measured from the APM cluster redshift survey. The cluster power spectrum constrains the amplitude of density fluctuations, as measured by the linear rms variance in spheres of radius 8 h,1 Mpc, denoted by ,8. When combined with the constraints on ,8 and the density parameter , derived from the local abundance of clusters, we find a best-fitting cold dark matter model with and , for a power spectrum shape that matches that measured for galaxies. However, for the best-fitting value of , and given the value of Hubble's constant from recent measurements, the assumed shape of the power spectrum is incompatible with the most readily motivated predictions from the cold dark matter paradigm. [source] | ||||||||||