Showing papers on "Cluster (physics) published in 1995"
TL;DR: In this paper, the authors used spectroscopic and photometric data for the old open clusters to define disk abundance gradients and the cluster age-metallicity relationship, and they point to a complex history of chemical enrichment and mixing in the disk.
Abstract: The Galactic open clusters, in particular the oldest members, serve as excellent probes of the structure and evolution of the Galactic disk. Individual clusters provide excellent tests of stellar and dynamical evolution. Cluster spatial and age distributions provide insight into the processes of cluster formation and destruction that have allowed substantial numbers of old open clusters to survive. Spectroscopic and photometric data for the old clusters yield kinematic, abundance, and age information that clarifies the relationship between the old open cluster population and other Galactic populations. New samples of old open clusters, which span a large range in distance and age, are used to define disk abundance gradients and the cluster age-metallicity relationship, and they point to a complex history of chemical enrichment and mixing in the disk.
482 citations
TL;DR: In this paper, the structure of the global minimum of clusters bound by the Morse potential has been investigated and the effect of decreasing the range of the potential is shown to destabilize strained structures.
Abstract: We investigate the structures of clusters bound by the Morse potential by mapping the structure of the global minimum as a function of both cluster size and the range of the pair potential. We consider values of the range parameter appropriate to a loosely bound diatomic molecule (longest), two C60 molecules (shortest), and at regular intervals between these two limits. We have studied all cluster sizes with 25 atoms or less and a selection of sizes containing between 35 and 80 atoms. The effect of decreasing the range of the potential is to destabilize strained structures. For the larger clusters the structure of the global minimum changes from icosahedral to decahedral to face‐centered cubic as the range is decreased. We have also investigated the effects of temperature on the equilibrium structure by performing a model calculation for a 75‐atom cluster.
360 citations
TL;DR: In this article, a higher resolution magnetic bottle photoelectron spectrometer for the study of the electronic structure of size-selected metal clusters is presented, and the initial study on Fe−n (n=3−24) is reported at a photon energy of 3.49 eV.
Abstract: A higher resolution magnetic bottle photoelectron spectrometer for the study of the electronic structure of size‐selected metal clusters is presented. The initial study on Fe−n (n=3–24) is reported at a photon energy of 3.49 eV. The photoelectron spectra of these clusters exhibit sharp features throughout the size range. The spectra for Fe−3–8 show large size dependence with many resolved features. The spectra for Fe−9–15 exhibit some similarity with each other, all with a rather sharp feature near the threshold. An abrupt spectral change occurs at Fe−16, then again at Fe−19 and Fe−23. These photoelectron spectral changes coincide remarkably with changes of the cluster reactivity with H2. Extended Huckel molecular orbital (EHMO) calculations are performed for all the clusters to aid the spectral interpretations. The calculations yield surprisingly good agreement with the experiment for clusters beyond Fe9 when body‐centered cubic (bcc) structures are assumed for Fe9–15 and a similarly close‐packed structu...
354 citations
TL;DR: In this article, the authors observed the multiple pickup of up to 30 foreign particles by large (N≳103 atoms) liquid helium clusters and the formation of clusters of the foreign particles within the helium cluster.
Abstract: The multiple pickup of up to 30 foreign particles by large (N≳103 atoms) liquid helium clusters and the formation of clusters of the foreign particles within the helium cluster has been observed in a molecular beam experiment for Ar, Kr, Xe, H2O, and SF6. Evaporation of helium atoms due to the pickup process has been measured quantitatively by two methods. The measured apparent cross sections for capture and coagulation of these particles are significantly smaller than the total scattering cross sections of the clusters. After electron impact ionization the size distribution of the foreign particle cluster ion fragments can be well described by a Poisson distribution. This is interpreted as indicating negligible fragmentation of the coagulated foreign particle clusters. The measured coagulation cross sections are smaller than the capture cross sections. This is explained through a model which involves only partial coagulation of the foreign particles. The observed processes allow the preparation of foreign particle clusters with well‐defined size distributions inside large helium clusters.
345 citations
TL;DR: The Palomar Distant Cluster Survey (PDCS) as mentioned in this paper was conducted in two broad band filters that closely resemble V$ and I$ and the limiting magnitudes for our 300 s exposures are~$\sim$~23.8~($V$) and~22.5~($I$).
Abstract: We present an optical/near IR selected catalog of 79 clusters distributed over an area of 5.1~square~degrees. The catalog was constructed from images obtained with the 4-Shooter CCD mosaic camera on the Hale 5m telescope operating in ``scan" mode. The survey, hereafter known as the Palomar Distant Cluster Survey (PDCS), was conducted in two broad band filters that closely resemble~$V$ and~$I$. The $4\sigma$ limiting magnitudes for our 300 s exposures are~$\sim$~23.8~($V$) and~22.5~($I$). A matched filter algorithm was developed and employed to identify the cluster candidates by using positional and photometric data simultaneously. The clusters cover the range $0.2 \simless z \simless 1.2$, based on the redshift estimates derived in the cluster detection procedure. An accurate selection function is generated from extensive simulations. We find that the cumulative surface density of clusters with richness class R $\ge$ 1 is about a factor of 5 higher than the extrapolated density of R $\ge$ 1 Abell clusters. The PDCS results are consistent with a constant comoving density of clusters to $z \simless 0.6$, albeit at the above high density level. Constraints on cluster abundances at $z > 0.6$ will be possible with the acquisition of spectroscopic redshifts for a large subset of these cluster candidates. We also present a supplemental catalog of 28 clusters that do not satisfy all our selection criteria but which include some of the most distant systems detected in the survey. Finding charts for all 107 cluster candidates are provided.
334 citations
TL;DR: A simple preparation of Cd17S4(SCH2CH2OH)26 clusters in aqueous solution leads to the formation of colorless blocky crystals that resemble the self-similarities known from fractal geometry.
Abstract: A simple preparation of Cd17S4(SCH2CH2OH)26 clusters in aqueous solution leads to the formation of colorless blocky crystals. X-ray structure determinations revealed a superlattice framework built up of covalently linked clusters. This superlattice is best described as two enlarged and interlaced diamond or zinc blende lattices. Because both the superlattice and the clusters display the same structural features, the crystal structure resembles the self-similarities known from fractal geometry. The optical spectrum of the cluster solution displays a sharp transition around 290 nanometers with a large absorption coefficient (∼84,000 per molar per centimeter).
316 citations
TL;DR: The formation of a porous film is calculated for clusters impinging with low kinetic energy, while for the clusters with the highest energy a dense mirrorlike film is obtained, in good agreement with experiment.
Abstract: Langevin-molecular-dynamics simulations of thin-film growth by energetic cluster impact were carried out. The impact of a ${\mathrm{Mo}}_{1043}$ cluster on a Mo(001) surface was studied for impact energies of 0.1, 1, and 10 eV/atom using the Finnis-Sinclair many-body potential. The characteristics of the collision range from a soft touchdown at 0.1 eV/atom, over a flattening collision at 1 eV/atom, to a meteoric impact at 10 eV/atom. The highest energy impact creates a pressure of about 100 GPa in the impact zone and sends a strong shock wave into the material. The cluster temperature reaches a maximum of 596 K for 0.1 eV/atom, 1799 K for 1 eV/atom, and 6607 K for 10 eV/atom during the first ps after the touchdown. For energies of 1 and 10 eV/atom the cluster recrystallizes after 20 ps. The consecutive collision of 50 ${\mathrm{Mo}}_{1043}$ clusters with a Mo(001) surface at T=300 K was simulated for the three impact energies. The formation of a porous film is calculated for clusters impinging with low kinetic energy, while for the clusters with the highest energy a dense mirrorlike film is obtained, in good agreement with experiment.
306 citations
Patent•
13 Sep 1995
TL;DR: In this article, a semiconductor nonvolatile mass storage memory is partitioned into user files and system files, each partition having a plurality of sectors, each cluster stores the system file for a single predetermined LBA.
Abstract: A semiconductor non-volatile mass storage memory is partitioned into user files and system files. The system files partition is further subdivided into clusters, each cluster having a plurality of sectors. Each cluster stores the system file for a single predetermined LBA. As the information within the LBA is changed, the new information is written into an empty sector within the cluster. Once the cluster is filled, the system either erases for recycling the cluster or preferably locates an empty cluster and repeats the process with that new cluster. Once all the clusters are filled, all clusters containing old data are erased for recycling.
248 citations
TL;DR: The approach used here for the controlled synthesis of bioinorganic nanocomposites could be useful for the nanoscale engineering of dispersed materials with biocompatible and bioactive properties.
Abstract: Amorphous iron sulfide minerals containing either 500 or 3000 iron atoms in each cluster have been synthesized in situ within the nanodimensional cavity of horse spleen ferritin. Iron-57 Mossbauer spectroscopy indicated that most of the iron atoms in the 3000-iron atom cores are trivalent, whereas in the 500-iron atom clusters, approximately 50 percent of the iron atoms are Fe(III), with the remaining atoms having an effective oxidation state of about +2.5. Iron K-edge extended x-ray absorption fine structure data for the 500-iron atom nanocomposite are consistent with a disordered array of edge-shared FeS4 tetrahedra, connected by Fe(S)2Fe bridges with bond lengths similar to those of the cubane-type motif of iron-sulfur clusters. The approach used here for the controlled synthesis of bioinorganic nanocomposites could be useful for the nanoscale engineering of dispersed materials with biocompatible and bioactive properties.
247 citations
TL;DR: In this paper, the spectral properties such as the energy spectrum, the eigenmodes, and the density of states of a classical finite system of two-dimensional charged particles which are confined by a quadratic potential were studied.
Abstract: We present a study of the spectral properties such as the energy spectrum, the eigenmodes, and the density of states of a classical finite system of two-dimensional charged particles which are confined by a quadratic potential. Using the method of Newton optimization we obtain the ground state and the metastable states. For a given configuration the eigenvectors and eigenfrequencies for the normal modes are obtained using the Householder diagonalization technique for the dynamical matrix whose elements are the second derivative of the potential energy. For small clusters the lowest excitation corresponds to an intershell rotation. The energy barrier for such rotations is calculated. For large clusters the lowest excitation consists of a vortex/antivortex pair. The Lindeman melting criterion is used to calculate the order-disorder transition temperature for intershell rotation and intershell diffusion. The value of the transition temperature at which intershell rotation becomes possible depends very much on the configuration of the cluster, i.e., the distribution of the particles between the different shells. Magic numbers are associated with clusters which are most stable against intershell rotation. The specific heat of the cluster is also calculated using the Monte Carlo technique, which we compare with an analytical calculation where effects due to anharmonicity are incorporated.
216 citations
TL;DR: In this article, an artificial solid with extremely narrow mini or hopping bands depending on the chemically adjustable thickness of the ligand shell and its properties is described as a ligand-stabilized colloidal quantum dot.
Abstract: Small metal clusters, like Au55(PPh3)12Cl6, which fall in the size regime of 1–2 nm are colloidal nanoparticles with quantum properties in the transitional range between metals and semiconductors. These chemically tailored quantum dots show regarding the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small particle sizes to the molecular state. The organic ligand shell surrounding the cluster acts like a dielectric “spacer” generating capacitances between neighboring clusters down to 10−18 F. Therefore, charging effects superposed by level spacing effects can be observed. The ligand-stabilized colloidal quantum dots in condensed state can be described as a novel kind of artificial solid with extremely narrow mini or hopping bands depending on the chemically adjustable thickness of the ligand shell and its properties. Since its discovery, the Single Electron Tunneling (SET) effect has been recognized to be the fundamental concept for ultimate miniaturization in microelectronics. The controlled transport of charge carriers in arrangements of ligand-stabilized clusters has been observed already at room temperature through Impedance Spectroscopy (IS) and Scanning Tunneling Spectroscopy (STS). This reveals future directions with new concepts for the realization of simple devices for Single Electron Logic (SEL).
TL;DR: In this paper, the authors used a representative sample of 65 galaxy clusters observed with the Einstein IPC to constrain the range of cluster X-ray morphologies, including the distribution of emission weighted centroid variation, axial ratio, orientation, and radial fall-off.
Abstract: We use a representative sample of 65 galaxy clusters observed with the Einstein IPC to constrain the range of cluster X-ray morphologies. We develop and apply quantitative and reproducible measures to constrain the intrinsic distributions of emission weighted centroid variation, axial ratio, orientation, and the radial fall--off. We then use the range of cluster X--ray morphologies to constrain three generic cosmological models (Omega=1, Omega_0=0.2, and Omega_0=0.2 & lambda_0=0.8). For each of these models, we evolve eight sets of Gaussian random initial conditions consistent with an effective power spectrum $P(k)\propto k^{-1}$ on cluster scales. Using this sample of 24 numerical cluster simulations, we compare the X--ray morphologies of the observed and simulated clusters. The comparisons indicate that: (i) cluster centroid variations, axial ratios, and radial fall-offs are sensitive to the underlying cosmological model, and (ii) galaxy clusters with the observed range of X--ray morphologies are very unlikely in low Omega_0 cosmologies. The analysis favors the Omega=1 model, though some discrepancies remain. We discuss the effects of changing the initial conditions and including additional physics in the simulations.
TL;DR: In this article, the authors analyze three clusters that exhibit large arcs, whose X-ray surface brightness profiles have been observed, and whose gas temperatures have been determined, and find that the central mass implied by lensing is a factor of $2$--$2.5$ too large for the gas at the observed temperature to be in hydrostatic equilibrium solely due to thermal pressure support.
Abstract: Long arcs in clusters of galaxies, produced by gravitational lensing, can be used to estimate the mass interior to the arcs and therefore, constrain the cluster mass distribution. The radial density distribution of the intracluster gas (ICM) can be extracted from the X-ray surface brightness observations. If the gas temperature is also known, it is then possible to probe the dynamical state of the gas and test whether the ICM is in hydro- static equilibrium within the gravitational potential of the cluster as a result of thermal pressure support. We analyze three clusters that exhibit large arcs, whose X-ray surface brightness profiles have been observed, and whose gas temperatures have been determined. In two of the clusters, A2218 and A1689, the central mass implied by lensing is a factor of $2$--$2.5$ too large for the gas at the observed temperature to be in hydrostatic equilibrium solely due to thermal pressure support. In other words, if we accept the mass estimate derived from the lensing analysis and demand that the X-ray surface brightness profile be consistent with the observations, the required gas temperature is a factor of $2$--$2.5$ higher than observed. The results for the third cluster, A2163 (the most luminous and the hottest cluster known), are more ambiguous. The discrepancy between the X-ray and the lensing mass estimates arise because the presence of arcs imply a highly concentrated cluster mass distribution whereas the observed X-ray profiles imply a more extended mass distribution. The large X-ray core radii are not the result of the limited resolution of the X-ray detectors. We consider various possibilities that could account for the discrepancy.
TL;DR: In this paper, the specific properties of free clusters and the formation of new cluster-assembled materials using the low energy cluster beam deposition (LECBD) technique are discussed with special attention to new observed structures.
Abstract: In this paper the specific properties of free clusters and the formation of new cluster-assembled materials using the low energy cluster beam deposition (LECBD) technique are discussed. Recent results obtained for free clusters are summarized with special attention to new observed structures. As for the specific structures and properties of cluster-assembled materials, two main aspects are specially emphasized: the memory effect of the free cluster properties leading to the formation of new phases and the effect of the specific nanostructure of the cluster-assembled materials related to the random cluster stacking mechanism characteristic of the LECBD. These effects and the corresponding potential applications are illustrated using some selected examples: new diamond-like carbon films produced by fullerene depositions (memory effect) and grain effect on the magnetic properties of cluster-assembled transition metal films.
TL;DR: In this article, the authors quantify the morphologies and dynamical states of 59 galaxy clusters using the power-ratio technique of Buote & Tsai applied to ROSAT PSPC X-ray images.
Abstract: We quantify the morphologies and dynamical states of 59 galaxy clusters using the power-ratio technique of Buote & Tsai applied to ROSAT PSPC X-ray images. The clusters exhibit a particularly strong $P_2/P_0 - P_4/P_0$ correlation in the $1h^{-1}_{80}$ Mpc aperture which may be interpreted as an evolutionary track; the location of a cluster on the correlation line indicates the dynamical state of the cluster and the distribution of clusters along this track measures the rate of formation and evolution of clusters in our sample. The power ratios anti-correlate with the cooling-flow rate indicating a reasonable dependence of the flow rate on cluster morphology. The relationship of the power ratios to the optical Bautz-Morgan (BM) Type is more complex. This is because the power ratios are sensitive to unrelaxed regions of clusters within a specified scale, whereas BM types are sensitive to unrelaxed regions over many scales. We discuss further astrophysical applications exploiting the relationship between the power ratios and the evolutionary states of clusters.
TL;DR: In this article, the authors presented models and connections between microscopic and macroscopic level, regardless of whether there already exist suitable nanoscale metal cluster compounds, and is aimed at the ultimate properties for a possible application in microelectronics.
Abstract: Small metal clusters, like Au 55 (PPh 3 ) 12 Cl 6 , which fall in the size regime of 1 - 2 nm are colloidal nanoparticles with quantum properties in the transitional range between metals and semiconductors These chemically tailored quantum dots show by the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small particle sizes to the molecular state The organic ligand shell surrounding the cluster acts like a dielectric «spacer» generating capacitances between neighboring clusters down to 10 -18 F Therefore, charging effects superposed by level spacing effects can be observed The ligand-stabilized colloidal quantum dots in condensed state can be described as a novel kind of artificial solid with extremely narrow mini or hopping bands depending on the chemically adjustable thickness of the ligand shell and its properties Since its discovery, the Single Electron Tunneling (SET) effect has been recognized to be the fundamental concept for ultimate miniaturization in microelectronics The controlled transport of charge carriers in arrangements of ligand-stabilized clusters has been observed already at room temperature through Impedance Spectroscopy (IS) and Scanning Tunneling Spectroscopy (STS) This reveals future directions with new concepts for the realization of simple devices for Single Electron Logic (SEL) Part II presents models and connections between microscopic and macroscopic level, regardless of whether there already exist suitable nanoscale metal cluster compounds, and is aimed at the ultimate properties for a possible application in microelectronics
TL;DR: In this paper, the initial phase of carbonaceous cluster growth is studied in detail and it is shown that the increase in cluster growth with energy density is much slower than the one of radical formation and conductivity.
Abstract: Carbonaceous clusters-supposed to be the carriers of electric conductivity-are formed along latent tracks of energetic ions in polymers. The different experimental techniques for cluster determination are summarized. Here we present some new results which have been derived from UV-Vis spectrometric examinations. Especially the initial phase of cluster growth is studied in detail. There are hints that a threshold energy density has to be deposited in the polymer before cluster growth sets in. This threshold is similar to the one for producing radicals (as seen by EPR studies), and to the one for the onset of strong polymeric conductivity. The cluster growth is shown to scale rather well with the mean transferred electronic energy density. The increase in cluster growth with energy density is much slower than the one of radical formation and conductivity.
TL;DR: In this article, a method to quantitatively classify clusters of galaxies according to their projected morphologies was proposed, which is derived from the two-dimensional multipole expansion of the projected gravitational potential and yields dimensionless power ratios as morphological statistics.
Abstract: We describe and test a method to quantitatively classify clusters of galaxies according to their projected morphologies. This method will be subsequently used to place constraints on cosmological parameters ($\Omega$ and the power spectrum of primordial fluctuations on scales at or slightly smaller than that of clusters) and to test theories of cluster formation. We specifically address structure that is easily discernible in projection and dynamically important to the cluster. The method is derived from the two-dimensional multipole expansion of the projected gravitational potential and yields dimensionless {\it power ratios} as morphological statistics. If the projected mass profile is used to characterize the cluster morphology, the power ratios are directly related to the cluster potential. However, since detailed mass profiles currently exist for only a few clusters, we use the X-ray--emitting gas as an alternative tracer of cluster morphology. In this case, the relation of the power ratios to the potential is qualitatively preserved. We demonstrate the feasibility of the method by analyzing simulated observations of simple models of X-ray clusters using the instrument parameters of the ROSAT PSPC. For illustrative purposes, we apply the method to ROSAT PSPC images of A85, A514, A1750, and A2029. These clusters, which differ substantially in their X-ray morphologies, are easily distinguished by their respective power ratios. We discuss the suitability of this method to address the connection between cluster morphology and cosmology and to assess whether an individual cluster is sufficiently relaxed for analysis of its intrinsic shape using hydrostatic methods. Approximately 50 X-ray observations of Abell clusters with the PSPC will be amenable to morphological analysis using the method of this paper.
TL;DR: In this article, a vector empirical orthogonal function analysis and fuzzy cluster algorithm are applied to a 9-yr dataset to define six recurrent 700-mb circulation patterns that represent large-scale variabilities associated with the monsoon trough and subtropical ridge.
Abstract: The basic structure of the variability of the large-scale circulations over the tropical western Pacific is investigated with respect to its influence on tropical cyclone characteristics. A vector empirical orthogonal function analysis and fuzzy cluster algorithm are applied to a 9-yr dataset to define six recurrent 700-mb circulation patterns that represent large-scale variabilities associated with the monsoon trough and subtropical ridge. Five of the cluster patterns, which contain 48% of the sample, define combinations of active (inactive) monsoon trough and strong (weak) subtropical ridge circulations. The sixth cluster, which contains 26% of the data sample, depicts small deviations from the long-term climatology. After the cluster centers are defined, the fuzzy cluster coefficients are used to identify a seventh cluster, which contains the remaining 26% of the circulation patterns that could not be classified within any of the original six clusters. The 700-mb circulation patterns are physi...
TL;DR: In this article, a large and well-controlled sample of clusters of galaxies was used to investigate the relation between cluster velocity dispersions and X-ray temperatures of intra-cluster gas.
Abstract: Using a large and well-controlled sample of clusters of galaxies, we investigate the relation between cluster velocity dispersions and X-ray temperatures of intra-cluster gas. In order to obtain a reliable estimate of the total velocity dispersion of a cluster, independent of the level of anisotropies in galaxy orbits, we analyze the integrated velocity dispersion profiles over increasing distances from the cluster centers. Distortions in the velocity fields, the effect of close clusters, the presence of substructures, and the presence of a population of (spiral) galaxies not in virial equilibrium with the cluster potential are taken into account. Using our final sample of 37 clusters, for which a reliable estimate of the velocity dispersion could be obtained, we derive a relation between the velocity dispersions and the X-ray temperatures, with a scatter reduced by more than 30 % with respect to previous works. A chi square fit to the temperature-velocity dispersion relation does not exclude the hypothesis that the ratio between galaxy and gas energy density (the so-called spectral beta) is a constant for all clusters. In particular, the value of beta=1, corresponding to energy equipartition, is acceptable.
TL;DR: In this paper, the vibrational energy levels of acetylene, C2H2, up to 12,000 cm−1 were fitted simultaneously to a model based on the clustering of the levels induced by a set of eight anharmonic resonances.
Abstract: We have gathered 122 known experimental data concerning the vibrational energy levels of acetylene, C2H2, up to 12 000 cm−1. We have fitted the data simultaneously to a model based on the clustering of the levels induced by a set of eight anharmonic resonances. That set is carefully built from the literature information on various isotopomers of acetylene. The model takes full advantage of the anharmonic pattern and systematically block diagonalizes the entire vibrational energy matrix. The 122 input energies are reproduced within a standard deviation of 0.74 cm−1 with 35 fitted parameters. Decisive support to the model is brought by using the resulting vibrational parameters and matrix eigenvectors to reproduce energies, principal rotational parameters, and relative intensity features. The cluster picture is discussed, in terms of the 7 normal modes of vibration in acetylene, according to the theoretical model developed by Kellman [M. E. Kellman and G. Chen, J. Chem. Phys. 95, 8671 (1991)].
TL;DR: A review of the current knowledge on carbon fullerenes doped with foreign atoms and heteroatom-containing fullerene-like structures and nanotubes is provided Strong covalent bonds lend high specificity and stabilize the hollow-cage and symmetric structure of these materials.
Abstract: A review of the current knowledge on carbon fullerenes doped with foreign atoms and heteroatom-containing fullerene-like structures and nanotubes is provided Strong covalent bonds lend high specificity and stabilize the hollow-cage and symmetric structure of these moieties These structures are distinct from noble-gas and metallic clusters, where either weak van der Waals forces or stronger metallic bonds, which are not very specific, hold the cluster atoms together In the latter kind of clusters, atoms gain stability through close packing and large coordination numbers and consequently they cannot afford a hollow core Nonetheless some intermetallic nanoparticles exhibit truncated icosahedral symmetry The field is divided, somewhat artificially, into two separate categories One family consists of fullerene-like clusters assembled from different atoms which do not have a bulk counterpart of similar chemical formula The other group is that of fullerene-like nanostructures which are obtained mainly from ubiquitous 2-D layered compounds; various elements and compounds with 3-D character and also from certain metallic alloys It is shown that nanoparticles of 2-D compounds are unstable in the planar form and they reconstruct into hollow-cage nanoparticles, spontaneously Nanosolids of this kind may reveal vastly different properties from their bulk predecessors Numerous applications for the doped and heteroatom fullerene-like materials in the fields of catalysis, lubrication, electronic and photonic devices, alternative energy sources, etc are expected upon further study and development
TL;DR: In this paper, the geometrical structures of triniobium monoxide, Nb3O, and its cation, NB3O+, have been determined by an experimental and theoretical study.
Abstract: The geometrical structures of the ground states of triniobium monoxide, Nb3O, and its cation, Nb3O+, have been determined by an experimental and theoretical study. Vibrationally resolved photoelectron spectra of an Nb3O cluster beam were obtained at 100 and 300 K using the pulsed field ionization‐zero electron kinetic energy technique. The spectra were simulated by calculating multidimensional Franck–Condon factors using the geometries and harmonic vibrational frequencies obtained from density functional theory for the minimum energy structures of the ion and neutral molecule. The rather remarkable agreement between the experiment and the simulated spectra establishes that Nb3O and Nb3O+ have planar C2v structures with the oxygen atom bridging two niobium atoms. These are the most complex transition metal cluster structures to date to be characterized by gas phase spectroscopic techniques.
TL;DR: In this paper, the first results of a serendipitous search for clusters of galaxies in deep ROSAT position sensitive proportional counter (PSPC) pointed observations at high Galactic latitude were presented.
Abstract: We present the first results of a serendipitous search for clusters of galaxies in deep ROSAT position sensitive proportional counter (PSPC) pointed observations at high Galactic latitude. The survey is being carried out using a wavelet-based detection algorithm which is not biased against extended, low surface brightness sources. A new flux-diameter limited sample of 10 cluster candidates has been created from approximately 3 deg(exp 2) surveyed area. Preliminary CCD observations have revealed that a large fraction of these candidates correspond to a visible enhancement in the galaxy surface density, and several others have been identified from other surveys. We believe these sources to be either low- to moderate-redshift groups or intermediate- to high-redshift clusters. We show X-ray and optical images of some of the clusters identified to date. We present, for the first time, the derived number density of the galaxy clusters to a flux limit of 1 x 10(exp -14) ergs cm(exp -2) s(exp -1) (0.5-2.0 keV). This extends the log N-log S of previous cluster surveys by more than one decade in flux. Results are compared to theoretical predictions for cluster number counts.
Abstract: Photoelectron spectra of Ag−n clusters with n=1–21 recorded at different photon energies (hν=4.025, 4.66, 5.0, and 6.424 eV) are presented. Various features in the spectra of Ag−2–Ag−9 can be assigned to electronic transitions predicted from quantum chemical ab initio calculations. While this comparison with the quantum chemical calculations yields a detailed and quantitative understanding of the electronic structure of each individual cluster, a discussion in terms of the shell model is able to explain trends and dominant patterns in the entire series of spectra up to Ag−21.
TL;DR: In this paper, a review of the current state of knowledge of the structure and activity of bimetallic Pt-Re-Al 2 O 3 catalysts used in petroleum reforming and of the known heteronuclear PRe-Re cluster complexes is presented.
TL;DR: In this paper, a series of vertex-sharing polyicosahedral clusters containing group 11 (Au,Ag,Cu) and group 10 (Pt,Pd,Ni) metals are discussed.