Influence Of Cluster Size Research Articles

Defining Cell Cluster Size by Dielectrophoretic Capture at an Array of Wireless Electrodes of Several Distinct Lengths.

Clusters of biological cells play an important role in normal and disease states, such as in the release of insulin from pancreatic islets and in the enhanced spread of cancer by clusters of circulating tumor cells. We report a method to pattern cells into clusters having sizes correlated to the dimensions of each electrode in an array of wireless bipolar electrodes (BPEs). The cells are captured by dielectrophoresis (DEP), which confers selectivity, and patterns cells without the need for physical barriers or adhesive interactions that can alter cell function. Our findings demonstrate that this approach readily achieves fine control of cell cluster size over a broader range set by other experimental parameters. These parameters include the magnitude of the voltage applied externally to drive capture at the BPE array, the rate of fluid flow, and the time allowed for DEP-based cell capture. Therefore, the reported method is anticipated to allow the influence of cluster size on cell function to be more fully investigated.

Cluster-Dependent Charge-Transfer Dynamics in Iron-Sulfur Proteins.

Photoinduced charge-transfer dynamics and the influence of cluster size on the dynamics were investigated using five iron-sulfur clusters: the 1Fe-4S cluster in Pyrococcus furiosus rubredoxin, the 2Fe-2S cluster in Pseudomonas putida putidaredoxin, the 4Fe-4S cluster in nitrogenase iron protein, and the 8Fe-7S P-cluster and the 7Fe-9S-1Mo FeMo cofactor in nitrogenase MoFe protein. Laser excitation promotes the iron-sulfur clusters to excited electronic states that relax to lower states. The electronic relaxation lifetimes of the 1Fe-4S, 8Fe-7S, and 7Fe-9S-1Mo clusters are on the picosecond time scale, although the dynamics of the MoFe protein is a mixture of the dynamics of the latter two clusters. The lifetimes of the 2Fe-2S and 4Fe-4S clusters, however, extend to several nanoseconds. A competition between reorganization energies and the density of electronic states (thus electronic coupling between states) mediates the charge-transfer lifetimes, with the 2Fe-2S cluster of Pdx and the 4Fe-4S cluster of Fe protein lying at the optimum leading to them having significantly longer lifetimes. Their long lifetimes make them the optimal candidates for long-range electron transfer and as external photosensitizers for other photoactivated chemical reactions like solar hydrogen production. Potential electron-transfer and hole-transfer pathways that possibly facilitate these charge transfers are proposed.

Adsorption sensitivity of nanocrystalline B-substituted H-ZSM-5 and alkali metal-exchanged M-ZSM-5 zeolites towards parent nitrosamine: A B97D study

In this work, the adsorption of parent nitrosamine (NA) on the Brønsted acid sites of B-substituted H-ZSM-5 and alkali metal-exchanged zeolites was investigated using the quantum 10T cluster at B97D/6-311++G(d,p) level and 46T model at the ONIOM(B97D/6-311++G(d,p):HF/STO-3G) level of theory. The influence of cluster size on the interaction between NA and zeolites was explored. The extended zeolite framework significantly increased the adsorption energy of NA on the zeolites. From the comparison of adsorption energies, the trend for acid strength of acidic sites was predicted to be B/ZSM-5<Al/ZSM-5. The adsorption energies of NA on alkali metal-exchanged zeolites were decreased when the cations were changed from Li+ to Na+, in agreement with the lower acidity of the Na+ ion compared to the Li+. In addition to the main H(M)z⋯O interaction, stability of all complexes was affected by the NH⋯OZ interactions. Besides, interaction between NA and the ZSM-5 zeolites was examined using the atoms in molecules (AIM) and natural bond orbital (NBO) analyses. The comparison of ρ(r) at O⋯HZ(M) BCP of Al/10T and B/10T complexes showed that the interactions in Al complexes are stronger than B ones. We have found a correlation between calculated adsorption energies and CT values.

Optical properties of silver and copper clusters with up to 150 atoms

Optical absorption spectra of the lowest-energy structures of small and medium-sized transition-metal clusters, AgN and CuN with N up to 150, are investigated within the classical Mie–Gans theory. The global-minima structures of these clusters have been determined in our previous studies using an unbiased structure-optimization approach combined with the embedded-atom total-energy method. The influence of cluster size, shape and metal on the peak positions and the relative intensities in the absorption spectra is studied systematically. Our studies give information on differences/similarities between optical absorption spectra of different metal clusters and their isomers. The main features of the obtained optical spectra for silver clusters are in good agreement with the available experiments and with results of the computationally much more advanced TDDFT calculations.

Influence of cluster size and surface functionalization of ZnO nanoparticles on the morphology, thermomechanical and piezoelectric properties of P(VDF-TrFE) nanocomposite films

Few studies have been reported concerning the nanocomposites of copolymers of vinylidene difluoride and trifluoroethylene (P(VDF-TrFE)) with piezoelectric nanofillers. This study deals with the preparation and characterization of piezoelectric nanocomposite films based on P(VDF-TrFE) filled with several ZnO piezoelectric nanoparticles with different sizes and surface states. The influence of cluster size and surface state of ZnO nanoparticles on the morphology and electromechanical properties of (PVDF-TrFE) nanocomposite films is investigated.The dispersion of nanoparticles and the microstructure of nanocomposite are observed by Environmental Scanning Electron Microscope (ESEM) and Transmission Electron Microscopy (TEM). The crystallinity of the copolymer matrix is characterized by X-ray diffraction and Differential Scanning Calorimetry (DSC). The piezoelectric and mechanical properties are measured to evaluate the influence of cluster size and surface functionalization with respect to the P(VDF-TrFE) matrix. The nanocomposites filled with 10% nanoparticles showed an increase up to 25% of storage modulus while keeping a high piezoelectric activity. Furthermore, storage modulus of nanocomposites slightly linearly increased with decreasing cluster size of nanoparticles.

Variable RyR Cluster Morphology in Sheep Atrial Myocytes: Super Resolution Measurement and Ca2+ Release Simulation

Conventional methods used to examine antibody labeled proteins are impeded by the resolution limits of light microscopy. We report new measurements of ryanodine receptor (RyR) clusters using the stimulated emission depletion (STED) microscopy method and correlate RyR morphology with function using a fully stochastic model of Ca2+ release. Sheep atrial myocytes were fixed and RyRs were antibody labeled and fluorescently tagged with Atto-647N. Two pulsed lasers were used for STED microscopy; a 635 nm pulsed at 80 MHz for 80ps to excite and a 780 nm laser, with a donut shaped beam was pulsed at 80MHz for 100fs for depletion. Acquired images showed ∼3.5x increase in resolution compared to conventional confocal methods. After deconvolution, further improvements in both signal-to-noise ratio and resolution were observed. Gaussian fitting of the smallest detectable clusters showed a >4x improvement in resolution, allowing a typical lateral resolution of 40-65 nm. Using the protein size predicted from ultrastructure and as documented in rat ventricular myocytes, calculations of cluster size yielded a mean cluster size of 21 RyRs, with a standard deviation of 33. Over 50% of the clusters measured had a size of <7, but many small clusters were grouped in a secondary level of organisation, The influence of cluster size and geometry on Ca2+ spark generation were probed using a Monte Carlo model of Ca2+ release sites. The model contained a main release site and a smaller peripheral cluster placed at various distances from the main site to assess the affect of one cluster firing on the probability and latency of release of the associated cluster. This study highlights the usefulness of this super-resolution method to determine realistic cluster geometries and the probable consequences for the regulation of Ca2+ release.

Strong-field ionization and dissociation studies of small early transition metal oxide clusters

We present the results of a systematic experimental approach utilizing time-of-flight mass spectrometry (TOF-MS) to investigate changes in maximum ionization states as the result of femtosecond pulse ionization. Strong-field gas-phase ionization experiments were performed on well characterized distributions of small early transition metal oxide (M x O y ) clusters, where M = Ti, V, Cr, Nb, or Ta, created as a molecular beam via supersonic expansion. Utilizing high resolution TOF-MS enabled the observation of highly charged ions resulting from ionization and subsequent fragmentation via Coulomb explosion. Maximum charge states for each cluster distribution are reported as observed under various ionization conditions. Evidence for direct correlation with previously reported ionization energies of the component species is presented. Regardless of metal composition, it is observed that every cluster distribution gains approximately the same amount of energy from the external field. The extreme ionization of the targeted clusters produced ions of Ti 10+, V 9+, Cr 8+, Nb 11+, Ta 11+, and O 6+, requiring up to 216 eV of energy to create these maximum charge states via sequential ionization. Several enhanced ionization models are discussed with relation to our experimental data. Systematic investigations on the influence of cluster size and ionization laser pulse width indicate enhanced ionization contributions from the ionization ignition and charge-resonance enhanced ionization mechanisms.

Influence of cluster size and ion activation method on the dissociation of cesium iodide clusters

Cesium iodide clusters (CsI) are simple ionic structures that are composed of different combinations of the same two atoms, cesium and iodine. When these clusters are generated by electrospray ionization, mass spectrometry analysis shows the generation of a broad m/ z distribution with one or two residual cesium ions as the charge carrier(s). The formation of larger cluster assemblies was ion source dependent, and significantly influenced by source pressure. The gas-phase dissociation of these clusters was studied by collision-induced dissociation (CID) and surface-induced dissociation (SID) in a quadrupole time-of-flight mass spectrometer. SID was found to deposit more internal energy into these clusters, providing access to alternative, high energy dissociation pathways. The most significant differences were observed for larger cluster systems. Doubly charged clusters were observed to dissociate via one or two pathways, a mass stripping process and a charge splitting process. While SID yielded both fragmentation pathways, CID only accessed the mass stripping pathway.

Magnetic moments, exchange coupling, and crossover temperatures of Co clusters onPt(111) and Au(111)

The influence of cluster size and of cluster–substrate interaction on the magnetic propertiesof Co clusters of 1–10 atoms on Pt(111) and Au(111) is studied by fully relativistic ab initiocalculations. The focus is on systematic trends of the spin and orbital magnetic moments,the exchange coupling, and the crossover temperature. The spin magnetic moments of Coclusters are larger for the Pt substrate than for the Au substrate, while the reverse is truefor the orbital magnetic moments. The local magnetic moments of Co atoms generallyincrease if the number of Co neighbours decreases. The exchange coupling constantsJij depend on the cluster size and on the location of respective atoms. The crossovertemperature increases monotonically with cluster size and is larger for clusters on Pt thanfor clusters on Au.

Spin-dependent transport in cluster-assembled nanostructures: influence of cluster size and matrix material

Spin-dependent transport in granular metallic nanostructures has been investigated by means of a thermoelectric measurement. Cobalt clusters of well-defined size ( = 15 and 600), embedded in copper and silver matrices, show magnetic field responses of up to several hundred percent at low temperature. The experimental observations are identified as due to spin mixing. The influence of cluster size and matrix are discussed.

Irradiation of silicon surface by Ar cluster ion beam: Cluster size effects

The influence of cluster size on damage layer thickness produced by Ar gas cluster ion beam (GCIB) irradiation is presented. The GCIB has a wide cluster size distribution which has been difficult to control. To obtain a narrow size distribution of the GCIB, the mass filter containing a strong permanent magnet is developed. In this study, the size-selected Ar-GCIB irradiates the Si substrates. The cluster size is varied between 500 and 20,000atoms/cluster. After irradiation, the damage layer thickness on Si substrates is measured by ellipsometry. The results of size-selected Ar-GCIB irradiation on Si substrates at acceleration energy of 5keV show that the damage decreases very quickly, from 7.9nm to 0.3nm with increasing the cluster size from 500 to 5000atoms/cluster. This tendency is in agreement with the results calculated by molecular dynamics simulation. These results suggest that the GCIB process is promising for low damage processing of semiconductor material.

Gadolinium Nitride Gd3N in Carbon Cages: The Influence of Cluster Size and Bond Strength

Gadolinium Nitride Gd₃N in Carbon Cages: The Influence of Cluster Size and Bond Strength

DFT Investigation of Alkoxide Formation from Olefins in H-ZSM-5

We present a density functional theory (DFT) study of propene, 1-hexene, and 3-hexene protonation over representative H-ZSM-5 clusters to give covalent alkoxide intermediates. The influence of cluster size, olefin carbon number, olefin conformation, proton siting, aluminum siting, and bonding configuration (primary vs secondary) of the alkoxide intermediate was analyzed. We found the formation of a physisorbed π-complex involving the olefin double bond and the acidic proton to be relatively independent of olefin structure and site geometry. However, we show that the proton-transfer process for formation of the covalent alkoxide intermediate involves a carbenium-ion-like transition state, with an activation energy that is (1) dependent on the protonation site of the olefin and (2) relatively independent of the carbon number and double bond location of the olefin. Accessibility of the alkoxide oxygen site in the cavity was observed to play a significant role in the stability of the alkoxy species. We find t...

Structure character in small-carbon-cluster deposition on diamond surface

Experimentally, hydrogen-free diamond-like carbon (DLC) films were assembled by means of pulsed laser deposition (PLD), where energetic small-carbon-clusters were deposited on the substrate. In this paper, the chemisorption of energetic C2 and C10 clusters on diamond (001)-( 2×1) surface was investigated by molecular dynamics simulation. The influence of cluster size and the impact energy on the structure character of the deposited clusters is mainly addressed. The impact energy was varied from a few tens eV to 100 eV. The chemisorption of C10 was found to occur only when its incident energy is above a threshold value ( E th). While, the C2 cluster was easily to adsorb on the surface even at much lower incident energy. With increasing the impact energy, the structures of the deposited C2 and C10 are different from the free clusters. Finally, the growth of films synthesized by energetic C2 and C10 clusters were simulated. The statistics indicate the C2 cluster has high probability of adsorption and films assembled of C2 present slightly higher SP3 fraction than that of C10-films, especially at higher impact energy and lower substrate temperature. Our result supports the experimental findings. Moreover, the simulation underlines the deposition mechanism at atomic scale.

Ab initio Cluster Calculations of the Electric Field Gradients at the Nb Site in the LiNbO3 Crystal

Calculations of the electric field gradients at the niobium site for the LiNbO3 crystal have been carried out within the temperature range 298 to 1505 K using the ab initio cluster approach. The influence of cluster size and basis sets on the niobium quadrupole coupling constant was considered. It was shown that the calculations for the minimal cluster (NbO6)—7 using the TZV basis set for oxygen and the (14s8p7d) basis set augmented with two diffuse p-functions (0.074 and 0.023) for the niobium yield a good agreement with experimental data. Results of the ab initio cluster calculations were compared with those obtained within the framework of the point-multipole model.

Size dependence in adsorption on model surfaces

Considering the chemisorption of atomic oxygen on Li(001) surface, the size dependence in adsorption on the model surfaces has been investigated. All-electron density functional calculations within the local density approximation have been applied to cluster models with increasing size. The influence of cluster size on the physics and chemistry of adsorption has been investigated.

Molecular-dynamics study of the structural rearrangements of Cu and Au clusters softly deposited on a Cu(001) surface

The soft deposition of copper and gold clusters on the Cu(001) surface is studied by constant energy molecular-dynamics simulations. The atomic interactions are mimicked by a many-body potential based on the tight-binding model. The influence of cluster size, substrate temperature, and incident kinetic energy (in the low-energy limit) is analyzed. Some of the simulations are extended up to a few hundred picoseconds and within this simulation time the cluster flattens and partially spreads over the surface, and the degree of spreading depends on the above variables. The influence of surface steps has also been studied and the deposited atoms seem to have a strong affinity for step-edge sites.

Influence of cluster size on the normal- and superconducting-state properties of granular Bi films

The Hall coefficient ${R}_{H}$ and the magnetic-field dependence of the superconducting transition temperature ${T}_{c}$ of granular films built from well defined Bi clusters has been measured as a function of Bi cluster size L $(3.5&lt;~L&lt;~10\mathrm{nm})$ in magnetic fields up to 8 T and at temperatures $T&gt;1.8\mathrm{K}.$ From these experimental results we can conclude that with decreasing L the original rhombohedral bulk structure of the Bi clusters becomes more and more distorted (increasing number of defects), until at ${L=L}^{*}\ensuremath{\approx}4.0\mathrm{nm}$ the structure changes into the ``amorphous'' Bi structure. For ${L=L}^{*}$ the Bi conduction electrons become almost localized and ${(dB}_{c2}{/dT)}_{{T}_{c}}$ has an unusually large value of -16.7 T/K. The good agreement between the L dependencies of normal and superconducting properties indicates that the electronic structure of the Bi clusters changes with L, but is rather homogeneous for a given L.

Resonant x-ray absorption of neon clusters: The influence of cluster size on the character of core excited states.

First resonant $K$-shell absorption spectra of atomic clusters covering the size range from the atom to the solid are reported. Discrete absorption into Rydberg states as well as the near edge ionization continuum (XANES/EXAFS) of neon clusters ($N\ensuremath{\approx}15\ensuremath{-}4000$) is investigated with excellent spectral resolution. Shifts and splittings of the absorption features ($1s\ensuremath{\rightarrow}3p,4p$) provide information on local properties of the different atomic sites. Besides identifying surface and bulk contributions we observe how the character of a transition changes from a Rydberg orbital in a small cluster into a bulk excitation in larger systems.

Ab initio models for ZnS surfaces: the influence of cluster size on surface properties: II. Three-dimensional models

Models for zinc sulfide surfaces varying from 2D slabs to 3D zinc blende clusters containing several ZnS layers were studied. The energies and electronic properties are shown to converge monotonically as the model size increases. In some cases some size-dependent variation was found. The influence of edges and vacancies remains local, damping quickly beyond the neighboring atoms.