Two-dimensional Clusters Research Articles

Spin Structures of the Hubbard Clusters and the Pseudogap

The spin and charge structures formed in the Hubbard model for a finite two-dimensional cluster have been studied in the mean field approximation. The self-consistent iterative procedure reduces an uncorrelated initial spin distribution into stable structures with spectral properties typical of stripes. It is shown that the density of states of the system for any doping has a sharp minimum at the Fermi level, the pseudogap. The pinning of the gap at the Fermi level is characteristic not only of a superconducting state, but also typical of a normal state of spin glasses. Our results support conception of the PG state as a state with frozen locally nematic spin structures of antiferromagnetic domains.

Quantum monte carlo simulation of FeAs-based superconductors

The results for the calculation of the thermodynamic characteristics of finite two-dimensional FeAs clusters simulating iron-based superconductors have been obtained. The generalized quantum Monte Carlo algorithm is modified and used to calculate the energy and occupation numbers of finite FeAs clusters in the two-orbital model. The results for a cluster of 3 × 3 FeAs cells have been reported.

Optimal transport exponent in spatially embedded networks

The imposition of a cost constraint for constructing the optimal navigation structure surely represents a crucial ingredient in the design and development of any realistic navigation network. Previous works have focused on optimal transport in small-world networks built from two-dimensional lattices by adding long-range connections with Manhattan length r(ij) taken from the distribution P(ij)~r(ij)(-α), where α is a variable exponent. It has been shown that, by introducing a cost constraint on the total length of the additional links, regardless of the strategy used by the traveler (independent of whether it is based on local or global knowledge of the network structure), the best transportation condition is obtained with an exponent α=d+1, where d is the dimension of the underlying lattice. Here we present further support, through a high-performance real-time algorithm, on the validity of this conjecture in three-dimensional regular as well as in two-dimensional critical percolation clusters. Our results clearly indicate that cost constraint in the navigation problem provides a proper theoretical framework to justify the evolving topologies of real complex network structures, as recently demonstrated for the networks of the US airports and the human brain activity.

Cytomorphological features of metastatic squamous cell carcinoma in serous effusions

To study the cytomorphological features of squamous cell carcinoma (SCC) in serous effusions. Conventional smears from 23 SCC were reviewed for the following features: cellularity, single cells, cell clusters, long cords, squamous pearls, cell-in-cell, 'windows', polygonal cells, anucleated cells, tadpole cells, fibre cells, third-type cells, refractile cytoplasmic ring, two-tone cytoplasm, cytoplasmic density, cytoplasmic vacuoles, signet ring cells, nuclear/cytoplasmic ratio, nuclear hyperchromasia, irregular nuclear membrane, nuclear centricity, double or multiple nuclei, nucleolus, anaplastic cells and mitosis. Subsequently, we also reviewed 15 reactive mesothelium, 18 mesotheliomas and 24 adenocarcinomas for comparison. Most SCC smears comprised mixed populations of single cells and cell clusters. Keratinized squamous cells and squamous pearls were diagnostic for well-differentiated SCC. Squamous eddies, appreciated on the cell block sections appearing as two-dimensional cell clusters with a swirling pattern, were characteristic for SCC. Poorly differentiated/third-type cells with atypical cytoplasmic keratinization, manifest as two-tone cytoplasm with a well-defined border and occasionally a refractile central ring, were an important clue for the squamous origin of the cells. Features including cell-in-cell, cytoplasmic vacuolation, double or multinucleated cells, anaplastic cells and mitotic figures were present in various degrees, and were not of diagnostic value. Certain cytological features are diagnostic for SCC, whereas other features of poorly differentiated SCC often overlap with those of reactive mesothelial cells, mesothelioma, metastatic adenocarcinoma or urothelial carcinoma in serous effusions. The combination of clinical history, appropriate immunohistochemical panel and cytomorphological features are important to ensure a correct diagnosis.

Efficient generation of two-dimensional cluster states in a cavity QED

We propose a scheme to achieve a kind of nontrivial multipartite pair-wise controlled phase operation in a cavity QED setup. The operation implemented is of geometrical nature and is not sensitive to the thermal state of the cavity. In particular, we have managed to avoid the conventional dispersive coupling so that high speed gate operation is achieved which is very important in view of decoherence. We show that this multipartite pair-wise controlled phase operation makes the generation of two-dimensional cluster states very efficient.

Multifractal scaling of flux penetration in the iron-based superconductor Ba(Fe0.93Co0.07)2As2

The penetration of magnetic flux fronts in the optimally doped iron-based superconductor Ba(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{2}$As${}_{2}$ ($x=0.07\ifmmode\pm\else\textpm\fi{}0.005$) is studied by means of magneto-optical imaging and Bitter decoration. The higher-order analysis of roughening and growth of the magnetic flux front reveals anomalous scaling properties, indicative of non-Gaussian correlations of the disorder potential. While higher-order spatial correlation functions reveal multifractal behavior for the roughening, the usual Kardar-Parisi-Zhang growth exponent is found. Both exponents are found to be independent of temperature. The scaling behavior is manifestly different from that found for other modes of flux penetration, such as that mediated by avalanches, suggesting that multiscaling is a powerful tool for the characterization of roughened interfaces. We propose a scenario for vortex penetration based on two-dimensional percolation and cluster aggregation for an inhomogeneously disordered superconductor.

Analyzing the liquid state of two-dimensional dust clusters: The instantaneous normal mode approach

The liquid state and the freezing transition of finite two-dimensional dust systems are studied using the instantaneous normal mode (INM) analysis. This technique measures the instantaneous unstable modes of a cluster configuration and relates them to the liquid properties of the system. Here, the INM analysis has been applied to experiments on laser-heated dust clusters. From the experiments, diffusion constants and melting temperatures for clusters of different size have been derived. The INM diffusion constants have been compared to those derived from other standard approaches. The scatter of the diffusion constant retrieved by the INM is smaller than that retrieved by other methods, allowing a more reliable determination of melting temperatures. Moreover, the behavior of double-well and escape modes, which reflect certain topological properties of unstable modes, correlates very well with the behavior of the diffusion constant. Further, the dynamic nature of the unstable modes has been determined as mostly shearlike. Finally, the INM results on the experiments are checked against those from Langevin simulations.

Self-Assembly of Two-Dimensional Colloidal Clusters by Tuning the Hydrophobicity, Composition, and Packing Geometry

We study the structure of binary monolayers of large (3 μm diameter) very hydrophobic (A) and large (3 μm diameter) hydrophilic (B) or small (1 μm diameter) hydrophilic (C) silica particles at an octane-water interface. By tuning the composition and packing geometry of the mixed monolayer, we find that a rich variety of two-dimensional hexagonal superlattices of mixed A/B or A/C clusters are formed, stabilized by short-ranged electrostatic induced dipole interactions. The cluster structures obtained are in excellent agreement with zero temperature calculations, indicating that the self-assembly process can be effectively controlled.

A semi-supervised hierarchical approach: two-dimensional clustering of microarray gene expression data

Micro array technologies have become a widespread research technique for biomedical researchers to assess tens of thousands of gene expression values simultaneously in a single experiment. Micro array data analysis for biological discovery requires computational tools. In this research a novel two-dimensional hierarchical clustering is presented. From the review, it is evident that the previous research works have used clustering which have been applied in gene expression data to create only one cluster for a gene that leads to biological complexity. This is mainly because of the nature of proteins and their interactions. Since proteins normally interact with different groups of proteins in order to serve different biological roles, the genes that produce these proteins are therefore expected to co express with more than one group of genes. This constructs that in micro array gene expression data, a gene may makes its presence in more than one cluster. In this research, multi-level micro array clustering, performed in two dimensions by the proposed two-dimensional hierarchical clustering technique can be used to represent the existence of genes in one or more clusters consistent with the nature of the gene and its attributes and prevent biological complexities.

Photodissociation of methyl iodide adsorbed on low-temperature amorphous ice surfaces

Photodissociation dynamics of methyl iodide (CH3I) adsorbed on both amorphous solid water (ASW) and porous amorphous solid water (PASW) has been investigated. The ejected ground-state I((2)P3∕2) and excited-state I((2)P1∕2) photofragments produced by 260- and 290-nm photons were detected using laser resonance-enhanced multiphoton ionization. In contrast to gas-phase photodissociation, (i) the I((2)P3∕2) photofragment is favored compared to I((2)P1∕2) at both wavelengths, (ii) I((2)P3∕2) and I((2)P1∕2) have velocity distributions that depend upon ice morphology, and (iii) I2 is produced on ASW. The total iodine [I((2)P3∕2)+I((2)P1∕2)+I2] yield varies with substrate morphology, with greater yield from ASW than PASW using both 260- and 290-nm photons. Temperature-programmed desorption studies demonstrate that ice porosity enhances the trapping of adsorbed CH3I, while pore-free ice likely allows monomer adsorption and the formation of two-dimensional CH3I clusters. Reactions or collisions involving these clusters, I atomic fragments, or I-containing molecular fragments at the vacuum-surface interface can result in I2 formation.

Two-dimensional magnetic clusters in Lan(Ti1−xFex)nO3n+2 (n = 5 with x = 0.2 and n = 6 with x = 0.33)

Crystal structure analyses of the layered compounds Lan(Ti1−xFex)nO3n+2, with nominal compositions x = 0.2 for n = 5 and x = 0.33 for n = 6, show that the iron is concentrated at the centers of the slabs. The spatial arrangements of the iron ions can be approximated by two-dimensional square lattices with strong magnetic interactions between neighboring sites, albeit with fractional occupancies of the sites of an average of 0.67 magnetic ions in n = 6 and 0.42 magnetic ions in n = 5 compounds. A previously described (Lichtenberg et al 2008 Prog. Solid State Chem. 36 253) crossover of magnetic behavior of n = 6 at room temperature is explained by the formation of two-dimensional, ferromagnetically organized magnetic clusters with an average size of 52 Fe3+ ions. The absence of long-range magnetic order follows from the fractional occupancy of the sites by the magnetic ions. The lower concentration of magnetic ions in n = 5 explains why crossover behavior is not found and clusters do not form in that compound.

Are large perimeter- minimizing two-dimensional clusters of equal-area bubbles hexagonal or circular?

A computer study of clusters of up to N =200 000 equal-area bubbles shows for the first time that partially rounding conjectured optimal hexagonal planar soap bubble clusters reduces perimeter. Different methods of creating optimal clusters are compared, and new candidate minimizers for several N are given.

Aberrant promoter methylation of the CD4 gene in peripheral blood cells of mastitic dairy cows

Bovine mastitis is the most common and costly disease of dairy cattle. Cluster of differentiation 4 (CD4) is closely related to the immune response in mastitis. We quantified promoter CpG methylation levels of the CD4 gene in Chinese Holsteins with clinical mastitis (CM) and in healthy controls; these levels were quantitatively detected with bisulfite pyrosequencing assays and confirmed by cloning sequencing. We found that the bovine CD4 promoter had 16% more methyl groups in the cows with CM (75.0 ± 5.8%) compared to the controls (59.0 ± 8.5%). The decreased expression level of CD4 in CM cows may be downregulated by the increased DNA methylation levels in the CD4 promoter. Two-dimensional hierarchical clustering analyses showed large differences in promoter CD4 methylation between mastitic and healthy cows; the dendrogram clearly distinguished the cows with clinical mastitis from healthy controls based on methylation levels. The DNA methylation level of the CD4 gene was strongly influenced by mastitis status in all comparisons. We suggest that the DNA methylation level of the CD4 promoter can be used as a molecular marker for clinical mastitis in dairy cows.

One-Way Quantum Computation with Cluster State and Probabilistic Gate

We present a scheme for efficiently constructing a two-dimensional cluster state, which serves as the central physical resource for one-way quantum computation. In this scheme, we successfully make the required computational overhead scale efficiently with the qubit number by using a probabilistic entangling quantum gate.

Effect of Dispersion on Catalytic Performance of Supported Pt Catalysts for CO Oxidation

A series of ceria, silica, and γ-alumina-supported platinum catalysts were prepared by the incipient-wetness impregnation method. Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to determine the dispersion of Pt. For the Pt/CeO 2 catalysts, XRD studies suggest that Pt was better dispersed as its concentration decreased. This observation correlated well with XPS analysis. For catalysts with the same Pt mass loading, TEM and XRD results suggest that Pt dispersion displays an increasing order as Pt/SiO 2 < Pt/γ-Al 2 O 3 < Pt/CeO 2 . Catalytic activities for CO oxidation were investigated. Results showed that the 0.25 wt% Pt/CeO 2 exhibited a higher activity than other oxide supported catalysts with a turnover frequency of 2.2 × 10 −3 CO 2 per total Pt per second at room temperature. 以氧化铈、氧化硅和氧化铝为载体, 采用浸渍法制备了一系列不同负载量的 Pt 基催化剂, 并利用透射电子显微镜、X 射线粉末衍射和 X 射线光电子能谱等技术对催化剂进行了表征. 结果表明, 对于 Pt/CeO 2 催化剂, 随着负载量减小, Pt 的分散度提高; 对于相同负载量的 Pt 基催化剂, 各催化剂上 Pt 分散情况为: Pt/SiO 2 < Pt/γ-Al 2 O 3 < Pt/CeO 2 . CO 氧化反应结果表明, 0.25% Pt/CeO 2 催化剂表现出更加优良的低温活性, 室温下其单位 Pt 原子上 CO 2 的生成速率为 2.2 × 10 −3 s −1 . Highly dispersed Pt species, including single atom and two-dimensional clusters, are active for CO oxidation at room temperature.

Symmetry protection of measurement-based quantum computation in ground states

The two-dimensional cluster state, a universal resource for measurement-based quantum computation, is also the gapped ground state of a short-ranged Hamiltonian. Here, we examine the effect of perturbations to this Hamiltonian. We prove that, provided the perturbation is sufficiently small and respects a certain symmetry, the perturbed ground state remains a universal resource. We do this by characterizing the operation of an adaptive measurement protocol throughout a suitable symmetry-protected quantum phase, relying on generic properties of the phase rather than any analytic control over the ground state.

Interactions and Self-Assembly of Stable Hydrocarbon Radicals on a Metal Support.

Stable hydrocarbon radicals are able to withstand ambient conditions. Their combination with a supporting surface is a promising route toward novel functionalities or carbon-based magnetic systems. This will remain elusive until the interplay of radical–radical interactions and interface effects is fundamentally explored. We employ the tip of a low-temperature scanning tunneling microscope as a local probe in combination with density functional theory calculations to investigate with atomic precision the electronic and geometric effects of a weakly interacting metal support on an archetypal hydrocarbon radical model system, i.e., the exceptionally stable spin-1/2 radical α,γ-bisdiphenylene-β-phenylallyl (BDPA). Our study demonstrates the self-assembly of stable and regular one- and two-dimensional radical clusters on the Au(111) surface. Different types of geometric configurations are found to result from the interplay between the highly anisotropic radical–radical interactions and interface effects. We investigate the interaction mechanisms underlying the self-assembly processes and utilize the different configurations as a geometric design parameter to demonstrate energy shifts of up to 0.6 eV of the radicals’ frontier molecular orbitals responsible for their electronic, magnetic, and chemical properties.

Characteristics of clustered particles in skimming flows on a stepped spillway

Air–water flows at hydraulic structures are commonly observed and called white waters. The free-surface aeration is characterised by some intense exchanges of air and water leading to complex air–water structures including some clustering. The number and properties of clusters may provide some measure of the level of particle-turbulence and particle–particle interactions in the high-velocity air–water flows. Herein a re-analysis of air–water clusters was applied to a highly aerated free-surface flow data set (Chanson and Carosi, Exp Fluids 42:385–401, 2007). A two-dimensional cluster analysis was introduced combining a longitudinal clustering criterion based on near-wake effect and a side-by-side particle detection method. The results highlighted a significant number of clustered particles in the high-velocity free-surface flows. The number of bubble/droplet clusters per second and the percentage of clustered particles were significantly larger using the two-dimensional cluster analysis than those derived from earlier longitudinal detection techniques only. A number of large cluster structures were further detected. The results illustrated the complex interactions between entrained air and turbulent structures in skimming flow on a stepped spillway, and the cluster detection method may apply to other highly aerated free-surface flows.

Deciduoid mesothelioma: Cytologic presentation and diagnostic pitfalls

We report two cases of malignant deciduoid mesothelioma (MDM), a very rare variant of malignant mesothelioma (MM). Case 1: An 18-year-old male with no history of asbestos exposure presented with worsening abdominal pain, anorexia, and vomiting after a motor vehicle accident. A CT scan showed small amount of ascites and abdominal mass. An exploratory laparotomy revealed multiple yellow tan, firm nodules on the peritoneum and omentum. He received palliative treatment and died 5 months after the diagnosis. Case 2: A 64-year-old female with history of asbestos exposure initially presented with abdominal distension. CT scan showed abdominal mass with a large amount of ascites. A diagnostic laparoscopy revealed multiple peritoneal nodules. She underwent several regimens of chemotherapy over a period of 69 months and is still alive to date. In both cases, features of mesothelial origin were subtle and the smears showed predominantly single cells with marked nuclear atypia. The second case also contained few two-dimensional loose cell clusters with scalloped or hobnail borders. The clusters often exhibited a pseudoacinar structure surrounding a globular extracellular material. Groups of three to four cells often formed doublets and triplets with cell-to-cell windows. Our results show that MDM may not present with the traditional cytological features described in MM and can manifest with more nuclear pleomorphism resulting in erroneous diagnosis. Recognition of the subtle mesothelial features along with the appropriate ancillary tests is essential for accurate diagnosis.

Polarization Selection Rules for Surface-Enhanced Raman Scattering from Anisotropic Microstructured Surfaces

From a study of the polarization dependence of the surface-enhanced Raman (SERS) modes of a probe molecule (pyridine) adsorbed on a locally anisotropic, metallic surface, we show that the polarization asymmetry associated with the in-plane (ring stretching) vibrational modes is consistently correlated with the morphological anisotropy, while the out-of-plane (ring deformation) modes are almost insensitive to it. As a direct application of this “polarization selection rule” for SERS, we further show that the polarization asymmetry of the in-plane vibrational modes provides a quantitative estimate of the degree of local structural anisotropies in the system. Such mesoscale, locally ordered, anisotropic structures occur naturally in a wide variety of aggregated and self-assembled systems. As a model system for this study, we have used metal nanorod arrays, whose tips can be made to form two-dimensional clusters that exhibit anisotropy at mesoscopic length scales.