Presence Of Large Clusters Research Articles

The cooperative effect of HX (X = Br, F) acids in CH3SH clusters

In this study, the cooperative effect of clusters of HBr, HF and CH3SH was investigated. Therefore, (HX)n…(CH3SH)m, (X = Br, F; n, m = 1, 2) clusters were calculated using B3LYP at DFT level and aug-cc-pVDZ and aug-cc-pVTZ basis sets at MP2 level.Structures, energies and infrared vibrational frequencies are all used to discuss the results in this study. It was observed that the cooperative effect makes a significant contribution to the total interaction energies of the cyclic conformers of (HX)n…(CH3SH)m. In addition, it was determined that the double addition potential cannot be neglected in the simulations where it is applied. Tetramer complexes were studied to evaluate behavior in the presence of larger clusters. Furthermore, thermodynamic parameters were calculated for each cluster examined.These results show that the sulfur's hydrogen bond accepting ability increases further in the presence of HBr, HF and exhibits hydrogen bonding behavior in the clusters.

Ion-induced changes in DNA gels.

Small angle neutron scattering (SANS) measurements are reported for DNA gels under near physiological conditions in which the concentration of monovalent and divalent counter-ions and the pH are varied. The scattering intensity I(q) is described by a two-term equation, one due to osmotic concentration fluctuations and the other coming from static inhomogeneities frozen in by the cross-links. SANS in the low q range indicates the presence of large clusters and the size of which exceeds the resolution of the experiment. In the intermediate q-range, the intensity increases with the CaCl2 concentration and the slope approaches -1, corresponding to linear (rod-like) scatterers. In the highest q region, the scattering response is governed by the local chain geometry. Screening of electrostatic interactions by sodium chloride causes a moderate increase in the SANS intensity that is accompanied by an increase in the mesh size L of the network. Addition of calcium chloride, or a decrease in pH, produces similar trends, and ultimately leads to phase separation. The scattering intensity at q = 0, estimated from independent measurements of the osmotic pressure Π, is in excellent agreement with I(0) from the SANS measurements. Anomalous small angle X-ray scattering (ASAXS) measurements on the uncross-linked DNA show that the monovalent ion cloud is only weakly influenced by the addition of divalent ions. Conversely, the divalent counter-ion cloud tightly follows the contour of polymer chains.

On the Role of Stirring on Microstructure and Ductility of Rheocast Al Alloys

Two alloys containing different Mg contents have been used to study the combined effect of stirring and oxidation on microstructure and ductility. The results show that intensive stirring can sufficiently disperse the α-Al particles and enable better liquid feeding during solidification and consequently reduce the porosity. The morphology of the oxides is determined by the amount of both Mg and stirring. With lower Mg content, the oxides present as oxide films, which can be broken up during stirring. In alloy with higher Mg content, the oxides exist as particles with numerous cracks, and the particle size increases slightly after stirring. In the Magsimal 59 alloy, due to the presence of large clusters of pores in the fracture surface, the influence of the small oxide particles on the ductility is negligible. In contrast, in the 42000 alloy, large oxide films on the fracture surface are correlated with the ductility.

Preparation and Characterization of Composite of Polyamide 6/Nickel Ferrite

The research in composites attempt to predict the physico-chemical and mechanical a given mixture of materials. In this work, a composite was produced using as the polyamide 6 matrix and how the burden of nickel ferrite was incorporated as powders calcined at 1200°C and concentration of 50 wt.%. This mixture was compacted in a hydraulic press with heating and characterized by XRD, SEM and TG. XRD results showed the characteristic peaks of polyamide 6 and ferrite. SEM results showed a good dispersion of nickel ferrite loading in the matrix, the presence of larger clusters and evenly distributed load for the composite calcined at 1200 ° C. TG curves showed that the addition of loading of calcined nickel ferrite promoted an increase in thermal stability of the composite compared to pure polyamide.

Infrared spectra of CO2-doped hydrogen clusters, (H2)N–CO2

Clusters of para-H(2) and/or ortho-H(2) containing a single carbon dioxide molecule are studied by high resolution infrared spectroscopy in the 2300 cm(-1) region of the CO(2) ν(3) fundamental band. The (H(2))(N)-CO(2) clusters are formed in a pulsed supersonic jet expansion from a cooled nozzle and probed using a rapid scan tunable diode laser. Simple symmetric rotor type spectra are observed with little or no resolved K-structure, and prominent Q-branch features for ortho-H(2) but not para-H(2). Observed rotational constants and vibrational shifts are reported for ortho-H(2) up to N = 7 and para-H(2) up to N = 15, with the N > 7 assignments only made possible with the help of theoretical simulations. The para-H(2) cluster with N = 12 shows clear evidence for superfluid effects, in good agreement with theory. The presence of larger clusters with N > 15 is evident in the spectra, but specific assignments are not possible. Mixed para- + ortho-H(2) cluster transitions are well predicted by linear interpolation between corresponding pure cluster line positions.

Additive Mixed Effect Model for Clustered Failure Time Data

We propose an additive mixed effect model to analyze clustered failure time data. The proposed model assumes an additive structure and includes a random effect as an additional component. Our model imitates the commonly used mixed effect models in repeated measurement analysis but under the context of hazards regression; our model can also be considered as a parallel development of the gamma-frailty model in additive model structures. We develop estimating equations for parameter estimation and propose a way of assessing the distribution of the latent random effect in the presence of large clusters. We establish the asymptotic properties of the proposed estimator. The small sample performance of our method is demonstrated via a large number of simulation studies. Finally, we apply the proposed model to analyze data from a diabetic study and a treatment trial for congestive heart failure.

The Multiple Faces of Carcinoid Tumor: Performance Characteristics of Low-Grade Neuroendocrine Carcinoma Metastatic to the Liver in an Educational Interlaboratory Slide Comparison Program

Cytologic features of low-grade neuroendocrine carcinoma are well described in primary sites. There are fewer reports of the cytologic features specific to metastatic liver lesions or the frequency of misdiagnosis. To identify discriminating cytologic features and characterize the rate of misdiagnosis of low-grade neuroendocrine tumors metastatic to the liver in an educational interlaboratory slide comparison program. Glass slides with the specific reference diagnosis of metastatic low-grade neuroendocrine tumor involving liver were circulated to 175 laboratories, with 575 participant responses in the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytology. Eight specific cytologic features were assessed to identify predictors of poor performance (>10% misdiagnosis). There was an exact match diagnosis in 496 of 575 responses (86%); 555 of 575 responses (96.5%) were correctly identified as malignant. Incorrect responses included adenocarcinoma (27), hepatocellular neoplasm (21), small cell carcinoma (11), benign neoplasm not otherwise specified (6), benign liver (3) and inflammation (3). Three features were significantly associated with the misdiagnosis of adenocarcinoma: presence of large clusters (P = .02), lack of single-cell pattern (P = .02), and lack of stripped nuclei (P = .01). Participants often recognize metastatic low-grade neuroendocrine carcinoma in an educational glass-slide program. Adenocarcinoma was the most common incorrect diagnosis, especially in the presence of large cellular clusters or absence of a single-cell pattern or stripped nuclei.

Interpreting genotype cluster sizes of Mycobacterium tuberculosis isolates typed with IS6110 and spoligotyping

Molecular techniques such as IS6110-RFLP typing and spacer oligonucleotide typing (spoligotyping) have aided in understanding the transmission patterns of Mycobacterium tuberculosis. The degree of clustering of isolates on the basis of genotypes is informative of the extent of transmission in a given geographic area. We analyzed 130 published data sets of M. tuberculosis isolates, each representing a sample of bacterial isolates from a specific geographic region, typed with either or both of the IS6110-RFLP and spoligotyping methods. We explored common features and differences among these samples. Using population models, we found that the presence of large clusters (typically associated with recent transmission) as well as a large number of singletons (genotypes found exactly once in the data set) is consistent with an expanding infectious population. We also estimated the mutation rate of spoligotype patterns relative to IS6110 patterns and found the former rate to be about 10–26% of the latter. This study illustrates the utility of examining the full distribution of genotype cluster sizes from a given region, in the light of population genetic models.

Effect of cationic size on gelation temperature and properties of gelatin hydrogels

Effect of Na +, K + and Ca 2+ on gel transition temperature ( T g) of gelatin hydrogels (5%, w/v) has been studied by oscillatory rheology in the salt concentration range I = 0.01–0.1 M, which showed increase in T g with salt concentration with the trend for T g showing Ca 2+ > K + > Na +. The dynamic light scattering (DLS) measurements in the sol state ( T > T g) showed two distinct relaxation modes whereas only a gel mode was observed in the gel state in all the samples which contained significant amount of heterodyne contribution. Low frequency (1.5 rad/s) isochronal storage modulus data revealed the formation of strong gel in presence of CaCl 2 compared to that of NaCl and KCl situations. The slow mode relaxation and heterodyne parameter obtained from DLS data indicate the presence of larger clusters in Ca 2+ gels.

Multiscale simulation of laser ablation of organic solids: evolution of the plume

A computational approach that combines the molecular dynamics (MD) breathing sphere model for simulation of the initial stage of laser ablation and the direct simulation Monte Carlo (DSMC) method for simulation of the multi-component ablation plume development on the time- and length-scales of real experimental configurations is presented. The combined multiscale model addresses different processes involved in the laser ablation phenomenon with appropriate resolutions and, at the same time, accounts for the interrelations among the processes. Preliminary results demonstrate the capabilities of the model and provide new insights into complex processes occurring during the ablation plume expansion. The spatial distribution of monomers in the plume is found to be strongly affected by the presence of large clusters. Interaction between the clusters and monomers can result in splitting of the monomer distribution into faster and slower components. The overall spatial mass distribution is found to have little relation with the monomer distribution.

Association of cellular prion protein with gangliosides in plasma membrane microdomains of neural and lymphocytic cells.

In this report we demonstrated that cellular prion protein is strictly associated with gangliosides in microdomains of neural and lymphocytic cells. We preliminarily investigated the protein distribution on the plasma membrane of human neuroblastoma cells, revealing the presence of large clusters. In order to evaluate its possible role in tyrosine signaling pathway triggered by GEM, we analyzed PrPc presence in microdomains and its association with gangliosides, using cholera toxin as a marker of GEM in neuroblastoma cells and anti-GM3 MoAb for identification of GEM in lymphoblastoid cells. In neuroblastoma cells scanning confocal microscopical analysis revealed a consistent colocalization between PrPc and GM1 despite an uneven distribution of both on the cell surface, indicating the existence of PrPc-enriched microdomains. In lymphoblastoid T cells PrPc molecules were mainly, but not exclusively, colocalized with GM3. In addition, PrPc was present in the Triton-insoluble fractions, corresponding to GEM of cell plasma membrane. Additional evidence for a specific PrPc-GM3 interaction in these cells was derived from the results of TLC analysis, showing that prion protein was associated with GM3 in PrPc immunoprecipitates. The physical association of PrPc with ganglioside GM3 within microdomains of lymphocytic cells strongly suggests a role for PrPc-GM3 complex as a structural component of the multimolecular signaling complex involved in T cell activation and other dynamic lymphocytic plasma membrane functions.

Oscillatory regimes of vapor condensation

The problem of the condensation of supersaturated vapor in an open system at a constant rate of production of a monomer and a continuous flow of a carrier gas that removes the products of condensation from the system is considered. It is shown both analytically and by numerical experiment that with a decreasing rate of the carrier gas to below a critical magnitude, the condensation regime becomes oscillatory; namely, time oscillations of the cluster-size distribution in the vapor to be condensed are set in. The cause of the phenomenon is in the suppression of the rate of nucleation and the presence of large clusters.

Clustering-induced nonsaturable absorption phenomenon in heavily erbium-doped silica fibers

Nonsaturable absorption experiments in heavily erbium-doped fibers demonstrate that the behavior of the absorption with pump power cannot be interpreted with an ion-pair model but requires that the presence of larger clusters be taken into account. Numerical modeling permits the determination of the percentage of ions organized in clusters, as much as 52% of the dopants in the tested fiber, and the intracluster transfer rate, up to 2 × 106 s−1.

On the role of dissociative ionization in the formation of argon dimer ions

The formation of Ar 2 + ions has been investigated by means of the threshold photoelectron photoion coincidence (TPEPICO) technique. Two pathways for the formation of Ar 2 + ions are important. One is a direct path via excitation of Rydberg states of Ar2 with consecutive autoionization. The other path is dissociative ionization of larger argon clusters, in this case argon trimers. These two pathways lead to Ar 2 + ions with different internal energy. The pathways are easily distinguished in the TPEPICO-TOF spectra by the kinetic energy released (KER) in the dissociative ionization. The KER for the reaction Ar 3 + → Ar 2 + + Ar was measured as a function of the photon energy and compared to the KER expected from statistical theory. The agreement is satisfying and confirms that Ar 3 + ions do indeed dissociate at the thermochemical threshold. At higher photon energy the excited2Π(3/2)g state of Ar 3 + is also detected from a second component in the KER. By applying a kinetic energy discrimination it is possible to measure cluster ion spectra in the presence of larger clusters but essentially without interference from the latter.

Dynamic simulation of bimodal suspensions of hydrodynamically interacting spherical particles

Stokesian dynamics is used to simulate the dynamics of a monolayer of a suspension of bimodally distributed spherical particles subjected to simple shearing flow. Hydrodynamic forces only are considered. Many-body far-field effects are calculated using the inverse of the grand mobility matrix. Near-field effects are calculated from the exact equations for the interaction between two unequal-sized spheres. Both the detailed microstructure (e.g. pair-distribution function and cluster formation) and the relative viscosity are determined for bimodal suspensions having particle size ratios of 2 and 4. The flow of an ‘infinite’ suspension is simulated by considering 25, 49, 64, and 100 particles to be ‘one’ cell of an infinite periodic array. The effects of both the size ratio and the relative fractions of the different-sized particles are examined. When the area fraction, ϕa, is less than 0.4 the particle size distribution does not affect the calculated viscosity. For ϕa > 0.4, and for a fixed fraction of small spheres, the bimodal suspensions generally have lower viscosities than monodispersed suspensions, with the size of this effect increasing with ϕa. These results compare favourably with experiment when ϕa and the volume fraction, ϕv, are normalized by the maximum packing values in two and three dimensions, respectively. At the microstructural level, viscosity reduction is related to the influence of particle size distribution on the average number of particles in clusters. At a fixed area fraction, the presence of smaller particles tends to reduce average cluster size, particularly at larger ϕa, where significant viscosity reductions are observed. Since the presence of large clusters in monodispersed suspensions has been directly linked to high viscosities, this provides a dynamic mechanism for the viscosity reduction in bimodal suspensions.

Cluster beam analysis via photoionization

A photoionization method for quantitatively analyzing the neutral products of free jet expansions is described. The basic principle is to measure the yield of an ion characterization of each component cluster at a photon energy just below that at which production of the same ion from larger clusters can be detected. Since there is then no problem with fragmentation, the beam density of each neutral cluster can be measured in the presence of larger clusters. Although these measurements must be done in the test ions' onset regions where their yields are often quite small, the technique is made highly practicable by the large intensities of widely tunable vacuum-ultraviolet synchrotron light now available at electron storage rings. As an example, the method is applied to the analysis of cluster beams collimated from the free jet expansion of a 200:1 ammonia-chlorobenzene mixture.

Evidence for ethylene-molecule clusters in a gas jet system

Abstract The presence of large clusters in the input carrier gas of a gas jet recoil transport system has been estbilished from light-scattering experiments. With a 90° scattering geometry a λ−1 dependence was observed for light scattered by flowing ethylene gas, obtained from a reservoir that was maintained above the critical pressure. Estimates of lifetimes, diameter and density of clusters in the flowing gas are provided.