The Role of Interface on the Properties of Cluster Assemblies

Atomic clusters characterized by finite size, low dimensionality, and reduced coordination number exhibit many novel properties that are very different from their bulk. As these clusters are assembled, their properties can be significantly altered due to the interaction of these clusters with each other as well as with their support. This paper provides a brief review of the cluster properties that are affected when clusters are deposited on metallic or organic substrates, isolated in matrices or in zeolite cages, coated with acetate ligands, or simply allowed to self-assemble without the presence of any reactive species. It is shown that the interface between the clusters and their support can play an important role on the properties of clusters as their unique characteristics do.     

Synthesis of Some Novel bis‐Spiro[indole‐pyrazolinyl‐thiazolidine]‐2,4′‐diones

The reaction of 1H‐indol‐2,3‐diones with 1,6‐dibromohexane has resulted in the formation of new 1H‐indol‐2,3‐diones‐1,1′‐(1,6‐hexanediyl)bis in quantitative yields. These compounds have been used for the synthesis of novel [3′‐(2,3‐dimethyl‐5‐oxo‐1‐phenyl‐3‐pyrazolin‐4‐yl)spiro[3H‐indol‐3,2′‐thiazolidine]‐2,4′‐dione]‐1,1′‐(1,6‐hexanediyl)bis via bis Schiff's bases, [3‐(2,3‐dimethyl‐5‐oxo‐1‐phenyl‐3‐pyrazolin‐4‐yl) imino‐1H‐indol‐2‐one]‐1,1′‐(1,6‐hexanediyl)bis.     

Highly dispersed clay-polyolefin nanocomposites free of compatibilizers, via the in situ polymerization of alpha-olefins by clay-supported catalysts

In situ polymerization by certain transition metal catalysts supported on and activated by acid-treated montmorillonite produces well-dispersed clay-polyolefin nanocomposites, without requiring either organic surfactants to be present in the clay phase or modification of the polyolefin structure.     

Quantum corrections to electro-weak form factors of nucleons in the skyrme model

We calculate0(1/N) corrections to electro-weak currents of nucléons in the Skyrme model. In contrast with the corresponding correction to the Skyrmion mass, these corrections are negligibly small.     

Memory effects in polymers. V. Processing history versus thermally induced self-orientation of unoriented poly(chlorotrifluoroethylene) films

A peculiar phenomenon is reported whereby a melt-extruded, low-crystallinity, unoriented film of poly(chlorotrifluoroethylene) upon unconstrained thermal treatment, self-extends in the machine direction (MD) while shrinking along the transverse (TD) and normal/thickness (ND) directions. In addition to the expected increase in crystallinity, the annealing process leads to an unexpected development of crystalline orientation along the MD. This phenomenon is an example of “processing-induced memory effects” since it depends on the processing history of the starting film, e.g., melt-extrusion leads to the subject behavior whereas compression molding does not. We must mention that the melt-extruded films of poly(chlorotrifluoroethylene) are isotropic to start with, that is, MD and TD are indistinguishable prior to the annealing process. Furthermore, this phenomenon has not been observed for any other semicrystalline polymer and is believed to be the first citation for poly(chlorotrifluoroethylene) since its commercialization in 1957. Thermomechanical analysis (TMA) is the analytical technique that led to this novel phenomenon which was later substantiated by x-ray diffraction (XRD). ©1995 John Wiley & Sons, Inc.     

Pulse-number distribution for the neural spike train in the cat's auditory nerve

Pulse-number distributions (PNDs) were recorded from primary afferent fibers in the auditory nerve of the cat, using standard extracellular microelectrode recording techniques. Pure-tone and broadband-noise stimuli were used. The number of neural spikes (pulses) n was measured in a set of contiguous intervals, each of duration T seconds. The quantity n varies from one interval to another. These data were then used to determine the PND, which is the probability p(n,T) of occurrence of n spikes in the time T, versus the number n. The estimated mean and variance of p(n,T) were obtained. Two different values of T were used. An unexpected observation was that the count mean-to-variance ratio R is relatively constant and independent of the stimulus intensity. Use of the PND as a statistical measure of the underlying neural point process has a number of virtues. For example, the PND readily exhibits the existence of spike clusters (e.g., pairs) for some units. The PND is essentially unaffected by time jitter and time quantization and provides a statistically significant measure for units firing at low rates. A study of the scaled and unscaled pulse-interval distributions (PIDs), under conditions of spontaneous firing, demonstrates that the occurrences of neural events are generally not describable by a renewal process. Our investigation shows that none of the point processes customarily used to model the auditory neural spike train is consistent with all of the data. It appears that the encoding of acoustic information into nerve spikes in the peripheral auditory system takes the form of a cluster point process similar to the Neyman-Scott type. For pure-tone excitation, the PND will be well represented as a multinomial distribution in this case.