Effect of scale and surface chemistry on the mechanical properties of carbon nanotubes‐based composites

In this article, Multi‐Walled Carbon Nanotubes (MWCNTs) of varying diameters, both untreated and polycarboxylated, were dispersed at constant weight percentage in an epoxy matrix, and resulting fracture toughnesses (K_Ic) were measured in each case. We show that changing the MWCNT diameter has two effects on the composite fracture toughness: (i) a small MWCNT diameter enables larger interfacial surface for adhesion maximization, which increases toughness; (ii) at the same time, it limits the available pull‐out energy and reduces the MWCNT ability to homogeneously disperse in the matrix due to this same large active surface: this decreases toughness. Most commercially available MWCNTs have a length range of several μm, thus an optimal diameter exists which depends on MWCNT wall thickness and surface treatment. Such optimal diameter maximizes pull‐out energy and thus composite fracture toughness. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Variational Bayesian Inference for Nonlinear Hawkes Process with Gaussian Process Self-Effects

Traditionally, Hawkes processes are used to model time-continuous point processes with history dependence. Here, we propose an extended model where the self-effects are of both excitatory and inhibitory types and follow a Gaussian Process. Whereas previous work either relies on a less flexible parameterization of the model, or requires a large amount of data, our formulation allows for both a flexible model and learning when data are scarce. We continue the line of work of Bayesian inference for Hawkes processes, and derive an inference algorithm by performing inference on an aggregated sum of Gaussian Processes. Approximate Bayesian inference is achieved via data augmentation, and we describe a mean-field variational inference approach to learn the model parameters. To demonstrate the flexibility of the model we apply our methodology on data from different domains and compare it to previously reported results.     

A conformationally flexible tetrahydroxycalix[4]arene adopting the unusual 1,3-alternate conformation

The use of a chiral solvating agent enabled the determination of the NMR-silent ring-inversion process of the ketocalixarene 3. Spectroscopic and crystal data indicate that 3 adopts the unusual 1,3-alternate conformation.     

Enhanced light‐vapor interactions and all optical switching in a chip scale micro‐ring resonator coupled with atomic vapor

The coupling of atomic and photonic resonances serves as an important tool for enhancing light‐matter interactions and enables the observation of multitude of fascinating and fundamental phenomena. Here, by exploiting the platform of atomic‐cladding wave guides, the resonant coupling of rubidium vapor and an atomic cladding micro ring resonator is experimentally demonstrated. Specifically, cavity‐atom coupling in the form of Fano resonances having a distinct dependency on the relative frequency detuning between the photonic and the atomic resonances is observed. Moreover, significant enhancement of the efficiency of all optical switching in the V‐type pump‐probe scheme is demonstrated. The coupled system of micro‐ring resonator and atomic vapor is a promising building block for a variety of light vapor experiments, as it offers a very small footprint, high degree of integration and extremely strong confinement of light and vapor. As such it may be used for important applications, such as all optical switching, dispersion engineering (e.g. slow and fast light) and metrology, as well as for the observation of important effects such as strong coupling, and Purcell enhancement.

     

Time-varying many-server finite-queues in tandem: Comparing blocking mechanisms via fluid models

This paper focuses on the mechanism of Blocking Before Service (BBS), in time-varying many-server queues in tandem. BBS arises in telecommunication networks, production lines and healthcare systems. We model a stochastic tandem network under BBS and develop its corresponding fluid limit, which includes reflection due to jobs lost. Comparing our fluid model against simulation shows that the model is accurate and effective. This gives rise to design/operational insights regarding network throughput, under both BBS and BAS (Blocking After Service).     

H2O‐Catalyzed Route to Early Lanthanide Tribromide THF and DME Solvates from Oxides

A convenient one‐pot synthetic protocol towards THF and DME solvates of lanthanum and other early lanthanide tribromides was developed using the water‐catalyzed reaction of lanthanide(III) oxides with highly reactive Me₃SiBr in situ formed from commercially available disilane Si₂Me₆ and Br₂. This practical route allows to obtain the target lanthanum tribromide solvates [LaBr₃(thf)₄] ( 1a ) and [LaBr₃(dme)₂]₂ ( 1b ) as well as analogous early lanthanide molecular tribromide solvates [NdBr₃(thf)₄] ( 2a ), [NdBr₃(dme)₂] ( 2b ), [SmBr₃(thf)₂] ( 3a ), and [SmBr₃(dme)₂] ( 3b ) difficult to prepare by other solution‐based procedures. The molecular structure of 1b· 2CH₂Cl₂ was determined by an XRD study.     

Tetraaddition of PhLi to a ketocalixarene derivative

[reaction: see text] Reaction of a ketocalixarene with 2.2 equiv or an excess of PhLi affords diaddition and tetraaddition products, respectively. Ionic hydrogenation of the tetraalcohol 8a yields a calix[4]arene monosubstituted by phenyl groups at all four methylene bridges.     

Structure selection based on high vertical electron affinity for TiO2 clusters

We study the structure and electronic properties of (TiO2)(2-10) clusters by using basin hopping based on density functional theory, combined with many-body perturbation theory. We show that in photoemission experiments performed on anions isomers with high electron affinity are selectively observed rather than those with the lowest energy. These isomers possess a highly reactive Ti3+ site. The selectivity for highly reactive clusters may be exploited for applications in catalysis.