Quest for frustration driven distortion in Y2(Mo2)O(7)

We investigated the nature of the freezing in the geometrically frustrated Heisenberg spin glass Y2(Mo2)O(7) by measuring the temperature dependence of the static internal magnetic field distribution above the spin-glass temperature, Tg, using the muon spin relaxation technique. The evolution of the field distribution cannot be explained by changes in the spin susceptibility alone and suggests a lattice deformation. This possibility is addressed by numerical simulations of the Heisenberg Hamiltonian with magnetoelastic coupling at T > 0.     

Persistent Chemiluminescent Glow of Phenoxy-dioxetane Luminophore Enables Unique CRET-Based Detection of Proteases

Chemiluminescence is being considered an effective imaging modality as it offers low background and high sensitivity. Recent discovery by our group has led to development of new phenoxy-dioxetane chemiluminescence luminophores, which are highly bright under physiological conditions. However, the current scope of probes based on these luminophores is limited, as they can only be turned on by phenol protecting group removal. Here we present a new chemiluminescence resonance energy transfer (CRET) system, Glow-CRET, in which light emission is triggered by proteolytic cleavage of a peptide substrate that links a dioxetane luminophore and a quencher. In order to compose such system, a new phenoxy-dioxetane luminophore, 7-HC-CL, was developed. This luminophore exhibits intense and persistent glow chemiluminescence; it undergoes very slow chemiexcitation, and it has the highest chemiluminescence quantum yield ever reported under physiological conditions. Based on 7-HC-CL, a Glow-CRET probe for matrix metalloproteinases, MMP-CL, was synthesized. Incubation of MMP-CL with its cognate protease resulted in 160-fold increase in chemiluminescence signal. MMP-CL was also able to detect matrix metalloproteinase activity in cancer cells with significantly higher signal-to-background ratio than an analogous fluorescence resonance energy transfer (FRET)-based probe. This work is expected to open new horizons in chemiluminescence imaging, as it enables to use the dioxetanes in ways that had not been possible. We anticipate that 7-HC-CL and future derivatives will be utilized not only for the construction of further Glow-CRET probes, but also for other applications, such as chemiluminescence tagging of proteins.     

Harmonic Cheeger–Simons characters with applications

We initiate the study of harmonic Cheeger–Simons characters, with applications to smooth versions of the Geometric Langlands program in the abelian case.     

A model for codependent reversible/irreversible growth processes

A model for codependent growth that combines reversible and irreversible bond formation is developed. The system is composed of two processes: A reversible process which is fast but does not lead to a stable growth by itself, while the irreversible process is stable but is too slow to occur by itself. Therefore, neither the reversible nor the irreversible growth processes will occur separately, but their combination is shown to yield a new type of stable, codependent growth. Using kinetic Monte Carlo techniques we simulate and analyze the general properties of this codependent growth. We discuss the general conditions for such growth and its applications to self-organization processes.     

Gas-phase nazarov cyclization of protonated 2-methoxy and 2-hydroxychalcone: An example of intramolecular proton-transport catalysis

Upon CA, ESI generated [M + H]⁺ ions of chalcone (benzalacetophenone) and 3-phenyl-indanone both undergo losses of H₂O, CO, and the elements of benzene. CA of the [M + H]⁺ ions of 2-methoxy and 2-hydroxychalcone, however, prompts instead a dominant loss of ketene. In addition, CA of the [M + H]⁺ ions of 2-methoxy-β-methylchalcone produces an analogous loss of methylketene instead. Furthermore, the [M + D]⁺ ion of 2-methoxychalcone upon CA eliminates only unlabeled ketene, and the resultant product, the [M + D − ketene]⁺ ion, yields only the benzyl-d ₁ cation upon CA. We propose that the 2-methoxy and 2-hydroxy (ortho) substituents facilitate a Nazarov cyclization to the corresponding protonated 3-aryl-indanones by mediating a critical proton transfer. The resultant protonated indanones then undergo a second proton transport catalysis facilitated by the same ortho substituents producing intermediates that eliminate ketene to yield 2-methoxy- or 2-hydroxyphenyl-phenyl-methylcarbocations, respectively. The basicity of the ortho substituent is important; for example, replacement of the ortho function with a chloro substituent does not provide an efficient catalyst for the proton transports. The Nazarov cyclization must compete with an alternate cyclization, driven by the protonated carbonyl group of the chalcone that results in losses of H₂O and CO. The assisted proton transfer mediated by the ortho substituent shifts the competition in favor of the Nazarov cyclization. The proposed mechanisms for cyclization and fragmentation are supported by high-mass resolving power data, tandem mass spectra, deuterium labeling, and molecular orbital calculations.     

Schottky diode characteristics: Aluminium with 500 and 1000 Å thicknesses on p type WSe2 crystal

The conduction properties of Al‐p WSe₂ Schottky barrier diodes prepared identically but with different metal thickness are reported here. The p type WSe₂ semiconducting crystals used in the present study was grown by direct vapour transport technique. The current‐voltage characteristics of these diodes were analyzed from 140 K to 300 K on the basis of thermionic emission theory applying Gaussian distribution. Below 200 K, deviations were observed in barrier height, ideality factor and Richardson plot. Hence at lower temperatures, a model has been considered where the total current is assumed to be the sum of thermionic emission, generation recombination and tunneling components. The observed deviations in the diode parameters were successfully interpreted in terms of the contribution of these multiple charge transport mechanisms across the interface of the fabricated diodes. The diode with a thickness of 500 Å Al showed more homogeneous nature than with 1000 Å. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Topology and Flux of T-Dual Manifolds with Circle Actions

We present an explicit formula for the topology and H-flux of the T-dual of a general type II, compactification, significantly generalizing earlier results. Our results apply to T-dualities with respect to any circle action on spacetime X. As before, T-duality exchanges type IIA and type IIB string theories. A new consequence is that the T-dual spacetime is a singular space when the fixed point set ${X^\mathbb{T}}$ is non-empty; the singularities correspond to Kaluza-Klein monopoles. We propose that the Ramond-Ramond charges of type II string theories on the singular dual are classified by twisted equivariant cohomology groups. We also discuss the K-theory approach.     

On Noncentral Generalized Laplacianness of Quadratic Forms in Normal Variables

A general distribution which will be called the noncentral generalized Laplacian (NGL) is introduced and its properties studied. Then a set of results are obtained which will give the necessary and sufficient conditions for a bilinear expression or a quadratic expression to be distributed as a NGL.