Mössbauer effect studies of spin disturbances in dilute ferromagnetic alloys

¹¹⁹Sn Mössbauer effect studies of dilute Pt Fe, Pd Fe and Ni Fe alloys are reported. For Pt Fe an oscillatory spatial dependence of the spin-polarization about the Fe atoms is observed. The range increases with increasing temperature. For Pd Fe and Ni Fe the host properties are masked by the magnetic disturbances induced by the tin probe atoms.     

The Remarkable Stable Emerald Green C60F15[CBr(CO2Et)2]3: The First [60]Fullerene That Is also the First [18]Trannulene

No Abstract     

Duals Invert

Monoidal objects (or pseudomonoids) in monoidal bicategories share many of the properties of the paradigmatic example: monoidal categories. The existence of (say, left) duals in a monoidal category leads to a dualization operation which was abstracted to the context of monoidal objects by Day et al. (Appl Categ Struct 11:229–260, 2003). We define a relative version of this called exact pairing for two arrows in a monoidal bicategory; when one of the arrows is an identity, the other is a dualization. In this context we supplement results of Day et al. (Appl Categ Struct 11:229–260, 2003) (and even correct one of them) and only assume the existence of biduals in the bicategory where necessary. We also abstract recent work of Day and Pastro (New York J Math 14:733–742, 2008) on Frobenius monoidal functors to the monoidal bicategory context. Our work began by focusing on the invertibility of components at dual objects of monoidal natural transformations between Frobenius monoidal functors. As an application of the abstraction, we recover a theorem of Walters and Wood (Theory Appl Categ 3:25–47, 2008) asserting that, for objects A and X in a cartesian bicategory , if A is Frobenius then the category Map(X,A) of left adjoint arrows is a groupoid. Also, the characterization in Walters and Wood (Theory Appl Categ 3:25–47, 2008) of left adjoint arrows between Frobenius objects of a cartesian bicategory is put into our current setting. In the same spirit, we show that when a monoidal object admits a dualization, its lax centre coincides with the centre defined in Street (Theory Appl Categ 13:184–190, 2004). Finally we look at the relationship between lax duals for objects and adjoints for arrows in a monoidal bicategory.     

Robust strategic bidding in auction-based markets

In this paper, we propose an alternative methodology for devising revenue-maximizing strategic bids under uncertainty in the competitors’ bidding strategy. We focus on markets endowed with a sealed-bid uniform-price auction with multiple divisible products. On recognizing that the bids of competitors may deviate from equilibrium and are of difficult statistical characterization, we proposed a two-stage robust optimization model with equilibrium constraints aiming to devise risk-averse strategic bids. The proposed model is a trilevel optimization problem that can be recast as a particular instance of a bilevel program with equilibrium constraints. Reformulation procedures are proposed to find a single-level equivalent formulation suitable for column-and-constraint generation (CCG) algorithm. Results show that even for the case in which an imprecision of 1% is observed on the rivals’ bids in the equilibrium point, the robust solution provides a significant risk reduction (of 79.9%) in out-of-sample tests. They also indicate that the best strategy against high levels of uncertainty on competitors’ bid approaches to a price-taker offer, i.e., bid maximum capacity at marginal cost.     

Anomalous surface photoconductivity in hydrogenated amorphous silicon

The intensity and time dependence of the source-drain photocurrent is measured on hydrogenated amorphous silicon (a-Si:H) field effect transistors as a function of gate bias. The photocurrent increases rapidly, becomes weakly dependent on excitation intensity, and exhibits long decay times. A model in which the relaxation of the space charge dominates the photocurrent quantitatively predicts the experimental data. The results show that anomalous surface photoconductivity is often the dominant photoresponse of a-Si:H.     

Polymerization in catalyst particles: Calculation of molecular weight distribution

Factors which affect and broaden molecular weight distributions are investigated for polymerizations in catalyst particles which are accumulating polymer, such as Ziegler polymerizations of olefins. Expressions for the Q value, or ratio of weight-average to number-average molecular weight, are derived for simple, but important linear models. These expressions are of the form Q = FSX for a kinetic scheme in which polymer chains have an infinite growing lifetime, and Q = 2FGSX for a kinetic scheme in which termination by hydrogen is dominant and each site produces many chains. The factors F, G, S, and X are equal to or greater than unity: F depends on particle geometry and the nature of diffusion and reaction; G depends on environmental history of the particle; S depends on the distribution of site activities; and X depends on the distribution of particle sizes. Effects of reactor type are also studied quantitatively.     

Luminescence and ESR studies of defects in hydrogenated amorphous silicon

New experimental information on luminescence and light induced ESR (LESR) in hydrogenated amorphous silicon is described. We demonstrate that the two experiments involve identical recombination transitions, and identify two separate processes. One process involves defect states, and from the doping dependence of LESR we deduce that the electronically active defects are dangling bonds with positive electronic correlation energy.     

Refinement of structures previously proposed for gum arabic and other acacia gum exudates

In the light of advances in structural gum-chemistry, the analytical data available from earlier analytical and structural studies of gum arabic (Acacia Senegal Willd.), and of the gum exudates from Acacia laeta, A. campylacantha and A. seyal, have been re-interpreted. The structures originally suggested were based on random arbitrary assignments of substituent sugars without an attempt to establish regular structures. Modelling considerations and recalculations show that the data can also be interpreted in terms of more ordered structures. These are consistent with almost all of the available experimental data and give a much clearer insight into the nature and extent of the structural differences shown by the two Acacia gums of commercial importance. Acacia senegal (gum arabic, gum hashab) and Acacia seyal (gum talha).