Effect of disorder on transport properties in a tight-binding model for lead halide perovskites

The hybrid organic-inorganic lead halide perovskite materials have emerged as remarkable materials for photovoltaic applications. Their strengths include good electric transport properties in spite of the disorder inherent in them. Motivated by this observation, we analyze the effects of disorder on the energy eigenstates of a tight-binding model of these materials. In particular, we analyze the spatial extension of the energy eigenstates, which is quantified by the inverse participation ratio. This parameter exhibits a tendency, and possibly a phase transition, to localization as the on-site energy disorder strength is increased. However, we argue that the disorder in the lead halide perovskites corresponds to a point in the regime of highly delocalized states. Our results also suggest that the electronic states of mixed-halide materials tend to be more localized than those of pure materials, which suggests a weaker tendency to form extended bonding states in the mixed-halide materials and is therefore not favourable for halide mixing.Comment: 24 pages (preprint), 11 figure

Quasi-Monte Carlo, Discrepancies and Error Estimates

We discuss the problem of defining an estimate for the error in quasi-Monte Carlo integration. The key issue is the definition of an ensemble of quasi-random point sets that, on the one hand, includes a sufficiency of equivalent point sets, and on the other hand uses information on the degree of uniformity of the point set actually used, in the form of a discrepancy or diaphony. A few examples of such discrepancies are given. We derive the distribution of our error estimate in the limit of large number of points. In many cases, Gaussian central limits are obtained. We also present numerical results for the quadratic star-discrepancy for a number of quasi-random sequences

The effect of population variation on the accuracy of sex estimates derived from basal occipital discriminant functions

Multiple discriminant functions that estimate sex from the dimensions of the basal occipital have been published. However, as there is limited exploration of basal dimension variation between groups, the accuracy of these functions when applied to archaeological material is unknown. This study compares basal dimensions between four known sex-at-death post-medieval European samples and explores how metric differences impact on the accuracy of sex assessment discriminant functions. Published data from St Bride’s, London (n = 146) and the Georges Olivier collection, Paris (n = 68) were compared with new data from the eighteenth to nineteenth century Dutch Middenbeemster sample (n = 74) and the early twentieth century Rainer sample, Romania (n = 282) using independent t tests. The Middenbeemster and Rainer data were substituted into six published discriminant functions derived from the St Bride’s and the Georges Olivier samples, and the results were compared to their known sex. Multiple statistically significant differences were found between the four groups. Of the six discriminant functions tested, five failed to reach the published accuracy and fell below chance. In addition, even where the samples were statistically comparable in means, trends for difference also impacted the accuracy of discriminant functions. Enough variation in basal occipital dimensions existed in the European groups to decrease the accuracy of sex estimation discriminant functions to unusable. Possible inter-observer error, varying genetic, socioeconomic, and geographical factors are likely causes of dimension variation. This research further highlights the dangers of using sex estimation discriminant functions on samples that differ to the original derivative population and demonstrates the need for more rigorous testing

Monte Carlo Renormalization of the 3-D Ising model: Analyticity and Convergence

We review the assumptions on which the Monte Carlo renormalization technique is based, in particular the analyticity of the block spin transformations. On this basis, we select an optimized Kadanoff blocking rule in combination with the simulation of a d=3 Ising model with reduced corrections to scaling. This is achieved by including interactions with second and third neighbors. As a consequence of the improved analyticity properties, this Monte Carlo renormalization method yields a fast convergence and a high accuracy. The results for the critical exponents are y_H=2.481(1) and y_T=1.585(3).Comment: RevTeX, 4 PostScript file

Transverse and longitudinal characterization of electron beams using interaction with optical near-fields

We demonstrate an experimental technique for both transverse and longitudinal characterization of bunched femtosecond free electron beams. The operation principle is based on monitoring of the current of electrons that obtained an energy gain during the interaction with the synchronized optical near-field wave excited by femtosecond laser pulses. The synchronous accelerating/decelerating fields confined to the surface of a silicon nanostructure are characterized using a highly focused sub-relativistic electron beam. Here the transverse spatial resolution of 450 nm and femtosecond temporal resolution achievable by this technique are demonstrated

Pion Mass Effects in the Large NN Limit of \chiPT

We compute the large $N$ effective action of the $O(N+1)/O(N)$ non-linear sigma model including the effect of the pion mass to order $m^2_{\pi}/f_{\pi}^2$. This action is more complex than the one corresponding to the chiral limit not only because of the pion propagators but also because chiral symmetry produce new interactions proportional to $m^2_{\pi}/f_{\pi}^2$. We renormalize the action by including the appropriate counter terms and find the renormalization group equations for the corresponding couplings. Then we estudy the unitarity propierties of the scattering amplitudes. Finally our results are applied to the particular case of the linear sigma model and also are used to fit the pion scattering phase shifts.Comment: FT/UCM/18/9

Analysis of Bose-Einstein correlations in e+e- -> W+W- events including final state interactions

Recently DELPHI Collaboration reported new data on Bose-Einstein correlations (BEC) measured in e+e- -> W^+W^- events. Apparently no enhancement has been observed. We have analyzed these data including final state interactions (FSI) of both Coulomb and strong (s-wave) origin and found that there is enhancement in BEC but it is overshadowed by the FSI which are extremely important for those events. We have found the following values for the size of the interaction range beta and the degree of coherence lambda: beta=0.87 +/- 0.31fm and lambda=1.19 +/- 0.48, respectively.Comment: 7pages, 4 figure

WW Cross-sections and Distributions

We present the results obtained by the "WW Cross-sections and Distributions" working group during the CERN Workshop "Physics at LEP2" (1994/1995)Comment: 61 pages, tar'ed gzip'ed uuencoded files, LaTeX, 4 Postscript figures. To appear in "Physics at LEP2", G.Altarelli and F.Zwirner eds., CERN Report 199

A global fit of ππ\pi\pi and πK\pi K elastic scattering in ChPT with dispersion relations

We apply the one-loop results of the $SU(3)_L\times SU(3)_R$ ChPT suplemented with the inverse amplitude method to fit the available experimental data on $\pi\pi$ and $\pi K$ scattering. With esentially only three parameters we describe accurately data corresponding to six different channels, namely $(I,J)=(0,0), (2,0), (1,1), (1/2,0), (3/2,0)$ and $(1/2,1)$. In addition we reproduce the first resonances of the $(1,1)$ and $(1/2,1)$ channel with the right mass corresponding to the $\rho$ and the $K^*(892)$ particles.Comment: 19 pages, 5 figures available on request, FT/UCM/10/9