Hadronisation at LEP

An overview of recent results from LEP concerning the hadronisation process is presented. Emphasis is placed on the $b$-quark. The first presented analysis is the measurement of the $b$-quark fragmentation function. It includes a new, hadronic-model independent method to extract the x-dependence of the non-perturbative QCD component from the measured fragmentation function. This is followed by the results of two analyses on, respectively, production rates of b-excited states and branching fractions of b-quarks to neutral and charged b-hadrons. Multiplicity in the final state is also discussed concerning the difference in multiplicities between b and light quark initiated events, and total multiplicities in three jet events. Finally, recent measurements of \omega and \eta meson production rates are given.Comment: Talk given at XXXVIII Rencontres de Moriond, March 23rd - 29th, 200

Blind Minimax Estimation

We consider the linear regression problem of estimating an unknown, deterministic parameter vector based on measurements corrupted by colored Gaussian noise. We present and analyze blind minimax estimators (BMEs), which consist of a bounded parameter set minimax estimator, whose parameter set is itself estimated from measurements. Thus, one does not require any prior assumption or knowledge, and the proposed estimator can be applied to any linear regression problem. We demonstrate analytically that the BMEs strictly dominate the least-squares estimator, i.e., they achieve lower mean-squared error for any value of the parameter vector. Both Stein's estimator and its positive-part correction can be derived within the blind minimax framework. Furthermore, our approach can be readily extended to a wider class of estimation problems than Stein's estimator, which is defined only for white noise and non-transformed measurements. We show through simulations that the BMEs generally outperform previous extensions of Stein's technique.Comment: 12 pages, 7 figure

Home bias in financial markets: robust satisficing with info gaps

The observed patterns of equity portfolio allocation around the world are at odds with predictions from a capital asset pricing model (CAPM). What has come to be called the “home-bias” phenomenon is that investors tend to hold a disproportionately large share of their equity portfolio in home country stocks as compared with predictions of the CAPM. This paper provides an explanation of the home-bias phenomenon based on information-gap decision theory. The decision concept that is used here is that profit is satisficed and robustness to uncertainty is maximized rather than expected profit being maximized. Furthermore, uncertainty is modeled nonprobabilistically with info-gap models of uncertainty, which can be viewed as a possible quantification of Knightian uncertainty.

Cryopreservation of a whole liver

Preservation of vascularized organs such as the liver is limited to 24hrs. before destructive processes disqualify it for transplantation. This narrow time window prevents surgeons from performing optimal pathogen screening and matching tests which often lead to re-transplantation. Numerous problems are associated with viably freezing and thawing a whole liver: complicated geometry, poor heat transfer, release of latent heat and the difficulty of generating a uniform cooling rate. Our past success led us to apply our novel freezing technique to a larger solid organ, the liver. Whole livers were frozen/thawed using a directional solidification apparatuses; viability was tested by means of integrity and functionality in vitro and in auxiliary liver transplantation. Thawed livers were intact with over 80% viability; histology revealed normal architecture, bile production and blood flow following auxillary transplantation where normal. Our results suggest a novel cryopreservation method and may enable better organ donor-recipient matching in the futur

Price-Based vs. Quantity-Based Environmental Regulation under Knightian Uncertainty: An Info-Gap Robust Satisficing Perspective

Conventional wisdom among environmental economists is that the relative slopes of the marginal social benefit and marginal social cost functions determine whether a price-based or quantity-based environmental regulation leads to higher expected social welfare. We revisit the choice between price-based vs. quantity-based environmental regulation under Knightian uncertainty; that is, when uncertainty cannot be modeled with known probability distributions. Under these circumstances, the policy objective cannot be to maximize the expected net benefits of emissions control. Instead, we evaluate an emissions tax and an aggregate abatement standard in terms of maximizing the range of uncertainty under which the welfare loss from error in the estimates of the marginal benefits and costs of emissions control can be limited. The main result of our work is that the same criterion involving the relative slopes of the marginal benefit and cost functions determines whether price-based or quantity-based control is more robust to unstructured uncertainty. Hence, not only does the relative slopes criterion lead to the policy that maximizes the expected net benefits of control under structured uncertainty, it also leads to the policy that maximizes robustness to unstructured uncertainty.emissions control, environmental regulation, info-gap, Knightian uncertainty, robustness, satisficing

Spontaneous and Directed Symmetry Breaking in the Formation of Chiral Nanocrystals

The homochirality of biomolecules remains one of the outstanding puzzles concerning the beginning of life. Chiral amplification of a randomly perturbed racemic mixture of chiral molecules is a well-accepted prerequisite for all routes to biological homochirality. Some models have suggested that such amplification occurred due to asymmetric discrimination of chiral biotic or prebiotic molecules when they adsorbed onto crystalline surfaces. While chiral amplification has been demonstrated on surfaces of both chiral and achiral crystals, the mechanism that would produce an enantiomeric imbalance in the chiral surfaces themselves has not been addressed. Here we report strong chiral amplification in the colloidal synthesis of intrinsically chiral lanthanide phosphate nanocrystals, quantitatively measured via the circularly polarized luminescence of the lanthanide ions within the nanocrystals. The amplification involves spontaneous symmetry breaking into either left- or right-handed nanocrystals below a critical temperature. Furthermore, chiral tartaric acid molecules in the solution act as an external chiral field, sensitively directing the amplified nanocrystal handedness through a discontinuous transition between left- and right-handed excess. These characteristics suggest a conceptual framework for chiral amplification, based on the statistical thermodynamics of critical phenomena, which we use to quantitatively account for the observations. Our results demonstrate how chiral minerals with high enantiomeric excess could have grown locally in a primordial racemic aqueous environment.Comment: 9 pages, 4 figure