Strange kinetics: conflict between density and trajectory description

We study a process of anomalous diffusion, based on intermittent velocity fluctuations, and we show that its scaling depends on whether we observe the motion of many independent trajectories or that of a Liouville-like equation driven density. The reason for this discrepancy seems to be that the Liouville-like equation is unable to reproduce the multi-scaling properties emerging from trajectory dynamics. We argue that this conflict between density and trajectory might help us to define the uncertain border between dynamics and thermodynamics, and that between quantum and classical physics as well.Comment: submitted to Chemical Physic

On manifolds with nonhomogeneous factors

We present simple examples of finite-dimensional connected homogeneous spaces (they are actually topological manifolds) with nonhomogeneous and nonrigid factors. In particular, we give an elementary solution of an old problem in general topology concerning homogeneous spaces

Anomalous diffusion and the first passage time problem

We study the distribution of first passage time (FPT) in Levy type of anomalous diffusion. Using recently formulated fractional Fokker-Planck equation we obtain three results. (1) We derive an explicit expression for the FPT distribution in terms of Fox or H-functions when the diffusion has zero drift. (2) For the nonzero drift case we obtain an analytical expression for the Laplace transform of the FPT distribution. (3) We express the FPT distribution in terms of a power series for the case of two absorbing barriers. The known results for ordinary diffusion (Brownian motion) are obtained as special cases of our more general results.Comment: 25 pages, 4 figure

Is there H2O stacking disordered ice I in the Solar System?

Water ice exists in large quantities across the Solar System, and it is involved in a wide range of atmospheric and geological processes. Here we focus on the question if stacking disordered ice I (ice Isd) is present in the Solar System. The conditions required to form ice Isd are described and we argue that previous descriptions of ‘cubic ice’ (ice Ic) in the literature may in fact have been concerned with ice Isd. In contrast to the stable hexagonal ice I (ice Ih) and ice Ic, ice Isd is a highly complex material that encompasses a wide range of possible stacking regimes and structures. The most fundamental quantity to describe a given ice Isd sample is its cubicity which reflects the fraction of cubic stacking. Following an introduction into the characterisation techniques used to identify and characterise ice Isd, we discuss the various environments in the Solar System where ice Isd may exist and the relevance its existence may have. This includes the atmospheres of the inner planets, various icy moons as well as comets and other icy objects in the far reaches of the Solar System. The details of the stacking disorder may contain information about the formation and thermal history of ice Isd samples. This offers the exciting prospect of using ice Isd as a marker material for atmospheric and geological processes. The crystallographic space group of ice Isd allows polar structures which could be an important factor for the accretion of ice particles in space. We conclude that ice Isd should exist at several locations in the Solar System and in potentially large quantities. The definitive identification of ice Isd in a natural environment is a next major milestone in our understanding of the importance of water ice across the Solar System

High-efficiency Bragg grating enhanced on-chip photon-number-resolving detectors

The recent trend towards integration of quantum optics experiments has produced a demand for on-chip single photon detectors with high quantum efficiencies. In previous work we demonstrated integrated photon number resolving detectors for use at telecommunications wavelengths [1], here we outline developments of this design which have enabled improvements in the quantum efficiency, permitting an on-chip detection efficiency of 92% to be obtained in the device of Fig. 1. ..

Regulatory objectivity in action: Mild cognitive impairment and the collective production of uncertainty

In this paper, we investigate recent changes in the definition and approach to Alzheimer’s disease brought about by growing clinical, therapeutic and regulatory interest in the prodromal or preclinical aspects of this condition. In the last decade, there has been an increased interest in the biomolecular and epidemiological characterization of pre-clinical dementia. It is argued that early diagnosis of dementia, and particularly of Alzheimer‘s disease, will facilitate the prevention of dementing processes and lower the prevalence of the condition in the general population. The search for a diagnostic category or biomarker that would serve this purpose is an ongoing but problematic endeavour for research and clinical communities in this area. In this paper, we explore how clinical and research actors, in collaboration with regulatory institutions and pharmaceutical companies, come to frame these domains as uncertainties and how they re-deploy uncertainty in the ‘collective production’ of new diagnostic conventions and bioclinical standards. While drawing as background on ethnographic, documentary and interview data, the paper proposes an in-depth, contextual analysis of the proceedings of an international meeting organized by the Peripheral and Central Nervous System Drug Advisory Committee of the US Food and Drug Administration to discuss whether or not a particular diagnostic convention — mild cognitive impairment — exists and how best it ought to be studied. Based on this analysis we argue that the deployment of uncertainty is reflexively implicated in bioclinical collectives’ search for rules and conventions, and furthermore that the collective production of uncertainty is central to the ‘knowledge machinery’ of regulatory objectivity