Gerd Baumann

Meaningful Interpretation of Subdiffusive Measurements in Living Cells (Crowded Environment) by Fluorescence Fluctuation Microscopy

In living cell or its nucleus, the motions of molecules are complicated due to the large crowding and expected heterogeneity of the intracellular environment. Randomness in cellular systems can be either spatial (anomalous) or temporal (heterogeneous). In order to separate both processes, we introduce anomalous random walks on fractals that represented crowded environments. We report the use of numerical simulation and experimental data of single-molecule detection by fluorescence fluctuation microscopy for detecting resolution limits of different mobile fractions in crowded environment of living cells. We simulate the time scale behavior of diffusion times τD(τ) for one component, e.g. the fast mobile fraction, and a second component, e.g. the slow mobile fraction. The less the anomalous exponent α the higher the geometric crowding of the underlying structure of motion that is quantified by the ratio of the Hausdorff dimension and the walk exponent d f /dw and specific for the type of crowding generator used. The simulated diffusion time decreases for smaller values of α ≠ 1 but increases for a larger time scale τ at a given value of α ≠ 1. The effect of translational anomalous motion is substantially greater if α differs much from 1. An α value close to 1 contributes little to the time dependence of subdiffusive motions. Thus, quantitative determination of molecular weights from measured diffusion times and apparent diffusion coefficients, respectively, in temporal auto- and crosscorrelation analyses and from time-dependent fluorescence imaging data are difficult to interpret and biased in crowded environments of living cells and their cellular compartments; anomalous dynamics on different time scales τ must be coupled with the quantitative analysis of how experimental parameters change with predictions from simulated subdiffusive dynamics of molecular motions and mechanistic models. We first demonstrate that the crowding exponent α also determines the resolution of differences in diffusion times between two components in addition to photophyscial parameters well-known for normal motion in dilute solution. The resolution limit between two different kinds of single molecule species is also analyzed under translational anomalous motion with broken ergodicity. We apply our theoretical predictions of diffusion times and lower limits for the time resolution of two components to fluorescence images in human prostate cancer cells transfected with GFP-Ago2 and GFP-Ago1. In order to mimic heterogeneous behavior in crowded environments of living cells, we need to introduce so-called continuous time random walks (CTRW). CTRWs were originally performed on regular lattice. This purely stochastic molecule behavior leads to subdiffusive motion with broken ergodicity in our simulations. For the first time, we are able to quantitatively differentiate between anomalous motion without broken ergodicity and anomalous motion with broken ergodicity in time-dependent fluorescence microscopy data sets of living cells. Since the experimental conditions to measure a selfsame molecule over an extended period of time, at which biology is taken place, in living cells or even in dilute solution are very restrictive, we need to perform the time average over a subpopulation of different single molecules of the same kind. For time averages over subpopulations of single molecules, the temporal auto- and crosscorrelation functions are first found. Knowing the crowding parameter α for the cell type and cellular compartment type, respectively, the heterogeneous parameter γ can be obtained from the measurements in the presence of the interacting reaction partner, e.g. ligand, with the same α value. The product α⋅γ=γ˜ is not a simple fitting parameter in the temporal auto- and two-color crosscorrelation functions because it is related to the proper physical models of anomalous (spatial) and heterogeneous (temporal) randomness in cellular systems. We have already derived an analytical solution for γ˜ in the special case of γ = 3/2 . In the case of two-color crosscorrelation or/and two-color fluorescence imaging (co-localization experiments), the second component is also a two-color species gr, for example a different molecular complex with an additional ligand. Here, we first show that plausible biological mechanisms from FCS/ FCCS and fluorescence imaging in living cells are highly questionable without proper quantitative physical models of subdiffusive motion and temporal randomness. At best, such quantitative FCS/ FCCS and fluorescence imaging data are difficult to interpret under crowding and heterogeneous conditions. It is challenging to translate proper physical models of anomalous (spatial) and heterogeneous (temporal) randomness in living cells and their cellular compartments like the nucleus into biological models of the cell biological process under study testable by single-molecule approaches. Otherwise, quantitative FCS/FCCS and fluorescence imaging measurements in living cells are not well described and cannot be interpreted in a meaningful way.

Transcultural journalism and the politics of translation: Interrogating the BBC World Service

When George Orwell worked for the BBC Eastern Services during the Second World War, he regarded it as ‘an organ of colonial discourse propagating the word and world view of the metropolitan centre to its peripheral subject people’ (Kerr, 2002: 473–90). Orwell’s misgivings about his own journalistic practice and the BBC Eastern Service’s suspected ideological functions may pose an enduring dilemma for some journalists, but many are delighted to endure the processes of recruitment, induction, training and enculturation into the BBC’s hegemonic, globally diffused brand of impartial journalism. This is called, with some self-irony, ‘being BBCed’ by journalists working in, or for, Bush House. The BBC’s overseas services (now the World Service) have long relied on an army of diasporic translators and ‘the right kind of voice’ to disseminate news across the globe. The long-standing reputation of the BBC World Service (BBCWS) among the world’s pre-eminent broadcasters and its credibility have depended on the largely undocumented and unexplored everyday transcultural encounters and translation practices that have taken place in the diasporic and cosmopolitan contact zones of Bush House. This special issue draws on a collaborative empirical research project on the BBC World Service to examine wider issues of the politics, ethics and practices of transcultural journalism and the politics of translation.

Fluorescence Molecule Counting for Single-Molecule Studies in Crowded Environment of Living Cells without and with Broken Ergodicity

We present a new approach to distinguish between non-ergodic and ergodic behavior. Performing ensemble averaging in a subpopulation of individual molecules leads to a mean value that can be similar to the mean value obtained in an ergodic system. The averaging is carried out by minimizing the variation between the sum of the temporal averaged mean square deviation of the simulated data with respect to the logarithmic scaling behavior of the subpopulation. For this reason, we first introduce a kind of Continuous Time Random Walks (CTRW), which we call Limited Continuous Time Random Walks (LCTRW) on fractal support. The random waiting time distributions are sampled at points which fulfill the condition N < 1, where N is the Poisson probability of finding a single molecule in the femtoliter-sized observation volume ΔV at the single-molecule level. Given a subpopulation of different single molecules of the same kind, the ratio T/ Tm between the measurement time T and the meaningful time Tm, which is the time for observing just one and the same single molecule, is the experimentally accessible quantity that allows to compare different molecule numbers in the subpopulation. In addition, the mean square displacement traveled by the molecule during the time t is determined by an upper limit of the geometric dimension of the living cell or its nucleus.

Fractals for multicyclic synthesis conditions of biopolymers examples of oligonucleotide synthesis measured by high-performance capillary electrophoresis and ion-exchange high-performance liquid chromatography

We have developed models of patterns for nucleotide chain growth. These patterns are measurable by high-performance capillary electrophoresis and ion-exchange high-performance liquid chromatography in crude products of solid-phase synthesized 30mer and 65mer oligodeoxyribonucleotide target sequences N. We introduce mathematical methods for finding characteristic values d(o) and p(o) for constant chemical modes of growth as well as d and p for non-constant chemical modes of growth (d = probability of propagation, p = probability of termination). These methods are employed by presenting the accompanying computer software developed by us in C code, Mathematica R languages, and Fortran. Characteristic values of the parameters d, p, and the target nucleotide length N describe the complete composition of the crude product. From this we have developed the relation 2 - [N/(N - 1)]/Da, measurable(N,d) as a universal quantitative measure for multicyclic synthesis conditions (D, fractal dimension and similarity exponent, respectively). We use this mathematical treatment to compare the efficiency of oligodeoxyribonucleotide syntheses of different target length N on polymer support materials. Further, we analyze selected syntheses of short and long oligodeoxyribonucleotides as well as single-stranded DNA sequences by well-known empirical autocorrelation, fast Fourier transformation, and embedding dimension techniques.

Broadcasting britishness, strategic challenges and the ecology of overseas broadcasting by the BBC

In December 2007, the BBC World Service celebrated 75 years of broadcasting overseas: from the first transmission on the original Empire Service to the explosion in foreign language services induced by the Second World War and the subsequent establishment and continuous re-development of a post-war pattern of broadcasting around the world that still bears an imprint on output today. Yet despite global public familiarity with the World Service as an institution, symbolised by its home at Bush House in London and the unmistakable Britishness of the ‘voice’ that emanates from it, the history of overseas broadcasting by the Corporation is little known and perhaps even less understood. It is more than a little surprising that the BBC World Service, or the External Services as they were known prior to a name change in 1988, have still to receive anything like the kind of critical and detailed examination warranted by their role in the political, diplomatic and cultural lives of those countries and diasporas to which they broadcast. Notwithstanding Asa Briggs’ colossal and extensive official history of the BBC up to the mid-1970s, Bush House remains an icon, though a relatively unexplained one. There has been a general failure in the academic community, as Philip Taylor has pointed out, to sufficiently mesh the media and other forms of cultural exchange into mainstream political and administrative histories and this remains the case today.

Anomalous behavior in length distributions of 3D random Brownian walks and measured photon count rates within observation volumes of single-molecule trajectories in fluorescence fluctuation microscopy

Based on classical mean-field approximation using the diffusion equation for ergodic normal motion of single 24-nm and 100-nm nanospheres, we simulated and measured molecule number counting in fluorescence fluctuation microscopy. The 3D-measurement set included a single molecule, or an ensemble average of single molecules, an observation volume DeltaV and a local environment, e.g. aqueous solution. For the molecule number N << 1 per DeltaV, there was only one molecule at a time inside DeltaV or no molecule. The mean rate k of re-entries defined by k = N/tau(dif) was independent of the geometry of DeltaV but depended on the size of DeltaV and the diffusive properties tau(dif). The length distribution l of single-molecule trajectories inside DeltaV and the measured photon count rates I obeyed power laws with anomalous exponent kappa =-1.32 approximately -4/3.

Editorial The BBC World Service and the Middle East: comparisons, contrasts, conflicts

The author reflects on the development of the British Broadcasting Corp. (BBCs) international broadcasting services in which the Middle East has played a vital role. He discusses that BBC adopted Arabic as its first foreign language service in January 1938 because of the threat of World War II. BBC decided to expand its radio service in Turkey and Persia.

Epilogue: The BBC World Service and the Middle East: past, present, and future dilemmas

The article offers information on the company BBC World Service (BBCWS) and its development and struggle in the Middle East. It also explains the relationship between BBCWS and British Foreign and Commonwealth office (FCO). Public diplomacy is stated to have altered the perceived and potential role of the BBC in the region.

The BBC World Service in the Middle East: Claims to impartiality, or a politics of translation?

As the World Service’s first foray into foreign-language broadcasting (Guardian, 1938) and its first initiative to branch out into non-English-language television (1994—96; 2008 to present), BBC Arabic has played a central role for the Corporation. Distrust of its claims to impartiality, however, persists. To assess both claims and critiques, we examine its politics of translation under four headings: transporting data from the field to the broadcaster; translating from one language into another; transposing data and message by inflexions of tone; and transmitting the result to selected audiences at selected times. We do so from both an etic (‘outsiders’) analysis of BBC output and an emic (‘insiders’) analysis of what audiences perceive and react to by way of critical receptions and reactions.

Introduction - South Asian diasporas and the BBC World Service: contacts, conflicts, and contestations

This article sets out the analytical framework of this special issue and outlines the development of BBC radio broadcasting in South Asia. It analyses the ways in which the BBC in South Asia is integrally and indissolubly intertwined with ‘critical events’ and shifting geopolitical priorities: from the imperial and diasporic imaginings of the Empire Service, to its dissolution and the expansion of South Asian language services during World War II for the purpose of countering ‘enemy broadcasts’; from independence, partition and decolonisation, including the BBCs subsequent role in mediating postcolonial conflicts and wars and Cold War tensions, to its most recent ‘war on terror’ phase with its unspoken aim of promoting a British version liberal democracy around the globe. The article highlights how the often intimate engagements of diverse audiences in South Asia and its diasporas with the BBC have changed in response to technological innovation and geopolitics. We emphasise the distinctiveness of the BBC voice, especially the ‘right kind of diasporic voice’, and its acoustic power and presence in South Asia. We highlight how the rapid expansion of South Asian mediascapes – especially in India is unsettling the privileged position that the BBC South Asian services have enjoyed for nearly eight decades. Digital technologies are facilitating the emergence of ‘digital diasporas’ as South Asians across the world log on to consume news with alternative perspectives to news providers in South Asia and to engage in diasporic debates, often with unintended and unforeseen consequences.