Efficiency of autonomous soft nano-machines at maximum power

We consider nano-sized artificial or biological machines working in steady state enforced by imposing non-equilibrium concentrations of solutes or by applying external forces, torques or electric fields. For unicyclic and strongly coupled multicyclic machines, efficiency at maximum power is not bounded by the linear response value 1/2. For strong driving, it can even approach the thermodynamic limit 1. Quite generally, such machines fall in three different classes characterized, respectively, as "strong and efficient", "strong and inefficient", and "balanced". For weakly coupled multicyclic machines, efficiency at maximum power has lost any universality even in the linear response regime

Stochastic thermodynamics of chemical reaction networks

For chemical reaction networks described by a master equation, we define energy and entropy on a stochastic trajectory and develop a consistent nonequilibrium thermodynamic description along a single stochastic trajectory of reaction events. A first-law like energy balance relates internal energy, applied (chemical) work and dissipated heat for every single reaction. Entropy production along a single trajectory involves a sum over changes in the entropy of the network itself and the entropy of the medium. The latter is given by the exchanged heat identified through the first law. Total entropy production is constrained by an integral fluctuation theorem for networks arbitrarily driven by time-dependent rates and a detailed fluctuation theorem for networks in the steady state. Further exact relations like a generalized Jarzynski relation and a generalized Clausius inequality are discussed. We illustrate these results for a three-species cyclic reaction network which exhibits nonequilibrium steady states as well as transitions between different steady states.Comment: 14 pages, 2 figures, accepted for publication in J. Chem. Phy

Brainstem: Neglected Locus in Neurodegenerative Diseases

The most frequent neurodegenerative diseases (NDs) are Alzheimer’s disease (AD), Parkinson’s disease (PD), and frontotemporal lobar degeneration associated with protein TDP-43 (FTLD–TDP). Neuropathologically, NDs are characterized by abnormal intracellular and extra-cellular protein deposits and by disease-specific neuronal death. Practically all terminal stages of NDs are clinically associated with dementia. Therefore, major attention was directed to protein deposits and neuron loss in supratentorial (telencephalic) brain regions in the course of NDs. This was also true for PD, although the pathological hallmark of PD is degeneration of pigmented neurons of the brainstem’s substantia nigra (SN). However, PD pathophysiology was explained by dopamine depletion in the telencephalic basal ganglia due to insufficiency and degeneration of the projection neurons located in SN. In a similar line of argumentation AD- and FTLD-related clinical deficits were exclusively explained by supratentorial allo- and neo-cortical laminar neuronal necrosis. Recent comprehensive studies in AD and PD early stages found considerable and unexpected involvement of brainstem nuclei, which could have the potential to profoundly change our present concepts on origin, spread, and early clinical diagnosis of these diseases. In contrast with PD and AD, few studies addressed brainstem involvement in the course of the different types of FTLD–TDP. Some of the results, including ours, disclosed a higher and more widespread pathology than anticipated. The present review will focus mainly on the impact of brainstem changes during the course of the most frequent NDs including PD, AD, and FTLD–TDP, with special emphasis on the need for more comprehensive research on FTLDs

Efficiency of a Brownian information machine

A Brownian information machine extracts work from a heat bath through a feedback process that exploits the information acquired in a measurement. For the paradigmatic case of a particle trapped in a harmonic potential, we determine how power and efficiency for two variants of such a machine operating cyclically depend on the cycle time and the precision of the positional measurements. Controlling only the center of the trap leads to a machine that has zero efficiency at maximum power whereas additional optimal control of the stiffness of the trap leads to an efficiency bounded between 1/2, which holds for maximum power, and 1 reached even for finite cycle time in the limit of perfect measurements.Comment: 9 pages, 2 figure

Unbalancierte chromosomale Aberrationen beim Plattenepithelkarzinom des Penis

Das Peniskarzinom gehört in Europa mit einer Prävalenz von knapp 1% zu den seltenen Malignomen. Daher sind verfügbare Daten über molekulargenetische Veränderungen dieser Neoplasie bisher gering. Mit dem Auftreten einer lymphogenen Metastasierung verschlechtert sich die Prognose der Erkrankung drastisch. Somit ist die Einschätzung des Tumorverhaltens bereits aus Parametern des Primärtumors von großer klinischer Bedeutung. Mit dem Ziel der Entwicklung eines genetischen Profils für das Peniskarzinom wurden 33 Gewebeproben von Plattenepithelkarzinomen am Penis mittels komparativer genomischer Hybridisierung (CGH) untersucht. Damit konnten spezifische unbalancierte Aberrationen des Tumorgenoms auf chromosomaler und subchromosomaler Ebene getrennt nach nichtmetastasierenden - und (lymphogen) metastasierenden Primärtumoren gezeigt werden. Bei Tumoren ohne Lymphknotenmetastasen fanden sich durchschnittlich 7,2 chromosomale Aberrationen, die gleichmäßig mit je 3,6 Verlusten - bzw. Zugewinnen von DNA-Abschnitten verteilt waren, während es in Fällen mit lymphogener Metastasierung respektive nur 2,4 bzw. 3,2 Aberrationen waren. Ebenso zeigt sich tendenziell eine Assoziation zwischen kürzerer Überlebenszeit und einer geringeren Zahl chromosomaler Aberrationen. Die in beiden Gruppen aufgetretenen Veränderungen -8p; +8q und +9p scheinen ein Indiz für eine Tumorprogression zu sein, während der Verlust der Region -10q und der Zugewinn des gesamten Chromosoms +9 in der ermittelten Häufigkeit ausschließlich in den N+-Tumoren deutliche Hinweise auf eine lymphogene Metastasierung darstellen

Portfolio Analysis Models: A Review

This study, which is qualitative in nature, examined the concept of portfolio analysis with focus on business portfolio analysis. Four portfolio analysis models: Boston Consulting growth-share matrix, General Electric industry-attractiveness matrix, Shell directional policy matrix, and Arthur D. Little strategic condition matrix, were discussed in terms of their nature, characteristics, relevance and strategic implications to marketing and management. The limitations of each of these strategic tools were expounded and some newer variants of portfolio analysis models that emerged as a result of these limitations were briefly discussed. The study revealed that each of the four portfolio models has its own merits and demerits and none can be said to be superior as their proponents had advanced.  Instead, each can be applied depending on the need of the organization and the environment in which it operates and they could sometime be employed in an integrative manner. It also revealed that the newer variants though theoretically sound are not popular in marketing and management literatures and in practice.  The study concluded that most of the criticisms leveled against these strategic tools are as a result of the misplaced role these tools are expected to play.  Portfolio analysis, the study concluded is not to dictate or recommend strategic decision but to provide strategists with the data needed to making informed decision. Keywords: Portfolio analysis, Boston Consulting growth-share matrix, General Electric industry-attractiveness matrix, Shell directional policy matrix, Arthur D. Little strategic condition matri