Contexts of social action: guest editors' introduction

Cataloged from PDF version of article.In traditional linguistic accounts of context, one thinks of the immediate features of a speech situation, that is, a situation in which an expression is uttered. Thus, features such as time, location, speaker, hearer and preceding discourse are all parts of context. But context is a wider and more transcendental notion than what these accounts imply. For one thing, context is a relational concept relating social actions and their surroundings, relating social actions, relating individual actors and their surroundings, and relating the set of individual actors and their social actions to their surroundings

Robustness from flexibility in the fungal circadian clock

Background Robustness is a central property of living systems, enabling function to be maintained against environmental perturbations. A key challenge is to identify the structures in biological circuits that confer system-level properties such as robustness. Circadian clocks allow organisms to adapt to the predictable changes of the 24-hour day/night cycle by generating endogenous rhythms that can be entrained to the external cycle. In all organisms, the clock circuits typically comprise multiple interlocked feedback loops controlling the rhythmic expression of key genes. Previously, we showed that such architectures increase the flexibility of the clock's rhythmic behaviour. We now test the relationship between flexibility and robustness, using a mathematical model of the circuit controlling conidiation in the fungus Neurospora crassa. Results The circuit modelled in this work consists of a central negative feedback loop, in which the frequency (frq) gene inhibits its transcriptional activator white collar-1 (wc-1), interlocked with a positive feedback loop in which FRQ protein upregulates WC-1 production. Importantly, our model reproduces the observed entrainment of this circuit under light/dark cycles with varying photoperiod and cycle duration. Our simulations show that whilst the level of frq mRNA is driven directly by the light input, the falling phase of FRQ protein, a molecular correlate of conidiation, maintains a constant phase that is uncoupled from the times of dawn and dusk. The model predicts the behaviour of mutants that uncouple WC-1 production from FRQ's positive feedback, and shows that the positive loop enhances the buffering of conidiation phase against seasonal photoperiod changes. This property is quantified using Kitano's measure for the overall robustness of a regulated system output. Further analysis demonstrates that this functional robustness is a consequence of the greater evolutionary flexibility conferred on the circuit by the interlocking loop structure. Conclusions Our model shows that the behaviour of the fungal clock in light-dark cycles can be accounted for by a transcription-translation feedback model of the central FRQ-WC oscillator. More generally, we provide an example of a biological circuit in which greater flexibility yields improved robustness, while also introducing novel sensitivity analysis techniques applicable to a broader range of cellular oscillators

Ignition of a Large Volume Plasma with a Plasma Jet

Here we report on a method to generate a long plasma plume and to ignite a large volume plasma by means of the jet. The plasma plume is generated by our tube reactor and then introduced into a chamber where the pressure is controlled. We discovered there are three operating phases:Aphasewhere the plume length remains approximately constant, followed by a second phase where the jet increases in length as the pressure decreases. Then at pressures below 70 Torr a mode transition occurs where the plume length decreases and the plasma expands until the entire chamber is filled

Complementary approaches to understanding the plant circadian clock

Circadian clocks are oscillatory genetic networks that help organisms adapt to the 24-hour day/night cycle. The clock of the green alga Ostreococcus tauri is the simplest plant clock discovered so far. Its many advantages as an experimental system facilitate the testing of computational predictions. We present a model of the Ostreococcus clock in the stochastic process algebra Bio-PEPA and exploit its mapping to different analysis techniques, such as ordinary differential equations, stochastic simulation algorithms and model-checking. The small number of molecules reported for this system tests the limits of the continuous approximation underlying differential equations. We investigate the difference between continuous-deterministic and discrete-stochastic approaches. Stochastic simulation and model-checking allow us to formulate new hypotheses on the system behaviour, such as the presence of self-sustained oscillations in single cells under constant light conditions. We investigate how to model the timing of dawn and dusk in the context of model-checking, which we use to compute how the probability distributions of key biochemical species change over time. These show that the relative variation in expression level is smallest at the time of peak expression, making peak time an optimal experimental phase marker. Building on these analyses, we use approaches from evolutionary systems biology to investigate how changes in the rate of mRNA degradation impacts the phase of a key protein likely to affect fitness. We explore how robust this circadian clock is towards such potential mutational changes in its underlying biochemistry. Our work shows that multiple approaches lead to a more complete understanding of the clock

A novel and robust parameter training approach for HMMs under noisy and partial access to states

Cataloged from PDF version of article.This paper proposes a new estimation algorithm for the parameters of an HMM as to best account for the observed data. In this model, in addition to the observation sequence, we have partial and noisy access to the hidden state sequence as side information. This access can be seen as "partial labeling" of the hidden states. Furthermore, we model possible mislabeling in the side information in a joint framework and derive the corresponding EM updates accordingly. In our simulations, we observe that using this side information, we considerably improve the state recognition performance, up to 70%, with respect to the "achievable margin" defined by the baseline algorithms. Moreover, our algorithm is shown to be robust to the training conditions. (C) 2013 Elsevier B.V. All rights reserved

Pengaruh Faktor Internal dan Eksternal Motivasi terhadap Mutu Pendidikan di Universitas Al Washliyah (UNIVA) Medan

Secara umum penelitian ini bertujuan untuk mengetahui pengaruh motivasi dalam meningkatkan mutu pendidikan di Universitas Al Washliyah (UNIVA) Medan. Penelitian ini termasuk Metode penelitian yang digunakan penulis dalam menyusun laporan tugas akhir ini menggunakan metode deskriptif, yaitu yang mengungkapkan gambaran masalah yang terjadi pada saat penelitian ini berlangsung dan metode kuantitatif, yaitu metode untuk menghitung seberapa besar pengaruh variabel bebas teradap variabel terikatnya. Dalam penelitian ini analisis data yang digunakan adalah analisis jalur dimaksudkan untuk mengetahui adakah pengaruh faktor-faktor internal dan eksternal yang mempengaruhi Perubahan Mutu Pendidikan Universitas Al Washliyah Medan dengan persamaan. Berdasarkan hubungan antar variabel diketahui bahwa ketiga hubungan yang memiliki hubungan yang tidak signifikan yaitu antara Mutu Pendidikan (Y) dengan Faktor Internal (X1), Mutu Pendidikan (Y) dengan Faktor Eksternal (X2) dan Faktor Internal (X1) dengan Faktor Eksternal (X2). Dari aspek variabel Faktor Internal dan Faktor Eksternal secara simultan berpengaruh signifikan terhadap Mutu Pendidikan. Pada uji F, terdapat kecocokan antara model dengan data. Sehingga model analisis jalur yang didapat layak untuk digunakan. Secara parsial koefisien Faktor Internal berpengaruh signifikan terhadap Mutu Pendidikan dan Faktor Eksternal tidak berpengaruh secara signifikan. Pengaruh langsung variabel Faktor Internal (X1) terhadap Mutu Pendidikan (Y) adalah sebesar 0,032041 atau 3,2041% dan pengaruh tidak langsung melalui Faktor Internal (X2) adalah 0,00159847 atau 0,159847% sehingga total pengaruh yang diberikan variabel Faktor Internal (X1) adalah 0,03363947 atau sebesar 3,363947% terhadap Mutu Pendidikan (Y). Ini berarti Faktor Internal memiliki pengaruh yang kecil terhadap Mutu Pendidikan.Pengaruh langsung variabel Faktor Eksternal (X2) terhadap Mutu Pendidikan (Y) adalah sebesar 0,002209 atau 0,2209% dan pengaruh tidak langsung melalui Faktor Internal (X1) adalah 0,00159846 atau 0,159846% sehingga total pengaruh yang diberikan variabel Faktor Eksternal (X2) adalah 0,00380747 atau 0,380747% terhadap Mutu Pendidikan (Y). Ini berarti Faktor Ekstrnal memiliki pengaruh yang besar terhadap Mutu Pendidikan. Nilai R square sebesar 4%, ini menunjukkan bahwa dengan menggunakan model analisis jalur yang didapatkan dimana variabel eksogen yaitu Faktor Internal (X1) dan Faktor Eksternal (X2), memiliki pengaruh terhadap variabel Mutu Pendidikan (Y) sebesar 4%, namun pengaruhnya sangatlah kecil. Sedangkan sisanya (100%-4% = 96%) adalah kemungkinan terdapat aspek-aspek lain yang memiliki pengaruh terhadap Perubahan variabel Mutu Pendidikan (Y). Hal ini sesuai dengan nilai error yang muncul pada path diatas yaitu sebesar 0,63