Steady-state fluctuations of a genetic feedback loop:an exact solution

Genetic feedback loops in cells break detailed balance and involve bimolecular reactions; hence exact solutions revealing the nature of the stochastic fluctuations in these loops are lacking. We here consider the master equation for a gene regulatory feedback loop: a gene produces protein which then binds to the promoter of the same gene and regulates its expression. The protein degrades in its free and bound forms. This network breaks detailed balance and involves a single bimolecular reaction step. We provide an exact solution of the steady-state master equation for arbitrary values of the parameters, and present simplified solutions for a number of special cases. The full parametric dependence of the analytical non-equilibrium steady-state probability distribution is verified by direct numerical solution of the master equations. For the case where the degradation rate of bound and free protein is the same, our solution is at variance with a previous claim of an exact solution (Hornos et al, Phys. Rev. E {\bf 72}, 051907 (2005) and subsequent studies). We show explicitly that this is due to an unphysical formulation of the underlying master equation in those studies.Comment: 31 pages, 3 figures. Accepted for publication in the Journal of Chemical Physics (2012

Cálculo de los tiempos de circularvección en una población con patología vestibular. Influencia del estímulo visual

[corrected] To describe the results obtained for circularvection times (tCV) in a study of the phenomenon of visual-vestibular interaction for a population with vestibular pathology and to analyze differences in its calculation among patients reporting a worsening of their symptoms with visual stimuli. MATERIAL AND METHODS: A detailed case history was taken for all patients, followed by a sensory organization test using computerized dynamic posturography and the calculation of their tCV. RESULTS: The mean tCV results were: tCV2= 6.32+/-3.17 s; tCV3=6.57+/-3.68 s; tCVr=6.27+/-6.02 s. Significant differences were obtained in tCV2 (P=.046) and tCVr (P=.023). CONCLUSIONS: tCV is a diagnostic test using simple tools that can help differentiate patients in whom the visual stimulus is influenced

Sampling bias in systems with structural heterogeneity and limited internal diffusion

Complex systems research is becomingly increasingly data-driven, particularly in the social and biological domains. Many of the systems from which sample data are collected feature structural heterogeneity at the mesoscopic scale (i.e. communities) and limited inter-community diffusion. Here we show that the interplay between these two features can yield a significant bias in the global characteristics inferred from the data. We present a general framework to quantify this bias, and derive an explicit corrective factor for a wide class of systems. Applying our analysis to a recent high-profile survey of conflict mortality in Iraq suggests a significant overestimate of deaths

How accurate are the non-linear chemical Fokker-Planck and chemical Langevin equations?

The chemical Fokker-Planck equation and the corresponding chemical Langevin equation are commonly used approximations of the chemical master equation. These equations are derived from an uncontrolled, second-order truncation of the Kramers-Moyal expansion of the chemical master equation and hence their accuracy remains to be clarified. We use the system-size expansion to show that chemical Fokker-Planck estimates of the mean concentrations and of the variance of the concentration fluctuations about the mean are accurate to order $\Omega^{-3/2}$ for reaction systems which do not obey detailed balance and at least accurate to order $\Omega^{-2}$ for systems obeying detailed balance, where $\Omega$ is the characteristic size of the system. Hence the chemical Fokker-Planck equation turns out to be more accurate than the linear-noise approximation of the chemical master equation (the linear Fokker-Planck equation) which leads to mean concentration estimates accurate to order $\Omega^{-1/2}$ and variance estimates accurate to order $\Omega^{-3/2}$. This higher accuracy is particularly conspicuous for chemical systems realized in small volumes such as biochemical reactions inside cells. A formula is also obtained for the approximate size of the relative errors in the concentration and variance predictions of the chemical Fokker-Planck equation, where the relative error is defined as the difference between the predictions of the chemical Fokker-Planck equation and the master equation divided by the prediction of the master equation. For dimerization and enzyme-catalyzed reactions, the errors are typically less than few percent even when the steady-state is characterized by merely few tens of molecules.Comment: 39 pages, 3 figures, accepted for publication in J. Chem. Phy

Adicción al ejercicio medida a través del Exercise Addiction Inventory (EAI) y salud en deportistas habituales. Una revisión sistemática y meta-análisis

Cada vez es más frecuente la investigación sobre adicción al ejercicio debido a la importancia del exceso de actividad física en la salud general. Diferentes estudios han investigado la prevalencia del riesgo de adicción al ejercicio (RAE) y sus consecuencias, existiendo contradicciones con respecto a la asociación entre el RAE y las variables asociadas al entrenamiento. Uno de los objetivos de esta revisión sistemática fue analizar los estudios que han usado el Exercise Addiction Inventory (EAI) para valorar el RAE, así como realizar un meta-análisis para observar las posibles diferencias entre grupos con y sin RAE respecto a la prevalencia, edad, variables de salud (calidad de vida física y mental, desórdenes alimentarios) o de entrenamiento físico (horas/semana). Las búsquedas de estudios se realizaron en bases de datos electrónicas como Pubmed, SPORTDiscus o Scopus, y se hicieron utilizando términos de indexación y palabras clave relacionados con materias médicas o ciencias del deporte. Los criterios de inclusión fueron: participantes evaluados con el EAI; resultados reportados de prevalencia de RAE y/o puntuación en dicho cuestionario; diseño observacional. Veinte estudios cumplieron los criterios de elegibilidad para la revisión sistemática y 17 fueron incluidos en el meta-análisis. Los resultados mostraron peores valores en calidad de vida mental y trastornos de alimentación en el grupo con RAE comparado con el grupo sin RAE. Además, el grupo con RAE era más joven y realizaba más horas de entrenamiento semanal. No obstante, es necesaria más investigación. Research on physical exercise addiction is becoming more frequent due to the importance of excessive physical activity on health in general. Different studies have investigated the prevalence of risk of exercise addiction (REA) and its consequences. Furthermore, there exist a series of contradictions regarding the relationship between REA and other variables associated with physical training. One goal of this systematic review and meta-analysis consists of analysing possible differences in prevalence, age, general health (mental and physical quality of life, eating disorders) and physical training (hours/week) between groups with REA and non-addicted groups. The Exercise Addiction Inventory (EAI) was used to undertake this research. Research was carried out in electronic databases such as Pubmed, SPORTDiscus or Scopus. Inclusion criteria: Studies were eligible as long as participants were measured with EAI, results showed prevalence of REA and/or EAI score, and the study was observational. Twenty studies met the established eligibility criteria for inclusion in the systematic review, whereas seventeen studies were included in the meta-analysis. Regarding mental quality of life, results showed lower values for the exercise addiction risk group, compared with the nonaddicted group. The exercise addiction group was younger than the non-addicted group and dedicated more weekly hours to physical training. Subjects with REA have a lower health profile than those with non-REA. However, more research is required, given the lack of consensus on how to measure exercise addiction and the scarce number of studies to date

Uso de dispositivos fitness por parte de usuarios de gimnasios

El objetivo del presente estudio fue analizar los hábitos y nivel de uso de tecnologías aplicadas al deporte por parte de usuarios de centros de fitness. La muestra fue de 126 usuarios de centros fitness (61, 9% hombres y 38, 1% mujeres) de la ciudad de Zaragoza. El 66% de los sujetos realizaban un mínimo de 4 días semanales de actividad física y más del 30% realizaba 3 días de ejercicio físico semanal en el centro de fitness. Se observó que casi un 70% de los usuarios utilizan tecnología para realizar sus entrenamientos. Cabe destacar que las disciplinas deportivas en las que más uso se hizo de dispositivos tecnológicos fueron el running y el ciclo indoor (como actividad dirigida). Con respecto a los principales motivos que tienen los usuarios para utilizar tecnología durante su entrenamiento, destacan el de controlar la intensidad del mismo y el de mejorar su salud. Por el contrario, se observó que las personas que no usan dispositivos para realizar ejercicio físico afirman que éstos no responden a sus necesidades o no tienen suficientes conocimientos para saber utilizarlos. Dicho esto, resaltar que la mayoría de los sujetos del estudio afirmaron que la tecnología que se usaba, por muy avanzada o práctica que fuese, no podía sustituir a los profesionales de la ciencia de la actividad física y el deporte. The aim of the present study was to analyze sports habits and use of technology applied to sport by fitness center users. The sample was composed by 126 fitness center users (61, 9% men and 38, 1% women) belonging to private mid-market fitness centers of Zaragoza. A total of 66% of the subjects trained at least four days per week, while more than 30% carried out three days of physical exercise per week in a fitness center. We observed that around 70% of the sample used technology to carry out their training. It should be pointed out that the sports disciplines with the highest use of devices were running and spinning (directed activity). Regarding the main reasons for using technology during training, control of training intensity and improving health were the most common. On the contrary, we noticed that those persons who did not use gadgets during the practice of physical exercise stated that such devices were not useful or that they did not have enough knowledge to use them correctly. With this in mind, it is necessary to emphasize that the majority of the subjects from the present study affirmed that technology cannot replace sports and physical activity sciences professionals

Effects of bursty protein production on the noisy oscillatory properties of downstream pathways

Experiments show that proteins are translated in sharp bursts; similar bursty phenomena have been observed for protein import into compartments. Here we investigate the effect of burstiness in protein expression and import on the stochastic properties of downstream pathways. We consider two identical pathways with equal mean input rates, except in one pathway proteins are input one at a time and in the other proteins are input in bursts. Deterministically the dynamics of these two pathways are indistinguishable. However the stochastic behavior falls in three categories: (i) both pathways display or do not display noise-induced oscillations; (ii) the non-bursty input pathway displays noise-induced oscillations whereas the bursty one does not; (iii) the reverse of (ii). We derive necessary conditions for these three cases to classify systems involving autocatalysis, trimerization and genetic feedback loops. Our results suggest that single cell rhythms can be controlled by regulation of burstiness in protein production

Relación entre la adicción al ejercicio, el uso de dispositivos fitness y la ansiedad rasgo

El reciente auge de la tecnología y su protagonismo en el mundo del fitness han desencadenado la publicación de libros e investigaciones científicas. Además, la reciente preocupación de muchos investigadores por la adicción al ejercicio y sus conse cuencias para la salud aumentan la importancia de investigar si estas variables (tecnología, adicción al ejercicio y salud) podrían esta r relacionadas de algún modo. Por ello, el objetivo del presente estudio fue investigar si existe o no una asociación entre el uso de disposit ivos fitness , la adicción al ejercicio y la ansiedad-rasgo. Para llevar a cabo el presente estudio se analizó una muestra de 102 usuarios de cen tros deportivos con una media de 30 años de edad, a los cuales se les proporcionó cuestionarios para evaluar el uso de las tecnologí as, la adicción al ejercicio ( Exercise Addiction Inventory ) y el nivel de ansiedad-rasgo ( State-Trait Anxiety Inventory ). Los resultados mostraron que la mayoría de los sujetos de centros fitness empleaban tecnologías durante sus entrenamientos, siendo mayor el porcentaje de hombres que hacían uso de ellas que de hombres. También se hallaron interesantes correlaciones entre la edad y la adicción al e jercicio físico, así como entre ansiedad-rasgo y adicción al ejercicio físico. Con respecto a qué dispositivos son los más utilizados, l os wearables y las apps móviles obtuvieron el mayor porcentaje. No obstante, se hacen necesarias más investigaciones experimentales con mues tras más amplias que evalúen un mayor rango de variables asociadas a la salud. Recently, the growth of technology and its prominent importance in the world of fitness have triggered the publication of several books and research papers. Moreover, there are a strong concern about exercise addiction and its health consequences among the research community. Variables such as technology, exercise addiction and health could be related with the issue. This study aims at investigating whether there is an association between the use of fitness devices, exercise addiction and trait anxiety. The investigation analyzes a simple of 102 users of fitness centers located in Zaragoza with a mean age of 30 years old. The study uses different questionnaires in order to evaluate: i) the use of technology (own questionnaire), exercise addiction (ExerciseAddic (ion Inventory) and iii) the level of trait anxiety (State-Trait Anxiety Inventory). Results indicates that most of the users use technology during their training sessions, being larger the percentage of men than women. Further, interesting associations between age and exercise addiction were found, as well as, between trait anxiety and exercise addiction. In addition, the study highlights that wearables and mobile apps are the trendy devices. Nevertheless, greater range of variables associated with health calls for more experimental studies with larger samples

Ultra-soft 100 nm Thick Zero Poisson’s Ratio Film with 60% Reversible Compressibility

About a 100 nm thick multilayer film of nanoparticle monolayers and polymer layers is shown to behave like cellular-foam with a modulus below 100 KPa. The 1.25 cm radius film adhered to a rigid surface can be compressed reversibly to 60% strain. The more than four orders of magnitude lower modulus compared to its constituents is explained by considering local bending in the (nano)cellular structure, similar to cork and wings of beetles. As the rigidity of the polymer backbone is increased in just four monolayers the modulus of the composite increases by over 70%. Electro-optical map of the strain distribution over the area of compression and increase in modulus with thickness indicates the films have zero Poisson’s ratio