The role of sigma factor competition in bacterial adaptation under prolonged starvation

The study of adaptive microbial evolution in the laboratory can illuminate the genetic mechanisms of gaining fitness under a pre-defined set of selection factors. Laboratory evolution of bacteria under long-term starvation has gained importance in recent years because of its ability to uncover adaptive strategies that overcome prolonged nutrient limitation, a condition often encountered by natural microbes. In this evolutionary paradigm, bacteria are maintained in an energy-restricted environment in a growth phase called long-term stationary phase (LTSP). This phase is characterized by a stable, viable population size and highly dynamic genetic changes. Multiple independent iterations of LTSP evolution experiments have given rise to mutants that are slow-growing compared to the ancestor. Although the antagonistic regulation between rapid growth and the stress response is well-known in bacteria (especially Escherichia coli), the growth deficit of many LTSP-adapted mutants has not been explored in detail. In this review, I pinpoint the trade-off between growth and stress response as a dominant driver of evolutionary strategies under prolonged starvation. Focusing on mainly E. coli-based research, I discuss the various affectors and regulators of the competition between sigma factors to occupy their targets on the genome, and assess its effect on growth advantage in stationary phase (GASP). Finally, I comment on some crucial issues that hinder the progress of the field, including identification of novel metabolites in nutrient-depleted media, and the importance of using multidisciplinary research to resolve them

Solar activity forecast with a dynamo model

Although systematic measurements of the solar polar magnetic field exist only from mid 1970s, other proxies can be used to infer the polar field at earlier times. The observational data indicate a strong correlation between the polar field at a sunspot minimum and the strength of the next cycle, although the strength of the cycle is not correlated well with the polar field produced at its end. This suggests that the Babcock Leighton mechanism of poloidal field generation from decaying sunspots involves randomness, whereas the other aspects of the dynamo process must be reasonably ordered and deterministic. Only if the magnetic diffusivity within the convection zone is assumed to be high, we can explain the correlation between the polar field at a minimum and the next cycle. We give several independent arguments that the diffusivity must be of this order. In a dynamo model with diffusivity like this, the poloidal field generated at the mid latitudes is advected toward the poles by the meridional circulation and simultaneously diffuses towards the tachocline, where the toroidal field for the next cycle is produced. To model actual solar cycles with a dynamo model having such high diffusivity, we have to feed the observational data of the poloidal field at the minimum into the theoretical model. We develop a method of doing this in a systematic way. Our model predicts that cycle 24 will be a very weak cycle. Hemispheric asymmetry of solar activity is also calculated with our model and compared with observational data.Comment: 17 pages, 18 figures, submitted to MNRA

Outstanding Issues in Solar Dynamo Theory

The magnetic activity of the Sun, as manifested in the sunspot cycle, originates deep within its convection zone through a dynamo mechanism which involves non-trivial interactions between the plasma and magnetic field in the solar interior. Recent advances in magnetohydrodynamic dynamo theory have led us closer towards a better understanding of the physics of the solar magnetic cycle. In conjunction, helioseismic observations of large-scale flows in the solar interior has now made it possible to constrain some of the parameters used in models of the solar cycle. In the first part of this review, I briefly describe this current state of understanding of the solar cycle. In the second part, I highlight some of the outstanding issues in solar dynamo theory related to the the nature of the dynamo $\alpha$-effect, magnetic buoyancy and the origin of Maunder-like minima in activity. I also discuss how poor constraints on key physical processes such as turbulent diffusion, meridional circulation and turbulent flux pumping confuse the relative roles of these vis-a-vis magnetic flux transport. I argue that unless some of these issues are addressed, no model of the solar cycle can claim to be ``the standard model'', nor can any predictions from such models be trusted; in other words, we are still not there yet.Comment: To appear in "Magnetic Coupling between the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200

How does culture impinge upon managers' demeanor of earnings management? Evidence from cross-country analysis

We examine the impact of national culture on earnings. Specifically, we examine managers’ likelihood of using accrual or real earnings management and the role of culture on various attributes of earnings (accruals quality, persistence, smoothing, and predictability). We measure national culture using Hofstede’s six dimensions of culture (1984, 2001, and 2010). Using data from 36 countries during 1997-2018, we find that managers are likely to use both accruals and real earnings management in high power distance countries. In long-term oriented countries, managers are more likely to use real earnings management. In uncertainty avoidance countries, in high individualist countries, and in higher indulgent versus restraint countries, managers are less likely to use either type of earnings management. In masculine countries, managers tend to use lower accruals management rather and rely on production cost real earnings management. We also find the use of accruals management and the use of real earnings management are substitutes for each other. In addition, we are able to classify countries into four earnings quality groups based on the culture impact on the earnings attributes (primarily driven by accruals quality, predictability, and smoothing). Persistence is generally not significant in classifying countries by earnings attributes. Our findings indicate that a universal set of accounting standards is a challenging goal to achieve given the cultural diversity across countries. To improve the existing corporate governance framework and to ensure high quality and uniform financial statements, the enforcement of standards should be tailored to specific cultures, or at a minimum, corporate boards need to be more culturally diversified

Estimation of osmotic potential and free amino acids in some mangroves of the Sundarbans, India

Osmotic potential (OP) of root and leaf was measured in 19 species of mangroves collected from the Sundarbans, India. Leaf OP was estimated in 11 taxa from among them, grown in fresh water and compared with that deriving from taxa grown in saline water. Free amino acids were estimated from leaves of 16 mangrove species of the Sundarbans. The osmotic potential in leaves collected from their natural habitat was more negative than that from those grown in fresh water conditions. Seedlings grown without salt provided less negative leaf OPthan those treated with 0.1 mol dm–3 NaCl. The more negative OP was found in more saline soil, which might be related to adaptation to facilitate water uptake from a highly saline and frequently waterlogged anaerobic substratum. Aspartic acid, alanine, proline, tryptophan, tyrosine and phenylalanine are the major free amino acids detected in the leaves. Leucine was recorded only in Avicennia spp., where phenylalanine content was negligible. Proline content was estimated in seven species. The positive linear trend obtained between leaf OP and proline content points to its role as an osmoticum in mangrove leaves. Cysteine, aspartic acid, alanine and phenylalanine were determined in seedlings, while proline could be estimated only in X. mekongensis. Cysteine and proline content in seedling leaves were gradually reduced with increasing soil salinity. Lack of cysteine in mature leaves and its decrease in more saline soil probably indicates salinity as a photorespiration restricting factor. A more or less inverse relationship was found between proline and alanine content both in seedlings and mature plants

Q-curvature and Path Integral Complexity

We discuss the interpretation of path integral optimization as a uniformization problem in even dimensions. This perspective allows for a systematical construction of the higher-dimensional path integral complexity in holographic conformal field theories in terms of Q-curvature actions. We explore the properties and consequences of these actions from the perspective of the optimization programme, tensor networks and penalty factors. Moreover, in the context of recently proposed holographic path integral optimization, we consider higher curvature contributions on the Hartle-Hawking bulk slice and study their impact on the optimization as well as their relation to Q-curvature actions and finite cut-off holography

The Waldmeier Effect in Sunspot Cycles

We discuss two aspects of the Waldmeier Effect, namely (1) the rise times of sunspot cycles are anti-correlated to their strengths (WE1) and (2) the rates of rise of the cycles are correlated to their strengths (WE2). From analysis of four different data sets we conclude that both WE1 and WE2 exist in all the data sets. We study these effects theoretically by introducing suitable stochastic fluctuations in our regular solar dynamo model.Comment: Magnetic Coupling between the Interior and Atmosphere of the Sun; Astrophysics and Space Science Proceeding