Simple models for the heat flux from the Atlantic meridional overturning cell to the atmosphere

It has been suggested that a slowdown of the Atlantic meridional overturning cell (AMOC) would cause the Northern Hemisphere to cool by a few degrees. We use a sequence of simple analytical models to show that due to the nonlinearity of the system, the simplified heat flux from the modeled AMOC to the atmosphere above is so robust that even changes of as much as 50% in the present AMOC transport are not enough to significantly change the temperature of the outgoing warmed atmosphere (i.e., the fraction of the atmosphere warmed by the AMOC). Our most realistic model (which is still a far cry from reality) involves a warm ocean losing heat to an otherwise motionless and colder atmosphere. As a result, the compressible atmosphere convects, and the generated airflow ultimately penetrates horizontally into the surrounding air. The behavior of the system is attributable to four key aspects of the underlying physical processes: (1) convective atmospheric transport increases by warming the atmosphere, (2) the ocean is warmer than the atmosphere, (3) the surface heat flux is usually proportional to the temperature difference between the ocean and the atmosphere, and (4) the specific heat capacity of water is much larger than that of the air. Taken together, these properties of the system lead to the existence of a dynamic “asymptotic” state, a modeled regime, in which even significant changes in the AMOC transport have almost no effect on the ocean-atmosphere heat flux and the resulting outgoing atmospheric temperature. In the hypothetical limit of an infinitely large specific heat capacity of water, Cpw there is no change in either the atmospheric transport or the temperatures of the ocean and the atmosphere, regardless of how large the reduction in the AMOC transport is. Although our models may be too simple to allow for a direct application to the ocean and atmosphere, they do shed light on the processes in question

Unstaggered-staggered solitons in two-component discrete nonlinear Schr\"{o}dinger lattices

We present stable bright solitons built of coupled unstaggered and staggered components in a symmetric system of two discrete nonlinear Schr\"{o}dinger (DNLS) equations with the attractive self-phase-modulation (SPM) nonlinearity, coupled by the repulsive cross-phase-modulation (XPM) interaction. These mixed modes are of a "symbiotic" type, as each component in isolation may only carry ordinary unstaggered solitons. The results are obtained in an analytical form, using the variational and Thomas-Fermi approximations (VA and TFA), and the generalized Vakhitov-Kolokolov (VK) criterion for the evaluation of the stability. The analytical predictions are verified against numerical results. Almost all the symbiotic solitons are predicted by the VA quite accurately, and are stable. Close to a boundary of the existence region of the solitons (which may feature several connected branches), there are broad solitons which are not well approximated by the VA, and are unstable

Unstaggered-staggered solitons on one- and two-dimensional two-component discrete nonlinear Schr\"{o}dinger lattices

We study coupled unstaggered-staggered soliton pairs emergent from a system of two coupled discrete nonlinear Schr\"{o}dinger (DNLS) equations with the self-attractive on-site self-phase-modulation nonlinearity, coupled by the repulsive cross-phase-modulation interaction, on 1D and 2D lattice domains. These mixed modes are of a "symbiotic" type, as each component in isolation may only carry ordinary unstaggered solitons. While most work on DNLS systems addressed symmetric on-site-centered fundamental solitons, these models give rise to a variety of other excited states, which may also be stable. The simplest among them are antisymmetric states in the form of discrete twisted solitons, which have no counterparts in the continuum limit. In the extension to 2D lattice domains, a natural counterpart of the twisted states are vortical solitons. We first introduce a variational approximation (VA) for the solitons, and then correct it numerically to construct exact stationary solutions, which are then used as initial conditions for simulations to check if the stationary states persist under time evolution. Two-component solutions obtained include (i) 1D fundamental-twisted and twisted-twisted soliton pairs, (ii) 2D fundamental-fundamental soliton pairs, and (iii) 2D vortical-vortical soliton pairs. We also highlight a variety of other transient dynamical regimes, such as breathers and amplitude death. The findings apply to modeling binary Bose-Einstein condensates, loaded in a deep lattice potential, with identical or different atomic masses of the two components, and arrays of bimodal optical waveguides.Comment: to be published in Communications in Nonlinear Science and Numerical Simulatio

Statistical mechanics of chromosomes: In vivo and in silico approaches reveal high-level organization and structure arise exclusively through mechanical feedback between loop extruders and chromatin substrate properties

The revolution in understanding higher order chromosome dynamics and organization derives from treating the chromosome as a chain polymer and adapting appropriate polymer-based physical principles. Using basic principles, such as entropic fluctuations and timescales of relaxation of Rouse polymer chains, one can recapitulate the dominant features of chromatin motion observed in vivo. An emerging challenge is to relate the mechanical properties of chromatin to more nuanced organizational principles such as ubiquitous DNA loops. Toward this goal, we introduce a real-time numerical simulation model of a long chain polymer in the presence of histones and condensin, encoding physical principles of chromosome dynamics with coupled histone and condensin sources of transient loop generation. An exact experimental correlate of the model was obtained through analysis of a model-matching fluorescently labeled circular chromosome in live yeast cells. We show that experimentally observed chromosome compaction and variance in compaction are reproduced only with tandem interactions between histone and condensin, not from either individually. The hierarchical loop structures that emerge upon incorporation of histone and condensin activities significantly impact the dynamic and structural properties of chromatin. Moreover, simulations reveal that tandem condensin-histone activity is responsible for higher order chromosomal structures, including recently observed Z-loops

Continuity Culture: A Key Factor for Building Resilience and Sound Recovery Capabilities

This article investigates the extent to which Jordanian service organizations seek to establish continuity culture through testing, training, and updating of their business continuity plans. A survey strategy was adopted in this research. Primary and secondary data were used. Semistructured interviews were conducted with five senior managers from five large Jordanian service organizations registered with the Amman Stock Exchange. The selection of organizations was made on the basis of simple random sampling. Interviews targeted the headquarters only in order to obtain a homogenous sample. Three out of five organizations could be regarded as crisis prepared and have better chances for recovery. The other two organizations exhibited characteristics of standard practice that only emphasizes the recovery aspect of business continuity management (BCM), while paying less attention to establishing resilient cultures and embedding BCM. The findings reveal that the ability to recover following major incidents can be improved by embedding BCM in the culture of the organization and by making BCM an enterprise-wide process. This is one of few meticulous studies that have been undertaken in the Middle East and the first in Jordan to investigate the extent to which service organizations focus on embedding BCM in the organizational culture

Fractional diffusion equation for an n-dimensional correlated Lévy walk.

Lévy walks define a fundamental concept in random walk theory that allows one to model diffusive spreading faster than Brownian motion. They have many applications across different disciplines. However, so far the derivation of a diffusion equation for an n-dimensional correlated Lévy walk remained elusive. Starting from a fractional Klein-Kramers equation here we use a moment method combined with a Cattaneo approximation to derive a fractional diffusion equation for superdiffusive short-range auto-correlated Lévy walks in the large time limit, and we solve it. Our derivation discloses different dynamical mechanisms leading to correlated Lévy walk diffusion in terms of quantities that can be measured experimentally

Small Scale Aquaculture

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