Energy Cascade in a Nonlinear Mechanistic Model of Turbulence

Energy transfer plays an essential role in many natural and engineering processes which include different scales. Understanding how the energy cascade (which refers to the energy transfer among the different scales) works is of primary importance. One notable example is the energy cascade in turbulent flow whose kinetic energy is transferred from large eddies to smaller ones. Below a threshold scale the energy is dissipated due to viscous friction. We introduce a nonlinear phenomenological mechanistic model of turbulence which consists of masses connected by springs arranged in a binary tree structure. To represent the various scales, the masses are gradually decreased in lower levels. The bottom level of the model consists of nonlinear energy sinks to provide dissipation. Based on previous research, we choose the system parameters and analyze its behavior for simple impulsive excitations. The decay of the total mechanical energy and the discrete energy spectrum of the system are compared for different impulse magnitudes. It is demonstrated that the dissipation is much more significant compared to the linear model, if the input energy is large enough. The energy spectra are compared with that of the linear model. We find that the energy spectrum of the nonlinear model better highlights the cut-off feature of the Kolmogorov spectrum

Visualized effect of oxidation on magnetic recording fidelity in pseudo-single-domain magnetite particles

Magnetite (​Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism. However, reliable interpretation of the recording fidelity of ​Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance. Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale ​Fe3O4 particles as they transform towards γ-Fe2O3. Magnetic induction maps demonstrate a change in both strength and direction of remanent magnetization within ​Fe3O4 particles in the size range dominant in rocks, confirming that oxidation can modify the original stored magnetic information

Controllability and controller-observer design for a class of linear time-varying systems

“The final publication is available at Springer via http://dx.doi.org/10.1007/s10852-012-9212-6"In this paper a class of linear time-varying control systems is considered. The time variation consists of a scalar time-varying coefficient multiplying the state matrix of an otherwise time-invariant system. Under very weak assumptions of this coefficient, we show that the controllability can be assessed by an algebraic rank condition, Kalman canonical decomposition is possible, and we give a method for designing a linear state-feedback controller and Luenberger observer

Cytogerontology since 1881: A reappraisal of August Weismann and a review of modern progress

Cytogerontology, the science of cellular ageing, originated in 1881 with the prediction by August Weismann that the somatic cells of higher animals have limited division potential. Weismann's prediction was derived by considering the role of natural selection in regulating the duration of an organism's life. For various reasons, Weismann's ideas on ageing fell into neglect following his death in 1914, and cytogerontology has only reappeared as a major research area following the demonstration by Hayflick and Moorhead in the early 1960s that diploid human fibroblasts are restricted to a finite number of divisions in vitro. In this review we give a detailed account of Weismann's theory, and we reveal that his ideas were both more extensive in their scope and more pertinent to current research than is generally recognised. We also appraise the progress which has been made over the past hundred years in investigating the causes of ageing, with particular emphasis being given to (i) the evolution of ageing, and (ii) ageing at the cellular level. We critically assess the current state of knowledge in these areas and recommend a series of points as primary targets for future research

Organic Geochemical Studies. I. Molecular Criteria for Hydrocarbon Genesis

In recent years the search for life-forms at the earliest periods of geological time has been continued not only at the morphological level but also at the molecular level. This has been possible as a result of the increase in the biochemical knowledge and with the advent of analytical techniques that are capable of describing the intimate molecular architecture of individual molecules in acute detail. The fundamental premises upon which this organic geochemical approach rest are the following: that certain molecules, possessing a characteristic structural skeleton, show a reasonable stability to degradation over long periods of geological time; that their structural specificity can be understood in terms of known biosynthetic sequences; and that their formation by any non-biological means is of negligible probability. In this manuscript it is proposed to critically re-examine these premises and to establish criteria whereby one can differentiate molecules derived from biological systems from those that have their origin in non-biological processes. The importance of establishing such criteria lies in the significance these criteria have in determining whether life exists, or has existed, on other planets. Within the very near future it may be possible to provide an initial answer to this question when the first lunar samples are returned to the earth for analysis

Conditional Transgenesis Using Dimerizable Cre (DiCre)

Cre recombinase is extensively used to engineer the genome of experimental animals. However, its usefulness is still limited by the lack of an efficient temporal control over its activity. We have recently developed a conceptually new approach to regulate Cre recombinase, that we have called Dimerizable Cre or DiCre. It is based on splitting Cre into two inactive moieties and fusing them to FKBP12 (FK506-binding protein) and FRB (binding domain of the FKBP12-rapamycin associated protein), respectively. These latter can be efficiently hetero-dimerized by rapamycin, leading to the reinstatement of Cre activity. We have been able to show, using in vitro approaches, that this ligand-induced dimerization is an efficient way to regulate Cre activity, and presents a low background activity together with a high efficiency of recombination following dimerization. To test the in vivo performance of this system, we have, in the present work, knocked-in DiCre into the Rosa26 locus of mice. To evaluate the performance of the DiCre system, mice have been mated with indicator mice (Z/EG or R26R) and Cre-induced recombination was examined following activation of DiCre by rapamycin during embryonic development or after birth of progenies. No recombination could be observed in the absence of treatment of the animals, indicating a lack of background activity of DiCre in the absence of rapamycin. Postnatal rapamycin treatment (one to five daily injection, 10 mg/kg i.p) induced recombination in a number of different tissues of progenies such as liver, heart, kidney, muscle, etc. On the other hand, recombination was at a very low level following in utero treatment of DiCre×R26R mice. In conclusion, DiCre has indeed the potentiality to be used to establish conditional Cre-deleter mice. An added advantage of this system is that, contrary to other modulatable Cre systems, it offers the possibility of obtaining regulated recombination in a combinatorial manner, i.e. induce recombination at any desired time-point specifically in cells characterized by the simultaneous expression of two different promoters

Activity patterns of free-ranging koalas (Phascolarctos cinereus) revealed by accelerometry

An understanding of koala activity patterns is important for measuring the behavioral response of this species to environmental change, but to date has been limited by the logistical challenges of traditional field methodologies. We addressed this knowledge gap by using tri-axial accelerometer data loggers attached to VHF radio collars to examine activity patterns of adult male and female koalas in a high-density population at Cape Otway, Victoria, Australia. Data were obtained from 27 adult koalas over two 7-d periods during the breeding season: 12 in the early-breeding season in November 2010, and 15 in the late-breeding season in January 2011. Multiple 15 minute observation blocks on each animal were used for validation of activity patterns determined from the accelerometer data loggers. Accelerometry was effective in distinguishing between inactive (sleeping, resting) and active (grooming, feeding and moving) behaviors. Koalas were more active during the early-breeding season with a higher index of movement (overall dynamic body acceleration [ODBA]) for both males and females. Koalas showed a distinct temporal pattern of behavior, with most activity occurring from mid-afternoon to early morning. Accelerometry has potential for examining fine-scale behavior of a wide range of arboreal and terrestrial species