Simulations of the nonlinear stage of Farley-Buneman instability with allowance for electron thermal effects

The Farley-Buneman instability is a two-stream instability observed in the weakly ionized plasma of the E region of the Earth’s ionosphere. In the present paper, the effect of nonisothermal behavior of electrons on the development of this instability is investigated by numerical simulations. The instability is described using fluid equations for the electron density and temperature, a kinetic equation for ions, and Poisson’s equation. In contrast to most previous studies, the simulations are performed by numerically solving partial differential equations, rather than by the particle method. With allowance for thermal effects, the simulation results become more realistic, because the amplitudes of the perturbed electric field and plasma oscillations decrease and the instability develops over a longer time. It is shown that the influence of electron thermal effects is more pronounced at low values of the external electric field.     

Nonlinear regimes of Farley-Buneman instability

The dynamic suppression of the instability of a quasi-monochromatic wave by nonlinear wave-wave interaction is considered. It is shown that, near the threshold of linear instability, the process of decay into two strongly damped waves leads to the onset of a quasi-periodic or a stochastic nonlinear stabilization regime involving a small number of modes. A case study is made of the Farley-Buneman instability in an isothermal magnetized current-carrying plasma in which particle collisions play an important role. Typical characteristic features of different stabilization regimes are analyzed as functions of current and other plasma parameters.     

Quasilinear theory of the ion Weibel instability in the Earth's magnetospheric tail

The quasilinear equation for the ion Weibel instability is solved for waves propagating along the magnetic field. The energy of the excited waves is estimated and the moments of the ion distribution function in the saturation stage are determined as functions of the current velocity for parameters characteristic of the neutral sheet of the Earth's magnetotail. The question is studied of whether the current disruption at the beginning of the explosive phase of a substorm can be explained as being due to the onset of the ion Weibel instability.     

Effect of the normal component of the magnetic field on the kink instability of the Earth’s magnetospheric current sheet

The kink instability of a thin anisotropic current sheet is analyzed. It is shown that, for highly anisotropic current sheets, the instability growth rate is larger than that previously obtained using the Harris isotropic sheet model. The calculated oscillation period is a few minutes. The results of calculations are compared to the observed oscillations of the magnetotail current sheet. The results obtained indicate that kink instability can significantly contribute to large-scale variations in the structure of the Earth’s magnetotail current sheet.     

An Efficient Wavelet-Based Approximation Method to Gene Propagation Model Arising in Population Biology

In this paper, we have applied an efficient wavelet-based approximation method for solving the Fisher’s type and the fractional Fisher’s type equations arising in biological sciences. To the best of our knowledge, until now there is no rigorous wavelet solution has been addressed for the Fisher’s and fractional Fisher’s equations. The highest derivative in the differential equation is expanded into Legendre series; this approximation is integrated while the boundary conditions are applied using integration constants. With the help of Legendre wavelets operational matrices, the Fisher’s equation and the fractional Fisher’s equation are converted into a system of algebraic equations. Block-pulse functions are used to investigate the Legendre wavelets coefficient vectors of nonlinear terms. The convergence of the proposed methods is proved. Finally, we have given some numerical examples to demonstrate the validity and applicability of the method.     

Charles Mills for and against liberalism

Charles Mills both severely criticizes and reluctantly accepts liberal political theory’s approach to race and racism. In this new book, he develops contract theory’s understanding of race and racism in the effort to resuscitate liberalism from the racist deathbed on which it lies. To do this he must wrestle with political forms of black resistance that comport uneasily with liberalism, at best: nationalism notably, but also other types of racially oriented collective subjectivity, for example, identity politics. The book represents a major advance in Mills’s thought, but his work remains uneasy about the instability of race and the flexibility of racism.     

Stability of dust acoustic wavepackets suffering from polarization force due to the presence of trapped ions

The combined effects of the polarization force, free and trapped ions, and dust charge variation are incorporated in a rigorous study of the nonlinear dust acoustic waves (DAWs) propagating in an unmagnetized dusty plasma. Owing to the departure from the Boltzmann ion distribution, it is found that the nonlinear DAWs are governed by a modified Korteweg?de Vries (mKdV) equation. The association between the mKdV solitary wave and the DAW envelope in the system under consideration is discussed. A modified nonlinear Schrödinger equation appropriate for describing the modulated DAWs is derived. The modulation instability (MI) and the dependence of the system physical parameters on the polarization force, trapped ions, and dust charge variation have been analyzed. It is found that the critical curve separating the stable/unstable regions is strongly influenced by both of the polarization and the ion trapping parameters. Moreover, increasing the polarization leads to an increase of the critical wave number, while increasing the trapping parameter yields the opposite effect. The MI maximum growth rate decreases (increases) as the polarization (trapped ion) increases. The obtained results may be helpful in better understanding of space observations of the solar energetic particle flows in interplanetary space and the energetic particle events in the Earth’s magnetosphere.     

On a Reproductive Stage-Structured Model for the Population Dynamics of the Malaria Vector

A reproductive stage-structured deterministic differential equation model for the population dynamics of the human malaria vector is derived and analysed. The model captures the gonotrophic and behavioural life characteristics of the female Anopheles sp. mosquito and takes into consideration the fact that for the purposes of reproduction, the female Anopheles sp. mosquito must visit and bite humans (or animals) to harvest necessary proteins from blood that it needs for the development of its eggs. Focusing on mosquitoes that feed exclusively on humans, our results indicate the existence of a threshold parameter, the vectorial reproduction number, whose size increases with increasing number of gonotrophic cycles, and is also affected by the female mosquito’s birth rate, its attraction and visitation rate to human residences, and its contact rate with humans. A stability analysis of the model indicates that the mosquito can establish itself in the environment if and only if the value of the vectorial reproduction number exceeds unity and that mosquito eradication is possible if the vectorial reproduction number is less than unity, since, then, the trivial steady state which always exist is unique and is globally and asymptotically stable. When a persistent vector population steady state exists, it is locally and asymptotically stable for a range of reproduction numbers, but can also be driven to instability via a Hopf bifurcation as the reproduction number increases further away from unity. The model derivation identifies and characterizes control parameters relating to activities such as human-mosquito contact and the mosquito’s survival chances between blood meals and egg laying. Our results show that the total mosquito population size increases with increasing number of gonotrophic cycles. Therefore understanding the fundamental aspects of the mosquito’s behaviour provides a pathway for the study of human-mosquito contact and mosquito population control. Control of the mosquito population densities would ultimately lead to malaria control.     

Cleavage of BLM and Sensitivity of Bloom’s Syndrome Cells to Hydroxurea

Patients with Bloom’s syndrome (BS) show a strong genetic instability and a predisposition to all types of cancer. Here, we report that the Bloom’s syndrome protein (BLM) is cleaved in response to hydroxyurea (HU)- or UVC-induced apoptosis. The appearance and solubility of BLM proteolytic products differed according to whether proteolysis occurred in response to HU or UVC. One BS cell line homozygous for a null mutation in BLM was resistant to both UVC- and HU-induced apoptosis, while another one expressing a mutated BLM protein was resistant to HU-induced apoptosis but displayed normal sensitivity to UVC. Thus, UVC and HU appear to induce apoptosis through distinct pathways.

Key Words:

Bloom’s syndrome, Apoptosis, Hydroxyurea, Ultraviolet C radiation, RecQ helicase     

Generation of zonal flows and large-scale magnetic fields by drift-Alfvén turbulence

The possibility of generating zonal perturbations by drift-Alfvén turbulence in a plasma with a finite pressure (1>β>m_e/m_i) is investigated. A set of coupled equations is derived that includes the equation for the spectral function of the turbulence and the averaged equations for zonal perturbations. It is shown that, in particular cases, the equation for the spectral function possesses action invariants; i.e., it takes the form of a conservation law for some quantities that are proportional to the spectral function of turbulence. Two types of instability of the zonal perturbations are revealed. The first type of instability generates only a zonal flow. Two regimes of this instability—resonant and hydrodynamic regimes—are examined, and the corresponding instability growth rates are determined. The second type of instability takes place when the resonant interaction of drift-Alfvén waves with electrons is taken into account. Because of this instability, the generation of a zonal magnetic field is inevitably accompanied by the generation of a zonal flow. It is found that the growth rate of the second type of instability is slower than that of the first type.     

Wave-Block Due to a Threshold Gradient Underlies Limited Coordination in Pancreatic Islets

Two models for coupled pancreatic β cells are used to investigate excited wave propagation in spatially inhomogeneous islets of Langerhans. The application concerns spatial variation of glucose concentration across the islet. A comprehensive model of coupled cells shows that wave blocking occurs as the conductance of adenosine triphosphate regulated potassium channels increases, corresponding to spatially decreasing glucose concentration. A simplified model based on a perturbed version of Fisher’s equation has been investigated using perturbation theory. We show that the perturbed Fisher’s equation likewise can exhibit wave blocking.     

Numerical Investigation of the Instability-Based Power Emission from an Ungated Plasmonic HEMT Using Complete Hydrodynamic Model

The full-wave analysis of the Dyakonov–Shur instability in an ungated short-channel high electron mobility transistor (HEMT) is investigated in this paper. This mechanism causes the emission of electromagnetic radiations by the device. The accurate analysis of the device is important especially when large electric fields are present. Herein, to analyze such structures, the complete hydrodynamic model, which is the simultaneous solution of Maxwell’s equations and the first three moments of the Boltzmann transport equation, is used. This model well describes the electron-wave interactions by considering the transport parameter variations with the electron energy and temperature. These variations are especially considerable when the emitter operates at high electromagnetic fields and were not considered in previous studies. The obtained results demonstrate the oscillation current along the channel and consequently the radiated power of the device are severely influenced by the transport parameter variations. The developed analysis method describes the behavior of the device as a terahertz emitter more accurately than the available ones.

     

Association between knee extensor force steadiness and postural stability against mechanical perturbation in patients with Parkinson’s disease

ObjectiveLower extremity force steadiness has been shown to decrease with aging and neuromotor dysfunction and to be associated with physical function and fall. Although patients with Parkinson’s disease (PD) experience decreased force steadiness, whether the extent of force steadiness differs according to target force or whether this steadiness is associated with postural control remain unclear. Therefore, this study aimed to compare the force steadiness while steadily exerting low and moderate levels of knee extensor force between individuals with and without PD and to examine the association between force steadiness and postural instability against mechanical perturbation in PD.MethodsA total of 33 patients with PD (mean age, 71.7 years) and 33 healthy controls (72.2 years) participated in this study. Participants with PD were classified into postural stability or instability groups based on the Movement Disorder Society-sponsored revision of the Unified Parkinson’s Disease Rating Scale motor exam item 12. Participants performed steady task of the knee isometric extension at two levels (10% and 50% of maximal voluntary contraction [MVC]).ResultsForce steadiness at 10% MVC was lower in postural instability group than that in the control and postural stability groups (P < 0.05) after adjusting for age, sex, and body mass index, whereas it was not significantly different at 50% MVC among the three groups.DiscussionThese results suggest that the knee extensor force steadiness is affected in patients with PD having postural instability against mechanical perturbation during low intensity force exertion and is not affected regardless of the presence of postural instability during moderate intensity force exertion.     

Parental Socioeconomic Instability and Child Obesity

Using data from the 1986 to 2010 National Longitudinal Study of Youth (NLSY) and the NLSY Child and Young Adult Supplement, this research explores how changes in parental socioeconomic status relate to child obesity over time. Results from linear mixed-effects models indicate that maternal educational gains and maternal employment transitions significantly increased their child’s body mass index (BMI). This finding suggests that mothers who work may have less time to devote to monitoring their child’s food intake and physical activity, which places their children at higher risks of becoming overweight or obese over time. Conversely, father’s work transitions and educational gains contribute to decreases in child’s BMI. Thus, work instability and increasing educational attainment for the traditional breadwinner of the household corresponds to better child weight outcomes. Results also suggest that there are racial differences in child BMI that remain after adjusting for changes in socioeconomic status, which indicate that the same structural disadvantages that operate to keep minorities in lower social class standings in society also work to hinder minorities from advancing among and out of their social class. Policy implications related to curbing child obesity are discussed.     

Dynamic mutations in human genes: A review of trinucleotide repeat diseases

Dynamic mutations in human genes result from unstable trinucleotide repeats embedded within the transcribed region. The changeable nature of these mutations from generation to generation is in contrast to the static inheritance of other single-gene mutational events, e.g. point mutations, deletions, insertions and inversions, typically associated with Mendelian inheritance patterns. Intergenerational instability of dynamic mutations within families has provided an explanation for the genetic anticipation, leading to increasing severity or earlier age of onset in successive generations, associated with certain inherited disorders. While models for genomic instability presume that trinucleotide repeat expansion results from disruption of the DNA replication process, experimental evidence has not yet been obtained in support of this contention. Nevertheless, examples of unstable trinucleotide repeats continue to increase, although not all are associated with a specific phenotype. Five disorders resulting from small-scale expansions of CAG repeats within the protein-coding region are known: spinobulbar muscular atrophy, Huntington’s disease, spinocerebellar ataxia type 1, dentatorubral-pallidoluysian atrophy (DRPLA) and Machado-Joseph disease. A sixth disorder, Haw River syndrome, is allelic to DRPLA. Five folate-sensitive chromosomal fragile sites characterized to date, viz. FRAXA, FRAXE, FRAXF, FRA11B and FRA16A, all have large-scale CGG repeat expansion. Two disorders, fragile X syndrome and FRAXE mental retardation, result from instability of CGG repeats in the 5’ untranslated region ofFMR1 andF M R2 genes respectively. FRA11B lies close to chromosome 1 1q deletion endpoints in many Jacobsen syndrome patients and may be related to the deletion event producing partial aneuploidy for 1lq. Expansion of FRAXF and FRA16A has not been associated with a phenotype. Myotonic dystrophy results from a large-scale CTG expansion in the 3’ untranslated region of the myotonin protein kinase gene while Friedreich’s ataxia has recently been found to have a large-scale GAA repeat in the first intron ofX25. This article reviews the characteristics of trinucleotide repeat disorders and summarizes current understanding of the molecular pathophysiology.     

Retaliation in Response to Castration Promotes a Low Level of Virulence in an Ant–Plant Mutualism

The diversion of a host’s energy by a symbiont for its own benefit is a major source of instability in horizontally-transmitted mutualisms. This instability can be counter-balanced by the host’s retaliation against exploiters. Such responses are crucial to the maintenance of the relationship. We focus on this issue in an obligate ant–plant mutualism in which the ants are known to partially castrate their host plant. We studied plant responses to various levels of castration in terms of (1) global vegetative investment and (2) investment in myrmecophytic traits. Castration led to a higher plant growth rate, signalling a novel case of gigantism induced by parasitic castration. On the other hand, completely castrated plants produced smaller nesting and food resources (i.e. leaf pouches and extra floral nectaries). Since the number of worker larvae is correlated to the volume of the leaf pouches, such a decrease in the investment in myrmecophytic traits demonstrates for the first time the existence of inducible retaliation mechanisms against too virulent castrating ants. Over time, this mechanism promotes an intermediate level of castration and enhances the stability of the mutualistic relationship by providing the ants with more living space while allowing the plant to reproduce.     

DNA Repair Mechanisms in Huntington’s Disease

The human genome is under continuous attack by a plethora of harmful agents. Without the development of several dedicated DNA repair pathways, the genome would have been destroyed and cell death, inevitable. However, while DNA repair enzymes generally maintain the integrity of the whole genome by properly repairing mutagenic and cytotoxic intermediates, there are cases in which the DNA repair machinery is implicated in causing disease rather than protecting against it. One case is the instability of gene-specific trinucleotides, the causative mutations of numerous disorders including Huntington’s disease. The DNA repair proteins induce mutations that are different from the genome-wide mutations that arise in the absence of repair enzymes; they occur at definite loci, they occur in specific tissues during development, and they are age-dependent. These latter characteristics make pluripotent stem cells a suitable model system for triplet repeat expansion disorders. Pluripotent stem cells can be kept in culture for a prolonged period of time and can easily be differentiated into any tissue, e.g., cells along the neural lineage. Here, we review the role of DNA repair proteins in the process of triplet repeat instability in Huntington’s disease and also the potential use of pluripotent stem cells to investigate neurodegenerative disorders.     

Grafen,the Price equations,fitness maximization,optimisation and the fundamental theorem of natural selection

This paper is a commentary on the focal article by Grafen and on earlier papers of his on which many of the results of this focal paper depend. Thus it is in effect a commentary on the “formal Darwinian project”, the focus of this sequence of papers. Several problems with this sequence are raised and discussed. The first of these concerns fitness maximization. It is often claimed in these papers that natural selection leads to a maximization of fitness and that this view is claimed in Fisher’s “fundamental theorem of natural selection”. These claims are refuted, and various incorrect statements about the meaning and interpretation of the fundamental theorem of natural selection, in this sequence and in other papers by other authors, are discussed. Next, much of the work in this sequence rests on the first Price equation. In the deterministic (infinite population) case this equation is no more than the standard classical equation relating to changes in gene frequencies. In the stochastic case the equation gives the change in gene frequencies as the sum of two terms (the second of which vanishes in the deterministic case). These two terms are of essentially equal importance in the situation considered in the focal article, yet one of Grafen’s results ignores the second term in the stochastic analysis. This is associated with a wavering between deterministic and stochastic analyses and the use of the Price fitness concept and the classical fitness concept. These comments cast doubts on Grafen’s optimization theory.