Tidal deformations of slowly spinning isolated horizons

It is generally believed that tidal deformations of a black hole in an external field, as measured using its gravitational field multipoles, vanish. However, this does not mean that the black hole horizon is not deformed. Here we shall discuss the deformations of a black hole horizon in the presence of an external field using a characteristic initial value formulation. Unlike existing methods, the starting point here is the black hole horizon itself. The effect of, say, a binary companion responsible for the tidal deformation is encoded in the geometry of the spacetime in the vicinity of the horizon. The near horizon spacetime geometry, i.e. the metric, spin coefficients, and curvature components, are all obtained by integrating the Einstein field equations outwards starting from the horizon. This method yields a reformulation of black hole perturbation theory in a neighborhood of the horizon. By specializing the horizon geometry to be a perturbation of Kerr, this method can be used to calculate the metric for a tidally deformed Kerr black hole with arbitrary spin. As a first application, we apply this formulation here to a slowly spinning black hole and explicitly construct the spacetime metric in a neighborhood of the horizon. We propose natural definitions of the electric and magnetic surficial Love numbers based on the Weyl tensor component $\Psi_2$. From our solution, we calculate the tidal perturbations of the black hole, and we extract both the field Love numbers and the surficial Love numbers which quantify the deformations of the horizon.Comment: 36 pages, 3 pages of supplementary material, 3 figures. Typos corrected, references added, update of Fig.2 (content unchanged), the discussion in section VIIC has been extended (results unchanged), and a small summary of the main results has been added in section

Tidal deformations of slowly spinning isolated horizons

It is generally believed that tidal deformations of a black hole in anexternal field, as measured using its gravitational field multipoles, vanish.However, this does not mean that the black hole horizon is not deformed. Herewe shall discuss the deformations of a black hole horizon in the presence of anexternal field using a characteristic initial value formulation. Unlikeexisting methods, the starting point here is the black hole horizon itself. Theeffect of, say, a binary companion responsible for the tidal deformation isencoded in the geometry of the spacetime in the vicinity of the horizon. Thenear horizon spacetime geometry, i.e. the metric, spin coefficients, andcurvature components, are all obtained by integrating the Einstein fieldequations outwards starting from the horizon. This method yields areformulation of black hole perturbation theory in a neighborhood of thehorizon. By specializing the horizon geometry to be a perturbation of Kerr,this method can be used to calculate the metric for a tidally deformed Kerrblack hole with arbitrary spin. As a first application, we apply thisformulation here to a slowly spinning black hole and explicitly construct thespacetime metric in a neighborhood of the horizon. We propose naturaldefinitions of the electric and magnetic surficial Love numbers based on theWeyl tensor component $\Psi_2$. From our solution, we calculate the tidalperturbations of the black hole, and we extract both the field Love numbers andthe surficial Love numbers which quantify the deformations of the horizon.<br

Black hole tomography: Unveiling black hole horizon dynamics via ringdown observations

During the post-merger regime of a binary black hole merger, thegravitational wave signal consists of a superposition of quasi-normal modes(QNMs) of the remnant black hole. It has been observed empirically, primarilythrough numerical simulations and heuristic arguments, that the infallingradiation at the horizon is also composed of a superposition of QNMs. In thispaper, we provide an analytic explanation for this observation in theperturbative regime. Our analysis is based on a characteristic initial valueformulation where data is prescribed on the horizon (modeled as a perturbedisolated horizon), and on a transversal null-hypersurface which registers theoutgoing radiation. This allows us to reformulate the traditional QNM problemin a fully 4-dimensional setting. Using a mode-decomposition, we demonstratethat the radiation modes crossing $\mathcal{H}$ are highly correlated with theoutgoing modes crossing $\mathcal{I}$, and provide explicit expressions linking$\widetilde{\Psi}_0$ at the horizon with $\widetilde{\Psi}_4$ at null infinity.<br

In vitro mycorrhization of micropropagated plants: studies on Castanea sativa Mill.

In vitro mycorrhization can be made by several axenic and nonaxenic techniques but criticism exists about their artificiality and inability to reproduce under natural conditions. However, artificial mycorrhization under controlled conditions can provide important information about the physiology of symbiosis. Micropropagated Castanea sativa plants were inoculated with the mycorrhizal fungus Pisolithus tinctorius after in vitro rooting. The mycorrhizal process was monitored at regular intervals in order to evaluate the mantle and hartig net formation, and the growth rates of mycorrhizal and nonmycorrhizal plants. Plant roots show fungal hyphae adhesion at the surface after 24 hours of mycorrhizal induction. After 20 days a mantle can be observed and a hartig net is forming although the morphology of the epidermal cells remains unaltered. At 30 days of root–fungus contact the hartig net is well developed and the epidermal cells are already enlarged. After 50 days of mycorrhizal induction, growth was higher for mycorrhizal plants than for nonmycorrhizal ones. The length of the major roots was lower in mycorrhizal plants after 40 days. Fresh and dry weights were higher in mycorrhizal plants after 30 days. The growth rates of chestnut mycorrhizal plants are in agreement with the morphological development of the mycorrhizal structures observed at each mycorrhizal time. The assessment of symbiotic establishment takes into account the formation of a mantle and a hartig net that were already developed at 30 days, when differences between fresh and dry weights of mycorrhizal and nonmycorrhizal plants can be quantified. In vitro conditions, mycorrhization influences plant physiology after 20 days of root–fungus contact, namely in terms of growth rates. Fresh and dry weights, heights, stem diameter and growth rates increased while major root growth rate decreased in mycorrhizal plants.Springe

Fostering employee creativity through creativity-contingent extrinsic and intrinsic rewards that emphasise creativity: A systematic review of creativity academic papers

Creativity is widely believed to be necessary to increase quality performance. Thus, in today’s more challenging and competitive environment, the contemporary organization frequently utilizes rewards practices to stimulate creative activities among employees. Existing research on reward practices shows evidence that creativity contingent rewards play a vital role in improving employee creative performance. This study presents a systematic review of extrinsic and intrinsic rewards that contribute to creativity and their effect on employee creativity. The findings show that regardless of the degree of importance of the rewards perceived by the employee, both the extrinsic and intrinsic rewards were positively correlated with the behaviour of creativity behavior. Interestingly, the results showed that creativity-contingent intrinsic rewards have relatively stronger effects on employee creativity when compared to creativity-contingent extrinsic rewards

Active behaviour during early development shapes glucocorticoid reactivity

TGlucocorticoids are the final effectors of the stress axis, with numerous targets in the central nervous system and the periphery. They are essential for adaptation, yet currently it is unclear how early life events program the glucocorticoid response to stress. Here we provide evidence that involuntary swimming at early developmental stages can reconfigure the cortisol response to homotypic and heterotypic stress in larval zebrafish (Danio rerio), also reducing startle reactivity and increasing spontaneous activity as well as energy efficiency during active behaviour. Collectively, these data identify a role of the genetically malleable zebrafish for linking early life stress with glucocorticoid function in later life

Generation of a reference transcriptome for evaluating rainbow trout responses to various stressors

<p>Abstract</p> <p>Background</p> <p>Fish under intensive culture conditions are exposed to a variety of acute and chronic stressors, including high rearing densities, sub-optimal water quality, and severe thermal fluctuations. Such stressors are inherent in aquaculture production and can induce physiological responses with adverse effects on traits important to producers and consumers, including those associated with growth, nutrition, reproduction, immune response, and fillet quality. Understanding and monitoring the biological mechanisms underlying stress responses will facilitate alleviating their negative effects through selective breeding and changes in management practices, resulting in improved animal welfare and production efficiency.</p> <p>Results</p> <p>Physiological responses to five treatments associated with stress were characterized by measuring plasma lysozyme activity, glucose, lactate, chloride, and cortisol concentrations, in addition to stress-associated transcripts by quantitative PCR. Results indicate that the fish had significant stressor-specific changes in their physiological conditions. Sequencing of a pooled normalized transcriptome library created from gill, brain, liver, spleen, kidney and muscle RNA of control and stressed fish produced 3,160,306 expressed sequence tags which were assembled and annotated. SNP discovery resulted in identification of ~58,000 putative single nucleotide polymorphisms including 24,479 which were predicted to fall within exons. Of these, 4907 were predicted to occupy the first position of a codon and 4110 the second, increasing the probability to impact amino acid sequence variation and potentially gene function.</p> <p>Conclusion</p> <p>We have generated and characterized a reference transcriptome for rainbow trout that represents multiple tissues responding to multiple stressors common to aquaculture production environments. This resource compliments existing public transcriptome data and will facilitate approaches aiming to evaluate gene expression associated with stress in this species.</p

Adrenocorticotropic Hormone Suppresses Gonadotropin-Stimulated Estradiol Release from Zebrafish Ovarian Follicles

While stress is known to impact reproductive performance, the pathways involved are not entirely understood. Corticosteroid effects on the functioning of the hypothalamus-pituitary-gonadal axis are thought to be a key aspect of stress-mediated reproductive dysfunction. A vital component of the stress response is the pituitary secretion of adrenocorticotropic hormone (ACTH), which binds to the melanocortin 2 receptor (MC2R) in the adrenal glands and activates cortisol biosynthesis. We recently reported MC2R mRNA abundance in fish gonads leading to the hypothesis that ACTH may be directly involved in gonadal steroid modulation. Using zebrafish (Danio rerio) ovarian follicles, we tested the hypothesis that acute ACTH stimulation modulates cortisol and estradiol (E2) secretion. ACTH neither affected cortisol nor unstimulated E2 release from ovarian follicles. However, ACTH suppressed human chorionic gonadotropin (hCG)-stimulated E2 secretion in a dose-related manner, with a maximum decrease of 62% observed at 1 I.U. ACTH mL−1. This effect of ACTH on E2 release was not observed in the presence of either 8-bromo-cAMP or forskolin, suggesting that the mechanism(s) involved in steroid attenuation was upstream of adenylyl cyclase activation. Overall, our results suggest that a stress-induced rise in plasma ACTH levels may initiate a rapid down-regulation of acute stimulated E2 biosynthesis in the zebrafish ovary, underscoring a novel physiological role for this pituitary peptide in modulating reproductive activity