560 research outputs found
Spectral analysis of gravitational waves from binary neutron star merger remnants
No full textIn this work we analyze the gravitational wave signal from hypermassive neutron stars formed after the merger of binary neutron star systems, focusing on its spectral features. The gravitational wave signals are extracted from numerical relativity simulations of models already considered by De Pietri et al. [Phys. Rev. D 93, 064047 (2016)], Maione et al. [Classical Quantum Gravity 33, 175009 (2016)], and Feo et al. [Classical Quantum Gravity 34, 034001 (2017)], and allow us to study the effect of the total baryonic mass of such systems (from 2.4M(circle dot) to 3M(circle dot)), the mass ratio (up to q = 0.77), and the neutron star equation of state, in both equal and highly unequal mass binaries. We use the peaks we find in the gravitational spectrum as an independent test of already published hypotheses of their physical origin and empirical relations linking them with the characteristics of the merging neutron stars. In particular, we highlight the effects of the mass ratio, which in the past was often neglected. We also analyze the temporal evolution of the emission frequencies. Finally, we introduce a modern variant of Prony's method to analyze the gravitational wave postmerger emission as a sum of complex exponentials, trying to overcome some drawbacks of both Fourier spectra and least-squares fitting. Overall, the spectral properties of the postmerger signal observed in our simulation are in agreement with those proposed by other groups. More specifically, we find that the analysis of Bauswein and Stergioulas [Phys. Rev. D 91, 124056 (2015)] is particularly effective for binaries with very low masses or with a small mass ratio and that the mechanical toy model of Takami et al. [Phys. Rev. D 91, 064001 (2015)] provides a comprehensive and accurate description of the early stages of the postmerger
Exosome mediated communication in cancer: melanoma and sarcoma models
No full textExosomes (EXOs) are nanovesicles of diameter ranging between 50 to 140 nm, distinguished from other cell-derived vesicles by their origin, size, morphology and composition. Their stimulatory or inhibitory signaling activities are mediated by their content (mRNAs, microRNAs and proteins) that can be transferred from the cells of origin to recipient cells, influencing the surrounding microenvironment besides cell behavior. In this study we investigated EXO-mediated communications in two cancer models, melanoma and Ewing’s sarcoma.
In view of our previous results demonstrating miR-221&222 as key factors for melanoma development and dissemination, we demonstrated that the EXO-mediated horizontal transfer of miR-222 was competent to deliver miR-222-associated properties increasing tumor malignancy.
Melanoma-purified vesicles were characterized and investigated for the functionality of miR-222 in EXO-mediated tumorigenesis. Our data showed that EXOs secreted by miR-222-overexpressing cells induced a protumorigenic program in target cells, mainly through the upmodulation of the PI3K/AKT pathway. The reverse effects were obtained with EXOs recovered after inhibition of endogenous miR-221 and miR-222 by antagomir transfections. The possible differential significance of PI3K/AKT blockade in miR-222-transduced vs control cells was assessed by using BKM120, a pan inhibitor of PI3K. Results showed the capability of miR-222 overexpression to overcome BKM120-dependent effects.
We then demonstrated the role of Ewing’s sarcoma-derived EXOs as mediators of signals involved in cancer growth, metastases and differentiation. Ewing’s sarcoma (EWS) is an aggressive childhood bone tumor characterized in the majority of cases by the presence of the fusion oncoprotein EWS-FLI1 and by high expression of the membrane glycoprotein CD99. These features, which are the necessary conditions for the pathogenesis of EWS, mediate tumor progression and maintain the cells in a dedifferentiated state. We evaluated the ability of EXOs, expressing or not CD99, to modulate the phenotype of EWS cells. We observed that the delivery of EXOs devoid of CD99 was sufficient to induce neural differentiation in EWS recipient cells through the inhibition of Notch-NF-kB signaling mediated by miR-34a overexpression.
All together these observations would provide a significant step toward new biomarker discovery and innovative therapeutic options. These data on one side support miR-222 responsibility in the exosome-associated melanoma properties, on the other the role of CD99-shRNA/miR-34a-derived EXOs to induce differentiation in EWS, thus further indicating microRNAs as potential diagnostic, prognostic and eventually therapeutic biomarkers
Food Chains in the Chemostat: Relationships Between Mean Yield and Complex Dynamics
No full textA tritrophic food chain chemostat model composed of a prey with Monod type nutrient uptake, a Holling type II predator and a Holling type II exploited superpredator is considered in this paper. The bifurcations of the model show that dynamic complexity first increases and then decreases with the nutrient supplied to the bottom of the food chain. Extensive simulations prove that the same holds for food yield, i.e., there exists an optimum nutrient supply which maximizes mean food yield. Finally, a comparative analysis of the results points out that the optimum nutrient supply practically coincides with the nutrient supply separating chaotic dynamics from high-frequency cyclic dynamics. This reinforces the idea, already known for simpler models, that food yield maximization requires that the system behaves on the edge of chaos. -- 1 -- Food Chains in the Chemostat: Relationships Between Mean Yield and Complex Dynamics Alessandra Gragnani Oscar De Feo Sergio Rinaldi 1 Introduction Ai..
Utility and prognostic significance of leukocyte ratios in dogs with Primary Immune-Mediated Hemolytic Anemia
No full textCanine immune-mediated hemolytic anemia (IMHA) is a life-threatening condition that is commonly associated with neutrophilia and monocytosis. Leukocyte ratios have been found to have prognostic value in humans and animals affected by a range of inflammatory, infectious, and neoplastic disorders. We hypothesized that in primary IMHA, neutrophil to lymphocyte (NLR), neutrophil to monocyte (NMR), band neutrophil to segmented neutrophil (BNR) and monocyte to lymphocyte (MLR) ratios would be higher in dogs that did not survive to discharge. Medical records of dogs diagnosed with IMHA at two veterinary teaching hospitals were retrospectively reviewed. Twenty-three of the 72 included dogs did not survive to discharge. NLR, NMR, BNR and MLR ratios were compared between dogs that survived to discharge and dogs that died or were euthanized. None of the ratios were significantly different between survivors and non-survivors (P = 0.14–0.99). Area under the Receiver Operating Characteristic (ROC) curve for prediction of non-survival ranged from 0.5 (95% confidence interval 0.38–0.62) for MLR to 0.61 (0.49–0.72) for NMR and was not significantly different from 0.5 for any ratio (P = 0.29–0.99). After exclusion of 31 dogs that received one or both immunosuppressive medications and blood transfusion before presentation, the area under the ROC curve for prediction of survival was significantly different from 0.5 for MLR (0.78, P = 0.01) and NMR (0.78, P = 0.0002). This study suggests that lower MLR and higher NMR may predict poorer prognosis in untreated dogs with IMHA
Food Chains in the Chemostat: Relationships Between Mean Yield and Complex Dynamics
No full textA tritrophic food chain chemostat model composed of a prey with Monod type nutrient uptake, a Holling type II predator and a Holling type II exploited superpredator is considered in this paper. The bifurcations of the model show that dynamic complexity first increases and then decreases with the nutrient supplied to the bottom of the food chain. Extensive simulations prove that the same holds for food yield, i.e., there exists an optimum nutrient supply which maximizes mean food yield. Finally, a comparative analysis of the results points out that the optimum nutrient supply practically coincides with the nutrient supply separating chaotic dynamics from high-frequency cyclic dynamics. This reinforces the idea, already known for simpler models, that food yield maximization requires that the system behaves on the edge of chaos
Modeling equal and unequal mass binary neutron star mergers using public codes
No full textWe present three-dimensional simulations of the dynamics of binary neutron star mergers from the late stage of the inspiral process up to ∼20 ms after the system has merged, either to form a hypermassive neutron star or a rotating black hole. We investigate five equal mass models of total gravitational mass 2.207, 2.373, 2.537, 2.697, and 2.854M, respectively, and four unequal mass models with MADM≃2.53 M and q≃0.94, 0.88, 0.83, and 0.77 (where q=M(1)/M(2) is the mass ratio). We use a semirealistic equation of state, namely, the seven-segment piecewise polytropic SLyPP with a thermal component given by Γth=1.8. We have also compared the resulting dynamics (for one model) using both the BSSN-NOK and CCZ4 methods for the evolution of the gravitational sector and also different reconstruction methods for the matter sector, namely, PPM, WENO, and MP5. Our results show agreement at high resolution, but superiority of BSSN-NOK supplemented by WENO reconstruction at lower resolutions. One of the important characteristics of the present investigation is that for the first time it has been done using only publicly available open source software: the Einstein Toolkit code, deployed for the dynamical evolution, and the LORENE code, for the generation of the initial models. All of the source code and parameters used for the simulations have been made publicly available. This not only makes it possible to rerun and reanalyze our data but also enables others to directly build upon this work for future research
Neutron star instabilities in full general relativity using a Γ=2.75 ideal fluid
No full textWe present results about the effect of the use of a stiffer equation of state, namely the ideal-fluid Γ=2.75 one, on the dynamical bar-mode instability in rapidly rotating polytropic models of neutron stars in full general relativity. We determine the change on the critical value of the instability parameter β for the emergence of the instability when the adiabatic index Γ is changed from 2 to 2.75 in order to mimic the behavior of a realistic equation of state. In particular, we show that the threshold for the onset of the bar-mode instability is reduced by this change in the stiffness and give a precise quantification of the change in value of the critical parameter βc. We also extend the analysis to lower values of β and show that low-beta shear instabilities are present also in the case of matter described by a simple polytropic equation of state
Binary neutron star merger simulations with different initial orbital frequency and equation of state
No full textWe present results from three-dimensional general relativistic simulations of binary neutron star coalescences and mergers using public codes. We considered equal mass models where the baryon mass of the two neutron stars. is 1.4M(circle dot), described by four different equations of state (EOS) for the cold nuclear matter (APR4, SLy, H4, and MS1; all parametrized as piecewise polytropes). We started the simulations from four different initial interbinary distances (40, 44.3, 50, and 60 km), including up to the last 16 orbits before merger. That allows us to show the effects on the gravitational wave (GW) phase evolution, radiated energy and angular momentum due to: the use of different EOS, the orbital eccentricity present in the initial data and the initial separation (in the simulation) between the two stars. Our results show that eccentricity has a major role in the discrepancy between numerical and analytical waveforms until the very last few orbits, where 'tidal' effects and missing high-order post-Newtonian coefficients also play a significant role. We test different methods for extrapolating the GW signal extracted at finite radii to null infinity. We show that an effective procedure for integrating the Newman-Penrose psi(4) signal to obtain the GW strain h is to apply a simple high-pass digital filter to h after a time domain integration, where only the two physical motivated integration constants are introduced. That should be preferred to the more common procedures of introducing additional integration constants, integrating in the frequency domain or filtering psi(4) before integration
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