Quenched Galaxies are Important Host Candidates of Binary Black Hole and Binary Neutron Star Mergers

In this work,we present the probabilities of mergers of binary black holes(BBHs)and binary neutron stars(BNSs)as functions of stellar mass,metallicity,specific star formation rate(sSFR),and age for galaxies with redshift z≤0.1.Using the binary-star evolution(BSE)code and some fitting formulae,we construct a phenomenological model of cosmic gravitational wave(GW)merger events.By using the Bayesian analysis method and the observations from Advanced LIGO and Virgo,we obtain the relevant parameters of the phenomenological model(such as the maximum black hole mass is 93_(-22)^(+73)M_(⊙)).Combining the above model results with the galaxy catalog given by the EMERGE empirical galaxy model,we find the normalized probability of occurrence of a merger event varying with log10 sSFR yr(-1)for galaxies with z≤0.1 is different from that in previous studies,that is,two peaks exist in this work while there is only one peak(log_(10)(sSFR/yr^(−1))=−10)in the previous work.The sSFR value corresponding to the new peak is log_(10)(sSFR/yr^(−1))=−12 and in line with the value(log_(10)(sSFR yr^-1)=-12.65_(-0.66)^(+0.44)of NGC 4493,the host galaxy of BNS merger event GW170817.The new peak is caused by today’s quenched galaxies,which give a large contribution to the total SFR at high redshift in the EMERGE empirical galaxy model.Moreover,we find that the BNS mergers are most likely detected in galaxies with age∼11 Gyr,which is greater than previous results(6−8Gyr)and close to the age of NGC 4993,13.2_(-0.9)^(+0.5)Gyr.

A prediction of in vivo mechanical stresses in blood vessels using thermal expansion method and its application to hypertension and vascular stenosis

Mechanical stimuli play critical roles in cardiovascular diseases,in which in vivo stresses in blood vessels present a great challenge to predict.Based on the structural-thermal coupled finite element method,we propose a thermal expansion method to estimate stresses in multi-layer blood vessels under healthy and pathological conditions.The proposed method provides a relatively simple and convenient means to predict reliable in vivo mechanical stresses with accurate residual stress.The method is first verified with the opening-up process and the pressure-radius responses for single and multi-layer vessel models.It is then applied to study the stress variation in a human carotid artery at different hypertension stages and in a plaque of vascular stenosis.Our results show that specific or optimal residual stresses exist for different blood pressures,which helps form a homogeneous stress distribution across vessel walls.High elastic shear stress is identified on the shoulder of the plaque,which contributes to the tearing effect in plaque rupture.The present study indicates that the proposed numerical method is a capable and efficient in vivo stress evaluation of patient-specific blood vessels for clinical purposes.

Numerical study of clathrin-mediated endocytosis of nanoparticles by cells under tension

In this study, a three-dimensional mathematical model was used to study the contribution of clathrins during the process of cellular uptake of spherical nanoparticles under different membrane tensions. The clathrin-coated pit (CCP) that forms around the inward budding of the cell membrane was modeled as a vesicle with bending rigidity. An optimization algorithm was proposed for minimizing the total energy of the system, which comprises the deforming nanoparticle, receptor-ligand bonds, cell membrane, and CCP, in which way, the profile of the system is acquired. The results showed that the CCP enable full wrapping of the nanoparticles at various membrane tensions. When the cell membrane tension increases, the total deformation energy also increases, but the ratio of CCP bending to the minimum value of the total energy of the system decreases. The results also showed that the diameter of the endocytic vesicles determined by the competition between the stretching of the cell membrane and confinement of the coated pits are much larger than the nanoparticles, which is quit different as the results in passive endocytosis that is not facilitated by the CCPs. The present results indicate that variations of tension on cell membranes constitutes a biophysical marker for understanding the size distribution of CCPs observed in experiments. The present results also suggest that the early abortion of endocytosis is related to that the receptor-ligand bonds cannot generate adequate force to wrap the nanoparticles into the cell membrane before the clathrins respond to support the endocytic vesicles. Correspondingly, late abortion may relate to the inability of CCPs to confine the nanoparticles until the occurrence of the necking stage of endocytosis.

A Numerical Study of Passive Receptor-Mediated Endocytosis of Nanoparticles:The Effect of Mechanical Properties

In this work,a three-dimensional axisymmetric model with nanoparticle,receptor-ligand bonds and cell membrane as a system was used to study the quasi-static receptor-mediated endocytosis process of spherical nanoparticles in drug delivery.The minimization of the system energy function was carried out numerically,and the deformations of nanoparticle,receptor-ligand bonds and cell membrane were predicted.Results show that passive endocytosis may fail due to the rupture of receptor-ligand bonds during the wrapping process,and the size and rigidity of nanoparticles affect the total deformation energy and the terminal wrapping stage.Our results suggest that,in addition to the energy requirement,the success of passive endocytosis also depends on the maximum strength of the receptor-ligand bonds.

Numerical study of biomechanical characteristics of plaque rupture at stenosed carotid bifurcation:a stenosis mechanical property-specific guide for blood pressure control in daily activities

Acute stress concentration plays an important role in plaque rupture and may cause stroke or myocardial infarction.Quantitative evaluation of the relation between in vivo plaque stress and variations in blood pressure and flow rates is valuable to optimize daily monitoring of the cardiovascular system for high-risk patients as well as to set a safe physical exercise intensity for better quality of life.In this study,we constructed an in vivo stress model for a human carotid bifurcation with atherosclerotic plaque,and analyzed the effects of blood pressure,flow rates,plaque stiffness,and stenosis on the elastic stress and fluid viscous stress around the plaque.According to the maximum values of the mechanical stress,we define a risk index to predict the risk level of plaque rupture under different exercise intensities.For a carotid bifurcation where the blood flow divides,the results suggest that the stenosis ratio determines the ratio of the contributions of elastic shear stress and viscous shear stress to plaque rupture.A n increase of the plaque stiffness enhances the maximum elastic shear stress in the plaque,indicating that a high-stiffness plaque is more prone to rupture for given stenosis ratio.High stress co-localization at the shoulder of plaques agrees with the region of plaque injury in clinical observations.It is demonstrated that,due to the stress-shield effect,the rupture risk of a high-stiffness plaque tends to decrease under high-stenosis conditions,suggesting the existence of a specific stenosis corresponding to the maximum risk.This study may help to complement risk stratification of vulnerable plaques in clinical practice and provides a stenosis mechanical property-specific guide for blood pressure control in cardiovascular health management.

A Full Eulerian Fluid-Membrane Coupling Method with a Smoothed Volume-of-Fluid Approach

A novel full Eulerian fluid-elastic membrane coupling method on the fixed Cartesian coordinate mesh is proposed within the framework of the volume-of-fluid approach.The present method is based on a full Eulerian fluid-(bulk)structure coupling solver(Sugiyama et al.,J.Comput.Phys.,230(2011)596–627),with the bulk structure replaced by elastic membranes.In this study,a closed membrane is considered,and it is described by a volume-of-fluid or volume-fraction information generally called VOF function.A smoothed indicator(or characteristic)function is introduced as a phase indicator which results in a smoothed VOF function.This smoothed VOF function uses a smoothed delta function,and it enables a membrane singular force to be incorporated into a mixture momentum equation.In order to deal with a membrane deformation on the Eulerian mesh,a deformation tensor is introduced and updated within a compactly supported region near the interface.Both the neo-Hookean and the Skalak models are employed in the numerical simulations.A smoothed(and less dissipative)interface capturing method is employed for the advection of the VOF function and the quantities defined on the membrane.The stability restriction due to membrane stiffness is relaxed by using a quasi-implicit approach.The present method is validated by using the spherical membrane deformation problems,and is applied to a pressure-driven flow with the biconcave membrane capsules(red blood cells).

A numerical method to predict the membrane tension distribution of spreading cells based on the reconstruction of focal adhesions

Changes in membrane tension significantly affect the physiological functions of cells in various ways.However,directly measuring the spatial distribution of membrane tension remains an ongoing issue.In this study,an algorithm is proposed to determine the membrane tension inversely by executing a particle-based method and searching for the minimum deformation energy based on the cell images and focal adhesions.A standard spreading cell model is established using 3D reconstructions with images from structured illumination microscopy as the reference cell shape.The membrane tension distribution,forces across focal adhesions,and profile of the spread cell are obtained using this method,until the cell deformation energy function optimization converges.Qualitative and quantitative comparisons with previous experimental results validated the reliability of this method.The results show that in the standard spreading cell model,the membrane tension decreases from the bottom to the top of the membrane.This method can be applied to predict the membrane tension distribution of cells freely spreading into different shapes,which could improve the quantitative analysis of cellular membrane tension in various studies for cell mechanics.

The possible equation of state of dark matter in low surface brightness galaxies

The observed rotation curves of low surface brightness(LSB)galaxies play an essential role in studying dark matter,and indicate the existence of a central constant density dark matter core.However,the cosmological N-body simulations of cold dark matter predict an inner cusped halo with a power-law mass density distribution,and cannot reproduce a central constant-density core.This phenomenon is called cusp-core problem.When dark matter is quiescent and satisfies the condition for hydrostatic equilibrium,the equation of state can be adopted to obtain the density profile in the static and spherically symmetric space-time.To address the cusp-core problem,we assume that the equation of state is independent of the scaling transformation.Its lower order approximation for this type of equation of state can naturally lead to a special case,i.e.,■,where p andρrepresent the pressure and density,respectively,V_(rot) depicts the rotation velocity of galaxy,andζandεare positive constants.It can obtain a density profile that is similar to the pseudo-isothermal halo model whenεis approximately 0.15.To obtain a more universally used model,let the equation of state include the polytropic model,i.e.■,from which we can obtain other types of density profiles,such as the profile that is nearly same as the Burkert profile,where s and ρ_(0) are positive constants.

A case study of aggregation behaviors of titanium dioxide nanoparticles in the presence of dodecylbenzene sulfonate in natural water

The present work aims to ascertain the mechanisms of surfactant（dodecylbenzene sulfonate; DBS） effects on the aggregation behaviors of TiO2 nanoparticles（TiO2-NPs） in natural water samples. Aggregation experiments were conducted at a TiO2-NPs concentration of 10 mg/L in deionized water and in natural water samples via dynamic light scattering and Zeta potential determination. Average attachment efficiency was calculated to compare the aggregation behaviors of nanoparticles in the two aqueous media. Results showed that the effects of DBS on aggregation could be interpreted by both Derjaguin–Landau–Verwey–Overbeek（DLVO） and non-DLVO mechanisms. In natural water samples,aggregation did not occur rapidly and was able to develop slowly under all conditions, and the roles of DBS were obvious at high DBS concentration owing to the impacts of inherent components of natural water samples, such as colloids and natural organic compounds.Future aggregation studies should concentrate on multi-factor, multi-colloidal and dynamic aspects under similar environmental conditions.