Strength Of Attractive Interaction Research Articles

Bose-Einstein condensate in an elliptical waveguide

We investigate the effects of spatial curvature for an atomic Bose-Einstein condensate confined in an elliptical waveguide. The system is well described by an effective 1D Gross-Pitaevskii equation with a quantum-curvature potential, which has the shape of a double-well but crucially depends on the eccentricity of the ellipse. The ground state of the system displays a quantum phase transition from a two-peak configuration to a one-peak configuration at a critical attractive interaction strength. In correspondence of this phase transition the superfluid fraction strongly reduces and goes to zero for a sufficiently attractive Bose-Bose interaction.

Vesicle Geometries Enabled by Semiflexible Polymer.

Understanding and controlling vesicle shapes is fundamental challenge in biophysics and materials design. In this paper, we employ the Monte Carlo method to investigate the shape of soft vesicle induced by semiflexible polymer outside in two dimensions. The effect of bending stiffness of polymer and the strength of attractive interaction between vesicle and polymer on the shape of vesicle is discussed in detail in the present paper. It is found that the shape of vesicle is influenced by and . Typical shape of vesicles is observed, such as circular, cigar-like, double vesicle, and racquet-like. To engineer vesicle shape transformations is helpful for exploiting the richness of vesicle geometries for desired applications.

Pluronic F127/carfilzomib-based nanomicelles as promising nanocarriers: synthesis, characterization, biological, and in silico evaluations

In this work, we designed a drug delivery nanosystem based on oil-in-water Pluronic F127 nanomicelles to encapsulate and control the release of the antineoplasic drug carfilzomib (CFZ), and hypothesized that CFZ entrapment might result in a better effective and more localized cytotoxic effect on cancerous cells and to reduce its undesirable side effects for in vitro and in vivo applications. Pluronic F127/CFZ nanomicelles showed a high drug encapsulation efficiency (74.8%) and were allowed to achieve a sustained release pattern. Computational analyses were conducted to increase understanding of the nature and strength of mutual interactions between Pluronic F127 and CFZ. Simulation data indicated that the position of heteroatoms on CFZ influences the strength of attractive interactions in the Pluronic F127/CFZ nanomicelles. Cytotoxic activity of free and encapsulated CFZ was assayed in several cancerous cell lines, SHY-SY5Y human neuroblastoma, MCF7 breast, and HeLa cervical cancer cells employing the MTT colorimetric assay. We found that Pluronic F127/CFZ nanomicelles exhibited greater anti-proliferative activity than free CFZ (lower IC50s) and induced evident morphological alterations in cancer cells. Caspase-3 activity was assessed to determine the main mechanism of drug-induced cell death. Compared to free CFZ, our formulation only increased caspase-3 activity in HeLa cells. To examine the short-term toxicity of F127/CFZ nanomicelles, intravenous injections of free CFZ and F127/CFZ nanomicelles at three doses of 0.25 mg/kg, 0.5 mg/kg, and 1 mg/kg for five consecutive days were administered to an animal model. The potential anti-bactericidal activity of this new formulation was also assayed against four standard bacteria, including Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, and Enterococcus faecalis. Unfortunately, no significant bacteria-killing effects were detected despite other drugs of the same family showing promising results. Still, our new formulation showed desirable anti-cancer effects and might be a good therapeutic modality for cancer treatment.

Linear and Ring Polymer Brushes: A Density Functional Theory Study

AbstractMonomer resolved density functional theory is employed to study structural properties and interactions between polymer‐grafted flat walls. Both linear and ring polymer brushes are considered. The three major control parameters are the grafting density, the grafted chain length, and temperature. The effect of these parameters on the brush–brush overlap and attractive interaction strength is analyzed. It is found that ring brushes provide better steric stabilization compared to their linear counterparts, in agreement with available experimental and simulation data.

Interactions between Sterically Stabilized Nanoparticles: The Effects of Brush Bidispersity and Chain Stiffness.

Density Functional Theory is employed to study structural properties and interactions between solvent-free polymer-grafted nanoparticles. Both monodisperse and bidisperse polymer brushes with variable chain stiffness are considered. The three major control parameters are the grafting density, the grafted chain length, and its stiffness. The effect of these parameters on the brush-brush overlap and attractive interaction strength is analyzed. The Density Functional Theory results are compared with the available simulation data, and good quantitative agreement is found.

Realization of a Townes Soliton in a Two-Component Planar Bose Gas.

Most experimental observations of solitons are limited to one-dimensional (1D) situations, where they are naturally stable. For instance, in 1D cold Bose gases, they exist for any attractive interaction strength g and particle number N. By contrast, in two dimensions, solitons appear only for discrete values of gN, the so-called Townes soliton being the most celebrated example. Here, we use a two-component Bose gas to prepare deterministically such a soliton: Starting from a uniform bath of atoms in a given internal state, we imprint the soliton wave function using an optical transfer to another state. We explore various interaction strengths, atom numbers, and sizes and confirm the existence of a solitonic behavior for a specific value of gN and arbitrary sizes, a hallmark of scale invariance.

Pairing and Pair Superfluid Density in One-Dimensional Two-Species Fermionic and Bosonic Hubbard Models.

We use unbiased computational methods to elucidate the onset and properties of pair superfluidity in two-species fermionic and bosonic systems with onsite interspecies attraction loaded in a uniform, i.e., with no confining potential, one-dimensional optical lattice. We compare results from quantum MonteCarlo (QMC) and density matrix renormalization group (DMRG), emphasizing the one-to-one correspondence between the Drude weight tensor, calculated with DMRG, and the various winding numbers extracted from the QMC. Our results show that, for any nonvanishing attractive interaction, pairs form and are the sole contributors to superfluidity; there are no individual contributions due to the separate species. For weak attraction, the pair size diverges exponentially, i.e., Bardeen-Cooper-Schrieffer (BCS) pairing, requiring huge systems to bring out the pair-only nature of the superfluid. This crucial property is largely overlooked in many studies, thereby misinterpreting the origin and nature of the superfluid. We compare and contrast this with the repulsive case and show that the behavior is very different, contradicting previous claims about drag superfluidity and the symmetry of properties for attractive and repulsive interactions. Finally, our results show that the situation is similar for soft-core bosons: superfluidity is due only to pairs, even for the smallest attractive interaction strength compatible with the largest system sizes that we could attain.

Finite-size effects in a bosonic Josephson junction

We investigate finite-size quantum effects in the dynamics of $N$ bosonic particles which are tunneling between two sites adopting the two-site Bose-Hubbard model. By using time-dependent atomic coherent states (ACS) we extend the standard mean-field equations of this bosonic Josephson junction, which are based on time-dependent Glauber coherent states. In this way we find $1/N$ corrections to familiar mean-field (MF) results: the frequency of macroscopic oscillation between the two sites, the critical parameter for the dynamical macroscopic quantum self trapping (MQST), and the attractive critical interaction strength for the spontaneous symmetry breaking (SSB) of the ground state. To validate our analytical results we perform numerical simulations of the quantum dynamics. In the case of Josephson oscillations around a balanced configuration we find that also for a few atoms the numerical results are in good agreement with the predictions of time-dependent ACS variational approach, provided that the time evolution is not too long. Also the numerical results of SSB are better reproduced by the ACS approach with respect to the MF one. Instead the onset of MQST is correctly reproduced by ACS theory only in the large $N$ regime and, for this phenomenon, the $1/N$ correction to the MF formula is not reliable.

Mechanical disorder of sticky-sphere glasses. I. Effect of attractive interactions.

Recent literature indicates that attractive interactions between particles of a dense liquid play a secondary role in determining its bulk mechanical properties. Here we show that, in contrast with their apparent unimportance to the bulk mechanics of dense liquids, attractive interactions can have a major effect on macro- and microscopic elastic properties of glassy solids. We study several broadly applicable dimensionless measures of stability and mechanical disorder in simple computer glasses, in which the relative strength of attractive interactions-referred to as "glass stickiness"-can be readily tuned. We show that increasing glass stickiness can result in the decrease of various quantifiers of mechanical disorder, on both macro- and microscopic scales, with a pair of intriguing exceptions to this rule. Interestingly, in some cases strong attractions can lead to a reduction of the number density of soft, quasilocalized modes, by up to an order of magnitude, and to a substantial decrease in their core size, similar to the effects of thermal annealing on elasticity observed in recent works. Contrary to the behavior of canonical glass models, we provide compelling evidence indicating that the stabilization mechanism in our sticky-sphere glasses stems predominantly from the self-organized depletion of interactions featuring large, negative stiffnesses. Finally, we establish a fundamental link between macroscopic and microscopic quantifiers of mechanical disorder, which we motivate via scaling arguments. Future research directions are discussed.

Mechanical disorder of sticky-sphere glasses. II. Thermomechanical inannealability.

Many structural glasses feature static and dynamic mechanical properties that can depend strongly on glass formation history. The degree of universality of this history dependence and what it is possibly affected by are largely unexplored. Here we show that the variability of elastic properties of simple computer glasses under thermal annealing depends strongly on the strength of attractive interactions between the glasses' constituent particles-referred to here as glass "stickiness." We find that in stickier glasses the stiffening of the shear modulus with thermal annealing is strongly suppressed, while the thermal-annealing-induced softening of the bulk modulus is enhanced. Our key finding is that the characteristic frequency and density per frequency of soft quasilocalized modes becomes effectively invariant to annealing in very sticky glasses; the latter are therefore deemed "thermomechanically inannealable." The implications of our findings and future research directions are discussed.

Shear stress dependence of force networks in 3D dense suspensions.

The geometric organization and force networks of 3D dense suspensions that exhibit both shear thinning and thickening have been examined as a function of varying strength of interparticle attractive interactions using lubrication flow discrete element simulations. Significant rearrangement of the geometric topology does not occur at either the local or global scale as these systems transition across the shear thinning and shear thickening regimes. In contrast, massive rearrangements in the balance of attractive, lubrication, and contact forces are observed with interesting behavior of network growth and competition. In agreement with prior work, in shear thinning regions the attractive force is dominant, however as the shear thickening region is approached there is growth of lubrication forces. Lubrication forces oppose the attraction forces, but as viscosity continues to increase under increasing shear stress, the lubrication forces are dominated by contact forces that also resist attraction. Contact forces are the dominant interactions during shear thickening and are an order of magnitude higher than their values in the shear-thinning regime. At high attractive interaction strength, contact networks can form even under shear thinning conditions, however high shear stress is still required before contact networks become the driving mechanism of shear thickening. Analysis of the contact force network during shear thickening generally indicates a uniformly spreading network that rapidly forms across empty domains; however the growth patterns exhibit structure that is significantly dependent upon the strength of interparticle interactions, indicating subtle variations in the mechanism of shear thickening.

Simplified approach of investigation of binding energy for fermionic pairing in two dimensional Fermi liquid type superconducting materials at finite low temperature

Relation between the binding energy of pair of fermions and the magnitude of the attractive interaction between them is investigated theoretically with the help of mean field approximation, for a two-dimensional (2D) Fermi liquid type superconducting material. Here the fermion pair has finite center of mass momentum (CMM). The fermion pair is considered to be formed in the presence of an active Fermi sea having multiple pairs with inclusion of the effect of Pauli exclusion principle, at finite low temperature. Our calculations show that co-existence of true bound state (TB) and Cooper pair state (CP) with various CMMs can occur only beyond a critical attractive interaction strength which is similar to the results obtained at T=0 K[1]. We establish that Coopers pair state to true bound state crossover can be possible to achieve controlling the value of CMM of the fermion pairs. This could lead to the well-studied phenomena Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein Condensed (BEC) crossover and also the formation of incoherent pairs, under strong coupling regime. This throws a significant emphasis on the normal state anomalies seen in some of the exotic superconductors.

A Lamin-Associated Chromatin Model for Chromosome Organization

We propose a simple model for chromatin organization based on the interaction of the chromatin fibers with lamin proteins along the nuclear membrane. Lamin proteins are known to be a major factor that influences chromatin organization and hence gene expression in the cells. We provide a quantitative understanding of lamin-associated chromatin organization in a crowded macromolecular environment by systematically varying the heteropolymer segment distribution and the strength of the lamin-chromatin attractive interaction. Our minimal polymer model reproduces the formation of lamin-associated-domains and provides an in silico tool for quantifying domain length distributions for different distributions of heteropolymer segments. We show that a Gaussian distribution of heteropolymer segments, coupled with strong lamin-chromatin interactions, can qualitatively reproduce observed length distributions of lamin-associated-domains. Further, lamin-mediated interaction can enhance the formation of chromosome territories as well as the organization of chromatin into tightly packed heterochromatin and the loosely packed gene-rich euchromatin regions.

Blow-up profile of neutron stars in the Hartree–Fock–Bogoliubov theory

We consider the gravitational collapse for neutron stars in the Hartree-Fock-Bogoliubov theory. We prove that when the number particle becomes large and the gravitational constant is small such that the attractive interaction strength approaches the Chandrasekhar limit mass slowly, the minimizers develop a universal blow-up profile. It is given by the Lane-Emden solution.

Many-body blow-up profile of boson stars with external potentials

We consider a 3D quantum system of [Formula: see text] identical bosons in a trapping potential [Formula: see text], with [Formula: see text], interacting via a Newton potential with an attractive interaction strength [Formula: see text]. For a fixed large [Formula: see text] and the coupling constant [Formula: see text] smaller than a critical value [Formula: see text] (Chandrasekhar limit mass), in an appropriate sense, the many-body system admits a ground state. We investigate the blow-up behavior of the ground state energy as well as the ground states when [Formula: see text] approaches [Formula: see text] sufficiently slowly in the limit [Formula: see text]. The blow-up profile is given by the Gagliardo–Nirenberg solutions.

Formula omitted] normalized solutions for nonlinear Schrödinger systems in [formula omitted

In this paper we consider the existence and phase separation of L2 normalized solutions for the nonlinear Schrödinger systems −Δu1+V1(x)u1=μ1u1+a1|x|u13−β|x|u22u1inR3,−Δu2+V2(x)u2=μ2u2+a2|x|u23−β|x|u12u2inR3,where ai>0,μi∈R,i=1,2,β>0 and V1 and V2 are two nonnegative trapping potentials. We address the existence and nonexistence of L2 normalized solutions, which relate generally to the comparison between the strength (a1,a2) of attractive intraspecies interactions and (a∗,a∗), where a∗=‖Q‖22 and Q is the unique positive radial solution of −Δu+u−|x|u3=0 in R3. Specially, our analytic results show that the existence occurs at the case where a1+a2≤2a∗, and ai=a∗ for i=1 or 2, which depends heavily on the behaviors of V1(0) and V2(0). We also study the limit behavior of L2 normalized solutions in the repulsive case β→+∞, and phase separation is expected.

Blow-up profile of neutron stars in the Chandrasekhar theory

We study the Chandrasekhar variational model for neutron stars, with or without an external potential. We prove the existence of minimizers when the attractive interaction strength τ is strictly smaller than the Chandrasekhar limit τc and investigate the blow-up phenomenon in the limit τ ↑ τc. We show that the blow-up profile of the minimizer(s) is given by the Lane–Emden solution.

Local structure, thermodynamics, and phase behavior of asymmetric particle mixtures: Comparison between integral equation theories and simulation.

We study the structural pair correlations, thermodynamics, and fluid-fluid demixing phase behavior of dense binary sphere mixtures as predicted by integral equation theories with diverse closure approximations. The focus is on mixtures with a large size asymmetry over a wide range of compositions and strengths of interparticle attractive interactions with an emphasis on the nonperturbative strong bridging or network forming regime. Quantitative comparisons with simulations are carried out. At high volume fractions of the larger species, we find that all studied closures are reasonably good. However, large quantitative or even qualitative discrepancies compared with simulations emerge when the large species is the volumetrically minority component, under both entropic depletion and strong enthalpic bridging conditions. Overall, we find that using the modified-Verlet (MV) closure approximation for all three correlation functions leads to good predictions for structure, phase behavior, and the equation-of-state, along with assuring pair correlation functions which are rigorously positive. This symmetric or "triple MV" approximation has the advantage that the same closure can be used for any size ratio in all thermodynamic state regimes, in contrast to asymmetric closures. The good accuracy of the triple MV closure for particle mixtures provides as basis for developing improved theoretical descriptions of polymer nanocomposites and will serve as a crucial input to microscopic theories of slow dynamics in glass and gel forming systems.

Molecular dynamics simulation of thermo-mechanical behaviour of elastomer cross-linked via multifunctional zwitterions.

Coarse-grained (CG) molecular dynamics simulations have been employed to study the thermo-mechanical response of a physically cross-linked network composed of zwitterionic moieties and fully flexible elastomeric polymer chains. In this work, we used the effective Lennard-Jones interactions for our bead-spring model of zwitterionic cross-linkers (ZCLs). The effects of ZCL functionality, its chain length and the attractive interaction strength (ε) of end-groups on the thermo-mechanical properties are explored. We developed one particular system with versatile functionality of ZCLs at constant molecular weight with variable functional sites, observing that the stress-strain curve is increased with the functionality, evidenced by the bond orientation through the second-order Legendre polynomials. In the case of the length of the tri-functional ZCL, we found that a shorter length leads to a higher modulus and a relatively greater value of glass-transition temperature (Tg). In addition, we found that with the increase of the attractive interaction strength (ε) on the tri-functional ZCL, the stress-strain behaviour and the chain orientation are reinforced, accompanied by an enhancement of Tg. Lastly, we examined the effect of the cross-linker functionality on the tension-recovery process, as well as the fracture behaviour, by performing the typical tri-axial deformation. The results of tension-recovery and tri-axial deformation correspondingly proved the presence of physical linkages of end-groups, and strong attractive forces between end-linking groups were revealed through visual molecular dynamics (VMD) analysis. Generally, we anticipate that our work could provide some guidelines for the rational design and preparation of high performance zwitterionic cross-linked elastomeric materials.

Charge Oscillations Emerging after Application of an Intense Light Field to Superconductors on a Dimer Lattice

Motivated by recent experimental findings for an organic superconductor, charge oscillations that emerge after a strong pulse of an oscillating electric field is applied are studied in electron systems in a superconducting phase on a lattice with a dimerized structure. They are analyzed using Fourier spectra of charge densities whose time profiles are obtained by numerically solving the time-dependent Schr\"odinger equation within a mean-field approximation. Depending on the strengths of attractive interactions, different charge-oscillation modes appear. For weak attractions, the charge-oscillation mode is an electronic breathing mode, which was previously found for repulsive interactions. For strong attractions, it is a pair analog of the electronic breathing mode (a `pair' breathing mode). For intermediate attractions, it is another mode whose transient current distributions are considerably different from those of the breathing modes. We investigate how their frequencies and amplitudes depend on interactions and transfer integrals.