Strong Long-range Interactions Research Articles

Universal Defects Statistics with Strong Long-Range Interactions.

Quasi-static transformations, or slow quenches, of many-body quantum systems across quantum critical points generate topological defects. The Kibble-Zurek mechanism regulates the appearance of defects in a local quantum system through a classical combinatorial process. However, long-range interactions disrupt the conventional Kibble-Zurek scaling and lead to a density of defects that is independent of the rate of the transformation. In this Letter, we analytically determine the complete full counting statistics of defects generated by slow annealing a strong long-range system across its quantum critical point. We demonstrate that the mechanism of defect generation in long-range systems is a purely quantum process with no classical equivalent. Furthermore, universality is not only observed in the defect density but also in all the moments of the distribution. Our findings can be tested on various experimental platforms, including Rydberg gases and trapped ions.

Physics-based discrete models for magneto-mechanical metamaterials

Magneto-mechanical metamaterials are emerging smart materials whose mechanical responses can be tailored through structure architecture and magnetic interactions. The latter provides additional freedom in the material design space and leads to novel behaviors due to its nonlocal nature. The enriched functionalities open new possibilities in various applications, such as actuators, energy absorbers, and soft robots. However, the nonlinear and nonlocal coupling between elastic and magnetic forces poses a great challenge in the modeling and simulation of these systems, further hindering theory-based rational design strategies. Here, we focus on a class of magneto-mechanical metamaterials comprising elastic solids embedded with rigid permanent magnets. The clear separation between elastic and magnetic forces simplifies the design and fabrication process, yet their nonlocal interplay still allows for complex behaviors. We present a simulation framework for such magneto-mechanical metamaterials by combining a lattice spring model for the elastic solid with the dipole model for the magnetic interactions and implementing it in the LAMMPS molecular dynamics software. We demonstrate the capabilities of our framework by simulating a few representative structures, including shape-locking lattice metamaterials, a soft cellular solid with controllable buckling, and a metamaterial chain with phase-transforming behavior. For the shape-locking lattice metamaterials, we successfully capture the magnetic-actuation-driven reconfiguration and the nonlinear mechanical response of the curved lattices. For the soft cellular solid, we identify its buckling patterns under external non-uniform magnetic fields and simulate a buckling evolution process consistent with experiments. For the metamaterial chain, we include the strong long-range interactions among the embedded magnets and reproduce the controllable phase transitions in the experiments. Our work provides a simple yet versatile simulation methodology to investigate the nonlinear mechanical behaviors in the presence of strong external and internal magnetic forces, which will facilitate the design and analysis of magneto-mechanical materials. It can also be applied to other magnetically-driven smart structures, such as soft robots.

The Paradoxical Behavior of Rough Colloids at Fluid Interfaces.

Colloidal particles adsorb and remain trapped at immiscible fluid interfaces due to strong interfacial adsorption energy with a contact angle defined by the chemistry of the particle and fluid phases. An undulated contact line may appear due to either particle surface roughness or shape anisotropy, which results in a quadrupolar interfacial deformation and strong long-range capillary interaction between neighboring particles. While each effect has been observed separately, here we report the paradoxical impact of surface roughness on spherical and anisotropic ellipsoidal polymer colloids. Using a seeded emulsion polymerization technique, we synthesize spherical and ellipsoidal particles with controlled roughness magnitudes and topography (convex/concave). Via in situ measurement of the interfacial deformation around colloids at an air-water interface, we find that while surface roughness strengthens the quadrupolar deformation in spheres as expected by theory, in stark contrast, it weakens the same in ellipsoids. As roughness increases, particles of both shapes become more hydrophilic, and their apparent contact angle decreases. Using numerical predictions, we show that this partially explains the decreased interfacial deformation and capillary interactions between the ellipsoids. Therefore, particle surface engineering has the potential to decrease the capillary deformation by asymmetric particles via changing their capillary pinning, as well as wetting behavior at fluid interfaces.

Extensive long-range polycomb interactions and weak compartmentalization are hallmarks of human neuronal 3D genome.

Chromatin architecture regulates gene expression and shapes cellular identity, particularly in neuronal cells. Specifically, polycomb group (PcG) proteins enable establishment and maintenance of neuronal cell type by reorganizing chromatin into repressive domains that limit the expression of fate-determining genes and sustain distinct gene expression patterns in neurons. Here, we map the 3D genome architecture in neuronal and non-neuronal cells isolated from the Wernicke's area of four human brains and comprehensively analyze neuron-specific aspects of chromatin organization. We find that genome segregation into active and inactive compartments is greatly reduced in neurons compared to other brain cells. Furthermore, neuronal Hi-C maps reveal strong long-range interactions, forming a specific network of PcG-mediated contacts in neurons that is nearly absent in other brain cells. These interacting loci contain developmental transcription factors with repressed expression in neurons and other mature brain cells. But only in neurons, they are rich in bivalent promoters occupied by H3K4me3 histone modification together with H3K27me3, which points to a possible functional role of PcG contacts in neurons. Importantly, other layers of chromatin organization also exhibit a distinct structure in neurons, characterized by an increase in short-range interactions and a decrease in long-range ones.

SCA-Former: transformer-like network based on stream-cross attention for medical image segmentation

Objective. Deep convolutional neural networks (CNNs) have been widely applied in medical image analysis and achieved satisfactory performances. While most CNN-based methods exhibit strong feature representation capabilities, they face challenges in encoding long-range interaction information due to the limited receptive fields. Recently, the Transformer has been proposed to alleviate this issue, but its cost is greatly enlarging the model size, which may inhibit its promotion. Approach. To take strong long-range interaction modeling ability and small model size into account simultaneously, we propose a Transformer-like block-based U-shaped network for medical image segmentation, dubbed as SCA-Former. Furthermore, we propose a novel stream-cross attention (SCA) module to enforce the network to focus on finding a balance between local and global representations by extracting multi-scale and interactive features along spatial and channel dimensions. And SCA can effectively extract channel, multi-scale spatial, and long-range information for a more comprehensive feature representation. Main results. Experimental results demonstrate that SCA-Former outperforms the current state-of-the-art (SOTA) methods on three public datasets, including GLAS, ISIC 2017 and LUNG. Significance. This work exhibits a promising method to enhance the feature representation of convolutional neural networks and improve segmentation performance.

Highly-excited Rydberg excitons in synthetic thin-film cuprous oxide

Cuprous oxide (hbox {Cu}{}_2hbox {O}) has recently emerged as a promising material in solid-state quantum technology, specifically for its excitonic Rydberg states characterized by large principal quantum numbers (n). The significant wavefunction size of these highly-excited states (proportional to n^2) enables strong long-range dipole-dipole (proportional to n^4) and van der Waals interactions (proportional to n^{11}). Currently, the highest-lying Rydberg states are found in naturally occurring hbox {Cu}_2hbox {O}. However, for technological applications, the ability to grow high-quality synthetic samples is essential. The fabrication of thin-film hbox {Cu}{}_2hbox {O} samples is of particular interest as they hold potential for observing extreme single-photon nonlinearities through the Rydberg blockade. Nevertheless, due to the susceptibility of high-lying states to charged impurities, growing synthetic samples of sufficient quality poses a substantial challenge. This study successfully demonstrates the CMOS-compatible synthesis of a hbox {Cu}{}_2hbox {O} thin film on a transparent substrate that showcases Rydberg excitons up to n = 8 which is readily suitable for photonic device fabrications. These findings mark a significant advancement towards the realization of scalable and on-chip integrable Rydberg quantum technologies.

Crystal dipolar bosons in optical lattice: A review

Crystals are ubiquitous, occurring in diverse materials. Herein, we review the formation and detection of quantum crystals that are produced via strong long-range dipolar interaction. We explore the rich physics of the emergent phases that form due to the long-range interactions. We describe the characteristic density signature of these phases. We discuss how we can characterize these crystal states through an order parameter and describe an experimental protocol to detect them. We finally discuss the coherence properties of these emergent phases.

Rigidity of dipolar coupled H2O molecular network in external electric field

We have performed the first study of the effect of an external electric field on the quantum paraelectric state of the electric dipolar lattice of polar water molecules confined within nano-sized cages of beryl crystal lattice. The complex dielectric permittivity ε* = ε'+iε" of a water subsystem in hydrous beryl is measured at frequencies 1 Hz-1 MHz in the temperature interval 10–300 K both in zero and 7 kV/cm external field. For comparison, we measure dielectric response of conventional quantum paraelectric KTaO3. In KTaO3, the application of electric field of several kV/cm suppresses quantum fluctuations and leads to a shallow maximum of ε′(T) around 15 K that could indicate a diffuse phase transition. In hydrous beryl, however, a bias electric field of up to 7 kV/cm has no effect on the dielectric response of the water molecules network. This result is confirmed by Monte Carlo simulations. We attribute the enhanced rigidity of the water dipolar subsystem to the strong long-range dipole-dipole interaction between separate H2O molecules. The field that could affect the polarization state of the dipoles is estimated to be of the order of 100 kV/cm.

Domain statistics in the relaxation of the one-dimensional Ising model with strong long-range interactions

After a zero temperature quench, we study the kinetics of the one-dimensional Ising model with long-range interactions between spins at distance r decaying as r−α, with α≤1. As shown in our recent study (Corberi et al., 2021) that only a fraction of the non-equilibrium trajectories is characterised by the presence of coarsening domains while in the remaining ones the system is quickly driven towards a magnetised state. Restricting to realisations displaying coarsening we compute numerically the probability distribution of the size of the domains and find that it exhibits a scaling behaviour with an unusual α-dependent power-law decay. This peculiar behaviour is also related to the divergence of the average size of domains with system size at finite times. Such a scenario differs from the one observed when α>1, where the distribution decays exponentially. Finally, based on numerical results and on analytical calculations we argue that the average domain size grows asymptotically linearly in time.

On Pseudoconformal Blow-Up Solutions to the Self-Dual Chern-Simons-Schrödinger Equation: Existence, Uniqueness, and Instability

We consider the self-dual Chern-Simons-Schrödinger equation (CSS), also known as a gauged nonlinear Schrödinger equation (NLS). CSS is L 2 L^{2} -critical, admits solitons, and has the pseudoconformal symmetry. These features are similar to the L 2 L^{2} -critical NLS. In this work, we consider pseudoconformal blow-up solutions under m m -equivariance, m ≥ 1 m\geq 1 . Our result is threefold. Firstly, we construct a pseudoconformal blow-up solution u u with given asymptotic profile z ∗ z^{\ast } : \[ [ u ( t , r ) − 1 | t | Q ( r | t | ) e − i r 2 4 | t | ] e i m θ → z ∗ in H 1 \Big [u(t,r)-\frac {1}{|t|}Q\Big (\frac {r}{|t|}\Big )e^{-i\frac {r^{2}}{4|t|}}\Big ]e^{im\theta }\to z^{\ast }\qquad \text {in }H^{1} \] as t → 0 − t\to 0^{-} , where Q ( r ) e i m θ Q(r)e^{im\theta } is a static solution. Secondly, we show that such blow-up solutions are unique in a suitable class. Lastly, yet most importantly, we exhibit an instability mechanism of u u . We construct a continuous family of solutions u ( η ) u^{(\eta )} , 0 ≤ η ≪ 1 0\leq \eta \ll 1 , such that u ( 0 ) = u u^{(0)}=u and for η > 0 \eta >0 , u ( η ) u^{(\eta )} is a global scattering solution. Moreover, we exhibit a rotational instability as η → 0 + \eta \to 0^{+} : u ( η ) u^{(\eta )} takes an abrupt spatial rotation by the angle \[ ( m + 1 m ) π \Big (\frac {m+1}{m}\Big )\pi \] on the time interval | t | ≲ η |t|\lesssim \eta . We are inspired by works in the L 2 L^{2} -critical NLS. In the seminal work of Bourgain and Wang (1997), they constructed such pseudoconformal blow-up solutions. Merle, Raphaël, and Szeftel (2013) showed an instability of Bourgain-Wang solutions. Although CSS shares many features with NLS, there are essential differences and obstacles over NLS. Firstly, the soliton profile to CSS shows a slow polynomial decay r − ( m + 2 ) r^{-(m+2)} . This causes many technical issues for small m m . Secondly, due to the nonlocal nonlinearities, there are strong long-range interactions even between functions in far different scales. This leads to a nontrivial correction of our blow-up ansatz. Lastly, the instability mechanism of CSS is completely different from that of NLS. Here, the phase rotation is the main source of the instability. On the other hand, the self-dual structure of CSS is our sponsor to overcome these obstacles. We exploited the self-duality in many places such as the linearization, spectral properties, and construction of modified profiles.

Perfect optomechanically induced transparency and slow light in an Rydberg atom-assisted optomechanical system

Rydberg atoms have attracted considerable attention due to their several singular properties, such as strong long-range interactions, extremely long lifetimes, and very large polarizability. These characteristics make Rydberg atoms a good candidates for cavity quantum electrodynamics, quantum information, and many-body physics. Recently, the study of optomechanics has become a rapidly developing field due to its important applications in cooling of mechanical resonators, implementing precision measurements, slowing light, and preparing quantum entanglement. Obviously, optomechanical systems pave the way for quantum information processing and quantum communication. Specially, there is significant interest in quantum optomechanics due to its high compatibility that can be combined, to build hybrid systems for certain purposes, with the ultracold atoms, a superconducting single electron transistor, a magnetostrictive actuation, a charged oscillator resonator, etc. In this work, we investigate the optomechanically induced transparency (OMIT) and the resulting effect of slow light in a hybrid system composed of a Rydberg atomic ensemble embedded inside a simple optomechanical cavity. As a typical effect of destructive quantum interference, OMIT is widely used in quantum optics and quantum information processing. Based on the Rydberg blockade effect, a Rydberg atomic ensemble in the same blockade region embedded inside an optomechanical cavity can be regarded as a superatom that contains only a single Rydberg excitation. Therefore, the problem of exponentially increasing system size with the number of atoms increasing can be circumvented easily. The hybrid system becomes a coupling between a Rydberg superatom and an optomechanical cavity and the coupling strength is enhanced by a factor of square root of the number of atoms in the ensemble. In this system, the perfect OMIT, namely, an ideal OMIT dip with a very narrow window, can be attained when an effect of non-rotating wave approximation (NRWA) is considered. Further, we demonstrate that the term of NRWA plays a key important role in achieving perfect OMIT by comparing the optomechanical spectra obtained with and without NRWA effects. Our results show that in the resolved sideband regime the higher the quality factor of cavity is, the stronger the slow light effect becomes in the window of the perfect OMIT. Particularly, in achieving the ultraslow light, the long lifetime of the Rydberg atom shows its superiority.

Effects of long-range inter-particle interactions and isolated defect on quantum walks of two hard-core bosons in one-dimensional lattices

The quantum walk of two hard-core bosons in one-dimensional lattice under the effect of long-range inter-particle interaction is studied in detail. We also simulate the influence of an isolated defect that may exist in the lattice on the quantum walk of two particles by adding an additional potential energy to a certain lattice site. Using exact diagonalization method, the continuous-time quantum walk is directly simulated. The numerical simulations show that the range of interaction (long-range or short-range), the strength of the inter-particle interaction, the initial state of the two particles and the presence of the isolated defect have great influences on the quantum walk. Under the effect of strong long-range interaction, the particles initially located on the non-adjacent lattice sites have a co-walking behavior, while under the short-range interactions (nearest-neighbor interactions) only two particles initially located on the neighboring lattice sites can exhibit co-walking. After introducing the isolated defect into the system with strong interaction, two particles residing on the same side of the isolated defect keep co-walking, while two particles located on either sides of the isolated defect or one particle located on the isolated defect and the other particle staying on the side of the isolated defect, the two particles keep stationary or co-walking near the defect, displaying the characteristics of localization. By using the second-order perturbation theory of degenerate quantum system, a comprehensive theoretical analysis of the above numerical results is given. The theoretical analysis reveals the underlying physical law of quantum walks of two particles in one-dimensional lattice under the effects of strong long-range interaction and isolated defect in the lattice.

Demonstration of a Quantum Gate Using Electromagnetically Induced Transparency.

We demonstrate a native CNOT gate between two individually addressed neutral atoms based on electromagnetically induced transparency. This protocol utilizes the strong long-range interactions of Rydberg states to enable conditional state transfer on the target qubit when operated in the blockade regime. An advantage of this scheme is it enables implementation of multiqubit CNOT^{k} gates using a pulse sequence independent of qubit number, providing a simple gate for efficient implementation of digital quantum algorithms and stabilizer measurements for quantum error correction. We achieve a loss corrected gate fidelity of F_{CNOT}^{cor}=0.82(6), and prepare an entangled Bell state with F_{Bell}^{cor}=0.66(5), limited at present by laser power. We present a number of technical improvements to advance this to a level required for fault-tolerant scaling.

Signatures of the long-range phase transition in topological Josephson junctions

The extended Kitaev models spark a recent surge of interest due to its unprecedented topological phase with fractional invariants. In this extended model of topological superconductors, long-range pairing interactions can induce a pair of subgap massive edge modes (MEMs), posing novel challenges to the unambiguous detection of Majorana bound states (MBSs) sustained by the same model in the short-range limit. Here we investigate the effect of a power-law decayed long-range pairing on the dc and ac Josephson currents between two Majorana nanowires. By varying the magnetic field and long-range pairing, the nanowires can be driven into different phases hosting MEMs, MBSs, or trivial Andreev bound states (ABSs), which considerably modulate the Josephson current. For weakly linked Josephson junctions, we show that the MEMs emerging in the long-range phases can induce a zigzag profile in the dc current-phase relation featured by two sign reversals deviating from the point where the superconducting phase difference $\ensuremath{\phi}=\ensuremath{\pi}$. In contrast, the Josephson current indicates a sharp sign reversal at $\ensuremath{\phi}=\ensuremath{\pi}$ in the short-range phase that hosts MBSs, while a smooth sinelike dc Josephson current appears in the presence of ABSs. In the nonequilibrium junction biased by a voltage, we identify a $4\ensuremath{\pi}$ ac Josephson current in the short-range phases, indicating a MBSs-mediated tunneling process dominating the supercurrents. Differently, when the system enters MEMs-hosted long-range phases, the ordinary ac Josephson current with $2\ensuremath{\pi}$ periodicity can be restored. In addition, we find the ac Josephson current induced by MEMs is significantly suppressed under the strong long-range pairing interactions. These signatures can serve as probes to discriminate MBSs from MEMs and ABSs.

Long-range order and quantum criticality in antiferromagnetic chains with long-range staggered interactions.

We study quantum phase transitions in Heisenberg antiferromagnetic chains with a staggered power-law decaying long-range interactions. Employing the density-matrix renormalization group (DMRG) algorithm and the fidelity susceptibility as the criticality measure, we establish more accurate values of quantum critical points than the results obtained from the spin-wave approximation, quantum Monte Carlo, and DMRG in literatures. The deviation is especially evident for strong long-range interactions. We extend isotropic long-range interactions to the anisotropic cases and find that kaleidoscope of quantum phases emerge from the interplay of anisotropy of the long-range exchange interaction and symmetry breaking. We demonstrate nonfrustrating long-range interactions induce the true long-range order in Heisenberg antiferromagnetic chains with a continuous symmetry breaking, lifting the restrictions imposed by the Mermin-Wagner theorem.

Numerical optimization of dc wire parameters for mitigation of the long range beam-beam interactions in High Luminosity Large Hadron Collider

Several configurations of the High Luminosity Large Hadron Collider, whose performance at collision is mainly limited due to the strong beam-beam long-range interactions, are studied in the presence of dc wire compensators. This analysis is based on analytical and numerical calculations where the main observables are the dynamic aperture (correlated to the beam lifetime) and the frequency map analysis. It is demonstrated that, with a proper optimization of the wire compensator parameters (distance from the beam and wire current) and without violating the machine protection restrictions, these long range beam-beam interactions can be very well mitigated, making these scenarios viable and complementary with respect to the present HL-LHC baseline. The impact in the integrated luminosity and the operational flexibility gained are also presented.

Characterization of a HBB -Locus Fetal Chromatin Domain Region during Adult Erythropoiesis

The hemoglobinopathies including sickle cell disease (SCD) and β-thalassemia are the most common genetic disorders in the world producing significant morbidity and mortality. Drug-mediated fetal hemoglobin (HbF) induction ameliorates the clinical severity of SCD and improves long-term survival. To define mechanisms of γ-globin regulation, previously we demonstrated the role of the Gγ-globin cAMP response element, in drug-mediated HbF induction (Sangerman et al., Blood 2006). Subsequently, data generated by the ENCODE project led us to investigate a region 4 kb upstream of Gγ-globin, which harbors a DNase hypersensitive site and enrichment of the histone 3 lysine 4, mono-methylated (H3K4Me1) enhancer mark, that we named the Fetal Chromatin Domain (FCD). Recently, a synthetic zinc finger DNA-binding domain targeting this region was shown to reduce γ-globin gene expression in K562 cells (Shen et al., Blood 128:320, 2016). Initially, we performed multispecies sequence alignments which revealed the FCD is located in a genomic region shared by Old World monkeys (humans and Baboons) with a delayed fetal to adult globin switch that occurs after birth. By contrast, the FCD region is absent in New World monkeys where the switch occurs during the fetal developmental stage. These findings support involvement of the FCD region in γ-globin regulation during hemoglobin switching.Subsequent studies were performed to define the functional role of the FCD during erythropoiesis. ENCODE long RNA-sequencing assay detected PolyA RNA species throughout the FCD region in K562 cells. Based on these findings, we designed two small-interference RNA molecules targeting the core FCD (siFCD). Both siFCD molecules were transfected into KU812 cells and individual γ-globin gene expression measured using RT-qPCR with gene-specific primers. The level of Gγ-globin mRNA increased by 64%, while Aγ-globin transcription was reduced 38%. These results suggest the FCD facilitates differential regulation of the γ-globin genes. To further characterize FCD function, a series of γ-globin promoter luciferase reporters were constructed with the sense or antisense 500-bp core FCD region, cloned downstream of the luciferase gene. In KU812 stable cell lines, the sense FCD construct enhanced Aγ-globin promoter activity 10-fold, whereas the antisense construct repressed promoter activity. By contrast, the FCD in both orientations silenced Gγ-globin promoter activity. These results support unidirectional gene-specific enhancer properties of the FCD. Subsequent pulldown assay with a 34-bp biotinylated FCD probe confirmed NFE2, BHLHE40 and cMyc binding, which was abolished by mutation of the E-box sequence (CACGTG) in the FCD core.To build on the KU812 cell data, we performed μChIP assay using primary erythroid progenitors generated from adult CD34+ stem cells (Zhu et al., Haematologica 2017). In our system, the γ-globin to β-globin gene switch occurred on day 4 in culture. Initially, we measured levels of acetylated histone H3 (AcH3), H3K4Me1, and TFIID binding in the β-globin locus control region hypersensitivity site 2 (HS2) and FCD. As expected, high AcH3 and H3K4Me1 marks occurred in HS2 consistent with its enhancer function. Similar patterns of histone marks and binding of TFIID, NFE2 and BHLHE40 occurred in HS2 and FCD region. It is known that HS2 participates in DNA looping to accomplish developmentally regulated globin gene expression during hemoglobin switching therefore chromosome conformation capture (3C) assay was performed in primary erythroid progenitors to determine if the FCD facilitates changes in chromatin structure. We observed strong long-range interactions between the FCD and HS2 with 4.4-fold maximal chromatin enrichment on day 5; likewise the FCD showed interactions with Aγ-globin (4.7-fold) and Gγ-globin (3.5-fold) by day 3 before switching occurred. Of note, low level interactions occurred between the FCD and β-globin gene at all time points tested.Collectively, these data support the FCD as a unidirectional enhancer element involved in γ-globin regulation during erythropoiesis. To further define mechanisms of FCD function, the effects of CrisprCas9-mediated deletions in the FCD on globin gene expression will be explored. DisclosuresNo relevant conflicts of interest to declare.

Asymmetric Rydberg blockade of giant excitons in Cuprous Oxide

The ability to generate and control strong long-range interactions via highly excited electronic states has been the foundation for recent breakthroughs in a host of areas, from atomic and molecular physics to quantum optics and technology. Rydberg excitons provide a promising solid-state realization of such highly excited states, for which record-breaking orbital sizes of up to a micrometer have indeed been observed in cuprous oxide semiconductors. Here, we demonstrate the generation and control of strong exciton interactions in this material by optically producing two distinct quantum states of Rydberg excitons. This is made possible by two-color pump-probe experiments that allow for a detailed probing of the interactions. Our experiments reveal the emergence of strong spatial correlations and an inter-state Rydberg blockade that extends over remarkably large distances of several micrometers. The generated many-body states of semiconductor excitons exhibit universal properties that only depend on the shape of the interaction potential and yield clear evidence for its vastly extended-range and power-law character.

Excitons dynamic in a three-stranded $$\alpha $$-helix protein chains with diagonal and off-diagonal couplings: effects of strong long-range interactions

Exciton dynamics through a three-stranded -helix protein chain in the presence of inter-spines and diagonal and off-diagonal couplings as well as long-range interactions are investigated. Its is shown that the behavior of the system is governed by three-coupled modified continuous nonlinear Schrodinger equations. Performing a modulational instability analysis, it appears that both the off-diagonal coupling and the long-range interaction reduce the instability regions and the amplitude of the growth rate. More analytical insights of the system dynamics are obtained by constructing its solutions with the F-expansion method. Many families of solutions are unveiled among them are bright and dark solitary waves, Jacobian elliptic function solutions and hyperbolic function solutions to name just a few. Intensive numerical simulations carried corroborate the analytical solutions found with a good accuracy. In addition, our numerical findings prove that the long-range interactions increase the energy of the waves propagating through the protein chain. From a biological point of view, the model used in the current work better describes the energy transport in protein chains.

Gold nanoparticles obtained by ns-pulsed laser ablation in liquids (ns-PLAL) are arranged in the form of fractal clusters

Gold nanoparticles (AuNPs), synthesized by ns-pulsed laser ablation in liquid (ns-PLAL) in the absence of any capping agents, are potential model systems to study the interactions with biological structures unencumbered by interference from the presence of stabilizers and capping agents. However, several aspects of the physics behind these AuNPs solutions deserve a detailed investigation. The structure in solution of ns-PLAL-synthesized AuNPs was investigated in solution by means of small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Furthermore, the (dried) NPs have been examined using TEM. The analysis of the SAXS curve shows the presence of a large number of small aggregates with a fractal structure stabilized by strong long-range repulsive interactions. Fitting of the SAXS curve to a suitable “fractal model” allows the estimation of the features of the fractal including the fractal dimension d = 1.9. The latter allows to estimate the fraction of light scattered by fractals of different sizes and thus permits a fair comparison between the DLS and TEM data. Here, a stable abundant population of fractal clusters is reported reflecting a mechanism where primary AuNPs (size 7.6 nm) are forced to aggregate forming clusters during the collapse of the cavitation bubble. When these clusters are released in the aqueous phase, their large negative charge builds up repulsive interactions that prevent cluster-cluster aggregation imparting colloidal stability.