The European Physical Journal E最新文献

{"title":"Reinforcement learning of a biflagellate model microswimmer","authors":"Sridhar Bulusu,&nbsp;Andreas Zöttl","doi":"10.1140/epje/s10189-025-00513-3","DOIUrl":"10.1140/epje/s10189-025-00513-3","url":null,"abstract":"<p>Many microswimmers are able to swim through viscous fluids by employing periodic non-reciprocal deformations of their appendages. Here we use a simple microswimmer model inspired by swimming biflagellates which consists of a spherical cell body and two small spherical beads representing the motion of the two flagella. Using reinforcement learning, we identify for different microswimmer morphologies quasi-optimized swimming strokes. For all studied cases, the identified strokes result in symmetric and quasi-synchronized beating of the two flagella beads. Interestingly, the stroke-averaged flow fields are of pusher type, and the observed swimming gaits outperform previously used biflagellate microswimmer models relying on predefined circular flagella-bead motion.</p>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 8-9","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1140/epje/s10189-025-00513-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144832332","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimizing metachronal paddling with reinforcement learning at low Reynolds number","authors":"Alana A. Bailey,&nbsp;Robert D. Guy","doi":"10.1140/epje/s10189-025-00511-5","DOIUrl":"10.1140/epje/s10189-025-00511-5","url":null,"abstract":"<p>Metachronal paddling is a swimming strategy in which an organism oscillates sets of adjacent limbs with a constant phase lag, propagating a metachronal wave through its limbs and propelling it forward. This limb coordination strategy is utilized by swimmers across a wide range of Reynolds numbers, which suggests that this metachronal rhythm was selected for its optimality of swimming performance. In this study, we apply reinforcement learning to a swimmer at zero Reynolds number and investigate whether the learning algorithm selects this metachronal rhythm, or if other coordination patterns emerge. We design the swimmer agent with an elongated body and pairs of straight, inflexible paddles placed along the body for various fixed paddle spacings. Based on paddle spacing, the swimmer agent learns qualitatively different coordination patterns. At tight spacings, a back-to-front metachronal wave-like stroke emerges which resembles the commonly observed biological rhythm, but at wide spacings, different limb coordinations are selected. Across all resulting strokes, the fastest stroke is dependent on the number of paddles; however, the most efficient stroke is a back-to-front wave-like stroke regardless of the number of paddles.</p>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 8-9","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12334496/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144797916","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Linear dielectric spectroscopy of a polymer network stabilizing a ferroelectric liquid crystal","authors":"Mohammed Hanine,&nbsp;Abdelylah Daoudi,&nbsp;Jamal Hemine","doi":"10.1140/epje/s10189-025-00504-4","DOIUrl":"10.1140/epje/s10189-025-00504-4","url":null,"abstract":"<div><p>In this study, the linear dielectric characterization of a ferroelectric liquid crystal (FLC) stabilized by an anisotropic polymer network (PSFLC) was investigated. The liquid crystal employed in the PSFLC composites exhibited the chiral smectic C phase (SmC*), with a short helical pitch, a high tilt angle, and a high degree of spontaneous polarization. Dielectric spectroscopy was preceded by polarizing optical microscopy, as well as structural and electro-optical studies on pure FLC and PSFLC composites at different polymer concentrations. These studies enabled the determination of the pitch of the helix, the tilt angle, and the spontaneous polarization as a function of temperature and electric field. In the absence of a DC voltage, the dielectric response indicated the relaxation of the Goldstone mode as well as a reduction in tilt angle, spontaneous polarization and relaxation amplitude as the polymer density increased. By integrating the experimental data with the Landau model, the physical parameters, including the torsional elastic constant and rotational viscosity, were identified for pure FLC and PSFLC films. In addition, the impact of polymer density on these physical parameters was explored.</p><h3>Graphic Abstract</h3>\u0000<div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 8-9","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144793121","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Simulated interference colors chart from birefringence measurements in lyotropic calamitic nematic–biaxial nematic—discotic nematic phases","authors":"D. D. Lüders,&nbsp;E. Akpinar","doi":"10.1140/epje/s10189-025-00510-6","DOIUrl":"10.1140/epje/s10189-025-00510-6","url":null,"abstract":"<div><p>In this study, Nematic Discotic (N_D)—Nematic Biaxial (N_B)—Nematic Calamitic (N_C) phase sequences are investigated for some surfactant-based lyotropic mixtures. From the microscopic analysis point of view, the nematic phases, especially N_B one, are characterized by a methodology we developed to create a resultant image via composition of many microscopic textures (images). The resultant image permits recognizing the N_B phase bordered by two verticals imaginary lines contrasting two distinct colors. To consolidate our methodology, we simulated the interference colors chart of the samples for the first time via birefringence measurements performed by laser conoscopy technique. The simulated and experimental results are in good accordance.</p><h3>Graphical abstract</h3><div><figure><div><div><picture><source><img></source></picture></div><div><p>Interference color chart for Calamitic Nematic - Biaxial Nematic - Discotic Nematic phases obtained via birefringence measurements</p></div></div></figure></div></div>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 8-9","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144787963","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mixed convection in thermo-gravitational column: a continuous species separation","authors":"Khairi Sioud,&nbsp;Abdelkader Mojtabi,&nbsp;Marie-Catherine Charrier-Mojtabi,&nbsp;Ali Abdennadher,&nbsp;Alain Bergeon","doi":"10.1140/epje/s10189-025-00512-4","DOIUrl":"10.1140/epje/s10189-025-00512-4","url":null,"abstract":"<div><p>So far, species separation has been achieved in closed vertical thermogravitational columns (TGC). To obtain continuous separation, the initially homogeneous binary solution with a positive thermodiffusion coefficient was introduced at a constant volumetric flow rate through one of the two vertical slots of the TGC and retrieved through the opposite slot. This process required the horizontal dimension separating the two slots to be sufficiently large for the mass regime at the exit slot to reach the steady state associated with a vertical stratification of the mass fraction. Analytical resolution and numerical simulations were developed and showed good agreement between theoretical and numerical results.</p></div>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 8-9","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12325451/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144783181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Local stress-geometry equation of 2D frictionless granular systems","authors":"Xinggang Zhang,&nbsp;Dan Dai,&nbsp;Yan Tang","doi":"10.1140/epje/s10189-025-00506-2","DOIUrl":"10.1140/epje/s10189-025-00506-2","url":null,"abstract":"<p>For a static granular system, the constitutive equation of its stress tensor is of great significance for understanding its mechanical behaviors. Under isostatic state, it can have the form of stress-geometry equation. To investigate the force moment tensor and the stress-geometry equation of a two-dimensional (2D) granular system in theory, we propose some algebraic theories such as the decomposition formula of a second-order tensor and the cross-product of two symmetric tensors for the dyadic space <span>(mathbb {T}^{2}(mathbb {R}^{2}))</span>. For a 2D frictionless disk packing, the local stress-geometry equation for a disk with three or four contacts is derived based on the definition of force moments tensor and the equilibrium equation of contact forces. The definition of the geometry tensor in the stress-geometry equation shows complex associations between the contact branch vectors of a disk with three or four contacts. For a disk with four contacts, its local Janssen coefficient can be given from the eigenvalues of its geometry tensor. Discrete element method (DEM) simulations for random frictionless disk packings are performed to verify two local stress-geometry equations in this paper, and the numerical results are in good agreement with the theoretical predictions. The local stress-geometry equations are convenient for obtaining some information about the stress tensors according to the contact structures without knowing the details of the deformations and the intergranular interactions.</p>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 8-9","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144758872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The effect of self-induced Marangoni flow on polar-nematic waves in active-matter systems","authors":"Andrey Pototsky,&nbsp;Uwe Thiele","doi":"10.1140/epje/s10189-025-00508-0","DOIUrl":"10.1140/epje/s10189-025-00508-0","url":null,"abstract":"<p> We study the formation of propagating large-scale density waves of mixed polar-nematic symmetry in a colony of self-propelled agents that are bound to move along the planar surface of a thin viscous film. The agents act as an insoluble surfactant, i.e. the surface tension of the liquid depends on their density. Therefore, density gradients generate a Marangoni flow. We demonstrate that for active matter in the form of self-propelled surfactants with local (nematic) aligning interactions such a Marangoni flow nontrivially influences the propagation of the density waves. Upon gradually increasing the Marangoni parameter, which characterises the relative strength of the Marangoni flow as compared to the self-propulsion speed, the density waves broaden while their speed may either increase or decrease depending on wavelength and overall mean density. A further increase in the Marangoni parameter eventually results in the disappearance of the density waves. This may occur either discontinuously at finite wave amplitude via a saddle-node bifurcation or continuously with vanishing wave amplitude at a wave bifurcation, i.e. a finite-wavelength Hopf bifurcation.</p>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 8-9","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12310849/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144740805","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Conformational properties of strictly two-dimensional equilibrium polymers","authors":"J. P. Wittmer,&nbsp;A. Cavallo,&nbsp;A. Johner","doi":"10.1140/epje/s10189-025-00505-3","DOIUrl":"10.1140/epje/s10189-025-00505-3","url":null,"abstract":"<p>Two-dimensional monodisperse linear polymer chains are known to adopt for sufficiently large chain lengths <i>N</i> and surface fractions <span>(phi )</span> compact configurations with fractal perimeters. We show here by means of Monte Carlo simulations of reversibly connected hard disks (without branching, ring formation and chain intersection) that polydisperse self-assembled equilibrium polymers with a finite scission energy <i>E</i> are characterized by the same universal exponents as their monodisperse peers. Consistently with a Flory-Huggins mean-field approximation, the polydispersity is characterized by a Schulz–Zimm distribution with a susceptibility exponent <span>(gamma =19/16)</span> for all not dilute systems and the average chain length <span>(left&lt;N right&gt;propto exp (delta E) phi ^{alpha })</span> thus increases with an exponent <span>(delta = 16/35)</span>. Moreover, it is shown that <span>(alpha =3/5)</span> for semidilute solutions and <span>(alpha approx 1)</span> for larger densities. The intermolecular form factor <i>F</i>(<i>q</i>) reveals for sufficiently large <span>(left&lt;N right&gt;)</span> a generalized Porod scattering with <span>(F(q) propto 1/q^{11/4})</span> for intermediate wavenumbers <i>q</i> consistently with a fractal perimeter dimension <span>(d_s=5/4)</span>.\u0000</p><p>Snapshot of a subvolume of a much larger configuration of strictly two-dimensional equilibrium polymers as considered in this study for a broad range of surface fractions and scission energies. Despite the low dimensionality and the strong polydispersity of the annealed chain systems, the same univeral scaling relations and asymptotic exponents as for their monodisperse quenched peers are found as suggested by a simple Flory-Huggins type mean-field approximation. This holds especially for semidilute solutions and dense melts where the chains are demonstrated to adopt compact configurations of a fractal perimeter dimension 5/4. The intermolecular form factor <i>F</i>(<i>q</i>) thus reveals a generalized Porod scattering with <span>(F(q) propto 1/q^{11/4})</span> for intermediate wavenumbers <i>q</i> Snapshot of a subvolume of a much larger configuration of strictly two-dimensional equilibrium polymers as considered in this study for a broad range of surface fractions and scission energies. Despite the low dimensionality and the strong polydispersity of the annealed chain systems, the same univeral scaling relations and asymptotic exponents as for their monodisperse quenched peers are found as suggested by a simple Flory-Huggins type mean-field approximation. This holds especially for semidilute solutions and dense melts where the chains are demonstrated to adopt compact configurations of a fractal perimeter dimension 5/4. The intermolecular form factor <i>F</i>(<i>q</i>) thus reveals a generalized Porod scattering with <span>(F(q) propto 1/q^{11/4})</span> for intermediate wavenumbers <i>q</i></p>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 6-7","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144688561","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of photothermal therapy using PANI-Fe₂O₃-Cys nanocomposites on breast cancer cells with antibacterial activity and cytotoxicity study","authors":"Huda Abdul Redha Abdullah,&nbsp;Mohanad Q. Fahem,&nbsp;Zahraa T. Turki,&nbsp;Mohammed H. Jawad","doi":"10.1140/epje/s10189-025-00507-1","DOIUrl":"10.1140/epje/s10189-025-00507-1","url":null,"abstract":"<div><p>This study discusses the effect of photothermal therapy using PANI-conductive polymer composites with iron oxide and the amino acid cysteine ​​(Cys) on breast cancer cells. The study focused on the biological and toxicological effects associated with the treatment process and its impact on these cancer cells. The materials were prepared using a very simple chemical oxidation method to produce polymer nanoparticles to which iron and cysteine ​​molecules are attached. These composites were used as therapeutic agents in photothermal therapy, which relies primarily on the process of converting light into heat energy to kill cancer cells. The results showed that photothermal therapy using PANI-Fe₂O₃-Cys composites with near-infrared (NIR) light was significantly more effective in inhibiting breast cancer cells (MDA-MB-231) than using the composites without a laser. Significant changes in the morphology of the cancer cells were observed after treatment, demonstrating the treatment’s effectiveness in destroying cancer cells. On the other hand, there was a slight and negligible effect on healthy cells, demonstrating the successful formulation and targeting of the treatment for cancerous tumors. Antibacterial evaluations also demonstrated effective activity against <i>Staphylococcus aureus</i> and <i>Klebsiella</i> bacteria. This study supports the use of composite nanomaterials in photothermal therapy as a targeted treatment for breast cancer, as well as enhancing the effectiveness of this treatment with lasers. It also explains how these materials could be used in future medical applications, particularly in cancer treatment, using methods that are considered less invasive and safer.</p><h3>Graphic abstract</h3><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 6-7","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144688563","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Density-dependent cell migration in the absence of social interactions: a case study of Acanthamoeba castellanii","authors":"Nasser Ghazi,&nbsp;Mete Demircigil,&nbsp;Olivier Cochet-Escartin,&nbsp;Amandine Chauviat,&nbsp;Sabine Favre-Bonté,&nbsp;Christophe Anjard,&nbsp;Jean-Paul Rieu","doi":"10.1140/epje/s10189-025-00502-6","DOIUrl":"10.1140/epje/s10189-025-00502-6","url":null,"abstract":"<div><p>Cell migration is often influenced by intercellular or social interactions, ranging from long-range diffusive cues to direct contacts that can trigger biochemical signaling within the cell and affect the cell protruding activity or direction of turns. Here we study the density-dependent migration of the amoeba <i>Acanthamoeba castellanii (Ac)</i>, a unicellular eukaryote that moves without social interactions. Using experiments and mean free path theory, we characterize how collisions affect motility parameters in crowded environments. We identify the collision rate as a key parameter linking cell density to the collision-induced reorientation rate, and we show its consistency across multiple independent approaches. Our findings reveal that the intrinsic migration speed remains constant, while persistence time and effective diffusion are entirely governed by collisions. At high densities, cells exhibit nearly ballistic trajectories between collisions, a behavior rarely reported in eukaryotes. These results establish <i>Ac</i> as a minimal model for motility in the absence of biochemical signaling, with implications for testing behaviors in complex crowded environments and pre-jamming dynamics.</p><h3>Graphical Abstract</h3><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":790,"journal":{"name":"The European Physical Journal E","volume":"48 6-7","pages":""},"PeriodicalIF":2.2,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144688562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}