物理最新文献

This study explores the thermal optimization of a cold square enclosure containing a heated circular cylinder, where the cylinder’s position varies along the vertical centerline of the enclosure. The cavity is filled with a suspension of nano-encapsulated phase change materials (NEPCMs) in a non-Newtonian fluid to enhance thermal performance. The primary aim is to examine the flow patterns, phase change dynamics, and overall thermal efficiency of the system. The governing equations for the NEPCMs nanofluid are reformulated into a dimensionless form and solved using the finite element method. Key parameters such as the cylinder’s position ((delta )), the power-law index (n), the NEPCMs particle volume fraction ((phi )), the fusion temperature ((varTheta _F)), and the Rayleigh number (Ra) are systematically analyzed to assess their influence on thermal performance. The findings of the study indicate that the region of active NEPCM fusion grows with increasing NEPCM concentration, except in the case of pseudoplastic fluids. The vertical position of the heated cylinder acts as an effective passive control parameter. Increasing NEPCM concentration consistently enhances overall heat transfer for all fluid types.

A high-energy acousto-optic Q-switched dual-crystal Tm:YAP laser at 1 kHz repetition rate was investigated. Using two b-cut Tm:YAP crystals in an L-shaped resonator with laser diode dual-end pumped at 793 nm, a pulse energy of 22.31 mJ at 1938.86 nm with 0.19 nm linewidth was achieved, corresponding to a 65 ns pulse width and 343.2 kW peak power, with beam quality factor M² ~ 3.4. In addition, when the pump power was 137.4 W, an average power of 29.96 W was obtained in continuous wave mode. To the best of our knowledge, this work represents the highest pulse energy reported of acousto-optic Q-switched Tm:YAP oscillator lasers at 1.94 μm.

This study explores the potential for high-harmonic generation (HHG) from argon atomic gas and single attosecond pulse generation by leveraging amplified and hyper-focused short laser pulses through a plasmonic nanostructure. The plasmonic nanostructure features triangular nanobowties with multilayer compositions of dielectrics and metals, supported by an insulating substrate. Within the nanobowtie gap, localized surface plasmons significantly enhance the laser field intensity over a substantial volume of the gap. Fine-tuning the geometric parameters of this structure achieves up to 45-fold amplification (< 17 dB) within the central wavelength of 800 nm of a standard titanium–sapphire laser. This enhancement enables the argon atoms introduced via a gas jet to exhibit a pronounced nonlinear response, leading to high-intensity HHG under incident pulses of relatively low intensity (10¹² W/cm²). Based on the harmonic spectrum observed, the generation of isolated attosecond pulses with a temporal width of 33.37 attoseconds is achievable, notably without necessitating chirp mitigation techniques.

Graphical abstract

The low-lying structure of the well-deformed nucleus (^{158})Gd has been revisited to elucidate the nature of the low-lying states in (^{158})Gd. Earlier (p, t) studies identified numerous 0(^+) states below 4.3 MeV, prompting questions about whether these states correspond to collective vibrations or shape coexistence. New and previously reported ((n,n^prime gamma )) measurements are combined, including (gamma )-(gamma ) coincidences, excitation functions, and angular distributions, to extract lifetimes and transition probabilities for 44 excited states up to 2.7 MeV, including 32 previously unmeasured levels. Our results confirm or revise (gamma )-ray placements and provide detailed transition strengths, revealing both weakly collective and strongly enhanced B(E2) and B(E1) transition probabilities. In particular, a tentative 0(^+) state at 2437.8 keV exhibits a strong interband B(E2) transition, which may be a candidate for a possible two-phonon ((beta beta )) excitation. Systematic comparisons with neighboring Gd isotopes, Hartree–Fock–Bogoliubov, and interacting-boson model predictions suggest that the first excited 0(^+) state in (^{158})Gd is predicted to be a (beta )-vibration, although it is weakly collective.

We also present results for lifetimes and transition probabilities for a number of negative parity states, including (hbox {K}^{pi }=0^-,1^-,2^-) sequences, perhaps providing insight into octupole collectivity and the interplay between quadrupole and octupole vibrations in deformed nuclei. The systematic presence of low-lying negative-parity bands and their interband transition strengths suggest that (^{158})Gd’s potential energy surface may support both quadrupole and octupole vibrational modes, in agreement with microscopic calculations [1,2,3].

In this paper we study the first nonlinear stage of modulation instability (NLSMI) of x-periodic anomalous waves (AWs) in multidimensional generalizations of the focusing nonlinear Schrödinger (NLS) equation, like the non-integrable elliptic and hyperbolic NLS equations in (2+1) and (3+1) dimensions. In the quasi one-dimensional (Q1D) regime, where the wavelength in the x direction of propagation is significantly smaller than in the transversal directions, the behavior at leading order is universal, independent of the particular model, and described by adiabatic deformations of the Akhmediev breather solution of NLS. Varying the initial data, the first NLSMI shows various combinations of basic processes, like AW growth from the unstable background, followed by fission in the slowly varying transversal directions, and the inverse process of fusion, followed by AW decay to the background. Fission and fusion are critical processes showing similarities with multidimensional wave breaking, and with phase transitions of second kind and critical exponent 1/2. In (3+1) dimensions with radial symmetry in the transversal plane, fission consists in the formation of an opening smoke ring, while if the symmetry is hyperbolic in the transversal plane, the growing Q1D AW is an X-wave undergoing fission into branches of hyperbolas. In the long wave limit, the Q1D Akhmediev breather reduces to the Q1D analogue of the Peregrine instanton, rationally localized in space. Numerical experiments on the hyperbolic NLS equation show that the process of “AW growth + fission” is not restricted to the Q1D regime, extending to a finite region of the modulation instability domain. At last, we pose and solve the “inverse time-scattering problem of AWs”: the reconstruction of the (O({epsilon })) initial perturbation of the background, from the knowledge of the first nonlinear stages of modulation instability for positive and negative times. The universality of these processes suggests their observability in natural phenomena related to AWs in contexts such as water waves, nonlinear optics, plasma physics, and Bose–Einstein condensates.

The demand for antibacterial surfaces has intensified since the recent pandemic, underscoring the need to prevent microbial adhesion on high-contact surfaces. Metallic and metal oxide nanostructures exhibit intrinsic antibacterial properties, motivating the development of scalable, cost-effective fabrication routes for functional coatings. In this study, copper oxide (CuO) thin films were deposited by magnetron sputtering and further nanostructured via glancing angle deposition (GLAD). The films exhibited pronounced antibacterial efficacy, inactivating Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) with efficiencies over 98% after 8 h of exposure. Increasing the deposition angle enhanced surface roughness and hydrophobicity, which directly correlated with higher bacterial inactivation. Longer exposure further improved antibacterial performance, demonstrating time-dependent activity. These results establish GLAD-fabricated CuO thin films as a promising, industrially scalable strategy for next-generation antimicrobial surface coatings.

We study symmetric and asymmetric cumulants as well as rapidity-even dipolar flow in ({}^{16})O+({}^{16})O collisions at (sqrt{s_{NN}} = 200) GeV to explore (alpha )-clustering phenomena in light nuclei within the viscous relativistic hydrodynamics framework. Signatures of (alpha )-clustering manifest in the anisotropic flow coefficients and their correlations – particularly in observables involving elliptic-triangular flow correlations. We show that final-state symmetric and asymmetric cumulants – especially (textrm{NSC}(2,3)) and (textrm{NAC}_{2,1}(2,3)) – are sensitive to the initial nuclear geometry. Additionally, we observe a significant difference in rapidity-even dipolar flow, (v_1^{text {even}}), between (alpha )-clustered and Woods–Saxon configurations in high-multiplicity events. These findings underscore the pivotal role of nuclear structure in heavy-ion collision dynamics and provide observables for distinguishing nuclear geometries, particularly in ultra-central collisions.

Human exploration beyond low Earth orbit poses unique health and operational challenges, with space radiation recognized as one of the most significant hazards. This comprehensive review examines the complex nature of the space radiation environment, its biological effects on humans and life support systems, and current strategies for risk assessment and mitigation. It details the composition and properties of galactic cosmic rays (GCRs) and solar particle events (SPEs), their interactions with spacecraft shielding, and the resulting biological impacts ranging from DNA damage to systemic effects including cancer, cardiovascular disease, and central nervous system impairments. Special emphasis is given to the combined effects of radiation and microgravity, which together alter cellular function and influence health outcomes. The paper also explores the effects of radiation on plants and microorganisms as biological components of bioregenerative life support systems (BLSS). The issue of radiation-induced degradation of food and pharmaceuticals is also considered. Existing and emerging countermeasures, encompassing passive and active shielding, pharmacological agents, nutrition, physiological adaptations like synthetic hibernation, and personalized risk assessment through targeted crew selection are critically reviewed. Additionally, the work highlights the importance of high-fidelity analog studies, space-based experiments, and advanced risk models integrating physical, biological, and operational data to inform future mission planning. Finally, the paper reviews existing infrastructures, experimental platforms, and European research programs, emphasizing the critical role of ground-based accelerators, space analog environments, and in-flight studies in advancing our understanding of radiation risks. By identifying key knowledge gaps and proposing a structured mitigation framework, this study presents a strategic roadmap for protecting human health and sustaining life during long-duration missions to the Moon, Mars, and beyond. (The review work described in the paper stems from the discussions within the working group on Radiation sponsored by the Italian Space Agency.)

Nonlinear wave phenomena play a central role in fluid dynamics and plasma physics. Soliton interaction is a key feature of such systems. The coupled Korteweg–de Vries (KdV) equations describe these nonlinear and dispersive waves. However, obtaining accurate and stable solutions remains difficult. This study presents a combined analytical and machine-learning approach. Analytical two-soliton solutions are derived using Hirota’s bilinear method. Dispersion relations and interaction properties are obtained to explain the evolution of wave profiles. Interaction times and peak positions are computed numerically to track soliton behavior before, during, and after collision. A modified physics-informed neural network (PINN) is then developed. Global physical constraints, such as energy conservation, are included directly in the loss function. This ensures that the learned solutions remain consistent with the underlying physics. Numerical experiments show that the PINN framework provides improved stability and accuracy. The model captures long-term nonlinear wave interactions with higher fidelity. The proposed method offers a reliable computational framework for analyzing coupled KdV systems and other nonlinear dispersive wave models.

This paper investigates the shadow and quasinormal modes (QNMs) of a Schwarzschild black hole (BH) embedded in a Hernquist dark matter (DM) halo, focusing on the influence of DM parameters – specifically the core radius (r_{s}) and core density (rho _{s}) – on BH observational signatures. We analyze the structure of the BH shadow, lensing ring, and photon ring, showing that the shadow radius increases with both (r_{s}) and (rho _{s}). Using the WKB approximation, Padé approximants, and time-domain integration, we compute the QNMs for scalar, electromagnetic, and axial gravitational perturbations. Our results reveal that the DM halo modifies the spacetime’s effective potential: larger values of (r_{s}) or (rho _{s}) reduce the peak of the potential barrier, leading to lower oscillation frequencies and slower wavefunction damping. These findings highlight the systematic impact of DM on strong-field observables and suggest that BH shadows and QNMs provide a viable means to probe DM profiles in galactic nuclei.