arXiv subjects

N. Mendez

Publications and source records attributed to N. Mendez.

3 recordsLinked to original sources

arXiv2026

Atomistic insights into the structural, thermal, and mechanical evolution of $Zr_{47.5}Cu_{47.5}Ag_{5}$ bulk metallic glass

Bulk metallic glasses (BMGs) are distinguished by amorphous atomic structures that confer superior mechanical performance; however, the evolution of these properties in ternary bulk configurations remains insufficiently explored. In this study, we employed large-scale molecular dynamics simulations to investigate the structural, thermal, and mechanical properties of $Zr_{47.5}Cu_{47.5}Ag_{5}$ BMGs. Our thermodynamic and topological analyses, utilizing potential energy regression and the Modified Wendt-Abraham parameter, identified a glass transition temperature ($T_g$) of approximately $692\text{ K}$. Structural characterization via Voronoi tessellation and partial radial distribution functions reveals that the amorphous matrix is stabilized by icosahedral clusters, with Ag atoms inducing significant chemical heterogeneity through localized nano-clustering. Thermal transport properties, computed via the Green-Kubo formalism, demonstrate a monotonic decrease in conductivity with temperature, consistent with structural scattering saturation in disordered lattices. Mechanical tensile testing reveals that the material exhibits robust rate- and temperature-dependent behavior, with yield strengths reaching $\approx 2.3\text{ GPa}$ at room temperature. We show that macroscopic strain-softening is intrinsically linked to the thermally induced collapse of rigid icosahedral motifs, which facilitates shear band percolation. These findings provide a structural rationale for the beneficial role of Ag dopants in enhancing the resilience of multicomponent metallic glasses.

cond-mat.mtrl-sci↗

arXiv2026

Multifractal Signatures of Hamiltonian Chaos in Hyperion's Rotational Dynamics

The chaotic rotation of Saturn's moon Hyperion is a paradigmatic example of Hamiltonian chaos in a natural system. Although its tumbling motion is well established theoretically, identifying a robust observational signature of chaos from sparse and noisy astronomical time series remains a major challenge, making phase-space reconstruction techniques impractical under realistic conditions. In this work, we show that multifractal detrended fluctuation analysis (MFDFA) provides an effective alternative for detecting chaotic dynamics directly from photometric observations. Using historical ground-based light curves and synthetic datasets, we demonstrate that the intermittency associated with chaotic tumbling produces a broad multifractal singularity spectrum. While multifractality is a known feature of Hamiltonian chaos, we show that it can serve as a practical observational diagnostic when traditional chaos indicators fail because of sparse sampling. In particular, the multifractal spectrum remains detectable after realistic observational filtering and distinguishes chaotic tumbling from aliased regular rotation. By contrast, regular resonant rotation exhibits a significantly narrower spectrum, approaching the monofractal behavior expected for uncorrelated noise. For the observational data, we measure a broad spectral width consistent with the synthetic chaotic model, statistically distinct from surrogate datasets, and robust against finite time-series length. These results establish multifractal scaling as a viable observational signature of Hamiltonian chaos in sparse astronomical datasets, bridging nonlinear dynamics and planetary photometry.

astro-ph.EP↗

arXiv2025

Neutron-induced reaction cross section measurements on carbon at neutron energies up to 55 MeV at LANSCE

Background: Single-crystal chemical vapor deposited (sCVD) diamond detectors offer a unique method to study cross sections of reactions on carbon since they can be used as active targets. Previous studies analyzing neutrons on carbon using these detectors were primarily focused on lower energy neutrons and reactions, and some of these did not have sufficient energy resolution to isolate the contributions of reaction channels with similar Q values. Purpose: This work extends neutron-induced reaction cross section measurements to higher energies, relevant to rare isotope facilities. These measurements can be used to inform and benchmark simulation of experiments that require neutron detection, particularly those utilizing organic scintillators. For some experiments, simulations are used to extract physics information from experimental data, reinforcing the need for accurate simulations. Methods: Two sCVD diamond detectors were used as active targets at LANSCE, where neutrons up to 800 MeV are produced via spallation. Results: Relative cross sections are reported from incident neutron (kinetic) energies E$_n$ = 12 MeV up to 55 MeV for $^{12}$C(n,$α_0$), up to 46 MeV for $^{12}$C(n,d$_0$), and up to 27 MeV for $^{12}$C(n,p$_0$) and $^{12}$C(n,p$_1$). These measurements extend these cross sections to higher energies than those of previous studies. Conclusions: Good agreement is found between this work and recent experimental data from the EXFOR database in the neutron energies where the studies overlap. This work supports the need to update the ENDF evaluation for the (n,$α_0$) channel with more recent data, and provides data that could allow for an evaluation of the (n,p$_0$), (n,p$_1$), and (n,d$_0$) channels. These cross sections will increase the accuracy of simulations by extending the energy range for which empirical cross sections are available.

nucl-ex↗