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Concrete is the most widely manufactured material in the world. Its binding phase, calcium-silicate-hydrate (C-S-H), is responsible for its mechanical properties and has an atomic structure fairly similar to that of usual calcium silicate glasses, which makes it appealing to study this material with tools and theories traditionally used for non-crystalline solids. Here, following this idea, we use molecular dynamics simulations to evaluate the fracture toughness of C-S-H, inaccessible experimentally. This allows us to discuss the brittleness of the material at the atomic scale. We show that, at this scale, C-S-H breaks in a ductile way, which prevents one from using methods based on linear elastic fracture mechanics. Knowledge of the fracture properties of C-S-H at the atomic scale opens the way for an upscaling approach to the design of tougher cement paste, which would allow for the design of slender environment-friendly infrastructures, requiring less material.

Background: Elemental analysis of teeth allows for exposure assessment during critical windows of development and is increasingly used to link early life exposures and health. The measurement of inorganic elements in teeth is challenging; laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is the most widely used technique., Objective: Both synchrotron x-ray fluorescence (SXRF) and LA-ICP-MS have the capability to measure elemental distributions in teeth with each having distinct advantages and disadvantages., Methods: In our study, we compared these two methods for teeth elemental quantification. SXRF was able to achieve spatial resolutions of 0.3 µm and is non-destructive while giving similar elemental quantification results to LA-ICP-MS., Results: For particular elements, SXRF can offer lower detection limits but depends on the specific beam intensity. The comparison between methods revealed less than 10% disagreement between quantification results from LA-ICP-MS and SXRF., Impact: Synchrotron x-ray fluorescence can be used to effectively quantify elemental distributions in teeth at a nanoscale resolution and is comparable to current laser ablation inductively coupled plasma mass spectrometry. Both methods offer advantages and disadvantages with LA-ICP-MS offering in-lab analyses, whereas SXRF offers much finer spatial and temporal scales and better detection capabilities. For studies focused on fine scale changes in structure, SXRF is more appropriate than LA-ICP-MS., Competing Interests: Ethics approval and consent to participate: The study received IRB approval from Harvard University and adhered to all guidelines and regulations set forth. Informed consent was obtained from all study participants. Competing interests: The authors declare no competing interests., (© 2025. The Author(s), under exclusive licence to Springer Nature America, Inc.)

Porosity affects key astromaterial processes from disruption in our atmosphere and impact with the ground, to the comminution of boulders by thermal and impact processes and slope mechanics on asteroid surfaces, to access and utilization of in-situ resources. Whereas the bulk porosity of clay-rich meteorites is well established, the magnitude of their surface area and nano-scale porosity is poorly known. Here we use N 2 BET gas adsorption to measure the specific surface area and nanoscale pore distribution in several clay-rich meteorites. Two recent falls Tarda (C2-ung) and Aguas Zarcas (CM2) have specific surface areas of 72.5 and 16.5 m 2 /g, respectively. However, the specific surface area of Tarda ranges from 33.7 to 81.6 m 2 /g depending on outgassing conditions. The Tarda surface area is dominated by an interconnected network of ~ 3-nm-sized pores, whereas Aguas Zarcas shows a lower density of ~ 3 nm pores and broader size distribution around 40 nm. In contrast, Ivuna and Orgueil (CI1) have surface areas of ~ 15 to 18 m 2 /g: the low values compared to Tarda are likely due to the neoformation of pore-blocking minerals during atmospheric exposure. These data suggest that returned samples from asteroids Ryugu and Bennu, which are mineralogically and texturally similar to Tarda, also have interconnected nano-scale porosity with high surface area., (© 2024. The Author(s).)

While family engagement at the individual level of health care, such as families partnering with providers in decision-making about health care for an individual child has been well studied, family engagement in systems-level activities (e.g., participation in advisory and other decision-making groups, or creation and revision of policies) that impact the health services families and children receive has not. This note from the field presents a framework that describes the information and supports that help families partner with professionals and contribute to systems-level activities. Without attention to these components of family engagement, family presence and participation may be only token. We engaged an expert Family/Professional Workgroup whose members represented key constituencies and diverse geography, race/ethnicity, and areas of expertise; conducted a review of peer-reviewed publications and grey literature; and conducted a series of key informant interviews to identify best practices for supporting meaningful family engagement at the systems level. Based on an analysis of the findings, the authors identified four action-oriented domains of family engagement and key criteria that support and strengthen meaningful family engagement in systems-level initiatives. Child- and family-serving serving organizations can use this Family Engagement in Systems framework to support meaningful family engagement in the design of policies, practices, services, supports, quality improvement projects, research, and other systems-level activities., (© 2023. The Author(s).)

Caregiving encompasses the nurturing, tasks, resources, and services that meet the day-to-day needs of children and youth with special health care needs (CYSHCN) at home. Many gaps exist in the strategies currently offered by the health care system to meet the caregiving needs of CYSHCN. The work of family caregivers of CYSHCN is known to be extensive, but it is so poorly understood that it has been described as "invisible". This invisibility leads to poor communication and gaps in understanding between professional health care providers and family caregivers. To address these gaps, health care researchers must work with family caregivers to incorporate their expertise on caregiving and create meaningful and sustainable research partnerships. A growing body of research is attempting to remedy the problem of caregiving invisibility and lay better foundations for successful integration between health care settings, family caregiving, professional caregiving, and community supports for families of CYSHCN. We identify high-priority gaps in CYSHCN caregiving research and propose research questions that are designed to accelerate growth in evidence-based understanding of the work of family caregivers of CYSHCN and how best to support them., (Copyright © 2021 Academic Pediatric Association. Published by Elsevier Inc. All rights reserved.)

Families of children and youth with special health care needs (CYSHCN) can face challenges with regard to health and well-being. Health systems are designed to support CYSHCN but do not often consider the health and well-being of their family. Despite a growing body of literature, substantial gaps remain in our understanding of the impact of caregiving on family health and well-being and mechanisms of supporting families. In order to better understand and address these gaps, a national CYSHCN network developed a national research agenda to prioritize key areas of insufficient understanding of health and well-being for families of CYSHCN. Questions identified by the research agenda include: 1) How can family resiliency and adaptability be measured and improved? 2) How can we better assess family mental health needs and implement appropriate interventions? 3) What is the impact of family health on CYSHCN health outcomes? This paper describes a review of what is currently known regarding health for families of CYSHCN, gaps in the literature focused on the research agenda questions, and recommendations for future research. Based on the research agenda and current state of research for family health of CYSHCN, the authors recommend focusing on resiliency and adaptability as outcomes, using implementation science to address mental health concerns of family members and to further assess the impact of family health on health outcomes of CYSHCN. In addition, research should have a special focus on diverse populations of families and consider these questions in the context of different family structures., (Copyright © 2021 Academic Pediatric Association. Published by Elsevier Inc. All rights reserved.)

Time-reversible dynamical simulations of nonequilibrium systems exemplify both Loschmidt's and Zermélo's paradoxes. That is, computational time-reversible simulations invariably produce solutions consistent with the irreversible Second Law of Thermodynamics (Loschmidt's) as well as periodic in the time (Zermélo's, illustrating Poincaré recurrence). Understanding these paradoxical aspects of time-reversible systems is enhanced here by studying the simplest pair of such model systems. The first is time-reversible, but nevertheless dissipative and periodic, the piecewise-linear compressible Baker Map. The fractal properties of that two-dimensional map are mirrored by an even simpler example, the one-dimensional random walk, confined to the unit interval. As a further puzzle the two models yield ambiguities in determining the fractals' information dimensions. These puzzles, including the classical paradoxes, are reviewed and explored here.

This is our current research perspective on models providing insight into statistical mechanics. It is necessarily personal, emphasizing our own interest in simulation as it developed from the National Laboratories' work to the worldwide explosion of computation of today. We contrast the past and present in atomistic simulations, emphasizing those simple models that best achieve reproducibility and promote understanding. Few-body models with pair forces have led to today's "realistic" simulations with billions of atoms and molecules. Rapid advances in computer technology have led to change. Theoretical formalisms have largely been replaced by simulations incorporating ingenious algorithm development. We choose to study particularly simple, yet relevant, models directed toward understanding general principles. Simplicity remains a worthy goal, as does relevance. We discuss hard-particle virial series, melting, thermostatted oscillators with and without heat conduction, chaotic dynamics, fractals, the connection of Lyapunov spectra to thermodynamics, and finally simple linear maps. Along the way, we mention directions in which additional modeling could provide more clarity and yet more interesting developments in the future.

Objectives: In this study, we sought to establish priorities for a national research agenda for children and youth with special health care needs (CYSHCN) through a structured, multistakeholder, mixed-methods approach., Methods: Using surveys, we solicited responses from >800 members of expert-nominated stakeholder organizations, including CYSHCN families, health care providers, researchers, and policymakers, to identify what research with or about CYSHCN they would like to see in a national research agenda. From 2835 individual free-text responses, 96 research topics were synthesized and combined. Using an adapted RAND/UCLA Appropriateness Method (a modified Delphi approach), an expert panel rated research topics across 3 domains: need and urgency, research impact, and family centeredness. Domains were rated on 9-point Likert scales. Panelist ratings were used to sort research topics into 4 relative-priority ranks. Rank 1 (highest priority) research topics had a median of ≥7 in all domains., Results: The RAND/UCLA Appropriateness Method was used to prioritize CYSHCN research topics and depict their varying levels of stakeholder-perceived need and urgency, research impact, and family centeredness. In the 15 topics that achieved rank 1, social determinants of health (disparities and rurality), caregiving (family resilience and care at home), clinical-model refinement (effective model elements, labor divisions, telemedicine, and system integration), value (stakeholder-centered value outcomes, return on investment, and alternative payment models), and youth-adult transitions (planning, insurance, and community supports) were emphasized., Conclusions: High-priority research topics identified by CYSHCN experts and family leaders underscore CYSHCN research trends and guide important directions. This study is the first step toward an efficient and cohesive research blueprint to achieve highly-effective CYSHCN health systems., Competing Interests: POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose., (Copyright © 2020 by the American Academy of Pediatrics.)

Strength and other mechanical properties of cement and concrete rely upon the formation of calcium-silicate-hydrates (C-S-H) during cement hydration. Controlling structure and properties of the C-S-H phase is a challenge, due to the complexity of this hydration product and of the mechanisms that drive its precipitation from the ionic solution upon dissolution of cement grains in water. Departing from traditional models mostly focused on length scales above the micrometer, recent research addressed the molecular structure of C-S-H. However, small-angle neutron scattering, electron-microscopy imaging, and nanoindentation experiments suggest that its mesoscale organization, extending over hundreds of nanometers, may be more important. Here we unveil the C-S-H mesoscale texture, a crucial step to connect the fundamental scales to the macroscale of engineering properties. We use simulations that combine information of the nanoscale building units of C-S-H and their effective interactions, obtained from atomistic simulations and experiments, into a statistical physics framework for aggregating nanoparticles. We compute small-angle scattering intensities, pore size distributions, specific surface area, local densities, indentation modulus, and hardness of the material, providing quantitative understanding of different experimental investigations. Our results provide insight into how the heterogeneities developed during the early stages of hydration persist in the structure of C-S-H and impact the mechanical performance of the hardened cement paste. Unraveling such links in cement hydrates can be groundbreaking and controlling them can be the key to smarter mix designs of cementitious materials.

Structurally stable atomistic one-dimensional shock waves have long been simulated by injecting fresh cool particles and extracting old hot particles at opposite ends of a simulation box. The resulting shock profiles demonstrate tensor temperature, Txx≠Tyy and Maxwell's delayed response, with stress lagging strain rate and heat flux lagging temperature gradient. Here this same geometry, supplemented by a short-ranged external "plug" field, is used to simulate steady Joule-Kelvin throttling flow of hot dense fluid through a porous plug, producing a dilute and cooler product fluid.

We use nonequilibrium molecular dynamics to analyze and illustrate the qualitative differences between the one-thermostat and two-thermostat versions of equilibrium and nonequilibrium (heat-conducting) harmonic oscillators. Conservative nonconducting regions can coexist with dissipative heat conducting regions in phase space with exactly the same imposed temperature field.

Guided by molecular dynamics simulations, we generalize the Navier-Stokes-Fourier constitutive equations and the continuum motion equations to include both transverse and longitudinal temperatures. To do so we partition the contributions of the heat transfer, the work done, and the heat flux vector between the longitudinal and transverse temperatures. With shockwave boundary conditions time-dependent solutions of these equations converge to give stationary shockwave profiles. The profiles include anisotropic temperature and can be fitted to molecular dynamics results, demonstrating the utility and simplicity of a two-temperature description of far-from-equilibrium states.

The anisotropy of temperature is studied here in a strong two-dimensional shock wave, simulated with conventional molecular dynamics. Several forms of the kinetic temperature are considered, corresponding to different choices for the local instantaneous stream velocity. A local particle-based definition omitting any "self"-contribution to the stream velocity gives the best results. The configurational temperature is not useful for this shock-wave problem. The configurational temperature is subject to a shear instability and can give local negative temperatures in the vicinity of the shock front. The decay of sinusoidal shock-front perturbations shows that strong two-dimensional planar shock waves are stable to such perturbations.

We compare nonlinear stresses and temperatures for adiabatic-shear flows, using up to 262, 144 particles, with those from corresponding homogeneous and inhomogeneous flows. Two varieties of kinetic temperature tensors are compared to the configurational temperatures. This comparison of temperatures led us to two findings beyond our original goal of analyzing shear algorithms. First, we found an improved form for local instantaneous velocity fluctuations, as calculated with smooth-particle weighting functions. Second, we came upon the previously unrecognized contribution of rotation to the configurational temperature.

Many recent papers have questioned Irving and Kirkwood's atomistic expression for stress. In Irving and Kirkwood's approach both interatomic forces and atomic velocities contribute to stress. It is the velocity-dependent part that has been disputed. To help clarify this situation we investigate (i) a fluid in a gravitational field and (ii) a steadily rotating solid. For both problems we choose conditions where the two stress contributions, potential and kinetic, are significant. The analytic force-balance solutions of both these problems agree very well with a smooth-particle interpretation of the atomistic Irving-Kirkwood stress tensor.

Homogeneous shear flows (with constant strainrate dv(x)/dy) are generated with the Doll's and Sllod algorithms and compared to corresponding inhomogeneous boundary-driven flows. We use one-, two-, and three-dimensional smooth-particle weight functions for computing instantaneous spatial averages. The nonlinear normal-stress differences are small, but significant, in both two and three space dimensions. In homogeneous systems the sign and magnitude of the shearplane stress difference, Pxx-Pyy, depend on both the thermostat type and the chosen shearflow algorithm. The Doll's and Sllod algorithms predict opposite signs for this normal-stress difference, with the Sllod approach definitely wrong, but somewhat closer to the (boundary-driven) truth. Neither of the homogeneous shear algorithms predicts the correct ordering of the kinetic temperatures: Txx > Tzz > Tyy.

We analyze temperature and thermometry for simple nonequilibrium heat-conducting models. We also show in detail, for both two- and three-dimensional systems, that the ideal-gas thermometer corresponds to the concept of a local instantaneous mechanical kinetic temperature. For the phi4 models investigated here the mechanical temperature closely approximates the local thermodynamic equilibrium temperature. There is a significant difference between the kinetic temperature and nonlocal configurational temperature. Neither obeys the predictions of extended irreversible thermodynamics. Overall, we find that the kinetic temperature, as modeled and imposed by the Nosé-Hoover thermostats developed in 1984, provides the simplest means for simulating, analyzing, and understanding nonequilibrium heat flows.

We consider and compare four Hamiltonian formulations of thermostated mechanics, three of them kinetic, and the other one configurational. Though all four approaches "work" at equilibrium, their application to many-body nonequilibrium simulations can fail to provide a proper flow of heat. All the Hamiltonian formulations considered here are applied to the same prototypical two-temperature "phi4" model of a heat-conducting chain. This model incorporates nearest-neighbor Hooke's-Law interactions plus a quartic tethering potential. Physically correct results, obtained with the isokinetic Gaussian and Nose-Hoover thermostats, are compared with two other Hamiltonian results. The latter results, based on constrained Hamiltonian thermostats, fail to model correctly the flow of heat.

Stable fluid and solid particle phases are essential to the simulation of continuum fluids and solids using smooth particle applied mechanics. We show that density-dependent potentials, such as Phi rho=1/2 Sigma(rho-rho 0)2, along with their corresponding constitutive relations, provide a simple means for characterizing fluids and that special stabilization potentials, with density gradients or curvatures, such as Phi inverted Delta rho=1/2 Sigma(inverted Delta rho)2, not only stabilize crystalline solid phases (or meshes) but also provide a surface tension which is missing in the usual density-dependent-potential approach. We illustrate these ideas for two-dimensional square, triangular, and hexagonal lattices.

Smooth-particle applied mechanics (SPAM) provides several approaches to approximate solutions of the continuum equations for both fluids and solids. Though many of the usual formulations conserve mass, (linear) momentum, and energy, the angular momentum is typically not conserved by SPAM. A second difficulty with the usual formulations is that tensile stress states often exhibit an exponentially fast high-frequency short-wavelength instability, "tensile instability." We discuss these twin defects of SPAM and illustrate them for a rotating elastic body. We formulate ways to conserve angular momentum while at the same time delaying the symptoms of tensile instability for many sound-traversal times. These ideas should prove useful in more general situations.

We study the relative usefulness of static and dynamic boundary conditions as a function of system dimensionality. In one space dimension, dynamic boundaries, with the temperatures and velocities of external mirror-image boundary particles linked directly to temperatures and velocities of interior particles, perform qualitatively better than the simpler static-mirror-image boundary condition with fixed boundary temperatures and velocities. In one space dimension, the Euler-Maclaurin sum formula shows that heat-flux errors with dynamic temperature boundaries vary as h(-4), where h is the range of the smooth-particle weight function w(r

The authors thermostat a qp harmonic oscillator using the two additional control variables zeta and xi to simulate Gibbs' canonical distribution. In contrast to the motion of purely Hamiltonian systems, the thermostated oscillator motion is completely ergodic, covering the full four-dimensional [q,p,zeta,xi] phase space. The local Lyapunov spectrum (instantaneous growth rates of a comoving corotating phase-space hypersphere) exhibits singularities like those found earlier for Hamiltonian chaos, reinforcing the notion that chaos requires kinetic-as opposed to statistical-study, both at and away from equilibrium. The exponent singularities appear to have a fractal character.

The Kaplan-Yorke information dimension of phase-space attractors for two kinds of steady nonequilibrium many-body flows is evaluated. In both cases a set of Newtonian particles is considered which interacts with boundary particles. Time-averaged boundary temperatures are imposed by Nose-Hoover thermostat forces. For both kinds of nonequilibrium systems, it is demonstrated numerically that external isothermal boundaries can drive the otherwise purely Newtonian flow onto a multifractal attractor with a phase-space information dimension significantly less than that of the corresponding equilibrium flow. Thus the Gibbs' entropy of such nonequilibrium flows can diverge.

A particularly simple chaotic nonequilibrium open system with two Cartesian degrees of freedom, characterized by two distinct temperatures T(x) and T(y), is introduced. The two temperatures are maintained by Nose-Hoover canonical-ensemble thermostats. Both the equilibrium (no net heat transfer) and nonequilibrium (dissipative) Lyapunov spectra are characterized for this simple system.

Purified bovine brain calmodulin was biotinylated with biotinyl-epsilon-aminocaproic acid N-hydroxysuccinimide. Biotinylated calmodulin was used to detect and quantify calmodulin-binding proteins following both protein blotting and slot-blot procedures by using alkaline phosphatase or peroxidase coupled to avidin. When purified bovine brain calcineurin, a calmodulin-dependent protein phosphatase, was immobilized on nitrocellulose slot blots, biotinylated calmodulin bound in a calcium-dependent saturable manner; these blots were then quantified by densitometry. Biotinylated calmodulin was able to detect as little as 10 ng of calcineurin, and the binding was competitively inhibited by addition of either native calmodulin or trifluoperazine. When biotinylated calmodulin was used to probe protein blots of crude brain cytosol and membrane preparations after gel electrophoresis, only protein bands characteristic of known calmodulin-binding proteins (i.e., calmodulin-dependent protein kinase, calcineurin, spectrin) were detected with avidin-peroxidase or avidin-alkaline phosphatase procedures. Purified calcineurin was subjected to one- and two-dimensional gel electrophoresis and protein blotting; as expected, only the 61-kDa calmodulin-binding subunit was detected. When the two-dimensional protein blot was incubated with biotinylated calmodulin and detected with avidin-alkaline phosphatase, several apparent forms of the 61-kDa catalytic subunit were detected, consistent with isozymic species of the enzyme. The results of these studies suggest that biotinylated calmodulin can be used as a simple, sensitive, and quantifiable probe for the study of calmodulin-binding proteins.