Classical Predictions Research Articles

Quantification of thermal and contact resistances of scanning thermal probes

Scanning thermal probes are widely used for imaging temperature fields with nanoscale resolution, for studying near-field radiative heat transport and for locally heating samples. In all these applications, it is critical to know the thermal resistance to heat flow within the probe and the thermal contact resistance between the probe and the sample. Here, we present an approach for quantifying the aforementioned thermal resistances using picowatt resolution heat flow calorimeters. The measured contact resistance is found to be in good agreement with classical predictions for thermal contact resistance. The techniques developed here are critical for quantitatively probing heat flows at the nanoscale.

Do rich households live farther away from their workplaces?

One of the classic predictions of urban economic theory is that high-income and low-income households choose different residential locations and therefore, conditional on workplace location, have different commuting patterns. The effect of household income on commuting distance may be positive, because of an increased demand for housing as house prices are lower further from workplace locations, or negative, because of an increase in the value of travel time. In addition, the sign of this effect may depend on the location of residential amenities relative to workplaces. Empirical tests of this effect are not standard, due to reverse causation and lack of good control variables. To address reverse causation, this effect is derived using changes in household income and distance through residential moves keeping workplace location constant. Our results contradict previous results in the literature. We show that for Denmark, conditional on the workplace location, the income elasticity of distance is negative and in the order of −0.18. This elasticity is larger for single-earner than for dual-earner households. Conditional on that the household moves residence between municipalities, the elasticity is suggested to be around −0.60.

Optimization of the Coupled Cluster Implementation in NWChem on Petascale Parallel Architectures.

The coupled cluster singles and doubles (CCSD) algorithm in the NWChem software package has been optimized to alleviate the communication bottleneck. This optimization provided a 2-fold to 5-fold speedup in the CCSD iteration time depending on the problem size and available memory, and improved the CCSD scaling to 20 000 nodes of the NCSA Blue Waters supercomputer. On 20 000 XE6 nodes of Blue Waters, a complete conventional CCSD(T) calculation of a system encountering 1042 basis functions and 103 occupied correlated orbitals obtained a performance of 0.32 petaflop/s and took 5 h and 24 min to complete. The reported time and performance included all stages of the calculation from initialization to termination for iterative single and double excitations as well as perturbative triples correction. In perturbative triples alone, the computation sustained a rate of 1.18 petaflop/s. The CCSD and (T) phases took approximately (3)/4 and (1)/4 of the total time to solution, respectively, showing that CCSD is the most time-consuming part at the large scale. The MP2, CCSD, and CCSD(T) computations in 6-311++G** basis set performed on guanine-cytosine deoxydinucleotide monophosphate probed the conformational energy difference between the A- and B-conformations of single stranded DNA. Good agreement between MP2 and coupled cluster methods has been obtained, suggesting the utility of MP2 for conformational analysis in these systems. The study revealed a significant discrepancy between the quantum mechanical and classical force field predictions, suggesting a need to improve the dihedral parameters.

In situ TEM imaging of CaCO₃ nucleation reveals coexistence of direct and indirect pathways.

Mechanisms of nucleation from electrolyte solutions have been debated for more than a century. Recent discoveries of amorphous precursors and evidence for cluster aggregation and liquid-liquid separation contradict common assumptions of classical nucleation theory. Using in situ transmission electron microscopy (TEM) to explore calcium carbonate (CaCO3) nucleation in a cell that enables reagent mixing, we demonstrate that multiple nucleation pathways are simultaneously operative, including formation both directly from solution and indirectly through transformation of amorphous and crystalline precursors. However, an amorphous-to-calcite transformation is not observed. The behavior of amorphous calcium carbonate upon dissolution suggests that it encompasses a spectrum of structures, including liquids and solids. These observations of competing direct and indirect pathways are consistent with classical predictions, whereas the behavior of amorphous particles hints at an underlying commonality among recently proposed precursor-based mechanisms.

Rayleigh instability at small length scales.

The Rayleigh instability (also called the Plateau-Rayleigh instability) of a nanosized liquid propane thread is investigated using molecular dynamics (MD). The validity of classical predictions at small length scales is verified by comparing the temporal evolution of liquid thread simulated by MD against classical predictions. Previous works have shown that thermal fluctuations become dominant at small length scales. The role and influence of the stochastic nature of thermal fluctuations in determining the instability at small length scale is also investigated. Thermal fluctuations are seen to dominate and accelerate the breakup process only during the last stages of breakup. The simulations also reveal that the breakup profile of nanoscale threads undergo modification due to reorganization of molecules by the evaporation-condensation process.

Bridging high pressure rheology and film-forming capacity of polymer-base oil solutions in EHL

The development of high value-added lubricants which overcome more drastic operating conditions, are fuel-efficient and provide excellent performance for a long life remains a huge challenge for oil makers. This article sheds light on the tribological response of an EHD circular rolling–sliding contact for a base oil and three polymers mixed in solutions in order to understand the relationship between physico-chemistry and tribology. The final aim is to help formulators select the appropriate chemicals meeting engine specifications. Central and minimal film thickness measurements were run on a ball-on-disc tribometer and determined through white light optical interferometry. Experiments were compared with classical analytical predictions and with the results of a finite element numerical solver based on the generalized Reynolds’ equation including the modelled rheological behavior established from high-pressure and high-stress viscosity measurements and density variations. Moreover, the role played by thermal effects and variable slide-to-roll ratio were discussed.

Confinement degradation by Alfvén-eigenmode induced fast-ion transport in steady-state scenario discharges

Analysis of neutron and fast-ion Dα data from the DIII-D tokamak shows that Alfvén eigenmode activity degrades fast-ion confinement in many high βN, high qmin, steady-state scenario discharges. (βN is the normalized plasma pressure and qmin is the minimum value of the plasma safety factor.) Fast-ion diagnostics that are sensitive to the co-passing population exhibit the largest reduction relative to classical predictions. The increased fast-ion transport in discharges with strong AE activity accounts for the previously observed reduction in global confinement with increasing qmin; however, not all high qmin discharges show appreciable degradation. Two relatively simple empirical quantities provide convenient monitors of these effects: (1) an ‘AE amplitude’ signal based on interferometer measurements and (2) the ratio of the neutron rate to a zero-dimensional classical prediction.

Loop-Closure and Gaussian Models of Collective Structural Characteristics of Capped PEO Oligomers in Water.

Parallel-tempering MD results for a CH3(CH2-O-CH2)mCH3 chain in water are exploited as a database for analysis of collective structural characteristics of the PEO globule with a goal of defining models permitting statistical thermodynamic analysis of dispersants of Corexit type. The chain structure factor, relevant to neutron scattering from a deuterated chain in null water, is considered specifically. The traditional continuum-Gaussian structure factor is inconsistent with the simple k → ∞ behavior, but we consider a discrete-Gaussian model that does achieve that consistency. Shifting and scaling the discrete-Gaussian model helps to identify the low-k to high-k transition near k ≈ 2π/0.6 nm when an empirically matched number of Gaussian links is about one-third of the total number of effective atom sites. This short distance-scale boundary of 0.6 nm is directly verified with the r space distributions, and this distance is thus identified with a natural size for coarsened monomers. The probability distribution of Rg(2) is compared with the classic predictions for both the Gaussian model and freely jointed chains. ⟨Rg(2)(j)⟩, the contribution of the jth chain segment to ⟨Rg(2)⟩, depends on the contour index about as expected for Gaussian chains despite significant quantitative discrepancies that express the swelling of these chains in water. Monomers central to the chain contour occupy the center of the chain globule. The density profiles of chain segments relative to their center of mass can show distinctive density structuring for smaller chains due to the close proximity of central elements to the globule center. However, that density structuring washes out for longer chains where many chain elements additively contribute to the density profiles. Gaussian chain models thus become more satisfactory for the density profiles for longer chains.

Reproductive cessation and post-reproductive lifespan in Asian elephants and pre-industrial humans.

IntroductionShort post-reproductive lifespan is widespread across species, but prolonged post-reproductive life-stages of potential adaptive significance have been reported only in few mammals with extreme longevity. Long post-reproductive lifespan contradicts classical evolutionary predictions of simultaneous senescence in survival and reproduction, and raises the question of whether extreme longevity in mammals promotes such a life-history. Among terrestrial mammals, elephants share the features with great apes and humans, of having long lifespan and offspring with long dependency. However, little data exists on the frequency of post-reproductive lifespan in elephants. Here we use extensive demographic records on semi-captive Asian elephants (n = 1040) and genealogical data on pre-industrial women (n = 5336) to provide the first comparisons of age-specific reproduction, survival and post-reproductive lifespan in both of these long-lived species.ResultsWe found that fertility decreased after age 50 in elephants, but the pattern differed from a total loss of fertility in menopausal women with many elephants continuing to reproduce at least until the age of 65 years. The probability of entering a non-reproductive state increased steadily in elephants from the earliest age of reproduction until age 65, with the longer living elephants continuing to reproduce until older ages, in contrast to humans whose termination probability increased rapidly after age 35 and reached 1 at 56 years, but did not depend on longevity. Post-reproductive lifespan reached 11–17 years in elephants and 26–27 years in humans living until old age (depending on method), but whereas half of human adult lifespan (of those reproductive females surviving to the age of 5% fecundity) was spent as post-reproductive, only one eighth was in elephants. Consequently, although some elephants have long post-reproductive lifespans, relatively few individuals reach such a phase and the decline in fertility generally parallels declines in survivorship in contrast to humans with a decoupling of senescence in somatic and reproductive functions.ConclusionsOur results show that the reproductive and survival patterns of Asian elephants differ from other long-lived animals exhibiting menopause, such as humans, and extreme longevity alone does not promote the evolution of menopause or post-reproductive lifespan, adding weight to the unusual kin-selected benefits suggested to favour such traits in humans and killer whales.

Extrapair behaviour reveals flexible female choosiness and mixed support for classic good genes in blue-footed boobies

The good genes hypothesis has long been a major focus of research on the function of extrapair (EP) behaviour by socially monogamous females. It predicts that females should be less faithful when paired to low-quality males and, as EP males become increasingly superior to their social mates, that EP males should be of higher quality than the males they cuckold. Evaluations have yielded mixed results, perhaps in part due to an overly strict interpretation of these predictions. A recent theoretical model demonstrated that while females with high-quality mates should be selective, those with low-quality males may gain good genes benefits by random EP mating, provided EP choosiness has costs, phenotypic indicators are imperfect and sperm competition favours genetic quality. We tested these classic and modified behavioural predictions in the blue-footed booby, Sula nebouxii , at two critical steps of EP interactions: courtship and copulation. Support for the classic good genes predictions was limited: EP courtship was more common in females with younger mates, but EP copulation following courtship was not predicted by social mate or relative male age, body size, condition, foot colour (a dynamic ornament) or breeding success, and these characteristics did not differ consistently between social and EP males. However, EP copulation increased with relative attractiveness (greener feet) of the EP male only when the social male was attractive, supporting the model's prediction that female choosiness should increase with social male attractiveness. Moreover, EP copulation probability decreased as EP males became increasingly superior to unattractive females, suggesting that EP males can also be choosy and may constrain female behaviour. Our results confirm that EP interactions involve more complexity than originally envisioned, warranting further studies that focus on behaviour and include all three main players: female, social mate and EP male. • We evaluated the good genes hypothesis of extrapair (EP) courtship and copulation in blue-footed boobies. • We also tested whether females with high-quality mates are choosier towards EP males. • Young males were more likely to be cuckolded, but social and EP male quality was similar. • Superior EP attractiveness increased EP copulation only in mates of attractive males. • Evidence for good genes was mixed, but results support flexible female EP choosiness.

Electron-beam dynamics in a strong laser field including quantum radiation reaction

The evolution of an electron beam colliding head-on with a strong plane-wave field is investigated in the framework of strong-field QED including radiation-reaction effects due to photon emission. Employing a kinetic approach to describe the electron and the photon distribution it is shown that at a given total laser fluence the final electron distribution depends on the shape of the laser envelope and on the pulse duration, in contrast to the classical predictions of radiation reaction based on the Landau-Lifshitz equation. Finally, it is investigated how the pair-creation process leads to a nonlinear coupled evolution of the electrons in the beam, of the produced charged particles, and of the emitted photons.

Self-energy-modified Poisson-Nernst-Planck equations: WKB approximation and finite-difference approaches.

We propose a modified Poisson-Nernst-Planck (PNP) model to investigate charge transport in electrolytes of inhomogeneous dielectric environment. The model includes the ionic polarization due to the dielectric inhomogeneity and the ion-ion correlation. This is achieved by the self energy of test ions through solving a generalized Debye-Hückel (DH) equation. We develop numerical methods for the system composed of the PNP and DH equations. Particularly, toward the numerical challenge of solving the high-dimensional DH equation, we developed an analytical WKB approximation and a numerical approach based on the selective inversion of sparse matrices. The model and numerical methods are validated by simulating the charge diffusion in electrolytes between two electrodes, for which effects of dielectrics and correlation are investigated by comparing the results with the prediction by the classical PNP theory. We find that, at the length scale of the interface separation comparable to the Bjerrum length, the results of the modified equations are significantly different from the classical PNP predictions mostly due to the dielectric effect. It is also shown that when the ion self energy is in weak or mediate strength, the WKB approximation presents a high accuracy, compared to precise finite-difference results.

Vacuum Stability of the Wrong Sign (−ϕ 6) Scalar Field Theory

We apply the effective potential method to study the vacuum stability of the bounded from above (−ϕ 6) (unstable) quantum field potential. The stability (∂E/∂b = 0) and the mass renormalization (∂ 2 E/∂b 2 = M 2) conditions force the effective potential of this theory to be bounded from below (stable). Since bounded from below potentials are always associated with localized wave functions, the algorithm we use replaces the boundary condition applied to the wave functions in the complex contour method by two stability conditions on the effective potential obtained. To test the validity of our calculations, we show that our variational predictions can reproduce exactly the results in the literature for the \(\mathcal {PT}\)-symmetric ϕ 4 theory. We then extend the applications of the algorithm to the unstudied stability problem of the bounded from above (−ϕ 6) scalar field theory where classical analysis prohibits the existence of a stable spectrum. Concerning this, we calculated the effective potential up to first order in the couplings in d space-time dimensions. We find that a Hermitian effective theory is instable while a non-Hermitian but \(\mathcal {PT}\)-symmetric effective theory characterized by a pure imaginary vacuum condensate is stable (bounded from below) which is against the classical predictions of the instability of the theory. We assert that the work presented here represents the first calculations that advocates the stability of the (−ϕ 6) scalar potential.

Frame dependence of stationary heat transfer in an inert mixture of ideal gases

This paper is devoted to the study of a stationary heat transfer problem in an inert binary mixture of ideal gases. The mixture is enclosed between two coaxial cylinders, kept at two different constant temperatures and at rest in a non-inertial frame. In particular, the frame is assumed to rotate with a constant angular velocity around the cylinder axes. The phenomenon is described by the linearized equations of extended thermodynamics with 13 moments. Integration of the field equations requires the assignment of non-controllable boundary values, which are determined through a fluctuation principle. It turns out that the temperature field presents boundary layers. Moreover, in agreement with the predictions of the kinetic theory, the tangential components of the heat and of the diffusion fluxes cannot vanish. We also show that the mixture and its constituents cannot be at rest in the rotating frame. An analysis is proposed concerning the combined effects of thermo-diffusion and rotation in the separation of mixture components. A comparison between classical and extended thermodynamics predictions is also proposed.

Structural interdependence within top management teams: A key moderator of upper echelons predictions

Studies of the effects of top management team (TMT) composition on organizational outcomes have yielded mixed and confusing results. A possible breakthrough resides in the reality thatTMTs vary in how they are fundamentally structured. Some are structured such that members operate independently of each other, while others are set up such that roles are highly interdependent. We examine the potential for three facets of structural interdependence—horizontal, vertical, and reward interdependence—to resolve ambiguities regarding effects ofTMTheterogeneity. Based on a sample ofTMTs in technology firms, we find that the three facets of structural interdependence are potent moderators of two classic predictions: the positive association betweenTMTheterogeneity and member departures, and betweenTMTheterogeneity and firm performance. Copyright © 2014 John Wiley & Sons, Ltd.

Quantum molecular dynamics study of warm dense iron.

The equation of state, the self-diffusion coefficient and viscosity of fluid iron in the warm dense regime at densities from 12.5 to 25.0 g/cm(3), and temperatures from 0.5 to 15.0 eV have been calculated via quantum molecular dynamics simulations. The principal Hugoniot is in good agreement with nuclear explosive experiments up to ∼ 50 Mbar but predicts lower pressures compared with high intensity laser results. The self-diffusion coefficient and viscosity have been simulated and have been compared with the one-component plasma model. The Stokes-Einstein relationship, defined by connections between the viscosity and the self-diffusion coefficient, has been determined and has been found to be fairly well described by classical predictions.

PREDICTION OF FLUID SLIP AT GRAPHENE AND CARBON NANOTUBE INTERFACES

The hydrodynamic boundary condition is now a subject of greater interest than ever before, even though the problem of formulating the correct boundary condition has existed from the beginning of the 19th century. Since then, many researchers have attempted to formulate a general boundary condition for fluid-solid interfaces. The 21st century has seen revolutionary advancement in nanoscale science and technology, which in turn, poses many fundamental questions about the nature of fluid flow in nanometric pores such as carbon nanotubes (CNTs) and aquaporins. Among them, one of the most important is the boundary condition. In this work, based on a statistical mechanics approach, we present a method to calculate the intrinsic interfacial friction coefficient between a fluid and solid at a planar and cylindrical interface, which determines the slip and boundary condition. We apply the method in conjunction with equilibrium molecular dynamics (EMD) simulation technique to fluids such as argon, methane and water flowing in planar graphene nanoslit pores and CNTs. We compare our model predictions against direct non-equilibrium molecular dynamics (NEMD) simulations and find excellent agreement. We identify several limitations of generally used NEMD methods to predict the slip and boundary condition and show that great care needs to be taken in analyzing the results of NEMD slip data for high-slip systems. We suggest some procedures to increase the reliability of the slip estimates. We also study the shear rate and external field dependent behavior of slip in Couette and Hagen-Poiseuille type flows. The slip length remains constant (indicating a linear response of the fluid to the external perturbation) only for low shear rates/external fields and as the field increases, the slip length increases rapidly. At these high fields the Navier-slip model breaks down. We attempt to resolve the highly debated issue of flow rates of water in carbon nanotubes, the values of which are scattered over 1 to 5 orders of magnitude in literature. We accurately predict these flow rates using both the CNT diameter dependent interfacial friction coefficient between water-CNTs and NEMD simulations streaming velocity profiles. Very narrow tubes show higher flow rate enhancements and as the tube diameter increases, the flow rates approach classical Navier-Stokes predictions with the no slip boundary condition. As the diameter of the tube increases, the slip length decreases monotonically and asymptotically approaches a constant value, which is equal to the slip length on a planar graphene surface. Our model gives the linear regime slip length which corresponds to experimental condition flow rates, which is otherwise cumbersome to find using NEMD simulation techniques. The proposed method is robust, general and can be used to find the slip and boundary condition accurately at any fluid-solid interface.

Effects of Extrinsic Mortality on the Evolution of Aging: A Stochastic Modeling Approach

The evolutionary theories of aging are useful for gaining insights into the complex mechanisms underlying senescence. Classical theories argue that high levels of extrinsic mortality should select for the evolution of shorter lifespans and earlier peak fertility. Non-classical theories, in contrast, posit that an increase in extrinsic mortality could select for the evolution of longer lifespans. Although numerous studies support the classical paradigm, recent data challenge classical predictions, finding that high extrinsic mortality can select for the evolution of longer lifespans. To further elucidate the role of extrinsic mortality in the evolution of aging, we implemented a stochastic, agent-based, computational model. We used a simulated annealing optimization approach to predict which model parameters predispose populations to evolve longer or shorter lifespans in response to increased levels of predation. We report that longer lifespans evolved in the presence of rising predation if the cost of mating is relatively high and if energy is available in excess. Conversely, we found that dramatically shorter lifespans evolved when mating costs were relatively low and food was relatively scarce. We also analyzed the effects of increased predation on various parameters related to density dependence and energy allocation. Longer and shorter lifespans were accompanied by increased and decreased investments of energy into somatic maintenance, respectively. Similarly, earlier and later maturation ages were accompanied by increased and decreased energetic investments into early fecundity, respectively. Higher predation significantly decreased the total population size, enlarged the shared resource pool, and redistributed energy reserves for mature individuals. These results both corroborate and refine classical predictions, demonstrating a population-level trade-off between longevity and fecundity and identifying conditions that produce both classical and non-classical lifespan effects.

Charge-Tunable Quantum Plasmons in Colloidal Semiconductor Nanocrystals

Nanomaterials exhibiting plasmonic optical responses are impacting sensing, information processing, catalysis, solar, and photonics technologies. Recent advances have expanded the portfolio of plasmonic nanostructures into doped semiconductor nanocrystals, which allow dynamic manipulation of carrier densities. Once interpreted as intraband single-electron transitions, the infrared absorption of doped semiconductor nanocrystals is now commonly attributed to localized surface plasmon resonances and analyzed using the classical Drude model to determine carrier densities. Here, we show that the experimental plasmon resonance energies of photodoped ZnO nanocrystals with controlled sizes and carrier densities diverge from classical Drude model predictions at small sizes, revealing quantum plasmons in these nanocrystals. A Lorentz oscillator model more adequately describes the data and illustrates a closer link between plasmon resonances and single-electron transitions in semiconductors than in metals, highlighting a fundamental contrast between these two classes of plasmonic materials.

Quantum Plasmonics: Optical Properties of a Nanomatryushka

Quantum mechanical effects can significantly reduce the plasmon-induced field enhancements around nanoparticles. Here we present a quantum mechanical investigation of the plasmon resonances in a nanomatryushka, which is a concentric core-shell nanoparticle consisting of a solid metallic core encapsulated in a thin metallic shell. We compute the optical response using the time-dependent density functional theory and compare the results with predictions based on the classical electromagnetic theory. We find strong quantum mechanical effects for core-shell spacings below 5 Å, a regime where both the absorption cross section and the local field enhancements differ significantly from the classical predictions. We also show that the workfunction of the metal is a crucial parameter determining the onset and magnitude of quantum effects. For metals with lower workfunctions such as aluminum, the quantum effects are found to be significantly more pronounced than for a noble metal such as gold.