Dimensional Bulk Research Articles

Exploring unique quasinormal modes of a massive scalar field in brane-world scenarios

We compute precise values of quasinormal modes of a massive scalar field in the background of the Schwarzschild-like brane-localised black holes. It is shown that the quasinormal spectrum of the massive field differs qualitatively from that previously known for other black hole models, due to the presence of two kinds of modes: those whose damping rate vanishes as the mass of the field μ increases up to some critical value, and those whose real oscillation frequency vanishes at a certain value of μ. While the first type of modes, which are arbitrarily long-lived, are recognized in various four-dimensional backgrounds as quasi-resonances, the second type is a novel feature for asymptotically flat black holes. When Re(ω) reaches zero, the fundamental mode disappears from the spectrum and the first overtone becomes the fundamental mode. We also demonstrate that quasi-resonances may not exist for brane-localised black holes immersed in D≥6 - dimensional bulk.

Multifactorial impacts of B-doping on Fe81Ga19 alloys prepared by laser-beam powder bed fusion: Microstructure, magnetostriction, and osteogenesis

Magnetostrictive Fe-Ga alloys have captivated substantial focus in biomedical applications because of their exceptional transition efficiency and favorable cytocompatibility. Nevertheless, Fe-Ga alloys always exhibit frustrating magnetostriction coefficients when presented in bulk dimensions. It is well-established that the magnetostrictive performance of Fe-Ga alloys is intimately linked to their phase and crystal structures. In this study, various concentrations of boron (B) were doped into Fe81Ga19 alloys via the laser-beam powder bed fusion (LPBF) technique to tailor the crystal and phase structures, thereby improving the magnetostrictive performance. The results revealed the capacity for quick solidification of the LPBF process in expediting the solid solution of B element, which increased both lattice distortion and dislocations within the Fe-Ga matrix. These factors contributed to an elevation in the density of the modified-D03 phase structure. Moreover, the prepared Fe-Ga-B alloys also exhibited a 〈001〉 preferred grain orientation caused by the high thermal gradients during the LPBF process. As a result, a maximum magnetostriction coefficient of 105 ppm was achieved in the (Fe81Ga19)98.5B1.5 alloy. In alternating magnetic fields, all the LPBF-prepared alloys showed good dynamic magnetostriction response without visible hysteresis, while the (Fe81Ga19)98.5B1.5 alloy presented a notable enhancement of ∼30 % in magnetostriction coefficient when compared with the Fe81Ga19 alloy. Moreover, the (Fe81Ga19)98.5B1.5 alloy exhibited favorable biocompatibility and osteogenesis, as confirmed by increased alkaline phosphatase (ALP) activity and the formation of mineralized nodules. These findings suggest that the B-doped Fe-Ga alloys combined with the LPBF technique hold promise for the development of bulk magnetostrictive alloys that are applicable for bone repair applications.

The cosmological constant problem and the extra dimensions of [formula omitted]=2 [formula omitted]=5 supergravity

We propose an interpretation for the cosmological constant problem based on modeling the universe as a 3-brane embedded in the bulk of 5-dimensional supergravity with hypermultiplets. When solving the modified Friedmann equations the complex structure moduli of the Calabi-Yau manifold cancel the large value of the vacuum energy density on the brane, wherein this value transfers to an Anti-de Sitter fifth dimensional bulk compactified on a scale (∼10−26m). An effective dark energy density is produced on the brane which equals the observed value responsible for the late-time acceleration of the universe. The bulk undergoes a decelerated contraction while we show that cosmic expansion of the brane-universe consists with the recent observed data of the ΛCDM model. On the other hand, through this model, the hierarchy between the electroweak scale (MEW=100GeV) and the Planck scale (Mpl∼1018GeV) is interpreted by compactifying the 6-extra dimensions of D=5 supergravity on a sub-millimeters scale, where the fundamental scale of gravity within these extra dimensions is MEW.

Nanostructured Materials, Structures and Mechanical Properties, Processing and Applications

Nanomaterials are becoming an integral part of high-performance products and services. As technology advances, the possibilities for engineering components with nanomaterials are more numerous, taking advantage of the benefits that these materials have the potential to provide. Nanostructured materials have bulk dimensions with a structure that includes nanoscale features, and have been around for quite some time, hidden in everyday items. More recently, they have been made possible to be analysed and manipulated with increasingly sophisticated instruments and processes. This ability has made them more accessible, however, challenges still remain in the more widespread adoption of these materials for exploiting their advantages. The present paper outlines the position and emergence of nanostructured materials in the broader context of nanomaterials, examining their mechanical properties, production methods and applications.

Mechanical behavior of bio‐inspired composites made of co‐continuous geopolymer and 3D‐printed polymer

AbstractGeopolymers (GPs) are emerging, low‐density ceramic materials that are simple to manufacture, with high elastic modulus and strength, albeit with low toughness. Fiber reinforcements have been used to achieve varied ductile behaviors, but little is known about the GP addition to polymeric frame structures. Thus, drawing inspiration from the nanostructure of bones, this paper investigated an interpenetrating, co‐continuous composite consisting of a GP as the stiff but brittle phase, and a 3D‐printed polymer (PA12 White) as the soft and deformable phase. The composite mechanical properties and failure modes were studied experimentally using uniaxial compression and four‐point bending tests. The co‐continuous network constrained brittle cracking within the GP and reduced strain localization in the polymer. The results showed that the composite had higher strength (56.11 ± 2.12 MPa) and elastic modulus (6.08 ± 1.37 GPa) than the 3D‐printed polymer and had higher toughness (5.98 ± 0.24 MJ/mm3) than the GP for the specific geometries examined. The shape effect study demonstrated that cubic structures had higher elastic modulus and strength but at the expense of lower toughness when compared to rectangular prism structures. The study of scale effects indicated that increasing the number of periodic unit cells while maintaining consistent bulk dimensions led to augmented strength and toughness, albeit without statistically significant alterations in elastic modulus. Thus, this paper presents an experimental realization of a novel, bio‐inspired, interpenetrating, GP–polymer composite design, offering improved strength and toughness. It also provides valuable insights into the shape and size effects on the mechanical properties of this new composite.

Carrollian structure of the null boundary solution space

We study pure D dimensional Einstein gravity in spacetimes with a generic null boundary. We focus on the symplectic form of the solution phase space which comprises a 2D dimensional boundary part and a 2(D(D − 3)/2 + 1) dimensional bulk part. The symplectic form is the sum of the bulk and boundary parts, obtained through integration over a codimension 1 surface (null boundary) and a codimension 2 spatial section of it, respectively. Notably, while the total symplectic form is a closed 2-form over the solution phase space, neither the boundary nor the bulk symplectic forms are closed due to the symplectic flux of the bulk modes passing through the boundary. Furthermore, we demonstrate that the D(D − 3)/2 + 1 dimensional Lagrangian submanifold of the bulk part of the solution phase space has a Carrollian structure, with the metric on the D(D − 3)/2 dimensional part being the Wheeler-DeWitt metric, and the Carrollian kernel vector corresponding to the outgoing Robinson-Trautman gravitational wave solution.

Systems biology analysis reveals distinct molecular signatures associated with immune responsiveness to the BNT162b COVID-19 vaccine

Human immune responses to COVID-19 vaccines display a large heterogeneity of induced immunity and the underlying immune mechanisms for this remain largely unknown. Using a systems biology approach, we longitudinally profiled a unique cohort of female high and low responders to the BNT162b vaccine, who were known from previous COVID-19 vaccinations to develop maximum and minimum immune responses to the vaccine. We utilized high dimensional flow cytometry, bulk and single cell mRNA sequencing and 48-plex serum cytokine analyses. We revealed early, transient immunological and molecular signatures that distinguished high from low responders and correlated with B and T cell responses measured 14 days later. High responders featured a distinct transcriptional activity of interferon-driven genes and genes connected to enhanced antigen presentation. This was accompanied by a robust cytokine response related to Th1 differentiation. Both transcriptome and serum cytokine signatures were confirmed in two independent confirmatory cohorts. Collectively, our data contribute to a better understanding of the immunogenicity of mRNA-based COVID-19 vaccines, which might lead to the optimization of vaccine designs for individuals with poor vaccine responses. German Center for Infection Research, German Center for Lung Research, German Research Foundation, Excellence Strategy EXC 2155 "RESIST" and European Regional Development Fund.

Soft particles and infinite-dimensional geometry

In the sigma model, soft insertions of moduli scalars enact parallel transport of S-matrix elements about the finite-dimensional moduli space of vacua, and the antisymmetric double-soft theorem calculates the curvature of the vacuum manifold. We explore the analogs of these statements in gauge theory and gravity in asymptotically flat spacetimes, where the relevant moduli spaces are infinite-dimensional. These models have spaces of vacua parameterized by (trivial) flat connections on the celestial sphere, and soft insertions of photons, gluons, and gravitons parallel transport S-matrix elements about these infinite-dimensional manifolds. We argue that the antisymmetric double-soft gluon theorem in d + 2 bulk dimensions computes the curvature of a connection on the infinite-dimensional space Map, where G is the global part of the gauge group. The analogous metrics in abelian gauge theory and gravity are flat, as indicated by the vanishing of the antisymmetric double-soft theorems in those models. In other words, Feynman diagram calculations not only know about the vacuum manifold of Yang–Mills theory, they can also be used to compute its curvature. The results have interesting implications for flat space holography.

Torrefaction for Upgrading the Quality of Merbau Wood Waste Pellets

Recently, biofuels are intensively studied regarding the need of alternative renewable energy sources. Woody biomass has been one of the raw materials which are used in various ways including biofuels. As for biofuels, woody biomass has yet to possess some disadvantages such as bulk dimension, low density, non-uniformity, and high moisture content. Pelletizing has been one of the ways to improve the quality of woody biomass to be a proper biofuel. However, wood pellets also still offer downside such as hygroscopicity. Torrefaction is one of the methods to upgrade pellets quality such as high calorific value, fixed carbon, and hydrophobicity. In this study, merbau wood waste pellets were dry torrefied at a temperature of 200°C and 250°C for 15 and 30 minutes. The data obtained showed that torrefaction applied on merbau wood waste pellets could produce high quality pellets.

Towards non-invertible anomalies from generalized Ising models

We present a general approach to the bulk-boundary correspondence of noninvertible topological phases, including both topological and fracton orders. This is achieved by a novel bulk construction protocol where solvable (d+1)(d+1)-dimensional bulk models with noninvertible topology are constructed from the so-called generalized Ising (GI) models in dd dimensions. The GI models can then terminate on the boundaries of the bulk models. The construction generates abundant examples, including not only prototype ones such as \mathbb{Z}_2ℤ2 toric code models in any dimensions no less than two, and the X-cube fracton model, but also more diverse ones such as the \mathbb{Z}_2x \mathbb{Z}_2ℤ2xℤ2 topological order, the 4d \mathbb{Z}_2ℤ2 topological order with pure-loop excitations, etc. The boundary of the solvable model is potentially anomalous and corresponds to precisely only sectors of the GI model that host certain total symmetry charges and/or satisfy certain boundary conditions. We derive a concrete condition for such bulk-boundary correspondence. The condition is violated only when the bulk model is either trivial or fracton ordered. A generalized notion of Kramers-Wannier duality plays an important role in the construction. Also, utilizing the duality, we find an example where a single anomalous theory can be realized on the boundaries of two distinct bulk fracton models, a phenomenon not expected in the case of topological orders. More generally, topological orders may also be generated starting with lattice models beyond the GI models, such as those with symmetry protected topological orders, through a variant bulk construction, which we provide in an appendix.

Boundaries and interfaces with localized cubic interactions in the O(N) model

We explore a new approach to boundaries and interfaces in the O(N) model where we add certain localized cubic interactions. These operators are nearly marginal when the bulk dimension is 4 − ϵ, and they explicitly break the O(N) symmetry of the bulk theory down to O(N − 1). We show that the one-loop beta functions of the cubic couplings are affected by the quartic bulk interactions. For the interfaces, we find real fixed points up to the critical value Ncrit ≈ 7, while for N > 4 there are IR stable fixed points with purely imaginary values of the cubic couplings. For the boundaries, there are real fixed points for all N, but we don’t find any purely imaginary fixed points. We also consider the theories of M pairs of symplectic fermions and one real scalar, which have quartic OSp(1|2M) invariant interactions in the bulk. We then add the Sp(2M) invariant localized cubic interactions. The beta functions for these theories are related to those in the O(N) model via the replacement of N by 1 − 2M. In the special case M = 1, there are boundary or interface fixed points that preserve the OSp(1|2) symmetry, as well as other fixed points that break it.

A Review of Nano and Microscale Heat Transfer: An Experimental and Molecular Dynamics Perspective

Significant progress in the development of micro and nanoscale devices has been observed for the past three decades. The thermal transportation in these small-length scales varies significantly, and it is difficult to explain the underlying physics using the pre-existing theoretical formulations. When the bulk dimension of a system is comparable to or smaller than the mean free path (MFP) of the thermal carriers, classical theories, such as Fourier’s Law of heat conduction, are unable to accurately explain the system energy dynamics. The phenomena of energy transit and conversion at the micro to nanoscale is an interesting topic of research due to the substantial changes in behavior that are documented when compared to those at the macro size. This review article is broadly divided into two parts. Initially, the recent development in the field of molecular dynamic (MD) simulations is emphasized. Classical MD simulation is such a powerful tool that provides insight into the length scales where the conventional continuum approaches cease to be valid. Several examples of recent developments in the applicability of MD simulations for micro and nanoscale thermal transportation are reviewed. However, there are certain limitations of the MD simulations where the results deviate from experimental validation due to the lack of knowledge of the appropriate force fields. Hence the experimental development of micro and nanoscale thermal transportation processes is briefly reviewed and discussed in the other section of this review article.

Mathematical Models and Methods on Higher Dimensional Bulk Viscous String Cosmology with the Framework of Lyra Geometry

We investigate a cosmological scenario generated by a cloud of strings containing particles in the framework of the Lyra geometry by considering five-dimensional Bianchi type-III line element. We assume two physically plausible conditions (i) shear scalar (σ) proportional to the expansion factor (θ), which leads to P = Qn; n ≠ 0 is a constant, P and Q being scale factors and (ii) ξ = ξ0 = constant, ξ being the coefficient of bulk viscosity, deterministic models of our Universe are obtained. We have solved the modified Einstein’s field equations of a homogeneous Bianchi type-III metric. The bihaviors of cosmographic parameters for the different values of time (t) and redshift (z) are presented in detail to study the proposed model. It has been found that the displacement vector (β) behaves itself like the cosmological term, and the solution is consistent with the recent observations of SNeIa. The physical and geometrical properties of the model are premeditated, and it has been discussed in detail regarding the possibilities and prospects that can be happen throughout the evolution of the Universe. It is found that the bulk viscosity plays a crucial role in the evolution of the Universe, and the strings dominate in the early Universe and eventually disappear from the Universe during a sufficiently large time. So, our model can be treated as a realistic one.

Growth and Characterization of Organic 2-Chloro 5-Nitroaniline Crystal Using the Vertical Bridgman Technique

In this article, we discuss the preparation of organic 2-chloro-5 nitroaniline (2C5NA) crystals and their different kinds of physical, chemical, and mechanical properties. The vertical Bridgman approach was used to effectively produce the bulk organic 2C5NA crystal. To produce a good-quality bulk crystal, the shape, dimensions, and cone angle of the ampoule were optimized. Also, the temperature profile was set for the 2C5NA crystal. The growth atmosphere and the lowering rate were identified to obtain a homogeneous mixture of the compounds and initiate the nucleation process. Single-crystal X-ray diffraction (XRD), powder XRD, proton Fourier transform nuclear magnetic resonance (FT-NMR), and Fourier transform infrared investigations were used to confirm the crystal structure, molecular structure, and presence of functional groups in the formed crystal. The formed crystal has a monoclinic crystal structure with the space group P21/c, according to single-crystal XRD analysis. The thermal stability and kinetic parameters were examined using thermogravimetric analysis and differential thermal curves. From dielectric analysis, the electrical conductivity and dielectric behavior of 2C5NA were investigated with variations in frequency and temperature. The organic 2-chloro-5-nitroaniline crystal demonstrates that the indentation size effect is observed in the Vickers micro-hardness test, which was also carried out.

Pole-skipping points in 2D gravity and SYK model

We represent the first investigation of pole-skipping on both the gravity and field theory sides. In contrast to the higher dimensional models, there is no momentum degree of freedom in (1 + 1)−dimensional bulk theory. Thus, we then consider a scalar field mass as our degree of freedom for the pole-skipping phenomenon instead of momentum. The pole-skipping frequencies of the scalar field in 2D gravity are the same as higher dimensional cases: ω = −i2πTn for positive integers n. At each of these frequencies, there is a corresponding pole-skipping mass, so the pole-skipping points exist in (ω, m) space. We also compute the pole-skipping points of the SYK model in (ω, h) space where h is the dimension of the bilinear primary operator. We find that there is a one-to-one correspondence of the pole-skipping points between the JT gravity and the SYK model. To obtain the pole-skipping points, we need to consider the parameter ϵ related to the chemical potential on the horizon of charged JT gravity and the particle-hole asymmetric parameter mathcal{E} of the complex SYK model as shift parameters. This highlights the ϵ − mathcal{E} correspondence in relation to pole-skipping phenomenon.

De Sitter versus Anti de Sitter flows and the (super)gravity landscape

Generic solutions are studied in Einstein-scalar gravity in an ansatz that can interpolate between de Sitter and Anti-de Sitter regimes. The classification of regular solutions of [1, 2] is first extended to the dS regime. This implies, among others, the existence of cosmic clocks that reverse direction without passing through a curvature singularity. We then consider an ansatz for solutions that interpolate between the dS and AdS regimes. The structure of such more general solutions and their singularities are studied. It is shown that there are no regular solutions that interpolate between dS and AdS extrema for generic potentials. This is unlike the Centaur solutions that were shown to exist in two bulk dimensions. We also comment on the potential interplay with recent dS conjectures and the dS BF bounds.

Operator growth and black hole formation

When two particles collide in an asymptotically AdS spacetime with high enough energy and small enough impact parameter, they can form a black hole. Motivated by dual quantum circuit considerations, we propose a threshold condition for black hole formation. Intuitively the condition can be understood as the onset of overlap of the butterfly cones describing the ballistic spread of the effect of the perturbations on the boundary systems. We verify the correctness of the condition in three bulk dimensions. We describe a six-point correlation function that can diagnose this condition and compute it in two-dimensional CFTs using eikonal resummation.

Tree-inspired and scalable high thermal conductivity ethylene–vinyl acetate copolymer/expanded graphite/paraffin wax phase change composites for efficient thermal management

Bioinspired fabrication of high thermal conductivity phase change composites has great prospects for efficient thermal management. However, the direct and partial imitations of nature are not facile to the full realization of natural systematic advantages and scalable production. Herein, inspired by the tree’s transportation system, this study adopted a bottom-up strategy to mimic the tree’s sophisticated hierarchy at both micro and bulk dimensions. The composites employed a phloem-mimic crosslinking ethylene–vinyl acetate copolymer/paraffin wax (EVA/PW) film as the intelligent heat storage and release medium, and the xylem-imitated roll-to-roll directional EVA/expanded graphite (EVA/EG) film with enhanced high thermal conductivity (51.1 W m−1 K−1 with the enhancement of 26,894 %) as fast heat conduction pathway. Above two components were assembled to develop phase change composites (PCCs) with annual-ring and multilayered structures. Both computational and experimental results revealed that the assembled tree-inspired structures significantly improve the heat conduction performances of PCCs. The tree-inspired PCCs showed significantly high thermal conductivity (7.01 W m−1 K−1 with the enhancement of 2821 %) with a low filler content (9.0 vol%). Meanwhile, obtained PCCs with high phase change enthalpy exhibited excellent temperature regulation performance. This work offers a promising route for the scalable manufacture of advanced PCCs for efficient thermal management, and a general strategy to realize the natural systematic advantages via the bottom-up strategy.

A variational approach to hyperbolic evolutions and fluid-structure interactions

We show the existence of a weak solution for a system of partial differential equations describing the motion of a flexible solid inside a fluid: A nonlinear, viscoelastic, n -dimensional bulk solid governed by a PDE including inertia is interacting with an incompressible fluid governed by the ( n -dimensional) Navier–Stokes equation for n\geq 2 . The result is the first allowing for large bulk deformations in the regime of long time existence for fluid-structure interactions. The existence is achieved by introducing a novel variational scheme involving two time-scales that allows us to extend the method of minimizing movements to hyperbolic problems involving nonconvex and degenerate energies.

Sub-100 mA/cm2 CO2-to-CO Reduction Current Densities in Hierarchical Porous Gold Electrocatalysts Made by Direct Ink Writing and Dealloying.

While most research efforts on CO2-to-CO reduction electrocatalysts focus on boosting their selectivity, the reduction rate, directly proportional to the reduction current density, is another critical parameter to be considered in practical applications. This is because mass transport associated with the diffusion of reactant/product species becomes a major concern at a high reduction rate. Nanostructured Au is a promising CO2-to-CO reduction electrocatalyst for its very high selectivity. However, the CO2-to-CO reduction current density commonly achieved in conventional nanostructured Au electrocatalysts is relatively low (in the range of 1-10 mA/cm2) for practical applications. In this work, we combine direct ink writing-based additive manufacturing and dealloying to design a robust hierarchical porous Au electrocatalyst to improve the mass transport and achieve high CO2-to-CO reduction current densities on the order of 64.9 mA/cm2 with CO partial current density of 33.8 mA/cm2 at 0.55 V overpotential using an H-cell configuration. Although the current density achieved in our robust hierarchical porous Au electrocatalyst is one order of magnitude higher than the one achieved in conventional nanostructured electrocatalysts, we found that the selectivity of our system is relatively low, namely 52%, which suggests that mass transport remains a critical issue despite the hierarchical porous architecture. We further show that the bulk dimension of our electrocatalyst is a critical parameter governing the interplay between selectivity and reduction rate. The insights gained in this work shed new light on the design of electrocatalysts toward scale-up CO2 reduction and beyond.