Void Interior Research Articles

Arrays of ZnO/MoS2 nanorods and MoS2 nanotubes for spectral enhancement and self-cleaning

Structure and heterojunction of substrates are widely regarded as critical factors to improve Raman detection and recyclibility, but the exact roles are rarely explored for the mixed contributions. Herein, the arrays of ZnO/MoS2 coaxial nanorods (NRs) and MoS2 nanotubes (NTs) were successfully constructed for the surface-enhanced Raman scattering (SERS). The influences of NR and NT length on the morphology, light absorption and emission, as well as SERS performance were systematically investigated. Both the arrays grown for 40 min displayed optimal SERS performance, in which MoS2 NT array owned stronger enhancement with a detection limit of 5 × 10−7 M than that of 1 × 10−6 M for ZnO/MoS2 NR array. The NTs also effectively enhanced photocatalysis, in which rhodamine 6G pollutant was completely degraded within 140 min under ultraviolet light, surpassing that by the NRs. The analysis revealed that band alignment and structure characteristic of the specimens played critical roles in the spectral enhancement and self-cleaning, while the nanostructure surpassed heterojunction as it supplied void interior for extending light propagation and more contact area for adsorbing pollutants. These results would contribute to a better understanding of the Raman enhancement and could be extended to the design of SERS substrates to harness their potential application.

How galaxies populate haloes in very low-density environments

Context. Evidence shows that properties of dark matter haloes may vary with large-scale environment. Studying the halo occupation distribution in cosmic voids makes it possible to obtain useful information that can shed light on the subject. The history of the formation of the haloes and galaxies residing in these regions is likely to differ from the global behaviour given their extreme environment. Aims. Our goal is to characterise the halo occupation distribution in the interior of cosmic voids and compare with the general results to unveil the way galaxies populate haloes in simulated galaxy catalogues. Methods. We used two publicly accessible simulated galaxy catalogues constructed with different methods: a semi-analytical model and a hydrodynamic simulation. In both cases, we identified cosmic voids, and we measured the halo occupation distribution inside these regions for different absolute magnitude thresholds. We compared these determinations with the overall results, and we studied the dependence of different characteristics of the voids. We also analysed the stellar content and the formation time of the haloes inside voids and confronted the general halo population results. Results. Inside the voids, we find a significantly different halo occupation distribution with respect to the general results. This is present in all absolute magnitude ranges explored. We obtain no signs of variation related to void characteristics, indicating that the effects depend only on the density of the large-scale environment. Additionally, we find that the stellar-mass content also differs within voids that host haloes with less massive central galaxies (∼10%), as well as satellites with significantly lower stellar-mass content (∼30%). Finally, we find a slight difference between the formation times of the younger haloes in voids than the average population. These characteristics indicate that haloes populating voids have had a different formation history, inducing significant changes on the halo occupation distribution.

The bias of cosmic voids in the presence of massive neutrinos

Cosmic voids offer an extraordinary opportunity to study the effects of massive neutrinos on cosmological scales. Because they are freely streaming, neutrinos can penetrate the interior of voids more easily than cold dark matter or baryons, which makes their relative contribution to the mass budget in voids much higher than elsewhere in the Universe. In simulations it has recently been shown how various characteristics of voids in the matter distribution are affected by neutrinos, such as their abundance, density profiles, dynamics, and clustering properties. However, the tracers used to identify voids in observations (e.g., galaxies or halos) are affected by neutrinos as well, and isolating the unique neutrino signatures inherent to voids becomes more difficult. In this paper we make use of the DEMNUni suite of simulations to investigate the clustering bias of voids in Fourier space as a function of their core density and compensation. We find a clear dependence on the sum of neutrino masses that remains significant even for void statistics extracted from halos. In particular, we observe that the amplitude of the linear void bias increases with neutrino mass for voids defined in dark matter, whereas this trend gets reversed and slightly attenuated when measuring the relative void-halo bias using voids identified in the halo distribution. Finally, we argue how the original behaviour can be restored when considering observations of the total matter distribution (e.g. via weak lensing), and comment on scale-dependent effects in the void bias that may provide additional information on neutrinos in the future.

Hierarchical molybdenum-doped cobaltous hydroxide nanotubes assembled by cross-linked porous nanosheets with efficient electronic modulation toward overall water splitting

Designing hierarchical nanostructures of earth-abundant electrocatalysts for enhanced overall water splitting performance is of great significance. Herein, Mo-doped Co(OH)2 hierarchical nanotubes (Mo-Co(OH)2 HNTs) assembled by cross-linked porous nanosheets are designed and synthesized through a sacrificial template strategy. Benefiting from the hierarchical structures based on porous nanosheets with void interior as well as modified electronic structure of higher intensity of Co3+ species by Mo6+ doping, the Mo-Co(OH)2 HNTs demonstrate superior electrocatalytic performance, achieving an current density of 10 mA cm−2 at the low overpotentials of 218 mV and 125 mV for oxygen and hydrogen evolution reactions, respectively. Furthermore, an overall water splitting cell was assembled with the Mo-Co(OH)2 electrocatalyst as both the anode and cathode materials, which exhibits a driving voltage of as low as 1.62 V. The facile strategy presented in this work can be extended to the construction of various hollow/porous nanostructures with effective heteroatom doping to achieve low-cost, bifunctional and high-performance electrocatalysts for overall water splitting.

An accurate linear model for redshift space distortions in the void–galaxy correlation function

Redshift space distortions within voids provide a unique method to test for environmental dependence of the growth rate of structures in low density regions, where effects of modified gravity theories might be important. We derive a linear theory model for the redshift space void-galaxy correlation that is valid at all pair separations, including deep within the void, and use this to obtain expressions for the monopole $\xi^s_0$ and quadrupole $\xi^s_2$ contributions. Our derivation highlights terms that have previously been neglected but are important within the void interior. As a result our model differs from previous works and predicts new physical effects, including a change in the sign of the quadrupole term within the void radius. We show how the model can be generalised to include a velocity dispersion. We compare our model predictions to measurements of the correlation function using mock void and galaxy catalogues modelled after the BOSS CMASS galaxy sample using the Big MultiDark $N$-body simulation, and show that the linear model with dispersion provides an excellent fit to the data at all scales, $0\leq s\leq120\;h^{-1}$Mpc. While the RSD model matches simulations, the linear bias approximation does not hold within voids, and care is needed in fitting for the growth rate. We show that fits to the redshift space correlation recover the growth rate $f(z=0.52)$ to a precision of $2.7\%$ using the simulation volume of $(2.5\;h^{-1}\mathrm{Gpc})^3$.

Observation of microscale nonparaxial optical bottle beams.

We predict and experimentally observe three-dimensional microscale nonparaxial optical bottle beams based on the generation of a caustic surface under revolution. Such bottle beams exhibit high contrast between the surrounding surface and the effectively void interior. Via caustic engineering, we can precisely control the functional form of the high-intensity surface to achieve microscale bottle beams with longitudinal and transverse dimensions of the same order of magnitude. Although, in general, the phase profile at the input plane can be computed numerically, we find closed-form expressions for bottle beams with various types of surfaces both in the real and in the Fourier space.

The Architectonic Experience of Body and Space in Augmented Interiors.

The environment shapes our experience of space in constant interaction with the body. Architectonic interiors amplify the perception of space through the bodily senses; an effect also known as embodiment. The interaction of the bodily senses with the space surrounding the body can be tested experimentally through the manipulation of multisensory stimulation and measured via a range of behaviors related to bodily self-consciousness. Many studies have used Virtual Reality to show that visuotactile conflicts mediated via a virtual body or avatar can disrupt the unified subjective experience of the body and self. In the full-body illusion paradigm, participants feel as if the avatar was their body (ownership, self-identification) and they shift their center of awareness toward the position of the avatar (self-location). However, the influence of non-bodily spatial cues around the body on embodiment remains unclear, and data about the impact of architectonic space on human perception and self-conscious states are sparse. We placed participants into a Virtual Reality arena, where large and narrow virtual interiors were displayed with and without an avatar. We then applied synchronous or asynchronous visuotactile strokes to the back of the participants and avatar, or, to the front wall of the void interiors. During conditions of illusory self-identification with the avatar, participants reported sensations of containment, drift, and touch with the architectonic environment. The absence of the avatar suppressed such feelings, yet, in the large space, we found an effect of continuity between the physical and the virtual interior depending on the full-body illusion. We discuss subjective feelings evoked by architecture and compare the full-body illusion in augmented interiors to architectonic embodiment. A relevant outcome of this study is the potential to dissociate the egocentric, first-person view from the physical point of view through augmented architectonic space.

Topology optimization of 3D shell structures with porous infill

This paper presents a 3D topology optimization approach for designing shell structures with a porous or void interior. It is shown that the resulting structures are significantly more robust towards load perturbations than completely solid structures optimized under the same conditions. The study indicates that the potential benefit of using porous structures is higher for lower total volume fractions. Compared to earlier work dealing with 2D topology optimization, we found several new effects in 3D problems. Most notably, the opportunity for designing closed shells significantly improves the performance of porous structures due to the sandwich effect. Furthermore, the paper introduces improved filter boundary conditions to ensure a completely uniform coating thickness at the design domain boundary.

The void galaxy survey: photometry, structure and identity of void galaxies

We analyze photometry from deep B-band images of 59 void galaxies in the Void Galaxy Survey (VGS), together with their near-infrared 3.6$\mu$m and 4.5$\mu$m Spitzer photometry. The VGS galaxies constitute a sample of void galaxies that were selected by a geometric-topological procedure from the SDSS DR7 data release, and which populate the deep interior of voids. Our void galaxies span a range of absolute B-magnitude from $\rm{M_B=-15.5}$ to $\rm{M_B=-20}$, while at the 3.6$\mu$m band their magnitudes range from $\rm{M_{3.6}=-18}$ to $\rm{M_{3.6}=-24}$. Their B-[3.6] colour and structural parameters indicate these are star forming galaxies. A good reflection of the old stellar population, the near-infrared band photometry also provide a robust estimate of the stellar mass, which for the VGS galaxies we confirm to be smaller than $3 \times 10^{10}$ M$_\odot$. In terms of the structural parameters and morphology, our findings align with other studies in that our VGS galaxy sample consists mostly of small late-type galaxies. Most of them are similar to Sd-Sm galaxies, although a few are irregularly shaped galaxies. The sample even includes two early-type galaxies, one of which is an AGN. Their S\'{e}rsic indices are nearly all smaller than $n=2$ in both bands and they also have small half-light radii. In all, we conclude that the principal impact of the void environment on the galaxies populating them mostly concerns their low stellar mass and small size.

Morphology and molecular dynamics investigation of PDMS adsorbed on titania nanoparticles: Effects of polymer molecular weight

Morphology, thermal transitions and molecular dynamics of polydimethylsiloxane (PDMS) adsorbed onto low specific surface area (25m2/g) spherical-like titania (TiO2) nanoparticles were studied employing adsorption–desorption nitrogen isotherms, morphology (SEM), calorimetry (DSC) and dielectric (BDS) techniques. The initial titania particles (crystallites of 40–140nm in diameter) were found to aggregate forming voids of a broad range. PDMS was adsorbed in the interior of voids in aggregates and onto external surfaces of the aggregates. With nanoparticles content increasing an increase in the glass transition temperature, Tg, is observed in DSC, accompanied by a broadening of the glass transition step and a decrease in the heat capacity step, ΔCp. According to BDS the interfacial polymer fraction is larger and exhibits slower dynamics (αint relaxation) in the case of shorter PDMS chains (∼22 monomers/chain) as compared to longer chains (∼105 monomers/chain). Changes in the interfacial polymer fraction correlate well with changes in the specific surface area of the aggregates, as recorded by gas molecules adsorption–desorption, and with morphology (SEM). Comparison with previous results obtained with PDMS-based nanocomposites suggests that interfacial polymer fraction and dynamics are dominated by the concentration of polymer–particle contact points (increased for shorter chains due to more free chain ends), rather than by the strength of polymer–filler physical bonds.

Self-similarity and universality of void density profiles in simulation and SDSS data

The stacked density profile of cosmic voids in the galaxy distribution provides an important tool for the use of voids for precision cosmology. We study the density profiles of voids identified using the zobov watershed transform algorithm in realistic mock luminous red galaxy (LRG) catalogues from the Jubilee simulation, as well as in void catalogues constructed from the SDSS LRG and Main Galaxy samples. We compare different methods for reconstructing density profiles scaled by the void radius and show that the most commonly used method based on counts in shells and simple averaging is statistically flawed as it underestimates the density in void interiors. We provide two alternative methods that do not suffer from this effect; one based on Voronoi tessellations is also easily able to account from artefacts due to finite survey boundaries and so is more suitable when comparing simulation data to observation. Using this method, we show that the most robust voids in simulation are exactly self-similar, meaning that their average rescaled profile does not depend on the void size. Within the range of our simulation, we also find no redshift dependence of the mean profile. Comparison of the profiles obtained from simulated and real voids shows an excellent match. The mean profiles of real voids also show a universal behaviour over a wide range of galaxy luminosities, number densities and redshifts. This points to a fundamental property of the voids found by the watershed algorithm, which can be exploited in future studies of voids.

Facile Synthesis of 3D Hierarchical Flower-like Co3-xFexO4 ferrite on Nickel Foam as High-Performance Electrodes for Supercapacitors

A facile hydrothermal method combined with a post solution reaction is developed to synthesize interconnected three-dimension (3D) hierarchical Co3-xFexO4 ferrite (CF) on nickel foam. By controlling the experimental parameters, the structures of the products are tailored from nanoflowers to microflowers with different sized void interiors. The obtained 3D hierarchical flower-like CF are characterized by field emission scanning electron microscopy, X-ray diffraction, and inductively coupled plasma mass spectrometer analysis. The 3D hierarchical flower-like CF-nickel foam with the rational structural feature could be used as binder and conductive agent-free supercapacitor electrodes directly. Such integrated electrodes exhibit a high specific capacitance and well cycling stability when the charge-discharge current density is high. Remarkably, the 3D hierarchical CF microflowers exhibit specific capacitance values of 768Fg−1 at a constant current density of 6Ag−1. The CF microflowers also show high charge-discharge reversibility with an efficiency of 79.2% after 5000 cycles.

Effects of hydrogen and impurities on void nucleation in copper: simulation point of view

The mechanisms of hydrogen influence on vacancy cluster formation in copper are studied using numerical simulations. Vacancy agglomeration in clusters larger than divacancies is found to be energetically favourable, but in pure copper the cluster creation is prevented by the lack of binding between single vacancies. Hydrogen dissolved in the lattice readily accumulates in vacancy-type defects, changing their properties. A single vacancy can accommodate up to six hydrogen atoms. Hydrogen stabilizes divacancies and promotes vacancy cluster nucleation. In larger vacancy clusters, accumulated hydrogen prevents cluster collapse into stacking fault tetrahedra. In small voids, hydrogen prefers to remain in atomic form at the void surface, but when voids become sufficiently large, hydrogen molecules in the void interior can also be formed. Some common impurities in copper (O, S, P and Ag) contribute to void formation by capturing vacancies in their vicinity. In contrast, substitutional Ni has little effect on vacancy clustering but tends to capture interstitial hydrogen.

Voids and the Cosmic Web: cosmic depression & spatial complexity

AbstractVoids form a prominent aspect of the Megaparsec distribution of galaxies and matter. Not only do they represent a key constituent of the Cosmic Web, they also are one of the cleanest probes and measures of global cosmological parameters. The shape and evolution of voids are highly sensitive to the nature of dark energy, while their substructure and galaxy population provides a direct key to the nature of dark matter. Also, the pristine environment of void interiors is an important testing ground for our understanding of environmental influences on galaxy formation and evolution. In this paper, we review the key aspects of the structure and dynamics of voids, with a particular focus on the hierarchical evolution of the void population. We demonstrate how the rich structural pattern of the Cosmic Web is related to the complex evolution and buildup of voids.

Co3O4 nanocages with highly exposed {110} facets for high-performance lithium storage

Functional materials with both exposed highly reactive planes and hollow structures have attracted considerable attentions with respect to improved catalytic activity and enhanced electrochemical energy storage. Herein, we report the synthesis of unusual single-crystal Co3O4 nanocages with highly exposed {110} reactive facets via a one-step solution method. When tested as anode materials in lithium-ion batteries, these Co3O4 nanocages deliver a high reversible lithium storage capacity of 864 mAh g−1 at 0.2C over 50 cycles and exhibit an excellent rate capability. The dominantly exposed {110} planes, a high density of atomic steps in nanocages, and the large void interiors lead to the regarded superior electrochemical performance.

Distance deviation measure of contouring variability

BackgroundSeveral methods that are currently used for contouring analysis have problems providing reliable and/or meaningful results. In this paper a solution to these problems is proposed in a form of a novel measure, which was developed based on requirements defined for contouring studies.Materials and methodsThe proposed distance deviation measure can be understood as an extension of the closest point measures in such a way that it does not measure only distances between points on contours but rather analyse deviation of distances to both/all contours from each image point/voxel. The obtained result is information rich, reliable and provided in a form of an image, enabling detailed topographic analysis. In addition to image representation, results can be further processed into angular representation for compact topographic analysis or into overall scalar estimates for quick assessment of contour disagreement.ResultsDistance deviation method is demonstrated on a multi observer contouring example with complex contour shapes, i.e., with pronounced extremes and void interior. The results are presented using the three proposed methods.ConclusionsThe proposed method can detect and measure contour variation irrespective of contour complexity and number of contour segments, while the obtained results are easy to interpret. It can be used in various situations, regarding the presence of reference contour or multiple test contours.

Hierarchical flower-like Co3−xFexO4 ferrite hollow spheres: facile synthesis and catalysis in the degradation of methylene blue

A facile method is proposed for the synthesis of three-dimensional (3D) flower-like Co3-xFexO4 ferrite (CF) hollow spheres, using SiO2@FeOOH as precursor. The CF hollow spheres are efficient for the catalytic degradation of methylene blue (MB) in the presence of H2O2 at 80 °C. The obtained CF hollow spheres were characterized using transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction, X-ray photo-electron spectroscopy, and N2 adsorption-desorption isotherm measurements. The formation of 3D hierarchical flower-like superstructure was influenced by the relative amount of urea used. As the mole ratio of CoCl2 and urea decreased, the structure of the products was tailored from yolk-like spheres to hollow spheres with different sized void interiors. Moreover, N2 adsorption-desorption isotherm analysis showed that the CF hollow spheres have a large specific surface area (163 m(2) g(-1)) which provided more activity sites. The CF hollow spheres can catalyze the oxidation of MB efficiently. These results indicate that the designed CF hollow spheres exhibit promising capability for the degradation of dyes.

Hollow ZnO/Zn2SiO4/SiO2 sub-microspheres with mesoporous shells: Synthesis, characterization, adsorption and photoluminescence

The multifunctional versatile ZnO/Zn2SiO4/SiO2 hollow microspheres with porous structures on the shells are successfully fabricated by the sequential deposition of amino-functionalized SiO2 and then ZnO layers on the prepared polystyrene (PS) colloidal templates, and the subsequent calcination process. The formation of hollow morphology was confirmed by scanning electron microscope (SEM) and transmission electron microscope (TEM). Nitrogen sorption measurements also verify the presence of the mesoporous structure scattered on the shells. The application of the absorption capacity to remove toxic metal ions in water is performed. Furthermore, the photoluminescence (PL) results indicate that hollow composites prepared in our experiment have excellent optical properties. The origin of various PL bands is discussed as well. The high surface areas, together with void interiors and mesoporous walls make composites an efficient adsorbent and promising platform for optoelectronics and nanomedicine applications.

Comparative structural and functional analysis of two octaheme nitrite reductases from closely related Thioalkalivibrio species

Octaheme nitrite reductase from the haloalkaliphilic bacterium Thioalkalivibrioparadoxus was isolated and characterized. A comparative structural and functional analysis of two homologous octaheme nitrite reductases from closely related Thioalkalivibrio species was performed. It was shown that both enzymes have similar catalytic properties, owing to high structural similarity. Both enzymes are characterized by specific structural features distinguishing them from pentaheme cytochromec nitrite reductases, such as the Tyr-Cys bond in the active site, the hexameric structure resulting in the formation of a void space inside the hexamer, and the product channel that opens into the void interior space of the hexamer. It is suggested that these specific structural features are responsible for the higher nitrite reductase activity, the greater preference for nitrite than for sulfite as a substrate, and the wider pH range of the catalytic activity of octaheme nitrite reductases than of pentaheme homologs. Nucleotide sequence data are available in the GenBank database under the accession number HQ665012.1. Structural data are available in the RCSB Protein Data Bank database under the accession numbers 3SXQ and 3TTB STRUCTURED DIGITAL ABSTRACT: TvPaRandTvPaRbindbyx-ray crystallography(View interaction).

Investigation on mechanism of type IV cracking in P92 steel at 650 °C

Abstract