Central Void Research Articles

Identification of a robust bacterial pyranose oxidase that displays an unusual pH dependence

Pyranose oxidases are valuable biocatalysts, yet only a handful of bacterial pyranose oxidases are known. These bacterial enzymes exhibit noteworthy distinctions from their extensively characterized fungal counterparts, encompassing variations in substrate specificity and structural attributes. Herein a bacterial pyranose oxidase from Oscillatoria princeps (OPOx) was biochemically characterized in detail. In contrast to the fungal pyranose oxidases, OPOx could be well expressed in Escherichia coli as soluble, fully flavinylated and active oxidase. It was found to be highly thermostable (melting temperature >90 ⁰C) and showed activity on glucose, exhibiting an exceptionally low KM value (48 μM). Elucidation of its crystal structure revealed similarities with fungal pyranose oxidases, such as being a tetramer with a large central void leading to a narrow substrate access tunnel. In the active site, the FAD cofactor is covalently bound to a histidine. OPOx displays a relatively narrow pH optimum for activity with a sharp decline at relatively basic pH values which is accompanied with a drastic change in its flavin absorbance spectrum. The pH-dependent switch in flavin absorbance features and oxidase activity was shown to be fully reversible. It is hypothesized that a glutamic acid helps to stabilize the protonated form of the histidine that is tethered to the FAD. OPOx presents itself as a valuable biocatalyst as it is highly robust, well-expressed in E. coli, shows low KM values for monosaccharides and has a peculiar pH dependent “on-off switch”.

Void closure in a pulsed complex plasma in microgravity

A new experimental method for creating void-free complex (dusty) plasmas under microgravity conditions is presented. The method is based on a pulsed operation mode of a four-channel radio frequency generator for plasma sustainment. A dust cloud of micrometer-sized particles can be immersed in the bulk of a low temperature plasma under microgravity conditions. It typically contains a central volume depleted of particles—the void—that prevents the generation of large, continuous clouds. Experiments performed at different neutral gas pressures and discharge volumes during the microgravity phase of a parabolic flight show that the central void is closed completely once the pulsed operation mode is applied. The particle cloud shape and the density distribution within the cloud are practically independent of the pulse period within the investigated parameter range and mainly depend on the overall discharge parameters neutral gas pressure and discharge volume. This indicates that the pulsed operation of the plasma source does not introduce new physical effects on the particles aside from the void closure. The proposed method has great potential for future application in experimental facilities dedicated to fundamental studies of large three-dimensional, homogeneous complex plasma systems in microgravity.

Kirkendall effect-induced uniform stress distribution stabilizes nickel-rich layered oxide cathodes

Nickel-rich layered oxide cathodes promise ultrahigh energy density but is plagued by the mechanical failure of the secondary particle upon (de)lithiation. Existing approaches for alleviating the structural degradation could retard pulverization, yet fail to tune the stress distribution and root out the formation of cracks. Herein, we report a unique strategy to uniformize the stress distribution in secondary particle via Kirkendall effect to stabilize the core region during electrochemical cycling. Exotic metal/metalloid oxides (such as Al2O3 or SiO2) is introduced as the heterogeneous nucleation seeds for the preferential growth of the precursor. The calcination treatment afterwards generates a dopant-rich interior structure with central Kirkendall void, due to the different diffusivity between the exotic element and nickel atom. The resulting cathode material exhibits superior structural and electrochemical reversibility, thus contributing to a high specific energy density (based on cathode) of 660 Wh kg−1 after 500 cycles with a retention rate of 86%. This study suggests that uniformizing stress distribution represents a promising pathway to tackle the structural instability facing nickel-rich layered oxide cathodes.

Strength evaluation of alkali treated Sabai Grass (Eulaliopsis binata) fibers and its reinforced composites

This investigation aims to use Sabai grass fiber as a substitute reinforcement in epoxy-based composite systems, which is environment friendly and performs similarly to other natural fibers. Composite laminates are prepared with treated and untreated Sabai fibers reinforcement layered in different orientations using vacuum resin transfer molding method. Fabricated composite laminates have been evaluated for their mechanical properties (tensile strength, flexural strength, and impact strength). The effect of varying concentrations (3%, 5%, 7%, and 9 wt.%) of NaOH treatment and fiber reinforcement angle on Sabai fiber-reinforced composite laminates on its physical and mechanical properties are experimentally evaluated. The specimen made with 5 wt.% of NaOH-treated has shown maximum tensile properties because of the higher fiber concentration in the composite laminate. The thickness of fibers gets reduced as the central voids contract after the treatment. The treated strand reinforced (0°/0°/0°/0°) composite laminate has maximum tensile (103.15 MPa) and flexural strength (143 MPa). In addition, it has a higher density (1.20 g/cm3) and less porosity contents (0.70%). The untreated reinforcement has a higher impact strength. The adhesion mechanism at the fiber matrix interface has been studied using field emission scanning electron microscopy by analyzing the fiber surface morphology after treatment and in the fractured samples. The correlation of the mechanical properties of the laminate has been discussed with consideration of interfacial adhesion mechanism, fiber pull-outs, and fiber-matrix cracking phenomenon. FTIR analyses confirm the removal of the peak at around 1735 cm−1 that belongs to the acetyl group of hemicellulose attributed to C=O stretching vibration, and the peak at 1253 cm−1 is associated with the lignin, which is in close agreement with chemical analysis.

Bifunctional magnetic nanoparticles with ion imprinting for improving the flow through determination of ultratraces of Cd(II) using magnetic preconcentration.

A novel bifunctional magnetic sorbent with mercapto and amino groups and ion imprinting (MBII) was synthesized using a one-step aqueous sol-gel process for preconcentration and determination of Cd(II) ions. MBII was employed as a microcolumn (MC) filler in a flow-through system coupled to GFAAS. The magnetic properties of the solid allowed microcolumn magnetic solid-phase extraction (MCMSPE) to be performed by simply including a single circular magnet around the MC. This assembly enabled complete attachment of the solid to the MC wall leaving a central void to facilitate higher sample flow rates without blockage or material loss. For comparison, a bifunctional magnetic solid without imprinting (MBNI) was also synthesized and evaluated. Both MBII and MBNI were characterized by FTIR, SEM, EDX, BET and magnetization measurements. The results showed the preservation of the magnetic core, its superparamagnetism and the functional groups in the solid. Batch studies revealed a maximum adsorption capacity for both materials at pH around 6 with equilibrium reached within 5 minutes. The advantages were reflected in the maximum adsorption capacity of MBII, which was found to be 2.5 times greater than that of MBNI. Both adsorbents were compared as MC fillers for dynamic preconcentration in MCMSPE systems. Under optimized conditions, MBNI showed a PCF of 125 and MBII of 250. The higher selectivity of MBII was corroborated by interfering ion studies. The analytical performance parameters for the proposed method using MBII as an adsorbent showed a detection limit of 0.05 ng L-1, a linear range of 2.0-80 ng L-1, an RSD% of 2.2 (n = 7; 20 ng L-1) and a lifetime of more than 300 preconcentration-elution cycles without loss of sensitivity or need for refilling. The method was successfully applied to the determination of trace Cd(II) in osmosis, lake and tap water with recoveries ranging from 98 to 105%. Comparison of these results with those of similar reported methods showed a considerable improvement primarily attributed to the combined effect of MBII's higher retention capacity and its magnetic properties that allowed higher sample flow rates and, thus, enhanced figures of merit.

INVESTIGATION OF THERMODYNAMIC PROPERTIES AND ANISOTROPIC FACTORS OF PERFECT AND DEFECTIVE TUNGSTEN THROUGH CORRELATION WITH ELASTIC CONSTANTS: A MOLECULAR DYNAMICS STUDY

In this study, the thermodynamic properties and anisotropic factors of perfect and defective tungsten were investigated through their correlation with elastic constants. The study examined sound velocities, Debye temperature, minimum thermal conductivity, melting point, and elastic anisotropy factors at various temperatures and pressures. The utilized elastic constants were calculated by molecular dynamics simulations. We used three different interatomic potentials in the simulations involving two embedded atoms and one modified embedded-atom method. The findings indicated that temperature and pressure were positively correlated with anisotropic factors, with increased values leading to an increase in metal anisotropy. Also, defects were found to cause an increase in anisotropy, with a single vacancy having a greater impact on elastic anisotropy compared to a central void in the crystal structure. The study also found that the fundamental thermodynamic characteristics of pure tungsten crystal including density, sound velocities, Debye temperature, and Grüneisen parameter in the ambient conditions for all three potentials were in good agreement with previous experimental and theoretical calculations. The results showed that defective structures displayed the same trend as perfect crystals for elastic constant-related properties. The presence of defects in the crystal caused a decrease in thermodynamic properties at all temperatures and pressures, with the degree of decrease directly correlated with the fraction of crystal defects. The study also found that the minimum thermal conductivity as a key parameter of tungsten showed a downward trend with temperature and upward with pressure.

Engineering Significance of Annular Raft Foundations over Solid Raft FoundationsJ

Abstract: Raft foundations play a pivotal role in distributing structural loads to the underlying soil, thereby ensuring the stability and integrity of various civil engineering structures. The choice between different types of raft foundations, such as solid and annular rafts, significantly impacts the overall performance and durability of a structure. This paper explores the engineering significance of annular raft foundations in comparison to solid raft foundations. The traditional solid raft foundation offers uniform load distribution and settlement control; however, it often encounters challenges when dealing with non-uniform soil profiles, differential settlements, and expansive soils. Annular raft foundations, a relatively innovative approach, address these challenges by featuring a central void within the raft. This void introduces a controlled differential settlement mechanism, enabling the foundation to accommodate non-uniform soil conditions effectively. Moreover, annular rafts offer improved structural performance in regions prone to ground movements, as the central void allows the foundation to adjust to soil displacements more flexibly than a solid raft. The engineering significance of annular rafts extends to their enhanced loadbearing capacity and reduction in material usage compared to solid rafts. The design of annular rafts takes advantage of the arching effect within the void, which enables the foundation to support heavier loads while minimizing the amount of concrete and reinforcement required. This not only contributes to cost savings but also aligns with sustainable construction practices by reducing the environmental impact associated with excessive material consumption.

A biofunctional review of C-reactive protein (CRP) as a mediator of inflammatory and immune responses: differentiating pentameric and modified CRP isoform effects.

C-reactive protein (CRP) is an acute phase, predominantly hepatically synthesized protein, secreted in response to cytokine signaling at sites of tissue injury or infection with the physiological function of acute pro-inflammatory response. Historically, CRP has been classified as a mediator of the innate immune system, acting as a pattern recognition receptor for phosphocholine-containing ligands. For decades, CRP was envisioned as a single, non-glycosylated, multi-subunit protein arranged non-covalently in cyclic symmetry around a central void. Over the past few years, however, CRP has been shown to exist in at least three distinct isoforms: 1.) a pentamer of five identical globular subunits (pCRP), 2.) a modified monomer (mCRP) resulting from a conformational change when subunits are dissociated from the pentamer, and 3.) a transitional isoform where the pentamer remains intact but is partially changed to express mCRP structural characteristics (referred to as pCRP* or mCRPm). The conversion of pCRP into mCRP can occur spontaneously and is observed under commonly used experimental conditions. In careful consideration of experimental design used in published reports of in vitro pro- and anti-inflammatory CRP bioactivities, we herein provide an interpretation of how distinctive CRP isoforms may have affected reported results. We argue that pro-inflammatory amplification mechanisms are consistent with the biofunction of mCRP, while weak anti-inflammatory mechanisms are consistent with pCRP. The interplay of each CRP isoform with specific immune cells (platelets, neutrophils, monocytes, endothelial cells, natural killer cells) and mechanisms of the innate immune system (complement), as well as differences in mCRP and pCRP ligand recognition and effector functions are discussed. This review will serve as a revised understanding of the structure-function relationship between CRP isoforms as related to inflammation and innate immunity mechanisms.

Experimental study on the thermal evolution of silicon defects with zonal characteristics induced by precisely localized irradiation of focused helium ion beams

The thermal evolution of defects introduced in silicon by line scanning with helium ion microscopy was investigated, confirming that the evolution of the defective structure after annealing at 650 °C for 1 h results in a central void channel and a sector ring of cavities surrounding it, located in the amorphous and transition regions of the unannealed pre-irradiated sample, respectively. The variation of defective structures with annealing temperature and ion dose indicates that high temperature is favorable for the formation of void channels and cavities, and the coarsening and recrystallization processes compete in the shaping of a void channel. The total volume of the defective structure is linearly related to the ion dose, while the zoning phenomenon is attributed to the differences in the vacancy amounts within their locations. These results provide direct experimental evidence for the thermal evolution of defects with zonal characteristics induced by precisely localized helium irradiation.

Hexanuclear and octanuclear metal complexes of octadecaazamacrocycle based on diaminocyclohexane and pyridine units

An extended macrocyclic amine L derived from the [6+6] condensation of trans-1,2-diaminocyclohexane and 2,6-diformylpyridine contains 18 nitrogen atoms in its main cycle. All of these atoms can be engaged in the formation of polynuclear complexes with transition metal ions and the macrocycle L is able to bind six Cu(II), Ni(II) or Zn(II) ions within its interior. X-ray crystal structures of these complexes indicate variable coordination numbers of metal ions as well as various conformations adopted by the macrocyclic ligand. In the hexanuclear Cu(II) complex with coordinated nitrate anions Cu(II) ions are hexacoordinate and exhibit highly distorted octahedral geometry, while in analogous complexes with coordinated sulphate anions Cu(II) ions are pentacoordinate of distorted square pyramid geometry. Both complexes are relatively symmetric having (approximate) S6 axis and adopt a circular doughnut shape with a central void not occupied by metal ions. The NMR spectrum of the zinc(II) derivative also reflects the symmetrical coordination. In contrast, the macrocycle L is squeezed and less symmetric in the octanuclear chloride derivative where two additional Cu(II) ions are linked to a hexanuclear macrocyclic unit via chloride bridges. The macrocycle is also squeezed in the hexanuclear Ni(II) complex containing metal ions of approximate octahedral geometry. In all three Cu(II) complexes the macrocycle provides N3 donor set for each metal ion, while in the Ni(II) complex alternating N3 and N4 environments of the metal ions are observed.

URBAN LEFT-OVER SPACE: CHARACTERISTIC IDENTIFICATION OF THE IN-BETWEEN SPACES IN RIVERSIDE SETTLEMENT (CASE STUDY: MARTAPURA RIVERSIDE SETTLEMENT AT SASIRANGAN VILLAGE)

The identity of "Thousand Rivers' City" makes the river have the meaning of identity and life orientation. River-oriented life inflicted an adaptive behavior called budaya sungai. However, the globalization process has caused a shift from river-oriented to land-oriented and creates heterogeneity in riverside settlements. Creating variations of typology such as atas sungai, bantaran sungai, and tepian sungai. The emergence of these typologies indirectly creates urban leftover space as a transition called the in-between space. This research aims to identify the characteristic of the in-between spaces in riverside settlements so that the space does not become negative and can be utilized to meet the living needs of people who live in riverside settlements. The research used explanatory sequential design methods, based on the quantitative phase, a figure-ground analysis identified curvilinear as the typological patterns and homogenous as textural patterns of the riverside settlement. The map shows a high-density level of solids with no central open system void. Based on the qualitative phase, all in-between spaces have linear patterns and are mostly made of wood materials. 76.47% of enclosures are open but in contrast to land use which is mostly private. 2 out of 17 in-between spaces could not be characterized.

Poly(ethylene imine) stabilized metal hydroxide nanoaggregates in reverse microemulsion system enabling synthesis of hollow silica catalytic nanoreactors as highly efficient semihydrogenation catalysts

In this work, we report a generic method of reverse microemulsion for syntheses of uniform and well-dispersed hollow porous silica nanospheres with metal (oxide) nanoparticles inside their cavities (MxOy@HPSNs or M@HPSNs), where the water phase consists of poly(ethylene imine) stabilized metal hydroxide nanoaggregates. During silica deposition, the mentioned nanoaggregates function as void templates as well as a platform to deliver catalytic functionality into voids. The subsequent calcination simultaneously gives hollow nanostructures and metal (oxide) nanoparticles inside central voids. The method applies to the metals that have hydroxide precipitates at basic conditions, and is suitable for most of catalytically active metals. As a demonstration, Pd@HPSNs illustrate high catalytic efficiency for selective hydrogenation of phenylacetylene at ambient H2 pressure, and the enhancement could be assigned to the effect of void confinement.

A comprehensive assessment of endogenous bubbles properties in fluidized bed reactors via X-ray imaging

Properties of endogenous bubbles released during the devolatilization of a single biomass particle under inert conditions have been investigated by means of advanced X-ray imaging techniques. Distribution of void fraction showed that endogenous bubbles structure resembles that of classic bubbles observed in fluidized bed reactors, constituted by a cloud, wake and a central void region. A value of about 0.25 for the wake fraction has been obtained from experiments, which is in agreement with literature data for Geldart B particles. Volume of cloud region as a function of relative bubble velocity was generally well-described by the theoretical models of Davidson and Murray, showing effective recirculation of volatile matter around the bubble. Moreover, lack of mixing between bubbles and emulsion phase, as predicted by the Davidson's theory for classic bubbles, confirmed the bypass phenomenon observed for endogenous bubbles in previous studies. Owing to the non-invasive nature of the X-ray technique employed, it was possible to estimate the main features of endogenous bubbles with high accuracy. Knowledge provided in this work can be easily implemented to improve modelling of fluidized bed reactors applied to advanced thermochemical conversions, such as gasification and pyrolysis, of biomass and waste materials. • Devolatilization of biomass in fluidized beds generates endogenous bubbles • Advanced X-ray imaging provided comprehensive assessment of endogenous bubbles • Bubbles void fraction distribution is obtained by means of the Beer-Lambert law • Endogenous bubbles consist of a wake, cloud, and central gas-rich region • Endogenous bubbles strongly resemble traditional bubbles in bubbling regime

Pt nanoparticles confined in hollow silica nanoreactors as highly efficient catalysts for semihydrogenations of alkynes at atmospheric H2 pressure.

In this work, Pt nanoparticles encapsulated hollow porous silica nanoreactors (Pt@HPSNs) was synthesized in one-pot by a reverse microemulsion system, and they exhibit good catalytic efficiency and stability for semihydrogenations of alkynes. The key design concept is to form Pt hydroxide nanoparticles mixed poly(ethyleneimine) nano-aggregates in water droplets, which further functions as seeds for silica deposition and the void templates to form the central voids. The Pt@HPSNs illustrate a wide adaptability for semihydrogenations of a series of terminal alkynes to the corresponding alkenes at mild reaction conditions, and demonstrate high yields of styrene for semihydrogenation of phenylacetylene, showing good catalytic efficiency for hydrogenation of phenylacetylene to styrene at atmospheric H2 pressure. The enhanced catalytic performance of Pt@HPSNs are ascribed to their hollow porous nanostructures, where the confinement of Pt nanoparticles in voids increase the structural stability and the confinement effect may increase the collision of reactants and Pt, resulting in improved catalytic efficiency.

Au–CuxOy Nanoparticles Encapsulated in Hollow Porous Silica Nanospheres as Efficient Catalysts for Nitrophenol Reduction

In this work, Au–CuxOy hybrid nanoparticle-encapsulated hollow porous silica nanospheres (Au–CuxOy in HPSNs) were synthesized by immobilizing the catalytic functionality inside hollow cavities by using polyethyleneimine in a reverse microemulsion system as the void template as well as the platform to deliver the metals into the central voids. Compared with individual Au in HPSNs and CuxOy in HPSNs, the prepared Au–CuxOy in HPSNs demonstrate significantly improved catalytic efficiency for the reduction of various nitrophenols with NaBH4. At the molar ratio of 4-nitrophenol/Au of 30/1, the 4-nitrophenol conversions over Au–CuxOy in HPSNs reach 100% within 5.5 min, and catalytic efficiency is maintained during five cycles of catalytic reactions. The enhanced performance can be ascribed to the synergistic effect between Au and CuxOy, and the protection of silica shells to inner Au–CuxOy improve their catalytic stability.

Void fraction measurement and calculation model of vertical upward co-current air–water slug flow

The focus of this paper is on the measurement and calculation model of void fraction for the vertical upward co-current air–water slug flow in a circular tube of 15 mm inner diameter. High-speed photography and optical probes were utilized, with water superficial velocity ranging from 0.089 to 0.65 m·s −1 and gas superficial velocity ranging from 0.049 to 0.65 m·s −1 . A new void fraction model based on the local parameters was proposed, disposing the slug flow as a combination of Taylor bubbles and liquid slugs. In the Taylor bubble region, correction factors of liquid film thickness C δ and nose shape C Z* were proposed to calculate α TB . In the liquid slug region, the radial void fraction distribution profiles were obtained to calculate α LS , by employing the image processing technique based on supervised machine learning. Results showed that the void fraction proportion in Taylor bubbles occupied crucial contribution to the overall void fraction. Multiple types of void fraction predictive correlations were assessed using the present data. The performance of the Schmidt model was optimal, while some models for slug flow performed not outstanding. Additionally, a predictive correlation was correlated between the central local void fraction and the cross-sectional averaged void fraction, as a straightforward form of the void fraction calculation model. The predictive correlation showed a good agreement with the present experimental data, as well as the data of Olerni et al. , indicating that the new model was effective and applicable under the slug flow conditions.

Gravitational entropy in Szekeres class I models

Developing a self-consistent notion of gravitational entropy in the context of cosmological structure formation has been so far an elusive task. Various theoretical proposals have been presented, initially based on Penrose’s Weyl curvature hypothesis, and variations of it. A more recent proposal by Clifton, Ellis, and Tavakol (CET) considered a novel approach by defining such entropy from a Gibbs equation constructed from an effective stress–energy tensor that emerges from the ‘square root’ algebraic decomposition of the Bel–Robinson tensor, the simplest divergence-less tensor related to the Weyl tensor. Since, so far all gravitational entropy proposals have been applied to highly restrictive and symmetric spacetimes, we probe in this paper the CET proposal for a class of much less idealized spacetimes (the Szekeres class I models) capable of describing the joint evolution of arrays of arbitrary number of structures: overdensities and voids, all placed on selected spatial locations in an asymptotic ΛCDM background. By using suitable covariant variables and their fluctuations, we find the necessary and sufficient conditions for a positive CET entropy production to be a negative sign of the product of the density and Hubble expansion fluctuations. To examine the viability of this theoretical result we examine numerically the CET entropy production for two elongated over dense regions surrounding a central spheroidal void, all evolving jointly from initial linear perturbations at the last scattering era into present day Mpc-size CDM structures. We show that CET entropy production is positive for all times after last scattering at the precise spatial locations where structure growth occurs and where the exact density growing mode is dominant. The present paper provides the least idealized (and most physically robust) probe of a gravitational entropy proposal in the context of structure formation.

Pt-NixOy heteroaggregate nanoparticles confined in hollow mesoporous silica nanospheres for enhanced hydrolysis of ammonia borane

In this work, Pt-NixOy heteroaggragate nanoparticles confined in hollow mesoporous silica nanospheres (Pt-NixOy@HMSNs) are synthesized in one-pot, which features Pt-NixOy hybrid nanoparticles inside hollow cavities of mesoporous silica nanospheres. Through adjusting the ratios of Pt2+/Ni2+ in micelles, Pt-NixOy@HMSNs with different Pt/Ni ratios are synthesized. The obtained materials were tested for hydrolysis of ammonia borane with detailed kinetic studies. Compared to Pt@HMSNs and Ni@HMSNs, Pt4-(NixOy)1/x@HMSNs show the enhanced performance in AB hydrolysis. The catalytic activity improvement is ascribed to the synergistic effect of Pt-NixOy and the void confinement, where the interfaces of Pt-NixOy greatly enhance the hydrolysis activity and the confinement of functional nanoparticles inside the central voids increases their structural and catalytic stability.

Gapless-REMA100: A gapless 100-m reference elevation model of Antarctica with voids filled by multi-source DEMs

The digital elevation model (DEM) of Antarctica is a fundamental dataset for a wide range of glaciological applications, from fieldwork planning to ice sheet dynamics analysis. The DEM data at high spatial resolution provides a more detailed depiction of the topography. The reference elevation model of Antarctica (REMA) mosaic is a recently released high-resolution Antarctic DEM product with a high absolute vertical accuracy of 1 m or less. The REMA mosaic was generated using an optical photogrammetry technique and can reflect the surface elevation of the ice sheet. However, the REMA mosaic has a large number of data voids of various spatial sizes, which affects its wide glaciological application. Therefore, we propose the generation of a gapless 100-m reference elevation model of Antarctica (Gapless-REMA100) with the voids filled by combining multi-source DEMs. In this study, the best-fit fill DEMs were automatically selected between almost all available circum-Antarctica or regional DEMs. Targeting numerous voids in large areas of the 100-m REMA mosaic, we propose a novel hierarchical delta surface method for interpolating the created delta surface to achieve an efficient, unbiased, and continuous filled surface. High-precision laser altimetry data were used to evaluate the vertical accuracy of the REMA mosaic. To eliminate the influence of the temporal surface elevation change and penetration depth between the DEM and laser altimetry data, we developed a new local contrast evaluation method by calculating the vertical accuracy of the equal-area buffer as a control to that of the center void. The experimental results with the Ice, Cloud and Land elevation Satellite-2 (ICESat-2) laser altimetry data validate that the filled 100-m REMA mosaic of voids can reach an elevation accuracy similar to that of the original REMA dataset for the west and east Antarctic ice sheet as well as the entire continent. In the Antarctic Peninsula area, the vertical accuracy of the filled REMA mosaic by the proposed method is superior to that of the officially released version of the Polar Geospatial Center. This is the first time that a gapless, seamless, and accurate 100-m REMA mosaic has been released which has the potential to be extensively used in glaciological applications. The proposed methods can also be used in void-filling of different types of DEM products and their elevation accuracy evaluations.

Re-examination of several key aspects of an earlier model analysis on cylinder hydrodynamics under self-gravity

In several astrophysical and cosmological contexts, long dynamic filamentary structures emerge ubiquitously in observations and numerical simulations. For theoretical understanding, such filaments may be idealized as self-similar hydrodynamic cylinders under self-gravity of infinite length with axisymmetry and axial uniformity. We review and present analytical results of such a self-similar dynamic cylinder, including asymptotic solutions both towards the symmetry axis and at large radii, asymptotic solution just outside a dynamically expanding central void cylinder and a dimensional energy conservation equation. We introduce a velocity potential and derive cylindrical Bernoulli relations in similarity forms. Besides, the sonic critical curve (SCC) for γ=1 is treated and examined. A thorough classification of the SCC of this kind is done. Most importantly, intrinsic invariance of the general polytropic dynamic cylinder emerges when γ=1, which builds connections among individual self-similar solutions of the same kind. We re-examine several key aspects of the study by Holden et al. (2009) and find that some of their results and conclusions to be misleading and incomplete. We pinpoint the sources of their errors and offer our correct results. Finally, we numerically compute self-similar solutions with a central free-fall behaviour as well as solutions that go across either the upper or the lower branch of the SCC once and show the corresponding global solution profiles.