Empty Structure Research Articles

Selective Laser Melting (SLM) Technology for Jewelry Design and Its Application

With the rapid development of 3D printing technology, applications in jewelry design and the other fields are also increasing. Selective Laser Melting (SLM) technology is also one of the important ways to make metal jewelry by one-time printing. In terms of jewelry design, it can print almost any shape of works, including empty shell structure, movable structure and special structure. However, there are still many design principles that need to pay attention to in the application of SLM technology in jewelry design. For example support structure design, internal structure design, mold polishing difficulty and post-processing design. This paper focuses on the support structure design and movable structure design, highlighting the great impact of SLM technology on jewelry manufacturing and processing process. Based on this technology, jewelry design and related exploration can not only meet the aesthetic needs of traditional jewelry, but also reflect the technical advantages of 3D printing in manufacturing, and can meet the actual needs in production more efficiently.

Theoretical study of the self-preservation effect in CF4 gas hydrates

This work studies thermodynamic properties of CF4 gas hydrates using the statistical thermodynamic model of inclusion compounds, developed in our laboratory and closely associated with Quasiharmonic Lattice Dynamic (QLD) and Molecular Dynamic Simulation (MD). Thermal expansion coefficient of CF4 gas hydrate is calculated at different hydrate composition. The thermal expansion coefficient is shown to be lesser than the thermal expansion coefficient of CH4 hydrates, but larger than ice Ih, that still indicates the presence of the self-preservation effect. The thermal expansion coefficient is very sensitive to the composition of the hydrate and can vary in a wide range. The same is true for the hydrate lattice parameter as well; it is shown that at certain conditions it may be even less than for hypothetical empty hydrate structure. The self-preservation effect may be applied for many aspects related to CF4 compound, especially for storage and transportation purposes in producing semiconductor electronics.

First Report of aacC5-aadA7Δ4 Gene Cassette Array and Phage Tail Tape Measure Protein on Class 1 Integrons of Campylobacter Species Isolated from Animal and Human Sources in Egypt.

Simple SummaryCampylobacter species are among the major causes of bacterial foodborne infections. Here, we investigate, for the first time, class 1 integrons and associated gene cassettes among pan drug-resistant (PDR), extensively drug-resistant (XDR), and multidrug-resistant (MDR) Campylobacter species isolated from livestock animals and humans in Egypt. Our results revealed alarming PDR (2.55%) and inordinate XDR (68.94%) and MDR (28.5%) Campylobacter isolates. None of the examined isolates were pan-susceptible. The existence of a novel gene cassette array, namely aacC5-aadA7Δ4 and a putative phage tail tape measure protein on class 1 integrons of Campylobacter species is the most highlighted novelty of the current study. Evidence from this study showed the possibility of Campylobacter–bacteriophage interactions as well as treatment failure in animals and humans due to horizontal gene transfer mediated by class 1 integrons.Campylobacter species are common commensals in the gastrointestinal tract of livestock animals; thus, animal-to-human transmission occurs frequently. We investigated for the first time, class 1 integrons and associated gene cassettes among pan drug-resistant (PDR), extensively drug-resistant (XDR), and multidrug-resistant (MDR) Campylobacter species isolated from livestock animals and humans in Egypt. Campylobacter species were detected in 58.11% of the analyzed chicken samples represented as 67.53% Campylobacter jejuni (C. jejuni) and 32.47% Campylobacter coli (C. coli). C. jejuni isolates were reported in 51.42%, 74.28%, and 66.67% of examined minced meat, raw milk, and human stool samples, respectively. Variable antimicrobial resistance phenotypes; PDR (2.55%), XDR (68.94%), and MDR (28.5%) campylobacters were reported. Molecular analysis revealed that 97.36% of examined campylobacters were integrase gene-positive; all harbored the class 1 integrons, except one possessed an empty integron structure. DNA sequence analysis revealed the predominance of aadA (81.08%) and dfrA (67.56%) alleles accounting for resistance to aminoglycosides and trimethoprim, respectively. This is the first report of aacC5-aadA7Δ4 gene cassette array and a putative phage tail tape measure protein on class 1 integrons of Campylobacter isolates. Evidence from this study showed the possibility of Campylobacter–bacteriophage interactions and treatment failure in animals and humans due to horizontal gene transfer mediated by class 1 integrons.

Low-velocity impact response of tube-reinforced honeycomb sandwich structure

To improve the load carrying capacity, structural stiffness, and impact resistance of a honeycomb sandwich structure, the honeycomb holes are filled with metallic tubes. Experimentally and numerically studies were carried out on the drop weight impact response of the tube-reinforced honeycomb sandwich structure. The results show that the stiffness and peak load of the honeycomb sandwich structure were increased by the metallic tube filler. The addition of tube filler made the Mises stress and deformation distribution of the front and back face-sheets more uniform. In addition, the tube-reinforced structure absorbed the impact energy more quickly than the empty honeycomb sandwich structure and the front face-sheet deformation was markedly reduced by tube reinforcement. The peak load and contact energy (the energy absorbed by the local deformation of sandwich structures) were predicted theoretically for both empty honeycomb sandwich structure and tube-reinforced honeycomb sandwich structure. The finite element parametric study shown that, compared with the empty honeycomb sandwich structure, the maximum deflections of the front and back face-sheets of the globally filled tube-reinforced honeycomb sandwich structure were reduced by 18.6% and 36.4% respectively. The tube-reinforced honeycomb sandwich structure is a promising structure for weight sensitive applications owing to its improved load carrying capacity and impact resistance.

Mesoporous Metal-Organic Framework MIL-101 at High Pressure.

The chromium terephthalate MIL-101 is a mesoporous metal-organic framework (MOF) with unprecedented adsorption capacities due to the presence of giant pores. The application of an external pressure can effectively modify the open structure of MOFs and its interaction with guest molecules. In this work, we study MIL-101 under pressure by synchrotron X-ray diffraction and infrared (IR) spectroscopy with several pressure transmitting media (PTM). Our experimental results clearly show that when a solid medium as NaCl is employed, an irreversible amorphization of the empty structure occurs at about 0.4 GPa. Using a fluid PTM, as Nujol or high-viscosity silicone oil, results in a slight lattice expansion and a strong modification of the peak frequency and shape of the MOF hydroxyl vibration below 0.1 GPa. Moreover, the framework stability is enhanced under pressure with the amorphization onset shifted to about 7 GPa. This coherent set of results points out the insertion of the fluid inside the MIL-101 pores. Above 7 GPa, concomitantly to the nucleation of the amorphous phase, we observe a peculiar medium-dependent lattice expansion. The behavior of the OH stretching vibrations under pressure is profoundly affected by the presence of the guest fluid, showing that OH bonds are sensitive vibrational probes of the host-guest interactions. The present study demonstrates that even a polydimethylsiloxane silicone oil, although highly viscous, can be effectively inserted into the MIL-101 pores at a pressure below 0.2 GPa. High pressure can thus promote the incorporation of large polymers in mesoporous MOFs.

Synthesis of New Hollow Nanocomposite Photocatalysts: Sunlight Applications for Removal of Gaseous Organic Pollutants

ABSTRACT Synthesis of novel sunlight-driven hollow nano-composite photocatalysts has been considered as a future innovation technology to address air pollution remediation. The present work deals with the primary Pt-doped/TiO2 hollow nano-sized photocatalysts using carbon colloidal spheres as a sacrificial hard template. Then Cu2+ and Cd2+ as a co-doping operator were introduced, which balanced out the empty structure at higher temperature and controlled the Pt oxidation process. Here, the generation of sulfuric hollow of CuS/Pt–TiO2 and CuS-CdS/Pt–TiO2 via thermal treatment with H2S at 180∘C for 12h was performed as a new technique. The morphological structure of novel photocatalysts was characterized and their ability to decompose the isopropanol gas under solar irradiation was investigated; which is about 20 times higher than that of the conventional catalyst TiO2–P25. This presents for the first time one of the best TiO2 based photonanocatalysts under solar or visible light for promising environmental and industrial applications.

Out-of-plane crushing response of aluminum honeycombs in-situ filled with graphene-reinforced polyurethane foam

This work reports the out-of-plane crushing response of aluminum honeycomb (HC) filled with polyurethane (PU) foams. For the filling of the HC, two types of PU foams were manufactured: unreinforced PU (UR/PU) foam and PU foam reinforced (GR/PU) with reduced graphene oxide (rGO) flakes. In this investigation, the static and low velocity impact compressive tests were performed on the separate constituents (UR/PU foam, GR/PU foam and empty HC) and their combinations (UR/PU foam-filled HC and GR/PU foam-filled HC). By the addition of 0.02% rGO flakes, to UR/PU, an increase (over 41%) of the strength and energy absorption properties was obtained. Moreover, due to the interaction effect, the foam-filled HC composite highlights better properties (up to 61%) than the empty HC structure. Further, it has been observed that exposure of the specimens to ultraviolet (UV) radiation do not change the foam density, but their properties increase by up to 30%. Finally, it was noticed that the in-situ foam-filled HC manufacturing technique is clearly superior to the ex-situ method, while the foam material dictates the filled HC collapse mechanisms considerably.

Illuminating the Mechanism of MHC-I Folding and Antigen Repertoire Selection Using Deep Mutational Scanning and Biophysical Studies

Abstract Chaperones Tapasin and TAP-binding protein related (TAPBPR) perform the important functions of stabilizing nascent MHC-I molecules (chaperoning), and selecting high affinity peptide cargo in the MHC-I groove (editing). While X-ray and cryoEM snapshots of MHC-I molecules prepared in complex with TAPBPR and Tapasin, respectively, have provided important insights into the empty MHC-I groove structure, the molecular mechanism through which these chaperones influence the selection of specific amino acid sequences remains incompletely characterized. Of particular importance is a 16 aa loop region in TAPBPR (corresponding to 11 residues in the sequence of Tapasin), which has been suggested to actively compete with incoming peptides by forming direct contacts with the F-pocket of the empty MHC-I groove. Using a deep mutational scanning functional analysis of TAPBPR, we find that important residues for its chaperoning activity are located on the major interaction surfaces with nascent MHC-I molecules, excluding the loop. However, interactions with properly conformed molecules toward editing of their peptide cargo are influenced by loop mutations, in an MHC-I allele- and peptide-dependent manner, as shown in MHC-I tetramer staining experiments using a TAPBPR library expressed on the surface of yeast. Detailed biophysical characterization by NMR and ITC reveal that the loop does not interact with the empty MHC-I groove to compete with incoming peptides, but instead promotes peptide loading by acting as a kinetic “trap”. Our results suggest that, by utilizing a longer loop, TAPBPR lowers the affinity requirements for peptide selection relative to Tapasin to promote loading under conditions of reduced peptide concentration.

Learning Densities in Feature Space for Reliable Segmentation of Indoor Scenes

Deep learning has enabled remarkable advances in scene understanding, particularly in semantic segmentation tasks. Yet, current state of the art approaches are limited to a closed set of classes, and fail when facing novel elements, also known as out of distribution (OoD) data. This is a problem as autonomous agents will inevitably come across a wide range of objects, all of which cannot be included during training. We propose a novel method to distinguish any object (foreground) from empty building structure (background) in indoor environments. We use normalizing flow to estimate the probability distribution of high-dimensional background descriptors. Foreground objects are therefore detected as areas in an image for which the descriptors are unlikely given the background distribution. As our method does not explicitly learn the representation of individual objects, its performance generalizes well outside of the training examples. Our model results in an innovative solution to reliably segment foreground from background in indoor scenes, which opens the way to a safer deployment of robots in human environments.

“There are significant differences…”: The secret life of existential there in academic writing

While numerous interactive aspects of academic writing have attracted attention in recent years, one common feature which has escaped scrutiny is “existential there” (as in “there are significant differences”). Based on a corpus of 80 research articles from four disciplines, this study explores the ‘secret life’ of this construction, revealing how academic writers use it to organise their arguments and persuade peers of their claims. In contrast to the style guides which regard existential there as an “empty structure” to be avoided, our data show that academic authors make considerable use of it across different sections of the research article to achieve their persuasive purposes. We also discuss differences in how writers in different disciplines favour diverse accompanying head nouns to foreground the particular aspect of information their readers are likely to find most familiar and persuasive. We conclude that existential there is a key feature in the academic author's rhetorical toolbox, allowing them to build interaction with readers and claim credit for their ideas.

Gain and Bandwidth Improvement of Empty Substrate Integrated Waveguide H-plane Horn Antenna at W-band

A high-gain broadband empty substrate integrated waveguide (ESIW) H-plane horn antenna constructed by four low-cost printed circuit board (PCB) layers is proposed in this paper. The empty structure is fabricated by using high-precision laser engraving technology. A slotted rectangular dielectric load (SRDL) is introduced by simply extending the substrates, resulting a 4-dB gain enhancement and a 31% bandwidth improvement. The proposed antenna gives a measured realized gain at 14.5-dBi level with a relative impedance bandwidth larger than 19.6% (|S11| ≤ − 10 dB). The proposed antenna features the merits of low cost, high gain, and broad bandwidth.

Computational analysis of vibrational spectrum and hydrogen bonds of ice XVII

Based on first-principles density functional theory, we investigated the relationship between the vibrational normal modes and the spectrum of the newest laboratory-prepared ice phase, an empty clathrate hydrate structure from gas hydrate named ice XVII. A 48-molecule supercell was designed to mimic the hydrogen-disordered structure. Despite its much lower density than ice Ih, its phonon density of states shows features very similar to those of that phase. In our previous studies of ice Ic and ice XIV, we found two basic hydrogen bond vibrational modes in these hydrogen-ordered ice phases, which contribute two sharp hydrogen bond peaks in the translation region. In this study, we found that this rule also holds in the hydrogen-disordered phase ice XVII. A water molecule vibrating along its angle bisector possesses strong energy, because this vibrational mode involves oscillation against four bonded neighbors. In contrast, a water molecule vibrating perpendicular to its angle bisector has low energy because this mode involves only two of the molecule’s hydrogen bonds. This is an evidence in hydrogen-disordered ice and strengthens our proposal that the existence of two basic hydrogen bond vibrational modes is a general rule among ice family.

Analysis of structures subjected to crowd loads

The movement of people on any structure induces dynamic crowd load. The enthusiastic potential behavior of people from overwhelming happiness in concert, shows etc. on structures such as stadiums, auditorium, grandstands, bridges, malls and convention centers causes synchronized rhythmic movements. Resonance between forcing frequency and one or more natural frequencies of the structure resulting from human-structure synchronization leads to strong vibrations. Such vibrations not only affect structural stability, but also create discomfort among people. Pedestrian induced lateral vibration of Millennium Bridge, London is a classic example for the same. Crowd loads impose vertical as well as horizontal loads on the structure. Both these loads induce vibrations in corresponding directions. Beyond an acceptable limit of vibration level, people may feel uncomfortable. If there is a mode of low natural frequency, even a significantly low forcing frequency can lead to strong vibrations, which in turn may cause panic. The present research focuses on analysis of a simply supported slab strip subjected to crowd load. The crowd-structure interaction is analytically modelled and the modal parameters and the response of the occupied structure are determined. Furthermore, the effect of various parameters such as crowd size, crowd location and crowd activity on the behavior of occupied structure is studied. The comfort level of the people on the structure is also estimated. It is observed that crowd parameters affect the behavior of the system as well as the comfort level of the occupants. It is further seen that the trend of variation of natural frequency of the occupied structure with variation in crowd properties changes with change in the empty structure properties.

Compact Microstrip to Empty Substrate-Integrated Coaxial Line Transition

Substrate-integrated waveguides (SIWs) are increasingly being used due to their capability of combining the advantages of planar circuits and traditional waveguides. The development of empty SIWs has substantially reduced the related insertion losses, since waves propagate through air instead of propagating through a lossy dielectric medium. Recently, a new empty coaxial structure, completely built with printed circuit boards and integrated in a substrate, has been proposed. It has been named empty substrate-integrated coaxial line (ESICL). The resulting coaxial line has low cost, easy manufacturing, low radiation, low losses, high-quality factor, and nondispersive. A transition from grounded coplanar waveguide to ESICL already exists. In this letter, a transition from microstrip to ESICL is presented for the first time. In order to demonstrate its feasibility, a back-to-back structure and a bandpass filter have been manufactured and measured.

Plastic collapse and energy absorption of empty circular aluminum tube under transverse quasi-static loading

This paper presents an experimental investigation on plastic collapse and energy absorption of empty circular aluminum tubes under quasi-static transverse loading. Tubular structures being a critical demand as material saving, high energy absorption and good strength characteristics were of major concerns due to its wall thinness, and so, its various diameter-to-thickness (D/t) ratios and span lengths. Studies found that empty circular Al-tube structure subjected to transverse standard three-point bending loading undergone three plastic deformation phases, starting with crumpling phase, crumpling and buckling phase, and lastly the structural collapse. The results found that energy absorption of empty aluminum tubes for a constant D/t ratio decreases as span length. On the contrary, the energy absorption of empty aluminum tubes for a given constant span length increases with the increase in D/t ratio.

Hepatitis A Virus Capsid Structure.

Hepatitis A virus (HAV) has been enigmatic, evading detailed structural analysis for many years. Its recently determined high-resolution structure revealed an angular surface without the indentations often characteristic of receptor-binding sites. The viral protein 1 (VP1) β-barrel shows no sign of a pocket factor and the amino terminus of VP2 displays a "domain swap" across the pentamer interface, as in a subset of mammalian picornaviruses and insect picorna-like viruses. Structure-based phylogeny confirms this placement. These differences suggest an uncoating mechanism distinct from that of enteroviruses. An empty capsid structure reveals internal differences in VP0 and the VP1 amino terminus connected with particle maturation. An HAV/Fab complex structure, in which the antigen-binding fragment (Fab) appears to act as a receptor-mimic, clarifies some historical epitope mapping data, but some remain difficult to reconcile. We still have little idea of the structural features of enveloped HAV particles.

A framework for quantification of human-structure interaction in vertical direction

In lightweight structures, there is increasing evidence of the existence of interaction between pedestrians and structures, now commonly termed pedestrian-structure interaction. The presence of a walker can alter the dynamic characteristics of the human-structure system compared with those inherent to the empty structure. Conversely, the response of the structure can influence human behaviour and hence alter the applied loading. In the past, most effort on determining the imparted footfall-induced vertical forces to the walking surface has been conducted using rigid, non-flexible surfaces such as treadmills. However, should the walking surface be vibrating, the characteristics of human walking could change to maximize comfort. Knowledge of pedestrian-structure interaction effects is currently limited, and it is often quoted as a reason for our inability to predict vibration response accurately. This work aims to quantify the magnitude of human-structure interaction through an experimental-numerical programme on a full-scale lively footbridge. An insole pressure measurement system was used to measure the human-imparted force on both rigid and lively surfaces. Test subjects, walking at different pacing frequencies, took part in the test programme to infer the existence of the two forms of human-structure interaction. Parametric statistical hypothesis testing provides evidence on the existence of human-structure interaction. In addition, a non-parametric test (Monte Carlo simulation) is employed to quantify the effects of numerical model error on the identified human-structure interaction forms. It is concluded that human-structure interaction is an important phenomenon that should be considered in the design and assessment of vibration-sensitive structures.

A description of hydroquinone clathrates using molecular dynamics: Molecular model and crystalline structures for CH4 and CO2 guests.

The crystalline structure of hydroquinone clathrates has been studied using molecular dynamics. A flexible non-polarizable all-atom molecular model, based on the original Optimized Potentials for Liquid Simulations force field with recalculated point electric charges, has been used to describe the hydroquinone molecule, and the crystalline solid structure of the α native phase has been analyzed. Then, the β clathrates have been studied, considering CO2 and CH4 as guest molecules, and also the empty clathrate structure. In all cases, the lattice parameters obtained through molecular simulation show excellent agreement with reported experimental values, showing that the molecular model selected is able to reproduce both the native crystalline phase and also the clathrate structures. In addition, the process of clathrate guest molecule release upon heating has been characterized, and the simulations show a good correspondence with the very recent experimental trends observed for both guest molecules analyzed.

Near-infrared optical characteristics of composite Ag-porous Si dielectric film for solar devices

Ag-porous Si (Ag-pSi) composite as metallo-dielectric based periodical lattice nanostructure is proposed and studied to improve the light efficiency in such structure in near-infrared range of 750–3000 nm. To achieve this, Finite-Differential Time-Domain (FDTD) implements were applied in analyzing the effects of number of layers (nLs) as well as porosity on optical characteristics of reflection, transmission and absorption using “FDTD solutions”. Perfectly matched layers (PML) and periodic boundary conditions (PBC) were selected as suitable boundaries for this simulation. The results revealed that these highlighted optical properties through the composite are influenced by variation in the nLs and porosity in near-infrared wavelengths. The reflection and transmission spectra presented contrasting patterns. Optimum transmission was attained at 80% porosity with the thickness higher than 500 nm. For the composite Ag-pSi, all the peaks found in these optical properties tended towards higher wavelengths as compared to the case of the composite Ag-Air which had an empty structure. The optimum absorption was improved by 10% with the incorporation of pSi into the Ag material. Therefore, the enhancement of optical properties in this proposed design can be achieved by controlling both the nLs and porosity.

Optimization of honeycomb strength assignment for a composite energy-absorbing structure

This study proposes a new composite structure to promote energy absorption capability of railway vehicles by integrating characteristics of a thin-walled steel structure and aluminum honeycomb fillers. Non-linear explicit code LS_DYNA3D(971) was utilized in building detailed finite element models, which were also validated by previous test data. Considering the expensive selling price, complicated fabricating technology and low production rate of high strength honeycomb, honeycombs with appropriate strength should be selected to fill in the steel structure. Therefore, scientific sampling points were chosen from the design space using Box-Behnken design method. Analysis of variance was performed in order to explore the effects of distributed honeycomb strength in four levels on crashworthiness indicators. Response surface methodology (RSM) was well applied to perform both parametric analysis and multiobjective optimization for searching the optimal configurations. Here, two different criterion were conducted in optimization process by adopting desirability approach. It was find that the composite structure with high strength honeycombs in level-1 and level-2 and relatively low strength honeycombs in level-3 and level-4 are preferable for use. Comparing with the empty steel structure, the optimal EA capacity is promoted by 35.32% in criterion 1 and 34.35% in criterion 2, being able to bear the condition with crashing speed of 36 km/h and impacting mass of 55.3 t. It illustrates that the new composite structures can be recommended as excellent crashworthy devices.