Ac Layers Research Articles

Influence of bonding condition of different interfaces on the mechanical responses and failure mode of asphalt pavement

In this study, a finite element model was established to compute the responses of asphalt pavement with various bonding conditions between the asphalt concrete layers (AC-AC interface) and between the asphalt concrete layer and base (AC-Base interface). The influence of bonding conditions of different interfaces on failure mode of asphalt pavement was discussed. The results indicated that poor bonding condition would increase longitudinal tensile strain at the bottom of the AC layers and vertical compressive strain at the top of subgrade, and the negative effects of two interfaces on pavement would enhance each other. It was observed that insufficient bonding strength would reduce the predicted life of pavement and, more importantly, debonding of AC-AC interface or two interfaces simultaneously would change pavement failure mode. Additionally, it should be noted that the fully-unbonded condition of AC-AC interface would affect the critical location for crack initiation in AC layers.

Constructing Dual-Transport Pathways by Incorporating Beaded Nanofillers in Mixed Matrix Membranes for Efficient CO2 Separation.

Mixed matrix membranes (MMMs) have attracted significant attention in the field of CO2 separation because MMMs have potential to overcome an undesirable "trade-off" effect. In this study, the beaded nanofillers of ZIF-8@aminoclay (ZIF-8@AC) were synthesized using an in situ growth method, and they were doped into a Pebax MH 1657 (Pebax) matrix to fabricate MMMs for efficient CO2 separation. The beaded structure was formed by ZIF-8 particles joined together during the process of AC coating on the ZIF-8 surface. ZIF-8@AC played a vital role in the improvement of gas separation performance. It was mainly attributed to the following reasons: First, the inherent micropores of ZIF-8 constructed the internal pathways for gas transport in the beaded nanofillers, benefiting the improvement of gas permeability. Second, the staggered AC layers constructed the external pathways for gas transport in the beaded nanofillers, increasing the tortuosity of gas transport for larger molecules and favoring the improvement of gas selectivity. Therefore, the internal and external pathways of ZIF-8@AC co-constructed the dual-transport pathways for CO2 transport in MMMs. In addition, the abundant amino groups of the beaded nanofillers provided abounding carriers for CO2, facilitating CO2 transport in the dual-transport pathways. Therefore, the CO2 separation performance of Pebax/ZIF-8@AC-1 MMMs was significantly improved. The CO2 permeability and CO2/CH4 separation factor of Pebax/ZIF-8@AC-1-7 MMM were 620 ± 10 Barrer and 40 ± 0.4, which were 2.3 and 1.6 times those of a pure Pebax membrane, respectively. Furthermore, the CO2/CH4 separation performance of Pebax/ZIF-8@AC-1-7 MMM overcame successfully the "trade-off" effect and approached the 2019 upper bound. It is a novel strategy to design a beaded nanofiller doped into MMMs for carbon capture.

RELATIONSHIP BETWEEN PHYSICAL AND CHEMICAL PROPERTIES OF ENTISOLS-FLUVENTS AND EROSION IN THE SÃO FRANCISCO RIVER

ABSTRACT The intense anthropization in the lower São Francisco River and surrounding areas can lead to environmental degradation risks and, above all, makes the area more susceptible to soil erosion. This study aimed to identify and correlate the physical and chemical properties able to enhance erosive processes and slope instability in the watercourse margins of the lower São Francisco River, in Sergipe State, Brazil. To this end, disturbed and undisturbed samples of an Entisol-Fluvent soil were collected in the region, specifically in the city of Amparo de São Francisco. Physical (density, porosity, and texture) and chemical (pH, cation exchange capacity, base saturation, micro-, and macronutrients) analyses were performed. All physical properties and organic carbon contents were higher in the surface layers (Ap and AC) compared to the others. Organic carbon, phosphorus, and micronutrients had a negative correlation with soil density, showing higher contents and lower soil densities in the Ap and AC layers. The pedological characteristics of the evaluated soil layers are unable to provide soil resistance to water erosion.

A planning framework for AC-DC bilayer microgrids

This paper proposes a novel stochastic planning framework for bilayer microgrids (BμGs), which facilitates the integration of different types (AC and DC) of loads and distributed generations (DGs). In contrast to the conventional μG configurations that adopt single layer, the bilayer configuration has an AC layer in addition to a DC layer, where all the AC/DC loads and DGs are connected directly to the corresponding AC/DC layer. The interconnection between the AC and DC layers is achieved through one or more interlinking converters (ICs). Depending on the types, locations, and specifications of the μG loads and DGs, the planning framework allows each node to be a universal node that can include two buses (AC and DC) or a single bus (AC or DC). The network wiring can also be universal (AC, DC, or both) to facilitate the connection between the system nodes. The framework determines the optimal BμG configuration that minimizes the system total costs by providing the following decisions: the AC-layer connection; the DC-layer connection; and the number, locations and sizes of the ICs. Two case studies have been implemented and solved using different μG configurations to demonstrate the effectiveness of the proposed framework and the benefits of the BμG.

Dual-emitting barium based metal-organic nanosheets as a potential sensor for temperature and anthrax biomarkers

The development of novel 2D materials, due to the promising applications they have enabled through their unique properties, has attracted increasingly more research interest. In this regard, novel dual-emitting coordination polymer nanosheets were developed by doping Eu3+ and Tb3+ ions into the nanostructures of the [Ba(DPA)2(H2O)2]n (DPA = dipicolinic acid) coordination polymer (BCP). Single crystal x-ray crystallography revealed that BCP is a 1D coordination polymer and its three-dimensional supramolecular architecture is constructed with a relatively strong hydrogen bonding in the ac crystallographic plane and weak non-covalent interactions along the b axis. Using energetic ultrasound irradiations, synthesis of nanoscale BCP along with the unzipping of the weak interactions between the ac layers was accomplished. The resulting BCP nanosheets was used as the host lattice and was doped with Eu3+ and Tb3+ ions. Remarkably, the sensing ability of both Eu3+ and Tb3+ doped coordination polymer (Ln@BCP) nanosheets towards temperature and the DPA anthrax biomarker were investigate. The high relative sensitivity value of 2.42% K−1 and their reusability, makes Ln@BCP nanosheets an ideal candidate for the nanothermometry. They also exhibited high selective detection characteristics towards the DPA anthrax biomarker with a 0.03 nM detection limit. Therefore, Ln@BCP nanosheets can also be considered as an efficient multi-responsive optical sensor.

Influence of viscoelastic properties of cold recycled asphalt mixtures on pavement response by means of temperature instrumentation

Cold recycled asphalt mixtures (CRAMs) have been widely used in pavement construction and rehabilitation of base courses. Some studies describe it as granular materials, without stiffness dependency regarding temperature or frequency variation, while other researches state that it resembles a viscoelastic material. This indicates that the CRAMs mechanical behaviour is not fully understood. In the present study, dynamic modulus tests were conducted with CRAMs samples and the master curves suggested a viscoelastic behaviour for this type of mixture. The dynamic modulus results were used as input data in 3D-Move Analysis software and the pavement structure was simulated at different temperature conditions based on temperature instrumentation data collected from the field. It was found that the temperature dependency of CRAMs’ stiffness influences pavement mechanical behaviour. Besides, the relative stiffness between CRAMs and AC layers plays a major role in pavement response for varying temperatures. Therefore, CRAM's viscoelastic properties cannot be neglected.

Effects of dietary total sulphur amino acids to lysine ratio on performance, nitrogen utilization of Ac layers (black-boned chicken)

A study was conducted to evaluate the effects of dietary total sulphur amino acids (TSAA) to lysine (Lys) ratio on performance of Ac layers (black-boned chicken). A total of 800 laying hens from 38 to 50 weeks old was allocated according to a completely randomized design with five treatments and 20 replicates of 8 birds each. The basal diet was formulated with 16% crude protein (CP), 2755 kcal/kg of metabolizable energy (ME), 0.482% methionine, 0.925% TSAA and 1.12% lysine. The TSAA/Lys ratio of the basal diet was 0.85. The basal diet plus four diets were formulated, two with TSSA levels at 10% and 20% below and two at 10% and 20% above that of the basal diet, giving 0.762%, 0.857%, 1.047% and 1.142% TSAA, respectively with the basal at 0.925% TSAA. The 10% decrease or increase in TSAA from 0.952% did not affect feed intake or egg production. However, further TSAA decreases from 0.857% to 0.762% led to reducing egg weight, which increased with a curvilinear trend as the level of TSAA in the diets was increased. TSAA influenced nitrogen retention in a quadratic trend, with hens fed diets containing 0.952% and 1.047 % TSAA retaining more nitrogen than the other treatments. Increasing dietary TSAA increased the white and yolk index and Haugh unit, whereas egg shell thickness, yolk colour and egg components were not influenced. The TSAA/Lys ratio of 0.85 improved egg weight and nitrogen retention of Ac layers. Keywords: Egg weight, feed intake, performance, production, nitrogen retention, sulphur amino acid

Cage Based Crystalline Covalent Organic Frameworks

The first two cage based crystalline covalent organic frameworks, cage-COF-1 and cage-COF-2, were constructed from a prism-like three-aldehyde-containing molecular cage. The cage contains two horizontal phloroglucinol and three vertical triazine moieties forming three identical V-shaped cavities. By reacting with p-phenylenediamine and 4,4'-biphenyldiamine, the two cage-COFs were formed with a hexagonal skeleton and possess a unique structure. Due to the pillared cage nodes, the linkers are hanging with their π-surfaces but not C-H sites exposed to the pore, and enjoy certain rotational dynamics as suggested by 13C CP/MAS NMR. The antidirection of the diimine linkages leads to rippled layers which pack in unique ABC mode through alternate stacking of the cage twosided faces in both AB and AC layers. Such packing forms trigonal channels along c axis which are interconnected in ab plane due to the large open space created across the hanging linkers, resembling the porous characteristics of 3D COFs. The cage-COFs have a permanent porosity and can adsorb CO2 facilitated by the intrinsic cage cavities that serve as prime adsorption sites. The unprecedented cage-COFs not only merge the borderline of 2D and 3D COFs but also bridge porous organic cages to extended crystalline organic frameworks.

Temperature adjustment of Surface Curvature Index from Traffic Speed Deflectometer measurements

ABSTRACT Pavement structural condition evaluation plays an important role in assessing rehabilitation needs and making prudent investment decisions. Recently the use of Traffic Speed Deflectometer (TSD), is being considered for pavement structural evaluation especially for network level pavement management applications. Among various TSD data measurements and indices, Surface Curvature Index (SCITSD), is a widely-used index for assessing the structural condition of the AC layers. Since asphalt modulus is temperature sensitive, measured deflections and consequently the computed SCITSD are also affected by pavement temperature at the time of testing. For consistent pavement evaluation, SCITSD computed across sections and over time should be adjusted to a reference temperature. This study presents an applied method for adjusting SCITSD to a reference temperature. The method was based on a model developed from a dataset built from responses computed with dynamic-viscoelastic analyses under TSD moving load in a wide range of pavement properties. The method was field evaluated with TSD data from three locations within the US and one location each in Europe and Australia. The results showed that the proposed method can reasonably adjust SCITSD to a reference temperature which enables its application in pavement structural assessment and subsequent use in pavement management activities.

Oxide-free aC/Zr0.65Al0.075Cu0.275/aC phase plates for transmission electron microscopy

Thin-film phase plates (PP) have become a valuable tool for the imaging of organic objects in transmission electron microscopy (TEM). The thin film usually consists of amorphous carbon (aC), which undergoes rapid aging under intense illumination with high-energy electrons. The limited lifetime of aC film PPs calls for alternative PP materials with improved material stability. This work presents thin-film PPs fabricated from the metallic glass alloy Zr0.65Al0.075Cu0.275 (ZAC), which was identified as a promising PP material with beneficial properties, such as a large inelastic mean free path. An adverse effect of the ZAC alloy is the formation of a surface oxide layer in ambient air, which reduces the electrical conductivity and causes electrostatic charging in the electron beam. To avoid surface oxidation, the ZAC alloy is enclosed by thin aC layers. The resulting aC/ZAC/aC layer system is used to fabricate Zernike and Hilbert PPs. Phase-contrast TEM imaging is demonstrated for a sample of carbon nanotubes, which show strong contrast enhancement in PP TEM images.

Nanocomposites of silicon and carbon derived from coal tar pitch: Cheap anode materials for lithium-ion batteries with long cycle life and enhanced capacity

ABSTRACT From energy and environmental consideration, an industrial waste product, coal tar pitch (CTP), is used as the carbon source for Si/AC composite. We exploited a facile sintering method to largely scale up Si/amorphous carbon nanocomposite. The composites with 20 wt.% silicon with PVdF binder exhibited stable lithium storage ability for prolonged cycling. The composite anode delivered a capacity of 400.3 mAh g−1 with a high capacity retention of 71.3% after 1000 cycles. Various methods are used to investigate the reason for the outstanding cyclability. The results indicate that the silicon nanoparticles are wrapped by amorphous SiOx and AC in Si/AC composite. This uniform structure is very favorable to lithium storage, the SiOx and AC layers can supply sufficient conductivity and strong elasticity to suppress the stress resulting from the reaction of Si with Li during charge/discharge process.

Surface impedance of k-(BEDT-TTF)2Cu[N(CN)2]Br crystals

Precision measurements of the real and imaginary parts of the microwave surface impedance Zac(T) = Rac(T) + iXac(T) of the conducting ac layers of the k-(BEDT-TTF)2Cu[N(CN)2]Br crystals in the temperature interval of 0.5 40 K increases in comparison with Rac(T); (iv) the dependence Rac(T) at T > 40 K is nonmonotonic in thin crystals. These features of the impedance Zac(T) with increasing T are interpreted in terms of (i) the d-type symmetry of the superconducting order parameter, (ii) normal skin effect, (iii) manifestations of the antiferromagnetic fluctuations, and (iv) the size effect. The electrodynamic parameters of k-(BEDT-TTF)2Cu[N(CN)2]Br have been determined.

Monoclinic and Triclinic δ-Clathrates of Syndiotactic Polystyrene

The paper compares X-ray diffraction patterns of δ-clathrates of s-PS with a large number of guests, having molecular volume in the range 0.058−0.195 nm3, mainly focusing on the distance between the ac layers of enantiomorphous polymer helices (d010), as precisely evaluated by measurements on films exhibiting the a∥c∥ uniplanar orientation. The reported data and the crystal structure determination of the δ-clathrates with dinitrobenzene and dibenzofuran allow concluding that beside the already known large number of δ-clathrates of s-PS with monoclinic unit cells there is also a large number δ-clathrates of s-PS with triclinic unit cells. In particular, monoclinic or triclinic δ-clathrates are generally obtained with guests whose molecular volume is lower or higher with respect to the cavity of the δ nanoporous crystalline form (≈ 0.125 nm3). Small guests are easily accommodated in the cavities of the δ phase, thus maintaining its monoclinic unit cell and P21/a symmetry. Bulky guests, on the contrary, can be accommodated by substantial changes of the structural organization of the starting δ nanoporous form, leading to the occupation of only half of the cavities initially present while the other half is lost. This new kind of structural organization of the triclinic δ clathrates allows the inclusion of guest molecules definitely bigger than until now expected, although it halves the maximum guest/styrenic-unit molar ratio, which is reduced from the usual 1/4 to 1/8.

Investigation on the Oxidation Mechanism of Cobalt Hydroxide to Cobalt Oxyhydroxide

Cobalt hydroxide and cobalt oxyhydroxide derive their crystal structure from brucite mineral. Cobalt hydroxide crystallizes in hexagonal 1H polytype while cobalt oxyhydroxide in rhombohedral symmetry. In spite of the isostructural relationship between cobalt hydroxide and oxyhydroxide, we observe different symmetries. Hexagonal and rhombohedral polytypes are related to each other by a simple translation vector. Translation of AC layers by (1/3, 2/3, 1) and (2/3, 1/3, 1) with respect to each other generates the 3R polytype. Careful evaluation of the X-ray powder diffraction (PXRD) patterns of cobalt oxyhydroxide reveals the exact stacking sequence to be AC CB BA. The structural transformation of cobalt hydroxide to cobalt oxyhydroxide is reported.

Layers of Close-Packed Alternated Enantiomorphous Helices and the Three Different Uniplanar Orientations of Syndiotactic Polystyrene

Thorough analyses of X-ray diffraction patterns of syndiotactic polystyrene (s-PS) films, exhibiting different crystalline and co-crystalline phases, and related evaluations of degrees of orientation have allowed to give a more accurate as well as simpler description of the three known uniplanar orientations. This new description involves the three simplest orientations of the high density ac layers (i.e. of the layers of close-packed alternated enantiomorphous s-PS helices) with respect to the film plane. On this basis it is proposed that the three uniplanar orientations should be named a∥c∥, a∥c⊥ and a⊥c∥, i.e., by a nomenclature which also presents the advantage to be independent of the helical crystalline or co-crystalline s-PS phase.

Polymer/Gas Clathrates for Gas Storage and Controlled Release

The nanoporous crystalline phase of a cheap commercial polymer shows, already at room temperature, large uptake of gas molecules (e.g., butadiene and carbon dioxide) leading to polymer/gas clathrate phases. These clathrate phases have been characterized by X-ray diffraction and infrared linear dichroism measurements. Gas release kinetics are strongly reduced as a consequence of clathrate formation and can be further reduced by (010) orientation of the host phase, i.e., by placing the ac layers of close-packed enantiomorphous polymer helices nearly parallel to the film plane. The reported results indicate that this robust and easy-to-process polymeric crystalline framework is suitable for gas storage and controlled release.

Integration of field and laboratory testing to determine the causes of a premature pavement failure

The main objective of the forensic study was to identify the cause(s) of the pavement failure on a temporary detour of an interstate highway in Austin, Texas. Ground penetrating radar (GPR), falling weight deflectometer (FWD), coring, trenching, and comprehensive laboratory tests were performed. It was found that the main cause of the premature failure was attributed to material and construction practices. The base material used on this project did not meet the Triaxial class 1 requirement; it tested as a class 2.3 material. The base material was found to be highly moisture susceptible; it did not meet the Texas Department of Transportation's (TxDOT's) compressive strength requirements when subjected to capillary soaking. In addition, the repetitive triaxial test results revealed that the stiffness and load-carrying capability and resistance to permanent deformation became inadequate when the base material was exposed to moisture. It is believed that moisture entered this pavement primarily through poorly compacted AC layers and longitudinal joints. Cores taken in March 2004 from the original type B and C layers confirmed that the majority of cores have air voids exceeding 9%. The lower type B layer was also badly segregated and debonded from the upper type C layer at some locations. GPR results also indicated that the joints in the pavement were excessively porous. Further tests on the recovered binder for the type B layer indicated that the binder was prematurely aged, most probably from overheating during production.Key words: pavement failure, forensic, ground penetrating radar (GPR), falling weight deflectometer (FWD), laboratory testing.

Syndiotactic Polystyrene Physical Gels: Guest Influence on Structural Order in Molecular Complex Domains and Gel Transparency

Correlation lengths of crystalline domains of syndiotactic polystyrene (sPS) gels prepared in different solvents, and those of derived aerogels, have been investigated by wide-angle X-ray diffraction. The correlation length (D010), along the direction perpendicular to the ac layers of close-packed enantiomorphous s(2/1)2 helices, is strongly dependent on the chemical nature of the guest molecules not only for molecular complex phases of gels but also for the nanoporous crystalline δ phase of aerogels. Moreover, for a large series of solvents, it has been clearly established that sPS gel transparency is markedly dependent on the solvent and regularly increased as D010 correlation length is decreased.

Control of Crystal Size and Orientation in Polymer Films by Host−Guest Interactions

The unprecedented occurrence of two different kinds of uniplanar orientation by solution casting, observed for syndiotactic polystyrene (s-PS) films, has been rationalized in terms of host−guest interactions into molecular complex phases. Correlation lengths along different crystallographic directions (Dhkl), of molecular complex crystalline domains of s-PS with several different guest molecules, have been investigated by wide-angle X-ray diffraction. The chemical nature of the guest has a strong influence on the correlation length perpendicular to the ac plane (i.e., perpendicular to the layers of close-packed enantiomorphous helices) and a weak influence on the correlation lengths along a and c (chain) axes. Less and more favorable host−guest interactions lead to molecular complex domains with low and high degree of order perpendicular to the ac layers (D010 < 6 nm and D010 > 7 nm) and generate cast films with uniplanar (010) and (002) orientations, respectively.

Crystalline structures of intercalate molecular complexes of syndiotactic polystyrene with two fluorescent guests: 1,3,5-Trimethyl-benzene and 1,4-dimethyl-naphthalene

The crystal structures of two molecular complex phases of syndiotactic polystyrene (s-PS) with 1,3,5-trimethyl-benzene (TMB) and 1,4-dimethyl-naphthalene (DMN) have been described. These structures present a monoclinic unit cell in which the s(2/1)2 polymer helices and guest molecules are packed according the space group P21/a and unit cell constants: a=17.3Å, b=15.4Å, c=7.8Å and γ=95.7° for s-PS/TMB and a=17.4Å, b=17.2Å, c=7.8Å and γ=116.4° for s-PS/DMN. Both structures can be described as intercalates, since they present ac layers of polymer helices alternated to layers of contiguous guest molecules and a guest/monomeric-unit molar ratio of 1/2, as recently observed only for s-PS/norbornadiene molecular complex. On the basis of a comparison between crystalline structures and X-ray diffraction data of several s-PS molecular complexes, a simple criterion to anticipate their clathrate or intercalate nature has been suggested.