Free Volume Space Research Articles

Multi-Color Spaceplates in the Visible.

The ultimate miniaturization of any optical system relies on the reduction or removal of free-space gaps between optical elements. Recently, nonlocal flat optic components named "spaceplates" were introduced to effectively compress space for light propagation. However, space compression over the visible spectrum remains beyond the reach of current spaceplate designs due to their inherently limited operating bandwidth and functional inefficiencies in the visible range. Here, we introduce "multi-color" spaceplates performing achromatic space compression at three distinct color channels across the visible spectrum to markedly miniaturize color imaging systems. In this approach, we first design monochromatic spaceplates with high compression factors and high transmission amplitudes at visible wavelengths based on a scalable structure and dielectric materials widely used in the fabrication of meta-optical components. We then show that the dispersion-engineered combination of monochromatic spaceplates with suitably designed transmission responses forms multicolor spaceplates that function achromatically. The proposed multicolor spaceplates, composed of amorphous titanium dioxide and silicon dioxide layers, efficiently replace free-space volumes with compression ratios as high as 4.6, beyond what would be achievable by a continuously broadband spaceplate made of the same materials. Our strategy for designing monochromatic and multicolor spaceplates, along with the presented theoretical and computational results, show that strong space-compression effects can be achieved in the visible range. Our findings may ultimately enable a new generation of ultrathin optical devices for various applications.

Near-strain-free anode architecture enabled by interfacial diffusion creep for initial-anode-free quasi-solid-state batteries

Anode-free (or lithium-metal-free) batteries with garnet-type solid-state electrolytes are considered a promising path in the development of safe and high-energy-density batteries. However, their practical implementation has been hindered by the internal strain that arises from the repeated plating and stripping of lithium metal at the interlayer between the solid electrolyte and negative electrode. Herein, we utilize the titanium nitrate nanotube architecture and a silver-carbon interlayer to mitigate the anisotropic stress caused by the recurring formation of lithium deposition layers during the cycling process. The mixed ionic-electronic conducting nature of the titanium nitrate nanotubes effectively accommodates the entry of reduced Li into its free volume space via interfacial diffusion creep, achieving near-strain-free operation with nearly tenfold volume suppressing capability compared to a conventional Cu anode counterpart during the lithiation process. Notably, the fabricated Li6.4La3Zr1.7Ta0.3O12 (LLZTO)-based initial-anode-free quasi-solid-state battery full cell, coupled with an ionic liquid catholyte infused high voltage LiNi0.33Co0.33Mn0.33O2-based cathode with an areal capacity of 3.2 mA cm−2, exhibits remarkable room temperature (25 °C) cyclability of over 600 cycles at 1 mA cm−2 with an average coulombic efficiency of 99.8%.

Distribution of the adsorbed density of supercritical CO2 onto the anthracite and its implication for CO2 geologic storage in deep coal

CO2 geological storage in deep coal has been a research hotspot in carbon capture and storage under the background of carbon neutrality. Understanding supercritical CO2 adsorption onto coals has been significant for accurately evaluating deep coal's CO2 geological storage capacity and further determining the deployment of a CO2-ECBM project. The supercritical CO2 adsorption experiments on dry Qinshui anthracite coal were conducted. The adsorbed CO2 density and average number of adsorbed molecule layers were calculated. The effects of temperature, pressure, and pore size on the density of the adsorbed phase were discussed using the simplified local density (SLD) adsorption model, and the distribution of adsorbed CO2 on the coal surface was disclosed. Finally, the modified method for calculating CO2 geological storage in coal was proposed. The results show that: (1) The average adsorbed density of supercritical CO2 onto the anthracite at the experimental temperatures ranged from 1.073 to 1.088 g/cm3, and the average number of adsorbed molecular layer ranged from 1.15 to 1.26, indicating the coexistence of micropore filling and multilayer adsorption. (2) The SLD theory demonstrated that the distribution of the adsorbed CO2 density is jointly controlled by temperature, pressure, pore size, and CO2 phase. The supercritical CO2 can form a second layer of adsorbed molecules. The minimum pore size to keep the adsorbed CO2 density unchanged on the pore wall is around 0.82 nm for subcritical CO2 and 3 nm for supercritical CO2. (3) The real average adsorbed CO2 density is always lower than that of the first adsorbed molecular layer and the density under extreme pressure. There are four different distributions of free and adsorbed CO2 on the surface of the coal with the changes in temperature and pressure, consisting of subcritical, gas-like supercritical, liquid-like supercritical, and extreme states. (4) The modified method of CO2 storage capacity for coal, based on excess adsorption and equivalent free CO2 in the total pore, avoids the error caused by the uncertainty of adsorbed CO2 density and free space volume. It is recommended that this method should be preferentially adopted during the selection of the potential target area for CO2 geological storage in deep coal. The study aims to provide a new idea for the mechanism of supercritical CO2 adsorption on coal and the assessment of supercritical CO2 geologic storage capacity in deep coal.

Investigation on absorption separation characteristics of R134a, R1234yf, R22, R410A, and R404A using MWCNT-[HMIM][Tf2N] ionanofluid

In this study, refrigerant absorption characteristics of R134a, R1234yf, R22, R410A, and R404A were investigated using MWCNT-[HMIM][Tf2N] ionanofluid (IONF) for environmental improvement towards a sustainable future. During the absorption experiment, the remaining free volume space was reduced when the refrigerant was recharged in Cycle-2, and the average pressure reduction rate in Cycle-1 was increased by 18.2 % compared to Cycle-2. In addition, the solubility between the refrigerant and IONF had a more significant influence on the absorption performance than the concentration. The relative refrigerant absorption performance for the separation of mixed refrigerants increased by interfering with the absorption of refrigerants with relatively large molecular sizes as the concentration of IONF increased. Compared to 0 wt%, the relative absorption performance at 0.5 wt% concentration of MWCNT-[HMIM][Tf2N] IONF increased by 123.9 %, 26.4 %, and 123.9 %, respectively, for R22/R134a, R22/R1234yf, and R134a/R1234yf. It was confirmed that the refrigerant recovery and waste refrigerant treatment using MWCNT-[HMIM][Tf2N] IONF have sufficient potential to reduce environmental degradation and considered to be aneconomically viable method.

Hop, Skip, and Jump: Hydrogen Molecular Transport through Amorphous Polyethylene Matrices Studied via Molecular Dynamics Simulations.

In the pursuit of advancing and diversifying energy technologies for a more sustainable future, the possibilities of hydrogen (H2) usage will broaden, as will our understanding of its containment materials. Polyethylene (PE) has a vast assortment of uses and applications, which are growing with demands for alternative energy possibilities. One use of PE liner is as a prime candidate for nonmetallic piping and pressurized type IV storage devices. Such applications require PE to effectively prevent H2 transport through containment systems. To study the molecular transport mechanism of hydrogen through polymeric barriers, a system containing hydrogen molecules absorbed within amorphous PE is modeled here using molecular dynamics simulations. The simulations are conducted within a range of temperatures that span the glass transition temperature of amorphous PE. The simulated PE displays bulk density, radius of gyration, and self-diffusion coefficient that are consistent with experimental data. The simulated trajectories are interrogated to study the movement of the guest gas molecules. The results show that the diffusion coefficients increase with temperature, as expected. However, the mobility of the PE chains is found to affect the mobility of absorbed H2 molecules to a much lower extent than it affects that of CH4 molecules because of the much smaller size of the former than of the latter guest. From a molecular perspective, a "hopping" mechanism is observed, according to which H2 molecules hop between one vacant free volume space to another within the polymer matrix, in combination with longer, straight, undisturbed "jumps" or "skips" along directions aligned with regions of ordered PE chains. This suggests that the orientation of the crystallites within the semicrystalline PE matrix affects the H2 containment. Implications of these findings toward PE usage as containment material are discussed.

Shock-induced energy localization and reaction growth considering chemical-inclusions effects for crystalline explosives

Chemical inclusions significantly alter shock responses of crystalline explosives in macroscale gap experiments but their microscale dynamics origin remains unclear. Herein shock-induced energy localization, overall physical responses, and reactions in α-1,3,5-trinitro-1,3,5-triazinane (α-RDX) crystal entrained various chemical inclusions were investigated by the multi-scale shock technique implemented in the reactive molecular dynamics method. Results indicated that energy localization and shock reaction were affected by the intrinsic factors within chemical inclusions, i.e., phase states, chemical compositions, and concentrations. The atomic origin of chemical-inclusions effects on energy localization is dependent on the dynamics mechanism of interfacial molecules with free space volume, which includes homogeneous intermolecular compression, interfacial impact and shear, and void collapse and jet. As introducing various chemical inclusions, the initiation of those dynamics mechanisms triggers diverse decay rates of bulk RDX molecules and hereby impacts on growth speeds of final reactions. Adding chemical inclusions can reduce the effectiveness of the void during the shock impacting. Under the shockwave velocity of 9 km/s, the parent RDX decay rate in RDX entrained amorphous carbon decreases the most and is about one fourth of that in RDX with a vacuum void, and solid HMX and TATB inclusions are more reactive than amorphous carbon but less reactive than dry air or acetone inclusions. The less-dense shocking system denotes the greater increases in local temperature and stress, the faster energy liberation, and the earlier final reaction into equilibrium, revealing more pronounced responses to the present intense shockwave. The quantitative models associated with the relative system density (RDsys) were proposed for indicating energy-localization mechanisms and evaluating initiation safety in the shocked crystalline explosive. RDsys is defined by the density ratio of defective RDX to perfect crystal after dynamics relaxation and reveals the global density characteristic in shocked systems filled with chemical inclusions. When RDsys is below 0.9, local hydrodynamic jet initiated by void collapse dominates upon energy localization instead of interfacial impact. This study sheds light on novel insights for understanding the shock chemistry and physical-based atomic origin in crystalline explosives considering chemical-inclusions effects.

Porous anion exchange membranes fabricated by phase inversion and in‐situ modification for acid recovery

AbstractDiffusion dialysis (DD) for acid recovery is significantly restricted by the poor acid dialysis coefficient () of anion exchange membranes (AEMs). To overcome such problem, porous AEMs with extremely high free space volume have been fabricated herein based on porous membrane substrate, drawing inspiration from the dissolution‐diffusion concept. Specifically, chloromethylated polyethersulfone (CMPES) has been used as the starting material to create the porous substrate via non‐solvent phase inversion, then in‐situ crosslinked and quaternized using ethylenediamine (EDA) and N‐methylimidazole (NMI), respectively. In this study, the degrees of modification of EDA and NMI are controlled to adjust the microstructure and DD performance of the produced porous AEMs. The ideal AEM's and acid/salt separation factor (S) are 4.3 and 2.6 times greater, respectively, than those of the commercial DF‐120 membrane at the same condition. Additionally, it shows strong organic solvent resistance and thermal stability, and therefore demonstrate the potential for widespread use.

Influence of nanosized defects on photoluminescence efficiency of Er3+ ions co-doped with Au2 O3 in a lead boroselenate glass ceramic system: a novel approach using positron annihilation lifetime spectroscopy.

This study consists of the results of an investigation into the influence of the free-volume space (fv ) defects on luminescence efficiency (LE) of erbium ions in Au2 O3 -doped PbO-B2 O3 -SeO2 (PBS) glass ceramics. Glass ceramics containing fixed concentrations of Er3+ ions and varied concentrations of Au2 O3 were synthesized. X-ray diffraction studies indicated that the samples contained Au2 (SeO3 )3 crystalline phase and nano gold metallic particles. The concentration of defects entrenched in the glass ceramics estimated in terms of Au2 O3 content using positron annihilation lifetime spectroscopy measurement indicated the highest content in the glass ceramic containing 0.075 mol% of Au2 O3 . Optical absorption and the photoluminescence (PL) spectra of the glass ceramics were studied in the visible region. The observed increase of PL efficiency was attributed to the enhanced concentration of free-volume imperfections in the samples. A perfect correlation could be achieved between the free-volume fraction and the PL efficiency of erbium ions in these glass ceramics.

To what extent can space be compressed? Bandwidth limits of spaceplates

Spaceplates are novel flat-optic devices that implement the optical response of a free-space volume over a smaller length, effectively “compressing space” for light propagation. Together with flat lenses such as metalenses or diffractive lenses, spaceplates have the potential to enable the miniaturization of any free-space optical system. While the fundamental and practical bounds on the performance metrics of flat lenses have been well studied in recent years, a similar understanding of the ultimate limits of spaceplates is lacking, especially regarding the issue of bandwidth, which remains as a crucial roadblock for the adoption of this platform. In this work, we derive fundamental bounds on the bandwidth of spaceplates as a function of their numerical aperture and compression ratio (ratio by which the free-space pathway is compressed). The general form of these bounds is universal and can be applied and specialized for different broad classes of space-compression devices, regardless of their particular implementation. Our findings also offer relevant insights into the physical mechanism at the origin of generic space-compression effects and may guide the design of higher performance spaceplates, opening new opportunities for ultra-compact, monolithic, planar optical systems for a variety of applications.

Enhanced dielectric and electrostatic energy density of electronic conductive organic-metal oxide frameworks at ultra-high frequency

High-density energy materials comprise high dielectric strength, and rapid charge transport leads to improved microwave absorbance, maximum electromagnetic wave (EM) attenuation, and wideband characteristics. This work exhibits hierarchical polyaniline (PANI) functionalized polycrystalline hybrid units. Comprehensive band structures, increased electron conduction, high charge polarization, and definite EM wave absorption could be tuned by the featured morphologies. Filler material's (RGO/ZnO) intercalated structures have substantial free space volume. It could facilitate notable dielectric permittivity (∼2562 F m−1), give rise to higher charge polarization and excellent charge storage performance (∼112 F). This electrostatic charge proficiency could recognize with generous electron density corresponding to stimulated surface charge density (σs, ∼8.66×103 C m−2). Quality factor (Q) of 0.056 (∼ 7.1×106Hz) with minimized losses attributed to higher energy density (Ue, ∼1530 J cm−3) at low electric field strength ∼ 450 V m−1, which could resemble a variable Ue performance at lower to a higher percolation threshold voltage. Incorporated ZnO and RGO nanostructures are well organized, with the PANI matrix providing good interfacial adhesion. It significantly raises the EM wave losses (– 28 dB) of ∼0.300 mm thick specimen at ∼ 18.42 GHz. We envisioned that the multifunctional response of the PANI-RGO-ZnO 2:1 hybrid might manifest potential energy storage and microwave absorption as electrode materials that may be useful in solid-state devices used in modern communication systems.

Natal philopatry is associated with smaller nest size in a cavity-nesting bird with consequences for nest box temperature

Considerable within-population variation in nest size exists among cavity nesters. We sought to explain this by studying a multi-brooded population of Eastern Bluebirds (Sialia sialis) breeding in nest boxes. We examined seasonal change in nest weights and compared the weights of nests built by immigrant and resident females. We further investigated whether nest weight correlated with maternal condition or breeding success. Nest weight measured after broods fledged was correlated with nest height at the start of incubation. Breeders spent fewer days building and built successively smaller, lighter nests in later nesting attempts. Female bluebirds performed the majority of nest construction. Nests built by immigrant females were significantly larger on average than those built by female recruits hatched on site, and the seasonal decline in nest weight was more pronounced for natally philopatric females. For the first time, we present evidence that the weights of philopatric females’ first nests were significantly positively correlated with the weights of the nests they were raised in, suggesting an effect of natal memory. Contrary to expectation, neither maternal condition nor reproductive success (clutch size, hatching success, brood size, and fledging success) was related to nest weight. To investigate whether smaller nests provided a thermal advantage in summer nest attempts when afternoon box temperatures can exceed 41°C, we measured the temperature within nest boxes using programmable data loggers. Mean daily maximum box temperatures during incubation were significantly positively related to nest weight and significantly negatively related to the volume of free space above the nest. Increased air circulation above the nest likely contributed to cooling the boxes when ambient temperatures were high. Reducing nest size was therefore advantageous, especially in later nesting attempts when ambient temperatures were warmest. Seasonal decline in nest weights and differences between immigrant and natally philopatric females merits further investigation.

Effect of non-condensable gas in steam condensation at sub-atmospheric pressure condition

In the International Thermonuclear Experimental Reactor (ITER), a postulated Loss Of Coolant Accident (LOCA) in the Vacuum Vessel (VV) has to be managed with a pressure suppression system working at sub-atmospheric pressure. The operating conditions considerably differ from those experienced in the fission nuclear power plants such as BWR, since the ITER Tokamak works at very low pressure conditions and can withstand a maximum pressure of 0.15 MPa. For this reason, the pressure value must not exceed 10 kPa for a water temperature of 30 °C inside the Vapour Suppression Tanks (VSTs) that are the fundamental components of the Vacuum Vessel Pressure Suppression System (VVPSS). During a LOCA some non-condensable gases (mainly hydrogen and oxygen gases due to the water radiolysis or thermolysis) may be mixed in the steam and this could impair the condensation efficiency. In order to investigate the effects of non-condensable gas on DCC, we conducted a research program funded by ITER Organization at the laboratory of the University of Pisa: we designed and built a small-scale experimental rig to study the steam Direct Contact Condensation (DCC) with the presence of non-condensable gas and simulate the behaviour of a VST. Since DCC can occur with different characteristics, we ran 12 closed mode tests exploring all condensation regimes injecting a certain mass of air with the steam discharged in the subcooled water. The tests started at the saturation pressures corresponding to water temperatures ranging from 40 °C to 80 °C and ended when the free space volume reached the atmospheric pressure. From the analysis of the data acquired during the tests we observed that the condensation efficiency remained higher than 95%. We observed that despite this, the presence of a certain quantity of non-condensable gas has negative aspects on condensation: the condensation regime never reaches stability (the regimes quickly shift towards instability). Furthermore, the presence of air triggers a turbulence of the flow which interferes with the transfer of heat from the steam to the water. Not only the introduction of air into the flow increases linearly the pressure above the water head but its high temperature further contributes to the pressure increase. The air mixed with the flow also forms eddies that can trap the steam and transport it out of the water, preventing it from condensing. Apart from condensation, the most noticeable problem is the rapid increase in pressure inside the condensation tank.

Comparison of thermal runaway pressures within sealed enclosures for nickel manganese cobalt and iron phosphate cathode lithium-ion cells

Mining vehicle manufacturers are developing lithium-ion (Li-ion) battery electric vehicles as an alternative to diesel-powered vehicles. In gassy underground mines, explosion-proof (XP) enclosures are commonly used to enclose electrical ignition sources to prevent propagation of an internal methane-air explosion to a surrounding explosive atmosphere. Li-ion batteries can create pressurized explosions within sealed enclosures due to thermal runaway (TR). NIOSH researchers measured TR pressures of nickel manganese cobalt (NMC) cathode type 18650 Li-ion cells, model MH1, as a function of free space within sealed enclosures and observed an inverse power relationship. TR pressure-rise rates, gas quantities, and temperatures were also measured. A confined NMC cell with 92.5 mL of free space produced 232 bar of pressure, far exceeding minimum pressure containment specifications for conventional XP enclosures. Approximately 287 times the cell volume of free space would be needed to reduce the TR pressure of these cells to 8.62 barg (125 psig) per U.S. Code of Federal Regulations, Title 30, Part 18. The NMC cell TR pressures were significantly higher than those measured previously for iron phosphate cathode Li-ion cells under comparable confinement conditions.

Chemical Engineering for Improvement of the Efficiency of Microwave Energy Use in Processing of Plant Biomass

Combined coaxial-circular waveguide equipped with protective module allowing the transmission of microwave energy of three magnetrons with the output of 0.9 kW per each into the pressurized reaction chamber and capable of operating at temperatures of up to 250 °C and a pressure of up to 10 bars was designed and tested. Choke flange junction of the waveguide sections was used instead of contact flange connection. The developed waveguide construction allows to place the radio transparent partition inside the free space volume of a choke flange junction performing protection of emitters and summing of microwave energy of three magnetrons with an efficiency close to 100% that was proven by tests with fresh water as a microwave energy absorber. The extraction set-up equipped with the above-mentioned waveguide has demonstrated the stable and safety operation of the transmitting block and the accurate automatic control of the temperature and pressure inside the reaction chamber in the presence of a strong electromagnetic field. The construction of the microwave extraction set-up allows to use the impact of the combination of temperature and pressure on the cell wall, promoting the high rate isolation of secondary metabolites from biomass that was demonstrated by water extraction of black alder bark.

About copying a free-space electromagnetic field by an invisible object

The structure of a monochromatic electromagnetic field inside a spherical object that does not distort the wave field of external sources outside its surface has been studied using transformation optics methods. It is assumed that the object is made of isotropic materials with equal values of permittivity and permeability and consists of a spherical volume of material with a positive spatially uniform refractive index and an adjacent spherical layer of material with a negative inhomogeneous refractive index (i.e., it is a spherical superlens made of isotropic materials). It is shown that the field inside a sphere with a positive refractive index is the reduced-size copy of the field in which the object was located. This copy contains information about the radiation field of external sources in a spherical free-space volume whose radius depends on the object parameters and can be significantly larger than the radius of the object. It is shown that the copying properties of the object with given dimensions can be fully preserved if its outer layer is made of anisotropic materials.

Boosting cyclability performance of GeP anode via in-situ generation of free expansion volume

Among the germanium-based composites, germanium phosphide (GeP) is a promising anode material for lithium-ion batteries (LiBs) because of its good electronic conductivity, low binding energy and high theoretical energy density. Nevertheless, the severe volume variation and sluggish reaction kinetics hindered its applications. To solve the above issues, this work come up with a killer idea that inspired by the free volume theory of polymers, which was mainly involved creation of free volume into GeP matrix. Specifically, structural design that elaborately deals with severe aggregation while helps alleviating volume expansion and contraction of GeP have being made by a facile ball milling-assisted in-situ generation of free expansion volume. Compared with pristine GeP and direct ball milled GeP, the addition of NaCl as grinding agent plays a very positive role on generating free volume space in flake-like GeP particles, which was assembled by numerous amorphous GeP granules. In this way, the as obtained GeP particles exhibited enhanced reversible capacity, improved cyclability and rate performance (883mAhg−1 at 0.2 C after 100th cycle, and 680mAhg−1 at 2 C) when served as anode material in LiBs. This study highlights a highly efficient and cost effective approach in advancing the high performance GeP towards practical applications for energy storage.

Effect of Immersion in Water or Alkali Solution on the Structures and Properties of Epoxy Resin.

The durability of fiber-reinforced polymer (FRP) composites is significantly dependent on the structures and properties of the resin matrix. In the present paper, the effects of physical or chemical interactions between the molecular chain of the epoxy resin matrix and water molecules or alkaline groups on the water absorption, mechanical structures, and microstructures of epoxy resin samples were studied experimentally. The results showed that the water uptake curves of the epoxy resin immersed in water and an alkali solution over time presented a three-stage variation. At different immersion stages, the water uptake behavior of the resin showed unique characteristics owing to the coupling effects of the solution concentration gradient diffusion, molecular hydrolysis reaction, and molecular segment movement. In comparison with the water immersion, the alkali solution environment promoted the hydrolysis reaction of the epoxy resin molecular chain. After the immersion in water or the alkali solution for one month, the water uptake of the resin was close to saturate, and the viscoelasticity was observed to decrease significantly. The micropore and free volume space on the surface and in the interior of the resin gradually increased, while the original large-scale free volume space decreased. The tensile strength decreased to the lowest point after the immersion in water and the alkali solution for one month, and the decrease percentages at 20 °C and 60 °C water or 60 °C alkali solution were 24%, 28%, and 22%, respectively. Afterward, the tensile strength recovered with the further extension of immersion time. In addition, it can be found that the effect of the alkali solution and water on the tensile strength of the epoxy resin was basically the same.

Exploration of nano sized defects in Fe2O3 doped lead zirconium silicate glass ceramics by using positron annihilation lifetime spectroscopy

This work is focused on the evaluation of the free volume space and the concentration of nano-sized cavities trapped in Fe2O3 mixed lead zirconium silicate glass ceramics using positron annihilation lifetime spectroscopy (PALS) studies with 22Na (0.1MBq) positron source. Such imperfections are anticipated to have strong bearing on physical characteristics of the glass ceramic. The glasses of a particular composition viz., 36PbO–4ZrO2–(60–x)SiO2: xFe2O3 (0 ≤ x ≤ 0.5 in the intervals of 0.1) were synthesized by traditional melting and quenching techniques. The lifetime of the positrons measured in these samples is found to be strongly reliant on the content of Fe2O3. The results have suggested the increased fraction of free volume imperfections (fv), and radius of the cavities (R) with increase of Fe2O3 content from 0.2 to 0.5 mol%. The spectroscopic studies of these samples indicated that iron ions predominantly existed in Fe3+ state and occupied octahedral positions with FeO6 structural units, acted as modifiers and induced several imperfections. The estimated maximal concentration of imperfections in the glass ceramic sample F5 by PALS studies is attributed to such reasons. The inferences drawn from PALS studies regarding the concentration of defects in these samples are found to be in agreement with the results of third harmonic generation (THG) studies and conductivity studies.

Dielectric Nonlocal Metasurfaces for Fully Solid-State Ultrathin Optical Systems

Most optical systems involve a combination of lenses separated by free-space regions where light acquires the required angle-dependent phase delay for a certain functionality. Very recently, flat-optics structures have been proposed to compress these large free-space volumes and miniaturize the overall optical system. However, these early designs can only replace free-space volumes of limited length, or operate in a very narrow angular range, or require a high-index background. These issues raise questions about the applicability of these devices in practical scenarios. Here, we first derive a fundamental trade-off between the length of compressed free space and the operating angular range, which explains some of the limitations of earlier designs, and we then propose a solution to relax this trade-off using nonlocal metasurface structures composed of suitably coupled resonant layers. This strategy, inspired by coupled-resonator-based band-pass filters, allows replacing free-space volumes of arbitrary length over wide angular ranges, and with very high transmittance. Finally, we theoretically demonstrate, for the first time, the potential of combining local and nonlocal metasurfaces to realize compact, fully solid-state, planar structures for focusing, imaging, and magnification, in which the focal length of the lens (and hence its magnifying power) does not dictate the actual distance at which focusing is achieved. Our findings are expected to extend the reach of the field of metasurfaces and open new unexplored opportunities.

Encapsulation of Clove Oil within Ca-Alginate-Gelatine Complex: Effect of Process Variables on Encapsulation Efficiency

Owing to the properties such as analgesic, clove oil is commonly used as medicine, antibacterial, antioxidant, and antimicrobial drugs. The possibility of clove oil encapsulation as a solid macrocapsule was studied by making Ca-Alginate-Gelatine macrocapsules. The process variables used were variations in Alginate concentration of 1% and 1.5% w/v, and the mass ratio between alginate-gelatine was varied between 1: 4, 1: 6, and 1: 8 w/w. In addition, variations in the concentration of CaCl2 (10%, 20% and 30% w/v) as a cross-linking agent for the formation of Ca-Alginate complexes were also used as process variables. The increase of alginate, gelatine and CaCl2 concentration seems to decreased the encapsulation efficiency because of the limitation of the free space volume formed in the Ca-Alginate-Gelatine matrix. The highest encapsulation efficiency (93.08%) was obtained in the use of Alginate 1% w/v, with a ratio of alginate to gelatine 1: 4 and cross-linking in a 10% w/v CaCl2 solution for 15 minutes.