Arrays Of Islands Research Articles

Characterization of Liquid Film Distribution and Sub-Flow Regimes of Annular Flow in Helically Coiled Tubes Using Ring Island Array Sensor

Characterization of Liquid Film Distribution and Sub-Flow Regimes of Annular Flow in Helically Coiled Tubes Using Ring Island Array Sensor

Dynamic vortex Mott transition in triangular superconducting arrays

The proximity-coupled superconducting island arrays on a metallic film provide an ideal platform to study the phase transition of vortex states under mutual interactions between the vortex and potential landscape. We have developed a top-down microfabrication process for Nb island arrays on Au film by employing an Al hard mask. A current-induced dynamic vortex Mott transition has been observed under the perpendicular magnetic fields of f magnetic flux quantum per unit cell, which is characterized by a dip-to-peak reversal in differential resistance d V/d I vs. f curve with the increasing current. The d V/d I vs. I characteristics show a scaling behavior near the magnetic fields of f = 1/2 and f = 1, with the critical exponents ε of 0.45 and 0.3, respectively, suggesting different universality classes at these two fields.

Densely Packed Tethered Polymer Nanoislands: A Simulation Study.

COordinated Responsive Arrays of Surface-Linked polymer islands (CORALS) allow for the creation of molecular surfaces with novel and switchable properties. Critical components of CORALs are the uniformly distributed islands of densely grafted polymer chains (nanoislands) separated by regions of bare surface. The grafting footprint and separation distances of nanoislands are comparable to that of the constituent polymer chains themselves. Herein, we characterize the structural features of the nanoislands and semiflexible polymers within to better understand this critical constituent of CORALs. We observe different characteristics of grafted semiflexible polymers depending on the polymer island’s size and distance from the center of the island. Specifically, the characteristics of the chains at the island periphery are similar to isolated tethered polymer chains (full flexible chains), while chains in the center of the island experience the neighbor effect such as chains in the classic polymer brush. Chains close to the edge of the islands exhibit unique structural features between these two regimes. These results can be used in the rational design of CORALs with specific interfacial characteristics and predictable responses to external stimuli. It is hoped that this the discussion of the different morphologies of the polymers as a function of distance from the edge of the polymer will find applications in a wide variety of systems.

Josephson Currents and Gap Enhancement in Graph Arrays of Superconductive Islands.

Evidence is reported that topological effects in graph-shaped arrays of superconducting islands can condition superconducting energy gap and transition temperature. The carriers giving rise to the new phase are couples of electrons (Cooper pairs) which, in the superconducting state, behave as predicted for bosons in our structures. The presented results have been obtained both on star and double comb-shaped arrays and the coupling between the islands is provided by Josephson junctions whose potential can be tuned by external magnetic field or temperature. Our peculiar technique for probing distribution on the islands is such that the hopping of bosons between the different islands occurs because their thermal energy is of the same order of the Josephson coupling energy between the islands. Both for star and double comb graph topologies the results are in qualitative and quantitative agreement with theoretical predictions.

Stretchable array of CdSe/ZnS quantum-dot light emitting diodes for visual display of bio-signals

Display devices that can visually present various bio-signals are a core future technology required for skin attachable wearable electronics. Quantum dot light emitting diodes (QD-LEDs), which can be used as high performance display devices, exhibit many advantages such as a narrow bandwidth, high color purity, high environmental stability, easy and fast processing, and a high brightness at low voltage. In this study, we report on the fabrication of a stretchable QD-LED array for the visual display of body movement and skin temperature signals from skin-attached sensors. After forming an array of a rigid NOA63 islands, an array of CdSe/ZnS QD-LEDs is fabricated on top of that island array and electrically connected using liquid metal Galinstan interconnections. Finally, the array of QD-LEDs on the NOA63 islands is transferred onto a stretchable elastomer substrate of Ecoflex/PDMS. Of particular importance, for stable performance of the QD-LEDs under deformation, in replacement of the conventionally used ITO, a flexible and highly transparent electrode of Au grid/Ethylene glycol doped PEDOT:PSS is used. Such a design architecture can minimize the strain applied to the QD-LEDs by concentrating the strain onto the soft elastomer film substrate and the Galinstan interconnections. As a result, the fabricated QD-LED array exhibits stable operation under both 50% uniaxial and 30% biaxial strains. After attachment of the stretchable QD-LED array onto skin, the extent of knee bending, and changes in skin temperature are displayed as changes in the pattern of the QD-LED array. This work demonstrates the potential application of our stretchable array of QD-LEDs for easy and daily monitoring of health conditions through a visual display.

A wave propagation algorithm for nonlinear site response analysis of layered soil accounting for liquefaction

A constitutive model is developed for the ground response analysis of layered sites. The model is a one-dimensional version of Ta-Ger (2016) and involves critical state compatibility, anisotropic plastic flow rule and Bouc-Wen type hardening law. After being downgraded to the p-q stress space the model is reformulated to provide a unified framework of analysis for both drained and undrained loading conditions and for sand and clay. The calibration of the model parameters for sand is based on a procedure that targets to the optimum performance in both drained and undrained load conditions by simultaneously matching the response in terms of: (a) the cyclic resistance ratio curves as per the NCEER/NSF methodology, and (b) widely-used experimental shear modulus and damping ratio curves available in the literature. For the clay-like soil the calibration involves only the second step under the assumption of fully undrained conditions. The model is implemented through an explicit finite difference algorithm into an in-house computer code which performs integration of the wave equations to obtain the non-linear response of the soil. The accuracy of the algorithm is verified through comparison with analytical solutions for the amplification function of soil deposits with linearly increasing Vs, subjected to vertically propagating shear waves. It is then validated against experimental data from two centrifuge experiments. Finally, the records of the Port Island array from Kobe 1995 earthquake are employed to test the ability of the model to predict the observed response.

Identifying suitable time periods for infrasound measurement system response estimation using across-array coherence

SUMMARY Microbarometers deployed to measure atmospheric infrasound are often connected to, or housed within, a wind noise reduction system (WNRS). At infrasound arrays of the International Monitoring System (IMS), being deployed as part of Comprehensive Nuclear-Test-Ban Treaty verification measures, the WNRS typically comprises an 18 m diameter pipe array. Over the past decade an in situ method has been developed to estimate the measurement system (sensor + WNRS) response characteristics, by comparing its recordings with those made on a colocated reference sensor with known response and no WNRS. The method relies upon the identification of time periods for which the reference sensor and measurement system are subject to the same input pressure field. It has proven difficult to reliably identify such time periods at frequencies $\lt 0.1\,$ Hz using recordings at a single location, resulting in a negative bias in estimated measurement system gain values (the ‘dip artefact’) in the 0.02–0.1 Hz passband. The IMS is deploying arrays of microbarometers, and we show that a measure of across-array coherence can be used to identify time periods associated with acoustic signal propagation. Amplitude response estimates, using 1 yr of data from four IMS arrays, indicate that the dip artefact can be removed by retaining for analysis only those time periods that exhibit high across-array coherence. Moreover, our analysis confirms the hypothesis that the dip artefact is associated with time periods during which wind-generated pressure fluctuations dominate, leading to partial suppression of noise with length scales less than the extent of the WNRS. At two arrays within continental forests accurate amplitude responses are estimated across the 0.02–4 Hz passband, as acoustic signals at all frequencies can be identified. At two oceanic island arrays, the low numbers of time windows with above-noise acoustic signal in the 0.02–0.1 Hz passband make reliable response estimation at these frequencies difficult or impossible. It is recommended that the methodology for estimating the response of an infrasound measurement system at an array should incorporate a multichannel coherence measure; data centres may already routinely compute such measures in their signal detection algorithms.

Epitaxial growth of peculiar GeSn and SiSn nanostructures using a Sn island array as a seed

The regularities of the GeSn and SiSn nanostructure formation on Si and Ge(100) substrates on the vapor–liquid-crystal mechanism were studied. It was shown that either thread-like nanostructures or mushroom-shaped islands containing truncated icosahedrons in the upper Ge part can appear on a Ge(100) substrate. A Sn-rich island array with faceted silicon pedestals was formed during the Si growth over the Sn island array obtained on a Si(100) substrate. Two characteristic island shapes with lenticular and conical shapes were found by transmission electron microscopy (TEM). Lenticular islands consist of β-Sn and are buried in Si, while cone-shaped islands, in addition to β-Sn, contain a SiSn solid solution region in their lower part. The Sn content, estimated from interplanar spacing changes, is about 5%. The region between the islands also contains the SiSn solid solution layer. In addition, it has a nanostructured faceted morphology. The photoluminescence signal from structures with the SiSn island array with silicon pedestals was observed in the region from 1.25 to 3 μm with a maximum of about 2 μm. The nanostructured faceted surface formation was studied by self-organization. The appearance of GeSn cross-structures was revealed during the GeSn deposition on a nanostructured faceted surface. The near-infrared photoluminescence increase by a factor of 3.5 was demonstrated in the samples with cross-structures.

Robust anomalous metallic states and vestiges of self-duality in two-dimensional granular In-InOx composites

Many experiments investigating magnetic-field tuned superconductor-insulator transition (H-SIT) often exhibit low-temperature resistance saturation, which is interpreted as an anomalous metallic phase emerging from a ‘failed superconductor’, thus challenging conventional theory. Here we study a random granular array of indium islands grown on a gateable layer of indium-oxide. By tuning the intergrain couplings, we reveal a wide range of magnetic fields where resistance saturation is observed, under conditions of careful electromagnetic filtering and within a wide range of linear response. Exposure to external broadband noise or microwave radiation is shown to strengthen the tendency of superconductivity, where at low field a global superconducting phase is restored. Increasing magnetic field unveils an ‘avoided H-SIT’ that exhibits granularity-induced logarithmic divergence of the resistance/conductance above/below that transition, pointing to possible vestiges of the original emergent duality observed in a true H-SIT. We conclude that anomalous metallic phase is intimately associated with inherent inhomogeneities, exhibiting robust behavior at attainable temperatures for strongly granular two-dimensional systems.

Optical Properties of Three-Dimensional InGaP(As) Islands Formed by Substitution of Fifth-Group Elements

The optical properties of three-dimensional quantum-size InGaPAs islands, which are formed by substitution of phosphorous by arsenic in an InGaPAs layer deposited on GaAs directly during the epitaxial growth, are studied by photoluminescence (PL) spectroscopy. The PL line of the formed array of island lies in the range of 950–1000 nm at room temperature. The PL studies in the temperature range of 78–300 K indicate significant inhomogeneity of the island array, existence of nonradiative recombination centers, and transport of carriers between islands. The photoluminescence excitation spectra exhibit a line related to the absorption in the residual two-dimensional InGaPAs layer. Annealing of the structures allowed us to increase the PL intensity at room temperature up to 300% with a slight short-wavelength shift of the island emission line and to improve the homogeneity inside the island array.

DNA methylation changes in the hippocampus of learning and memory disorder offspring rats of lead exposure during pregnant and lactation period.

Pregnant female rats exposed to lead may give birth to offspring with learning and memory disorders. Many studies have shown that there are many mechanisms that cause learning and memory impairment. Epigenetic mechanisms may play an important function in the learning and memory impairment. We examined DNA methylation changes in the hippocampus of rats with learning and memory disorder that were the offsprings of rats exposed to lead during pregnant and lactation period. The Morris Water Maze was applied as a learning and memory test, and a Roche NimbleGen's rat DNA methylation 385K Promoter Plus CpG Island Array was used for array hybridization. The results of the integrated navigation and spacial exploration test showed that until 21 days after birth and the lactation period, the learning and memory abilities of offsprings with lead exposure during pregnant and lactation period were significantly lower than those of the control group. The hippocampus DNA methylation levels of the three types of promoters increased compared with those of the control group. According to the Gene Ontology (GO) terms, metal ion transport, cell connections, the lamellar body, the axon bulge, and methylation of various metal transporters were found to be significantly enriched. Pathway analysis showed that the hedgehog signaling pathway, neuroactive receptor-ligand interaction with the ligase pathway, and interaction between cytokines had high methylation. DNA methylation of the whole genome in the hippocampus of the rats with learning and memory impairment induced by perinatal lead contact showed a lot of changes compared with that in the group of control.

An H/V geostatistical approach for building pseudo-3D Vs models to account for spatial variability in ground response analyses Part I: Model development

Many recent studies have shown that we are generally unable to accurately replicate recorded ground motions at most borehole array sites using available subsurface geotechnical information and one-dimensional (1D) ground response analyses (GRAs). When 1D GRAs fail to accurately predict recorded site response, the site is often considered too complex to be effectively modeled as 1D. While three-dimensional (3D) numerical GRAs are possible and believed to be more accurate, there is rarely a 3D subsurface model available for these analyses. The lack of affordable and reliable site characterization methods to quantify spatial variability in subsurface conditions, particularly regarding shear wave velocity (Vs) measurements needed for GRAs, has pushed researchers to adopt stochastic approaches, such as Vs randomization and spatially correlated random fields. However, these stochastically generated models require the assumption of generic, or guessed, input parameters, introducing significant uncertainties into the site response predictions. This article describes a new geostatistical approach that can be used for building pseudo-3D Vs models as a means to rationally account for spatial variability in GRAs, increase model accuracy, and reduce uncertainty. Importantly, it requires only a single measured Vs profile and a number of simple, cost-effective, horizontal-to-vertical spectral ratio (H/V) noise measurements. Using Gaussian geostatistical regression, irregularly sampled estimates of fundamental site frequency from H/V measurements ( f0,H/V) are used to generate a uniform grid of f0,H/V across the site with accompanying Vs profiles that have been scaled to match each f0,H/V value, thereby producing a pseudo-3D Vs model. This approach is demonstrated at the Treasure Island and Delaney Park Downhole Array sites (TIDA and DPDA, respectively). While the pseudo-3D Vs models can be used to incorporate spatial variability into 1D, two-dimensional (2D), or 3D GRAs, their implementation in 1D GRAs at TIDA and DPDA is discussed in a companion paper.

An H/V geostatistical approach for building pseudo-3D Vs models to account for spatial variability in ground response analyses Part II: Application to 1D analyses at two downhole array sites

Common procedures used to account for spatial variability of shear wave velocity (Vs) in one-dimensional (1D) ground response analyses (GRAs), such as stochastic randomization of Vs or increasing small-strain damping, have been shown to improve seismic site response predictions relative to 1D GRAs where no attempts are made to account for spatial variability. However, even after attempting to account for spatial variability using common procedures, 1D GRAs often still yield results that are different than ground motions recorded at many downhole array sites. When 1D predictions differ from observations, the site is typically considered to be too spatially variable to effectively use 1D GRAs. While there is no doubt that some sites are indeed too variable for 1D GRAs, it is also possible that simple 1D analyses could still be effectively used at many sites if spatial variability is accounted for through a more rational, site-specific approach. In this study, an H/V geostatistical approach for building pseudo-3D Vs models is implemented to account for spatial variability in 1D GRAs. The geostatistical approach is used to generate a uniform grid of Vs profiles that have been scaled to match fundamental site frequency estimates from horizontal-to-vertical spectral ratio (H/V) noise measurements. In this article, 1D GRAs are performed for each grid point and the results are statistically combined to reflect the average site response and its variability. This 1D application is demonstrated at the Treasure Island and Delaney Park Downhole Array sites, where it is shown to produce superior fits to the small-strain recorded site response relative to existing approaches used to account for spatial variability in 1D GRAs. Using the proposed approach, we also investigate the lateral area that is likely influencing site response at each site and show that it could extend to significant distances (as much as 1 km) from the boreholes.

Оптические свойства трехмерных островков InGaP(As), сформированных методом замещения элементов пятой группы

Photoluminescence spectroscopy (PL) has been used to study the optical properties of three-dimensional quantum-sized InGaPAs islands formed by substituting phosphorus by arsenic in an InGaP layer deposited on GaAs directly during epitaxial growth. PL line of the formed array of islands is in the range of 950–1000 nm at room temperature. Studies of PL in the temperature range 78–300 K indicate a significant inhomogeneity of the island array, the presence of nonradiative recombination centers, and carrier transport between islands. We observe in the photoluminescence excitation spectra a line associated with absorption in the residual two-dimensional InGaPAs layer. Annealing of the structures results in 300% increase of the PL intensity at room temperature with an insignificant short-wavelength shift of the island PL line, and also in improvement of the homogeneity within the island array.

Monitoring Vocalizing Species by Engaging Community Volunteers Using Cell Phones

ABSTRACTBiodiversity monitoring is important for species and habitat management, although it can be costly in terms of personnel time and expertise. Citizen Science projects that engage community participants to collect species distribution data can provide high volumes of data at little cost, but data are often associated with unknown observer error. Projects that remove decision‐making (e.g., species identification) allow for higher participation because expertise requirements are eliminated. We piloted a project using Citizen Science principles to solve logistical challenges for a synoptic amphibian survey across an island array in the United States Virgin Islands by inviting the community to collect recordings of frogs using cell phones. We received >270 recordings and location data from community participants during a 2‐week survey window; these were processed manually, using bioacoustics analysis software for species identification and location. Species detections were comparable to previous methods of survey although new distribution records were substantially increased. Utilizing Citizen Scientists to conduct recorded surveys of amphibians using cell phones offers a low‐cost method for expanding survey effort for predictably‐vocalizing species. © 2020 The Wildlife Society.

Chiral topologically ordered insulating phases in arrays of interacting integer quantum Hall islands

We study networks of Coulomb-blockaded integer quantum Hall islands with even fillings $\nu=2k$ ($k$ being an integer), including cases with $2k$ layers each of $\nu=1$ fillings. Allowing only spin-current interactions between the islands (i.e., without any charge transfer), we obtain solvable models leading to a rich set of insulating $SU(2)_k$ topologically ordered phases. The case with $k=1$ is dual to the Kalmeyer-Laughlin phase, $k=2$ to Kitaev's chiral spin liquid and the Moore-Read state, and $k=3$ contains a Fibonacci anyon that may be utilized for universal topological quantum computation. Additionally, we show how the $SU(2)_k$ topological phases may be obtained also in an array of islands with $\nu=2k$ integer quantum Hall states and critical spin chains in a checkerboard pattern. The array and checkerboard constructions gap out the charge mode and additional "flavor" modes by virtue of their geometry. Furthermore, we find that a fine tuning of the system parameter is not needed in the checkerboard configuration and the $\nu=2$ case. We also discuss their bulk excitations, and show that their thermal Hall conductance is universal, reflecting the central charge $c=3k/(k+2)$ of the chiral edge modes.

Improvement of viewing angle dependence of bottom-emitting green organic light-emitting diodes with a strong microcavity effect.

The current efficiency and color purity of organic light-emitting diodes (OLEDs) can be easily improved by means of a microcavity structure, but this improvement is typically accompanied by a deterioration in the characteristics of viewing angle. To minimize the angular dependence of the color characteristics exhibited by these strong microcavity devices, we investigated the changes in the optical properties of the green OLED with a bottom resonant structure. This investigation was based on varying the hole transport layer and semitransparent anode thicknesses. The results of optical simulations revealed that the current efficiency and viewing angle characteristics can be simultaneously improved by adjusting the thickness of the two layers. Furthermore, optical simulations predicted that the angular color dependence could be limited to 0.019 in the International Commission on Illumination (CIE) 1976 coordinate system. This optimum condition yielded a current efficiency of ∼134 cd/A. To further reduce this color shift, a nanosized island array (NIA) was introduced through the dewetting process of cesium chloride. By employing NIAs, the color coordinate shift value was reduced to 0.016 in the CIE 1976 coordinate system, and a current efficiency of 130.7 cd/A was achieved.

Molecular Beam Epitaxy of Strained Nanoheterostructures Based on Si, Ge, and Sn

The results of investigating the generation of strained nanoheterostructures based on compounds with materials of group IV (Ge, Si, Sn) are presented. It is established how silver, tin, and lead atoms diffuse over the surface and what temperature dependences of diffusion coefficients are specific to atoms of these elements. It is shown that the diffusion of silver, tin, and lead atoms follows the mechanism of solid-phase wetting with generation of surface phases. The experimental data are provided that indicate the dominating role of edge dislocations and dislocation complexes of edge type in relaxation of Ge/Ge $${}_{0.5}$$ Si $${}_{0.5}$$ /Si(001) heterostructure. Tin-rich islands with Si pedestal on Si(001) substrate were obtained by the molecular beam epitaxy method. Firstly, the Sn film was applied on the Si surface. During the subsequent annealing an array of Sn islands, which were further used as catalysts for growing nanoobjects, was formed. Tin-rich islands with Si pedestal are formed after deposition of silicon at temperatures of 300–450 $${}^{\circ}$$ C on the surface with Sn islands. The growth of islands with pedestal occurred by the vapor–liquid–crystal mechanism. Intense photoluminescence was revealed from the tin-rich islands with Si pedestals in the wavelength range 1.3–1.7 $$\mu$$ m.

Realizing Stretchable OLEDs: A Hybrid Platform Based on Rigid Island Arrays on a Stress‐Relieving Bilayer Structure

AbstractOptoelectronic devices that are stretchable can revolutionize various fields by enabling the functionalities that are not accessible from conventional rigid platforms. In this respect, many efforts are made to realize stretchable organic light‐emitting diodes (OLEDs) for their compatibility with various deformable substrates. Two representative examples of such efforts include a method based on intrinsically stretchable materials and a method to attach ultrathin OLEDs on a prestrained elastomer substrate. However, both of those methods have limitations either in material availability for high performance or in optical clarity. Here a hybrid platform is proposed for stretchable OLEDs free from such limitations. The proposed platform is composed of an array of rigid islands connected by serpentine‐shaped interconnectors formed on a bilayer elastomer substrate in which the top layer has an ultralow Young's modulus of ≈0.9 kPa, greatly relieving the rigid islands and interconnectors of the mechanical stress applied to them when stretched. With the proposed platform, stretchable OLEDs are demonstrated that can be repeatedly stretched by 140% and are based on thermally evaporable materials well established for fabrication of high‐performance OLEDs.

Luminescence of Spatially Ordered Self-Assembled Solitary Ge(Si) Nanoislands and their Groups Incorporated into Photonic Crystals

The luminescence properties of arrays of spatially ordered self-assembled solitary Ge(Si) nanoislands and their groups, including those embedded in two-dimensional photonic crystals, are studied. It is shown that the incorporation of an array of ordered solitary Ge(Si) islands and their groups into photonic crystals results in an increase in the intensity of their photoluminescence signal at liquid-nitrogen temperature. The maximum increase in the intensity (by a factor of up to ~30) is observed for an ordered array of solitary Ge(Si) islands. The increase in the intensity is attributed to the interaction of emission from islands with photonic-crystal radiative modes. This interaction is more efficient in the case of an array of solitary islands. Due to such interaction the luminescence signal from ordered solitary Ge(Si) islands incorporated into photonic crystals is observed at up to room temperature.