Spatial Homogeneity Research Articles

The optimization of vertical bifacial photovoltaic farms for efficient agrivoltaic systems

An unprecedented demand for Food, Energy, and Water (FEW) resources over coming decades and the rising climate concerns require integrated FEW innovations with least environmental footprint. Collocating photovoltaic (PV) technology with agriculture is a promising approach towards dual land productivity that could locally fulfill growing food and energy demands particularly in rural areas. This ‘agrivoltaic’ (AV) solution can be highly suitable for hot and arid climates where an optimized solar panel coverage could prevent excessive thermal stress during harsh weather thereby increasing the crop yield and lowering the water budget. One of the concerns with using standard fixed tilt solar array structure that faces North/South (N/S) direction for AV farming is the spatial heterogeneity in the daily sunlight distribution for crops and soil water contents, both of which could affect crop yield. Dynamic tilt control through a tracking system can eliminate this problem but could increase the system cost and complexity. Here we present the investigation of vertically tilted bifacial AV farms which can be especially attractive for climates where PV losses due to dust are high. The relative food-energy performance for the vertical East/West faced bifacial panel (bi-E/W) scheme is compared with the standard monofacial tilted panels facing North/South (mono-N/S) through integrated models for energy conversion, spatial/temporal shade patterns, and the crop yield that is benchmarked against the reported field experiments for lettuce. We show that both schemes have similar food-energy yields for shade-sensitive crops which require a relatively low array density (i.e.⩽1/2 of that for the standard ground mounted PV systems). On the other hand, the two PV schemes have remarkably different food-energy yields for denser PV array configuration for which bi-E/W provides higher crop yield and mono-N/S exhibits higher energy yield. To preserve ⩾80% of lettuce yield, the maximum array density is limited from half to twice of the standard PV systems corresponding to the varying shade response for the crop. Similarly, to preserve 80% of the energy yield, the lettuce yield is predicted to vary from 65% (shade-sensitive) to 100% (shade-tolerant). The vertical bi-E/W scheme is although not superior in terms of the combined food-energy performance, it could be attractive for its distinct advantages such as spatial homogeneity for shades and rainfall under panels, convenient architecture for farm machinery mobility, and an inherent resilience to soiling.

Estimating Mean Surface Backscatter from GPM Surface Backscatter Observations

The radar on the Global Precipitation Measurement (GPM) mission observes precipitation at 13.6 GHz (Ku-band) and 35.6 GHz (Ka-band) and also receives echoes from the earth’s surface. Statistics of surface measurements for non-raining conditions are saved in a database for later use in estimating the precipitation path-integrated attenuation. Previous work by Meneghini and Jones (2011) showed that while averaging over larger latitude/longitude bins increase the number of samples, it can also increase sample variance due to spatial inhomogeneity in the data. As a result, Meneghini and Kim (2017) proposed a new, adaptive method of database construction, in which the number of measurements averaged depends on the spatial homogeneity. The purpose of this work is to re-visit previous, single-frequency results using dual-frequency data and optimal interpolation (kriging). Results include that (1) temporal inhomogeneity can create similar results as spatial, (2) Ka-band behavior is similar to Ku-band, (3) the Ku-/Ka-band difference has less spatial inhomogeneity than either band by itself, and (4) kriging and the adaptive method can reduce the sample variance. The author concludes that finer spatial and temporal resolution is necessary in constructing the database for single frequencies but less so for the Ku-/Ka-band difference. The adaptive approach reduces sample standard deviation with a relatively modest computational increase.

Exploration of a singular fluid spacetime

We investigate the properties of a special class of singular solutions for a self-gravitating perfect fluid in general relativity: the singular isothermal sphere. For arbitrary constant equation-of-state parameter w=p/rho , there exist static, spherically-symmetric solutions with density profile propto 1/r^2, with the constant of proportionality fixed to be a special function of w. Like black holes, singular isothermal spheres possess a fixed mass-to-radius ratio independent of size, but no horizon cloaking the curvature singularity at r=0. For w=1, these solutions can be constructed from a homogeneous dilaton background, where the metric spontaneously breaks spatial homogeneity. We study the perturbative structure of these solutions, finding the radial modes and tidal Love numbers, and also find interesting properties in the geodesic structure of this geometry. Finally, connections are discussed between these geometries and dark matter profiles, the double copy, and holographic entropy, as well as how the swampland distance conjecture can obscure the naked singularity.

Construction and characterization of a high luminance level source based on high power multi-chip white LEDs

In order to calibrate the luminance measurement devices at higher luminance ranges, a luminous source with a high-level light output is required. Such sources are usually provided by halogen lamps. However, with the developing semiconductor technologies in recent years, the creation of light sources with high-power white light-emitting diodes (LEDs) has begun to be included in the field of metrology. For this reason, a luminous source having a wide range of luminance production capabilities has been developed. The source was based on an integrating sphere with two high-power white LEDs and a variable power supply. Forced convection was utilized by using a cooling fan to increase the heat transfer together with the existing heat sink to prevent the LEDs from being damaged at high current levels and to provide stable optical output. The cooling performance of the LEDs and optical characterization studies such as the spectral characteristics and produced luminance depend on driving currents and spatial surface homogeneity of the constructed luminance source were also carried out. With the constructed luminance source, luminance calibration of a meter up to 200000 cd/m2 level can be performed.

Single-stage few-cycle nonlinear compression of milliJoule energy Ti:Sa femtosecond pulses in a multipass cell.

We report on the nonlinear temporal compression of mJ energy pulses from a Ti:Sa chirped pulse amplifier system in a multipass cell filled with argon. The pulses are compressed from 30 fs down to 5.3 fs, corresponding to two optical cycles. The post-compressed beam exhibits excellent spatial quality and homogeneity. These results provide guidelines for optimizing the compressed pulse quality and further scaling of multipass-cell-based post-compression down to the single-cycle regime.

Enhancing the capture efficiency and homogeneity of single-layer flow-through trapping microfluidic devices using oblique hydrodynamic streams

With the aim to parallelize and monitor biological or biochemical phenomena, trapping and immobilization of objects such as particles, droplets or cells in microfluidic devices has been an intense area of research and engineering so far. Either being passive or active, these microfluidic devices are usually composed of arrays of elementary traps with various levels of sophistication. For a given array, it is important to have an efficient and fast immobilization of the highest number of objects, while optimizing the spatial homogeneity of the trapping over the whole chip. For passive devices, this has been achieved with two-layer structures, making the fabrication process more complex. In this work, we designed small microfluidic traps by single-layer direct laser writing into a photoresist, and we show that even in this simplest case, the orientation of the main flow of particles with respect to the traps have a drastic effect on the trapping efficiency and homogeneity. To better understand this phenomenon, we have considered two different flow geometries: parallel and oblique with respect to the traps array, and compared quantitatively the immobilization of particles with various sizes and densities. Using image analysis, we show that diagonal flows gives a spatial distribution of the trap loading that is more homogeneous over the whole chip as compared to the straight ones, and by performing FEM and trapping simulation, we propose a qualitative explanation of this phenomenon.

Extracting Terrain Texture Features for Landform Classification Using Wavelet Decomposition

Accurate landform classification is a crucial component of geomorphology. Although extensive classification efforts have been exerted based on the terrain factor, the scale analysis to describe the macro and micro landform features still needs standard measurement. To obtain the appropriate analysis scale of landform structure feature, and then carry out landform classification using the terrain texture, the texture feature is introduced for reflecting landform spatial differentiation and homogeneity. First, applying the ALOS World 3D-30m (AW3D30) DEM and selecting typical landforms of the southwest Tibet Plateau, the discrete wavelet transform (DWT), which acts as the texture feature analysis method, is executed to dissect the multiscale structural features of the terrain texture. Second, through the structural indices of reconstructed texture images, the optimum decomposition scale of DWT is confirmed. Under these circumstances, wavelet coefficients and wavelet energy entropy are extracted as texture features. Finally, the random forest (RF) method is utilized to classify the landform. Results indicate that the texture feature of DWT can achieve higher classification accuracy, which increases by approximately 11.8% compared with the gray co-occurrence matrix (GLCM).

다양한 유사성 척도를 이용한 바람권역의 군집분석

To assess wind resources in a given area, it is necessary to select a representative measurement point by identifying a wind zone where the wind resource characteristics are homogeneous. In this study, to identify the spatial homogeneity of wind resources, it was necessary to test several similarity measures for clustering analysis, such as time-series wind vector similarity, Pearson's correlation coefficient of time-series wind speed, the cosine distance of time-series wind direction, the index of agreement of time-series wind speed, the 24-hour autocorrelation function, and the principal components of wind resource factors. It was found that the primary components of wind resources were the Weibull scale and shape factors of wind speed distribution, while terrain elevation and the 24-hour autocorrelation function were chosen as the secondary components. The similarity measures were applied to Jeju Island, which has a simple topography, and the Pohang region, which has a complex mountainous topography, to classify the wind zones; while poly-serial correlation coefficients, together with box plots, were used to evaluate whether there was a significant statistical difference in the wind resource factors within a given cluster. In conclusion, it was confirmed that the time-series wind vector similarity and the primary components of wind resource factors are the most effective similarity measures of clustering analysis.

Application-driven synthesis and characterization of hexagonal boron nitride deposited on metals and carbon nanotubes

Hexagonal boron nitride (h-BN) is unique among two-dimensional materials, with a large band gap (∼6 eV) and high in-plane thermal conductivity (>400 W m−1 K−1), second only to diamond among electrical insulators. Many studies to date have relied on exfoliated h-BN, however, for large-scale applications the material must be synthesized by methods such as chemical vapor deposition (CVD). Here, we first investigate single-layer h-BN synthesized by CVD on single crystal platinum (Pt), comparing these films with h-BN deposited on more commonly used polycrystalline Pt and Cu. The h-BN film grown on single crystal Pt has the lowest surface roughness and best spatial homogeneity, and our electrochemical transfer process allows the Pt to be reused with no measurable degradation. We also demonstrate direct capping of carbon nanotubes (CNTs) with as-grown h-BN, but we find that the direct growth partly degrades the CNT electrical conductivity. On the other hand, we show that transferred monolayer h-BN can serve as an ultrathin barrier which protects MoS2 from damage at high temperatures and discuss other applications that take advantage of the conformal h-BN deposition.

Assessment of LST spatial and temporal changes in Jazmourian basin, southeast Iran

ABSTRACT Land surface temperature (LST) is an atmosphere-land interaction, which represents the first thermal reaction of the environmental changes occurring in the earth surface, being one of the most important factors used in the earth sciences. Jazmourian basin, in the southeast of Iran, is a fertile agricultural land with diverse topography and unique climatic conditions. Due to its significance as one of the most important agricultural poles of Iran, the LST variations are of great interest due to their high impact on the environmental processes, especially in the land cover. In recent years, Moderate Resolution Imaging Spectroradiometer images have been extensively used to estimate the LST due to their spatial and temporal homogeneity and freely available showing improved capabilities of climate analysis in the areas with scarce observation networks. We used a combination of MOD11C3 and MYD11C3 products of daytime and nighttime LST, covering the complete circadian cycle over Jazmourian basin, from 2003 to 2019. Results showed varied trends by months with a significantly positive increase in January. The spatial distribution revealed a generalized positive anomaly in the whole study area, with the highest values in central lowlands and lowest at eastern high elevations of the basin. The temporal and spatial analyses indicated high temperature differences between months and seasons as well as a wide range from −10°C to 65°C.

Microstructural effects on the dynamical relaxation of glasses and glass composites: A molecular dynamics study

One way to increase the ductility of metallic glasses is to induce heterogeneous microstructures, as for example in nanoglasses and crystal-glass composites. The heterogeneities have important consequences not only on the development of shear bands, but also on the structural relaxations in the glass phase. Experiments using dynamic mechanical spectroscopy (DMS) have been conducted, but an atomic-scale picture is still lacking. Here we apply DMS within molecular dynamics simulations to a classical CuZr metallic glass to study how structural relaxations and mechanical energy dissipation are affected by different microstructures, including nanoglasses, crystal-glass nanolaminates and glasses with spherical crystalline inclusions. We find that in a fully glassy system, not only the fraction but also the spatial homogeneity of “hard” icosahedral environments matter. When hard crystalline particles are introduced, the storage modulus simply results from volumetric averages consistent with the classical Voigt and Reuss bounds. On the other hand, loss moduli are much more complex and can be smaller or larger than in a pure glass depending on the microstructure and loading condition. Atomistic processes leading to these evolutions are discussed and remaining open questions are highlighted.

Highly Sensitive and Spatially Homogeneous Surface-Enhanced Raman Scattering Substrate under Plasmon–Nanocavity Coupling

We fabricated a plasmon–nanocavity coupling structure composed of Au nanoparticles (Au-NPs), titanium dioxide, and Au-film (ATA) as a highly sensitive and spatially homogeneous surface-enhanced Raman scattering (SERS) substrate. The SERS intensity of the ATA was ∼11 times higher than that of the Au-NPs/TiO2 substrates without cavity enhancement. This SERS enhancement was attributed to the remarkable near-field enhancement of Au-NPs under coupling with cavity resonance. Under the present experimental conditions, crystal violet (CV) molecule decorated ATA prepared from a concentration as low as 10–7 mol/L could be detected, which is 1 order of magnitude higher sensitivity than the samples without cavities. More importantly, a spatially homogeneous SERS signal distribution of Raman mapping on the ATA was demonstrated over a 20 × 20 μm2 area on the sample, attributed to the homogeneous near-field distribution over the Au-NPs under coherent coupling between plasmon resonance and cavity resonance. We envision that this plasmon–nanocavity coupling SERS structure with high sensitivity, repeatability, and spatial homogeneity can be practically used in chemical and biomolecule detection devices.

MOMENTUM OF AN ELECTROMAGNETIC WAVE IN TIME-VARYING DIELECTRIC MEDIA

In the context of the Abraham–Minkowski controversy, the problem of the propagation of electromagnetic waves in a linear dielectric medium with a time-varying dielectric constant is considered. It is shown that the momentum of an electromagnetic wave in the form of Minkowski is preserved with an instantaneous change in the dielectric permittivity of the medium. At the same time, the Abraham momentum is not conserved, despite the spatial homogeneity of the problem. This circumstance is interpreted as a manifestation of the Abraham force.

A novel marine spatial management tool for multiple conflicts recognition and optimization of marine functional zoning in the East China sea

Marine spatial planning (MSP) is to manage incompatible functional use for achieving spatial homogeneity in sea. However most MSP strategies focus on single-target sea use demand ignoring multiple-conflicts of different demands. Thus, this study develops a spatial management model and quantitatively recognizes two types of spatial conflicts among eight sea use functions in the Zhejiang coasts, China. Under the simulation of three different management scenarios including independent, joint and overall-value managements respectively, we further propose a conflict optimization scheme in the scenarios of sea uses with different intensities, different types of sea use combinations, and different site selection. Most importantly, this study demonstrates the spatial management model is a powerful and efficient tool for spatial multiple-conflicts trade-off and matching sea use demands under the practical approach of marine functional zoning (MFC) in China.

Spatial-temporal evolution and influencing factors of total factor productivity in China's logistics industry under low-carbon constraints.

Behind the rapid development of China's logistics industry, there are problems of high energy consumption and high pollution. Under the dual constraints of resources and environment, promoting the low-carbon transformation of the logistics industry is the key to achieving sustainable development of the logistics industry. This paper applies the epsilon-based measure (EBM) model which considers undesirable output and global Malmquist-Luenberger (GML) index to measure the logistics efficiency under the low-carbon constraints of 30 provinces in China from 2005 to 2017, that is, the green total factor productivity (GTFP), and characterizes its temporal and spatial evolution characteristics through visualization and spatial analysis methods. Then, this paper uses the geographically weighted regression (GWR) model to analyze the influence of industrial agglomeration level, informatization level, foreign direct investment, logistics energy intensity, traffic network density, and technological innovation capability on the GTFP of the logistics industry. The findings of this paper show that (1) during the inspection period, the overall average GTFP of the logistics industry was 0.992, which did not reach the effective level, and the spatial differentiation showed that the average GTFP of eastern was greater than that of in central, and that of in central was greater than that of in western. (2) The GTFP of the logistics industry has experienced an alternating process of rising and falling in time, with large fluctuations. Also, in terms of spatial dimension, there is a trend that high-level areas gradually gather to the southeast, and there is significant spatial autocorrelation. (3) For the logistics industry, high-efficiency areas and high-output areas show significant spatial homogeneity. (4) The estimation results of the GWR show that the direction and intensity of the multi-dimensional driving factors on the GTFP of the logistics industry are different in different regions, showing obvious spatial non-stationary characteristics.

Analysis of climate change in Terskol over the last 60 years

In connection with the ongoing climatic changes, the tasks of monitoring the climate of the high-mountainous zone of the Caucasus are of particular importance. Climatological studies in this work are based on the material of long-term meteorological observations from 1961 to 2020. according to the Terskol weather station. Correlation analysis showed the spatial homogeneity of temperature changes in Terskol and weather stations of all climatic zones of southern Russia, in contrast to the regional precipitation regime with a small scale of coherence (up to 200 km). In the modern period (1991-2020), the change in average temperatures in comparison with climatic norms (1961-1990) is not confirmed by statistical estimates, with the exception of the summer season. Over the 60-year period, from 1961 to 2020, there was a statistically significant increase in average summer temperatures by 0.31 °C/10 years (D = 26.8%). At the turn of the 20th and 21st centuries a steady increase in winter, spring and annual temperatures is formed, while summer temperatures maintain a positive trend, but statistically insignificant at this time interval. Period from 2006 characterized by the addition of a statistically significant increase in the absolute maximums of all seasonal temperatures, in contrast to the sums and daily maximum precipitation, the decrease in which in the winter season is statistically insignificant, and there are no trends in other seasons. Such a prevailing thermal and precipitation regime in recent decades has become the main component of many factors leading to dangerous slope phenomena, glacier degradation and significant changes in the hydrological regime.

Photocatalytic Degradation of 2-propanol Over TiO2-based Thin Films in a Simulated Pilot Microreactor

Background: Microreactor devices have attracted increasing attention over the last years due to their high surface-to-volume ratio, which ensures a high heat and mass transfer, short molecular diffusion distance and greater spatial illumination homogeneity compared to the traditional reactors. Objective: The aim of this study was to model the kinetics of photo-degradation of 2-propanol over TiO2-based thin films in a gas-phase batch-reactor and simulate their performance in a microreactor device. Methods: The reaction was carried out in a gas-phase batch-reactor, assessing the reactivity of singlelayer nitrogen (N)-doped TiO2 and a bilayer consisting of N-doped TiO2 as a bottom layer and copper (Cu)-doped TiO2 as a top layer. The kinetics of the photocatalytic process was modelled by Langmuir– Hinshelwood (LH) model. The constants obtained from the LH model were used to simulate the performance of the photocatalysts in a microreactor, operating in a continuous flow mode and investigating the effect of the volumetric flow rate (Q), initial concentration of pollutant (Co), number of microchannels (n) and microchannel length (l) on the photo-degradation of 2-propanol. Results: N-Cu-TiO2 exhibited a higher reactivity but a lower adsorption ability towards the target pollutant compared to N-TiO2. To maximize and leverage the advantages of a microreactor, optimal operating conditions for a continuous flow mode, at a steady-state, should be moderately low Q and Co, long l and n that minimizes flow maldistribution in parallel. Conclusion: The findings in this work could serve as a basis to design and fabricate efficient microreactors for the removal of VOC in air purification applications.

Sharing spaces: niche differentiation in diet and substrate use among wild capuchin monkeys

Understanding variation in social grouping patterns among animal taxa is an enduring goal of ethologists, who seek to evaluate the selective pressures shaping the evolution of sociality. Cohesive association with conspecifics increases intragroup feeding competition and may impose constraints on group size. Furthermore, in sexually dimorphic species, males and females may have different nutritional requirements, which can lead to suboptimal foraging in mixed-sex groups. How do animals living in permanent social groups mitigate these foraging costs? Niche differentiation is often hypothesized as a mechanism, but rigorous and detailed tests of the extent and context of differences in diet and habitat use, key tenets of this hypothesis, are rare. We investigated the potential for niche differentiation in foraging activity budget and environment use in a population of wild white-faced capuchin monkeys, Cebus imitator , in northwestern Costa Rica. Using a robust data set of 15 879 foraging scan samples collected from four groups over 13 months, we found that smaller individuals – e.g. juveniles and females – forage more often on smaller branches. We additionally found clear evidence of predator-sensitive foraging wherein the smallest individuals spent less time on the ground during invertebrate foraging. Importantly, niche differentiation was far more evident overall during invertebrate foraging, likely due to spatial constraints and environmental homogeneity imposed by fruit patches. In summary, we found considerable variation in habitat use across age and sex classes, likely attributable to differences in size and relative predation risk. These variables likely reduce intraspecific feeding competition by promoting differential diet and habitat use. Our results also provide insight into the limits of niche differentiation as a strategy for competition reduction and may shed light on the evolution of fission–fusion dynamics in highly frugivorous species. • Niche differentiation was apparent during invertebrate, but not fruit, foraging. • Use of the forest strata was consistent with predator-sensitive foraging. • Foraging time on difficult-to-access foods did not differ for juveniles and adults. • Smaller individuals – juveniles and females – used smaller substrates more often. • Support substrates affected microhabitat differentiation but are often overlooked.

Enhancing and quantifying spatial homogeneity in monolayer WS2

Controlling the radiative properties of monolayer transition metal dichalcogenides is key to the development of atomically thin optoelectronic devices applicable to a wide range of industries. A common problem for exfoliated materials is the inherent disorder causing spatially varying nonradiative losses and therefore inhomogeneity. Here we demonstrate a five-fold reduction in the spatial inhomogeneity in monolayer WS2, resulting in enhanced overall photoluminescence emission and quality of WS2 flakes, by using an ambient-compatible laser illumination process. We propose a method to quantify spatial uniformity using statistics of spectral photoluminescence mapping. Analysis of the dynamic spectral changes shows that the enhancement is due to a spatially sensitive reduction of the charged exciton spectral weighting. The methods presented here are based on widely adopted instrumentation. They can be easily automated, making them ideal candidates for quality assessment of transition metal dichalcogenide materials, both in the laboratory and industrial environments.

Superconductivity of highly spin-polarized electrons in FeSe probed by Se77 NMR

A number of recent experiments indicate that the iron-chalcogenide FeSe provides the long-sought possibility to study bulk superconductivity in the cross-over regime between the weakly coupled Bardeen-Cooper-Schrieffer (BCS) pairing and the strongly coupled Bose-Einstein condensation (BEC). We report on $^{77}\mathrm{Se}$ nuclear magnetic resonance experiments of FeSe, focused on the superconducting phase for strong magnetic fields applied along the $c$ axis, where a distinct state with large spin polarization was reported. We determine this high-field state as bulk superconducting with high spatial homogeneity of the low-energy spin fluctuations. Further, we find that the static spin susceptibility becomes unusually small at temperatures approaching the superconducting state, despite the presence of pronounced spin fluctuations. Taken together, our results clearly indicate that FeSe indeed features an unusual field-induced superconducting state of a highly spin-polarized Fermi liquid in the BCS-BEC crossover regime.