Spatial Extension Research Articles

The peculiar ejecta of the nova V1425 Aquilae

Many important details of the mechanisms underlying the ejection of material during a (classical) nova eruption are still not understood. Here we present optical spectroscopy and narrow-band images of the nova V1425 Aql, 23 yr after the nova eruption. We find that the ejecta consist of two significantly different components. The first resembles what is commonly seen in novae, that is, a symmetric distribution centred on the position of the underlying cataclysmic binary and presenting both allowed (hydrogen and helium) and forbidden ([O III] and [N II]) transitions. The second one, on the other hand, consists of material travelling at an approximately three times higher velocity that is not visible in the allowed transitions, presents a significantly different [N II]–[O III] ratio, and is located at approximately 2.3 arcsec to the southwest of the position of the binary. Comparing the velocities and spatial extensions of the two ejecta, we find that both originated in the same nova eruption. We explore possible extrinsic and intrinsic mechanisms for the asymmetry of the high-velocity material in the form of asymmetrically distributed interstellar material and magnetic accretion, respectively, but find the available data to be inconclusive. From the expansion parallax, we derive a distance for the nova of 3.3(3) kpc.

Subgap spectroscopy along hybrid nanowires by nm-thick tunnel barriers

Tunneling spectroscopy is widely used to examine the subgap spectra in semiconductor-superconductor nanostructures when searching for Majorana zero modes (MZMs). Typically, semiconductor sections controlled by local gates at the ends of hybrids serve as tunnel barriers. Besides detecting states only at the hybrid ends, such gate-defined tunnel probes can cause the formation of non-topological subgap states that mimic MZMs. Here, we develop an alternative type of tunnel probes to overcome these limitations. After the growth of an InSb-Al hybrid nanowire, a precisely controlled in-situ oxidation of the Al shell is performed to yield a nm-thick AlOx layer. In such thin isolating layer, tunnel probes can be arbitrarily defined at any position along the hybrid nanowire by shadow-wall angle-deposition of metallic leads. In this work, we make multiple tunnel probes along single nanowire hybrids and successfully identify Andreev bound states (ABSs) of various spatial extension residing along the hybrids.

Effect of Storm Size on Sea Surface Cooling and Tropical Cyclone Intensification in the Western North Pacific

Abstract The effect of tropical cyclone (TC) size on TC-induced sea surface temperature (SST) cooling and subsequent TC intensification is an intriguing issue without much exploration. Via compositing satellite-observed SST over the western North Pacific during 2004–19, this study systematically examined the effect of storm size on the magnitude, spatial extension, and temporal evolution of TC-induced SST anomalies (SSTA). Consequential influence on TC intensification is also explored. Among the various TC wind radii, SSTA are found to be most sensitive to the 34-kt wind radius (R34) (1 kt ≈ 0.51 m s−1). Generally, large TCs generate stronger and more widespread SSTA than small TCs (for category 1–2 TCs, R34: ∼270 vs 160 km; SSTA: −1.7° vs −0.9°C). Despite the same effect on prolonging residence time of TC winds, the effect of doubling R34 on SSTA is more profound than halving translation speed, due to more wind energy input into the upper ocean. Also differing from translation speed, storm size has a rather modest effect on the rightward shift and timing of maximum cooling. This study further demonstrates that storm size regulates TC intensification through an oceanic pathway: large TCs tend to induce stronger SST cooling and are exposed to the cooling for a longer time, both of which reduce the ocean’s enthalpy supply and thereby diminish TC intensification. For larger TCs experiencing stronger SST cooling, the probability of rapid intensification is half of smaller TCs. The presented results suggest that accurately specifying storm size should lead to improved cooling effect estimation and TC intensity prediction. Significance Statement Storm size has long been speculated to play a crucial role in modulating the TC self-induced sea surface temperature (SST) cooling and thus potentially influence TC intensification through ocean negative feedback. Nevertheless, systematic analysis is lacking. Here we show that larger TCs tend to generate stronger SST cooling and have longer exposure to the cooling effect, both of which enhance the strength of the negative feedback. Consequently, larger TCs undergo weaker intensification and are less likely to experience rapid intensification than smaller TCs. These results demonstrate that storm size can influence TC intensification not only from the atmospheric pathway, but also via the oceanic pathway. Accurate characterization of this oceanic pathway in coupled models is important to accurately forecast TC intensity.

Extending gestures and global city-making: Analyzing extending urbanization at multiple scales

The strength of the analysis of extended urbanization proposed in Simone et al.'s (2023) ‘Inhabiting the Extensions’ resides in its fascinating ability to bring together a focus on micro gestures and individual decisions with a structural analysis of global capital flows, geopolitics, and climate change. The collective work of ethnographically diving in nine locations across the world, and bringing together these reflections, generated a rich and complex understanding of city-making processes through spatial and temporal extensions.

Combined Effects of Intense THz Laser Field and Applied Electric Field on Binding Energy of Exciton in GaAs/GaAlAs Finite Spherical Quantum Dot

This paper describes the combined effects of intense THz laser field and electric field on the ground state binding energy of heavy hole excitons confined in GaAs/ GaAlAs spherical finite quantum dots. The formulation is based on the model of “laser dressed potential” which combines Coulomb interaction and field effect in only one potential as reported in the literature. The calculation is performed by using the variational method in the framework of the single band effective mass theory. Our results show that (i) the laser field increases the electron and hole confinement energy that form the exciton in the QD until they reach a maximum, then they become almost constant for an intense laser field, (ii)the electric field and the laser field lowers the binding energy for all quantum dot radii making the exciton stabilized and clustered near the center of the dot, and iii)the laser field increases the spatial extension of exciton but the electric field decreases it linearly.

A High-mass, Young Star-forming Core Escaping from Its Parental Filament

We studied the unique kinematic properties in massive filament G352.63-1.07 at 103 au spatial scale with the dense molecular tracers observed with the Atacama Large Millimeter/submillimeter Array. We find the central massive core M1 (12 M ⊙) being separated from the surrounding filament with a velocity difference of and a transverse separation within 3″. Meanwhile, as shown in multiple dense-gas tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament toward both its ends. M1 thus represents a very beginning state for a massive, young star-forming core escaping from the parental filament, within a timescale of ∼4000 yr. Based on its kinetic energy (3.5 × 1044 erg), the core escape is unlikely solely due to the original filament motion or magnetic field but requires more energetic events such as a rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental turbulence. This may help the filament to become stabilized again.

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite-Water Interface by Adsorption of Rb+ and Halides (Cl- , Br- , I- ) at High Salinity.

Classical electric double layer (EDL) models have been widely used to describe ion distributions at charged solid-water interfaces in dilute electrolytes. However, the chemistry of EDLs remains poorly constrained at high ionic strength where ion-ion correlations control non-classical behavior such as overcharging, i. e., the accumulation of counter-ions in amounts exceeding the substrate's surface charge. Here, we provide direct experimental observations of correlated cation and anion distributions adsorbed at the muscovite (001)-aqueous electrolyte interface as a function of dissolved RbBr concentration ([RbBr]=0.01-5.8 M) using resonant anomalous X-ray reflectivity. Our results show alternating cation-anion layers in the EDL when [RbBr]≳100 mM, whose spatial extension (i. e., ~20 Å from the surface) far exceeds the dimension of the classical Stern layer. Comparison to RbCl and RbI electrolytes indicates that these behaviors are sensitive to the choice of co-ion. This new in-depth molecular-scale understanding of the EDL structure during transition from classical to non-classical regimes supports the development of realistic EDL models for technologies operating at high salinity such as water purification applications or modern electrochemical storage.

3D Point Cloud Semantic Segmentation Through Functional Data Analysis

Here, we propose a method for the semantic segmentation of 3D point clouds based on functional data analysis. For each point of a training set, a number of handcrafted features representing the local geometry around it are calculated at different scales, that is, varying the spatial extension of the local analysis. Calculating the scales at small intervals allows each feature to be accurately approximated using a smooth function and, for the problem of semantic segmentation, to be tackled using functional data analysis. We also present a step-wise method to select the optimal features to include in the model based on the calculation of the distance correlation between each feature and the response variable. The algorithm showed promising results when applied to simulated data. When applied to the semantic segmentation of a point cloud of a forested plot, the results proved better than when using a standard multiscale semantic segmentation method. The comparison with two popular deep learning models showed that our proposal requires smaller training samples sizes and that it can compete with these methods in terms of prediction.

Looking for a New Approach to Measuring the Spatial Concentration of the Human Population

Abstract In the article a new approach for measuring the spatial concentration of human population is presented and tested. The new procedure is based on the concept of concentration introduced by Gini and, at the same time, on its spatial extension (i.e., taking into account the concept of spatial autocorrelation, polarization). The proposed indicator, the Spatial Gini Index, is then computed by using two different kind of territorial partitioning methods: MaxMin (MM) and the Constant Step (CS) distance. In this framework an ad hoc extension of the Rey and Smith decomposition method is then introduced. We apply this new approach to the Italian and foreign population resident in almost 7,900 statistical units (Italian municipalities) in 2002, 2010 and 2018. All elaborations are based on a new ad hoc library developed and implemented in Python.

Heatwave Characteristics in the Recent Climate and at Different Global Warming Levels: A Multimodel Analysis at the Global Scale

AbstractThe representation of heatwaves (HWs) in the Coupled Model Intercomparison Project phase 6 (CMIP6) models is analyzed. This study (a) evaluates the performance of CMIP6 simulations against global reanalysis and observations regarding time‐ and intensity‐related criteria and (b) investigates how HWs are projected to change at different global warming levels (GWLs). During 1979–2014, the dispersion of the models is comparable to the observational uncertainty for the time indices (duration, frequency, number of events). It is of the order of one event per year, 1 day for the duration of the events and 2 days for the frequency, with tendencies for over‐ or underestimation, depending on the reference data set and the region considered. For the HW magnitude, the models' dispersion can reach 15°C for a given region and is significantly higher than the observational uncertainty. The mean intensity of HWs tends to be overestimated, which is partly attributed to overly pronounced drying of the soil during HW events. The contribution of the soil moisture anomaly to the temperature anomaly during recent specific HWs is shown to reach up to 30% of the signal. For a given GWL, intensification of HW occurrence, spatial extension, and duration is detected worldwide, but it is modulated at the regional scale and strongly model dependent. For time‐related indices, tropical regions and the Arabian Peninsula will be most impacted, but the maximum temperature will strongly increase in mid‐latitude regions. Time–space analyses of the evolution of HW properties for a given GWL are discussed.

Lagrangian studies of coherent sets and heat transport in constant heat flux-driven turbulent Rayleigh–Bénard convection

We explore the mechanisms of heat transfer in a turbulent constant heat flux-driven Rayleigh–Bénard convection flow, which exhibits a hierarchy of flow structures from granules to supergranules. Our computational framework makes use of time-dependent flow networks. These are based on trajectories of Lagrangian tracer particles that are advected in the flow. We identify coherent sets in the Lagrangian frame of reference as those sets of trajectories that stay closely together for an extended time span under the action of the turbulent flow. Depending on the choice of the measure of coherence, sets with different characteristics are detected. First, the application of a recently proposed evolutionary spectral clustering scheme allows us to extract granular coherent features that are shown to contribute significantly less to the global heat transfer than their spatial complements. Moreover, splits and mergers of these (leaking) coherent sets leave spectral footprints. Second, trajectories which exhibit a small node degree in the corresponding network represent objectively highly coherent flow structures and can be related to supergranules as the other stage of the present flow hierarchy. We demonstrate that the supergranular flow structures play a key role in the vertical heat transport and that they exhibit a greater spatial extension than the granular structures obtained from spectral clustering.

A MUSE/VLT spatially resolved study of the emission structure of Green Pea galaxies

Green Pea galaxies (GPs) present among the most intense starbursts known in the nearby Universe. These galaxies are regarded as local analogs of high-redshift galaxies, making them a benchmark in the understanding of the star formation processes and the galactic evolution in the early Universe. In this work, we performed an integral field spectroscopic (IFS) study for a set of 24 GPs to investigate the interplay between its ionized interstellar medium (ISM) and the massive star formation that these galaxies present. Observations were taken in the optical spectral range (λ4750 Å–λ9350 Å) with the MUSE spectrograph attached to the 8.2 m telescope VLT. Spatial extension criteria were employed to verify which GPs are spatially resolved in the MUSE data cubes. We created and analyzed maps of spatially distributed emission lines (at different stages of excitation), continuum emission, and properties of the ionized ISM (e.g., ionization structure indicators, physical-chemical conditions, dust extinction). We also took advantage of our IFS data to produce integrated spectra of selected galactic regions in order to study their physical-chemical conditions. Maps of relevant emission lines and emission line ratios show that higher-excitation gas is preferentially located in the center of the galaxy, where the starburst is present. The continuum maps, with an average angular extent of 4″, exhibit more complex structures than the emission line maps. However, the [O III]λ5007 Å emission line maps tend to extend beyond the continuum images (the average angular extent is 5.5″), indicating the presence of low surface brightness ionized gas in the outer parts of the galaxies. Hα/Hβ, [S II]/Hα, and [O I]/Hα maps trace low-extinction, optically thin regions. The line ratios [O III]/Hβ and [N II]/Hα span extensive ranges, with values varying from 0.5 dex to 0.9 dex and from −1.7 dex to −0.8 dex, respectively. Regarding the integrated spectra, the line ratios were fit to derive physical properties including the electron densities ne = 30 − 530 cm−3, and, in six GPs with a measurable [O III]λ4363 Å line, electron temperatures of Te = 11 500 K–15 500 K, so the direct method was applied in these objects to retrieve metallicities 12 + log(O/H)≃8. We found the presence of the high-ionizing nebular He IIλ4686 Å line in three GPs, where two of them present among the highest sSFR values (> 8 × 108 yr−1) in this sample. Non-Wolf-Rayet (WR) features are detected in these galaxy spectra.

Influence of spatial extension of impurity on the nonlinear optical properties of doped GaAs quantum dot in presence of noise

This work examines the role of spatial impurity extension (SIE) on a few nonlinear optical (NLO) properties of impurity-doped GaAs quantum dot (QD). The NLO properties considered are the nonlinear optical rectification (NOR), the second harmonic generation (SHG) and the third harmonic generation (THG). The study also includes 1 (GWN) which has been incorporated into the doped QD through additive and multiplicative pathways. The study uncovers the delicate interplay between GWN and SIE which ultimately fabricates the said NLO properties. NOR, SHG and THG manifest red-shift with enhancement of SIE both with and without GWN. The study also shows possibilities of attaining maximum NLO response by prudently applying GWN in a particular pathway. Depending upon the particular NLO property concerned, the presence of noise and its mode of application can either deplete or amplify it to different extents with respect to the noise-free situation.

Robust Behavior of Charge Density Wave Quantum Motif Star-of-David in 2D NbSe2 Nanocrystals.

Charge density wave (CDW) is a typical collective phenomenon, and the phase change is generally accompanied by electronic transition with potential device applications. For the continuous miniaturization of devices, it is important to investigate the size effect down to the nanoscale. In this work, single-layer (SL) 1T-NbSe2 islands provide an ideal research platform to investigate the size effect on CDW arrangement and electronic states. The CDW motifs (Star-of-David [SOD]) at the island border are along the edge, and those at the interior tend to arrange in a triangular lattice for islands as small as 5nm. Interestingly, in some small islands, the SOD clusters rearrange into a square-like lattice, and each SOD cluster remains robust as a quantum motif, both in the sense of geometry and electronic structures. Moreover, the electronic structure at the center of the small islands is downwards shifted compared to the big islands, explained by the spatial extension of the band bending originating from the edge of the islands. These findings reveal the robust behavior of CDW motifs down to the nanoscale and provide new insights into the size-limiting effect on 2D2D CDW ordering and electronic states down to a few nanometer extremes.

Analytical formulation for exciton in semiconductor quantum dot with parabolic confinement

The exciton properties in cubical quantum dot (CQD), with parabolic confining potential, are theoretically investigated. We have used the two-band model, the effective mass approximation, and the variational method. The analytical expressions of the binding energy, the normalized photoluminescence (PL) energy transition, the spatial extension, and the oscillator strength of the exciton, in the ground state, have been obtained. The numerical calculations for the typical GaAs/Al x Ga1− x As CQD are presented. The effects of the CQD length and the Al concentration on the exciton properties are discussed. The results of the calculation illuminate that Al concentration and the CQD length can make an important impact on the exciton binding energy and the PL peak energy.

3T vs. 7T fMRI: capturing early human memory consolidation after motor task utilizing the observed higher functional specificity of 7T.

Functional magnetic resonance imaging (fMRI) visualizes brain structures at increasingly higher resolution and better signal-to-noise ratio (SNR) as field strength increases. Yet, mapping the blood oxygen level dependent (BOLD) response to distinct neuronal processes continues to be challenging. Here, we investigated the characteristics of 7 T-fMRI compared to 3 T-fMRI in the human brain beyond the effect of increased SNR and verified the benefits of 7 T-fMRI in the detection of tiny, highly specific modulations of functional connectivity in the resting state following a motor task. 18 healthy volunteers underwent two resting state and a stimulus driven measurement using a finger tapping motor task at 3 and 7 T, respectively. The SNR for each field strength was adjusted by targeted voxel size variation to minimize the effect of SNR on the field strength specific outcome. Spatial and temporal characteristics of resting state ICA, network graphs, and motor task related activated areas were compared. Finally, a graph theoretical approach was used to detect resting state modulation subsequent to a simple motor task. Spatial extensions of resting state ICA and motor task related activated areas were consistent between field strengths, but temporal characteristics varied, indicating that 7 T achieved a higher functional specificity of the BOLD response than 3 T-fMRI. Following the motor task, only 7 T-fMRI enabled the detection of highly specific connectivity modulations representing an "offline replay" of previous motor activation. Modulated connections of the motor cortex were directly linked to brain regions associated with memory consolidation. These findings reveal how memory processing is initiated even after simple motor tasks, and that it begins earlier than previously shown. Thus, the superior capability of 7 T-fMRI to detect subtle functional dynamics promises to improve diagnostics and therapeutic assessment of neurological diseases.

Analysis of the spatial extension of pineapple monocultures in northern Costa Rica using heterogeneous geographic data

Abstract. In recent years, Costa Rica has become the world's leading producer and exporter of pineapple, with more than 65.000 hectares of its territory dedicated to this crop. The development of these intensive pineapple crops is mainly concentrated in the north of the country, especially in the border area with Nicaragua. This rapid expansion in these regions has many economic, social and environmental consequences. In order to understand the local impact of this phenomenon, a first analysis of land use changes for the benefit of pineapple monocultures must be performed. For this purpose, pineapple crop delineation layers in 2000 and 2019 were provided by MOCUPP, a United Nations agency responsible for monitoring agricultural areas in Costa Rica. Landsat 5 satellite images from 1998 and 2001 were also used to generate land cover classifications. The pineapple crop delineation layers produced by MOCUPP are characterized by heterogeneous granularities and positional accuracies, complicating the analysis of land cover changes through the generation of artefacts. To address this problem, an artefact removal procedure was conducted, based on the use of minimum shape and size indicators. The assignment of land use changes to pineapple crops allowed the assessment of deforested areas between 2000 and 2019. Thus, over this period, more than 6300 hectares of forest were lost to pineapple crops, mainly in the cantons of Los Chiles and San Carlos, in the northern part of the country. Finally, this article illustrates the problems associated with the use of heterogeneous data to analyse land cover changes. To avoid these problems, the use of prior data integration procedures, such as data matching algorithms, is recommended.

Mapping of Soil Erosion Using Remote Sensing and GIS: Case of The Oued Bouhamdane Watershed (North-East of Algeria)

The northern region of Algeria is experiencing a real threat to the spatial extension of soil erosion. The Oued Bouhamdane watershed, part of this region, brings together all the natural and anthropogenic conditions that accelerate its degradation. This study is based on the use of remote sensing and GIS to map soil erosion in the Oued Bouhamdane watershed in north-eastern Algeria, using the Gavrilovic equation. The combination of data from different sources and field observation has made it possible to draw up a contextualized map of all the factors of soil erosion. Integrating the model into the GIS made it possible to give a first estimate of the annual volume of eroded soils, i.e., 14.57% of the total area of the Oued Bouhamdane watershed is affected, where soil losses are estimated on average at 941.13m3/Km2/year. This modest cartographic result is a perfect base for environmental monitoring and managing water resources in this watershed.

Nonlinear optical properties of doped GaAs quantum dot modulated by noise: Role of impurity spread

This paper explores the role of spatial extension of impurity (SEI) on two nonlinear optical (NLO) properties and two other related properties of impurity doped GaAs quantum dot (QD). The NLO properties include the electro-optic effect (EOE) and the third-order nonlinear optical susceptibility (TONOS) whereas the other two related properties being total optical dielectric function (TODF) and the intraband transition lifetime (ITL). The study also involves Gaussian white noise (GWN) which has been introduced to the doped QD through additive and multiplicative pathways. The investigation unveils the subtle interplay between GWN and SEI which ultimately fine-tunes the said NLO properties. TODF, EOE and TONOS manifest red-shift with enhancement of SEI both with and without GWN. The ITL, on the other hand, exhibits monotonic growth with increase in SEI under all conditions. Moreover, the application of GWN causes noticeable quenching of the NLO properties. And the quenching becomes more stringent in presence of multiplicative noise than its additive counterpart.

Construction of a feature enhancement network for small object detection

Limited by the size, location, number of samples and other factors of the small object itself, the small object is usually insufficient, which degrades the performance of the small object detection algorithms. To address this issue, we construct a novel Feature Enhancement Network (FENet) to improve the performance of small object detection. Firstly, an improved data augmentation method based on collision detection and spatial context extension (CDCI) is proposed to effectively expand the possibility of small object detection. Then, based on the idea of Granular Computing, a multi-granular deformable convolution network is constructed to acquire the offset feature representation at the different granularity levels. Finally, we design a high-resolution block (HR block) and build High-Resolution Block-based Feature Pyramid by parallel embedding HR block in FPN (HR-FPN) to make full use different granularity and resolution features. By above strategies, FENet can acquire sufficient feature information of small objects. In this paper, we firstly applied the multi-granularity deformable convolution to feature extraction of small objects. Meanwhile, a new feature fusion module is constructed by optimizing feature pyramid to maintain the detailed features and enrich the semantic information of small objects. Experiments show that FENet achieves excellent performance compared with performance of other methods when applied to the publicly available COCO dataset, VisDrone dataset and TinyPerson dataset. The code is available at https://github.com/cowarder/FENet.