► Managers are looking to natural disturbance regimes to model harvest guidelines. ► We review field methods for sampling gaps and common gap models. ► We discuss the attributes of natural and ...man-made gaps. ► We make recommendations for future gap research.
As silvicultural objectives have changed over the last several decades, managers are increasingly designing cutting regimes that mimic natural disturbance with the hopes that such systems will restore forests to a more natural condition while optimizing harvest yield. Treefall gaps, canopy openings caused by the death of one or more trees, are the dominant form of disturbance in many forest systems worldwide. These gaps play an important role in forest ecology by helping to maintain bio- and pedo-diversity, influencing nutrient cycling, and preserving the uneven-age nature of late-successional forests. In gap literature, there are inconsistencies with regard to gap terminology, methods for identifying and studying gaps, and modeling gap disturbances. From the papers reviewed, the size of treefall gaps ranges widely from 10 to >5000
m
2; we suggest that the maximum gap size should be set at 1000
m
2. Larger openings tend to have microclimates and return intervals significantly different than smaller treefall gaps. Two main definitions of treefall gaps exist:
canopy gap: a ‘hole’ in the forest through all levels down to an average height of 2
m above ground and
extended gap: canopy gap plus the area that extends to the bases of surrounding canopy trees. Although researchers have assumed a variety of gap shapes to simplify measuring gap size, gaps are often irregularly shaped and so we recommend that gap areas and shapes be determined from detailed field measurements. Gap age may be determined from tree ring analysis of released trees in or near the gap edge, the spacing of whorls on released saplings, or from decomposition of gap-making trees. Windthrow is the main cause of canopy gaps in a variety of ecosystems; other causes include insects, diseases, acidic deposition, drought, and climate change. Treefall-gap models have been developed to predict the following processes during gap making or infilling: (i) gap abundance, (ii) forest structure, (iii) spatial and temporal variations in light levels, (iv) canopy dynamics, and (v) soil nutrient and water regimes. We recommend a protocol for gap studies and identify future research topics.
An ultrawideband (UWB) full-metal planar array antenna based on a combination of ridge gap waveguide (RGW) and E-plane groove gap waveguide (E-GGW) is presented for millimeter-wave (mmWave) ...applications. First, the radiation element of a double-step double-ridged slot structure is proposed and designed. By removing the vertical walls of the cavity in the H-plane, the impedance matching characteristics presents a UWB bandwidth of 53%. Second, a UWB double-layer feeding network is achieved by combining RGWs and double-side-pin E-GGWs for the radiation elements. Finally, an 8 <inline-formula> <tex-math notation="LaTeX">\times </tex-math></inline-formula> 8 full-metal planar array antenna with the presented elements and network is designed, prototyped, and measured. The measured results agree well with the simulated results. The proposed antenna provides an impedance matching bandwidth (<inline-formula> <tex-math notation="LaTeX">\vert \text{S}_{11}\vert < -10 </tex-math></inline-formula> dB) of 46.8% from 18.8 to 30.3 GHz. The maximum gain is 27.7 dBi at 27 GHz and a stable gain of 26 <inline-formula> <tex-math notation="LaTeX">\pm ~1.7 </tex-math></inline-formula> dBi is obtained over the operation band.
This letter presents an all-metal three-layer monopulse antenna based on Gap Waveguide technology operating in Ka-band. (specifically from 29 to 31 GHz) for direction-finding applications. This ...contribution stands out mainly for the simplicity of its single-layer comparator network (layer 1) composed of a combination of ridge and groove gap waveguides. Also, the compactness of the feed network (layer 2) allows for a low-profile monopulse antenna comprising only three aluminum pieces. The antenna is bottom-fed through three ports connected, two of them to the comparator network, and one directly to the corporate-feed network, to achieve one sum (<inline-formula><tex-math notation="LaTeX">\Sigma</tex-math></inline-formula>) and two difference patterns (<inline-formula><tex-math notation="LaTeX">\Delta _{H}</tex-math></inline-formula>, <inline-formula><tex-math notation="LaTeX">\Delta _{E}</tex-math></inline-formula>). Experimental results validate the concept, showing a close agreement with simulations. The measured null depth is close to -30 dB in both difference patterns, and the sum pattern achieves 26.9 dBi directivity with a realized radiation efficiency greater than 80<inline-formula><tex-math notation="LaTeX">\%</tex-math></inline-formula>.
Glial cells are now recognized as active communication partners in the central nervous system, and this new perspective has rekindled the question of their role in pathology. In the present study we ...analysed functional properties of astrocytes in hippocampal specimens from patients with mesial temporal lobe epilepsy without (n = 44) and with sclerosis (n = 75) combining patch clamp recording, K(+) concentration analysis, electroencephalography/video-monitoring, and fate mapping analysis. We found that the hippocampus of patients with mesial temporal lobe epilepsy with sclerosis is completely devoid of bona fide astrocytes and gap junction coupling, whereas coupled astrocytes were abundantly present in non-sclerotic specimens. To decide whether these glial changes represent cause or effect of mesial temporal lobe epilepsy with sclerosis, we developed a mouse model that reproduced key features of human mesial temporal lobe epilepsy with sclerosis. In this model, uncoupling impaired K(+) buffering and temporally preceded apoptotic neuronal death and the generation of spontaneous seizures. Uncoupling was induced through intraperitoneal injection of lipopolysaccharide, prevented in Toll-like receptor4 knockout mice and reproduced in situ through acute cytokine or lipopolysaccharide incubation. Fate mapping confirmed that in the course of mesial temporal lobe epilepsy with sclerosis, astrocytes acquire an atypical functional phenotype and lose coupling. These data suggest that astrocyte dysfunction might be a prime cause of mesial temporal lobe epilepsy with sclerosis and identify novel targets for anti-epileptogenic therapeutic intervention.
As a highly stable band gap semiconductor, antimonene is an intriguing two‐dimensional (2D) material in optoelectronics. However, its short layer distance and strong binding energy make it ...challenging to prepare high‐quality large 2D antimonene; therefore, its predicted tunable band gap has not been experimentally confirmed. Now, an approach to prepare smooth and large 2D antimonene with uniform layers that uses a pregrinding and subsequent sonication‐assisted liquid‐phase exfoliation process has been established. Mortar pregrinding provides a shear force along the layer surfaces, forming large, thin antimony plates, which can then easily be exfoliated into smooth, large antimonene, avoiding long sonication times and antimonene destruction. The resulting antimonene also enabled verification of the tunable band gap from 0.8 eV to 1.44 eV. Hole extraction and current enhancement by about 30 % occurred when the antimonene was used as a hole transport layer in perovskite solar cells.
Chasing antimonene: The Group 15 2D material antimonene was successfully prepared by pregrinding and a subsequent liquid‐phase exfoliation process. The uniform antimonene thus obtained provided an opportunity for an experimental study of the band gap dependence on the antimonene thickness, indicating that the band gap is finely tunable between 0.8 eV and 1.44 eV.
Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2AgBiBr6, shows ...attractive optical and electronic features, making it promising for high‐efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal‐engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs2AgBiBr6 under ambient conditions. The band‐gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first‐principles calculations indicate that enhanced Ag–Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band‐gap narrowing effect. This work provides new insights for achieving lead‐free double perovskites with suitable band gaps for optoelectronic applications.
Disorderly conduct: A crystal‐engineering strategy has been introduced to narrow the band gap of benchmark double perovskite Cs2AgBiBr6. The band gap of Cs2AgBiBr6 crystals can be reduced from 1.98 eV to 1.72 eV, reaching the smallest reported band gap for Cs2AgBiBr6 under ambient conditions. DFT calculations indicate that Ag–Bi disorder in the crystal structure could lead to band‐gap narrowing.
The gap‐prepulse inhibition of the acoustic startle (GPIAS) paradigm is the primary test used in animal research to identify gap detection thresholds and impairment. When a silent gap is presented ...shortly before a loud startling stimulus, the startle reflex is inhibited and the extent of inhibition is assumed to reflect detection. Here, we applied the same paradigm in humans. One hundred and fifty‐seven normal‐hearing participants were tested using one of five gap durations (5, 25, 50, 100, 200 ms) in one of the following two paradigms—gap‐embedded in or gap‐following—the continuous background noise. The duration‐inhibition relationship was observable for both conditions but followed different patterns. In the gap‐embedded paradigm, GPIAS increased significantly with gap duration up to 50 ms and then more slowly up to 200 ms (trend only). In contrast, in the gap‐following paradigm, significant inhibition—different from 0—was observable only at gap durations from 50 to 200 ms. The finding that different patterns are found depending on gap position within the background noise is compatible with distinct mechanisms underlying each of the two paradigms.
Connexins are chordate gap junction channel proteins that, by enabling direct communication between the cytosols of adjacent cells, create a unique cell signalling network. Gap junctional ...intercellular communication (GJIC) has important roles in controlling cell growth and differentiation and in tissue development and homeostasis. Moreover, several non-canonical connexin functions unrelated to GJIC have been discovered. Of the 21 members of the human connexin family, connexin 43 (Cx43) is the most widely expressed and studied. The long cytosolic C-terminus (CT) of Cx43 is subject to extensive post-translational modifications that modulate its intracellular trafficking and gap junction channel gating. Moreover, the Cx43 CT contains multiple domains involved in protein interactions that permit crosstalk between Cx43 and cytoskeletal and regulatory proteins. These domains endow Cx43 with the capacity to affect cell growth and differentiation independently of GJIC. Here, we review the current understanding of the regulation and unique functions of the Cx43 CT, both as an essential component of full-length Cx43 and as an independent signalling hub. We highlight the complex regulatory and signalling networks controlled by the Cx43 CT, including the extensive protein interactome that underlies both gap junction channel-dependent and -independent functions. We discuss these data in relation to the recent discovery of the direct translation of specific truncated forms of Cx43. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.
•The Cx43 C-terminus (CT) is fundamental for correct function of Cx43 gap junctions.•The Cx43 CT is highly regulated post-translationally, e.g. by phosphorylation.•The Cx43 CT endows Cx43 with unique isoform-specific functions.•The Cx43 CT interacts with many proteins and have channel-independent functions.•Truncated forms of Cx43 containing the CT can be synthesized independently.
The main objective of this paper is to initiate a systematic application of gap metric techniques to the performance analysis and design issues of detecting and isolating multiplicative faults in ...uncertain systems. To be specific, in the first part of this paper, the K-gap and L2-gap metrics are introduced, which measure the distance between two kernel subspaces and serve as an efficient tool to deal with fault detection and isolation issues. Based on it, the K-gap and L2-gap aided analysis of residual dynamics with respect to model uncertainties is presented for the open-loop and feedback control systems, respectively. Furthermore, they are applied to deal with the performance analysis of fault detection systems. For this purpose, the concepts of fault detectability indicators and fault-to-uncertainty ratio are introduced. The second part of this paper is dedicated to the isolation of multiplicative faults. To this end, the definition for fault isolability is studied first with the aid of K-gap metric. The further efforts are devoted to the application of K-gap metric to two online fault isolation algorithms. The first one is an observer-based scheme, which adopts a bank of residual generators and an observer-based decision unit. The second scheme is based on the data-driven identification of the kernel representation of the faulty plant and the data-driven computation of the K-gap metric. Case and example studies are finally given to illustrate the proposed approaches.
Communication is important to ensure the correct and efficient flow of information, which is required to sustain active social networks. A fine-tuned communication between cells is vital to maintain ...the homeostasis and function of multicellular or unicellular organisms in a community environment. Although there are different levels of complexity, intercellular communication, in prokaryotes to mammalians, can occur through secreted molecules (either soluble or encapsulated in vesicles), tubular structures connecting close cells or intercellular channels that link the cytoplasm of adjacent cells. In mammals, these different types of communication serve different purposes, may involve distinct factors and are mediated by extracellular vesicles, tunnelling nanotubes or gap junctions. Recent studies have shown that connexin 43 (Cx43, also known as GJA1), a transmembrane protein initially described as a gap junction protein, participates in all these forms of communication; this emphasizes the concept of adopting strategies to maximize the potential of available resources by reutilizing the same factor in different scenarios. In this Review, we provide an overview of the most recent advances regarding the role of Cx43 in intercellular communication mediated by extracellular vesicles, tunnelling nanotubes and gap junctions.
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