Aperture Region Research Articles

Experimental and numerical investigation of the squeegee process during stencil printing of thick adhesive sealings

ABSTRACT To reliably compensate fuel cell stack tolerances, sealings with a layer thickness of at least 500 µm are necessary. Additionally, threads positioned at the upper region of the stencil apertures need to be integrated to print closed-loop designs under cycle times of as low as 3 seconds. All these requirements can intensify the occurrence of print defects and diminish the process stability. This paper addresses the issues of incomplete regions and air bubbles emerging during the squeegee process. It was detected that the cleanliness state of the stencil directly impacts the formation of incomplete regions by affecting venting conditions inside the aperture. Moreover, it was identified that bubbles are either transferred from the adhesive roll into the aperture or created due to interactions between the moving adhesive and stencil threads. Further, it was shown that bubbles cannot be completely eliminated using a stencil with threads but their size can remain smaller than 300 µm when printing with a new adhesive roll. Finally, distinct strategies were derived and verified experimentally to successfully print a basic sealing design. By introducing a small local gap between substrate and stencil, the entire sealing aperture was reliably filled without the need of a cleaning step.

Shifted super transformed nested array for DOA estimation of non-circular signals with increased uDOFs and reduced mutual coupling

In this work, a scheme for array structure design is proposed to maximize uniform degrees of freedom (uDOFs) and reduce mutual coupling. It starts by exchanging the positions of two subarrays within the nested array, followed by mitigating mutual coupling through sensor relocation due to the dense subarray, and ultimately increasing uDOFs by globally shifting the entire array to the right. Following this scheme, the concept of Shifted Super Transformed Nested Array (SSTNA) is introduced and general guidelines for the construction of SSTNA are provided. Analytical expressions for the continuous region of the virtual apertures and uDOFs are derived. Furthermore, the optimal shifting parameter and the first three weight functions are determined for SSTNA. Theoretical analysis shows that SSTNA can effectively reduce mutual coupling while maintaining high uDOFs. In strong mutual coupling scenarios, simulation results are provided to demonstrate the effectiveness and superiority of the proposed design.

The evaluation of nasolacrimal duct injury in Le Fort I osteotomy patients.

Although Le Fort I surgeries are safe and successful procedures; nasolacrimal duct injuries may be observed due to these surgeries. The study aimed to investigate the prevalence of nasolacrimal duct injury in Le Fort I osteotomy patients. The authors conducted a retrospective cohort study consisting of patients who underwent Le Fort I osteotomies between 2017 and 2021 in the Erciyes University Faculty of Dentistry. The primary predictor variables were the distance of the nasolacrimal canal to the outer cortex of the maxilla and the nasal floor, as well as the superior-inferior level of the superiorly positioned screw inserted in the maxilla aperture region relative to the nasolacrimal canal. The outcome variable was the presence of a nasolacrimal duct injury. Mann Whitney U test was used for quantitative variables between the two groups. A Pearson chi-squared analysis was used to compare categorical data. A p-value <0.05 was considered statistically significant. A total of 290 nasolacrimal canals were evaluated in 145 patients, 87 females, and 58 males. The mean age was 23.47± 6.67. There was a statistically significant relationship between screw level and nasolacrimal canal perforation (p<0,001). The distance between the most anterior border of the nasolacrimal canal and the outer cortical of the maxilla was significantly less in the perforation group (p<0,001). The fixation screw was significantly closer to the nasolacrimal canal in the perforation group (p<0,001). In Le Fort I surgery, nasolacrimal duct injury may occur during screw fixation to the aperture region. Superiorly positioned fixation screws in the aperture region may damage the nasolacrimal canal. In patients where the nasolacrimal canal is close to the outer cortex, care should be taken when applying the fixation screws to the aperture region to avoid damaging the canal.

Contribution to the pollen morphology of Astragalus L. section Aegacantha Bunge (Galegeae-Fabaceae) and its systematic significance

Astragalus L. sect. Aegacantha Bunge includes 57 described species, mostly confined to Southwest Asia and Central Asia. We studied the pollen morphology of 17 species of this section present in Pakistan. Pollen morphology of sect. Aegacantha species is poorly investigated despite its systematic importance. The main aim of this study is to determine and document the pollen characters that can assist in the taxonomic identification of species in this difficult section. Pollen slides were prepared following acetolysis and examined by both light and scanning electron microscopy. Pollen size varies, with the polar axis ranging from 32.91 to 43.10 μm and the equatorial axis from 22.91 to 28.47 μm. Pollen is sub-prolate (1.15–1.33) to prolate (1.34–2.00) in shape, small to medium in size, radially symmetrical, isopolar, trizonocolporate to tricolporate, and monad. Sculpture variations (i.e. reticulate, microreticulate, perforate, microperforate, regulate, microregulate and granulate) were observed around the apertural, meridional and polar regions. Ordination analysis (principal component analysis (PCA)) revealed that the quantitative characters of pollen morphology are the most reliable characters for delimitation of species within section Aegacantha. Cluster analysis (unweighted pair group method using arithmetic average (UPGMA)) shows a partial relationship between the Aegacantha taxa clustered based on pollen characters and supports the general morphology. Further, this study shows that the pollen traits provide a baseline for phylogenetic optimisation in the investigated Aegacantha section.

Cavity Mode-Matching InGaN Aperture-Emitting Device with a Nanoporous GaN Reflector via Ion Implantation

Cavity mode-matching InGaN resonant-cavity light-emitting diodes (RC-LEDs) with aperture size-dependent emission have been demonstrated through nitrogen ion (N+) implantation and electrochemical wet etching processes. The RC-LED structure consisted of 570 nm-depth ion-implanted regions and an embedded 17-pair nanoporous-GaN/n-GaN distributed Bragg reflector (DBR) outside the aperture, while there existed a full 20-pair DBR structure within the aperture regions. Shorter and mode-matching cavity lengths were fabricated, confirmed by transmission electron microscopy and angle-resolved photoluminescence spectra inside the aperture area without subjecting to the N+ implantation. By reducing the aperture sizes, higher current density and narrower far-field electroluminescence emission patterns were observed in the RC-LED with an aperture size of 40 μm-diameter. These results demonstrate that the cavity mode-matching RC-LEDs with optical/electrical confinements and controllable cavity length mismatch features can be applied in a wide range of optoelectronic-based device applications.

Swirl-like Acoustofluidic Stirring Facilitates Microscale Reactions in Sessile Droplets.

Sessile droplets play a crucial role in the microreactors of biochemical samples. Acoustofluidics provide a non-contact and label-free method for manipulating particles, cells, and chemical analytes in droplets. In the present study, we propose a micro-stirring application based on acoustic swirls in sessile droplets. The acoustic swirls are formed inside the droplets by asymmetric coupling of surface acoustic waves (SAWs). With the merits of the slanted design of the interdigital electrode, the excitation position of SAWs is selective by sweeping in wide frequency ranges, allowing for the droplet position to be customized within the aperture region. We verify the reasonable existence of acoustic swirls in sessile droplets by a combination of simulations and experiments. The different periphery of the droplet meeting with SAWs will produce acoustic streaming phenomena with different intensities. The experiments demonstrate that acoustic swirls formed after SAWs encountering droplet boundaries will be more obvious. The acoustic swirls have strong stirring abilities to rapidly dissolve the yeast cell powder granules. Therefore, acoustic swirls are expected to be an effective means for rapid stirring of biomolecules and chemicals, providing a new approach to micro-stirring in biomedicine and chemistry.

Investigation of pollen morphology of the genera Grammosciadium, Vinogradovia and Caropodium (Apiaceae)

In this study, detailed light microscopy (LM) and scanning-electron microscopy (SEM) analyses of pollen grains belonging to 11 taxa of genera Grammosciadium, Vinogradovia and Caropodium were performed. The pollen is radially symmetrical and generally isopolar with the exception of Grammosciadium macrodan ssp. nezaketiae where 65% of the grains have asymmetrical appearance. All the taxa are tricolporate. Ectoapertures are discontinuous (colpus length: 14.7 ± 0.8 and colpus width: 21.20 ± 2.28) with narrow and acute at the ends extending to the subpolar region. Endoapertures are in the mid-section of the ectoapertures, which is lolangate, prolate-spheroidal in Grammosciadium scabridum, while lalongate, ellipsoidal, oblate or suboblate in the other taxa. Pollen shape is triangular and semi-triangular in polar-view. Pollen outline in equatorial view is subrectangular-straight in G. scabridum and Caropodium platycarpum, however, those were subrectangular and slightly constricted in equatorial region in all others. Based on the P/E ratio, it is prolate in G. macrodon ssp. macrodon while it is perprolate in the other taxa. Ornamentation variation (i.e. psilate, psilate-perforate, psilate-rugulate, rugulate and rugulate-perforate) was observed around the apertural, equatorial and polar regions. This character has been found as taxonomically important for the studied taxa.

On the exine ultrastructure of fossil ginkgoaleans: In situ pollen of Sorosaccus Harris

The morphology and exine ultrastructure have been studied of pollen grains from pollen cones of Sorosaccus sibiricus Prynada from the Ust’-Baley (Aalenian, Siberia), Sorosaccus sp. from the Vladimirovka (Aalenian-Bajocian, Siberia), and S. ex gr. sibiricus Prynada from the Tyrma (Tithonian–Berriasian, Russian Far East) localities. The pollen grains are boat-shaped and monosulcate. A finely granulate pattern is discernible under high magnification of light microscope in pollen grains from Vladimirovka and Tyrma; SEM shows that this pattern is formed by flat verrucae. TEM shows that sculptural elements are present on the surface of pollen grains from Ust’-Baley, although it is not evident in LM and SEM. By previous data on modern and fossil members, we believed that ginkgoalean pollen grains can be differentiated from similar boat-shaped monosulcate pollen of other affinities by a ratio of ectexinal sublayers (a thick homogeneous tectum, a thin infratectum of one row of structural elements, and a thin foot layer) in combination with an ectexine that is greatly reduced in the aperture region. Freshly obtained data have revealed another set of characters, with a less prominent tectum by comparison to underlying sublayers, an infratectum with small granules within the alveoli, and a prominent verrucate surface pattern that is distinguishable even in transmitted light. Ginkgoaleans are characterized by more than one set of ultrastructural characters of the exine.

Improving Signal Integrity by Reducing Mode Conversion in Differential Pairs on a Meshed Ground in Flexible Printed Circuit Boards

Asymmetry in a differential pair leads to deterioration of signal integrity. Differential pairs on a meshed ground often encounter asymmetry in return current paths. In this paper, we propose an offset mesh as an improved mesh structure that offsets asymmetry between a solid region and an aperture region. The offset mesh mitigates the asymmetry in the conventional mesh structure without additional design elements. The proposed structure has been verified to be effective in reducing mode conversion, intra-pair and inter-pair skews, and characteristic impedance variation in the time and frequency domains. This enables high-density routing of differential pairs.

The morphology and affinity of anabaritids revealed by their internal molds from the Cambrian Fortunian, southern Shaanxi, China

Anabaritids are a group of tubular skeletal fossils known from the lower Cambrian worldwide. Many previously collected specimens of anabaritids lack both the apical and apertural regions, and thus their complete morphology and growth patterns are not fully understood. Here we describe a number of internal molds of Anabarites from the lower Cambrian (Fortunian Stage) Zhangjiagou Lagerstätte, southern Shaanxi Province. Our new specimens preserved the apex, the aperture with three lobes, and three longitudinal grooves initiating apically rather than adapically as previously reported. This work enriches the morphology of anabaritids, casting doubt on the previous proposition that anabaritids originated from a cylindrical tubular ancestor. It is proposed here that a triradial symmetry may have been established in very early ontogenetic stages of some anabaritids; furthermore, the aperture with three lobes resembles those of olivooids and thus supports a possible close relationship between anabaritids and olivooid scyphozoans.

Wideband double-mode bulk acoustic wave resonator filters on lithium niobate using periodically slotted electrodes

This paper discusses applicability of periodically slotted electrodes for realization of wideband transversely coupled double-mode resonator filters using lithium niobate thin plates. First, two-dimensional analysis is carried out, and it is shown that the periodic structure is effective to control the frequency separation between two resonance modes, and synthesis of the fractional bandwidth larger than 24% is achievable. Next, three-dimensional analysis is performed for suppression of spurious resonances. It is shown that mass loading at the aperture edges is effective for piston mode operation, and transverse modes can be well suppressed. It is also pointed out that the bottom electrode should cover only the aperture region and be removed from the busbar and gap regions for suppression of unwanted resonances. With these proper edge treatments, spurious-free and wide passbands can be synthesized.

Improvement on the uniformity of deep reactive ion etch for electrically isolated silicon-based substrates

Substrate-free micro-electro-mechanical systems (MEMS) devices are becoming the hotspots for microsystems. The fabrication of substrate-free MEMS devices usually involves the release of backside silicon by the inductively coupled plasma deep reactive ion etch (ICP-DRIE) process. However, when using DRIE to etch electrically isolated samples, significant non-uniformity in the etch profile were often observed. Compared to grounded silicon samples, the electrically isolated counterparts after DRIE showed a faster etch rate at the edge and a slower one in the center. This phenomenon is believed to be caused by the interaction between the deflection of charge-bearing ions entering the aperture region and the accumulated charges on the sidewall during DRIE. Simulation results with ICP showed that the electric field and ion distribution can be affected in electrically isolated substrates. After the isolated samples were electrically grounded, the charge accumulation on the sidewall was reduced and 12% etch uniformity was obtained. This technique helps in the fabrication of substrate-free MEMS devices.

Pollen morphology, ultrasculpture and ultrastructure of Poiretia Vent. (Leguminosae – Papilionoideae – Dalbergieae – Adesmia informal clade)

Pollen morphology, ultrasculpture and ultrastructure were investigated for Poiretia in search of morphological characters of taxonomic importance using light microscopy as well as scanning and transmission electron microscopy. Additionally, principal components analysis was done to elucidate patterns of variation among the species. Pollen grains are small to medium size, isopolar, prolate spheroidal to prolate, 3-zonocolporate, colporus with operculum, membrane and margo are ornamented. Five pollen types are recognised and described based on mesocolpium exine ultrasculpture. Exine consists of a compact tectum, eutectate, tectate perforate to semitectate, the infratectum is collumelar and granular, foot layer discontinuous to absent in aperture region and endexine is continuous. A comprehensive description of the operculum, membrane ornamentations and the ultrastructure of exine were given for all species in the genus, nine of which were not previously analysed palynologically. Systematic implications of the palynological variations found in the literature and through light, scanning and transmission electron microscopical analyses were discussed. This article describes the importance of the characterisation of Poiretia pollen grains, which contributes to the systematics of the Adesmia informal clade. The class of endoaperture, ultrasculpture of mesocolpium and apocolpium, and ultrastructure of tectum, foot layer, and endexine support the eurypalynous status of Poiretia and are useful to recognise some species that have problematic delimitation (P. latifolia, P. coriifolia, P. unifoliolata, P. mattogrossensis, P. elegans, P. marginata) as well as groups of species.

Пространственно-временные процессы в позиционно-чувствительном детекторе с подвижной вольт-амперной характеристикой

Abstract. The paper considers the features of transient phenomena during output signal generation in position-sensitive detectors (PSD) with a moving current-voltage (I-V) characteristic. The dependence of the linear and exponential parts of the movement trajectory of the I-V characteristic on the magnitude of the voltage distributed over the resistive divider is studied. It is shown that optimizing the operating modes of the investigated PSDs in order to obtain maximum operation speed and maintain the specified resolution of the sensor requires maintaining a balance between the minimum of the applied voltage and the slope of the I-V characteristic in the aperture region. Key words: position-sensing detector, moving current-voltage characteristic, operation speed.

Spatio-temporal processes in the position-sensitive detector with moving current-voltage characteristic

The paper considers the features of transient phenomena during output signal generation in a position-sensitive detector (PSD) with a moving current-voltage (I-V) characteristic. The dependence of the linear and exponential parts of the movement trajectory of the I-V characteristic on the magnitude of voltage distributed over the resistive divider is studied. It is shown that optimizing the operating modes of the investigated PSDs in order to obtain maximum operation speed and maintain the specified resolution of the sensor requires maintaining a balance between the minimum of the applied voltage and the slope of the I-V characteristic in the aperture region. Keywords: position-sensing detector, moving current-voltage characteristic, operation speed.

Kleptoplast distribution, photosynthetic efficiency and sequestration mechanisms in intertidal benthic foraminifera

Foraminifera are ubiquitously distributed in marine habitats, playing a major role in marine sediment carbon sequestration and the nitrogen cycle. They exhibit a wide diversity of feeding and behavioural strategies (heterotrophy, autotrophy and mixotrophy), including species with the ability of sequestering intact functional chloroplasts from their microalgal food source (kleptoplastidy), resulting in a mixotrophic lifestyle. The mechanisms by which kleptoplasts are integrated and kept functional inside foraminiferal cytosol are poorly known. In our study, we investigated relationships between feeding strategies, kleptoplast spatial distribution and photosynthetic functionality in two shallow-water benthic foraminifera (Haynesina germanica and Elphidium williamsoni), both species feeding on benthic diatoms. We used a combination of observations of foraminiferal feeding behaviour, test morphology, cytological TEM-based observations and HPLC pigment analysis, with non-destructive, single-cell level imaging of kleptoplast spatial distribution and PSII quantum efficiency. The two species showed different feeding strategies, with H. germanica removing diatom content at the foraminifer’s apertural region and E. williamsoni on the dorsal site. All E. williamsoni parameters showed that this species has higher autotrophic capacity albeit both feeding on benthic diatoms. This might represent two different stages in the evolutionary process of establishing a permanent symbiotic relationship, or may reflect different trophic strategies.

RETRACTED: Design, Development and Performance Testing of a Novel Utility Solar Cooker with Highlighting Its Significance in Current Scenario

Abstract In most developing worlds, cooking with heat has been a technically feasible replacement for fuelwood in food production as the need of the hour. Cooking energy accounts for 36% of India's gross primary energy use. Non-commercial oils are used mainly by the rural and urban populations to fulfil their energy requirements. Solar cooking is one potential alternative, but it has been met with some resistance due to some obstacles. Simple box-type solar cookers are an easy way to cook food utilizing solar energy throughout the day, but cooking is not feasible all across the night-time. In this research, a box-type solar cooker with energy storage is developed, and a performance study is conducted to enable food to be cooked at odd hours. Thermal energy has been stored using phase change content (PCM). The amount of energy retained, the amount of heat lost during the charging and discharging period, and the amount of PCM needed are all calculated. Experiments were carried out with two continuous loads in a cooker with a 0.5 m2 aperture region and PCM (Erythritol). While the performance of the PCM cooker is comparable to that of a simple box-type cooker, cooking during off-sunshine hours is not feasible with the simple box-type cooker, according to the report. However, by utilizing the specially built and manufactured PCM cooker, cooking can be done at any time of day. As a result, this paper aims to summarise the research on solar cooking systems that incorporate phase shift materials (PCMs).

Targeted defect analysis in VCSEL oxide windows using 3D slice and view

We report on high resolution analysis of vertical cavity surface emitting lasers (VCSELs) to detect and assess defects in sub-surface layers. We employ a focussed ion beam scanning electron microscope (FIB-SEM) to sputter and image successive cross sections (slice and view technique) in order to produce a 3D reconstruction of the oxide aperture region. High resolution images and measurements of the multilayers and oxide apertures of VCSEL devices were obtained. The process took ∼2.5 h and produced over 270 slice SEM images for a device volume of approximately 13.2 × 16.0 × 13.8 μm3, with a voxel size of 50 nm. On-wafer, single mode VCSEL devices with high and low output powers were analysed to compare their oxide apertures and distributed Bragg reflector (DBR) layer structures. It was found that the low output power VCSEL had DBR layer defects and a 41.8% reduction of effective oxide aperture area, explaining the lower power obtained. The results provide evidence that oxide aperture area and structural defects are major factors that affect the optical output power of VCSEL devices. Outcomes in this work show FIB-SEM slice and view is a valuable method for 3D reconstruction of VCSEL devices, which enables top view, cross-sectional view and angled view of the whole device region as well as designated structures such as oxide aperture or structural defects in various layers. This work demonstrates a promising technique with high resolution (50 nm) 3D imaging for analysis of complex semiconductor devices.

Pollen development in three selected species of Rubiaceae provides ontogenetic evidence for pollen evolution

Pollen development in Ixora chinensis, Pentas lanceolata, and Spermacoce pusilla was investigated. Simultaneous cytokinesis at meiosis, a persistent epidermis, fibrous thickenings in the endothecium, an ephemeral middle layer, and a secretory tapetum that remains uninucleate were observed in all examined species and constitute a family character in Rubiaceae. The main ontogenetic sequence of sporoderm development is generally centripetal and shows major similarities among the studied species, with slight differences in the timing of specific events. Tapetum degradation starts slightly later in I. chinensis than in P. lanceolata and S. pusilla, while intine formation may be slightly later in S. pusilla than in the other two species. Occurrences of orbicules, white-line-centered endexine lamellae and apertural intine projections were observed in I. chinensis and P. lanceolata but not in S. pusilla. Columellae are well-developed in I. chinensis and P. lanceolata but are simplified in S. pusilla. Carbohydrate reserves in mature pollen grains also vary among these three species. Thickened endexine at the apertural sites and a membranous granular layer are shared by the three species. White-line-centered lamellae might represent a common mechanism for endexine formation in the family. Endexine dilations and thickening occurred in the apertural region represent a common character in the family. The ephemeral membranous granular layer developed beneath the endexine is a very common feature for Rubiaceae. Our study shows that ultrastructural and developmental studies are essential in illustrating micromorphological features of pollen especially these ephemeral characters. Thus, application of palynological ontogenetic data to phylogenetic problems deserves more attention.

Growth and Fabrication of Quasivertical Current Aperture Vertical Electron Transistor Structures

The current aperture vertical electron transistor (CAVET) combines the high carrier mobility of the AlGaN/GaN heterostructure with the better electric field distribution of the vertical topology, allowing for higher power densities if compared with lateral high electron mobility transistors (HEMTs). The formation of a current blocking layer (CBL), without degenerating the aperture region and the subsequently overgrown AlGaN/GaN heterostructure is the key building block of such devices. Herein, a comparison of GaN:Mg nonplanar selective area growth (SAG) and Mg‐ion implantation is carried out primarily focusing on structural evolution, Mg distribution, and 2D electron gas (2DEG) performance. The epitaxial growth process in SAG is correlated to local growth increase and ridge development, and then optimized regarding mesa filling. AlGaN/GaN regrowth is analyzed regarding structural evolution after overgrowth and Mg distribution into the GaN channel. Considerably lower Mg‐distribution into subsequently grown layers is detected for implanted samples in agreement with the electrical performance of the overgrown AlGaN/GaN heterostructures. A GaN‐on‐Si quasivertical CAVET structure with an Mg‐implanted CBL and 250 nm channel thickness is fabricated. High surface quality and proper 2DEG performance demonstrate the potential use of GaN‐on‐Si CAVET's using Mg implantation for CBL fabrication.