Small Pyramids Research Articles

Maxillary Sinus Volume in Patients With Unilateral Cleft Lip and Palate by CBCT.

Cleft lip and palate (CLP) is one of the most common congenital craniofacial anomalies, which can change the morphology of the skull, face, and maxillary sinus due to the disruption in the fusion of palatal shelves. This study aimed to investigate the volume and dimensions of the maxillary sinus in unilateral CLP patients along with comparing the healthy and affected sides. This cross-sectional study was conducted on 27 cone-beam computed tomography stereotypes (14 male and 13 female) of patients with unilateral CLP. Maxillary sinuses were traced separately on each side and analyzed by OnDemand3D software in a separate room with low light. The height and base area of the maxillary sinuses were measured on each side. After dividing each sinus into smaller pyramids, the volume of the sinus was obtained using the partial frustum model method and analyzed by paired t test. There was no significant difference between cleft and noncleft sides in terms of mean volume and height of the sinus ( P > 0.05). The average area of the sinus base on the cleft side was 32.77mm 2 more than the noncleft side, and this difference was statistically significant ( P = 0.027). The mean upper maxillary sinus volume on the cleft side was 541.62mm 3 larger than the noncleft side, but this difference was not statistically significant ( P = 0.075). Considering the age groups, the average upper sinus volume on the cleft side in patients under 20 years old was 4.66mm 3 less than the noncleft side. In the age group of more than 20 years, the average volume of the upper sinus on the cleft side was 978.66mm 3 more than the noncleft side. The mean volume of the lower sinus on the cleft side was 505.92mm 3 lower than the noncleft side, and this difference was statistically significant ( P = 0.010). The average area of the sinus base of the cleft side was significantly higher than the noncleft side. Also, the lower sinus volume of the cleft side was significantly lower than the noncleft side. However, no significant difference was observed in upper sinus volume between the cleft and noncleft sides.

In(Ga)N 3D Growth on GaN-Buffered On-Axis and Off-Axis (0001) Sapphire Substrates by MOCVD.

In(Ga)N epitaxial layers were grown on on-axis and off-axis (0001) sapphire substrates with an about 1100 nm-thick GaN buffer layer stack using organometallic chemical vapor deposition at 600 °C. The In(Ga)N layers consisted of a thin (~10–25 nm) continuous layer of small conical pyramids in which large conical pyramids with an approximate height of 50–80 nm were randomly distributed. The large pyramids were grown above the edge-type dislocations which originated in the GaN buffer; the dislocations did not penetrate the large, isolated pyramids. The large pyramids were well crystallized and relaxed with a small quantity of defects, such as dislocations, preferentially located at the contact zones of adjacent pyramids. The low temperature (6.5 K) photoluminescence spectra showed one clear maximum at 853 meV with a full width at half maximum (FWHM) of 75 meV and 859 meV with a FWHM of 80 meV for the off-axis and on-axis samples, respectively.

Ultrafast Random‐Pyramid Texturing for Efficient Monocrystalline Silicon Solar Cells

Herein, an ultrafast random‐pyramid texturing process is proposed for monocrystalline silicon (mono‐Si) solar cells by combining metal‐catalyzed chemical etching (MCCE) and the standard alkaline texturing process. Namely, large numbers of artificial defects are introduced on the wafer surface in 3 min by MCCE; therefore, the process duration of alkaline texturing is largely shortened from 420 s for the as‐cut wafer to 180 s for the wafer with artificial defects due to its high surface reactivity. Moreover, those tiny artificial defects are apt to form small pyramids, resulting in a better light‐trapping performance. As a demonstration, the passivated emitter rear contact solar cell with ultrafast random pyramid texture achieves a power conversion efficiency of 23.02%. Therefore, such a cost‐effective ultrafast texturing strategy can open a promising new route toward the mass production of high‐efficiency industrial mono‐Si solar cells.

Texture engineering of mono-crystalline silicon via alcohol-free alkali solution for efficient PERC solar cells

Control of texture structures is an effective method to reduce surface reflectivity and enhance the efficiency of solar cells. In this paper, pyramid structures are prepared on mono-crystalline silicon wafers by cyclodextrin as surfactant to slow down the etching rate in alcohol-free alkali solution. Compared with volatile alcohol surfactant (e.g. isopropanol, IPA), the cyclodextrin not only possesses a relative high boiling point (1534.4 ℃), but displays non-toxic and biodegradable properties. Furthermore, the surface morphology, average reflectivity, surface recombination of mono-crystalline silicon wafers were studied in detail. The results show that cyclodextrin can decrease the size and depth of pyramid structures, and thus a lower average reflectivity of 7.5% was obtained. In addition, ray tracing simulation was performed to calculate the photo-generated carrier concentration of PN junction with different sizes of pyramids, and the conclusion is that the carrier concentration of small pyramids is much higher than that of large pyramids. Finally, the average efficiency of large-area mono-crystalline silicon PERC solar cells fabricated by cyclodextrin surfactant was 22.69%, which was 0.43% absolutely higher than that of conventional IPA surfactant.

Bloomsbury in Winter—2020

Bloomsbury in Winter—2020

Does Size Matter? The Case of the Courtship Pyramids in Red Sea Ghost Crabs (Ocypode saratan).

Simple SummaryMale ghost crabs (Ocypode spp.) are known to build sand structures near the entrance to their burrows. It has always been assumed that the structure played a role in sexual selection and mate attraction. We hypothesized that the larger males would make relatively larger pyramids in order to enhance fitness. We studied Red Sea ghost crabs at Eilat, Israel, and found that the larger crabs actually did not put much effort into building pyramids, and it was the medium-sized crabs that invested the most in building the pyramids.Display, wherein males attempt to maximize fitness by attracting sexually mature females to mate, is known to drive speciation by Sexual Selection. We researched the Red Sea Ghost Crab (Ocypode saratan; RSGC), in which males build display pyramids to attract females. The study was conducted at the beach in Eilat, Israel. At each session, we measured the height (in cm) of all pyramids and the dimensions (height, breadth; in cm) of the burrow entrance. We assumed that the size of the entrance represented the relative size of the carapace width of the occupant. The mean (± SE) entrance volume was 230.8 ± 11.7 cm, and the height of the pyramid was 11.8 ± 0.49 cm (n = 54). The results of our study did not support our hypothesis because we had expected to find a linear correlation between body size and pyramid height, i.e., the larger the male, the larger the pyramid. However, our results show that the largest males in the population either built small pyramids or not at all, and the cut-off of the larger crab’s body size appears to be around 350 cm3. We discovered a step-wise function in the data in that crabs with the smallest body size of ca. 250 cm3 constructed the highest pyramids, with a declining tendency between 250–350 cm3 and extremely low pyramids beyond 350 cm3. However, our findings need to be further studied with a stress on the ambiance and elucidate whether the habitats differ in temperature, humidity, prey-base, etc., before concluding as to why the larger males desist from building pyramids. This study underwrites the importance of studying the mating systems of the macro-fauna of the beaches that are fast disappearing owing to anthropogenic development.

Multimodal Microscale Imaging of Textured Perovskite-Silicon Tandem Solar Cells.

Halide perovskite/crystalline silicon (c-Si) tandem solar cells promise power conversion efficiencies beyond the limits of single-junction cells. However, the local light-matter interactions of the perovskite material embedded in this pyramidal multijunction configuration, and the effect on device performance, are not well understood. Here, we characterize the microscale optoelectronic properties of the perovskite semiconductor deposited on different c-Si texturing schemes. We find a strong spatial and spectral dependence of the photoluminescence (PL) on the geometrical surface constructs, which dominates the underlying grain-to-grain PL variation found in halide perovskite films. The PL response is dependent upon the texturing design, with larger pyramids inducing distinct PL spectra for valleys and pyramids, an effect which is mitigated with small pyramids. Further, optimized quasi-Fermi level splittings and PL quantum efficiencies occur when the c-Si large pyramids have had a secondary smoothing etch. Our results suggest that a holistic optimization of the texturing is required to maximize light in- and out-coupling of both absorber layers and there is a fine balance between the optimal geometrical configuration and optoelectronic performance that will guide future device designs.

Influence of the textured pyramid size on the performance of silicon heterojunction solar cell

By adjusting the KOH/H2O texturing condition intendedly, different random pyramidal textures with the average pyramid size of 8 μm (large), 4 μm (medium) and 1.5 μm (small) were prepared on N type M2 monocrystalline silicon substrates for the fabrication of silicon heterojunction (SHJ) solar cell. It was evidenced that the pyramid morphology not only impacted the reflection of incident light and the heterojunction interface passivation quality but also affected the interface contact property between transparent conductive oxide (TCO) layer and Ag electrode. The texture with small pyramids presented the best anti-reflective and passivation performance due to the pyramidal size distribution uniformity, which brought the SHJ solar cell the highest short-circuit current density (JSC) and open-circuit voltage (VOC). However, the texture with small pyramids also led to the worst fill factor (FF). As a result, there was no obvious difference on the conversion efficiency for the textures with different pyramidal size. By characterizing the TCO/Ag contact, the FF reduction induced by the small pyramid texture could be attributed to the increased specific contact resistance of the TCO/Ag contact, which resulted from the fact that there were lots of voids between the TCO layer and Ag electrode, since Ag particles with a larger size than the small pyramids could not fill into the limited space between the adjacent pyramids. As a result, in order to realize the potential to enhance the SHJ solar cell conversion efficiency by adopting the texture with small pyramids, new Ag paste with smaller Ag particles should be adopted.

Degradation study of carrier selective contact silicon solar cells with ageing: Role of silicon surface morphology

Ageing effect on the performance of Ag/ITO/MoOx/n-Si/LiFx/Al carrier selective contact (CSC) silicon solar cells has been investigated based on silicon surface morphology (planar, different pyramid sizes, and chemical polishing of pyramids). The cells with small silicon pyramids (~2 µm) have shown better stability with time than the medium/large pyramids (~5/~8 µm). The chemical polishing of pyramid peaks and valleys has further reduced the cells ageing effect due to minimization of the microstructural stress (tensile in the valleys and compressive at the peaks) at the MoOx/n-Si interface, which has been verified indirectly with cells fabricated on a planar surface. The cell’s performance degradation based on morphology points out the instability of the MoOx layer and Schottky barrier reduction, which results in hole-transport hindrance at the MoOx/n-Si junction with the S-shape in J-V graphs under illumination. The ageing effect on device performance is further investigated using the Sentaurus TCAD simulations with the MoOx layer work function variation, and the study indicates the band bending reduction (minimal carrier inversion) and hole transport barrier at the junction region.

Highly reproducible c-Si texturing by metal-free TMAH etchant and monoTEX agent

Surface texturing of a silicon solar cell is critical to provide surface antireflection and light trapping. The common texturing method based on KOH as an etchant with isopropyl alcohol (IPA) as a wetting agent suffers two disadvantages: introducing metal contamination and low repeatability. To circumvent the limitation of the KOH-IPA method, we develop a new texturing regime by substituting TMAH for KOH, and a commercial surfactant RENA monoTEX for IPA. This TMAH-monoTEX method shows advantages of non-metal contamination, high reproducibility, short process time and small random pyramids. IBC solar cells fabricated with the TMAH-monoTEX texture achieved an efficiency of 25% with Jsc of 42.9 mA/cm2, Voc of 719 mV and FF of 81.1%.

К. Schaffer: Zur feineren Struktur der Hirnrinde und über funktionelle Bedeutung der Nervenzellenfortsätze. Arch. f. Mikrosk. Anatomie. XLVIIL 4 Heft. 1897. S. S. 550—572

The author's research refers to the anterior cerebral cortex of a newborn dog. The author studies in detail the so-called tiny pyramidal cells, lying between the pluripolar cells of the molecular layer and the small (true) pyramidal cells. Already R. y Cajal drew attention to polygonal or core-shaped cells, the cells that lie behind the layer of the outermost cells (pluripolare Nervenzellen von R. y Cajal), but did not separate them into a special group, believing that these cells were gradually changing vid, go into the small pyramids, to which he numbered them. Schaffer separates these cells into a special group, calling it the layer of surface polymorphic cells. These cells have a dark variety of shapes (fusiform, oval, roundish, pear-shaped, polygonal) and lie in approximately four (4) rows. Dendrites go then, mainly, in two opposite directions (for fusiform cells), then they move radially in all directions (for round and polygonal cells). The number of dendrites is sometimes strikingly abundant. Dendrites going to the surface of the brain reach it, while dendrites of the opposite direction sometimes go down to the ammonium formations of the cerebral cortex. Special attention should be paid to the axial cylinder of the disassembled cells; on the basis of the features of this appendix, the author distinguishes 3 types of disassembled cells.

Passivation of textured crystalline silicon with small pyramids by silicon nitride films formed by catalytic chemical vapor deposition and phosphorus catalytic impurity doping

Abstracts Silicon nitride (SiNx) films formed by catalytic chemical vapor deposition (Cat-CVD) and phosphorus (P) catalytic impurity doping (Cat-doping) are applied on textured crystalline silicon (c-Si) wafers with a pyramid size of 1–2 µm to reduce the surface recombination of minority carriers. SiNx single layer passivation realizes a surface recombination velocity (SRV) of less than 10 cm/s. The addition of a P Cat-doped layer results in a reduction in a SRV to ~7 cm/s owing to field-effect passivation. These values are comparable to those obtained in our previous study for textured c-Si surface with larger-sized pyramids, indicating the high passivation ability of Cat-CVD SiNx films and P Cat-doping independent of the size of pyramids. In addition to the double-side textured wafers, we also prepare a single-side textured wafer using Cat-CVD SiNx as an etching barrier. We find that Cat-CVD SiNx films can be utilized as an etching barrier against alkali solution, and a high effective minority carrier lifetime (τeff) of 2.3 ms has been obtained by the passivation with Cat-CVD SiNx films. These achievements will contribute to an improvement in the performance of back-contact c-Si solar cells.

Numerical simulation of the hydrodynamics and mass transfer in the capping of large size Z-cut plates

Numerical simulation of the hydrodynamics and mass transfer involved in the capping of large size Z-cut KDP plates has been performed. The variations of surface supersaturation with thin layer height, bulk supersaturation and rotation rate are analyzed. The results show that keeping still is very unfavorable for the growth of thin layer, a certain rotation rate should be applied to the Z-cut plate to increase the concentration gradient across the (0 0 1) face, thus making sure that thin layers can grow from the edges while small pyramids barely grow from the face center. Given the result that end faces of thin layers nearly bear a bulk supersaturation, a relative low bulk supersaturation will be better to ensure both the growth of thin layers and the good surface uniformity brought by low supersaturation. Moreover, as thin layers grow, rotation rate should be increased to make up the insufficient solute supply resulting from the decreasing linear speed. The optimal parameters for rapid and high-quality capping of large size Z-cut plates are suggested, the relevant simulation results are also presented.

Effect of textured silicon pyramids size and chemical polishing on the performance of carrier-selective contact heterojunction solar cells

Role of textured crystalline silicon pyramids size and chemical polishing (CP) for isotropic etching of pyramid peaks/valleys are investigated from carrier-selective contact silicon heterojunction solar cell performance. With an increase of average pyramids size from 2 to 8 µm, the effective minority carrier lifetimes (τeff) are reduced from ∼126 to ∼65 µs with molybdenum oxide (MoOx) surface passivation layers. After the CP treatment, an increase in the τeff is observed for the same respective textures (from ∼154 to ∼99 µs) due to reduction of charge carrier recombination. The solar cell structure of Ag/ITO/MoOx/n-Si/LiFx/Al is fabricated at room temperature. With small pyramids (∼2 µm), the cell has shown the better power conversion efficiency of ∼14.53%, but, after the CP treatment not much efficiency variation is observed. Whereas; the CP treatment is beneficial for medium/large pyramids (∼5–8 µm) based cells, which has enhanced the open-circuit voltage (45–63 mV) after smoothing/rounding of sharp peak/valley surfaces. But, we have observed a reduction in photocurrent due to an increase of light reflection from smoothened pyramid surfaces. Quantum efficiency analysis has provided the better insight with the silicon surface morphology dependent energy conversion. The cells’ reverse saturation currents also have analyzed to understand the silicon surface passivation and MoOx/n-Si junction quality. The performance variation of cells is explained by considering low-barrier shunts at the pyramids’ peaks/valleys, which influence the junction built-in potential at the depletion region.

Plasma etched c-Si wafer with proper pyramid-like nanostructures for photovoltaic applications

Dry and maskless texturing process of mono-crystalline silicon wafers using CF4/O2 plasma in a reactive ion etching (RIE) system has been developed with the aim of obtaining optimized surface texture characterized by low optical reflection loss for photovoltaic applications. In this study c-Si has been successfully subjected to plasma etching at unusual process conditions, specifically high value of substrate temperature (15 °C) coupled with high value of process pressure (40 Pa). Different c-Si surface textures are produced at different etch durations.Specifically, pyramid-like morphology appears at very short etch time and crater-like nanostructures form at longer etch time, whereas the former gives the lowest average reflectance (<5%). Furthermore, we clearly observe a slowing down of the etching rate starting from 5 min and in correspondence with the appearance of the sponge-like structure coupled with pores formation. Geometric parameters of morphological features, such as RMS and average inclination angle of the surface features, have been correlated with some specific texture functions such as angular distribution of scattered light Ps(θ) obtained by Angular Resolved Scattering (ARS) technique. Shape and slope of the texture features strongly determine the amount of forward scattered light and, as a consequence, the amount of reflectance decrease. Surface texture obtained after only 3 min of etch and characterized both by well distributed small normal pyramids and by high average inclination angle, proves to be more effective in giving reflection reduction respect to other surface textures characterized by inhomogeneously distributed large cavities. Finally, we can well suppose that this small pyramid-like texture on Si-substrates can be used for the preparation of highly efficient heterojunction-based solar cells (Si-HJT).

Differences in cytoarchitecture of Broca's region between human, ape and macaque brains

Areas 44 and 45 have been identified in non-human primates as homologs of the human Broca region. Distribution of large and smaller pyramids and the ventro-lateral localization in the posterior frontal lobe enable their identification in non-human primates. Since only humans hold the ability of language, it has been hypothesized that differences in microstructure may, together with other anatomical factors, e.g., white matter tract connectivity, volumes of cortical areas and their molecular differentiation, be responsible for the lack (non-human primates) or ability (humans) of language. We sought to identify microstructural differences, by quantitatively studying the cytoarchitecture of areas 44 and 45 using layer-specific grey level indices (volume proportion of neuropil and cell bodies) in serially sectioned and cell body stained human, bonobo, chimpanzee, gorilla, orangutan and Macaca fascicularis brains. The main results are the interspecies differences in neuropil volume relative to cell bodies in all layers of both areas which allows a grouping of the different species into three major groups: Homo sapiens has the largest, great apes a markedly lower, and macaque the lowest neuropil volume. This indicates considerably more space for local and interregional connectivity in human brains, which matches recent studies of fiber tracts and spacing of cortical minicolumns because increasing connectivity also requires more space for axons and dendrites in the neuropil. The evolutionary enlargement of neuropil is, therefore, a major structural difference between humans and non-human primates which may correspond to the underlying functional differences.

Influence of small size pyramid texturing on contact shading loss and performance analysis of Ag-screen printed mono crystalline silicon solar cells

Front side textured random pyramids are widely utilized in major industries for the performance enhancement of crystalline silicon (c-Si) solar cells. Random pyramids not only reduce the surface reflectance but also improve the light trapping effect. Therefore, it is necessary to understand the pyramid height affecting the cell performance, further improving cell efficiency. In this work, we present an experimental study to investigate the influence of pyramids size on the contact shading loss mechanism of silver (Ag) screen-printed p-type c-Si solar cells. Three alkaline texture solutions with sodium silicate additives were optimized to develop the small pyramid (0.5–2.0 µm) size, middle pyramid (5.0–9.0 µm) size and large pyramid (10–15 µm) size on the c-Si surface, respectively. It was noticed that screen-printed finger width strongly depends on pyramid size. Even though, same mesh patterns and screen printing conditions resulted in 20 µm widening of metal finger width on the large pyramids as compared to the small pyramids. This was attributed to the increase in the size of cell surface pyramids that not only varied the gap between the screen mesh and cell surface while screen-printing but also hindered the contraction of metal electrodes during the firing process. The c-Si solar cells with large pyramids suffered from an extra shading loss during fabrication, thus, led to the reduction of the short circuit current density (~0.7 mA/cm2) resulting in lower efficiency (~17.72%) as compared to efficiency (~18.60%) of small pyramid based cells.

Surface Morphology Study of Chemical Vapor Transport of ZnO Crystals.

A chemical vapor transport (CVT) method was implemented to grow bulk ZnO crystals. X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), and optical microscope (OM) studies were carried out to characterize the surface properties of the grown crystal. The XRD result indicated the exposed solid-vapor interface of the as-grown crystal was composed of (0001) and faces. Using SEM and OM, we observed small hexagonal pyramids and microstructures formed of crosslines on the as-grown crystal and found hexagonal thermal etching pits on the surfaces of seed crystals. The formation, evolution, and distribution mechanisms of the microstructures were investigated.

Congenital Zika virus infection: a neuropathological review.

A relationship between Zika virus (ZikV) infection in pregnancy and the occurrence of microcephaly was established during the Zika outbreak in Brazil (2015-2016). Neuropathological findings in congenital Zika syndrome helped to understand its pathogenetic mechanisms. The most relevant postmortem findings in the central nervous system (CNS) of fetuses and neonates infected with ZikV early in gestation are microcephaly with ex-vacuo ventriculomegaly and large head circumference associated with obstructive hydrocephalus due to severe midbrain and aqueduct distortion. Babies with severe brain lesions are born with arthrogryposis. Histologically, there is extensive destruction of the hemispheric parenchyma, calcifications, various disturbances of neuronal migration, reactive gliosis, microglial hyperplasia and occasional perivascular cuffs of lymphocytes, also in the meninges. Hypoplastic lesions secondary to the lack of descending nerve fibers include small basis pontis, pyramids and spinal corticospinal tracts. Cerebellar hypoplasia is also common. Severe nerve motor nerve cell loss is observed in the anterior horn of the spinal cord. A spectrum of neuropathological changes, from severe microcephaly to obstructive hydrocephalus was observed. The severity of the lesions is directly related to the gestational age, the most severe occurring when the mother is infected in the first trimester. Infection of progenitor cells at the germinal matrix was demonstrated. The lack of spinal motor neurons is responsible for fetal acynesia and consequent arthrogryposis.

Passivation of textured crystalline silicon surfaces by catalytic CVD silicon nitride films and catalytic phosphorus doping

Silicon nitride (SiNx) films formed by catalytic chemical vapor deposition (Cat-CVD) and phosphorus (P)-doped layers formed by catalytic impurity doping (Cat-doping) are applied for the passivation of pyramid-shaped textured crystalline Si (c-Si) surfaces formed by anisotropic etching in alkaline solution. Lower surface recombination velocities (SRVs) tend to be obtained when smaller pyramids are formed on c-Si surfaces. P Cat-doping is effective for reducing the SRV of textured c-Si surfaces as in the case of flat c-Si surfaces. We realize SRVs of textured c-Si surfaces of ∼8.0 and ∼6.7 cm/s for only SiNx passivation and for the combination of SiNx and P Cat-doping, respectively. These structures also have high optical transparency and low Auger recombination loss, and are of great worth in application for the surface passivation of interdigitated back-contact c-Si solar cells.