Pillar-like Structures Research Articles

Ultrastructure of the digestive system of Ramazzottius tribulosus and Macrobiotus richtersi (Eutardigrada) in relationship with diet

The ultrastructure of the digestive system of tardigrades was already described in some species, but it has never been studied in relationship to diet. We performed ultrastructural analyses of the midgut and hindgut of phytophagous Ramazzottius tribulosus and zoophagous Macrobiotus richtersi. In addition, the foregut of R. tribulosus was analyzed. New ultrastructural details have been observed. Among them are: (a) distinct transverse pillar-like structures, lacking in electron-dense and compact cuticle of the buccal tube; (b) a hole or groups of holes sometimes present in the buccal tube; (c) a large cavity within each of the salivary glands where secreted mucus accumulates; and (d) already found in zoophagous Isohypsibius prosostomus, one valve, formed by folds of the pharynx and located at the transition from pharynx to esophagus. In both analyzed species the increase of midgut surface is identified by two orders of folds of the gut wall and by microvilli. In R. tribulosus there are many first-order folds and few second-order folds, whereas in M. richtersi the opposite pattern is found. A peritrophic membrane and microvilli with a well developed glycocalyx are found only in the midgut lumen of R. tribulosus. The density of microvilli and the ratio between the real surface with microvilli and the hypothetical surface without microvilli is lower in zoophagous M. richtersi and I. prosostomus than in phytophagous R. tribulosus. All of these data represent an indirect indication of differences in digestive physiology between phytophagous and zoophagous tardigrade species. The shape of the hindgut is similar in both species and the lumen of the hindgut looks like a heartshaped cavity with some narrow cell evaginations.

Characteristics and impact of Taq enzyme adsorption on surfaces in microfluidic devices

We investigated the adsorption of Taq enzyme, using sessile droplets, on different microfluidic materials. In propagating adsorption materials, the contact angle (CA) of a sessile Taq droplet continually recedes and collapses due to adsorption. Contrastingly, in contained adsorption materials it exhibits an initial reduced CA due to an instantaneous adsorption, however remains time-invariant. Spectrophotometer analysis on SU8, a propagating adsorption material, reveals a gradual loss of Taq from the droplet onto the surface during droplet collapsing, as opposed to a rapid saturated adsorption in Teflon, a contained adsorption material. AFM micrographs of the adsorbed surfaces suggest a network-like structure in SU8 and distinctly different pillar-like structures in Teflon. With this understanding, we have successfully applied a SU8-Teflon coating to impart a time-invariant contact angle with minimal loss of Taq in surface microfluidic devices.

Silicidation in Ni/Si thin film system investigated by X-ray diffraction and Auger electron spectroscopy

Silicide formation induced by thermal annealing in Ni/Si thin film system has been investigated using glancing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES). Silicide formation takes place at 870 K with Ni 2Si, NiSi and NiSi 2 phases co-existing with Ni. Complete conversion of intermediate silicide phases to the final NiSi 2 phase takes place at 1170 K. Atomic force microscopy measurements have revealed the coalescence of pillar-like structures to ridge-like structures upon silicidation. A comparison of the experimental results in terms of the evolution of various silicide phases is presented.

Triggered star formation in the environment of young massive stars

AbstractRecent observations with the Spitzer Space Telescope show clear evidence that star formation takes place in the surrounding of young massive O-type stars, which are shaping their environment due to their powerful radiation and stellar winds. In this work we investigate the effect of ionising radiation of massive stars on the ambient interstellar medium (ISM): In particular we want to examine whether the UV-radiation of O-type stars can lead to the observed pillar-like structures and can trigger star formation. We developed a new implementation, based on a parallel Smooth Particle Hydrodynamics code (called IVINE), that allows an efficient treatment of the effect of ionising radiation from massive stars on their turbulent gaseous environment. Here we present first results at very high resolution. We show that ionising radiation can trigger the collapse of an otherwise stable molecular cloud. The arising structures resemble observed structures (e.g. the pillars of creation in the Eagle Nebula, M16, or the Horsehead Nebula, B33). Including the effect of gravitation we find small regions that can be identified as formation places of individual stars. We conclude that ionising radiation from massive stars alone can trigger substantial star formation in molecular clouds.

Ultrastructural anatomy of CALT follicles in the rabbit reveals characteristics of M-cells, germinal centres and high endothelial venules.

Conjunctiva-associated lymphoid tissue (CALT) is a part of the eye-associated lymphoid tissue (EALT) at the ocular surface. Its lymphoid follicles are usually characterized by using light microscopy, but its ultrastructure remains largely unknown. In this study, flat whole-mount conjunctival tissues (n = 42) from 21 young adult rabbits were investigated native in reflected light, and further stained and cleared (n = 6), in paraffin histology sections (n = 6), scanning electron microscopy (SEM, n = 4) and transmission electron microscopy (TEM, n = 4). Secondary lymphoid follicles accumulated into a dense group nasally towards the lacrimal punctum of the lower lid. High endothelial venules (HEV) with typical ultrastructure occurred in the parafollicular zone. The bright germinal centre (GC) contained lymphoblasts, follicular dendritic cells, apoptotic cells and tingible body macrophages. The follicle-associated epithelium (FAE) was devoid of goblet cells and contained groups of lymphoid cells. TEM showed these cells to be located in cytoplasmic pockets of superficial electron-lucent cells with a thin cytoplasmic luminal lining that contained a fine filament meshwork and numerous endocytotic vesicles. These M-cells were sitting between and on top of the ordinary dense epithelial cells that were located basally and formed pillar-like structures. In stereoscopic SEM, the surface cells were very large, had a polygonal outline and covered cavernous spaces. The rabbit has a CALT with typical follicular morphology, including HEV for regulated lymphocyte migration and epithelial cells with ultrastructural characteristics of M-cells that allow antigen transport as indicated by the GC-reaction. The arrangement of these M-cells on top of and between epithelial pillar cells may reflect a special structural requirement of the multilayered CALT FAE.

Influence of process variables on electron beam chemical vapor deposition of platinum

Electron beam chemical vapor deposition was performed in a modified environmental scanning electron microscope to deposit platinum structures. Process variables including voltage, beam current, deposition time, dwell time, and line time were studied in statistically designed and analyzed experiments on fiber (pillar-like structures) and line (wall-like structures) deposition. Deposition rates and geometric features such as aspect ratio were optimized. Results from the experimentation showed the importance of the beam current, voltage, and adsorbate replenishment to the deposition process. Growth rates up to 0.9μm∕min were obtained for short deposition times.

Inductively coupled plasma etching of poly-SiC in SF6 chemistries

A study was made to find a low-cost and robust etching solution for silicon carbide (SiC) using a commercially available inductively coupled plasma etching tool. Sulfur hexafluoride (SF6) was selected because of its high degree of F dissociation and nonhazardous nature. A parametric study of the etching characteristics of poly-SiC in inductively coupled plasma (ICP) SF6 chemistries was performed. Etch chemistry was found to greatly affect etch rate, selectivity, and the postetch surface condition. Etch rates as high as 5884Å∕min were achieved with high SiC∕Cr selectivity (36) using a SF6∕CF4∕He gas mixture, but the etched surface was relatively rough (134 Å rms). He addition was found to increase the SiC etch rate, and this effect is believed to be caused by increased ionization of SF6 in the plasma and the resulting increases in the SF3+ and fluorine (F) radical concentrations. The formation of pillar-like structures and sidewall deposition was observed on the etched SiC surfaces under some conditions. These unwanted etch byproducts exhibited a high concentration of chromium (Cr) and fluorine. However, an argon (Ar) plasma preclean of the substrate, high ICP, and/or bias powers, and CF4 addition reduced the pillar formation significantly.

A Novel Isolation of Pillarlike Structures by CMP and Etchback Processes

A Novel Isolation of Pillarlike Structures by CMP and Etchback Processes

Ceratamines, Structurally Simple Microtubule-Stabilizing Antimitotic Agents with Unusual Cellular Effects

Ceratamine A and ceratamine B are heterocyclic alkaloids recently identified in a screen for compounds that arrest cells in mitosis. Treatment of breast carcinoma MCF-7 cells causes a concentration-dependent block of cell cycle progression exclusively at mitosis. In vitro studies with purified tubulin indicate that the ceratamines directly stimulate microtubule polymerization in the absence of microtubule-associated proteins. Cells treated with ceratamines show a dense perinuclear microtubule network in interphase and multiple pillar-like tubulin structures in mitotic cells. The ceratamines do not compete with paclitaxel for binding to microtubules in vitro. Unlike other microtubule-stabilizing agents, the ceratamines have simple structures with no chiral centers, making them attractive drug leads.

Fabrication of TiO2 composite materials for air purification by magnetic field effect and electrocodeposition

Novel air purification materials were fabricated by the application of a magnetic field. In a magnetic field perpendicular to a copper plate, nickel particles with a diameter of 10 μ m were arranged to form numerous pillar-like structures on the matrix surface, and copper as a binder was deposited onto the three-dimensional surface. The total surface area of the pillars and the matrix increased with the magnetic flux density, up to about 800 cm2 per cm2 of the original matrix surface at 6.2 T. After successful codeposition of TiO2 particles on the fabricated materials by electroplating, their photocatalytic activities were evaluated on the basis of the removal efficiency of nitrogen oxides (NOx), which are some of the most hazardous air pollutants. It was concluded that the samples with the pillar-like structures had two opposite characteristics: large surface area as a positive effect and shadowing against ultraviolet (UV) irradiation as a negative effect. However, total photocatalytic activity increased to twice as much as that of the flat sample by improving the UV irradiation method and the preparation condition of the materials

Environmental signals and regulatory pathways that influence biofilm formation.

In nature, bacteria often exist as biofilms. Here, we discuss the environmental signals and regulatory proteins that affect both the initiation of bacterial biofilm formation and the nature of the mature biofilm structure. Current research suggests that the environmental signals regulating whether bacterial cells will initiate a biofilm differ from one bacterial species to another. This may allow each bacterial species to colonize its preferred environment efficiently. In contrast, some of the environmental signals that have currently been identified to regulate the structure of a mature biofilm are nutrient availability and quorum sensing, and are not species specific. These environmental signals evoke changes in the nature of the mature biofilm that may ensure optimal nutrient acquisition. Nutrient availability regulates the depth of the biofilm in such a way that the maximal number of cells in a biofilm appears to occur at suboptimal nutrient concentrations. At either extreme, nutrient-rich or very nutrient-poor conditions, greater numbers of cells are in the planktonic phase where they have greater access to the local nutrients or can be distributed to a new environment. Similarly, quorum-sensing control of the formation of channels and pillar-like structures may ensure efficient nutrient delivery to cells in a biofilm.

Effects of Surface Structure on the Hydrophobicity and Sliding Behavior of Water Droplets

Hydrophobicity and sliding behavior of water droplets were investigated on various hydrophobic pillarlike and groove structures prepared on a silicon wafer by dicing and subsequently coating with fluoroalkylsilane. The dominant hydrophobicity mode was changed from Wenzel's mode to Cassie's mode at a smaller roughness than that expected from the calculation based on the sinusoidal surface by Johnson and Dettre. The effect of water intrusion on the microstructure due to droplet weight was revealed to be an important factor governing the water sliding angle on the surface. In a comparison of the sliding behavior of water droplets over pillarlike and groove structures, it was demonstrated that a proper design of the surface with respect to shape and extent of the three-phase line is more effective than the increase of contact angles merely by decreasing the solid−water contact area.

Growing pillars of densely packed carbon nanotubes on Ni-coated silica

We report the growth of pillar-like cylindrical structures consisting of densely packed and vertically aligned multiwalled carbon nanotubes by exposing Ni-coated oxidized-Si (001) substrates to a xylene–ferrocene mixture. The nanotube pillars have a diameter between 10 and 100 μm, and lengths of several tens of micrometres. Formation of circular microcracks in the film allows ferrocene and xylene molecules to reach the underlying SiO 2 layer where pillars nucleate and grow out of the plane of the film surface. The nanotube pillars are attractive for applications such as energy storage, electrodes, and composite reinforcements.

Electrodes modified with synthetic anionic clays

Anionic clays Zn 2Cr(OH) 6C1·2H 2O, denoted [ZnCrCI], and Zn 3A1(OH) 8C1·2H 2O, denoted [ZnAlCl], are rapidly exchanged with electroactive organic sulfonate anion such as 2,2′-azinobis 3-ethylbenzothiazoline-6-sulfonate (ABTS). These samples are prepared by a simple exchange reaction or by the coprecipitation method. High degrees of exchange are obtained and pillar-like layered structures are formed. Clay-carbon paste modified electrodes have been produced using these materials and the precursor [ZnCrCl]. The electrochemical behaviour of the intercalated substrate has been studied using cyclic voltammetry. The electrogenerated radical of intercalated [ZnAl-ABTS] has been characterized by EPR.

Anion-exchanging clay-modified electrodes: synthetic layered double hydroxides intercalated with electroactive organic anions

The layered double hydroxide (LDH) Zn 2Cr(OH) 6Cl · 2H 2O, denoted [Zn-Cr-Cl], which is an anion-exchanging clay, is rapidly exchanged with electroactive organic sulphonate anions such as m-nitrobenzene sulphonate and anthraquinone mono- and disulphonates. High degrees of reaction are attained, and pillar-like layered structures are formed. Clay-modified electrodes have been produced using these materials and the precursor LDH [Zn-Cr-Cl]. The electrochemical behaviour of the substrates listed above, either intercalated or simply adsorbed on the LDH particles, has been studied using cyclic voltammetry.

Current-distribution effects in microstructures for perpendicular magnetoresistance experiments

We present a simple Ohmic model to calculate the current distribution in small pillar-like structures for perpendicular magnetoresistance experiments. These calculations are consistent with three-dimensional electrostatic simulations, based on the finite element method, and facilitate the analysis of magnetoresistance data of microstructured multilayers.

Ultrastructural observation of the trans-Golgi associated plate-like cisterna in the secretory cells of the rat anterior pituitary gland with special reference to the intracisternal skeleton.

A well-developed plate-like cisterna (PLC) associated with trans-Golgi elements was observed in the Golgi apparatus of secretory cells in the rat anterior pituitary gland. This structure corresponds to the trans-most sacculotubular network. The PLC maintains a remarkably uniform thickness of about 33 nm, as measured between the outer leaflets of its unit membrane structure. As to the mechanism by which this peculiar construction of the PLC is maintained, pillar-like structures were noted in the PLC intracisternal space, apparently acting as supports to keep the intermembrane distance constant. The PLC was especially well developed in hypertrophied cells such as gonadotrophs following castration. One noteworthy feature was that the PLC frequently ran parallel with the rough endoplasmic reticulum (RER), maintaining a constant distance from the latter in hypertrophied cells, but no membrane continuity between the PLC and RER was seen.

Structure and formation of egg membranes in Aedes aegypti. (L.) (Diptera: Culicidae)

An ultrastructural study of mosquito ovarioles reveals that both the vitelline membrane and the endochorion are secreted by the follicular epithelium. The presecretory phase is characterized by the hypertrophy of endoplasmic reticulum and Golgi complex in the follicle cells. Synthesis of vitelline membrane precursors begins immediately after yolk protein uptake by micropinocytosis. Secretory droplets are budded off Golgi cisternae and released into the follicle cell-oocyte interface by exocytosis. The vitelline membrane first appears as dense plaques which eventually fuse to form a single homogeneous layer. Two types of secretory material are identified in the follicle cells prior to the formation of the endochorion. Golgi cisternae bud off small droplets similar in size and appearance to the precursors of the vitelline membrane. These migrate to the apical surface and accumulate between surface folds in the plasma membrane. The second type is a fibrous material formed in endoplasmic reticulum. When fully secreted, the endochorion is a 2-layered structure. The lower layer is comprised of pillar-like structures alternating with fibrous mesh-like areas. The pillars are formed by the coalescence of droplets released from Golgi, while the mesh-like areas presumably arise from the fibrous material. The outer layer is also fibrous. The follicle cells degenerate once the endochorion is laid down.