Needle-shaped Structures Research Articles

A novel method for the preparation of NH 3 sensors based on ZnO-In thin films

This paper reports the preparation of ZnO-In thin films that are capable of detecting low ammonia concentrations in air. Indium and zinc layers are subsequently deposited by thermal evaporation at 70 °C onto an alumina substrate; the metal-semiconductor phase transformation is obtained on thermal cycling of the films in a synthetic air flow at a maximum temperature of 500 °C. XRD analysis shows that these films are polycrystalline and are slightly oriented in the (002) direction. SEM micrographs show that the surface of the metal-oxide film presents a needle-shaped structure; the needle size ranges between 1 and 3 μm. ZnO-In thin films can detect ammonia concentrations in the range 1–10 ppm by operating between 200 and 500 °C and are selective towards reducing gases like CO and CH 4; a good response towards a few ppm NO x is also observed in the same temperature range. This sensor seems to be suitable for detecting some ppm of ammonia in air.

Structure of Polyglycine Crystals Formed by Thermal Solid State Polymerization.

Structure of polyglycine crystal synthesized by solid-state polymerization from α-form single crystal of glycine monomer was examined by X-ray diffraction and scanning electron microscopy (SEM). The X-ray diffraction patterns showed biaxially oriented type-I crystal of polyglycine. The SEM results suggested that crossing laminar and needle-shaped structures were responsible for the biaxial crystalline orientation.

Morphogenesis of Calcification in Porcine Bioprosthesis: Insight from High Resolution Electron Microscopic Investigation at Molecular and Atomic Resolution

High resolution electron microscopy (HREM) coupled with energy dispersive X-ray microanalysis were used to investigate the morphogenesis of calcification in 28 explanted porcine bioprosthetic heart valves. Different morphology and compositions of calcific deposits were consistently observed in various valvular structures of all explanted porcine bioprostheses. The most common forms of calcific deposits were present as spherical particles and needle-shaped structures. HREM investigation of spherical particles of calcium phosphate revealed very fine electron-dense dots about 0.3-1.0 nm in diameter which were packed to form sphere-like clusters of about 2.0-3.5 nm in diameter in the particles. HREM observations of the microneedle-shaped structures even as small as 1.9 nm in thickness could identify the lattice fringes with center-to-center spacings of about 0.8-0.9 nm. Energy dispersive X-ray microanalysis defined the components of needle-shaped calcification as calcium and phosphorus in a ratio typical of hydroxyapatite crystals. The calcific deposits in the collagen tissue have been shown to be at discrete sites on or in the collagen fibrils as the spherical particles or homogeneous electron-dense masses. Based on HREM observations of different types of morphogenesis of calcification it is suggested that chemical processes of calcification accompanying the deposition of calcium in the implanted bioprosthetic heart valves are specific to each substrate system. The formation of amorphous calcium phosphate precursors and direct deposition of microcrystalline hydroxyapatites are considered to be the primary mechanisms of calcification occurring in implanted porcine bioprostheses.

Morphological features of spermatozoa of Paragonimus ohirai (Trematoda: Platyhelminthes) examined by a silver nitrate staining technique

The mature thread-like spermatozoon of Paragonimus ohirai was shown to be composed of 7 distinct segments which have morphologically different characteristics, following staining with silver nitrate. The first segment (1S) is a needle-shaped structure with a perforatorium. The 2S is composed of two filaments loosely paired; 3S consists of a somewhat coarse thread (vestige of the cytoplasmic projection); 4S is composed of two flagella tightly paired; in 5S, two silver-positive filaments are independently seen as in 2S; 6S has a 'spiral' structure composed of two flagella; in 7S, two filaments are seen dissociated from each other. The sperm nucleus exists within the 'spiral' structure of 6S and this structure may serve to hold and/or protect the nucleus. The technique presented here is useful for gross morphological observations of the long sperm of flatworms.

A Progesterone-Modulated, Low-Molecular-Weight Protein from the Uterus of the Sheep is Associated with Crystalline Inclusion Bodies in Uterine Epithelium and Embryonic Trophectoderm1

A protein of Mr 14,000 (14K protein) has been identified in the medium after culturing sheep conceptuses in vitro. However, it was also a component of uterine flushes of nonpregnant ewes during the luteal phase of the estrous cycle. The 14K protein, which consists of several isoforms, was purified from conceptus culture medium by a simple three-step procedure, involving ammonium sulfate precipitation, high-performance anion-exchange chromatography, and gel filtration on Sephacryl S-200. Western blotting procedures with an anti-14K antiserum showed that endometrium from ovariectomized ewes began to release the 14K protein after 6 to 14 days of progesterone treatment. Immunostaining of tissue from Day 16 pregnant ewes and from ewes treated with progesterone for 14 or 30 days showed the protein to be confined to the surface and upper glandular epithelium of the endometrium and to be absent from the deep glands. It was also present in trophectoderm of Day 16 conceptuses. Immunogold labeling in conjunction with electron microscopy revealed that within trophectoderm the 14K protein was localized to large, membrane-bound rhomboidal or needle-shaped crystal structures, and it seems likely that the protein was accumulated by the conceptus as a result of uptake of uterine histotroph. In the uterine epithelium, immunogold label was again most strongly concentrated over crystal-like structures but was also uniformly present over the cytoplasm and nucleoplasm. It was absent over mitochondria, over lipid droplets, and over non-epithelial types of endometrial cell. Such a cellular distribution for a secretory protein is novel, and it remains unclear whether the protein is synthesized by these cells.

Clear cell carcinoma of the skin: a tricholemmal carcinoma?

We report the light and electron microscopic findings of an unusual, locally aggressive cutaneous clear cell carcinoma involving extensively the left cheek and upper lip of a 61-year-old woman. The patient remained free of recurrence 5 years after wide local excision. Microscopically, the tumor was a poorly circumscribed and deeply invasive clear cell neoplasm characterized by large lobules and convoluted trabeculae of polygonal and columnar cells with palisading of the peripheral cells rimmed by thick basement membranes, and horn microcysts with tricholemmal keratinization. The tumor infiltrated the muscle and the salivary glands. Only slight cytologic atypia and a few mitotic figures were present. No definite ductal differentiation was found. Immunoperoxidase staining for carcinoembryonic and epithelial membrane antigens was negative. Ultrastructurally, the tumor cells were joined by desmosomes, and surrounded by thick basal lamina. The cytoplasm contained large pools of glycogen. Peculiar whorls of tonofilaments and aggregates of needle-shaped and club-shaped structures were observed in a small keratinizing focus. The tumor showed features resembling the outer root sheath of the hair follicle microscopically. Furthermore, the lack of duct-like structures and immunoreactivity of carcinoembryonic antigen tend to favor tricholemmal over sweat gland differentiation in this tumor which possibly represents a rare example of tricholemmal carcinoma.

The influence of Mo2C morphology and distribution on the fatigue crack initiation and propagation behavior of Fe-C-Mo dual-phase steels

Dual-phase microstructures consisting of ferrite with carbides (Mo2C) surrounding equiaxed martensite packets have been developed in two alloys, Fe-O. 2C-4Mo and Fe-O. 2C-2Mo. These alloys were chosen because of the presence of two distinct carbide morphologies: (1) a needle-shaped interphase carbide structure, and (2) a fibrous carbide structure. Isothermal transformations were used to control the carbide morphology and distribution in the ferritic regions of the dual-phase microstructures. In the present research the effects of changes in carbide structure on low cycle fatigue (LCF) and fatigue crack growth (FCG) behavior were studied. Crack initiation was observed at prior austenite grain boundaries in the fibrous microstructure, and along intrusion/extrusion defects in the interphase needle microstructures for LCF tests. TEM studies revealed a carbide free region at prior austenite grain boundaries where initiation occurs for the fibrous case. The cyclic stress/strain response of the ferritic portions of the microstructure is determined by the ability of the carbides to homogenize the strain found there. This affects the stress/strain distribution in the composite ferrite-martensite microstructure by changing the hardness ratio of the two phases and subsequently alters the fatigue crack growth behavior and the macroscopic cyclic stress/strain response. Strain localization was also found to affect the roughness induced closure found for fatigue crack growth tests for low R tests (R = 0.1).

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Cementifying fibroma is a rare neoplasm of the bone with a predilection for the mandible. We experienced a case of cementifying fibroma of the right lower posterior region of the mandible in a 61-year-old male. The tumor was surgically removed under local anesthesia. The obtained specimen was examined with light and electron microscopes.Light microscopic findings: The tumor was composed of delicate interlacing collagen fi bers, interspersed with large numbers of cellular elements and cementum-like hard tissues.Transmission electron microscopic findings: The tumor was found to consist of fibroblastlike cells, cementblast-like cells and hard tissues. The fibroblast-like cells assuming spindle or polyhedral shape, contained abundant cytoplasmic organelles and large nuclei. The nuclei varied from elongated ovoid shapes with smooth outline to polyhedral shapes with deep invagination. Intracytoplasmically, there were well developed rER, Golgi apparatus and several mitochondria. Some cementoblast-like cells also contained abundant amounts of 10 nm filaments and 10-400 nm electron-dense microgranules. The intracytoplasma of these cells usually contained electron-dense deposits and needle-shaped crystal-like structures. Within the fibrous matrix, amorphous electron-dense deposits on the collagen fiber bed were usually noted. Occasionally a small number of matrix vesicle-like structures were also present on the collagen fi bers. These matrix vesicle-like structures included electron-dense deposits or needle-shaped crystal like structures.Scanning electron microscopic findings: In the collagen fibrous matrix, there were numerous rounds or ovoid, structureless calcified clusters and cellular elements. Early calcifying deposition on the delicately interlacing fibrous network could also be observed around the cementum-like structure. Occasionally, coalescence of a round calcifying structure into a large cluster was also observed.X-ray microanalysis revealed that these clusters contain a high concentration of phosphate and calcium.

Magnetic field dependence of ultrasonic response times in ferrofluids

A continuous wave method has been used to investigate the influence of a magnetic field upon the ultrasonic response times in a water-base ferrofluid. Values of response times as long as several seconds were observed. Measurements were made of response times versus field angle at 2.262 MHz and at 830 KHz. It was found that the response time is a strong function of the field angle; also it was unusually long at some angles of rotation. This long reponse time was interpreted as an indication of the formation of larger agglomerate or needle-shaped structures due to the external magnetic field. It was concluded that ultrasonic measurements can he a powerful tool for studying the dynamics of ferrofluids under the action of an external magnetic field.