DC heating induced shape transformation of Ge structures on ultraclean Si(5 5 12) surfaces.

We report the growth of Ge nanostructures and microstructures on ultraclean, high vicinal angle silicon surfaces and show that self-assembled growth at optimum thickness of the overlayer leads to interesting shape transformations, namely from nanoparticle to trapezoidal structures, at higher thickness values. Thin films of Ge of varying thickness from 3 to 12 ML were grown under ultrahigh vacuum conditions on a Si(5 5 12) substrate while keeping the substrate at a temperature of 600 °C. The substrate heating was achieved by two methods: (i) by heating a filament under the substrate (radiative heating, RH) and (ii) by passing direct current through the samples in three directions (perpendicular, parallel and at 45° to the (110) direction of the substrate). We find irregular, more spherical-like island structures under RH conditions. The shape transformations have been found under DC heating conditions and for Ge deposition more than 8 ML thick. The longer sides of the trapezoid structures are found to be along (110) irrespective of the DC current direction. We also show the absence of such a shape transformation in the case of Ge deposition on Si(111) substrates. Scanning transmission electron microscopy measurements suggested the mixing of Ge and Si. This has been confirmed with a quantitative estimation of the intermixing using Rutherford backscattering spectrometry (RBS) measurements. The role of DC heating in the formation of aligned structures is discussed. Although the RBS simulations show the presence of a possible SiO(x) layer, under the experimental conditions of the present study, the oxide layer would not play a role in determining the formation of the various structures that were reported here.

Formation of aligned nanosilicide structures in a MBE-grown Au/Si(110) system: a real-time temperature-dependent TEM study.

Thin Au films (∼2 nm) were deposited on an Si(110) substrate epitaxially under ultra-high vacuum (UHV) conditions in a molecular beam epitaxy (MBE) system. Real-time in situ transmission electron microscopy (TEM) measurements were carried out at various temperatures (from room temperature to 700 °C), which shows the formation and growth of aligned gold silicide nanorod-like structures. The real-time selected-area electron diffraction patterns show the presence of silicon and unreacted gold at lower temperatures (up to 363 °C), while at higher temperatures only the signature of silicon has been observed. The diffraction analysis from room temperature cooled systems show the presence of gold silicide structures. Around 700 °C, 97% of the nanostructures were found to be aligned nanosilicide-rod-like structures with a longer side of ≈37 nm and aspect ratio of 1.38. For a high temperature annealed system (at 600 °C), selected-area diffraction (SAD) and high resolution lattice (after cooling down to room temperature) confirmed the formation of nano- Au(5)Si(2) structures. The alignment of gold silicide structures has been explained on the basis of lattice matching between the substrate silicon and silicide structures.

Congenital granular cell lesion "congenital epulis"--report of a case.

Congenital granular cell lesion (CGCL) or "congenital epulis" is a rare lesion of newborn also known as Neuman's Tumor, which is benign in nature, mostly occurs as a single tumour but rarely as multiple. The histogenesis and natural clinical history of the lesion remains obscure. Even with the advent of modem histopathological techniques, it has not been possible to depict specific cellular features unique to this lesion. This lesion arises from mucosa of gingiva either from maxillary or mandibular alveolar ridge. The appearance of the lesion is most common in maxillary alveolar ridge than mandibular with predominance in females than in the males. The present report describes a case of congenital granular cell lesion (CGCL) in the incisor region of mandibular alveolar ridge. This lesion was causing feeding problem and was excised under local anaesthesia.

Talon cusp associated with other dental anomalies: a case report.

Talon cusp is an uncommon dental anomaly referring to an accessory cusp projecting from the cingulum area, or cemento-enamel junction of maxillary or mandibular anterior teeth, in both the primary and permanent dentition. This paper reports a rare case of talon cusp affecting the mandibular right central incisor and maxillary right lateral incisor, together with other dental abnormalities, viz. an inverted impacted migrating mandibular right second premolar; complete agenesis of the maxillary and mandibular third molars, the maxillary right second permanent molar, and the mandibular left permanent central incisor; severe crowding; deep bite; hypoplastic teeth; bilateral reverse cross-bite in the premolar region; and a retrognathic mandible. The presence of this number of dental anomalies in a single patient is rare.

Mandibular lateral incisor-canine transposition (Mn.12.C): a case report.

Tooth transposition is a rare developmental anomaly of the teeth characterized by positional interchange of permanent tooth leading to disintegration in the alignment in the affected segment, shifting of midline and malocclusion of teeth. This article reports a rare case of Mn.12.C anomaly affecting right mandibular arch of a (11 year old) female child causing shifting of midline and crowding.

Prevalence of supernumerary teeth in deciduous and mixed dentition.

Supernumerary teeth are the extra teeth which may have either erupted or unerupted in addition to normal dentition and are seen both in deciduous as well as permanent dentition. The incidence of supernumerary teeth shows more frequent occurrence in permanent dentition than deciduous dentition, affecting both the sexes. The etiology of supernumerary teeth is still unknown and not well understood, but thought to be the result from disturbance during the initiation and proliferation stages of tooth development. In the present study an attempt has been made to asses, its prevalence in deciduous and mixed dentition phase.

A study of behaviour patterns of normal children in a dental situation and its relationship with socioeconomic status, family type and sibling position.

Different psychosocial variables, such as socioeconomic status, family type and sibling position may be considered to be of great significance as it may influence child behaviour pattern in a dental treatment situation. 143 children in the age group of 3-14 years were selected randomly from the out patient department of Pediatric Dentistry, Dental Wing, S. C. B. Medical College, Cuttack with an aim of assessing relationship, if any, between the magnitude of behaviour and the above mentioned psychosocial variables. Behaviour rating was done using Frankl behaviour rating scale. The results of the study reveals no significant relationship between socio economic status, family type and sibling position with child behaviour pattern, but a trend has been observed that children of high socio economic back ground behave more positively, children of a nuclear family exhibit more negative attitude and middle siblings show less negative behaviour than youngest and eldest.

Prevalence of dental caries and treatment needs among children of Cuttack (Orissa).

An epidemiological investigation was carried out to know the prevalence of Dental Caries amongst 1257 children in the age group of 5, 8, 11 & 15 years respectively attending schools in the city of Cuttack, Orissa. The examination was carried out under natural light and dental caries was diagnosed according to W.H.O. Criteria 1983. The point prevalence of dental caries was recorded to be 64.3% with an average DMFT of 2.38. The prevalence of caries showed a pattern of occurrence i.e. prevalence consistantly increased from 5 years to 8 years age group and subsequently decreased at 11 years and 15 years age. Regarding treatment needs, 63.6% children required dental treatment for various reason and it is in accordance with dental caries prevalence of different age group.

Identification and partial characterization of Arkansas isolates of chicken anemia virus.

Chickens from both broiler and broiler breeder pullet flocks experiencing symptoms of chicken anemia virus (CAV) infection were first observed at the Poultry Health Research Laboratory at the University of Arkansas in September 1992. Flocks had experienced higher than normal mortality with subcutaneous hemorrhages on the wings, neck, and thorax. Postmortem and histopathologic evaluation revealed thymus and bursal atrophy and lesions consistent with those reported for CAV infection. Because this infection had not previously been observed by Poultry Health Research Laboratory personnel in Arkansas-grown chickens, the establishment of a definitive diagnosis was deemed important. The presence of CAV was established by infecting MSB-1 cells with pooled liver homogenates from groups of 10 specific-pathogen-free chickens that had previously been inoculated in an attempt to experimentally reproduce the disease observed in the field. Cytopathic effects in the infected MSB-1 cells were first evident following the fifth passage. Indirect fluorescent antibody technique identified infected MSB-1 cells following at least five blind passages. To further confirm the presence of CAV, a polymerase chain reaction (PCR) technique was used to amplify a specific portion of the virus genome from infected MSB-1 cells and tissue extracts from several submitted chickens. Sequence analysis of a 186-bp PCR amplification product revealed that the Arkansas isolate was very similar to the Cuxhaven-1 isolate (99.5% sequence identity).