Nonlinear I-V characteristics of nanocrystalline SnO2

Current versus voltage characteristics (I-V) of nanocrystalline SnO2 materials have been investigated in air at room temperature. The samples were prepared by the inert gas condensation technique (IGCT) as well as by chemical methods. X-ray diffraction studies showed a tetragonal rutile structure for all the samples. Microstructural studies were performed with transmission electron microscopy. All the samples exhibited nonlinear I-V characteristics of the current-controlled negative resistance (CCNR) type. The results show that the threshold field (break down) voltage is higher for the samples prepared by the IGCT method than for those prepared by the chemical method due to the formation of a tin oxide layer over the crystalline tin. It is also found that the threshold field increases with the decrease in grain size.

Molecular and Clinical Characteristics of Pituitary Adenoma Predisposition (PAP)

Pituitary adenomas are common benign neoplasms. Although most of them are sporadic, a minority occurs in familial settings. Heterozygous germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene were found to underlie familial pituitary adenomas, a condition designated as pituitary adenoma predisposition (PAP). PAP confers incomplete penetrance of mostly growth hormone (GH) secreting adenomas in young patients, who often lack a family history of pituitary adenomas. This thesis work aimed to clarify the molecular and clinical characteristics of PAP. Applying the multiplex ligation-dependent probe amplification assay (MLPA), we found large genomic AIP deletions to account for a subset of PAP. Therefore, MLPA could be considered in PAP suspected patients with no AIP mutations found with conventional sequencing. We generated an Aip mouse model to examine pituitary tumorigenesis in vivo. The heterozygous Aip mutation conferred complete penetrance of pituitary adenomas that were mostly GH-secreting, rendering the phenotype of the Aip mouse similar to that of PAP patients. We suggest that AIP may function as a candidate gatekeeper gene in somatotrophs. To clarify molecular mechanisms of tumorigenesis, we elucidated the expression of AIP-related molecules in human and mouse pituitary tumors. The expression of aryl hydrocarbon receptor nuclear translocator (ARNT) was reduced in mouse Aip-deficient adenomas, and similar ARNT reduction was also evident in human AIP mutation positive adenomas. This suggests that in addition to participating in the hypoxia pathway, estrogen receptor signaling and xenobiotic response pathways, ARNT may play a role in AIP-related tumorigenesis. We also studied the characteristics and the response to therapy of PAP patients and found them to have an aggressive disease phenotype with young age at onset. Therefore, improvement in treatment outcomes of PAP patients would require their efficient identification and earlier diagnosis of the pituitary adenomas. The possible role of the RET proto-oncogene in tumorigenesis of familial AIP mutation negative pituitary adenomas was evaluated, but none of the found RET germline variants were considered pathogenic. Surprisingly, RET immunohistochemistry suggested possible underexpression of RET in AIP mutation positive pituitary adenomas an observation that merits further investigation.

Impedance‐frequency characteristics of metal‐oxide‐semiconductor structures on polycrystalline silicon

This paper reports the variations in impedance with frequency of metal‐oxide‐semiconductor (MOS) structures on polycrystalline silicon. The origin of these impedance‐frequency characteristics are qualitatively explained. These characteristics indicate that the MOS structure on polycrystalline silicon can be exploited to realize voltage controlled filters.

Investigation of the effect of nonlocal scale on ultrasonic wave dispersion characteristics of a monolayer graphene

In this article, an ultrasonic wave propagation in graphene sheet is studied using nonlocal elasticity theory incorporating small scale effects. The graphene sheet is modeled as an isotropic plate of one-atom thick. For this model, the nonlocal governing differential equations of motion are derived from the minimization of the total potential energy of the entire system. An ultrasonic type of wave propagation model is also derived for the graphene sheet. The nonlocal scale parameter introduces certain band gap region in in-plane and flexural wave modes where no wave propagation occurs. This is manifested in the wavenumber plots as the region where the wavenumber tends to infinite or wave speed tends to zero. The frequency at which this phenomenon occurs is called the escape frequency. The explicit expressions for cutoff frequencies and escape frequencies are derived. The escape frequencies are mainly introduced because of the nonlocal elasticity. Obviously these frequencies are function of nonlocal scaling parameter. It has also been obtained that these frequencies are independent of y-directional wavenumber. It means that for any type of nanostructure, the escape frequencies are purely a function of nonlocal scaling parameter only. It is also independent of the geometry of the structure. It has been found that the cutoff frequencies are function of nonlocal scaling parameter (e(0)a) and the y-directional wavenumber (k(y)). For a given nanostructure, nonlocal small scale coefficient can be obtained by matching the results from molecular dynamics (MD) simulations and the nonlocal elasticity calculations. At that value of the nonlocal scale coefficient, the waves will propagate in the nanostructure at that cut-off frequency. In the present paper, different values of e(o)a are used. One can get the exact e(0)a for a given graphene sheet by matching the MD simulation results of graphene with the results presented in this paper. (C) 2010 Elsevier B.V. All rights reserved.

On formation, growth and concentrations of air ions

Aerosol particles have effect on climate, visibility, air quality and human health. However, the strength of which aerosol particles affect our everyday life is not well described or entirely understood. Therefore, investigations of different processes and phenomena including e.g. primary particle sources, initial steps of secondary particle formation and growth, significance of charged particles in particle formation, as well as redistribution mechanisms in the atmosphere are required. In this work sources, sinks and concentrations of air ions (charged molecules, cluster and particles) were investigated directly by measuring air molecule ionising components (i.e. radon activity concentrations and external radiation dose rates) and charged particle size distributions, as well as based on literature review. The obtained results gave comprehensive and valuable picture of the spatial and temporal variation of the air ion sources, sinks and concentrations to use as input parameters in local and global scale climate models. Newly developed air ion spectrometers (Airel Ltd.) offered a possibility to investigate atmospheric (charged) particle formation and growth at sub-3 nm sizes. Therefore, new visual classification schemes for charged particle formation events were developed, and a newly developed particle growth rate method was tested with over one year dataset. These data analysis methods have been widely utilised by other researchers since introducing them. This thesis resulted interesting characteristics of atmospheric particle formation and growth: e.g. particle growth may sometimes be suppressed before detection limit (~ 3 nm) of traditional aerosol instruments, particle formation may take place during daytime as well as in the evening, growth rates of sub-3 nm particles were quite constant throughout the year while growth rates of larger particles (3-20 nm in diameter) were higher during summer compared to winter. These observations were thought to be a consequence of availability of condensing vapours. The observations of this thesis offered new understanding of the particle formation in the atmosphere. However, the role of ions in particle formation, which is not well understood with current knowledge, requires further research in future.

Flow structure and heat transfer characteristics behind a diaphragm in the presence of a diffusion flame

The characteristics of the separated flow behind a diaphragm over a burning surface are investigated experimentally. This complex problem of practical significance involving recirculation, blowing and combustion reactions is studied in a two-dimensional combustion tunnel. The flame structure, recirculation patterns and heat transfer to the surface are presented for a range of values of free stream and fuel injection velocities as well as for different heights of the diaphragm. The trends of heat transfer vs axial distance are shown to be similar to those resulting from a non-reactive heated stream with a diaphragm. Treating the case of a boundary layer diffusion flame as that corresponding to the zero height of the diaphragm, the heat transfer augmentation due to recirculation is estimated. It is found that at considerable downstream distances (xfh > 3), the heat transfer rates with diaphragm overtake the rates from a developing boundary layer case. Flow visualization studies with particle track photography show that there are many similarities between the reactive and the non-reactive cases.

Classification of Protein Kinases on the Basis of Both Kinase and Non-Kinase Regions

Background: Protein phosphorylation is a generic way to regulate signal transduction pathways in all kingdoms of life. In many organisms, it is achieved by the large family of Ser/Thr/Tyr protein kinases which are traditionally classified into groups and subfamilies on the basis of the amino acid sequence of their catalytic domains. Many protein kinases are multidomain in nature but the diversity of the accessory domains and their organization are usually not taken into account while classifying kinases into groups or subfamilies. Methodology: Here, we present an approach which considers amino acid sequences of complete gene products, in order to suggest refinements in sets of pre-classified sequences. The strategy is based on alignment-free similarity scores and iterative Area Under the Curve (AUC) computation. Similarity scores are computed by detecting common patterns between two sequences and scoring them using a substitution matrix, with a consistent normalization scheme. This allows us to handle full-length sequences, and implicitly takes into account domain diversity and domain shuffling. We quantitatively validate our approach on a subset of 212 human protein kinases. We then employ it on the complete repertoire of human protein kinases and suggest few qualitative refinements in the subfamily assignment stored in the KinG database, which is based on catalytic domains only. Based on our new measure, we delineate 37 cases of potential hybrid kinases: sequences for which classical classification based entirely on catalytic domains is inconsistent with the full-length similarity scores computed here, which implicitly consider multi-domain nature and regions outside the catalytic kinase domain. We also provide some examples of hybrid kinases of the protozoan parasite Entamoeba histolytica. Conclusions: The implicit consideration of multi-domain architectures is a valuable inclusion to complement other classification schemes. The proposed algorithm may also be employed to classify other families of enzymes with multidomain architecture.

Understorey vegetation as an indicator of forest site potential in Southern Finland.

The relationship between site characteristics and understorey vegetation composition was analysed with quantitative methods, especially from the viewpoint of site quality estimation. Theoretical models were applied to an empirical data set collected from the upland forests of southern Finland comprising 104 sites dominated by Scots pine (Pinus sylvestris L.), and 165 sites dominated by Norway spruce (Picea abies (L.) Karsten). Site index H100 was used as an independent measure of site quality. A new model for the estimation of site quality at sites with a known understorey vegetation composition was introduced. It is based on the application of Bayes' theorem to the density function of site quality within the study area combined with the species-specific presence-absence response curves. The resulting posterior probability density function may be used for calculating an estimate for the site variable. Using this method, a jackknife estimate of site index H100 was calculated separately for pine- and spruce-dominated sites. The results indicated that the cross-validation root mean squared error (RMSEcv) of the estimates improved from 2.98 m down to 2.34 m relative to the "null" model (standard deviation of the sample distribution) in pine-dominated forests. In spruce-dominated forests RMSEcv decreased from 3.94 m down to 3.16 m. In order to assess these results, four other estimation methods based on understorey vegetation composition were applied to the same data set. The results showed that none of the methods was clearly superior to the others. In pine-dominated forests, RMSEcv varied between 2.34 and 2.47 m, and the corresponding range for spruce-dominated forests was from 3.13 to 3.57 m.

Structural, optical and electrical characteristics of transparent bismuth vanadate films deposited on indium tin oxide coated glass substrates

Bismuth vanadate (BVO) thin films were fabricated on indium tin oxide (ITO) coated glass substrates using pulsed laser ablation technique and investigated their structural, optical and electrical properties. The use of the indium tin oxide coated glass substrate resulted in reducing the leakage current characteristics of crystalline BVO thin films. The X-ray diffraction (XRD) studies confirmed the monophasic nature of the post annealed (500 A degrees C/1 h) films. The atomic force microscopy indicated the homogeneous distribution of crystallites in the as-deposited films. The as-deposited and the post annealed films were almost 90% transparent (380-900 nm) as confirmed by optical transmission studies. Dielectric constant of around 52 was attained accompanied by the low dielectric loss of 0.002 at 10 kHz for post annealed films. The leakage current of the post annealed BVO films on ITO coated glass substrates measured at room temperature was 8.1 x 10(-8) A at an applied electric field of 33 kV/cm, which was lower than that of the films with platinum and SrRuO3 as the bottom electrodes.