Composite Filler Characterization by Scanning Electron Microscopy, Image Analysis and Thermogravimetry

The morphological and compositional characterization of the filler particles in selected dental composites has been accomplished by a combination of backscattered electron imaging, digital imaging , energy dispersive X-ray analysis and thermogravimetry. Backscattered electron images provide excellent composition contrast between the filler and the matrix in this analysis . Qualitative energy dispersive spectroscopy was used to classify the filler composition in the composites studied. The digital imaging technique of feature analysis was utilized to quantitatively characterize the particle morphological parameters and their distributions. Several parameters were determined of which the particle area, breadth, height and Waddel diameter are emphasized. Particle size distribution histograms were also obtained. The filler contents in commercial composites were also determined by thermogravimetry. Thus a comprehensive method has been developed and applied to characterize filler morphology in particulate dental composites, which include both commercial and experimental systems. The commercial systems show variations in filler composition, filler size and distribution as well as filler loading levels. The experimental systems confirm variations in particle size and size distributions as a function of filler processing time

Properties of a New Dental Porcelain

A high strength dental porcelain OPTEC, HSP™ has recently been introduced for use in the fabrication of crowns, three-unit anterior bridges with a single pontic, inlays, on lays, veneers, etc., without a metal substrate. This investigation reports the results of our research involving the characterization of the structure properties and thermally induced transformations of this porcelain. It has been found that the material possesses superior strength and other properties relative to conventional porcelains. The improved properties appear to result from the presence of a very fine and relatively dense distribution of leucite crystals. Scanning electron microscopy indicates, however, that the new product needs additional optimization to improve uniformity of crystallite distribution. Scanning electron microscopy and X-ray diffraction studies also reveal well defined structural and crystallographic transformations during thermal treatment at selected temperature ranges. The primary transformation appears to be crystallization of metastable sanidine from the glass matrix. The crystallization of sanidine leads to a translucent to opaque transition. The transformations appear to follow the phase transitions expected from the phase diagrams

Evaluation of Erbium:YAG Laser Radiation of Hard Dental Tissues: Analysis of Temperature Changes, Depth of Cuts and Structural Effects

Temperature elevations, depths of cuts and structural changes produced by 2.94 micron pulsed Erbium:YAG laser radiation of hard dental tissues, at different power levels and exposure times of the laser, were studied. The depth of cut produced was found to vary significantly as a function of power level and exposure time on dry teeth. The mean temperature rise with laser radiation was also influenced both by power level and time of exposure. The effect of water flow on the teeth during laser exposure was evaluated; the results indicate that the ablation efficiency was better, temperature elevations lower and structural changes minimal to absent in the presence of water as compared to teeth that were dry during laser radiation

RNA polymerase activity in isolated nuclei of Nicotiana sanderae callus: characteristics and modulation during differentiation

Isolated nuclei from differentiating cultures of Nicotiana sanderae showed increased levels of RNA polymerase activity as compared to the nuclei from callus cultures. The RNA synthetic activity was dependent on nucleotide triphosphates and Mg2+ and was destroyed by RNase. Maximum activity was obtained in the presence of 50 mM (NH4)2 SO4 and α-amanitin inhibited 40% and 55% of the activity in the nuclei from callus and differentiating tissue respectively. The nuclei from differentiating tissue elicited a 3-fold increase in RNA polymerase I and a 4-fold augmentation in RNA polymerase II activities

Effect of phytohormones on nuclear RNA synthesis in germinating seeds of Trigonella foenumgraeceum and its callus

Treatment of Trigonella foenumgraeceum (fenugreek) seedlings with naphthalene acetic acid plus gibberellic acid enhanced the RNA synthesising capacity of nuclei isolated from the hypocotyl and cotyledonary regions. This increase was more pronounced in the nuclei from the hypocotyl region than from the cotyledonary region. In vitro addition of these phytohormones did not stimulate RNA synthesis by nuclei. The RNA synthesis by mitochondria was not affected by preincubating the seedlings with the hormones. The nuclei isolated from callus cultures of fenugreek hypocotyl treated with the hormone also showed increased RNA synthesis

An Eight-Term Novel Four-Scroll Chaotic System with Cubic Nonlinearity and its Circuit Simulation

This research work proposes an eight-term novel four-scroll chaotic system with cubic nonlinearity and analyses its fundamental properties such as dissipativity, equilibria, symmetry and invariance, Lyapunov exponents and KaplanYorke dimension. The phase portraits of the novel chaotic system, which are obtained in this work by using MATLAB, depict the four-scroll attractor of the system. For the parameter values and initial conditions chosen in this work, the Lyapunov exponents of the novel four-scroll chaotic system are obtained as L1 = 0.75335, L2 = 0 and L3 = −22.43304. Also, the Kaplan-Yorke dimension of the novel four-scroll chaotic system is obtained as DKY = 2.0336. Finally, an electronic circuit realization of the novel four-scroll chaotic system is presented by using SPICE to confirm the feasibility of the theoretical model

Problems in early diagnosis of bladder cancer in a spinal cord injury patient: Report of a case of simultaneous production of granulocyte colony stimulating factor and parathyroid hormone-related protein by squamous cell carcinoma of urinary bladder

BACKGROUND: Typical symptoms and signs of a clinical condition may be absent in spinal cord injury (SCI) patients. CASE PRESENTATION: A male with paraplegia was passing urine through penile sheath for 35 years, when he developed urinary infections. There was no history of haematuria. Intravenous urography showed bilateral hydronephrosis. The significance of abnormal outline of bladder was not appreciated. As there was large residual urine, he was advised intermittent catheterisation. Serum urea: 3.5 mmol/L; creatinine: 77 umol/L. A year later, serum urea: 36.8 mmol/l; creatinine: 632 umol/l; white cell count: 22.2; neutrophils: 18.88. Ultrasound: bilateral hydronephrosis. Bilateral nephrostomy was performed. Subsequently, blood tests showed: Urea: 14.2 mmol/l; Creatinine: 251 umol/l; Adjusted Calcium: 3.28 mmol/l; Parathyroid hormone: < 0.7 pmol/l (1.1 – 6.9); Parathyroid hormone-related protein (PTHrP): 2.3 pmol/l (0.7 – 1.8). Ultrasound scan of urinary bladder showed mixed echogenicity, which was diagnosed as debris. CT of pelvis was interpreted as vesical abscess. Urine cytology: Transitional cells showing mild atypia. Bladder biopsy: Inflamed mucosa lined by normal urothelial cells. A repeat ultrasound scan demonstrated a tumour arising from right lateral wall; biopsy revealed squamous cell carcinoma. In view of persistently high white cell count and high calcium level, immunohistochemistry for G-CSF and PTHrP was performed. Dense staining of tumour cells for G-CSF and faintly positive staining for C-terminal PTHrP were observed. This patient expired about five months later. CONCLUSION: This case demonstrates how delay in diagnosis of bladder cancer could occur in a SCI patient due to absence of characteristic symptoms and signs

Novel Synthesis of Cellulose-Based Diblock Copolymer of Poly(hydroxyethyl methacrylate) by Mechanochemical Reaction

The mechanical fracture of polymer produces polymeric free radical chain-ends, by which liner block copolymers have been synthesized. A diblock copolymer of microcrystalline cellulose (MCC) and poly 2-hydroxyethyl methacrylate (pHEMA) was produced by the mechanochemical polymerization under vacuum and room temperature. The fraction of pHEMA in MCC-blockpHEMA produced by the mechanochemical polymerization increased up to 21 mol% with increasing fracture time (∼6 h). Then, the tacticities of HEMA sequences in MCC-block-pHEMA varied according to the reaction time. In the process of mechanochemical polymerization, cellulose could play the role of a radical polymerization initiator capable of controlling stereoregularity

Frame Theory for Signal Processing in Psychoacoustics

This review chapter aims to strengthen the link between frame theory and signal processing tasks in psychoacoustics. On the one side, the basic concepts of frame theory are presented and some proofs are provided to explain those concepts in some detail. The goal is to reveal to hearing scientists how this mathematical theory could be relevant for their research. In particular, we focus on frame theory in a filter bank approach, which is probably the most relevant view-point for audio signal processing. On the other side, basic psychoacoustic concepts are presented to stimulate mathematicians to apply their knowledge in this field