Charles V. Sammut

In Situ Assessment of the Setting of Tricalcium Silicate–based Sealers Using a Dentin Pressure Model

INTRODUCTION EndoSequence BC Sealer (Brasseler, Savannah, GA) is a premixed tricalcium silicate-based root canal sealer that requires moisture from the root dentin to hydrate. The aim of this study was to investigate the setting of EndoSequence BC Sealer and other sealers in contact with human dentin in a simulated clinical environment. METHODS EndoSequence BC Sealer, MTA Fillapex (Angelus, Londrina, Brazil), Septodont Sealer (Septodont, Saint Maur-des-Fosses, France), and Apexit Plus (Ivoclar, Schaan, Lichtenstein) were assessed. Caries-free lower premolars extracted for orthodontic purposes in patients aged 13-16 years were standardized to a 10-mm root length and were filled with test sealers and set up in a dentin pressure model for 14 days. In addition, set sealers immersed in physiologic solution for 14 days were also assessed. The set materials in solution and materials retrieved from the dentin pressure setup were characterized by scanning electron microscopy and X-ray diffraction analysis. The setting time and radiopacity were assessed using ISO 6876:2002 specifications. Furthermore, mineral ion leaching was evaluated by inductively coupled plasma mass spectrometry. RESULTS All the sealers tested exhibited formation of a calcium phosphate phase when in contact with physiologic solution. Septodont Sealer and Apexit Plus did not exhibit the formation of a calcium phosphate phase in the dentin pressure setup. The fluid in the system was enough to allow the setting of EndoSequence BC Sealer, which did not set in a dry environment. All materials leached calcium with the Septodont Sealer, exhibiting double the calcium ion leaching compared with EndoSequence BC Sealer. CONCLUSIONS Using the dentinal fluid pressure system resulted in an adequate flow of dentinal fluid that allowed EndoSequence BC Sealer to set inside the root canal. Although the sealers tested were tricalcium silicate based, the hydration reaction and bioactivity in the presence of dentinal fluid were different to hydration in vitro. Thus, clinically, material bioactivity cannot be assumed.

Dielectric properties of muscle and liver from 500 MHz–40 GHz

Dielectric properties are the most important parameters determining energy deposition when biological tissues are exposed to radio frequency and microwave fields. Energy absorption is determined by the specific absorption rate (SAR). SAR distributions can be computed accurately only if the complex relative permittivity of the target tissue is known to a sufficiently high accuracy, and currently there is a lack of data on the dielectric properties of biological tissues at high frequencies. In this study, tissue dielectric properties are measured using an open-ended coaxial probe technique from 500 MHz up to 40 GHz. We present dielectric data for ex vivo bovine and porcine muscle and liver tissues at 37 °C. One-pole Cole–Cole model is used to fit the measured data as a function of frequency and the dispersion parameters are presented. This data is supported by an accurate study on reference liquids such as methanol and ethanediol.

Eddy current sensing using planar coils

Sensors are used in various everyday practices, and therefore, there are different types of sensors suitable for innumerable applications. The type of sensor discussed in this paper is the proximity sensor based on eddy current theory, which measures the distance between the sensor and the target plate with no physical contact [1].

Accurate in vivo dielectric properties of liver from 500 MHz to 40 GHz and their correlation to ex vivo measurements

ABSTRACT In this article, we report on the characterization of the dielectric properties of in vivo rat liver at 36.4°C from 500 MHz up to 40 GHz with less than 5% uncertainty. The measured data were fitted to a Cole–Cole model and dielectric parameters are presented together with their respective 95% confidence interval. The root mean square error is 0.42. Moreover, ex vivo measurements were conducted in situ at 1, 2, 4 and 6 min after animal death and are compared to in vivo measurements. The results show that immediate changes in and are within experimental uncertainty, and therefore changes between in vivo and published ex vivo dielectric properties can be attributed to tissue hydration.

Experimental analysis of radiographer exposure to the static field from a 1.5-T magnetic resonance imaging machine

Introduction. This study measures the exposure of occupational therapists from a 1.5-T magnetic resonance imaging (MRI) machine. Method. A total of 14 time-series on each of the chest, head and hand were taken before and after different MRI procedures. The peak values were noted in each case together with an average of all data recorded in the time-series. Results. The highest exposure recorded was observed on the hand, followed by the head and the chest. The overall maximum exposure (1479.40 mT) recorded was observed on the hand during a change of coil. It was also observed that the recorded exposure of experienced radiographers working in the MRI environment was less than that of junior staff due to different practices. Conclusion. This study is of significant importance in Malta since it is the first conducted in a MRI environment, especially because the results were compared with limits imposed by EU Directive 2013/35/EU which has to be implemented by July 2016.

Comparison of measured and computed conversion loss from a resonant tunneling device multiplier

The behavior of a resonant tunneling device (RTD) as a multiplier over a range of bias voltage is investigated. The experimental results agree well with large-signal simulations based on a simple equivalent circuit with element values derived from the I-V characteristic and low-frequency small-signal impedance measurements. This technique can be extended to assist in the design and realization of millimeter and submillimeter RTD multipliers.<<ETX>>

Near-Field to Far-Field pattern measurements for a mid-aperture FR-ORA array

In this communication Near-Field to Far-Field (NF/FF) measurements are employed to characterize the radiation pattern of a prototype of 9 × 9 finite array antenna element proposed for radio astronomy. The antenna design is a tightly coupled phased array designed to function in the 0.3 - 1.3 GHz band. The developed antenna is a composite structure to achieve ultra-wideband performance. It is likely to be competitive over related technologies because of its exceptional bandwidth, its light weight construction, its low cost (because of the planar design and significantly lower metal content in the fractal elements), its low profile (planar structure), with dual polarisation and the potential steerability of the individual elements. Another unique feature of the open octagonal ring array is that the center frequency and bandwidth can be tailored to any specific application by scaling the element sizes in the active layer. Through the validation of three-dimensional electromagnetic simulations, the NF/FF transformation has proven to be a convenient and cost-effective method to determine far-field patterns of the array elements.

Ultra-wideband tightly coupled fractal octagonal phased array antenna

This paper presents a low profile ultrawideband tightly coupled phased array antenna with integrated feedlines. The aperture array consists of planar element pairs with fractal geometry. In each element these pairs are set orthogonal to each other for dual polarisation. The design is an array of closely capacitively coupled pairs of fractal octagonal rings. The adjustment of the capacitive load at the tip end of the elements and the strong mutual coupling between the elements, enables a wideband conformal performance. Adding a ground plane below the array partly compensates for the frequency variation of the array impedance, providing further enhancement in the array bandwidth. Additional improvement is achieved by placing another layer of conductive elements at a defined distance above the radiating elements. A Genetic Algorithm was scripted in MATLAB and combined with the HFSS simulator, providing an easy optimisation tool across the operational bandwidth for the array unit cell design parameters. The proposed antenna shows a wide-scanning ability with a low cross-polarisation level over a wide bandwidth.

Accurate small-signal modelling of a double barrier resonant tunnelling diode (DBRTD)

A small-signal equivalent circuit model for a double-barrier resonant tunneling diode (DBRTD) over the frequency range of 45 MHz to 13 GHz is developed. This model is capable of predicting small-signal microwave properties to within +or-5% of measurement. This model is based on frequency-independent parameters and accurately predicts the small-signal properties of the device using voltage-dependent differential conductance obtained from the DC I-V characteristic, and capacitance determined over the entire test frequency range. It is believed that this was made possible primarily by an accurate de-embedding technique which was facilitated by the choice of package and simple mount design, which together allowed S11 measurements to be made within an almost entirely uniform 3.5-mm coaxial line.<<ETX>>

Fractal analysis correlation of the images from scanning laser microscopy techniques and atomic force microscopy

The laser scanning laser microscopy techniques and atomic force microscopy give complementary information at micro- and nano-scales regarding the surface samples. By using a multimodal microscopy system, having more optical techniques based on far field and near field and an atomic force microscope the same area of the investigated samples. The system is able to acquire the optical images having hundred nanometers or nanometers resolutions and surface topography at nanoscale. Fractal analysis is a very useful tool for quantifying and simulating the complex patterns encountered in microscopic images. The objective of this work is to perform a study of the complex optical and morphological features of certain biological tissues by using fractal geometry. It is shown a correlation between optical images and surface morphology regarding fractal geometry and that fractal dimension is a good candidate to quantify the different images.