Factors Affecting the Hydrophobic Property of Stearic Acid Self-Assembled on the TiO2 Substrate.

The self-assembled monolayer (SAM) on inorganic metal oxides is highly applicable in making different kinds of surface phenomena such as superhydrophobicity, functional group-modified surfaces, corrosion resistance, and so on. The formation of stearic acid SAMs on the TiO2 substrate depends on a few factors, and the cleanability of the substrate surface can be considered as the critical criterion for the formation of the SAM layer. The solvent, concentration of the adsorbate, immersion time, and temperature can be identified as other factors that are crucial for growing a uniform and highly dense monolayer. SAM layers always build up spontaneously on a suitable substrate, but the growth rate and arrangement can be changed by varying the external factors. These factors highly affect the chemisorption of stearic acid molecules onto the TiO2 substrate and building a well-ordered pattern on the surface without defects. This study mainly focuses on identifying the critical conditions of the external factors in obtaining a high-performance superhydrophobic surface. The crystal structure and surface morphologies of the substrate materials are characterized by powder X-ray diffraction and scanning electron microscopy, and the surface wettability is characterized by contact angle measurements. High superhydrophobicity is observed at the optimum conditions of the factors. Ethanol is used as the solvent; the temperature is about 40 °C; and 600 ppm of stearic acid is the critical concentration in obtaining a superhydrophobic surface with 100 min of immersion time, while the contact angle is 151.38°. Simultaneously, if the concentration is 1000 ppm and the immersion time is 120 min, the surface shows high superhydrophobicity with a contact angle of 162.06°. These critical conditions are found to be adequate for building well-ordered stearic acid SAMs on the TiO2 substrate.

Responses of Sri Lankan indigenous goats and their Jamnapari crosses to artificial challenge with Haemonchus contortus.

Goat farming plays an important role in the Sri Lankan rural economy. Sri Lankan indigenous (SLI) goats and their crossbreds are reared mainly under extensive management and indiscriminately exposed to pathogens and parasites. This study was designed to evaluate resistance to haemonchosis in SLI goats and their Jamnapari crossbreds (JCB) in the dry zone of Sri Lanka. Twenty SLI and 20 JCB 4-month-old male goats were artificially challenged with 5000 H. contortus L3 larvae. Faecal egg counts (FEC), body weights, FAffa MAlan CHArt (FAMACHA®) scores, packed cell volumes (PCV), red blood cell counts, total and differential white blood cell counts, blood haemoglobin contents, serum total protein and albumin contents, and serum pepsinogen and antibody levels were determined at 0, 21, 28, 35 and 42days after challenge. Effects of measurement time were significant for all variables (P<0.05). Breed effects approached significance (P=0.06) and measurement time×breed interaction was significant (P<0.05) for FEC. Peak FEC occurred at day 35 in both goat types, and JCB goats had higher FEC than SLI goats at days 28 (P<0.001), 35 (P<0.10), and 42 (P<0.10). Means for FEC at day 35 were 1783±446 eggs per gram of feces (epg) for SLI kids and 3329±850 epg for JCB kids. Haematological parameters, serum chemistry, and FAMACHA scores suggested that SLI goats were recovering from parasitic infection by day 42, whereas JCB goats had increasing severity of anaemia. Means for PCV in SLI goats decreased from 26.8±0.7% at day 0 to 19.7±0.9% at day 35 and thereafter increased to 20.2±0.9% at day 42. Means for PCV in JCB goats declined from 25.9±0.6% at day 0 to 17.2±0.9% at day 42. Eosinophilia was observed in both genotypes. The JCB goats were heavier than SLI goats and had higher antibody titres, reflecting higher levels of parasitism. Both goat types significantly increased in body weight during the experiment and therefore tolerated parasite infection without severe production losses. We concluded that SLI goats were more resistant to haemonchosis than JCB goats, but that JCB goats were somewhat resilient to parasitic infection. Substantial variability in measurements associated with parasite infection in both breeds indicated potential to improve parasite resistance. Phenotypic information should be coupled with genomic information to identify appropriate breeding goals for future selection programs.

A retrospective analysis to determine factors contributing to the survival of patients with oral squamous cell carcinoma.

The clinical outcome of patients with OSCC is assessed based on TNM system and currently it is the most reliable indicator on which therapeutic decisions are made. The patients with advanced disease are managed with combined treatment modalities. The aim of this retrospective study was to identify the factors which influence survival of patients with OSCC in Sri Lanka. Four hundred and thirty patients who have been managed surgically using either (1) local excision, (2) local excision+supraomohyoid neck dissection, (3) local excision+modified radical neck dissection, (4) local excision+radical neck dissection, (5) local excision+contra-lateral neck dissection depending on TNM stage, with or without post-operative radiotherapy. Patients with incompletely excised tumours showed statistically significant poor survival which improved with radiotherapy (stage II P=0.002, stage III P=0.017). With reference to TNM stage IV tumours, the patients who had received surgical option 4, showed poor survival compared to surgical options 2, 3, and 5 (P=0.001). However, within the group of patients who had received surgical option 4, those who had nodal metastasis showed poorer survival compared to patients without nodal metastasis. In addition, survival improved in patients who had been treated with surgical option 4, with radiotherapy. Furthermore, margin status was also found to significantly influence the survival of patients with TNM stage IV tumours (P=0.003). The main factors that had significant impact on the survival were TNM stage, nodal metastasis and the state of excision margins.

Study of dirofilariasis in a selected area in the Western Province.

INTRODUCTION: Human dirofilariasis is a zoonotic infection caused by the filarial worm, Dirofilaria (Nochtiella) repens, whose primary host is the dog. This infection is on the increase over the past decade in Sri Lanka and the prevalence of canine dirofilariasis in the country is also believed to be high. We present here a study on public awareness of dirofilariasis and the prevalence of this infection in dogs in Negombo, an urban area that has a high domestic canine population. OBJECTIVE: To assess the awareness of dirofilariasis infection among residents and study the prevalence of this infection in domestic dogs in Negombo. DESIGN: Prospective study. SETTING: Department of Parasitology, Faculty of Medicine, University of Colombo, Colombo 8, Sri Lanka. METHODS: A descriptive cross-sectional study within the city of Negombo during September and November 2003 using a pre-tested, interviewer-administered questionnaire with cluster sampling was done. Two hundred seventy adults, including 132 dog owners, were included in the study. Data analysis was done using the Epilnfo programme. The prevalence of canine dirofilariasis was studied in a group of 65 dogs over the age of 1 year. They were selected by cluster sampling with random choice of the streets within the study area. Stained thick blood films, made following an earlobe-prick at any time during the day, were microscopically examined for the presence of microfilariae. RESULTS: Forty nine of the respondents (18%) were aware of the existence of canine dirofilariasis while human dirofilariasis was known only to 6%. Awareness was related to the level of education. Knowledge of canine filariasis was better among pet owners (32/132) when compared to others (18/138; p < 0.05). Veterinary surgeons were acknowledged as the source of information by 38% of those who were aware of the disease. Forty five per cent (n = 29) of the dogs screened were positive for microfilariae. Out of these 18 and two dogs were infected with D repens. and B. ceylonensis, respectively, while nine others were co-infected with the two parasites. CONCLUSIONS: The knowledge of dirofilariasis is extremely poor in the study area. The high prevalence of filarial infections in dogs highlights the importance of improving the public awareness of this disease, especially among the dog owners. Proper management of this condition in dogs-the reservoirs of infection for human dirofilariasis, is important for the control of this zoonotic infection.

A case of sebaceous carcinoma of the parotid gland.

Sebaceous carcinoma of salivary gland origin is an extremely rare malignancy. It occurs mainly in the parotid gland. This is a case report of a sebaceous carcinoma in a 57-year-old woman who had a lump over the right parotid region for 8-9 months. The tumour was composed of small basaloid cells and large foamy cells. Sebaceous differentiation was evident in some tumour islands. This is the first case reported in the Department of Oral Pathology, Faculty of Dental Sciences, University of Peradeniya.

Extension of CadPlan algorithm to model the dose distribution under a motorized wedge.

The CadPlan treatment planning system models the dose distribution in the non-wedge direction under a wedged field by converting the wedge thickness to an equivalent water thickness. The algorithm estimates the off-axis ratio (OAR) in the non-wedged direction using the open field OAR at a depth deeper by this equivalent water thickness. This model has been shown to work well for a Siemens Mevatron KD-2 Linac. However, the motorized wedge of the Elekta (formerly Philips) accelerators is tapered off-axis to give a flat dose profile in the non-wedged direction. The CadPlan model assumes that the wedge has a uniform thickness in the non-wedged direction and so cannot model the off-axis dose for the motorized wedge. For a 4 MV beam of a SL75/5 accelerator this leads to a 7% overestimate and a 9% underestimate of the OAR under the thin and thick edge of the wedge respectively. For 6 and 18 MV beams of a SL20 accelerator and a 6 MV beam of a SL75/5 accelerator, the model underestimates the OAR in the order of 10% under the thick end of the wedge. We have shown that by appropriate modification of the effective water thickness values at off-axis distances, the algorithm models the OAR in the non-wedged direction to within 2.5% of the measured values for the 4, 6 and 18 MV beams, for the Elekta motorized wedge.

The use of an electronic portal imaging system to measure portal dose and portal dose profiles.

The dosimetric characteristics of a scanning liquid-filled ionization chamber (SLIC) electronic portal imaging device have been investigated. To assess the system's response in relation to incident radiation beam intensity, a series of characteristic curves are obtained for various field sizes and nominal energies of 6 and 10 MV photons. The response of the imaging system is dependent on incident radiation intensity and can be described to within 1% accuracy on central axis using a square root function. Portal dose measurements with the SLIC at the plane of the detector, on central axis of the beam using homogeneous attenuating phantom materials show that the imaging system is capable of measuring the portal (transmission) dose to within 3% of the ionization chamber results for homogeneous material. For two-dimensional dosimetry applications, the system is calibrated with a 10 cm Perspex block used as beam flattening material on the detector cassette to correct for variations in individual ion chamber sensitivity and the effect of nonuniform beam profiles produced by the flattening filter. Open and wedged dose profiles measured with the SLIC agreed with ion chamber measured profiles to within 3.5% accuracy.

A quality control test for electronic portal imaging devices.

A quality control (QC) test suitable for routine daily use has been developed for video based electronic portal imaging devices. It provides an objective and quantitative test for acceptable image quality on the basis of the high contrast spatial resolution and the contrast-to-noise ratio (CNR). The test uses a phantom consisting of five sets of high-contrast rectangular bar patterns with spatial frequencies of 0.1, 0.2, 0.25, 0.4, and 0.75 lp/mm. Data obtained during a one month calibration period were used to determine a critical frequency fc for the relative square wave modulation transfer function and a critical contrast-to-noise ratio (CNRc). Subsequent measurements indicating significant deviations from these critical values result in warning messages to the operator indicating potential problems in system performance. Measurements over a period of two years show that the QC test provides a sensitive indication of imaging performance.

Assessing radiation and light field congruence with a video based electronic portal imaging device.

Projected light fields are used on treatment simulators and teletherapy treatment units to delineate the size and position of the radiation beam. Any discrepancy between these fields will lead to a systematic field placement error, with possibly serious implications with regard to the accuracy of the delivered dose distribution in the patient. Conventionally, film has been used for regular quality control tests of light and radiation field congruence, but this is a time consuming method and is not suitable for daily checks. A new method is described that uses a specially designed test phantom, a video-based electronic portal imaging device and a personal computer to test for radiation and light field congruence on treatment accelerators. This method consists of aligning the test phantom in the light field of a treatment linac and acquiring an electronic portal image. A computer program then automatically analyzes the image and determines the degree of congruence between the two fields. The final result of the test is a go, warning, or no go decision depending on the extent of misalignment between the light and radiation fields. Two algorithms were tested for reproducibility (<0.4 mm), sensitivity to noise (<0.2 mm), and positional accuracy (<0.4 mm) and are shown to give results comparable to the conventional film method. Daily testing of field congruence over a period of 84 days demonstrated differences in the results determined by the two algorithms of less than 0.1 +/- 0.2 mm (standard deviation) at 6 MV and 0.22 +/- 0.13 mm at 23 MV. Routine testing is possible as the effort and time required are minimal, and the test can be performed during daily routine start-up procedures.

Noise analysis in real-time portal imaging. I. Quantization noise.

The limit at which quantization noise becomes dominant in video-based real-time portal imaging has been studied. Quantization noise due to truncation in integer frame averaging is shown to be dominant over the input analog-to-digital converter (A/D) quantization noise, unless image addition is used in video-based real-time portal imaging systems. Portal images acquired with the Newvicon camera by averaging more than 64 frames are found to be dominated by the quantization noise due to truncation. It has shown that the signal-to-noise ratio (SNR) is limited to 886.8 when using an 8-bit A/D with digital frame averaging, but higher values can be achieved with digital frame addition. It is also shown that digital frame addition together with 16-bit processing can achieve higher contrast resolution than digital frame averaging and 8-bit processing.

Pseudocorrelation: a fast, robust, absolute, grey-level image alignment algorithm.

A new image alignment algorithm--pseudocorrelation--has been developed based on the application of Monte Carlo techniques to the calculation of a cross-correlation integral for grey-scale images. It has many advantages over cross-correlation: it is at least a factor of 10 faster than fast-Fourier-transform-based cross-correlation, and requires 8 times less memory. Its high speed allows for the search space of geometric transformations between images to include magnification and rotation as well as translations without the search time becoming too long. It allows noise to be taken into account, making calculation of a robust, absolute probability of good alignment possible. It is relatively insensitive to differences in quality between images. This article describes the pseudocorrelation algorithm in detail and presents the results of tests of the effects of contrast enhancement, resolution differences, and noise on the algorithm's performance. These tests show that the algorithm is well suited to the task of automated alignment of very low contrast images from video electronic portal imaging devices.

Optimization of metal/phosphor screens for on-line portal imaging.

Studies were conducted to determine the optimal metal/phosphor screen for on-line video verification of radiation treatment portals. Screens were evaluated for luminance and spatial resolution as a function of composition and thickness at 6- and 23-MV x-ray energies. A new video technique was used to determine modulation transfer functions. Gd2O2S was found to be the most efficient (brightest) phosphor for this application. Luminance was found to vary linearly with phosphor thickness up to a thickness of 500 mg/cm2. Metal plates made of iron, brass, copper, lead, and sintered tungsten of various thicknesses were also tested for luminance and resolution with Gd2O2S phosphor. Brightness peaked at about 2-mm thickness for most metals. Significant contributions to the brightness were found to come from x rays interacting with the phosphor itself.

Monte Carlo optimization of metal/phosphor screens at megavoltage energies.

The physics of imaging with metal/phosphor (Gd2O2S:Tb on brass) screens at megavoltage energies has been investigated using Monte Carlo simulation. It has been found that pair production is a significant contributor to energy deposition for Bremsstrahlung beams with energies greater than 6 MV. The effects of different thicknesses of phosphor and metal have been studied, and it is shown that the metal plays a significant role in establishing electronic equilibrium in the phosphor. The transport of optical photons through the phosphor has been modeled, and was found that only 10% to 20% of the light created in the phosphor escapes from the surface, with much of the loss being due to total internal reflection at the surface. Calculated results have been compared with experimental measurements of screen brightness for different phosphor and metal thicknesses. The SNR of a video electronic portal imaging device (VEPID) has been calculated as a function of x-ray and optical photon detection efficiency. The non-Poisson distribution of energy deposition in the phosphor is an important contributor to the SNR. The results of this paper should serve as a useful guide to the engineering design of future electronic portal imaging systems.