Heterogeneous condensation of the Lennard-Jones vapour onto nanoscale particles

The heterogeneous condensation of a vapour onto a substrate is a key step in a wide range of chemical and physical process that occur in both nature and technology. For example, dust and pollutant aerosol particles, ranging in size from several microns down to just a few nanometers, serve as cloud condensation nuclei in the atmosphere, and nanoscale structured surfaces provide templates for the controlled nucleation and growth of variety of complex materials. While much is known about the general features of heterogeneous nucleation onto macroscopic surfaces, much less is understood about both the dynamics and thermodynamics of nucleation involving nanoscale heterogeneities. The goal of this thesis is to understand the general features of condensation of vapours onto different types of nanoscale heterogeneity that range in degree of solubility from being insoluble, to partially miscible through to completely miscible. The heterogeneous condensation of the Lennard-Jones vapour onto an insoluble nanoscale seed particle is studied using a combination of molecular dynamics simulations and thermodynamic theory. The nucleation rate and free energy barrier are calculated from molecular dynamics using the mean first passage time method. These results show that the presence of a weakly interacting seed has no effect on the formation of small cluster embryos but accelerates the rate by lowering the free energy barrier of the larger clusters. A simple phenomenological model of film formation on a small seed is developed by extending the capillarity based liquid drop model. It captures the general features of heterogeneous nucleation, but a comparison with the simulation results show that the model significantly overestimates the height of the nucleation barrier while providing good estimates of the critical film size. A non-volatile liquid drop model that accounts for solution non-ideality is developed to describe the thermodynamics of partially miscible and fully miscible droplets in a solvent vapour. The model shows ideal solution drops dissolve always spontaneously, but partially miscible drops exhibit a free energy surface with two minima, associated with a partially dissolved drop and a fully dissolved drop, separated by a free energy barrier. The solubility transition between the two drops is shown to follow a hysteresis loop as a function of system volume similar to that observed in deliquescence. A simple lattice gas model describing the absorption of mono-layers of vapour onto the particle is also developed. Finally, molecular dynamics simulation of miscible and partially miscible binary Lennard-Jones mixtures are also used to study this system. For all cases studied, condensation onto the drop occurs spontaneously. Sub-monolayers of the solvent phase form when the system volume is large. At smaller system volumes, complete film formation is observed and the dynamics of film growth are dominated by cluster-cluster coalescence. Some degree of mixing into the core of the particle is observed for the miscible mixtures for all volumes. However, mixing of the solvent into the particle core only occurs below an onset volume for the partially miscible case, suggesting the presence of a solubility transition similar to the one described by the thermodynamic model

Heterogeneous condensation of the Lennard-Jones vapor onto a nanoscale seed particle

The heterogeneous condensation of a Lennard-Jones vapor onto a nanoscale seed particle is studied using molecular dynamics simulations. Measuring the nucleation rate and the height of the free energy barrier using the mean first passage time method shows that the presence of a weakly interacting seed has little effect on the work of forming very small cluster embryos but accelerates the rate by lowering the barrier for larger clusters. We suggest that this results from a competition between the energetic and entropic features of cluster formation in the bulk and at the heterogeneity. As the interaction is increased, the free energy of formation is reduced for all cluster sizes. We also develop a simple phenomenological model of film formation on a small seed that captures the general features of the nucleation process for small heterogeneities. A comparison of our simulation results with the model shows that heterogeneous classical nucleation theory provides a good estimate of the critical size of the film but significantly over-estimates the size of the barrier.Comment: 9 pages, 10 figures, In Print J. Chem. Phy

A new method for the diffraction problems

Bu çalışmada, dielektrik kamadan kırınım problemlerine yeni bir yaklaşımla yeni bir yöntem geliştirilmiştir. Bugüne kadar, kırınım problemlerinde kırınım alanını hesaplamada kullanılan köşeden saçılma yaklaşımından farklı olarak, boşluktaki eşdeğer yüzey akımları kullanılmıştır. Teklik teoremi ve Huygens ilkesi çerçevesinde, Stratton’un eşdeğer yüzey akımlarını kullanan yeni yöntemle, dielektrik kama için gölge bölgesinde bulunan tek alan bileşeni olan kırınım alanı ifadeleri semer noktası yaklaşıklığıyla elde edilmiştir. Bu yöntemle, diğer çalışmalarda sonsuz değerler veren gölge bölgesi geçiş sınırı ifadeleri de kesin olarak bulunmuştur. Önerilen yeni yöntem, literatürde rastlanan tek çalışmayla karşılaştırıldığında analitik olarak identik çıkmasının yanısıra, sayısal hesaplamaların daha hızlı olmasıyla, bilgisayar maliyetini düşürmektedir.Anahtar Kelimeler: Saçılma problemi, kırınım, kırınmış alanlar, dielektrik kama, eşdeğer yüzey akımları. In this study, a new method with a new approach for diffraction problems of a dielectric wedge is developed. The main purpose of the study is to obtain the expressions of diffracted field terms in the region called shadow region for a dielectric wedge, when an electromagnetic plane wave propagating in the space strikes an obstacle or discontinuity. To date, diffracted fields were described as the fields due to the discontinuity such as knife-edge or sharp point of the obstacle. In this study, the fields in the shadow region caused by surface currents sources of the incident field on the shadow boundary are taken into consideration by considering diffraction phenomenon as the penetration of the illuminated region towards to the region behind sharp edge. The approach using equivalent source currents in the space to find diffraction fields is totally different from ray theory and scattering at the edges, used for diffraction problems to date. Shadow region fields with saddle point approximation were obtained for a dielectric wedge by new method using Stratton's equivalent source currents with the frame of uniqueness theorem and Huygens Principle. By this method, expressions on the shadow transition boundary are also obtained exactly, although they give infinite values for other diffraction formulas. Keywords: Scattering problem, diffraction, diffracted field, dielectric wedge, equivalent surface currents

Elli beş yaşındaki bir kadında ki-67 ekspresyonu olmamasının düşük malign potansiyeli yansıttığı muhtemel olarak wolffian kaynaklı dişi adneksial tümör

Female adnexial tumors of probable Wolffian origin (FATWO) are rare tumors derived from the remnants of the mesonephric duct. These tumors generally exhibit a low malignant potential, but recurrence and or metastasis is possible during the course of the disease according to the tumors’ possible malignant potential. We report a case of FATWO without estrogen and progesterone receptors and with negative immunostaining for Ki-67 (a proliferation marker) as a probable low-malignant-potential tumor. A 55-year-old woman presented with a complaint of heavy menstrual bleeding and pelvic pain. Preoperative ultrasonographic evaluation revealed an intramural uterine leiomyoma of 4 cm in diameter and a right adnexial solid mass measuring 5 cm in diameter. Following total abdominal hysterectomy and bilateral salpingo-oophorectomy, immunostaining based on the labeled streptavidin-biotin method was performed on sections from representative blocks of paraffin-embedded tissues sampled from the mass, revealing a low mitotic index with negative Ki-67 immunostaining. Immunohistochemical staining with promising new markers and pathological investigation of the entire tumor are needed to determine the malignant behavior of an individual FATWO. Ki-67 is a helpful marker for determining Wolffian duct tumors’ potential malignant behavior

Prevention of adhesion formation in wistar-albino rats by increased bowel movements achieved with oral ricinus oil use for 8 days postoperatively: an experimental study

Objective: Adhesion formation frequently occurs after abdominopelvic surgery and can cause significant morbidity for patients. Meticulous hemostasis, minimal access surgery and utilization of surgical adjuvants intraoperatively are clinically useful measures to minimize adhesion formation. We investigated the clinical efficiency of oral Ricinus oil treatment for 8 days postoperatively to decrease adhesion formation in this case-control study in a rat model. Study design: Following computer-generated randomization, 24 female Wistar-albino rats were operated on, with 10 standard cautery lesions on the right uterine horn and two simple suture lesions on left uterine horn generated with absorbable material. Half (n = 12) the rats received 0.13 g (0.2 ml) Ricinus oil emulsion (40 g/60 ml) via the oral route during the first 8 days postoperatively, and the remaining rats (n = 11) were considered as controls. The extent, severity, degree, total adhesion scores and histopathological features of the adhesions were the main outcome measures. Results: The degree and total adhesion formation scores in the Ricinus oil group and control group revealed significant differences in adhesion extent and severity. The total adhesion scores of the Ricinus oil and control groups were 3.00 +/- 2.21 and 5.18 +/- 2.78 respectively (P 0.05). Conclusions: Ricinus oil treatment following abdominopelvic surgery for the 8-day period that covers the completion of tissue healing process may be a promising, cheap and cost-effective treatment strategy for patients. (C) 2012 Elsevier Ireland Ltd. All rights reserved

Antituberculosis drug resistance patterns in two regions of Turkey: a retrospective analysis

BACKROUND: The emergence of Mycobacterium tuberculosis strains resistant to antituberculosis agents has recently received increased attention owing largely to the dramatic outbreaks of multi drug resistance tuberculosis (MDR-TB). METHODS: Patients residing in Zonguldak and Kayseri provinces of Turkey with, pulmonary tuberculosis diagnosed between 1972 and 1999 were retrospectively identified. Drug susceptibility tests had been performed for isoniazid (INH), rifampin (RIF), streptomycin (SM), ethambutol (EMB) and thiacetasone (TH) after isolation by using the resistance proportion method. RESULTS: Total 3718 patients were retrospectively studied. In 1972–1981, resistance rates for to SM and INH were found to be 14.8% and 9.8% respectively (n: 2172). In 1982–1991 period, resistance rates for INH, SM, RIF, EMB and TH were 14.2%, 14.4%, 10.5%, 2.7% and 2.9% (n: 683), while in 1992–1999 period 14.4%, 21.1%, 10.6%, 2.4% and 3.7% respectively (n: 863). Resistance rates were highest for SM and INH in three periods. MDR-TB patients constituted 7.3% and 6.6% of 1982–1991 and 1992–1999 periods (p > 0.05). CONCLUSION: This study demonstrates the importance of resistance rates for TB. Continued surveillance and immediate therapeutic decisions should be undertaken in order to prevent the dissemination of such resistant strains

Real-world efficacy and safety of Ledipasvir plus Sofosbuvir and Ombitasvir/Paritaprevir/Ritonavir +/- Dasabuvir combination therapies for chronic hepatitis C: A Turkish experience

Background/Aims: This study aimed to evaluate the real-life efficacy and tolerability of direct-acting antiviral treatments for patients with chronic hepatitis C (CHC) with/without cirrhosis in the Turkish population.Material and Methods: A total of 4,352 patients with CHC from 36 different institutions in Turkey were enrolled. They received ledipasvir (LDV) and sofosbuvir (SOF)+/- ribavirin (RBV) ombitasvir/paritaprevir/ritonavir +/- dasabuvir (PrOD)+/- RBV for 12 or 24 weeks. Sustained virologic response (SVR) rates, factors affecting SVR, safety profile, and hepatocellular cancer (HCC) occurrence were analyzed.Results: SVR12 was achieved in 92.8% of the patients (4,040/4,352) according to intention-to-treat and in 98.3% of the patients (4,040/4,108) according to per-protocol analysis. The SVR12 rates were similar between the treatment regimens (97.2%-100%) and genotypes (95.6%-100%). Patients achieving SVR showed a significant decrease in the mean serum alanine transaminase (ALT) levels (50.90 +/- 54.60 U/L to 17.00 +/- 14.50 U/L) and model for end-stage liver disease (MELD) scores (7.51 +/- 4.54 to 7.32 +/- 3.40) (p<0.05). Of the patients, 2 were diagnosed with HCC during the treatment and 14 were diagnosed with HCC 37.0 +/- 16.0 weeks post-treatment. Higher initial MELD score (odds ratio [OR]: 1.92, 95% confidence interval [CI]: 1.22-2.38; p=0.023]), higher hepatitis C virus (HCV) RNA levels (OR: 1.44, 95% CI: 1.31-2.28; p=0.038), and higher serum ALT levels (OR: 1.38, 95% CI: 1.21-1.83; p=0.042) were associated with poor SVR12. The most common adverse events were fatigue (12.6%), pruritis (7.3%), increased serum ALT (4.7%) and bilirubin (3.8%) levels, and anemia (3.1%).Conclusion: LDV/SOF or PrOD +/- RBV were effective and tolerable treatments for patients with CHC and with or without advanced liver disease before and after liver transplantation. Although HCV eradication improves the liver function, there is a risk of developing HCC.Turkish Association for the Study of The Liver (TASL