Viscosity critical behaviour at the gel point in a 3d lattice model

Within a recently introduced model based on the bond-fluctuation dynamics we study the viscoelastic behaviour of a polymer solution at the gelation threshold. We here present the results of the numerical simulation of the model on a cubic lattice: the percolation transition, the diffusion properties and the time autocorrelation functions have been studied. From both the diffusion coefficients and the relaxation times critical behaviour a critical exponent k for the viscosity coefficient has been extracted: the two results are comparable within the errors and are in close agreement with the Rouse model prediction and with some experimental results. In the critical region below the transition threshold the time autocorrelation functions show a long time tail which is well fitted by a stretched exponential decay.Comment: 14 pag., RevTex, 9 figure

Gastric cancer missed at endoscopy

Stomach cancer is the fourth most common malignancy worldwide. Endoscopy (with biopsies) is the gold standard for its diagnosis but missed oesophageal and gastric cancers are not infrequent in patients who have undergone previous endoscopy. Errors by the endoscopist account for the majority of these missed lesions. The following report describes an incident in which there was a diagnostic error that led to a failed diagnosis of gastric cancer at first endoscopy. The implications for clinical and endoscopic practice are discussed.Keywords: Gastric cancer; Misdiagnoses; Diagnostic error; Endoscop

Complex viscosity behavior and cluster formation in attractive colloidal systems

The increase of the viscosity, which is observed in attractive colloidal systems by varying the temperature or the volume fraction, can be related to the formation of structures due to particle aggregation. In particular we have studied the non trivial dependence of the viscosity from the temperature and the volume fraction in the copolymer-micellar system L64. The comparison of the experimental data with the results of numerical simulations in a simple model for gelation phenomena suggests that this intriguing behavior can be explained in terms of cluster formation and that this picture can be quite generally extended to other attractive colloidal systems.Comment: 5 pages, 4 figure

On mean coordination and structural heterogeneity in model amorphous solids

We propose a simple route to analytically evaluate the average coordination of model disordered solids with maximally homogeneous distribution of the particles in space. The model yields the average number of contacts (z) as a function of volume fraction (phi) of a hard-sphere connected system and recovers the critical jamming point of hard spheres (z=6 at phi=0.64). Numerical simulations of Lennard-Jones glasses with a varying attraction range are used to investigate the volume fraction dependence of the average coordination in the presence of attraction. It is observed that upon decreasing phi below 0.6, structural heterogeneity is reflected in values of the coordination number which are higher than those predicted by the model for a statistically homogeneous distribution of particles in space due to the attraction-induced local aggregation. Thus the model can be usefully employed as a quantitative reference to assess the degree of structural heterogeneity in glasses in terms of a directly accessible structural parameter such as the mean number of contacts

Static and dynamic heterogeneities in a model for irreversible gelation

We study the structure and the dynamics in the formation of irreversible gels by means of molecular dynamics simulation of a model system where the gelation transition is due to the random percolation of permanent bonds between neighboring particles. We analyze the heterogeneities of the dynamics in terms of the fluctuations of the intermediate scattering functions: In the sol phase close to the percolation threshold, we find that this dynamical susceptibility increases with the time until it reaches a plateau. At the gelation threshold this plateau scales as a function of the wave vector $k$ as $k^{\eta -2}$, with $\eta$ being related to the decay of the percolation pair connectedness function. At the lowest wave vector, approaching the gelation threshold it diverges with the same exponent $\gamma$ as the mean cluster size. These findings suggest an alternative way of measuring critical exponents in a system undergoing chemical gelation.Comment: 4 pages, 4 figure

Dynamic heterogeneities in attractive colloids

We study the formation of a colloidal gel by means of Molecular Dynamics simulations of a model for colloidal suspensions. A slowing down with gel-like features is observed at low temperatures and low volume fractions, due to the formation of persistent structures. We show that at low volume fraction the dynamic susceptibility, which describes dynamic heterogeneities, exhibits a large plateau, dominated by clusters of long living bonds. At higher volume fraction, where the effect of the crowding of the particles starts to be present, it crosses over towards a regime characterized by a peak. We introduce a suitable mean cluster size of clusters of monomers connected by "persistent" bonds which well describes the dynamic susceptibility.Comment: 4 pages, 4 figure

Prevalence of reflux esophagitis among patients undergoing endoscopy in a secondary referral hospital in Giza, Egypt

Background: Gastro-esophageal reflux disease (GERD) is one of the most prevalent diseases seen in western countries. The prevalence of GERD is lower in the Asian population and the spectrum of the disease is mild. Data from Africa and the Middle East are sparse.Aim: The aim of the study was to determine the prevalence, severity and risk factors of reflux esophagitis (RE) among patients undergoing endoscopy in a secondary referral hospital in Egypt.Materials and methods: This was a retrospective study. Data on patients presenting with gastroesophageal reflux symptoms (RS) and scheduled for upper gastrointestinal endoscopy between January 2000 and January 2013 were collected.Results: Four hundred and thirty-three patients were assessed. Two hundred and fifty-four (59%) were male. Ages ranged from 18 to 85 years, mean 45± 15 years. One hundred and forty-four patients (33%) had a history of smoking, 120 (28%) were taking aspirin or non-steroidal anti-inflammatory drugs and 8 (2%) were consuming alcohol. The duration of RS ranged from one month to 20 years, mean 21 ± 30 months. One hundred and forty-six patients (34%) had the RS daily, 70 (16%) classified RS as severe intensity and 99 (23%) had acid regurgitation. One hundred and six patients (24%) were found to have RE. Ninety-eight of them (23%) showed grade 1. Barrett’s esophagus (BE) was diagnosed in seven patients (2%) and esophageal stricture in one (0.2%). One hundred and four patients (24%) had hiatus hernia (HH), 16 (4%) gastric ulcers and 45 (10%) duodenal ulcers. In multivariate analysis, male sex and HH were two independent risk factors for the development of RE.Conclusion: The prevalence of RE is low among patients undergoing endoscopy. Most of the patients had a mild degree of esophagitis. BE and stricture were rarely seen. Male sex and HH were risk factors of RE

Colorectal cancer in Egypt is commoner in young people: Is this cause for alarm?

Background: Colorectal cancer (CRC) is the third most common cancer worldwide after lung and breast cancers with two-thirds of all CRCs occurring in the more developed regions of the world. CRC affects men and women of all racial and ethnic groups, and is most often found in those aged 50 years or older. Aim: The aim of the study was to determine the prevalence of CRC among patients undergoing colonoscopy in Egypt. Materials and methods: This was a descriptive cross-sectional hospital-based study. A total of 412 consecutive patients who underwent planned pancolonoscopy from January 2000 to January 2012 at our institution were assessed. All endoscopic examinations leading to a diagnosis of CRC were evaluated. The following parameters were analyzed: frequency of CRC, patient characteristics, indication for endoscopic examination, endoscopic findings, localization of CRC and histopathology. Results: CRC was diagnosed in 57 patients (14% of all colonoscopies). Fifty-six percent were female. The mean age was 51± 15 years (age range: 16–80 years). Twenty-five percent of cancers occurred in patients aged less than 40 years. The most frequent indication for colonoscopy was rectal bleeding (39%). The most common colonoscopy finding was mass (96%). Sixty-eight percent of CRC were located in the left colon and rectum. Ninety-one percent of CRC wereAdenocarcinoma. Conclusions: CRC is not uncommon among Egyptian patients subjected to colonoscopy. Thereare relatively higher CRC rates in patients under 40 years of age than reported in the West. This has implications relating to future epidemiological trends in Egypt. Physicians must have a greater awareness of the potential for CRC in young people in the Middle East.Keywords: Colorectal cancer; Birth cohort; Egypt 

Improving the quality of endoscopic polypectomy by introducing a colonoscopy quality assurance program

Background: Colonoscopy is a routine procedure in patients who present with bowel symptoms. Polyps can be identified and removed during colonoscopy. A colonoscopy quality-assurance program (CQAP) was instituted in 2003.Aim: The aim of the study was to determine the effect of instituting a CQAP on the quality of endoscopic polypectomy (EP) in our patients.Patients and methods: An Initial assessment of EP practice in 2003 showed that four patients had polyps. Cecal intubation had been achieved in only two patients and a complete polyp description (CPD) had not been documented. Polypectomy was performed in two patients but the completeness of removal and retrieval of the polyps had not been assessed and histology had not been recorded. A quality improvement process was therefore instituted. This required full colonoscopy to the cecum, CPD and polypectomy to be performed for every polyp. There should be a 90% retrieval rate of all excised polyps and follow up of all histology reports. Seventy-six patients were assessed prospectively over the period 2004–2011.Results: Cecal intubation rates increased from 65% in years 2004–2007 to 90% in years 2008–2011 (t-proportion = 2.4 & CI= 4.7, highly significant). CPD rates increased from 35% to 100% (t-proportion = 6.5 & CI= 12.7,  highly significant). EP rates increased from 59% to 100% (t-proportion = 3.5 & CI= 6.9, highly significant). Percentage of procedures in which all polyps were judged completely removed increased from 41% to 86% (t-proportion = 3.6 & CI= 7, highly significant). Polyp retrieval rates, with retrieval of P90% of all excised polyps, increased from 80% to 92% (t-proportion = 0.87 & CI= 1.7, significant). Polyp histology documentation rates increased from 41% to 88% (t-proportion =3.7 & CI= 7.3, highly significant).Conclusion: The implementation of a quality assurance and improvement program improved the quality of EP in patients with polyp(s) detected during colonoscopy.Keywords: Colonoscopy; Polypectomy; Quality assurance; Juvenile polyp