An experimental and numerical study of particle nucleation and growth during low-pressure thermal decomposition of silane

Abstract This paper discusses an experimental and numerical study of the nucleation and growth of particles during low-pressure (∼1:0 Torr) thermal decomposition of silane (SiH 4 ). A Particle Beam Mass Spectrometer was used to measure particle size distributions in a parallel-plate showerhead-type semiconductor reactor. An aerosol dynamics moment-type formulation coupled with a chemically reacting uid ow model was used to predict particle concentration, size, and transport in the reactor. Particle nucleation kinetics via a sequence of chemical clustering reactions among silicon hydride molecular clusters, growth by heterogeneous chemical reactions on particle surfaces and coagulation, and transport by convection, di usion, and thermophoresis were included in the model. The e ect of pressure, temperature, ow residence time, carrier gas, and silane concentration were examined under conditions typically used for low-pressure (∼1 Torr) thermal chemical vapor deposition of polysilicon. The numerical simulations predict that several pathways involving linear and polycyclic silicon hydride molecules result in formation of particle "nuclei," which subsequently grow by heterogeneous reactions on the particle surfaces. The model is in good agreement with observations for the pressure and temperature at which particle formation begins, particle sizes and growth rates, and relative particle concentrations at various process conditions. A simpliÿed, computationally inexpensive, quasi-coupled modeling approach is suggested as an engineering tool for process equipment design and contamination control during low-pressure thermal silicon deposition.

Occult hepatitis C virus infection is more common than hepatitis B infection in maintenance hemodialysis patients

Patients of end stage renal disease on maintenance hemodialysis were enrolled to study the prevalence of occult and dual hepatitis B virus (HBV) and hepatitis C virus (HCV) infection and non-occult hepatitis B and C virus infection. One hundred and two patients were enrolled. Thirty patients had HCV infection, three of them were positive in anti-HCV. So, 27 (90%) of HCV-positive patients had occult HCV infection. Eleven (11%) patients had HBV infection. Five patients were positive in anti-HBc or HBV-DNA, but negative in HBsAg (occult HBV infection). Three (3%) patients had dual HBV and HCV infection. None of the patients showed changes in viral markers during the follow-up of 8 mo on average (1-12 mo)

Refractory benign esophageal strictures

Refractory benign esophageal stricture (RBES) is a frequently encountered problem worldwide. These strictures arise from various causes such as corrosive injury, radiation therapy, peptic origin, ablative therapy, and after surgery. Most strictures can be treated successfully with endoscopic dilatation using bougies or balloons, with only a few complications. Those patients who fail after serial dilatation with bougies or balloons will come to the category of refractory strictures. Dilatation combined with intralesional steroid injections can be considered for peptic strictures, whereas incisional therapy has been demonstrated to be effective for short anastomotic strictures. When these therapeutic options do not resolve the stenosis, stent placement should be considered. Self-bougienage can be proposed to a selected group of patients with a proximal stenosis. Most of the patients of RBES respond to above-mentioned treatment and occasional patient may require surgery as the final treatment option. This review aims to provide a comprehensive approach toward endoscopic management of RBESs based on current literature and personal experience

Endoscopic management of ingested foreign bodies and food impaction in esophagus

Foreign body (FB) in the esophagus is a common emergency presentation in all age groups, especially in children. The immediate risk can range from a minimal one to a life-threatening scenario. Food impactions generally occur when there is altered anatomy (rings, webs or strictures) or motility disorders of the esophagus. The initial management approach includes a thorough history and physical examination followed by radiological investigations. Flexible endoscopy not only confirms the diagnosis but also is the therapeutic modality of choice for removing FBs and relieving the obstruction. This review aims to provide a comprehensive approach towards endoscopic management of esophageal FBs based on current literature and personal experience. The management problems associated with different types of FBs have also been highlighted

15 cm long impacted chewing wood stick in stomach: Endoscopic removal

We report a case of long rigid radiolucent foreign body “chewing wood stick (datun)” impacted in the stomach of a 50-year-old man. He was literate, without any history of psychiatric illness and had been using “datun” to clean his teeth for last 15 years. He presented with a history of accidental ingestion of “datun” 3 months back, it was found impacted in the stomach on percutaneous ultrasonography and was removed with endoscopy using rat tooth forceps and snare

Unique Removal of a Kinked Nasogastric Tube

Nasogastric (NG) tube insertion is a common clinical procedure used for both diagnostic and therapeutic purposes. As the importance of enteral nutrition is being increasingly recognized; the use of NG tube insertion has steadily increased. Here, we present an interesting case in which a kinked NG tube was removed in a unique manner with “push and pull” technique without untoward trauma

Over-the-scope clip

The endoscopic clips were first described by Hayashi in Japan in 1975. Since then, many different types of clips have been introduced to the gastroenterology practice. Over-the-scope clip (OTSC) or the “beer claw” was introduced in the year 2010. It works on the principle of dynamic compression and is applied over the scope like a band ligator. OTSC is a new endoscopic modality which can be used in acute gastrointestinal hemorrhage, iatrogenic perforation, anastomotic leak, and chronic fistula treatment with fairly good success rate and therefore, is now being considered as an alternative to surgery, especially in situations where surgery is not feasible