ABSTRACT
Air-stable magnetic cobalt nanocrystals have been conveniently prepared via a reverse micellar synthesis, followed by a hydrothermal treatment. The synthesis was carried out by first mixing an aqueous solution containing cobalt chloride and poly(sodium 4-styrenesulfonate) (PSS) with an organic mixture containing cetyltrimethylammonium bromide (CTAB) to form reverse micelles, followed by reducing cobalt ions with sodium borohydride. The resultant nanoparticles were then undergone a hydrothermal treatment at 165 degrees C for 8 h to generate well-dispersed CTAB/PSS-encapsulated cobalt nanocrystals with an average diameter of 3.5 +/- 0.5 nm. The nanoparticles were highly crystalline with a hexagonal close-packed crystal phase. The presence of CTAB/PSS complex coatings was identified by FT-IR and UV-vis spectroscopies as well as thermogravimetry analyses. The nanocrystals exhibited superparamagnetic property at room temperature with a saturation magnetization (M(s)) of 95 emu/g. The magnetization could be largely preserved after storage at room temperature for 4 months as the M(s) value only slightly decreased to 88 emu/g (measured at 300 K). Thus, the polymer encapsulation could not only improve thermal stability of the micelles for the growth and nucleation of Co atoms but also protect the resulting cobalt nanocrystals from oxidation through forming an oxygen impermeable sheath.
Subject(s)
Cobalt/chemistry , Nanoparticles/chemistry , Polymers/chemistry , Surface-Active Agents/chemistry , Cetrimonium , Cetrimonium Compounds/chemistry , Metal Nanoparticles/chemistry , Nanotechnology/methodsABSTRACT
A prism-coupler technique was introduced to determine the refractive indices and thermo-optic coefficients of epitaxial Sr(0.6)Ba(0.4)Nb(2)O(6) (SBN) waveguides, in a temperature range covering the ferroelectric-paraelectric phase transition. A strong enhancement in the TO coefficient is observed near T(c). This strong enhancement is related to the critical change of the polarization. The values of dn(e)/dT are significantly larger than dn(o)/dT due to the larger quadratic electro-optic coefficient in TM polarization. In TM mode, the refractive index of SBN is increased by 1.3% as the temperature is increased to 160 degrees C. Our results suggest that SBN waveguide is a potential candidate for thermo-optic modulators and switches.
Subject(s)
Glass/chemistry , Optical Devices , Refractometry/instrumentation , Telecommunications/instrumentation , Transducers , Computer Simulation , Computer-Aided Design , Equipment Design , Equipment Failure Analysis , Light , Models, Theoretical , Scattering, Radiation , TemperatureABSTRACT
BACKGROUND: The feasibility, efficacy, and safety of the TriClip in the management of peptic ulcer hemorrhage in human beings are scarcely reported in the literature. OBJECTIVE: A pilot study was conducted to assess the feasibility, efficacy, and safety of the TriClip endoscopic clipping device in the control of peptic ulcer hemorrhage. DESIGN: Prospective evaluation. SETTING: Regional government hospital. PATIENTS: From July 2004 to January 2005, patients older than 16 years and with Forrest type I and IIa peptic ulcer hemorrhages were included in the study. INTERVENTIONS: TriClips were used for initial hemostasis. Salvage procedures, including adrenalin injection, heat probe application, argon plasma coagulation, or surgery will be carried out appropriately if TriClip failed to control bleeding alone. An endoscopy was repeated 24 hours later for the security of the TriClip and for any endoscopic evidence of recurrent bleeding. A follow-up endoscopy was performed 8 weeks later to assess ulcer healing. MAIN OUTCOME MEASUREMENTS: Procedure time, successful hemostatic rate, number of clips used, ulcer recurrent bleeding rate, complications, and ulcer healing rate were measured. LIMITATIONS: No comparative arm; pilot study only. RESULT: A total of 27 cases (11 women, 16 men) were included in the study, with a median age of 70 years (range 18-88 years). There were 19 cases of duodenal ulcer and 8 cases of gastric ulcer, with median size of 8 mm (range 2-20 mm). The rate of successful hemostasis in the first endoscopy by TriClips alone was 81.5% (22/27), with a median procedure time of 10 minutes (range 3-30 minutes). In the second endoscopy, the endoscopic recurrent bleeding rate was 14.8% (4/27) and the TriClips were found dislodged in 11 patients (40.7%). The permanent hemostasis rate was 67% (18/27). The overall failure rate was 33% (9/27). Three patients required blood transfusion before the first endoscopy. There was no morbidity or mortality observed in all cases. All ulcers healed after 8 weeks. CONCLUSIONS: The use of the TriClip is feasible in the initial control of peptic ulcer hemorrhage. However, we could not detect any obvious advantages in arresting bleeding vessels by using this new clipping device.
