PubMed Health⌕ Search

Biomedical subjects

P S Yen

Publications and source records attributed to P S Yen.

8 recordsLinked to original sources
PubMed2002

Advective flow and floc permeability.

This work monitored advection flow through a floc by bubble tracking. Close examination of the motion of a swarm of hydrogen bubbles that passed over a free-falling floc allowed the extent of advection flow to be estimated at 53% for the original activated sludge floc, and 12% for the flocculated floc. The interior permeability of the sludge flocs was estimated from this information. The fluid force exerted on the falling floc was also considered.

Journal Article↗
PubMed2001

Reinforcement of acrylic denture base resin by incorporation of various fibers.

This study was designed to evaluate improvements in the mechanical properties of acrylic resin following reinforcement with three types of fiber. Polyester fiber (PE), Kevlar fiber (KF), and glass fiber (GF) were cut into 2, 4, and 6 mm lengths and incorporated at concentrations of 1, 2, and 3% (w/w). The mixtures of resin and fiber were cured at 70 degrees C in a water bath for 13 h, then at 90 degrees C for 1 h, in 70 x 25 x 15 mm stone molds, which were enclosed by dental flasks. The cured resin blocks were cut to an appropriate size and tested for impact strength and bending strength following the methods of ASTM Specification No. 256 and ISO Specification No. 1567, respectively. Specimens used in the impact strength test were reused for the Knoop hardness test. The results showed that the impact strength tended to be enhanced with fiber length and concentration, particularly PE at 3% and 6 mm length, which was significantly stronger than other formulations. Bending strength did not change significantly with the various formulations when compared to a control without fiber. The assessment of Knoop hardness revealed a complex pattern for the various formulations. The Knoop hardness of 3%, 6 mm PE-reinforced resin was comparable to that of the other formulations except for the control without fiber, but for clinical usage this did not adversely affect the merit of acrylic denture base resin. It is concluded that, for improved strength the optimum formulation to reinforce acrylic resin is by incorporation of 3%, 6 mm length PE fibers.

Acrylic Resins↗
PubMed2001

High-speed sludge freezing.

The investigation examined the feasibility of applying a "high-speed freezing technique, using liquid nitrogen freezing, to condition activated sludges and alum sludges. Experimental results indicate that the freezing speed is much faster than that adopted in most previous works on sludge freezing. Although the filterability and settleability of the alum sludge is improved by 3-min liquid nitrogen freezing, no similar improvement is observed for activated sludge. Moreover, curing affects neither sludge after liquid nitrogen freezing, but affects the slow-freezing activated sludge.

Alum Compounds↗
PubMed2001

Errors in bound water measurements using centrifugal settling method.

Centrifugal settling method (CSM) is commonly used to estimate the bound water content in sludges. The sludge sediment matrix should be purely plastic for accurate measurements to the bound water content. This communication, however, addressed for the first time that, owing to the inhibited elasticity of the sludge matrix, sediment height rebound was commonly observed for the flocculated sludge. Also, different sludges could have distinct elastic responses after centrifugation. There existed no simple correlation to incorporate the elastic rebound of sludge sediment in bound water measurement. The possible errors incorporated into CSM for measuring bound water contents were highlighted.

Centrifugation↗
PubMed1998

Preoperative embolization of meningiomas: comparison of superselective and subselective techniques.

We retrospectively compared the efficacy of preoperative superselective and subselective embolization for intracranial meningiomas. Between January and December 1996, 22 patients (7 men, 15 women, mean age 51 +/- 15.5 yr) underwent superselective embolization with 45 to 150 mm polyvinyl alcohol particles after superselective catheterization of the feeding vessels with a microcatheter system. Another 30 patients (12 men, 18 women, mean age 50 +/- 12.9 yr) underwent subselective embolization between January and December 1995 with 150 to 300 mm Gelfoam particles after catheterization of the terminal external carotid artery just proximal to the orifice of the maxillary artery with a 4- or 5-F angiocatheter. The mean intraoperative blood loss (918 versus 1450 mL, p < 0.05), amount of blood transfused (4.9 versus 7.5 units, p = 0.09), and surgical resection time (422 versus 529 min, p < 0.05) were all lower in the superselective group than in the subselective group, while the occurrence of fresh ischemic necrosis (59% versus 53%, p = 0.68), hemorrhage (77% versus 60%, p = 0.19), and embolic material (55% versus 13%, p < 0.05) on pathologic examination were higher in the superselective group. No procedure-related complications occurred in the superselective group, whereas two patients in the subselective group had postoperative scalp necrosis. Our findings show that superselective embolization is more effective than subselective embolization for preoperative endovascular devascularization of meningiomas, with significant reductions in intraoperative blood loss and surgery time. Preoperative embolization of meningiomas, if indicated, should be done with the superselective technique whenever feasible.

Adult↗
PubMed1997

Nasopharyngeal carcinoma: MRI and CT assessment.

Precise assessment of the extent of nasopharyngeal carcinoma (NPC) represents the basic step towards optimal treatment. We compared the capacity of CT and MRI in assessing the extent of NPC in 67 patients. MRI was superior to CT in demonstrating lesions in the retropharyngeal node, skull base, intracranial area, carotid space, longus colli muscle and levator palatini muscle. Of 25 cases in which retropharyngeal adenopathy was recognised only on MRI, seven had been reported as showing oropharyngeal involvement and 18 as primary extension to the carotid space on CT. MRI showed skull-base involvement in 40 patients compared with 27 on CT and intracranial involvement in 38 patients versus 24 on CT. There was not a single case in which skull base invasion was seen on CT but not on MRI. MRI enabled improved recognition of tumour infiltration of longus colli muscles (34 cases compared with 15 on CT). It allowed us to clarify 12 questionable sinonasal opacities on CT. Overall, T-staging was changed in 18 of 67 patients (26.9%), including upstaging in 15 cases and down-staging in 3 cases, after comparing CT with MRI. The nodel status was changed from negative on CT to positive on MRI in 4 of 67 patients (6%). We believe that MRI allows more accurate evaluation of the extent of NPC than CT and should be the primary mode of investigation.

Adolescent↗
PubMed1997

CT angiography of intracranial aneurysms: advantages and pitfalls.

OBJECTIVE: To determine the clinical usefulness of computed tomography (CT) angiography in the evaluation of cerebral aneurysms. MATERIALS AND METHODS: From October 1994 through April 1996, 26 patients with 30 surgical proven intracranial aneurysms underwent both CT angiography and catheter cerebral angiography. The findings of the two methods were reviewed independently and then compared with each other. RESULTS: Comparing with catheter angiography, CT angiography was superior in demonstrating the aneurysmal neck in seven aneurysms but was inferior in one. The thrombosed part and calcification of aneurysms were clearly demonstrated on CT angiograms. CT angiography also aided in differentiating tight vascular loops from aneurysms. On CT angiograms, one posterior communicating arterial aneurysm was overlooked and another anterior choroidal artery aneurysm was misinterpreted as a posterior communicating artery aneurysm. Of note were two patients in whom the infundibulum of the orbitofrontal artery was misinterpreted as the anterior communicating artery aneurysm. CONCLUSION: CT angiography can compliment conventional catheter angiography for its better demonstration of the 3-dimensional anatomy. It can provide surgical information about the neck, calcification and thrombosed part of an aneurysm and its relation to adjacent structures. However, caution is advocated because CT angiography may fail to demonstrate small but important vessels such as posterior communicating, anterior choroidal and orbitofrontal arteries. Recognition of the limitations of CT angiography is important in minimizing interpretation errors.

Adult↗