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S Lyon

Publications and source records attributed to S Lyon.

13 recordsLinked to original sources
PubMed2006

Intervalley gap anomaly of two-dimensional electrons in silicon.

We report here a systematic study of the energy gaps at the odd-integer quantum Hall states nu = 3 and 5 under tilted magnetic (B) fields in a high quality Si two-dimensional electron system. Out of the coincidence region, the valley splitting is independent of the in-plane fields. However, the nu = 3 valley gap differs by about a factor of 3 (Deltav approximately 0.4 vs 1.2 K) on different sides of the coincidence. More surprisingly, instead of reducing to zero, the energy gaps at nu = 3 and 5 rise rapidly when approaching the coincidence angles. We believe that such an anomaly is related to strong couplings of the nearly degenerate Landau levels.

Journal Article↗
PubMed2004

Two-flux composite fermion series of the fractional quantum Hall states in strained Si.

Magnetotransport properties are investigated in a high-mobility two-dimensional electron system in the strained Si quantum well of a (100) Si(0.75)Ge(0.25)/Si/Si(0.75)Ge0.25 heterostructure, at temperatures down to 30 mK and in magnetic fields up to 45 T. We observe around nu=1/2 the two-flux composite fermion (CF) series of the fractional quantum Hall effect (FQHE) at nu=2/3, 3/5, 4/7, and at nu=4/9, 2/5, 1/3. Among these FQHE states, the nu=1/3, 4/7, and 4/9 states are seen for the first time in the Si/SiGe system. Interestingly, of the CF series, the 3/5 state is weaker than the nearby 4/7 state and the 3/7 state is conspicuously missing, resembling the observation in the IQHE regime that the nu=3 is weaker than the nearby nu=4 state. Our results can be quantitatively understood in the picture of CF's with the valley degree of freedom.

Journal Article↗
PubMed2002

Displacement of occluded plastic endoprostheses into the duodenum during percutaneous biliary drainage: description of an under-reported technique.

AIM: Percutaneous transhepatic biliary drainage (PTBD) is occasionally requested in patients with an occluded plastic stent in situ. We describe a technique for dislodging the stent into the duodenum during PTBD. MATERIALS AND METHODS: Twelve patients (M:F, 9:3 mean age 70 years) with plastic stents in the common bile duct (CBD) underwent PTBD. Eleven patients had malignant obstruction and one patient had Mirizzi's syndrome and a large duodenal diverticulum. PTBD was performed using right lobe access in nine patients and a left hepatic access in three patients. The level of biliary obstruction was at the lower CBD in five patients, mid-CBD in four patients and upper CBD in three patients. After standard percutaneous biliary access was established, an 8mm by 4 cm balloon catheter was gently inflated alongside the upper end of the plastic stent and advanced over a stiff guidewire, towards the duodenum, to dislodge the plastic stent. RESULTS: Plastic stents were successfully dislodged in all 11 patients with malignancy and metallic stents were deployed for palliation. In nine of 11 patients with malignant lesions the PTBD dislodgement of the plastic stent and insertion of a metallic stent was carried out as a single-step procedure. In two patients with biliary sepsis, a two-step procedure was necessary. In the patient with Mirizzi's syndrome the plastic stent could not be dislodged. No complications were observed. CONCLUSION: Plastic stents, inserted at ERCP, can be dislodged in the majority of cases at PTBD using a balloon catheter inserted alongside the failed stent without complication.

Aged↗
PubMed1995

A role for nitric oxide in X-ray contrast material toxicity.

RATIONALE AND OBJECTIVES: We assessed the role that nitric oxide (NO) plays in contrast media (CM) toxicity, using 100% lethal dose (LD100) studies in hyperimmune Brown Norway (BN) rats. METHODS: Ninety-two BN rats and 41 Sprague-Dawley (SD) rats underwent CM LD100 tail vein injections with methylglucamine iothalamate or sodium iothalamate to the point of cessation of respiration. Methylglucamine hydrochloride also was injected. The injections were accompanied by L-arginine (L-Arg) or D-arginine (D-Arg) analogues or by an H1 blocker. L-Arg analogues inhibit NO formation, and D-Arg analogues do not. RESULTS: An L-Arg analogue, but not a D-Arg analogue, increased the tolerance of BN rats (p < .005) for methylglucamine iothalamate but not for sodium iothalamate. The L-Arg analogue also protected BN rats against methylglucamine chloride injections (p < .002). H1 blockade protected BN rats against methylglucamine iothalamate (p < .0005) and methylglucamine chloride (p < .005) injections. None of these measures altered the CM tolerance of SD rats. In SD rats, injections of either methylglucamine iothalamate or sodium iothalamate along with a D-Arg analogue or normal saline were better tolerated than similar injections in BN rats (p < .01 and .002 for methylglucamine iothalamate and sodium iothalamate, respectively). In SD rats but not BN rats, sodium iothalamate was better tolerated than was methylglucamine iothalamate (p < .0005). CONCLUSION: NO appears to play a significant role in BN rats LD100 CM toxicity and has been implicated by others in the blood pressure fall characterizing some forms of antigen-induced anaphylaxis [1, 2]. The results of the current study and the literature suggest that methylglucamine-modulated release of histamine from mast cells may underlie the NO production.

Anaphylaxis↗
PubMed1986

Aluminum ingestion and behavior in the Long-Evans rat.

A variety of behaviors was measured in adult Long-Evans male rats fed ground rat chow containing either no added aluminum, low aluminum (1500 mg/kg), moderate aluminum (2500 mg/kg), or high aluminum (3500 mg/kg). There were no effects of aluminum on either body weight or mouse killing. There was an inverse relationship between brain aluminum and open-field activity. Elevated brain aluminum was correlated with relatively poor performance on a single-trial passive-avoidance task and on a visual discrimination with reversal task.

Aggression↗
PubMed1977

Steroids: theoretical and experimental basis for utilization in prevention of contrast media reactions.

In vitro and in vivo studies were done to examine the effects of methylprednisolone on the adverse reactions induced by contrast media. At very high concentrations, the steroid potentiated the complement-activating effect produced in vitro by iodipamide, but inhibited the immune and nonimmune mechanisms of hemolysis. Rabbits pretreated for 3 days with intramuscular methylprednisolone (at high or low dosages) were significantly protected against an LD47 challenging dose of iodipamide. Those treated once with a low intravenous dose immediately prior to iodipamide challenge were protected to a lesser degree. Rabbits treated once with a very high intravenous dose of steroid evidenced no protection. A hyper-responsive dog was consistently protected against adverse reactions to injected sodium iothalamate by a 3-day steroid pretreatment.

Animals↗
PubMedDate not supplied

Acute traumatic renal artery to inferior vena cava fistula treated with a covered stent.

A 34-year-old man presented within hours of suffering a penetrating stab wound and was diagnosed with a right renal artery to inferior vena cava fistula. Initial attempts at excluding the fistula with a balloon were unsuccessful. He was subsequently treated with a covered stent inserted into the right renal artery which successfully excluded the fistula.

Acute Disease↗