Dileptons and Photons from Coarse-Grained Microscopic Dynamics and Hydrodynamics Compared to Experimental Data

We compute the radiation of dileptons and photons using relativistic hydrodynamics and a coarse-grained version of the microscopic event generator UrQMD, both of which provide a good description of the hadron spectra. The currently most accurate dilepton and photon emission rates from perturbative QCD and from experimentally-based hadronic calculations are used. Comparisons are made to data on central Pb-Pb and Pb-Au collisions taken at the CERN SPS at a beam energy of 158 A GeV. Both hydrodynamics and UrQMD provide very good descriptions of the photon transverse momentum spectrum measured between 1 and 4 GeV, but very slightly underestimate the low mass spectrum of e+e- pairs, even with greatly broadened rho and omega vector mesons.Comment: 4 pages, 10 figures, Quark Matter 2002 proceeding

A Comprehensive Simulation Model for Floating Gate Transistors

Floating-gate transistors have proven to be extremely useful devices in the development of analog systems; however, the inability to properly simulate these devices has held back their adoption. The objective of this work was to develop a complete simulation model for a floating-gate (FG) MOSFET using both standard SPICE primitives and also MOSFET models taken directly from foundry characterizations. This new simulation model will give analog designers the ability simulate all aspects of floating-gate device operation including transient, AC and DC characteristics. This work describes the development of this model and demonstrates its use in various applications

Electric conductivity of hot pion matter

The determination of transport coefficients plays a central role in characterizing hot and dense nuclear matter. Currently, there are significant discrepancies between various calculations of the electric conductivity of hot hadronic matter. In the present work we calculate the electric conductivity of hot pion matter by extracting it from the electromagnetic spectral function, via its zero energy limit at vanishing 3-momentum, within the Vector Dominance Model (VDM). Since within the VDM the photon couples to the hadronic currents primarily through the $\rho$ meson, we use hadronic many-body theory to calculate the $\rho$-meson's self-energy in hot pion matter, by dressing its pion cloud with thermal $\pi$-$\rho$ and $\pi$-$\sigma$ loops including vertex corrections to maintain gauge invariance. In particular, we analyze the low-energy transport peak of the spectral function, extract its behavior with temperature and compare to (the results of) existing approaches in the literature

Lock and Dam No. 26 R, Lock Cofferdam, Construction Sequencing

Construction of a new lock and dam to replace existing Locks and Dam No. 26 required construction to be accomplished in three separate stages. Each portion of the new structure would be constructed inside cellular cofferdams. The construction of each cofferdam would require model tests to determine compatibility with design flow requirements relative to constructability of coffercells, scour of riverbed material, and navigation of river vessels. Compatibility of the lock cofferdam geometry was verified using model studies along with sequence for construction of the cofferdam cells. Construction of the second stage cofferdam was successfully completed in December 1985, followed by dewatering and construction of the 1,200 foot lock structure

Contrast material–enhanced MRA overestimates severity of carotid stenosis, compared with 3D time-of-flight MRA

AbstractObjectiveNon–contrast-enhanced magnetic resonance angiography (MRA) carotid imaging with the time-of-flight (TOF) technique compares favorably with angiography, ultrasound, and excised plaques. However, gadolinium contrast-enhanced MRA (CE-MRA) has almost universally replaced TOF-MRA, because it reduces imaging time (25 seconds vs 10 minutes) and improves signal-to-noise ratio. In our practice we found alarming discrepancies between CE-MRA and TOF-MRA, which was the impetus for this study.Study designTo compare the two techniques, we measured stenosis, demonstrated on three-dimensional images obtained at TOF and CE-MRA, in 107 carotid arteries in 58 male patients. The measurements were made on a Cemax workstation equipped with enlargement and measurement tools. Measurements to 0.1 mm were made at 90 degrees to the flow channel at the area of maximal stenosis and distal to the bulb where the borders of the internal carotid artery lumen were judged to be parallel (North American Symptomatic Carotid Endarterectomy Trial criteria). Experiments with carotid phantoms were done to test the comtribution of imaging software to image quality.ResultsTwelve arteries were occluded. In the remaining 95 arteries, compared with TOF-MRA, CE-MRA demonstrated a greater degree of stenosis in 42 arteries, a lesser degree of stenosis in 14 arteries, and similar (±5%) stenosis in 39 arteries (P = .02, χ2 analysis). The largest discrepancies were arteries with 0% to 70% stenosis. In those arteries in which CE-MRA identified a greater degree of stenosis than shown with TOF-MRA, mean increase was 21% for 0% to 29% stenosis, 36% for 30% to 49% stenosis, and 38% for of 50% to 69% stenosis. The carotid phantom experiments showed that the imaging parameters of CE-MRA, particularly the plane on which frequency encoding gradients were applied, reduced signal acquisition at the area of stenosis.ConclusionsCollectively these data demonstrate that CE-MRA parameters must be retooled if the method is to be considered reliable for determination of severity of carotid artery stenosis. CE-MRA is an excellent screening technique, but only TOF-MRA should be used to determine degree of carotid artery stenosis

Double-lumen carotid plaque: A morbid configuration

AbstractDuring analysis of carotid plaque anatomy for a multicenter carotid imaging trial, we examined plaque specimens from 5 patients with double internal carotid artery lumina. Four of the 5 patients had symptoms referable to the lesion. The second lumen was noted when the plaque specimens were examined ex vivo with high-resolution (200 μm3) magnetic resonance imaging. Plaque structure was correctly identified in only 1 patient preoperatively. However, during retrospective review of the preoperative imaging studies, the second internal carotid artery lumen was identified in 3 patients

Adjunctive primary stenting of Zenith endograft limbs during endovascular abdominal aortic aneurysm repair: Implications for limb patency

ObjectiveEndograft limb occlusion is an infrequent but serious complication of endovascular abdominal aortic aneurysm (AAA) repair. The insertion of additional stents within the endograft limb may prevent future occlusion. This study evaluates limb patency with and without adjunctive stenting of endograft limbs at the time of endovascular AAA repair.MethodsWe performed a retrospective review of 248 patients who underwent endovascular abdominal aortic aneurysm repair with the Zenith AAA endovascular graft between 1999 and 2004. Among these patients, two groups were identified: 64 patients with adjunctive stents placed in 85 limbs and 184 patients without additional bare stent placement in endograft limbs at the time of endovascular AAA repair.ResultsWomen comprised 23% of stented and 11% of unstented patients (P = .02). The mean length of follow-up in the stented and unstented groups was 2.0 years. There were 13 instances of limb thrombosis in 13 patients (5.2% of patients, 2.7% of limbs), all in the unstented group. No limb occlusions occurred in the presence of adjunctive bare metal stents. Seventy-three percent of the occlusions occurred ≤6 months of endovascular AAA repair. Two patients (15%) had no symptoms of lower-extremity ischemia despite graft limb occlusion and did not undergo intervention. The others underwent thrombectomy (n = 2), thrombectomy with bare stent placement (n = 3), femoral-femoral bypass (n = 4), thrombolysis (n = 1), and thrombolysis with bare stent placement (n = 1). Of the seven who underwent thrombectomy or thrombolysis, three had no additional stents placed at the secondary procedure, and two of these three went on to rethrombose. By life-table analysis, primary patency at 3 years in the stented and nonstented limbs was 100% ± 0% and 94% ± 3%, respectively (P = .05).ConclusionsThe intraoperative insertion of additional bare metal stents appeared to eliminate the risk of thrombosis and was without complication. Of the 85 stented limbs in this series, not one occluded. The overall rate of limb thrombosis was low, with most limb occlusions occurring ≤6 months of stent-graft insertion, and would probably have been even lower had we been able to identify all high-risk cases for prophylactic adjunctive stenting. Limb occlusion denotes an underlying problem with the graft, which if left untreated after thrombectomy or thrombolysis will lead to rethrombosis. Postoperative imaging was of little value in detecting impending limb occlusion. Based on these findings, we believe one should identify and stent any limbs that appear to be at risk for thrombosis, but this study lacks the data to predict which limbs need stenting

Endovascular treatment of thoracoabdominal aortic aneurysms

ObjectiveThis study assessed the role of multibranched stent grafts for thoracoabdominal aortic aneurysm (TAAA) repair.MethodsSelf-expanding covered stents were used to connect the caudally directed cuffs of an aortic stent graft with the visceral branches of a TAAA in 22 patients (16 men, 6 women) with a mean age of 76 ± 7 years. All patients were unfit for open repair, and nine had undergone prior aortic surgery. Customized aortic stent grafts were inserted through surgically exposed femoral (n = 16) or iliac (n = 6) arteries. Covered stents were inserted through surgically exposed brachial arteries. Spinal catheters were used for cerebrospinal fluid pressure drainage in 22 patients and for and spinal anesthesia in 11.ResultsAll 22 stent grafts and all 81 branches were deployed successfully. Aortic coverage as a percentage of subclavian-to-bifurcation distance was 69% ± 20%. Mean contrast volume was 203 mL, mean blood loss was 714 mL, and mean hospital stay was 10.9 days. Two patients (9.1%) died perioperatively: one from guidewire injury to a renal arterial branch and the other from a medication error. Serious or potentially serious complications occurred in 9 of 22 patients (41%). There was no paraplegia, renal failure, stroke, or myocardial infarction among the 20 surviving patients. Two patients (9.1%) underwent successful reintervention: one for localized intimal disruption and the other for aortic dissection, type I endoleak, and stenosis of the superior mesenteric artery. One patient has a type II endoleak. Follow-up is >1 month in 19 patients, >6 months in 12, and >12 months in 8. One branch (renal artery) occluded for a 98.75% branch patency rate at 1 month. The other 80 branches remain patent. There are no signs of stent graft migration, component separation, or fracture.ConclusionsMultibranched stent graft implantation eliminates aneurysm flow, preserves visceral perfusion, and avoids many of the physiologic stresses associated with other forms of repair. The results support an expanded role for this technique in the treatment of TAAA