bluuebunny/crossref_metadata_2025 huggingface dataset:
E-049 Single versus staged stent assisted coiling techniques for intracranial aneurysms: comparison of complication rates, and immediate and long term angiographic outcome in a single institution experience
Authors: Alaraj A , Hage Z , Munson T , Amin-Hanjani S , Charbel F , Aletich V
Published: December 2010

Introduction

Endovascular management of intracranial aneurysms include stent assisted techniques for wide neck complex aneurysm. Two approaches are being used for stent assisted coiling, single versus staged coiling after stent ‘endothelialization’. Comparative outcomes of these two methods are the purpose of this study.

Methods

Medical records and angiographic results were reviewed for 133 aneurysms treated between October 2003 and November 2008 with stent assisted coiling, single stage (62 aneurysms) or staged treatments (71 aneurysms). Demographics, outcomes and angiographic features were reviewed.

Results

Patient demographics between the two cohorts were not statistically different by univariate analysis in terms of age, clinical presentation, aneurysm location, follow-up duration and presence of fusiform aneurysms. Aneurysm characteristics in single versus staged treatment were: average neck diameter (5.2±1.6 mm) versus (6.0±2.9 mm) (p=0.07); dome diameter (7.5±3.4 mm) versus (8.9±0.2 mm) (p=0.42); and dome/neck ratio (1.5±0.4) versus (1.4±0.6) (p=0.39) respectively. Fusiform aneurysms were comparable in the two groups. There was a statistically significant difference in immediate, good angiographic results (95–100% occlusion) (55.6% vs 44.5%; p=0.04) but not in long term angiographic results (46.2% vs 53.8%), the need for treatment (11.3% vs 12.6%) or in the rate of in-stent stenosis (7.6% vs 7.6%) in single versus staged treatment. There was no difference in complication rates with regard to coil protrusion (p=0.3), clot/emboli formation (p=0.3) or rupture/dissection (p=0.5). Two patients had rebleeding from a ruptured aneurysm postpartial treatment with single staged stent assisted coiling 3 days after the treatment.

Conclusions

In a controlled cohort, aneurysms treated with single stage had a similar long term angiographic results with the same complication rates compared with multistage treatment.
E-005 Preliminary result of carotid artery stenting using angioguard XP/precise stent with technique of mild post-angioplasty
Authors: Fujii M , Uemura A , Matsukawa H , Yamamoto D , Kobayashi N , Numaguchi Y , Murakata A , Shinoda M , Ishikawa R
Published: December 2010

Carotid artery stenting (CAS) using Angioguard XP/Precise stent (AG/PS) has been widely used for treating carotid artery stenosis. However, the use of this device was considered to cause a relatively high occurrence rate of embolic complications compared with the use of other off labeled occlusion or protection devices. One of the reasons is thought to be the excessive pressing on the atheroma plaque lesion post-angioplasty after stenting. Here, we report the preliminary results of CAS with AG/PS using mild post-angioplasty (mild post-PTA) in a small number of patients at our institution. CAS was successfully performed in 12 patients (men, 11; women, one; average age 70.6 years; six patients under general anesthesia) using this technique over a 10 month period. Eight patients showed symptomatic carotid artery stenosis. The preoperative carotid artery average per cent stenosis by NASCET criteria was 73.8%. Furthermore, we discuss the postoperative carotid artery per cent stenosis, cerebral ischemic complication, other complication events, no flow/slow flow event and carotid artery restenosis rate. The postoperative carotid artery average per cent stenosis was improved to 7.5%. Moreover, good dilatation was achieved after stenting using mild post-PTA. Postoperative diffusion weighted MR images showed high intensity spotty lesions. One patient (8.3%) presented with motor speech disturbance and asymptomatic no flow event. Perioperative complication and carotid artery restenosis after stenting have not occurred so far during a short follow-up period, indicating a relatively acceptable result of CAS with AG/PS using mild post-PTA. Other procedures to achieve good stenting results using mild post-PTA are needed, as well as data from long term follow-up at our own institution.
E-050 Stent assisted coil embolization for large and giant fusiform dissecting aneurysms: a series of 38 cases
Authors: Choulakian A , Eboli P , Mukherjee D , Alexander M
Published: December 2010

Introduction

Fusiform aneurysms present a challenge for treatment since their dome to neck ratios are often less than 1. These are cases that are excluded from most aneurysm series, and prior to intracranial stents were thought not to be treatable by embolization, except by parent artery occlusion.

Methods

This is a retrospective analysis of a prospectively collected database of 38 patients who had stent assisted coil embolization of a large or giant fusiform aneurysms. A total of 21 patients had two telescoping stents placed and four patients had three telescoping stents. There is an analysis of the procedure related complications, re-treatments, symptomatology and delayed follow-up.

Results

The average aneurysm size treated was 21.4 mm (range 12–61), with an average neck of 18.6 mm. In the periprocedural period there was a 10% complication rate with two strokes and two increased cranial neuropathies. Nine of the patients required re-treatment during a mean follow-up time of 38 months. There were two deaths in the follow-up period: one due to subarachnoid hemorrhage, another presumed due to respiratory arrest.

Conclusions

Although stand alone flow diversion devices are being developed and evaluated, stent assisted coil embolization is an effective alternative to fusiform and fusiform dissecting aneurysms. The periprocedural complication rates are reasonable (10%), and although re-treatment is frequently necessary, the long term outcomes are better than the natural history of this disease.
E-051 Upper cervical spinal dural arteriovenous fistulae: an under recognized entity?
Authors: Gandhi D , Huang J , Choudhary A , Kathuria S
Published: December 2010

Introduction

Spinal dural arteriovenous fistulae (dAVFs) are uncommon lesions that often present with slowly progressive myelopathy. These shunts are located most commonly in the thoracolumbar region. A location in the cervical spine is considered exceedingly rare and has been reported most often in the context of subarachnoid hemorrhage. We report a series of five cases of upper cervical dAVFs and describe the clinical and angiographic characteristics of these lesions.

Materials and methods

A review of interventional neuroradiology database identified five patients with upper cervical dural arteriovenous fistulae (CdAVFs). We performed a review of the patient charts, imaging studies, including digital subtraction angiography (DSA) and C arm CTs (when available), and the operative records. The imaging studies were reviewed by two neuroradiologists with experience in spinal angiography and interventions. We also performed a detailed review of the English literature on this entity.

Results

Mean age of the patients was 61.6 years (range 45–75 years). There were three men and two women. Four of the five patients presented with subarachnoid hemorrhage (SAH) that could be attributed to the CdAVF. One patient had an incidental detection of the CdAVF while undergoing cerebral angiography for a ruptured left posterior communicating aneurysm. The fistulae were located at C1 or C2 level and supplied by C1/C2 radicular arteries. Small branches of anterior or lateral spinal artery were noted to supply the fistulae in four of the five patients. Embolization was performed in 3/5 lesions and was curative in one. Reduction in flow was accomplished in 2/5 but definitive cure using endovascular therapy was not possible due to small size of the feeder vessels and/or supply from ASA. One of these two patients has had microsurgical obliteration of the fistula. Two patients are being medically observed, one with incidentally detected fistula and another who refused microsurgical therapy.

Conclusion

Upper cervical dAVFs may possibly be an under recognized entity. Approximately half of the reported cases have presented with SAH. Endovascular therapy is often difficult due to small size, eloquent nature and multiplicity of feeder vessels. Microsurgical therapy is also difficult but may offer a chance of complete obliteration in selected cases. In high risk cases, expectant management may be reasonable since the clinical course from the hemorrhage seems to be fairly benign and significant complications from SAH are uncommon. We advocate bilateral selective vertebral angiography (in addition to usual DSA workup) with the inclusion of their cervical segments in evaluation of any patient with hemorrhage in the region of the foramen magnum/upper cervical spine. These lesions have a higher chance of detection if the upper cervical spine is included in the imaging field of view.
E-055 Mechanical thrombectomy with the Penumbra System for treatment of venous sinus thrombosis
Authors: Choulakian A , Alexander M
Published: December 2010

Objective

Venous sinus thrombosis can be a fatal condition. When systemic anticoagulation therapy fails or is high risk, endovascular chemical thrombolysis or mechanical thrombectomy may be necessary. We report our experience using the Penumbra System (PS; Penumbra, Alameda, California, USA) in a series of four patients with venous sinus thrombosis.

Methods

Four patients were treated with mechanical thrombectomy using the PS for venous sinus thrombosis. Three of these patients also underwent balloon angioplasty following the PS device. Utility of this technique was evaluated by procedural success, improvement in neurological condition, avoidance of complications and follow-up imaging.

Results

Technical success was achieved in all four patients with restoration of flow in the occluded sinuses without the use of chemical thrombolysis (Abstract E-055 table 1). No complications were encountered during the procedure and no postprocedural complications were attributable to the thrombectomy. One patient with glioblastoma died 6 weeks after the procedure. No new intracerebral hemorrhages (ICH) were caused and there was no exacerbation of pretreatment ICHs. Follow-up imaging was available in all but one patient to documented continued sinus patency. Neurologic improvement was seen in all patients after thrombectomy. Two patients have returned for outpatient follow-up and both are doing well.

Abstract E-055 Table 1

Results for the four patients

Patient NoPresenting symptomsRisk factorsAnticoagulationICHThrombosed sinusesTime to treatmentProcedureFollow-up imagingNeurologic status1Decreased LOCHITLepirudin post-procedurePreprocedureSSS<1 dayPenumbra, balloon angioplastyStable CTVImproved mental status2Headache, nausea, vomitingMastoiditisHeparin pre and postprocedureNoneR TS R SS R IJ4 daysPenumbra, balloon angioplastyStable MRVMild headache at 3 months3Iatrogenic SSS injuryHypercoagulableNoneNoneSSS R TS<1 dayPenumbraStable angiogramDead at 6 weeks (GBM)4Quadriplegia, aphasia, lethargyBirth control pillsHeparin postprocedurePreprocedureSSS8 daysPenumbra, balloon angioplastyNoneNormal at 3 months

Conclusion

Endovascular treatment for venous sinus thrombosis with the PS is a safe and efficacious alternative to the other forms of mechanical thrombectomy reported in the literature. Good clinical and radiographic results can be obtained without the need for chemical thrombolysis.

Abstract E-055 Figure 1Abstract E-055 Figure 2
E-058 Basilar artery recanalization status after endovascular therapy does not predict outcome
Authors: Raghuram K , Rai A
Published: December 2010

Purpose

Basilar artery occlusion is a devastating event without treatment. With the advent of mechanical and endovascular therapy, one would expect an improvement in outcomes.

Materials and methods

We retrospectively reviewed patient records on 17 patients who presented with acute basilar artery thromboembolism and underwent an interventional procedure. The admission clinical findings, CT and CT angiogram, angiographic images and follow-up CT/MRI were reviewed. Clinical follow-up was also recorded. Statistical methods to analyze the findings were performed using JMP software.

Results

12% of patients had a good outcome and 18% were lost to follow-up. NIH stroke scale at admission had a direct correlation with outcome (modified Rankin scale). Recanalization did not directly correlate with outcome. Postprocedure hemorrhage was higher with larger doses of tissue plasminogen activator (tPA) and adding a mechanical device (MERCI) did not significantly improve outcome compared with tPA. Older age, higher admission National Institutes of Health Stroke Scale (NIHSS) were indicators of an adverse outcome. Complete basilar occlusion was associated with a worse outcome than a partial occlusion but the difference did not approach statistical significance.

Conclusions

In this single center experience analysis, we were unable to identify any statistically significant angiographic predictors of outcome. Specifically, recanalization of the basilar artery did not correlate with good outcome. NIHSS at admission was an independent predictor of outcome. Basilar occlusion remains a complex and debilitating condition that is not satisfactorily treated by any current methods, including interventional techniques.
E-006 Urgent recanalization using stents for acute internal carotid artery occlusion in progressive stroke patients
Authors: Lee T , Sung S , Lee S
Published: December 2010

Background

Re-establishing cerebral blood flow in a timely fashion during an acute stroke has been shown to be efficacious in improving patient outcomes. Complete occlusion of the internal carotid artery (ICA) in progressive stroke patients would be expected to bring about devastating neurological sequelae and probably not be compatible with survival unless it could be treated. We retrospectively analyzed the feasibility, safety and effectiveness of the urgent recanalization using stents for acute ICA occlusion in the progressive stroke syndromes.

Methods

Between January 2008 and December 2009, urgent recanalization using stents for acute ICA occlusion was performed in 21 progressive stroke patients. The group of patients comprised 16 men and five women, aged 52–83 years (mean age 68.8 years). The occlusion segments of ICA were extracranial in nine patients and intracranial in 12 patients. A 0.014 inch microwire was placed into the distal ICA or middle cerebral artery, crossing the occluded segment. The stent was then advanced over the microwire and deployed in the lesion.

Results

We achieved successfully complete recanalization using stents in 19 of 21 patients (90.1%). We could not advance the stent delivery system into the lesion in two patients because of the vascular tortuousness. During the procedure, ICA dissection occurred in two patients (9.5%) and was treated with additional stent placement. There was no symptomatic thromboembolic complication. Fifteen of 19 patients (78.9%) showed the stable or improved neurologic signs and favorable clinical outcomes. Four patients (21.1%) showed brain edema and aggravating neurologic signs and two of them (10.5%) expired due to massive brain edema and herniation.

Conclusion

Urgent recanalization using stents for acute ICA occlusion may salvage the vessel and promise better clinical outcome in the progressive stroke patients. Endovascular recanalization for ICA occlusion is feasible with acceptable early clinical result.
E-063 Cardiothoracic surgery does not pose significant risk of aneurysmal subarachnoid hemorrhage
Authors: Moskowitz S , Ching E Cheng , Teng Q , Hui F
Published: December 2010

Objective

Neurologic imaging prior to cardiac surgery often identifies incidental intracranial vascular pathology. The risk of hemorrhage from these lesions during an open cardiothoracic surgical procedure is unknown, preventing appropriate patient and surgeon counseling. We sought to identify the risk of aneurismal subarachnoid hemorrhage (SAH) in this population.

Background

Patients undergoing cardiothoracic surgery often sustain significant hemodynamic fluctuations during and after their procedure. Since the incidence of cerebral aneurysms is estimated as 1–8% based on non-invasive imaging and autopsy studies, the number of patients harboring aneurysms is significant. It is unknown whether the cardiothoracic procedure impacts on the risk of aneurysm rupture.

Methods

A prospective database of all cardiothoracic procedures is maintained for a large tertiary care center. Demographic, clinical, procedural and complication data are routinely collected. Data from this were reviewed for all procedures between 2001 and 2009 and neurologic complications identified. All identified strokes were reviewed for ischemia or hemorrhage, and the imaging reviewed for all hemorrhages to describe the pattern with focus on SAH and potential for aneurysms as contributory.

Results

In this time period, over 10 000 procedures were performed. Neurologic events occurred in 617, of which 71 were hemorrhages. Hemorrhagic transformation of an ischemic stroke accounted for 49 (HI-1, 27; HI-2, 10; PH-1, 8; PH-2, 4). Two subdural hematomas were identified and nine intraparenchymal hemorrhages were seen. SAH occurred in 11, consisting of three as a direct result of a complication from intra-arterial thrombectomy. Seven were small convexity bleeds for which three had vascular imaging performed (all negative). One SAH was the result of a fusiform supraclinoid mycotic aneurysm which developed as a result of bacterial endocarditis. This aneurysm was not present on preoperative vascular imaging and required vessel sacrifice as it continued to grow rapidly and ruptured. No cases of SAH associated with a saccular aneurysm were identified.

The incidence of cerebral aneurysms of 1–9% suggests that in this population, 100–900 aneurysms should exist. With no SAH cases identified, the periprocedural risk from aneurysm rupture is less than 0.01–0.001%.

Conclusions

Aneurysm SAH as a direct result of open cardiothoracic surgery represents a very small risk. Consideration for management should be driven by cardiac indications with insignificant additional risk added by the incidental cerebral aneurysm found preoperatively.
E-064 Endovascular treatment of intracranial aneurysm with stents: experience of a Latin American Country
Authors: Pabon B , Vargas S , Urena P
Published: December 2010

Objective

To report our experiences in the treatment of wide necked, giant and complex intracranial aneurysms (IAs) with stents.

Materials and methods

From June 2002 to January 2010, a total of 205 patients with 214 aneurysms were treated in our institutions with stent technique. Data regarding technical success, initial and final angiographic results, mortality, morbidity and final clinical outcome were collected and analyzed retrospectively.

Results

205 patients with 214 IAs were treated. 47% of the cases had a history of hemorrhage. Regarding the procedure strategy, in 71% of the cases we used stent assisted coiling. Clinical and radiological mid and long term follow-up was obtained in 75% and 56%, respectively. Morbidity was 5.5% and mortality procedure related was 3% (six patients).

Conclusion

Endovascular reconstruction with stent only or stent assisted coiling represents a safe, durable and curative treatment alternative for selected wide necked, large and giant intracranial aneurysms.
E-065 Revascularization of internal carotid artery occlusion by using a flow reversal system
Authors: Buciuc R , Luzardo G , Khan M , Schlackman B , Uschman H , Wineman R
Published: December 2010

Introduction and purpose

To assess the feasibility and safety of carotid revascularization in subacute conditions, using a flow reversal system.

Materials and method

A total of five patients presenting with subacute carotid occlusion and non-disabling neurologic deficits underwent endovascular revascularization of their occluded vessel by using a flow reversal system as a protection device against embolic phenomena. In two cases, in addition to the flow reversal system a protective filter has been added on prior to completion of revascularization. All patients underwent the intervention under general anesthesia. After revascularization, all patients underwent placement of stents at the locations presumed responsible for their occlusions. All patients were managed immediately in the neurointensive care unit under strict blood pressure control.

Results

Technically, all of the procedures were successful with no embolic phenomena. In patients where a filter device was used in addition to the flow reversal system, the filter was inspected visually after removal and no clots or debris were identified.

There were no neurological deficits associated with the procedure. There were no systemic or local complications associated.

In one patient a 6 month clinic and angiographic follow-up was obtained. This demonstrated patency of the stent. The patient did not develop any additional neurological deficits.

Conclusion

Preliminary results of using a flow reversal system in carotid artery subacute revascularization suggest that this technique is feasible and effective. A larger patient cohort would be necessary to further address the safety of the procedure, indications and long term results.
E-066 Dural sinus stenting for advanced pseudotumor cerebri with papilledema: patient selection and results
Authors: Kumpe D , Seinfeld J
Published: December 2010

Pseudotumor cerebri in its advanced form creates severe papilledema which can threaten vision or cause blindness. A subgroup of pseudotumor patients with this advanced clinical picture have intracranial dural sinus outflow obstruction which is completely reversible with elimination of the offending venous pressure gradient by stent placement over the focal lesion causing the gradient. This procedure corrects the underlying cause of the increased intracranial pressure. Traditional surgical corrections, including shunts—lumboperitoneal, ventriculoperitoneal or ventriculoatrial—and optic nerve sheath fenestration do not correct the underlying hemodynamic abnormality and have high failure rates in follow-up. Dural sinus stents, on the other hand, have remained uniformly patent and our patients’ papilledemas have not recurred. This procedure should replace traditional surgical approaches in appropriately selected patients. The presentation will focus on the clinical evaluation and selection of these patients for treatment. Our clinical results (currently 19 stent placements in 18 patients) will be presented, with follow-up extending to 10 years.
A BOXCARS investigation of the interspecies V–V energy transfer from highly excited SF6 to CH4
Authors: Wang Lixin , Jones W. E.
Published: December 2010

The BOXCARS technique was used to investigate the V–V energy transfer between highly excited SF6 and CH4. The rates and the amounts of energy transferred to both the ν1 and ν3 modes depend strongly on excitation intensity and partial pressure of SF6 and CH4, and within experimental error, the variation of these quantities in both modes is identical, which is contrary to the situation in other polyatomic molecules. The results indicate that V–T energy transfer in CH4 plays an important role in the relaxation of the excess vibrational energy transferred from SF6 to CH4, and that the intermode V–V energy transfer between the ν1 and ν3 modes of CH4 is much faster than the interspecies V–V energy transfer between highly excited SF6 and CH4.
Interaction of light with a lattice of dipoles: A new approach
Authors: Dormale Bernard M. de
Published: December 2010

We present a new way to compute reflection–transmission coefficients of a two-dimensional lattice of spheres subject to dipole–dipole interaction. Our method proves to be numerically both efficient and accurate.
Ion-beam-assisted deposition of nonhydrogenated a-Si:C films
Authors: Tucker C. D. , Brodie D. E.
Published: December 2010

Amorphous silicon carbide (a-Si:C) films were prepared by low-energy ion-beam-assisted deposition (IBAD) in an attempt to remove structural defects in the "lattice" and improve the electrical characteristics of the film. The ion beam was generated by electron cyclotron resonance from an ultra-high-purity argon plasma. The deposition environment was first evacuated to a very high vacuum to eliminate all but trace amounts of water vapour and other gases so that improvements in the electrical and (or) structural properties of the film would be attributable to the influence of the densification by ion bombardment and not to contaminants. The IBAD process does improve the film characteristics by reducing the density of localized states at the Fermi level and the porosity of the film. However, even though these films have the best electrical characteristics obtained thus far for these kind of films, none of them exhibited device quality and none were observed to be photoconducting. A large density (≈1 at.%) of implanted argon atoms may be limiting the reduction in the defect density that might otherwise be achievable.
Modified shifted 1/N expansion for relativistic Yukawa and Hulthen potentials
Authors: Panchanan Swati , Roychoudhury Rajkumar , Varshni Y. P.
Published: December 2010

The shifted 1/N expansion technique is applied to the radial Dirac equation. It is shown that the fixing condition E1 = 0 produces an enhanced accuracy for Yukawa and Hulthen potentials. The modified shifted 1/N expansion results are compared with the exact numerical results and results obtained by other approximate methods.
Phonon self-energy with layered anisotropy: Strong coupling finite temperature and impurities
Authors: Jiang C. , Carbotte J. P.
Published: December 2010

We present a generalized, real frequency axis, Eliashberg formulation for the change in phonon self energy on entering the superconducting state which is valid for a solid with layered anisotropy. For simplicity, we assume free electron isotropic propagation in the planes with a hopping probability from plane to plane and cylindrical symmetry. Numerical results are given, at zero temperature, for different amounts of anisotropy and coupling strengths. Finite temperature and impurity effects are also considered.
Theoretical study of the electronic structure of the low-lying states of the Li2H molecule
Authors: Allouche A. R. , Aubert-Frecon M. , Spiegelmann F.
Published: December 2010

Results of a complete active space self-consistent field treatment of the two lowest states of each symmetry 2A1, 2B1, and 2B2 of Li2H are reported. An isosceles triangle is predicted for the equilibrium geometry of the ground state (1)2A1 (RLiLi = 2.48 Å, RLiH = 1.70 Å) (1 Å = 10−10 m) and of the excited state (1)2B1 (RLiLi = 2.91 Å, RLiH = 1.58 Å) while a linear geometry is predicted for the (1)2B2, (2)2A1, (2)2B2, and (2)2B1 states with the following values for RLiH = RLiLi/2: 1-66, 1.57, 1.66, and 1.57 Å, respectively. Fitted analytical forms of the potential energy surfaces for the six states investigated are also displayed.
An explanation of a difficulty with Huygens' secondary wavelets
Authors: Daniels J. M.
Published: December 2010

Huygens' construction for the propagation of a wave front using secondary wavelets gives rise to a paradox, that a backward travelling wave is predicted, but this wave does not exist. This paradox is resolved by postulating two wavelets that cancel in the backward direction. Kirchhoff's diffraction integral is examined in the light of this postulate.
Surface light-induced flux magnitude at low radiation intensities
Authors: Vaksman Michael A. , Podgorski Isabela
Published: December 2010

Surface light-induced drift (SLID) of a rarefied gas in rectangular geometry is analyzed. In the case of low radiation intensities, the expressions for SLID flux and the relative pressure drop along the cell are found to contain a factor diverging logarithmically with the rise of the parameter L/R (L is the length of the cell, R is the distance between the walls). This divergence is attributed to the contribution to the SLID flux of the molecules moving to the wall at grazing angles.
Quantization of the double pendulum
Authors: Ali M. K.
Published: December 2010

The double pendulum is one of the best tools for demonstrating classical chaos and yet its quantization has somehow escaped attention. An attempt is made to fill this gap. We show that the constraint-induced Riemann curvature scalar plays an important role in the proper quantization and evaluation of the energy spectra of this system. The quantum energies are compared with the semiclassical results obtained earlier by resumming the Birkhoff–Gustavson normal form series. The general agreement between the two sets of energies demonstrates how a proper resummation makes it possible to use a divergent normal form series for semiclassical analyses.
Calculation of the singlet–triplet energy differences using the universal function
Authors: Chen Zhifan , Msezane Alfred Z.
Published: December 2010

A method to calculate the singlet–triplet energy differences in electron–atom (molecule) scattering is developed. The method uses the recently developed universal function, which can extrapolate the generalized oscillator strength through the nonphysical region to K2 (momentum transfer squared) = 0, to calculate the integral of the energy difference in the small K2 region. Cubic spline is used for the experimental data to evaluate the contribution to the integral numerically. The energy differences in the transitions 11S–21,3P in e–He and X1 Σ+–A1,3 Π in e–CO scattering are calculated and compared with measurements as illustrative examples.
The properties of lead titanate thin films produced by chemical vapour deposition
Authors: Madsen Lynnette D. , Weaver Louise , Clark Alison J.
Published: December 2010

This project focused on advancing the knowledge of chemical vapour deposition (CVD) of lead titanate (PbTiO3) thin films for future work on lead zirconate titanate or PZT (PbZrxTi1−xO3) through an understanding of the structural, chemical, and electrical properties of the material. A low-pressure, low-temperature process for PbTiO3 was developed. The major factors in controlling the film composition and thickness uniformity were identified as substrate temperature and the partial pressures of the reactive gases. The formation sequence for CVD PbTiO3 films involved individual oxides of Ti and Pb, rather than pyrochlore-type phases. A Pb-rich composition ensured the formation of perovskite, however, it resulted in the formation of a thin PbOx surface layer. Removal of this layer by etching gave improved electrical properties. Capacitance measurements typically varied less than 1% over the frequency range and gave ε′ values from 60 to 155. At 1 kHz, tan ∂ was ~0.01 and the, resistivity was ~1011 Ω cm. Transmission electron microscopy examination of as-deposited films of PbTiO3 revealed no macrodomains existed. After post-deposition rapid thermal annealing (RTA), twinned structures, apparently acting as domains, were found in ~0.1 μm diameter grains. The multilayered bottom electrode of Pt and Ti used in this study was found to react at temperatures ≤ 515 °C. At higher RTA temperatures (698 °C), the Ti layer was completely consumed, however the top surface of the Pt layer remained unaffected.
Blackening and expansion in elastic hadron scattering
Authors: Menon Márcio José
Published: December 2010

Through a diffractive approach to elastic scattering, it is shown that hadrons become blacker and larger as the energy increases in the ISR–Tevatron domain. Comparisons are made with the predictions from geometrical models and hybrid eikonal models (Lipatov Pomeron, dual analytical approach). Connections between blackening–expansion effects and hadronic form factors – elementary amplitudes are also reviewed and discussed.
Some new formulas for multipole field calculations
Authors: Dormale Bernard M. de
Published: December 2010

We provide new formulas to compute the multipole moments of a free field from the values of a finite number of its derivatives at the origin. We also show how to replace a localized current density with point multipoles radiating the same field.
Measurement of sheath characteristics in the presence of convection and ionization
Authors: Clements R. M. , Dawe J. R. , Rizvi S. A. H. , Smy P. R.
Published: December 2010

A flame plasma whose electron and (or) ion density can be varied over several orders of magnitude is constrained to flow perpendicular to a planar grid Langmuir probe. The probe is biased negative to the plasma, and the current–voltage characteristics and the thickness of the ion sheath formed at the probe are measured. The level of the electron and (or) ion density is set within a range at which the probe current due to thermal ionization throughout the sheath is comparable with the current of ions convected into the sheath. The experimental results are compared with the predictions of a recent theoretical paper that calculates the effect of recombination upon the characteristics of planar, cylindrical, and spherical probes with boundary layer sheaths. The theoretical predictions and experimental results for an idealized planar configuration show good agreement over wide ranges of variation of probe bias and plasma electron and (or) ion density. This verification of the theoretical planar electrode – perpendicular-flow model, which is the basis for all three boundary layer relations, is seen as providing strong backing for these relations, which have application to ionization measurements in various forms of recombinant plasma.
On the integrability properties of variable coefficient Korteweg – de Vries equations
Authors: Güngör F. , Sanielevici M. , Winternitz P.
Published: December 2010

All variable coefficient Korteweg – de Vries (KdV) equations with three-dimensional Lie point symmetry groups are investigated. For such an equation to have the Painlevé property, its coefficients must satisfy seven independent partial differential equations. All of them are satisfied only for equations equivalent to the KdV equation itself. However, most of them are satisfied in all cases. If the symmetry algebra is either simple, or nilpotent, then the equations have families of single-valued solutions depending on two arbitrary functions of time. Symmetry reduction is used to obtain particular solutions. The reduced ordinary differential equations are classified.
Absolute differential cross sections for double–photon Compton scattering
Authors: Sandhu B. S. , Singh B. , Ghumman B. S.
Published: December 2010

The differential cross sections for double-photon Compton scattering were measured as functions of independent final-photon energy with the two detectors placed at 90° to the incident beam and 135° to each other. The energy of the incident photons was 661.65 keV as produced by an 8 Ci (1 Ci = 37 GBq) 137Cs radioactive source. Many systematic effects contributing to true events have been taken into account. The measured energy spectra of two emitted photons and differential cross sections agree with the theory within experimental estimated error.
Flat-field-grating demultiplexer for WDM
Authors: McGreer K. A.
Published: December 2010

A concave grating etched into a planar waveguide can be used to demultiplex signals from a wavelength division multiplexed telecommunication system. After the effective index of the waveguide is specified, a grating can be designed so that each channel receives light of desired wavelength. In the manufacturing process, the effective index of the waveguides may differ slightly from the specified value. The error will cause the wavelength of light entering each channel to shift. A design is presented here that has an input focal curve that is flat and oriented along the edge of the device. During the packaging process, the position of the input fibre along the input focal plane can be adjusted to compensate for the shift caused by an error in the effective index of the waveguide. This offers an alternative to thermal tuning and brings reasonable performance specifications of the demultiplexer within fabrication capability.
Optical waveguide intensity modulator in silicon, based on carrier injection in a Si1−xGex pin heterostructure
Authors: Fernando C. , Janz S. , Normandin R. , Noël J. P. , Tarr N. G. , Wight J. S.
Published: December 2010

A Si1−xGex pin optical waveguide modulator operating at a wavelength of λ = 1.3 μm was designed and demonstrated. The free carrier absorption by carriers injected into the i region under high forward bias was used to attenuate the guided mode intensity. Numerical simulations indicate that this structure can operate at speeds up to 200 MHz. A maximum modulation depth of 85% was measured for a 2 mm long waveguide using a peak modulation current of 4200 A cm−2.
Transparency of band-gap-shifted InGaAsP/lnP quantum-well waveguides
Authors: He J. -J. , Koteles Emil S. , Davis M. , Poole P. J. , Dion M. , Feng Y. , Charbonneau S. , Piva P. , Buchanan M. , Goldberg R. , Mitchell I.
Published: December 2010

The properties of band-gap-shifted InGaAsP/InP quantum-well waveguides were investigated. A 90 nm blue-shift of the band gap was obtained by phosphorus ion implantation followed by rapid thermal annealing. It was shown that the absorption constant at the original band edge was reduced from 110 to only 4 cm−1. No waveguide excess loss was observed due to the QW-intermixing process. Good electrical properties of the pin diode were also maintained.
Indium-induced smoothing of GaAs films during MBE growth
Authors: Lavoie C. , Pinnington T. , Tiedje T. , Hutter J. L. , Soerensen G. , Streater R.
Published: December 2010

A new technique is reported for obtaining a smooth growth surface during molecular beam epitaxy growth of GaAs on (001) GaAs substrates. The smoothing is achieved by exposing the surface to an indium flux during growth of the GaAs buffer layer at high substrate temperature (590 °C). In situ light scattering shows a dramatic reduction in surface roughness along the [110] direction during this process, consistent with ex situ scanning force microscopy measurements on the films, which reveal atomically flat terraces oriented along the <110> directions. The surface reconstruction shifts from (2 × 4) to (4 × 2) under the indium flux, as revealed by reflection high-energy electron diffraction. The sticking coefficient of the indium as determined by secondary-ion mass spectroscopy is less than 10%. We attribute the observed effects to a transition from group V to group III termination, induced by surface segregation of the nonincorporated indium.
A low-temperature ion vapor deposition technique for silicon and silicon–germanium epitaxy
Authors: Mohajerzadeh S. , Selvakumar C. R. , Brodie D. E. , Robertson M. D. , Corbett J. M.
Published: December 2010

Ion beam vapor deposition is a new technique to grow Si and SiGe layers on Si substrates at low temperatures. The growth of Si and SiGe layers reported in this paper involves ion-assisted dissociation of SiH4 into Si and H2 where Si is deposited. The Ge incorporation is achieved through thermal co-evaporation of elemental Ge. The SiGe films deposited at temperatures below 350 °C are planar and epitaxially grown, as confirmed by Rutherford back scattering, transmission electron microscopy, and electron diffraction analysis. The in situ cleaning is achieved by Ar ion bombardment followed by an in situ thermal annealing to repair the damage. Polycrystalline SiGe films are also deposited on substrate surfaces coated with a thin oxide.
Experimental investigations of anisotropic etching of Si in tetramethyl ammonium hydroxide
Authors: Naseh S. , Landsberger L. M. , Kahrizi M. , Paranjape M.
Published: December 2010

Anisotropic etching of silicon in tetramethyl ammonium hydroxide (TMAH) is receiving attention as a relatively nontoxic alternative anisotropic etchant for silicon (Si), for the fabrication of microelectromechanical systems, sensors, and actuators. This work presents experimental investigations on several aspects of anisotropic etching of Si in TMAH. The effects of temperature and concentration on etch rates of {100} and {110} wafers are characterized. Several previously unreported experimental findings aimed at better understanding the atomic level mechanisms are presented: underetch-rate variation with mask-edge deviation, an investigation of stirring, and a subtle effect of applied bending stress.
Schottky contacts to GaxIn1−xP barrier enhancement layers on InP and InGaAs
Authors: Pang Z. , Mascher P. , Simmons J. G. , Thompson D. A.
Published: December 2010

In our investigations, Au, Al, Ni, Pt, Ti, and combinations thereof were deposited on InP and InGaAs by e-beam evaporation to form Schottky contacts. The Schottky-barrier heights of these diodes determined by forward I–V and (or) reverse C–V measurements lie between 0.38–0.48 eV. To increase the Schottky-barrier height, a strained GaxIn1−xP layer was inserted between the electrode metal(s) and the semiconductor. This material, which has a band-gap larger than InP, was grown by gas-source molecular beam epitaxy. The Schottky-barrier heights, which generally depend on the gallium fraction, x, and the thickness of the strained GaxIn1−xP layer, increase and are in the range of 0.56–0.65 eV in different contact schemes.
Piezoresistance characterization of commercial CMOS gate polysilicon and its application in biomass microsensors
Authors: Chen J. M. , Parameswaran M. , Paranjape M.
Published: December 2010

This paper presents experimental results on the piezoresistance characterization of gate polysilicon available from two commercial CMOS processes. It is shown that the gate polysilicon is very strain-sensitive, and a gauge factor of about 25 can be readily achieved. This value can allow standard gate polysilicon to be used as a strain-sensing element for integrated microsensor applications. As an example, a sub-nanogram mass sensor was fabricated using commercially available CMOS technology and is presented. The device incorporates gate polysilicon of the CMOS process as the sensing material, and is subjected to low levels of strain in order to measure small masses (< 10−9 g). A potential application for this sensor is to monitor the growth of biological cell cultures in a liquid environment.
Si-Ge heterojunction bipolar technology for high-speed integrated circuits
Authors: Ahlgren D. C. , Jeng S. J. , Nguyen-Ngoc D. , Stein K. , Sunderland D. , Gilbert M. , Malinowski J. , Schonenberg K. , Soyuer M. , Meyerson B. , Harame D.
Published: December 2010

This review discusses the fundamentals of SiGe epitaxial base heterojunction bipolar transistor (HBT) technology that have been developed for use in analog and mixed-signal applications in the 1–20 GHz range. The basic principles of operation of the graded base SiGe HBT are reviewed. These principles are then used to explore the design optimization for analog applications. Device results are presented that illustrate some important trade-offs in device design. A discussion of the use of UHV/CVD for the deposition of the epitaxial base profile is followed by an overview of the integrated process. This process, which has been installed on 200 mm wafers in IBM's Advanced Semiconductor Technology Center in Hopewell Junction, N.Y., also includes a full range of support devices. The process has demonstrated SiGe HBT performance, reliability, and yield in a CMOS fabrication with the addition of only one tool for UHV/CVD deposition of the epi-base and, with minimal additional process steps, can be used to fabricate full BiCMOS designs. This paper concludes with a discussion of high-performance circuits fabricated to date, including ECL ring'oscillators, power amplifiers, low-noise amplifiers, voltage-controlled oscillators, and finally a 12-bit DAC that features nearly 3000 SiGe HBT devices demonstrating medium-scale integration.
DC extraction of the base and emitter resistances in polysilicon-emitter npn BJTs
Authors: Van V. , Deen M. J. , Kendall J. , Malhi D. S. , Voinigescu S. , Schrofer M.
Published: December 2010

Five DC techniques of extracting the base and emitter resistances of polysilicon-emitter npn bipolar junction transistors (BJTs) are presented and compared. The five techniques include three previously published techniques and two new techniques, constant base current and IB–IE plane fitting. Application of the five methods to a 0.8 × 16 μm2 npn BJT shows that all but the method of impact ionization yield comparable Rc and Rbb values at high currents. The impact ionization method, which extracts Rc and Rbb in the impact ionization region and at low base currents, yields markedly different Rc and Rbb values, indicating that the values of the parasitic resistances depend on the current range over which the extraction is performed. Thus the choice of which method is best to use depends on the current range over which Rc and Rbb are to be measured, and the validity of the assumptions used in the method when applied to the device.
Current distributions in silicon–germanium p-MOSFETs
Authors: McAlister S. P. , McKinnon W. R. , Bradford T.
Published: December 2010

Simulations of the current distributions in Si–Ge p–MOSFETs are presented for Si–Ge channel designs that have a triangular or a uniform Ge profile. The distributions of current show why the triangular design is better than the uniform Ge profile. Contributions to the transconductance in both designs are dominated by the Si–Ge channel in the −0.5 to −1.5 V gate-voltage range but the contribution to the device performance from the current parallel to the top oxide/Si interface dominates the response by −2.5 V.
High-frequency noise modelling and the scaling of the noise parameters of polysilicon emitter bipolar junction transistors
Authors: Deen M. Jamal
Published: December 2010

This paper presents detailed results from modelling the four noise parameters: minimum noise figure (NFMIN), noise resistance (RN), optimal source resistance (RS,OPT), and reactance (XS,OPT) as functions of frequency and collector-biasing current. Compared to previous BJT (bipolar junction transistor) high-frequency noise models, we include the emitter resistance, which results in an increased input device impedance, and a degeneration of the device transconductance. We also give an explicit formula for the noise resistance. We present noise results for polysilicon emitter bipolar transistors as a function of emitter areas to demonstrate how the noise parameters scale with emitter areas over a range of frequencies. However, these results are given only for devices in which the pad impedances are much larger than the device input impedance, so that very little input signal is lost through the pads to ground.
Optical characterization of silicon carbide polytypes
Authors: Bowron J. W. , Damaskinos S. , Dixon A. E.
Published: December 2010

A modified experimental scanning laser photoluminescence microscope was used to perform spatially and spectrally resolved measurements on a SiC sample. A scanning grating monochromator integrated into the detection arm of the microscope yielded a high photon collection efficiency at the detector. A cold-finger stage mounted directly onto the X-Y translation stages of the microscope allowed low-temperature PL measurements to be made. One object of the experiment was to test the hypothesis that spectrally and spatially resolved PL could be used to identify different polytypes associated with the grain structure observed in reflected light. Four different regions of the SiC sample were identified and three of these were correlated with low spatial resolution X-ray measurements and found to be polytypes 4H, 6H, and 33R–(α)SiC. Room-temperature photoluminescence was used to map the distribution of a deep impurity level and to map crystal defects. Reflected-light measurements were used to map different grain orientations of SiC. The sample was observed to be polycrystalline with most of the grains at the outer edge of the sample.