Effect of transluminal angioplasty on cerebral blood flow in the management of symptomatic vasospasm following aneurysmal subarachnoid hemorrhage

In this study the authors have examined the effects of transluminal angioplasty on cerebral blood flow (CBF) in the management of intractable vasospasm following aneurysmal subarachnoid hemorrhage (SAH). Fourteen consecutively enrolled patients underwent attempted angioplasty with or without intraarterial infusion of papaverine. Twelve patients underwent pre- and postangioplasty xenon-enhanced computerized tomography (Xe-CT) scanning to measure regional CBF in 55 to 65 regions of interest (ROIs) per patient. Angioplasty was possible in 13 (93%) of 14 patients, with angiographically demonstrated improvement in all 13. Twelve (92%) of the 13 patients were neurologically improved following angioplasty; seven (58%) of the 12 patients who improved had a complete reversal of all delayed ischemic deficits. Angioplasty significantly decreased the mean number of ROIs at risk (11.4 ROIs pre- and 0.9 ROIs postangioplasty) (p < 0.00005, t-test). All patients had a reduction in the number of ROIs at risk after angioplasty; six (50%) of 12 no longer had any ROIs remaining at risk after angioplasty. Angioplasty significantly increased the mean CBF within at-risk ROIs (13 ml/100 g/minute pre- and 44 ml/100 g/minute postangioplasty) (p < 0.00005, t-test). All patients experienced an improvement in mean CBF in at-risk ROIs after angioplasty, with the mean CBF improving to above 20 ml/100 g/minute in all cases. No differences in the degree of improvement were found in patients who received intraarterial papaverine compared with those who did not. In the majority of patients with refractory vasospasm following SAH, angioplasty effectively dilated spastic arteries, reversed delayed neurological deficits, and significantly improved CBF in areas of brain at risk of infarction.     

Oscillating superleak transducer of second sound: Amplitude and linewidth

Two oscillating superleak transducers, one serving as generator, the other as detector, of first and second sound, situated at opposite ends of a one-dimensional resonance cavity, are considered. Included in the analysis are the dissipative effects of normal viscous slip and thermal diffusion through the porous membrane. The calculated amplitude and linewidth of the receiver response, both close to and away from the membrane resonance, show good agreement with available experimental data.     

Snowpack response in the Assiniboine-Red River basin associated with projected global warming of 1.0 °C to 3.0 °C

This study assesses snow response in the Assiniboine-Red River basin, located in the Lake Winnipeg watershed, due to anthropogenic climate change. We use a process-based distributed snow model driven by an ensemble of eight statistically downscaled global climate models (GCMs) to project future changes under policy-relevant global mean temperature (GMT) increases of 1.0 °C to 3.0 °C above the pre-industrial period. Results indicate that basin scale seasonal warmings generally exceed the GMT increases, with greater warming in winter months. The majority of GCMs project wetter winters and springs, and drier summers, while autumn could become either drier or wetter. An analysis of snow water equivalent (SWE) responses under GMT changes reveal higher correlations of snow cover duration (SCD), snowmelt rate, maximum SWE (SWE_max) and timing of SWE_max with winter and spring temperatures compared to precipitation, implying that these variables are predominantly temperature controlled. Consequently, under the GMT increases from 1.0 °C to 3.0 °C, the basin will experience successively shorter SCD, slower snowmelt, smaller monthly SWE and SWE_max, earlier SWE_max, and a transition from snow-dominated to rain-snow hybrid regime. Further, while the winter precipitation increases for some GCMs compensate the temperature-driven changes in SWE, the increases for most GCMs occur as rainfall, thus limiting the positive contribution to snow storage. Overall, this study provides a detailed diagnosis of the snow regime changes under the policy-relevant GMT changes, and a basis for further investigations on water quantity and quality changes.     

Der Stand der Forschung zur Erfolgsmessung von Informationssystemen

Measuring information systems (IS) success is of great interest to both researchers and practitioners. This article examines multidimensional approaches to measuring IS success and explores the current state of IS success research through a literature review and by classifying articles published between 2003 and 2007. Based on a total of 41 academic journal and conference publications, the relevant research carried out is identified, while the research results are categorized, consolidated, and discussed. The results show that the dominant empirical research analyzes the individual impact of a certain type of information system by ascertaining users’ evaluation of it by means of surveys and then applying structural equation modeling. The DeLone and McLean Information Systems Success Model is the main theoretical basis of the reviewed empirical studies. This article provides researchers with a comprehensive review and structuring of IS success research. Furthermore, opportunities for additional development are identified and future research directions suggested.     

An amorphous silicon thin film transistor: Theory and experiment

The volt-ampere characteristics for a thin film transistor fabricated with vacuum deposited amorphous silicon as the semiconductor is presented. The substrate is single crystalline silicon with a 3000 Å layer of thermally grown silicon dioxide as the insulator. The gate is a buried N⁺ phosphorus diffused region while the source and drain contacts are interdigited fingers of aluminum. By using the Cohen-Fritzsche-Ovshinsky model for the density of localized states in the mobility gap, the V_G vs I_D characteristic at small values of V_D is predicted and experimentally verified. This characteristic is used to theoretically predict the family of I_D curves for the TFT over a range of V_G and V_D. The theory and experiment agree exceptionally well below the gate-drain pinch-off, thereby verifying the theory of a TFT with a uniform distribution of traps in the band-gap.     

R-Curve Behavior and Crack-Closure Stresses in Barium Titanate and (Mg,Y)-PSZ Ceramics

R -curves, process zones, and shielding stresses of barium titanate (BaTiO₃) and partially stabilized zirconia (PSZ) have been studied using compact-tension (CT) specimens. BaTiO₃ and PSZ exhibited pronounced R -curves that rose over similar crack lengths and showed steady-state toughnesses of 0.7 and 6.4 MPa·m^1/2, respectively. Both steady-state toughnesses were ∼80% larger than the initial fracture toughnesses. Ferroelastic domain switching was the main toughening mechanism in BaTiO₃, whereas, in PSZ, transformation toughening was the main toughening mechanism. The crack process zone and crack-opening-displacement (COD) profile of each material was studied in detail using atomic force microscopy. Crack-closure-stress distributions were extracted from the COD profiles, using weight-function methods. The resulting stress profiles indicated that compressive residual stresses of 40 MPa in BaTiO₃ and 400 MPa in PSZ acted in a limited region behind the crack tip. In the PSZ, crack bridging seemed to be a competing mechanism to transformation toughening.     

Effect of MnO2 on the dielectric and piezoelectric properties of alkaline niobate based lead free piezoelectric ceramics

Lead free ferroelectric ceramics of the KNN–LiTaO₃–LiSbO₃ system were prepared using the mixed oxide route. This work reports the effect of doping (K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.1Sb_0.04)O₃ produced through the conventional solid state sintering method with different amounts of MnO₂. With 1 mol% of the dopant, ～96.5% of the theoretical density of the ceramics was achieved while grain growth inhibition was attained through pinning of the grain boundary movement. A polymorphic phase transition (PPT) was induced in the ceramic from the orthorhombic crystal structure to the tetragonal structure with increasing dopant amount. At lower temperatures, the doped samples had higher epsilon values but there was a decrease in both T_c (from 333 °C to 249 °C) and epsilon value at T_c (from ≈9500 to <6000). At temperatures below 300 °C however, the loss tangent in the doped samples (≈2.5 mol%) was much lower and steady when compared to the undoped one. The ferroelectric properties were slightly lowered with the addition of MnO₂. The remnant polarisation (P_r) was lowered from ～18 μC/cm² to ～9 μC/cm², the coercive field (E_c) from ～8.5 kV/cm to ～6.2 kV/cm and the piezoelectric charge coefficient (d₃₃) decreased as well.     

A particularly strong organic acceptor for tuning the hole-injection barriers in modern organic devices

A better understanding of metal-organic interfaces combined with means to control their properties is crucial for the further improvement of organic (opto)electronic devices. In this context, the use of organic acceptors is an efficient tool to modify metal work functions and hole-injection barriers, which has the potential to considerably improve the performance of organic devices. Here, we use density functional theory based calculations to discuss a particularly potent acceptor suitable for that purpose, 3,5-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane (F2HCNQ), which clearly outperforms the frequently applied and in the meantime prototypical system 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Comparative calculations for a single monolayer of the two molecules adsorbed on an Ag(1 1 1) surface reveal that (i) the work-function increase induced by F2HCNQ is more than 20% higher than for F4TCNQ and that (ii) at the same time the adsorption energy basically is unaffected, while (iii) the electronic structure is slightly modified. In the end of the day, F2HCNQ is a highly promising candidate for applications in organic devices.     

Effect of Ta on structure and mechanical properties of (Ti,Ta,W)(C,N)–Co cermets

The effect of Ta on the structure and mechanical properties of (Ti,Ta,W)(C,N)–Co cermets was investigated. A series of alloys of varying nominal composition were manufactured following normal powder metallurgical procedures. The alloys were characterized and their performance in metal cutting was evaluated. It was found that Ta enhances the resistance to plastic deformation (PD) of this system. By combining sets of alloys, several explanations for this enhancement could be eliminated. Plastic deformation was found to be caused by grain boundary sliding. Ta is believed to influence the interfacial energies of the system, yielding a stronger hard phase skeleton, which restricts grain boundary sliding.