The objective gradation of stenosing coronary artery processes by means of the quantification of pathologic-anatomical data and their relations. 2. Development and presentation of the model

In order to objectify the judgement of the coronary arteriosclerosis the influence values position x obstruction on the left side and on the right side as well as the mass of the heart are mathematically valued with the aim to achieve a good separation between the infarction group and the control group and an insignificant false coordination of test persons. The optimation carried out for this purpose must be brought into accordance by means of technically ascertained recognitions and necessary practicability concerning valuations which are to be proposed. According to the results obtained on 174 test persons an obstruction on the right side below 50% has a higher importance than on the left side. In the positions of the obstruction the proximal as well as the medium third of the right coronary arteries a higher valuation must be ascribed. Compared with this the trunk of the left coronary artery has a significance corresponding possibly to the proximal third of this vessel. A more insignificant importance than hitherto taken into consideration belongs to the medium third of the left coronary artery. The valuations proposed lead to a highly significant improvement of the separation ability in contrast to the comparable valuations. The false coordination of the test persons at the same time decreases to 11 in the group with infarctions and to 2 in the control group. This equals 10.1 or 4.5%, respectively. In the present number of patients the barriers of the ostium and the type of supply have no statistically ascertained influence on the separation ability.     

Complex hydrides as solid storage materials: First safety tests

Hydrogen technology requires efficient and safe hydrogen storage systems. For this purpose, storage in solid materials, such as high capacity complex hydrides, is studied intensely. Independent from the actual material to be used eventually, any tank design will combine nanoscale powders of highly reactive material with pressurized hydrogen gas and so far, little is known about the behavior of these mixtures in case of incidents. For a first evaluation of a complex hydride in case of a tank failure, NaAlH₄ (doped with Ti) was investigated in a small-scale tank failure test. 80–100 ml of the material was filled into a heat exchanger tube, and sealed under argon atmosphere with a burst disk. Subsequently, the NaAlH₄ was partially desorbed by heating. When the powder temperature reached 130 °C and the burst disk ruptured at 9 bar hydrogen overpressure the behavior of the expelled powder was monitored using a high speed camera, an IR camera as well as sound level meters. Expulsion of the hydrogen storage material into (dry) ambient atmosphere yields a dust cloud of finely dispersed powder which does not ignite spontaneously. Similar experiments including an external source of ignition (spark/water reacting with NaAlH₄) yield a flame of reacting powder. The intensity will be compared to the reaction of an equivalent amount of pure hydrogen.     

Accurate extraction of the mechanical properties of thin films by nanoindentation for the design of reliable MEMS

Traditional procedures for the extraction of mechanical properties of thin films by nanoindentation measurements have shown problems in terms of accuracy and in the ability to support sophisticated constitutive models. In this paper, an inverse modeling procedure based on finite element analysis is presented to solve these limitations. Finite element simulation is used to predict the relationships between the indentation load and depth. The developed approach is applied to extract the viscoplastic properties of aluminum single grain, the viscoelastic properties of acrylic resin films, and the residual strain in stainless steel.     

Zirconia with Defined Particle Morphology and Hierarchically Structured Pore System Synthesized via Combined Exo‐ and Endotemplating

Highly porous zirconia with defined particle morphology can be prepared by impregnation of spherical activated carbon as an exotemplate with a zirconia nanoparticle sol. The resulting zirconia spheres show a particle size distribution between 0.2 and 0.4 mm and exhibit high specific surface areas and specific pore volumes up to 104 m²g^–1 and 0.56 cm³g^–1, respectively. Addition of a triblockcopolymer (TBC) as an endotemplate during the synthesis leads to the formation of an additional pore system. The corresponding spherical zirconia products possess a hierarchically structured pore system with a bimodal pore size distribution with maxima at ca. 3 and 20 nm. The relative fraction of pores originating from the endotemplate can be varied by changing the endotemplate content in the zirconia nanoparticle sol. The presence of the TBC also has an influence on the specific surface area and the specific pore volume. Using the ratio of TBC to zirconium of n_TBC/n_Zr = 0.027, a material can be prepared that exhibits a specific surface area and a specific pore volume of 161 m²g^–1 and 0.62 cm³g^–1, respectively. These values are more than twice as high as for zirconia prepared by a conventional precipitation method (68 m²g^–1 and 0.11 cm³g^–1, respectively).     

Cover Picture: Nanotechnological Aspects in Materials for Hydrogen Storage (Adv. Eng. Mater. 6/2005)

The cover shows the schematic structure of an aluminum and magnesium containing hydrogen storage material. More about nanotechnological aspects in materials for hydrogen storage can be found in the article by M. Fichtner on page 443. A nanotechnological app#roach aims at making tailor‐made developments for storage materials by combining different scientific disciplines and focussing on processes on the microscale. The approach has already been successful in achieving major advances in the field of novel solid materials for hydrogen storage. However, further breakthroughs are necessary to reach the goal of storage systems for fuel cell‐driven, mobile applications.     

Experimental study of powder bed behavior of sodium alanate in a lab-scale H2 storage tank with flow-through mode

Chemical hydrogen storage in complex hydrides offers the potential of high gravimetric storage densities compared to intermetallic hydrides, and is therefore a promising technology for mobile applications. The main challenge for mobile application is still the required high refuelling rate of the hydrogen storage tanks. Since hydrogen is bonded by an exothermal chemical reaction in complex hydrides, appropriate storage tanks require high heat transfer rates for the cooling of the tank. Hydride tanks that are state of the art rely on an indirect cooling and are additionally equipped with e.g. finns, foams, etc. to improve the heat transfer rate. For the present study, an improved laboratory tank, which allows for indirect as well as direct cooling by excess H₂ gas (flow-through mode), has been designed and built. This laboratory tank is filled with 87 g of NaAlH₄ (doped with 2 mol% CeCl₃) and equipped with 8 thermocouples as well as two pressure sensors. Experimental results presented in this paper show a significant influence of the cooling by gaseous excess H₂ on the flow-directional temperature profiles at the part of the reaction bed close to the inlet. Considering the overall conversion, this influence is rather small due to the low heat capacity flux (ρc_p)_H2. Furthermore, it is shown that changes in material properties, attributed to the effects of heat and mass transport as well as intrinsic reaction kinetics, can be measured and assessed by the temperature and pressure sensors. After about 10 complete charging and discharging cycles, the initial permeability K of the bed has decreased by 50% to 1.6·10⁻¹² m². In the same time, the initial thermal conductivity has increased by a factor of 1.3 to values reported in literature (0.67 Wm⁻¹ K⁻¹) and remains constant during further cycles. Additionally, it is observed that the reaction rate of the second absorption step improves, even after a total of 36 cycles.     

Influence of nanoconfinement on morphology and dehydrogenation of the Li11BD4-Mg(11BD4)2 system

The decomposition of a nanoconfined mixture of lithium-magnesium borohydride, Li(11)BD(4)-Mg((11)BD(4))(2), has been investigated and compared to the corresponding mixture in the bulk form. The systems were investigated by thermal analysis, small-angle neutron scattering, (11)B nuclear magnetic resonance and transmission electron microscopy. The dehydrogenation temperatures decreased by up to 60?°C in the nanoconfined system, with gas evolution following different steps, compared to the behaviour of the bulk material under the same conditions. Most importantly, desorption from the nanoconfined hydride proceeds without formation of diborane, B(2)D(6), which evolves from the bulk mixture. From small-angle neutron scattering, differences in morphology between the bulk and the nanoconfined systems are also demonstrated. Evidence of a complete decomposition has been found in the nanoconfined system, after heating up to 460?°C. Furthermore, (11)B NMR data show that nanoconfinement inhibits the formation of dodecaborane, [B(12)D(12)](2-), during decomposition, a result which is important for practical applications of borohydrides.     

Efficient Monte Carlo device modeling

A single-particle approach to full-band Monte Carlo device simulation is presented which allows an efficient computation of drain, substrate and gate currents in deep submicron MOSFETs. In this approach, phase-space elements are visited according to the distribution of real electrons. This scheme is well adapted to a test-function evaluation of the drain current, which emphasizes regions with large drift velocities (i.e., in the inversion channel), a substrate current evaluation via the impact ionization generation rate (i.e., in the LDD region with relatively high electron temperature and density) and a computation of the gate current in the dominant direct-tunneling regime caused by relatively cold electrons (i.e., directly under the gate at the source well of the inversion channel). Other important features are an efficient treatment of impurity scattering, a phase-space steplike propagation of the electron allowing to minimize self-scattering, just-before-scattering gathering of statistics, and the use of a frozen electric field obtained from a drift-diffusion simulation. As an example an 0.1-μm n-MOSFET is simulated where typically 30 minutes of CPU time are necessary per bias point for practically sufficient accuracy