Magnetic resonance imaging of disseminated sclerosis

Multiple sclerosis is a chronic demyelinating disease. Paraclinical examinations may contribute to the diagnosis of multiple sclerosis. Magnetic resonance imaging (MRI) has a very high sensitivity concerning multiple sclerosis, and has made it possible to visualize multiple sclerosis plaques in vivo, to follow each plaque over the course of time and in this way to obtain information about the pathogenesis. MRI has shown that the size of plaques may vary considerably, and that plaques are dynamic structures with the ability to change in size over few weeks. By using MRI and the contrast agent Gadolinium-DTPA, it is possible to distinguish a newly developed plaque from an older one. Therefore, MRI has become an important examination in therapeutic trials. Just now, MRI with Gadolinium-DTPA is being used to evaluate the efficacy of plasmapheresis and immunoglobulin treatment in a joint study between Rigshospitalet and Hvidovre Hospital.     

Synchronization of quadrature-quadrature phase-shift keying signals

The key synchronization aspects in the system design of a QQPSK (quadrature-quadrature phase-shift-keying) modem are addressed. The sensitivity of the data demodulator to synchronization errors is discussed, and contextually the performances of some IF and baseband carrier phase and symbol timing recovery schemes are evaluated both theoretically and by computer simulations. In particular, a fourth-power IF carrier/clock regenerator and two baseband clock recovery schemes, with and without the aid of data decisions, respectively, are taken into account. The analysis shows on the one hand the substantial robustness of QQPSK to carrier phase errors and the adequacy of the examined carrier extraction scheme. On the other hand, the remarkable sensitivity of QQPSK to symbol timing inaccuracy is stressed and the need to resort to the newly proposed decision-aided baseband clock recovery scheme is pointed out     

Inhibition of monocyte leukotriene B4 production after aspirin desensitization

Aspirin-sensitive patients may be desensitized through a graded series of exposures to aspirin. We investigated the underlying mechanism of aspirin desensitization by measuring the release of leukotrienes B4 and C4 from calcium ionophore-stimulated peripheral blood monocytes. Compared with monocytes from normal volunteers (n = 5), monocytes from patients with aspirin-sensitive asthma (n = 10) released increased amounts of thromboxane B2 (1060 +/- 245 pg/ml vs 456 +/- 62 pg/ml), leukotriene B4 (861 +/- 139 pg/ml vs 341 +/- 44 pg/ml), and leukotriene C4 (147 +/- 31 pg/ml vs 56 +/- 6 pg/ml) at baseline. After aspirin desensitization, thromboxane B2 release was almost completely suppressed in both groups. Leukotriene B4 release was significantly decreased in the aspirin-sensitive group (484 +/- 85 pg/ml) but not in the normal subject group (466 +/- 55 pg/ml). The need for prednisone decreased significantly after patients were desensitized to aspirin (10.4 +/- 2.2 mg/day to 1.6 +/- 2.8 mg/day). These results demonstrate that desensitization to aspirin results in decreased monocyte leukotriene B4 release. On the basis of the bronchospastic and inflammatory potential of leukotrienes, the decrease in leukotriene release may contribute to the clinical improvement seen after aspirin desensitization.     

Investigations of two-stage-pseudospark switches for high-currentapplications

To avoid the lowering of the holdoff voltage due to the electrode erosion in one stage high current pseudospark switches (PSS), a two stage PSS with no axial aperture in the intermediate electrode was tested. For investigations a pulse generator was used generating peak currents up to 120 kA at a maximum voltage of 30 kV with a period length of 5 μs of a weakly damped sine wave with 90% current reversal. In comparison with a one stage PSS the breakdown characteristic was shifted to higher pressure. With a free floating intermediate electrode, the device could not be triggered, however, with additional capacities of a few nF between the three electrodes the discharge was ignited. The discharge in the second gap is triggered by the pseudospark discharge in the cathode gap, discharging the auxiliary capacities. Simultaneously, observation of both gaps with fast shutter photography showed an independent movement of the discharges in the two gaps. In the cathode gap as current increases, the discharge moves away from the center to the plane electrode surface as has been observed in the one stage PSS. However, in the anode gap the discharge moves away from the center after a contraction to the center. The two discharges are transmitted to metal vapor arc type discharges as the erosion patterns prove. With this kind of a two stage PSS holdoff voltages exceeding 35 kV would be possible. The characteristic switch data, i.e., delay and jitter, are nearly equal to a one stage PSS     

Creating geometrically robust designs for highly sensitive problems using topology optimization

Resonance and wave-propagation problems are known to be highly sensitive towards parameter variations. This paper discusses topology optimization formulations for creating designs that perform robustly under spatial variations for acoustic cavity problems. For several structural problems, robust topology optimization methods have already proven their worth. However, it is shown that direct application of such methods is not suitable for the acoustic problem under consideration. A new double filter approach is suggested which makes robust optimization for spatial variations possible. Its effect and limitations are discussed. In addition, a known explicit penalization approach is considered for comparison. For near-uniform spatial variations it is shown that highly robust designs can be obtained using the double filter approach. It is finally demonstrated that taking non-uniform variations into account further improves the robustness of the designs.     

3D interactive topology optimization on hand-held devices

This educational paper describes the implementation aspects, user interface design considerations and workflow potential of the recently published TopOpt 3D App. The app solves the standard minimum compliance problem in 3D and allows the user to change design settings interactively at any point in time during the optimization. Apart from its educational nature, the app may point towards future ways of performing industrial design. Instead of the usual geometrize, then model and optimize approach, the geometry now automatically adapts to the varying boundary and loading conditions. The app is freely available for iOS at Apple’s App Store and at http://www.topopt.dtu.dk/TopOpt3D for Windows and OSX.     

The Formation of Calcified Nanospherites during Micropetrosis Represents a Unique Mineralization Mechanism in Aged Human Bone

Osteocytes—the central regulators of bone remodeling—are enclosed in a network of microcavities (lacunae) and nanocanals (canaliculi) pervading the mineralized bone. In a hitherto obscure process related to aging and disease, local plugs in the lacuno‐canalicular network disrupt cellular communication and impede bone homeostasis. By utilizing a suite of high‐resolution imaging and physics‐based techniques, it is shown here that the local plugs develop by accumulation and fusion of calcified nanospherites in lacunae and canaliculi (micropetrosis). Two distinctive nanospherites phenotypes are found to originate from different osteocytic elements. A substantial deviation in the spherites' composition in comparison to mineralized bone further suggests a mineralization process unlike regular bone mineralization. Clearly, mineralization of osteocyte lacunae qualifies as a strong marker for degrading bone material quality in skeletal aging. The understanding of micropetrosis may guide future therapeutics toward preserving osteocyte viability to maintain mechanical competence and fracture resistance of bone in elderly individuals.     

Monoethlenic C20 and C22 fatty acids in marine oil and rapeseed oil. Studies on their oxidation and on their relative ability to inhibit palmitate oxidation in heart and liver mitochondria

1. Carnitine esters of erucic acid (22:1 n-9 cis), cetoleic acid (22:1 n-11 cis), brassidic acid (22:1 n-9 trans), gadoleic acid (20:1 n-9 cis) and oleic acid (18:1 n-9 cis) have been compared as mitochondrial substrates and as inhibitors of palmitoylcarnitine oxidation in heart and liver mitochondria. 2. Both the rate of intramitochondrial-CoA acylation and the rate of beta-oxidation decreases as the chain length increases from C18 to C22. There are no significant differences among the three C22 isomers as oxidizable substrates. 3. All the tested acylcarnitines inhibit palmitoylcarnitine oxidation. The C18 and C20 acylcarnitines inhibit by virtue of being competing substrates; i.e. the respiration is not inhibited. The C22-isomers inhibit also respiration; this shows that the inhibition of palmitolycarnitine oxidation is not compensated for by oxidation of C22-acylcarnitines. Brassidoylcarnitine inhibits the oxidation of palmitoylcarnitine and respiration less than erucoyl-and cetoleoylcarnitine. The different behaviour of the C22-isomers is probably due to the difference in their competitive properties with respect to long-chain acyl-CoA dehydrogenase. 4. All C22 acylcarnitines seem to be relatively better oxidized in the liver than in the heart mitochondria while their inhibitory effect on the usage of the radioactive palmitoylcarnitine is very similar. 5. Palmitoylcarnitine inhibits almost completely the "endogenous" formation of acetyl-CoA presumably from malate via pyruvate in the liver mitochondria while the C22-acylcarnitines cause only a partial inhibiton of this acetyl-CaO formation.     

Constitutive equations for the nonlinear elastic response of rubbers

Summary A constitutive model is derived for the elastic behavior of rubbers at three-dimensional deformations with finite strains. An elastomer is thought of as an incompressible network of flexible chains bridged by permanent junctions that move affinely with the bulk medium. The constraints imposed by surrounding macromolecules on configurations of an individual chain are introduced by combining the Flory–Erman and Erman–Monnerie approaches. To describe inter-chain interactions in a tractable way, the conventional picture of a tube where a chain is confined is replaced by geometrical restrictions on the positions of its ends and center of mass. The constraints on the chain ends are formulated within the traditional Flory concept, whereas those on the position of center of mass are described following the Ronca–Allegra scenario. Stress–strain relations for a network of constrained chains are derived by using the laws of thermodynamics. The constitutive equations involve four adjustable parameters with transparent physical meaning. The material constants are found by fitting experimental data on elastomers at uniaxial and equi-biaxial tensions and pure shear. It is demonstrated that (i) the model provides an acceptable prediction of stresses in a test with one deformation mode, when its parameters are found by matching observations in an experiment with another mode, and (ii) material constants are affected by chemical composition of elastomers in a physically plausible way.     

Wafer Direct Bonding: From Advanced Substrate Engineering to Future Applications in Micro/Nanoelectronics

Wafer direct bonding refers to the process of adhesion of two flat mirror-polished wafers without using any intermediate gluing layers in ambient air or vacuum at room temperature. The adhesion of the two wafers occurs due to attractive long range van der Waals or hydrogen bonding forces. At room temperature the bonding energy of the interface is low and higher temperature annealing of the bonded wafer pairs has to be carried out to enhance the bonding energy. In this paper, we describe the prerequisites for the wafer-bonding process to occur and the methods to prepare the suitable surfaces for wafer bonding. The characterization techniques to assess the quality of the bonded interfaces and to measure the bonding energy are presented. Next, the applications of wafer direct bonding in the fabrication of novel engineered substrates such as "silicon-on-insulator" and other "on-insulator" substrates are detailed. These novel substrates, often called hybrid substrates, are fabricated using wafer bonding and layer splitting via a high dose hydrogen/helium implantation and subsequent annealing. The specifics of this process, also known as the smart-cut process, are introduced. Finally, the role of wafer bonding in future nanotechnology applications such as nanotransistor fabrication, three-dimensional integration for high-performance micro/nanoelectronics, nanotemplates based on twist bonding, and nano-electro-mechanical systems is discussed