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151.
KT Baudendistel JR Reichenbach R Metzner J Schroeder LR Schad 《Canadian Metallurgical Quarterly》1998,16(8):989-991
Functional magnetic resonance imaging (fMRI) of the brain using blood oxygenation level dependent (BOLD) contrast relies on the changes of paramagnetic deoxyhemoglobin concentration, which affects brain parenchyma and draining venous vessels. These changes in deoxyhemoglobin concentration in venous vessels can also be monitored using a high-resolution susceptibility-based MR-venography technique. Four volunteers participated in the study in which functional MR-venograms were compared with conventional echo-planar imaging (EPI)-BOLD-fMRI. In all cases, small venous vessels could be identified close to the areas of activation detected by conventional fMRI. In the venograms, task performance (finger tapping) resulted in a loss of venous vessel contrast compared to the resting state, which is consistent with a local decrease of deoxyhemoglobin concentration. MR-venography allows a direct visualization of the BOLD-effect at high spatial resolution. In combination with conventional fMRI, this technique may help to separate the contribution of brain parenchyma and venous vessels in fMRI studies. 相似文献
152.
Two-dimensional cubic convolution 总被引:2,自引:0,他引:2
The paper develops two-dimensional (2D), nonseparable, piecewise cubic convolution (PCC) for image interpolation. Traditionally, PCC has been implemented based on a one-dimensional (1D) derivation with a separable generalization to two dimensions. However, typical scenes and imaging systems are not separable, so the traditional approach is suboptimal. We develop a closed-form derivation for a two-parameter, 2D PCC kernel with support [-2,2]/spl times/[-2,2] that is constrained for continuity, smoothness, symmetry, and flat-field response. Our analyses, using several image models, including Markov random fields, demonstrate that the 2D PCC yields small improvements in interpolation fidelity over the traditional, separable approach. The constraints on the derivation can be relaxed to provide greater flexibility and performance. 相似文献
153.
Tomislav B. Šekara 《Electrical Engineering (Archiv fur Elektrotechnik)》2006,89(2):137-147
The novel transformation polynomials for discretization of analogue systems have been presented. A generalization of some
of the existing transformation methods has also been done. A comparative analysis, through the corresponding examples involving
several known discretization methods, has been carried out. It has been demonstrated that the application of these transformation
polynomials allows the reduction of discretization error compared to other approximation methods. The response to an arbitrary
excitation of the discrete system obtained by these transformations is approximately equal to that of the original analogue
system. The transformations are rational since variable s
−
n
,n ∈ N, transforms to the quotient of two linear functions of variable z. 相似文献
154.
Tomislav Sonja Mislav 《AEUE-International Journal of Electronics and Communications》2008,62(2):148-154
This paper presents a novel algorithm for intermodulation products counting in multicarrier systems. Intermodulation products are caused by the nonlinearity of the amplifiers’ transfer characteristic. Along the transmission network, broadband amplifiers are needed to boost up the signal level and compensate the signal attenuation. When the number of carriers increases, the number of intermodulation products also increases extremely fast. In our approach, selective counting procedure by grouping intermodulation products was introduced. The presented solution shows considerable reduction in computational effort in counting the number of intermodulation products in the individual channel, especially if the number of products is very large. 相似文献
155.
Processing images acquired by multi-camera systems is nowadays an effective and convenient way of performing 3D reconstruction.
The basic output, i.e. the 3D location of points, can easily be further processed to also acquire information about additional
kinematic data: velocity and acceleration. Hence, many such reconstruction systems are referred to as 3D kinematic systems
and are very broadly used, among other tasks, for human motion analysis. A prerequisite for the actual reconstruction of the
unknown points is the calibration of the multi-camera system. At present, many popular 3D kinematic systems offer so-called
wand calibration, using a rigid bar with attached markers, which is from the end user’s point of view preferred over many
traditional methods. During this work a brief criticism on different calibration strategies is given and typical calibration
approaches for 3D kinematic systems are explained. In addition, alternative ways of calibration are proposed, especially for
the initialization stage. More specifically, the proposed methods rely not only on the enforcement of known distances between
markers, but also on the orthogonality of two or three rigidly linked wands. Besides, the proposed ideas utilize common present
calibration tools and shorten the typical calibration procedure. The obtained reconstruction accuracy is quite comparable
with that obtained by commercial 3D kinematic systems. 相似文献
156.
Tomislav Reichenbach 《Artificial Life and Robotics》2009,13(2):561-565
Computer simulation is an essential step in the design and construction of various mechanical structures, including biped
robots, because it enables rapid testing and virtual prototyping during the construction phase. Although many different simulators
are available, this article gives an overview and a motivation for building a new dynamic multibody simulator. The simulator
is especially adapted to humanoid robot Archie, developed at the IHRT Institute at the Technical University of Vienna. In
addition, it is shown how the simulator can be used not only in the controller design, but also in the online control loop
to extend the available sensors: a virtual sensors principle.
This work was presented in part at the First European Workshop on Artificial Life and Robtics, Vienna, Austria, July 12–13,
2007 相似文献
157.
Goran Petrovic Tomislav Kilic Bozo Terzic 《Mechanical Systems and Signal Processing》2009,23(3):931-939
In this paper a sensorless speed detection method of induction squirrel-cage machines is presented. This method is based on frequency determination of the stator neutral point voltage primary slot harmonic, which is dependent on rotor speed. In order to prove method in steady state and dynamic conditions the simulation and experimental study was carried out. For theoretical investigation the mathematical model of squirrel cage induction machines, which takes into consideration actual geometry and windings layout, is used. Speed-related harmonics that arise from rotor slotting are analyzed using digital signal processing and DFT algorithm with Hanning window. The performance of the method is demonstrated over a wide range of load conditions. 相似文献
158.
Sanja Vidaček Tibor Janči Zdenka Brdek Doris Udovičić Nives Marušić Helga Medić Tomislav Petrak Igor Lacković 《International Journal of Food Science & Technology》2012,47(8):1757-1764
The potential of electrical impedance was investigated to differentiate thawed sea bass fillets (Dicentrarchus labrax) previously subjected to different freezing conditions. The HP 4284A Precise LCR meter was used to measure impedance magnitude (|Z|) and phase (?) at 27 frequencies from 0.1 to 1000 kHz. A needle‐type multi electrode array was tested as a probe for impedance measurements. The study showed that fast and non‐invasive control method based on measurement of ? on thawed fillets could assess the freezing conditions of white fish at higher frequencies of measurements (500–1000 kHz). The advantages of ? when compared with |Z| include its independence on temperature, on puncture depth of the probe and on duration of storage prior to freezing. Usage of a needle‐type multi electrode array reduced the effect of muscle tissue anisotropy; however, even at 1 MHz, the differences in electrical measurements varied around 10–11% depending on muscle fibre direction. 相似文献
159.
Joaquim Salvi Author Vitae Sergio Fernandez Author Vitae Tomislav Pribanic Author Vitae 《Pattern recognition》2010,43(8):2666-2680
Shape reconstruction using coded structured light is considered one of the most reliable techniques to recover object surfaces. Having a calibrated projector-camera pair, a light pattern is projected onto the scene and imaged by the camera. Correspondences between projected and recovered patterns are found and used to extract 3D surface information. This paper presents an up-to-date review and a new classification of the existing techniques. Some of these techniques have been implemented and compared, obtaining both qualitative and quantitative results. The advantages and drawbacks of the different patterns and their potentials are discussed. 相似文献
160.