After the primary anterior-posterior patterning of the neural plate, a subset of wnt signaling molecules including Xwnt-1, Xwnt-2b, Xwnt-3A, Xwnt-8b are still expressed in the developing brain in a region spanning from the posterior part of the diencephalon to the mesencephalon/metencephalon boundary. In this expression field, they are colocalized with the HMG-box transcription factor XTcf-4. Using antisense morpholino loss-of-function strategies, we demonstrate that the expression of this transcription factor depends on Xwnt-2b, which itself is under the control of XTcf-4. Marker gene analyses reveal that this autoregulatory loop is important for proper development of the midbrain and the isthmus. Staining for NCAM reveals a lack of dorsal neural tissue in this area. This reduction is caused by a reduced proliferation rate as shown by staining for PhosphoH3 positive nuclei. In rescue experiments, we demonstrate that individual isoforms of XTcf-4 control the development of different parts of the brain. XTcf-4A restored the expression of the mesencephalon marker genes pax-6 and wnt-2b but not the isthmus marker gene en-2. XTcf-4C, in contrast, restored en-2, but had only weak effects on pax-6 and wnt-2b. Thus, autoregulation of canonical Wnt signaling and alternative expression of different isoforms of XTcf-4 is essential for specifying the developing CNS.

The kinetics of proteins passing through individual nuclear pore complexes (NPCs) of the nuclear envelope (NE) was studied using near-field scanning optical microscopy (NSOM) in combination with fluorescence correlation spectroscopy (FCS). The NSOM probe was placed over a single pore in an unsupported native NE to observe fluorescence-labeled NTF2 moving in the transport channel. A correlation analysis of the arising fluorescence fluctuations enabled us to characterize the translocation as driven by Brownian motion and to determine the related kinetic constants. Though trapped in the pore, NTF2 turned out to be highly mobile within a large axial extension. Our findings support the idea that molecules in transit interact with NPC proteins containing phenylalanine-glycine-repeat domains at the periphery of the channel. NSOM-FCS may help to understand the facilitated translocation in more detail and offers a new way to study single molecule mobility on a nanoscale.

For investigating influences of vehicle components on the acoustic comfort at low frequencies, e.g., the booming noise behavior of a vehicle, building a whole car simulation model is useful. To reduce the model’s complexity and to save resources in the validation process, we first identify relevant components before building the model. Based on previous studies, we focus on the vehicle’s body and the rear axle. In this paper, we analyze which axle and body elements are crucial for describing road booming noise. For this purpose, we use impact measurements to examine noise transfer functions of the body and a vibro-acoustical modal analysis to identify coupled modes between the body’s structure and the interior cavity. For investigating relevant force paths from the rear axle to the body, we used a chassis test bench. We identify the main transmission paths of road booming noise and highlight which axle and body components have an influence on them. Mainly the rear axle in its upright direction in combination with a rigid body movement of the rear tailgate coupled with the first longitudinal mode of the airborne cavity causes road booming noise. Furthermore, the rear axle steering, the active roll stabilization and the trim elements of the vehicle’s body are essential to describe road booming noise. The results can be used to set priorities in the validation of individual axle and body components for future simulation models. We found that the ventilation openings, the front seats, the headliner, and the cockpit of a vehicle have little influence on its noise transfer functions from the rear axle connection points to the driver’s ear between 20 and 60 Hz.

Sound power levels were measured for an axial-flow fan and a centrifugal fan, both having 600-mm-diam impellers. One-third-octave-band sound power levels were measured by microphones at essentially free-field locations and in the test ducts for two installation configurations: "1… an open inlet and an anechoic outlet duct and "2… an open outlet and an anechoic inlet duct. Two parallelepiped ''rectangular box'' measurement surfaces and a hemispherical measurement surface were used for free-field tests. The requirement in ISO 3744 that the environmental correction be not more than 2 dB was not satisfied at some frequencies in the frequency range of interest. On average, the smallest environmental corrections were observed for the smallest measurement surface. Differences, as great as 4 dB, between the free-field sound power levels were largest at frequencies for which the environmental correction was also large. For plane sound waves, in-duct sound power levels were greater than the free-field sound power levels. At frequencies where higher-order-mode sounds propagated through the test ducts, sound power levels determined by the in-duct method were less than those determined by the free-field method. This paper discusses reasons for the differences between the sound power levels by the two methods. © 1995 Institute of Noise Control Engineering.

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