Analysis of Transit Time Effects on Doppler Flow Measurement

A relation is derived between the transmitted spectral density and the output spectral density of broad bandwidth, random signal, Doppler flow measurement systems operating under conditions where the fluid transit time is limited by the transmitted signal bandwidth and not by beam geometry. The fact that this result is already known to hold for pulsed radio frequency (RF) Doppler proves that random or pseudorandom Dopplers will give the same output spectrum as pulsed RF Dopplers, provided that the transmitted spectral density of the RF system has the same envelope as that of the noise system.     

Evidence for regulation of cartilage differentiation by the homeobox gene Hoxc-8

Homeobox genes of the Hox class are required for proper patterning of skeletal elements, but how they regulate the differentiation of specific tissues is unclear. We show here that overexpression of a Hoxc-8 transgene causes cartilage defects whose severity depends on transgene dosage. The abnormal cartilage is characterized by an accumulation of proliferating chondrocytes and reduced maturation. Since Hoxc-8 is normally expressed in chondrocytes, these results suggest that Hoxc-8 continues to regulate skeletal development well beyond pattern formation in a tissue-specific manner, presumably by controlling the progression of cells along the chondrocyte differentiation pathway. The comparison to Hoxd-4 and Isl-1 indicates that this role in chondrogenesis is specific to proteins of the Hox class. Their capacity for regulation of cartilage differentiation suggests that Hox genes could also be involved in human chondrodysplasias or other cartilage disorders.     

Endothelium-derived relaxing factor activates calcium-activated potassium channels of resistance vessel smooth muscle cells

Direct observation was made by using the patch-clamp technique with a specially designed microperfusion system to investigate the effect of acetylcholine (Ach 10(-6) mol/L) elicited endothelium-derived relaxing factor (EDRF) on the calcium-activated potassium channel (IK(Ca)) in the smooth muscle cells of mesenteric resistance vessels in Wistar rats. Activation of IK(Ca) was firstly observed by inducing the elicited EDRF or sodium nitroprusside (SNP 10(-8) mol/L) under various clamping voltages in cell-attached configuration. While the pipette solution contained KCl 126 mmol/L and the bath solution contained KCl 5.9 mmol/L, two types of conductances of calcium-activated potassium current being 76.4 +/- 2.3 pS (mean +/- S.E. n = 7) and 160.3 +/- 7.5 pS (mean +/- S.E. n = 7) were recorded during the EDRF activation, one type of conductance being 100.5 +/- 2.8 pS (mean +/- S.E. n = 6) was activated by nitric oxide (NO) which is an effective component from SNP. Differences in kinetic characteristics of these channels between EDRF and NO activation were found, particularly the probability of the channel being open in EDRF activation was obviously greater than that in NO stimulation. It has been shown that the potassium channel mechanisms involved in the EDRF and NO actions might be different.     

Primary ciliary dyskinesia: ultrastructural defects and clinical features

Golden hamsters were exposed to conditions of 2.5 times normal gravity (hypergravity, HG) for 4 months. During this period, tests were carried out to study equilibrium maintenance, swimming behaviour and open-field behaviour of these HG hamsters and of control hamsters living in a normal-gravity environment. The tests proved to be useful devices for detecting differences in perceptive-motor behaviour between HG hamsters and control hamsters. The HG hamsters had more difficulties in balancing on tubes and orientation during swimming. In the open-field study, the HG hamsters showed less locomotor activity than control hamsters. However, no differences were observed between the groups in washing, rearing and number of times having defaecation. These findings indicate that the daily transition from 2.5 to 1 g was not experienced as stressful by the hamsters, although performance on several perceptive-motor tasks was decreased, especially during the first weeks.     

Ultrasound Doppler Probing of Flows Transverse with Respect to Beam Axis

It is an accepted fact that transverse Doppler effects of the first order in v/c are nonexistent for all physical wave phenomena, including acoustics, i.e., the Doppler effect is zero for radiation normal to the direction of motion. However, this statement assumes that the incident field is a plane wave, which is not true in general for finite aperture sources. Consequently, the probing of flows transverse to the axis of finite diameter beams, particularly focused beams, is feasible. This geometry will be advantageous in many applications where the classical orientation of the sound beam, oblique to the flow, is not possible. With this motivation in mind, the theory and experimental feasibility of measuring Doppler spectra in transverse geometries is presently investigated.     

Cre/loxP-mediated excision and amplification of large segments of the Escherichia coli genome

The isolation and amplification of large, predetermined segments of a genome from its host have been explored. The prototype of our approach was the excisional replication of some viruses such as the lambda-lysogen. Similar machinery was used to excise and amplify large genomic segments of Escherichia coli in its host. Two loxP sequences for a site-specific recombinase Cre, together with a conditional replication origin (pi-dependent gamma-ori), were inserted into the genome by homologous recombination at predetermined sites, 50-100 kb apart. Cre and pir200 which encodes the site-specific recombinase Cre and an ori-specific replication protein pi, respectively, were also introduced into the genome. The predetermined genomic segments flanked by the loxP sequences were excised and amplified upon induction of the cre and pir200 genes which were under the control of the tet promoter. This excised and amplified DNA could be easily purified as a large plasmid. This procedure can provide an alternative to conventional cloning methods by obtaining predetermined large genomic segments directly from the original organisms. In this study, using the Cre/loxP site-specific recombination and pi/gamma-ori replication system of plasmid R6K, a procedure was devised that could isolate a large segment of the E. coli genome and demonstrated the feasibility of the procedure by excising and amplifying the 50-kb trg-narZ and 100-kb trg-hipA regions of the E. coli W3110 genome.