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The articles in this special feature of Measurement Science and Technology are devoted to an exciting area of fluid metrology pursuing the registration of flow velocities in three dimensions by particle holography—commonly termed holographic particle image velocimetry (HPIV) (Hinsch 2002). Already in 1993 this technique was considered to 'revolutionize the acquisition of velocity data in much the same way as did the inventions of hot wire anemometry and laser Doppler velocimetry' as E P Rood states in his foreword to the proceedings of the first workshop dedicated to the topic at the Washington ASME Fluid Engineering Conference (Rood 1993). The big step forward is to eliminate most of the depth-of-focus restrictions of classical PIV by a holographic recording of tracer particles. Thus, even non-stationary flows can be registered in a single record.A central concern of the early days was to explore optical set-ups suitable for improving particle-position resolution by using large recording apertures and for suppressing coherent noise. Furthermore, the evaluation of the holographic images required efficient hardware and software to scan and process the coordinates of particle images in a reasonable time. A sophisticated system relying on the state-of-the art experience and the utmost in processing hardware was producing first fields of thousands of three-dimensional velocity vectors (Barnhart et al 1994). Much profound research work on the main issues has been carried out in the meantime. Advances toward practical systems, however, needed fuelling by the recent technological developments of high-energy pulsed lasers and electronic image acquisition as well as the increasing performance of digital image processing.This recent progress led to a session on HPIV during the international PIV'01 conference at Göttingen, Germany (Kompenhans 2001), the creation of a worldwide working group (photon.physik.uni-oldenburg.de/hpiv) and in May 2003 an international workshop on holographic metrology in fluid mechanics at Loughborough University, UK (Coupland 2003). These workshop presentations have been elaborated and supplemented in the present special feature.The holographic velocimetry work presented here can be grouped into two sections according to the type of hologram recording—using either a physical carrier material or an electronic image sensor. Most researchers still use the somewhat anachronistic silver-halide emulsion of photographic film, especially when high resolving power is needed as in several application-specific topics. It offers still an unequalled resolution of up to 5000 line-pairs/mm at reasonable sensitivities to record even the low-power light scattered by tiny tracer particles, yet it requires laborious wet chemical processing.A good impression of the huge amount of data that can be stored on photographic film and the immense effort needed to analyse the reconstructed holographic images is given in the paper by E Malkiel et al. A straightforward in-line recording layou...

Holography is truly the key to three dimensions in particle image velocimetry, i.e. the measurement of all spatial components of the velocity vector-and this over a deep measuring field. Sophisticated instruments have been designed that successfully tackle practical problems such as the low scattering efficiency of particles, the inferior depth resolution or the aberrations and distortions in the reconstruction. Furthermore, efficient strategies are introduced to interrogate the holographic storage and process the huge amount of data towards a final flow field representation. Recently, phase-sensitive metrology, familiar in many fields of experimental mechanics, has been examined for use in particle velocimetry. Suitable methods are holographic and speckle interferometry or the optical processing of data for three-dimensional correlation. While in these techniques the power of optics is unrivalled, the practical advantage of video and digital techniques over photographic recording is obvious. The electronic version of speckle interferometry (ESPI/DSPI) is a well-established method used in laser metrology and has received further exploitation for applications in flow analysis recently. Finally, the state-of-the-art of digital particle holography is reviewed to allow estimates of its future in experimental flow analysis.

The primary structure of the 70 kDa subunit of soluble bovine guanylate cyclase, which catalyzes the formation of cyclic GMP from GTP, has been determined. The alignment of six different clones out of two bovine libraries yielded a total of 3.1 kb with a coding region of 1857 bases. The open reading frame encodes a protein of 619 amino acids and a molecular mass of 70.5 kDa. Antibodies raised against a synthetic peptide, which corresponded to the C-terminus of the deduced sequence precipitated guanylate cyclase activity from guanylate cyclase-enriched preparations.

Biochemical studies suggest that stimulation of aldosterone secretion by angiotensin II involves activation of voltage‐dependent Ca2+ channels. We used an adrenocortical cell line (Y1) to study the effect of angiotensin II on transmembranous currents. The hormone (1 nM to 1 microM) caused depolarization of the plasma membrane (from −35 to 10 mV) and elicited repetitive action potentials. Using the whole‐cell clamp technique, we identified two types of voltage‐dependent Ca2+ currents which differed with respect to their threshold potential and time course of inactivation. Angiotensin II (1 nM to 1 microM) stimulated a slowly inactivating Ca2+ current on average up to 1.7‐fold whereas a fast inactivating Ca2+ current remained almost unaffected by the hormone. Ca2+ currents were not influenced by forskolin (1 microM) or intracellularly applied cAMP (50 microM). Pretreatment of cells with pertussis toxin abolished the hormonal stimulation of the slowly inactivating Ca2+ current but was without effect on control currents. The toxin ADP‐ribosylated a single membranous peptide of 40 kd Mr. An antiserum raised against a synthetic peptide corresponding to a region common to all sequenced alpha‐subunits of guanine nucleotide‐binding proteins (G‐proteins) and an antiserum raised against a peptide corresponding to a region of alpha‐subunits of Gi‐like G‐proteins reacted with membranous 40 kd peptides, whereas an antiserum raised against a synthetic peptide corresponding to a region specific for the alpha‐subunit of the G‐protein, G0, failed to recognize a peptide in the 39 to 40 kd region.(ABSTRACT TRUNCATED AT 250 WORDS)