For a number of years, observations have been made of contour-like patterns created by the moiré interference of a grid with its shadow cast onto a surface. The conditions under which these patterns correspond to planar contours are derived, and systems to generate these contours are suggested. It is shown that moiré contour patterns provide a useful and flexible means of contouring surfaces. Experimental results are presented.

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The reaction of pyridinio-iV-phosphonates with pyridines in aqueous buffers has been demonstrated to involve nucleophilic attack at phosphorus. The second-order rate constants obey the equation log kxpy

An optical velocimeter employing a linear array of photodiodes has been developed and utilized for measuring erythrocyte velocities in the microcirculation. A magnified image of a microvessel is projected and aligned on a one-dimensional array of photodiodes. Photocurrent from odd-ordered diodes is summed, photocurrent from even-ordered diodes is summed, and a signal proportional to the difference between these two currents is produced by a differential amplifier. The center frequency of the output signal of the differential amplifier is proportional to the erythrocyte velocity. After lowpass filtering the output of the differential amplifier, a signal proportional to its frequency and therefore velocity is produced by a frequency-voltage converter. In vitro calibration with a moving dried smear of erythrocytes illustrated a linear relation between the output of the frequency-voltage converter and erythrocyte velocity for a wide range of velocities and magnifications. The system produces a stable zero output at zero velocity and had an estimated frequency response of greater than 40 Hz in vivo. Volumetric flow rates computed from velocity and diameter measurements at arteriolar bifurcations in the rat cremaster muscle were consistent with mass conservation.

Thieno [3,4-b]pyridine (5) was synthesized by means of the successive steps of (a) photochlorination of 2,3-dimethylpyridine to the bis(chloromethy1) compound, (b) condensation with sodium sulfide, (c) oxidation to the sulfoxide, and (d) catalytic dehydration by means of alumina. Thien0[3,4c]pyridine (6) was obtained in an analogous manner. Spectral properties indicate that 5 and 6 have aromatic character.Of the six possible isomeric thienopyridines (1-6) syntheses on a preparative scale of 1 (4), 2 (5-7), 3 (6,7) and 4 (4,5a) have been reported in recent years. We now present details on the practical syntheses of thieno[3,4-6]pyridine (5) and thieno[3,4c]pyridine (6), originally reported in a brief communication (8). 6a3 Na3 N \ ' ' 3 1 2 3 4 5 6Prior to our studies parent compounds 5 and ti were unknown. Russian workers (9) had reported the condensation of a 3-aminothiophene salt with methyl vinyl ketone to give a mixture of 7-methyl-4 and 7-methyl-5. However, repetition of this reaction and structural studies on the two isolable products (4) indicated that one obtains a mixture of 5and 7-methyl-4, instead. Recently, Spinner and Yeoh (10) reported syntheses of derivatives OH (7) of the 1,3-dihydro-5 system. Treatment of 7a and 7b with acetic acid-hydrogen peroxide gave the corresponding sulfones. Methylation of 7a (with diazomethane) formed 8b, while methylation of 7b (with methyl iodide) gave a product to which an S-methyl structure was assigned. The sulfone of 8b, plus studies on ionization constants and tautomerization of hydroxy compounds, were also described.