Pulse amplitude modulation (PAM) fluorometer techniques provide unique information on photosynthetic activity of CAM (crassulacean acid metabolism) plants such as the orchid Dendrobium spp. (cv. Viravuth Pink). CAM plants close their stomata for at least part of the day, creating a sealed compartment in the stems and leaves that precludes measurement of the light reactions of photosynthesis by any gas exchange-based method. PAM machines calculate photosynthesis as the electron transport rate (ETR) through PSII (four electrons per O 2 produced) as mol m À2 s À1. Photosynthesis-versus-irradiance (P-vs.-E) curves fitted the waiting-in-line function (ETR ¼ ETR max 3 E=E opt À Á 3 e 1ÀE=Eopt), allowing half-saturating and optimal irradiances (E opt) to be estimated. Effective quantum yield (Y max), ETR (ETR max), and the nonphotochemical quenching parameter NPQ max all vary on a diurnal (circadian) cycle, but the parameter qN max does not show a systematic variation over a diurnal period. Dendrobium Viravuth is a ''sun plant,'' with E opt between 404 and 539 mmol m À2 s À1 PAR but photosynthetic capacity is very low in the late afternoon. Total CO 2 fixed nocturnally as C4-dicarboxylic acids by leaves was only %120 mg C m À2 d À1. Titratable acid of leaves was depleted by ;1500 hours and shows a classical CAM diurnal cycle. Dendrobium Viravuth stores only enough CO 2 as C4 acids to account for ;10% of the daily gross photosynthesis estimated with the PAM machine (%1.4 g C m À2 d À1). Dendrobium Viravuth is an orchid cultivar with very limited capacity to fix and store C4 acids at night. It is probably a CAM-cycling orchid.

An analysis has been made of the dielectrophoretic ͑DEP͒ forces acting on a spheroidal particle in a traveling alternating electric field. The traveling field can be generated by application of alternating current signals to an octapair electrode array arranged in phase quadrature sequence. The frequency dependent force can be resolved into two orthogonal forces that are determined by the real and the imaginary parts of the Clausius-Mossotti factor. The former is determined by the gradient in the electric field and directs the particle either toward or away from the tip of the electrodes in the electrode array. The force determined by the imaginary component is in a direction along the track of the octapair interdigitated electrode array. The DEP forces are related to the dielectric properties of the particle. Experiments were conducted to determine the DEP forces in such an electrode arrangement using yeast cells ͑Saccharomyces cervisiate TISTR 5088͒ with media of various conductivities. Experimental data are presented for both viable and nonviable cells. The dielectric properties so obtained were similar to those previously reported in literature using other DEP techniques.

PAM (Pulse Amplitude Modulation) fluorometer techniques directly measure the light reactions of photosynthesis that are otherwise difficult to estimate in CAM (Crassulacean Acid metabolism) plants such as pineapple (Ananas comosus comosus cv. Phuket). PAM machines calculate photosynthesis as the Electron Transport Rate (ETR) through PSII (4 electrons per O 2 produced) as mol m −2 s −1 . P vs. E curves fitted the waiting-in-line function (an equation of the form ETR ¼ ETR max  ð E=E opt Þ:e 1ÀE=Eopt ) allowing half-saturating and optimal irradiances (E opt ) to be estimated. Effective Quantum Yield (Y max ), Electron Transport Rate (ETR max ) and the NonPhotochemical Quenching parameter, NPQ max all vary on a diurnal cycle but the parameter qN max does not show a systematic variation over a diurnal period. Phuket pineapple is a "sun plant" with Optimum Irradiance (E opt ) from 755 to 1,130 μmol m −2 s −1 (

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Proper models of cell geometry are needed for biophysical analysis of cellular electrical phenomena. This work compares various mathematical volume-models for normal human erythrocytes (discocyte) possessing biconcave-discoid form to simulate translational dielectrophoretic velocity spectra of erythrocyte suspensions induced in a traveling electric field over a frequency range from 1 kHz to 15 MHz. The non-spherical volumes of the oblate-spheroid, the prolate-spheroid, and the oval of Cassini and the “Bun-model” were numerically evaluated according to the normal range of cellular dimension values for mammalian erythrocytes. The latter model is the novel approach derived to provide a more realistic model for the shape of discocytes in the thin biconcave-disc form with a toroidal rim. The bun model is also more rugged than the Cassini equation. Using the actual cell dimensions for calculations, the numerical results among these calculated cell volumes revealed large and significant differences with respect to the Bun-model of +32.09%, +8.95%, and −8.45% for prolate-spheroid, Cassini's equation, and oblate-spheroid, respectively. These large volume deviations shift the magnitude of the sharp peak in dielectrophoretic velocity spectra to lower values with differences of +189.28%, +7.66%, and −9.49%, respectively. For traveling wave dielectrophoresis, similar results were found for the sharp peak of +145.76%, +7.71%, and −9.50%, respectively. The suitability of the Bun-model was verified by curve-fitting of the cell velocity spectra between experimental and theoretical curves, which gave the maximum discrepancies of less than ±10%.