Numbers Of Flashes Research Articles

The cloud flash‐to‐ground flash ratio and other lightning occurrence characteristics in Kathmandu thunderstorms

Lightning and thunderstorm observations have been made in Kathmandu, Nepal (27.4°N, 85.2°E) over the 21‐month period March 1987 to November 1988 inclusive, using direct observations of thunder and lightning, and the registrations of a CGR3 lightning flash counter that provided records of the approximate numbers of cloud flashes, positive ground flashes, and negative ground flashes with an effective range of about 14 km. The observation period effectively covered two thunderstorm seasons as almost no lightning occurred during the winter months. During 1987 and 1988 the mean thunderdays per year was 42. The principal use of the CGR3 registrations was to estimate the long‐term ratio of cloud flashes to ground flashes, denoted z; it was found that z was 2.1 in 1987 and 3.0 in 1988, with a two‐season mean of 2.7. The uncertainty in ratio values is about 30%. The registrations also enabled lightning flash densities to be estimated with an uncertainty of about 40%. The two‐season mean ground flash, cloud flash, and total flash densities were 2.4, 6.6, and 9.0 km−2 yr−1, respectively. There were well‐marked seasonal variations in occurrence, with about 82% of all lightning occurring between mid‐February and the end of May. During this premonsoon period there were steady rises to maximum values in May of the thunderdays per month (to 10), the monthly total flash density (to 2.9 km−2 month−1), and the monthly value of z (to 3.6). The range of values of z calculated from the records for individual thunderstorm days was 0.17 to infinity, but very little lightning was associated with the extreme values. A distribution of values of the ratio with respect to cumulative lightning occurrence shows that 80% of all lightning was associated with values of z (calculated on a thunderstorm day basis) between 1.3 and 6.7. There is reasonably good agreement between the value of z for Kathmandu and values of z for other places at similar latitudes. However, major differences have been found for low latitudes between recently measured values of z and earlier predictions of the latitudinal variation of z.

Storage of abnormal oxidants ‘∑ 1’, ‘∑ 2’ and ‘∑ 3’ in photosynthetic water oxidases inhibited by Cl −-removal

The Cl − requirement of photosynthetic O 2 evolution was studied by thermoluminescence measurements with purified Photosystem II-containing membrane particles from chloroplast thylakoids. When Cl anions had been removed from the particles either by an alkaline shock in a Cl −-free medium, or by treatment with SO 2− 4, the pattern of the thermoluminescence emission after illumination with increasing numbers of flashes suggested that the oxidant storage in the water oxidase could only proceed up to the final step. The final step itself. i.e., the advance to the water-oxidizing S 4 state, apparently was blocked. An upward shift of the emission temperatures of the thermoluminescence bands was seen both in the absence and in the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethyl urea, indicating that the stored oxidants had redox properties different from those of normal, Cl −-sufficient preparations. These properties were readily interconvertible by addition or removal of Cl −. We postulate that in Cl −-deficient water oxidases abnormal S 1, S 2 and S 3 states, symbolized as ∑ 1, ∑ 2 and ∑ 3, respectively, are formed which are in a Cl −-dependent equilibrium with the corresponding normal S states. An oxidation of ∑ 3 to a ∑ 4 state is not possible. It is proposed that Cl − controls the oxidation potential of the stored oxidants by regulating events associated with the binding and/or oxidative modification of water molecules at the water oxidase.

Thermoluminescence study of charge recombination in Photosystem II at low temperatures. II. Oscillatory properties of the Z v and A thermoluminescence bands in chloroplasts dark-adapted for various time periods

The oscillations of the Z V and A thermoluminescence bands were investigated in spinach chloroplasts which had been dark-adapted for various time periods and subjected to a series of flashes at +2°C before continuous illumination at various low temperatures. When excited with continuous light below −65°C, the Z V band exhibited period-4 oscillation, with maxima on preflashes 0, 4 and 8. Above −65°C, the oscillation pattern depended greatly on the dark-adaptation period of the chloroplasts. In preilluminated samples (15 s light followed by 3 min dark), when the Q B pool is half oxidized, the oscillation of the thermoluminescence intensity measured at −50°C was similar to that observed below −65°C. However, after the thorough dark-adaptation of the chloroplasts (6 h), when the major fraction of the Q B pool is assumed to be oxidized, a binary oscillation appeared in the oscillation pattern, with maxima at odd flash numbers. Below −65°C, period-2 oscillation of the Z V band could not be induced by the dark-adaptation of the chloroplasts, suggesting an inhibition of electron exchange between Q A and Q B. Upon excitation of the chloroplasts with continuous light at −30°C, the A band oscillated with a periodicity of 4 with maxima at preflash numbers 2 and 6. At pH 7.5, the period-4 oscillation was converted into a period-2 oscillation by thorough dark-adaptation of the chloroplasts (24 h). Model calculations of the oscillatory patterns suggest that the period-4 oscillations of the Z V and A bands are determined by the concentrations [S 0] + [S 1] and [S 2] + [S 3], respectively, which are present after the preflashes prior to the low-temperature continuous illumination. The period-2 oscillations in the amplitudes of the Z V and A bands reflect the changes occurring in the redox state of the Q B pool in a sequence of flashes. The possible relationship between the characteristics of the Z V and A bands and the temperature-dependence of the S state transitions was investigated. Comparison of the amplitudal changes of the B (S 2Q − B and S 3Q − B recombination) and Q (S 2Q − A recombination) thermoluminescence bands as a function of the excitation temperature suggests that the S 2 → S 3 and S 3 → S 4 transitions are blocked at about −65 and −40°C, respectively. It is also concluded that the thermoluminescence intensity emitted by the reaction center is about twice as high in the S 3 state as in the S 2 state.

Oscillation of delayed luminescence from PS II: recombination of S 2Q −B and S 3Q −B

Luminescence decaying in the seconds to minutes time scale was studied in spinach chloroplasts and the following results were obtained: (1) After a series of flashes a slow phase which decays in the tens of seconds to minutes time scale was observed to oscillate with a pattern characteristic of S 2Q − B and S 3Q − B recombination. This phase was lost upon Tris-treatment or upon the addition of DCMU. (2) After every flash a small faster phase of luminescence decaying in the seconds time scale was also present. This phase progressively increased with increasing numbers of flashes but when methyl viologen was present no such progressive increase of this phase occurred. In the presence of DCMU this seconds time scale luminescence was greatly increased. This phase of luminescence is attributed to S 2Q − A recombination. (3) Tris-treatment resulted in the appearance of an even faster phase of luminescence which may be due to Z +Q − B recombination. These results demonstrate a close correlation of the kinetics of luminescence decay with thermoluminescence emission temperature.

Charge accumulation and recombination in Photosystem II studied by thermoluminescence. II. Oscillation of the C band induced by flash excitation

The characteristics of the thermoluminescence band appearing at +50°C in the glow curve (C band) was investigated in maize chloroplasts. The C band, which had a half-time of 10 min, could be charged in the presence of DCMU, and its amplitude significantly increased if preilluminated chloroplasts were reexcited after DCMU addition. Inactivation of the water-splitting system by hydroxylamine- or Tris-treatment did not abolish the C band. In chloroplasts subjected to various numbers of flashes before DCMU addition, the amplitude of the C band exhibited oscillation patterns which were markedly dependent upon dark adaptation of chloroplasts. Flash excitation of chloroplasts preilluminated by continuous light for 30 s prior to 5 min dark adaptation resulted in a period-4 oscillation with maxima occurring at flash numbers 0, 4, 8, 12. After a 6-h dark-adaptation of chloroplasts the period-4 oscillation was superimposed with a period-2 oscillation. The oscillatory patterns were simulated by model calculations and the possible origin of the C band is discussed.

Charge accumulation and recombination in Photosystem II studied by thermoluminescence. I. Participation of the primary acceptor Q and secondary acceptor B in the generation of thermoluminescence of chloroplasts

In the glow curves of chloroplasts excited by a series of flashes at +1°C the intensity of the main thermoluminescence band appearing at +30°C (B band; B, secondary acceptor of Photosystem II) exhibits a period-4 oscillation with maxima on the 2nd and 6th flashes indicating the participation of the S 3 state of the water-splitting system in the radiative charge recombination reaction. After long-term dark adaptation of chloroplasts (6 h), when the major part of the secondary acceptor pool (B pool) is oxidized, a period-2 contribution with maxima occurring at uneven flash numbers appears in the oscillation pattern. The B band can even be excited at −160°C as well as by a single flash in which case the water-splitting system undergoes only one transition (S 1 → S 2). The experimental observations and computer simulation of the oscillatory patterns suggest that the B band originates from charge recombination of the S 2B − and S 3B − redox states. The half-time of charge recombination responsible for the B band is 48 s. When a major part of the plastoquinone pool is reduced due to prolonged excitation of the chloroplasts by continuous light, a second band (Q band; Q, primary acceptor of Photosystem II) appears in the glow curve at +10°C which overlaps with the B band. In chloroplasts excited by flashes prior to DCMU addition only the Q band can be observed showing maxima in the oscillation pattern at flash numbers 2, 6 and 10. The Q band can also be induced by flashes after DCMU addition which allows only one transition of the water-splitting system (S 1 → S 2). In the presence of DCMU, electrons accumulate on the primary acceptor Q, thus the Q band can be ascribed to the charge recombination of either the S 2Q − or S 3Q − states depending on whether the water-splitting system is in the S 2 or the S 3 state. The half-time of the back reaction of Q − with the donor side of PS II (S 2 or S 3 states) is 3 s. It was also observed that in a sequence of flashes the peak positions of the Q and B bands do not depend on the advancement of the water-splitting system from the S 2 state to the S 3 state. This result implies that the midpoint potential of the water-splitting system remains unmodified during the S 2 → S 3 transition.

Effects of selective attention on the late components of evoked potentials in man

Vertex and specific evoked potentials to visual and cutaneous stimuli were recorded in 6 subjects. The delivery of roughly equal numbers of flashes and shocks was paced by the subjects themselves. They also had to choose which stimulus they would be given next; 9 times out of 10 the stimulus matched the subject's expectation and stimuli from the unexpected modality were given randomly 1 time out of 10 on the average. No task was required after the stimulus occurrence. Cortical evoked potentials (CEPs) to unexpected stimuli were averaged and compared with CEPs the major difference consisted in large N 2 and P 3 waves in response to unexpected stimuli; no difference was observed in the amplitude of the N 1 wave. In specific CEPs unexpected stimuli also elicited N 2 and P 3 waves; in addition N 1 showed a slight tendency to be higher in CEPs to unexpected stimuli.

The Effect of Bicarbonate on Photosynthetic Oxygen Evolution in Flashing Light in Chloroplast Fragments

The ability of bicarbonate ion (HCO(3) (-)) to stimulate photosynthetic oxygen evolution in maize chloroplast fragments exposed to continuous light depends on light intensity. Stimulation by HCO(3) (-) is less at low intensities. In HCO(3) (-)-depleted chloroplasts exposed to brief saturating light flashes, period 4 oscillations (in O(2) yield per flash) are damped within three cycles. Readdition of HCO(3) (-) to these preparations restores the oscillatory pattern to higher flash numbers, indicating that HCO(3) (-) reduces the probability of "misses" in the photosystem II reaction center. The rate of the dark relaxation reaction S(n) (') --> S(n+1) (where S refers to the oxidation state of the oxygen-evolving mechanism and n = 0, 1, or 2), after a photoact in the photosystem II reaction center, is retarded in HCO(3) (-)-depleted chloroplasts compared to the rate for this reaction in depleted chloroplasts to which HCO(3) (-) has been resupplied. However, the final oxygen-evolving reaction after the accumulation of four positive charges appears to be independent of HCO(3) (-). Bicarbonate has no effect on the dark deactivation of the higher oxidation states (S(2) and S(3)) of the positive charge-accumulating system. We propose two alternate ways in which the kinetic model of oxygen evolution developed by Kok et al. [(1970) Photochem. Photobiol. 11, 457-475] can be extended to include the action of HCO(3) (-).

The action of tetraphenylboron as a system II electron donor and its effect on the decay of the electrical field across the thylakoid membrane

The effect of tetraphenylboron on the O 2 evolution, the electron transport in normal and in Tris-washed chloroplasts, and on the decay of the electrical field across the thylakoid membrane has been investigated in spinach chloroplasts. It was found that: 1. 1. The average O 2 yield per flash as a function of the tetraphenylboron concentration is dependent on the number of excitation flashes. With increasing flash number, the tetraphenylboron concentration which is required for 50% suppression of the average O 2 yield per flash shifts toward higher values. 2. 2. After the irreversible consumption of tetraphenylboron by System II oxidizing equivalents, the O 2 evolution reappears. 3. 3. The electron flow from System II to System I, as indicated by the amplitude of the reduction kinetics of the 703 nm absorption change, remains unaffected in the tetraphenylboron concentration range and at flash numbers where the O 2 evolution is totally suppressed. 4. 4. Tetraphenylboron restores electron transport in Tris-washed chloroplasts. This tetraphenylboron-mediated electron transport is completely blocked by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). 5. 5. Preliminary titration experiments favor the assumption that tetraphenyl-boron acts in chloroplasts rather as a 1-electron donor than as a 2-electron donor. 6. 6. Tetraphenylboron accelerates the decay of the electrical field across the thylakoid membrane. Because of its ability to act as a System II electron donor, the accelerating effect on the electrical field is transitory if System II is active. By contrast, in DCMU-blocked chloroplasts with active System I electron transport [mediated by the 2,6-dichlorophenolindophenol (DCIP) cycle], a permanent accelerating effect on the electrical field is observed. From these results it has been concluded, that tetraphenylboron acts as an efficient 1-electron donor for System II. The functional integrity of the water-splitting enzyme system Y is not required for this donation. Tetraphenylboron itself does not destroy the O 2 evolution capability of chloroplasts, it rather acts as a competitive electron donor. However, an inhibitory effect arises probably from the oxidation products of tetraphenylboron. The possible modes of action of tetraphenylboron are discussed.

Increment thresholds for multiple identical flashes in the peripheral retina.

With a 1° field presented at 14° in the temporal retina, light-detection thresholds were determined for various numbers of flashes n, with each flash by itself subliminal. When the flash duration t equals the interval i between successive flashes, the threshold luminance I is described by the equation, I = a + (b/n t), where a and b are constants. This equation is analogous to the law of Blondel and Rey, I = a + (b/T), where T is the duration of a single flash. In fact, when t = i, and t equals 5, 10, or 20 ms, a plot of I vs T for single flashes is identical with a plot of I vs nt for multiple flashes. When the interval i is held constant at 30 ms, the total threshold energy E increases linearly with the number of flashes regardless of the durations of the identical flashes in the train. As the interval between two successive subliminal flashes increases, E increases until it reaches a value that is roughly equal to twice its initial value, and thereafter it remains constant.

The effect of dithionite on fluorescence and luminescence of chloroplasts

The kinetics of dithionite-induced changes in fluorescence and luminescence of isolated chloroplasts were studied as function of dithionite concentration and number of preilluminating short saturating flashes. 1. 1. The kinetics of the dithionite-induced fluorescence increase were found to be of an apparently biphasic n ature. A relatively small, rapid, increase (accounting for about 15% of the maximum increase that could be obtained with light) was followed by a “slow” increase. This second, “slow”, phase, in contrast to the first phase, was strongly dependent on the number of preilluminating flashes. It was slowest after two flashes and most rapid after three. 2. 2. The first phase of the dithionite-induced fluorescence increase was approximately correlated with reduction of the largest part of the total pool of primary and secondary acceptors of Photosystem II. 3. 3. The kinetics of luminescence induced by dithionite were correlated with the rapid phase of fluorescence increase. The highest emission intensity of luminescence was observed after two flashes, but apart from a proportionality factor the kinetics were almost the same after different numbers of flashes. The results indicate that the luminescence is produced by a reaction between an oxidized product, which is the same after different numbers of preilluminating flashes, and reduced quencher, formed mainly during the “rapid” phase of the dithionite-induced fluorescence increase. 4. 4. The results are discussed in relation to existing hypotheses, involving the existence of two primary acceptors of Photosystem II. It is argued that our results do not support these hypotheses and that the effects of dithionite may be explained in terms of a single primary acceptor (and quencher), reduced by dithionite via the secondary acceptor pool.

Sense modality switching and serial leaming

This investigation examined the effect of sense modality switching ofinformation at various positions of a serial learning task. Different numbers of flashes of light and different numbers of “blips” ofa pure tone were used as signalsin a four-position serial learning task. The design of the study involved a switch in sense modality at each one of the four possible positions in the series. Thus, it was possible to determine if the transmission of information through one sense modality makes it progressively more difficult or more time consuming to switch to another source of information transmitted through another modality. The results generally supported the contention that, as information is received through a particular modality, there is a build-up of the disruption involved in switching sense modality.

Perceptual additions with four 90 degrees arcs as stimuli.

The stimulus, 4 black 90° arcs of concentric circles, was viewed under the following three sets of conditions: (a) stroboscopic lighting of 10.5 cps with an increasing number of flashes from 1 to 95, (b) continuous stroboscopic lighting of 10.5 cps, and (c) constant lighting. Ss reported different kinds of experience apart from the perception of the 4 arcs of 90°. These include forms, mainly elongations of the 4 arcs, and additions between the 4 arcs, plus radii, the three forms of which were perceived both in stroboscopic lighting and in constant lighting. Elongations and arc additions become longer and longer with increasing numbers of stroboscopic flashes, and at a certain number of flashes they often grow into circles of 360°. When the number of stroboscopic flashes is increased Ss usually observe an increasing number of radii which, for instance, around 15 flashes reach maximum number of about 16. Elongations and arc additions of 360° and a great number of radii often appear under continued stroboscopic lighting. This new perceptual situation elicits characteristic results from each S, but most Ss form groups with particular characteristics.