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At least 595 records · Page 33Linked to original sources
PubMed1988

Driver behavior at flashing-light, rail-highway crossings.

The risk of accident at flashing-light, rail-highway crossings has been found to be ten times higher than at crossings equipped with barriers. The purpose of the present investigation was to study driver behavior in rail-highway crossings and to relate measures of driver behavior to variables believed to be associated with increased risks of accident. About 2,000 drivers were observed in 16 different crossings with driver head movements as the major dependent variable. This variable exhibits wide variability among drivers as well as satisfactory interobserver reliability. The results showed that many drivers turned their head to look for trains in rail-highway crossings although the crossings were equipped with flashing warning lights. However, fewer drivers looked when the visibility was restricted, a factor that is associated with increased risk of accident, and in crossings with few trains per day. The conclusion from the present study is that flashing-light crossings should be designed in a way that redundant information about approaching trains should be easily available to the drivers.

Automobile Driving↗
PubMed1979

Elevations in skin temperature of the finger as an objective index of postmenopausal hot flashes: standardization of the technique.

The present study was designed to validate and standardize a technique of continuous recording of skin temperature of the finger as an objective index of hot flashes. Significant skin temperature rises (greater than 1 degree C) were recorded in close temporal relationship to 69% of subjective hot flashes experienced by seven postmenopausal women. The temperature elevations occurred at an interval of 54 +/- 10 minutes (mean +/- standard error) and lasted an average of 31 minutes. The mean increase was 2.7 degrees +/- 0.2 degrees C. The extent of the temperature elevations found in the postmenopausal subjects was significantly greater than in premenopausal control subjects (P less than 0.05) and was reduced by estrogen treatment (P less than 0.02). This study substantiates that the recording of skin temperature changes of the finger provides an objective index of hot flashes. This should assist in the investigation of the underlying disturbance and provide more accurate evaluation of modes of therapy.

Adult↗
PubMed1975

Multiple-flash activation of the water-photolysis system in wheat leaves as observed by delayed emission.

The chloroplasts from wheat leaves greened under intermittent illuminations (1 ms in duration) at long intervals (5 min) are capable of photoreducing DCIP (2,6-dichlorophenolindophenol) with diphenylcarbazide as an electron donor but are incapable of photoreducing DCIP with water as the donor. On exposure of such intermittently illuminated leaves to flashes spaced at intervals of less than 10s, the delayed light emission from the leaves was greatly enhanced in parallel with the generation of Hill activity. The mechanism of this photoactivation was studied by following the changes of the delayed emission from intermittently illuminated leaves exposed to short-interval flashes programmed in various ways. Analysis of the kinetic data indicated that the photoactivation involves three consecutive photoreactions with a rate-limiting dark reaction between them; P-light leads to A0-light leads to A1-dark leads to A2-light leads to A3 in which P is a precursor convertible to A0, the first intermediate with a longer lifetime of t 1/2 approximately 100s and A3 is the final activated compound or state converted by short-interval flashes from A0 through A1 and A2, two other intermediates with shorter lifetimes of t 1/2 approximately 0.4s and 5s, respectively.

2,6-Dichloroindophenol↗
PubMed1975

Electrical potential changes, H+ translocation and phosphorylation induced by short flash excitation in Rhodopseudomonas sphaeroides chromatophores.

1. The basal decay of the carotenoid shift of chromatophores from photosynthetic bacteria following short flash excitation is approximately biphasic. The decay indicates the dissipation of the transmembrane electrical potential. 2. The H+ efflux following rapid H+ binding after a flash, measured from the colour change of added cresol red, shows very similar kinetics to the carotenoid shift decay suggesting that the dissipation of the electric potential decay is a consequence of the H+ efflux. 3. The electric potential decay is stimulated when the chromatophore suspension is supplemented with ADP and Pi (in either the presence or absence of antimycin A). 4. The stimulated electric potential decay by ADP and Pi has a similar pH dependence to that of phosphorylation in continuous light. 5. The stimulation of the electric potential decay by ADP and Pi is reversed, by aurovertin, an antibiotic which inhibits phosphorylation. 6. The stimulation of the electric potential decay by ADP+Pi is also reversed by the inhibitors oligomycin and venturicidin. These inhibitors, but not aurovertin, also inhibit the fast phase of the decay under non-phosphorylating conditions. 7. Valinomycin accelerates the overall rate of decay of the electric potential, inhibits the ADP and Pi stimulated electric potential decay, and inhibits the flash-induced phosphorylation. The decay rate of the H+ efflux however, is slower in the presence of this ionophore. 8. Nigericin-type ionophores accelerate the overall decay rate of the H+ efflux and inhibit the ADP and Pi stimulated electric potential decay. The basal rate of the electric potential decay is unaffected by treatment with these ionophores. 9. When a coupling factor associated with the chromatophore ATPase is removed from the membrane, both the stimulation of the electric potential decay by ADP and Pi and ADP phosphorylation are inhibtied. Both reactions are completely restored after reconstitution with the crude coupling factor extract. The basal electric potential decay rate is not affected by the removal of coupling factor.

Adenosine Diphosphate↗
PubMed1976

Determination of H+/e- ratios in chloroplasts with flashing light.

Using a rapid pH electrode, measurements were made of the flash-induced proton transport in isolated spinach chloroplasts. To calibrate the system, we assumed that in the presence of ferricyanide and in steady-state flashing light, each flash liberates from water one proton per reaction chain. We concluded that with both ferricyanide and methylviologen as acceptors two protons per electron are translocated by the electron transport chain connecting Photosystem II and I. With methyl viologen but not with ferricyanide as an acceptor, two additional protons per electron are taken up due to Photosystem I activity. One of these latter protons is translocated to the inside of the thylakoid while the other is taken up in H2O2 formation. Assuming that the proton released during water splitting remains inside the thylakoid, we compute H+/e- ratios of 3 and 4 for ferricyanide and methylviologen, respectively. In continuous light of low intensity, we obtained the same H+/e- ratios. However, with higher intensities where electron transport becomes rate limited by the internal pH, the H+/e- ratio approached 2 as a limit for both acceptors. A working model is presented which includes two sites of proton translocation, one between the photoacts, the other connected to Photosystem I, each of which translocates two protons per electron. Each site presents a approximately 30 ms diffusion barrier to proton passage which can be lowered by uncouplers to 6-10 ms.

Chloroplasts↗
PubMed1977

Ubiquinone reduction and proton uptake by chromatophores of Rhodopseudomonas sphaeroides R-26: periodicity of two in consecutive light flashes.

Chromatophores of Rhodopseudomonas sphaeroides strain R-26 were subjected to a series of brief flashes of light in the presence of diaminodurene as an electron donor. Odd-numbered flashes induced the reduction of ubiquinone to the anionic semiquinone, as indicated by absorbance changes near 450 nm. This reaction was not attended by proton binding. Even-numbered flashes caused disappearance of the semiquinone, presumably by conversion to the fully reduced form. This reaction was attended by proton uptake.

Bacterial Chromatophores↗
PubMed1979

The buffering capacity of the internal phase of thylakoids and the magnitude of the pH changes inside under flashing light.

The buffering capacity inside thylakoids is determined and the magnitude of flash-induced pH changes inside is calibrated in the pH range from 6.4 to 8.1. The work is based on flash-induced absorption changes of neutral red in a chloroplast suspension in which the outer phase is strongly buffered by bovine serum albumin. It is shown that neutral red is bound inside thylakoids. The binding can be described by a simple isotherm with an apparent Km = 4 microM and satruation at 1 neutral red per 17 chlorophylls. The apparent pK of neutral red is shifted from 6.6 in solution to 7.25 when bound inside. It is demonstrated that neutral red is a clean indicator of pH changes inside, i.e. when properly used it shows no response to other events. Although bound it reports pH changes which occur in the internal osmolar (aqueous) volume of thylakoids. This is obvious from the influence of chemically very different buffers on the magnitude of the absorption changes of neutral red. These act in a manner proportional to their calculated buffering capacity in aqueous solution. The intrinsic buffering capacity of the internal phase is determined with the aid of these buffers, at pH 7.2 it is between 0.8 and 1 mM (at 60 mosM). The absence of large variations in the buffering capacity in the range from pH 6.4 to 8.1 suggests that proteinaceous groups are involved in addition to the lipids which may dominate the buffering capacity at lower pH. The magnitude of the internal pH change is arrpox. 0.6 (at pH 7.3) under stimulation of both photosystems with a short xenon flash of light.

Chloroplasts↗
PubMed1980

Periodic changes in the oxidation state of manganese in photosynthetic oxygen evolution upon illumination with flashes.

The pattern of manganese released from chloroplast membranes by a rapid temperature shock after various illumination regimes indicates that changes in the oxidation state of bound manganese occur during photosynthesis. Continuous illumination decreases by 35-40% the amount of Mn(II) released in the presence of K3Fe(CN)6 compared with a dark-adapted control. Following illumination and heat treatment, the addition of the reductant H2O2 to the samples causes an increase in the level of electron paramagnetic resonance (EPR)-detectable manganese. The pH dependence of the H2O2 reduction indicates that the non-EPR-detectable manganese present in the heated sample after illumination is in the form of higher oxidation state compounds, e.g. MnO2. The light-induced Mn(II) decrease is reversible in the dark with t 1/2 approx. 40 s and can be prevented by the presence of the Photosystem II inhibitors 3-(3,4-dichlorophenyl)-1,1-dimethyl urea or fluorocarbonylcyanide phenylhydrazone during the illumination period. After a series of brief flashes of light the Mn(II) released by heat treatment oscillates over periods of four flashes. The pattern is similar to the O2 yield flash pattern and suggests that a cycling of manganese oxidation states is involved in the O2 evolution mechanism. The oscillations in the Mn(II) release are analyzed in terms of the current four-step model for O2 evolution. The analysis suggests that manganese is successively oxidized in the first two steps, but undergoes a partial reduction on the third step. This result is consistent with the concept that water undergoes a partial oxidation prior to the release of O2 from the water-splitting complex.

Chloroplasts↗
PubMed1992

Thermoluminescence and flash-induced oxygen yield in herbicide resistant mutants of the D1 protein in Synechococcus PCC7942.

Several strains of Synechococcus PCC7942 carrying point mutations in the gene psbA were studied by thermoluminescence and polarographic measurement of flash-induced oxygen yield. The following results were obtained: (a) Replacement of Ser-264 in D1 by Ala (mutant Di1) or Gly (mutant G264) resulting in DCMU and atrazine resistance leads to a downshift of the thermoluminescence (TL) B-band peak temperature from 40 degrees C in wild-type thylakoids to about 30 degrees C. In dark adapted samples of both mutants the TL and oxygen yield pattern induced by a train of single turnover flashes were strongly damped indicative of a high miss factor. (b) In contrast to Ser-264 mutants, replacement of Phe-255 in D1 by Tyr (mutant Tyr5) induced strong resistance to atrazine but not to DCMU and did not affect the peak termperature of the B-band and the flash-induced TL and oxygen yield patterns. In this respect mutant Tyr5 resembles the wild type. (c) No significant differences have been found between strains with single site mutations in psbAI and normal psbAII/psbAIII genes, and strains with same mutations in psbAI but additional deletion of psbAII and psbAIII. Obviously in strains were psbAI is present, PS II complexes containing gene products of psbAII and psbAIII are not assembled in detectable amounts. (d) Strains with double mutations at positions 264 and 255 display a downshift of the B-band peak temperature. Their oscillatory patterns of B-band intensity and oxygen yield are highly damped. This behaviour is similar to strains D1 and G264 which are modified at position 264 only. We extend reports on additivity of mutation effects on herbicide binding to binding of QB. (e) Mutations at the QB site not only influence the binding of QB and herbicides but also change the thermoluminescence quantum yield and the lifetimes of the redox states S2 and S3 of the water oxidase. This finding might indicate long ranging effects on Photosystem II exerted by structural modifications of the QB site. From these data we conclude that Ser-264 is essential for binding of atrazine, DCMU and QB, whereas Phe-255 is involved in atrazine binding and its substitution by Tyr does not markedly affect QB or DCMU binding in Synechococcus PCC7942.

Atrazine↗
PubMed1983

Multiple component self-control program for menopausal hot flashes.

Four menopausal women served as their own controls in a study of the application of behavioral methods to the treatment of hot flashes. After a 3-or 4-week baseline period, they received 10 sessions of training in a variety of stress and temperature control techniques, including relaxation, self-suggestions of cool thoughts and images, marital contingency contracting and temperature feedback. The percentage reductions in number of flashes between the last 2 weeks of baseline and the last 2 weeks of training were 41, 75, 76 and 90 for the 4 participants. Treatment gains were maintained at 6-months follow-up. These substantial reductions in frequency of hot flashes offer strong support for the further investigation of the use of behavioral methods as alternatives or additions to medicative therapies.

Adult↗
PubMed1981

Checkerboard reversal pattern and flash VEPs in dialysed and non-dialysed subjects.

In forty-three patients suffering from chronic renal failure (CRF; 32 non-dialysed, 11 dialysed) the flash VEP and the pattern VEP to different spatial (7.5', 15', 30', 60' checks) and temporal (2, 10, 20, 40 Hz) frequencies were investigated. Abnormally delayed flash VEPs were obtained in 53.6% of the cases; transient pattern VEPs had a delayed major positive deflection in 46% of the tested eyes and altered steady-state response in 58% with a total of 65% abnormal responses. Chronically dialysed subjects showed higher levels of altered VEPs for both the techniques. The shorter latencies normally observed with coarser checks in healthy people were maintained in CRF patients, resulting in an abnormal prolongation of the shift between high and low spatial frequencies. Higher statistical correlations linked the pattern VEP with blood urea nitrogen (P less than 0.001) and other renal chemistry than the flash VEP. These and other features could be ascribed to a specific involvement of a maculo-calcarine channel devoted to 'detailed' vision and suggest the usefulness of this method to provide a tool for the early detection of an encephalopathic uraemia.

Adult↗
PubMed1989

Peak N160 of rat flash evoked potential: does it reflect habituation or sensitization?

Flash evoked potentials recorded from awake rats contain a negative peak occurring about 160 msec after the flash (N160). This peak has been associated with a specific level of arousal, and/or habituation by various authors. The current studies attempted to determine whether changes in N160 amplitude which accompany repeated testing reflect processes associated with sensitization or habituation. This paper describes experiments in Long-Evans hooded rats which demonstrate the effects of repeated testing, varying stimulus intensity, varying stimulus frequency, and discharging an alarm bell before and during a test session. Repeated testing produced increases in N160 amplitude which were greater at high than low stimulus intensities. Repeated exposure to the test chamber without flashing did not alter N160 amplitude, nor did altering stimulus rate within the range of 0.5 to 4.0 Hz. Discharging an alarm increased N160 amplitude. Taken together, the data suggest that amplitude of N160 more closely reflects sensitization to the stimulus than habituation to either the stimulus or any feature of the test situation.

Animals↗
PubMed1983

The products of photoreversing rhodopsin bleaching by microsecond flashes in the isolated vertebrate retina.

Bleaching experiments were carried out at room temperature on rhodopsin in isolated rat, frog and rat retinas with blue and orange laser flashes of very high energy and duration less than 3 microseconds. Blue flashes bleached a maximum of about 50% at the highest energies; orange ones bleached about 30% at intermediate energies but the value decreased to below 20% as the energy increased. This bleaching behaviour can be explained in terms of a kinetic model which assumes that bleaching is photoreversed during the flashes and which incorporates the relevant properties of rhodopsin, isorhodopsin, bathorhodopsin and lumirhodopsin.

Animals↗
PubMed1987

Light adaptation and responses to contrast flashes in cones of the walleye retina.

The effects of light adaptation on the intracellular responses of cones to incremental and decremental light flashes were investigated in the superfused walleye retina. The time course of light adaptation was relatively slow, some 10-20 min being required to reach steady-state conditions. Under steady-state conditions: (1) both dark-adapted and light-adapted amplitude/intensity data were well described by the Michaelis-Menten relation, (2) the incremental response did not saturate on intense backgrounds and (3) the cone sensitivity conformed closely to Weber's law. Effects of the polarity and magnitude of the flash contrast were analyzed by deriving "equivalent contrast" relations for cones and comparing the results to those of recent psychophysical experiments. Results based on the response amplitude suggest that responses to negative contrast flashes may be enhanced by post-receptor mechanisms. Results based on cone latency suggest that equivalent contrast relations for visual latency may be largely shaped in the very early, quasi-linear phase of the cone response.

Action Potentials↗
PubMed1990

The oscillatory potentials in response to stimuli of photopic intensities delivered in dark-adaptation: an explanation for the conditioning flash effect.

Previous studies reported that the oscillatory potentials (OPs) evoked to the first flash of a series were always smaller than those produced by the later flashes. This conditioning flash effect (CFE) was suggested to arise from rod inhibition of cone-mediated OPs. We investigated this CFE with the use of two stimulus intensities: 10 cd sec m-2 and 1 cd sec m-2. While the highest intensity did yield the previously reported CFE, the dimmest intensity did not. Our results further indicated that with the brightest stimulus, there is a significant increase in the interpeak interval of the OPs, while dimmest stimuli failed to reveal a similar marked increase. We also noted a significant correlation between the frequency domain of the OPs (as estimated with the interpeak interval) and the amplitude of the OPs (individual or collective: SOPs). Our results would also suggest that the observed CFE could result from a cone inhibition of rod-mediated OPs.

Adaptation, Ocular↗
PubMed1994

Separable red-green and luminance detectors for small flashes.

Detection contours were measured in L and M cone contrast coordinates for foveal flashes of 200 msec duration and 2.3, 5, 10 and 15 min arc diameter on a bright yellow field. The test flash consisted of simultaneous incremental and decremental red and green lights in various amplitude ratios. At all sizes, the most sensitive detection mechanism was not a luminance mechanism, but rather a red-green mechanism that responds to the linear difference of equally weighted L and M cone contrasts, and signals red or green sensations at the detection threshold. Both temporal and spatial integration were greater for red-green detection than luminance detection. A coincident, subthreshold, yellow flash (a luminance pedestal) did not affect the threshold of the red-green mechanism. Such a pedestal is a sum of equal L and M cone contrast--it represents a vector parallel to the red-green detection contour and thus is expected not to stimulate directly the red-green mechanism. When suprathreshold, the coincident pedestal facilitated chromatic detection by approximately 2x at all tested sizes; intense pedestals did not mask chromatic detection. This insensitivity to intense luminance pedestals further indicates that the red-green mechanism has fixed spectral tuning with balanced opponent L and M contrast inputs. This view of fixed spectral weights contrasts with the "variable tuning hypothesis", which postulates that the weights change with spatial-temporal variations in the test stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Color Perception↗
PubMed1988

Characterization of the indole triplet excited state in proteins utilizing laser flash photolysis.

The triplet-triplet absorption spectrum of the sole indole side chain of human serum albumin and its decay kinetics were previously characterized, at room temperature, by using a conventional flash photolysis method [(1978) Proc. Natl. Acad. Sci. USA 75, 1172-1175]. Exploitation of this potentially useful long lived reporter group in protein studies was limited by the excessively large sample size required by that apparatus. The 265 nm laser flash instrument used in the present work avoids this problem at the price of a loss in photo-selectivity. We report that the latter concern can be mitigated. Melittin was studied first because this polypeptide contains a single aromatic residue (W-19), and because its monomeric and tetrameric forms are good models for solvent exposed and buried indole side chains of proteins. For both forms, the indole triplet and neutral radical absorption spectra could be readily time resolved and identified on the basis of shape and differential dioxygen sensitivity. The single tryptophan containing protein human serum albumin was studied next because it contains a large number of other 265 nm absorbing moieties whose transient spectra might complicate the detection of the indole triplet. These transients were shown to not interfere significantly in the wavelength region 450 nm to 600 nm, and, in contrast to the indole triplet, they were relatively dioxygen insensitive. Thus, a facile means is available by which the indole triplet of proteins may be characterized. Subsequently the question of whether this species could be detected in the presence of nuclei acid components was investigated by flashing the phage fd. The putative nucleic acid transients were shown not to interfere and the absorbance of the indole triplet was readily time resolved. The spectral assignment was persuasively confirmed by showing that the indole triplet absorption and phosphorescence emission spectra decay with the same lifetime. The present work thus provides additional evidence for the general applicability of the indole triplet excited state as a long lived intrinsic protein reporter group.

Bacteriophages↗
PubMed1983

Circadian changes in the response of the rabbits retina to flashes.

It was previously shown that in rabbits the electroretinogram (ERG) and the visually evoked potential show a circadian rhythm consisting of a stable phase during which the animals respond to flashes with day time potentials and another phase with night time potentials (NTPs) and that the occurrence of the sharp phase transitions is programmed by the time course of the preceding light-dark schedule. From the present investigation it follows that photic sensitivity to flashes is markedly higher during the NTP-phase than in the other phase, whereas dark adaptation runs the same time course in both phases. With respect to the ERG it appears that, over a wide range of flash intensities its b wave only is affected by phase of the rhythm. The differences in photic responses between the 2 phases are discussed in the light of possibly synchronous changes in the influence of sympathetic nerve fibres on eye structures.

Animals↗