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PubMed1999

Modulation of flash-induced photosystem II fluorescence by events occurring at the water oxidizing complex.

The mechanism of flash-induced changes with a periodicity of four in photosystem II (PSII) fluorescence was investigated with the aim of further using fluorescence measurements as an approach to studying the structural and functional organization of the water-oxidizing complex (WOC). The decay of the flash-induced high fluorescence state of PSII was measured with pulse amplitude modulated fluorometry in thylakoids and PSII enriched membrane fragments. Calculated QA- decay was well described by three exponential decay components, reflecting QA- reoxidation with halftimes of 450 and 860 micros, 2 and 7.6 ms, and 111 and 135 ms in thylakoids and PSII membranes, respectively. The effect of modification of the PSII donor side by changing pH or by removal of the extrinsic 17 and 24 kDa proteins on period four oscillations in both maximum fluorescence yield and the relative contribution of QA- reoxidation reactions was compared to flash-induced oxygen yield. The four-step oxidation of the manganese cluster of the WOC was found to be necessary but not sufficient to produce modulation of PSII fluorescence. The capacity of the WOC to generate molecular oxygen was also required to observe a period four in the fluorescence; however, direct quenching by oxygen was not responsible for the modulation. Potential mechanisms responsible for the periodicity of four in both maximum fluorescence yield pattern and flash-dependent changes in proportion of centers with different QA- reoxidation rates are discussed with respect to intrinsic deprotonation events occurring at the WOC.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed2001

Laser flash photolysis study of Jacobsen catalyst and related manganese(III) salen complexes. Relevance to catalysis.

The laser flash photolysis and emission properties of a set of five-coordinate manganese(III) Schiff-base complexes have been examined. In contrast to the intramolecular electron transfer between Mn3+ and the equatorial salen ligand reported to occur in the absence of axial coordination, our laser flash photolysis study has shown that the reactivity of the respective excited states is appreciably influenced by the electron donor strength of the apical ligand at the metal center. In fact, homolytic and heterolytic photocleavage of the metal-ligand apical bond can be the most important processes upon laser excitation, their relative contribution being influenced by medium effects and the sigma-charge donation of the axial ligand. On the other hand, the detection of reactive intermediates such as the oxomanganese(V) salen complex (lambda(max) 530 nm) by laser flash photolysis opens the way to apply this fast detection technique to the study of reaction mechanisms in catalysis by metallic complexes. As a matter of fact, quenching of oxomanganese(V) salen by simple alkenes has been observed by laser flash.

Journal Article↗
PubMed1997

The use of flash photolysis for a high-resolution temporal and spatial analysis of bacterial chemotactic behaviour: CheZ is not always necessary for chemotaxis.

The purpose of this work was to develop a high-resolution analysis of behaviour as an assay of the physiological consequences of mutations in the che genes and also to examine the role of CheZ in chemotaxis. Recent advances in flash photolysis have made it possible to expose cells to an unstable chemical gradient created by a square-wave increase in attractant concentration. The response of individual cells can be tracked in the order of milliseconds using real-time motion analysis. The tumble frequency of wild-type Escherichia coli exposed to photoreleased aspartate falls very quickly to smooth-swimming levels, and the swimming speed of these cells rises. As a consequence of these behavioural changes, there is an increase in the number of bacteria present in the centre of the flashed area, that is the bacteria's response to the transient gradient generated by flash photolysis was to swim into the centre of the flash area. This allowed the rapid quantitative measurement of chemotaxis. Deletion of various che genes resulted in predictable changes in chemotactic behaviour. cheZ null mutants are non-chemotactic when measured by classical techniques but demonstrate a definite chemotactic response to photoreleased attractant.

Bacterial Proteins↗
PubMed2001

Age-related changes in the flash electroretinogram and oscillatory potentials in individuals age 75 and older.

OBJECTIVES: To evaluate whether the inner plexiform layer of the retina is altered during senescence by examining the oscillatory potentials (OPs) of the flash electroretinogram (fERG) in individuals age 75 and older. DESIGN: Cross-sectional, observational study. SETTING: A university-based center. PARTICIPANTS: Fifty-six healthy volunteers (age 20-88 years). MEASUREMENTS: fERGs and OPs were first evaluated in scotopic conditions, following pupillary dilation and dark adaptation, in young (20-32 years; n = 30) and older (75-88 years; n = 26) individuals. Electrical signals were recorded with a Dawson-Trick-Litzkow type (DTL) fiber electrode in response to blue and white flashes. Red flashes were subsequently delivered to the test eye for photopic fERG and OP recordings following a period of light adaptation. RESULTS: The amplitude of the a- and b-waves in response to blue and white flashes was significantly decreased in older people and their implicit time was increased. The latency of the a- and b-waves under photopic conditions was also prolonged with senescence, but only the amplitude of the b-wave was reduced. The amplitude of most OPs recorded under both scotopic and photopic conditions decreased with age, whereas their implicit times were prolonged. CONCLUSIONS: Our results confirm previous findings regarding the age dependency of the fERG a- and b-waves. Furthermore, we provide novel information concerning the detrimental effects of age on the OPs, indicating that the neuronal elements within the inner plexiform layer of the retina are compromised with senescence.

Adult↗
PubMed2005

[Simplified production of multimedia based radiological learning objects using the flash format].

PURPOSE: Evaluation of the applicability of the Flash Format for the production of radiological learning objects used in an e-learning environment. MATERIAL AND METHODS: Five exemplary learning objects with different didactic purposes referring to radiological diagnostics are presented. They have been intended for the use within the multimedia, internet-based e-learning environment LaMedica. Interactive learning objects were composed using the Flash 5.0 software (Macromedia, San Francisco, USA) on the basis of digital CT and MR images, digitized conventional radiographs and different graphical elements prepared as TIFF files or in a vector graphics format. RESULTS: After a short phase of initial skill adaptation training, a radiologist author was soon able to create independently all learning objects. The import of different types of images and graphical elements was carried out without complications. Despite manifold design options, handling of the program is easy due to clear arrangement and structure, thus enabling the creation of simple as well as complex learning objects that provided a high degree of attractiveness and interaction. Data volume and bandwidth demand for online use was significantly reduced by the Flash Format compression without a substantial loss of visual quality. CONCLUSION: The universally compatible Flash Format offers an opportunity for the simple production of radiological learning objects that fulfill all relevant needs of modern internet based e-learning environments, such as interactivity, employment of multimedia and convertibility.

Computer Graphics↗
PubMed1989

[T2*-weighted MR images of gynecologic tumors with the FLASH sequence: the initial experiences at 1.5 T].

To speed up the time taken for MR examinations, 20 patients with malignant gynaecological lesions (carcinoma of the cervix, uterus or ovary) and two operative specimen (carcinoma of the cervix) were examined by T2*-weighted flash sequences; the results were compared with T2-weighted spin echo sequences. In ten out of 20 in vivo examinations, the flash method produced a similar contrast range between tumour and normal tissues, cystic lesions being particularly well seen in gradient echo sequences. In the remaining patients, and in the surgical specimen, demarcation of the tumour was significantly poorer on the flash sequences. There was also loss of anatomic detail and an increased susceptibility to artifacts. The flash sequence as used here can therefore not be regarded as of the same diagnostic value as T2-weighted spin echo sequences in the diagnosis of gynaecological malignancies.

Carcinoma↗
PubMed2005

Asymmetric mislocalization of a visual flash ahead of and behind a moving objectt.

When subjects localize a flash relative to another stationary stimulus, the flash appears displaced in the direction of nearby motion signals (position capture; Whitney and Cavanagh, 2000 Nature Neuroscience 3 954-959). Our previous study had suggested that the position capture is larger for a flash presented ahead of a moving stimulus than for a flash behind it (Watanabe et al, 2003 Perception 32 545-559). In the present study, I investigated the spatial asymmetry of position capture. Experiment 1 demonstrated that asymmetric position capture occurs primarily in a moving-object-centered coordinate. Experiment 2 showed evidence that the asymmetric position capture operates after individuation of single visual objects. Finally, experiment 3 demonstrated that, when attention was reduced with a dual-task procedure, the asymmetric position capture increased. These results suggest that the spatial asymmetry of position capture occurs without attention but the spatial bias can be reduced by attention. Therefore, the underlying mechanism for the asymmetric spatial bias may be different from attentive tracking (Cavanagh, 1992 Science 257 1563-1565) and mislocalization during smooth pursuit (Brenner et al, 2001 Vision Research 41 2253-2259).

Attention↗
PubMed1996

Oxidation states of the manganese cluster during the flash-induced S-state cycle of the photosynthetic oxygen-evolving complex.

The Mn K-edge x-ray absorption spectra for the pure S states of the tetranuclear Mn cluster of the oxygen-evolving complex of photosystem II during flash-induced S-state cycling have been determined. The relative S-state populations in samples given 0, 1, 2, 3, 4, or 5 flashes were determined from fitting the flash-induced electron paramagnetic resonance (EPR) multiline signal oscillation pattern to the Kok model. The edge spectra of samples given 0, 1, 2, or 3 flashes were combined with EPR information to calculate the pure S-state edge spectra. The edge positions (defined as the zero-crossing of the second derivatives) are 6550.1, 6551.7, 6553.5, and 6553.8 eV for S0, S1, S2, and S3, respectively. In addition to the shift in edge position, the S0--> S1 and S1--> S2 transitions are accompanied by characteristic changes in the shape of the edge, both indicative of Mn oxidation. The edge position shifts very little (0.3 eV) for the S2--> S3 transition, and the edge shape shows only subtle changes. We conclude that probably no direct Mn oxidation is involved in this transition. The proposed Mn oxidation state assignments are as follows: S0 (II, III, IV, IV) or (III, III, III, IV), S1 (III, III, IV, IV), S2 (III, IV, IV, IV), S3 (III, IV, IV, IV).

Journal Article↗
PubMed1995

Oscillations of reaction center II-D1 protein degradation in vivo induced by repetitive light flashes. Correlation between the level of RCII-QB- and protein degradation in low light.

The D1 protein subunit of the photochemical reaction center II (RCII) turns over rapidly in oxygenic photosynthetic organisms exposed to the light. At high photon flux densities (PFD), photoinactivation of RCII precedes the degradation of the D1 protein. We found that the apparent quantum yield for the D1 protein degradation in Chlamydomonas cells is severalfold higher at low PFDs (10-100 mumol m-2 s-1) as compared to that observed at PFDs which induce photoinactivation of RCII (1.5-3 x 10(3) mumol m-2 s-1). Relative high levels of reduced RCII secondary plastoquinone acceptor, QB-, are induced in cells exposed to low PFDs as determined by thermoluminescence measurements. The probability of generating elevated levels of QB- which may recombine with the S2,3 oxidized states of the oxygen evolving complex decreases with increase in the light intensities at which consecutive double reduction of QB and exchange with the plastoquinone pool prevail. We have used light flashes to test if a correlation exists between the degradation of D1 protein and the relative level of QB-. D1 protein degradation could be induced in dark-incubated cells exposed to a series of 1.4 x 10(3) single light flashes given at intervals compatible with generation of elevated levels of QB- and its decay by charge recombination. Oscillations of the QB- level in cells exposed to 960-1440 series of 1 to several flashes correlated with oscillations of the D1 protein degradation in Chlamydomonas cells and in the Scenedesmus wild type but not in the LF-1 mutant lacking photosystem II donor side activity. In this mutant the "S state cycle" and QB- oscillations are abolished. We propose that the process of recombination of long lived RCII-QB- with the S2,3 states may involve damaging events related to the D1 protein degradation induced by light flashes or continuous low light in vivo.

Animals↗
PubMed1997

Optimal MR protocol for hepatic hemangiomas. Comparison of conventional spin-echo sequences with T2-weighted turbo spin-echo and serial gradient-echo (FLASH) sequences with gadolinium enhancement.

PURPOSE: To compare conventional spin-echo (SE) sequences with T2-weighted turbo SE and serial gadolinium-enhanced T1-weighted FLASH sequences in the detection and characterization of hepatic hemangiomas, and to describe the enhancement characteristics of the lesions on dynamic MR imaging. MATERIAL AND METHODS: Forty-two patients with 66 hemangiomas were studied at 1.0 T or 1.5 T by using conventional SE sequences (T1-weighted, T2-weighted, and heavily T2-weighted), T2-weighted turbo SE sequences, and breath-hold T1-weighted FLASH sequences acquired before, immediately after, and 1, 2, 3, 5, and 10 min after injection of a bolus of gadopentetate dimeglumine. Images were quantitatively analyzed for lesion-to-liver contrast-to-noise (C/N) ratios, and qualitatively analyzed for lesion conspicuity. The enhancement pattern and the rapidity of enhancement were analyzed in small (<15 mm), medium (15-39 mm), and large (>39 mm) hemangiomas. RESULTS: In T2-weighted images, T2-weighted turbo SE and heavily T2-weighted SE images had higher C/N ratios than T2-weighted SE images (p=0.003). Lesion conspicuity was not significantly different in these 3 sequences (p=0.307). In T1-weighted images, T1-weighted FLASH images had higher C/N (p<0.001) and also better lesion conspicuity (p<0.001) than T1-weighted SE images. Immediate uniform enhancement was seen in 43% of small hemangiomas (9 of 21 lesions), and persistent central hypointensity was seen in 73% of large hemangiomas (11 of 15 lesions). Rapid enhancement was seen in 62% of small hemangiomas (13 of 21 lesions) and in 31% of medium or large hemangiomas (14 of 45 lesions). CONCLUSION: Further clinical study is needed for evaluating the differential diagnostic advantages of turbo SE T2-weighted imaging compared to the calculation of T2-values by means of a SE T2-weighted sequence. However, the results of the present study suggest that T2-weighted turbo SE imaging and precontrast and serial gadolinium-enhanced FLASH imaging have the potential to replace conventional SE imaging in the evaluation of hepatic hemangiomas.

Contrast Media↗
PubMed1988

Synchronous rhythmic flashing of fireflies. II.

Synchronized flashing by males of some firefly species involves a capacity for visually coordinated, rhythmically coincident, inter-individual behavior that is apparently unique in the animal kingdom except for a few other arthropods and for man. This paper reviews (1) diverse communicative interactions that have evolved from elementary photic signals, (2) physiological mechanisms of synchronism, and (3) theories about its biological meaning. Work of the past 20 years shows that flash synchrony is widespread geographically and taxonomically, appears in an astonishing range of spectacular display types, utilizes several neural flash-control mechanisms and is pervasively but enigmatically involved in courtship. No proposed function for synchrony has been fully established but theory and physiology concur in indicating that synchrony aids male orientation toward the female, female recognition of male flashing, or both. Increased mate choice for the female is one likely ultimate benefit.

Animals↗
PubMed1987

Pathology of the optic nerve and visual association areas. Information given by the flash and pattern visual evoked potential, and the temporal and spatial contrast sensitivity function.

Spatial and temporal contrast sensitivity functions (CSF) were compared with visual evoked potentials (VEP) in two groups of patients with pathology selectively affecting different parts of the visual pathway. These consisted of 10 patients with a selective delay of the pattern VEP due to demyelination of one optic nerve (unilateral optic neuritis) and 11 patients with a selective delay of the flash VEP due to pathology of the visual association areas (primary presenile dementia, or Alzheimer's disease). The results led to the following conclusions. Comparison of the VEP and CSF results indicated that VEP latency was more closely associated with the temporal CSF than the spatial CSF. Pathology of the visual association areas which selectively increased the latency of the flash P2 component also reduced sensitivity at low and medium temporal frequencies. In demyelination of the optic nerve, a highly significant correlation was found between the delay of the pattern reversal VEP and sensitivity at high temporal frequencies. Comparison of the results in these two types of pathology suggests that the pattern VEP and flash P1 component, the spatial CSF, and temporal CSF at high temporal frequencies are all processed in the geniculostriate pathway. The flash P2 component and temporal CSF at low and medium frequencies were affected differently from the other measures. The possibility that these processes are transmitted by nongeniculate pathways is discussed.

Adult↗
PubMed1994

Deaths due to flash floods in Puerto Rico, January 1992: implications for prevention.

BACKGROUND: In January 1992, the Commonwealth of Puerto Rico sustained unusually heavy rainfall, which caused flash floods and deaths. METHODS: We conducted a descriptive study and a case-control study to determine the circumstances of these deaths and to identify mortality-prevention strategies. We describe the time, place, and circumstances of each death, and compare this information with water-level and rainfall data and the timing of warnings. Using controls selected from the affected population, we estimated the risk of death by age, sex, and vehicle occupancy during the flood. RESULTS: Within 7 hours, 23 people died in 17 incidents; 20 of the decedents (87%) were occupants of motor vehicles. The estimated risk of mortality was significantly elevated for motorists (odds ratio = 16, 95% confidence interval: 3.5-144). Being in a vehicle to evacuate a flash flood area was protective; however, being in a vehicle during the flood for other reasons further increased the risk of mortality. Deaths occurred early during the rapid rise of water and before official warnings were issued. CONCLUSION: We recommend improving the sensitivity of the warning system and its ability to disseminate appropriate information rapidly. We also recommend educating officials and the public about the risks of driving on flooded roads and in potential flash flood conditions; and about the unique flash flood risks associated with specific topographical features in their region.

Adolescent↗
PubMed1985

Coronary angiography with flashing tomosynthesis.

Thirty-four patients with coronary artery disease were studied with standard 35 mm coronary cineangiography and flashing tomosynthesis, to assess the value of the latter technique to detect stenotic coronary arteries. All occluded vessels and all coronary stenoses seen by cineangiography were also found by flashing tomosynthesis. A correlation coefficient of r = 0.85 (P less than 0.001) was determined between the degrees of stenosis obtained by the two techniques. With flashing tomosynthesis, less contrast medium was needed, the investigation time was shorter, and the radiation exposure markedly reduced. At present, dynamic events, such as collateral blood flow, cannot be evaluated. We conclude that coronary arterial stenoses and occlusions can be reliably evaluated by flashing tomosynthesis. Further technological developments are necessary for the technique to gain clinical acceptance.

Adult↗
PubMed1987

Flash-induced proton release in Rhodopseudomonas sphaeroides spheroplasts.

Proton release by flash excitations was measured with right-side-out vesicles prepared from Rhodopseudomonas sphaeroides by lysozyme-EDTA treatment followed by hypotonic treatment. Absorbance change at 586 nm in the presence of bromcresol purple was measured to monitor the pH change. In the presence of horse heart cytochrome c, which catalyzes the electron transfer from the cytochrome b-c1 complex to the primary electron donor, the single-turnover flash elicited release of about two protons per primary electron donor, which was rereduced rapidly by the added cytochrome c. The halftime of the proton release was about 70 ms at pH 6.3 and at a redox potential of about 150 mV. The rate was considerably lower than that of the electron transfer from the cytochrome b-c1 complex to cytochrome c. However, multiple flashes with intervals of 60 ms caused release of the same amount of protons as that by flashes with longer intervals. This indicated that the proton release itself was rapid, but delocalization was slower. Antimycin A inhibited the proton release, and myxothiazol almost completely abolished it.

Biological Transport↗
PubMed1982

A flash-photometric method for determination of reactivity of superoxide: application to superoxide dismutase assay.

Pulse-generation of O2- by a flash was used to determine the reactivity of O2-, O2- was produced within 10 ms by a flash of light through the excitation of FMN in the presence of N,N,N',N'-tetramethylethylenediamine and oxygen. Kinetic analysis of cytochrome c reduction by O2- generated by flash yielded the reaction rate constant between cytochrome c and O2- and the spontaneous disproportionation rate constant of O2-. We applied it for superoxide dismutase assay using a linear relation between superoxide dismutase concentration and the apparent rate constant of cytochrome c reduction by O2-. The catalytic rate constant and activation energy at pH 7.3 of bovine liver Cu,Zn-superoxide dismutase were found to be 1.75 x 10(9) M-1 . s-1 at 25 degrees C and 26.9 kJ . M-1, respectively. The kinetics of O2- decay can be also monitored at 240 nm in this flash-photometric system and gave the spontaneous disproportionation rate constant of O2- and the catalytic rate constant of superoxide dismutase.

Animals↗
PubMedDate not supplied

Rapid three-dimensional MR imaging using the FLASH technique.

Fast low-angle shot (FLASH) imaging is a new technique for rapid magnetic resonance (MR) imaging that reduces acquisition times to seconds while retaining spatial resolution. This article deals with a three-dimensional (3D) variant of the FLASH method that allows the recording of a 3D-data set of 128 X 128 X 128 pixels within an acquisition time of only 4 min. The method is demonstrated using a 2.35 T 40 cm bore MR system. Experiments are carried out on rabbit head and human extremities. Depending on the field of view, the isotropic resolution is 1 mm or even less leading to cross-sectional images with a 1 mm slice thickness. In principle, FLASH imaging techniques are applicable to any MR system without the need of major hardware modifications. However, high-speed computers, large storage capacity, and rapid image display routines greatly facilitate an advantageous use of the 3D-FLASH variant.

Animals↗
PubMed1985

Repetitively pulsed small spot light flashes. Depression of steady-state pattern visual evoked potentials.

Steady-state visual evoked potentials (VEP's) were elicited from human volunteers by contrast reversal of a 43% contrast checkerboard pattern resolvable with 6/24 (20/80) Snellen acuity. Superimposed on the fixation point was a Xenon flash lamp subtending 0.358 degrees visual angle, which produced a 0.05 J/cm2 sr flash in 2 microseconds (full width, half maximum). Single pulses of light had no significant effect on the VEP. Increasingly significant decreases in VEP signal magnitude were noted with 2 and 5 pulses of 20 Hz white light. No disruption of VEP phase entrainment was noted with any of the flash exposures. Partial reciprocity was demonstrated between number of flashes at this frequency and response decrement.

Adolescent↗