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PubMed2004

Explosion caused by flashing liquid in a process vessel.

An explosion occurred at a polyvinyl chloride (PVC) resin manufacturing plant. The explosion originated at an atmospheric storage vessel when it received a slurry discharge from a suspension polymerization reactor. The pressure rise caused by the uncontrolled flashing of superheated liquid vinyl chloride resulted in the complete separation of the roof from the tank shell. A cloud of vinyl chloride vapor was released and ignited resulting in a vapor cloud explosion. The accident caused significant property damage but no serious injuries. An investigation was conducted to determine the causes of the accident. It was discovered that the facility had experienced numerous overpressure incidents in the atmospheric storage vessels used as slurry tanks. Many of these incidents resulted in modest structural damage to these slurry tanks. It was determined by Exponent that the rapid flashing of residual liquid monomer present in the product slurry stream caused the earlier overpressure incidents. The facility operator did not adequately investigate or document these prior overpressure events nor did it communicate their findings to the operating personnel. Thus, the hazard of flashing liquid vinyl chloride was not recognized. The overpressure protection for the slurry tanks was based on a combination of a venting system and a safety instrumentation system (SIS). The investigation determined that neither the venting system nor the SIS was adequate to protect the slurry tank from the worst credible overpressure scenario. Fundamentally, this is because the performance objectives of the venting system and SIS were not clearly defined and did not protect against the worst credible overpressure scenario. The lessons learned from this accident include: use prior incident data for recognizing process hazards; identify targets vulnerable to these hazards; explicitly define performance objectives for safeguards to protect against the worst credible overpressure scenario. The ultimate lesson learned here is that a liquid trapped under pressure above its normal boiling point represents an overpressure hazard. To avoid exceeding the design pressure of the receiving vessel, the superheated liquid must be discharged slowly so that the vapor production rate caused by flashing does not exceed the venting rate of the receiving vessel.

Accidents, Occupational↗
PubMed2006

A general model for predicting the flash point of miscible mixtures.

A mathematical model is presented for predicting the flash point of miscible mixtures. This model is reducible and adequate for some specified systems as proposed previously. Except for multiple aqueous-organic solutions, the predictive capability of the reduced form for other miscible mixtures, including binary aqueous-organic solutions and flammables-only analogues, has been verified previously. The model was validated using the ternary aqueous-organic solutions, water+methanol+ethanol/isopropanol. The results of the study confirm that the model predicts the flash points of these solutions by utilizing the flash points of the individual components. Further, if the binary interaction parameters for a ternary aqueous-organic solution are not accessible, a model based upon the binary interaction parameters of the binary solutions may provide a very acceptable means of predicting the flash point for such a ternary solution through comparison of the predicted and experimental data, as demonstrated in this study.

2-Propanol↗
PubMed2006

A non-ideal model for predicting the effect of dissolved salt on the flash point of solvent mixtures.

Flash point is one of the major quantities used to characterize the fire and explosion hazard of liquids. Herein, a liquid with dissolved salt is presented in a salt-distillation process for separating close-boiling or azeotropic systems. The addition of salts to a liquid may reduce fire and explosion hazard. In this study, we have modified a previously proposed model for predicting the flash point of miscible mixtures to extend its application to solvent/salt mixtures. This modified model was verified by comparison with the experimental data for organic solvent/salt and aqueous-organic solvent/salt mixtures to confirm its efficacy in terms of prediction of the flash points of these mixtures. The experimental results confirm marked increases in liquid flash point increment with addition of inorganic salts relative to supplementation with equivalent quantities of water. Based on this evidence, it appears reasonable to suggest potential application for the model in assessment of the fire and explosion hazard for solvent/salt mixtures and, further, that addition of inorganic salts may prove useful for hazard reduction in flammable liquids.

Models, Chemical↗
PubMed2005

Flashes are localised as if they were moving with the eyes.

Targets that are flashed during smooth pursuit are mislocalised in the direction of the pursuit. It has been suggested that a similar mislocalisation of moving targets could help to overcome processing delays when hitting moving objects. But are moving targets really mislocalised in the way that flashed ones are? To find out we asked people to indicate where targets that were visible for different periods of time had appeared. The targets appeared while the subjects' eyes were moving, and were either moving with the eyes or static. For flashed targets we found the usual systematic mislocalisation. For targets that moved with the eyes the mislocalisation was at least as large, irrespective of the presentation time. For static targets the mislocalisation decreased with increasing presentation time, so that by the time the presentations reached about 200 ms the targets were not mislocalised at all. A simple model that combines smooth retinal motion with information about the velocity of smooth pursuit could account for the measured tapping errors. These findings support the notion that the systematic mislocalisation of flashed targets is related to the way in which people intercept moving objects.

Humans↗
PubMed2006

Capture of visual direction in dynamic vergence is reduced with flashed monocular lines.

The visual direction of a continuously presented monocular object is captured by the visual direction of a closely adjacent binocular object, which questions the reliability of nonius lines for measuring vergence. This was shown by Erkelens, C. J., and van Ee, R. (1997a,b) [Capture of the visual direction: An unexpected phenomenon in binocular vision. Vision Research, 37, 1193-1196; Capture of the visual direction of monocular objects by adjacent binocular objects. Vision Research, 37, 1735-1745] stimulating dynamic vergence by a counter phase oscillation of two square random-dot patterns (one to each eye) that contained a smaller central dot-free gap (of variable width) with a vertical monocular line oscillating in phase with the random-dot pattern of the respective eye; subjects adjusted the motion-amplitude of the line until it was perceived as (nearly) stationary. With a continuously presented monocular line, we replicated capture of visual direction provided the dot-free gap was narrow: the adjusted motion-amplitude of the line was similar as the motion-amplitude of the random-dot pattern, although large vergence errors occurred. However, when we flashed the line for 67 ms at the moments of maximal and minimal disparity of the vergence stimulus, we found that the adjusted motion-amplitude of the line was smaller; thus, the capture effect appeared to be reduced with flashed nonius lines. Accordingly, we found that the objectively measured vergence gain was significantly correlated (r=0.8) with the motion-amplitude of the flashed monocular line when the separation between the line and the fusion contour was at least 32 min arc. In conclusion, if one wishes to estimate the dynamic vergence response with psychophysical methods, effects of capture of visual direction can be reduced by using flashed nonius lines.

Convergence, Ocular↗
PubMed2006

Retinal adaptation responses revealed by global flash multifocal electroretinogram are dependent on the degree of myopic refractive error.

PURPOSE: There is evidence that the inner retina is involved in eye growth control processes and the development of myopia. We sought to investigate the response dynamics of the inner retina of adult emmetropes and myopes using the global flash multifocal electroretinogram (mfERG) paradigm. METHODS: Fourteen myopes and 10 emmetropic subjects (mean age: 21.0+/-2.8 years) underwent mfERG testing using VERIS 5.1.5X. The global flash stimulus array consisted of 103-scaled hexagons which flickered according to a pseudorandom binary m-sequence (2(13)-1). The stimulation sequence was modified by inserting three frames, a dark frame, a global (full screen) flash, and another dark frame. The amplitude and implicit time of the two distinct waveform features, an early direct component (DC) and a later induced component (IC) of the first-order kernel were analyzed. Retinal responses were averaged over rings of increasing eccentricity, or into nasal and temporal hemifields. RESULTS: There was a significant correlation between the DC and IC response amplitude and myopic refractive error, i.e., the greater the myopic error, the greater the response amplitude. However, when comparing between the two refractive error groups, DC and IC response amplitudes of emmetropes and myopes were similar, even after compensating for the effect of axial length. There were no significant differences in implicit times of the DC and IC in emmetropes and myopes. CONCLUSIONS: Global flash mfERG responses of emmetropes and myopes were not found to be significantly different. The measured retinal adaptation response however varied according to the degree of myopia. We hypothesize that dopamine, a neurotransmitter that plays a key role in retinal adaptation and is known to be reduced in myopic eyes, may be involved in the retinal adaptation effect observed.

Adaptation, Ocular↗
PubMed2002

A process for improving flash sterilization.

In reviewing OR policies and procedures for flash sterilization, staff members at Presbyterian Hospital of Dallas discovered that their process of biological monitoring and flash sterilization needed improvement, and they implemented changes to correct the process. These changes led to questions regarding biological indicators and the flash sterilization container systems being used. As a result, the overall time required for flash sterilization was increased to validate the sterilization process.

Environmental Monitoring↗
PubMed1997

Evidence for the first phase of the reprotonation switch of bacteriorhodopsin from time-resolved photovoltage and flash photolysis experiments on the photoreversal of the M-intermediate.

The kinetics of the photoreversal reaction of the M-intermediate of bacteriorhodopsin (bR) was investigated by time-resolved optical absorption spectroscopy and photovoltage measurements using double-flash excitation (a green flash (532 nm) followed by a blue flash (400 nm) after a variable delay). The sign of the photovoltage and the 1H/2H kinetic isotope effect indicate that the Schiff base is reprotonated by a group between the Schiff base and the extracellular surface, probably Asp85. Analysis of the kinetic data shows that the charge movement in 150 mM KCl at 12 degrees C is characterized by two components with time constants of approximately 100 ns and approximately 600 ns, respectively, which are independent of the delay time between the flashes and the pH. The amplitudes of the fast and slow components depend on the delay and the pH. The slower component starts to contribute to the charge movement only after delays longer than 100 micros, is absent at low pH, and increases in amplitude with a pKa of approximately 6. Because the proton release group deprotonates after 70-100 micros and has a transient pKa of 5.8, these results suggest the following assignment: the fast and the combination of fast and slow components represent photoreversal from two M states, with the release group protonated and deprotonated, respectively. The slow phase of the photoreversal starts from a state with the release group deprotonated, and with the pK of Asp85 elevated, and is probably due to the restoration of the pK of Asp85 to its initial low value. This provides further evidence for coupling between the pK's of Asp85 and the release group and suggests that proton release is the first step in the reprotonation switch. At alkaline pH the amplitude of the electrical signal from the back photoreaction decreases with an apparent pK of 8, without a corresponding decrease in the amount of M. At neutral pH the movement of the positively charged guanidinium group of Arg82 from a position near the release group on the surface to Asp85 makes a substantial contribution to the electrical photoreversal amplitude. Above the pK of the release group in the unphotolysed state (approximately 8), Arg82 stays near the surface, leading to a corresponding signal reduction.

Bacteriorhodopsins↗
PubMed1985

Hot flashes in postmenopausal women ameliorated by danazol.

Six postmenopausal women with hot flashes were studed for two 8-week periods during which they received low-dose danazol (100 mg/24 hours) for one time interval and placebo for the other in a randomized double-blind manner. The patients recorded the number and severity of their hot flashes daily. On the last day of each period the patients were admitted to the research center overnight for an 8-hour monitoring of forehead skin temperatures and for continuous withdrawal of blood to determine 20-minute integrated levels of luteinizing hormone. Three of the six patients responded to danazol with a mean reduction of 88% in the number of hot flashes and a 53% decrease in the severity of hot flashes. Responders differed from nonresponders in that on treatment the frequency of nocturnal pulses of luteinizing hormone was reduced more (36.1% versus 14.4%), the increase in amplitude of the pulses was greater (+30.7% versus -11.8%), and the fall in the mean level of luteinizing hormone was more marked (19.0% versus 10.5%). The findings suggest that danazol may be a reasonable alternative to estrogen in the treatment of postmenopausal women with severe vasomotor symptoms.

Danazol↗
PubMed1994

Transdermal clonidine for ameliorating post-orchiectomy hot flashes.

To determine the efficacy of transdermal clonidine for alleviating post-orchiectomy hot flashes, a randomized, double-blind, crossover clinical trial was designed including 70 men with a history of prostate cancer who had undergone a medical or surgical orchiectomy and were suffering from hot flashes. The results of this study demonstrated that clonidine did not significantly decrease hot flash frequency or severity. Future research is necessary to find effective means of alleviating hot flashes in post-orchiectomy patients.

Adult↗
PubMed2002

Shifts in perceived position of flashed stimuli by illusory object motion.

Moving stimuli cause the position of flashed stimuli to appear shifted in the direction of motion (position capture). To examine whether position capture depends on low-level motion interactions or perception of integrated object motion, we employed a slit-view display. Two line-drawn diamonds translated horizontally in opposite directions, one above and one below the fixation cross, either behind an occluding surface with a narrow slit or without occluding surface. When the diamonds were in vertical alignment, two vertical bars were flashed, one in the center of each diamond. In the slit-view condition, the diamonds were visible through a 4-, 2-, or 1-pixel vertical slit; the width of the flashed bars always matched the width of the slit. Even though the horizontal component of physical motion was greatly reduced or absent in the slit-view conditions, observers perceived diamonds moving behind the occluding surface. Furthermore, the position of the flashed bar was captured by the moving diamonds such that each bar appeared shifted in the direction of perceived motion. We conclude that the position capture reported here has a component based on high-level motion processing that is responsible for dynamically integrating object motion and shape.

Analysis of Variance↗
PubMed1999

Resetting the rat circadian clock by ultra-short light flashes.

We examined the effects that ultra-brief, intense, light flashes have on the rat circadian clock, the suprachiasmatic nucleus of the hypothalamus (SCN). We found that as few as five intense flashes, each 10-micros in duration (1 per s), can produce both phase shifts in free-running activity rhythms and Fos expression in the SCN in rats kept in constant darkness. After pre-exposure to such flashes, phase shifts in response to a continuous light pulse delivered 2 h later were potentiated, but Fos expression in the SCN was decreased as following pre-exposure to continuous light. These results show that flashes induce behavioral and cellular effects indicative of clock resetting similar to those induced by light stimuli of longer duration. Extremely brief but intense, light stimuli may be much more important to clock resetting than had been previously known.

Animals↗
PubMedDate not supplied

[Value of visual evoked potentials in multiple sclerosis (MS). Comparative study of results obtained by light flash and checkerboard reversal stimulation].

Evoked visual potentials were studied in 12 subjects diagnosed or suspected of having MS. A comparison was made between these subjects and results obtained with single eye stimulation using a flash of light (101 subjects) or by using a reversible checker-board pattern (58 subjects). Reversible checker-board pattern simulation showed pathological unilateral or bilateral increase in the latency of the main positive spike in the response of 80% of the verified MS cases and 50% of the probable or possible MS cases. These percentages were 25% lower when flashes of light were used as stimulation. 58% of those patients who have never presented ophtalmological symptoms have abnormal latency in responses invoked by the reversible checker-board pattern, as opposed to 20% using flashes of light for stimulation. Study of E.V.P. in normal subjects indicates that the better results obtained with reversible checker-board stimulation can be attributed to greater reproductibility of the response. Analysis of the overall morphology of the responses significantly increases E.V.P. examination efficiency when using flashes of light as stimulation. However, in our series, it does not change the results obtained by only calculating the latency of response to reversal of a checker-board pattern.

Adult↗
PubMed2001

Optimization and validation of a rapid high-resolution T1-w 3D FLASH water excitation MRI sequence for the quantitative assessment of articular cartilage volume and thickness.

In view of follow up, survey and development of therapeutic strategies for osteoarthritis where cartilage deterioration plays an important role, a non invasive, reliable and quantitative assessment of the articular cartilage is desirable. The currently available high resolution T(1)-weighted (T1-w) 3D FLASH pulse sequences with frequency selective fat suppression are very time consuming. We have 1) optimized a high resolution T1-w 3D FLASH water excitation (WE) sequence for short acquisition time and cartilage visualization, and 2) validated this sequence for cartilage volume and thickness quantification. The spectral fat presaturation was replaced by selective water excitation. The flip angle of the WE sequence was optimized for the contrast to noise (C/N(cart)) ratio of cartilage. Sagittal datasets (voxel size: 0.31 x 0.31 x 2 mm(3)) of the knees of nine healthy volunteers were acquired both, with the 3D FLASH WE (17.2/6.6/30 degrees ) sequence (WE) and a previously validated 3D FLASH fat saturated (42/11/30 degrees ) sequence (FS). For validation of the WE sequence, cartilage volume, mean and maximal cartilage thickness of the two sequences were compared. Reproducibility was assessed by calculating the coefficient of variation (COV %) of 4 consecutive WE data sets in the volunteers. The acquisition time was reduced from 16'30" (FS) down to 7'14" for the WE sequence. Image contrast and visualization of the cartilage was very similar, but delineation of the basal layer of the cartilage was slightly improved with the WE sequence. A flip angle of 30 degrees provided the best C/N(cart) ratios (WE). Reproducibility (COV) was between 1.9 and 5.9%. Cartilage volume and thickness agreed within 4% between FS and WE sequence. The WE sequence allows for rapid, valid and reproducible quantification of articular cartilage volume and thickness, prerequisites for follow-up examinations. The reduced acquisition time (50% of FS) enables routine clinical application and thus may contribute to a broader assessment of osteoarthritis.

Adult↗
PubMed1998

Flash decaging of tyrosine sidechains in an ion channel.

A nonsense codon suppression technique was employed to incorporate ortho-nitrobenzyl tyrosine, "caged tyrosine," in place of tyrosine at any of three positions (93, 127, or 198) in the alpha subunit of the muscle nicotinic ACh receptor (nAChR) expressed in Xenopus oocytes. The ortho-nitrobenzyl group was then removed by 1 ms flashes at 300-350 nm to yield tyrosine itself while macroscopic currents were recorded during steady ACh exposure. Responses to multiple flashes showed (1) that each flash decages up to 17% of the tyrosines and (2) that two tyrosines must be decaged per receptor for a response. The conductance relaxations showed multiple kinetic components; rate constants (<0.1 s(-1) to 10(3) s(-1)) depended on pH and the site of incorporation, and relative amplitudes depended on the number of prior flashes. This method, which is potentially quite general, (1) provides a time-resolved assay for the behavior of a protein when a mutant sidechain is abruptly changed to the wild-type residue and (2) will also allow for selective decaging of sidechains that are candidates for covalent modification (such as phosphorylation) in specific proteins in intact cells.

Acetylcholine↗
PubMed1987

An evaluation of three biological indicator systems in flash sterilization.

An evaluation of two flash-sterilization-specific biological indicators (BI) and a traditional spore strip indicator was performed to assess sensitivity and reliability as reflected in survive/kill ratios. The BIs tested included: 3M's Attest #1261, Amsco's Proof Flash, and Castle Tec Test. Survival after "come-up" time alone, (0 exposure) and one-, two-, and three-minute exposures at 273 degrees F in a gravity displacement sterilizer was measured by media color change or turbidity after incubation at 55 degrees C. Each cycle was replicated three times on two separate days with six of each BI per run. Positive BIs were subcultured as necessary. Proof Flash presented technical difficulties due to incomplete or impossible crushing of media vials, unexpected media color changes, and evaporation of media. Tec Test was not sufficiently resistant as survivors were not detected at any exposure time. The Attest had 100% survival at zero and one-minute exposures and 94% survival after the two-minute exposure. No survivors were detected after the three-minute exposure. Although each institution should evaluate BIs for their own use independently, the data indicate that Attest #1261 monitored the three-minute flash cycles more satisfactorily than the other BIs tested.

Bacillus subtilis↗
PubMedDate not supplied

Flashing anomalous color contrast.

A new visual phenomenon that we call flashing anomalous color contrast is described. This phenomenon arises from the interaction between a gray central disk and a chromatic annulus surrounded by black radial lines. In an array of such figures, the central gray disk no longer appears gray, but assumes a color complementary to that of the surrounding annulus. The induced color appears: (1) vivid and saturated; (2) self-luminous, not a surface property; (3) flashing with eye or stimulus movement; (4) floating out of its confines; and (5) stronger in extrafoveal than in foveal vision. The strength of the effect depends on the number, length, width, and luminance contrast of the radial lines. The results suggest that the chromatic ring bounding the inner tips of the black radial lines induces simultaneous color contrast, whereas the radial lines elicit, in conjunction with the gray disk and the ring, the flashing, vividness, and high saturation of the effect. The stimulus properties inducing the illusion suggest that flashing anomalous color contrast may be based on asynchronous interactions among multiple visual pathways.

Adaptation, Ocular↗
PubMed1986

Photochemical properties of Escherichia coli DNA photolyase: a flash photolysis study.

Escherichia coli DNA photolyase contains a stable flavin neutral blue radical that is involved in photosensitized repair of pyrimidine dimers in DNA. We have investigated the effect of illumination on the radical using light of lambda greater than 520 nm from either a camera flash or laser. We find that both types of irradiations result in the photoreduction of the flavin radical with a quantum yield of 0.10 +/- 0.02. While photoreduction with the camera flash is minimal in the absence of an electron donor (dithiothreitol), laser flash photolysis at 532 nm reduces the flavin to the same extent in the presence or absence or an electron donor. Thus, it is concluded that the primary step in photoreduction involves an electron donor that is a constituent of the enzyme itself. Laser flash photolysis produces a transient absorption band at 420 nm that probably represents the absorption of the lowest excited doublet state (2(1)IIII*) of the radical and decays with first-order kinetics with k1 = 0.8 X 10(6) s-1. The photoreduction data combined with the results of recent studies on the activity of dithionite-reduced enzyme suggest that electron donation by excited states of E-FADH2 is the mechanism of flavin photosensitized dimer repair by E. coli DNA photolyase.

Deoxyribodipyrimidine Photo-Lyase↗