Denitrification mitigates N flux through the stream-floodplain complex of a desert city.

The Indian Bend Wash (IBW) flood-control project relies on a greenbelt to carry floods through Scottsdale, Arizona, USA. The greenbelt is characterized by a chain of shallow artificial lakes in a larger floodplain of irrigated turf, which has been protected from encroaching urban development. As such, this urban stream-floodplain complex can be divided into three subsystems: artificial lakes, channelized stream segments, and floodplain. We conducted experiments to evaluate which, if any, of these subsystems were important sites of denitrification, and to explore factors controlling denitrification rates. Denitrification enzyme activity (DEA) bioassays were conducted on sediments from eight lake and six stream segments as well as soil samples from eight floodplain transects. Mass-specific potential denitrification rates were significantly higher in lakes than in streams or floodplains. Nutrient limitation bioassays revealed that nitrate (NO3-) limited denitrification in lake sediments, a surprising finding given that NO3(-)-rich groundwater additions frequently raised lake NO3(-) concentration above 1 mg N/L. Experiments on intact lake cores suggested that denitrification was limited by the rate NO3(-) diffused into sediments, rather than its availability in overlying water. Floodplain denitrification was limited by water content, not NO3(-) or C, and irrigation of soils stimulated denitrification. We constructed a N budget for the IBW stream-floodplain complex based on our experimental results. We found that both lakes and floodplains removed large quantities of N, with denitrification removing 261 and 133 kg N ha(-1) yr(-1) from lake sediments and floodplain soils, respectively, indicating that lakes are hotspots for denitrification. Nevertheless, because floodplain area was >4.5 times that of lakes, floodplain soils removed nearly 2.5 times as much N as lake sediments. Given the desert's low annual precipitation, a finding that floodplain soils are active sites of denitrification might seem implausible; however, irrigation is common in urban landscapes, and it elevated annual denitrification in IBW. Based on our results, we conclude that construction of artificial lakes created hotspots while application of irrigation water created hot moments for denitrification in the stream-floodplain complex, demonstrating that management decisions can improve the ability of urban streams to provide critical ecosystem services like N retention.

Nutrient variation in an urban lake chain and its consequences for phytoplankton production.

In the Central Arizona-Phoenix (CAP) ecosystem, managers divert mixed stream water and groundwater to maintain an artificial lake chain in Indian Bend Wash (IBW), a historically flashy, ephemeral, desert stream. Nutrient concentrations in the CAP ecosystem's groundwater, stream water, and floodwater differ: stream water has low concentrations of both inorganic N and P, while groundwater is low in inorganic P but rich in nitrate (NO(3)(-)). Consequently, groundwater contribution drives inorganic N concentrations in the lake chain. In contrast, floodwater typically has high P concentrations while remaining low in N. Thus we expected N and P concentrations in IBW lakes to vary with the mix of water flowing through them. Elevated NO(3)(-) and low inorganic P concentrations were predicted when groundwater pumping was pronounced and this prediction was supported. We hypothesized that these predictable changes in water chemistry would affect nutrient limitation of phytoplankton. Laboratory nutrient-addition bioassays demonstrated that phytoplankton growth was P-limited throughout the summer of 2003 when N/P was high. However, after a late-season flood drove N/P below 31:1, the expected threshold between N and P limitation, N limitation was observed. Our results indicate that effects of floods, the preeminent historic drivers of Sonoran Desert stream biogeochemistry, are mitigated in urban ecosystems by decisions about which spigots to turn. Consequently, nutrient limitation of urban streams is driven as much by management decisions as by natural hydrologic variation.

Shifts in Ectomycorrhizal Fungal Communities and Exploration Types Relate to the Environment and Fine-Root Traits Across Interior Douglas-Fir Forests of Western Canada.

Large-scale studies that examine the responses of ectomycorrhizal fungi across biogeographic gradients are necessary to assess their role in mediating current and predicted future alterations in forest ecosystem processes. We assessed the extent of environmental filtering on interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) ectomycorrhizal fungal communities across regional gradients in precipitation, temperature, and soil fertility in interior Douglas-fir dominated forests of western Canada. We also examined relationships between fine-root traits and mycorrhizal fungal exploration types by combining root and fungal trait measurements with next-generation sequencing. Temperature, precipitation, and soil C:N ratio affected fungal community dissimilarity and exploration type abundance but had no effect on α-diversity. Fungi with rhizomorphs (e.g., Piloderma sp.) or proteolytic abilities (e.g., Cortinarius sp.) dominated communities in warmer and less fertile environments. Ascomycetes (e.g., Cenococcum geophilum) or shorter distance explorers, which potentially cost the plant less C, were favored in colder/drier climates where soils were richer in total nitrogen. Environmental filtering of ectomycorrhizal fungal communities is potentially related to co-evolutionary history between Douglas-fir populations and fungal symbionts, suggesting success of interior Douglas-fir as climate changes may be dependent on maintaining strong associations with local communities of mycorrhizal fungi. No evidence for a link between root and fungal resource foraging strategies was found at the regional scale. This lack of evidence further supports the need for a mycorrhizal symbiosis framework that is independent of root trait frameworks, to aid in understanding belowground plant uptake strategies across environments.

Intraspecific Fine-Root Trait-Environment Relationships across Interior Douglas-Fir Forests of Western Canada.

Variation in resource acquisition strategies enables plants to adapt to different environments and may partly determine their responses to climate change. However, little is known about how belowground plant traits vary across climate and soil gradients. Focusing on interior Douglas-fir (Pseudotsuga menziesii var. glauca) in western Canada, we tested whether fine-root traits relate to the environment at the intraspecific level. We quantified the variation in commonly measured functional root traits (morphological, chemical, and architectural traits) among the first three fine-root orders (i.e., absorptive fine roots) and across biogeographic gradients in climate and soil factors. Moderate but consistent trait-environment linkages occurred across populations of Douglas-fir, despite high levels of within-site variation. Shifts in morphological traits across regions were decoupled from those in chemical traits. Fine roots in colder/drier climates were characterized by a lower tissue density, higher specific area, larger diameter, and lower carbon-to-nitrogen ratio than those in warmer/wetter climates. Our results showed that Douglas-fir fine roots do not rely on adjustments in architectural traits to adapt rooting strategies in different environments. Intraspecific fine-root adjustments at the regional scale do not fit along a single axis of root economic strategy and are concordant with an increase in root acquisitive potential in colder/drier environments.

Porcine skin visible lesion thresholds for near-infrared lasers including modeling at two pulse durations and spot sizes.

With the advent of such systems as the airborne laser and advanced tactical laser, high-energy lasers that use 1315-nm wavelengths in the near-infrared band will soon present a new laser safety challenge to armed forces and civilian populations. Experiments in nonhuman primates using this wavelength have demonstrated a range of ocular injuries, including corneal, lenticular, and retinal lesions as a function of pulse duration. American National Standards Institute (ANSI) laser safety standards have traditionally been based on experimental data, and there is scant data for this wavelength. We are reporting minimum visible lesion (MVL) threshold measurements using a porcine skin model for two different pulse durations and spot sizes for this wavelength. We also compare our measurements to results from our model based on the heat transfer equation and rate process equation, together with actual temperature measurements on the skin surface using a high-speed infrared camera. Our MVL-ED50 thresholds for long pulses (350 micros) at 24-h postexposure are measured to be 99 and 83 J cm(-2) for spot sizes of 0.7 and 1.3 mm diam, respectively. Q-switched laser pulses of 50 ns have a lower threshold of 11 J cm(-2) for a 5-mm-diam top-hat laser pulse.

Differentiation of fetal pig endocrine cells after allografting into the thymus gland.

BACKGROUND: The thymus of large animals, such as the pig, is thought to be an appropriate site for transplanting adult islets, which contain numerous beta cells, for the purpose of reversing diabetes. Whether fetal islet-like cell clusters (ICCs), which contain few beta cells, will develop at this site, so that adequate amounts of insulin can be produced, is unknown. METHODS: Between 15,000 and 40,000 ICCs were injected into the thymus gland of six juvenile immunosuppressed pigs, and the animals were killed up to 30 days later. The graft was then examined histologically and comparisons made with untransplanted ICCs and those grafted into the omentum of immunosuppressed pigs. RESULTS: At transplantation, the percentage of cells in the ICCs containing insulin, glucagon, somatostatin, or pancreatic polypeptide was 9+/-1%, 13+/-2%, 9+/-1%, and 3+/-1% respectively. Within 9-30 days of transplantation into the thymus, the percentage of all endocrine cells increased, insulin to 41+/-3%, glucagon to 43+/-6%, somatostatin to 26+/-4%, and pancreatic polypeptide to 9+/-3%. There was co-localization of more than one hormone in some cells. Omental grafts contained a similar percentage of insulin and glucagon-containing cells, but significantly fewer somatostatin and pancreatic polypeptide-containing cells. CONCLUSIONS: Endocrine cells from the fetal pig pancreas will differentiate when transplanted into the thymus gland of the pig, making this a suitable site for grafting ICCs to test their ability to normalize blood glucose levels of diabetic recipients.

Pathology of macular lesions from subnanosecond pulses of visible laser energy.

PURPOSE: To demonstrate how current theories regarding ultrashort laser pulse effects may apply to ocular tissue, a prospective clinicopathologic study of macular lesions from ultrashort laser pulses compared the pathologic effects with the clinical and fluorescein angiographic appearance of the laser lesions. METHODS: Ninety-femtosecond, 3-picosecond, and 60-picosecond laser pulses, throughout a range of energies, were delivered to the retina of Macaca mulatta. Clinical examination and fluorescein angiography were performed at 1 hour in all eyes and 24 hours after exposure in selected eyes. Eyes were enucleated at 1 or 24 hours after lesion placement. The structure and extent of retinal lesions were scored for comparison with the clinical findings. RESULTS: Focal retinal pathologic appearance correlated well with a clinically visible lesion observed 24 hours after laser delivery. Retinal lesions were small foci of retinal pigment epithelium (RPE) and retinal disruption, without choriocapillaris involvement. Lesions that contained focal RPE vacuoles or lifting of the RPE also demonstrated leakage, in fluorescein angiographic studies. Suprathreshold laser delivery frequently caused focal columns of retinal injury and intraretinal hemorrhages from retinal vessel bleeding, with no rupture of choroidal blood vessels. CONCLUSIONS: The retinal response to ultrashort laser pulses at moderate energy followed a pattern of focal damage from laser-induced breakdown without significant thermal spread.

Retinal effects of ultrashort laser pulses in the rabbit eye.

PURPOSE: To evaluate the effects of ultrashort laser pulses from femtoseconds to nanoseconds on the retinas of live rabbit eyes and to determine the energy requirements for visible lesion development. METHODS: The retinal effects of laser exposures were examined for laser exposures with pulsewidths ranging from 4 ns to 90 fs, with visible wavelengths of 532 nm for durations > 5 ps and 580 nm for durations < 5 ps. The authors examined and scored all laser impact sites in the retina ophthalmoscopically--with fundus photography and with fluorescein angiography--to identify evidence of visible laser effects. RESULTS: The laser energy required for retinal minimal visible lesions was found to be slightly less for pulsewidths < 5 ps and varied from 5 microJ at 4 ns to 1.1 microJ at 90 fs for the 1-hour ophthalmoscopic reading. Lesions from higher energy pulses (7 to 120 microJ) were examined at all pulsewidths. For 90-fs high-energy pulse delivery, an increased intensity of retinal lesions and the development of several subretinal hemorrhages were demonstrated at peak energies of 30 microJ. Fluorescein angiography was found to be much more sensitive as an indicator of retinal damage for both femtosecond pulsewidths. CONCLUSIONS: The low energies required for visible lesion production in live rabbit eyes raise new questions surrounding ultrashort pulse propagation in ocular media, energy deposition at the retina, and mechanisms limiting retinal damage from ultrashort laser pulses.

Visible retinal lesions from ultrashort laser pulses in the primate eye.

PURPOSE: To evaluate the effects of ultrashort laser pulses of visible wavelengths on the retinas of rhesus monkey eyes and to perform threshold measurements for minimum visible lesions (MVLs) at pulsewidths from nanoseconds to femtoseconds. METHODS: Single laser pulses at visible wavelengths were placed within the macular area of live rhesus monkey eyes at varying pulse energies at five pulsewidths (4 ns, 60 ps, 3 ps, 600 fs, and 90 fs). The number of visible lesions was determined after 1 hour and 24 hours postexposure, and a probit analysis was performed for the dosage, causing 50% probability for damage (ED50) as well as the 95% fiducial intervals for ED50. Fluorescein angiography (FA) was performed, and hemorrhagic lesions were recorded as they became visible. RESULTS: The ED50 threshold doses at the 1-hour reading, calculated from the measured data, decreased from 1.5 microJ at 4 ns to 0.60 microJ at 600 fs, but it increased to 1.18 microJ at 90 fs. At the 24-hour reading, the ED50 calculated doses decreased from 0.90 microJ at 4 ns down to 0.26 microJ at 600 fs, but it increased to 0.43 microJ at 90 fs. Fluorescein angiography visible lesion ED50 values were all higher than MVL values, showing that FA was not as sensitive in determining damage levels. CONCLUSIONS: Laser pulses for pulsewidths between 4 ns and 90 fs are capable of producing visible lesions in monkey eyes with energies less than 1 microJ. Fluorescein angiography is not as sensitive in determining threshold levels as visually observing the retina through a fundus camera.

A comparison of retinal morphology viewed by optical coherence tomography and by light microscopy.

OBJECTIVE: To compare the cross-sectional images of primate retinal morphology obtained by optical coherence tomography (OCT) with light microscopy to determine the retinal components represented in OCT images. METHODS: Laser pulses were delivered to the retina to create small marker lesions in a Macaca mulatta. These lesions were used to align in vivo OCT scans and ex vivum histologic cross sections for image comparison. RESULTS: The OCT images demonstrated reproducible patterns of retinal morphology that corresponded to the location of retinal layers seen on light microscopic overlays. Layers of relative high reflectivity corresponded to horizontally aligned retinal components such as the nerve fiber layer and plexiform layers, as well as to the retinal pigment epithelium and choroid. In contrast, the nuclear layers and the photoreceptor inner and outer segments demonstrated relative low reflectivity by OCT. CONCLUSIONS: Retinal morphology and macular OCT imaging correlate well, with alignment of areas of high and low reflectivity to specific retinal and choroidal elements. Resolution of retinal structures by OCT depends on the contrast in relative reflectivity of adjacent structures. Use of this tool will enable expanded study of retinal morphology, both normal and pathologic, as it evolves in vivo.

Argon laser retinal lesions evaluated in vivo by optical coherence tomography.

PURPOSE: To assess the in vivo evolution of argon laser retinal lesions by correlating the cross-sectional structure from sequential optical coherence tomography with histopathologic sectioning. METHODS: Argon laser lesions were created in the retinas of Macaca mulatta and evaluated by cross-section optical coherence tomography, which was compared at selected time points with corresponding histopathology. RESULTS: Argon laser lesions induced an optical coherence tomography pattern of early outer retinal relative high reflectivity with subsequent surrounding relative low reflectivity that correlated well with histopathologic findings. The in vivo optical coherence tomography images of macular laser lesions clearly demonstrated differences in pathologic response by retinal layer over time. CONCLUSION: The novel sequential imaging of rapidly evolving macular lesions with optical coherence tomography provides new insight into the patterns of acute tissue response by cross-sectional layer. This sequential imaging technique will aid in our understanding of the rapid evolution of retinal pathology and response to treatment in the research and clinical setting.

Comparison of optical coherence tomography imaging of cataracts with histopathology.

This paper presents a comparison of in vivo optical coherence tomography (OCT) captured cataract images to subsequent histopathological examination of the lenticular opacities. OCT imaging was performed on anesthetized Rhesus monkeys, known as the delayed effects colony (DEC), with documented cataracts. These monkeys were exposed to several types of radiation during the mid and late 1960s. The radiation and age related cataracts in these animals were closely monitored using a unique grading system developed specifically for the DEC. In addition to this system, a modified version of a common cataract grading scheme for use in humans was applied. Of the original 18 monkeys imaged, lenses were collected at necropsy from seven of these animals, processed, and compared to OCT images. Results showed a direct correlation between the vertical OCT images and the cataractous lesions seen on corresponding histopathologic sections of the lenses. Based on the images obtained and their corresponding documented comparison to histopathology, OCT showed tremendous potential to aid identification and characterization of cataracts. There can be artifactual problems with the images related to movement and shadows produced by opacities. However, with the advent of increased speed in imaging and multiplanar imaging, these disadvantages may easily be overcome. © 1999 Society of Photo-Optical Instrumentation Engineers.

Median effective dose determination and histologic characterization of porcine (Sus scrofa domestica) dermal lesions induced by 1540-nm laser radiation pulses.

BACKGROUND AND PURPOSE: Light amplification by stimulated emission of radiation (laser) systems operating in the so-called "eye safe" region are gaining widespread use in industry, medicine, and military applications. This research effort was geared to study the effects of laser tissue interaction on human skin by using in vivo porcine skin as an animal model. The goals of the study were to determine the median effective dose (ED50) for 1540-nm laser exposures, to evaluate the Yorkshire pig and the Yucatan mini-pig as animal models for laser exposure, and to characterize laser-induced skin lesions histologically. METHODS: A 1540-nm wavelength laser was used to expose multiple sites on the flanks of 10 pigs, using 0.8-ms pulses, ranging from 7 to 96 joules (J)/cm2. Single pulses were delivered to the flank of Yorkshire and Yucatan pigs in a grid pattern. Exposure sites were evaluated immediately after exposure and at 1 hour and 24 hours for presence of gross lesions. Representative biopsy specimens were collected from lesion sites for histologic evaluation at the 24-hour endpoint. RESULTS: The ED50 for the two breeds differed in the amount of energy required to induce dermal lesions. Grossly, lesions in each breed were well demarcated and pale gray to brightly erythematous. Microscopically, lesions had epidermal layer damage as cellular swelling and nuclear pyknosis, loss of cellular detail, and coagulation necrosis at the dermal layer. CONCLUSIONS: Findings suggest the presence of a different mechanism of laser-tissue damage in these two breeds. Photo-thermal mechanism appears to induce the skin lesions in the Yorkshire pig, whereas photo-thermal and photochemical mechanisms appear to be involved in lesion formation in the Yucatan mini-pig. All data obtained in this study will become part of database used by the American National Standards Institute (ANSI) to recommend laser safety standards for the occupational health and safety programs (OHSP), which will be used by industry and the military to base and update their current OHSP.

Study of corneal lesions induced by 1,318-nm laser radiation pulses in Dutch belted rabbits (Oryctolagus cuniculus).

BACKGROUND AND PURPOSE: Use of high-energy near-infrared lasers is becoming more prevalent in today's industries, such as technology, medicine, and military operations. Despite wide-range use of these lasers, threshold, median effective dose (ED50), and the mechanism of laser-tissue interaction are not well defined at the 1,318-nm wavelength for human corneal exposures. The goals of the study reported here were to establish the ED50 for single-pulse, 1,318-nm laser exposures on the Dutch Belted rabbit cornea and to characterize microscopic changes. Results of this study were then compared with those of previous corneal studies. METHODS: A neodymium:yttrium aluminum garnet (Nd:YAG) laser was used to deliver single 1,318-nm wavelength pulses to the corneas of 10 female Dutch Belted rabbits (Oryctolagus cuniculus). Single pulses of 0.5-ms duration and radiant energy ranging from 116 to 2,250 J/cm2 irradiated the exposure sites. Sites were clinically evaluated for presence of a lesion at one hour and 24-h after exposure. Results of the 24-h evaluation were used to determine the (ED50). Corneas were subsequently collected at the 24-h endpoint for microscopic evaluation. RESULTS: The ED50 for 1,318-nm exposures to the rabbit cornea was determined to be 382 J/cm2, as measured at the 1/e2 (0.865 times that of the peak power per unit area). At each exposure site, there was a small (< 1 mm in diameter), white, circular, well demarcated corneal lesion characterized histologically by a band of stromal coagulative necrosis and endothelial necrosis, with sparing of the anterior epithelium. In addition, there appeared some potential for damage to Descemet's membrane at the highest energy level tested. CONCLUSIONS: Findings indicate that the rabbit corneais subject to injury at the 1,318-nm wavelength with the established ED50.

Comparison of two porcine (Sus scrofa domestica) skin models for in vivo near-infrared laser exposure.

BACKGROUND AND PURPOSE: The current safety standards for lasers operating in the 1,400- to 2,000-nanometer (nm) wavelength region are based on only a few observations at specific wavelengths. On the basis of experimental results conducted with Yorkshire pigs (Sus scrofa domestica), these standards may not accurately reflect the potential for laser injury when humans are exposed to these wavelengths. It is our belief that one of the damage mechanisms involved in these laser injuries results from energy absorption by skin pigmentation (melanin), and a more highly pigmented animal model, the Yucatan hairless minipig, may be a more suitable subject for laser exposure studies. METHODS: Skin specimens were collected from Yorkshire pigs and Yucatan minipigs for histologic examination, and the thickness of the epidermis was measured. Epidermal thickness of human skin also was determined, and a qualitative assessment of the melanin content in the epidermal layers was conducted. RESULTS: Mean +/- SD thicknesses of the Yucatan minipig flank and dorsal neck epidermis were 68 +/- 34 and 68 +/- 25 microm, respectively. Thicknesses of the Yucatan minipig skin were closely comparable to the thicknesses of human epidermis from the face (68 +/- 26 microm), neck (65 +/- 24 microm) and arms (68 +/- 21 microm). The Yorkshire pig lacks substantial melanin in the epidermis, whereas the skin of the Yucatan minipig is more similar to that of humans. CONCLUSION: On the basis of epidermal skin thickness measurements and melanin assessment, the flank and dorsal neck of the Yucatan minipig are better suited to laser injury studies than are the Yorkshire pig models of human skin.

Acquisition of a conditioned reflex in New Zealand white rabbits from three sources.

In studies of learning using rabbits, there has been standardization of behavioural procedures across laboratories. Less attention has been paid to variation that may arise from genetic differences and/or differences in rearing conditions. The present experiment revealed that acquisition of a conditioned reflex can be affected dramatically by such differences. Specifically, the acquisition of a conditioned reflex in New Zealand White (NZW) rabbits from 3 different suppliers was compared. All rabbits received behavioural training in which a tone or a light signalled an electrotactile stimulation of the trigeminal nerve near the rabbits' right eye. This tactile stimulus reliably elicited an eyeblink. Repeated presentations of the auditory and visual signals followed by the tactile stimulus yielded the acquisition of a conditioned response (CR), namely closure of the eyelids during the warning period provided by the signal stimuli. Two of the groups showed steady CR acquisition at a rate that matched previous results in other laboratories as well as in the senior author's laboratory. However, the third group of rabbits showed very slow acquisition, and some rabbits failed to show any CR acquisition.

Proposed maximum permissible exposure limits for ultrashort laser pulses.

Recent studies have provided considerable ED50 data for both visible and near infrared wavelengths from single laser pulses below one nanosecond of exposure. The current ANSI Z136.1 standard does not offer an approved maximum permissible exposure limit for subnanosecond single laser pulses and the current suggested maximum permissible exposure limit may be overly conservative. Lacking an approved standard industrial, medical, educational, and military uses of these types of laser systems may be limited or prohibited. A new set of laser maximum permissible exposure limits for subnanosecond visible and near infrared single laser pulses is recommended, along with the steps taken to develop the proposed standard.

Ultrashort laser pulse effects in ocular and related media.

Relatively little experimental and theoretical data exist on the retinal hazards of ultrashort laser pulses operating in the visible and near infrared spectral regions. Because of potential nonlinear effects that can occur from high-peak irradiance, ultrashort laser pulses propagate from the cornea to the retina, we have developed four projects within our Ultrashort Pulse Effects program. First, we discuss preliminary ED50 threshold values for nanosecond (ns), picosecond (ps), and femtosecond (fs) single pulses for in-vivo ocular exposures in Dutch Belted Rabbits using pulses in the visible spectral region. Then we examine two experiments that study nonlinear absorption using water tubes and measure the nonlinear refractive index of ocular tissue using the Z-Scan technique. Finally, we determine laser-induced breakdown thresholds in ultrahigh purity water. These studies give reasonable estimates of the damage thresholds and insight into the biophysics of how ultrashort pulses interact with ocular media.

Ultrashort laser pulse bioeffects and safety.

Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than 1 ns than that for longer pulses. It has also been shown that more energy is required for near-infrared (NIR) wavelengths than in the visible because the light focuses behind the retina, requiring more energy to produce a damaging fluence on the retina. We review the progress made in determining the trends in retinal damage from laser pulses of 1 ns to 100 fs in the visible and NIR wavelength regimes. We have determined the most likely damage mechanism(s) operative in this pulse width regime.

Overruled: objections to optical disk archiving.

In summary, while the Federal Rules of Evidence neglect to specifically address the admission of optical disk evidence, the Rules do recognize the reliability and admissibility of records maintained with modern computer storage techniques. In certain cases, information stored on optical disk will constitute original information; in others, the information will constitute an admissible duplicate. Regardless of the classification, the optical disk evidence should be admissible if the party offering the evidence can establish that the optical disk storage and retrieval process accurately reproduces the original document. The admission of medical records stored on optical disk will be challenged. The technology involved in optical disk storage, however, makes optical disk information more reliable than magnetic disk information. As a result, optical disk evidence currently should survive challenges more readily than magnetic disk evidence.