Main-Channel Slopes of Selected Streams in Iowa for Estimation of Flood-Frequency Discharges, November 2004

This report describes a statewide study conducted to develop main-channel slope (MCS) curves for 138 selected streams in Iowa with drainage areas greater than 100 square miles. MCS values determined from the curves can be used in regression equations for estimating flood frequency discharges. Multi-variable regression equations previously developed for two of the three hydrologic regions defined for Iowa require the measurement of MCS. Main-channel slope is a difficult measurement to obtain for large streams using 1:24,000-scale topographic maps. The curves developed in this report provide a simplified method for determining MCS values for sites located along large streams in Iowa within hydrologic Regions 2 and 3. The curves were developed using MCS values quantified for 2,058 selected sites along 138 selected streams in Iowa. A geographic information system (GIS) technique and 1:24,000-scale topographic data were used to quantify MCS values for the stream sites. The sites were selected at about 5-mile intervals along the streams. River miles were quantified for each stream site using a GIS program. Data points for river-mile and MCS values were plotted and a best-fit curve was developed for each stream. An adjustment was applied to all 138 curves to compensate for differences in MCS values between manual measurements and GIS quantification. The multi-variable equations for Regions 2 and 3 were developed using manual measurements of MCS. A comparison of manual measurements and GIS quantification of MCS indicates that manual measurements typically produce greater values of MCS compared to GIS quantification. Median differences between manual measurements and GIS quantification of MCS are 14.8 and 17.7 percent for Regions 2 and 3, respectively. Comparisons of percentage differences between flood-frequency discharges calculated using MCS values of manual measurements and GIS quantification indicate that use of GIS values of MCS for Region 3 substantially underestimate flood discharges. Mean and median percentage differences for 2- to 500-year recurrence-interval flood discharges ranged from 5.0 to 5.3 and 4.3 to 4.5 percent, respectively, for Region 2 and ranged from 18.3 to 27.1 and 12.3 to 17.3 percent for Region 3. The MCS curves developed from GIS quantification were adjusted by 14.8 percent for streams located in Region 2 and by 17.7 percent for streams located in Region 3. Comparisons of percentage differences between flood discharges calculated using MCS values of manual measurements and adjusted-GIS quantification for Regions 2 and 3 indicate that the flood-discharge estimates are comparable. For Region 2, mean percentage differences for 2- to 500-year recurrence-interval flood discharges ranged between 0.6 and 0.8 percent and median differences were 0.0 percent. For Region 3, mean and median differences ranged between 5.4 to 8.4 and 0.0 to 0.3 percent, respectively. A list of selected stream sites presented with each curve provides information about the sites including river miles, drainage areas, the location of U.S. Geological Survey stream flowgage stations, and the location of streams Abstract crossing hydro logic region boundaries or the Des Moines Lobe landforms region boundary. Two examples are presented for determining river-mile and MCS values, and two techniques are presented for computing flood-frequency discharges.

Estimating Design-Flood Discharges for Streams in Iowa Using Drainage-Basin and Channel-Geometry Characteristics, HR-322, 1993

Drainage-basin and channel-geometry multiple-regression equations are presented for estimating design-flood discharges having recurrence intervals of 2, 5, 10, 25, 50, and 100 years at stream sites on rural, unregulated streams in Iowa. Design-flood discharge estimates determined by Pearson Type-III analyses using data collected through the 1990 water year are reported for the 188 streamflow-gaging stations used in either the drainage-basin or channel-geometry regression analyses. Ordinary least-squares multiple-regression techniques were used to identify selected drainage-basin and channel-geometry regions. Weighted least-squares multiple-regression techniques, which account for differences in the variance of flows at different gaging stations and for variable lengths in station records, were used to estimate the regression parameters. Statewide drainage-basin equations were developed from analyses of 164 streamflow-gaging stations. Drainage-basin characteristics were quantified using a geographic-information-system (GIS) procedure to process topographic maps and digital cartographic data. The significant characteristics identified for the drainage-basin equations included contributing drainage area, relative relief, drainage frequency, and 2-year, 24-hour precipitation intensity. The average standard errors of prediction for the drainage-basin equations ranged from 38.6% to 50.2%. The GIS procedure expanded the capability to quantitatively relate drainage-basin characteristics to the magnitude and frequency of floods for stream sites in Iowa and provides a flood-estimation method that is independent of hydrologic regionalization. Statewide and regional channel-geometry regression equations were developed from analyses of 157 streamflow-gaging stations. Channel-geometry characteristics were measured on site and on topographic maps. Statewide and regional channel-geometry regression equations that are dependent on whether a stream has been channelized were developed on the basis of bankfull and active-channel characteristics. The significant channel-geometry characteristics identified for the statewide and regional regression equations included bankfull width and bankfull depth for natural channels unaffected by channelization, and active-channel width for stabilized channels affected by channelization. The average standard errors of prediction ranged from 41.0% to 68.4% for the statewide channel-geometry equations and from 30.3% to 70.0% for the regional channel-geometry equations. Procedures provided for applying the drainage-basin and channel-geometry regression equations depend on whether the design-flood discharge estimate is for a site on an ungaged stream, an ungaged site on a gaged stream, or a gaged site. When both a drainage-basin and a channel-geometry regression-equation estimate are available for a stream site, a procedure is presented for determining a weighted average of the two flood estimates.

Production of nanometric particles in radio frequency glow discharges in mixtures of silane and methane

The formation of silicon particles in rf glow discharges has attracted attention due to their effect as a contaminant during film deposition or etching. However, silicon and silicon alloy powders produced by plasma¿enhanced chemical vapor deposition (PECVD) are promising new materials for sintering ceramics, for making nanoscale filters, or for supporting catalytic surfaces. Common characteristics of these powders are their high purity and the easy control of their stoichiometry through the composition of the precursor gas mixture. Plasma parameters also influence their structure. Nanometric powders of silicon¿carbon alloys exhibiting microstructural properties such as large hydrogen content and high surface/volume ratio have been produced in a PECVD reactor using mixtures of silane and methane at low pressure (-1 Torr) and low frequency square¿wave modulated rf power (13.56 MHz). The a¿Si1¿xCx:H powders were obtained from different precursor gas mixtures, from R=0.05 to R=9, where R=[SiH4]/([SiH4]+[CH4]). The structure of the a¿Si1¿xCx:H powder was analyzed by several techniques. The particles appeared agglomerated, with a wide size distribution between 5 and 100 nm. The silane/methane gas mixture determined the vibrational features of these powders in the infrared. Silicon-hydrogen groups were present for every gas composition, whereas carbon¿hydrogen and silicon¿carbon bonds appeared in methane¿rich mixtures (R-0.6). The thermal desorption of hydrogen revealed two main evolutions at about 375 and 660¿°C that were ascribed to hydrogen bonded to silicon and carbon, respectively. The estimated hydrogen atom concentration in the sample was about 50%.

Stimulus-induced rhythmic, periodic or ictal discharges (SIRPIDs) in comatose survivors of cardiac arrest: Characteristics and prognostic value.

OBJECTIVES: To analyze the prevalence of stimulus-induced rhythmic, periodic or ictal discharges (SIRPIDs) in patients with coma after cardiac arrest (CA) and therapeutic hypothermia (TH) and to examine their potential association with outcome. METHODS: We studied our prospective cohort of adult survivors of CA treated with TH, assessing SIRPIDs occurrence and their association with 3-month outcome. Only univariated analyses were performed. RESULTS: 105 patients with coma after CA who underwent electroencephalogram (EEG) during TH and normothermia (NT) were studied. Fifty-nine patients (56%) survived, and 48 (46%) had good neurological recovery. The prevalence of SIRPIDs was 13.3% (14/105 patients), of whom 6 occurred during TH (all died), and 8 in NT (3 survived, 1 with good neurological outcome); none had SIRPIDs at both time-points. SIRPIDs were associated with discontinuous or non-reactive EEG background and were a robustly related to poor neurological outcome (p<0.001). CONCLUSION: This small series provides preliminary univariate evidence that in patients with coma after CA, SIRPIDs are associated with poor outcome, particularly when occurring during in therapeutic hypothermia. However, survival with good neurological recovery may be observed when SIRPIDs arise in the post-rewarming normothermic phase. SIGNIFICANCE: This study provides clinicians with new information regarding the SIRPIDs prognostic role in patients with coma after cardiac arrest.

Techniques for Estimating Flood-Frequency Discharges for Streams in Iowa, HR-395A, 2001

A statewide study was conducted to develop regression equations for estimating flood-frequency discharges for ungaged stream sites in Iowa. Thirty-eight selected basin characteristics were quantified and flood-frequency analyses were computed for 291 streamflow-gaging stations in Iowa and adjacent States. A generalized-skew-coefficient analysis was conducted to determine whether generalized skew coefficients could be improved for Iowa. Station skew coefficients were computed for 239 gaging stations in Iowa and adjacent States, and an isoline map of generalized-skew-coefficient values was developed for Iowa using variogram modeling and kriging methods. The skew map provided the lowest mean square error for the generalized-skew- coefficient analysis and was used to revise generalized skew coefficients for flood-frequency analyses for gaging stations in Iowa. Regional regression analysis, using generalized least-squares regression and data from 241 gaging stations, was used to develop equations for three hydrologic regions defined for the State. The regression equations can be used to estimate flood discharges that have recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years for ungaged stream sites in Iowa. One-variable equations were developed for each of the three regions and multi-variable equations were developed for two of the regions. Two sets of equations are presented for two of the regions because one-variable equations are considered easy for users to apply and the predictive accuracies of multi-variable equations are greater. Standard error of prediction for the one-variable equations ranges from about 34 to 45 percent and for the multi-variable equations range from about 31 to 42 percent. A region-of-influence regression method was also investigated for estimating flood-frequency discharges for ungaged stream sites in Iowa. A comparison of regional and region-of-influence regression methods, based on ease of application and root mean square errors, determined the regional regression method to be the better estimation method for Iowa. Techniques for estimating flood-frequency discharges for streams in Iowa are presented for determining ( 1) regional regression estimates for ungaged sites on ungaged streams; (2) weighted estimates for gaged sites; and (3) weighted estimates for ungaged sites on gaged streams. The technique for determining regional regression estimates for ungaged sites on ungaged streams requires determining which of four possible examples applies to the location of the stream site and its basin. Illustrations for determining which example applies to an ungaged stream site and for applying both the one-variable and multi-variable regression equations are provided for the estimation techniques.

Methods for Estimating Annual Exceedance-Probability Discharges for Streams in Iowa, Based on Data through Water Year 2010, TR-519, 2013

A statewide study was performed to develop regional regression equations for estimating selected annual exceedance- probability statistics for ungaged stream sites in Iowa. The study area comprises streamgages located within Iowa and 50 miles beyond the State’s borders. Annual exceedanceprobability estimates were computed for 518 streamgages by using the expected moments algorithm to fit a Pearson Type III distribution to the logarithms of annual peak discharges for each streamgage using annual peak-discharge data through 2010. The estimation of the selected statistics included a Bayesian weighted least-squares/generalized least-squares regression analysis to update regional skew coefficients for the 518 streamgages. Low-outlier and historic information were incorporated into the annual exceedance-probability analyses, and a generalized Grubbs-Beck test was used to detect multiple potentially influential low flows. Also, geographic information system software was used to measure 59 selected basin characteristics for each streamgage. Regional regression analysis, using generalized leastsquares regression, was used to develop a set of equations for each flood region in Iowa for estimating discharges for ungaged stream sites with 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities, which are equivalent to annual flood-frequency recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years, respectively. A total of 394 streamgages were included in the development of regional regression equations for three flood regions (regions 1, 2, and 3) that were defined for Iowa based on landform regions and soil regions. Average standard errors of prediction range from 31.8 to 45.2 percent for flood region 1, 19.4 to 46.8 percent for flood region 2, and 26.5 to 43.1 percent for flood region 3. The pseudo coefficients of determination for the generalized leastsquares equations range from 90.8 to 96.2 percent for flood region 1, 91.5 to 97.9 percent for flood region 2, and 92.4 to 96.0 percent for flood region 3. The regression equations are applicable only to stream sites in Iowa with flows not significantly affected by regulation, diversion, channelization, backwater, or urbanization and with basin characteristics within the range of those used to develop the equations. These regression equations will be implemented within the U.S. Geological Survey StreamStats Web-based geographic information system tool. StreamStats allows users to click on any ungaged site on a river and compute estimates of the eight selected statistics; in addition, 90-percent prediction intervals and the measured basin characteristics for the ungaged sites also are provided by the Web-based tool. StreamStats also allows users to click on any streamgage in Iowa and estimates computed for these eight selected statistics are provided for the streamgage.

Comparisons of Estimates of Annual Exceedance-Probability Discharges for Small Drainage Basins in Iowa, Based on Data through Water Year 2013, TR-678, 2015

Traditionally, the Iowa Department of Transportation has used the Iowa Runoff Chart and single-variable regional-regression equations (RREs) from a U.S. Geological Survey report (published in 1987) as the primary methods to estimate annual exceedance-probability discharge (AEPD) for small (20 square miles or less) drainage basins in Iowa. With the publication of new multi- and single-variable RREs by the U.S. Geological Survey (published in 2013), the Iowa Department of Transportation needs to determine which methods of AEPD estimation provide the best accuracy and the least bias for small drainage basins in Iowa. Twenty five streamgages with drainage areas less than 2 square miles (mi2) and 55 streamgages with drainage areas between 2 and 20 mi2 were selected for the comparisons that used two evaluation metrics. Estimates of AEPDs calculated for the streamgages using the expected moments algorithm/multiple Grubbs-Beck test analysis method were compared to estimates of AEPDs calculated from the 2013 multivariable RREs; the 2013 single-variable RREs; the 1987 single-variable RREs; the TR-55 rainfall-runoff model; and the Iowa Runoff Chart. For the 25 streamgages with drainage areas less than 2 mi2, results of the comparisons seem to indicate the best overall accuracy and the least bias may be achieved by using the TR-55 method for flood regions 1 and 3 (published in 2013) and by using the 1987 single-variable RREs for flood region 2 (published in 2013). For drainage basins with areas between 2 and 20 mi2, results of the comparisons seem to indicate the best overall accuracy and the least bias may be achieved by using the 1987 single-variable RREs for the Southern Iowa Drift Plain landform region and for flood region 3 (published in 2013), by using the 2013 multivariable RREs for the Iowan Surface landform region, and by using the 2013 or 1987 single-variable RREs for flood region 2 (published in 2013). For all other landform or flood regions in Iowa, use of the 2013 single-variable RREs may provide the best overall accuracy and the least bias. An examination was conducted to understand why the 1987 single-variable RREs seem to provide better accuracy and less bias than either of the 2013 multi- or single-variable RREs. A comparison of 1-percent annual exceedance-probability regression lines for hydrologic regions 1–4 from the 1987 single-variable RREs and for flood regions 1–3 from the 2013 single-variable RREs indicates that the 1987 single-variable regional-regression lines generally have steeper slopes and lower discharges when compared to 2013 single-variable regional-regression lines for corresponding areas of Iowa. The combination of the definition of hydrologic regions, the lower discharges, and the steeper slopes of regression lines associated with the 1987 single-variable RREs seem to provide better accuracy and less bias when compared to the 2013 multi- or single-variable RREs; better accuracy and less bias was determined particularly for drainage areas less than 2 mi2, and also for some drainage areas between 2 and 20 mi2. The 2013 multi- and single-variable RREs are considered to provide better accuracy and less bias for larger drainage areas. Results of this study indicate that additional research is needed to address the curvilinear relation between drainage area and AEPDs for areas of Iowa.

Chemical and isotopic equilibrium between CO2 and CH4 in fumarolic gas discharges: Generation of CH4 in arc magmatic-hydrothermal systems

The chemical and isotopic composition of fumarolic gases emitted from Nisyros Volcano, Greece, and of a single gas sample from Vesuvio, Italy, was investigated in order to determine the origin of methane (CH,) within two subduction-related magmatic-hydrothermal environments. Apparent temperatures derived from carbon isotope partitioning between CH4 and CO2 of around 340degreesC for Nisyros and 470degreesC for Vesuvio correlate well with aquifer temperatures as measured directly and/or inferred from compositional data using the H2O-H-2-CO2-CO-CH4 geothermometer. Thermodynamic modeling reveals chemical equilibrium between CH4, CO2 and H2O implying that carbon isotope partitioning between CO2 and CH, in both systems is controlled by aquifer temperature. N-2/(3) He and CH4/(3) He ratios of Nisyros fumarolic gases are unusually low for subduction zone gases and correspond to those of midoceanic ridge environments. Accordingly, CH4 may have been primarily generated through the reduction of CO, by H, in the absence of any organic matter following a Fischer-Tropsch-type reaction. However, primary occurrence of minor amounts of thermogenic CH4 and subsequent re-equilibration with co-existing CO2 cannot be ruled out entirely- CO2/He-3 ratios and delta(13)C(CO2) values imply that the evolved CO2 either derives from a metasomatized mantle or is a mixture between two components, one outgassing from an unaltered mantle and the other released by thermal breakdown of marine carbonates. The latter may contain traces of organic matter possibly decomposing to CH4 during thermometamorphism. Copyright (C) 2004 Elsevier Ltd.

Properties of amorphous silicon thin films grown in square wave modulated silane rf discharges.

Hydrogenated amorphous silicon (a‐Si:H) thin films have been obtained from pure SiH4 rf discharges by using the square wave modulation (SQWM) method. Film properties have been studied by means of spectroellipsometry, thermal desorption spectrometry, photothermal deflection spectroscopy and electrical conductivity measurements, as a function of the modulation frequency of the rf power amplitude (0.2-4000 Hz). The films deposited at frequencies about 1 kHz show the best structural and optoelectronic characteristics. Based upon the experimental results, a qualitative model is presented, which points up the importance of plasma negative ions in the deposition of a‐Si:H from SQWM rf discharges through their influence on powder particle formation.

Weakened functional connectivity in patients with psychogenic non-epileptic seizures (PNES) converges on basal ganglia.

BACKGROUND: Psychogenic non-epileptic seizures (PNES) are involuntary paroxysmal events that are unaccompanied by epileptiform EEG discharges. We hypothesised that PNES are a disorder of distributed brain networks resulting from their functional disconnection.The disconnection may underlie a dissociation mechanism that weakens the influence of unconsciously presented traumatising information but exerts maladaptive effects leading to episodic failures of behavioural control manifested by psychogenic 'seizures'. METHODS: To test this hypothesis, we compared functional connectivity (FC) derived from resting state high-density EEGs of 18 patients with PNES and 18 age-matched and gender-matched controls. To this end, the EEGs were transformed into source space using the local autoregressive average inverse solution. FC was estimated with a multivariate measure of lagged synchronisation in the θ, α and β frequency bands for 66 brain sites clustered into 18 regions. A multiple comparison permutation test was applied to deduce significant between-group differences in inter-regional and intraregional FC. RESULTS: The significant effect of PNES-a decrease in lagged FC between the basal ganglia and limbic, prefrontal, temporal, parietal and occipital regions-was found in the α band. CONCLUSION: We believe that this finding reveals a possible neurobiological substrate of PNES, which explains both attenuation of the effect of potentially disturbing mental representations and the occurrence of PNES episodes. By improving understanding of the aetiology of this condition, our results suggest a potential refinement of diagnostic criteria and management principles.

Electrolocation-communication discharges of the fish Gymnotus carapo L. (Gymnotidae: Gymnotiformes) during behavioral sleep

Technical problems have hampered the study of sleep in teleosts. The electrical discharges of Gymnotus carapo L. (Gymnotidae: Gymnotiformes) were monitored to evaluate their ease and reliability as parameters to study sleep. The discharges were detected by electrodes immersed in a glass aquarium and were recorded on a conventional polygraph. G. carapo showed conspicuous signs of behavioral sleep. During these periods, opercular beat rates were counted, electric discharges recorded, and the "sharp discharge increase" (SDI) of the orienting reflex was investigated. All 20 animals monitored maintained electrical discharges during behavioral sleep. The discharge frequencies during sleep (50.3 ± 10.4 Hz) were not significantly different from those observed when the fish was awake and inactive (57.2 ± 12.1 Hz) (Wilcoxon matched-pairs signed-ranks test, P>0.05). However, the SDI, which was prevalent in the awake fish, was not observed during periods of behavioral sleep. Additional observations showed that the species had cannibalistic habits. When presented with electrical discharges from a conspecific, the sleeping fish showed an initial decrease or pause in discharge frequency, while the awake fish did not have this response. We conclude that the electrical discharges of G. carapo were not conspicuous indicators of behavioral sleep. Discharges may have been maintained during sleep for sensory purposes, i.e., conspecific detection and avoidance of cannibalistic attacks.

Protein tyrosine kinase inhibitors modify kainic acid-induced epileptiform activity and mossy fiber sprouting but do not protect against limbic cell death

Intrahippocampal administration of kainic acid (KA) induces synaptic release of neurotrophins, mainly brain-derived neurotrophic factor, which contributes to the acute neuronal excitation produced by the toxin. Two protein tyrosine kinase inhibitors, herbimycin A and K252a, were administered intracerebroventricularly, in a single dose, to attenuate neurotrophin signaling during the acute effects of KA, and their role in epileptogenesis was evaluated in adult, male Wistar rats weighing 250-300 g. The latency for the first Racine stage V seizure was 90 ± 8 min in saline controls (N = 4) which increased to 369 ± 71 and 322 ± 63 min in animals receiving herbimycin A (1.74 nmol, N = 4) and K252a (10 pmol, N = 4), respectively. Behavioral alterations were accompanied by diminished duration of EEG paroxysms in herbimycin A- and K252a-treated animals. Notwithstanding the reduction in seizure severity, cell death (60-90% of cell loss in KA-treated animals) in limbic regions was unchanged by herbimycin A and K252a. However, aberrant mossy fiber sprouting was significantly reduced in the ipsilateral dorsal hippocampus of K252a-treated animals. In this model of temporal lobe epilepsy, both protein kinase inhibitors diminished the acute epileptic activity triggered by KA and the ensuing morphological alterations in the dentate gyrus without diminishing cell loss. Our current data indicating that K252a, but not herbimycin, has an influence over KA-induced mossy fiber sprouting further suggest that protein tyrosine kinase receptors are not the only factors which control this plasticity. Further experiments are necessary to elucidate the exact signaling systems associated with this K252a effect.

Photoemission optogalvanic effect studies in N2, NO2 and Ar discharges under pulsed laser excitation

A two-photon induced photoemission optogalvanic effect which brings about a change in the discharge voltage when a pulsed dye laser beam is focused on a tungsten electrode has been described. The experiment is performed with N2, NO2 and Ar discharges. The magnitude of the signal voltage is studied as a function of laser energy and discharge current. The effective quantum efficiency in the discharge is found to be larger than that in the vacuum condition.