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co-auteur étranger; International audience; Melt inclusions with large, positive Sr anomalies have been described in multiple tectonic settings, and the origins of this unusual geochemical feature are debated. Three origins have been proposed involving plagioclase as the source of the elevated Sr: (i) direct assimilation of plagioclase-rich lithologies, (ii) recycled lower oceanic gabbro in the mantle source, and (iii) shallow-level diffusive interaction between present day lower oceanic crust (i.e., plagioclase-bearing lithologies) and the percolating melt. A “ghost plagioclase” signature (i.e., a large, positive Sr anomaly without associated high Al2O3) is present in melt inclusions from Mauna Loa. We present new 87Sr/86Sr measurements of individual olivine-hosted melt inclusions from three Hawaiian volcanoes, Mauna Loa, Loihi, and Koolau. The dataset includes a Mauna Loa melt inclusion with the highest reported Sr anomaly (or highest (Sr/Ce)N, which is 7.2) for Hawai'i. All melt inclusions have 87Sr/86Sr values within the range reported previously for the lavas from each volcano. Critically, the 87Sr/86Sr of the high (Sr/Ce)N melt inclusion lies within the narrow range of Mauna Loa melts that lack high (Sr/Ce)N signatures. To explain the high (Sr/Ce)N ratio of the ghost plagioclase signature using an ancient recycled gabbro would therefore require the gabbro-infused mantle source to evolve, by chance, to have the same 87Sr/86Sr as the source of the Mauna Loa melts that lack a recycled gabbro (ghost plagioclase) signature. Alternatively, shallow-level diffusive interactions between Mauna Loa plagioclase-rich cumulates and a percolating mantle-derived melt provides a simpler explanation for the presence of the high (Sr/Ce)N Mauna Loa melts.

The nature of Earth’s earliest crust and the processes by which it formed remain major issues in Precambrian geology. Due to the absence of a rock record older than ∼4.02 Ga, the only direct record of the Hadean is from rare detrital zircon and that largely from a single area: the Jack Hills and Mount Narryer region of Western Australia. Here, we report on the geochemistry of Hadean detrital zircons as old as 4.15 Ga from the newly discovered Green Sandstone Bed in the Barberton greenstone belt, South Africa. We demonstrate that the U-Nb-Sc-Yb systematics of the majority of these Hadean zircons show a mantle affinity as seen in zircon from modern plume-type mantle environments and do not resemble zircon from modern continental or oceanic arcs. The zircon trace element compositions furthermore suggest magma compositions ranging from higher temperature, primitive to lower temperature, and more evolved tonalite-trondhjemite-granodiorite (TTG)-like magmas that experienced some reworking of hydrated crust. We propose that the Hadean parental magmas of the Green Sandstone Bed zircons formed from remelting of mafic, mantle-derived crust that experienced some hydrous input during melting but not from the processes seen in modern arc magmatism.

Lavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high 87Sr/86Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high 87Sr/86Sr lava from Savai’i Island, Samoa for detailed analyses of 87Sr/86Sr and 143Nd/144Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of 87Sr/86Sr—including the highest observed in an oceanic hotspot lava—encompassing ~30% of the oceanic mantle’s total variability. These new isotopic data, data from other Samoan lavas, and magma mixing calculations are consistent with clinopyroxene 87Sr/86Sr variability resulting from magma mixing between a high silica, high 87Sr/86Sr (up to 0.7316) magma, and a low silica, low 87Sr/86Sr magma. Results provide insight into the composition of magmas derived from a sediment-infiltrated mantle source and document the fate of sediment recycled into Earth’s mantle., Subduction of oceanic crust and sediments contributes to heterogeneities in the mantle, which are sampled by mantle plumes. Here, the authors find that extreme isotopic heterogeneity in Samoan clinopyroxenes can help constrain the composition of mantle sources containing sediment recycled into the Earth’s mantle.

Geodynamic processes on early Earth, especially the interaction between the crust and deep mantle, are poorly constrained and subject to much debate. The rarity of fresh igneous materials more than 3 billion years old accounts for much of this uncertainty. Here we examine 3.27-billion-year-old komatiite lavas from Weltevreden Formation in the Barberton greenstone belt, which is part of the Kaapvaal Craton in Southern Africa. We show that primary magmatic compositions of olivine are well preserved in these lavas based on major and trace element systematics. These komatiitic lavas represent products of deep mantle plumes. Oxygen isotope compositions (δ18O) of the fresh olivine measured by laser fluorination are consistently lighter (about 2‰) than those obtained from modern mantle-derived volcanic rocks. These results suggest a mantle source for the Weltevreden komatiites that is unlike the modern mantle and one that reflects mantle heterogeneity left over from a Hadean magma ocean. The anomalously light δ18O may have resulted from fractionation of deep magma ocean phases, as has been proposed to explain lithophile and siderophile isotope compositions of Archaean komatiites. Lavas sourced from Archaean mantle plumes have anomalously light oxygen isotope signatures, according to geochemical analyses of lava samples from southern Africa. The results imply that Earth’s early mantle was heterogeneous.

Thorough physical and chemical characterization of plutonium–beryllium (PuBe) neutron sources is an important capability with applications ranging from material accountancy to nuclear forensics. Characterization of PuBe sources is not trivial owing to range of existing source designs and the need for adequate infrastructure to deal with radiation and protect the analyst. This study demonstrates a method for characterization of three PuBe sources that includes physical inspection and imaging followed by controlled disassembly and destructive analysis.

Author(s): Willhite, Lori Nicole | Advisor(s): Jackson, Matthew G | Abstract: The Icelandic hotspot has erupted the highest terrestrial mantle-derived 3He/4He over a period spanning much of the Cenozoic, from the early-Cenozoic Baffin Island-West Greenland flood basalt province (49.8 RA), to the mid-Miocene lavas in northwest Iceland (40.2 to 47.5 RA), to Pleistocene lavas in Iceland’s neovolcanic zone (34.3 RA). This study provides a detailed geochemical data set—He-O-Sr-Nd-Hf-Pb isotopic compositions, as well as whole rock major and trace element concentrations—for a suite of 18 Baffin Island lavas. The Baffin Island lavas transited through and potentially assimilated variable degrees of Precambrian continental basement. We therefore use geochemical indicators sensitive to continental crust assimilation (whole rock Nb/Th, Ce/Pb, MgO) to identify the least crustally-contaminated lavas in the suite. Four lavas, identified as “least crustally-contaminated”, have high MgO (g15 wt.%) and Nb/Th and Ce/Pb ratios that fall within the mantle range (Nb/Th=15.6±2.6, Ce/Pb=24.3±4.3). These four lavas have 3He/4He up to 39.9 RA and mantle-like δ18O of 5.03 to 5.21‰, 87Sr/86Sr = 0.703008–0.703021, 143Nd/144Nd = 0.513094–0.513128, 176Hf/177Hf = 0.283265–0.283284, 206Pb/204Pb = 17.7560–17.9375, and are located on or near the 4.5 Ga Pb isotope geochron. The radiogenic isotopic compositions of the least crustally-contaminated Baffin Island lavas are offset to more geochemically depleted compositions compared to high-3He/4He lavas from Iceland, a shift that cannot be explained by continental crust assimilation in the Baffin suite. While Sr-Nd-Pb isotopic heterogeneity among high-3He/4He localities has been previously observed, this is an important observation of geochemically distinct high-3He/4He endmembers within a single hotspot. Additionally, the least crustally-contaminated primary melts from Baffin Island-West Greenland have higher mantle potential temperatures (1510 to 1630 °C) than global MORB primary magmas located far from hotspots (1320 to 1480 °C), which supports a hot, buoyant plume origin for these early Iceland plume lavas. These observations support the contention that the geochemically heterogeneous high-3He/4He domain is dense, located in the deep mantle, and sampled by only the hottest plumes.

Parent–progeny isotope relationships provide critical signatures in forensic efforts designed to determine the history of interdicted nuclear materials. Unfortunately, there is substantial need for new standards and QC strategies yielding confidence in such chronometric measurements. Here, we investigate the initial isolation of progeny uranium in certified reference material-126a for use as a precision comparator in a thermal ionization mass spectrometry-based QC strategy seeking to provide improved uncertainties in isotopic and chronometric measurements for nuclear materials containing elevated U-236, such as plutonium. Application to real-world Pu either preserved or improved upon uncertainties associated with key parent–daughter ratios and further constrained associated chronometric windows.

Nuclear forensic publications, performance tests, and research and development efforts typically target the bulk global inventory of intentionally safeguarded materials, such as plutonium (Pu) and uranium (U). Other materials, such as neptunium (Np), pose a nuclear security risk as well. Trafficking leading to recovery of an interdicted Np sample is a realistic concern especially for materials originating in countries that reprocesses fuel. Using complementary forensic methods, potential signatures for an unknown Np oxide sample were investigated. Measurement results were assessed against published Np processes to present hypotheses as to the original intended use, method of production, and origin for this Np oxide.

In this study, a certified plutonium metal reference material (CRM 126) with a known production history is examined using analytical methods that are commonly employed in nuclear forensics for provenancing and attribution. The measured plutonium isotopic composition and actinide assay are consistent with values reported on the reference material certificate. Model ages from U/Pu and Am/Pu chronometers agree with the documented production timeline. The results confirm the utility of these analytical methods and highlight the importance of a holistic approach for forensic study of unknown materials.

This study presents a method for destructive analysis of irradiated uranium (U) targets, with a focus on collection and measurement of long-lived (t 1/2 > ~10 years) and stable fission product isotopes of ruthenium and cesium. Long-lived and stable isotopes of these elements can provide information on reactor conditions (e.g. flux, irradiation time, cooling time) in old samples (>5–10 years) whose short-lived fission products have decayed away. The separation and analytical procedures were tested on archived U reactor targets at Los Alamos National Laboratory as part of an effort to evaluate reactor models at low-burnup.

Our study of Colorado Plateau and Rio Grande rift spinel peridotite xenoliths determined bulk Lu–Hf budgets and cpx, opx, and whole rock 176Hf/177Hf to evaluate the potential age significance of Lu/Hf–Hf isotope correlations in sub-continental lithospheric mantle (SCLM) derived xenoliths. The samples have fertilities (spinel Cr# range from 0.1 to 0.5), and equilibration temperatures (950–1050 °C) that overlap with those of spinel peridotites commonly used in Lu–Hf dating studies. The Lu/Hf of clinopyroxene (cpx) and its associated whole rock (WR) are similar in fertile samples, but cpx has a lower Lu/Hf than that of the WR in refractory samples. Orthopyroxene (opx) has systematically higher Lu/Hf than cpx, but in many samples, the opx and cpx have identical 176Hf/177Hf, suggesting that the Hf isotope composition of these minerals is supported by the Lu/Hf of the WR rather than that of the individual minerals. Many opx fractions and whole rocks have less radiogenic 176Hf/177Hf than their corresponding cpx (but similar to that of the host magma), reflecting contamination. Because the 176Hf/177Hf of cpx is supported by the WR Lu/Hf, it is necessary to use the latter rather than the cpx Lu/Hf for isochron dating. However, because the actual WR Lu/Hf values are susceptible to secondary overprinting, we recommend using model WR Lu/Hf values (determined from mineral Lu and Hf concentrations and modal abundances) to construct external cpx isochrons. Model WR and measured cpx 176Hf/177Hf are correlated (r2 = 0.98) in a suite of eastern Colorado Plateau xenoliths and yield an apparent age of 1.2 Ga (versus 1.5 Ga when – incorrectly – using cpx Lu/Hf). Despite the good correlation between Lu/Hf and 176Hf/177Hf, we do not find correlations between indicators of melt depletion and Lu/Hf or 176Hf/177Hf. This suggests that Lu/Hf–176Hf/177Hf correlations are not the result of melt depletion. Instead, we propose that Lu/Hf–176Hf/177Hf correlations are the result of mixing between depleted and enriched components (e.g. metasomatism of depleted lithospheric mantle). We emphasize that additional data should be utilized (e.g. whole rock Lu–Hf budget, degree of metasomatism, opx 176Hf/177Hf) when interpreting apparent Lu–Hf isochrons for age significance.

Actinide isotope measurements are a critical signature capability in the modern nuclear forensics "toolbox", especially when interrogating anthropogenic constituents in real-world scenarios. Unfortunately, established methodologies, such as traditional total evaporation via thermal ionization mass spectrometry, struggle to confidently measure low abundance isotope ratios (

We test common fluence diagnostics in the regime of very low burnup natural uranium reactor samples. The fluence diagnostics considered are the uranium isotopics ratios $^{235}$U/$^{238}$U and $^{236}$U/$^{235}$U, for which we find simple analytic formulas agree well with full reactor simulation predictions. Both ratios agree reasonably well with one another for fluences in the mid $10^{19}\,\mathrm{n/cm^2}$ range. However, below about $10^{19}\,\mathrm{n/cm^2}$ the concentrations of $^{236}$U are found to be sufficiently low that the measured $^{236}$U/$^{235}$U ratios become unreliable. We also derive and test diagnostics for determining sample cooling times in situations where very low burnup and very long cooling times render many standard diagnostics, such as the $^{241}$Am/$^{241}$Pu ratio, impractical. We find that using several fragment ratios are necessary to detect the presence of systematic errors, such as fractionation., 7 pages, 4 figures

The Lena Trough is a highly oblique, sparsely magmatic, ultra-slow spreading center located at the smallest distance between North America and Eurasia in the Arctic basin. Competing models suggest that it is either floored by oceanic mantle abyssal peridotites (APs) exposed by lithospheric necking, or by subcontinental mantle exposed in a still juvenile rift. To distinguish between these hypotheses, we have examined mineral major and trace element and whole rock Os-isotope variations in Lena Trough peridotites. Lena Trough peridotites are predominantly LREE-depleted, similar to other AP suites, and have 187Os/188Os ranging from ∼0.118 to 0.130 ( Ave. = 0.1244 ). This distribution is nearly identical to that of abyssal peridotites globally. Both the REE patterns and the Os-isotope distribution of the Lena Trough peridotites differ starkly from subcontinental mantle xenoliths sampled at Svalbard adjacent to Lena Trough. This suggests that Lena Trough is a site of oceanic spreading, although mid-ocean ridge volcanism as such has not yet begun. Highly refractory APs from several settings have Os- and Hf-isotope compositions indicating ancient (>1 Ga) melt depletion. Some researchers have proposed that at least some APs do not directly sample the convecting upper mantle source of MORB, but instead sample highly melt-depleted residues either entrained in the convecting mantle or present as a buoyant “slag” floating atop the less-depleted MORB-source mantle. However, ocean island peridotite xenoliths and APs reveal an essentially identical, non-Gaussian distribution of Os-isotopes and also span a similar range in Hf-isotopes. The similar mean and distribution of Os-isotopes between APs and ocean island xenoliths indicate that these two sample types derive from the same heterogeneous mantle reservoir. This similarity is inconsistent with the AP “slag hypothesis” due to the significantly greater depth of origin of ocean island xenoliths with respect to APs. Global correlation between peridotite fertility indices (e.g., whole rock Al2O3, spinel Cr#) and 187Os/188Os in both APs and ocean island xenoliths suggests ancient melting events have played a role in their petrogenesis, with an average age of melt depletion of ∼1.5 Ga. However, APs display a much steeper correlation than ocean island xenoliths, but have a similar y-intercept. The contrasting trends can be explained by recent on-ridge melt extraction superimposed on an ancient melt-depletion trend. The average Os-isotope composition of both APs and ocean island xenoliths is distinctly sub-chondritic, and requires significantly greater average melt depletion of the upper mantle (>10%) than suggested by previous inversions of MORB compositions.

Mid-oceanic-ridge basalts (MORB) form by partial melting of material in the convecting upper mantle. The range in isotopic compositions observed in MORB is inconsistent with the ultradepleted isotopic compositions observed in many abyssal peridotites. These results have called into question the prevailing hypothesis that abyssal peridotites (APs) are simple residues of recent MORB melting, which should result in the two reservoirs having the same range in isotopic compositions. We examined xenoliths that, based on their chemical features (e.g., light rare earth element depleted, fertile major element compositions, Sr-Nd-Pb isotopes similar to estimates for depleted MORB mantle), are interpreted to be derived from the convecting upper mantle, in order to evaluate the potential for isotopically ultradepleted domains to contribute significantly to MORB petrogenesis. Our data support the idea that isotopically ultradepleted peridotite is widely distributed in the upper mantle, and we demonstrate that ultradepleted domains are capable of contributing to MORB petrogenesis. An isotopically enriched component, such as recycled oceanic crust, in the MORB source mantle can account for the lack of MORB with ultradepleted isotopic compositions.

Background Atypical melanocytic neoplasms present a therapeutic dilemma. Current consensus is to perform a sentinel lymph node (SLN) biopsy as part of management. However, it is unclear whether this is required in all patients. We present our experience with sentinel lymphadenectomy in these patients and examine the clinical and pathologic variables associated with a positive SLN. Study Design A prospectively maintained melanoma database was queried for patients with controversial melanocytic lesions. All patients between January 1997 and January 2009 were included. Demographic and pathologic information was collected and correlated with results of SLN biopsy. Results Thirty-one patients underwent SLN biopsy. Median patient age was 19 years (range 5 to 59 years) and median tumor Breslow depth was 1.35 mm. Five patients (16%) had a positive SLN. Those with a positive SLN were younger (median 11 vs 23.5 years, p=0.02) and had a greater Breslow depth (median 1.90 vs 1.09; p=0.03) than those who were SLN negative. Median follow-up was16 months for patients with at least 6 months of follow-up time and there have been no recurrences identified. Conclusions We report an SLN positive rate of 16% in patients with atypical melanocytic tumors. Younger age and greater Breslow depth are associated with having a positive SLN. These results confirm earlier work demonstrating the importance of SLN biopsy in this disease and highlight the need to measure Breslow depth in these lesions so that they can be appropriately stratified as to the need for SLN biopsy.

The purpose of this study was to evaluate the relative sensitivity of neonatal and adult CD rats to manganese-induced neurotoxicity. Identical oral manganese chloride (MnCl(2)) doses (0, 25, or 50 mg kg(-1) body wt. day(-1)) were given to neonatal rats throughout lactation (i.e. from postnatal day (PND) 1 through 21) and to adult male rats for 21 consecutive days. The MnCl(2) doses administered to neonates were ca. 100-fold higher than those resulting from the consumption of an equivalent volume of rat's milk. Rats were assessed using similar behavioral and neurochemical evaluations. Several statistically significant changes occurred in Mn-exposed rats relative to control animals. Neonates given the high dose of MnCl(2) had reduced body weight gain. An increased pulse-elicited acoustic startle response amplitude was observed in neonates from both MnCl(2) treatment groups on PND 21. Increased striatal, hippocampal, hindbrain and cortical Mn concentrations were observed in all Mn-exposed neonates on PND 21. Increased hypothalamic and cerebellar Mn concentrations were also observed on PND 21 in neonates from the high-dose group only. Increased striatal, cerebellar and brain residue Mn concentrations were observed in adult rats from the high-dose group. Increased striatal dopamine and 3,4-dihydroxyphenylacetic acid levels were observed only in PND 21 neonates from the high-dose group. No treatment-related changes were observed in clinical signs, motor activity (assessed in neonates on PND 13, 17, 21 +/- 1 and in adults), passive avoidance (assessed in neonates on PND 20 +/- 1 and in adults) or neuropathology (assessed in PND 21 neonates only). The results of our experiment suggest that neonates may be at greater risk for Mn-induced neurotoxicity when compared to adults receiving similar high oral levels of Mn.

A number of Drosophila learning mutants have defective intracellular second-messenger systems. In an effort to develop techniques that will allow direct measurement of the effects of these mutations on whole-cell neuronal membrane currents, the perforated-patch whole-cell (PPWC) technique has been applied to cleavage-arrested cultured embryonic Drosophila neurons. This technique permits the measurement of membrane currents without disturbing the intracellular environment. As a result of the maintenance of the intracellular environment, Drosophila neuron currents are found to be much more stable than when measured using the conventional whole-cell (CWC) patch-clamp technique. Ca2+ channel currents, which typically ‘wash out’ within a few minutes of the beginning of CWC recording, are stable for the duration of the seal (tens of minutes) when measured using the PPWC technique. Since the learning mutations dunce and rutabaga disrupt cyclic AMP signalling, the actions of externally applied dibutyryl cyclic AMP (db-cAMP) and theophylline on Ca2+ and K+ channel currents were studied. db-cAMP and theophylline enhanced the Ba2+ current, carried by Ca2+ channels, but had no effect on the K+ current in the cleavage-arrested neurons. However, the large variability and reduction in density of Ba2+ and K+ currents raise questions about the suitability of using these cleavage-arrested cells as models for Drosophila neurons.

Aims This clinical trial assessed whether a potent, selective GPR109A agonist, GSK256073, could, through inhibition of lipolysis, acutely improve glucose homeostasis in subjects with type 2 diabetes mellitus. Methods Thirty-nine diabetic subjects were enrolled in the randomized, single-blind, placebo-controlled, three-period crossover trial. Each subject received placebo and two of four regimens of GSK256073 for 2 days. GSK256073 was dosed 5 mg every 12 h before breakfast and supper (BID), 10 mg every 24 h before breakfast (QD), 25 mg BID and 50 mg QD. Results The change from baseline weighted mean glucose concentration for an interval from 24 to 48 h after the initial drug dose was significantly reduced for all GSK256073 regimens, reaching a maximum of -0.87 mmol/l (-1.20, -0.52) with the 25 mg BID dose. Sustained suppression of non-esterified fatty acid (NEFA) and glycerol concentrations was observed with all GSK256073 doses throughout the 48-h dosing period. Serum insulin and C-peptide concentrations fell in concert with glucose concentrations and calculated HOMA-IR scores decreased 27-47%, consistent with insulin sensitization. No marked differences were evident between either 10 and 50 mg total daily doses or QD versus BID dosing. Conclusions Administration of a GPR109A agonist for 2 days significantly decreased serum NEFA and glucose concentrations in diabetic subjects. Glucose improvements were associated with decreased insulin concentrations and measures of enhanced insulin sensitivity. Improved glucose control occurred with GSK256073 doses that were generally safe and not associated with events of flushing or gastrointestinal disturbances.

Use of high flow nasal cannula on a pediatric burn patient with inhalation injury and post-extubation stridor Faera L. Byerly , John A. Haithcock , Ian B. Buchanan , Kathy A. Short , Bruce A. Cairns d,* NC Jaycee Burn Center, Department of Surgery, University of North Carolina at Chapel Hill, NC 27514, USA Department of Respiratory Care, UNC Hospitals, NC, USA Department of Surgery, University of North Carolina at Chapel Hill, NC, USA Associate Director, North Carolina Jaycee Burn Center, Division of Trauma, Critical Care, and Burns, Department of Surgery, University of North Carolina at Chapel Hill, 101 Manning Drive, NC Jaycee Burn Center CB#7600, Chapel Hill, NC 27514, USA

AGEP (acute generalized exanthematous pustulosis) is a relatively rare exfoliative skin syndrome consisting of generalized eruption of pustules in response to medication or infection. Because AGEP may have other systemic manifestations, such as renal failure, hyperthermia, lab abnormalities, and/or hemodynamic instability, it is important to make the distinction between AGEP and other life-threatening generalized skin diseases, such as toxic epidermal necrolysis (TEN). Here we present a case of AGEP in response to valdecoxib, which has not previously been described in the literature. The patient presented with profound hypotension requiring fluid and vasopressor support and was referred to the burn service for treatment of TEN, but her skin lesions were inconsistent with this diagnosis. A dermatology consult was obtained and suggested a diagnosis of AGEP, which a biopsy confirmed. TEN and AGEP present with similar history, types of associated drugs, and immunology. Both can be associated with antibiotics, non-steroidals, and anticonvulsants, but AGEP is more frequent with aminopenicillins, while TEN is associated more often with sulfonamide antibiotics. Both disorders have a proposed T cell-mediated immune response, but they differ in the mechanism. A description of valdecoxib and its role as a sulfonamide in producing cutaneous reactions is also provided.

During long-duration spaceflight, astronauts experience progressive muscle atrophy and often perform strenuous extravehicular activities. Post-flight, there is a lengthy recovery period with an increased risk for injury. Currently, there is a critical need for an enabling tool to optimize muscle performance and to minimize the risk of injury to astronauts while on-orbit and during post-flight recovery. Consequently, these studies were performed to develop a method to address this need.Eight test subjects performed a repetitive dynamic exercise to failure at 65% of their upper torso weight using a Lordex spinal machine. Surface electromyography (SEMG) data was collected from the erector spinae back muscle. The SEMG data was evaluated using a 5th order autoregressive (AR) model and linear regression analysis.The best predictor found was an AR parameter, the mean average magnitude of AR poles, with r = 0.75 and p = 0.03. This parameter can predict performance to failure as early as the second repetition of the exercise.A method for predicting human muscle performance early during dynamic repetitive exercise was developed. The capability to predict performance to failure has many potential applications to the space program including evaluating countermeasure effectiveness on-orbit, optimizing post-flight recovery, and potential future real-time monitoring capability during extravehicular activity.

The purpose of this study was to evaluate the relative sensitivity of neonatal and adult CD rats to manganese-induced neurotoxicity. Identical oral manganese chloride (MnCl(2)) doses (0, 25, or 50 mg kg(-1) body wt. day(-1)) were given to neonatal rats throughout lactation (i.e. from postnatal day (PND) 1 through 21) and to adult male rats for 21 consecutive days. The MnCl(2) doses administered to neonates were ca. 100-fold higher than those resulting from the consumption of an equivalent volume of rat's milk. Rats were assessed using similar behavioral and neurochemical evaluations. Several statistically significant changes occurred in Mn-exposed rats relative to control animals. Neonates given the high dose of MnCl(2) had reduced body weight gain. An increased pulse-elicited acoustic startle response amplitude was observed in neonates from both MnCl(2) treatment groups on PND 21. Increased striatal, hippocampal, hindbrain and cortical Mn concentrations were observed in all Mn-exposed neonates on PND 21. Increased hypothalamic and cerebellar Mn concentrations were also observed on PND 21 in neonates from the high-dose group only. Increased striatal, cerebellar and brain residue Mn concentrations were observed in adult rats from the high-dose group. Increased striatal dopamine and 3,4-dihydroxyphenylacetic acid levels were observed only in PND 21 neonates from the high-dose group. No treatment-related changes were observed in clinical signs, motor activity (assessed in neonates on PND 13, 17, 21 +/- 1 and in adults), passive avoidance (assessed in neonates on PND 20 +/- 1 and in adults) or neuropathology (assessed in PND 21 neonates only). The results of our experiment suggest that neonates may be at greater risk for Mn-induced neurotoxicity when compared to adults receiving similar high oral levels of Mn.

The results of a study of second-harmonic emission from a gyrotron designed for high-power high-frequency operation at the fundamental of the cyclotron frequency are presented. Stable, very narrow bandwidth second-harmonic cavity emission from 209 GHz to 302 GHz has been observed. An output power of 25 kW and efficiency of 6·5% in the TE11, 2, 1, mode at 241 GHz is reported; this represents the highest power obtained to date from a high-frequency (> 100 GHz) harmonic gyrotron. These experiments have been carried out in a cavity for which the mode density is very high; the cavity diameter is approximately six free-space wavelengths for emission at the second harmonic. Mode competition between fundamental and second-harmonic modes is discussed. It is also shown that, in general, gyrotrons designed for high-power low-Q operation in overmoded cavities at the fundamental will also have high efficiencies and strong emission in second-harmonic modes. Prospects for high-frequency harmonic gyrotrons for p...

The effects of ruthenium red (RuR) were tested on the membrane currents of internally perfused, voltage-clamped nerve cell bodies from the snail Limnea stagnalis. Bath application of nanomolar concentrations of RuR produces a prolonged Na current that decays approximately 40 times slower than the normal Na current in these cells. The relationship between the reversal potential for the prolonged Na current and the intracellular concentration of Na+ agrees well with the constant-field equation, assuming a small permeability for Cs+. Because a strong correlation was found between the magnitude of the normal Na current and that of the prolonged Na current, it is concluded that the prolonged Na current flows through the normal Na channels. This conclusion is supported by the similar selectivities, voltage dependencies, and tetrodotoxin (TTX) sensitivities of these two currents. This action of RuR to slow the inactivation of the Na channel was not observed at concentrations below 1 nM, but was complete at 10 nM. When the concentration of RuR is increased to 0.1 mM, the Ca current in these cells is blocked; but at this high concentration RuR also reduces the outward voltage-dependent currents and resting membrane resistance. Therefore, RuR is not a good Ca blocker because of its lack of specificity. However, its action of slowing Na current inactivation is very specific and could prove to be useful in studying the inactivation of the Na channel.

Drosophila offers a unique opportunity to determine how the genome codes for ionic channels in an organized nervous system. Considerable progress has already been made in studying the molecular biology of Drosophila K channels. In order for similar progress to be made on neuronal voltage-dependent Ca channels, a physiological preparation is needed in which the function of these channels can be directly studied. The patch-clamp studies reported here show that cultures of embryonic Drosophila cells (Seecof and Unanue, 1968) meet this need. These cultures provide the first opportunity to study with voltage-clamp techniques the Ca and Na currents of Drosophila neurons. The focus of these studies is on the Ca current; however, descriptions of the K and Na currents are also given since they help to characterize the cells studied and the quality of the voltage clamp. The voltage-dependent K, Na, and Ca currents of Drosophila neurons are very similar to those of molluscan neurons and other better studied neurons. The K currents are the largest currents in these neurons, averaging over 300 pA at +20 mV. There are 2 classes of Ca-independent K currents, inactivating currents that are 4-AP sensitive, and noninactivating currents that are insensitive to 4-AP. A large fraction of the K currents are located in the somal membrane. The Na currents are TTX sensitive and probably located in the processes. The peak amplitudes of the Ca currents vary from 0 to over 100 pA in these neurons, averaging 40 pA. With 5 mM external Ca2+ or Ba2+, the Ba currents are about twice as large as the Ca currents. Although 100 microM Cd2+ completely blocks the Ca current, organic blockers have very little effect. Variable inactivation characteristics and sensitivity to washout suggest the possibility of multiple types of Ca channels. A search for single-channel Ba currents in the somal membrane was unsuccessful.

A machine has been developed to accurately count and size large populations of the small nematode Caenorhabditis elegans with minimal effort. Like the related Coulter counter, this machine detects the change in electrical current which a particle (nematode) produces as it passes between two electrodes in a small transducer. Despite the use of alternating current, detailed analysis shows that detection is based primarily on resistance changes. The machine also employs a sheathed‐flow system to orient the long thin animals reproducibly in the transducer, so that resistance changes correspond directly to animal size. Accurate, non‐destructive measurement of live nematodes which have a 20‐fold length‐to‐width ratio and vary over a 103 range in volume can be achieved at a counting rate of 103 per min with 1% coincidence. Sources of measurement errors have been identified and controlled or eliminated. The machine has been calibrated against the optically measured lengths of nematodes in all stages of the life c...

Cells from the circumoesophageal nerve ring of the pond snail Lymnaea stagnalis were internally perfused with solutions containing Cs aspartate, EGTA and pH buffers. Time-dependent, voltage-dependent 'residual' outward currents were observed at positive potentials. They were found to be carried largely by H+. The outward H+ currents were reduced by high internal pH, low external pH, external Cd2+ and 4-aminopyridine. External tetraethylammonium ions reduced the H+ currents but had a more effective blocking action on the K+ currents in these cells. All five agents reduced the maximum H+ conductance. In addition Cd2+, low external pH and high internal pH were found to shift the voltage dependence of the H+ current to more positive potentials. There was no significant difference between H+ currents recorded with the internal pCa2+ about 7 and those recorded with the internal pCa2+ near 5. It is likely that the H+ channel described here provides the basis for the increase in H+ permeability described by Thomas & Meech (1982) in depolarized Helix neurones. As judged by their sensitivity to different antagonists, H+ channels are unlike any other previously described channel. They are highly selective for protons and we suggest that their role in molluscan neurones is to compensate for the rapid intracellular acidification which is generated by trains of action potentials (Ahmed & Connor, 1980).

Both the activation kinetics and the magnitude of the Ca current in Lymnaea are strongly dependent on temperature. The Q10 for the reciprocal of the activation time constant is 4.9 +/- 0.2 and the Q10 for the maximum current is 2.3 +/- 0.1. By lowering the temperature to 7-10 degrees C, we have been able to resolve the Ca tail currents. The block of Ca current by Cd2+ is voltage dependent, being more effective at more positive potentials. As determined from the magnitude of the tail currents, the Ca permeability is not maximally activated until the membrane potential is greater than +70 mV. The Ca permeability is half activated in the range 30-35 mV. The open-channel current-voltage relation for the Ca current is in rough agreement with the prediction of the constant-field equation. There is no indication of current saturation at negative potentials for potentials down to -60 mV. The Ca tail current decays with at least two time constants, one 200-400 microseconds and the other 2-4 ms. Although these time constants are not strongly voltage dependent, the ratio of the amplitude of the fast component of the tail current to that of the slow component is much larger at -60 mV than at 0 mV. The time course of the Ba tail current is very similar to that of the Ca tail current. The time course of the activation of the Ca current follows m2 kinetics and does not show evidence for a Cole-Moore-type shift for holding potentials between -50 and -110 mV. During a second positive pulse applied 1 ms after the first, the Ca current activates more rapidly, without the delay characteristic of the Ca current of a single positive pulse. The activation of the Ca current can be represented by a linear sequential model. The simplest model that describes both the turn-on and the turn-off of the Ca current must have at least three closed states, followed by a single open state.

A simple method for characterizing the development and reproduction of mutant strains of the small nematode Caenorhabditis elegans has been developed. “3-egg” populations of nematodes, started with three synchronously laid eggs and allowed to develop undisturbed for about two generations, are measured on the electronic nematode counter, and the resulting size distributions are interpreted by a computer. The computer compares the observed distribution to an expected distribution, generated by assuming the developmental curves previously measured for the wild-type C. elegans; if the distributions do not agree, the computer independently varies scale factors for developmental rate, size, egg-laying rate, and spread until the expected distribution best approximates the observed one. The resulting factors quantify any mutant defect of growth or reproduction, and the poorness of fit tells how greatly the mutant's development differs from that of the wild-type in ways other than those allowed for by the four scale changes. The computer program is shown to be able to fit wild-type C. elegans 3-egg populations grown for various lengths of time at 20°C. Three-egg populations of wild-type animals grown at 16 and 25°C are fitted by the computer and give altered developmental parameters consistent with those previously measured by more direct means. Nine behavioral and morphological mutants have been analyzed by this method. All show some developmental alterations from the wild-type. Fertility seems to be more adversely affected than growth. One mutant has been studied in more detail to determine the specific ways in which it differs from the wild-type.

Isolated nerve cell bodies from Lymnaea stagnalis were internally perfused and voltage-clamped. The magnitude of the Ca2+ current was monitored while perfusing with various intracellular solutions. When the intracellular perfusate was unenriched (containing only inorganic ions, 100 mM-HEPES and 5 mM-EGTA), the Ca2+ current was found to 'wash out', falling to half of its maximum value approximately 30-40 min from the beginning of perfusion. Stopping the flow of the perfusing solution increased this half-time to more than 50 min. The current-voltage relationship changed only slightly during wash-out. The addition of 2 mM-ATP and 1 mM-Mg2+ to the internal perfusate prevented, and even reversed, wash-out of the Ca2+ current. Both ATP and Mg2+ were necessary for maximal effect. Such current loss as occurred in the presence of ATP and Mg2+ was associated with a decrease in the capacitance of the cell and probably resulted from membrane being pulled into the pipette. The rate of inactivation of the Ca2+ current increased during perfusion with an unenriched internal solution, but decreased to initial values when ATP and Mg2+ were added to the internal perfusate. Although intracellular Mg2+ was necessary for the prevention of wash-out, levels higher than 1 mM had a blocking effect on the Ca2+ current. Certain factors that promote cyclic AMP-dependent protein phosphorylation (internal: cyclic AMP, theophylline and catalytic subunit of cyclic AMP-dependent protein kinase; external: dibutyryl cyclic AMP, 8-bromo cyclic AMP and forskolin) had no effect on the magnitude of the Ca2+ current in cells perfused with ATP and Mg2+. Externally applied theophylline blocked the Ca2+ current. The mechanism through which ATP and Mg2+ act to prevent wash-out of the Ca2+ current may be to enhance the ability of the cell to lower the Ca2+ concentration near the inner surface of the plasma membrane. This would prevent both the reversible block of Ca2+ current by intracellular Ca2+ and an irreversible loss of current due to high levels of intracellular Ca2+.