Lines Of Different Slopes Research Articles

Measuring H2O concentrations in olivine by secondary ion mass spectrometry: Challenges and paths forward

Abstract Trace concentrations of H2O in olivine strongly affect diverse mantle and magmatic processes. H2O in olivine has been difficult to accurately quantify due to challenges in sample preparation and measurement, as well as significant uncertainties in standard calibrations. Here we directly compare secondary-ion mass spectrometry (SIMS) measurements of the olivine standards of Bell et al. (2003, hereafter Bell03) and Withers et al. (2012, hereafter Withers12) upon which most SIMS and Fourier transform infrared (FTIR) spectroscopy analyses are based. In the same SIMS session, we find that the olivine standards from the two studies are offset by ~50%, forming lines of different slope when comparing SIMS measurements to the independent nuclear reaction analysis (NRA) in Bell03 and elastic recoil detection analysis (ERDA) in Withers12. This offset is similar to the ~40% offset that exists in the FTIR absorption coefficients determined by those two studies, and points to the NRAERDA data as the cause for the offset more than different IR absorption characteristics of the different olivines. We find that the Withers12 olivine standards form the most precise calibration line, and that the measured Bell03 olivine standards have issues of reproducibility and accuracy due to the presence of hydrous inclusions (as documented previously by Mosenfelder et al. 2011). Owing to the limited availability of the Withers12 olivine standards, however, we recommend using orthopyroxene standards (Kumamoto et al. 2017) to calibrate H2O in olivine by SIMS due to similar calibration slopes. We revise the reference values of current orthopyroxene standards to account for uncertainties in the Bell et al. (1995) manometry data. With these revised values, the orthopyroxene calibration line is within 12% of the Withers12 olivine line, which is within the long-term uncertainty of the SIMS olivine measurements. We apply our SIMS calibration protocol to revise estimates of the partition coefficients for H2O between olivine and melt, resulting in a value of 0.0009 ± 0.0003 at pressures ~0.2–2 GPa. This brings into closer agreement between the partition coefficients determined from experimental studies and those based on natural studies of olivine-hosted melt inclusions.

A highly tunable quadruple quantum dot in a narrow bandgap semiconductor InAs nanowire.

Quantum dots (QDs) made from semiconductors are among the most promising platforms for the development of quantum computing and simulation chips, and they have the advantages of high density integration and compatibility with the standard semiconductor chip fabrication technology compared to other platforms. However, the development of a highly tunable semiconductor multiple QD system still remains a major challenge. Here, we demonstrate the realization of a highly tunable linear quadruple QD (QQD) in a narrow bandgap semiconductor InAs nanowire via a fine finger gate technique. The QQD is studied by electron transport measurements in the linear response regime. Characteristic two-dimensional charge stability diagrams containing four groups of resonant current lines of different slopes are obtained for the QQD. It is shown that these current lines arise from and can be individually assigned to resonant electron transport through the energy levels of different QDs. Benefitting from the excellent gate tunability, we also demonstrate the tuning of the QQD to regimes where the energy levels of two QDs, three QDs and all four QDs are energetically in resonance, respectively, with the Fermi level of the source and drain contacts. A capacitance network model is developed for the linear QQD and the simulated charge stability diagrams based on this model show good agreement with the experiments. Our work provides solid experimental evidence that narrow bandgap semiconductor nanowire multiple QDs could be used as a versatile platform to achieve integrated qubits for quantum computing and to perform quantum simulations of complex many-body systems.

Detection of charge states of an InAs nanowire triple quantum dot with an integrated nanowire charge sensor

A linear triple quantum dot (TQD) integrated with a quantum dot (QD) charge sensor is realized. The TQD and the charge sensor are built from two adjacent InAs nanowires by the fine finger gate technique. The charge state configurations of the nanowire TQD are studied by measurements of the direct transport signals of the TQD and by detection of the charge state transitions in the TQD via the nanowire QD sensor. Excellent agreement in the charge stability diagrams of the TQD obtained by the direct transport measurements and by the charge-state transition detection measurements is achieved. It is shown that the charge stability diagrams are featured by three groups of charge state transition lines of different slopes, corresponding to the changes in the electron occupation numbers of the three individual QDs in the TQD. It is also shown that the integrated nanowire QD sensor is highly sensitive and can detect the charge state transitions in the cases where the direct transport signals of the TQD are too weak to be measurable. Tuning to a regime, where all three QDs in the TQD are close to being on resonance with the Fermi level of the source and drain reservoirs and co-existence of triple and quadruple points becomes possible, has also been demonstrated with the help of the charge sensor in the region where the direct transport signals of the TQD are hardly visible.

Robust Method to Determine Critical Micelle Concentration via Spreading Oil Drops on Surfactant Solutions.

The spreading of a liquid on another is often encountered in oil spills and coatings and is also of industrial relevance in pharmaceuticals and petrochemicals. In this study, the spreading of oil drops on aqueous solutions containing cationic, anionic, and nonionic surfactants over a wide range of surfactant concentrations is investigated. The spreading behavior quantified by measuring the time evolution of the projected area of the oil lens reveals the occurrence of a maximum, which is strongly dependent on the concentration of the surfactant in the aqueous solution. Our experiments show that this dependence is different at concentrations above and below the critical micelle concentration (CMC) of the surfactant and can be captured by two straight lines of different slopes. Interestingly, these two straight lines intersect at a concentration that coincides with the CMC of the surfactants in solution. We find that this behavior is universal as shown by performing experiments with different types of surfactants, their purity, and other system variables. Thus, we propose a method to unambiguously determine the CMC of surfactant solutions compared to the conventional techniques. The proposed method is simple, versatile, and applicable for the determination of CMC of both ionic and nonionic surfactants.

Array Codes With Local Properties

In general, array codes consist of m × n arrays and in many cases, the arrays satisfy parity constraints along lines of different slopes (generally with a toroidal topology). Such codes are useful for RAID type of architectures, since they allow to replace finite field operations by XORs. We present expansions to traditional array codes of this type, like Blaum-Roth (BR) and extended EVENODD codes, by adding parity on columns. This vertical parity allows for recovery of one or more symbols in a column locally, i.e., by using the remaining symbols in the column without invoking the rest of the array. Properties and applications of the new codes are discussed, in particular to Locally Recoverable (LRC) codes.

A Study on the Evaporation of Water–Ethanol Mixture Using Rainbow Refractometry

Evaporation of droplets of liquid mixture is a subject of interest in combustion studies, e.g., combustion of bioethanol blends. In this paper, experimental investigation, using rainbow refractometry, on the variations of droplet diameter and composition during the evaporation of water–ethanol droplet in quiescent atmosphere is studied. The droplet is suspended on the tip of 125 μm-diameter fiberglass rod. The initial diameter is around 1000–1100 μm, and the initial composition is varied from 0% to 100% of ethanol by volume. The scattered rainbow signal from the evaporating droplet is fitted to the Airy theory to extract information on the diameter and refractive index of the liquid droplet against evolution time. To determine the accuracy of droplet diameter measurements using this technique, the diameter is also measured from the shadow image of droplet simultaneously. At 0–60% of ethanol by volume, the diameter and volume fraction accuracies are within ±30 μm and 10%, respectively, even though the temperature and composition gradients inside a droplet are neglected. The results show that the water–ethanol mixture evaporates faster at the beginning due to the higher amount of the volatile component, i.e., ethanol. The D2–t curve appears as a series of two straight lines of different slopes: a steep one initially and a moderate one at later stage. The slope at the initial or the transition stage increases with the ethanol composition, while the slope at later stage (steady stage) is equivalent to that of pure water. Likewise, the refractive index decreases rapidly at the beginning and becomes steady reaching a final value of 1.333, which is close to the refractive index of pure water.

Characterization and Electrical Conductivity of Electron Beam Irradiated Metal Phthalocyanine Complexes

Variation of DC electrical conductivity with temperature from 273-473 K of electron beam irradiated Tetra-nitro zinc, and Cu-Pcs, were carried out. It shows semiconductor behavior and resistivity varies from 0.043×10 5 Ω -cm to 64.61×10 5 Ω -cm for all complexes. Variation of conductivity with temperature shows two straight lines of different slopes the first line (LT), resembles the α– phase, (Ea 1 ) = 0.226 eV while the second line at 362 K resembles the β - phase (Ea 2 ) = 0.460 eV (for Cu- Pcs). The β -phase shows higher activation energy than the α -phase, and the X-ray diffraction studies reveal that the crystals are monoclinic. The conductivity is explained on the basis of Davis and Mott model. The conduction mechanism at lower temperature is explained in terms of hoping through a band of localized states and at higher temperatures in terms of thermal excitation of carriers to the band edge.

Coherent Transport in a Linear Triple Quantum Dot Made from a Pure-Phase InAs Nanowire.

A highly tunable linear triple quantum dot (TQD) device is realized in a single-crystalline pure-phase InAs nanowire using a local finger gate technique. The electrical measurements show that the charge stability diagram of the TQD can be represented by three kinds of current lines of different slopes and a simulation performed based on a capacitance matrix model confirms the experiment. We show that each current line observable in the charge stability diagram is associated with a case where a QD is on resonance with the Fermi level of the source and drain reservoirs. At a triple point where two current lines of different slopes move together but show anticrossing, two QDs are on resonance with the Fermi level of the reservoirs. We demonstrate that an energetically degenerated quadruple point at which all three QDs are on resonance with the Fermi level of the reservoirs can be built by moving two separated triple points together via sophistically tuning of energy levels in the three QDs. We also demonstrate the achievement of direct coherent electron transfer between the two remote QDs in the TQD, realizing a long-distance coherent quantum bus operation. Such a long-distance coherent coupling could be used to investigate coherent spin teleportation and superexchange effects and to construct a spin qubit with an improved long coherent time and with spin state detection solely by sensing the charge states.

Liquid-Cell Transmission Electron Microscopy of Localized Corrosion of Aluminum

While the growth of pits in passive metals exposed to chloride solutions is well understood, the processes associated with the initiation and propagation of stable pits, versus pits that form and then re-passivate, are still a matter of conjecture. This study uses potentiostatic polarization to determine the pitting potential of aluminum as a function of chloride activity at constant pH. In contrast to earlier studies there is a departure from linearity as the solution becomes increasingly dilute, suggesting a new mechanism for the initiation of pits in less aggressive environments. This is shown in Figure 1, where a line has been fit both to the entire dataset, and two lines have been fit to their respective high and low portions of the dataset. The data at low chloride concentrations do not agree with the formulation developed by McCafferty [1] unless fit separately as two lines of different slope. Pitting corrosion is directly observed in situ in a liquid cell transmission electron microscope (TEM) [2]. Figure 2 shows a schematic of our corrosion cell design that we incorporate into this holder. The sample is created using standard electron beam evaporation, sputter deposition, and shadow mask methods. Current is supplied with titanium leads to the aluminum. This configuration allows pitting corrosion to be randomly distributed over the entire aluminum field. The influence of the microscope induced electron dose on the corrosion properties has been investigated and found to be controllable and consistent. We have characterized the thin film aluminum electrochemical behavior by generating Tafel curves within the liquid cell, and found the observations in situ to be largely representative of the bulk behavior. In Figure 3 this comparison is shown for nominally pure aluminum in the bulk case, versus the thin film samples, both in and out of the TEM. At low chloride concentration the curves have similar characteristics, such as similar anodic current slope, but are translated to more noble potentials and higher current densities for pitting behavior. Changes in the open circuit potential between the two thin film samples; in the microscope and external to it, are partially explained by the bias applied by the goniometer. The difference between open circuit potential in the bulk and thin film cases is consistent over several measurements, but the reason for the shift is a topic of further research. Current work is probing the relationship between thickness of the thin film and behavior compared to the bulk. In all cases we observed current transients representative of metastable pitting. We were able to relate crystalline features found in situ with topographic features using atomic force microscopy (AFM), as seen in this group’s earlier work [3]. Coupled with a depth profile from Auger Electron Spectroscopy of the pit this suggests that the ridges observed around the pit cusp in AFM are metallic aluminum. Pit growth is observed in situ, as seen in Figure 4, and suggests a redeposition of aluminum from the pit anolyte as seen in the red-circled features. Redeposition could result in conditions for repassivation by depriving the system of the critical concentration of aluminum ions [4]. Future work will include oxidation of the aluminum film in situ to examine changes from radiolysis by the beam, and effects of chloride on a fully oxidized aluminum film (no remaining underlying aluminum metal). It is expected this will reveal the influence of chloride on the surface-oxide interface and lead to greater detailed understanding of the oxide film’s role in passivation. This work is funded by NSF, under NSF-DMR 1309509. We acknowledge See Wee Chee and Brent Engler for collaboration, R. Dove and R. Planty for technical assistance and facilities within the Nanoscale Characterization Core operated by the Center for Materials Devices and Integrated Systems at RPI.

Kinetic analysis of Li|Li+ interphase in an ionic liquid electrolyte

Kinetic analysis of the Li|Li+ interphase in an electrolyte based on N-metyl-N-propylpyrrolidinium bis(trifluoromethanesulfon)imide ionic liquid (MPPyrrTFSI) and lithium bis(trifluoromethanesulfon)imide salt (LiTFSI) was performed. Li|electrolyte|Li and LiC6|electrolyte|Li cells were galvanostatically charged/discharged in order to form solid electrolyte interphase (SEI) protecting layer. SEM images showed that the surface of both Li and LiC6 anodes was covered with small particles. The fitting procedure of electrochemical impedance data taken at different temperatures gave three resistances (R el, R SEI, R ct) and hence, three lnR = f(T −1) straight lines of different slopes. Specific conductivity and activation energy of the conduction process of the liquid electrolyte, were ca. σ = 2.5 mS cm−1 (at T = 25.0 °C) and $$ E_{\text{el}}^{\# } $$ = 15 kJ mol−1. Activation energy for the conduction process in the SEI layer was ca. 56 kJ mol−1 in the case of the metallic lithium and 62 kJ mol−1 for the graphite anode. Activation energy of the charge transfer process, $$ E_{\text{ct}}^{\# } $$ , for Li and LiC6 anodes was 71 and 65 kJ mol−1, respectively. Analysis of literature data for different electrolytes suggests that the $$ E_{\text{ct}}^{\# } $$ value for Li+ reduction may be approximated by 57 ± 5 kJ mol−1. Activation energy for the diffusion processes in the graphite electrode, detected from the Warburg coefficient, was ca 74 kJ mol−1.

Kinetics of Li+ reduction in 1-methyl-3-propylpiperidinium bis(trifluoromethylsulfonyl) imide room temperature ionic liquid

Separation of the total Li/LiTFSI+MPPipTFSI/Li cell impedance into single contributions was performed with the use of electrochemical impedance spectroscopy (EIS). The structure of the electrode was observed by scanning electron microscopy (SEM). The charge transfer process occurs at a solid|solid Li+(SEI)→Li(metal) interphase (SEI is the solid electrolyte interphase). SEM images show that the structure of the electrode surface (and of the interphase) is grain-like. The kinetics of Li+ reduction in ionic liquids is interesting as the Li+ desolvation step (which takes place in classical solutions) does not take place which leads to a simpler process. Deconvolution of the EIS spectra indicates three resistances and corresponding three lnR=f(T−1) straight lines of different slopes, associated with the resistance of liquid electrolyte, SEI and the charge transfer process, respectively. Activation energy for the Li+ conduction process in the liquid electrolyte and solid SEI is 23 and 32kJmol−1, respectively. Activation energy for the charge transfer process Li+(SEI)→Li is 62kJmol−1 and the corresponding exchange current density at T=298K is 1.92×10−5Acm−2. As the process occurs at the SEI|Li interphase, the concentration independent rate constant cannot be calculated.

Temperature-dependent leakage current behavior of epitaxial Bi0.5Na0.5TiO3-based thin films made by pulsed laser deposition

This paper discusses the electrical conduction mechanisms in a 0.88 Bi0.5Na0.5TiO3-0.08 Bi0.5K0.5TiO3-0.04 BaTiO3 thin film in the temperature range of 200-350 K. The film was deposited on a SrRuO3/SrTiO3 substrate by pulsed laser deposition technique. At all measurement temperatures, the leakage current behavior of the film matched well with the Lampert’s triangle bounded by three straight lines of different slopes. The relative location of the triangle sides varied with temperature due to its effect on the density of charge carriers and un-filled traps. At low electric fields, the ohmic conduction governed the leakage mechanism. The calculated activation energy of the trap is 0.19 eV implying the presence of shallow traps in the film. With increasing the applied field, an abrupt increase in the leakage current was observed. This was attributed to a trap-filling process by the injected carriers. At sufficiently high electric fields, the leakage current obeyed the Child’s trap-free square law suggesting the space charge limited current was the dominant mechanism.

Indentation size effect at the initiation of plasticity for ceramics and metals

In nanoindentation, the plasticity size effect has been observed for several years, where a higher hardness is measured as contact size decreases. For spherical indenters, Lim and Chaudhri (1999 Phil. Mag. 79 2979) first showed that the entire flow curve appears at higher contact pressures for smaller radius indenters in copper. However, few papers have reported the initial yield size effect due to the difficulty in defining the yield point. Recently, Spary et al (2006 Phil. Mag. 86 5581) demonstrated that the initial yield strength of metals increases linearly with inverse cube root of indenter radius, by nanoindentation together with finite elemental modelling. Here, we use a clear method to determine the onset of plasticity in spherical nanoindentation without the uncertainties of modelling. This enables us to measure the yield pressure of tungsten metal and a series of ceramics with a high degree of accuracy and over a large range of indenter radii (hundreds of nanometres to several tens of micrometres). Our data of all ceramics and metals show clearly that there is a significant yield strength enhancement, which is inversely proportional to the cube root of the indenter radius. Normalizing the data for each material by its yield pressure for an infinite radius indenter, we find that the data for metals and ceramics fall on lines of different slope, indicating that material parameters influence the indentation yield strength size effect as well as the geometrical size effect.

MDS array codes for correcting a single criss-cross error

We present a family of maximum-distance separable (MDS) array codes of size (p-1)/spl times/(p-1), p a prime number, and minimum criss-cross distance 3, i.e., the code is capable of correcting any row or column in error, without a priori knowledge of what type of error occurred. The complexity of the encoding and decoding algorithms is lower than that of known codes with the same error-correcting power, since our algorithms are based on exclusive-OR operations over lines of different slopes, as opposed to algebraic operations over a finite field. We also provide efficient encoding and decoding algorithms for errors and erasures.

Optimizing The Metalloid Content in Bulk Metallic Glasses

AbstractWe have studied the effect of phosphorus content on the formation and properties of bulk Pd-Cu-P and Pd-Ni-P metallic glasses. It was found that the molar volumes of the Pd-Ni-P bulk glasses plotted as a function of P content follow a straight line whereas those for the Pd-Cu-P glasses follow two straight lines of different slopes, intersecting at a critical P concentration. The transition in molar volume behavior is attributed to a change in the alloy's short-range order with increasing P content. The origin of this structural change is discussed based on x-ray photoelectron spectroscopy (XPS) measurements.

Assessment of the effect of molecular size on the electrophoretic mobility of humic substances

SummaryThe basic principles of the electrophoretic behaviour of humic substances (HS) still need to be systematically investigated. HS extracted from a Cryorthod (HS–1) and from an Haplumbrept (HS–2) were first fractionated by ultrafiltration to obtain two series of fractions of reduced polydispersity with a nominal mean relative molecular mass (M) of 7500, 20000, 40000, 75000 and 200 000 Da. Fractions extracted from the same soil behaved like an homologous series when tested by size exclusion chromatography, showing a linear relation of M with molecular size. When plotted against their mean M, the elution volumes of HS fractions extracted from the two different soils originated lines of different slope. Absolute electrophoretic mobilities of the fractions were determined in polyacrylamide gel slabs of increasing polyacrylamide concentration using a single buffer system; in all gels there was a close linear relation between the electrophoretic mobility and the logarithm of the mean M of HS fractions. Extrapolation of mobilities of HS–1 at zero gel concentration gave intercepts that did not differ significantly, showing that there was a constant mobility for all fractions in free solution. These results mean that charge differences have little effect on the electrophoretic mobilities of HS extracted from the same soil and imply the theoretical possibility of determining M distributions of HS by polyacrylamide gel electrophoresis in a single buffer system. Mobilities of HS–2 fractions were compared with those of HS–1: the latter fitted the regression equations of mobility against logarithm of the molecular weight obtained from HS–1 humic substances only in gels of small acrylamide concentration. Deviations were larger at small M, probably because of the increasing fulvic character of the fractions, and increased in gels of greater acrylamide concentration, indicating that charge differences may not be negligible when comparing humic substances extracted from different soils.

Binding of alpha-thrombin to fibrin depends on the quality of the fibrin network.

Binding of human alpha-thrombin to fibrin was studied in a purified system at pH 7.35, I 0.08 and 37 degrees C. Binding experiments with active thrombin resulted in fibrin clots of variable quality, depending on the thrombin concentration: opaque gels composed of 'coarse' network were produced at low thrombin concentrations, while increasing concentrations of thrombin led to more translucent 'fine' gels. Scatchard analysis showed a non-linear dependence of thrombin binding to fibrin, suggesting the existence in fibrin(ogen) of multiple classes of binding sites for thrombin. Binding of catalytic-site-inhibited thrombin was investigated in clots of defined quality produced with three different concentrations of a thrombin-like enzyme, batroxobin (EC 3.4.21.29). Straight lines of different slopes were established by Scatchard analysis of binding data at each fixed batroxobin concentration. These results favour a model according to which binding affinity for thrombin depends on the thickness of fibrin bundles. Labelled active-site-inactivated thrombin incorporated in batroxobin-induced clots was only sparingly released during incubation for 24 h in the presence of a 200-fold excess of unlabelled thrombin, indicating that thrombin binding to fibrin is not reversible and that Scatchard analysis is not appropriate for quantification of binding parameters. Irreversible binding of thrombin appears to reflect trapping of thrombin molecules within fibrin fibres. The amount of trapped thrombin depends on the quality of the fibrin fibres, which in turn is determined by the concentration of the clotting enzyme.

Capillary flow properties of PVC melts (abstract)

The effects of degree of polymerization and temperature on flow properties of PVC melts have been studied by using a Koka Flow Tester. Each flow curve is expressed by two straight lines of different slopes which meet at a breaking point. The critical shear rate γ̇wc’ at the breaking point increases as the degree of polymerization decreases or the temperature increases. The critical shear stress τc at γ̇wc’ increases as the degree of polymerization decreases, being almost independent of the temperature. The end correction coefficient ν shows a minimum or begins to increase around γ̇wc’. The coefficient ν increases as the degree of polymerization increases or the temperature decreases. The extrudate is smooth on the surface at low shear rates, shows a small wavy roughness (shark skin) at shear rates just below γ̇wc’, becomes fairly smooth again beyond γ̇wc’, and then shows intensive irregular roughness (melt fracture) at higher shear rates. The die swell becomes notable as degree of polymerization decreases or the temperature increases. The die swell takes a maximum at a shear rate just below γ̇wc’, where a shark skin appears on the extrudate. Differing from usual thermoplastic resin melts, PVC melts show a negative correlation between the die swell ratio and the end correction coefficient. This seems to be due to the following reason: PVC melts have high viscosities and have long relaxation times for strain recovery, and thus the extrudates solidify without being fully relaxed. This tendency of solidification without relaxation is more noticeable as the degree of polymerization increases or the temperature decreases.

Capillary Flow Properties of PVC Melts

The effects of degree of polymerization and temperature on flow properties of PVC melts have been studied by using a Koka Flow Tester. Each flow curve is expressed by two straight lines of different slopes which meet at a breaking point. The critical shear rate γ′wc at the breaking point increases as the degree of polymerization decreases or the temperature increases. The critical shear stress τc at γ′wc increases as the degree of polymerization decreases, being almost independent of the temperature. The end correction coefficient ν shows a minimum or begins to increase around γ′wc. The coefficient ν increases as the degree of polymerization increases or the temperature decreases. The extrudate is soomth on the surface at low shear rates, shows a small wavy roughness (shark skin) at shear rates just below γ′wc, becomes fairly smooth again beyond γ′wc, and then shows intensive irregular roughness (melt fracture) at higher shear rates. The die swell becomes notable as degree of ploymerization decreases or the temperature increases. The die swell takes a maximum at a shear rate just below γ′wc, where a shark skin appears on the extrudate. Differing from usual thermpolastic resin melts, PVC melts shows a negative correlation between the die swell ratio and the end correction coefficient. This seems to be due to the following reason: PVC melts have high viscosities and have long relaxation times for strain recovery, and thus the extrudates solidify without being fully relaxed. This tendency of solidification without relaxation is more noticeable as the degree of polymerization increases or the temperature decreases.

The relationship between reaction kinetics and mutagenic action of monofunctional alkylating agents in higher eukaryotic systems: IV. The effects of the excision-defective mei-9L1 and mus(2)201D1 mutants on alkylation-induced genetic damage in Drosophila

Repair-defective mutants of Drosophila melanogaster which identify two major DNA excision repair loci have been examined for their effects on alkylation-induced mutagenesis using the sex-linked recessive lethal assay as a measure of genotoxic endpoint. The alkylating agents (AAs) chosen for comparative analysis were selected on the basis of their reaction kinetics with DNA and included MMS, EMS, MNU, DMN, ENU, DEN and ENNG. Repair-proficient males were treated with the AAs and mated with either excision-defective mei-9 L1 or mus(2)201 D1 females or appropriate excision-proficient control females. The results of the present work suggest that a qualitative and quantitative relationship exists between the nature and the extent of chemical modification of DNA and the induction of genetic alterations. The presence of either excision-defective mutant can enhance the frequency of mutation (hypermutability) and this hypermutability can be correlated with the Swain-Scott constant S of specific AAs such that as the S N1 character of the DNA alkylation reaction increases, the difference in response between repair-deficient and repair-proficient females decreases. The order of hypermutability of AAs with relative to mei-9 L1 is MMS > MNU > DMN = EMS > iPMS = ENU = DEN = ENNG. When the percentage of lethal mutations induced in mei-9 L1 females are plotted against those determined for control females, straight lines of different slopes are obtained. These mei-9 L1/ mei-9 + indices are: MMS = 7.6, MNU = 5.4, DMN = 2.4, EMS = 2.4 and iPMS = ENU = DEN = ENNG = 1. An identical order of hypermutability with similar indices is obtained for the mus(2)201 mutants: MMS(7.3) > MNU(5.4) > EMS(2.0) > ENU(1.1). Thus, absence of excision repair function has a significant effect on mutation production by AAs efficient in alkylating N-atoms in DNA but no measurable influence on mutation production by AAs most efficient in alkylating O-atoms in DNA. The possible nature of these DNA adducts has been discussed in relation to repair of alkylated DNA. In another series of experiments, the effect of alkylation mutagenesis of was studied in males, by comparing mutation induction in males vs. activity in Berlin K (control). Although these experiments suggested the existence of DNA repair in postmeiotic cells during spermatogenesis, no quantitative comparisons could be made. The inherent problem with this approach, mutagen treatment of two different genotypes, is that factors entirely unrelated to DNA repair, e.g., differences in metabolism, may influence the outcome of the comparison. Utilization of the mutant in low dosage experiments did out measurably improve the sensitivity of the assay for sex-linked recessive lethals. Because the mei-9 L1 allele has not been characterized biochemically, we cannot determine at present whether excision deficiency, per se, will not lead to notable shifts in lowest effective concentrations (LECs) or whether the mei-9 L1 allele is ‘leaky’ and providing some wild-type function at low mutagen doses. Nevertheless, ‘high-exposure-level’ experiments with strong reference mutagens may not be indicative of the situation relevant at low genotoxic activities and this aspect should be given special attention in considerations dealing with the possible use of the specific repair-defective alleles in genetic toxicology testing.