Order Of Magnitude Drop Research Articles

Liver repopulation with xenogenic hepatocytes in B and T cell-deficient mice leads to chronic hepadnavirus infection and clonal growth of hepatocellular carcinoma.

To investigate host and viral mechanisms determining hepadnaviral persistence and hepatocarcinogenesis, we developed a mouse model by transplanting woodchuck hepatocytes into the liver of mice that contain the urokinase-type plasminogen activator transgene (uPA) and lack mature B and T lymphocytes due to a recombination activation gene 2 (RAG-2) gene knockout. The woodchuck hepatocytes were transplanted via intrasplenic injection and were found to integrate into the recipient mouse liver cord structure. Normal adult woodchuck hepatocytes proliferated and reconstituted up to 90% of the uPA/RAG-2 mouse liver. uPA/RAG-2 mice containing woodchuck hepatocytes were infectable with woodchuck hepatitis virus (WHV) and showed WHV replication for at least 10 months with titers up to 1 x 10(11) virions per ml in the peripheral blood. WHV-infected hepatocytes from chronic carrier woodchucks also established a persistent infection in uPA/RAG-2 mice after an 8- to 12-week lag period of viremia. Although WHV envelope, core, and X proteins were produced in the uPA/RAG-2 mice, no inflammatory host immune response was observed in the liver of WHV-replicating mice. A first antiviral test demonstrated a greater than four orders of magnitude drop in WHV titer in response to interferon alpha treatment. WHV replication was up-regulated by dexamethasone treatment. Comparison of precancerous lesions in donor woodchucks versus recipient uPA/RAG-2 mice revealed an enrichment of dysplastic precancerous hepatocytes in transplanted mice. Clonal amplification of hepatocytes from a woodchuck with hepatocellular carcinomas was demonstrated by the detection of unique WHV DNA integration patterns in hepatocellular carcinomas that arose in uPA/RAG-2 mice. In the absence of B or T cell-mediated immune responses, WHV establishes a persistent noncytotoxic infection of woodchuck hepatocytes in uPA/RAG-2 chimeric mouse livers. Further studies of the kinetics of hepadnavirus infection and replication in quiescent and proliferating hepatocytes should increase our understanding of hepadnavirus spread and aid in the design of therapies to block or cure persistent infection.

Measurement of hydraulic conductivity in oil sand tailings slurries: Reply

The authors thank the discusser for his interest in the paper. The authors agree with the discusser that the flow pump technique is an excellent method to determine hydraulic conductivity and have used this technique to measure hydraulic conductivity in conventional soils. The fine tails, however, are slurries with void ratios up to 10. At these high void ratios, the initial effective stress, at which hydraulic conductivity had to be measured, was only 0.2 kPa. Only very small head differences of approximately 0.02 kPa could be allowed to prevent consolidation during the test, and it was easier to control this with the constant head horizontal burette technique. The discusser suggests measuring the inflow and outflow to determine the volume change of the specimen. The authors did not want the specimen to change volume during flow, as this would have changed the hydraulic conductivity in these high void ratio materials. To ensure that there was no volume change, the inflow and outflow were measured and compared. Figure 1 indicates that there was no volume change during the entire hydraulic conductivity test as the inflow and outflow flow velocities are always equal. The suggestion to plot the ratio of flows with time is interesting and Fig. 2 plots the data from Fig. 1 in this manner. As the ratio is always one, it does show that no volume change was occurring. However, it fails to show an interesting property of high void ratio slurries: the almost two orders of magnitude drop in hydraulic conductivity at the beginning of the test. The reasons for this behavior are given in the paper. The authors did not have any problem distinguishing the steady state from transient state in the constant head tests. The constant head tests were performed for about 10 to 15 h, which is not dissimilar to the 26 h time for the flow pump test shown in the discussion. The authors agree that long-term tests are uneconomical, and the test results may be susceptible to physical and chemical changes in the specimen. In the flow pump test, a known quantity of flow is forced thorough the specimen and the corresponding pressure difference is measured, which is used to determine the hydraulic gradient. This is exactly the opposite of the constant head test. Aiban and Znidarcic (1989) reported that the constant head test and flow pump test yield the same hydraulic conductivity values when the specimenis tested under similar conditions. References

Comparison of nonequilibrium solution algorithms applied to chemically stiff hypersonic flows

Three solution algorithms, explicit under-relaxation, point implicit, and lower-upper symmetric Gauss-Seidel, are used to compute nonequilibrium flow around the Apollo 4 return capsule at the 62-km altitude point in its descent trajectory. By varying the Mach number, the efficiency and robustness of the solution algorithms were tested for different levels of chemical stiffness. The performance of the solution algorithms degraded as the Mach number and stiffness of the flow increased. At Mach 15 and 30, the lower-upper symmetric Gauss-Seidel method produces an eight order of magnitude drop in the energy residual in one-third to one-half the Cray C-90 computer time as compared to the point implicit and explicit under-relaxation methods. The explicit under-relaxation algorithm experienced convergence difficulties at Mach 30 and above. At Mach 40 the performance of the lower-upper symmetric Gauss-Seidel algorithm deteriorates to the point that it is out performed by the point implicit method. The effects of the viscous terms are investigated. Grid dependency questions are explored.

Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

Relaxation times (T1) and lineshapes were examined as a function of temperature through the α-β transition for 29Si in a single crystal of amethyst, and for 29Si and 17O in cristobalite powders. For single crystal quartz, the three 29Si peaks observed at room temperature, representing each of the three differently oriented SiO4 tetrahedra in the unit cell, coalesce with increasing temperature such that at the α-β transition only one peak is observed. 29Si T1's decrease with increasing temperature up to the transition, above which they remain constant. Although these results are not uniquely interpretable, hopping between the Dauphine twin related configurations, α1 and α2, may be the fluctuations responsible for both effects. This exchange becomes observable up to 150° C below the transition, and persists above the transition, resulting in β-quartz being a time and space average of α1 and α2. 29Si T1's for isotopically enriched powdered cristobalite show much the same behavior as observed for quartz. In addition, 17O T1's decrease slowly up to the α-β transition at which point there is an abrupt 1.5 order of magnitude drop. Fitting of static powder 17O spectra for cristobalite gives an asymmetry parameter (η) of 0.125 at room T, which decreases to <0.040 at the transition temperature. The electric field gradient (EFG) and chemical shift anisotropy (CSA), however, remain the same, suggesting that the decrease in η is caused by a dynamical rotation of the tetrahedra below the transition. Thus, the mechanisms of the α-β phase transitions in quartz and cristobalite are similar: there appears to be some fluctuation of the tetrahedra between twin-related orientations below the transition temperature, and the β-phase is characterized by a dynamical average of the twin domains on a unit cell scale.

A quantitative study of copper segregation in silicon under oxygen ion beam bombardment using SIMS

Abstract The segregation of Cu in Si under oxygen ion bombardment has been investigated using secondary ion mass spectrometry (SIMS). The decay length of the Cu signal observed when depth profiling a Cu implanted (100) n-type Si wafer has been measured as a function of the angle of incidence and the primary beam energy. The decay length at normal incidence is found to vary linearly as a function of energy, between 2.5 and 14 keV O 2 atom. The dependence with angle was measured at 14 keV O 2 atom and is found to be much stronger. From normal incidence to 20° the decay length decreases rapidly from 3000 to 311 nm. From 20 to 30° another order of magnitude drop in decay length is observed with most of the drop occurring between 20 and 25°. Past 30° the decay length is almost constant with a value of approximately 32 nm. These changes in decay length with energy and angle are discussed with reference to the nature of the altered layer formed under oxygen bombardment of Si.

The influence of interstitial Ga and interfacial Au2P3 on the electrical and metallurgical behavior of Au-contacted III-V semiconductors

The introduction of a very small amount of Ga into Au contact metallization on InP is shown to have a significant effect on both the metallurgical and electrical behavior of that contact system. Ga atoms in the interstices of the Au lattice are shown to be effective in preventing the solid-state reactions that normally take place between Au and InP during contact sintering. In addition to suppressing the metallurgical interaction, the presence of small amounts of Ga is shown to cause an order of magnitude reduction in the specific contact resistivity. Evidence is presented that the reactions of GaP and GaAs with Au contacts are also drastically affected by the presence of Ga. The sintering behavior of the Au-GaP and the Au-GaAs systems (as contrasted with that of the Au-InP system) is explained as due to the presence of interstitial Ga in the contact metallization. Finally the large, two-to-three order of magnitude drop in the contact resistance that occurs in the Au-InP system upon sintering at 400 °C is shown to be a result of the formation of an Au2P3 layer at the metal-semiconductor interface. Contact resistivities in the 10−6 Ω cm2 range are obtained for as-deposited Au on InP when a thin (20 Å) layer of Au2P3 is introduced between the InP and the Au contacts.

Processing of polymer latex emulsion: Batch coagulation

AbstractA small‐scale batch experiment has been developed to establish processing conditions for latex coagulation in an extruder environment—characterized by the prevailing flow field, temperature, and pressure. Our experiments have shown that the most effective processing means to control the particle size distribution and also the particle morphology is the coagulation temperature. The changes in hydrodynamics, introduced by variations in the channel depth and rotor speed, affect the average particle size to a lesser degree. The morphology of the coagulated particles and their size distribution have been found to play an important role in the latex dewatering process. By coagulating well above the glass transition temperature(s) of the polymer, an order of magnitude drop in the specific surface area of the coagulated particles has been observed.

Influence of molybdenum on the creep properties of nickel-base superalloy single crystals

The influence of Mo on the creep properties of single crystals of a model nickel-base superalloy has been investigated. The Mo content was systematically varied from 9.8 to 14.6 wt pet in an alloy series based on Ni-6 wt pet Al-6 wt pet Ta. The optimum initial γ-γ′ microstructure for raft development and creep strength was produced in each alloy prior to testing. The creep lives at 982 °C and 234 MPa exhibited a steep peak as a function of Mo content, with the maximum in life occurring at about 14.0 wt pet Mo. Deviations of less than 1 wt pet Mo from the optimum composition resulted in an order of magnitude drop in properties. As the Mo content was increased from 9.8 to 14.0 wt pct, the magnitude of lattice mismatch significantly increased, which was believed to be beneficial because of stronger γ-γ′ interfaces. As the Mo content was increased further from 14.0 to 14.6 w/o, the mechanical properties degraded because of the precipitation of a deleterious third phase. The results suggest that small variations in refractory metal content and initial gg′ size can have profound effects on mechanical properties. Hence, composition ranges and microstructures for the attainment of optimum mechanical properties may be somewhat limited and require close process control.

Electrochemical synthesis and optical analysis of poly[(2,2′‐dithienyl)‐5,5′‐diylvinylene

AbstractThe electrochemical synthesis of poly[(2,2′‐dithienyl)‐5,5′‐diylvinylene tetrafluoroborate] (PDTE/BF4) has been accomplished and provides coppery‐black free‐standing films with a room‐temperature four‐probe conductivity as high as 15 (Ω cm)−1. The conductivity and morphology of the films were found to be strongly dependent on synthetic conditions. The oxidized form of PDTE is not air stable, as evidenced by a rapid, three order of magnitude drop in the conductivity. Optoelectrochemical experiments demonstrate that bipolarons are the main charge‐carrying species in conductive PDTE and allow their evolution to be followed as a function of oxidation.

A review of lunar paleointensity data and implications for the origin of lunar magnetism

The saturation remanence normalization method of paleointensity estimation has been applied to more than 50 lunar samples, and has been calibrated in terms of standard intensity determinations done on 14 samples. These results suggest that a lunar surface field, comparable in intensity to the earth's magnetic field, existed from about 3.6 to 3.8 AE. Absolute paleointensity estimates and lunar surface field strength determinations are consistent with this observation. The data presented here differ from previous descriptions of the variation in the lunar field with time in that (A) the oldest samples (&gt;3.9 AE) are among the most weakly magnetized; and (B) an order of magnitude drop in paleointensity is suggested between the time of extrusion of the Apollo 11 low and high potassium basalts. The limited range in age of the strongly magnetized lunar samples and the absence of shocked samples in this set argues against a solar source for the lunar paleofield or for fields arising from transient phenomena such as impacts. The coincidence of this high field era with the termination of basin forming impacts and the beginning of mare basalt extrusion suggests a common cause. A close approach of the moon to the earth at about 3.8 AE might account for all three phenomena. The confined duration of the strong lunar field may allow for the assignment of relative ages for certain lunar samples and surface features.

An intrinsic oxygen fugacity study of platinum-carbon associations in layered intrusions

That some value of the f (sub S 2 ) /f (sub O 2 ) ratio must be exceeded to stabilize sulfide immiscibility in gabbroic magmas is the working hypothesis for the formation of platinum-enriched horizons in the Bushveld and Stillwater Complexes. Intrinsic f (sub O 2 ) measurements from 900 degrees to 1,160 degrees C are given for eight eastern and three western Bushveld samples representative of the chromitites within 970 m of the stratigraphy containing the reef. Similarly, f (sub O 2 ) -T data for five samples of anorthosites and one sample of chromitite are given for 370 m of the stratigraphy enclosing the Stillwater J-M reef platiniferous horizon.In the eastern Bushveld, the f (sub O 2 ) decreases (more reduced) with elevation; in the Merensky Reef footwall about a three order of magnitude drop from f (sub O 2 ) = 10 (super -11) to f (sub O 2 ) = 10 (super -13.7) was measured at 1,150 degrees C for the respective horizons of -869.8 m and -687 m (base of the Merensky Reef as zero datum elevation). From the -687-m horizon to the Merensky Reef, the f (sub O 2 ) values at 1,150 degrees C range between 10 (super -13) to 10 (super -14) with one western Bushveld Merensky Reef sample at 10 (super -15.6) .In the Stillwater Complex, original igneous f (sub O 2 ) values and later serpentinization produce f (sub O 2 ) values at 1,150 degrees C that vary from 10 (super -12.0) (deep footwall) to 10 (super -9.8) (zone of interest). The serpentinization has erased the original igneous redox equilibria for several meters on each side of the zone of interest.Six lines of evidence are reviewed that suggest the Bushveld Merensky event was the result of a system open to volatile composition changes and that the Bushveld chamber may have hovered close to the sulfide immiscibility during 677.3 m of accumulation. In our model, at the Merensky formation time a final perturbation in the f (sub S 2 ) /f (sub O 2 ) ratio triggered the sulfide immiscibility. Spatial constraints and mass balance calculations are presented to test this model.The Merensky Reef and the Stillwater zone of interest both display visual graphite, potholes, and enigmatic platinum-group element concentrations, as well as other discussed similarities that suggest the presented model for the Bushveld may have been originally operative for the Stillwater as well.

A review of lunar paleointensity data

An extension of the saturation remanence normalization method to over 50 samples implies that a lunar surface field, comparable in intensity to the Earth's magnetic field, existed from about 3.65 to 3.85 AE. Absolute paleointensity estimates published to date, and surface field strengths, as measured by the Apollo subsatellites, are in general agreement with this observation. The data presented here differ from previous descriptions of the variation of the lunar field with time in that A) the oldes samples (>3.85 AE) are found to be amongst the most weakly magnetized; B) an order of magnitude drop in paleointensity is suggested between the time of extrusion of the Apollo 11 low and high potassium basalts. The confined time envelope of the strongly magnetized lunar samples, and the absence of shocked samples in the set, argues against an external, solar source for the lunar paleofield, or for a strong magnetic field arising from some transient phenomena (i.e. shock). A lunar dynamo, perhaps triggered by the close approach of the Moon to the Earth seems the best explanation for the limited period of intense lunar magnetic activity.

Effect of pressure on electrical resistivity and thermoelectric power of FeS

Electrical resistivity and thermoelectric power (TEP) measurements upto 70 Kbar were performed on FeS crystals grown from 53 atom % Fe melts. The phase transitions, earlier reported by the X-ray diffraction and Mossbauer measurements, were found at 28 and 54 Kbar. The first transition is characterized by a nearly two orders of magnitude drop in resistivity and a large decrease in TEP, and the second transition is marked by an increase in the resistivity and TEP parallel to the C-axis.

A model for Archean tectonism. Part 2. Numerical models of vertical tectonism in greenstone belts

A tectonic model that attempts to explain common features of Archean geology is investigated. The model supposes the accumulation, by volcanic eruptions, of a thick basaltic pile on a granitoid crust. The thermal blanketing effect of this lava raises the temperature of the granitic crust and eventually softens it enough that gravitational slumping and downfolding of the lava follows.Numerical models of the thermal and mechanical evolution of a granitoid crust covered with a thick lava sequence indicate that such an evolution is possible when reasonable assumptions are made about the temperature dependence of the viscosity in crustal rocks. These models show the lava sinking in relatively narrow regions while wider granite diapirs appear in between. The convection produces strong horizontal temperature gradients that may cause lateral changes in metamoprhic facies. A one order of magnitude drop in accumulated strain occurs between the granite–basalt interface and the center of the granite diaper at a depth of 10–15 km.