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  • 1
    Electronic Resource
    Electronic Resource
    Shear stabilization of a solidifying front: Weakly nonlinear analysis in a long-wave limit (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 2319-2336 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The manufacturing of single crystals of multi-component materials with uniform material properties is frequently hampered by the presence of morphological instabilities during the solidification. In this paper we extend into the nonlinear regime our previous work on the influence of shear flows on the linear stability of the solid/liquid interface during the directional solidification of binary alloys. The flows are generated by unidirectional or nonplanar harmonic oscillations of the crystal parallel to the mean interface position, and oscillations with physically realizable amplitudes and frequencies are found to be useful for stabilization purposes. A strongly nonlinear equation which governs the evolution of the interface in the limit of high surface energy, a weak flow and thermodynamic equilibrium is derived, and a weakly nonlinear analysis of this equation is performed. For the unidirectional case, it is found that oscillations with sufficiently large amplitude will change the initial bifurcation from super- to subcritical. For the nonplanar case, it is found that subcritical instability of roll, square and hexagonal cells is favored as the amplitude of the flow is increased. Thus, some of the stabilization due to the flow may be lost at finite amplitude, but substantial stabilization can be retained. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869019
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  • 2
    Electronic Resource
    Electronic Resource
    The low-lying electronic states of CoF (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6949-6955 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The emission spectrum of CoF has been investigated in the 820 nm–3.5 μm spectral region using a Fourier transform spectrometer. The bands were excited in a carbon tube furnace by the reaction of cobalt metal vapor and CF4 at a temperature of about 2300 °C. The bands observed in the 3000–9000 cm−1 region have been classified into three new transitions. The bands with 0-0 R-heads at 3458 cm−1, 3759 cm−1, and 4012 cm−1 have been assigned as the 3Δ1–3Φ2, 3Δ2–3Φ3, and 3Δ3–3Φ4 subbands of the C 3Δ–X 3Φi electronic transition. To higher wave numbers, two bands with R-heads at 8396 cm−1 and 8565 cm−1 have been assigned as the 3Δ2–3Φ3 and 3Δ3–3Φ4 subbands of the D 3Δ–X 3Φi transition. In addition, the bands with R-heads at 6339 cm−1 and 6542 cm−1 have been assigned as the 0-0 3Φ4–3Δ3 and 3Φ3–3Δ2 subbands of the G 3Φ–C 3Δ transition. The G 3Φ–X 3Φ transition has been reported previously as the [10.3]3Φ–X 3Φ transition. The rotational analysis of many bands of these transitions has been obtained and the molecular constants for the two new low-lying excited states have been extracted. Six new band involving the high vibrational levels of ground state (up to v=6) have been identified in the 3Φ4–3Φ4 subband of the G 3Φ–X 3Φ transition. The rotational analysis of these bands provides improved constants for the ground state. We have noticed, as have previous workers, the strong correspondence that exists between the states of transition metal monofluorides and monohydrides. In addition, all of the low-lying states of CoF and CoH are related to the low-lying terms of the Co+ atom. We discuss these correlations between the energy levels of CoF, CoH, and Co+. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471411
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  • 3
    Electronic Resource
    Electronic Resource
    Estimation of the Poly(ethylene glycol) Chain Length of L-Polylactide-Polyethylene Glycol in Aqueous Dispersions Using Viscoelastic Measurements (1995)
    s.l. : American Chemical Society
    Langmuir 11 (1995), S. 1482-1485 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00005a013
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  • 4
    Electronic Resource
    Electronic Resource
    The spreading of volatile liquid droplets on heated surfaces (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 248-265 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional volatile liquid droplet on a uniformly heated horizontal surface is considered. Lubrication theory is used to describe the effects of capillarity, thermocapillarity, vapor recoil, viscous spreading, contact-angle hysteresis, and mass loss on the behavior of the droplet. A new contact-line condition based on mass balance is formulated and used, which represents a leading-order superposition of spreading and evaporative effects. Evolution equations for steady and unsteady droplet profiles are found and solved for small and large capillary numbers. In the steady evaporation case, the steady contact angle, which represents a balance between viscous spreading effects and evaporative effects, is larger than the advancing contact angle. This new angle is also observed over much of the droplet lifetime during unsteady evaporation. Further, in the unsteady case, effects which tend to decrease (increase) the contact angle promote (delay) evaporation. In the "large'' capillary number limit, matched asymptotics are used to describe the droplet profile; away from the contact line the shape is determined by initial conditions and bulk mass loss, while near the contact-line surface curvature and slip are important. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868623
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  • 5
    Electronic Resource
    Electronic Resource
    The mechanism of water-stress-induced embolism in two species of chaparral shrubs (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 18 (1995), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The mechanism of water-stress-induced embolism of xylem was investigated in Malosma laurina and Heteromeles arbutifolia, two chaparral shrub species of southern California. We tested the hypothesis that the primary cause of xylem dysfunction in these species during dehydration was the pulling of air through the pores in the cell walls of vessels (pores in pit membranes) as a result of high tensions on xylem water. First, we constructed vulnerability-to-embolism curves for (i) excised branches that were increasingly dehydrated in the laboratory and (ii) hydrated branches exposed to increasing levels of external air pressure. Branches of M. laurina that were dehydrated became 50% embolized at a xylem pressure potential of -1.6 MPa, which is equal in magnitude but opposite in sign to the +1.6 MPa of external air pressure that caused 50% embolism in hydrated stems. Dehydrated and pressurized branches of H. arbutifolia reached a 50% level of embolism at -6.0 and +6.4 MPa, respectively. Secondly, polystyrene spheres ranging in diameter from 20 to 149 nm were perfused through hydrated stem segments to estimate the pore size in the vessel cell walls (pit membranes) of the two species. A 50% or greater reduction in hydraulic conductivity occurred in M. laurina at perfusions of 30, 42, 64 and 82 nm spheres and in H. arbutifolia at perfusions of 20 and 30 nm spheres. Application of the capillary equation to these pore diameters predicted 50% embolism at xylem tensions of -2.2 MPa for M. laurina and -6.7 MPa for H. arbutifolia, which are within 0.7 MPa of the actual values. Our results suggest that the size of pores in pit membranes may be a factor in determining both xylem efficiency and vulnerability to embolism in some chaparral species. H. arbutifolia, with smaller pores and narrower vessels, withstands lower water potentials but has lower transport efficiency. M. laurina, with wider pores and wider vessels, has a greater transport efficiency but requires a deeper root system to help avoid catastro-phically low water potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1995.tb00352.x
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  • 6
    Electronic Resource
    Electronic Resource
    New evidence for large negative xylem pressures and their measurement by the pressure chamber method (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Pressure probe measurements have been interpreted as showing that xylem pressures below c. –0.4 MPa do not exist and that pressure chamber measurements of lower negative pressures are invalid. We present new evidence supporting the pressure chamber technique and the existence of xylem pressures well below –0.4 MPa. We deduced xylem pressures in water-stressed stem xylem from the following experiment: (1) loss of hydraulic conductivity in hydrated stem xylem (xylem pressure = atmospheric pressure) was induced by forcing compressed air into intact xylem conduits; (2) loss of hydraulic conductivity from cavitation and embolism in dehydrating stems was measured, and (3) the xylem pressure in dehydrated stems was deduced as being equal and opposite to the air pressure causing the same loss of hydraulic conductivity in hydrated stems. Pressures determined in this way are only valid if cavitation was caused by air entering the xylem conduits (air-seeding). Deduced xylem pressure showed a one-to-one correspondence with pressure chamber measurements for 12 species (woody angiosperms and gymnosperms); data extended to c. –10 MPa. The same correspondence was obtained under field conditions in Betula occidentalis Hook., where pressure differences between air- and water-filled conduits were induced by a combination of in situ xylem water pressure and applied positive air pressure. It is difficult to explain these results if xylem pressures were above –0.4 MPa, if the pressure chamber was inaccurate, and if cavitation occurred by some mechanism other than air-seeding. A probable reason why the pressure probe does not register large negative pressures is that, just as cavitation within the probe limits its calibration to pressures above c. –0.5 MPa, cavitation limits its measurement range in situ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00334.x
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  • 7
    Electronic Resource
    Electronic Resource
    Expression of the butyrophilin gene, a milk fat globule membrane protein, is associated with the expression of the αS1casein gene (1995)
    Springer
    Journal of molecular histology 27 (1995), S. 388-394 
    Details
    ISSN: 1573-6865
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Previous in situ hybridization studies from our laboratory have shown that expression of certain milk protein genes, e.g. α-lactalbumin, is very high in most parts of the mammary glands of sheep and cattle, while in other areas containing an abundance of fat globules it is virtually zero (Molenaar et al., 1992). One possible explanation is that some areas of the mammary gland are dedicated to protein synthesis and some to fat synthesis. To check this possibility, the cRNA for butyrophilin, a milk-fat globule membrane protein, and hence a putative marker of milk fat synthesis, was used as a probe in in situ hybridization studies. The results show quite clearly that the patterns of expression for this gene are similar, cell type for cell type, as those for milk protein genes such as α-lactalbumin and αs1casein. In addition, we found that butyrophilin gene expression more closely matches that of αS1casein than that of α-lactalbumin. If it is shown in the future that butyrophilin is indeed a marker for milk fat synthesis, then these results support the current assumption that fat and protein synthesis do occur in the same cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00179564
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  • 8
    Electronic Resource
    Electronic Resource
    Expression of the butyrophilin gene, a milk fat globule membrane protein, is associated with the expression of the αS1casein gene (1995)
    Springer
    Journal of molecular histology 27 (1995), S. 388-394 
    Details
    ISSN: 1573-6865
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Previousin situ hybridization studies from our laboratory have shown that expression of certain milk protein genes, e.g. α-lactalbumin, is very high in most parts of the mammary glands of sheep and cattle, while in other areas containing an abundance of fat globules it is virtually zero (Molenaaret al., 1992). One possible explanation is that some areas of the mammary gland are dedicated to protein synthesis and some to fat synthesis. To check this possibility, the cRNA for butyrophilin, a milk-fat globule membrane protein, and hence a putative marker of milk fat synthesis, was used as a probe inin situ hybridization studies. The results show quite clearly that the patterns of expression for this gene are similar, cell type for cell type, as those for milk protein genes such as α-lactalbumin and αs1casein. In addition, we found that butyrophilin gene expression more closely matches that of αS1casein than that of α-lactalbumin. If it is shown in the future that butyrophilin is indeed a marker for milk fat synthesis, then these results support the current assumption that fat and protein synthesis do occur in the same cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02389025
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  • 9
    Electronic Resource
    Electronic Resource
    Degassing and surface analysis of gas atomized aluminium alloy powders (1995)
    Springer
    Journal of materials science 30 (1995), S. 3811-3819 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The degassing behaviour and surface characterization of Al-Mg base alloys has been investigated using quadrupole mass spectrometry (QMS) and X-ray photoelectron spectroscopy (XPS). The alloy composition, particle size and the nature of the atomizing gas have been studied in terms of gas evolution and surface composition. XPS has been used both to measure oxide thicknesses and magnesium enrichment ratios. XPS results show that magnesium segregation increases for larger particle sizes and this is supported by QMS, with a correspondingly higher hydrogen evolution on heating being observed for the larger size fractions. High-resolution XPS of the carbon 1s photoelectron peak (C1s) indicates the presence of carbonate component on the as-received magnesium-containing powders. This component is less pronounced on degassed powders indicating the evolution of CO2 on heating. This observation is supported by thermodynamic calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01153939
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  • 10
    Electronic Resource
    Electronic Resource
    Nanospheres prepared from poly(β-malic acid) benzyl ester copolymers: evidence for their in vitro degradation (1996)
    Springer
    Journal of materials science 7 (1996), S. 161-166 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: The in vitro degradation of nanospheres perpared from three benzyl ester derivatives of poly (β-malic acid) containing 80, 90 and 100% of benzylated malic acid units was studied. The progressive decrease in the molecular weight of the copolymers was observed as the nanospheres degraded, demonstrating that the degradation under the experimental conditions occurred by a simple hydrolytic cleavage of the ester bond between the monomeric units. The degradation was slow, with the weight average molecular weight decreasing to about 70% of the initial value in 5 months for all the nanosphere systems. A comparison of degradation rates for benzyl ester copolymers with the degradation rate of poly (β-malic acid) homopolymer demonstrated a decreased degradation rate of benzylated copolymers which suggests that the introduction of a pendent benzyl ester function in proximity to the ester bond in the main chain, reduces the rate of the bond cleavage. No significant difference in the degradation behaviour of highly benzylated copolymers, containing 90 and 80% of benzylated malic acid units, and fully benzylated polymer could be detected to prove an autocatalytic role on degradation of the free pendent carboxyl group in the former two copolymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00121255
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