DNA condensation in vivo relies on electrostatic complexation with small cations or large histones. We report a synchrotron x-ray study of the phase behavior of DNA complexed with synthetic cationic dendrimers of inte...
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DNA condensation in vivo relies on electrostatic complexation with small cations or large histones. We report a synchrotron x-ray study of the phase behavior of DNA complexed with synthetic cationic dendrimers of intermediate size and charge. We encounter unexpected structural transitions between columnar mesophases with in-plane square and hexagonal symmetries, as well as liquidlike disorder. The isoelectric point is a locus of structural instability. A simple model is proposed based on competing long-range electrostatic interactions and short-range entropic adhesion by counterion release.
In this paper, we study the pH response of a buried channel SOI MOSFET integrated with a nanofluidic cell. The surface of the device is exposed to solutions of different pH to validate the sensitivity of the device to...
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In this paper, we study the pH response of a buried channel SOI MOSFET integrated with a nanofluidic cell. The surface of the device is exposed to solutions of different pH to validate the sensitivity of the device to different chemical and biological environments.
Single-phase Pr5Ni1.9Si3 and PrNi were prepared and characterized by using differential thermal analysis, single crystal, and powder x-ray diffraction. Their thermal and magnetic properties were studied by measuring h...
Single-phase Pr5Ni1.9Si3 and PrNi were prepared and characterized by using differential thermal analysis, single crystal, and powder x-ray diffraction. Their thermal and magnetic properties were studied by measuring heat capacity as a function of temperature in magnetic fields up to 100 kOe and magnetization as a function of magnetic field up to 50 kOe over the temperature range from 5 to 400 K. Pr5Ni1.9Si3 orders magnetically at 50 K, and it undergoes a second transition at 25 K. As inferred from the behavior of the magnetization and magnetocaloric effect (MCE), both ferromagnetic and antiferromagnetic components are present in the magnetic ground state of the material. The heat capacity and magnetocaloric effect of PrNi confirm that it orders ferromagnetically at 19 K. Both Pr5Ni1.9Si3 and PrNi exhibit moderate magnetocaloric effects. The maximum MCE for Pr5Ni1.9Si3 is 3.4 K and it is observed at 50 K for a magnetic field change from 0 to 75 kOe. The maximum MCE for PrNi is 4.2 K, which occurs at 19 K for a magnetic field change from 0 to 100 kOe.
Thermal transport properties have been determined for a decagonal Al74Ni10Co16 quasicrystal in the temperature range 373–873 K. Differential scanning calorimetry and a laser flash method were employed in the determin...
Thermal transport properties have been determined for a decagonal Al74Ni10Co16 quasicrystal in the temperature range 373–873 K. Differential scanning calorimetry and a laser flash method were employed in the determination of heat capacity and thermal diffusivity, respectively. Thermal conductivity was determined from the product of diffusivity, heat capacity, and density. A high degree of anisotropy was observed between the aperiodic and periodic axes. The anisotropic heat flow is described using the thermal ellipsoid model. The model was applied to a surface oriented 45° to the major axes and substantiated from bulk measurements obtained from a sample cut along this orientation. Within this temperature range, the thermal transport of this two-dimensional quasicrystal may be described in a manner similar to anisotropic metallic single crystals.
Carbon nanotubes (CNTs) were stabilized in solution through sonication-induced polymerization of acrylated epoxidized soybean oil (AESO) monomer. Transmission electron microscopy and atomic force microscopy showed tha...
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Carbon nanotubes (CNTs) were stabilized in solution through sonication-induced polymerization of acrylated epoxidized soybean oil (AESO) monomer. Transmission electron microscopy and atomic force microscopy showed that the resulting polymer coatings of nanotubes in solution were approximately 10–30 nm in thickness. Raman spectroscopy suggests that AESO intercalates Nanocyl bundles and coats the exterior of HiPco bundles. Using sonication a stable dispersion of as-produced carbon nanotube powder was formed. Mechanical measurements on macroscale composites samples showed modulus enhancement consistent with a lower bound rule of mixtures.
Phase contrast in intermittent-contact atomic force microscopy (AFM) reveals in-plane structural and mechanical properties of polymer monolayers. This is surprising, because measurements of nanoscale in-plane properti...
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Phase contrast in intermittent-contact atomic force microscopy (AFM) reveals in-plane structural and mechanical properties of polymer monolayers. This is surprising, because measurements of nanoscale in-plane properties typically require contact mode microscopies. Our measurements are possible because the tip oscillates not just perpendicular but also parallel to the sample surface along the long axis of the cantilever. This lateral tip displacement is virtually universal in AFM, implying that any oscillating-tip AFM technique is sensitive to in-plane material properties.
Myelin figures are densely packed stacks of coaxial cylindrical bilayers that are unstable to the formation of coils or double helices. These myelin figures appear to have no intrinsic chirality. We show that such cyl...
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Myelin figures are densely packed stacks of coaxial cylindrical bilayers that are unstable to the formation of coils or double helices. These myelin figures appear to have no intrinsic chirality. We show that such cylindrical membrane stacks can develop an instability when they acquire a spontaneous curvature or when the equilibrium distance between membranes is decreased. This instability breaks the chiral symmetry of the stack and may result in coiling. A unilamellar cylindrical vesicle, on the other hand, will develop an axisymmetric instability, possibly related to the pearling instability.
作者：
R. S. LakesDepartment of Engineering Physics
Engineering Mechanics Program Materials Science Program University of Wisconsin 147 ERB 1500 Engineering Drive Madison Wisconsin 53705
Composites with negative stiffness inclusions in a viscoelastic matrix are shown to have higher stiffness and mechanical damping tanδ than that of either constituent and exceeding conventional bounds. The causal mech...
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Composites with negative stiffness inclusions in a viscoelastic matrix are shown to have higher stiffness and mechanical damping tanδ than that of either constituent and exceeding conventional bounds. The causal mechanism is a greater deformation in and near the inclusions than the composite as a whole. Though a block of negative stiffness is unstable, negative stiffness inclusions in a composite can be stabilized by the surrounding matrix. Such inclusions may be made from single domains of ferroelastic material below its phase transition temperature or from prebuckled lumped elements.
In recent years, experimental and computational studies have demonstrated that the dynamics of glass-forming liquids are spatially heterogeneous, exhibiting regions of temporarily enhanced or diminished mobility. Here...
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In recent years, experimental and computational studies have demonstrated that the dynamics of glass-forming liquids are spatially heterogeneous, exhibiting regions of temporarily enhanced or diminished mobility. Here we present a detailed analysis of dynamical heterogeneity in a simulated “bead-spring” model of a low-molecular-weight polymer melt. We investigate the transient nature and size distribution of clusters of “mobile” chain segments (monomers) as the polymer melt is cooled toward its glass transition. We also explore the dependence of this clustering on the way in which the mobile subset is defined. We show that the mean cluster size is time dependent with a peak at intermediate time, and that the mean cluster size at the peak time grows with decreasing temperature T. We show that for each T a particular fraction of particles maximizes the mean cluster size at some characteristic time, and this fraction depends on T. The growing size of the clusters demonstrates the growing range of correlated motion, previously reported for this same system [C. Beneman et al. Nature (London) 399, 246 (1999)]. The distribution of cluster sizes approaches a power law near the mode-coupling temperature, similar to behavior reported for a simulated binary mixture and a dense colloidal suspension, but with a different exponent. We calculate the correlation length of the clusters, and show that it exhibits similar temperature- and time-dependent behavior as the mean cluster size, with a maximum at intermediate time. We show that the characteristic time of the maximum cluster size follows the scaling predicted by mode-coupling theory (MCT) for the β time scale, revealing a possible connection between spatially heterogeneous dynamics and MCT.
Recoil implantation was performed to create ultra shallow Sb doped layers in an Si (001) substrate. The technique consists of the initial deposition of thin (40 to 140 nm) Sb layers followed by high energy Ar+ ion irr...
Recoil implantation was performed to create ultra shallow Sb doped layers in an Si (001) substrate. The technique consists of the initial deposition of thin (40 to 140 nm) Sb layers followed by high energy Ar+ ion irradiation and final chemical stripping of the residual Sb film. The resulting Sb atoms are recoil implanted into the underlying Si substrate. The results show a linear dependence of Sb concentration with Ar+ ion dose. High resolution Medium Energy Ion Scattering (MEIS) measurements have shown the projected range to be 3.0 nm with a doped layer width of 2.8 nm. The deposited Sb layer thickness is also shown to be a weakly dependent parameter in determining the Sb concentration for a given ion energy and dose.
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