Direct Observation of Aggregation‐Induced Backbone Conformational Changes in Tau Peptides

In tau proteins, the hexapeptides in the R2 and R3 repeats are known to initiate tau fibril formation, which causes a class of neurodegenerative diseases called the taupathies. We show that in R3, in addition to the presence of the hexapeptides, the correct turn conformation upstream to it is also essential for producing prion‐like fibrils that are capable of propagation. A time‐dependent NMR aggregation assay of a slow fibril forming R3‐S316P peptide revealed a trans to cis equilibrium shift in the peptide‐bond conformation preceding P316 during the growth phase of the aggregation process. S316 was identified as the key residue in the turn that confers templating capacity on R3 fibrils to accelerate the aggregation of the R3‐S316P peptide. These results on the specific interactions and conformational changes responsible for tau aggregation could prove useful for developing an efficient therapeutic intervention in Alzheimer's disease.     

On the propensity of magnetism in 3d transition-metal-MgCNi3 alloys

The effects of disorder and incipient magnetism in MgC(_Ni1-xTx)3$\mathrm{MgC}({\mathrm{Ni}}_{1-x}{\mathrm{T}}_x{)}_3$ (T≡Fe$\mathrm{T}\equiv \mathrm{Fe}$, Co or Cu) alloys are studied using coherent-potential approximation and Ginzburg–Landau coefficients. The first-principles, local-density-functional-based calculations for substitutionally disordered Fe and Co impurities in the Ni sub-lattice of MgCNi₃, in low concentrations, show that incipient magnetism resides in these materials. The overestimation of the calculated magnetic properties points to the limitations of the local-density approximation. However, using a phenomenological approach based on Ginzburg–Landau coefficients and the fixed-spin moment method, we show that MgC(_Ni1-xTx)3$\mathrm{MgC}({\mathrm{Ni}}_{1-x}{\mathrm{T}}_x{)}_3$ alloys remain paramagnetic. At expanded volumes, we also find the possibility of a ferromagnetic state for MgC(_{Ni0.95Fe0.05)3}$\mathrm{MgC}({\mathrm{Ni}}_{0.95}{\mathrm{Fe}}_{0.05}{)}_3$ and MgC(_{Ni0.90Co0.10)3}$\mathrm{MgC}({\mathrm{Ni}}_{0.90}{\mathrm{Co}}_{0.10}{)}_3$ alloys.     

Dielectric behavior and transport properties of ZnO nanorods

Highly optical, good crystalline and randomly aligned ZnO nanorods were synthesized by the hydrothermal method. The dielectric properties of ZnO nanorods were attributed to the interfacial polarization at low frequencies (below 10 kHz) and orientational polarization at higher frequencies. The observed ω^(n?1) dependence of dielectric loss was discussed on the basis of the Universal model of dielectric response. Dielectric loss peak was composed of the Debye like loss peak at higher frequencies and interfacial loss peak at lower frequencies. Charge transport through the grain and grain boundary region was investigated by impedance spectroscopy. At higher temperatures the conductivity of the nanorod was mainly through the grain interior and the overall impedance was contributed by the grain boundary region. The activation energy of nanorod was calculated as 0.078 eV, which is slightly higher than the reported bulk value.     

Pressure distribution near wedges for separated supersonic turbulent flow

Summary A theoretical analysis of the pressure distribution in the vicinity of a wedge for separated turbulent flow is made. The solution is based on Vasiliu's analysis of the pressure distribution for step-induced separation using the Crocco-Lees mixing coefficient and Chapman's dividing streamline model. Theoretical results are compared with experimental data by Sterrett and Emery for Mach 5.8 and wedge angles of 28° and 34.17°.Nomenclature b mixing coefficient distribution factor - C _p pressure coefficient - F() defined by equation (3) - f ₁() defined by equation (5) - f() defined by equation (10) - I ₁ momentum integral, reference 4 - K mixing coefficient, defined by equation (4) - K _j jet flow parameter, reference 4 - K ₀ value of K at separation - K _0r value of K in the reattachment zone - () defined by equation (11) - M Mach number - M free stream Mach number - P pressure - P _S pressure at the separation point - P free stream pressure - r _S defined as P _S/P - X distance from the separation point - X _n distance from separation to reattachment point - X _W distance from separation point to wedge corner - wedge angle - specific heats ratio - mixing layer thickness - _j mixing layer thickness in jet flow solution - _j ^* displacement thickness in jet flow solution - _S boundary layer thickness at separation - dimensionless coordinate, defined as X/ _S - _n value of at the reattachment point - deflection angle of flow outside the mixing layer - jet flow parameter, reference 4 - dimensionless pressure, defined as P/P _S - [ _c ]_max jet flow parameter, reference 4 - _c jet spread factor, reference 4     

The annealing of chemical radiation damage in acetatopentamminecobalt/III/nitrate

The kinetics of isothermal annealing of NO ₂ ⁻ in γ-irradiated acetatopentamminecobalt/III/ nitrate in the range 95–115 °C is a combination of a first order process affecting 28% of the damage fragments and a second order process, governing the behaviour of the remainder. The annealing data have also been analyzed on the basis of models developed by Fletcher and Brown and by Waite.     

Nanocrystalline GdBa2HfO5.5 perovskite dielectric material—A single-step synthesis and its characterization

Nanocrystals of GdBa₂HfO_5.5 perovskite ceramic materials, of the family A₂(BB′)O₆, were synthesized using an auto-igniting combustion of a precursor solution containing metal ions, oxidant and a fuel. Phase purity and particulate properties of the as-prepared powder were examined using X-ray diffraction, differential thermal and thermogravimetric analyses, Fourier-transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopic techniques. These nanocrystals were sintered to high density (～98% of the theoretical density) at ～1620 °C for 2 h.The sintering behavior, dielectric constant and dielectric loss factor of the samples showed variations in magnitude with that of the samples prepared by conventional solid-state route.     

Lubricated revolute joints in rigid multibody systems

The main purpose of this work is to present a general methodology for modeling lubricated revolute joints in constrained rigid multibody systems. In the dynamic analysis of journal-bearings, the hydrodynamic forces, which include both squeeze and wedge effects, generated by the lubricant fluid, oppose the journal motion. The hydrodynamic forces are obtained by integrating the pressure distribution evaluated with the aid of Reynolds’ equation, written for the dynamic regime. The hydrodynamic forces built up by the lubricant fluid are evaluated from the system state variables and included into the equations of motion of the multibody system. Numerical examples are presented in order to demonstrate the use of the methodologies and procedures described in this work.     

Crystal structure and dielectric properties of a new complex perovskite oxide Ba<Subscript>2</Subscript>LaSbO<Subscript>6</Subscript>

The crystal structure and dielectric properties of a new perovskite material Ba₂LaSbO₆ are reported. Ba₂LaSbO₆ was synthesized for the first time by conventional solid state reaction process. X-ray diffraction (XRD) measurements and Rietveld analysis revealed that, contrary to the other Ba₂RESbO₆ (RE=Rare-Earth other than La) complex perovskites, which are cubic, Ba₂LaSbO₆ crystallizes in a monoclinic system having space group P2₁/n. Dielectric properties of Ba₂LaSbO₆ at frequencies up to 40 GHz and in temperatures ranging from 50 to 350 K were determined by analyzing the resonant modes in cavities totally filled with the measured material. The dielectric constant ()=15.8±0.2% and at 77 K loss factor (tg)9×10^-4. Preliminary studies reveal that at the processing temperatures, Ba₂LaSbO₆ do not react with YBa₂Cu₃O_7- (YBCO) and Bi₂Sr₂CaCu₂O_x [Bi (2212)] superconductors. Having appropriate dielectric properties along with chemical stability with superconductors Ba₂LaSbO₆ can be used as a precursor as substrate for deposition of various passive HTS devices, or as an insulator in the active SIS structures. PACS 61.66.Fn; 61.10.Nz; 77.22.-d; 74.72.-h     

Transient temperature response of a porous matrix entering a planetary atmosphere

Summary An analysis is made of the transient temperature behavior of a transpiration-cooled porous matrix entering a planetary atmosphere with constant velocity and negative entry angle. The analysis is based on one dimensional heat conduction in a porous plate subjected to a time dependent heat flux at one side and cooled internally by mass injection from a constant temperature reservoir at the opposite side. An exact closed-form solution is obtained and temperature charts are presented for a wide range of Fourier number and coolant flow parameters.Nomenclature A surface area, ft² - C constant, 17,600 Btu/ft^3/2-sec - C _c constant pressure specific heat of coolant, Btu/lb_m-°F - g local gravitational acceleration, ft/sec² - g _c coolant flow parameter, defined by equation (15) - h height of entry above planet surface, ft - K ₁ ratio of local heat flux to stagnation point heat flux - K thermal conductivity of plate material, Btu/sec-ft-°F - L plate thickness, ft - m constant, 3.15 - m _c coolant mass flow rate, lb_m/sec - M _n roots of equation (33) - n constant, 0.50 - N defined by equation (30) - P porosity - q surface heat flux, Btu/ft²-sec - q ₀ surface heat flux at t=0, Btu/ft²-sec, defined by (6) - r distance from planet center, ft - R radius of curvature at stagnation point, ft - t time, sec - T temperature, °F - T _c coolant supply temperature, °F - V velocity, ft/sec - x normal coordinate through plate, ft - y altitude, ft - thermal diffusivity of plate, ft²/sec - atmospheric density decay parameter, 1/23500 ft^–1 - flight path angle relative to local horizontal direction, positive for climbing and negative for descent, deg - dimensionless temperature parameter, defined by (12) - dimensionless distance, defined by (13) - free stream atmospheric density, slug/ft³ - ₀ atmospheric density at reference state, slug/ft³ - Fourier number, defined by (14) - 1/sec, defined by (7) - flight entry parameter, defined by (16)