High‐Throughput Method for Determining Modulus of Polymer Blends

Summary: A method for rapidly determining the modulus of polymer blends was developed. A polymer blend gradient library of poly(L ‐lactic acid) (PLLA) and poly(D ,L ‐lactic acid) (PDLLA) was created in the form of a strip‐shaped film and characterized with FTIR microspectroscopy. Nanoindentation measurements were made along the gradients to obtain modulus data over a wide range of PLLA‐PDLLA blend compositions. This novel, high‐throughput approach to material characterization provides engineers with a technique to accelerate the development of materials.

Deposition of the polymer composition gradient.     

Tracking pore to pore exchange using relaxation exchange spectroscopy

We observe the movement of water over time between pores of differing sizes in Castlegate sandstone. To achieve this, we perform an NMR transverse relaxation exchange experiment for several mixing times. The resulting data are converted to 2D T2 distributions using a 2D inverse Laplace transform (ILT). We show for the first time that quantitative analysis of ILT distributions enables one to extract characteristic times for different pores sizes. This information is potentially useful for permeability determination as well as better understanding of exchange between specific pore subpopulations.     

Torsional response and stiffening of individual multiwalled carbon nanotubes

We report on the characterization of torsional oscillators which use multiwalled carbon nanotubes as the spring elements. Through atomic-force-microscope force-distance measurements we are able to apply torsional strains to the nanotubes and measure their torsional spring constants, and estimate their effective shear moduli. The data show that the nanotubes are stiffened by repeated flexing. We speculate that changes in the intershell mechanical coupling are responsible for the stiffening.     

Die Bestimmung des Calciums

Ohne Zusammenfassung     

Zur Bestimmung der elektrolytischen Leitf?higkeit w?ssriger L?sungen

Ohne Zusammenfassung     

Finite method for a nonlinear allocation problem

The problem considered is as follows:m resources are to be allocated ton activities, with resourcei contributing linearly to the potential for activityj according to the coefficientE(i,j). The objective is to minimize some nonlinear function of the potentials. If the objective function is sufficiently well behaved, the problem can be solved in finitely many steps using the method described in this paper.The author thanks S. Toi Lawphongpanich for several helpful references and suggestions.     

Recent Fourier and Laplace perspectives for multidimensional NMR in porous media

Multidimensional NMR techniques used in the measurement of molecular displacements, whether by diffusion or advection, and in the measurement of nuclear spin relaxation times are categorised. Fourier-Fourier, Fourier-Laplace and Laplace-Laplace methods are identified, and recent developments discussed in terms of the separation, correlation and exchange perspective of multidimensional NMR spectroscopy.     

Effects of a parallel magnetic field on the metal-insulator transition in a dilute two-dimensional electron system

The temperature dependence of conductivity sigma(T) of a two-dimensional electron system in silicon has been studied in parallel magnetic fields B. At B = 0, the system displays a metal-insulator transition at a critical electron density n(c)(0), and dsigma/dT>0 in the metallic phase. At low fields ( B < or approximately equal to 2 T), n(c) increases as n(c)(B)-n(c)(0) proportional, variant Bbeta ( beta approximately 1), and the zero-temperature conductivity scales as sigma(n(s),B,T = 0)/sigma(n(s),0,0) = f(B(beta)/delta(n)), where delta(n) = [n(s)-n(c)(0)]/n(c)(0) and n(s) is electron density, as expected for a quantum phase transition. The metallic phase persists in fields of up to 18 T, consistent with the saturation of n(c) at high fields.     

Phase-locked, erbium-fiber-laser-based frequency comb in the near infrared

A phase-locked frequency comb in the near infrared is demonstrated with a mode-locked, erbium-doped, fiber laser whose output is amplified and spectrally broadened in dispersion-flattened, highly nonlinear optical fiber to span from 1100 to >2200 nm. The supercontinuum output comprises a frequency comb with a spacing set by the laser repetition rate and an offset by the carrier-envelope offset frequency, which is detected with the standard f-to-2f heterodyne technique. The comb spacing and offset frequency are phase locked to a stable rf signal with a fiber stretcher in the laser cavity and by control of the pump laser power, respectively. This infrared comb permits frequency metrology experiments in the near infrared in a compact, fiber-laser-based system.