Nodal order parameter in electron-doped Pr(2-x)CexCuO(4-delta) superconducting films

The London penetration depth, lambda(ab)(T), is reported for thin films of the electron-doped superconductor Pr(2-x)Ce(x)CuO(4-delta) with varying Ce concentration, x=0.13, 0.15, and 0.17. Measurements down to 0.35 K were carried out using a tunnel-diode oscillator with excitation fields applied both perpendicular and parallel to the conducting planes. Films at all three doping levels exhibited power law behavior indicative of d-wave pairing with impurity scattering. These results are fully consistent with previous measurements on single crystals.     

Interplay between nonlinearity,scan speed,damping, and electronics in frequency modulation atomic-force microscopy

Numerical simulations of the frequency modulation atomic force microscope, including the whole dynamical regulation by the electronics, show that the cantilever dynamics is conditionally stable and that there is a direct link between the frequency shift and the conservative tip-sample interaction. However, a soft coupling between the electronics and the nonlinearity of the interaction may significantly affect the damping. A resonance between the scan speed and the response time of the system can provide a simple explanation for the spatial shift and contrast inversion between topographical and damping images, and for the extreme sensitivity of the damping to a tip change.     

Two-dimensional oxide on Pd(111)

The oxidation of Pd(111) leads to an incommensurate surface oxide, which was studied by the use of scanning tunneling microscopy, surface x-ray diffraction, high resolution core level spectroscopy, and density functional calculations. A combination of these methods reveals a two-dimensional structure having no resemblance to bulk oxides of Pd. Our study also demonstrates how the atomic arrangement of a nontrivial incommensurate surface can be solved by molecular dynamics in a case where experimental techniques alone give no solution.     

Heating of thin foils with a relativistic-intensity short-pulse laser

K-shell x-ray spectroscopy of sub-100 nm Al foils irradiated by high contrast, spatially uniform, 150 fs, Ilambda (2)=2 x 10(18) W microm(2)/cm(2), laser pulses is obtained with 500 fs time resolution. Two distinct phases occur: At /=500 fs the resonance transitions dominate. Initial satellites arise from a large area, high density, low temperature (approximately 100 eV) plasma created by fast electrons. Thus, contrary to predictions, a short, high intensity laser incident on a thin foil does not create a uniform, hot dense plasma.     

Single-shot spectral interferometry with chirped pulses

We present a method for obtaining time-resolved measurements of the amplitude modulation and the phase shift of a chirped probe pulse interacting with a femtosecond-laser-produced plasma. Based on spectral interferometry, the technique allows for single-shot measurements and keeps the temporal resolution associated with the full bandwidth of the probe pulse. We demonstrate the efficiency of this technique by probing femtosecond-laser breakdown of plastic targets.     

Novel Experimental Technique for the Determination of Monomer Droplet Size Distribution in Miniemulsion

Summary: The lack of accurate knowledge for measuring monomer droplet size and droplet size distribution has hampered the further progress of miniemulsion polymerization. Monomer droplet size is probably the most important characteristics of a miniemulsion, influencing the miniemulsion stability and the nucleation mechanism. To date, several experimental techniques have been tested to measure miniemulsion droplet size, but none are convenient and accurate. This work presents a novel experimental technique, using a powerful new scanning transmission electron microscopy (STEM) imaging system, which allows transmission observations of wet samples in an environmental scanning electron microscopy (ESEM). This new imaging technique is a useful technique to directly measure droplet size and droplet size distribution.

Miniemulsion droplets in dark field wet STEM imaging conditions.     

Risk exposure and Lagrange multipliers of nonanticipativity constraints in multistage stochastic problems

We take advantage of the interpretation of stochastic capacity expansion problems as stochastic equilibrium models for assessing the risk exposure of new equipment in a competitive electricity economy. We develop our analysis on a standard multistage generation capacity expansion problem. We focus on the formulation with nonanticipativity constraints and show that their dual variables can be interpreted as the net margin accruing to plants in the different states of the world. We then propose a procedure to estimate the distribution of the Lagrange multipliers of the nonanticipativity constraints associated with first stage decisions; this gives us the distribution of the discounted cash flow of profitable plants in that stage.     

Stability of the molecular bond of benzene up to 40 GPa. A brillouin study

Abstract

The variation of the elastic constant of an oriented C₆H₆ monocrystal shows the occ urenre of an irreversible process above 20 GPa. This process leads to the format ion of a polymer- as it was shown by IR study. The bulk modulus of the recovered product is one order of magni t ude above that of solid benzene, this gives ev idence for a reconstruct ion of the bonds in the sample.

La mesure de constantes élastiques réalisée sur un monocristal orienté de benzene montre qu' un processus irréversible se développe au-delá de 20 GPa. La formation d'un Polymére Peut ětre constatée aprés I'exdpérience. Le module de rigidité du produit formé, un ordre de grandeur au-dessus de Celui du benzene solide, montre clairement qu'une reconstruction des liaisons a eu lieu.     

Synthesis of arborescent styrene homopolymers and copolymers from epoxidized substrates

The synthesis of arborescent styrenic homopolymers and copolymers was achieved by anionic polymerization and grafting. Styrene and p‐(3‐butenyl)styrene were first copolymerized using sec‐butyllithium in toluene, to generate a linear copolymer with a weight‐average molecular weight M_w = 4000 and M_w/M_n = 1.05. The pendant double bonds of the copolymer were then epoxidized with m‐chloroperbenzoic acid. A comb‐branched (or arborescent generation G0) copolymer was obtained by coupling the epoxidized substrate with living styrene‐p‐(3‐butenyl)styrene copolymer chains with M_w ≈ 5000 in a toluene/tetrahydrofuran mixture. Further cycles of epoxidation and coupling reactions while maintaining M_w ≈ 5000 for the side chains yielded arborescent copolymers of generations G1–G3. A series of arborescent styrene homopolymers was also obtained by grafting M_w ≈ 5000 polystyrene side chains onto the linear and G0–G2 copolymer substrates. Size exclusion chromatography measurements showed that the graft polymers have low polydispersity indices (M_w/M_n = 1.02–1.15) and molecular weights increasing geometrically over successive generations. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012