Non-existence of infinitesimally invariant measures on loop groups

Let G be a compact Lie group, L(G) the associated loop group, ω the canonical symplectic form on L(G). Set H the Hamiltonian function for which the associated ω-Hamiltonian vector field is the infinitesimal rotation. Then H generates a canonical semi-definite Riemannian structure on L(G), which induces a Riemannian structure on the free loop groupL(G)/G=L₀(G). This metric corresponds to the Sobolev norm H¹. Using orthonormal frame methodology the positivity and finiteness of the Ricci curvature of L₀(G) is proved. By studying the dissipation towards high modes of a unitary group valued SDE it is proved that the loop group does not have any infinitesimally invariant measure.     

Surface and bulk elasticity determined fluctuation regimes in smectic membranes

We report combined x-ray photon correlation spectroscopy (XPCS) and neutron spin echo (NSE) measurements of the layer-displacement fluctuations in smectic liquid-crystal membranes in the range from 10 ns to 10 micros. NSE reveals a new regime, determined by bulk elasticity, in which relaxation times decrease with the wave vector of the fluctuations. XPCS probes slower surface-tension-dominated relaxation times, independent of the wave vector. XPCS gives a difference in correlation times at specular and off-specular positions that can be related to different detection schemes.     

Potentials and limitations of robotics: Guides to managerial evaluations

This article primarily focuses on: the place of robotics within current and prospective advances in manufacturing technology, the impacts of increasing robot utilization on the productivity and costs of users, and resulting effects on the international competitiveness of domestic industries.     

PELDOR at S- and X-band frequencies and the separation of exchange coupling from dipolar coupling

A pulsed electron double resonance (PELDOR) setup working at S-band frequencies is introduced and its performance compared with an X-band setup. Furthermore, to verify experimentally that it is possible to disentangle the dipolar coupling nu(Dip) from the exchange coupling J by PELDOR we synthesized and investigated four bisnitroxide radicals. They exhibit in pairs the same distances r(AB) between the nitroxide moieties but only one of each pair possesses a non-zero J. The experimental values for r(AB) match the ones from molecular modeling very well for the molecules without exchange coupling. For one bisnitroxide it was possible to separate nu(Dip) from J and to ascertain the magnitude and sign of J to +11 MHz (antiferromagnetic spin-spin coupling).     

Quantum chemical analysis of the unfolding of a penta-glycyl 3(10)-helix initiated by HO(●), HO2(●), and O2(-●)

In this study, the thermodynamic functions of hydrogen abstraction from the C(α) and amide nitrogen of Gly(3) in a homo-pentapeptide (N-Ac-GGGGG-NH(2); G5) by HO(●), HO(2)(●), and O(2)(-●) were computed using the Becke three-parameter Lee-Yang-Parr (B3LYP) density functional. The thermodynamic functions, standard enthalpy (ΔH°), Gibbs free energy (ΔG°), and entropy (ΔS°), of these reactions were computed with G5 in the 3(10)-helical (G5(Hel)) and fully-extended (G5(Ext)) conformations at the B3LYP/6-31G(d) and B3LYP/6-311+G(d,p) levels of theory, both in the gas phase and using the conductor-like polarizable continuum model implicit water model. H abstraction is more favorable at the C(α) than at the amide nitrogen. The secondary structure of G5 affects the bond dissociation energy of the H-C(α), but has a negligible effect on the dissociation energy of the H-N bond. The HO(●) radical is the strongest hydrogen abstractor, followed by HO(2)(●), and finally O(2)(-●). The secondary structure elements, such as H-bonds in the 3(10)-helix, protect the peptide from radical attack by disabling the potential electron delocalization at the C(α), which is possible when G5 is in the extended conformation. The unfolding of the peptide radicals is more favorable than the unfolding of G5(Hel); however, only the HO(●) can initiate the unfolding of G5(Hel) and the formation of G5(Ext)(●). These results are relevant to peptides that are prone to undergoing transitions from helical structures to β-sheets in the cellular condition known as "oxidative stress" and the results are discussed in this context.     

A Synthetic Bioinspired Carbohydrate Polymer with Mucoadhesive Properties

Mucoadhesive polymers are of significant interest to the pharmaceutical, medical device, and cosmetic industries. Polysaccharides possessing charged functional groups, such as chitosan, are known for mucoadhesive properties but suffer from poor chemical definition and solubility, while the chemical synthesis of polysaccharides is challenging with few reported examples of synthetic carbohydrate polymers with engineered‐in ionic functionality. We report the design, synthesis, and evaluation of a synthetic, cationic, enantiopure carbohydrate polymer inspired by the structure of chitosan. These water‐soluble, cytocompatible polymers are prepared via an anionic ring‐opening polymerization of a bicyclic β‐lactam sugar monomer. The synthetic method provides control over the site of amine functionalization and the length of the polymer while providing narrow dispersities. These well‐defined polymers are mucoadhesive as documented in single‐molecule scale (AFM), bulk solution phase (FRAP), and ex vivo tissue experiments. Polymer length and functionality affects bioactivity as long, charged polymers display higher mucoadhesivity than long, neutral polymers or short, charged polymers.     

Enhancing dominant modes in nonstationary time series by means of the symbolic resonance analysis

We present the symbolic resonance analysis (SRA) as a viable method for addressing the problem of enhancing a weakly dominant mode in a mixture of impulse responses obtained from a nonlinear dynamical system. We demonstrate this using results from a numerical simulation with Duffing oscillators in different domains of their parameter space, and by analyzing event-related brain potentials (ERPs) from a language processing experiment in German as a representative application. In this paradigm, the averaged ERPs exhibit an N400 followed by a sentence final negativity. Contemporary sentence processing models predict a late positivity (P600) as well. We show that the SRA is able to unveil the P600 evoked by the critical stimuli as a weakly dominant mode from the covering sentence final negativity.     

Measurement of absolute absorption cross sections for nitrous acid (HONO) in the near-infrared region by the continuous wave cavity ring-down spectroscopy (cw-CRDS) technique coupled to laser photolysis

Absolute absorption cross sections for selected lines of the OH stretch overtone 2ν(1) of the cis-isomer of nitrous acid HONO have been measured in the range 6623.6-6645.6 cm(-1) using the continuous wave cavity ring-down spectroscopy (cw-CRDS) technique. HONO has been generated by two different, complementary methods: in the first method, HONO has been produced by pulsed photolysis of H(2)O(2)/NO mixture at 248 nm, and in the second method HONO has been produced in a continuous manner by flowing humidified N(2) over 5.2 M HCl and 0.5 M NaNO(2) solutions. Laser photolysis synchronized with the cw-CRDS technique has been used to measure the absorption spectrum of HONO produced in the first method, and a simple cw-CRDS technique has been used in the second method. The first method, very time-consuming, allows for an absolute calibration of the absorption spectrum by comparison with the well-known HO(2) absorption cross section, while the second method is much faster and leads to a better signal-to-noise ratio. The strongest line in this wavelength range has been found at 6642.51 cm(-1) with σ = (5.8 ± 2.2) × 10(-21) cm(2).     

Features of magnetic resonance in nanoporous carbon with pores filled with transition-metal atoms

Properties of nanoporous carbon (NPC) free of metal atoms and NPC containing atoms of Ni, Co and Pd in their pores are studied by electron spin resonance (ESR). The asymmetrical ESR line with the so-called Dyson line shape points out that charge carriers are responsible for the resonance spectrum in metal-free NPC. Although the amount of Ni, Co, and Pd introduced into nanopores is small, the NPC properties change significantly. A bulk ferromagnetism is observed in the case of NPC with Co and Pd, but not in NPC:Ni. Co atoms in pores of NPC cause the formation of a new material, namely, a disordered ferromagnetic medium with some features in the Co atom distribution. Magnetic properties are strongly temperature-dependent. The temperature dependences of the conductivity and ESR integral intensity in NPC:Ni reveal an exponential growth with the same activation energy. The magnetic resonance spectrum of NPC:Pd consists of four signals for NPC which is produced from SiC. There are one ferromagnetic and three paramagnetic signals belonging to the carbon dangle sp³- and sp²-bonds kind and to the paramagnetic clusters of Pd atoms.     

Concentration fluctuations in polymer gel investigated by neutron scattering: static inhomogeneity in swollen gel

By using small-angle neutron scattering (SANS) and neutron spin echo (NSE), we have quantitatively investigated the static inhomogeneity in poly (N-isopropyl acrylamide) gel (PNIPA) in microscopic length scales of 0.015相似文献