Efficient magnetization reversal with noisy currents

We propose to accelerate reversal of the ferromagnetic order parameter in spin valves by electronic noise. By solving the stochastic equations of motion we show that the current-induced magnetization switching time is drastically reduced by a modest level of externally generated current (voltage) noise. This also leads to a significantly lower power consumption for the switching process.     

Conformational stability from temperature-dependent fourier transform infrared spectra of noble gas solutions, r0 structural parameters, and barriers to internal rotation for ethylamine

Variable temperature (-55 to -145 degrees C) studies of the infrared spectra (3500 to 100 cm(-1)) of ethylamine, CH(3)CH(2)NH(2), dissolved in liquid krypton and/or xenon have been recorded. From these data, the enthalpy differences have been determined to be 54 +/- 4 cm(-1) (0.65 +/- 0.05 kJ/mol), with the trans conformer (methyl group relative to the lone pair of electrons on nitrogen) being the more stable form. It is estimated that there is 61 +/- 1% of the doubly degenerate gauche form present at ambient temperature. The conformational energetics have been calculated with the M?ller-Plesset perturbation method to the second order (MP2(full)) and the fourth order (MP4(SDTQ)) as well as with density functional theory by the B3LYP method utilizing a variety of basis sets. Basis sets with diffuse functions lead to incorrect prediction of the conformational stability. On the basis of the frequencies of the torsional transitions along with the determined experimental enthalpy difference and gauche dihedral angle, the potential function governing conformational interchange has been obtained, and the determined Fourier cosine coefficients are V(1) = -207 +/- 48, V(2) = 320 +/- 67, V(3) = 1072 +/- 25, V(4) = 55 +/- 11, and V(5) = -96 +/- 28 cm(-1), with a trans-to-gauche barrier of 1286 cm(-1), and a gauche-to-gauche barrier of 715 cm(-1). The 3-fold methyl rotational barriers have been determined to be 1241 +/- 4 and 1281 +/- 10 cm(-1) for the gauche and trans conformers, respectively. By utilizing the previously reported microwave rotational constants combined with the structural parameters predicted at the MP2(full)/6-311+ G(d,p) level, adjusted r(0) structural parameters have been obtained. A complete vibrational assignment is given for the trans conformer, which is supported by normal coordinate calculations utilizing scaled force constants from ab initio B3LYP/6-311++G(3df,3pd) calculations. Proposed assignments are also made for the fundamentals of the gauche conformer. The results of these spectroscopic and theoretical studies are discussed and compared to the corresponding results for similar molecules.     

In-source CID of guanosine: Gas phase ion-molecule reactions

In-source collision induced dissociation was applied to access second generation ions of protonated guanosine. The in-source gas-phase behavior of [BH2]+-NH3 (m/z 135, C5H3N4O+) was investigated. Adduct formation and reactions with available solvent molecules (H2O and CH3OH) were demonstrated. Several addition/elimination sequences were observed for this particular ion and solvent molecules. Dissociation pathways for the newly formed ions were developed using a QqTOF mass spectrometer, permitting the assignment of elemental compositions of all product ions produced. Reaction schemes were suggested arising from the ring-opened intermediate of the protonated base moiety [BH2]+, obtained from fragmentation of guanosine. The mass spectral data revealed that the in-source CH3OH-reaction product underwent more complex fragmentations than the comparable ion following reaction with H2O. A rearrangement and a parallel radical dissociation pathway were discerned. Apart from the mass spectrometric evidence, the fragmentation schemes are supported by density functional theory calculations, in which the reaction of the ring-opened protonated guanine intermediate with CH3OH and a number of subsequent fragmentations were elaborated. Additionally, an in-source transition from the ring-opened intermediate of protonated guanine to the ring-opened intermediate of protonated xanthine was suggested. For comparison, a low-energy collision induced dissociation study of xanthosine was performed. Its dissociation pathways agreed with our assumption.     

Atomic force microscopy on chromosomes, chromatin and DNA: A review

The purpose of this review is to discuss the achievements and progress that has been made in the use of atomic force microscopy in DNA related research in the last 25 years. For this review DNA related research is split up in chromosomal-, chromatin- and DNA focused research to achieve a logical flow from large- to smaller structures. The focus of this review is not only on the AFM as imaging tool but also on the AFM as measuring tool using force spectroscopy, as therein lays its greatest advantage and future. The amazing technological and experimental progress that has been made during the last 25 years is too extensive to fully cover in this review but some key developments and experiments have been described to give an overview of the evolution of AFM use from 'imaging tool' to 'measurement tool' on chromosomes, chromatin and DNA.     

Characterization of a photonic strain sensor in silicon-on-insulator technology

Recently there has been growing interest in sensing by means of optical microring resonators in photonic integrated circuits that are fabricated in silicon-on-insulator (SOI) technology. Taillaert et al. [Proc. SPIE 6619, 661914 (2007)] proposed the use of a silicon-waveguide-based ring resonator as a strain gauge. However, the strong lateral confinement of the light in SOI waveguides and its corresponding modal dispersion where not taken into account. We present a theoretical understanding, as well as experimental results, of strain applied on waveguide-based microresonators, and find that the following effects play important roles: elongation of the racetrack length, modal dispersion of the waveguide, and the strain-induced change in effective refractive index.     

Thermo‐Responsive Solid‐Phase Extraction Using Poly(methyl vinyl ether)–Containing Segmented Polymer Networks

Segmented polymer networks containing poly(methyl vinyl ether) (PMVE) segments were prepared by free‐radical‐initiated copolymerization of PMVE‐α,ω‐dimethacrylate with styrene or 2‐hydroxyethyl methacrylate (HEMA). These networks were evaluated as thermo‐responsive solid‐phase extraction materials. Suspension‐derived polymer networks consisting of 80% of PMVE and 20% of HEMA adsorb toluene from an aqueous solution at 40°C and release the adsorbed toluene quantitatively at 20°C.     

The sol-gel approach towards thermo-responsive poly(N-isopropyl acrylamide) hydrogels with improved mechanical properties

A new type of thermo-responsive hydrogels based on the polymer poly(N-isopropyl acrylamide) (PNIPAA) has been synthesized with the sol-gel technology. For the preparation of this type of nano-structured hydrogels, the inorganic silica phase was synthesized by the sol-gel process in the presence of an aqueous solution of high molecular weight PNIPAA. This combination of the organic and inorganic phases forms hybrid hydrogels with a semi-IPN morphology. The unique structure of these hydrogels improves the mechanical stability to a great extent as compared to conventional PNIPAA-hydrogels. This was shown by stress-strain experiments and the capability to absorb and desorb large amounts of water. The silica only slightly influences the transition temperature of the hydrogels but allows us to vary the thermo-responsive properties of the materials to a great extent.     

Polymer networks containing crystallizable poly(octadecyl vinyl ether) segments for shape‐memory materials

New polymer networks were prepared by free radical initiated copolymerization of crystallizable α,ω‐bismethacrylate‐terminated poly(octadecyl vinyl ether) (polyODVE) with butyl acrylate (BA). The polyODVE bismacromonomers were obtained by end‐capping the bifunctionally living cationic polymerization of ODVE with 2‐hydroxyethyl methacrylate (HEMA). The segmented networks show a high degree of phase separation over a wide range of compositions. The shape memory properties of a material containing 20 wt.‐% of polyODVE are reported.