Linewidth Data Research Articles

Amyloid-β Protofibrils Differ from Amyloid-β Aggregates Induced in Dilute Hexafluoroisopropanol in Stability and Morphology

The brains of Alzheimer's disease (AD) patients contain large numbers of amyloid plaques that are rich in fibrils composed of 40- and 42-residue amyloid-beta (Abeta) peptides. Several lines of evidence indicate that fibrillar Abeta and especially soluble Abeta aggregates are important in the etiology of AD. Recent reports also stress that amyloid aggregates are polymorphic and that a single polypeptide can fold into multiple amyloid conformations. Here we demonstrate that Abeta-(1-40) can form soluble aggregates with predominant beta-structures that differ in stability and morphology. One class of aggregates involved soluble Abeta protofibrils, prepared by vigorous overnight agitation of monomeric Abeta-(1-40) at low ionic strength. Dilution of these aggregation reactions induced disaggregation to monomers as measured by size exclusion chromatography. Protofibril concentrations monitored by thioflavin T fluorescence decreased in at least two kinetic phases, with initial disaggregation (rate constant approximately 1 h(-1)) followed by a much slower secondary phase. Incubation of the reactions without agitation resulted in less disaggregation at slower rates, indicating that the protofibrils became progressively more stable over time. In fact, protofibrils isolated by size exclusion chromatography were completely stable and gave no disaggregation. A second class of soluble Abeta aggregates was generated rapidly (<10 min) in buffered 2% hexafluoroisopropanol (HFIP). These aggregates showed increased thioflavin T fluorescence and were rich in beta-structure by circular dichroism. Electron microscopy and atomic force microscopy revealed initial globular clusters that progressed over several days to soluble fibrous aggregates. When diluted out of HFIP, these aggregates initially were very unstable and disaggregated completely within 2 min. However, their stability increased as they progressed to fibers. Relative to Abeta protofibrils, the HFIP-induced aggregates seeded elongation by Abeta monomer deposition very poorly. The techniques used to distinguish these two classes of soluble Abeta aggregates may be useful in characterizing Abeta aggregates formed in vivo.

On the Titanium Oxide Neutral Cluster Distribution in the Gas Phase: Detection through 118 nm Single-Photon and 193 nm Multiphoton Ionization

Titanium oxide clusters are generated in a supersonic expansion by laser ablation of the metal and reaction with oxygen (0.1-6%) in He expansion gas. Mass spectra of the titanium oxide clusters are observed by photoionization with lasers of three different wavelengths: 118, 193, and 355 nm. Only the 118 nm (10.5 eV) light can ionize Ti(m)O(n) neutral clusters without fragmentation. Both the 193 nm (6.4 eV) and 355 nm (3.5 eV) multiphoton ionization cause fragmentation of the neutral clusters during the ionization process and, thus, can complicate the determination of the stable neutral Ti(m)O(n) gas-phase species. Employing 118 nm single-photon ionization and line-width data, the Ti(m)O(2m) and Ti(m)O(2m+1) series are found to be the most stable neutral cluster species for high oxygen content in the expansion gas. Fragmentation during the multiphoton ionization process for 193 nm light yields the cluster ions Ti(m)O(2m-1,-2)+. These ions are formed by the loss of one or two oxygen atoms from Ti(m)O(2m,2m+1) neutral species. The dominant cluster growth process is suggested to be through the addition of TiO2 species. For low oxygen content (<2%) in the expansion gas, oxygen-deficient clusters of the form Ti(m)O(2m-1,-2) are also observed. These latter series are not fragmented by the 193 nm ionization process.

Extrinsic contribution to Gilbert damping in sputtered NiFe films by ferromagnetic resonance

We quantitatively determine the intrinsic and extrinsic contribution to frequency (Δfres) and field (ΔH) linewidths using Network Analyzer ferromagnetic resonance (NA-FMR) (using two different excitation cells) and conventional ferromagnetic resonance (FMR) techniques in sputtered thin permalloy (NiFe) films. There are some common features in these two FMR measurements, which allow us to get important information on damping mechanisms and structural magnetic qualities. The NA-FMR data show an increase in frequency linewidth (Δfres) as magnetic field (H) increases. A distinct change in the slope of this increase is noted for a field above 200Oe. To explain this result, we consider available theories including the “two-magnon” model, and the “local-resonance” model. From a fitting of Δfres versus H data to the Arias-Mills’ two-magnon model results, we obtain the Gilbert damping parameters. The frequency variation of conventional FMR linewidth (ΔH) data also yields an effective value for the Gilbert damping (αeff=0.0128), in good agreement with the data from the Network Analyzer data (0.013±0.004). In addition to the theoretical analysis presented in this paper, we compare our experimental results from RF-excitation cell to the commonly used co-planer waveguide technique.

Semiclassical calculations of collision line broadening in Raman spectra of N2 and CO mixtures.

We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N(2) and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N(2), the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N(2) and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N(2). The central results of this work are the Q-branch linewidths of N(2)-CO and CO-N(2), which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules.

Magnetic susceptibility and spin dynamics of a polyoxovanadate cluster: A proton NMR study of a model spin tetramer

We report susceptibility and nuclear magnetic resonance (NMR) measurements in a polyoxovanadate compound with formula $(\mathrm{NHEt}{)}_{3}[{\mathrm{V}}_{8}^{\mathrm{IV}}{\mathrm{V}}_{4}^{\mathrm{V}}{\mathrm{As}}_{8}{\mathrm{O}}_{40}({\mathrm{H}}_{2}\mathrm{O})]\ensuremath{\cdot}{\mathrm{H}}_{2}\mathrm{O}\ensuremath{\equiv}{\mathrm{V}12}.$ The magnetic properties can be described by considering only the central square of localized ${\mathrm{V}}^{4+}$ ions and treated by an isotropic Heisenberg Hamiltonian of four intrinsic spins 1/2 coupled by nearest-neighbor antiferromagnetic interaction with $J\ensuremath{\sim}17.6\mathrm{K}.$ In this simplified description the ground state is nonmagnetic with ${S}_{T}=0.$ The ${}^{1}H$ NMR linewidth (full width at half maximum) data depend on both the magnetic field and temperature, and are explained by the dipolar interaction between proton nuclei and ${\mathrm{V}}^{4+}$ ion spins. The behavior of the nuclear spin-lattice relaxation rate ${T}_{1}^{\ensuremath{-}1}$ in the temperature range (4.2--300 K) is similar to that of $\ensuremath{\chi}T$ vs T and it does not show any peak at low temperatures contrary to previous observations in antiferromagnetic rings with larger intrinsic spins. The results are explained by using the general features of the Moriya formula and by introducing a single T-independent broadening parameter for the electronic spin system. From the exponential T dependence of ${T}_{1}^{\ensuremath{-}1}$ at low $T(2.5\mathrm{K}&lt;T&lt;4.2\mathrm{K})$ we have obtained a field dependent gap following the linear relation ${\ensuremath{\Delta}}_{\mathrm{NMR}}={\ensuremath{\Delta}}_{0}\ensuremath{-}g{\ensuremath{\mu}}_{B}H,$ with the gap ${\ensuremath{\Delta}}_{0}\ensuremath{\sim}17.6\mathrm{K}$ in agreement with the susceptibility data. Below 2.5 K the proton ${T}_{1}^{\ensuremath{-}1}$ deviates from the exponential decrease indicating the presence of a small, almost temperature independent, but strongly field dependent, nuclear relaxation contribution, which we will investigate in detail in the near future.

Processing chemically amplified resists on advanced photomasks using a thermal array

A thermal array, which consists of a dense distribution of multivariate controlled heat/chill elements, is developed to achieve temperature uniformity of a quartz photomask throughout the processing temperature cycle of ramp, hold and quench. The thermal array spatially tunes the uniformity in response to calibrated feedback provided by temperature sensor instrumented masks or by linewidth data. The system can stabilize to decreases in temperature setpoints at fast rates, about 40 °C/min, to improve the throughput of the tool for situations requiring switching between operating temperatures. The thermal array is a likely aid to improve critical dimension distribution on expensive photomasks by providing uniform thermal processing conditions.

Near theoretical microwave loss in hot isostatic pressed (hipped) polycrystalline yttrium iron garnet

The ferromagnetic resonance (FMR) linewidth, the field dependent effective linewidth, and the parallel pump spin wave linewidth were measured for spheres and disks prepared from a block of hot isostatic pressed (hipped) polycrystalline yttrium iron garnet (YIG). All linewidths as well as static magnetization data indicate close to 100% density. Vibrating sample magnetometer measurements give an average saturation induction 4πMs of 1825 G. The FMR half-power linewidths for the spheres at 9.5 GHz were 13 Oe. Linewidths measured over the 9.5–18 GHz frequency range show a small but distinct drop and agree with Schlömann’s theory of anisotropy-dominated two-magnon scattering for polycrystalline ferrites. The effective linewidth versus field data at 10 GHz show a region of strong absorption that corresponds to the width of the spin wave manifold for low wave numbers and a high field value of about 2 Oe. Parallel pumping measurements give minimum spin wave linewidths of 1.2 and 0.6 Oe at 9 and 16.7 GHz, respectively. The 16.7 GHz spin wave linewidths correspond to half-frequency spin waves at 8.35 GHz. The extrapolated linewidths at zero wave number are about 0.5 Oe and match the established intrinsic linewidths expected for YIG single crystals at 8–9 GHz. The spin wave linewidths increase linearly with wave number and are consistent with a transit time scattering process with scattering lengths that are about ten times greater than the average grain size.

Optimized pulsed laser deposited barium ferrite thin films with narrow ferromagnetic resonance linewidths

Hexagonal M-type barium ferrite (BaM) films have been prepared by pulsed laser deposition. Optimal preparation conditions gave pure single phase films with the narrowest possible ferromagnetic resonance (FMR) linewidths. The films were deposited on c-plane sapphire substrates with a KrF excimer laser at wavelength of 248 nm and fluence of 1.7 J/cm2. The minimum linewidth films were obtained for an oxygen partial pressure of 300 mTorr and a substrate temperature of 910 °C, and were 0.85 μm thick. X-ray diffraction indicated pure single crystal BaM phase with local c-axis deviations less than 0.15°. Vibrating sample magnetometry data gave hysteresis loops with minimal hysteresis and small coercive force, saturation induction 4πMs of 4.2 kG and uniaxial anisotropy field HA of 16.4 kOe. The HA matches the anisotropy for bulk and the 4πMs is about 10% below literature values for the bulk. The FMR spectra were measured from 50 to 75 GHz by shorted wave guide techniques with the static field perpendicular to the film. The optimized film uniform mode half power FMR linewidth at 60.3 GHz was 27 Oe. This linewidth was a linear function of the frequency with a response coefficient of 0.5 Oe/GHz and nearly zero frequency intercept. Within experimental error, this linewidth response is the same as for bulk crystals. The FMR spectra show additional standing spin wave (SSW) resonances which could be indexed to give field positions that scale with the square of index n except for low order modes. The scaling gave a standard exchange energy parameter, Aex, of 6.4×10−7 erg/cm. The SSW linewidths scaled with n2. Application of the Kittel thickness variation model to the SSW linewidth data gave an estimated thickness variation of the film of about 7%.

Trapped ion optical frequency standards

Optical frequency standards based on narrow absorptions in laser-cooledsingle trapped ions have recently begun to demonstrate stabilities that arecompetitive with cold atom fountain microwave standards. This paperpresents a short review of the wider state-of-the-art development of thesesingle cold trapped ion frequency standards, coupled with a more detailedaccount of recent results achieved at National Physical Laboratory inrespect of single ion systems based on 88Sr+, 87Sr+ and 171Yb+.Narrow linewidth data for the optical clock quadrupole and octupoletransitions respectively at 674 nm in 88Sr+and 467 nm in 171Yb+, arepresented, together with a discussion of current systematics and futureprojections. The potential for optical clock operation is outlined.

Quality assessment of chalcopyrite thin films using Raman spectroscopy

The relationship of the linewidth of the Raman A 1-mode of CuInS 2-based thin films is investigated. Thereby it is assumed that the linewidth is predictive for the crystal quality. Comparison with the parameters of the solar cells formed out of these thin films reveal a direct correlation between the linewidth and solar cell data, such as open circuit voltage and fill factor. A correlation of the linewidth with the crystal sizes as determined by SE images is also found. For small linewidths, a saturation of the solar cell data is found. This behaviour indicates other origins of performance limitation to be present in CuInS 2-based devices.

Frequency-dependent exchange bias in NiFe/NiO films

Ferromagnetic (FM) resonance and magnetization curve measurements were performed at room temperature for a polycrystalline ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ coupled to NiO. It was observed that the shape of the angular variation of the resonance field is frequency dependent, with the curve at 9.65 GHz typical for a strongly exchange-coupled bilayer, while the 34.0 GHz curve is characteristic for relatively weak interactions. Numerical simulations of the resonance field and of the hysteresis loop shift, carried out through the domain wall formation model, as well as the resonance linewidth data indicated that there must be two fractions in the antiferromagnetic part of the interface, with stable and unstable grains. Only the stable grains contribute to the exchange bias. In our sample, whether an interfacial antiferromagnetic grain is stable or not is predominantly determined by the strength of the exhange coupling between this grain and the adjacent FM domain. The stable antiferromagnetic grains, whose contribution is sensed by the resonance experiment, are the smaller ones, which are more strongly coupled to the ferromagnet than the larger grains.

Exploring the active site of human factor Xa protein by NMR screening of small molecule probes.

A collection of small molecules (MW < 350 Da) was screened for binding to human factor Xa using saturation transfer difference NMR spectroscopy to detect binding. The NMR screening experiments identified four hits. Binding isotherms constructed from NMR linewidth data showed that the binding affinities of the hits were all in the 30-210 microM range. Competition binding experiments showed that three of the ligands were displaced by a known microM inhibitor of factor Xa. The success of the method for identifying new ligands and the relevance of this information to the design of new factor Xa inhibitors are discussed.

Measurements of line intensities and line widths in the ν3-fundamental band of nitrous oxide at atmospheric temperatures

We present measurements of the absolute intensities, N 2-, O 2-, and air-broadened half-widths of spectral lines in the 4.5 μm ( ν 3-fundamental) band of 14 N 2 16 O at 216, 250 and 296 K . These data were obtained using a high-resolution ( 0.002 cm −1) Fourier-transform spectrometer. The variation of the line widths with temperature and the rotational quantum number m (| m| is J in the P-branch and J+1 in the R-branch, with J being the rotational quantum number of a linear molecule) is examined. Simple empirical polynomial (quartic) fits of the measured half-widths are presented. A new improved method of extrapolation of line-width data to higher values of m has also been devised.

Demixing of Fluorinated and Hydrogenated Surfactants into Distinct Aggregates and into Distinct Regions within Aggregates. A Combined NMR, Fluorescence Quenching, and Cryo-TEM Study

The formation of two different kinds of micelles in the cationic surfactant mixture of HFDePC and CTAC as well as the increased mixing with increasing temperature has been investigated. A critical temperature of demixing was appreciated to 42 °C. NMR self-diffusion measurements reveal to us a coexistence of larger fluorocarbon-rich and smaller hydrocarbon-rich micelles, which is also observed using cryo-TEM. We also suggest, from 19F line width data, that the two surfactant species constituting the demixed micelles are “microphase-separated”. The existence of such aggregates has earlier only been speculated upon. From time-resolved fluorescence quenching measurements, we have estimated the fraction of fluorocarbon surfactant in the hydrocarbon-rich micelles to larger than 0.1.

Structural and Single Crystal EPR Studies of the Complex Copper L-Glutamine: A Weakly Exchange-Coupled System with syn-anti Carboxylate Bridges

We report the molecular structure and a single crystal EPR study at 9.8 and 33.9 GHz of a new copper(II) compound with the amino acid L-Glutamine, Cu[NH2CO2CH(CH2)2CONH2]2. The CuII ion is in an elongated octahedral environment equatorially trans-coordinated by two glutamine molecules acting as bidentate ligands through the nitrogen atom and one oxygen atom of each amino acid group, and axially by two carboxylate oxygen atoms of two neighboring glutamine molecules. Copper ions are arranged in layers connected by syn-anti carboxylate bridges that provide equatorial and apical ligands to the copper ions. Neighboring layers are connected by long chemical paths, which include two amino acid side chains connected by H bonds. Single crystal EPR spectra show a single exchange-collapsed resonance at both microwave frequencies for any magnetic field orientation. The evaluation of the molecular g-tensor from the angular variation of the EPR line position yielded g⊥ = 2.051 and g|| = 2.248, which indicates a d ground orbital for the Cu ions. The angular variation of the EPR line width displays a contribution that is typical of a 2-D magnetic system, and another contribution depending on the microwave frequency, which is attributed to the incomplete collapse of the resonances corresponding to magnetically nonequivalent copper ions. A quantitative analysis of the line width data allowed us to estimate a mean exchange coupling constant |J/k| = 0.42(2) K, which is assigned to the syn-anti carboxylate chemical path that connects neighboring copper ions within a layer. The results are discussed and compared with those observed in similar systems. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Stark widths dependence on the upper level ionization potential and the rest core charge of the emitter within 3 s–3 p and 3 p–3 d transition arrays

Stark width simultaneous dependence on the upper level ionization potential and rest core charge of the emitter has been evaluated and discussed. It has been verified that the found relations, connecting Stark broadening parameters with upper level ionization potential and rest core charge of the emitters for particular electron temperature and density, can be used for prediction of Stark line width and shift data in case of ions for which observed data, or more detailed calculations, are not yet available.

Multiwatt CW diode end-pumped Nd:YAP laser at 1.08 and 1.34 μm: influence of Nd doping level

A CW diode-pumped Nd:YAP laser delivering an output power of 3.7 W at 1.34 μm is described. The laser operates in an end-pumped configuration using a fiber bundle optically coupled to the laser rod with only two lenses. A maximum optical slope efficiency of 35.7% was measured with respect to the incident pump power on the laser crystal, with a threshold as low as 1.5 W. A comparison between Nd:YAP and Nd:YAG crystals in the same pumping configuration is given at both wavelengths of 1.06 and 1.34 μm. The influence of Nd doping level in YAP crystal on laser efficiency is presented with results obtained at 0.77, 0.85, 0.95, and 1.05 at.% Nd concentrations, respectively. Thermal induced lens and spectral linewidth data are also given.

Experimental measurements and analysis of thermal magnetization noise in GMR sensors

High-frequency measurements and theoretical analysis of data on giant magnetoresistance thermal magnetization fluctuation noise are presented. An experimental setup for the measurement of this noise at high frequencies is proposed. The measured noise increases with bias current and demonstrates two distinct resonance peaks within 6 GHz. Damping parameters are extracted from resonance linewidth data. Small variations are seen within a given manufacturing batch of eight heads. Data fitting to the measured-noise power spectrum and comparison between eigenmode and Landau-Lifshitz-Gilbert theories.

Heterogeneous solvent dynamics and time-resolved optical linewidths

The time resolved inhomogeneous optical linewidth observed in solvation dynamics experiments is sensitive to the nature of the solvent dynamics, homogeneous or heterogeneous. Linewidth data are assessed with regard to intrinsic non-exponentiality, the length scale of heterogeneity, and the time scale of rate exchange. For the glass-forming solvent under study, heterogeneity is found for average relaxation times in the range 3 ms to 54 s and in the regime of nanosecond dynamics.

Molecular Mechanism of Lateral Diffusion of Fluorosurfactants. A 19F NMR Study

The focus of this thesis has been on the effects of segregation in mixtures of amphiphilic molecules. Two different systems were investigated: fluorocarbon-hydrocarbon surfactant mixtures and lipid-surfactant mixtures.In fluorocarbon-hydrocarbon surfactant mixtures the repulsive interactions between the chains can lead to a demixing into different types of coexisting micelles, fluorocarbon rich and hydrocarbon rich. From NMR self-diffusion measurements such a demixing was found to occur in the mixture of the partially fluorinated surfactant HFDePC and C16TAC. We furthermore suggested a demixing also within the micelles to explain 19F-NMR line width data and results from neutron scattering.In lipid-surfactant mixtures, a segregation of the molecules may instead be caused by a difference in the preferred curvature of the lipid and the surfactant residing within the same aggregate. Using a surfactant selective electrode, binding isoterms of four different cationic surfactants (C12TAC, C14TAC, C16TAC and HFDePC) to preformed lipid (GMO) vesicles were determined. Perforated vesicles were observed by cryo-TEM in the mixture with C16TAC. To explain the results from the binding isoterms, the formation of pores in the bilayer was regarded as a cooperative process, similar to micelle formation. The surfactant accumulates at the edges of the pores, and increasing the surfactant concentration results in an increased number of pores with a constant surfactant/lipid ratio at the edges.The lipid-surfactant mixtures were also studied at the solid/solution interface using AFM. An adsorbed mesh structure, a counterpart to the bulk perforated lamellar phase, was observed for the first time.