Peak Spectral Width Research Articles

Si nanoripples: A growth dynamical study

Si(100) surface was physically eroded using 1keV O2+ ion beam and the resultant surface was studied by atomic force microscopy (AFM). The data were analyzed within the framework of dynamic scaling theory. Results indicate two growth regimes during the evolution of ripples on the surface. The first growth regime which is an unstable one continues for around 35min and has an exponential growth exponent. The second growth regime on the other hand sets in after this time and exhibits a growth exponent of 0.38. However, for the entire bombarding period a single coarsening exponent (1/z=0.44) extracted from the power spectral density peak widths of the acquired AFM images is observed. The ripple amplitudes however show an exponential increase over the time domain studied in agreement with the Bradley–Harper theory. Finally, roughness measurements clearly indicate transition regions of sputter yield variations and the onset of ripple formation.

Absorption spectrophotometry signal de-noising using invariant wavelets

Diseases such as cancer, hepatitis and AIDS cause body fluid concentration and amount to become modified; their measurement can thus be useful as a diagnostic technique. Spectroscopy is one of the most widely used techniques for biological substance detection and quantification. The presence of unwanted signals is the main limiting factor for sensitivity and quality; this is called noise. Noise has different backgrounds which range from physical assumptions to environmental influence. Eliminating or reducing noise in spectroscopy has thus been studied for many years and the applicability of wavelet transform has been demonstrated in recent decades. This paper presents invariant wavelet transform for increasing signal to noise ratio in spectrophotometer signals and thus improve the quality of spectrophotometric analysis and biological substance quantification. The proposed technique was applied to artificially-generated signals and signals from two spectrometers, one having a continuum source and another with a laser radiation source. The results obtained with this technique were compared to those obtained from traditional filters: Gaussian, Wiener and orthogonal wavelets. This technique's main advantages are a substantial increase in signal to noise ratio and preservation of spectral peak location and width. These advantages increase biological substance detection and quantification quality and accuracy and allow automatic analysis of the spectrum. They can also lead to better understanding of experimental limitations and allow a quantitative study of the influence of changes in substance concentration in related diseases.

First Distance-of-Flight Instrument: Opening a New Paradigm in Mass Spectrometry

A new instrumental concept, distance-of-flight mass spectrometry (DOFMS), is demonstrated experimentally. In DOFMS the mass-to-charge ratio of ions is determined by the distance each ion travels during a fixed time period; the mass spectrum is then recorded with a position-sensitive detector. The DOF approach provides a new way to separate and quantify components of complex samples. Initial results are demonstrated with a glow discharge ion source and a microchannel plate-phosphor screen detector assembly for atomic ion determination. This detection system demonstrated mass spectral peak widths of approximately 0.65 mm, corresponding to resolving powers of approximately 400-600 for a number of elemental samples.

Theoretical and experimental study of the achievable separation power in resistive‐glass atmospheric pressure ion mobility spectrometry

We present a detailed investigation of the performance of our previously reported nanoelectrospray high-resolution resistive-glass atmospheric pressure drift tube ion mobility spectrometer constructed with monolithic resistive-glass desolvation and drift regions. Using experimental spectral data and theoretical pulse width and diffusion variables, we compare theoretical and experimental resolving powers achievable under a variety of field strengths and ion gate pulse widths. The effects of instrumental and operational parameters on the resolution achievable in chromatographic terms are also discussed. Following characterization of the separation power of the instrument, experimental spectral peak width data is fitted by a least-squares procedure to a pre-existing semi-empirical model developed to study contributions to peak width other than initial pulse width and diffusional broadening. The model suggests possible contributions to the final measured peak width from electric field inhomogeneity and minor contributions from instrumental parameters such as anode size, anode-to-anode grid distance and drift gas flow rate. The model also reveals an unexpected ion gate width dependence on the final measured peak width that we attribute to non-ideal performance of the Bradbury-Nielsen ion gate and limitations in the design of our pulsing-electronics.

Possibilities for measurement of nano-crystallites size with use of parametric X-ray radiation

Spectral and angular properties of the parametric X-ray radiation (PXR) of relativistic particles emitted in the backward direction from a thin crystalline layer and polycrystal are considered. The shapes of the natural spectral peak of the PXR from a crystalline ball and spectral distribution of PXR from a polycrystal are estimated. It is shown that the natural spectral peak width determines the PXR spectral peak width emitted in backward direction from crystalline layer and grains with size of nanometer range. The method for measurements of crystalline layer thickness and crystalline grains size of nanometer range with use of spectral peak width of the PXR emitted in the backward direction is discussed.

Supraspinal contribution to splanchnic sympathetic activity in neonatal mouse and rat brainstem–spinal cord in vitro

Under optimal in vitro conditions, isolated spinal cords of neonatal Sprague–Dawley (SD) rats spontaneously generate sympathetic nerve discharge (SND). To aid future studies involving genetically modified mice, we established a preparation to assess SND generation within the mouse spinal cord. Brainstem–spinal cord–splanchnic nerve preparations of neonatal 129S6/SvEvTac (129S6) mice, C57BL/6 (B6) mice, Long-Evan (LE) rats, and SD rats were used. The contributions of the brainstem to splanchnic SND (sSND) were not significantly affected by cervical cord transections in LE and SD rats. However, the transections caused approximately a 70% reduction in sSND in both mice species. Power spectral analyses characterized distinct features of sSND oscillations. With intact brainstem–spinal cord, comparable maximal power peaks at ∼ 1–2 Hz were observed in mouse and rat spectra, although the spectral peak widths were broader in mice. Cervical cord transections reduced the maximal peak powers and the peak widths in mice but not in rats. For comparisons across animal groups, the amounts of sSND were normalized to ambient current noise and expressed in signal/noise units. Similar amounts of normalized sSND were recorded from mice and rats with intact brainstem–spinal cords. However, the level of mouse sSND was reduced following cervical cord transection, whereas rat sSND was not. Our results demonstrate a species related difference in sSND recorded from neonatal rat and mouse spinal cord preparations in vitro. The current experimental model is applicable to evaluate the SND strength in neonatal rodents of various genetic backgrounds.

Fermi surface of Co(0001) and initial-state linewidths determined by soft x-ray angle-resolved photoemission spectroscopy

Soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) reveals the band dispersion and Fermi surface of bulk ferromagnetic Co(0001). The spectral peak widths are narrower than previously observed in low-energy ARPES experiments. From very general considerations and in contrast to low-energy experiments, we show that the final-state broadening is significantly reduced in the experimentally measured linewidth. SX-ARPES yields the intrinsic initial-state lifetime ${\ensuremath{\Gamma}}_{i}=1/2{\ensuremath{\Sigma}}_{i}(\stackrel{P\vec}{k},E)$, the latter being the initial state self-energy, quantifying the correlations and indicating an energy and momentum dependence. Our results open a way to a direct measurement of the many-particle effects in solid-state physics, which does not require a modeling of the final state and provides a genuine description of the initial state.

Nest and colony-specific spectra in the weaver ant Oecophylla smaragdina

Animals in social groups need to differentiate between group members and others. In very large groups, such as those formed by many ant species, it is not possible to rely on individually specific cues to identify colonymates. Instead, recognition must be based on the colony-specific cues. Individual ant colonies tend to have a specific chemical gestalt that is maintained by the continual exchange of chemicals between workers. In very large polydomous colonies, the exchange of chemicals may be limited between nests within the colony, resulting in inter-nest variation in colony odour that might hinder identification of colonymates or conspecific intruders. We used near-infrared spectroscopy to explore variation in the chemical profile between and within colonies of the weaver ant Oecophylla smaragdina. We found that differences between colonies were reflected in the position, amplitude and width of spectral peaks, while differences between nests within colonies were reflected mainly in amplitude. Furthermore, in the context of colonymate recognition, the behaviour of the ants themselves was positively correlated with colony-specific spectral characteristics, rather than with nest-specific characteristics. Thus, colony spectra have features that are not obscured by intra-colonial variation and may potentially encode the chemical characteristics used by workers to identify colonymates.

Average Predictability Time. Part I: Theory

AbstractThis paper introduces the average predictability time (APT) for characterizing the overall predictability of a system. APT is the integral of a predictability measure over all lead times. The underlying predictability measure is based on the Mahalanobis metric, which is invariant to linear transformation of the prediction variables and hence gives results that are independent of the (arbitrary) basis set used to represent the state. The APT is superior to some integral time scales used to characterize the time scale of a random process because the latter vanishes in situations when it should not, whereas the APT converges to reasonable values. The APT also can be written in terms of the power spectrum, thereby clarifying the connection between predictability and the power spectrum. In essence, predictability is related to the width of spectral peaks, with strong, narrow peaks associated with high predictability and nearly flat spectra associated with low predictability. Closed form expressions for the APT for linear stochastic models are derived. For a given dynamical operator, the stochastic forcing that minimizes APT is one that allows transformation of the original stochastic model into a set of uncoupled, independent stochastic models. Loosely speaking, coupling enhances predictability. A rigorous upper bound on the predictability of linear stochastic models is derived, which clarifies the connection between predictability at short and long lead times, as well as the choice of norm for measuring error growth. Surprisingly, APT can itself be interpreted as the “total variance” of an alternative stochastic model, which means that generalized stability theory and dynamical systems theory can be used to understand APT. The APT can be decomposed into an uncorrelated set of components that maximize predictability time, analogous to the way principle component analysis decomposes variance. Part II of this paper develops a practical method for performing this decomposition and applies it to meteorological data.

Analysis of Distortion Product Otoacoustic Emission Spectra in Normal-Hearing Adults

To evaluate the ability of distortion product otoacoustic emission (DPOAE) spectral characteristics to distinguish between ears with variable hearing sensitivity within the normal range. Distortion product grams (DP-grams) were acquired with primary tones decremented in 1/8-octave steps and primary-tone levels presented at 65 dB SPL (L1) and 45 dB SPL (L2) across an f2 frequency range of 842-7996 Hz from 22 normal-hearing adults (44 ears). Hearing thresholds of ears classified in Group A (n = 22) were better than ears classified in Group B (n = 22). Examined parameters of the DP-grams included spectral peak occurrence, peak height, peak width, and DPOAE levels. Analyses of variance were conducted to determine whether DP-gram parameters differed between Group A and Group B. For the low-resolution DP-grams examined in this study, no significant between-group differences in peak occurrence, peak height, and peak width were observed. DPOAE levels were significantly higher in ears classified in Group A compared with ears classified in Group B in individuals with symmetrical hearing. Although spectral peaks are evident in DP-grams acquired with low resolution of the primary tones, DPOAE levels are more effective in distinguishing ears with greater hearing sensitivity from less sensitive ears.

Performance Enhancements of Mass Selective Axial Ejection from a Linear Ion Trap

Mass selective axial ejection (MSAE) of ions from a linear ion trap (LIT) takes advantage of the rf fringing fields at the end of the linear quadrupole to convert radial ion excitation into axial ejection. Ions gain radial amplitude via a mass selective resonance excitation process and are ejected axially over an electrostatic DC barrier. The extraction efficiency and resolution are determined by the length and shape of the extraction region in the vicinity of the exit aperture. In the work presented here, axial DC fields, created by auxiliary electrodes, were used to modify the shape of the trapping electrostatic fields along the quadrupole axis and to increase the density of the ions in the extraction region. Better confinement and ion cloud coherence increased the extraction efficiency and the spectral resolution. As a result, extraction efficiency can be increased by up to one order of magnitude at fast scan rates, i.e., 10 and 20 kTh/s, and a factor of 2-3 at the slower scan speed of 1 kTh/s. The length of the extraction region was also modified by application of a portion of the drive rf voltage to the end lens of the LIT. A comparison of the MSAE spectra at different scan rates and rf levels showed that extraction efficiencies increase at scan rates of 10 kTh/s or higher, with associated improvements in mass spectral peak widths.

Ripplon on high viscosity liquid

A ripplon is a thermally excited capillary wave propagating on liquid surface. Propagation of the ripplon reflects surface mechanical properties such as surface tension and viscoelasticity of the liquid. An optical beating ripplon spectroscopy technique developed by us was applied mainly to the observation of various surface phenomena on a lowly viscous liquid surface in the frequency range from 1 kHz to several 10 MHz. In this study, we carried out a light scattering observation of the highly damped ripplon on the surface of the viscous liquid. The spectral peak width of the damped ripplon was smaller for the higher viscosity and the optical beating technique could resolve such a structure. A strict description of the dynamic structure factor of the ripplon was employed to fit the experimental power spectrum of overdamped ripplon to viscosity up to 1000 cS.

Petroleomics: Chemistry of the underworld

Each different molecular elemental composition-e.g., C(c)H(h)N(n)O(o)S(s)-has a different exact mass. With sufficiently high mass resolving power (m/Deltam(50%) approximately 400,000, in which m is molecular mass and Deltam(50%) is the mass spectral peak width at half-maximum peak height) and mass accuracy (<300 ppb) up to approximately 800 Da, now routinely available from high-field (>/=9.4 T) Fourier transform ion cyclotron resonance mass spectrometry, it is possible to resolve and identify uniquely and simultaneously each of the thousands of elemental compositions from the most complex natural organic mixtures, including petroleum crude oil. It is thus possible to separate and sort petroleum components according to their heteroatom class (N(n)O(o)S(s)), double bond equivalents (DBE = number of rings plus double bonds involving carbon, because each ring or double bond results in a loss of two hydrogen atoms), and carbon number. "Petroleomics" is the characterization of petroleum at the molecular level. From sufficiently complete characterization of the organic composition of petroleum and its products, it should be possible to correlate (and ultimately predict) their properties and behavior. Examples include molecular mass distribution, distillation profile, characterization of specific fractions without prior extraction or wet chemical separation from the original bulk material, biodegradation, maturity, water solubility (and oil:water emulsion behavior), deposits in oil wells and refineries, efficiency and specificity of catalytic hydroprocessing, "heavy ends" (asphaltenes) analysis, corrosion, etc.

Nonlinear processes upon doubling the period of self-modulation oscillations in a solid-state ring laser

Nonlinear phenomena appearing in a solid-state ring laser upon approaching the period-doubling bifurcation point of self-modulation oscillations and inside the doubling region are studied theoretically and experimentally. The bifurcation appears due to the parametric interaction of self-modulation oscillations of the first kind with relaxation oscillations. It is found that the bifurcation diagrams, time dependences of the intensities and power spectrum can significantly differ for counterpropagating waves because of the amplitude nonreciprocity of the ring resonator and the inequality of the moduli of the feedback coefficients. It is shown that when the self-modulation period is doubled, the widths of spectral peaks corresponding the self-modulation frequency and the fundamental relaxation frequency decrease. Noise precursors of doubling bifurcation are studied. It is found that the distance between the peaks of noise precursors increases with increasing the noise intensity. It is demonstrated experimentally that the noise modulation leads to the bifurcation point displacement, which increases with increasing the noise.

Peak width issues with generalised 2D correlation NMR spectroscopy

Two-dimensional spectral correlation analysis is shown to be sensitive to fluctuations in spectral peak width as a function of perturbation variable. This is particularly significant where peak width fluctuations are of similar order of magnitude as the peak width values themselves and where changes in peak width are not random but are, for example, proportional to intensity. In such cases these trends appear in the asynchronous matrix as false peaks that serve to interfere with interpretation of the data. Complex, narrow band spectra such as provided by 1H NMR spectroscopy are demonstrated to be prone to such interference. 2D correlation analysis was applied to a series of NMR spectra corresponding to a commercial wine fermentation, in which the samples collected over a period of several days exhibit dramatic changes in concentration of minor and major components. The interference due to changing peak width effects is eliminated by synthesizing the recorded spectra using a constant peak width value prior to performing 2D correlation analysis.

ESI FT-ICR mass spectral analysis of coal liquefaction products

We have applied electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyze the pyridine soluble fraction of a distillation resid and a further processed liquid product in a coal liquefaction process. The inherent high resolving power ( m/Δ m 50%>300,000, in which Δ m 50% is full mass spectral peak width at half-maximum peak height) and mass accuracy (<1 ppm) of FT-ICR MS makes it possible to resolve and identify polar heteroatomic species. The resid contains more heteroatomic compounds and a higher molecular weight distribution whereas the liquid sample is lower in average mass and more saturated. The data confirms that the liquefaction process produces lower mass, hydrogenated liquid product whereas the resid (highly aromatic and of high heteroatom content) must be recycled to reduce its heteroatom content and increase its degree of saturation.

Dynamics of amorphous polymers in the temperature region 2– [formula omitted] where the standard model of low-temperature glasses begin to fail: studies by single molecule spectroscopy and comparison with photon echo data

Spectra of single tetra-tert-butylterrylene molecules incorporated in purely amorphous polyisobutylene matrix have been measured at 2, 4.5 and 7 K (244, 381 and 187 molecules, correspondingly). This is a temperature region, where the main assumptions of the standard two-level system (TLS) model of low-temperature glasses begin to be not valid. At T=2 K the main parameters of most of the registered spectra were found to be consistent with the standard TLS model. At T=4.5 and 7 K some deviations from predictions of this model were observed. The detailed analysis reveals that increasing of temperature leads to additional, in comparison with the predictions of the standard TLS model, line broadening of spectral peaks. This additional line broadening was attributed to the influence of quasi-local low-frequency modes (LFMs) of the amorphous matrix in system under study at T=4.5 and 7 K . Distributions of single spectral peak widths of the detected spectra (the line width distributions) have been calculated and compared with the line width distributions simulated for the same system. Comparative analysis of experimental and simulated distributions allows to evaluate the value of LFM contribution at 4.5 and 7 K . The single molecule spectroscopy data were compared with the literature values of inverse optical dephasing times, 1/ πT 2, as measured for the same system by photon echo (S.J. Zilker et al., J. Chem. Phys. 109 (1998) 6780).

有機π配位子による金ナノ粒子の機能化とネットワーク化

Thiol-derivatized gold nanoparticles has drawn much attention as a building block of nano-scaled electronic devises. As a fuctional thiol ligand, π-conjugated radical thiols, e.g p-mercaptophenyl nitronyl nitroxide, etc., have been synthesized. Nanoparitcles with the average particle size of 4 nm were chemisorbed by 100 lignads of p-mercaptophenyl nitronyl nitroxde and they were isolated and characterized. The ESR spectral peak width of the radical thiol on the nanoparticle was extremely broadened (ΔHpp= 30 mT at RT), suggesting the significant magnetic interaction between an unpaired electron of the radical uint and conduction electrons of gold nanoparticles.Network structures of gold nanopartilces connected by σ- or π-molecular nanowires made of alkanedithiol or oligothiophene with protected thiol groups were also prepared. It is to be noted that the network structures of nanaoparticles connected with molecular wires were prepared through a self-organization process. They are semiconductors with small activation energies (ca. 20 meV at temperatures higher than 40 K, and ca. 6 meV at lower than 40 K), suggesting a hopping mechanism for the electronic transportation in a higher temperatures region (T = 40 K) and a tunneling mechanism in the lower temperature (T < 40 K).

Dynamics of a doped polymer at temperatures where the two-level system model of glasses fails: Study by single-molecule spectroscopy

We investigated the spectra of a large number of single tetra-tert-butylterrylene molecules embedded in an amorphous polyisobutylene matrix and analyzed the distributions of their linewidths (widths of single spectral peaks). The measurements were performed at 2, 4.5, and 7 K. This is a temperature region, where the standard two-level system (TLS) model of low-temperature glasses begins to fail. At T=2 K the temporal behavior (history of frequency jumps) of most of the measured spectra and their linewidth distributions were found to be consistent with the TLS model. At higher temperatures the main features of individual spectra (number of spectral peaks, temperature variation of peak widths, ratio of intensities of different peaks, etc.) still appear consistent with the predictions of this model. An increase of temperature leads mainly to the broadening of spectral peaks. A detailed analysis of the linewidth distributions reveals deviations from a standard TLS model at T=4.5 and 7 K. This difference is attributed to the influence of quasi-local low-frequency modes (LFM) of the amorphous matrix. By comparing the measured linewidth distributions with computer simulations, we quantitatively determined the LFM contribution to the single-molecule spectra in our dye-matrix system at different temperatures.

New techniques in electron energy-loss spectroscopy and energy-filtered imaging

This article is a survey of hardware and software advances that promise to increase the power and sensitivity of electron energy-loss spectroscopy (EELS) and energy-filtered imaging (EFTEM) in a transmission electron microscope. Recent developments include electron-gun monochromators, lens-aberration correctors, and software for spectral sharpening, spectral processing and interpretation of fine structure. Future improvements could include the deployment of new electron sources. The expected enhancements in energy and spatial resolution are compared with fundamental limitations that arise from the natural widths of spectral peaks, the delocalization of inelastic scattering and the problem of electron-irradiation damage.