Spectral Character Research Articles

Random vibration analysis of switching apparatus based on Monte Carlo method

The performance in vibration environment of switching apparatus containing mechanical contact is an important element when judging the apparatus’s reliability. A piecewise linear two-degrees-of-freedom mathematical model considering contact loss was built in this work, and the vibration performance of the model under random external Gaussian white noise excitation was investigated by using Monte Carlo simulation in Matlab/Simulink. Simulation showed that the spectral content and statistical characters of the contact force coincided strongly with reality. The random vibration character of the contact system was solved using time (numerical) domain simulation in this paper. Conclusions reached here are of great importance for reliability design of switching apparatus.

Global spectral classification of Martian low‐albedo regions with Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) data

Martian low‐albedo surfaces (defined here as surfaces with Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) albedo values ≤0.15) were reexamined for regional variations in spectral response. Low‐albedo regions exhibit spatially coherent variations in spectral character, which in this work are grouped into 11 representative spectral shapes. The use of these spectral shapes in modeling global surface emissivity results in refined distributions of previously determined global spectral unit types (Surface Types 1 and 2). Pure Type 2 surfaces are less extensive than previously thought, and are mostly confined to the northern lowlands. Regional‐scale spectral variations are present within areas previously mapped as Surface Type 1 or as a mixture of the two surface types, suggesting variations in mineral abundance among basaltic units. For example, Syrtis Major, which was the Surface Type 1 type locality, is spectrally distinct from terrains that were also previously mapped as Type 1. A spectral difference also exists between southern and northern Acidalia Planitia, which may be due in part to a small amount of dust cover in southern Acidalia. Groups of these spectral shapes can be averaged to produce spectra that are similar to Surface Types 1 and 2, indicating that the originally derived surface types are representative of the average of all low‐albedo regions.

Score–moment combined linear discrimination analysis (SMC-LDA) as an improved discrimination method

A new discrimination method called the score-moment combined linear discrimination analysis (SMC-LDA) has been developed and its performance has been evaluated using three practical spectroscopic datasets. The key concept of SMC-LDA was to use not only the score from principal component analysis (PCA), but also the moment of the spectrum, as inputs for LDA to improve discrimination. Along with conventional score, moment is used in spectroscopic fields as an effective alternative for spectral feature representation. Three different approaches were considered. Initially, the score generated from PCA was projected onto a two-dimensional feature space by maximizing Fisher's criterion function (conventional PCA-LDA). Next, the same procedure was performed using only moment. Finally, both score and moment were utilized simultaneously for LDA. To evaluate discrimination performances, three different spectroscopic datasets were employed: (1) infrared (IR) spectra of normal and malignant stomach tissue, (2) near-infrared (NIR) spectra of diesel and light gas oil (LGO) and (3) Raman spectra of Chinese and Korean ginseng. For each case, the best discrimination results were achieved when both score and moment were used for LDA (SMC-LDA). Since the spectral representation character of moment was different from that of score, inclusion of both score and moment for LDA provided more diversified and descriptive information.

The rocks of Gusev Crater as viewed by the Mini‐TES instrument

The Miniature Thermal Emission Spectrometer (Mini‐TES) on board the Mars Exploration Rover Spirit is part of a payload designed to investigate whether a lake once existed in Gusev Crater. Mini‐TES has observed hundreds of rocks along the rover's traverse into the Columbia Hills, yielding information on their distribution, bulk mineralogy, and the potential role of water at the site. Although dust in various forms produces contributions to the spectra, we have established techniques for dealing with it. All of the rocks encountered on the plains traverse from the lander to the base of the Columbia Hills share common spectral features consistent with an olivine‐rich basaltic rock known as Adirondack Class. Beginning at the base of the West Spur of the Columbia Hills and across its length, the rocks are spectrally distinct from the plains but can be grouped into a common type called Clovis Class. These rocks, some of which appear as in‐place outcrop, are dominated by a component whose spectral character is consistent with unaltered basaltic glass despite evidence from other rover instruments for significant alteration. The northwest flank of Husband Hill is covered in float rocks known as Wishstone Class with spectral features that can be attributed uniquely to plagioclase feldspar, a phase that represents more than half of the bulk mineralogy. Rare exceptions are three classes of basaltic “exotics” found scattered across Husband Hill that may represent impact ejecta and/or float derived from local intrusions within the hills. The rare outcrops observed on Husband Hill display distinctive spectral characteristics. The outcrop called Peace shows a feature attributable to molecular bound water, and the outcrop that hosts the rock called Watchtower displays a dominant basaltic glass component. Despite evidence from the rover's payload for significant alteration of some of the rocks, no unambiguous detection of crystalline phyllosilicates or other secondary silicates has been observed by Mini‐TES. The mineralogical results supplied by Mini‐TES provide no clear evidence that a lake once existed in Gusev Crater.

Study of Spectral Character of Alkali Metals Using Microwave Plasma Torch Simultaneous Spectrometer

A microwave plasma torch (MPT) simultaneous spectrometer was used to study the spectral character and the matrix effect on alkali metal ions in solution. The main parameters were optimized. The microwave forward power was 100 W. The argon flow rate that was used to sustain the Ar-MPT included the flow rate of carrier gas and the flow rate of support gas, which were 0.8 and 1.0 L/min, respectively. The HC1 concentration in the solution was 0.02 mol/L. The observation height was 9.0 mm. The detection limits of Li, Na, K, Rb, and Cs were 0.0003, 0.0004, 0.009, 0.07 and 2.4 mg/L, respectively, and the results obtained by the Ar-MPT were compared with those obtained by argon inductively coupled plasma(Ar-ICP) and argon microwave induced plasma(Ar-MIP). The interference effects of several matrix elements were also studied.

Optimum segmentation of simple objects in high-resolution remote sensing imagery in coastal areas

The optimum segmentation of ground objects in a landscape is essential for interpretation of high-resolution remotely sensed imagery and detection of objects; and it is also a technical foundation to efficiently use spatial information in remote sensing imagery. Landscapes are complex system composed of a large number of heterogeneous components. There are many explicit homogeneous image objects that have similar spectral character and yet differ from surrounding objects in high-resolution remote sensing imagery. Thereby, a new concept of Distinctive Feature of fractal is put forward and used in deriving Distinctive Feature curve of fractal evolution in multiscale segmentation. Through distinguishing the extremum condition of Distinctive Feature curve and the inclusion relationship of fractals in multiscale representation the Scalar Order is built. This can help to determinate the optimum scale in image segmentation for simple-objects, and the potential meaningful image-object fitting the intrinsic scale of the dominant landscape object can be obtained. Based on the application in high-resolution remote sensing imagery in coastal areas, a satisfactory result was acquired.

Global-scale surface spectral variations on Titan seen from Cassini/VIMS

We present global-scale maps of Titan from the Visual and Infrared Mapping Spectrometer (VIMS) instrument on Cassini. We map at 64 near-infrared wavelengths simultaneously, covering the atmospheric windows at 0.94, 1.08, 1.28, 1.6, 2.0, 2.8, and 5 μm with a typical resolution of 50 km/pixel or a typical total integration time of 1 s. Our maps have five to ten times the resolution of ground-based maps, better spectral resolution across most windows, coverage in multiple atmospheric windows, and represent the first spatially resolved maps of Titan at 5 μm. The VIMS maps provide context and surface spectral information in support of other Cassini instruments. We note a strong latitudinal dependence in the spectral character of Titan's surface, and partition the surface into 9 spectral units that we describe in terms of spectral and spatial characteristics.

Femtosecond Time- and Wavelength-Resolved Fluorescence and Absorption Spectroscopic Study of the Excited States of Adenosine and an Adenine Oligomer

By employing broadband femtosecond Kerr-gated time-resolved fluorescence (KTRF) and transient absorption (TA) techniques, we report the first (to our knowledge) femtosecond combined time- and wavelength-resolved study on an ultraviolet-excited nucleoside and a single-stranded oligonucleotide (namely adenosine (Ado) and single-stranded adenine oligomer (dA)(20)) in aqueous solution. With the advantages of the ultrafast time resolution, the broad spectral and temporal probe window, and a high sensitivity, our KTRF and TA results enable the real time monitoring and spectral characterization of the excited-state relaxation processes of the Ado nucleoside and (dA)(20) oligonucleotide investigated. The temporal evolution of the 267 nm excited Ado KTRF spectra indicates there are two emitting components with lifetimes of approximately 0.13 ps and approximately 0.45 ps associated with the L(a) and L(b) pipi* excited states, respectively. These Ado results reveal no obvious evidence for the involvement of the npi* state along the irradiative internal conversion pathway. A distinct mechanism involving only the two pipi* states has been proposed for the ultrafast Ado deactivation dynamics in aqueous solution. The time dependence of the 267 nm excited (dA)(20) KTRF and TA spectra reveals temporal evolution from an ultrafast "A-like" state (with a approximately 0.39 ps decay time) to a relatively long-lived E(1) "excimer" (approximately 4.3 ps decay time) and an E(2) "excimer-like" (approximately 182 ps decay time) state. The "A-like" state has a spectral character closely resembling the excited state of Ado. Comparison of the spectral evolution between the results for Ado and (dA)(20) provides unequivocal evidence for the local excitation character of the initially photoexcited (dA)(20). The rapid transformation of the locally excited (dA)(20) component into the delocalized E(1) "excimer" state which then further evolves into the E(2) "excimer-like" state indicates that base stacking has a high ability to modify the excited-state deactivation pathway. This modification appears to occur by suppressing the internal conversion pathway of an individually excited base component where the stacking interaction mediates efficient interbase energy transfer and promotes formation of the collective excited states. This feature of the local excitation that is subsequently followed by rapid energy delocalization into nearby bases may occur in many base multimer systems. Our results provide an important new contribution to better understanding DNA photophysics.

Spectral analysis of 10-m resolution temperature profiles from balloon soundings over Beijing

Abstract. Vertical temperature profiles with a height resolution of 10 m have been measured in the troposphere and lower stratosphere during March and April 2003 over the Beijing Meteorological Observatory. This resolution allows us to study temperature spectra up to higher wave numbers than many published papers. Our purposes in this study are to examine the spectral character of normalized temperature fluctuations in the 2.90–8.01 km (troposphere) and 14.65–19.76 km (lower stratosphere) altitude ranges and to compare them with model spectra. Vertical wave number spectra of six temperature profiles are presented. Results indicate that mean spectral slopes are about −1.9 in the troposphere and −2.2 in the lower stratosphere, which is believed to be the shallowest slopes ever measured by balloon-borne radiosonde soundings. Mean spectral amplitudes at m=1/(100 m) are about 17 times larger in the troposphere and 4 times larger in the lower stratosphere than the predicted saturated spectral amplitudes. These results show that the observed temperature spectra do not obey current gravity wave saturation models, the "universal" atmospheric spectrum model, or the wind-shifting model, in both slope and amplitude.

Retrieval of atmospheric horizontal visibility by statistical regression from NOAA/AVHRR satellite data

Based on the atmospheric horizontal visibility data from forty-seven observational stations along the eastern coast of China near the Taiwan Strait and simultaneous NOAA/AVHRR multichannel satellite data during January 2001 to December 2002, the spectral characters associated with visibility were investigated. Successful retrieval of visibility from multichannel NOAA/AVHRR data was performed using the principal component regression (PCR) method. A sample of retrieved visibility distribution was discussed with a sea fog process. The correlation coefficient between the observed and retrieved visibility was about 0.82, which is far higher than the 99.9% confidence level by statistical test. The rate of successful retrieval is 94.98% of the 458 cases during 2001–2002. The error distribution showed that high visibilities were usually under-estimated and low visibilities were over-estimated and the relative error between the observed and retrieved visibilities was about 21.4%.

The multiscale spectral and spatial character of photoresponse in CdZnTe crystals

Experiments give evidence of the spectral and spatial instabilities of the photoresponse in CdZnTe crystals, which are caused by the transformation of fields created by ensembles of structural defects of various types and scales. Wavelet analysis of the photocurrent as a function of the light wavelength (I = f(λ)) and the spatial coordinate (I = f(x)) reveal a correlation between the spectral instability and the spatial arrangement of crystal regions where this instability arises.

Emission spectral characteristics of Cu, Ag, Zn, and Cd neutral atoms in a glow discharge

Detailed spectra highlighting the neutral atom emission characteristics (i.e. I lines) for Cu, Zn, Ag and Cd in a glow discharge device are presented in this study. A particular focus is the presentation of spectra that document the many high excitation energy neutral atom lines that are observed in these spectra. For Cu, several spectral lines originating from levels close to the ionization potential of copper are observed including lines from the so-called autoionizing levels which are actually just above the ionization potential for copper. Generally similar results are seen for Ag, Zn and Cd, including the observation of many high excitation energy neutral atom lines of Zn originating from the upper levels on the triplet side of the energy level diagram. The spectral data point to ion–electron recombination processes followed by stepwise de-excitation and radiative decay as a key mechanism in setting the spectral character of neutral atom emission in a glow discharge device. Unambiguous identification of spectral lines for specific transitions was facilitated by the acquisition of all spectral data utilizing a UV–visible Fourier transform spectrometer. This spectrometer provided complete and continuous coverage of the spectral region from 200 to 650 nm and allowed spectral lines to be identified with an accuracy of 1–2 pm.

Analysis of a spectrally unique deposit in the dissected Noachian terrain of Mars

We have analyzed a spectrally anomalous dark intracrater deposit and an adjacent lighter‐toned fan‐shaped deposit in the dissected Noachian terrain of Mars using a combination of high spatial and spectral resolution remote sensing data sets. The spatial proximity of these two deposits and their dust‐free spectral character make these prime targets for (1) determining whether the dark‐toned deposit is derived from the fan‐shaped deposit and (2) constraining the nature and mineralogy of the fan‐shaped deposit. Stereo observations and derived digital elevation models of the of the fan‐shaped deposit show a set of three flows lobes. Calculations of the yield strength, based on morphometry of the lobes, indicate yield strengths consistent with those of other volcanic flows on Mars, although an aqueous origin cannot be discounted. The dark deposit consists of a mantle that forms dunes at its thickest portions and extends as a thinner veneer. We find no obvious morphologic association between the dark deposit and adjacent fan. Multispectral imaging from the THEMIS VIS and IR instruments show that the two deposits have different spectral characteristics, probably caused by differences in their mineralogy rather than their physical properties. Finally, modeling of MGS/TES spectra of the combined deposits indicates a feldspar‐rich composition that is possibly complemented by smaller quantities of alteration products such as carbonates, and possibly sulfates and clays. These results indicate that (1) there is no association between these deposits and (2) the combined deposits have a primarily igneous mineralogy, although some aqueous alteration may have occurred.

Movement of the Magnetic Structure in the Plasma Sheet Observed by Cluster II

AbstractUsing the data of the FGM instrument onboard of Cluster II, we can calculate the velocity of the magnetic structure. Data observed by Cluster II in the plasma sheet were analyzed during the storm (1 and 2 August, 2002) and the geomagnetism quiet (6 and 7 August, 2002) in GSM (Geocentric Solar Magnetospheric System) coordinates. After analyzing the statistical characteristics and the spectral character of the velocity, we conclude the followings: (1) The variation of the velocity is an irregular oscillation. (2) The width of the distribution of Vz is nearly equal to that of Vy and they are both bigger than that of Vx. This may be caused by the windsock mechanism. (3) On the dawn side of the plasma sheet, the average of Vx and Vz are nearly equal to 0, but the average of Vy is in the order of –10km/s. It may be caused by the compressed Pc5 wave which moves in the plasma sheet. (4) All the spectra of Vx, Vy, Vz have apices between 0.033 min−1 and 0.035 min−1.

SwiftObservations of the X‐Ray–Bright GRB 050315

This paper discusses Swift observations of the gamma-ray burst GRB 050315 (z=1.949) from 80 s to 10 days after the onset of the burst. The X-ray light curve displayed a steep early decay (t^-5) for ~200 s and several breaks. However, both the prompt hard X-ray/gamma-ray emission (observed by the BAT) and the first ~ 300 s of X-ray emission (observed by the XRT) can be explained by exponential decays, with similar decay constants. Extrapolating the BAT light curve into the XRT band suggests the rapidly decaying, early X-ray emission was simply a continuation of the fading prompt emission; this strong similarity between the prompt gamma-ray and early X-ray emission may be related to the simple temporal and spectral character of this X-ray rich GRB. The prompt (BAT) spectrum was a steep down to 15 keV, and appeared to continue through the XRT bandpass, implying a low peak energy, inconsistent with the Amati relation. Following the initial steep decline the X-ray afterglow did not fade for ~1.2*10^4 s, after which time it decayed with a temporal index of alpha ~ 0.7, followed by a second break at ~2.5*10^5 s to a slope of alpha ~ 2. The apparent `plateau' in the X-ray light curve, after the early rapid decay, makes this one of the most extreme examples of the steep-flat-steep X-ray light curves revealed by Swift. If the second afterglow break is identified with a jet break then the jet opening angle was theta_0 ~ 5 deg, and implying E_gamma > 10^50 erg.

Photoluminescence of acupoint “Waiqiu” in human superficial fascia

The spectral characters of an acupuncture point named “Waiqiu” in superficial fascia tissue have been studied by photoluminescence (PL) spectroscopy under the excitation of 457.9 nm. The PL around “Waiqiu” acupuncture point consists of two sub-bands resulting from the flavin adenine dinucleotide (FAD) and phospholipids, and the porphyrins (including purine, isoxanthopterin and tryptophan), respectively. More emission due to FAD and phospholipids is found inside the acupuncture effect area of “Waiqiu” than its marginal or outside acupuncture regions. The ratio of emission intensity of FAD and phospholipids to one of porphyrins gradually decreases along the direction away from the center of the acupuncture point. It implies that the component proportion changes between FAD, phospholipids and porphyrins around the “Waiqiu” acupuncture point. We suggest that there might be a certain relationship between redox function of FAD and “Waiqiu” acupuncture effect.

A Unified Near‐Infrared Spectral Classification Scheme for T Dwarfs

A revised near infrared classification scheme for T dwarfs is presented, based on and superseding prior schemes developed by Burgasser et al. and Geballe et al., and defined following the precepts of the MK Process. Drawing from two large spectroscopic libraries of T dwarfs identified largely in the Sloan Digital Sky Survey and the Two Micron All Sky Survey, nine primary spectral standards and five alternate standards spanning spectral types T0 to T8 are identified that match criteria of spectral character, brightness, absence of a resolved companion and accessibility from both northern and southern hemispheres. The classification of T dwarfs is formally made by the direct comparison of near infrared spectral data of equivalent resolution to the spectra of these standards. Alternately, we have redefined five key spectral indices measuring the strengths of the major H$_2$O and CH$_4$ bands in the 1-2.5 micron region that may be used as a proxy to direct spectral comparison. Two methods of determining T spectral type using these indices are outlined and yield equivalent results. These classifications are also equivalent to those from prior schemes, implying that no revision of existing spectral type trends is required. The one-dimensional scheme presented here provides a first step toward the observational characterization of the lowest luminosity brown dwarfs currently known. Future extensions to incorporate spectral variations arising from differences in photospheric dust content, gravity and metallicity are briefly discussed. A compendium of all currently known T dwarfs with updated classifications is presented.

Single attosecond pulse generation by nonlinear Thomson scattering in a tightly focused intense laser beam

The relativistic nonlinear Thomson scattering of a tightly focused intense laser pulse by an electron is investigated, and the temporal and spectral characters of the radiation are discussed. In a tightly focused laser pulse with an intensity of approximately 1020W∕cm2 and a pulse duration of 20fs, the electron is scattered away from the focus quickly by the ponderomotive force and therefore the radiation emitted at the focus is much higher than that at other regions. As a result, a single ultrashort pulse of 3.8 as is generated and its corresponding spectrum is broadened to 200 orders of the frequency of the driving laser. With increasing the laser intensity, the signal-to-noise of the radiated pulse increases, and the pulse duration decreases. Moreover, the phase behavior of the spectral components and the dependence of the radiated power on the laser intensity are discussed.

Mechanisms of core‐mantle angular momentum exchange and the observed spectral properties of torsional oscillations

Torsional oscillations of the fluid core produce decadal variations in the Earth's magnetic field and in the length of day. The magnetic field variations can be used to infer the fluid velocity of the oscillations. An additional constraint is imposed by the length‐of‐day variations because coupling mechanisms are required to transfer angular momentum between the core and mantle. Proposed mechanisms included electromagnetic, topographic, and gravitational couplings. We make use of a finite volume model of the core‐mantle system to evaluate each of these mechanisms with respect to observed spectral properties of torsional oscillations. We find that the different coupling mechanisms have different spectral characters which may be useful in distinguishing their importance within the Earth's core‐mantle system. For reasonable values of core and mantle properties, gravitational coupling between the mantle and inner core is the candidate mechanism most likely to be able to reproduce all spectral features of the observed transfer of angular momentum between the core and mantle. Possible spatial distributions of the torsional oscillation excitation source are also investigated.

WAVELET TRANSFORMATION METHOD OF REMOTE SENSING IMAGES FUSION BASED ON EDGE FEATURES

How to fuse all kinds of images with various spatial resolution, to retain its spectral character, and to improve classification accuracy and spatial resolution is a hotspot in data fusion on remote sensing images. Based on wavelet transformation, the paper has extracted edge information of high spatial resolution image, and fused it with multi-spectral images. We chose IRS, SPOT and ETM images to do this experiment. The experimental results showed that it could improve spatial resolution of the multi-spectral images, while at the same time it also could retain spectral character very well with the method. Furthermore it is superior to other methods based on wavelet transformation in data fusion on remote sensing images with high spatial resolution difference.