Presence Of Broad Band Research Articles

Standard models of spatial vision mispredict edge sensitivity at low spatial frequencies

One well-established characteristic of early visual processing is the contrast sensitivity function (CSF) which describes how sensitivity varies with the spatial frequency (SF) content of the visual input. The CSF prompted the development of a now standard model of spatial vision. It represents the visual input by activity in orientation- and SF selective channels which are nonlinearly recombined to predict a perceptual decision. The standard spatial vision model has been extensively tested with sinusoidal gratings at low contrast because their narrow SF spectra isolate the underlying SF selective mechanisms. It is less studied how well these mechanisms account for sensitivity to more behaviourally relevant stimuli such as sharp edges at high contrast (i.e. object boundaries) which abound in the natural environment and have broader SF spectra. Here, we probe sensitivity to edges (2-AFC, edge localization) in the presence of broadband and narrowband noises. We use Cornsweet luminance profiles with peak frequencies at 0.5, 3 and 9 cpd as edge stimuli. To test how well mechanisms underlying sinusoidal contrast sensitivity can account for edge sensitivity, we implement a single- and a multi-scale model building upon standard spatial vision model components. Both models account for most of the data but also systematically deviate in their predictions, particularly in the presence of pink noise and for the lowest SF edge. These deviations might indicate a transition from contrast- to luminance-based detection at low SFs. Alternatively, they might point to a missing component in current spatial vision models.

On the flotation activity of reagents with a nitrile group in the flotation of copper-nickel ores

This paper considers the use of compounds having a nitrile group, such as Tecflote S10, S11, S12, and S13, as potential collectors in the flotation of sulfide copper-nickel ore. Tecflote S12, S10, and S13 reagents are substituted aminonitriles with one or two nitrile groups, differing by the hydrocarbon radical R, with its length in the range of C10–18. Tecflote S11 is a dimer with only two nitrile groups. Respective copper- and nickel-containing minerals were subjected to test hydrophobization when exposed to these reagents in frothless flotation using two ore samples characterized by higher chalcopyrite/pentlandite and nickel-bearing pyrotine grades. This paper shows the distribution of copper and nickel in the resulting frothless flotation products. A comparison of the results obtained when using aqueous and hexane solutions of the collector has demonstrated that Tecflote S12 is more efficient for nickel-containing minerals due to the possibility of direct interaction of the mineral particle with the collector in the volume of the solution. The formation of a Tecflote S12 complex with non-ferrous metal atoms is evidenced by the presence of broad bands corresponding to copper and nickel ions in the region of 290–360 cm–1 Raman spectrum in the compounds obtained by extraction from the aqueous solutions of copper and nickel chlorides. The flotation tests carried out using a sample of finely disseminated refractory copper-nickel ore from the Pechenga ore field have showed that feeding Tecflote S12 into the main flotation cycle, combined with xanthate and aeroflot, allows improving the yield of the finished concentrate and ensures lower nickel losses with tailings.

Spectroscopic and luminescent properties of Ce3+ -doped TeO2-WO3-GeO2 glasses

Different concentrations of Ce3+-doped TeO2-WO3-GeO2-Ce2O3 (TWGCe) glasses were prepared by melt-quenching method and characterized. Different spectroscopic and luminescence properties were evaluated using room temperature absorption and emission spectra. The absence of sharp X-ray diffraction peaks and the presence of broad band from 18° to 35° shows the amorphous phase of studied glasses. The Fourier transform infrared absorption spectra show the presence of various vibrational bonds. The optical properties of TWGCe glasses were studied by exciting the glass samples at 323 nm ultraviolet wavelength. The quenching in luminescence is noticed at × = 0.5 mol% along with a red-shift at higher Ce3+ concentrations. The decay time was found decrease with increase of concentration of Ce3+ ions. These glasses emit intense blue luminescence with CIE coordinates (0.161, 0.018) when excited at 323 nm radiation. These glasses are favourable as blue light sources in the design of phosphor-based white LEDs.

Active vibration control for the time-varying systems with a new adaptive algorithm

This paper proposes a new adaptive algorithm for the active vibration control of time-varying systems in the presence of broadband or narrowband disturbances. The new algorithm combines the conventional filtered-x least mean square algorithm with the recursive prediction error (RPE) algorithm after the gradient modification of the RPE algorithm. The modified RPE algorithm is used to estimate the model of the control path online. The well-known filtered-x least mean square (FxLMS) algorithm is effective for the uncertain or time-varying systems, and adopts an auxiliary white noise approach to estimate the model of the control path online. However, the auxiliary excitation will degrade the control performance to some extent. In the new algorithm, the auxiliary excitation is eliminated at the expense of a larger computational burden. The influence of the estimated finite impulse response series on the convergence is also discussed. A propulsion shafting model with the time-varying dynamics is established by frequency response function synthesis. Numerical simulation for the established model is presented to demonstrate the superior performance of the proposed algorithm as compared with the FxLMS algorithm.

Optical and crystal-chemical changes in aquamarines and yellow beryls from Thanh Hoa province, Vietnam induced by heat treatment

Optical and crystal-chemical changes in two beryl varieties after the heat treatment were determined using a wide spectrum of analytical methods. Studied aquamarines are generally more enriched in Fe (up to 0.25 apfu) and alkali (up to 0.08 apfu) than yellow beryls (up to 0.07 apfu Fe, up to 0.04 apfu alkali). The determined c/a ratio of 0.997–0.998 classified all our studied beryls as “normal” beryls. While no crystal structure changes were observed in samples heated to 700 °C, those heated to 900 and 1,100 °C exhibited cracks and fissures. Reduced Fe occurred in samples heated between 300 and 700 °C, and subsequent oxidation from 900 to 1,100 °C induced changes in their colour and clarity. The Fe-bearing beryl colour is controlled by the position of the absorption edge and the presence of a broad band attributed to Fe2+ in the NIR region. Blue colour results from the absorption edge located deeper in the UV region and the presence of broad band in the NIR region. Shift of absorption edge to the visible region at the presence of the broad band gives a yellow colour. Although our studied beryls are enriched in H2O I molecule due to their low alkali content, the H2O II molecule is also present. The following two dehydration processes were observed: (1) release of one double-coordinating H2O II molecule at 300–500 °C and (2) total dehydration at 900–1,100 °C. The observed cracks and fissures likely resulted from channel water release in large beryl crystals.

Characteristics of flux-time profiles, temporal evolution, and spatial distribution of radiation-belt electron precipitation bursts in the upper ionosphere before great and giant earthquakes

The analysis of energetic electron observations made by the DEMETER satellite reveals that radiation belt electron precipitation (RBEP) bursts are observed in general several (~1-6 days) before a large (M > 6.5) earthquake (EQ) in the presence of broad band (~1-20 kHz) VLF waves. The EBs show in general a relative peak-to-background flux increase usually < 100, they have a time duration of ~0.5 – 3 min, and their energy spectrum reach up to energies <~500 keV. The RBEP activity is observed as one, two or three EBs throughout a semi-orbit, depended on the magnetic field structure above the EQ epicenter. A statistical analysis has been made for earthquakes in Japan, which reveals a standard temporal variation of the number of EBs, which begins with an incremental rate several days before major earthquakes, and after a maximum, decreases so that the electron precipitation ceases above the epicenter. Some earthquake induced EBs were observed not only in the nightside ionosphere, but also in the dayside ionosphere.

Broadband vibration-based energy harvesting improvement through frequencyup-conversion by magnetic excitation

Traditional vibration-based energy harvesters are designed for a specific base excitationfrequency by matching its fundamental natural frequency. This work presentsthe modeling and analysis of a nonlinear, magnetically excited energy harvesterthat exhibits efficient broadband, frequency-independent performance utilizing apassive auxiliary structure that remains stationary relative to the base motion.This system is especially effective in the regime of driving frequencies well belowits fundamental frequency, thus enabling a more compact design solution overtraditional topologies. A model based on Euler–Bernoulli beam theory is coupled to alinear circuit and a model of the nonlinear, magnetic interaction to produce adistributed parameter magneto-electromechanical system. This model is used in bothharmonic and stochastic base excitation case studies. The results of these simulationsdemonstrate multiple-order-of-magnitude power harvesting performance improvementat low driving frequencies and an insensitivity to time-varying base excitation.Furthermore, the proposed system is shown to outperform an optimally designed,standard energy harvester in the presence of broadband, random base excitation.

Symbol error rate of the dm-mpsk under the influence of jamming signals

Focusing on the performance of the chirp spread spectrum (CSS) communication system under the influence of jamming, we analytically derive the symbol error rate (SER) for the direct modulation CSS system with M-ary phase shift keying in the presence of broadband and tone jamming signals. From numerical results, it is confirmed that the analytic result agrees closely with the empirical SER.

Leakage current, ferroelectric and structural properties in Pb 1−xBa xTiO 3 thin films prepared by chemical route

Single-phase perovskite structure Pb 1− x Ba x TiO 3 thin films ( x=0.30, 0.50 and 0.70) were deposited on Pt/Ti/SiO 2/Si substrates by the spin-coating technique. The dielectric study reveals that the thin films undergo a diffuse type ferroelectric phase transition, which shows a broad peak. An increase of the diffusivity degree with the increasing Barium contents was observed, and it was associated to a grain decrease in the studied composition range. The temperature dependence of the phonon frequencies was used to characterize the phase transition temperatures. Raman modes persist above tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of breakdown of the local cubic symmetry by chemical disorder. The absence of a well-defined transition temperature and the presence of broad bands in some interval temperature above FE–PE phase transition temperature suggested a diffuse type phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in these thin films. The leakage current density of the PBT thin films was studied at different temperatures and the data follow the Schottky emission model. Through this analysis the Schottky barrier height values 0.75, 0.53 and 0.34 eV were obtained to the PBT70, PBT50 and PBT30 thin films, respectively.

Study of phase transition in (Pb,Ba)TiO3 thin films

Dielectric and Raman scattering experiments were performed on polycrystalline Pb1−xBaxTiO3 thin films (x=0.40 and 0.60) as a function of temperature. The dielectric study on single phase compositions revealed that a diffuse-type phase transition occurred upon transformation of the cubic paraelectric to the tetragonal ferroelectric phase in all thin films, which showed a broadening of the dielectric peak. Diffusivity was found to increase with increasing barium contents in the composition range under study. In addition, the temperature dependence of Raman scattering spectra was investigated through the ferroelectric phase transition. The temperature dependence of the phonon frequencies was used to characterize the phase transitions. Raman modes persisted above the tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted as a breakdown of the local cubic symmetry by chemical disorder. The lack of a well-defined transition temperature and the presence of broadbands in some temperature intervals above the paraferroelectric phase transition temperature suggest a diffuse-type phase transition.

Raman and infrared studies ofLa1−ySryMn1−xMxO3(M=Cr, Co, Cu, Zn, Sc or Ga): Oxygen disorder and local vibrational modes

We present results of our study of polarized Raman scattering and infrared reflectivity of rhombohedral ceramic ${\mathrm{La}}_{1\ensuremath{-}y}{\mathrm{Sr}}_{y}{\mathrm{Mn}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{O}}_{3}$ manganites in the temperature range between 77 and $320\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In our samples, a part of the Mn atoms is substituted by $M=\mathrm{Cr}$, Co, Cu, Zn, Sc, or Ga with $x$ in the range 0--0.1. The hole concentration was kept at the optimal value of about 32% by tuning the Sr content $y$. We have monitored distortions of the oxygen sublattice by the presence of broad bands in the Raman spectra, the increase of dc resistivity extracted from the infrared reflectivity, and the change of the critical temperature of the ferromagnetic transition. Our results support the idea that these properties are mainly determined by the radius of the substituent ion, its electronic and magnetic structure playing only a minor role. Furthermore, the Raman spectra exhibit an additional ${A}_{g}$-like high frequency mode attributed to the local breathing vibration of oxygens surrounding the substituent ion. Its frequency and intensity strongly depend on the type of the substituent. In the Co-substituted sample, the mode anomalously softens when going from $300\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}77\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The frequency of the bulk ${A}_{1g}$ mode depends linearly on the angle of the rhombohedral distortion.

Investigation of phase transition in ferroelectric Pb0.70Sr0.30TiO3 thin films

We have carried out dielectric and Raman spectroscopy studies at the 298–623 K temperature range in polycrystalline Pb0.70Sr0.30TiO3 thin films grown by a soft chemical method. The diffuse phase-transition behavior of the thin films was observed by means of the dielectric constant versus temperature curves, which show a broad peak. Such behavior was confirmed later by Raman spectroscopy measurements up to 823 K, indicating that a diffuselike phase transition takes place at around 548–573 K. The damping factor of the E(1TO) soft mode was calculated using the damped simple harmonic oscillator model. On the other hand, Raman modes persist above the tetragonal to cubic phase transition temperature although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of a breakdown of the microscopic local cubic symmetry by chemical disorder. The lack of a well-defined transition temperature and the presence of broad bands at some temperature interval above the ferroelectric-paraelectric phase-transition temperature suggested a diffuse nature of the phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in this thin film.

A Raman and dielectric study of a diffuse phase transition in (Pb1-xCax)TiO3 thin films

Dielectric and Raman scattering experiments were performed on polycrystalline Pb1-xCaxTiO3 thin films (x=0.10, 0.20, 0.30, and 0.40) as a function of temperature. The results showed no shift in the dielectric constant (K) maxima, a broadening with frequency, and a linear dependence of the transition temperature on increasing Ca2+ content. On the other hand, a diffuse-type phase transition was observed upon transforming from the cubic paraelectric to the tetragonal ferroelectric phase in all thin films. The temperature dependence of Raman scattering spectra was investigated through the ferroelectric phase transition. The temperature dependence of the phonon frequencies was used to characterize the phase transitions. Raman modes persisted above the tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of a breakdown of the local cubic symmetry due to chemical disorder. The lack of a well-defined transition temperature and the presence of broad bands in some temperature interval above the FE–PE phase transition temperature suggested a diffuse-type phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in these thin films.

Electrical Properties of n-GaN/p-SiC and n-AlGaN/p-SiC Heterojunction Diodes

AbstractProperties of n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions prepared by HVPE on 4H SiC substrates were studied by means of C-V, C/G-T, C-f, I-V and DLTS. It is shown, in agrrement with earlier publications, that the GaN/p-SiC HJ is staggered type II with ΔEc=-0.4 eV andΔEv=0.6 eV. Whenchanging GaN for AlGaN with Al mole fraction of x=0.25-0.3 the band alignment becomes normal type I with ΔEc=0.2 eV andΔEv=0.6 eV. I-V characteristics of both heterojunctions bear evidence of strong tunneling via defect states, particularly centers with activation energy of 1.25 eV for GaN/4H SiC HJ. The tunneling was found to be more pronounced in the AlGaN/SiC HJs even though these HJs showed no evidence of formation of dark line defects at the interface, in contrast to GaN/SiC. DLTS measurements on both types of HJs revealed the presence of broad bands whose behavior is indicative of these bands being related to continuous states in the gap, most likely near the nitride/carbide interface.

Electrical Properties of n-GaN/p-SiC and n-AlGaN/p-SiC Heterojunction Diodes

AbstractProperties of n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions prepared by HVPE on 4H SiC substrates were studied by means of C-V, C/G-T, C-f, I-V and DLTS. It is shown, in agreement with earlier publications, that the GaN/p-SiC HJ is staggered type II with ΔEc=-0.4 eV andΔEv=0.6 eV. Whenchanging GaN for AlGaN with Al mole fraction of x=0.25-0.3 the band alignment becomes normal type I with ΔEc=0.2 eV andΔEv=0.6 eV. I-V characteristics of both heterojunctions bear evidence of strong tunneling via defect states, particularly centers with activation energy of 1.25 eV for GaN/4H SiC HJ. The tunneling was found to be more pronounced in the AlGaN/SiC HJs even though these HJs showed no evidence of formation of dark line defects at the interface, in contrast to GaN/SiC. DLTS measurements on both types of HJs revealed the presence of broad bands whose behavior is indicative of these bands being related to continuous states in the gap, most likely near the nitride/carbide interface.

Ethene/propene copolymerisations with rac-EBTHIZrR 2/alumoxane: σ-ligands effect

We report here about the role played by the σ-ligands of a metallocene in ethene/propene (E/P) copolymerisations promoted by rac-[ethylenebis(4,5,6,7-tetrahydro-1-indenyl)]zirconium dichloride 1, and its corresponding dimethyl derivative rac-EBTHIZrMe 2 2 and binaphtholate rac-EBTHIZr(BNP) 3 derivative, in the presence of several alumoxanes. Alumoxanes alternative to the traditional polymethylalumoxane (MAO) were synthesised and characterised. They are based on Al(2,4,4-trimethylpentyl) 3 (TIOA) 4 and were prepared by reaction of 4 with water to give either tetraisooctylalumoxane (TIOAO) 5 or polyisooctylalumoxane (TAO) 6 depending on the stoichiometry of the reaction. 1H NMR spectra of these products are characterised by the presence of broad bands and of resolved multiplets. Their relative amount in the region between 1.9 and 2.5 ppm was identified as the “fingerprint” of the polymerisation activity. A comparison of the results obtained in polymerisation with metallocenes having different σ-ligands allowed us to shed more light on the role played by those species. In conclusion, the nature of the σ-ligands of a metallocene affects its catalytic activity in polymerisation, as a function of the alumoxane employed and of the relative ratio with the metallocene, and this effect is enhanced in “critical conditions,” i.e. with a weakly activating cocatalyst or at a low Al/Zr ratio.

Perception of speech and non-speech sounds by listeners with real and simulated sensorineural hearing loss

The effects of sensorineural and simulated hearing loss on the perception of speech and non-speech sounds are evaluated and compared. Two simulations of hearing loss are considered: one introduces additive masking noise to elevate the detection thresholds of listeners with normal hearing, the other applies multiband dynamic expansion to attenuate sound components towards these detection thresholds. Measures of speech perception are derived from intelligibility tests for consonant-vowel syllables presented in a background of speech-spectrum noise. The perception of non-speech sounds was evaluated through measurements of the detection of tones in quiet and in the presence of broadband and narrowband masking noise, psychoacoustic tuning curves measured under forward masking conditions, and intensity discrimination for tone pulses. For mild and moderate hearing losses, both types of simulation alter the perception of speech in noise in a manner similar to sensorineural impairment. These simulations also produce effects similar to sensorineural impairment on the detection of tones in quiet and on simultaneous and forward masking. The expansion simulation tends to improve the ability to discriminate tone intensities, an effect generally not seen in listeners with sensorineural impairments.

Squeezed-radiation-enhanced four-wave mixing in intense pumps.

The nature of the nonlinear response of a quantum system in the presence of broadband squeezed radiation is examined. The relaxation of the system in the presence of squeezed radiation leads to enhancement of the four-wave-mixing signal.

Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). II: Effects of broadband noise level and high-pass masker cutoff frequency across click polarity.

Two experiments concerning the effects of masking noise on the gerbil brain-stem auditory-evoked response (BAER) are reported. Experiment 1 evaluated the effects of broadband masking noise on the BAER obtained to condensation and rarefaction clicks. With increasing noise level, there was an increase in BAER peak latencies, an increase in the i-v interval, and a decrease in peak amplitudes. Experiment 2 evaluated the effects of high-pass masking noise on the BAER obtained to condensation and rarefaction clicks. Both high-pass responses and derived-band responses were evaluated. For high-pass responses, with decreasing masker cutoff frequency, there was an increase in BAER peak latencies, a decrease in the i-v interval, and a decrease in peak amplitudes. For derived-band responses, with decreasing derived-band frequency, there was an increase in peak latencies and a decrease in the i-v interval. A comparison of wave i and wave v amplitudes across derived-band frequency demonstrates a greater contribution of high-frequency cochlear regions to wave i than wave v. Small, insignificant, effects of click polarity on BAER peak amplitudes were observed. These trends were in the direction seen in a companion paper [R. Burkard and H. F. Voigt, J. Acoust. Soc. Am. 85, 2514-2525 (1989)] and were, in general, reduced by the presence of broadband or high-pass maskers.

Infrared and Raman studies of amorphous MoS 3 and poorly crystalline MoS 2

Amorphous MoS 3 and poorly crystalline MoS 2 have been studied using infrared and Raman spectroscopies. While poorly crystalline MoS 2 exhibits sharp infrared bands at 385 and 470 cm −1, broad bands at 287, 335, 373, and 522 cm −1 were observed for the amorphous MoS 3. In contrast to poorly crystalline MoS 2 where sharp Raman peaks were measured at 384 and 408 cm −1, the Raman spectrum of amorphous MoS 3 showed broad peaks at 215, 317, 431, and 528 cm −1. The band profiles of both the ir and Raman spectra of the MoS 3 sample indicate the amorphous nature of the material. This is consistent with results obtained by other techniques. The comparison of the Raman spectrum of MoS 3 and that of amorphous MoS 2 reported in the literature indicates that local bondings in these materials are dissimilar. The presence of broad bands at 522 cm −1 in ir and 528 cm −1 in Raman spectra of MoS 3 is evidence for polysulfide bonds indicated by the XPS spectrum of the material. These results support a chain-like structural model for amorphous MoS 3 similar to that for crystalline MS 3 (M = Ti, Zr, Hf, Nb, Ta, and U). The thermal stability of MoS 3 and the effect of laser power on the Raman spectrum of MoS 3 were also studied.