1st Harmonics Research Articles

Plasma condensation in coronal loops

Aims. Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we seek to investigate plasma condensation through the use of spectroscopic analysis. Methods. Using a space-time (X-T) type plot we show, for a number of transition region (TR) and coronal lines, the variation of intensity (radiant flux) with time in an o -limb loop system. Noting a number of pixels where the intensity shows a sharp jump in value for the TR lines and a corresponding sharp decrease for the coronal lines, we investigate further and plot the intensity and velocity for these pixels as a function of time. Using standard Fourier techniques, together with a pre-whitening method, we measure all statistically significant frequencies present in the time series so created. Results. We find that, for the cooler lines of Hei 584 A and Ov 629 A, there are sharp increases in intensity, accompanied by large blueshifted velocities. In the case of Ov there is a substantial rebound to redshifted velocities when the strong brightening fades. The sharp increase in intensity and blueshifted velocity in the cooler lines is accompanied by a corresponding decrease in the intensity of the coronal lines (Mgx 624 A, Fexvi 360 A, Sixii 520 A), but with no corresponding change in their velocity values implying an evacuation of plasma. From the Fourier analysis, evidence is found for possible 1st and 2nd harmonics in the Hei and Ov lines, indicative of standing waves in loops. Conclusions. We conclude that what we are seeing is the first spectroscopic evidence of plasma condensation taking place in coronal loops.

Influence of Grain Boundaries and Sn Distribution on the H-T Phase Diagram of ${\rm Nb}_{3}{\rm Sn}$

We measured the 1st and 3rd harmonics of the AC magnetic susceptibility as a function of the temperature and the DC magnetic field, on several Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn samples (single crystal, polycrystalline samples and multifilamentary wires), with different pinning properties. From these measurements, the Bragg phase, the disordered one and the irreversibility line have been identified in the H-T phase diagram of analysed samples. We observed that the presence of the pinning due to grain boundaries increases the region of the disordered phase in respect to the pinning due to point defects, and gives the possibility to detect an irreversibility line. Nevertheless it is possible to observe a phase transition between the Bragg and the disordered phase if the sample has an almost spatially uniform tin content. On the contrary, in a sample characterized by similar grain boundaries properties but where a tin gradient is present, the Bragg glass phase tends to disappear.

Optical spectroscopy of the radio pulsar PSR B0656+14

We have obtained the spectrum of a middle-aged PSR B0656+14 in the 4300–9000 A range with the ESO/VLT/FORS2. Preliminary results show that at 4600–7000 A the spectrum is almost featureless and flat with a spectral index αν≃−0.2 that undergoes a change to a positive value at longer wavelengths. Combining with available multiwavelength data suggests two wide, red and blue, flux depressions whose frequency ratio is about 2 and which could be the 1st and 2nd harmonics of electron/positron cyclotron absorption formed at magnetic fields ∼108 G in upper magnetosphere of the pulsar.

X-Ray and Electrooptical Studies of Liquid Crystal Siloxane with a de Vries SmA* Phase

We present the X-ray diffraction, polarizing optical microscopy and electrooptic response studies of the chiral liquid crystal siloxane DSi3-MR11 [1] with a de Vries-type behavior. In a wide temperature range (Δ T ∼ 50°C) the material shows no layer shrinkage but a weak nearly linear layer spacing variation with temperature. Neither discontinuity nor slope change occurs at the SmA*-SmC* transition. In addition, using the X-ray data, the unusual electrooptic response in both 1st and 2nd harmonics together with known thermal behavior of birefringence, we evidence the cross-over from the classical orthogonal to the de Vries-like SmA* regime in DSi3-MR11 siloxane.

Investigations of Magnetic Behavior in Various&lt;tex&gt;$rm Nb_3rm Sn$&lt;/tex&gt;Multifilamentary Wires by Means of the 1st and 3rd Harmonics of the AC Magnetic Susceptibility

The 1st and 3rd harmonics of the AC magnetic susceptibility were measured as a function of the temperature on Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn multifilamentary wires, produced by different processes: bronze route (home made) and internal tin diffusion (Oxford) These measurements were performed both with and without a DC magnetic field, up to 19T. We observed that the magnetic response of the bronze route wire is mainly characterized by vortex dynamical phenomena, such as flux creep. This is in contrast with the internal tin wire, where the static hysteretic Bean model is sufficient to describe the magnetic behavior. Moreover, by using the 3rd harmonics measurements, it has been possible to get indication about the phase transition in the vortex lattice between the Bragg Glass phase and the disordered phase, which is absent in the bronze route multifilamentary wire. The H-T phase diagram has been obtained for both samples and has been compared with the previously analyzed one for the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn single crystals and polycrystalline samples

Nb3Sn single crystals, polycrystals and multifilamentary wires: common and different features in the magnetic response

The magnetic response of different Nb3Sn samples has been investigated studying the temperature dependence of both the 1st and 3rd harmonics of the AC magnetic susceptibility, in presence of a DC field up to 19 T. In single crystal and in polycrystalline samples, the occurrence of a Peak Effect was observed within DC magnetic fields ranging from 3 T to about 13 T. It corresponds to a transition in the vortex lattice between the Bragg Glass phase and a disordered phase. This transition has been also detected at higher magnetic fields in both the samples, thanks to the 3rd harmonics measurements. In contrast to single crystals and polycrystals, no Peak Effect and no indications about the Bragg/disordered phase transition have been detected in the analysed multifilamentary wires.

Transition between the Bragg glass and the disordered phase inNb3Sndetected by third harmonics of the ac magnetic susceptibility

We report additional experimental evidences about the presence of an universal behavior in the Field-Temperature Phase Diagram of Type II Superconductors. This behavior is characterized by a phase transition in the vortex matter between the disordered and the Bragg Glass phase. The experimental detection of a Peak Effect phenomenon has been proved to be strictly connected to the existence of this phase transition. In this paper, we show the first observation of a Peak Effect in the compound Nb3Sn, by using 1st harmonics of the AC magnetic susceptibility. Peak Effect has been detected at fields between 3T and 13T, whereas it is not observable at higher fields. This seems to be in contrast with the theoretical predictions of such a phase transition at all fields. Nevertheless, by measuring the 3rd harmonics of the AC susceptibility, this phase transition has been detected up to our highest available field (19 T), thus demonstrating the necessity of the higher harmonics analysis in studying these topics and moreover proving the validity of the theoretical predictions.

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables - IV. Observations of frequency doubling and tripling in VW Hyi

We present new observations of the rapid oscillations in the dwarf nova VW Hyi, made late in outburst. These dwarf nova oscillations (DNOs) increase in period until they reach 33 s, when a transition to a strong 1st harmonic and weak fundamental takes place. After further period increase the 2nd harmonic appears; often all three components are present simultaneously. This 1:2:3 frequency suite is similar to what has been seen in some neutron star and black hole X-Ray binaries, but has not previously been seen in a cataclysmic variable. When studied in detail the fundamental and 2nd harmonic vary similarly in phase, but the 1st harmonic behaves independently, though keeping close to twice the frequency of the fundamental. The fundamental period of the DNOs, as directly observed or inferred from the harmonics, increases to ~100 s before the oscillation disappears as the star reaches quiescence. Its maximum period is close to that of the `longer period' DNOs observed in VW Hyi. The quasi-periodic oscillations (QPOs), which have fundamental periods 400 -- 1000 s, behave in the same way, showing 1st and 2nd harmonics at approximately the same times as the DNOs. We explore some possible models. One in which the existence of the 1st harmonic is due to transition from viewing a single accretion region to viewing two regions, and the rate of accretion onto the primary is modulated at the frequency of the 1st harmonic, as in the `beat frequency model', can generate the suite of DNO frequencies observed. But the behaviour of the QPOs is not yet understood.

Measurement of Flexoelectric Coefficients in Nematic Liquid Crystals Using Shallow Grating Devices

A nematic device with a shallow grating and homeotropic anchoring is used to probe the flexoelectric effect. Applying a sinusoidally varying voltage across the cell, the transmittance of the device between crossed polarisers is found to consist of a mixture of 1st and 2nd harmonics, corresponding to the flexoelectric and dielectric responses of the director to the applied electric field. The results are compared with theoretical ones generated using a 1-dimensional approximation to the cell structure, and a value for the sum of the flexoelectric coefficients determined.

Frequency-Based Analysis of Diastolic Function: The Early Rapid Filling Phase Generates Negative Intraventricular Wave Reflections

ACS ∗,† To assess global diastolic function (DF), both invasive and noninvasive methods have been utilized. Except for the end-diastolic pressure–volume relationship, currently all proposed parameters for diastolic function are derived purely from pressure or flow. To characterize the physiology of diastole in the context of atrioventricular pressure gradient generated transmitral flow, and in analogy to frequency-based characterization of ventricular–vascular coupling, we subjected the simultaneously recorded transmitral flow (E-wave) and micromanometric intraventricular pressure (LVP) waveforms to Fourier analysis in 20 subjects. This permitted computation of input impedance, characteristic impedance, the phase angle φ relating pressure to flow, and the complex reflection coefficient R ∗ during the E-wave. We found that the magnitudes of input impedance were 32 ± 12, 13.9 ± 4.4, 37 ± 13, and 53 ± 23 mmHg s/m for DC, 1st, 2nd, and 3rd harmonics, respectively. The characteristic impedance was 30 ± 15 mmHg s/m. The magnitude and phase angle of complex reflection coefficient R ∗ were 0.43 ± 0.11 and 3.58 ± 0.52 rad, respectively. The magnitude of the input impedance carrying most oscillatory power (1st harmonic) is lower than the characteristic impedance, verifying our finding that the real portion of R ∗ was negative. We also found that E waves with prolonged deceleration time (DT > 180 ms—“delayed relaxation” pattern) manifest increased phase differences between pressure and flow, voiding an optimal pressure–flow relationship. These findings elucidate the frequency-based (amplitude/phase) mechanisms

Response of glass and liquid phases in the vortex lattice to an external AC magnetic field at different frequencies

We individuated a method to distinguish a glass phase from a highly viscous liquid phase in a lattice of vortices, established in type-two superconductors. Our analysis is based on the study of the temperature dependence of numerically obtained 1st and 3rd harmonics curves of the AC magnetic susceptibility, by changing the frequency of the applied AC magnetic field. The harmonics are obtained by integrating the non-linear diffusion equation for the magnetic field, with different voltage–current characteristics, corresponding to the two different phases. This method could be applied to the analysis of experimental curves in order to determine if the detected magnetic response of superconducting samples may be interpreted in terms of vortex glass or Kim–Anderson model.

Novel design for small-size coplanar waveguide frequency tripler

This letter presents a novel design for a small-size coplanar waveguide frequency tripler. In this study, a new BPF has been replaced the conventional stub lines in the output termination of the multiplier. Not only enhance the performance of the tripler, but also reduce the whole circuit size. to 2.125/spl times/2.275 cm/sup 2/ in the frequency 0.8/2.4 GHz, The spurious suppressions are 37.48, 33.38, and 32.08 dBc for the 1st, 2nd, and 4th harmonics, respectively. It reveals the best output power of -1.92 dBm for a 0 dBm input signal and maximum conversion gain of -1.92 dB. It is very useful for applications in the wireless communication and radar systems.

Third harmonics of the AC magnetic susceptibility: a method for the study of flux dynamics in high temperature superconductors

The temperature dependence of the 1st and 3rd harmonics ( $\chi^{\prime ,\prime\prime}_{1,3}$ ) of the AC magnetic susceptibility has been measured on melt grown YBCO samples for different frequencies and amplitudes of the AC magnetic field and intensity of a contemporaneously applied DC field. With the help of critical state models and of numerical simulations [22], we have devised a novel method, based on the combined analysis of the 1st and the 3rd harmonics (specifically on the comparison between $\chi"_1$ and $\chi'_3$ ), that allows to distinguish different temperature ranges dominated by the different dissipative magnetic flux regimes. In particular, we identified three principal “zones” in the temperature dependence of the real part of the 3rd harmonic: the “zone 1”, in the temperature range below the peak of the imaginary part of the 1st harmonic, $T_{p}(\chi"_1)$ , and the “zone 2”, characterized by $\chi'_3$ negative values in a temperature region just above $T_{p}(\chi"_1)$ , both dominated by the creep regime; the zone 3, just below T c , in which we revealed the presence of Thermally Assisted Flux Flow (TAFF). By the identification of these “zones”, an estimation of the value of the pinning potential can be obtained.

Development Research of Variable Resonance-Mode Type of Side-Branch Resonators.

The variable resonance-mode type of side-branch resonators which can be adjusted freely at the desired resonance modes (i.e., desired resonance frequencies and mode shapes) with a single closed-end tube configuration, unlike a conventional side branch, are newly developed and their attenuation characteristics are investigated theoretically and experimentally. The mechanism of variable-mode is based on the principle that the resonance mode of fluid wave motion in a side-branch tube can be changed arbitrarily with the adjustment of reflection factors at the choke orifices which are inserted in it. The present variable resonance-mode type of side-branch resonators are devised in order to reduce the several harmonics of the fixed discrete-frequency pressure pulsation such as those generated by a fixed speed hydraulic pump. A successful mathematical means (optimum design method) of sizing the desired lengths and diameters of n number of choke orifices and lengths of divided n+1 number of side-branch tube parts so as to coincide resonance frequencies with the desired one is outlined. It has been confirmed in the bench tests that the proposed side-branch resonators yield the satisfactory insertion loss characteristics so far as they are used in a hydraulic circuit with very short length of outlet pipe in which the influence of standing wave is negligible. Further, the present side-branch designed so as to reduce the 1st and 2nd harmonics of pressure pulsation has proven to be very successful also in application to a real hydraulic excavator for reduction of air-borne noise as well as pressure pulsation of these harmonics.

The extended E-J characteristics of flux diffusion and their role in the self-field AC losses in Ag-sheathed PbBi2223 tapes

The interplay between the flux pinning of the critical state and flux diffusion has an important effect on the hysteresis losses at high frequencies (>200Hz). This interplay between the two mechanisms has been seen in the dB/dt dependence of the magnetization and AC losses in a varying external field. In order to study this effect in the self-field situation we have separated the eddy current losses and hysteresis losses, of an Ag-sheathed PbBi2223 tape, by making measurements of the 1st and 3rd harmonics of the electric field, at various frequencies. These measurements show as expected that the hysteresis loss per cycle decreases for increasing frequency. Our data shows that, for a given frequency and transport current, there exists an equivalent critical current, which when plotted against the corresponding loss electric field is coincident with the DC E-J characteristics of the tape. This demonstrates that the hysteresis losses are determined by the extended E-J characteristics of the tape.

Investigation of ECCD on the first and second harmonics ECR

Electron cyclotron current drive (ECCD) on the 1st and 2nd harmonics of the electron cyclotron resonance (ECR) is considered. Mainly the T-10 experimental results are described and comparison with the experimental data from various devices is performed. Features of ECCD are studied by comparison of Fokker-Planck (FP) calculations with measurements of X-ray spectra in discharges with ECCD. It is shown that ECCD efficiency is in a good agreement with FP calculations. Database obtained on various devices allows to assume that in ITER the ECCD efficiency can be achieved as high as eta CD=0.3*1020A/Wm2.

First results from the high energy resolution photoemission beam line at ELETTRA

We report the first results obtained from the high energy resolution beam line at the storage ring ELETTRA of Trieste. The beam line has been designed to perform photoemission experiments in the vacuum ultraviolet (VUV) and soft X-ray (SXR) energy range. The radiation source is an undulator which consists of three sections, with 36 periods and a period length of 12.5 cm. It allows scanning of an energy range 17–900 eV using the 1st, 3rd and 5th harmonics. The monochromator is a spherical grating type and the resolving power at 400 eV, estimated from the K-shell photoabsorption of the N 2 molecule is well above 10 000. The spectra are better than any other spectra taken while operating with high flux, i.e. first order diffraction and grating not masked. Measurements taken at the oxygen and neon K-edges, the argon L 23 edges and of the helium double ionization spectra, indicate that the resolution is excellent from 65 to 870 eV.

The Effect of UV Light on IR Absorption in Chemically Vapor Deposited a-SiNx:H Films

ABSTRACTWe have measured the optical absorption properties of Plasma Enhanced Chemically Vapor Deposited (PECVD) films of hydrogenated amorphous silicon nitride (a-SiNx:H) over the energy range from 0.54 to 2 eV using Photothermal Deflection Spectroscopy (PDS). The near-infrared absorption properties of these films provide a quantitative estimate of the amount of H bonded to Si or N as well as a measure of the the density of electronic gap states due to species like Si dangling bonds. Typical PDS spectra obtained on as-deposited films show a broad absorption tail with a large number of narrow absorption peaks. Using the phase sensitive feature of this spectroscopy we are able to separate nitride-related absorption from that arising from the fused quartz substrates. In addition to the broad, featureless band tail, whose magnitude is quite sensitive to optical excitation with light above ̃3.9 eV, we observe a number of narrow absorption peaks which we identify as overtones of localized vibrational modes. Specifically, we see peaks at 0.82 and 1.20 eV which we identify as the 1st and second harmonics of N-H stretching vibrations, and several other peaks whose origins remain undetermined. Prolonged UV excitation produces no detectable change in these vibrational modes, although large changes are seen in the underlying absorption tail. This reinforces previous suggestions that photoinduced changes in these films do not arise from rearrangement of the bonded hydrogen.

Abnormalities of left ventricular shape in patients with stable angina

In this study, left ventricular shape was evaluated quantitatively by calculating the power spectrum and the regional curvatures of angiographic outlines as seen in the right oblique anterior projection. Two groups of patients were studied: 16 normal subjects and 16 patients with stable angina who were selected because of normal left ventricular function (normal left ventricular volumes, pressures, ejection fraction and no regional wall motion abnormality at subjective analysis of ventriculograms). The two groups did not differ in terms of mean age of the patients. Regional curvatures were calculated using the Frenet-Serret formula starting from the mitral corner (point 1) and extending to the aortic corner (point 90). The power spectrum was calculated by means of Fourier analysis. The ventricular shape during diastole of the patients with angina differed significantly from that of the normal group in that there was a greater posterobasal curvature; a lower curvature of the inferior wall showing an inward convexity; a greater parietal curvature of the inferoapical region and a minor curvature of the anterobasal region. The power spectrum differed significantly from that of the normal subjects. The 1st and 2nd harmonics were reduced and the 3rd, 4th, 5th and 6th ones increased. The end-systolic contour of the group of patients with stable angina showed a higher amplitude of the 3rd and 5th harmonics and a lower amplitude of the 1st, 2nd, 9th, 10th and 11th harmonics with respect to the group of normal patients. Regional curvatures showed significant differences between the two groups in the antero-basal region. These modifications of left ventricular shape in patients with stable angina did not appear to be related to age and/or heart rate; to abnormalities in hemodynamics and wall motion; or to acute ischemia. Abnormalities of shape in patients with stable angina, therefore, may indicate a remodeling of the left ventricle due to the structural effects (myocardial and/or interstitial) of chronic ischemia.

Direct-writing recorder of the frequency dependence of dynamic compliance analyzed from one cycle of breathing and pulmonary resistance: effect of fenoterol on asthmatic subjects.

We developed a new method of direct-writing recording of the frequency dependence of dynamic compliance analysed from one cycle of breathing and pulmonary resistance. Both pulmonary resistance (RL) and frequency dependence of dynamic compliance (Cdyn.f) are calculated by Fourier-series analysis of flow and transpulmonary pressure in a single cycle of breathing. RL was obtained from fundamental harmonics. Cdyn.f was calculated from 1st and 2nd harmonics and estimated by the ratio of Cdyn at 0.5 Hz to Cdyn at zero frequency, C0.5/C0. We used fenoterol aerosol which contained 0.2 mg of fenoterol with one puff of aerosol. Two puffs of fenoterol aerosol were used in each subject and followed changes of RL, C0 and C0.5 as long as 30 min. After fenoterol inhalation RL decreased considerably and C0.5/C0 cont [C0.5/(control C0)] increased. With time, while RL was kept stable, C0.5/C0 cont increased further. We suggest that fenoterol has a potent effect on the small airways which is enhanced with time.