Multi-frequency Pulse Research Articles

FREQUENCY DEPENDENCE OF PULSE WIDTH FOR 150 RADIO NORMAL PULSARS

The frequency dependence of pulse width is studied for 150 normal pulsars, mostly selected from the European Pulsar Network, for which the 10\% multifrequency pulse widths can be well fit with the Thorsett relationship W_{10}=A\nu^{\mu}+W_{\rm 10, min}. The relative fraction of pulse width change between 0.4~GHz and 4.85~GHz, \eta=(W_{4.85}-W_{0.4})/W_{0.4}, is calculated in terms of the best-fit relationship for each pulsar. It is found that 81 pulsars (54\%) have $\eta<-10$\% (group A), showing considerable profile narrowing at high frequencies, 40 pulsars (27\%) have $-$10\%$\leq\eta\leq 10$\% (group B), meaning a marginal change in pulse width, and 29 pulsars (19\%) have $\eta>10$\% (group C), showing a remarkable profile broadening at high frequencies. The fractions of the group-A and group-C pulsars suggest that the profile narrowing phenomenon at high frequencies is more common than the profile broadening phenomenon, but a large fraction of the group-B and group-C pulsars (a total of 46\%) is also revealed. The group-C pulsars, together with a portion of group-B pulsars with a slight pulse broadening, can hardly be explained using the conventional radius-to-frequency mapping, which only applies to the profile narrowing phenomenon. Based on a recent version of the fan beam model, a type of broadband emission model, we propose that the diverse frequency dependence of pulse width is a consequence of different types of distribution of emission spectra across the emission region. The geometrical effect predicting a link between the emission beam shrinkage and the spectrum steepening is tested but disfavored.

Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation

Electronic spin transport properties of graphene nanoribbons (GNRs) are influenced by the presence of adatoms, adsorbates and edge functionalization. To improve the understanding of the factors that influence the spin properties of GNRs, local (element) spin-sensitive techniques such as electron spin resonance (ESR) spectroscopy are important for spintronics applications. Here, we present results of multi-frequency continuous wave (CW), pulse and hyperfine sublevel correlation (HYSCORE) ESR spectroscopy measurements performed on oxidatively unzipped graphene nanoribbons (GNRs), which were subsequently chemically converted (CCGNRs) with hydrazine. ESR spectra at 336 GHz reveal an isotropic ESR signal from the CCGNRs, of which the temperature dependence of its line width indicates the presence of localized unpaired electronic states. Upon functionalization of CCGNRs with 4-nitrobenzene diazonium tetrafluoroborate, the ESR signal is found to be 2 times narrower than that of pristine ribbons. NH3 adsorption/desorption on CCGNRs is shown to narrow the signal, while retaining the signal intensity and g value. The electron spin-spin relaxation process at 10 K is found to be characterized by slow (163 ns) and fast (39 ns) components. HYSCORE ESR data demonstrate the explicit presence of protons and 13C atoms. With the provided identification of intrinsic point magnetic defects such as proton and 13C has been reported, which are roadblocks to spin travel in graphene-based materials, this work could help in advancing the present fundamental understanding on the edge-spin (or magnetic)-based transport properties of CCGNRs.

Effects of neuromuscular electrical stimulation on arterial hemodynamic properties and body composition in paretic upper extremities of patients with subacute stroke.

Neuromuscular electric stimulation (NMES) induces repeated muscular contraction, possibly promoting the perfusion/oxygenation of the regional tissues. It remains unclear how NMES influences vascular hemodynamic property and segmental fluid distribution/composition in paretic extremities of hemiplegic patients. Eleven hemiplegic patients aged 62.6 ± 12.5 years in the subacute stage of stroke received NMES for paretic wrist extensor and flexor muscles 30 min daily, 5 days per week for 4 weeks. The non-paretic upper extremities (NPUE) that did not receive NMES served as control. Distribution of fluid to intra/extracellular milieu and arterial hemodynamic properties were determined by using the multi-frequency bioelectrical impedance and pulse wave analysis, respectively. Compared with NPUE without NMES, paretic upper extremity (PUE) with NMES revealed a significantly less decrease in arterial blood flow, impedance quotient, slope quotient, and less increase in crest width and crest time of arterial pulse wave. NMES for 4 weeks increased body cell mass in PUE. Furthermore, NPUE without NMES reduced intracellular water, whereas PUE with NMES retarded loss of intracellular water after stroke. NMES therapy increases body cell mass, attenuates reduction of intracellular water, and alleviates arterial hemodynamic disturbance in PUE in subacute stroke. However, stroke-related physical deconditioning may negatively regulate body composition and impair hemodynamic function in NPUE.

Properties of the Umov vector in shallow water and its dependence on sea surface conditions

In this work, the effects of a rough sea surface on shallow water acoustic propagation are examined using experimental data collected during the ONR sponsored Target and Reverberation Experiment (TREX) off of the coast of Panama City, Florida, in May 2013. The acoustic data were collected from a bottom deployed recording tower that coherently recorded data on a horizontal line array (HLA), a vertical line array (VLA), and on an accelerometer-based vector sensor which was combined with a co-located hydrophone to formulate the Umov vector, or instantaneous intensity vector. The source was lowered from the stern of a research vessel to a depth one-third and two-thirds of the water depth (18 m), and transmitted a multi-frequency pulse from 1 to 4 kHz. These measurements were repeated at positions approximately 10, 20, and 40 water depths away from the tower, along a bearing perpendicular and parallel to the surface wave-crests. During the experiment, the sea surface directional-wave spectrum was measured by a Datawell Waverider buoy moored at the experimental site. Properties of the Umov vector are shown to relate to roughness and directional characteristics of the sea surface. The Umov vector is also studied in relation to the HLA and VLA measurements.

A New Water Electrode Method for Short‐Time Testing of Water Treeing and Consideration of Temperature Effects of Water Tree Initiation and Propagation

AbstractWater treeing occurs when an AC voltage is applied to an electrical insulation system such as those in power cables and power apparatus. From a practical viewpoint, research on water treeing has mostly been performed under high‐frequency AC voltage application. However, power cables and power apparatus are also used under DC voltage application owing to progress in inverter technology. Inverter drive of rotating electrical machines has spread and expanded for global warming prevention and maintenance improvement. Underwater motors are used in water. In an underwater motor driven by the voltage of an inverter, it is necessary to consider water treeing of the motor insulation and cable insulation connected with a drive board. Thus far, a water electrode method that utilizes an AC voltage of high frequency has been used in the accelerated water treeing experimental method for a long time. On the other hand, an inverter with a surge voltage generates an equivalent AC frequency by the application of a multifrequency pulse voltage similar to a pulse width modulation (PWM) control wave. Therefore, there is a possibility of mistakes in real‐machine reliability evaluation because the initiation and propagation mechanisms are different from those in a real machine, even if we can reproduce water treeing by increasing the basic frequency. This paper reports our investigation of a new water electrode method and of temperature effects on water tree initiation and propagation. We also compare experimental results between 500 Hz and 50 Hz using the new water electrode method from the viewpoint of temperature. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 1–9, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22422

The evaluation of sugar content and firmness of non-climacteric pears based on voltammetric electronic tongue

The sugar content and firmness of non-climacteric pear of different cultivars were studied by a voltammetric electronic tongue (VE-tongue). The VE-tongue self-developed in this study comprised six working electrodes (gold, silver, platinum, palladium, tungsten, and titanium electrode), an Ag/AgCl reference electrode, and a platinum auxiliary electrode. The multi-frequency large amplitude pulse voltammetry (MLAPV) was applied to the working electrodes as the scanning potential waveform,and it consisted of four frequency segments of 1Hz, 10Hz, 100Hz, and 1000Hz. In this study, five cultivars of pear from different geographical origins were tested by VE-tongue, and the firmness and sugar content of pears were tested by the traditional methods. The characteristic data (the maximum and minimum values) obtained by VE-tongue were compressed by principal component analysis (PCA), and the principal components (PCs) were taken as the input variables of principal component regression (PCR), partial least squares regression (PLSR), and least squared-support vector machines (LS-SVMs) to predict sugar content and firmness. All the models showed good results, and LS-SVM preformed best in the prediction.

Monitoring of quality and storage time of unsealed pasteurized milk by voltammetric electronic tongue

A voltammetric electronic tongue (VE-tongue) was self-developed and applied to monitor the quality and storage time of unsealed pasteurized milk. The VE-tongue comprised four working electrodes: gold, silver, platinum, and palladium electrode. Two potential waveforms: Multi-frequency rectangle pulse voltammetry (MRPV) and multi-frequency staircase pulse voltammetry (MSPV) were applied to working electrodes in the study, and both of MRPV and MSPV consisted of three frequency segments: 1Hz, 10Hz, and 100Hz. The total areas under the corresponding curves obtained by VE-tongue in the three frequencies were applied as characteristic data, which were evaluated by the principal component analysis (PCA) and cluster analysis (CA). The results of PCA and CA indicate that the milk samples of different storage time could be successfully classified by the VE-tongue based on MRPV and MSPV, respectively. Combining the areas obtained by the VE-tongue based on MRPV and MSPV, the classification results of PCA and CA were improved evidently. The total bacterial count, acidity and viscosity of the milk samples were also measured during the storage, and those physicochemical characteristics showed regular configuration in PCA and CA plots. Furthermore, the total bacterial count and viscosity properties were predicted by partial least squares regression (PLSR) and least squares-support vector machines (LS-SVM), and the combination of the areas obtained by the VE-tongue based on the MRPV and MSPV were applied as the input data of PLSR and LS-SVM. Both the prediction techniques performed well in predicting viscosity and total bacterial count, and the prediction results of LS-SVM were better than that of PLSR. Those results demonstrate that the VE-tongue could be applied to monitor the quality storage time of unsealed pasteurized milk.

Sinusoidal envelope voltammetry as a new readout technique for electronic tongues

We introduce a novel voltammetric method, so-called sinusoidal envelope voltammetry, for use in electronic tongues. Fourier transformation was used to transform the data of the signal from the time domain to the frequency domain. The four taste substances, acesulfame potassium, monosodium glutamate, potassium chloride and tartaric acid, are shown to exhibit abundant frequency characteristics in the power spectrum of a Fourier transformation. This indicates that the power spectrum from sinusoidal envelope voltammetry can be used as fingerprints of samples for classification. Principal component analysis along with discrimination index and multi-frequency large amplitude pulse voltammetry as a reference technique is used to evaluate the separation ability of sinusoidal envelope voltammetry. The score plots of the method for the four taste substances and for the five brands of Jiafan rice wine show better discrimination ability than multi-frequency large amplitude pulse voltammetry. Sinusoidal envelope voltammetry is considered to be a promising technique for use in voltammetric electronic tongues.

Phase-Resolved Spectra of PSR B0525+21 and PSR B2020+28

Using the published data of multi-frequency time-aligned pulse profiles from Kuzmin et al. (1998), we calculate the phase-resolved spectra of PSRs B0525+21 and B2020+28. The results reveal that conal-double pulsars have common ‘M’-shaped phase-resolved spectra.

Classification and prediction of rice wines with different marked ages by using a voltammetric electronic tongue

A voltammetric electronic tongue (VE-tongue) was developed to discriminate the difference between Chinese rice wines in this research. Three types of Chinese rice wine with different marked ages (1, 3, and 5 years) were classified by the VE-tongue by principal component analysis (PCA) and cluster analysis (CA). The VE-tongue consisted of six working electrodes (gold, silver, platinum, palladium, tungsten, and titanium) in a standard three-electrode configuration. The multi-frequency large amplitude pulse voltammetry (MLAPV), which consisted of four segments of 1 Hz, 10 Hz, 100 Hz, and 1000 Hz, was applied as the potential waveform. The three types of Chinese rice wine could be classified accurately by PCA and CA, and some interesting regularity is shown in the score plots with the help of PCA. Two regression models, partial least squares (PLS) and back-error propagation-artificial neural network (BP–ANN), were used for wine age prediction. The regression results showed that the marked ages of the three types of Chinese rice wine were successfully predicted using PLS and BP–ANN.

A Multi-Frequency Pulse EPR and ENDOR Approach to Study Strongly Coupled Nuclei in Frozen Solutions of High-Spin Ferric Heme Proteins

In spite of the tremendous progress in the field of pulse electron paramagnetic resonance (EPR) in recent years, these techniques have been scarcely used to investigate high-spin (HS) ferric heme proteins. Several technical and spin-system-specific reasons can be identified for this. Additional problems arise when no single crystals of the heme protein are available. In this work, we use the example of a frozen solution of aquometmyoglobin (metMb) to show how a multi-frequency pulse EPR approach can overcome these problems. In particular, the performance of the following pulse EPR techniques are tested: Davies electron nuclear double resonance (ENDOR), hyperfine correlated ENDOR (HYEND), electron-electron double resonance (ELDOR)-detected NMR, and several variants of hyperfine sublevel correlation (HYSCORE) spectroscopy including matched and SMART HYSCORE. The pulse EPR experiments are performed at X-, Q- and W-band microwave frequencies. The advantages and drawbacks of the different methods are discussed in relation to the nuclear interaction that they intend to reveal. The analysis of the spectra is supported by several simulation procedures, which are discussed. This work focuses on the analysis of the hyperfine and nuclear-quadrupole tensors of the strongly coupled nuclei of the first coordination sphere, namely, the directly coordinating heme and histidine nitrogens and the 17O nucleus of the distal water ligand. For the latter, 17O-isotope labeling was used. The accuracy of our results and the spectral resolution are compared in detail to an earlier single-crystal continuous-wave ENDOR study on metMb, and it will be shown how additional information can be obtained from the multi-frequency approach. The current work is therefore prone to become a template for future EPR/ENDOR investigations of HS ferric heme proteins for which no single crystals are available.

Protein−Protein Interactions Studied by EPR Relaxation Measurements: Cytochrome c and Cytochrome c Oxidase

The complex formed between cytochrome c oxidase from Paracoccus denitrificans and its electron-transfer partner cytochrome c has been studied by multi-frequency pulse electron paramagnetic resonance spectroscopy. The dipolar relaxation of a fast-relaxing paramagnetic center induced on a more slowly relaxing center can be used to measure their distance in the range of 1-4 nm. This method has been used here for the first time to study transient protein-protein complex formation, employing soluble fragments for both interacting species. We observed significantly enhanced transversal relaxation of the CuA center in cytochrome c oxidase due to the fast-relaxing iron of cytochrome c upon complex formation. The possibility to measure cytochrome c oxidase in the presence and absence of cytochrome c permitted us to separate the dipolar relaxation from other relaxation contributions. This allowed a quantitative simulation and interpretation of the relaxation data. The specific temperature dependence of the dipolar relaxation together with the high orientational selectivity achieved at high magnetic field values may provide detailed information on distance and relative orientation of the two proteins with respect to each other in the complex. Our experimental results cannot be explained by any single well-defined structure of the complex of cytochrome c oxidase with cytochrome c, but rather suggest that a broad distribution in distances and relative orientations between the two proteins exist within this complex.

Continuous-Wave and Pulse EPR Study of the Copper(II) Complex of N-Confused Tetraphenylporphyrin: Direct Observation of a σ Metal−Carbon Bond

N-confused or inverted porphyrins, a family of porphyrin isomers that contain a confused pyrrole ring connected through its alpha and beta' positions in the macrocycle, exhibit unique physical and chemical properties, like, for instance, the ability to stabilize unusual oxidation states of metals due to the reactivity of the inverted pyrrole. In this Article, a combined multifrequency continuous-wave and pulse electron paramagnetic resonance (EPR) study of the copper(II) complex of N-confused tetraphenylporphyrin (TPP) is presented. By use of pulse EPR methods like ENDOR and HYSCORE, the magnetic interactions between the unpaired electron of the compound and the surrounding nitrogen nuclei were revealed. Through 13C labeling of the macrocycle, a detailed study of the carbon hyperfine interaction became possible and provided further insight into the character of the metal-carbon bond. The observed hyperfine couplings of the ligand atoms in the first coordination sphere showed the presence of a remarkably strong sigma Cu-C bond and allowed for a detailed analysis of the spin delocalization over the porphyrin macrocycle. Interestingly, it was found that the observed delocalization is approximately 11% larger than the corresponding one for CuTPP.

Synthesis of Dendritic Metalloporphyrins with Distal H‐Bond Donors as Model Systems for Hemoglobin

AbstractWe report the synthesis of the first‐ (G1) and second‐generation (G2) dendritic FeII porphyrins 1⋅Fe–4⋅Fe (G1) and 6⋅Fe (G2) bearing distal H‐bond donors ideally positioned for stabilization of FeIIO2 adducts by H‐bonding (Fig. 1). A first approach towards the construction of these novel biomimetic systems failed unexpectedly: the Suzuki cross‐coupling between appropriately functionalized ZnII porphyrins and ortho‐ethynylated aryl derivatives, serving as anchors for the distal H‐bond donor moieties, was unsuccessful (Schemes 1, 3, and 5), presumably due to steric hindrance resulting from unfavorable coordination of the ethynyl residue to the Pd species in the catalytic cycle (Scheme 6). The target molecules were finally prepared by a route in which the ortho‐ethynylated meso‐aryl ring is introduced during porphyrin construction in a mixed condensation involving the two dipyrrylmethanes 33 and 34, and aldehyde 36 (Schemes 7 and 8). Following attachment of the dendrons (Scheme 11), the distal H‐bond donors were introduced by Sonogashira cross‐coupling (Scheme 12), and subsequent metallation afforded the dendritic FeII porphyrins 1⋅Fe–6⋅Fe. 1H‐NMR Spectroscopy proved the location of the H‐bond donor moiety atop the porphyrin surface, and X‐ray crystal‐structure analysis of model system 45 (Fig. 2) revealed that this moiety would not sterically interfere with gas binding. With 1,2‐dimethyl‐1H‐imidazole (DiMeIm) as ligand, the dendritic FeII porphyrins formed five‐coordinate high‐spin complexes (Figs. 3 and 4) and addition of CO led reversibly to the corresponding stable six‐coordinate gas complexes (Fig. 6). Oxygenation, however, did not result in defined FeIIO2 complexes as rapid decomposition to FeIII species took place immediately, even in the case of the G2 dendrimer 6⋅Fe(DiMeIm) (Fig. 7). In contrast, stable gas adducts are formed between dendritic CoII porphyrins and O2 in the presence of DiMeIm as axial ligand, as revealed by electron paramagnetic resonance (EPR). The possible stabilization of these complexes through H‐bonding involving the distal ligand is currently under investigation in multidimensional and multifrequency pulse EPR experiments.

Use of spatial encoding in NMR photography

NMR photography has gained significant attention as a method of storing and retrieving information using NMR spectroscopy. Among the commonly practiced methods the most important is the frequency encoding by use of a multi-frequency pulse on a liquid crystal molecule. We propose and demonstrate another robust method which relies on spatial encoding. Spatial information is mapped onto the spectrum, if excited and recorded in the presence of a gradient. The encoding is performed by applying a multi-frequency pulse in the presence of a gradient. The subsequent acquisition, under a gradient, helps storing this spatial information on a one-dimensional spectrum. Series of such spectra can also store two-dimensional patterns. This procedure is described and exemplified in this paper.

Design of data acquisition and control subsystem of the ktm tokamak multifrequency pulse radar reflectometer

A Kazakhstan Tokamak for Material studies (KTM) [1] Azizov, E. A., Dokouka, V. N.Dvorkin, N. Ya. (2003). Kazakhstan tokamak for material testing (KTM). Plasma Devices and Operations, 11(1): 39–55. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar] is being developed by Russian and Kazakh scientists for modeling plasma-material interactions in the divertor region under conditions expected for ITER. The first results of designing a KTM radar reflectometer data acquisition and control subsystem (DACS) are presented. General requirements to the data acquisition and processing are defined. Problems of real-time processing and transmitting information to a Plasma Control System (PCS) are solved. A desirable time diagram of the DACS operation is shown and design approaches confirming it feasibility are given.

A simple method for NMR photography

The application of a multi-frequency weak pulse to a liquid crystal can excite narrow 1H NMR peaks at the applied frequencies. By using two-level amplitude coding, namely setting the amplitudes of some of the harmonics to zero, this method can be used to store up to 1024 bits of binary information in the liquid crystal molecules. When the information is retrieved in the form of a spectrum, which is plotted as an array of 32 or 16 segments, the stack of spectral segments reproduces a 2D input pattern quite well. This technique is called “NMR photography.” The original method was a pseudo-2D technique that applies the 1024-frequency pulse in the first step, and reads the signal row-by-row in the second step. The present improvement involves subtracting two spectra obtained with the same 1024-frequency pulse but with different durations, so that the method becomes a 1D technique, with a tremendous saving of experimental time. Several examples are given to illustrate the results.

Simultaneous single-pulse observations of radio pulsars

We present the first results from a programme of multi-frequency simultaneous single pulse observations carried out as part of the European Pulsar Network. We detail the main data analysis methods and apply them to simultaneous observations of the strong pulsar B0329+54 at 1.4 and 2.7 GHz using the Jodrell Bank and Effelsberg radio telescopes respectively. The pulses at different frequencies are highly correlated in their total intensity, as seen in previous experiments, and generally show consistent position angles of the linearly polarized component. In contrast, the circularly polarized emission sometimes shows clear differences between pulses received at different frequencies. These results are unexpected and warrant further follow-up studies to interpret them in the context of the intrinsic bandwidth of pulsar radiation.

Contour Hologram Recording under the Formation of Multifrequency Pulsed Radiation Using Stimulated Brillouin Scattering

A ruby light source is described that emits a giant multifrequency pulse, in which each spectral line, except for the initiating radiation line, is a Stokes component of the stimulated Brillouin scattering of the preceding adjacent line. The results of experimental studies of the temporal, spectral, and energy characteristics of radiation are presented. It is shown that the radiation formed can be used for the holographic recording of contour maps with a narrower fringe than that obtained with a two-frequency laser.

An inverse Compton scattering (ICS) model of pulsar emission

The shapes of pulse profiles, especially their variations with respect to observing frequencies, are very important to understand emission mechanisms of pulsars. However, no previous attempt has been made to interpret their complicated phenomenology. In this paper, we present theoretical simulations for the integrated pulse profiles and their frequency evolution within the framework of the inverse Compton scattering (ICS) model proposed by Qiao ([CITE]) and Qiao & Lin ([CITE]). Using the phase positions of the pulse components predicted by the "beam-frequency figure" of the ICS model, we present Gaussian fits to the multi-frequency pulse profiles for some pulsars. It is shown that the model can reproduce various types of the frequency evolution behaviors of pulse profiles observed.