磁性颗粒复合体磁渗流区矫顽力异常的研究

制备了MnZn铁氧体/SiO₂颗粒复合体.研究了磁性颗粒复合体的有效磁导率μ、 比磁化强度σ以及矫顽力H_c随磁性颗粒含量的变化.研究发现，在MnZn铁氧体体积百分含 量为90%—98%的区域，复合体的有效磁导率μ的变化速率发生突变，出现磁渗流现象，从实验得到的体系磁渗流阈值V_c=97.9%.在磁渗流区，矫顽力表现出异常行为.结果表明 ，这种异常行为与复合体微观结构有着密切关系.在磁渗流前，矫顽力H_c的变化主要来 源于磁 关键词： 颗粒复合体 磁渗流 矫顽力     

Exciplex parameters: key factors in the dielectric behaviour of magnetodynamics

Photoinduced electron transfer reactions in solution produce two primary geminate radical ion pairs: contact ion pair or exciplex and solvent-separated ion pair. The magnetodynamics of radical ion pairs involves suppression of the spin-evolution between singlet and triplet states of a fraction of solvent-separated ion pairs, the partners of which undergo prior diffusion to attain the distance where exchange interaction is negligible, in the presence of an external low magnetic field of the order of the hyperfine interactions present in the system. This results in an increase in geminate recombination of the singlet solvent-separated ion pairs and enhancement in exciplex luminescence since the precursor radical ion pair is singlet. Although seemingly magnetodynamics is a diffusion-controlled phenomenon that should depend mainly on the dielectric constant of the medium (keeping viscosity almost constant), it is not true for all the exciplex systems since the nature of the magnetic field effect versus medium dielectric curves differ from each other in peak positions, peak heights and onset points. To investigate this differential nature, magnetic field effects among exciplex systems consisting of different derivatives of carbazole as electron donors are compared with a universal acceptor, 1,4-dicyano-benzene, with the pyrene—N,N-dimethylaniline exciplex system as reference. It was found that, apart from the solvent dielectric, the exciplex energy and the bulk effect of the steric constraints present on either donor or acceptor site, regulating the optimum inter-radical distance in the initially formed radical ion pair, are the key factors in controlling the magnetodynamic behaviour.     

Incidence of supraglottic activity in males and females: a preliminary report

Supraglottic activity was rated from flexible endoscopic video recordings of subjects with normal laryngeal structure and function as they sustained vowels and repeated syllables and sentences. Judges rated these recordings for false vocal fold (FVF) adduction and anterior-to-posterior (A-P) compression at the initiation of the speech task, throughout the whole speech task (static supraglottic activity), and as brief individual adductions within a speech task (dynamic supraglottic activity). Significant differences in A-P (p < 0.0003) and FVF (p < 0.0000001) compression were found between tasks. Dynamic FVF activity was associated with glottal stops. Static A-P and FVF activities were present in males significantly more (p < 0.0001) than females. FVF activity associated with speech initiation was found in females significantly more (p = 0.0256) than males. Supraglottic activity plays a role in normal speech production, and should not necessarily be considered suggestive of a voice use pattern with excessive muscle tension.     

Time-resolved and high-resolution MRA in a rabbit model of pulmonary embolism at 7 T: preliminary results

Purpose

Evaluate feasibility of using time-resolved and high-resolution, contrast-enhanced magnetic resonance angiography (MRA) at 7 T for characterization of an animal model of pulmonary embolism.

Methods

MRAs were performed in five rabbits using a 7-T MR scanner. Preceding the MR studies, each rabbit underwent a pulmonary artery catheterization with balloon placement. Two doses of gadodiamide were injected: first during a time-resolved MRA, immediately followed by a high-resolution acquisition. Balloon was then deflated, permitting reperfusion for 5 min. A second dose was then injected and another high-resolution MRA acquired. Measurements of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and vessel cross-sections down to fourth-order branches were made, among other parameters.

Results

Occlusion was detected in all rabbits. Despite a TE of 0.58 ms for the time-resolved MRA, regions of nonuniform enhancement attributed to susceptibility effects at the 7-T field were observed in perfused lung. Mean SNR=7.5±3.3 and 134.2±46.5 for the lung and aorta, respectively, and mean CNR=126.7±46.4 for aorta versus lung were obtained. Diameters of vessels in lung that was never occluded were not statistically different from those in reperfused lung.

Conclusion

Results show that time-resolved and high-resolution MRA of the lung are feasible at 7 T and provide high SNR, CNR and resolution, but TEs smaller than 0.58 ms are required to avoid susceptibility artifacts in time-resolved MRAs.     

Electronic structure,magnetic properties,and microstructural analysis of thiol-functionalized Au nanoparticles: role of chemical and structural parameters in the ferromagnetic behaviour

The present work describes the field emission characteristics of nanocrystalline metal clusters decorated multi walled carbon nanotubes (MWNT) field emitters fabricated over flexible graphitized carbon cloth. MWNT have been synthesized by catalytic chemical vapour decomposition (CCVD) of acetylene over Rare Earth (RE) based AB₂ (DyNi₂) alloy hydride catalyst. Fine powders of RE based AB₂ alloy hydride catalysts have been prepared by hydrogen decrepitation technique. The as-grown carbon nanotubes (CNTs) are purified by acid and heat treatments and characterized using XRD, SEM and TEM. Purified MWNT have been decorated with nanocrystalline Pd, Pt and Pt–Ru metal clusters using a simple chemical reduction method. The characterization of metal decorated CNTs were done by using XRD, SEM, TEM, HRTEM and EDX. Nanocrystalline Pd, Pt and Pt–Ru metal clusters decorated MWNT field emitters have been fabricated over graphitized carbon fabric using spin coating method. The field emission characteristics have been studied using an indigenously fabricated set up and the results are discussed. The samples show excellent emission properties with a fairly stable emission current over a period of 4 h. As the presence of the graphitic layer provides strong adhesion between the nanotubes and carbon cloth, the use of graphitized carbon cloth as substrate opens new possibilities for CNT field emitters.     

Populations in the U.S. workforce who rely on voice as a primary tool of trade: a preliminary report

The United States Bureau of Labor Statistics and other sources wereconsulted about the percentages of the working population that we identified as professional voice users. The largest percentage may be in sales and sales related occupations (13%), but the exact breakdown of those who approach their clients vocally rather than by mail is still uncertain. The second largest population is teachers, who comprise 4.2% percent of the U.S. workforce (1994 statistic). Teachers have been identified as having the greatest incidence of voice disorders. Population data are also given for professional voice users who could present a significant hazard to public safety if their vocal communication skills were severely impaired.     

芦山4.20地震的一段学校疏散录像——初步分析及其对应急避险的统计物理模型的意义

真实灾害情境下的人群撤离录像对约束应急避险的统计物理模型具有不可取代的意义.文章分析了中央电视台《新闻联播》播出的2013年4月20日芦山地震时一段教室疏散的视频,讨论了其对应急避险模型的意义.与2008年汶川地震的情况比较,似可看出受过应急训练的人群与未受过训练的人群在撤离时有不同的表现.     

Prediction of the ground motion in Italy: a preliminary attempt

Summary The strong-motion accelerograms written by moderate and strong earthquakes occurring in Central Italy in recent years have been used to estimate physical quantities characterizing the spectrum of motion in the band of engineering interest (0.1 Hz≲f≲20 Hz). The source, propagation and site response parameters obtained in these analyses have therefore been employed to check if theoretical models may be used to correctly predict the trend of the peak values of seismic excitationvs. earthquake size in the areas investigated. For the selected data set, representative of a seismotectonic environment generating earthquakes with prevalent normal faulting (up to a magnitudeM _l ∼7, at depths varying roughly from 5 to 15 km), the assumed spectral model allows successful statistical predictions showing that specific site response is the main factor responsible for the large fluctuations often observed in the data behaviour, at similar magnitudes and distances from focus.

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Riassunto Gli accelerogrammi registrati in occasione di terremoti da moderati a forti nell'Italia Centrale negli ultimi anni sono stati utilizzati per la stima delle grandezze fisiche che caratterizzano lo spettro del moto nella banda di interesse ingegneristico (0.1 Hz≲f≲20 Hz). La parametrizzazione ottenuta per descrivere, mediamente, i meccanismi della sorgente, della propagazione e degli effetti di sito è stata quindi usata per verificare se i modelli teorici possono essere utilmente usati per prevedere gli andamenti dei valori di picco del moto in funzione dell'entità del terremoto. Per i dati selezionati, rappresentativi di un ambiente sismotettonico in grado di generare terremoti con meccanismi prevalentemente distensivi (fino ad una magnitudoM _l ∼7, con profondità variabile all'incirca tra 5 e 15 km), il modello spettrale prescelto consente delle previsioni soddisfacenti da un punto di vista statistico, mostrando che la specifica risponsta dei siti è probabilmente il fattore che provoca le sensibili fluttuazioni spesso osservate per i valori di picco del moto, anche a parità di magnitudo e distanza dal fuoco.

     

An investigation of the correlation between NIR spectrum of the northern sky and atmospheric parameters from April to December in Toyama,Japan by compact spectrometer system

Optical Review - We report on the prediction of the next day’s weather parameters, such as temperature, ground pressure, and water vapor content, utilizing the near-infrared spectrum of the...     

Relaxation and conductivity behaviour in the compounds: FeRGe2O7 (R=Pr,Tb)

AC measurements were performed on the thortveitite-like layered compounds, FeRGe₂O (R=Pr,Tb) in order to study their dielectric features, e.g. as a function of temperature. The main electrical response lies on impedance plots composed of two successive arcs with depressed centers. Bulk conductivity behavior is mostly Arrhenius for the measured temperatures. The associated bulk activation energies are close to 1 eV. Raw data were used to follow the temperature dependence of the dynamic parameters, ε′(ω) and σ′(ω). From logarithmic σ′(ω) vs. ω curves the dc component was obtained. ε′(ω) vs. log ω curves exhibit a dispersive behavior at low frequencies, reflecting blocking effects. E_dc and E_ac activation energies were also calculated, the last one obtained from σ′(ω) vs. 1000/T plots. Conductivity results suggest the occurrence of an extrinsic conducting mechanism. A structural instability was detected via the temperature dependence of permittivity, which has been ascribed to the presence of Ga-O-Ga bonds having associated angles different of 180°. Analyses of the results show that the interchange of Tb and Pr in the general formula FeRGe₂O₇ (R=Pr, Tb) involves only small differences in their global ac and dc behavior.     

Critical behaviour of invariant curves in the standard map: a perturbative approach

The classical perturbation series is used to follow an invariant curve, of fixed winding number, up to its break-up point. The result obtained for the critical value of the perturbation and the corresponding behaviour of the invariant curve are in complete agreement with the results of Kadanoff and Shenker.     

Relaxation behaviour of a biased two-level system,in metals in the weak damping limit

The dynamic properties of a biased two-level system in contact with a dissipative bath are studied in the weak coupling limit using a resolvent expansion method. The theory yields consistent results at low temperatures, a regime in which the widely used dilute bounce gas approximation (DBGA) to an underlying functional integral expression breaks down. The present results are however equivalent to a recently adapted functional integral technique that goes beyond the DBGA. The calculated expressions are relevant for analyzing the neutron scattering data on tunneling of light interstitials, e.g., hydrogen, in metals, at very low temperatures.     

Evaluation of the role of magnetization transfer imaging in prostate: a preliminary study

Results of the preliminary study on the evaluation of the role of magnetization transfer imaging (MTI) of prostate in men who had raised prostate-specific antigen (PSA) (>4 ng/ml) or abnormal digital rectal examination (DRE) are reported. MT ratio (MTR) was calculated for 20 patients from the hyper- (normal) and hypo-intense regions (area suspicious of malignancy as seen on T2-weighted MRI) of the peripheral zone (PZ) and the central gland (CG) at 1.5 T. In addition, MTR was calculated for three healthy controls. Mean MTR was also calculated for the whole of the PZ (including hyper- and hypo-intense area) in all patients. Out of 20 patients, biopsy revealed malignancy in 12 patients. Mean MTR value (8.29+/-3.49) for the whole of the PZ of patients who were positive for malignancy on biopsy was statically higher than that observed for patients who were negative for malignancy (6.18+/-3.15). The mean MTR for the whole of the PZ of controls was 6.18+/-1.63 and is similar to that of patients who were negative for malignancy. Furthermore, for patients who showed hyper- (normal portion) and hypo-intense (region suspicious of malignancy) regions of the PZ, the MTR was statistically significantly different. These preliminary results reveal the potential role of MT imaging in the evaluation of prostate cancer.     

Measurement of the parameters of a pulse propagation path in a medium with noise, dispersion, and selective absorption

A method of signal processing is proposed that allows one to determine the propagation time of pulsed signals, the dispersion, and the selective absorption in the medium when the shape of the pulses is substantially distorted under the effect of the two aforementioned factors and noise. The method is based on measuring the complex frequency response of the propagation path for a narrow frequency band within which the frequency response is governed by the desired parameters of the medium. To determine the parameters of the path from the data of acoustic measurements, both cepstral analysis and numerical differentiation are used. The data of numerical experiments are presented.     

数值地震预测的关键物理问题

数值地震预测是地震物理研究中的一个重要课题,具有基础性的科学意义和潜在的应用价值。文章介绍了数值地震预测的三个关键物理问题——地震发生率与应力变化的关系、地震断层的摩擦函数、地球中应力的传递问题,讨论了这些问题的意义、研究现状和发展趋势。     

数值地震预测的关键物理问题*

数值地震预测是地震物理研究中的一个重要课题,具有基础性的科学意义和潜在的应用价值.文章介绍了数值地震预测的三个关键物理问题——地震发生率与应力变化的关系、地震断层的摩擦函数、地球中应力的传递问题,讨论了这些问题的意义、研究现状和发展趋势.     

High temperature corrosion behaviour of some Fe-, Co- and Ni-base superalloys in the presence of Y2O3 as inhibitor

High temperature corrosion is accelerated degradation of materials at higher temperatures of operation caused by the presence of a deposit of salt or ash. Inhibitors and fuel additives have been investigated with varying success to control this type of corrosion. In this work, effect of an oxide additive namely Y₂O₃ on the hot corrosion behaviour of some superalloys viz Superfer 800H (alloy A), Superco 605 (alloy B) and Superni 75 (alloy C) has been investigated in an Na₂SO₄-60%V₂O₅ environment at 900 °C for 50 cycles. Each cycle consisted of 1 h heating in a Silicon Carbide Tube Furnace followed by 20 min cooling in ambient air. Weight data were taken by an electronic balance having an accuracy of 0.01 mg after each cycle. Subsequently, the exposed alloys were characterized by XRD, SEM and EPMA analyses to evaluate the role of the oxide additive. In the Na₂SO₄-60%V₂O₅ environment, the corrosion rate for the Co-base alloy was found to be highest, whereas that for the Ni-base Superni 75 the lowest. Superficially applied Y₂O₃ was observed to be useful in reducing the high temperature corrosion of the alloys. It was found to be most effective for the alloy A for which the oxide scale was continuous and rich in protective Cr. Alloy B showed the formation of medium size scale rich in Cr and Co. The oxide scale for the alloy C contained mainly Cr and Ni.