Documents disponibles écrits par cet auteur

Design and evaluation of damped air bearings at head-disk interface / Jianhua Li in Transactions of the ASME . Journal of tribology, Vol. 132 N° 3 (Juillet 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 132 N° 3 (Juillet 2010) . - 13 p. Titre : Design and evaluation of damped air bearings at head-disk interface Type de document : texte imprimé Auteurs : Jianhua Li, Auteur ; Junguo Xu, Auteur ; Yuki Shimizu, Auteur Année de publication : 2011 Article en page(s) : 13 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Damping  Elastic  constants  Frequency  response  Machine  bearings  Magnetic  heads  Modal  analysis Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Perturbation and modal-analysis methods were employed to systematically study a damped slider's dynamic characteristics, including an air-bearing slider's stiffness, damping coefficient, frequency response to translation and wavy motion, natural frequencies, damping ratios, and modal shape-node line. We found that a design with grooves distributed on a trailing pad effectively improved the slider's damping ratio in the second pitch mode; however, parametric studies revealed that the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider we designed with distributed damped grooves on a trailing pad had a higher damping ratio in the second pitch mode, and hence, its responses in the second pitch mode were greatly reduced, which were clarified through simulation and an experiment. Some issues on air-bearing stiffness reduction and negative damping at low frequency and contamination and lube pickup on the damped grooves were also evaluated in the experiment. No degradation could be found in the damped slider. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Design and evaluation of damped air bearings at head-disk interface [texte imprimé] / Jianhua Li, Auteur ; Junguo Xu, Auteur ; Yuki Shimizu, Auteur . - 2011 . - 13 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 132 N° 3 (Juillet 2010) . - 13 p. Mots-clés : Damping  Elastic  constants  Frequency  response  Machine  bearings  Magnetic  heads  Modal  analysis Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : Perturbation and modal-analysis methods were employed to systematically study a damped slider's dynamic characteristics, including an air-bearing slider's stiffness, damping coefficient, frequency response to translation and wavy motion, natural frequencies, damping ratios, and modal shape-node line. We found that a design with grooves distributed on a trailing pad effectively improved the slider's damping ratio in the second pitch mode; however, parametric studies revealed that the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider we designed with distributed damped grooves on a trailing pad had a higher damping ratio in the second pitch mode, and hence, its responses in the second pitch mode were greatly reduced, which were clarified through simulation and an experiment. Some issues on air-bearing stiffness reduction and negative damping at low frequency and contamination and lube pickup on the damped grooves were also evaluated in the experiment. No degradation could be found in the damped slider. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]

Performance of active and passive methods for measuring low-frequency surface wave dispersion curves / Brent L. Rosenblad in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 10 (Octobre 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 10 (Octobre 2009) . - pp. 1419–1428 Titre : Performance of active and passive methods for measuring low-frequency surface wave dispersion curves Type de document : texte imprimé Auteurs : Brent L. Rosenblad, Auteur ; Jianhua Li, Auteur Année de publication : 2009 Article en page(s) : pp. 1419–1428 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Surface  wavesSpectral  analysisSignal  processingGeophysical  surveysMeasurement Résumé : This paper examines the consistency between surface wave dispersion curves measured at wavelengths of up to 600 m using active and passive methods at sites in the Mississippi Embayment. Large-diameter (200 m) circular receiver arrays were deployed at five deep soil sites located in Tennessee, Arkansas, and Missouri to record ambient ground vibrations at low frequencies. Measurements were performed at the same locations using linear receiver arrays and actively generated low-frequency energy using the recently developed Network for Earthquake Engineering Simulation (NEES) field vibrator (termed Liquidator). Characteristics of the ambient wavefield measured at the five sites in the Mississippi Embayment are presented along with comparisons between the surface wave dispersion curves obtained from the active and passive measurements at each site. The ambient wavefield measurements exhibited peak levels in the frequency range of 1–5 Hz. Surface wave dispersion curves developed from frequency-wavenumber (f-k) processing of the active and passive methods were in good agreement at four of the sites, with phase velocities from the passive measurements within 5–10 % of the active-source measurements out to wavelengths of about 550 m. Improved comparisons were obtained at the fifth site by applying high-resolution f-k processing. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000100 [article] Performance of active and passive methods for measuring low-frequency surface wave dispersion curves [texte imprimé] / Brent L. Rosenblad, Auteur ; Jianhua Li, Auteur . - 2009 . - pp. 1419–1428. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 10 (Octobre 2009) . - pp. 1419–1428 Mots-clés : Surface  wavesSpectral  analysisSignal  processingGeophysical  surveysMeasurement Résumé : This paper examines the consistency between surface wave dispersion curves measured at wavelengths of up to 600 m using active and passive methods at sites in the Mississippi Embayment. Large-diameter (200 m) circular receiver arrays were deployed at five deep soil sites located in Tennessee, Arkansas, and Missouri to record ambient ground vibrations at low frequencies. Measurements were performed at the same locations using linear receiver arrays and actively generated low-frequency energy using the recently developed Network for Earthquake Engineering Simulation (NEES) field vibrator (termed Liquidator). Characteristics of the ambient wavefield measured at the five sites in the Mississippi Embayment are presented along with comparisons between the surface wave dispersion curves obtained from the active and passive measurements at each site. The ambient wavefield measurements exhibited peak levels in the frequency range of 1–5 Hz. Surface wave dispersion curves developed from frequency-wavenumber (f-k) processing of the active and passive methods were in good agreement at four of the sites, with phase velocities from the passive measurements within 5–10 % of the active-source measurements out to wavelengths of about 550 m. Improved comparisons were obtained at the fifth site by applying high-resolution f-k processing. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000100

Synthesis of photoactive magnetic nanoparticles with atomic layer deposition / Yun Zhou in Industrial & engineering chemistry research, Vol. 49 N° 15 (Août 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 15 (Août 2010) . - pp 6964–6971 Titre : Synthesis of photoactive magnetic nanoparticles with atomic layer deposition Type de document : texte imprimé Auteurs : Yun Zhou, Auteur ; David M. King, Auteur ; Jianhua Li, Auteur Année de publication : 2010 Article en page(s) : pp 6964–6971 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Photoactive  Magnetic  Nanoparticles. Résumé : Iron-based magnetic nanoparticles have been produced by decomposition of iron oxalate powder. The micrometer-size iron oxalate powder was first ground by use of a cryogenic milling process. A titanium dioxide (TiO2) thin film was then deposited on the synthesized iron nanoparticles with an in situ atomic layer deposition (ALD) process at 100 °C with TiCl4 and H2O2 as precursors. However, because of the high surface area, the iron nanoparticles were unstable and spontaneously oxidized when exposed to H2O2 during the TiO2 ALD process, thus reducing the magnetic moment of the core particles. As an improvement in the process, prior to the TiO2 deposition, an aluminum nitride (AlN) film was deposited in situ to coat and passivate the iron core particles. The AlN ALD was performed at 250 °C with trimethylaluminium (TMA) and ammonia (NH3) as precursors. This passivation provided a significant decrease in the iron oxidation as determined by X-ray diffraction and magnetization measurements. Photoactivity of the TiO2 film was demonstrated by decomposition of methylene blue solution under ultraviolet irradiation. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901712q [article] Synthesis of photoactive magnetic nanoparticles with atomic layer deposition [texte imprimé] / Yun Zhou, Auteur ; David M. King, Auteur ; Jianhua Li, Auteur . - 2010 . - pp 6964–6971. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 15 (Août 2010) . - pp 6964–6971 Mots-clés : Photoactive  Magnetic  Nanoparticles. Résumé : Iron-based magnetic nanoparticles have been produced by decomposition of iron oxalate powder. The micrometer-size iron oxalate powder was first ground by use of a cryogenic milling process. A titanium dioxide (TiO2) thin film was then deposited on the synthesized iron nanoparticles with an in situ atomic layer deposition (ALD) process at 100 °C with TiCl4 and H2O2 as precursors. However, because of the high surface area, the iron nanoparticles were unstable and spontaneously oxidized when exposed to H2O2 during the TiO2 ALD process, thus reducing the magnetic moment of the core particles. As an improvement in the process, prior to the TiO2 deposition, an aluminum nitride (AlN) film was deposited in situ to coat and passivate the iron core particles. The AlN ALD was performed at 250 °C with trimethylaluminium (TMA) and ammonia (NH3) as precursors. This passivation provided a significant decrease in the iron oxidation as determined by X-ray diffraction and magnetization measurements. Photoactivity of the TiO2 film was demonstrated by decomposition of methylene blue solution under ultraviolet irradiation. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901712q