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Determination of the Magnetocrystalline Anisotropy Constant from the Frequency Dependence of the Specific Absorption Rate in a Frozen Ferrofluid
No full textColloidal suspensions of superparamagnetic nanoparticles, known as ferrofluids, are promising candidates for the mediation of magnetic fluid hyperthermia (MFH). In such materials, the dissipation of heat occurs as a result of the relaxation of the particles in an applied ac magnetic field via the Brownian and Neel mechanisms. In order to isolate and study the role of the Neel mechanism in this process, the sample can be frozen, using liquid nitrogen, in order to suppress the Brownian relaxation. In this experiment, dextran-coated Fe3O4 nanoparticles synthesized via co-precipitation and characterized via transmission electron microscopy and dc magnetization are used as MFH mediators over the temperature range between −70°C to −10°C (Brownian-suppressed state). Heating the nanoparticles using ac magnetic field (amplitude ∼ 300 Oe), the frequency dependence of the specific absorption rate (SAR) is calculated between 150 kHz and 350 kHz and used to determine the magnetocrystalline anisotropy of the sample
Plasma Engineered Surfaces for Orthopedic Devices
No full textAtmospheric pressure plasma was used to graft various biocompatible polymers to the surface of ultra-high molecular weight polyethylene (UHMWPE). Polymers used as grafts in this study were poly(2-hydroxyethylmethacrylate) (PHEMA) and polyethylene glycol (PEG). A significant decrease in contact angle was noted for grafted surfaces, indicating increased hydrophilicity. Surface functionalities were verified using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The wear properties of the coatings were determined by weight loss under conditions of a random motion pin-on-plate apparatus with the coated polyethylene plaques immersed in DI water. Based on these tests, the grafted surfaces exhibited an improved resistance to wear, compared to UHMWPE. Cell viability studies were used to confirm that the plasma treatment had no negative effects on the surface bio-toxicity. Based on the results, it is anticipated that the incorporation of these biocompatible polymer-grafted UHMWPE surfaces in metal-on-plastic orthopedic implants should improve their performance and longevity
Paired vehicle occupant analysis indicates age and crash severity moderate likelihood of higher severity injury in second row seated adults in frontal crashes
No full textThe majority of advances in occupant protection systems for motor vehicle occupants have focused on occupants seated in the front row of the vehicle. Recent studies suggest that these systems have resulted in lower injury risk for front row occupants as compared to those in the second row. However, these findings are not universal. In addition, some of these findings result from analyses that compare groups of front and second row occupants exposed to dissimilar crash conditions, raising questions regarding whether they might reflect differences in the crash rather than the front and second row restraint systems. The current study examines factors associated with injury risk for pairs of right front seat and second row occupants in frontal crashes in the United States using paired data analysis techniques. These data indicate that the occupant seated in the front row frequently experiences the more severe injury in the pair, however there were no significant differences in the rate of occurrence of these events and events where the more severe injury occurs in the second row occupant of the pair. A logistic regression indicated that the likelihood of the more severe injury occurring in the second row seated occupant of the pair increased as crash severity increased, consistent with data from anatomic test dummy (ATD) tests. It also indicated that the second row occupant was more likely to have the more severe injury in the pair if that occupant was the older occupant of the pair. These findings suggest that occupant protection systems which focus on providing protection specifically for injuries experienced by older occupants in the second row in higher severity crash conditions might provide the greatest benefit
Discovering Urban Social Functional Regions Using Taxi Trajectories
No full textSocial function refers to the recognized human use of urban land. Detailed urban land social function identification is an integral part of urban planning. This paper focuses on discovering the social functions of urban hot areas by using taxi trajectory data. The dataset is collected in Shanghai, China, over 1.5 years. Firstly, we propose a new method to find the urban hot areas. Secondly, we classify these areas into our predefined 10 kinds of social function by depicting the characteristics of them explicitly. Thirdly, we analyze the various temporal features of ten classes in detail