Spark plasma sintering synthesis of porous nanocrystalline titanium alloys for biomedical applications.

The reason for the extended use of titanium and its alloys as implant biomaterials stems from their lower elastic modulus, their superior biocompatibility and improved corrosion resistance compared to the more conventional stainless steel and cobalt-based alloys [Niinomi, M., Hattori, T., Niwa, S., 2004. Material characteristics and biocompatibility of low rigidity titanium alloys for biomedical applications. In: Jaszemski, M.J., Trantolo, D.J., Lewandrowski, K.U., Hasirci, V., Altobelli, D.E., Wise, D.L. (Eds.), Biomaterials in Orthopedics. Marcel Dekker Inc., New York, pp. 41-62]. Nanostructured titanium-based biomaterials with tailored porosity are important for cell-adhesion, viability, differentiation and growth. Newer technologies like foaming or low-density core processing were recently used for the surface modification of titanium alloy implant bodies to stimulate bone in-growth and improve osseointegration and cell-adhesion, which in turn play a key role in the acceptance of the implants. We here report preliminary results concerning the synthesis of mesoporous titanium alloy bodies by spark plasma sintering. Nanocrystalline cp Ti, Ti-6Al-4V, Ti-Al-V-Cr and Ti-Mn-V-Cr-Al alloy powders were prepared by high-energy wet-milling and sintered to either full-density (cp Ti, Ti-Al-V) or uniform porous (Ti-Al-V-Cr, Ti-Mn-V-Cr-Al) bulk specimens by field-assisted spark plasma sintering (FAST/SPS). Cellular interactions with the porous titanium alloy surfaces were tested with osteoblast-like human MG-63 cells. Cell morphology was investigated by scanning electron microscopy (SEM). The SEM analysis results were correlated with the alloy chemistry and the topographic features of the surface, namely porosity and roughness.

The influence of short-time ball-milling on the stability of amorphous CoFeB alloys.

The influence of short-time milling on the atomic structure of amorphous Co(70.3)Fe(4.7)B(25) has been investigated by differential scanning calorimetry (DSC), x-ray powder diffraction (XRD), vibrating sample magnetometer (VSM) and x-ray absorption fine-structure (XAFS) techniques. Our results prove that the milling process crystallizes the initially amorphous sample and that the degree of inherent crystallization is inversely proportional to the powder particle size. The investigation of the local atomic structure documents very similar environments around the Co and Fe atoms. The high-energy ball-milling of amorphous precursor represents a practical way to prepare powders having the desired amorphous/nanocrystalline microstructure.

Imaging the magnetic spin structure of exchange-coupled thin films.

We have investigated the magnetic spin structure of a soft-magnetic film that is exchange-coupled to a hard-magnetic layer to form an exchange-spring layer system. The depth dependence of the magnetization direction was determined by nuclear resonant scattering of synchrotron radiation from ultrathin 57Fe probe layers. In an external field a magnetic spiral structure forms that can be described within a one-dimensional micromagnetical model. The experimental method allows one to image vertical spin structures in stratified media with unprecedented accuracy.

Observation of the 22.5-keV resonance in (149)Sm by the nuclear lighthouse effect.

We have observed coherent nuclear resonant scattering of synchrotron radiation at the 22.5-keV resonance of (149)Sm. High-speed rotational sample motion led to an angular deflection of the resonantly scattered radiation off the nonresonant primary beam. This allowed us to determine the resonance energy of the first excited nuclear level of (149)Sm to be 22496(4) eV. Because of the angular deflection of the resonant photons, time spectra of coherent nuclear resonant scattering can be recorded as a function of a spatial coordinate. Time resolutions of a few 10 ps can be expected, which are beyond the limits of existing x-ray detection schemes.

Perpendicular spin orientation in ultrasmall Fe islands on W(110).

We have studied the magnetism of Ag-coated Fe islands on W(110) by nuclear resonant scattering of synchrotron radiation at the 14.4 keV resonance of (57)Fe. Separated islands with an average diameter of 2.0 nm and monolayer thickness are formed at a Fe coverage of theta = 0.57 bulk monolayers. Time spectra of the nuclear decay were measured in the temperature range from 4.5 to 300 K. We find strong evidence for perpendicular spin orientation, which most likely results from the interplay of shape anisotropy and elastic strain in the islands.

Coherent resonant x-ray scattering from a rotating medium.

A coherently excited nuclear state in a rotating sample acquires a phase shift during its time evolution that is proportional to its angular momentum and the rotation angle. As a consequence, the radiative decay of the excited state proceeds into the rotated direction, and the time spectrum of the nuclear decay is mapped onto an angular scale. This effect has been observed in nuclear resonant scattering of synchrotron radiation from a 57Fe metal foil rotating at 18 kHz.

First observation of inelastic X-ray scattering from condensed (4)He using high energy resolution.

Recently, the suitability of inelastic X-ray scattering for the investigation of solid and fluid (4)He has been demonstrated. For the test experiments an energy resolution of the order of 10-15 meV was used at the backscattering spectrometer INELAX at the storage ring DORIS of DESY, Hamburg. Lattice excitations were observed for momentum transfers along the c axis of h.c.p. helium crystals which were grown in situ at pressures of 54-63 MPa and at temperatures of 4.2-6.4 K. At 10 K above the melting point, energy-loss signals could also be detected from the liquid helium at equivalent momentum transfers.

Myocardial infarction and the weather: a significant positive correlation between the onset of heart infarct and 28 KHz atmospherics--a pilot study.

The date of occurrence of a heart infarct was tabulated for 162 patients admitted to four Munich clinics with cardiology departments from January 1 to July 31, 1981. This occurrence calendar was correlated with the daily average density of 28 KHz and 10 KHz atmospheric (atm) impulses and several classic weather parameters. The occurrence of heart infarcts has a certain positive correlation with the increased appearance of "pure" 28 KHz impulses, the correlation with 10 KHz impulses is very slight. Among the classic weather parameters, the average daily humidity has the highest negative correlation coefficient.