The impact of carbon coating on the synthesis and properties of α''-Fe16N2 powders.

This paper presents the preparation of carbon composite Fe16N2 powders, and the influence of a protective carbon coating on the yield and magnetic properties of Fe16N2. Nanoparticle precursors with and without carbon were reacted under ammonia gas flow to produce Fe16N2. Neutron and X-ray powder diffraction indicate that the powders contain typically 40-60% Fe16N2, with the remaining phases being unreacted iron, Fe4N or Fe3N. Transmission electron microscopy demonstrates that the carbon coating is effective at reducing the level of sintering of Fe nanoparticles during the reduction stage prior to ammonolysis. XPS results support the retention of a carbon coating on the surface after ammonolysis, and that there is Fe-C bonding present at the particle surface. In situ TEM was used to observe loss of ordering in the nitrogen sublattice of carbon composite Fe16N2 powders in the range of 168 °C to 200 °C. Magnetic susceptibility measurements show maximum values for saturation magnetization in the range of 232 emu g(-1), and for coercivity near 930 Oe, for different samples measured up to 2 T applied field at 300 K.

Direct photonic coupling of a semiconductor quantum dot and a trapped ion.

Coupling individual quantum systems lies at the heart of building scalable quantum networks. Here, we report the first direct photonic coupling between a semiconductor quantum dot and a trapped ion and we demonstrate that single photons generated by a quantum dot controllably change the internal state of a Yb^{+} ion. We ameliorate the effect of the 60-fold mismatch of the radiative linewidths with coherent photon generation and a high-finesse fiber-based optical cavity enhancing the coupling between the single photon and the ion. The transfer of information presented here via the classical correlations between the σ_{z} projection of the quantum-dot spin and the internal state of the ion provides a promising step towards quantum-state transfer in a hybrid photonic network.

Photon emission and absorption of a single ion coupled to an optical-fiber cavity.

We present a light-matter interface which consists of a single 174Yb+ ion coupled to an optical fiber cavity. We observe that photons at 935 nm are mainly emitted into the cavity mode and that correlations between the polarization of the photon and the spin state of the ion are preserved despite the intrinsic coupling into a single-mode fiber. Complementary, when a faint coherent light field is injected into the cavity mode, we find enhanced and polarization dependent absorption by the ion.

Formation of ultrasharp vertically aligned Cu-Si nanocones by a DC plasma process.

We report an effective method for the production of ultrasharp vertically oriented silicon nanocones with tip radii as small as 5 nm. These silicon nanostructures were shaped by a high-temperature acetylene and ammonia dc plasma reactive ion etch (RIE) process. Thin-film copper deposited onto Si substrates forms a copper silicide (Cu3Si) during plasma processing, which subsequently acts as a seed material masking the single-crystal cones while the exposed silicon areas are reactive ion etched. In this process, the cone angle is sharpened continually as the structure becomes taller. Furthermore, by lithographically defining the seed material as well as employing an etch barrier material such as titanium, the cone location and substrate topography can be controlled effectively.

Regulatory approach toward vaccines against cancer: the benefit/risk ratio.

Decisions regarding investigational new drug applications for testing of all biologicals to be used in humans, including those designed to prevent or treat cancers, must be considered in terms of benefit/risk ratios. In order for a regulatory organization to make the appropriate decision regarding the testing of new biologicals in humans, it must have an extremely broad dialog within the critical scientific public and the general public, which are represented on committees functioning in the Bureau of Biologics. There must be a generaly consensus regarding the benefit/risk ratio of proposed new biologicals for scientific progress and the effective regulation of biologicals.

Antibody persistence after primary immunization with trivalent oral poliovirus vaccine.

Five years after primary infant immunization with trivalent oral poliovirus vaccine, employing either a three-dose primary series as recommended by the U.S. Public Health Service Advisory Committee on Immunization Practices (ACIP) or a four-dose series as recommended by the Committee on Infectious Diseases of the American Academy of Pediatrics. 115 children were serologically tested for persistence of neutralizing antibodies by the microneutralization test. Of the 57 individuals immunized according to the ACIP recommendation, antibody persistence was demonstrated in 92% for type 1 poliovirus, 98% for type 2, and 84% for type 3. Of those 58 individuals originally receiving a four-dose primary infant immunization series, the persistence of antibody was 98% to type 1, 98% to type 2, and 87% to type 3. Twenty-one of 24 negative sera showed neutralizing ability when tested by a more sensitive plaque reduction test. Thus, individuals completing either immunization schedule demonstrated satisfactory persistence of neutralizing antibody to all three poliovirus types over a five-year period.

Evaluation of hepatitis B antigen testing in federally licensed blood banks in the United States.

Between August 1972 and January 1974, the Burear of Biologics distributed four panels of 20 coded serum samples to all federally licensed blood banks for hepatitis B antigen testing. Initially, all but six blood banks reported results by counterelectrophoresis (CEP) only, but by January 1974, 152 of 247 banks reported results by radioimmunoassay (RIA). On the four panels distributed, correct results were reported for 63 to 83% of all potentially detectable samples by CEP and for 98 to 100% of all samples potentially detectable by RIA. Perfect scores were obtained by only 5 to 25% of blood banks using CEP but by 77 to 100% using RIA. Nonreproducible results on duplicate reactive samples, included to evaluate internal consistency, ranged from 0.5 to 25% by CEP and from zero to 5% by RIA. These results demonstrate greater reliability in addition to greater sensitivity of "third generation" RIA testing in comparison with "second generation" CEP testing.

Control of measles and rubella through use of attenuated vaccines.

A summary report of the current status of morbidity and mortality associated with measles and rubella vis á vis immunization practices in the United States since these vaccines were licensed in 1963 (measles) and 1969 (rubella) is presented.

Review of existing vaccines for influenza.

The problems of producing and distributing influenza vaccines are described as well as effectiveness and adverse reactions. It appears that Guillain-Barré (GBS) is likely to be encountered with the use of any of the inactivated influenza vaccines.

Food and Drug Administration responses to the challenges of AIDS.

Rarely has a public health issue emerged that has had impact on so many aspects of the responsibilities of the Food and Drug Administration. In a curious sense, the emergence of AIDS as a national problem has been timely. Only a few years ago, the scientific basis did not exist for performing studies of the immunology and pathogenesis of the syndrome--studies that should be helpful in directing therapeutic and preventive measures. Many of the techniques for studying AIDS and for manufacturing products to treat it involve modern technology. Research and policy actions that FDA has initiated have been designed to ensure as fully as possible the safety and effectiveness of regulated products that are relevant to AIDS and to apply new technology to this important public health problem.

Responses of bone-forming cells on pre-immersed Zr-based bulk metallic glasses: Effects of composition and roughness.

Bulk metallic glasses (BMGs) demonstrate attractive properties for potential biomedical applications, owing to their amorphous structure. The present work has investigated the biocompatibility of Zr-based BMGs by studying the cellular behavior of bone-forming mouse MC3T3-E1 pre-osteoblast cells. A Ti-6Al-4V alloy was used as a reference material. Pre-immersion treatment was performed on BMG samples in phosphate-buffered saline prior to cell experiments. The effects of 1at.% yttrium alloying and surface roughness on cellular behavior were examined. The general biosafety of Zr-based BMGs for MC3T3-E1 cells was revealed as normal cell responses. Pre-immersion treatment was found to effectively reduce the surface concentrations of alloying elements. Micro-alloying with 1 at.% yttrium did not significantly affect cell adhesion and proliferation, but slightly decreased alkaline phosphatase (ALP) activity on rough surfaces. Lower cell adhesion and proliferation were found on smooth surfaces of Zr-based BMGs compared to their rougher counterparts. Higher ALP activity was detected on rougher surfaces. To obtain a mechanistic understanding surface free energy was correlated with cell adhesion.

Creep-resistant, Al2O3-forming austenitic stainless steels.

A family of inexpensive, Al2O3-forming, high-creep strength austenitic stainless steels has been developed. The alloys are based on Fe-20Ni-14Cr-2.5Al weight percent, with strengthening achieved through nanodispersions of NbC. These alloys offer the potential to substantially increase the operating temperatures of structural components and can be used under the aggressive oxidizing conditions encountered in energy-conversion systems. Protective Al2O3 scale formation was achieved with smaller amounts of aluminum in austenitic alloys than previously used, provided that the titanium and vanadium alloying additions frequently used for strengthening were eliminated. The smaller amounts of aluminum permitted stabilization of the austenitic matrix structure and made it possible to obtain excellent creep resistance. Creep-rupture lifetime exceeding 2000 hours at 750 degrees C and 100 megapascals in air, and resistance to oxidation in air with 10% water vapor at 650 degrees and 800 degrees C, were demonstrated.

Experimental secondary electron spectra under SEM conditions.

Secondary electron spectra have been collected from both pure elements and from compounds examined under conditions approximating those found in a scanning electron microscope. Despite the presence of substantial surface contamination these spectra are found to be reproducible and characteristic of the underlying material. Typically the peak in such spectra is found to be at an energy of about 5 eV, and 50% of the total secondary electron emission falls within the range 0-12 eV. These data may be of value for the design of detectors for scanning microscopy and might have applications for microanalysis.