Hydrogen adsorption studies in micro-size cobalt dots

Hydrogen desorption curves were obtained from a sample composed of a square arrangement of Co dots with average diameter of 4.4 μm, separated by a distance of 11.6 μm. A macroscopic sample of Co dots grown on a 2.5 × 2.5 cm Si substrate was made by standard lithographic techniques and used in these experiments. Thermal programmed desorption (TPD) was performed under ultra-high vacuum conditions. Hydrogen TPD curves were obtained from a 1 × 1 cm Co dots samples displaying a maximum of intensity at 425 K. Hydrogen TPD curve was also obtained from 1 cm× 1 cm samples of Co films and Co foils for comparison. The hydrogen TPD curves have decreasing intensity from the Co foils to the Co dots and finally to the Co films. This indicates that there are more sites for hydrogen adsorption on the Co dots than in the Co films. This is a surprising result because there is approximately 8.7 times less Co atoms exposed in the Co dots that in the Co film sample. A desorption energy of 27 kcal/mol was obtained for the Co dots suggesting that hydrogen is adsorbed on an hcp hollow site of the Co dot crystalline structure.     

The hypersonic environment: Required operating conditions and design challenges

Hypersonic flight powered by airbreathing engines offers the potential for faster response time at long ranges, and reduced cost for access-to-space. In the present paper the operating environment of typical hypersonic vehicles are discussed, including results for the radiation equilibrium wall temperature of external vehicle surfaces and the flow properties through three sample engines spanning the range of hydrocarbon-fueled Mach 4-8 flight and hydrogen-fueled flight at speeds up to Mach 17. Flow conditions at several locations through the sample engines were calculated to provide indications of the required operating flow environment. Additional system consideration such a seals, joints, vehicle integration and in-service engineering are addressed.     

Doped silicon and NIS junctions for bolometer applications

We discuss the performance, of a normal metal hot electron bolometer (NHEB) that we have measured at 0.3 K. We found that the noise equivalent power was limited by the amplifier noise. To improve the NHEB power response and to make it more robust and reliable we propose to substitute the normal metal with heavily doped silicon. The heavily doped silicon behaves like a metal with lower carrier concentration and has a smaller electron–phonon thermal coupling. We have fabricated superconductor-doped silicon-superconductor contacts (S-Sm-S) and we have used them as thermometers and coolers.     

From biological inspiration toward next-generation manipulators: manipulator control focused on human tasks

This paper presents our approach to extend the niche of behavior-based robotics toward manipulation. We use results from neuroscience to derive some qualitative design rules for the mechanics of the manipulator, resulting in a next-generation manipulator, the "soft arm". By defining the basic behaviors of the manipulator as trajectory-producing behaviors (which is also biologically plausible), we have designed a first test case: writing on a board with a mobile manipulator. The soft arm has not yet been developed; therefore, we have emulated such a soft robot arm on an industrial robot.     

Spectrally pure excitation signals: only a dream?

For accurate testing of a nonlinear device-under-test (DUT), the spectral purity of the input signal is utterly important. This paper describes a method to create very pure signals, such as sine waves, dual-tones, or multitones, using only power measurements. The signals are generated with an arbitrary waveform generator. Any unwanted spectral line is removed, independent of its exact origin. This allows to apply the correct signal to the DUT, even if the signal source is not perfect or is followed by filters or amplifiers with a small nonlinear distortion. Measurements are used to demonstrate the capabilities of the method.     

Stability studies on methyl and ethyl fatty acid esters of sunflowerseed oil

Fatty acid esters, high in linoleic acid, were prepared and stored for long-term engine tests. Storage tests with these esters were undertaken to obtain more information on optimal storage requirements and general stability characteristics. Samples were kept at three temperature levels (20 C, 30 C and fluctuating around 50 C) for a 90-day period and were removed at regular intervals for chemical and physical analysis. The influence of air, temperature, light, TBHQ and contact with mild steel was evaluated by comparing the free fatty acid, peroxide, anisidine, ultraviolet absorption, viscosity and induction periods. A statistical model was used to evaluate the data and to reduce the large number of data points to comparable curves. Storage of esters in contact with air, especially at a temperature above 30 C, resulted in significant increases in peroxide, ultraviolet absorption, free fatty acid, viscosity and anisidine values. Exclusion of air retarded oxidation at all temperature levels. A direct relationship between viscosity increases and oxidation parameters was evident. Exposure to light caused a small increase in the oxidation parameters of esters stored at the highest temperature level. Addition of TBHQ prevented oxidation of samples stored under moderate conditions. Under unfavorable storage conditions the anti-oxidant was no longer effective. Mild steel had very little effect on the oxidation parameters. Only the anisidine values of samples stored at the highest temperature level were slightly increased. Methyl esters performed slightly better than ethyl esters during the storage test. The following practical guidelines for storage of fatty acid ester fuels are: (i) airtight containers should be used; (ii) the storage temperature should be <30 C; (iii) mild steel (rust free) containers may be used, and (iv) TBHQ has a beneficial effect on oxidation stability.     

Expansion in bioreactors of human progenitor populations from cord blood and mobilized peripheral blood

Umbilical cord blood (UCB) and mobilized peripheral blood (MPB) provide an alternate source to bone marrow for transplantation. Expansion in vitro of stem/progenitor cell populations from these sources may provide adult-sized grafts otherwise not attainable because of the limited cell numbers available in the case of UCB or because of numerous rounds of apheresis required for sufficient MPB cells. We asked whether continuous perfusion culture could be employed in ex vivo expansion to produce clinically relevant numbers of stem/progenitor cells from these sources. To evaluate MPB, 1-10 million leukocytes, from patients who had received either granulocyte colony-stimulating factor (G-CSF) or cyclophosphamide and granulocyte-macrophage colony-stimulating factor (GM-CSF), were inoculated into bioreactors, with or without irradiated, allogeneic stroma. The growth factor combination in the perfusion medium consisted of interleukin-3 (IL-3), stem cell factor (SCF), GM-CSF and erythropoietin (Epo). Under the best conditions tested, total cell numbers, granulocyte-macrophage colony-forming units (CFU-GM), and long-term culture-initiating cell (LTC-IC) populations were expanded by about 50-, 80-, and 20-fold, respectively, over 14 days. At low cell inocula (1 million), the presence of stroma enhanced the expansion of total cells and CFU-GM but not of LTC-IC. When SCF was not included in the medium, both total cells and CFU-GM expanded to a much lesser extent, but again the expansion of LTC-IC was not affected. At the higher cell inoculum (10 million), expansions of total cells and CFU-GM were equivalent with or without stroma. To evaluate UCB, cells were placed into bioreactors with or without irradiated, allogeneic stroma, and the bioreactors were perfused with medium containing the four standard growth factors. After 6-14 days, in several independent experiments, 20-24 million cells were harvested from bioreactors perfused with SCF-containing medium, irrespective of the presence or absence of preformed stroma. Similarly, in reactors perfused with SCF-containing medium (with or without stroma), an average 40- to 60-fold expansion of CFU-GM was obtained, yielding an average of 1.5-1.8 x 10(5) CFU-GM per reactor. Harvested cells were thus up to 40-fold enriched in CFU-GM in comparison to the inoculum. In the absence of SCF, cell expansions averaged 1.5- to 2-fold, and CFU-GM were expanded only 10- to 14-fold by day 14. As before, the presence of preformed stroma did not affect either cell or CFU-GM yields, provided the cell inoculum was at least 4.5 million cells.(ABSTRACT TRUNCATED AT 400 WORDS)