Turbulence is investigated in the lee of an open-cell metal foam layer. In contrast to canonical grids, metal foams are locally irregular but statistically isotropic. The solid matrix is ...characterised by two lengths, the ligament thickness $d_f$ and the pore diameter $d_p$. A direct numerical simulation is conducted on a realistic metal foam geometry for which $d_f/d_p = 0.14$ and the porous layer thickness is five times the pore diameter. The Reynolds number based on the pore size is ${\textit {Re}}_{d_p} = 4000$, corresponding to a Taylor-scale Reynolds number ${\textit {Re}}_\lambda \approx 80$. Closer to the foam than two pore diameters, the pressure and turbulent transports of turbulent kinetic energy are non-negligible. In the same region, ${\textit {Re}}_\lambda$ undergoes a steep decrease whereas the dissipation coefficient $C_{\epsilon }$ increases like ${\textit {Re}}_\lambda ^{-1}$. At larger distances from the porous layer, the classical grid turbulence situation is recovered, where the mean advection of turbulent kinetic energy equals dissipation. This entails a power-law decay of turbulent quantities and characteristic lengths. The decaying exponents of integral, Taylor and Kolmogorov scales are close to one-half, indicating that the turbulence simulated here differs from Saffman turbulence. Analysis of the scaling exponents of structure functions and the decorrelation length of dissipation reveals that small-scale fluctuations are weakly intermittent.
NASA is a critical information source in this Age of Information. With the advent and maturity of the Internet, the demand for NASA information has grown beyond science data archives to near real ...time and even real time data, particularly on the Earth and near Earth ecosystems. NASA also has prospered a policy of sharing mission responsibility with non-NASA entities, which still require tracking support from the NASA network. This paper discusses the issues in conflict when trying to solve the paradox of securing a critical national resource and participating as a good citizen of the Information Age. By illustrating several ground network architecture examples, these issues are highlighted. Recommendations for using the NASA tracking networks are given.
International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California
The NASA Communications (Nascom) Division has been ...directed to deploy Internet Protocol (IP) based technology for the ground segments of all present and future spaceflight telemetry networks. The Nascom network supports all NASA spaceflight telemetry, command and status requirements, from sounding rockets and balloons to the Hubble Space Telescope and the Space Shuttle. This paper discusses the challenges of transitioning a 35 year old, custom engineered, worldwide legacy telemetry network to IP, and the resulting, new NASA IP Operational Network for ground transport of spacecraft telemetry and command.
TINA and the Internet: an evaluation of some scenarios Licciardi, C.A.; Minerva, R.; Moiso, C. ...
Proceedings TINA '97 - Global Convergence of Telecommunications and Distributed Object Computing,
1997
Conference Proceeding
The paper is an attempt to analyze the applicability of TINA in an Internet context considering the usefulness and the need of TINA solutions from a business point of view and not in its ...applicability "per se". For this reason some applicability scenarios have been chosen. They describe the applicability in a general framework more than describing the technicalities. The results are that TINA should pay more attention to the developments of the Internet in terms of protocols, APIs and products so that it could be a useful "component based architecture" for building servers and services over the Internet.
Ultrasonic backscatter techniques are being developed to diagnose osteoporosis. Tissues that lie between the transducer and the ultrasonically interrogated region of bone may produce errors in ...backscatter measurements. The goal of this study is to investigate the effects of intervening tissues on ultrasonic backscatter measurements of bone. Measurements were performed on 24 cube shaped specimens of human cancellous bone using a 5 MHz transducer. Measurements were repeated after adding a 1 mm thick plate of cortical bone to simulate the bone cortex and a 3 cm thick phantom to simulate soft tissue at the hip. Signals were analyzed to determine three apparent backscatter parameters (apparent integrated backscatter, frequency slope of apparent backscatter, and frequency intercept of apparent backscatter) and three backscatter difference parameters normalized mean backscatter difference (nMBD), normalized slope of the backscatter difference, and normalized intercept of the backscatter difference. The apparent backscatter parameters were impacted significantly by the presence of intervening tissues. In contrast, the backscatter difference parameters were not affected by intervening tissues. However, only one backscatter difference parameter, nMBD, demonstrated a strong correlation with bone mineral density. Thus, among the six parameters tested, nMBD may be the best choice for in vivo backscatter measurements of bone when intervening tissues are present.
The densification of undoped zirconia nanopowder was performed using the High-Pressure Field Assisted Sintering technique, with the aim of preparing bulk size-stabilized tetragonal zirconia. The role ...played by the structural and microstructural properties of the starting powders on the characteristics of the sintered materials was investigated by exploring several different synthetic routes. Nanopowders prepared by solvothermal methods were proven to give the most satisfactory results thanks to their microstructure, particularly characterized by uniform spherical microaggregates. Using solvothermally synthesized powder as a starting material, nearly fully dense (97% relative density) samples of undoped size-stabilized tetragonal zirconia were obtained with a sintering cycle of 5
min under a uniaxial pressure of 700
MPa, at sintering temperatures as low as 900
°C.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Second harmonic generation properties have been studied in 23
K
2O
·
27Nb
2O
5
·
50 SiO
2 glass subjected to thermal poling. The poling-induced optical nonlinearity, with
χ
(2)
=
3.8
pm/V, has been ...related to structural modifications within a surface layer of a few microns on the anode side, as evidenced by means of confocal micro-Raman mapping along the sample thickness. The data indicate that the structural changes result from a charge transport process that causes network modifications in an alkali depleted layer whose thickness is comparable with that of the non-linear region. The Raman data also indicate that in the alkali depleted layer the network polymerization degree increases as a consequence of ion migration. The origin of the nonlinearity and the mechanisms activated by poling are discussed. The mechanism of non-bridging-oxygen to bridging-oxygen bond switching is proposed to explain ion migration and the subsequent structural changes in the glass.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The radioluminescence (RL) properties of Ce-doped silica glasses prepared by sol−gel method were investigated as a function of the dopant amount in a wide range of concentrations (Ce:Si molar ratios ...from 1 × 10-5 to 5 × 10-2). The effects of xerogel densification temperature and of a postdensification thermal treatment were also considered. In order to understand the microstructural features governing Ce3+ luminescence efficiency, optical absorption measurements in the ultraviolet, visible, and infrared regions and time-resolved photoluminescence experiments were performed. The complex dependence of RL intensity upon rare-earth (RE) concentration and thermal treatment was attributed to the role of OH vibrations as nonradiative recombination channels, as well as to the formation of RE aggregates in the silica matrix. Specifically, the segregation of CeO2 nanoparticles, in which Ce4+ does not supply any radiative emission, has been revealed by infrared absorption measurements, in agreement with previous Raman, transmission electron microscopy, and X-ray diffraction data. Moreover, an optical absorption band, centered at 2.4 eV and whose intensity increases with the square of cerium concentration, was observed and tentatively assigned to an intervalence electron-transfer transition involving Ce3+−Ce4+ dimers. Postdensification thermal treatments markedly reduce the intensity of this band and increase RL intensity. The relationship between the 2.4 eV band and the RL properties will be outlined. In particular, the increase in RL intensity will be discussed, mainly as a consequence of microscopic modifications leading to an improvement of the charge-transfer efficiency toward emitting centers.
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IJS, KILJ, NUK, PNG, UL, UM
The synthesis of Ni/YSZ cermet with controlled microstructural characteristics presents a lot of interest for many solid-state electrochemical applications. These materials are generally obtained by ...reducing poorly sintered mixtures of YSZ with nickel oxide by hydrogen. We recently proposed an alternative route based on a thermite reaction performed in a combustion regime. This method makes it possible, in one step, to synthesize highly porous cermet, to sinter the ceramic fraction, and to dope it with yttria. Such an approach represents an application of combustion synthesis or the self-propagating high-temperature synthesis (SHS) technique. We present here electrical characteristics of Ni/YSZ cermets produced by this method. The total electronic conductivity shows an unusually smooth percolation threshold. This fact makes it possible to obtain a fairly high electronic conductivity even at relatively low metal volume fractions. The ceramic fraction shows an excellent degree of sintering and an ionic conductivity not too different from the conductivity of YSZ single crystals with the same composition.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The phosphoprotein p53 is involved in transcriptional regulation and is detected in hematologic malignancies. In vitro incubation of acute myelogenous leukemia with OL(1)p53, a 20-mer ...phosphorothioate oligonucleotide complementary to p53 mRNA, results in leukemic cell death. A phase I dose-escalating trial was conducted to determine the toxicity of OL(1)p53 following systemic administration to patients with hematologic malignancies.
Sixteen patients with either refractory acute myelogenous leukemia (n = 6) or advanced myelodysplastic syndrome (n = 10) participated in the trial. Patients were given OL(1)p53 at doses of 0.05 to 0.25 mg/kg/h for 10 days by continuous intravenous infusion.
No specific toxicity was directly related to the administration of OL(1)p53. One patient developed transient nonoliguric renal failure. One patient died of anthracycline-induced cardiac failure. Approximately 36% of the administered dose of OL(1)p53 was recovered intact in the urine. Plasma concentrations and area under the plasma concentration curves were linearly correlated with dose. Leukemic cell growth in vitro was inhibited as compared with pretreatment samples. There were no clinical complete responses.
A phosphorothioate oligonucleotide, OL(1)p53, can be administered systemically without complications. This type of modified oligonucleotide can be administered without complete degradation, as it was recovered from the urine intact. This oligonucleotide may be useful in combination with currently available chemotherapy agents for the treatment of malignancies.
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