Are Diamond Surface Coatings Immune to Dry Running?

It is well understood that mechanical seal performance is dependent upon the tribology of the seal face materials. Published material is available claiming the advantages of Polycrystalline Diamond (PCD) and its suitability for extended running under dry conditions; indeed, one such claim suggests that PCD coated faces are immune to dry running. In order to investigate this claim, the author undertook a series of rigorously controlled tests to evaluate the performance of mechanical seal faces coated with a Polycrystalline Diamond coating (PCD) against others with Diamond - Like Carbon (DLC) coatings. Seal surface topography was accurately measured before and after testing and was used to evaluate the wear behaviour. From the test results obtained it is concluded that neither coatings are suitable for extended dry running use. However, it was evident that seal faces coated with a new form of DLC identified as, Plasma Assisted - Chemical Vapour Deposition (PA-CVD) performed 18 times longer than the PCD coated ones before reaching a predetermined friction induced temperature. Publications can be cited as evidence that PCD coated seal faces are capable of producing very high frictional temperatures that could, in a dry running situation, allow certain liquid fuels such as flashing hydrocarbons to reach their auto-ignition temperatures. In addition, it was revealed that the PCD coated seal units are being sold at a higher cost than the equivalent DLC coated ones by a factor of three

Extraction of frequency-dependent electrical characteristics of biological tissues using ultra-wideband electromagnetic pulse

There have been many important contributions to imaging for biomedical applications. The most popular methods include X-ray mammography, magnetic resonance imaging (MRI), ultrasound, and most recently, microwave imaging. While the first three of these have been used for biomedical applications for over three decades, microwave imaging has seen many developments over the last few years. This is primarily due to the large contrast in electrical parameters between different body tissues (including differences between healthy and diseased tissues) at microwave frequencies. There are also vast improvements possible for the comfort of the patient undergoing such imaging as compared to mammography. However, there has been no relevant work to date on extraction of the electrical characteristics of tissues within a living patient. Rather, all of the work in the field of microwave imaging has focused on utilizing the vast contrast in electrical parameters to create an image of internal body structures. The electrical properties of human body tissues can be considered as non-magnetic, lossy, frequency-dependent dielectrics in the general case. All that is needed to fully describe these tissues is the frequency-dependent complex relative permittivity. The present work focuses on a unique application of Ultra-Wideband (UWB) radar to extract the frequency-dependent electrical properties of tissues modeled as multiple layers of dielectric regions. By applying an incident pulse to this series of dielectric regions, and by analyzing the reflected signals, the electrical characteristics can be extracted. The results can be expressed in terms of frequency-dependent relative permittivity and conductivity. This work focuses on the time-domain processing to determine the thickness of dielectric regions. Also, a calibration method is proposed to remove interference from the outer dielectric region. Finally, a generalized methodology is proposed to extract the electrical parameters of multiple dielectric regions in the frequency-domain. In all cases, excellent agreement is found between extracted and expected results

7-Tetrahydrobiopterin is an uncoupled cofactor for rat hepatic phenylalanine hydroxylase

AbstractRat hepatic phenylalanine hydroxylase requires both a tetrahydropterin cofactor and molecular oxygen to convert phenylalanine to tyrosine. During the physiological hydroxylation, a single mol of the natural cofactor, tetrahydrobiopterin, is oxidized for each mol of phenylalanine converted to tyrosine. Artificial conditions have been devised in which the oxidation of the tetrahydropterin is uncoupled from the hydroxylation of the aromatic amino acid substrate. Recently, an isomer of tetrahydrobiopterin, 7-tetrahydrobiopterin, has been isolated from the urine of certain mildly hyperphenylalaninemic children. We report in this communication that 7-tetrahydrobiopterin may be an inefficient cofactor for phenylalanine hydroxylase because, in vitro, the phenylalanine-dependent oxidation of 7-tetrahydrobiopterin is accompanied by the hydroxylation of the aromatic amino acid substrate only about 15% of the time, i.e. the enzymatic oxidation of 7-tetrahydrobiopterin is about 85% uncoupled from the hydroxylation of the amino acid substrate

Maximum versus Meaningful Discrimination in Scale Response: Implications for Validity of Measurement of Consumer Perceptions about Products

This paper argues for the use of the number of response categories that are meaningful to respondents as a criterion in designing attribute rating scales in marketing in contrast to a focus in past research on using scales to maximize the discrimination elicited from respondents. Whereas scales eliciting a maximum level of discrimination may be more reliable than scales eliciting a meaningful level of discrimination, the latter are argued to be more valid in measuring sameness and difference between brands that are meaningful to respondents. Specifically, a distinction is drawn in this paper between the maximum number of categories that consumers can discriminate between and the number of categories that are meaningful to them. The meaningful number of categories refers to the number of categories that individuals typically use in thinking about an attribute in such situations as making a choice or judgment. Thus, the unique perspective of consumer behavior with its central focus on phenomena such as product judgment and choice is incorporated into the measurement of consumers\u27 perceptions about attributes. Several studies were conducted to test hypotheses generated on the basis of the notion of the meaningful number of categories. The first study used an open-ended method (i.e., a sorting task) to measure the number of categories that are meaningful to consumers for specific attributes. Using the results of the first study as a basis, two studies demonstrated the effect of the meaningful number of categories for an attribute on scale response such that fewer scale points were used to rate products on attributes with fewer meaningful numbers of categories. Another study showed that a scale with the meaningful number of categories might be more accurate than other scales in predicting sameness and difference between brands that are meaningful to consumers. The significance of using scales with a meaningful number of categories is in validly measuring differences between products that are meaningful to consumers

Subclasses of Presburger Arithmetic and the Weak EXP Hierarchy

It is shown that for any fixed $i>0$, the $\Sigma_{i+1}$-fragment of Presburger arithmetic, i.e., its restriction to $i+1$ quantifier alternations beginning with an existential quantifier, is complete for $\mathsf{\Sigma}^{\mathsf{EXP}}_{i}$, the $i$-th level of the weak EXP hierarchy, an analogue to the polynomial-time hierarchy residing between $\mathsf{NEXP}$ and $\mathsf{EXPSPACE}$. This result completes the computational complexity landscape for Presburger arithmetic, a line of research which dates back to the seminal work by Fischer & Rabin in 1974. Moreover, we apply some of the techniques developed in the proof of the lower bound in order to establish bounds on sets of naturals definable in the $\Sigma_1$-fragment of Presburger arithmetic: given a $\Sigma_1$-formula $\Phi(x)$, it is shown that the set of non-negative solutions is an ultimately periodic set whose period is at most doubly-exponential and that this bound is tight.Comment: 10 pages, 2 figure

Transient Mathematical Modeling for Liquid Rocket Engine Systems: Methods, Capabilities, and Experience

The subject of mathematical modeling of the transient operation of liquid rocket engines is presented in overview form from the perspective of engineers working at the NASA Marshall Space Flight Center. The necessity of creating and utilizing accurate mathematical models as part of liquid rocket engine development process has become well established and is likely to increase in importance in the future. The issues of design considerations for transient operation, development testing, and failure scenario simulation are discussed. An overview of the derivation of the basic governing equations is presented along with a discussion of computational and numerical issues associated with the implementation of these equations in computer codes. Also, work in the field of generating usable fluid property tables is presented along with an overview of efforts to be undertaken in the future to improve the tools use for the mathematical modeling process

Multiresolution Analysis of Substructure in Dark Matter Halos

Multiresolution analysis is applied to the problem of halo identification in cosmological N-body simulations. The procedure makes use of a discrete wavelet transform known as the algorithme a trous and segmentation analysis. It has the ability to find subhalos in the dense regions of a parent halo and can discern the multiple levels of substructure expected in the hierarchical clustering scenario. As an illustration, a 500,000 particle dark matter halo is analyzed and over 600 subhalos are found. Statistical properties of the subhalo population are discussed.Comment: 22 pages, 12 figures, substantial changes and additions over original submission, to be published in the Astrophysical Journal, Oct, 200

Short-range ordering in a battery electrode, the 'cation-disordered' rocksalt Li1.25Nb0.25Mn0.5O2.

Cation order, with a local structure related to γ-LiFeO2, is observed in the nominally cation-disordered Li-excess rocksalt Li1.25Nb0.25Mn0.5O2via X-ray diffraction, neutron pair distribution function analysis, magnetic susceptibility and NMR spectroscopy. The correlation length of ordering depends on synthesis conditions and has implications for the electrochemistry of these phases.EPSRC: EP/L015978/1 Basic Energy Science, US Department of Energy: DE-SC001258

Structural origins of voltage mysteresis in the Na-Ion cathode P2-Na0.67[Mg0.28Mn0.72]O2 : A combined spectroscopic and density functional theory study

Funding Information: E.N.B. acknowledges funding from the Engineering Physical Sciences Research Council (EPSRC) via the National Productivity Interest Fund (NPIF) 2018 and is also grateful for use of the ARCHER UK National Supercomputing Service via our membership in the UK’s HEC Materials Chemistry Consortium, funded by the EPSRC (EP/L000202). Research was also carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, through the U.S. Department of Energy, Office of Basic Energy Sciences, Contract DE-AC02-98CH10866. P.J.R. thanks the Northeast Centre for Chemical Energy Storage (NECCES), an Energy Frontier Research Centre funded by the US Department of Energy, Office of Basic Energy Sciences, award DE-SC0012583. M.A.J. is grateful for the financial support of the EPSRC Centre for Doctoral Training (CDT) in Nanoscience and Nanotechnology Award EP/L015978/1. J.L. was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (no. 2019R1A6A1A10073437). E.N.B. also wishes to thank Dr M.F. Groh for assistance with setting up capillary XRD measurements. Publisher Copyright: ©Peer reviewedPublisher PD