Small, high-speed bearing technology for cryogenic turbo-pumps

The design of 20-mm bore ball bearings is described for cryogenic turbo-machinery applications, operating up to speeds of 120,000 rpm. A special section is included on the design of hybrid bearings. Each hybrid bearing is composed of a ball bearing in series with a conventional pressurized fluid-film journal bearing. Full details are presented on the design of a test vehicle which possesses the capability of testing the above named bearings within the given speed range under externally applied radial and axial loads

An information-bearing seed for nucleating algorithmic self-assembly

Self-assembly creates natural mineral, chemical, and biological structures of great complexity. Often, the same starting materials have the potential to form an infinite variety of distinct structures; information in a seed molecule can determine which form is grown as well as where and when. These phenomena can be exploited to program the growth of complex supramolecular structures, as demonstrated by the algorithmic self-assembly of DNA tiles. However, the lack of effective seeds has limited the reliability and yield of algorithmic crystals. Here, we present a programmable DNA origami seed that can display up to 32 distinct binding sites and demonstrate the use of seeds to nucleate three types of algorithmic crystals. In the simplest case, the starting materials are a set of tiles that can form crystalline ribbons of any width; the seed directs assembly of a chosen width with >90% yield. Increased structural diversity is obtained by using tiles that copy a binary string from layer to layer; the seed specifies the initial string and triggers growth under near-optimal conditions where the bit copying error rate is 17 kb of sequence information. In sum, this work demonstrates how DNA origami seeds enable the easy, high-yield, low-error-rate growth of algorithmic crystals as a route toward programmable bottom-up fabrication

Breakdown of albumin and haemalbumin by the cysteine protease interpain A, an albuminase of Prevotella intermedia

BACKGROUND: Prevotella intermedia is a Gram-negative black-pigmenting oral anaerobe associated with periodontitis in humans, and has a haem requirement for growth, survival and virulence. It produces an iron porphyrin-containing pigment comprising monomeric iron (III) protoporphyrin IX (Fe(III)PPIX.OH; haematin). The bacterium expresses a 90-kDa cysteine protease termed interpain A (InpA) which both oxidizes and subsequently degrades haemoglobin, releasing haem. However, it is not known whether the enzyme may play a role in degrading other haem-carrying plasma proteins present in the gingival sulcus or periodontal pocket from which to derive haem. This study evaluated the ability of InpA to degrade apo- and haem-complexed albumin. RESULTS: Albumin breakdown was examined over a range of pH and in the presence of reducing agent; conditions which prevail in sub- and supra-gingival plaque. InpA digested haemalbumin more efficiently than apoalbumin, especially under reducing conditions at pH 7.5. Under these conditions InpA was able to substantially degrade the albumin component of whole human plasma. CONCLUSIONS: The data point to InpA as an efficient “albuminase” with the ability to degrade the minor fraction of haem-bound albumin in plasma. InpA may thus contribute significantly to haem acquisition by P. intermedia under conditions of low redox potential and higher pH in the inflamed gingival crevice and diseased periodontal pocket where haem availability is tightly controlled by the host

HmuY Haemophore and Gingipain Proteases Constitute a Unique Syntrophic System of Haem Acquisition by Porphyromonas gingivalis

Haem (iron protoporphyrin IX) is both an essential growth factor and virulence regulator for the periodontal pathogen Porphyromonas gingivalis, which acquires it mainly from haemoglobin via the sequential actions of the R- and K-specific gingipain proteases. The haem-binding lipoprotein haemophore HmuY and its cognate receptor HmuR of P. gingivalis, are responsible for capture and internalisation of haem. This study examined the role of the HmuY in acquisition of haem from haemoglobin and the cooperation between HmuY and gingipain proteases in this process. Using UV-visible spectroscopy and polyacrylamide gel electrophoresis, HmuY was demonstrated to wrest haem from immobilised methaemoglobin and deoxyhaemoglobin. Haem extraction from oxyhaemoglobin was facilitated after oxidation to methaemoglobin by pre-treatment with the P. gingivalis R-gingipain A (HRgpA). HmuY was also capable of scavenging haem from oxyhaemoglobin pre-treated with the K-gingipain (Kgp). This is the first demonstration of a haemophore working in conjunction with proteases to acquire haem from haemoglobin. In addition, HmuY was able to extract haem from methaemalbumin, and could bind haem, either free in solution or from methaemoglobin, even in the presence of serum albumin

Perfect hypermomentum fluid: variational theory and equations of motion

The variational theory of the perfect hypermomentum fluid is developed. The new type of the generalized Frenkel condition is considered. The Lagrangian density of such fluid is stated, and the equations of motion of the fluid and the Weyssenhoff-type evolution equation of the hypermomentum tensor are derived. The expressions of the matter currents of the fluid (the canonical energy-momentum 3-form, the metric stress-energy 4-form and the hypermomentum 3-form) are obtained. The Euler-type hydrodynamic equation of motion of the perfect hypermomentum fluid is derived. It is proved that the motion of the perfect fluid without hypermomentum in a metric-affine space coincides with the motion of this fluid in a Riemann space.Comment: REVTEX, 23 pages, no figure

Constraints on stellar convection from multi-colour photometry of Delta Scuti stars

In Delta Scuti star models, the calculated amplitude ratios and phase differences for multi-colour photometry exhibit a strong dependence on convection. These observables are tools for determination of the spherical harmonic degree of the excited modes. The dependence on convection enters through the complex parameter f, which describes bolometric flux perturbation. We present a method of simultaneous determination of f and spherical harmonic degree from multi-colour data and apply it to three Delta Scuti stars. The method indeed works. Determination of the degree appears unique and the inferred f's are sufficiently accurate to yield a useful constraint on models of stellar convection. Furthermore, the method helps to refine stellar parameters, especially if the identified mode is radial.Comment: 9 pages, 12 figures, to appear in Astronomy and Astrophysic

Bounds for the time to failure of hierarchical systems of fracture

For years limited Monte Carlo simulations have led to the suspicion that the time to failure of hierarchically organized load-transfer models of fracture is non-zero for sets of infinite size. This fact could have a profound significance in engineering practice and also in geophysics. Here, we develop an exact algebraic iterative method to compute the successive time intervals for individual breaking in systems of height $n$ in terms of the information calculated in the previous height $n-1$. As a byproduct of this method, rigorous lower and higher bounds for the time to failure of very large systems are easily obtained. The asymptotic behavior of the resulting lower bound leads to the evidence that the above mentioned suspicion is actually true.Comment: Final version. To appear in Phys. Rev. E, Feb 199

Probabilistic Approach to Time-Dependent Load-Transfer Models of Fracture

A probabilistic method for solving time-dependent load-transfer models of fracture is developed. It is applicable to any rule of load redistribution, i.e, local, hierarchical, etc. In the new method, the fluctuations are generated during the breaking process (annealed randomness) while in the usual method, the random lifetimes are fixed at the beginning (quenched disorder). Both approaches are equivalent.Comment: 13 pages, 4 figures. To appear in Phys.Rev.