F-15 flight flutter test program

The modes to be observed during the F-15 flight flutter test program were selected on the basis of the results of analytical studies, wind tunnel tests, and ground vibration tests. The modes (both symmetrical and antisymmetrical) tracked on this basis were: fin first bending, fin torsion, fin tip roll, stabilator bending, stabilator pitch, boom lateral bending, boom torsion, boom vertical bending, wing first bending, wing second bending, wing first torsion, outer wing torsion, and aileron rotation. Data obtained for these various modes were evaluated in terms of damping versus airspeed at 1525 m (5000 ft), damping versus altitude at the cross-section Mach numbers (to extrapolate to the damping value to be expected at sea level), and flutter boundaries on the basis of flutter margin of various modal pairs representing potential flutter mechanisms. Results of these evaluations are summarized in terms of minimum predicted flutter margin for the various mechanisms

Soft deformable self-propelled particles

In this work we investigate the collective behavior of self-propelled particles that deform due to local pairwise interactions. We demonstrate that this deformation alone can induce alignment of the velocity vectors. The onset of collective motion is analyzed. Applying a Gaussian-core repulsion between the particles, we find a transition to disordered non-collective motion under compression. We here explain that this reflects the reentrant fluid behavior of the general Gaussian-core model now applied to a self-propelled system. Truncating the Gaussian potential can lead to cluster crystallization or more disordered cluster states. For intermediate values of the Gaussian-core potential we for the first time observe laning for deformable self-propelled particles. Finally, without the core potential, but including orientational noise, we connect our description to the Vicsek approach for self-propelled particles with nematic alignment interactions.Comment: 6 pages, 7 figure

Constraining the CKM Parameters using CP Violation in semi-leptonic B Decays

We discuss the usefulness of the CP violating semi-leptonic asymmetry a_{SL} not only as a signal of new physics, but also as a tool in constraining the CKM parameters. We show that this technique could yield useful results in the first years of running at the B factories. We present the analysis graphically in terms of M_{12}, the dispersive part of the B-Bbar mixing amplitude. This is complementary to the usual unitarity triangle representation and often allows a cleaner interpretation of the data.Comment: 15 pages REVTEX, 7 figure

A consistent picture for large penguins in D -> pi+ pi-, K+ K-

A long-standing puzzle in charm physics is the large difference between the D0 -> K+ K- and D0 -> pi+ pi- decay rates. Recently, the LHCb and CDF collaborations reported a surprisingly large difference between the direct CP asymmetries, Delta A_CP, in these two modes. We show that the two puzzles are naturally related in the Standard Model via s- and d-quark "penguin contractions". Their sum gives rise to Delta A_CP, while their difference contributes to the two branching ratios with opposite sign. Assuming nominal SU(3) breaking, a U-spin fit to the D0 -> K+ pi-, pi+ K-, pi+ pi-, K+ K- decay rates yields large penguin contractions that naturally explain Delta A_CP. Expectations for the individual CP asymmetries are also discussed.Comment: 24 pages, 8 figure

Towards granular hydrodynamics in two-dimensions

We study steady-state properties of inelastic gases in two-dimensions in the presence of an energy source. We generalize previous hydrodynamic treatments to situations where high and low density regions coexist. The theoretical predictions compare well with numerical simulations in the nearly elastic limit. It is also seen that the system can achieve a nonequilibrium steady-state with asymmetric velocity distributions, and we discuss the conditions under which such situations occur.Comment: 8 pages, 9 figures, revtex, references added, also available from http://arnold.uchicago.edu/?ebn

Velocity correlations in granular materials

A system of inelastic hard disks in a thin pipe capped by hot walls is studied with the aim of investigating velocity correlations between particles. Two effects lead to such correlations: inelastic collisions help to build localized correlations, while momentum conservation and diffusion produce long ranged correlations. In the quasi-elastic limit, the velocity correlation is weak, but it is still important since it is of the same order as the deviation from uniformity. For system with stronger inelasticity, the pipe contains a clump of particles in highly correlated motion. A theory with empirical parameters is developed. This theory is composed of equations similar to the usual hydrodynamic laws of conservation of particles, energy, and momentum. Numerical results show that the theory describes the dynamics satisfactorily in the quasi-elastic limit, however only qualitatively for stronger inelasticity.Comment: 12 pages (REVTeX), 15 figures (Postscript). submitted to Phys. Rev.

Organization of Multinational Activities and Ownership Structure

We develop a model in which multinational investors decide about the modes of organization, the locations of production, and the markets to be served. Foreign investments are driven by market-seeking and cost-reducing motives. We further assume that investors face costs of control that vary among sectors and increase in distance. The results show that (i) production intensive sectors are more likely to operate a foreign business independent of the investment motive, (ii) that distance may have a non-monotonous effect on the likelihood of horizontal investments, and (iii) that globalization, if understood as reducing distance, leads to more integration

Quantitative Relative Comparison of CFD Simulation Uncertainties for a Transonic Diffuser Problem

Different sources of uncertainty in CFD simulations are illustrated by a detailed study of two-dimensional, turbulent, transonic flow in a converging-diverging channel. Runs were performed with the commercial CFD code GASP using different turbulence models, grid levels, and flux-limiters to see the effect of each on the CFD simulation uncertainties. Two flow conditions were studied by changing the exit pressure ratio: the first is a complex case with a strong shock and a separated flow region, the second is the weak shock case with no separation. The uncertainty in CFD simulations has been studied in terms of four contributions: (1) discretization error, (2) error in geometry representation, (3) turbulence model, and (4) the downstream boundary condition. In this paper, we have quantified the relative contribution and the importance of each source of uncertainty and shown the level of scatter in results that a well informed CFD user may obtain in a typical design activity. The nozzle efficiency results obtained in this study showed that the range of variation for the strong shock case was much larger than that observed in the weak shock case. The discretization errors were up to 6% and the relative uncertainty originating from the selection of different turbulence models was as large as 9% for the strong shock case. Furthermore, the results demonstrated that grid convergence is not achieved with grid levels that have moderate mesh sizes and showed that highly refined grids are required to obtain solutions with an acceptable level of accuracy in design problems that involve simulations of complex flow fields. The results illustrated the interaction of different sources of uncertainty and showed that the magnitudes of numerical errors are influenced by the physical models used

Piericiden A Sensitivity, Site 1 Phosphorylation, and Reduced Nicotinamide Adenine Dinucleotide Dehydrogenase during Iron-limited Growth of Candida utilis

It has been reported that cells of Candida utilis, grown in continuous culture under iron-limited conditions, develop site 1 phosphorylation, without the appearance of piericidin sensitivity and without changes in the iron-sulfur centers of NADH dehydrogenase, on aeration in the presence of cycloheximide, as well as on increasing the supply of iron during growth. These findings were reinvestigated in the present study. The parameters and properties followed during these transitions were sensitivity of NADH oxidation to piericidin, presence or absence of coupling site 1, EPR signals appearing on reduction with NADH or dithionite, the specific activities of NADH oxidase, NADH-ferricyanide reductase, and NADH-5-hydroxy-1,4-naphthoquinone (juglone) reductase, and the kinetic behavior of NADH dehydrogenase in the ferricyanide assay. Monitoring the rates of oxidation of NADH in submitochondrial particles with artificial oxidants, observing the kinetics of the ferricyanide assay, and measuring the concentration of iron-sulfur centers elicited by EPR permitted ascertaining the type of NADH dehydrogenase present and its relative concentration in different experimental situations. It was found that on gradually increasing the concentration of iron during continuous culture (transition from ironlimited to iron- and substrate-limited growth), as well as on aeration of iron-limited cells, coupling site 1, piericidin sensitivity, NADH-ferricyanide activity, and iron-sulfur centers 1 and 2 increased concurrently, with concomitant decline of NADH-juglone reductase activity. Cycloheximide prevented all these changes. Iron-sulfur centers 3 plus 4 underwent relatively little increase during these transitions. It is concluded that in both of these experimental conditions a replacement of the type of NADH dehydrogenase present in exponential phase cells by that characteristic of stationary phase cells occurs and that the appearance of site 1 phosphorylation, piercidin sensitivity, and iron-sulfur centers 1 plus 2, all associated with the latter enzyme, is a consequence of this replacement. No evidence was found for the development of coupling site 1 without the appearance of piericidin sensir t

Reduced Nicotinamide Adenine Dinucleotide Dehydrogenase, Piericidin Sensitivity, and Site 1 Phosphorylation in Different Growth Phases of Candida utilis

Reports in the literature indicate that during the exponential phase of growth of Candida utilis NADH oxidation is insensitive to rotenone, that rotenone sensitivity is acquired during the transition to the late stationary phase and is again lost on catabolite repression. The acquisition and loss of rotenone sensitivity appears to be accompanied by similar changes in Site 1 phosphorylation but does not appear to be reflected in the rate of oxidation of NADH (by mitochondria) or of NAD-linked substrates (by mitochondria or whole cells). In the present paper evidence is presented that these fluctuations in sensitivity to inhibitors of NADH oxidation reflect the presence of different types of inner membrane-bound NADH dehydrogenases in different phases of growth. Thus inner membrane preparations from exponential phase cells contain an NADH dehydrogenase which reacts equally well with ferricyanide and juglone as electron acceptor, appears to be very labile, and lacks EPR signals corresponding to iron-sulfur Centers 1 and 2, whereas a new species, probably an iron-sulfur protein, with resonances at g|| = 2.01, and g⊥ = 1.92 in the reduced state, is present. This species is not significantly reduced by NADH. In corresponding preparations from late stationary phase cells NADH-ferricyanide activity is high, juglone reductase activity is low, and the enzyme is stable and exhibits the EPR signals of iron-sulfur Centers 1 and 2, whereas the EPR signals of iron-sulfur Centers 3 + 4 change very little on transition from exponential to stationary phase cells. There is also a decrease in cytochrome concentration. Most prominent among these is a b-type cytochrome (g = 2.54; 2.23; 1.87) which decreases 2- to 3-fold. The EPR detectable species with g|| = 2.01 and g⊥ = 1.92 in the reduced state is no longer detected. On catabolite repression of late stationary phase cells there is an 80 to 90% decline in NADH-ferricyanide activity, of iron-sulfur Centers 1 and 2, a 50 to 60% decrease of Centers 3 + 4, and an increase in a b cytochrome, but the specific activity in NADH-juglone reductase and NADH oxidase assays increases, the enzyme becomes once again labile, and the EPR detectable species with g|| = 2.01 and g⊥ = 1.92 appears on reduction with dithionite. All these changes are prevented by cycloheximide. The data suggest that sensitivity to piericidin A and coupling to energy conservation Site 1 are properties of the type of NADH dehydrogenase present in late stationary phase cells but not in exponential phase or of catabolite-repressed cells