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rss_1.0 Recursos de colección

Caltech Authors (105,723 recursos)
Repository of works by Caltech published authors.

Type = Report or Paper

Mostrando recursos 1 - 20 de 2,865

1. Revisiting the AMBA AHB bus case study - Filippidis, Ioannis; Murray, Richard M.
This report describes a number of changes to the ARM AMBA bus case study from Bloem et al. that lead to significant reduction in synthesis time. In addition, it identifies the reason of blowup for the synthesized strategies in earlier studies as lack of binary decision diagram (BDD) reordering during strategy construction. Enabling dynamic BDD reordering with the group sifting algorithm, we synthesized strategies for as many as 18 masters, with both the original and revised specifications. This conclusion is based on detailed experimental measurements that show the changes of BDD sizes over time for the fixpoint and other variables...

2. A polynomial time algorithm for the ground state of 1D gapped local Hamiltonians - Landau, Zeph; Vazirani, Umesh; Vidick, Thomas
Computing ground states of local Hamiltonians is a fundamental problem in condensed matter physics. We give the first randomized polynomial-time algorithm for finding ground states of gapped one-dimensional Hamiltonians: it outputs an (inverse-polynomial) approximation, expressed as a matrix product state (MPS) of polynomial bond dimension. The algorithm combines many ingredients, including recently discovered structural features of gapped 1D systems, convex programming, insights from classical algorithms for 1D satisfiability, and new techniques for manipulating and bounding the complexity of MPS. Our result provides one of the first major classes of Hamiltonians for which computing ground states is provably tractable despite the...

3. Open Channel Siphon with Viscoelastic Fluids - James, David F.
Viscoelastic fluids show many remarkable phenomena, the best known of which is probably the Weissenberg effect. Because such fluids produce normal stresses in a plane perpendicular to that in which shear takes place, they will climb up a rotating shaft (for example, a stirring rod) immersed in the liquid. A more direct illustration of the elastic properties of the fluid is provided when a rotating flow comes to rest; tracer particles within the flow indicate that the fluid first stops and then flows in the opposite direction for a short duration. An apparently unreported but equally spectacular effect with this...

4. An Experimental Study of Longitudinal Strain Pulse Propagation in Wide Rectangular Bars - Jones, Orval; Ellis, Albert T.
The plane-stress theory presented in Part I is shown to qualitatively predict the warping of plane sections observed in transient fringe patterns obtained using birefringent coatings and in dynamic photoelastic pictures obtained by other investigators. Measurements using conventional techniques are described in which wide rectangular bars were subjected to a longitudinal step-function pressure loading produced by a shock tube. Comparisons show that the gross features of the experimental records for the head of the pulse are qualitatively predicted by the theory. Both theory and experiment show that short-wavelength second mode disturbances arrive very early. Experimentally it is observed that these disturbances...

5. Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion, and its stabilization of rutile TiO_2 - Lan, Tian; Li, C. W.; Hellman, O.; Muñoz, J. A.; Smith, H.; Abernathy, D. L.; Fultz, B.
Although the rutile structure of TiO_2 is stable at high temperatures, the harmonic approximation predicts that several acoustic phonons decrease anomalously to zero frequency with thermal expansion, incorrectly predicting a structural collapse at temperatures well below 1000 K. Inelastic neutron scattering was used to measure the temperature dependence of the phonon density of states (DOS) of rutile TiO_2 from 300 to 1373 K. Surprisingly, these anomalous acoustic phonons were found to increase in frequency with temperature. First-principles calculations showed that with lattice expansion, the potentials for the anomalous acoustic phonons transform from quadratic to quartic, stabilizing the rutile phase at...

6. An Experiment Concerning Partly Closed Cavities Behind a Surface-Piercing Rod - Meijer, M. C.
Thomsen in Ref. (1) emphasizes three different states of ventilation occurring at surface-piercing rods, as observed by Hay (2). Hay has towed cylindrical rods which intersect the water surface, at different speeds and at different depths of submergence. From his photographic records, the following observations have been made. At relatively low speeds, an air filled cavity is formed in the wake of the rod, which is open to atmosphere and which extends downwards to a point above the base of the rod. With increasing speed, this point moves downward towards the base of the rod. This form of cavity has been called the...

7. Water Tunnel Experiments on Spheres in Cavity Flow - Hsu, En-Yun; Perry, Byrne
A program of experimental work on air-supported cavity flow has been in progress in the Free Surface Tunnel for some time now and a considerable amount of data has been taken. Most of this work has been concerned with cones and disks, which have distinct points at which the cavity separates from the nose, but it was thought worthwhile to extend the investigations to include continuously curving noses with shapes such as spheres and ellipsoids. As a start in this direction, a number of tests have been made on spheres with attached cavities. The sphere was selected as a convenient shape because...

8. Water Entry Study of the MK 25 Torpedo with 3.5-Calibre 70-Degree Spherogive Head - Wilcox, G. M.; Waugh, J. G.
This report describes a study conducted jointly by the Hydrodynamics Laboratory of the California Institute of Technology and the Pasadena Annex of the Naval Ordnance Test Station, Inyokern. Air to water launchings were made with a full-size (22.42-in. dia.) dummy Mk 25 aircraft torpedo with a 3-l/2-cal. 70° spherogive nose and with a 2-in. dia. model of the same shape. The purpose of this investigation was to study the problems associated with water entry modeling. Froude scaling was used to determine model entry velocity and the air pressure in the model system was reduced until the cavitation number of the model equaled that...

9. Drag Studies in Water Entry of the MK 13-6 Torpedo - Wilcox, Genevieve M.
An experimental investigation was made of the drag characteristics of a 2-in. diameter model of the standard (Head F) Mk 13-6 torpedo during the cavity phase of the underwater trajectory. The data used in this analysis were available from a previously completed trajectory study. These data were sufficient to determine the instantaneous velocity of the model along its trajectory. Hence, the deceleration and the instantaneous drag coefficient could be determined. The model was dynamically and geometrically similar to the prototype; its entry velocity of 120 fps was scaled from the prototype velocity of 406 fps in accordance with the Froude law. Results from model runs made at nominal atmospheric pressures of 1,...

10. A Preliminary Investigation of the Behavior of Condensable Jets Discharged into Water - Kiceniuk, Taras
Preliminary observations of the behavior of submerged steam nozzles discharging into stationary and moving water are described, and photographs ate presented to show the changes in appearance of the steam jet due to changes in chamber pressure and/or water velocity. The measured static pressure distributions along the longitudinal axis of both a converging nozzle and one of the de Laval type have been plotted showing the contrast between the operation of a steam nozzle discharging into air and that of one submerged in water. A missile running in an air-supported cavity was studied to determine the effect of the discharge of a condensable-jet propulsion...

11. The Effect of Aspect Ratio on the Lift of Flat Planing Surfaces - Perry, Byrne
Previous theories and empirical formulas for the lift of flat planing surfaces are reviewed, and the resemblance of the planing surface to the airfoil noted, A simple expression, which converges to the correct limits for exactly known cases, is assumed for the ratio of planing to airfoil lift, and the planing lift is then estimated by using airfoil experimental data. The resulting calculated values are in satisfactory agreement with planing experiments.

12. An Experimental Study of Axial Flow Pump Cavitation - Guinard, P.; Fuller, T.; Acosta, A. J.
A qualitative study of the effects of cavitation on the performance of an axial flow pump was n1ade. Photographic evidence shows that cavitation need not occur first on the blade surface but could occur in the free stream. This phenomenon is ascribed to a flow through the tip clearance space. Cavitation similarity was found to be determined by the cavitation number K, Thoma's σ, or the suction specific speed S for the conditions of these tests.

13. Dynamic Coefficients of the MK-13 Torpedo - Kiceniuk, Taras
The forces and moments which act on a submerged body undergoing unsteady motion can be described in terms of selected dimensionless constant hydrodynamic coefficients if the instantaneous angles of attack are kept small. To determine the values of these coefficients a model of the body can be supported from the spindle of a dynamic balance (1) in the flowing stream of a water tunnel working section. This procedure was carried out for certain coefficients on a 2-inch diameter model of the Mk-13 torpedo (Fig. 1) using the Angular Dynamic Balance in conjunction with the High Speed Water Tunnel at the California Institute...

14. Forces on a Cylinder Planing in a Vapor Cavity - Kermeen, R. W.
The results of an experimental program carried out in the High Speed Water Tunnel to measure the forces on a cylinder planing on the inside surface of a vapor cavity are pre sen ted. Curves of lift, drag, and pitching moment coefficients and position of the center of pressure of the planing cylinder are given as functions of planing angle and draught. A brief description of the vapor cavity, spray configurations, and cylinder cavitation are included.

15. Report on Design and Construction of the Axial Flow Pump Test Facility - Fuller, T. W.; Acosta, A. J.
In studies concerned with the application of pumps to underwater jet propulsion, it has been pointed out that cavitation may be avoided or suppressed by enclosing the pump (or propeller) in a suitably shaped shroud. The advantages of avoiding cavitation are clear; namely, the elimination of much noise, damage and vibration in addition to increasing the allowable speed. However, a general discussion of the various flow processes which lead to cavitation is not yet possible. For propellers, cavitation is observed in helical trailing vortices and also on the blade surface proper, but for other types of propulsion systems, notably pump jets, neither...

16. Terminal Sinking Velocities for a Series of Flat Nosed Bodies - Waid, R. L.
Drag studies were made on a series of models having varying degrees of bluntness and varying length-to-diameter ratios. Using the drag coefficients obtained from the tests, terminal sinking velocities in sea water were calculated for various volumes and densities. It was found that the terminal sinking velocity of a blunt-nosed body could be increased 15 percent if the length-to-diameter ratio was increased from 7 to 14 for the same volume. The terminal sinking velocity of a fine-nosed body could be increased only 2 percent if the length-to-diameter ratio was increased from 6 to 12.

17. A Scale Model Investigation of the Effect of Jet Configuration on Skin Friction for the MK-40 Torpedo - Waid, R. L.
An analytical study, combining jet diffusion patterns and jet velocities, indicates that there are four methods of eliminating the clinging jet phenomenon which occurs on the Mk-40 Torpedo Test Vehicle. It is shown that extension of the nozzles along the existing nozzle axis appears to present the simplest method of design improvement. Experiments were conducted on a modified model of the Mk-40 to verify the analysis. It was found that for the operational jet-to-model velocity ratio, (U/V) of 2, a nozzle extension of 6 nozzle diameters is the minimum required to provide cling-free performance. All experiments and calculations were made for the case...

18. Resistance Tests on the 5-in. A. S. Projectile and the 6-in. Projector Charge - Kermeen, R. W.
Resistance tests were conducted in the High Speed Water Tunnel on 2-in. diameter models of the 5-in. A. S. Projectile, Ex 30, and the 6-in. Projector Charge, Ex 1. The 5-in. A. S. Projectile was found to have a terminal sinking velocity of 39.4 fps with armed nose fuse and 35.7 fps for the flat nose projectile without fuse. The terminal sinking velocity for the 6-in. Projector Charge was 34.3 fps with armed nose fuse and 32.6 without the fuse.

19. Final Report [Apra Harbor, Guam] - Carr, John H.
Contract NOy-12561 was initiated 28 June 1945 for the purpose of conducting hydraulic model experiments to guide the extensive harbor improvements then in process and planned for, at Apra Harbor, Guam, M. I. The contract was continued through change orders and finally terminated on 30 November 1954. The Apra Harbor investigation was completed at the end of 1948, and during the following contract period activity was directed along the lines of basic investigations of wave phenomena as they affect harbors and harbor structures. The program of the Laboratory was formulated and directed by Robert T. Knapp, Professor of Hydraulics, during the Apra Harbor studies...

20. Hydrostatic Tensile Fracture of a Polyurethane Elastomer - Lindsey, Gerald H.
The investigation of fracture of polymeric materials in hydrostatic tensile fields constitutes an avenue of approach to the study of fracture in more general three-dimensional environments. The advantages created by the symmetry of the stress field are considerable and, in one of the cases studied, facilitates a theoretical treatment that includes large deformations, which are characteristic of this class of materials. The analysis is developed through the concept of fracture originating from a flaw, which in this instance is taken to be a spherical cavity. Through the application of energy principles, a theoretical prediction of ultimate strength is made for hydrostatic tensile fields. Experiments were conducted...

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