Proposed Modifications to the Los Angeles Rattler Test

The amount of highway construction is increasing every year. As a result, there is an ever increasing demand for mineral aggregates. Engineers classify these mineral aggregates as the smaller rocks which are composed of one or more minerals. In the state of California, between one-fifth and one-third of the 300 million dollars spent annually for the construction of highways is used for the procurement and placement of aggregates. (l) This cost is steadily increasing because of the depletion of the more accessible and higher quality aggregates. Because the traffic volume and loads are steadily increasing, the Interstate system as well as many other primary roads being built demand durable aggregates. The selecting of high quality aggregates is not a new problem. Back in Roman times it was necessary to select suitable rocks for use as flag stones, a surfacing material of the time. Some of the highways of that era remain in excellent condition today as a result of the prudent selection of surfacing material. It was not until the late nineteenth century, however, that the use of machines to simulate field conditions for the purpose of determining the durability of aggregates began. The first successful test for abrasion of aggregates was the Deval test. At the present time the Los Angeles rattler tests used by most of the State Highway Departments. It is considered the most effective test for determining the structural and abrasive qualities of an aggregate. In the late 1940\u27s however, it was observed that aggregates which had passed the Los Angeles rattler test were failing under field conditions. In 1947, Melville investigated a failure in Route 250 near Charlottesville, Virginia. From his investigation he concluded that the aggregates had weathered sufficiently to produce a layer of plastic fines which caused the failure. (2) Since then there have been many similar cases reported, especially in the western states. As a consequence of· these failures, many of the western states have been attempting to develop an empirical test that will determine the tendency of an aggregate to produce plastic fines. Washington, Oregon, Idaho, California, and South Dakota, as well as other states, have developed tests to determine the durability characteristics of aggregates. At the present time, none of these tests are universally accepted by other states or by the American Society for Testing and Materials. The Los Angeles rattler test is a very simple test and requires little time to perform. The amount of time required to conduct a test is becoming increasingly important because labor costs are steadily rising. Also, with the high production of modern aggregate contractors, it is important to have a test which can be accomplished in a short period of time. The Los Angeles rattler machine is an expensive piece of equipment and one that all state highway departments regard as standard equipment. Accordingly, this study was made with a view toward modifying the Los Angeles rattler test to include wet abrasion. This would make it possible to obtain the necessary durability information from a single laboratory test without appreciably adding to the cost of equipment

The Chandra X-Ray Observatory's Radiation Environment and the AP-8/AE-8 Model

The Chandra X-ray Observatory (CXO) was launched on July 23, 1999 and reached its final orbit on August 7, 1999. The CXO is in a highly elliptical orbit, approximately 140,000 km x 10,000 km, and has a period of approximately 63.5 hours (~ 2.65 days). It transits the Earth's Van Allen belts once per orbit during which no science observations can be performed due to the high radiation environment. The Chandra X-ray Observatory Center (CXC) currently uses the National Space Science Data Center's ``near Earth'' AP-8/AE-8 radiation belt model to predict the start and end times of passage through the radiation belts. However, our scheduling software uses only a simple dipole model of the Earth's magnetic field. The resulting B, L magnetic coordinates, do not always give sufficiently accurate predictions of the start and end times of transit of the Van Allen belts. We show this by comparing to the data from Chandra's on-board radiation monitor, the EPHIN (Electron, Proton, Helium Instrument particle detector) instrument. We present evidence that demonstrates this mis-timing of the outer electron radiation belt as well as data that also demonstrate the significant variablity of one radiation belt transit to the next as experienced by the CXO. We also present an explanation for why the dipole implementation of the AP-8/AE-8 model is not ideally suited for the CXO. Lastly, we provide a brief discussion of our on-going efforts to identify a model that accounts for radiation belt variability, geometry, and one that can be used for observation scheduling purposes.Comment: 12 pgs, 6 figs, for SPIE 4012 (Paper 76

Coulomb Charging at Large Conduction

We discuss the suppression of Coulomb charging effects on a small metallic island coupled to an electrode by a tunnel junction. At high temperatures the quantum corrections to the classical charging energy $E_c=e^2/2C$, where $C$ is the island capacitance, are evaluated. At low temperatures the large quantum fluctuations of the island charge cause a strong reduction of the effective $E_c$ which is determined explicitly in the limit of a large tunneling conductance.Comment: 4 page

Using High Resolution Images to Investigate Fatigue Crack Initiation of Alloys at the Microstructural Level

Microstructural features within a material dictate the material’s mechanical behavior and lead to localized strains as the sample is deformed. In order to further understand structural failure, an improved understanding of how microstructural features influence failure is necessary. Fatigue is one common mode of failure for aerospace applications, and a better understanding of the conditions of crack initiation can provide information that ultimately may increase longevity of aerospace systems. This paper investigates the hypothesis that fatigue crack initiation for a cyclically loaded sample is correlated to areas of higher localized strain. The experiment was conducted using a Ti-6Al-4V sample subjected to low amplitude fatigue ratio. For sample preparation, a titanium nanopowder solution is applied to an area of interest. The titanium particles on the sample are then imaged in an optical microscope, and the displacement of each particle is measured after loading the sample. The resultant displacement field is converted into a strain field, which will indicate locations on the sample with higher localized strains. When comparing sites of crack initiation to the strain field map, there is a tendency for cracks to initiate near locations with high localized strains. This knowledge can lead to an improved ability to predict fatigue crack initiation locations, and can also be used to improve structural designs at the microstructural level

A Tableaux Calculus for Reducing Proof Size

A tableau calculus is proposed, based on a compressed representation of clauses, where literals sharing a similar shape may be merged. The inferences applied on these literals are fused when possible, which reduces the size of the proof. It is shown that the obtained proof procedure is sound, refutationally complete and allows to reduce the size of the tableau by an exponential factor. The approach is compatible with all usual refinements of tableaux.Comment: Technical Repor

Relativistic entanglement of two massive particles

We describe the spin and momentum degrees of freedom of a system of two massive spin--$\tfrac{1}{2}$ particles as a 4 qubit system. Then we explicitly show how the entanglement changes between different partitions of the qubits, when considered by different inertial observers. Although the two particle entanglement corresponding to a partition into Alice's and Bob's subsystems is, as often stated in the literature, invariant under Lorentz boosts, the entanglement with respect to other partitions of the Hilbert space on the other hand, is not. It certainly does depend on the chosen inertial frame and on the initial state considered. The change of entanglement arises, because a Lorentz boost on the momenta of the particles causes a Wigner rotation of the spin, which in certain cases entangles the spin- with the momentum states. We systematically investigate the situation for different classes of initial spin states and different partitions of the 4 qubit space. Furthermore, we study the behavior of Bell inequalities for different observers and demonstrate how the maximally possible degree of violation, using the Pauli-Lubanski spin observable, can be recovered by any inertial observer.Comment: 17 pages, 4 figure

The Midpoint Rule as a Variational--Symplectic Integrator. I. Hamiltonian Systems

Numerical algorithms based on variational and symplectic integrators exhibit special features that make them promising candidates for application to general relativity and other constrained Hamiltonian systems. This paper lays part of the foundation for such applications. The midpoint rule for Hamilton's equations is examined from the perspectives of variational and symplectic integrators. It is shown that the midpoint rule preserves the symplectic form, conserves Noether charges, and exhibits excellent long--term energy behavior. The energy behavior is explained by the result, shown here, that the midpoint rule exactly conserves a phase space function that is close to the Hamiltonian. The presentation includes several examples.Comment: 11 pages, 8 figures, REVTe