Robust Quantum Communication Using A Polarization-Entangled Photon Pair

Noise and imperfection of realistic devices are major obstacles for implementing quantum cryptography. In particular birefringence in optical fibers leads to decoherence of qubits encoded in polarization of photon. We show how to overcome this problem by doing single qubit quantum communication without a shared spatial reference frame and precise timing. Quantum information will be encoded in pair of photons using ``tag'' operations which corresponds to the time delay of one of the polarization modes. This method is robust against the phase instability of the interferometers despite the use of time-bins. Moreover synchronized clocks are not required in the ideal situation no photon loss case as they are only necessary to label the different encoded qubits.Comment: 4 pages, 2 figure

Information Flow of quantum states interacting with closed timelike curves

Recently, the quantum information processing power of closed timelike curves have been discussed. Because the most widely accepted model for quantum closed timelike curve interactions contains ambiguities, different authors have been able to reach radically different conclusions as to the power of such interactions. By tracing the information flow through such systems we are able to derive equivalent circuits with unique solutions, thus allowing an objective decision between the alternatives to be made. We conclude that closed timelike curves, if they exist and are well described by these simple models, would be a powerful resource for quantum information processing.Comment: Now includes appendix proving Deutsch's maximum entropy conjectur

Geometric effects in applied-field MPD thrusters

Three applied-field magnetoplasmadynamic (MPD) thruster geometries were tested with argon propellant to establish the influence of electrode geometry on thruster performance. The thrust increased approximately linearly with anode radius, while the discharge and electrode fall voltages increased quadratically with anode radius. All these parameters increased linearly with applied-field strength. Thrust efficiency, on the other hand, was not significantly influenced by changes in geometry over the operating range studied, though both thrust and thermal efficiencies increased monotonically with applied field strength. The best performance, 1820 sec I(sub sp) at 20 percent efficiency, was obtained with the largest radius anode at the highest discharge current (1500 amps) and applied field strength (0.4 Tesla)

Remanent magnetization and 3-dimensional density model of the Kentucky anomaly region

A three-dimensional model of the Kentucky body was developed to fit surface gravity and long wavelength aeromagnetic data. Magnetization and density parameters for the model are much like those of Mayhew et al (1982). The magnetic anomaly due to the model at satellite altitude is shown to be much too small by itself to account for the anomaly measured by Magsat. It is demonstrated that the source region for the satellite anomaly is considerably more extensive than the Kentucky body sensu stricto. The extended source region is modeled first using prismatic model sources and then using dipole array sources. Magnetization directions for the source region found by inversion of various combinations of scalar and vector data are found to be close to the main field direction, implying the lack of a strong remanent component. It is shown by simulation that in a case (such as this) where the geometry of the source is known, if a strong remanent component is present its direction is readily detectable, but by scalar data as readily as vector data

Updated measurements of the dark matter halo masses of obscured quasars with improved WISE and Planck data

Using the most recent releases of WISE and Planck data, we perform updated measurements of the bias and typical dark matter halo mass of infrared-selected obscured and unobscured quasars, using the angular autocorrelation function and cosmic microwave background (CMB) lensing cross-correlations. Since our recent work of this kind, the WISE Allwise catalogue was released with improved photometry, and the Planck mission was completed and released improved products. These new data provide a more reliable measurement of the quasar bias and provide an opportunity to explore the role of changing survey pipelines in results downstream. We present a comparison of IR color-selected quasars, split into obscured and unobscured populations based on optical-IR colors, selected from two versions of the WISE data. Which combination of data is used impacts the final results, particularly for obscured quasars, both because of mitigation of some systematics and because the newer catalogue provides a slightly different sample. We show that Allwise data is superior in several ways, though there may be some systematic trends with Moon contamination that were not present in the previous catalogue. We opt currently for the most conservative sample that meet our selection criteria in both the previous and new WISE catalogues. We measure a higher bias and halo mass for obscured quasars ($b_{\textrm{obsc}} \sim 2.1$, $b_{\textrm{unob}} \sim 1.8$) --- at odds with simple orientation models --- but at a reduced significance ($\sim$1.5$\sigma$) as compared to our work with previous survey data.Comment: 20 pages, 15 figures, accepted for publication in MNRA

A modified proximity approach in the fusion of heavy-ions

By using a suitable set of the surface energy coefficient, nuclear radius, and universal function, the original proximity potential 1977 is modified. The overestimate of the data by 4 % reported in the literature is significantly reduced. Our modified proximity potential reproduces the experimental data nicely compared to its older versions.Comment: 9 pages, 5 figures, Chin. Phys. lett.(2010) in pres

MPD thruster technology

MPD (MagnetoPlasmaDynamic) thrusters demonstrated between 2000 and 7000 seconds specific impulse at efficiencies approaching 40 percent, and were operated continuously at power levels over 500 kW. These demonstrated capabilities, combined with the simplicity and robustness of the thruster, make them attractive candidates for application to both unmanned and manned orbit raising, lunar, and planetary missions. To date, however, only a limited number of thruster configurations, propellants, and operating conditions were studied. The present status of MPD research is reviewed, including developments in the measured performance levels and electrode erosion rates. Theoretical studies of the thruster dynamics are also described. Significant progress was made in establishing empirical scaling laws, performance and lifetime limitations and in the development of numerical codes to simulate the flow field and electrode processes

Lunar contour mapping system /lucom/ final report, 5 aug. 1964 - 18 mar. 1965

Radar sensor system for acquisition of lunar surface data - Lunar contour mapping syste