An extensive and autonomous deep space navigation system using radio pulsars

Interstellar navigation poses significant challenges in all aspects of a spacecraft. One of them is reliable, low-cost, real-time navigation, especially when there is a considerable distance between Earth and the spacecraft in question. In this paper, a complete system for navigation using pulsar radio emissions is described and analysed. The system uses a pulsar‟s emissions in the radio spectrum to create a novel system capable of fully autonomous navigation. The system is roughly divided into two parts, the front - end and the back - end, as well as their subdivisions. The front - end performs initial signal reception and pre-processing. It applies time-based coherent de-dispersion to allow for low-power on-board processing, and uses a very wide bandwidth to limit the required antenna size. As a result, the electronics required performing the processing is complex, but the system is well limited in both size and power consumption

Synergistic toughening and compatibilisation effect of Poly(butylene succinate) in PLA/poly-caprolactone blends

YesBinary and ternary blends of a polylactic acid matrix with polycaprolactone (PCL) and polybutylene succinate (PBS) were produced by twin screw extrusion, containing up to 30 wt% loading. Mechanical, thermal and rheological characterisation techniques were used to quantify properties of the different blend formulations and miscibility was investigated using scanning electron microscopy. PCL is known to act as an impact modifier in PLA but to cause a corresponding reduction in strength. Results showed that addition of both PBS and PCL seperatly caused a reduction in melt viscosity, elastic modulus and tensile strength, but an increase in impact strength and strain at break. Analysis of morphology suggested that immiscibility was evident, particularly at higher PCL and PBS loadings. Results indicated that incorporation of a small loading of PBS had a synergistic effect on the PLA-PCL blend properties. Miscibility was improved and enhanced mechanical properties were observed for a ternary blend containing 5 wt% of both PBS and PCL compared to blends containing 10% of each polymer alone.Financial support of Floreon- Transforming Packaging Ltd through the PhD sponsorship and materials provision

Growth of laser host thin-film optical waveguides by pulsed laser deposition

Optical waveguides of laser gain media are highly desirable because the high intensity-length product and good pump-signal mode overlap, which can be achieved in the waveguide geometry, leads to a reduced threshold pump power as compared to bulk lasers. Pulsed laser deposition (PLD) has emerged as a viable means of depositing epitaxial thin films of the correct composition. We report here the deposition of GGG and YGG thin films on YAG substrates and the deposition of sapphire on sapphire substrates

Two Mathematically Equivalent Versions of Maxwell's Equations

This paper is a review of the canonical proper-time approach to relativistic mechanics and classical electrodynamics. The purpose is to provide a physically complete classical background for a new approach to relativistic quantum theory. Here, we first show that there are two versions of Maxwell's equations. The new version fixes the clock of the field source for all inertial observers. However now, the (natural definition of the effective) speed of light is no longer an invariant for all observers, but depends on the motion of the source. This approach allows us to account for radiation reaction without the Lorentz-Dirac equation, self-energy (divergence), advanced potentials or any assumptions about the structure of the source. The theory provides a new invariance group which, in general, is a nonlinear and nonlocal representation of the Lorentz group. This approach also provides a natural (and unique) definition of simultaneity for all observers. The corresponding particle theory is independent of particle number, noninvariant under time reversal (arrow of time), compatible with quantum mechanics and has a corresponding positive definite canonical Hamiltonian associated with the clock of the source. We also provide a brief review of our work on the foundational aspects of the corresponding relativistic quantum theory. Here, we show that the standard square-root and the Dirac equations are actually two distinct spin-$\tfrac{1}{2}$ particle equations.Comment: Appeared: Foundations of Physic

The Relativistic Electrodynamics Least Action Principles Revisited: New Charged Point Particle and Hadronic String Models Analysis

The classical relativistic least action principle is revisited from the vacuum field theory approach. New physically motivated versions of relativistic Lorentz type forces are derived, a new relativistic hadronic string model is proposed and analyzed in detail.Comment: n/

Laser operation of an Nd:Gd₃Ga₅O₁₂ thin-film optical waveguide fabricated by pulsed laser deposition

We report the laser operation of a thin-film waveguide structure grown by the pulsed laser deposition technique. A 2.7-µm-thick crystalline film of neodymium doped Gd3Ga5O12 (Nd:GGG) lases at a wavelength centered at 1.06µm when pumped by a Ti:sapphire laser at 808 nm

First Measurement of A_N at sqrt(s)=200 GeV in Polarized Proton-Proton Elastic Scattering at RHIC

We report on the first measurement of the single spin analyzing power (A_N) at sqrt(s)=200GeV, obtained by the pp2pp experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). Data points were measured in the four momentum transfer t range 0.01 < |t| < 0.03 (GeV/c)^2. Our result, averaged over the whole t-interval is about one standard deviation above the calculation, which uses interference between electromagnetic spin-flip amplitude and hadronic non-flip amplitude, the source of A_N. The difference could be explained by an additional contribution of a hadronic spin-flip amplitude to A_N.Comment: 13 pages, 5 figures. New values of polarization errors. Final version submitted to Phys. Lett.

First Measurement of Proton-Proton Elastic Scattering at RHIC

The first result of the pp2pp experiment at RHIC on elastic scattering of polarized protons at sqrt{s} = 200 GeV is reported here. The exponential slope parameter b of the diffractive peak of the elastic cross section in the t range 0.010 <= |t| <= 0.019 (GeV/c)^2 was measured to be b = 16.3 +- 1.6 (stat.) +- 0.9 (syst.) (GeV/c)^{-2} .Comment: 9 pages 5 figure

An Automated Algorithm to Distinguish and Characterize Solar Flares and Associated Sequential Chromospheric Brightenings

We present a new automated algorithm to identify, track, and characterize small-scale brightening associated with solar eruptive phenomena observed in H{\alpha}. The temporal spatially-localized changes in chromospheric intensities can be separated into two categories: flare ribbons and sequential chromospheric brightenings (SCBs). Within each category of brightening we determine the smallest resolvable locus of pixels, a kernel, and track the temporal evolution of the position and intensity of each kernel. This tracking is accomplished by isolating the eruptive features, identifying kernels, and linking detections between frames into trajectories of kernels. We fully characterize the evolving intensity and morphology of the flare ribbons by observing the tracked flare kernels in aggregate. With the location of SCB and flare kernels identified, they can easily be overlaid on top of complementary data sets to extract Doppler velocities and magnetic field intensities underlying the kernels. This algorithm is adaptable to any dataset to identify and track solar features.Comment: 22 pages, 9 figure

Semiparametric theory and empirical processes in causal inference

In this paper we review important aspects of semiparametric theory and empirical processes that arise in causal inference problems. We begin with a brief introduction to the general problem of causal inference, and go on to discuss estimation and inference for causal effects under semiparametric models, which allow parts of the data-generating process to be unrestricted if they are not of particular interest (i.e., nuisance functions). These models are very useful in causal problems because the outcome process is often complex and difficult to model, and there may only be information available about the treatment process (at best). Semiparametric theory gives a framework for benchmarking efficiency and constructing estimators in such settings. In the second part of the paper we discuss empirical process theory, which provides powerful tools for understanding the asymptotic behavior of semiparametric estimators that depend on flexible nonparametric estimators of nuisance functions. These tools are crucial for incorporating machine learning and other modern methods into causal inference analyses. We conclude by examining related extensions and future directions for work in semiparametric causal inference