The planar spectrum in U(N)-invariant quantum mechanics by Fock space methods: I. The bosonic case

Prompted by recent results on Susy-U(N)-invariant quantum mechanics in the large N limit by Veneziano and Wosiek, we have examined the planar spectrum in the full Hilbert space of U(N)-invariant states built on the Fock vacuum by applying any U(N)-invariant combinations of creation-operators. We present results about 1) the supersymmetric model in the bosonic sector, 2) the standard quartic Hamiltonian. This latter is useful to check our techniques against the exact result of Brezin et al. The SuSy case is where Fock space methods prove to be the most efficient: it turns out that the problem is separable and the exact planar spectrum can be expressed in terms of the single-trace spectrum. In the case of the anharmonic oscillator, on the other hand, the Fock space analysis is quite cumbersome due to the presence of large off-diagonal O(N) terms coupling subspaces with different number of traces; these terms should be absorbed before taking the planar limit and recovering the known planar spectrum. We give analytical and numerical evidence that good qualitative information on the spectrum can be obtained this way.Comment: 17 pages, 4 figures, uses youngtab.sty. Final versio

Study of corrosion of 1100 aluminum

Corrosion of 1100 aluminum in oxygen-saturated water at 70 degrees C under experimental conditions was studied, emphasizing effects of exposure interruption, the number of specimens, and the refreshment rate. A logarithmic equation was derived to express the corrosion rate

Study of crevice-galvanic corrosion of aluminum

Corrosion effects of aluminum-copper and aluminum-nickel couples in oxygenated distilled water, and aluminum alloys in oxygenated copper sulfate solution were studied. One of each of the couples had a water tight seal, and showed no substantial corrosion, and of the unsealed couples, only the aluminum-copper developed corrosion

Transverse self-modulation of ultra-relativistic lepton beams in the plasma wakefield accelerator

The transverse self-modulation of ultra-relativistic, long lepton bunches in high-density plasmas is explored through full-scale particle-in-cell simulations. We demonstrate that long SLAC-type electron and positron bunches can become strongly self-modulated over centimeter distances, leading to wake excitation in the blowout regime with accelerating fields in excess of 20 GV/m. We show that particles energy variations exceeding 10 GeV can occur in meter-long plasmas. We find that the self-modulation of positively and negatively charged bunches differ when the blowout is reached. Seeding the self-modulation instability suppresses the competing hosing instability. This work reveals that a proof-of-principle experiment to test the physics of bunch self-modulation can be performed with available lepton bunches and with existing experimental apparatus and diagnostics.Comment: 8 pages, 8 figures, accepted for publication in Physics of Plasma

Continuous maintenance and the future – Foundations and technological challenges

High value and long life products require continuous maintenance throughout their life cycle to achieve required performance with optimum through-life cost. This paper presents foundations and technologies required to offer the maintenance service. Component and system level degradation science, assessment and modelling along with life cycle ‘big data’ analytics are the two most important knowledge and skill base required for the continuous maintenance. Advanced computing and visualisation technologies will improve efficiency of the maintenance and reduce through-life cost of the product. Future of continuous maintenance within the Industry 4.0 context also identifies the role of IoT, standards and cyber security

Gamma-Ray Burst Spectral Features: Interpretation as X-ray Emission From A Photoionized Plasma

Numerous reports have been made of features, either in emission or absorption, in the 10 - 1000 keV spectra of some gamma-ray bursts. Originally interpreted in the context of Galactic neutron star models as cyclotron line emission and $e^+ - e^-$ annihilation features, the recent demonstration that the majority of GRBs lie at cosmological distances make these explanations unlikely. In this letter, we adopt a relativistic fireball model for cosmological GRBs in which dense, metal rich blobs or filaments of plasma are entrained in the relativistic outflow. In the context of this model, we investigate the conditions under which broadband features, similar to those detected, can be observed. We find a limited region of parameter space capable of reproducing the observed GRB spectra. Finally, we discuss possible constraints further high-energy spectral observations could place on fireball model parameters.Comment: Accepted for publication in Astrophysical Journal Letters Four pages, 2 figure

Ion motion in the wake driven by long particle bunches in plasmas

We explore the role of the background plasma ion motion in self-modulated plasma wakefield accelerators. We employ J. Dawson's plasma sheet model to derive expressions for the transverse plasma electric field and ponderomotive force in the narrow bunch limit. We use these results to determine the on-set of the ion dynamics, and demonstrate that the ion motion could occur in self-modulated plasma wakefield accelerators. Simulations show the motion of the plasma ions can lead to the early suppression of the self-modulation instability and of the accelerating fields. The background plasma ion motion can nevertheless be fully mitigated by using plasmas with heavier plasmas.Comment: 23 pages, 6 figure