Studies of auroral X-ray imaging from high altitude spacecraft

Results of a study of techniques for imaging the aurora from a high altitude satellite at X-ray wavelengths are summarized. The X-ray observations allow the straightforward derivation of the primary auroral X-ray spectrum and can be made at all local times, day and night. Five candidate imaging systems are identified: X-ray telescope, multiple pinhole camera, coded aperture, rastered collimator, and imaging collimator. Examples of each are specified, subject to common weight and size limits which allow them to be intercompared. The imaging ability of each system is tested using a wide variety of sample spectra which are based on previous satellite observations. The study shows that the pinhole camera and coded aperture are both good auroral imaging systems. The two collimated detectors are significantly less sensitive. The X-ray telescope provides better image quality than the other systems in almost all cases, but a limitation to energies below about 4 keV prevents this system from providing the spectra data essential to deriving electron spectra, energy input to the atmosphere, and atmospheric densities and conductivities. The orbit selection requires a tradeoff between spatial resolution and duty cycle

Shuttle/TDRSS modelling and link simulation study

A Shuttle/TDRSS S-band and Ku-band link simulation package called LinCsim was developed for the evaluation of link performance for specific Shuttle signal designs. The link models were described in detail and the transmitter distortion parameters or user constraints were carefully defined. The overall link degradation (excluding hardware degradations) relative to an ideal BPSK channel were given for various sets of user constraint values. The performance sensitivity to each individual user constraint was then illustrated. The effect of excessive Spacelab clock jitter on the return link BER performance was also investigated as was the problem of subcarrier recovery for the K-band Shuttle return link signal

Dynamic evolution of the source volumes of gradual and impulsive solar flare emissions

This study compares flare source volumes inferred from impulsive hard X-rays and microwaves with those derived from density sensitive soft X-ray line ratios in the O VII spectrum. The data for this study were obtained with the SMM Hard X-Ray Burst Spectrometer, Earth-based radio observatories, and the SOLEX-B spectrometer on the P78-1 satellite. Data were available for the flares of 1980 April 8, 1980 May 9, and 1981 February 26. The hard X-ray/microwave source volume is determined under the assumption that the same electron temperature or power law index characterizes both the source of hard X-rays and the source of microwaves. The O VII line ratios yield the density and volume of the 2 X 10 to the 6th K plasma. For all three flares, the O VII source volume is found to be smallest at the beginning of the flare, near the time when the impulsive hard X-ray/microwave volume reaches its first maximum. At this time, the O VII volume is three to four orders of magnitude smaller than that inferred from the hard X-ray/microwave analysis. Subsequently, the O VII source volume increases by one or two orders of magnitude then remains almost constant until the end of the flare when it apparently increases again

Phase diagram of the one-dimensional Holstein model of spinless fermions

The one-dimensional Holstein model of spinless fermions interacting with dispersionless phonons is studied using a new variant of the density matrix renormalisation group. By examining various low-energy excitations of finite chains, the metal-insulator phase boundary is determined precisely and agrees with the predictions of strong coupling theory in the anti-adiabatic regime and is consistent with renormalisation group arguments in the adiabatic regime. The Luttinger liquid parameters, determined by finite-size scaling, are consistent with a Kosterlitz-Thouless transition.Comment: Minor changes. 4 pages, 4 figures. To appear in Physical Review Letters 80 (1998) 560

Comment on "Plasma ionization by annularly bounded helicon waves" [Phys . Plasmas 13, 063501 (2006)]

The neoclassical calculation of the helicon wave theory contains a fundamental flaw. Use is made of a proportional relationship between the magnetic field and its curl to derive the Helmholtz equation describing helicon wave propagation; however, by the fundamental theorem of Stokes, the curl of the magnetic field must be perpendicular to that portion of the field contributing to the local curl. Reexamination of the equations of motion indicates that only electromagnetic waves propagate through a stationary region of constant pressure in a fully ionized, neutral medium.Comment: 7 pages, 1 figure, to be published in Phys. Plasmas, http://link.aip.org/link/?PHPAEN/16/054701/

Quantum Entanglement in the Two Impurity Kondo Model

In order to quantify quantum entanglement in two impurity Kondo systems, we calculate the concurrence, negativity, and von Neumann entropy. The entanglement of the two Kondo impurities is shown to be determined by two competing many-body effects, the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, $I$. Due to the spin-rotational invariance of the ground state, the concurrence and negativity are uniquely determined by the spin-spin correlation between the impurities. It is found that there exists a critical minimum value of the antiferromagnetic correlation between the impurity spins which is necessary for entanglement of the two impurity spins. The critical value is discussed in relation with the unstable fixed point in the two impurity Kondo problem. Specifically, at the fixed point there is no entanglement between the impurity spins. Entanglement will only be created (and quantum information processing (QIP) be possible) if the RKKY interaction exchange energy, $I$, is at least several times larger than the Kondo temperature, $T_K$. Quantitative criteria for QIP are given in terms of the impurity spin-spin correlation.Comment: 7 pages, 3 figures, 1 tabl

Superconducting Pairing Symmetries in Anisotropic Triangular Quantum Antiferromagnets

Motivated by the recent discovery of a low temperature spin liquid phase in layered organic compound $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ which becomes a superconductor under pressure, we examine the phase transition of Mott insulating and superconducting (SC) states in a Hubbard-Heisenberg model on an anisotropic triangular lattice. We use a renormalized mean field theory to study the Gutzwiller projected BCS wavefucntions. The half filled electron system is a Mott insulator at large on-site repulsion $U$, and is a superconductor at a moderate $U$. The symmetry of the SC state depends on the anisotropy, and is gapful with $d_{x^2-y^2}+id_{xy}$ symmetry near the isotropic limit and is gapless with $d_{x^2-y^2}$ symmetry at small anisotropy ratio.Comment: 6 pages, 5 figure

Movin\u27 on Up: An Examination of Value-Added Growth During School Transition Years in Arkansas

This study assesses the impact school transitions have on grade-level value-added growth scores in Arkansas. Arkansas is unique in that the autonomy of setting building level transitions is left to individual districts. This distinction allows researchers to make comparisons between student groups that where students transitioned upward to a new building and those who did not. Using data covering five different school years, this study evaluates mathematics and English language-arts value-added growth scores of grade levels that transitioned to a new building and compared them to grade-level growth scores of buildings where students did not make a transition. Using regression analyses, we find that overall, there are not consistent results showing less growth during a transition year. However, we find a pattern that shows that students who transition in 6th and 7th grade, common transition years in Arkansas, demonstrate lower value-added growth-scores compared to student groups who did not transition. These results are similar for both mathematics and ELA. This study adds to current literature about value-added growth in Arkansas. We discuss our findings in the context of prior transition year literature and conclude with policy suggestion

The Pen Duick Escarpment off Morocco: A promising biogeochemically active carbonate mound laboratory (MiCROSYSTEMS)

Carbonate mud mounds, found in marine environments from shallow- to deep-water settings, span from Proterozoic to recent times. During the past decades, numerous active venting fields were discovered in deep marine environments and became a subject of extensive study for marine scientists. Mound building seems to be a fundamental but still enigmatic strategy for life. Various arguments suggest that microorganisms are playing a major role in the reef development, mound formation and biodiversity. Therefore, it is important to evaluate the microbial mediated processes of carbonate precipitation.Cold-water coral reefs thriving on carbonate mounds were discovered in the late 1990’s off western Ireland. An exploratory cruise of RV Belgica in 2002 off Morocco has led to the discovery of apparently juvenile mounds in water depths of 500-600 m, topping a cliff - the Pen Duick escarpment - flanked by giant mud volcanoes. Subsequent cruises have confirmed the colonization by deep-water corals and have unveiled extensive fields of seep-related carbonate crusts in the off-reef regions. Long cores taken in 2004 indicate that the ‘Pen Duick’ mounds, in which microbial action was demonstrated by a strong emission of hydrogen sulphide, may be considered as giant biogeochemical reactors. The mound sediments were dated 2 kyrs B.P. at the surface and 20 kyrs B.P. in a depth of 6 mbsf.A 450 cm long gravity core, coming from one of these juvenile mounds, was sampled and analyzed for mineralogy, stable isotopes composition, geochemistry, and microbial communities. Most of the sediment consists of calcite (coccoliths), quartz and dolomite. At a depth of 4 mbsf, we found hardened nodule-like structures, embedded in grey mud containing cold-water coral pieces. The presence of 20-30% of dolomite, in the carbonate phase, suggests a microbial influence during mineral formation. Preliminary results of the pore water geochemistry indicate a reactive sulphate – methane interface at 3.8 mbsf. In this layer we focused our studies on the microbial communities, such as methanogens, methanotrophs and sulphate reducers. The trend of the d13C values in digenetic carbonate supports the assumption of microbial activity in this section of the core. In order to define the primary microbial community involved in carbonate precipitation, we did direct culturing, DNA isolation and PCR analysis of three functional genes, the a subunit (mcrA) of the methyl-coenzyme M reductase (MCR), the a subunit (pmoA) of the particulate methane monooxygenase (MMO) and the a and ß subunits (dsrA and dsrB, respectively) of the dissimilatory sulfite reductase (DSR). These enzymes are involved in methanogenesis, methanotrophy and sulphate reduction biochemical pathways, respectively. In summary, our initial results demonstrate that the Pen Duick carbonate mound can be considered as a natural laboratory in which to study cold-water coral ecosystems associated with microbial activity

Entanglement Sharing and Decoherence in the Spin-Bath

The monogamous nature of entanglement has been illustrated by the derivation of entanglement sharing inequalities - bounds on the amount of entanglement that can be shared amongst the various parts of a multipartite system. Motivated by recent studies of decoherence, we demonstrate an interesting manifestation of this phenomena that arises in system-environment models where there exists interactions between the modes or subsystems of the environment. We investigate this phenomena in the spin-bath environment, constructing an entanglement sharing inequality bounding the entanglement between a central spin and the environment in terms of the pairwise entanglement between individual bath spins. The relation of this result to decoherence will be illustrated using simplified system-bath models of decoherence.Comment: 5 pages, 1 figure v2: 6 pages 2 figures, additional example and reference