Ultrastructure of Teliospores and Promycelium and Basidiospore Formation in the Four-Spored Form of Gymnoconia Nitens, One of the Causes of Orange Rust of Rubus

Orange rust of Rubus is an interesting disease because of the fact that it can be caused by three different rust fungi that produce virtually identical symptoms. One is Gymnoconia peckiana (Howe in Peck) Trotter, which is a demicyclic species, while the other two are endocyclic forms historically referred to as Gymnoconia nitens (Schwein.) Kern & H.W. Thurston. Although the spores produced on infected Rubus leaves by these latter two forms are morphologically identical to the aeciospores of G. peckiana, they actually function as teliospores. However, the teliospores of one of the forms gives rise to two-celled promycelia that bear only two basidiospores, while teliospores of the other produce four-celled promycelia bearing four basidiospores. Here, we examined the teliospores of the four-spored form along with the sequence of events that lead to basidiospore development. Developing and mature teliospores were binucleate, and we saw no evidence that karyogamy occurred in these spores. Upon germination, both spore nuclei migrated into the promycelium and underwent mitosis to form a total of four nuclei. Four transverse septa then developed, creating four uninucleate cells. A tapered sterigma arose from each cell and gave rise to a basidiospore. These findings indicate that the basidiospores of the four-spored form of G. nitens were formed in an asexual fashion

Quantum theory for electron spin decoherence induced by nuclear spin dynamics in semiconductor quantum computer architectures: Spectral diffusion of localized electron spins in the nuclear solid-state environment

We consider the decoherence of a single localized electron spin due to its coupling to the lattice nuclear spin bath in a semiconductor quantum computer architecture. In the presence of an external magnetic field and at low temperatures, the dominant decoherence mechanism is the spectral diffusion of the electron spin resonance frequency due to the temporally fluctuating random magnetic field associated with the dipolar interaction induced flip-flops of nuclear spin pairs. The electron spin dephasing due to this random magnetic field depends intricately on the quantum dynamics of the nuclear spin bath, making the coupled decoherence problem difficult to solve. We provide a formally exact solution of this non-Markovian quantum decoherence problem which numerically calculates accurate spin decoherence at short times, which is of particular relevance in solid-state spin quantum computer architectures. A quantum cluster expansion method is developed, motivated, and tested for the problem of localized electron spin decoherence due to dipolar fluctuations of lattice nuclear spins. The method is presented with enough generality for possible application to other types of spin decoherence problems. We present numerical results which are in quantitative agreement with electron spin echo measurements in phosphorus doped silicon. We also present spin echo decay results for quantum dots in GaAs which differ qualitatively from that of the phosphorus doped silicon system. Our theoretical results provide the ultimate limit on the spin coherence (at least, as characterized by Hahn spin echo measurements) of localized electrons in semiconductors in the low temperature and the moderate to high magnetic field regime of interest in scalable semiconductor quantum computer architectures.Comment: 23 pages, 15 figure

Wavefunction considerations for the central spin decoherence problem in a nuclear spin bath

Decoherence of a localized electron spin in a solid state material (the ``central spin'' problem) at low temperature is believed to be dominated by interactions with nuclear spins in the lattice. This decoherence is partially suppressed through the application of a large magnetic field that splits the energy levels of the electron spin and prevents depolarization. However, dephasing decoherence resulting from a dynamical nuclear spin bath cannot be removed in this way. Fluctuations of the nuclear field lead to uncertainty of the electron's precessional frequency in a process known as spectral diffusion. This article considers the effect of the electron's wavefunction shape upon spectral diffusion and provides wavefunction dependent decoherence time formulas for free induction decay as well as spin echoes and concatenated dynamical decoupling schemes for enhancing coherence. We also discuss dephasing of a qubit encoded in singlet-triplet states of a double quantum dot. A central theoretical result of this work is the development of a continuum approximation for the spectral diffusion problem which we have applied to GaAs and InAs materials specifically

Interactions between vaccinia virus and sensitized macrophages in vitro

The action of peritoneal exudate cells (PEC) from normal and vaccinia virus infected mice on infectious vaccinia virus particles was investigatedin vitro. PEC from immune mice showed a significantly higher infectivity titre reduction (virus clearance, VC) than normal cells. This effect could be clearly attributed to the macrophage. Vaccinia virus multiplied in PEC from normal animals while there was no virus propagation in cells from immunized mice. The release of adsorbed or engulfed virus was reduced significantly in PEC from immunized animals. Anti-vaccinia-antibodies seem to activate normal macrophages to increased virus clearance. This stimulating effect was demonstrable only in the IgG fraction of the antiserum. The activity of macrophages from mice injected three times over a period of 14 days with vaccinia virus could be entirely blocked with anti-mouse-IgG, while PEC from mice injected one time six days previously were not inhibited

The MY NASA DATA Project

On the one hand, locating the right dataset, then figuring out how to use it, is a daunting task that is familiar to almost any scientist or graduate student in the fields of Earth system science. On the other hand, the ability to explore authentic Earth system science data, through inquiry-based education, is an important goal in US national education standards. Fortunately, in the digital age, tools are emerging that can make such data exploration commonplace at all educational levels. This paper describes the conception and development of one project that aims to bridge this gap: Mentoring and inquiry using NASA Data on Atmospheric and Earth science for Teachers and Amateurs (MY NASA DATA; mynasadata.larc.nasa.gov). With funding from NASA's Science Mission Directorate, this project was launched in early 2004 with the aim of developing microsets and identifying other enablers for making data accessible. A key feature of the project is a Live Access Server, the first educational implementation of this open source software, developed by NOAA, that makes it possible to explore multiple data formats through a single interface. This powerful tool is made more useful to the primary target audiences (K-12 and amateur scientists) through careful selection of the data offered, user-friendly explanations of the tool itself, and age-appropriate explanations of the parameters. However experience already shows that graduate students and even practicing scientists can also make use of this resource. The website also hosts teacher-contributed lesson plans, and seeks to feature reports of research projects that use the data

Spectroscopic investigations of a Ti:Tm:LiNbO3 waveguide for photon-echo quantum memory

We report the fabrication and characterization of a Ti$^{4+}$:Tm$^{3+}$:LiNbO$_3$ optical waveguide in view of photon-echo quantum memory applications. In particular, we investigated room- and cryogenic-temperature properties via absorption, spectral hole burning, photon echo, and Stark spectroscopy. We found radiative lifetimes of 82 $\mu$s and 2.4 ms for the $^3$H$_4$ and $^3$F$_4$ levels, respectively, and a 44% branching ratio from the $^3$H$_{4}$ to the $^3$F$_4$ level. We also measured an optical coherence time of 1.6 $\mu$s for the $^3$H$_6\leftrightarrow{}^3$H$_4$, 795 nm wavelength transition, and investigated the limitation of spectral diffusion to spectral hole burning. Upon application of magnetic fields of a few hundred Gauss, we observed persistent spectral holes with lifetimes up to seconds. Furthermore, we measured a linear Stark shift of 25 kHz$\cdot$cm/V. Our results are promising for integrated, electro-optical, waveguide quantum memory for photons.Comment: 11 pages, 14 figure