One-dimensional spin-liquid without magnon excitations

It is shown that a sufficiently strong four-spin interaction in the spin-1/2 spin ladder can cause dimerization. Such interaction can be generated either by phonons or (in the doped state) by the conventional Coulomb repulsion between the holes. The dimerized phases are thermodynamically undistinguishable from the Haldane phase, but have dramatically different correlation functions: the dynamical magnetic susceptibility, instead of displaying a sharp single magnon peak near $q = \pi$, shows only a two-particle threshold separated from the ground state by a gap.Comment: 9 pages, LaTex, to be published in Phys. Rev. Lett., vol. 78, May 199

The Origin of the Hot Gas in the Galactic Halo: Confronting Models with XMM-Newton Observations

We compare the predictions of three physical models for the origin of the hot halo gas with the observed halo X-ray emission, derived from 26 high-latitude XMM-Newton observations of the soft X-ray background between l=120\degr and l=240\degr. These observations were chosen from a much larger set of observations as they are expected to be the least contaminated by solar wind charge exchange emission. We characterize the halo emission in the XMM-Newton band with a single-temperature plasma model. We find that the observed halo temperature is fairly constant across the sky (~1.8e6-2.3e6 K), whereas the halo emission measure varies by an order of magnitude (~0.0005-0.006 cm^-6 pc). When we compare our observations with the model predictions, we find that most of the hot gas observed with XMM-Newton does not reside in isolated extraplanar supernova remnants -- this model predicts emission an order of magnitude too faint. A model of a supernova-driven interstellar medium, including the flow of hot gas from the disk into the halo in a galactic fountain, gives good agreement with the observed 0.4-2.0 keV surface brightness. This model overpredicts the halo X-ray temperature by a factor of ~2, but there are a several possible explanations for this discrepancy. We therefore conclude that a major (possibly dominant) contributor to the halo X-ray emission observed with XMM-Newton is a fountain of hot gas driven into the halo by disk supernovae. However, we cannot rule out the possibility that the extended hot halo of accreted material predicted by disk galaxy formation models also contributes to the emission.Comment: 20 pages, 14 figures. New version accepted for publication in ApJ. Changes include new section discussing systematic errors (Section 3.2), improved method for characterizing our model spectra (4.2.2), changes to discussion of other observations (5.1). Note that we can no longer rule out possibility that extended hot halo of accreted material contributes to observed halo emission (see 5.2.1

FUSE Detection of Galactic OVI Emission in the Halo above the Perseus Arm

Background observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) toward l=95.4, b=36.1 show OVI 1032,1038 in emission. This sight line probes a region of stronger-than-average soft X-ray emission in the direction of high-velocity cloud Complex C above a part of the disk where Halpha filaments rise into the halo. The OVI intensities, 1600+/-300 ph/s/cm^2/sr (1032A) and 800+/-300 ph/s/cm^2/sr (1038A), are the lowest detected in emission in the Milky Way to date. A second sight line nearby (l=99.3, b=43.3) also shows OVI 1032 emission, but with too low a signal-to-noise ratio to obtain reliable measurements. The measured intensities, velocities, and FWHMs of the OVI doublet and the CII* line at 1037A are consistent with a model in which the observed emission is produced in the Galactic halo by hot gas ejected by supernovae in the Perseus arm. An association of the observed gas with Complex C appears unlikely.Comment: accepted for publication in ApJL, 11 pages including 3 figure

Developing a National Perspective of Interrelated Preparation: Educational Administration Leading Teacher Leadership Programs

This NCPEA Position Paper articulates a national perspective for the development of teacher leadership programs with leadership from educational administration professors. The National Council of Professors of Educational Administration (NCPEA), as the professional organization that provides direction and leadership for its members, presents a vision for dialogue and action to collaboratively develop teacher leadership programs among professors of educational administration and teacher education faculty. We believe that leadership matters and thus we submit there is a sense of urgency for professors to collaboratively develop teacher leadership programs embedded within educational administration programs. It is crucial that these programs articulate knowledge and skills aligned to the national standards for preparing school leaders–leaders who know excellent instruction, but who also are excellent leaders. We envision programs of teacher leadership that include both content and leadership instruction, integrating concepts from curriculum from teacher education, and leadership from educational administration that cultivate skills. These leadership skills are applied in authentic educational environments where experiences are cultivated and guided by both university professors and school practitioners. Appropriate instructional methods for adults provide learning through problem-based concepts where teacher leader candidates can plan, experience, and evaluate on-the-job activities to develop voice, confidence, and actions as leaders and change agents, without ever assuming an official role or title of school administrators. In this document we present three principles for consideration, which correlate with three audiences that could advance these principles

Surprisingly Little O VI Emission Arises in the Local Bubble

This paper reports the first study of the O VI resonance line emission (1032, 1038 Angstroms) originating in the Local Bubble (or Local Hot Bubble) surrounding the solar neighborhood. In spite of the fact that O VI absorption within the Local Bubble has been observed, no resonance line emission was detected during our 230 ksec Far Ultraviolet Spectroscopic Explorer observation toward a ``shadowing'' filament in the southern Galactic hemisphere. As a result, tight 2 sigma upper limits are set on the intensities in the 1032 and 1038 Angstrom emission lines: 500 and 530 photons cm^{-2} s^{-1} sr^{-1}, respectively. These values place strict constraints on models and simulations. They suggest that the O VI-bearing plasma and the X-ray emissive plasma reside in distinct regions of the Local Bubble and are not mixed in a single plasma, whether in equilibrium with T ~ 10^6 K or highly overionized with T ~ 4 to 6 x 10^4 K. If the line of sight intersects multiple cool clouds within the Local Bubble, then the results also suggest that hot/cool transition zones differ from those in current simulations. With these intensity upper limits, we establish limits on the electron density, thermal pressure, pathlength, and cooling timescale of the O VI-bearing plasma in the Local Bubble. Furthermore, the intensity of O VI resonance line doublet photons originating in the Galactic thick disk and halo is determined (3500 to 4300 photons cm^{-2} s^{-1} sr^{-1}), and the electron density, thermal pressure, pathlength, and cooling timescale of its O VI-bearing plasma are calculated. The pressure in the Galactic halo's O VI-bearing plasma (3100 to 3800 K cm^{-3}) agrees with model predictions for the total pressure in the thick disk/lower halo. We also report the results of searches for other emission lines.Comment: accepted by ApJ, scheduled for May 2003, replacement astro-ph submission corrects typos and grammatical errors in original versio

Dolomitization and Dolomite Neomorphism: Trenton and Black River Limestones (Middle Ordovician) Northern Indiana, U.S.A.

The Trenton and Black River Limestones are dolomitized extensively along the axis of the Kankakee Arch in Indiana, with the proportion of dolomite decreasing to the south and southeast of the arch. Planar and nonplanar dolomite replacement textures and rhombic (type 1) and saddle (type 2) void-filling dolomite cements are present. Three stages of dolomitization, involving different fluids, are inferred on the basis of petrographic and geochemical characteristics of the dolomites. Nonferroan planar dolomite has relatively high δ18O values (-1.8 to -6.1‰ PDB) and has 87Sr/86Sr ratios (0.70833 to 0.70856) that overlap those of Middle Ordovician seawater. Petrography, geochemistry, and the geometry of the dolomitized body suggest that the planar dolomite was formed in Middle and Late Ordovician seawater during the deposition of the overlying Maquoketa Shale. Ferroan planar and nonplanar dolomite occurs in the upper few meters of the Trenton Limestone, confined to areas underlain by planar dolomite. This dolomite contains patches of nonferroan dolomite with cathodoluminescence (CL) characteristics similar to underlying planar dolomite. Ferroan dolomite has relatively low δ18O values (-5.1 to -7.3‰ PDB) and has slightly radiogenic 87Sr/86Sr ratios (0.70915 to 0.70969) similar to those obtained for the overlying Maquoketa Shale. These data indicate that ferroan dolomite formed by neomorphism of nonferroan planar dolomite as fluids were expelled from the overlying Maquoketa Shale during burial. The absence of ferroan dolomite at the Trenton-Maquoketa contact, in areas where the earlier-formed nonferroan planar dolomite also is absent, indicates that the fluid expelled from the overlying shale did not contain enough Mg2+ to dolomitize limestone. Type 1 dolomite cement has isotopic compositions similar to those of the ferroan dolomite, suggesting that it also formed from shale-derived burial fluids. CL growth zoning patterns in these cements suggest that diagenetic fluids moved stratigraphically downward and toward the southeast along the axis of the Kankakee Arch. Type 2 saddle dolomite cements precipitated late; their low δ18O values (-6.0 to -7.0‰ PDB) are similar to those of the type 1 dolomite cement. However, fluid-inclusion data indicate that the saddle dolomite was precipitated from more saline, basinal fluids and at higher temperatures (94° to 143°C) than the type 1 cements (80° to 104°C). A trend of decreasing fluid-inclusion homogenization temperatures and salinities from the Michigan Basin to the axis of Kankakee Arch suggests that these fluids emerged from the Michigan Basin after precipitation of type 1 cement

Sensitive PCR Method for Detection of Escherichia coli 0157:H7 and Other Shiga toxin-producing Bacteria in Ground Meat

Sensitivity of a polymerase chain reaction (PCR) procedure was evaluated for Escherichia coli O157:H7 and Shiga toxin gene (stx) detection in ground beef and ground pork at contamination levels of 0.14, 1.4, and 14 colony forming units per gram (CFU/g) of meat. The PCR procedure, developed during our previous research, amplifies three target genes simultaneously: uidA that is specific for E. coli O157:H7, and stx1 and stx2, the genes for Shiga toxins 1 and 2, respectively. Detection of the uidA gene by the PCR was 91% sensitive in beef and 55% sensitive in pork, and 90% and 71% sensitive for stx gene detection in beef and pork, respectively. In comparison, detection of E. coli O157:H7 by culture, done simultaneously with PCR, was 53% sensitive in beef and 11% sensitive in pork. Results indicate that this PCR procedure is a rapid and sensitive method for STEC and E. coli O157:H7 detection in meat at contamination levels less than 1 CFU/g

Triplex PCR for Rapid Detection of Escherichia coli O157:H7 Directly from Ground Pork

A polymerase chain reaction (PCR) procedure is being developed to detect Escherichia coli O157:H7 and associated Shiga-like toxins (STX1 and STX2) directly from pork, bypassing the time-consuming microbial culture steps for identification. A triplex PCR procedure was adapted and conditions experimentally determined to efficiently amplify three target genes: uidA with unique sequence in E. coli O157:H7, and stx1 and stx2. A meat sample preparation technique developed in previous research was modified to allow detection of 0.2-2.0 colony forming units per gram (CFU./g.) of meat. Time required to complete the procedure after overnight incubation of samples is seven hours

Coulomb Blockade Regime of a Single-Wall Nanotube

A model of carbon nanotube at half filling is studied. The Coulomb interaction is assumed to be unscreened. It is shown that this allows to develop the adiabatic approximation which leads to considerable simplifications in calculations of the excitation spectrum. We give a detailed analysis of the spectrum and the phase diagram at half filling and discuss effects of small doping. At small doping several phases develop strong superconducting fluctuations corresponding to various types of pairing

2012 National Turfgrass Evaluation Program Tall Fescue Test: 2016 Data

Research efforts to improve cultivar quality include selecting for stress tolerance and disease resistance as well as finer leaf texture, a rich green color, and better sward density. Several cultivars included in the 2012 National Turfgrass Evaluation Program Tall Fescue Test performed well and showed good brown patch resistance in south central Kansas during the 2016 growing season