Cross-correlation of the unresolved X-ray background with faint galaxies

At the faint end of the deepest X-ray surveys, a population of X-ray luminous galaxies is seen. In this paper, we present the results of a cross-correlation between the residual, unresolved X-ray photons in a very deep X-ray survey and the positions of faint galaxies, in order to examine the importance of these objects at even fainter flux levels. We measure a significant correlation on all angular scales up to ~1 arcmin. This signal could account for a significant fraction of the unresolved X-ray background, approximately 35 per cent if the clustering is similar to optically selected galaxies. However, the angular form of the correlation is seen to be qualitatively similar to that expected for clusters of galaxies and the X-ray emission could be associated with hot gas in clusters or with QSOs within galaxy clusters rather than emission from individual faint galaxies. The relative contribution from each of these possibilities cannot be determined with the current data.Comment: 7 pages LaTeX including 9 EPS figures. Uses mn.sty. Accepted for publication by MNRA

The discovery of very red counterparts to faint X-ray sources

We present deep K-band imaging at the positions of four very faint X-ray sources found in the UK ROSAT Deep Survey to have no optical counterpart brighter than R~23. Likely identifications are found within the ROSAT error circle in all four fields with R-K colours of between 3.2 +/- 0.4 and 6.4 +/- 0.6. From a consideration of the R-K colours and X-ray to optical luminosity ratios of the candidate identifications, we tentatively classify two of the X-ray sources as very distant (z ~ 1) clusters of galaxies, one as a narrow emission line galaxy and one as an obscured QSO.Comment: 7 pages, LaTeX, 7 figures (1 postscript file each). Uses mn.sty and epsf.sty. Accepted by MNRAS. For more information see http://www.astro.soton.ac.uk/~amn/UKdee

"Non-metabolizable" glucose analogue shines new light on primingmechanisms: Triggering of microbial metabolism

The rhizosphere and detritusphere are characterized by increased carbon availability, including low-molecular weight organic substances. Such easily biodegradable organic substances can change the mineralization rates of pre-existing soil organic matter, a phenomenon termed priming. Priming of soil organic matter decomposition has attracted much research interest, yet a conclusive mechanistic explanation remains elusive. One proposal is that low molecular weight organic substances might “trigger” an acceleration of microbial metabolism. For the first time, we applied a glucose analogue to soil to demonstrate triggering of microbial metabolism, and to estimate its relative contribution to priming. “Non-metabolizable” glucose analogues have been widely used in pure culture studies to mimic glucose, but never in soil biochemistry. We hypothesized that analogue molecules will elicit a metabolic response in microorganisms despite limited catabolism, and thereby confirm the proposed triggering. The effect of 14C-labeled 3-O-methyl-D-glucose (OMG) – a common “non-metabolizable” glucose analogue – on soil organic matter mineralization was compared to that of 14C-labeled D-glucose. OMG was mineralized, but its mineralization was initially impeded and substantially delayed, relative to glucose. OMG caused brief but strong priming in the first 24 h, increasing unlabeled CO2 efflux by 173%, 89% and 36% above control for additions of 0.49, 2.4 and 4.9 mmol OMG g-1 soil, respectively. In contrast, glucose caused low or negative priming on the first day. On the first day after OMG addition, a negative correlation between priming and OMG mineralization indicated that triggering is a valid mechanism of microbial activation during a famine-feast transition, but is short-lived. Glucose mineralization peaked on the second day for medium and high additions, coinciding with peaks in positive priming. Maximum substrate mineralization also coincided with peaks in priming for medium and high OMG levels, but these occurred 9 and 11 days after addition, respectively. This revealed non-triggering priming mechanisms, which contributed most to priming and were closely coupled to substrate mineralization. By separating energy- and substrate-dependent metabolic processes from triggering processes, the glucose analogue 3-O-methyl-D-glucose enabled triggering to be demonstrated, but triggering by glucose occurs without contributing greatly to priming

What Does an Exemplary Middle School Mathematics Teacher Look Like? The Use of a Professional Development Rubric

A School University Research Network (SURN) committee composed of current mathematics teachers, central office math supervisors, building administrators, mathematicians, and mathematics educators researched numerous sources regarding best practices in mathematics instruction. The resulting professional development rubric synthesizes their findings and can serve a professional development role by providing teachers and administrators with a tool to develop clarity and consensus on best mathematics instructional practices, and how these practices are implemented in the classroom. It is also being used as a tool for cooperating teachers in their supervision of student teachers and as a reflective method for self-evaluation

Correlation of the Quasi-Periodic Oscillation Frequencies of White Dwarf, Neutron Star, and Black Hole Binaries

Using data obtained in 1994 June/July with the Extreme Ultraviolet Explorer deep survey photometer and in 2001 January with the Chandra X-ray Observatory Low Energy Transmission Grating Spectrograph, we investigate the extreme-ultraviolet (EUV) and soft X-ray oscillations of the dwarf nova SS Cyg in outburst. We find quasi-periodic oscillations (QPOs) at nu_0 ~ 0.012 Hz and nu_1 ~ 0.13 Hz in the EUV flux and at nu_0 ~ 0.0090 Hz, nu_1 ~ 0.11 Hz, and possibly nu_2 ~ nu_0 + nu_1 ~ 0.12 Hz in the soft X-ray flux. These data, combined with the optical data of Woudt & Warner for VW Hyi, extend the Psaltis, Belloni, & van der Klis nu_high-nu_low correlation for neutron star and black hole low-mass X-ray binaries (LMXBs) nearly two orders of magnitude in frequency, with nu_low ~ 0.08 nu_high. This correlation identifies the high-frequency quasi-coherent oscillations (so-called ``dwarf nova oscillations'') of cataclysmic variables (CVs) with the kilohertz QPOs of LMXBs, and the low-frequency QPOs of CVs with the horizontal branch oscillations (or the broad noise component identified as such) of LMXBs. Assuming that the same mechanisms produce the QPOs in white dwarf, neutron star, and black hole binaries, we find that the data exclude the relativistic precession model and the magnetospheric and sonic-point beat-frequency models (as well as any model requiring the presence or absence of a stellar surface or magnetic field); more promising are models that interpret QPOs as manifestations of disk accretion onto any low-magnetic field compact object.Comment: 15 pages including 4 encapsulated postscript figures; LaTeX format, uses aastex.cls; accepted on 2002 July 23 for publication in The Astrophysical Journa

Evaluation of bcl-2 protein expression and 14;18 translocation as prognostic markers in follicular lymphoma.

Conflicting results have been published on the prognostic significance of t(14;18) in follicular lymphoma: Yunis et al. (1989) reported that its presence indicated poor response to therapy and short survival, whereas Levine et al. (1988) showed no difference in prognosis between cases with and without the translocation. However these results were based on small series of cases and on follow-up periods (no longer than 7 years) which are relatively short for a disease with such a slow clinical evolution. Here we report an investigation of 70 cases of follicular lymphoma with long term follow-up data (up to 17 years). This series has been studied for the presence of the 14;18 translocation and for the expression of bcl-2 protein. Our results show that there are no grounds for considering either the 14;18 translocation or the expression of the bcl-2 protein to be useful prognostic markers in clinical practice

Contrasting effects of organic and mineral nitrogen challenge the N-Mining Hypothesis for soil organic matter priming

© 2018 Elsevier Ltd Addition of easily available organic substances to soil often increases the CO2 efflux from pre-existing soil carbon (C). This phenomenon is often explained in terms of the Nitrogen (N)-Mining Hypothesis. According to this proposed – but never conclusively proven – mechanism, increased C availability induces N limitation in microbes, which then access N by degrading soil organic matter (SOM) – a priming effect. This is supported by some experiments demonstrating reduced CO2 efflux after mineral N addition. However, amino acids cause priming, despite their very low C:N ratios and rapid deamination to mineral N. To explore this contradiction, we applied 14C- and 15N-labelled C and N sources (glucose, alanine and ammonium sulfate) to rigorously test two key predictions of the N-Mining Hypothesis: (i) an amino acid should stimulate much less priming than glucose, and (ii) priming should be similarly suppressed for an amino acid or a stoichiometrically equivalent addition of glucose plus mineral N. Both of these key predictions of the N-Mining Hypothesis failed. Efflux of CO2 from native C was essentially determined by the type and amount of C added, with alanine stimulating more priming than glucose (16–50% cumulative increase relative to control, versus 0–25%, respectively). Higher C additions caused more priming than low additions. Mineral N reduced native-C-derived CO2 efflux when added alone or with organic substrates, but this effect was independent of the organic C additions and did not influence C-induced priming. These results were inconsistent with the hypothesized role of N mining in priming. We conclude that the N-Mining Hypothesis, at least in its current form, is not a universal explanation for observed priming phenomena. Instead, we observed a strong correlation between the rates of priming and the mineralization of the added substrates, especially during the first 8 days. This indicated that priming was best explained by energy-induced synthesis of SOM-degrading exoenzymes, possibly in combination with apparent priming from accelerated turnover of microbial biomass

Mineralization of "non-metabolizable" Glucose analogues in soil: Potential chemosensory mimics of Glucose

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Glucose is widely used to study the dynamics of easily available organics in soil. Pure culture studies have revealed that many microorganisms can sense and respond to glucose through chemosensory mechanisms that are not directly reliant on energy catabolism. However, the rapid mineralization of glucose by microorganisms makes it difficult to disentangle its energy effects from such non-catabolic interactions. "Non-metabolizable" glucose analogues have proven useful in mechanistic studies of glucose in pure culture, but have never been applied to complex microbial communities in soil. We sought to determine how their mineralization in soil differs from that of glucose, and whether they have potential as a new approach for investigating chemosensory mechanisms in soil microbiology. We incubated soil from an agricultural Haplic Luvisol under controlled conditions for 24 d and monitored CO 2 efflux after addition of (1) glucose, and three "non-metabolizable" glucose analogues: (2) 2-deoxyglucose (DG), (3) a-methylglucoside (aMG), and (4) 3-O-methyl-glucose (OMG), at three concentration levels, along with a control. All three analogues did in fact produce a large increase in soil CO 2 efflux, but the dynamics of their mineralization differed from the rapid degradation seen for glucose. At medium and high concentrations, CO 2 efflux peaked between 2.5 and 4 d after amendment with DG and aMG, and was delayed by about one week for OMG. The markedly different patterns of mineralization between glucose and OMG offer a new tool for investigating the behavior of glucose in soil. By using OMG as a glucose model, chemosensory mechanisms could be studied with limited interference from energy catabolism

Mineralization of “non-metabolizable” glucose analogues in soil: potential chemosensory mimics of glucose

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimGlucose is widely used to study the dynamics of easily available organics in soil. Pure culture studies have revealed that many microorganisms can sense and respond to glucose through chemosensory mechanisms that are not directly reliant on energy catabolism. However, the rapid mineralization of glucose by microorganisms makes it difficult to disentangle its energy effects from such non-catabolic interactions. “Non-metabolizable” glucose analogues have proven useful in mechanistic studies of glucose in pure culture, but have never been applied to complex microbial communities in soil. We sought to determine how their mineralization in soil differs from that of glucose, and whether they have potential as a new approach for investigating chemosensory mechanisms in soil microbiology. We incubated soil from an agricultural Haplic Luvisol under controlled conditions for 24 d and monitored CO2 efflux after addition of (1) glucose, and three “non-metabolizable” glucose analogues: (2) 2-deoxyglucose (DG), (3) α-methylglucoside (αMG), and (4) 3-O-methyl-glucose (OMG), at three concentration levels, along with a control. All three analogues did in fact produce a large increase in soil CO2 efflux, but the dynamics of their mineralization differed from the rapid degradation seen for glucose. At medium and high concentrations, CO2 efflux peaked between 2.5 and 4 d after amendment with DG and αMG, and was delayed by about one week for OMG. The markedly different patterns of mineralization between glucose and OMG offer a new tool for investigating the behavior of glucose in soil. By using OMG as a glucose model, chemosensory mechanisms could be studied with limited interference from energy catabolism