Accretion column disruption in GX 1+4

Daily observations of the binary X-ray pulsar GX 1+4 were made with the Rossi X-ray Timing Explorer (RXTE) satellite between 1997 May 16-20 as part of a four-month monitoring program. On May 17 the sharp dips normally observed in the lightcurve were all but absent, resulting in a pulse fraction f_p approx. 0.5 instead of the more typical value of approx. 0.8 measured before and after. Also observed was a dramatic hardening of the 2-40 keV phase-averaged spectrum. The power-law photon index was 1.16 +/- 0.02, whereas values of 1.6-2.0 are more typical. In terms of a Comptonization continuum component, the optical depth for scattering was tau approx 19, with 4-6 the usual range for RXTE spectra (Galloway 2000). Pulse-phase spectrosopy indicates that tau is decreased relative to the phase-averaged value around the primary minimum, where an increase is normally observed. The reduced depth of the dip is interpreted as disruption of the accretion column, and the accompanying spectral variation suggests a substantially different accretion regime than is usual for this source.Comment: 10 pages, 2 figures, minor abstract typo and wording of final paragraph correcte

Discovery of optical pulsations in V2116 Ophiuchi/GX 1+4

We report the detection of pulsations with $\sim 124$ s period in V2116 Oph, the optical counterpart of the low-mass X-ray binary GX 1+4. The pulsations are sinusoidal with modulation amplitude of up to 4% in blue light and were observed in ten different observing sessions during 1996 April-August using a CCD photometer at the 1.6-m and 0.6-m telescopes of Laborat\'orio Nacional de Astrof\'{\i}sica, in Brazil. The pulsations were also observed with the $UBVRI$ fast photometer. With only one exception the observed optical periods are consistent with those observed by the BATSE instrument on board the Compton Gamma Ray Observatory at the same epoch. There is a definite correlation between the observability of pulsations and the optical brightness of the system: V2116~Oph had $R$ magnitude in the range $15.3-15.5$ when the pulsed signal was detected, and $R = 16.0-17.7$ when no pulsations were present. The discovery makes GX 1+4 only the third of $\sim 35$ accretion-powered X-ray pulsars to be firmly detected as a pulsating source in the optical. The presence of flickering and pulsations in V2116 Oph adds strong evidence for an accretion disk scenario in this system. The absolute magnitude of the pulsed component on 1996 May 27 is estimated to be $M_V \sim -1.5$. The implied dimensions for the emitting region are 1.1 R_{\sun}, 3.2 R_{\sun}, and 7.0 R_{\sun}, for black-body spectral distributions with $T = 10^5$ K, $2 \times 10^4$ K, and $1 \times 10^4$ K, respectively.Comment: 9 pages, 3 figures in PostScript, latex, accepted for publication on the Astrophysical Journal Letter

The Cellular Distribution of Serotonin Transporter Is Impeded on Serotonin-Altered Vimentin Network

BACKGROUND:The C-terminus of the serotonin transporter (SERT) contains binding domains for different proteins and is critical for its functional expression. In endogenous and heterologous expression systems, our proteomic and biochemical analysis demonstrated that an intermediate filament, vimentin, binds to the C-terminus of SERT. It has been reported that 5HT-stimulation of cells leads to disassembly and spatial reorientation of vimentin filaments. METHODOLOGY/PRINCIPAL FINDINGS:We tested the impact of 5HT-stimulation on vimentin-SERT association and found that 5HT-stimulation accelerates the translocation of SERT from the plasma membrane via enhancing the level of association between phosphovimentin and SERT. Furthermore a progressive truncation of the C-terminus of SERT was performed to map the vimentin-SERT association domain. Deletion of up to 20, but not 14 amino acids arrested the transporters at intracellular locations. Although, truncation of the last 14 amino acids, did not alter 5HT uptake rates of transporter but abolished its association with vimentin. To understand the involvement of 5HT in phosphovimentin-SERT association from the plasma membrane, we further investigated the six amino acids between Delta14 and Delta20, i.e., the SITPET sequence of SERT. While the triple mutation on the possible kinase action sites, S(611), T(613), and T(616) arrested the transporter at intracellular locations, replacing the residues with aspartic acid one at a time altered neither the 5HT uptake rates nor the vimentin association of these mutants. However, replacing the three target sites with alanine, either simultaneously or one at a time, had no significant effect on 5HT uptake rates or the vimentin association with transporter. CONCLUSIONS/SIGNIFICANCE:Based on our findings, we propose that phosphate modification of the SITPET sequence differentially, one at a time exposes the vimentin binding domain on the C-terminus of SERT. Conversely, following 5HT stimulation, the association between vimentin-SERT is enhanced which changes the cellular distribution of SERT on an altered vimentin network

Effects of climate and atmospheric nitrogen deposition on early to mid-term stage litter decomposition across biomes

Litter decomposition is a key process for carbon and nutrient cycling in terrestrial ecosystems and is mainly controlled by environmental conditions, substrate quantity and quality as well as microbial community abundance and composition. In particular, the effects of climate and atmospheric nitrogen (N) deposition on litter decomposition and its temporal dynamics are of significant importance, since their effects might change over the course of the decomposition process. Within the TeaComposition initiative, we incubated Green and Rooibos teas at 524 sites across nine biomes. We assessed how macroclimate and atmospheric inorganic N deposition under current and predicted scenarios (RCP 2.6, RCP 8.5) might affect litter mass loss measured after 3 and 12 months. Our study shows that the early to mid-term mass loss at the global scale was affected predominantly by litter quality (explaining 73% and 62% of the total variance after 3 and 12 months, respectively) followed by climate and N deposition. The effects of climate were not litter-specific and became increasingly significant as decomposition progressed, with MAP explaining 2% and MAT 4% of the variation after 12 months of incubation. The effect of N deposition was litter-specific, and significant only for 12-month decomposition of Rooibos tea at the global scale. However, in the temperate biome where atmospheric N deposition rates are relatively high, the 12-month mass loss of Green and Rooibos teas decreased significantly with increasing N deposition, explaining 9.5% and 1.1% of the variance, respectively. The expected changes in macroclimate and N deposition at the global scale by the end of this century are estimated to increase the 12-month mass loss of easily decomposable litter by 1.1-3.5% and of the more stable substrates by 3.8-10.6%, relative to current mass loss. In contrast, expected changes in atmospheric N deposition will decrease the mid-term mass loss of high-quality litter by 1.4-2.2% and that of low-quality litter by 0.9-1.5% in the temperate biome. Our results suggest that projected increases in N deposition may have the capacity to dampen the climate-driven increases in litter decomposition depending on the biome and decomposition stage of substrate

Alzheimer's disease cerebrospinal fluid biomarker in cognitively normal subjects

In a large multicentre study, Toledo et al. examine core Alzheimer's disease CSF biomarkers in 1233 cognitively normal subjects aged 40-85 years. Alzheimer disease-like changes in Aβ1-42 are seen as early as middle age, while APOE genotype strongly modifies age-related effects on both Aβ1-42 and phosphorylated/total ta

How Past and Present Influence the Foraging of Clonal Plants?

Clonal plants spreading horizontally and forming a network structure of ramets exhibit complex growth patterns to maximize resource uptake from the environment. They respond to spatial heterogeneity by changing their internode length or branching frequency. Ramets definitively root in the soil but stay interconnected for a varying period of time thus allowing an exchange of spatial and temporal information. We quantified the foraging response of clonal plants depending on the local soil quality sampled by the rooting ramet (i.e. the present information) and the resource variability sampled by the older ramets (i.e. the past information). We demonstrated that two related species, Potentilla reptans and P. anserina, responded similarly to the local quality of their environment by decreasing their internode length in response to nutrient-rich soil. Only P. reptans responded to resource variability by decreasing its internode length. In both species, the experience acquired by older ramets influenced the plastic response of new rooted ramets: the internode length between ramets depended not only on the soil quality locally sampled but also on the soil quality previously sampled by older ramets. We quantified the effect of the information perceived at different time and space on the foraging behavior of clonal plants by showing a non-linear response of the ramet rooting in the soil of a given quality. These data suggest that the decision to grow a stolon or to root a ramet at a given distance from the older ramet results from the integration of the past and present information about the richness and the variability of the environment

Inequalities in the use of secondary prevention of cardiovascular disease by socioeconomic status: evidence from the PURE observational study

Background: There is little evidence on the use of secondary prevention medicines for cardiovascular disease by socioeconomic groups in countries at different levels of economic development. Methods: We assessed use of antiplatelet, cholesterol, and blood-pressure-lowering drugs in 8492 individuals with self-reported cardiovascular disease from 21 countries enrolled in the Prospective Urban Rural Epidemiology (PURE) study. Defining one or more drugs as a minimal level of secondary prevention, wealth-related inequality was measured using the Wagstaff concentration index, scaled from −1 (pro-poor) to 1 (pro-rich), standardised by age and sex. Correlations between inequalities and national health-related indicators were estimated. Findings: The proportion of patients with cardiovascular disease on three medications ranged from 0% in South Africa (95% CI 0–1·7), Tanzania (0–3·6), and Zimbabwe (0–5·1), to 49·3% in Canada (44·4–54·3). Proportions receiving at least one drug varied from 2·0% (95% CI 0·5–6·9) in Tanzania to 91·4% (86·6–94·6) in Sweden. There was significant (p<0·05) pro-rich inequality in Saudi Arabia, China, Colombia, India, Pakistan, and Zimbabwe. Pro-poor distributions were observed in Sweden, Brazil, Chile, Poland, and the occupied Palestinian territory. The strongest predictors of inequality were public expenditure on health and overall use of secondary prevention medicines. Interpretation: Use of medication for secondary prevention of cardiovascular disease is alarmingly low. In many countries with the lowest use, pro-rich inequality is greatest. Policies associated with an equal or pro-poor distribution include free medications and community health programmes to support adherence to medications. Funding: Full funding sources listed at the end of the paper (see Acknowledgments)

Spin period evolution of GX 1+4

We aim both to complement the existing data on the spin history of the peculiar accreting X-ray pulsar GX 1+4 with more past and current data from BeppoSAX, INTEGRAL, and Fermi and to interpret the evolution in the framework of accretion theory. We used source light curves obtained from BeppoSAX/WFC and INTEGRAL/ISGRI to derive pulse periods using an epoch-folding analysis. Fermi/GBM data were analyzed by fitting a constant plus a Fourier expansion to background-subtracted rates, and maximizing the Y2 statistic. We completed the sample with hard X-ray light curves from Swift/BAT. The data were checked for correlations between flux and changes of the pulsar spin on different timescales. The spin-down of the pulsar continues with a constant change in frequency, i.e., an apparently accelerating change in the period. Over the past three decades, the pulse period has increased by about ~50%. Short-term fluctuations on top of this long-term trend do show anti-correlation with the source flux. Possible explanations of the observed long-term frequency and its dependence on flux are discussed.Comment: Accepted for publication in A&