Ultrasensitive gene regulation by positive feedback loops in nucleosome modification

Eukaryotic transcription involves the synergistic interaction of many different proteins. However, the question remains how eukaryotic promoters achieve ultrasensitive or threshold responses to changes in the concentration or activity of a single transcription factor (TF). We show theoretically that by recruiting a histone-modifying enzyme, a TF binding non-cooperatively to a single site can change the balance between opposing positive feedback loops in histone modification to produce a large change in gene expression in response to a small change in concentration of the TF. This mechanism can also generate bistable promoter responses, allowing a gene to be on in some cells and off in others, despite the cells being in identical conditions. In addition, the system provides a simple means by which the activities of many TFs could be integrated at a promoter

Point-of-care laboratory analyses of intraosseous, arterial and central venous samples during experimental cardiopulmonary resuscitation

Introduction: Screening and correcting reversible causes of cardiac arrest (CA) are an essential part of cardiopulmonary resuscitation (CPR). Point-ofcare (POC) laboratory analyses are used for screening pre-arrest pathologies, such as electrolyte disorders and acid-base balance disturbances. The aims of this study were to compare the intraosseous (10), arterial and central venous POC values during CA and CPR and to see how the CPR values reflect the pre-arrest state. Methods: We performed an experimental study on 23 anaesthetised pigs. After induction of ventricular fibrillation (VF), we obtained POC samples from the 10 space, artery and central vein simultaneously at three consecutive time points. We observed the development of the values during CA and CPR and compared the CPR values to the pre-arrest values. Results: The 10, arterial and venous values changed differently from one another during the course of CA and CPR. Base excess and pH decreased in the venous and 10 samples during untreated VF, but in the arterial samples, this only occurred after the onset of CPR. The 10, arterial and venous potassium values were higher during CPR compared to the pre-arrest arterial values (mean elevations 4.4 mmol/l (SD 0.72), 3.3 mmol/l (0.78) and 2.8 mmol/l (0.94), respectively). Conclusions: A dynamic change occurs in the common laboratory values during CA and CPR. POC analyses of lactate, pH, sodium and calcium within 10 samples are not different from analyses of arterial or venous blood. Potassium values in 10, arterial and venous samples during CPR are higher than the pre-arrest arterial values.Peer reviewe

The 1966-1967 Outburst of V1647 Orionis and the Appearance of McNeil's Nebula

We present the results of an investigation aimed at characterizing previous eruptions of V1647 Orionis, the illuminating star of McNeil's Nebula. Photographic plates and films from the Asiago Observatory (1960-1998) and Harvard Observatory (1898-1974) collections were inspected for the nebula. We have determined that, to the plate limits, the known eruption of 1966-1967 is the only one detected during the 38 yr period covered by the Asiago archive. In the Harvard collection, we did not find any additional occurrences in approximately 400 plates of the region taken over the last 100 yr. Based on the Asiago material, we here present a study of the 1966-1967 event. McNeil's Nebula and V1647 Ori are clearly visible on 19 plates obtained with the Asiago 67/92 cm Schmidt telescope from 1966 October 22 to 1967 March 4. The object is not seen on plates taken in 1966 March nor in 1967 November, thus setting a minimum duration time for the eruptive event of 5 months and a maximum of 20 months. The 19 plates showing McNeil's Nebula were digitized, and a morphological and photometric analysis of the object was undertaken. These data show temporal photometric variability, as well as structural differences between different color bands. We finally compare the 1966-1967 event to the recent 2003-2006 eruption and consider the nature of V1647 Ori within the framework of EX Lupi- and FU Orionis-type eruptions

Exploring the parent population of beamed NLS1s: from the black hole to the jet

The aim of this work is to understand the nature of the parent population of beamed narrow-line Seyfert 1 galaxies (NLS1s), by studying the physical properties of three parent candidates samples: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s and disk-hosted radio-galaxies. In particular, we focused on the black hole mass and Eddington ratio distribution and on the interactions between the jet and the narrow-line region.Comment: 6 pages, 2 figures, to appear in Proceedings of High Energy Phenomena in Relativistic Outflows (HEPRO) V, Workshop Series of the Argentinian Astronomical Societ

Symbiotic Stars in OGLE Data I. Large Magellanic Cloud Systems

Symbiotic stars are long-orbital-period interacting-binaries characterized by extended emission over the whole electromagnetic range and by complex photometric and spectroscopic variability. In this paper, the first of a series, we present OGLE light curves of all the confirmed symbiotic stars in the Large Magellanic Cloud, with one exception. By careful visual inspection and combined time-series analysis techniques, we investigate for the first time in a systematic way the photometric properties of these astrophysical objects, trying in particular to distinguish the nature of the cool component (e.g., Semi-Regular Variable vs. OGLE Small-Amplitude Red Giant), to provide its first-order pulsational ephemerides, and to link all this information with the physical parameters of the binary system as a whole. Among the most interesting results, there is the discovery of a 20-year-long steady fading of Sanduleak's star, a peculiar symbiotic star known to produce the largest stellar jet ever discovered. We discuss by means of direct examples the crucial need for long-term multi-band observations to get a real understanding of symbiotic and other interacting binary stars. We eventually introduce BOMBOLO, a multi-band simultaneous imager for the SOAR 4m Telescope, whose design and construction we are currently leading.Comment: 16 pages, 4 Tables, 12 Figures. Accepted for publication in MNRA

Unveiling the parent population of beamed narrow-line Seyfert 1s

Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN) recently identified as a new class of $\gamma$-ray sources. The high energy emission is explained by the presence of a relativistic jet observed at small angles, just like in the case of blazars. When the latter are observed at larger angles they appear as radio-galaxies, but an analogue parent population for beamed NLS1s has not yet been determined. In this work we analyze this problem by studying the physical properties of three different samples of parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s, and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In our approach, we first derived black hole mass and Eddington ratio from the optical spectra, then we investigated the interaction between the jet and the narrow-line region from the [O III] $\lambda\lambda$4959,5007 lines. Finally, the radio luminosity function allowed us to compare their jet luminosity and hence determine the relations between the samples.Comment: 6 pages, no figures. Proceedings of the 28th Texas Symposium, Geneva, December 13-18, 201

Soil ecosystem services of the under different uses in the Colombian Amazonia

Agroforestry systems (AFs), where agricultural and livestock crops are associated with woody plants, are known as sustainable systems, that conserve biodiversity and improve the provision of ecosystem services without compromising productivity. This work focuses mainly on cacao AFs, which have been related to different ecosystem services in tropical regions. Especially, our study focuses on the ability of the cacao AFs to improve soil ecosystem services in the Colombian Amazon region. We focused on soil ecosystems ecosystem services in the Colombian Amazonia because: of the social importance of cacao production system in the study region, specifically within the post conflict context; the lack of knowledge on the capacity of cacao AFs to offer soil ecosystem services in the study zone and its capacity in restoring ecosystem services in degraded soils. Aim The objective of our work was to evaluate the soil quality in different cacao agroforestry systems in the Colombian Amazonia, and to compare these evaluated soil quality of soil quality in Forest and Pasture. Material and methods The study was conducted at the Macagual Amazon Research Center, located west of the Colombian Amazon. We evaluated soil quality in four types of AFs Cacao, presenting different establishment, composition and structural characteristics; but also in a plot of native forest composed of characteristic species of the area, and in a plot of pasture composed of grasses. In the different plot of each land use, we evaluated the diversity of macrofauna, the morphology of aggregate, the physical properties and the soil chemistry. We summarized these variables in a General Indicator of Soil Quality GISQ, characterizing soil quality in the different land uses. Major results and Conclusion It was found that the level of intensification among land uses (Bosque>AFs>Pasture) affects the decrease of the macrofauna populations, which was related to soil compaction (physical properties). Chemical fertility improved with the establishment of AFs influenced by the application of amendments and organic fertilizers. When establishing agroforestry systems from pasture areas at a certain level of degradation, the GISQ scale was found to increase by 42%. Our results indicate that AFs practices can definitely be used as a restoration strategy, for the recovery of degraded areas

Discovery of a new photometric sub-class of faint and fast classical novae

We present photometric and spectroscopic follow-up of a sample of extragalactic novae discovered by the Palomar 60-inch telescope during a search for "Fast Transients In Nearest Galaxies" (P60-FasTING). Designed as a fast cadence (1-day) and deep (g < 21 mag) survey, P60-FasTING was particularly sensitive to short-lived and faint optical transients. The P60-FasTING nova sample includes 10 novae in M31, 6 in M81, 3 in M82, 1 in NGC2403 and 1 in NGC891. This significantly expands the known sample of extragalactic novae beyond the Local Group, including the first discoveries in a starburst environment. Surprisingly, our photometry shows that this sample is quite inconsistent with the canonical Maximum Magnitude Rate of Decline (MMRD) relation for classical novae. Furthermore, the spectra of the P60-FasTING sample are indistinguishable from classical novae. We suggest that we have uncovered a sub-class of faint and fast classical novae in a new phase space in luminosity-timescale of optical transients. Thus, novae span two orders of magnitude in both luminosity and time. Perhaps, the MMRD, which is characterized only by the white dwarf mass, was an over-simplification. Nova physics appears to be characterized by quite a rich four-dimensional parameter space in white dwarf mass, temperature, composition and accretion rate.Comment: Submitted to ApJ, 12 pages. High resolution version at http://www.astro.caltech.edu/~mansi/msFasting.pd