Scaling law in target-hunting processes

We study the hunting process for a target, in which the hunter tracks the goal by smelling odors it emits. The odor intensity is supposed to decrease with the distance it diffuses. The Monte Carlo experiment is carried out on a 2-dimensional square lattice. Having no idea of the location of the target, the hunter determines its moves only by random attempts in each direction. By sorting the searching time in each simulation and introducing a variable $x$ to reflect the sequence of searching time, we obtain a curve with a wide plateau, indicating a most probable time of successfully finding out the target. The simulations reveal a scaling law for the searching time versus the distance to the position of the target. The scaling exponent depends on the sensitivity of the hunter. Our model may be a prototype in studying such the searching processes as various foods-foraging behavior of the wild animals.Comment: 7 figure

Oxygen isotopes implanted in the LDEF spacecraft

Secondary ion mass spectrometry was used to study oxygen implanted in the surface of copper from the Long Duration Exposure Facility (LDEF). Oxidation that occurred in orbit shows a characteristic oxygen isotope composition, depleted in O-18. The measured depletion is comparable to the predicted depletion (45 percent) based on a model of the gravitational separation of the oxygen isotopes. The anomalous oxygen was contained within 10nm of the surface. Tray E10 was calculated to have received 5.14 x 10(exp 21) atoms of oxygen cm(sup -2) during the LDEF mission and so there is sufficient anomalous implanted oxygen present in the surface to obtain a reliable isotopic profile

A high Eddington-ratio, true Seyfert 2 galaxy candidate: implications for broad-line-region models

A bright, soft X-ray source was detected on 2010 July 14 during an XMM--Newton slew at a position consistent with the galaxy GSN 069 (z=0.018). Previous ROSAT observations failed to detect the source and imply that GSN 069 is now >240 times brighter than it was in 1994 in the soft X-ray band. We report here results from a ~1 yr monitoring with Swift and XMM-Newton, as well as from optical spectroscopy. GSN 069 is an unabsorbed, ultra-soft source in X-rays, with no flux detected above ~1 keV. The soft X-rays exhibit significant variability down to timescales of hundreds of seconds. The UV-to-X-ray spectrum of GSN 069 is consistent with a pure accretion disc model which implies an Eddington ratio of ~0.5 and a black hole mass of ~ 1.2 million solar masses. A new optical spectrum, obtained ~3.5 months after the XMM-Newton slew detection, is consistent with earlier spectra and lacks any broad line component, classifying the source as a Seyfert 2 galaxy. The lack of cold X-ray absorption and the short timescale variability in the soft X-rays rule out a standard Seyfert 2 interpretation of the X-ray data. We discuss our results within the framework of two possible scenarios for the broad-line-region (BLR) in AGN, namely the two-phase model (cold BLR clouds in pressure equilibrium with a hotter medium), and models in which the BLR is part of an outflow, or disc-wind. Finally, we point out that GSN 069 may be a member of a population of super-soft AGN whose SED is completely dominated by accretion disc emission, as it is the case in some black hole X-ray binary transients during their outburst evolution. The disc emission for a typical AGN with larger black hole mass than GSN 069 does not enters the soft X-ray band, so that GSN 069-like objects would likely be missed by current X-ray surveys, or mis-classified as Compton-thick candidates. (ABRIDGED)Comment: Accepted for publication in MNRA

Optical, near-IR and XX-ray observations of SN 2015J and its host galaxy

SN 2015J was discovered on April 27th 2015 and is classified as a type IIn supernova. At first, it appeared to be an orphan SN candidate, i.e. without any clear identification of its host galaxy. Here, we present the analysis of the observations carried out {by the VLT 8-m class telescope with the FORS2 camera in the R band and the Magellan telescope (6.5 m) equipped with the IMACS Short-Camera (V and I filters) and the FourStar camera (Ks filter)}. We show that SN 2015J resides in what appears to be a very compact galaxy establishing a relation between the SN event and its natural host. We also present and discuss archival and new $X$-ray data centred on SN 2015J. At the time of the supernova explosion, Swift/XRT observations were made and a weak X-ray source was detected at the location of SN 2015J. Almost one year later, the same source was unambiguously identified during serendipitous observations by Swift/XRT and $XMM$-Newton, clearly showing an enhancement of the 0.3-10 keV band flux by a factor $\simeq 30$ with respect to the initial state. Swift/XRT observations show that the source is still active in the $X$-rays at a level of $\simeq 0.05$ counts s$^{-1}$. The unabsorbed X-ray luminosity derived from the {\it XMM}-Newton slew and SWIFT observations, $L_{x}\simeq 5\times10^{41}$ erg s$^{-1}$, places SN 2015J among the brightest young supernovae in X-rays.Comment: The Astrophysical Journal, Volume 850, Number

Unusual Response to a Localized Perturbation in a Generalized Elastic Model

The generalized elastic model encompasses several physical systems such as polymers, membranes, single file systems, fluctuating surfaces and rough interfaces. We consider the case of an applied localized potential, namely an external force acting only on a single (tagged) probe, leaving the rest of the system unaffected. We derive the fractional Langevin equation for the tagged probe, as well as for a generic (untagged) probe, where the force is not directly applied. Within the framework of the fluctuation-dissipation relations, we discuss the unexpected physical scenarios arising when the force is constant and time periodic, whether or not the hydrodynamic interactions are included in the model. For short times, in case of the constant force, we show that the average drift is linear in time for long range hydrodynamic interactions and behaves ballistically or exponentially for local hydrodynamic interactions. Moreover, it can be opposite to the direction of external disturbance for some values of the model's parameters. When the force is time periodic, the effects are macroscopic: the system splits into two distinct spatial regions whose size is proportional to the value of the applied frequency. These two regions are characterized by different amplitudes and phase shifts in the response dynamics

Knee joint neuromuscular activation performance during muscle damage and superimposed fatigue

This study examined the concurrent effects of exercise-induced muscle damage and superimposed acute fatigue on the neuromuscular activation performance of the knee flexors of nine males (age: 26.7 ± 6.1yrs; height 1.81 ± 0.05m; body mass 81.2 ± 11.7kg [mean ± SD]). Measures were obtained during three experimental conditions: (i) FAT-EEVID, involving acute fatiguing exercise performed on each assessment occasion plus a single episode of eccentric exercise performed on the first occasion and after the fatigue trial; (ii) FAT, involving the fatiguing exercise only and; (iii) CON consisting of no exercise. Assessments were performed prior to (pre) and at lh, 24h, 48h, 72h, and 168h relative to the eccentric exercise. Repeated-measures ANOVAs showed that muscle damage within the FAT-EEVID condition elicited reductions of up to 38%, 24%) and 65%> in volitional peak force, electromechanical delay and rate of force development compared to baseline and controls, respectively (F[io, 80] = 2.3 to 4.6; p to 30.7%>) following acute fatigue (Fp; i6] = 4.3 to 9.1; p ; Fp, iq = 3.9; p <0.05). The safeguarding of evoked muscle activation capability despite compromised volitional performance might reveal aspects of capabilities for emergency and protective responses during episodes of fatigue and antecedent muscle damaging exercise

Disappearance of quasi-periodic-eruptions (QPEs) in GSN 069, simultaneous X-ray re-brightening, and predicted QPE re-appearance

We study the short- and long-timescale properties of quasi-periodic eruptions (QPEs) in GSN 069 and its overall X-ray evolution over the past 11 yr using 11 XMM-Newton and 1 Chandra observations from December 2010 to December 2021. QPEs are a transient phenomenon in GSN 069 last detected in January 2020 with a life-time between 1 and 5.5 yr. On short timescales, the QPE intensity and recurrence time oscillate defining alternating strong/weak QPEs and long/short recurrence times. The quiescent level variability in observations with QPEs exhibits a quasi-periodic oscillation (QPO) at the average observation-dependent recurrence time peaking with a delay of a few hr w.r.t. the preceding QPE. A significant late-time X-ray re-brightening starting with the QPE disappearance is observed in the long-term light curve of the quiescent emission, and the overall X-ray evolution follows the relation expected from constant-area blackbody emission. QPEs in GSN 069 are consistent with being produced by repeating tidal stripping events of a white dwarf (WD) donor in a highly eccentric orbit around the supermassive black hole, one QPE being produced at each pericenter passage. Our data suggest that the WD was partially disrupted when QPEs disappeared in GSN 069, giving rise to the observed X-ray re-brightening. We predict the re-appearance of QPEs in GSN 0699 in the near future with different recurrence times than currently detected QPEs, as the surviving core will again suffer a series of tidal stripping events at pericenter passage.Comment: Submitted to A&A. Comments welcom

TYC 8380-1953-1: Discovery of an RS CVn binary through the XMM-Newton slew survey

In this paper we report the discovery of the chromospherically active (RS CVn type) binary TYC 8380-1953-1 through the XMM-Newton slew survey and present results of our optical and X-ray follow-up. With a flux limit of $6 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the soft band ($0.2 - 2$ keV), the XMM-Newton slew has a similar sensitivity to the ROSAT All Sky Survey allowing interesting sources to be identified by their long-term variability. Two different types of stellar sources are detected in shallow X-ray surveys: young stars (both pre-main and main sequence stars) and chromospherically active binaries (BY Dra and RS CVn type systems). The discovery of stars in such surveys and the study of their nature through optical follow-ups is valuable to determine their spatial distribution and scale height in the Galaxy. Our analysis shows that TYC 8380-1953-1 is a double-lined spectroscopic binary with both components having similar spectral type (likely K0/2+K3/5) and luminosity. With a typical coronal temperature for an RS CVn system ($kT \sim 1.15$ keV) and an X-ray luminosity in the $0.3-10$ keV energy band higher than $4 \times 10^{31}$ erg\,s$^{-1}$, TYC 8380-1953-1 lies among the most X-ray luminous RS CVn binaries.Comment: Accepted for publication in the PASP. 18 pages, 10 figure

Microbial Communities Under Distinct Thermal and Geochemical Regimes in Axial and Off-Axis Sediments of Guaymas Basin

Cold seeps and hydrothermal vents are seafloor habitats fueled by subsurface energy sources. Both habitat types coexist in Guaymas Basin in the Gulf of California, providing an opportunity to compare microbial communities with distinct physiologies adapted to different thermal regimes. Hydrothermally active sites in the southern Guaymas Basin axial valley, and cold seep sites at Octopus Mound, a carbonate mound with abundant methanotrophic cold seep fauna at the Central Seep location on the northern off-axis flanking regions, show consistent geochemical and microbial differences between hot, temperate, cold seep, and background sites. The changing microbial actors include autotrophic and heterotrophic bacterial and archaeal lineages that catalyze sulfur, nitrogen, and methane cycling, organic matter degradation, and hydrocarbon oxidation. Thermal, biogeochemical, and microbiological characteristics of the sampling locations indicate that sediment thermal regime and seep-derived or hydrothermal energy sources structure the microbial communities at the sediment surface

Candidate tidal disruption events from the XMM-Newton Slew Survey

In recent years, giant amplitude X-ray flares have been observed from a handful of non-active galaxies. The most plausible scenario of these unusual phenomena is tidal disruption of a star by a quiescent supermassive black hole at the centre of the galaxy. Comparing the XMM-Newton Slew Survey Source Catalogue with the ROSAT PSPC All-Sky Survey five galaxies have been detected a factor of up to 88 brighter in XMM-Newton with respect to ROSAT PSPC upper limits and presenting a soft X-ray colour. X-ray luminosities of these sources derived from slew observations have been found in the range 10^41-10^44 erg s^-1, fully consistent with the tidal disruption model. This model predicts that during the peak of the outburst, flares reach X-ray luminosities up to 10^45 erg s^-1, which is close to the Eddington luminosity of the black hole, and afterwards a decay of the flux on a time scale of months to years is expected. Multi-wavelength follow-up observations have been performed on these highly variable objects in order to disentangle their nature and to investigate their dynamical evolution. Here we present sources coming from the XMM-Newton Slew Survey that could fit in the paradigm of tidal disruption events. X-ray and optical observations revealed that two of these objects are in full agreement with that scenario and three other sources that, showing signs of optical activity, need further investigation within the transient galactic nuclei phenomena.Comment: 4 pages, 4 figures, A&A accepte