Separation and fractionation of order and disorder in highly polydisperse systems

We study a polydisperse soft-spheres model for colloids by means of microcanonical Monte Carlo simulations. We consider a polydispersity as high as 24%. Although solidification occurs, neither a crystal nor an amorphous state are thermodynamically stable. A finite size scaling analysis reveals that in the thermodynamic limit: a the fluid-solid transition is rather a crystal-amorphous phase-separation, b such phase-separation is preceded by the dynamic glass transition, and c small and big particles arrange themselves in the two phases according to a complex pattern not predicted by any fractionation scenario.

Simultaneous optical and X-ray observations of flares and rotational modulation on the RS CVn binary HR 1099 (V711 Tau) from the MUSICOS 1998 campaign

We present simultaneous and continuous observations of the Hα, Hβ, He I D_3, Na I D_1,D_2 doublet and the Ca II H&K lines for the RS CVn system HR 1099. The spectroscopic observations were obtained during the MUSICOS 1998 campaign involving several observatories and instruments, both echelle and long-slit spectrographs. During this campaign, HR 1099 was observed almost continuously for more than 8 orbits of 2^d.8. Two large optical flares were observed, both showing an increase in the emission of Hα, Ca II H K, Hβ and He I D_3 and a strong filling-in of the Na I D_1, D_2 doublet. Contemporary photometric observations were carried out with the robotic telescopes APT-80 of Catania and Phoenix-25 of Fairborn Observatories. Maps of the distribution of the spotted regions on the photosphere of the binary components were derived using the Maximum Entropy and Tikhonov photometric regularization criteria. Rotational modulation was observed in Hα and He I D_3 in anti-correlation with the photometric light curves. Both flares occurred at the same binary phase (0.85), suggesting that these events took place in the same active region. Simultaneous X-ray observations, performed by ASM on board RXTE, show several flare-like events, some of which correlate well with the observed optical flares. Rotational modulation in the X-ray light curve has been detected with minimum flux when the less active G5 V star was in front. A possible periodicity in the X-ray flare-like events was also found.

Comment Letter: The NYSE and the End of the Structural Separation between Regulatory and Commercial Interests of the Exchange

The NYSE transformed into a for profit entity in 2006. As part of the approval process, the NYSE agreed to structurally separate the regulatory function from the business function. In doing so, the NYSE created NYSE Regulation, a non-profit with an independent board, to handle most regulatory matters. During the comment period, a spirited debate arose over the ability of a for profit company to carry out a regulatory mission. Some suggested that the regulatory function was incompatible with a "for profit" motive and that NYSE Regulation should be spun off. Others accepted the proposed structure but called for additional changes designed to reduce the possible influence of the public holding company over the regulatory function. In the end, the SEC approved the structure but with a number of prophylactic safeguards including the requirement that NYSE Regulation have a board consisting of all independent directors (save the CEO) and that directors from the for profit holding company could not make up a majority of the board. More recently, however, the NYSE has proposed to end the structural separation of the two functions and instead put in place a functional separation. The proposal would result in the termination of the delegation agreement between the Exchange and NYSE Regulation and the creation of both a Regulatory Oversight Committee of the Board of Directors of the Exchange and the creation of a Chief Regulatory Officer. This letter examines the history of the separation of the two functions and critiques the NYSE's proposal.

Analysis of the zone connecting consecutive sectors in distillation columns by the Ponchon-Savarit method

McCabe-Thiele and Ponchon-Savarit methods are two classical graphical methods for the design of binary distillation columns very useful for didactical purposes and for preliminary calculations. Nevertheless, their description in the literature is not complete and not all the cases are analysed. To complete the academic literature dealing with this subject we have generalized equations for the operating lines or DP that define the change between two consecutive sectors ΔkC for any feed condition, together with the different possibilities to extract products or to add or remove heat. A consistent analysis of what may happen when changing between sectors in the column is presented.

Correlation of the liquid–liquid equilibrium data for specific ternary systems with one or two partially miscible binary subsystems

This paper presents the results of a liquid–liquid equilibrium data correlation for 11 ternary systems which have not been previously fitted using the NRTL model or, when they have, the results presented in the literature are inconsistent with the experimental behavior of the system. These ternary systems include mixtures with one or two partially miscible pairs. During the correlation process, new restrictions were imposed on the values for the NRTL binary parameters to ensure correct prediction of the total or partial miscibility for the binary pairs involved. In addition, topological concepts related to the Gibbs stability test have been applied in order to validate the results in the whole range of compositions.

Spin separation in digital ferromagnetic heterostructures

In a study of the ferromagnetic phase of a multilayer digital ferromagnetic semiconductor in the mean-field and effective-mass approximations, we find the exchange interaction to have the dominant energy scale of the problem, effectively controlling the spatial distribution of the carrier spins in the digital ferromagnetic heterostructures. In the ferromagnetic phase, the majority-spin and minority-spin carriers tend to be in different regions of the space (spin separation). Hence, the charge distribution of carriers also changes noticeably from the ferromagnetic to the paramagnetic phase. An example of a design to exploit these phenomena is given here.

An algorithm to hide information in binary images

The objective of this paper is to develop a method to hide information inside a binary image. An algorithm to embed data in scanned text or figures is proposed, based on the detection of suitable pixels, which verify some conditions in order to be not detected. In broad terms, the algorithm locates those pixels placed at the contours of the figures or in those areas where some scattering of the two colors can be found. The hidden information is independent from the values of the pixels where this information is embedded. Notice that, depending on the sequence of bits to be hidden, around half of the used pixels to keep bits of data will not be modified. The other basic characteristic of the proposed scheme is that it is necessary to take into consideration the bits that are modified, in order to perform the recovering process of the information, which consists on recovering the sequence of bits placed in the proper positions. An application to banking sector is proposed for hidding some information in signatures.

Astrophysical parameters of LS 2883 and implications for the PSR B1259-63 gamma-ray binary

Only a few binary systems with compact objects display TeV emission. The physical properties of the companion stars represent basic input for understanding the physical mechanisms behind the particle acceleration, emission, and absorption processes in these so-called gamma-ray binaries. Here we present high-resolution and high signal-to-noise optical spectra of LS 2883, the Be star forming a gamma-ray binary with the young non-accreting pulsar PSR B1259-63, showing it to rotate faster and be significantly earlier and more luminous than previously thought. Analysis of the interstellar lines suggests that the system is located at the same distance as (and thus is likely a member of) Cen OB1. Taking the distance to the association, d = 2.3 kpc, and a color excess of E(B – V) = 0.85 for LS 2883 results in MV ≈ –4.4. Because of fast rotation, LS 2883 is oblate (R eq sime 9.7 R ☉ and R pole sime 8.1 R ☉) and presents a temperature gradient (T eq≈ 27,500 K, log g eq = 3.7; T pole≈ 34,000 K, log g pole = 4.1). If the star did not rotate, it would have parameters corresponding to a late O-type star. We estimate its luminosity at log(L */L ☉) sime 4.79 and its mass at M * ≈ 30 M ☉. The mass function then implies an inclination of the binary system i orb ≈ 23°, slightly smaller than previous estimates. We discuss the implications of these new astrophysical parameters of LS 2883 for the production of high-energy and very high-energy gamma rays in the PSR B1259-63/LS 2883 gamma-ray binary system. In particular, the stellar properties are very important for prediction of the line-like bulk Comptonization component from the unshocked ultrarelativistic pulsar wind.

The masses of the neutron and donor star in the high-mass X-ray binary IGR J18027-2016

Aims. We report near-infrared observations of the supergiant donor to the eclipsing high mass X-ray binary pulsar IGR J18027-2016. We aim to determine its spectral type and measure its radial velocity curve and hence determine the stellar masses of the components. Methods. ESO/VLT observations of the donor utilising the NIR spectrograph ISAAC were obtained in the H and K bands. The multi-epoch H band spectra were cross-correlated with RV templates in order to determine a radial solution for the system. Results. The spectral type of the donor was confirmed as B0-1 I. The radial velocity curve constructed has a semi-amplitude of 23.8 ± 3.1 km s-1. Combined with other measured system parameters, a dynamically determined neutron star mass of 1.4  ±  0.2–1.6  ±  0.3 M⊙ is found. The mass range of the B0-B1 I donor was 18.6  ±  0.8–21.8  ±  2.4 M⊙. These lower and upper limits were obtained under the assumption that the system is viewed edge-on (i = 90° with β = 0.89) for the lower limit and the donor fills its Roche lobe (β = 1 with i = 73.1°) for the upper limit respectively.

The supergiant B[e] star LHA 115-S 18 - binary and/or luminous blue variable?

Context. The mechanism by which supergiant (sg)B[e] stars support cool, dense dusty discs/tori and their physical relationship with other evolved, massive stars such as luminous blue variables is uncertain. Aims. In order to investigate both issues we have analysed the long term behaviour of the canonical sgB[e] star LHA 115-S 18. Methods. We employed the OGLE II-IV lightcurve to search for (a-)periodic variability and supplemented these data with new and historic spectroscopy. Results. In contrast to historical expectations for sgB[e] stars, S18 is both photometrically and spectroscopically highly variable. The lightcurve is characterised by rapid aperiodic ` aring' throughout the 16 years of observations. Changes in the high excitation emission line component of the spectrum imply evolution in the stellar temperature - as expected for luminous blue variables - although somewhat surprisingly, spectroscopic and photometric variability appears not to be correlated. Characterised by emission in low excitation metallic species, the cool circumstellar torus appears largely unaffected by this behaviour. Finally, in conjunction with intense, highly variable He ii emission, X-ray emission implies the presence of an unseen binary companion. Conclusions. S18 provides observational support for the putative physical association of (a subset of) sgB[e] stars and luminous blue variables. Given the nature of the circumstellar environment of S18 and that luminous blue variables have been suggested as SN progenitors, it is tempting to draw a parallel to the progenitors of SN1987A and SN2009ip. Moreover the likely binary nature of S18 strengthens the possibility that the dusty discs/tori that characterise sgB[e] stars are the result of binary-driven mass-loss; consequently such stars may provide a window on the short lived phase of mass-transfer in massive compact binaries.

GRO J1008−57: an (almost) predictable transient X-ray binary

A study of archival RXTE, Swift, and Suzaku pointed observations of the transient high-mass X-ray binary GRO J1008−57 is presented. A new orbital ephemeris based on pulse arrival-timing shows the times of maximum luminosities during outbursts of GRO J1008−57 to be close to periastron at orbital phase − 0.03. This makes the source one of a few for which outburst dates can be predicted with very high precision. Spectra of the source in 2005, 2007, and 2011 can be well described by a simple power law with high-energy cutoff and an additional black body at lower energies. The photon index of the power law and the black-body flux only depend on the 15–50 keV source flux. No apparent hysteresis effects are seen. These correlations allow us to predict the evolution of the pulsar’s X-ray spectral shape over all outbursts as a function of just one parameter, the source’s flux. If modified by an additional soft component, this prediction even holds during GRO J1008−57’s 2012 type II outburst.

Accreting magnetars: a new type of high-mass X-ray binaries?

The discovery of very slow pulsations (Pspin =5560 s) has solved the long-standing question of the nature of the compact object in the high-mass X-ray binary 4U 2206+54 but has posed new ones. According to spin evolutionary models in close binary systems, such slow pulsations require a neutron star magnetic field strength larger than the quantum critical value of 4.4 × 1013 G, suggesting the presence of a magnetar. We present the first XMM–Newton observations of 4U 2206+54 and investigate its spin evolution. We find that the observed spin-down rate agrees with the magnetar scenario. We analyse Integral Spacecraft Gamma-Ray Imager (ISGRI)/INTErnational Gamma-RAy Laboratory (INTEGRAL) observations of 4U 2206+54 to search for the previously suggested cyclotron resonance scattering feature at ∼30 keV. We do not find a clear indication of the presence of the line, although certain spectra display shallow dips, not always at 30 keV. The association of these dips with a cyclotron line is very dubious because of its apparent transient nature. We also investigate the energy spectrum of 4U 2206+54 in the energy range 0.3–10 keV with unprecedented detail and report for the first time the detection of very weak 6.5 keV fluorescence iron lines. The photoelectric absorption is consistent with the interstellar value, indicating very small amount of local matter, which would explain the weakness of the florescence lines. The lack of matter locally to the source may be the consequence of the relatively large orbital separation of the two components of the binary. The wind would be too tenuous in the vicinity of the neutron star.

The evolution and masses of the neutron star and donor star in the high mass X-ray binary OAO 1657−415

We report near-infrared radial velocity (RV) measurements of the recently identified donor star in the high mass X-ray binary (HMXB) system OAO 1657−415 obtained in the H band using ISAAC on the Very Large Telescope. Cross-correlation methods were employed to construct a RV curve with a semi-amplitude of 22.1 ± 3.5 km s−1. Combined with other measured parameters of this system it provides a dynamically determined neutron star (NS) mass of 1.42 ± 0.26 M⊙ and a mass of 14.3 ± 0.8 M⊙ for the Ofpe/WN9 highly evolved donor star. OAO 1657−415 is an eclipsing HMXB pulsar with the largest eccentricity and orbital period of any within its class. Of the 10 known eclipsing X-ray binary pulsars OAO 1657−415 becomes the ninth with a dynamically determined NS mass solution and only the second in an eccentric system. Furthermore, the donor star in OAO 1657−415 is much more highly evolved than the majority of the supergiant donors in other HMXBs, joining a small but growing list of HMXBs donors with extensive hydrogen depleted atmospheres. Considering the evolutionary development of OAO 1657−415, we have estimated the binding energy of the envelope of the mass donor and find that there is insufficient energy for the removal of the donor’s envelope via spiral-in, ruling out a common envelope evolutionary scenario. With its non-zero eccentricity and relatively large orbital period the identification of a definitive evolutionary pathway for OAO 1657−415 remains problematic, we conclude by proposing two scenarios which may account for OAO 1657−415 current orbital configuration.

The X-ray quiescence of Swift J195509.6+261406 (GRB 070610): an optical bursting X-ray binary?

We report on an ~63 ks Chandra observation of the X-ray transient Swift J195509.6+261406 discovered as the afterglow of what was first believed to be a long-duration gamma-ray burst (GRB 070610). The outburst of this source was characterized by unique optical flares on timescales of second or less, morphologically similar to the short X-ray bursts usually observed from magnetars. Our Chandra observation was performed ~2 years after the discovery of the optical and X-ray flaring activity of this source, catching it in its quiescent state. We derive stringent upper limits on the quiescent emission of Swift J195509.6+261406, which argues against the possibility of this object being a typical magnetar. Our limits show that the most viable interpretation on the nature of this peculiar bursting source is a binary system hosting a black hole or a neutron star with a low-mass companion star (<0.12 M ☉) and with an orbital period smaller than a few hours.

High selectivity of TiC-CDC for CO2/N2 separation

A series of carbide-derived carbons (CDC) have been prepared starting from TiC and using different chlorine treatment temperatures (500–1200 °C). Contrary to N2 adsorption measurements at −196 °C, CO2 adsorption measurements at room temperature and high pressure (up to 1 MPa) together with immersion calorimetry measurements into dichloromethane suggest that the synthesized CDC exhibit a similar porous structure, in terms of narrow pore volume, independently of the temperature of the reactive extraction treatment used (samples synthesized below 1000 °C). Apparently, these carbide-derived carbons exhibit narrow constrictions were CO2 adsorption under standard conditions (0 °C and atmospheric pressure) is kinetically restricted. The same accounts for a slightly larger molecule as N2 at a lower adsorption temperature (−196 °C), i.e. textural parameters obtained from N2 adsorption measurements on CDC must be underestimated. Furthermore, here we show experimentally that nitrogen exhibits an unusual behavior, poor affinity, on these carbide-derived carbons. CH4 with a slightly larger diameter (0.39 nm) is able to partially access the inner porous structure whereas N2, with a slightly smaller diameter (0.36 nm), does not. Consequently, these CDC can be envisaged as excellent sorbent for selective CO2 capture in flue-gas streams.