Quiescent System Research Articles

Transient dynamics in dense colloidal suspensions under shear: shear rate dependence

A combination of confocal microscopy and rheology experiments, Brownian dynamics (BD) and molecular dynamics (MD) simulations and mode coupling theory (MCT) have been applied in order to investigate the effect of shear rate on the transient dynamics and stress–strain relations in supercooled and glassy systems under shear. Immediately after shear is switched on, the microscopic dynamics display super-diffusion and the macroscopic rheology a stress overshoot, which become more pronounced with increasing shear rate. MCT relates both to negative sections of the generalized shear modulus, which grow with increasing shear rate. When the inverse shear rate becomes much smaller than the structural relaxation time of the quiescent system, relaxation through Brownian motion becomes less important. In this regime, larger stresses are accumulated before the system yields and the transition from localization to flow occurs earlier and more abruptly.

Using Resistivity Arrays to Monitor Groundwater Impacts near Runoff Holding Ponds

Mineral and organic salts from beef manure contained in precipitation runoff from feedyard pen surfaces can alter the conductivity properties of soil and water receiving it. Typically, holding ponds are constructed to control runoff from concentrated animal feeding operations. The integrity of these holding ponds has come under increased scrutiny since leakage has the potential to affect soil and groundwater quality. Traditionally, ponds are monitored by installing monitoring wells at key locations to evaluate the impact of these ponds on the environment. These monitoring wells are expensive and subject to ambiguous interpretation. A subsurface resistivity array was installed at a beef cattle feedyard located at the U.S Meat Animal Research Center, Clay Center, Nebraska (Feedyard A) and at a cattle feeding cooperator site (Feedyard B). Array probes were permanently installed at Feedyard A (16 probes spaced 6.1-m apart at a depth of 30 cm) and at Feedyard B (32 probes spaced 3.05-m apart at a depth of 50 cm). Weekly readings from each site were evaluated to monitor the stability of the zone of hydration near the pond. The low hydraulic conductivity soils at Feedyard A provided a very quiescent environmental system to evaluate the resistivity array's inherent measurement stability. Seasonal changes could easily be accounted for by variation in seasonal soil temperatures. The Feedyard B site was typified by coarse textured parent material that had high hydraulic conductivity properties. This site experienced dynamic changes week to week and throughout the season. The resistivity array system was able to adequately measure these dynamics. Additional analysis using difference maps improved the illustration of the resulting dynamic. The results of this study indicate that the resistivity array system has the potential to improve monitoring of runoff holding ponds and warrants additional validation.

ON THE PROGENITORS OF GALACTIC NOVAE

Of the approximately 400 known Galactic classical novae, only ten of them, the recurrent novae, have been seen to erupt more than once. At least eight of these recurrents are known to harbor evolved secondary stars, rather than the main sequence secondaries typical in classical novae. In this paper, we propose a new nova classification system, based solely on the evolutionary state of the secondary, and not (like the current schemes) based on the properties of the outbursts. Using archival optical and near-infrared photometric observations of a sample of thirty eight quiescent Galactic novae we show that the evolutionary state of the secondary star in a quiescent system can predicted and several objects are identified for follow-up observations; CI Aql, V2487 Oph, DI Lac and EU Sct.

Historical light curve and search for previous outbursts of Nova KT Eridani (2009)

Context. Nova Eridani (2009) caught the eye of the nova community due to its fast decline from maximum, which was initially missed, and its subsequent development in the radio and X-ray wavelengths. This system also exhibits properties similar to those of the much smaller class of recurrent novae; themselves potential progenitors of Type Ia Supernovae. Aims. We aim to determine the nature and physical parameters of the KT Eri progenitor system. Methods. We searched the Harvard College Observatory archive plates for the progenitor of KT Eri to determine the nature of the system, particularly the evolutionary stage of the secondary.We used the data obtained to search for any periodic signal and the derived luminosity to estimate a recurrence timescale. Furthermore, by comparing the colours of the quiescent system on a colour-magnitude diagram we may infer the nature of the secondary star. Results. We identified the progenitor system of KT Eri and measured a quiescent magnitude of < B >= 14.7 \pm 0.4. No previous outburst was found. However, we suggest that if the nova is recurrent it should be on a timescale of centuries. We find a periodicity at quiescence of 737 days which may arise from reflection effects and/or eclipses in the central binary. The periodicity and the quiescence magnitude of the system suggest that the secondary star is evolved and likely in, or ascending, the Red Giant Branch. A second period is evident at 376 days which has a sinusoidal like light curve. Furthermore, the outburst amplitude of ~ 9 magnitudes is inconsistent with those expected for fast classical novae (~ 17 magnitudes) which may lend further support for an evolved secondary. (Abridged)

Characterization of CO 2 hydrate formation by temperature vibration

A method of temperature vibration was proposed to promote CO 2 hydrate formation based on the dual nature of CO 2 solubility in hydrate-forming regions. The effects on carbon dioxide hydrate formation were investigated in a small scale reactor. The results show that the hydrate formation with distilled water in a quiescent system can be improved effectively by temperature vibration, and the pressure drop is increased by 30%. The effect is especially evident with 0.3% sodium dodecyl sulfate (SDS) additive using temperature vibration method, and large amount of hydrates are formed. The rest gas pressure is very close to the phase equilibrium value at setting temperature. Moreover, the pressure drop of CO 2 gas in the reactor is about 2.6 times of that without temperature vibration. With appropriate operation time of temperature vibration, hydrate formation period can be greatly shortened.

High-Pressure Differential Scanning Calorimetry Measurements of the Mass Transfer Resistance across a Methane Hydrate Film as a Function of Time and Subcooling

High pressure differential scanning calorimetry was utilized to study the mass transfer rates across methane hydrate films grown at hydrocarbon−water interfaces in a quiescent system, as a function...

The quiescent spectral energy distribution of V404 Cyg

We present a multiwavelength study of the black hole X-ray binary V404 Cyg in quiescence, focusing upon the spectral energy distribution (SED). Radio, optical, UV, and X-ray coverage is simultaneous. We supplement the SED with additional non-simultaneous data in the optical through infrared where necessary. The compiled SED is the most complete available for this, the X-ray and radio brightest quiescent black hole system. We find no need for a substantial contribution from accretion light from the near-UV to the near-IR, and in particular the weak UV emission constrains published spectral models for V404 Cyg. We confirm that no plausible companion spectrum and interstellar extinction can fully explain the mid-IR, however, and an IR excess from a jet or cool disc appears to be required. The X-ray spectrum is consistent with a Gamma~2 power-law as found by all other studies to date. There is no evidence for any variation in the hardness over a range of a factor of 10 in luminosity. The radio flux is consistent with a flat spectrum (in f(nu)). The break frequency between a flat and optically thin spectrum most likely occurs in the mid or far-IR, but is not strongly constrained by these data. We find the radio to be substantially variable but with no clear correlation with X-ray variability.

Transport and adsorption of antibiotics by marine sediments in a dynamic environment

Bed sediments are the major sink for many contaminants in aquatic environments. With increasing knowledge of and research on the environmental occurrence of antibiotics, there has been growing interest in their behaviour and fate in aquatic environments. However, there is little information about the behaviour of antibiotics in a dynamic water/sediment environment, such as river and coastal marine water. Therefore, the aims of the present study were: (1) to study the transport and distribution of four common antibiotics between water and sediment in both dynamic and quiescent water/sediment systems and (2) to understand the persistence and possible degradation of the four antibiotics in the two different systems. A lid-driven elongated annular flume, designed to reduce the centrifugal effect, was used to simulate a dynamic water environment. In addition, a quiescent water/sediment experiment was conducted for comparison with the dynamic water system. The seawater and sediment, used in both experiments of flowing and quiescent water/sediment systems, were collected from Victoria Harbour, a dynamic coastal environment in an urban setting. The four antibiotics selected in this study were ofloxacin (OFL), roxithromycin (RTM), erythromycin (ETM), and sulfamethoxazole (SMZ), the most commonly used antibiotics in South China. Antibiotics in an overlying solution decreased very quickly in the flume system due to the sorption to suspended particles and surface sediment. There were significant differences in the adsorption of the four antibiotics in sediment. OFL showed a high tendency to be adsorbed by sediment with a high K (d) value (2980 L/Kg), while the low K (d) values of SMZ indicated that there was a large quantity in water. The four antibiotics reached a depth of 20-30 mm in the sediment over a period of 60 days in the flume system. However, the compounds were only found in surface sediment (above 10 mm) in the quiescent system, indicating the influence of the dynamic flume system on the distribution of antibiotics in sediment. OFL showed a moderate persistence in the dynamic flume system, while other three antibiotics had less persistence in sediment. However, all of the four compounds showed moderate persistence in the quiescent system. The study showed the rapid diffusive transfer of antibiotics from water to sediment in the dynamic flume system. The four antibiotics exhibited larger differences in their adsorption to sediment in both dynamic and quiescent systems due to their different K (d) values. The high sorption of antibiotics to marine sediment may reduce their availability to benthic invertebrates.

A mode coupling theory for Brownian particles in homogeneous steady shear flow

A microscopic approach is presented for calculating general properties of interacting Brownian particles under steady shearing. We start from exact expressions for shear-dependent steady-state averages, such as correlation and structure functions, in the form of generalized Green–Kubo relations. To these we apply approximations inspired by the mode coupling theory (MCT) for the quiescent system, accessing steady-state properties by integration through the transient dynamics after startup of steady shear. Exact equations of motion, with memory effects, for the required transient density correlation functions are derived next; these can also be approximated within an MCT-like approach. This results in closed equations for the nonequilibrium stationary state of sheared dense colloidal dispersions, with the equilibrium structure factor of the unsheared system as the only input. In three dimensions, these equations currently require further approximation prior to numerical solution. However, some universal aspects can be analyzed exactly, including the discontinuous onset of a yield stress at the ideal glass transition predicted by MCT. Using these methods we additionally discuss the distorted microstructure of a sheared hard-sphere colloid near the glass transition, and consider how this relates to the shear stress. Time-dependent fluctuations around the stationary state are then approximated and compared to data from experiment and simulation; the correlators for yielding glassy states obey a “time-shear-superposition” principle. The work presented here fully develops an approach first outlined previously [Fuchs and Cates, Phys. Rev. Lett. 89, 248304 (2002)], while incorporating a significant technical change from that work in the choice of mode coupling approximation used, whose advantages are discussed.

Chandra and Swift observations of the quasi-persistent neutron star transient EXO 0748—676 back to quiescence

Abstract The quasi-persistent neutron star X-ray transient and eclipsing binary EXO 0748−676 recently started the transition to quiescence following an accretion outburst that lasted more than 24 years. We report on two Chandra and 12 Swift observations performed within five months after the end of the outburst. The Chandra spectrum is composed of a soft, thermal component that fits to a neutron star atmosphere model with kT∞∼ 0.12keV, joined by a hard power-law tail that contributes ∼20 per cent of the total 0.5–10 keV unabsorbed flux. The combined Chandra/Swift data set reveals a relatively hot and luminous quiescent system with a temperature of kT∞∼ 0.11–0.13keV and a bolometric thermal luminosity of ∼8.1 × 1033–1.6 × 1034(d/7.4kpc)2ergs −1. We discuss our results in the context of cooling neutron star models.

A nonmolecular derivation of Maxwell’s thermal-creep boundary condition in gases and liquids via application of the LeChatelier–Braun principle to Maxwell’s thermal stress

According to the LeChatelier–Braun principle, when a closed quiescent system initially in an equilibrium or unstressed steady state is subjected to an externally imposed “stress” it responds in a manner tending to alleviate that stress. Use of this entropically based qualitative rule, in combination with the notion of Maxwell thermal stresses existing in nonisothermal gases and liquids, enables one to (i) derive Maxwell’s thermal-creep boundary condition prevailing at the boundary between a solid and a fluid (either gas or liquid) and (ii) rationalize the phenomenon of thermophoresis in liquids, for which, in contrast with the case of gases, an elementary explanation is currently lacking. These two objectives are achieved by quantitatively interpreting the heretofore qualitative LeChatelier–Braun notion of stress in the present context as being the fluid’s stress tensor, the latter including Maxwell’s thermal stress. In effect, thermophoretic particle motion is interpreted as the manifestation of the fluid’s attempt to expel the particle from its interior so as to alleviate the thermal stress that would otherwise ensue were the particle to remain at rest (thus obeying the traditional no slip rather than thermal-creep boundary condition) following its introduction into the previously stress-free quiescent fluid. With Kn the Knudsen number in the case of rarefied gases, Maxwell’s thermal stress constitutes a noncontinuum phenomenon of O(Kn2), whereas his thermal-creep phenomenon constitutes a continuum phenomenon of O(Kn). That these two phenomena can, nevertheless, be proved to be synonymous (in the sense, so to speak, of being two sides of the same coin), as is done in the present paper, supports the “ghost effect” findings of Sone [Y. Sone, “Flows induced by temperature fields in a rarefied gas and their ghost effect on the behavior of a gas in the continuum limit,” Annu. Rev. Fluid Mech 32, 779 (2000)], which, philosophically, imply the artificiality of the distinction currently existing between continuum- and noncontinuum-level phenomena.

The matter-flow structure in the SS Cyg system in its quiescent state from comparisons of observational and synthetic Doppler tomograms

Doppler tomograms are constructed for the quiescent state of the SS Cyg system based on Hβ and Hγ spectral-line observations carried out in August 2006 with the 2-m telescope at Terskol Peak. Gasdynamical simulations combined with the Doppler tomograms enable identification of the main features of the flow. Comparisons of synthetic tomograms with observations indicate that an accretion disk is present in the quiescent system. In the tomograms, the luminosity is maximum at the arms of the spiral tidal shock at the shock front due to the interaction between the gas of the circum-binary envelope and material in the stream issuing from the Lagrangian point L1 (the “hot line”), and in the region behind the bow shock due to the motion of the accretor and disk in the gas of the envelope. The contribution of this last element results in appreciable asymmetry of the tomograms.

Does SDS micellize under methane hydrate-forming conditions below the normal Krafft point?

Sodium dodecyl sulfate (SDS) can accelerate nucleation and growth of gas hydrates in a quiescent system. The objective of this paper is to investigate whether or not SDS micelles form in the meta-stable region of methane hydrates by the direct measurement of aqueous SDS concentration. The SDS solubility in water with high-pressure methane is identical to that under atmospheric pressure at a temperature range of 270–282 K; thus, the Krafft point under these methane hydrate-forming conditions does not shift from the normal Krafft point (281–289 K) under atmospheric pressure. The mole fraction of methane in SDS solution is independent of aqueous SDS concentration at a hydrate-forming condition. These results suggest that at temperatures below the normal Krafft point, no SDS micelles are present in the aqueous phase even in a high-pressure methane environment.

Microfabrication by X‐ray‐induced polymerization above the lower critical solution temperature

AbstractA polymer synthesis method is presented in which chain growth driven by exothermic reaction stimulates a gradual chain collapse. The globular precipitates in such systems can be restrained from coalescing by polymerizing in a quiescent environment. Time‐resolved small‐angle scattering study of the methacrylic acid polymerization kinetics in a quiescent system above its lower critical solution temperature (LCST) in water reveals the following features of this method: (a) growing oligomers remain as rigid chains until a critical chain length is reached, at which they undergo chain collapse, (b) radius of gyration increases linearly with time until a critical conversion is reached, and (c) radius of gyration remains constant after the critical conversion, even while conversion is gradually increasing. Following this self‐stabilizing growth mechanism, we show that nanoparticles can be directly synthesized by polymerizing N‐isopropylacrylamide above its LCST in water. The average size of nanoparticles obtained from a polymer–solvent system is expected to be the maximum extent of reaction spread at that monomer concentration. This hypothesis was then verified by polymerizing N‐isopropylacrylamide above their LCST in water, but by initiating the reaction with X‐rays shielded by a mask. The microfabricated patterns conform well to the size and shape of the mask used confirming that the growing chains do not propagate beyond the exposed regions as long as the reaction temperature is maintained above the LCST. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 429–425, 2006

Preparation of Enzyme Crystals with Tunable Morphology in Membrane Crystallizers

Trypsins were crystallized by using membrane crystallization techniques, both in static and dynamic configurations. Crystal size distribution analysis revealed the high uniformity in size of the products that is achievable. Crystals produced by using membrane crystallization methods are more uniform than those obtained in conventional batch experiments. Crystals produced in forced solution flow are even more uniform than those obtained in a quiescent membrane system. Typical values obtained of percent standard deviation and Span are comparable to or even better than those reported in the literature. Crystal growth rate is favorably affected by solution convective motions in forced solution flow, by increasing solution velocity up to a maximum, which, in the best case, has been observed to be ca. 1500 μm/s. These high values of suitable velocities are characteristics of the membrane system; as with traditional method, growth rate deceleration was already visible at 250 μm/s. The maximum seems to be shifted according to the kinematic viscosity of the crystallizing solutions. Some crystals were assessed by X-ray crystallographic analysis, which demonstrated that dynamically grown crystals show no loss in diffraction quality with respect to static membrane crystallized proteins.

Phenotypic, Functional, and Kinetic Parameters Associated with Apparent T-Cell Control of Human Immunodeficiency Virus Replication in Individuals with and without Antiretroviral Treatment

The human immunodeficiency virus (HIV)-mediated immune response may be beneficial or harmful, depending on the balance between expansion of HIV-specific T cells and the level of generalized immune activation. The current study utilizes multicolor cytokine flow cytometry to study HIV-specific T cells and T-cell activation in 179 chronically infected individuals at various stages of HIV disease, including those with low-level viremia in the absence of therapy ("controllers"), low-level drug-resistant viremia in the presence of therapy (partial controllers on antiretroviral therapy [PCAT]), and high-level viremia ("noncontrollers"). Compared to noncontrollers, controllers exhibited higher frequencies of HIV-specific interleukin-2-positive gamma interferon-positive (IL-2(+) IFN-gamma(+)) CD4(+) T cells. The presence of HIV-specific CD4(+) IL-2(+) T cells was associated with low levels of proliferating T cells within the less-differentiated T-cell subpopulations (defined by CD45RA, CCR7, CD27, and CD28). Despite prior history of progressive disease, PCAT patients exhibited many immunologic characteristics seen in controllers, including high frequencies of IL-2(+) IFN-gamma(+) CD4(+) T cells. Measures of immune activation were lower in all CD8(+) T-cell subsets in controllers and PCAT compared to noncontrollers. Thus, control of HIV replication is associated with high levels of HIV-specific IL-2(+) and IFN-gamma(+) CD4(+) T cells and low levels of T-cell activation. This immunologic state is one where the host responds to HIV by expanding but not exhausting HIV-specific T cells while maintaining a relatively quiescent immune system. Despite a history of advanced HIV disease, a subset of individuals with multidrug-resistant HIV exhibit an immunologic profile comparable to that of controllers, suggesting that functional immunity can be reconstituted with partially suppressive highly active antiretroviral therapy.

Characterization of Multiple Flow Morphologies within the Trickle Flow Regime

The existence of multiple hydrodynamic states in the trickle flow regime is a well documented, but as yet poorly quantified phenomenon. The prewetting procedure is known to drastically impact the hydrodynamic state and morphology of the liquid flow. In this work, three limiting cases for the case of no gas flow are identified: Nonprewetted, Levec-prewetted, and pseudo-Kan-prewetted. For the quiescent air-distilled water-3 mm glass spheres system, it is shown that bed-scale maldistribution exists in all three modes of operation, but is more severe in the Levec- and nonprewetted modes. The incorporation of a novel volumetric utilization coefficient into an existing momentum balance-based holdup model is sufficient to accurately model the holdup in all prewetted modes (AARE = 9.2%). This results in the first holdup model that takes the prewetting procedure into account. Present results support the notion that Kan-type prewetting results in film flow, while Levec- and nonprewetted modes are dominated by rivulet flow.

The Hard Quiescent Spectrum of the Neutron Star X‐Ray Transient EXO 1745−248 in the Globular Cluster Terzan 5

We present a Chandra observation of the globular cluster Terzan 5 during times when the neutron star X-ray transient EXO 1745-248 located in this cluster was in its quiescent state. We detected the quiescent system with a (0.5-10 keV) luminosity of ~2 × 1033 ergs s-1. This is similar to several other neutron-star transients observed in their quiescent states. However, the quiescent X-ray spectrum of EXO 1745-248 was dominated by a hard power-law component instead of the soft component that usually dominates the quiescent emission of other neutron star X-ray transients. This soft component could not conclusively be detected in EXO 1745-248, and we conclude that it contributed at most 10% of the quiescent flux in the energy range 0.5-10 keV. EXO 1745-248 is only the second known neutron-star transient whose quiescent spectrum is dominated by the hard component (SAX J1808.4-3658 is the other one). We discuss possible explanations for this unusual behavior of EXO 1745-248, its relationship to other quiescent neutron-star systems, and the impact of our results on understanding quiescent X-ray binaries. We also discuss the implications of our results on the way that the low-luminosity X-ray sources in globular clusters are classified.

The Discovery of Optical Bursts from MS 1603.6+2600 (UW Coronae Borealis)

We report the discovery of several optical burstlike events from the low-mass X-ray binary MS 1603.6+2600 (UW CrB). The events last for a few tens of seconds, exhibit a very fast rise and slow decay, and involve optical brightening of a factor of 2-3. The flares appear distinct from the lower level flickering and instead strongly resemble reprocessed type I X-ray bursts as seen in a number of other neutron star low-mass X-ray binaries. In conjunction with the previously reported candidate X-ray burst, these confirm that the compact object in UW CrB is a neutron star. We examine the optical burst brightness and recurrence times and discuss how the nature of the system can be constrained. We conclude that the source is most likely an accretion disk corona source at an intermediate distance, rather than a nearby quiescent system or very distant dipper.

Angiostatin.

The quiescent vascular system in the adult body represents the imbalanced net outcome of overproduction of endogenous angiogenesis inhibitors and reduced levels of angiogenic factors. While some endogenous inhibitors are expressed under physiological conditions, they can also be generated in association with tumor growth. Angiostatin is such a specific angiogenesis inhibitor produced by tumors. It inhibits primary and metastatic tumor growth by blocking tumor angiogenesis. Having demonstrated potent antitumor activity in animal studies, angiostatin is now in clinical trials for human cancer therapy. Angiostatin is not a novel protein molecule coded by novel DNA sequences. Instead, it is an internal proteolytic fragment of a known protein, plasminogen. Surprisingly, most kringle domains of plasminogen only inhibit angiogenesis when cleaved as fragments from their parent protein that lacks antiangiogenic activity. These findings suggest that they are cryptic fragments hidden in large protein molecules. Thus, proteolytic processing plays a critical role in down-regulation of angiogenesis. Despite proteolytic processing, the antiangiogenic mechanism of angiostatin remains an enigma. Without knowing the mechanisms, it is difficult to predict the ultimate outcome of ongoing clinical trials. In this article, we discuss what is known about angiostatin and how this molecule specifically inhibits angiogenesis. We hope that the information will be useful for further development of angiostatin and its related inhibitors as therapeutic agents.