Aging Regime Research Articles

Characterisation of materials causing discolouration in potable water systems

Discoloured water is one of the main causes of customer complaints received by UK water suppliers. Flushing is recognised as a means of preventing red water events by mobilising material with the potential to cause discolouration. The understanding of the mechanisms and materials causing discolouration is limited. It is therefore necessary to characterise the materials mobilised by flushing, which are responsible for discolouration. The University of Sheffield and two UK water companies embarked on an in-depth programme of monitoring mains flushing. The programme involves collecting discrete samples during flushing of pipes of differing materials, diameters, age, source water and hydraulic regime. The results show iron to be the dominant material mobilised irrespective of pipe material. All samples indicate a direct correlation between turbidity, iron and manganese, and to a lesser extent with metals lead, copper, aluminium and zinc. Concentration of metals mobilised is independent of pipe material, diameter or age.

Quasiequilibrium during aging of the two-dimensional Edwards-Anderson model

We test the quasiequilibrium picture of the aging dynamics--strictly valid in the asymptotic dynamical regime of aging systems--in the preasymptotic aging regime of the two-dimensional Edwards-Anderson spin glass model. We compare the fluctuation-dissipation characteristic for spin autocorrelation function and response with a corresponding one obtained for a suitably defined correlation function and its conjugated response. In agreement with the quasiequilibrium picture we find that after a short transient the two corresponding fluctuation-dissipation ratios (FDR's) coincide at equal times. Moreover we show that, as it happens for the usual FDR, the dynamic FDR at finite time coincides with the static one at finite size.

Aging dynamics of heterogeneous spin models

We investigate numerically the dynamics of three different spin models in the aging regime. Each of these models is meant to be representative of a distinct class of aging behavior: coarsening systems, discontinuous spin glasses, and continuous spin glasses. In order to study dynamic heterogeneities induced by quenched disorder, we consider single-spin observables for a given disorder realization. In some simple cases we are able to provide analytical predictions for single-spin response and correlation functions. The results strongly depend upon the model considered. It turns out that, by comparing the slow evolution of a few different degrees of freedom, one can distinguish between different dynamic classes. As a conclusion we present the general properties which can be induced from our results, and discuss their relation with thermometric arguments.

A far-from-equilibrium fluctuation–dissipation relation for an Ising–Glauber-like model

We derive an exact expression of the response function to an infinitesimal magnetic field for an Ising-Glauber-like model with arbitrary exchange couplings. The result is expressed in terms of thermodynamic averages and does not depend on the initial conditions or on the dimension of the space. The response function is related to time-derivatives of a complicated correlation function and so the expression is a generalisation of the equilibrium fluctuation-dissipation theorem in the special case of this model. Correspondence with the Ising-Glauber model is discussed. A discrete-time version of the relation is implemented in Monte Carlo simulations and then used to study the aging regime of the ferromagnetic two-dimensional Ising-Glauber model quenched from the paramagnetic phase to the ferromagnetic one. Our approach has the originality to give direct access to the response function and the fluctuation-dissipation ratio.

Dynamic heterogeneities in the out-of-equilibrium dynamics of simple spherical spin models.

The response of spherical two-spin interaction models, the spherical ferromagnet (s-FM) and the spherical Sherrington-Kirkpatrick (s-SK) model, is calculated for the protocol of the so-called nonresonant hole burning (NHB) experiment for temperatures below the respective critical temperatures. It is shown that it is possible to select dynamic features in the out-of-equilibrium dynamics of both models, one of the hallmarks of dynamic heterogeneities. The behavior of the s-SK model and the s-FM model in three dimensions is very similar, showing dynamic heterogeneities in the long-time behavior, i.e., in the aging regime. The appearance of dynamic heterogeneities in the s-SK model explicitly demonstrates that these are not necessarily related to spatial heterogeneities. For the s-FM model, it is shown that the nature of the dynamic heterogeneities changes as a function of dimensionality. With the increasing dimension, the frequency selectivity of the NHB diminishes and the dynamics in the mean-field limit of the s-FM model becomes homogeneous.

Concentration and stable carbon isotopic composition of ethane and benzene using a global three‐dimensional isotope inclusive chemical tracer model

A three‐dimensional global chemical tracer model of the atmosphere has been adapted to include the stable carbon isotopic composition and isotopic fractionation of ethane and benzene. For computational efficiency the chemistry was based on a prescribed OH‐radical concentration field, and therefore the feedback of ethane and benzene chemistry on the atmospheric OH‐radical concentrations was not considered. The Emission Database for Global Atmospheric Research (EDGAR) V2.0 emission database used needed to be scaled by a factor of 2.22 in order to have good agreement between observed and modeled concentrations. Modeled isotopic compositions were consistent with the few published observations. The global distribution of modeled stable carbon isotope ratios and the derived mean photochemical ages of ethane and benzene are presented. The model predicts distinct regimes of photochemical aging and air mass mixing for polar regions.

Linear and nonlinear response in the aging regime of the one-dimensional trap model

We investigate the behavior of the response function in the one-dimensional trap model using scaling arguments that we confirm by numerical simulations. We study the average position of the random walk at time t(w)+t, given that a small bias h is applied at time t(w). Several scaling regimes are found, depending on the relative values of t, t(w), and h. Comparison with the diffusive motion in the absence of bias allows us to show that the fluctuation-dissipation relation is valid even in the aging regime, at least for times such that linear response is obeyed. However, for sufficiently long times, the response always becomes nonlinear in h.

Effects of Sulfur Dioxide and Polyvinylpolypyrrolidone on the Flavor Stability of Beer as Measured by Sensory and Chemical Analysis

A sensory panel was trained to articulate and quantify aged characters in ales and lagers. Key terms used to describe aging were hay/straw aroma, cardboard flavor, and apple/wine flavor. The panel was employed to detect the merits of adding sulfur dioxide (SO2) at levels that would be permissible without labeling in the United States. Although some benefit was observed, few of the differences were robust statistically. The observations made by the panel were compared with the observed impact of SO2 on total levels of carbonyl substances measured in the same beers. The reduction in carbonyls was similar irrespective of whether SO2 was added before or after accelerated aging regimes, whereas the limited benefits seen via sensory evaluation were only observed for sulfite addition prior to aging. It is inferred that the limited protective action of SO2 is as an antioxidant rather than as a binder of carbonyls through adduct formation. The taste panel was also used to demonstrate that the partial removal of polyphenols by polyvinylpolypyrrolidone was without any significant effect on the flavor stability of the beers studied.

Aging at criticality in model-C dynamics.

We study the off-equilibrium two-point critical response and correlation functions for the relaxational dynamics with a coupling to a conserved density (model C) of the O(N) vector model. They are determined in an epsilon=4-d expansion for vanishing momentum. We briefly discuss their scaling behaviors and the associated scaling forms are determined up to first order in epsilon. The corresponding fluctuation-dissipation ratio has a nontrivial large time limit in the aging regime and, up to one-loop order, it is the same as that of the model A for the physically relevant case N=1. The comparison with predictions of local scale invariance is also discussed.

Microscopic description of aging dynamics: fluctuation-dissipation relations, effective temperature, and heterogeneities.

We consider the dynamics of a diluted mean-field spin glass model in the aging regime. The model presents a particularly rich heterogeneous behavior. In order to catch this behavior, we perform a spin-by-spin analysis for a given disorder realization. We confirm the connection between statics and dynamics at the level of single degrees of freedom. Moreover, working with single-site quantities, we can introduce a new response-vs-correlation plot, which clearly shows how heterogeneous degrees of freedom undergo coherent structural rearrangements. We discuss the general scenario which emerges from our work and (possibly) applies to more realistic glassy models. Interestingly enough, some features of this scenario can be understood recurring to thermometric considerations.

Aging and fluctuation-dissipation ratio for the dilute Ising model

We consider the out-of-equilibrium, purely relaxational dynamics of a weakly diluted Ising model in the aging regime at criticality. We derive at first order in a $\sqrt{\epsilon}$ expansion the two-time response and correlation functions for vanishing momenta. The long-time limit of the critical fluctuation-dissipation ratio is computed at the same order in perturbation theory.

Two-loop critical fluctuation-dissipation ratio for the relaxational dynamics of the O(N) Landau-Ginzburg Hamiltonian.

The off-equilibrium purely dissipative dynamics (model A) of the O(N) vector model is considered at criticality in an epsilon=4-d>0 expansion up to O(epsilon(2)). The scaling behavior of two-time response and correlation functions at zero momentum, the associated universal scaling functions and the nontrivial limit of the fluctuation-dissipation ratio are determined in the aging regime.

Influence of high electrical fields on ageing and polarization properties of polyethylene

AbstractThe influence of high electrical fields (above 20 kV mm−1) on ageing, polarization and morphology of polyethylene (PE) is discussed. Infrared and positron annihilation spectroscopy measurements together with capacitance measurements tend to indicate that polymer morphology is modified by high fields. We show that accelerated electrical ageing characteristics of PE are directly linked to morphology changes induced by the field. Below a so‐called critical field, the activation volume of the ageing process is dependent on field‐induced strain. Above the critical field, the amorphous phase is significantly deformed and weak van der Waals bonds are broken, leading to another faster ageing regime. There is excellent agreement between the proposed model and experimental data obtained with PE‐insulated high voltage cables. The possible relation between the submicrocavity formation proposed in our ageing model and various polarization measurements is discussed. It is our contention that strong charge injection occurs only after submicrocavity formation, ie after weak bonds are broken. As is well known, polarization currents obtained under high fields are controlled by space charges. It seems that wave packets and the negative resistance observed above 100 kV mm−1 in PE are associated with a steady state in field‐induced defect formation. This suggests that space charges are related to the formation of submicrocavities and, therefore, are a consequence and not a cause of high field ageing.© 2002 Society of Chemical Industry

Developmental and food-access-dependent changes in effector systems activated by leptin.

In small mammals leptin reduces fat stores not only by inhibiting food intake but also by disinhibiting metabolic cold defense. Presuming that postnatal age and feeding regime set the conditions for either mode of leptin action, we compared the caloric equivalents of changes in fat mass, metabolic rate (MR) and food intake (FI) induced by 10-day treatments with leptin, in rats treated from postnatal days 7, 15, 25 onward and in adult mice that were free-feeding or food restricted. Whereas MR changes are known to dominate from postnatal days 7-16, changes in MR explained only about 50% and 30% of the leptin-induced changes in fat mass between days 15-24 and days 25-34, respectively. In adult mice of similar body weights, leptin-induced reductions in fat mass under free-feeding conditions were due only to FI decreases but due only to MR increases under food-restricted conditions. Thus, the same leptin treatment induces the same percentage decrease in body fat content by driving the two effectors differently, depending on age and feeding conditions. Consequently, in assessing the effects of leptin under various physiological conditions, short-term measurements of FI or MR alone are not sufficient. Instead, determination of the resultant decreases in total body fat is required.

Production of Filth Fly Parasitoids (Hymenoptera: Pteromalidae) on Fresh and on Freeze-killed and Stored House Fly Pupae

Laboratory experiments were performed to assess the effects of age, status (fresh versus freezekilled), and storage regime on the suitability of house fly, Musca domestica L. (Diptera: Muscidae) pupae as hosts for Muscidifurax raptor Girault & Saunders, M. raptorellus Kogan & Legner, M. zaraptor Kogan & Legner, Spalangia cameroni Perkins, Trichomalopsis sarcophagae (Gahan) and Urolepis rufipes (Ashmead) (Hymenoptera: Pteromalidae). Production of all species was maximized on pupae aged 24 + h post-pupation. Fresh pupae could not be refrigerated at 10°C or less, or at 15°C without a significant decline in their suitability as hosts. Although production of S. cameroni was essentially limited to the use of fresh house fly pupae, M. raptor , M. raptorellus , M. zaraptor , T. sarcophagae and U. rufipes could be reared on either fresh or freeze-killed pupae stored at - 20 °C for up to 6 months prior to parasitism. The suitability of freeze-killed pupae declined during storage when used for production of male and female M. raptorellus and M. zaraptor , and possibly for male T. sarcophagae . No other effects of storage on parasitoid production were detected. These results suggest that insectaries can stockpile fly pupae in freezers during times of overproduction for future use in mass-rearing M. raptor, M. raptorellus, M. zaraptor, T. sarcophagae and U. rufipes as biocontrol agents of filth flies.

Effect of double nursing on some anatomical and physiological properties of the digestive tract of rabbits between 23 and 44 days of age.

Anatomical and physiological properties of the digestive tract were examined and compared in young rabbits nursed either by one (SS) or by two does (DD) daily up to the age of 35 days. At the age of 23, 30, 37 and 44 days, 8 young per treatment were euthanised. Double suckling and the subsequent higher level of solid feed intake after weaning were found to exert a stronger influence on the weight of the entire gastrointestinal tract and that of its individual parts (the stomach, small intestine, caecum and colon) than on its length. The quantity of the gastric content was found to rise with advancing age in both groups (from 36 to 70 g and from 37.5 to 79 g). In both groups the pH of the stomach was higher during the suckling period (4.5-5.3) than subsequent to weaning (1.6-2.4). The quantity of the caecal content also increased with age (from 4 or 8 g), but on the 37th day significantly higher quantities of caecal content were recorded in DD rabbits (50.5 g compared with 35 g). The pH of the caecal content decreased more slowly from an initial high value (6.0 and 6.5 in SS and DD rabbits, respectively), and by the 37th day had settled at a low value (5.7-5.8) in both groups. The dry matter content of the caecal content decreased from 270-273 g to 188-207 g in both groups. Total volatile fatty acid (tVFA) and acetic acid (C2) concentration, which amounted to 66-88% of tVFA, rose; in SS rabbits they were at higher levels by the 30th day (53.6 and 42.2 mmol/L, respectively), and remained at an increased level until the 44th day (P < 0.05). The ratio of C3: C4 was high on the 23rd day (2.5 and 2.4), but dropped at the age of 30 days (0.5 in SS and 1.7 in DD, P < 0.05) and, further, by the 37th day (0.2 in SS). In SS rabbits coliform count proved significantly lower (10(5)) on the 23rd day than in DD rabbits (10(6)). By the 37th day this count had decreased in both groups and subsequently remained at a low level (< 10(4)). By the 23rd day Bacteroides were present in large quantities (10(8)) in the caecum and showed no change with advancing age or feeding regime.

Intrauterine insemination with frozen donor sperm. Pregnancy outcome in relation to age and ovarian stimulation regime.

The success of intrauterine insemination with donor semen (IUI-DI) is likely to be influenced by a number of variables, including age and ovarian stimulation (OS) regime. A retrospective analysis of 1056 treatment cycles in 261 women (212 single heterosexuals and 49 lesbians) was conducted to assess the influence of these two variables on pregnancy outcome during IUI-DI. The overall pregnancy rate was 10.6%, being 18.5% for women <35 years, 11.9% in women 35-40 years and 5.4% in women >40 years (P < 0.05). The cumulative pregnancy rate (CPR) after eight cycles was 0.86, 0.51 and 0.32 respectively (P < 0.05). A total of 445 inseminations were performed following spontaneous ovulation, 360 following OS with clomiphene citrate (CC) and 251 with hMG, the pregnancy rate per cycle being 13, 7.2 and 11.2% respectively. There was no statistically significant difference in the pregnancy rate per cycle, CPR or multiple pregnancy rate in the three treatment groups. These results indicate that the use of OS with either CC or hMG in women without ovulatory dysfunction does not improve the pregnancy rate during IUI-DI. The only factor associated with reduced effectiveness of fertility treatment was age, confirming that IUI is a poor treatment option for women >40 years of age.

Global Significance of a Sub-Moho Boundary Layer (SMBL) Deduced from High-Resolution Seismic Observations

We infer the fine structure of a sub-Moho boundary layer (SMBL) at the top of the lithospheric mantle from high-resolution seismic observations of Peaceful Nuclear Explosions (PNE) on superlong-range profiles in Russia. Densely recorded seismograms permit recognition of previously unknown features of teleseismic propagation of the well known Pn and Sn phases, such as a band of incoherent, scattered, high-frequency seismic energy, developing consistently from station to station, apparent velocities of sub-Moho material, and high-frequency energy to distances of more than 3000 km with a coda band, incoherent at 10 km spacing and yet consistently observed to the end of the profiles. Estimates of the other key elements of the SMBL were obtained by finite difference calculations of wave propagation in elastic 2D models from a systematic grid search through parameter space. The SMBL consists of randomly distributed, mild velocity fluctuations of 2% or schlieren of high aspect ratios (≥40) with long horizontal extent (~20 km) and therefore as thin as 0.5 km only; SMBL thickness is 60-100 km. It is suggested that the SMBL is of global significance as the physical base of the platewide observed high-frequency phases Pn and Sn. It is shown that wave propagation in the SMBL waveguide is insensitive to the background velocity distribution on which its schlieren are superimposed. This explains why the Pn and Sn phases traverse geological provinces of various age, heat flow, crustal thickness, and tectonic regimes. Their propagation appears to be independent of age, temperature, pressure, and stress. Dynamic stretching of mantle material during subduction or flow, possibly combined with chemical differentiation have to be considered as scale-forming processes in the upper mantle. However, it is difficult to distinguish with the present sets of Pn/Sn array data whether (and also where) the boundary layer is a frozen-in feature of paleo-processes or whether it is a response to an on-going processes; nevertheless, the derived quantitative estimates of the SMBL properties provide important constraints for any hypothesis on scale-forming processes. Models to be tested by future numerical and field experiments are, for example, repeated subduction-convection stretching of oceanic lithosphere (marble-cake model) and schlieren formation at mid-ocean ridges. It is also proposed that the modeling of the observed blocking of Sn and Pn propagation at active plate margins offers a new tool to study the depth range of tectonics below the crust-mantle boundary. Finally, the deduced schlieren structure of the SMBL closes an important scale gap of three to four orders of magnitude between structural dimensions studied in petrological analysis of mantle samples (xenoliths or outcrop of oceanic lithosphere) and those imaged in classical seismological studies of the lithosphere.

Response of non-equilibrium systems with long-range initial correlations

The long-time dynamics of the d-dimensional spherical model with a non-conserved order parameter and quenched from an initial state with long-range correlations is studied through the exact calculation of the two-time autocorrelation and autoresponse functions. In the ageing regime, these are given in terms of non-trivial universal scaling functions of both time variables. At criticality, five distinct types of ageing are found, depending on the form of the initial correlations, while at low temperatures only a single type of ageing exists. The autocorrelation and autoresponse exponents are shown to be generically different and to depend on the initial conditions. The scaling form of the two-time response functions agrees with a recent prediction coming from conformal invariance.

Aging in ferromagnetic systems at criticality near four dimensions.

We study the off-equilibrium response and correlation functions and the corresponding fluctuation-dissipation ratio for a purely dissipative relaxation of an O(N) symmetric vector model (model A) below its upper critical dimension. The scaling behavior of these quantities is analyzed and the associated universal functions are determined at first order in epsilon=4-d in the high-temperature phase and at criticality. A nontrivial limit of the fluctuation-dissipation ratio is found in the aging regime X( infinity )=1/2(1-(epsilon/4)(N+2)/(N+8))+O(epsilon(2)).