Independent Time Scales Research Articles

Inferring Advective Timescales and Overturning Pathways of the Deep Western Boundary Current in the North Atlantic Through Labrador Sea Water Advection

AbstractThe Subpolar North Atlantic plays a critical role in the formation of the deep water masses which drive Atlantic Meridional Overturning Circulation (AMOC). Labrador Sea Water (LSW) is formed in the Labrador Sea and exported predominantly via the Deep Western Boundary Current (DWBC). The DWBC is an essential component of the AMOC advecting deep waters southward, flowing at depth along the continental slope of the western Atlantic. By combining sustained hydrographic observations from the Labrador Sea to 26.5°N, we investigate the signal propagation and advective timescales of LSW via the DWBC from its source region to the Tropical Atlantic through various approaches using robust neutral density classifications. Two individually defined LSW classes are observed to advect on timescales that support a new plausible hydrographically observed advective pathway. We find each LSW class to advect on independent timescales, and validate a hypothesized alternative‐interior advection pathway branching from the DWBC by observing the arrival of LSW outside of the DWBC in the Bermuda basin on timescales similar to arriving at 26.5°N, 10–15 yr after leaving the source region. Advective timescales estimated herein indicate that this interior pathway is likely the main advective pathway; it remains uncertain whether a direct pathway plays a significant advective role. Using LSW convective signals as advective tracers along the DWBC permits the estimation of advective timescales from the subpolar to tropical latitudes, illuminating deep water advection pathways across the North Atlantic and the lower‐limb of AMOC as a whole.

The Pedagogy of Bafflement: Bernard Bailyn's History 2910, Fall 1996

The Pedagogy of Bafflement: Bernard Bailyn's History 2910, Fall 1996

Identification of energy dependent synchronization in coupled pendulums using semi-analytical method

The synchronization pattern of the coupled pendulums is vital in the design of pendulum energy harvesters. This understanding will help in optimizing the design of the harvester. Typically, the numerical solutions of these problems are initial-condition dependent and solved using time-consuming numerical integration techniques. Semi-analytical methods can effectively find system responses compared to nonlinear normal modes and then calculate the response. Semi-analytical methods are faster as one looks for periodic/quasi-periodic solutions. However, direct application in solving homogeneous equations using semi-analytical methods is complex. Hence, in the present paper, the synchronization nature of multi-degrees of freedom pendulum system was evaluated using multi-harmonic energy balance method (MHEBM), with different energy distribution between mass elements. Here, the proposed method is validated using a 2 DOF system with one pendulum and a 3 DOF system with two pendulums. The present study considers MHEBM with two independent time scales for solving quasi-periodic responses. Numerical integration results and analytical solutions for the linearized system (derived and solved using the method of characteristics) validate the proposed method. The ability of the system to get into in-phase and out-of-phase synchronization with different energy distributions is also demonstrated.

BGK source terms for out-of-equilibrium two-phase flow models

A modified form of BGK source terms is proposed for modeling two-phase flows with thermodynamical disequilibrium. The novelty is that three independent time-scales allow to manage the return to the thermodynamical equilibrium while remaining in agreement with the second law of thermodynamics. This is achieved thanks to the definition of a “local-in-time” equilibrium state which tends toward the asymptotic equilibrium state when time increases. The thermodynamical paths of the system are then modified with respect to the classical BGK source terms used for two-phase flow modeling, and the relaxation process of the system toward the asymptotic equilibrium state can be defined with additional degrees of freedom. In a numerical point of view, both the classical and the modified BGK source terms have advantages. The choice between these two forms strongly depends on the numerical strategy used to perform simulations.

Formula omitted] network optimization for edge consensus

This paper examines the H∞ performance problem of the edge agreement protocol for networks of agents operating on independent time scales, connected by weighted edges, and corrupted by exogenous disturbances. H∞-norm expressions and bounds are computed that are then used to derive new insights on network performance in terms of the effect of time scales and edge weights on disturbance rejection. We use our bounds to formulate a convex optimization problem for time scale and edge weight selection. Numerical examples are given to illustrate the applicability of the derived H∞-norm bound expressions, and the optimization paradigm is illustrated via a formation control example involving non-homogeneous agents.

The interplay of a fault zone and a volcanic reservoir from 3D elasto-plastic models: Rheological conditions for mutual trigger based on a field case from the Andean Southern Volcanic Zone

The Southern Andes margin hosts active and fossil volcanic, geothermal, and mineralized systems documenting intense geofluid migration through the crust. Fluid flow is also spatially associated with crustal faults that accommodate the bulk deformation arising from oblique plate convergence. Although recognized, the precise local mechanical interaction between faults and crustal reservoirs is yet to be better understood. Here we present 3D numerical models of a magmatic reservoir and a fault zone set about 4 km apart, inspired by the Tatara-San Pedro volcanic complex in the Southern Volcanic Zone (~36°S), which displays a geothermal field and a margin-parallel dextral active fault zone constrained by published magnetotelluric profiles and crustal seismicity respectively. We investigate elasto-plastic deformation and stress patterns in the intermediate bedrock space between the reservoir and the fault zone and test how shear stress, volumetric strain, and plastic strain develop. We also test the potential of enabling brittle failure of their counterpart by imposing either (1) a strike-slip displacement along the fault zone, or (2) a magmatic overpressure at the cavity walls. Parametric tests of Young's modulus and frictional strength provide the conditions for macro-scale brittle failure and show the development of diffuse domains of dilational strain of the order of 10−5 –10−3 in the intervening bedrock. This dilation is a proxy to the opening of voids or volumetric cracking in the bedrock, which tends to increase porosity and permeability allowing over-pressurized geofluids to migrate within these domains. Our results show that a minimum of 60 m of fault displacement is required to trigger brittle failure of an upper crustal cavity if the bedrock is stiff, whereas, for a more compliant bedrock, more than 100 m of localized slip motion is required. This implies that it is rather the accumulated effect of repeated crustal fault displacement that potentially favors fluid pathways upwards, rather than a single seismic event. On the other hand, a minimum of 7.5 MPa of fluid overpressure is required for a mid-crustal cavity (15 km depth) to trigger brittle failure of the fault zone. This threshold overpressure increases up to 50 MPa when the cavity is shallower (6 km depth). Our results show that in general, shallow reservoirs must be very close to fault zones (less than 1–2 km apart) to reactivate them. The models show that localized strike-slip tectonics and magma intrusions build a dilational stress field at the scale of several kilometers, that promotes fluid pathways to the surface. Further combining this interaction with the regional transpressional stress field may explain observations of transient fluid pathways on seemingly independent timescales along the Andean margin.

New chronology of the Chinese loess-paleosol sequence by leaf wax δD records during the past 800 k.y.

Abstract The Chinese loess-paleosol sequences provide important archives for studying paleoenvironmental changes. However, the lack of independent and accurate time scales hinders the study between loess and other records. Asian stalagmite δ18O records indicate synchronous patterns of paleoprecipitation δ18O over large geographic regions. The record of hydrogen isotopic composition of plant wax (δDwax) in Chinese loess is also controlled by rainwater δD. Both share a common origin. The linear relationship between rainfall δ18O and δD variance provides the basis to tie together chronologies of the same climate event in different records. Here, we show a new loess chronology by correlating chronologies of marker boundaries of the prominent climate chronozones in stalagmite δ18O and summer insolation to the equivalent climate stratigraphy in the loess δDwax sequence. We first developed and tested this novel methodology with data since the last interglacial on a millennial scale, and then applied this approach to the loess δDwax sequence for the past 800 k.y. to improve the traditional chronology based on magnetic susceptibility and grain size. The new δDwax time series provides not only an improved chronology for studying paleoclimate changes during interglacial intervals, it also represents a unique database with which to better understand the links between the Asian monsoon changes in the Chinese loess and other global climate events, especially for the periods prior to 640 ka, for which stalagmite records are not available.

Relaxation-time approximation with pair production and annihilation processes

We extend the Boltzmann equation in the relaxation time approximation to explicitly include transitions between particles forming an interacting mixture. Using the detailed balance condition as well as conditions of energy-momentum and current conservation, we show that only two independent relaxation time scales are allowed in such an interacting system. Dissipative hydrodynamic equations and the form of transport coefficients is subsequently derived for this case. We find that the shear and bulk viscosity coefficients, as well as the baryon charge conductivity are independent of the transition time scale. However, the bulk viscosity and conductivity coefficients that can be attributed to the individual components of the mixture depend on the transition time.

High-precision nonlocal temporal correlation identification of entangled photon pairs for quantum clock synchronization.

High-precision nonlocal temporal correlation identification in entangled photon pairs is critical to measure the time offset between remote independent time scales for many quantum information applications. The first nonlocal correlation identification was reported in 2009, which extracts the time offset via the algorithm of iterative fast Fourier transformations and their inverse. The best identification resolution is restricted by the peak identification threshold of the algorithm, and thus the time offset calculation precision is limited. In this paper, an improvement for the identification is presented both in resolution and precision via a modified algorithm of direct cross correlation extraction. A flexible resolution down to 1 ps is realized, which is only dependent on the least significant bit resolution of the time-tagging device. The attainable precision is shown to be mainly determined by the inherent timing jitter of single photon detectors, the acquired pair rate, and acquisition time, and a sub-picosecond precision (0.72 ps) has been achieved at an acquisition time of 4.5 s. This high-precision nonlocal measurement realization provides a solid foundation for the field applications of entanglement-based quantum clock synchronization, ranging, and communications.

Formation of S0s in extreme environments II: The star-formation histories of bulges, discs, and lenses

ABSTRACT Different processes have been proposed to explain the formation of S0s, including mergers, disc instabilities, and quenched spirals. These processes are expected to dominate in different environments, and thus leave characteristic footprints in the kinematics and stellar populations of the individual components within the galaxies. New techniques enable us to cleanly disentangle the kinematics and stellar populations of these components in IFU observations. In this paper, we use buddi to spectroscopically extract the light from the bulge, disc, and lens components within a sample of eight S0 galaxies in extreme environments observed with MUSE. While the spectra of bulges and discs in S0 galaxies have been separated before, this work is the first to isolate the spectra of lenses. Stellar populations analysis revealed that the bulges and lenses have generally similar or higher metallicities than the discs, and the α-enhancement of the bulges and discs are correlated, while those of the lenses are completely unconnected to either component. We conclude that the majority of the mass in these galaxies was built up early in the lifetime of the galaxy, with the bulges and discs forming from the same material through dissipational processes at high redshift. The lenses, on the other hand, formed over independent time-scales at more random times within the lifetime of the galaxy, possibly from evolved bars. The younger stellar populations and asymmetric features seen in the field S0s may indicate that these galaxies have been affected more by minor mergers than the cluster galaxies.

Multiple time scale analysis of pressure oscillations in solid rocket motors

In this study, acoustic pressure oscillations for single and coupled longitudinal acoustic modes in Solid Rocket Motor (SRM) are investigated using Multiple Time Scales (MTS) method. Two independent time scales are introduced. The oscillations occur on fast time scale whereas the amplitude and phase changes on slow time scale. Hopf bifurcation is employed to investigate the properties of the solution. The supercritical bifurcation phenomenon is observed for linearly unstable system. The amplitude of the oscillations result from equal energy gain and loss rates of longitudinal acoustic modes. The effect of linear instability and frequency of longitudinal modes on amplitude and phase of oscillations are determined for both single and coupled modes. For both cases, the maximum amplitude of oscillations decreases with the frequency of acoustic mode and linear instability of SRM. The comparison of analytical MTS results and numerical simulations demonstrate an excellent agreement.

Analysis of Flow Timescales on a Periodically Pitching/Surging Airfoil

Time-resolved velocity fields around a pitching and surging NACA 0018 airfoil were analyzed to investigate the influence of three independent timescales associated with the unsteady flowfield. The first of these timescales, the period of the pitch/surge motion, is directly linked to the development of dynamic stall. A simplified model of the flow using only a time constant mode and the first two harmonics of the pitch surge frequency has been shown to accurately model the flow. Full stall and leading-edge flow separation, however, were found to take place before the maximum angle of attack, indicating that a different timescale was associated with leading-edge vortex formation. This second, leading-edge vortex, timescale was found to depend on the airfoil convection time and compare well with the universal vortex formation time. Finally, instantaneous non-phase-averaged measurements were investigated to identify behavior not directly coupled to the airfoil motion. From this analysis, a third timescale associated with quasi-periodic Strouhal vortex shedding was found before flow separation. The interplay between these three timescales is discussed in detail, particularly as they relate to the periodic velocity and angle-of-attack change apparent to the blades of a vertical axis wind turbine.

A statistical characterization of the Galileo-to-GPS inter-system bias

Global navigation satellite system operates using independent time scales and thus inter-system time offsets have to be determined to enable multi-constellation navigation solutions. GPS/Galileo inter-system bias and drift are evaluated here using different types of receivers: two mass market and two professional receivers. Moreover, three different approaches are considered for the inter-system bias determination: in the first one, the broadcast Galileo to GPS time offset is used to align GPS and Galileo time scales. In the second, the inter-system bias is included in the multi-constellation navigation solution and is estimated using the measurements available. Finally, an enhanced algorithm using constraints on the inter-system bias time evolution is proposed. The inter-system bias estimates obtained with the different approaches are analysed and their stability is experimentally evaluated using the Allan deviation. The impact of the inter-system bias on the position velocity time solution is also considered and the performance of the approaches analysed is evaluated in terms of standard deviation and mean errors for both horizontal and vertical components. From the experiments, it emerges that the inter-system bias is very stable and that the use of constraints, modelling the GPS/Galileo inter-system bias behaviour, significantly improves the performance of multi-constellation navigation.

Tephrochronology and the extended intimate (integration of ice-core, marine and terrestrial records) event stratigraphy 8–128 ka b2k

The comparison of palaeoclimate records on their own independent timescales is central to the work of the INTIMATE (INTegrating Ice core, MArine and TErrestrial records) network. For the North Atlantic region, an event stratigraphy has been established from the high-precision Greenland ice-core records and the integrated GICC05 chronology. This stratotype provides a palaeoclimate signal to which the timing and nature of palaeoenvironmental change recorded in marine and terrestrial archives can be compared. To facilitate this wider comparison, without assuming synchroneity of climatic change/proxy response, INTIMATE has also focussed on the development of tools to achieve this. In particular the use of time-parallel marker horizons e.g. tephra layers (volcanic ash). Coupled with the recent temporal extension of the Greenland stratotype, as part of this special issue, we present an updated INTIMATE event stratigraphy highlighting key tephra horizons used for correlation across Europe and the North Atlantic. We discuss the advantages of such an approach, and the key challenges for the further integration of terrestrial palaeoenvironmental records with those from ice cores and the marine realm.

Chrono- and sequence-stratigraphy of the Mid-Permian to Early Triassic Khuff sequences of the Arabian Plate

ABSTRACTThe Middle Permian (Guadalupian), Upper Permian (Lopingian) and Lower Triassic Khuff and correlative formations in the Arabian Plate consist of six “third-order” sequences, from oldest to youngest KS6 to KS1, and at least 45 “fourth-order” sequences. They are here dated using biostratigraphic constraints and correlated to two independent sequence-stratigraphic time scales: (1) global sequences calibrated in the Geological Time Scale GTS 2012; and (2) orbital-forcing glacio-eustatic sequences that track the 0.405 million year (Myr) orbital eccentricity signal in the M&H-2010 scale (Matthews and Al-Husseini, 2010). The chronostratigraphic calibration of the Khuff sequences provides a reference section and common nomenclature that can be used for regional and global correlations. It permits positioning the hydrocarbon reservoirs of the Khuff and equivalent formations in a sequence-stratigraphic framework that can be used in exploration and reservoir characterization.The lower sequence boundary of the Khuff Formation (Khuff SB) is correlated to global Wordian SB Wor1 near the Roadian/Wordian Boundary at 268.8 ± 0.5 Ma, and correlative SB 19C at 268.9 Ma in the M&H-2010 scale. The upper sequence boundary of the Khuff Formation with the overlying Sudair Formation (Sudair SB) is correlated to Olenekian SB Ole1 near the Induan/Olenekian Boundary at 250.0 ± 0.5 Ma, and correlative SB 17 at 249.5 Ma in the M&H-2010 scale. These calibrations imply the Khuff was deposited in about 19.4 Myr, and consists of 48 “stratons”; i.e. transgressive-regressive (T-R) depositional subsequences with an average duration of 0.405 Myr corresponding to long-eccentricity orbital cycles 664 to 617. The 48 stratons are predicted to form four “dozons” (19C, 18A, 18B and 18C), each consisting of 12 stratons. Individual dozons lasted 4.86 Myr and are separated by regional sequence boundaries (SB 19C to SB 17A).In Oman, Khuff Sequence KS6 on the Saiq Plateau is correlated to the subsurface Lower Khuff Member, and both are interpreted to consist of 12 subsequences that are correlated to stratons 664–653 forming Dozon 19C between 268.9–264.0 Ma. KS6 is correlated to the four global sequences Wordian Wor1 to Capitanian Cap1 dated between 268.8–264.0 Ma in GTS 2012. Khuff Sequence KS5 corresponds to the Middle Khuff Member up to the top of Middle Khuff Anhydrite in subsurface Oman. On the Saiq Plateau, KS5 potentially consists of 12 cycle sets (Koehrer et al., 2010) that are correlated to stratons 652–641 of Dozon 18A, between 264.0–259.2 Ma. It is correlated to global sequences Capitanian Cap2 and Cap3 dated between 264.0–259.8 Ma in GTS 2012. Khuff Sequence KS4 consists of 11 cycle sets on the Saiq Plateau and other localities in Al Jabal al-Akhdar in Oman (Koehrer et al., 2010, 2012). It is assumed that one cycle set remains unidentified in KS4, completing its correlation to stratons 640–629 of Dozon 18B between 259.2–254.3 Ma. KS4 correlates to the global sequences Wuchiapingian Wuc1 and Wuc2 dated between 259.8–254.2 in GTS 2012. Khuff sequences KS3, KS2 and KS1 combined consist of 10 cycle sets in Al Jabal al-Akhdar (Koehrer et al., 2010, 2012), and two are presumed unidentified so as to correlate to the 12 stratons 628–617 of Dozon 18C between 254.3–249.5 Ma. Sequence KS3 correlates to Changhsingian global sequences Cha1 and Cha2 dated between 254.2–252.5, and KS2 and KS1 to latest Permian–Early Triassic global sequences Cha 3 and Induan–Olenekian Ind1 dated between 252.5–249.9 Ma in GTS 2012. The Permian/Triassic Boundary (PTB), dated at 252.2 ± 0.5 Ma in GTS 2012, occurs in lowermost Khuff Sequence KS2, in cycle set KCS 2.3, and based on the orbital calibration of the Upper Permian (Lopingian) Series in South China, it occurs in Straton 623 between 252.3 and 251.9 Ma.

Long Duration, Single-Molecule Monitoring of Lysozyme Kinetics

Tethering a single molecule of T4 lysoyzme to a carbon nanotube field effect transistor resulted in a novel technique for monitoring single-molecule enzymatic activity. Continuous electronic monitoring readily resolved lysozyme as a processive enzyme, since substrate release was clearly distinguished from serial hydrolysis of glycosidic bonds. On average, we observed hydrolysis of 100 consecutive bonds at 15 Hz rates when lysozyme processed natural peptidoglycan. Furthermore, long duration measurements allowed statistically-meaningful analysis of thousands of chemical events by the same molecule, uncovering seven independent timescales governing lysozyme's activity, including minute-by-minute dynamic disorder. Stability of the lysozyme-transistor method allowed these timescales to be studied as a function of environmental conditions such as substrate, pH, or temperature, in order to produce a detailed map of factors that affect single molecule processivity. For example, variations in pH do not change any of the rate constants of lysozyme's motions, but rather decrease enzyme activity by increasing the proportion of time stuck in an inactive, closed conformation. As another example, we found that peptidoglycan cross-links are directly responsible for a 50% drop in effective activity. Using a synthetic, linear substrate without cross-links, we observed long, uninterrupted processing runs to the end of individual substrate molecules. By comparison, lysozyme spends approximately half its time traversing the cross-links present in wild-type substrate. Rather than releasing substrate at a cross-link, however, lysozyme instead changes to an alternate, non-processive motion with which it can sidestep the cross-link. The combination of processive and non-processive motions allow lysozyme to remain effective and zigzag through wild-type substrate.

Out of tune: the dangers of aligning proxy archives

Tuning is a widespread technique to combine, date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives. The approach will be reviewed by discussing a number of literature examples, ranging from peat and tephra layers to orbital tuning and δ18O series from marine and ice deposits. Potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties, and some solutions suggested. Fossil proxy research could become enhanced if tuning were approached in a more quantitative, reliable and objective way, and especially if individual proxy archives were non-tuned and kept on independent time-scales.

Constrained sintering of an air-plasma-sprayed thermal barrier coating

A micromechanical model is presented for the constrained sintering of an air-plasma-sprayed, thermal barrier coating upon a thick superalloy substrate. The coating comprises random splats with intervening penny-shaped cracks. The crack faces make contact at asperities, which progressively sinter in-service by interfacial diffusion, accommodated by bulk creep. Diffusion is driven by the reduction in interfacial energy at the developing contacts and by the local asperity contact stress. At elevated operating temperature, both sintering and creep strains accumulate within the plane of the coating. The sensitivities of sintering rate and microstructure evolution rate to the kinetic parameters and thermodynamic driving forces are explored. It is demonstrated that the sintering response is governed by three independent timescales, as dictated by the material and geometric properties of the coating. Finally, the role of substrate constraint is assessed by comparing the rate of constrained sintering with that for free sintering.

Self-Propelled Particles with Fluctuating Speed and Direction of Motion in Two Dimensions

We study general aspects of active motion with fluctuations in the speed and the direction of motion in two dimensions. We consider the case in which fluctuations in the speed are not correlated to fluctuations in the direction of motion, and assume that both processes can be described by independent characteristic time scales. We show the occurrence of a complex transient that can exhibit a series of alternating regimes of motion, for two different angular dynamics which correspond to persistent and directed random walks. We also show additive corrections to the diffusion coefficient. The characteristic time scales are also exposed in the velocity autocorrelation, which is a sum of exponential forms.

On the Dynamics of Kac p-Spin Glasses

This paper discusses the dynamical properties of p-spin models with Kac interactions. For large but finite interaction range R one finds two different well separated time scales for relaxation. A first short time scale, roughly independent of R, on which the system remains confined to limited regions of the configuration space and an R dependent long time scale on which the system is able to escape from the confining regions. I will argue that the R independent time scales can be described through dynamical mean field theory, while non-perturbative new techniques have to be used to deal with the R dependent scales.