Slow Decay Rate Research Articles

Recycling concrete: An undiscovered source of ultrafine particles

While concrete recycling is practiced worldwide, there are many unanswered questions in relation to ultrafine particle (UFP; Dp < 100 nm) emissions and exposure around recycling sites. In particular: (i) Does recycling produce UFPs and in what quantities? (ii) How do they disperse around the source? (iii) What impact does recycling have on ambient particle number concentrations (PNCs) and exposure? (iv) How effective are commonly used dust respirators to limit exposure? We measured size-resolved particles in the 5–560 nm range at five distances between 0.15 and 15.15 m that were generated by an experimentally simulated concrete recycling source and found that: (i) the size distributions were multimodal, with up to ∼93% of total PNC in the UFP size range; and (ii) dilution was a key particle transformation mechanism. UFPs showed a much slower decay rate, requiring ∼62% more distance to reach 10% of their initial concentration compared with their larger counterparts in the 100–560 nm size range. Compared with typical urban exposure during car journeys, exposure decay profiles showed up to ∼5 times higher respiratory deposition within 10 m of the source. Dust respirators were found to remove half of total PNC; however the removal factor for UFPs was only ∼57% of that observed in the 100–560 nm size range. These findings highlight a need for developing an understanding of the nature of the particles as well as for better control measures to limit UFP exposure.

High-resolution ac-pulse modulated electrohydrodynamic jet printing on highly insulating substrates

This paper presents a new high-resolution ac-pulse modulated electrohydrodynamic (EHD)-jet printing technology on highly insulating substrates for drop-on-demand fabrication of electrical features and interconnects using silver nanoink. In traditional EHD-jet printing, the remained charge of the printed droplets changes the electrostatic field distribution and interrupts the follow-on printing behavior, especially for highly insulating substrates which have slow charge decay rates. The residue charge makes the control of EHD-jet printing very challenging for high-resolution continuous features. In this paper, by using modulated ac-pulsed voltage, the EHD-jet printing process switches the charge polarity of the consequent droplets to neutralize the charge on the substrate. The effect of the residue charge is minimized, which enables high-resolution printing of continuous patterns. Moreover, by modulating the pulse frequency, voltage, and duration, the EHD-jet printing behavior can be controlled with respect to printing speed/frequency and droplet size. Printing frequency is directly controlled by the pulse frequency, and the droplet dimension is controlled by the voltage and the duration of the pulse. We demonstrated that ac-pulse modulated EHD-jet printing can overcome the long-predicated charge accumulation problem on highly insulating substrates, and potentially be applied to many flexible electronics applications.

Correlation between native defects and dopants in colloidal lanthanide-doped Ga2O3nanocrystals: a path to enhance functionality and control optical properties

We report the synthesis and study of the photoluminescence properties of colloidal lanthanide(III)-doped Ga2O3 nanocrystals. The Ga2O3 nanocrystal host lattice acts as a sensitizer of the Eu3+ dopant red emission arising from intra-4f orbital transitions, and concurrently exhibits a strong blue photoluminescence originating from defect-based donor–acceptor pair (DAP) recombination. The Eu3+ sensitization, enabled by the energy transfer from the nanocrystal host lattice to the dopant centers, allows for the generation of dual blue-red emission. Increasing doping concentration leads to a decrease in the donor activation energy allowing for simultaneous control of the optical and electrical properties of these multifunctional nanocrystals. Analyses of the steady-state and time-resolved photoluminescence spectra suggest that Eu3+ ions occupy at least two different sites, which were tentatively designated as the six-coordinate internal and surface-related dopants. Uniquely, both DAP and Eu3+ emissions have long lifetimes (in milliseconds), although Eu3+ luminescence has a slower decay rate. These phenomena enable a temporal modulation of the dual emission and photoluminescence chromaticity on the millisecond timescale. The generality of these findings was demonstrated by preparing Tb3+-doped Ga2O3 nanocrystals, as a blue-green dual emitter. Owing to their optical transparency, electrical properties, emission color versatility, robustness, and fabricability, colloidal lanthanide(III)-doped Ga2O3 nanocrystals are a promising class of multifunctional materials and complex phosphors.

Cooperative amplification of energy transfer in plasmonic systems

We study cooperative effects in energy transfer (ET) from an ensemble of donors to an acceptor near a plasmonic nanostructure. We demonstrate that in cooperative regime ET takes place from plasmonic superradiant and subradiant states rather than from individual donors leading to a significant increase of ET efficiency. The cooperative amplification of ET relies on the large coupling of superradiant states to external fields and on the slow decay rate of subradiant states. We show that superradiant and subradiant ET mechanisms are efficient in different energy domains and therefore can be utilized independently. We present numerical results demonstrating the amplification effect for a layer of donors and an acceptor on a spherical plasmonic nanoparticle.

Millennial stocks and fluxes of large woody debris in lakes of the North American taiga

Summary Large woody debris (LWD) is an important cross‐boundary subsidy that enhances the productivity of lake ecosystems and the stability of aquatic food webs. LWD may also be an important carbon sink because LWD pieces are preserved for centuries in the littoral zone of lakes and rivers. However, a long‐term analysis of LWD stocks and fluxes in lakes, coupled with the reconstruction of past disturbances at the site level, has never been attempted. Large woody debris was sampled in five lakes of the Quebec taiga. Actual LWD stocks were described and residence time of the LWD pieces was established using tree‐ring and radiocarbon dating. LWD losses by decomposition and burial and other factors influencing LWD residence time were investigated using linear regressions. Impacts of wildfires on LWD fluxes during the last 1400 years were reconstructed separately for the five lakes using piecewise regression models. Fire years at each site were identified from the recruitment dates of charred LWD pieces. Large woody debris volume ranged between 0.92 and 1.57 m3 per 100 m of shoreline, and extrapolating these results to the landscape scale, it was concluded that LWD littoral carbon pools represent a minimal portion of boreal carbon storage. Large woody debris residence time in boreal lakes was confirmed to be very long. Tree‐ring dates of 1571 LWD pieces, mainly black spruce (Picea mariana (Mill.) BSP.), spanned the last 1400 years, while LWD specimens of older floating chronologies were preserved from decomposition for up to five millennia. The most influential variables explaining the variation in LWD residence time were the degree of burial and the distance from the shore. Large woody debris recruitment rates averaged 5.8 pieces per century per 100 m of shoreline. Fourteen wildfires were the primary cause for changes in the rates of tree establishment in the riparian forests and of LWD recruitment in the lakes. Synthesis. Interactions between terrestrial and aquatic ecosystems in northern boreal regions are strongly influenced by wildfires whose effects can last for centuries due to the slow large woody debris decay rate. Actual LWD stocks and carbon pools are a legacy of the past fire history.

Decay of spin coherences in one-dimensional spin systems

Strategies to protect multi-qubit states against decoherence are difficult to formulate because of their complex many-body dynamics. A better knowledge of the decay dynamics would help in the construction of dynamical decoupling control schemes. Here we use solid-state nuclear magnetic resonance techniques to experimentally investigate decay of coherent multi-spin states in linear spin chains. Leveraging on the quasi-one-dimension geometry of fluorapatite crystal spin systems, we can gain a deeper insight on the multi-spin states created by the coherent evolution, and their subsequent decay, than it is possible in three-dimensional (3D) systems. We are then able to formulate an analytical model that captures the key features of the decay. We can thus compare the decoherence behavior for different initial states of the spin chain and link their decay rate to the state characteristics, in particular their coherence and long-range correlation among spins. Our experimental and theoretical study shows that the spin chains undergo a rich dynamics, with a slower decay rate than for the 3D case, and thus might be more amenable to decoupling techniques.

POLYNOMIAL DECAY OF CORRELATIONS IN THE GENERALIZED BAKER'S TRANSFORMATION

We introduce a family of area preserving generalized baker's transformations acting on the unit square and having sharp polynomial rates of mixing for Hölder data. The construction is geometric, relying on the graph of a single variable "cut function". Each baker's map B is nonuniformly hyperbolic and while the exact mixing rate depends on B, all polynomial rates can be attained. The analysis of mixing rates depends on building a suitable Young tower for an expanding factor. The mechanisms leading to a slow rate of correlation decay are especially transparent in our examples due to the simple geometry in the construction. For this reason, we propose this class of maps as an excellent testing ground for new techniques for the analysis of decay of correlations in non-uniformly hyperbolic systems. Finally, some of our examples can be seen to be extensions of certain 1D non-uniformly expanding maps that have appeared in the literature over the last twenty years, thereby providing a unified treatment of these interesting and well-studied examples.

Rapid litter production and accumulation in Bornean mangrove forests

Litter fall and accumulation were measured weekly for one year (January–December 2007) at five mangrove forests within the Apar‐Adang Nature Reserve, East Kalimantan, Indonesia. Three forests were located near the sea edge, each co‐dominated by combinations of Sonnertia alba, Rhizophora apiculata, and Bruguiera parviflora; two forests were co‐dominated by Ceriops decandra, Exocoecaria agallocha, and Bruguiera sexangula (site IV), and by B. parviflora and B. sexangula (site V) and located further inland but subjected to intermittant freshwater inputs. Mean rates of annual litter production at forests I to V were 20.3, 19.7, 27.2, 24.2 and 27.6 Mg DW ha−1 yr−1 (mean of all forests = 23.7 Mg DW ha−1 yr−1) and rates of litter accumulation were 44.4, 50.2, 45.9, 61.3 and 66.2 Mg DW ha−1 yr−1 (mean of all forests = 57.8 Mg DW ha−1 yr−1), respectively, exhibiting peaks in the wet and dry seasons. Litter accumulation was greater than litter fall due to tidal advection of litter from forests closer to the sea edge coupled with slow decay rates. These rates of aboveground litter production and accumulation are the highest recorded for mangroves and higher than rates measured in tropical humid evergreen forests, suggesting that large expanses of equatorial mangrove forest, such as those on Borneo, may constitute an immense sink for coastal carbon.

Decay Properties of Klein‐Gordon Fields on Kerr‐AdS Spacetimes

This paper investigates the decay properties of solutions to the massive linear wave equation for g being the metric of a Kerr‐AdS spacetime satisfying satisfying the Breitenlohner‐Freedman bound. We prove that the nondegenerate energy of ψ with respect to an appropriate foliation of spacelike slices decays like (log t⋆)−2. Our estimates are expected to be sharp from heuristic and numerical arguments in the physics literature suggesting that general solutions will only decay logarithmically. The underlying reason for the slow decay rate can be traced back to a stable trapping phenomenon for asymptotically anti‐de Sitter black holes, which is in turn a consequence of the reflecting boundary conditions at null infinity.© 2013 Wiley Periodicals, Inc.

A Free-Floating PIV System: Measurements of Small-Scale Turbulence under the Wind Wave Surface

Abstract An in situ free-floating underwater miniature particle image velocimetry (UWMPIV) system is developed and applied to measure the structure of turbulence in the aqueous side of the wind wave surface boundary layer. The UWMPIV system provides a direct way to measure the aqueous side turbulence dissipation rate and vortex structures immediately below the air–water interface, which are important parameters that determine the gas exchange rate across the air–water interface subjected to a low-to-moderate wind shear. The impact of platform motion on the measurement of small-scale turbulence is discussed and found to be insignificant. A series of field experiments under a near “zero-fetch” wind wave condition and one open water experiment under a low wind condition were conducted on Lake Michigan to demonstrate the capabilities of the free-floating particle image velocimetry (PIV) system. The dissipation rate estimated with a “direct method” and with a “spectra fitting” method are compared. Vertical profiles of the turbulence dissipation rate suggest a power-law dependency with depth below the water surface. Surface shear velocities estimated through the aqueous side Reynolds stress distribution agreed well with wind stresses estimated by the classic drag law for zero-fetch wind wave conditions, where the primary source of turbulence was wind shear. For the open water experiment under a very low wind condition, a high dissipation rate was observed near the water surface, suggesting a high turbulence production rate by surface waves, and the profile of dissipation rate showed a slower decay rate with depth in the presence of waves.

Interpretation of thermal dependence of magnetic aftereffect for magnetic nanocomposite with slow decay rates

A new experimental characterization is presented of time-, field-, and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay. Field and temperature variations of irreversible susceptibility, χ irr , decay coefficient, S, fluctuation field, hf , and activation volume, V, have been calculated for the nanocomposite sample (Co80Ni20) using a recently developed modified Preisach–Arrhenius (MPA) model. The sample is composed of non-interacting nanoparticles having negligible reversible magnetization. Non-Arrhenius behavior is observed in both the maximum decay coefficient, S max, and the fluctuation field, hf , as a function of temperature T. The peak of both temperature curves are identical and occur at a critical temperature Tk of ∼50 K, which agrees with our experimental results. Based on the effect of a temperature-dependent chemical potential on energy barrier, hf is studied for T < Tk and T ≥ Tk , respectively. A more complete MPA model that can predict the magnetization as function of time, field and temperature for a magnetic material with slow decay rates is proposed. This model uses a multi-variable analytical formula, , which incorporates the characteristic parameters.

Does litterfall from native trees support rainfed agriculture? Analysis of Ficus trees in agroforestry systems of southern dry agroclimatic zone of Karnataka, southern India

Trees of the genus Ficus, integral components of indigenous rainfed agro-ecosystems of the southern dry agro-climatic zone of Karnataka, southern India, have traditionally been associated with the ecological service of soil quality enhancement in addition to various direct use benefits. We assessed the soil enrichment service of Ficus benghalensis L. a common Ficus species in these agroforestry systems, by quantifying nutrient return via litter fall. Litterfall estimation and chemical analysis of litter showed that F. benghalensis trees produce 3,512 kg·ha−1 of litter annually which, on decomposition, can satisfy up to 76.70 % of N, 20.24% of P and 67.76% of K requirements of dryland crops annually per hectare. This can lead to an avoided cost of compost of US $ 36.46 ha−1·a−1 in dryland farming systems. The slow rate of decay of Ficus litter, as revealed in litter decomposition studies indicates its potential as ideal mulch for dryland soils. We discuss the complementarity between Ficus litterfall and cropping patterns in Mandya, and its implications for rainfed agricultural systems.

Electronic and magnetic structure of the Cr(001) surface

Density functional theory (DFT) calculations are carried out to study the electronic and magnetic structure of the (001) surface of chromium. Our aim is to identify and characterize the most prominent electronic surface states and make the connection with the main experimental results. We show that a low dispersive minority spin surface state at the center of the surface Brillouin zone plays a crucial role. This surface state of Δ1 symmetry at 0.58 eV above the Fermi level exhibits a predominantly dz2 as well as pz orbital character. Local density of states (LDOS) analysis in the vacuum above the surface shows that the sharp feature originating from this surface state persists far away above the surface because of the slow decay rate of the pz wavefunction. Finally, by artificially lowering the surface magnetic moment on the outermost surface layer we find excellent agreement with experiments for . In addition, we propose that some extra spin polarized scanning tunneling spectroscopy (SP-STS) experiments should be made at smaller tip–surface distances to reveal additional features originating from the majority spin dz2 surface state.

Hierarchical nanostructured composite cathode with carbon nanotubes as conductive scaffold for lithium-sulfur batteries

Carbon nanotubes (CNTs) are excellent scaffolds for advanced electrode materials, resulting from their intrinsic sp2 carbon hybridization, interconnected electron pathway, large aspect ratio, hierarchical porous structures, and low cost at a large-scale production. How to make full utilization of the mass produced CNTs as building blocks for nanocomposite electrodes is not well understood yet. Herein, a composite cathode containing commercial agglomerated multi-walled CNTs and S for Li-S battery was fabricated by a facile melt-diffusion strategy. The hierarchical CNT@S coaxial nanocables exhibited a discharging capacity of 1020 and 740 mAh ·g–1 at 0.5 and 2.0 C, respectively. A rapid capacity decay of 0.7% per cycle at the initial 10 cycles and a slow decay rate of 0.14% per cycle for the later 140 cycles were detected. Such hierarchical agglomerated CNT@S cathodes show advantages in easy fabrication, environmentally benign, low cost, excellent scalability, and good Li ion storage performance, which are extraordinary composites for high performance Li-S battery.

Bulk solid state rechargeable lithium ion battery fabrication with Al-doped Li7La3Zr2O12 electrolyte and Cu0.1V2O5 cathode

A simple, low-temperature route was developed to process bulk solid-state Li-ion batteries employing Al-doped Li7La3Zr2O12 solid electrolyte (thickness: ∼ 0.5mm; 25°C conductivity: ∼ 2×10−4 S cm−1). A composite Cu0.1V2O5–based slurry was directly painted on Li7La3Zr2O12 and dried at 120°C to prepare the cathode film. The opposite side of the electrolyte was subsequently exposed to molten Li to form the anode. The discharge capacity of the solid state battery was 53mAhg−1 (calculated based on the weight of active cathode material) at room temperature with 5μAcm−2 discharging current. Severe capacity decay occurred after the initial discharging. A comparable liquid electrolyte battery was tested at room temperature for comparison and had a much slower decay rate. However, when the operating temperature of the solid state battery was increased to 50°C, the cell performance significantly improved. At 50°C, the battery exhibited 176mAhg−1 initial discharging capacity at 5μAcm−2 current density and 93mAhg−1 initial capacity under a 10μAcm−2 discharging current density. After 20 cycles, the capacity decayed to 68.6mAhg−1 when cycled at a 10μAcm−2 current density. Impedance spectroscopy was used to investigate the interface resistance of the battery at different temperatures. The results indicated that both the cathode and anode interface resistance were dramatically reduced at 50°C. The decrease in interface resistances at elevated temperature is proposed as the main reason for the observed battery performance enhancement.

Influence of Steps on the Tilting and Adsorption Dynamics of Ordered Pentacene Films on Vicinal Ag(111) Surfaces

Here we present a structural study of pentacene (Pn) thin films on vicinal Ag(111) surfaces by He atom diffraction measurements and density functional theory (DFT) calculations supplemented with van der Waals (vdW) interactions. Our He atom diffraction results suggest initial adsorption at the step edges evidenced by initial slow specular reflection intensity decay rate as a function of Pn deposition time. In parallel with the experimental findings, our DFT+vdW calculations predict the step edges as the most stable adsorption site on the surface. An isolated molecule adsorbs as tilted on the step edge with a binding energy of 1.4 eV. In addition, a complete monolayer (ML) with pentacenes flat on the terraces and tilted only at the step edges is found to be more stable than one with all lying flat or tilted molecules, which in turn influences multilayers. Hence our results suggest that step edges can trap Pn molecules and act as nucleation sites for the growth of ordered thin films with a crystal structure similar to that of bulk Pn.

Heteroskedasticity of Market Return: A Look at the All Nigerian Stock Exchange Index Time Series

With increasing importance of the capital market in the capital formation process, greater research interest is required towards understanding the behaviour of volatility and by extension, price generating dynamics in the market. Of the deluge of models that have emerged to explain and predict market behaviour, the pre-dominant ones are undoubtedly the unconditional mean-variance frameworks typified by the CAPM Class of models. Unfortunately these models have manifested critical defects in theory and evidence. This paper follows the lead of Engle (1982), Bollerslev (1986), and Nelson (1991) to model the All Nigerian Stock Exchange Index times series between January 2004 and December 2007 within the AR(3) EGARCH (1, 1) in-Mean framework with a view to explain those stylized facts of volatility like asymmetry, persistence, clustering, positive risk premium etc commonly associated with other advanced and rapidly developing markets. Using 978 observations comprised in the weekly sample Index Return, the exponential model which tended to be white noise was found to be substantially well specified, and able to explain some of the puzzles thrown up by the normative frameworks as in Amah (2004). The research result shows that the market exhibited the phenomenon of mean/volatility persistence, a symptom typically associated with market inefficiency. Basically the auto-regressive scheme of the first and second moments provided the right basis to predict future behaviour of returns. There seems therefore to be a predictable component in the conditional variance over time such that increases in present volatility leads to subsequent increases in future volatility. This also suggests that the market has what analysts have come to know as long memory and slow auto-correlation decay rate which contradicts the intuition behind random walk hypothesis. Finally research findings suggest that the market did not exhibit ‘leverage effects’, a phenomenon of volatility asymmetry found in most advanced markets.

Transition from interpulse to afterglow plasmas driven by repetitive short-pulse microwaves in a multicusp magnetic field

In the power-off phase, plasmas generated by repetitive short-pulse microwaves in a multicusp magnetic field show a transitive nature from interpulse to afterglow as a function of pulse duration tw = 20–200 μs. The ionized medium can be driven from a highly non equilibrium to an equilibrium state inside the pulses, thereby dictating the behavior of the plasma in the power-off phase. Compared to afterglows, interpulse plasmas observed for tw &amp;lt; 50 μs are characterized by a quasi-steady-state in electron density that persists for ∼ 20–40 μs even after the end of the pulse and has a relatively slower decay rate (∼ 4.3 × 104 s−1) of the electron temperature, as corroborated by optical measurements. The associated electron energy probability function indicates depletion in low energy electrons which appear at higher energies just after the end of the pulse. The transition occurs at tw ∼ 50 μs as confirmed by time evolution of integrated electron numbers densities obtained from the distribution function.

Luciferase from Fulgeochlizus bruchi (Coleoptera:Elateridae), a Brazilian click-beetle with a single abdominal lantern: molecular evolution, biological function and comparison with other click-beetle luciferases

Bioluminescent click-beetles emit a wide range of bioluminescence colors (λ(Max) = 534-594 nm) from thoracic and abdominal lanterns, which are used for courtship. Only the luciferases from Pyrophorus and Pyrearinus species were cloned and sequenced. The Brazilian Fulgeochlizus bruchi click-beetle, which inhabits the Central-west Cerrado (Savannas), is noteworthy because, differently from other click-beetles, the adult stage displays only a functional abdominal lantern, which produces a bright green bioluminescence for sexual attraction purposes, and lacks functional thoracic lanterns. We cloned the cDNA for the abdominal lantern luciferase of this species. Notably, the primary sequence of this luciferase showed slightly higher identity with the green emitting dorsal lantern luciferases of the Pyrophorus genus instead of the abdominal lanterns luciferases. This luciferase displays a blue-shifted spectrum (λ(Max) = 540 nm), which is pH-insensitive from pH 7.5 to 9.5 and undergoes a slight red shift and broadening above this pH; the lowest K(M) for luciferin among studied click-beetle luciferases, and the highest optimum pH (9.0) ever reported for a beetle luciferase. At pH 9.0, the K(M) for luciferin increases, showing a decrease of affinity for this substrate, despite the higher activity. The slow luminescence decay rate of F. bruchi luciferase in vitro reaction could be an adaptation of this luciferase for the long and sustained in vivo luminescence display of the click-beetle during the courtship, and could be useful for in vivo intracellular imaging.

Effect of decomposing post-fire coarse woody debris on soil fertility and nutrient availability in a Mediterranean ecosystem

Post-fire coarse woody debris can repre- sent a valuable nutrient reservoir for a regenerating ecosystem, helping to prevent soil fertility losses after a wildfire. However, there is scarce information on its effect on soil nutrient cycling and availability. We established three study sites along an altitudinal gradient in a burnt pine forest (SE Spain). At each site we determined: (1) decomposition rates and nutrient dynamics in charred logs left on the ground, 2 and 4 years after the fire, and (2) available nutrients in the soil and in the microbial fraction below charred logs and in bare soil areas. Despite the relatively slow decay rates in this Mediterranean climate (ca. 10 % of dry weight lost after 4 years), N and P were progres- sively released by logs, accounting for ca. 40 and 65 % of the initial content respectively after 4 years. This implies that the total aboveground biomass of the burnt forest released around 20 kg ha -1 of N and 2k g ha -1 of P during this period. The presence of post fire coarse woody debris consistently increased soil organic matter by around 18 %, total C and N by 42 and 26 %, respectively, dissolved organic C and N by 47 %, available inorganic P by 68 %, and microbial biomass and nitrogen by some 36 and 48 %, respec- tively. By contrast, soil bulk density decreased by ca. 18 % under logs compared to bare areas. Thus, the fire-killed wood was useful in the recovery of soil fertility and nutrient availability. Leaving the post-fire woody debris on site can enhance the biogeochemical sustainability, microbiological processes and soil ecological functioning. The detrimental effect of post-fire salvage logging on soil fertility should be therefore considered when making management decisions.