First-order Loss Research Articles

Damping performance and its influencing factors of wind turbine towers with constrained layer damping treatment

Constrained layer damping (CLD) is proposed as an energy dissipation measure for vibration control of offshore monopile wind turbine towers (OMWTT). The damping performance and influencing factors of OMWTT with CLD treatment are studied in this paper. First, a theory for calculating the first-order modal loss factor provided by CLD for composite structures is derived using the modal strain energy (MSE) method; second, the error of the theoretical formulation is analyzed using the finite element method; and finally, the influence of each parameter of the CLD on the first-order modal loss factor is discussed. The modal loss factor’s temperature dependence is described with the theory’s aid. The modal damping calculation theory proposed in this paper can rapidly determine the optimal design of CLD, considering the influence of multiple parameters and a complex environment, which could be helpful in the efficient vibration reduction of OMWTT.

On the intrinsic reaction rate of polyethylene pyrolysis and its interplay with mass transfer

An attempt to determine the the intrinsic kinetic of polyolefins pyrolysis is presented. For this, pyrolysis experiments of polyethylene were performed in a screen heater reactor, where the effects of mass and heat transfer on the pyrolysis process are minimized. First-order mass loss rate constants obtained at 500 °C were circa 0.5 and 1.3 s−1 for HDPE and LDPE, respectively, which are significantly higher than the majority of the values reported in the literature. At 450 °C, the mass loss rate of HDPE was lower, circa 10−2 s−1. Additionally, we have observed that the interplay between mass transfer and the depolymerization reactions can be used to steer the product distribution. For instance, in a 50 g scale batch reactor, the product obtained at 420 °C (only oil) is much lighter than at 500 °C (mixture of oil and wax), which can be attributed to the much lower evaporation rate of larger cracking products at 420 °C as a result of which these fragments crack further in the reacting liquid phase.

Dynamic performance of co-cured composite structure with sandwich damping film

In this paper, a research on theoretical analysis and finite element simulation of the damping sandwich composite plate with fixed support condition is carried out, and the dynamic characteristics of composite plates are explored by modal experiments. The vibration equilibrium equation of damping sandwich composite plate with fixed support condition is derived by combining first-order shear deformation theory, variational principle, and Hamilton principle. A set of modal basis functions satisfying the fixed support condition are established. The analytical solution is obtained via Galerkin weighted residual theory. The influence of structural parameters on the free vibration characteristics of the sandwich composite plates is investigated based on the mutual verification of theoretical calculation, numerical simulation, and modal test results. When the damping layer (0.2 mm) is located on the surface of the skin (2 mm), the first-order mode frequency and first-order loss factor are 196.66 Hz and 0.01, respectively. When the damping layer is in the neutral layer, the first-order mode frequency and first-order loss factor are 189.99 Hz and 0.14, respectively. Compared with the damping layer in the skin, the first-order mode frequency is reduced by 3.39%, while the first-order loss factor is 14 times higher. The results show that the damping performance of the structure is optimal when the damping layer is located in the neutral layer, and the structural stiffness is higher when the damping layer is close to the skin. The work provides theoretical guidance for the development and application of lightweight composite structures with large damping and high stiffness.

Effect of 3D Printing Process Parameters on Damping Characteristic of Cantilever Beams Fabricated Using Material Extrusion

The present paper aims to investigate the process parameters and damping behaviour of the acrylonitrile butadiene styrene (ABS) cantilever beam manufactured using material extrusion (MEX). The research outcome could guide the manufacture of MEX structures to suit specific operating scenarios such as energy absorption and artificially controlled vibration responses. Our research used an experimental approach to examine the interdependencies between process parameters (nozzle size, infill density and pattern) and the damping behaviour (first-order modal damping ratio and loss factor). The impact test was carried out to obtain the damping ratio from the accelerometer. A dynamic mechanical analysis was performed for the loss factor measurement. The paper used statistical analysis to reveal significant dependencies between the process parameters and the damping behaviour. The regression models were also utilised to evaluate the mentioned statistical findings. The multiple third-order polynomials were developed to represent the relation between process parameters and modal damping ratio using stiffness as the mediation variable. The obtained results showed that the infill density affected the damping behaviour significantly. Higher infill density yielded a lower damping ratio. Nozzle size also showed a notable effect on damping. A high damping ratio was observed at a significantly low value of nozzle size. The results were confirmed using the theoretical analysis based on the underlying causes due to porosity in the MEX structure.

Incremental Evaluation Model for the Analysis of Indoor Air Measurements

The investigation of the cleaning effectiveness of air cleaners under realistic conditions is challenging. Mathematical models are needed to extract characteristic properties of the air cleaning system from experimental data. An incremental evaluation model based on a source term and a total first-order loss coefficient in each segment was developed to analyze indoor particle measurements. The application of the model is demonstrated using two scenarios, one in a well-mixed testing room and another in a fully equipped aircraft cabin at 750 hPa with a typical aircraft ventilation system. In the first scenario, a normalized version of the model is used to eliminate the source’s influence. For the investigation in the aircraft cabin, the model served to extract temporal and spatial resolved source terms and first-order loss coefficients. The incremental evaluation model is applicable to enhance the certification of air cleaners. The application of the model is not only limited to particles; measurements of gaseous compounds like ozone, carbon dioxide, or volatile organic compounds can be evaluated analogously. The model’s utility for the data analysis of experiments with complex flow conditions should be studied in further investigations.

Light intensity dependence of the photocurrent in organic photovoltaic devices

The competition between recombination and extraction of carriers defines the charge collection efficiency and, therefore, the overall performance of organic photovoltaic devices, including solar cells and photodetectors. In this work, we describe different components of the steady-state light intensity-dependent photocurrent (IPC) and charge collection efficiency under operational conditions. Further, we demonstrate how different loss mechanisms can be identified based on their unique signatures in the IPC. In particular, we show how IPC can be used to distinguish first-order, trap-assisted recombination from other first-order photocurrent loss mechanisms, which dominate at the low-intensity characteristic of indoor light-harvesting applications. The theoretical framework is presented and verified by a one-dimensional drift-diffusion device model. Finally, the extended IPC methodology is validated on organic thin-film photovoltaic devices. We conclude that the relatively straightforward measurement of IPC over a large dynamic range can be a powerful tool for understanding solar and indoor device fundamentals. • IPC is a tool for understanding photovoltaic device fundamentals • Photocurrent loss mechanisms are identified based on their signatures in IPC • The theoretical framework is verified with a drift-diffusion device model • Experimental demonstration of IPC method on state-of-the-art organic solar cells Zeiske et al. present a combined theoretical and experimental study of intensity-dependent photocurrent (IPC), a tool for understanding solar and indoor device fundamentals, to identify different photovoltaic device performance-limiting photocurrent loss mechanisms based on their unique signatures in IPC.

Angled Flip-Chip Integration of VCSELs on Silicon Photonic Integrated Circuits

An investigation of angled flip-chip integration of a singlemode 850 nm vertical-cavity surface-emitting laser (VCSEL) on a silicon nitride photonic integrated circuit (PIC) is presented. Using numerical FDTD simulations, we consider the conditions under which the VCSEL can be integrated at an angle over a grating coupler with high coupling efficiency and low optical feedback. With both coupling efficiency and feedback decreasing with increasing angle, there is a trade-off. With co-directional coupling, first-order diffraction loss sets in at a critical angle, which further reduces the coupling efficiency. No such critical angle exists for contra-directional coupling. We also experimentally demonstrate angled flip-chip integration of GaAs-based 850 nm single transverse and polarization mode VCSELs over grating couplers on a silicon-nitride PIC. At the output grating coupler, light is either collected by an optical fiber or converted to a photocurrent using a flip-chip integrated GaAs-based photodetector. The latter forms an on-PIC optical link. We measured an insertion loss of 21.9, 17.6 and 20.1 dB with a singlemode fiber, multimode fiber and photodetector over the output grating coupler, respectively.

A comparative experimental study on damping properties of epoxy nanocomposite beams reinforced with carbon nanotubes and graphene nanoplatelets

Abstract Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) are extremely ideal nanofillers for applications in damping polymer. This work explores the damping behavior of polymer nanocomposite beams made of epoxy resin reinforced with CNTs and GNPs experimentally. Beam specimens for the vibration tests together with dynamic mechanical analysis (DMA) are fabricated with different weight ratios of CNTs and GNPs, upon which DMA and free vibration tests are conducted. Scanning electron microscope images are also obtained to check the dispersion of nanofillers in microscale. It is found that the first-order loss factor of composite beam specimens shows a rise of 41.1% at 0.4 wt% CNT content compared with that of pure epoxy, while the first-order loss factor of composite beam specimens with 0.025 wt% GNP content increases up by 128.9%. The maximum value of the first-order loss factor of nanocomposite beams with GNP reinforcement is 62.2% higher than that with CNTs.

Contributions of Coagulation, Deposition, and Ventilation to the Removal of Airborne Nanoparticles in Indoor Environments.

Airborne nanoparticles are frequently released in occupied spaces due to episodic indoor source activities. Once generated, nanoparticles undergo aerosol transformation processes such as coagulation and deposition. These aerosol processes lead to changes in particle concentration and size distribution over time and accordingly affect human exposure to nanoparticles. The present study establishes a framework for an indoor particle dynamic model that can predict time- and size-dependent particle concentrations after episodic indoor emission events. The model was evaluated with six experimental data sets obtained from previous measurement studies in the literature. The indoor particle dynamic model quantified the relative contributions of three particle loss mechanisms (i.e., coagulation, deposition, and ventilation) to the total reduction in number concentration. The results show that particle coagulation and indoor surface deposition are two dominant processes responsible for temporal changes in particle size and concentration following indoor emission events. The first-order equivalent coagulation loss rate notably varies with indoor emission source and accounts for up to 59% of the total particle loss for burning a candle, 42% for broiling a fish, and 10% for burning incense. The results reveal that while the coagulation loss rate changes markedly with the particle concentration and source type, the deposition loss rate is more dependent on particle size. Compared to coagulation and deposition, the effect of ventilation is marginal for most of the nanoparticle emission events indoors; however, ventilation loss becomes pronounced with the decrease of particle concentration below 5 × 104 cm-3, especially for particles larger than 100 nm in aerodynamic diameter.

Direct observation of trap-assisted recombination in organic photovoltaic devices

Trap-assisted recombination caused by localised sub-gap states is one of the most important first-order loss mechanism limiting the power-conversion efficiency of all solar cells. The presence and relevance of trap-assisted recombination in organic photovoltaic devices is still a matter of some considerable ambiguity and debate, hindering the field as it seeks to deliver ever higher efficiencies and ultimately a viable new solar photovoltaic technology. In this work, we show that trap-assisted recombination loss of photocurrent is universally present under operational conditions in a wide variety of organic solar cell materials including the new non-fullerene electron acceptor systems currently breaking all efficiency records. The trap-assisted recombination is found to be induced by states lying 0.35-0.6 eV below the transport edge, acting as deep trap states at light intensities equivalent to 1 sun. Apart from limiting the photocurrent, we show that the associated trap-assisted recombination via these comparatively deep traps is also responsible for ideality factors between 1 and 2, shedding further light on another open and important question as to the fundamental working principles of organic solar cells. Our results also provide insights for avoiding trap-induced losses in related indoor photovoltaic and photodetector applications.

Quality, phenolic content, antioxidant activity, and the degradation kinetic of some quality parameters in strawberry fruit coated with salicylic acid andAloe veragel

The aim of this study was to evaluate the effect of salicylic acid (SA), Aloe vera gel (AV), and SA + AV on quality parameters of strawberry over 15 days. Weight loss, decay, and firmness increased, while ascorbic acid (AAC), total anthocyanin (TAC), total phenolic (TPC) contents, total antioxidant activity (TAA), and sensory attributes decreased significantly during the storage time in all samples. All treatments suppressed water loss, decay, and firmness and maintained higher AAC, TAA, and TPC compared to the control. AAC loss followed a first-order kinetic model, but TPC and TAC loss followed a zero-order kinetic until day 5 or 10 and a first-order reaction until the end of storage. Most of the recorded quality attributes were better preserved in the SA + AV samples, followed by the AV and then the SA treatments. The data of this study confirmed that the postharvest application of 1 mM SA + AV can improve the quality attributes of strawberry during storage. Practical applications As strawberry is mainly lost during the postharvest period, it is important to take proper strategies to overcome this problem. The results of the present study showed that the coating of the strawberry fruit with AV + SA (especially at 1 mM) retained fruit firmness, AAC, TPC, sensory attributes, and TAA and delayed strawberry decay as well. Besides, the function of AV in keeping the quality parameters of the strawberry fruit was better than that of SA. When SA is to be used as a postharvest treatment, 2 mM SA might give better results in the retention of AAC, TAC, and TPC, and 1 mM SA might give fruits with more firmness and less decay. The results of this study showed that strawberry is a good source of AAC (276.35 mg/100 g) and TPC (1,146.69 mg gallic acid equivalent/100 g) that declined to 186 and 480 mg/100 g, respectively, in the control sample after 15 days of storage, which were still high values. Meanwhile, in the samples treated with 1 mM SA + AV, AAC and TPC were 240 and 758.54 mg/100 g after 15 days of storage, respectively. In conclusion, the use of SA and AV, either alone or particularly in combination, may enhance the health aspects of strawberry through retaining AAC and TPC and therefore, increasing TAA of strawberry and also, maintaining a lower rate of weight and firmness loss.

Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies.

Potted plants have demonstrated abilities to remove airborne volatile organic compounds (VOC) in small, sealed chambers over timescales of many hours or days. Claims have subsequently been made suggesting that potted plants may reduce indoor VOC concentrations. These potted plant chamber studies reported outcomes using various metrics, often not directly applicable to contextualizing plants' impacts on indoor VOC loads. To assess potential impacts, 12 published studies of chamber experiments were reviewed, and 196 experimental results were translated into clean air delivery rates (CADR, m3/h), which is an air cleaner metric that can be normalized by volume to parameterize first-order loss indoors. The distribution of single-plant CADR spanned orders of magnitude, with a median of 0.023 m3/h, necessitating the placement of 10-1000 plants/m2 of a building's floor space for the combined VOC-removing ability by potted plants to achieve the same removal rate that outdoor-to-indoor air exchange already provides in typical buildings (~1 h-1). Future experiments should shift the focus from potted plants' (in)abilities to passively clean indoor air, and instead investigate VOC uptake mechanisms, alternative biofiltration technologies, biophilic productivity and well-being benefits, or negative impacts of other plant-sourced emissions, which must be assessed by rigorous field work accounting for important indoor processes.

First-Order Seismic Loss Assessment at Urban Scale: A Case Study of Skopje, North Macedonia

ABSTRACT Relatively simple method for seismic loss assessment is presented based on probabilistic hazard, event scenarios and local building inventory. EMS98-dependent vulnerability model is transformed to continuous fragility functions correlating damage probability to peak ground acceleration. The proposed method illustrated over 59,950 inventoried buildings and evaluated with replacement cost of $25.5B. For a repeat of the M6.1 1963 earthquake, simulations predict immediate losses of about $6.8B and 1,908 red-tagged buildings, compared to about $5B and 15,800 red-tagged building at the time. Average losses from probabilistic scenarios range from $1.6B (return period of 100y) to $17.8B (10,000y).

Measurements of HO2 uptake coefficient on aqueous (NH4)2SO4 aerosol using aerosol flow tube with LIF system

Laboratory studies of HO2 uptake coefficients, γ(HO2), were conducted at room temperature using an aerosol flow tube coupled with a laser induced fluorescence (LIF) system. The measurement was conducted with atmospherically relevant HO2 concentrations (∼1×109molecule/cm3) at 51% RH. The measured γ(HO2) onto aqueous (NH4)2SO4 aerosol was 0.001 ± 0.0007, which was consistent with the relatively low first-order loss rate of HO2 onto aqueous (NH4)2SO4 aerosol. The γ(HO2) was elevated with increase of Cu(II) concentrations in aqueous (NH4)2SO4 aerosol. The threshold of Cu(II) concentration was 10−3 mol/L for the dramatic increase of γ(HO2). It was found that γ(HO2) reached 0.1 when Cu(II) concentration in aerosol was larger than 10−3 mol/L, suggesting that γ(HO2) is very sensitive to concentration of transition metal ions in aerosol.

Theoretical evaluation of different factors affecting the HO2 uptake coefficient driven by aqueous-phase first-order loss reaction

The heterogeneous loss on aerosols is an important sink of HO2, affecting the radical chemistry and cycling, and thus it plays a key role in the atmospheric photochemistry. Gaining a reasonable HO2 uptake coefficient (γHO2) would be of great importance in evaluating the heterogeneous loss rate of HO2 on aerosols. This work was motivated by the large variance of reported HO2 mass accommodation coefficients (αHO2) in laboratory studies (0.1–1), which can cause consequent bias in the parameterized HO2 uptake coefficient (γHO2). We conducted a theoretical analysis of the roles of several key factors or parameters in determining γHO2 on a sphere droplet with adjustable Cu2+ ion concentration including αHO2, aqueous-phase acidity, the first-order loss-rate constant KI value, and the aqueous phase production of HO2. The results intuitively demonstrate that utilizing a single γHO2 value for aerosols of different sizes, compositions or hygroscopic states is unsafe in atmospheric models. The theoretical analysis indicated that for a single aerosol experiencing hygroscopic growth, γHO2 decreased with increasing aerosol size, because of the increased gas phase diffusion resistance and dilution of aqueous-phase HO2 consuming ions. Aerosol pH and metal abundance influence γHO2 by determining the aqueous-phase loss-rate constants, and these two factors were found to be only predominant for large particles/droplets (Rp > 1 μm). For small and middle size aerosols, the mass accommodation process plays the determining role in controlling HO2 uptake. Considering ambient aerosols rarely grow to cloud droplet size on sunny days when photochemical budget of HO2 radicals is of more concern, it is crucial to adopt appropriate αHO2 in models, as arbitrarily choosing the αHO2 value can lead to large bias when simulating HO2 heterogeneous process on ambient aerosols.

Analysis of a series of urban-scale chlorine dispersion experiments and implications on indoor health consequences

In the United States, industrial compounds are routinely transported by rail in pressurized vessels, often near urban areas. A rupture of a vessel, for example due to a derailment, can result in the rapid release of a liquid-aerosol-gas mixture. The health consequences of such a release, especially close to population centers, are not well understood. To address this question, a series of controlled experimental releases of pressurized chlorine (Cl2) was conducted at the Dugway Proving Ground (Dugway, Utah). Each trial consisted of the sudden breach of a tank containing at least 4,500 kg (kg) of pressurized liquid Cl2. In this paper, we report on measured Cl2 concentrations in three test structures downwind of the release. Based on these data, we estimate the indoor-outdoor exchange, transport through a multi-room structure, and the first-order loss rate due to reaction or sorption. This loss rate is particularly important for consequence assessment. For example, in a mobile office with a ventilation rate of about three air changes per hour, the reaction loss rate was approximately 2.5 h−1. This accounts for a nearly 20 percent reduction in toxic load to indoor occupants. Finally, the paper discusses the modeling and analysis of a typical urban hazard assessment.

Solubility and solution-phase chemistry of isocyanic acid, methyl isocyanate, and cyanogen halides

Abstract. Condensed-phase uptake and reaction are important atmospheric removal processes for reduced nitrogen species, isocyanic acid (HNCO), methyl isocyanate (CH3NCO), and cyanogen halides (XCN, X = Cl, Br, I); yet many of the fundamental quantities that govern this chemistry have not been measured or are not well studied. These nitrogen species are of emerging interest in the atmosphere as they have either biomass burning sources, i.e., HNCO and CH3NCO, or, like the XCN species, have the potential to be a significant condensed-phase source of NCO− and therefore HNCO. Solubilities and the first-order reaction rate of these species were measured for a variety of solutions using a bubble flow reactor method with total reactive nitrogen (Nr) detection. The aqueous solubility of HNCO was measured as a function of pH and had an intrinsic Henry's law solubility of 20 (±2) M atm−1 and a Ka of 2.0 (±0.3) × 10−4 M (pKa = 3.7±0.1) at 298 K. The temperature dependence of HNCO solubility was very similar to other small nitrogen-containing compounds, such as HCN, acetonitrile (CH3CN), and nitromethane, and the dependence on salt concentration exhibited the “salting out” phenomenon. The rate constant of reaction of HNCO with 0.45 M NH4+, as NH4Cl, was measured at pH = 3 and found to be 1.2 (±0.1) × 10−3 M−1 s−1, faster than the rate that would be estimated from rate measurements at much higher pHs. The solubilities of HNCO in the non-polar solvents n-octanol (n-C8H17OH) and tridecane (C13H28) were found to be higher than aqueous solution for n-octanol (87±9 M atm−1 at 298 K) and much lower than aqueous solution for tridecane (1.7±0.17 M atm−1 at 298 K), features that have implications for multi-phase and membrane transport of HNCO. The first-order loss rate of HNCO in n-octanol was determined to be relatively slow, 5.7 (±1.4) × 10−5 s−1. The aqueous solubility of CH3NCO was found to be 1.3 (±0.13) M atm−1 independent of pH, and CH3NCO solubility in n-octanol was also determined at several temperatures and ranged from 4.0 (±0.5) M atm−1 at 298 K to 2.8 (±0.3) M atm−1 at 310 K. The aqueous hydrolysis of CH3NCO was observed to be slightly acid-catalyzed, in agreement with literature values, and reactions with n-octanol ranged from 2.5 (±0.5) to 5.3 (±0.7) × 10−3 s−1 from 298 to 310 K. The aqueous solubilities of XCN, determined at room temperature and neutral pH, were found to increase with halogen atom polarizability from 1.4 (±0.2) M atm−1 for ClCN and 8.2 (±0.8) M atm−1 for BrCN to 270 (±54) M atm−1 for ICN. Hydrolysis rates, where measurable, were in agreement with literature values. The atmospheric loss rates of HNCO, CH3NCO, and XCN due to heterogeneous processes are estimated from solubilities and reaction rates. Lifetimes of HNCO range from about 1 day against deposition to neutral pH surfaces in the boundary layer, but otherwise can be as long as several months in the middle troposphere. The loss of CH3NCO due to aqueous-phase processes is estimated to be slower than, or comparable to, the lifetime against OH reaction (3 months). The loss of XCNs due to aqueous uptake is estimated to range from being quite slow, with a lifetime of 2–6 months or more for ClCN and 1 week to 6 months for BrCN to 1 to 10 days for ICN. These characteristic times are shorter than photolysis lifetimes for ClCN and BrCN, implying that heterogeneous chemistry will be the controlling factor in their atmospheric removal. In contrast, the photolysis of ICN is estimated to be faster than heterogeneous loss for average midlatitude conditions.

Energy Deposition by Energetic Electrons in a Diffusive Collisional Transport Model.

A considerable fraction of the energy in a solar flare is released as suprathermal electrons; such electrons play a major role in energy deposition in the ambient atmosphere, and hence the atmospheric response to flare heating. Historically, the transport of these particles has been approximated through a deterministic approach in which first-order secular energy loss to electrons in the ambient target is treated as the dominant effect, with second-order diffusive terms (in both energy and angle) being generally either treated as a small correction or neglected. However, it has recently been pointed out that while neglect of diffusion in energy may indeed be negligible, diffusion in angle is of the same order as deterministic scattering and hence must be included. Here we therefore investigate the effect of angular scattering on the energy deposition profile in the flaring atmosphere. A relatively simple compact expression for the spatial distribution of energy deposition into the ambient plasma is presented and compared with the corresponding deterministic result. For unidirectional injection there is a significant shift in heating from the lower corona to the upper corona; this shift is much smaller for isotropic injection. We also compare the heating profiles due to return current ohmic heating in the diffusional and deterministic models.

Effect of sample holding time on bioaccessibility and sediment ecotoxicological assessments

The ecotoxicological effects of hydrophobic organic compound (HOC) contamination in sediment are often assessed using laboratory exposures of cultured invertebrates to field-collected sediment. The use of a sediment holding time (storage at 4 °C) between field sampling and the beginning of the bioassay is common practice, yet the effect of holding time on the reliability of bioassay results is largely unknown, especially for current-use HOCs, such as pyrethroid insecticides. Single-point Tenax extraction can be used to estimate HOC concentrations in the rapidly desorbing phase of the organic carbon fraction of sediment (i.e., bioaccessible concentrations), which relate to sediment toxicity and bioaccumulation in invertebrates. In this study, repeated measurements of bioaccessible concentrations (via Tenax), were made as a function of sediment holding time using pyrethroid-contaminated field sediment, and Hyalella azteca 10-d survival and growth was measured concurrently for comparison. Similarly, bioaccessible concentrations and 14-d bioaccumulation were measured in Lumbriculus variegatus as a comparison using the legacy HOCs, polychlorinated biphenyls (PCBs). While the bioaccessible and bioaccumulated PCB concentrations did not change significantly through 244 d of holding time, the bioaccessible pyrethroid concentrations were more varied. Depending on when pyrethroid-contaminated sediments were sampled, the bioaccessible pyrethroid concentrations showed first-order loss with half-lives ranging from 3 to 45 d of holding, or slower, linear decreases in concentrations up to 14% decrease over 180 d. These findings suggest that at least for some contaminants in sediments, holding the sediments prior to bioassays can bias toxicity estimates.

Improved methodology for analyzing relations between starch digestion kinetics and molecular structure

A new combined methodology for obtaining relations between starch molecular structure and digestion kinetics of starch-based foods is illustrated using published data on cooked rice. Digestibility data are treated with the logarithm of slopes method, giving region(s) where first-order loss kinetics are applicable; accurate values for the rate parameters are obtained by non-linear least-squares. A new method is developed to find independent structural variables for whole and enzymatically-debranched starches. Chain-length distributions of amylose and amylopectin are fitted with models using biologically-meaningful parameters, including accounting for SEC band broadening. While slower digestion rate usually means higher residual starch, this is not always so; both digestion parameters must be considered separately. The treatment shows that digestion kinetics depend on amylose content and also amylose molecular fine structure: the amount of shorter amylose chains and total amylose molecular size. The new combined data-treatment methodology is applicable to a wide range of food systems.