Quasi-equilibrium Conditions Research Articles

Analytical time-coordinated entry guidance for multi-hypersonic vehicles within three-dimensional corridor

A coordinated entry mission requires multiple hypersonic vehicles to arrive at the designated area simultaneously from different times and locations. To satisfy the coordinated entry mission, this paper investigates the coordinated entry guidance problem for multi-hypersonic vehicles. An analytical time-coordinated entry guidance method is proposed based on the algorithms of analytical prediction, profile correction, and coordination time determination. Firstly, considering the altitude variations of the trajectory, high-precision analytical solutions for the remaining flight time and range are derived based on quasi-equilibrium glide conditions. Compared to the traditional numerical integration prediction methods, this analytical prediction method achieves superior computational efficiency while ensuring high-precision prediction. Subsequently, a flight corridor based on longitudinal lift-to-drag ratio is constructed, extending from the traditional two-dimensional corridor to a three-dimensional one. Within the corridor, the analytical lift-to-drag ratio profile is corrected by minimizing the prediction errors, and the guidance commands for both angle of attack and bank angle can be generated directly without tracking law. With the above analytical solutions and algorithms, the coordinated entry guidance method enables rapid generation of guidance commands for each hypersonic vehicle. Finally, numerical simulations under dispersed launching time and launching location conditions are performed, and the simulation results verify the effectiveness and robustness of the proposed time-coordination entry guidance algorithm.

How the Quasi-Eqilibrium Condition Has Obfuscated Electrochemistry in General and the HOR/HER Discussion in Particual (Part 1)

Most reactions in electrocatalysis involve the transfer of multiple electrons. Due to the unlikely transfer of more than one electron at once, such reactions are multistep reactions. However, electrochemical textbooks focus heavily on the one-electron one-step reaction and there seem to be no consensus in the literature on how to treat multistep reactions.We will elucidate how multistep reactions can be treated in a straightforward manner. In this process we explain that the Tafel slope, despite common practice and a recent IUPAC report, cannot be used to determine the reaction mechanism. This misconception stems from the inappropriate use of the quasi-equilibrium condition in the electrochemical literature.We continue to show that the concept of the exchange current density cannot be universally defined for multistep reactions and that it is in almost no cases possible to accurately fit a multistep reaction by a simple Butler-Volmer equation.Finally, we present how the HOR/HER reaction mechanism on Pt can be identified when the Butler-Volmer model is rigorously applied on the two HOR/HER paths dominating the discussion, namely the Tafel-Volmer and Heyrovský-Volmer. Figure 1

Magnetic Spectra Comparison for Kappa-distributed Whistler Electron Fluctuations

In the inner heliosphere, space measurements have revealed that plasma is well described by the kappa distributions, which are characterized by the value of the κ parameter. This parameter indicates how far plasma is from the ideal Maxwell–Boltzmann equilibrium distribution and gives the distribution a typical high-energy power-law tail. In these quasi-equilibrium conditions, the plasma spontaneously emits electromagnetic fluctuations. When suprathermal electrons are involved, these spontaneous emissions get enhanced, and the kappa distributions improve the description of the related nonthermal effects by taking into account the contribution of these high-energy electrons. Nevertheless, the kappa distributions describe different scenarios in which the velocity distribution may obey a power-law decay. Here, we present a systematic and quantitative comparison of kappa-distributed magnetized plasma through a comparison of magnetic spectra for electron cyclotron whistler mode fluctuations. Our results show that for a kappa distribution with a thermal speed equal to the one obtained in thermal equilibrium, the magnetic field fluctuations exhibit higher energy levels that scale with increasing values of β and decreasing values of κ, even though the same thermal speed is considered for all studied cases. Conversely, for a kappa distribution with a kappa-dependent thermal speed, the magnetic field fluctuations tend to exhibit less total energy with lower kappa values, even when compared to the Maxwellian distribution equilibrium results in the same range of parameters.

A Study toward the Model Independence of Various Heating Rates Method in Thermoluminescence Glow Curve Analysis

This study analyzes thermoluminescence (TL) glow curves simulated in general order kinetics (GOK), one trap one recombination center (OTOR), and non‐interactive multi‐trap system (NMTS) models using various heating rates (VHR) method in linear heating scheme to extract the activation energy. A theoretical analysis to determine activation energy from TL curves using OTOR and NMTS models in an iterative manner, where the TL intensity is determined by using the Lambert‐W function, is proposed with its limitations. It is established that the activation energies in OTOR and NMTS models consist of the relevant GOK term and a respective correction term. Systematic analysis is carried out to study the improvement of the accuracy of activation energy derived from OTOR and NMTS model TL curves over the GOK model calculation. A quantitative analysis of the quasi‐equilibrium (QE) approximations is carried out for choosing appropriate system parameters. The validity of QE conditions are determined by studying variations of full width at half maximum as well as area under the curve as a function of heating rate. The present method is applied on some experimental data to estimate activation energies. This investigation reveals that the activation energy derived in VHR method has negligible dependence on the underlying theoretical models, i.e., the activation energy derived from GOK model calculation is significantly accurate for experimental scenario.

A rapid time-coordinated longitudinal guidance method for high-speed vehicle

Compared to the traditional method of adjusting flight time by increasing lateral maneuverability [1-2], a faster time-coordinated longitudinal guidance method for unpowered high-speed vehicles has been proposed in this paper. Firstly, the centroid dynamics model and flight constraint model of unpowered high-speed vehicles were established, and the angle of attack corridor was derived based on quasi-equilibrium gliding conditions (QEGC). Then, to plan a reasonable angle of attack profile, the flight capability of a single vehicle under different constant angles of attack is analyzed, including terminal altitude, terminal velocity, and terminal arrival time. Furthermore, to achieve a long-term high angle of attack flight, a rapid time-coordinated longitudinal guidance method based on a trapezoidal angle of attack profile was proposed. Finally, using the vehicle and its performance parameters from Chapter 3 [3], numerical simulations were conducted under nominal tasks and multi-vehicle collaborative tasks. The simulation results show that under different expected arrival times, this method can quickly plan the angle of attack profile that satisfies time constraints, with high computational efficiency. Moreover, the arrival time adjustment ability of this method is large, which can fully utilize the arrival time capability of the high-speed vehicle. The above research provides more convenient conditions for a collaborative flight of multiple vehicles.

Hybrid density functional theory simulation of sodium impurity and impurity–vacancy defect complexes in germanium: perspectives of defect engineering for activation of shallow donors

At present, germanium (Ge) as a high-mobility material is considered as a possible replacement for Si in microelectronics. The main obstacle in the method is the large vacancy concentration obtained after the implantation of shallow donors. This prevents the formation of n+ regions and has a negative impact on device performance. One way to eliminate the detrimental effects of such defects is through the codoping approach. In this study, the behavior of Na impurities in germanium together with the formation of defect complexes with vacancies, divacancies and shallow donors (P and As) were investigated using hybrid density functional theory calculations. The site preference, diffusion barriers, charge states and binding energies of various complexes, as well as the activation of donor–vacancy complexes with both F and Na codoping were investigated. For this purpose, two extreme cases were considered. Firstly, we calculate the concentrations of substitutional and interstitial Na together with monovacancies in the case of quasi-equilibrium conditions realized for doping from melt. Another extreme case is Na codoping during ion implantation. Our calculations show that Na passivates vacancies, divacancies and donor–vacancy complexes (E-centers) with a large energy gain, which prevents rapid donor diffusion similar to the case of doping with fluorine. We have shown that the passivation of E-centers with both F and Na impurities leads to the back transformation of such complexes into shallow donors. This means that codoping with Na may neutralize the harmful effects of vacancies and is a perspective for defect engineering.

Rings, Shells, and Arc Structures Around B[e] Supergiants. I. Classical Tools of Nonlinear Hydrodynamics

Structures in circumstellar matter reflect both fast processes and quasi-equilibrium states. A geometrical diversity of emitting circumstellar matter is observed around evolved massive stars, in particular around B[e] supergiants. We recapitulate classical analytical tools of linear and nonlinear potential theory, such as Cole–Hopf transformation and Grad–Shafranov theory, and develop them further to explain the occurrence of the circumstellar matter structures and their dynamics. We use potential theory to formulate the nonlinear hydrodynamical equations and test dilatations of the quasi-equilibrium initial conditions. We find that a wide range of flow patterns can basically be generated and the timescales can switch, based on initial conditions, and lead to eruptive processes, reinforcing that the nonlinear fluid environment includes both quasi-stationary structures and fast processes like finite-time singularities. Some constraints and imposed symmetries can lead to Keplerian orbits, while other constraints can deliver quasi-Keplerian ones. The threshold is given by a characteristic density at the stellar surface.

Seasonal Variations in Eddy-Induced Atmospheric Perturbations in the South China Sea

Abstract This study investigates the impact of eddy-induced sea surface temperature (SST) anomalies on the overlying atmosphere in the South China Sea, utilizing observational and reanalysis datasets. The results reveal that SST anomalies caused by anticyclonic or cyclonic eddies have a significant impact on the acceleration or deceleration of surface winds, with a stronger response in summer compared to winter. Moreover, atmospheric responses, such as heat flux, precipitation, and marine atmospheric boundary layer (MABL) depth above anticyclonic or cyclonic eddies, exhibit in-phase seasonal variations as surface winds. The study also explores the mechanisms leading to atmospheric response, pointing toward the vertical mixing mechanism as the dominant cause, supported by both the in-phase relationship between SST and surface wind anomalies and the linear relationship between the wind stress divergence anomaly and downwind SST gradient anomaly. Seasonal variations in coupling intensity are attributed to varying background atmospheric conditions, with more effective vertical turbulence mixing and stronger coupling intensity caused by more unstable MABL and enhanced large-scale vertical wind shear during summer than winter. Besides, the atmosphere above eddies is under a quasi-equilibrium condition, in which the surface wind stress increases monotonically with the depth of MABL. Given that the MABL depth response to eddy-induced SST anomaly is stronger in summer than in winter, it is reasonable to expect a more intense wind response during this season. Thus, the MABL depth coupling works together with the vertical mixing mechanism to explain the proportional relationship between SST and wind anomalies, and why the atmospheric response is stronger in summer than in winter. Significance Statement The atmosphere exerts a significant influence on the ocean, with strong winds cooling the sea surface temperature on a large scale (more than 1000 km). Conversely, the ocean tends to drive the atmosphere at a mesoscale level (10–1000 km), whereby a warm sea surface temperature causes surface wind to accelerate. This study aims to better understand how mesoscale eddies in the South China Sea influence the overlying atmosphere in different seasons. Our research explores factors that control mesoscale air–sea coupling, and highlights the importance of stability and depth change of marine atmospheric boundary layer. These results will establish a foundation for future research examining how the atmospheric perturbations caused by mesoscale eddies can in turn impact both ocean circulation and eddies.

(Invited) Potentiometric Entropy Measurements and Isothermal Operando Calorimetry to Identify the Charging Mechanisms of Battery Materials

This talk presents recent development in potentiometric entropy measurements and isothermal operando calorimetry to gain insight into the charging mechanisms of lithium ion batteries. First, the concept, design, and operation of two unique experimental apparatuses will be presented. Then, the effects of material composition, crystallographic structure, and particle size on the cell’s thermodynamic behavior, polarization, and lithium ion transport will be discussed for different Wadsley-Roth materials (e.g., TiNb2O7, PNb9O25, (W0.2V0.8)3O7) under quasi-equilibrium conditions. Particular attention will be paid to phase transition, lithium ion intercalation and ion ordering in solid solution, and/or two-phase coexistence occurring during charging/discharging. Finally, instantaneous heat generation rates measured by isothermal operando calorimetry at each electrode will be used to identify the causes of energy dissipation and to provide insight into the transport and interfacial phenomena taking place in the electrodes at different states of charge and charging rates. Here, special emphasis will be placed on the contributions of Joule heating associated with resistive losses, heat of mixing due to ion concentration gradient, and reversible entropic changes.

Nanoscale Investigation into Dynamics of Thin Liquid Films during Bouncing and Attachment of Rising Air Bubbles on Hydrophilic and Hydrophobic Surfaces.

Investigations on bouncing and attachment of free-rising air bubbles on hydrophobic surfaces have been limited to side-view, high-speed photography of the bubble-plate attachment process. In this work, an investigation of the dynamics as well as stability of thin liquid films (TLFs) between free-rising air bubbles and quartz surfaces was performed using a newly developed multiple-wavelength synchronized reflection interferometry microscopy (SRIM) technique. The effect of surface hydrophobicity on both the stability and critical rupture thickness of TLFs was investigated. Results showed that the TLF ruptured at a critical rupture thickness of 100-1000 nm or beyond during bubble's impact on hydrophobic quartz surfaces. The critical rupture thicknesses varied depending on the surface hydrophobicity as well as surface asperity. A higher surface hydrophobicity, in general, contributed to a higher critical rupture thickness. In addition, the effect of n-octanol on the stability of the TLFs was investigated. Results showed that film stability increased with increasing the concentration of n-octanol, which was accompanied by a significant decrease in the critical rupture thickness. The present result illustrates, for the first time, the dynamics of TLFs on hydrophobic surfaces under a dynamic condition compared with previous studies under a quasi-equilibrium condition. The information revealed from the present work has a significant implication to many industrial applications, including froth flotation and other biological and semiconductor applications.

Analytic Time Reentry Cooperative Guidance for Multi-Hypersonic Glide Vehicles

Aiming at the cooperative guidance problem of multi-hypersonic glide vehicles, a cooperative guidance method based on a parametric design and an analytical solution of time-to-go is proposed. First, the hypersonic reentry trajectory optimization problem was transformed into a parameter optimization problem. The parameters were optimized to determine the angle of attack profile and the time to enter the altitude velocity reentry corridor. Then, using the quasi-equilibrium glide condition, the estimation form of the remaining flight time was analytically derived to satisfy accurately the cooperative time constraint. Using the remaining time-to-go and range-to-go, combined with the heading angle deviation corridor, the bank angle command was further calculated. Finally, the swarm intelligence optimization algorithm was used to optimize the design parameters to obtain the cooperative guidance trajectory satisfying the time constraint. Simulations showed that the analytical time reentry cooperative guidance algorithm proposed in this paper can accurately meet the time constraints and cooperative flight accuracy. Monte Carlo simulation experiments verified that the proposed algorithm demonstrates a robust performance.

Simulation of thermoluminescence signals at very low dose rates and low doses: Implications for dosimetric applications

During luminescence dosimetry applications, samples are irradiated in the laboratory with irradiation dose rates of the order of 0.1 Gy/s. By contrast, samples in nature are irradiated with a dose rate many orders magnitude smaller, typically 1 mGy/year. In this paper, the effect of very low dose rates and also low doses on thermoluminescence (TL) signals is investigated using the basic one-trap one-recombination center model (OTOR). The simulations showed that at very low dose rates the assumptions of quasi-equilibrium conditions (QE) are violated. This violation of QE conditions results in a significant distortion of the shapes of TL glow curves, with the result that the peak shape methods of analysis fail to produce the correct activation energy E of the traps. At the same time, the estimated half-life of the electrons traps is found to increase significantly at very low doses. The dose response of the sample at very low dose rates is simulated for both the irradiation stage and the subsequent heating stage. The dose response of the integrated TL signal is found to coincide with the dose response during the irradiation stage. However, the TL dose response measured in terms of the peak height shows a significant under-response at very low doses, making the whole dose response curve superlinear before the onset of saturation. The peak height under-response is due to the clear violation of QE conditions at very low doses and dose rates. The reported distortion of the TL glow curves and the existence of superlinearity of the TL signals at low dose rates, have important implications for the analysis of TL signals. Researchers need to be aware of the possibility that both of these effects may be present, since they can influence the analysis of experimental data and can lead to the wrong conclusions in dosimetric applications.

Flow Dynamics and Pollutant Transport at an Artificial Right-Angled Open-Channel Junction with a Deformed Bed

Artificial open-channel junctions have sharp corners and a smaller width-to-depth ratio. Despite numerous studies on channel junctions, knowledge on turbulent structures and their role in mixing at artificial junctions is lacking. To fill this research gap, the present study uses a large-eddy simulation (LES) model to investigate the three-dimensional (3D) turbulent structures and their role in pollutant transport at a right-angled laboratory open-channel junction with a deformed bed. The deformed-bed junction represents a quasi-equilibrium condition and consists of a scour zone and deposition bar. The numerical model is validated against experimental data of the velocity field and turbulent kinetic energy. Comparisons of the flow field between the flat-bed condition and quasi-equilibrium deformed-bed condition showed a reduced flow separation zone and less developed recirculating gyre in the latter case because of the strong secondary currents. The coherence of the turbulent structures was drastically disrupted at the deformed-bed junction because the Kelvin-Helmholtz (KH) instability results in more randomly oriented residuals. In contrast, the breakdown of the shear layer at a flat-bed junction displayed the trail of the arch-shaped vortices. The role of turbulent structures in pollutant transport is elucidated by using a neutrally buoyant conservative tracer. Large turbulent structures associated with the KH instability help the tracer evolve faster at the deformed-bed junction.

Astrochemically relevant H-atom-abstraction and H-atom-addition reactions connecting fulminic acid (HCNO) and formaldoxime (H2CNOH)

ABSTRACT While fulminic acid (HCNO) is a well-known interstellar molecule, its partially hydrogenated form, formaldoxime (H2CNOH), has not been detected yet in the interstellar medium (ISM). A possible reason for the non-detection of H2CNOH can be that in the presence of H atoms the quasi-equilibrium between these species is shifted towards HCNO. To support this hypothesis, the H-atom-abstraction and H-atom-addition reactions of HCNO and H2CNOH were investigated in solid para-H2 matrix at 3.1 K. The reactions were followed by IR spectroscopy. The experiments proved that both the H-atom-addition reaction to HCNO and the H-atom-abstraction reaction from H2CNOH proceed at low temperatures, and these reactions yield H2CNO radical. In addition, H-atom-addition reaction can also take place with H2CNOH, leading to the formation of H3CNOH radical. Both H2CNO and H3CNOH radicals can react with H atoms, either in a H-atom-addition reaction or in a H-atom-abstraction reaction. Although all of these reactions are barrierless, experimentally the H-atom-addition reactions were not observed, revealing that the H-atom-abstraction reactions of these radicals are more effective. Therefore, in the case of a quasi-equilibrium condition, the abundance of H2CNOH in the ISM is expected to be lower than that of HCNO. Furthermore, the results also indicate that the H-atom-addition and H-atom-abstraction reactions between H2CNOH and HCNO can act as catalytic cycles for interstellar H2 formation.

Surface plasmon coupling effects on the behaviors of radiative and non-radiative recombination in an InGaN/GaN quantum well

Although surface plasmon (SP) coupling has been widely used for enhancing the emission efficiency of an InGaN/GaN quantum well (QW) structure, the interplay of the carrier transport behavior in the QW with SP coupling, which is a crucial mechanism controlling the SP-coupling induced QW emission enhancement, is still an issue not well explored yet. To understand the effects of SP coupling on the radiative and non-radiative recombination behaviors of carriers in a QW structure, the temperature-dependent time-resolved photoluminescence spectroscopies of two QW samples of different indium contents with surface Ag nanoparticles are studied. A two-single-exponential model is used for calibrating their radiative and non-radiative decay times. The SP coupling process, which transfers carrier energy from a QW into the SP resonance mode for effective radiation and increases the effective radiative recombination rate, produces energy-dependent carrier depletion and, hence, disturbs the quasi-equilibrium condition of carrier distribution. In this situation, a strong carrier transport process occurs targeting a new quasi-equilibrium condition that enhances non-radiative recombination and, hence, reduces the benefit of using the SP coupling technique. To alleviate this problem of SP-coupling induced energy loss, a weak energy-dependent or broad-spectrum SP coupling process is recommended.

Three-dimensional Self-organization of Tetraphenylporphyrin and its Composites with C60: Structure and Optical Properties

Background: Thin films of a 5,10,15,20-tetraphenylporphyrin (H2TPP) and its metal complexes (MeTPP, where Me = Co, Cu, Zn, Fe-Cl) were obtained by vacuum thermal evaporation under quasi-equilibrium conditions (hot wall method) and by coating from a toluene solution on various substrates. It was shown that H2TPP, CuTPP and CoTPP have an ability to selforganization into linear structures during crystallization (nanowhiskers, nanowires, or nanorods), regardless of our obtaining method. Methods: FeClTPP and ZnTPP crystallize into planar films with the same preparation technique. Co-deposition with fullerene C60 allows obtaining fullerene crystallites on the surface of tetraphenylporphyrin, subsequently creating the so-called bulk heterojunctions. Results: The possibility of controlling the shape of obtained crystallites by changing technological parameters and substrates has been shown for metal free tetraphenylporphyrin. High degree crystalline ZnTPP and H2TPP films are characterized by a red shift of photoluminescence and absorption spectra under crystallization. Conclusion: A change in the relative intensity of the photoluminescence spectrum maxima of various nature is observed during transition from amorphous to crystalline structure of H2TPP.

Catalytic Biosensors Operating under Quasi-Equilibrium Conditions for Mitigating the Changes in Substrate Diffusion.

Despite the success of continuous glucose measuring systems operating through the skin for about 14 days, long-term implantable biosensors are facing challenges caused by the foreign-body reaction. We present a conceptually new strategy using catalytic enzyme-based biosensors based on a measuring sequence leading to minimum disturbance of the substrate equilibrium concentration by controlling the sensor between "on" and "off" state combined with short potentiometric data acquisition. It is required that the enzyme activity can be completely switched off and no parasitic side reactions allow substrate turnover. This is achieved by using an O2 -independent FAD-dependent glucose dehydrogenase embedded within a crosslinked redox polymer. A short measuring interval allows the glucose concentration equilibrium to be restored quickly which enables the biosensor to operate under quasi-equilibrium conditions.

Phase constitution and glass formation of U-Pd-Ni-Si alloys

In order to explore U-based alloys having high glass forming ability (GFA), a series of U-Pd-Ni-Si alloys with 60% U were designed on the basis of the eutectic features of U-Ni and U-Pd base systems together with the Si addition. Their ingots and ribbons were prepared by arc-melting and melt-spinning methods and further examined to reveal the phase constitution and amorphization behavior mainly by X-ray diffraction and differential scanning calorimetry. The results show that these alloys can form U6Ni type (NU) and/or α-U type (AU) phases under a quasi-equilibrium or equilibrium condition and amorphous phase, completely for most of them, under a non-equilibrium condition. A possibly Pd-based glassy phase seemed to unexpectedly arise in two Pd-rich alloy ingots, which would be the first observation of glass formation in U-based alloys solidified at low cooling rates. Within all the U-Pd-Ni-Si alloys, the ones with a big Ni/Pd ratio, thus tending to get NU phase, can achieve substantially higher GFA than the others with small Ni/Pd and a tendency to AU phase. Especially, U60Pd7.5Ni25Si7.5 and U60Pd5Ni25Si10 displayed firstly the reduced glass transition temperature Tg/TL of > 0.6 and a wide supercooled liquid region of ~100 K, exhibiting a GFA level superior to the whole reported U-based metallic glasses (MGs) and comparable to some traditional bulk MGs. All the yields reflect that Ni plays stronger roles in both compounding with U and the glass formation than Pd and Si in these alloys, and also offer guidance for creating novel U-based metallic materials including better MGs.

Stimulated emission in 24–31 μ m range and «Reststrahlen» waveguide in HgCdTe structures grown on GaAs

Long-wavelength stimulated emission (SE) is studied in optically pumped HgCdTe quantum well heterostructures with dielectric waveguides. Continuous temperature tuning of the wavelength from 27 to 18 μm is achieved in structures with optimized waveguides. Above 27 μm, SE clamps at 31 μm wavelength, where mode leaking is reduced due to the Reststrahlen effect in the GaAs substrate. The operating temperature is mainly limited by the activation of Auger recombination in quasi-equilibrium conditions, while at low temperatures, we expect that lowering initial carrier heating would enhance the gain considerably. We conclude that exploiting the Reststrahlen effect should allow one to achieve continuous wavelength tuning around 30 μm and operating wavelengths up to 40 μm with technologically attainable epistructure thickness.

The use of the IAEA MARIS database in determining the variability of sediment distribution coefficients in the marine environment and potential implications for marine dispersion modelling

A prototype tool has been developed for deriving sediment distribution coefficients, K d, in the marine environment by harvesting simultaneous measurements of activity concentrations of radionuclides in seawater and sediments based on the International Atomic Energy Agency’s Marine Radioactivity Information System (MARIS). As a case study, the K d variability in the Baltic Sea was investigated as this region has been extensively monitored by HELCOM since 1984 resulting in a comprehensive dataset with good spatial and temporal coverage and required ancillary parameters. The prototype tool was used to derive a dataset of in-situ apparent K d(a) values derived from measurements of seawater and sediment in quasi-equilibrium conditions from the Baltic Sea over a period of approximately 35 years. For Cs, a comprehensive analysis of the Baltic Sea K d(a) dataset was undertaken, focusing on the temporal trend of K d(a) and comparing the results to K d values derived elsewhere. For Sr and Pu, for which there were fewer data records available a more rudimentary analysis was carried out. The Cs K d(a) median values derived from 137Cs data in this study were estimated to be 2154 l kg−1 for seabed sediment and 10 000 l kg−1 for suspended sediment. The value derived for seabed sediment is in good agreement with the previously recommended ocean margin Cs K d value of 4000 l kg−1. The analysis demonstrated the important distinction in the Baltic Sea between K d values for seabed sediment and suspended sediments, which differed by an order of magnitude. The analysis also highlighted the dependence of K d values on the variation in both the salinity of seawater and the type of seabed sediment. Such variability can significantly influence outcomes when modelling the behaviour of radionuclides in marine dispersion modelling.