Unit Cell Mass Research Articles

Application of nonlocal strain gradient theory for the analysis of bandgap formation in metamaterial nanobeams

The aim of this paper is to investigate bandgap formation in an Euler-Bernoulli nanobeam using the nonlocal strain gradient theory. Such a model enables the capture of both softening and stiffening size-dependent behavior of the nanobeams using two length-scale parameters, namely, a nonlocal parameter and a strain gradient parameter. Hamilton's principle is used to develop the normalized equation of motion yielding a sixth order differential equation. The nanobeam is assumed to be infinitely long and the dispersion of an elastic wave in a single representative periodic unit cell of the structure is used to estimate the bandgap edge frequencies. To this end, two unit cell approaches are employed to obtain the dispersion relations, namely, the homogenization and transfer matrix approaches. Both methods yield similar dispersion curves and showed good agreement with classical cases from the literature. A parametric study was carried out to investigate the effect of several parameters on the bandgap formation in the metamaterial nanobeams. These parameters include, the nonlocal parameter, the strain gradient parameter, the length of the unit cell and the resonator mass to unit cell mass ratio. The study conducted using a purely strain gradient model showed a comparable response to that of the classical macro problem with the usual hardening when increasing the value of the strain gradient length scale. Nonlocal and nonlocal strain gradient models introduced coupling between parameters of the study with the occasional introduction of non-monotonic dispersion curves. Such non-monotonic behavior is believed to be characteristic of large values of the nonlocal length-scale.

Kinetic modeling of xylonic acid production by Gluconobacter oxydans: effects of hydrodynamic conditions

In this study, the synthesis of xylonic acid from xylose by Gluconobacter oxydans NL71 has been investigated. According to the relationship between oxygen transfer rate and oxygen uptake rate, three different kinetic models of product formation were established and the nonlinear fitting was carried out. The results showed that G. oxydans has critical dissolved oxygen under different strain concentrations, and the relationship between respiration intensity and dissolved oxygen conformed to the Monod equation [Formula: see text]. The maximum reaction rate per unit cell mass and the theoretical maximum specific productivity of G. oxydans obtained by the kinetic model are 0.042mol/L/h and 6.97g/gx/h, respectively. These results will assist in determining the best balance between the airflow rate and cell concentration in the reaction and improve the production efficiency of xylonic acid.

Bandgap merging and backward wave propagation in inertial amplification metamaterials

The aim of this study is to investigate the wave propagation characteristics of one-dimensional inertial amplification (IA) metamaterials with double resonators. The IA Angle is introduced by the IA mechanism as a critical parameter to modulate elastic waves. Double attenuation peaks in the bandgaps caused by coupling the IA mechanism and local resonance can be created in different ranges by adjusting the IA Angle. Moreover, a novel phenomenon of negative relative group velocity is observed in the region of double-negative effective properties, denoting negative energy flow. Numerical simulations using Gaussian pulse excitation are performed to validate the existence of a backward wave corresponding to the negative relative group velocity in the time domain. Furthermore, bandgap merging occurs in the region of double-zero effective properties, resulting in broadband wave attenuation. In particular, instead of using traditional metamaterials, two local resonator bandgaps can be merged to expand the bandgap range by at least 30% without changing the unit cell mass. The research results can be used to tune wave propagation in metamaterials, providing ideas for metamaterial design.

Free vibration analysis and multi-objective optimization of lattice sandwich beams

The free vibration dynamic modellings of sandwich beams with periodic lattice truss cores are established by combining the Bernoulli–Euler beam theory and Timoshenko beam theory, and the fundamental frequency and unit cell mass of lattice sandwich beams are optimized based on the non-dominated sorting genetic algorithm-II (NSGA-II). Firstly, the vibration control equation of lattice sandwich beams is derived using Hamilton’s principle. Then, it is compared and verified by modal experiment and finite element numerical simulation. On this basis, the influence of different truss cores on the structure’s natural frequency is further analyzed. Finally, taking the sheet thickness, core thickness, and radius of the truss as the optimization design variables and taking the structural fundamental frequency maximization and mass minimization as the optimization objectives, the Pareto front is obtained by NSGA-II, and the optimization results are verified by theoretical and numerically. The research results show that the theoretical method in this article can well predict the natural frequencies of sandwich beams with different truss cores. The optimized sandwich structure has higher fundamental frequency with lighter weight, which effectively improves the anti-vibration ability.

Source Apportionment of Speciated Mercury in Chinese Rice Grain Using a High-Resolution Model.

Rice grain consumption is a primary pathway of human mercury exposure. To trace the source of rice grain mercury in China, we developed a rice paddy mercury transport and transformation model with a grid resolution of 1 km × 1 km by using the unit cell mass conservation method. The simulated total mercury (THg) and methylmercury (MeHg) concentrations in Chinese rice grain ranged from 0.08 to 243.6 and 0.03 to 238.6 μg/kg, respectively, in 2017. Approximately, 81.3% of the national average rice grain THg concentration was due to atmospheric mercury deposition. However, soil heterogeneity, especially the variation in soil mercury, led to the wide rice grain THg distribution across grids. Approximately, 64.8% of the national average rice grain MeHg concentration was due to soil mercury. In situ methylation was the main pathway via which the rice grain MeHg concentration was increased. The coupled impact of high mercury input and methylation potential led to extremely high rice grain MeHg in partial grids among Guizhou province and junctions with surrounding provinces. The spatial variation in soil organic matter significantly impacted the methylation potential among grids, especially in Northeast China. Based on the high-resolution rice grain THg concentration, we identified 0.72% of grids as heavily polluted THg grids (rice grain THg > 20 μg/kg). These grids mainly corresponded to areas in which the human activities of nonferrous metal smelting, cement clinker production, and mercury and other metal mining were conducted. Thus, we recommended measures that are targeted at the control of heavy pollution of rice grain by THg according to the pollution sources. In addition, we observed a wide spatial variation range of MeHg to THg ratios not only in China but also in other regions of the world, which highlights the potential risk of rice intake.

Parametric characteristics analysis of three cells in 3D and five-directional annular braided composites.

On the basis of analyzing the movement law of 3D circular braided yarn, the three-cell model of 3D five-direction circular braiding composite material is established. By analyzing the node position relationship in various cell models, the calculation formulas of braiding angle, cell volume, fiber volume and fiber volume content in various cell models are obtained. It is found that there are four different braiding angles in four internal cells, and the braiding angles in internal cells gradually increase from inside to outside. The braiding angles of upper and lower surface cells are approximately equal. With the increase of the length of the knuckles, the braiding angles of each cell decrease, and the braiding angles of the four inner cells decrease greatly, while the braiding angles of upper and lower surfaces decrease slightly. The results of parametric analysis showed that with the increase of the length of the knuckles and the inner diameter of cells, the mass of cells increased proportionally, while the total fiber volume content of cells decreased. With the increase of braiding yarn number and axial yarn number, the unit cell mass decreases in direct proportion, and the unit cell total fiber volume content increases. Through the research results of this paper, the geometrical characteristics of the cell model under different braided parameters can be obtained, which greatly improves the analysis efficiency.

On the Interrelationship Between Static and Vibration Mitigation Properties of Architected Metastructures

Continuous demand for improvement of material performance in structural applications pushes the need for materials that are able to fulfill multiple functions. Extensive work on effective static properties of different architected materials have shown their ability to push the modulus-density design space, in terms of high effective moduli at low relative density. On the other hand, variations in geometry allow for these materials to manipulate mechanical wave propagation, producing band gaps at certain frequency ranges. The enhanced static and vibration properties of architected metamaterials make them ideal candidates for multi-functional purposes. In this paper, we take inspiration from the mass-efficient static behavior of different lattice geometries to fully explore the capabilities of a periodic and locally resonant metastructure design platform. We numerically study the influence of four different lattice topologies on the dynamic and static behavior of metastructures that combine a periodic lattice geometry with locally resonant inclusions. We analyze the influence of lattice geometry on band gap frequencies in terms of the lattice effective static properties. We show that vibration mitigation over a wide range of frequencies is achieved by tailoring the lattice geometry for constant unit cell mass and size. Specifically, by selectively placing material inside the unit cell, we achieve up to a 6-fold change of lower edge band gap frequency and up to an 8-fold change of normalized band gap width, for metastructures with low-density lattices. We introduce multi-functional performance parameters to evaluate the metastructures in terms of their effective static stiffness and band gap properties. These parameters can inform the design of tailored materials that have desired mechanical and dynamic properties for applications in e.g. aerospace and automotive components, and energy infrastructure.

Intracellular versus extracellular accumulation of Hexavalent chromium reduction products by Geobacter sulfurreducens PCA

Hexavalent chromium (Cr(VI)) reduction by Geobacter sulfurreducens PCA was evaluated in batch experiments, and the form and amounts of intracellular and extra-cellular Cr(VI) reduction products were determined over time. The first-order Cr(VI) reduction rate per unit mass of cells was consistent for different initial cell concentrations, and approximately equal to (2.065 ± 0.389) x 10−9 mL CFU−1 h−1. A portion of the reduced Cr(VI) products precipitated on Geobacter cell walls as Cr(III) and was bound via carboxylate functional groups, a portion accumulated inside Geobacter cells, and another portion existed as soluble Cr(III) or organo-Cr(III) released to solution. A mass balance analysis of total chromium in aqueous media, on cell walls, and inside cells was determined as a function of time, and with different initial cell concentrations. Mass balances were between 92% and 98%, and indicated Cr(VI) reduction products accumulate more on cell walls and inside cells with time and with increasing initial cell concentration, as opposed to particulates in aqueous solution. Reduced Cr(VI) products both in solution and on cell surfaces appear to form organo-Cr(III) complexes, and our results suggest that such complexes are more stable to reoxidation than aqueous Cr(III) or Cr(OH)3. Chromium inside cells is also likely more stable to reoxidation, both because it can form organic complexes, and it is separated by the cell membrane from solution conditions. Hence, Cr(VI) reduction products in groundwater during bioremediation may become more stable against re-oxidation, and may pose a lower risk to human health, over time and with greater initial biomass densities.

Carrier concentration effect and other structure-related parameters on lattice thermal conductivity of Si nanowires

Lattice thermal conductivity (LTC) of Si bulk and nanowires (NWs) with diameter 22, 37, 50, 56, 98 and 115 nm was investigated in the temperature range 3–300 K using a modified Callaway model that contains both longitudinal and transverse modes. Using proper equations, mean bond length, lattice parameter, unit cell volume, mass density, melting temperature, longitudinal and transverse Debye temperature and group velocity for all transverse and longitudinal modes were calculated for each NW diameter mentioned. Surface roughness, Gruneisen parameter and impurity were used as adjustable parameters to fit theoretical results with experimental curves. In addition, values of electron concentration and dislocation density were determined. There are some phonon scattering mechanisms assumed, which are Umklapp and normal processes, imperfections, phonon confinement, NW boundaries, electrons scattering and dislocation. Dislocation density less than 10 $$^{{14}}$$ m $$^{{-2}}$$ for NWs and 10 $$^{{12}}$$ m $$^{{-2}}$$ for bulk has no effect on LTC. Also, electron concentration less than 10 $$^{{22}}$$ m $$^{{-3}}$$ for NWs and 10 $$^{{16}}$$ m $$^{{-3}}$$ for the bulk has no effect. On increasing dislocation density and electron concentration, LTC comparably decreases.

High molecular weight β-poly(l-malic acid) produced by A. pullulans with Ca2+ added repeated batch culture

β-Poly(malic acid) (PMLA) has attracted increasing attentions because of its potential application in medicine and other industries. In this study, the variation of PMLA molecular weight (Mw) in the batch culture and the strategies to enhance PMLA Mw were studied. Adding exogenous Ca2+ (0.1g/L CaCl2) to the medium caused a significant increase in both PMLA concentration and Mw (11.38% and 26.3%, respectively) when Na2CO3 was used as the neutralizer. The Mw of PMLA during the process of batch culture, which associated with the specific PMLA production per unit cell mass (Yp/x) before glucose was depleted, increased from 12.522KDa to its maximum 18.693KDa and then kept decreasing until the end of the culture. Compared with the results in batch culture, Mw increased by 84.4% (up to 19.51kDa) with a productivity of 1.1gh−1L−1 when the cells were maintained in exponential growth phase during Ca2+ added repeated batch culture. The present work provides an efficient approach to obtain superior quality PMLA product with high Mw.

Efficient ethanol production from potato and corn processing industry waste using E. coli engineered to express Vitreoscilla haemoglobin

Engineering of ethanologenic E. coli to express the haemoglobin (VHb) from the bacterium Vitreoscilla has been shown to enhance ethanol production by fermentation of pure sugars, sugars from hydrolysis of lignocellulose, components of whey, and sugars from wastewater produced during potato processing. Here, these studies were extended to see whether the same effect could be seen when a mixture of waste materials from processing of potatoes and corn into potato and corn chips were used as sugar sources. Consistent increases in ethanol production coincident with VHb expression were seen in shake flasks at both low aeration and high aeration conditions. The ethanol increases were due almost entirely to increases in the amount of ethanol produced per unit of cell mass. The VHb strategy for increasing fermentation to ethanol (and perhaps other valuable fermentation products) may be of general use, particularly regarding conversion of otherwise discarded materials into valuable commodities.

Acoustic metamaterial plates for elastic wave absorption and structural vibration suppression

This article presents the design and modeling techniques and design guidelines, and reveals the actual working mechanism of acoustic metamaterial plates for elastic wave absorption and structural vibration suppression. Each of the studied metamaterial plates is designed by integrating two (or one) isotropic plates with distributed discrete mass-spring-damper subsystems that act as local vibration absorbers. For an infinite metamaterial plate, its stopband is obtained by dispersion analysis on an analytical unit cell. For a finite metamaterial plate with specific boundary conditions, frequency response analysis of its full-size finite-element model is performed to show its stopband behavior, and the stopband behavior is further confirmed by transient analysis based on direct numerical integration of the finite-element equations. Influences of the vibration absorbers׳ local resonant frequencies and damping ratios and the plate׳s damping, boundary conditions, and natural frequencies and mode shapes are thoroughly examined. The concepts of negative effective mass and spring and acoustic and optical wave modes are explained in detail. The working mechanism of acoustic metamaterial plates is revealed to be based on the concept of conventional vibration absorbers. An absorber׳s resonant vibration excited by the incoming elastic wave generates a concentrated inertial force to work against the plate׳s internal shear force, straighten the plate, and attenuate/stop the wave propagation. Numerical results show that the stopband׳s location is determined by the local resonant frequency of absorbers, the stopband׳s width increases with the (absorber mass)/(unit cell mass) ratio, and increase of absorbers׳ damping significantly increases the stopband׳s width and reduces low-frequency vibration amplitudes. However, too much damping may deactivate the stopband effect, and the plate׳s material damping is not as efficient as absorbers׳ damping for suppression of low-frequency vibrations.

Enhanced cellulose fermentation and end-product synthesis by Clostridium thermocellum with varied nutrient compositions under carbon-excess conditions

Sixteen combinations of seven growth nutrients, namely α-cellulose, yeast extract (YE), urea, CaCl2·2H2O, MgCl2·6H2O, FeSO4·6H2O and vitamins, were studied to improve direct cellulose fermentation by Clostridium thermocellum DSM 1237 under carbon-excess conditions. Varied nutrient compositions improved cellulose fermentation conditions for C. thermocellum and displayed two major types of effects: a general growth enhancement effect and a carbon-flux shifting effect. Different concentrations of the four most influential nutrients (YE, α-cellulose, CaCl2 and MgCl2) resulted in enhanced yields of ethanol or H2. High ethanol yields, high ethanol to acetate (E/A) ratios, and low acetate and H2 yields were obtained when YE, α-cellulose and CaCl2 were present at high concentrations, in combination with low concentrations of magnesium. Vitamins were identified as a relatively less influential nutrient, but high concentrations of vitamins supported enhanced yields of acetate and H2. High urea and YE in combination with low MgCl2 concentrations enhanced cellulose utilization per unit mass of cells and cell-specific yields of both ethanol and H2. Volumetric yields for ethanol and H2 were improved by 2.3-fold (76.5 mM) and 2.04-fold (71.22 mmol per liter), respectively, compared with the basic combination. The highest hydrogen yield (1.64 mol/mol glucose) was obtained in the combination with the lowest ethanol yields while the lowest hydrogen yielding combination had the highest ethanol yield of 1.36 mol/mole glucose, representing 68% of the theoretical maximum for ethanol. The culture conditions determined by this study can be optimized further for enhanced production of either ethanol or H2 by direct cellulose fermentation.

The low frequency performance of metamaterial barriers based on cellular structures

The high sound transmission loss (STL) metamaterials that have been suggested to-date commonly require the introduction of relatively heavy resonating or constraining components which limit the applicability of these solutions in typical noise control applications where it is desirable to minimize the treatment mass at a given STL. Here it is proposed that a panel consisting of an array of cellular unit structures can possess a high STL within a specified low frequency range without an undue mass penalty. The cellular acoustical metamaterial considered comprises a periodic arrangement of unit cells consisting of plates held in a grid-like frame (which itself is unsupported). It is suggested here that such a cellular panel can yield enhanced STL if the unit cell mass is apportioned appropriately between the unit cell plate and the surrounding grid-like frame, the effect being similar to the high STL observed in the low frequency range for a plate clamped along its edges. A finite element-model of a single unit cell was used to predict the normal incidence transmission loss of the periodic array by imposing boundary conditions that enforce spatial periodicity. Two material designs were compared: one in which the densities of the materials used for the unit plate panel and the grid were changed relative to each other, and a second where the relative thicknesses of the unit plate panel and the grid frame were varied. The numerical simulations indicate that benefits can be achieved in either case. However, the design based on density variations appears to be more effective than the approach based on geometry alteration in creating a relatively broad range of low frequency transmission loss enhancement.

Algal Biogeography: Metagenomics Shows Distribution of a Picoplanktonic Pelagophyte

How can we determine the distribution of uncultured marine microorganisms? Targeted metagenomics has provided the complete chloroplast genome sequence, and the distribution, for a picoplanktonic pelagophyte alga.

Aerobic TCE degradation by encapsulated toluene-oxidizing bacteria, Pseudomonas putida and Bacillus spp.

The degradation rates of toluene and trichloroethylene (TCE) by Pseudomonas putida and Bacillus spp. that were encapsulated in polyethylene glycol (PEG) polymers were evaluated in comparison with the results of exposure to suspended cultures. PEG monomers were polymerized together with TCE-degrading microorganisms, such that the cells were encapsulated in and protected by the matrices of the PEG polymers. TCE concentrations were varied from 0.1 to 1.5 mg/L. In the suspended cultures of P. putida, the TCE removal rate decreased as the initial TCE concentration increased, revealing TCE toxicity or a limitation of reducing power, or both. When the cells were encapsulated, an initial lag period of about 10-20 h was observed for toluene degradation. Once acclimated, the encapsulated P. putida cultures were more tolerant to TCE at an experimental range of 0.6-1.0 mg/L and gave higher transfer efficiencies (mass TCE transformed/mass toluene utilized). When the TCE concentration was low (e.g., 0.1 mg/L) the removal of TCE per unit mass of cells (specific removal) was significantly lower, probably due to a diffusion limitation into the PEG pellet. Encapsulated Bacillus spp. were able to degrade TCE cometabolically. The encapsulated Bacillus spp. gave significantly higher values than did P. putida in the specific removal and the transfer efficiency, particularly at relatively high TCE concentration of approximately 1.0±0.5 mg/L. The transfer efficiency by encapsulated Bacillus spp. in this study was 0.27 mgTCE/mgToluene, which was one to two orders of magnitude greater than the reported values.

The activity of β-galactosidase and lactose metabolism in Kluyveromyces lactis cultured in cheese whey as a function of growth rate

Kluyveromyces lactis was cultured in cheese whey permeate on both batch and continuous mode to investigate the effect of time course and growth rate on beta-galactosidase activity, lactose consumption, ethanol production and protein profiles of the cells. Cheese whey was the substrate to grow K. lactis as a batch or continuous culture. In order to precise the specific growth rate for maximum beta-galactosidase activity a continuous culture was performed at five dilution (growth) rates ranging from 0.06, 0.09, 0.12, 0.18 to 0.24 h(-1). The kinetics of lactose consumption and ethanol production were also evaluated. On both batch and continuous culture a respirofermentative metabolism was detected. The growth stage for maximum beta-gal activity was found to be at the transition between late exponential and entrance of stationary growth phase of batch cultures. Fractionating that transition stage in several growth rates at continuous culture a maximum beta-galactosidase activity at 0.24 h(-1) was observed. Following that stage beta-gal activity undergoes a decline which does not correlate to the density of its corresponding protein band on the gel prepared from the same samples. The maximum beta-galactosidase activity per unit of cell mass was found to be 341.18 mmol ONP min(-1) g(-1) at a dilution rate of 0.24 h(-1). The physiology of K. lactis growing in cheese whey permeate can proven useful to optimize the conversion of that substrate in biomass rich in beta-gal or in ethanol fuel. In addition to increasing the native enzyme the conditions established here can be set to increase yields of recombinant protein production based on the LAC4 promoter in K. lactis host.

Data from necropsy studies and in vitro tissue studies lead to a model for allometric scaling of basal metabolic rate

BackgroundThe basal metabolic rate (BMR) of a mammal of mass M is commonly described by the power function αMβ where α and β are constants determined by linear regression of the logarithm of BMR on the logarithm of M (i. e., β is the slope and α is the intercept in regression analysis). Since Kleiber's demonstration that, for 13 measurements of BMR, the logarithm of BMR is closely approximated by a straight line with slope 0.75, it has often been assumed that the value of β is exactly 3/4 (Kleiber's law).ResultsFor two large collections of BMR data (n = 391 and n = 619 species), the logarithm of BMR is not a linear function of the logarithm of M but is a function with increasing slope as M increases. The increasing slope is explained by a multi-compartment model incorporating three factors: 1) scaling of brain tissue and the tissues that form the surface epithelium of the skin and gastrointestinal tract, 2) scaling of tissues such as muscle that scale approximately proportionally to body mass, and 3) allometric scaling of the metabolic rate per unit cell mass. The model predicts that the scaling exponent for small mammals (body weight < 0.2 kg) should be less than the exponent for large mammals (> 10 kg). For the simplest multi-compartment model, the two-compartment model, predictions are shown to be consistent with results of analysis using regression models that are first-order and second-order polynomials of log(M). The two-compartment model fits BMR data significantly better than Kleiber's law does.ConclusionThe F test for reduction of variance shows that the simplest multi-compartment allometric model, the two-compartment model, fits BMR data significantly better than Kleiber's law does and explains the upward curvature observed in the BMR.

Permanent changes in growth and physiology of Bacillus subtilis ToC46 after loss of a recombinant plasmid

The physiology and growth of plasmid-bearing Bacillus subtilis carrying plasmid pPFF1, the non-transformed host, and cells after loss of the plasmid (so-called plasmid-cured cells) were investigated. It was found that, following plasmid loss, cells exhibited phenotypic characteristics different from those of the non-transformed host strains. Compared to plasmid-bearing cells and non-transformed host cells, an approximate 25% increase in the maximum specific growth rate and a more rapid increase in total RNA per unit cell mass were observed in plasmid-cured cells. The total enthalpy associated with irreversible denaturation events was determined in whole cells by differential scanning calorimetry. This showed higher enthalpies for plasmid-cured cells compared with the non-transformed host, which suggests increased ribosome numbers. The result from cellular DNA hybridisation suggests that there was no direct evidence of plasmid integration into the host chromosome.

Kinetics and Equilibrium of Cadmium Biosorption by Yeast Cells S. cerevisiae and K. fragilis

The biosorption of cadmium metal ions by Saccharomyces cerevisiae and Kluyveromyces fragilis yeast cells was studied under various operating conditions in a batch system using shaker flasks and a 2-L double draft tube fluidized bioreactor system. The effects of key parameters such as solution pH, initial metal concentration, biosorbent concentration, and age of the biosorbent cells were investigated. The experiments were carried out at room temperature and pH values of 3.5, 4.5 and 5.0. Three biosorbent yeast cells concentrations (2.5, 5.0 and 7.5 g dry wt./L) were employed with aqueous solutions having initial cadmium concentrations of 50, 100 and 200 mg/L. The solution pH was found to play a critical role in the biosorption process and the metal uptake increased with an increase in pH value. The optimum pH was found to be 5.0. Also, increasing the metal concentration and decreasing the biosorbent concentration increased the final metal uptake per unit cell mass. At a sufficiently high cadmium concentration of 200 mg/L, the effect of initial metal concentration became the dominant factor, since the metal uptake became constant with respect to the initial metal concentration, regardless of pH value. The results showed that the effect of biosorbent concentration on metal uptake was less significant than those of the cadmium concentration and the pH. It was also found that the younger the yeast biosorbent, the higher the metal uptake capacity. Generally, the cadmium uptake was found to take place rapidly, whereby almost 90% uptake occurred within the first five minutes of exposure. The equilibrium of cadmium biosorption was investigated under the same operating conditions. The Langmuir and the Freundlich adsorption isotherms were used to fit the experimental data. However, both of these conventional adsorption models did not fit the experimental data accurately. The maximum uptake capacity was estimated to be close to 35 and 40 mg Cd/g DW cell for S. cerevisiae and K. fragilis, respectively at a pH value of 5.0.