bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sample introduction techniques for microfabricated separation devices
Authors: Roddy Elizabeth S. , Xu Hongwei , Ewing Andrew G. 
Published: January 2004

AbstractA great deal of progress has been made toward the development of the micro total analysis system (μ‐TAS) since its inception in 1990. A wide variety of applications, including genomics, proteomics and drug discovery, have prompted the development of analytical methods capable of very high throughput while maintaining low cost. The μ‐TAS concept addresses both of these requirements. Electrophoresis has been a key element in the development of the μ‐TAS. Most chemical and biochemical assays utilize a separation component at some point during analysis. Genomics, in particular, depends almost exclusively on electrophoresis for size‐based separations of DNA. This review examines sample introduction into microfabricated electrophoretic devices, or chips, primarily for DNA analysis. Sample introduction is an important component of these systems and is an essential process for making chip electrophoresis a widely applicable analytical technique. Specific issues, such as automation, the delivery of large numbers of samples to microfabricated devices and injection of picoliter‐sized sample plugs into a separation lanes on chips, are presented.
Fluid mechanics of electroosmotic flow and its effect on band broadening in capillary electrophoresis
Authors: Ghosal Sandip 
Published: January 2004

AbstractElectroosmotic flow (EOF) usually accompanies electrophoretic migration of charged species in capillary electrophoresis unless special precautions are taken to supress it. The presence of the EOF provides certain advantages in separations. It is an alternative to mechanical pumps, which are inefficient and difficult to build at small scales, for transporting reagents and analytes on microfluidic chips. The downside is that any imperfection that distorts the EOF profile reduces the separation efficiency. In this paper, the basic facts about EOF are reviewed from the perspective of fluid mechanics and its effect on separations in free solution capillary zone electrophoresis is discussed in the light of recent advances.
Determination of the cis‐trans isomerization barrier of enalaprilat by dynamic capillary electrophoresis and computer simulation
Authors: Trapp Oliver , Trapp Gabriele , Schurig Volker 
Published: January 2004

AbstractDynamic capillary electrophoresis (DCE) and computer simulation of the elution profiles with the stochastic model has been applied to determine the isomerization barriers of the angiotensin converting enzyme inhibitor enalaprilat. The separation of the rotational cis‐trans isomeric drug has been performed in an aqueous 20 mM borate buffer at pH 9.3. Interconversion profiles featuring plateau formation and peak broadening were observed. To evaluate the rate constants kcis→trans and ktrans→cis of the cis‐trans isomerization from the experimental electropherograms obtained by dynamic capillary electrophoresis, elution profiles were analyzed by a simulation with iterative convergence to the experimental data using the ChromWin software which requires the total migration times of the individual isomers tR, the electroosmotic break‐through time t0, the plateau height hplateau, the peak widths at half height of the individual isomers wh, as well as the peak ratio of the isomers as experimental data input. From temperature‐dependent measurements between 0° and 15°C the thermodynamic parameters ΔG, ΔH and ΔS, the rate constants kcis→trans and ktrans→cis and the kinetic activation parameters ΔG≠, ΔH≠, and ΔS≠ of the cis‐trans isomerization of enalaprilat were obtained. From the activation parameters the isomerization barriers at 37°C were calculated to be ΔG≠trans→cis = 87.2 kJ·mol−1 and ΔG≠cis→trans = 91.9 kJ·mol−1.
Effect of Joule heating on efficiency and performance for microchip‐based and capillary‐based electrophoretic separation systems: A closer look
Authors: Petersen Nickolaj J. , Nikolajsen Rikke P. H. , Mogensen Klaus B. , Kutter Jörg P. 
Published: January 2004

AbstractAn attempt is made to revisit the main theoretical considerations concerning temperature effects (“Joule heating”) in electro‐driven separation systems, in particular lab‐on‐a‐chip systems. Measurements of efficiencies in microfabricated devices under different Joule heating conditions are evaluated and compared to both theoretical models and measurements performed on conventional capillary systems. The widely accepted notion that planar microdevices are less susceptible to Joule heating effects is largely confirmed. The heat dissipation from a nonthermostatically controlled glass microdevice was found to be comparable to that from a liquid‐cooled‐fused silica capillary. Using typically dimensioned glass and glass/silicon microdevices, the experimental results indicate that 5–10 times higher electric field strengths can be applied than on conventional capillaries, before detrimental effects on the separation efficiency occur. The main influence of Joule heating on efficiency is via the establishment of a radial temperature profile across the lumen of the capillary or channel. An overall temperature increase of the buffer solution has only little influence on the quality of the separation. Still, active temperature control (cooling, thermostatting) can help prevent boiling of the buffer and increase the reproducibility of the results.
High‐resolution computer simulation of the dynamics of isoelectric focusing of proteins
Authors: Thormann Wolfgang , Huang Tiemin , Pawliszyn Janusz , Mosher Richard A. 
Published: January 2004

AbstractA dynamic electrophoresis simulator that accepts 150 components and voltage gradients employed in the laboratory was used to provide a detailed description of the focusing process of proteins under conditions that were hitherto inaccessible. High‐resolution focusing data of four hemoglobin variants in a convection‐free medium are presented for pH 3–10 and pH 5–8 gradients formed with 20 and 40 carrier ampholytes/pH unit, respectively. With 300 V/cm, focusing is shown to occur within 5–10 min, whereas at 600 V/cm separation is predicted to be complete between 2.5 and 5 min. The time interval required for focusing of proteins is demonstrated to be dependent on the input protein charge data and, however less, on the properties of the carrier ampholytes. The simulation data reveal that the number of transient protein boundaries migrating from the two ends of the column towards the focusing positions is equal to the number of sample components. Each protein is being focused via the well‐known double‐peak approach to equilibrium, a process that is also characteristic for focusing of the carrier ampholytes. The predicted focusing dynamics for the hemoglobin variants in pH 3–10 and pH 5–8 gradients are shown to qualitatively agree well with experimental data obtained by whole‐column optical imaging.
Zeta potential of microfluidic substrates: 1. Theory, experimental techniques, and effects on separations
Authors: Kirby Brian J. , Hasselbrink Ernest F. 
Published: January 2004

AbstractThis paper summarizes theory, experimental techniques, and the reported data pertaining to the zeta potential of silica and silicon with attention to use as microfluidic substrate materials, particularly for microchip chemical separations. Dependence on cation concentration, buffer and cation type, pH, cation valency, and temperature are discussed. The Debye‐Hückel limit, which is often correctly treated as a good approximation for describing the ion concentration in the double layer, can lead to serious errors if it is extended to predict the dependence of zeta potential on the counterion concentration. For indifferent univalent electrolytes (e.g., sodium and potassium), two simple scalings for the dependence of zeta potential on counterion concentration can be derived in high‐ and low‐ζ limits of the nonlinear Poisson‐Boltzman equation solution in the double layer. It is shown that for most situations relevant to microchip separations, the high‐ζ limit is most applicable, leading to the conclusion that the zeta potential on silica substrates is approximately proportional to the logarithm of the molar counterion concentration. The ζ vs. pH dependence measurements from several experiments are compared by normalizing the ζ based on concentration.
Peak dispersion and contributions to plate height in nonaqueous capillary electrophoresis at high electric field strengths: Ethanol as background electrolyte solvent
Authors: Palonen Sami , Jussila Matti , Porras Simo P. , Riekkola Marja‐Liisa 
Published: January 2004

AbstractNonaqueous capillary electrophoretic separations were performed under high electric field strengths (up to 2000 Vcm−1) in ethanolic background electrolyte solution and the contributions of different band broadening effects to plate height were evaluated. Under optimum conditions, increasing the field strength will provide faster separations and increased separation efficiency. Decrease in the separation efficiency at high field strengths was, however, observed in a previous study and now in the present paper an attempt is made to quantify various band broadening effects by applying a plate height model, which included the contributions of the injection plug length, diffusion, electromigration dispersion, Joule heating, analyte adsorption to the capillary wall, and detector slit aperture length. Of special interest were the contributions of Joule heating and analyte adsorption to the capillary wall. Poly(glycidylmethacrylate‐co‐N‐vinylpyrrolidone)‐coated fused‐silica capillaries were used with internal diameters (ID) ranging from 30 to 75 μm. The separation efficiencies obtained experimentally were compared with the theoretically calculated efficiencies and fairly good agreement was observed for the 30 μm ID capillary. Relatively large deviation from the predictions of the model was found for the other capillary diameters especially at higher field strengths. The possible reasons for the deviation were discussed.
Urinary mutagenesis and fried red meat intake: Influence of cooking temperature, phenotype, and genotype of metabolizing enzymes in a controlled feeding study
Authors: Peters Ulrike , Sinha Rashmi , Bell Douglas A. , Rothman Nathaniel , Grant Delores J. , Watson Mary A. , Kulldorff Martin , Brooks Lance R. , Warren Sarah H. , DeMarini David M. 
Published: January 2004

AbstractMeat cooked at high temperatures contains potential carcinogenic compounds, such as heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). Samples from a 2‐week controlled feeding study were used to examine the relationship between the intake of mutagenicity from meat fried at different temperatures and the levels of mutagenicity subsequently detected in urine, as well as the influence of the genotype of drug metabolizing enzymes on urinary mutagenicity. Sixty subjects consumed ground beef patties fried at low temperature (100°C) for 1 week, followed by ground beef patties fried at high temperature (250°C) the second week. Mutagenicity in the meat was assayed in Salmonella typhimurium TA98 (+S9), and urinary mutagenicity was determined using Salmonella YG1024 (+S9). Genotypes for NAT1, NAT2, GSTM1, and UGT1A1 were analyzed using blood samples from the subjects. Meat fried at 100°C was not mutagenic, whereas meat fried at 250°C was mutagenic (1023 rev/g). Unhydrolyzed and hydrolyzed urine samples were 22× and 131× more mutagenic, respectively, when subjects consumed red meat fried at 250°C compared with red meat fried at 100°C. We found that hydrolyzed urine was ∼8× more mutagenic than unhydrolyzed urine, likely due to the deconjugation of mutagens from glucuronide. The intake of meat cooked at high temperature correlated with the mutagenicity of unhydrolyzed urine (r = 0.32, P = 0.01) and hydrolyzed urine (r = 0.34, P = 0.008). Mutagenicity in unhydrolyzed urine was not influenced by NAT1, NAT2, or GSTM1 genotypes. However, a UGT1A1*28 polymorphism that reduced UGT1A1 expression and conjugation modified the effect of intake of meat cooked at high temperature on mutagenicity of unhydrolyzed urine (P for interaction = 0.04). These mutagenicity data were also compared with previously determined levels of HCAs (measured as MeIQx, DiMeIQx, and PhIP) and polycyclic aromatic hydrocarbons (PAHs) in the meat, levels of HCAs in the urine, and CYP1A2 and NAT2 phenotypes. The levels of mutagenicity in the meat fried at low and high temperatures correlated with levels of HCAs, but not levels of PAHs, in the meat. Also, levels of mutagenicity in unhydrolyzed urine correlated with levels of MeIQx in unhydrolyzed urine (r = 0.36; P = 0.01), and the levels of mutagenicity of hydrolyzed urine correlated with levels of MeIQx (r = 0.34; P = 0.01) and PhIP (r = 0.43; P = 0.001) of hydrolyzed urine. Mutagenicity in unhydrolyzed urine was not influenced by either the CYP1A2 or NAT2 phenotype. The data from this study indicate that urinary mutagenicity correlates with mutagenic exposure from cooked meat and can potentially be used as a marker in etiological studies on cancer. Environ. Mol. Mutagen. 43:53–74, 2004. Published 2004 Wiley‐Liss, Inc.
Blown‐sand transport rate
Authors: Ni Jinren , Li Zhenshan , Mendoza Cesar 
Published: January 2004

AbstractSeveral sand transport rate data sets and eight representative transport rate formulae are transformed using the dimensionless parameters ϕ = gQ/ρU3* and r = U*t/U* and the results compared on the (ϕ, r) plane. The formulae generate three different geometric patterns – constant, monotonic decreasing and concave downward – and the corresponding data displayed one more pattern, a monotonic increasing one. Stimulated by this discrepancy, a new general formula for the sand transport rate with ϕ and r as its basis is introduced; each of the representative formulae is either a particular case of it or an approximation to it. The four parameters in the new formula are determined for description of the four possible patterns exhibited by the data; their variation is established and their physical interpretation is discussed in relation to measured data of the characteristic parameters of wind ﬂow and sand. Copyright © 2004 John Wiley & Sons, Ltd.
A distribution‐free statistical method for the spatial characterization of dune granulometry: an example from the Strzelecki Desert, South Australia
Authors: Bishop Mark A. 
Published: January 2004

AbstractDistribution‐free statistical methods of comparative data analysis have identiﬁed subtle granulometric differences attributed to the evolution of barchan form at Gurra‐Gurra waterhole. Geomorphic locations on the barchan dunes display statistically signiﬁcant grain‐size differences that assist in the interpretation of aeolian processes. In summer, very ﬁne sands mantle the dunescape and are the fraction that most affects the parameters of sorting and skewness. The surﬁcial sedimentological character is one of subtle contrasts between the processes of grain winnowing and intergranular protection. The second and third moment measures are parameters that best demonstrate the spatial granulometric differences. Dune‐forming processes at Gurra‐Gurra have produced dune sands that have a very narrow range of grain size, which, in turn, reﬂects textural and mineralogical maturity, and hence an extensive transport history. The statistical techniques employed in this study can also be used for the comparison of temporal (seasonal) sedimentological change, and for the granulometric analysis and association of process for dunes of different morpho‐types. Copyright © 2004 John Wiley & Sons, Ltd.
Channels, wetlands and islands in the Okavango Delta, Botswana, and their relation to hydrological and sedimentological processes
Authors: Gumbricht T. , McCarthy J. , McCarthy T. S. 
Published: January 2004

AbstractThe Okavango wetland in northern Botswana is one of the world's largest inland deltas. The delta is a dynamic environment with shifting channel routes, causing growth and decay of ﬂanking wetlands, and giving birth to islands. Primary island nuclei are formed by ﬂuvial processes and bioengineering, and subsequently grow into secondary larger islands of irregular shape by clastic and chemical sedimentation, and later by coalescence. This article presents classiﬁcations and quantitative estimations of channels, wetlands and islands of the Okavango Delta. Islands were classiﬁed dependent on composition, pattern of composition, shape and juxtaposition. 90 per cent of all islands in the entire wetland were identiﬁed, with a classiﬁcation accuracy of 60 to 85 per cent. Smaller islands of the nucleus types dominate the upper parts of the delta, whereas larger secondary islands are more common in the distal part, a reﬂection of the age of the islands. Islands in the entry valley of the delta, the Panhandle, are larger in the top end – the primary region of recent clastic sedimentation. The overall size distribution of islands in the delta, however, shows no clumps, indicating that island growth is a uniform process over time and space. The total area ﬂooded at least every decade is approximately 14 000 km2, of which 9000 km2 is classiﬁed as actual wetland. Channel meandering decreases from the Panhandle to the distal part of the delta, with the abandoned Thaoge channel as an exception. Occurrence of ﬂuvially formed islands in the distal delta indicates that the water ﬂow and area of inundation must once have been much larger. Copyright © 2004 John Wiley & Sons, Ltd.
Evidence for freeze–thaw events and their implications for rock weathering in northern Canada
Authors: Hall Kevin 
Published: January 2004

AbstractDiscussions regarding weathering in cold environments generally centre on mechanical processes and on the freeze–thaw mechanism in particular. Despite the almost ubiquitous assumption of freeze–thaw weathering, unequivocal proof of interstitial rock water actually freezing and thawing is singularly lacking. Equally, many studies have used the crossing of 0 °C, or values close to that, as the basis for determining the number of ‘freeze–thaw events’. In order to assess the weathering regime at a site in northern Canada, temperatures were collected at the surface, 1 cm and 3 cm depth for sets of paving bricks, with exposures both vertical and at 45°, orientated to the four cardinal directions. Temperature data were collected at 1 min intervals for 1 year. These data provide unequivocal proof for the occurrence of the freezing and thawing of water on and within the rock (freeze–thaw events). The freeze event is evidenced by the exotherm associated with the release of latent heat as the water actually freezes. This is thought to be the ﬁrst record of such events from a ﬁeld situation. More signiﬁcantly, it was found that the temperature at which freezing occurred varied signiﬁcantly through the year and that on occasion the 1 cm depth froze prior to the rock surface. The change in freeze temperature is thought to be due to the chemical weathering of the material (coupled with on‐going salt inputs via the melting of snowfall), which, it is shown, could occur throughout the winter despite air temperatures down to −30 °C. This ﬁnding regarding chemical weathering is also considered to be highly signiﬁcant. A number of thermal stress events were also recorded, suggesting that rock weathering in cold regions is a synergistic combination of various chemical and mechanical weathering mechanisms. Copyright © 2003 John Wiley & Sons, Ltd.
Patterns of sediment slug translation and dispersion following typhoon‐induced disturbance, Oyabu Creek, Kyushu, Japan
Authors: Kasai Mio , Marutani Tomomi , Brierley Gary J. 
Published: January 2004

AbstractA six‐year monitoring programme characterized the migration/dispersion patterns of sediment slugs generated following typhoon‐induced disturbances in 1993 and 1997 along a single‐thread gravel‐bed stream, Oyabu Creek, on Kyushu Island, Japan. This laterally conﬁned creek comprises rifﬂe–pool sequences with intervening bedrock outcrops. The passage of sediment pulses associated with sediment slug processes reﬂected, and was controlled by, the rifﬂe–pool structures which provided channel bed roughness, the volume of sediment stored along valley ﬂoors, and the distribution of bedrock outcrops. Changes to bed material size following major sediment inputs during the disturbance events also exerted an inﬂuence on subsequent sediment slug processes. The sequence of rainfall events, together with changes to channel bed structure, induced different phases in the sediment slug processes. The capacity of a reach to store or trap sediment, as recorded by the longitudinal structure of the channel, varied during these differing phases. Copyright © 2004 John Wiley & Sons, Ltd.
Crater formation in soils by raindrop impact
Authors: Ghadiri Hossein 
Published: January 2004

AbstractThe process of crater formation by the impact of water drops on soil, sand and various other target material was studied. Craters of various shapes and sizes were observed on different target materials or conditions, ranging from circumferential depression to completely hemispherical shape. Crater shape was dependent upon target material, its ﬂow stress or shear strength and the presence and thickness of water on the surface. Between 5 and 22 per cent of impact energy was spent on cratering, but the relationship between crater volume and kinetic energy of a raindrop was curvilinear, indicating a lower efﬁciency of impact energy in removing target material as the energy increases. Impact impulse, on the other hand, showed a more linear relationship with crater volume, and the ratio of impulse over crater volume (I/V) remained constant for the entire range of drop sizes, impact velocities, and surface conditions used in this study. Surface shear strength, represented by the penetration depth of fall‐cone penetrometer, appeared to be a key factor involved in this process. An equation was developed which related crater volume to cone penetration depth and impact impulse. Crater volume, which appeared to be a better indicator of the total amount of material dislodged by a raindrop than splash amount, can thus be predicted using this equation. Copyright © 2004 John Wiley & Sons, Ltd.
Longitudinal velocity patterns and bed morphology interaction in a rill
Authors: Giménez Rafael , Planchon Olivier , Silvera Norbert , Govers Gerard 
Published: January 2004

AbstractPresent‐day understanding of rill dynamics is hampered by a lack of detailed data on velocity distributions in rills. The latter are difﬁcult to collect with traditional techniques due to the very low water depths and the relatively high ﬂow velocities in rills. The objectives of this paper were to investigate the feasibility of miniaturized acoustic Doppler velocimeter (mADV) measurements in rill ﬂow and to explore longitudinal variations in ﬂow velocities and their relationship with rill bed morphology. Detailed data on longitudinal ﬂow velocity were required to achieve these objectives.A 1·8 m long rill was formed freely in a ﬂume at 5° slope and 0·001 m3 s−1 discharge. Rill topography was characterized by an alternation of steps and pools. The ﬂume surface was then ﬁxed to preserve rill roughness. A topographical scanning of the entire ﬂume surface was made. Velocity was measured with a mADV along the rill, and at different depths. Flow depth in a longitudinal direction was also measured using an elevation gauge.A strong relationship exists between rill topography and ﬂow hydraulics. Over steps, ﬂow was unidirectional and rapidly accelerating until a threshold Froude number (Fn) value between 1·3 and 1·7 was reached and a hydraulic jump occurred leading to the formation of a pool. In the pool, the ﬂow pattern was multidirectional and complex. The ﬂow was subcritical when leaving the pool and accelerated over the next step until the threshold Froude number value was again reached. Energy loss in the rill was concentrated in the pools, mainly due to the action of a hydraulic jump. This mechanism of energy dissipation appeared to be an essential factor in rill formation and bedform evolution. Copyright © 2004 John Wiley & Sons, Ltd.