bluuebunny/crossref_metadata_2025_split huggingface dataset:
System peaks and their positive and negative aspects in chromatographic techniques
Authors: Srbek Jan , Coufal Pavel , Bosáková Zuzana , Tesařová Eva 
Published: July 2005

AbstractWhenever a mobile phase contains more than one component, additional signals commonly called system peaks can appear. The origin of these signals is explained through loss of equilibrium in the separation column caused by injection of analyte dissolved in a different solvent than the mobile phase. The system peaks are then generated by a relaxation process started by the non‐equilibrium state. An overview of the theory and applications of the system peaks in separation methods, mainly in liquid chromatography, is presented in this paper. Only a brief theoretical discussion of the system peak origin is given as the theoretical aspects of system peak formation have already been published in many papers. The main focus of this review is to summarize applications, in which system peaks were used to measure physical or physicochemical data. Signals of system peaks are often misinterpreted but they offer valuable information about thermodynamics and kinetics of the separation process that takes place in chromatographic column.
Zone electrophoresis separation of perfluorocarboxylic acids on a chip with conductivity detection
Authors: Masár Marián , Wójcik Lena , Kaniansky Dušan , Trojanowicz Marek 
Published: July 2005

AbstractPerfluorinated carboxylic acids (PFCAs), amphiphiles of anthropogenic origin, are spread worldwide throughout the environment. This work deals with their zone electrophoresis (ZE) separation on a chip with coupled columns and integrated conductivity detection. Analogies with the electrophoretic behavior of PFCAs and fatty acids were employed in a search for electrolyte conditions suitable for their separation. ZE separations in the water‐ethanol electrolyte systems, based on differences in the ionic mobilities of the anions of PFCAs, provided favorable resolution and detection conditions of the homologues containing up to 10 carbon atoms in the alkyl chain. Concentration limits of detection of 0.3–6.5 μmol/L were attained for PFCAs (loaded by a 900 nL volume sample injection channel of the chip) under these separation conditions. The material of which the chip was made [poly(methylmethacrylate)] restricted its use in investigations of the separations of higher PFCA homologues as it was damaged by ethanolic and/or methanolic background electrolyte solutions required in experiments with these amphiphilic compounds.
Effect of surfactant counterion and organic modifier on the properties of surfactant vesicles in electrokinetic chromatography
Authors: Schuster Stephanie A. , Foley Joe P. 
Published: July 2005

AbstractCounterion and organic modifier are two parameters in EKC that can be varied in order to obtain improved solubility, selectivity, and efficiency. The effect of changing surfactant counterion and/or organic modifier on the chromatographic and electrophoretic properties of cetyltrimethylammonium bromide (CTAB)/sodium octyl sulfate (SOS) vesicles is examined in EKC. The vesicles are prepared in a 1:3.66 cationic/anionic mole ratio for a total surfactant concentration of 69 mM. The cationic CTAB is replaced by cetyltrimethylammonium chloride (CTAC) and the first use of CTAC/SOS vesicles is reported. The mean diameter of the CTAC/SOS vesicles is 96 nm while that of the CTAB/SOS vesicles is 85 nm. A class I modifier (2‐amino‐1‐butanol) and a class II modifier (acetonitrile) have similar effects on the EOF, elution range, methylene selectivity, and the efficiency of the CTAB/SOS vesicles and the CTAC/SOS vesicles. Upon addition of 10% ACN, there is roughly a 10‐fold increase in the efficiency of heptanophenone, a model hydrophobic compound, compared to the efficiency using unmodified vesicles. Linear free energy relationship (LFER) analysis using the Abraham solvation model is employed to characterize solute‐vesicle interactions. The results suggest that organic modifier‐vesicle interactions depend somewhat on the counterion.
How different reforestation approaches affect red soil properties in southern China
Authors: Zheng H. , Ouyang Z. Y. , Wang X. K. , Miao H. , Zhao T. Q. , Peng T. B. 
Published: July 2005

AbstractSignificant differences were found in soil physicochemical and biological effects between various forest restoration approaches of a hilly red‐soil region, southern China. Soil quality was the highest in natural secondary forest (0·95), while in sites revegetated with tea‐oil camellia (Camellia oleifera), Chinese fir (Cunninghamia lanceolata) and slash pine (Pinus elliottii) and control sites, integrated soil quality indices were 0·68, 0·55, 0·36 and 0·04 respectively. The lower soil quality of plantations and controls resulted from increased disruption of soil physical structure, lower quality litter fall, lower litter fall production, reduction in microbial biomass, decline of microbial function and loss of soil nutrients due to periodically artificial tending and accelerated soil erosion. Improvement in soil physicochemical properties and enhanced soil microbial function at a natural secondary forest site demonstrated the inherent restoration of these soils. Hence, natural restoration, as well as reducing human disturbance, is a better approach to improving soil properties than returning farmland to planted woodlands. Copyright © 2005 John Wiley & Sons, Ltd.
Reducing water erosion in a gypsic soil by combined use of organic amendment and shrub revegetation
Authors: Marqués M. J. , Jiménez L. , Pérez‐Rodríguez R. , GarcÍa‐Ormaechea S. , Bienes R. 
Published: July 2005

AbstractDegraded gypsic soils in the centre of Spain can be rehabilitated with organic amendment and shrub revegetation. Erosion has been measured on plots of 2×0·5 m2 under simulated rainfall of 70 mm h−1 and a kinetic energy of 18 J mm−1 m−2. Samples of water runoff and sediments were studied in the summer of the years 2002 and 2003. The presence of shrub Atriplex halimus (Chenonodiaceae) significantly reduces runoff from 16·9 to 6·7 ml m−2 min−1 and sediments from 0·16 to 0·02 g m−2 min−1. When sewage sludge is applied the differences among plots with and without bushes disappear. Although both treatments independently applied are efficient as erosion control measures, the combined use of revegetation and organic amendment allows a reduced dose of sewage sludge with the same effect on erosion. A low dose of sludge is desirable in view of the accumulation of toxic chemicals. Copyright © 2005 John Wiley & Sons, Ltd.
Desertification in north China: background, anthropogenic impacts and failures in combating it
Authors: Chen Y. , Tang H. 
Published: July 2005

AbstractDesertification in north China is ongoing despite the endeavours to mitigate it over the past 50 years. Overall examination of the context of desertification and defects of desertification‐combating programmes is a prerequisite for desertification control, which is now attracting general concern in China. The physiographic circumstances of north China, including the dry, continental, mid‐latitude climate, easily erodible soil surface and water shortage, provide the background to desertification. Climatic aridity and the evolution of land use and land management in recent decades have produced great stress on the land. The ineffectiveness of anti‐desertification measures ascribed to inadequate scientific involvement in decision‐making, neglect of the human dimension and the lack of a well‐organized desertification monitoring system are discussed in this paper. Copyright © 2005 John Wiley & Sons, Ltd.
Measurement of skeletal muscle perfusion during postischemic reactive hyperemia using contrast‐enhanced MRI with a step‐input function
Authors: Thompson Richard B. , Aviles Ronnier J. , Faranesh Anthony Z. , Raman Venkatesh K. , Wright Victor , Balaban Robert S. , McVeigh Elliot R. , Lederman Robert J. 
Published: July 2005

AbstractThe regional distribution of skeletal muscle blood flow was measured during postischemic reactive hyperemia using Gd‐DTPA contrast‐enhanced (CE) MRI. The release of an occlusive thigh cuff was used to deliver a step‐input of contrast concentration that was coincident with the onset of reactive hyperemia. A first‐order tracer kinetic equation was used to estimate the unidirectional influx constant, Ki (ml/100 g/min), and the distribution volume of Gd‐DTPA in the tissue, ve, from T1‐weighted images acquired with saturation recovery (SR) steady‐state free precession (SSFP) and spoiled gradient‐echo (SPGR) protocols. The capillary permeability surface (PS) area increased significantly during reactive hyperemia, which facilitated rapid extraction of Gd‐DTPA during the first pass. Regional muscle group studies from 11 normal volunteers yielded blood flow (Ki) values of 108.3 ± 34.1 ml/100 g/min in the gastrocnemius, 184.3 ± 41.3 ml/100 g/min in the soleus, and 122.4 ± 34.4 ml/100 g/min in the tibialis anterior. The distribution volumes (ve) in the corresponding muscle groups were respectively 8.3% ± 2.1%, 9.3% ± 1.9%, and 7.9% ± 1.8% from the kinetic model, and 8.8% ± 2.4%, 9.1% ± 1.9%, and 7.2% ± 1.4% from tissue relaxometry studies. Bulk blood flow studies in the same volunteers using phase‐contrast velocimetry (popliteal artery) yielded significantly lower flow values, but with a correlation coefficient R2 = 0.62 and P = 0.004. Magn Reson Med 54:289–298, 2005. Published 2005 Wiley‐Liss, Inc.
Visibility of vascular phenylalanine in dynamic uptake studies in humans using magnetic resonance spectroscopy
Authors: Kreis Roland , Salvisberg Christian , Lutz Thomas , Boesch Chris , Pietz Joachim 
Published: July 2005

AbstractIn general, vascular contributions to the in vivo magnetic resonance (MR) brain spectrum are too small to be relevant. In cerebral uptake studies, however, vascular contributions may constitute a major confounder. MR visibility of vascular Phe was investigated by recording localized spectra from fully oxygenated and well‐mixed whole blood. Blood Phe levels determined by MR spectroscopy (MRS) and ion‐exchange chromatography showed excellent correlation. In addition, effects of blood flow were shown to have a small effect on signal amplitude with the MRS methodology used. Hence, blood Phe is almost completely MR visible at 1.5 T, even though it is severely broadened at higher fields. Without appropriate correction, cerebral Phe influx in studies of brain Phe uptake in phenylketonuria patients or healthy subjects would appear to be faster and lead to higher levels. Similar effects are envisaged for studies of ethanol or glucose uptake across the blood–brain barrier. Magn Reson Med 54:435–438, 2005. © 2005 Wiley‐Liss, Inc.
Water in tendon: Orientational analysis of the free induction decay
Authors: Krasnosselskaia Lada V. , Fullerton Gary D. , Dodd Stephen J. , Cameron Ivan L. 
Published: July 2005

AbstractThe orientation dependence of the free induction decay (FID) of1H NMR water signal in ex vivo bovine digital flexor tendon at the native level of hydration is reported. Residual dipolar coupling due to the overall tissue anisotropy produces a 6:1 change in the signal intensity as an angle between the long axis of a specimen and the external magnetic field is changed from the “magic angle” of 54.7° to 0°. The strength of residual dipolar interactions between water protons was estimated by orientational analysis of the signal intensity to be equal to 780 Hz. Apparent signal maxima are observed at orientations 8–13° away from 54.7° due to an inhomogeneous contribution to the decay. A small fraction of total water in tendon is detectable at all orientations and exhibits a shift in the precession frequency. It is hypothesized that this water fraction resides in the interconnecting gaps at the ends of collagen molecules. The gaps have a disordered environment that allows for a zero time average of dipolar interactions. Measured frequency and phase shifts are interpreted as signatures of the bulk magnetic susceptibility effect due to geometry of the cavity formed by adjacent gaps at the ends of the collagen molecules. The multiexponentiality of the FID decay is hypothesized to be due to the exchange between orientationally restricted water structured along the length of the collagen molecule and disordered water in the cavity. Magn Reson Med 54:280–288, 2005. © 2005 Wiley‐Liss, Inc.
Application of model‐free analysis in the MR assessment of pulmonary perfusion dynamics
Authors: Chuang Kai‐Hsiang , Wu Ming‐Ting , Lin Yi‐Ru , Hsieh Kai‐Sheng , Wu Ming‐Long , Tsai Shang‐Yueh , Ko Cheng‐Wen , Chung Hsiao‐Wen 
Published: July 2005

AbstractDynamic contrast‐enhanced (DCE) MRI has been used to quantitatively evaluate pulmonary perfusion based on the assumption of a gamma‐variate function and an arterial input function (AIF) for deconvolution. However, these assumptions may be too simplistic and may not be valid in pathological conditions, especially in patients with complex inflow patterns (such as in congenital heart disease). Exploratory data analysis methods make minimal assumptions on the data and could overcome these pitfalls. In this work, two temporal clustering methods—Kohonen clustering network (KCN) and Fuzzy C‐Means (FCM)—were concatenated to identify pixel time‐course patterns. The results from seven normal volunteers show that this technique is superior for discriminating vessels and compartments in the pulmonary circulation. Patient studies with five cases of acquired or congenital pulmonary perfusion disorders demonstrate that pathologies can be highlighted in a concise map that combines information of the mean transit time (MTT) and pulmonary blood volume (PBV). The method was found to provide greater insight into the perfusion dynamics that might be overlooked by current model‐based analyses, and may serve as a basis for optimal hemodynamic quantitative modeling of the interrogated perfusion compartments. Magn Reson Med 54:299–308, 2005. © 2005 Wiley‐Liss, Inc.
Functional MRI using regularized parallel imaging acquisition
Authors: Lin Fa‐Hsuan , Huang Teng‐Yi , Chen Nan‐Kuei , Wang Fu‐Nien , Stufflebeam Steven M. , Belliveau John W. , Wald Lawrence L. , Kwong Kenneth K. 
Published: July 2005

AbstractParallel MRI techniques reconstruct full‐FOV images from undersampled k‐space data by using the uncorrelated information from RF array coil elements. One disadvantage of parallel MRI is that the image signal‐to‐noise ratio (SNR) is degraded because of the reduced data samples and the spatially correlated nature of multiple RF receivers. Regularization has been proposed to mitigate the SNR loss originating due to the latter reason. Since it is necessary to utilize static prior to regularization, the dynamic contrast‐to‐noise ratio (CNR) in parallel MRI will be affected. In this paper we investigate the CNR of regularized sensitivity encoding (SENSE) acquisitions. We propose to implement regularized parallel MRI acquisitions in functional MRI (fMRI) experiments by incorporating the prior from combined segmented echo‐planar imaging (EPI) acquisition into SENSE reconstructions. We investigated the impact of regularization on the CNR by performing parametric simulations at various BOLD contrasts, acceleration rates, and sizes of the active brain areas. As quantified by receiver operating characteristic (ROC) analysis, the simulations suggest that the detection power of SENSE fMRI can be improved by regularized reconstructions, compared to unregularized reconstructions. Human motor and visual fMRI data acquired at different field strengths and array coils also demonstrate that regularized SENSE improves the detection of functionally active brain regions. Magn Reson Med 54:343–353, 2005. © 2005 Wiley‐Liss, Inc.
Efficiency of inversion pulses for background suppressed arterial spin labeling
Authors: Garcia Dairon M. , Duhamel Guillaume , Alsop David C. 
Published: July 2005

AbstractBackground suppression strategies for arterial spin labeling (ASL) MRI offer reduced noise from motion and other system instabilities. However, the inversion pulses used for suppression can also attenuate the ASL signal, which may offset the advantages of background suppression. Numerical simulations were used to optimize the inversion efficiency of four candidate pulses over a range of radiofrequency (RF) and static magnetic field variations typical of in vivo imaging. Optimized pulses were then used within a pulsed ASL sequence to assess the pulses' in vivo inversion efficiencies for ASL. The measured in vivo inversion efficiency was significantly lower than theoretical predictions (e.g., 93% experimental compared to 99% theoretical) for the tangent hyperbolic pulse applied in a background suppression scheme. This inefficiency was supported by an in vitro study of human blood. These results suggest that slow magnetization transfer (MT) in blood, either with bound water or macromolecular protons, dominates the inversion inefficiency in blood. Despite the attenuated signal relative to unsuppressed ASL, the signal‐to‐noise ratio (SNR) with suppression was improved by 23–110% depending on the size of the region measured. Knowledge of efficiency will aid optimization of the number of suppression pulses and provide more accurate quantification of blood flow. Magn Reson Med 54:366–372, 2005. © 2005 Wiley‐Liss, Inc.
Free‐breathing whole‐heart coronary MRA with 3D radial SSFP and self‐navigated image reconstruction
Authors: Stehning C. , Börnert P. , Nehrke K. , Eggers H. , Stuber M. 
Published: July 2005

AbstractRespiratory motion is a major source of artifacts in cardiac magnetic resonance imaging (MRI). Free‐breathing techniques with pencil‐beam navigators efficiently suppress respiratory motion and minimize the need for patient cooperation. However, the correlation between the measured navigator position and the actual position of the heart may be adversely affected by hysteretic effects, navigator position, and temporal delays between the navigators and the image acquisition. In addition, irregular breathing patterns during navigator‐gated scanning may result in low scan efficiency and prolonged scan time. The purpose of this study was to develop and implement a self‐navigated, free‐breathing, whole‐heart 3D coronary MRI technique that would overcome these shortcomings and improve the ease‐of‐use of coronary MRI. A signal synchronous with respiration was extracted directly from the echoes acquired for imaging, and the motion information was used for retrospective, rigid‐body, through‐plane motion correction. The images obtained from the self‐navigated reconstruction were compared with the results from conventional, prospective, pencil‐beam navigator tracking. Image quality was improved in phantom studies using self‐navigation, while equivalent results were obtained with both techniques in preliminary in vivo studies. Magn Reson Med 54:476–480, 2005. © 2005 Wiley‐Liss, Inc.
Liver regeneration in humans is characterized by significant changes in cellular phosphorus metabolism: Assessment using proton‐decoupled 31P‐ magnetic resonance spectroscopic imaging
Authors: Zakian Kristen L. , Koutcher Jason A. , Malhotra Sandeep , Thaler Howard , Jarnagin William , Schwartz Lawrence , Fong Yuman 
Published: July 2005

AbstractIn the present study we applied proton‐decoupled 31P magnetic resonance spectroscopic imaging (MRSI) to noninvasively assess liver metabolism in patients who had undergone a partial hepatectomy (PH). Proton‐decoupled 31P chemical shift imaging was performed in 47 patients 2–28 days following major hepatectomy, and the results were compared with those from eight control subjects. All studies were performed on a 1.5T MR imager (General Electric, Milwaukee, WI) equipped with a stand‐alone proton decoupler. A 31P‐1H resonator pair was used for data acquisition, and 31P data were obtained in 34 min. Liver regeneration was characterized by increases in phosphoethanolamine (PE), and decreases in nucleoside triphosphates (NTP), glycerophosphoethanolamine (GPE), and glycerophosphocholine (GPC). These alterations were most marked 48–72 hr after hepatectomy and returned to baseline within 3 weeks. The level of PE measured by MRSI was also found to depend on the percentage of liver that was removed, while changes in levels of cellular high energy phosphates were independent of the size of liver resection. Implementation of proton‐decoupling was critical for assessing individual phosphomonoester and phosphodiester components. This study demonstrates that 31P MRSI can be used to assess metabolic changes in humans during liver regeneration, and may be useful for assessing derangement of the regenerative process or guiding adjuvant chemotherapies. Magn Reson Med 54:264–271, 2005. © 2005 Wiley‐Liss, Inc.
Brain γ‐aminobutyric acid measurement by proton double‐quantum filtering with selective J rewinding
Authors: Choi Changho , Coupland Nicholas J. , Hanstock Christopher C. , Ogilvie Catherine J. , Higgins Andrea C. M. , Gheorghiu Dan , Allen Peter S. 
Published: July 2005

AbstractAn optimized single‐shot proton double‐quantum (DQ) filter for the quantification of γ‐aminobutyric acid (GABA) levels in human brain is reported. It is demonstrated that creation of DQ coherences following dual‐resonance‐selective refocusing gives a theoretical editing efficiency of 50% for the detection of the GABA resonance at 3.01 ppm. The sequence times are optimized with both numerical and experimental analyses of the editing performance, giving an experimental editing efficiency of 42%. It is acknowledged that homocarnosine is partially coedited, leading to a 20% contribution to the edited signal; however, macromolecule contamination is negligible in vivo under these experimental conditions. The GABA concentration in human prefrontal cortex is estimated to be 0.8 ± 0.1 μmol/g (mean ± SD, n = 6), with reference to the internal standard creatine at 9 μmol/g. Magn Reson Med 54:272–279, 2005. © 2005 Wiley‐Liss, Inc.
On the cause of spatial displacement of long T1 species in segmented inversion recovery prepared imaging
Authors: Goldfarb James W. , Arnold Sheeba , Schapiro William , Reichek Nathaniel 
Published: July 2005

AbstractUsing inversion recovery steady‐state free precession segmented k‐space imaging for the detection of myocardial infarction, we noticed that some structures appeared in the wrong locations of the image. In this work, the spatial displacement is demonstrated and explained from both theoretical and experimental points of view. The effect is due to a change in phase from segment to segment of the detected magnetization from species with long T1's such as cysts, fluid collections, and cerebrospinal fluid. Depending on the number of k‐space segments and view ordering, structures can be replicated throughout the image or displaced by half of the phase‐encoding field of view. Magn Reson Med 54:481–485, 2005. © 2005 Wiley‐Liss, Inc.