bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glacier variations, mudflow activity and landscape development in the Aksay Valley (Tian Shan) during the late Holocene
Authors: Solomina O.N. , Savoskul O.S. , Cherkinsky A.E. 
Published: November 2007

The object of this paper is to reconstruct the history of glaciation and the dynamics of mudflow activity as part of the development of landscapes in the Aksay Valley, Kirgizsky Ridge, over the last 2000 years. Glacial, mudflow and slope deposits were dated by lichenometry and the radiocarbon method. The results of 14C dating of buried soils shows that at about 1700 BP a period of activization of slope processes took place in the valley. The zone of alpine meadow was situated at that time at an elevation of about 2750 m and glacier termini were situated at about 3100-3200 m. The oldest mudflow surface, which was investigated by lichenometry, dates from the same time. New equations for the rate of growth of the lichens Aspicilia tianshanica and Rhizocarpon geographicum use the oldest mudflow surface as a control point. Two periods of reduced mudflow activity are identified by lichenometry, i.e., 350-450 and 130-240 BP, and the latter is confirmed by 14C dating of peat-soil interlayers in a mudflow stratum with the specific activity of samples exceeding NBS standard. Thus, a new modification of the 14C-dating method is demonstrated. Lichenometry on moraines of the Aksay Glacier shows that advances of the glacier took place in the fourteenth and late- nineteenth centuries as well as at the beginning of this century. The depression of equilibrium-line altitude (ELA) for the fourteenth and nineteenth centuries was 150-170 m and 100-120 m, respectively.
Holocene palaeochannels at SiSatchanalai, north-central Thailand: ages, significance and palaeoenvironmental indications
Authors: Bishop Paul , Godley David 
Published: November 2007

Radiocarbon dating of sediments infilling palaeochannels in the northern part of the Central Plain of Thailand shows that they probably date from the early to mid-Holocene. The composition of bed material of the palaeochannels and the Yom River (the modern river) confirms that the palaeochannels represent earlier courses of the Yom. The most recent palaeochannel was abandoned about 1700 years ago when the modern course of the Yom was established, probably by avulsion during a period of increased runoff and flood activity which has also been identified in northeast Thailand. Bankfull discharges ( Qbf) of the palaeochannels are estimated in two ways. The 'hydraulic' approach combines a palaeochannel's bankfull cross-sectional area and an estimate of the average velocity needed to transport the coarse fraction of the channel's bed material. The 'geomorphological' approach relies on published equations relating Qbf and channel dimensions. When applied to the grain-size and dimensional characteristics of the modern Yom, both methods give results consistent with modem gauging data. The palaeodischarge estimations indicate the greatest bankfull discharges in the early- to mid-Holocene palaeochannel; slightly lower, but still comparable, discharges in the present channel; and lower to substantially lower discharges during the mid- to late-Holocene. The modem discharge may be affected by human activity, indicating that the highest discharges of the Holocene occurred during the early- to mid-Holocene. This sequence of Holocene environments is in close agreement with independ ently derived regional palaeoclimatic reconstructions, suggesting that these fluctuations in discharge have been externally climatically controlled, and that they are not the result of internal adjustments associated with multiple channels during phases of channel avulsion. The possibility of one phase of coeval distributary flow through the two mid- to late-Holocene palaeochannels does not change this conclusion, but it lessens the inferred decline in precipitation between the early and late-Holocene.
Holocene glacial activity and climatic variations in the Swiss Alps: reconstructing a continuous record from proglacial lake sediments
Authors: Leemann Andreas , Niessen Frank 
Published: November 2007

Cores recovered from proglacial Lake Silvaplana (Swiss Alps) were investigated to examine the influence of Holocene glaciers on lacustrine sedimentation. During times of glacial activity in the catchment the sedimentation in the lake is dominated by the input of silt and clay-sized material delivered by glacial meltwaters. The deposition of fine-grained material and the formation of varves reflect the existence of glaciers in the catchment and can therefore be used for the reconstruction of glacial history. Sedimentation rates are up to nine times higher in the varved than in the non-varved sediments, indicating significantly higher erosion rates under glaciated catchment conditions. Glacial varves were deposited in Lake Silvaplana during glacial retreat in the latest Pleistocene and early Holocene until 9400BP. Non-varved deposits having a higher organic content and coarser grain- sizes accumulated at lower rates when glacial activity was absent or negligible within the catchment between 9400 and 3300 BP. The continuous deposition of varves after 3300 BP indicates that Neoglacia tion provided glacial cover for part of the catchment since then. Long-term variation in varve thickness is interpreted as being controlled by the size of the glaciers in the catchment. Maximal varve thicknesses are observed from AD 1790 to 1870. Since the changes in glacial activity for this area seem to be mainly controlled by temperature rather than precipitation, we suggest that the entire lacustrine sediment record of Lake Silvaplana reflects relative changes of summer air temperature during the Holocene.
Fisher's method of scoring in statistical image reconstruction: comparison of Jacobi and Gauss-Seidel iterative schemes
Authors: Hudson H Malcolm , Jun Ma  
Published: November 2007

Many algorithms for medical image reconstruction adopt versions of the expectation-maximization (EM) algorithm. In this approach, parameter estimates are obtained which maximize a complete data likelihood or penalized likelihood, in each iteration. Implicitly (and sometimes explicitly) penalized algorithms require smoothing of the current reconstruction in the image domain as part of their iteration scheme. In this paper, we discuss alternatives to EM which adapt Fisher's method of scoring (FS) and other methods for direct maximization of the incomplete data likelihood. Jacobi and Gauss-Seidel methods for non-linear optimization provide efficient algorithms applying FS in tomography. One approach uses smoothed projection data in its iterations. We investigate the convergence of Jacobi and Gauss-Seidel algorithms with clinical tomographic projection data.
The analysis of the EEG
Authors: Gasser Theo , Molinari Luciano 
Published: November 2007

The quantitative analysis of the electroencephalogram (EEG) relies heavily on methods of time series analysis. A quantitative approach seems indispensable for research (be it clinical or basic neurophysical research), but it can also be a useful information for purely clinical purposes. Apart from the ongoing spontaneous EEG, evoked potentials (EPs) also play an important role. They can be elicited by simple sensory stimuli or more complex stimuli. Their analysis requires methods which are different from those for the spontaneous EEG. Those methods operate usually in the time domain and offer many challenging problems to statisticians. Methods for analysing the spontaneous EEG usually work in the frequency domain in terms of spectra and coherences. Biomedical engineers who take care of the equipment are usually also trained in time series analysis. Thus, they have contributed much more to methodological progress for analysing EEGs and EPs, compared with statisticians. However, the availability of a sample of subjects, and the associated problems in modelling followed by an inferential analysis could make a larger influence from the statistical side quite profitable. This paper tries to give an overview of a fascinating area. In doing so we treat more extensively problems with some statistical appeal. This leads inevitably to some overlap with our own work.
Nitric Oxide Synthesis Inhibition and Role of P-selectin in Leukocyte Adhesion to Vascular Tissues
Authors: Yang B.C. , Mehta P. , Mehta J.L. 
Published: November 2007

Background: This study was designed to examine the role of P-selectin expression in leuko cyte adhesion to endothelium caused by inhibition of nitric oxide synthesis. Methods and Results: Rat aortic rings were treated with the nitric oxide synthesis inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) for 2 hours. Parallel sets of aortic rings were pretreated with the nitric oxide precursor L-arginine or posttreated with a specific mono clonal antibody against P-selectin. Some rings were used for determination of vasoreactivity in response to norepinephrine and acetylcholine, while other rings were incubated with autol ogous unlabeled leukocytes or Biotin-FITC labeled leukocytes for 30 minutes. Leukocyte adhesion to vascular endothelium was determined by scanning electron microscopy. L-NAME enhanced the contractile response in response to norepinephrine, suppressed the relaxant response to acetyleholine, promoted leukocyte adherence to the endothelium and resulted in P-selectin expression on the aortic endothelium. Pretreatment of aortic rings with L-arginine reversed the L-NAME-mediated changes in vasoreactivity in response to nore pinephrine and acetyleholine and attenuated the L-NAME-enhanced leukocyte adhesion to endothelial intima. P-selectin treatment, on the other hand, had no effect on L-NAME-medi ated changes. Intrtperitoneal administration of L-NAME resulted in a significant decrease in plasma nitrite level, a small, but significant, increase in lung and spleen myeloperoxidase activity, and a significant increase in leukocyte deposition in lung and spleen. The L-NAME- mediated increase in myelopcroxidase activity and leukocyte deposition in the spleen, but not in the lungs, was abolished by treatment of rats with the P-selectin antagonist CY 1503 administered 30 minutes prior to L-NAME. Conclusions: These observations indicate that a reduction in nitric oxide synthesis enhances leukocyte adhesion to aortic endothelium and in visceral tissues. While P-selectin expression is evident in some of the experimental models of leukocyte adhesion to endothelium under conditions of nitric oxide inhibition, the role of P-selectin expression remains unclear.
Antiarrhythmic and Arrhythmogenic Actions of Varying Levels of Extracellular Magnesium: Possible Cellular Basis for the Differences in the Efficacy of Magnesium and Lidocaine in Torsade de Pointes
Authors: Takanaka Chiei , Ogunyankin Kofo O. , Sarma J.S.M. , Singh Bramah N. 
Published: November 2007

Background: In recent years, there has been an increasing use of antiarrhythmic drugs that act predominantly by prolonging myocardial repolarization. An inevitable electrophysiologic con sequence of these drugs is the development of torsade de pointes as a proarrhythmic reaction. Both intravenous lidocaine and magnesium sulphate have been used in the acute control of such a proarrhythmia. Their electrophysiologic mechanisms in this setting are not well defined. Methods and Results: Using the standard microelectrode techniques, the effects of magne sium (Mg) and lidocaine on action potential duration (APD), and on barium-induced sponta neous action potentials, were studied in canine Purkinje fiber preparations. The objective was to clarify the direct and indirect effects of magnesium on triggered activities due to early afterdepolarizations. Superfusion in media with 0.1 mM Mg and 2.5 mM K produced more pronounced increases in APD measured at -20mV repolarization time [APD20] than those in a solution with 5 mM K. This effect was further enhanced at lower stimulation frequencies. The striking prolongation of APD20 by solutions with low potassium concentrations dimin ished as the Mg concentration was increased. In solutions with 2.5 mM K, Mg produced con centration-dependent decreases in APD20. This effect was greater at lower stimulation fre quencies. Lidocaine at 4.0 × 10-5 M produced a marked shortening of the APD in the entire voltage range. On barium-induced automaticity, Mg markedly suppressed the spontaneous firing frequency of the abnormal automaticity in a concentration-dependent manner. With 10 mM Mg, such action potentials appeared only sporadically. Magnesium also decreased the amplitude and the maximum upstroke velocity of these action potentials. In contrast, lido caine at 4.0 × 10-5 M exhibited no significant effects on action potentials due to barium- induced abnormal automaticity, or on additional depolarizations developing from the repolar ization phase of these action potentials. Conclusions: The data indicate that (i) hypomagnesemia may be arrhythmogenic when com bined with hypokalemia and bradycardia leading to a prolongation of the plateau phase of the action potential, (ii) magnesium administration may suppress triggered activities mainly by a direct inhibition of the development of triggered potentials, and (iii) lidocaine may suppress triggered potentials only indirectly by preventing the development of early afterdepolariza tions due to the shortening effect on the APD. These findings are consistent with the clinical observation of a high incidence of torsade de pointes in the setting of hypokalemia and hypo magnesemia induced by a chronic diuretic therapy. They are also consistent with the marked effectiveness of intravenous Mg relative to the inconsistent clinical effects of lidocaine in controlling torsade de pointes.
Adrenergic-dependent Effect of Adenosine-induced Ventricular Fibrillation in the Isolated Rabbit Heart
Authors: Friedrichs Gregory S. , Chi Liguo , Park James L. , Lucchesi Benedict R. 
Published: November 2007

Background: The present study examined the contributory role of endogenous cate cholamines in adenosine-induced ventricular fibrillation in isolated rabbit hearts. Methods and Results: Cardiac catecholamine depletion was induced in eleven rabbits by the administration of 6-hydroxydopamine (2 x 30 mg/kg, every 12 hours intramuscularly). Hearts were removed 24 hours later, and subjected to 12 minutes of hypoxic perfusion fol lowed by 40 minutes of reoxygenation while heart rate was maintained with atrial pacing. One of six, and one of five hearts from 6-hydroxydopamine treated rabbits developed ventric ular fibrillation during hypoxia-reoxygenation when exposed to 3,7-dimethyl-1-propar gylzanthine (DMPX) (10 μM) + adenosine (ADO) (1 μM) and DMPX (10 μM) + ADO (10 μM), respectively. In hearts from a control group, not exposed to 6-hydroxydopamine, ven tricular fibrillation developed in each of five (100% incidence) hearts when perfused in the presence of DMPX (10 μM) + ADO (10 μM) ( P < .05). Nadolol (1 μM), a β-adrenoceptor antagonist, decreased the incidence of ventricular fibrillation (30%) in a separate group of DMPX (10 μM) + ADO (10 μM) treated hearts (n = 6, P < .05 vs DMPX + ADO treated hearts). To ensure catecholamine depletion. spontancously beating isolated hearts from vehi cle and 6-hydroxydopamine treated rabbits were perfused under normoxic conditions while exposed to increasing concentrations of tyramine ( 1, 3, 10 mM) and the change in heart rate was determined. A concentration-related, positive chronotropic response to tyramine was obtained in hearts from the vehicle treated group that was absent in hearts from 6-hydroxy dopamine treated rabbits or hearts perfused in the presence of nadolol. Conclusions: The results demonstrate that inhibition of the cardiac adenosine A2 receptor, unmasks an adenosine A1 receptor profibrillatory effect that is dependent upon endogenous cardiac catecholamines and β-adrenoreceptor activation during myocardial hypoxia-reoxy genation.
Electrocardiographic Changes and Mortality Due to Myocardial Infarction in Rats With or Without Imidapril Treatment
Authors: Ren Bin , Lukas Anton , Shao Qiming , Guo Min , Takeda Nobuakira , Aitken Randy M. , Dhalla Naranjan S. 
Published: November 2007

Background: Various angiotensin-converting enzyme inhibitors are known to improve heart function and prolong survival in patients and animals after myocardial infarction. Because myocardial infarction is known to induce arrhythmias, this study tested the hypoth esis that early treatment with the angiotensin-converting enzyme inhibitor imidapril reduces mortality during acute myocardial infarction because of protective effects against arrhythmogenesis. Methods and Results: Rats were randomly divided into four groups: sham control, myocar dial infarction, sham plus imidapril, and myocardial infarction plus imidapril. Myocardial infarction was produced by ligation of the left anterior descending coronary artery. Treated rats received imidapril (1 mg/kg/day) through a gastric tube beginning 1 hour after coronary occlusion; control rats received tap water. Electrocardiograms (ECGs) were recorded 1, 3, 7, and 21 days postocclusion. Infarct size and scar weight were determined at 21 days in the myocardial infarction groups with and without imidapril treatment. ECGs of untreated rats showed ST-segment changes, abnormal Q waves, premature ventricular complexes, and QTc prolongation 1-21 days after coronary occlusion. Total mortality in 21 days averaged 35% in untreated rats; mortality within 48 hours was 30%. On the other hand, imidapril-treated rats showed fewer ST-segment changes, fewer abnormal Q waves, and a decreased inci dence of premature ventricular complexes after coronary occlusion; the ST-segment and QTc interval returned to basal values within 1 week after occlusion. Imidapril treatment did not affect the ECG pattern in sham-treated control animals. Total mortality in the imidapril- treated group in 21 days after infarction was 22.5%; mortality within 48 hours was 20% ( P < .05 compared with the untreated infarction group). Infarct size and scar weight caused by coronary occlusion did not differ in the untreated and imidapril-treated groups. Conclusions: Early treatment with imidapril markedly decreases mortality in rats after acute myocardial infarction. The lower mortality is not associated with a decrease in infarct size but is consistent with a protective effect of the drug against arrhythmogenesis.
Formation of Reactive Oxygen Species in Various Vascular Cells During Glyceryltrinitrate Metabolism
Authors: Dikalov S. , Fink B. , Skatchkov M. , Sommer O. , Bassenge E. 
Published: November 2007

Background: Anti-ischemic therapy with organic nitrates as nitric oxide (NO) donors is complicated by the induction of tolerance. When nitrates are metabolized to release NO, there is a considerable coproduction of reactive oxygen species (superoxide radical and per oxynitrite) in vessels leading to inactivation of NO, to diminished cyclic quanosine mono phosphate production in smooth muscle cells (SMC), to impaired vasomotor responses to the endothelium-derived relaxation factor (EDRF), and to formation of nitrotyrosine as a marker of glyceryltrinitrate (GTN)-induced formation of peroxynitrite. The aim of the study was to analyze in vitro the formation of superoxide radicals and of peroxynitrite in GTN-treated endothelial and smooth muscle cells and in washed ex vivo platelets using electron spin resonance and spin-trapping techniques. Methods and Results: Using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap, it was shown that in platelets, smooth muscle, and endothelial cells incubated acutely for 15 minutes with 0.5 mM GTN, the rate of generation of reactive oxygen species (ROS) was twice as high as under control conditions. Using the new spin-trap 2H-imidazole-1-oxide (TMIO), a GTN-induced peroxynitrite formation was detected in SMC and in platelets incubated with 0.5 mM GTN for 15 minutes. Spin-trap 1-hydroxy-3-carboxy-pyrrolidine (CP-H) was used to estimate the rate of ROS formation in platelets incubated for 15 min utes with 0.5 mM GTN; the rate amounted to 14.6 ± 1.1 nM/min/mg protein compared with 4.0 ± 0.4 nM/min/mg protein in controls. The rate of ROS formation in SMCs was substan tially increased (240 ± 16%) after initiation of GTN tolerance by treatment of the cells in culture with 100 μM GTN for 24 hours. Conclusions: GTN increases the formation of superoxide radicals in endothelial cells, SMCs, and platelets. Peroxynitrite is formed during GTN metabolism in vascular cells and may contribute to the development of tolerance. A decrease in the nitrate-induced inhibi tion of platelet aggregation during GTN tolerance is associated with oxidative actions of ROS formed in platelets during GTN metabolism.
Effect of Nifedipine on the Steady-State Pharmacokinetics and Pharmacodynamics of Irbesartan in Healthy Subjects
Authors: Marino M.R. , Hammett J.L. , Ferreira I. , Ford N.F. , Uderman H.D. 
Published: November 2007

Background: In clinical practice, nifedipine has the potential to alter the pharmacokinetics, and therefore possibly the pharmacodynamics and efficacy or safety, of irbesartan. The objectives of the current study were to determine the effects of concomitant administration of nifedipine on the steady-state pharmacokinetics and pharmacodynamics of irbesartan in 12 healthy subjects. Methods and Results: This was an open-label, randomized, crossover study. Each subject received irbesartan 300 mg once daily for 4 days in one period and irbesartan 300 mg once daily plus long-acting nifedipine (Procardia XL, Pratt Pharmaceuticals, New York, NY) 30 mg once daily for 4 days in the other period. The order of treatment periods was random ized, and a minimum 7-day washout phase separated the two periods. Steady state was achieved by day 3. On day 4, no significant differences were observed between the two treatments with respect to maximum concentration of irbesartan at the end of the dosing interval (Cmax) or the area under the plasma concentration versus time curve during a dos ing interval (AUCtau) of irbesartan. Steady-state Cmax and AUCtau met the criteria for bioequivalence when irbesartan was administered alone or with nifedipine. On day 4, mean plasma renin activity was somewhat higher at every point but one when irbesartan was administered with nifedipine; however, no significant difference was observed between the two treatments in mean 24-hour AUC values. On day 4, there was a modest overall decrease from baseline in mean blood pressure for both treatments. No significant differences were observed between the two treatments in mean 24-hour AUC values for seated diastolic or systolic blood pressure. No serious adverse events were reported. Conclusions: Concomitant administration of nifedipine 30 mg with irbesartan 300 mg for 4 days in healthy subjects (1) does not alter the steady-state pharmacokinetic parameters of irbesartan, (2) results in Cmax and AUCtau values for irbesartan that meet the criteria for bioequivalence, and (3) is well tolerated.