bluuebunny/crossref_metadata_2025_split huggingface dataset:
Force development, energy state and ATP production of cardiac muscle from turtles and trout during normoxia and severe hypoxia
Authors: Overgaard Johannes , Gesser Hans 
Published: April 2004

SUMMARYThe effects of hypoxia on energy economy of cardiac muscle were compared between the hypoxia-tolerant freshwater turtle at 20°C and the hypoxia-sensitive rainbow trout at 15°C. Isolated ventricular preparations were left either at rest or stimulated at 30 min-1 to develop isometric twitch force. Under oxygenated conditions, twitch force and oxygen consumption were similar for the two species. Overall metabolism was reduced during severe hypoxia in both resting and stimulated preparations and under these conditions most of the ATP production was derived from anaerobic metabolism. During hypoxia, a metabolic depression of approximately 2/3 occurred for non-contractile processes in both turtle and trout preparations. During hypoxia, lactate production and residual oxygen consumption were similar in turtle and trout. Cellular energy state and phosphorylation potential decreased during severe hypoxia in both species and this reduction was more severe in preparations stimulated to contraction. However, in turtle ventricular preparations the energy state and phosphorylation potential stabilised at higher levels than in trout, and turtle preparations also maintained a higher twitch force throughout the hypoxic period. Moreover,twitch force relative to total ATP hydrolysis was markedly increased during hypoxia in turtle while this ratio was unchanged for trout. The main findings of this study are: (1) cellular energy liberation and the energy demand of non-contractile processes decreased to similar levels in hypoxic turtle and trout myocardium; (2) turtle myocardium maintained a substantially higher cellular energy state and twitch force development than trout myocardium during hypoxia and (3) the ratio of twitch force to ATP hydrolysis increased during hypoxia in turtle but was unchanged in trout. It is possible that this superior economy of the contracting turtle myocardium contributes to the remarkable hypoxia tolerance of freshwater turtles.
Swimming gaits, passive drag and buoyancy of diving sperm whalesPhyseter macrocephalus
Authors: Miller Patrick J. O. , Johnson Mark P. , Tyack Peter L. , Terray Eugene A. 
Published: April 2004

SUMMARYDrag and buoyancy are two primary external forces acting on diving marine mammals. The strength of these forces modulates the energetic cost of movement and may influence swimming style (gait). Here we use a high-resolution digital tag to record depth, 3-D orientation, and sounds heard and produced by 23 deep-diving sperm whales in the Ligurian Sea and Gulf of Mexico. Periods of active thrusting versus gliding were identified through analysis of oscillations measured by a 3-axis accelerometer. Accelerations during 382 ascent glides of five whales (which made two or more steep ascents and for which we obtained a measurement of length) were strongly affected by depth and speed at Reynold's numbers of 1.4–2.8×107. The accelerations fit a model of drag, air buoyancy and tissue buoyancy forces with an r2 of 99.1–99.8% for each whale. The model provided estimates (mean ± s.d.) of the drag coefficient(0.00306±0.00015), air carried from the surface (26.4±3.9 l kg-3 mass), and tissue density (1030±0.8 kg m-3)of these five animals. The model predicts strong positive buoyancy forces in the top 100 m of the water column, decreasing to near neutral buoyancy at 250–850 m. Mean descent speeds (1.45±0.19 m s-1) were slower than ascent speeds (1.63±0.22 m s-1), even though sperm whales stroked steadily (glides 5.3±6.3%) throughout descents and employed predominantly stroke-and-glide swimming (glides 37.7±16.4%)during ascents. Whales glided more during portions of dives when buoyancy aided their movement, and whales that glided more during ascent glided less during descent (and vice versa), supporting the hypothesis that buoyancy influences behavioural swimming decisions. One whale rested at∼10 m depth for more than 10 min without fluking, regulating its buoyancy by releasing air bubbles.
Dynamics of pectoral fin rowing in a fish with an extreme rowing stroke:the threespine stickleback (Gasterosteus aculeatus)
Authors: Walker Jeffrey A. 
Published: April 2004

SUMMARYThe dynamics of pectoral fin rowing in the threespine stickleback are investigated by measuring the instantaneous force balance on freely swimming fish throughout the stroke cycle and comparing the measured forces with fin motions and an unsteady, blade-element model of pectoral fin propulsion. Both measured and modeled forces suggest that attached vortex and circulatory forces and not inertial (added mass) forces dominate the force balance. Peak forces occur at midstrokes. There is no evidence for large force peaks at the stroke transitions due to either rapid fin rotation (supination) or rapid fin closure against the body. The energetics of pectoral fin rowing are estimated using the unsteady blade-element model and an indirect method based on the center of mass dynamics. The results indicate that the mechanical efficiency of pectoral fin rowing is low (0.1–0.3) relative to a flapping mechanism and possibly relative to axial undulation at comparable speeds.
Quantitative structure–activity relationships (QSARs) as a tool for predicting the sorption of organic chemicals in soils
Authors: Gerstl Zev 
Published: April 2004

AbstractThe use of quantitative structure‐activity relationships (QSARs) based on linear free‐energy relationships (LFERs), molecular connectivity (MC) indices, and on more sophisticated quantum mechanical approaches, for predicting soil sorption coefficients is reviewed. The nature and energetics of sorption of organic chemicals by soils are also briefly reviewed.On the basis of the data presented we may conclude that from the large body of physicochemical parameters, the n‐octanol/water partition coefficient (Kow) has been most successful in modeling sorption data of organic chemicals. From the large set of nonempirical parameters that are defined in terms of a compound's 2‐ or 3‐dimensional structure and can be derived for any chemical without experimental efforts, the MC indices have proven the most reliable and easily available.
Diffusion Parameters of the Extracellular Space
Authors: Syková Eva 
Published: April 2004

AbstractExtrasynaptic communication between neurons or neurons and glia is mediated by the diffusion of neuroactive substances in the extracellular space (ECS). Diffusion in the central nervous system (CNS) is inhomogeneous and often anisotropic. Changes in ECS volume and geometry accompany physiological neuronal activity, development, lactation, stimulation, and aging, as well as pathological states, e.g., anoxia/ischemia, seizures, injury, demyelination, and tumors. Ionic changes and amino acid release result in cellular swelling, compensated for by ECS shrinkage and a decrease in the apparent diffusion coefficients of neuroactive substances or water (ADCW) as determined by diffusion analysis using the real‐time iontophoretic tetramethylammonium (TMA+) method or diffusion‐weighted NMR. The diffusion parameters of the CNS in adult mammals (including humans), ECS volume fraction α (α = ECS volume/total tissue volume) 0.20–0.25 and tortuosity 1.5‐1.6, hinder the diffusion of neuroactive substances and water. A significant decrease in ECS volume (to 0.16) and an increase in diffusion barriers (tortuosity), accompanied by learning deficits, occur in aging CNS, accompanied by astrogliosis, rearrangement of astrocytic processes, and a loss of extracellular matrix. Decreases in ADCTMA and ADCW due to astrogliosis and increased proteoglycan expression were found after brain injury and in grafts of embryonic tissue. Tenascin‐R‐deficient mice also revealed significant changes in ADCTMA and ADCW. Plastic changes in ECS volume, tortuosity, and anisotropy significantly affect neuron–glia communication, the spatial relation of glial processes towards synapses, glutamate or GABA “spillover”, and synaptic cross‐talk. The various changes occur during pathological states and, as such, can be important for diagnosis, drug delivery, and treatment.
Some “Reflections” on the Effects of Finite Gradient Pulse Lengths in PGSE NMR Experiments in Restricted Systems
Authors: Price William S. , Söderman Olle 
Published: April 2004

AbstractIt is generally difficult to analytically derive models describing the echo attenuation in pulsed gradient spin‐echo (PGSE) experiments for even the simplest porous systems that are commonly studied—especially when the gradient pulse (δ) is of finite length compared to the timescale of the diffusion measurement (Δ). Consequently, various levels of approximation are used to evaluate PGSE experiments. In the present paper, a conceptual view ofq‐space is given and two of the most common approximations, the short gradient pulse (SGP) and Gaussian phase distribution (GPD) approximations, are compared in detail with a recent matrix method, which provides “analytically” exact results giving a visual representation of the limitations of these approximations. The simulations are performed for diffusion between a pair of reflecting planes separated by a distancea.A modification that is sometimes applied to the short gradient pulse approximation in attempting to extend it to finite gradient pulses is also compared. The simulations reveal that, except when the experimental conditions closely match the requirements of the SGP and GPD simulations, the matrix method must be used in order to correctly interpret the data.
Effect of oxic state on nonpolar organic contaminant distribution, mobility, and bioavailability in estuarine sediments
Authors: Pedersen Joel A. , Schweitzer Linda E. , Lin Chen‐Hung Michael , Suffet I.H.(Mel) 
Published: April 2004

AbstractDissolved and particle‐associated natural organic matter plays an important role in nonpolar organic chemical distribution, mobility, and bio‐availability in sediment environments. We investigated the influence of oxic state on the association of a model hydrophobic organic chemical (HOC), 2,2',4,4'‐tetrachlorobiphenyl (TeCB), with dissolved and particle‐associated organic matter in estuarine sediments. Site‐specific distribution data were used to model the effect of oxic state on diffusive flux of TeCB across the sediment‐water interface. Additional experiments examined the role of oxic state in TeCB bioavailability to a deposit‐feeding epibenthic echinoderm.Aeration of estuarine sediment pore waters induced a negligible change to greater than an order of magnitude decrease in the dissolved organic carbon (DOC)–water distribution coefficient, Kpwdoc, in all but one system examined. Correspondingly, oxidation of sediment solids effected a negligible to 0.5 log unit decrease in the particle associated organic carbon‐water distribution coefficient, Koc. These results indicate that aeration of anoxic estuarine sediments induced by dredging, bioturbation, or storm events may result in release of HOCs from particle‐associated and dissolved organic matter, increasing the concentration of the truly dissolved compound.Model simulations indicated that oxygenation of anoxic sediments would result in a 34–100% increase in TeCB diffusive flux. Pore water dissolved organic matter (DOM)facilitated TeCB transport across the sediment‐water interface and increased diffusive flux by up to a factor of 1.7. A sensitivity analysis indicated that facilitation of diffusive transport by DOM would be significant in the systems under investigation when log Kpwdoc exceeded approximately 5.7. Therefore, disturbing anoxic sediments can mobilize HOCs. In bioaccumulation assays using sea urchins, TeCB bioavailability temporarily increased after anoxic sediments were disturbed and aerated, but long‐term bioavailability remained unaltered when sediment reduction potential returned to the level of the unaerated control.
Microprobe laser mass spectrometry studies of polycyclic aromatic hydrocarbon distributions on harbor sediments and coals
Authors: Seb Gillette J. , Ghosh Upal , Mahajan Tania B. , Zare Richard N. , Luthy Richard G. 
Published: April 2004

AbstractMicroprobe two‐step laser mass spectrometry (μL2MS) was used to assess the distribution and origin of polycyclic aromatic hydrocarbons (PAHs) on sediment particles dredged from the harbor of Milwaukee, Wisconsin. PAH concentrations are largely associated with coal‐derived particles and other carbonaceous environments. PAH distributions on these coal‐derived particles and carbonaceous environments, which are thought to have separate origins, were found to be quite similar. μL2MS data of coal and thermally‐processed coal showed profound differences from μL2MS data obtained from the coal‐derived particles in the sediment. The results of these experiments indicate that the coal‐derived particles are not the source of PAHs in the sediment but are scavengers of PAH contaminants in the Milwaukee Harbor sediments.
Targeting of phosphonoacetate to the liver: Synthesis of a phosphonoacetate—trilactoside conjugate
Authors: Bhat Shridhar , Vaino Andrew R. , Szarek Walter A. 
Published: April 2004

AbstractAs part of continuing studies on drug delivery to the human liver, a phosphonoacetate—trilactoside conjugate (12) has been synthesized in an overall yield of 23%. The shortness of the synthesis of this conjugate hinges upon a successful Michaelis—Arbuzov reaction of bromoacetamide 8 with tris‐(trimethylsilyl) phosphite.
Design and preparation of polyphenyl distance markers for solid‐state 19F NMR
Authors: Monde Kenji , Tomita York , Gilchrist M. Lane , McDermott Ann E. , Nakanishi Koji 
Published: April 2004

AbstractWith 13C‐labeled samples, it is possible to measure internuclear distances up to 7 Å by solid‐state NMR, thus providing a powerful tool for probing ligand—receptor interactions. However, limitations in measurable distances and appreciable natural abundant 13C background signals present problems in solid‐state 13C NMR. In order to overcome these disadvantages, a set of reference compounds with known F—F distances, namely, quinolinol, p‐biphenyl, and p‐terphenyl‐bearing trifluoromethyl and trifluoromethylthio groups, have been synthesized. The preparation of these reference compounds and means for diluting these references in solid‐state NMR are described.
Quantum simulations of vibrational dephasing of molecules in a cryogenic environment: HArF in an argon cluster
Authors: Jungwirth Pavel , Gerber R. Benny , Ratner Mark A. 
Published: April 2004

AbstractThe Classical Separable Potential (CSP) method, which is a meanfield approximation to multidimensional quantum dynamics, is applied to the dephasing process of a vibrationally excited HArF molecule in an argon cluster at low temperatures. Dephasing timescales of the order of 1 ps are estimated for dynamics following fundamental excitation of either the H–Ar or the Ar–F stretching mode of HArF. The CSP approach is valid over such timescales, and it is thus a viable approach to quantum simulations of dephasing at low temperatures. Vibrational relaxation is much slower: Quasi‐classical molecular dynamics simulations yield a relaxation time around 100 ps for the initial v = 1 Ar–F stretching excitation. Such timescales are beyond the validity range of CSP; therefore, this or similar separable methods are inapplicable for vibrational energy decay.
NMR Studies of Diffusion‐Coherence Phenomena in Red Cell Suspensions: Current Status
Authors: Regan David G. , Kuchel Philip W. 
Published: April 2004

AbstractPulsed field‐gradient spin‐echo (PGSE) nuclear magnetic resonance (NMR) diffusion experiments conducted on some heterogeneous systems have been observed to show periodicities in the data. These “coherence patterns” are manifest in the normalized PGSE signal intensities as a function of the spatial wave vector q in so‐called q‐space plots. The sample that to our knowledge best reveals these coherence patterns is suspensions of red blood cells (RBC). The origin of these patterns and their mathematical and physical underpinnings are now well established. We have used computer simulations of molecular diffusion in lattices of RBC and other cells to aid in the interpretation and analysis of the corresponding experimental data. The aim of this review is to present the current status of NMR q‐space studies of RBC suspensions that show the diffusion‐coherence effect.
Cadmium (zinc) manganese sulfide nanocrystalline (Cd1‐xMnxS and Zn1‐xMnxS) dilute magnetic semiconductors. synthesis, annealing, and effects of surface oxidation on magnetic properties
Authors: Dang Qianyu , Wen Genwang , Sorensen Christopher M. , Klabunde Kenneth J. 
Published: April 2004

AbstractCd1‐xMnxS and Zn1‐xMnxS dilute magnetic semiconductor nanocrystals were prepared in aqueous and non‐aqueous solutions by simple precipitation methods with x values ranging from 0.1 to 0.5. X‐ray powder diffraction showed the asprepared sample crystal sizes were about 2–3 nm with zinc blende cubic structure. After thermal annealing, the crystals converted to the hexagonal wurzite structure as the crystallite size reached 100–120 nm. The manganese ions on the surface were very easily oxidized in the air and were the cause of an antiferromagnetic transition at near 37 K.
Family of thiomercuric derivatives of sugars: Synthesis, fungicidal/herbicidal activity, and application to the X‐ray structure determination of the corresponding enzymes
Authors: Belakhov Valery , Dor Evgenia , Hershenhorn Joseph , Botoshansky Mark , Bravman Tsafrir , Kolog Mirit , Shoham Yuval , Shoham Gil , Baasov Timor 
Published: April 2004

AbstractA series of thiomercuric derivatives of mono‐ and disaccharides 1–7, in which methylmercury or phenylmercury is covalently attached to anomeric thioglycosides, were synthesized for structure—function studies of glycosidases. Thiomethylmercuryl xylobiosides 5 and 6 were found to inhibit intracellular xylanase‐T6 in a competitive manner, with Ki values of 0.35 mM and 0.01 mM, respectively. These inhibitors have been co‐crystallized with the enzyme and are being used for X‐ray analysis. 1‐(Thiomethylmercuric)‐ß‐D‐xyloside (3) affords crystals belonging to the orthorhombic space group P212121 and at 293(2) K: a = 6.7510(2), b = 9.7140(2), c = 29.4770(9) Å, V = 1933.08(9) Å, Z = 8, R(F2) = 0.0329, and Rw(F2) = 0.0626. There are two molecules (A and B) in the asymmetric unit, and each one shows an almost linear S–Hg–C arrangement. Biological tests on 1–7 indicated that they exhibit potent fungicidal and herbicidal activities.
Description and importance of interchain excited states in conjugated polymer photophysics
Authors: Jakubiak Rachel , Yan Ming , Wan Wai Chou , Hsieh Bing R. , Rothberg Lewis J. 
Published: April 2004

AbstractWe compare the photoluminescence (PL) of poly‐p‐phenyl‐enevinylene (PPV) to that of one of its soluble derivatives, poly (2‐methoxy, 5‐(21‐ethylhexoxy)‐p‐phenylenevinylene) (MEH‐PPV). We show that excimers due to π‐orbital overlap of adjacent polymer backbones are formed in MEH‐PPV in high quantum yield. They do not emit light at room temperature, potentially explaining the reduction of PL yield in MEH‐PPV films relative to solution. The herringbone packing of polymer chains in PPV prevents π‐π stacking, but low PL yields are observed anyway. We conclude that polymer design to inhibit interchain registration is a questionable strategy to increase luminescence yields. The low PL yield in PPV is ascribed to bound polaron pair formation and preliminary data suggest that these may also form upon photoexcitation of MEH‐PPV films.
Sonochemical synthesis of crystalline nanoporous zinc oxide spheres and their application in dye‐sensitized solar cells
Authors: Chen Siguang , Kumar Rangari Vijaya , Gedanken Aharon , Zaban Arie 
Published: April 2004

AbstractA composite material made of zinc oxide and polyvinyl alcohol was prepared by a sonochemical method. Annealing of the composite under air removed the polymer, leaving porous spheres of ZnO. This change was accompanied by a change of the surface area from 2 m2/g to 34 m2/g. The porous ZnO particles were used as the electrode material for dye‐sensitized solar cells (DSSCs). It was tested by forming a film of the doped porous ZnO on a conductive glass support. The performance of the solar cell is reported.
Application of time‐dependent density‐functional theory to electron—ion coupling in ethylene
Authors: Bertsch George F. , Giansiracusa Jeffrey , Yabana Kazuhiro 
Published: April 2004

AbstractTo examine the applicability of the time‐dependent density‐functional theory (TDDFT) for treating the electron–nucleus coupling in excited states, we calculate the strength distribution associated with the π–π* transition in ethylene. The observed optical transition strength in the 7–8.5 eV region shows a complex structure arising from coupling to C–C stretch motion, to torsional motion, and to Rydberg excitations. The mean energy of the observed peak is reproduced to about 0.2 eV accuracy by the TDDFT in the local density approximation (LDA). The reflection approximation is used to calculate the peak broadening. Roughly half of the broadening can be attributed to the fluctuation in the C–C coordinate. The asymmetry in the line shape is also qualitatively reproduced by the C–C coordinate fluctuation. We find, in agreement with other theoretical studies, that the torsional motion is responsible for the progression of weak transition strength extending from the peak down to about 6 eV. The LDA reproduces the strength in this region to a factor of about 3. We conclude that the TDDFT is rather promising for calculating the electron–nucleus coupling at short times.
Synthesis and structural studies of “branched” 2‐linked trisaccharides related to h‐type 2 blood group determinants
Authors: Duus Jens Ø. , Nifant'ev Nikolay E. , Shashkov Alexander S. , Khatuntseva Elena A. , Bock Klaus 
Published: April 2004

AbstractA series of fucosylated trisaccharides l‐Fuc‐(1→2)‐ß‐d‐Gal‐(1→4)‐ß‐X‐OMe (1‐6, X = d‐GlcNAc, d‐Qui (6‐deoxy‐Glc), d‐Xyl) related to H type 2 blood group determinant have been synthesized both as their α‐ and ß‐ L‐Fuc anomers together with the component disaccharide starting compounds (7‐11). The conformational properties of the trisaccharides together with their parent disaccharides have been investigated by NMR spectroscopy (proton and carbon chemical shifts and proton NOEs) in combination with computer modeling using the Monte Carlo approach and the HSEA force field using the GEGOP program with the main focus on the α‐linked fucose series.The series of compounds allow for the investigation of interaction between the sugar units in the—in principle—linear structures, which in practice behave as branched trisaccharides.The interaction between the terminal fucose unit and the unit at the reducing end has been probed by substitution of the bulky CH2OH group with CH3 and H substituents, respectively. Compounds with severe steric interactions can be identified by the non‐additivity of their carbon chemical shifts and subsequently confirmed by the detailed conformational assessment by NOEs and computer modeling. The most severe contacts arise in the GlcNAc and Qui trisaccharide series, whereas the Xyl‐containing trisaccharide derivatives only exhibit weak steric interaction as probed by the NMR parameters.