bluuebunny/crossref_metadata_2025_split huggingface dataset:
van der Waals and hygroscopic forces of adhesion generated by spider capture threads
Authors: Hawthorn Anya C. , Opell Brent D. 
Published: October 2003

SUMMARYCribellar thread is the most primitive type of sticky prey capture thread found in aerial spider webs. Its outer surface is formed of thousands of fine fibrils that issue from a cribellum spinning field. The fibrils of primitive cribellar thread are cylindrical, whereas those of derived threads have nodes. Cribellar threads snag on insect setae but also adhere to smooth surfaces. A previous study showed empirically that cylindrical fibrils use only van der Waals forces to stick to smooth surfaces, as their stickiness is the same under different humidity. By contrast, noded fibrils are stickier under high humidity, where they are presumed to adsorb atmospheric water and implement hygroscopic (capillary) adhesion. Here, we model thread stickiness according to these two adhesive mechanisms. These models equate stickiness with the force necessary to overcome the adhesion of fibril contact points in a narrow band along each edge of the contact surface and to initiate peeling of the thread from the surface. Modeled and measured thread stickiness values are similar, supporting the operation of the hypothesized adhesive forces and portraying an important transition in the evolution of spider threads. Cribellar threads initially relied only on van der Waals forces to stick to smooth surfaces. The appearance of fibril nodes introduced hydrophilic sites that implemented hygroscopic force and increased thread stickiness under intermediate and high humidity.
Sensory innervation of the ovotestis in the snailHelix aspersa
Authors: Antkowiak Tomasz , Chase Ronald 
Published: October 2003

SUMMARYBecause oviposition in the land snail Helix aspersa is a metabolically expensive process coupled to a high fixed cost, one expects oviposition to occur only when the clutch size surpasses a minimum value at which the reproductive benefit exceeds the cost. We propose that neural innervation of the gonad allows H. aspersa to monitor oocyte production and ensure an adequate supply of gametes prior to ovulation. The ovotestis is innervated by a branch of the intestinal nerve in which the majority of axon fibres measure &lt;0.2 μm in diameter. We found a strong positive correlation between the number of mature oocytes in the ovotestis and the frequency of spontaneous afferent spikes in the nerve branch. Tactile stimulation of the ovotestis resulted in a 20-fold increase in afferent spikes and an efferent reflex directed towards the ovotestis and the pericardium. Afferent activity also increased 10-fold after an experimentally induced increase in the volume of the ovotestis. These results suggest that the growing oocytes expand the walls of the acini and trigger action potentials in the mechanosensitive nerve terminals that lie within the acinar walls. We hypothesize that the resulting tonic signal is permissive for ovulation. In addition, a phasic sensory signal may occur during ovulation to trigger CNS motor output related to oviposition.
Burrow surveillance in fiddler crabs I. Description of behaviour
Authors: Hemmi Jan M. , Zeil J. 
Published: October 2003

SUMMARYWhen defending resources, animals need to reliably detect and identify potential competitors. Animals that live at high population densities would be expected to be efficient in this aspect of resource defence since the time lost in false alarms could be substantial and the failure of identifying a competitor could be very costly. How does an animal decide whether another animal is or is not a threat to a resource or a territory?Fiddler crabs [Uca vomeris (McNeill)] operate from burrows that they guard and defend vigorously against other crabs. The crabs live in dense populations, with many animals inhabiting one square metre of mudflat. We describe here the behavioural responses of foraging crabs to repeated presentations of small crab-like dummies approaching their burrows. We explore the relationship between the probability and the timing of burrow defence responses, the crab's behavioural state, and the visual appearance and direction of approach of the dummies. We find that the probability of response of resident crabs is independent of the relative position of crab and dummy but is strongly affected by the dummy's position and movement direction relative to the crab's burrow. The critical stimuli are the dummy's distance from the crab's burrow and whether the dummy is moving towards the burrow or not. The response distance (dummy-burrow distance) increases with the crab's own distance from the burrow, indicating that the crabs modify their assessment of threat depending on their own distance away from the burrow. Differences in dummy size and brightness do not affect the probability or the timing of the response.We discuss these results in the context of fiddler crab social life and, in a companion paper, identify the visual and non-visual cues involved in burrow defence.
Slow death in the leopard frogRana pipiens: neurotransmitters and anoxia tolerance
Authors: Milton Sarah L. , Manuel Liscia , Lutz Peter L. 
Published: October 2003

SUMMARYWhile frogs such as Rana temporaria are known to withstand 4-5 h anoxia at room temperature, little is known about the neurological adaptations that permit this. Previous research has shown that changes in neuroactive compounds such as glutamate and dopamine in anoxia-sensitive (mammalian)brains follow a strikingly different pattern than is observed in truly anoxia-tolerant vertebrates such as the freshwater turtle. The present study measured changes in the levels of whole brain and extracellular amino acids,and extracellular dopamine, in the normoxic and 3-4 h anoxic frog Rana pipiens, in order to determine whether their neurotransmitter responses resemble the anoxia-vulnerable or anoxia-tolerant response. Increases in whole brain serine, glycine, alanine and GABA levels were similar to those seen in anoxia-tolerant species, although the levels of glutamine, taurine and glutamate did not increase as occurs in true facultative anaerobes. Extracellular levels of aspartate, taurine and GABA also increased significantly, while glutamate levels decreased. The maintenance of low extracellular glutamate was the most significant difference between the frog and the anoxic/ischemic mammalian brain, although aspartate did increase 215%over a 4 h period of anoxia. A 12-fold increase in extracellular dopamine levels during anoxia was the biggest contrast between anoxia-tolerant vertebrates and R. pipiens. The frog could thus be an interesting model in which to examine the mechanisms of dopamine failure in early anoxia,which occurs rapidly in the mammal but over a period of hours in the `slow death' of the anoxic frog brain.
Waved albatrosses can navigate with strong magnets attached to their head
Authors: Mouritsen Henrik , Huyvaert Kathryn P. , Frost Barrie J. , Anderson David J. 
Published: October 2003

SUMMARYThe foraging excursions of waved albatrosses Phoebastria irrorataduring incubation are ideally suited for navigational studies because they navigate between their Galápagos breeding site and one specific foraging site in the upwelling zone of Peru along highly predictable,straight-line routes. We used satellite telemetry to follow free-flying albatrosses after manipulating magnetic orientation cues by attaching magnets to strategic places on the birds' heads. All experimental, sham-manipulated and control birds, were able to navigate back and forth from Galápagos to their normal foraging sites at the Peruvian coast over 1000 km away. Birds subjected to the three treatments did not differ in the routes flown or in the duration and speed of the trips. The interpretations and implications of this result depend on which of the current suggested magnetic sensory mechanisms is actually being used by the birds.
Energy metabolism and valve closure behaviour in the Asian clamCorbicula fluminea
Authors: Ortmann Christian , Grieshaber Manfred K. 
Published: October 2003

SUMMARYSince its invasion of Europe in the early 1980s, the Asian clam Corbicula fluminea has become very abundant in nearly all western river systems. Today this species is one of the most important biomass producers in the River Rhine. Monitoring the valve movements of C. fluminea over a period of 2 years revealed a circadian rhythm in summer,with extended periods (10-12 h) of valve closure, predominantly in the morning hours. Altogether valve movements were very scarce, frequently fewer than four movements per individual per day.Simultaneous measurements of heat dissipation and oxygen consumption(calorespirometry) revealed an intermittent metabolism in the clam. With the onset of valve closure, C. fluminea reduced its metabolic rate to 10%of the standard metabolic rate (SMR) measured when the valves were open. Nevertheless, this depressed metabolism remained aerobic for several hours,enabling the clam to save energy and substrates compared to the requirements of the tenfold higher SMR. Only during long-lasting periods of valve closure(more than 5-10 h) did the clams become anaerobic and accumulate succinate within their tissues (2 μmol g-1 fresh mass). Succinate is transported into the mantle cavity fluid, where it reaches concentrations of 4-6 mmol l-1. Because this succinate-enriched fluid must pass the gills when the valves open again, we suggest that this anaerobic end product is at least partly reabsorbed, thus reducing the loss of valuable substrates during anaerobiosis. Propionate was also produced, but only during experimental N2-incubation, under near-anoxic conditions.The intermittent metabolism of C. fluminea is discussed as an adaption to efficiently exploit the rare food supply, saving substrates by the pronounced metabolic depression during valve closure.
Sol‐Gel‐Derived Sb‐Doped SnO2 Nanoparticles Controlled in Size by Nb2O5
Authors: Zhu X. , Geis‐Gerstorfer J. 
Published: October 2003

AbstractNanocrystalline Sb‐doped SnO2 particles were prepared by sol‐gel and their particle growth was controlled by niobium oxide. In the present synthesis, SnCl4 and SbCl3, as precursors, were dissolved and hydrolyzed in ethylene glycol at 80–120 °C, and further 0.1 mol.‐% Nb2O5 through its precursor NbCl5 was mixed to the above solution. The mixture was then dried at 120–150 °C and calcinated at 600 °C for 2 hours. By XRD and TEM, Sb‐doped SnO2 nanoparticles were highly crystalline and their mean crystal size was ca.10–20 nm with narrow particle size distribution. As the addition of antimony increased, the crystallinity and particle size distribution of SnO2 particles had the trend to decrease.
Disorder‐induced heating of ultracold plasmas
Authors: Gericke D.O. , Murillo M.S. 
Published: October 2003

AbstractWe report calculations for the disorder‐induced heating of the ions in ultracold plasmas that were created by ionization of ultracold, trapped gases. Since the ions gain a large amount of kinetic energy while building up negative potential energy, plasmas are usually heated to a moderately coupled state that is almost independent of the initial temperature. We show how this process is related to the establishment of Coulomb structure in the final plasma state. Several possibilities for reducing the heating by the introduction of structure in the initial state, i.e., the gas before ionization, are then discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of partial hepatectomy on in vivo engraftment after intravenous administration of human adipose tissue stromal cells in mouse
Authors: Kim Dong Heon , Je Chang Min , Sin Jin Yong , Jung Jin Sup 
Published: October 2003

AbstractTheir multidifferentiation potential makes human mesenchymal stem cells (hMSCs) candidates for cell‐based therapeutic strategies for tissue injuries and for hematopoietic disorders by both local and systemic application. Despite their potential clinical utility in cellular and gene therapy, the fate of adipose stromal cells (ATSCs) after systemic administration is mostly unknown. In this study, we investigated the distribution of ATSCs injected intravenously and the effect of partial hepatectomy on their distribution. Adipose tissue stromal cells (hATSCs) were obtained from adipose tissues of adult human donors. Under appropriate culture conditions, hATSCs were induced to differentiate into osteocytes and adipocyte lineages. The hATSCs were marked by infection with the lacZ‐adeno virus, and the distribution of injected cells was examined by X‐Gal staining. Immunosuppression was achieved by the administration of cyclosporin into mice. The hATSCs were engrafted onto various tissues, including brain, thymus, heart, liver, and lung, after intravenous administration. Liver regeneration induced by partial hepatectomy enhanced the integration of hATCSCs into the liver. These results demonstrate that hATSCs have the ability to proliferate extensively in culture, and that they maintain their multilineage differentiation potential in vitro, establishing their progenitor cell nature. These cells are promising candidates for developing novel cell‐based therapeutic approaches to postnatal tissue repair. © 2003 Wiley‐Liss, Inc. MICROSURGERY 23:424–431 2003
Nanoscale structure–property relationships in conjugated polymers: Implications for present and future device applications
Authors: Winokur M. J. , Chunwachirasiri W. 
Published: October 2003

AbstractThe most prevalent molecular level structures and structure–property relationships for three basic classes of conjugated polymers are summarized. This discussion encompasses linear unsubstituted conducting polymers and those containing linear side‐chain and branched side‐chain substituents. The impact of these structural attributes on charge transport and photophysics is emphasized. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2630–2648, 2003
Imprecise color constancy versus color realism
Authors: Funt Brian V. 
Published: October 2003

AbstractByrne & Hilbert's thesis, that color be associated with reflectance-type, is questioned on the grounds that it is far from clear that the human visual system is able to determine a surface's reflectance-type with sufficient accuracy. In addition, a (friendly) suggestion is made as to how to amend the definition of reflectance-type in terms of CIE (Commission Internationale de l'Eclairage) coordinates under a canonical illuminant.
Dynamic Force Properties of Soleus, And Sensorimotor Interactions of Soleus, Medial Gastrocnemius, and Tibialis Anterior in the Freely Moving Cat
Authors: Herzog W. , Leonard T. R. 
Published: October 2003

The dynamic properties of the cat soleus muscle were studied in freely walking animal preparations. The force and EMG responses of the soleus following supramaximal, ins tants of the step cycle. The sensorimotor interactions of soleus with the medial head of the gastrocnemius (a functional agonist of the soleus at the ankle) and the tibialis anterior (a functional antagonist of soleus at the ankle) were studied by measuring their force and EMG responses following the artifical stimulation of the soleus nerve. Supramaximal nerve stimulation showed distinct increases in the soleus forces during the entire swing phase and the second part (after peak forces had been reached) of the stance phase. Soleus forces could only be increased slightly in the first part of stance (from paw contact to peak force). These results suggest that force production of the soleus is virtually maximal during the early phases of stance but is submaximal for the remainder of the step cycle. Forces and EMGs of the medial gastrocnemius muscle were affected by the soleus nerve stimulation only in the latter part of the swing phase. In these cases, the force and EMG of the medial gastrocnemius were reduced significantly for the step cycle following the perturbation. The active force production of soleus during late swing causes an inhibition of medial gastrocnemius activity and force. Forces and EMGs of the tibialis anterior muscle were always affected by the soleus nerve stimulation during the swing phase of the step cycle. In these case, the force EMG of the medial gastrocnemius were reduced significantly for the step cycle following the perturbation. The active force production of soleus during late swing causes an inhibition of medial gastrocnemius activity and force. Forces and EMGs of the tibialis anterior muscle were always affected by the soleus nerve stimulation during the swing phase of the step cycle. In these instances, forces and EMGs of the tibialis anterior were significantly increased compared to step cycles preceding or following the perturbation. Part of the force enhancement is caused by the stretch of the activated tibialis anterior by the soleus, and part of the enhancement is caused by reflex activation. No effects on forces or EMGs of the tibialis anterior were observed when the soleus nerve stimulation showed its effects during the stance phase of the step cycle. The results of theis study suggest that the magnitude and the quality of ensorimotor interactions of soleus with medial gastrocnemius and tibialis anterior depend on the phase of the step cycle. The strongest interactions appear to exist during the swing phase; no observable interactions were found during stance.
Analysis ofmyostatingene structure, expression and function in zebrafish
Authors: Xu Cheng , Wu Gang , Zohar Yonathan , Du Shao-Jun 
Published: October 2003

SUMMARYMyostatin is a member of the TGF-β family that functions as a negative regulator of skeletal muscle development and growth in mammals. Recently,Myostatin has also been identified in fish; however, its role in fish muscle development and growth remains unknown. We have reported here the isolation and characterization of myostatin genomic gene from zebrafish and analysis of its expression in zebrafish embryos, larvae and adult skeletal muscles. Our data showed that myostatin was weakly expressed in early stage zebrafish embryos, and strongly expressed in swimming larvae, juvenile and skeletal muscles of adult zebrafish. Transient expression analysis revealed that the 1.2 kb zebrafish myostatin 5′ flanking sequence could direct green fluorescent protein (GFP) expression predominantly in muscle cells, suggesting that the myostatin 5′ flanking sequence contained regulatory elements required for muscle expression. To determine the biological function of Myostatin in fish, we generated a transgenic line that overexpresses the Myostatin prodomain in zebrafish skeletal muscles using a muscle-specific promoter. The Myostatin prodomain could act as a dominant negative and inhibit Myostatin function in skeletal muscles. Transgenic zebrafish expressing the Myostatin prodomain exhibited no significant change in myogenic gene expression and differentiation of slow and fast muscle cells at their embryonic stage. The transgenic fish, however,exhibited an increased number of myofibers in skeletal muscles, but no significant difference in fiber size. Together, these data demonstrate that Myostatin plays an inhibitory role in hyperplastic muscle growth in zebrafish.
Structure and Reactivity of Ziegler–Natta Catalyst Intermediates
Authors: Sobota Piotr 
Published: October 2003

AbstractThis paper provides a survey of our recent research on chemistry that occurs among components of Ziegler–Natta catalysts. Since the amount of information regarding this topic is enormous we have focused on alkoxo compounds, which are attracting more and more attention in polymer industry. In this concept article we discuss recent studies on the inherently very complex catalyst system that involve isolation of various solid polynuclear metal‐containing species, determination of their structures by X‐ray crystallography, and relating their structures to the activity in polymerization. The presented research may be useful in predicting trends for the development of new single‐site catalysts as well as new co‐catalysts.
Transition‐Metal Complexes as Enzyme‐Like Reagents for Protein Cleavage: Complexcis‐[Pt(en)(H2O)2]2+as a New Methionine‐Specific Protease
Authors: Milović Nebojša M. , Dutcǎ Laura‐M. , Kostić Nenad M. 
Published: October 2003

AbstractComplexcis‐[Pt(en)(H2O)2]2+promotes selective hydrolytic cleavage of two proteins, horse cytochromecand bovineβ‐casein. The cleavage is completed in 24 h under relatively mild conditions, at about pH 2.5, and a temperature as low as 40 °C. The results of HPLC and TSDS PAGE separations, MALDI mass spectrometry, and Edman sequencing showed that cleavage occurred exclusively at the peptide bond involving the C‐terminus of each methionine residue, both such residues in cytochromecand all six such residues inβ‐casein. While having the same selectivity as cyanogen bromide (CNBr), the most common chemical protease,cis‐[Pt(en)(H2O)2]2+has several advantages. It is nonvolatile, easy to handle, and recyclable. Its cleavage is residue‐selective, the rest of the polypeptide backbone remains intact, and the other side chains remain unmodified. It is applied in approximately equimolar amounts with respect to methionine residues, creates free amino and carboxylic groups, and cleaves even the MetPro bond, which is resistant to CNBr and most proteolytic enzymes. Finally the complex also works in the presence of the denaturing reagent sodium dodecyl sulfate. Experiments with the synthetic peptides, AcAla‐Lys‐Tyr‐Gly‐Gly‐Met‐Ala‐Ala‐Arg‐Ala (termed Met‐peptide) and AcVal‐Lys‐Gly‐Gly‐His‐Ala‐Lys‐Tyr‐Gly‐Gly‐Met‐Ala‐Ala‐Arg‐Ala (termed HisMet‐peptide) as substrates, revealed structural and mechanistic features of the proteolytic reactions. We explain why two similar complexes with similar metal ions,cis‐[Pt(en)(H2O)2]2+andcis‐[Pd(en)(H2O)2]2+, differ in selectivity as proteolytic reagents. The selectivity of cleavage is governed by the selectivity of thecis‐[Pt(en)(H2O)2]2+binding to the methionine side chain. The proteolytic activity is governed by the modes of coordination, which control the approach of the anchored PtIIion to the scissile peptide bond. The cleavage occurs with a small, but significant, catalytic turnover of more than 18 after 7 days. The ability ofcis‐[Pt(en)(H2O)2]2+to cleave proteins at relatively few sites, with explicable selectivity and catalytic turnover, bodes well for its use in biochemical practice.
Relaxation of a quantum many‐body system from a correlated initial state. A general and consistent approach
Authors: Semkat D. , Bonitz M. , Kremp D. 
Published: October 2003

AbstractVarious approaches to a theoretical treatment of the dynamics of quantum many‐body systems starting from a correlated initial state are discussed. In particular, we compare the concept of the BBGKY–hierarchy (singletime reduced density operators) and that of nonequilibrium Green's functions (two‐time correlation functions). Conditions for physically meaningful initial correlations are established. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)