bluuebunny/crossref_metadata_2025 huggingface dataset:
Action Potential-Evoked and Ryanodine-Sensitive Spontaneous Ca2+Transients at the Presynaptic Terminal of a Developing CNS Inhibitory Synapse
Authors: Conti Rossella , Tan Yusuf P. , Llano Isabel
Published: August 2004

The existence of spontaneous calcium transients (SCaTs) dependent on intracellular store activation has been reported in putative axonal terminals of cerebellar basket interneurons. We used the two-photon imaging technique to optically identify basket terminals in acute cerebellar slices of young rats (11-16 d old) and study the properties of SCaTs unambiguously localized in these regions. The whole-cell recording configuration and preloading technique were alternatively used to load the calcium-dependent dye in the interneuron and compare SCaTs with action potential evoked calcium transients. SCaTs were observed in the basket terminals at frequencies that were significantly increased after bath application of 10 μmryanodine and did not depend on P/Q- or N-type voltage-dependent calcium channel activation. They originated at specific sites where bursts of events with temporal separation as small as 200 msec could be generated. Their sites of origin were spaced on average 6 μm apart and were preferentially located near axonal endings. SCaTs had amplitudes comparable with those of Ca2+rises evoked by single action potentials that lead to release of neurotransmitter, as confirmed by parallel recordings of preloaded terminals and evoked IPSCs in the postsynaptic Purkinje cells. These results support the hypothesis that SCaTs at basket terminals underlie the large miniature IPSCs characteristic of Purkinje cells.
Natural Stimulus Statistics Alter the Receptive Field Structure of V1 Neurons
Authors: David Stephen V. , Vinje William E. , Gallant Jack L.
Published: August 2004

Studies of the primary visual cortex (V1) have produced models that account for neuronal responses to synthetic stimuli such as sinusoidal gratings. Little is known about how these models generalize to activity during natural vision. We recorded neural responses in area V1 of awake macaques to a stimulus with natural spatiotemporal statistics and to a dynamic grating sequence stimulus. We fit nonlinear receptive field models using each of these data sets and compared how well they predicted time-varying responses to a novel natural visual stimulus. On average, the model fit using the natural stimulus predicted natural visual responses more than twice as accurately as the model fit to the synthetic stimulus. The natural vision model produced better predictions in >75% of the neurons studied. This large difference in predictive power suggests that natural spatiotemporal stimulus statistics activate nonlinear response properties in a different manner than the grating stimulus. To characterize this modulation, we compared the temporal and spatial response properties of the model fits. During natural stimulation, temporal responses often showed a stronger late inhibitory component, indicating an effect of nonlinear temporal summation during natural vision. In addition, spatial tuning underwent complex shifts, primarily in the inhibitory, rather than excitatory, elements of the response profile. These differences in late and spatially tuned inhibition accounted fully for the difference in predictive power between the two models. Both the spatial and temporal statistics of the natural stimulus contributed to the modulatory effects.
Coordinating Structural and Functional Synapse Development: Postsynaptic p21-Activated Kinase Independently Specifies Glutamate Receptor Abundance and Postsynaptic Morphology
Authors: Albin Stephanie D. , Davis Graeme W.
Published: August 2004

Here, we show that postsynaptic p21-activated kinase (Pak) signaling diverges into two genetically separable pathways at theDrosophilaneuromuscular junction. One pathway controls glutamate receptor abundance. Pak signaling within this pathway is specified by a required interaction with the adaptor protein Dreadlocks (Dock). We demonstrate that Dock is localized to the synapse via an Src homology 2-mediated protein interaction. Dock is not necessary for Pak localization but is necessary to restrict Pak signaling to control glutamate receptor abundance. A second genetically separable function of Pak kinase signaling controls muscle membrane specialization through the regulation of synaptic Discs-large. In this pathway, Dock is dispensable. We present a model in which divergent Pak signaling is able to coordinate two different features of postsynaptic maturation, receptor abundance, and muscle membrane specialization.
Altered Prelimbic Cortex Output during Cue-Elicited Drug Seeking
Authors: Miller Courtney A. , Marshall John F.
Published: August 2004

Cocaine treatment paired with environmental cues establishes a conditioned place preference (CPP) for that environment. After expression of this preference, rats show elevated levels of immediate early genes (IEGs; e.g. c-fos) in the prelimbic cortex (PrL), basolateral amygdala complex (BLC), and nucleus accumbens core (NAcc) compared with drug-unpaired controls. These findings, together with the known connections between these regions, suggest that they function as a circuit contributing to cue-elicited craving. To investigate the function of this circuit during drug-seeking, we characterized Fos immunoreactivity of particular neuron classes in each region. To distinguish between IEG activation of GABAergic and non-GABAergic (principally, excitatory projection) neurons, we combined Fos immunohistochemistry with immunohistochemistry for glutamic acid decarboxylase 67 (GAD67) or calcium/calmodulin-dependent protein kinase II (CAMKII) proteins. Within the BLC and NAcc of drug-paired and drug-unpaired animals tested for CPP, we observed no significant differences in the percentage of Fos-immunoreactive (IR) cells that were also GAD67-IR. We also observed no group difference in the degree of Fos/CAMKII overlap in the BLC. However, in PrL, the degree of Fos/GAD67overlap in the drug-paired group was significantly higher than in the drug-unpaired group. Also, the Fos/CAMKII overlap in the entire PrL as well as just its layer V was significantly lower in the drug-paired animals compared with controls. These findings suggest that, during CPP expression in cocaine-paired animals, the PrL GABAergic interneurons are preferentially activated while PrL output is attenuated, perhaps through greater inhibition of layer V pyramidal neurons. These results suggest a shifting prefrontal cortex cell population response during cocaine-seeking.
Opioid Receptors in the Midbrain Periaqueductal Gray Regulate Extinction of Pavlovian Fear Conditioning
Authors: McNally Gavan P. , Pigg Michael , Weidemann Gabrielle
Published: August 2004

Four experiments studied the role of opioid receptors in the midbrain periaqueductal gray matter (PAG), an important structure eliciting conditioned fear responses, in the extinction of Pavlovian fear. Rats received pairings of an auditory conditioned stimulus (CS) with a foot shock unconditioned stimulus (US). The freezing conditioned response (CR) elicited by the CS was then extinguished via nonreinforced presentations of the CS. Microinjection of the opioid receptor antagonist naloxone into the ventrolateral PAG (vlPAG) before nonrein-forced CS presentations impaired development of extinction, but such microinjections at the end of extinction did not reinstate an already extinguished freezing CR. This role for opioid receptors in fear extinction was specific to the vlPAG because infusions of naloxone into the dorsal PAG did not impair fear extinction. Finally, the impairment of fear extinction produced by vlPAG infusions of naloxone was dose-dependent. These results show for the first time that the midbrain PAG contributes to fear extinction and specifically identify a role for vlPAG opioid receptors in the acquisition but not the expression of such extinction. Taken together with our previous findings, we suggest that, during fear conditioning, activation of vlPAG opioid receptors contributes to detection of the discrepancy between the actual and expected outcome of the conditioning trial. vlPAG opioid receptors regulate the learning that accrues to the CS and other stimuli present on a trial because they instantiate an associative error correction process influencing US information reaching the site of CS-US convergence in the amygdala. During nonreinforcement, this vlPAG opioid receptor contribution signals extinction.
Czochralski‐grown Single Crystals with Acentric Symmetry Group 32
Authors: Heimann R.B. , Hengst M.
Published: August 2004

Single crystals with calcium gallium germanate (Ca3Ga2Ge4O14, CGG) structure such as langasite La3Ga5SiO14 (LGS), its niobium (‘langanite’, La3Ga5.5Nb0.5O14, LGN) and tantalum (‘langataite’, La3Ga5.5Ta0.5O14, LGT) analogs as well as strontium niobium gallium silicate (Sr3NbGa3Si2O14, SNGS) and strontium tantalum gallium silicate (Sr3TaGa3Si2O14, STGS) were grown with high perfection by the Czochralski pulling technique. Specific electric conductivity, optical activity, and dielectric, piezoelectric, bulk and surface acoustic, elastic, and electro‐optic properties were measured.
Studies on a Novel Route to C/SiC
Authors: Müller E. , Dittrich R. , Moritz K.
Published: August 2004

Electrophoresis was used for infiltration of two‐dimensional woven carbon fibre fabrics with ethanolic SiC powder suspension for producing fibre reinforced ceramic‐matrix composites. In these experiments, due to the electrical conductivity of the carbon fibers, the fabrics were used as deposition electrode. In an applied electric DC field the powder particles move into the fabric where they were deposited also within the spaces between single filaments of fiber rovings. By using SiC slurries containing additional sintering aids a high degree of infiltration was obtained within processing times of only a few seconds for a single fabric. Laminated green bodies consisting of stacked single fabrics were slowly dried to avoid crack formation. Pressureless sintering and hot pressing were compared as sintering methods.
Biaxial Fracture Test of Silicon Wafers
Authors: Funke C. , Kullig E. , Kuna M. , Möller H.J.
Published: August 2004

The statistical fracture stress distribution of silicon wafers was obtained by biaxial plate bending tests in combination with finite element calculations. For the correct interpretation of these tests it is important that the finite element calculations imply wafer thickness and elastic properties of the multicrystalline silicon wafer, otherwise the resulting stresses will be estimated to high. The Weibull distribution of fracture stresses yields different parameters for each test series of silicon, depending on the surface preparation and wafer manufacturing condition.
New Developments in Vertical Gradient Freeze Growth
Authors: Pätzold O. , Wunderwald U. , Bellmann M. , Gumprich P. , Buhrig E. , Cröll A.
Published: August 2004

The Vertical Gradient Freeze (VGF) technique is an important method for growing high quality compound semiconductors such as GaAs. Results obtained with a novel VGF set‐up developed for the growth under influence of a rotating magnetic field (RMF) and under vapour pressure control are presented in this paper. The RMF is shown to be a powerful tool to affect the heat and mass transport within the melt in a definite way. In GaAs:Si growth, RMF induced flow results in a decreased curvature of a nominally concave‐shaped interface, i.e., it contributes to an axial heat transfer at the solid‐liquid interface. The axial dopant segregation of Ga in Ge is found to be improved under continuous RMF action due to better mixing of the melt. The set‐up also allowed to determine the influence of carbon and the arsenic vapour pressure on the dopant incorporation and crystal quality.
Fatigue Behaviour of Cast Iron with Globular Graphite
Authors: Hübner P. , Pusch G. , Krodel L.
Published: August 2004

Cast iron with bainitic matrix and globular graphite, so called austempered ductile iron (ADI), allows the substitution of heat‐treatable steels. The use of ADI in safety‐relevant components requires knowledge of the fracture and fatigue behaviour. Cyclic stress strain behaviour and fatigue life at total strain control and random loading have been investigated at ADI (EN‐GJS‐1000‐5) and pearlitic cast iron (EN‐GJS‐600‐3). In addition fracture mechanic tests at cyclic loading at various stress ratios were carried out.
On the Deformation Behaviour and Martensitic Transformations of Metastable Austenitic Steels
Authors: Onyuna M. , Oettel H. , Martin U. , Weiß A.
Published: August 2004

Deformation behaviour of Type AISI 304 stainless steel was evaluated by uniaxial tensile testing at different temperatures ranging from –60 °C to 200 °C. The strengthening mechanisms of strain‐induced transformation of austenite to martensite and variant conversions have been discussed. Ludwigson and Berger's transformation kinetics relationship has been modified to take into consideration temperature during isothermal deformation. A plastic work interpretation of the maximum uniform elongation attained when taking into consideration the various phase transformations during deformation is presented. It has been demonstrated that finite element method (FEM) can be used with a limited number of parameters to predict the flow curves of these steels.
Prevalence of Jews as subjects in genetic research: Figures, explanation, and potential implications
Authors: Carmeli Daphna Birenbaum
Published: August 2004

Geneticists' view of ‘population isolates’ as bearing special utility for research often translates into the targeting of such groups as study popuations. This paper aims to outline the prevalence and structure of reference to one such group—that of the Jews—in genetic research publications. The paper uses three prevalence scores, calculated on the basis of a search of the PubMed database, conducted in September–October 2002. A systematic comparison to other population groups shows that in relation to the population size and in relation to the general bioscientific reference to this group, Jews are over‐represented in human genetic literature, particularly in mutation‐related contexts. This pattern is interpreted as representing geneticists' interest in Jewish communities, which are comparatively endogamous yet sizeable. It is also attributed to geneticists' access to Jewish communities, which is facilitated by the participation of Jewish scientists that alleviates ethical concerns as well. The geographical proximity of the largest Jewish communities to major research centers, and previous acquaintance with the genetic paradigm that many Jewish persons possess, further enhance this trend. The paper ends by pointing at potential extra‐medical implications of this increased prevalence. © 2004 Wiley‐Liss, Inc.
Compliant walking in primates: Elbow and knee yield in primates compared to other mammals
Authors: Larney Eileen , Larson Susan G.
Published: July 2004

It has been suggested that primates utilize a compliant gait to help reduce peak locomotor stresses on their limbs (Schmitt [1994] J. Hum. Evol. 26:441–458; Schmitt [ 1998] Primate Locomotion, p. 175–200; Schmitt [ 1999] J. Zool. Lond. 248:149–160). However, the components of such a gait, i.e., increased step length, prolonged contact time, and substantial limb yield, have only been documented on a handful of primate species. In order to explore the generality of this claim, elbow and knee angles during walking were documented at touchdown, midstance, and liftoff in a sample of primates, carnivores, marsupials, rodents, and artiodactyls, all under 25 kg. Limb yield was calculated as the change in angle from touchdown to midstance, and re‐extension as the change in angle from midstance to liftoff for both forelimbs and hind limbs. Use of a compliant gait (as reflected in significant limb yield) in primates was confirmed for both forelimbs and hind limbs. However, there was variability within primates in the degree of either elbow or knee yield. Surprisingly, marsupials were found to exhibit almost as much elbow yield and even greater knee yield than primates. Carnivores and rodents display a modest amount of limb yield during walking, while artiodactyls appear to display a relatively stiff gait. These data are consistent with the suggestion that the use of a compliant gait to attenuate peak substrate reaction forces may have facilitated the primate invasion of a small‐branch niche. However, limb compliance (as reflected by elbow or knee yield) does not appear to be exclusive to the primate order. Am J Phys Anthropol, 2003. © 2003 Wiley‐Liss, Inc.
Social and seasonal influences on the reproductive cycle in female mandrills (Mandrillus sphinx)
Authors: Setchell Joanna M. , Wickings E. Jean
Published: July 2004

We present 12 years of perineal swelling data for a semifree‐ranging colony of mandrills (Mandrillus sphinx), and evaluate the influence of rank, parity, and seasonality on reproductive parameters. Female sexual swellings showed a seasonal pattern, with August the median month of ovulation. Overlapping periovulatory periods did not decrease the likelihood of conception. Females showed their first genital swelling at age 3.6 years (n = 28; range, 3.2–4.6 years), and higher‐ranking females experienced their first swelling earlier than low‐ranking females. Median postpartum amenorrhea (PPA) duration was 208 days (n = 92; range, 74–538 days). PPA was longer in primiparous females than in multiparous females, but PPA duration was unrelated to female rank. Median follicular phase duration was 24 days for the first cycle after parturition (n = 84; range, 12–40 days), shortening to 17 days in subsequent cycles (n = 55; range, 6–39 days). The follicular phase was longer in nulliparous females than in parous females, but was unrelated to female rank. Median cycle length (from one sexual swelling breakdown to the next) was 38 days (n = 57; range, 18–108 days). Eighty‐seven percent of conceptions occurred within two cycles, and half of the nulliparous females conceived during their first swelling cycle. Lower‐ranking females were more likely to require more cycles to conceive than higher‐ranking females. The cycling phase was significantly longer in nulliparous females than in parous females, and was also significantly longer in lower‐ranking females than in higher‐ranking females. We discuss the influence of provisioning on female reproductive parameters, the influence of parity and rank on the different phases of the interbirth interval, and the evolution of long and variable follicular phases in mandrills. Am J Phys Anthropol, 2004. © 2004 Wiley‐Liss, Inc.
Clinical implications of benign multiple sclerosis: A 20‐year population‐based follow‐up study
Authors: Pittock Sean J. , McClelland Robyn L. , Mayr William T. , Jorgensen Neal W. , Weinshenker Brian G. , Noseworthy John , Rodriguez Moses
Published: July 2004

In 2001, we followed up all patients from the 1991 Olmsted County Multiple Sclerosis (MS) prevalence cohort. We found that the longer the duration of MS and the lower the disability, the more likely a patient is to remain stable and not progress. This is particularly powerful for patients with benign MS with Expanded Disability Status Scale score of 2 or lower for 10 years or longer who have a greater than 90% chance of remaining stable. This is important because these patients represent 17% of the entire prevalence cohort. These data should assist in the shared therapeutic decision‐making process of whether to start immunomodulatory medications. Ann Neurol 2004;56:303–306
Development of halogen‐free flame‐retardant thermoplastic elastomer polymer blend
Authors: Pal Kiran , Rastogi J. N.
Published: August 2004

Ethylene‐propylene diene rubber (EPDM) and isotactic polypropylene (iPP) blends have widest industrial applications that require a degree of flame retardancy. Halogen‐free intumescent technology based on phosphorous salt is a significantly advanced approach to make the polymer flame‐retardant. Both ammonium polyphosphate and ethylenediamine phosphate are important intumescent compounds. Their combination with carbonific and spumific agents were studied in binary blends of EPDM/PP. The polymer system was vulcanized online during melt mixing. Intumescent flame‐retardant polymer systems exhibit good flame‐retardancy with optimum comparable physiomechanical, electrical, and fluid resistance properties, including lower smoke emission, which is essential to protect people because the visibility remains unaffected in the event of fire. Pronounced charring and intumescent effect appear to enhance the flame‐retardancy of the polymers. Possible expected intumescent mechanism is proposed based on the nonpyrolysis mechanism for the flame‐retarded polymer and the intumescent components. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 407–415, 2004
Synthesis of high rubber styrene–EPDM–acrylonitrile graft copolymer and its toughening effect on SAN
Authors: Zeng Zhiping , Wang Lianshi , Cai Tongmin , Zeng Xiangbin
Published: August 2004

High rubber styrene–EPDM–acrylonitrile (AES) was prepared by the graft copolymerization of styrene (St) and acrylonitrile (AN) onto ethylene–propylene–diene terpolymer (EPDM) in n‐heptane/toluene cosolvent using benzoyl peroxide as an initiator. The effects of reaction conditions, such as reaction temperature, initiator concentration, EPDM content, the solvent component, and reaction time, on the graft copolymerization are discussed. In addition, according to the research on mechanical properties of the SAN/AES blend, a remarkable toughening effect of AES on SAN resin was found. By means of scanning electron microscopy, the toughening mechanism is proposed to be crazing initiation from rubber particles and shear deformation of SAN matrix. Uniform dispersion of rubber particles, as shown by transmission electron microscopy, is attributed to the good compatibility of SAN and AES. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 416–423, 2004
Preparation and properties of ethylene–propylene–diene rubber/organomontmorillonite nanocomposites
Authors: Li Wei , Huang Yu Dong , Ahmadi Seyed Javad
Published: August 2004

Ethylene–propylene–diene rubber (EPDM)/organomontmorillonite (OMMT) nanocomposites were prepared with a maleic anhydride grafted EPDM oligomer as a compatibilizer via melt intercalation. X‐ray diffraction and transmission electron microscopy indicated that the silicate layers of OMMT were exfoliated and dispersed uniformly as a few monolayers in nanocomposites. The change in the crystallization behavior of the nanocomposites was examined. The nanocomposites exhibited great improvements in the tensile strength and tensile modulus. The incorporation of OMMT gave rise to a considerable reduction of tan δ and an increase in the storage modulus. Moreover, the solvent resistance of the nanocomposites increased remarkably. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 440–445, 2004
Study on fiber structure formation in wet spinning of aliphatic polyketone using aqueous solution of complex metal salts—Characteristics of solid structure formation in drying step and its effects on superdrawing step
Authors: Morita Toru , Taniguchi Ryu , Kato Jinichiro
Published: August 2004

Solid structure formation in the drying step for wet spinning of poly(1‐oxotrimethylene) using as a solvent an aqueous solution of complex metal salts of calcium chloride/zinc chloride was studied. Because the degree of structural densification and the crystal structure both differ depending on the drying temperature, the drying temperature had a major effect on the drawing behavior and the strength achieved after drawing. With higher drying temperature, the denseness increased due to smaller voids in the dried undrawn fiber, while there was also a tendency toward higher strength with respect to the draw ratio. However, an excessively high drying temperature altered the crystal structure from a rough crystalline form to a dense crystalline form and reduced both the maximum draw ratio and strength. Mechanical cleavage of the molecular chains occurred between the ethylene groups and carbonyl groups of the main chains in the drawing step. This cleavage made it possible to suppress the inhibition of drawing due to entanglement of the molecular chains, thereby enabling superdrawing to afford a high performance fiber. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 446–452, 2004
The effect of storage temperatures below 100°C on the viscosity of a novolak resin propylene glycol solution
Authors: Wells Lisa J. , Spinks Geoffrey M. , Nightingale Sharon A.
Published: July 2004

The aging of a novolak resin solution used in iron‐making blast furnace taphole clays is reported. The novolak resin propylene glycol solution was aged at temperatures between 2 and 80°C for up to 56 days. The viscosity was measured to evaluate the change in the resin's behavior. A cure reaction was found to occur with the addition of hexamethylenetetramine (HMTA) at temperatures lower than had previously been reported. Methods for handling and storage of taphole clay to avoid excessive increases in viscosity due to aging are discussed. An approach for estimating the long term aging at temperatures of 30 to 50°C was considered using shorter term aging data obtained at 70 and 80°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 267–276, 2004
Morphology and properties of PVC/clay nanocomposites via in situ emulsion polymerization
Authors: Pan Mingwang , Shi Xudong , Li Xiucuo , Hu Haiyan , Zhang Liucheng
Published: July 2004

PVC/Na+–montmorillonite (MMT) nanocomposites were prepared via a simple technique of emulsion polymerization at several different MMT clay concentrations. X‐ray diffraction and transmission electron microscopy studies revealed the formation of a mixture of intercalated and exfoliated nanostructure. Tensile testing results showed that the tensile modulus of the nanocomposites increased with the addition of clay, while the tensile strength decreased little. The notched impact strength of the nanocomposites was also improved. For systems containing clay in the range of 2.1 to 3.5 wt %, the impact strength was almost two times as large as that of pure PVC. However, those mechanical properties began to decrease with the continuously increasing amount of clay. The fracture surface of pure PVC and the nanocomposites was observed by scanning electron microscope. Thermal properties of the nanocomposites were found to increase as a result of clay incorporation. The glass transition temperatures of the PVC/clay nanocomposites were nearly identical to that of pure PVC. The Vicat softening points exhibited a progressively increasing trend with the clay content added. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 277–286, 2004
Strain rate effects on the mechanical properties of polymer composite materials
Authors: Jacob George C. , Starbuck J. Michael , Fellers John F. , Simunovic Srdan , Boeman Raymond G.
Published: July 2004

This paper is a detailed review of the strain rate dependence of some mechanical properties of polymer composite materials. An attempt is made to present and summarize much of the published work relating to the effect of strain rate studies done in the past on the tensile, shear, compressive, and flexural properties of composite materials to better understand the strain rate effects on these mechanical properties of fiber‐reinforced polymer composite materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 296–301, 2004
Synthesis of molecularly imprinted microspheres for recognition of trans‐aconitic acid
Authors: Jiang Yong , Tong Ai‐Jun
Published: August 2004

In the presence of a template molecule, trans‐aconitic acid and, using acetonitrile as solvent and dispersing medium, monodispersed microspheres with a diameter of 600–700 nm bearing molecularly imprinted binding sites were prepared by precipitation polymerization. It was found that the concentrations of template, monomer, and crosslinking agent as well as the chemical structure of the template greatly affect the polymer configuration. Microspheres are produced only when the concentration of the template molecule and the functional monomer are finely tuned. Comparison with the performance of a conventional imprinted polymer monolith showed that the imprinted microsphere had obvious advantages in specific binding to template molecule. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 542–547, 2004
Investigation of the viscoelastic and transport properties of interfacially polymerized barrier layers using pendant drop mechanical analysis
Authors: Khare Vivek P. , Greenberg Alan R. , Krantz William B.
Published: August 2004

Pendant drop mechanical analysis (PDMA) enables the mechanical and transport characterization of unsupported interfacially polymerized (IP) thin films. PDMA was used to study the viscoelastic and permeation behavior of films formed by the interfacial polymerization of m‐phenylenediamine (MPD) and trimesoyl chloride (TMC). The viscoelastic properties were obtained by stress‐relaxation experiments wherein IP films on the surface of aqueous MPD drops were deformed and the decrease in the internal pressure resulting from stress relaxation was monitored with time. The stress‐relaxation behavior was interpreted using the fractional exponential relaxation model. The two model parameters, τ and β, are related to the degrees of crosslinking and branching, respectively. Water transport was generated by an osmotic gradient across the IP films, and permeation data were obtained by monitoring the increase in the drop size with time. Whereas the network structure was relatively insensitive to MPD concentration, the TMC concentration had a significant effect on the degrees of crosslinking and branching; τ evidenced a maximum at 0.1 wt % TMC concentration and β decreased monotonically with TMC concentration. The effect of organic‐phase reactant functionality was studied by incorporating isophthaloyl chloride (difunctional) with TMC. For TMC fractions > 25 wt %, the network structure was relatively insensitive to TMC fraction in the isophthaloyl chloride–TMC mixture. The transport experiments enabled the determination of a membrane constant A. The transport results generally corroborated the trends observed in the stress‐relaxation experiments, thus demonstrating the close association between the network structure and transport behavior. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 558–568, 2004
Decomposition of poly(ethylene glycol) in nanocomposites
Authors: Chen Biqiong , Evans Julian R. G. , Holding Steve
Published: August 2004

Poly(ethylene glycol) (PEG) has been widely used in studies of polymer–clay nanocomposites because it readily intercalates in smectite clays. Nanocomposites were formed from PEG with molecular weights (Mw) ranging from 300 to 20,000, as evidenced by expansion of the basal planar spacing of the clay (d001) in X‐ray diffraction. However PEG with high molecular weight (≥ 10,000) readily underwent degradation during preparation of composites when heated at low temperature (60°C) due to oxidative attack. Molecular weight distribution determined by gel permeation chromatography showed that this degradation always happened with or without the presence of clay and it became more serious when the molecular weight was higher. The reduction in pH of aqueous PEG solutions after degradation increased with molecular weight. Since d001 was independent of molecular weight over a wide range, such degradation cannot be detected by this method. Precautions against oxidative attack are therefore recommended to avoid decomposition when preparing PEG–clay nanocomposites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 548–552, 2004
QSAR Analysis of Some Fused Pyrazoles as Selective Cyclooxygenase‐2 Inhibitors: A Hansch Approach
Authors: Prasanna Sivaprakasam , Manivannan Elangovan , Chaturvedi Subash Chandra
Published: July 2004

Quantitative structure activity relationships (QSAR) for two unique series of centrally fused pyrazole ring systems have been studied for selective cyclooxygenase‐2 inhibitory activity. Several statistically significant QSAR models were developed and suggest that hydrophobicity of entire molecules and a fluorine atom substitution at position 8 of the non benzene sulphonyl ring fused with central pyrazole core of series 1 compounds is crucial for improved COX‐2 selectivity. Various structural and physicochemical stipulations to improve the inhibitory activities of the enzymes among individual series of compounds are also discussed. The conclusions derived may serve as an example to advance the design of new selective COX‐2 inhibitors.
Dimensionierung von Grundwasserabsenkungen – Probleme und Lösungen
Authors: Weyrauch Fritz , Schöffel Georg
Published: July 2004

Diese Arbeit beschäftigt sich mit der Analyse von Anomalien der Funktion Qs, die den Wasserandrang zu einer Baugrube beschreibt. Ihre Ursache liegt in der unbedachten Verwendung der Sichardtschen Reichweitenformel. Es wird eine Lösung vorgeschlagen, die die Anomalien beseitigt. Außerdem werden Verfahren zur Berechnung der erforderlichen Brunnenzahl bei gegebener Absenktiefe bzw. der erzielten Absenkung bei gegebener Brunnenzahl und des k‐Wertes bei einem Pumpversuch entwickelt.
Ein neues FEM‐Stabelement für nachgiebige Verbundquerschnitte
Authors: Gollwitzer Thomas , Gebbeken Norbert
Published: July 2004

Ein neues FEM‐Stabelement für einen n‐teiligen, nachgiebigen Verbundquerschnitt wird vorgestellt. Mit Hilfe des Prinzips der virtuellen Arbeit wird die Steifigkeitsmatrix des Elements hergeleitet. Sie besteht aus der Summe der Steifigkeitsmatrizen der Einzelstäbe und der Summe der Steifigkeitsmatrizen der Verbundfugen. Anhand einer bekannten analytischen Lösung des γ‐Verfahrens wird die Lösung verifiziert und validiert. Dem Anwender wird eine maximale Elementlänge ℓ, empfohlen.
Zur praktischen Ermittlung von statischen Windlasten an Bauwerken mit der Singularitätenmethode
Authors: Rosemeier Gustav‐Erich
Published: July 2004

In Fortführung des bisherigen Konzeptes [1] wird gezeigt, wie statische Windlasten bei Hochbauten in guter Näherung rechnerisch ermittelt werden können. Dabei lassen sich die bisherigen Ergebnisse von Standardprofilen nützlich verwenden. Als Ziel der vorgelegten Untersuchungen soll eine übergeordnete Systematik einer Strömungsmechanik mit abgelösten turbulenten Strömungszonen (Totwasser) erkennbar sein.
Zur aushubbedingten Reduktion des Drucksondierwiderstandes
Authors: Grabe Jürgen , König Florian
Published: July 2004

Mit Hilfe einer Finite‐Element‐Modellierung wird der Penetrationsvorgang einer Drucksonde in nichtbindige Böden simuliert. Es wird der Einfluß des Spannungszustandes und der Lagerungsdichte auf den Drucksondierwiderstand untersucht. Dadurch wird eine Einschätzung der Reduktion des Drucksondierwiderstandes infolge einer Spannungsänderung, wie beispielsweise infolge Bodenaushub, ermöglicht.
Phenotypic variability in human embryonic holoprosencephaly in the Kyoto Collection
Authors: Yamada Shigehito , Uwabe Chigako , Fujii Shingo , Shiota Kohei
Published: August 2004

Background

Holoprosencephaly (HPE) is one of the most common developmental disorders of the brain associated with specific craniofacial dysmorphogenesis. Although numerous postnatal cases have been reported, early phases of its pathogenesis are not well understood. We examined over 200 cases of HPE human embryos both grossly and histologically, and studied their phenotypic variability and stage‐specific characteristics.

METHODS

Among over 44,000 human embryos in the Kyoto Collection of Human Embryos, 221 embryos have been diagnosed as HPE. Their developmental stages ranged from Carnegie stage (CS) 13 to CS 23. They were examined grossly and were also serially sectioned for detailed histological analysis.

RESULTS

HPE embryos after CS 18 were classified into complete (true) cyclopia, synophthalmia (partially fused eyes in a single eye fissure), closely apposed separate eyes (possible forerunners of ethmocephaly and cebocephaly), and milder HPE with median cleft lip (premaxillary agenesis). At CS 13–17, when facial morphogenesis is not completed, HPE embryos had some facial characteristics that are specific to these stages and different from those in older HPE embryos. The midline structures of the brain, including the pituitary gland, were lacking or seriously hypoplastic in HPE embryos. Complete cyclopia was found in two cases after CS 18 but none at earlier stages.

CONCLUSIONS

The early development of HPE in human embryos was systematically studied for the first time. The pathogenesis of craniofacial abnormalities, especially eye anomalies, in HPE was discussed in the light of recent studies with mutant laboratory animals. Birth Defects Research (Part A), 2004. © 2004 Wiley‐Liss, Inc.
Clonazepam use in pregnancy and the risk of malformations
Authors: Lin Angela E. , Peller Allyson J. , Westgate Marie‐Noel , Houde Kara , Franz Aleda , Holmes Lewis B.
Published: August 2004

BACKGROUND

Clonazepam (Klonopin) is a benzodiazepine that has been used widely to treat seizures and conditions such as panic attacks and anxiety disorder. However, the current findings about its use in pregnancy are derived from limited studies of small sample size. Because it is commonly prescribed during pregnancy, more information about its safety is needed.

METHODS

The medical records of 28,565 infants were surveyed as part of a hospital‐based malformation surveillance program to identify those who had been exposed prenatally to an anticonvulsant, including clonazepam.

RESULTS

During a 32‐month period, 166 anticonvulsant‐exposed infants were identified; 52 had been exposed to clonazepam, 43 as monotherapy. A total of 33 (76.7%) of the monotherapy infants were exposed during the first trimester. One (3.0%) infant had dysmorphic features, growth retardation, and a heart malformation (tetralogy of Fallot).

CONCLUSIONS

This study did not observe an increase in major malformations in births exposed to clonazepam monotherapy. However, this study is not large enough to have adequate power to determine whether or not the rate of major malformations is increased in clonazepam‐exposed pregnancies. No increase has been identified in three other case series. Although the number of patients in this series was larger than previous reports, continued monitoring of pregnancies is needed to determine whether or not clonazepam is teratogenic. Birth Defects Research (Part A), 2004. © 2004 Wiley‐Liss, Inc.
Kreative Uhren in unserem Kopf: Experimente zum Hören und Nachdenken
Authors: Euler Manfred
Published: July 2004

Es werden Hörexperimente vorgestellt, die sich mit einem Computer und einem Sound‐Editor‐Programm leicht durchführen lassen. Sie erlauben einen Blick aus der Innenperspektive auf die konstruktive Rolle neuronaler Synchronisationsprozesse bei der Sprach‐ und Musikwahrnehmung. Die Synchronisation von Uhren stellt ein Basismodell für das Verständnis neuronaler Prozesse dar, die für die Konstruktion von Wirklichkeit zentral sind.
Die Vielfalt neotropischer Fledermäuse: Fliegende Alleskönner
Authors: Wilcken Sandra , Kalko Elisabeth K. V.
Published: July 2004

Fledermäuse sind vielseitige Lebenskünstler. Kaum eine andere Tiergruppe ist in Verhalten und Ökologie so vielfältig, keine Säugerordnung außer den Nagern ist artenreicher. Sie trinken Nektar, fressen Früchte, fangen Fische und jagen Insekten. In dunkelster Nacht orientieren sich die fliegenden Säuger per Ultraschall, riechen oder hören ihre Beute. Sogar Wärmestrahlung und UV‐Licht können manche Arten wahrnehmen. Die Nutzung unterschiedlicher ökologischer Nischen ermöglicht vor allem in tropischen Ökosystemen die Koexistenz zahlreicher Arten. Obwohl Fledermäuse für den Erhalt und die Regeneration tropischer Wälder eine wichtige Rolle spielen, ist das Geheimnis ihrer Vielfalt bislang nur in Ansätzen verstanden.
Geschwisterkonflikte bei Tölpel: Brudermörder und Desperados
Authors: Bucher Kirsten
Published: July 2004

Sowohl Blaufußtölpel als auch Brauntölpel zeigen aggressive Brutreduktion. Dabei führen offene Geschwisterkämpfe unter den beiden ungleich alten Küken zum Tod des jüngeren Geschwisters. Doch während bei Blaufußtölpeln Geschwistermord nur fakultativ auftritt, überleben beim obligaten Geschwistermord der Brauntölpel weniger als zehn Prozent der jüngeren Küken. Der Ausgang der Kämpfe hängt offensichtlich von der zukünftigen Verfügbarkeit der Nahrung ab: Während sie bei Blaufußtölpeln normalerweise für beide Geschwister ausreicht, können Brauntölpeleltern meist nur ein Küken bis zum Flüggewerden durchfüttern. Obwohl das zweite Brauntölpelküken vermutlich nur als „Versicherung”︁ gegen den Verlust des ersten Kükens dient, wird es häufig getötet, bevor das Überleben des Älteren sichergestellt ist. Eine Erklärung für das frühe Timing des obligaten Geschwistermordes liefert die Desperado‐Sibling‐Hypothese, die davon ausgeht, dass das jüngere Küken nur eine Chance hat: Es muss versuchen, seinen Gegner mit totaler Gewalt zu vernichten. Experimentelle Untersuchungen des agonistischen Verhaltens jüngerer Brauntölpel unterstützen die Hypothese und verdeutlichen gleichzeitig die Kosten, die dem älteren Küken durch einen potenziellen Desperado entstehen können.
Den Nachwuchs mit anderen Augen sehen
Authors: Wendler Silke
Published: July 2004

Wie erkennen und unterscheiden Vogeleltern, deren Nester in dunklen Höhlen liegen, die aufgesperrten Schnäbel ihrer Brut? Hier kommt den Vögeln eine Fähigkeit zugute, über die wir Menschen nicht verfügen. Sie haben eine zusätzliche Klasse von Photorezeptoren (Zapfen) in der Retina ihrer Augen. Dies befähigt sie, Wellenlängen zwischen 320 und 400 nm wahrzunehmen und damit den nahen UV‐Bereich einzuschließen.
EU‐Erweiterung ‐ Herausforderung an die Kontrolle des Artenhandels
Authors: Irsch Wilhelm
Published: July 2004

Die zehn neuen EU‐Mitgliedsstaaten sind ebenfalls Unterzeichner des Washingtoner Artenschutzübereinkommens (CITES), doch die Unterschiede zwischen CITES und den engeren Verordnungen der EU, die auf eine einheitliche Umsetzung des weltweiten Artenschutzübereinkommes für die Mitgliedstaaten Europas abzielen, geben Artenschützern Anlass zur Besorgnis.
Diplom ‐ Bachelor ‐ Master: Wo geht's lang?
Authors: Liebig Karin , Wolk Andrea , Frings Stephan
Published: July 2004

Interessenten an einem Biologiestudium haben an vielen Universitäten zur Zeit noch die Wahl zwischen einem Diplomstudiengang und einem oder mehreren Bachelor‐Studiengängen. Vor die Entscheidung gestellt, den richtigen Ausbildungsweg einzuschlagen, sind viele Abiturienten ratlos, und es zeigt sich, dass Chancen und Risiken der neuen zweistufigen Studiengänge (Bachelor und Master) noch unzureichend bekannt sind. Wir wollen hier versuchen, den Studierenden einige Kriterien für ihre Entscheidung an die Hand zu geben, um ihnen den Start in ein erfolgreiches Biologiestudium zu erleichtern.
Die gründliche Vorbereitung, Teil 2
Authors: Debus‐Spangenberg Isolde
Published: July 2004

In BIUZ 3/2004 beschrieb die Medienwissenschaftlerin und Karriereberaterin Isolde Debus‐Spangenberg, wo und wie interessante Stellenangebote für Biologen zu finden sind. Wer alle beschriebenen Recherche‐ Wege genutzt hat, der hat sicher auch bereits das eine oder andere attraktive Angebot entdeckt. Doch bevor Sie jetzt aktiv werden und den direkten Kontakt zum Unternehmen suchen, haben Sie noch eine Vorarbeit zu leisten: die Recherche über den potenziellen Arbeitgeber.
Survival after treatment for breast cancer in a geographically defined population
Authors: Tejler G , Norberg B , Dufmats M , Nordenskjöld B
Published: July 2004

Background

South East Sweden with 976 000 inhabitants is served by nine hospitals with specialized breast surgeons. Population-based mammographic screening was introduced in 1986 for women aged 40–74 years. Patients with primary breast cancer were treated according to a joint management programme.

Methods

All patients were reported to a regional cancer registry from which breast cancer incidence, treatment and survival in this defined population were reported.

Results

A total of 7892 women had their first invasive breast cancer diagnosed between 1986 and 1999. The median tumour size was 17 mm and 29·9 per cent had axillary metastases. Some 49·8 per cent of these women had a modified radical mastectomy and 31·9 per cent had a segmental resection with axillary clearance. Postoperative radiotherapy was given to 40·3 per cent of the women after mastectomy and to 87·1 per cent after breast-conserving surgery. Tamoxifen and chemotherapy were used as adjuvant treatment except in low-risk patients. Breast cancer-specific survival rate for all stages was 83·5 per cent at 5 years and 74·0 per cent at 10 years. Respective values were 95·8 and 90·9 per cent for patients with stage T1 N0 M0 tumours, and 77·7 and 62·4 per cent for those with T1–2 N1 M0 tumours.

Conclusion

Breast specialists treating women with breast cancer according to a joint management programme have achieved very good survival rates.
DEUSS: A Perdeuterated Poly(oxyethylene)‐Based Resin for Improving HRMAS NMR Studies of Solid‐Supported Molecules
Authors: Poschalko Alexander , Lancelot Nathalie , Marin Julien , Larras Virginie , Limal David , Elbayed Karim , Raya Jesus , Piotto Martial , Briand Jean‐Paul , Guichard Gilles , Bianco Alberto
Published: July 2004

A novel resin called DEUSS (perdeuterated poly(oxyethylene)‐based solid support) has been prepared by anionic polymerization of deuterated [D4]ethylene oxide, followed by cross‐linking with deuterated epichlorohydrin. DEUSS can be suspended in a wide range of solvents including organic and aqueous solutions, in which it displays a high swelling capacity. As measured by proton HRMAS of the swollen polymer, the signal intensity of the oxyethylene protons is reduced by a factor of 110 relative to the corresponding nondeuterated poly(oxyethylene)poly(oxypropylene) (POEPOP) resin, thus facilitating detailed HRMAS NMR studies of covalently linked molecules. This 1H NMR invisible matrix was used for the solid‐phase synthesis of peptides, oligoureas, and a series of amides as well as their characterization by HRMAS NMR spectroscopy. On‐bead NMR spectra of high quality and with resolution comparable to that of liquid samples were obtained and readily interpreted. The complete absence of the parasite resin signals will be of great advantage, for example, for the optimization of multistep solid‐phase stereoselective reactions, and for the conformational study of resin‐bound molecules in a large variety of solvents.
Eintrag und Elimination von gefährlichen Stoffen in kommunalen Kläranlagen
Authors: Fahlenkamp H. , Hannich C. B. , Möhle E. , Nöthe T. , Ries T.
Published: July 2004

No abstracts.
Differenzialkreislaufreaktoren zur Gewinnung reaktionskinetischer Daten für festbettkatalytische Reaktionen – Teil 2: Theorie und Realverhalten
Authors: Hesselbarth B. , Adler R.
Published: July 2004

No abstracts.
Stoffaustauschmessungen an Einzeltropfen mittels Laser induzierter Fluoreszenz (LIF)
Authors: Gneist G. , Schollenberger S. , Bart H.‐J.
Published: July 2004

No abstracts.
Erhöhung der Abscheidung ultrafeiner Dieselrußpartikeln durch Mikrokugelbeschichtung auf metallträgerbasierten Katalysatorstrukturen
Authors: Messerer A. , Schmid H.‐J. , Knab C. , Pöschl U. , Nießner R.
Published: July 2004

No abstracts.
Lineare Stabilitätsanalyse der Strömung einer drainierenden Schaumlamelle
Authors: Runowski T. , Pahl M. H.
Published: July 2004

No abstracts.
Zu den Anfängen der Analytischen Chemie: Wider Fälscher und Betrüger
Authors: Volke Klaus
Published: July 2004

Bereits im Altertum gab es chemisch‐analytische Nachweisverfahren und Prüfmethoden vor allem für die Edelmetalle, die nicht nur der Anfertigung von Kunst‐ und Kultgegenständen sowie der Prägung von Münzen dienten, sondern auch Bestandteil von Tributleistungen waren. Das Wechselspiel zwischen dem Bemühen der Metallurgen, möglichst reine Metalle herzustellen, und der Kunstfertigkeit der Fälscher, möglichst echt wirkende Fälschungen herzustellen, hat nicht nur die Kenntnisse über die metallurgischen Prozesse gefördert, sondern auch zu ersten Analysenmethoden geführt.