bluuebunny/crossref_metadata_2025 huggingface dataset:
Just do it? impact of a science apprenticeship program on high school students' understandings of the nature of science and scientific inquiry
Authors: Bell Randy L. , Blair Lesley M. , Crawford Barbara A. , Lederman Norman G.
Published: April 2003

The purpose of this study was to explicate the impact of an 8‐week science apprenticeship program on a group of high‐ability secondary students' understandings of the nature of science and scientific inquiry. Ten volunteers (Grades 10–11) completed a modified version of the Views of Nature of Science, Form B both before and after their apprenticeship to assess their conceptions of key aspects of the nature of science and scientific inquiry. Semistructured exit interviews provided an opportunity for students to describe the nature of their apprenticeship experiences and elaborate on their written questionnaire responses. Semistructured exit interviews were also conducted with the scientists who served as mentors for each of the science apprentices. For the most part, students held conceptions about the nature of science and scientific inquiry that were inconsistent with those described in current reforms. Participating science mentors held strong convictions that their apprentices had learned much about the scientific enterprise in the course of doing the science in their apprenticeship. Although most students did appear to gain knowledge about the processes of scientific inquiry, their conceptions about key aspects of the nature of science remained virtually unchanged. Epistemic demand and reflection appeared to be crucial components in the single case where a participant experienced substantial gains in her understandings of the nature of science and inquiry. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 487–509, 2003
Intentions and beliefs in students' understanding and acceptance of biological evolution
Authors: Sinatra Gale M. , Southerland Sherry A. , McConaughy Frances , Demastes James W.
Published: April 2003

We examined the intersection of students' understanding and acceptance of evolution and their epistemological beliefs and cognitive dispositions. Based on previous research, we hypothesized there would be a relation between understanding and acceptance. We also hypothesized that students who viewed knowledge as changing and who have a disposition toward open‐minded thinking would be more likely to accept the scientific explanation of human evolution, and that beliefs and dispositions would not be related to acceptance of a topic that is generally perceived as noncontroversial. Ninety‐three undergraduate students enrolled in a nonmajors biology class completed measures of their (a) content knowledge of evolution and photosynthesis and respiration; (b) acceptance of theories of animal evolution, human evolution, and photosynthesis; and (c) epistemological beliefs and cognitive dispositions. Although our findings did reveal a significant relation between knowledge and reported acceptance for photosynthesis, there was no relation between knowledge and acceptance of animal or human evolution. Epistemological beliefs were related to acceptance, but only to the acceptance of human evolution. There was no relation between students' epistemological beliefs and their general acceptance of animal evolution or photosynthesis. Three subscales, Ambiguous Information, Actively Open‐Minded Thinking, and Belief Identification, were significantly correlated with understanding evolutionary theory. We argue these findings underscore the importance of intentional level constructs, such as epistemological beliefs and cognitive dispositions, in the learning of potentially controversial topics. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 510–528, 2003
Cell and Molecular Regulation of Endothelin-1 Production during Hepatic Wound Healing
Authors: Shao Rong , Shi Zengdun , Gotwals Philip J. , Koteliansky Victor E. , George Jacob , Rockey Don C.
Published: April 2003

During hepatic wound healing, activation of key effectors of the wounding response known as stellate cells leads to a multitude of pathological processes, including increased production of endothelin-1 (ET-1). This latter process has been linked to enhanced expression of endothelin-converting enzyme-1 (ECE-1, the enzyme that converts precursor ET-1 to the mature peptide) in activated stellate cells. Herein, we demonstrate up-regulation of 56- and 62-kDa ECE-1 3′-untranslated region (UTR) mRNA binding proteins in stellate cells after liver injury and stellate cell activation. Binding of these proteins was localized to a CC-rich region in the proximal ECE-1 3′ UTR base pairs (the 56-kDa protein) and to a region between 60 and 193 base pairs in the ECE-1 3′ UTR mRNA (62 kDa). A functional role for the 3′ UTR mRNA/protein interaction was established in a series of reporter assays. Additionally, transforming growth factor-β1, a cytokine integral to wound healing, stimulated ET-1 production. This effect was due to ECE-1 mRNA stabilization and increased ECE-1 expression in stellate cells, which in turn was a result of de novo synthesis of the identified 56- and 62-kDa ECE-1 3′ UTR mRNA binding proteins. These data indicate that liver injury and the hepatic wound healing response lead to ECE-1 mRNA stabilization in stellate cells via binding of 56- and 62-kDa proteins, which in turn are regulated by transforming growth factor-β. The possibility that the same or similar regulatory events are present in other forms of wound healing is raised.
Functional cdc25C Dual-Specificity Phosphatase Is Required for S-Phase Entry in Human Cells
Authors: Turowski Patric , Franckhauser Celine , Morris May C. , Vaglio Philippe , Fernandez Anne , Lamb Ned J. C.
Published: April 2003

In view of the common regulatory mechanism that induces transcription of the mitotic phosphatase cdc25C and cyclin A at the beginning of S-phase, we investigated whether cdc25C was required for S-phase transit. Here, we show that in both nontransformed human fibroblasts and HeLa cells, cdc25C protein levels significantly increased concomitant with S-phase onset and cyclin A synthesis. Activity measurements on immunoprecipitates from synchronized HeLa cells revealed a sharp rise in cdc25C-associated phosphatase activity that coincided with S-phase. Microinjection of various antisense-cdc25C molecules led to inhibition of DNA synthesis in both HeLa cells and human fibroblasts. Furthermore, transfection of small interfering RNA directed against cdc25C specifically depleted cdc25C in HeLa cells without affecting cdc25A or cdc25B levels. Cdc25C RNA interference was also accompanied by S-phase inhibition. In cells depleted of cdc25C by antisense or siRNA, normal cell cycle progression could be re-established through microinjection of wild-type cdc25C protein but not inactive C377S mutant protein. Taken together, these results show that cdc25C not only plays a role at the G2/M transition but also in the modulation of DNA replication where its function is distinct from that of cdc25A.
Association of Chromatin Proteins High Mobility Group Box (HMGB) 1 and HMGB2 with Mitotic Chromosomes
Authors: Pallier Coralie , Scaffidi Paola , Chopineau-Proust Stéphanie , Agresti Alessandra , Nordmann Patrice , Bianchi Marco E. , Marechal Vincent
Published: April 2003

High mobility group box (HMGB) 1 and 2 are two abundant nonhistone nuclear proteins that have been found in association with chromatin. Previous studies based on immunofluorescence analysis indicated that HMGB1 dissociates from chromosomes during mitosis. In the present work, HMGB1 and 2 subcellular localization was reinvestigated in living cells by using enhanced green fluorescent protein- and Discosome sp. red fluorescent protein-tagged proteins. Contrary to previous reports, HMGB1 and 2 were shown to be present under two forms in mitotic cells, i.e., free and associated with the condensed chromatin, which rapidly exchange. A detailed analysis of HMGB2 interaction with mitotic chromosomes indicated that two sites encompassing HMG-box A and B are responsible for binding. Importantly, this interaction was rapidly inactivated when cells were permeabilized or exposed to chemical fixatives that are widely used in immunodetection techniques. A comparable behavior was also observed for two proteins of the HMG-nucleosome binding (HMGN) group, namely, HMGN1 and HMGN2.
Irod/Ian5: An Inhibitor of γ-Radiation- and Okadaic Acid-induced Apoptosis
Authors: Sandal Tone , Aumo Linda , Hedin Lars , Gjertsen Bjørn T. , Døskeland Stein O.
Published: April 2003

Protein phosphatase-directed toxins such as okadaic acid (OA) are general apoptosis inducers. We show that a protein (inhibitor of radiation- and OA-induced apoptosis, Irod/Ian5), belonging to the family of immune-associated nucleotide binding proteins, protected Jurkat T-cells against OA- and γ-radiation-induced apoptosis. Unlike previously described antiapoptotic proteins Irod/Ian5 did not protect against anti-Fas, tumor necrosis factor-α, staurosporine, UV-light, or a number of chemotherapeutic drugs. Irod antagonized a calmodulin-dependent protein kinase II-dependent step upstream of activation of caspase 3. Irod has predicted GTP-binding, coiled-coil, and membrane binding domains. Irod localized to the centrosomal/Golgi/endoplasmic reticulum compartment. Deletion of either the C-terminal membrane binding domain or the N-terminal GTP-binding domain did not affect the antiapoptotic function of Irod, nor the centrosomal localization. The middle part of Irod, containing the coiled-coil domain, was therefore responsible for centrosomal anchoring and resistance toward death. Being widely expressed and able to protect also nonimmune cells, the function of Irod may not be limited to the immune system. The function and localization of Irod indicate that the centrosome and calmodulin-dependent protein kinase II may have important roles in apoptosis signaling.
Subcellular Localization and Activity of Multidrug Resistance Proteins
Authors: Rajagopal Asha , Simon Sanford M.
Published: April 2003

The multidrug resistance (MDR) phenotype is associated with the overexpression of members of the ATP-binding cassette family of proteins. These MDR transporters are expressed at the plasma membrane, where they are thought to reduce the cellular accumulation of toxins over time. Our data demonstrate that members of this family are also expressed in subcellular compartments where they actively sequester drugs away from their cellular targets. The multidrug resistance protein 1 (MRP1), P-glycoprotein, and the breast cancer resistance protein are each present in a perinuclear region positive for lysosomal markers. Fluorescence-activated cell sorting analysis suggests that these three drug transporters do little to reduce the cellular accumulation of the anthracycline doxorubicin. However, whereas doxorubicin enters cells expressing MDR transporters, this drug is sequestered away from the nucleus, its subcellular target, in vesicles expressing each of the three drug resistance proteins. Using a cell-impermeable inhibitor of MRP1 activity, we demonstrate that MRP1 activity on intracellular vesicles is sufficient to confer a drug resistance phenotype, whereas disruption of lysosomal pH is not. Intracellular localization and activity for MRP1 and other members of the MDR transporter family may suggest different strategies for chemotherapeutic regimens in a clinical setting.
TINA Interacts with the NIMA Kinase inAspergillus nidulansand Negatively Regulates Astral Microtubules during Metaphase Arrest
Authors: Osmani Aysha H. , Davies Jonathan , Oakley C. Elizabeth , Oakley Berl R. , Osmani Stephen A.
Published: April 2003

The tinA gene of Aspergillus nidulans encodes a protein that interacts with the NIMA mitotic protein kinase in a cell cycle-specific manner. Highly similar proteins are encoded in Neurospora crassa and Aspergillus fumigatus. TINA and NIMA preferentially interact in interphase and larger forms of TINA are generated during mitosis. Localization studies indicate that TINA is specifically localized to the spindle pole bodies only during mitosis in a microtubule-dependent manner. Deletion of tinA alone is not lethal but displays synthetic lethality in combination with the anaphase-promoting complex/cyclosome mutation bimE7. At the bimE7 metaphase arrest point, lack of TINA enhanced the nucleation of bundles of cytoplasmic microtubules from the spindle pole bodies. These microtubules interacted to form spindles joined in series via astral microtubules as revealed by live cell imaging. Because TINA is modified and localizes to the spindle pole bodies at mitosis, and lack of TINA causes enhanced production of cytoplasmic microtubules at metaphase arrest, we suggest TINA is involved in negative regulation of the astral microtubule organizing capacity of the spindle pole bodies during metaphase.
Cortactin Tyrosine Phosphorylation Requires Rac1 Activity and Association with the Cortical Actin Cytoskeleton
Authors: Head Julie A. , Jiang Dongyan , Li Min , Zorn Lynda J. , Schaefer Erik M. , Parsons J. Thomas , Weed Scott A.
Published: April 2003

Cortactin is an F-actin binding protein that activates actin-related protein 2/3 complex and is localized within lamellipodia. Cortactin is a substrate for Src and other protein tyrosine kinases involved in cell motility, where its phosphorylation on tyrosines 421, 466, and 482 in the carboxy terminus is required for cell movement and metastasis. In spite of the importance of cortactin tyrosine phosphorylation in cell motility, little is known regarding the structural, spatial, or signaling requirements regulating cortactin tyrosine phosphorylation. Herein, we report that phosphorylation of cortactin tyrosine residues in the carboxy terminus requires the aminoterminal domain and Rac1-mediated localization to the cell periphery. Phosphorylation-specific antibodies directed against tyrosine 421 and 466 were produced to study the regulation and localization of tyrosine phosphorylated cortactin. Phosphorylation of cortactin tyrosine 421 and 466 was elevated in response to Src, epidermal growth factor receptor and Rac1 activation, and tyrosine 421 phosphorylated cortactin localized with F-actin in lamellipodia and podosomes. Cortactin tyrosine phosphorylation is progressive, with tyrosine 421 phosphorylation required for phosphorylation of tyrosine 466. These results indicate that cortactin tyrosine phosphorylation requires Rac1-induced cortactin targeting to cortical actin networks, where it is tyrosine phosphorylated in hierarchical manner that is closely coordinated with its ability to regulate actin dynamics.
Villidin, a Novel WD-repeat and Villin-related Protein fromDictyostelium,Is Associated with Membranes and the Cytoskeleton
Authors: Gloss Annika , Rivero Francisco , Khaire Nandkumar , Müller Rolf , Loomis William F. , Schleicher Michael , Noegel Angelika A.
Published: April 2003

Villidin is a novel multidomain protein (190 kDa) from Dictyostelium amoebae containing WD repeats at its N-terminus, three PH domains in the middle of the molecule, and five gelsolin-like segments at the C-terminus, followed by a villin-like headpiece. Villidin mRNA and protein are present in low amounts during growth and early aggregation, but increase during development and reach their highest levels at the tipped mound stage. The protein is present in the cytosol as well as in the cytoskeletal and membrane fractions. GFP-tagged full-length villidin exhibits a similar distribution as native villidin, including a distinct colocalization with Golgi structures. Interestingly, GFP fusions with the gelsolin/villin-like region are uniformly dispersed in the cytoplasm, whereas GFP fusions of the N-terminal WD repeats codistribute with F-actin and are associated with the Triton-insoluble cytoskeleton. Strains lacking villidin because of targeted deletion of its gene grow normally and can develop into fruiting bodies. However, cell motility is reduced during aggregation and phototaxis is impaired in the mutant strains. We conclude that villidin harbors a major F-actin binding site in the N-terminal domain and not in the villin-like region as expected; association of villidin with vesicular membranes suggests that the protein functions as a linker between membranes and the actin cytoskeleton.
Variation in Gene Expression Patterns in Human Gastric Cancers
Authors: Chen Xin , Leung Suet Y. , Yuen Siu T. , Chu Kent-Man , Ji Jiafu , Li Rui , Chan Annie S.Y. , Law Simon , Troyanskaya Olga G. , Wong John , So Samuel , Botstein David , Brown Patrick O.
Published: April 2003

Gastric cancer is the world's second most common cause of cancer death. We analyzed gene expression patterns in 90 primary gastric cancers, 14 metastatic gastric cancers, and 22 nonneoplastic gastric tissues, using cDNA microarrays representing ∼30,300 genes. Gastric cancers were distinguished from nonneoplastic gastric tissues by characteristic differences in their gene expression patterns. We found a diversity of gene expression patterns in gastric cancer, reflecting variation in intrinsic properties of tumor and normal cells and variation in the cellular composition of these complex tissues. We identified several genes whose expression levels were significantly correlated with patient survival. The variations in gene expression patterns among cancers in different patients suggest differences in pathogenetic pathways and potential therapeutic strategies.
Dependence of Endoplasmic Reticulum-associated Degradation on the Peptide Binding Domain and Concentration of BiP
Authors: Kabani Mehdi , Kelley Stephanie S. , Morrow Michael W. , Montgomery Diana L. , Sivendran Renuka , Rose Mark D. , Gierasch Lila M. , Brodsky Jeffrey L.
Published: April 2003

ER-associated degradation (ERAD) removes defective and mis-folded proteins from the eukaryotic secretory pathway, but mutations in the ER lumenal Hsp70, BiP/Kar2p, compromise ERAD efficiency in yeast. Because attenuation of ERAD activates the UPR, we screened for kar2 mutants in which the unfolded protein response (UPR) was induced in order to better define how BiP facilitates ERAD. Among the kar2 mutants isolated we identified the ERAD-specific kar2-1 allele (Brodsky et al. J. Biol. Chem. 274, 3453–3460). The kar2-1 mutation resides in the peptide-binding domain of BiP and decreases BiP's affinity for a peptide substrate. Peptide-stimulated ATPase activity was also reduced, suggesting that the interdomain coupling in Kar2-1p is partially compromised. In contrast, Hsp40 cochaperone-activation of Kar2-1p's ATPase activity was unaffected. Consistent with UPR induction in kar2-1 yeast, an ERAD substrate aggregated in microsomes prepared from this strain but not from wild-type yeast. Overexpression of wild-type BiP increased substrate solubility in microsomes obtained from the mutant, but the ERAD defect was exacerbated, suggesting that simply retaining ERAD substrates in a soluble, retro-translocation-competent conformation is insufficient to support polypeptide transit to the cytoplasm.
SWAP-70 Identifies a Transitional Subset of Actin Filaments in Motile Cells
Authors: Hilpelä Pirta , Oberbanscheidt Pia , Hahne Penelope , Hund Martin , Kalhammer Georg , Small J. Victor , Bähler Martin
Published: April 2003

Functionally different subsets of actin filament arrays contribute to cellular organization and motility. We report the identification of a novel subset of loose actin filament arrays through regulated association with the widely expressed protein SWAP-70. These loose actin filament arrays were commonly located behind protruding lamellipodia and membrane ruffles. Visualization of these loose actin filament arrays was dependent on lamellipodial protrusion and the binding of the SWAP-70 PH-domain to a 3′-phosphoinositide. SWAP-70 with a functional pleckstrin homology-domain lacking the C-terminal 60 residues was targeted to the area of the loose actin filament arrays, but it did not associate with actin filaments. The C-terminal 60 residues were sufficient for actin filament association, but they provided no specificity for the subset of loose actin filament arrays. These results identify SWAP-70 as a phosphoinositide 3-kinase signaling-dependent marker for a distinct, hitherto unrecognized, array of actin filaments. Overexpression of SWAP-70 altered the actin organization and lamellipodial morphology. These alterations were dependent on a proper subcellular targeting of SWAP-70. We propose that SWAP-70 regulates the actincytoskeletonasaneffectororadaptorproteininresponsetoagoniststimulatedphosphatidylinositol (3,4)-bisphosphate production and cell protrusion.
Nek2A kinase stimulates centrosome disjunction and is required for formation of bipolar mitotic spindles
Authors: Faragher Alison J. , Fry Andrew M.
Published: April 2003

Nek2A is a cell cycle-regulated kinase of the never in mitosis A (NIMA) family that is highly enriched at the centrosome. One model for Nek2A function proposes that it regulates cohesion between the mother and daughter centriole through phosphorylation of C-Nap1, a large coiled-coil protein that localizes to centriolar ends. Phosphorylation of C-Nap1 at the G2/M transition may trigger its displacement from centrioles, promoting their separation and subsequent bipolar spindle formation. To test this model, we generated tetracycline-inducible cell lines overexpressing wild-type and kinase-dead versions of Nek2A. Live cell imaging revealed that active Nek2A stimulates the sustained splitting of interphase centrioles indicative of loss of cohesion. However, this splitting is accompanied by only a partial reduction in centriolar C-Nap1. Strikingly, induction of kinase-dead Nek2A led to formation of monopolar spindles with unseparated spindle poles that lack C-Nap1. Furthermore, kinase-dead Nek2A interfered with chromosome segregation and cytokinesis and led to an overall change in the DNA content of the cell population. These results provide the first direct evidence in human cells that Nek2A function is required for the correct execution of mitosis, most likely through promotion of centrosome disjunction. However, they suggest that loss of centriole cohesion and C-Nap1 displacement may be distinct mitotic events.
Oligomerization of a Cargo Receptor Directs Protein Sorting into COPII-coated Transport Vesicles
Authors: Sato Ken , Nakano Akihiko
Published: April 2003

Secretory proteins are transported from the endoplasmic reticulum (ER) to the Golgi complex in vesicles coated with coat protein complex II (COPII). The incorporation of certain transport molecules (cargo) into the COPII vesicles is thought to be mediated by cargo receptors. Here we show that Emp47p, a type-I membrane protein, is specifically required for the transport of an integral membrane protein, Emp46p, from the ER. Exit of Emp46p from the ER was saturable and dependent on the expression level of Emp47p. Emp46p binding to Emp47p occurs in the ER through the coiled-coil region in the luminal domains of both Emp47p and Emp46p, and dissociation occurs in the Golgi. Further, this coiled-coil region is also required for Emp47p to form an oligomeric complex of itself in the ER, which is essential for exit of Emp47p from the ER. Our results suggest that Emp47p is a receptor protein for Emp46p that allows for the selective transport of this protein, and this event involves receptor oligomerization.
Arfophilins Are Dual Arf/Rab 11 Binding Proteins That Regulate Recycling Endosome Distribution and Are Related toDrosophilaNuclear Fallout
Authors: Hickson Gilles R.X. , Matheson Johanne , Riggs Blake , Maier Valerie H. , Fielding Andrew B. , Prekeris Rytis , Sullivan William , Barr Francis A. , Gould Gwyn W.
Published: April 2003

Arfophilin is an ADP ribosylation factor (Arf) binding protein of unknown function. It is identical to the Rab11 binding protein eferin/Rab11-FIP3, and we show it binds both Arf5 and Rab11. We describe a related protein, arfophilin-2, that interacts with Arf5 in a nucleotide-dependent manner, but not Arf1, 4, or 6 and also binds Rab11. Arfophilin-2 localized to a perinuclear compartment, the centrosomal area, and focal adhesions. The localization of arfophilin-2 to the perinuclear compartment was selectively blocked by overexpression of Arf5-T31N. In contrast, a green fluorescent protein-arfophilin-2 chimera or arfophilin-2 deletions were localized around the centrosome in a region that was also enriched for transferrin receptors and Rab11 but not early endosome markers, suggesting that the distribution of the endosomal recycling compartment was altered. The arfophilins belong to a conserved family that includes Drosophila melanogaster nuclear fallout, a centrosomal protein required for cellularization. Expression of green fluorescent protein-nuclear fallout in HeLa cells resulted in a similar phenotype, indicative of functional homology and thus implicating the arfophilins in mitosis/cytokinesis. We suggest that the novel dual GTPase-binding capacity of the arfophilins could serve as an interface of signals from Rab and Arf GTPases to regulate membrane traffic and integrate distinct signals in the late endosomal recycling compartment.
An Estimator for Some Binary-Outcome Selection Models Without Exclusion Restrictions
Authors: Sartori Anne E.
Published: April 2003

This article provides a new maximum-likelihood estimator for selection models with dichotomous dependent variables when identical factors affect the selection equation and the equation of interest. Such situations arise naturally in game-theoretic models where selection is typically nonrandom and identical explanatory variables influence all decisions under investigation. When identical explanatory variables influence selection and a subsequent outcome of interest, the commonly used Heckman-type estimators identify from distributional assumptions about the residuals alone. When its own identifying assumption is reasonable, the new estimator allows the researcher to avoid the painful choice between identifying from distributional assumptions alone and adding a theoretically unjustified variable to the selection equation in a mistaken attempt to “boost” identification. The article uses Monte Carlo methods to compare the small-sample properties of the estimator with those of the Heckman-type estimator and ordinary probit.
Small-angle X-ray scattering studies on oxide layer thickness at the porous silicon interface
Authors: Björkqvist M. , Salonen J. , Laine E.
Published: April 2003

We have determined the thickness of an oxide layer at the p+-type porous silicon interface as a function of oxidation time, by using a small angle X-ray scattering (SAXS). The scattering experiments were carried out using a Kratky camera with a step-scanning device. Oxidation was achieved by storing the porous silicon samples in various temperatures under high relative humidity. The negative deviations from Porod's law were observed from the scattering curves of oxidized samples. The oxide layer thickness was determined from the scattering curve using a sigmoidal-gradient approximation for the diffuse boundary. The oxide layer thickness values as a function of oxidation time, obtained using SAXS are compared to measured weight increase values, caused by the oxidation.
The small-angle scattering structure functions of the single tetrahedron
Authors: Gille W.
Published: April 2003

Basic properties of the SAS correlation function γ (r) and related functions are represented for a tetrahedron of edge length a. An interval splitting into four basic r-intervals in a sequence of cases for averaging the intersection volume between two tetrahedrons has been performed. Remarkably simple analytic expressions result in the first r-interval. Indeed, γ(r) is a polynomial of degree three. The coefficients are given explicitly. The asymptotic expansion I_\infty (h) is compared with the exact scattering intensity I(h).
Total reflection X-ray fluorescence study of Langmuir monolayers on water surface
Authors: Novikova Natalia N. , Zheludeva Svetlana I. , Konovalov Oleg V. , Kovalchuk Mikhail V. , Stepina Nina D. , Myagkov Igor V. , Godovsky Yulij K. , Makarova Nina N. , Tereschenko Elena Yu. , Yanusova Ludmila G.
Published: April 2003

X-ray total external reflection fluorescence has been applied to detect an angular dependence of fluorescence yield modulated by evanescent/X-ray standing wave pattern from metal-rich organic monolayer alone on water surface. Theoretical consideration reveals that electric field intensity in a molecular monolayer is completely determined by an area per one molecule value that can be obtained from pressure-area isotherm. This allows getting an ion position inside a monolayer from the corresponding fluorescence angular dependence. The possibilities of the technique have been used at the SR beamline ID10B (ESRF) to characterize Langmuir monolayers of phthalocyanines and cyclolinear polyorganosiloxanes formed on air/water interface.
Small-angle X-ray scattering characterization of porous glasses
Authors: Walter G. , Kranold R. , Enke D. , Goerigk G.
Published: April 2003

Small-angle X-ray scattering has been used to examine porous glasses. The experiment and analysis of the extracted data are described with specific concern for the quantitative characterization of the pore structure. The techniques used are illustrated by the results obtained from two selected porous glasses. Small-angle X-ray scattering data of two series of novel porous glass systems are presented and discussed.
Benefits of polarized small-angle neutron scattering on magnetic nanometer scale structure modeling
Authors: Heinemann André , Wiedenmann Albrecht
Published: April 2003

Recent use of polarized neutron technique in small-angle scattering (SANS) have led to impressive results in the case of magnetic nanometer-scale structure analysis. In some particular cases this method offers the possibility to survey structure models with the necessary accuracy for the first time. The different cross sections for spin-up and spin-down neutron scattering on magnetic precipitates can be combined with the method of chemical contrast variation. All data fitting using structure models will benefit of that kind of constraints. The analysis of the interference term of nuclear and magnetic scattering respectively enables the extraction of additional information about the composition and magnetization profiles of the samples. Here we place emphasis on the difference of spin-up and spin-down neutron scattering intensities to obtain this information. This technique profits by the clear distinction between magnetic and nonmagnetic scattering contributions and the strong auxiliary conditions for model fitting procedures. Depending on the relative orientations of the external magnetic field, the local magnetization of the precipitates and the scattering vector, significant scattering patterns can be scrutinized. Beside general formulas for some special cases of present experimental interest we exercise the approach to a nontrivial case of data obtained from polarised SANS experiments at the Berlin Neutron Scattering Center (BENSC).
In situ study of the formation of CdS nanoparticles by small-angle X-ray scattering
Authors: Meneau Florian , Cristol Sylvain , Sankar Gopinathan , Dolbnya Igor P , Bras Wim , Catlow C Richard A , Thomas John M , Greaves G Neville
Published: April 2003

Time-resolved in situ small angle X-ray scattering measurements were carried out to monitor the formation of nanoparticles of cadmium sulfide, from a solution containing the corresponding acetate and thioacetamide under solvothermal conditions. Analysis of the SAXS data shows that spherical cadmium sulfide particles of ca 105 Å in radius form within the first minutes of the reaction and then grow uniformly to form cylindrical nanoclusters over a period of a few hours, resulting in a highly monodispersed particles distribution.
Prototype of a database for rapid protein classification based on solution scattering data
Authors: Sokolova Anna V. , Volkov Vladimir V. , Svergun Dmitri I.
Published: April 2003

Finding similarities in sequences and/or structures is one of the fastest ways of characterizing proteins. Similarity in atomic structure of proteins is generally more recognizable than similarity in sequence and may be more closely related to similarity in function. If the atomic structure is not available, useful information can be obtained by X-ray solution scattering. Ab initio methods to analyse the scattering data require longer computation time and yield low resolution models only. We present an approach to rapidly characterize proteins with unknown structure based on comparison of experimental scattering profiles with a database of scattering patterns calculated from known structures.
Structure factor for polydisperse fluids of particles with surface adhesion
Authors: Gazzillo Domenico , Giacometti Achille
Published: April 2003

An exactly solvable model for polydisperse fluids of particles with surface adhesion is discussed. For this model, alternative to Baxter's one and with factorized stickiness coefficients, all scattering functions can be computed analytically for an arbitrary number of components. An application to experimental small-angle scattering results on sterically stabilized colloidal particles interacting via an attractive short-ranged attraction shows the usefulness of this model. However, results on its thermodynamic properties reveal some intrinsic inconsistencies. A way out from this drawbacks is discussed in terms of a new potential.
Small-angle scattering characterization of n-aliphatic alcohol films adsorbed on hydroxyled porous silicas
Authors: Pikus S. , Kobylas E. , Ciccariello S.
Published: April 2003

The thickness of a film deposited on a porous sample can be determined by comparing the tail behaviour of the relevant small-angle scattering intensity with that predicted on the basis of some theoretical models of the film structure. A critical comparison of the present models is reported. The model depicting the film as a third homogeneous phase of the coated sample is the most predictive one because it allows us to determine also the surface area per coating molecule. This conclusion is checked by analyzing the small-angle scattering intensities of a set of samples obtained by coating, via an evaporative technique, a hydroxyled silica gel with different amounts of octadecanol or dodecanol.
Use of anomalous small-angle X-ray scattering for the investigation of highly charged colloids
Authors: Dingenouts N. , Merkle R. , Guo X. , Narayanan T. , Goerigk G. , Ballauff M.
Published: April 2003

We present a study of the radial structure of a spherical polyelectrolyte brushes by anomalous small-angle X-ray scattering. The spherical polyelectrolyte brushes consist of a solid poly(styrene) core of ca 100 nm diameter onto which long linear chains of poly(acrylic acid) (PAA) are densely grafted. A sufficiently high pH, these polyelectrolyte chains are fully charged. Rubidium ions are used as counterions because their adsorption edge (15 199.6 eV) can be conventiently reached by synchrotron radiation. By performing small-angle X-ray scattering studies at different energies of the incident radiation, the contribution of the Rb+ counterions can be analyzed separately. The scattering contribution of the counterions can be derived and compared to the scattering intensity of the entire particle. The distributions of the macro-ion and of the counterions are shown to be very similiar. This shows that the counterions must be confined within the brush.
Uniqueness of ab initio shape determination in small-angle scattering
Authors: Volkov Vladimir V. , Svergun Dmitri I.
Published: April 2003

Scattering patterns from geometrical bodies with different shapes and anisometry (solid and hollow spheres, cylinders, prisms) are computed and the shapes are reconstructed ab initio using envelope function and bead modelling methods. A procedure is described to analyze multiple solutions provided by bead modeling methods and to estimate stability and reliability of the shape reconstruction. It is demonstrated that flat shapes are more difficult to restore than elongated ones and types of shapes are indicated, which require additional information for reliable shape reconsrtuction from the scattering data.
Some key issues pertaining to analysis of small-angle scattering data affected by multiple scattering
Authors: Mazumder S. , Sen D. , Patra A.K.
Published: April 2003

The relevance of accounting for multiple scattering effects in small-angle scattering studies has increased today as more number of high resolution small-angle scattering facilities are available to probe large inhomogeneities. The effect of multiple scattering and the data analysis procedure depends upon the degree of multiple scattering whose measure in a specimen is conveniently expressed by N (= t/L the ratio of specimen thickness t to scattering mean free path L). It also depends upon the relative magnitude of the scattering mean free path L of radiation inside the matrix vis-a-vis the linear dimension R of the inhomogeneities. For L>>R, the scattering medium can be treated in a mean field way as far as the description of multiple scattering is concerned. Such a medium is termed as `effective medium'. But when the condition L>>R is invalidated, the statistical nature of the medium manifests. In the present paper, some key issues pertinent to analysis of small-angle scattering data affected by multiple scattering are addressed.
Small-angle neutron scattering by porous alumina membranes made of aligned cylindrical channels
Authors: Marchal Damien , Demé Bruno
Published: April 2003

Small-angle neutron scattering is used to investigate porous alumina membranes (γ-Al2O3) made of parallel channels with cylindrical shape. The membranes are produced by anodization of thin aluminium sheets. The scattering experiments are performed in a coaxial geometry where the cylindrical pores are oriented with their long axis parallel to the incident beam resulting in isotropic scattering patterns due to the circular symmetry. The results obtained with commercial Anodisc® membranes and membranes synthesized in our laboratory are compared to radialy averaged 2D Fourier transforms of electron microscopy images of the alumina membrane surface and to known values of the materials' porosity.
Small-angle neutron scattering analysis of the precipitation behaviour in a maraging steel
Authors: Staron P. , Jamnig B. , Leitner H. , Ebner R. , Clemens H.
Published: April 2003

Maraging steels are widely used in many technological sectors such as aerospace and military as well as for tools and dies because of their high strength and toughness. For further improvement of these mechanical properties, which are mainly controlled by intermetallic precipitates in the nanometer size range, fundamental understanding of the influence of composition and heat treatment on the microstructural development is necessary. Quantitative characterisation of the precipitate dispersion based on transmission electron microscopy (TEM) is complicated because of the small size of the precipitates. Therefore, small-angle neutron scattering (SANS) was used in addition to determine precipitate size distributions and volume fractions. SANS and TEM measurements were carried out on a cobalt-free corrosion resistant maraging steel after different ageing treatments. The SANS results showed that after ageing for 15 min a large number of precipitates with radii less than 1 nm have been formed. An analysis of the chemical composition of the nanometer-sized precipitates by direct methods is rather difficult. Therefore, the ratio of magnetic to nuclear scattering intensity was additionally analysed in order to gain information on the composition of the precipitates. From the results it is concluded that the precipitates consist of the intermetallic Ti6Si7Ni16 phase.
Ultra small-angle X-ray scattering: conditions, limits and results in speckle experiments
Authors: Livet Frédéric , Bley Françoise , Ehrburger-Dolle Françoise , Geissler Erik , Lebolloc'h David , Schulli Tobias
Published: April 2003

To carry out small-angle scattering experiments with X-rays in the scattering vector range q < 10−3 Å−1 with area detectors, background must be carefuly reduced. The principal source of background is slit scattering. Careful polishing of slits allows slit diffraction to be observed, which can be calculated from wave equations. In this case, the background takes the shape of thin streaks perpendicular to the slit edges. This introduces the design of new beamstops, which are cross-shaped. Typical results obtained on the D2AM beamline of the ESRF are shown, especially for the case of coherent scattering.
Change in the nano-structure of Al-base alloy ribbons in response to tensile stress – a small-angle X-ray scattering study
Authors: Kamiyama Tomoaki , Kimura Hisamichi , Sasamori Kenichiro , Inoue Akihisa
Published: April 2003

The microstructure of aluminum-base alloys consists of icosahedral or amorphous particles 3 to 10 nm in size distributed in the face centered Al-rich matrix. These particles are considered to cause high mechanical strength. Structural changes due to the deformation were detected for some Al-base alloys by small-angle X-ray scattering, even after very weak plastic deformation. An increase in the scattering intensities parallel to the uniaxial tensile stress was detected for scattering vectors near 0.02 Å-1, and can be attributed to the increase in the structure factor for the correlation between particles. This indicates that the degree of particle ordering is increased in the direction of the uniaxial tension with the motion of dislocations under tensile stress.
Optimisation of a crystal design for a Bonse–Hart camera
Authors: Villa Mario , Baron Matthias , Hainbuchner Martin , Jericha Erwin , Leiner Vincent , Schwahn Dieter , Seidl Erwin , Stahn Jochen , Rauch Helmut
Published: April 2003

Bonse-Hart double-crystal diffractometers (DCDs) with multi-bounce channel-cut crystals show rocking curves that depart dramatically from dynamical diffraction theory in their wings. The intrinsic background is many orders of magnitude higher than the predictions of dynamical diffraction theory. This effect was studied at the ultra-small-angle neutron scattering facility at the Atominstitut in Wien and at facilities in Grenoble, Jülich and Villigen. The scattering intensity contains Bragg reflections from the front and the back faces, and thermal diffuse scattering from the internal volume. The aim of this study was to eliminate this contamination and develop a new crystal design which provides optimal resolution. Therefore different ways were tested. In the first step the contamination was eliminated by cutting a groove in the middle of the back plate of the channel-cut crystals and inserting a cadmium absorber in this groove. With this modification an additional suppression of the wings of the rocking curve of about one order of magnitude was achieved. After this, we developed a new design for a DCD. The concept for this new crystal design was to avoid the back reflection and the thermal diffuse scattering. The different steps on the way to produce these crystals are presented in a detailed way. The crystal preparation and the different instruments where these crystals have been tested are also described.
Small-angle scattering in materials science - a short review of applications in alloys, ceramics and composite materials
Authors: Fratzl Peter
Published: April 2003

Since the early days of small-angle scattering (SAS), this technique has been used to characterize the structure of solid materials on the nanometer scale. Some recent developments in this field will be reviewed, focusing on alloys, ceramics and (nano-) composite materials. The large field of SAS from polymeric systems will not be covered. Classical applications of SAS are the characterization of pores or precipitates in alloys, for instance. In more recent years, a range of new applications for X-ray SAS has emerged owing to the availability of more and more brilliant (synchrotron) X-ray sources. Examples include grazing-incidence SAXS, used increasingly to characterize nano-structured surfaces on semiconductors and also on other materials. The use of a narrow X-ray beam also allows the investigation of extremely inhomogeneous or hierarchically structured materials by scanning SAXS. In this approach, the specimen is moved step by step across an X-ray beam with a diameter of a few micrometers (or even less), collecting a SAXS pattern at each step. In neutron SAS, the systematic use of magnetic cross-sections has brought considerable progress in the study of magnetic nano-particles or nano-composites. Single crystalline or textured materials are being studied under several orientations with respect to the primary beam to yield three-dimensional (neutron or X-ray) SAS patterns. In many cases, SAS is combined with other techniques, such as electron microscopy, spectroscopy or mechanical characterization, the most elegant being an in-situ combination. A number of recent examples for the above-mentioned approaches will be given.
Grazing incidence small-angle X-ray scattering of BN-Fe and BN-Ag nanocomposite films obtained by cosputtering and multilayer deposition techniques
Authors: Babonneau David , Camelio Sophie , Girardeau Thierry , Jaouen Michel , Lyon Olivier
Published: April 2003

We have elaborated BN-Fe and BN-Ag nanocomposite films by ion-beam sputtering codeposition and multilayer deposition. Grazing incidence small-angle X-ray scattering experiments have been performed to study the nanostructure of the films as a function of the deposition conditions and of the metallic species. The results show that the multilayer method generates a self-organized growth from plane to plane and a small polydispersity. The cosputtering technique displays a more random arrangement of nanoparticles but has the advantage of leading to a columnar growth when assisting the deposition with a nitrogen ion beam. Furthermore, the presence of two families of nanoparticles (small elongated clusters within the matrix and large particles on the surface) has been evidenced in the case of codeposition of BN and Ag under assistance.
Cold neutron beam focusing by a superconducting sextupole magnet
Authors: Suzuki Jun-ichi , Oku Takayuki , Adachi Tomohiro , Shimizu Hirohiko M. , Hirumachi Tamiko , Tsuchihashi Takahiro , Watanabe Ikuo
Published: April 2003

We have developed a superconducting sextupole magnet with about 50 mm in bore diameter to focus cold neutron beams with large cross-section and have investigated its focusing and polarizing effect. Large gain in neutron intensity and high neutron polarization have been obtained by numerical simulation for highly collimated neutron beams. We discuss applications of this magnet for small-angle neutron scattering experiments.
Grazing incidence small-angle X-ray scattering study of defects in deuterium implanted monocrystalline silicon
Authors: Dubček P. , Pivac B. , Bernstorff S. , Corni F. , Tonini R. , Ottaviani G.
Published: April 2003

Grazing incidence small-angle X-ray scattering was used to study monocrystalline silicon samples implanted with deuterium ions at an energy of 24 keV and to the dose of 2 × 1016 ions/cm2. Samples were annealed isochronally at different temperatures in the range from 393 to 973 K. Due to the relaxation of the defects structures, i.e. redistribution of vacancies and deuterium, strong particle like contribution is observed in addition to the rough surface scattering, already at 393 K annealing. During the annealing, this particles (agglomerations of vacancies) are gradually dissolved till 623 K annealing temperature. Another agglomeration mechanism takes over at about 773 K when a different type of particle growth is observed, and these are dissolved again at about 973 K. The sizes of detected particles are in 2–3 nm range. Also, the interference type of scattering from a film of about 30 nm thickness (the top layer, mostly unaffected by implantation) is observed. This film is gradually getting thinner with the increasing annealing temperature, due to the redistribution of the defects and the structure relaxation.