bluuebunny/crossref_metadata_2025 huggingface dataset:
How do we know that the Antarctic environment is fine?
Authors: Walton D.W.H.
Published: April 2004

One might imagine that the only continent in the world devoted to peace and science would be certain to play a leadership role in global questions that needed a scientific answer. Indeed, to a dispassionate observer, the present situation with respect to reporting on the state of the Antarctic environment must seem bizarre. All the Antarctic Treaty Consultative Parties are members of the United Nations Environment Programme, and all are apparently committed to providing State of the Environment Reports for their respective regions. Why then have some of these very nations been so reluctant to accept that Antarctica is a key part of this world and, to provide the holistic view required, needs to be included in the reporting? The list of excuses for delay is lengthy: no money; no secretariat to organize through; likely to be too expensive; no clear reason to undertake it; not needed at present; who would be the audience; how would we maintain political oversight; etc. but none of them ever appeared insoluble. This has been clearly demonstrated by the recent publication by New Zealand of a State of the Environment Report for the Ross Sea Region.
The treatment of spatial autocorrelation in biological surveys: the case of line transect surveys
Authors: Ferguson J.W.H. , Bester M.N.
Published: April 2004

Marked spatial autocorrelation was encountered in an extensive data set on Antarctic seal densities as well as Antarctic pack ice characteristics. Whilst the methodology of measuring spatial autocorrelation is well developed, there is no established infrastructure for statistical inference in terms of correlation analysis or ANOVA. We survey the literature that deals with these problems, as well as some of the approaches that have been proposed for taking autocorrelation into account in inferential statistics. We apply these approaches to a data set comprising Antarctic pack ice seal counts as well as a few environmental measures. In contrast to the predictions from the existing literature, nonlinear estimation suggested that Pearson's r substantially overestimates the true correlation between seal densities and environmental variables. When compared to spatially adjusted analysis of variance, conventional ANOVA that compared seal densities or pack ice characteristics in different areas overestimated the degree of difference between these areas in proportion to the degree of spatial autocorrelation of the particular data set. In our case, the effects of spatial autocorrelation were not neutralised by treating entire transects as single points. These results emphasise the need for a methodology that takes spatial autocorrelation into account for interpreting the spatial data on Antarctic seals collected during the Antarctic pack ice seal (APIS) program. New software written for performing these analyses is available from the senior author.
Analysis of acoustic dot echo signature over an Antarctic ice shelf: the possible remote sensing of Antarctic petrels
Authors: Anderson Philip S.
Published: April 2004

Data from a monostatic acoustic radar operating at British Antarctic Survey's Halley station on a coastal Antarctic ice shelf show a band of small target echoes at an altitude of 700–1000 m during spring 1991. Statistical analysis of the echo signature show that the targets are spread more evenly in the horizontal than would be expected for a random signature, whilst the local distribution in the vertical is Gaussian. Similar echo signatures have been observed previously, and are attributed to birds, bats or insects: the Antarctic data are also consistent with bird targets, but the case is not proven. No birds have been observed directly, but at 700 m they would be barely visible to the naked eye. The nearest nesting area with suitably large numbers of birds (Antarctic petrels, Thalassoica antarctica) is a few hundred kilometres away. Estimates of velocity and target density imply that the Halley site would need to be specially favoured by the colony for their acoustic signature to be observed in such numbers, but such might be the case due to the presence of perennial coastal open water to the west of the station.
Seasonality of volcanic eruptions
Authors: Mason B. G. , Pyle D. M. , Dade W. B. , Jupp T.
Published: April 2004

An analysis of volcanic activity during the last three hundred years reveals that volcanic eruptions exhibit seasonality to a statistically significant degree. This remarkable pattern is observed primarily along the Pacific “Ring of Fire” and locally at some individual volcanoes. Globally, seasonal fluctuations amount to 18% of the historical average monthly eruption rate. In some regions, seasonal fluctuations amount to as much as 50% of the average eruption rate. Seasonality principally reflects the temporal distribution of the smaller, dated eruptions (volcanic explosivity index of 0–2) that dominate the eruption catalog. We suggest that the pattern of seasonality correlates with the annual Earth surface deformation that accompanies the movement of surface water mass during the annual hydrological cycle and illustrate this with respect to global models of surface deformation and regional measurements of annual sea level change. For example, seasonal peaks in the eruption rate of volcanoes in Central America, the Alaskan Peninsula, and Kamchatka coincide with periods of falling regional sea level. In Melanesia, in contrast, peak numbers of volcanic eruptions occur during months of maximal regional sea level and falling regional atmospheric pressure. We suggest that the well‐documented slow deformation of Earth's surface that accompanies the annual movements of water mass from oceans to continents acts to impose a fluctuating boundary condition on volcanoes, such that volcanic eruptions tend to be concentrated during periods of local or regional surface change rather than simply being distributed randomly throughout the year. Our findings have important ramifications for volcanic risk assessment and volcanoclimate feedback mechanisms.
Field measurements of water vapor continuum absorption in the visible and near‐infrared
Authors: Sierk B. , Solomon S. , Daniel J. S. , Portmann R. W. , Gutman S. I. , Langford A. O. , Eubank C. S. , Dutton E. G. , Holub K. H.
Published: April 2004

We carried out a spectroscopic field experiment designed to measure water vapor continuum absorption in the visible and near‐infrared spectral regions. Atmospheric spectra at ∼1 nm resolution were recorded using direct sunlight at high solar zenith angles during sunrise. Simultaneously radiosonde soundings and a network of geodetic Global Positioning System (GPS) receivers were deployed to constrain the water vapor amount along the absorption path. The solar spectra were analyzed using the Differential Optical Absorption Spectroscopy technique, while the GPS and radiosonde observations were used as input data to a line‐by‐line radiative transfer model to compute theoretical differential absorption spectra. The difference between the measurements and the simulated spectra provides information regarding the additional absorption owing to the H2O continuum. The data are compared to predictions of the widely used Clough‐Kneizys‐Davies continuum model as well as with theoretically derived spectra of water dimer. The results show that continuum absorption contributes significantly to solar absorption even in highly saturated H2O bands. The comparisons provide the needed observations to improve future continuum parameterizations.
Temporal and latitudinal distributions of stratospheric N2O isotopomers
Authors: Toyoda Sakae , Yoshida Naohiro , Urabe Taichiro , Nakayama Yusuke , Suzuki Takeshi , Tsuji Kazuhide , Shibuya Kazuhiko , Aoki Shuji , Nakazawa Takakiyo , Ishidoya Shigeyuki , Ishijima Kentaro , Sugawara Satoshi , Machida Toshinobu , Hashida Gen , Morimoto Shinji , Honda Hideyuki
Published: April 2004

Temporal and latitudinal variations of vertical profiles of N2O isotopomers were observed in the stratosphere over Japan (39°N, 142°E), Sweden (68°N, 20°E), and Antarctica (69°N, 40°E) during the period between 1990 and 2001. Samples were collected with a balloon‐borne cryogenic sampler and analyzed by mass spectrometry in the laboratory. Observed enrichment factors for heavier isotopomers (15N14N16O, 14N15N16O, and 14N14N18O) relative to 14N14N16O were nearly constant in the lower stratosphere (less than ∼22 km) but increased at higher altitudes (∼22–35 km) while showing seasonal and latitudinal differences. Enrichment factors during the photolysis and photo‐oxidation of N2O were also obtained in laboratory experiments and compared with those observed. We found that in the higher‐altitude region (1) fractionation of the isotopomers is mainly determined by photolysis, but is also affected by physical processes, (2) subsidence of air masses in the winter polar vortex induces the intrusion of an upper stratospheric air mass depleted in N2O, and (3) decay of the vortex in the local spring leads to rapid horizontal advection of midlatitude air masses. At lower altitudes, isotopomer ratios are determined by photolysis, photo‐oxidation, and the mixing of air masses within the stratosphere or between the stratosphere and the troposphere. Secular trend of isotopomer profiles was not detectable over Japan during 11 years. Assuming that the lower stratospheric air over midlatitudes is exchanged with the troposphere, isotopomer ratios of the N2O “back‐flux” from the stratosphere were estimated. These values can be used in the isotopomeric mass balance model to constrain the global N2O budget.
Enzymic characterization with progress curve analysis of a collagen peptidase from an enthomopathogenic bacterium, Photorhabdus luminescens
Authors: MAROKHÁZI Judit , KÓCZÁN György , HUDECZ Ferenc , GRÁF László , FODOR András , VENEKEI István
Published: April 2004

A proteolytic enzyme, Php-B (Photorhabdus protease B), was purified from the entomopathogenic bacterium, Photorhabdus luminescens. The enzyme is intracellular, and its molecular mass is 74 kDa. Tested on various peptide and oligopeptide substrates, Php-B hydrolysed only oligopeptides, with significant activity against bradykinin and a 2-furylacryloyl-blocked peptide, Fua-LGPA (2-furylacryloyl-Leu-Gly-Pro-Ala; kcat=3.6×102 s−1, Km=5.8×10−5 M−1, pH optimum approx. 7.0). The pKa1 and the pKa2 values of the enzyme activity (6.1 and 7.9 respectively), as well as experiments with enzyme inhibitors and bivalent metal ions, suggest that the activity of Php-B is dependent on histidine and cysteine residues, but not on serine residues, and that it is a metalloprotease, which most probably uses Zn2+ as a catalytic ion. The enzyme's ability to cleave oligopeptides that contain a sequence similar to collagen repeat (-Pro-Xaa-Gly-), bradykinin and Fua-LGPA (a synthetic substrate for bacterial collagenases and collagen peptidases), but not native collagens (types I and IV) or denatured collagen (gelatin), indicates that Php-B is probably a collagen peptidase, the first enzyme of this type to be identified in an insect pathogen, that might have a role in the nutrition of P. luminescens by degrading small collagen fragments. For the determination of enzyme kinetic constants, we fitted a numerically integrated Michaelis–Menten model to the experimental progress curves. Since this approach has not been used before in the characterization of proteases that are specific for the P1´–P4´ substrate sites (e.g. collagenolytic enzymes), we present a comparison of this method with more conventional ones. The results confirm the reliability of the numerical integration method in the kinetic analysis of collagen-peptide-hydrolysing enzymes.
DES2 protein is responsible for phytoceramide biosynthesis in the mouse small intestine
Authors: OMAE Fumio , MIYAZAKI Masao , ENOMOTO Ayako , SUZUKI Minoru , SUZUKI Yusuke , SUZUKI Akemi
Published: April 2004

The C-4 hydroxylation of sphinganine and dihydroceramide is a rate-limiting reaction in the biosynthesis of phytosphingolipids. Mouse DES1 (MDES1) cDNA homologous to the Drosophila melanogaster degenerative spermatocyte gene-1 (des-1) cDNA leads to sphingosine Δ4-desaturase activity, and another mouse homologue, MDES2, has bifunctional activity, producing C-4 hydroxysphinganine and Δ4-sphingenine in yeast [Ternes, Franke, Zahringer, Sperling and Heinz (2002) J. Biol. Chem. 277, 25512–25518]. Here, we report the characterization of mouse DES2 (MDES2) using an in vitro assay with a homogenate of COS-7 cells transfected with MDES2 cDNA and N-octanoyl-sphinganine and sphinganine as substrates. MDES2 protein prefers dihydroceramide as a substrate to sphinganine, and exhibits dihydroceramide Δ4-desaturase and C-4 hydroxylase activities. MDES2 mRNA content was high in the small intestine and abundant in the kidney. In situ hybridization detected signals of MDES2 mRNA in the crypt cells. Immunohistochemistry using an anti-MDES2 peptide antibody stained the crypt cells and the adjacent epithelial cells. These results suggest that MDES2 is the dihydroceramide C-4 hydroxylase responsible for the biosynthesis of enriched phytosphingoglycolipids in the microvillous membranes of intestinal epithelial cells.
Identification and characterization of plant glycerophosphodiester phosphodiesterase
Authors: van der REST Benoît , ROLLAND Norbert , BOISSON Anne-Marie , FERRO Myriam , BLIGNY Richard , DOUCE Roland
Published: April 2004

GPX-PDE (glycerophosphodiester phosphodiesterase; EC 3.1.4.46) is a relatively poorly characterized enzyme that catalyses the hydrolysis of various glycerophosphodiesters (glycerophosphocholine, glycerophosphoethanolamine, glycerophosphoglycerol, glycerophosphoserine and bis-glycerophosphoglycerol), releasing sn-glycerol 3-phosphate and the corresponding alcohol. In a previous study, we demonstrated the existence of a novel GPX-PDE in the cell walls and vacuoles of plant cells. Since no GPX-PDE had been identified in any plant organism, the purification of GPX-PDE from carrot cell walls was attempted. After extraction of cell wall proteins from carrot cell suspension cultures with CaCl2, GPX-PDE was purified up to 2700-fold using, successively, ammonium sulphate precipitation, gel filtration and concanavalin A–Sepharose. Internal sequence analysis of a 55 kDa protein identified in the extract following 2700-fold purification revealed strong similarity to the primary sequence of GLPQ, a bacterial GPX-PDE. To confirm the identity of plant GPX-PDE, an Arabidopsis thaliana cDNA similar to that encoding the bacterial GPX-PDE was cloned and overexpressed in a bacterial expression system, and was used to raise antibodies against the putative Arabidopsis thaliana GPX-PDE. Immunochemical assays performed on carrot cell wall proteins extracted by CaCl2 treatment showed a strong correlation between GPX-PDE activity and detection of the 55 kDa protein, validating the identity of the plant GPX-PDE. Finally, various properties of the purified enzyme were investigated. GPX-PDE is a multimeric enzyme, specific for glycerophosphodiesters, exhibiting a Km of 36 µM for glycerophosphocholine and active within a wide pH range (from 4 to 10). Since these properties are similar to those of GLPQ, the bacterial GPX-PDE, the similarities between plant and bacterial enzymes are also discussed.
Identification and characterization of the conserved nucleoside-binding sites in the Epstein-Barr virus thymidine kinase
Authors: WU Chung-Chun , CHEN Min-Che , CHANG Ya-Ru , HSU Tsuey-Ying , CHEN Jen-Yang
Published: April 2004

Thymidine kinase (TK), encoded by EBV (Epstein–Barr virus), is an attractive target for antiviral therapy and provides a novel approach to the treatment of EBV-associated malignancies. Despite the extensive use of nucleoside analogues for the treatment of viral infections and cancer, the structure–function relationship of EBV TK has been addressed rarely. In the absence of any structural information, we sought to identify and elucidate the functional roles of amino acids in the nucleoside-binding site using site-directed mutagenesis. Through alignment with other human herpesviral TK protein sequences, we predicted that certain conserved regions comprise the nucleoside-binding site of EBV TK and, through site-directed mutagenesis, showed significant changes in activity and binding affinity for thymidine of site 3 (-DRH-) and 4 (-VFP-) mutants. For site 3, only mutants D392E (Asp392→Glu) and R393H retain activity, indicating that a negative charge is important for Asp392 and a positive charge is required for Arg393. The increased binding affinities of these two mutants for 3´-deoxy-2´,3´-didehydrothymidine suggest that the two residues are also important for substrate selection. Interestingly, the changed metal-ion usage pattern of D392E reveals that Asp392 plays multiple roles in this region. His394 cannot be compensated by other amino acids, also indicating a crucial role. In site 4, the F402Y mutant retains full activity; however, F402S retains only 60% relative activity. Strikingly, when Phe402 is substituted with serine residue, the original preferred pyrimidine substrates, such as 3´-azido-3´-deoxythymidine, iododeoxyuridine and β-l-5-iododioxolane uracil (l-form substrate), have decreased competitiveness with thymidine, suggesting that Phe402 plays a crucial role in substrate specificity and that the aromatic ring is important for function.
Identification of furin pro-region determinants involved in folding and activation
Authors: BISSONNETTE Lyne , CHAREST Gabriel , LONGPRÉ Jean-Michel , LAVIGNE Pierre , LEDUC Richard
Published: April 2004

The pro-region of the subtilisin-like convertase furin acts early in the biosynthetic pathway as an intramolecular chaperone to enable proper folding of the zymogen, and later on as an inhibitor to constrain the activity of the enzyme until it reaches the trans-Golgi network. To identify residues that are important for pro-region function, we initially identified amino acids that are conserved among the pro-regions of various mammalian convertases. Site-directed mutagenesis of 17 selected amino acids within the 89-residue pro-region and biosynthetic labelling revealed that I60A-furin and H66A-furin were rapidly degraded in a proteasome-dependent manner, while W34A-furin and F67A-furin did not show any autocatalytic activation. Intriguingly, the latter mutants proteolytically cleaved pro-von Willebrand factor precursor to the mature polypeptide, suggesting that the mutations permitted proper folding, but did not allow the pro-region to exercise its role in inhibiting the enzyme. Homology modelling of furin's pro-region revealed that residues Ile-60 and His-66 might be crucial in forming the binding interface with the catalytic domain, while residues Trp-34 and Phe-67 might be involved in maintaining a hydrophobic core within the pro-region itself. These results provide structural insights into the dual role of furin's pro-region.
Putrescine biosynthesis in mammalian tissues
Authors: COLEMAN Catherine S. , HU Guirong , PEGG Anthony E.
Published: April 2004

l-Ornithine decarboxylase provides de novo putrescine biosynthesis in mammals. Alternative pathways to generate putrescine that involve ADC (l-arginine decarboxylase) occur in non-mammalian organisms. It has been suggested that an ADC-mediated pathway may generate putrescine via agmatine in mammalian tissues. Published evidence for a mammalian ADC is based on (i) assays using mitochondrial extracts showing production of 14CO2 from [1-14C]arginine and (ii) cloned cDNA sequences that have been claimed to represent ADC. We have reinvestigated this evidence and were unable to find any evidence supporting a mammalian ADC. Mitochondrial extracts prepared from freshly isolated rodent liver and kidney using a metrizamide/Percoll density gradient were assayed for ADC activity using l-[U-14C]-arginine in the presence or absence of arginine metabolic pathway inhibitors. Although 14CO2 was produced in substantial amounts, no labelled agmatine or putrescine was detected. [14C]Agmatine added to liver extracts was not degraded significantly indicating that any agmatine derived from a putative ADC activity was not lost due to further metabolism. Extensive searches of current genome databases using non-mammalian ADC sequences did not identify a viable candidate ADC gene. One of the putative mammalian ADC sequences appears to be derived from bacteria and the other lacks several residues that are essential for decarboxylase activity. These results indicate that 14CO2 release from [1-14C]arginine is not adequate evidence for a mammalian ADC. Although agmatine is a known constituent of mammalian cells, it can be transported from the diet. Therefore l-ornithine decarboxylase remains the only established route for de novo putrescine biosynthesis in mammals.
Non-protein bound iron release during chemotherapy in cancer patients
Authors: WEIJL N. I. , ELSENDOORN T. J. , MOISON R. M. W. , LENTJES E. G. W. M. , BRAND R. , BERGER H. M. , OSANTO S.
Published: April 2004

Non-protein bound iron (NPBI) is able to catalyse oxidative reactions, causing damage to vital structures. Adverse effects induced by cisplatin seem, in part, to be mediated by free radicals. In the present study, we have measured plasma NPBI, various other iron parameters and antioxidants in 28 cancer patients undergoing cisplatin-based chemotherapy at various time points before and during chemotherapy. No NPBI was present prior to therapy, but within 1–4 days following the first administration of chemotherapy, mean NPBI rose significantly to 10.6±6.6 µmol/l (range, 0.6–21.3 µmol/l) in 18 (64.3%) of the 28 patients measured. The rise in NPBI was accompanied by a significant rise in total plasma iron and ferritin and a marked decrease in the latent iron-binding capacity. Concomitantly, plasma vitamins C and E decreased significantly, indicating consumption of antioxidants. Similar observations were also made during the fourth chemotherapy cycle. The increase in NPBI preceded and correlated significantly with chemotherapy toxicity, such as a decrease in leucocyte count and haemoglobin, with a transient rise in various liver enzymes and with known cisplatin-related toxicity, i.e. the loss of renal and hearing function. In conclusion, cisplatin chemotherapy induces oxidative damage which rapidly leads to release of iron from intracellular proteins and the appearance of NPBI. Bone marrow, red blood cells, liver and kidney seem to be a likely source of NPBI. The observed high levels of NPBI may be a major causative determinant in chemotherapy-induced toxicity.
Patterning-free integration of polymer light-emitting diode and polymer transistor
Authors: Li Z. L. , Yang S. C. , Meng H. F. , Chen Y. S. , Yang Y. Z. , Liu C. H. , Horng S. F. , Hsu C. S. , Chen L. C. , Hu J. P. , Lee R. H.
Published: April 2004

We demonstrate an integration of polymer light-emitting diode (LED) and polymer transistor in which no patterning of the organic layers is needed. Intrinsic high-mobility semiconducting conjugated polymer poly(3-hexylthiophene)(P3HT) is used as the hole-transport layer for polymer LED. The light emission efficiency is only slightly lower than the LED with conventional heavily doped hole-transport layer. Such LED is easily integrated with a P3HT transistor without patterning.
Light-modulated scanning tunneling spectroscopy for nanoscale imaging of surface photovoltage
Authors: Takeuchi Osamu , Yoshida Shoji , Shigekawa Hidemi
Published: April 2004

Light-modulated scanning tunneling spectroscopy (LM–STS) is proposed as a useful method for investigating spatially resolved surface photovoltage (SR–SPV). LM–STS provides the dependences of SR–SPV on bias voltage under constant tip-sample distance simultaneously with the entire dark/illuminated I–V curves. With this method, it is shown that SPV of a metallic Si(111) surface can be bias-dependent and SPV at zero bias voltage for Si(001) can be tip-sample-distance-dependent under conditions of small tip-sample distance and high illumination intensity. The importance of the experimental condition for interpreting experimentally obtained SR–SPV was suggested.
Avoiding cracks in self-assembled photonic band-gap crystals
Authors: Chabanov A. A. , Jun Y. , Norris D. J.
Published: April 2004

Thin colloidal crystals (or synthetic opals) composed of Stöber silica spheres typically develop cracks when they are utilized to obtain photonic band-gap crystals (or inverted opals). We find that, by sintering the silica spheres prior to assembly of the opal, these cracks can be avoided. We report the effects of temperature and duration of the heat treatment on 850 nm silica spheres using electron microscopy, thermogravimetry, and light scattering. We also find a large dependence of the refractive index of the silica on the temperature of the heat treatment. This may allow tuning of the refractive index of silica spheres.
Luminescence from processible quantum dot-polymer light emitters 1100–1600 nm: Tailoring spectral width and shape
Authors: Bakueva L. , Konstantatos G. , Levina L. , Musikhin S. , Sargent E. H.
Published: April 2004

Electroluminescent devices combining two families of PbS colloidal quantum dots to achieve spectrally tailored two-color emission are reported. Depending on device structure selected—the use of two separated layers versus a mixture of nanocrystals—the structures demonstrated light emission either in two infrared frequency peaks corresponding to the spectral region 1.1–1.6 μm or in a wide band spanning this same spectral region. Separated-layer devices exhibit wide tunability in the relative intensity of the two peaks by varying excitation conditions. Replacing oleate with octodecylamine ligands increases the internal electroluminescence efficiency to 3.1%.
p-type behavior in phosphorus-doped (Zn,Mg)O device structures
Authors: Heo Y. W. , Kwon Y. W. , Li Y. , Pearton S. J. , Norton D. P.
Published: April 2004

The characteristics of device structures that employ phosphorus-doped (Zn,Mg)O have been examined in a effort to delineate the carrier type behavior in this material. The capacitance–voltage properties of metal/insulator/P-doped (Zn,Mg)O diode structures were measured and found to exhibit a polarity consistent with the P-doped (Zn,Mg)O layer being p type. In addition, thin-film junctions comprising n-type ZnO and P-doped (Zn,Mg)O display asymmetric I–V characteristics that are consistent with the formation of a p–n junction at the interface. Although Hall measurements of the P-doped (Zn,Mg)O thin films yielded an indeterminate Hall sign due to a small carrier mobility, these results are consistent with previous reports that phosphorus can yield an acceptor state and p-type behavior in ZnO materials.
Continuous-wave operation of distributed feedback interband cascade lasers
Authors: Yang Rui Q. , Hill C. J. , Yang B. H. , Wong C. M. , Muller R. E. , Echternach P. M.
Published: April 2004

Continuous-wave distributed feedback interband cascade lasers operating near 3.3 μm are reported. Single longitudinal mode emission is achieved with side mode suppression ratio greater than 30 dB at temperatures up to 175 K. A clear Bragg stop band in the laser emission spectrum indicates a dominant index coupling with the first-order grating. Detailed characteristics of these lasers are discussed.
Very high spin polarization in GaAs by injection from a (Ga,Mn)As Zener diode
Authors: Van Dorpe P. , Liu Z. , Van Roy W. , Motsnyi V. F. , Sawicki M. , Borghs G. , De Boeck J.
Published: April 2004

We demonstrate an electrically injected electron spin polarization in GaAs of 80% at 4.6 K by interband tunneling from the valence band of (Ga,Mn)As into an (Al,Ga)As light-emitting diode. The polarization is analyzed by the oblique Hanle effect and vanishes at 120 K, the Curie temperature of the (Ga,Mn)As injector. The temperature and the bias dependence of the polarization are explained in terms of the properties of the (Ga,Mn)As/GaAs diode.
Near-bandedge cathodoluminescence of an AlN homoepitaxial film
Authors: Silveira E. , Freitas J. A. , Kneissl M. , Treat D. W. , Johnson N. M. , Slack G. A. , Schowalter L. J.
Published: April 2004

Cathodoluminescence experiments were performed on a high-quality AlN epitaxial film grown by organometallic vapor phase epitaxy on a large single crystal AlN substrate. The low-temperature near-bandedge spectra clearly show six very narrow lines. The thermal quenching behavior of these emission lines provides insight on how to assign them to free and bound exciton recombination processes. The binding energy for the free-exciton-A in AlN was found to be nearly twice that in GaN. The observation of the free-exciton-A first excited state permitted us to estimate its reduced effective mass and, by using recent reported values for the hole effective mass in Mg-doped AlN, the electron effective mass in AlN has been deduced.
Epitaxial growth of AlxGa1−xN on Si(111) via a ZrB2(0001) buffer layer
Authors: Tolle John , Kouvetakis John , Kim Dae-Woo , Mahajan S. , Bell A. , Ponce Fernando A. , Tsong I. S. T. , Kottke Michael L. , Chen Zhihao D.
Published: April 2004

Epitaxial growth of an Al0.2Ga0.8N(0001) film by metalorganic chemical vapor deposition (MOCVD) at 1050 °C on a Si(111) substrate via a ZrB2(0001) buffer layer has been accomplished free of unintentional Si doping. The in-plane lattice mismatch between Al0.2Ga0.8N(0001) and ZrB2(0001) is only 0.3% and good epitaxial relation is established with [112_0]AlGaN//[112_0]ZrB2//[1_10]Si. The cathodoluminescence (CL) spectrum of the Al0.2Ga0.8N shows a band-edge emission at 3.87 eV with full width at half maximum (FWHM) of 40 meV. Both the intensity and FWHM of the CL emission are comparable to those from a high-quality undoped Al0.2Ga0.8N film grown by MOCVD on sapphire. The close lattice match and the reflective nature of the ZrB2(0001) buffer layer are both attributes accountable for the optical quality of the Al0.2Ga0.8N grown on Si(111).
Sublobaric Acid and Oxolobaric Acid, Two New Depsidones from the Lichen Anzia hypoleucoides
Authors: Elix John A. , Wardlaw Judith H. , Yoshimura Isao
Published: April 2004

The depsidones sublobaric acid
(8-hydroxy-3-methoxy-11-oxo-1-propanoyl-6-pentyl-11H-dibenzo[b,e][1,4]-
dioxepin-7-carboxylic acid) (6) and oxolobaric acid
(1-(1′,4′-dioxopentyl)-8-hydroxy-3-methoxy-11-oxo-6-pentyl-11H-dibenzo[b,e][1,4]dioxepin-7-carboxylic
acid) (7) have been isolated from the
lichenAnzia hypoleucoides together with atranorin,
chloroatranorin, divaricatic acid and lobaric acid (1). The structure of
compounds (6) and (7) followed from a combination of spectroscopic data.
Pigments of Fungi. LII Anisochiral Flavomannin 6,6′,8-Tri-O-methyl Ether from an Australian Dermocybe Toadstool
Authors: Buchanan Malcolm S. , Gill Melvyn , Gimenez Alberto , Phonh-Axa Somphone , Raudies Evelin , Yu Jin , Palfreyman Anna R.
Published: April 2004

Flavomannin 6,6′,8-tri-O-methyl ether occurs in
the fruiting bodies of the Australian toadstool
Dermocybe sp. WAT 24274 as an anisochiral mixture of the
(3S,3′S,P)-
and
(3R,3′R,M)-enantiomers
(5) and (7), respectively, in which the former predominates to the extent of
50% e.e. The structure of the natural product is determined by
spectroscopic methods and the absolute configuration and enantiomeric purity
are deduced from the c.d. spectrum and by chemical degradation of the natural
product to a mixture of stereoisomeric dihydroanthracenones that has been
analysed by chiral h.p.l.c.
A Comparison of the Flash Vacuum Pyrolysis Products of Some N-Acylbenzotriazoles and N-Acylbenzisoxazolones
Authors: Baradarani Mehdi M. , Khalafy Jabbar , Prager Rolf H.
Published: April 2004

The flash vacuum pyrolysis (f.v.p.) products of
2-(1H-benzotriazol-1-ylcarbonyl)benzonitrile, methyl
2-(1H-benzotriazol-1-ylcarbonyl)benzoate and
1-(2-chloromethylbenzoyl)-1H-benzotriazole and the cor-
responding benzisoxazolones have been characterized. The benzotriazole
derivatives gave compounds whose origin suggests the predominance of radical
processes. At lower temperatures the benzisoxa- zolones gave benzoxazole
products consistent with a singlet carbene intermediate, but which had triplet
diradical properties at higher temperatures, leading to the formation of
acridine from the chloromethyl compound. The major low-temperature f.v.p.
product from the (chloromethylbenzoyl)benzisoxazolone was
indolo[1,2-b]benzoxazole.
From IUPAC. Specification of Components, Methods and Parameters in Fourier Transform Spectroscopy by Michelson and Related Interferometers
Authors: Bertie John E.
Published: April 2004

With the goal of ensuring that adequate information is presented in the
scientific literature to permit the reproduction of measurements in different
laboratories, this paper presents short lists of components, methods and
parameters that should be reported in papers that focus on spectra recorded on
Fourier transform spectrometers.
spectroscopy at modest resolution (0.25-8 cm-1) spectroscopy at high resolution (0.01 cm-1) Raman spectroscopy at modest resolution
Mechanism of homophilic adhesion by the neural cell adhesion molecule: Use of multiple domains and flexibility
Authors: Johnson C. P. , Fujimoto I. , Perrin-Tricaud C. , Rutishauser U. , Leckband D.
Published: April 2004

The extracellular regions of adhesion proteins of the Ig superfamily comprise multiple, tandemly arranged domains. We used directforce measurements to investigate how this modular architecture contributes to the adhesive interactions of the neural cell adhesion molecule (NCAM), a representative of this protein class. The extracellular region of NCAM comprises five immunoglobulin and two fibronectin domains. Previous investigations generated different models for the mechanism of homophilic adhesion that each use different domains. We use force measurements to demonstrate that NCAM binds in two spatially distinct configurations. Igdomain deletion mutants identified the domains responsible for each of the adhesive bonds. The measurements also confirmed the existence of a flexible hinge that alters the orientation of the adhesive complexes and the intermembrane distance. These results suggest that a combination of multiple bound states and internal molecular flexibility allows for sequentially synergistic bond formation and the ability to accommodate differences in intercellular space.
Requirement for a conserved Toll/interleukin-1 resistance domain protein in the
Caenorhabditis elegans
immune response
Authors: Liberati Nicole T. , Fitzgerald Katherine A. , Kim Dennis H. , Feinbaum Rhonda , Golenbock Douglas T. , Ausubel Frederick M.
Published: April 2004

The p38 mitogen-activated protein kinase pathway regulates innate immune responses in evolutionarily diverse species. We have previously shown that the
Caenorhabditis elegans
p38 mitogen-activated protein kinase, PMK-1, functions in an innate immune response pathway that mediates resistance to a variety of microbial pathogens. Here, we show that
tir-1,
a gene encoding a highly conserved Toll/IL-1 resistance (TIR) domain protein, is also required for
C. elegans
resistance to microbial pathogens. RNA interference inactivation of
tir-1
resulted in enhanced susceptibility to killing by pathogens and correspondingly diminished PMK-1 phosphorylation. Unlike all known TIR-domain adapter proteins, overexpression of the human TIR-1 homologue, SARM, in mammalian cells was not sufficient to induce expression of NF-κB or IRF3-dependent reporter genes that are activated by Toll-like receptor signaling. These data reveal the involvement of a previously uncharacterized, evolutionarily conserved TIR domain protein in innate immunity that is functionally distinct from other known TIR domain signaling adapters.
Biologically active noncalcemic analogs of 1α,25-dihydroxyvitamin D with an abbreviated side chain containing no hydroxyl
Authors: Plum Lori A. , Prahl Jean M. , Ma Xiaohong , Sicinski Rafal R. , Gowlugari Sumithra , Clagett-Dame Margaret , DeLuca Hector F.
Published: April 2004

Since the discovery of the active metabolite of vitamin D, i.e., 1α,25-dihydroxyvitamin D
3
, there has been a continuous effort to synthesize analogs able to carry out many of the functions of the native hormone without raising serum calcium concentration. The present report provides a series of previously undescribed analogs wherein this goal is realized. We have prepared 2-methylene-19-nor-1α-hydroxyvitamin D analogs of 1,25-(OH)
2
D
3
that possess only two to four carbons of the side chain without a hydroxyl thereon. Compared to 1,25-(OH)
2
D
3
, these analogs are slightly less active in binding to the vitamin D receptor, in causing HL-60 differentiation, and are slightly less active in
in vitro
transcription assays using the 24-hydroxylase promoter attached to a luciferase reporter gene. Of considerable importance is that these analogs, given to rats at daily doses of up to 70 μg/kg of body weight per day, are either unable or only slightly able to raise serum calcium concentration but are nevertheless able to suppress parathyroid hormone levels in plasma up to 100% and induce 24-hydroxylase mRNA in skin. Because of their ability to act
in vivo
without raising serum calcium levels, they may be of considerable interest for the systemic treatment of diseases such as psoriasis, cancer, and secondary hyperparathyroidism of renal failure, where a rise in serum calcium is undesirable.
Properties of Switch-like Bioregulatory Networks Studied by Simulation of the Hypoxia Response Control System
Authors: Kohn Kurt W. , Riss Joseph , Aprelikova Olga , Weinstein John N. , Pommier Yves , Barrett J. Carl
Published: April 2004

A complex bioregulatory network could be more easily comprehended if its essential function could be described by a small “core” subsystem, and if its response characteristics were switch-like. We tested this proposition by simulation studies of the hypoxia response control network. We hypothesized that a small subsystem governs the basics of the cellular response to hypoxia and that this response has a sharp oxygen-dependent transition. A molecular interaction map of the network was prepared, and an evolutionarily conserved core subsystem was extracted that could control the activity of hypoxia response promoter elements on the basis of oxygen concentration. The core subsystem included the hypoxia-inducible transcription factor (HIFα:ARNT heterodimer), proline hydroxylase, and the von Hippel-Lindau protein. Simulation studies showed that the same core subsystem can exhibit switch-like responses both to oxygen level and to HIFα synthesis rate, thus suggesting a mechanism for hypoxia response promoter element-dependent responses common to both hypoxia and growth factor signaling. The studies disclosed the mechanism responsible for the sharp transitions. We show how parameter sets giving switch-like behavior can be found and how this type of behavior provides a foundation for quantitative studies in cells.
Interaction of the S-phase cyclin Clb5 with an 'RXL' docking sequence in the initiator protein Orc6 provides an origin-localized replication control switch
Authors: Wilmes Gwendolyn M. , Archambault Vincent , Austin Richard J. , Jacobson Matthew D. , Bell Stephen P. , Cross Frederick R.
Published: April 2004

Cyclin-dependent kinases are critical regulators of eukaryotic DNA replication. We show that the S-phase cyclin Clb5 binds stably and directly to the origin recognition complex (ORC). This interaction is mediated by an “RXL” target sequence, or “Cy” motif, in the Orc6 subunit that is recognized by the “hydrophobic patch” region on Clb5. The Clb5-Orc6 interaction requires replication initiation, and is maintained throughout the remainder of S phase and into M phase. Eliminating the Clb5-Orc6 interaction has no effect on initiation of replication but instead sensitizes cells to lethal overreplication. We propose that Clb5 binding to ORC provides an origin-localized replication control switch that specifically prevents reinitiation at replicated origins.
Accreditation and library collections: the monographic holdings of academic libraries that support AACSB accredited and non‐accredited MBA programs in the state of Pennsylvania, USA
Authors: McGuigan Glenn S. , Crawford Gregory A. , Kubiske Jessica L.
Published: April 2004

This research used a sample of titles drawn from the Harvard Business School Core Collection to examine the holdings of libraries of institutions offering the Master of Business Administration degree within the state of Pennsylvania. Of  the  82 books selected from the Core Collection, the average number of books owned by the libraries was 25.3 (30.8 percent). In addition, the results showed that those libraries supporting AACSB accredited MBA programs owned significantly more of the sample of titles (37.06, 45.2 percent) than did libraries supporting non‐AACSB accredited programs (16.9, 20.6 percent).
Metadata for harvesting: the Open Archives Initiative, and how to find things on the Web
Authors: Hunter Philip , Guy Marieke
Published: April 2004

The Open Archives Initiative (OAI) protocol for metadata harvesting offers the prospect of resource discovery tools far beyond what is currently available to users of the Web via standard search engines. This article illustrates how existing information about available resources can be repurposed fairly easily and cheaply using standard tools. However the publishing of this information throws up a number of practical and philosophical questions which have to be addressed by projects and institutions.
Discretization of the magnetic field in MPD thrusters
Authors: Heiermann Jörg , Auweter‐Kurtz Monika
Published: April 2004

For the numerical simulation of magnetoplasmadynamic (MPD) self‐field thruster flow, the solution of one of the two dynamical Maxwell equations – Faraday's law – is required. The Maxwell equations and Ohm's law for plasmas can be summarized in one equation for the stream function so that the two‐dimensional, axisymmetric magnetic field can be calculated. The finite volume (FV) discretization of the equation on unstructured, adaptive meshes is presented in detail and solutions for different thruster currents are shown. The calculated thrust is compared with the experimental data.
A study of inadvertent domestication selection during start‐feeding of brown trout families
Authors: Glover K. A. , Taggart J. B. , Skaala Ø. , Teale A. J.
Published: April 2004

A study was undertaken to compare first‐feeding mortality among 10 brown trout families fed high (100%) and low (25%) rations in replicate mixed family tanks. Microsatellite DNA profiling was used to assign individual brown trout to family of origin. At the end of the 35 day experimental period, highly significant differences in overall mortality were observed between the two treatments, and within the treatments there were highly significant differences in family mortality. Both replicates displayed similar patterns of family mortality. Notably, the distribution of mortality among families differed significantly between the two ration treatments, although this was more distinct for some families than others. No correlation between mean family egg diameter and family mortality were observed within either feeding treatment, although a significant positive correlation between mean family egg diameter and timing of family mortality was observed. It is suggested that these data indicate the existence of a genotype x environment interaction relating to feeding level during the critical start‐feeding period.
First record of Diaphus dumerilii(Myctophiformes: Myctophidae) off the Portuguese mainland coast
Authors: Costa P. M.
Published: April 2004

Diaphus dumerilii, a myctophid, was recorded for the first time with the capture of a single specimen off Algarve, southern Portugal.
Ultraviolet light‐induced impairment of goldfish embryo development and evidence for photorepair mechanisms
Authors: Wiegand M. D. , Young D. L. W. , Gajda B. M. , Thuen D. J. M. , Rittberg D. A. H. , Huebner J. D. , Loadman N. L.
Published: April 2004

Goldfish Carassius auratus embryos were subjected to artificial ultraviolet‐B (UVB) radiation (280–320 nm) at various times during development to evaluate the effects on production of anatomically normal larvae. The UVB radiation used in these experiments included a higher proportion of shorter wavelengths compared to the natural spectrum. The development of embryos exposed to UVB for 2 or 4 h at 26 h post‐fertilization was severely impaired whereas similar exposures at 50 or 74 h post‐fertilization had no effect. A 2 h exposure to UVB commencing at 2 h post‐fertilization did not adversely affect embryonic development whereas a 4 h exposure to a lower dose did. At 50 h post‐fertilization, when embryos were normally resistant to UVB, denial of access to visible light and UVA before, during and after exposure to UVB caused impairment of development. Analysis of DNA fragment length after incubation with an endonuclease suggested that UVB damage at 50 h was caused by formation of pyrimidine dimers. This study demonstrated that the sensitivity of goldfish embryos to UVB varied during development and that resistance to UVB in later developmental stages included a photorepair mechanism.
Comparative proximate body composition of Atlantic salmon with emphasis on parr from fluvial and lacustrine habitats
Authors: Dempson J. B. , Schwarz C. J. , Shears M. , Furey G.
Published: April 2004

The nutritional status of Atlantic salmon Salmo salar parr was assessed by examining how proximate body composition and energy content (kJ g−1) were associated with the habitat rearing origin of parr utilizing fluvial or lacustrine areas. Comparisons were made among sampling sites within the two habitats, as well as between the two major habitat types applying both fixed effect and random effect models. Mean protein concentration varied from 13·87 to 15·67% among fluvial sites, and from 14·96 to 16·38% among lacustrine sampling locations. Mean fat concentration ranged from 1·71 to 3·32% and from 2·22 to 4·29% among fluvial and lacustrine locations, respectively, with energy concentration, on average, c. 11% higher in lacustrine parr. Interpretation of results of comparisons between habitats was dependent upon the statistical model used. Benefits associated with lacustrine rearing, such as greater body size and nutritional status, have implications for overwintering survival in fresh water as well as subsequent survival during initial sea entrance as smolts.
The role of microtubules in cellular organization and endocytosis in the plant pathogen Ustilago maydis
Authors: Steinberg G. , Fuchs U.
Published: April 2004

Microtubules are an important part of the eukaryotic cytoskeleton, which participates in numerous essential cellular processes. In fungi interphase microtubules mediate cell polarity and participate in polar growth. However, our understanding of their detailed role in fungal growth is just at the beginning. In growing cells of the plant pathogenic fungus Ustilago maydis microtubules are organized by polar microtubule organizing centres that focus the microtubule minus ends at the small bud. Two opposing motor complexes utilize this microtubule polarity. Cytoplasmic dynein and a kinesin of the Unc104/Kif1A family of kinesins mediate rapid bi‐directional transport of early endosomes. A balance of their activity is required for cell cycle‐dependent accumulation of early endosomes at the growth site, the rear cell pole and the region of cell cleavage. Mutant phenotypes suggest that these endosomes participate in polar growth, bud site selection and cell separation. Therefore, our data suggest that endocytotic membrane recycling participates in local exocytosis, and that the microtubule cytoskeleton has a crucial role in this process.