bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixture of Covariance Structure Models to Identify Different Types of Life Style
Authors: Stein Petra
Published: July 2006

A central topic of empirical social research is the problem of unobserved heterogeneity. To solve this problem at least partially, a statistical model is presented: the finite mixture of conditional mean and covariance structure models. In this approach, the expected values in each component of a mixture may depend on normally or nonnormally distributed regressor variables. The expected value and the covariance matrix in each component of the mixture are parameterized using conditional mean and covariance structure models. Three different procedures for estimating the parameters of these models are briefly discussed. The model and the estimation procedures are applied to data of the German General Social Survey 1998 to identify heterogenous types of life style. Since different regression models with latent variables may be used for each type, it is not only possible to cover different types of life style, but also different types of relationships between life style dimensions and the influences of sociodemographic variables on life style.
Evaluation of ozone and water vapor fields from the ECMWF reanalysis ERA‐40 during 1991–1999 in comparison with UARS satellite and MOZAIC aircraft observations
Authors: Oikonomou E. K. , O'Neill A.
Published: July 2006

The European Centre for Medium‐Range Weather Forecasts (ECMWF) 40‐year Re‐analysis (ERA‐40) ozone and water vapor reanalysis fields during the 1990s have been compared with independent satellite data from the Halogen Occultation Experiment (HALOE) and Microwave Limb Sounder (MLS) instruments on board the Upper Atmosphere Research Satellite (UARS). In addition, ERA‐40 has been compared with aircraft data from the Measurements of Ozone and Water Vapour by Airbus In‐Service Aircraft (MOZAIC) program. Overall, in comparison with the values derived from the independent observations, the upper stratosphere in ERA‐40 has about 5–10% more ozone and 15–20% less water vapor. This dry bias in the reanalysis appears to be global and extends into the middle stratosphere down to 40 hPa. Most of the discrepancies and seasonal variations between ERA‐40 and the independent observations occur within the upper troposphere over the tropics and the lower stratosphere over the high latitudes. ERA‐40 reproduces a weaker Antarctic ozone hole, and of less vertical extent, than the independent observations; values in the ozone maximum in the tropical stratosphere are lower for the reanalysis. ERA‐40 mixing ratios of water vapor are considerably larger than those for MOZAIC, typically by 20% in the tropical upper troposphere, and they may exceed 60% in the lower stratosphere over high latitudes. The results imply that the Brewer‐Dobson circulation in the ECMWF reanalysis system is too fast, as is also evidenced by deficiencies in the way ERA‐40 reproduces the water vapor “tape recorder” signal in the tropical stratosphere. Finally, the paper examines the biases and their temporal variation during the 1990s in the way ERA‐40 compares to the independent observations. We also discuss how the evaluation results depend on the instrument used, as well as on the version of the data.
Dynamics of diffusive bubble growth and pressure recovery in a bubbly rhyolitic melt embedded in an elastic solid
Authors: Chouet Bernard , Dawson Phillip , Nakano Masaru
Published: July 2006

We present a model of gas exsolution and bubble expansion in a melt supersaturated in response to a sudden pressure drop. In our model, the melt contains a suspension of gas bubbles of identical sizes and is encased in a penny‐shaped crack embedded in an elastic solid. The suspension is modeled as a three‐dimensional lattice of spherical cells with slight overlap, where each elementary cell consists of a gas bubble surrounded by a shell of volatile‐rich melt. The melt is then subjected to a step drop in pressure, which induces gas exsolution and bubble expansion, resulting in the compression of the melt and volumetric expansion of the crack. The dynamics of diffusion‐driven bubble growth and volumetric crack expansion span 9 decades in time. The model demonstrates that the speed of the crack response depends strongly on volatile diffusivity in the melt and bubble number density and is markedly sensitive to the ratio of crack thickness to crack radius and initial bubble radius but is relatively insensitive to melt viscosity. The net drop in gas concentration in the melt after pressure recovery represents only a small fraction of the initial concentration prior to the drop, suggesting the melt may undergo numerous pressure transients before becoming significantly depleted of gases. The magnitude of pressure and volume recovery in the crack depends sensitively on the size of the input‐pressure transient, becoming relatively larger for smaller‐size transients in a melt containing bubbles with initial radii less than 10−5 m. Amplification of the input transient may be large enough to disrupt the crack wall and induce brittle failure in the rock matrix surrounding the crack. Our results provide additional basis for the interpretation of volume changes in the magma conduit under Popocatépetl Volcano during Vulcanian degassing bursts in its eruptive activity in April–May 2000.
Ice core evidence for a second volcanic eruption around 1809 in the Northern Hemisphere
Authors: Yalcin Kaplan , Wake Cameron P. , Kreutz Karl J. , Germani Mark S. , Whitlow Sallie I.
Published: July 2006

A volcanic signal observed in ice cores from both polar regions six years prior to Tambora is attributed to an unknown tropical eruption in 1809. Recovery of dacitic tephra from the 1809 horizon in a Yukon ice core (Eclipse) that is chemically distinct from andesitic 1809 tephra found in Antarctic ice cores indicates a second eruption in the Northern Hemisphere at this time. Together with the similar magnitude and timing of the 1809 volcanic signal in the Arctic and Antarctic, this could suggest a large tropical eruption produced the sulfate and Antarctic tephra and a minor Northern Hemisphere eruption produced the Eclipse tephra. Nonetheless, the possibility that there were coincidental eruptions of similar magnitude in both hemispheres, rather than a single tropical eruption, should not be discounted. Correctly attributing the source of the 1809 volcanic signal has important implications for modeling the magnitude and latitudinal distribution of volcanic radiative forcing.
Europa control of Jovian radio emission: A Galileo study
Authors: Higgins C. A. , Menietti J. D. , Christopher I. W.
Published: July 2006

Jupiter decameter wavelength emissions (DAM) have a well‐known correlation with the orbital phase of Io. Menietti et al. (1998, 2001) showed that the Galileo spacecraft data show correlations with the orbital phase of Ganymede and Callisto. Using more Galileo data we study the influence of Europa using a unique occurrence probability data compilation technique that includes rotation period averaging and removal of Io influence. We also remove the known effects of Ganymede and Callisto. From occurrence probability graphs, we find a small but significant correlation between the 2.0–5.6 MHz band of the DAM emission and the orbital phase of Europa. Statistical tests show significance values much greater than the 99% confidence level (Z‐test > 5σ) for a Europa phase interval of 260°–290°. These analyses give further evidence for Alfvénic interactions between Europa and Jupiter.
Radiative transfer in clouds with small‐scale inhomogeneities: Microphysical approach
Authors: Mishchenko Michael I.
Published: July 2006

Several recent publications have indicated that cloud droplets belonging to a particular size range may tend to cluster by forming small random particle groups imbedded in an otherwise uniform cloud. To analyze radiative transfer in clouds with such small‐scale inhomogeneities, we invoke the concepts of statistical electromagnetics. We show that as long as the assumptions of ergodicity and spatial uniformity hold, one can still apply the classical radiative transfer equation in which the participating extinction and phase matrices are obtained by averaging the respective single‐particle matrices over all the particles constituting the cloud. This result implies that comparisons of in situ and remote‐sensing retrievals of the cloud‐particle size distribution can be problematic and should be performed with caution.
Origin of second harmonic generation optical activity of a tryptophan derivative at the air/water interface
Authors: Mitchell S. A.
Published: July 2006

Second harmonic generation optical activity (SHG-OA) of chiral monolayers of the tryptophan derivative Nα-(tert-butoxycarbonyl)-tryptophan (BOC-Trp) at an air/water interface has been studied in detail. In combination with previously reported experimental measurements with the fundamental frequency ℏω=2.20eV (λ=564nm), new measurements with λ=564 and 800nm fully characterize the nonlinear susceptibility tensors of chiral and achiral (racemic) monolayers under two-photon resonant and nonresonant conditions of the fundamental frequency. A realistic computational approach including semiempirical, intermediate neglect of differential overlap (ZINDO/S) calculations has been used to calculate the nonlinear susceptibilities of model achiral and chiral monolayers composed of indole chromophores. There is satisfactory agreement between calculated and observed nonlinear susceptibilities, which constrains certain structural parameters of the monolayers including the absolute orientation of the long molecular axis of indole at the air/water interface. The origin of SHG-OA of BOC-Trp monolayers is discussed with reference of two distinct mechanisms at the microscopic level, designated type I or chiral assembly and type II or electronic coupling. Both mechanisms are studied in detail within the framework of ZINDO/S calculations. The dominant effect for the BOC-Trp monolayers is type I, involving chiral assembly of indole chromophores.
Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV
Authors: Elles Christopher G. , Jailaubekov Askat E. , Crowell Robert A. , Bradforth Stephen E.
Published: July 2006

Transient absorption measurements monitor the geminate recombination kinetics of solvated electrons following two-photon ionization of liquid water at several excitation energies in the range from 8.3to12.4eV. Modeling the kinetics of the electron reveals its average ejection length from the hydronium ion and hydroxyl radical counterparts and thus provides insight into the ionization mechanism. The electron ejection length increases monotonically from roughly 0.9nm at 8.3eV to nearly 4nm at 12.4eV, with the increase taking place most rapidly above 9.5eV. We connect our results with recent advances in the understanding of the electronic structure of liquid water and discuss the nature of the ionization mechanism as a function of excitation energy. The isotope dependence of the electron ejection length provides additional information about the ionization mechanism. The electron ejection length has a similar energy dependence for two-photon ionization of liquid D2O, but is consistently shorter than in H2O by about 0.3nm across the wide range of excitation energies studied.
Dielectric secondary relaxations in polypropylene glycols
Authors: Grzybowska K. , Grzybowski A. , Zioło J. , Paluch M. , Capaccioli S.
Published: July 2006

Broadband dielectric measurements of polypropylene glycol of molecular weight Mw=400g∕mol (PPG 400) were carried out at ambient pressure over the wide temperature range from 123to353K. Three relaxation processes were observed. Besides the structural α relaxation, two secondary relaxations, β and γ, were found. The β process was identified as the true Johari-Goldstein relaxation by using a criterion based on the coupling model prediction. The faster γ relaxation, well separated from the primary process, undoubtedly exhibits the anomalous behavior near the glass transition temperature (Tg) which is reflected in the presence of a minimum of the temperature dependence of the γ-relaxation time. We successfully applied the minimal model [Dyre and Olsen, Phys. Rev. Lett. 91, 155703 (2003)] to describe the entire temperature dependence of the γ-relaxation time. The asymmetric double-well potential parameters obtained by Dyre and Olsen for the secondary relaxation of tripropylene glycol at ambient pressure were modified by fitting to the minimal model at lower temperatures. Moreover, we showed that the effect of the molecular weight of polypropylene glycol on the minimal model parameters is significantly larger than that of the high pressure. Such results can be explained by the smaller degree of hydrogen bonds formed by longer chain molecules of PPG at ambient pressure than that created by shorter chains of PPG at high pressure.
The WD40 and FYVE domain containing protein 2 defines a class of early endosomes necessary for endocytosis
Authors: Hayakawa Akira , Leonard Deborah , Murphy Stephanie , Hayes Susan , Soto Martha , Fogarty Kevin , Standley Clive , Bellve Karl , Lambright David , Mello Craig , Corvera Silvia
Published: July 2006

The FYVE domain binds with high specificity and avidity to phosphatidylinositol 3-phosphate. It is present in ≈30 proteins in humans, some of which have been implicated in functions ranging from early endosome fusion to signal transduction through the TGF-β receptor. To develop a further understanding of the biological roles of this protein family, we turned to the nematode
Caenorhabditis elegans
, which contains only 12 genes predicted to encode for phosphatidylinositol 3-phosphate binding, FYVE domain-containing proteins, all of which have homologs in the human genome. Each of these proteins was targeted individually by RNA interference. One protein, WDFY2, produced a strong inhibition of endocytosis when silenced. WDFY2 contains WD40 motifs and a FYVE domain, is highly conserved between species, and localizes to a set of small endosomes that reside within 100 nm from the plasma membrane. These endosomes are involved in transferrin uptake but lack the classical endosomal markers Rab5 and EEA1. Silencing of WDFY2 by siRNA in mammalian cells impaired transferrin endocytosis. These studies reveal the important, conserved role of WDFY2 in endocytosis, and the existence of a subset of early endosomes, closely associated with the plasma membrane, that may constitute the first stage of endocytic processing of internalized cargo.
Functional development of Src tyrosine kinases during evolution from a unicellular ancestor to multicellular animals
Authors: Segawa Yuko , Suga Hiroshi , Iwabe Naoyuki , Oneyama Chitose , Akagi Tsuyoshi , Miyata Takashi , Okada Masato
Published: July 2006

The Src family of tyrosine kinases play pivotal roles in regulating cellular functions characteristic of multicellular animals, including cell–cell interactions, cell-substrate adhesion, and cell migration. To investigate the functional alteration of Src kinases during evolution from a unicellular ancestor to multicellular animals, we characterized Src orthologs from the unicellular choanoflagellate
Monosiga ovata
and the primitive multicellular sponge
Ephydatia fluviatilis
. Here, we show that the
src
gene family and its C-terminal Src kinase (Csk)-mediated regulatory system already were established in the unicellular
M. ovata
and that unicellular Src has unique features relative to multicellular Src: It can be phosphorylated by Csk at the negative regulatory site but still exhibits substantial activity even in the phosphorylated form. Analyses of chimera molecules between
M. ovata
and
E. fluviatilis
Src orthologs reveal that structural alterations in the kinase domain are responsible for the unstable negative regulation of
M. ovata
Src. When expressed in vertebrate fibroblasts,
M. ovata
Src can induce cell transformation irrespective of the presence of Csk. These findings suggest that a structure of Src required for the stable Csk-mediated negative regulation still is immature in the unicellular
M. ovata
and that the development of stable negative regulation of Src may correlate with the evolution of multicellularity in animals.
Mice with the R176Q cardiac ryanodine receptor mutation exhibit catecholamine-induced ventricular tachycardia and cardiomyopathy
Authors: Kannankeril Prince J. , Mitchell Brett M. , Goonasekera Sanjeewa A. , Chelu Mihail G. , Zhang Wei , Sood Subeena , Kearney Debra L. , Danila Cristina I. , De Biasi Mariella , Wehrens Xander H. T. , Pautler Robia G. , Roden Dan M. , Taffet George E. , Dirksen Robert T. , Anderson Mark E. , Hamilton Susan L.
Published: July 2006

Mutations in the cardiac ryanodine receptor 2 (RyR2) have been associated with catecholaminergic polymorphic ventricular tachycardia and a form of arrhythmogenic right ventricular dysplasia. To study the relationship between RyR2 function and these phenotypes, we developed knockin mice with the human disease-associated
RyR2
mutation R176Q. Histologic analysis of hearts from
RyR2

R176Q
/+

mice revealed no evidence of fibrofatty infiltration or structural abnormalities characteristic of arrhythmogenic right ventricular dysplasia, but right ventricular end-diastolic volume was decreased in
RyR2

R176Q
/+

mice compared with controls, indicating subtle functional impairment due to the presence of a single mutant allele. Ventricular tachycardia (VT) was observed after caffeine and epinephrine injection in
RyR2

R176Q
/+

, but not in WT, mice. Intracardiac electrophysiology studies with programmed stimulation also elicited VT in
RyR2

R176Q
/+

mice. Isoproterenol administration during programmed stimulation increased both the number and duration of VT episodes in
RyR2

R176Q
/+

mice, but not in controls. Isolated cardiomyocytes from
RyR2

R176Q
/+

mice exhibited a higher incidence of spontaneous Ca
2+
oscillations in the absence and presence of isoproterenol compared with controls. Our results suggest that the R176Q mutation in
RyR2
predisposes the heart to catecholamine-induced oscillatory calcium-release events that trigger a calcium-dependent ventricular arrhythmia.
Checkpoint kinase 1 (Chk1) is required for mitotic progression through negative regulation of polo-like kinase 1 (Plk1)
Authors: Tang Jiabin , Erikson Raymond L. , Liu Xiaoqi
Published: July 2006

Although the essential function of checkpoint kinase 1 (Chk1) in DNA damage response has been well established, the role of Chk1 in normal cell cycle progression is unclear. By using RNAi to specifically deplete Chk1, we determined loss-of-function phenotypes in HeLa cells. A vector-based RNAi approach showed that Chk1 is required for normal cell proliferation and survival, inasmuch as a dramatic cell-cycle arrest at G
2
/M phase and massive apoptosis were observed in Chk1-deficient cells. Coupling of siRNA with cell synchronization further revealed that Chk1 depletion leads to metaphase block, as indicated by various mitotic markers. Neither bipolar spindle formation nor centrosome functions were affected by Chk1 depletion; however, the depleted cells exhibited chromosome misalignment during metaphase, chromosome lagging during anaphase, and kinetochore defects within the regions of misaligned/lagging chromosomes. Moreover, we showed that Chk1 is a negative regulator of polo-like kinase 1 (Plk1), in either the absence or presence of DNA damage. Finally, Chk1 depletion leads to the activation of the spindle checkpoint because codepletion of spindle checkpoint proteins rescues the Chk1 depletion-induced mitotic arrest.
Synergistic Sedation With Oral Midazolam as a Premedication and Intravenous Propofol Versus Intravenous Propofol Alone in Upper Gastrointestinal Endoscopies in Children
Authors: Paspatis Gregorios A. , Charoniti Ioanna , Manolaraki Maria , Vardas Emmanouil , Papanikolaou Nikolaos , Anastasiadou Almout , Gritzali Aliki
Published: July 2006

Objectives:

The primary objective of the present study was to compare the required dose of intravenous (IV) propofol between group A (synergistic sedation with an oral dose of midazolam combined with IV propofol) and group B (IV propofol alone), in diagnostic upper gastrointestinal endoscopy (UGIE) in pediatric patients. The secondary objective was to compare the safety, the efficacy, the ease of IV line placement and the ease of separation from parents between the 2 groups.

Methods:

Fifty‐four consecutive children (aged 3 y or older) who underwent UGIE were randomly assigned to 1 of the 2 medication regimens. Patients in group A (n = 26, mean age: 8.1 y) received midazolam (0.5 mg/kg) orally. Thirty minutes after the midazolam dose was given, repeated IV doses of propofol 0.5 mg/kg were administered titrated to achieve the level of deep sedation. Patients in group B (n = 28, mean age: 9 y) received IV propofol alone with the same methodology and sedation end point.

Results:

The mean dose (1.8 ± 0.7 mg/kg) of propofol administered in group A patients was remarkably lower compared with that (2.9 ± 0.9 mg/kg) of group B. Multivariate stepwise logistic regression analysis revealed that among sex, age, ASA grade and the type of sedation, the synergistic sedation was the only factor associated with the ease of IV line placement (χ2 = 16.3, P < 0.001) and the ease of separation from parents (χ2 = 41.6, P < 0.001). Additional multivariate stepwise logistic regression analysis revealed that among sex, age, ASA grade and the type of sedation, synergistic sedation was the only factor associated with a higher level of patient comfort (χ2 = 35.5, P < 0.001). The recovery time was significantly shorter in group B patients (7.7 ± 3.6 min) compared with that of group A (25.9 ± 4.1 minutes) (P < 0.01). The 2 regimens were equally safe.

Conclusions:

Our data suggest that synergistic sedation with an oral dose of midazolam combined with propofol may benefit the children who undergo UGIE with regard to lower mean dose of propofol used, easier IV line placement, easier separation from the parents, less pain induced by the IV line placement and greater patient comfort.
Evaluation of Cardiac Function by Tissue Doppler Imaging in Children With Chronic Hepatitis
Authors: Bora Polat Tugcin , Urganci Nafiye , Yalcin Yalim , Akdeniz Celal , Zeybek Cenap , Erdem Abdullah , Celebi Ahmet
Published: July 2006

Objectives:

Pathoanatomic changes in cirrhosis result in impaired ventricular filling and diastolic dysfunction and were named as cirrhotic cardiomyopathy. However, cardiac functions have not been studied in patients with chronic hepatitis. We hypothesized that such patients might have subclinical ventricular dysfunction, detectable by tissue Doppler echocardiography and related to the severity of hepatic inflammation and fibrosis.

Methods:

We studied 63 clinically stable patients, 27 patients with mild chronic hepatitis (group 1), 22 patients with moderate chronic hepatitis (group 2) and 14 patients with severe chronic hepatitis (group 3) according to the scoring system of Knodell, and 36 age‐matched healthy subjects.

Results:

Patients with severe chronic hepatitis had impaired right ventricular diastolic function. The early diastolic velocity of the tricuspid valve annulus was lower in patients from group 3 than in healthy subjects (P < 0.001). Patients in group 3 had a greater isovolumic relaxation time (P < 0.001), indicating right ventricular diastolic dysfunction. Comparing group 3 with the healthy subjects, the ratio of peak early myocardial tissue velocity and peak late (or atrial) myocardial tissue velocity was significantly decreased (P < 0.001), at 1.4 (0.7) and 1.9 (0.7), respectively. There was also a slightly lower peak early myocardial tissue velocity and peak late (or atrial) myocardial tissue velocity ratio and a slightly longer isovolumic relaxation time in patients from group 2 than in healthy subjects (P < 0.05).

Conclusions:

We detected subclinical dysfunction of the right ventricle in children with chronic hepatitis in whom hepatic inflammation and fibrosis is prominent. Tissue Doppler echocardiography provides a quantifiable indicator useful for detection and monitoring of disease progression.
Hyaluronic Acid Predicts Hepatic Fibrosis in Children With Hepatic Disease
Authors: Hartley Jane L. , Brown Rachel M. , Tybulewicz Aniela , Hayes Peter , Wilson David C. , Gillett Peter , McKiernan Patrick
Published: July 2006

Background:

Hyaluronic acid (HA) is removed by the liver via sinusoidal cell adhesion molecules. This is impeded in fibrosis, leading to a rise in serum HA. As a noninvasive marker of fibrosis, HA may obviate the need for liver biopsy.

Objective:

To evaluate HA as a marker of hepatic fibrosis, in unselected children undergoing liver biopsy.

Methods:

Ninety‐three unselected consecutive children (median age, 7.5 years; range, 0.07‐19 years) undergoing a liver biopsy between April 2003 and March 2004 were prospectively recruited. Liver biopsy and fasting HA levels were taken simultaneously. The Ishak score was used to stage fibrosis. Scores of 3 or greater were regarded as significant fibrosis. Hyaluronic acid levels were measured using an enzyme‐linked binding protein assay (2002 Corgenix, Inc) (adult reference range, 0‐75 ng/mL; pediatric reference range, 0‐30 ng/mL).

Results:

Twenty‐three (25%) of 93 biopsies had significant fibrosis, and HA levels in this group were significantly higher than those with mild fibrosis (Ishak score, <3), (median level, 72 ng/mL vs 30 ng/mL; Mann‐Whitney U test; P < 0.005). Hyaluronic acid level of 50 ng/mL had a positive predictive value 40% and negative predictive value 86% for significant fibrosis. An HA level 200 ng/mL has a sensitivity of 26% and specificity of 90%.

Conclusions:

Hyaluronic Acid is a valid noninvasive predictor of hepatic fibrosis in unselected children with liver disease. An HA level of 200 ng/mL strongly suggests significant fibrosis. Hyaluronic acid level of less than 50 ng/mL accurately identifies those who do not have significant fibrosis.
Increased mobility in the membrane targeting PX domain induced by phosphatidylinositol 3‐phosphate
Authors: Cheever Matthew L. , Kutateladze Tatiana G. , Overduin Michael
Published: July 2006

Phosphoinositides (PIs) are concentrated in specific subcellular membranes in order to recruit and regulate cytosolic proteins responsible for vesicular trafficking, cytoskeletal rearrangement, and eukaryotic cell growth, differentiation, and survival. Phox homology (PX) domains are found in proteins that are integral players in endocytic pathways. For example, Vam7p is targeted by its PX domain to phosphatidylinositol 3‐phosphate [PtdIns(3)P] in the yeast vacuole, where it interacts with other SNARE proteins and GTPases of the vesicular membrane fusion machinery. Although several PX structures have been solved, the role of dynamics in their interactions with membrane lipids is unclear. Here, we present the first detailed characterization of the backbone dynamics of a PX domain, that of Vam7p, in the presence and absence of its ligand. The structure appears to tumble more rapidly in solution upon binding PtdIns(3)P, revealing a conformational change that includes adjustments in the flexible membrane insertion loop (MIL). The flexibilities of the MIL and domain termini are pronounced in both states, while the α1 and α2 helices are rigid. Dynamic effects are spread across the binding pocket, with PtdIns(3)P inducing altered mobility of different residues on multiple timescales, including a shift in the MIL to slower timescale motions. The bound state is more dynamic overall, particularly in the β‐sheet lobe, which packs against the ligand's 3‐phosphate. Thus, the induced dynamic and structural effects are transduced from the buried heart of the binding pocket in the helical lobe through the β‐sheet lobe to the exposed surface of the bilayer‐inserted protein.
The CXXC motif at the N terminus of an α‐helical peptide
Authors: Iqbalsyah Teuku M. , Moutevelis Efrosini , Warwicker Jim , Errington Neil , Doig Andrew J.
Published: July 2006

An active site containing a CXXC motif is always found in the thiol‐disulphide oxidoreductase superfamily. A survey of crystal structures revealed that the CXXC motif had a very high local propensity (26.3 ± 6.2) for the N termini of α‐helices. A helical peptide with the sequence CAAC at the N terminus was synthesized to examine the helix‐stabilizing capacity of the CXXC motif. Circular dichroism was used to confirm the helical nature of the peptide and study behavior under titration with various species. With DTT, a redox potential of Eo = −230 mV was measured, indicating that the isolated peptide is reducing in nature and similar to native human thioredoxin. The pKa values of the individual Cys residues could not be separated in the titration of the reduced state, giving a single transition with an apparent pKa of 6.74 (±0.06). In the oxidized state, the N‐terminal pKa is 5.96 (±0.05). Analysis of results with the modified helix‐coil theory indicated that the disulfide bond stabilized the α‐helical structure by 0.5 kcal/mol. Reducing the disulfide destabilizes the helix by 0.9 kcal/mol.
An amino acid “transmembrane tendency” scale that approaches the theoretical limit to accuracy for prediction of transmembrane helices: Relationship to biological hydrophobicity
Authors: Zhao Gang , London Erwin
Published: July 2006

Hydrophobicity analyses applied to databases of soluble and transmembrane (TM) proteins of known structure were used to resolve total genomic hydrophobicity profiles into (helical) TM sequences and mainly “subhydrophobic” soluble components. This information was used to define a refined “hydrophobicity”‐type TM sequence prediction scale that should approach the theoretical limit of accuracy. The refinement procedure involved adjusting scale values to eliminate differences between the average amino acid composition of populations TM and soluble sequences of equal hydrophobicity, a required property of a scale having maximum accuracy. Application of this procedure to different hydrophobicity scales caused them to collapse to essentially a single TM tendency scale. As expected, when different scales were compared, the TM tendency scale was the most accurate at predicting TM sequences. It was especially highly correlated (r = 0.95) to the biological hydrophobicity scale, derived experimentally from the percent TM conformation formed by artificial sequences passing though the translocon. It was also found that resolution of total genomic sequence data into TM and soluble components could be used to define the percent probability that a sequence with a specific hydrophobicity value forms a TM segment. Application of the TM tendency scale to whole genomic data revealed an overlap of TM and soluble sequences in the “semihydrophobic” range. This raises the possibility that a significant number of proteins have sequences that can switch between TM and non‐TM states. Such proteins may exist in moonlighting forms having properties very different from those of the predominant conformation.
Sediment microbial enzyme activity as an indicator of nutrient limitation in Great Lakes coastal wetlands
Authors: HILL B. H. , ELONEN C. M. , JICHA T. M. , COTTER A. M. , TREBITZ A. S. , DANZ N. P.
Published: July 2006

1. We compared the extracellular enzyme activity (EEA) of sediment microbial assemblages with sediment and water chemistry, gradients in agricultural nutrient loading (derived from principal component analyses), atmospheric deposition and hydrological turnover time in coastal wetlands of the Laurentian Great Lakes.

2. There were distinct increases in nutrient concentrations in the water and in atmospheric N deposition along the gradient from Lake Superior to Lake Ontario, but few differences between lakes in sediment carbon (C), nitrogen (N) or phosphorus (P). Wetland water and sediment chemistry were correlated with the agricultural stress gradient, hydrological turnover time and atmospheric deposition.

3. The N : P ratio of wetland waters and sediments indicated that these coastal wetlands were N‐limited. Nutrient stoichiometry was correlated with the agricultural stress gradient, hydrological turnover time and atmospheric deposition.

4. Extracellular enzyme activity was correlated with wetland sediment and water chemistry and stoichiometry, atmospheric N deposition, the agricultural stress gradient and the hydrological turnover time. The ratios of glycosidases to peptidases and phosphatases yielded estimates of nutrient limitation that agreed with those based solely on nutrient chemistry.

5. This study, the first to link microbial enzyme activities to regional‐scale anthropogenic stressors, suggests that quantities and ratios of microbial enzymes are directly related to the concentrations and ratios of limiting nutrients, and may be sensitive indicators of nutrient dynamics in wetland ecosystems, but further work is needed to elucidate these relationships.
Dynamics of yeast prion aggregates in single living cells
Authors: Kawai‐Noma Shigeko , Ayano Satoru , Pack Chan‐Gi , Kinjo Masataka , Yoshida Masasuke , Yasuda Kenji , Taguchi Hideki
Published: July 2006

Prions are propagating proteins that are ordered protein aggregates, in which the phenotypic trait is retained in the altered protein conformers. To understand the dynamics of the prion aggregates in living cells, we directly monitored the fate of the aggregates using an on‐chip single‐cell cultivation system as well as fluorescence correlation spectroscopy (FCS). Single‐cell imaging revealed that the visible foci of yeast prion Sup35 fused with GFP are dispersed throughout the cytoplasm during cell growth, but retain the prion phenotype. FCS showed that [PSI+] cells, irrespective of the presence of foci, contain diffuse oligomers, which are transmitted to their daughter cells. Single‐cell observations of the oligomer‐based transmission provide a link between previous in vivo and in vitro analyses of the prion and shed light on the relationship between the protein conformation and the phenotype.
Reproductive allocation in a gender dimorphic shrub: anomalous female investment in Gynatrix pulchella?
Authors: LEIGH ANDREA , COSGROVE MEREDITH J. , NICOTRA ADRIENNE B.
Published: July 2006

In gender dimorphic species, reproductive allocation (RA, the ratio of reproductive to vegetative biomass) is predicted to be greater in female plants than in male plants. Empirical research on dimorphic plant species supports this hypothesis. To date, of 44 dimorphic angiosperms for which RA has been reported in the literature, RA is greater in females than males in 40 species, is equal in four, and in no species is it greater in males.

In many instances where differential RA occurs, sexual dimorphism in morphological or physiological traits has been reported. This dimorphism is often attributed to the differing costs of reproduction or to selection to counteract such costs.

We investigated RA and other morphological and physiological characters in Gynatrix pulchella, a dimorphic species that we found ranges from dioecious to subdioecious or gynodioecious, depending on season and locality. Our results showed that contrary to our predictions functionally male plants allocated significantly more biomass to reproduction than female plants across three populations. Greater male RA was due to a combination of larger, more numerous flowers and lower leaf biomass per branch than females.

There were no detectable costs of greater RA in males in terms of decreased overall growth or increased mortality. Additionally, leaf nitrogen content was greater in males than in females and there were no between‐sex differences in gas exchange.

The finding that male plants allocate significantly more resources to reproduction than females in G. pulchella is apparently a unique case. However, equivalent RA for the sexes does occur in gynodioecious species and we suggest that higher male RA in gynodioecious plants may be more common than predictions based on sexual systems involving pure males.

Our results challenge accepted theory that allocation to reproduction should be greater in female plants than in males. In light of these findings, predictions regarding which sex should allocate more to reproduction need to be revised to accommodate the diversity of plant sexual systems.
On the effectiveness of higher taxonomic ranks for vegetation analysis
Authors: DALE M. B. , CLIFFORD H. T.
Published: July 2006

The ecological value of employing taxonomic categories other than species to describe vegetation is examined by comparing the results of numerical classification. Using presence data only and an unsophisticated classification method with data from a small area, it is found that the use of generic and subgeneric categories instead of species causes little loss in interpretability. At the family and subfamily levels more sophisticated analyses probably employing quantitative data, are apparently required to achieve similar levels of interpretability. The transformation between categories is shown to be a simple matrix multiplication and some alternative transformations are briefly outlined. It is suggested that the use of different taxonomic categories in a sequence of analyses beginning with the highest category would provide a useful means of planning which could reduce the overall time required for the analysis of large data sets.
The effect of prescribed burning on the soil fauna and on litter decomposition in Western Australian forests
Authors: SPRINGETT JOSEPHINE A.
Published: July 2006

The effect of mild fires on the soil fauna was examined in a Pinus pinaster plantation and in Jarrah (Eucalyptus marginata) and Karri (E. diversicolor) forests. In the pine plantation, litter decomposition ceases until four years after burning. In both native forests, species diversity and density are reduced after burning and do not recover their pre‐burning values during a normal prescribed burning rotation. Prescribed burning on a five to seven year rotation is likely to permanently simplify the litter fauna and flora, with far‐reaching effects on forest and hygiene.
A photographic method and a ranking procedure for estimating numbers of the rose aphid, Macrosiphum rosae (L.), on rose buds
Authors: Maelzer D. A.
Published: July 2006

Two sampling methods for aphids are described. The first is a photographic method that allows sampling with replacement for use in field experiments and in which a linear regression technique is used to estimate the errors of sampling. The second method is a ranking procedure for sampling natural populations in which regressions of aphid numbers on ‘colony length’ are used to minimize bias.
Sequential decision plans for the management of cotton arthropods in south‐east Queensland
Authors: STERLING WINFIELD L.
Published: July 2006

An outline of a pest management plan for cotton insects has been developed that is essentially based on three sets of sequential sampling plans. These plans utilize the binomial sampling theory and treatment levels for pests during three phenological stages of cotton plant growth. The plans also provide a known level of accuracy in making management decisions and frequently will require less time than other sampling techniques.
Host specificity of insects in a community of three co‐dominant Eucalyptus species
Authors: MORROW P. A.
Published: July 2006

In a subalpine association of three Eucalyptus species, phytophagous insects showed strong host preferences even among very closely related Eucalyptus species. Sixty‐three per cent of insect species attacked only one eucalypt species, 30% attacked two species and only 8% fed on all three. Ninety‐seven per cent of individuals belonged to species using one or two hosts. The results are discussed in relation to the degree of host specificity that might be expected when most potential hosts are members of a single genus, the way in which host specificity is determined, and the potential of insects with host preferences to affect the dynamics of plant communities.
The Macquarie perch, Macquria australasica (Pisces: Percichthyidae), of Lake Eildon, Victoria
Authors: CADWALLADER P. L. , ROGAN P. L.
Published: July 2006

The results of a field study carried out between 1966 and 1969 indicate that the spawning migrations of Macquarie perch, Macquaria australasica, from Lake Eildon, Victoria, into the inflowing Delatite, Howqua, Jamieson, Goulburn and Big Rivers occurred when water temperatures in the rivers reached 16.5°C. Because of different temperature regimes the times of the spawning migration and spawning differed from river to river. Migrating fish were of a uniform size and were in their fifth to tenth years of life. Recaptures of tagged fish suggest that some fish use the same river each year for spawning. Observations on pre‐spawning and spawning behaviour and on the characteristics of the spawning site are recorded. Fecundity of fourteen fish in the size range 305–405 mm standard length varied from 50189 to 107 724 eggs per fish. The virtual disappearance of Macquarie pereh from Lake Eildon was probably caused by a combination of several factors, including changed habitat, overfishing of the spawning stock and predation by, and competition for food with, introduced fish.
The ecology of Araucaria species in New Guinea. II. Pattern in the distribution of young and mature individuals and light requirements of seedlings.
Authors: ENRIGHT N. J.
Published: July 2006

Conventional pattern analysis and segregation analysis were used to investigate the hypothesis that young and mature individuals of Araucaria hunsteinii were not usually found growing in close association whilst the distribution of young and mature individuals of A. cunninghamii was essentially random. It was considered that this pattern reflected a difference in regeneration strategy between the two species, A. hunsteinii being a gap regenerator and A. cunninghamii a shade‐tolerant species. A seedling growth‐experiment using three different shade treatments and four temperature treatments tested this hypothesis further. Results show that A. hunsteinii is more dependent on high light intensity than A. cunninghamii for the production of biomass. A. cunninghamii produces more biomass than A. hunsteinii under all treatment conditions.
Litter fall and nutrient cycling in karri (Eucalyptus diversicolor F. Muell.) forest in relation to stand age
Authors: O'CONNELL A. M. , MENAGÉ P. M. A.
Published: July 2006

Annual litter fall, nutrient concentrations in litter components and annual weight of nutrients in litter fall have been estimated for karri forest stands aged 2, 6, 9 and 40 years and in mature forest. The weight of litter falling annually increases with stand age, ranging from 1.13 t/ha in 2‐year‐otd regeneration to 9.45 t/ha in mature forest. This increase is due mainly to greater amounts of twigs, bark and fruit falling in older stands. Leaf fait is relatively independent of stand age once the canopy of regenerating stands closes and the understorey has developed.

Concentrations of N, P, K, S and Mn in karri leaf litter differ significantly between sites and the differences appear to be related to stand age. Highest levels of these elements are found in karri leaf litter from the youngest stand and the concentrations decrease with increasing stand age. The amounts of annual litter fall and of nutrients cycling in litter are among the largest reported for Australian forests. In particular cycling of Ca, K and Mg in mature karri forest is greater than has been reported for any other eucalypt forest. Karri forest understorey plays a key rote in nutrient cycling in these ecosystems, contributing 30–70% of the weight of many of the nutrients in the leaf component of titter. Understorey leaf material is particularly important in the cycling of N, S and the micro‐nutrients Cu and Zn.
A new approach to the species classification problem in floristic analysis
Authors: AUSTIN M. P. , BELBIN L.
Published: July 2006

A new method of species (inverse) classification of vegetation data, i.e. classification of species into groups with similar ecological tolerances, is presented which overcomes the problems of species abundance distorting the results. The algorithm TWO‐STEP is based on the use of an asymmetric measure of dissimilarity:

image

where i, j are species, h is the stand, n is the total number of stands, and xih is the amount of species i in stand h.

The algorithm uses the rows of the asymmetric dissimilarity matrix generated as above to form a second symmetric dissimilarity matrix using the measure:

image

where m is the number of species and k the species.

Flexible sorting is applied to generate a species classification. Comparison of results after applying the TWO‐STEP algorithm and a standard alternative to an artificial data set demonstrates its efficacy. TWO‐STEP also shows considerable advantages over previous analyses for a Queensland rainforest data set (quantitative) and an English heath (qualitative) data set. Normalization of species data appears advantageous for quantitative data only.
Modelling the lineage of a growing population as an age‐dependent branching process
Authors: WOODWARD IAN O.
Published: July 2006

A new model for population growth as a branching process is described. It requires knowledge of the population's age‐specific survivorship and fecundity curves. The total population size at any time is calculated by summing across all branches of the tree representing the population's lineage and thus the model also allows the lineage of the developing population to be traced. Use of the model is demonstrated by a hypothetical example. The model could be of particular value in tracing the phylogenetic development of populations and/or species.
Does Araucaria hunsteinii compete with its neighbours?
Authors: ENRIGHT N. J.
Published: July 2006

A comparison of the proportion of total stand basal area contributed by Araucaria hunsteinii, as opposed to the rest of the forest, in a number of 0.5 ha plots from New Guinea rainforest is presented. Results suggest that A. hunsteinii avoids competition with other tree species. Several hypotheses which may explain this phenomenon are advanced.
Do waxes on Eucalyptus leaves provide protection from grazing insects?
Authors: EDWARDS PENELOPE B.
Published: July 2006

Evidence is presented which indicates that the removable wax layer on juvenile leaves of several species of Encalyptus provides protection from grazing by the Eucalyptus tortoise beetle, Paropsis charybdis, by preventing the adult beetles from gaining a foothold. Other possible roles of Eucalyptus leaf waxes, particuarly those related to frost resistance, are considered in the light of the present observations.
Short Note Simpson Desert dunecrest assemblages
Authors: BUCKLEY R.
Published: July 2006

There are two distinct plant assemblages on the dunecrests of the Simpson Desert. The first is characterized by Zygochloa paradoxa and Chamaesyce wheeled. The second is marked by the presence of Calotis erinacea and Helichrysum ambiguum. There are no consistent differences in texture or fertility between the soils occupied by these four species on the sandridges though there are some differences in other habitats. Hence static soil differences cannot account for the distribution of the two assemblages. It is suggested that the Calotis patches represent populations spread from focal plants established after the 1960s drought, but this remains untested.
An energy and water budget for a population of the arid zone scorpion Urodacus yaschenkoi (Birula 1903)
Authors: MARPLES T. G. , SHORTHOUSE D. J.
Published: July 2006

A population energy budget and water relations of the arid zone scorpion Urodacus yaschenkoi (Birula 1903) is described. The standing crop varied between 1945 and 4043 kJ in 2240 m2. The annual population respiration was 191 l of oxygen or 3562 kJ. Ecological efficiencies using laboratory and field measurements of energy flow were calculated for each instar. Water loss was extrapolated from laboratory studies and was shown to be more critical to the survival of the population than energy demand.