bluuebunny/crossref_metadata_2025 huggingface dataset:
Tectonic evolution of the eastern margin of the Thaumasia Plateau (Mars) as inferred from detailed structural mapping and analysis
Authors: Borraccini F. , Di Achille G. , Ori G. G. , Wezel F. C.
Published: May 2007

The eastern margin of the Thaumasia Plateau (EMTP) is characterized by a diversity of tectonic features, which recorded its complex, and still controversial, tectonic history. A detailed structural survey and analyses have been carried out in order to assess the kinematics and relative age of the main deformational events. Combining results from statistics of lineament orientations and density of fault length for each geologic unit and taking into account crosscutting relationships among tectonic structures, three main deformational events have been recognized. The early stage of the tectonic evolution of EMTP is recorded by Noachian units at the southern edge of Melas Dorsa and is represented by N‐S oriented grabens sutured by Early Hesperian formations. Starting from Late Noachian, the extensional stress field became NE‐SW oriented and resulted in the formation of NW‐SE striking sets of grabens. At the boundary between Noachian and Hesperian, the most important change in tectonic regime occurred. The Hesperian tectonics are characterized by an E‐W shortening possibly related to an eastward motion of the Thaumasia Plateau. This tectonic phase likely produced a N‐S‐oriented wrinkle ridges as well as regional folds and thrust faults. E‐W‐oriented preexisting tectonic lineaments could have been reactivated forming regional transfer zones. In this scenario, Coprates Rise, Melas Dorsa, and Thaumasia Ridge could be interpreted as mountain belts resulting from buckling and thrust faulting of the eastern and southern margins of the Thaumasia plateau. The proto‐Valles Marineris could have experienced a left‐lateral component of displacement and played a role of a transfer shear zone.
Tectonic accretion versus erosion along the southern Chile trench: Oblique subduction and margin segmentation
Authors: Polonia A. , Torelli L. , Brancolini G. , Loreto M.‐F.
Published: May 2007

The southernmost tip of South America is an active continental margin where oblique convergence between plates, transcurrent motion, and tectonic rotation on land make the geodynamic setting more complex than that of the central Andes. A multichannel seismic data set has been used in conjunction with multibeam and altimetry data to clarify the regional architecture of the continental margin from 50°S to 57°S. Despite the thick sedimentary section in the trench and the slow plate convergence rate peculiar of typical accretionary margins, seismic reflection profiles image widely varying frontal wedge morphologies, different rates of accretion, a high degree of structural diversity, and different modes of continental building (offscraping, underplating, tectonic erosion). Correlation between structural parameters (depth of the décollement level, width of the wedge, accretionary rates, Moho depth) suggests large‐scale structural control on margin geometry and structural diversity. The transition from tectonic accretion to erosion and general structural variations do not show any gradual trend, but rather, they occur along oblique structural trends that produce a tectonic segmentation of the margin. This is mainly related to tectonic processes on the overriding plate (block rotations along strike‐slip faults), while local disturbances on the incoming plate (seamounts, fracture zones, and oceanic fabric relative orientation) add further structural complexity. Altimetry data, in conjunction with structural analysis, suggest that large‐scale tectonic variations and structural development are related to trench‐parallel gravity anomaly variations and, ultimately, to basal friction on the plate interface. Strong negative gravity anomalies are associated with sedimentary basins, wide wedges, and accretionary domains, while positive gravity anomalies mainly refer to transverse structural highs and narrow wedges.
Parameter interdependence and uncertainty induced by lumping in a hydrologic model
Authors: Gallagher Mark R. , Doherty John
Published: May 2007

Throughout the world, watershed modeling is undertaken using lumped parameter hydrologic models that represent real‐world processes in a manner that is at once abstract, but nevertheless relies on algorithms that reflect real‐world processes and parameters that reflect real‐world hydraulic properties. In most cases, values are assigned to the parameters of such models through calibration against flows at watershed outlets. One criterion by which the utility of the model and the success of the calibration process are judged is that realistic values are assigned to parameters through this process. This study employs regularization theory to examine the relationship between lumped parameters and corresponding real‐world hydraulic properties. It demonstrates that any kind of parameter lumping or averaging can induce a substantial amount of “structural noise,” which devices such as Box‐Cox transformation of flows and autoregressive moving average (ARMA) modeling of residuals are unlikely to render homoscedastic and uncorrelated. Furthermore, values estimated for lumped parameters are unlikely to represent average values of the hydraulic properties after which they are named and are often contaminated to a greater or lesser degree by the values of hydraulic properties which they do not purport to represent at all. As a result, the question of how rigidly they should be bounded during the parameter estimation process is still an open one.
New constraints on the upper mantle structure of the Slave craton from Rayleigh wave inversion
Authors: Chen Chin‐Wu , Rondenay Stéphane , Weeraratne Dayanthie S. , Snyder David B.
Published: May 2007

Rayleigh wave phase and amplitude data are analyzed to provide new insight into the velocity structure of the upper mantle beneath the Slave craton, in the northwestern Canadian Shield. We invert for phase velocities at periods between 20 s–142 s (with greatest sensitivity at depths of 28–200 km) using crossing ray paths from events recorded by the POLARIS broadband seismic network and the Yellowknife array. Phase velocities obtained for the Slave province are comparable to those from other cratons at shorter periods, but exceed the global average by ∼2% at periods above 60 s, suggesting that the Slave craton may be an end member in terms of its high degree of mantle depletion. The one‐dimensional inversion of phase velocities yields high upper‐mantleS‐wave velocities of 4.7 ± 0.2 km/s that persist to 220 ± 65 km depth and thus define the cratonic lithosphere. Azimuthal anisotropy is well resolved at all periods with a dominant fast direction of N59°E ± 20°, suggesting that upper mantle anisotropy beneath the Slave craton is influenced by both lithospheric fabric and sub‐lithospheric flow.
Identification and localization of soluble sulfotransferases in the human gastrointestinal tract
Authors: Teubner Wera , Meinl Walter , Florian Simone , Kretzschmar Michael , Glatt Hansruedi
Published: May 2007

Soluble SULTs (sulfotransferases) are important in the regulation of messenger molecules and the elimination of xenobiotics. However, sulfo-conjugation of various substrates can also lead to the formation of reactive metabolites that may induce cancer and cause other damage. The aim of the present study was to identify the SULT forms expressed in the human gastrointestinal tract, especially the colon and rectum (common sites for cancer), and to determine their cellular localization. Normal colonic or rectal tissue, resected with tumours, was obtained from 39 subjects. For comparison, we additionally studied one to four samples from stomach, jejunum, ileum, cecum and liver. SULTs were detected by immunoblotting, immunohistochemistry and measurement of enzyme activities. SULT1A1, 1A3 and 1B1 were found in all parts of the gastrointestinal tract, often exceeding levels in liver (where these forms were present at high, undetectable and low levels respectively). They were predominantly localized in differentiated enterocytes. SULT1E1 and 2A1 were only detected in liver, jejunum, ileum and cecum. SULT1C1 was readily found in stomach, but was negligible elsewhere. SULT1A2 was present at low levels in individual samples. The remaining forms were not detected with the limitation that only high levels could be recognized with the antisera used. In conclusion, SULTs are abundant in the gastrointestinal tract of man. We suspect that they are involved in the presystemic elimination of bioactive food-borne components, including aglycones released by gut microbiota, as well as the bioactivation of some procarcinogens.
Modulation of Aβ generation by small ubiquitin-like modifiers does not require conjugation to target proteins
Authors: Dorval Véronique , Mazzella Matthew J. , Mathews Paul M. , Hay Ronald T. , Fraser Paul E.
Published: May 2007

The sequential processing of the APP (amyloid precursor protein) by the β- and γ-secretase and generation of the Aβ (amyloid-β) peptide is a primary pathological factor in AD (Alzheimer's disease). Regulation of the processing or turnover of these proteins represents potential targets for the development of AD therapies. Sumoylation is a process by which SUMOs (small ubiquitin-like modifiers) are covalently conjugated to target proteins, resulting in a number of functional consequences. These include regulation of protein–protein interactions, intracellular trafficking and protein stability, which all have the potential to impact on several aspects of the amyloidogenic pathway. The present study examines the effects of overexpression and knockdown of the major SUMO isoforms (SUMO1, 2 and 3) on APP processing and the production of Aβ peptides. SUMO3 overexpression significantly increased Aβ40 and Aβ42 secretion, which was accompanied by an increase in full-length APP and its C-terminal fragments. These effects of SUMO3 were independent of its covalent attachment or chain formation, as mutants lacking the motifs responsible for SUMO chain formation or SUMO conjugation led to similar changes in Aβ. SUMO3 overexpression also up-regulated the expression of the transmembrane protease BACE (β-amyloid-cleaving enzyme), but failed to affect levels of several other unrelated proteins. Suppression of SUMO1 or combined SUMO2+3 by RNA interference did not affect APP levels or Aβ production. These findings confirm a specific effect of SUMO3 overexpression on APP processing and the production of Aβ peptides but also suggest that endogenous sumoylation is not essential and likely plays an indirect role in modulating the amyloid processing pathway.
Phosphorylation of the 12 S globulin cruciferin in wild-type and abi1-1 mutant Arabidopsis thaliana (thale cress) seeds
Authors: Wan Lianglu , Ross Andrew R. S. , Yang Jingyi , Hegedus Dwayne D. , Kermode Allison R.
Published: May 2007

Cruciferin (a 12 S globulin) is the most abundant storage protein in the seeds of Arabidopsis thaliana (thale cress) and other crucifers, sharing structural similarity with the cupin superfamily of proteins. Cruciferin is synthesized as a precursor in the rough endoplasmic reticulum. Subunit assembly is accompanied by structural rearrangements involving proteolysis and disulfide-bond formation prior to deposition in protein storage vacuoles. The A. thaliana cv. Columbia genome contains four cruciferin loci, two of which, on the basis of cDNA analysis, give rise to three alternatively spliced variants. Using MS, we confirmed the presence of four variants encoded by genes At4g28520.1, At5g44120.3, At1g03880.1 and At1g3890.1 in A. thaliana seeds. Two-dimensional gel electrophoresis, along with immunological detection using anti-cruciferin antiserum and antibodies against phosphorylated amino acid residues, revealed that cruciferin was the major phosphorylated protein in Arabidopsis seeds and that polymorphism far exceeded that predicted on the basis of known isoforms. The latter may be attributed, at least in part, to phosphorylation site heterogeneity. A total of 20 phosphorylation sites, comprising nine serine, eight threonine and three tyrosine residues, were identified by MS. Most of these are located on the IE (interchain disulfide-containing) face of the globulin trimer, which is involved in hexamer formation. The implications of these findings for cruciferin processing, assembly and mobilization are discussed. In addition, the protein phosphatase 2C-impaired mutant, abi1-1, was found to exhibit increased levels of cruciferin phosphorylation, suggesting either that cruciferin may be an in vivo target for this enzyme or that abi1-1 regulates the protein kinase/phosphatase system required for cruciferin phosphorylation.
2-Aminoadipic acid is a marker of protein carbonyl oxidation in the aging human skin: effects of diabetes, renal failure and sepsis
Authors: Sell David R. , Strauch Christopher M. , Shen Wei , Monnier Vincent M.
Published: May 2007

We hypothesized that the ϵ-amino group of lysine residues in longlived proteins oxidatively deaminates with age forming the carbonyl compound, allysine (α-aminoadipic acid-δ-semialdehyde), which can further oxidize into 2-aminoadipic acid. In the present study, we measured both products in insoluble human skin collagen from n=117 individuals of age range 10–90 years, of which n=61 and n=56 were non-diabetic and diabetic respectively, and a total of n=61 individuals had either acute or chronic renal failure. Allysine was reduced by borohydride into 6-hydroxynorleucine and both products were measured in acid hydrolysates by selective ion monitoring gas chromatography (GC)-MS. The results showed that 2-aminoadipic acid (P<0.0001), but not 6-hydroxynorleucine (P=0.14), significantly increased with age reaching levels of 1 and 0.3 mmol/mol lysine at late age respectively. Diabetes in the absence of renal failure significantly (P<0.0001) increased 2-aminoadipic acid up to <3 mmol/mol, but not 6-hydroxynorleucine (levels<0.4 mmol/mol, P=0.18). Renal failure even in the absence of diabetes markedly increased levels reaching up to <0.5 and 8 mmol/mol for 6-hydroxynorleucine and 2-aminoadipic acid respectively. Septicaemia significantly (P<0.0001) elevated 2-aminoadipic acid in non-diabetic, but not diabetic individuals, and mildly correlated with other glycoxidation markers, carboxymethyl-lysine and the methylglyoxal-derived products, carboxyethyl-lysine, argpyrimidine and MODIC (methylglyoxal-derived imidazolium cross-link). These results provide support for the presence of metal-catalysed oxidation (the Suyama pathway) in diabetes and the possible activation of myeloperoxidase during sepsis. We conclude that 2-aminoadipic acid is a more reliable marker for protein oxidation than its precursor, allysine. Its mechanism of formation in each of these conditions needs to be elucidated.
Tailoring structure–function properties of L-asparaginase: engineering resistance to trypsin cleavage
Authors: Kotzia Georgia A. , Lappa Katerina , Labrou Nikolaos E.
Published: May 2007

Bacterial L-ASNases (L-asparaginases) catalyse the conversion of L-asparagine into L-aspartate and ammonia, and are widely used for the treatment of ALL (acute lymphoblastic leukaemia). In the present paper, we describe an efficient approach, based on protein chemistry and protein engineering studies, for the construction of trypsin-resistant PEGylated L-ASNase from Erwinia carotovora (EcaL-ASNase). Limited proteolysis of EcaL-ASNase with trypsin was found to be associated with a first cleavage of the peptide bond between Lys53 and Gly54, and then a second cleavage at Arg206-Ser207 of the C-terminal fragment, peptide 54–327, showing that the initial recognition sites for trypsin are Lys53 and Arg206. Site-directed mutagenesis of Arg206 to histidine followed by covalent coupling of mPEG-SNHS [methoxypoly(ethylene glycol) succinate N-hydroxysuccinimide ester] to the mutant enzyme resulted in an improved modified form of EcaL-ASNase that retains 82% of the original catalytic activity, exhibits enhanced resistance to trypsin degradation, and has higher thermal stability compared with the wild-type enzyme.
Control over action potential, calcium peak and average fluxes in the cyclic quasi-steady-state ion transport system in cardiac myocytes: in silico studies
Authors: Dzbek Jaroslaw , Korzeniewski Bernard
Published: May 2007

MCA (metabolic control analysis) was originally developed to deal with steady-state systems. In the present theoretical study, the control analysis is applied to the cyclic quasi-steady-state system of ion transport in cardiac myocytes. It is demonstrated that the metabolic control of particular components (channels, exchangers, pumps) of the system over such quasi-steady-state variables as action potential amplitude, action potential duration, area under the Ca2+ peak and average fluxes through particular channels during one oscillation period can be defined and calculated. It is shown that the control over particular variables in the analysed, periodical system is distributed among many (potentially all) components of the system. Nevertheless, some components seem to exert much more control than other components, and different variables are controlled to the greatest extent by different channels. Finally, it is hypothesized that the Na+ and K+ transport system exerts a significant control over the Ca2+ transport system, but not vice versa.
Mice develop normally in the absence of Smad4 nucleocytoplasmic shuttling
Authors: Biondi Christine A. , Das Debipriya , Howell Michael , Islam Ayesha , Bikoff Elizabeth K. , Hill Caroline S. , Robertson Elizabeth J.
Published: May 2007

Smad4 in partnership with R-Smads (receptor-regulated Smads) activates TGF-β (transforming growth factor-β)-dependent signalling pathways essential for early mouse development. Smad4 null embryos die shortly after implantation due to severe defects in cell proliferation and visceral endoderm differentiation. In the basal state, Smad4 undergoes continuous shuttling between the cytoplasm and the nucleus due to the combined activities of an N-terminal NLS (nuclear localization signal) and an NES (nuclear export signal) located in its linker region. Cell culture experiments suggest that Smad4 nucleocytoplasmic shuttling plays an important role in TGF-β signalling. In the present study we have investigated the role of Smad4 shuttling in vivo using gene targeting to engineer two independent mutations designed to eliminate Smad4 nuclear export. As predicted this results in increased levels of Smad4 in the nucleus of homozygous ES cells (embryonic stem cells) and primary keratinocytes, in the presence or absence of ligand. Neither mutation affects Smad4 expression levels nor its ability to mediate transcriptional activation in homozygous cell lines. Remarkably mouse mutants lacking the Smad4 NES develop normally. Smad4 NES mutants carrying one copy of a Smad4 null allele also fail to display developmental defects. The present study clearly demonstrates that Smad4 nucleocytoplasmic shuttling is not required for embryonic development or tissue homoeostasis in normal, healthy adult mice.
High-affinity binding by the periplasmic iron-binding protein from Haemophilus influenzae is required for acquiring iron from transferrin
Authors: Khan Ali G. , Shouldice Stephen R. , Kirby Shane D. , Yu Rong-hua , Tari Leslie W. , Schryvers Anthony B.
Published: May 2007

The periplasmic iron-binding protein, FbpA (ferric-ion-binding protein A), performs an essential role in iron acquisition from transferrin in Haemophilus influenzae. A series of site-directed mutants in the metal-binding amino acids of FbpA were prepared to determine their relative contribution to iron binding and transport. Structural studies demonstrated that the mutant proteins crystallized in an open conformation with the iron atom associated with the C-terminal domain. The iron-binding properties of the mutant proteins were assessed by several assays, including a novel competitive iron-binding assay. The relative ability of the proteins to compete for iron was pH dependent, with a rank order at pH 6.5 of wild-type, Q58L, H9Q>H9A, E57A>Y195A, Y196A. The genes encoding the mutant FbpA were introduced into H. influenzae and the resulting strains varied in the level of ferric citrate required to support growth on iron-limited medium, suggesting a rank order for metal-binding affinities under physiological conditions comparable with the competitive binding assay at pH 6.5 (wild-type=Q58L>H9Q>H9A, E57A>Y195A, Y196A). Growth dependence on human transferrin was only obtained with cells expressing wild-type, Q58L or H9Q FbpAs, proteins with stability constants derived from the competition assay >2.0×1018 M−1. These results suggest that a relatively high affinity of iron binding by FbpA is required for removal of iron from transferrin and its transport across the outer membrane.
Testing the adaptive selection of human mtDNA haplogroups: an experimental bioenergetics approach
Authors: Elson Joanna L. , Turnbull Douglass M. , Taylor Robert W.
Published: May 2007

The evolution of human mtDNA (mitochondrial DNA) has been characterized by the emergence of distinct haplogroups, which are associated with the major global ethnic groups and defined by the presence of specific mtDNA polymorphic variants. A recent analysis of complete mtDNA genome sequences has suggested that certain mtDNA haplogroups may have been positively selected as humans populated colder climates due to a decreased mitochondrial coupling efficiency, in turn leading to increased generation of heat instead of ATP synthesis by oxidative phosphorylation. If this is true, implying different evolutionary processes in different haplogroups, this could potentially void the usefulness of mtDNA as a genetic tool to study the timing of major events in evolutionary history. In this issue of the Biochemical Journal, Taku Amo and Martin Brand present experimental biochemical data to test this hypothesis. Measurements of the bioenergetic capacity of cybrid cells harbouring specific Arctic or tropical climate mtDNA haplogroups on a control nuclear background reveal no significant changes in coupling efficiency between the two groups, indicating that mtDNA remains a viable evolutionary tool to assess the timing of major events in the history of humans and other species.
The lipoprotein lipase gene serine 447 stop variant influences hypertension-induced left ventricular hypertrophy and risk of coronary heart disease
Authors: Talmud Philippa J. , Flavell David M. , Alfakih Khaled , Cooper Jackie A. , Balmforth Anthony J. , Sivananthan Mohan , Montgomery Hugh E. , Hall Alistair S. , Humphries Steve E.
Published: May 2007

LVH [LV (left ventricular) hypertrophy] is an independent risk factor for CHD (coronary heart disease). During LVH, the preferred cardiac energy substrate switches from FAs (fatty acids) to glucose. LPL (lipoprotein lipase) is the key enzyme in triacylglycerol (triglyceride) hydrolysis and supplies FAs to the heart. To investigate whether substrate utilization influences cardiac growth and CHD risk, we examined the association between the functional LPL S447X (rs328) variant and hypertension-induced LV growth and CHD risk. LPL-X447 has been shown to be more hydrolytically efficient and would therefore release more free FAs than LPL-S477. In a cohort of 190 hypertensive subjects, LPL X447 was associated with a greater LV mass index [85.2 (1.7) in S/S compared with 91.1 (3.4) in S/X+X/X; P=0.01], but no such association was seen in normotensive controls (n=60). X447 allele frequency was higher in hypertensives with than those without LVH {0.14 [95% CI (confidence interval), 0.08–0.19] compared with 0.07 (95% CI, 0.05–0.10) respectively; odds ratio, 2.52 (95% CI, 1.17–5.40), P=0.02}. The association of LPL S447X with CHD risk was then examined in a prospective study of healthy middle-aged U.K. men (n=2716). In normotensive individuals, compared with S447 homozygotes, X447 carriers were protected from CHD risk [HR (hazard ratio), 0.48 (95% CI, 0.23–1.00); P=0.05], whereas, in the hypertensives, X447 carriers had increased risk [HR, 1.54 (95% CI, 1.13–2.09) for S/S (P=0.006) and 2.30 (95% CI, 1.53–3.45) for X447+ (P<0.0001)] and had a significant interaction with hypertension in CHD risk determination (P=0.007). In conclusion, hypertensive LPL X447 carriers have increased risk of LVH and CHD, suggesting that altered FA delivery constitutes a mechanism through which LVH and CHD are associated in hypertensive subjects.
The dopaminergic system in hypertension
Authors: Zeng Chunyu , Zhang Meng , Asico Laureano D. , Eisner Gilbert M. , Jose Pedro A.
Published: May 2007

Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport, vascular smooth muscle contractility and production of reactive oxygen species and by interacting with the renin–angiotensin and sympathetic nervous systems. Dopamine receptors are classified into D1-like (D1 and D5) and D2-like (D2, D3 and D4) subtypes based on their structure and pharmacology. Each of the dopamine receptor subtypes participates in the regulation of blood pressure by mechanisms specific for the subtype. Some receptors regulate blood pressure by influencing the central and/or peripheral nervous system; others influence epithelial transport and regulate the secretion and receptors of several humoral agents. This review summarizes the physiology of the different dopamine receptors in the regulation of blood pressure, and the relationship between dopamine receptor subtypes and hypertension.
Factors Affecting the Buy vs Build Decision in Large Australian Organisations
Authors: Hung Patrick , Low Graham Cedric
Published: May 2007

When developing an information system, organisations are faced with a fundamental choice: to buy a pre-developed package (potentially customise it or redesign/reengineer the business processes of the company concerned to fit the package), or to build the system in-house. Past literature has indicated the importance of the buy vs build decision to the organisation even suggesting that correctly managing the choice could be the key to managing IT. This research aims to identify the factors that an organisation should consider when making an information systems buy vs build decision. Interviews were conducted with 10 organisations across a spread of industries, involving key strategic IT decision-making personnel at the senior IT executive level. By examining the operational approaches adopted in each of these organisations and the key drivers behind these approaches, we identify the core factors that affect real-world buy vs build decisions in large Australian organisations with a turnover in excess of $750 million. We found that a number of core factors - strategy, commodity and competitive advantage, maturity, cost and requirements fit - critically affect buy vs build, while peripheral factors - risk, time and timing, political factors, and ongoing support - are secondary considerations.
Re-Engineering at LeCroy Corporation: The Move to Component-Based Systems
Authors: Kotlarsky Julia
Published: May 2007

This case study discusses two related aspects that are becoming increasingly important in today's software development practice: re-engineering of a monolithic system into a component-based system (the focus of this case) and globally distributed work. Component-based (software) development (CBD) involves (i) the development of software components and (ii) the building of software systems through the integration of preexisting software components (developed in-house or procured from the component market). For companies involved in software development, CBD offers agility in design by basing software development on methodologies that support the recombination of reusable components, being an approach that rapidly expands product variation and sustains the build-up of product families. It also promises significant improvements in software development through shorter time-to-market and reduced development costs. However, being an innovative approach to software development that emerged in the mid-1990s, the adoption of CBD requires companies to re-engineer existing software systems (products) or to develop new systems from scratch using component technologies and to deal with additional challenges associated with the management of CBD. LeCroy Corporation was one of the early adopters of CBD that decided to adopt CBD to gain competitive advantage in its markets. The case describes an actual situation at LeCroy Corporation, involving several decisions, challenges and opportunities faced by the managers of a globally distributed software development team over a period of time when they re-engineered a monolithic system into a component-based system.
Low dimensional intermediate valence fluctuation in single crystalline YbB4
Authors: Kim J. Y. , Cho B. K. , Lee H. J. , Kim H.-C.
Published: May 2007

Temperature-dependent magnetization M(T), resistivity ρ(T), and specific heat Cp(T) were measured for single crystalline YbB4. M(T) showed a large anisotropy, that is M‖(T)>M⊥(T), for fields parallel and perpendicular, respectively, to the c axis. While M‖(T) followed Curie-Weiss behavior with slight crystalline electric field splittings, M⊥(T) showed a typical temperature dependence of intermediate valence (IV) fluctuation, which implies that YbB4 is a rare compound with two-dimensional IV fluctuation. ρ(T) followed ρ0+AT2 below Tcoh≈5K, indicating a low-temperature Fermi liquid state of YbB4. In addition, anomalies were also found at ≈Tcoh in M(T), ρ(T), and Cp(T).
Explicit solutions for exit-only radioactive decay chains
Authors: Yuan Ding , Kernan Warnick
Published: May 2007

In this study, we extended Bateman’s [Proc. Cambridge Philos. Soc. 15, 423 (1910)] original work for solving radioactive decay chains and explicitly derived analytic solutions for generic exit-only radioactive decay problems under given initial conditions. Instead of using the conventional Laplace transform for solving Bateman’s equations, we used a much simpler algebraic approach. Finally, we discuss methods of breaking down certain classes of large decay chains into collections of simpler chains for easy handling.
On the performance of different bimetallic combinations in surface plasmon resonance based fiber optic sensors
Authors: Sharma Anuj K. , Gupta B. D.
Published: May 2007

In the present work, we have investigated the capability of different bimetallic combinations to be used in a fiber optic sensor based on the technique of surface plasmon resonance. The metals considered for the present analysis are silver, gold, copper, and aluminum. The performance of the sensor with different bimetallic combinations is evaluated and compared numerically. The performance is analyzed in terms of three parameters: sensitivity, signal-to-noise ratio (SNR), and operating range. On the basis of the comparison and some logical criteria, the best possible bimetallic combination along with requisite thickness distribution is predicted. The bimetallic combination is capable of simultaneously providing the larger values of sensitivity, SNR, and operating range, which is not possible with any single metallic layer.
The development of laser- and beam-driven plasma accelerators as an experimental field
Authors: Joshi C.
Published: May 2007

Since its inception in the early 1980s, the field of plasma-based particle accelerators has made remarkable advances. Robust plasma accelerating structures can now be excited over centimeter scales using short laser pulses and over meter scales using ultrarelativistic particle beams. Accelerating fields in excess of tens of GV/m can be sustained over these lengths. Laser-driven plasma accelerators now routinely produce monoenergetic, low divergence electron beams in the 100MeV–1GeV range, whereas electron-beam driven plasma accelerators have demonstrated the ability to double the energy of 42GeV electrons using a high-energy collider beam in less than one meter. The development of this field is traced through a series of path breaking experiments.
Theoretical investigation of the ground and low-lying excited states of nickel carbide, NiC
Authors: Tzeli Demeter , Mavridis Aristides
Published: May 2007

The electronic structure and bonding of 19 states of the diatomic nickel carbide (NiC) has been studied by multireference methods. Potential energy curves have been constructed for all states, whereas for the three lowest states of symmetries XΣ+1, aΠ3, and AΠ1 well separated from the rest of the states, special attention was paid through the use of very large basis sets and the calculation of core-valence correlation and scalar relativistic effects. The recommended binding energies for these states are 91, 67, and 54kcal∕mol with respect to the ground state atoms. Our results in general can be considered in fair agreement with the limited experimental findings.
Marginally unstable Holmboe modes
Authors: Alexakis Alexandros
Published: May 2007

Marginally unstable Holmboe modes for smooth density and velocity profiles are studied. For a large family of flows and stratification that exhibit Holmboe instability, it is shown that the modes with phase velocity equal to the maximum or the minimum velocity of the shear are marginally unstable. This allows us to determine the critical value of the control parameter R (expressing the ratio of the velocity variation length scale to the density variation length scale) above which Holmboe instability is present, Rcrit=2. Furthermore, systems for which the parameter R is very close to this critical value Rcrit are examined. For this case, an analytical expression for the dispersion relation of the complex phase speed c(k) in the unstable region is derived. The growth rate and the width of the region of unstable wavenumbers has a very strong (exponential) dependence on the deviation of R from the critical value. Two specific examples are examined and a physical interpretation of the results is described.
Fronts from complex two-dimensional dispersal kernels: Theory and application to Reid’s paradox
Authors: Fort Joaquim
Published: May 2007

Bimodal dispersal probability distributions with characteristic distances differing by several orders of magnitude have been derived and favorably compared to observations by Nathan et al. [Nature (London) 418, 409 (2002)]. For such bimodal kernels, we show that two-dimensional molecular dynamics computer simulations are unable to yield accurate front speeds. Analytically, the usual continuous-space random walks (CSRWs) are applied to two dimensions. We also introduce discrete-space random walks and use them to check the CSRW results (because of the inefficiency of the numerical simulations). The physical results reported are shown to predict front speeds high enough to possibly explain Reid’s paradox of rapid tree migration. We also show that, for a time-ordered evolution equation, fronts are always slower in two dimensions than in one dimension and that this difference is important both for unimodal and for bimodal kernels.
Visualization of induced charge in an organic thin-film transistor by cross-sectional potential mapping
Authors: Ikeda Susumu , Shimada Toshihiro , Kiguchi Manabu , Saiki Koichiro
Published: May 2007

Kelvin probe force microscopy was applied to the cross-sectional potential imaging of a working organic thin-film transistor (OTFT). The bottom-contact-type OTFT with an active layer of copper-phthalocyanine (CuPc) was cleaved and internal potential distribution of its channel region was visualized. The potential distribution on the cross section changed depending on the applied drain and gate voltage. Horizontal potential distribution in the semiconductor film from source to drain direction was roughly consistent with the results of surface potential imaging previously reported. Vertical potential distribution from bottom (gate) to top (CuPc film) showed that a potential peak appeared along the semiconductor/insulator interface when a negative voltage was applied to the gate. The charge injection process is discussed based on the visualized potential peak at the interface.
Electron mobility in tris(8-hydroxyquinoline)aluminum (Alq3) films by transient electroluminescence from single layer organic light emitting diodes
Authors: Park Hoon , Shin Dong-Sub , Yu Hee-Sung , Chae Hee-Baik
Published: May 2007

Single layer devices of indium tin oxide/Alq3∕Al were constructed with varying the active areas from 1to8mm2 and the thicknesses from 30to50nm. Average electric field across the Alq3 layer during the transient state was estimated from the accumulated charges at the interfaces of the devices. The electron mobility could thus be calculated by assuming that the injected charge carriers moved under the average electric field rather than the instantaneous field. The resulting mobility could be determined uniquely in a device thickness. The electron drift mobility was shown to behave similarly to the time-of-flight results.
Eutactic star closest to a given star
Authors: Gómez A. , Torres M. , Aragón J. L.
Published: May 2007

A eutactic star is a set of M vectors in Rn (M>n) that are projections of M orthogonal vectors in RM. Eutactic stars have remarkable properties that have been exploited in several fields such as crystallography, graph theory, wavelets, and quantum measurement theory. In this work we show that given an arbitrary star of vectors, there exists a closest eutactic star in the Frobenius norm. An algorithm for calculating this star is presented. Additionally, the distance between both stars provides a new measure of eutacticity.
Extended reduction criterion and lattice states
Authors: Benatti Fabio , Floreanini Roberto , Liguori-Schremp Alexandar M.
Published: May 2007

We study a particular class of states of a bipartite system consisting of two four-level parties. By means of an adapted extended reduction criterion we associate their properties to the geometric patterns of a planar lattice consisting of 16 points.
Invited Article: Linearization and signal recovery in photoacoustic infrared spectroscopy
Authors: Michaelian K. H.
Published: May 2007

Photoacoustic (PA) infrared spectroscopy enables the characterization of a wide variety of materials, affording the spectroscopist several advantages over more traditional infrared methods. While PA spectra are readily acquired using commercial instrumentation, the quality of the data can be improved substantially through the use of specialized numerical and experimental procedures. Two of these methods are the subject of this review. Specifically, this article describes (a) linearization of PA infrared spectra, a calculation that incorporates phase and amplitude information to extend the range of linearity for strongly absorbing samples, and (b) lock-in and digital signal-recovery procedures in step-scan phase-modulation PA infrared spectroscopy. Linearization yields significant improvement in band definition, especially in the low-wavenumber region. This numerical method succeeds in situations where the PA phase of the sample is less than that of the reference (carbon black). When this criterion is not met initially, the sample or reference interferograms can be manipulated prior to the calculation. The steps involved in linearization are illustrated in detail and approximations are discussed. Lock-in demodulation of the step-scan phase-modulation signal is compared to digital (software) demodulation in this study; the lock-in technique is found to be superior in several cases. The imaginary interferograms in these experiments sometimes lack a strong central feature, a situation that necessitates the application of less commonly used methods for phase correction and spectrum calculation. These methods, which are available in commercial software, include two-quadrant and stored-phase corrections. The PA phase spectrum resembles amplitude and absorption spectra when real and imaginary PA spectra are correctly calculated.
Fully automated time domain spectrometer for the absorption and scattering characterization of diffusive media
Authors: Pifferi Antonio , Torricelli Alessandro , Taroni Paola , Comelli Daniela , Bassi Andrea , Cubeddu Rinaldo
Published: May 2007

We describe a system for absorption and scattering spectroscopy of diffusive media based on time-resolved reflectance and transmittance measurements. The system is operated with mode-locked lasers tunable in the 550–1050nm spectral range and on a detection chain based on time-correlated single-photon counting. All measurement procedures such as laser tuning and optimization, signal conditioning, data acquisition, and analysis are completely automated, permitting spectral measurements over the whole range in a few minutes. The criticalities of the system are discussed together with the strategies to compensate them. The Medphot protocol devised for the characterization of photon migration instruments was applied to assess the system performances in terms of accuracy, linearity, noise, stability, and reproducibility. Finally, an example of application of the instrument to the spectroscopy of powders is presented.
Spatial normalization of the high-frequency ultrasound energy loss in open-cell foams
Authors: Gómez Álvarez-Arenas T. E. , González Gómez I.
Published: May 2007

Wide-band and air-coupled ultrasound pulses are propagated through slabs of open-cell reticulated solid foams and the transmission coefficient is measured. Under these conditions, fluid in the pores and solid skeleton are strongly decoupled; in addition, at frequencies well over that of the relaxation of the influence of the tortuosity, it is observed that energy loss approaches to a constant value: ∣γ∣∞. Internal surface area (Si) and the length dimension parameter (Λ) of the foams are independently measured. Results reveal that ∣γ∣∞ vs Λ or Si follows a power law very close to linear, suggesting a possible spatial normalization for ∣γ∣∞.
Finite element analysis of the effect of electrode resistivity on resistivity measurement in a diamond anvil cell
Authors: Huang Xiaowei , Gao Chunxiao , Zhang Dongmei , Li Ming , He Chunyuan , Hao Aimin , Yu Cuiling , Sang Chong , Liu Cailong , Wang Yue , Guan Rui , Li Dongmei , Zou Guangtian , Ma Yanzhang
Published: May 2007

The effect of electrode resistivity on the in situ resistivity measurement in a diamond anvil cell was studied using finite element analysis. The theoretical analysis reveals that the origin of significant error for a thin sample is mainly caused by the resistivity difference between the electrodes and the sample. The authors found that reducing such resistivity differences can improve the accuracy. The result shows that the van der Pauw method [L. J. van der Pauw, Philips Tech. Rev. 20, 220 (1958)] can provide more accurate results for thin samples compared with the four-point probe method. This approach provides means to simulate actual experiments and to eliminate the measurement error.
Strained Si n-channel metal-oxide-semiconductor field-effect transistors formed on very thin SiGe relaxed layer fabricated by ion implantation technique
Authors: Sawano K. , Fukumoto A. , Hoshi Y. , Shiraki Y. , Yamanaka J. , Nakagawa K.
Published: May 2007

Strained Si n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated on the Si0.83Ge0.17 relaxed thin layer formed by ion implantation technique. Although the SiGe thickness was as small as 100nm, the relaxation was highly enhanced thanks to the pre-ion-implantation into the Si substrate and the strained Si channel with very smooth surface was obtained. A nMOSFET was fabricated in this structure and 100% drive current improvement and 60% mobility enhancement over the control Si MOSFET were achieved. This indicates that the ion implantation technique is very promising for realization of relaxed-SiGe-based devices with very high performances.
Ion irradiation effects on ionic liquids interfaced with rf discharge plasmas
Authors: Baba K. , Kaneko T. , Hatakeyama R.
Published: May 2007

The availability of plasma ion irradiation toward a gas-liquid interface is investigated in a rf discharge system incorporating an ionic liquid. The introduction of the ionic liquid to the plasma causes the formation of a sheath electric field on the ionic liquid surface, resulting in the acceleration of the ions to the ionic liquid and the generation of secondary electrons from the ionic liquid by the ion irradiation. These effects are found to advance the discharge process and enhance the plasma production.
Study of the initial nucleation and growth of catalyst-free InAs and Ge nanowires
Authors: Park Hyun D. , Prokes S. M.
Published: May 2007

The authors have examined the nucleation conditions in the growth of catalyst-free InAs and Ge nanowires (NWs) on porous Si, as well as the growth of InAs NWs on a SiO2 substrate using 10nm sized In nanoparticles. The NW growths were performed in a closed system. The results suggest that all the NWs grew from a solid nucleation state. For the growth using In nanoparticles, the results suggest that the growth mechanism is very different from the vapor-liquid-solid, in that the nanowire growth only begins after the nucleation particle solidifies.
Thermal stability of nanoscale Ge metal-oxide-semiconductor capacitors with ZrO2 high-k gate dielectrics on Ge epitaxial layers
Authors: Oh Jungwoo , Majhi Prashant , Kang Chang Yong , Yang Ji-Woon , Tseng Hsing-Huang , Jammy Raj
Published: May 2007

The authors report on the thermal stability of Ge metal-oxide-semiconductor (MOS) devices. Ge MOS capacitors with ZrO2 high-k gate dielectric and TaN metal gates were fabricated on Ge epitaxial films. Ge MOS capacitors exhibited a very low gate leakage current density of ∼1×10−6A∕cm2 with a capacitance equivalent thickness of 13Å. The excellent electrical characteristics, however, degraded when Ge∕ZrO2 gate stacks were subsequently annealed at elevated temperatures that are potentially used for transistor fabrication. The thermal degradation was due primarily to the formation of interfacial Ge oxides. Ge oxidation temperature was identified using surface analysis and correlated with electrical characteristics.
Generation of cylindrically symmetric converging shock waves by underwater electrical explosion of wire array
Authors: Fedotov A. , Grinenko A. , Efimov S. , Krasik Ya. E.
Published: May 2007

It is shown that the originally corrugated shock wave generated in the process of an underwater electrical explosion of a cylindrical wire array is self-aligned into a cylindrically symmetric converging front. It was found that by increasing the number of the wires in the array this self-alignment process occurs faster. It is also demonstrated that in the case of a large wire number (>20), one-dimensional calculations can be successfully employed for theoretical analysis.
The Science Park and the Governance Challenge of the Movement of the High-Tech Urban Region towards Polycentricity: The Hsinchu Science-Based Industrial Park
Authors: Chou Tsu-Lung
Published: May 2007

In this paper I explore the governance challenges of science-park-based urban regions by exploring the case study of the Hsinchu science-based industrial park in Taiwan. In contrast to the economic emphasis of new regionalism on regional learning, I investigate the change and development of the high-tech Hsinchu region as it moves towards polycentricity, by exploring how the political processes of multiple and interconnected forces, from international to national and subnational levels, affect spatial-construction and regional governance issues. With reference to the analytical tool of the polycentric urban region (PUR), I highlight that international, national, and subnational forces caused the polycentric development, which in turn has led to governance contradictions and has politically affected the implementations of an ideal mode of the PUR.