bluuebunny/crossref_metadata_2025 huggingface dataset:
DFT studies on the multi‐channel reaction of CH3S+NO2
Authors: Tang Yi‐Zhen , Sun Hao , Pan Ya‐Ru , Pan Xiu‐Mei , Wang Rong‐Shun
Published: December 2006

The mechanisms for the reaction of CH3S with NO2 are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) on both single and triple potential energy surfaces (PESs). The geometries, vibrational frequencies, and zero‐point energy (ZPE) correction of all stationary points involved in the title reaction are calculated at the B3LYP/6‐311++G(d,p) level. More accurate energies are obtained at the QCISD(T)/6‐311++G(d,p). The results show that 5 intermediates and 14 transition states are found. The reaction is more predominant on the single PES, while it is negligible on the triple PES. Without any barrier height for the whole process, the main channel of the reaction is to form CH3SONO and then dissociate to CH3SO+NO. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Certification process artifacts defined as measurable units for software assurance
Authors: Lee Seok‐Won , Gandhi Robin A. , Ahn Gail‐Joon
Published: December 2006

Certification and Accreditation (C&A) process artifacts for software‐intensive systems are characterized by the metrics and measures required to be produced from their units of analysis for assessing system behaviour. Software‐intensive systems are complex clusters of closely interdependent system of systems that include underlying software, systems, people, processes, and operational environments. Naturally, such systems require carefully designed C&A artifacts that consider metrics and measures from multiple dimensions at different levels of abstraction in the Universe of Discourse (UoD) in order to understand, predict, and control their emergent behaviour. Hence, C&A artifacts defined as measurable units for software assurance should be the result of an aggregated reasoning of evidences from various dimensions, while maintaining traceability and alignment to real world goals/objectives in all stages of the system lifecycle. To address these research objectives, we present a novel integration framework that promotes cohesion and traceability among metrics and measures from multiple dimensions in the problem domain on the basis of the definition of a common language. By applying our framework to automate the Department of Defense Information Technology Security Certification and Accreditation Process (DITSCAP), we also motivate the design principles and modelling techniques necessary to generalize a course of action to conduct C&A processes with appropriate tool support for software‐intensive systems. Copyright © 2006 John Wiley & Sons, Ltd.
The KlSTE2 and KlSTE3 genes encode MATα‐ and MATa‐specific G‐protein‐coupled receptors, respectively, which are required for mating of Kluyveromyces lactis haploid cells
Authors: Torres‐Quiroz Francisco , Kawasaki Laura , Rodríguez‐González Miriam , Patrón‐Soberano Araceli , Coria Roberto
Published: December 2006

Mating in yeast is initiated by binding of pheromone to G‐protein‐coupled receptors expressed in haploid cells. We analysed the role of KlSte2p and KlSte3p receptors in the Kluyveromyces lactis mating pathway. By sequence analysis, KlSte2p and KlSte3p are the homologues of the Saccharomyces cerevisiae α‐pheromone and a‐pheromone receptors, respectively. However, by expression experiments, we determined that KlSTE2 gene is expressed in the cells typified as MATα and therefore is the receptor for the K. lactis a‐pheromone and KlSTE3 gene is expressed in the MATa cells and binds the α‐pheromone. The KlSTE2 gene is silent in MATa cells, while it is highly expressed in MATα cells, and conversely the KlSTE3 gene is expressed in MATa cells and repressed in MATα cells. Disruption mutants of both genes were found to be sterile, and this defect is reversed by plasmidic copies of each gene. The cytoplasmic C‐terminus of KlSte3p interacts strongly with the KlGpa1p (Gα) subunit, which is involved in the transduction of the pheromone stimulus to induce mating. Remarkably, this same domain does not interact with a constitutive active allele of the Gα subunit, indicating that the C‐terminus is able to discriminate between the active (GTP‐bound) and inactive (GDP‐bound) forms of the Gα subunit. Copyright © 2007 John Wiley & Sons, Ltd.
Accuracy of complex lower-limb deformity correction with external fixation: A comparison of the Taylor Spatial Frame with the Ilizarov ring fixator
Authors: Manner Hans Michael , Huebl Michael , Radler Christof , Ganger Rudolf , Petje Gert , Grill Franz
Published: December 2006

Purpose

Circular external fixators have several advantages over other surgical options in the treatment of limb length discrepancy and axial deformity. The innovative Taylor Spatial Frame (TSF) combines a rigid hexapod fixation system with the support of a web-based software program, and thus offers the possibility of simultaneous corrections of multidirectional deformities. Whilst there is still some scepticism of many Ilizarov device users about the advantages of the TSF, the purpose of the study was to perform a comparison between the TSF and the Ilizarov ring fixator (IRF) with regard to the accuracy of deformity correction in the lower limb.

Methods

Two hundred and eight consecutive deformity corrections in 155 patients were retrospectively evaluated. There were 79 cases treated with the IRF and 129 cases treated with the TSF. The mean age of the patients at the time of surgery was 13.2 years (range; 2–49 years). Standing anteroposterior and lateral radiographs were evaluated preoperatively and immediately after removal of the frames. The final result was compared to the preoperatively defined aim of the deformity correction. According to the treated count of dimensions, we differentiated four types of deformity corrections. The results were graded into four groups based on the persisting axial deviation after removal of the frame.

Results

The aim of the deformity correction was achieved in a total of 90.7% in the TSF group, compared to 55.7% in the IRF group. On the basis of the count of dimensions, the TSF achieved obviously higher percentages of excellent results (one dimension: TSF 100%; IRF 79.3%; two dimensions: TSF 91.8%; IRF 48.6%; three dimensions: TSF 91.1%; IRF 28.6%; four dimensions: TSF 66.7%; IRF 0%). In addition, the degree of the persisting deformity increased with the number of planes of the deformity correction.

Conclusions

The TSF allowed for much higher precision in deformity correction compared to the IRF. In two-, three- and four-dimensional deformity corrections in particular, the TSF showed clear advantages. This may derive from the TSF-specific combination of a hexapod fixator with the support of an Internet-based software program, enabling precise simultaneous multiplanar deformity corrections.
Energies of \( S^{2} \)-valued harmonic maps on polyhedra with tangent boundary conditions
Authors: Majumdar A. , Robbins J.M. , Zyskin M.
Published: December 2006

A unit-vector field

\mathbf{n}\:\text{:}P\rightarrow S^{2}

on a convex polyhedron

P \subset \mathbb{R}^{3}

satisfies tangent boundary conditions if, on each face of

P

,

\mathbf{n}

takes values tangent to that face. Tangent unit-vector fields are necessarily discontinuous at the vertices of

P

. We consider fields which are continuous elsewhere. We derive a lower bound

E_{P}^{−}(h)

for the infimum Dirichlet energy

E_{P}^{\mathrm{\inf }}(h)

for such tangent unit-vector fields of arbitrary homotopy type

h

.

E_{P}^{−}(h)

is expressed as a weighted sum of minimal connections, one for each sector of a natural partition of

S^{2}

induced by

P

. For

P

a rectangular prism, we derive an upper bound for

E_{P}^{\mathrm{\inf }}(h)

whose ratio to the lower bound may be bounded independently of

h

. The problem is motivated by models of nematic liquid crystals in polyhedral geometries. Our results improve and extend several previous results.
Semi-strong convergence of sequences satisfying a variational inequality
Authors: Briane Marc , Mokobodzki Gabriel , Murat François
Published: December 2006

In this paper we study the properties of any sequence

(u_{n})_{n⩾1}

weakly converging to a nonnegative function

u

in

W_{0}^{1,p}(\Omega )

,

p > 1

, and satisfying a variational inequality of type

−\mathrm{div}(a_{n}( \cdot ,\mathrm{∇}u_{n}))⩾f_{n}

, where

(a_{n})_{n⩾1}

is a suitable sequence of monotone operators and

(f_{n})_{n⩾1}

is any strongly convergent sequence in the dual space

W^{−1,p^{′}}(\Omega )

. We prove that the sequence

(u_{n}−(1−ɛ)u)^{−}

strongly converges to 0 in

W_{0}^{1,p}(\Omega )

for any

ɛ \in (0,1)

. We show by a counter-example that the result does not hold true if

ɛ = 0

. A remarkable corollary of these strong

ɛ

-convergences is that the sequence

(u_{n})_{n⩾1}

satisfies, up to a subsequence, a kind of semi-strong convergence:

(u_{n})_{n⩾1}

can be bounded from below by a sequence which converges to the same limit

u

but strongly in

W_{0}^{1,p}(\Omega )

. We also give an example of a nonnegative weakly convergent sequence which does not satisfy this semi-strong convergence property and hence cannot satisfy any variational inequality of the previous type. Finally, in the linear case of a sequence of highly-oscillating matrices, we improve the strong

ɛ

-convergences by replacing the arbitrary small constant

ɛ > 0

by a sequence

(ɛ_{n})_{n⩾1}

converging to 0.

Dans cet article, on étudie les propriétés de toute suite

(u_{n})_{n⩾1}

qui converge faiblement dans

W_{0}^{1,p}(\Omega )

,

p > 1

, vers une fonction positive

u

et qui satisfait une inégalité variationnelle du type

−\mathrm{div}(a_{n}( \cdot ,\mathrm{∇}u_{n}))⩾f_{n}

, où

(a_{n})_{n⩾1}

est une suite convenable d'opérateurs monotones et où

(f_{n})_{n⩾1}

est une suite fortement convergente dans l'espace dual

W^{−1,p^{′}}(\Omega )

. On montre que, pour tout

ɛ \in ]0,1[

, la suite

(u_{n}−(1−ɛ)u)^{−}

converge fortement vers 0 dans

W_{0}^{1,p}(\Omega )

, et, à l'aide d'un contre-exemple, que cette convergence n'est pas en général vraie lorsque

ɛ = 0

. Un corollaire remarquable de ces

ɛ

-convergences fortes est que la suite

(u_{n})_{n⩾1}

satisfait, à une sous-suite près, une sorte de semi-convergence forte : la suite

(u_{n})_{n⩾1}

peut en effet être minorée par une suite qui converge fortement dans

W_{0}^{1,p}(\Omega )

vers la même limite

u

. On explicite aussi un exemple d'une suite positive et faiblement convergente qui ne vérifie pas la semi-convergence forte et qui par conséquent, n'est solution d'aucune inéquation variationnelle du type précédent. Enfin, dans le cas linéaire d'une suite fortement oscillante de matrices, on améliore la

ɛ

-convergence en remplaçant la constante arbitraire

ɛ > 0

par une suite

(ɛ_{n})_{n⩾1}

convergeant vers 0.
Mid‐trimester dilation and evacuation with laminaria does not increase the risk for severe subsequent pregnancy complications
Authors: Jackson J.E. , Grobman W.A. , Haney E. , Casele H.
Published: December 2006

Objective: To evaluate subsequent pregnancy outcomes in women with a previous mid‐trimester (12–24 weeks) pregnancy termination by dilation and evacuation (D&E) as compared to women without a previous D&E. Method: Medical records for women who underwent a D&E between 1995 and 2003 were identified and reviewed. Women with subsequent pregnancies were compared on a 1:2 basis with women in a control group who had viable pregnancies and no previous mid‐trimester DE. Outcomes of interest included preterm labor, placental abnormalities, and a composite complication outcome. Results: Of the 317 women who underwent a D&E, 85 had viable subsequent pregnancies. These women delivered slightly earlier than the 170 controls (38.9 versus 39.5 weeks, p = 0.001), although there was no statistically significant difference between the two groups with regard to birth weights, spontaneous preterm delivery, abnormal placentation, and overall complication rate. Conclusions: Mid‐trimester termination by D&E does not increase the rate of clinically significant subsequent pregnancy complications.
Treatment of Scaphoid Non-Unions by a Palmar Approach with Vascularised Bone Graft Harvested from the Thumb
Authors: BERTELLI J. A. , PERUCHI F. M. , ROST J. R. , TACCA C. P.
Published: December 2006

Ten patients with scaphoid non-unions which had been present for longer than 2 years were treated using a vascularised bone graft harvested from the thumb and pedicled on the first dorsal metacarpal artery. Bone harvesting and grafting were performed by a single palmar approach. Concomitant cancellous bone graft was not used. Bone healing was confirmed by CT scans in nine of the ten patients. Persistence of the non-union was observed in one patient who was the oldest in this series, had the longest standing non-union and was a heavy smoker. Twelve months after surgery, nine of the ten patients had significant pain relief with an improved range of motion and grip strength.
High‐Level Recombinant Protein Production in CHO Cells Using an Adenoviral Vector and the Cumate Gene‐Switch
Authors: Gaillet Bruno , Gilbert Rénald , Amziani Rachid , Guilbault Claire , Gadoury Christine , Caron Antoine W. , Mullick Alaka , Garnier Alain , Massie Bernard
Published: December 2006

To facilitate and accelerate the production of eukaryotic proteins with correct post‐translational modifications, we have developed a protein production system based on the transduction of Chinese hamster ovary (CHO) cells using adenovirus vectors (AdVs). We have engineered a CHO cell line (CHO‐cTA) that stably expresses the transactivator (cTA) of our newly developed cumate gene‐switch transcription system. This cell line is adapted to suspension culture and can grow in serum‐free and protein‐free medium. To increase the transduction level of AdVs, we have also generated a cell line (CHO‐cTA‐CAR) that expresses additional amounts of the coxackievirus and adenovirus receptor (CAR) on its surface. Recombinant protein production was tested using an AdV carrying the secreted alkaline phosphatase (SEAP) under the control of the CR5 promoter, which is strongly and specifically activated by binding to cTA. The SEAP expression was linked to the expression of the green fluorescent protein (GFP) through an internal ribosome entry site (IRES) to facilitate titration of the AdV. We monitored SEAP expression on a daily basis for 9 days after transduction of CHO‐cTA and CHO‐cTA‐CAR using different quantities of AdVs at 37 and 30 °C. Incubation at the latter temperature increased the production of SEAP at least 10‐fold, and the presence of CAR increased the transduction level of the AdV. Maximum SEAP production (63 mg/L) was achieved at 6–7 days post‐infection at 30 °C by transducing CHO‐cTA‐CAR with 500 infectious particles/cell. Because numerous AdVs can now be generated within a few weeks and large‐scale production of AdVs is now a routine procedure, this system could be used to produce rapidly milligram quantities of a battery of recombinant proteins as well as for large‐scale protein production.
Electrochemical Regeneration of NADH Using Conductive Vanadia‐Silica Xerogels
Authors: Siu Eulalia , Won Keehoon , Park Chan Beum
Published: December 2006

Electrically conductive sol‐gel matrices have been first introduced in order to enhance the efficiency of electrochemical NADH regeneration systems for biocatalysis. Vanadia‐silica mixed gels as conductive sol‐gels were synthesized using vanadium (V) oxytripropoxide (VOTP) and tetramethyl orthosilicate (TMOS) as precursors. Direct electrochemical reductions of NAD+ were carried out in the presence of vanadia‐silica xerogels using unmodified platinum electrodes. Vanadia‐silica gels from higher ratios of VOTP to TMOS could effectively improve electrochemical generations of NADH from NAD+. Direct electrochemical regenerations of NADH were coupled to the synthesis of l‐glutamate from α‐ketoglutarate catalyzed by glutamate dehydrogenases (GDH). In this case, vanadia‐silica gels were used as matrices for enzyme encapsulation, as opposed to serving as additives. When GDH were entrapped in “nonconductive” silica gels, synthesized using only TMOS, in the control experiment, the initial supply of NADH exhausted quickly and a final conversion of 30% was obtained. However, the use of conductive vanadia‐silica gels with encapsulated GDH resulted in complete conversion of α‐ketoglutarate to l‐glutamate. A turnover number of a cofactor was also enhanced 3‐fold by the application of conductive vanadia‐silica gels.
Intrinsic and apparent short‐time limits for fault healing: Theory, observations, and implications for velocity‐dependent friction
Authors: Nakatani Masao , Scholz Christopher H.
Published: December 2006

The time‐dependent healing of frictional strength, whose underlying mechanism may vary, is often logarithmic with time, after a certain time duration called the cutoff time. We theoretically show that the cutoff time depends on the initial strength at the beginning of quasi‐stationary contact. This comes from the fact that the healing rate depends negatively and exponentially on the current strength. If healing starts with the minimum strength attained instantaneously upon the application of normal load, “intrinsic” cutoff time tcx, which reflects the reaction rate constant of the underlying physico‐chemical process, will be observed. In general, the observed cutoff time is the sum of tcx and the effective contact time tini of asperities at the beginning of the healing. Hence, in slide‐hold‐slide (SHS) experiments, where tini is inversely proportional to the slip velocity Vprior in the sliding preceding the hold, two regimes are predicted. For high Vprior (tini ≪ tcx), the observed cutoff time is independent of Vprior, being ∼tcx. For low Vprior (tini ≫ tcx), the observed cutoff time is “apparent,” being ∼tini inversely proportional to Vprior. Both regimes have been identified in laboratory data. Incorporation of the present cutoff time theory into the rate and state evolution laws predicts that the velocity dependence of steady state will diminish at high velocities where effective contact time is ≪tcx. Furthermore, the two regimes for SHS tests are divided by this cutoff velocity. This also has been confirmed with laboratory data. Implications on the very long cutoff time observed for natural repeating earthquakes are discussed.
Possible overestimation of shallow‐depth calcium carbonate dissolution in the ocean
Authors: Friis K. , Najjar R. G. , Follows M. J. , Dutkiewicz S.
Published: December 2006

We argue that diagnostics of excess dissolved calcium carbonate (TA*) above the saturation horizon cannot be unambiguously interpreted in terms of local in situ dissolution. We examine a three‐dimensional numerical model of global ocean circulation and biogeochemistry with explicit representation of the formation and dissolution of calcium carbonate. In particular, dissolution is only allowed to occur below the saturation horizon. The model qualitatively captures the observed basin‐ and global‐scale patterns of alkalinity and TA* as well as the relationship between TA* and chlorofluorocarbon age in the thermocline. The existence of TA* above the saturation horizon in the model can only be explained in terms of transport subsequent to dissolution. The model study does not rule out the possibility of shallow‐depth calcium carbonate dissolution but suggests that dissolution rates derived from tracer observations have not adequately accounted for the influence of transport.
Robust increases in midlatitude static stability in simulations of global warming
Authors: Frierson Dargan M. W.
Published: December 2006

We examine changes in the static stability of the midlatitude troposphere in simulations of global warming using 21 coupled climate models in the AR4 archive. The dry static stability within the midlatitudes exhibits a robust increase in the simulations, with upper tropospheric warming outpacing the lower troposphere by approximately 2 K. The increase in stability is especially evident in the summer season, and is more prominent in the Southern Hemisphere than in the Northern. The moist static stability is largely unchanged, on the other hand, showing that moist convection plays a dominant role in determining the temperature structure of the midlatitudes. We compare bulk measures of the stability with changes in meridional gradients for each individual model simulation, and find that moist theories work well in predicting the stability with the primary exception of the Northern Hemisphere summer, where enhanced surface warming over land reduces the increase in stability.
Is regional air quality model diversity representative of uncertainty for ozone simulation?
Authors: Vautard R. , Van Loon M. , Schaap M. , Bergström R. , Bessagnet B. , Brandt J. , Builtjes P. J. H. , Christensen J. H. , Cuvelier C. , Graff A. , Jonson J. E. , Krol M. , Langner J. , Roberts P. , Rouil L. , Stern R. , Tarrasón L. , Thunis P. , Vignati E. , White L. , Wind P.
Published: December 2006

We examine whether seven state‐of‐the‐art European regional air quality models provide daily ensembles of predicted ozone maxima that encompass observations. Using tools borrowed from the evaluation of ensemble weather forecasting, we analyze statistics of simulated ensembles of ozone daily maxima over an entire summer season. Although the model ensemble overestimates ozone, the distribution of simulated concentrations is representative of the uncertainty. The spread of simulations is due to random fluctuations resulting from differences in model formulations and input data, but also to the spread between individual model systematic biases. The ensemble average skill increases as the spread decreases. The skill of the ensemble in giving probabilistic predictions of threshold exceedances is also demonstrated. These results allow for optimism about the ability of this ensemble to simulate the uncertainty of the impact of emission control scenarios.
Observations of the impact of a major Saharan dust storm on the atmospheric radiation balance
Authors: Slingo A. , Ackerman T. P. , Allan R. P. , Kassianov E. I. , McFarlane S. A. , Robinson G. J. , Barnard J. C. , Miller M. A. , Harries J. E. , Russell J. E. , Dewitte S.
Published: December 2006

Saharan dust storms have often been observed from space, but the full impact on the Earth's radiation balance has been difficult to assess, due to limited observations from the surface. We present the first simultaneous observations from space and from a comprehensive new mobile facility in Niamey, Niger, of a major dust storm in March 2006. The results indicate major perturbations to the radiation balance both at the top of the atmosphere and at the surface. Combining the satellite and surface data, we also estimate the impact on the radiation balance of the atmosphere itself. Using independent data from the mobile facility, we derive the optical properties of the dust and input these and other information into two radiation models to simulate the radiative fluxes. We show that the radiation models underestimate the observed absorption of solar radiation in the dusty atmosphere.
SAM and regional rainfall in IPCC AR4 models: Can anthropogenic forcing account for southwest Western Australian winter rainfall reduction?
Authors: Cai Wenju , Cowan Tim
Published: December 2006

Winter rainfall over southwest Western Australia (SWWA) has decreased by 20% since the late 1960s. Why has the reduction occurred in the Southern Hemisphere (SH) winter months but not in summer? To what extent is this reduction attributable to anthropogenic forcing and congruent with the Southern Annular Mode (SAM)? Using reanalysis data and the Intergovernmental Panel on Climate Change 4th Assessment Report (IPCC AR4) 20th century model experiments, we show that a SAM‐SWWA relationship exists in winter and not in other seasons. An ensemble result from 71 experiments reveals that anthropogenic forcing contributes to about 50% of the observed rainfall decline. Approximately 70% of the observed trend is congruent with the SAM trend, whereas for the models it is 46%. Our result suggests that other forcing factors must be invoked to fully account for the observed rainfall reduction.
Influence of methane hydrate content on electrical sediment properties
Authors: Spangenberg Erik , Kulenkampff Johannes
Published: December 2006

The electrical resistivity of an originally fully water saturated glass bead sample during the process of hydrate formation from methane dissolved in the pore water without a free gas phase was measured. In addition to the sample resistivity we measured the resistivity of the circulating water in order to determine the amount of water consumed by hydrate formation from the increase of salinity and to determine the formation resistivity factor and resistivity index. The resistivity of the sample increased from 5.1 Ωm at 100% water saturation to 265 Ωm at about 95% hydrate saturation whereas the water resistivity decreased from 1.39 Ωm to 1.08 Ωm. The observed dependence of the resistivity index versus water saturation cannot be described with the Archie‐equation using a constant saturation exponent, but corresponds to what was predicted by a cubic sphere pack model.
Meteor induced ridge and trough formation and the structuring of the nighttime E‐region ionosphere
Authors: Oppenheim Meers M. , Dimant Yakov
Published: December 2006

When meteor‐generated plasma trails diffuse into the ionosphere they create large ambipolar electric fields mainly perpendicular to the Earth's geomagnetic field (B) and extending many kilometers from the trail along B. These fields will cause ionospheric plasma to collect into ridges extending from the trail along B, enhancing the density by as much as a factor of 2, and they will also remove up to 90% of the plasma on each side of the ridge. We predict that meteor‐induced density perturbations may fill as much as 20% of the ionosphere between 95 and 120 km altitude. This paper presents simulations and theory to show how meteors produce plasma ridges and troughs. We estimate the extent of these as a function of altitude and meteor density. This process may explain observations of extensive nighttime E‐region density structures made by rockets and radars.
Continental deformation in Asia from a combined GPS solution
Authors: Calais E. , Dong L. , Wang M. , Shen Z. , Vergnolle M.
Published: December 2006

After decades of research on continental tectonics, there is still no consensus on the mode of deformation of continents or on the forces that drive their deformation. In Asia the debate opposes edge‐driven block models, requiring a strong lithosphere with strain localized on faults, to buoyancy‐driven continuous models, requiring a viscous lithosphere with pervasive strain. Discriminating between these models requires continent‐wide estimates of lithospheric strain rates. Previous efforts have relied on the resampling of heterogeneous geodetic and Quaternary faulting data sets using interpolation techniques. We present a new velocity field based on the rigorous combination of geodetic solutions with relatively homogeneous station spacing, avoiding technique‐dependent biases inherent to interpolation methods. We find (1) unresolvable strain rates (<3 × 109/yr) over a large part of Asia, with current motions well‐described by block or microplate rotations, and (2) internal strain, possibly continuous, limited to high‐elevation areas.
Decontaminating tide gauge records for the influence of glacial isostatic adjustment: The potential impact of 3‐D Earth structure
Authors: Kendall Roblyn A. , Latychev Konstantin , Mitrovica Jerry X. , Davis Jonathan E. , Tamisiea Mark E.
Published: December 2006

We investigate the potential impact of lateral variations in mantle viscosity and lithospheric thickness on predictions of present‐day relative sea‐level change due to glacial isostatic adjustment (GIA). We consider three viscoelastic Earth models. The first is a 1‐D model with a lithospheric thickness of 120 km and upper and lower mantle viscosities of 5 × 1020 Pa s and 5 × 1021 Pa s, respectively. The second model includes global lithospheric thickness variations and lateral heterogeneities in upper mantle viscosity ranging over three orders of magnitude, while the third model includes lateral variations in lower mantle viscosity alone. We find that the impact of 3‐D structure is significant. Indeed, the difference between the 3‐D and 1‐D model predictions at ∼300 sites with tide gauge records longer than 40 years duration is greater than 0.2 mm/yr and 0.5 mm/yr for 50% and 25% of the sites, respectively. The maximum difference exceeds several mm/yr. We conclude that efforts to decontaminate tide gauge records for ongoing GIA, to determine the rate and origin of global sea‐level rise, should incorporate 3‐D mantle structure into the GIA modelling.
O(1S → 1D,3P) branching ratio as measured in the terrestrial nightglow
Authors: Slanger T. G. , Cosby P. C. , Sharpee B. D. , Minschwaner K. R. , Siskind D. E.
Published: December 2006

The branching ratio of the two optically forbidden atmospheric emission lines, O(1S − 1D) at 557.7 nm and O(1S − 3P) at 297.2 nm, is a fixed number in the upper atmosphere because the O(1S) level is common to both lines. The value for the ratio A(557.7)/A(297.2) currently recommended by NIST is 16.7, and the ratio found in the laboratory is somewhat larger. Field observations require space‐based instruments, in which case calibration between the two wavelength regions is the critical issue. We circumvent this problem by using the O2(A‐X) Herzberg I emission system as a bridge between the UV region below 310 nm and the ground‐accessible region above that wavelength. These two spectral regions can be separately calibrated in terms of intensity, and the results of a disparate set of observations (satellite, rocket, ground‐based sky spectra) lead to a quite consistent value of 9.8 ± 1.0 for A(557.7)/A(297.2). This conclusion has consequences for auroral and dayglow processes and for spectral calibration. It is particularly important to ascertain the cause of the substantial difference between this value and those from theory.
Ion acoustic‐like waves triggered by nonlinear circularly polarized waves in the presence of an alpha particle beam
Authors: Gomberoff L.
Published: December 2006

We consider a fast solar wind‐type plasma consisting of electrons, a protons background, and a much more tenuous alpha particle beam. It is shown that such system is unstable against ion acoustic‐like waves triggered by finite‐amplitude left‐hand polarized waves propagating in the direction of the interplanetary magnetic field. The ion acoustic‐like waves have similar properties to those found in a plasma with a much denser proton beam (Gomberoff, 2006b). Although the alpha particle beam is much more tenuous than the proton beam, the system is equally able to trigger ion acoustic‐like waves. Therefore we believe that this effect should be taken into account in the evolution of the fast solar wind.
Effects of internal mineral structures on the magnetic remanence of silicate‐hosted titanomagnetite inclusions: An electron holography study
Authors: Feinberg Joshua M. , Harrison Richard J. , Kasama Takeshi , Dunin‐Borkowski Rafal E. , Scott Gary R. , Renne Paul R.
Published: December 2006

Titanomagnetite inclusions in pyroxene and plagioclase are carriers of stable magnetic remanence in some slowly cooled rocks such as gabbros, anorthosites, granulites, and diorites. Needle‐shaped inclusions with average dimensions of 1 × 1 × >25 μm form epitaxially by exsolution from their host silicate. Close examination of clinopyroxene‐hosted inclusions reveals an internal microstructure, which consists of magnetite (Fe3O4) prisms and ulvöspinel (Fe2TiO4) lamellae that formed as a result of phase unmixing during initial cooling. This internal structure exerts a profound influence on the magnetic remanence properties of each inclusion, primarily by transforming it from a multidomain grain into an assemblage of magnetostatically interacting single‐domain prisms. Here we use off‐axis electron holography to image the magnetization states of individual prisms and the magnetostatic interactions between them. We show that the inclusions exhibit both single‐domain and collective magnetic states that depend primarily on the shape anisotropies of individual magnetite prisms, magnetostatic interactions between closely spaced prism stacks, and the shape anisotropy of the needle itself. Prisms that are separated by thick ulvöspinel lamellae show uniformly magnetized and/or vortex states. In contrast, closely spaced magnetite prisms behave as multipart vortices or as long composite columns, whose strong net magnetization may not be related directly to the orientation and shape of either the needle or the constituent prisms. The overall remanence direction recorded by clinopyroxene crystals containing finely exsolved inclusions is a reflection of both the inclusions' elongation directions and the prism arrangements within them.
The rocks of Gusev Crater as viewed by the Mini‐TES instrument
Authors: Ruff S. W. , Christensen P. R. , Blaney D. L. , Farrand W. H. , Johnson J. R. , Michalski J. R. , Moersch J. E. , Wright S. P. , Squyres S. W.
Published: December 2006

The Miniature Thermal Emission Spectrometer (Mini‐TES) on board the Mars Exploration Rover Spirit is part of a payload designed to investigate whether a lake once existed in Gusev Crater. Mini‐TES has observed hundreds of rocks along the rover's traverse into the Columbia Hills, yielding information on their distribution, bulk mineralogy, and the potential role of water at the site. Although dust in various forms produces contributions to the spectra, we have established techniques for dealing with it. All of the rocks encountered on the plains traverse from the lander to the base of the Columbia Hills share common spectral features consistent with an olivine‐rich basaltic rock known as Adirondack Class. Beginning at the base of the West Spur of the Columbia Hills and across its length, the rocks are spectrally distinct from the plains but can be grouped into a common type called Clovis Class. These rocks, some of which appear as in‐place outcrop, are dominated by a component whose spectral character is consistent with unaltered basaltic glass despite evidence from other rover instruments for significant alteration. The northwest flank of Husband Hill is covered in float rocks known as Wishstone Class with spectral features that can be attributed uniquely to plagioclase feldspar, a phase that represents more than half of the bulk mineralogy. Rare exceptions are three classes of basaltic “exotics” found scattered across Husband Hill that may represent impact ejecta and/or float derived from local intrusions within the hills. The rare outcrops observed on Husband Hill display distinctive spectral characteristics. The outcrop called Peace shows a feature attributable to molecular bound water, and the outcrop that hosts the rock called Watchtower displays a dominant basaltic glass component. Despite evidence from the rover's payload for significant alteration of some of the rocks, no unambiguous detection of crystalline phyllosilicates or other secondary silicates has been observed by Mini‐TES. The mineralogical results supplied by Mini‐TES provide no clear evidence that a lake once existed in Gusev Crater.
Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 2. Opportunity
Authors: Johnson Jeffrey R. , Grundy William M. , Lemmon Mark T. , Bell James F. , Johnson Miles J. , Deen Robert , Arvidson R. E. , Farrand W. H. , Guinness E. , Hayes Alexander G. , Herkenhoff K. E. , Seelos F. , Soderblom J. , Squyres S.
Published: December 2006

The Panoramic Camera (Pancam) on the Mars Exploration Rover Opportunity acquired visible/near‐infrared multispectral observations of soils and rocks under varying viewing and illumination geometries that were modeled using radiative transfer theory to improve interpretations of the microphysical and surface scattering nature of materials in Meridiani Planum. Nearly 25,000 individual measurements were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles (0–150°) at Eagle crater, in the surrounding plains, in Endurance crater, and in the plains between Endurance and Erebus craters through Sol 492. Corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission. Disparity maps created from Pancam stereo images allowed inclusion of local facet orientation estimates. Outcrop rocks overall exhibited the highest single scattering albedos (≤0.9 at 753 nm), and most spherule‐rich soils exhibited the lowest (≤0.6 at 753 nm). Macroscopic roughness among outcrop rocks varied but was typically larger than spherule‐rich soils. Data sets with sufficient phase angle coverage (resulting in well‐constrained Hapke parameters) suggested that models using single‐term and two‐term Henyey‐Greenstein phase functions exhibit a dominantly broad backscattering trend for most undisturbed spherule‐rich soils. Rover tracks and other compressed soils exhibited forward scattering, while outcrop rocks were intermediate in their scattering behaviors. Some phase functions exhibited wavelength‐dependent trends that may result from variations in thin deposits of airfall dust that occurred during the mission.
Constraints on dust aerosols from the Mars Exploration Rovers using MGS overflights and Mini‐TES
Authors: Wolff M. J. , Smith M. D. , Clancy R. T. , Spanovich N. , Whitney B. A. , Lemmon M. T. , Bandfield J. L. , Banfield D. , Ghosh A. , Landis G. , Christensen P. R. , Bell J. F. , Squyres S. W.
Published: December 2006

Overflights of the Mars Exploration Rovers (MER) by the Mars Global Surveyor (MGS) provide a unique opportunity to examine some of the basic properties of dust aerosols, starting with one of the most fundamental, the indices of refraction (m = n + ik) in the infrared. The upward‐viewing geometry of the Miniature Thermal Emission Spectrometer (Mini‐TES) and the combined contemporaneous observations from both MER and MGS are powerful tools. Their use allows atmospheric retrievals to directly determine n and k while offering constraints for the menagerie of other radiative transfer input parameters. We exploit these coordinated observing campaigns, along additional data sources, to carry out series of radiative transfer analyses that ultimately return the set of refractive indices. We apply the resulting m to a larger sample of Mini‐TES data to both further validate our approach and retrieve several other aerosol properties, including dust optical depth, dust size, and a measure of the vertical mixing profile. We find good agreement with the empirical approach of Smith et al. (2006), in terms of both the optical depths themselves and the frequency dependence of their extinction cross section and single scattering albedo. The retrieved dust sizes vary from near 1.3 μm to 1.8 μm within the selected sample, with a precision estimated to be ≃0.1–0.2 μm. The vertical mixing profile evolves from well‐mixed to appreciably confined by LS ∼ 30°. For Spirit (MER‐A), there is an abrupt transition back to a more well‐mixed vertical profile with the onset of regional dust activity at LS ∼ 140°. We discuss the lack of a definitive detection of water ice clouds in Mini‐TES observations and the potential effects of vertical gradients in particle size distribution. Finally, as part of coordinated overflight analyses, an atmospherically corrected TES Lambert albedo map is derived and presented in Appendix A.
On the use of the Boussinesq equation for interpreting recession hydrographs from sloping aquifers
Authors: Rupp David E. , Selker John S.
Published: December 2006

The method of recession analysis proposed by Brutsaert and Nieber (1977) remains one of the few analytical tools for estimating aquifer hydraulic parameters at the field scale and beyond. In the method, the recession hydrograph is examined as −dQ/dt = f(Q), where Q is aquifer discharge and f is an arbitrary function. The observed function f is parameterized through analytical solutions to the one‐dimensional Boussinesq equation for unconfined flow in a homogeneous and horizontal aquifer. While attractive in its simplicity, as originally presented it is not applicable to settings where slope is an important driver of flow, or where hydraulic parameters vary greatly with depth. We compare analytical solutions to the linearized one‐dimensional Boussinesq equation for a sloping aquifer to numerical solutions of the full nonlinear equation. The behavior of the nonlinear Boussinesq equation is also assessed when the aquifer is heterogeneous wherein the lateral saturated hydraulic conductivity k varies as a power law with height z above the impermeable layer (k ∼ zn, n constant ≥ 0). All of the analytical solutions differ in key aspects from the nonlinear solution when plotted as −dQ/dt = f(Q) and thus are inappropriate for a Brutsaert and Nieber‐type analysis. However, new analytical solutions for a sloping aquifer are derived “empirically” from the numerical simulations that are applicable during the late period of recession when the recession curve converges to −dQ/dt = aQb, where b = (2n + 1)/(n + 1) and a is a function of the dimensions and hydraulic properties of the aquifer.
Blood-Oxygen-Level-Dependent Magnetic Resonance Signal and Cerebral Oxygenation Responses to Brain Activation are Enhanced by Concurrent Transient Hypertension in Rats
Authors: Qiao Min , Rushforth Dave , Wang Rong , Shaw R Anthony , Tomanek Boguslaw , Dunn Jeff F , Tuor Ursula I
Published: December 2006

Neuronal activation results in increases in blood-oxygen-level-dependent (BOLD) signal increases in magnetic resonance images, increases in cerebral blood flow (CBF), and changes in tissue oxygenation. We hypothesized that transient hypertension concurrent with neuronal activation would interfere with the normal physiological responses to neuronal activation potentially leading to additive responses. Anesthetized rats were prepared for functional magnetic resonance imaging studies in which increases in BOLD signal were measured in response to: (1) electrical forepaw stimulation, (2) different graded levels of transient hypertension produced with norepinephrine, and both 1 and 2. In other experiments with a similar protocol, changes in CBF and cortical oxyhemoglobin (oxyHb) and deoxyhemoglobin (deoxyHb) were measured using Laser Doppler Flowmetry and near-infrared (IR) spectroscopy. BOLD signal within the sensory-motor cortex increased during forepaw stimulation. These matched increases in CBF and oxyHb and decreases in deoxyHb. During moderate or severe transient hypertension, there was a blood pressure-dependent increase in BOLD signal, CBF, and oxyHb; and a decrease in deoxyHb. When transient hypertension and forepaw stimulation were combined, the responses of oxyHb, deoxyHb, or BOLD signal were generally a summation of each response. In contrast, the CBF response to forepaw stimulation was relatively unaffected by transient hypertension. We conclude that during stimulation with concurrent hypertension, the normal changes in tissue oxygenation that accompany neuronal activation are enhanced by the increases produced by hypertension despite an excellent autoregulation of CBF. The latter could reflect highly transient decreases in oxygen consumption or likely a redistribution of flow through more nonexchange vessels.
Quantification of Dopamine Transporter Binding Using [18F]FP-β-CIT and Positron Emission Tomography
Authors: Yaqub Maqsood , Boellaard Ronald , van Berckel Bart NM , Ponsen Mirthe M , Lubberink Mark , Windhorst Albert D , Berendse Henk W , Lammertsma Adriaan A
Published: December 2006

The purpose of this study was to compare different kinetic and semi-quantitative methods for analysing human [18F]FP-β-CIT studies: plasma input models, simplified (SRTM) and full (FRTM) reference tissue models, standard uptake values (SUV) and SUV ratios (SUVr). Both simulations and clinical evaluations were performed to determine the effects of noise, scan duration and blood volume on Akaike model selection, and on precision and accuracy of estimated parameters. For typical noise levels (COV ∼ 2.5%) and scan durations (< 90 mins), simulations provided poor fits (Akaike criterion) in case of reversible plasma input models showing a relatively high number of outliers compared with the two-tissue irreversible model. Reference tissue models provided more reliable fits, which were nearly independent of noise and scan duration. For clinical data, two tissue irreversible and reversible plasma input models fitted striatum curves equally well (Akaike criterion). BP with plasma input models were less precise and contained more outliers than BP obtained with SRTM or FRTM. Among all methods tested, SRTM showed the highest contrast between patients and controls. When differentiating between patients and controls, SUVr performed almost equally well as SRTM, although contrast between striatum and background was lower. In conclusion, SRTM provided BP estimates with the highest precision and accuracy. Moreover, SRTM provided good contrast between patients and controls, and between striatum and background. SRTM is therefore the method of choice for quantitative [18F]FP-β-CIT studies. SUVr might be an alternative for larger clinical trials.
Toxin–antitoxin systems are ubiquitous and plasmid-encoded in vancomycin-resistant enterococci
Authors: Moritz Elizabeth M. , Hergenrother Paul J.
Published: December 2006

Vancomycin-resistant enterococci (VRE) are common hospital pathogens that are resistant to most major classes of antibiotics. The incidence of VRE is increasing rapidly, to the point where over one-quarter of enterococcal infections in intensive care units are now resistant to vancomycin. The exact mechanism by which VRE maintains its plasmid-encoded resistance genes is ill-defined, and novel targets for the treatment of VRE are lacking. In an effort to identify novel protein targets for the treatment of VRE infections, we probed the plasmids obtained from 75 VRE isolates for the presence of toxin–antitoxin (TA) gene systems. Remarkably, genes for one particular TA pair, the
mazEF
system (originally identified on the
Escherichia coli
chromosome), were present on plasmids from 75/75 (100%) of the isolates. Furthermore,
mazEF
was on the same plasmid as
vanA
in the vast majority of cases (>90%). Plasmid stability tests and RT-PCR raise the possibility that this plasmid-encoded
mazEF
is indeed functional in enterococci. Given this ubiquity of
mazEF
in VRE and the deleterious activity of the MazF toxin, disruption of
mazEF
with pharmacological agents is an attractive strategy for tailored antimicrobial therapy.
Resolution limit in community detection
Authors: Fortunato Santo , Barthélemy Marc
Published: December 2006

Detecting community structure is fundamental for uncovering the links between structure and function in complex networks and for practical applications in many disciplines such as biology and sociology. A popular method now widely used relies on the optimization of a quantity called modularity, which is a quality index for a partition of a network into communities. We find that modularity optimization may fail to identify modules smaller than a scale which depends on the total size of the network and on the degree of interconnectedness of the modules, even in cases where modules are unambiguously defined. This finding is confirmed through several examples, both in artificial and in real social, biological, and technological networks, where we show that modularity optimization indeed does not resolve a large number of modules. A check of the modules obtained through modularity optimization is thus necessary, and we provide here key elements for the assessment of the reliability of this community detection method.