bluuebunny/crossref_metadata_2025 huggingface dataset:
DNA barcoding of Cuban freshwater fishes: evidence for cryptic species and taxonomic conflicts
Authors: LARA ARIAGNA , PONCE de LEÓN JOSÉ LUIS , RODRÍGUEZ RODET , CASANE DIDIER , CÔTÉ GUILLAUME , BERNATCHEZ LOUIS , GARCÍA‐MACHADO ERIK
Published: October 2009

Despite ongoing efforts to protect species and ecosystems in Cuba, habitat degradation, overuse and introduction of alien species have posed serious challenges to native freshwater fish species. In spite of the accumulated knowledge on the systematics of this freshwater ichthyofauna, recent results suggested that we are far from having a complete picture of the Cuban freshwater fish diversity. It is estimated that 40% of freshwater Cuban fish are endemic; however, this number may be even higher. Partial sequences (652 bp) of the mitochondrial gene COI (cytochrome c oxidase subunit I) were used to barcode 126 individuals, representing 27 taxonomically recognized species in 17 genera and 10 families. Analysis was based on Kimura 2‐parameter genetic distances, and for four genera a character‐based analysis (population aggregation analysis) was also used. The mean conspecific, congeneric and confamiliar genetic distances were 0.6%, 9.1% and 20.2% respectively. Molecular species identification was in concordance with current taxonomical classification in 96.4% of cases, and based on the neighbour‐joining trees, in all but one instance, members of a given genera clustered within the same clade. Within the genus Gambusia, genetic divergence analysis suggests that there may be at least four cryptic species. In contrast, low genetic divergence and a lack of diagnostic sites suggest that Rivulus insulaepinorum may be conspecific with Rivulus cylindraceus. Distance and character‐based analysis were completely concordant, suggesting that they complement species identification. Overall, the results evidenced the usefulness of the DNA barcodes for cataloguing Cuban freshwater fish species and for identifying those groups that deserve further taxonomic attention.
Ocular blood flow assessment using continuous laser Doppler flowmetry
Authors: Riva Charles E. , Geiser Martial , Petrig Benno L. ,   for the Ocular Blood Flow Research Association
Published: October 2009

Acta Ophthalmol. 2010: 88: 622–629

This article describes the technique of continuous laser Doppler flowmetry (LDF) as applied to the measurement of the flux of red blood cells in the optic nerve head, iris and subfoveal choroid. Starting with the exposition of the physical principles underlying LDF, we first describe the various devices developed to perform LDF in these vascular beds. We then discuss the clinical protocols, blood flow parameters, calibration procedures, reproducibility and limitations of the LDF technique. Various problems still need to be solved in order to bring to light the full potential of LDF in the assessment of microcirculatory haemodynamics.
On the deformation chirality of real cubic fourfolds
Authors: Finashin S. , Kharlamov V.
Published: October 2009

According to our previous results, the conjugacy class of the involution induced by the complex conjugation in the homology of a real non-singular cubic fourfold determines the fourfold up to projective equivalence and deformation. Here, we show how to eliminate the projective equivalence and obtain a pure deformation classification, that is, how to respond to the chirality problem: which cubics are not deformation equivalent to their image under a mirror reflection. We provide an arithmetical criterion of chirality, in terms of the eigen-sublattices of the complex conjugation involution in homology, and show how this criterion can be effectively applied taking as examples M-cubics (that is, those for which the real locus has the richest topology) and (M−1)-cubics (the next case with respect to complexity of the real locus). It happens that there is one chiral class of M-cubics and three chiral classes of (M−1)-cubics, in contrast to two achiral classes of M-cubics and three achiral classes of (M−1)-cubics.
Linear free divisors and Frobenius manifolds
Authors: Gregorio Ignacio de , Mond David , Sevenheck Christian
Published: October 2009

We study linear functions on fibrations whose central fibre is a linear free divisor. We analyse the Gauß–Manin system associated to these functions, and prove the existence of a primitive and homogenous form. As a consequence, we show that the base space of the semi-universal unfolding of such a function carries a Frobenius manifold structure.
On the Effects of Elastic Nonlinearity in Metals
Authors: Wong T. E. , Johnson G. C.
Published: October 2009

The variation in Young’s modulus and Poisson’s ratio of metals during uniaxial deformation is examined. Predictions are made on the basis of a nonlinear description of the constitutive relation between stress and strain involving both second- and third-order elastic constants. A comparison of measured and predicted variations shows good agreement, with the relative change in Young’s modulus being on the order of 10 times the elastic strain for most metals. The material nonlinearity is then examined as a possible cause for changes in the natural frequency of a beam subject to an axial residual stress. An upper bound for the frequency change involving the maximum stress, initial Young’s modulus and a nonlinearity parameter is derived.
Measurement of Non-Uniform Residual Stresses Using the Hole-Drilling Method. Part II—Practical Application of the Integral Method
Authors: Schajer G. S.
Published: October 2009

The Integral Method for calculating non-uniform residual stress fields using strain relaxation data from the incremental hole-drilling method is examined in detail. Finite element calculations are described which evaluate the calibration coefficients required for practical applications of the method. These calibration data are tabulated for a range of hole sizes and depths. It is found that the hole drilling method is not well adapted to measuring stresses remote from the surface, and a theoretical depth limit for stress measurements of 0.5 of the mean radius of the strain gauge rosette, rm, is identified. A practical depth limit is in the range 0.3–0.4 rm.
One-Dimensional Density Distributions of Powder Media in Dies Subjected to Multishock Compactions
Authors: Sano Y.
Published: October 2009

A theoretical attempt to clarify the reason why the compacts of powder media have uniform density distributions as the density of the compacts becomes high, is made for the compaction of the copper powder medium of a simple type by punch impaction. Based on the one-dimensional equation of motion including the effect of die wall friction force, there are two main factors which influence the density distribution of the medium during the compaction process; one is the propagation of the shock wave passing through the medium, while the other is the friction force between the circumferential surface of the medium and the die wall. The equation reveals that the effect of the force increases little as the density becomes high as a result of the repetitive traveling of the shock wave between the punch and plug. The propagation or more definitely the repetitive traveling, on the other hand, increasingly unformalizes the density distribution during the process as the number of the traveling increases. Owing to the aforementioned effects of the two factors on the density distribution during the process, the high density compacts become uniform.
Yield Surfaces of SUS304 Under Cyclic Loading
Authors: Ishikawa H. , Sasaki K.
Published: October 2009

To formulate the constitutive equations for cyclic plasticity, the subsequent yield surfaces should be examined carefully. In this paper, the subsequent yield surfaces have been examined from the experiment for the initially isotropic material of SUS304 subject to cyclic loading, using a 50µm/m offset strain criterion for yielding probed at the current center of the yield surface. The experiment shows a translation, distorsion, and rotation of the subsequent yield surfaces because of the deformation-induced-anisotropy due to proportional or nonproportional cyclic loading in tension-torsion space. These yield surfaces could be represented by the quadratic function of stresses with fourth rank anisotropic coefficient tensor components. These anisotropic coefficient tensor components are found to be represented by the strain amplitude of cyclic loading. As a result, the loading function obtained shows availability to derive the constitutive equations of cyclic plasticity.
Modeling Quenching to Predict Residual Stress and Microstructure Distribution
Authors: Li Y. Y. , Chen Y.
Published: October 2009

A mathematical model was developed for calculating the temperature, stress-strain field, and their interaction in a metallic material undergoing phase transformation during quenching processes. The model considers the fully coupled thermomechanical field equations, with coupling through the dilatational work, the plastic work, and the heat release during phase transformation in the energy equation. Computations were performed for a hollow steel cylinder. Several test problems were evaluated to make certain that the computer model worked properly. Final results demonstrate qualitative agreement with experiments. They also reveal detailed descriptions of material response.
Analysis of Neck Propagation in Polymeric Fibres Including the Effects of Viscoplasticity
Authors: Tug¯cu P. , Neale K. W.
Published: October 2009

The effects of material strain-rate dependence on necking and neck propagation in polymeric fibres are analyzed. Using a finite element scheme together with an elastic-viscoplastic constitutive model the entire load-deformation histories of round specimens are computed. Stress-strain distributions as well as the evolution of the specimen profiles are given at various stages of the axisymmetric stretching process. Comparisons with rate-independent response are also presented.
Damage evolution in GaN under MeV heavy ion implantation
Authors: Gao Yuan , Xue Jianming , Zhang Dongzheng , Wang Zilong , Lan Chune , Yan Sha , Wang Yugang , Xu Fujun , Shen Bo , Zhang Yanwen
Published: October 2009

Damage evaluation processes in patterned GaN implanted by 3 MeV Au2+ ions were investigated as a function of ion fluences and annealing temperatures. Surface swelling was observed by using atomic force microscopy and the results showed that the swelling height depends on ion fluence and annealing temperature. The authors observed four-stage implantation-induced damage evolution including point-defect formation, defect clustering, amorphization/bubble formation, and eventually, decomposition. This evolution is contributed to irradiation-induced defect production and defect migration/accumulation occurred at different levels of displacement per atom. Craterlike holes were observed on the surface of GaN implanted at the ion fluence of 2×1016 cm−2, which is evidence of N loss, and broken bubbles formed during implantation.
Planarian Hh Signaling Regulates Regeneration Polarity and Links Hh Pathway Evolution to Cilia
Authors: Rink Jochen C. , Gurley Kyle A. , Elliott Sarah A. , Sánchez Alvarado Alejandro
Published: October 2009

Hedgehog, Flatworms, and Regeneration

The Hedgehog (Hh) signaling pathway plays pivotal roles during embryonic development, post-embryonic tissue maintenance, and disease. In spite of having at its core a collection of highly conserved components, the Hh pathway displays unusual differences in signal transduction mechanisms among flies, fish, and mammals. Using planarians (nonparasitic flatworms),

Rink
et al.

(p.
1406
, published online 22 October) report a key role for Hh signaling during adult regeneration and provide evidence that the perplexing diversity of transduction mechanisms may have arisen from animal-specific losses of an ancestral association between cilia and Hh signaling.
Medication use by athletes during the Athens 2004 Paralympic Games
Authors: Tsitsimpikou C , Jamurtas A , Fitch K , Papalexis P , Tsarouhas K
Published: October 2009

Objective:

To examine the use of food supplements and pharmaceutical preparations by elite Paralympic athletes.

Design:

Survey study.

Setting:

Athens 2004 Paralympic Games.

Participants:

Data obtained from two sources: (i) athletes’ declaration of intake of drugs/supplements recorded on the Doping Control Official Record during sample collection for doping control; (ii) athletes’ application forms for granting of a therapeutic use exemption.

Main outcome measures:

Classification of declared food supplements according to the active ingredient and medications according to therapeutic actions and active compounds.

Results:

64.2% of the athletes tested for doping control declared use of medications or food supplements, and 81.3% of these athletes declared intake of fewer than four preparations. Non-invasive routes of administration dominated. Food supplements (42.1%) were popular, and drugs used to treat several pathological conditions noted. Non-steroidal anti-inflammatory agents and analgesics were commonly used (9.8% and 5.6%, respectively). The prevalence of inhaled β2-agonist use (4.8%) was higher than expected and exceeded that at the Athens Olympic Games.

Conclusions:

This review, the first to examine elite Paralympic athletes, shows a more rational approach to the use of medication and food supplements, but a similar consumption pattern to that of athletes at the Athens Olympic Games. Because of the dearth of such studies, consumption trends among Paralympic athletes remain unclear. The need to counsel athletes with disabilities on their nutritional needs is confirmed, and close monitoring by healthcare professionals is recommended.
Decreased incidence of knee posterior cruciate ligament injury in Australian Football League after ruck rule change
Authors: Orchard J W , Seward H
Published: October 2009

Objective:

To assess whether a rule change introduced in the Australian Football League (AFL) before the start of the 2005 season, to limit the run-up of ruckmen at the centre bounce, has been successful in reducing the incidence of knee posterior cruciate ligament (PCL) injuries

Design:

Cohort study with historical control.

Setting:

The AFL competition from 1992 to 2008 inclusive.

Assessment of risk factors:

The presence of a rule change (four seasons) compared with the previous 13 seasons (divided into two eras of seven and six seasons).

Main outcome measure:

Occurrence of knee PCL injury during a regular season or finals match, both from all causes and specifically from centre bounce ruck collision mechanisms.

Results:

From 1992 to 1998 there were 11.0 PCL injuries per 10 000 player-hours, with 0.8 ruck injuries per 10 000 centre bounces. From 1999 to 2004, the rates increased to 12.9 per 10 000 player-hours and 5.6 ruck injuries per 10 000 centre bounces (p<0.01). The rates reduced to 5.9 PCL injuries per 10 000 player-hours and 0.9 ruck injuries per 10 000 centre bounces in the period 2005–2008 following the rule change (p<0.01). There was a lower relative risk in 2005–2008 than in 1999–2004 of incurring a centre bounce ruck PCL injury (0.16 (95% CI 0.04 to 0.69)) or of sustaining any PCL injury (0.45 (95% CI 0.28 to 0.75)).

Conclusion:

A rule change in the AFL to limit the run-up of ruckmen at the centre bounce has successfully reduced the rate of PCL injuries with this mechanism, with the total incidence of PCL injuries also falling.
Optimal pacing strategy: from theoretical modelling to reality in 1500-m speed skating
Authors: Hettinga F J , De Koning J J , Schmidt L J I , Wind N A C , MacIntosh B R , Foster C
Published: October 2009

Purpose

Athletes are trained to choose the pace which is perceived to be correct during a specific effort, such as the 1500-m speed skating competition. The purpose of the present study was to “override” self-paced (SP) performance by instructing athletes to execute a theoretically optimal pacing profile.

Methods

Seven national-level speed-skaters performed a SP 1500-m which was analysed by obtaining velocity (every 100 m) and body position (every 200 m) with video to calculate total mechanical power output. Together with gross efficiency and aerobic kinetics, obtained in separate trials, data were used to calculate aerobic and anaerobic power output profiles. An energy flow model was applied to SP, simulating a range of pacing strategies, and a theoretically optimal pacing profile was imposed in a second race (IM).

Results

Final time for IM was ∼2 s slower than SP. Total power distribution per lap differed, with a higher power over the first 300 m for IM (637.0 (49.4) vs 612.5 (50.0) W). Anaerobic parameters did not differ. The faster first lap resulted in a higher aerodynamic drag coefficient and perhaps a less effective push-off.

Conclusion

Experienced athletes have a well-developed performance template, and changing pacing strategy towards a theoretically optimal fast start protocol had negative consequences on speed-skating technique and did not result in better performance.
Liver allograft pathology: approach to interpretation of needle biopsies with clinicopathological correlation
Authors: Adeyi O , Fischer S E , Guindi M
Published: October 2009

The spectrum of diseases encountered in post-transplant liver pathology biopsies is broad. In this review, these have been divided as belonging to one of three categories: (1) new-onset/de novo post-transplant abnormalities (early and late), (2) rejection, and (3) recurrence of original disease. The clinical and pathological features of the entities making up each category, with the relevant differential diagnosis and overlaps between and within these groups, are discussed and illustrated. Recurrent or de novo neoplasms make up a fourth category not included in this review. Early new-onset conditions are mostly related to surgical complications, donor factors and ischaemia to the graft. These include reperfusion/preservation injury, lipopeliosis, small-for-size-syndrome, biliary sludge syndrome and hepatic artery thrombosis. The various forms of rejection (cellular, chronic, antibody-mediated, and late atypical rejection) are detailed. Most chronic liver diseases can and do recur in the graft. They may display features that overlap with de novo conditions (eg, primary sclerosing cholangitis versus chronic rejection). As with most cases of allograft biopsy interpretation, accurate diagnosis rests with careful correlation of histological features with clinical, imaging and laboratory findings, and often comparison with previous sequential and follow-up biopsies. Late-onset new diseases include biliary strictures, idiopathic chronic hepatitis and de novo autoimmune hepatitis, among others. This review provides a practical approach to the interpretation of these challenging biopsies. Selected difficult scenarios or conundrums are identified and discussed in the relevant sections.
Legislating tolerance: Spain's national public smoking law
Authors: Muggli Monique E , Lockhart Nikki J , Ebbert Jon O , Jiménez-Ruiz Carlos A , Riesco Miranda Juan Antonio , Hurt Richard D
Published: October 2009

While Spain's national tobacco control legislation prohibits smoking in many indoor public places, the law provides for an exception to the prohibition of smoking by allowing separate seating sections and ventilation options in certain public places such as bars and restaurants, hotels and airports. Accordingly, Spain's law is not aligned with Article 8 Guidelines of the World Health Organization's Framework Convention on Tobacco Control, which requires parties to ensure universal protection against secondhand smoke exposure in all enclosed public places, workplaces and on all means of public transport. Spain's law is currently being promoted by the tobacco companies in other countries as a model for smoke-free legislation. In order to prevent weakening of smoke-free laws in other countries through industry-supported exceptions, we investigated the tactics used by the tobacco companies before the implementation of the new law and assessed the consequences of these actions in the hospitality sector. Internal tobacco industry documents made public through US litigation settlements dating back to the 1980s were searched in 2008–9. Documents show that tobacco companies sought to protect hospitality venues from smoking restrictions by promoting separate seating for smokers and ineffective ventilation technologies, supporting an unenforceable voluntary agreement between the Madrid local government and the hospitality industry, influencing ventilation standards setting and manipulating Spanish media. The Spanish National Assembly should adopt comprehensive smoke-free legislation that does not accommodate the interests of the tobacco industry. In doing so, Spain's smoke-free public places law would be better aligned with the Framework Convention on Tobacco Control.
Electrical resistivity sounding as a technique for studying crustal dilatancy prior to earthquakes
Authors: Drury M. J.
Published: October 2009

The usefulness of monitoring electrical resistivity changes in a stressed crust as a means of studying crustal behaviour during dilatancy prior to earthquakes is considered. Examination of published laboratory data shows that much of the large decrease of resistivity of stressed rocks prior to failure is accounted for by 'surface conductivity' in electrical double layers at rock–fluid interfaces in microcracks. Resistivity changes in the crust might be observed before other dilatancy-induced precursory phenomena are seen because of the strong effect of the surface conductivity. Measurements of resistivity changes alone with time cannot be used for predicting the time of occurrence of an earthquake because of uncertainties in factors such as pore fluid pressure and degree of saturation of newly formed cracks. However, observations of time-dependent resistivity (or impedance) variations might provide information on crustal behaviour during dilatancy, since as cracks begin to open in some preferred direction the impedance anisotropy of the crust should change. Such changes would be seen in the magnetotelluric impedance tensor elements. Information on crustal behaviour during dilatancy is required if a means of predicting the time and location of earthquakes using observations of time-dependent, dilatancy-induced precursory phenomena is to be developed.
Selective weathering of granitic clasts
Authors: Bustin R. M. , Mathews W. H.
Published: October 2009

Disintegration of isolated clasts of tonalite and granodiorite in some glacial and glaciofluvial deposits in southwestern British Columbia has been examined. Degree of disintegration is highly variable and neighboring clasts of similar lithology may be completely unaltered. Friability of some clasts is so great that the concept of transport from an already weathered parent bedrock is dismissed. Disintegration is associated with the biotite content of the rock and with numerous microfractures radiating from expanded biotite crystals. It is concluded that alteration and expansion of biotite has been responsible for the microfractures and has facilitated further chemical weathering of the rock. Optical, X-ray, and scanning electron-microscope studies indicate that the biotite has been converted first to trioctohedral vermiculite, and minor biotite-vermiculite random mixed-layer mineral by leaching of potassium and expansion of the phyllosilicate lattice, followed by precipitation of hydroxyl-Al and -Fe(?) in the interlayer position. Mildly acid solutions percolating downward from the present, or former, soil surface, is considered to be the prime agent for the alteration. Differences in biotite content, in grain size, in degree of rounding and of polishing of the clast surfaces, and perhaps in hydrothermal alterations of the rock prior to glacial transport account for the variable degree of disintegration at their present sites.
The identification of single-domain titanomagnetite particles by means of transmission electron microscopy
Authors: Smith P. P. K.
Published: October 2009

A basalt sample dredged from the axis of the Mid-Atlantic Ridge has been ion-thinned and examined by transmission electron microscopy. Finely dispersed particles as small as 0.04 μm in diameter, occurring in amorphous patches of the rock, have been identified as titanomagnetite by means of electron diffraction and microanalysis. These small particles have dimensions appropriate to single magnetic domain behaviour, and are considered to be largely responsible for the strong and very stable natural remanent magnetization of this rock.
Wave properties of isothermal magneto-rotational fluids
Authors: Sharif M. , Sheikh Umber
Published: October 2009

In this paper, the isothermal plasma-wave properties in the neighborhood of the pair-production region for the Kerr black-hole magnetosphere are discussed. We consider the Fourier-analyzed form of the perturbed general relativistic magnetohydrodynamical equations whose determinant leads to a dispersion relation. For the special scenario, the x-components of the complex wave vectors are calculated numerically. Respective components of the propagation vector, attenuation vector, phase and group velocities are shown in graphs. We have investigated, in particular, the existence of a Veselago medium and wave behavior (modes of waves dispersion).
Slip flow in peristaltic transport of a Carreau fluid in an asymmetric channel
Authors: Sobh Ayman Mahmoud
Published: October 2009

In this paper, peristaltic transport of a Carreau fluid in an asymmetric channel is studied theoretically under zero Reynolds number and long-wavelength approximation for both slip and no-slip flow (Kn  =  0). The problem is analyzed using a perturbation expansion in terms of the Weissenberg number as a parameter. Analytic forms for the axial velocity component and the pressure gradient are obtained to second order. The pressure rise is computed numerically and explained graphically. Moreover, the effects of the slip parameter, Weissenberg number, power-law index, and phase difference on the pressure gradient, the axial velocity, and the trapping phenomena have been discussed.
Transformation properties and symmetry behaviour of ELKO spinors
Authors: Wunderle K. E. , Dick R.
Published: October 2009

We review the transformation properties of ELKO spinors (Eigenspinoren des Ladungskonjugationsoperators) under charge conjugation, parity, and time reversal. Our calculations confirm that ELKO spinors are not eigenspinors of the helicity operator and satisfy [Formula: see text] which identifies them as a representation of a nonstandard Wigner class. However, we find that ELKO spinors transform symmetrically under parity instead of the previously assumed asymmetry. Furthermore, we demonstrate that ELKO spinors transform asymmetrically under time reversal, which is opposite to the previously reported symmetric behaviour. These changes affect the (anti)commutation relations that are satisfied by the operators acting on ELKO spinors. We are also able to show that ELKO spinors actually satisfy the same (anti)commutation relations as Dirac spinors, even though they belong to two different representations.
The mass-number dependence studies for the multiplicity of shower particles produced in interactions of different projectiles with emulsion nuclei at 3.7 GeV/n in the framework of the modified Glauber models I and II
Authors: El-Din M. S.M. Nour , Solite M. E.
Published: October 2009

In the present work, we calculate the total reaction cross sections for the reactions of the following projectiles: P, 12C, 14N, 16O, 22Ne, 24Mg, 28Si, and 32S with emulsion nuclei, at incident energy ELab = 3.7 GeV/n, in the framework of the modified Glauber models I and II (Gl-I and Gl-II approaches). At the same time the number of interacted nucleons from these projectiles and the emulsion target nuclei beside the number of their binary collisions are calculated. Also the multiplicity of the shower particles produced in these reactions are calculated. A comparison between the calculated values of these total reaction cross sections and their multiplicities of the produced shower particles in these reactions, with the corresponding measured values, had been done within both: Gl-I and Gl-II approaches and in accordance to the zero-range considerations. As a result of this comparison we have not obtained an agreement between the calculated values and the corresponding experimental data in case of the total reaction cross sections, but we have got, in general, a good agreement for the comparison in the case of the particle multiplicities calculations. It should be noted, for the last comparison, that the theoretical calculations in the framework of Gl-II approach give, in general, agreement with the corresponding experimental data better than those we have obtained for the theoretical calculations in the framework of the Gl-I approach.
The effect of interactive lecture experiments on student academic achievement and attitudes towards physics
Authors: Moll Rachel F. , Milner-Bolotin Marina
Published: October 2009

This paper examines the effects of computer-based Interactive Lecture Experiments (ILEs) in a large introductory physics course on student academic achievement and attitudes towards physics. ILEs build on interactive lecture demonstrations by requiring students to analyze data during and after lecture demonstrations. Academic achievement was measured using the Force Concept Inventory (FCI) and final examinations' grades; and student attitudes were measured using a Colorado Learning Attitudes about Science Survey (CLASS). FCI results showed a general positive shift (about average for an interactive course) but could not detect improvements in student understanding of specific topics addressed by ILEs. However, open-ended questions on the final exam showed differences between sections on topics that were addressed by ILEs. Attitude survey results showed a negative shift in student attitudes over the semester, which is a typical result for an introductory physics course. This finding suggests that ILE pedagogy alone is insufficient to significantly improve student attitudes toward science. The study also revealed possible improvements to implementing ILEs such as working in groups, ongoing feedback for students, and linking assessment to pedagogical practices.
Large-scale CIV3 calculations of fine-structure energy levels and radiative rates in Al-like copper
Authors: Gupta G. P. , Msezane A. Z.
Published: October 2009

We have performed large-scale CIV3 calculations of excitation energies from the ground state for 97 fine-structure levels as well as of oscillator strengths and radiative decay rates for all electric-dipole-allowed and intercombination transitions among the fine-structure levels of the terms belonging to the (1s22s22p6)3s23p, 3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2, 3s24s, 3s24p, 3s24d, 3s24f, and 3s3p4s configurations of Cu XVII. These states are represented by very extensive configuration-interaction (CI) wave functions obtained with the CIV3 (Configuration-Interaction Version 3) computer code of Hibbert. The important relativistic effects in intermediate coupling are incorporated by means of the Breit–Pauli Hamiltonian, which consists of the nonrelativistic term plus the one-body mass correction, Darwin term, and spin–orbit, spin–other-orbit, and spin–spin operators. To keep our calculated energy splittings as close as possible to the experimental values (wherever available), we have made small adjustments to the diagonal elements of the Hamiltonian matrices. Our calculated excitation energies, including their ordering, are in excellent agreement with the available experimental results. From our radiative decay rates we have also calculated radiative lifetimes of some fine-structure levels. The mixing among several fine-structure levels is found to be so strong that the correct identification of these levels becomes very difficult. We believe that our extensive calculations will be useful to experimentalists in identifying the fine-structure levels in their future work. In this calculation we also predict new data for several fine-structure levels where no other theoretical and (or) experimental results are available.
Observation of the chemiluminescent NO + O → NO2 + hν reaction in the upper mesospheric dark polar regions by OSIRIS on Odin
Authors: Gattinger R. L. , Evans W. F.J. , McDade I.C. , Degenstein D. A. , Llewellyn E. J.
Published: October 2009

The visible and near infrared continuum spectrum produced by the NO + O → NO2 + hv chemiluminescent reaction has been detected in the upper mesospheric dark polar regions by OSIRIS on the Odin spacecraft. Averaged observed NO2 emission spectral shapes are obtained by spectrally resolving the NO + O continuum from the blended strong upper mesospheric OH vibration–rotation airglow bands. The observed continuum spectral shape when compared with laboratory measurements is shifted to lower wavelengths by approximately 20 nm in the steeply sloped 400 to 500 nm region. The observed laboratory continuum spectral shape for upper mesospheric ambient pressure is presented for reference over the 400 to 800 nm region. An example of an NO2 continuum volume emission-rate altitude profile derived from a single OSIRIS limb scan is also included. Limb radiances up to 3 × 109 photons cm–2 nm–1 s–1 are observed at the peak of the NO2 continuum corresponding to total volume emission rates of approximately 2 × 104 photons cm–3 s–1. Data extracted from numerous single-volume emission-rate altitude profiles obtained over approximately a 24 h period are assembled into a Southern Hemisphere polar map of the 90 km NO2 continuum emission. The map illustrates the considerable spatial brightness variation typically observed in the dark Antarctic polar region throughout the OSIRIS mission dataset. After further analysis these measurements will assist in quantifying the role of thermospheric formed NOx in the catalytic removal of ozone in the upper stratosphere.
Implementation of a perturbation model for a dilute binary liquid and comparison of model mass diffusion coefficients with microgravity experiment results for liquid Pb 1 wt % Au
Authors: Scott Paul J. , Smith Reginald W.
Published: October 2009

The estimation of mass diffusion coefficients, through Earth-bound experiments, remains difficult, due to the frequent occurrence of dominating convective flows resulting from gravity-driven density gradients caused by temperature and concentration gradients. To partly remedy this, a series of capillary mass diffusion experiments has been performed in microgravity on a number of different space platforms, sometimes performed on a microgravity isolation mount, to further reduce the platform operational noise referred to as “g-jitter”. Theoretical comparisons are sought for the experimental observations. Two numerical models have been developed based on perturbation theory. We have used the Lado criteria for minimizing the difference in free energy between the multispecies liquid of interest and a reference hard-sphere liquid. The hard-sphere liquid is characterized by the rational function approximation of the partial radial distribution functions. The effective embedded atom like glue potential has been used to model the liquid of interest. This has necessitated introducing the mean coordination number as an additional parameter. Isothermal compressibility has been used to determine the mean coordination number. The initialization of the numerical solutions, and the extension of solutions over the experimental range of temperatures have been demonstrated for Pb 1 wt % Au. The model results have been used to estimate the mass diffusion coefficients by applying the Enskog equation to the reference hard-sphere liquid. For consideration of capillary experiments, a definition of total mass diffusion coefficient, Dtot, has been introduced to characterize reverse Kirkaldy simultaneous diffusion. The mixed diffusion coefficient estimate is in good agreement with the mixed diffusion coefficient estimated from the velocity correlation of molecular dynamic simulations. Dtot and D11 are in good agreement with the experimental results indicating that reverse Kirkaldy simultaneous diffusion has had an influence on the experiment. Good agreement between the mixed mass diffusion coefficient and the result from molecular dynamic simulation indicates the perturbation models can predict the mixed coefficient. These models may assist in the analysis of data from both Earth-bound and microgravity, mass diffusion experiments when the required embedded atom type potentials are available.
Structural analysis of phosphatidyl choline lipids and glycerol precursors
Authors: Goursot Annick , Mineva Tzonka , Krishnamurty Sailaja , Salahub Dennis R.
Published: October 2009

The structures and stabilities of the glycerol (G) and glycerol 3-phosphate (G3P) isomers have been calculated in the gas phase, using an ab initio density functional theory (DFT) method. The different conformational structures are shown to be at the origin of the various phospholipid conformers, except, obviously, for the alkyl chain torsions. The G3P conformations have been examined taking into account the experimental structures of the complexation sites in the glycerol kinase (GK) and glycerol 3-phosphate acyl transferase (G3PAT) enzymes, which correspond to the first and second steps of the “de novo” phospholipid biogenesis, respectively. The conformational analysis of the glycerophosphate skeleton is shown to determine most of the structural characteristics of the phosphatidyl choline lipids, which differ by the length of their diacyl chains, i.e., dilauroyl (DL), dimyristoyl (DM), and dipalmitoyl (DP) phosphatidylcholines (PC). Higher energy conformers with kinks in the acyl chains have been found, in preparation for molecular dynamics studies of the chain melting phase transformation.
Exact exchange-correlation potentials in spin-density functional theory and their discontinuities at unit electron number
Authors: Perdew John P. , Sagvolden Espen
Published: October 2009

The exact exchange-correlation potential of Kohn–Sham density functional theory is known to jump discontinuously by a spatial constant as the average electron number, N, crosses an integer in an open system of fluctuating electron number, with important physical consequences for charge transfers and band gaps. We have recently constructed an essentially exact exchange-correlation potential vxc for N electrons (0 ≤ N ≤ 2) in the presence of a –1/r external potential, i.e., for a ground ensemble of H+ ion, H atom, and H– ion densities. That construction illustrates the discontinuity at N = 1, where it equals IH – AH, the positive difference between the ionization energy and the electron affinity of the hydrogen atom. Here we construct the corresponding essentially exact spin-up and spin-down exchange-correlation potentials vxc,↑ and vxc,↓ of the Kohn–Sham spin-density functional theory, more commonly used for electronic structure calculations, for the ground ensemble with most-negative z-component of spin (or equivalently in the presence of a uniform magnetic field of infinitesimal strength). The potentials vxc, vxc,↑, and vxc,↓, which vanish as r → ∞ (except when N approaches an integer from above), are identical for 0 ≤ N ≤ 1 and for N = 2 but not for 1 < N < 2. We find that the majority or spin-down potential has a spatially constant discontinuity at N = 1 equal to IH – AH. The minority or spin-up potential has a discontinuity which is this constant in one order of limits, but is a spatially varying function in a different order of limits. This order-of-limits problem is a consequence of a special circumstance: the vanishing of the spin-up density at N = 1.
Towards a computational treatment of polyoxometalates in solution using QM methods and explicit solvent molecules
Authors: Miró Pere , Poblet Josep M. , Ávalos Josep Bonet , Bo Carles
Published: October 2009

This study is aimed at developing an explicit solvent model for highly charged species such as polyoxometalates. The model includes solvent molecules in the first solvation shell explicitly, and long-range bulk effects and counter-ions as a set of single point charges. The model strongly stabilizes the electronic structure of the Keggin anion. The energies of the Kohn–Sham orbitals obtained using our model lie very close to those computed using the COSMO continuum solvent model; moreover, the total solvation energy evaluated with our model compares well to the value calculated by COSMO.
Kohn–Sham DFT and ligand-field theory — Is there a synergy?
Authors: Schäffer Claus E. , Bendix Jesper
Published: October 2009

In forming electronic states of the partially filled shell of transition-metal atomic and molecular systems, real, symmetry-based, fixed, Kohn–Sham eigenorbitals can be used to bridge KS-states with strong-field, ligand-field states. Thereby, DFT computations, restrained by the use of these frozen orbitals of the so-called average-of-configuration type, allow a central-field modeling of the partially filled shell whose Hamiltonian matrix consists of mutually orthogonal diagonal and non-diagonal parts, of which only the former can be computed. Mutually orthogonal operators of ligand-field theory are particularly suited to parameterize the energy “data” obtained from the bridges between molecular Kohn–Sham DFT states and ligand-field states. With the d2 configuration as the simplest example encompassing both ligand-field and interelectronic repulsion, each one-electron parameter, though defined by energy differences of perturbed d orbitals, is associated with a 45 × 45, diagonal, theoretical, strong-field-type coefficient matrix of the ligand field repulsion model (LFR), which is mapped in a one-to-one fashion onto a likewise diagonal KS-DFT computational energy matrix. For sets of mutually orthogonal operators, the mapping determines the value of any such ligand-field parameter as a scalar product between the DFT matrix and the coefficient matrix of the associated ligand-field operator. Each and every two-electron parameter of LFR is in the same strong-field function basis associated with a 45 × 45 coefficient matrix that includes a non-diagonal part. This matrix, nevertheless, by the formation of a scalar product with the appropriate diagonal, computational DFT matrix, provides the value of the two-electron parameter. In spite of the lacking non-diagonal DFT information, its non-diagonal elements of the two-electron interelectronic repulsion matrices are indirectly accessible through the parameterization based upon the computed diagonal DFT matrices combined with the mapping of the DFT energy results onto the parametric LFR. In this way, LFR delivers back to DFT a quantification of the deviation of the systems’ eigenbasis from the DFT-computed states, which are defined by having unit occupation numbers. This work focuses firstly on using the LFR model for forming a full DFT energy matrix and dissecting it into mutually orthogonal one- and two-electron parts and secondly on the use of the two-electron parts to obtain a complete ligand-field image of a nephelauxetic, molecular atom, intrinsic of the chemical system.
NMR line shapes from AB spin systems in solids — The role of antisymmetric spin–spin coupling
Authors: Harris Kristopher J. , Bryce David L. , Wasylishen Roderick E.
Published: October 2009

NMR parameters such as indirect nuclear spin–spin coupling (J), nuclear magnetic shielding (σ), direct dipolar coupling (D), and electric field gradient (V) are properly described by second-rank tensors. Each may be decomposed into isotropic, symmetric, and antisymmetric components; the number of these three components which may be nonzero is a distinguishing attribute of each interaction tensor. The rank-1 antisymmetric portion of J (Janti) holds the distinction of remaining the only nonzero part of these fundamental NMR interaction tensors which has never been observed experimentally. Accordingly, effects from Janti are usually ignored, but it is important to consider when this is valid. An experimental strategy for observing Janti in powdered samples of tightly coupled homonuclear spin pairs, based on ideas originally presented by Andrew and Farnell ( Mol. Phys. 1968, 15, 157 ), is described. The theory of Andrew and Farnell is extended to powder samples, and methods for analyzing NMR spectra from powdered samples are presented. It is found that, in certain rare cases, Janti has the potential to affect the NMR line shapes from AB spin systems, but that even in these systems, the most intense features of the spectra are not affected and may be analyzed independently of Janti. Furthermore, Janti will only have an observable effect on the NMR spectra when its magnitude is comparable with that of Jiso and with the difference in chemical shifts (in Hz) between the two sites. Finally, the first experimental attempts to measure Janti are reported, and experimental proof that no elements of Janti(119Sn,119Sn) in hexa(p-tolyl)ditin are larger than 2900 Hz is given. The benefits of modern double-quantum filtering NMR pulse sequences in isolating effects from Janti are also illustrated.
Mechanism of dihydride formation and hydrogen/deuterium exchange in a cationic iridium(III) complex
Authors: Cavallo Luigi , Nolan Steven P. , Jacobsen Heiko
Published: October 2009

In this manuscript, we provide a theoretical rationalization of the mechanisms that control double H2 addition to an unsaturated 14 e cationic Ir(III) complex to yield a dihydride Ir(III) complex. Further, we also present two mechanisms that can explain the experimentally observed incorporation of deuterium into the tert-Butyl (tBu) groups of the N-heterocyclic ItBu ligands.
DFT studies of complexes between ethylenediamine tetraacetate and alkali and alkaline earth cations
Authors: Gajewski Melissa , Klobukowski Mariusz
Published: October 2009

Density functional theory (DFT) calculations for M–(C10H12N2O84–) and M–(H2O)6, where M = Na+, K+, Rb+, Mg2+, Ca2+, and Sr2+, and (C10H12N2O84–) = EDTA4–, were carried out at both all-electron and pseudopotential levels. Results from these four methods were compared, and it was found that the ions bind to EDTA4– with selectivity of Mg2+ > Ca2+ > Sr2+ > Na+ > K+ > Rb+.
Validation of broken-symmetry density functional methods for the calculation of electron paramagnetic resonance parameters of dinuclear mixed-valence MnIVMnIIIcomplexes
Authors: Schinzel Sandra , Kaupp Martin
Published: October 2009

. The EPR parameters of a series of dinuclear manganese(III,IV) complexes with mono(μ-oxo), bis(μ-oxo), (μ-oxo)(μ-carboxylato), bis(μ-oxo)(μ-carboxylato), and (μ-oxo)bis(μ-carboxylato) bridges were studied by broken-symmetry density functional (DFT) methods. The influence of the exchange-correlation functional on the agreement with experiment has been evaluated systematically for g tensors;55Mn,14N, and1H hyperfine coupling tensors; and Heisenberg exchange couplings.14N and1H hyperfine couplings,55Mn hyperfine anisotropies, g tensors, and exchange couplings are well described by hybrid functionals with moderate exact-exchange admixtures such as B3LYP. The isotropic55Mn hyperfine couplings require larger exact-exchange admixtures. However, the errors of the B3LYP calculations are systematic and may be corrected by a constant scaling factor, providing good predictive power for a wide range of EPR parameters with broken-symmetry DFT and standard functionals. The influence of terminal and bridging ligands on structure, spin-density distributions, and EPR parameters are evaluated systematically. Computed hyperfine and g tensors are not covariant to each other. This may have consequences for spectra simulations. The nature of the broken-symmetry state and the origin of its spin contamination were analyzed by an expansion into restricted determinants, based on paired orbitals.