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Children with the neurofibromatosis type 1 (NF1) inherited tumor predisposition syndrome are at risk for the development of brain tumors. In addition, children with neurofibromatosis type 1 often exhibit low tone (hypotonia). In this study, the authors explored the hypothesis that hypotonia could be a clinical indicator of glioma in children with neurofibromatosis type 1. A total of 56 children between 1 and 7 years of age with a confirmed diagnosis of neurofibromatosis type 1 were evaluated. Brain magnetic resonance imaging (MRI) was available for 19 of these children. Chi-square analysis demonstrated a statistically significant correlation between hypotonia and glioma in children with neurofibromatosis type 1 (90% sensitivity and 78% specificity). These results suggest that hypotonia might be a clinically useful indicator of brain tumor in this at-risk population.

The cyanobacterium Synechocystis sp. PCC 6803 is a photosynthetic organism capable of efficient harnessing of solar energy while capturing CO(2) from the environment. Methods to genetically alter its genomic DNA are essential for elucidating gene functions and are useful tools for metabolic engineering. In this study, a novel counter-selection method for the genetic alteration of Synechocystis was developed. This method utilizes the nickel inducible expression of mazF, a general protein synthesis inhibitor, as a counter-selection marker. Counter-selection is particularly useful because the engineered strain is free of any markers which make further genetic modification independent of available antibiotic resistance genes. The usability of this method was further demonstrated by altering genes at several loci in two variants of Synechocystis.

Density functional theory calculations of the electronic structure of Ce- and Pu-based heavy fermion superconductors in the so-called 115 family are performed. The gap equation is used to consider which superconducting order parameters are most favorable assuming a pairing interaction that is peaked at (\pi,\pi,q_z) - the wavevector for the antiferromagnetic ordering found in close proximity. In addition to the commonly accepted $d_{x^2-y^2}$ order parameter, there is evidence that an extended s-wave order parameter with nodes is also plausible. We discuss whether these results are consistent with current observations and possible measurements that could help distinguish between these scenarios., Comment: 8 pages, 4 figures; Accepted for publication in JPCM

Background and Purpose. High-voltage pulsed current (HVPC) has been used to promote the healing of decubitus ulcers and surgical wounds. The benefits of HVPC are thought to include an antimicrobial action. This study was undertaken to explore the development of an in vitro system for the systematic evaluation of the effects of HVPC. Methods. Using agarose-based media, the system allows for examination of the direct effect of HVPC on microorganisms as well as exploration of the possible in situ generation of bacteriostatic or bactericidal factors by the action of HVPC on constituents of the media. The solid media also allow characterization of the spatial extent of the current's effects such as changes in temperature or pH. The system was used to examine the effects of HVPC on four different species of bacteria: Escherichia coli, Klebsiella, Pseudomonas aeruginosa, and Staphylococcus aureus. Results. Both direct and indirect bactericidal effects were observed at either the positive or negative electrode, or both, for each of the organisms, although zones of inhibition varied. Temperature and pH were examined as possible mechanisms for the indirect effect. Temperature changes observed during the application of HVPC were minimal and did not contribute to the antimicrobial effect. Extreme pH changes did not appear to be the major cause of the indirect effect because the zones of inhibition observed were generally larger than the zones of extremely acid or basic pHs. Conclusion and Discussion. High-voltage pulsed current produced antimicrobial effects in this in vitro study. Additional studies are needed to elucidate the mechanisms and to determine whether the mechanisms occur in vivo.

By including dynamic fluctuations around the local-density-approximation (LDA) electronic structure we find good agreement for the specific-heat mass-enhancement factors for U[ital X][sub 3] ([ital X]=Ir, Pt, Au). The fluctuations, which are calculated through to second-order in the perturbation, are restricted to those caused by strong, local, uranium 5[ital f] electron-electron interactions, for which the calculated effective interaction strength is 2 eV. The strong material dependence of the second-order mass-enhancement factors is related to the composition dependence of the Fermi energy and the underlying one-electron LDA density of states.

The dynamic fluctuations due to localized Hubbard type of effective interactions, U and J, are calculated perturbatively up to second order around the local density approximation (LDA) electronic structure. We have found for UX3 (X  Ir, Pt, or Au), the mass-enhancement factors are in good agreement with experiment for U = 2eV, and that the trends in the enhancement factors are systematically related to changes in the underlying LDA electronic structure. As for La2CuO4 we find that the dynamic fluctuations are small despite the large effective interaction. Further, our approach reproduces the insulating ground state and the magnetic moment correctly. For the doped case [La2-xBaxCuO4 (x ≠ 0)] we find that even though the mass enhancement is small, there is a significant broadening of the quasiparticles close to the Fermi energy.

The phase stability and site occupancy of bcc (body centered cubic) Nb(5)Al and slightly rearranged atomic structures have been examined by means of first-principles calculations. In order to use first-principles methods, a periodic cell is required and we used ordered Nb(5)Al compounds as a tractable example of a low Al concentration Nb(1 - x)Al(x) alloy (in this case, for about 17 at.% Al). The instability against an ω-structure atomic displacement was also studied, since this structure is detrimental to ductility. Mulliken population analysis was used to provide an understanding of the hybridization between the atoms and the electronic origin of the site occupancy and instability of the underlying bcc structures. By making calculations for several different configurations of the Nb-Al system we estimated the strengths of the Nb-Nb and Nb-Al bonds. It is shown that the stability of the underlying bcc phases is directly related to Nb-Nb and Nb-Al first-nearest-neighbor interactions. The first-principles calculations were extended to finite temperature by including various contributions to the free energy. In particular, the vibrational free energy was calculated within the quasiharmonic approximation, and it is shown that the contribution of the low energy modes to the lattice entropy helps to stabilize ordered bcc phases against ω-type phase transformations. Semi-quasi-random structures were employed to study the stability of the ordered and disordered bcc phases. Our study showed, in agreement with experiment, that the ω, ordered, and disordered phases can coexist in a nonequilibrium state at finite temperature.

Using density-functional perturbation theory, we have calculated the elastic constants for the ground-state crystal structures of the light actinide metals both at their equilibrium volumes (for Th through Np) and as a function of pressure (for Th through U). As necessary, we take into account the effects of atomic relaxation and show that these can be neglected for α-U, but are crucial for α-Np. The elastic constants of Th and U are compared with experimental measurements near ambient conditions and good agreement is found. Studies of the Born stability criteria in pressure reveal that Th and Pa are mechanically unstable while U remains stable up to 85 GPa, as is observed in diamond anvil cell experiments.

Objective The aim of the study was to explore the sensitivity and robustness of T2 mapping in the detection and quantification of early degenerative cartilage changes at the patella. Materials and methods Forty-two patients (22 women, 20 men) with a mean age of 30.3 years and a symptomatic cartilage defect of ICRS grade ≤2 were examined using a 3 T MRI with an 8-channel knee coil. The cartilage lesion was graded based on high-resolution PD TSE and 3D isotropic TrueFISP images. T2 maps were calculated from a standard MESE-sequence, performed at the beginning and at the end of the scan (40 min in-between). Depending on the defect size, a region-of-interest (ROI) analysis was performed on 1–3 consecutive slices. Mean T2 values for the deep, superficial, and global layer as well as the zonal variation were compared among defect grades (ANOVA, post hoc Duncan-test) and over time (Student's t-test). Results T2-measurements directly correlated with the extent of cartilage defect (ICRS grade) at all layers and at both time-points. However, correlations were closer for the second measurement at the end of the scan. In this unloaded state, differences in T2-values became more pronounced and were significant even between cartilage of normal appearance adjacent to the defect and healthy cartilage of control patients (both ICRS grade 0). In contrast, there were no such differences among grades in the zonal variation at any time. Conclusion T2 mapping might be a sensitive method for the detection of early cartilage degeneration at the patella in the unloaded joint.

We have performed first-principles local-density-approximation (LDA) electronic-structure calculations of the of the neutral MX chain compounds and fitted their band structures to a two-band tight-binding Hamiltonia. Using two slightly different approaches based on constrained occupancies in the Kohn-Sham LDA, we have calculated from first principles the Hubbard parameters for the neutral halogen-bridged transition-metal (MX) linear chain systems (M  Ni or Pt, and X  Cl, Br, or I). For PtX (XCl, Br) the Pt onsite U is almost three times larger than the PtX hopping integral, and is almost twice as large for the NiX compounds, which are very strongly correlated and are likely to have a spin-density-wave or antiferromagnetic ground state.

Both local density-functional (LDF) Stoner theory and spin-polarized LDF, each in conjunction with the scalar relativistic linear muffin-tin orbital technique, are used to study the magnetic properties of the neutral halogen-bridged transition-metal linear chains, denoted by MX (MNi or Pt, and XCl, Br, or I). Both approaches show the Ni-based compounds are antiferomagnetic, whereas the Pt-based compounds are paramagnetic. Besides these calculations, we have also studied the magnetism of the MX chain systems using the new density functional, which takes orbital polarization into account and uses a Hubbard interaction instead of the Stoner parameter. Despite the additional sophistication of this approach, very similar results are obtained.

We present first-principles all-electron local-density-approximation (LDA) electronic-structure calculations of the neutral halogen-bridged transition-metal linear-chain compound (MX chain system) Pt 2 Br 6 (NH 3 ) 4 ; the results agree well with the experimental lattice dimerization, band gap, and the Raman breathing mode.

Results of first-principles density-functional calculations on single chains of NiN, CaNiN, and K 2 NiN are reported. It is demonstrated that the main features of the true three-dimensional CaNiN material can be understood from a ‘single-chain’ point of view. The inclusion of the Ca (or K) atoms around the NiN chain leads to noteworthy modifications in the electronic properties, but all materials are metallic. We propose that upon replacing parts of the Ca atoms with other atoms one may vary the electrical conductivity. Finally, our results demonstrate the capability of the LMTO method for helical polymers to describe the properties of transition-metal compounds.

Using spark-source mass spectrometry, atomic absorption spectrometry and various optical techniques, a study is made of the concentrations of impurities (total and point-defect concentrations), charge carriers and precipitates as well as of their axial distributions in Bridgman crystals grown with and without an extra Cd source. It is found that the concentrations of substitutional impurities are controlled by Cd and Te vacancies which form during the growth process. When the crystals are cooled after growth, part of the Cd vacancies are occupied by impurity atoms, while part of them cluster to form Te precipitates. The vacancy concentrations are modified, and the latter reaction is suppressed, in the case of growth under Cd overpressure. Intentional doping with halogens leads to formation of persistent Te-site donor/Cd-vacancy complexes.

Background Primary upper endoscopy (EGD) and transabdominal US (TUS) are often performed in patients with upper abdominal pain. Objective Primary: Determine whether the combination of EGD and EUS was equivalent to EGD plus TUS in the diagnostic evaluation of upper abdominal pain. Secondary: Compare EUS versus TUS in detecting abdominal lesions, and compare EGD by using an oblique-viewing echoendoscope versus the standard, forward-viewing endoscope in detecting mucosal lesions. Design Prospective, paired design. Setting Six academic endoscopy centers. Patients This study involved patients with upper abdominal pain referred for endoscopy. Intervention All patients had EGD, EUS, and TUS. The EGD was done using both an oblique-viewing echoendoscope and the standard, forward-viewing endoscope (randomized order) by two separate endoscopists in a blinded fashion, followed by EUS. TUS was performed within 4 weeks of EGD/EUS, also in a blinded fashion. Follow-up: telephone interviews and chart reviews. Main Outcome Measurements Diagnose possible etiology of upper abdominal pain and detect clinically significant lesions. Results A diagnosis of the etiology of upper abdominal pain was made in 66 of 172 patients (38%). The diagnostic rate was 42 of 66 patients (64%) for EGD plus EUS versus 41 of 66 patients (62%) for EGD plus TUS, which was statistically equivalent (McNemar test; P = .27). One hundred ninety-eight lesions were diagnosed with either EUS or TUS. EUS was superior to TUS for visualizing the pancreas ( P P = .03). Two biliary stones were detected only by EUS. Two hundred fifty-one mucosal lesions were similarly diagnosed with EGD with either the standard, forward-viewing endoscope or the oblique-viewing echoendoscope (kappa = 0.48 [95% CI, .43-.54]). EGD with the standard, forward-viewing endoscope was preferred for biopsies. Limitations No cost analysis. Conclusion The combination of EGD with EUS is equivalent to EGD plus TUS for diagnosing a potential etiology of upper abdominal pain. EUS is superior to TUS for detecting chronic pancreatitis. EGD combined with EUS should be considered in the first-line diagnostic evaluation of patients with upper abdominal pain.

High-order scattering is found to be essential for the convergence of the multiple-scattering (MS) theory of x-ray-absorption fine structure, both in the near-edge and the extended regimes. These contributions are calculated using an ab initio curved-wave scattering-matrix formalism. Convergence to full MS accuracy is demonstrated for fcc Cu, as well as for molecular ${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$, where our approach provides a high-order MS interpretation of the ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ shape resonances.

All-electron local-density-approximation electronic-structure calculations show how the ligand structure of a neutral halogen-bridged transiton-metal linear-chain compound, Pt{sub 2}Br{sub 6}(NH{sub 3}){sub 4}, modifies the electronic structure to reduce it to an effective one-dimensional system. The dimerization and opening of the band gap is then understood on the basis of a conventional two-band Su-Schrieffer-Heeger model for isolated chains. Despite the strong {ital pd}{sigma} coupling between the Pt {ital d}{sub 3{ital z}}{sup 2}{minus}{ital r}{sup 2} and Br {ital p}{sub {ital z}} orbitals along the chains, the system will not dimerize in the absence of the ligand structure.

To examine the prognostic value of routine postinfarction exercise tests in young patients, exercise tests were carried out at 3 and 6 weeks and 18 months after infarction in 149 patients aged under 55 years at the time of the index infarction. The patients also had coronary angiography and left ventriculography a mean of 3 months after infarction. Three years after infarction, only two of the 149 patients have died, reinfarction occurred in only seven (4.7%) patients; unstable angina in four (3%) patients and coronary artery surgery was needed in 31 (20.8%) patients; 16 in the first, 10 in the second, and 5 in the third year of follow-up. Angina on exercise testing at 6 weeks was the only variable with any predictive value. Eighteen (38%) of the 47 patients with, compared to 12 (11.8%) of the 102 patients without, angina on exercise testing at 6 weeks had coronary surgery (less than 0.001). None of the other exercise variables reliably predicted death, or other complications, including coronary surgery. Ten (13.8%) of the 75 patients excluded from the study died during follow-up; six of them within 6 weeks of infarction. Four (67%) of these patients were excluded from the study because of heart failure. Therefore, the 3-year outcome in young survivors of a myocardial infarction is good and is not reliably predicted by exercise testing at 3 and 6 weeks or 18 months.

Advances in remote sensing from ground-based and space-borne systems, expanded in-situ observation networks, and increased low-cost computer capability, will allow an unprecedented view of mesoscale weather systems from the local weather office. However, the volume of data from these new instruments, the nonconventional quantities measured, and a frequent operational cycle, require the development of systems to translate this information into products aimed specifically at aiding the forecaster in zero to six hour prediction. An observing network now exists in northeast Colorado that is similar to what a local weather office will have available within 5–7 years. With GOES and TIROS satellites, Doppler radar, wind profilers, and surface mesonet stations, we have a unique opportunity to explore the use of such data in nowcasting weather phenomena. The scheme, called LAPS (the Local Analysis and Prediction System), objectively analyzes data on a high-resolution (10-km), three-dimensional grid. The analyzed fields are used to generate mesoscale forecast products currently aimed at convection and aircraft icing. Substantial skill was demonstrated during a convective forecasting experiment. While preliminary results from the icing experiment indicate improvements are needed with fine detail, the results are useful in an areally averaged sense.

For narrow electronic bands in metals, we seek improvement over the local-density approximation (LDA) by including the on-site Coulomb interaction between localized electrons. For the 3{ital d} ferromagnetic series of Fe, Co, and Ni, by treating fluctuations to second order in the on-site interaction around the LDA solution, in comparison with experiment a distinct improvement over the conventional LDA is obtained for a number of properties: effective masses, x-ray photoemission spectra, and results derived from angle-resolved photoemission spectra, such as exchange splittings and quasiparticle bands. In addition, the predicted quasiparticle broadenings and satellite features, which are not present in standard LDA calculations, are in reasonable agreement with observation.

Using the linear muffin-tin orbital method and the virtual-crystal approximation, we have calculated from first principles the spin and orbital moments of Fe-Co and Co-Ni alloys. The spin-orbit interaction was included at the variational step. The calculations also incorporated orbital polarization, which improved the agreement with the experimental orbital moments. While the spin moments were fairly insensitive to the level of approximation and followed the Slater-Pauling curve, the orbital moments exhibited a more complex behavior, where, for example, the crystal structure plays a most decisive role. Finally, enhanced orbital moments are predicted for ${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$ alloys with x\ensuremath{\sim}0.25--0.5 in a hypothetical bcc structure, and for ${\mathrm{Fe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$ alloys with x\ensuremath{\sim}0.25 in a hypothetical fcc structure.

We present theoretical evidence for ferromagnetism in Ru and Rh overlayers on Ag(001). These predictions are based on ab-initio, spin-polarized, electronic-structure calculations within the framework of the local spin-density approximation. For Tc, Ru, Rh and Pd overlayers chemisorbed on Ag(001), only Ru and Rh exhibited ferromagnetism. Several metamagnetic spin states were found for the Ru overlayers.

We have determined theoretically both the orbital and the spin contribution to the magnetic moment on the (001) surfaces of fcc Mn, bcc and fcc Fe, hcp Co, and fcc Ni. We used a surface geometry that corresponds to the bulk crystal structure (except for Mn) with no relaxation of the surface. In addition to enhanced spin moments at the surface we find that the orbital moment for surface states is greatly enhanced (sometimes by more than 100%). We also present calculations for different spin configurations in fcc Fe, and we find that two competing spin configurations exists. fcc Mn is found to have a surface spin moment slightly larger than the surface moment of bcc Fe. Detailed information from the calculations is presented, i.e., density of states, charge-density contour plots, and orbital-projected spin moments.

Objective To evaluate the predictive utility of the number and morphologic appearance of isolated cafe au lait macules (CALMs) in establishing the diagnosis of neurofibromatosis type 1 (NF1) in a cohort of children referred to an NF1 subspecialty clinic. Design Retrospective study of patients seen between the years 2004 and 2007. Setting Tertiary care neurofibromatosis referral clinic at St Louis Children's Hospital. Patients The study population comprised 110 patients who presented with CALMs and no other diagnostic features of NF1. The median number of CALMs at initial presentation was 6, while the median age of the patients was 33 months. The median age at the last follow-up examination was 76.5 months. Main Outcome Measures Number and morphologic appearance of CALMs and diagnosis of NF1. Results Thirty-four of the children met diagnostic criteria for NF1 during the study period. Thirty-two children met criteria prior to age 72 months, and 2 children met criteria after 72 months. The mean number of CALMs at presentation in children eventually diagnosed as having NF1 (11.8 CALMs) was significantly higher than the mean number of CALMs in children not diagnosed as having NF1 (4.6 CALMs). Of the 44 children who had 6 or more typical CALMs at presentation, 34 children met criteria for NF1. Sixty-eight patients had CALMs described as “typical,” while 42 patients had “atypical” CALMs. Only 2 patients with atypical CALMs met criteria for NF1. Conclusion The majority of patients with 6 or more CALMs will eventually meet diagnostic criteria for NF1, typically by age 6 years, and this likelihood increases with increasing number and typical morphologic appearance of CALMs.

The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many-body techniques such as using dynamical mean-field theory. We review the physics underlying these approaches and discuss their strengths and weaknesses in terms of the larger issues of electronic structure that they involve. In particular, we argue that the common assumptions made to justify such calculations are inconsistent with what the calculations actually do. Although many of these calculations are often treated as essentially first-principles calculations, in fact, we argue that they should be viewed from an entirely different point of view, namely, as based on phenomenological many-body corrections to band-structure theory. Alternatively, it may also be considered that they are just based on a Hubbard model that is more complex than the simple one- or few-band models traditionally used in many-body theories of solids.

We extend a tight-binding method to include the effects of spin-orbit coupling and apply it to the study of the electronic properties of the actinide elements Th, U, and Pu. These tight-binding parameters are determined for the fcc crystal structure using the equivalent equilibrium volumes. In terms of the single-particle energies and the electronic density of states, the overall quality of the tight-binding representation is good and of the same quality as without spin-orbit coupling. The values of the optimized tight-binding spin-orbit coupling parameters are comparable to those determined from purely atomic calculations.

We consider the effect of electron-phonon coupling in semimetals in high magnetic fields, with regard to elastic modes that can lead to a redistribution of carriers between pockets. We show that in a clean three dimensional system, at each Landau level crossing, this leads to a discontinuity in the magnetostriction, and a divergent contribution to the elastic modulus. We estimate the magnitude of this effect in the group V semimetal Bismuth., Comment: 2 figures

We present results for the electronic structure of plutonium by using a recently developed quasiparticle self-consistent $GW$ method (\qsgw). We consider a paramagnetic solution without spin-orbit interaction as a function of volume for the face-centered cubic (fcc) unit cell. We span unit-cell volumes ranging from 10% greater than the equilibrium volume of the $\delta$ phase to 90 % of the equivalent for the $\alpha$ phase of Pu. The self-consistent $GW$ quasiparticle energies are compared to those obtained within the Local Density Approximation (LDA). The goal of the calculations is to understand systematic trends in the effects of electronic correlations on the quasiparticle energy bands of Pu as a function of the localization of the $f$ orbitals. We show that correlation effects narrow the $f$ bands in two significantly different ways. Besides the expected narrowing of individual $f$ bands (flatter dispersion), we find that an even more significant effect on the $f$ bands is a decrease in the crystal-field splitting of the different bands., Comment: 9 pages, 7 figures, 3 tables

Advances in remote sensing from earth- and spaceborne systems, expanded in situ observation networks, and increased low-cost computer capability will allow an unprecedented view of mesoscale weather systems from the local weather office. However, the volume of data from these new instruments, the nonconventional quantities measured, and the need for a frequent operational cycle require development of systems to translate this information into products aimed specifically at aiding the forecaster in 0- to 6-h prediction. In northeast Colorado an observing network now exists that is similar to those that a local weather office may see within 5–7 years. With GOES and TIROS satellites, Doppler radar, wind profilers, and surface mesonet stations, a unique opportunity exists to explore the use of such data in nowcasting weather phenomena. The scheme, called LAPS (the Local Analysis and Prediction System), objectively analyzes data on a high-resolution, three-dimensional grid. The analysed fields are use...

The most important elements of {ital ab} {ital initio} calculations of x-ray-absorption fine structure (XAFS) are studied. To obtain accurate results without {ital ad} {ital hoc} adjustable parameters, we find it essential to include (i) curved-wave effects, (ii) a complex, energy-dependent self-energy, (iii) an approximate molecular potential, and (iv) a fixed energy reference for the photoelectron wave number. Based on these findings, an automated code has been developed for {ital ab} {ital initio} calculations of single-scattering XAFS, in which curved-wave effects are treated exactly in terms of effective backscattering amplitudes, inelastic losses and self-energy shifts are incorporated with use of a Hedin-Lundqvist self-energy, an automated relativistic overlapping-atom muffin-tin potential is used, and the energy threshold is estimated from electron-gas theory. The efficiency of the code is made possible by analytic expressions for the Hedin-Lundqvist self-energy. This code replaces existing tables of XAFS phases and scattering amplitudes and yields reliable theoretical XAFS standards for arbitrary pairs of atoms throughout the Periodic Table ({ital Z}{le}94). These results are comparable to those from self-consistent calculations and are valid to within about 20 eV of the absorption edge. Comparisons with experiment are presented for Cu, Ge, Pt, Br{sub 2}, and GeCl{sub 4}. The calculatedmore » XAFS amplitudes are found to be accurate to within 15%; XAFS phases are accurate to within 0.2 rad; and nearest-neighbor distances are typically accurate to within 0.02 A.« less

We have, for the first time, theoretically determined the self-consistent orbital contribution to the magnetic moment on the (001) surfaces of Fe, Co and Ni. We used a surface geometry that corresponds to the bulk crystal structure with no relaxation of the surface. In addition to enhanced spin moments at the surface, we find that the orbital moment for surface states is greatly enhanced (sometimes by over 100%).

We present first-principles local-density-approximation (LDA) calculations on the electronic structure of the mixed-valence halogen-bridged transition-metal (MX) linear chain compound Pt2Br4(NH3)4 in simplified geometries; neither the ammonia ligands nor the dimerization were included. We present results on equilibrium lattice constants and on the tight-binding and Coulomb parameters needed for many-body models of this system.

The importance of including all of Hund’s rules in self‐consistent electronic‐structure calculations in solids is pointed out. We present a scheme that accounts for the interactions that lead to these rules, and we give examples of when these interactions become important. Calculated ground state properties (chemical bonding, magnetic moment, magnetic form factor) of actinide and rare earth systems are found to agree better with experiment when all Hund’s rules are accounted for. On the other hand, but also in agreement with experiment, we find that Hund’s second and third rule contributions for Fe, Co, and Ni are small.

Using an all-electron, self-consistent, full-potential, linear muffin-tin-orbitals method within the local-density approximation of density-functional theory, we have studied the structural properties and the elastic constants of Mo and MoSi{sub 2}. The Mo and MoSi{sub 2} ground-state properties, lattice parameters, cohesive energy, and (for Mo) elastic constants are found to be in good agreement with the experimental results. Different structures in the angle-integrated photoemission spectrum of MoSi{sub 2} can be satisfactorily explained in terms of various features present in the calculated total density of states. Since there have been no previous theoretical or experimental determinations, our calculations provide the first available information on the elastic constants of MoSi{sub 2}. For both Mo and MoSi{sub 2} we have calculated the stress tensors for the experimental structures and have minimized their elastic energies. We have found that the lattice parameters and the ground-state total energies of Mo and MoSi{sub 2} obtained from both the elastic energy and the total-energy minimizations are about the same, and that the lattice parameters are close to their experimental values.

The surface electronic structure of Ce in the {alpha} and {gamma} phase has been calculated using a film linearized-muffin-tin-orbitals method. The bonding in Ce is found to be mainly metallic in character. The width of the 4{ital f} band in {alpha}-Ce is found to be about 0.7 eV both in the bulk and at the surface; in {gamma}-Ce it is slightly narrower, about 0.6 eV. The calculated work function of {alpha}-Ce is in good agreement with experimental data. Cross sections for the bremsstrahlung isocromat (BIS) processes have been calculated in a fully relativistic framework, and good agreement with experiment is obtained for the itinerant peak in the BIS data near {ital E}{sub {ital F}}. We find our results consistent with an itinerant {ital f}-electron picture for {alpha}-Ce, and thereby consistent with a picture for the {gamma}{r arrow}{alpha} transition that is from localized (and magnetic) to itinerant (bonding and nonmagnetic) {ital f}-electron behavior, i.e., a Mott transition, as opposed to a Kondo volume collapse picture involving a transition between localized states of the {ital f} electrons. We also predict that the surface of {alpha}-cerium is {gamma}-like.

We use a recently developed self-consistent GW approximation to present first principles calculations of the conduction band spin splitting in GaAs under [110] strain. The spin orbit interaction is taken into account as a perturbation to the scalar relativistic hamiltonian. These are the first calculations of conduction band spin splitting under deformation based on a quasiparticle approach; and because the self-consistent GW scheme accurately reproduces the relevant band parameters, it is expected to be a reliable predictor of spin splittings. We also discuss the spin relaxation time under [110] strain and show that it exhibits an in-plane anisotropy, which can be exploited to obtain the magnitude and sign of the conduction band spin splitting experimentally., 8 pages, 4 figures, 1 table

We present results for the electronic structure of alpha uranium using a recently developed quasiparticle self-consistent GW method (QSGW). This is the first time that the f-orbital electron-electron interactions in an actinide has been treated by a first-principles method beyond the level of the generalized gradient approximation (GGA) to the local density approximation (LDA). We show that the QSGW approximation predicts an f-level shift upwards of about 0.5 eV with respect to the other metallic s-d states and that there is a significant f-band narrowing when compared to LDA band-structure results. Nonetheless, because of the overall low f-electron occupation number in uranium, ground-state properties and the occupied band structure around the Fermi energy is not significantly affected. The correlations predominate in the unoccupied part of the f states. This provides the first formal justification for the success of LDA and GGA calculations in describing the ground-state properties of this material., 4 pages, 3 fihgures

Attempts to go beyond the local density approximation (LDA) of Density Functional Theory (DFT) have been increasingly based on the incorporation of more realistic Coulomb interactions. In their earliest implementations, methods like LDA+$U$, LDA + DMFT (Dynamical Mean Field Theory), and LDA+Gutzwiller used a simple model interaction $U$. In this article we generalize the solution of the full Coulomb matrix involving $F^{(0)}$ to $F^{(6)}$ parameters, which is usually presented in terms of an $\ell m_\ell$ basis, into a $jm_{j}$ basis of the total angular momentum, where we also include spin-orbit coupling; this type of theory is needed for a reliable description of $f$-state elements like plutonium, which we use as an example of our theory. Close attention will be paid to spin-flip terms, which are important in multiplet theory but that have been usually neglected in these kinds of studies. We find that, in a density-density approximation, the $jm_j$ basis results provide a very good approximation to the full Coulomb matrix result, in contrast to the much less accurate results for the more conventional $\ell m_\ell$ basis.

This paper presents results of scale model testing of. the Glenmore Water Treatment Plant NE Clearwell in Calgary, Alberta, Canada. This clearwell has a perforated baffle wall at its inlet, a 4-pass serpentine system, and a weir at the outlet. The model was operated based on Froude similarity and had a scale of 1:19. Tracer studies and flow visualization were carried out for three flow rates. From the residence time distribution developed from the tracer tests, it was seen the baffle factor and Morril Dispersion index were affected by the time between when the flow in the model and tracer test was initiated. It took approximately 10 h of flow development time for the results to reach steady-state values for the minimum flow rate. At higher flows, the baffle factor was not as strongly affected by flow development time, however the Morril Dispersion index better matched prototype values at longer times.

A long-standing problem in Pu science is the crystallographic mechanism for the $\ensuremath{\delta}\ensuremath{\rightarrow}{\ensuremath{\alpha}}^{\ensuremath{'}}$ ($\mathrm{fcc}\ensuremath{\rightarrow}\mathrm{\text{monoclinic}}$) transformation. Orientation relations between the two structures impose severe restrictions on the possible mechanisms and require the transition to be reconstructive, which we describe as a sequence of three displacive transitions: $\mathrm{fcc}\ensuremath{\rightarrow}\mathrm{\text{trigonal}}\ensuremath{\rightarrow}\mathrm{\text{hexagonal}}\ensuremath{\rightarrow}\mathrm{\text{monoclinic}}$. We predict instabilities along the $\ensuremath{\Lambda}$ and $\ensuremath{\Sigma}$ branches in the phonon dispersion of the $\ensuremath{\delta}$ phase and formulate a free energy to describe the displacement of atoms across the transition. We suggest that the $\ensuremath{\delta}\ensuremath{\rightarrow}{\ensuremath{\alpha}}^{\ensuremath{'}}$ transition in Pu lies at the threshold of a change in character of the orientation relationship from lighter to heavier actinides, correlating with changes in electron itinerancy, magnetism, and volume.

Extended X-ray absorption fine structure (EXAFS) measurements on shocked polycrystalline iron have provided further evidence for the shock induced alpha - epsilon phase transition in iron. However, recent molecular dynamics investigation of this system has suggested the presence of fcc material in the shocked region. In this paper we will investigate the difficulties in simulating EXAFS signals from molecular dynamics data. We will aim to show that in the case of the shock induced a - E transition EXAFS is insensitive to the type of close packing of the product phase.

We report on large-scale non-equilibrium atomistic simulations of shock-induced transformations in poly crystalline iron samples. These simulations show that, depending on the crystallographic orientation of the body-centered-cubic (bcc) parent phase grains with respect to the shock direction, a significant fraction of the product phase can be face-centered-cubic (fcc) instead of the expected hexagonal-close-packed (hcp) structure. This observation is explained by the existence of different transformation mechanisms for shocks along different crystallographic directions. We conclude that the observation of different product phases can be explained by simple geometric considerations of the involved transformation mechanisms between the parent bcc structure and the product hcp and fcc structures. Ultrafast high-energy laser-based experiments are underway to further investigate this subject. © 2007 American Institute of Physics.

By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of δ-plutonium with varying 5f occupancy. The LDA Hamiltonian is extracted from a tight-binding (TB) fit to full-potential linearized augmented plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We show the strong sensitivity of the spectral properties to the 5f occupancy, which suggests using this occupancy as a fitting parameter in addition to the Hubbard U. By comparing with PES data, we conclude that the “open shell” 5f5 configuration gives the best agreement, resolving the controversy over 5f “open shell” versus “close shell” atomic configurations in δ-Pu.