Search

(a) Institut de Physique et Chimie desMate´riaux de Strasbourg (IPCMS), UMR 7504duCNRS,Universite´LouisPasteur,23rueduLoess,F-67037StrasbourgCedex,France(b)Max-Planck-Institutfu¨rFestko¨rperforschung,Heisenbergstr.1,D-70569Stuttgart,Germany(ReceivedAugust28,2000)Thepressuredependencesofthephononlifetimesofzone-centeropticalphononsofvariousgroupIVand III–V semiconductors are calculated from first principles using third-order density-func-tionalperturbationtheory.Themicroscopicmechanismresponsible,i.e.theanharmonicdecayofaphonon into phonons of different energy, is revealed and the sensitive dependence on pressure isstudiedindetail.Theresults arecomparedwithrecentmeasurements of thepressure dependenceofthelinewidthsofthefirstorderRamanlinesofSi,Ge,andSiC.

We present an ab initio calculation of the real part of the phonon self energy for longitudinal and transverse optical Raman phonons in GaAs, AlAs, GaP and InP. The calculated temperature dependences of transverse and longitudinal modes at the Γ-point are in good agreement with available experimental data. This calculation permits us to analyze the different contributions to the real part of the phonon self-energy. In particular we are able to reproduce the observed asymmetry of the Raman line of the transverse optical mode in GaP. Furthermore, we explain why the frequency of this mode changes less with temperature than that of the transverse mode in the other materials investigated. The pressure dependence of the real and the imaginary parts of the phonon self-energy are also discussed.

We have measured the phonon dispersion of wurtzite CdSe along ΓA by inelastic neutron scattering at room temperature. The sample was grown with the very weakly neutron absorbing isotope 116Cd and natural selenium. These experiments extend the picture so far obtained from earlier measurements on 114CdS and deliver more information on the accuracy of theoretical models. The experimental data are compared with ab initio and shell model calculations.

We present first principles calculations of the real part of the self energy for the transverse optical phonon at the Brillouin zone center in GaAs. The various contributions at zero temperature are analyzed and discussed. Our result for the temperature dependence of the real part of the phonon self energy is in good agreement with the available experimental data.

We have studied the pressure dependence of the linewidths of the longitudinal and transverse optical phonons at the Brillouin-zone center in $3C\ensuremath{-}\mathrm{S}\mathrm{i}\mathrm{C}.$ Raman measurements at 6 K, which cover the pressure range up to 15 GPa, are in good agreement with first-principles calculations also reported here. These results differ considerably from previous experimental data. While the linewidth of the transverse mode remains practically unchanged within our pressure range (up to 35 GPa for the calculation), that of the longitudinal mode shows a monotonic increase up to 26 GPa, decreasing abruptly above this pressure. The mechanisms responsible for this anomalous behavior are identified and discussed. Experimental and theoretical results concerning the pressure dependence of phonon frequencies and related quantities complete the work.

By density functional supercell calculations we have studied the magnetic properties of intrinsic vacancies in ZnO doped with diluted Fe impurities. We found that the more energetically favored Fe Zn – V O configuration corresponds to the one in which the two defects are far apart. On the contrary, among the investigated configurations of Fe Zn – V Zn , the one having the lower formation energy corresponds to the complex in which one defect is in the next nearest neighbor position with respect to the other. For Zn-poor growth condition the thermal population of the latter complex provide a key to understand the magnetism of the system.

We examine the dependence on size distribution of the Raman line shape of optical vibron modes in CdSe dots. A detailed comparison with the theory of electron-hole correlated Raman scattering in spherical quantum dots, which includes LO-confined modes, is carried out. The obtained CdSe vibron frequencies are found to map well on the ab initio calculated LO phonon dispersion relations of wurtzite CdSe along the [001] direction of the Brillouin zone.

We have measured the pressure dependence of the width of the first-order Raman lines in Si and Ge at low temperature. The width increases linearly with hydrostatic pressure, which implies a decrease of the lifetime of the long-wavelength optical phonons. The results are compared with recent first-principles calculations of anharmonic decay into two phonons of lower energy, based on third-order density-functional perturbation theory. Provided the calculations are slightly adjusted so that the relevant frequencies agree exactly with the measured ones, the agreement for the linewidths between theory and experiment is excellent.

Neuroendoscopy is presently a routine procedure in most neurosurgical services. It was originally developed to deal with obstructive hydrocephalus, but modern technical advancements have made possible to face also other neurological diseases including brain tumors. Presently, small endoscopes with exquisite detail visualization, high resolution screens, 3D cameras, dedicated ultrasonic aspirators and laser beams offer therapeutic options which could be just dreamed a few years ago. The friendly interface with image-guided systems further improves the technique. Nowadays, the golden standard treatment of ventricular tumors includes biopsy under endoscopic control and (if necessary) treatment of the associated hydrocephalus during the same procedure. Endoscopic biopsy may be followed (if indicated) by traditional microsurgery, but it may also remain the only surgical procedure needed since several midline tumors either do not require surgical excision or may be managed by radiosurgery, chemotherapy, and/or radiation-therapy. Another endoscopic option is the fenestration/aspiration of cystic space occupying lesions. This technique may result very useful in selected cases of craniopharyngioma, metastases, abscesses and cystic tumors in general. This treatment aims to the endoscopic cyst shrinkage followed by radiosurgery or other adjunctive therapies. Moreover, there are particular expansive lesions which may be even endoscopically excised. This is especially the case of 3rd ventricle colloid cysts, for which endoscopy has become the first choice treatment in a lot of neurosurgical units. Finally, most CSF-cysts (arachnoid, choroid, ependymal, post-surgical, post-hemorrhagic) may be endoscopically treated thus avoiding open surgery or cysto-peritoneal shunting.

Vittorio Marchi was an Italian neuroscientist who lived during the second half of the 19th century. He is generally remembered for developing a novel staining method to trace the degeneration of nervous fibers in lesions of the central nervous system. This osmium-based method was used worldwide for approximately a century and continues to be cited in modern textbooks. Despite several important original scientific contributions, Marchi was never awarded a university chair. Discouraged, he left to practice neurology in a rural area but continued to write outstanding articles, and in 1897, he became a pioneer of meningioma surgery. Today, he is remembered only in specialized contexts. We hope this article can provide the recognition that Marchi deserves.

In this study we explore, both from theoretical and experimental side, the effect of Fe doping in ZrO2 (ZrO2:Fe). By means of first principles simulation, we study the magnetization density and the magnetic interaction between Fe atoms. We also consider how this is affected by the presence of oxygen vacancies and compare our findings with models based on impurity band (J.M.D. Coey, M. Venkatesan, C.B. Fitzgerald, Nat. Mater. 4, 173 (2005)) and carrier mediated magnetic interaction (T. Dietl, H. Ohno, F. Matsukura, J. Cibert, D. Ferrand, Science 287, 1019 (2000)). Experimentally, thin films (≈20 nm) of ZrO2:Fe at high doping concentration are grown by atomic layer deposition. We provide experimental evidence that Fe is uniformly distributed in the ZrO2 by transmission electron microscopy and energy dispersive X-ray mapping, while X-ray diffraction evidences the presence of the fluorite crystal structure. Alternating gradient force magnetometer measurements show magnetic signal at room temperature, how- ever, with low magnetic moment per atom. Results from experimental measures and theoretical simulations are compared.

In this paper we study, both with theoretical and experimental approach, the effect of iron doping in zirconia. Combining density functional theory (DFT) simulations with the experimental characterization of thin films, we show that iron is in the Fe3+ oxidation state and accordingly that the films are rich in oxygen vacancies (VO). VO favor the formation of the tetragonal phase in doped zirconia (ZrO2:Fe) and affect the density of state at the Fermi level as well as the local magnetization of Fe atoms. We also show that the Fe(2p) and Fe(3p) energy levels can be used as a marker for the presence of vacancies in the doped system. In particular the computed position of the Fe(3p) peak is strongly sensitive to the VO to Fe atoms ratio. A comparison of the theoretical and experimental Fe(3p) peak position suggests that in our films this ratio is close to 0.5. Besides the interest in the material by itself, ZrO2:Fe constitutes a test case for the application of DFT on transition metals embedded in oxides. In ZrO2:Fe the inclusion of the Hubbard U correction significantly changes the electronic properties of the system. However the inclusion of this correction, at least for the value U = 3.3 eV chosen in the present work, worsen the agreement with the measured photo-emission valence band spectra., 24 pages, 8 figures

STUDY DESIGN Retrospective study. OBJECTIVE The aim of this study is to show that a single traumatic fracture of the atlas is unusual but not rare and requires specific management strategies, which can be highlighted by the study of the junctional ligaments and membranes. SUMMARY OF BACKGROUND DATA A single traumatic fracture of the atlas arch is considered a rare event and has been analyzed in few case reports. Ligaments and membranes play a primary role in providing stability to the craniovertebral junction area. METHODS Here, we report 10 cases of a single traumatic fracture of the atlas arch: 4 cases were part of our series of spine injuries and were studied by magnetic resonance imaging during the acute phase to assess the junctional ligaments. The remaining 6 cases were obtained from the Literature. RESULTS Indirect signs of a traumatic ligamentous injury were found only in 1 patient. However, in all cases, these fractures were considered biomechanically stable and all patients were discharged with a rigid collar. During the follow-up, all patients reported an improvement in their neck pain and tenderness, with radiologic signs of bone healing. CONCLUSIONS A single fracture of the atlas arch is an unusual traumatic event that results from slow-force impact. Medical experience in treating this specific fracture subtype is nowadays poor because of the paucity of the literature; thus, this unusual condition may either be underestimated or even overstudied and overtreated. Nowadays, it seems reasonable to assume that the management should be conservative in all cases and that magnetic resonance imaging often plays only a marginal role.

The craniovertebral junction is a specific region of the spine with unique anatomical and biomechanical properties that yields a wide variety of injury patterns. Junctional traumatic fractures and/or dislocations are widely reported in clinical practice, but we could identify only a subgroup of upper cervical spine traumatic injuries with very few cases reported in the literature, and for this reason may be considered rare. In some of these cases, the absence of spinal biomechanical instability, in association with moderate clinical symptoms (neck stiffness and pain) and the difficulty in fracture identification through standard cervical radiographs, leads to a high percentage of missed injuries. In other cases, traumatic events have been commonly described only in autopsy series due to the high degree of spinal biomechanical instability. Herein, we have summarized all the relevant literature concerning this issue and also included our cases, with the aim of emphasizing prompt diagnosis and correct management. We provide a guide for correctly identifying “rare” craniovertebral junction traumatic injuries.

Objective This study aims to identify the angiographic parameters that could help predict the risks of hyperemic complications (HCs) in the treatment of cerebral arteriovenous malformations (AVMs). Methods The charts and the pre- and post-treatment angiographies of 400 consecutively treated patients with cerebral AVMs were retrospectively reviewed. Several parameters were analyzed: grade, size, drainage depth, number of the “recruited veins” (veins coming from the brain and joining the main AVM drainage), and “venous times” (the times of visualization of the nidus and the main drainage, of the “recruited veins,” and finally of the normal cerebral veins). On this basis, two groups were identified: group 1, consisting of 309 patients (77.3%) with normal/subnormal venous times, and group 2, consisting of 91 patients (22.7%) with altered venous times and venous engorgement. Finally, the weight of the various parameters was measured by univariate and multivariate analyses. Results An overall number of 245 patients (61.2%) achieved favorable outcomes. HCs occurred in a total of 28 patients (7%): No patient belonged to group 1, so that these adverse effects were reported in 30.7% of group 2 patients. The presence of deep drainage and the number of recruited veins resulted in statistically significantly different impacts on the risk of the different grades. Conclusions The statistical analysis allowed the identification of three different risk scores, which were named Nig-scores (Niguarda scores). Nig-score 0 means no risk of HCs and concerns patients without altered venous times; Nig-score 1 represents patients with intermediate risk, that is, with moderately altered venous times and few recruited veins; Nig-score 2 indicates high risk of HCs and refers to patients with markedly altered venous times.

Achieving high temperature ferromagnetism by doping transition metals thin films is seen as a viable approach to integrate spin-based elements in innovative spintronic devices. In this work we investigated the effect of Fe doping on structural properties of ZrO2 grown by atomic layer deposition (ALD) using Zr(TMHD)4 for Zr and Fe(TMHD)3 for Fe precursors and ozone as oxygen source. The temperature during the growth process was fixed at 350{\deg}C. The ALD process was tuned to obtain Fe doped ZrO2 films with uniform chemical composition, as seen by time of flight secondary ion mass spectrometry. The control of Fe content was effectively reached, by controlling the ALD precursor pulse ratio, as checked by X-ray photoemission spectroscopy (XPS) and spectroscopic ellipsometry. From XPS, Fe was found in Fe3+ chemical state, which maximizes the magnetization per atom. We also found, by grazing incidence X-ray diffraction, that the inclusion of Fe impurities in ZrO2 induces amorphization in thin ZrO2 films, while stabilizes the high temperature crystalline tetragonal/cubic phase after rapid thermal annealing at 600{\deg}C., Comment: 11 pages, 7 figures, 1 Table

The aim of this study is to review the clinical outcome of patients treated for spinal dural arteriovenous malformations and investigate the presence of pretreatment indicators of outcome after short- and midterm follow-up. The authors retrospectively reviewed the records of 65 consecutive patients treated either surgically or endovascularly in 3 neurosurgery departments between 1989 and 2009. After treatment, 80% of patients reported improvement of at least 1 symptom. Motor symptoms improved more than sensory disorders, pain, or sphincter impairment. Spinal dural arteriovenous fistulas at the thoracic level, and in particular at the lower level, responded better than those in other spinal areas. Spinal dural arteriovenous fistula is a rare pathology with a malignant course that should be treated aggressively. This study appears to confirm that neurological status before treatment, anatomical location of the fistula, and symptoms at presentation are all factors that can predict outcome. Early diagnosis of spinal dural arteriovenous malformations in the lower thoracic area in patients with an Aminoff scale score < 3 was associated with the most favorable outcome.

Spondylodiscitis mainly affects the anterior part of the spine. In this paper, we retrospectively analyze our experience with the anterior stand-alone approach (ASAA) in the treatment of spinal infections.Forty consecutive patients with severe spondylodiscitis underwent the ASAA during the acute infective phase. Treatment consisted of disease debridement, vertebral body reconstruction using titanium expandable prostheses and anterior fixation.There was neither mortality nor major morbidity. Successful arthrodesis was achieved in 39 out of 40 patients who remained disease free throughout the follow-up period. Six months after treatment, one patient experienced pseudarthrosis and required supplemented posterior spinal fixation for vertebral instability. However, adequate arthrodesis was eventually obtained even in this patient.ASAA with spine reconstruction using synthetic materials during the acute infection phase was safe and effective. The infections were rapidly defeated, the patients were allowed to stand up early after the procedure and the length of hospital stay was significantly reduced.

I present an ab initio study of the phase stability and dielectric constant (${\ensuremath{\kappa}}_{0}$) of ${\mathrm{Hf}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}{\mathrm{O}}_{2}$ alloy as a function of Ge concentration in the range $0\ensuremath{\le}x\ensuremath{\le}0.25$. I determine the critical concentration ${x}_{c}$ at which the monoclinic structure (the stable phase at low $x$ and at low temperatures) has a phase transition into the high-${\ensuremath{\kappa}}_{0}$ fluorite structure. I found that, at ${x}_{c}$, the fluorite phase presents a dielectric constant that is more than 50$%$ higher than the orientationally averaged dielectric constant of undoped bulk monoclinic phase. I studied the effect of temperature on this phase transition. I identified the microscopic mechanisms which influence the dielectric properties of the fluorite phase finding that the decrease of the Born effective charge of Ge with respect to that of Hf is locally compensated by a variation of the Born effective charge of the O atoms which are neighbors of the Ge. I predict that the bulk modulus of this superhard oxide increases as a function of doping. My results are relevant to improve, by Ge alloying, the dielectric and mechanical properties of hafnia in advanced technological applications.

We propose a first-principles scheme for the description of the magneto-optical kerr effect within density functional theory (DFT). Though the computation of Kerr parameters is often done within DFT, starting from the conductivity or the dielectric tensor, there is no formal justification to this choice. As a first steps, using as reference materials iron, cobalt and nickel we show that pseudo-potential based calculations give accurate predictions. Then we derive a formal expression for the full dielectric tensor in terms of the density-density correlation function. The derived equation is exact in systems with an electronic gap, with the possible exception of Chern insulators, and whenever the time reversal symmetry holds and can be used as a starting point for the inclusion of local fields and excitonic effects within time-dependent DFT for such systems. In case of metals instead we show that, starting from the density-density correlation function, the term which describes the anomalous Hall effect is neglected giving a wrong conductivity., Comment: 8 pages, 4 figures

We describe, within an ab initio approach, the stabilization of the tetragonal phase versus the monoclinic one in yttrium-doped zirconia. The process is believed to be influenced from different mechanisms. Indeed, we show that there is a delicate balance between the change in electrostatic and kinetic energy and exchange-correlation effects. In the tetragonal phase, the perturbation induced by doping is better screened at the price of sacrificing correlation energy. Our work opens the opportunity to use the same approach to predict the tetragonal phase stabilization of materials such as zirconia or hafnia, with different and less characterized dopants.

We report a density functional study of the electronic properties and hyperfine structure of substitutional selenium in silicon nanowires using plane-wave pseudopotential techniques. We simulated hydrogen passivated [001] oriented nanowires with a diameter up to 2 nm, analyzing the effect of quantum confinement on the defect formation energy and on the hyperfine parameters as a function of the diameter and of the defect position. We show that substitutional Se in silicon has favorable configurations for positions near the surface with possible formation of chalcogen - hydrogen complexes. We also show that hyperfine interactions increase at small diameters, as long as the nanowire is large enough to prevent surface distortion which modifies the symmetry of the donor wave function. Moreover, surface effects lead to strong differences in the hyperfine parameters depending on the Se location inside the nanowire, allowing the identification of an impurity site on the basis of electron paramagnetic resonance spectra.

Traumatic (Type II) odontoid fractures are very common injuries. Nevertheless, their connection with transverse atlantal ligament injury is controversial and poorly defined. The aim of this study is to report a single case of traumatic (type II) odontoid fracture with transverse atlantal ligament injury and to critically analyze the role of ligaments and membranes together with neuroradiological tools in the management of craniovertebral junction-traumatized patients.We report 27 consecutive cases of traumatic (type II) odontoid fractures who underwent magnetic resonance imaging (MRI) in the acute phase injury (72 hours), focusing our attention on the transverse atlantal ligament.One patient (3.7%) demonstrated a transverse atlantal ligament injury on MRI. The patient underwent surgery.Traumatic (type II) odontoid fracture with transverse atlantal ligament avulsion can be considered an unusual event. It is our opinion that the routine use of MRI for all patients with type II odontoid fracture could be unjustified in clinical practice. Strict clinical surveillance of all patients managed conservatively and the use of MRI in selected cases could be a reasonable management option.

By density factional supercell calculations we computed the total energy and the magnetic properties of isolated complexes formed in wurtzite ZnO doped with diluted Fe impurities in the presence of interstitial atoms of Zn or O. Interstitial O occupies preferentially a site with octahedral symmetry with substitutional Fe in the first neighbor shell, thus forming the complex Fe${}_{\mathrm{Zn}}$-I${}_{\mathrm{O}}$. In contrast, the complex Fe${}_{\mathrm{Zn}}$-I${}_{\mathrm{Zn}}$ is energetically unfavored with respect to the case where the two components are far apart. For oxygen-rich growth conditions, a significant population of complexes Fe${}_{\mathrm{Zn}}$-I${}_{\mathrm{O}}$ is stable at (and above) room temperature, providing a key to understanding the room-temperature magnetism of this system. Interstitial oxygen, coupled with diluted Fe impurities, exhibit a density of states spin polarized at the Fermi energy.

In ZrO2 crystals, the highest dielectric constant (k) is ascribed to the tetragonal phase. By the use of density functional theory and synchrotron radiation x-ray diffraction, we show how the a and c lattice parameters of the tetragonal phase influence the resulting k. Highest k values are obtained at increasing both a and c, while k is reduced for compressive strained cells. The determination of a and c on La-doped ZrO2 and ZrO2 thin films deposited by atomic layer deposition on Ge (001) allowed us to elucidate the influence of La doping and Ge diffusion on the k value.

Ab initio density-functional theory in generalized gradient approximation is used to perform calculations on the magnetic structure of Mn thin films and Mn-Ni ordered surface alloys on Ni/Cu. For the Mn monolayer on Ni(001), Ni(011), and Ni (111), we found that the ground state corresponds to an antiferromagnetic coupling between Mn atoms. Ni subsurface atoms adjacent to Mn surface display two different values (0.26 mu(B) and 0.13 mu(B)) of the magnetic moment in the (111) crystallographic face. For the ordered Mn0.5Ni0.5 monolayer on Ni a ferromagnetic configuration has been obtained. At variance, for the ordered Mn0.5Ni0.5 two-layers thick on Ni an antiferromagnetic coupling between Mn atom nearest-neighboring positions are depicted for the (001) and (011) crystallographic faces whereas it is ferromagnetic for (111) one. Ni magnetic moments at surface alloy are killed (-0.04 mu(B)). Mn overlayer and 1-2 ML surface alloy always present a large rippling, in qualitative agreement with experimental measurements

By means of the effective mass approximation we have computed without any adjustable parameters the energy levels and hyperfine splitting of a P impurity in silicon spherical nanocrystals as a function of the nanocrystal radius. Confinement effects produce an enhancement of the energy levels and of the hyperfine splitting as the crystal radius is decreased. Our results are in good agreement with available experimental data.

Within the framework of density functional theory we have computed the total energy and the magnetic properties of wurtzite ZnO doped with diluted impurities of Co or of Ni in the presence of intrinsic vacancies. The complex M Zn –V Zn (M=Co,Ni) , where the Zn-vacancy ( V Zn ) is in the next nearest neighbour site with respect the transition metal M atom, is energetically favored with respect to the configuration in which the two defects are far apart. Also for the more favourite thermodynamic growth condition the probability to find these types of complex at room temperature is relatively small (of the order of 10 −7 or less).

Within the framework of the envelope function approximation we have computed – without adjustable parameters and with a reduced computational effort due to analytical expression of relevant Hamiltonian terms – the energy levels of the shallow P impurity in silicon and the hyperfine and superhyperfine splitting of the ground state. We have studied the dependence of these quantities on the applied external electric field along the [001] direction. Our results reproduce correctly the experimental splitting of the impurity ground states detected at zero electric field and provide reliable predictions for values of the field where experimental data are lacking. Further, we have studied the effect of confinement of a shallow state of a P atom at the center of a spherical Si-nanocrystal embedded in a SiO2 matrix. In our simulations the valley–orbit interaction of a realistically screened Coulomb potential and of the core potential are included exactly, within the numerical accuracy due to the use of a finite basis set, while band-anisotropy effects are taken into account within the effective-mass approximation.

Rare earth oxides (REOs) have lately received extensive attention in relation to the continuous scaling down of non-volatile memories (NVMs). In particular, La2O3 films are promising for integration into future NVMs because they are expected to crystallize above 400 degrees C in the hexagonal phase (h-La2O3) which has a higher K value than the cubic phase (c-La2O3) in which most of REOs crystallize. In this work, La2O3 films are grown on Si by atomic layer deposition using La(C5H5)(3) and H2O. Within the framework of the h-La2O3 formation, we systematically study the crystallographic evolution of La2O3 films versus annealing temperature (200-600 degrees C) by Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction (GIXRD). As-grown films are chemically unstable in air since a rapid transformation into monoclinic LaO(OH) and hexagonal La(OH)(3) occurs. Vacuum annealing of sufficiently thick (> 100 nm) La(OH)(3) layers induces clear changes in FTIR and GIXRD spectra: c-La2O3 gradually forms in the 300-500 degrees C range while annealing at 600 degrees C generates h-La2O3 which exhibits, as inferred from our electrical data, a desirable k similar to 27. A quick transformation from h-La2O3 into La(OH)(3) occurs due to H2O absorption, indicating that the annealed films are chemically unstable. This study extends our recent work on the h-La2O3 formation. (C) 2008 Elsevier B.V. All rights reserved.

We propose a mechanism leading to the local epitaxy observed in $\mathrm{Hf}{\mathrm{O}}_{2}$ films grown on Ge(001). Our model is based on state-of-the-art ab initio calculations compared with available experimental data. According to the proposed model, the observed preferential orientation of the monoclinic structure is related to the relaxation of the epitaxially stabilized anatase phase when a critical thickness is reached. In fact, the preferential orientation of the monoclinic structure follows the in-plane axis of the anatase phase, as proven by accurate x-ray scattering data. We predict that the anatase phase, which has no bulk counterpart and has a calculated dielectric constant comparable to the bulk monoclinic one, is almost lattice matched with the Ge(001) substrate. Although the observation of the anatase phase is still missing, its stabilization would allow a control at the atomic level of the $\mathrm{Hf}{\mathrm{O}}_{2}∕\mathrm{Ge}(001)$ interface, possibly providing better performances in the next generation complementary-metal-oxide-semiconductor devices.

La2O3 films are obtained by annealing in vacuum La(OH)(3) layers produced upon air exposure of La2O3 layers grown using atomic layer deposition. Sample thickness determines whether hexagonal or cubic La2O3 form. The observed infrared active phonon mode with minimum frequency for hexagonal La2O3 films is located at 198 cm(-1), in good agreement with the first principles calculations, and at a lower frequency than the corresponding mode for cubic La2O3 is at 235 cm(-1). Accordingly, electrical measurements reveal a dielectric constant around 27 for hexagonal La2O3 films, significantly higher than the one around 17 derived for cubic La2O3 layers. (C) 2007 American Institute of Physics.

We compute within the effective-mass theory and without adjustable parameters the Stark effect for shallow P donors in Si with anisotropic band structure. Valley-orbit coupling is taken into account in a nonperturbative way and scattering effects of the impurity core are included to properly describe low-lying impurity states. The ground-state energy slightly decreases with increasing electric field up to a critical value ${E}_{\mathit{cr}}\ensuremath{\sim}25\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{cm}$, at which the donor can be ionized by tunneling due to a field-induced mixing of the ``$1s$-like'' singlet ground state with a ``$2{p}_{0}$-like'' excited state in zero field. The resulting ground-state wave function at high field extends significantly outside the potential barrier surrounding the impurity. Calculations of the hyperfine splitting and of the $A$-shell superhyperfine coupling constants as a function of the electric field complete the work.

Low back pain (LBP) is a widespread health problem and a major contributor to increasing health costs and lost work days. Different pathologies cause LBP and one of these is lumbar degenerative spondylolisthesis (SPL). There are no generally accepted and standardized methods for assessing the outcome of patients treated for degenerative lumbar SPL. This study aims to assess quality of life after surgery for lumbar degenerative SPL through the adoption of outcome measures. We studied 76 patients treated, for degenerative lumbar SPL, with spinal stabilization, decompression and bilateral dorsolateral fusion, followed up for at least two years. We used the Roland-Morris (RM) scale and the Oswestry Disability Index (ODI) to assess the quality of life of the patients before surgery and at follow up. Each patient was pre-operatively studied through standard and dynamic x-rays, CT scan and MRI of lumbar column. Relationships between clinical, radiological and disability scores, grouped by categories, were tested. The sample comprised 25 males and 51 females. Mean age was 59.6 years (SD 12.2). The mean duration of symptoms (from clinical onset to surgery) was 23.42 months (median 13, range 4-100 months). In about half of the cases, duration of symptoms before surgery was12 months. At follow up, the fusion rate was 85.5%, and the ODI score was significantly reduced: an improvement of20 points in 35.7% of patients, and of20 points in 55.7%. On the RM scale, 59.4% of patients had a reduction5 points, 13.1% a reduction of 2-4 points, and 27.5% an unchanged or worse score. There was no significant reduction in RM scale and ODI scores in patients with fusion versus pseudoarthrosis. Instrumental pedicle screw fixation and arthorodesis seem to be very effective in improving quality of life, as shown by the reduced disability scores at follow up.

Far-infrared reflectivity spectra are measured to investigate the role of both phonon anharmonicity and disorder in ${\mathrm{MgAl}}_{2}{\mathrm{O}}_{4}$ spinel at low temperature. Damping constants induced by phonon anharmonicity and disorder are investigated to tentatively discriminate these two effects. Using density-functional perturbation theory, ab initio one- and two-phonon density of states are computed for the nondisordered spinel. It is shown that both the frequency and temperature dependences of the experimental damping factors agree well with the calculated imaginary parts of the two-phonon density of states. Moreover, first-order phonon mode Gr\"uneisen parameters are calculated and compared to experiments. Finally, the origin of the low intensity of the polar mode near $565\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ of ${T}_{1u}$ symmetry is understood.

Within the framework of density functional theory, we have computed structural and vibrational properties of high-K dielectric oxides, HfO2 and TiO2. We have considered different polytypes of these oxides and computed the corresponding static dielectric constants in order to investigate what are the more promising materials suitable for technological application. We found the flourite phase of hafnium dioxide, that is a promising candidate as gate oxide in ultra-scaled complementary metal-oxide-semiconductor (CMOS) technology, is structurally unstable due to the presence of soft phonon modes that have wave-vectors in the region of the Brillouin zone containing the K- and X-points. According to our results, the fluorite TiO2 is structurally unstable as well but, contrary to HfO2, the soft phonon modes have wave-vectors in the whole Brilouin zone. Calculations of the thermodynamical properties of the baddeleyite HfO2, the stable phase at ambient condition, complete the work. (c) 2006 Elsevier Ltd. All rights reserved.

The half-metallic NiMnSb compound is recently attracting renewed interest for its application in devices making use of spin polarized charges injected into conventional semiconductor. For technological purposes it is desirable to design interfaces where the peculiar half-metallic character of NiMnSb is not degraded. We focus here on the NiMnSb/GaAs(0 0 1) heterojunction that we investigate by accurate pseudopotential density functional—local spin density calculations. We find in general that the half-metallicity is lost when NiMnSb is joined with the semiconductor, even at the interface with a mixed (Mn,As) plane which is one of the most promising for maintaining the desired half-metallicity. In this case, however, the effect is localized just on the interfacial atoms. Electronic and magnetic bulk properties are recovered within a couple of atomic planes far from the interface, so that the band alignments are well defined.

The records of 403 patients treated for herniated lumbar disc disease were analysed in a retrospective observational study in order to verify how three outcome measures, i.e., satisfaction with the outcome of surgery, the degree of return to activities of daily living including work (ADL), and duration of interruption of ADL, may be influenced by clinical variables. Age, type of disc herniation, radiological evidence of recurrence (radiological recurrence), and need for a second surgical operation for disc herniation (surgical recurrence) were found to be significantly related to the patient's satisfaction with the outcome of surgery at follow up. Satisfaction with the outcome of surgery was not found to depend on the interval between clinical onset and radiological diagnosis, or on the timing of surgery. The degree of return to ADL was found to be significantly related to age, surgical recurrence, type of disc herniation, and timing of surgery. The results of the present study suggest that age and type of disc herniation are among the most important factors to consider when deciding whether or not to operate on a patient for herniated lumbar disc and that return to ADL after surgery is closely correlated with disc disease recurrence.

We propose ${\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$ alloys as suitable candidates for spintronic applications. Remarkably, our first-principles investigation explains, within the local spin density approximation, the microscopic mechanism that stabilizes the half metallicity in Si matrices under Ge alloying and shows that it can spontaneously occur: in fact, half metallicity is determined by $p\text{\ensuremath{-}}d$ hybridization in the presence of Ge atoms surrounding Mn impurities, and this particular environment is energetically favored over other possible local composition fluctuations, such as excess of Si atoms around Mn. A detailed discussion of the trends of defect formation energy and of magnetization as a function of alloy composition and configuration completes the present work.

The temperature dependence of the frequencies and linewidths of the Raman-active longitudinal optical (LO) phonons in GaAs and AlAs have been measured. The low-temperature lifetime of the LO phonon in AlAs is found to be 9.7 ps, very close to the corresponding GaAs value of 9.5 ps. This contradicts early theoretical predictions. The agreement between theory and experiment can be restored when the accidental degeneracy between the AlAs LO phonon frequency and a feature in the two-phonon density of states is taken into account.

The dependence of the crystal lattice constant on isotopic substitution of atomic masses is investigated in GaAs and ZnSe using perturbation theory in a density-functional framework. The temperature dependence of the derivatives of the lattice constant with respect to both the anion and the cation mass is computed. Results for additional lattice properties, such as the linear thermal expansion coefficients and mode Gr\"uneisen parameters, are reported and compared with available experimental data. Chemical trends are discussed. \textcopyright{} 1996 The American Physical Society.

An 11-year-old girl was treated by corpectomy and anterior fusion because of the destruction of the C7 vertebral body. Pathological studies were not conclusive. The outcome was excellent, but 18 months later, she required thoracic corpectomy with anterior fusion owing to the impending kyphotic fracture of the Th8 vertebral body. Langerhans cell histiocytosis was now recognised and chemotherapy was given. 3 years later, the disease appears well controlled with normal shape of both the operated vertebral levels and maintenance of the movements of the adjacent vertebrae.

The anharmonic lifetimes of zone-center optical phonons in C, Si, and Ge are calculated along with their temperature and pressure dependences, using third-order density-functional perturbation theory. Our basic ingredients are by-products of a standard linear-response calculation of phonon dispersions in the harmonic approximation, resulting in a similarly good agreement with experiments. The microscopic mechanisms responsible for the decay are revealed and shown to be different for different materials and to depend sensitively on the applied pressure.

We present a formulation of third-order density-functional perturbation theory which is manifestly invariant with respect to unitary transfomations within the occupied-states manifold and is particularly suitable for a practical implementation of the so called `2n+1' theorem. Our implementation is demonstrated with the calculation of the third-order anharmonic coupling coefficients for some high-simmetry phonons in Silicon., Comment: 6 pages, Plane Tex, SISSA Ref. 78/94/CM/SC (June 94)

Following the submission of Fig. 4 in the correct electronic format to the editorial office, an error occurred during the final stage of the editing process which resulted in the inset of the specific figure to have been erroneously reproduced in the published version of our article. This erratum provides the corrected inset to Fig. 4 (the whole Fig. 4 is attached). We would like to apologize for this mistake, noting that it does not invalidate any relevant statements and quantitative analysis presented in the originally published article.

The authors report on the calculation, by density functional theory, of the total energy and of the magnetic properties of wurtzite ZnO doped with diluted Fe impurities in the presence of vacancies. They found that the complex FeZn–VZn—where the Zn vacancy (VZn) occupies the next nearest neighbor position to Fe atom—is energetically favored compared with the isolated FeZn and VZn. An opposite situation was obtained for FeZn and VO. For Zn-poor growth condition, the room temperature population of the FeZn–VZn complex provides a key to understand the magnetism of this system.

This research was partially funded by the ERC starting grant No. 713927, the ISF grant No. 447/16, the CERCA Programme of the Generalitat de Catalunya, Centre de Recerca Matemàticaca, Fundació Ferran Sunyer i Balaguer from Institut d'Estudis Catalans, and the MTM2014-59174-P grant. We obtain necessary and sufficient conditions on weights for the generalized Fourier-type transforms to be bounded between weighted Lp-Lq spaces. As an important example, we investigate transforms with kernel of power type, as for instance the sine, Hankel, or Hα transforms. The obtained necessary and sufficient conditions are given in terms of weights, but not in terms of their decreasing rearrangements, as in several previous investigations.