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Synthetic two-dimensional (2D) mono-elemental crystals, namely X-enes, have recently emerged as a new frontier for atomically thin nanomaterials with on-demand properties. Among X-enes, antimonene, the β-phase allotrope of antimony, is formed by atoms arranged in buckled hexagonal rings bearing a comparatively higher environmental stability with respect to other players of this kind. However, the exploitation of monolayer or few-layer antimonene and other 2D materials in novel opto-electronic devices is still hurdled by the lack of scalable processes. Here, we demonstrated the viability of a bottom-up process for the epitaxial growth of antimonene-like nanocrystals (ANCs), based on a Metal-Organic Chemical Vapor Deposition (MOCVD) process, assisted by gold nanoparticles (Au NPs) on commensurate (1 1 1)-terminated Ge surfaces. The growth mechanism was investigated by large- and local-area microstructural analysis, revealing that the etching of germanium, catalyzed by the Au NPs, led to the ANCs growth on the exposed Ge (1 1 1) planes. As a supportive picture, ab-initio calculations rationalized this epitaxial relationship in terms of compressively strained β-phase ANCs. Our process could pave the way to the realization of large-area antimonene layers by a deposition process compatible with the current semiconductor manufacturing technology.

We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic structure of the active sites during 2-propanol oxidation to acetone on the Co3O4 (001) surface in humid conditions. In the gas phase, the O K-edge spectra of 2-propanol and acetone as well that of 2-propoxide considered as reaction intermediate, present no pre-edge peaks. Upon 2-propanol adsorption at the Co site of Co3O4 (001) surface, the O K-edge spectrum presents a distinct peak preceded by a bumb in the pre-edge region, both due to dipole transitions from O 1s to 2p states hybridized with Co 3d empty states. The formation of 2- propoxide leads to two distinct pre-edge peaks due to the increase of 3d empty states. A further increment of these pre-edge peaks is observed when acetone is formed and is rather ascribed to the new contributions of carbon 2p empty states in the transitions occurring in the pre-edge region. The changes observed in the pre-edge peak along the oxidation were correlated to the electronic configuration and hybridization of the cobalt atom directly bonded to alcohol. The variation of electron densities was also monitored for all surface cobalt atoms including the ones on which molecular and dissociated water are adsorbed. The PDOS analysis and crystal field theory showed that adsorption of 2-propanol and molecular water on the surface does not change the oxidation state of +3, while surface cobalt atoms bonded to OH groups have an oxi- dation state of +4. The 3d Loewdin charges analysis shows pronounced cooperative effects between both Co sites during the last oxidation step which corresponds to the decomposition of 2-propoxide to acetone.

BACKGROUND Management of complex thrombosed aneurysms of the middle cerebral artery (MCA) is challenging. Lesions not amenable to endovascular techniques or direct clipping might require a bypass procedure with subsequent aneurysm occlusion. Various bypass techniques followed by surgical or endovascular closure of the aneurysm are available, but an unpredictable extension of the thrombus to the parent vessel and/or to perforator vessels can occur. We present a multidisciplinary technique with the aim to reduce invasiveness and complications. METHODS We present two patients, harboring a thrombosed giant MCA bifurcation aneurysm, who were treated with a minimally invasive three-steps multimodality procedure. In both cases, through a limited exposure of the sylvian fissure, a side-to-side anastomosis between the two M2 branches was performed, followed in the immediate post-op by an endovascular occlusion of the frontal M2 branch, with the aim of transforming a bifurcation aneurysm in a sidewall aneurysm, that was then treated a few days later by flow diverter deployment. RESULTS Both patients had excellent outcomes and were discharged after 7 days without neurological deficits. CONCLUSIONS Treatment of complex thrombosed MCA aneurysms is challenging. Side- to-side M2 anastomosis with the aim of transforming a bifurcation aneurysm in a sidewall aneurysm, suitable to be treated few days later by flow diverter deployment, offers a minimally invasive multimodal approach with the possibility of reducing serious complications.

Truncating the Fourier transform averaged by means of a generalized Hausdorff operator, we approximate functions and the adjoint to that Hausdorff operator of the given function. We find estimates for the rate of approximation in various metrics in terms of the parameter of truncation and the components of the Hausdorff operator. Explicit rates of approximation of functions and comparison with approximate identities are given in the case of continuous functions from the class $\text {Lip }\alpha $ .

We prove that for any convex polytope $\Omega \subset \mathbb{R}^d$ which is centrally symmetric and whose faces of all dimensions are also centrally symmetric, there exists a Riesz basis of exponential functions in the space $L^2(\Omega)$. The result is new in all dimensions $d$ greater than one., Comment: To appear in Journal of the European Mathematical Society (JEMS)

Chalcogens are extremely promising for hyperdoping Si because of their superior electronic properties with respect to group V elements of the periodic table traditionally employed as dopants. Within the framework of plane-wave pseudopotential techniques we computed the formation energy of different types of defects formed by dopants in Se-hyperdoped Si, as a function of the dopant concentration. Moreover, we studied the possibility of tailoring the electronic properties of the system, by tuning the probability that each type of defect can form. In particular, by using supercells exceeding thousands of atoms we characterized the double impurity band (IB) structure of S e S i 3 − V S i complex, formed by a Si vacancy surrounded by three Se, which presents a shallow metallic IB and a deep insulating IB in the Si band gap, thus allowing sub-threshold photon absorption, and suggesting that a significant improvement in the performance of Se-hyperdoped Si as an infrared detector, can be achieved by increasing the population of S e S i 3 − V S i complexes. Our findings relate the range of microscopic sizes in which dopants can diffuse to the population of different types of complexes, revealing the possibility of engineering the critical concentration at which the insulator-to-metal transition occurs by varying the diffusion length of the dopant. These results pave the way for the exploitation of Se-hyperdoped Si as a building block in newly conceived ultra-scaled nano-electronic devices, infra-red detectors and intermediate-band photovoltaic applications.

By first principles simulations we systematically investigate Se hyperdoped silicon by computing, for different types of Se complexes, the formation energy as a function of dopant concentration. We identify the microscopic mechanisms responsible for the dramatic reduction of electrical deactivation defects as the dopant concentration approaches the critical value

We show that if the Gabor system $\{ g(x-t) e^{2\pi i s x}\}$, $t \in T$, $s \in S$, is an orthonormal basis in $L^2(\mathbb{R})$ and if the window function $g$ is compactly supported, then both the time shift set $T$ and the frequency shift set $S$ must be periodic. To prove this we establish a necessary functional tiling type condition for Gabor orthonormal bases which may be of independent interest., Comment: To appear in Mathematische Annalen

Using first-principles density functional theory calculations, combined with a topological analysis, we have investigated the electronic properties of ${\text{Cd}}_{3}{\text{As}}_{2}$ and ${\text{Na}}_{3}\text{Bi}$ Dirac topological semimetals doped with nonmagnetic and magnetic impurities. Our systematic analysis shows that the selective breaking of the inversion, rotational, and time-reversal symmetry, controlled by specific choices of the impurity doping, induces phase transitions from the original Dirac semimetal to a variety of topological phases such as topological insulator, trivial semimetal, nonmagnetic and magnetic Weyl semimetal, and Chern insulator. The Dirac semimetal phase can exist only if the rotational symmetry ${C}_{n}$ with $ng2$ is maintained. One particularly interesting phase emerging in doped ${\text{Cd}}_{3}{\text{As}}_{2}$ is a coexisting Dirac-Weyl phase, which occurs when only inversion symmetry is broken while time-reversal symmetry and rotational symmetry are both preserved. To further characterize the low-energy excitations of this phase, we have complemented our density functional results with a continuum four-band $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ model, which indeed displays nodal points of both Dirac and Weyl types. The coexisting phase appears as a transition point between two topologically distinct Dirac phases but may also survive in a small region of parameter space controlled by external strain.

Hyperdoping Si with chalcogens is a topic of great interest due to the strong sub-bandgap absorption exhibited by the resulting material, which can be exploited to develop broadband room-temperature infrared photodetectors using fully Si-compatible technology. Here, we report on the critical behavior of the impurity-driven insulator-to-metal transition in Te-hyperdoped Si layers fabricated via ion implantation followed by nanosecond pulsed-laser melting. Electrical transport measurements reveal an insulator-to-metal transition, which is also confirmed and understood by density functional theory calculations. We demonstrate that the metallic phase is governed by a power law dependence of the conductivity at temperatures below 25 K, whereas the conductivity in the insulating phase is well described by a variable-range hopping mechanism with a Coulomb gap at temperatures in the range of 2-50 K. These results show that the electron wave-function in the vicinity of the transition is strongly affected by the disorder and the electron-electron interaction., Comment: 19 pages, 6 figures

By plane-wave pseudopotential techniques we simulated structural and electronic properties of novel two-dimensional (2D) materials composed of Si and Ge randomly placed at the lattice sites of a honeycomb structure: 2D-Si1−xGex, and 2D-(H@Si)1−x(Ge@H)x, the corresponding H-passivated alloy. We investigated the formation of a random network of Si and Ge in 2D-honeycomb structure and proved the thermal stability of H-passivated SiGe alloy by computing the formation energy of these 2D-compounds. The 2D-Si1−xGex random alloy is a semi-metal and presents at the Fermi energy a density of states resembling the one produced by the Dirac’s cone of silicene and germanene, suggesting the possibility to induce, in 2D-Si1−xGex Dirac’s cone, a population of high velocity carriers that behaves like massless Dirac fermions. The 2D-(H@Si)1−x(Ge@H)x random alloy is a semiconductor and presents a tunable direct bandgap that doubles by decreasing the concentration from x = 1 to x = 0.25, making this 2D-alloy suitable for opto-electronic applications. The lattice parameter of both 2D-alloys increases linearly with Ge concentration, thus providing a microscopic mechanism to engineer the lattice parameter and/or the electronic properties of 2D-heterostructures based on these 2D-materials. The study of elastic properties of 2D-@Si1−xGex and 2D-(H@Si)1−x(Ge@H)x as a function of x for possible use in flexible electronics and the investigation of magnetic properties of partially H-passivated 2D-(H@Si)1−xGex random alloy for concentration close to x = 0.5 for spintronic applications complete the work.

Exploiting first-principles simulations and x-ray absorption near edge spectroscopy (XANES) in high magnetic fields, we investigated the magnetic properties of thin films of zirconia doped with Fe impurities. In our ${\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{2\ensuremath{-}y}$ samples, grown by atomic layer deposition (ALD), the Fe dopants are uniformly distributed, ranging from diluted ($x\ensuremath{\simeq}2\text{--}3%$) up to high ($x\ensuremath{\simeq}25%$) atomic concentration. By x-ray magnetic circular dichroism (XMCD), we carefully analyzed, for samples having different Fe concentration, the magnetic moments as a function of temperature, in the range from 5 K up to 150 K, studying the best dopant concentration range maximizing the magnetic signal. Surprisingly, the iron magnetic moment measured for diluted concentrations degrades as the concentration of magnetic dopant increases. On the basis of ab initio simulations, we propose that the microscopic mechanisms responsible for the peculiar magnetic properties of this compound can be explained by oxygen-mediated superexchange mechanism between the Fe dopants producing, at high dopant concentration, an antiferromagnetic coupling between two Fe atoms. We identify and discuss the role of O vacancies to control such microscopic mechanisms.

We have computed from first principles the structural, magnetic and optical properties of zig-zag oriented silicene nanoribbons. The minimal width for structurally stable planar structure having zig-zag edges corresponds to a 4-chains ribbon. Its ground state presents reconstructed and spin polarized edges, coupled antiferromagnetically. For this state, and for the corresponding excited state with ferromagnetically coupled edges, we computed the optical absorption spectra within the independent particle approximation, including local field effect corrections, for light polarized in the directions parallel and perpendicular to the ribbon axis. For the “parallel” light polarization the inclusion of local fields effects is limited to a slight reduction of the intensity of the main peak in the infrared region, as well as that of some minor peaks in the visible-ultraviolet structure. Conversely, the computed optical spectrum for light polarized perpendicularly to the ribbon axis shows that the short-width zig-zag nanoribbons are basically transparent in the infrared and visible region, because of the effect of electronic confinement combined with local fields. Keywords: Silicene, Optoelectronic properties, First principles simulations, 2D materials, Optical spectra, Nanoribbons.

Background Arteriovenous malformation surgery is particularly demanding owing to the need to control bleeding of small, deep white matter vessels during and after removal of the nidus; this is probably one of the most critical moments of arteriovenous malformation surgery. The aim of this article is to describe a useful technique based on the use of tweezers to temporarily stop the blood flow followed by coagulation with the thulium laser. Methods Surgery was performed in 20 patients with unruptured cerebral arteriovenous malformations. In each case, the superficial feeder vessels were easily coagulated with nonstick bipolar tips. The finer and deeper feeder vessels were coagulated with use of tweezers and thulium laser. Results All patients were treated successfully. Optimal intraoperative hemostasis was achieved. Conclusions Results were good with no postoperative complications. Our results could encourage a more standardized use of the described technique.

We obtain necessary and sufficient conditions for the uniform convergence of sine integrals ∫0∞g(t)sinξtdt, where g satisfies general monotonicity conditions. In contrast with the previous results on this topic, here we do not assume g≥0.

The halo vest is widely used throughout the world to manage craniovertebral and cervical instabilities. It can be used for postoperative immobilization or as an alternative to surgical fixation.In this paper we present some cases of severe complications from our own practice and review the literature on halo complications.Like any therapeutic manoeuvre, halo placement may be followed by various complications. In the meantime, modern techniques of fixation offer safe and immediate stabilization.The halo vest remains a formidable method for cervical immobilization. However, it should not be used a priori instead of surgery.

We present first-principles calculations of structural, electronic, magnetic, and optical properties of zigzag-oriented silicene nanoribbons, which, being endowed with spin-polarized edge states, are promising candidates as building blocks of future spintronic devices. The minimal width for a structurally stable planar structure having zigzag edges corresponds to a 4-chain ribbon, whose ground state presents antiferromagnetically coupled spin-polarized edges, and a lattice parameter along the nanoribbon axis contracted ($\ensuremath{\sim}5%$) with respect to the bulk value. Starting from the dependence of structural and electronic properties on the ribbon width, we present theoretical predictions for the optical spectra of narrow nanoribbons, in which excitonic effects are relevant due to the confinement in a quasi-one-dimensional structure. Especially for light polarized parallel to the ribbon axis, we find significant differences in the position of optical absorption peaks of ribbons with ferro- or antiferromagnetically coupled edges, showing that optical spectra can be used as a fingerprint of the magnetic coupling of electronic edge states.

Background: The halo vest is widely used throughout the world to manage craniovertebral and cervical instabilities. It can be used for postoperative immobilization or as an alternative to surgical fixation.

We show that the Hankel transform of a general monotone function converges uniformly if and only if the limit function is bounded. To this end, we rely on an Abel–Olivier test for real-valued functions. Analogous results for cosine series are derived as well. We also show that our statements do not hold without the general monotonicity assumption in the case of cosine integrals and series.

N-type doping in Si by shallow impurities, such as P, As and Sb, exhibits an intrinsic limit due to the Fermi-level pinning via defect complexes at high doping concentrations. Here we demonstrate that doping Si with the chalcogen Te by non-equilibrium processing, a deep double donor, can exceed this limit and yield higher electron concentrations. In contrast to shallow impurities, both the interstitial Te fraction decreases with increasing doping concentration and substitutional Te dimers become the dominant configuration as effective donors, leading to a non-saturating carrier concentration as well as to an insulator-to-metal transition. First-principle calculations reveal that the Te dimers possess the lowest formation energy and donate two electrons per dimer to the conduction band. These results provide novel insight into physics of deep impurities and lead to a possible solution for the ultra-high electron concentration needed in today's Si-based nanoelectronics., 26 pages, including the suppl information

Arteriovenous malformations (AVMs) are rare entities and therefore considered the main challenge for a neurosurgeon. Since the publication of the ARUBA study, one of the most popular debate regards the actual surgical indication for unruptured AVMs. Our group recently published a multicenter review of more than 500 cases underlying the important role of surgery. Over the last few decades, the expanding technologies used in the treatment of AVMs have shown an ongoing improvement overcoming some of the existing difficulties and shortcomings. In this paper, we reviewed the present literature to illustrate the main contemporary tools that, in our opinion, are crucial to obtain the best surgical and clinical outcome. Indocyanin green is nowadays considered a gold standard to identify arterial feeders, draining veins, and to detect any eventual residual. The use of non-stick, bipolar, 2-mm blade microclips, and thulium laser allows to obtain a better bleeding control and nidus removal. The development of the intraoperative ultrasound with neuronavigation, angiosonography, and color-Doppler improves the accuracy of AVM resection. Moreover, improvements have been developed with the use of intraoperative micro-Dopplers combined with flow measurements, which consent to verify the gradual reduction of flow through draining veins. The possibility to perform functional preoperative studies and intraoperative monitoring can be considered as an essential point in the decision making in eloquent or near-eloquent AVMs. Furthermore, the hybrid operating room represents the best expression of an excellent neurovascular team where the use of the intraoperative angiography allows neurosurgeons and neurointerventional radiologists to work at the same time in a combined approach to achieve the best surgical removal.

Traumatic injuries of the craniovertebral junction (CVJ) area are common and frequently the outcome of motor vehicle accidents, falls, and diving accidents. To define and characterize CVJ traumatic injuries, some international classifications are currently in use, and they are thought and focused on junction bone fracture. However, recent data point out a major important role of the CVJ ligaments and membranes in traumatic injuries with a secondary function of the osseous structures. Emphasizing the correct role of the ligaments and membranes is extremely important for determining appropriate medical or surgical planning for patients and also to design new CVJ injury classifications. We reviewed every recent major publication on the ligaments and membranes of the CVJ area. We divided the information into sections concerning anatomy, embryology, biomechanics, trauma, and CVJ bone fractures. A role of the ligaments and membranes in the traumatic injuries of the CVJ area has often been recognized; but only recently, with the increase in the knowledge of the anatomic and biomechanical junction area, supported by neuroradiological tools (magnetic resonance imaging) and a more detailed traumatic injuries assessment, has the role of the ligaments and membranes been highlighted. Ligaments and membranes have a pivotal role in each junctional ability and are the key to orienting any medical or surgical indications in this unique area of the spine.

Background Torcular meningiomas involving major dural venous sinuses are rare entities and a great challenge for neurosurgeons. The deep knowledge of the patency of occlusion of the sinuses, the extent of the occlusion and potentially new developing of extra and intracranial collateral venous drainage as compensatory venous channels, are at the base of a correct operative strategy. Case Description A 45-year-old woman presented with persistent headache. Magnetic resonance imaging of the brain and digital subtraction angiography demonstrated a huge torcular meningioma with complete multi-venous sinus occlusion and a wide venous network for brain and tumor drainage. In these rare cases, we have hypothesized the presence of venous drainage shared by the brain and the tumor, which could generate undesirable venous occlusion during operative resection. This could be a cause of the well-known surgical complications, such as brain swelling and hemorrhagic infarction. Conclusions We report our experience with a huge torcular meningioma with multi-venous sinus invasion and a literature review, with a special emphasis on compensatory drainage veins and surgical strategy.

In December of 2016, a Consensus Conference on unruptured AVM treatment, involving 24 members of the three European societies dealing with the treatment of cerebral AVMs (EANS, ESMINT, and EGKS) was held in Milan, Italy. The panel made the following statements and general recommendations: (1) Brain arteriovenous malformation (AVM) is a complex disease associated with potentially severe natural history; (2) The results of a randomized trial (ARUBA) cannot be applied equally for all unruptured brain arteriovenous malformation (uBAVM) and for all treatment modalities; (3) Considering the multiple treatment modalities available, patients with uBAVMs should be evaluated by an interdisciplinary neurovascular team consisting of neurosurgeons, neurointerventionalists, radiosurgeons, and neurologists experienced in the diagnosis and treatment of brain AVM; (4) Balancing the risk of hemorrhage and the associated restrictions of everyday activities related to untreated unruptured AVMs against the risk of treatment, there are sufficient indications to treat unruptured AVMs grade 1 and 2 (Spetzler-Martin); (5) There may be indications for treating patients with higher grades, based on a case-to-case consensus decision of the experienced team; (6) If treatment is indicated, the primary strategy should be defined by the multidisciplinary team prior to the beginning of the treatment and should aim at complete eradication of the uBAVM; (7) After having considered the pros and cons of a randomized trial vs. a registry, the panel proposed a prospective European Multidisciplinary Registry.

Object The goal of this study was to compare long-term results of surgery with the outcomes of conservative treatment in patients with asymptomatic lipomas of the conus medullaris. Methods The parents of 56 consecutive children with a diagnosis of asymptomatic lipoma of the conus medullaris underwent detailed neurosurgical consultation. The pros and cons of both prophylactic surgery and conservative treatment were carefully presented. Both options were offered, and the parents were free to choose the preferred management. A total of 32 children underwent surgical treatment, and 24 were conservatively treated. Afterward, all patients entered the same protocol of serial neurological and urological follow-up at the Centro Spina Bifida. The mean follow-up periods were 9.7 years in the surgical treatment group and 10.4 years in the conservative treatment group. Results Permanent surgical morbidity was 3.1% (1 patient). During follow-up, tethered cord syndrome occurred in 9.7% of the surgically treated patients (3 of 32 patients) and in 29.1% of the conservatively managed children (7 of 24 patients). This difference did not result in statistical significance, but a clear trend in favor of surgery emerged. Young age at surgery and a cord/sac ratio < 50% appeared to be determining factors in the prevention of subsequent tethered cord syndrome. Conclusions The small size of this series does not provide enough statistical evidence that surgical treatment can really improve the natural history of asymptomatic lipomas of the conus medullaris. Nevertheless, surgery appears at least advisable since it reduces by 75% the odds of TCS (p = 0.067), which is quite close to statistical significance.

The localization of the donor electron wave function can be of key importance in various silicon applications, since for example it determines the interactions between neighboring donors. Interestingly, the physical confinement of the electrons in quasi-one-dimensional nanostructures, like silicon nanowires, noticeably affects this property. Using fully ab initio calculations, we show that the delocalization of the donor electron wave function along the axis of a nanowire is much greater in [011] oriented nanowires for phosphorus and selenium donors. We also demonstrate that its value can be controlled by applying a compressive or tensile uniaxial strain. Finally, we discuss the implications of these features from both an experimental and a theoretical point of view. © 2013 American Chemical Society.

Among the novel two-dimensional (2D) materials, silicene and germanene, which are two honeycomb crystal structures composed of a monolayer of Si and Ge, respectively, have attracted the attention of material scientists because they combine the advantages of the new 2D ultimate-scaled electronics with their compatibility with industrial processes presently based on Si and Ge. We envisage pseudomorphic lateral heterostructures based on ribbons of silicene and germanene, which are the 2D analogs of conventional 3D Si/Ge superlattices and quantum wells. In spite of the considerable lattice mismatch ($\ensuremath{\sim}4%$) between free-standing silicene and germanene, our ab initio simulations predict that, considering striped 2D lateral heterostructures made by alternating silicene and germanene ribbons of constant width, the silicene/germanene junction remains pseudomorphic---i.e., it maintains lattice-matched edges---up to critical ribbon widths that can reach some tens of nanometers. Such critical widths are one order of magnitude larger than the critical thickness measured in 3D pseudomorphic Si/Ge heterostructures and the resolution of state-of-the-art lithography, thus enabling the possibility of lithography patterned silicene/germanene junctions. We computed how the strain produced by the pseudomorphic growth modifies the crystal structure and electronic bands of the ribbons, providing a mechanism for band-structure engineering. Our results pave the way for lithography patterned lateral heterostructures that can serve as the building blocks of novel 2D electronics.

BACKGROUND: Intracranial cysts containing cerebrospinal fluid (CSF) may be developmental or acquired. OBJECTIVE: To analyze the results of endoscopic neurosurgery in the management of intracranial CSF cysts. METHODS: In a 7-year period, 64 consecutive patients underwent endoscopic neurosurgery for CSF cysts. Group 1 consisted of 13 patients with acquired cysts; group 2 included 51 patients with developmental cysts. In all cases, the cyst walls were fenestrated through small burr holes with frameless guided operative endoscopes. Follow-up ranged from 1 to 6 years (mean, 3.4 years). RESULTS: There were no mortality and no permanent morbidity, apart from a patient (1.6%) who remained neurologically intact but required ventriculoperitoneal shunting because of intraoperative hemorrhage. The planned fenestrations could be performed in all patients except 2, owing to thick, opaque cyst walls. In group 1, 6 patients fully recovered and remained intact throughout the follow-up, whereas 7 improved but had various degrees of neurological disabilities that were related to their initial diseases. Radiological results were excellent in all cases. In group 2, there were 7 asymptomatic patients who remained unchanged and 44 "symptomatic" patients: 40 (91 %) clinically improved, 4 (9%) remained unchanged, and none worsened. Cyst size decreased in 37 patients (74%) and remained unchanged in 13 (26%). CONCLUSION: In this series, patients of different ages, harboring cysts of various sizes and locations, could be satisfactorily treated with endoscopic neurosurgery.

The possibility of an association between Dandy-Walker malformation and occipital meningocele is well-known. However, just an overall number of about 40 cases have been previously reported. Giant occipital meningocele has been described only in three newborns. Incidence, pathology, clinical presentation, and proper management of this association are still poorly defined.An 8-year-old boy with Dandy-Walker malformation and giant (25 cm in diameter) occipital meningocele is presented. This boy was born without any apparent occipital mass and harbored no other significant malformations including hydrocephalus. On admission, he was neurologically intact and the giant occipital mass presented partially calcified cyst walls. Treatment consisted of the excision of the occipital malformation, cranioplasty, and cysto-peritoneal shunt. Outcome was excellent.To the best of our knowledge, among the few reported patients with Dandy-Walker malformation associated to occipital meningocele, this is the oldest one and the one with the largest occipital meningocele; he is unique with calcified walls of the occipital meningocele and the only one who survived the repair of the giant malformation. In Dandy-Walker malformation, occipital meningocele may develop and grow regardless of hydrocephalus. Giant size may be reached and the cyst may become calcified. Surgical repair may warrant favorable outcome.

The authors investigated the magnetic properties of Fe-doped zirconia, ZrO2:Fe, grown by atomic layer deposition, for different concentrations of Fe dopant, a substitutional impurity to Zr. Their growth recipe allows the deposition of films in which the percentage of Fe, x, ranges from diluted (x ∼ 1–2 at. %) up to high (x ∼ 25 at. %) concentrations. By x-ray magnetic circular dichroism, the authors carefully analyzed the magnetic moments of these dilute magnetic oxides at low temperature (T = 5 K), determining the best dopant range maximizing the magnetic signal. In particular, the authors found that the magnetic signal decreases as the Fe concentration increases. By comparison with ab initio simulations, the authors enlighten the microscopic mechanisms responsible for this peculiar behavior.

ObjectThe authors report on a series of 145 consecutive patients with different types of spine lesions surgically treated via an anterior approach (AA) at the thoracic and lumbar levels during the past 10 years. Indications, techniques, and surgical results are described.MethodsThis series included 92 patients with fractures, 30 with neoplasms, 13 with thoracic disc hernias, and 10 with spinal infections. Based on the lesion to be addressed, the AA was used for lesion excision, corpectomy, vertebral body reconstruction with cages, realignment, and/or plating or screwing. The approach was extracavitary in 55 patients and intracavitary in 90. In 126 patients (86.8%), neural decompression and spine stabilization were achieved via a stand-alone AA (SA-AA), whereas 19 patients (13.1%) were treated using a 2-stage anteroposterior approach. This circumferential approach was reserved for select cases of severe traumatic dislocation, particular types of tumors, or specific anatomical locations. The authors developed a simple neuronavigation-based method of identifying the severely injured patients who were eligible for the SA-AA by evaluating the angle of lateral dislocation.ResultsThere were no deaths and no instances of major surgery-related morbidity. Minor morbidity was almost always transitory and was reported in 13 patients (8.9%). Neurological improvement was reported in 20% of injured patients with a preoperative incomplete lesion. Postoperatively, all patients were able to stand or at least sit without load pain. During the follow-up (mean ± standard deviation 3.8 ± 2.4 years), there were no cases of failure, fracture, dislocation, or bending of the anterior instrumentation, and the rate of pseudarthrosis was 0%.ConclusionThe anterior route provides direct access to most spine diseases and allows optimal neural decompression and the possibility of adequate realignment and strong reconstruction/fixation. Stability of the vertebral column is achieved, resolution of clinical pain is rapid and almost complete, and the rate of surgical complications is very low. The authors assert that the SA-AA offers so many advantages and has such good results that the 2-stage anteroposterior approach can be reserved for a minority of select cases and that the time for using the posterior approach alone is over.

On the basis of ab initio simulations, the formation of an epitaxial phase that has the anatase structure has been proposed as the microscopic mechanism responsible for the preferential orientation of monoclinic HfO2 films on the high-mobility (0 0 1) oriented Ge and GaAs substrates. In fact, the oriented monoclinic structure follows the in-plane axis of the anatase phase as proved by X-ray scattering measurements. The fact that epitaxial HfO2 anatase has no bulk counterpart is explained by our calculations as due to the unfavorable Helmholtz free energy of anatase phase when the condition of epitaxy is released.

Due to the confinement effect, the donor wave functions in nanostructures are highly localized on the defect and can even be deformed by the local geometry of the system. This can have relevant consequences on the hyperfine structure of the defect that can be exploited for advanced electronic applications. In this work we employ ab initio density functional calculations to explore the hyperfine structure of S and Se substitutional defects in silicon and germanium nanowires. We show that, if the tetrahedral symmetry is preserved, the hyperfine contact term is only marginally dependent on the nanowire orientation, while it can undergo drastic changes if the symmetry is lost. In addition, we provide an analysis of the strain dependence of the hyperfine structure for the different orientations of the nanowires.

Due to the confinement effect, the donor wave functions in nanostructures are highly localized on the defect and can even be deformed by the local geometry of the system. This can have relevant consequences on the hyperfine structure of the defect that can be exploited for advanced electronic applications. In this work we employ ab initio density functional calculations to explore the hyperfine structure of S and Se substitutional defects in silicon and germanium nanowires. We show that, if the tetrahedral symmetry is preserved, the hyperfine contact term is only marginally dependent on the nanowire orientation, while it can undergo drastic changes if the symmetry is lost. In addition, we provide an analysis of the strain dependence of the hyperfine structure for the different orientations of the nanowires.

We report on a theoretical study of the electronic, optical and magneto-optical properties of digital ferromagnetic hetero-structures based on $Mn$ $\delta$--doped $GaAs$. We consider different structures corresponding to $Mn$ contents within the range 12-50\% and we study how the system changes as a function of the doping concentration. Our first--principles approach includes the spin-orbit interaction in a fully relativistic pseudopotential scheme and the local fields effect in the description of the optical absorption. We show that $Mn$ $\delta$-doped $GaAs$ shares many properties with the uniformly doped $Ga_{1-x}Mn_xAs$ system, i.e. half-metallicity, similar absorption spectra, and moderate Kerr rotation angles in the visible spectral region., Comment: in press on Physical Review B

We present first-principles calculations of NiMnSb/GaAs(001) junction within the framework of density functional theory (DFT) by using the plane wave pseudopotential method. After optimization of the atomic positions, we have investigated the main electronic and magnetic properties. We extract the band alignments for the majority and the minority spin channels. We found that the half-metallicity, which characterizes the NiMnSb in its bulk and epitaxial phase, is lost at the junction.

The MnAs compound is presently of increasing interest for spintronic applications. By means of accurate first-principles pseudopotential calculations, we investigate its structural, electronic and magnetic properties under different strain/stress conditions, starting from its stable bulk free standingphase which has the hexagonal structure of NiAs. The other structures considered here simulate the pseudomorphic growth on substrates with different orientation and lattice mismatch. The effects of stress on the magnetic properties are linear over a limited range, which is typically accessible to measurements, but sizeable and strongly nonlinear for higher stress, suggesting a magnetic phase transition.

We study the physical properties of MnAs under strain by using accurate first-principles pseudopotential calculations. Our results provide new insight on the physics of strained multilayer that are grown epitaxially on different lattice mismatched substrates and which are presently of interest for spintronic applications. We compute the strain dependence of the structural parameters, electronic bands, density of states and magnetization. In the region of strain/stress that is easily directly accessible to measurements, the effects on these physical quantities are linear. We also address the case of uniaxial stress inducing sizeable and strongly non linear effects on electronic and magnetic properties.

Pressure dependence of lifetime of transverse optical phonons in GaP with different isotopic composition is computed by first principles and compared with available experimental data. The anharmonic mechanisms responsible for the anomalous line shape of the Raman spectra are discussed in term of microscopic quantities. The scattering processes responsible for line width are computed within the plane-waves pseudopotential method in the framework of density functional theory.

We present an experimental study of x-ray absorption near edge structure (XANES) at ${L}_{2,3},\phantom{\rule{0.16em}{0ex}}{M}_{2,3}$, and $K$ edges of, respectively, Fe, Zr, and O in iron-doped zirconia $({\mathrm{ZrO}}_{2}:\mathrm{Fe})$ for different Fe dopant concentrations $x$ (from $x\ensuremath{\sim}6%$ to $x\ensuremath{\sim}25%$ at.) and make the comparison with ab initio simulations at the O $K$-edge. The x-ray magnetic circular dichroism (XMCD) measurements show no evidence of ferromagnetic (FM) order for all the analyzed samples in agreement with our ab initio simulations, which show an antiferromagnetic (AFM) order. We found that substituting Zr with Fe atoms leads to a radical change in the O $K$-edge XANES spectrum, especially in the pre-edge region where a pre-edge peak appears. This pre-edge peak is ascribed to dipole transitions from O $1s$ to O $2p$ states that are hybridized with the unoccupied Fe $3d$ states. Both theoretical and experimental results reveal that the intensity of the pre-edge peak increases with Fe concentration, suggesting the increase of unoccupied Fe $3d$ states. The increase of Fe concentration increases oxygen vacancies as required for charge neutrality and consequently improves AFM ordering. According to our first-principles calculations, the effect of one Fe atom is mostly localized in the first oxygen shell and vanishes as one moves far from it. Thus the increase of the O $K$-pre-edge peak with increasing Fe concentration is due to the increase of percentage of oxygen atoms that are near neighbors to Fe atoms.

The aim of this paper is to discuss the problems of craniocervical instability and craniocervical fusion in infancy. Despite the relative frequency of carniovertebral joint malformations, actual instability is quite rare in infancy. An infant 8 months of age presented with tetraparesis and sleep apnea due to a complex malformation of her craniovertebral joint. An initial attempt at conservative treatment using a rigid neck collar failed, so the patient was surgically managed by the onlay placement of two autologous rib grafts. The rigid collar was maintained for 5 months. Both rib grafts progressively reabsorbed within a few months, while the clinical deficits recurred. Reoperation consisted of occipitocervical interposition of two robust struts of banked cadaveric adult fibula. This time, the skull appeared mature enough to allow immobilization by the halo system. Adequate occipitocervical fusion was eventually achieved, and the patient fully recovered. To the best of our knowledge, there is no other reported case of an infant undergoing craniovertebral fusion using cadaveric adult bone. When screw placement is not considered advisable to manage small infants, appropriate stability may be obtained using struts of robust cadaveric bone. A meticulous carpentry technique with graft interposition under compression and adequate postoperative immobilization remains mandatory.