Heat transfer in rough nanofilms and nanowires using full band ab initio Monte Carlo simulation.

The Boltzmann transport equation is one of the most relevant frameworks to study the heat transport at the nanoscale, beyond the diffusive regime and up to the micrometer-scale. In the general case of 3D devices, the particle Monte Carlo approach of phonon transport is particularly powerful and convenient, and requires reasonable computational resources. In this work, we propose an original and versatile particle Monte Carlo approach parametrized by using ab initio data. Both the phonon dispersion and the phonon-phonon scattering rates have been computed by DFT calculation in the entire 3D Brillouin zone. To treat the phonon transport at rough interfaces, a combination of specular and diffuse reflections has been implemented in phase space. Thermal transport has been investigated in nanowires and thin films made of cubic and hexagonal Silicon, including edge roughness, in terms of effective thermal conductivity, phonon band contributions and heat flux orientation. It is shown that the effective thermal conductivity in quasi-ballistic regime obtained from our Monte Carlo simulation cannot be accurately fitted by simple semi-analytical Matthiessen-like models and that spectral approaches are mandatory to get good results. Our full band approach shows that some phonon branches exhibiting a negative group velocity in some parts of the Brillouin zone may contribute negatively to the total thermal flux. Besides, the thermal flux clearly appears to be oriented along directions of high density of states. The resulting anisotropy of the heat flux is discussed together with the influence of rough interfaces.

[Reversible posterior leukoencephalopathy syndrome in a patient presenting granulomatosis with polyangiitis]. / Syndrome d'encéphalopathie postérieure réversible au cours d'une granulomatose avec polyangéite.

BACKGROUND: Reversible posterior leukoencephalopathy syndrome (RPLS) is characterised by clinical neurological features of sudden onset and brain MRI findings such as T2/Flair white matter hyperintensities. RPLS can occur in autoimmune diseases, and rarely in systemic vasculitis. We report a case of RPLS in a woman presenting granulomatosis with polyangiitis (Wegener's granulomatosis). PATIENTS AND METHODS: A 22-year-old female patient was treated with methylprednisolone pulses for granulomatosis with polyangiitis and neurological impairment. A few hours after the second pulse, the patient had seizures, blindness and confusion associated with high blood pressure and acute renal failure. MRI revealed a high-intensity area on T2-Flair weighted images of the occipital-temporal lobes. The patient was treated with antiepileptic and antihypertensive medications, oral steroids and cyclophosphamide; the clinical and radiological findings proved reversible over the ensuing days. DISCUSSION: The occurrence of RPLS in systemic vasculitis is rare. Six cases of RPLS associated with granulomatosis and polyangiitis have been reported. It appears important to screen for high blood pressure in patients recently treated with corticosteroids for vasculitis as this condition may represent a precipitating factor for RPLS.

Understanding the insulating nature of alkali-metal/Si(111):B interfaces.

We have recently revisited the phase diagram of alkali-metal/Si(111):B semiconducting interfaces previously suggested as the possible realization of a Mott-Hubbard insulator on a triangular lattice. The insulating character of the 2√[3] × 2√[3]R30 surface reconstruction observed at the saturation coverage, i.e. 0.5 ML, has been shown to find its origin in a giant alkali-metal-induced vertical distortion. Low energy electron diffraction, photoemission spectroscopy and scanning tunneling microscopy and spectroscopy experiments coupled with linear augmented plane-wave density functional theory calculations allow a full understanding of the k-resolved band structure, explaining both the inhomogeneous charge transfers into an Si-B hybridized surface state and the opening of a band gap larger than 1 eV. Moreover, √[3] × âˆš[3]R30, 3 × 3 and 2√[3] × 2√[3]R30 surface reconstructions observed as a function of coverage may reveal a filling-controlled transition from a half-filled correlated magnetic material to a strongly distorted band insulator at saturation.

Giant alkali-metal-induced lattice relaxation as the driving force of the insulating phase of alkali-metal/Si(111):B.

Ab initio density-functional theory calculations, photoemission spectroscopy (PES), scanning tunneling microscopy, and spectroscopy (STM, STS) have been used to solve the 2sqrt[3]×2sqrt[3]R30 surface reconstruction observed previously by LEED on 0.5 ML K/Si:B. A large K-induced vertical lattice relaxation occurring only for 3/4 of Si adatoms is shown to quantitatively explain both the chemical shift of 1.14 eV and the ratio 1/3 measured on the two distinct B 1s core levels. A gap is observed between valence and conduction surface bands by ARPES and STS which is shown to have mainly a Si-B character. Finally, the calculated STM images agree with our experimental results. This work solves the controversy about the origin of the insulating ground state of alkali-metal/Si(111):B semiconducting interfaces which were believed previously to be related to many-body effects.

Nonlocal activation of a bistable atom through a surface state charge-transfer process on Si(100)-(2×1):H.

The reversible hopping of a bistable atom on the Si(100)-(2×1):H surface is activated nonlocally by hole injection into Si-Si bond surface states with a low temperature (5 K) scanning tunneling microscope. In the contact region, at short distances (<1.5 nm) between the hole injection site and the bistable atom, the hopping yield of the bistable atom exhibits remarkable variations as a function of the hole injection site. It is explained by the density of state distribution along the silicon bond network that shows charge-transfer pathways between the injection sites and the bistable atom.

Ankylosing spondylitis: a family study.

Of the first degree relatives of B27 positive spondylitis probands, 10.2% demonstrated an associated disease, i.e., ankylosing spondylitis, Reiter's syndrome, peripheral arthritis, or acute anterior uveitis; all were B27 positive. Eighteen, i.e., only 13.7% of the B27 positive subjects had sacroiliitis; 4 were asymptomatic. We would therefore caution against the previous over-estimation of disease prevalence in "randomly selected" HLA-B27 positive individuals. None of the B27 negative relatives had any uveitis or spondyloarthropathy.

The pattern of facial growth before and during puberty, as shown by French-Canadian girls.

The results are reported for an analysis of longitudinal sequences of lateral head X-rays of 50 Montreal girls, taken annually between the ages of 6 and 15 years. Mean size changes for distances within the cranial base, the maxilla and the mandible, as well as those outlining the facial polygon, are displayed on a common proportional scale based on mean sizes at 15 years old. Mean growth velocities are displayed on both a chronological age scale and on one relative to the individual age of peak growth velocity in stature. A distinct facial pattern of growth is established, In terms of the proportion of final size achieved during childhood, it is below the cranial pattern, but above the general skeletal one. This facial pattern shows a pubertal peak in growth, but one quantitatively less important than that for stature. The timing of the two peaks is closely aligned, although the evidence favours a slightly later development for the face. The mandibular ramus provided the sole exception to this common facial pattern, though some questions on maxillary growth remain open.