57 research outputs found
Low-Temperature Expansion for a First Order Surface Transition
The question concerning the possibility of a first order surface transition
in a semi--infinite Blume--Capel model is addressed by means of low temperature
expansions. It is found that such a transition can exist, according to mean
field and cluster variation approximations, and contrarily to renormalization
group results.Comment: 9 pages (plain TeX) + 1 figure (PostScript, appended),
POLFIS-TH.03/9
Reconstructing the somatotopic organization of the corticospinal tract remains a challenge for modern tractography methods
The corticospinal tract (CST) is a critically important white matter fiber
tract in the human brain that enables control of voluntary movements of the
body. Diffusion MRI tractography is the only method that enables the study of
the anatomy and variability of the CST pathway in human health. In this work,
we explored the performance of six widely used tractography methods for
reconstructing the CST and its somatotopic organization. We perform experiments
using diffusion MRI data from the Human Connectome Project. Four quantitative
measurements including reconstruction rate, the WM-GM interface coverage,
anatomical distribution of streamlines, and correlation with cortical volumes
to assess the advantages and limitations of each method. Overall, we conclude
that while current tractography methods have made progress toward the
well-known challenge of improving the reconstruction of the lateral projections
of the CST, the overall problem of performing a comprehensive CST
reconstruction, including clinically important projections in the lateral (hand
and face area) and medial portions (leg area), remains an important challenge
for diffusion MRI tractography.Comment: 41 pages, 19 figure
Pressure Effects and Large Polarons in Layered MgB_2 Superconductor
We consider the dependence of the MgB_2 superconducting critical temperature
on the pressure. Our model exploits the influence of the large polarons on the
band structure of the layered MgB_2 superconductor. Namely, the hole
Pekar-Froehlich polarons form quasi two-dimensional potential wells in the
boron plane which shift the positions of the sigma- and pi-bands. This energy
shift depends on the pressure and the Cooper pairing of the correlated
sigma-electrons happens inside polaron wells. The results obtained are as
follows: dT_c/dp = -\alpha (5.2 \pm 0.9) K/GPa or dT_c/dp = -\alpha (6.9\pm
1.1) K/GPa for a different choice of the Grueneisen parameter. Being compared
with known experimental data they give us a resonable interval for the value of
the Froehlich electron-phonon coupling constant: \alpha = 0.15 - 0.45.Comment: 6 pages, 1 fig, LaTeX, subm. to Phys. Rev.
Microsurgery can cure most intracranial dural arteriovenous fistulae of the sinus and non-sinus type
There is consensus that intracranial dural arteriovenous fistulae (dAVF) with direct (non-sinus-type) or indirect (sinus-type) retrograde filling of a leptomeningeal vein should be treated due to the high risk of neurological deficits and hemorrhage. No consensus exists on treatment modality (surgery and/or embolization) and, if surgery is performed, on the best surgical strategy. This series aims to evaluate the role of surgery in the management of aggressive dAVFs. Forty-two patients underwent surgery. Opening and packing the sinus with thrombogenic material was performed in 9 of the 12 sinus-type dAVFs. In two sinus-type fistulae of the cavernous sinus and 1 of the torcular, microsurgery was used as prerequisite for subsequent embolization by providing access to the sinus. In the 30 non-sinus-type dAVFs, surgery consisted of interruption of the draining vein at the intradural entry point. In 41 patients undergoing 43 operations, elimination of the dAVF was achieved (97.6%). In one case, a minimal venous drainage persisted after surgery. The transient surgical morbidity was 11.9% (n = 5) and the permanent surgical morbidity 7.1% (n = 3). Our surgical strategy was to focus on the arterialized leptomeningeal vein in the non-sinus-type and on the arterialized sinus segment in the sinus-type dAVFs allowing us to obliterate all but one dAVF with a low morbidity rate. We therefore propose that microsurgery should be considered early in the treatment of both types of aggressive dAVFs. In selected cases of cavernous sinus dAVFs, the role of microsurgery is reduced to that of an adjunct to endovascular therapy
Intermediate-coupling exciton in a quantum well
The interaction expression of the surface-optical phonons with an electron (a hole) in a slab is extended to the case of a quantum well and the Hamiltonian H of the exciton-phonon system allowing for the Gabovish image potential is obtained for the first time. A double-time unitary transformation to the Hamiltonian H is carried out to obtain the Hamiltonian Hex of the exciton in a quantum well, and the motion of the exciton in the z direction is discussed in detail. The result obtained is suitable not only for a weak-coupling exciton system but also for an intermediate-coupling exciton system
Effect of electric field on chemical bonds of carbon-doped silicon oxide as evidenced by in situ Fourier transform infrared spectroscopy
10.1116/1.1865114Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures232433-436JVTB
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