81 research outputs found
Decoupling of diffusion from structural relaxation and spatial heterogeneity in a supercooled simple liquid
We report a molecular dynamics simulation of a supercooled simple monatomic
glass-forming liquid. It is found that the onset of the supercooled regime
results in formation of distinct domains of slow diffusion which are confined
to the long-lived icosahedrally structured clusters associated with deeper
minima in the energy landscape. As these domains, possessing a low-dimensional
geometry, grow with cooling and percolate below , the critical temperature
of the mode coupling theory, a sharp slowing down of the structural relaxation
relative to diffusion is observed. It is concluded that this latter anomaly
cannot be accounted for by the spatial variation in atomic mobility; instead,
we explain it as a direct result of the configuration-space constraints imposed
by the transient structural correlations. We also conjecture that the observed
tendency for low-dimensional clustering may be regarded as a possible mechanism
of fragility.Comment: To be published in PR
Физико-химические характеристики электрохимически активированного раствора хлорида натрия
НАТРИЯ ХЛОРИДВОДЫ ОЧИСТК
A Structural Model for Octagonal Quasicrystals Derived from Octagonal Symmetry Elements Arising in -Mn Crystallization of a Simple Monatomic Liquid
While performing molecular dynamics simulations of a simple monatomic liquid,
we observed the crystallization of a material displaying octagonal symmetry in
its simulated diffraction pattern. Inspection of the atomic arrangements in the
crystallization product reveals large grains of the beta-Mn structure aligned
along a common 4-fold axis, with 45 degree rotations between neighboring
grains. These 45 degree rotations can be traced to the intercession of a second
crystalline structure fused epitaxially to the beta-Mn domain surfaces, whose
primitive cell has lattice parameters a = b = c = a_{beta-Mn}, alpha = beta =
90 degrees, and gamma = 45 degrees. This secondary phase adopts a structure
which appears to have no known counterpart in the experimental literature, but
can be simply derived from the Cr_3Si and Al_3Zr_4 structure types. We used
these observations as the basis for an atomistic structural model for octagonal
quasicrystals, in which the beta-Mn and the secondary phase structure unit
cells serve as square and rhombic tiles (in projection), respectively. Its
diffraction pattern down the octagonal axis resembles those experimentally
measured. The model is unique in being consistent with high-resolution electron
microscopy images showing square and rhombic units with edge-lengths equal to
that of the beta-Mn unit cell. Energy minimization of this configuration, using
the same pair potential as above, results in an alternative octagonal
quasiperiodic structure with the same tiling but a different atomic decoration
and diffraction pattern.Comment: 25 pages, 10 figure
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ICP Etching of SiC
A number of different plasma chemistries, including NF{sub 3}/O{sub 2}, SF{sub 6}/O{sub 2}, SF{sub 6}/Ar, ICl, IBr, Cl{sub 2}/Ar, BCl{sub 3}/Ar and CH{sub 4}/H{sub 2}/Ar, have been investigated for dry etching of 6H and 3C-SiC in a Inductively Coupled Plasma tool. Rates above 2,000 {angstrom} cm{sup {minus}1} are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl{sub 2}-based etching does not provide high rates, even though the potential etch products (SiCi{sub 4} and CCl{sub 4}) are volatile. Photoresist masks have poor selectivity over SiC in F{sub 2}-based plasmas under normal conditions, and ITO or Ni are preferred
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Low damage, highly anisotropic dry etching of SiC
A parametric study of the etching characteristics of 6H p{sup +} and n{sup +} SiC and thin film SiC{sub 0.5}N{sub 0.5} in Inductively Coupled Plasma NF{sub 3}/O{sub 2} and NF{sub 3}/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF{sub 3} percentage and rf chuck power. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tin-oxide (ITO) masks display relatively good etch selectivity over SiC (maximum of {approximately} 70:1), while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF{sub 3}:O{sub 2} conditions
Imaging practice in low-grade gliomas among European specialized centers and proposal for a minimum core of imaging
Objective: Imaging studies in diffuse low-grade gliomas (DLGG) vary across centers. In order to establish a minimal core of imaging necessary for further investigations and clinical trials in the field of DLGG, we aimed to establish the status quo within specialized European centers. Methods: An online survey composed of 46 items was sent out to members of the European Low-Grade Glioma Network, the European Association of Neurosurgical Societies, the German Society of Neurosurgery and the Austrian Society of Neurosurgery. Results: A total of 128 fully completed surveys were received and analyzed. Most centers (n=96, 75%) were academic and half of the centers (n=64, 50%) adhered to a dedicated treatment program for DLGG. There were national differences regarding the sequences enclosed in MRI imaging and use of PET, however most included T1 (without and with contrast, 100%), T2 (100%) and TIRM or FLAIR (20, 98%). DWI is performed by 80% of centers and 61% of centers regularly performed PWI.ConclusionA minimal core of imaging composed of T1 (w/wo contrast), T2, TIRM/FLAIR, PWI and DWI could be identified. All morphologic images should be obtained in a slice thickness of 3mm. No common standard could be obtained regarding advanced MRI protocols and PET. Importance of the study: We believe that our study makes a significant contribution to the literature because we were able to determine similarities in numerous aspects of LGG imaging. Using the proposed minimal core of imaging in clinical routine will facilitate future cooperative studies
Imaging practice in low-grade gliomas among European specialized centers and proposal for a minimum core of imaging.
OBJECTIVE: Imaging studies in diffuse low-grade gliomas (DLGG) vary across centers. In order to establish a minimal core of imaging necessary for further investigations and clinical trials in the field of DLGG, we aimed to establish the status quo within specialized European centers. METHODS: An online survey composed of 46 items was sent out to members of the European Low-Grade Glioma Network, the European Association of Neurosurgical Societies, the German Society of Neurosurgery and the Austrian Society of Neurosurgery. RESULTS: A total of 128 fully completed surveys were received and analyzed. Most centers (n = 96, 75%) were academic and half of the centers (n = 64, 50%) adhered to a dedicated treatment program for DLGG. There were national differences regarding the sequences enclosed in MRI imaging and use of PET, however most included T1 (without and with contrast, 100%), T2 (100%) and TIRM or FLAIR (20, 98%). DWI is performed by 80% of centers and 61% of centers regularly performed PWI. CONCLUSION: A minimal core of imaging composed of T1 (w/wo contrast), T2, TIRM/FLAIR, PWI and DWI could be identified. All morphologic images should be obtained in a slice thickness of ≤ 3 mm. No common standard could be obtained regarding advanced MRI protocols and PET. IMPORTANCE OF THE STUDY: We believe that our study makes a significant contribution to the literature because we were able to determine similarities in numerous aspects of LGG imaging. Using the proposed "minimal core of imaging" in clinical routine will facilitate future cooperative studies
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