New structural motif of 18 valence electron molecules with a planar tetracoordinate heavier group 14 center: Unique stabilization effect of a π-type skeleton

2017 ◽  
Vol 117 (22) ◽  
pp. e25436 ◽  
Author(s):  
Shuang Yu ◽  
Yi-Hong Ding
Author(s):  
R. H. Duff

A material irradiated with electrons emits x-rays having energies characteristic of the elements present. Chemical combination between elements results in a small shift of the peak energies of these characteristic x-rays because chemical bonds between different elements have different energies. The energy differences of the characteristic x-rays resulting from valence electron transitions can be used to identify the chemical species present and to obtain information about the chemical bond itself. Although these peak-energy shifts have been well known for a number of years, their use for chemical-species identification in small volumes of material was not realized until the development of the electron microprobe.


Author(s):  
Stuart A. Maloy

MoSi2 has recently been investigated as a potential material for high temperature structural applications. It has excellent oxidation resistance up to 1700°C, a high melting temperature, 2030°C, and a brittle-to-ductile transition temperature at 900-1000°C. WSi2 is isomorphous with MoSi2 and has a body-centered tetragonal unit cell of the space group 14/mmm. The lattice parameters are a=3.20 Å and c=7.84 Å for MoSi2 and a=3.21 Å and c=7.88 Å for WSi2. Therefore, WSi2 was added to MoSi2 to improve its strength via solid solution hardening. The purpose of this study was to investigate the slip systems in polycrystalline MoSi2/WSi2 alloys.


Author(s):  
A. Howie ◽  
D.W. McComb

The bulk loss function Im(-l/ε (ω)), a well established tool for the interpretation of valence loss spectra, is being progressively adapted to the wide variety of inhomogeneous samples of interest to the electron microscopist. Proportionality between n, the local valence electron density, and ε-1 (Sellmeyer's equation) has sometimes been assumed but may not be valid even in homogeneous samples. Figs. 1 and 2 show the experimentally measured bulk loss functions for three pure silicates of different specific gravity ρ - quartz (ρ = 2.66), coesite (ρ = 2.93) and a zeolite (ρ = 1.79). Clearly, despite the substantial differences in density, the shift of the prominent loss peak is very small and far less than that predicted by scaling e for quartz with Sellmeyer's equation or even the somewhat smaller shift given by the Clausius-Mossotti (CM) relation which assumes proportionality between n (or ρ in this case) and (ε - 1)/(ε + 2). Both theories overestimate the rise in the peak height for coesite and underestimate the increase at high energies.


Author(s):  
J. Liu ◽  
J. M. Cowley

The low energy loss region of a EELS spectrum carries information about the valence electron excitation processes (e.g., collective excitations for free electron like materials and interband transitions for insulators). The relative intensities and the positions of the interband transition energy loss peaks observed in EELS spectra are determined by the joint density of states (DOS) of the initial and final states of the excitation processes. Thus it is expected that EELS in reflection mode could yield information about the perturbation of the DOS of the conduction and valence bands of the bulk crystals caused by the termination of the three dimensional periodicity at the crystal surfaces. The experiments were performed in a Philipps 400T transmission electron microscope operated at 120 kV. The reflection EELS spectra were obtained by a Gatan 607 EELS spectrometer together with a Tracor data acquisition system and the resolution of the spectrometer was about 0.8 eV. All the reflection spectra are obtained from the specular reflection spots satisfying surface resonance conditions.


2020 ◽  
Vol 26 (1) ◽  
pp. 31-36
Author(s):  
Md Zakaria Sarkar ◽  
AHM Ferdows Nur ◽  
Utpal Kumar Dutta ◽  
Muhammad Rafiqul Islam ◽  
Debabrota Roy ◽  
...  

Objective: The aim of this study was to evaluate hearing outcome after stapedotomy in patients with Otosclerosis. Methods: This cross sectional study was carried out from July 2017 to January 2019 in National Institute of ENT, Unit V. About 22 patients with Otosclerosis were included in this study. Diagnosis of Otosclerosis was based on the history, medical status with Otoscopy, Tuning fork tests and Audiometric tests. We compiled data on the pre and post operative air-bone gap (ABG) at 0.5, 1, 2 KHZ. The ABG was Calculated using AC and BC thresholds on the same audiogram. Post operative hearing gain was then Calculated from the ABG before the operation minus the ABG of the last follow up examination Results: In this study most of the cases were age group 14-30 years (72.7%), female (54.5%). Most common symptoms was progressive hearing loss, tinnitus (77.8%).The average preoperative hearing loss in this study was (AC) was 48.31±7.68. The average post opt. hearing (AC) at follow up was 28.95±10.30 with an average hearing gain of 15.40±8.53 dB which was significant. The average pre-operative ABG was 28.99 dB ± 8.10. The average post opt. ABG was analyzed at 1 follow up showed ABG 13.18±8.09 dB which was found to be significant. Conclusion: Stapedotomy is an effective surgical procedure for the treatment of otosclerosis which leads to improvement in patient’s quality of life. A favorable hearing outcome can be obtained by the combination of experienced hands with minimal surgical trauma and appropriate surgical technique. Bangladesh J Otorhinolaryngol; April 2020; 26(1): 31-36


2015 ◽  
Vol 11 (3) ◽  
pp. 3224-3228
Author(s):  
Tarek El-Ashram

In this paper we derived a new condition of formation and stability of all crystalline systems and we checked its validity andit is found to be in a good agreement with experimental data. This condition is derived directly from the quantum conditionson the free electron Fermi gas inside the crystal. The new condition relates both the volume of Fermi sphere VF andvolume of Brillouin zone VB by the valence electron concentration VEC as ;𝑽𝑭𝑽𝑩= 𝒏𝑽𝑬𝑪𝟐for all crystalline systems (wheren is the number of atoms per lattice point).


Author(s):  
Olivier Charles Gagné ◽  
Frank Christopher Hawthorne

Bond-length distributions are examined for three configurations of the H+ ion, sixteen configurations of the group 14-16 non-metal ions and seven configurations of the group 17 ions bonded to oxygen. Lone-pair stereoactivity for ions bonded to O<sup>2-</sup> is discussed, as well as the polymerization of the PO<sub>4</sub> group.


2020 ◽  
Author(s):  
Nidhi Gour ◽  
Bharti Koshti

Aggregation of amyloid beeta 1-42 (Aβ<sub>42</sub>) peptide causes the formation of clustered deposits knows as amyloid plaques in the brain which leads to neuronal dysfunction and memory loss and associated with many neurological disorders including Alzheimer’s and Parkinson’s. Aβ<sub>42</sub> has core structural motif with phenylalanine at the 19 and 20 positions. The diphenylalanine (FF) residue plays a crucial role in the formation of amyloid fibers and serves as model peptide for studying Aβ<sub>42 </sub>aggregation. FF self-assembles to well-ordered tubular morphology via aromatic pi-pi stackings. Our studies, suggest that the aromatic rings present in the anti-amyloidogenic compounds may interact with the pi-pi stacking interactions present in the FF. Even the compounds which do not have aromatic rings, like cyclodextrin and cucurbituril show anti-amyloid property due to the binding of aromatic ring inside the guest cavity. Hence, our studies also suggest that compounds which may have a functional moiety capable of interacting with the aromatic stacking interactions might be tested for their anti-amyloidogenic properties. Further, in this manuscript, we have proposed two novel nanoparticle based assays for the rapid screening of amyloid inhibitors. In the first assay, interaction between biotin-tagged FF peptide and the streptavidin labelled gold nanoparticles (s-AuNPs) were used. In another assay, thiol-Au interactions were used to develop an assay for detection of amyloid inhibitors. It is envisaged that the proposed analytical method will provide a simple, facile and cost effective technique for the screening of amyloid inhibitors and may be of immense practical implications to find the therapeutic remedies for the diseases associated with the protein aggregation.


2019 ◽  
Author(s):  
Hassan Harb ◽  
Lee Thompson ◽  
Hrant Hratchian

Lanthanide hydroxides are key species in a variety of catalytic processes and in the preparation of corresponding oxides. This work explores the fundamental structure and bonding of the simplest lanthanide hydroxide, LnOH (Ln=La-Lu), using density functional theory calculations. Interestingly, the calculations predict that all structures of this series will be linear. Furthermore, these results indicate a valence electron configuration featuring an occupied sigma orbital and two occupied pi orbitals for all LnOH compounds, suggesting that the lanthanide-hydroxide bond is best characterized as a covalent triple bond.


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