The valence bands in two-dimensional graphite

1955 ◽  
Vol 227 (1170) ◽  
pp. 330-349 ◽  
Keyword(s):  
Normal Structure ◽  
Theoretical Treatment ◽  
Two Dimensional ◽  
Linear Combinations ◽  
X Ray ◽  
Atomic Orbitals ◽  
Idempotent Operators ◽  
Valence Bands ◽  
The One

A group-theoretical treatment of the spatial symmetry of two-dimensional graphite leads to a classification of the one-electron eigenstates. The method of idempotent operators is used to derive Bloch orbitals for the crystal valence bands as linear combinations of the atomic orbitals 2 p x , 2 p y and 2 s . The functions 2 p z form the conduction band. The energy of the electrons in such orbitals is estimated in terms of four overlap integrals between nearest neighbour atoms, and four corresponding Hamiltonian integrals. The deduced band structure is not sensitive to the precise values of these integrals, and cannot be changed materially by the inclusion of further neighbours. The states form three touching bands, all fully occupied by electrons in the normal structure. The large band width of some 10 eV affects previous discussions of soft X-ray experiments.

A one-dimensional cobalt(II) coordination polymer based on 2,4′-oxydibenzoic acid: poly[[[diaquabis[2-(4-carboxyphenoxy)benzoato-κO1]cobalt(II)]-μ-4,4′-bipyridine-κ2N:N′] dihydrate]

2014 ◽  
Vol 70 (7) ◽  
pp. 654-658 ◽  
Author(s):  
Long Tang ◽  
Feng Fu ◽  
Ji-Jiang Wang ◽  
Qi-Rui Liu ◽  
Hang-Hang Zhao
Keyword(s):  
Coordination Polymer ◽  
Hydrothermal Condition ◽  
Dimensional Chain ◽  
Supramolecular Architecture ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
One Dimensional ◽  
X Ray ◽  
The One ◽  
Two Sides

The reaction of CoSO4with 2,4-oxydibenzoic acid (H2oba) and 4,4′-bipyridine (bipy) under hydrothermal condition yielded a new one-dimensional cobalt(II) coordination polymer, {[Co(C14H9O5)2(C10H8N2)(H2O)2]·2H2O}n, which was characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, magnetic properties and single-crystal X-ray diffraction. The CoIIions are connected by bipy ligands into infinite one-dimensional chains. The Hoba−ligands extend out from the two sides of the one-dimensional chain. O—H...O hydrogen bonding extends these chains into a two-dimensional supramolecular architecture.

A Study on the Application of Learning Vector Quantization Neural Network in Pattern Classification

2014 ◽  
Vol 525 ◽  
pp. 657-660 ◽  
Author(s):  
Shuo Ding ◽  
Xiao Heng Chang ◽  
Qing Hui Wu
Keyword(s):  
Neural Network ◽  
Pattern Classification ◽  
Vector Quantization ◽  
Bp Neural Network ◽  
Back Propagation ◽  
Learning Vector Quantization ◽  
Classification Method ◽  
Two Dimensional ◽  
The One

Standard back propagation (BP) neural network has disadvantages such as slow convergence speed, local minimum and difficulty in definition of network structure. In this paper, an learning vector quantization (LVQ) neural network classifier is established, then it is applied in pattern classification of two-dimensional vectors on a plane. To test its classification ability, the classification results of LVQ neural network and BP neural network are compared with each other. The simulation result shows that compared with classification method based on BP neural network, the one based on LVQ neural network has a shorter learning time. Besides, its requirements for learning samples and the number of competing layers are also lower. Therefore it is an effective classification method which is powerful in classification of two-dimensional vectors on a plane.

Effective aperture of X-ray compound refractive lenses

2017 ◽  
Vol 24 (3) ◽  
pp. 609-614 ◽  
Author(s):  
V. G. Kohn
Keyword(s):  
Integral Intensity ◽  
Two Dimensional ◽  
One Dimensional ◽  
X Ray ◽  
The Real ◽  
A Value ◽  
Effective Aperture ◽  
The One ◽  
Definition Of ◽  
Focusing Properties

A new definition of the effective aperture of the X-ray compound refractive lens (CRL) is proposed. Both linear (one-dimensional) and circular (two-dimensional) CRLs are considered. It is shown that for a strongly absorbing CRL the real aperture does not influence the focusing properties and the effective aperture is determined by absorption. However, there are three ways to determine the effective aperture in terms of transparent CRLs. In the papers by Kohn [(2002). JETP Lett. 76, 600–603; (2003). J. Exp. Theor. Phys. 97, 204–215; (2009). J. Surface Investig. 3, 358–364; (2012). J. Synchrotron Rad. 19, 84–92; Kohn et al. (2003). Opt. Commun. 216, 247–260; (2003). J. Phys. IV Fr, 104, 217–220], the FWHM of the X-ray beam intensity just behind the CRL was used. In the papers by Lengeler et al. [(1999). J. Synchrotron Rad. 6, 1153–1167; (1998). J. Appl. Phys. 84, 5855–5861], the maximum intensity value at the focus was used. Numerically, these two definitions differ by 50%. The new definition is based on the integral intensity of the beam behind the CRL over the real aperture. The integral intensity is the most physical value and is independent of distance. The new definition gives a value that is greater than that of the Kohn definition by 6% and less than that of the Lengeler definition by 41%. A new approximation for the aperture function of a two-dimensional CRL is proposed which allows one to calculate the two-dimensional CRL through the one-dimensional CRL and to obtain an analytical solution for a complex system of many CRLs.

scholarly journals A Review of the Classification of Opal with Reference to Recent New Localities

Minerals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 299 ◽  
Author(s):  
Neville J. Curtis ◽  
Jason R. Gascooke ◽  
Martin R. Johnston ◽  
Allan Pring
Keyword(s):  
Resonance Spectroscopy ◽  
X Ray Diffraction ◽  
Xrd Pattern ◽  
X Ray ◽  
Additional Information ◽  
Acceptable Alternative ◽  
Infra Red ◽  
New Localities ◽  
The One

Our examination of over 230 worldwide opal samples shows that X-ray diffraction (XRD) remains the best primary method for delineation and classification of opal-A, opal-CT and opal-C, though we found that mid-range infra-red spectroscopy provides an acceptable alternative. Raman, infra-red and nuclear magnetic resonance spectroscopy may also provide additional information to assist in classification and provenance. The corpus of results indicated that the opal-CT group covers a range of structural states and will benefit from further multi-technique analysis. At the one end are the opal-CTs that provide a simple XRD pattern (“simple” opal-CT) that includes Ethiopian play-of-colour samples, which are not opal-A. At the other end of the range are those opal-CTs that give a complex XRD pattern (“complex” opal-CT). The majority of opal-CT samples fall at this end of the range, though some show play-of-colour. Raman spectra provide some correlation. Specimens from new opal finds were examined. Those from Ethiopia, Kazakhstan, Madagascar, Peru, Tanzania and Turkey all proved to be opal-CT. Of the three specimens examined from Indonesian localities, one proved to be opal-A, while a second sample and the play-of-colour opal from West Java was a “simple” Opal-CT. Evidence for two transitional types having characteristics of opal-A and opal-CT, and “simple” opal-CT and opal-C are presented.

Theoretical and Experimental Ti-K NEXAFS of Various Ti-Oxides

2005 ◽  
Vol 475-479 ◽  
pp. 3119-3122
Author(s):  
Teruyasu Mizoguchi ◽  
Masaki Sakurai ◽  
Atsutomo Nakamura ◽  
Takeo Sasaki ◽  
Yukio Sato ◽  
...  
Keyword(s):  
First Principles ◽  
Main Peak ◽  
Theoretical Studies ◽  
Linear Combinations ◽  
Edge Structure ◽  
X Ray ◽  
Atomic Orbitals ◽  
Ti Oxides ◽  
X Ray Absorption ◽  
Experimental And Theoretical Studies

Near-edge structure of X-ray absorption spectrum (NEXAFS) of various Ti-oxides were investigated by combined with first principles orthogonalized linear combinations of atomic orbitals (OLCAO) method. From experimental and theoretical studies on the NEXAFS of the tetravalent and trivalent Ti-oxides, including rutile, anatase, brookite, columbite, and Ti2O3, it was found that the valence state of Ti can be identified by regarding the positions of the spectral onset and the shoulder in the main-peak of Ti-K NEXAFS.

scholarly journals Contributions to Developments of Photoelectron Spectroscopy and X-ray Absorption Fine Structure Applied to Materials Studies

2021 ◽  
Vol 31 (2) ◽  
pp. 113
Author(s):  
Nguyen Van Hung
Keyword(s):  
Fine Structure ◽  
Photoelectron Spectroscopy ◽  
Melting Curve ◽  
Debye Model ◽  
Near Neighbor ◽  
X Ray ◽  
Absorption Fine ◽  
Valence Bands ◽  
The One ◽  
X Ray Absorption

This work reviews the contributions of author to the developments and applications of Photoelectron Spectroscopy (PES) and X-ray Absorption Fine Structure (XAFS) to materials studies. Focusing on Angle resolved PES (ARPES) the energy distribution is discussed for angle-resolved photoemission from valence bands of single crystals. The important influence of the spectrometer angle of acceptance on the results of X-ray PES (XPS) is investigated in detail. The Plane Density of States (PDOS) is introduced as a new property of the electronic structure. Most meaningful contributions to XAFS consist of the developments of multiple-scattering and anharmonic XAFS theory. Anharmonic correlated Einstein model (ACEM) and anharmonic correlated Debye model (ACDM) have been derived to obtain Debye-Waller factors (DWF) presented in terms of cumulant expansion which describe the thermodynamic properties and anharmonic effects in XAFS of substances contributing to their accurate structural determination. The anharmonic effective potential (AEP) procedure and first shell near neighbor contributions approach have developed to include many-body effects in the one-dimensional model by a simple measure. Based on DWFs a thermodynamic lattice theory has been derived for studying melting curve and eutectic points of binary alloys. Several applications of the derived methods are performed and the good agreement of the calculated results with experiment illustrate the advantages and efficiencies of the achieved developments.

Tubulin structure at intermediate resolution

1995 ◽  
Vol 53 ◽  
pp. 852-853
Author(s):  
K. H. Downing ◽  
S. G. Wolf ◽  
E. Nogales
Keyword(s):  
High Resolution ◽  
Structural Data ◽  
Therapeutic Drug ◽  
Zinc Ions ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Negative Stain ◽  
Functional Mechanisms ◽  
Tubulin Structure

Microtubules are involved in a host of critical cell activities, many of which involve transport of organelles through the cell. Different sets of microtubules appear to form during the cell cycle for different functions. Knowledge of the structure of tubulin will be necessary in order to understand the various functional mechanisms of microtubule assemble, disassembly, and interaction with other molecules, but tubulin has so far resisted crystallization for x-ray diffraction studies. Fortuitously, in the presence of zinc ions, tubulin also forms two-dimensional, crystalline sheets that are ideally suited for study by electron microscopy. We have refined procedures for forming the sheets and preparing them for EM, and have been able to obtain high-resolution structural data that sheds light on the formation and stabilization of microtubules, and even the interaction with a therapeutic drug.Tubulin sheets had been extensively studied in negative stain, demonstrating that the same protofilament structure was formed in the sheets and microtubules. For high resolution studies, we have found that the sheets embedded in either glucose or tannin diffract to around 3 Å.

Two dimensional Sr silicate grown on Si(001) studied using X-ray Photoelectron Spectroscopy

2006 ◽  
Vol 132 ◽  
pp. 87-90
Author(s):  
M. El Kazzi ◽  
G. Delhaye ◽  
S. Gaillard ◽  
E. Bergignat ◽  
G. Hollinger
Keyword(s):  
Photoelectron Spectroscopy ◽  
Two Dimensional ◽  
X Ray

F.VIII R:Ag in Hepatitis

1979 ◽  
Author(s):  
R. Kotitschke ◽  
J. Scharrer
Keyword(s):  
Chronic Hepatitis ◽  
Blood Donors ◽  
Blood Donation ◽  
Normal Population ◽  
Rabbit Antiserum ◽  
Two Dimensional ◽  
Plastic Plate ◽  
Significant Difference ◽  
Acute Hepatitis B ◽  
The One

F.VIII R:Ag was determined by quantitative immunelectrophoresis (I.E.) with a prefabricated system. The prefabricated system consists of a monospecific f.VIII rabbit antiserum in agarose on a plastic plate for the one and two dimensional immunelectrophoresis. The lognormal distribution of the f.VIII R:Ag concentration in the normal population was confirmed (for n=70 the f.VIII R:Ag in % of normal is = 95.4 ± 31.9). Among the normal population there was no significant difference between blood donors (one blood donation in 8 weeks; for n=43 the f.VIII R:Ag in % of normal is = 95.9 ± 34.0) and non blood donors (n=27;f.VIII R:Ag = 94.6 ± 28.4 %). The f.VIII R:Ag concentration in acute hepatitis B ranged from normal to raised values (for n=10, a factor of 1.8 times of normal was found) and was normal again after health recovery (n=10, the factor was 1.0). in chronic hepatitis the f.VIII R:Ag concentration was raised in the majority of the cases (for n=10, the factor was 3.8). Out of 22 carrier sera 20 showed reduced, 2 elevated levels of the f.VIII R:Ag concentration. in 5 sera no f.VIII R:Ag could be demonstrated. The f.VIII R:Ag concentration was normal for n=10, reduced for n=20 and elevated for n=6 in non A-non B hepatitis (n=36). Contrary to results found in the literature no difference in the electrophoretic mobility of the f.VIII R:Ag was found between hepatitis patients sera and normal sera.

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