On the qualitative theory of Shockley surface states of the (111) face of NbC and the nature of bonding in this compound

1980 ◽  
Vol 45 (5) ◽  
pp. 1317-1322 ◽  
Author(s):  
Mojmír Tomášek ◽  
Štěpán Pick ◽  
Karlheinz Schwarz
Keyword(s):  
Fermi Energy ◽  
Niobium Carbide ◽  
Surface States ◽  
Qualitative Theory ◽  
The Other ◽  
Covalent Component

Qualitative theory of Shockley surface states is applied to the analysis of the (111) surface of the niobium carbide crystal. The existence of Shockley states is predicted in two hybridizational gaps. One of (p, t2g) character lies just below the Fermi energy and the other of (eg, t2g) character is at higher energies. The relation between Shockey states and bonding is discussed. A strong (p, t2g) covalent component of the metal-nonmetal bond is found.

scholarly journals A Qualitative Theory of Cognitive Attitudes and their Change

2021 ◽  
pp. 1-31
Author(s):  
EMILIANO LORINI
Keyword(s):  
Belief Change ◽  
Qualitative Theory ◽  
The Other ◽  
Logical Framework ◽  
Basic Logic ◽  
Conditional Belief ◽  
Concepts Of Knowledge ◽  
Cognitive Attitudes ◽  
Qualitative Decision Theory ◽  
Qualitative Decision

Abstarct We present a general logical framework for reasoning about agents’ cognitive attitudes of both epistemic type and motivational type. We show that it allows us to express a variety of relevant concepts for qualitative decision theory including the concepts of knowledge, belief, strong belief, conditional belief, desire, conditional desire, strong desire, and preference. We also present two extensions of the logic, one by the notion of choice and the other by dynamic operators for belief change and desire change, and we apply the former to the analysis of single-stage games under incomplete information. We provide sound and complete axiomatizations for the basic logic and for its two extensions.

scholarly journals Studies on the origin of the interfacial superconductivity of Sb2Te3/Fe1+yTe heterostructures

2019 ◽  
Vol 117 (1) ◽  
pp. 221-227 ◽  
Author(s):  
Jing Liang ◽  
Yu Jun Zhang ◽  
Xiong Yao ◽  
Hui Li ◽  
Zi-Xiang Li ◽  
...  
Keyword(s):  
Layer Thickness ◽  
Topological Insulator ◽  
Surface States ◽  
The Other ◽  
Majorana Fermions ◽  
Bulk Conductivity ◽  
Indirect Coupling ◽  
Topological Surface ◽  
Excess Fe

The recent discovery of the interfacial superconductivity (SC) of the Bi2Te3/Fe1+yTe heterostructure has attracted extensive studies due to its potential as a novel platform for trapping and controlling Majorana fermions. Here we present studies of another topological insulator (TI)/Fe1+yTe heterostructure, Sb2Te3/Fe1+yTe, which also has an interfacial 2-dimensional SC. The results of transport measurements support that reduction of the excess Fe concentration of the Fe1+yTe layer not only increases the fluctuation of its antiferromagnetic (AFM) order but also enhances the quality of the SC of this heterostructure system. On the other hand, the interfacial SC of this heterostructure was found to have a wider-ranging TI-layer thickness dependence than that of the Bi2Te3/Fe1+yTe heterostructure, which is believed to be attributed to the much higher bulk conductivity of Sb2Te3that enhances indirect coupling between its top and bottom topological surface states (TSSs). Our results provide evidence of the interplay among the AFM order, itinerant carries from the TSSs, and the induced interfacial SC of the TI/Fe1+yTe heterostructure system.

C band radar crops monitoring at high temporal frequency: first results of the MOCTAR campaign

2020 ◽  
Author(s):  
Pierre-Louis Frison ◽  
Adnane Chakir ◽  
Jamal Ezzahar ◽  
Pascal Fanise ◽  
Ludovic Villard ◽  
...  
Keyword(s):  
Temporal Frequency ◽  
Surface States ◽  
The Other ◽  
Thermal Dissipation ◽  
Full Potential ◽  
Time Step ◽  
Crop Fields ◽  
First Results ◽  
Olive Trees ◽  
Semi Arid

<p>This work deals with crops monitoring in a semi-arid environment, the Mediterranean region, where up to 90% of available water is used for irrigation. In addition to help for yield predictions, temporal monitoring at a regular time basis can help for the optimization of water use. We focused on the daily cycle of the backscattering radar coefficient over two different crop Mediterranean types: olive trees and wheat. With a six-day period between two consecutive acquisitions, the Sentinel-1 mission improves significantly the potential of SAR data for seasonal monitoring of earth surfaces. The available temporal frequency allows for the first time the temporal monitoring of natural surfaces in relation with seasonal changes. However, they are still many issues for better understanding Sentinel-1 temporal signatures and the full potential of these data over crop fields. Indeed, crop fields are characterized by contrasted surface states between bare soils and densely vegetated, with sudden changes due to field works (changing dramatically soil roughness or moisture) or harvests.  The MOCTAR experiment consists in the acquisitions of radar fully polarimetric interferometric C-band data acquired continuously at 10 min time step from the top of a tower. The study site is located in the Haouz plain, near the city of Marrakech, in the Chichaoua region, in Morocco. The region is characterized by a semi-arid Mediterranean climate, with an average of 250 mm of yearly precipitation. The region is characterized by two main seasons: wet and dry, extended from October to April and from May to September respectively. Maximum temperatures occur in July-August (average of 27.2 °C) and minimum in January (10.8° C). The study site is composed of two plots of 2.50 ha each, one consisting in olive trees, the other in wheat (Fig. 1). Both are irrigated with drip technique. The study site is documented for more than 10 years, and in situ measurements such as soil moisture, biomass, sapflow sensors (thermal dissipation method) and a micrometric dendrometer are regularly collected.</p><p>The radar antennas are fixed on a 20 m height tower, in a similar way than the TropiScat experiment They have been installed in May 2019. Four L-band antennas, two emitting and two receiving, one in H and the other in V polarizations, are visible on the bottom row. Above, six antennas operating at C band are mounted on two rows: four on the bottom one (two emitting and two receiving in H and V pol.) and above two receiving antennas in H and V pol. This configuration allows for interferometric fully polarimetric acquisitions also called PolInSAR. The acquisitions are made continuously with a 10 min time step.</p><p>First results show pronounced daily cycles, with amplitude of about 2 dB. These cycles are likely correlated to diurnal variations of tree water content and sap flow, but need to be further investigated sap flows and dielectric constant measurements made on the trunks. These results will be analyzed by comparison with Sentinel-1 temporal profiles.</p>

Dirac States of 2D Topological Insulators: Effect of Heterovalent Dopant-Content

2019 ◽  
Vol 25 (6) ◽  
pp. 1437-1441 ◽  
Author(s):  
Salma Khatun ◽  
Amlan J. Pal
Keyword(s):  
Fermi Energy ◽  
Dirac Point ◽  
Surface States ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Metallic State ◽  
X Ray Diffraction ◽  
Dopant Content ◽  
X Ray ◽  
Transmission Electron

AbstractWe have studied Bi2Se3 at its 2D-limit using scanning tunneling spectroscopy (STS). Bulk Bi2Se3 is a well-known topological insulator having gapless surface states. In the 2D limit, the interior of the material exhibits a band gap, whereas the periphery shows a gapless metallic state having a Dirac point. We demonstrate a method to tune the Fermi energy and hence the Dirac point of Bi2Se3 nanoplates through doping at the anionic site. For this purpose, STS measurements were carried out on the Bi2Se3 system. We have used bromide as a dopant, which turns the material to n-type in nature. As a result, STS studies infer that the Fermi energy (EF) shifted toward the conduction band and consequently the Dirac point could be found to move away from Fermi energy. Through STS measurements, we have demonstrated a correlation between the shift of Dirac point position and the dopant content. The size, shape, and compositions of Bi2Se3 nanoflakes and concentration of bromine in the doped nanostructures were determined using transmission electron microscopy, associated energy dispersive X-ray spectroscopy analysis, and X-ray diffraction.

ON THE SLIDING BIFURCATION OF A CLASS OF PLANAR FILIPPOV SYSTEMS

2013 ◽  
Vol 23 (03) ◽  
pp. 1350040 ◽  
Author(s):  
DINGHENG PI ◽  
JIANG YU ◽  
XIANG ZHANG
Keyword(s):  
Limit Cycles ◽  
Homoclinic Bifurcation ◽  
Qualitative Theory ◽  
Piecewise Smooth ◽  
The Other ◽  
Heteroclinic Cycle ◽  
Differential Systems ◽  
Sliding Bifurcation ◽  
Bifurcation Phenomena ◽  
Limit Cycle Bifurcation

In this paper, we study the sliding bifurcation phenomena of a class of planar piecewise smooth differential systems consisting of linear and quadratic subsystems. Using the differential inclusion and the qualitative theory of ordinary differential equations, we find some new interesting phenomena appearing in the piecewise smooth differential systems. In brief, we prove that the system may have sliding homoclinic bifurcation, sliding cycle bifurcation, semistable limit cycle bifurcation and heteroclinic cycle bifurcation. In addition, the mentioned systems can have at most two limit cycles, and the maximal number of limit cycles can be realized and central nested with one bifurcated from the sliding–crossing bifurcation of a sliding cycle and the other from the saddle homoclinic bifurcation. These two limit cycles collide and then both disappear. This novel scenario is verified by our systems.

scholarly journals Dynamic Modification of Fermi Energy in Single-Layer Graphene by Photoinduced Electron Transfer from Carbon Dots

Nanomaterials ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 528 ◽  
Author(s):  
Angelo Armano ◽  
Gianpiero Buscarino ◽  
Fabrizio Messina ◽  
Alice Sciortino ◽  
Marco Cannas ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Fermi Energy ◽  
Carbon Dots ◽  
Mutual Influence ◽  
Solid Phase ◽  
Surface States ◽  
Single Layer ◽  
Single Layer Graphene ◽  
N Doping ◽  
Carbon Based Nanomaterials

Graphene (Gr)—a single layer of two-dimensional sp2 carbon atoms—and Carbon Dots (CDs)—a novel class of carbon nanoparticles—are two outstanding nanomaterials, renowned for their peculiar properties: Gr for its excellent charge-transport, and CDs for their impressive emission properties. Such features, coupled with a strong sensitivity to the environment, originate the interest in bringing together these two nanomaterials in order to combine their complementary properties. In this work, the investigation of a solid-phase composite of CDs deposited on Gr is reported. The CD emission efficiency is reduced by the contact of Gr. At the same time, the Raman analysis of Gr demonstrates the increase of Fermi energy when it is in contact with CDs under certain conditions. The interaction between CDs and Gr is modeled in terms of an electron-transfer from photoexcited CDs to Gr, wherein an electron is first transferred from the carbon core to the surface states of CDs, and from there to Gr. There, the accumulated electrons determine a dynamical n-doping effect modulated by photoexcitation. The CD–graphene interaction unveiled herein is a step forward in the understanding of the mutual influence between carbon-based nanomaterials, with potential prospects in light conversion applications.

scholarly journals Tunable Optical Bistability in One-Dimensional Photonic Crystal with a Nonlinear Defect Coupled by Graphene Sheets

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Zhiwei Zheng ◽  
Leyong Jiang ◽  
Jun Guo ◽  
Xiaoyu Dai ◽  
Yuanjiang Xiang
Keyword(s):  
Photonic Crystal ◽  
Fermi Energy ◽  
Optical Bistability ◽  
Lateral Shift ◽  
The Other ◽  
Graphene Sheets ◽  
Hysteresis Width ◽  
One Dimensional ◽  
Graphene Layers ◽  
Dimensional Photonic Crystal

The optical bistability in one-dimensional photonic crystal (1DPC) with a nonlinear defect is investigated. It is demonstrated that, by introducing graphene layers into the nonlinear defect, the optical bistability in 1DPC can be changed significantly. The hysteresis threshold increases with the number of graphene monolayers and can be lowered or enhanced by tuning the Fermi energy of graphene. On the other hand, the hysteresis width and the nonlinear lateral shift can also be controlled by varying the Femi energy and the number of graphene monolayers. These results may be useful for controlling the optical bistability and nonlinear lateral shift in 1DPCs.

Structure of Etched {00.1} CdS Surfaces

1970 ◽  
Vol 28 ◽  
pp. 476-477
Author(s):  
G. Shimaoka ◽  
S. C. Chang
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Physical Properties ◽  
Surface States ◽  
Wurtzite Structure ◽  
The Other

CdS has a wurtzite structure and two types of {00.1} surfaces exist along the {00.1} direction in CdS: one, (00.1), consisting entirely of Cd atoms and the other, (00.1), of S atoms. Many interesting reports have been published on differences in chemical and physical properties between the two faces. Properties of surface states of CdS crystal, particularly their stabilities, have been computed and discussed theoretically. In the present study we have investigated microstructure of etched {00.1} surfaces of CdS crystal by means of electron microscopy and electron diffraction.

Stability of fast elaborated small CdS quantum dots

2011 ◽  
Vol 1286 ◽  
Author(s):  
M. Fregnaux ◽  
S. Dalmasso ◽  
J.-J. Gaumet ◽  
J.-P. Laurenti
Keyword(s):  
Absorption Spectra ◽  
Broad Band ◽  
Surface States ◽  
The Other ◽  
Cds Quantum Dots ◽  
Other Hand ◽  
Direct Exposure ◽  
Single Source Precursor ◽  
Excitonic Transition ◽  
Excitonic Emission

ABSTRACTSmall size CdS QDs were synthesized by (i) the single source precursor methodology and by (ii) the microwave synthetic route. The consequences of CdS QD direct exposure to air for a period of 7 days were investigated by following the evolution of the photoluminescence (PL) and absortion spectra. For QDs obtained by (i), the excitonic emission band (3.0 ‑ 3.1 eV) decreases in intensity, relatively to the low energy one (2.2 ‑ 2.5 eV) tentatively associated to midgap surface states. This suggests arising of new recombination path(s) associated to degradations during aging, possibly an oxidative formation of a CdO surface layer. On the other hand, no significant change is observed in the absorption spectra. For QDs obtained by (ii), no degradation is revealed by the PL spectra which remain unchanged. On the other hand, the absorption spectra are dominated by an unexplained broad band around 3.6 eV which tends to hide the fundamental excitonic transition one and increases in intensity with aging.

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