189 research outputs found
The difference of boundary effects between Bose and Fermi systems
In this paper, we show that there exists an essential difference of boundary
effects between Bose and Fermi systems both for Dirichlet and Neumann boundary
conditions: at low temperatures and high densities the influence of the
boundary on the Bose system depends on the temperature but is independent of
the density, but for the Fermi case the influence of the boundary is
independent of the temperature but depends on the density, after omitting the
negligible high-order corrections. We also show that at high temperatures and
low densities the difference of the influence of the boundary between Bose and
Fermi systems appears in the next-to-leading order boundary contribution, and
the leading boundary contribution is independent of the density. Moreover, for
calculating the boundary effects at high temperatures and low densities, since
the existence of the boundary modification causes the standard virial expansion
to be invalid, we introduce a modified virial expansion.Comment: 8 page
Thermodefect voltage in graphene nanoribbon junctions
Thermoelectric junctions are often made of components of different materials
characterized by distinct transport properties. Single material junctions, with
the same type of charge carriers, have also been considered to investigate
various classical and quantum effects on the thermoelectric properties of
nanostructured materials. We here introduce the concept of defect-induced
thermoelectric voltage, namely, {\it thermodefect voltage}, in graphene
nanoribbon (GNR) junctions under a temperature gradient. Our thermodefect
junction is formed by two GNRs with identical properties except the existence
of defects in one of the nanoribbons. At room temperature the thermodefect
voltage is highly sensitive to the types of defects, their locations, as well
as the width and edge configurations of the GNRs. We demonstrate that the
thermodefect voltage can be as high as mV/K for - defects in
semiconducting armchair GNRs. We further investigate the Seebeck coefficient,
electrical conductance, and electronic thermal conductance, and also the power
factor of the individual junction components to explain the thermodefect
effect. Taken together, our study presents a new pathway to enhance the
thermoelectric properties of nanomaterials.Comment: 11 pages, 6 figure
All unitary cubic curvature gravities in D dimensions
We construct all the unitary cubic curvature gravity theories built on the
contractions of the Riemann tensor in D -dimensional (anti)-de Sitter
spacetimes. Our construction is based on finding the equivalent quadratic
action for the general cubic curvature theory and imposing ghost and tachyon
freedom, which greatly simplifies the highly complicated problem of finding the
propagator of cubic curvature theories in constant curvature backgrounds. To
carry out the procedure we have also classified all the unitary quadratic
models. We use our general results to study the recently found cubic curvature
theories using different techniques and the string generated cubic curvature
gravity model. We also study the scattering in critical gravity and give its
cubic curvature extensions.Comment: 24 pages, 1 figure, v2: A subsection on cubic curvature extensions of
critical gravity is added, v3: The part regarding critical gravity is
revised. Version to appear in Class. Quant. Gra
Comparison of chemotherapy and hematopoietic stem cell transplantation pre and postterm DMFT scores: A preliminary study
Aims: Chemotherapy is frequently used as a conditioning regimen to destroy malignant marrow cells before transplantation. Xerostomia, dysphagia, altered taste perception, mucositis, soft‑tissue ulceration, and infection are common adverse oral effects of chemotherapy. The study was aimed to compare decayed, missing, filled teeth (DMFT) scores before and after hematopoietic stem cell transplantation (HSCT) and chemotherapy.Materials and Methods: Thirty‑six patients undergoing HSCT were included in the study. Apre‑HSCT dental treatment protocol was implemented that consisted of restoration of all active carious lesions, treatment of periodontal infections, and extraction of all teeth with advanced periodontal disease. Upon completion of dental treatment, the importance of rigorous and effective oral hygiene was reemphasized, and patients were recalled 6 months later. DMFT scores were calculated prior to the initiation of HSCT treatment and 6 months after transplantation.Statistical Analysis Used: Regression analysis was used to evaluate the effects of HSCT and chemotherapy on DMFT scores.Results: Wilcoxon T test showed a statistically significant difference in DMFT scores before and after HSCT (P < 0.001). Conclusions: DMFT scores were found to increase after chemotherapy and HSCT, suggesting that the risk of infection is higher among HSCT patients when compared to other individuals. The results emphasize the need for dental examinations as an integral part of examination and treatment planning for patients undergoing HSCT and chemotherapy.Key words: Chemotherapy, decayed missing filled teeth scores, hematopoietic stem cell transplantatio
LWIR all-atomic layer deposition ZnO bilayer microbolometer for thermal imaging
We propose an all-ZnO bilayer microbolometer, operating in the long-wave infrared regime that can be implemented by consecutive atomic layer deposition growth steps. Bilayer design of the bolometer provides very high absorption coefficients compared to the same thickness of a single ZnO layer. High absorptivity of the bilayer structure enables higher performance (lower noise equivalent temperature difference and time constant values) compared to single-layer structure. We observe these results computationally by conducting both optical and thermal simulations. © 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
A Complete Classification of Higher Derivative Gravity in 3D and Criticality in 4D
We study the condition that the theory is unitary and stable in
three-dimensional gravity with most general quadratic curvature,
Lorentz-Chern-Simons and cosmological terms. We provide the complete
classification of the unitary theories around flat Minkowski and (anti-)de
Sitter spacetimes. The analysis is performed by examining the quadratic
fluctuations around these classical vacua. We also discuss how to understand
critical condition for four-dimensional theories at the Lagrangian level.Comment: 20 pages, v2: minor corrections, refs. added, v3: logic modified, v4:
typos correcte
Noncritical Einstein-Weyl Gravity and the AdS/CFT Correspondence
We explore four-dimensional Einstein-Weyl gravity and supergravity on anti-de
Sitter spacetime. For a specific range of the coupling with appropriate
boundary conditions, we show the effective equivalence of the theory with
Einstein gravity and AdS supergravity at the quadratic Lagrangian level.
Furthermore we show that these equivalences can be promoted to the full
nonlinear level. We also show that the similar behavior holds for the
generalized Gibbons-Hawking terms. From this we find that the correlation
functions in the dual conformal field theory of Einstein-Weyl gravity and
supergravity can be readily read off from corresponding ones from Einstein
gravity and AdS supergravity. We also give comments on some issues in critical
gravity and supergravity as well as conformal gravity and supergravity.Comment: 20 pages, 1 figure: v2, references and footnote added, typos
correcte
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