3,050 research outputs found
The chemical potential for the inhomogeneous electron liquid in terms of its kinetic and potential parts with special consideration of the surface pote ntial step and BCS-BEC crossover
The chemical potential of a many-body system is valuable since it
carries fingerprints of phase changes. Here, we summarize results for for
a thre e-dimensional electron liquid in terms of average kinetic and potential
energie s per particle. The difference between and the energy per
particle is fou nd to be exactly the electrostatic potential step at the
surface. We also prese nt calculations for an integrable one-dimensional
many-body system with delta f unction interactions, exhibiting a BCS-BEC
crossover. It is shown that in the B CS regime the chemical potential can be
expressed solely in terms of the ground -state energy per particle. A brief
discussion is also included of the strong c oupling BEC limit.Comment: 4 pages 3 figure
A simple interpretation of quantum mirages
In an interesting new experiment the electronic structure of a magnetic atom
adsorbed on the surface of Cu(111), observed by STM, was projected into a
remote location on the same surface. The purpose of the present paper is to
interpret this experiment with a model Hamiltonian, using ellipses of the size
of the experimental ones, containing about 2300 atoms. The charge distribution
for the different wavefunctions is analyzed, in particular, for those with
energy close to the Fermi energy of copper Ef. Some of them show two symmetric
maxima located on the principal axis of the ellipse but not necessarily at the
foci. If a Co atom is adsorbed at the site where the wavefunction with energy
has a maximum and the interaction is small, the main effect of the
adsorbed atom will be to split this particular wavefunction in two. The total
charge density will remain the same but the local density of states will
present a dip at Ef at any site where the charge density is large enough. We
relate the presence of this dip to the observation of quantum mirages. Our
interpretation suggests that other sites, apart from the foci of the ellipses,
can be used for projecting atomic images and also indicates the conditions for
other non magnetic adsorbates to produce mirages.Comment: 3 pages, 3 Fig
Cause and Consequences of Genetic and Epigenetic Alterations in Human Cancer
Both genetic and epigenetic changes contribute to development of human cancer. Oncogenomics has primarily focused on understanding the genetic basis of neoplasia, with less emphasis being placed on the role of epigenetics in tumourigenesis. Genomic alterations in cancer vary between the different types and stages, tissues and individuals. Moreover, genomic change ranges from single nucleotide mutations to gross chromosomal aneuploidy; which may or may not be associated with underlying genomic instability. Collectively, genomic alterations result in widespread deregulation of gene expression profiles and the disruption of signalling networks that control proliferation and cellular functions. In addition to changes in DNA and chromosomes, it has become evident that oncogenomic processes can be profoundly influenced by epigenetic mechanisms. DNA methylation is one of the key epigenetic factors involved in regulation of gene expression and genomic stability, and is biologically necessary for the maintenance of many cellular functions. While there has been considerable progress in understanding the impact of genetic and epigenetic mechanisms in tumourigenesis, there has been little consideration of the importance of the interplay between these two processes. In this review we summarize current understanding of the role of genetic and epigenetic alterations in human cancer. In addition we consider the associated interactions of genetic and epigenetic processes in tumour onset and progression. Furthermore, we provide a model of tumourigenesis that addresses the combined impact of both epigenetic and genetic alterations in cancer cells
Switcher-random-walks: a cognitive-inspired mechanism for network exploration
Semantic memory is the subsystem of human memory that stores knowledge of
concepts or meanings, as opposed to life specific experiences. The organization
of concepts within semantic memory can be understood as a semantic network,
where the concepts (nodes) are associated (linked) to others depending on
perceptions, similarities, etc. Lexical access is the complementary part of
this system and allows the retrieval of such organized knowledge. While
conceptual information is stored under certain underlying organization (and
thus gives rise to a specific topology), it is crucial to have an accurate
access to any of the information units, e.g. the concepts, for efficiently
retrieving semantic information for real-time needings. An example of an
information retrieval process occurs in verbal fluency tasks, and it is known
to involve two different mechanisms: -clustering-, or generating words within a
subcategory, and, when a subcategory is exhausted, -switching- to a new
subcategory. We extended this approach to random-walking on a network
(clustering) in combination to jumping (switching) to any node with certain
probability and derived its analytical expression based on Markov chains.
Results show that this dual mechanism contributes to optimize the exploration
of different network models in terms of the mean first passage time.
Additionally, this cognitive inspired dual mechanism opens a new framework to
better understand and evaluate exploration, propagation and transport phenomena
in other complex systems where switching-like phenomena are feasible.Comment: 9 pages, 3 figures. Accepted in "International Journal of
Bifurcations and Chaos": Special issue on "Modelling and Computation on
Complex Networks
A Multicenter Study Of Students Sensitivity To Screen-Update Delay
In a climate of shrinking educational budgets, online learning courses offer many advantages; however there are several possible problems associated with electronic learning. There may be problems associated with learning style preferences, student apathy, instructional support, accessibility, and problems with technology. This paper examines a technological problem associated with the effects of screen-update-delay and student enjoyment, student self-reported comprehension, and student objective comprehension. In particular, this paper attempts to identify the point at which longer screen updates will be detrimental to the students enjoyment and/or have a significant negative impact on the students self-reported comprehension and retention of material
Similar Endothelial Glycocalyx Structures in Microvessels from a Range of Mammalian Tissues: Evidence for a Common Filtering Mechanism?
AbstractThe glycocalyx or endocapillary layer on the luminal surface of microvessels has a major role in the exclusion of macromolecules from the underlying endothelial cells. Current structural evidence in the capillaries of frog mesentery indicates a regularity in the structure of the glycocalyx, with a center-to-center fiber spacing of 20 nm and a fiber width of 12 nm, which might explain the observed macromolecular filtering properties. In this study, we used electron micrographs of tissues prepared using perfusion fixation and tannic acid treatment. The digitized images were analyzed using autocorrelation to find common spacings and to establish whether similar structures, hence mechanisms, are present in the microvessel glycocalyces of a variety of mammalian tissues. Continuous glycocalyx layers in mammalian microvessels of choroid, renal tubules, glomerulus, and psoas muscle all showed similar lateral spacings at ∼19.5 nm (possibly in a quasitetragonal lattice) and longer spacings above 100 nm. Individual glycocalyx tufts above fenestrations in the first three of these tissues and also in stomach fundus and jejunum showed evidence for similar short-range structural regularity, but with more disorder. The fiber diameter was estimated as 18.8 (± 0.2) nm, but we believe this is an overestimate because of the staining method used. The implications of these findings are discussed
Spin Forming of an Aluminum 2219-T6 Aft Bulkhead for the Orion Multi-Purpose Crew Vehicle: Phase II Supplemental Report
The principal focus of this project was to assist the Orion Multi-Purpose Crew Vehicle (MPCV) Program in developing a spin forming fabrication process for manufacture of the aft bulkhead of the pressure vessel. The spin forming process will enable a single piece aluminum (Al) 2219 aft bulkhead which will eliminate the current multiple piece welded construction, simplify fabrication, and lead to an enhanced design that will reduce vehicle weight by eliminating welds. Phase I of this assessment explored spin forming the single-piece forward pressure vessel bulkhead from aluminum-lithium 2195
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