1,354 research outputs found
Kaluza-Klein description of geometric phases in graphene
In this paper, we use the Kaluza-Klein approach to describe topological
defects in a graphene layer. Using this approach, we propose a geometric model
allowing to discuss the quantum flux in -spin subspace. Within this model,
the graphene layer with a topological defect is described by a four-dimensional
metric, where the deformation produced by the topological defect is introduced
via the three-dimensional part of metric tensor, while an Abelian gauge field
is introduced via an extra dimension. We use this new geometric model to
discuss the arising of topological quantum phases in a graphene layer with a
topological defect.Comment: 16 pages, version accepted to Annals of Physic
Mechanical design of NASA Ames Research Center vertical motion simulator
NASA has designed and is constructing a new flight simulator with large vertical travel. Several aspects of the mechanical design of this Vertical Motion Simulator (VMS) are discussed, including the multiple rack and pinion vertical drive, a pneumatic equilibration system, and the friction-damped rigid link catenaries used as cable supports
The effect of delayed harvest upon yield of grain
In 1927 yield and moisture data were secured at semi-weekly harvest intervals for four varieties of oats, two of winter wheat and two of barley. In 1928 this experiment was repeated using six varieties of oats, two of winter wheat and four of barley.
The data secured in these studies show increases in yields which indicate that photosynthesis and translocation of food material to the kernel may continue much longer than has been previously reported. The yields continued to rise until the moisture content of the grain had fallen to percentages varying, in 1927, between 33.6 and 10.0, and in 1928 between 45.0 and 19.4, as shown in table I, page 335.
The results of these experiments indicate that a considerable part of the grain crop is usually harvested before maximum production has been attained. In 1927 several of the varieties increased in yield as much as 10 percent after the date on which they normally would have been harvested. In some cases these increases extended over a period of 10 days. In 1928, probably due to intermittent storms, the increases were much smaller than in the previous year, but continued over approximately the same length of time.
The results confirm the accepted idea that the corresponding losses from delayed harvesting are lower for wheat than for other grains.
The experiments with oats show a distinct relation between varieties and the length of profitable harvest period
Detailed analysis of radiation data from the Gemini 4 and Gemini 7 proton-electron spectrometer experiments Final report, 13 Jun. 1967 - 30 Dec. 1968
Detailed analysis of radiation data from Gemini 4 and 7 proton-electron spectrometer experiment
rab7b controls trafficking from endosomes to the tgn
Rab7b is a recently identified member of the Rab GTPase protein family and has high similarity to Rab7. It has been reported that Rab7b is lysosome associated, that it is involved in monocytic differentiation and that it promotes lysosomal degradation of TLR4 and TLR9. Here we investigated further the localization and function of this GTPase. We found that wild-type Rab7b is lysosome associated whereas an activated, GTP-bound form of Rab7b localizes to the Golgi apparatus. In contrast to Rab7, Rab7b is not involved in EGF and EGFR degradation. Depletion of Rab7b or expression of Rab7b T22N, a Rab7b dominant-negative mutant, impairs cathepsin-D maturation and causes increased secretion of hexosaminidase. Moreover, expression of Rab7b T22N or depletion of Rab7b alters TGN46 distribution, cation-independent mannose-6-phosphate receptor (CI-MPR) trafficking, and causes an increase in the levels of the late endosomal markers CI-MPR and cathepsin D. Vesicular stomatitis virus G protein (VSV-G) trafficking, by contrast, is normal in Rab7b-depleted or Rab7b-T22N-expressing cells. In addition, depletion of Rab7b prevents cholera toxin B-subunit from reaching the Golgi. Altogether, these data indicate that Rab7b is required for normal lysosome function, and, in particular, that it is an essential factor for retrograde transport from endosomes to the trans-Golgi network (TGN)
Interacting damage models mapped onto Ising and percolation models
We introduce a class of damage models on regular lattices with isotropic
interactions, as e.g. quasistatic fiber bundles. The system starts intact with
a surface-energy threshold required to break any cell sampled from an
uncorrelated quenched-disorder distribution. The evolution of this
heterogeneous system is ruled by Griffith's principle which states that a cell
breaks when the release in elastic energy in the system exceeds the
surface-energy barrier necessary to break the cell. By direct integration over
all possible realizations of the quenched disorder, we obtain the probability
distribution of each damage configuration at any level of the imposed external
deformation. We demonstrate an isomorphism between the distributions so
obtained and standard generalized Ising models, in which the coupling constants
and effective temperature in the Ising model are functions of the nature of the
quenched-disorder distribution and the extent of accumulated damage. In
particular, we show that damage models with global load sharing are isomorphic
to standard percolation theory, that damage models with local load sharing rule
are isomorphic to the standard Ising model, and draw consequences thereof for
the universality class and behavior of the autocorrelation length of the
breakdown transitions corresponding to these models. We also treat damage
models having more general power-law interactions, and classify the breakdown
process as a function of the power-law interaction exponent. Last, we also show
that the probability distribution over configurations is a maximum of Shannon's
entropy under some specific constraints related to the energetic balance of the
fracture process, which firmly relates this type of quenched-disorder based
damage model to standard statistical mechanics.Comment: 16 pages, 3 figure
Effect of topological defects and Coulomb charge on the low energy quantum dynamics of gapped graphene
We study the combined effect of a conical topological defect and a Coulomb
charge impurity on the dynamics of Dirac fermions in gapped graphene. Beyond a
certain strength of the Coulomb charge, quantum instability sets in, which
demarcates the boundary between sub and supercritical values of the charge. In
the subcritical regime, for certain values of the system parameters, the
allowed boundary conditions in gapped graphene cone can be classified in terms
of a single real parameter. We show that the observables such as local density
of states, scattering phase shifts and the bound state spectra are sensitive to
the value of this real parameter, which is interesting from an empirical point
of view. For a supercritical Coulomb charge, we analyze the system with a
regularized potential as well as with a zigzag boundary condition and find the
effect of the sample topology on the observable features of the system.Comment: 22 pages, 23 figure
Relativistic Landau quantization for a neutral particle
In this contribution we study the Landau levels arising within the
relativistic quantum dynamics of a neutral particle which possesses a permanent
magnetic dipole moment interacting with an external electric field. We consider
the Aharonov-Casher coupling of magnetic dipole to the electric field to
investigate an an analog of Landau quantization in this system and solve the
Dirac equation for two different field configurations. The eigenfunctions and
eigenvalues of Hamiltonian in both cases are obtained.Comment: 9 pages, no figure
Noninertial effects on a Dirac neutral particle inducing an analogue of the Landau quantization in the cosmic string spacetime
We discuss the behaviour of external fields that interact with a Dirac
neutral particle with a permanent electric dipole moment in order to achieve
relativistic bound states solutions in a noninertial frame and in the presence
of a topological defect spacetime. We show that the noninertial effects of the
Fermi-Walker reference frame induce a radial magnetic field even in the absence
of magnetic charges, which is influenced by the topology of the cosmic string
spacetime. We then discuss the conditions that the induced fields must satisfy
to yield the relativistic bound states corresponding to the
Landau-He-McKellar-Wilkens quantization in the cosmic string spacetime. Finally
we obtain the Dirac spinors for positive-energy solutions and the Gordon
decomposition of the Dirac probability current.Comment: 15 pages, no figure, this paper will be published in volume 42 of the
Brazilian Journal of Physic
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