2,706 research outputs found
Unsolvability of the Halting Problem in Quantum Dynamics
It is shown that the halting problem cannot be solved consistently in both
the Schrodinger and Heisenberg pictures of quantum dynamics. The existence of
the halting machine, which is assumed from quantum theory, leads into a
contradiction when we consider the case when the observer's reference frame is
the system that is to be evolved in both pictures. We then show that in order
to include the evolution of observer's reference frame in a physically sensible
way, the Heisenberg picture with time going backwards yields a correct
description.Comment: 4 pages, 3 figure
On the positive mass theorem for manifolds with corners
We study the positive mass theorem for certain non-smooth metrics following
P. Miao's work. Our approach is to smooth the metric using the Ricci flow. As
well as improving some previous results on the behaviour of the ADM mass under
the Ricci flow, we extend the analysis of the zero mass case to higher
dimensions.Comment: 21 pages, incorporated referee's comment
Effects of Sand Addition to Heavy Saline-Alkali Soil on the Infiltration and Salt Leaching in Hetao Irrigation District, China
Proceeding PaperSoil salinity is a matter of great economic and environmental implications. In Hetao
Irrigation District, soil salinity limits crop productivity affecting about 69% of its total cultivated
land due to natural soil salinisation and salt accumulation caused by irrigation. The goal of this
study is to contribute to the alleviation of this problem through the technique of adding wind-sand to
the top layer of heavy saline-alkali soil, and to evaluate and analyse their effects on the infiltration
and salt leaching. The experiment was carried out on a laboratory scale. Clayey soil with 21 g/kg
of salts collected at the Ulat Front Banner site was used. Wind-sand was added to the top 30 cm
layer of this soil. The infiltration tests were carried out in plastic columns with 9 cm diameter and
45 cm high, loaded with a soil and wind-sand mixture (from 2% to 30% ratio), supplied by a constant
hydraulic head. Soil water samples were collected for 15 days for quantification of the soil salt
leaching. A significant increase of the infiltration rate was observed in the first infiltration hour, rising
from 1 to 9 mm/h, in response to the addition of 8% and 30% of sandy particles, respectively. The
effects of wind-sand in salt leaching were relevant in the top 20 cm layer. After 7 days of infiltration
there was a decrease in the salt content in soils with 4%, 8%, and 30% of sand particles added, of 35%,
55%, and 95%, respectively, in relation to the control. In conclusion, the practice of adding sandy
particles to the topsoil is a soil melioration method that allows a positive impact on soil infiltration
and salt leaching. An addition of 8% of sand seems to be a good choice, as it favours an increase in
salt leaching of about 55% after 7 days. These results are encouraging and appeal to field studies
to assess the impact on a field-scale system, and the effects of this soil melioration on irrigation,
drainage, and agronomic aspectsinfo:eu-repo/semantics/publishedVersio
Electronic structure of a Si δ-doped layer in a GaAs/AlxGa1-xAs/GaAs quantum barrier
We present a theoretical study of the electronic structure of a heavily Si d-doped layer in a GaAs/ AlxGa1-xAs/GaAs quantum barrier. In this class of structures the effect of DX centers on the electronic properties can be tuned by changing the AlxGa1-xAs barrier width and/or the Al concentration, which leads to a lowering of the DX level with respect to the Fermi energy without disturbing the wave functions much. A self-consistent approach is developed in which the effective confinement potential and the Fermi energy of the system, the energies, the wave functions, and the electron densities of the discrete subbands have been obtained as a function of both the material parameters of the samples and the experimental conditions. The effect of DX centers on such structures at nonzero temperature and under an external pressure is investigated for three different models: (1) the DXnc0 model with no correlation effects, (2) the d+/DX0 model, and (3) the d+/DX- model with inclusion of correlation effects. In the actual calculation, influences of the background acceptors, the discontinuity of the effective mass of the electrons at the interfaces of the different materials, band nonparabolicity, and the exchange-correlation energy of the electrons have been taken into account. We have found that (1) introducing a quantum barrier into d-doped GaAs makes it possible to control the energy gaps between different electronic subbands; (2) the electron wave functions are more spread out when the repellent effect of the barriers is increased as compared to those in d-doped GaAs; (3) increasing the quantum-barrier height and/or the application of hydrostatic pressure are helpful to experimentally observe the effect of the DX centers through a decrease of the total free-electron density; and (4) the correlation effects of the charged impurities are important for the systems under study
Wireless multimedia sensor network for plant disease detections
International audienceTo minimize pesticide use it is necessary to detect at the early stage the present of plant disease and perform local treatment instead of global systematic treatment. To achieve this goal, one of the techniques may be used is image processing through the deployment of WMSN in the cultivated field. However, transmitting massive image data wirelessly will increase significantly network traffic and particularly energy consumption. In this paper, we propose a plant disease detection approach which is designed to run on the resource-constrained WMSN nodes. Through the analysis of plant images acquired by the node, this new approach is able to make a preliminary local decision on the health condition of the plant and determine the necessity of sending back images to the control centre for further inspection, thus improving the efficiency of the monitoring network. The complete method includes image segmentation based on both color and shape, and uses 2D histogram as the feature for classification. Experiments on the plant images with nutrient deficiency symptoms show the classification accuracy of the new method reaches 87.5%
Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials
We investigate the cosmological evolution of the tachyon and phantom-tachyon
scalar field by considering the potential parameter () as a function of another potential parameter
(), which correspondingly extends the
analysis of the evolution of our universe from two-dimensional autonomous
dynamical system to the three-dimension. It allows us to investigate the more
general situation where the potential is not restricted to inverse square
potential and .One result is that, apart from the inverse square potential,
there are a large number of potentials which can give the scaling and dominant
solution when the function equals for one or some
values of as well as the parameter satisfies
condition Eq.(18) or Eq.(19). We also find that for a class of different
potentials the dynamics evolution of the universe are actually the same and
therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal
C(2010), online first,
http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=
Electron mobility in Si δ-doped GaAs with spatial correlationsin the distribution of charged impurities
We present a theoretical study of electron mobility in heavily Si d-doped GaAs in the presence of applied hydrostatic pressure. At low temperature the electron-ionized impurity scattering is the most important scattering mechanism. The presence of DX centers in Si-doped GaAs results in spatial correlations of the charged impurities, which increase the electron mobility through the structure factor of the charged-impurity distribution and/or a decrease in the density of the charged dopants. A Monte Carlo approach has been developed to simulate this distribution in two dimensions for the d+/DX0 and d+/DX- models. In the mobility calculation, both intrasubband and intersubband scatterings are considered with the electron-electron screening within the random-phase approximation. A detailed comparison between experiment and theory shows that theory excluding the correlation effects underestimates the electron mobility systematically. In cooperation with other mechanisms, e.g., self-compensation of Si dopants, in the d layer, both DX-center models can explain the experimental results well. This indicates that in order to effectively study the electronic properties of DX centers via the electron mobility in d-doped structures, the samples must have a relatively low doping concentration in order to prevent self-compensation
Transient domain walls and lepton asymmetry in the Left-Right symmetric model
It is shown that the dynamics of domain walls in Left-Right symmetric models,
separating respective regions of unbroken SU(2)_L and SU(2)_R in the early
universe, can give rise to baryogenesis via leptogenesis. Neutrinos have a
spatially varying complex mass matrix due to CP-violating scalar condensates in
the domain wall. The motion of the wall through the plasma generates a flux of
lepton number across the wall which is converted to a lepton asymmetry by
helicity-flipping scatterings. Subsequent processing of the lepton excess by
sphalerons results in the observed baryon asymmetry, for a range of parameters
in Left-Right symmetric models.Comment: v2 version accepted for publication in Phys. Rev. D. Discussion in
Introduction and Conclusion sharpened. Equation (12) corrected. 16 pages, 3
figure files, RevTeX4 styl
Global Monopole in Asymptotically dS/AdS Spacetime
In this paper, we investigate the global monopole in asymptotically dS/Ads
spacetime and find that the mass of the monopole in the asymptotically dS
spacetime could be positive if the cosmological constant is greater than a
critical value. This shows that the gravitational field of the global monopole
could be attractive or repulsive depending on the value of the cosmological
constant.Comment: 5 pages, 1 figure, to appear in Phys. Rev.
BPS R-balls in N=4 SYM on R X S^3, Quantum Hall Analogy and AdS/CFT Holography
In this paper, we propose a new approach to study the BPS dynamics in N=4
supersymmetric U(N) Yang-Mills theory on R X S^3, in order to better understand
the emergence of gravity in the gauge theory. Our approach is based on
supersymmetric, space-filling Q-balls with R-charge, which we call R-balls. The
usual collective coordinate method for non-topological scalar solitons is
applied to quantize the half and quarter BPS R-balls. In each case, a different
quantization method is also applied to confirm the results from the collective
coordinate quantization. For finite N, the half BPS R-balls with a U(1)
R-charge have a moduli space which, upon quantization, results in the states of
a quantum Hall droplet with filling factor one. These states are known to
correspond to the ``sources'' in the Lin-Lunin-Maldacena geometries in IIB
supergravity. For large N, we find a new class of quarter BPS R-balls with a
non-commutativity parameter. Quantization on the moduli space of such R-balls
gives rise to a non-commutative Chern-Simons matrix mechanics, which is known
to describe a fractional quantum Hall system. In view of AdS/CFT holography,
this demonstrates a profound connection of emergent quantum gravity with
non-commutative geometry, of which the quantum Hall effect is a special case.Comment: 42 pages, 2 figures; v3: a new paragraph on counting unbroken susy of
NC R-balls and references adde
- …