28,676 research outputs found
Phenological response of vegetation to upstream river flow in the Heihe Rive basin by time series analysis of MODIS data
Liquid and solid precipitation is abundant in the high elevation, upper reach of the Heihe River basin in northwestern China. The development of modern irrigation schemes in the middle reach of the basin is taking up an increasing share of fresh water resources, endangering the oasis and traditional irrigation systems in the lower reach. In this study, the response of vegetation in the Ejina Oasis in the lower reach of the Heihe River to the water yield of the upper catchment was analyzed by time series analysis of monthly observations of precipitation in the upper and lower catchment, river streamflow downstream of the modern irrigation schemes and satellite observations of vegetation index. Firstly, remotely sensed NDVI data acquired by Terra-MODIS are used to monitor the vegetation dynamic for a seven years period between 2000 and 2006. Due to cloud-contamination, atmospheric influence and different solar and viewing angles, however, the quality and consistence of time series of remotely sensed NDVI data are degraded. A Fourier Transform method – the Harmonic Analysis of Time Series (HANTS) algorithm – is used to reconstruct cloud- and noise-free NDVI time series data from the Terra-MODIS NDVI dataset. Modification is made on HANTS by adding additional parameters to deal with large data gaps in yearly time series in combination with a Temporal-Similarity-Statistics (TSS) method developed in this study to seek for initial values for the large gap periods. Secondly, the same Fourier Transform method is used to model time series of the vegetation phenology. The reconstructed cloud-free NDVI time series data are used to study the relationship between the water availability (i.e. the local precipitation and upstream water yield) and the evolution of vegetation conditions in Ejina Oasis from 2000 to 2006. Anomalies in precipitation, streamflow, and vegetation index are detected by comparing each year with the average year. The results showed that: the previous year total runoff had a significant relationship with the vegetation growth in Ejina Oasis and that anomalies in the spring monthly runoff of the Heihe River influenced the phenology of vegetation in the entire oasis. Warmer climate expressed by the degree-days showed positive influence on the vegetation phenology in particular during drier years. The time of maximum green-up is uniform throughout the oasis during wetter years, but showed a clear S-N gradient (downstream) during drier years
SPSA-Based Tracking Method for Single-Channel-Receiver Array
A novel tracking method in the phased antenna array with a single-channel receiver for the moving signal source is presented in this paper. And the problems of the direction-of-arrival track and beamforming in the array system are converted to the power maximization of received signal in the free-interference conditions, which is different from the existing algorithms that maximize the signal to interference and noise ratio. The proposed tracking method reaches the global optimum rather than local by injecting the extra noise terms into the gradient estimation. The antenna beam can be steered to coincide with the direction of the moving source fast and accurately by perturbing the output of the phase shifters during motion, due to the high efficiency and easy implementation of the proposed beamforming algorithm based on the simultaneous perturbation stochastic approximation (SPSA). Computer simulations verify that the proposed tracking scheme is robust and effective
Entangling a series of trapped ions by moving cavity bus
Entangling multiple qubits is one of the central tasks for quantum
information processings. Here, we propose an approach to entangle a number of
cold ions (individually trapped in a string of microtraps) by a moved cavity.
The cavity is pushed to include the ions one by one with an uniform velocity,
and thus the information stored in former ions could be transferred to the
latter ones by such a moving cavity bus. Since the positions of the trapped
ions are precisely located, the strengths and durations of the ion-cavity
interactions can be exactly controlled. As a consequence, by properly setting
the relevant parameters typical multi-ion entangled states, e.g., state for
10 ions, could be deterministically generated. The feasibility of the proposal
is also discussed.Comment: 8 pages, 2 figures, 1 tabl
Electron-Phonon Interactions for Optical Phonon Modes in Few-Layer Graphene
We present a first-principles study of the electron-phonon (e-ph)
interactions and their contributions to the linewidths for the optical phonon
modes at and K in one to three-layer graphene. It is found that due to
the interlayer coupling and the stacking geometry, the high-frequency optical
phonon modes in few-layer graphene couple with different valence and conduction
bands, giving rise to different e-ph interaction strengths for these modes.
Some of the multilayer optical modes derived from the - mode of
monolayer graphene exhibit slightly higher frequencies and much reduced
linewidths. In addition, the linewidths of K- related modes in
multilayers depend on the stacking pattern and decrease with increasing layer
numbers.Comment: 6 pages,5 figures, submitted to PR
Deprojection technique for galaxy cluster considering point spread function
We present a new method for the analysis of Abell 1835 observed by
XMM-Newton. The method is a combination of the Direct Demodulation technique
and deprojection. We eliminate the effects of the point spread function (PSF)
with the Direct Demodulation technique. We then use a traditional depro-jection
technique to study the properties of Abell 1835. Compared to that of
deprojection method only, the central electron density derived from this method
increases by 30%, while the temperature profile is similar.Comment: accepted for publication in Sciences in China -- G, the Black Hole
special issu
Relaxed 2-D Principal Component Analysis by Norm for Face Recognition
A relaxed two dimensional principal component analysis (R2DPCA) approach is
proposed for face recognition. Different to the 2DPCA, 2DPCA- and G2DPCA,
the R2DPCA utilizes the label information (if known) of training samples to
calculate a relaxation vector and presents a weight to each subset of training
data. A new relaxed scatter matrix is defined and the computed projection axes
are able to increase the accuracy of face recognition. The optimal -norms
are selected in a reasonable range. Numerical experiments on practical face
databased indicate that the R2DPCA has high generalization ability and can
achieve a higher recognition rate than state-of-the-art methods.Comment: 19 pages, 11 figure
From Supercurrents to Soft Terms
In this paper,hidden sectors of Ferrara-Zumino multiplets with contributions
to soft terms coming from quantum supergravity are investigated in framework of
gravity mediation. The two-point correlator of Ferrara-Zumino multiplets can be
parameterized, which implies the wave function renormalizations of components
fields in gravity supermultiplet can be evaluated in relatively simple form.
Soft terms are calculated via supercurrent approach. We find gaugino masses are
independent of sfermion masses on general grounds. The unification of gaugino
masses is not universal. In comparison with general gauge mediation, there are
no sum rules for sfermion masses of each generation.Comment: v3, 9 p
Coulomb Screening of 2D Massive Dirac Fermions
A model of 2D massive Dirac fermions, interacting with a instantaneous
Coulomb interaction, is presented to mimic the physics of gapped graphene. The
static polarization function is calculated explicitly to analyze screening
effect at the finite temperature and density. Results are compared with the
massless case . We also show that various other works can be reproduced within
our model in a straightforward and unified manner
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