194 research outputs found
Adaptive impedance control of robot manipulators based on Q-learning and disturbance observer
In this paper, an adaptive impedance control combined with disturbance observer (DOB) is developed for a general class of uncertain robot manipulators in discrete time. The impedance control is applied to realize the interaction force control of robot manipulators in unknown, time-varying environments. The optimal reference trajectory is produced by impedance control, and the impedance parameters are achieved using Q-learning technique, which is implemented based on trajectory tracking errors. The position control with DOB of robot manipulators is implemented to track the virtual desired trajectory, and the DOB is designed to compensate for unknown compounded disturbance function by bounding both tracking error inputs and compounded disturbance inputs in a permitted control region, of which the compounded disturbance function is taken into account of all uncertain terms and external disturbances. The appropriate DOB parameters are selected applying linear matrix inequalities (LMIs) method. Both the impedance control and the bounded DOB control can well guarantee semiglobal uniform boundness of the closed-loop robot systems based on Lyapunov analysis and Schur complement theory. Simulation results are performed to test and verify effectiveness of the investigated combining adaptive impedance control with DOB
Deep Interest Evolution Network for Click-Through Rate Prediction
Click-through rate~(CTR) prediction, whose goal is to estimate the
probability of the user clicks, has become one of the core tasks in advertising
systems. For CTR prediction model, it is necessary to capture the latent user
interest behind the user behavior data. Besides, considering the changing of
the external environment and the internal cognition, user interest evolves over
time dynamically. There are several CTR prediction methods for interest
modeling, while most of them regard the representation of behavior as the
interest directly, and lack specially modeling for latent interest behind the
concrete behavior. Moreover, few work consider the changing trend of interest.
In this paper, we propose a novel model, named Deep Interest Evolution
Network~(DIEN), for CTR prediction. Specifically, we design interest extractor
layer to capture temporal interests from history behavior sequence. At this
layer, we introduce an auxiliary loss to supervise interest extracting at each
step. As user interests are diverse, especially in the e-commerce system, we
propose interest evolving layer to capture interest evolving process that is
relative to the target item. At interest evolving layer, attention mechanism is
embedded into the sequential structure novelly, and the effects of relative
interests are strengthened during interest evolution. In the experiments on
both public and industrial datasets, DIEN significantly outperforms the
state-of-the-art solutions. Notably, DIEN has been deployed in the display
advertisement system of Taobao, and obtained 20.7\% improvement on CTR.Comment: 9 pages. Accepted by AAAI 201
Three-dimensionality of the bulk electronic structure in WTe2
We use temperature- and field-dependent resistivity measurements
[Shubnikov--de Haas (SdH) quantum oscillations] and ultrahigh resolution,
tunable, vacuum ultraviolet (VUV) laser-based angle-resolved photoemission
spectroscopy (ARPES) to study the three-dimensionality (3D) of the bulk
electronic structure in WTe2, a type-II Weyl semimetal. The bulk Fermi surface
(FS) consists of two pairs of electron pockets and two pairs of hole pockets
along the X-Gamma-X direction as detected by using an incident photon energy of
6.7 eV, which is consistent with the previously reported data. However, if
using an incident photon energy of 6.36 eV, another pair of tiny electron
pockets is detected on both sides of the Gamma point, which is in agreement
with the small quantum oscillation frequency peak observed in the
magnetoresistance. Therefore, the bulk, 3D FS consists of three pairs of
electron pockets and two pairs of hole pockets in total. With the ability of
fine tuning the incident photon energy, we demonstrate the strong
three-dimensionality of the bulk electronic structure in WTe2. The combination
of resistivity and ARPES measurements reveal the complete, and consistent,
picture of the bulk electronic structure of this material.Comment: 6 pages, 3 figure
Observation of Fermi Arcs in Type-II Weyl Semimetal Candidate WTe2
We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved
photoemission spectroscopy (ARPES) to study the electronic properties of
WTe, a material that was predicted to be a type-II Weyl semimetal. The Weyl
fermion states in WTe2 were proposed to emerge at the crossing points of
electron and hole pockets; and Fermi arcs connecting electron and hole pockets
would be visible in the spectral function on (001) surface. Here we report the
observation of such Fermi arcs in WTe2 confirming the theoretical predictions.
This provides strong evidence for type-II Weyl semimetallic states in WTe2.Comment: 5 pages, 4 figure
Temperature induced Lifshitz transition in WTe2
We use ultra-high resolution, tunable, VUV laser-based, angle-resolved
photoemission spectroscopy (ARPES) and temperature and field dependent
resistivity and thermoelectric power (TEP) measurements to study the electronic
properties of WTe2, a compound that manifests exceptionally large, temperature
dependent magnetoresistance. The temperature dependence of the TEP shows a
change of slope at T=175 K and the Kohler rule breaks down above 70-140 K
range. The Fermi surface consists of two electron pockets and two pairs of hole
pockets along the X-Gamma-X direction. Upon increase of temperature from 40K,
the hole pockets gradually sink below the chemical potential. Like BaFe2As2,
WTe2 has clear and substantial changes in its Fermi surface driven by modest
changes in temperature. In WTe2, this leads to a rare example of temperature
induced Lifshitz transition, associated with the complete disappearance of the
hole pockets. These dramatic changes of the electronic structure naturally
explain unusual features of the transport data.Comment: 5 pages, 3 figure
Passively Q-switched erbium-doped fiber laser using evanescent field interaction with gold-nanosphere based saturable absorber
We demonstrate an all-fiber passively Q-switched erbiumdoped fiber laser (EDFL) using a gold-nanosphere (GNS) based saturable absorber (SA) with evanescent field interaction. Using the interaction of evanescent field for fabricating SAs, long nonlinear interaction length of evanescent wave and GNSs can be achieved. The GNSs are synthesized from mixing solution of chloroauricacid (HAuCl4) and sodium citrate by the heating effects of the microfiber's evanescent field radiation. The proposed passively Q-switched EDFL could give output pulses at 1562 nm with pulse width of 1.78 ÎĽs, a repetition rate of 58.1 kHz, a pulse energy of 133 nJ and a output power of 7.7 mWwhen pumped by a 980 nm laser diode of 237 mW
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