13,635 research outputs found
Q & A Experiment to Search for Vacuum Dichroism, Pseudoscalar-Photon Interaction and Millicharged Fermions
A number of experiments are underway to detect vacuum birefringence and
dichroism -- PVLAS, Q & A, and BMV. Recently, PVLAS experiment has observed
optical rotation in vacuum by a magnetic field (vacuum dichroism). Theoretical
interpretations of this result include a possible pseudoscalar-photon
interaction and the existence of millicharged fermions. Here, we report the
progress and first results of Q & A (QED [quantum electrodynamics] and Axion)
experiment proposed and started in 1994. A 3.5-m high-finesse (around 30,000)
Fabry-Perot prototype detector extendable to 7-m has been built and tested. We
use X-pendulums and automatic control schemes developed by the
gravitational-wave detection community for mirror suspension and cavity
control. To polarize the vacuum, we use a 2.3-T dipole permanent magnet, with
27-mm-diameter clear borehole and 0.6-m field length,. In the experiment, the
magnet is rotated at 5-10 rev/s to generate time-dependent polarization signal
with twice the rotation frequency. Our
ellipsometer/polarization-rotation-detection-system is formed by a pair of
Glan-Taylor type polarizing prisms with extinction ratio lower than 10-8
together with a polarization modulating Faraday Cell with/without a quarter
wave plate. We made an independent calibration of our apparatus by performing a
measurement of gaseous Cotton-Mouton effect of nitrogen. We present our first
experimental results and give a brief discussion of our experimental limit on
pseudo-scalar-photon interaction and millicharged fermions.Comment: 21 pages, 13 figures, submitted to Modern Physics Letter
Optimization of MPPT step size in stand-alone solar pumping systems
In a stand-alone solar pumping system with a pump driven by an induction motor, the step size in maximum power point tracking (MPPT) methods greatly affects the dynamics and stability of the system. In this paper, we analyze some phenomena appearing in the contrastive experiments which have been carried out for about one year, and give a solution to determine the step size based on system parameters and controller capabilities. The contrastive experiments show that the system performance can be obviously improved by the optimized step size together with an adequate smoothing capacitor. © 2006 IEEE.published_or_final_versio
Raman spectroscopy of epitaxial graphene on a SiC substrate
The fabrication of epitaxial graphene (EG) on SiC substrate by annealing has
attracted a lot of interest as it may speed up the application of graphene for
future electronic devices. The interaction of EG and the SiC substrate is
critical to its electronic and physical properties. In this work, Raman
spectroscopy was used to study the structure of EG and its interaction with SiC
substrate. All the Raman bands of EG blue shift from that of bulk graphite and
graphene made by micromechanical cleavage, which was attributed to the
compressive strain induced by the substrate. A model containing 13 x 13
honeycomb lattice cells of graphene on carbon nanomesh was constructed to
explain the origin of strain. The lattice mismatch between graphene layer and
substrate causes the compressive stress of 2.27 GPa on graphene. We also
demonstrate that the electronic structures of EG grown on Si and C terminated
SiC substrates are quite different. Our experimental results shed light on the
interaction between graphene and SiC substrate that are critical to the future
applications of EG.Comment: 20 pages, 5 figure
Incorporating UPFC model into the power system toolbox of theMATLAB for transient stability study
In this paper, power frequency model for unified power flow controller (UPFC) is presented with its DC link capacitor dynamics included. A novel interface of UPFC to AC network for transient stability study is then suggested and realised using Power System Toolbox (PST) of MATLAB. The control strategies for UPFC shunt and series elements are also discussed. Computer results on a 4-generator interconnected test power system show that the convergence and accuracy of the suggested interface are challenging and the suggested interface makes it very easy to incorporate the UPFC model into the conventional transient stability programme. The results also show that the UPFC control strategy had strong impacts on the performance of UPFC.published_or_final_versio
Temperature dependence of electron-spin relaxation in a single InAs quantum dot at zero applied magnetic field
The temperature-dependent electron spin relaxation of positively charged
excitons in a single InAs quantum dot (QD) was measured by time-resolved
photoluminescence spectroscopy at zero applied magnetic fields. The
experimental results show that the electron-spin relaxation is clearly divided
into two different temperature regimes: (i) T < 50 K, spin relaxation depends
on the dynamical nuclear spin polarization (DNSP) and is approximately
temperature-independent, as predicted by Merkulov et al. (ii) T > about 50 K,
spin relaxation speeds up with increasing temperature. A model of two LO phonon
scattering process coupled with hyperfine interaction is proposed to account
for the accelerated electron spin relaxation at higher temperatures.Comment: 10 pages, 4 figure
On resonant scatterers as a factor limiting carrier mobility in graphene
We show that graphene deposited on a substrate has a non-negligible density
of atomic scale defects. This is evidenced by a previously unnoticed D peak in
the Raman spectra with intensity of about 1% with respect to the G peak. We
evaluated the effect of such impurities on electron transport by mimicking them
with hydrogen adsorbates and measuring the induced changes in both mobility and
Raman intensity. If the intervalley scatterers responsible for the D peak are
monovalent, their concentration is sufficient to account for the limited
mobilities achievable in graphene on a substrate.Comment: version 2: several comments are taken into account and refs adde
Temporal and spatial changes of water quality and management strategies of Dianchi Lake in southwest China
Temporal and spatial changes to the water quality of Dianchi Lake in
southwest China were investigated using monthly monitoring data from 2005 to
2012. Dianchi Lake is divided into two parts, Caohai Lake and Waihai Lake,
by a man-made dike. Caohai Lake lies at the north of Dianchi Lake, while
Waihai Lake is the main water body of Dianchi Lake and accounts for 96.7%
of the whole area of the lake. Based on the analysis of total phosphorus
(TP), total nitrogen (TN), and chlorophyll <i>a</i> (Chl <i>a</i>) concentrations, it was
determined that, in Caohai Lake, the annual concentrations of these
variables ranged from 0.19–1.46 mg L<sup>−1</sup>, 6.11–16.79 mg L<sup>−1</sup>, 0.06–0.14 mg L<sup>−1</sup>,
respectively. In addition, the annual concentrations of TP, TN and Chl <i>a</i> in
Waihai Lake ranged between 0.13 and 0.20 mg L<sup>−1</sup>, 1.82 and 3.01 mg L<sup>−1</sup>, and 0.04 and 0.09 mg L<sup>−1</sup>,
respectively. Cluster analysis (CA) classified the 10 monitoring sites into
two clusters (cluster A and cluster B) based on similarities of water
quality characteristics. Our data revealed that the current status of water
quality within Caohai Lake was much worse than that of Waihai Lake. Water
quality was seriously degraded during the economic boom near the period of
the "Eleventh Five-Year Plan" (2005–2010), and gradually improved from
2010 to 2012 because of the "standard emission directive to industry". The
main factors that influenced the spatial and temporal changes to water
quality were natural factors including lake evolution and regional
characteristic as well as human factors such as pollution load into the lake
and management strategies that were already adopted. Some activities and
regulations were implemented to enhance the lake environment by controlling
wastewater emissions and establishing regulations to protect the lakes in
the Yunnan Province. However, problems with institutional fragmentation
(horizontal and vertical), simple treatment methods, low-intensity
investment in pollution control, and lack of meaningful endogenous pollution
control strategies were still present in the lake management strategy. To
solve these problems, suitable control measures are needed, especially
considering the current old-age status of Dianchi Lake. The fundamental
improvement of the water quality within Caohai Lake was dependent on the
measures taken in the upper reaches of the Caohai Watershed, including
further recovery of submerged plants, resource utilization by floating
plants and the reinforcement of sediment disposal. Management strategies for
endogenous pollution in Waihai Lake were mainly dependent on restocking
algae-eating fish and the ecological restoration of macrophytes. In this
way, the swamping trend and the ageing process that is occurring in Dianchi
Lake can be stunted. And the management strategies would be a contribution
to the management of water conflicts between mankind and ecosystems in similar
lakes
System Framework for Digital Monitoring of the Construction of Asphalt Concrete Pavement Based on IoT, BeiDou Navigation System, and 5G Technology
In the construction of asphalt pavement, poor quality is often the main reason for damage to the pavement, which necessitates the use of monitoring systems during the construction stage. Therefore, this study focuses on building an asphalt concrete pavement construction monitoring system to monitor the construction phase. Through a literature review and semi-structured interviews with industry experts, this paper provides an in-depth understanding of the goals and obstacles of asphalt pavement monitoring and discusses directions for improvement. Subsequently, based on the analysis of the interview results, a system framework for asphalt concrete pavement construction monitoring was constructed, and the system was successfully developed and applied to a highway construction project. The results show that the monitoring system significantly improves the construction quality of asphalt concrete pavement, improves the intelligent level of pavement construction management, and promotes the digital development of highway construction
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