774 research outputs found
High Current Matching over Full-Swing and Low-Glitch Charge Pump Circuit for PLLs
A high current matching over full-swing and low-glitch charge pump (CP) circuit is proposed. The current of the CP is split into two identical branches having one-half the original current. The two branches are connected in source-coupled structure, and a two-stage amplifier is used to regulate the common-source voltage for the minimum current mismatch. The proposed CP is designed in TSMC 0.18µm CMOS technology with a power supply of 1.8 V. SpectreRF based simulation results show the mismatch between the current source and the current sink is less than 0.1% while the current is 40 µA and output swing is 1.32 V ranging from 0.2 V to 1.52 V. Moreover, the transient output current presents nearly no glitches. The simulation results verify the usage of the CP in PLLs with the maximum tuning range from the voltage-controlled oscillator, as well as the low power supply applications
Thermal stability and oxidation of layer-structured rhombohedral In3Se4 nanostructures
The thermal stability and oxidation of layer-structured rhombohedral In3Se4 nanostructures have been investigated. In-situ synchrotron X-ray diffraction in a sealed system reveals that In3Se4 has good thermal stability up to 900 degrees C. In contrast, In3Se4 has lower thermal stability up to 550 or 200 degrees C when heated in an atmosphere flushed with Ar or in air, respectively. The degradation mechanism was determined to be the oxidation of In3Se4 by O-2 in the heating environment. This research demonstrates how thermal processing conditions can influence the thermal stability of In3Se4, suggesting that appropriate heating environment for preserving its structural integrity is required. (C) 2013 AIP Publishing LLC
Magnetotransport properties of Cd3As2 nanostructures
Three-dimensional (3D) topological Dirac semimetal is a new kind of material
that has a linear energy dispersion in 3D momentum space and can be viewed as
an analog of graphene. Extensive efforts have been devoted to the understanding
of bulk materials, but yet it remains a challenge to explore the intriguing
physics in low-dimensional Dirac semimetals. Here, we report on the synthesis
of Cd3As2 nanowires and nanobelts and a systematic investigation of their
magnetotransport properties. Temperature-dependent ambipolar behavior is
evidently demonstrated, suggesting the presence of finite-size of bandgap in
nanowires. Cd3As2 nanobelts, however, exhibit metallic characteristics with a
high carrier mobility exceeding 32,000 cm2V-1s-1 and pronounced anomalous
double-period Shubnikov-de Haas (SdH) oscillations. Unlike the bulk
counterpart, the Cd3As2 nanobelts reveal the possibility of unusual change of
the Fermi sphere owing to the suppression of the dimensionality. More
importantly, their SdH oscillations can be effectively tuned by the gate
voltage. The successful synthesis of Cd3As2 nanostructures and their rich
physics open up exciting nanoelectronic applications of 3D Dirac semimetals.Comment: 18 pages, 5 figure
Suppression of Black-body Radiation Induced Zeeman Shifts in the Optical Clocks due to the Fine-structure Intramanifold Resonances
The roles of the fine-structure intramanifold resonances to the Zeeman shifts
caused by the blackbody radiation (BBRz shifts) in the optical clock
transitions are analyzed. The clock frequency measurement in the
clock transition of the singly charged aluminium ion (Al) has already been
reached the level at which the BBRz effect can be significant in
determining the uncertainty. In view of this, we probe first the BBRz shift in
this transition rigorously and demonstrate the importance of the contributions
from the intramanifold resonances explicitly. To carry out the analysis, we
determine the dynamic magnetic dipole (M1) polarizabilities of the clock states
over a wide range of angular frequencies by employing two variants of
relativistic many-body methods. This showed the BBRz shift is highly suppressed
due to blue-detuning of the BBR spectrum to the fine-structure
intramanifold resonance in Al and it fails to follow the usually assumed
static M1 polarizability limit in the estimation of the BBRz shift. The
resonance also leads to a reversal behavior of the temperature dependence and a
cancellation in the shift. After learning this behavior, we extended our
analyses to other optical clocks and found that these shifts are of the order
of micro-hertz leading to fractional shifts in the clock transitions at the
level or below
Beimingwu: A Learnware Dock System
The learnware paradigm proposed by Zhou [2016] aims to enable users to reuse
numerous existing well-trained models instead of building machine learning
models from scratch, with the hope of solving new user tasks even beyond
models' original purposes. In this paradigm, developers worldwide can submit
their high-performing models spontaneously to the learnware dock system
(formerly known as learnware market) without revealing their training data.
Once the dock system accepts the model, it assigns a specification and
accommodates the model. This specification allows the model to be adequately
identified and assembled to reuse according to future users' needs, even if
they have no prior knowledge of the model. This paradigm greatly differs from
the current big model direction and it is expected that a learnware dock system
housing millions or more high-performing models could offer excellent
capabilities for both planned tasks where big models are applicable; and
unplanned, specialized, data-sensitive scenarios where big models are not
present or applicable.
This paper describes Beimingwu, the first open-source learnware dock system
providing foundational support for future research of learnware paradigm.The
system significantly streamlines the model development for new user tasks,
thanks to its integrated architecture and engine design, extensive engineering
implementations and optimizations, and the integration of various algorithms
for learnware identification and reuse. Notably, this is possible even for
users with limited data and minimal expertise in machine learning, without
compromising the raw data's security. Beimingwu supports the entire process of
learnware paradigm. The system lays the foundation for future research in
learnware-related algorithms and systems, and prepares the ground for hosting a
vast array of learnwares and establishing a learnware ecosystem
Calibration of Temperature in the Lower Stratosphere from Microwave Measurements Using COSMIC Radio Occultation Data: Preliminary Results
Accurate, consistent, and stable observations from different satellite missions are crucial for climate change detection. In this study, we use Global Positioning System (GPS) Radio Occultation (RO) data from the early phase of the FORMOSAT-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission, which was successfully launched on 15 April 2006, to inter-calibrate Temperature in the Lower Stratosphere (TLS) taken from Advanced Microwave Sounding Unit (AMSU) microwave measurements from different satellites for potential improvements of stratospheric temperature trend analysis. Because of the limited number of COSMIC soundings in the early phase of the mission, these results are considered preliminary. In this study, we use COSMIC RO data to simulate microwave brightness temperatures for comparison with AMSU Ch9 measurements (e.g., TLS) on board NOAA15, 16, and 18. Excellent correlation was found between synthetic COSMIC brightness temperatures (Tbs) and Tbs from NOAA15, NOAA16, and NOAA18, respectively. However, systematic differences on the order of 0.7 to 2 K were found between COSMIC and AMSU observations over Antarctica. Our results demonstrate that synthetic COSMIC Tbs are very useful in identifying inter-satellite offsets among AMSU measurements from different satellites. To demonstrate the long-term stability of GPS RO data, we compare COSMIC dry temperature profiles to those from collocated CHAMP profiles, where CHAMP was launched in 2001. The fact that the CHAMPand COSMIC dry temperature difference between 500 and 10 hPa ranges from -0.35 K (at 10 hPa) to 0.25 K (at 30 hPa) and their mean difference is about -0.034 K demonstrates the long-term stability of GPS RO signals. In order to demonstrate the potential usage of the GPS RO calibrated AMSU Tbs to inter-calibrate other overlapping AMSU Tbs, we examine the uncertainty of the calibration coefficients derived from AMSU-GPS RO pairs. We found the difference between COSMIC calibrated AMSU Tbs and those from CHAMP to be in the range of __0.07 K with a 0.1 K standard deviation. This demonstrates the robustness of the calibration coefficients found from AMSU-GPS RO pairs and shows the potential to use the calibrated AMSU Tbs to calibrate other overlapping AMSU Tbs where no coincident GPS RO data are available
Dimensionality-confined superconductivity within SrNbO3-SrTiO3 heterostructures
Interfaces between transition-metal oxides are able to host two-dimensional
electron gases (2DEGs) and exhibit exotic quantum phenomena. Here we report the
observation of superconductivity below 230 mK for the heterostructure composed
of SrNbO3 (SNO) and SrTiO3 (STO). Different from some other counterparts with
two insulators, the metallic SNO provides a novel mechanism to form a quasi
2DEG by charge transfer from bulk towards interface under strain. The
superconductivity, residing within the strained SNO layer near the interface,
is contributed by an electron system with record-low carrier density. Notably,
although embedded in a normal metallic layer with a carrier density 4 to 5
orders higher, the electron system is still uniquely well-protected to retain
high mobility and lies deep in extreme quantum regime
Pretreating anaerobic fermentation liquid with calcium addition to improve short chain fatty acids extraction via in situ synthesis of layered double hydroxides
In situ synthesis of layered double hydroxides (LDHs) was proved to be an effective way to extract short chain fatty acids (SCFAs) from anaerobic fermentation liquid (AFL) as carbon source for biodenitrification, but the SCFAs content in SCFAs-LDH was unsatisfactory because of the existence of much carbonate in AFL. Pretreatment of AFL with calcium addition was investigated to remove carbonate and improve SCFAs extraction via LDHs synthesis. Results of batch tests showed that, the carbonate removal efficiency was as high as 76.6% when the calcium addition was 0.06 mol/L at pH 12. When using the optimal SCFAs/Al3+ ratio of 3.0, the total SCFAs content in SCFAs-LDH with pretreatment was improved to 46.5 mg COD/g LDH, which was 4.5 times of the control (10.4 mg COD/g LDH). These results suggest that adding calcium to AFL was an effective way to eliminate the negative effect of carbonates on SCFAs-LDH synthesis
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