24,064 research outputs found
Nonlinear dynamics of a cigar-shaped Bose-Einstein condensate coupled with a single cavity mode
We investigate the nonlinear dynamics of a combined system which is composed
of a cigar-shaped Bose-Einstein condensate and an optical cavity. The two sides
couple dispersively. This system is characterized by its nonlinearity: after
integrating out the freedom of the cavity mode, the potential felt by the
condensate depends on the condensate itself. We develop a discrete-mode
approximation for the condensate. Based on this approximation, we map out the
steady configurations of the system. It is found that due to the nonlinearity
of the system, the nonlinear levels of the system can fold up in some parameter
regimes. That will lead to the breakdown of adiabaticity. Analysis of the
dynamical stability of the steady states indicates that the same level
structure also results in optical bistability.Comment: 8 pages, 5 figure
An experimental study for a miniature Stirling refrigerator
Experimental results of a miniature two-stage Stirling cryocooler are introduced. The influence of filling gas pressure and refrigeration temperature on the refrigerating capacity along with the relationship between parameters was measured. The valley pressure corresponding to the lowest refrigeration temperature and the cooldown time versus operating pressure are discussed. The coefficient of performance and thermodynamic efficiency of the cryocooler are calculated based on experimental data
Vector magnetic field sensing by single nitrogen vacancy center in diamond
In this Letter, we proposed and experimentally demonstrated a method to
detect vector magnetic field with a single nitrogen vacancy (NV) center in
diamond. The magnetic field in parallel with the axis of the NV center can be
obtained by detecting the electron Zeeman shift, while the Larmor precession of
an ancillary nuclear spin close to the NV center can be used to measure the
field perpendicular to the axis. Experimentally, both the Zeeman shift and
Larmor precession can be measured through the fluorescence from the NV center.
By applying additional calibrated magnetic fields, complete information of the
vector magnetic field can be achieved with such a method. This vector magnetic
field detection method is insensitive to temperature fluctuation and it can be
applied to nanoscale magnetic measurement.Comment: 5 pages, 5 figure
Reduction effect of individual N, P, K fertilization on antibiotic resistance genes in reclaimed water irrigated soil
The transfer of antibiotic resistance genes (ARGs) in soil under reclaimed water irrigation poses a potential environmental risk. Regulation of NPK fertilizer could influence the behavior of bacterial communities, mobile genetic elements (MGEs), and soil properties, which determine the fate of ARGs. To identify the key element in NPK fertilizer and realize efficient regulation, we explored the effect of individual N, P, K fertilization on ARGs variation in tomato rhizosphere and bulk soils. Compared with an unfertilized treatment, N fertilization resulted in greater decreases in the abundance of ARGs (decreases of 24.06%‒73.09%) than did either P fertilization (increases of up to 35.84%, decreases of up to 58.80%) or K fertilization (decreases of 13.47%‒72.47%). The influence of different forms of N (CO(NH2)2, NaNO3, and NH4HCO3), P (Ca(H2PO4)2 and CaMgO4P+), and K (KCl and K2(SO4)) fertilizers was also investigated in this study, and showed the influence of NaNO3, CaMgO4P+, and K2(SO4) on reducing ARGs abundance was greater in different types of N, P, K fertilizers. Bacterial communities showed the strongest response to N fertilization. The reduced bacterial diversity and abundance of ARG-host and non-host organisms explained the decline of total ARG abundance in soil. In soils fertilized with either P or K, the effect of soil properties, especially total nitrogen and pH, on ARGs variation was greater than that of bacterial community and MGEs. These results suggest that N regulation of in NPK fertilizer may be an effective way to reduce the risks of ARGs in soil associated with reclaimed water irrigation
Inelastic cotunneling induced decoherence and relaxation, charge and spin currents in an interacting quantum dot under a magnetic field
We present a theoretical analysis of several aspects of nonequilibirum
cotunneling through a strong Coulomb-blockaded quantum dot (QD) subject to a
finite magnetic field in the weak coupling limit. We carry this out by
developing a generic quantum Heisenberg-Langevin equation approach leading to a
set of Bloch dynamical equations which describe the nonequilibrium cotunneling
in a convenient and compact way. These equations describe the time evolution of
the spin variables of the QD explicitly in terms of the response and
correlation functions of the free reservoir variables. This scheme not only
provides analytical expressions for the relaxation and decoherence of the
localized spin induced by cotunneling, but it also facilitates evaluations of
the nonequilibrium magnetization, the charge current, and the spin current at
arbitrary bias-voltage, magnetic field, and temperature. We find that all
cotunneling events produce decoherence, but relaxation stems only from {\em
inelastic} spin-flip cotunneling processes. Moreover, our specific calculations
show that cotunneling processes involving electron transfer (both spin-flip and
non-spin-flip) contribute to charge current, while spin-flip cotunneling
processes are required to produce a net spin current in the asymmetric coupling
case. We also point out that under the influence of a nonzero magnetic field,
spin-flip cotunneling is an energy-consuming process requiring a sufficiently
strong external bias-voltage for activation, explaining the behavior of
differential conductance at low temperature: in particular, the splitting of
the zero-bias anomaly in the charge current and a broad zero-magnitude "window"
of differential conductance for the spin current near zero-bias-voltage.Comment: 15 pages, 5 figures, published version, to appear in Phys. Rev.
An Accretion-Jet Model for Black Hole Binaries: Interpreting the Spectral and Timing Features of XTE J1118+480
Multi-wavelength observations of the black hole X-ray binary XTE J1118+480
have offered abundant spectral and timing information about the source, and
have thus provided serious challenges to theoretical models. We propose a
coupled accretion-jet model to interpret the observations. We model the
accretion flow as an outer standard thin accretion disk truncated at a
transition radius by an inner hot accretion flow. The accretion flow accounts
for the observed UV and X-ray emission, but it substantially under-predicts the
radio and infrared fluxes, even after we allow for nonthermal electrons in the
hot flow. We attribute the latter components to a jet. We model the jet
emission by means of the internal shock scenario which is widely employed for
gamma-ray bursts. In our accretion-jet model of XTE J1118+480, the jet
dominates the radio and infrared emission, the thin disk dominates the UV
emission, and the hot flow produces most of the X-ray emission. The optical
emission has contributions from all three components: jet, thin disk, and hot
flow. The model qualitatively accounts for timing features, such as the
intriguing positive and negative time lags between the optical and X-ray
emission, and the wavelength-dependent variability amplitude.Comment: 27 pages, 4 figures (one in color); to appear in ApJ in Feb. 200
Analytical model of non-Markovian decoherence in donor-based charge quantum bits
We develop an analytical model for describing the dynamics of a donor-based
charge quantum bit (qubit). As a result, the quantum decoherence of the qubit
is analytically obtained and shown to reveal non-Markovian features: The
decoherence rate varies with time and even attains negative values, generating
a non-exponential decay of the electronic coherence and a later recoherence.
The resulting coherence time is inversely proportional to the temperature, thus
leading to low decoherence below a material dependent characteristic
temperature.Comment: 19 pages, 3 figure
Numerical simulation of welding of intersecting line joints of 6061-T6 aluminum alloy bicycle frame
The joints of aluminum alloy frames are usually welded by manual TIG welding. In order to study the distribution law of welding stress level and welding temperature field of intersecting joints of 6061-T6 aluminum alloy bicycle frames, a intersecting joints model of welding parts was established by Finite Element Model (FEM), Software. Based on ABAQUS software, the welding temperature field and welding stress field were studied and analyzed by using direct thermal coupling method. The accuracy of welding simulation is fully verified, which can meet the simulation requirements required for the subsequent optimization process design, and achieve the purpose of shortening the time required for the accumulation of practical inspection
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