1,047 research outputs found
Charged particles in a rotating magnetic field
We study the valence electron of an alkaline atom or a general charged
particle with arbitrary spin and with magnetic moment moving in a rotating
magnetic field. By using a time-dependent unitary transformation, the
Schr\"odinger equation with the time-dependent Hamiltonian can be reduced to a
Schr\"odinger-like equation with a time-independent effective Hamiltonian.
Eigenstates of the effective Hamiltonian correspond to cyclic solutions of the
original Schr\"odinger equation. The nonadiabatic geometric phase of a cyclic
solution can be expressed in terms of the expectation value of the component of
the total angular momentum along the rotating axis, regardless of whether the
solution is explicitly available. For the alkaline atomic electron and a strong
magnetic field, the eigenvalue problem of the effective Hamiltonian is
completely solved, and the geometric phase turns out to be a linear combination
of two solid angles. For a weak magnetic field, the same problem is solved
partly. For a general charged particle, the problem is solved approximately in
a slowly rotating magnetic field, and the geometric phases are also calculated.Comment: REVTeX, 13 pages, no figure. There are two minor errors in the
published version due to incorrect editing by the publisher. The "spin-1" in
Sec. I and the "spin 1" in Sec. II below Eq. (2c) should both be changed to
"spin" or "spin angular momentum". The preferred E-mail for correspondence is
[email protected] or [email protected]
Geometric phases for neutral and charged particles in a time-dependent magnetic field
It is well known that any cyclic solution of a spin 1/2 neutral particle
moving in an arbitrary magnetic field has a nonadiabatic geometric phase
proportional to the solid angle subtended by the trace of the spin. For neutral
particles with higher spin, this is true for cyclic solutions with special
initial conditions. For more general cyclic solutions, however, this does not
hold. As an example, we consider the most general solutions of such particles
moving in a rotating magnetic field. If the parameters of the system are
appropriately chosen, all solutions are cyclic. The nonadiabatic geometric
phase and the solid angle are both calculated explicitly. It turns out that the
nonadiabatic geometric phase contains an extra term in addition to the one
proportional to the solid angle. The extra term vanishes automatically for spin
1/2. For higher spin, however, it depends on the initial condition. We also
consider the valence electron of an alkaline atom. For cyclic solutions with
special initial conditions in an arbitrary strong magnetic field, we prove that
the nonadiabatic geometric phase is a linear combination of the two solid
angles subtended by the traces of the orbit and spin angular momenta. For more
general cyclic solutions in a strong rotating magnetic field, the nonadiabatic
geometric phase also contains extra terms in addition to the linear
combination.Comment: revtex, 18 pages, no figur
Time evolution, cyclic solutions and geometric phases for general spin in an arbitrarily varying magnetic field
A neutral particle with general spin and magnetic moment moving in an
arbitrarily varying magnetic field is studied. The time evolution operator for
the Schr\"odinger equation can be obtained if one can find a unit vector that
satisfies the equation obeyed by the mean of the spin operator. There exist at
least cyclic solutions in any time interval. Some particular time
interval may exist in which all solutions are cyclic. The nonadiabatic
geometric phase for cyclic solutions generally contains extra terms in addition
to the familiar one that is proportional to the solid angle subtended by the
closed trace of the spin vector.Comment: revtex4, 8 pages, no figur
First evidence of middle atmospheric HO_2 response to 27 day solar cycles from satellite observations
HO_2 and OH, also known as HO_x, play an important role in controlling middle atmospheric O_3. Due to their photochemical production and short chemical lifetimes, HO_x are expected to respond rapidly to solar irradiance changes, resulting in O_3 variability. While OH solar cycle signals have been investigated, HO_2 studies have been limited by the lack of reliable observations. Here we present the first evidence of HO_2 variability during solar 27âday cycles by investigating the recently developed HO_2 data from the Aura Microwave Limb Sounder (MLS). We focus on 2012â2015, when solar variability is strong near the peak of Solar Cycle 24. The features of HO_2 variability, with the strongest signals at 0.01â0.068âhPa, correlate well with those of solar Lyman α. When continuous MLS OH observations are not available, the new HO_2 data could be a promising alternative for investigating HO_x variability and the corresponding impacts on O_3 and the climate
Levinson's Theorem for the Klein-Gordon Equation in Two Dimensions
The two-dimensional Levinson theorem for the Klein-Gordon equation with a
cylindrically symmetric potential is established. It is shown that
, where denotes
the difference between the number of bound states of the particle
and the ones of antiparticle with a fixed angular momentum , and
the is named phase shifts. The constants and
are introduced to symbol the critical cases where the half bound
states occur at .Comment: Revtex file 14 pages, submitted to Phys. Rev.
Accounting for aerosol scattering in the CLARS retrieval of column averaged CO_2 mixing ratios
The California Laboratory for Atmospheric Remote Sensing Fourier transform spectrometer (CLARSâFTS) deployed at Mount Wilson, California, has been measuring column abundances of greenhouse gases in the Los Angeles (LA) basin in the nearâinfrared spectral region since August 2011. CLARSâFTS measures reflected sunlight and has high sensitivity to absorption and scattering in the boundary layer. In this study, we estimate the retrieval biases caused by aerosol scattering and present a fast and accurate approach to correct for the bias in the CLARS column averaged CO2 mixing ratio product, X_(CO2). The high spectral resolution of 0.06âcm^(â1) is exploited to reveal the physical mechanism for the bias. We employ a numerical radiative transfer model to simulate the impact of neglecting aerosol scattering on the CO_2 and O_2 slant column densities operationally retrieved from CLARSâFTS measurements. These simulations show that the CLARSâFTS operational retrieval algorithm likely underestimates CO_2 and O_2 abundances over the LA basin in scenes with moderate aerosol loading. The bias in the CO_2 and O_2 abundances due to neglecting aerosol scattering cannot be canceled by ratioing each other in the derivation of the operational product of X_(CO2). We propose a new method for approximately correcting the aerosolâinduced bias. Results for CLARS X_(CO2) are compared to directâSun X_(CO2) retrievals from a nearby Total Carbon Column Observing Network (TCCON) station. The biasâcorrection approach significantly improves the correlation between the X_(CO2) retrieved from CLARS and TCCON, demonstrating that this approach can increase the yield of useful data from CLARSâFTS in the presence of moderate aerosol loading
Prevalence of the Cryptosporidium Pig Genotype II in Pigs from the Yangtze River Delta, China
Background: Cryptosporidium spp. is prevalent globally, pigs are an important Cryptosporidium reservoir. In China, little data regarding rates of Cryptosporidium infections in pigs are available. The present study was therefore aimed at characterizing the distribution of Cryptosporidium species in pigs from two different cities, Shaoxing and Shanghai, from the Yangtze River delta. Methodology/Principal Findings: Nested PCR to amplify the 18S rRNA locus on DNA extracted from fecal samples (n = 94) revealed the positive rate of Cryptosporidium in pigs from two cities was approximately 17.0%. The positive rates in Shanghai and Shaoxing were 14.3 % and 25.0 % respectively. Amplified sequences were verified by sequencing. The identified strain belonged to the C. pig genotype II using BLAST analysis in the NCBI database. Conclusion/Significance: Our finding of Cryptosporidium pig genotype II in pigs in the Yangtze River delta area suggests that pig farms in this region must be considered a public health threat and proper control measures be introduced
Hydroclimate in the Pamirs Was Driven by Changes in PrecipitationâEvaporation Seasonality Since theLast Glacial Period
The Central Asian Pamir Mountains (Pamirs) are a highâaltitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacialâinterglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31âkyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. ÎŽD values of terrestrial biomarkers showed insolationâdriven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive ÎŽD shifts driven by changes in precipitation seasonality were observed at ca. 31â30, 28â26, and 17â14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitationâevaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant
Quantum Fluctuations of Vortex-Lattice State in Ultrafast Rotating Bose Gas
Quantum fluctuations in an ultrafast rotating Bose gas at zero temperature
are investigated. We calculate the condensate density perturbatively to show
that no condensate is present in the thermodynamic limit. The excitation from
Gaussian fluctuations around the mean field solution causes infrared
divergences in loop diagrams, nevertheless, in calculating the atom number
density, the correlation functions and the free energy, we find the sum of the
divergences in the same loop order vanishes and obtain finite physical
quantities. The long-range correlation is explored and the algebraic decay
exponent for the single-particle correlation function is obtained. The atom
number density distribution is obtained at the one-loop level, which
illustrates the quantum fluctuation effects to melt the mean field
vortex-lattice. By the non-perturbative Gaussian variational method, we locate
the spinodal point of the vortex-lattice state.Comment: 14 pgaes, 4 figure
Quantum-mechanical model for particles carrying electric charge and magnetic flux in two dimensions
We propose a simple quantum mechanical equation for particles in two
dimensions, each particle carrying electric charge and magnetic flux. Such
particles appear in (2+1)-dimensional Chern-Simons field theories as charged
vortex soliton solutions, where the ratio of charge to flux is a constant
independent of the specific solution. As an approximation, the charge-flux
interaction is described here by the Aharonov-Bohm potential, and the
charge-charge interaction by the Coulomb one. The equation for two particles,
one with charge and flux () and the other with () where
is a pure number is studied in detail. The bound state problem is solved
exactly for arbitrary and when . The scattering problem is
exactly solved in parabolic coordinates in special cases when takes integers or half integers. In both cases the cross sections obtained
are rather different from that for pure Coulomb scattering.Comment: 12 pages, REVTeX, no figur
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