1,743 research outputs found
Fermi-Bose transformation for the time-dependent Lieb-Liniger gas
Exact solutions of the Schrodinger equation describing a freely expanding
Lieb-Liniger (LL) gas of delta-interacting bosons in one spatial dimension are
constructed. The many-body wave function is obtained by transforming a fully
antisymmetric (fermionic) time-dependent wave function which obeys the
Schrodinger equation for a free gas. This transformation employs a differential
Fermi-Bose mapping operator which depends on the strength of the interaction
and the number of particles.Comment: 4+ pages, 1 figure; added reference
Momentum distribution of a freely expanding Lieb-Liniger gas
We numerically study free expansion of a few Lieb-Liniger bosons, which are
initially in the ground state of an infinitely deep hard-wall trap. Numerical
calculation is carried out by employing a standard Fourier transform, as
follows from the Fermi-Bose transformation for a time-dependent Lieb-Liniger
gas. We study the evolution of the momentum distribution, the real-space
single-particle density, and the occupancies of natural orbitals. Our numerical
calculation allows us to explore the behavior of these observables in the
transient regime of the expansion, where they are non-trivially affected by the
particle interactions. We derive analytically (by using the stationary phase
approximation) the formula which connects the asymptotic shape of the momentum
distribution and the initial state. For sufficiently large times the momentum
distribution coincides (up to a simple scaling transformation) with the shape
of the real-space single-particle density (the expansion is asymptotically
ballistic). Our analytical and numerical results are in good agreement.Comment: small changes; references correcte
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Agricultural management and plant selection interactively affect rhizosphere microbial community structure and nitrogen cycling.
BACKGROUND:Rhizosphere microbial communities are key regulators of plant performance, yet few studies have assessed the impact of different management approaches on the rhizosphere microbiomes of major crops. Rhizosphere microbial communities are shaped by interactions between agricultural management and host selection processes, but studies often consider these factors individually rather than in combination. We tested the impacts of management (M) and rhizosphere effects (R) on microbial community structure and co-occurrence networks of maize roots collected from long-term conventionally and organically managed maize-tomato agroecosystems. We also explored the interaction between these factors (M × R) and how it impacts rhizosphere microbial diversity and composition, differential abundance, indicator taxa, co-occurrence network structure, and microbial nitrogen-cycling processes. RESULTS:Host selection processes moderate the influence of agricultural management on rhizosphere microbial communities, although bacteria and fungi respond differently to plant selection and agricultural management. We found that plants recruit management-system-specific taxa and shift N-cycling pathways in the rhizosphere, distinguishing this soil compartment from bulk soil. Rhizosphere microbiomes from conventional and organic systems were more similar in diversity and network structure than communities from their respective bulk soils, and community composition was affected by both M and R effects. In contrast, fungal community composition was affected only by management, and network structure only by plant selection. Quantification of six nitrogen-cycling genes (nifH, amoA [bacterial and archaeal], nirK, nrfA, and nosZ) revealed that only nosZ abundance was affected by management and was higher in the organic system. CONCLUSIONS:Plant selection interacts with conventional and organic management practices to shape rhizosphere microbial community composition, co-occurrence patterns, and at least one nitrogen-cycling process. Reframing research priorities to better understand adaptive plant-microbe feedbacks and include roots as a significant moderating influence of management outcomes could help guide plant-oriented strategies to improve productivity and agroecosystem sustainability
Discretized vs. continuous models of p-wave interacting fermions in 1D
We present a general mapping between continuous and lattice models of Bose-
and Fermi-gases in one dimension, interacting via local two-body interactions.
For s-wave interacting bosons we arrive at the Bose-Hubbard model in the weakly
interacting, low density regime. The dual problem of p-wave interacting
fermions is mapped to the spin-1/2 XXZ model close to the critical point in the
highly polarized regime. The mappings are shown to be optimal in the sense that
they produce the least error possible for a given discretization length. As an
application we examine the ground state of a interacting Fermi gas in a
harmonic trap, calculating numerically real-space and momentum-space
distributions as well as two-particle correlations. In the analytically known
limits the convergence of the results of the lattice model to the continuous
one is shown.Comment: 7 pages, 5 figure
Attempted Bethe ansatz solution for one-dimensional directed polymers in random media
We study the statistical properties of one-dimensional directed polymers in a
short-range random potential by mapping the replicated problem to a many body
quantum boson system with attractive interactions. We find the full set of
eigenvalues and eigenfunctions of the many-body system and perform the
summation over the entire spectrum of excited states. The analytic continuation
of the obtained exact expression for the replica partition function from
integer to non-integer replica parameter N turns out to be ambiguous.
Performing the analytic continuation simply by assuming that the parameter N
can take arbitrary complex values, and going to the thermodynamic limit of the
original directed polymer problem, we obtain the explicit universal expression
for the probability distribution function of free energy fluctuations.Comment: 32 pages, 1 figur
Magnetic anomalies in Nd6Co(1.67)Si3: Surprising first order transitions in the low-temperature isothermal magnetization
We present the results of magnetic measurements on Nd6Co(1.67)Si3, a compound
recently reported to crystallize in a hexagonal structure (space group P6_3/m)
and to undergo long range magnetic ordering below 84 K. The results reveal that
the magnetism of this compound is quite complex with additional magnetic
anomalies near 50 and 20 K. There are qualitative changes in the isothermal
magnetization behavior with the variation of temperature. Notably, there is a
field-induced spin reorientation as the temperature is lowered below 20 K. A
finding we stress is that this transition is discontinuous for 1.8K in the
virgin curve, but the first order character appears only after a field-cycling
for a narrow higher temperature range near 5 K. Thus, this compound serves as
an example for the stabilisation of first-order transition induced by
magnetic-field-cycling. The issues of 'Phase co-existence' and 'meta-stability'
after a field-cycling at low temperatures in this compound are also addressed
Current induced domain wall dynamics in the presence of spin orbit torques
Current induced domain wall (DW) motion in perpendicularly magnetized
nanostripes in the presence of spin orbit torques is studied. We show using
micromagnetic simulations that the direction of the current induced DW motion
and the associated DW velocity depend on the relative values of the field like
torque (FLT) and the Slonczewski like torques (SLT). The results are well
explained by a collective coordinate model which is used to draw a phase
diagram of the DW dynamics as a function of the FLT and the SLT. We show that a
large increase in the DW velocity can be reached by a proper tuning of both
torques.Comment: 9 pages, 3 figure
Extended trigonometric Cherednik algebras and nonstationary Schr\"odinger equations with delta-potentials
We realize an extended version of the trigonometric Cherednik algebra as
affine Dunkl operators involving Heaviside functions. We use the quadratic
Casimir element of the extended trigonometric Cherednik algebra to define an
explicit nonstationary Schr\"odinger equation with delta-potential. We use
coordinate Bethe ansatz methods to construct solutions of the nonstationary
Schr\"odinger equation in terms of generalized Bethe wave functions. It is
shown that the generalized Bethe wave functions satisfy affine difference
Knizhnik-Zamolodchikov equations in their spectral parameter. The relation to
the vector valued root system analogs of the quantum Bose gas on the circle
with pairwise delta-function interactions is indicated.Comment: 23 pages; Version 2: expanded introduction and misprints correcte
Pairing states of a polarized Fermi gas trapped in a one-dimensional optical lattice
We study the properties of a one-dimensional (1D) gas of fermions trapped in
a lattice by means of the density matrix renormalization group method, focusing
on the case of unequal spin populations, and strong attractive interaction. In
the low density regime, the system phase-separates into a well defined
superconducting core and a fully polarized metallic cloud surrounding it. We
argue that the superconducting phase corresponds to a 1D analogue of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, with a quasi-condensate of
tightly bound bosonic pairs with a finite center-of-mass momentum that scales
linearly with the magnetization. In the large density limit, the system allows
for four phases: in the core, we either find a Fock state of localized pairs or
a metallic shell with free spin-down fermions moving in a fully filled
background of spin-up fermions. As the magnetization increases, the Fock state
disappears to give room for a metallic phase, with a partially polarized
superconducting FFLO shell and a fully polarized metallic cloud surrounding the
core.Comment: 4 pages, 5 fig
Exact Results for Three-Body Correlations in a Degenerate One-Dimensional Bose Gas
Motivated by recent experiments we derive an exact expression for the
correlation function entering the three-body recombination rate for a
one-dimensional gas of interacting bosons. The answer, given in terms of two
thermodynamic parameters of the Lieb-Liniger model, is valid for all values of
the dimensionless coupling and contains the previously known results
for the Bogoliubov and Tonks-Girardeau regimes as limiting cases. We also
investigate finite-size effects by calculating the correlation function for
small systems of 3, 4, 5 and 6 particles.Comment: 4 pages, 2 figure
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