1,518 research outputs found
Optical ladder operators in the Glauber-Fock oscillator array
In this study, we investigate the stationary states of the Glauber-Fock
oscillator waveguide array. We begin by transforming the associated Hamiltonian
into the form of a quantum harmonic oscillator Hamiltonian, allowing the
implementation of a supersymmetric (SUSY) approach. By considering the simplest
case for the intertwining operator, the optical ladder operators are
straightforwardly constructed and shown to map eigensolutions into
eigensolutions of the corresponding Hamiltonian operator, in pretty much the
same manner as it is done for the quantum harmonic oscillator case. The ladder
of the corresponding (eigen) supermodes is then easily established
Temporal factorization of a non-stationary electromagnetic cavity field
When an electromagnetic field is confined in a cavity of variable length,
real photons may be generated from vacuum fluctuations due to highly
nonadiabatic boundary conditions. The corresponding effective Hamiltonian is
time-dependent and contains infinite intermode interactions. Considering one of
the cavity mirrors fixed and the other describing uniform motion (zero
acceleration), we show that it is possible to factorize the entire temporal
dependency and write its formal solution, i.e., the Hamiltonian becomes a
product of a time-dependent function and a time-independent operator. With this
factorization, we prove in detail that the photon production is proportional to
the Planck factor involving a velocity-dependent effective temperature. This
temperature significantly limits photon generation even for ultra-relativistic
motion. The time-dependent unitary transformations we introduce to obtain
temporal factorization help establishing connections with the shortcuts to
adiabaticity of quantum thermodynamics and with the quantum Arnold
transformation.Comment: 10 pages, 4 figures. Accepted in Phys. Rev.
Exact Solution to the Driven Jaynes-Cummings System
We investigate the dynamics of the driven Jaynes-Cummings model, where a
two-level atom interacts with a quantized field and both, atom and field, are
driven by an external classical field. Via an invariant approach, we are able
to transform the corresponding Hamiltonian into the one of the standard
Jaynes-Cummings model. Subsequently, the exact analytical solution of the
Schr\"odinger equation for the driven system is obtained and employed to
analyze some of its dynamical variables.Comment: 7 pages, 5 figure
A counterfactual impact evaluation of a bilingual program on students’ grade point average at a spanish university
This observational study intends to estimate the causal effects of an English as a Medium of Instruction (EMI)
program (as predictor) on students Grade Point Average (GPA) (as outcome) at a particular University in Spain
by using a Counterfactual Impact Evaluation (CIE). The need to address the crucial question of causal inferences
in EMI programs to produce credible evidences of successful interventions contrasts, however, with the absence
of experimental or quasi-experimental research and evaluation designs in the field. CIE approach is emerging as
a methodologically viable solution to bridge that gap. The program evaluated here consisted in delivering an
EMI program in a Primary Education Teacher Training Degree group. After achieving balance on the observed
covariates and recreating a situation that would have been expected in a randomized experiment, three matching
approaches such as genetic matching, nearest neighbor matching and Coarsened Exact Matching were used to
analyze observational data from a total of 1288 undergraduate students, including both treatment and control
group. Results show unfavorable effects of the bilingual group treatment condition. Potential interpretations and
recommendations are provided in order to strengthen future causal evidences of bilingual education programs’
effectiveness in Higher Education.This work was supported by the Junta de AndalucÃa-funded
Proyecto de Excelencia: “Análisis y GarantÃa de Calidad de la Educación
Superior Plurilingüe en la Educación Superior de AndalucÃa [Junta de
Andalusia-funded Project of Excelence: Analysis and Warrantee of the
Quality of Plurilingual Higher Education in Andalucia] (AGCEPESA;
Grant Agreement No. P12-SEJ − 1588)
Cauchy-Riemann beams
By using operator techniques, we solve the paraxial wave equation for a field
given by the multiplication of a Gaussian function and an entire function. The
latter possesses a unique property, being an eigenfunction of the {\it
perpendicular} Laplacian with a zero eigenvalue, a consequence of the
Cauchy-Riemann equations. We demonstrate, both theoretically and
experimentally, the inherent rotation of this field during its propagation. The
explanation for these rotations lies in the utilization of the quantum (Bohm)
potential. The simplicity of this outcome reveals promising prospects: it
enables the analytical deduction of the Fraunhofer or Fresnel diffraction
pattern. In essence, this means that obtaining the Fresnel or Fourier transform
of a function satisfying the Cauchy-Riemann equations becomes a straightforward
task
Vibrational and thermal studies of essential oils derived from Cistus ladanifer and Erica arborea shrubs
Essential oils from the two most representative shrub species from the Iberian Peninsula (namely Cistus ladanifer L. and Erica arborea L.) have been characterized by Fourier transform infrared spectroscopy (FTIR) and thermoanalytical techniques (TG/DTG and DSC). Vibrational spectra have been compared with those of components of the plants, and with those of oils, gums and resins from other species. The different content in terpenoids of C. ladanifer oil (mainly mono-and sesquiterpenoids) and E. arborea oil (mainly triterpenoids) is reflected in the ATR-FTIR by the position of the bands at around 2873 cm-1, 1730 cm-1 and 1678 cm-1. As regards their thermal behavior, C. ladanifer-derived oil evinced higher thermal stability than that of obtained from E. arborea: The pyrolysis of the former was sensitized at 210°C, whereas for the later it occurred at 143°C. These temperatures are high enough to state that thermolabile constituents such as terpenoids are conserved in the hydrodistillation and that this extraction process ensures the recovery of the main constituents of both essential oils
Furfural, 5-HMF, acid-soluble lignin and sugar contents in C. ladanifer and E. arborea lignocellulosic biomass hydrolysates obtained from microwave-assisted treatments in different solvents
Cistus ladanifer L. and Erica arborea L. are the two most representative shrub species from the Iberian Peninsula. With a view to their valorization, their biomass hydrolysate components, obtained from microwave-assisted treatments with choline chloride/urea - HNO3 10%, N,N-dimethylacetamide/NaHCO3 and N,N-dimethylacetamide/CH3OK as solvents, have been measured using a spectrophotometric method. Concentrations of furfural and 5-(hydroxymethyl)furfural (5-HMF) in the filtrate have been determined after reduction with NaBH4. The production of total sugars, reducing sugars and non-reducing sugars has also been assessed. The obtained results support the choice of microwave-assisted choline chloride/urea deep eutectic solvent in acid media as the preferred method (over the polar aprotic solvent-based alternatives) for the extraction of lignin, furfural, 5-HMF and sugars from C. ladanifer and E. arborea biomass, attaining the best production yields for 60¿min exposure times. Another is the case if the aim of the treatments is to recovery sugars from both shrubs for subsequent enzymatic saccharification: the very low 5-HMF contents resulting from the dimetylacetamide systems (especially is association with CH3OK) make them highly advantageous as compared to the traditional method using NaOH
Crystallinity of cellulose microfibers derived from Cistus ladanifer and Erica arborea shrubs
The effectiveness of the use of cellulose fibers as particulates/composite reinforcers involves the assessment of the crystallinity of such fibers. The aim of the present work is to provide information on the degree of crystallinity of the cellulose microfibers obtained from the stems of Cistus ladanifer and Erica arborea shrubs through two different methods, namely an alkaline treatment and a microwave-assisted deep eutectic solvent (DES) method. The crystallinity indexes (CrI) obtained from X-ray powder diffraction patterns indicated that higher CrI were attained for cellulose obtained from the DES treatment. Complementary information on the degree of crystallinity was also retrieved from attenuated total reflection- Fourier transform infrared spectroscopy (ATR-FTIR) vibrational spectra, scanning electron microscopy (SEM) micrographs, and accessibility data for the DES-treated celluloses from the two species. The crystallinity results for the fibers derived from these two Mediterranean shrubs were within the range of the results for those derived from wood pulp, opening the door to their valorization for cellulose-derived packing applications or for their use as reinforcers in composite materials in combination with other biopolymers
Temporal evolution of a driven optomechanical system in the strong coupling regime
We obtain a time-evolution operator for a forced optomechanical quantum
system using Lie algebraic methods when the normalized coupling between the
electromagnetic field and a mechanical oscillator, , is not
negligible compared to one. Due to the forcing term, the interaction picture
Hamiltonian contains the number operator in the exponents, and in order to deal
with it, we approximate these exponentials by their average values taken
between initial coherent states. Our approximation is justified when we compare
our results with the numerical solution of the number of photons, phonons,
Mandel parameter, and the Wigner function, showing an excellent agreement.Comment: 21 pages, 11 figure
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