Longitudinal Modulation Research Articles

Transverse dynamical response of laser frequency-shifted feedback with mode mismatch

The transverse mode mismatch between the echo wave and optical fields in the laser cavity substantially impacts the responses of the laser frequency-shifted feedback (LFSF) system. This mismatch widely exists in experiments, which limits the detection sensitivity and degrades the signal-to-noise ratio. However, current research on the dynamic response of LFSF has predominantly concentrated on longitudinal modes and intensity modulation, with a lack of quantitative analysis regarding the dynamic response of the transverse modes. In this paper, we establish a transverse dynamical response model of LFSF considering the mode-mismatch. A calculation method of the effective reflectivity (ER) and mode-matching factor (MMF) is presented by decomposing the echo wave to the eigenmodes of the laser. The theoretical model is highly consistent with the experimental data. Finally, with this transverse dynamical response model, we develop a simple scheme to calibrate the effective reflectivity of scattering surfaces by employing a cat's eye retroreflector. Overall, this paper provides a detailed demonstration of the mismatch, which promises an effective theoretical basis to make full use of the high sensitivity of LFSF and apply it over a long distance.

Quasi-soliton control in optical lattices with longitudinal exponentially modulation

The dynamical evolution of one-dimensional quasi-soliton in Kerr-type linear-nonlinear optical lattices with the exponential asymptotically longitudinal modulation is investigated. The optical lattice features both the transverse linear refractive index modulation and the nonlinear coefficient periodically modulation. The analytical solutions of the integral beam center, the mean square of the beam width, and the critical incident angle are obtained by adopting the effective particle approach. The dynamical trapping and switching phenomena have been observed. Moreover, the introduction of the longitudinal modulation improves greatly the mobility of the soliton. The propagation states of the quasi-soliton can be controlled by varying a variety of parameters, such as the depths of the linear nonlinear lattices, the form factor and the incident angle of soliton, as well as the asymptotic rate of longitudinal modulation. Thus our results offer a new opportunity for the all optical manipulation of light beam.

Corrigendum: Longitudinal modulation of Marangoni wave patterns in thin film heated from below: instabilities and control

Corrigendum: Longitudinal modulation of Marangoni wave patterns in thin film heated from below: instabilities and control

Examining the change of half-period voltage in longitudinal electro-optic modulation and residual stress of potassium dihydrogen phosphate crystal.

In this paper, the voltage-transmittance curvesKDP crystals were measured accurately between two crossed or parallel polarizers using longitudinal electro-optic effect. The end faces of rectangular KDP samples were coated with ring-shaped electrodes using conductive silver paint (CSP). The change of half period voltage U i has been investigated. A method for quantitative characterization of residual stress has been proposed, based on deviation voltage U d. The results demonstrate that loading voltage is close to the integration of electric field intensity in crystal along the optical path when the CSP ring electrodes have a large outer radius R, small inner radius r, and long-distance d. The half-period voltage U i is also close to longitudinal half-wave voltage U π in these circumstances. The unclamped electro-optic coefficient γ63σ of KDP crystal at room temperature was measured as 10.24±0.05p m/V at the wavelength of 632.8nm.

Generation of attosecond micro bunched beam using ionization injection in laser wakefield acceleration.

Micro bunched electron beams with periodic longitudinal density modulation at optical wavelengths give rise to coherent light emission. In this paper, we show attosecond micro bunched beam generation and acceleration in laser-plasma wakefield via particle-in-cell simulations. Due to the near-threshold ionization with the drive laser, the electrons with phase-dependent distributions are non-linearly mapped to discrete final phase spaces. Electrons can preserve this initial bunching structure during the acceleration, leading to an attosecond electron bunch train after leaving the plasma with separations of the same time scale. The modulation of the comb-like current density profile is about 2k0 ∼ 3k0, where k0 is the wavenumber of the laser pulse. Such pre-bunched electrons with low relative energy spread may have potential in applications related to future coherent light sources driven by laser-plasma accelerators and broad application prospects in attosecond science and ultrafast dynamical detection.

Evidence of magnetoelectronic electromagnon-mediated transport in flexoelectronic heterostructures

The superposition of atomic vibrations and flexoelectronic effect gives rise to a cross correlation between free charge carriers and temporal magnetic moment of phonons in conducting heterostructures under an applied strain gradient. The resulting dynamical coupling is expected to give rise to quasiparticle excitations called magnetoelectronic electromagnons that carry electronic charge and temporal magnetic moment. Here, we report experimental evidence of magnetoelectronic electromagnons in the freestanding degenerately doped $p$-Si based heterostructure thin film samples. These quasiparticle excitations give rise to long-distance ($>100 \ensuremath{\mu}\mathrm{m}$) spin transport, demonstrated using spatially modulated transverse magnetothermoelectric and nonlocal resistance measurements. The magnetoelectronic electromagnons are nonreciprocal and give rise to large magnetochiral anisotropy $(0.352\phantom{\rule{0.16em}{0ex}}{\mathrm{A}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1})$ that diminishes at lower temperatures. The superposition of nonreciprocal magnetoelectronic electromagnons gives rise to longitudinal and transverse modulations in charge carrier density, spin density, and magnetic moment, demonstrated using the Hall effect and edge dependent magnetoresistance measurements, which can also be called inhomogeneous magnetoelectronic multiferroic effect. These quasiparticle excitations are analogous to photons where time dependent polarization and temporal magnetic moment replace electric and magnetic field, respectively, and most likely topological because they manifest topological Nernst effect. Hence, the magnetoelectronic electromagnon can potentially give rise to quantum interference and entanglement effects in conducting solid state systems at room temperature in addition to efficient spin transport.

Three techniques for measuring the transverse relaxation time of cesium atoms

The transverse relaxation time (T2) is an important indicator to determine the fundamental sensitivity limit of alkali-metal atomic magnetometers. We propose a method based on the principle of longitudinal field modulation that obtains T2 by scanning the transverse static magnetic field. The previous technique of extracting T2 from the linewidth of the modulation frequency and the traditional magnetic-resonance-broadening-fitting method are also described. The T2 measurements of Cesium (Cs) atoms are carried out through these three methods, whose operating environments are applicable to different atomic magnetometers, respectively. The method that we propose can be used for obtaining the T2 of Cs atoms as well as detecting the transverse static magnetic field and is customized for the study of the Cs–Xenon ensemble for the construction of nuclear magnetic resonance gyroscopes. Moreover, the relationship between the limit sensitivities and cell temperatures is further studied in the experiment.

Teaching primary care theory to promote general practice among medical students

Here we describe and reflect upon teaching primary care theory within a fourth-year longitudinal module in general practice at Brighton and Sussex Medical School (2012 to 2021). Primary care theory teaching adopts a ‘hearts and minds’ approach towards promoting general practice. It appeals to students’ ‘hearts’ by highlighting the social justice function of general practice: tackling health inequalities by ensuring patients are treated in the right place, reducing cost and widening access to healthcare. These benefits also point to the place of general practice in promoting environmentally sustainable healthcare. By presenting evidence for the role of general practice in tackling health inequalities, we believe that our teaching also appeals to students' ‘minds’. Both approaches are important in order to counter the ‘hidden curriculum’ in undergraduate medicine which conveys negative messages about general practice.

Comparisons of in situ ionospheric density using ion velocity meters onboard FORMOSAT-7/COSMIC-2 and ICON missions

We report the preliminary inter-satellite comparisons of the in situ ion density measurements by the ion velocity meter (IVM) onboard FORMOSAT-7/COSMIC-2 (F7/C2) and Ionospheric Connection Explorer (ICON) missions, during the solar minimum period of December 2019 to November 2020. The initial comparisons reveal identical diurnal, seasonal, and latitude/longitude variations in the two ion-density measurements, with F7/C2 consistently yielding stronger values than ICON, which could partly result from the difference in their orbit altitudes. The diurnal variation in the equatorial region did not show any effect of pre-reversal enhancement (PRE) during 2019–2020. The daytime plasma distributions show larger ion densities over a narrow latitudinal belt around the geomagnetic equator in all seasons, and the low-latitude densities reveal signatures of hemispherical asymmetry, with larger values occurring in the summer hemisphere. The observations also reveal distinct wavenumber-4 longitudinal modulation, which is most prominent in equinox and becomes less distinguishable during December solstice months. The simultaneous observations from F7/C2 IVM and ICON IVM also provide opportunities to study the spatial configuration and time evolution of ionospheric irregularities in the equatorial and low latitude regions. The F7/C2 and ICON simultaneously observed the equatorial plasma bubbles (EPBs) occurring around Taiwan on 18 October 2020, and the observations are consistent with each other. The EPBs were also observed by an all-sky imager located in Taiwan, comparing the satellite observations.Graphical

Waveguiding driven by the Pancharatnam-Berry phase

We theoretically and numerically investigate the properties of waveguides based on the Pancharatnam-Berry phase, obtained by a longitudinally periodic rotation of the optic axis in a transversely twisted birefringent medium. In this paper we study the case where the period of the longitudinal modulation is chosen so that a net accumulation of geometric phase in propagation occurs. First, the interplay between different contributions to the optical potential is addressed. Second, a continuous evolution of the polarization structure of the quasimodes is observed in the numerical simulations. We explain it by a combination of plane-wave-based models and gauge transformations. We discover that, beyond the longitudinal oscillations, the polarization of the quasimode also varies through its cross section. The analogies with respect to charged particles moving in a magnetic field are outlined.

Cultivating patient-centered care skills through engagement in difficult conversations

Background and purposeAppropriately engaging with patients around sensitive, challenging, or uncomfortable topics, often termed “difficult conversations,” is a facet of patient-centered care. Development of such skills prior to practice often occurs in the hidden curriculum. Instructors implemented and evaluated a longitudinal simulation-based module aimed at advancing students' understanding and abilities to use patient-centered care skills to navigate difficult conversations within the formal curriculum. Educational activity and settingThe module was embedded within the third professional year of a skills-based laboratory course. Four simulated patient encounters were revised to increase opportunities to practice patient-centered skills during difficult conversations. Preparatory discussions and pre-simulation assignments delivered foundational knowledge, and post-simulation debriefing allowed for feedback and reflection. Students completed pre- and post-simulation surveys to measure understanding of patient-centered care, empathy, and perceived ability. Instructors assessed student performance in eight skill areas using the Patient-Centered Communication Tools. FindingsOf 137 students, 129 completed both surveys. Students' definitions of patient-centered care grew in accuracy and detail following module completion. Eight of the 15 empathy items were significantly changed from pre- to post-module, signifying enhanced empathy. Student perception of ability to perform patient-centered care skills significantly improved from baseline to post-module. Across the semester, student performance on simulations significantly improved on six out of eight patient-centered care skills. SummaryStudents deepened their understanding of patient-centered care, grew in aspects of empathy, and improved actual and perceived ability to deliver care that is patient-centered during challenging encounters.

Prediction of longitudinal growth and growth modulation after VBT surgery: A comparative analysis of different skeletal maturity staging systems

Prediction of longitudinal growth and growth modulation after VBT surgery: A comparative analysis of different skeletal maturity staging systems

Contactless wide-range ferromagnetic high-current converters for monitoring and control systems in the electric power industry

The paper shows that the impossibility of breaking the current circuit for the production necessity of temporarily switching on electrical measuring instruments, large power losses on shunts, and the need to obtain quick information about the quality of the functioning of technological processes have led to the widespread use of non-contact conversion and measurement of high direct currents in circuits without breaking them. Light detachable wide-range stationary and portable non-contact transducers and meters of high direct currents are not yet mass-produced. In this regard, it is expedient to develop and study non-contact converters and meters of high direct currents, which are distinguished by a wide range of converted currents, small dimensions and weight, increased accuracy, and sensitivity of electric power facilities. The questions of sensitivity of magneto-modulation non-contact transducers are considered. The expression for the optimal static characteristic of the developed magneto-modulation non-contact transducer is determined and analyzed. Its maximum deviation from the calculated value does not exceed 6%. The expressions for the current, average sensitivity, and sensitivity regarding the magnitude of the excitation of a magneto-modulation non-contact transducer are obtained and investigated. In this case, the maximum sensitivity of the transducer reaches a value of 0.425 with an optimal excitation value of 1.65. It is recommended to take the allowable limit of the input value of the converter to be less than one. Its input value must be taken equal to 0.7. The developed magneto-modulation non-contact transducer has an increased sensitivity due to longitudinal modulation. It can be widely applied in control and management systems in melioration and irrigation, water supply, industry, metallurgy, railway transport, science, technology, GIS technology, and, in particular, digital coverage and database visualization, and as well as for checking electric meters at the place of their installation for non-contact control of direct, as well as alternating currents.

Longitudinal Modulation of Loco-Regional Immunity in Ovarian Cancer Patients Receiving Intraperitoneal Chemotherapy.

The immune tumor microenvironment (TME) of epithelial ovarian cancer (EOC) carries both effector and suppressive functions. To define immune correlates of chemotherapy-induced tumor involution, we performed longitudinal evaluation of biomarker expression on serial biological specimens collected during intraperitoneal (IP) platinum-based chemotherapy. Serial biological samples were collected at several time points during IP chemotherapy. RNA from IP fluid cells and tumor tissue was analyzed via NanoString. Meso Scale Discovery (MSD) multiplex assay and ELISA for MUC1 antibodies were performed on plasma and IP fluid. Differentially expressed genes in IP fluid demonstrate an upregulation of B cell function and activation of Th2 immune response along with dampening of Th1 immunity during chemotherapy. MSD analysis of IP fluid and gene expression analysis of tumor tissue revealed activation of Th2 immunity and the complement system. Anti-MUC1 antibodies were detected in IP fluid samples. IP fluid analysis in a secondary cohort also identified chemotherapy-induced B cell function genes. This study shows that serial IP fluid sampling is an effective method to capture changes in the immune TME during chemotherapy and reveals treatment induced changes in B cell function and Th2 immunity.

Two-dimensional Thouless pumping of light in photonic moiré lattices

Continuous and quantized transports are profoundly different. The latter is determined by the global rather than local properties of a system, it exhibits unique topological features, and its ubiquitous nature causes its occurrence in many areas of science. Here we report the first observation of fully-two-dimensional Thouless pumping of light by bulk modes in a purpose-designed tilted moiré lattices imprinted in a photorefractive crystal. Pumping in such unconfined system occurs due to the longitudinal adiabatic and periodic modulation of the refractive index. The topological nature of this phenomenon manifests itself in the magnitude and direction of shift of the beam center-of-mass averaged over one pumping cycle. Our experimental results are supported by systematic numerical simulations in the frames of the continuous Schrödinger equation governing propagation of probe light beam in optically-induced photorefractive moiré lattice. Our system affords a powerful platform for the exploration of topological pumping in tunable commensurate and incommensurate geometries.

A dual-axis high-order harmonic and single-axis phase-insensitive demodulation atomic magnetometer for in situ NMR detection of Xe

Based on the parametric oscillation process, we demonstrate the dual-axis phase-sensitive demodulation (PSD) and single-axis phase-insensitive demodulation (PISD) for the atomic magnetometer in an in situ nuclear magnetic resonance (NMR) detection system, which can separate the precession signals of NMR from the oscillating magnetic fields. The two orthogonal magnetic fields can be detected simultaneously and independently by selecting the optimal demodulation phases with the traditional PSD method. The response signals of the parametric modulation magnetometer demodulated with high order harmonic signals are evaluated, which is a new exploration. The first order harmonic demodulation can present the best sensitivity about 250 fT/Hz1/2. The high order harmonic demodulation technology supplies a twofold 3 dB bandwidth. With the PISD method, a single-axis demodulation technique is proposed. The transverse nuclear spin precession magnetic fields can be extracted effectively with the demodulation R signal outputs by setting a specific longitudinal modulation magnetic field amplitude, which is a new demodulation strategy compared with the traditional demodulation method for the NMR system.

Ausmaß und Integration von Wissenschaftsmodulen in das Medizinstudium an den staatlichen Fakultäten und den privaten staatlich anerkannten Fakultäten in Deutschland: eine Querschnittsstudie

BackgroundAt the end of November 2020, four years after the adoption of the Masterplan Medizinstudium 2020, the Federal Ministry of Health presented the draft bill for the revision of the medical licensing regulations. This was adapted in August 2021 and stipulates, among other things, the completion of a mandatory scientific project up to the second stage of the medical examination, which is to be conducted within twelve weeks and based on the structured teaching of scientific skills using longitudinal courses. This study examines to what extent the mentioned aspects of the draft bill are already included in the current compulsory curricula in German medical study programs. MethodsIn a cross-sectional study, we conducted a document analysis and an online survey of the student deaneries of state and private, state-recognized faculties of medicine in Germany. The objective was to assess the integration of curricular science projects and longitudinal science modules. The data was analyzed descriptively. ResultsIn total, 40 (93%) of 43 faculties were included in the document analysis. 26 (60.5%) of 43 academic deans responded to the online questionnaire. Only twelve (30%) of the faculties offer a mandatory science project according to the document analysis and eight (30.8%) according to the evaluation of the online survey. In relative terms, a mandatory science project is already a curricular component in the majority of model and reform degree programs (document analysis: 83.3%, n=10 / N=12; questionnaire: 87.5%, n=7 / N=8). This contrasts with a significantly smaller number of regular degree programs that currently offer a science project as a mandatory component (document analysis: 16.7%, n=2 / N=12; questionnaire: 12.5%, n=1 / N=8). In the majority of the model and reform courses, a compulsory (longitudinal) science module has already been integrated into the curriculum (document analysis: 75%, n=12 / N=16; questionnaire: 55.5%, n=6 / N=11). This is only true for 25% (n=4 / N=12; document analysis) and 44.5% (n=5 / N=11; questionnaire) of the regular courses. DiscussionThe results of the surveys indicate that the regular study programs, in particular, need to be restructured in order to integrate the intended time frame of twelve weeks for an obligatory science project into the current curriculum. How this is to be achieved without reducing the existing study content seems to be still unclear. Regardless of the current draft bill, however, this step appears to be necessary in order to strengthen the acquisition of scientific competencies in medical studies and to adapt it to international medical education. ConclusionThe majority of the current model and reformed medical study courses already fulfill the requirements of the draft bill for the new licensing regulations with regard to the curricular integration of an obligatory scientific project and longitudinal strand on scientific work, which offer hints on design possibilities for further faculties.

Micromagnetics of magnetic chemical modulations in soft-magnetic cylindrical nanowires

We analyze the micromagnetics of short longitudinal modulations of a high-magnetization material in cylindrical nanowires made of a soft-magnetic material of lower magnetization such as permalloy, combining magnetic microscopy, analytical modeling, and micromagnetic simulations. The mismatch of magnetization induces curling of magnetization around the axis in the modulations, in an attempt to screen the interfacial magnetic charges. The curling angle increases with modulation length, until a plateau is reached with nearly full charge screening for a specific length scale~$\Delta_\mathrm{mod}$, larger than the dipolar exchange length of any of the two materials. The curling circulation can be switched by the Oersted field arising from a charge current with typical magnitude $10^{12} A/m^{2}$ for a diameter of $\sim$100 nm, and reaching a maximum for $\Delta_\mathrm{mod}$.

Numerical simulations of a continuously injected relativistic electron beam relaxation into a plasma with large-scale density gradients

In this paper the influence of large-scale decreasing and increasing gradients of the density of magnetized plasma on the relaxation process of a continuously injected relativistic electron beam with an energy of 660 keV (vb=0.9c) and a pitch-angle distribution is studied using particle-in-cell numerical simulations. It is found that for the selected parameters in the case of a smoothly decreasing gradient and in a homogeneous plasma the formation of spatially limited plasma oscillations of large amplitude occurs. In such cases, modulation instability develops and a long-wave longitudinal modulation of the ion density is formed. In addition, the large amplitude of plasma waves accelerates plasma electrons to energies on the order of the beam energy. In the case of increasing and sharply decreasing gradients, a significant decrease in the amplitude of plasma oscillations and the formation of a turbulent ion density spectrum are observed. The possibility of acceleration of beam electrons to energies more than 2 times higher than the initial energy of the beam particles is also demonstrated. This process takes place not only during beam propagation in growing plasma density, but also in homogeneous plasma due to interaction of beam particles with plasma oscillations of large amplitude.

Enabling non-isocentric dynamic trajectory radiotherapy by integration of dynamic table translations

Objective. The purpose of this study is to develop a treatment planning process (TPP) for non-isocentric dynamic trajectory radiotherapy (DTRT) using dynamic gantry rotation, collimator rotation, table rotation, longitudinal, vertical and lateral table translations and intensity modulation and to validate the dosimetric accuracy. Approach. The TPP consists of two steps. First, a path describing the dynamic gantry rotation, collimator rotation and dynamic table rotation and translations is determined. Second, an optimization of the intensity modulation along the path is performed. We demonstrate the TPP for three use cases. First, a non-isocentric DTRT plan for a brain case is compared to an isocentric DTRT plan in terms of dosimetric plan quality and delivery time. Second, a non-isocentric DTRT plan for a craniospinal irradiation (CSI) case is compared to a multi-isocentric intensity modulated radiotherapy (IMRT) plan. Third, a non-isocentric DTRT plan for a bilateral breast case is compared to a multi-isocentric volumetric modulated arc therapy (VMAT) plan. The non-isocentric DTRT plans are delivered on a TrueBeam in developer mode and their dosimetric accuracy is validated using radiochromic films. Main results. The non-isocentric DTRT plan for the brain case is similar in dosimetric plan quality and delivery time to the isocentric DTRT plan but is expected to reduce the risk of collisions. The DTRT plan for the CSI case shows similar dosimetric plan quality while reducing the delivery time by 45% in comparison with the IMRT plan. The DTRT plan for the breast case showed better treatment plan quality in comparison with the VMAT plan. The gamma passing rates between the measured and calculated dose distributions are higher than 95% for all three plans. Significance. The versatile benefits of non-isocentric DTRT are demonstrated with three use cases, namely reduction of collision risk, reduced setup and delivery time and improved dosimetric plan quality.