Slow Mode Research Articles

Upgrade of SARAF fast beam chopper and its applications in Phase I and Phase II of SARAF linac

A fast chopper system has been developed for single-bunch selection for Phase I of the Soreq Applied Research Accelerator Facility (SARAF) in Israel. Further upgrade of the fast chopper system has improved its performance by enabling single-bunch selection for protons and deuterons at a repetition rate up to 220 kHz, with bunch transmission of up to 65% and with neighboring bunch contamination of less than 15%. The upgrade included (1) the redesign of the chopper deflection plates to minimize the electric-field asymmetry and provide more effective single-bunch selection, (2) a new trigger system with better trigger time resolution and better control capabilities, (3) an upgrade of the chopper electronics to increase the repetition rate, (4) the design of the chopper machine protection system, and (5) a general upgrade of the chopper concept to allow for operation in fast and slow modes. The implemented upgrades and the performance of the upgraded system are described. In addition, examples of the first experiments using the neutron time-of-flight (TOF) technique are presented. A fast neutron TOF facility, based on the upgraded fast chopper, is planned for SARAF Phase II. The high neutron flux at SARAF Phase II combined with the upgraded fast chopper system will make SARAF competitive with other advanced neutron research facilities.

Role of slow out-of-equilibrium modes on the dynamic structure factor near the QCD critical point

The role of slow out of equilibrium modes (OEM), introduced to extend the validity of hydrodynamics near the QCD critical point on the power spectrum of dynamical density fluctuations has been studied. We have used the equation of motion of slow modes for the situation when the extensive nature of thermodynamics is not altered due to the introduction of OEM. We find that the extensivity condition puts an extra constraint on the coupling of OEM with the four divergence of velocity. The dynamic structure factor (Snn) in presence of the OEM shows four Lorentzian peaks asymmetrically positioned about $\omega (\text{frequency})=0$, whereas the dynamic structure factor without the presence of any OEM shows three well-known Lorentzian peaks. The width of the peaks are reduced in presence of OEM. We find that the asymmetric peaks originate due to the coupling of the out-of-equilibrium modes with the hydrodynamic modes. It is also shown that the OEM has negligible effects on Snn if first order hydrodynamics (relativistic Navier-Stokes) is used. The introduction of OEM reduces the width of the Rayleigh peak indicating the reduction in the decay rate of the fluctuation which leads to slowing down, a well-known characteristics of the critical end point (CEP).

Modification of coconut residue fiber and its bile salt adsorption mechanism: Action mode of insoluble dietary fibers probed by microrheology

The effect of dietary fiber on lowering blood cholesterol level depends on its ability to separate bile salt (BS) and prevent its recycling. The effects of composition and microstructure of coconut residue fiber (CRF) by modifying on BS retention and adsorption process were studied, and the adsorption mechanism of BS by insoluble dietary fiber (IDF) was investigated. We proved for the first time that adding 0.38 wt% of chitosan to assist in CRF self-assembly could improve effectively IDF's ability to retain multiple BS molecules. The adsorption of CRF to BS was a combination of two modes: rapid adsorption at the initial stage and slow adsorption after the initial stage. The fast adsorption mode plays a dominant role during the early stage of adsorption and is correlated with the viscosity and soluble diary fiber (SDF) content in dietary fiber (DF). In contrast, the slow adsorption mode occurs during the whole adsorption process while plays a dominant role during the middle and late adsorption stages. This mode is also correlated with the non-covalent transient network formed by DF in the system. The formation of a non-covalent transient network is a dynamic process in which the formation and collapse of the system occurs alternately; and this formation relies on the content of free H-bonds in IDF. This study can be helpful for the understanding of the BS-adsorption mechanism of ordinary diary fiber.

Discontinuous curvilinear collocated grid combined with nonuniform time step Runge-Kutta scheme for poroelastic finite-difference modeling

For poroelastic media, the existence of a slow P-wave mode, next to the standard fast P and S waves, hinders efficient numerical implementations to propagate poroelastic waves through arbitrary seismic models. The slow P-wave speed can be an order of magnitude smaller than the fast P-wave speed. Hence, a stable and accurate simulation that can capture the slow P wave requires a fine grid and a small time step, which increases the overall computation cost greatly. To decrease the computation cost, we propose a poroelastic finite-difference simulation method that combines a discontinuous curvilinear collocated-grid method with a nonuniform time step Runge-Kutta (NUTS-RK) scheme. The fine grid and small time step are only used for areas near interfaces, where the contribution of the slow P wave is nonnegligible. The NUTS-RK scheme is derived from a Taylor expansion and it can circumvent the need for interpolations or extrapolations otherwise required by communications between different time levels. The accuracy and efficiency of the proposed method are verified by numerical tests. Compared with the curvilinear collocated-grid finite-difference method that uses a globally uniform space grid as well as a uniform time step, the proposed method requires fewer computing resources and can reduce the computing time greatly.

Slow-light effect in symmetry-reduced non-defect photonic crystals

In this study, a two-dimensional low-symmetric photonic crystal (PC) configuration with elliptical geometry is presented and its slow-light (SL) effect is investigated. Reducing the symmetry in the PC unit cell provides slow modes at the higher transverse electric bands. The calculated group index and the corresponding normalized bandwidth equal to {ng, BW}={63.56, 0.0065}. That corresponds to a value of figure of merit (FOM)=0.4344 defined by the product of the average group index and the normalized bandwidth, FOM=〈ng〉BW, which is comparable to the values available in literature. Tracing the whole edges of the Brillouin zone, strongly excited SL modes are observed only along Γ-X but not along Γ-X’ or Γ-M. That condition allows for the design of low-symmetric PC waveguides with finite thicknesses at the expense of lowering group index value. The SL effect is still obtained for the proposed low-symmetric PCs having finite thicknesses, which is numerically proved via finite-difference time-domain methods. It is important to note that non-dispersive SL Bloch modes exist through the non-zero k-vector components of Brillouin zone. Hence, such a defect-free (without either point- or line- defect) SL PC design may have a great potential for the use of compact photonic devices such as in optical switching and biochemical sensing applications.

The Effect of Conductive Heat Transfer on the Morphology Formation in Polymer Solutions Undergoing Thermally Induced Phase Separation.

Owing to the fact that heat transfer during the thermally induced phase separation process is limited, a quench rate is inevitably entailed, which leads to the existence of temporal and spatial variations in temperature. Hence, it is of great importance to take into account the nonisothermality during the phase separation process, especially in high viscosity polymer solutions. In this study, the influence of conductive heat transfer on the morphology formation during the thermally induced phase separation process was investigated theoretically in terms of quench depth, boundary conditions, and enthalpy of demixing to elucidate the interaction between temperature and concentration through incorporating the nonlinear Cahn-Hilliard equation and the Fourier heat transfer equation in two dimensions. The Flory-Huggins free energy theory for the thermodynamics of phase separation, slow mode theory, and Rouse law for polymer diffusion without entanglements were taken into account in the model development. The simulation results indicated a strong interaction between heat transfer and phase separation, which impacted the morphology formation significantly. Results confirmed that quench depth had an indispensable impact on phase separation in terms of higher characteristic frequency by increasing the driving force for heat transfer. Applying quench from various boundaries led to a difference in the quench rate due to the high viscosity of the polymer solution. This led to a gradation in pore size and anisotropic morphology formation. The degree and direction of anisotropy depended on quench depth and rate, quench time, heat conduction rate inside the solution, solution viscosity, temperature evolution, and the enthalpy of demixing. It was also verified that the influence of enthalpy of demixing on phase separation could not be neglected as it increased the solution temperature and led to phase separation being accomplished at a higher temperature than the initial quench temperature.

The relationship between walkability and QOL outcomes in residential evaluation

To improve social factors related to quality of life (QOL), slow travel modes, represented by walking, may enable more opportunities for physical activities/social contacts. The impacts of walking may vary by the walkability of spatial environments, namely, by how accessible activities are by walking, and how safe, comfortable, and pleasant neighborhood streets are for walking. Little is yet known about the influence of walkability on various QOL outcomes, especially in car-oriented Asian cities. This study aimed to comprehensively explore the relationship between walkability and QOL outcomes by assessing the relationship between their multiple indicators. We first defined the indicators of walkability and QOL. Then, a questionnaire-based survey was administered to 500 inhabitants of Nagoya city (Japan) for evaluations of their neighborhoods with the indicators of walkability (neighborhood street accessibility and street quality) and QOL (work, health, social relationship, and attachment). Finally, the relationships between walkability and QOL outcomes were analyzed using structural equation modeling (SEM). Results showed that, neighborhood street quality (particularly pleasurability) affected the QOL outcomes through the interrelationship among the outcomes, more significantly than accessibility. The findings suggest the importance of street quality in land-use transport planning.

Comparison of Exact and Approximate MHD Slow Body Mode Solutions in Photospheric Waveguides

In this study, we explore the possibility of simplifying the modeling of magnetohydrodynamic slow body modes observed in photospheric magnetic structures such as the umbrae of sunspots and pores. The simplifying approach assumes that the variation of the eigenvalues of slow body waves can be derived by imposing that the longitudinal component of velocity with respect to the tube axis is zero at the boundary of the magnetic flux tube, which is in good agreement with observations. To justify our approach, we compare the results of our simplified model for slow body modes in cylindrical flux tubes with the model prediction obtained by imposing the continuity of the radial component of the velocity and total pressure at the boundary of the flux tube. Our results show that, to a high accuracy (less than 1% for the considered model), the conditions of continuity of the component of transversal velocity and pressure at the boundary can be neglected when modeling slow body modes under photospheric conditions.

Thin Filaments in an Average Magnetosphere: Pure Interchange Versus Ballooning Oscillations

AbstractThis paper describes magnetospheric waves of very long wavelength in thin magnetic filaments. We consider an average magnetospheric configuration with zero ionospheric conductance and calculate waves using two different formulations: classic interchange theory and ideal magnetohydrodynamic (MHD) ballooning. Classic interchange theory, which is developed in detail in this paper, is basically analytic and is relatively straightforward to determine computationally, but it cannot offer very high accuracy. The eigenfrequencies from the two formulations cover a range of a factor of seven and generally agree with a root‐mean‐square difference between the common logarithms of interchange and MHD frequencies to be ∼0.054. The pressure perturbations in the classic interchange theory are assumed constant along each field line, but the MHD computed pressure perturbations along the field line vary in a range ∼30% in the plasma sheet but are larger in the inner magnetosphere. The parallel and perpendicular displacements, which are very different in the plasma sheet and inner magnetosphere, show good qualitative agreement between the two approaches. In the plasma sheet, the perpendicular displacements are strongly concentrated in the equatorial plane, whereas the parallel displacements are spread through most of the plasma sheet away from the equatorial plane; and can be regarded as buoyancy waves. In the inner magnetosphere, the displacements are more sinusoidal and are more like conventional slow modes. The different forms of the waves are best characterized by the flux tube entropy PVγ.

Broadband Electrostatic Waves near the Lower-hybrid Frequency in the Near-Sun Solar Wind Observed by the Parker Solar Probe

Using Parker Solar Probe observations, this Letter reports for the first time the existence of broadband electrostatic waves below the electron cyclotron frequency in the near-Sun solar wind and even in the extended solar corona. These waves have enhanced power spectral densities of the electric fields near the lower-hybrid frequency f LH, and their peak frequencies can be below or exceed f LH. The perturbed electric fields are distributed between about 0.1 and 50 mV m−1. Accompanying broadband electrostatic waves, strong electrostatic solitary structures can arise, and their peak amplitudes approach nearly 500 mV m−1. Due to the appearance of considerable electric field fluctuations perpendicular to the background magnetic field, the observed waves would propagate obliquely. Moreover, this Letter conjectures the wavenumber and frequency information for the candidate of the wave mode nature being the oblique slow mode wave, the ion Bernstein wave, or the oblique fast-magnetosonic whistler wave. One important consequence of the observed waves is that they may regulate the electron heat flux in the near-Sun solar wind and in the solar corona.

Momentum space entanglement from the Wilsonian effective action

The entanglement between momentum modes of a quantum field theory at different scales is not as well studied as its counterpart in real space, despite the natural connection with the Wilsonian idea of integrating out the high-momentum degrees of freedom. Here, we push such connection further by developing a novel method to calculate the R\'enyi and entanglement entropies between slow and fast modes, which is based on the Wilsonian effective action at a given scale. This procedure is applied to the perturbative regime of some scalar theories, comparing the lowest-order results with those from the literature and interpreting them in terms of Feynman diagrams. This method is easily generalized to higher-order or nonperturbative calculations. It has the advantage of avoiding matrix diagonalizations of other techniques.

Dentapen versus traditional syringe infiltration - which LA technique is preferred by patients?

Design Single-blind randomised cross-over trial.Intervention The study compared solution deposition pain of a maxillary lateral incisor infiltration between a computer-controlled local anaesthesia delivery device (Dentapen) and traditional syringe. The Dentapen was given with a slow flow rate of 1.8 mL/162 sec and ramp-up mode, and the traditional syringe infiltration was delivered at a flow rate of 1.8 ml/60 sec. Patients were randomly assigned to a sequence to receive both interventions at two separate appointments, with each participant acting as their own control. Patients rated the pain of each intervention using a Heft-Parker visual analogue scale and completed a preference survey at the conclusion of the second appointment.Case selection A total of 130 adult patients with ASA I or II were included in the study. Criteria for exclusion were patients under 18 years of age or older than 65, allergies to local anaesthetics or sulphites, pregnant or nursing, history of significant medical conditions (ASA III or higher), taking any medications that may affect pain assessment, active pathosis at the injection site, or inability to give informed consent.Data analysis Differences in pain of solution deposition for the Dentapen and traditional infiltration techniques were analysed using paired t-tests and odds ratios. Interactions between study groups, gender and anxiety were analysed using a linear mixed-effect model with a P value <0.05.Results Solution deposition pain was significantly less (P <0.001) with the Dentapen infiltration than the traditional infiltration. The preference survey revealed that 75% of patients preferred the Dentapen infiltration over the traditional technique.Conclusions The findings of this clinical trial suggest that pain during maxillary lateral incisor infiltrations can be reduced by using the Dentapen with a slow flow rate and ramp-up mode compared with the traditional syringe technique.

Experimental and numerical evidence of using a Phononic membrane with the coupling of Fano resonant modes as a highly sensitive temperature sensor

In this article, we present numerically and experimentally a tunable phononic membrane as an efficient temperature sensor based on the generation of slow modes (sharp resonance modes) in microcavities. The Phononic membrane is periodically perforated with subwavelength slits (apertures) to produce tunable modes in these cavities (mode corresponding to a cavity resonance). By emerging the silicon membrane in water, a coupling effect between acoustic waves through the slits occurs, which leads to multiple-wave interferences like Fabry Perot resonators. Besides, this design could secure the phenomenon of ultrasonic opacity through the perforated silicon membrane. Where a deep and large attenuation band with a relative bandwidth of 31 % and at the central frequency of 0.9 MHz is observed in the amplitude transmission spectra of the phononic membrane. Secondly, by modifying the temperature of the water, the position of the bandwidth is tuned, since, we could achieve high sensitivity of 2400 Hz °C-1 for a temperature change of 10–20 °C, which is considered a promising result for many important applications such as temperature sensors and biosensors.

Fast and slow light propagations in a four-level cascade atomic medium

Under weak probe field, rotating wave and electric dipole approximations, we have derived analytic expressions for absorption and dispersion coefficients, group index and group velocity in a four-level cascade atomic medium interacting with the probe and pump laser fields. The model is applied to 85Rb atomic system to study the control of the fast and slow light propagation of the probe beam according to the intensity and frequency of the pump laser beam. With this excitation model, we find two transparent domains and thus the light group velocity is also controlled at these two frequency domains. In particular, the amplitude and the sign of the group index are easily changed by adjusting the intensity or frequency of the pump laser. That is, the probe beam propagation can be changed between fast and slow light modes by adjusting the intensity or frequency of the pump laser. Our analytical results can be useful for related experimental studies.

Partially polaron-transformed quantum master equation for exciton and charge transport dynamics.

Polaron-transformed quantum master equation (PQME) offers a unified framework to describe the dynamics of quantum systems in both limits of weak and strong couplings to environmental degrees of freedom. Thus, the PQME serves as an efficient method to describe charge and exciton transfer/transport dynamics for a broad range of parameters in condensed or complex environments. However, in some cases, the polaron transformation (PT) being employed in the formulation invokes an over-relaxation of slow modes and results in premature suppression of important coherence terms. A formal framework to address this issue is developed in the present work by employing a partial PT that has smaller weights for low frequency bath modes. It is shown here that a closed form expression of a second order time-local PQME including all the inhomogeneous terms can be derived for a general form of partial PT, although more complicated than that for the full PT. All the expressions needed for numerical calculation are derived in detail. Applications to a model of a two-level system coupled to a bath of harmonic oscillators, with test calculations focused on those due to homogeneous relaxation terms, demonstrate the feasibility and the utility of the present approach.

Memory effects in the density-wave imbalance in delocalized disordered systems

Dynamics of the imbalance in occupations on even and odd sites of a lattice serves as one of the key characteristics for the identification of the many-body localization transition. In this work, we investigate the long-time behavior of the imbalance in disordered one- and two-dimensional many-body systems in the regime of diffusive or subdiffusive transport. We show that memory effects originating from a coupling between slow and fast modes lead to a power-law decay of the imbalance, with the exponent determined by the diffusive (or subdiffusive) transport law and the spatial dimensionality. Analytical results are supported by numerical simulations performed on a two-dimensional system in the regime of weak localization.

Slow Surface Eigenmodes Directed by the Mu-Negative Metamaterial Slab

The paper presents the results of the study of slow surface electromagnetic waves directed along the flat mu-negative metamaterial slab surrounded by ordinary dielectric material. It is considered the case of isotropic and homogeneous metamaterial without losses. This metamaterial possesses the positive permittivity and the negative permeability over a definite frequency band. It is found that two surface modes of TE polarization can propagate along such waveguide structure. The dispersion properties, the spatial distribution of the electromagnetic field, as well as the phase and group velocities of these slow modes are studied. The first mode is a conventional forward wave, and has a lower frequency and lower phase velocity than the second mode. The second mode may have zero group velocity at a certain frequency. Characteristics of these surface modes for different values of the mu-negative slab parameters have been studied. The studied surface electromagnetic waves can be used for practical applications as in laboratory experiments, as in various technologies.

Design of Microstructured Flat Optical Fiber for Multiaxial Strain Monitoring in Composite Materials

An innovative microstructured flat optical fiber is designed to obtain a multiaxial strain sensor for composite material monitoring. The sensing regions are constituted by the two eyelets where Bragg gratings are written. To achieve multiaxial sensing, a suitable microstructure is designed close to only one of the eyelets. The effect of the strain field, evaluated via a 3D finite element method approach, is considered to obtain the change of the refractive index distribution. The electromagnetic modal analysis and the coupled mode theory are exploited to evaluate the Bragg wavelength shift for the slow and fast axis fundamental modes, guided in the two eyelets and affecting the sensor response. The designed microstructured flat optical fiber is technologically feasible and promises sensing performance higher than that obtainable with the conventional optical fibers. In addition, flat optical fiber can be embedded in composite materials reducing the drawbacks related to both orientation and excess resin.

A prototype of beam profile measurement system for HIAF-HFRS beam line

ABSTRACT A prototype of beam profile measurement system developed by the Institute of Modern Physics, which can work in the proportional region and ionization region, respectively, by adjusting the pressure and voltage, has been tested several times and achieved the design expectation. When the working pressure of the detector is low enough, the system can work in the secondary electron mode to measure the fast extraction beam profile too. The measurement system has been used to measure the profile of carbon ion beam in the Second Radioactive Ion Beam Line in Lanzhou in slow extraction mode and fast extraction mode, respectively. It is confirmed that the measurement system can measure the profile of carbon ion beam with a dynamic range of beam intensity up to six orders of magnitude. We used the X-ray beam to simulate the Gaussian-like distribution for laboratory testing, and the results show that the measurement system has a better resolution than 0.1 mm for the beam position with a Sigma of about 1.6 mm. This measurement system, together with the harps measurement system, will be able to meet needs of most beam profile measurements in High energy Fragment Separator (HFRS) at High Intensity heavy-ion Accelerator Facility (HIAF).

Phonon focusing and anisotropy of drag thermopower in potassium thin films at low temperatures

We have investigated the influence of elastic energy anisotropy on the dependences of drag thermopower in potassium thin films on the orientation of the film planes, directions of heat flux, and their geometric parameters. It is shown that the drag thermopower in square-shaped potassium films with orientations {100} and {111} is isotropic in the film planes. Their anisotropy is determined by the orientation of the film plane. As for square-shaped films with {110} orientation, the drag thermopower dependences appear ellipsoidal, with a long axis that points towards the [100] direction. As the transverse parameters of potassium films with {100} and {111} orientations are increased, the drag thermopower anisotropy of the films in the [110] direction varies in a non-monotonic manner. This effect is due to the competition between the contributions of slow quasi-transverse modes and longitudinal phonons. The relaxation rate of the latter by electrons has proved to be 30 times higher than that for the slow mode. The drag thermopower and phonon mean free paths in potassium films with lengths much larger than their widths in the boundary scattering regime are found to become anisotropic. However, accounting for the electron–phonon relaxation leads to isotropization of these quantities in thin films with {100} and {111} film plane orientations, with the orientation anisotropy being retained. For long films with {110} orientation, the shape of the drag thermopower dependences remains ellipsoidal with a long axis along the [100] direction.