Momentum Change Research Articles

Vortex-bright soliton complexes in [formula omitted] rotating Bose–Einstein condensates

We investigate a novel class of states associated with rotating bosonic F=2 Bose–Einstein condensates (BECs). In the cyclic phase with weak spin-exchange interaction, no vortex core is observed when rotation is considered. However, strong spin-exchange interaction can induce vortex-bright soliton complex, inside which the massive solitons locate within the cores of vortices. Anticlockwise current of the aforementioned excitation is obtained through analysing the particle current of every component. Furthermore, various axisymmetric vortex-bright soliton textures are excited via stronger density-density interaction. Remarkably, all of the vortex-bright soliton complexes rotate following the rotation rate, as in scalar condensates. Subsequently, upon sweeping density-density interaction and rotation frequency in numerical calculation, first-order phase transitions are generated when angular momentum changes discontinuously. With the aid of these findings, nontrivial topological excitations are investigated and a new gate is opened for manipulating topological phase transition in high-spin systems.

ЭНЕРГЕТИКА ИЗЛУЧЕНИЯ ЭЛЕКТРИЧЕСКОГО ЗАРЯДА И ЕЕ СЛЕДСТВИЯ

It is believed that an electric charge moving along a circular path, i.e. with centripetal acceleration, it is necessary to emit electromagnetic waves. This applies, inter alia, to cyclotron radiation. The purpose of the work is to establish the conditions for the radiation of an electric charge, based on the significant differences between its tangential and centripetal accelerations. The relevance of the work is determined by the widespread use of devices that generate electromagnetic radiation due to the acceleration of electric charges, including X-ray units and magnetrons. The starting point is a credible statement. A number of mathematically correct transformations are performed with it. Therefore, the result is necessarily reliable. Sad experience shows that this logic is not available for many specialists. In the event that such a necessary reliable result contradicts the existing paradigm, preference is almost always given to the paradigm, regardless of the persuasiveness of the evidence. This circumstance is an almost insurmountable obstacle to obtaining new knowledge. After all, if it does not contradict the paradigm, then it is not new and does not represent any value. Electromagnetic radiation carries away energy. It follows from this that the energy of the radiating system changes during radiation. Associated with this is the well-known rule: the change in energy is equal to the perfect work. Four theorems are proved. Theorem 1. A tangentially accelerated charge emits electromagnetic waves. Theorem 2. A normally accelerated charge does not emit electromagnetic waves. Theorem 2 formalizes a circumstance well-known in mechanics that the centripetal force does not perform work (since the scalar product of orthogonal vectors must be zero). Theorem 3. Electric charge satisfies Newton's second law. When a hydrogen-like atom passes from one stationary state to another, the orbital angular momentum changes. The difference is attributed to a photon and is called the photon's spin. Theorem 4. The spin of a photon is zero. The defect in the angular momentum of an atom during radiation can easily be attributed to the nucleus of an atom and even to an electron.

Positive Correlation Between Learning Motivation and Student Learning Outcomes in Physics Subjects Momentum and Impulse Materials

Motivation is one of several things that determine the success of student learning. Without motivation, the learning process is difficult to achieve optimal success. The purpose of this study was to determine the effect of learning motivation on student learning outcomes in class XI. This type of research is quantitative research. The instruments used to collect data in this study were a learning interest questionnaire and multiple choice questions. The prerequisite test data analysis techniques were carried out including the correlation test with the help of SPSS 21 software. The data collection technique in this study used questions with 30 questions with momentum and impulse material changing regularly. The population of this study were students of class XI. The method used in this research is descriptive statistics. The data analysis requirements test used was a correlation test. The correlation test is used to determine how strong the relationship between the two data is whether the independent variable has a strong relationship to the dependent variable with the decision-making criteria, namely Sig. (2-tailed) < 𝛼 of 0.01. Based on the results of this study, it shows that there is a significant positive influence between students' motivation to learn physics in class XI students on learning outcomes on momentum and impulse materials.

Collisions of Small Kuiper Belt Objects With (486958) Arrokoth: Implications for Its Spin Evolution and Bulk Density

AbstractThe orientation and morphology of the bilobate, cold classical Kuiper belt object (486958) Arrokoth (formerly 2014 MU69) is consistent with a slow, tidal merger of a close binary. However, the discrepancy between Arrokoth's present‐day rotation (15.9 hr) and synchronous rotation for nominal cometary densities near ∼500 kg/m3 implies reduction (up to 30%) in post‐merger spin angular momentum. We investigate how collisions with dynamically cold and hot classical Kuiper belt objects might have affected Arrokoth's post‐merger spin. Using a dynamically equivalent triaxial ellipsoid, 5000 Monte Carlo simulations of 100 impacts each, consistent with Arrokoth's cratering record, were carried out. Starting from the assumption of critical, synchronous rotation for a given density, these simulations rarely reproduce Arrokoth's present spin period, unless its true density is near 250 kg/m3. We explore in greater depth the effects of formation of Arrokoth's largest crater (now officially named Sky, previously informally named Maryland). We adopt point‐source scaling and randomly select impact parameters that lead to the crater, using Arrokoth's full bilobate shape. Results from Sky's formation alone are similar to those considering a full range of impactor sizes, unless we adopt low cratering efficiency due to high porosity, which implies substantially larger Sky‐forming impactors. Overall, results imply that the probability of substantial angular momentum change due to impacts alone over Solar System history is unlikely, and spindown from a synchronous, tidal rotation rate to a 15.9‐hr period unlikely unless Arrokoth itself was and is a very low density object (∼250 kg/m3), though we cannot statistically rule out densities up to 400 kg/m3.

Study of Momentum Diffusion with the Effect of Adiabatic Focusing

Abstract The momentum diffusion of charged energetic particles is an important mechanism of the transport process in astrophysics, the physics of fusion devices, and laboratory plasmas. In addition to the momentum diffusion term for a uniform field, we obtain an additional momentum diffusion term due to the focusing effect of the large-scale magnetic field. After evaluating the coefficient of the additional momentum diffusion term, we find that it is determined by the sign of the focusing characteristic length and the cross helicity of the turbulent magnetic field. Furthermore, by deriving the mean momentum change rate contributed from the additional momentum diffusion term, we identify that the focused field provides an additional momentum loss or gain process.

Angular Momentum Removal by Neutron and γ-Ray Emissions during Fission Fragment Decays.

We investigate the angular momentum removal from fission fragments (FFs) through neutron and γ-ray emission, finding that about half the neutrons are emitted with angular momenta ≥1.5ℏ and that the change in angular momentum after the emission of neutrons and statistical γ rays is significant, contradicting usual assumptions. Per fission event, in our simulations, the neutron and statistical γ-ray emissions change the spin of the fragment by 3.5-5ℏ, with a large standard deviation comparable to the average value. Such wide angular momentum removal distributions can hide any underlying correlations in the fission fragment initial spin values. Within our model, we reproduce data on spin measurements from discrete transitions after neutron emissions, especially in the case of light FFs. The agreement further improves for the heavy fragments if one removes from the analysis the events that would produce isomeric states. Finally, we show that while in our model the initial FF spins do not follow a sawtoothlike behavior observed in recent measurements, the average FF spin computed after neutron and statistical γ emissions exhibits a shape that resembles a sawtooth. This suggests that the average FF spin measured after statistical emissions is not necessarily connected with the scission mechanism as previously implied.

Desolvation–Solvation-Induced Reversible On–Off Switching of Two Memory Channels in a Cobalt(II) Coordination Polymer: Overlay of Spin Crossover and Structural Phase Transition

Desolvation–Solvation-Induced Reversible On–Off Switching of Two Memory Channels in a Cobalt(II) Coordination Polymer: Overlay of Spin Crossover and Structural Phase Transition

Spontaneous symmetry breaking in persistent currents of spinor polaritons

We predict the spontaneous symmetry breaking in a spinor Bose–Einstein condensate of exciton-polaritons (polaritons) caused by the coupling of its spin and orbital degrees of freedom. We study a polariton condensate trapped in a ring-shaped effective potential with a broken rotational symmetry. We propose a realistic scheme of generating controllable spinor azimuthal persistent currents of polaritons in the trap under the continuous wave optical pump. We propose a new type of half-quantum circulating states in a spinor system characterized by azimuthal currents in both circular polarizations and a vortex in only one of the polarizations. The spontaneous symmetry breaking in the spinor polariton condensate that consists in the switching from co-winding to opposite-winding currents in opposite spin states is revealed. It is characterized by the change of the average orbital angular momentum of the condensate from zero to non-zero values. The radial displacement of the pump spot and the polarization of the pump act as the control parameters. The considered system exhibits a fundamental similarity to a superconducting flux qubit, which makes it highly promising for applications in quantum computing.

Two-Week Rehabilitation with Auditory Biofeedback Prosthesis Reduces Whole Body Angular Momentum Range during Walking in Stroke Patients with Hemiplegia: A Randomized Controlled Trial.

Walking rehabilitation is challenging in stroke patients with sensory impairments. In this study, we examined the two-week effect of an auditory biofeedback prosthesis, Auditory Foot (AF), on the change in the frontal whole body angular momentum (WBAM) range, before and after a two-week walking rehabilitation. We conducted a pilot randomized controlled trial (RCT). We employed statistical Bayesian modeling to understand the mechanism of the rehabilitation effect and predict the expected effect in new patients. The best-performing model indicated that the frontal WBAM range was reduced in the AF group by 12.9–28.7%. This suggests that the use of kinesthetic biofeedback in gait rehabilitation contributes to the suppression of frontal WBAM, resulting in an improved walking balance function in stroke patients.

The deceleration of small charged bodies in a rarefied plasma

The purpose of this work is to create a method for determining the aerodynamic characteristics of fine particles in a highly rarefied plasma. The created method is based on the theorem on the change in momentum imparted to the body. The “body+surrounding plasma” system was considered to be closed; therefore, the change in the momentum of the body is equal in the impulse of the incident flow and is opposite to it in direction. The change in the pulse flux is calculated using the statistical method. To compare the results and approbation of the calculation method, the deceleration forces of a spherical body in a flow of neutral gas were determined. Next, we calculated the drag coefficient from the side of the charged plasma component. The calculation results are presented in the graphs.

Subpolar Southern Ocean Response to Changes in the Surface Momentum, Heat, and Freshwater Fluxes under 2xCO2

AbstractThe Antarctic subpolar Southern Ocean (sSO) has fundamental climate importance. Antarctic Bottom Water (AABW) originates in the sSO and supplies the lower limb of the meridional overturning circulation (MOC), occupying 36% of ocean volume. Climate models struggle to represent continental shelf processes that form AABW. We explore sources of persistent model biases by examining response of the sSO to perturbations in surface forcing in a global ocean–sea ice model (ACCESS-OM2) that forms AABW both on shelf and in open ocean. The sSO response to individual and combined perturbations of surface heat, freshwater, and momentum fluxes follows the WCRP CMIP6 FAFMIP-protocol. Wind perturbation (i.e., a poleward shift and intensification of the westerlies) is dominant, enhancing AABW formation and accelerating the global MOC. This occurs through upwelling of warm waters and inhibition of sea ice growth during winter, which triggers large open water polynya (OWP) events with associated deep convection. These events occur in the Weddell and Ross Seas and their variability is associated with availability of heat at midocean depths. These OWPs cease when the heat reservoir is depleted. Effects of surface warming and freshening only partially compensate changes from increasing winds on ocean stratification and depletion of AABW formation. These results indicate that overly convective models, such ACCESS-OM2, can respond to CO2-perturbed scenarios by forming too much AABW in OWP, which might not hold in models without OWPs. This might contribute to the large intermodel spread thermosteric sea level projections, being relevant to the interpretation of future projections by current climate models.

Momentum conservation in the Biot–Savart law

We study a simple system of charges and currents, consisting of two electric dipoles that are driven by exponentially growing currents running between the ends of each dipole. The exponential time dependence allows the electric and magnetic fields to be calculated exactly. The forces between the dipoles must be evaluated carefully when the exponential growth is slow and are shown to not be equal and opposite. The imbalance is accounted for by the rate of change of momentum in the electromagnetic field, so that the total momentum is conserved even though Newton's third law fails. Implications for momentum conservation for “semistatic” slowly varying currents, for which the Biot–Savart law is applicable, are discussed.

Analytical and Numerical Study on the Performance of ‎Supersonic Ejector at Different Operating Conditions ‎and Working Fluids

The computation of ejector geometry for a given fluid is essential and plays a crucial role in creating an ejector profile and performance analysis. The current paper discusses the constant rate of momentum change (CRMC) approach using a real gas equation for ejector design. The numerical analysis is carried to validate the analytical geometry and the effect of operating parameters on the entrainment ratio. The variation in entrainment ratio for the different working fluids has also been studied on the geometry computed for water-vapour. It is observed that the entrainment ratio of the ejector significantly varies with the change in operating conditions and working fluids. The numerically predicted entrainment ratio is ~0.354 compared to the on-design entrainment ratio 0.4 for water vapor, while the predicted entrainment ratio for other working fluids is ~0.319, ~0.314, and ~0.36 for air, N2, and CO2, respectively‎.

A Direct Machine-Specific Parameters Incorporated Spot-Scanning Proton Arc (SPArc) Algorithm

To address the challenges of generating a deliverable and efficient spot-scanning proton arc (SPArc) plan for a proton therapy system. We developed a novel SPArc optimization algorithm (SPArcDMSP) by directly incorporating the machine-specific parameters such as mechanical constraints and delivery sequence.A SPArc delivery sequence model (DSMarc) was built based on the machine-specific parameters of the prototype arc delivery system. The SPArcDMSP resamples and adjusts each control point's delivery speed based on the DSMarc calculation through the iterative approach. Users could set the expected arc delivery time and gantry max acceleration as a mechanical constraint during the SPArcDMSP optimization. Four cases (brain, liver, head neck, liver, and lung cancer) were selected to test SPArcDMSP. Two kinds of SPArc plans were generated using the same planning objective functions: (1) SPArcDMSP plan meeting the maximum allowable gantry acceleration speed (0.6deg/s2); (2) SPArcDMSP-user-speed plan with a user pre-defined delivery time and acceleration speed < 0.1 deg/s2. Arc delivery sequence such as gantry speed, delivery time was simulated based on the DSMarc and was compared.With a similar objective value, number of energy layers and spots, both SPArcDMSP and SPArcDMSP-user-speed plans could be delivered continuously within the ± 1 degree tolerance window (Table 1). The SPArcDMSP-user-speed plan could minimize the gantry momentum change based on clinical users input compared to the SPArcDMSP, which could help relieve mechanical challenge to accelerate or decelerate the hundreds of tons of gantry.For the first time, clinical users not only could generate a SPArc plan meeting the mechanical constraint of their proton system but also directly controlled the arc treatment speed and momentum changes of the gantry during the plan optimization. This work paved the roadmap for the clinical implementation of proton arc therapy in the treatment planning system.

Potential Applications of MTS and HTS to MRI Imaging Systems for Particle Beam Therapy

<h3>Purpose/Objective(s)</h3> To explore the potential application of medium temperature superconductors (MTS) and high temperature superconductors (HTS) to the development of background magnets for MRI systems for use in combination with particle beam therapy (PBT) and the concept design for MRI-guided PBT. <h3>Materials/Methods</h3> In proton/heavy ion therapy, because of the sharp dose drop off owing to the Bragg peak effect, imaging guidance becomes crucial. Various imaging techniques have been considered, but MRI, with its soft tissue contrast, 3D imaging, high spatial resolution, and potential on-live monitoring feature would be particularly useful in combination with PBT. One of the key challenges is that the charged particle beam will be deflected in a transverse magnetic field. The deflection of the particle beam in the presence of the background B0 has received significant interest, and both in-line and transverse configurations have been considered. For in-line configurations, smaller deflections are seen, with some rotation, and for transverse, greater deflection, and momentum change. With the use of a pencil beam PCT approach in combination with computation, such deflections can in principle be compensated. However, if "real time" imaging is to be enabled, minimum computation and reconstruction time is desirable. For these reasons, minimizing and simplifying the deflection is desirable. This can be enabled with the use of the in-line configuration, but in this case an in-line system compacts enough to mount on a gantry may be of interest. This can be made more achievable with the use of MTS or HTS where less bulky magnets are possible, cooling is simplified, and systems are much less quench sensitive. At the same time, the minimization of fringe fields can also substantially simplify the particle beam trajectories and minimize their deflection. This may also be enabled for open configuration transverse configurations with the use of less bulky HTS and MTS magnets. For this work we performed magnetic modelling of several different configurations of MTS and HTS magnets, both in-line and transverse, using Vector fields and other modelling software. The sizes and configurations of the MTS and HTS systems as compared to potential competing LTS systems were then compared. Particle beam trajectories were then computed with GEANT software and compared. <h3>Results</h3> (1) MTS and HTS systems can allow the development of in-line MR which are sufficiently compact, open, and robust (to quench) to allow mounting on a gantry. This reduces particle beam deflection, while at the same time allowing rotation of the beam around the patient; (2) Several designs for minimized fringe fields are given, both for in-line and transverse configurations. <h3>Conclusion</h3> MTS and HTS have a significant potential for application to MRI-guided Particle Therapy based on their potential for mounting on a gantry, and enabling of more open background magnet configurations. Magnet designs with minimized fringe fields are also possible and useful.

Parametric control of a diffractive axicon beam rider.

A laser beam rider is a large-scale optical structure designed so that it is attracted toward the optical axis, while also affording forward propulsion via radiation pressure along the beam path. Such structures form the basis of laser-driven light sails. Experimental measurements are described whereby a thin diffractive axicon film is shown to exhibit a natural restoring force when its axis is displaced from the optical axis. This effect is attributed to the optical momentum change of diffracted light. Whereas continuous illumination supports harmonic motion, modulated illumination is shown to support both parametric gain and parametric damping. The 12.7µm period photopolymer axicon grating was suspended in a vacuum torsion oscillator and irradiated with a 1.5 W near-infrared laser modulated at a period of 38 s.

Ultrafast electronic linewidth broadening in the C 1s core level of graphene

Core level binding energies and absorption edges are at the heart of many experimental techniques concerned with element-specific structure, electronic structure, chemical reactivity, elementary excitations and magnetism. X-ray photoemission spectroscopy (XPS) in particular, can provide information about the electronic and vibrational many-body interactions in a solid as these are reflected in the detailed energy distribution of the photoelectrons. Ultrafast pump-probe techniques add a new dimension to such studies, introducing the ability to probe a transient state of the many-body system. Here we use a free electron laser to investigate the effect of a transiently excited electron gas on the core level spectrum of graphene, showing that it leads to a large broadening of the C 1s peak. Confirming a decade-old prediction, the broadening is found to be caused by an exchange of energy and momentum between the photoemitted core electron and the hot electron system, rather than by vibrational excitations. This interpretation is supported by a line shape analysis that accounts for the presence of the excited electrons. Fitting the spectra to this model directly yields the electronic temperature of the system, in agreement with electronic temperature values obtained from valence band data. Furthermore, making use of time- and momentum-resolved C 1s spectra, we illustrate how the momentum change of the outgoing core electrons leads to a small but detectable change in the time-resolved photoelectron diffraction pattern and to a nearly complete elimination of the core level binding energy variation associated with the narrow $\sigma$-band in the C 1s state. The results demonstrate that the XPS line shape can be used as an element-specific and local probe of the excited electron system and that X-ray photoelectron diffraction investigations remain feasible at very high electronic temperatures.

The Video-Based STEM Experiment: An Observation of the Momentum of a Bouncing Ball

We have performed a video-based STEM experiment of a bouncing ball using a force plate logger sensor and Neulog application. Our objective was to observe the students understanding the relationship between impulse and momentum, examine this relation by bouncing a ball on a force plate logger sensor, and calculate impulse and change in momentum. All the data, such as raw data of force and time, video recorded, and the questions given to the 10th-grade senior high school students. Then, their answer will be analyzed to confirm the understanding of momentum during the learning process by video-based STEM experiments.

The equations of a solid body motion

Traditionally, the equations of motion of a solid body uses the theorem of the center of mass motion and the theorem of change of angular momentum with respect to the center of mass (Koenig’s axes). However, in the investigation of a solid body motion in a number of cases, the generalized coordinates are advisable to choose coordinates of another point of a body (pole) does not match the center of mass of the body, and the angles of rotation around this point. We obtain the equations of a solid body motion for these generalized coordinates. This is important for mathematical modeling of the motion of various objects, including vehicles. During the motion of a vehicle, its mass-inertial characteristics may change, including the position of the center of mass and the direction of the main axes of inertia, body mass and moments of inertia.

Training of upgrading on unstable material surfaces and its effect on some special abilities, tack off variables and the achievement of the long jump for young women

The real goal of approaching and rising in the long jump is to maintain the slightest change in linear momentum during this stage in order to succeed in achieving a good locomotive path. This study focused on carrying out exercises on unstable rubber surfaces that give an imbalance in order to stimulate and mobilize the working muscles to produce the largest instantaneous force that helps to improve the improvement and achievement and enhance performance. The research was carried out on and proved the long-term young women for 8 weeks by two training units per week and the momentary strength and speed were measured The results showed a remarkable and significant development in the momentary strength, the special speed, and the starting and achievement variables for the experimental group.