Opposite Sense Of Rotation Research Articles

Rotationally symmetric hybrid-nanofluid flow over a stretchable rotating disk

Owing to the advanced thermophysical properties of hybrid nanofluids and stabilizing nature of surface stretching, the problem of rotationally symmetric flow and heat transfer induced over a rotating disk is extended to the case of a stretchable disk, considering Cu and TiO2 nanoparticles suspended in water. In addition, this study deals with four distinct shapes (sphere, brick, cylinder, platelet) of Cu and platelet-shaped TiO2 nanoparticles to elucidate the shape effects. Different from the traditionally applied external vertical magnetic field, the flow is investigated under the influence of a horizontal magnetic field. Moreover, the impact of solar radiation parameters is taken into account to inspect the radiated hybrid nanoparticles. For the same sense and weak & opposite sense (−0.161≤β≤0, here β signify the angular velocity ratio of fluid to disk ) of fluid and disk rotation, solutions are obtained in all cases. However, in the case of strong and opposite sense of rotation, physically acceptable solutions exist after a critical value of the stretching parameter (for example, when β=−0.8,Scr≈0.6). These numerical results have significant engineering applications to fluid flows in rotating machineries such as rotating heat exchangers, rotating disk air cleaners and gas turbine engines.

The wake of a rectangular flat plate

The mean wake of a three-dimensional surface-mounted rectangular flat plate was studied experimentally in a low-speed wind tunnel for four different aspect (height-to-width) ratios, AR = 3, 2, 1, and 0.5. The Reynolds number based on the plate width was Re = 3.8 × 104 and the boundary layer thickness on the ground plane, relative to the plate width, was δ/W = 1.1. The incidence angle of the plate was varied from α = 0° (where the plate is normal to the flow) to α = 90° (where the plate is parallel to the flow). The mean velocity and vorticity fields in the wake were measured using a seven-hole pressure probe. At α = 0°, the length of the recirculation zone behind the plate becomes progressively shorter as the aspect ratio is lowered and follows the same tendency as that of a finite square prism. The wakes of the slenderer flat plates of AR = 3 and 2 are characterised by two pairs of streamwise vortices: a pair of tip vortices in the upper wake and a pair of ground-plane vortices on the lower edges of the wake. With increasing incidence angle, a single tip vortex comes to dominate the wake, secondary vorticity is induced at various locations, a ‘traffic light’ vortex pattern may form, and ultimately a familiar wing-tip (trailing) vortex develops. In contrast, flow downstream of the less slender flat plates of AR = 1 and 0.5 is characterised by a single pair of large streamwise vortices, which become asymmetric with increasing incidence. Close to the flat plate of AR = 0.5, and at small incidence angles only, a unique pair of small inner vorticity concentrations, of opposite sense of rotation to the main streamwise vortices, is found in the upper part of the wake.

Magnetic ground state of supported monatomic Fe chains from first principles

A new computational scheme is presented based on a combination of the conjugate gradient and the Newton–Raphson method to self-consistently minimize the energy within local spin-density functional theory, thus to identify the ground state magnetic order of a finite cluster of atoms. The applicability of the new ab initio optimization method is demonstrated for Fe chains deposited on different metallic substrates. The optimized magnetic ground states of the Fe chains on Rh(111) are analyzed in details and a good comparison is found with those obtained from an extended Heisenberg model containing first principles based interaction parameters. Moreover, the effect of the different bilinear spin–spin interactions in the formation of the magnetic ground states is monitored. In case of Fe chains on Nb(110) spin-spiral configurations with opposite rotational sense are found as compared to previous spin-model results which hints on the importance of higher order chiral interactions. The wavelength of the spin-spiral states of Fe chains on Re(0001) was obtained in good agreement with scanning tunneling microscopy experiments.

Mechanisms leading to the formation of double-diffusive layers during unidirectional solidification of aqueous NH4Cl solution

Double diffusive layers (DDLs) are one of the flow patterns which arise due to the coupled effects of thermal and solutal gradients and find relevance in large-scale applications. We report observations of DDLs using unidirectional solidification of a binary mixture, which naturally introduces thermal and solutal buoyant flows. The convection rolls at the opposite sidewalls, having an opposite sense of rotation, ultimately merge to form the DDLs that expand throughout the breadth of the test chamber. Our research on exploring the mechanisms of DDLs uses a combination of nonintrusive techniques capturing full-field measurements in real-time to obtain insights on their evolution.

Large eddy simulation of an inclined jet in crossflow with vortex generators

ABSTRACT Film cooling is one of the essential approaches to cool high-performance turbine blades. Film cooling with delta winglet vortex generator pair (DWVGP) placed upstream of the cooling hole is investigated by large eddy simulation (LES) at the blowing ratio of M=1.0. Film cooling effectiveness and vortical structures are evaluated in the flow field of a jet in crossflow (JICF). Results indicate that film cooling effectiveness increases significantly for the DWVGP case. As a dominant vortex structure, the ubiquitous counter-rotating vortex pair (CRVP) is recognized in the flow field. It has a detrimental effect that lifts the coolant off the cooling surface. The DWVGP evolved anticounter-rotating vortex pair (anti-CRVP) has the opposite sense of rotation to the jet introduced CRVP, which undertakes vorticity decay when developing downstream of the cooling hole. With the downwash effect of anti-CRVP, the reattachment of coolant is earlier, and a wide region of enhanced film cooling effectiveness in the spanwise direction is achieved. The coherent vortex structures including the classical vortices in the flow field and the vortex generator pair introduced vortices are analyzed. The genesis and evolution mechanism of CRVP with and without the vortex generators are discussed. It indicates that three branches of upstream spiral structures from the nozzle tube contribute to the CRVP. The merging of CRVP upstream branches is delayed by the vortex generators evolved anti-CRVP, which postpones the formation of downstream CRVP.

Polarization properties of noise-initiated stimulated Brillouin scattering in linear birefringent fibers

The transient theory of stimulated Brillouin scattering (SBS) is developed for optical fibers with constant modal birefringence along its length and arbitrary polarization of the pump and Stokes fields. SBS is initiated by thermally excited acoustic waves distributed along the length of the optical fiber, and the generated Stokes field fluctuates in time. It is shown that when a single-frequency pump field is launched such that the fiber is nearly equally excited along the slow and fast axes, the generated Stokes field is partially polarized for fiber lengths longer than its polarization beat length, due to temporal fluctuations in power and polarization. The Stokes field degree of polarization is reduced as the birefringence of the fiber is increased. For launched pump polarizations resulting in nonequal excitation along the slow and fast axes of the fiber, the generated Stokes field is preferentially linearly polarized along the principal axis that exhibits the highest Brillouin gain for fibers with birefringence such that its length is greater than twice its polarization beat length. As the fiber birefringence is reduced, the generated Stokes field state of polarization moves towards the launched pump polarization state, with the opposite sense of rotation. Numerical results are presented to quantify these effects as a function of single-pass Brillouin gain, fiber birefringence, and launched pump polarization state.

Surface Stabilized Topological Solitons in Nematic Liquid Crystals

Photo-alignment is a versatile tool to pattern the alignment at the confining substrates in a liquid crystal (LC) cell. Arbitrary alignment patterns can be created by using projection with a spatial light modulator (SLM) for the illumination. We demonstrate that a careful design of the alignment patterns allows the stabilization of topological solitons in nematic liquid crystal (NLC) cells, without the need for chirality or strong confinement. The created LC configurations are stabilized by the anchoring conditions imposed at the substrates. The photo-aligned background at both substrates is uniformly planar aligned, and ring-shaped regions with a 180° azimuthal rotation are patterned with an opposite sense of rotation at the top and bottom substrate. A disclination-free structure containing a closed ring of vertically oriented directors is formed when the patterned rings at the top and bottom substrate overlap. Thanks to the topological stability, a vertical director orientation in the bulk is observed even when the centra of both patterned rings are shifted over relatively large distances. The combination of numerical simulations with experimental measurements allows identification of the 3D director configuration in the bulk. A finite element (FE) Q-tensor simulation model is applied to find the equilibrium director configuration and optical simulations are used to confirm the correspondence with experimental microscopy measurements. The created LC configurations offer opportunities in the field of optical devices, light guiding and switching, particle trapping and studies of topological LC structures.

Synthesis and crystal structure of two manganese-based 12-metallacrown-4 complexes: Na2(3-chloro-benzoate)2[12-MCMn(III)N(shi)-4](DMF)6 and MnNa(3-chloro-benzoate)3[12-MCMn(III)N(shi)-4](DMF)(H2O)4·4DMF·0.72H2O.

Similar synthetic schemes yield two different metallacrown (MC) complexes: bis-(μ-3-chloro-benzoato)hexa-kis-(di-methyl-formamide)-tetra-kis-(μ4-N,2-dioxido-benzene-1-carboximidato)tetra-manganese(III)disodium(I), [Mn4Na2(C7H4ClO2)2(C7H4NO3)4(C3H7NO)6] or Na2(3-chloro-benzoate)2[12-MCMn(III)N(shi)-4](DMF)6, 1, and tetra-μ-aqua-tris-(μ-3-chloro-benzoato)(di-methyl-formamide)-tetra-kis-(μ4-N,2-dioxido-benzene-1-carboximidato)penta-manganese(III)sodi-um(I) di-methyl-formamide tetra-solvate 0.72-hydrate, [Mn5Na(C7H4ClO2)3(C7H4NO3)4(C3H7NO)(H2O)4]·4C3H7NO·0.718H2O or MnNa(3-chloro-benzo-ate)3[12-MCMn(III)N(shi)-4](DMF)(H2O)4·4DMF·0.72H2O, 2, where shi3- is salicyl-hydrox-imate and DMF is N,N-di-methyl-formamide. Both complexes have the same framework consisting of four MnIII ions in the MC ring and four shi3- ligands, resulting in an overall square-shaped mol-ecule. The MnIII ions are either five- or six-coordinate with elongated bond lengths in the apical or axial direction, respectively. The structure of 1 is nearly planar, and the MC binds two Na+ ions on opposite faces of the MC central cavity. The 3-chloro-benzoate anions also bind on opposite faces of the MC and form bridges between the central Na+ ions and the ring MnIII ions. For 1 the metallacrown mol-ecule, except for the central Na+ ion, exhibits whole mol-ecule disorder over two sets of sites. Both moieties are centrosymmetric and are related to each other by a pseudo-mirror operation with opposite sense of rotation around the Na⋯Na axis. The occupancy ratio of the main disorder of the metallacrown mol-ecules and 3-chloro-benzoate anions refined to 0.9276 (9):0.0724 (9). The structure of 2 is slightly domed, and the MC binds both an MnII ion and an Na+ ion in the MC central cavity. The MnII ion is located on the convex side of the MC, while the Na+ ion binds to the concave side. Complex 2 represents the first instance of a [12-MCMn(III)N(shi)-4] mol-ecule binding both 3d transition metal and alkali metal ions in the central cavity. In addition, three 3-chloro-benzoate anions bind on the convex side of the MC and connect the MnII ion to three of the ring MnIII ions.

Emergence of self-organized multivortex states in flocks of active rollers

Active matter, both synthetic and biological, demonstrates complex spatiotemporal self-organization and the emergence of collective behavior. A coherent rotational motion, the vortex phase, is of great interest because of its ability to orchestrate well-organized motion of self-propelled particles over large distances. However, its generation without geometrical confinement has been a challenge. Here, we show by experiments and computational modeling that concentrated magnetic rollers self-organize into multivortex states in an unconfined environment. We find that the neighboring vortices more likely occur with the opposite sense of rotation. Our studies provide insights into the mechanism for the emergence of coherent collective motion on the macroscale from the coupling between microscale rotation and translation of individual active elements. These results may stimulate design strategies for self-assembled dynamic materials and microrobotics.

Hydrodynamics of Vortex Generation during Bell Contraction by the Hydromedusa Eutonina indicans (Romanes, 1876).

Swimming bell kinematics and hydrodynamic wake structures were documented during multiple pulsation cycles of a Eutonina indicans (Romanes, 1876) medusa swimming in a predominantly linear path. Bell contractions produced pairs of vortex rings with opposite rotational sense. Analyses of the momentum flux in these wake structures demonstrated that vortex dynamics related directly to variations in the medusa swimming speed. Furthermore, a bulk of the momentum flux in the wake was concentrated spatially at the interfaces between oppositely rotating vortices rings. Similar thrust-producing wake structures have been described in models of fish swimming, which posit vortex rings as vehicles for energy transport from locations of body bending to regions where interacting pairs of opposite-sign vortex rings accelerate the flow into linear propulsive jets. These findings support efforts toward soft robotic biomimetic propulsion.

Rotational synchronization of camphor ribbons.

Experiments on interacting pinned self-propelled rotators are presented. The rotators are made from paper with camphor infused in its matrix. The ribbons rotate due to Marangoni effect driven forces arising by virtue of surface tension gradients. Two such self-rotating camphor ribbons are observed to experience a repulsive coupling via the camphor layer in the common water medium. Lag synchronization in both corotating (same sense of rotation) and counterrotating (opposite sense of rotation) ribbons is reported for the experiments. This synchronization is found to be dependent on the pivot to pivot distance l. For distances less than the span of both the ribbons, l_{c}, the rotators successfully synchronize. Furthermore, it is experimentally perceived that synchronization in the counterrotating ribbons is more robust than in the corotating ribbons. We rationalize the mechanism of this synchronization via a theoretical model involving a Yukawa type interaction which is analyzed numerically.

Vortical structures in the near wake of tabs with various geometries

The vortical structures and turbulence statistics in the near wake of rectangular, trapezoidal, triangular and ellipsoidal tabs were experimentally studied in a refractive-index-matching channel. The tabs share the same bulk dimensions, including a 17 mm height, a 28 mm base width and a $24.5^{\circ }$ inclination angle. Measurements were performed at two Reynolds numbers based on the tab height, $Re_{h}\simeq 2000$ (laminar incoming flow) and 13 000 (turbulent incoming flow). Three-dimensional, three-component particle image velocimetry (PIV) was used to study the mean flow distribution and dominant large-scale vortices, while complementary high-spatial-resolution planar PIV measurements were used to quantify high-order statistics. Instantaneous three-dimensional fields revealed the coexistence of a coherent counter-rotating vortex pair (CVP) and hairpin structures. The CVP and hairpin vortices (the primary structures) exhibit distinctive characteristics and strength across $Re_{h}$ and tab geometries. The CVP is coherently present in the mean flow field and grows in strength over a significantly longer distance at the low $Re_{h}$ due to the lower turbulence levels and the delayed shedding of the hairpin vortices. These features at the low $Re_{h}$ are associated with the presence of Kelvin–Helmholtz instability that develops over three tab heights downstream of the trailing edge. Moreover, a secondary CVP with an opposite sense of rotation resides below the primary one for the four tabs at the low $Re_{h}$. The interaction between the hairpin structures and the primary CVP is experimentally measured in three dimensions and shows complex coexistence. Although the CVP undergoes deformation and splitting at times, it maintains its presence and leads to significant mean spanwise and wall-normal flows.

Scattering properties of the three-dimensional topological insulatorSb2Te3: Coexistence of topologically trivial and nontrivial surface states with opposite spin-momentum helicity

The binary chalcogenides ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ and ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ are the most widely studied topological insulators. Although the quantum anomalous Hall effect has recently been observed in magnetically doped ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$, this compound has been studied to a much lesser extent. Here, by using energy-resolved quasiparticle interference mapping, we investigate the scattering events of pristine ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ surfaces. We find that, in addition to the Dirac fermions, another strongly spin-polarized surface resonance emerges at higher energies in the unoccupied electronic states. Although the two surface states are of different origin, i.e., topologically protected and trivial, respectively, both show strongly directional scattering properties and absence of backscattering. A comparison with ab initio calculations demonstrates that this is a direct consequence of their spin-momentum--locked spin texture which is found to exhibit an opposite rotational sense for the trivial state and the Dirac state.

Experimental study on instantaneous thrust and lift of two plunging wings in tandem

Two tandem wings undergoing a two-dimensional sinusoidal plunging motion are studied in a low Reynolds number water tunnel. The influence of the phase angle and leading-edge vortex (LEV) on the peak value of the instantaneous thrust and lift is studied. The instantaneous lift and thrust are measured by a force sensor; the velocity and vorticity fields are captured by digital particle image velocimetry. For the forewing, noticeable differences at various phase angles are found in the peak value of the instantaneous lift and thrust rather than in their minimum value. The LEV of the hindwing increased the maximum effective angle of attack of the forewing and enhanced the jet-like flow behind the forewing, which accounts for the increase in peak value. For the hindwing, the phase angle determines the sign of the forewing-shed LEV when the hindwing encounters this LEV. If the forewing-shed LEV before the leading edge of the hindwing has the opposite sense of rotation as the LEV of the hindwing, the velocity of the flow on the windward side of the hindwing increases, resulting in high instantaneous thrust and lift. If the two LEVs have the same sense of rotation, the forewing-shed LEV hinders the growth of the hindwing LEV because of the small effective angle of attack, leading to low instantaneous thrust and lift. Non-circulatory forces on the wings are calculated according to a potential flow model. Results show that the non-circulatory force has important effects on the peak value and symmetry of the instantaneous lift and thrust curves.

Transient force augmentation due to counter-rotating vortex ring pairs

Of particular significance to biological locomotion is vortex ring interaction. In the wakes of animals, this unsteady process determines the changes in the impulse of counter-rotating vortex ring pairs (VRPs), which consist of two vortex rings with opposite sense of rotation. In this paper, these VRPs are proposed to be of particular importance to unsteady force generation. We carry out numerical computations, simulating the piston–cylinder apparatus, to study the transient changes in the impulse of counter-rotating VRPs composed of a positive and a negative vortex ring. We model the negative vortex ring (NeVR) of a VRP by making reasonable assumptions about their vorticity distributions and spatial locations, which are initially prescribed. The result of modelling is superimposed on the flow, which has a pre-existing positive vortex ring (PoVR), leading to a VRP. The simulation quantitatively demonstrates that the unsteady force resulting from a VRP is significantly larger compared with an isolated PoVR (without an NeVR). The force enhancement is also correlated to vortex configurations. A normalised force coefficient characterising force augmentation over the entire stroke is given. The force augmentation coefficient grows significantly and then reaches a plateau as the momentum input increases. The results are consistent with those in fully unsteady vortex interaction, which involves the generation of an NeVR. It is suggested that counter-rotating VRPs could offer a new perspective to explain unconventional force generation for biological swimming and flying.

Spin effects in Kapitza-Dirac scattering at light with elliptical polarization

The Kapitza-Dirac effect, which refers to electron scattering at standing light waves, is studied in the Bragg regime with counterpropagating elliptically polarized electromagnetic waves with the same intensity, wavelength, and degree of polarization for two different setups. In the first setup, where the electric-field components of the counterpropagating waves have the same sense of rotation, we find distinct spin effects. The spins of the scattered electrons and of the nonscattered electrons, respectively, precess with a frequency that is of the order of the Bragg-reflection Rabi frequency. When the electric-field components of the counterpropagating waves have an opposite sense of rotation, which is the second considered setup, the standing wave has linear polarization, and no spin effects can be observed. Our results are based on numerical solutions of the time-dependent Dirac equation and the analytical solution of a relativistic Pauli equation, which accounts for the leading relativistic effects.

Non-Newtonian perspectives on pulsatile blood-analog flows in a 180° curved artery model

Complex, unsteady fluid flow phenomena in the arteries arise due to the pulsations of the heart that intermittently pumps the blood to the extremities of the body. The many different flow waveform variations observed throughout the arterial network are a result of this process and a function of the vessel properties. Large scale secondary flow structures are generated throughout the aortic arch and larger branches of the arteries. An experimental 180° curved artery test section with physiological inflow conditions was used to validate the computational methods implemented in this study. Good agreement of the secondary flow structures is obtained between experimental and numerical studies of a Newtonian blood-analog fluid under steady-state and pulsatile, carotid artery flow rate waveforms. Multiple vortical structures, some of opposite rotational sense to Dean vortices, similar to Lyne-type vortices, were observed to form during the systolic portion of the pulse. Computational tools were used to assess the effect of blood-analog fluid rheology (i.e., Newtonian versus non-Newtonian). It is demonstrated that non-Newtonian, blood-analog fluid rheology results in shear layer instabilities that alter the formation of vortical structures during the systolic deceleration and onwards during diastole. Additional vortices not observed in the Newtonian cases appear at the inside and outside of the bend at various times during the pulsation. The influence of blood-analog shear-thinning viscosity decreases mean pressure losses in contrast to the Newtonian blood analog fluid.

A Study of Mixing in a Magnetohydrodynamic Microfluidic Cell By Numerical Simulation

A comprehensive study of a two dimensional MHD (magnetohydrodynamics) micro stirrer with different electrode configurations covering a wide parameter space has been conducted by using computational fluid dynamics simulations. The wall of the circular cavity stirrer acts as the counter electrode. Cylindrical rods ranging in number from one to four, placed inside the cavity act as working electrodes. When two fluids are placed initially in the two halves of the cavity separated by an axial plane, the periodic flow reversal causes stretching, folding and breaking of the interface between the two fluids; an increase in the interfacial area; and enhanced mixing. Parametric studies conducted by varying the time period of the potential difference and the magnitude of the magnetic field intensity show that both significantly influence mixing quality. By having more complex geometries by increasing the number of working electrodes and choosing their locations inside the cavity, and by implementing specific switching schemes for the potential difference on the electrode pairs, secondary flows could be generated which introduced complex chaotic advection and enhanced mixing compared to the configuration with a single working electrode. This work adds to the relatively small body of work that relies on numerical simulations to study MHD microfluidic mixing problems. It also establishes numerical simulations as a tool for optimal design of MHD-based lab-on-a-chip applications. The core microfluidic functions in lab-on-a-chip applications include pumping, mixing, and controlling fluid flow [1]. Among these, efficient and rapid mixing is an especially important task since it has an effect on chemical reaction rates, when multiple species are present. However, due to the small size of these devices (usually millimeters or even micrometers), the Reynolds number is low, and therefore turbulent mixing techniques cannot be implemented. Techniques for speeding up mixing by molecular diffusion, an inherently slow process, are needed to improve the mixing and chemical reaction functionalities of the LOAC devices. By applying time periodic potential differences to the electrode pairs, complex flow features and chaotic advection are introduced. The post-processed results from one simulation follow. The time evolution of species mass fraction with T=4s is shown in Figure 1. Though during the first 2s the flow generates only a few striations, the fluids are well mixed subsequently. This can be attributed to the fact that after the first 2s the fluid moves in the next 2s in a pattern that is not just a reversal of the pattern in the previous two seconds. This mode is repeated four times during the 16s observation time resulting in a more chaotic flow. The results from a series of simulations show that a certain level of mixing can be accomplished by the simple use of the sinusoidal potential boundary conditions on one pair of electrodes. Once a potential is applied on the electrode pair in the presence of the magnetic field, the flow is driven to move clockwise and counter-clockwise periodically, by the Lorentz force. As a result, the interface between the fluids stretches rapidly, and therefore good mixing can be achieved. Better mixing performance was observed for larger values of the sinusoidal potential wave period. Furthermore, for the cases considered, increasing the total operation time beyond where the mixing quality vs. time plot plateaus, the marginal increase in the mixing quality is small. Mixing performance can be enhanced by increasing the current or the magnetic field strength, thereby increasing the Lorentz force. By introducing two flow structures having opposite sense of rotation with the use of two electrode pairs, one can enhance mixing even better. By applying sine wave potentials with opposite signs on two working electrodes, two counter-rotational flows can be generated and better mixing quality obtained with a shorter mixing time (Scheme A). This idea was then extended to 4 electrode pairs in which two pairs were active at a given time by switching between two schemes identical to Scheme A. This scheme (Scheme B) in which the electrode pairs are made active or inactive during a half period according to the switching schedule, allows more complex chaotic advection that enhances mixing performance even with a smaller magnetic field intensity. In Scheme B, the unmixed regions near the wall found in previous cases are mostly eliminated. Acknowledgement We acknowledge support under the National Science Foundation grant award number CBET-1336722. Reference [1] Isaac, K.M.; Gonzales, C.; Sen, D. Modeling of redox electrochemical MHD and three-dimensional CFD simulations of transient phenomena in microfluidic cells. Microfluid Nano-fluid., 2014, DOI: 10.1007/s10404-014-1370-6. Figure 1

New spectroscopic and polarimetric observations of the A0 supergiant HD 92207

AbstractOur recent search for the presence of a magnetic field in the bright early A‐type supergiant HD 92207 using FORS 2 in spectropolarimetric mode revealed the presence of a longitudinal magnetic field of the order of a few hundred Gauss. However, the definite confirmation of the magnetic nature of this object remained pending due to the detection of shortterm spectral variability probably affecting the position of line profiles in left‐ and right‐hand polarized spectra. We present new magnetic field measurements of HD 92207 obtained on three different epochs in 2013 and 2014 using FORS 2 in spectropolarimetric mode. A 3σ detection of the mean longitudinal magnetic field using the entire spectrum, 〈Bz〉all = 104 ± 34 G, was achieved in observations obtained in 2014 January. At this epoch, the position of the spectral lines appeared stable. Our analysis of spectral line shapes recorded in opposite circularly polarized light, i.e. in light with opposite sense of rotation, reveals that line profiles in the light polarized in a certain direction appear slightly split. The mechanism causing such a behaviour in the circularly polarized light is currently unknown. Trying to settle the issue of short‐term variability, we searched for changes in the spectral line profiles on a time scale of 8–10 min using HARPS polarimetric spectra and on a time scale of 3–4 min using time series obtained with the CORALIE spectrograph. No significant variability was detected on these time scales during the epochs studied. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Atom-diatom scattering dynamics of spinning molecules.

We present full quantum mechanical scattering calculations using spinning molecules as target states for nuclear spin selective atom-diatom scattering of reactive D+H2 and F+H2 collisions. Molecules can be forced to rotate uni-directionally by chiral trains of short, non-resonant laser pulses, with different nuclear spin isomers rotating in opposite directions. The calculations we present are based on rotational wavepackets that can be created in this manner. As our simulations show, target molecules with opposite sense of rotation are predominantly scattered in opposite directions, opening routes for spatially and quantum state selective scattering of close chemical species. Moreover, two-dimensional state resolved differential cross sections reveal detailed information about the scattering mechanisms, which can be explained to a large degree by a classical vector model for scattering with spinning molecules.