Counterclockwise Sense Research Articles

Paleomagnetic Data Bearing on the Origin of the Supra‐ Subduction Zone Ophiolites in Southeast Anatolia and the Progressive Closure of the Neotethys Ocean in the Eastern Mediterranean

AbstractThe Late Cretaceous supra‐subduction zone (SSZ) ophiolites in SE Anatolia form two parallel belts: the northern ophiolitic belt, which was emplaced onto the Tauride platform and a second southern belt emplaced on the Arabian platform. There are controversial hypotheses about the geometry and tectonic process of these ophiolites, which are still not well understood. Here, we test three alternative tectonic models for; (a) One single ocean which is defined by the İzmir‐Ankara‐Erzincan Ocean; (b) A southern branch of the Neotethys Ocean; (c) Two separate oceanic basins, which are the Berit Ocean and the South Neotethys Ocean. We present paleomagnetic results from 161 sites focusing on the sheeted dyke complex, cumulate gabbros, extrusive and sedimentary sequences of the Upper Cretaceous ophiolites in the SE Anatolian region. We also sampled the unconformable cover units from Middle Eocene and Miocene sedimentary rocks to distinguish emplacement related tectonic rotations from post‐emplacement tectonic rotations. Our data indicate that the southern ophiolites (Hatay ophiolite, cumulate gabbro + lava) were formed at a paleolatitude of and those of the northern ophiolites (Göksun, İspendere, Guleman ophiolite, cumulate gabbro + lava) were formed at a paleolatitude of . We hypothesize that the northern ophiolites were derived from the Ocean in a NW‐SE directed subduction zone between the Taurides and the Bitlis Pütürge massif, while the southern ophiolites, in contrast, were formed in the South Neotethys Ocean in a NNW‐SSE directed subduction zone farther northeast of the Taurides. Both the ophiolites reached their present position during Late Cretaceous to Middle Miocene, affected by rigid‐block rotations almost in counterclockwise sense.

Magnon spectrum of Bloch hopfion beyond ferromagnetic resonance

With the development of new nanofabrication technologies and measurement techniques, the interest of researchers is moving toward 3D structures and 3D magnetization textures. Special attention is paid to the topological magnetization textures, particularly hopfions. In this paper, we investigate the magnetization dynamics of the hopfion through the numerical solution of the eigenvalue problem. We show that the spectrum of spin-wave modes of the hopfion is much richer than those attainable in ferromagnetic resonance experiments or time-domain simulations reported so far. We identified four groups of modes that differ in the character of oscillations (clockwise or counter-clockwise rotation sense), the position of an average amplitude localization along the radial direction, and different oscillations in the vertical cross section. The knowledge of the full spin-wave spectrum shall help in hopfion identification, understanding of the interaction between spin waves and hopfion dynamics as well as the development of the potential of hopfion in spintronic and magnonic applications.

Floquet-Weyl semimetals generated by an optically resonant interband transition

Floquet-Weyl semimetals (FWSMs) generated by irradiation of a continuous-wave laser with left-hand circular polarization (rotating in counterclockwise sense with time) on the group II--V narrow-gap semiconductor ${\mathrm{Zn}}_{3}{\mathrm{As}}_{2}$ are theoretically investigated, where the frequency of the laser is set nearly resonant with the band gap of the crystal. It is found that the excitation of the crystal by such a laser induces two types of FWSM phases that differ absolutely in character. To be specific, the associated two pairs of Weyl points are stably formed by band touching between Floquet sidebands ascribable to a valence band labeled ${J}_{z}=\ifmmode\pm\else\textpm\fi{}3/2$ and a conduction band labeled ${J}_{z}=\ifmmode\pm\else\textpm\fi{}1/2$, where ${J}_{z}$ represents the $z$ component of total angular-momentum quantum number of the $\mathrm{\ensuremath{\Gamma}}$ point and a double sign corresponds. Here, one FWSM state composed of the up-spin Floquet sidebands relevant to ${J}_{z}=3/2$ and $1/2$ shows almost quadratic band-touching in the vicinity of the associated pair of Weyl points, while the other FWSM state composed of the down-spin Floquet sidebands relevant to ${J}_{z}=\ensuremath{-}3/2$ and $\ensuremath{-}1/2$ shows linear band-touching. Furthermore, it is revealed that both up-spin and down-spin sidebands host nontrivial two-dimensional surface states that are pinned to the respective pairs of the Weyl points. Both surface states also show different energy dispersions and physical properties. A more detailed discussion is presented in the text on the origin of the above findings, the chirality of the FWSM phases, the alteration of topological order, laser-induced magnetic properties, and so on.

Neogene restoration of geometry of the Neotethyan suture zone in Central Anatolia (Turkey)

ABSTRACT We have restored the geometries of suture zones that involved various continental blocks in central Anatolia during the Neogene, using palaeomagnetic data. Previously, the Kırşehir Block was proposed to be an NNE-SSW striking tectonic block broken into three fragments that they underwent clockwise rotations in the north and counter-clockwise rotations in the south during the Palaeogene, due to collision and N-S shortening of the Kırşehir Block between Tauride-Menderes Block in the south and the Pontides in the north. Our new results point out five distinct Neogene tectonic domains with distinct rotation patterns that indicate the rotational deformation of Central Anatolia is far more complex than generally presumed. Among these, 1) Kırıkkale-Bala Domain is rotated ~18° clockwise, 2) the Tuz Gölü Domain underwent ~14° counter-clockwise rotation, 3) the Alcı-Orhaniye Domain rotated ~35° counter-clockwise sense, 4) the Northern Haymana Domain underwent ~12° counter-clockwise rotation while 5) the Southern Haymana Domain underwent very small (~5° clockwise) net rotation since the early Miocene. The results also indicated that pre-Neogene configuration of the Izmir-Ankara Suture Zone was striking almost E-W while Inner-Tauride and Ankara-Erzincan suture zones were almost N-S in the study area. In addition, the fault zones that define the these domains extend from the Kırşehir Block into the over-riding blocks (Pontides) continuously without any deflection indicating that they were active during the Neogene and fragmented and dislocated the suture zones in the region.

Analysis of the thermo-fluidic transport around counter-rotating tandem circular cylinders

The work physically relates to the influence of thermal buoyancy on the flow and heat transfer of an incompressible fluid around two counter-rotating circular cylinders arranged in tandem configuration within an unconfined domain. Two-dimensional numerical simulations are conducted using a finite volume based computational fluid dynamics tool to explore the problem. The Reynolds number is taken as 100 with Prandtl number 0.71, keeping the non-dimensional spacing between the cylinders fixed at 1.5. The cylinder rotations are considered in the range of a dimensionless speed of 0 to 5. The upstream cylinder is rotating in the clockwise sense, whereas, the downstream one in the counter-clockwise sense. The buoyancy effect is analyzed for the Richardson number range 0 to 1. The flow is unsteady periodic characterized by vortex shedding around the stationary cylinders at the chosen value of the Reynolds number. The flow shows unsteadiness with vortex shedding initially with increasing rotational speed; however, at a critical value of the rotation, the flow becomes stabilized with suppression of vortex shedding. On the contrary, the cross thermal buoyancy effect destabilizes the flow into an unsteady periodic pattern. This complex interplay among the free stream flow, cross buoyancy, and counter-rotation produces intriguing fluid dynamic and thermal phenomena. The critical rotational speeds for the range of Richardson numbers are obtained as [Formula: see text] respectively for Ri = 0, 0.25, 0.5 and 1. A corresponding regime diagram is also constructed to depict the unsteady and steady zones of operation.

Regulation of bacterial ATP synthase activity: A gear-shifting or a pawl-ratchet mechanism?

The F1 Fo -ATP synthase, a widely distributed nanomotor responsible of ATP synthesis, rotates its central rotor reversibly: In the clockwise direction when viewed from the Fo (with the observer facing the positive side of the energy transducing membrane and looking down into the negative side of the membrane), it functions as ATP synthase, while in counterclockwise sense, it operates as a proton-pumping ATP hydrolase. Regulation exerted by naturally occurring inhibitory proteins of the enzyme appears to function by avoiding ATP hydrolysis while preserving ATP synthesis. The work of Liu et al. describes an unbiased, elegant analytical pipeline that provides important insights into the inhibitory role of the ε-subunit of the bacterial F1 Fo -ATP synthase invivo. We discuss if a gear-shifting versus a pawl-ratchet mechanism may explain the regulatory role of the ε-subunit.

Control of rotation of the F1FO-ATP synthase nanomotor by an inhibitory α-helix from unfolded ε or intrinsically disordered ζ and IF1 proteins

The ATP synthase is a ubiquitous nanomotor that fuels life by the synthesis of the chemical energy of ATP. In order to synthesize ATP, this enzyme is capable of rotating its central rotor in a reversible manner. In the clockwise (CW) direction, it functions as ATP synthase, while in counter clockwise (CCW) sense it functions as an proton pumping ATPase. In bacteria and mitochondria, there are two known canonical natural inhibitor proteins, namely the ε and IF1 subunits. These proteins regulate the CCW F1FO-ATPase activity by blocking γ subunit rotation at the αDP/βDP/γ subunit interface in the F1 domain. Recently, we discovered a unique natural F1-ATPase inhibitor in Paracoccus denitrificans and related α-proteobacteria denoted the ζ subunit. Here, we compare the functional and structural mechanisms of ε, IF1, and ζ, and using the current data in the field, it is evident that all three regulatory proteins interact with the αDP/βDP/γ interface of the F1-ATPase. In order to exert inhibition, IF1 and ζ contain an intrinsically disordered N-terminal protein region (IDPr) that folds into an α-helix when inserted in the αDP/βDP/γ interface. In this context, we revised here the mechanism and role of the ζ subunit as a unidirectional F-ATPase inhibitor blocking exclusively the CCW F1FO-ATPase rotation, without affecting the CW-F1FO-ATP synthase turnover. In summary, the ζ subunit has a mode of action similar to mitochondrial IF1, but in α-proteobacteria. The structural and functional implications of these intrinsically disordered ζ and IF1 inhibitors are discussed to shed light on the control mechanisms of the ATP synthase nanomotor from an evolutionary perspective.

Evaluation and interpretation of the bucket test in healthy individuals

Objective: To determine and interpret the range of normal deviation of the bucket test in healthy subjectsSubjects and methods: Study design: Cross-sectional study in a secondary care center. Inclusion criteria: subjects ≥18 years old with no otologic or neurologic symptoms and normal complete neuro-otological examination. The subjective visual vertical was evaluated binocularly using the bucket test. Five measurements were made on the clockwise direction and five on the counterclockwise direction. The examiner selected the starting point, the patient then manipulated the bucket and it stopped when the volunteer considered the line reached the vertical position.Results: Fifty healthy volunteers were included, 16 (32%) were men, and 34 (68%) women with a mean age of 34 years. The mean value found clockwise was 1.93° ± 2.26° and counterclockwise sense was of 0.86° ± 2.44°. Mean normal values ranged from 1.4° ± 1.9°.Conclusions: The bucket test is easy and quick to perform; we recommend to use a range of −1.0° to +3.0° as normal values in the healthy population.

Understanding reversals of a rattleback

A counterintuitive unidirectional (say counterclockwise) motion of a toy rattleback takes place when it is started by tapping it at a long side or by spinning it slowly in the clockwise sense of rotation. We study the motion of a toy rattleback having an ellipsoidal-shaped bottom by using frictionless Newton equations of motion of a rigid body rolling without sliding in a plane. We simulate these equations for tapping and spinning initial conditions to see the contact trajectory, the force arm and the reaction force responsible for torque turning the rattleback in the counterclockwise sense of rotation. Long time behavior of such a rattleback is, however, quasi-periodic and a rattleback starting with small transversal oscillations turns in the clockwise direction.

Principal components of wrist circumduction from electromagnetic surgical tracking.

An electromagnetic (EM) surgical tracking system was used for a functionally calibrated kinematic analysis of wrist motion. Circumduction motions were tested for differences in subject gender and for differences in the sense of the circumduction as clockwise or counter-clockwise motion. Twenty subjects were instrumented for EM tracking. Flexion-extension motion was used to identify the functional axis. Subjects performed unconstrained wrist circumduction in a clockwise and counter-clockwise sense. Data were decomposed into orthogonal flexion-extension motions and radial-ulnar deviation motions. PCA was used to concisely represent motions. Nonparametric Wilcoxon tests were used to distinguish the groups. Flexion-extension motions were projected onto a direction axis with a root-mean-square error of [Formula: see text]. Using the first three principal components, there was no statistically significant difference in gender (all [Formula: see text]). For motion sense, radial-ulnar deviation distinguished the sense of circumduction in the first principal component ([Formula: see text]) and in the third principal component ([Formula: see text]); flexion-extension distinguished the sense in the second principal component ([Formula: see text]). The clockwise sense of circumduction could be distinguished by a multifactorial combination of components; there were no gender differences in this small population. These data constitute a baseline for normal wrist circumduction. The multifactorial PCA findings suggest that a higher-dimensional method, such as manifold analysis, may be a more concise way of representing circumduction in human joints.

A Circularly Polarized Antenna Based on the Unidirectional Resonant Modes of a Ferrite Disk

We propose a circularly polarized antenna with a wide axial ratio (AR) beamwidth that consists of a normally magnetized ferrite disk mounted on a ground plane. The device uses the resonant modes of the disk, which rotate only in the clockwise or counter-clockwise sense in the frequency range where the effective permeability of ferrite is negative. A semianalytical model is derived for the antenna fed by a single, conventional current probe and is validated numerically by finite element method. For a yttrium iron garnet disk with the radius and height of 5 and 1 mm, respectively, the results show a 3 dB AR beamwidth of 90 ° with an operation frequency, which can be tuned in the 4-4.5 GHz range by varying the magnetic bias field from 50 to 35000 A/m. Simulations show that higher AR beamwidths are achievable using finite ground conductors. Compared with previous papers, the fabrication requirements on this structure are not critical, which enhances its potential applicability.

The High Time Resolution Universe survey – IX. Polarimetry of long-period pulsars

We present a polarimetric analysis of 49 long-period pulsars discovered as part of the High Time Resolution Universe (HTRU) southern survey. The sources exhibit the typical characteristics of ‘old’ pulsars, with low fractional linear and circular polarization and narrow, multi-component profiles. Although the position angle swings are generally complex, for two of the analysed pulsars (J1622−3751 and J1710−2616) we obtained an indication of the geometry via the rotating vector model. We were able to determine a value of the rotation measure (RM) for 34 of the sources which, when combined with their dispersion measures (DM), yields an integrated magnetic field strength along the line of sight. With the data presented here, the total number of values of RM associated with pulsars discovered during the HTRU southern survey sums to 51. The RMs are not consistent with the hypothesis of a counter-clockwise direction of the Galactic magnetic field within an annulus included between 4 and 6 kpc from the Galactic Centre. A partial agreement with a counter-clockwise sense of the Galactic magnetic field within the spiral arms is, however, found in the area of the Carina-Sagittarius arm.

Tidal currents in the Adriatic as measured by surface drifters

Velocities of surface drifters are analyzed to study tidal currents throughout the Adriatic Sea. Spectral and harmonic analyses indicate that the M2, S2, and K1 constituents dominate. Maps of tidal characteristics show that M2 and S2 are rectilinear currents (reversing tides) aligned with the main axis of the Adriatic basin with maximum amplitude (~7 cm/s for M2 and ~4 cm/s for S2) in the northern area off the Istrian Peninsula. Near the northern coast, semidiurnal tidal currents decrease in amplitude and rotate in the counterclockwise sense. Near the Po River delta, M2 (S2) motions rotate in the counterclockwise (clockwise) sense. S2 rotation is also counterclockwise near the northeastern coast. M2 phases increase from about 130° on the eastern Croatian coast to 190° on the western Italian side. S2 phases range from 150° to 200°. In the middle and southern Adriatic, the semidiurnal tides are small (~1 cm/s). The diurnal tidal currents (K1) are strong across the basin at the levels of Monte Conero and the Gargano Peninsula with speed larger than 5 cm/s and mainly clockwise rotation, and also in coastal areas (e.g., on the Albanian shelf and close to the Otranto Channel). Phases increase from the east to the west coasts (by as much as 150°). These new results compare satisfactorily with previous observations and numerical simulations, although tidal amplitudes are under‐estimated with respect to mooring measurements. They extend for the first time the description of the Adriatic tidal currents to the entire basin based on direct velocity observations.

Enlarged helical twisting power in chiral cyclic dimers based on conventional chiral alkyl diols

We prepared a homologous series of chiral cyclic liquid crystal (LC) dimers containing two biphenyl mesogens linked by two alkyl spacers, one of which was based on a R-enantiomeric chiral diol. In solution, the circular dichroism spectra of all the R-enantiomeric dimers showed the first negative and second positive Cotton effects, which indicated that the two biphenyl mesogens were located in a skewed overlapping alignment with counter-clockwise helicity. The helical twisting power (HTP) of these cyclic dimers was confirmed by the cholesteric LCs in mixtures with the nematic host. The induced cholesteric LCs in all mixtures had the same counter-clockwise helical sense as the skewed conformation of the two biphenyl mesogens. Furthermore, HTP values and Cotton effect amplitudes were linearly correlated, indicating direct induction of cholesteric twisting by the skewed biphenyl moieties. The induced HTP values were quite large, irrespective of the use of conventional chiral diols; the largest HTP value exceeded 100 μm−1 and was obtained in the cyclic dimer based on the R,R-1,2-diphenylethane diol.

Analysis of superposed strain: A case study from Barr Conglomerate in the South Delhi Fold Belt, Rajasthan, India

The structural geometry in the Barr conglomerate and the neighboring rocks in the western flank of the Meso- to Neoproterozoic South Delhi Fold Belt indicate superposed deformation, with structures developed by horizontal dextral simple shear deformation superimposed on earlier structures formed during approximately ESE-WNW compression and subvertical maximum elongation. The first deformation produced NNE-SSW trending subvertical schistosity, and associated steeply plunging isoclinal folds, mineral lineation and pebble elongation lineation having almost downdip alignment on the schistosity surface. The second deformation produced dextral folds both on bedding and schistosity surfaces and modified the shape of the pebbles already deformed by the first deformation. On vertical sections perpendicular to the schistosity trace the pebbles show sub-ellipsoidal shape with their mean elongation direction parallel to the schistosity trace. On the horizontal section the pebbles often show asymmetrical shape and asymmetrical deflection of the schistosity surface around the pebbles. The mean elongation direction makes a small angle (2°–8°) in the counter-clockwise sense with the schistosity surface. This obliquity is due to modification of post-first-deformation sub-ellipsoidal shape by later horizontal simple shear using the schistosity surface as the movement plane. Analytical expressions are derived for the modification of an original ellipse by simple shear parallel to the long axis of the ellipse. A family of curves has been generated to depict the change in axial ratio and orientation of long axis for different initial axial ratios, and for different values of shear strain ( γ). Using these curves it has been possible to factorize the total strain into two components representing the earlier compression and the later simple shear. It is noted that the computed earlier shortening strain ellipsoids are consistently in the flattening field close to the line of pure oblate ellipsoids in the Flinn plot. There is no systematic spatial control on the variation in the values of shear strain ( γ), strain ellipsoid shape parameter ( k), and intensity of distortion ( d) as one proceeds south to north along the strike of the conglomerate.

SUNRISE/IMaX OBSERVATIONS OF CONVECTIVELY DRIVEN VORTEX FLOWS IN THE SUN

We characterize the observational properties of the convectively driven vortex flows recently discovered on the quiet Sun, using magnetograms, Dopplergrams, and images obtained with the 1 m balloon-borne Sunrise telescope. By visual inspection of time series, we find some 3.1 × 10−3 vortices Mm−2 minute−1, which is a factor of ∼1.7 larger than previous estimates. The mean duration of the individual events turns out to be 7.9 minutes, with a standard deviation of 3.2 minutes. In addition, we find several events appearing at the same locations along the duration of the time series (31.6 minutes). Such recurrent vortices show up in the proper motion flow field map averaged over the time series. The typical vertical vorticities are ≲6 × 10−3 s−1, which corresponds to a period of rotation of some 35 minutes. The vortices show a preferred counterclockwise sense of rotation, which we conjecture may have to do with the preferred vorticity impinged by the solar differential rotation.

The bases for understanding of the NW Dinarides and Istria Peninsula tectonics

Thrust structure of the northeastern part of the External Dinarides is depended upon paleogeography of the Adriatic-Dinaric Mesozoic Carbonate Platform, which was in the southeast (in the recent position) composed of Dinaric and Adriatic segment with intermediate Budva Trough. In the northwest in the area of the present Slovenia, it represents uniform platform. In the northwestern continuation of the Budva Trough, shallow halftrough formed and more to the west, shallow Friuli Paleogene Basin came in to being, which separated so called Friuli Carbonate Platform from the central part of the carbonate platform. Area of Istria was separated from Adriatic segment with Kvarner Fault, originated already in the Mesozoic. External Dinaric Thrust Belt formed in the final phase of the Dinarides overthrusting. It originated from Dinaric segment of the Mesozoic Carbonate Platform at the end of the Eocene and was thrusted on the Adriatic segment of the Mesozoic Carbonate Platform. Whole process also triggered formation of the External Dinaric Imbricate Belt with Thrust Front of the External Dinarides against Adriatic-Apulian Foreland. Later also represents rigid indenter of the Adria Lithospheric Microplate ("Adria"), and External Dinaric Imbricate Belt represents its deformed margin, therefore we place it to the rigid indenter. Segmentation of the "Adria" occurred in the Miocene or later. It roughly disintegrated in the Padan and Adriatic part along Kvarner Fault. During rotation of the Padan part in the counter clockwise sense, the corner part, representing Istria Peninsula, rotated and underthrusted towards northeast under External Dinarides. As a result, Istria- Friuli Underthrust Zone formed, structurally conditioned with the position of the Friuli Paleogene Basin, and vast Istria Pushed Area between Southern Alps, Velebit Mts. and Želimlje Fault. This process is still active recently. During Istria underthrusting and pushing in the northwest direction, Raša Fault and Thrust Front of the External Dinaric Thrust Belt bended, and as a consequence, strike-slip movements along those planes were hindered. From the tip of the Kvarner Bay towards Idrija and Ravne Faults in the Upper Soča Valley, conditions for formation of the en echalon strike-slip belt were set up. The strike-slip belt is defined with segment of the Raša Fault southeast from Ilirska Bistrica, seismically active area between Ilirska Bistrica - Hruševje stretch, Vipava Fault, Predjama Fault and northwestern part of the Idrija and Ravne Fault. Therefore we postulate, that a segment of the External Dinaric Thrust Belt Front and shear boundary between the tip of Kvarner Bay and Upper Soča Valley, with extended branches of the Idrija and Ravne Faults, represents new attached block of the Adria Microplate rigid indenter edge.

Kinematics of the southern Red Sea–Afar Triple Junction and implications for plate dynamics

GPS measurements adjacent to the southern Red Sea and Afar Triple Junction, indicate that the Red Sea Rift bifurcates south of 17° N latitude with one branch following a continuation of the main Red Sea Rift (∼150° Az.) and the other oriented more N‐S, traversing the Danakil Depression. These two rift branches account for the full Arabia–Nubia relative motion. The partitioning of extension between rift branches varies approximately linearly along strike; north of ∼16°N latitude, extension (∼15 mm/yr) is all on the main Red Sea Rift while at ∼13°N, extension (∼20 mm/yr) has transferred completely to the Danakil Depression. The Danakil Block separates the two rifts and rotates in a counterclockwise sense with respect to Nubia at a present‐day rate of 1.9 ± 0.1°/Myr around a pole located at 17.0 ± 0.2°N, 39.7 ± 0.2°E, accommodating extension along the rifts and developing the roughly triangular geometry of the Danakil Depression. Rotating the Danakil Block back in time to close the Danakil Depression, and assuming that the rotation rate with respect to Nubia has been roughly constant, the present width of the Danakil Depression is consistent with initiation of block rotation at 9.3 ± 4 Ma, approximately coincident with the initiation of ocean spreading in the Gulf of Aden, and a concomitant ∼70% increase in the rate of Nubia–Arabia relative motion.

DYNAMICS OF IONIZED GAS AT THE GALACTIC CENTER: VERY LARGE ARRAY OBSERVATIONS OF THE THREE-DIMENSIONAL VELOCITY FIELD AND LOCATION OF THE IONIZED STREAMS IN SAGITTARIUS A WEST

We present new results based on high-resolution observations of Sgr A West at the Galactic center with the Very Large Array (VLA) at 1.3 cm. By combining recent observations with those made at earlier epochs with the VLA at wavelengths of 1.3 and 3.6 cm, we measured proper motions for 71 compact H II components in the central 80 '' (3 pc, assuming D = 8 pc). Using VLA archival data for the H92 alpha radio recombination line, we also investigated radial velocities in the LSR velocity range from +200 to -415 km s(-1). Combining proper motion and radial velocity measurements, we have determined the three-dimensional velocity distribution in Sgr A West. We find that the three ionized streams (Northern Arm, Eastern Arm, and Western Arc) in the central 3 pc can be modeled with three bundles of Keplerian orbits around Sgr A*. Assuming that each of the observed streams of ionized gas follows a single orbit, we determined the five orbital parameters (a, e, Omega, omega, i) for each of them using least-square fitting to the loci of the streams. The degeneracy in the orbital solutions for both the direction of flow and the two mirror images can be further resolved using the information obtained from the velocity measurements. Our results confirm earlier results on the streams in the Western Arc and the Northern Arm to be in Keplerian orbits, suggesting that the stream in the Eastern Arm is also consistent with an elliptical orbit. All three are confined within the central 3 pc. Both the Northern and Eastern Arm streams have high eccentricities (e = 0.83 +/- 0.10 and 0.82 +/- 0.05, respectively), while the Western Arc stream is nearly circular, with e = 0.2 +/- 0.15. All three streams orbit around Sgr A* in a counterclockwise sense (viewed from the Earth) and have orbital periods in the range 4-8x10(4) yr. To verify the fit, the distributions of radial and transverse velocity vectors in Sgr A West were also computed using the Keplerian model and they show good agreement with both the proper motion and radial velocity data. In addition, the computed orbits suggest that the Northern and Eastern Arm streams may collide in the Bar region (a few arcsec south of Sgr A*) and that most of the orbiting ionized gas in the Bar region is located behind Sgr A*. We also report an ionized nebula associated with IRS 8, including a bow shock in radio continuum emission which shows excellent agreement with near infrared observations. From the H92a line data, we find evidence of substantial interaction between the IRS 8 nebula and the Northern Arm stream occurring in the bow-shock region. Other new morphological features revealed in our high-resolution image include (1) a helical structure in the Northern Arm, suggesting that MHD plays an important role in the motion of the ionized gas, in addition to the dynamics determined by the central gravitational field, and (2) a linear feature in the IRS 16 region, suggesting that the compressed edge of the Northern Arm may result from the collective winds and radiation pressure from the high mass stars in the IRS16 cluster.

Tectonic evolution of the northwestern Internal Dinarides as constrained by structures and rotation of Medvednica Mountains, North Croatia

Abstract This paper attempts to explain the tectonic history and possible reasons for the change of trend of the northwestern part of the Internal Dinarides in a transitional area between the Southeastern Alps, central Dinarides and Tisia, north of Zagreb. Structural and palaeomagnetic data collected in pre-Neogene rocks at Medvednica Mountains, combined with palaeomagnetic data available from Neogene rocks in the surrounding area, point to the following conclusions: (1) The reason for dramatic deflection in structural trend of the Internal Dinarides in the area north of Zagreb is a 130° clockwise rotation and eastward escape of a tectonic block comprising Medvednica Mountains and the surrounding inselbergs, bounded to the north by the easternmost tip of the Periadratic Lineament. In Medvednica Mountains, the main period of tectonic escape and associated clockwise rotation occurred in the Late Palaeogene, possibly in the Oligocene–earliest Miocene. (2) When rotated into the original position, the trend of observed pre-Neogene structures of Medvednica Mountains becomes parallel to the major structural trend of the central Dinarides. In view of their original orientation, these structures are interpreted in the following way: (a) The first D1 deformational event is attributed to the Aptian–Albian nappe stacking in the central–northern Dinarides that was accommodated by a top-to-the-north directed shearing and northward propagation of already obducted ophiolites of the Central Dinaridic ophiolite zone. This nappe stacking, which resulted in a weak regional metamorphism in tectonic units underlying the ophiolites, was orogen-parallel or at a very acute angle to known structural (and possibly palaeogeographic) trends. This implies a major left-lateral shear component along the former Adriatic margin and obducted Dinaridic ophiolite zone. (b) This was followed by Early Albian orogen-perpendicular shortening (D2) that was accommodated by folding and top-to-the-west thrusting. This deformation resulted in gradual cooling of the metamorphic stack and also in uplift and erosion of the higher structural units. (c) The D3 deformational event was driven by renewed E–W shortening that took place after the Paleocene, most probably during the Middle Eocene–Oligocene, i.e. synchronous with the main Dinaridic tectonic phase of the External Dinarides. This shortening was probably triggered by collision and thrusting of Tisia over the northern segment of the Internal Dinarides. (d) This was finally followed by D4 pervasive, right-lateral N–S shearing that is tentatively interpreted as being related to the right-lateral shearing of the Sava zone during the Eocene–Oligocene. (e) Following the main period of tectonic escape and induced clockwise rotation along the Periadriatic fault, possibly in the Oligocene–earliest Miocene, the Medvednica Mountains and the surrounding area were affected by repeated extensions and inversions since the Early Miocene to recent times. Palaeomagnetic data suggest that in the Early Miocene (but probably before the Karpatian) this area was part of a regional block that shifted northwards and rotated in a counter-clockwise sense. A second episode of counter-clockwise rotation occurred at the present latitude in post-Pontian times (since c . 5 Ma), driven by the counter-clockwise rotating Adriatic Plate.