Does the East Greenland Current exist in the northern Fram Strait?

Warm Atlantic Water (AW) flows around the Nordic Seas in a cyclonic boundary current loop. Some AW enters the Arctic Ocean where it is transformed to Arctic Atlantic Water (AAW) before exiting through the Fram Strait. There the AAW is joined by recirculating AW. Here we present the first summer synoptic study targeted at resolving this confluence in the Fram Strait which forms the East Greenland Current (EGC). Absolute geostrophic velocities and hydrography from observations in 2016, including four sections crossing the east Greenland shelf break, are compared to output from an eddy-resolving configuration of the sea ice–ocean model FESOM. Far offshore (120&thinsp;km at 80.8°&thinsp;N) AW warmer than 2&thinsp;°C is found in the northern Fram Strait. The Arctic Ocean outflow there is broad and barotropic, but gets narrower and more baroclinic toward the south as recirculating AW increases the cross-shelf-break density gradient. This barotropic to baroclinic transition appears to form the well-known EGC boundary current flowing along the shelf break farther south where it has been previously described. In this realization, between 80.2 and 76.5°&thinsp;N, the southward transport along the east Greenland shelf break increases from roughly 1&thinsp;Sv to about 4&thinsp;Sv and the proportion of AW to AAW also increases fourfold from 19±8&thinsp;% to 80±3&thinsp;%. Consequently, in the southern Fram Strait, AW can propagate into the Norske Trough on the east Greenland shelf and reach the large marine-terminating glaciers there. High instantaneous variability observed in both the synoptic data and the model output is attributed to eddies, the representation of which is crucial as they mediate the westward transport of AW in the recirculation and thus structure the confluence forming the EGC.</p

Shell-model test of the rotational-model relation between static quadrupole moments Q(2^+_1), B(E2)'s, and orbital M1 transitions

In this work, we examine critically the relation between orbital magnetic dipole (scissors mode) strength and quadrupole deformation properties. Assuming a simple K=0 ground state band in an even-even nucleus, the quantities Q(2^+_1) (i.e., the static quadrupole moment) and B(E2)_{0_1 \to 2_1} both are described by a single parameter--the intrinsic quadrupole moment Q_0. In the shell model, we can operationally define Q_0(Static) and Q_0(BE2) and see if they are the same. Following a brief excursion to the sd shell, we perform calculations in the fp shell. The nuclei we consider ({44,46,48}Ti and {48,50}Cr) are far from being perfect rotors, but we find that the calculated ratio Q_0(Static)/Q_0(BE2) is in many cases surprisingly close to one. We also discuss the collectivity of orbital magnetic dipole transitions. We find that the large orbital B(M1) strength in {44}Ti relative to {46}Ti and {48}Ti cannot be explained by simple deformation arguments.Comment: 12 pages, RevTeX4. Sections II (Quadrupole properties in the sd-shell) and V (Random interaction studies) added. Minor changes throughout the text and 48Cr added to present Table IV, as well as results for the lowest 100 state

Magnetic dipole probes of the sd and pf shell crossing in the A=36,38 argon isotopes

We have calculated the M1 strength distributions in the A=36,38 argon isotopes within large-scale shell model studies which consider valence nucleons in the sd and pf shells. While the M1 strength in 36Ar is well reproduced within the sd shell, the experimentally observed strong fragmentation of the M1 strength in 38Ar requires configuration mixing between the sd and the pf shells adding to our understanding of correlations across the N=20 shell gap.Comment: 14 pages, 8 figure

The magnetic susceptibility of disordered non-diffusive mesoscopic systems

Disorder-induced spectral correlations of mesoscopic quantum systems in the non-diffusive regime and their effect on the magnetic susceptibility are studied. We perform impurity averaging for non-translational invariant systems by combining a diagrammatic perturbative approach with semiclassical techniques. This allows us to study the entire range from clean to diffusive systems. As an application we consider the magnetic response of non-interacting electrons in microstructures in the presence of weak disorder. We show that in the ballistic case (elastic mean free path $\ell$ larger than the system size) there exist two distinct regimes of behaviour depending on the relative magnitudes of $\ell$ and an inelastic scattering length $L_{\phi}$. We present numerical results for square billiards and derive approximate analytical results for generic chaotic geometries. The magnetic field dependence and $L_{\phi}$ dependence of the disorder-induced susceptibility is qualitatively similar in both types of geometry.Comment: 11 pages, 7 eps figures, to be published in Phys. Rev.

Therapeutic options to prevent recurrence of an aggressive aneurysmatic bone cyst of the cervical spine of a 16 year old boy - a case report

The aneurysmatic bone cyst (ABC) is a benign primary bone tumour. If located in the cervical spine, its expansive growth and destructive behaviour may lead to instability and serious neurological impairment. We report a case of a 16-year-old boy with an aggressive ABC in the 7th cervical vertebra. Computertomographic and magnetic resonance imaging revealed the envelopment of the left 7th and 8th spinal nerve along with the anterior displacement of the left vertebral artery. The interdisciplinary surgical strategy consisted of a partially incomplete cyst resection, subtotal spondylectomy with posterior screw-and-rod fixation from C6-Th1, iliac crest bone grafting and anterior plating from C6-Th1. With regard to the high rate of recurrence after incomplete resection published in the recent literature, the patient was postoperatively treated by megavoltage radiotherapy with a total dose of 30Gy (daily dose of 1.8 Gy for 3 weeks). The clinical and radiographic follow-up showed complete recovery of all neurologic impairments and no signs of tumour recurrence at 3, 6 and 12 months after surgery. This case highlights diverse treatment regimens and shall outline the challenge and the problems of the interdisciplinary decision-making in adolescents presenting with ABC in high-demanding anatomical regions

Practical solution to the Monte Carlo sign problem: Realistic calculations of 54Fe

We present a practical solution to the "sign problem" in the auxiliary field Monte Carlo approach to the nuclear shell model. The method is based on extrapolation from a continuous family of problem-free Hamiltonians. To demonstrate the resultant ability to treat large shell-model problems, we present results for 54Fe in the full fp-shell basis using the Brown-Richter interaction. We find the Gamow-Teller beta^+ strength to be quenched by 58% relative to the single-particle estimate, in better agreement with experiment than previous estimates based on truncated bases.Comment: 11 pages + 2 figures (not included

Persistent currents in diffusive metallic cavities: Large values and anomalous scaling with disorder

The effect of disorder on confined metallic cavities with an Aharonov-Bohm flux line is addressed. We find that, even deep in the diffusive regime, large values of persistent currents may arise for a wide variety of geometries. We present numerical results supporting an anomalous scaling law of the average typical current $$ with the strength of disorder $w$, $\sim w^{- \gamma}$ with $\gamma < 2$. This is contrasted with previously reported results obtained for cylindrical samples where a scaling $\sim w^{-2}$ has been found. Possible links to, up to date, unexplained experimental data are finally discussed.Comment: 5 pages, 4 figure

Heat capacity and pairing transition in nuclei

A simple model based on the canonical-ensemble theory is outlined for hot nuclei. The properties of the model are discussed with respect to the Fermi gas model and the breaking of Cooper pairs. The model describes well the experimental level density of deformed nuclei in various mass regions. The origin of the so-called S-shape of the heat capacity curve Cv(T) is discussed.Comment: 6 pages + 8 figure

Studies of the Giant Dipole Resonance in 27^{27}Al, 40^{40}Ca, 56^{56}Fe, 58^{58}Ni and 208^{208}Pb with high energy-resolution inelastic proton scattering under 0∘^\circ

A survey of the fine structure of the Isovector Giant Dipole Resonance (IVGDR) was performed, using the recently commissioned zero-degree facility of the K600 magnetic spectrometer at iThemba LABS. Inelastic proton scattering at an incident energy of 200 MeV was measured on $^{27}$Al, $^{40}$Ca, $^{56}$Fe, $^{58}$Ni and $^{208}$Pb. A high energy resolution ($\rm{\Delta}\it{E} \simeq$ 40 keV FWHM) could be achieved after utilising faint-beam and dispersion-matching techniques. Considerable fine structure is observed in the energy region of the IVGDR and characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The comparison with Quasiparticle-Phonon Model (QPM) calculations provides insight into the relevance of different giant resonance decay mechanisms. Photoabsorption cross sections derived from the data assuming dominance of relativistic Coulomb excitation are in fair agreement with previous work using real photons.Comment: 15 pages, 15 figure