Current driven switching of magnetic layers

The switching of magnetic layers is studied under the action of a spin current in a ferromagnetic metal/non-magnetic metal/ferromagnetic metal spin valve. We find that the main contribution to the switching comes from the non-equilibrium exchange interaction between the ferromagnetic layers. This interaction defines the magnetic configuration of the layers with minimum energy and establishes the threshold for a critical switching current. Depending on the direction of the critical current, the interaction changes sign and a given magnetic configuration becomes unstable. To model the time dependence of the switching process, we derive a set of coupled Landau-Lifshitz equations for the ferromagnetic layers. Higher order terms in the non-equilibrium exchange coupling allow the system to evolve to its steady-state configuration.Comment: 8 pages, 2 figure. Submitted to Phys. Rev.

Commercial aspect, of the exploitation of narwhal (Monodon monoceros) in Greenland, with emphasis on tusk exports

This study presents and evaluates data on recent commercial exchanges in narwhal (Monodon monoceros) products, particularly tusks, from Greenland. No evidence was found of an export trade in narwhal blubber or skin (mattak), but since the mid-1960, mattak has been sold to the Royal Greenland Trade Department (or more recently Royal Greenland Production) for re-sale within Greenland. Since 1977 the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) ha, required documentation for the international trade in narwhal tusk. The Greenland Home Rule Government assumed responsibility for this documentation beginning in 1985. More than 90% of the tusks exported with CITES permits issued by the Home Rule Government have given Denmark as the declared destination. Of the total tusks re-exported from Denmark with CITES documentation between 1985 and 1992, approximately two-thirds had the United Kingdom as the declared destination. The monetary value of an "average" tusk-bearing narwhal to a Greenlandic hunter in 1990 was estimated as 7632 Dkr (1272 US dollars). This estimate includes the tusk (6 kg), mattak (80 kg) and meat (46 kg) that were sold but makes no allowance for the products consumed by the hunter and his family. The cash value of narwhal products has not diminished in spite of high inflation in Greenland since the late l960s

LICOR-Liquid Columns' Resonances

The aim of the experiment LICOR was the investigation of the axial resonances oi cylindrical liquid columns supported by equal circular coaxiaJ disks. In preparation ot the D-2 experiment a •heoreiical model has been developed, which exactly describes the small amplitude oscillations of finite cylindrical columns between coaxial circular disks. In addition, in terrestrial experiments the resonance frequencies of small liquid columns with up to 5 mm in diameter have been determined and investigations with density-matched liquids (silicon oil in a waierlmethanol mixture) have been performed. For the D-2 experiment LICOR the front disk and the rear disk lor use in the AFPM have been constructed and equipped with pressure sensors and the necessary electronics. The pressure exerted by the oscillating liquid column on trie supporting disks vsas as low as 10 Pa. Since the data downlink of the Materials Research Laboratory was just one signal oer second and channel, it was necessary to determine amplitude and phase of the pressure already in the LICOR disks. The D-2 experiment has been successfully performed. It has fully confirmed the theoretical models and remarkably supplements the experiments on small liquid columns and on density-matched columns

On the mixing property for a class of states of relativistic quantum fields

Let $\omega$ be a factor state on the quasi-local algebra $\cal{A}$ of observables generated by a relativistic quantum field, which in addition satisfies certain regularity conditions (satisfied by ground states and the recently constructed thermal states of the $P(\phi)_2$ theory). We prove that there exist space and time translation invariant states, some of which are arbitrarily close to $\omega$ in the weak* topology, for which the time evolution is weakly asymptotically abelian

Summer and Fall Movements of Narwhals (Monodon monoceros) from Northeastern Baffin Island towards Northern Davis Strait

Ten narwhals (Monodon monoceros) were instrumented with satellite-linked radio transmitters in Tremblay Sound in August 1997 (N = 5) and August 1998 (N = 5). All whales stayed in the waters around Bylot Island until the end of September. On the basis of these animals and others tagged previously (total N = 24), it is believed that the Bylot Island summering population has limited or no contact with other summering populations in Canada or Greenland. Four whales were monitored during their southward movement along the east coast of Baffin Island. Three of them travelled close to the shore, visiting several fjords and bays, during September and October. The fourth whale started the southward migration at the same time as the other three, but it returned to the area east of Pond Inlet and made two trips northeast of Bylot Island. It headed south on 21 October 1998. South of Royal Society Fiord, it travelled offshore along the continental slope (1000 to 1500 m), probably because of ice formation in inshore areas. This narwhal and another male tagged in 1997 moved east toward the northern parts of the Davis Strait, reaching an area midway between Canada and Greenland in early November. Their winter movements were monitored until 30 January. The same wintering area in northern Davis Strait was previously documented for two male narwhals tracked from Melville Bay, NW Greenland, in 1993 and 1994. The whales showed a preference for deep areas, including deep fjords and the continental slope, where depths ranged between 500 and 1500 m. Even deeper areas, where maximum daily dives exceeded 1000 m, were also visited occasionally.On a équipé 10 narvals (Monodon monoceros) d'émetteurs radioélectriques en liaison avec un satellite dans le détroit de Tremblay en août 1997 (N = 5) et en août 1998 (N = 5). Toutes les baleines sont restées dans les eaux entourant l'île Bylot jusqu'à fin septembre. En considérant ces animaux et d'autres équipés précédemment (N total = 24), on pense que la population estivale de l'île Bylot n'a que peu, sinon pas de contact avec d'autres populations estivales du Canada ou du Groenland. Quatre baleines ont fait l'objet d'un suivi au cours de leur déplacement vers le sud le long de la côte est de l'île de Baffin. Durant les mois de septembre et d'octobre, trois d'entre elles longeaient la côte de près, effectuant des pauses dans divers fjords et baies. La quatrième a commencé sa migration vers le sud en même temps que les trois autres, mais elle est retournée dans la zone à l'est de Pond Inlet et s'est rendue par deux fois au nord-est de l'île Bylot. Elle a mis le cap vers le sud le 21 octobre 1998. Au sud du fjord Royal Society, elle s'est dirigée vers le large et a longé la pente continentale (à environ 1000 à 1500 m du rivage), probablement en raison de la formation de glace dans la zone côtière. Ce narval ainsi qu'un autre mâle équipé en 1997 se déplaçaient en direction de l'est vers la partie nord du détroit de Davis, atteignant début novembre une zone située à mi-chemin entre le Canada et le Groenland. En hiver, leurs déplacements ont été suivis jusqu'au 30 janvier. La même zone d'hivernage dans le nord du détroit de Davis a déjà été rapportée pour deux narvals mâles suivis en 1993 et 1994 depuis la baie Melville, au N.-O. du Groenland. Les baleines affichaient une préférence pour des zones profondes, y compris des fjords encaissés et la pente continentale, où la profondeur allait de 500 à 1500 m. De temps à autre, les baleines se rendaient aussi dans des zones encore plus profondes, où les plongées maximales quotidiennes dépassaient les 1000 m

Electromagnetic vertex function of the pion at T > 0

The matrix element of the electromagnetic current between pion states is calculated in quenched lattice QCD at a temperature of $T = 0.93 T_c$. The nonperturbatively improved Sheikholeslami-Wohlert action is used together with the corresponding ${\cal O}(a)$ improved vector current. The electromagnetic vertex function is extracted for pion masses down to $360 {\rm MeV}$ and momentum transfers $Q^2 \le 2.7 {\rm GeV}^2$.Comment: 17 pages, 8 figure

Reactions of Narwhals, Monodon monoceros, to Killer Whale, Orcinus orca, Attacks in the Eastern Canadian Arctic

A Killer Whale attack on Narwhals was observed at Kakiak Point in Admiralty Inlet, Nunavut, Canada, in August 2005. Behavioral responses of both Narwhals and Killer Whales were documented by direct observation. Data collected from Narwhals instrumented with satellite-linked transmitters 5 days prior to the arrival of Killer Whales were used to examine changes in Narwhal movement patterns (e.g., dispersal and clumping) five days before the attack, during the attack, and five days after Killer Whales left the area. A minimum of four Narwhals were killed by 12-15 Killer Whales in a period of 6 hours. Narwhals showed a suite of behavioral changes in the immediate presence of Killer Whales including slow, quiet movements, travel close to the beach (<2 m from shore), use of very shallow water, and formation of tight groups at the surface. These behavioral changes are consistent with Inuit accounts of Killer Whale attacks on Narwhals. During the attack, Narwhals dispersed broadly, the groups were less clumped (standard deviation of inter-whale mean latitudes and longitudes), Narwhal space-use doubled from pre-attack home ranges of 347 km2 to 767 km2 (kernel 50% probability), and Narwhals shifted their distribution further south of the attack site. After the disappearance of Killer Whales, north-south dispersal of Narwhals contracted and was similar to pre-attack levels, total space use decreased slightly (599 km2), yet west-east dispersal remained high. Narwhals were distributed significantly (P < 0.001) more broadly offshore in areas not used before the occurrence of Killer Whales. In general, short-term reactions of Narwhals to Killer Whale presence were obvious; yet normal behavior (as observed from shore) resumed shortly after Killer Whales left the area. Long-term (five day) Narwhal behavioral responses included increased dispersal of Narwhal groups over large offshore areas. This is among the few reports of eyewitness Killer Whale attacks on Narwhals in the high Arctic and is the first time changes in Narwhal behavior have been documented in response to a predation event through the use of satellite telemetry