Dynamics of coupled vortices in layered magnetic nanodots

The spin dynamics are calculated for a model system consisting of magnetically soft, layered nanomagnets, in which two ferromagnetic (F) cylindrical dots, each with a magnetic vortex ground state, are separated by a non-magnetic spacer (N). This permits a study of the effects of interlayer magnetostatic interactions on the vortex dynamics. The system was explored by applying the equations of motion for the vortex core positions. The restoring force was calculated taking into account the magnetostatic interactions assuming a realistic surface charge free spin distribution. For tri-layer F/N/F dots with opposite chiralities and the same core polarizations (lowest energy state), two eigenmodes are predicted analytically and confirmed via micromagnetic simulations. One mode is in the sub-GHz range for submicron dot diameters and corresponds to quasi-circular rotation of the cores about the dot center. A second mode is in the MHz range corresponding to a small amplitude rotation of the mean core position. The eigenfrequencies depend strongly on the geometrical parameters of the system, suggesting that magnetostatic effects play a dominant role in determining the vortex dynamics.Comment: One PDF file including text and 4 figure

ON THE DYNAMICS OF THE ISRAELI-ARAB ARMS RACE

This paper investigates the causal relationships between the military expenditures and military burden of the four major sides of the Israeli-Arab conflict, namely, Egypt, Israel, Jordan and Syria over the period 1960-2004. We utilize both the causality test suggested by Toda and Yamamoto (1995) and the generalized forecast error variance decomposition method of Pesaran and Shin (1998). Our findings suggest weak causality that runs usually from Israel’s to Arab’s military spending. The strongest links are between Israel and Syria that are still in a state of enmity. No causality was detected between Israel’s and Jordan’s military spending.Arms race, Middle East, Israeli-Arab conflict, Causality, Generalized Forecast Error Variance Decomposition

STRUCTURAL BREAKS IN MILITARY EXPENDITURES: EVIDENCE FOR EGYPT, ISRAEL,JORDAN AND SYRIA

This paper endogenously determines the timing of structural breaks in military expenditures and military burdens for the major parties involved in the Israeli-Arab conflict, namely Egypt, Israel, Jordan, and Syria over the period 1960-2004. Utilizing a test proposed by Vogelsang (1997), we find that all these countries experienced structural breaks, though at different periods in the late 70s and during the 80s. These structural breaks mark a sharp decline in the military burden that can be attributed to the peace talks that were initiated shortly after the 1973 war. When applying the Bai and Perron (1998, 2003) multiple structural break tests we detect two structural breaks for every country. The first break occurred during the 60s and demonstrated a significant rise in the military burden prior to the 1973 war, whereas the second break occurred in the late 70s and during the 80s and was characterized by a sharp decline in the military burden following the instigation of peace negotiations.Military Expenditures, Military Burden, Middle-East, Israeli-Arab Conflict, Structural Breaks.

THE IMPACT OF GATT ON INTERNATIONAL TRADE: EVIDENCE FROM STRUCTURAL BREAK ANALYSIS

In this study we test for structural changes in international trade patterns of 77 countries over the post-WWII period, to examine if they experienced a substantial increase in their trade ratios following major GATT rounds such as the Kennedy Round, or after joining GATT. Our results show that trade ratios of most of these countries exhibited structural breaks in their time paths, however, most of the postbreak paths were below the extrapolated prebreak paths. Furthermore, while the significant break years coincided closely with major regional and international events such as the oil shocks of the 70s and the East-Asian financial crisis in 1997, they occurred far before or after the time of a country's accession to GATT or the time of the major GATT rounds.International Trade, Trade Liberalization, Structural Change, Oil Shocks, Kennedy Round, East Asia, Financial Crisis.

Suppression of spin-pumping by a MgO tunnel-barrier

Spin-pumping generates pure spin currents in normal metals at the ferromagnet (F)/normal metal (N) interface. The efficiency of spin-pumping is given by the spin mixing conductance, which depends on N and the F/N interface. We directly study the spin-pumping through an MgO tunnel-barrier using the inverse spin Hall effect, which couples spin and charge currents and provides a direct electrical detection of spin currents in the normal metal. We find that spin-pumping is suppressed by the tunnel-barrier, which is contrary to recent studies that suggest that the spin mixing conductance can be enhanced by a tunnel-barrier inserted at the interface

Fourier methods for the perturbed harmonic oscillator in linear and nonlinear Schr\"odinger equations

We consider the numerical integration of the Gross-Pitaevskii equation with a potential trap given by a time-dependent harmonic potential or a small perturbation thereof. Splitting methods are frequently used with Fourier techniques since the system can be split into the kinetic and remaining part, and each part can be solved efficiently using Fast Fourier Transforms. To split the system into the quantum harmonic oscillator problem and the remaining part allows to get higher accuracies in many cases, but it requires to change between Hermite basis functions and the coordinate space, and this is not efficient for time-dependent frequencies or strong nonlinearities. We show how to build new methods which combine the advantages of using Fourier methods while solving the timedependent harmonic oscillator exactly (or with a high accuracy by using a Magnus integrator and an appropriate decomposition).Comment: 12 pages of RevTex4-1, 8 figures; substantially revised and extended versio

Feasibility of using neutron radiography to inspect the Space Shuttle solid rocket booster aft skirt, forward skirt and frustum. Part 1: Summary report

The space shuttle's solid rocket boosters (SRB) include components made primarily of aluminum that are parachuted back for retrieval from the ocean and refurbished for repeated usage. Nondestructive inspection methods used on these aging parts to reduce the risk of unforeseen problems include x-ray, ultrasonics, and eddy current. Neutron radiography tests on segments of an SRB component show that entrapped moisture and naturally occurring aluminum corrosion can be revealed by neutron radiography even if present in only small amounts. Voids in sealant can also be evaluated. Three alternatives are suggested to follow-up this study: (1) take an SRB component to an existing neutron radiography system; (2) take an existing mobile neutron radiography system to the NASA site; or (3) plan a dedicated system custom designed for NASA applications