DC spin generation by junctions with AC driven spin-orbit interaction

An unbiased one-dimensional weak link between two terminals, subjected to the Rashba spin-orbit interaction caused by an AC electric field which rotates periodically in the plane perpendicular to the link, is shown to inject spin-polarized electrons into the terminals. The injected spin-polarization has a DC component along the link and a rotating transverse component in the perpendicular plane. In the adiabatic, low rotation-frequency regime, these polarization components are proportional to the frequency. The DC component of the polarization vanishes for a linearly-polarized electric field.Comment: published versio

Mechanically Induced Thermal Breakdown in Magnetic Shuttle Structures

A theory of a thermally induced single-electron "shuttling" instability in a magnetic nanomechanical device subject to an external magnetic field is presented in the Coulomb blockade regime of electron transport. The model magnetic shuttle device considered comprises a movable metallic grain suspended between two magnetic leads, which are kept at different temperatures and assumed to be fully spin polarized with antiparallel magnetizations. For a given temperature difference shuttling is found to occur for a region of external magnetic fields between a lower and an upper critical field strength, which separate the shuttling regime from normal small-amplitude "vibronic" regimes. We find that (i) the upper critical magnetic field saturates to a constant value in the high temperature limit and that the shuttle instability domain expands with a decrease of the temperature, (ii) the lower critical magnetic field depends not only on the temperature independent phenomenological friction coefficient used in the model but also on intrinsic friction (which vanishes in the high temperature limit) caused by magnetic exchange forces and electron tunneling between the quantum dot and the leads. The feasibility of using thermally driven magnetic shuttle systems to harvest thermal breakdown phenomena is discussed.Comment: 9 pages, 2 figure

REXEBIS the Electron Beam Ion Source for the REX-ISOLDE project

The REXEBIS is an Electron Beam Ion Source (EBIS) developed especially to trap and further ionise the sometimes rare and short-lived isotopes that are produced in the ISOLDE separator for the Radioactive beam EXperiment at ISOLDE (REX-ISOLDE). By promoting the single-charged ions to a high charge-state the ions are more efficiently accelerated in the following linear accelerator. The EBIS uses an electron gun capable of producing a 0.5 A electron beam. The electron gun is immersed in a magnetic field of 0.2 T, and the electron beam is compressed to a current density of >200 A/cm2 inside a 2 T superconducting solenoid. The EBIS is situated on a high voltage (HV) platform with an initial electric potential of 60 kV allowing cooled and bunched 60 keV ions extracted from a Penning trap to be captured. After a period of confinement in the electron beam (<20 ms), the single-charged ions have been ionised to a charge-to-mass ratio of approximately ¼. During this confinement period, the platform potential is decreased to about 20 kV, and an axial potential barrier is lowered to allow the now highly charged ions to be extracted from the EBIS at an energy matching the requirement of the Radio Frequency Quadrupole (RFQ). Several different topics are presented in this report, all connected with the design and construction of an EBIS. Old 'truths' have also been scrutinised, for instance alignment tolerances. A large part is devoted to the description of a novel EBIS simulation implementation. A complete injection, breeding and extraction cycle has been simulated to certify high injection and extraction efficiencies. The entire EBIS was modelled in an ion-tracing program called SIMION, and the accepted and emitted phase spaces were determined. Beam optics parameters such as lens positions, voltages, accepted beam-tilt and displacement tolerances at the focal points were also settled using SIMION. An analytically derived acceptance formula was verified with simulations, and general conclusions on acceptance, emittance and energy spread of an EBIS are presented in this report. Any possible correlation between the two transverse phase spaces was shown to be insignificant. Furthermore, continuous injection, and maximal obtainable efficiency for such an injection mode were studied theoretically. The electron reflection and back-scattering in the collector was simulated using a combination of EGUN and SIMION. The result showed that a much lower degree of electron back-scattering may be obtained with this design as compared to previously published estimations. Furthermore, the Penning trapping of electrons at the trap barrier (or the post anode) was addressed, and techniques to avoid it were evaluated. Vacuum considerations for residual gas in the warm-bore magnet chamber, and the back-flow of Ar cooling gas from the Penning trap, have also been addressed since there is a risk of outnumbering the small number of radioactive ions. Simulated extraction spectra for different pressure scenarios are presented. All different REXEBIS elements (magnet, electron gun, inner structure, collector etc) are described from a design and performance perspective, and preliminary investigations of the platform high voltage switching and the beam diagnostics are included as well. A very elegant and simple method to align the solenoid within the iron yoke was developed and used. The high experimental emittance value obtained for electron beam ion source at MSL in Stockholm (4 times larger than the absolute upper theoretical value) was reproduced in simulations and could be justified by aberrations in the small einzel lens following the collector. The result of this simulation also verified the validity of the developed EBIS code

Studi Kerapatan dan Perubahan Tutupan Mangrove Menggunakan Citra Satelit di Pulau Sebatik Kalimantan Utara

Hutan mangrove merupakan ekosistem yang rentan sehingga membutuhkan pemantauan terus menerus untuk mendeteksi berbagai ancaman seperti aktivitas manusia dan bencana alam. Penginderaan jarak jauh dan sistem informasi geografis (SIG) sangat efektif untuk digunakan dalam pemantauan ekosistem mangrove karena dapat menjangkau daerah yang luas dan dapat dilakukan sekala berkala. Penerapan teknologi penginderaan jarak jauh untuk memantau ekosistem mangrove di Pulau Sebatik belum pernah dilakukan sebelumnya. Penelitian ini penting untuk mengetahui Perubahan kondisi hutan mangrove di Pulau Sebatik. Tujuan dari penelitian ini adalah untuk menghitung akurasi klasifikasi tutupan lahan dengan resolusi spasial yang berbeda, mengukur Perubahan mangrove dari tahun 2005 sampai 2016, dan menganalisis korelasi antara nilai Normalized Different Vegetation Index (NDVI) dan persentase tutupannya. Klasifikasi tutupan lahan dalam penelitian ini menggunakan klasifikasi terbimbing dengan algoritma Maximum Likelihood. NDVI digunakan sebagai indikator kerapatan mangrove. Pengukuran data lapangan diambil untuk menghitung tutupan kanopi. Penilaian akurasi klasifikasi citra Landsat sekitar 83% dan citra SPOT 6 sekitar 90%. Mangrove di Pulau Sebatik mengalami peningkatan dari tahun 2005 sampai 2016 sebesar 31,27%. Korelasi antara tutupan NDVI dan kanopi dikategorikan tinggi dengan koefisien korelasi r = 0,82 (Landsat 8) dan 0,85 (SPOT 6)

Entanglement of distant optomechanical systems

We theoretically investigate the possibility to generate non-classical states of optical and mechanical modes of optical cavities, distant from each other. A setup comprised of two identical cavities, each with one fixed and one movable mirror and coupled by an optical fiber, is studied in detail. We show that with such a setup there is potential to generate entanglement between the distant cavities, involving both optical and mechanical modes. The scheme is robust with respect to dissipation, and nonlocal correlations are found to exist in the steady state at finite temperatures.Comment: 12 pages (published with minor modifications

The ALTO project at IPN Orsay

In order to probe neutron rich radioactive noble gases produced by photo-fission, a PARRNe1 experiment (Production d'Atomes Radioactifs Riches en Neutrons) has been carried out at CERN. The incident electron beam of 50 MeV was delivered by the LIL machine: LEP Injector Linac. The experiment allowed to compare under the same conditions two production methods of radioactive noble gases: fission induced by fast neutrons and photo-fission. The obtained results show that the use of the electrons is a promising mode to get intense neutron rich ion beams. Thereafter, the success of this photo-fission experiment, a conceptual design for the installation at IPN Orsay of a 50 MeV electron accelerator close to the PARRNe-2 device has been worked out: ALTO Project. This work has started within a collaboration between IPNO, LAL and CERN groups.Comment: 14 pages, pdf file, International School-Seminar on Heavy-Ion Physics 7 (2002

Theory of Thermoelectric Power in High-Tc Superconductors

We present a microscopic theory for the thermoelectric power (TEP) in high-Tc cuprates. Based on the general expression for the TEP, we perform the calculation of the TEP for a square lattice Hubbard model including all the vertex corrections necessary to satisfy the conservation laws. In the present study, characteristic anomalous temperature and doping dependences of the TEP in high-Tc cuprates, which have been a long-standing problem of high-Tc cuprates, are well reproduced for both hole- and electron-doped systems, except for the heavily under-doped case. According to the present analysis, the strong momentum and energy dependences of the self-energy due to the strong antiferromagnetic fluctuations play an essential role in reproducing experimental anomalies of the TEP.Comment: 5 pages, 8 figures, to appear in J. Phys. Soc. Jpn. 70 (2001) No.10. Figure 2 has been revise

Interplay between Coulomb Blockade and Resonant Tunneling studied by the Keldysh Green's Function Method

A theory of tunneling through a quantum dot is presented which enables us to study combined effects of Coulomb blockade and discrete energy spectrum of the dot. The expression of tunneling current is derived from the Keldysh Green's function method, and is shown to automatically satisfy the conservation at DC current of both junctions.Comment: 4 pages, 3 figures(mail if you need), use revtex.sty, error corrected, changed titl