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Low-energy dipole (LED) excitations in $^{18}\mathrm{O}$ were investigated using a combination of the variation after $K$ projection in the framework of antisymmetrized molecular dynamics with $\ensuremath{\beta}$ constraint with the generator coordinate method. We obtained two LED states, namely, the ${1}_{1}^{\ensuremath{-}}$ state with a dominant shell-model structure and the ${1}_{2}^{\ensuremath{-}}$ state with a large $^{14}\mathrm{C}+\ensuremath{\alpha}$ cluster component. Both these states had significant toroidal dipole (TD) and compressive dipole (CD) strengths, indicating that the TD and CD modes are not separated but mixed in the LED excitations of $^{18}\mathrm{O}$. This is unlike the CD and TD modes for well-deformed nuclei such as $^{10}\mathrm{Be}$, where the CD and TD modes are generated as ${K}^{\ensuremath{\pi}}={0}^{\ensuremath{-}}$ and ${K}^{\ensuremath{\pi}}={1}^{\ensuremath{-}}$ excitations, respectively, in a largely deformed state.

This paper shows that a dipole close to a subwavelength sphere can give rise to an anapole, namely the dipole-scatterer is a non-radiating system. This state can be achieved with either a dielectric (high refractive index) or metallic particle.

Low-energy dipole excitations in ${}^{10}$Be were investigated based on the generator coordinate method with $\alpha + {}^6$He and $\alpha + \alpha + 2n$ cluster models. We obtained three $1^-$ states in $E_{x} < 15$~MeV, which show different characters in the $E1$, compressive dipole, and toroidal dipole transition strengths. We found the strong toroidal dipole transition in the $1_1^-$ state, remarkable $E1$ strength in the $1^-_2$ state, and the strong $E1$ and compressive dipole strength in the $1^-_3$ state. The $1^-_1$ is described by the $\alpha + {}^6$He cluster structure, where as the $1^-_2$ and $1^-_3$ states are understood by three-body excitations of the $\alpha + \alpha + 2n$ clustering., Comment: 20 pages, 8 figures

The low-energy behavior of the strength function for the $1^-$ soft dipole excitation in $^{6}$He is studied theoretically. Use of very large basis sizes and well-grounded extrapolation procedures allows to move to energies as small as 1 keV, at which the low-energy asymptotic behavior of the E1 strength function seems to be achieved. It is found that the low-energy behavior of the strength function is well described in the effective three-body "dynamical dineutron model". The astrophysical rate for the $\alpha$+$n$+$n \rightarrow ^6$He+$\gamma$ is calculated. Comparison with the previous calculations is performed., Comment: 6 pages, 9 figures

By using the hybrid- TV model of the 4 He + n + n three-body system, the binding energy and excited states of "He are investigated. The binding energy 0.784 MeV is obtained for more realistic 4 He-n interaction. It is discussed that the n-n correlations, which are fully taken into account in the ECM bases, are very important to reproduce the binding energy of "He. The excited resonance states of the "He system are also calculated by applying the complex scaling method. The first excited z+ state obtained as a three-body resonance state is in good agreement with experiments. However, the excited 1- resonance states corresponding to the soft dipole excitation are not obtained at the low energy region.

The GTEM (GigaTEM) cell is proving a useful tool for characterizing the EM emission of objects under laboratory conditions. In order to enhance its practical use, however, it is essential to be able to identify and predict differences between tests in "open site" and in cell environment. The modes of the empty cell were previously reported. In this contribution, we address in the first time the problem of excitation by dipoles in the non uniform environment of the cell. Moreover, we present an analytical model of the scattering by a dielectric or conducting sphere in the cell. Numerical results are compared with experimental data, when possible, and with theoretical results for scattering by the same object in free space, showing very good agreement as regards the resonant frequencies. >

Based on the double folding potential of ion-ion interactions, an investigation of the fusion cross sections at low energies for the reactions of a very neutron-rich 11Li with 150,154Sm, within the framework of the coupled multi-channel approach, is performed by taking account of the interplay of the soft dipole excitation associated with 11Li and the low-lying collective surface modes associated with ASm. Both spherical and deformed target nuclei are considered.

International audience; This paper deals with the scattering by a perfectly conductive ellipsoid under magnetic dipolar excitation at low frequency. The source and the ellipsoid are embedded in an infinite homogeneous conducting ground. The main idea is to obtain an analytical solution of this scattering problem in order to have a fast numerical estimation of the scattered field that can be useful for real data inversion. Maxwell equations and boundary conditions, describing the problem, are firstly expanded using low-frequency expansion of the fields up to order three. It will be shown that fields have to be found incrementally. The static one (term of order zero) satisfies the Laplace equation. The next non-zero term (term of order two) is more complicated and satisfies the Poisson equation. The order-three term is independent of the previous ones and is described by the Laplace equation. They constitute three different scattering problems that are solved using the separated variables method in the ellipsoidal coordinate system. Solutions are written as expansions on the few analytically known scalar ellipsoidal harmonics. Details are given to explain how those solutions are achieved with an example of numerical results.

The mass-dependent structure of the composite nucleus is shown based on three-dimensional timedependent Hartree-Fock calculations with Skyrme interactions (SLy4d and SkM*). One remarkable result is that the isovector monopole excitation dominantly appears for collisions of heavy nuclei, and the isovector dipole excitation for those of light ones. Such a difference found in the dynamical structure of composite nucleus plays a role in the equilibration of charge.

The energy-weighted sum rule for an electric dipole transition operator of a Schiff type differs from the Thomas-Reiche-Kuhn sum rule by several corrective terms which depend on the number of system components, ${\cal N}$. The deviations are evaluated by two distinct approaches. One of them is based on the charge density expansion around an uniform distribution and provides an analytical ${\cal N}$ dependence for the sum rule while, the other one hinges of the RPA approach and yields compact expressions for corrections as function of the RPA amplitudes. Although the formalism might be considered for any many body system, we applied it for illustration, to the case of $Na$ clusters. One concludes that the RPA results for $Na$ clusters obey the modified TRK sum rule., arXiv admin note: substantial text overlap with arXiv:1004.3159

This paper has used the finite-difference time-domain (FDTD) computer simulation technique to investigate specific absorption rates (SAR) in different human head models with metallic jewellery. A dipole excitation has been placed in front of the nose of 4 anatomical heads including a 5 year old and a 12 year old child's head. Metallic tongue jewellery and orthodontist metallic braces were added to the models and the SAR was investigated over a range of communication frequencies.

We look for collective excitations originating from the strong surface pairing in unstable nuclei near the neutron drip-line. The soft dipole excitation is such a pairing mode as it exhibits a character of core-vs-dineutron motion. Possibility of the hydrodynamic phonon mode (the Anderson-Bogoliubov mode) is also discussed., Comment: 9 pages, a talk presented at Collective Motion in Nuclei under Extreme Conditions (COMEX2), June 20-23, 2006, St. Goar, Germany

The strength function of the linear response by the external field is calculated in the formalism of the absorbing boundary condition (ABC). The dipole excitation of a schematic two-body system is treated in the present study. The extended completeness relation, which is assumed on the analogy of the formulation in the complex scaling method (CSM), is applied to the calculation of the strength function. The calculation of the strength function is successful in the present formalism and hence, the extended completeness relation seems to work well in the ABC formalism. The contributions from the resonance and the non-resonant continuum is also analyzed according to the decomposition of the energy levels in the extended completeness relation.

The soft dipole modes in neutron rich even-even Ni-isotopes are investigated in the quasiparticle relativistic random phase approximation. We study the evolution of strengths distribution, centroid energies of dipole excitation in low-lying and normal GDR regions with the increase of the neutron excess. It is found in the present study that the centroid energies of the soft dipole strengths strongly depend on the thickness of neutron skin along with the neutron rich even-even Ni-isotopes., 14 pages, 7 figures

Özet ATOMLARIN METAL YÜZEYLERİNDE YATAY VE DÜŞEY YÖNDE KONTROLLÜ HAREKETLERİ Alper Buldum Fizik Yüksek Lisans Tez Yöneticisi: Prof. Salim Çıracı Kasım 1994 Geçenlerde bazı deneyler, tarama tünelleme mikroskobu (TTM) kullanılarak, metal yüzeylerinde bulunan atomların istenilen pozisyonlara taşınabileceğini gösterdi. Daha fazlası, bir atomun TTM'nin iki elektrodu arasında tersinir bir şekilde, kontrollü olarak hareket ettirilebileceği gösterildi ki bu durumda iki sabit iletkenlik değeri elde ediliyordu. Adsorbe olmuş atomların ya da moleküllerin kontrollü dinamiği yeni bir araştırma alanı açtı. Bu tez çalışması, bir asal gaz atomunun (Xe) metal yüzeylerinde, yatay ve düşey yönde kontrollü hareketlerinin teorik olarak incelenmesidir. Xe atomunun Ni(llO) ve Pt(lll) yüzeylerinde yatay hareketleri Tungsten bir iğne tarafından sağlanıyor. Bu atomun iğne ve metal yüzeğiyle etkileşim enerjisi amprik bir potansiyelle ifade edildi. Moleküler statik metoduyla potansiyel enerji yüzeyleri hesaplandı ve adsorbsiyon pozisyonları tayin edildi. Moleküler dinamik metoduyla, verilen bir iğne yüksekliğinde Xe atomunun koordinatlarındaki değişiklikler elde edildi. İğne yüksekliğine bağlı olarak Xe atomunun üç çeşit hareketi keşfedildi: 1) İtilme 2) Çekilme 3) İğneye yapışarak taşınma. Xe atomunun metal yüzeyi ile iğne arasındaki kontrollü ve tersinir hareketi iniki düzgün Pt(lll) yüzeğiyle çalışıldı. Xe atomunun Pt(lll) yüzeğiyle etkileşimi için kısa mesafe ve uzun mesafe etkileşimlerini içeren ve pek çok deneysel veriyle test edilmiş bir ampirik potansiyel kullanıldı. Atomun efektif yükü ve metal yüzeyi ile arasında oluşan dipol momenti, atomla metal yüzeyi arasındaki mesafenin bir fonksiyonu olarak hesaplandı. Xe atomunun iki Pt(lll) yüzeyi arasındaki potansiyel enerji eğrisi ve bu eğrinin özdeğerleri ve öz fonksiyonları uygulanan voltajın ve iki elektrot arasındaki mesafenin bir fonksiyonu olarak hesaplandı. Bu modelin içinde, Zenon'un tünellemesi, dipol uyarılması ve rezonant tünelleme, elektrogöç gibi Xe atomunun geçişinde rol oynayan çeşitli mekanizmalar incelendi. Xe atomunun geçiş hızı çeşitli mekanizmalara göre hesaplandı. Bu hızın uygulanan voltaja nasıl bağlı olduğu keşfedildi. Toplam geçiş hızının genel davranışı akımın ya da voltajın üstel bir fonksiyonu şeklinde değil. Düşük voltajda sıcaklık destekli atom tünellemesi etkili iken yüksek voltajda dipol uyarılması ve rezonant tünelleme daha etkin oluyor. Anahtar sözcükler: Tarama tünelleme mikroskobu, atom geçişi, atom anahtarı, tünelleme, fiziksel adsorbsiyon, kimyasal adsorbsiyon, Ander son Newns modeli, moleküler statik, moleküler dinamik, elastik olmayan elektron tünellemesi, elektrogöç, dipol uyarılması, rezonant tünelleme. iv Abstract CONTROLLED LATERAL AND PERPENDICULAR MOTION OF ATOMS ON METAL SURFACES Alper Buldum M. S. in Physics Supervisor: Prof. Salim Çıracı November 1994 Nanoscale modification of matter has been the subject of interest. Recently, several experimental studies have demonstrated that by using a scanning tunneling microscope one can translate atoms on metal surfaces to a desired position. Furthermore, it has been shown that an atom between surface and tip can be transferred reversibly which results in bistable conductance. The controlled dynamics of adsorbed species has opened a new field of research. This thesis work provides a theoretical investigation of the controlled lateral and perpendicular motion of an inert gas atom (Xe) on metal surfaces. The lateral motion of Xe on the Ni(llO) and Pt(lll) surfaces is manipulated by a W tip. The interaction energy of the physisorbed atom with the tip and metal surface is described by an empirical potential. Using molecular statics the energy surfaces are calculated and the adsorbtion sites are determined. By using the molecular dynamics calculations, the variation in the coordinates of the adsorbate Xe with the tip moving at a given height are obtained. Three different modes of Xe translation are distinguished depending on the height of the tip. These are i) carriage on the tip, ii) pushing and, iii) pulling modes. The rangeof the tip height where one of these modes occur is strongly depended on the relaxation of electrodes and the geometry of the tip. Controlled and reversible transfer of atoms between the metal surface and the tip is studied by the transfer of Xe between two flat Pt(lll) surfaces. Physisorption of Xe on the Pt(lll) surface is studied by an empirical potential including short and long-range interactions and yielding correct account of several experimental data. Effective charge on Xe and the dipole moment constructed therefrom are calculated as a function of the Xe-surface separation. The potential energy curve of Xe between two Pt(lll) surfaces and quantum states of Xe therein are calculated as a function of the applied voltage and separation between two Pt(lll) surfaces. Within this model, various mechanisms, such as tunneling of Xe, dipole excitation and resonant tunneling, electromigration contributing to the transfer of Xe are examined. The transfer rate of Xe is then calculated for different mechanisms. Its dependence on the bias voltage is explored. The overall behavior of the total transfer rate is not a power law. While at low bias voltages thermal assisted atom tunneling is effective, the dipole excitation and resonant tunneling becomes dominant at high bias voltages. Keywords: Scanning tunneling microscope, atom transfer, atom switch, physisorption, chemisorption, Anderson-Newns model, molec ular statics, molecular dynamics, inelastic electron tunneling, electromigration, dipole excitation, resonant tunneling. 11 69

We use a three-body model to discuss the role of dineutron correlation in the ground state and the dipole excitations of typical weakly-bound Borromean nuclei, 11Li and 6He. We first show that the wave function for the neutron pair in the ground state is strongly concentrated on the nuclear surface for both nuclei. We then show that the energy distributions for the two emitted neutrons from the dipole excitation, on the other hand, are considerably different between the two nuclei, even though they show similar strong dineutron correlations in the ground state to each other. Our calculation indicates that this different behaviour of the energy distribution primarily reflects the interaction between the neutron and the core nucleus, rather than the interaction between the valence neutrons.

Inelastic excitations have been studied in 48 MeV α-scattering from 208 Pb. A concentration of isoscalar L = 1 strength is observed at E x ≈ 5.5 Mev which is interpreted as a dipole excitation mode representing a dipole oscillation of the nuclear diffuseness. A consistent description of inelastic excitations and electromagnetic widths is obtained.

Bremsstrahlung-weighted cross-section (bwcs) measurements may be a decisive step to obtain information about the difference between neutron and proton radii. A model-independent relation is discussed between the total bwcs, the relative intensity of the bwcs of the upper ( T > ) fragment of the dipole excitation and the neutron and proton radii.