First-principles calculation of the polarization-dependent force driving the Eg mode in bismuth under optical excitation.

Science.gov (United States)

Murray, Eamonn; Fahy, Stephen

2014-03-01

Using first principles electronic structure methods, we calculate the induced force on the Eg (zone centre transverse optical) phonon mode in bismuth immediately after absorption of polarized light. When radiation with polarization perpendicular to the c-axis is absorbed in bismuth, the distribution of excited electrons and holes breaks the three-fold rotational symmetry and leads to a net force on the atoms in the direction perpendicular to the axis. We calculate the initial excited electronic distribution as a function of photon energy and polarization and find the resulting transverse and longitudinal forces experienced by the atoms. Using the measured, temperature-dependent rate of decay of the transverse force[2], we predict the approximate amplitude of induced atomic motion in the Eg mode as a function of temperature and optical fluence. This work is supported by Science Foundation Ireland and a Marie Curie International Incoming Fellowship.

Spin-polarized spin excitation spectroscopy

International Nuclear Information System (INIS)

Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J

2010-01-01

We report on the spin dependence of elastic and inelastic electron tunneling through transition metal atoms. Mn, Fe and Cu atoms were deposited onto a monolayer of Cu 2 N on Cu(100) and individually addressed with the probe tip of a scanning tunneling microscope. Electrons tunneling between the tip and the substrate exchange energy and spin angular momentum with the surface-bound magnetic atoms. The conservation of energy during the tunneling process results in a distinct onset threshold voltage above which the tunneling electrons create spin excitations in the Mn and Fe atoms. Here we show that the additional conservation of spin angular momentum leads to different cross-sections for spin excitations depending on the relative alignment of the surface spin and the spin of the tunneling electron. For this purpose, we developed a technique for measuring the same local spin with a spin-polarized and a non-spin-polarized tip by exchanging the last apex atom of the probe tip between different transition metal atoms. We derive a quantitative model describing the observed excitation cross-sections on the basis of an exchange scattering process.

Coupled spin and charge collective excitations in a spin polarized electron gas

International Nuclear Information System (INIS)

Marinescu, D.C.; Quinn, J.J.; Yi, K.S.

1997-01-01

The charge and longitudinal spin responses induced in a spin polarized quantum well by a weak electromagnetic field are investigated within the framework of the linear response theory. The authors evaluate the excitation frequencies for the intra- and inter-subband transitions of the collective charge and longitudinal spin density oscillations including many-body corrections beyond the random phase approximation through the spin dependent local field factors, G σ ± (q,ω). An equation-of-motion method was used to obtain these corrections in the limit of long wavelengths, and the results are given in terms of the equilibrium pair correlation function. The finite degree of spin polarization is shown to introduce coupling between the charge and spin density modes, in contrast with the result for an unpolarized system

Gravitational torque on the inner core and decadal polar motion

Science.gov (United States)

Dumberry, Mathieu

2008-03-01

A decadal polar motion with an amplitude of approximately 25 milliarcsecs (mas) is observed over the last century, a motion known as the Markowitz wobble. The origin of this motion remains unknown. In this paper, we investigate the possibility that a time-dependent axial misalignment between the density structures of the inner core and mantle can explain this signal. The longitudinal displacement of the inner core density structure leads to a change in the global moment of inertia of the Earth. In addition, as a result of the density misalignment, a gravitational equatorial torque leads to a tilt of the oblate geometric figure of the inner core, causing a further change in the global moment of inertia. To conserve angular momentum, an adjustment of the rotation vector must occur, leading to a polar motion. We develop theoretical expressions for the change in the moment of inertia and the gravitational torque in terms of the angle of longitudinal misalignment and the density structure of the mantle. A model to compute the polar motion in response to time-dependent axial inner core rotations is also presented. We show that the polar motion produced by this mechanism can be polarized about a longitudinal axis and is expected to have decadal periodicities, two general characteristics of the Markowitz wobble. The amplitude of the polar motion depends primarily on the Y12 spherical harmonic component of mantle density, on the longitudinal misalignment between the inner core and mantle, and on the bulk viscosity of the inner core. We establish constraints on the first two of these quantities from considerations of the axial component of this gravitational torque and from observed changes in length of day. These constraints suggest that the maximum polar motion from this mechanism is smaller than 1 mas, and too small to explain the Markowitz wobble.

Inner Core Tilt and Polar Motion: Probing the Dynamics Deep Inside the Earth

Science.gov (United States)

Dumberry, M.; Bloxham, J.

2003-12-01

A tilted inner core permits exchange of angular momentum between the core and the mantle through gravitational and pressure torques and, as a result, changes in the direction of Earth's axis of rotation with respect to the mantle. Some of the observed variations in the direction of Earth's rotation could then be caused by equatorial torques on the inner core which tilt the latter out of its alignment with the mantle. In this work, we investigate whether such a scenario could explain the decade polar motion known as the Markowitz wobble. We show that a decade polar motion of the same amplitude as the observed Markowitz wobble requires a torque of 1020 N m which tilts the inner core by 0.07 degrees. This result critically depends on the viscosity of the inner core; for a viscosity less than 5 x 1017 Pa s, larger torques are required. A torque of 1020 N m with decadal periodicity can perhaps be produced by electromagnetic coupling between the inner core and a component of the flow in the outer core known as torsional oscillations, provided that the radial magnetic field at the inner core boundary is on the order of 3 to 4 mT and satisfies certain geometrical constraints. The resulting polar motion thus produced is eccentric and polarized, in agreement with the observations. Our model suggests that equatorial torques at the inner core boundary might also excite the Chandler wobble, provided shorter wavelength torsional oscillations with higher natural frequencies have enough power or provided there exists another physical mechanism that can generate a large torque at a 14 month period.

Photophysics of Curcumin excited state in toluene-polar solvent mixtures: Role of H-bonding properties of the polar solvent

Energy Technology Data Exchange (ETDEWEB)

Saini, R.K.; Das, K., E-mail: kaustuv@rrcat.gov.in

2014-01-15

Excited state dynamics of Curcumin in binary solvent mixtures of toluene and polar H-bonding solvents were compared by using an instrument endowed with 40 ps time resolution. The solvation time constant of Curcumin increases significantly (and can therefore be measured) in polar solvents which have, either, both H-bond donating and accepting ability, or, only H-bond donating ability. These results suggest that the rate limiting step in the excited state dynamics of the pigment might be the formation and reorganization of the intermolecular H-bonding between the keto group of the pigment and the H-bond donating moieties of the polar solvent. -- Highlights: • Excited state dynamics of Curcumin in a binary solvent mixture of toluene and three polar H-bonding solvents were compared. • The solvation time constant increases significantly with polar solvents having, H-bond donating and accepting, or, H-bond donating ability. • Observed results suggest that H-bonding property of polar solvent plays an important role in the excited state dynamics. • Intermolecular H-bonding between the keto group of the pigment and polar solvent may be the rate limiting step.

Photophysics of Curcumin excited state in toluene-polar solvent mixtures: Role of H-bonding properties of the polar solvent

International Nuclear Information System (INIS)

Saini, R.K.; Das, K.

2014-01-01

Excited state dynamics of Curcumin in binary solvent mixtures of toluene and polar H-bonding solvents were compared by using an instrument endowed with 40 ps time resolution. The solvation time constant of Curcumin increases significantly (and can therefore be measured) in polar solvents which have, either, both H-bond donating and accepting ability, or, only H-bond donating ability. These results suggest that the rate limiting step in the excited state dynamics of the pigment might be the formation and reorganization of the intermolecular H-bonding between the keto group of the pigment and the H-bond donating moieties of the polar solvent. -- Highlights: • Excited state dynamics of Curcumin in a binary solvent mixture of toluene and three polar H-bonding solvents were compared. • The solvation time constant increases significantly with polar solvents having, H-bond donating and accepting, or, H-bond donating ability. • Observed results suggest that H-bonding property of polar solvent plays an important role in the excited state dynamics. • Intermolecular H-bonding between the keto group of the pigment and polar solvent may be the rate limiting step

Harmonic pulsed excitation and motion detection of a vibrating reflective target.

Science.gov (United States)

Urban, Matthew W; Greenleaf, James F

2008-01-01

Elasticity imaging is an emerging medical imaging modality. Methods involving acoustic radiation force excitation and pulse-echo ultrasound motion detection have been investigated to assess the mechanical response of tissue. In this work new methods for dynamic radiation force excitation and motion detection are presented. The theory and model for harmonic motion detection of a vibrating reflective target are presented. The model incorporates processing of radio frequency data acquired using pulse-echo ultrasound to measure harmonic motion with amplitudes ranging from 100 to 10,000 nm. A numerical study was performed to assess the effects of different parameters on the accuracy and precision of displacement amplitude and phase estimation and showed how estimation errors could be minimized. Harmonic pulsed excitation is introduced as a multifrequency radiation force excitation method that utilizes ultrasound tonebursts repeated at a rate f(r). The radiation force, consisting of frequency components at multiples of f(r), is generated using 3.0 MHz ultrasound, and motion detection is performed simultaneously with 9.0 MHz pulse-echo ultrasound. A parameterized experimental analysis showed that displacement can be measured with small errors for motion with amplitudes as low as 100 nm. The parameterized numerical and experimental analyses provide insight into how to optimize acquisition parameters to minimize measurement errors.

Excite fermions in polarized eγ collisions

International Nuclear Information System (INIS)

Eboli, O.J.P.

1994-01-01

We investigate some consequences of excite leptons with 1/2 and 3/2 spins predicted by compound models in eγ collisions. Also we examine the possibility of the next generation of linear accelerators, with polarized beams, to provide information on the spin and these particle coupling

Motion of particles and spin in polarized media

International Nuclear Information System (INIS)

Silenko, A.Ya.

2003-01-01

The equations of the particle and spin motion in media with polarized electrons placed in external fields are found. The exchange interaction affects the motion of electrons and their spin, and the annihilation interaction affects the motion of positrons and their spin. The second-order terms in spin are taken into account for particles with spin S ≥ 1. The found equations can be used for the description of the particle and spin motion in both magnetic and nonmagnetic media [ru

Direct excitation of resonant torsional Alfven waves by footpoint motions

NARCIS (Netherlands)

Ruderman, M. S.; Berghmans, D.; Goossens, M.; Poedts, S.

1997-01-01

The present paper studies the heating of coronal loops by linear resonant Alfven waves that are excited by the motions of the photospheric footpoints of the magnetic field lines. The analysis is restricted to torsionally polarised footpoint motions in an axially symmetric system so that only

Polarized fine structure in the excitation spectrum of a negatively charged quantum dot

OpenAIRE

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Badescu, S. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-01-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of qua...

Excitation of Earth Rotation Variations "Observed" by Time-Variable Gravity

Science.gov (United States)

Chao, Ben F.; Cox, C. M.

2005-01-01

Time variable gravity measurements have been made over the past two decades using the space geodetic technique of satellite laser ranging, and more recently by the GRACE satellite mission with improved spatial resolutions. The degree-2 harmonic components of the time-variable gravity contain important information about the Earth s length-of-day and polar motion excitation functions, in a way independent to the traditional "direct" Earth rotation measurements made by, for example, the very-long-baseline interferometry and GPS. In particular, the (degree=2, order= 1) components give the mass term of the polar motion excitation; the (2,O) component, under certain mass conservation conditions, gives the mass term of the length-of-day excitation. Combining these with yet another independent source of angular momentum estimation calculated from global geophysical fluid models (for example the atmospheric angular momentum, in both mass and motion terms), in principle can lead to new insights into the dynamics, particularly the role or the lack thereof of the cores, in the excitation processes of the Earth rotation variations.

Vibrational motions in rotating nuclei studied by Coulomb excitations

Energy Technology Data Exchange (ETDEWEB)

Shimizu, Yoshifumi R [Kyushu Univ., Fukuoka (Japan). Dept. of Physics

1998-03-01

As is well-known Coulomb excitation is an excellent tool to study the nuclear collective motions. Especially the vibrational excitations in rotating nuclei, which are rather difficult to access by usual heavy-ion fusion reactions, can be investigated in detail. Combined with the famous 8{pi}-Spectrometer, which was one of the best {gamma}-ray detector and had discovered some of superdeformed bands, such Coulomb excitation experiments had been carried out at Chalk River laboratory just before it`s shutdown of physics division. In this meeting some of the experimental data are presented and compared with the results of theoretical investigations. (author)

Electron-impact excitation rate-coefficients and polarization of subsequent emission for Ar"+ ion

International Nuclear Information System (INIS)

Dipti; Srivastava, Rajesh

2016-01-01

Electron impact excitation in Ar"+ ions has been studied by using fully relativistic distorted wave theory. Calculations are performed to obtain the excitation cross-sections and rate-coefficients for the transitions from the ground state 3p"5 (J=3/2) to fine-structure levels of excited states 3p"44s, 3p"44p, 3p"45s, 3p"45p, 3p"43d and 3p"44d. Polarization of the radiation following the excitation has been calculated using the obtained magnetic sub-level cross-sections. Comparison of the present rate-coefficients is also done with the previously reported theoretical results for some unresolved fine structure transitions. - Highlights: • Fully relativistic distorted wave theory has been used to study the excitation of fine-structure states of Ar"+. • We have calculated electron-impact excitation cross-sections for the wide range of incident electron energies. • Electron impact excitation rate-coefficients are calculated as a function of electron temperature. • Polarization of photons emitted following the decay of the excited fine-structure states are also reported.

Self-consistent hole motion and spin excitations in a quantum antiferromagnet

International Nuclear Information System (INIS)

Su, Z.B.; Yu, L.; Li, Y.M.; Lai, W.Y.

1989-12-01

A new quantum Bogoliubov-de Gennes (BdeG) formalism is developed to study the self-consistent motion of holes and spin excitations in a quantum antiferromagnet within the generalized t-J model. On the one hand, the effects of local distortion of spin configurations and the renormalization of the hole motion due to virtual excitations of the distorted spin background are treated on an equal footing to obtain the hole wave function and its spectrum, as well as the effective mass for a propagating hole. On the other hand, the change of the spin excitation spectrum and the spin correlations due to the presence of dynamical holes are studied within the same adiabatic approximation. The stability of the hole states with respect to such changes justifies the self-consistency of the proposed formalism. (author). 25 refs, 6 figs, 1 tab

Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot

Science.gov (United States)

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Bădescu, Ş. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-10-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions.

Polarized X-ray excitation for scatter reduction in X-ray fluorescence computed tomography.

Science.gov (United States)

Vernekohl, Don; Tzoumas, Stratis; Zhao, Wei; Xing, Lei

2018-05-25

X-ray fluorescence computer tomography (XFCT) is a new molecular imaging modality which uses X-ray excitation to stimulate the emission of fluorescent photons in high atomic number contrast agents. Scatter contamination is one of the main challenges in XFCT imaging which limits the molecular sensitivity. When polarized X-rays are used, it is possible to reduce the scatter contamination significantly by placing detectors perpendicular to the polarization direction. This study quantifies scatter contamination for polarized and unpolarized X-ray excitation and determines the advantages of scatter reduction. The amount of scatter in preclinical XFCT is quantified in Monte Carlo simulations. The fluorescent X-rays are emitted isotropically, while scattered X-rays propagate in polarization direction. The magnitude of scatter contamination is studied in XFCT simulations of a mouse phantom. In this study, the contrast agent gold is examined as an example but a scatter reduction from polarized excitation is also expected for other elements. The scatter reduction capability is examined for different polarization intensities with a monoenergetic X-ray excitation energy of 82 keV. The study evaluates two different geometrical shapes of CZT detectors which are modeled with an energy resolution of 1 keV FWHM at an X-ray energy of 80 keV. Benefits of a detector placement perpendicular to the polarization direction are shown in iterative and analytic image reconstruction including scatter correction. The contrast to noise ratio (CNR) and the normalized mean square error (NMSE) are analyzed and compared for the reconstructed images. A substantial scatter reduction for common detector sizes was achieved for 100% and 80% linear polarization while lower polarization intensities provide a decreased scatter reduction. By placing the detector perpendicular to the polarization direction, a scatter reduction by factor up to 5.5 can be achieved for common detector sizes. The image

Historical Variations in Inner Core Rotation and Polar Motion at Decade Timescales

Science.gov (United States)

Dumberry, M.

2005-12-01

Exchanges of angular momentum between the mantle, the fluid core and the solid inner core result in changes in the Earth's rotation. Torques in the axial direction produce changes in amplitude, or changes in length of day, while torques in the equatorial direction lead to changes in orientation of the rotation vector with respect to the mantle, or polar motion. In this work, we explore the possibility that a combination of electromagnetic and gravitational torques on the inner core can reproduce the observed decadal variations in polar motion known as the Markowitz wobble. Torsional oscillations, which involve azimuthal motions in the fluid core with typical periods of decades, entrain the inner core by electromagnetic traction. When the inner core is axially rotated, its surfaces of constant density are no longer aligned with the gravitational potential from mantle density heterogeneities, and this results in a gravitational torque between the two. The axial component of this torque has been previously described and is believed to be partly responsible for decadal changes in length of day. In this work, we show that it has also an equatorial component, which produces a tilt of the inner core and results in polar motion. The polar motion produced by this mechanism depends on the density structure in the mantle, the rheology of the inner core, and the time-history of the angle of axial misalignment between the inner core and the mantle. We reconstruct the latter using a model of torsional oscillations derived from geomagnetic secular variation. From this time-history, and by using published models of mantle density structure, we show that we can reproduce the salient characteristics of the Markowitz wobble: an eccentric decadal polar motion of 30-50 milliarcsecs oriented along a specific longitude. We discuss the implications of this result, noting that a match in both amplitude and phase of the observed Markowitz wobble allows the recovery of the historical

Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states

International Nuclear Information System (INIS)

Haag, M.; Brandt, B. van den; Eichhorn, T.R.; Hautle, P.; Wenckebach, W.Th.

2012-01-01

In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 T at a temperature of about 100 K and has performed reliably over periods of several weeks. The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of ∼0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process.

Excitation of a surface wave by an s-polarized electromagnetic wave incident upon a boundary of a dense magnetoactive plasma

International Nuclear Information System (INIS)

Dragila, R.; Vukovic, S.

1988-01-01

The properties of surfave waves that are associated with a boundary between a rare plasma and a dense magnetoactive plasma and that propagate along a dc magnetic field are investigated. It is shown that the presence of the magnetic field introduces symmetry in terms of the polarization of the incident electromagnetic wave that excites the surface waves. A surface wave excited by an incident p-polarized (s-polarized) electromagnetic wave leaks in the form of an s-polarized (p-polarized) electromagnetic wave. The rate of rotation of polarization is independent of the polarization of the incident wave. Because a surface wave can leak in the form of an s-polarized electromagnetic wave, it can also be pumped by such a wave, and conditions were found for excitation of a surface wave by an s-polarized incident electromagnetic wave

Use of polarization measurements in evaluating cascade contributions to optical excitation functions

International Nuclear Information System (INIS)

McConkey, J.W.

1981-01-01

Recent developments in theory and experimental measurements of rotational line polarization fractions of diatomic molecules following electron impact are used to show how in some instances cascade free optical excitation functions can be derived without additional measurements of the cascading contribution. The Lyman system of H 2 is presented as an example and some previously conflicting excitation cross-section measurements obtained by different techniques are reconciled

Very long baseline interferometry applied to polar motion, relativity, and geodesy. Ph.D. thesis

International Nuclear Information System (INIS)

Ma, C.

1978-01-01

The causes and effects of diurnal polar motion are described. An algorithm was developed for modeling the effects on very long baseline interferometry observables. A selection was made between two three-station networks for monitoring polar motion. The effects of scheduling and the number of sources observed on estimated baseline errors are discussed. New hardware and software techniques in very long baseline interferometry are described

Using Constraints from Satellite Gravimetry to Study Meteorological Excitations of the Chandler Wobble for an Earth Model with Frequency-dependent Responses

Science.gov (United States)

Chen, W.; Li, J.; Ray, J.; Cheng, M.; Chen, J.; Wilson, C. R.

2015-12-01

What maintain(s) the damping Chandler wobble (CW) is still under debate though meteorological excitations are now more preferred. However, controversial results have been obtained: Gross [2000] and Gross et al. [2003] suggested oceanic processes are more efficient to excite the CW than atmospheric ones during 1980 - 2000. Brzezinski and Nastula [2002] concluded that their contributions are almost the same, and they can only provide ~80% of the power needed to maintain the CW observed during 1985 - 1996. Polar motion excitations involve not only the perturbations within the Earth system (namely, mass redistributions and motions of relative to the mantle), but also the Earth's responses to those perturbations (namely, the rheology of the Earth). Chen et al. [2013a] developed an improved theory for polar motion excitation taking into account the Earth's frequency-dependent responses, of which the polar motion transfer functions are ~10% higher than those of previous theories around the CW band. Chen et al. [2013b] compared the geophysical excitations derived from various global atmospheric, oceanic and hydrological models (NCEP, ECCO, ERA40, ERAinterim and ECMWF operational products), and found significant and broad-band discrepancies for models released by different institutes. In addition, the atmosphere, ocean and hydrology models are usually developed in a somewhat independent manner and thus the global (atmospheric, oceanic and hydrological) mass is not conserved [e.g., Yan and Chao, 2012]. Therefore, the matter-term excitations estimated from those models are problematic. In one word, it is unlikely to obtain reliable conclusions on meteorological excitations of CW on the basis of the original meteorological models. Satellite gravimetry can measure mass transportations caused by atmospheric, oceanic and hydrological processes much more accurately than those provided by the original meteorological models, and can force the global (atmospheric, oceanic and

Robust automated classification of first-motion polarities for focal mechanism determination with machine learning

Science.gov (United States)

Ross, Z. E.; Meier, M. A.; Hauksson, E.

2017-12-01

Accurate first-motion polarities are essential for determining earthquake focal mechanisms, but are difficult to measure automatically because of picking errors and signal to noise issues. Here we develop an algorithm for reliable automated classification of first-motion polarities using machine learning algorithms. A classifier is designed to identify whether the first-motion polarity is up, down, or undefined by examining the waveform data directly. We first improve the accuracy of automatic P-wave onset picks by maximizing a weighted signal/noise ratio for a suite of candidate picks around the automatic pick. We then use the waveform amplitudes before and after the optimized pick as features for the classification. We demonstrate the method's potential by training and testing the classifier on tens of thousands of hand-made first-motion picks by the Southern California Seismic Network. The classifier assigned the same polarity as chosen by an analyst in more than 94% of the records. We show that the method is generalizable to a variety of learning algorithms, including neural networks and random forest classifiers. The method is suitable for automated processing of large seismic waveform datasets, and can potentially be used in real-time applications, e.g. for improving the source characterizations of earthquake early warning algorithms.

Convergence of environment polarization effects in multiscale modeling of excitation energies

DEFF Research Database (Denmark)

Beerepoot, Maarten; Steindal, Arnfinn Hykkerud; Ruud, Kenneth

2014-01-01

We present a systematic investigation of the influence of polarization effects from a surrounding medium on the excitation energies of a chromophore. We use a combined molecular dynamics and polarizable embedding time-dependent density functional theory (PE-TD-DFT) approach for chromophores in pr...

Active-flux based motion sensorless vector control of biaxial excitation generator/motor for automobiles (BEGA)

DEFF Research Database (Denmark)

Coroban-Schramel, Vasile; Boldea, Ion; Andreescu, Gheorghe-Daniel

2009-01-01

This paper proposes a novel, active-flux based, motion-sensorless vector control structure for biaxial excitation generator for automobiles (BEGA) for wide speed range operation. BEGA is a hybrid excited synchronous machine having permanent magnets on q-axis and a dc excitation on daxis. Using th...... electrical degrees in less than 2 ms test time....

Can GRACE Explain Some of the Main Interannual Polar Motion Signatures?

Science.gov (United States)

Adhikari, S.; Ivins, E. R.; Larour, E. Y.

2016-12-01

GRACE has provided a series of monthly solutions for water mass transport that now span a 14-year period. A natural question to ask is how much of this mass transport information might be used to reconstruct, theoretically, the non-tidal and non-Chandlerian polar motion at interannual time scales. Reconstruction of the pole position at interannual time scales since 2002 has been performed by Chen et al. (2013, GRL) and Adhikari and Ivins (2016, Science Advances). (The main feature of polar motion that has been evolving since the mid 1990's is the increasing dominance of Greenland ice mass loss.) Here we discuss this reconstruction and the level of error that occurs because of missing information about the spherical harmonic degree 1 and 2 terms and the lack of terms associated with angular momentum transfer in the Louiville equations. Using GRACE observations and complementary solutions of self-attraction/loading problem on an elastically compressible rotating earth, we show that ice mass losses from polar ice sheets, and when combined with changes in continental hydrology, explain nearly the entire amplitude (83±23%) and mean directional shift (within 5.9±7.6°) of recently observed eastward polar motion. We also show that decadal scale pole variations are directly linked to global changes in continental hydrology. The energy sources for such motions are likely to be associated with decadal scale ocean and atmospheric oscillations that also drive 20th century continental wet-dry variability. Interannual variability in pole position, therefore, offers a tool for assessing past stability of our climate, and for the future, now faced with an increased intensity in the water cycle and more vulnerable to ice sheet instability. Figure caption: Observed and reconstructed mean annual pole positions with respect to the 2003-2015 mean position. Blue error band is associated with the reconstructed solution; red signifies additional errors that are related to uncertainty in

Long-term simulations of polar motion: Variations of the Chandler oscillation over two centuries

Science.gov (United States)

Kirschner, Stephanie; Reinwald, Michael; Schmidt, Michael

2014-05-01

The Earth Rotation Parameters (ERP) polar motion and length-of-day have been observed with very high precision using space-geodetic techniques over many decades. Temporal changes of ERP on various temporal scales are directly connected with geophysical processes in the Earth system. Here we focus on long-term changes of polar motion, in particular on the development of the Chandler oscillation over a time-frame of two centuries. The study will be performed using five equiprobable ensemble runs of the consistently coupled atmosphere-hydrosphere model ECOCTH (1860-2060). Five respective long-term simulations with the Dynamic Model for Earth Rotation (DyMEG) result in five realizations of the Chandler oscillation. These will be analyzed for similarities and differences using different statistical methods and tools of signal analysis, e.g. wavelets. Furthermore it will be studied in which way the long time series of polar motion reflect effects of climate change as described by ECOCTH.

Polarized neutron determination of the magnetic excitations in YBa2Cu3O7

DEFF Research Database (Denmark)

Mook, H.A.; Yethiraj, M.; Aeppli, G.

1993-01-01

Polarization analysis has been used to identify the magnetic excitations in YBa2Cu3O7. The dominant feature in the spectra is a peak at the (pi,pi) reciprocal lattice position and centered at 41 meV. The behavior of the peak is shown to change dramatically at T(c), so that the magnetic excitations...

Measurement of Polarization Observables in the Electro-Excitation of the Proton to its First Excited State

Energy Technology Data Exchange (ETDEWEB)

Roche, Rikki [Florida State Univ., Tallahassee, FL (United States)

2003-08-01

This thesis reports results from the Thomas Jefferson National Accelerator Facility (Jefferson Lab) Hall A experiment E91-011, which measured double-polarization observables in the pion electroproduction reaction from the proton. Specifically, the experiment measured the recoil proton polarization, polarized response functions, and cross section for the p($\\vec{e}$, e' $\\vec{p}$) π° reaction at a center-of-mass energy centered at W = 1232 MeV--the peak of the Δ(1232) resonance--and at a four-momentum transfer squared of Q² = 1.0 GeV²/c². Both the recoil proton polarization and polarized response function results will be presented in this thesis. Data were collected at Jefferson Lab, located in Newport News, Virginia during the summer of 2000. A 4.53 GeV polarized electron beam was scattered off of a cryogenic hydrogen target. The recoil proton polarization was measured in the Focal Plane Polarimeter (FPP), located in one of the two High Resolution Spectrometers (HRS) in Hall A. A maximum likelihood method was used to determine the polarized response functions directly from the measured polarizations and cross sections. A simultaneous fit of the cross sections, the recoil proton polarizations, and angular distributions of the polarized response functions will provide a determination of individual multipole amplitudes. Some of these multipole amplitudes are related to the concept of proton deformation. Both the recoil proton polarizations and polarized response functions were compared to two phenomenological models: MAID and SAID, which have all free parameters fixed, based on fits to previous world data. The measured helicity dependent observables, which are dominated by imaginary parts of Δ(1232)-resonance excitation multipole amplitudes, agree very well with the two models. The measured helicity independent observables, which are dominated by real parts of background multipole amplitudes, do not agree completely with

Electric dipole excitation of {sup 208}Pb by polarized electron impact

Energy Technology Data Exchange (ETDEWEB)

Jakubassa-Amundsen, D.H. [University of Munich, Mathematics Institute, Munich (Germany); Ponomarev, V.Yu. [Technische Universitaet Darmstadt, Institut fuer Kernphysik, Darmstadt (Germany)

2016-03-15

The cross sections and spin asymmetries for the excitation of 1{sup -} states in {sup 208}Pb by transversely polarized electrons with collision energy of 30-180MeV have been examined within the DWBA scattering formalism. As examples, we have considered a low-lying 1{sup -} state and also states belonging to the pygmy dipole and giant dipole resonances. The structure of these states and their corresponding transition charge and current densities have been taken from an RPA calculation within the quasiparticle phonon model. The complex-plane rotation method has been applied to achieve the convergence of the radial DWBA integrals for backward scattering. We have studied the behaviour of the cross sections and spin asymmetries as a function of electron energy and scattering angle. The role of the longitudinal and transversal contributions to the excitation has been thoroughly studied. We conclude that the spin asymmetry S, related to unpolarized outgoing electrons, is mostly well below 1% even at the backward scattering angles and its measurement provides a challenge for future experiments with polarized electrons. (orig.)

Oral cancer detection based on fluorescence polarization of blood plasma at excitation wavelength 405 nm

Science.gov (United States)

Pachaiappan, Rekha; Prakasarao, Aruna; Manoharan, Yuvaraj; Dornadula, Koteeswaran; Singaravelu, Ganesan

2017-02-01

During metabolism the metabolites such as hormones, proteins and enzymes were released in to the blood stream by the cells. These metabolites reflect any change that occurs due to any disturbances in normal metabolic function of the human system. This was well observed with the altered spectral signatures observed with fluorescence spectroscopic technique. Previously many have reported on the significance of native fluorescence spectroscopic method in the diagnosis of cancer. As fluorescence spectroscopy is sensitive and simple, it has complementary techniques such as excitation-emission matrix, synchronous and polarization. The fluorescence polarization measurement provides details about any association or binding reactions and denaturing effects that occurs due to change in the micro environment of cells and tissues. In this study, we have made an attempt in the diagnosis of oral cancer at 405 nm excitation using fluorescence polarization measurement. The fluorescence anisotropic values calculated from polarized fluorescence spectral data of normal and oral cancer subjects yielded a good accuracy when analyzed with linear discriminant analysis based artificial neural network. The results will be discussed in detail.

Autoregressive harmonic analysis of the earth's polar motion using homogeneous international latitude service data

Science.gov (United States)

Fong Chao, B.

1983-12-01

The homogeneous set of 80-year-long (1900-1979) International Latitude Service (ILS) polar motion data is analyzed using the autoregressive method (Chao and Gilbert, 1980) which resolves and produces estimates for the complex frequency (or frequency and Q) and complex amplitude (or amplitude and phase) of each harmonic component in the data. Principal conclusion of this analysis are that (1) the ILS data support the multiple-component hypothesis of the Chandler wobble (it is found that the Chandler wobble can be adequately modeled as a linear combination of four (coherent) harmonic components, each of which represents a steady, nearly circular, prograte motion, a behavior that is inconsistent with the hypothesis of a single Chandler period excited in a temporally and/or spatially random fashion). (2) the four-component Chandler wobble model ``explains'' the apparent phase reversal during 1920-1940 and the pre-1950 empirical period-amplitude relation, (3) the annual wobble is shown to be rather stationary over the years both in amplitude and in phase and no evidence is found to support the large variations reported by earlier investigations. (4) the Markowitz wobble is found to support the large variations reported by earlier investigations. (4) the Markowitz wobble is found to be marginally retrograde and appears to have a complicated behavior which cannot be resolved because of the shortness of the data set.

Revised magnetic polarity time scale for the Paleocene and early Eocene and implications for Pacific plate motion

International Nuclear Information System (INIS)

Butler, R.F.; Coney, P.J.

1981-01-01

Magnetostratiographic studies of a continental sedimentary sequence in the Clark's Fork Basin, Wyoming and a marine sedimentary sequence at Gubbio, Italy indicate that the Paleocene--Eocene boundary occurs just stratigraphically above normal polarity zones correlative with magnetic anomaly 25 chron. These data indicate that the older boundary of anomaly 24 chron is 52.5 Ma. This age is younger than the late Paleocene age assigned by LaBrecque et al. [1977] and also younger than the basal Eocene age assigned by Ness et al. [1980]. A revised magnetic polarity time scale for the Paleocene and early Eocene is presented in this paper. Several changes in the relative motion system between the Pacific plate and neighboring plates occurred in the interval between anomaly 24 and anomaly 21. A major change in absolute motion of the Pacific plate is indicated by the bend in the Hawaiian--Emperor Seamount chain at approx.43 Ma. The revised magnetic polarity time scale indicates that the absolute motion change lags the relative motion changes by only approx.3--5 m.y. rather than by >10 m.y. as indicated by previous polarity time scales

Multi-pulse orbits and chaotic dynamics in motion of parametrically excited viscoelastic moving belt

International Nuclear Information System (INIS)

Zhang Wei; Yao Minghui

2006-01-01

In this paper, the Shilnikov type multi-pulse orbits and chaotic dynamics of parametrically excited viscoelastic moving belt are studied in detail. Using Kelvin-type viscoelastic constitutive law, the equations of motion for viscoelastic moving belt with the external damping and parametric excitation are given. The four-dimensional averaged equation under the case of primary parametric resonance is obtained by directly using the method of multiple scales and Galerkin's approach to the partial differential governing equation of viscoelastic moving belt. From the averaged equations obtained here, the theory of normal form is used to give the explicit expressions of normal form with a double zero and a pair of pure imaginary eigenvalues. Based on normal form, the energy-phrase method is employed to analyze the global bifurcations and chaotic dynamics in parametrically excited viscoelastic moving belt. The global bifurcation analysis indicates that there exist the heteroclinic bifurcations and the Silnikov type multi-pulse homoclinic orbits in the averaged equation. The results obtained above mean the existence of the chaos for the Smale horseshoe sense in parametrically excited viscoelastic moving belt. The chaotic motions of viscoelastic moving belts are also found by using numerical simulation. A new phenomenon on the multi-pulse jumping orbits is observed from three-dimensional phase space

Apparent Polar Wander of the Pacific Plate Since the Cretaeous and Implications for True Polar Wander and for the Plate Motion Circuit Through Antarctica

Science.gov (United States)

Gordon, R. G.; Woodworth, D.

2017-12-01

In this presentation we review prior work on Pacific plate apparent polar wander and its implications (1) for true polar wander since ≈125 Ma and (2) for testing the global plate motion circuit through Antarctica. We furthermore update prior analyses using our recently improved and expanded apparent polar wander path for the Pacific plate [Woodworth et al., this meeting]. Three episodes of rapid motion of Pacific hotspots relative to the spin axis have occurred in the past ≈125 Ma: a ≈15° shift near 85 Ma [Gordon, 1983; Sager and Koppers, 2000], an ≈8° shift near the age of the Hawaiian-Emperor Bend [Petronotis et al., 1994; Woodworth et al., this meeting], and a 3°-°4 shift since 12 Ma [Woodworth et al., this meeting]. These shifts are in general agreement with the shifts of Indo-Atlantic hotspots relative to the spin axis. It has long been recognized that paleomagnetic poles from the continents, when rotated into the Pacific plate reference frame through plate motion circuits through Antarctica, are inconsistent with indigenous Pacific plate paleomagnetic poles and paleolatitudes [Suárez and Molnar, 1980; Gordon and Cox, 1980; Acton and Gordon, 1994]. We update such tests using our new and improved Pacific apparent polar wander path and show that the plate motion circuit through Antarctica still fails such paleomagnetic tests of consistency. Implications for global plate reconstructions and the hotspot reference frame will be discussed.

Resonance Polarization and Phase-Mismatched CARS of Pheophytin b Excited in the Qy Band

NARCIS (Netherlands)

de Boeij, W.P.; Lucassen, G.W.; Lucassen, Gerald; Otto, Cornelis; Greve, Jan

1993-01-01

Resonance polarization and phase-mismatched coherent anti-Stokes Raman scattering (CARS) measurements were performed on pheophytin b dissolved in acetone excited in the Qy absorption band, where strong broad fluorescence makes spontaneous Raman spectroscopy impossible. The phase-mismatching

Dynamics of plasma ions motion in ultra-intense laser-excited plasma wakes

International Nuclear Information System (INIS)

Zhou Suyun; Li Jing

2013-01-01

The effects of heavy ions and protons motion in an ultra-intense laser-driven plasma wake are compared by rebuilding a plasma wake model. It is shown that with the same laser and plasma background electron density n 0 , the heavy ions' motion suppresses wake-field resonant excitation less than the protons' motion in their own plasma wake. Though heavy ions obtain more kinetic energy from the plasma wake, its energy density is less than that of the protons due to the ion density being far less than the proton density. As a result, the total energy of heavy ions obtained from the wake-field is far less than that of protons. The dependence of the kinetic energy and the energy density of protons and heavy ions on n 0 is discussed. (paper)

Do not resonate with actions: sentence polarity modulates cortico-spinal excitability during action-related sentence reading.

Directory of Open Access Journals (Sweden)

Marco Tullio Liuzza

Full Text Available BACKGROUND: Theories of embodied language suggest that the motor system is differentially called into action when processing motor-related versus abstract content words or sentences. It has been recently shown that processing negative polarity action-related sentences modulates neural activity of premotor and motor cortices. METHODS AND FINDINGS: We sought to determine whether reading negative polarity sentences brought about differential modulation of cortico-spinal motor excitability depending on processing hand-action related or abstract sentences. Facilitatory paired-pulses Transcranial Magnetic Stimulation (pp-TMS was applied to the primary motor representation of the right-hand and the recorded amplitude of induced motor-evoked potentials (MEP was used to index M1 activity during passive reading of either hand-action related or abstract content sentences presented in both negative and affirmative polarity. Results showed that the cortico-spinal excitability was affected by sentence polarity only in the hand-action related condition. Indeed, in keeping with previous TMS studies, reading positive polarity, hand action-related sentences suppressed cortico-spinal reactivity. This effect was absent when reading hand action-related negative polarity sentences. Moreover, no modulation of cortico-spinal reactivity was associated with either negative or positive polarity abstract sentences. CONCLUSIONS: Our results indicate that grammatical cues prompting motor negation reduce the cortico-spinal suppression associated with affirmative action sentences reading and thus suggest that motor simulative processes underlying the embodiment may involve even syntactic features of language.

Energy harvesting from coherent resonance of horizontal vibration of beam excited by vertical base motion

Energy Technology Data Exchange (ETDEWEB)

Lan, C. B.; Qin, W. Y. [Department of Engineering Mechanics, Northwestern Polytechnical University, Xi' an 710072 (China)

2014-09-15

This letter investigates the energy harvesting from the horizontal coherent resonance of a vertical cantilever beam subjected to the vertical base excitation. The potential energy of the system has two symmetric potential wells. So, under vertical excitation, the system can jump between two potential wells, which will lead to the large vibration in horizontal direction. Two piezoelectric patches are pasted to harvest the energy. From experiment, it is found that the vertical excitation can make the beam turn to be bistable. The system can transform vertical vibration into horizontal vibration of low frequency when excited by harmonic motion. The horizontal coherence resonance can be observed when excited by a vertical white noise. The corresponding output voltages of piezoelectric films reach high values.

Polarized beams in high energy storage rings

Energy Technology Data Exchange (ETDEWEB)

Montague, B W [European Organization for Nuclear Research, Geneva (Switzerland)

1984-11-01

In recent years there has been a considerable advance in understanding the spin motion of particles in storage rings and accelerators. The survey presented here outlines the early historical development in this field, describes the basic ideas governing the kinetics of polarized particles in electromagnetic fields and shows how these have evolved into the current description of polarized beam behaviour. Orbital motion of particles influences their spin precession, and depolarization of a beam can result from excitation of spin resonances by orbit errors and oscillations. Electrons and positrons are additionally influenced by the quantized character of synchrotron radiation, which not only provides a polarizing mechanism but also enhances depolarizing effects. Progress in the theoretical formulation of these phenomena has clarified the details of the physical processes and suggested improved methods of compensating spin resonances. Full use of polarized beams for high-energy physics with storage rings requires spin rotators to produce longitudinal polarization in the interaction regions. Variants of these schemes, dubbed Siberian snakes, provide a curious precession topology which can substantially reduce depolarization in the high-energy range. Efficient polarimetry is an essential requirement for implementing polarized beams, whose utility for physics can be enhanced by various methods of spin manipulation.

A Modified LS+AR Model to Improve the Accuracy of the Short-term Polar Motion Prediction

Science.gov (United States)

Wang, Z. W.; Wang, Q. X.; Ding, Y. Q.; Zhang, J. J.; Liu, S. S.

2017-03-01

There are two problems of the LS (Least Squares)+AR (AutoRegressive) model in polar motion forecast: the inner residual value of LS fitting is reasonable, but the residual value of LS extrapolation is poor; and the LS fitting residual sequence is non-linear. It is unsuitable to establish an AR model for the residual sequence to be forecasted, based on the residual sequence before forecast epoch. In this paper, we make solution to those two problems with two steps. First, restrictions are added to the two endpoints of LS fitting data to fix them on the LS fitting curve. Therefore, the fitting values next to the two endpoints are very close to the observation values. Secondly, we select the interpolation residual sequence of an inward LS fitting curve, which has a similar variation trend as the LS extrapolation residual sequence, as the modeling object of AR for the residual forecast. Calculation examples show that this solution can effectively improve the short-term polar motion prediction accuracy by the LS+AR model. In addition, the comparison results of the forecast models of RLS (Robustified Least Squares)+AR, RLS+ARIMA (AutoRegressive Integrated Moving Average), and LS+ANN (Artificial Neural Network) confirm the feasibility and effectiveness of the solution for the polar motion forecast. The results, especially for the polar motion forecast in the 1-10 days, show that the forecast accuracy of the proposed model can reach the world level.

Exotic nuclear excitations

CERN Document Server

Pancholi, S C

2011-01-01

By providing the reader with a foundational background in high spin nuclear structure physics and exploring exciting current discoveries in the field, this book presents new phenomena in a clear and compelling way. The quest for achieving the highest spin states has resulted in some remarkable successes which this monograph will address in comprehensive detail. The text covers an array of pertinent subject matter, including the rotational alignment and bandcrossings, magnetic rotation, triaxial strong deformation and wobbling motion and chirality in nuclei. Dr. Pancholi offers his readers a clearly-written and up-to-date treatment of the topics covered. The prerequisites for a proper appreciation are courses in nuclear physics and nuclear models and measurement techniques of observables like gamma-ray energies, intensities, multi-fold coincidences, angular correlations or distributions, linear polarization, internal conversion coefficients, short lifetime (pico-second range) of excited states etc. and instrum...

Earth orientation from lunar laser ranging and an error analysis of polar motion services

Science.gov (United States)

Dickey, J. O.; Newhall, X. X.; Williams, J. G.

1985-01-01

Lunar laser ranging (LLR) data are obtained on the basis of the timing of laser pulses travelling from observatories on earth to retroreflectors placed on the moon's surface during the Apollo program. The modeling and analysis of the LLR data can provide valuable insights into earth's dynamics. The feasibility to model accurately the lunar orbit over the full 13-year observation span makes it possible to conduct relatively long-term studies of variations in the earth's rotation. A description is provided of general analysis techniques, and the calculation of universal time (UT1) from LLR is discussed. Attention is also given to a summary of intercomparisons with different techniques, polar motion results and intercomparisons, and a polar motion error analysis.

Absolute plate motions and true polar wander in the absence of hotspot tracks.

Science.gov (United States)

Steinberger, Bernhard; Torsvik, Trond H

2008-04-03

The motion of continents relative to the Earth's spin axis may be due either to rotation of the entire Earth relative to its spin axis--true polar wander--or to the motion of individual plates. In order to distinguish between these over the past 320 Myr (since the formation of the Pangaea supercontinent), we present here computations of the global average of continental motion and rotation through time in a palaeomagnetic reference frame. Two components are identified: a steady northward motion and, during certain time intervals, clockwise and anticlockwise rotations, interpreted as evidence for true polar wander. We find approximately 18 degrees anticlockwise rotation about 250-220 Myr ago and the same amount of clockwise rotation about 195-145 Myr ago. In both cases the rotation axis is located at about 10-20 degrees W, 0 degrees N, near the site that became the North American-South American-African triple junction at the break-up of Pangaea. This was followed by approximately 10 degrees clockwise rotation about 145-135 Myr ago, followed again by the same amount of anticlockwise rotation about 110-100 Myr ago, with a rotation axis in both cases approximately 25-50 degrees E in the reconstructed area of North Africa and Arabia. These rotation axes mark the maxima of the degree-two non-hydrostatic geoid during those time intervals, and the fact that the overall net rotation since 320 Myr ago is nearly zero is an indication of long-term stability of the degree-two geoid and related mantle structure. We propose a new reference frame, based on palaeomagnetism, but corrected for the true polar wander identified in this study, appropriate for relating surface to deep mantle processes from 320 Myr ago until hotspot tracks can be used (about 130 Myr ago).

Inhomogeneous nuclear spin polarization induced by helicity-modulated optical excitation of fluorine-bound electron spins in ZnSe

Science.gov (United States)

Heisterkamp, F.; Greilich, A.; Zhukov, E. A.; Kirstein, E.; Kazimierczuk, T.; Korenev, V. L.; Yugova, I. A.; Yakovlev, D. R.; Pawlis, A.; Bayer, M.

2015-12-01

Optically induced nuclear spin polarization in a fluorine-doped ZnSe epilayer is studied by time-resolved Kerr rotation using resonant excitation of donor-bound excitons. Excitation with helicity-modulated laser pulses results in a transverse nuclear spin polarization, which is detected as a change of the Larmor precession frequency of the donor-bound electron spins. The frequency shift in dependence on the transverse magnetic field exhibits a pronounced dispersion-like shape with resonances at the fields of nuclear magnetic resonance of the constituent zinc and selenium isotopes. It is studied as a function of external parameters, particularly of constant and radio frequency external magnetic fields. The width of the resonance and its shape indicate a strong spatial inhomogeneity of the nuclear spin polarization in the vicinity of a fluorine donor. A mechanism of optically induced nuclear spin polarization is suggested based on the concept of resonant nuclear spin cooling driven by the inhomogeneous Knight field of the donor-bound electron.

New determination of period and quality factor of Chandler wobble, considering geophysical excitations

Czech Academy of Sciences Publication Activity Database

Vondrák, Jan; Ron, Cyril; Chapanov, Y.

2017-01-01

Roč. 59, č. 5 (2017), s. 1395-1407 ISSN 0273-1177 R&D Projects: GA ČR GA13-15943S Institutional support: RVO:67985815 Keywords : polar motion * chandler wobble * geophysical excitations Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 1.401, year: 2016

Agreement in polar motion measurements during the MERIT campaign

Science.gov (United States)

Djurovic, D.; Techy, C.; Paquet, P.

From the original polar motion (PM) measurements performed during the MERIT Campaign, the Chandler and the annual components are removed. The analysis of the residuals shows a high level of significant correlation between the various techniques mainly for phenomenon ranging from 30 days to a few months. For periods smaller than one month the series are not correlated except for the X component, deduced from laser and Doppler techniques, which remains significant at the 99 percent level. These results led to the belief for a new earth rotation service open to different sources of data.

Dynamic polarization by coulomb excitation in the closed formalism for heavy ion scattering

International Nuclear Information System (INIS)

Frahn, W.E.; Hill, T.F.

1978-01-01

We present a closed-form treatment of the effects of dynamic polarization by Coulomb excitation on the elastic scattering of deformed heavy ions. We assume that this interaction can be represented by an absorptive polarization potential. The relatively long range of this potential entails a relatively slow variation of the associated reflection function in l-space. This feature leads to a simple generalization of the closed formula derived previously for the elastic scattering amplitude of spherical heavy nuclei. We use both the polarization potential of Love et al. and the recent improved potential of Baltz et al. to derive explicit expressions for the associated reflection functions in a Coulomb-distorted eikonal approximation. As an example we analyze the elastic scattering of 90-MeV 18 O ions by 184 W and show that both results give a quantitative description of the data. (orig.) [de

A novel approach to dual excitation ratiometric optical mapping of cardiac action potentials with di-4-ANEPPS using pulsed LED excitation.

Science.gov (United States)

Bachtel, Andrew D; Gray, Richard A; Stohlman, Jayna M; Bourgeois, Elliot B; Pollard, Andrew E; Rogers, Jack M

2011-07-01

We developed a new method for ratiometric optical mapping of transmembrane potential (V(m)) in cardiac preparations stained with di-4-ANEPPS. V(m)-dependent shifts of excitation and emission spectra establish two excitation bands (481 nm) that produce fluorescence changes of opposite polarity within a single emission band (575-620 nm). The ratio of these positive and negative fluorescence signals (excitation ratiometry) increases V(m) sensitivity and removes artifacts common to both signals. We pulsed blue (450 ± 10 nm) and cyan (505 ± 15 nm) light emitting diodes (LEDs) at 375 Hz in alternating phase synchronized to a camera (750 frames-per-second). Fluorescence was bandpass filtered (585 ± 20 nm). This produced signals with upright (blue) and inverted (cyan) action potentials (APs) interleaved in sequential frames. In four whole swine hearts with motion chemically arrested, fractional fluorescence for blue, cyan, and ratio signals was 1.2 ± 0.3%, 1.2 ± 0.3%, and 2.4 ± 0.6%, respectively. Signal-to-noise ratios were 4.3 ± 1.4, 4.0 ± 1.2, and 5.8 ± 1.9, respectively. After washing out the electromechanical uncoupling agent, we characterized motion artifact by cross-correlating blue, cyan, and ratio signals with a signal with normal AP morphology. Ratiometry improved cross-correlation coefficients from 0.50 ± 0.48 to 0.81 ± 0.25, but did not cancel all motion artifacts. These findings demonstrate the feasibility of pulsed LED excitation ratiometry in myocardium. © 2011 IEEE

Impact polarization and alignment creation parameters via stepwise excitation processes

International Nuclear Information System (INIS)

Csanak, G.; Cartwright, D.C.; Kazantsev, S.A.; Bray, I.

1998-01-01

W report here results from first order many body theory, distorted wave approximation, and converged close coupling calculations for polarization fractions and alignment creation parameters in the case of 2 1 S → n 1 P(n 3 - 5), 2 3 S → n 1 P(n = 2 - 5), 2 1 S → n 1 D(n = 3 - 5), 2 3 S → n 1 D(n = 3 - 5), 2 3 S → n 3 D(n = 3 - 5), and 2 1 S → n 3 D(n = 3 - 5) excitations in helium for electron impact energies from threshold to several hundred eV. (author)

A photo-excited broadband to dual-band tunable terahertz prefect metamaterial polarization converter

Science.gov (United States)

Zhu, Jianfeng; Yang, Yang; Li, Shufang

2018-04-01

A new and simple design of photo-excited broadband to dual-band tunable terahertz (THz) metamaterial cross polarization converter is proposed in this paper. The tunable converter is a sandwich structure with the center-cut cross-shaped metallic patterned structure as a resonator, the middle dielectric layer as a spacer and the bottom metallic film as the ground. The conductivity of the photoconductive semiconductor (Silicon) filled in the gap of the cross-shaped metallic resonator can be tuned by the incident pump power, leading to an easy modulation of the electromagnetic response of the proposed converter. The results show that the proposed cross-polarization converter can be tuned from a broadband with polarization conversion ratio (PCR) beyond 95% (1.86-2.94 THz) to dual frequency bands (fl = 1 . 46 THz &fh = 2 . 9 THz). The conversion peaks can reach 99.9% for the broadband and, 99.5% (fl) and 99.7% (fh) for the dual-band, respectively. Most importantly, numerical simulations demonstrate that the broadband/dual-band polarization conversion mechanism of the converter originates from the localized surface plasmon modes, which make the design simple and different from previous designs. With these good features, the proposed broadband to dual-band tunable polarization converter is expected to be used in widespread applications.

Evidence of excited state localization and static disorder in LH2 investigated by 2D-polarization single-molecule imaging at room temperature.

Science.gov (United States)

Tubasum, Sumera; Camacho, Rafael; Meyer, Matthias; Yadav, Dheerendra; Cogdell, Richard J; Pullerits, Tõnu; Scheblykin, Ivan G

2013-12-07

Two-dimensional polarization fluorescence imaging of single light harvesting complexes 2 (LH2) of Rps. acidophila was carried out to investigate the polarization properties of excitation and fluorescence emission simultaneously, at room temperature. In two separate experiments we excited LH2 with a spectrally narrow laser line matched to the absorption bands of the two chromophore rings, B800 and B850, thereby indirectly and directly triggering fluorescence of the B850 exciton state. A correlation analysis of the polarization modulation depths in excitation and emission for a large number of single complexes was performed. Our results show, in comparison to B800, that the B850 ring is a more isotropic absorber due to the excitonic nature of its excited states. At the same time, we observed a strong tendency for LH2 to emit with dipolar character, from which preferential localization of the emissive exciton, stable for minutes, is inferred. We argue that the observed effects can consistently be explained by static energetic disorder and/or deformation of the complex, with possible involvement of exciton self-trapping.

The effect of motion on dynamic nuclear polarization: A new theoretical development

International Nuclear Information System (INIS)

Coffino, A.R.

1989-01-01

Dynamic Nuclear Polarization (DNP) is a magnetic resonance technique which uses two different radiation sources: a radiofrequency field and microwave field to radiate nuclei and electrons, respectively. The DNP experiment probes the nature of the interaction between nuclei and electrons. The maximum of the resonance signal from the nucleus is plotted as a function of microwave frequency for the case of the microwaves on and off. The DNP signal is the ratio of these two signals and is termed the enhancement of the nuclear signal. This thesis considers the theory of the DNP signal based on the density matrix formulation of the Stochastic Liouville Equation, which incorporates the spin-spin interactions, spin-field interactions and a stochastic dynamics process which modulates these interactions. The case of one electron coupled to one spin one-half nucleus is considered. Such a formulation has never been developed. The thesis demonstrates that previous partial theories have attempted to incorporate dynamics have been incorrect. This theoretical development demonstrates, for the first time, how dynamics affects the DNP lineshapes. This theory predicts that DNP spectra change smoothly from the no motion to the fast motion region, and reproduces the known analytic answers in both the no-motion and the fast-motion limit. The most important observation of the results is that a DNP signal for a motional rate in the intermediate motional region looks like a superposition of a no-motion and fast-motion signal

Nano-polarization-converter based on magnetic plasmon resonance excitation in an L-shaped slot antenna.

Science.gov (United States)

Yang, Jing; Zhang, Jiasen

2013-04-08

We propose a nano-polarization-converter made of a resonant L-shaped slot antenna in a gold film and study its optical properties using the finite-difference time-domain method. Phase retardation between the fast and slow axes of the nano-polarization-converter originates from the simultaneous excitation of both single-surface first-order magnetic plasmon resonance mode and second-order magnetic plasmon resonance mode at the working wavelength. By adjusting the size of the slot antenna, which is still much smaller than the wavelength, the working wavelength can be tuned within a large wavelength range.

CL 19: Anisotropy of the electron diffraction from femtosecond Laser excited Bismuth

International Nuclear Information System (INIS)

Zhou, P.; Ligges, M.; Streubuehr, C.; Brazda, Th.; Payer, Th.; Meyer zu Heringdorf, F.; Horn-von Hoegen, M.; Von der Linde, D.

2010-01-01

We report an electron diffraction experiment in Bi in which a linearly polarized E g optical phonon mode is detected after excitation of the material by a femtosecond laser pulse. Bismuth is a semimetal with rhombohedral crystal structure with two atoms in the unit cell. There are two types of optical phonon modes: (i) The totally symmetric A 1g mode which corresponds to a displacement of the atoms along the trigonal (111) direction, and (ii) the doubly degenerate E g mode which represents a motion in the plane perpendicular to (111). The A 1g mode can be coherently excited both by displacive excitation (DE) and by impulsive stimulated Raman scattering (ISRS). Symmetry properties prevent DE of E g modes leaving ISRS as a likely excitation mechanism. We performed time resolved electron diffraction experiments on femtosecond laser excited Bi membranes of 15 nm thickness which were grown on a NaCl crystal and detached by floating in water. The experimental setup is described elsewhere. The fundamental laser beam (800 nm) was used for the excitation of the Bi films. The films had a crystalline structure with the (111) axis perpendicular to the surface. The electron beam passed perpendicular to the surface through the film. In this geometry the diffraction pattern is insensitive to atomic displacements along the (111) direction, i.e. insensitive to A 1g phonon modes. On the other hand, the excitation of E g modes corresponding to atomic displacements in the plane normal to (111) decreases the intensity of particular diffraction orders. The individual cycles of the E g vibrations (duration 475 fs) could not be resolved because our time resolution about 700 fs was not sufficient. In our experiment excitation beam with a fluence of 1 mJ/cm 2 and variable linear polarization was incident from the backside at an angle of 40 degrees (counter propagating electron and laser beam). The diffraction patterns were recorded as a function of the delay time between laser pump and

Electron-spin polarization of photoions produced through photoionization from the laser-excited triplet state of Sr

International Nuclear Information System (INIS)

Yonekura, Nobuaki; Nakajima, Takashi; Matsuo, Yukari; Kobayashi, Tohru; Fukuyama, Yoshimitsu

2004-01-01

We report the detailed experimental study on the production of electron-spin-polarized Sr + ions through one-photon resonant two-photon ionization via laser-excited 5s5p 3 P 1 (M J =+1) of Sr atoms produced by laser-ablation. We have experimentally confirmed that the use of laser-ablation for the production of Sr atoms prior to photoionization does not affect the electron-spin polarization. We have found that the degree of electron-spin polarization is 64±9%, which is in good agreement with our recent theoretical prediction. As we discuss in detail, we infer, from a simple analysis, that photoelectrons, being the counterpart of electron-spin-polarized Sr + ions, have approximately the same degree of electron-spin polarization. Our experimental results demonstrate that the combined use of laser-ablation technique and pulsed lasers for photoionization would be a compact and effective way to realize a pulsed source for spin-polarized ions and electrons for the studies of various spin-dependent dynamics in chemical physics

Voiced Excitations

National Research Council Canada - National Science Library

Holzricher, John

2004-01-01

To more easily obtain a voiced excitation function for speech characterization, measurements of skin motion, tracheal tube, and vocal fold, motions were made and compared to EM sensor-glottal derived...

Nuclear-charge polarization at scission in fission from moderately excited light-actinide nuclei

International Nuclear Information System (INIS)

Nishinaka, Ichiro

2009-01-01

Fragment mass yields and the average neutron multiplicity in the proton-induced fission of 232 Th and 238 U were measured by a double time-of-flight method. The most probable charges of secondary fragments were evaluated from the fragment mass yields measured by the double time-of-flight method and the fractional cumulative and independent yields reported in literature. The nuclear-charge polarization of primary fragments at scission was obtained by correcting the most probable charge of secondary fragments for neutron evaporation. The results show that the nuclear-charge polarization at scission is associated with the liquid-drop properties of nuclei and the proton shell effect with Z = 50 of heavy fragments and that it is practically insensitive to mass and excitation energy of the fissioning nucleus in the region of light-actinide nuclei. (author)

Polar ionospheric responses to solar wind IMF changes

Directory of Open Access Journals (Sweden)

Y. Zhang

2000-06-01

Full Text Available Auroral and airglow emissions over Eureka (89° CGM during the 1997-98 winter show striking variations in relation to solar wind IMF changes. The period January 19 to 22, 1998, was chosen for detailed study, as the IMF was particularly strong and variable. During most of the period, Bz was northward and polar arcs were observed. Several overpasses by DMSP satellites during the four day period provided a clear picture of the particle precipitation producing the polar arcs. The spectral character of these events indicated excitation by electrons of average energy 300 to 500 eV. Only occasionally were electrons of average energy up to ~1 keV observed and these appeared transitory from the ground optical data. It is noted that polar arcs appear after sudden changes in IMF By, suggesting IMF control over arc initiation. When By is positive there is arc motion from dawn to dusk, while By is negative the motion is consistently dusk to dawn. F-region (anti-sunward convections were monitored through the period from 630.0 nm emissions. The convection speed was low (100-150 m/s when Bz was northward but increased to 500 m/s after Bz turned southward on January 20.Key words: Atmospheric composition and structure (airglow and aurora - Ionosphere (particle precipitation - Magnetospheric Physics (polar cap phenomena

Wave excited motion of a body floating on water confined between two semi-infinite ice sheets

Science.gov (United States)

Ren, K.; Wu, G. X.; Thomas, G. A.

2016-12-01

The wave excited motion of a body floating on water confined between two semi-infinite ice sheets is investigated. The ice sheet is treated as an elastic thin plate and water is treated as an ideal and incompressible fluid. The linearized velocity potential theory is adopted in the frequency domain and problems are solved by the method of matched eigenfunctions expansion. The fluid domain is divided into sub-regions and in each sub-region the velocity potential is expanded into a series of eigenfunctions satisfying the governing equation and the boundary conditions on horizontal planes including the free surface and ice sheets. Matching is conducted at the interfaces of two neighbouring regions to ensure the continuity of the pressure and velocity, and the unknown coefficients in the expressions are obtained as a result. The behaviour of the added mass and damping coefficients of the floating body with the effect of the ice sheets and the excitation force are analysed. They are found to vary oscillatorily with the wave number, which is different from that for a floating body in the open sea. The motion of the body confined between ice sheets is investigated, in particular its resonant behaviour with extremely large motion found to be possible under certain conditions. Standing waves within the polynya are also observed.

Magnetic excitations and polarized neutrons

International Nuclear Information System (INIS)

Shirane, G.

1985-01-01

We review the historical development of polarized beam techniques for studies of condensed matter physics. In particular we describe, in some detail, the recent advance of the triple axis technique with polarization analysis. It is now possible to carry out quantitative characterization of magnetic cross sections S(Q,ω), in absolute units, for a wide range of energy and momentum transfers. We will discuss some examples of recent inelastic measurements on 3d ferromagnets and heavy Fermions. 35 refs., 11 figs., 2 tabs

Atomic processes relevant to polarization plasma spectroscopy

International Nuclear Information System (INIS)

Fujimoto, T.; Koike, F.; Sakimoto, K.; Okasaka, R.; Kawasaki, K.; Takiyama, K.; Oda, T.; Kato, T.

1992-04-01

When atoms (ions) are excited anisotropically, polarized excited atoms are produced and the radiation emitted by these atoms is polarized. From the standpoint of plasma spectroscopy research, we review the existing data for various atomic processes that are related to the polarization phenomena. These processes are: electron impact excitation, excitation by atomic and ionic collisions, photoexcitation, radiative recombination and bremsstrahlung. Collisional and radiative relaxation processes of atomic polarization follow. Other topics included are: electric-field measurement, self alignment, Lyman doublet intensity ratio, and magnetic-field measurement of the solar prominence. (author)

Experimental investigation of snap-through motion of in-plane MEMS shallow arches under electrostatic excitation

KAUST Repository

Ramini, Abdallah

2015-12-11

We present an experimental investigation for the nonlinear dynamic behaviors of clamped–clamped in-plane MEMS shallow arches when excited by harmonic electrostatic forces. Frequency sweeps are conducted to study the dynamic behaviors in the neighborhoods of the first and third resonance frequencies as well as the super-harmonic resonances. Experimental results show local softening behavior of small oscillations around the first resonance frequency and hardening behavior at the third resonance frequency for small dc and ac loads. Interesting dynamic snap-through cross-well motions are observed experimentally at high voltages for the first time in the micro-scale world. In addition to the dynamic snap-through motion, the MEMS arch exhibits large oscillations of a continuous band of snap-through motion between the super-harmonic resonance regime and the first primary resonance regime. This continuous band is unprecedented experimentally in the micro/macro world, and is promising for a variety of sensing, actuation and communications applications.

Experimental investigation of snap-through motion of in-plane MEMS shallow arches under electrostatic excitation

KAUST Repository

Ramini, Abdallah; Bellaredj, Mohammed L F; Al Hafiz, Md Abdullah; Younis, Mohammad I.

2015-01-01

We present an experimental investigation for the nonlinear dynamic behaviors of clamped–clamped in-plane MEMS shallow arches when excited by harmonic electrostatic forces. Frequency sweeps are conducted to study the dynamic behaviors in the neighborhoods of the first and third resonance frequencies as well as the super-harmonic resonances. Experimental results show local softening behavior of small oscillations around the first resonance frequency and hardening behavior at the third resonance frequency for small dc and ac loads. Interesting dynamic snap-through cross-well motions are observed experimentally at high voltages for the first time in the micro-scale world. In addition to the dynamic snap-through motion, the MEMS arch exhibits large oscillations of a continuous band of snap-through motion between the super-harmonic resonance regime and the first primary resonance regime. This continuous band is unprecedented experimentally in the micro/macro world, and is promising for a variety of sensing, actuation and communications applications.

Proton polarization in photo-excited aromatic molecule at room temperature enhanced by intense optical source and temperature control

Energy Technology Data Exchange (ETDEWEB)

Sakaguchi, S., E-mail: sakaguchi@phys.kyushu-u.ac.jp [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Uesaka, T. [RIKEN Nishina Center, Saitama 351-0198 (Japan); Kawahara, T. [Department of Physics, Toho University, Chiba 274-8510 (Japan); Ogawa, T. [RIKEN Advanced Science Institute, Saitama 351-0198 (Japan); Tang, L. [Center for Nuclear Study, University of Tokyo, Tokyo 113-0001 (Japan); Teranishi, T. [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Urata, Y.; Wada, S. [RIKEN Advanced Science Institute, Saitama 351-0198 (Japan); Wakui, T. [Cyclotron and Radioisotope Center (CYRIC), Tohoku University, Miyagi 980-8578 (Japan)

2013-12-15

Highlights: • Proton polarization in p-terphenyl at room-temperature is enhanced by a factor of 3. • Intense laser and temperature control are critically important for high polarization. • Optimization of time structure of laser pulse is effective for further improvement. -- Abstract: Proton polarization at room temperature, produced in a p-terphenyl crystal by using electron population difference in a photo-excited triplet state of pentacene, was enhanced by utilizing an intense laser with an average power of 1.5 W. It was shown that keeping the sample temperature below 300 K is critically important to prevent the rise of the spin–lattice relaxation rate caused by the laser heating. It is also reported that the magnitude of proton polarization strongly depends on the time structure of the laser pulse such as its width and the time interval between them.

Energy harvesting from human motion: exploiting swing and shock excitations

International Nuclear Information System (INIS)

Ylli, K; Hoffmann, D; Willmann, A; Becker, P; Folkmer, B; Manoli, Y

2015-01-01

Modern compact and low power sensors and systems are leading towards increasingly integrated wearable systems. One key bottleneck of this technology is the power supply. The use of energy harvesting techniques offers a way of supplying sensor systems without the need for batteries and maintenance. In this work we present the development and characterization of two inductive energy harvesters which exploit different characteristics of the human gait. A multi-coil topology harvester is presented which uses the swing motion of the foot. The second device is a shock-type harvester which is excited into resonance upon heel strike. Both devices were modeled and designed with the key constraint of device height in mind, in order to facilitate the integration into the shoe sole. The devices were characterized under different motion speeds and with two test subjects on a treadmill. An average power output of up to 0.84 mW is achieved with the swing harvester. With a total device volume including the housing of 21 cm 3 a power density of 40 μW cm −3 results. The shock harvester generates an average power output of up to 4.13 mW. The power density amounts to 86 μW cm −3 for the total device volume of 48 cm 3 . Difficulties and potential improvements are discussed briefly. (paper)

Spin and parity assignments to dipole excitations of the odd-mass nucleus {sup 207}Pb from nuclear resonance fluorescence experiments with linearly-polarized {gamma}-ray beams

Energy Technology Data Exchange (ETDEWEB)

Pietralla, N; Fritzsche, M; Savran, D [Institut fuer Kernphysik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany); Li, T C [Nuclear Structure Laboratory, SUNY at Stony Brook, Stony Brook, NY 11794-3800 (United States); Ahmed, M W; Tonchev, A P; Tornow, W; Weller, H R [Triangle Universities Nuclear Laboratory (TUNL), Duke University, Durham, NC 27708 (United States); Werner, V, E-mail: pietralla@ikp.tu-darmstadt.d [A.W. Wright Nuclear Structure Laboratory (WNSL), Yale University, New Haven, CT (United States)

2010-01-01

Pb({gamma}-vector ,{gamma}') photon scattering reactions were studied [1] with the nearly monochromatic, linearly polarized photon beams at the High Intensity {gamma}-ray Source (HI{gamma}S) at the DFELL. Azimuthal scattering intensity asymmetries measured with respect to the polarization plane of the beam have been used for the first time to assign both the spin and parity quantum numbers of dipole excited states of {sup 206,207,208}Pb at excitation energies in the vicinity of 5.5 MeV. Evidence for dominant particle-core coupling is deduced from these results along with information on excitation energies and electromagnetic transition matrix elements.

Collective motion of active Brownian particles with polar alignment.

Science.gov (United States)

Martín-Gómez, Aitor; Levis, Demian; Díaz-Guilera, Albert; Pagonabarraga, Ignacio

2018-04-04

We present a comprehensive computational study of the collective behavior emerging from the competition between self-propulsion, excluded volume interactions and velocity-alignment in a two-dimensional model of active particles. We consider an extension of the active brownian particles model where the self-propulsion direction of the particles aligns with the one of their neighbors. We analyze the onset of collective motion (flocking) in a low-density regime (10% surface area) and show that it is mainly controlled by the strength of velocity-alignment interactions: the competition between self-propulsion and crowding effects plays a minor role in the emergence of flocking. However, above the flocking threshold, the system presents a richer pattern formation scenario than analogous models without alignment interactions (active brownian particles) or excluded volume effects (Vicsek-like models). Depending on the parameter regime, the structure of the system is characterized by either a broad distribution of finite-sized polar clusters or the presence of an amorphous, highly fluctuating, large-scale traveling structure which can take a lane-like or band-like form (and usually a hybrid structure which is halfway in between both). We establish a phase diagram that summarizes collective behavior of polar active brownian particles and propose a generic mechanism to describe the complexity of the large-scale structures observed in systems of repulsive self-propelled particles.

Investigation of polar and stereoelectronic effects on pure excited-state hydrogen atom abstractions from phenols and alkylbenzenes.

Science.gov (United States)

Pischel, Uwe; Patra, Digambara; Koner, Apurba L; Nau, Werner M

2006-01-01

The fluorescence quenching of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by 22 phenols and 12 alkylbenzenes has been investigated. Quenching rate constants in acetonitrile are in the range of 10(8)-10(9) M(-1)s(-1) for phenols and 10(5)-10(6) M(-1)s(-1) for alkylbenzenes. In contrast to the quenching of triplet-excited benzophenone, no exciplexes are involved, so that a pure hydrogen atom transfer is proposed as quenching mechanism. This is supported by (1) pronounced deuterium isotope effects (kH/kD ca 4-6), which were observed for phenols and alkylbenzenes, and (2) a strongly endergonic thermodynamics for charge transfer processes (electron transfer, exciplex formation). In the case of phenols, linear free energy relationships applied, which led to a reaction constant of rho = -0.40, suggesting a lower electrophilicity of singlet-excited DBO than that of triplet-excited ketones and alkoxyl radicals. The reactivity of singlet-excited DBO exposes statistical, steric, polar and stereoelectronic effects on the hydrogen atom abstraction process in the absence of complications because of competitive exciplex formation.

Spin-orbit splitted excited states using explicitly-correlated equation-of-motion coupled-cluster singles and doubles eigenvectors

Science.gov (United States)

Bokhan, Denis; Trubnikov, Dmitrii N.; Perera, Ajith; Bartlett, Rodney J.

2018-04-01

An explicitly-correlated method of calculation of excited states with spin-orbit couplings, has been formulated and implemented. Developed approach utilizes left and right eigenvectors of equation-of-motion coupled-cluster model, which is based on the linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] method. The spin-orbit interactions are introduced by using the spin-orbit mean field (SOMF) approximation of the Breit-Pauli Hamiltonian. Numerical tests for several atoms and molecules show good agreement between explicitly-correlated results and the corresponding values, calculated in complete basis set limit (CBS); the highly-accurate excitation energies can be obtained already at triple- ζ level.

Radial polar histogram: obstacle avoidance and path planning for robotic cognition and motion control

Science.gov (United States)

Wang, Po-Jen; Keyawa, Nicholas R.; Euler, Craig

2012-01-01

In order to achieve highly accurate motion control and path planning for a mobile robot, an obstacle avoidance algorithm that provided a desired instantaneous turning radius and velocity was generated. This type of obstacle avoidance algorithm, which has been implemented in California State University Northridge's Intelligent Ground Vehicle (IGV), is known as Radial Polar Histogram (RPH). The RPH algorithm utilizes raw data in the form of a polar histogram that is read from a Laser Range Finder (LRF) and a camera. A desired open block is determined from the raw data utilizing a navigational heading and an elliptical approximation. The left and right most radii are determined from the calculated edges of the open block and provide the range of possible radial paths the IGV can travel through. In addition, the calculated obstacle edge positions allow the IGV to recognize complex obstacle arrangements and to slow down accordingly. A radial path optimization function calculates the best radial path between the left and right most radii and is sent to motion control for speed determination. Overall, the RPH algorithm allows the IGV to autonomously travel at average speeds of 3mph while avoiding all obstacles, with a processing time of approximately 10ms.

Polarized-neutron-scattering study of the spin-wave excitations in the 3-k ordered phase of uranium antimonide.

Science.gov (United States)

Magnani, N; Caciuffo, R; Lander, G H; Hiess, A; Regnault, L-P

2010-03-24

The anisotropy of magnetic fluctuations propagating along the [1 1 0] direction in the ordered phase of uranium antimonide has been studied using polarized inelastic neutron scattering. The observed polarization behavior of the spin waves is a natural consequence of the longitudinal 3-k magnetic structure; together with recent results on the 3-k-transverse uranium dioxide, these findings establish this technique as an important tool to study complex magnetic arrangements. Selected details of the magnon excitation spectra of USb have also been reinvestigated, indicating the need to revise the currently accepted theoretical picture for this material.

Chaos and its control in the pitch motion of an asymmetric magnetic spacecraft in polar elliptic orbit

Energy Technology Data Exchange (ETDEWEB)

Inarrea, Manuel [Universidad de La Rioja, Area de Fisica Aplicada, 26006 Logrono (Spain)], E-mail: manuel.inarrea@unirioja.es

2009-05-30

We study the pitch attitude dynamics of an asymmetric magnetic spacecraft in a polar almost circular orbit under the influence of a gravity gradient torque. The spacecraft is perturbed by the small eccentricity of the elliptic orbit and by a small magnetic torque generated by the interaction between the Earth's magnetic field and the magnetic moment of the spacecraft. Under both perturbations, we show that the pitch motion exhibits heteroclinic chaotic behavior by means of the Melnikov method. Numerical methods applied to simulations of the pitch motion also confirm the chaotic character of the spacecraft attitude dynamics. Finally, a linear time-delay feedback method for controlling chaos is applied to the governing equations of the spacecraft pitch motion in order to remove the chaotic character of initially irregular attitude motions and transform them into periodic ones.

Chaos and its control in the pitch motion of an asymmetric magnetic spacecraft in polar elliptic orbit

International Nuclear Information System (INIS)

Inarrea, Manuel

2009-01-01

We study the pitch attitude dynamics of an asymmetric magnetic spacecraft in a polar almost circular orbit under the influence of a gravity gradient torque. The spacecraft is perturbed by the small eccentricity of the elliptic orbit and by a small magnetic torque generated by the interaction between the Earth's magnetic field and the magnetic moment of the spacecraft. Under both perturbations, we show that the pitch motion exhibits heteroclinic chaotic behavior by means of the Melnikov method. Numerical methods applied to simulations of the pitch motion also confirm the chaotic character of the spacecraft attitude dynamics. Finally, a linear time-delay feedback method for controlling chaos is applied to the governing equations of the spacecraft pitch motion in order to remove the chaotic character of initially irregular attitude motions and transform them into periodic ones.

Planar undulator motion excited by a fixed traveling wave. Quasiperiodic averaging normal forms and the FEL pendulum

Energy Technology Data Exchange (ETDEWEB)

Ellison, James A.; Heinemann, Klaus [New Mexico Univ., Albuquerque, NM (United States). Dept. of Mathematics and Statistics; Vogt, Mathias [Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany); Gooden, Matthew [North Carolina State Univ., Raleigh, NC (United States). Dept. of Physics

2013-03-15

We present a mathematical analysis of planar motion of energetic electrons moving through a planar dipole undulator, excited by a fixed planar polarized plane wave Maxwell field in the X-Ray FEL regime. Our starting point is the 6D Lorentz system, which allows planar motions, and we examine this dynamical system as the wave length {lambda} of the traveling wave varies. By scalings and transformations the 6D system is reduced, without approximation, to a 2D system in a form for a rigorous asymptotic analysis using the Method of Averaging (MoA), a long time perturbation theory. The two dependent variables are a scaled energy deviation and a generalization of the so- called ponderomotive phase. As {lambda} varies the system passes through resonant and nonresonant (NR) zones and we develop NR and near-to-resonant (NtoR) MoA normal form approximations. The NtoR normal forms contain a parameter which measures the distance from a resonance. For a special initial condition, for the planar motion and on resonance, the NtoR normal form reduces to the well known FEL pendulum system. We then state and prove NR and NtoR first-order averaging theorems which give explicit error bounds for the normal form approximations. We prove the theorems in great detail, giving the interested reader a tutorial on mathematically rigorous perturbation theory in a context where the proofs are easily understood. The proofs are novel in that they do not use a near identity transformation and they use a system of differential inequalities. The NR case is an example of quasiperiodic averaging where the small divisor problem enters in the simplest possible way. To our knowledge the planar prob- lem has not been analyzed with the generality we aspire to here nor has the standard FEL pendulum system been derived with associated error bounds as we do here. We briefly discuss the low gain theory in light of our NtoR normal form. Our mathematical treatment of the noncollective FEL beam dynamics problem in

Planar undulator motion excited by a fixed traveling wave. Quasiperiodic averaging normal forms and the FEL pendulum

International Nuclear Information System (INIS)

Ellison, James A.; Heinemann, Klaus; Gooden, Matthew

2013-03-01

We present a mathematical analysis of planar motion of energetic electrons moving through a planar dipole undulator, excited by a fixed planar polarized plane wave Maxwell field in the X-Ray FEL regime. Our starting point is the 6D Lorentz system, which allows planar motions, and we examine this dynamical system as the wave length λ of the traveling wave varies. By scalings and transformations the 6D system is reduced, without approximation, to a 2D system in a form for a rigorous asymptotic analysis using the Method of Averaging (MoA), a long time perturbation theory. The two dependent variables are a scaled energy deviation and a generalization of the so- called ponderomotive phase. As λ varies the system passes through resonant and nonresonant (NR) zones and we develop NR and near-to-resonant (NtoR) MoA normal form approximations. The NtoR normal forms contain a parameter which measures the distance from a resonance. For a special initial condition, for the planar motion and on resonance, the NtoR normal form reduces to the well known FEL pendulum system. We then state and prove NR and NtoR first-order averaging theorems which give explicit error bounds for the normal form approximations. We prove the theorems in great detail, giving the interested reader a tutorial on mathematically rigorous perturbation theory in a context where the proofs are easily understood. The proofs are novel in that they do not use a near identity transformation and they use a system of differential inequalities. The NR case is an example of quasiperiodic averaging where the small divisor problem enters in the simplest possible way. To our knowledge the planar prob- lem has not been analyzed with the generality we aspire to here nor has the standard FEL pendulum system been derived with associated error bounds as we do here. We briefly discuss the low gain theory in light of our NtoR normal form. Our mathematical treatment of the noncollective FEL beam dynamics problem in the

How Often Do Thermally Excited 630.0 nm Emissions Occur in the Polar Ionosphere?

Science.gov (United States)

Kwagala, Norah Kaggwa; Oksavik, Kjellmar; Lorentzen, Dag A.; Johnsen, Magnar G.

2018-01-01

This paper studies thermally excited emissions in the polar ionosphere derived from European Incoherent Scatter Svalbard radar measurements from the years 2000-2015. The peak occurrence is found around magnetic noon, where the radar observations show cusp-like characteristics. The ionospheric, interplanetary magnetic field and solar wind conditions favor dayside magnetic reconnection as the dominant driving process. The thermal emissions occur 10 times more frequently on the dayside than on the nightside, with an average intensity of 1-5 kR. For typical electron densities in the polar ionosphere (2 × 1011 m-3), we find the peak occurrence rate to occur for extreme electron temperatures (>3000 K), which is consistent with assumptions in literature. However, for extreme electron densities (>5 × 1011 m-3), we can now report on a completely new population of thermal emissions that may occur at much lower electron temperatures (˜2300 K). The empirical atmospheric model (NRLMSISE-00) suggests that the latter population is associated with enhanced neutral atomic oxygen densities.

Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole

KAUST Repository

Aly, Shawkat Mohammede

2015-02-12

The excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.

Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole

KAUST Repository

Aly, Shawkat Mohammede; Usman, Anwar; Alzayer, Maytham; Hamdi, Ghada A.; Alarousu, Erkki; Mohammed, Omar F.

2015-01-01

The excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.

Spin-isospin excitations studied by polarized beams

International Nuclear Information System (INIS)

Sakai, H.; Greenfield, M.B.; Hatanaka, K.

1996-01-01

The spin-parity J π of the spin dipole resonances (SDR) in 12 N and 12 B are investigated via the measurements of polarization observables, the transverse polarization transfer coefficient D NN for the (vector p, vector n) reaction at 197 and 295 MeV and the tensor analyzing power A xx for the (vector d, 2 He) reaction at 270 MeV. The polarization observables, D NN and A xx for the peak at 4.5 MeV are consistent with the DWIA prediction with 2 - but those for the peak at 7.5 MeV contradict the predictions with an expected J π =1 - . Neither polarization observables could detect any concentration of 0 - strength. The usefulness of these spin observables in identifying J π is shown. (orig.)

Inertial polarization of dielectrics

OpenAIRE

Zavodovsky, A. G.

2011-01-01

It was proved that accelerated motion of a linear dielectric causes its polarization. Accelerated translational motion of a dielectric's plate leads to the positive charge of the surface facing the direction of motion. Metal plates of a capacitor were used to register polarized charges on a dielectric's surface. Potential difference between the capacitor plates is proportional to acceleration, when acceleration is constant potential difference grows with the increase of a dielectric's area, o...

Magnetic field pitch angle diagnostic using the motional Stark effect (invited)

International Nuclear Information System (INIS)

Levinton, F.M.; Gammel, G.M.; Kaita, R.; Kugel, H.W.; Roberts, D.W.

1990-01-01

The Stark effect has been employed in a novel technique for obtaining the pitch angle profile and q(r) using polarimetry measurements of the Doppler shifted H α emission from a hydrogen diagnostic neutral beam. As a neutral beam propagates through a plasma, collisions of the beam particles with the background ions and electrons will excite beam atoms, leading to emission of radiation. The motional Stark effect, which arises from the electric field induced in the atom's rest frame due to the beam motion across the magnetic field (E=V beam xB), causes a wavelength splitting of several angstroms and polarization of the emitted radiation. The Δm=±1 transitions, or σ components, from the beam fluorescence are linearly polarized parallel to the direction of the local magnetic field when viewed transverse to the fields. Since the hydrogen beam provides good spatial localization and penetration, the pitch angle can be obtained anywhere in the plasma. A photoelastic modulator (PEM) is used to modulate the linearly polarized light. Depending on the orientation of the PEM, it can measure the sine or cosine of the angle of polarization. Two PEM's are used to measure both components simultaneously. Results of q(r) for both Ohmic and NBI heated discharges have been obtained in the Princeton Beta Experiment (PBX-M) tokamak, with an uncertainty of ∼6% for q(0)

Vibrational motions associated with primary processes in bacteriorhodopsin studied by coherent infrared emission spectroscopy.

Science.gov (United States)

Groma, Géza I; Colonna, Anne; Martin, Jean-Louis; Vos, Marten H

2011-03-16

The primary energetic processes driving the functional proton pump of bacteriorhodopsin take place in the form of complex molecular dynamic events after excitation of the retinal chromophore into the Franck-Condon state. These early events include a strong electronic polarization, skeletal stretching, and all-trans-to-13-cis isomerization upon formation of the J intermediate. The effectiveness of the photoreaction is ensured by a conical intersection between the electronic excited and ground states, providing highly nonadiabatic coupling to nuclear motions. Here, we study real-time vibrational coherences associated with these motions by analyzing light-induced infrared emission from oriented purple membranes in the 750-1400 cm(-)(1) region. The experimental technique applied is based on second-order femtosecond difference frequency generation on macroscopically ordered samples that also yield information on phase and direction of the underlying motions. Concerted use of several analysis methods resulted in the isolation and characterization of seven different vibrational modes, assigned as C-C stretches, out-of-plane methyl rocks, and hydrogen out-of-plane wags, whereas no in-plane H rock was found. Based on their lifetimes and several other criteria, we deduce that the majority of the observed modes take place on the potential energy surface of the excited electronic state. In particular, the direction sensitivity provides experimental evidence for large intermediate distortions of the retinal plane during the excited-state isomerization process. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Mapping the local organization of cell membranes using excitation-polarization-resolved confocal fluorescence microscopy.

Science.gov (United States)

Kress, Alla; Wang, Xiao; Ranchon, Hubert; Savatier, Julien; Rigneault, Hervé; Ferrand, Patrick; Brasselet, Sophie

2013-07-02

Fluorescence anisotropy and linear dichroism imaging have been widely used for imaging biomolecular orientational distributions in protein aggregates, fibrillar structures of cells, and cell membranes. However, these techniques do not give access to complete orientational order information in a whole image, because their use is limited to parts of the sample where the average orientation of molecules is known a priori. Fluorescence anisotropy is also highly sensitive to depolarization mechanisms such as those induced by fluorescence energy transfer. A fully excitation-polarization-resolved fluorescence microscopy imaging that relies on the use of a tunable incident polarization and a nonpolarized detection is able to circumvent these limitations. We have developed such a technique in confocal epifluorescence microscopy, giving access to new regions of study in the complex and heterogeneous molecular organization of cell membranes. Using this technique, we demonstrate morphological changes at the subdiffraction scale in labeled COS-7 cell membranes whose cytoskeleton is perturbed. Molecular orientational order is also seen to be affected by cholesterol depletion, reflecting the strong interplay between lipid-packing regions and their nearby cytoskeleton. This noninvasive optical technique can reveal local organization in cell membranes when used as a complement to existing methods such as generalized polarization. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Polar ionospheric responses to solar wind IMF changes

Directory of Open Access Journals (Sweden)

Y. Zhang

Full Text Available Auroral and airglow emissions over Eureka (89^° CGM during the 1997-98 winter show striking variations in relation to solar wind IMF changes. The period January 19 to 22, 1998, was chosen for detailed study, as the IMF was particularly strong and variable. During most of the period, B_z was northward and polar arcs were observed. Several overpasses by DMSP satellites during the four day period provided a clear picture of the particle precipitation producing the polar arcs. The spectral character of these events indicated excitation by electrons of average energy 300 to 500 eV. Only occasionally were electrons of average energy up to ~1 keV observed and these appeared transitory from the ground optical data. It is noted that polar arcs appear after sudden changes in IMF B_y, suggesting IMF control over arc initiation. When B_y is positive there is arc motion from dawn to dusk, while B_y is negative the motion is consistently dusk to dawn. F-region (anti-sunward convections were monitored through the period from 630.0 nm emissions. The convection speed was low (100-150 m/s when B_z was northward but increased to 500 m/s after B_z turned southward on January 20.

Key words: Atmospheric composition and structure (airglow and aurora - Ionosphere (particle precipitation - Magnetospheric Physics (polar cap phenomena

Polarization transfer from polarized nuclear spin to μ- spin in muonic atom

International Nuclear Information System (INIS)

Kuno, Yoshitaka; Nagamine, Kanetada; Yamazaki, Toshimitsu.

1987-02-01

A theoretical study of polarization transfer from an initially-polarized nuclear spin to a μ - spin in a muonic atom is given. The switching of the hyperfine interaction at excited muonic states as well as at the ground 1s state is taken into account. The upper state of hyperfine doublet at the muonic 1s state is considered to proceed down to the lower state. It is found that as the hyperfine interaction becomes effective at higher excited muonic orbitals, a less extent of polarization is transferred from the nuclear spin to the μ - spin. The theoretical values obtained are compared with the recent experiment of μ - repolarization in a polarized 209 Bi target. (author)

Proton polarization above 70% by DNP using photo-excited triplet states, a first step towards a broadband neutron spin filter

International Nuclear Information System (INIS)

Eichhorn, T.R.; Niketic, N.; Brandt, B. van den; Filges, U.; Panzner, T.; Rantsiou, E.; Wenckebach, W.Th.; Hautle, P.

2014-01-01

The use of polarized protons as neutron spin filter is an attractive alternative to the well established neutron polarization techniques, as the large, spin-dependent neutron scattering cross-section for protons is useful up to the sub-MeV region. Employing optically excited triplet states for the dynamic nuclear polarization (DNP) of the protons relieves the stringent requirements of classical DNP schemes, i.e low temperatures and strong magnetic fields, making technically simpler systems with open geometries possible. Using triplet DNP a record polarization of 71% has been achieved in a pentacene doped naphthalene single crystal at a field of 0.36 T using a simple helium flow cryostat for cooling. Furthermore, by placing the polarized crystal in a neutron optics focus and de-focus scheme, the actual sample cross-section could be increased by a factor 35 corresponding to an effective spin filter cross-section of 18×18mm 2

Proton polarization above 70% by DNP using photo-excited triplet states, a first step towards a broadband neutron spin filter

Energy Technology Data Exchange (ETDEWEB)

Eichhorn, T.R. [Laboratory for Developments and Methods (LDM), Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Laboratory of Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Niketic, N.; Brandt, B. van den; Filges, U.; Panzner, T.; Rantsiou, E.; Wenckebach, W.Th. [Laboratory for Developments and Methods (LDM), Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Hautle, P., E-mail: patrick.hautle@psi.ch [Laboratory for Developments and Methods (LDM), Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland)

2014-08-01

The use of polarized protons as neutron spin filter is an attractive alternative to the well established neutron polarization techniques, as the large, spin-dependent neutron scattering cross-section for protons is useful up to the sub-MeV region. Employing optically excited triplet states for the dynamic nuclear polarization (DNP) of the protons relieves the stringent requirements of classical DNP schemes, i.e low temperatures and strong magnetic fields, making technically simpler systems with open geometries possible. Using triplet DNP a record polarization of 71% has been achieved in a pentacene doped naphthalene single crystal at a field of 0.36 T using a simple helium flow cryostat for cooling. Furthermore, by placing the polarized crystal in a neutron optics focus and de-focus scheme, the actual sample cross-section could be increased by a factor 35 corresponding to an effective spin filter cross-section of 18×18mm{sup 2}.

(abstract) Effect of Long Period Ocean Tides on the Earth's Rotation

Science.gov (United States)

Gross, R. S.; Chao, B. F.; Desai, S.

1996-01-01

The second-degree zonal tide raising potential, which is responsible for tidal changes in the Earth's rotation rate and length-of-day, is symmetric about the polar axis and hence can excite the Earth's polar motion only through its action upon nonaxisymmetric features of the Earth such as the oceans. Ocean tidal excitation of polar motion in the diurnal and semidiurnal tidal bands has been previously detected and extensively examined. Here, the detection of ocean tidal excitation of polar motion in the long-period tidal band, specifically at the Mf' (13.63-day) and Mf (13.66-day) tidal frequencies, is reported.

MCSCF wave functions for excited states of polar molecules - Application to BeO. [Multi-Configuration Self-Consistent Field

Science.gov (United States)

Bauschlicher, C. W., Jr.; Yarkony, D. R.

1980-01-01

A previously reported multi-configuration self-consistent field (MCSCF) algorithm based on the generalized Brillouin theorem is extended in order to treat the excited states of polar molecules. In particular, the algorithm takes into account the proper treatment of nonorthogonality in the space of single excitations and invokes, when necessary, a constrained optimization procedure to prevent the variational collapse of excited states. In addition, a configuration selection scheme (suitable for use in conjunction with extended configuration interaction methods) is proposed for the MCSCF procedure. The algorithm is used to study the low-lying singlet states of BeO, a system which has not previously been studied using an MCSCF procedure. MCSCF wave functions are obtained for three 1 Sigma + and two 1 Pi states. The 1 Sigma + results are juxtaposed with comparable results for MgO in order to assess the generality of the description presented here.

Synchronization of Two Non-Identical Coupled Exciters in a Non-Resonant Vibrating System of Linear Motion. Part I: Theoretical Analysis

Directory of Open Access Journals (Sweden)

Chunyu Zhao

2009-01-01

Full Text Available In this paper an analytical approach is proposed to study the feature of frequency capture of two non-identical coupled exciters in a non-resonant vibrating system. The electromagnetic torque of an induction motor in the quasi-steady-state operation is derived. With the introduction of two perturbation small parameters to average angular velocity of two exciters and their phase difference, we deduce the Equation of Frequency Capture by averaging two motion equations of two exciters over their average period. It converts the synchronization problem of two exciters into that of existence and stability of zero solution for the Equation of Frequency Capture. The conditions of implementing frequency capture and that of stabilizing synchronous operation of two motors have been derived. The concept of torque of frequency capture is proposed to physically explain the peculiarity of self-synchronization of the two exciters. An interesting conclusion is reached that the moments of inertia of the two exciters in the Equation of Frequency Capture reduce and there is a coupling moment of inertia between the two exciters. The reduction of moments of inertia and the coupling moment of inertia have an effect on the stability of synchronous operation.

Circular motion of particles suspended in a Gaussian beam with circular polarization validates the spin part of the internal energy flow

DEFF Research Database (Denmark)

Angelsky, O. V.; Bekshaev, A. Ya.; Maksimyak, P. P.

2012-01-01

switching to the right (left) circular polarization, the particles performed spinning motion in agreement with the angular momentum imparted by the field, but they were involved in an orbital rotation around the beam axis as well, which in previous works [Y. Zhao et al, Phys. Rev. Lett. 99, 073901 (2007......Non-spherical dielectric microparticles were suspended in a water-filled cell and exposed to a coherent Gaussian light beam with controlled state of polarization. When the beam polarization is linear, the particles were trapped at certain off-axial position within the beam cross section. After...... of inhomogeneously polarized paraxial beams [A. Bekshaev et al, J. Opt. 13, 053001 (2011)]....

Associative ionization of two laser excited Na atoms

International Nuclear Information System (INIS)

Meijer, H.A.J.

1988-01-01

An investigation into the associative ionization of two sodium atoms excited by polarized laser beams is described. It was possible to excite the Na atoms in a velocity-selective way by exploiting the Doppler effect. The excitation of Na to the 3 2 P 3/2 , F=3 level is discussed on the basis of so-called saturation curves. Experiments with seven different combinations of polarization of the two exciting laser beams are described and the results discussed. 86 refs.; 53 figs.; 6 tabs

Investigations of fluctuation phenomena in the excitation functions of the cross-section by means of polarized particles

International Nuclear Information System (INIS)

Henneck, R.

1976-01-01

The present work concerns theoretical and experimental investigations of fluctuation phenomena, which appear in the excitation functions of the diff. cross-section and of the analyzing power, when bombarding nuclei with polarized particles in the energy range of strongly overlapping levels. We could show theoretically that model-dependent calculations (or assumptions), necessary for the determination of the relative amount of direct interaction contribution within the statistical model of Ericson, are not necessary for the elastic scattering of polarized spin-1/2- particles from spin-zero-target nuclei, if the additional observable analyzing power is included in the analysis. The proposed, new method hence presents an independent test for the consistency of the Hauser-Feshbach theory and its validity in the domain of strongly overlapping levels. (orig./WL) [de

High-spin excitations of atomic nuclei

International Nuclear Information System (INIS)

Xu Furong; National Laboratory of Heavy Ion Physics, Lanzhou; Chinese Academy of Sciences, Beijing

2004-01-01

The authors used the cranking shell model to investigate the high-spin motions and structures of atomic nuclei. The authors focus the collective rotations of the A∼50, 80 and 110 nuclei. The A∼50 calculations show complicated g spectroscopy, which can have significant vibration effects. The A≅80 N≅Z nuclei show rich shape coexistence with prolate and oblate rotational bands. The A≅110 nuclei near the r-process path can have well-deformed oblate shapes that become yrast and more stable with increasing rotational frequency. As another important investigation, the authors used the configuration-constrained adiabatic method to calculate the multi-quasiparticle high-K states in the A∼130, 180 and superheavy regions. The calculations show significant shape polarizations due to quasi-particle excitations for soft nuclei, which should be considered in the investigations of high-K states. The authors predicted some important high-K isomers, e.g., the 8 - isomers in the unstable nuclei of 140 Dy and 188 Pb, which have been confirmed in experiments. In superheavy nuclei, our calculations show systematic existence of high-K states. The high-K excitations can increase the productions of synthesis and the survival probabilities of superheavy nuclei. (authors)

An intense polarized beam by a laser ionization injection

International Nuclear Information System (INIS)

Ohmori, Chihiro; Hiramatsu, Shigenori; Nakamura, Takeshi.

1990-12-01

Accumulation of protons and polarized protons by photo-ionization injection are described. This method consists of (1)producing the neutral hydrogen beam by Lorentz stripping, (2)excitation of the neutral hydrogen beam with a laser, and (3)ionization of the hydrogen beam in the 2P excited state with another laser. When the laser for the excitation is circularly polarized, we can get a polarized proton beam. An ionization efficiency of 98% and a polarization of 80% can be expected by an intense laser beam from a FEL(Free Electron Laser). (author)

Jordan-Schwinger map, 3D harmonic oscillator constants of motion, and classical and quantum parameters characterizing electromagnetic wave polarization

International Nuclear Information System (INIS)

Mota, R D; Xicotencatl, M A; Granados, V D

2004-01-01

In this work we introduce a generalization of the Jauch and Rohrlich quantum Stokes operators when the arrival direction from the source is unknown a priori. We define the generalized Stokes operators as the Jordan-Schwinger map of a triplet of harmonic oscillators with the Gell-Mann and Ne'eman matrices of the SU(3) symmetry group. We show that the elements of the Jordan-Schwinger map are the constants of motion of the three-dimensional isotropic harmonic oscillator. Also, we show that the generalized Stokes operators together with the Gell-Mann and Ne'eman matrices may be used to expand the polarization matrix. By taking the expectation value of the Stokes operators in a three-mode coherent state of the electromagnetic field, we obtain the corresponding generalized classical Stokes parameters. Finally, by means of the constants of motion of the classical 3D isotropic harmonic oscillator we describe the geometrical properties of the polarization ellipse

Jordan Schwinger map, 3D harmonic oscillator constants of motion, and classical and quantum parameters characterizing electromagnetic wave polarization

Science.gov (United States)

Mota, R. D.; Xicoténcatl, M. A.; Granados, V. D.

2004-02-01

In this work we introduce a generalization of the Jauch and Rohrlich quantum Stokes operators when the arrival direction from the source is unknown a priori. We define the generalized Stokes operators as the Jordan-Schwinger map of a triplet of harmonic oscillators with the Gell-Mann and Ne'eman matrices of the SU(3) symmetry group. We show that the elements of the Jordan-Schwinger map are the constants of motion of the three-dimensional isotropic harmonic oscillator. Also, we show that the generalized Stokes operators together with the Gell-Mann and Ne'eman matrices may be used to expand the polarization matrix. By taking the expectation value of the Stokes operators in a three-mode coherent state of the electromagnetic field, we obtain the corresponding generalized classical Stokes parameters. Finally, by means of the constants of motion of the classical 3D isotropic harmonic oscillator we describe the geometrical properties of the polarization ellipse.

Jordan-Schwinger map, 3D harmonic oscillator constants of motion, and classical and quantum parameters characterizing electromagnetic wave polarization

Energy Technology Data Exchange (ETDEWEB)

Mota, R D [Unidad Profesional Interdisciplinaria de IngenierIa y TecnologIas Avanzadas, IPN. Av. Instituto Politecnico Nacional 2580, Col. La Laguna Ticoman, 07340 Mexico DF (Mexico); Xicotencatl, M A [Departamento de Matematicas del Centro de Investigacion y Estudios Avanzados del IPN, Mexico DF, 07000 (Mexico); Granados, V D [Escuela Superior de FIsica y Matematicas, Instituto Politecnico Nacional, Ed. 9, Unidad Profesional Adolfo Lopez Mateos, 07738 Mexico DF (Mexico)

2004-02-20

In this work we introduce a generalization of the Jauch and Rohrlich quantum Stokes operators when the arrival direction from the source is unknown a priori. We define the generalized Stokes operators as the Jordan-Schwinger map of a triplet of harmonic oscillators with the Gell-Mann and Ne'eman matrices of the SU(3) symmetry group. We show that the elements of the Jordan-Schwinger map are the constants of motion of the three-dimensional isotropic harmonic oscillator. Also, we show that the generalized Stokes operators together with the Gell-Mann and Ne'eman matrices may be used to expand the polarization matrix. By taking the expectation value of the Stokes operators in a three-mode coherent state of the electromagnetic field, we obtain the corresponding generalized classical Stokes parameters. Finally, by means of the constants of motion of the classical 3D isotropic harmonic oscillator we describe the geometrical properties of the polarization ellipse.

Polar and low polar solvents media effect on dipole moments of some diazo Sudan dyes

Science.gov (United States)

Zakerhamidi, M. S.; Golghasemi Sorkhabi, Sh.; Shamkhali, A. N.

2014-06-01

Absorption and fluorescence spectra of three Sudan dyes (SudanIII, SudanIV and Sudan black B) were recorded in various solvents with different polarity in the range of 300-800 nm, at room temperature. The solvatochromic method was used to investigate dipole moments of these dyes in ground and excited states, in different media. The solvatochromic behavior of these substances and their solvent-solute interactions were analyzed via solvent polarity parameters. Obtained results express the effects of solvation on tautomerism and molecular configuration (geometry) of Sudan dyes in solvent media with different polarity. Furthermore, analyze of solvent-solute interactions and value of ground and excited states dipole moments suggests different forms of resonance structures for Sudan dyes in polar and low-polar solvents.

Earth rotation excitation mechanisms derived from geodetic space observations

Science.gov (United States)

Göttl, F.; Schmidt, M.

2009-04-01

Earth rotation variations are caused by mass displacements and motions in the subsystems of the Earth. Via the satellite Gravity and Climate Experiment (GRACE) gravity field variations can be identified which are caused by mass redistribution in the Earth system. Therefore time variable gravity field models (GFZ RL04, CSR RL04, JPL RL04, ITG-Grace03, GRGS, ...) can be used to derive different impacts on Earth rotation. Furthermore satellite altimetry provides accurate information on sea level anomalies (AVISO, DGFI) which are caused by mass and volume changes of seawater. Since Earth rotation is solely affected by mass variations and motions the volume (steric) effect has to be reduced from the altimetric observations in order to infer oceanic contributions to Earth rotation variations. Therefore the steric effect is estimated from physical ocean parameters such as temperature and salinity changes in the oceans (WOA05, Ishii). In this study specific individual geophysical contributions to Earth rotation variations are identified by means of a multitude of accurate geodetic space observations in combination with a realistic error propagation. It will be shown that due to adjustment of altimetric and/or gravimetric solutions the results for polar motion excitations can be improved.

Nonlinear Gyrokinetic Theory With Polarization Drift

International Nuclear Information System (INIS)

Wang, L.; Hahm, T.S.

2010-01-01

A set of the electrostatic toroidal gyrokinetic Vlasov equation and the Poisson equation, which explicitly includes the polarization drift, is derived systematically by using Lie-transform method. The polarization drift is introduced in the gyrocenter equations of motion, and the corresponding polarization density is derived. Contrary to the wide-spread expectation, the inclusion of the polarization drift in the gyrocenter equations of motion does not affect the expression for the polarization density significantly. This is due to modification of the gyrocenter phase-space volume caused by the electrostatic potential [T. S. Hahm, Phys. Plasmas 3, 4658 (1996)].

Competitive photocyclization/rearrangement of 4-aryl-1,1-dicyanobutenes controlled by intramolecular charge-transfer interaction. Effect of medium polarity, temperature, pressure, excitation wavelength, and confinement.

Science.gov (United States)

Ito, Tadashi; Nishiuchi, Emi; Fukuhara, Gaku; Inoue, Yoshihisa; Mori, Tadashi

2011-09-01

A series of 4-aryl-1,1-dicyanobutenes (1a-1f) with different substituents were synthesized to control the intramolecular donor-acceptor or charge-transfer (C-T) interactions in the ground state. Photoexcitation of these C-T substrates led to competitive cyclization and rearrangement, the ratio being critically controlled by various environmental factors, such as solvent polarity, temperature and static pressure, and also by excitation wavelength and supramolecular confinement (polyethylene voids). In non-polar solvents, the rearrangement was dominant (>10 : 1) for all examined substrates, while the cyclization was favoured in polar solvents, in particular at low temperatures. Selective excitation at the C-T band further enhanced the cyclization up to >50 : 1 ratios. More importantly, the cyclization/rearrangement ratio was revealed to be a linear function of the C-T transition energy. However, the substrates with a sterically demanding or highly electron-donating substituent failed to give the cyclization product.

Seismic effects on the reliability of polar cranes for nuclear power plants

International Nuclear Information System (INIS)

Kaiser, W.; Friedrich, H.; Knoefel, L.

1985-01-01

In order to meet the requirements of nuclear safety reactor components have to be designed aseismically. A model for studying simulated seismic effects on the reliability of containment equipment polar cranes is presented. Based on this model vertical and horizontal motions of the crane are investigated. Emphasis is laid on non-linearities caused by malfunctions such as lift of the crane from the runaway, lift of the trolley from the beams, slackening of the ropes as well as sliding of blocked track wheels. Seismic excitations are simulated by computer produced accelerograms

Excited states

CERN Document Server

Lim, Edward C

1974-01-01

Excited States, Volume I reviews radiationless transitions, phosphorescence microwave double resonance through optical spectra in molecular solids, dipole moments in excited states, luminescence of polar molecules, and the problem of interstate interaction in aromatic carbonyl compounds. The book discusses the molecular electronic radiationless transitions; the double resonance techniques and the relaxation mechanisms involving the lowest triplet state of aromatic compounds; as well as the optical spectra and relaxation in molecular solids. The text also describes dipole moments and polarizab

Numerical simulation of the cavitation's hydrodynamic excitement

International Nuclear Information System (INIS)

Hassis, H.; Dueymes, E.; Lauro, J.F.

1993-01-01

First, we study the motion, the velocity, the phases plane and the acoustic sources associated to a spherical bubble in a compressible or incompressible medium. The bubble can be excited by periodic or random excitements. We study the parameters which influence their behaviour: periodicity or not of motion, implosion and explosion or oscillation of bubble. We take into account this behaviour in a model of cavitation: it is a numerical simulation using population of bubbles which are with positions (in the cavitation volume) and sizes are random. These bubbles are excited by a random excitement: a model of turbulent flow or implosion and explosion of bubble. (author)

Study of the motion of electrons in non polar classical liquids. Measurement of Hall effect and f.i.r. search for low energy traps. Progress report

International Nuclear Information System (INIS)

1981-01-01

Progress is reported on experiments aimed at the measurement of the Hall mobility of injected electrons in classical non polar insulating liquids and the optical absorption associated with electrons captured by shallow traps in the liquefied rare gases. Theoretical work aimed at a better understanding of the trapping kinetics of electrons by SF 6 and O 2 dissolved in rare gas liquids was also carried out. Its conclusion is that the electric field dependence of the trapping probability can be explained, basically without adjustable parameters, by considering the Poole-Frenkel-Schotky ionization of the excited state of the traps. From the analysis of published data on the motion of electrons in liquid ethane it is tentatively concluded that at low temperatures the trapping of electrons in the liquid involves a Jahn-Teller like distortion of a single ethane molecule while at higher temperatures it is necessary to consider a small molecular cluster, possibly made up of 2 molecules

Imaging Magnetic Vortices Dynamics Using Lorentz Electron Microscopy with GHz Excitations

Science.gov (United States)

Zhu, Yimei

2015-03-01

Magnetic vortices in thin films are naturally formed spiral spin configurations with a core polarization pointing out of the film plane. They typically represent ground states with high structural and thermal stability as well as four different chirality-polarity combinations, offering great promise in the development of spin-based devices. For applications to spin oscillators, non-volatile memory and logic devices, the fundamental understanding and precise control of vortex excitations and dynamic switching behavior are essential. The compact dimensionality and fast spin dynamics set grand challenges for direct imaging technologies. Recently, we have developed a unique method to directly visualize the dynamic magnetic vortex motion using advanced Lorentz electron microscopy combined with GHz electronic excitations. It enables us to map the orbit of a magnetic vortex core in a permalloy square with modality. Our approach is complementary to X-ray magnetic circular dichroism and is of general interest to the magnetism community as it paves a way to study fundamental spin phenomena with unprecedented resolution and accuracy. Collaborations with S.D. Pollard, J.F. Pulecio, D.A. Arena and K.S. Buchanan are acknowledged. Work supported by DOE-BES, Material Sciences and Engineering Division, under Contract No. DE-AC02-98CH10886.

6-C polarization analysis using point measurements of translational and rotational ground-motion: theory and applications

Science.gov (United States)

Sollberger, David; Greenhalgh, Stewart A.; Schmelzbach, Cedric; Van Renterghem, Cédéric; Robertsson, Johan O. A.

2018-04-01

We provide a six-component (6-C) polarization model for P-, SV-, SH-, Rayleigh-, and Love-waves both inside an elastic medium as well as at the free surface. It is shown that single-station 6-C data comprised of three components of rotational motion and three components of translational motion provide the opportunity to unambiguously identify the wave type, propagation direction, and local P- and S-wave velocities at the receiver location by use of polarization analysis. To extract such information by conventional processing of three-component (3-C) translational data would require large and dense receiver arrays. The additional rotational components allow the extension of the rank of the coherency matrix used for polarization analysis. This enables us to accurately determine the wave type and wave parameters (propagation direction and velocity) of seismic phases, even if more than one wave is present in the analysis time window. This is not possible with standard, pure-translational 3-C recordings. In order to identify modes of vibration and to extract the accompanying wave parameters, we adapt the multiple signal classification algorithm (MUSIC). Due to the strong nonlinearity of the MUSIC estimator function, it can be used to detect the presence of specific wave types within the analysis time window at very high resolution. We show how the extracted wavefield properties can be used, in a fully automated way, to separate the wavefield into its different wave modes using only a single 6-C recording station. As an example, we apply the method to remove surface wave energy while preserving the underlying reflection signal and to suppress energy originating from undesired directions, such as side-scattered waves.

Spurious Excitations in Semiclassical Scattering Theory.

Science.gov (United States)

Gross, D. H. E.; And Others

1980-01-01

Shows how through proper handling of the nonuniform motion of semiclassical coordinates spurious excitation terms are eliminated. An application to the problem of nuclear Coulomb excitation is presented as an example. (HM)

Transient, polarity-dependent dielectric response in a twisted nematic liquid crystal under very low frequency excitation.

Science.gov (United States)

Krishnamurthy, K S

2015-09-01

The electric Freedericksz transition is a second-order quadratic effect, which, in a planarly aligned nematic liquid crystal layer, manifests above a threshold field as a homogeneous symmetric distortion with maximum director-tilt in the midplane. We find that, upon excitation by a low frequency (wave field, the instability becomes spatially and temporally varying. This is demonstrated using calamitic liquid crystals, initially in the 90°-twisted planar configuration. The distortion occurs close to the negative electrode following each polarity switch and, for low-voltage amplitudes, decays completely in time. We use the elastically favorable geometry of Brochard-Leger walls to establish the location of maximum distortion. Thus, at successive polarity changes, the direction of extension of both annular and open walls switches between the alignment directions at the two substrates. For high voltages, this direction is largely along the midplane director, while remaining marginally oscillatory. These results are broadly understood by taking into account the time-varying and inhomogeneous field conditions that prevail soon after the polarity reverses. Polarity dependence of the instability is traced to the formation of intrinsic double layers that lead to an asymmetry in field distribution in the presence of an external bias. Momentary field elevation near the negative electrode following a voltage sign reversal leads to locally enhanced dielectric and gradient flexoelectric torques, which accounts for the surface-like phenomenon observed at low voltages. These spatiotemporal effects, also found earlier for other instabilities, are generic in nature.

Effect of interchain coupling on the excited polaron in conjugated polymers

International Nuclear Information System (INIS)

Li, Xiao-xue; Chen, Gang

2017-01-01

Based on the one-dimensional extended Su–Schrieffer–Heeger model, we theoretically investigate the effect of interchain coupling on the formation and polarization of the single-excited state of polaron in conjugated polymers. It is found that there exists a turnover value of the coupling strength, over which the excited polaron could not be formed in either of the two coupled chains. Instead, a polaron-like particle is localized at the center of each chain. In addition, we also find that the reverse polarization of the excited polaron could be enhanced for some cases in polymer when the interchain coupling becomes strong until it exceeds the critical value. - Highlights: • Effect of interchain coupling on the single-excited state of polaron is studied. • When coupling strength exceeds critical value, the excited polaron is dissociated. • Soliton pair could be dissociated into polaron-like particle with strong coupling. • Reverse polarization of excited polaron is enhanced by weak interchain coupling. • Reverse polarization is obtained more easily in solid film of polymer molecules.

Effect of interchain coupling on the excited polaron in conjugated polymers

Energy Technology Data Exchange (ETDEWEB)

Li, Xiao-xue, E-mail: sps_lixx@ujn.edu.cn; Chen, Gang, E-mail: ss_cheng@ujn.edu.cn

2017-02-05

Based on the one-dimensional extended Su–Schrieffer–Heeger model, we theoretically investigate the effect of interchain coupling on the formation and polarization of the single-excited state of polaron in conjugated polymers. It is found that there exists a turnover value of the coupling strength, over which the excited polaron could not be formed in either of the two coupled chains. Instead, a polaron-like particle is localized at the center of each chain. In addition, we also find that the reverse polarization of the excited polaron could be enhanced for some cases in polymer when the interchain coupling becomes strong until it exceeds the critical value. - Highlights: • Effect of interchain coupling on the single-excited state of polaron is studied. • When coupling strength exceeds critical value, the excited polaron is dissociated. • Soliton pair could be dissociated into polaron-like particle with strong coupling. • Reverse polarization of excited polaron is enhanced by weak interchain coupling. • Reverse polarization is obtained more easily in solid film of polymer molecules.

Recent advance in polar seismology: Global impact of the International Polar Year

Science.gov (United States)

Kanao, Masaki; Zhao, Dapeng; Wiens, Douglas A.; Stutzmann, Éléonore

2015-03-01

The most exciting initiative for the recent polar studies was the International Polar Year (IPY) in 2007-2008. The IPY has witnessed a growing community of seismologists who have made considerable efforts to acquire high-quality data in polar regions. It also provided an excellent opportunity to make significant advances in seismic instrumentation of the polar regions to achieve scientific targets involving global issues. Taking these aspects into account, we organize and publish a special issue in Polar Science on the recent advance in polar seismology and cryoseismology as fruitful achievements of the IPY.

Synchronization of Two Non-Identical Coupled Exciters in a Non-Resonant Vibrating System of Linear Motion. Part II: Numeric Analysis

Directory of Open Access Journals (Sweden)

Chunyu Zhao

2009-01-01

Full Text Available The paper focuses on the quantitative analysis of the coupling dynamic characteristics of two non-identical exciters in a non-resonant vibrating system. The load torque of each motor consists of three items, including the torque of sine effect of phase angles, that of coupling sine effect and that of coupling cosine effect. The torque of frequency capture results from the torque of coupling cosine effect, which is equal to the product of the coupling kinetic energy, the coefficient of coupling cosine effect, and the sine of phase difference of two exciters. The motions of the system excited by two exciters in the same direction make phase difference close to π and that in opposite directions makes phase difference close to 0. Numerical results show that synchronous operation is stable when the dimensionless relative moments of inertia of two exciters are greater than zero and four times of their product is greater than the square of their coefficient of coupling cosine effect. The stability of the synchronous operation is only dependent on the structural parameters of the system, such as the mass ratios of two exciters to the vibrating system, and the ratio of the distance between an exciter and the centroid of the system to the equivalent radius of the system about its centroid.

Baryon spectroscopy with polarization observables from CLAS

Energy Technology Data Exchange (ETDEWEB)

Strauch, Steffen [Univ. of South Carolina, Columbia, SC (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

2016-11-01

The spectrum of nucleon excitations is dominated by broad and overlapping resonances. Polarization observables in photoproduction reactions are key in the study of these excitations. They give indispensable constraints to partial-wave analyses and help clarify the spectrum. A series of polarized photoproduction experiments have been performed at the Thomas Jefferson National Accelerator Facility with the CEBAF Large Acceptance Spectrometer (CLAS). These measurements include data with linearly and circularly polarized tagged-photon beams, longitudinally and transversely polarized proton and deuterium targets, and recoil polarizations through the observation of the weak decay of hyperons. An overview of these studies and recent results will be given.

Polarization methods for diode laser excitation of solid state lasers

Science.gov (United States)

Holtom, Gary R.

2008-11-25

A mode-locked laser employs a coupled-polarization scheme for efficient longitudinal pumping by reshaped laser diode bars. One or more dielectric polarizers are configured to reflect a pumping wavelength having a first polarization and to reflect a lasing wavelength having a second polarization. A Yb-doped gain medium can be used that absorbs light having a first polarization and emits light having a second polarization. Using such pumping with laser cavity dispersion control, pulse durations of less than 100 fs can be achieved.

System for simultaneously measuring 6DOF geometric motion errors using a polarization maintaining fiber-coupled dual-frequency laser.

Science.gov (United States)

Cui, Cunxing; Feng, Qibo; Zhang, Bin; Zhao, Yuqiong

2016-03-21

A novel method for simultaneously measuring six degree-of-freedom (6DOF) geometric motion errors is proposed in this paper, and the corresponding measurement instrument is developed. Simultaneous measurement of 6DOF geometric motion errors using a polarization maintaining fiber-coupled dual-frequency laser is accomplished for the first time to the best of the authors' knowledge. Dual-frequency laser beams that are orthogonally linear polarized were adopted as the measuring datum. Positioning error measurement was achieved by heterodyne interferometry, and other 5DOF geometric motion errors were obtained by fiber collimation measurement. A series of experiments was performed to verify the effectiveness of the developed instrument. The experimental results showed that the stability and accuracy of the positioning error measurement are 31.1 nm and 0.5 μm, respectively. For the straightness error measurements, the stability and resolution are 60 and 40 nm, respectively, and the maximum deviation of repeatability is ± 0.15 μm in the x direction and ± 0.1 μm in the y direction. For pitch and yaw measurements, the stabilities are 0.03″ and 0.04″, the maximum deviations of repeatability are ± 0.18″ and ± 0.24″, and the accuracies are 0.4″ and 0.35″, respectively. The stability and resolution of roll measurement are 0.29″ and 0.2″, respectively, and the accuracy is 0.6″.

Effects of Long Period Ocean Tides on the Earth's Rotation

Science.gov (United States)

Gross, Richard S.; Chao, Ben F.; Desai, Shailen D.

1996-01-01

The spectra of polar motion excitation functions exhibit enhanced power in the fortnightly tidal band. This enhanced power is attributed to ocean tidal excitation. Ocean tide models predict polar motion excitation effects that differ with each other, and with observations, by factors as large as 2-3. There is a need for inproved models for the effect of long-period ocean tides on Earth's rotation.

Role of giant resonance excitation in heavy ion collisions

International Nuclear Information System (INIS)

Catara, F.; Chomaz, Ph.

1987-01-01

In this paper we discuss several aspects of heavy ion collisions involving collective vibrational modes. In our approach the relative motion is treated in a semiclassical approximation, while the intrinsic degrees of freedom are described microscopically within the RPA. The differences with respect to macroscopic models are analyzed in the appendix. First we present some results on the inelastic scattering cross section and we show that the structures observed experimentally can be explained in terms of multiple excitation of the Giant Quadrupole Resonance. After we calculate an adiabatic polarization potential describing the coupling to the collective vibrational modes and show that it produces a strong enhancement of the subbarrier fusion cross section. This enhancement is found to be enough to reproduce the experimental data for symmetric systems, while for asymmetric reactions the coupling to other degrees of freedom, like transfer, is needed. Finally we report some preliminary results on a dynamical calculation of the real and imaginary parts of the polarization potential. We show that at high incident energies (E/A > 20MeV) the role of the Giant Quadrupole Resonance becomes dominant

The evolution of tensor polarization

International Nuclear Information System (INIS)

Huang, H.; Lee, S.Y.; Ratner, L.

1993-01-01

By using the equation of motion for the vector polarization, the spin transfer matrix for spin tensor polarization, the spin transfer matrix for spin tensor polarization is derived. The evolution equation for the tensor polarization is studied in the presence of an isolate spin resonance and in the presence of a spin rotor, or snake

Competition between excited core states and 1homega single-particle excitations at comparable energies in {sup 207}Pb from photon scattering

Energy Technology Data Exchange (ETDEWEB)

Pietralla, N., E-mail: pietralla@ikp.tu-darmstadt.d [Institut fuer Kernphysik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany); Nuclear Structure Laboratory, SUNY at Stony Brook, Stony Brook, NY 11794-3800 (United States); Institut fuer Kernphysik, Universitaet zu Koeln, 50937 Koeln (Germany); Li, T.C. [Nuclear Structure Laboratory, SUNY at Stony Brook, Stony Brook, NY 11794-3800 (United States); Fritzsche, M. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany); Ahmed, M.W. [Triangle Universities Nuclear Laboratory (TUNL), Duke University, Durham, NC 27708 (United States); Ahn, T.; Costin, A. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany); Nuclear Structure Laboratory, SUNY at Stony Brook, Stony Brook, NY 11794-3800 (United States); Institut fuer Kernphysik, Universitaet zu Koeln, 50937 Koeln (Germany); Enders, J. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany); Li, J. [Duke Free Electron Laser Laboratory (DFELL), Duke University, Durham, NC 27708 (United States); Mueller, S.; Neumann-Cosel, P. von [Institut fuer Kernphysik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany); Pinayev, I.V. [Duke Free Electron Laser Laboratory (DFELL), Duke University, Durham, NC 27708 (United States); Ponomarev, V.Yu.; Savran, D. [Institut fuer Kernphysik, Technische Universitaet Darmstadt, 64289 Darmstadt (Germany); Tonchev, A.P.; Tornow, W.; Weller, H.R. [Triangle Universities Nuclear Laboratory (TUNL), Duke University, Durham, NC 27708 (United States); Werner, V. [A.W. Wright Nuclear Structure Laboratory (WNSL), Yale University, New Haven, CT (United States); Wu, Y.K. [Duke Free Electron Laser Laboratory (DFELL), Duke University, Durham, NC 27708 (United States); Zilges, A. [Institut fuer Kernphysik, Universitaet zu Koeln, 50937 Koeln (Germany)

2009-10-26

The Pb(gamma{sup -}>,gamma{sup '}) photon scattering reaction has been studied with the nearly monochromatic, linearly polarized photon beams at the High Intensity gamma-ray Source (HIgammaS) at the DFELL. Azimuthal scattering intensity asymmetries measured with respect to the polarization plane of the beam have been used for the first time to assign both the spin and parity quantum numbers of dipole excited states of {sup 206,207,208}Pb at excitation energies in the vicinity of 5.5 MeV. Evidence for dominant particle-core coupling is deduced from these results along with information on excitation energies and electromagnetic transition matrix elements. Implications of the existence of weakly coupled states built on highly excited core states in competition with 1homega single particle (hole) excitations at comparable energies are discussed.

Anomalous Late Jurassic motion of the Pacific Plate with implications for true polar wander

Science.gov (United States)

Fu, R. R.; Kent, D.

2017-12-01

True polar wander, or TPW, is the rotation of the entire mantle-crust system that results in simultaneous change in latitude and orientation for all lithospheric plates. One of the most recent candidate TPW events consists of a 30˚ rotation during Late Jurassic time (160 - 145 Ma). However, existing paleomagnetic documentation of this event derives exclusively from continental studies. Because all major landmasses except China were connected directly or via spreading centers in the Late Jurassic, the velocities of these continents were mutually constrained and their motion as a group over the underlying mantle would be indistinguishable from TPW using only continental data. On the other hand, plates of the Pacific Basin constituted a kinematically independent domain, interfacing with continents at subduction zones and slip-strike boundaries. Coherent motion of both Pacific Basin and continental plates would therefore indicate uniform motion of virtually the entire lithosphere, providing a means to distinguish TPW from continental drift. We performed thermal demagnetization on remaining samples from Ocean Drilling Program (ODP) Site 801B, which were cored from the oldest sampled oceanic crust in the Western Pacific, to determine its change in paleolatitude during the Late Jurassic and Early Cretaceous (167 - 134 Ma). We find that the Pacific Plate likely underwent a steady southward drift during this time period, consistent with previous results from magnetic anomalies, except for an episode of northward motion between Oxfordian and Tithonian time (161 - 147 Ma). Although the amplitude of this northward shift is subject to significant uncertainty due to the sparse recovery of core samples, the trajectory of the Pacific Plate is most simply explained by TPW in the 160 - 145 Ma interval as inferred from continental data. Furthermore, such an interpretation is consistent with the sense of shear inferred at the Farallon-North American Plate boundary, whereas uniform

Polarization-dependent solitons in the strong coupling regime of semiconductor microcavities

International Nuclear Information System (INIS)

Fu, Y.; Zhang, W.L.; Wu, X.M.

2015-01-01

This paper studies the influence of polarization on formation of vectorial polariton soliton in semiconductor microcavities through numerical simulations. It is found that the polariton solution greatly depends on the polarization of both the pump and exciting fields. By properly choosing the pump and exciting field polarization, bright–bright or bright–dark vectorial polariton solitons can be formed. Especially, when the input conditions of pump or exciting field of the two opposite polarizations are slightly asymmetric, an interesting phenomenon that the dark solitons transform into bright solitons occurs in the branch of soliton solutions.

Measurement of Polarization Observables in the Electro-Excitation of the Proton to its First Excited State

International Nuclear Information System (INIS)

Rikki Roche

2003-01-01

This thesis reports results from the Thomas Jefferson National Accelerator Facility (Jefferson Lab) Hall A experiment E91-011, which measured double-polarization observables in the pion electroproduction reaction from the proton. Specifically, the experiment measured the recoil proton polarization, polarized response functions, and cross section for the p(rvec e), e(prime) (rvec p) π o reaction at a center-of-mass energy centered at W = 1232 MeV--the peak of the Δ(1232) resonance--and at a four-momentum transfer squared of Q 2 = 1.0 GeV 2 /c 2 . Both the recoil proton polarization and polarized response function results will be presented in this thesis

Polarized wiggler for NSLS X-ray ring

International Nuclear Information System (INIS)

Friedman, A.; Zhang, X.; Krinsky, S.; Blum, E.B.

1993-01-01

We examine the properties of an elliptically polarized wiggler that will generate circularly polarized photons with energy spectrum of 3--12 KeV. The vertical wiggler magnetic field is produced by permanent magnets while the horizontal wiggler field is generated by electric coils capable of AC excitation. The radiation parameters of the wiggler is discussed. We consider AC excitation of the wiggler to produce the time modulation of the elliptic polarization. The power is dissipated in the vacuum chamber due to the eddy current

Study on characteristics of vertical strong motions

International Nuclear Information System (INIS)

Akao, Y.; Katukura, H.; Fukushima, S.; Mizutani, M.

1993-01-01

Statistic properties of vertical strong ground motions from near-field earthquakes are discussed in comparison with that of horizontal motions. It is a feature of this analysis that time history of each observed record is divided into direct P- and S-wave segments from a seismological viewpoint. Following results are obtained. Vertical motion energy excited by direct S-waves is about 0.6 times of horizontal ones at deep underground, and it approaches to 1.0 at shallow place. Horizontal motion energy excited by direct P-waves becomes 0.2 times (at deep) or more (at shallow) of vertical one. These results can be available in modeling of input motions for aseismic design. (author)

POLARIZED BEAMS: 1 - Longitudinal electron spin polarization at HERA

Energy Technology Data Exchange (ETDEWEB)

Anon.

1994-09-15

Wednesday 4 May marked a turning point in the art of the manipulation of spins in electron storage rings: longitudinal electron spin polarization (with the spins oriented along the electrons' direction of motion) was established in the electron ring of HERA, the electronproton collider at DESY in Hamburg. A polarization level of about 55% was obtained and polarizations of over 60% were reproducibly obtained in the following days. The beam energy was 27.52 GeV, corresponding to half integer spin tune of 62.5.

Magnetic field effects on ultrafast lattice compression dynamics of Si(111) crystal when excited by linearly-polarized femtosecond laser pulses

Science.gov (United States)

Hatanaka, Koji; Odaka, Hideho; Ono, Kimitoshi; Fukumura, Hiroshi

2007-03-01

Time-resolved X-ray diffraction measurements of Si (111) single crystal are performed when excited by linearly-polarized femtosecond laser pulses (780 nm, 260 fs, negatively-chirped, 1 kHz) under a magnetic field (0.47 T). Laser fluence on the sample surface is 40 mJ/cm^2, which is enough lower than the ablation threshold at 200 mJ/cm^2. Probing X-ray pulses of iron characteristic X-ray lines at 0.193604 and 0.193998 nm are generated by focusing femtosecond laser pulses onto audio-cassette tapes in air. Linearly-polarized femtosecond laser pulse irradiation onto Si(111) crystal surface induces transient lattice compression in the picosecond time range, which is confirmed by transient angle shift of X-ray diffraction to higher angles. Little difference of compression dynamics is observed when the laser polarization is changed from p to s-pol. without a magnetic field. On the other hand, under a magnetic field, the lattice compression dynamics changes when the laser is p-polarized which is vertical to the magnetic field vector. These results may be assigned to photo-carrier formation and energy-band distortion.

The Growth, Polarization, and Motion of the Radio Afterglow from the Giant Flare from SGR 1806-20

Energy Technology Data Exchange (ETDEWEB)

Taylor, G

2005-04-20

The extraordinary giant flare (GF) of 2004 December 27 from the soft gamma repeater (SGR) 1806-20 was followed by a bright radio afterglow. We present an analysis of VLA observations of this radio afterglow from SGR1806-20, consisting of previously reported 8.5 GHz data covering days 7 to 20 after the GF, plus new observations at 8.5 and 22 GHz from day 24 to 81. For a symmetric outflow, we find a deceleration in the expansion, from {approx}4.5 mas/day to <2.5 mas/day. The time of deceleration is roughly coincident with the rebrightening in the radio light curve, as expected to result when the ejecta from the GF sweeps up enough of the external medium, and transitions from a coasting phase to the Sedov-Taylor regime. The radio afterglow is elongated and maintains a 2:1 axis ratio with an average position angle of -40{sup o} (north through east), oriented perpendicular to the average intrinsic linear polarization angle. We also report on the discovery of motion in the flux centroid of the afterglow, at an average velocity of 0.26 {+-} 0.03 c (assuming a distance of 15 kpc) at a position angle of -45{sup o}. This motion, in combination with the growth and polarization measurements, suggests an initially asymmetric outflow, mainly from one side of the magnetar.

Search for nuclear excitation by laser-driven electron motion

International Nuclear Information System (INIS)

Bounds, J.A.; Dyer, P.

1992-01-01

It has been proposed that a nucleus may be excited by first exciting the atom's electrons with UV photons. The incident photons couple to the electrons, which would then couple via a virtual photon to the nucleus. As a test case, experiments with 235 U have been performed. A pulsed infrared laser produces an atomic vapor of 235 U which is then bombarded by a high-brightness UV laser beam. The resulting ions are collected. The first excited nuclear state of 235 U has a 26-min half-life and decays by internal conversion, resulting in emission of an atomic electron. These conversion electrons are detected by a channel electron multiplier. An upper limit of 4.0x10 -5 has been obtained for the probability of exciting the nucleus of a 235 U atom that is in the 248-nm UV beam for 700 fs at an irradiance in the range of 1.0x10 15 to 2.5x10 15 W/cm 2

Elementary spin excitations in ultrathin itinerant magnets

Energy Technology Data Exchange (ETDEWEB)

Zakeri, Khalil, E-mail: zakeri@mpi-halle.de

2014-12-10

Elementary spin excitations (magnons) play a fundamental role in condensed matter physics, since many phenomena e.g. magnetic ordering, electrical (as well as heat) transport properties, ultrafast magnetization processes, and most importantly electron/spin dynamics can only be understood when these quasi-particles are taken into consideration. In addition to their fundamental importance, magnons may also be used for information processing in modern spintronics. Here the concept of spin excitations in ultrathin itinerant magnets is discussed and reviewed. Starting with a historical introduction, different classes of magnons are introduced. Different theoretical treatments of spin excitations in solids are outlined. Interaction of spin-polarized electrons with a magnetic surface is discussed. It is shown that, based on the quantum mechanical conservation rules, a magnon can only be excited when a minority electron is injected into the system. While the magnon creation process is forbidden by majority electrons, the magnon annihilation process is allowed instead. These fundamental quantum mechanical selection rules, together with the strong interaction of electrons with matter, make the spin-polarized electron spectroscopies as appropriate tools to excite and probe the elementary spin excitations in low-dimensional magnets e.g ultrathin films and nanostructures. The focus is put on the experimental results obtained by spin-polarized electron energy loss spectroscopy and spin-polarized inelastic tunneling spectroscopy. The magnon dispersion relation, lifetime, group and phase velocity measured using these approaches in various ultrathin magnets are discussed in detail. The differences and similarities with respect to the bulk excitations are addressed. The role of the temperature, atomic structure, number of atomic layers, lattice strain, electronic complexes and hybridization at the interfaces are outlined. A possibility of simultaneous probing of magnons and phonons

Effect of horizontal displacements due to ocean tide loading on the determination of polar motion and UT1

Science.gov (United States)

Scherneck, Hans-Georg; Haas, Rüdiger

We show the influence of horizontal displacements due to ocean tide loading on the determination of polar motion and UT1 (PMU) on the daily and subdaily timescale. So called ‘virtual PMU variations’ due to modelling errors of ocean tide loading are predicted for geodetic Very Long Baseline Interferometry (VLBI) networks. This leads to errors of subdaily determination of PMU. The predicted effects are confirmed by the analysis of geodetic VLBI observations.

Excited State Spectra and Dynamics of Phenyl-Substituted Butadienes

DEFF Research Database (Denmark)

Wallace-Williams, Stacie E.; Schwartz, Benjamin J.; Møller, Søren

1994-01-01

indicate that phenyl torsional motion is not important to the excited-state dynamics and reveal alternative excited-state reaction pathways. The results demonstrate how molecular systems that are structually similar can exhibit different electronic properties and excited-state dynamics....

Optically induced rotation of Rayleigh particles by vortex beams with different states of polarization

International Nuclear Information System (INIS)

Li, Manman; Yan, Shaohui; Yao, Baoli; Liang, Yansheng; Lei, Ming; Yang, Yanlong

2016-01-01

Optical vortex beams carry optical orbital angular momentum (OAM) and can induce an orbital motion of trapped particles in optical trapping. We show that the state of polarization (SOP) of vortex beams will affect the details of this optically induced orbital motion to some extent. Numerical results demonstrate that focusing the vortex beams with circular, radial or azimuthal polarizations can induce a uniform orbital motion on a trapped Rayleigh particle, while in the focal field of the vortex beam with linear polarization the particle experiences a non-uniform orbital motion. Among the formers, the vortex beam with circular polarization induces a maximum optical torque on the particle. Furthermore, by varying the topological charge of the vortex beams, the vortex beam with circular polarization gives rise to an optimum torque superior to those given by the other three vortex beams. These facts suggest that the circularly polarized vortex beam is more suitable for rotating particles. - Highlights: • States of polarization of vortex beams affect the optically induced orbital motion of particles. • The dependences of the force and orbital torque on the topological charge, the size and the absorptivity of particles were calculated. • Focused vortex beams with circular, radial or azimuthal polarizations induce a uniform orbital motion on particles. • Particles experience a non-uniform orbital motion in the focused linearly polarized vortex beam. • The circularly polarized vortex beam is a superior candidate for rotating particles.

Polarization-controlled asymmetric excitation of surface plasmons

KAUST Repository

Xu, Quan; Zhang, Xueqian; Yang, Quanlong; Tian, Chunxiu; Xu, Yuehong; Zhang, Jianbing; Zhao, Hongwei; Li, Yanfeng; Ouyang, Chunmei; Tian, Zhen; Gu, Jianqiang; Zhang, Xixiang; Han, Jiaguang; Zhang, Weili

2017-01-01

Free-space light can be coupled into propagating surface waves at a metal–dielectric interface, known as surface plasmons (SPs). This process has traditionally faced challenges in preserving the incident polarization information and controlling

Harmonically excited orbital variations

International Nuclear Information System (INIS)

Morgan, T.

1985-01-01

Rephrasing the equations of motion for orbital maneuvers in terms of Lagrangian generalized coordinates instead of Newtonian rectangular cartesian coordinates can make certain harmonic terms in the orbital angular momentum vector more readily apparent. In this formulation the equations of motion adopt the form of a damped harmonic oscillator when torques are applied to the orbit in a variationally prescribed manner. The frequencies of the oscillator equation are in some ways unexpected but can nonetheless be exploited through resonant forcing functions to achieve large secular variations in the orbital elements. Two cases are discussed using a circular orbit as the control case: (1) large changes in orbital inclination achieved by harmonic excitation rather than one impulsive velocity change, and (2) periodic and secular changes to the longitude of the ascending node using both stable and unstable excitation strategies. The implications of these equations are also discussed for both artificial satellites and natural satellites. For the former, two utilitarian orbits are suggested, each exploiting a form of harmonic excitation. 5 refs

Polarization-Dependent Measurements of Molecular Super Rotors with Oriented Angular Momenta

Science.gov (United States)

Murray, Matthew J.; Toro, Carlos; Liu, Qingnan; Mullin, Amy S.

2014-05-01

Controlling molecular motion would enable manipulation of energy flow between molecules. Here we have used an optical centrifuge to investigate energy transfer between molecular super rotors with oriented angular momenta. The polarizable electron cloud of the molecules interacts with the electric field of linearly polarized light that angularly accelerates over the time of the optical pulse. This process drives molecules into high angular momentum states that are oriented with the optical field and have energies far from equilibrium. High resolution transient IR spectroscopy reveals the dynamics of collisional energy transfer for these super excited rotors. The results of this study leads to a more fundamental understanding of energy balance in non-equilibrium environments and the physical and chemical properties of gases in a new regime of energy states. Results will be presented for several super rotor species including carbon monoxide, carbon dioxide, and acetylene. Polarization-dependent measurements reveal the extent to which the super rotors maintain spatial orientation of high angular momentum states.

Excited state kinetics of anthracene-bridge-aniline intramolecular exciplexes

DEFF Research Database (Denmark)

Thyrhaug, Erling; Hammershøj, Peter; Kjær, Kasper Skov

2014-01-01

excited anthracene state (LE) and an excited state complex (exciplex, EP) in non-polar solvents. The kinetics of the excited state processes were established in decalin from the time-resolved emission, and was shown to be strongly influenced by an electron-transfer state (ET). For quantitative studies...

Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics

International Nuclear Information System (INIS)

Deyne, Andy Van Yperen-De; Pauwels, Ewald; Ghysels, An; Waroquier, Michel; Van Speybroeck, Veronique; Hemelsoet, Karen; De Meyer, Thierry; De Clerck, Karen

2014-01-01

A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed

Chemical modulation of electronic structure at the excited state

Science.gov (United States)

Li, F.; Song, C.; Gu, Y. D.; Saleem, M. S.; Pan, F.

2017-12-01

Spin-polarized electronic structures are the cornerstone of spintronics, and have thus attracted a significant amount of interest; in particular, researchers are looking into how to modulate the electronic structure to enable multifunctional spintronics applications, especially in half-metallic systems. However, the control of the spin polarization has only been predicted in limited two-dimensional systems with spin-polarized Dirac structures and is difficult to achieve experimentally. Here, we report the modulation of the electronic structure in the light-induced excited state in a typical half-metal, L a1 /2S r1 /2Mn O3 -δ . According to the spin-transport measurements, there appears a light-induced increase in magnetoresistance due to the enhanced spin scattering, which is closely associated with the excited spin polarization. Strikingly, the light-induced variation can be enhanced via alcohol processing and reduced by oxygen annealing. X-ray photoelectron spectroscopy measurements show that in the chemical process, a redox reaction occurs with a change in the valence of Mn. Furthermore, first-principles calculations reveal that the change in the valence of Mn alters the electronic structure and consequently modulates the spin polarization in the excited state. Our findings thus report a chemically tunable electronic structure, demonstrating interesting physics and the potential for multifunctional applications and ultrafast spintronics.

Acoustically levitated dancing drops: Self-excited oscillation to chaotic shedding

Science.gov (United States)

Lin, Po-Cheng; I, Lin

2016-02-01

We experimentally demonstrate self-excited oscillation and shedding of millimeter-sized water drops, acoustically levitated in a single-node standing waves cavity, by decreasing the steady acoustic wave intensity below a threshold. The perturbation of the acoustic field by drop motion is a possible source for providing an effective negative damping for sustaining the growing amplitude of the self-excited motion. Its further interplay with surface tension, drop inertia, gravity and acoustic intensities, select various self-excited modes for different size of drops and acoustic intensity. The large drop exhibits quasiperiodic motion from a vertical mode and a zonal mode with growing coupling, as oscillation amplitudes grow, until falling on the floor. For small drops, chaotic oscillations constituted by several broadened sectorial modes and corresponding zonal modes are self-excited. The growing oscillation amplitude leads to droplet shedding from the edges of highly stretched lobes, where surface tension no longer holds the rapid expanding flow.

Self-excited multi-scale skin vibrations probed by optical tracking micro-motions of tracers on arms

Science.gov (United States)

Chen, Wei-Chia; Chen, Hsiang-Ying; Chen, Yu-Sheng; Tian, Yong; I, Lin

2017-07-01

The self-excited multi-scale mechanical vibrations, their sources and their mutual coupling of different regions on the forearms of supine subjects, are experimentally investigated, using a simple noncontact method, optical video microscopy, which provides 1 μm and 25 ms spatiotemporal resolutions. It is found that, in proximal regions far from the radial artery, the vibrations are the global vibrations of the entire forearm excited by remote sources, propagating through the trunk and the limb. The spectrum is mainly composed of peaks of very low frequency motion (down to 0.05 Hz), low frequency respiration modes, and heartbeat induced modes (about 1 Hz and its harmonics), standing out of the spectrum floor exhibiting power law decay. The nonlinear mode-mode coupling leads to the cascaded modulations of higher frequency modes by lower frequency modes. The nearly identical waveforms without detectable phase delays for a pair of signals along or transverse to the meridian of regions far away from the artery rule out the detectable contribution from the propagation of Qi, some kind of collective excitation which more efficiently propagates along meridians, according to the Chinese medicine theory. Around the radial artery, in addition to the global vibration, the local vibration spectrum shows very slow breathing type vibration around 0.05 Hz, and the artery pulsation induced fundamental and higher harmonics with descending intensities up to the fifth harmonics, standing out of a flat spectrum floor. All the artery pulsation modes are also modulated by respiration and the very slow vibration.

Numerical simulations of convectively excited gravity waves

International Nuclear Information System (INIS)

Glatzmaier, G.A.

1983-01-01

Magneto-convection and gravity waves are numerically simulated with a nonlinear, three-dimensional, time-dependent model of a stratified, rotating, spherical fluid shell heated from below. A Solar-like reference state is specified while global velocity, magnetic field, and thermodynamic perturbations are computed from the anelastic magnetohydrodynamic equations. Convective overshooting from the upper (superadiabatic) part of the shell excites gravity waves in the lower (subadiabatic) part. Due to differential rotation and Coriolis forces, convective cell patterns propagate eastward with a latitudinally dependent phase velocity. The structure of the excited wave motions in the stable region is more time-dependent than that of the convective motions above. The magnetic field tends to be concentrated over giant-cell downdrafts in the convective zone but is affected very little by the wave motion in the stable region

Can Internal Conversion BE Controlled by Mode-Specific Vibrational Excitation in Polyatomic Molecules

Science.gov (United States)

Portnov, Alexander; Epshtein, Michael; Bar, Ilana

2017-06-01

Nonadiabatic processes, dominated by dynamic passage of reactive fluxes through conical intersections (CIs) are considered to be appealing means for manipulating reaction paths. One approach that is considered to be effective in controlling the course of dissociation processes is the selective excitation of vibrational modes containing a considerable component of motion. Here, we have chosen to study the predissociation of the model test molecule, methylamine and its deuterated isotopologues, excited to well-characterized quantum states on the first excited electronic state, S_{1}, by following the N-H(D) bond fission dynamics through sensitive H(D) photofragment probing. The branching ratios between slow and fast H(D) photofragments, the internal energies of their counter radical photofragments and the anisotropy parameters for fast H photofragments, confirm correlated anomalies for predissociation initiated from specific rovibronic states, reflecting the existence of a dynamic resonance in each molecule. This resonance strongly depends on the energy of the initially excited rovibronic states, the evolving vibrational mode on the repulsive S_{1} part during N-H(D) bond elongation, and the manipulated passage through the CI that leads to radicals excited with C-N-H(D) bending and preferential perpendicular bond breaking, relative to the photolyzing laser polarization, in molecules containing the NH_{2} group. The indicated resonance plays an important role in the bifurcation dynamics at the CI and can be foreseen to exist in other photoinitiated processes and to control their outcome.

Excitation methods for energy dispersive analysis

International Nuclear Information System (INIS)

Jaklevic, J.M.

1976-01-01

The rapid development in recent years of energy dispersive x-ray fluorescence analysis has been based primarily on improvements in semiconductor detector x-ray spectrometers. However, the whole analysis system performance is critically dependent on the availability of optimum methods of excitation for the characteristic x rays in specimens. A number of analysis facilities based on various methods of excitation have been developed over the past few years. A discussion is given of the features of various excitation methods including charged particles, monochromatic photons, and broad-energy band photons. The effects of the excitation method on background and sensitivity are discussed from both theoretical and experimental viewpoints. Recent developments such as pulsed excitation and polarized photons are also discussed

Polarization Nonlinear Optics of Quadratically Nonlinear Azopolymers

International Nuclear Information System (INIS)

Konorov, S.O.; Akimov, D.A.; Ivanov, A.A.; Petrov, A.N.; Alfimov, M.V.; Yakimanskii, A.V.; Smirnov, N.N.; Ivanova, V.N.; Kudryavtsev, V.V.; Podshivalov, A.A.; Sokolova, I.M.; Zheltikov, A.M.

2005-01-01

The polarization properties of second harmonic and sum-frequency signals generated by femtosecond laser pulses in films of polymers containing covalent groups of an azobenzothiazole chromophore polarized by an external electric field are investigated. It is shown that the methods of polarization nonlinear optics make it possible to determine the structure of oriented molecular dipoles and reveal important properties of the motion of collectivized πelectrons in organic molecules with strong optical nonlinearities. The polarization measurements show that the tensor of quadratic nonlinear optical susceptibility of chromophore fragments oriented by an external field in macromolecules of the noted azopolymers has a degenerate form. This is indicative of a predominantly one-dimensional character of motion of collectivized π electrons along an extended group of atoms in such molecules

Temporal evolution of atmosphere pressure plasma jets driven by microsecond pulses with positive and negative polarities

Science.gov (United States)

Shao, Tao; Yang, Wenjin; Zhang, Cheng; Fang, Zhi; Zhou, Yixiao; Schamiloglu, Edl

2014-09-01

Current-voltage characteristics, discharge images, and optical spectra of atmospheric pressure plasma jets (APPJs) are studied using a microsecond pulse length generator producing repetitive output pulses with different polarities. The experimental results show that the APPJs excited by the pulses with positive polarity have longer plume, faster propagation speed, higher power, and more excited species, such as \\text{N}2 , O, He, \\text{N}2+ , than that with the negatively excited APPJs. The images taken using an intensified charge-coupled device show that the APPJs excited by pulses with positive polarity are characterized by a bullet-like structure, while the APPJs excited by pulses with negative polarity are continuous. The propagation speed of the APPJs driven by a microsecond pulse length generator is about tens of km/s, which is similar to the APPJs driven by a kHz frequency sinusoidal voltage source. The analysis shows that the space charge accumulation effect plays an important role during the discharge. The transient enhanced electric field induced by the accumulated ions between the needle-like electrode and the nozzle in the APPJs excited by pulses with negative polarity enhances electron field emission from the cathode, which is illustrated by the bright line on the time-integrated images. This makes the shape of the APPJ excited using pulses with negative polarity different from the bullet-like shape of the APPJs excited by pulses with positive polarity.

Polarized electrons, trions, and nuclei in charged quantum dots

Science.gov (United States)

Bracker, A. S.; Tischler, J. G.; Korenev, V. L.; Gammon, D.

2003-07-01

We have investigated spin polarization in GaAs quantum dots. Excitons and trions are polarized directly by optical excitation and studied through polarization of photoluminescence. Electrons and nuclei are polarized indirectly through subsequent relaxation processes. Polarized electrons are identified by the Hanle effect for exciton and trion photoluminescence, while polarized nuclei are identified through the Overhauser effect in individual charged quantum dots.

Electrically small circularly polarized spherical antenna with air core

DEFF Research Database (Denmark)

Kim, O. S.

2013-01-01

An electrically small circularly polarized self-resonant spherical antenna with air core is presented. The antenna is a modified multiarm spherical helix exciting TM10 and TE10 spherical modes with equal radiated power, and thus yielding perfect circular polarization over the entire far......-field sphere (except the polar regions, where the radiation is low). The self-resonance is achieved by exciting higher-order TM modes, which provide the necessary electric stored energy in the near-field, while contributing negligibly to the far-field radiation of the antenna. The antenna has electrical size...

Observation of interface dependent spin polarized photocurrents in InAs/GaSb superlattice

Energy Technology Data Exchange (ETDEWEB)

Li, Yuan, E-mail: liyuan12@semi.ac.cn; Liu, Yu; Zhu, Laipan; Qin, Xudong; Wu, Qing; Huang, Wei; Chen, Yonghai, E-mail: yhchen@semi.ac.cn [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, 100083 Beijing (China); Niu, Zhichuan; Xiang, Wei; Hao, Hongyue [The State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, 100083 Beijing (China)

2015-05-11

In this letter, we investigated the spin polarized photocurrents excited by mid-infrared radiation and near-infrared radiation, respectively, in InAs/GaSb type II superlattices with different kinds of interfaces. By periodically varying the polarization state of the radiation, we analyzed Rashba-type and Dresselhaus-type spin polarized photocurrents, which present different features depending on the interface types and excitation conditions. Under mid-infrared excitation, the ratio of Rashba-type and Dresselhaus-type spin polarized photocurrents of the superlattice with InSb-like interface is obviously larger than that of the superlattice with GaAs-like interface, the ratio of the superlattice with alternate interface is in the middle. Whereas under near-infrared excitation, the ratios of the three superlattices are nearly the same. Further researches reveal the synactic effects of interface dependent strain and asymmetric interface potential on the spin splitting. Besides, the polarized Raman spectroscopies of these structures were also analyzed.

Observation of interface dependent spin polarized photocurrents in InAs/GaSb superlattice

International Nuclear Information System (INIS)

Li, Yuan; Liu, Yu; Zhu, Laipan; Qin, Xudong; Wu, Qing; Huang, Wei; Chen, Yonghai; Niu, Zhichuan; Xiang, Wei; Hao, Hongyue

2015-01-01

In this letter, we investigated the spin polarized photocurrents excited by mid-infrared radiation and near-infrared radiation, respectively, in InAs/GaSb type II superlattices with different kinds of interfaces. By periodically varying the polarization state of the radiation, we analyzed Rashba-type and Dresselhaus-type spin polarized photocurrents, which present different features depending on the interface types and excitation conditions. Under mid-infrared excitation, the ratio of Rashba-type and Dresselhaus-type spin polarized photocurrents of the superlattice with InSb-like interface is obviously larger than that of the superlattice with GaAs-like interface, the ratio of the superlattice with alternate interface is in the middle. Whereas under near-infrared excitation, the ratios of the three superlattices are nearly the same. Further researches reveal the synactic effects of interface dependent strain and asymmetric interface potential on the spin splitting. Besides, the polarized Raman spectroscopies of these structures were also analyzed

Anomalous Late Jurassic motion of the Pacific Plate with implications for true polar wander

Science.gov (United States)

Fu, Roger R.; Kent, Dennis V.

2018-05-01

True polar wander, or TPW, is the rotation of the entire mantle-crust system about an equatorial axis that results in a coherent velocity contribution for all lithospheric plates. One of the most recent candidate TPW events consists of a ∼30° rotation during Late Jurassic time (160-145 Ma). However, existing paleomagnetic documentation of this event derives exclusively from continents, which compose less than 50% of the Earth's surface area and may not reflect motion of the entire mantle-crust system. Additional paleopositional information from the Pacific Basin would significantly enhance coverage of the Earth's surface and allow more rigorous testing for the occurrence of TPW. We perform paleomagnetic analyses on core samples from Ocean Drilling Program (ODP) Site 801B, which were taken from the oldest available Pacific crust, to determine its paleolatitude during the Late Jurassic and Early Cretaceous (167-133 Ma). We find that the Pacific Plate underwent a steady southward drift of 0.49°-0.74° My-1 except for an interval between Kimmeridgian and Tithonian time (157-147 Ma), during which it underwent northward motion at 1.45° ± 0.76° My-1 (1σ). This trajectory indicates that the plates of the Pacific Basin participated in the same large-amplitude (∼30°) rotation as continental lithosphere in the 160-145 Ma interval. Such coherent motion of a large majority of the Earth's surface strongly supports the occurrence of TPW, suggesting that a combination of subducting slabs and rising mantle plumes was sufficient to significantly perturb the Earth's inertia tensor in the Late Jurassic.

Polarization of fast neutrons in VVR-M reactor

International Nuclear Information System (INIS)

Garusov, E.A.; Lifshits, E.P.; Petrov, Yu.V.

1987-01-01

Neutron polarization in the reactor leads to circular polarization of γ quanta emitted both in radiational capture of neutrons and in the transition of nuclei excited as a result of inelastic scattering to the ground state. This may be used to determine the polarization of reactor neutrons. The circular polarization of γ quanta at light-water and graphite targets at the center of the active zone of the VVR-M reactor at the B.P. Konstantinov Leningrad Institute of Nuclear Physics was recently measured. A simplified experimental scheme is shown. Fast neutrons leaving the active zone of the reactor were excited in the inelastic scattering at the target nuclei. The polarization of the γ quanta emitted by nuclei in transitions to the ground state was measured by a polarimeter positioned above the active zone. The reason for the circular polarization of γ quanta may also be nonconservation of P parity on account of weak interaction in the capture of a neutron by hydrogen

Efficient primary and parametric resonance excitation of bistable resonators

KAUST Repository

Ramini, Abdallah; Alcheikh, Nouha; Ilyas, Saad; Younis, Mohammad I.

2016-01-01

efficient and requires less power for primary resonance excitation. Moreover, unlike the classical method where the structure is vulnerable to the dynamic pull-in instability, the axial excitation technique can provide large amplitude motion while protecting

Stochastic ground motion simulation

Science.gov (United States)

Rezaeian, Sanaz; Xiaodan, Sun; Beer, Michael; Kougioumtzoglou, Ioannis A.; Patelli, Edoardo; Siu-Kui Au, Ivan

2014-01-01

Strong earthquake ground motion records are fundamental in engineering applications. Ground motion time series are used in response-history dynamic analysis of structural or geotechnical systems. In such analysis, the validity of predicted responses depends on the validity of the input excitations. Ground motion records are also used to develop ground motion prediction equations(GMPEs) for intensity measures such as spectral accelerations that are used in response-spectrum dynamic analysis. Despite the thousands of available strong ground motion records, there remains a shortage of records for large-magnitude earthquakes at short distances or in specific regions, as well as records that sample specific combinations of source, path, and site characteristics.

Contrast configuration influences grouping in apparent motion.

Science.gov (United States)

Ma-Wyatt, Anna; Clifford, Colin W G; Wenderoth, Peter

2005-01-01

We investigated whether the same principles that influence grouping in static displays also influence grouping in apparent motion. Using the Ternus display, we found that the proportion of group motion reports was influenced by changes in contrast configuration. Subjects made judgments of completion of these same configurations in a static display. Generally, contrast configurations that induced a high proportion of group motion responses were judged as more 'complete' in static displays. Using a stereo display, we then tested whether stereo information and T-junction information were critical for this increase in group motion. Perceived grouping was consistently higher for same contrast polarity configurations than for opposite contrast polarity configurations, regardless of the presence of stereo information or explicit T-junctions. Thus, while grouping in static and moving displays showed a similar dependence on contrast configuration, motion grouping showed little dependence on stereo or T-junction information.

Dynamics of Solid Body in Magnetic Suspension under Periodic Excitation

Directory of Open Access Journals (Sweden)

A. M. Gouskov

2017-01-01

Full Text Available The article studies dynamics of ferromagnetic body in hybrid magnetic suspension (HMS. The body is supposed to have one degree of freedom and a nonlinear magnetic force dependence on the current and displacement. The magnetic force induced in the HMS is divided into a passive component and an active one. Specifying the law of current variation in the coil allows us to generate nonlinear oscillations under electromagnet action. To provide periodic excitation the appropriate law of the current variation in the electromagnet coil is proposed. The mathematical model includes external periodic step-excitation. The equation of motion is formed. The scales of similarity are highlighted in the system, and the equation of motion is reduced to dimensionless form.The motion dynamics is studied numerically. The relaxation method was used to determine the periodic motions at different values of dimensionless frequency of the electromagnet excitation as well as to estimate the influence of other dimensionless parameters on the system dynamics. The amplitude-frequency curve analysis allows us to come to conclusion that the nature of system nonlinearity is rigid. Adding the external periodic step-excitation leads to the qualitative change in the nature of movement. This points to the occurrence of bifurcation.

Electron scattering by CO2: Elastic scattering, rotational excitation, and excitation of the asymmetric stretch at 10 eV impact energy

International Nuclear Information System (INIS)

Thirumalai, D.; Onda, K.; Truhlar, D.G.

1981-01-01

Coupled-channels calculations based on an effective potential are presented for electron scattering by CO 2 at 10 eV impact energy. The processes studied are pure elastic scattering, rotational excitation, and vibrational excitation of the asymmetric stretch; the vibrational excitation is always accompanied by rotational excitation. The quantities calculated are differential, partial, integral, and momentum transfer cross sections, both state to state and summed over final rotational states for a given final vibrational level. The effective potential is based on the INDOX2/1s method for the static and polarization potentials and the semiclassical exchange approximation for the exchange potential. There are no empirical parameters. The present calculations are compared to experiment and to previous calculations where available, and we also perform calculations with an altered polarization potential to further elucidate the reasons for the differences from one of the previous calculations. The agreement of the present results with the experimental rotationally summed, vibrationally inelastic differential cross section is excellent

Polarized wiggler for NSLS x-ray ring design considerations

International Nuclear Information System (INIS)

Friedman, A.; Krinsky, S.; Blum, E.

1992-03-01

We examine the properties of an elliptically polarized wiggler that will generate circularly polarized photons with energy spectrum of 3--12 KeV. The vertical wiggler magnetic field is produced by permanent magnets while the horizontal wiggler field is generated by electric coils capable of AC excitation. The radiation parameters of the wiggler are presented, including photon flux, circular and linear polarization and spectrum. These parameters are compared to the synchrotron radiation from a bending magnet. Numerical values are calculated for radiation from the wiggler and bending magnet for the NSLS X-ray ring parameters. A conceptual design for such a wiggler is discussed and several different alternatives are analyzed. We consider AC excitation of the wiggler to produce the time modulation of the elliptic polarization, and also to produce time modulated linearly polarized radiation

Circular polarization memory in single Quantum Dots

International Nuclear Information System (INIS)

Khatsevich, S.; Poem, E.; Benny, Y.; Marderfeld, I.; Gershoni, D.; Badolato, A.; Petroff, P. M.

2010-01-01

Under quasi-resonant circularly polarized optical excitation, charged quantum dots may emit polarized light. We measured various transitions with either positive, negative or no circular-polarization memory. We explain these observations and quantitatively calculate the polarization spectrum. Our model use the full configuration-interaction method, including the electron-hole exchange interaction, for calculating the quantum dot's confined many-carrier states, along with one assumption regarding the spin relaxation of photoexcited carriers: Electrons maintain their initial spin polarization, while holes do not.

Motion of particles of non-zero rest masses exterior to ...

African Journals Online (AJOL)

In this article, we extend the metric tensor exterior to astrophysically real or imaginary spherical distributions of mass whose tensor field varies with polar angle only; to derive equations of motion for test particles in this field. The time, radial, polar and azimuthal equations of motion for particles of non-zero rest masses moving ...

A polarized alkali ion source

International Nuclear Information System (INIS)

Boettger, R.; Tungate, G.; Bauer, B.; Egelhof, P.; Moebius, K.H.; Steffens, E.

1978-01-01

The beam foil technique has been applied to detect nuclear vector polarization of a 10 keV 23 Na + beam. The result was about 70% of the atomic beam polarization thus limiting the depolarization by the surface ionizer to at most 30%. In a Coulomb excitation experiment with a tensor polarized 42 MeV 23 Na 7+ beam an effect of 0.011 +- 0.003 was measured yielding a value of t 20 approx. 0.04 for the beam polarization. The depolarization during the acceleration process can be estimated to be about 0.8. (orig.) [de

Measuring fluorescence polarization with a dichrometer.

Science.gov (United States)

Sutherland, John C

2017-09-01

A method for obtaining fluorescence polarization data from an instrument designed to measure circular and linear dichroism is compared with a previously reported approach. The new method places a polarizer between the sample and a detector mounted perpendicular to the direction of the incident beam and results in determination of the fluorescence polarization ratio, whereas the previous method does not use a polarizer and yields the fluorescence anisotropy. A similar analysis with the detector located axially with the excitation beam demonstrates that there is no frequency modulated signal due to fluorescence polarization in the absence of a polarizer. Copyright © 2017. Published by Elsevier Inc.

Polarized neutron inelastic scattering experiments on spin dynamics

International Nuclear Information System (INIS)

Kakurai, Kazuhisa

2016-01-01

The principles of polarized neutron scattering are introduced and examples of polarized neutron inelastic scattering experiments on spin dynamics investigation are presented. These examples should demonstrate the importance of the polarized neutron utilization for the investigation of non-trivial magnetic ground and excited states in frustrated and low dimensional quantum spin systems. (author)

Polarization-Insensitive Surface Plasmon Polarization Electro-Absorption Modulator Based on Epsilon-Near-Zero Indium Tin Oxide

Science.gov (United States)

Jin, Lin; Wen, Long; Liang, Li; Chen, Qin; Sun, Yunfei

2018-02-01

CMOS-compatible plasmonic modulators operating at the telecom wavelength are significant for a variety of on-chip applications. Relying on the manipulation of the transverse magnetic (TM) mode excited on the metal-dielectric interface, most of the previous demonstrations are designed to response only for specific polarization state. In this case, it will lead to a high polarization dependent loss, when the polarization-sensitive modulator integrates to a fiber with random polarization state. Herein, we propose a plasmonic modulator utilizing a metal-oxide indium tin oxide (ITO) wrapped around the silicon waveguide and investigate its optical modulation ability for both the vertical and horizontal polarized guiding light by tuning electro-absorption of ITO with the field-induced carrier injection. The electrically biased modulator with electron accumulated at the ITO/oxide interface allows for epsilon-near-zero (ENZ) mode to be excited at the top or lateral portion of the interface depending on the polarization state of the guiding light. Because of the high localized feature of ENZ mode, efficient electro-absorption can be achieved under the "OFF" state of the device, thus leading to large extinction ratio (ER) for both polarizations in our proposed modulator. Further, the polarization-insensitive modulation is realized by properly tailoring the thickness of oxide in two different stacking directions and therefore matching the ER values for device operating at vertical and horizontal polarized modes. For the optimized geometry configuration, the difference between the ER values of two polarization modes, i.e., the ΔER, as small as 0.01 dB/μm is demonstrated and, simultaneously with coupling efficiency above 74%, is obtained for both polarizations at a wavelength of 1.55 μm. The proposed plasmonic-combined modulator has a potential application in guiding and processing of light from a fiber with a random polarization state.

Molecular alignment and orientation in short pulse laser fields

DEFF Research Database (Denmark)

Henriksen, Niels Engholm

1999-01-01

An analytical expression for the propagator associated with impulsive excitation is derived based on the Magnus expansion. We apply this expression to the excitation of angular motion out of a rotational eigenstate for a linear polar molecule in a plane polarized electromagnetic field. We show...

High-energy polarized proton beams a modern view

CERN Document Server

Hoffstaetter, Georg Heinz

2006-01-01

This monograph begins with a review of the basic equations of spin motion in particle accelerators. It then reviews how polarized protons can be accelerated to several tens of GeV using as examples the preaccelerators of HERA, a 6.3 km long cyclic accelerator at DESY / Hamburg. Such techniques have already been used at the AGS of BNL / New York, to accelerate polarized protons to 25 GeV. But for acceleration to energies of several hundred GeV as in RHIC, TEVATRON, HERA, LHC, or a VLHC, new problems can occur which can lead to a significantly diminished beam polarization. For these high energies, it is necessary to look in more detail at the spin motion, and for that the invariant spin field has proved to be a useful tool. This is already widely used for the description of high-energy electron beams that become polarized by the emission of spin-flip synchrotron radiation. It is shown that this field gives rise to an adiabatic invariant of spin-orbit motion and that it defines the maximum time average polarizat...

Polarization dependent effects in photo-fragmentation dynamics of free molecules

International Nuclear Information System (INIS)

Mocellin, A.; Marinho, R.R.T.; Coutinho, L.H.; Burmeister, F.; Wiesner, K.; Naves de Brito, A.

2003-01-01

We present multicoincidence spectra of nitrogen, formic acid and methyl methacrylate. We demonstrate how to probe the local symmetry of molecular orbitals from molecules core excited with linearly polarized synchrotron radiation. The intensity distribution of the photoelectron photo-ion photo-ion coincidence (PEPIPICO) spectrum reflects the selectivity and localization of core excitation by polarized light. By simulating the spectra the angular dependence of the fragmentation is determined

Polarization dependent effects in photo-fragmentation dynamics of free molecules

Energy Technology Data Exchange (ETDEWEB)

Mocellin, A.; Marinho, R.R.T.; Coutinho, L.H.; Burmeister, F.; Wiesner, K.; Naves de Brito, A

2003-04-01

We present multicoincidence spectra of nitrogen, formic acid and methyl methacrylate. We demonstrate how to probe the local symmetry of molecular orbitals from molecules core excited with linearly polarized synchrotron radiation. The intensity distribution of the photoelectron photo-ion photo-ion coincidence (PEPIPICO) spectrum reflects the selectivity and localization of core excitation by polarized light. By simulating the spectra the angular dependence of the fragmentation is determined.

A disordered polaron model for polarized fluorescence excitation spectra of LH1 and LH2 bacteriochlorophyll antenna aggregates

International Nuclear Information System (INIS)

Trinkunas, Gediminas; Freiberg, Arvi

2006-01-01

Excitonic polarons in antenna complexes are subject to static lattice disorder. A model has been developed to analyze polarized fluorescence excitation spectra of circular light-harvesting complexes from purple photosynthetic bacteria containing bacteriochlorophyll as the main photoactive pigment that includes both diagonal (energetic) and off-diagonal (structural) disorders. Essential differences of disorder realizations seem to exist between the core LH1 and peripheral LH2 complexes from the bacterium Rhodobacter sphaeroides. The disorder in LH1 appears to be dominated by the structural disorder, while that in LH2, by energetic one. These differences may be due to relatively bigger size of the LH1 complex and, consequently, with its enhanced structural flexibility

Excitation of high density surface plasmon polariton vortex array

Science.gov (United States)

Kuo, Chun-Fu; Chu, Shu-Chun

2018-06-01

This study proposes a method to excite surface plasmon polariton (SPP) vortex array of high spatial density on metal/air interface. A doughnut vector beam was incident at four rectangularly arranged slits to excite SPP vortex array. The doughnut vector beam used in this study has the same field intensity distribution as the regular doughnut laser mode, TEM01* mode, but a different polarization distribution. The SPP vortex array is achieved through the matching of both polarization state and phase state of the incident doughnut vector beam with the four slits. The SPP field distribution excited in this study contains stable array-distributed time-varying optical vortices. Theoretical derivation, analytical calculation and numerical simulation were used to discuss the characteristics of the induced SPP vortex array. The period of the SPP vortex array induced by the proposed method had only half SPPs wavelength. In addition, the vortex number in an excited SPP vortex array can be increased by enlarging the structure.

Dual-polarized feed antenna apparatus and method of use

Science.gov (United States)

Sarehraz, Mohammed (Inventor); Buckle, Kenneth A. (Inventor); Stefanakos, Elias (Inventor); Weller, Thomas (Inventor); Goswami, D. Yogi (Inventor)

2009-01-01

An antenna apparatus and method for the interception of randomly polarized electromagnetic waves utilizing a dual polarized antenna which is excited through a cross-slot aperture using two well-isolated orthogonal feeds.

A scalable piezoelectric impulse-excited energy harvester for human body excitation

International Nuclear Information System (INIS)

Pillatsch, P; Yeatman, E M; Holmes, A S

2012-01-01

Harvesting energy from low-frequency and non-harmonic excitations typical of human motion presents specific challenges. While resonant devices do have an advantage in environments where the excitation frequency is constant, and while they can make use of the entire proof mass travel range in the case of excitation amplitudes that are smaller than the internal displacement limit, they are not suitable for body applications since the frequencies are random and the amplitudes tend to be larger than the device size. In this paper a piezoelectric, impulse-excited approach is presented. A cylindrical proof mass actuates an array of piezoelectric bi-morph beams through magnetic attraction. After the initial excitation these transducers are left to vibrate at their natural frequency. This increases the operational frequency range as well as the electromechanical coupling. The principle of impulse excitation is discussed and a centimetre-scale functional model is introduced as a proof of concept. The obtained data show the influence of varying the frequency, acceleration and proof mass. Finally, a commercially available integrated circuit for voltage regulation is tested. At a frequency of 2 Hz and an acceleration of 2.7 m s −2 a maximal power output of 2.1 mW was achieved. (paper)

Physics with polarized beams above GeV region

International Nuclear Information System (INIS)

Yokosawa, A.

1980-01-01

During the past several years many exciting and unexpected results have been observed in experiments with polarized beams. Those results are reviewed briefly. A new polarized beam line up to 600 GeV/c is also discussed. 4 figures

Seismic structural response analysis for multiple support excitation

International Nuclear Information System (INIS)

Shaw, D.E.

1975-01-01

In the seismic analysis of nuclear power plant equipment such as piping systems situations often arise in which piping systems span between adjacent structures or between different elevations in the same structure. Owing to the differences in the seismic time history response of different structures or different elevations of the same structure, the input support motion will differ for different supports. The concept of a frequency dependent participation factor and rotational response spectra accounting for phase differences between support excitations is developed by using classical equations of motion to formulate the seismic response of a structure subjected to multiple support excitation. The essence of the method lies in describing the seismic excitation of a multiply excited structure in terms of translational and rotational spectra used at every support and a frequency dependent spatial distribution function derived from the phase relationships of the different support time histories. In this manner it is shown that frequency dependent participation factors can be derived from the frequency dependent distribution functions. Examples are shown and discussed relative to closed form solutions and the state-of-the-art techniques presently being used for the solution of problems of multiply excited structures

MEASUREMENT OF POLARIZATION OBSERVABLES IN VECTOR MESON PHOTOPRODUCTION USING A TRANSVERSELY-POLARIZED FROZEN-SPIN TARGET AND POLARIZED PHOTONS AT CLAS, JEFFERSON LAB

Energy Technology Data Exchange (ETDEWEB)

Roy, Priyashree [Florida State Univ., Tallahassee, FL (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

2016-11-30

The study of baryon resonances provides a deeper understanding of the strong interaction because the dynamics and relevant degrees of freedom hidden within them are re ected by the properties of the excited states of baryons. Higher-lying excited states at and above 1.7 GeV/c2 are generally predicted to have strong couplings to final states involving a heavier meson, e. g. one of the vector mesons, ρ, ω φ, as compared to a lighter pseudoscalar meson, e. g. π and η. Decays to the ππΝ final states via πΔ also become more important through the population of intermediate resonances. We observe that nature invests in mass rather than momentum. The excited states of the nucleon are usually found as broadly overlapping resonances which may decay into a multitude of final states involving mesons and baryons. Polarization observables make it possible to isolate single resonance contributions from other interference terms. The CLAS g9 (FROST) experiment, as part of the N* spectroscopy program at Je?erson Laboratory, accumulated photoproduction data using circularly- & linearly-polarized photons incident on a transversely-polarized butanol target (g9b experiment) in the photon energy range 0:3-2:4 GeV & 0:7-2:1 GeV, respectively. In this work, the analysis of reactions and polarization observables which involve two charged pions, either in the fully exclusive reaction γρ -> ρπ+π- or in the semi-exclusive reaction with a missing neutral pion, γρ -> ρπ+π-(π0) will be presented. For the reaction ρπ+π-, eight polarization observables (Is, Ic, Px, Py, Psx; y, Pcx; y) have been extracted. The high statistics data rendered it possible to extract these observables in three dimensions. All of them are first-time measurements. The fairly good agreement of Is, Ic obtained from this analysis with the experimental results from a previous CLAS experiment provides support for the first-time measurements. For the reaction γρ -> ρω -> ρπ+π(π0, five polarization

Acceleration of polarized proton beams

International Nuclear Information System (INIS)

Roser, T.

1998-01-01

The acceleration of polarized beams in circular accelerators is complicated by the numerous depolarizing spin resonances. Using a partial Siberian snake and a rf dipole that ensure stable adiabatic spin motion during acceleration has made it possible to accelerate polarized protons to 25 GeV at the Brookhaven AGS. Full Siberian snakes are being developed for RHIC to make the acceleration of polarized protons to 250 GeV possible. A similar scheme is being studied for the 800 GeV HERA proton accelerator

Geophysical excitation of the chandler wobble revisited

OpenAIRE

A. Brzezinski; Henryk Dobslaw; Robert Dill; Maik Thomas

2012-01-01

The 14-month Chandler wobble is a free motion of the pole excited by geophysical processes. Several recent studies demonstrated that the combination of atmospheric and oceanic excitations contains enough power at the Chandler frequency and is significantly coherent with the observed free wobble. This paper is an extension of earlier studies by Brzeziński and Nastula (Adv Space Res 30:195–200, 2002), Brzeziński et al. (Oceanic excitation of the Chandler wobble using a 50-year time series of oc...

Plasmonic rack-and-pinion gear with chiral metasurface

Science.gov (United States)

Gorodetski, Yuri; Karabchevsky, Alina

2016-04-01

The effect of circularly polarized beaming excited by traveling surface plasmons, via chiral metasurface is experimentally studied. Here we show that the propagation direction of the plasmonic wave, evanescently excited on the thin gold film affects the handedness of the scattered beam polarization. Nanostructured metasurface leads to excitation of localized plasmonic modes whose relative spatial orientation induces overall spin-orbit interaction. This effect is analogical to the rack-and-pinion gear: the rotational motion into the linear motion converter. From the practical point of view, the observed effect can be utilized in integrated optical circuits for communication systems, cyber security and sensing.

Long-lasting increase in axonal excitability after epidurally applied DC.

Science.gov (United States)

Jankowska, Elzbieta; Kaczmarek, Dominik; Bolzoni, Francesco; Hammar, Ingela

2017-08-01

Effects of direct current (DC) on nerve fibers have primarily been investigated during or just after DC application. However, locally applied cathodal DC was recently demonstrated to increase the excitability of intraspinal preterminal axonal branches for >1 h. The aim of this study was therefore to investigate whether DC evokes a similarly long-lasting increase in the excitability of myelinated axons within the dorsal columns. The excitability of dorsal column fibers stimulated epidurally was monitored by recording compound action potentials in peripheral nerves in acute experiments in deeply anesthetized rats. The results show that 1 ) cathodal polarization (0.8-1.0 µA) results in a severalfold increase in the number of epidurally activated fibers and 2 ) the increase in the excitability appears within seconds, 3 ) lasts for >1 h, and 4 ) is activity independent, as it does not require fiber stimulation during the polarization. These features demonstrate an unexplored form of plasticity of myelinated fibers and indicate the conditions under which it develops. They also suggest that therapeutic effects of epidural stimulation may be significantly enhanced if it is combined with DC polarization. In particular, by using DC to increase the number of fibers activated by low-intensity epidural stimuli, the low clinical tolerance to higher stimulus intensities might be overcome. The activity independence of long-lasting DC effects would also allow the use of only brief periods of DC polarization preceding epidural stimulation to increase the effect. NEW & NOTEWORTHY The study indicates a new form of plasticity of myelinated fibers. The differences in time course of DC-evoked increases in the excitability of myelinated nerve fibers in the dorsal columns and in preterminal axonal branches suggest that distinct mechanisms are involved in them. The results show that combining epidural stimulation and transspinal DC polarization may dramatically improve their outcome and

High-Frequency Ground-Motion Parameters from Weak-Motion Data in the Sicily Channel and Surrounding Regions

Science.gov (United States)

D'Amico, Sebastiano; Akinci, Aybige; Pischiutta, Marta

2018-03-01

In this paper we characterize the high frequency (1.0 - 10 Hz) seismic wave crustal attenuation and the source excitation in the Sicily Channel and surrounding regions using background seismicity from weak-motion database. The data set includes 15995 waveforms related to earthquakes having local magnitude ranging from 2.0 to 4.5 recorded between 2006 and 2012. The observed and predicted ground motions form the weak-motion data are evaluated in several narrow frequency bands from 0.25 to 20.0 Hz. The filtered observed peaks are regressed to specify a proper functional form for the regional attenuation, excitation and site specific term separately. The results are then used to calibrate effective theoretical attenuation and source excitation models using the Random Vibration Theory (RVT). In the log-log domain, the regional seismic wave attenuation and the geometrical spreading coefficient are modeled together. The geometrical spreading coefficient, g (r), modeled with a bilinear piecewise functional form and given as g (r) ∝ r-1.0 for the short distances (r selected reference distance with a magnitude independent roll-off spectral parameter, κ 0.04 s and with a Brune stress drop parameter increasing with moment magnitude, from Δσ = 2 MPa for Mw = 2.0 to Δσ = 13 MPa for Mw = 4.5. For events M≤4.5 (being Mwmax = 4.5 available in the dataset) the stress parameters are obtained by correlating the empirical/excitation source spectra with the Brune spectral model as function of magnitude. For the larger magnitudes (Mw>4.5) outside the range available in the calibration dataset where we do not have recorded data, we extrapolate our results through the calibration of the stress parameters of the Brune source spectrum over the Bindi et al. (2011) ground motion prediction equation (GMPE) selected as a reference model (hereafter also ITA10).

Quantized motion of trapped ions

International Nuclear Information System (INIS)

Steinbach, J.

1999-01-01

This thesis is concerned with a theoretical and numerical study of the preparation and coherent manipulation of quantum states in the external and internal degrees of freedom of trapped ions. In its first part, this thesis proposes and investigates schemes for generating several nonclassical states for the quantized vibrational motion of a trapped ion. Based on dark state preparation specific laser excitation configurations are presented which, given appropriately chosen initial states, realize the desired motional states in the steady-state, indicated by the cessation of the fluorescence emitted by the ion. The focus is on the SU(1,1) intelligent states in both their single- and two-mode realization, corresponding to one- and two-dimensional motion of the ion. The presented schemes are also studied numerically using a Monte-Carlo state-vector method. The second part of the thesis describes how two vibrational degrees of freedom of a single trapped ion can be coupled through the action of suitably chosen laser excitation. Concentrating on a two-dimensional ion trap with dissimilar vibrational frequencies a variety of quantized two-mode couplings are derived. The focus is on a linear coupling that takes excitations from one mode to another. It is demonstrated how this can result in a state rotation, in which it is possible to coherently transfer the motional state of the ion between orthogonal directions without prior knowledge of that motional state. The third part of this thesis presents a new efficient method for generating maximally entangled internal states of a collection of trapped ions. The method is deterministic and independent of the number of ions in the trap. As the essential element of the scheme a mechanism for the realization of a controlled NOT operation that can operate on multiple ions is proposed. The potential application of the scheme for high-precision frequency standards is explored. (author)

Theoretical and Experimental Study on Synchronization of the Two Homodromy Exciters in a Non-Resonant Vibrating System

Directory of Open Access Journals (Sweden)

Xue-Liang Zhang

2013-01-01

Full Text Available In this paper we give some theoretical analyses and experimental results on synchronization of the two non-identical exciters. Using the average method of modified small parameters, the dimensionless coupling equation of the two exciters is deduced. The synchronization criterion for the two exciters is derived as the torque of frequency capture being equal to or greater than the absolute value of difference between the residual electromagnetic torques of the two motors. The stability criterion of synchronous state is verified to satisfy the Routh-Hurwitz criterion. The regions of implementing synchronization and that of stability of phase difference for the two exciters are manifested by numeric method. Synchronization of the two exciters stems from the coupling dynamic characteristic of the vibrating system having selecting motion, especially, under the condition that the parameters of system are complete symmetry, the torque of frequency capture stemming from the circular motion of the rigid frame drives the phase difference to approach PI and carry out the swing of the rigid frame; that from the swing of the rigid frame forces the phase difference to near zero and achieve the circular motion of the rigid frame. In the steady state, the motion of rigid frame will be one of three types: pure swing, pure circular motion, swing and circular motion coexistence. The numeric and experiment results derived thereof show that the two exciters can operate synchronously as long as the structural parameters of system satisfy the criterion of stability in the regions of frequency capture. In engineering, the distance between the centroid of the rigid frame and the rotational centre of exciter should be as far as possible. Only in this way, can the elliptical motion of system required in engineering be realized.

Wobbling motion in high spin states

International Nuclear Information System (INIS)

Onishi, Naoki

1982-01-01

By generalizing the cranking model, interwoven motions of collective and non-collective rotation of nuclei are treated as three dimensional non-uniform rotations including precession and wobbling. Classical trajectories are obtained for the + j vector + = 30 h/2π sphere. A method of quantization for wobbling motions is discussed and is applied to estimate excitation energies. (author)

Wavelength Dependence of the Polarization Singularities in a Two-Mode Optical Fiber

Directory of Open Access Journals (Sweden)

V. V. G. Krishna Inavalli

2012-01-01

Full Text Available We present here an experimental demonstration of the wavelength dependence of the polarization singularities due to linear combination of the vector modes excited directly in a two-mode optical fiber. The coherent superposition of the vector modes excited by linearly polarized Gaussian beam as offset skew rays propagated in a helical path inside the fiber results in the generation of phase singular beams with edge dislocation in the fiber output. The polarization character of these beams is found to change dramatically with wavelength—from left-handed elliptically polarized edge dislocation to right-handed elliptically polarized edge-dislocation through disclinations. The measured behaviour is understood as being due to intermodal dispersion of the polarization corrections to the propagating vector modes, as the wavelength of the input beam is scanned.

Projectile Motion Hoop Challenge

Science.gov (United States)

Jordan, Connor; Dunn, Amy; Armstrong, Zachary; Adams, Wendy K.

2018-04-01

Projectile motion is a common phenomenon that is used in introductory physics courses to help students understand motion in two dimensions. Authors have shared a range of ideas for teaching this concept and the associated kinematics in The Physics Teacher; however, the "Hoop Challenge" is a new setup not before described in TPT. In this article an experiment is illustrated to explore projectile motion in a fun and challenging manner that has been used with both high school and university students. With a few simple materials, students have a vested interest in being able to calculate the height of the projectile at a given distance from its launch site. They also have an exciting visual demonstration of projectile motion when the lab is over.

Proton polarizing system with Ar-ion laser for p-vector-RI scattering experiments

International Nuclear Information System (INIS)

Wakui, T.; Hatano, M.; Sakai, H.; Uesaka, T.; Tamii, A.

2005-01-01

A proton polarizing system for use in scattering experiments with radioactive isotope beams is described. Protons in a naphthalene crystal doped with pentacene are polarized in a magnetic field of 0.3T at 100K by transferring a large population difference among the photo-excited triplet states of pentacene to the hydrogen nuclei. An Ar-ion laser, which demands minimal maintenance during scattering experiments, is employed to excite the pentacene molecules. A proton polarization of 37% is obtained

Dynamic behavior of three-dimensional composite beam under flapwise excitation

Energy Technology Data Exchange (ETDEWEB)

Eftekhari, Mojtaba [Dept. of Mechanical Engineering, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of)

2016-08-15

In this paper, dynamic response of a symmetrically laminated composite beam is studied under harmonic base excitation. The base is subjected to flapwise excitation tuned to the primary resonance in the presence of 2:1 internal resonance between the out-of-plane bending motion and the in-plane bending and torsional motions. In literature, modified modulation equations of composite beam have been derived and the stability of fixed points has been investigated in frequency and forced responses. However, post-critical behavior of the modulation equations is studied in this study. In bifurcation diagrams sketched near primary and internal resonances, it appears that detuning the flapwise excitation amplitude causes phenomena like jumps, period doubling, multi and quasi-periodic solutions to occur.

Interferometric polarization control

International Nuclear Information System (INIS)

Chuss, David T.; Wollack, Edward J.; Moseley, S. Harvey; Novak, Giles

2006-01-01

We develop the Jones and Mueller matrices for structures that allow control of the path length difference between two linear orthogonal polarizations and consider the effect of placing multiple devices in series. Specifically, we find that full polarization modulation (measurement of Stokes Q, U, and V) can be achieved by placing two such modulators in series if the relative angles of the beam-splitting grids with respect to the analyzer orientation are appropriately chosen. Such a device has several potential advantages over a spinning wave plate modulator for measuring astronomical polarization in the far infrared through millimeter: (i) The use of small, linear motions eliminates the need for cryogenic rotational bearings; (ii) the phase flexibility allows measurement of circular as well as linear polarization; and (iii) this architecture allows for both multiwavelength and broadband modulation. We also present initial laboratory results

Excited baryon program at the Bonn electron stretcher accelerator ELSA

International Nuclear Information System (INIS)

Menze, D.

1989-01-01

The Bonn electron stretcher accelerator ELSA is the first of a new generation of continuous beam machines in the GeV region. It is qualified for experiments with tagged photons and with polarized electrons on polarized nucleons to investigate the electromagnetic properties of excited baryon resonances

Past lessons and future importance of polarization

International Nuclear Information System (INIS)

Lipkin, H.J.

1980-01-01

Polarization and spin effects have traditionally brought surprises to physicists particularly to those who thought that such effects were unimportant. In hadron physics, large unexplained effects keep turning up and are still unresolved puzzles. A good measurement of the uninteresting beta ray polarization could have discovered parity nonconservation many years before its prediction by Lee and Yang. Nobody knows whether there are further exciting discoveries of this kind waiting for polarization experiments

Atomic Models for Motional Stark Effects Diagnostics

Energy Technology Data Exchange (ETDEWEB)

Gu, M F; Holcomb, C; Jayakuma, J; Allen, S; Pablant, N A; Burrell, K

2007-07-26

We present detailed atomic physics models for motional Stark effects (MSE) diagnostic on magnetic fusion devices. Excitation and ionization cross sections of the hydrogen or deuterium beam traveling in a magnetic field in collisions with electrons, ions, and neutral gas are calculated in the first Born approximation. The density matrices and polarization states of individual Stark-Zeeman components of the Balmer {alpha} line are obtained for both beam into plasma and beam into gas models. A detailed comparison of the model calculations and the MSE polarimetry and spectral intensity measurements obtained at the DIII-D tokamak is carried out. Although our beam into gas models provide a qualitative explanation for the larger {pi}/{sigma} intensity ratios and represent significant improvements over the statistical population models, empirical adjustment factors ranging from 1.0-2.0 must still be applied to individual line intensities to bring the calculations into full agreement with the observations. Nevertheless, we demonstrate that beam into gas measurements can be used successfully as calibration procedures for measuring the magnetic pitch angle through {pi}/{sigma} intensity ratios. The analyses of the filter-scan polarization spectra from the DIII-D MSE polarimetry system indicate unknown channel and time dependent light contaminations in the beam into gas measurements. Such contaminations may be the main reason for the failure of beam into gas calibration on MSE polarimetry systems.

Autoresonant Excitation of Antiproton Plasmas

CERN Document Server

Andresen, Gorm B; Baquero-Ruiz, Marcelo; Bertsche, William; Bowe, Paul D; Butler, Eoin; Carpenter, P T; Cesar, Claudio L; Chapman, Steven; Charlton, Michael; Fajans, Joel; Friesen, Tim; Fujiwara, Makoto C; Gill, David R; Hangst, Jeffrey S; Hardy, Walter N; Hayden, Michael E; Humphries, Andrew J; Hurt, J L; Hydomako, Richard; Jonsell, Svante; Madsen, Niels; Menary, Scott; Nolan, Paul; Olchanski, Konstantin; Olin, Art; Povilus, Alexander; Pusa, Petteri; Robicheaux, Francis; Sarid, Eli; Silveira, Daniel M; So, Chukman; Storey, James W; Thompson, Robert I; van der Werf, Dirk P; Wurtele, Jonathan S; Yamazaki, Yasunori

2011-01-01

We demonstrate controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense, and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination.

Tailoring the spin polarization in Ge/SiGe multiple quantum wells

International Nuclear Information System (INIS)

Giorgioni, Anna; Pezzoli, Fabio; Gatti, Eleonora; Grilli, Emanuele; Guzzi, Mario; Bottegoni, Federico; Cecchi, Stefano; Ciccacci, Franco; Isella, Giovanni; Trivedi, Dhara; Song, Yang; Li, Pengki; Dery, Hanan

2013-01-01

We performed spin-resolved photoluminescence measurements on Ge/SiGe multiple quantum wells with different well thickness and using different exciting power densities. The polarization of the direct emission strongly depends on the relative weight of electrons photoexcited from the light and the heavy hole subbands. The study of the polarization as a function of the exciting power highlights the role of the carrier-carrier interactions in determining spin depolarization

Watching Electrons at Conical Intersections and Funnels

Science.gov (United States)

Jonas, David M.; Smith, Eric R.; Peters, William K.; Kitney, Katherine A.

2009-06-01

The electronic motion at conical intersections and funnels is probed after polarized excitation of aligned electronic wavepackets. The pulses have bandwidth sufficient to observe vibrations mainly through their effect on the electrons. Vibrational symmetry can be identified by the polarization anisotropy of vibrational quantum beats. The polarized transients show signatures of electronic wavepacket motion (due to the energy gaps) and of electron transfer between orbitals (due to the couplings) driven by the conical intersection. For a conical intersection in a four-fold symmetric symmetry silicon naphthalocyanine molecule, electronic motions on a 100 fs timescale are driven by couplings of 1 meV. In the lower symmetry free-base naphthalocyanine, the conical intersection may be missed or missing (conical funnel), and the motions are nearly as rapid, but electronic equilibration is incomplete for red-edge excitation. These experiments probe non-adiabatic electronic dynamics with near-zero nuclear momentum - the electronic motions are determined by the principal slopes of the conical intersection and the width of the vibrational wavepacket.

From schooling to shoaling: patterns of collective motion in zebrafish (Danio rerio.

Directory of Open Access Journals (Sweden)

Noam Miller

Full Text Available Animal groups on the move can take different configurations. For example, groups of fish can either be 'shoals' or 'schools': shoals are simply aggregations of individuals; schools are shoals exhibiting polarized, synchronized motion. Here we demonstrate that polarization distributions of groups of zebrafish (Danio rerio are bimodal, showing two distinct modes of collective motion corresponding to the definitions of shoaling and schooling. Other features of the group's motion also vary consistently between the two modes: zebrafish schools are faster and less dense than zebrafish shoals. Habituation to an environment can also alter the proportion of time zebrafish groups spend schooling or shoaling. Models of collective motion suggest that the degree and stability of group polarization increases with the group's density. Examining zebrafish groups of different sizes from 5 to 50, we show that larger groups are less polarized than smaller groups. Decreased fearfulness in larger groups may function similarly to habituation, causing them to spend more time shoaling than schooling, contrary to most models' predictions.

Nested variant of the method of moments of coupled cluster equations for vertical excitation energies and excited-state potential energy surfaces.

Science.gov (United States)

Kowalski, Karol

2009-05-21

In this article we discuss the problem of proper balancing of the noniterative corrections to the ground- and excited-state energies obtained with approximate coupled cluster (CC) and equation-of-motion CC (EOMCC) approaches. It is demonstrated that for a class of excited states dominated by single excitations and for states with medium doubly excited component, the newly introduced nested variant of the method of moments of CC equations provides mathematically rigorous way of balancing the ground- and excited-state correlation effects. The resulting noniterative methodology accounting for the effect of triples is tested using its parallel implementation on the systems, for which iterative CC/EOMCC calculations with full inclusion of triply excited configurations or their most important subset are numerically feasible.

Investigation of wire motion in superconducting magnets

International Nuclear Information System (INIS)

Ogitsu, T.; Tsuchiya, K.; Devred, A.

1990-09-01

The large Lorentz forces occuring during the excitation of superconducting magnets can provoke sudden motions of wire, which eventually release enough energy to trigger a quench. These wire motions are accompanied by two electromagnetic effects: an induced emf along the moved wire, and a local change in flux caused by the minute dislocation of current. Both effects cause spikes in the coil voltage. Voltage data recorded during the excitation of a superconducting quadrupole magnet which early exhibit such events are here reported. Interpretations of the voltage spikes in terms of energy release are also presented, leading to insights on the spectrum of the disturbances which occur in real magnets. 15 refs

Controlling flexible rotor vibrations using parametric excitation

Energy Technology Data Exchange (ETDEWEB)

Atepor, L, E-mail: katepor@yahoo.co [Department of Mechanical Engineering, University of Glasgow, G12 8QQ (United Kingdom)

2009-08-01

This paper presents both theoretical and experimental studies of an active vibration controller for vibration in a flexible rotor system. The paper shows that the vibration amplitude can be modified by introducing an axial parametric excitation. The perturbation method of multiple scales is used to solve the equations of motion. The steady-state responses, with and without the parametric excitation terms, is investigated. An experimental test machine uses a piezoelectric exciter mounted on the end of the shaft. The results show a reduction in the rotor response amplitude under principal parametric resonance, and some good correlation between theory and experiment.

Relaxation of helium levels excited by heavy ion impact: III.- Orientation by anisotropic relaxation of excited atoms in previously aligned states

International Nuclear Information System (INIS)

Chamoun, E.; Lombardi, M.; Carre, M.; Gaillard, M.L.

1977-01-01

In the last paper of this series devoted to relaxation phenomena in a low pressure cell of helium excited by an accelerated ion beam, experimental evidence is given for a new mechanism of transfer between alignment and orientation through anisotropic relaxation of initially aligned excited states. The theory predicting this effect is briefly outlined and then description is given of the exact experimental conditions to detect the circularly polarized component of the light emitted by the target excited in the 4 1 D level of He I by Na + impact [fr

Effective inclusion of polarization effects in calculations of the oscillator strengths and transition energies in atoms and molecules using the equation-of-motion method

International Nuclear Information System (INIS)

Glushkov, A.V.; Kol'tsova, N.Yu.

1994-01-01

Equations of motion were solved by a modified method in a quasi-particle representation of the density functional taking into account the most important polarization effects, including the so-called 2p-2h two-particle-two-hole interactions. Based on these calculations, spectroscopic data on energies and oscillator strengths of the helium atom (the test computation), carbon monoxide, nitrogen molecule, and ethylene are presented that refine some previously reported experimental and theoretical results. It is shown that in some cases the inclusion of polarization corrections introduced by 2p-2h effects is of basic importance because it provides up to ∼30% contribution to the energies and oscillator strengths. 23 refs., 5 tabs

Spin characteristics of ion beams during the motion of electromagnetic elements

Science.gov (United States)

Zaika, N. I.; Magal, M. I.

The matrix method for description of the polarization components for ions moving through different electromagnetic systems: dipole magnets, cycle accelerators, quadrupole lenses, solenoids, wine filters, and electrostatic mirrors is developed in the paper. The expressions for elements of the transportation matrixes for the above-mentioned systems taking account of the projective trajectories are obtained. The program, TRANSPIN, for calculation of the beam polarization components after motion by ions of arbitrary number of electromagnetic elements along any possible trajectory is presented. The calculation results made for some of transportation lines for the isochronous cyclotron U-240 are discussed (trajectories for the ion motion were calculated by CERN-program TRANSPORT). The conditions for decrease of the polarization component dispersion because of difference between trajectories of the particles motion are also defined.

Frame by frame stop motion non-traditional approaches to stop motion animation

CERN Document Server

Gasek, Tom

2011-01-01

In a world that is dominated by computer images, alternative stop motion techniques like pixilation, time-lapse photography and down-shooting techniques combined with new technologies offer a new, tangible and exciting approach to animation. With over 25 years professional experience, industry veteran, Tom Gasek presents a comprehensive guide to stop motion animation without the focus on puppetry or model animation. With tips, tricks and hands-on exercises, Frame by Frame will help both experienced and novice filmmakers get the most effective results from this underutilized branch of animation

Nonlinear dynamics of trions under strong optical excitation in monolayer MoSe2.

Science.gov (United States)

Ye, Jialiang; Yan, Tengfei; Niu, Binghui; Li, Ying; Zhang, Xinhui

2018-02-05

By employing ultrafast transient reflection measurements based on two-color pump-probe spectroscopy, the population and valley polarization dynamics of trions in monolayer MoSe 2 were investigated at relatively high excitation densities under near-resonant excitation. Both the nonlinear dynamic photobleaching of the trion resonance and the redshift of the exciton resonance were found to be responsible for the excitation-energy- and density-dependent transient reflection change as a result of many-body interactions. Furthermore, from the polarization-resolved measurements, it was revealed that the initial fast population and polarization decay process upon strong photoexcitation observed for trions was determined by trion formation, transient phase-space filling and the short valley lifetime of excitons. The results provide a basic understanding of the nonlinear dynamics of population and valley depolarization of trions, as well as exciton-trion correlation in atomically thin MoSe 2 and other transition metal dichalcogenide materials.

Process and device for the selective excitation and separation of isotopes

International Nuclear Information System (INIS)

Ducas, T.W.

1976-01-01

Description is given of a method for selectively populating high-lying excited states of atoms or molecules. It comprises: excitation of atoms or molecules with a first circularly polarized pulsed radiation, the coherent frequency components of first pulsed radiation have frequencies corresponding to the energy difference between a lower energy level and the frequency split levels of an intermediate energy level, the duration of pulse being less than 2π/Δω, where Δω is the frequency difference of the split levels; applying a second circularly polarized pulsed radiation to atoms or molecules for a time subsequent to the termination of first radiation, the coherent frequency components of second pulsed radiation have frequencies corresponding to the energy difference between the split levels of intermediate energy level and an upper energy level, the duration of second pulse being less than 2π/Δω. The first and second radiation have the same handedness of circular polarization, whereby upper energy level has a greater population than prior to excitation by first and second radiation pulses [fr

Electron spin polarization in high-energy storage rings

International Nuclear Information System (INIS)

Mane, S.R.

1987-01-01

In a high energy storage ring, a single photon emission has relatively little effect on the orbital motion, but it can produce a relatively large change in the electron spin state. Hence the unperturbed orbital motion can be satisfactorily described using classical mechanics, but the spin must be treated quantum mechanically. The electron motion is therefore treated semi-classically in this thesis. It is explained how to diagonalize the unperturbed Hamiltonian to the leading order in Planck's constant. The effects of perturbations are then included, and the relevant time-scales and ensemble averages are elucidated. The Derbenev-Kondratenko formula for the equilibrium degree of polarization is rederived. Mathematical details of the rederivation are given. Since the original authors used a different formalism, a proof is offered of the equivalence between their method and the one used in this thesis. An algorithm is also presented to evaluate the equilibrium polarization. It has a number of new features, which enable the polarization to be calculated to a higher degree of approximation than has hitherto been possible. This facilitates the calculation of so-called spin resonances, which are points at which the polarization almost vanishes. A computer program has been written to implement the above algorithm, in the approximation of linear orbital dynamics, and sample results are presented

Determination of the polarization states of an arbitrary polarized terahertz beam: vectorial vortex analysis.

Science.gov (United States)

Wakayama, Toshitaka; Higashiguchi, Takeshi; Oikawa, Hiroki; Sakaue, Kazuyuki; Washio, Masakazu; Yonemura, Motoki; Yoshizawa, Toru; Tyo, J Scott; Otani, Yukitoshi

2015-03-24

Vectorial vortex analysis is used to determine the polarization states of an arbitrarily polarized terahertz (0.1-1.6 THz) beam using THz achromatic axially symmetric wave (TAS) plates, which have a phase retardance of Δ = 163° and are made of polytetrafluorethylene. Polarized THz beams are converted into THz vectorial vortex beams with no spatial or wavelength dispersion, and the unknown polarization states of the incident THz beams are reconstructed. The polarization determination is also demonstrated at frequencies of 0.16 and 0.36 THz. The results obtained by solving the inverse source problem agree with the values used in the experiments. This vectorial vortex analysis enables a determination of the polarization states of the incident THz beam from the THz image. The polarization states of the beams are estimated after they pass through the TAS plates. The results validate this new approach to polarization detection for intense THz sources. It could find application in such cutting edge areas of physics as nonlinear THz photonics and plasmon excitation, because TAS plates not only instantaneously elucidate the polarization of an enclosed THz beam but can also passively control THz vectorial vortex beams.

Integrated organic electronic based optochemical sensors using polarization filters

International Nuclear Information System (INIS)

Kraker, Elke; Haase, Anja; Lamprecht, Bernhard; Jakopic, Georg; Konrad, Christian; Koestler, Stefan

2008-01-01

A compact, integrated photoluminescence based oxygen and pH sensor, utilizing an organic light emitting device (OLED) as the light source and an organic photodiode (OPD) as the detection unit, is described. The main challenge in such an integrated sensor is the suppression of the excitation light at the detector, which is typically by many orders of magnitude higher in intensity than the emitted fluorescence. In our approach, we refrain from utilizing edge filters which require narrow band excitation sources and dyes with an adequate large Stokes shift. We rather developed an integrated sensor concept relying on two polarizers to separate the emission and excitation light. One polarizer is located right after the OLED, while the other one, oriented at 90 deg. to the first, is placed in front of the OPD. The main advantage of this solution is that any combination of excitation and emission light is acceptable, even if the two signals overlap spectrally. This is especially important for the use of OLEDs as the excitation sources, as these devices typically exhibit a broad spectral emission

Theories of Notation and Polar Motion I,

Science.gov (United States)

1980-12-01

relative motions such as ocean currents and winds, as we shall do. For the consideration of such effects see (Munk and Macdonald, 1960, p. 123; Lambeck...n)e ,uite general and niot irestricted to a solid body. In Fact, we na~it also in toe Poi ncar model . The equation K 12-1:: no;s the exponencial

Self-referenced coherent diffraction x-ray movie of Ångstrom- and femtosecond-scale atomic motion

International Nuclear Information System (INIS)

Glownia, J. M.; Natan, A.; Cryan, J. P.; Hartsock, R.; Kozina, M.

2016-01-01

Time-resolved femtosecond x-ray diffraction patterns from laser-excited molecular iodine are used to create a movie of intramolecular motion with a temporal and spatial resolution of 30 fs and 0.3 Å. This high fidelity is due to interference between the nonstationary excitation and the stationary initial charge distribution. The initial state is used as the local oscillator for heterodyne amplification of the excited charge distribution to retrieve real-space movies of atomic motion on ångstrom and femtosecond scales. This x-ray interference has not been employed to image internal motion in molecules before. In conclusion, coherent vibrational motion and dispersion, dissociation, and rotational dephasing are all clearly visible in the data, thereby demonstrating the stunning sensitivity of heterodyne methods.

Multi-modal vibration amplitudes of taut inclined cables due to direct and/or parametric excitation

Science.gov (United States)

Macdonald, J. H. G.

2016-02-01

Cables are often prone to potentially damaging large amplitude vibrations. The dynamic excitation may be from external loading or motion of the cable ends, the latter including direct excitation, normally from components of end motion transverse to the cable, and parametric excitation induced by axial components of end motion causing dynamic tension variations. Geometric nonlinearity can be important, causing stiffening behaviour and nonlinear modal coupling. Previous analyses of the vibrations, often neglecting sag, have generally dealt with direct and parametric excitation separately or have reverted to numerical solutions of the responses. Here a nonlinear cable model is adopted, applicable to taut cables such as on cable-stayed bridges, that allows for cable inclination, small sag (such that the vibration modes are similar to those of a taut string), multiple modes in both planes and end motion and/or external forcing close to any natural frequency. Based on the method of scaling and averaging it is found that, for sinusoidal inputs and positive damping, non-zero steady state responses can only occur in the modes in each plane with natural frequencies close to the excitation frequency and those with natural frequencies close to half this frequency. Analytical solutions, in the form of non-dimensional polynomial equations, are derived for the steady state vibration amplitudes in up to three modes simultaneously: the directly excited mode, the corresponding nonlinearly coupled mode in the orthogonal plane and a parametrically excited mode with half the natural frequency. The stability of the solutions is also identified. The outputs of the equations are consistent with previous results, where available. Example results from the analytical solutions are presented for a typical inclined bridge cable subject to vertical excitation of the lower end, and they are validated by numerical integration of the equations of motion and against some previous experimental

Toroidal silicon polarization analyzer for resonant inelastic x-ray scattering

Energy Technology Data Exchange (ETDEWEB)

Gao, Xuan [Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008-5252 (United States); Key Laboratory of Multi-scale Manufacturing Technology, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714 (China); Casa, Diego; Kim, Jungho; Gog, Thomas [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Li, Chengyang [Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008-5252 (United States); Department of Physics, South University of Science and Technology of China, Shenzhen 518055 (China); Burns, Clement [Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008-5252 (United States)

2016-08-15

Resonant Inelastic X-ray Scattering (RIXS) is a powerful probe for studying electronic excitations in materials. Standard high energy RIXS measurements do not measure the polarization of the scattered x-rays, which is unfortunate since it carries information about the nature and symmetry of the excitations involved in the scattering process. Here we report the fabrication of thin Si-based polarization analyzers with a double-concave toroidal surface, useful for L-edge RIXS studies in heavier atoms such as the 5-d transition metals.

A Fokker-Planck treatment of stochastic particle motion within the framework of a fully coupled 6-dimensional formalism for electron-positron storage rings including classical spin motion in linear approximation

International Nuclear Information System (INIS)

Barber, D.P.; Heinemann, K.; Mais, H.; Ripken, G.

1991-12-01

In the following report we investigate stochastic particle motion in electron-positron storage ring in the framework of a Fokker-Planck treatment. The motion is described by using the canonical variables χ, p χ , z, p z , σ = s - cxt, p σ = ΔE/E 0 of the fully six-dimensional formalism. Thus synchrotron- and betatron-oscillations are treated simultaneously taking into account all kinds of coupling (synchro-betatron coupling and the coupling of the betatron oscillations by skew quadrupoles and solenoids). In order to set up the Fokker-Planck equation, action-angle variables of the linear coupled motion are introduced. The averaged dimensions of the bunch, resulting from radiation damping of the synchro-betatron oscillations and from an excitation of these oscillations by quantum fluctuations, are calculated by solving the Fokker-Planck equation. The surfaces of constant density in the six-dimensional phase space, given by six-dimensional ellipsoids, are determined. It is shown that the motion of such an ellipsoid under the influence of external fields can be described by six generating orbit vectors which may be combined into a six-dimenional matrix B(s). This 'bunch-shape matrix', B(s), contains complete information about the configuration of the bunch. Classical spin diffusion in linear approximation has also been included so that the dependence of the polarization vector on the orbital phase space coordinates can be studied and another derivation of the linearized depolarization time obtained. (orig.)

Semiconductor color-center structure and excitation spectra: Equation-of-motion coupled-cluster description of vacancy and transition-metal defect photoluminescence

Science.gov (United States)

Lutz, Jesse J.; Duan, Xiaofeng F.; Burggraf, Larry W.

2018-03-01

Valence excitation spectra are computed for deep-center silicon-vacancy defects in 3C, 4H, and 6H silicon carbide (SiC), and comparisons are made with literature photoluminescence measurements. Optimizations of nuclear geometries surrounding the defect centers are performed within a Gaussian basis-set framework using many-body perturbation theory or density functional theory (DFT) methods, with computational expenses minimized by a QM/MM technique called SIMOMM. Vertical excitation energies are subsequently obtained by applying excitation-energy, electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC) methods, where appropriate, as well as time-dependent (TD) DFT, to small models including only a few atoms adjacent to the defect center. We consider the relative quality of various EOMCC and TD-DFT methods for (i) energy-ordering potential ground states differing incrementally in charge and multiplicity, (ii) accurately reproducing experimentally measured photoluminescence peaks, and (iii) energy-ordering defects of different types occurring within a given polytype. The extensibility of this approach to transition-metal defects is also tested by applying it to silicon-substituted chromium defects in SiC and comparing with measurements. It is demonstrated that, when used in conjunction with SIMOMM-optimized geometries, EOMCC-based methods can provide a reliable prediction of the ground-state charge and multiplicity, while also giving a quantitative description of the photoluminescence spectra, accurate to within 0.1 eV of measurement for all cases considered.

Symmetry-adapted-cluster configuration-interaction and equation-of-motion coupled-cluster studies of electronically excited states of copper tetrachloride and copper tetrabromide dianions

International Nuclear Information System (INIS)

Ehara, Masahiro; Piecuch, Piotr; Lutz, Jesse J.; Gour, Jeffrey R.

2012-01-01

Graphical abstract: Electronically excited states of CuCl 4 2- and CuBr 4 2- are determined using the scalar relativistic symmetry-adapted-cluster configuration-interaction and equation-of-motion coupled-cluster calculations. The results are compared with experimental spectra. Highlights: ► Electronic spectra of CuCl 4 2- and CuBr 4 2- are examined by SAC-CI and EOMCC methods. ► Relativistic SAC-CI and EOMCC results are compared with experimental spectra. ► An assignment of bands in the CuCl 4 2- and CuBr 4 2- absorption spectra is obtained. ► Relativistic effects affect excitation energies and ground-state geometries. ► The effect of relativity on the oscillator strengths is generally small. - Abstract: The valence excitation spectra of the copper tetrachloride and copper tetrabromide open-shell dianions, CuCl 4 2- and CuBr 4 2- , respectively, are investigated by a variety of symmetry-adapted-cluster configuration-interaction (SAC-CI) and equation-of-motion coupled-cluster (EOMCC) methods. The valence excited states of the CuCl 4 2- and CuBr 4 2- species that correspond to transitions from doubly occupied molecular orbitals (MOs) to a singly occupied MO (SOMO), for which experimental spectra are available, are examined with the ionized (IP) variants of the SAC-CI and EOMCC methods. The higher-energy excited states of CuCl 4 2- and CuBr 4 2- that correspond to transitions from SOMO to unoccupied MOs, which have not been characterized experimentally, are determined using the electron-attached (EA) SAC-CI and EOMCC approaches. An emphasis is placed on the scalar relativistic SAC-CI and EOMCC calculations based on the spin-free part of the second-order Douglass–Kroll–Hess Hamiltonian (DKH2) and on a comparison of the results of the IP and EA SAC-CI and EOMCC calculations with up to 2-hole-1-particle (2h-1p) and 2-particle-1-hole (2p-1h) excitations, referred to as the IP-SAC-CI SD-R and IP-EOMCCSD(2h-1p) methods in the IP case and EA-SAC-CI SD-R and EA

Polarization spectroscopy of positive and negative trions in an InAs quantum dot

Science.gov (United States)

Ware, Morgan E.; Bracker, Allan S.; Stinaff, Eric; Gammon, Daniel; Gershoni, David; Korenev, Vladimir L.

2005-02-01

Using polarization-sensitive photoluminescence and photoluminescence excitation spectroscopy, we study single InAs/GaAs self-assembled quantum dots. The dots were embedded in an n-type, Schottky diode structure allowing for control of the charge state. We present here the exciton, singly charged exciton (positive and negative trions), and the twice negatively charged exciton. For non-resonant excitation below the wetting layer, we observed a large degree of polarization memory from the radiative recombination of both the positive and negative trions. In excitation spectra, through the p-shell, we have found several sharp resonances in the emission from the s-shell recombination of the dot in all charged states. Some of these excitation resonances exhibit strong coulomb shifts upon addition of charges into the quantum dot. One particular resonance of the negatively charged trion was found to exhibit a fine structure doublet under circular polarization. This observation is explained in terms of resonant absorption into the triplet states of the negative trion.

Excitation of spin-1 states in 166168170Er using bremsstrahlung

International Nuclear Information System (INIS)

Metzger, F.R.

1976-01-01

Some 40 states in 166 , 168 , 170 Er, most of them previously unknown, have been excited using bremsstrahlung with < or =4.2 MeV endpoint energy. For all but three of these levels, the angular distribution of the resonantly scattered radiation favors the assignment of spin 1. For some of the strongly excited levels, linear polarization measurements have been performed. They indicate that these levels have positive parity. The branching ratios further characterize them as K=1 excitations

Characterization of excitation beam on second-harmonic generation in fibrillous type I collagen.

Science.gov (United States)

Chang, Ying; Deng, Xiaoyuan

2010-09-01

Following our established theoretical model to deal with the second-harmonic generation (SHG) excited by a linearly polarized focused beam in type I collagen, in this paper, we further quantitatively characterize the differences between SHG emissions in type I collagen excited by collimated and focused beams. The effects of the linear polarization angle (α) and the fibril polarity characterized by the hyperpolarizability ratio ρ on SHG emission has been compared under collimated and focused beam excitation, respectively. In particular, SHG emission components along the i axis [Formula: see text] (i = x,y,z), the induced SHG emission deviation angle γ(ij), and the detected SHG signals (I(2ω,ij)) in the ij plane by rotating the applied polarizer angle φ(ij) have been investigated (i = x, x, y; j = y, z, z). Results show that under our simulation model, SHG emission in the xy plane, such as I(2ω,x) ,I(2ω,y) ,γ(xy) and I(2ω,xy) varying as polarization angle (α) under collimated and focused light, presents no significant difference. The reverse of the fibril polarity has induced great impact on I(2ω,x) ,γ(xy) and I(2ω,xy) in both collimated and focused light. I(2ω,x) and γ(xy) show similarity, but I(2ω,xy) at α = 30° demonstrates a slight difference in focused light to that in collimated light. Under focused light, the reverse of fibril polarity causes obvious changes of the collected SHG intensity I(2ω,xz) and I(2ω,yz) at a special polarization angle α = 60° and γ(xz), γ(yz) along α.

Determination of Focal Mechanisms of Non-Volcanic Tremors Based on S-Wave Polarization Data Corrected for the Effects of Anisotropy

Science.gov (United States)

Imanishi, K.; Uchide, T.; Takeda, N.

2014-12-01

We propose a method to determine focal mechanisms of non-volcanic tremors (NVTs) based on S-wave polarization angles. The successful retrieval of polarization angles in low S/N tremor signals owes much to the observation that NVTs propagate slowly and therefore they do not change their location immediately. This feature of NVTs enables us to use a longer window to compute a polarization angle (e.g., one minute or longer), resulting in a stack of particle motions. Following Zhang and Schwartz (1994), we first correct for the splitting effect to recover the source polarization angle (anisotropy-corrected angle). This is a key step, because shear-wave splitting distorts the particle motion excited by a seismic source. We then determine the best double-couple solution using anisotropy-corrected angles of multiple stations. The present method was applied to a tremor sequence at Kii Peninsula, southwest Japan, which occurred at the beginning of April 2013. A standard splitting and polarization analysis were subject to a one-minute-long moving window to determine the splitting parameters as well as anisotropy-corrected angles. A grid search approach was performed at each hour to determine the best double-couple solution satisfying one-hour average polarization angles. Most solutions show NW-dipping low-angle planes consistent with the plate boundary or SE-dipping high-angle planes. Because of 180 degrees ambiguity in polarization angles, the present method alone cannot distinguish compressional quadrant from dilatational one. Together with the observation of very low-frequency earthquakes near the present study area (Ito et al., 2007), it is reasonable to consider that they represent shear slip on low-angle thrust faults. It is also noted that some of solutions contain strike-slip component. Acknowledgements: Seismograph stations used in this study include permanent stations operated by NIED (Hi-net), JMA, Earthquake Research Institute, together with Geological Survey of

Spin characteristics of ion beams during the motion of electromagnetic elements

International Nuclear Information System (INIS)

Zaika, N.I.; Magal', M.I.

1991-01-01

The matrix method for description of the polarization components for ions moving through different electromagnetic systems: dipole magnets, cycle accelerators, quadrupole lenses, solenoids, wine filters, electrostatic mirrors is developed in the paper. The expressions for elements of the transportation matrixes for the above-mentioned systems taking account of the projective trajectories are obtained. The programme TRANSPIN for calculation of the beam polarization components after motion by ions of arbitrary number of electromagnetic elements along any possible trajectory is worked out. The calculation results made for some of transportation lines for the isochronous cyclotron U-240 are discussed (trajectories for the ion motion were calculated by CERN-programme TRANSPORT). The conditions for decrease of the polarization component dispersion because of difference between trajectories of the particles motion are also defined. 6 refs.; 2 figs.; 4 tables. (author)

Terahertz radiation by subpicosecond spin-polarized photocurrent originating from Dirac electrons in a Rashba-type polar semiconductor

Science.gov (United States)

Kinoshita, Yuto; Kida, Noriaki; Miyamoto, Tatsuya; Kanou, Manabu; Sasagawa, Takao; Okamoto, Hiroshi

2018-04-01

The spin-splitting energy bands induced by the relativistic spin-orbit interaction in solids provide a new opportunity to manipulate the spin-polarized electrons on the subpicosecond timescale. Here, we report one such example in a bulk Rashba-type polar semiconductor BiTeBr. Strong terahertz electromagnetic waves are emitted after the resonant excitation of the interband transition between the Rashba-type spin-splitting energy bands with a femtosecond laser pulse circularly polarized. The phase of the emitted terahertz waves is reversed by switching the circular polarization. This suggests that the observed terahertz radiation originates from the subpicosecond spin-polarized photocurrents, which are generated by the asymmetric depopulation of the Dirac state. Our result provides a way for the current-induced terahertz radiation and its phase control by the circular polarization of incident light without external electric fields.

Self-excited vibration control for axially fast excited beam by a time delay state feedback

International Nuclear Information System (INIS)

Hamdi, Mustapha; Belhaq, Mohamed

2009-01-01

This work examines the control of self-excited vibration of a simply-supported beam subjected to an axially high-frequency excitation. The investigation of the resonant cases are not considered in this paper. The control is implemented via a corrective position feedback with time delay. The objective of this control is to eliminate the undesirable self-excited vibrations with an appropriate choice of parameters. The issue of stability is also addressed in this paper. Using the technique of direct partition of motion, the dynamic of discretized equations is separated into slow and fast components. The multiple scales method is then performed on the slow dynamic to obtain a slow flow for the amplitude and phase. Analysis of this slow flow provides analytical approximations locating regions in parameters space where undesirable self-excited vibration can be eliminated. A numerical study of these regions is performed on the original discretized system and compared to the analytical prediction showing a good agreement.

Particle hole excitations coupled to complex states in heavy-ion collisions

International Nuclear Information System (INIS)

Jolos, R.V.; Schmidt, R.

1982-01-01

The excitation of uncorrelated 1p-1h states in one nucleus due to the action of the time-dependent mean field of the other nucleus was studied earlier. No statistical assumptions or average procedures were made. Such a mechanism can be responsible for an appreciable excitation of the two nuclei during the short approach phase of the reaction (E* approximately> 100 MeV). The reversibility of the equations of motion leads to a deexcitation of the initially stored excitation energy into that of the relative motion for later times. This feedback behaviour of the internal excitation energy which results in particular to the deexcitation of high energetic 1p-1h pairs is probably not realistic due to the coupling of this states to more complex states with high density. It is studied the influence of this coupling due to the residual interaction between the nucleons on the dynamics of two colliding heavy ions

Experimental determination of the degree of polarization of quantum states

DEFF Research Database (Denmark)

Kothe-Termén, Christian; Madsen, Lars Skovgaard; Andersen, Ulrik Lund

2013-01-01

We demonstrate experimental excitation-manifold-resolved polarization characterization of quantum states of light ranging from the few-photon to the many-photon level. In contrast to the traditional characterization of polarization that is based on the Stokes parameters, we experimentally determine...... the Stokes vector of each excitation manifold separately. Only for states with a given photon number do the methods coincide. For states with an indeterminate photon number, for example Gaussian states, the employed method gives a richer and more accurate description. We apply the method both in theory...

Intershell interaction in excited atom and ion photoionization

International Nuclear Information System (INIS)

Amusia, M.Ya.; Avdonina, N.B.

1989-01-01

It is demonstrated, that the photoionization cross section of an excited electron in Cs atom isoelectronic sequence acquire additional structure if the virtual polarization of the core by the incident photon is taken into account. (orig.)

Polarization-dependent force driving the Eg mode in bismuth under optical excitation: comparison of first-principles theory with ultra-fast x-ray experiments

Science.gov (United States)

Fahy, Stephen; Murray, Eamonn

2015-03-01

Using first principles electronic structure methods, we calculate the induced force on the Eg (zone centre transverse optical) phonon mode in bismuth immediately after absorption of a ultrafast pulse of polarized light. To compare the results with recent ultra-fast, time-resolved x-ray diffraction experiments, we include the decay of the force due to carrier scattering, as measured in optical Raman scattering experiments, and simulate the optical absorption process, depth-dependent atomic driving forces, and x-ray diffraction in the experimental geometry. We find excellent agreement between the theoretical predictions and the observed oscillations of the x-ray diffraction signal, indicating that first-principles theory of optical absorption is well suited to the calculation of initial atomic driving forces in photo-excited materials following ultrafast excitation. This work is supported by Science Foundation Ireland (Grant No. 12/IA/1601) and EU Commission under the Marie Curie Incoming International Fellowships (Grant No. PIIF-GA-2012-329695).

Observations of Rabi oscillations in a non-polar InGaN quantum dot

Energy Technology Data Exchange (ETDEWEB)

Reid, Benjamin P. L., E-mail: benjamin.reid@physics.ox.ac.uk; Chan, Christopher C. S.; Taylor, Robert A. [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Kocher, Claudius [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Konstanz University, Konstanz (Germany); Zhu, Tongtong; Oehler, Fabrice; Emery, Robert; Oliver, Rachel A. [Department of Materials Science and Metallurgy, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

2014-06-30

Experimental observation of Rabi rotations between an exciton excited state and the crystal ground state in a single non-polar InGaN quantum dot is presented. The exciton excited state energy is determined by photoluminescence excitation spectroscopy using two-photon excitation from a pulsed laser. The population of the exciton excited state is seen to undergo power dependent damped Rabi oscillations.

Observations of Rabi oscillations in a non-polar InGaN quantum dot

International Nuclear Information System (INIS)

Reid, Benjamin P. L.; Chan, Christopher C. S.; Taylor, Robert A.; Kocher, Claudius; Zhu, Tongtong; Oehler, Fabrice; Emery, Robert; Oliver, Rachel A.

2014-01-01

Experimental observation of Rabi rotations between an exciton excited state and the crystal ground state in a single non-polar InGaN quantum dot is presented. The exciton excited state energy is determined by photoluminescence excitation spectroscopy using two-photon excitation from a pulsed laser. The population of the exciton excited state is seen to undergo power dependent damped Rabi oscillations.

Production of spin-polarized unstable nuclei by using polarized electron capture process

International Nuclear Information System (INIS)

Shimizu, S.

1998-01-01

Measurements of emitted radiation from spin polarized nuclei are used to get information on electromagnetic moment of ground state unstable nuclei together with spin or parity state of excited states of their decayed (daughter) nuclei. These data are known to be useful for experimental investigation into the structure of unstable nuclei far from the stability line. The present study aims to establish a general method applicable to 11 Be and 16 N nuclei. To produce spin polarization, a new method in which the electron spin polarization of Rb is firstly produced by laser pumping, then the electron is transferred to the unstable nuclear beam (RNB) when they passes through the Rb vapor is proposed. Finally the polarized RNB will be implanted into superfluid helium to remain with a long spin-relaxation time. Future experimental set up for the above measurement adopted in the available radioactive nuclear beam facilities is briefly described. (Ohno, S.)

Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells

International Nuclear Information System (INIS)

Davies, M. J.; Dawson, P.; Hammersley, S.; Zhu, T.; Kappers, M. J.; Humphreys, C. J.; Oliver, R. A.

2016-01-01

We report on a comparative study of efficiency droop in polar and non-polar InGaN quantum well structures at T = 10 K. To ensure that the experiments were carried out with identical carrier densities for any particular excitation power density, we used laser pulses of duration ∼100 fs at a repetition rate of 400 kHz. For both types of structures, efficiency droop was observed to occur for carrier densities of above 7 × 10 11  cm −2  pulse −1 per quantum well; also both structures exhibited similar spectral broadening in the droop regime. These results show that efficiency droop is intrinsic in InGaN quantum wells, whether polar or non-polar, and is a function, specifically, of carrier density.

Velocity Memory Effect for polarized gravitational waves

Science.gov (United States)

Zhang, P.-M.; Duval, C.; Gibbons, G. W.; Horvathy, P. A.

2018-05-01

Circularly polarized gravitational sandwich waves exhibit, as do their linearly polarized counterparts, the Velocity Memory Effect: freely falling test particles in the flat after-zone fly apart along straight lines with constant velocity. In the inside zone their trajectories combine oscillatory and rotational motions in a complicated way. For circularly polarized periodic gravitational waves some trajectories remain bounded, while others spiral outward. These waves admit an additional "screw" isometry beyond the usual five. The consequences of this extra symmetry are explored.

Manipulation of molecular vibrational motions via pure rotational excitations

DEFF Research Database (Denmark)

Shu, Chuan-Cun; Henriksen, Niels Engholm

2015-01-01

The coupling between different molecular degrees of freedom plays a decisive role in many quantum phenomena, including electron transfer and energy redistribution. Here, we demonstrate a quantum-mechanical time-dependent simulation to explore how a vibrational motion in a molecule can be affected...

Elementary excitations and phase transformations in solids

International Nuclear Information System (INIS)

Cowley, R.A.

1985-01-01

Neutron scattering is and will continue to be a uniquely powerful tool for the study of elementary excitations and phase transformations in solids. The paper examines a few recent experiments on molecular crystals, superionic materials, paramagnetic scattering and phase transitions to see what experimental features made these experiments possible, and hence to make suggestions about future needs. It is concluded that new instruments will extend the scope of neutron scattering studies to new excitations, that there is a need for higher resolution, particularly for phase transition studies, and that it will be important to use intensity information, discrimination against unwanted inelastic processes and polarization analysis to reliably measure the excitations in new materials. (author)

Excited state conformational dynamics in carotenoids: dark intermediates and excitation energy transfer.

Science.gov (United States)

Beck, Warren F; Bishop, Michael M; Roscioli, Jerome D; Ghosh, Soumen; Frank, Harry A

2015-04-15

A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors. Copyright © 2015 Elsevier Inc. All rights reserved.

Creating intense polarized electron beam via laser stripping and spin-orbit interaction

International Nuclear Information System (INIS)

Danilov, V.; Ptitsyn, V.; Gorlov, T.

2010-01-01

The recent advance in laser field make it possible to excite and strip electrons with definite spin from hydrogen atoms. The sources of hydrogen atoms with orders of magnitude higher currents (than that of the conventional polarized electron cathods) can be obtained from H - sources with good monochromatization. With one electron of H - stripped by a laser, the remained electron is excited to upper state (2P 3/2 and 2P 1/2 ) by a circular polarization laser light from FEL. Then, it is excited to a high quantum number (n=7) with mostly one spin direction due to energy level split of the states with a definite direction of spin and angular momentum in an applied magnetic field and then it is stripped by a strong electric field of an RF cavity. This paper presents combination of lasers and fields to get high polarization and high current electron source.

Electron-impact excitation of molecular ions

International Nuclear Information System (INIS)

Neufeld, D.A.; Dalgarno, A.

1989-01-01

A simple expression is derived that relates the rate coefficient for dipole-allowed electron-impact excitation of a molecular ion in the Coulomb-Born approximation to the Einstein A coefficient for the corresponding radiative decay. Results are given for several molecular ions of astrophysical interest. A general analytic expression is obtained for the equilibrium rotational level populations in the ground vibrational state of any molecular ion excited by collisions with electrons. The expression depends only upon the electron temperature, the electron density, and the rotational constant of the molecular ion. A similar expression is obtained for neutral polar molecules

Systematics in Rydberg state excitations for ion-atom collisions

International Nuclear Information System (INIS)

Andresen, B.; Jensen, K.; Petersen, N.B.; Veje, E.

1976-01-01

Rydberg state excitations in the Ne + , Mg + -He collisions have been studied in the projectile energy range 10-75 keV by means of optical spectrometry in a search for systematic trends. The relative excitation cross sections for levels of a Rydberg term series are found to follow a general (nsup(x))sup(P) behaviour with P < approximately -3 varying with collision energy and particles, regardless of whether the excited state population results from direct excitation, single electron transfer, or double electron transfer. At higher collision energies P is approximately -3 as predicted by theory. Polarization of the emitted line radiation indicates that there is no general rule for the relative excitation of the different magnetic substates of the same level. A statistical distribution of excitation is found for levels within the same term when the fine structure splitting is small. (Auth.)

Role of Many-Body Effects in Describing Low-Lying Excited States of pi-Conjugated Chromophores: High-Level Equation-of-Motion Coupled-Cluster Studies of Fused Porphyrin Systems

Energy Technology Data Exchange (ETDEWEB)

Kowalski, Karol; Olson, Ryan M.; Krishnamoorthy, Sriram; Tipparaju, Vinod; Apra, Edoardo

2011-07-12

The unusual photophysical properties of the pi-conjugated chrompohores makes them potential building blocks of various molecular devices. In particular, significant narrowing of the HOMO-LUMO gaps can be observed as an effect of functionalization chromophores with polycyclic aromatic hydrocabrons (PAHs). In this paper we present equation-of-motion coupled cluster calculations for vertical excitation energies of several functionalized forms of porphyrins. The results of free-base porphyrin (FBP) clearly demonstrate significant differences between functionalization of FBP with one- (anthracene) and two-dimensional (coronene) structures. We also compare the EOMCC results with the experimentally available results for the anthracene fused zinc porphyrin. The impact of various-type correlation effects is illustrated on several benchmark models where the comparison with the experiment is possible. In particular, we demonstrate that for all excited states considered in this paper, all of them being dominated by single excitations, the inclusion of triply excited configurations is crucial for attaining qualitative agreement with the experiment. We also demonstrate the parallel performance of the most computationally intensive part of the completely renormalized EOMCCSD(T) approach (CR-EOMCCSD(T)) across 120,000 cores.

Electron emission in the Auger neutralization of a spin-polarized He+ ion embedded in a free electron gas

International Nuclear Information System (INIS)

Juaristi, J.I.; Alducin, M.; Diez Muino, R.; Roesler, M.

2005-01-01

Results are presented for the energy distribution and spin polarization of the electrons excited during the Auger neutralization of a spin polarized He + ion embedded in a paramagnetic free electron gas. The screening of the He + ion is calculated using density functional theory within the local spin density approximation. The Auger rates, the energy distribution and the spin polarization of the excited electrons are obtained using the Fermi golden rule. The transport of the electrons is calculated within the Boltzmann transport equation formalism. The spin-polarization of the initially excited electrons is very high (>70%) and parallel to that of the electron bound to the He + ion. Nevertheless, the emitted electrons show a much lower degree of polarization, mainly in the low energy range, due to the creation of the unpolarized cascade of secondaries in the transport process

Polar motion as boundary condition in an adaptive Kalman filter approach for the determination of period and damping of the Chandler oscillation

Science.gov (United States)

Seitz, F.; Kirschner, S.; Neubersch, D.

2012-12-01

Earth rotation has been monitored using space geodetic techniques since many decades. The geophysical interpretation of observed time series of Earth rotation parameters (ERP) polar motion and length-of-day is commonly based on numerical models that describe and balance variations of angular momentum in various subsystems of the Earth. Naturally, models are dependent on geometrical, rheological and physical parameters. Many of these are weakly determined from other models or observations. In our study we present an adaptive Kalman filter approach for the improvement of parameters of the dynamic Earth system model DyMEG which acts as a simulator of ERP. In particular we focus on the improvement of the pole tide Love number k2. In the frame of a sensitivity analysis k2 has been identified as one of the most crucial parameters of DyMEG since it directly influences the modeled Chandler oscillation. At the same time k2 is one of the most uncertain parameters in the model. Our simulations with DyMEG cover a period of 60 years after which a steady state of k2 is reached. The estimate for k2, accounting for the anelastic response of the Earth's mantle and the ocean, is 0.3531 + 0.0030i. We demonstrate that the application of the improved parameter k2 in DyMEG leads to significantly better results for polar motion than the original value taken from the Conventions of the International Earth Rotation and Reference Systems Service (IERS).

Proton-proton elastic scattering excitation functions at intermediate energies: Cross sections and analyzing powers

CERN Document Server

Hinterberger, F; Altmeier, M; Bauer, F; Bisplinghoff, J; Büsser, K; Busch, M; Colberg, T; Diehl, O; Dohrmann, F; Engelhardt, H P; Eversheim, P D; Felden, O; Gebel, R; Glende, M; Greiff, J; Gross-Hardt, R; Hinterberger, F; Jahn, R; Jonas, E; Krause, H; Langkau, R; Lindemann, T; Lindlein, J; Maier, R; Maschuw, R; Mayer-Kuckuk, T; Meinerzhagen, A; Naehle, O; Prasuhn, D; Rohdjess, H; Rosendaal, D; Von Rossen, P; Schirm, N; Schulz-Rojahn, M; Schwarz, V; Scobel, W; Trelle, H J; Weise, E; Wellinghausen, A; Woller, K; Ziegler, R

2000-01-01

The EDDA experiment at the cooler synchrotron COSY measures proton-proton elastic scattering excitation functions in the momentum range 0.8 - 3.4 GeV/c. In phase 1 of the experiment, spin-averaged differential cross sections were measured continuously during acceleration with an internal polypropylene (CH sub 2) fiber target, taking particular care to monitor luminosity as a function of beam momentum. In phase 2, excitation functions of the analyzing power A sub N and the polarization correlation parameters A sub N sub N , A sub S sub S and A sub S sub L are measured using a polarized proton beam and a polarized atomic hydrogen beam target. The paper presents recent d sigma/d OMEGA and A sub N data. The results provide excitation functions and angular distributions of high precision and internal consistency. No evidence for narrow structures was found. The data are compared to recent phase shift solutions.

Theoretical resonant electron-impact vibrational excitation, dissociative recombination and dissociative excitation cross sections of ro-vibrationally excited BeH"+ ion

International Nuclear Information System (INIS)

Laporta, V.; Chakrabarti, K.; Celiberto, R.; Janev, R. K.; Mezei, J. Zs.; Niyonzima, S.; Tennyson, J.; Schneider, I.F.

2017-01-01

A theoretical study of resonant vibrational excitation, dissociative recombination and dissociative excitation processes of the beryllium monohydride cation, BeH"+ , induced by electron impact, is reported. Full sets of ro-vibrationally-resolved cross sections and of the corresponding Maxwellian rate coefficients are presented for the three processes. Particular emphasis is given to the high-energy behaviour. Potential curves of "2σ"+, "2σ and "2δ symmetries and the corresponding resonance widths, obtained from R-matrix calculations, provide the input for calculations which use a local complex-potential model for resonant collisions in each of the three symmetries. Rotational motion of nuclei and isotopic effects are also discussed. The relevant results are compared with those obtained using a multichannel quantum defect theory method. Full results are available from the Phys4Entry database.

Spin-orbit-coupled Bose-Einstein condensates of rotating polar molecules

Science.gov (United States)

Deng, Y.; You, L.; Yi, S.

2018-05-01

An experimental proposal for realizing spin-orbit (SO) coupling of pseudospin 1 in the ground manifold 1Σ (υ =0 ) of (bosonic) bialkali polar molecules is presented. The three spin components are composed of the ground rotational state and two substates from the first excited rotational level. Using hyperfine resolved Raman processes through two select excited states resonantly coupled by a microwave, an effective coupling between the spin tensor and linear momentum is realized. The properties of Bose-Einstein condensates for such SO-coupled molecules exhibiting dipolar interactions are further explored. In addition to the SO-coupling-induced stripe structures, the singly and doubly quantized vortex phases are found to appear, implicating exciting opportunities for exploring novel quantum physics using SO-coupled rotating polar molecules with dipolar interactions.

Penetration of geomagnetic pulsations from one polar cao cap to the other one

International Nuclear Information System (INIS)

Mal'tsev, Yu.P.; Lyatskij, V.B.

1982-01-01

A theoretical study is made of penetration of geomagnetic pulsations, excited in one polar cap in the region of open field lines, into the other one. The geomagnetic pulsations excited in a polar cap in the region of open field lines are also observed in the opposite polar cap. This is connected with the flow of ionospheric perturbation currents from one hemisphere to another over the boundary of the region with closed magnetic lines. In case of long-period oscillations under symmetrical conditions, both in the north and south polar caps, the ionospheric effect of the opposite hemisphere results in the fact that the electrical currents flowing from a source to the polar cap boundary grow 1.5 times as high. In case of short-period oscillations a portion of longitudinal current flowing between the hemispheres is branched away for polarization currents. As a result, the electrical field and currents in the ionosphere of the opposite hemisphere can substantially decrease as compared to the long-period oscillations

Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells

Energy Technology Data Exchange (ETDEWEB)

Davies, M. J.; Dawson, P.; Hammersley, S. [School of Physics and Astronomy, Photon Science Institute, University of Manchester, M13 9PL Manchester (United Kingdom); Zhu, T.; Kappers, M. J.; Humphreys, C. J.; Oliver, R. A. [Department of Material Science and Metallurgy, 27 Charles Babbage Road, University of Cambridge, Cambridge CB3 0FS (United Kingdom)

2016-06-20

We report on a comparative study of efficiency droop in polar and non-polar InGaN quantum well structures at T = 10 K. To ensure that the experiments were carried out with identical carrier densities for any particular excitation power density, we used laser pulses of duration ∼100 fs at a repetition rate of 400 kHz. For both types of structures, efficiency droop was observed to occur for carrier densities of above 7 × 10{sup 11 }cm{sup −2 }pulse{sup −1} per quantum well; also both structures exhibited similar spectral broadening in the droop regime. These results show that efficiency droop is intrinsic in InGaN quantum wells, whether polar or non-polar, and is a function, specifically, of carrier density.

Spin polarized semimagnetic exciton-polariton condensate in magnetic field.

Science.gov (United States)

Król, Mateusz; Mirek, Rafał; Lekenta, Katarzyna; Rousset, Jean-Guy; Stephan, Daniel; Nawrocki, Michał; Matuszewski, Michał; Szczytko, Jacek; Pacuski, Wojciech; Piętka, Barbara

2018-04-27

Owing to their integer spin, exciton-polaritons in microcavities can be used for observation of non-equilibrium Bose-Einstein condensation in solid state. However, spin-related phenomena of such condensates are difficult to explore due to the relatively small Zeeman effect of standard semiconductor microcavity systems and the strong tendency to sustain an equal population of two spin components, which precludes the observation of condensates with a well defined spin projection along the axis of the system. The enhancement of the Zeeman splitting can be achieved by introducing magnetic ions to the quantum wells, and consequently forming semimagnetic polaritons. In this system, increasing magnetic field can induce polariton condensation at constant excitation power. Here we evidence the spin polarization of a semimagnetic polaritons condensate exhibiting a circularly polarized emission over 95% even in a moderate magnetic field of about 3 T. Furthermore, we show that unlike nonmagnetic polaritons, an increase on excitation power results in an increase of the semimagnetic polaritons condensate spin polarization. These properties open new possibilities for testing theoretically predicted phenomena of spin polarized condensate.

Negative circular polarization emissions from WSe2/MoSe2 commensurate heterobilayers

KAUST Repository

Hsu, Wei-Ting; Lu, Li-Syuan; Wu, Po-Hsun; Lee, Ming-Hao; Chen, Peng-Jen; Wu, Pei-Ying; Chou, Yi-Chia; Jeng, Horng-Tay; Li, Lain-Jong; Chu, Ming-Wen; Chang, Wen-Hao

2018-01-01

Van der Waals heterobilayers of transition metal dichalcogenides with spin-valley coupling of carriers in different layers have emerged as a new platform for exploring spin/valleytronic applications. The interlayer coupling was predicted to exhibit subtle changes with the interlayer atomic registry. Manually stacked heterobilayers, however, are incommensurate with the inevitable interlayer twist and/or lattice mismatch, where the properties associated with atomic registry are difficult to access by optical means. Here, we unveil the distinct polarization properties of valley-specific interlayer excitons using epitaxially grown, commensurate WSe/MoSe heterobilayers with well-defined (AA and AB) atomic registry. We observe circularly polarized photoluminescence from interlayer excitons, but with a helicity opposite to the optical excitation. The negative circular polarization arises from the quantum interference imposed by interlayer atomic registry, giving rise to distinct polarization selection rules for interlayer excitons. Using selective excitation schemes, we demonstrate the optical addressability for interlayer excitons with different valley configurations and polarization helicities.

Negative circular polarization emissions from WSe2/MoSe2 commensurate heterobilayers

KAUST Repository

Hsu, Wei-Ting

2018-04-11

Van der Waals heterobilayers of transition metal dichalcogenides with spin-valley coupling of carriers in different layers have emerged as a new platform for exploring spin/valleytronic applications. The interlayer coupling was predicted to exhibit subtle changes with the interlayer atomic registry. Manually stacked heterobilayers, however, are incommensurate with the inevitable interlayer twist and/or lattice mismatch, where the properties associated with atomic registry are difficult to access by optical means. Here, we unveil the distinct polarization properties of valley-specific interlayer excitons using epitaxially grown, commensurate WSe/MoSe heterobilayers with well-defined (AA and AB) atomic registry. We observe circularly polarized photoluminescence from interlayer excitons, but with a helicity opposite to the optical excitation. The negative circular polarization arises from the quantum interference imposed by interlayer atomic registry, giving rise to distinct polarization selection rules for interlayer excitons. Using selective excitation schemes, we demonstrate the optical addressability for interlayer excitons with different valley configurations and polarization helicities.

Polarization preservation and control in a figure-8 ring

Energy Technology Data Exchange (ETDEWEB)

Derbenev, Yaroslav S. [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Morozov, Vasiliy [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Lin, Fanglei [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Zhang, Yuhong [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Kondratenko, A. M. [GOO Zaryad, Russkaya st., 41, Novosibirsk, 630058; Kondratenko, M. A. [GOO Zaryad, Russkaya st., 41, Novosibirsk, 630058; Filatov, Yuri [Joint Inst. for Nuclear Research (JINR), Dubna (Russian Federation); GOO Zaryad, Russkaya st., 41, Novosibirsk, 630058

2016-02-01

We present a complete scheme for managing the polarization of ion beams in Jefferson Lab's proposed Medium-energy Electron-Ion Collider (MEIC). It provides preservation of the ion polarization during all stages of beam acceleration and polarization control in the collider's experimental straights. We discuss characteristic features of the spin motion in accelerators with Siberian snakes and in accelerators of figure-8 shape. We propose 3D spin rotators for polarization control in the MEIC ion collider ring. We provide polarization calculations in the collider with the 3D rotator for deuteron and proton beams. The main polarization control features of the figure-8 design are summarized.

Proceedings of the Japan-US workshop on plasma polarization spectroscopy and the international seminar on plasma polarization spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Fujimoto, Takashi; Beiersdorfer, Peter [eds.

1998-06-01

The international meeting on Plasma Polarization Spectroscopy (PPS) was held in Kyoto during January 26-28, 1998. This Proceedings book includes the papers of the talks given at the meeting. These include: overviews of PPS from the aspects of atomic physics, and of plasma physics; several PPS and MSE (motional Stark effect) experiments on magnetically confined plasmas and a laser-produced plasma; polarized laser-induced fluorescence spectroscopy, several experiments on EBITs (electron beam ion trap) and their theoretical interpretations; polarized profiles of spectral lines, basic formulation of PPS; inelastic and elastic electron collisions leading to polarized atomic states; polarization in recombining plasma; relationship between the collisional polarization relaxation and the line broadening; and characteristics of the plasma produced by very short pulse and high power laser irradiation. The 19 of the presented papers are indexed individually. (J.P.N.)

High Frequency Near-Field Ground Motion Excited by Strike-Slip Step Overs

Science.gov (United States)

Hu, Feng; Wen, Jian; Chen, Xiaofei

2018-03-01

We performed dynamic rupture simulations on step overs with 1-2 km step widths and present their corresponding horizontal peak ground velocity distributions in the near field within different frequency ranges. The rupture speeds on fault segments are determinant in controlling the near-field ground motion. A Mach wave impact area at the free surface, which can be inferred from the distribution of the ratio of the maximum fault-strike particle velocity to the maximum fault-normal particle velocity, is generated in the near field with sustained supershear ruptures on fault segments, and the Mach wave impact area cannot be detected with unsustained supershear ruptures alone. Sub-Rayleigh ruptures produce stronger ground motions beyond the end of fault segments. The existence of a low-velocity layer close to the free surface generates large amounts of high-frequency seismic radiation at step over discontinuities. For near-vertical step overs, normal stress perturbations on the primary fault caused by dipping structures affect the rupture speed transition, which further determines the distribution of the near-field ground motion. The presence of an extensional linking fault enhances the near-field ground motion in the extensional regime. This work helps us understand the characteristics of high-frequency seismic radiation in the vicinities of step overs and provides useful insights for interpreting the rupture speed distributions derived from the characteristics of near-field ground motion.

LINEARLY POLARIZED PROBES OF SURFACE CHIRALITY

NARCIS (Netherlands)

VERBIEST, T; KAURANEN, M; MAKI, JJ; TEERENSTRA, MN; SCHOUTEN, AJ; NOLTE, RJM; PERSOONS, A

1995-01-01

We present a new nonlinear optical technique to study surface chirality. We demonstrate experimentally that the efficiency of second-harmonic generation from isotropic chiral surfaces is different for excitation with fundamental light that is +45 degrees and -45 degrees linearly polarized with

CLASSIFICATION FOR ANGLE-DEPENDENT POLARIZED PHOTOEMISSION SPECTRA USING MAGNETIC-MOMENTS ANALYSIS

NARCIS (Netherlands)

VANDERLAAN, G; THOLE, BT

The angular distribution of photoelectrons from a core level or localized valence level excited with circularly or linearly polarized Xrays is shown to contain the complete one-electron information of the ground state of a magnetic polarized atom. We generalize the definition of the fundamental

Measurement of spin motions in a storage ring outside the stable polarization direction

International Nuclear Information System (INIS)

Akchurin, N.; Badano, L.; Bravar, A.; Istituto Nazionale di Fisica Nucleare, Legnaro

1993-06-01

Polarized, stored beams are becoming a more and more important tool in nuclear and high energy physics. In order to measure the beam polarization in a storage ring the polarization vector of the stored beams has to aim, revolution for revolution, over a period of seconds to minutes, into the same, so-called ''stable'' direction. In this paper measurements at the Indiana University cooler ring (IUCF) are described in which for the first time in a storage ring oscillations of the polarization vector around this stable direction have been measured. The existence and the dynamics of such oscillations are, for instance, important for a new proposed technique for polarizing stored hadron beams

Measurement of spin motions in a storage ring outside the stable polarization direction

International Nuclear Information System (INIS)

Akchurin, N.; McPherson, J.; Olchowski, F.; Onel, Y.; Badano, L.; Conte, M.; Bravar, A.; Penzo, A.; Hall, J.; Kreiser, H.

1993-01-01

Polarized, stored beams are becoming a more and more important tool in nuclear and high energy physics. In order to measure the beam polarization in a storage ring the polarization vector of the stored beam has to aim, revolution for revolution, over a period of seconds to minutes, into the same, so-called open-quote stableclose quotes, direction. In this paper measurements at the Indiana University Cooler Ring (IUCF) are described in which for the first time in a storage ring oscillations of the polarization vector around this stable direction have been measured. The existence and the dynamics of such oscillations are, for instance, important for a new proposed technique for polarizing stored hadron beams

W-Band Circularly Polarized TE11 Mode Transducer

Science.gov (United States)

Zhan, Mingzhou; He, Wangdong; Wang, Lei

2018-06-01

This paper presents a balanced sidewall exciting approach to realize the circularly polarized TE11 mode transducer. We used a voltage vector transfer matrix to establish the relationship between input and output vectors, then we analyzed amplitude and phase errors to estimate the isolation of degenerate mode. A mode transducer with a sidewall exciter was designed based on the results. In the 88-100 GHz frequency range, the simulated axial ratio is less than 1.05 and the isolation of linearly polarization TE11 mode is higher than 30 dBc. In back-to-back measurements, the return loss is generally greater than 20 dB with a typical insertion loss of 1.2 dB. Back-to-back transmission measurements are in excellent agreement with simulations.

Complete electromagnetically induced transparency in sodium atoms excited by a multimode dye laser

International Nuclear Information System (INIS)

Alzetta, G.; Gozzini, S.; Lucchesini, A.; Cartaleva, S.; Karaulanov, T.; Marinelli, C.; Moi, L.

2004-01-01

Complete electromagnetically induced transparency (EIT) in sodium vapor is demonstrated experimentally by means of excitation with a broadband multimode dye laser tuned on the D 1 line. One hundred percent transparency is observed by excitation of the Na vapor with circularly polarized laser light. The linear polarization excitation produces, instead, complete destruction of the EIT resonance. For laser power density in the 0.1 to 1 W/cm 2 range, the linewidth of the EIT resonance remains in the interval of 90-400 kHz. This complete transparency of the medium in a narrow frequency interval is interesting for many applications where the enhancement of the refractive index is important and where the improvement of the signal-to-noise ratio of the dark resonances allows a more sensitive measurement of weak magnetic fields

Analytical formulation for modulation of time-resolved dynamical Franz-Keldysh effect by electron excitation in dielectrics

Science.gov (United States)

Otobe, T.

2017-12-01

Analytical formulation of subcycle modulation (SCM) of dielectrics including electron excitation is presented. The SCM is sensitive to not only the time-resolved dynamical Franz-Keldysh effect (Tr-DFKE) [T. Otobe et al., Phys. Rev. B 93, 045124 (2016), 10.1103/PhysRevB.93.045124], which is the nonlinear response without the electron excitation, but also the excited electrons. The excited electrons enhance the modulation with even harmonics of pump laser frequency, and generate the odd-harmonics components. The new aspect of SCM is a consequence of (i) the interference between the electrons excited by the pump laser and those excited by the probe-pulse laser and (ii) oscillation of the generated wave packed by the pump laser. When the probe- and pump-pulse polarizations are parallel, the enhancement of the even harmonics and the generation of the odd-harmonics modulation appear. However, if the polarizations are orthogonal, the effect arising from the electron excitations becomes weak. By comparing the parabolic and cosine band models, I found that the electrons under the intense laser field move as quasifree particles.

Negative circular polarization as a universal property of quantum dots

International Nuclear Information System (INIS)

Taylor, Matthew W.; Spencer, Peter; Murray, Ray

2015-01-01

This paper shows that negative circular polarization, a spin flip of polarized carriers resulting in emission of opposite helicity, can be observed in undoped, n-doped, and p-doped InAs/GaAs quantum dots. These results contradict the usual interpretation of the effect. We show using power dependent and time resolved spectroscopy that the generation of negative circular polarization correlates with excited state emission. Furthermore, a longer spin lifetime of negatively polarized excitons is observed where emission is largely ground state in character

Maturation of polarization and luminance contrast sensitivities in cuttlefish (Sepia officinalis).

Science.gov (United States)

Cartron, Lelia; Dickel, Ludovic; Shashar, Nadav; Darmaillacq, Anne-Sophie

2013-06-01

Polarization sensitivity is a characteristic of the visual system of cephalopods. It has been well documented in adult cuttlefish, which use polarization sensitivity in a large range of tasks such as communication, orientation and predation. Because cuttlefish do not benefit from parental care, their visual system (including the ability to detect motion) must be efficient from hatching to enable them to detect prey or predators. We studied the maturation and functionality of polarization sensitivity in newly hatched cuttlefish. In a first experiment, we examined the response of juvenile cuttlefish from hatching to the age of 1 month towards a moving, vertically oriented grating (contrasting and polarized stripes) using an optomotor response apparatus. Cuttlefish showed differences in maturation of polarization versus luminance contrast motion detection. In a second experiment, we examined the involvement of polarization information in prey preference and detection in cuttlefish of the same age. Cuttlefish preferentially chose not to attack transparent prey whose polarization contrast had been removed with a depolarizing filter. Performances of prey detection based on luminance contrast improved with age. Polarization contrast can help cuttlefish detect transparent prey. Our results suggest that polarization is not a simple modulation of luminance information, but rather that it is processed as a distinct channel of visual information. Both luminance and polarization sensitivity are functional, though not fully matured, in newly hatched cuttlefish and seem to help in prey detection.

Fast polarizers installation for ECRH and ECE in TCV

Energy Technology Data Exchange (ETDEWEB)

Silva, Miguel, E-mail: miguel.silva@epfl.ch [Ecole Polytechnique Federale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas (CRPP), Association EURATOM-Confederation Suisse, CH-1015 Lausanne (Switzerland); Goodman, Timothy; Felici, Federico; Porte, Laurie [Ecole Polytechnique Federale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas (CRPP), Association EURATOM-Confederation Suisse, CH-1015 Lausanne (Switzerland)

2011-10-15

We report on the installation of fast polarizers for ECRH injection and ECE diagnostics, in the TCV tokamak. The main goal is to change the polarization during a plasma shot and react to changing conditions such as: plasma current and position, ECRH injection angles as well as ECE oblique observation angle and correlation ECE frequency. This will allow tracking of plasma variations, find optimum parameters to maximize ECRH absorption and improve the quality and consistency of ECE measurements. The polarization is varied using two fast polarizers, from General Atomics, positioned either in the evacuated transmission line for ECRH, or in a similar non-evacuated line near a real-time moveable directional antenna for ECE. A programmable driver is used to control a servo-motor and allows three operation modes during a plasma shot: fixed angle position, pre-programmed reference waveform and following of a real-time reference waveform. Preliminary tests of the motor controller achieved an 8 Hz bandwidth for a {+-}4{sup o} amplitude motion and a 2.2 Hz bandwidth for a {+-}4{sup o} amplitude motion. The fast polarizers are presently in the ECE system and the control hardware is being installed.

The role of many-body effects in describing low-lying excited states of pi-conjugated chromophores: high-level equation-of-motion coupled-cluster studies of fused porphyrin systems

Energy Technology Data Exchange (ETDEWEB)

Kowalski, Karol [Pacific Northwest National Laboratory (PNNL); Olson, Ryan M [Cray, Inc.; Krishnamoorthy, Sriram [Pacific Northwest National Laboratory (PNNL); Tipparaju, Vinod [ORNL; Apra, Edoardo [ORNL

2011-01-01

The unusual photophysical properties of the {pi}-conjugated chromophores make them potential building blocks of various molecular devices. In particular, significant narrowing of the HOMO-LUMO gaps can be observed as an effect of functionalization chromophores with polycyclic aromatic hydrocarbons (PAHs). In this paper we present equation-of-motion coupled cluster (EOMCC) calculations for vertical excitation energies of several functionalized forms of porphyrins. The results for free-base porphyrin (FBP) clearly demonstrate significant differences between functionalization of FBP with one- (anthracene) and two-dimensional (coronene) structures. We also compare the EOMCC results with the experimentally available results for anthracene fused zinc-porphyrin. The impact of various types of correlation effects is illustrated on several benchmark models, where the comparison with the experiment is possible. In particular, we demonstrate that for all excited states considered in this paper, all of them being dominated by single excitations, the inclusion of triply excited configurations is crucial for attaining qualitative agreement with experiment. We also demonstrate the parallel performance of the most computationally intensive part of the completely renormalized EOMCCSD(T) approach (CR-EOMCCSD(T)) across 120000 cores.

Effects of uniform extracellular DC electric fields on excitability in rat hippocampal slices in vitro.

Science.gov (United States)

Bikson, Marom; Inoue, Masashi; Akiyama, Hiroki; Deans, Jackie K; Fox, John E; Miyakawa, Hiroyoshi; Jefferys, John G R

2004-05-15

The effects of uniform steady state (DC) extracellular electric fields on neuronal excitability were characterized in rat hippocampal slices using field, intracellular and voltage-sensitive dye recordings. Small electric fields (tips of basal and apical dendrites. The polarization was biphasic in the mid-apical dendrites; there was a time-dependent shift in the polarity reversal site. DC fields altered the thresholds of action potentials evoked by orthodromic stimulation, and shifted their initiation site along the apical dendrites. Large electric fields could trigger neuronal firing and epileptiform activity, and induce long-term (>1 s) changes in neuronal excitability. Electric fields perpendicular to the apical-dendritic axis did not induce somatic polarization, but did modulate orthodromic responses, indicating an effect on afferents. These results demonstrate that DC fields can modulate neuronal excitability in a time-dependent manner, with no clear threshold, as a result of interactions between neuronal compartments, the non-linear properties of the cell membrane, and effects on afferents.

Linear theory of beam depolarization due to vertical betatron motion

International Nuclear Information System (INIS)

Chao, A.W.; Schwitters, R.F.

1976-06-01

It is well known that vertical betatron motion in the presence of quantum fluctuations leads to some degree of depolarization of a transversely polarized beam in electron-positron storage rings even for energies away from spin resonances. Analytic formulations of this problem, which require the use of simplifying assumptions, generally have shown that there exist operating energies where typical storage rings should exhibit significant beam polarization. Due to the importance of beam polarization in many experiments, we present here a complete calculation of the depolarization rate to lowest order in the perturbing fields, which are taken to be linear functions of the betatron motion about the equilibrium orbit. The results are applicable to most high energy storage rings. Explicit calculations are given for SPEAR and PEP. 7 refs., 8 figs

Motion Analysis Based on Invertible Rapid Transform

Directory of Open Access Journals (Sweden)

J. Turan

1999-06-01

Full Text Available This paper presents the results of a study on the use of invertible rapid transform (IRT for the motion estimation in a sequence of images. Motion estimation algorithms based on the analysis of the matrix of states (produced in the IRT calculation are described. The new method was used experimentally to estimate crowd and traffic motion from the image data sequences captured at railway stations and at high ways in large cities. The motion vectors may be used to devise a polar plot (showing velocity magnitude and direction for moving objects where the dominant motion tendency can be seen. The experimental results of comparison of the new motion estimation methods with other well known block matching methods (full search, 2D-log, method based on conventional (cross correlation (CC function or phase correlation (PC function for application of crowd motion estimation are also presented.

Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

NARCIS (Netherlands)

Prins, M.W.J.; Jansen, R.; Kempen, van H.

1996-01-01

We describe a model as well as experiments on spin-polarized tunneling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate

Biological Studies with Laser-Polarized ^129Xe

Science.gov (United States)

Tseng, C. H.; Oteiza, E. R.; Wong, G. A.; Walsworth, R. L.; Albert, M. S.; Nascimben, L.; Peled, S.; Sakai, K.; Jolesz, F. A.

1996-05-01

We have studied several biological systems using laser-polarized ^129Xe. In certain tissues magnetic resonance imaging (MRI) using inhaled laser-polarized noble gases may provide images superior to those from conventional proton MRI. High resolution laser-polarized ^3He images of air spaces in the human lung were recently obtained by the Princeton/Duke group. However, ^3He is not very soluble in tissue. Therefore, we are using laser polarized ^129Xe (tissue-soluble), with the long term goal of biomedical functional imaging. We have investigated multi-echo and multi-excitation magnetic resonance detection schemes to exploit the highly non-thermal ^129Xe magnetization produced by the laser polarization technique. We have inhalated live rats with laser-polarized ^129Xe gas and measured three distinct ^129Xe tissue resonances that last 20 to 40 sec. As a demonstration, we obtained a laser polarized ^129Xe image of the human oral cavity. Currently we are measuring the polarization lifetime of ^129Xe dissolved in human blood, the biological transporting medium. These studies and other recent developments will be reported.

Electrical field excitation in non-uniform plasma by a modulated electron beam

International Nuclear Information System (INIS)

Anisimov, I.O.; Borisov, O.A.

2000-01-01

Excitation of electric fields due to a modulated electron beam in a warm non-uniform plasma is treated for weak beams in warm plasma. It is shown that the maximum electric field magnitude that is reached near the local plasma resonance point depends significantly on the direction of the electron stream motion. In collisional plasma the magnitude of the Langmuir wave that propagates to the subcritical plasma also depends on the direction of the electron stream motion. The motion of the modulated electron stream front results in beatings between oscillations on the modulation frequency and on the local electron plasma frequencies at the initial moment. Later these beatings damp in the supercritical plasma, whereas in the subcritical plasma they are transformed into spatial beatings between the field of the modulated electron stream and the excited Langmuir wave. (orig.)

First attempt of the measurement of the beam polarization at an accelerator with the optical electron polarimeter POLO

CERN Document Server

Collin, B; Essabaa, S; Frascaria, R; Gacougnolle, R; Kunne, Ronald Alexander; Aulenbacher, K; Tioukine, V

2004-01-01

The conventional methods for measuring the polarization of electron beams are either time consuming, invasive or accurate only to a few percent. We developped a method to measure electron beam polarization by observing the light emitted by argon atoms following their excitation by the impact of polarized electrons. The degree of circular polarization of the emitted fluorescence is directly related to the electron polarization. We tested the polarimeter on a test GaAs source available at the MAMI electron accelerator in Mainz, Germany. The polarimeter determines the polarization of a 50 keV electron beam decelerated to a few eV and interacting with an effusive argon gas jet. The resulting decay of the excited states produces the emission of a circularly polarized radiation line at 811.5 nm which is observed and analyzed.

Mexican waves in an excitable medium.

Science.gov (United States)

Farkas, I; Helbing, D; Vicsek, T

2002-09-12

The Mexican wave, or La Ola, which rose to fame during the 1986 World Cup in Mexico, surges through the rows of spectators in a stadium as those in one section leap to their feet with their arms up, and then sit down again as the next section rises to repeat the motion. To interpret and quantify this collective human behaviour, we have used a variant of models that were originally developed to describe excitable media such as cardiac tissue. Modelling the reaction of the crowd to attempts to trigger the wave reveals how this phenomenon is stimulated, and may prove useful in controlling events that involve groups of excited people.

Tracing Magnetic Fields With The Polarization Of Submillimeter Lines

Science.gov (United States)

Zhang, Heshou; Yan, Huirong

2017-10-01

Magnetic fields play important roles in many astrophysical processes. However, there is no universal diagnostic for the magnetic fields in the interstellar medium (ISM) and each magnetic tracer has its limitation. Any new detection method is thus valuable. Theoretical studies have shown that submillimeter fine-structure lines are polarized due to atomic alignment by Ultraviolet (UV) photon-excitation, which opens up a new avenue to probe interstellar magnetic fields. The method is applicable to all radiative-excitation dominant region, e.g., H II Regions, PDRs. The polarization of the submillimeter fine-structure lines induced by atomic alignment could be substantial and the applicability of using the spectro-polarimetry of atomic lines to trace magnetic fields has been supported by synthetic observations of simulated ISM in our recent paper. Our results demonstrate that the polarization of submillimeter atomic lines is a powerful magnetic tracer and add great value to the observational studies of the submilimeter astronomy.

Local polar fluctuations in lead halide perovskites

Science.gov (United States)

Tan, Liang; Yaffe, Omer; Guo, Yinsheng; Brus, Louis; Rappe, Andrew; Egger, David; Kronik, Leeor

The lead halide perovskites have recently attracted much attention because of their large and growing photovoltaic power conversion efficiencies. However, questions remain regarding the temporal and spatial correlations of the structural fluctuations, their atomistic nature, and how they affect electronic and photovoltaic properties. To address these questions, we have performed a combined ab initio molecular dynamics (MD) and density functional theory (DFT) study on CsPbBr3. We have observed prevalent anharmonic motion in our MD trajectories, with local polar fluctuations involving head-to-head motion of A-site Cs cations coupled with Br window opening. We calculate Raman spectra from the polarizability auto-correlation functions obtained from these trajectories and show that anharmonic A-site cation motion manifests as a broad central peak in the Raman spectrum, which increases in intensity with temperature. A comparison of the experimental Raman spectrum of hybrid organometallic MAPbBr3 and fully inorganic CsPbBr3 suggests that structural fluctuations in lead-halide perovskites is more general than rotation of polar organic cations and is intimately coupled to the inorganic framework.

Excitation of giant resonances through inelastic scattering

International Nuclear Information System (INIS)

Kailas, S.

1981-01-01

In the last few years, exciting developments have taken place in the study of giant resonances (GR). In addition to the already well known gjant dipole resonance (GDR), the presence of at least two more new GRs viz. giant quadrupole resonance (GQR) and giant monopole resonance (GMR) has been experimentally established. The systematics covering these GRs is found to be consistent with the theoretical expectation. Though the existence of higher multipoles has been predjcted by theory, so far only some of these have been found to be excited experimentally. Various probe particles - electrons, protons (polarized and unpolarized), light and heavy ions and pions - at different bombarding energies have been used to excite the GR region, primarily through the inelastic scattering process. Detailed experiments, looking at the decay modes of GR region, have also been performed. These studies have contributed significantly to a better understanding of the phenomenon of nuclear collective excitation. In this report, the current status of 'GR' research is reviewed. (author)

Comparison of exciplex generation under optical and X-ray excitation

Science.gov (United States)

Kipriyanov, A. A.; Melnikov, A. R.; Stass, D. V.; Doktorov, A. B.

2017-09-01

Exciplex generation under optical and X-ray excitation in identical conditions is experimentally compared using a specially chosen model donor-acceptor system, anthracene (electron acceptor) and N,N-dimethylaniline (electron donor) in non-polar solution, and the results are analyzed and interpreted based on analytically calculated luminescence quantum yields. Calculations are performed on the basis of kinetic equations for multistage schemes of bulk exciplex production reaction under optical excitation and combination of bulk and geminate reactions of radical ion pairs under X-ray excitation. These results explain the earlier experimentally found difference in the ratio of the quantum yields of exciplexes and excited electron acceptors (exciplex generation efficiency) and the corresponding change in the exciplex generation efficiency under X-irradiation as compared to the reaction under optical excitation.

The optics of secondary polarized proton beams

International Nuclear Information System (INIS)

Carey, D.C.

1990-05-01

Polarized protons can be produced by the parity-violating decay of either lambda or sigma hyperons. A secondary bema of polarized protons can then be produced without the difficult procedure of accelerating polarized protons. The preservation of the polarization while the protons are being transmitted to a final focus places stringent limitations on the optics of the beam line. The equations of motion of a polarized particle in a magnetic field have been solved to first order for quadrupole and dipole magnets. The lowest order terms indicate that the polarization vector will be restored to its original direction upon passage through a magnetic system if the momentum vector is unaltered. Higher-order terms may be derived by an expansion in commutators of the rotation matrix and its longitudinal derivative. The higher-order polarization rotation terms then arise from the non-commutivity of the rotation matrices by large angles in three-dimensional space. 5 refs., 3 figs

Effect of vacuum polarization on the excitation of hydrogen atom by electron impact

Directory of Open Access Journals (Sweden)

Sujata Bhattacharyya

1981-01-01

for 1S−2S excitation of the hydrogen atom by electron impact. The excitation amplitude calculated field theoretically is found to be lowered by 0.47t2/(t2+93 where t2=4|P−Q|2, P and Q being the momenta of the incident and scattered electrons respectively.

Seismic enhancement of multi-span continuous bridges subjected to three-directional excitations

Science.gov (United States)

Aryan, H.; Ghassemieh, M.

2015-04-01

Considering the seismic ground motions as the excitations in only two principal horizontal directions of the bridges and ignoring the third vertical direction is a disregard for the seismic conditions of the region and the bridge distance from epicenter. Numerous cases of substantial damages have been reported among the bridges tremendously suffered from being exposed to the simultaneous three-directional seismic ground motions. Besides the significant compression and tension damages in the columns due to the presence of vertical excitation, it could lead to unexpected shear and flexural failures in the columns and other components as well. Because the axial force variation in the columns due to three-directional excitations, could affect the demands and capacities of the bridge’s components. With respect to this issue, several studies on the bridge damages during the earthquakes have urged researchers to offer efficient methods for bridges handling of the three-directional seismic excitations. Thus, this paper presents and evaluates a superelastic based system for designing as well as retrofitting the multi-span continuous (MSC) bridges that can cope with two- and three-directional seismic excitations. Efficiency evaluation of the proposed system is conducted through various nonlinear time history analyses on a three-dimensional model of a detailed MSC bridge using a suite of developed ground motions for the bridge region. Also, all the analyses are fulfilled based on variation of one influential design characteristic of the proposed system in order to achieve the optimal design. Several pertinent assessment parameters are used during the evaluation of the proposed system. Finally, the efficiency of the new system subjected to the vertical and horizontal seismic excitations is confirmed according to reduction of the bridge responses and improvement in nonlinear performance of the columns in comparison with the as-built bridge results.

Modulating emission polarization of semiconductor quantum dots through surface plasmon of metal nanorod

Science.gov (United States)

Cheng, Mu-Tian; Liu, Shao-Ding; Wang, Qu-Quan

2008-04-01

We theoretically investigated the dynamics of exciton populations [ρyy(t ) and ρxx(t )] on two orthogonal polarization eigenstates (∣x⟩ and ∣y⟩) and the polarization ratio P(t )=[ρyy(t )-ρxx(t )]/[ρyy(t )+ρxx(t )] of an anisotropic InGaAs quantum dot modulated by the surface plasmon of an Au nanorod (NR). In the resonance of longitudinal surface plasmon of AuNR, the polarization ratio P(t ) increases from 0.22 to 0.99 during the excitation due to the efficient enhancement of Rabi frequency of the transition between the ∣y⟩ and vacuum states, and decreases from 0.02 to -0.92 after the excitation pulse due to the enhancement of decay rate of the ∣y⟩ state. This offers an approach to modulate the dynamic polarization ratio of radiative emissions.

Excited-State Dynamics of Carotenoids Studied by Femtosecond Transient Absorption Spectroscopy

International Nuclear Information System (INIS)

Lee, Ingu; Pang, Yoonsoo; Lee, Sebok

2014-01-01

Carotenoids, natural antenna pigments in photosynthesis share a symmetric backbone of conjugated polyenes. Contrary to the symmetric and almost planar geometries of carotenoids, excited state structure and dynamics of carotenoids are exceedingly complex. In this paper, recent infrared and visible transient absorption measurements and excitation dependent dynamics of 8'-apo-β-caroten-8'-al and 7',7'-dicyano-7'-apo-β-carotene will be reviewed. The recent visible transient absorption measurements of 8'-apo-β-caroten-8'-al in polar and nonpolar solvents will also be introduced to emphasize the complex excited-state dynamics and unsolved problems in the S 2 and S 1 excited states

Polarization dependent femtosecond laser modification of MBE-grown III-V nanostructures on silicon

OpenAIRE

Zandbergen, Sander R.; Gibson, Ricky; Amirsolaimani, Babak; Mehravar, Soroush; Keiffer, Patrick; Azarm, Ali; Kieu, Khanh

2017-01-01

We report a novel, polarization dependent, femtosecond laser-induced modification of surface nanostructures of indium, gallium, and arsenic grown on silicon via molecular beam epitaxy, yielding shape control from linear and circular polarization of laser excitation. Linear polarization causes an elongation effect, beyond the dimensions of the unexposed nanostructures, ranging from 88 nm to over 1 um, and circular polarization causes the nanostructures to flatten out or form loops of material,...

Near-field interference for the unidirectional excitation of electromagnetic guided modes.

Science.gov (United States)

Rodríguez-Fortuño, Francisco J; Marino, Giuseppe; Ginzburg, Pavel; O'Connor, Daniel; Martínez, Alejandro; Wurtz, Gregory A; Zayats, Anatoly V

2013-04-19

Wave interference is a fundamental manifestation of the superposition principle with numerous applications. Although in conventional optics, interference occurs between waves undergoing different phase advances during propagation, we show that the vectorial structure of the near field of an emitter is essential for controlling its radiation as it interferes with itself on interaction with a mediating object. We demonstrate that the near-field interference of a circularly polarized dipole results in the unidirectional excitation of guided electromagnetic modes in the near field, with no preferred far-field radiation direction. By mimicking the dipole with a single illuminated slit in a gold film, we measured unidirectional surface-plasmon excitation in a spatially symmetric structure. The surface wave direction is switchable with the polarization.

Nonlinear surge motions of a ship in bi-chromatic following waves

Science.gov (United States)

Spyrou, Kostas J.; Themelis, Nikos; Kontolefas, Ioannis

2018-03-01

Unintended motions of a ship operating in steep and long following waves are investigated. A well-known such case is ;surf-riding; where a ship is carried forward by a single wave, an event invoking sometimes lateral instability and even capsize. The dynamics underlying this behavior has been clarified earlier for monochromatic waves. However, the unsteadiness of the phase space associated with ship behavior in a multichromatic sea, combined with the intrinsically strong system nonlinearity, pose new challenges. Here, current theory is extended to cover surging and surf-riding behavior in unidirectional bi-chromatic waves encountering a ship from the stern. Excitation is provided by two unidirectional harmonic wave components having their lengths comparable to the ship length and their frequencies in rational ratio. The techniques applied include (a) continuation analysis; (b) tracking of Lagrangian coherent structures in phase space, approximated through a finite-time Lyapunov exponents' calculation; and (c) large scale simulation. A profound feature of surf-riding in bi-chromatic waves is that it is turned oscillatory. Initially it appears as a frequency-locked motion, ruled by the harmonic wave component dominating the excitation. Transformations of oscillatory surf-riding are realized as the waves become steeper. In particular, heteroclinic tanglings are identified, governing abrupt transitions between qualitatively different motions. Chaotic transients, as well as long-term chaotic motions, exist near to these events. Some extraordinary patterns of ship motion are discovered. These include a counterintuitive low speed motion at very high wave excitation level; and a hybrid motion characterized by a wildly fluctuating velocity. Due to the quite generic nature of the core mathematical model of our investigation, the current results are believed to offer clues about the behavior of a class of nonlinear dynamical systems having in their modeling some analogy with

Polarization of fluorescence: a probe of molecular autoionization

International Nuclear Information System (INIS)

Leroi, G.E.; Dehmer, J.L.; Parr, A.C.; Poliakoff, E.D.

1983-01-01

The polarization of fluorescence from excited-state molecular photoions provides a direct probe of the photoionization dynamics and the symmetry signatures of autoionizing resonances. Measurements on CO 2 and CS 2 are presented as examples

Gravitational Wave Polarizations in f (R Gravity and Scalar-Tensor Theory

Directory of Open Access Journals (Sweden)

Gong Yungui

2018-01-01

Full Text Available The detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory opens a new era to use gravitational waves to test alternative theories of gravity. We investigate the polarizations of gravitational waves in f (R gravity and Horndeski theory, both containing scalar modes. These theories predict that in addition to the familiar + and × polarizations, there are transverse breathing and longitudinal polarizations excited by the massive scalar mode and the new polarization is a single mixed state. It would be very difficult to detect the longitudinal polarization by interferometers, while pulsar timing array may be the better tool to detect the longitudinal polarization.

Anchored LH2 complexes in 2D polarization imaging.

Science.gov (United States)

Tubasum, Sumera; Sakai, Shunsuke; Dewa, Takehisa; Sundström, Villy; Scheblykin, Ivan G; Nango, Mamoru; Pullerits, Tõnu

2013-09-26

Protein is a soft material with inherently large structural disorder. Consequently, the bulk spectroscopies of photosynthetic pigment protein complexes provide averaged information where many details are lost. Here we report spectroscopy of single light-harvesting complexes where fluorescence excitation and detection polarizations are both independently rotated. Two samples of peripheral antenna (LH2) complexes from Rhodopseudomonas acidophila were studied. In one, the complexes were embedded in polyvinyl alcohol (PVA) film; in the other, they were anchored on the glass surface and covered by the PVA film. LH2 contains two rings of pigment molecules-B800 and B850. The B800 excitation polarization properties of the two samples were found to be very similar, indicating that orientation statistics of LH2s are the same in these two very different preparations. At the same time, we found a significant difference in B850 emission polarization statistics. We conclude that the B850 band of the anchored sample is substantially more disordered. We argue that both B800 excitation and B850 emission polarization properties can be explained by the tilt of the anchored LH2s due to the spin-casting of the PVA film on top of the complexes and related shear forces. Due to the tilt, the orientation statistics of two samples become similar. Anchoring is expected to orient the LH2s so that B850 is closer to the substrate. Consequently, the tilt-related strain leads to larger deformation and disorder in B850 than in B800.

Excited state intramolecular charge transfer reaction in non-aqueous ...

Indian Academy of Sciences (India)

polar phase and thus leading to less swelling of reverse .... ues were restricted up to the limit at which no phase separation was ..... The lower panel of figure 1 also indicates that the slopes of ... probe in its ground and excited states.55.

Multi-modal highlight generation for sports videos using an information-theoretic excitability measure

Science.gov (United States)

Hasan, Taufiq; Bořil, Hynek; Sangwan, Abhijeet; L Hansen, John H.

2013-12-01

The ability to detect and organize `hot spots' representing areas of excitement within video streams is a challenging research problem when techniques rely exclusively on video content. A generic method for sports video highlight selection is presented in this study which leverages both video/image structure as well as audio/speech properties. Processing begins where the video is partitioned into small segments and several multi-modal features are extracted from each segment. Excitability is computed based on the likelihood of the segmental features residing in certain regions of their joint probability density function space which are considered both exciting and rare. The proposed measure is used to rank order the partitioned segments to compress the overall video sequence and produce a contiguous set of highlights. Experiments are performed on baseball videos based on signal processing advancements for excitement assessment in the commentators' speech, audio energy, slow motion replay, scene cut density, and motion activity as features. Detailed analysis on correlation between user excitability and various speech production parameters is conducted and an effective scheme is designed to estimate the excitement level of commentator's speech from the sports videos. Subjective evaluation of excitability and ranking of video segments demonstrate a higher correlation with the proposed measure compared to well-established techniques indicating the effectiveness of the overall approach.

Effects of surface motion and electron-hole pair excitations in CO2 dissociation and scattering on Ni(100)

Science.gov (United States)

Luo, Xuan; Zhou, Xueyao; Jiang, Bin

2018-05-01

The energy transfer between different channels is an important aspect in chemical reactions at surfaces. We investigate here in detail the energy transfer dynamics in a prototypical system, i.e., reactive and nonreactive scattering of CO2 on Ni(100), which is related to heterogeneous catalytic processes with Ni-based catalysts for CO2 reduction. On the basis of our earlier nine-dimensional potential energy surface for CO2/Ni(100), dynamical calculations have been done using the generalized Langevin oscillator (GLO) model combined with local density friction approximation (LDFA), in which the former accounts for the surface motion and the latter accounts for the low-energy electron-hole pair (EHP) excitation. In spite of its simplicity, it is found that the GLO model yields quite satisfactory results, including the significant energy loss and product energy disposal, trapping, and steering dynamics, all of which agree well with the ab initio molecular dynamics ones where many surface atoms are explicitly involved with high computational cost. However, the GLO model fails to describe the reactivity enhancement due to the lattice motion because it intrinsically does not incorporate the variance of barrier height on the surface atom displacement. On the other hand, in LDFA, the energy transferred to EHPs is found to play a minor role and barely alter the dynamics, except for slightly reducing the dissociation probabilities. In addition, vibrational state-selected dissociative sticking probabilities are calculated and previously observed strong mode specificity is confirmed. Our work suggests that further improvement of the GLO model is needed to consider the lattice-induced barrier lowering.

Polarized object detection in crabs: a two-channel system.

Science.gov (United States)

Basnak, Melanie Ailín; Pérez-Schuster, Verónica; Hermitte, Gabriela; Berón de Astrada, Martín

2018-05-25

Many animal species take advantage of polarization vision for vital tasks such as orientation, communication and contrast enhancement. Previous studies have suggested that decapod crustaceans use a two-channel polarization system for contrast enhancement. Here, we characterize the polarization contrast sensitivity in a grapsid crab . We estimated the polarization contrast sensitivity of the animals by quantifying both their escape response and changes in heart rate when presented with polarized motion stimuli. The motion stimulus consisted of an expanding disk with an 82 deg polarization difference between the object and the background. More than 90% of animals responded by freezing or trying to avoid the polarized stimulus. In addition, we co-rotated the electric vector (e-vector) orientation of the light from the object and background by increments of 30 deg and found that the animals' escape response varied periodically with a 90 deg period. Maximum escape responses were obtained for object and background e-vectors near the vertical and horizontal orientations. Changes in cardiac response showed parallel results but also a minimum response when e-vectors of object and background were shifted by 45 deg with respect to the maxima. These results are consistent with an orthogonal receptor arrangement for the detection of polarized light, in which two channels are aligned with the vertical and horizontal orientations. It has been hypothesized that animals with object-based polarization vision rely on a two-channel detection system analogous to that of color processing in dichromats. Our results, obtained by systematically varying the e-vectors of object and background, provide strong empirical support for this theoretical model of polarized object detection. © 2018. Published by The Company of Biologists Ltd.

The scattering of polarized neutrons from statically polarized solid {sup 3}He

Energy Technology Data Exchange (ETDEWEB)

Haase, D.G.; Keith, C.D.; Gould, C.R.; Seely, M.L. [North Carolina State Univ., Raleigh, NC (United States)]|[Triangle Universities Nuclear Laboratory, Durham, NC 27708-0308 (United States); Huffman, P.R.; Roberson, N.R.; Tornow, W.; Wilburn, W.S. [Triangle Universities Nuclear Laboratory, Durham, NC 27708-0308 (United States)]|[Duke University, Durham, NC 27708-0308 (United States)

1998-01-11

We have constructed a 0.4 mole solid {sup 3}He target, cryogenically polarized at 12 mK in a field of 7 T. The 0.04 atoms/b target reached a polarization of 38% in 35 h. Such a target may be applied to any experiment which is tolerant of the large ambient magnetic field and which produces target heating of less than a microwatt. High energy neutron and photon scattering experiments meet these requirements. The target`s figure of merit for neutron transmission measurement exceeds that of polarized gas targets by greater than 35. At the Triangle Universities Nuclear Laboratory we have used the target to measure the total cross section differences {Delta}{sigma}{sub T} and {Delta}{sigma}{sub L} for incident polarized neutrons of energies 2-8 MeV. The cross section difference is sensitive to the excited state structure of the n-{sup 3}He system. The results have been compared to a recent R-matrix analysis of A=4 scattering and reaction data, and provide support for the {sup 4}He level scheme derived from that analysis. (orig.). 11 refs.

Influence of core flows on the decade variations of the polar motion

Science.gov (United States)

Hulot, G.; Le Huy, M.; Le Mouël, J.-L.

We address the possibility for the core flows that generate the geomagnetic field to contribute significantly to the decade variations of the mean pole position (generally called the Markowitz wobble). This assumption is made plausible by the observation that the flow at the surface of the core-estimated from the geomagnetic secular variation models-experiences important changes on this time scale. We discard the viscous and electromagnetic core-mantle couplings and consider only the pressure torque pf resulting from the fluid flow overpressure acting on the non-spherical core-mantle boundary (CMB) at the bottom of the mantle, and the gravity torque gf due to the density heterogeneity driving the core flow. We show that forces within the core balance each other on the time scale considered and, using global integrals over the core, the mantle and the whole Earth, we write Euler's equation for the mantle in terms of two more useful torques Pgeo and . The "geostrophic torque", γ Pgeo incorporates γpf and part of γgf, while γ is another fraction of γgf. We recall how the geostrophic pressure pgeo, and thus γPgeo for a given topography, can be derived from the flow at the CMB and compute the motion of the mean pole from 1900 to 1990, assuming in a first approach that the unknown γ can be neglected. The amplitude of the computed pole motion is three to ten times less than the observed one and out of the phase with it. In order to estimate the possible contribution of γ we then use a second approach and consider the case in which the reference state for the Earth is assumed to be the classical axisymmetric ellipsoidal figure with an almost constant ellipticity within the core. We show that (γPgeo + γ) is then equal to a pseudo-electromagnetic torque γL3, the torque exerted on the core by the component of the Lorentz force along the axis of rotation (this torque exists even though the mantle is assumed insulating). This proves that, at least in this case and

Motion sensing energy controller

International Nuclear Information System (INIS)

Saphir, M.E.; Reed, M.A.

1984-01-01

A moving object sensing processor responsive to slowly varying motions of a human being or other moving object in a zone of interest employs high frequency pulse modulated non-visible radiation generated by a radiation generating source, such as an LED, and detected by a detector sensitive to radiation of a preselected wavelength which generates electrical signals representative of the reflected radiation received from the zone of interest. The detectorsignals are processed to normalize the base level and remove variations due to background level changes, and slowly varying changes in the signals are detected by a bi-polar threshold detector. The control signals generated by the threshold detector in response to slowly varying motion are used to control the application of power to a utilization device, such as a set of fluoroescent lights in a room, the power being applied in response to detection of such motion and being automatically terminated in the absence of such motion after a predetermined time period established by a settable incrementable counter

Polar plot representation of time-resolved fluorescence.

Science.gov (United States)

Eichorst, John Paul; Wen Teng, Kai; Clegg, Robert M

2014-01-01

Measuring changes in a molecule's fluorescence emission is a common technique to study complex biological systems such as cells and tissues. Although the steady-state fluorescence intensity is frequently used, measuring the average amount of time that a molecule spends in the excited state (the fluorescence lifetime) reveals more detailed information about its local environment. The lifetime is measured in the time domain by detecting directly the decay of fluorescence following excitation by short pulse of light. The lifetime can also be measured in the frequency domain by recording the phase and amplitude of oscillation in the emitted fluorescence of the sample in response to repetitively modulated excitation light. In either the time or frequency domain, the analysis of data to extract lifetimes can be computationally intensive. For example, a variety of iterative fitting algorithms already exist to determine lifetimes from samples that contain multiple fluorescing species. However, recently a method of analysis referred to as the polar plot (or phasor plot) is a graphical tool that projects the time-dependent features of the sample's fluorescence in either the time or frequency domain into the Cartesian plane to characterize the sample's lifetime. The coordinate transformations of the polar plot require only the raw data, and hence, there are no uncertainties from extensive corrections or time-consuming fitting in this analysis. In this chapter, the history and mathematical background of the polar plot will be presented along with examples that highlight how it can be used in both cuvette-based and imaging applications.

Nonlinear Dynamic Behavior of a Flexible Structure to Combined External Acoustic and Parametric Excitation

Directory of Open Access Journals (Sweden)

Paulo S. Varoto

2006-01-01

Full Text Available Flexible structures are frequently subjected to multiple inputs when in the field environment. The accurate determination of the system dynamic response to multiple inputs depends on how much information is available from the excitation sources that act on the system under study. Detailed information include, but are not restricted to appropriate characterization of the excitation sources in terms of their variation in time and in space for the case of distributed loads. Another important aspect related to the excitation sources is how inputs of different nature contribute to the measured dynamic response. A particular and important driving mechanism that can occur in practical situations is the parametric resonance. Another important input that occurs frequently in practice is related to acoustic pressure distributions that is a distributed type of loading. In this paper, detailed theoretical and experimental investigations on the dynamic response of a flexible cantilever beam carrying a tip mass to simultaneously applied external acoustic and parametric excitation signals have been performed. A mathematical model for transverse nonlinear vibration is obtained by employing Lagrange’s equations where important nonlinear effects such as the beam’s curvature and quadratic viscous damping are accounted for in the equation of motion. The beam is driven by two excitation sources, a sinusoidal motion applied to the beam’s fixed end and parallel to its longitudinal axis and a distributed sinusoidal acoustic load applied orthogonally to the beam’s longitudinal axis. The major goal here is to investigate theoretically as well as experimentally the dynamic behavior of the beam-lumped mass system under the action of these two excitation sources. Results from an extensive experimental work show how these two excitation sources interacts for various testing conditions. These experimental results are validated through numerically simulated results

Critical excitation method for calculating earthquake effects on nuclear plant structures: an assessment study. Technical report

International Nuclear Information System (INIS)

Bedrosian, B.; Barbela, M.; Drenick, R.F.; Tsirk, A.

1980-10-01

The critical excitation method provides a new, alternative approach to methods presently used for seismic analysis of nuclear power plant structures. The critical excitation method offers the advantages that: (1) it side-steps the assumptions regarding the probability distribution of ground motions, and (2) it does not require an artificial, and to some extent arbitrarily generated, time history of ground motion, both features to which structural integrity analyses are sensitive. Potential utility of the critical excitation method is studied from the user's viewpoint. The method is reviewed and compared with the response spectrum method used in current practice, utilizing the reactor buildings of a PWR and a BWR plant in case studies. Two types of constraints on critical excitation were considered in the study. In one case, only an intensity limit was used. In the other case, imposition of an intensity limit together with limits on the maximum acceleration and/or velocity for the critical excitation is considered

Rotational damping motion in nuclei

International Nuclear Information System (INIS)

Egido, J.L.; Faessler, A.

1991-01-01

The recently proposed model to explain the mechanism of the rotational motion damping in nuclei is exactly solved. When compared with the earlier approximative solution, we find significative differences in the low excitation energy limit (i.e. Γ μ 0 ). For the strength functions we find distributions going from the Wigner semicircle through gaussians to Breit-Wigner shapes. (orig.)

Anatomical Reconstruction and Functional Imaging Reveal an Ordered Array of Skylight Polarization Detectors in Drosophila.

Science.gov (United States)

Weir, Peter T; Henze, Miriam J; Bleul, Christiane; Baumann-Klausener, Franziska; Labhart, Thomas; Dickinson, Michael H

2016-05-11

Many insects exploit skylight polarization as a compass cue for orientation and navigation. In the fruit fly, Drosophila melanogaster, photoreceptors R7 and R8 in the dorsal rim area (DRA) of the compound eye are specialized to detect the electric vector (e-vector) of linearly polarized light. These photoreceptors are arranged in stacked pairs with identical fields of view and spectral sensitivities, but mutually orthogonal microvillar orientations. As in larger flies, we found that the microvillar orientation of the distal photoreceptor R7 changes in a fan-like fashion along the DRA. This anatomical arrangement suggests that the DRA constitutes a detector for skylight polarization, in which different e-vectors maximally excite different positions in the array. To test our hypothesis, we measured responses to polarized light of varying e-vector angles in the terminals of R7/8 cells using genetically encoded calcium indicators. Our data confirm a progression of preferred e-vector angles from anterior to posterior in the DRA, and a strict orthogonality between the e-vector preferences of paired R7/8 cells. We observed decreased activity in photoreceptors in response to flashes of light polarized orthogonally to their preferred e-vector angle, suggesting reciprocal inhibition between photoreceptors in the same medullar column, which may serve to increase polarization contrast. Together, our results indicate that the polarization-vision system relies on a spatial map of preferred e-vector angles at the earliest stage of sensory processing. The fly's visual system is an influential model system for studying neural computation, and much is known about its anatomy, physiology, and development. The circuits underlying motion processing have received the most attention, but researchers are increasingly investigating other functions, such as color perception and object recognition. In this work, we investigate the early neural processing of a somewhat exotic sense, called

Polarization control of multi-photon absorption under intermediate femtosecond laser field

International Nuclear Information System (INIS)

Cheng Wenjing; Liang Guo; Wu Ping; Liu Pei; Jia Tianqing; Sun Zhenrong; Zhang Shian

2017-01-01

It has been shown that the femtosecond laser polarization modulation is a very simple and well-established method to control the multi-photon absorption process by the light–matter interaction. Previous studies mainly focused on the multi-photon absorption control in the weak field. In this paper, we further explore the polarization control behavior of multi-photon absorption process in the intermediate femtosecond laser field. In the weak femtosecond laser field, the second-order perturbation theory can well describe the non-resonant two-photon absorption process. However, the higher order nonlinear effect (e.g., four-photon absorption) can occur in the intermediate femtosecond laser field, and thus it is necessary to establish new theoretical model to describe the multi-photon absorption process, which includes the two-photon and four-photon transitions. Here, we construct a fourth-order perturbation theory to study the polarization control behavior of this multi-photon absorption under the intermediate femtosecond laser field excitation, and our theoretical results show that the two-photon and four-photon excitation pathways can induce a coherent interference, while the coherent interference is constructive or destructive that depends on the femtosecond laser center frequency. Moreover, the two-photon and four-photon transitions have the different polarization control efficiency, and the four-photon absorption can obtain the higher polarization control efficiency. Thus, the polarization control efficiency of the whole excitation process can be increased or decreased by properly designing the femtosecond laser field intensity and laser center frequency. These studies can provide a clear physical picture for understanding and controlling the multi-photon absorption process in the intermediate femtosecond laser field, and also can provide a theoretical guidance for the future experimental realization. (paper)

Correlations of mesospheric winds with subtle motion of the Arctic polar vortex

Directory of Open Access Journals (Sweden)

Y. Bhattacharya

2010-01-01

Full Text Available This paper investigates the relationship between high latitude upper mesospheric winds and the state of the stratospheric polar vortex in the absence of major sudden stratospheric warmings. A ground based Michelson Interferometer stationed at Resolute Bay (74°43' N, 94°58' W in the Canadian High Arctic is used to measure mesopause region neutral winds using the hydroxyl (OH Meinel-band airglow emission (central altitude of ~85 km. These observed winds are compared to analysis winds in the upper stratosphere during November and December of 1995 and 1996; years characterized as cold, stable polar vortex periods. Correlation of mesopause wind speeds with those from the upper stratosphere is found to be significant for the 1996 season when the polar vortex is subtly displaced off its initial location by a strong Aleutian High. These mesopause winds are observed to lead stratospheric winds by approximately two days with increasing (decreasing mesospheric winds predictive of decreasing (increasing stratospheric winds. No statistically significant correlations are found for the 1995 season when there is no such displacement of the polar vortex.

Some applications of polarized inelastic neutron scattering

Indian Academy of Sciences (India)

A brief account of applications of polarized inelastic neutron scattering in condensed matter research is given. ... the itinerant antiferromagnet chromium we demonstrate that the dynamics of the longitudinal and transverse excitations are very different, resolving a long standing puzzle concerning the slope of their dispersion.

Linearly polarized photoluminescence of InGaN quantum disks embedded in GaN nanorods.

Science.gov (United States)

Park, Youngsin; Chan, Christopher C S; Nuttall, Luke; Puchtler, Tim J; Taylor, Robert A; Kim, Nammee; Jo, Yongcheol; Im, Hyunsik

2018-05-25

We have investigated the emission from InGaN/GaN quantum disks grown on the tip of GaN nanorods. The emission at 3.21 eV from the InGaN quantum disk doesn't show a Stark shift, and it is linearly polarized when excited perpendicular to the growth direction. The degree of linear polarization is about 39.3% due to the anisotropy of the nanostructures. In order to characterize a single nanostructure, the quantum disks were dispersed on a SiO 2 substrate patterned with a metal reference grid. By rotating the excitation polarization angle from parallel to perpendicular relative to the nanorods, the variation of overall PL for the 3.21 eV peak was recorded and it clearly showed the degree of linear polarization (DLP) of 51.5%.

The excitation of plasma convection in the high-latitude ionosphere

International Nuclear Information System (INIS)

Lockwood, M.; Cowley, S.W.H.; Freeman, M.P.

1990-01-01

Recent observations of ionospheric flows by ground-based radars, in particular by the European Incoherent Scatter (EISCAT) facility using the Polar experiment, together with previous analyses of the response of geomagnetic disturbance to variations of the interplanetary magnetic field (IMF), suggest that convection in the high-latitude ionosphere should be considered to be the sum of two intrinsically time-dependent patterns, one driven by solar wind-magnetosphere coupling at the dayside magnetopause, the other by the release of energy in the geomagnetic tail (mainly by dayside and nightside reconnection, respectively). The flows driven by dayside coupling are largest on the dayside, where they usually dominate, are associated with an expanding polar cap area, and are excited and decay on ∼ 10-min time scales following southward and northward turnings of the IMF, respectively. The latter finding indicates that the production of new open flux at the dayside magnetopause excites magnetospheric and ionospheric flow only for a short interval, ∼ 10 min, such that the flow driven by this source subsequently decays on this time scale unless maintained by the production of more open flux tubes. Correspondingly, the flows excited by the release of energy in the tail, mainly during substorms, are largest on the nightside, are associated with a contracting polar cap boundary, and are excited on ∼ 1-hour time scales following a southward turn of the IMF. In general, the total ionospheric flow will be the sum of the flows produced by these two sources, such that due to their different response times to changes in the IMF, considerable variations in the flow pattern can occur for a given direction and strength ofthe IMF. Consequently, the ionospheric electric field cannot generally be regarded as arising from a simple mapping of the solar wind electric field along open flux tubes

Excited-state inter- and intramolecular proton transfer in methyl 3-hydroxy-2-quinoxalinate: effects of solvent and acid or base concentrations

International Nuclear Information System (INIS)

Dogra, S.K.

2005-01-01

Absorption, fluorescence excitation and fluorescence spectroscopy, combined with time-dependent spectroscopy and semi-empirical (AM1) and density functional theory using Gaussian 98 program calculations have been used to study the effects of solvent and acid or base concentration on the spectral characteristics of methyl 3-hydroxy-2-quinoxalinate (M3HQ). M3HQ is present as enol in less polar solvents and as keto in polar media. In non-polar solvents, large Stokes shifted fluorescence band is assigned to the phototautomer, formed by the excited-state intramolecular proton transfer, whereas fluorescence is only observed from keto in the polar solvents. In aqueous and polar solvents the monocation (MC5/MC6) is formed by protonating the carbonyl oxygen atom in the ground (S 0 ) and the first excited singlet states (S 1 ). Dication is formed by protonating one of ?N- atom of MC5/MC6. Monoanion is formed by deprotonating the phenolic proton of enol in the basic solution. pK a values for different prototropic equilibriums were determined in S 0 and S 1 states and discussed

Excited-State Dynamics of Carotenoids Studied by Femtosecond Transient Absorption Spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Lee, Ingu; Pang, Yoonsoo [Department of Physics and Photon Science, Gwangju (Korea, Republic of); Lee, Sebok [Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of)

2014-03-15

Carotenoids, natural antenna pigments in photosynthesis share a symmetric backbone of conjugated polyenes. Contrary to the symmetric and almost planar geometries of carotenoids, excited state structure and dynamics of carotenoids are exceedingly complex. In this paper, recent infrared and visible transient absorption measurements and excitation dependent dynamics of 8'-apo-β-caroten-8'-al and 7',7'-dicyano-7'-apo-β-carotene will be reviewed. The recent visible transient absorption measurements of 8'-apo-β-caroten-8'-al in polar and nonpolar solvents will also be introduced to emphasize the complex excited-state dynamics and unsolved problems in the S{sub 2} and S{sub 1} excited states.

Spin-polarized x-ray emission of 3d transition-metal ions : A comparison via K alpha and K beta detection

NARCIS (Netherlands)

Wang, Xin; deGroot, F.M.F.; Cramer, SP

1997-01-01

This paper demonstrates that spin-polarized x-ray-excitation spectra can be obtained using K alpha emission as well as K beta lines. A spin-polarized analysis of K alpha x-ray emission and the excitation spectra by K alpha detection on a Ni compound is reported. A systematic analysis of the

Time-resolved stimulated emission depletion and energy transfer dynamics in two-photon excited EGFP

Science.gov (United States)

Masters, T. A.; Robinson, N. A.; Marsh, R. J.; Blacker, T. S.; Armoogum, D. A.; Larijani, B.; Bain, A. J.

2018-04-01

Time and polarization-resolved stimulated emission depletion (STED) measurements are used to investigate excited state evolution following the two-photon excitation of enhanced green fluorescent protein (EGFP). We employ a new approach for the accurate STED measurement of the hitherto unmeasured degree of hexadecapolar transition dipole moment alignment ⟨α40 ⟩ present at a given excitation-depletion (pump-dump) pulse separation. Time-resolved polarized fluorescence measurements as a function of pump-dump delay reveal the time evolution of ⟨α40 ⟩ to be considerably more rapid than predicted for isotropic rotational diffusion in EGFP. Additional depolarization by homo-Förster resonance energy transfer is investigated for both ⟨α20 ⟩ (quadrupolar) and ⟨α40 ⟩ transition dipole alignments. These results point to the utility of higher order dipole correlation measurements in the investigation of resonance energy transfer processes.

Colloidal InP/ZnS core-shell nanocrystals studied by linearly and circularly polarized photoluminescence

International Nuclear Information System (INIS)

Langof, L.; Fradkin, L.; Ehrenfreund, E.; Lifshitz, E.; Micic, O.I.; Nozik, A.J.

2004-01-01

The magneto-optical properties of InP/ZnS core-shell nanocrystals (NCs) were investigated by measuring the degree of linear and circular polarization of photoluminescence (PL) spectra, in the presence of an external magnetic field under resonant or non-resonant excitation. The linearly polarized PL data strongly indicate that InP/ZnS NCs have a prolongated shape. The resonant-excited circularly polarized PL decay curves indicate that the spin relaxation time of the studied samples is shorter than the radiative lifetime of their exciton. Furthermore, the magnetic field-induced circularly polarized PL process reveals an exciton g factor (g ex ) of 0.55. Thus, such studies may serve as a tool to directly estimate the NC's shape anisotropy and to determine the g-factor of charge carriers and excitons in those NCs

Colloidal InP/ZnS core shell nanocrystals studied by linearly and circularly polarized photoluminescence

Science.gov (United States)

Langof, L.; Fradkin, L.; Ehrenfreund, E.; Lifshitz, E.; Micic, O. I.; Nozik, A. J.

2004-02-01

The magneto-optical properties of InP/ZnS core-shell nanocrystals (NCs) were investigated by measuring the degree of linear and circular polarization of photoluminescence (PL) spectra, in the presence of an external magnetic field under resonant or non-resonant excitation. The linearly polarized PL data strongly indicate that InP/ZnS NCs have a prolongated shape. The resonant-excited circularly polarized PL decay curves indicate that the spin relaxation time of the studied samples is shorter than the radiative lifetime of their exciton. Furthermore, the magnetic field-induced circularly polarized PL process reveals an exciton g factor ( gex) of 0.55. Thus, such studies may serve as a tool to directly estimate the NC's shape anisotropy and to determine the g-factor of charge carriers and excitons in those NCs.

Human motion sensing and recognition a fuzzy qualitative approach

CERN Document Server

Liu, Honghai; Ji, Xiaofei; Chan, Chee Seng; Khoury, Mehdi

2017-01-01

This book introduces readers to the latest exciting advances in human motion sensing and recognition, from the theoretical development of fuzzy approaches to their applications. The topics covered include human motion recognition in 2D and 3D, hand motion analysis with contact sensors, and vision-based view-invariant motion recognition, especially from the perspective of Fuzzy Qualitative techniques. With the rapid development of technologies in microelectronics, computers, networks, and robotics over the last decade, increasing attention has been focused on human motion sensing and recognition in many emerging and active disciplines where human motions need to be automatically tracked, analyzed or understood, such as smart surveillance, intelligent human-computer interaction, robot motion learning, and interactive gaming. Current challenges mainly stem from the dynamic environment, data multi-modality, uncertain sensory information, and real-time issues. These techniques are shown to effectively address the ...

Simulations of Polarization Levels and Spin Tune Biases in High Energy Leptons Storage Rings

Energy Technology Data Exchange (ETDEWEB)

Gianfelice, E. [Fermilab

2016-01-01

The use of resonant depolarization has been suggested for precise beam energy measurements in the 100 km long Future Circular Collider e+e-. The principle behind resonant depolarization is that a vertically polarized beam excited through an oscillating horizontal magnetic field gets depolarized when the excitation frequency is in a given relationship with the beam energy. In this paper the possibility of self- polarized leptons at 45 GeV (Z resonance) and 80 GeV (WW in presence of quadrupole vertical misalignment is investigated.

Software package for modeling spin-orbit motion in storage rings

Science.gov (United States)

Zyuzin, D. V.

2015-12-01

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 106-109 particles in a beam during 109 turns in an accelerator (about 1012-1015 integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin-orbit dynamics.

An efficient source of continuous variable polarization entanglement

DEFF Research Database (Denmark)

Dong, R.; Heersink, J.; Yoshikawa, J.-I.

2007-01-01

classical excitation in Ŝ3. Polarization entanglement was generated by interfering two independent polarization squeezed fields on a symmetric beam splitter. The resultant beams exhibit strong quantum noise correlations in the dark Ŝ1-Ŝ2 polarization plane. To verify entanglement generation, we......We have experimentally demonstrated the efficient creation of highly entangled bipartite continuous variable polarization states. Exploiting an optimized scheme for the production of squeezing using the Kerr non-linearity of a glass fibre we generated polarization squeezed pulses with a mean...... was found to depend critically on the beam-splitting ratio of the entangling beam splitter. Carrying out measurements on a different set of conjugate Stokes parameters, correlations of -3.6 ±0.3 and -3.4 ±0.3 dB have been observed. This result is more robust against asymmetries in the entangling beam...

Quantum mechanical equations of particle and spin motion in polarised medium

International Nuclear Information System (INIS)

Silenko, A.Ya.

2003-01-01

The quantum mechanical equations for the particles and spin motion in the media with polarized electrons by presence of the external fields are determined. The motion of the electrons and their spin are influenced by the exchange interaction whereas the motion of the positrons is the annihilation one. The second order summands by spin are accounted for the particles with the S≥1 spin. The obtained equations may applied for describing the particles and spin motion both in the magnetic and nonmagnetic media [ru

Robust structural design against self-excited vibrations

CERN Document Server

Spelsberg-Korspeter, Gottfried

2013-01-01

This book studies methods for a robust design of rotors against self-excited vibrations. The occurrence of self-excited vibrations in engineering applications if often unwanted and in many cases difficult to model. Thinking of complex systems such as machines with many components and mechanical contacts, it is important to have guidelines for design so that the functionality is robust against small imperfections. This book discusses the question on how to design a structure such that unwanted self-excited vibrations do not occur. It shows theoretically and practically that the old design rule to avoid multiple eigenvalues points toward the right direction and have optimized structures accordingly. This extends results for the well-known flutter problem in which equations of motion with constant coefficients occur to the case of a linear conservative system with arbitrary time periodic perturbations.

Creation of skyrmion through resonance excitation

Energy Technology Data Exchange (ETDEWEB)

Li, Zhi-xiong; Chen, Yi-fu; Zhou, Zhen-wei; Nie, Yao-zhuang; Xia, Qing-lin; Wang, Dao-wei; Guo, Guang-hua, E-mail: guogh@mail.csu.edu.cn

2017-07-01

Highlights: • Intrinsic oscillation modes of skyrmion are studied by using micromagnetic simulation. • Creation of skyrmion through resonant excitation is proposed. • The number of generated skyrmions can be effectively controlled by manipulating the driving field. • Skyrmion lattice in extended film is generated via resonant excitation. - Abstract: Controllable creation of magnetic skyrmions in nanostructures is a prerequisite for the application of skyrmions in spintronics. Here, we propose a new method for the creation of skyrmions. We show by using micromagnetic simulations that the skyrmions can be nucleated by resonantly exciting one of the skyrmion intrinsic oscillation modes. We first studied the dynamics of skyrmion in a ferromagnetic nanodisk with perpendicular anisotropy. One breathing mode and two non-degenerate gyrotropic modes are identified. Then we applied a circular-polarized microwave field to excite the uniformly magnetized nanodisk. When the frequency of the driving field is equal to the eigenfrequency of the skyrmion gyrotropic mode, stable skyrmions can be created from the initial uniform state. The number of skyrmions can be effectively controlled by appropriately choosing the duration of the driving field or tuning the field amplitude.

Observation of Polarization Vortices in Momentum Space

Science.gov (United States)

Zhang, Yiwen; Chen, Ang; Liu, Wenzhe; Hsu, Chia Wei; Wang, Bo; Guan, Fang; Liu, Xiaohan; Shi, Lei; Lu, Ling; Zi, Jian

2018-05-01

The vortex, a fundamental topological excitation featuring the in-plane winding of a vector field, is important in various areas such as fluid dynamics, liquid crystals, and superconductors. Although commonly existing in nature, vortices were observed exclusively in real space. Here, we experimentally observed momentum-space vortices as the winding of far-field polarization vectors in the first Brillouin zone of periodic plasmonic structures. Using homemade polarization-resolved momentum-space imaging spectroscopy, we mapped out the dispersion, lifetime, and polarization of all radiative states at the visible wavelengths. The momentum-space vortices were experimentally identified by their winding patterns in the polarization-resolved isofrequency contours and their diverging radiative quality factors. Such polarization vortices can exist robustly on any periodic systems of vectorial fields, while they are not captured by the existing topological band theory developed for scalar fields. Our work provides a new way for designing high-Q plasmonic resonances, generating vector beams, and studying topological photonics in the momentum space.

Angular momentum from CMIP5 climate change simulations, as related to Earth rotation excitation

Science.gov (United States)

Salstein, D.; Quinn, K.

2012-04-01

Atmospheric angular momentum parameters are calculated from revised scenarios of greenhouse gas concentration in use in the Coupled Model Intercomparison Project, phase 5, which investigates expected climate change. This phase includes new estimates for the so-called Representative Concentration Pathways (RCP), designed to simulate more realistically the future path of emissions of carbon dioxide and other greenhouse gases throughout the 21st century. From time series of atmosphere-ocean models that adopt these parameters, we calculate the impact on the excitations for length of day and polar motion through the course of the current century, and hence portions of the expected changes in the ERP's due to the atmosphere. We diagnose the most important geographic areas as regional sources of such variations; earlier such models revealed the particular importance of resulting relevant wind changes in the upper atmosphere of the middle latitudes and the southern hemisphere high latitudes. The spread among the RCP scenarios and among a number of different models gives us an understanding of possible uncertainties in the estimates. Earlier calculations were for the 20th and 21st centuries with less sophisticated greenhouse gas concentration scenarios. We can compare the Earth rotation excitations from the retrospective portions of the model-based estimates with atmospheric reanalyses that are in archives at the IERS Special Bureau for the Atmosphere.

Polarization-Sensitive Resonance CSRS of Deoxy- and Oxyhaemoglobin

NARCIS (Netherlands)

Voroshilov, A.; Voroshilov, Artemy; Lucassen, Gerald; Lucassen, Gerald W.; Otto, Cornelis; Greve, Jan

1995-01-01

Polarization-sensitive coherent Stokes Raman scattering (CSRS) measurements of oxy- and deoxyhaemoglobin in aqueous solutions are reported. The excitation wavelengths used were chosen in the region of the Q absorption bands to achieve twofold electronic resonance. The dispersion profiles of all

Analytic energy gradient of excited electronic state within TDDFT/MMpol framework: Benchmark tests and parallel implementation.

Science.gov (United States)

Zeng, Qiao; Liang, WanZhen

2015-10-07

The time-dependent density functional theory (TDDFT) has become the most popular method to calculate the electronic excitation energies, describe the excited-state properties, and perform the excited-state geometric optimization of medium and large-size molecules due to the implementation of analytic excited-state energy gradient and Hessian in many electronic structure software packages. To describe the molecules in condensed phase, one usually adopts the computationally efficient hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) models. Here, we extend our previous work on the energy gradient of TDDFT/MM excited state to account for the mutual polarization effects between QM and MM regions, which is believed to hold a crucial position in the potential energy surface of molecular systems when the photoexcitation-induced charge rearrangement in the QM region is drastic. The implementation of a simple polarizable TDDFT/MM (TDDFT/MMpol) model in Q-Chem/CHARMM interface with both the linear response and the state-specific features has been realized. Several benchmark tests and preliminary applications are exhibited to confirm our implementation and assess the effects of different treatment of environmental polarization on the excited-state properties, and the efficiency of parallel implementation is demonstrated as well.

Polarization of submillimetre lines from interstellar medium

Science.gov (United States)

Zhang, Heshou; Yan, Huirong

2018-04-01

Magnetic fields play important roles in many astrophysical processes. However, there is no universal diagnostic for the magnetic fields in the interstellar medium (ISM) and each magnetic tracer has its limitation. Any new detection method is thus valuable. Theoretical studies have shown that submillimetre fine-structure lines are polarized due to atomic alignment by ultraviolet photon-excitation, which opens up a new avenue to probe interstellar magnetic fields. We will, for the first time, perform synthetic observations on the simulated three-dimensional ISM to demonstrate the measurability of the polarization of submillimetre atomic lines. The maximum polarization for different absorption and emission lines expected from various sources, including star-forming regions are provided. Our results demonstrate that the polarization of submillimetre atomic lines is a powerful magnetic tracer and add great value to the observational studies of the submilimetre astronomy.

Excited-State Conformational/Electronic Responses of Saddle-Shaped N,N'-Disubstituted-Dihydrodibenzo[a,c]phenazines: Wide-Tuning Emission from Red to Deep Blue and White Light Combination.

Science.gov (United States)

Zhang, Zhiyun; Wu, Yu-Sin; Tang, Kuo-Chun; Chen, Chi-Lin; Ho, Jr-Wei; Su, Jianhua; Tian, He; Chou, Pi-Tai

2015-07-08

A tailored strategy is utilized to modify 5,10-dimethylphenazine (DMP) to donor-acceptor type N,N'-disubstituted-dihydrodibenzo[a,c]phenazines. The representative compounds DMAC (N,N'-dimethyl), DPAC (N,N'-diphenyl), and FlPAC (N-phenyl-N'-fluorenyl) reveal significant nonplanar distortions (i.e., a saddle shape) and remarkably large Stokes-shifted emission independent of the solvent polarity. For DPAC and FlPAC with higher steric hindrance on the N,N'-substituents, normal Stokes-shifted emission also appears, for which the peak wavelength reveals solvent-polarity dependence. These unique photophysical behaviors are rationalized by electronic configuration coupled conformation changes en route to the geometry planarization in the excited state. This proposed mechanism is different from the symmetry rule imposed to explain the anomalously long-wavelength emission for DMP and is firmly supported by polarity-, viscosity-, and temperature-dependent steady-state and nanosecond time-resolved spectroscopy. Together with femtosecond early dynamics and computational simulation of the reaction energy surfaces, the results lead us to establish a sequential, three-step kinetics. Upon electronic excitation of N,N'-disubstituted-dihydrodibenzo[a,c]phenazines, intramolecular charge-transfer takes place, followed by the combination of polarization stabilization and skeletal motion toward the planarization, i.e., elongation of the π-delocalization over the benzo[a,c]phenazines moiety. Along the planarization, DPAC and FlPAC encounter steric hindrance raised by the N,N'-disubstitutes, resulting in a local minimum state, i.e., the intermediate. The combination of initial charge-transfer state, intermediate, and the final planarization state renders the full spectrum of interest and significance in their anomalous photophysics. Depending on rigidity, the N,N'-disubstituted-dihydrodibenzo[a,c]phenazines exhibit multiple emissions, which can be widely tuned from red to deep blue and

Polarization Sensitive Coherent Raman Measurements of DCVJ

Science.gov (United States)

Anderson, Josiah; Cooper, Nathan; Lawhead, Carlos; Shiver, Tegan; Ujj, Laszlo

2014-03-01

Coherent Raman spectroscopy which recently developed into coherent Raman microscopy has been used to produce label free imaging of thin layers of material and find the spatial distributions of certain chemicals within samples, e.g. cancer cells.(1) Not all aspects of coherent scattering have been used for imaging. Among those for example are special polarization sensitive measurements. Therefore we have investigated the properties of polarization sensitive CARS spectra of a highly fluorescent molecule, DCVJ.(2) Spectra has been recorded by using parallel polarized and perpendicular polarized excitations. A special polarization arrangement was developed to suppress the non-resonant background scattering from the sample. These results can be used to improve the imaging properties of a coherent Raman microscope in the future. This is the first time coherent Raman polarization sensitive measurements have been used to characterize the vibrational modes of DCVJ. 1: K. I. Gutkowski, et al., ``Fluorescence of dicyanovinyl julolidine in a room temperature ionic liquid '' Chemical Physics Letters 426 (2006) 329 - 333 2: Fouad El-Diasty, ``Coherent anti-Stokes Raman scattering: Spectroscopy and microscopy'' Vibrational Spectroscopy 55 (2011) 1-37

Coherent Motion Reveals Non‐Ergodic Nature of Internal Conversion between Excited States

DEFF Research Database (Denmark)

Kuhlman, Thomas Scheby; Sølling, Theis I.; Møller, Klaus Braagaard

2012-01-01

for smaller molecules. Specifically, we focus on the S2→S1 internal conversion in cyclobutanone, cyclopentanone, and cyclohexanone. By means of time‐resolved mass spectrometry and photoelectron spectroscopy the relative rate of this transition is determined to be 13:2:1. Remarkably, we observe coherent......We found that specific nuclear motion along low‐frequency modes is effective in coupling electronic states and that this motion prevail in some small molecules. Thus, in direct contradiction to what is expected based on the standard models, the internal conversion process can proceed faster...

Ultra-Wideband, Dual-Polarized, Beam-Steering P-Band Array Antenna

Science.gov (United States)

duToit, Cornelis

2014-01-01

pair of elements: three apertures coupling to the patch elements were placed along the two symmetry lines of the antenna element pair. Two apertures were used in tandem to excite two of the stacked patch elements for one polarization; the other was used to excite one element from one side and the other element from the other side, opposite in phase, taking care of the remaining polarization. The apertures narrow down to a small gap where they are excited by a crossing microstrip line to prevent any asymmetrical excitation of the two sides of the aperture gap, minimizing port-to-port coupling. Using patches that are non-planar leads to higher mechanical rigidity and smaller patch sizes to fit into the available space. Aperture coupling minimizes direct metal-to-metal connections. Using an aperture coupling feed mechanism results in a feed network for two antenna elements with a total of three feed points, plus one simple in-phase combiner to reduce it to two ports. It greatly reduces the complexity of the alternative, but more conventional, way of feeding a pair of two dual-polarized elements with high port isolation.

Excitations in superfluid systems: contributions of the nuclear structure; Excitations dans les systemes superfluides: contributions de la structure nucleaire

Energy Technology Data Exchange (ETDEWEB)

Khan, E

2005-12-15

The author presents successively the theoretical aspect, the experimental aspect and the applied aspect of excitations in nuclear structures. The quasi-particle random phase approximation (QRPA) tool is first described. Recent approaches on QRPA are based on the theory of the density function where the ground state and excited states are described from the same nucleon-nucleon interaction. 2 methods for measuring the collective excitations are then presented: the proton scattering that has the potentiality to investigate the evolution of magicity, the second method is in fact a new method for measuring the giant mono-polar resonance (GMP) in exotic nuclei. Nuclear reactions are considered as a compulsory step on the way from observables like cross-sections to nuclear structure. The author highlights the assets of the convolution model that can generate the optical potential from the effective nucleon-nucleon interaction and from proton and neutron densities of the nuclei involved. R-processes in nucleosynthesis and neutron stars are reviewed as applications of collective excitations in the field of nuclear astrophysics. (A.C.)

Multiband Circular Polarizer Based on Fission Transmission of Linearly Polarized Wave for X-Band Applications

Directory of Open Access Journals (Sweden)

Farman Ali Mangi

2016-01-01

Full Text Available A multiband circular polarizer based on fission transmission of linearly polarized wave for x-band application is proposed, which is constructed of 2 × 2 metallic strips array. The linear-to-circular polarization conversion is obtained by decomposing the linearly incident x-polarized wave into two orthogonal vector components of equal amplitude and 90° phase difference between them. The innovative approach of “fission transmission of linear-to-circular polarized wave” is firstly introduced to obtain giant circular dichroism based on decomposition of orthogonal vector components through the structure. It means that the incident linearly polarized wave is converted into two orthogonal components through lower printed metallic strips layer and two transmitted waves impinge on the upper printed strips layer to convert into four orthogonal vector components at the end of structure. This projection and transmission sequence of orthogonal components sustain the chain transmission of electromagnetic wave and can achieve giant circular dichroism. Theoretical analysis and microwave experiments are presented to validate the performance of the structure. The measured results are in good agreement with simulation results. In addition, the proposed circular polarizer exhibits the optimal performance with respect to the normal incidence. The right handed circularly polarized wave is emitted ranging from 10.08 GHz to 10.53 GHz and 10.78 GHz to 11.12 GHz, while the left handed circular polarized wave is excited at 10.54 GHz–10.70 GHz and 11.13 GHz–11.14 GHz, respectively.

Effective interactions, elementary excitations, and transport in the helium liquids

International Nuclear Information System (INIS)

Pines, D.

1986-01-01

Polarization potentials, the self-consistent fields which describe the primary consequences of the strong atom-atom interaction in the helium liquids, are developed for liquid 4 He and 3 He. Emphasis is placed on the common physical origin of the effective interactions in all helium liquids, and the hierarchy of physical effects (very short-range atomic correlations, zero point motion, and the Pauli principle) which determine their strength is reviewed. An overview is then given of the application of polarization potential theory to experiment, including the phonon-maxon-roton spectra of 4 He and 3 He- 4 He mixtures, the phonon-maxon spectrum of normal and spin-polarized 3 He, and the transport properties of superfluid 4 He and of normal and spin-polarized 3 He

Moessbauer polarimetry using fluosilicates. Double motion drive and effective thickness measurements

Energy Technology Data Exchange (ETDEWEB)

Henry, M; Varret, F [Centre Universitaire du Mans, 72 (France)

1977-12-16

Calculations are made and spectra are obtained on linear experiments using single crystals. The energy coincidence between the source and the polarizer is achieved by using a double motion drive which moves the source at a constant velocity. Such an experiment provides an accurate determination of both the polarizer and the analyzer effective thicknesses.

Analysis of the multipactor effect in circular waveguides excited by two orthogonal polarization waves

Energy Technology Data Exchange (ETDEWEB)

Pérez, A. M.; Boria, V. E. [Departamento de Comunicaciones-iTEAM, Universidad Politécnica de Valencia Camino de Vera s/n, 46022 Valencia (Spain); Gimeno, B. [Departamento de Física Aplicada y Electromagnetismo-ICMUV, Universitat de València c/Dr. Moliner, 50, 46100 Valencia (Spain); Anza, S.; Vicente, C.; Gil, J. [Aurora Software and Testing S.L., Edificio de Desarrollo Empresarial 9B, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain)

2014-08-15

Circular waveguides, either employed as resonant cavities or as irises connecting adjacent guides, are widely present in many passive components used in different applications (i.e., particle accelerators and satellite subsystems). In this paper, we present the study of the multipactor effect in circular waveguides considering the coexistence of the two polarizations of the fundamental TE{sub 11} circular waveguide mode. For a better understanding of the problem, only low multipactor orders have been explored as a function of the polarization ellipse eccentricity. Special attention has been paid to the linear and circular polarizations, but other more general configurations have also been explored.

Analysis of the multipactor effect in circular waveguides excited by two orthogonal polarization waves

International Nuclear Information System (INIS)

Pérez, A. M.; Boria, V. E.; Gimeno, B.; Anza, S.; Vicente, C.; Gil, J.

2014-01-01

Circular waveguides, either employed as resonant cavities or as irises connecting adjacent guides, are widely present in many passive components used in different applications (i.e., particle accelerators and satellite subsystems). In this paper, we present the study of the multipactor effect in circular waveguides considering the coexistence of the two polarizations of the fundamental TE 11 circular waveguide mode. For a better understanding of the problem, only low multipactor orders have been explored as a function of the polarization ellipse eccentricity. Special attention has been paid to the linear and circular polarizations, but other more general configurations have also been explored

Analysis of Real Ship Rolling Dynamics under Wave Excitement Force Composed of Sums of Cosine Functions

International Nuclear Information System (INIS)

Zhang, Y. S.; Cai, F.; Xu, W. M.

2011-01-01

The ship motion equation with a cosine wave excitement force describes the slip moments in regular waves. A new kind of wave excitement force model, with the form as sums of cosine functions was proposed to describe ship rolling in irregular waves. Ship rolling time series were obtained by solving the ship motion equation with the fourth-order-Runger-Kutta method. These rolling time series were synthetically analyzed with methods of phase-space track, power spectrum, primary component analysis, and the largest Lyapunove exponent. Simulation results show that ship rolling presents some chaotic characteristic when the wave excitement force was applied by sums of cosine functions. The result well explains the course of ship rolling's chaotic mechanism and is useful for ship hydrodynamic study.

Colloidal InP/ZnS core-shell nanocrystals studied by linearly and circularly polarized photoluminescence

Energy Technology Data Exchange (ETDEWEB)

Langof, L.; Fradkin, L.; Ehrenfreund, E.; Lifshitz, E.; Micic, O.I.; Nozik, A.J

2004-02-16

The magneto-optical properties of InP/ZnS core-shell nanocrystals (NCs) were investigated by measuring the degree of linear and circular polarization of photoluminescence (PL) spectra, in the presence of an external magnetic field under resonant or non-resonant excitation. The linearly polarized PL data strongly indicate that InP/ZnS NCs have a prolongated shape. The resonant-excited circularly polarized PL decay curves indicate that the spin relaxation time of the studied samples is shorter than the radiative lifetime of their exciton. Furthermore, the magnetic field-induced circularly polarized PL process reveals an exciton g factor (g{sub ex}) of 0.55. Thus, such studies may serve as a tool to directly estimate the NC's shape anisotropy and to determine the g-factor of charge carriers and excitons in those NCs.

Non-iterative triple excitations in equation-of-motion coupled-cluster theory for electron attachment with applications to bound and temporary anions

Science.gov (United States)

Jagau, Thomas-C.

2018-01-01

The impact of residual electron correlation beyond the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) approximation on positions and widths of electronic resonances is investigated. To establish a method that accomplishes this task in an economical manner, several approaches proposed for the approximate treatment of triple excitations are reviewed with respect to their performance in the electron attachment (EA) variant of EOM-CC theory. The recently introduced EOM-CCSD(T)(a)* method [D. A. Matthews and J. F. Stanton, J. Chem. Phys. 145, 124102 (2016)], which includes non-iterative corrections to the reference and the target states, reliably reproduces vertical attachment energies from EOM-EA-CC calculations with single, double, and full triple excitations in contrast to schemes in which non-iterative corrections are applied only to the target states. Applications of EOM-EA-CCSD(T)(a)* augmented by a complex absorbing potential (CAP) to several temporary anions illustrate that shape resonances are well described by EOM-EA-CCSD, but that residual electron correlation often makes a non-negligible impact on their positions and widths. The positions of Feshbach resonances, on the other hand, are significantly improved when going from CAP-EOM-EA-CCSD to CAP-EOM-EA-CCSD(T)(a)*, but the correct energetic order of the relevant electronic states is still not achieved.

Electronic Excitations in Solution: The Interplay between State Specific Approaches and a Time-Dependent Density Functional Theory Description.

Science.gov (United States)

Guido, Ciro A; Jacquemin, Denis; Adamo, Carlo; Mennucci, Benedetta

2015-12-08

We critically analyze the performances of continuum solvation models when coupled to time-dependent density functional theory (TD-DFT) to predict solvent effects on both absorption and emission energies of chromophores in solution. Different polarization schemes of the polarizable continuum model (PCM), such as linear response (LR) and three different state specific (SS) approaches, are considered and compared. We show the necessity of introducing a SS model in cases where large electron density rearrangements are involved in the excitations, such as charge-transfer transitions in both twisted and quadrupolar compounds, and underline the very delicate interplay between the selected polarization method and the chosen exchange-correlation functional. This interplay originates in the different descriptions of the transition and ground/excited state multipolar moments by the different functionals. As a result, the choice of both the DFT functional and the solvent polarization scheme has to be consistent with the nature of the studied electronic excitation.

Optimized design of polarizers with low ohmic loss and any polarization state for the 28 GHz QUEST ECH/ECCD system

Energy Technology Data Exchange (ETDEWEB)

Tsujimura, Toru Ii, E-mail: tsujimura.tohru@nifs.ac.jp [National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292 (Japan); Idei, Hiroshi [Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580 (Japan); Kubo, Shin; Kobayashi, Sakuji [National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292 (Japan)

2017-01-15

Highlights: • Ohmic loss was calculated on the grooved mirror surface in simulated polarizers. • Polarizers with a low ohmic loss feature were optimally designed for 28 GHz. • Smooth rounded-rectangular grooves were made by mechanical machining. • The designed polarizers can realize all polarization states. - Abstract: In a high-power long-pulse millimeter-wave transmission line for electron cyclotron heating and current drive (ECH/ECCD), the ohmic loss on the grooved mirror surface of polarizers is one of the important issues for reducing the transmission loss. In this paper, the ohmic loss on the mirror surface is evaluated in simulated real-scale polarizer miter bends for different groove parameters under a linearly-polarized incident wave excitation. The polarizers with low ohmic loss are optimally designed for a new 28 GHz transmission line on the QUEST spherical tokamak. The calculated optimum ohmic loss is restricted to only less than 1.5 times as large as the theoretical loss for a copper flat mirror at room temperature. The copper rounded-rectangular grooves of the polarizers were relatively easy to make smooth in mechanical machining and the resultant surface roughness was not more than 0.15 μm, which is only 0.38 times as large as the skin depth. The combination of the designed elliptical polarizer and the polarization rotator can also realize any polarization state of the reflected wave.

Towards helium-3 neutron polarizers

International Nuclear Information System (INIS)

Tasset, F.

1995-01-01

With a large absorption cross-section entirely due to antiparallel spin capture, polarized helium-3 is presently the most promising broad-band polarizer for thermal and epithermal neutrons. Immediate interest was raised amongst the neutron community when a dense gaseous 3 He polarizer was used for the first time in 1988, on a pulsed neutron beam at Los Alamos. With 20 W of laser power on a 30 cm long, 8.6 atm target, 40% 3 He polarization was achieved in a recent polarized electron scattering experiment at SLAC. In this technique the 3 He nuclei are polarized directly at an appropriate high pressure through spin-exchange collisions with a thick, optically pumped rubidium vapor. A different and competitive approach is being presently developed at Mainz University in collaboration with ENS Paris and now the ILL. A discharge is established in pure 3 He at low pressure producing excited metastable atoms which can be optically pumped with infra-red light. Highly effective exchange collision with the atoms remaining in the ground state quickly produces 75% polarization at 1.5 mbar. A truly non-magnetic system then compresses the polarized gas up to several bars as required. The most recent machine comprises a two-stage glass-titanium compressor. In less than 1 h it can inflate a 100 cm 3 target cell with three bars of polarized gas. The very long relaxation times (several days) now being obtained at high pressure with a special metallic coating on the glass walls, the polarized cell can be detached and inserted in the neutron beam as polarizer. We expect 50% 3 He-polarization to be reached soon, allowing such filters to compete favorably with existing Heusler-crystal polarizers at thermal and short neutron wavelengths. It must be stressed that such a system based on a 3 He polarization factory able to feed several passive, transportable, polarizers is well matched to neutron scattering needs. (orig.)

Hotspot motion caused the Hawaiian-Emperor Bend and LLSVPs are not fixed

Science.gov (United States)

Tarduno, J. A.; Bono, R. K.

2017-12-01

Paleomagnetic study of volcanic rocks remains the gold standard on which to assess hotspot motion, true polar wander and plate motion recorded by oceanic plates. There is remarkable consistency between paleomagnetic results from basaltic lavas recovered by ocean drilling of the Emperor seamounts, and independent predictions of plate circuits. Both reveal greater than 40 mm/yr of southward hotspot motion; thus the dominant reason for the distinct bend morphology the Hawaiian-Emperor track is hotspot motion rather than plate motion. These findings provide the motivation for moving beyond hotspot fixity to understand mantle processes responsible for the observed motions. Global analyses as well as comparisons between the Hawaiian-Emperor and Louisville tracks indicate only a minor (if any) role for true polar wander. Two viable, non-mutually exclusive processes to explain the observed Hawaiian plume motion are: i. plume-ridge and ii plume-LLSVP interaction. Here we further explore these issues by paleomagnetic analyses of basalts from the Cenozoic Hawaiian chain and Late Cretaceous basalts of the southernmost Pacific Plate. The latter yield paleolatitudes consistent with those from the northern Pacific, indicating that long-standing non-dipole fields cannot have been large enough to affect conclusions on hotspot drift. Data from the former suggest some relative motions between the LLSVPs on tens-of-millions of year time scales, which probably record the continual reshaping of these provinces by plume motion in the lower mantle.

Software package for modeling spin–orbit motion in storage rings

Energy Technology Data Exchange (ETDEWEB)

Zyuzin, D. V., E-mail: d.zyuzin@fz-juelich.de [St. Petersburg State University (Russian Federation)

2015-12-15

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 10{sup 6}–10{sup 9} particles in a beam during 10{sup 9} turns in an accelerator (about 10{sup 12}–10{sup 15} integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin–orbit dynamics.

Semiclassical study of the collision of a highly excited Rydberg atom with the molecules HF and HCl

International Nuclear Information System (INIS)

Kimura, M.; Lane, N.F.

1990-01-01

The semiclassical impact-parameter method is applied to the processes of state changing and energy transfer in the collision of a highly excited Rydberg atom (n≥20) with the polar molecules HF and HCl. The relative motion of the molecule and atomic nucleus is taken to be rectilinear; the electron-molecule and ion core-molecule interactions are represented by cutoff dipole forms. Cross sections for transitions involving quantum numbers n and l of the atom and rotational quantum number j of the molecule are obtained for a range of collision energies and initial atomic and molecular states. Comparisons are made with the results of earlier classical studies and with the quantum-mechanical impulse approximation. Collision rates are calculated and compared with experimental values for l mixing and n and j changing. The agreement between experiment and theory is shown to be satisfactory, within the uncertainties of both the measurements and the theory. Cases of agreement and disagreement between various theories are examined. One finding of the present work is that the quantum-mechanical impulse approximation appears to significantly overestimate the values of various state-changing cross sections when the internal energy defect is small. The validity of the impulse approximation for collisions of Rydberg atoms with polar molecules is discussed

Two-photon spin-polarization spectroscopy in silicon-doped GaAs.

Science.gov (United States)

Miah, M Idrish

2009-05-14

We generate spin-polarized electrons in bulk GaAs using circularly polarized two-photon pumping with excess photon energy (DeltaE) and detect them by probing the spin-dependent transmission of the sample. The spin polarization of conduction band electrons is measured and is found to be strongly dependent on DeltaE. The initial polarization, pumped with DeltaE=100 meV, at liquid helium temperature is estimated to be approximately 49.5%, which is very close to the theoretical value (50%) permitted by the optical selection rules governing transitions from heavy-hole and light-hole states to conduction band states in a bulk sample. However, the polarization pumped with larger DeltaE decreases rapidly because of the exciting carriers from the split-off band.

Ultrafast equilibration of excited electrons in dynamical simulations.

Science.gov (United States)

Lin, Zhibin; Allen, Roland E

2009-12-02

In our density-functional-based simulations of materials responding to femtosecond-scale laser pulses, we have observed a potentially useful phenomenon: the excited electrons automatically equilibrate to a Fermi-Dirac distribution within ∼100 fs, solely because of their coupling to the nuclear motion, even though the resulting electronic temperature is one to two orders of magnitude higher than the kinetic temperature defined by the nuclear motion. Microscopic simulations like these can then provide the separate electronic and kinetic temperatures, chemical potentials, pressures, and nonhydrostatic stresses as input for studies on larger lengths and timescales.

Random forcing of geostrophic motion in rotating stratified turbulence

Science.gov (United States)

Waite, Michael L.

2017-12-01

Random forcing of geostrophic motion is a common approach in idealized simulations of rotating stratified turbulence. Such forcing represents the injection of energy into large-scale balanced motion, and the resulting breakdown of quasi-geostrophic turbulence into inertia-gravity waves and stratified turbulence can shed light on the turbulent cascade processes of the atmospheric mesoscale. White noise forcing is commonly employed, which excites all frequencies equally, including frequencies much higher than the natural frequencies of large-scale vortices. In this paper, the effects of these high frequencies in the forcing are investigated. Geostrophic motion is randomly forced with red noise over a range of decorrelation time scales τ, from a few time steps to twice the large-scale vortex time scale. It is found that short τ (i.e., nearly white noise) results in about 46% more gravity wave energy than longer τ, despite the fact that waves are not directly forced. We argue that this effect is due to wave-vortex interactions, through which the high frequencies in the forcing are able to excite waves at their natural frequencies. It is concluded that white noise forcing should be avoided, even if it is only applied to the geostrophic motion, when a careful investigation of spontaneous wave generation is needed.

Charge asymmetry in alignment of atoms excited by protons and antiprotons

International Nuclear Information System (INIS)

Balashov, V.V.; Sokolik, A.A.; Stysin, A.V.

2007-01-01

The multichannel diffraction approximation is used to consider excitation of lithium atom by proton and antiproton impact. Calculations are performed for the energy range 100 keV - 1 MeV of incoming proton and anti-proton which should be reliable enough due to the general requirements of the multichannel diffraction approximation. The sign-of-charge effect in the alignment of produced 1s 2 3d excited state and in the linear polarization of the subsequent spontaneous 1s 2 3d → 1s 2 2p radiation is expected to be considerable. The clear sign-of-charge effect in the polarization occurs for projectile energies below 1 MeV and become stronger when going to lower energies and the difference between the proton case and the anti-proton one looks considerable enough for experimental observation

On the polarized beam acceleration in medium energy synchrotrons

International Nuclear Information System (INIS)

Lee, S.Y.

1992-01-01

This lecture note reviews physics of spin motion in a synchrotron, spin depolarization mechanisms of spin resonances, and methods of overcoming the spin resonances during acceleration. Techniques used in accelerating polarized ions in the low/medium energy synchrotrons, such as the ZGS, the AGS, SATURNE, and the KEK PS and PS Booster are discussed. Problems related to polarized proton acceleration with snakes or partial snake are also examined

On the polarized beam acceleration in medium energy synchrotrons

Energy Technology Data Exchange (ETDEWEB)

Lee, S.Y.

1992-12-31

This lecture note reviews physics of spin motion in a synchrotron, spin depolarization mechanisms of spin resonances, and methods of overcoming the spin resonances during acceleration. Techniques used in accelerating polarized ions in the low/medium energy synchrotrons, such as the ZGS, the AGS, SATURNE, and the KEK PS and PS Booster are discussed. Problems related to polarized proton acceleration with snakes or partial snake are also examined.

Extreme secular excitation of eccentricity inside mean motion resonance. Small bodies driven into star-grazing orbits by planetary perturbations

Science.gov (United States)

Pichierri, Gabriele; Morbidelli, Alessandro; Lai, Dong

2017-09-01

Context. It is well known that asteroids and comets fall into the Sun. Metal pollution of white dwarfs and transient spectroscopic signatures of young stars like β-Pic provide growing evidence that extra solar planetesimals can attain extreme orbital eccentricities and fall into their parent stars. Aims: We aim to develop a general, implementable, semi-analytical theory of secular eccentricity excitation of small bodies (planetesimals) in mean motion resonances with an eccentric planet valid for arbitrary values of the eccentricities and including the short-range force due to General Relativity. Methods: Our semi-analytic model for the restricted planar three-body problem does not make use of series expansion and therefore is valid for any eccentricity value and semi-major axis ratio. The model is based on the application of the adiabatic principle, which is valid when the precession period of the longitude of pericentre of the planetesimal is much longer than the libration period in the mean motion resonance. In resonances of order larger than 1 this is true except for vanishingly small eccentricities. We provide prospective users with a Mathematica notebook with implementation of the model allowing direct use. Results: We confirm that the 4:1 mean motion resonance with a moderately eccentric (e' ≲ 0.1) planet is the most powerful one to lift the eccentricity of planetesimals from nearly circular orbits to star-grazing ones. However, if the planet is too eccentric, we find that this resonance is unable to pump the planetesimal's eccentricity to a very high value. The inclusion of the General Relativity effect imposes a condition on the mass of the planet to drive the planetesimals into star-grazing orbits. For a planetesimal at 1 AU around a solar mass star (or white dwarf), we find a threshold planetary mass of about 17 Earth masses. We finally derive an analytical formula for this critical mass. Conclusions: Planetesimals can easily fall into the central star

On the possibility of the autoresonant motion of an electron in a slow electromagnetic wave

International Nuclear Information System (INIS)

Milantiev, V.P.

1994-01-01

By autoresonant motion one usually means the motion when the condition of cyclotron resonance of gyrating particle with electromagnetic wave is conserved during all the time of the motion in spite of the relativistic mass increase. Such a motion takes place only in the case of vacuum wave, when the phase velocity ν p is equal to the speed of light in a vacuum C. Otherwise autoresonance is impossible, and energy of the particle oscillates in time. The authors now discuss the possibility of the autoresonance in a slow electromagnetic wave (ν p < c) propagating along the straight lines of the external magnetic field. It turns out that the autoresonant regime of the motion in a slow electromagnetic wave possible if some rather restrictive relations between the electric drift velocity and the phase velocity of wave take place. It depends also on the polarization of wave. The general case of the elliptical polarization is considered. The optimal regime corresponds to the wave with linear polarization in the direction of the constant electric field. For this case the calculations show that energy of the particle can unlimitedly increase (or decrease). The rate of acceleration can be even larger than in the case of vacuum wave. Radiation forces will restrict this process

The influence of autoionizing states on the excitation of helium by electrons

International Nuclear Information System (INIS)

Ittersum, T. van

1976-01-01

The work described in this thesis deals with resonance effects in the scattering of electrons by helium at energies near the threshold of the autoionizing states (50-70 eV). The investigation is performed by studying light emission following the excitation of singly excited states. In some cases, the polarization of the radiation was also investigated. The purpose of the research was (i) to enlarge our knowledge of triply excited negative ion states, i.e. resonance states which are formed by temporary binding of the incident electron to a doubly excited (autoionizing) state of neutral helium, and (ii) to clear up the nature of some resonance structures which could not be explained in terms of negative ion resonances

High luminosity polarized proton collisions at RHIC

International Nuclear Information System (INIS)

Roser, T.

2001-01-01

The Brookhaven Relativistic Heavy Ion Collider (RHIC) provides the unique opportunity to collide polarized proton beams at a center-of-mass energy of up to 500 GeV and luminosities of up to 2 x 10 32 cm -2 s -1 . Such high luminosity and high energy polarized proton collisions will open up the possibility of studying spin effects in hard processes. However, the acceleration of polarized beams in circular accelerators is complicated by the numerous depolarizing spin resonances. Using a partial Siberian snake and a rf dipole that ensure stable adiabatic spin motion during acceleration has made it possible to accelerate polarized protons to 25 GeV at the Brookhaven AGS. After successful operation of RHIC with gold beams polarized protons from the AGS have been successfully injected into RHIC and accelerated using a full Siberian snakes built from four superconducting helical dipoles. A new high energy proton polarimeter was also successfully commissioned. Operation with two snakes per RHIC ring is planned for next year

Bottom-up excited state dynamics of two cinnamate-based sunscreen filter molecules.

Science.gov (United States)

Peperstraete, Yoann; Staniforth, Michael; Baker, Lewis A; Rodrigues, Natércia D N; Cole-Filipiak, Neil C; Quan, Wen-Dong; Stavros, Vasilios G

2016-10-12

Methyl-E-4-methoxycinnamate (E-MMC) is a model chromophore of the commonly used commercial sunscreen agent, 2-ethylhexyl-E-4-methoxycinnamate (E-EHMC). In an effort to garner a molecular-level understanding of the photoprotection mechanisms in operation with E-EHMC, we have used time-resolved pump-probe spectroscopy to explore E-MMC's and E-EHMC's excited state dynamics upon UV-B photoexcitation to the S 1 (1 1 ππ*) state in both the gas- and solution-phase. In the gas-phase, our studies suggest that the excited state dynamics are driven by non-radiative decay from the 1 1 ππ* to the S 3 (1 1 nπ*) state, followed by de-excitation from the 1 1 nπ* to the ground electronic state (S 0 ). Using both a non-polar-aprotic solvent, cyclohexane, and a polar-protic solvent, methanol, we investigated E-MMC and E-EHMC's photochemistry in a more realistic, 'closer-to-shelf' environment. A stark change to the excited state dynamics in the gas-phase is observed in the solution-phase suggesting that the dynamics are now driven by efficient E/Z isomerisation from the initially photoexcited 1 1 ππ* state to S 0 .

Collisional redistribution of circularly polarized light in barium perturbed by argon

International Nuclear Information System (INIS)

Alford, W.J.; Andersen, N.; Belsley, M.; Cooper, J.; Warrington, D.M.; Burnett, K.

1984-01-01

We have measured the orientation of the Ba 6p 1 P level produced by collision-induced excitation from the ground state by circularly polarized light. The detuning dependence of the far-wing excited state orientation can be interpreted in terms of reorientation of molecular orbitals which occur during the collision. Effects due to rotational coupling are seen to occure at large blue wing detunings. We have also determined the collisional rate for destruction of orientation by measuring the pressure dependence of the excited state orientation. (orig.)

Tailoring polarization of electromagnetically induced transparency based on non-centrosymmetric metasurfaces

Science.gov (United States)

Li, Hai-ming; Xue, Feng

2017-09-01

In this manuscript, tailoring polarization of analogy of electromagnetically induced transparency (EIT-like) based on non-centrosymmetric metasurfaces has been numerically and experimentally demonstrated. The EIT-like metamaterial is composed of a rectangle ring and two cut wires. The rectangle ring and the cut wire are chosen as the bright mode and the quasi-dark mode, respectively. Under the incident electromagnetic wave excitation, a polarization insensitive EIT-like transmission window can be observed at specific polarization angles. Within the transmission window, the phase steeply changes, which leads to the large group index. Tailoring polarization of EIT-like metamaterial with large group index at specific polarization angles may have potential application in slow light devices.

Exciton induced directed motion of unconstrained atoms in an ultracold gas

Science.gov (United States)

Leonhardt, K.; Wüster, S.; Rost, J. M.

2017-03-01

We demonstrate that through localised Rydberg excitation in a three-dimensional cold atom cloud atomic motion can be rendered directed and nearly confined to a plane, without spatial constraints for the motion of individual atoms. This enables creation and observation of non-adiabatic electronic Rydberg dynamics in atoms accelerated by dipole-dipole interactions under natural conditions. Using the full l = 0, 1 m=0,+/- 1 angular momentum state space, our simulations show that conical intersection crossings are clearly evident, both in atomic position information and excited state spectra of the Rydberg system. Hence, flexible Rydberg aggregates suggest themselves for probing quantum chemical effects in experiments on length scales much inflated as compared to a standard molecular situation.

Multi-frequency response of a cylinder subjected to vortex shedding and support motions

Energy Technology Data Exchange (ETDEWEB)

Vikestad, Kyrre

1998-12-31

This thesis deals with an experimental investigation of vortex induced vibrations of a circular cylinder. The purpose of the experiment was to identify the influence from a controlled disturbance of the cylinder motions on the response caused by vortex shedding. The cylinder investigated is 2 m long and the diameter is 10 cm. The cylinder is elastically mounted in an apparatus using springs, where the foundation of one of the springs can have a harmonic motion. The apparatus is placed on a carriage in a 25 m long towing tank. Towing velocities are varied between 0.140 m/s and 0.655 m/s corresponding to reduced velocity range from 2.8 to 13.2. The still water natural frequency is 0.497 Hz, and the natural frequency in air is 0.634 Hz. The cylinder is only able to oscillate in the cross-flow direction. The support motion frequency was varied between 0.26 Hz and 1.01 Hz, and the force motion amplitude was varied using 2, 4 and 6 cm support amplitudes. Three sets of experiments were carried out: (1) Still water oscillations due to harmonic support motion excitation, support amplitude and frequencies varied, (2) Towing tests with no support motion, the velocity is varied, (3) Combined excitation: Towing tests with support motion. All possible combinations of experiments (1) and (2) are carried out. The two first experiments provide reference values for the combined excitation experiments and for verification purposes. The results reveal the ability of the external disturbance to influence the vortex shedding process both regarding frequency and the resulting response amplitudes. Results for added mass, in-line drag and damping are also obtained. The work may be of use in deep water floating petroleum production. 81 refs., 73 figs., 6 tabs.

Local and global nonlinear dynamics of a parametrically excited rectangular symmetric cross-ply laminated composite plate

International Nuclear Information System (INIS)

Ye Min; Lu Jing; Zhang Wei; Ding Qian

2005-01-01

The present investigation deals with nonlinear dynamic behavior of a parametrically excited simply supported rectangular symmetric cross-ply laminated composite thin plate for the first time. The governing equation of motion for rectangular symmetric cross-ply laminated composite thin plate is derived by using von Karman equation. The geometric nonlinearity and nonlinear damping are included in the governing equations of motion. The Galerkin approach is used to obtain a two-degree-of-freedom nonlinear system under parametric excitation. The method of multiple scales is utilized to transform the second-order non-autonomous differential equations to the first-order averaged equations. Using numerical method, the averaged equations are analyzed to obtain the steady state bifurcation responses. The analysis of stability for steady state bifurcation responses in laminated composite thin plate is also given. Under certain conditions laminated composite thin plate may have two or multiple steady state bifurcation solutions. Jumping phenomenon occurs in the steady state bifurcation solutions. The chaotic motions of rectangular symmetric cross-ply laminated composite thin plate are also found by using numerical simulation. The results obtained here demonstrate that the periodic, quasi-periodic and chaotic motions coexist for a parametrically excited fore-edge simply supported rectangular symmetric cross-ply laminated composite thin plate under certain conditions

Identification of the low-energy excitations in a quantum critical system

Directory of Open Access Journals (Sweden)

Tom Heitmann

2017-05-01

Full Text Available We have identified low-energy magnetic excitations in a doped quantum critical system by means of polarized neutron scattering experiments. The presence of these excitations could explain why Ce(Fe0.76Ru0.242Ge2 displays dynamical scaling in the absence of local critical behavior or long-range spin-density wave criticality. The low-energy excitations are associated with the reorientations of the superspins of fully ordered, isolated magnetic clusters that form spontaneously upon lowering the temperature. The system houses both frozen clusters and dynamic clusters, as predicted by Hoyos and Vojta [Phys. Rev. B 74, 140401(R (2006].

Solvent effects on the excited-state double proton transfer mechanism in the 7-azaindole dimer: a TDDFT study with the polarizable continuum model.

Science.gov (United States)

Yu, Xue-Fang; Yamazaki, Shohei; Taketsugu, Tetsuya

2017-08-30

Solvent effects on the excited-state double proton transfer (ESDPT) mechanism in the 7-azaindole (7AI) dimer were investigated using the time-dependent density functional theory (TDDFT) method. Excited-state potential energy profiles along the reaction paths in a locally excited (LE) state and a charge transfer (CT) state were calculated using the polarizable continuum model (PCM) to include the solvent effect. A series of non-polar and polar solvents with different dielectric constants were used to examine the polarity effect on the ESDPT mechanism. The present results suggest that in a non-polar solvent and a polar solvent with a small dielectric constant, ESDPT follows a concerted mechanism, similar to the case in the gas phase. In a polar solvent with a relatively large dielectric constant, however, ESDPT is likely to follow a stepwise mechanism via a stable zwitterionic intermediate in the LE state on the adiabatic potential energy surface, although inclusion of zero-point vibrational energy (ZPE) corrections again suggests the concerted mechanism. In the meantime, the stepwise reaction path involving the CT state with neutral intermediates is also examined, and is found to be less competitive than the concerted or stepwise path in the LE state in both non-polar and polar solvents. The present study provides a new insight into the experimental controversy of the ESDPT mechanism of the 7AI dimer in a solution.

Time-resolved resonance raman spectrum of all-trans-diphenylbutadiene in the lowest excited singlet state

DEFF Research Database (Denmark)

Wilbrandt, Robert Walter; Jensen, Niels-Henrik; Langkilde, F.W.

1984-01-01

The resonance Raman spectrwn of all-trans-diphenylbutadiene in its lowest excited S1 state excited in resonance with the S1 → Sn absorption band at 650 nm in non-polar solvents is reported. Three vibrational bands at 1572, 1481 and 1165 cm−1 are observed. A possible assignment of the the 1481 cm−...

Solvent polarity scale on the fluorescence spectra of a dansyl monomer copolymerizable in aqueous media

Science.gov (United States)

Ren, Biye; Gao, Feng; Tong, Zhen; Yan, Yu

1999-06-01

A copolymerizable fluorescent monomer N-[2-[[[5-(N,N-dimethylamino)-1-naphthalenyl]sulfonyl]-amino]ethyl]-2-propenamide (DANSAEP) was synthesized, which exhibits dual fluorescence due to the twisted intramolecular charge transfer in the excited state. The emission maximum λem shifts from 463.3 nm in n-hexane to 530.0 nm in water, showing solvent polarity dependence. The relations between λem and the conventional solvent polarity parameters ET(30) or Z are linear, dividing solvents into protic and aprotic groups. Kamlet's linear solvation energy relationship gives a good description for λem as a solvent polarity scale. The increment of dipole moment Δ μ at the excited state was estimated as 5.09 D with the solvatochromic analysis.

Fermionic Collective Excitations in a Lattice Gas of Rydberg Atoms

International Nuclear Information System (INIS)

Olmos, B.; Gonzalez-Ferez, R.; Lesanovsky, I.

2009-01-01

We investigate the many-body quantum states of a laser-driven gas of Rydberg atoms confined to a large spacing ring lattice. If the laser driving is much stronger than the van der Waals interaction among the Rydberg atoms, these many-body states are collective fermionic excitations. The first excited state is a spin wave that extends over the entire lattice. We demonstrate that our system permits us to study fermions in the presence of disorder although no external atomic motion takes place. We analyze how this disorder influences the excitation properties of the fermionic states. Our work shows a route towards the creation of complex many-particle states with atoms in lattices.

Nonlinear dynamic analysis of atomic force microscopy under deterministic and random excitation

International Nuclear Information System (INIS)

Pishkenari, Hossein Nejat; Behzad, Mehdi; Meghdari, Ali

2008-01-01

The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. This paper is devoted to the analysis of nonlinear behavior of amplitude modulation (AM) and frequency modulation (FM) modes of atomic force microscopy. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Using perturbation methods such as averaging, and Fourier transform nonlinear equations of motion are analytically solved and the advantageous results are extracted from this nonlinear analysis. The results of the proposed techniques for AM-AFM, clearly depict the existence of two stable and one unstable (saddle) solutions for some of exciting parameters under deterministic vibration. The basin of attraction of two stable solutions is different and dependent on the exciting frequency. From this analysis the range of the frequency which will result in a unique periodic response can be obtained and used in practical experiments. Furthermore the analytical responses determined by perturbation techniques can be used to detect the parameter region where the chaotic motion is avoided. On the other hand for FM-AFM, the relation between frequency shift and the system parameters can be extracted and used for investigation of the system nonlinear behavior. The nonlinear behavior of the oscillating tip can easily explain the observed shift of frequency as a function of tip sample distance. Also in this paper we have investigated the AM-AFM system response under a random excitation. Using two different methods we have obtained the statistical properties of the tip motion. The results show that we can use the mean square value of tip motion to image the sample when the excitation signal is random

Nonlinear dynamic analysis of atomic force microscopy under deterministic and random excitation

Energy Technology Data Exchange (ETDEWEB)

Pishkenari, Hossein Nejat [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Behzad, Mehdi [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)], E-mail: m_behzad@sharif.edu; Meghdari, Ali [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

2008-08-15

The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. This paper is devoted to the analysis of nonlinear behavior of amplitude modulation (AM) and frequency modulation (FM) modes of atomic force microscopy. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Using perturbation methods such as averaging, and Fourier transform nonlinear equations of motion are analytically solved and the advantageous results are extracted from this nonlinear analysis. The results of the proposed techniques for AM-AFM, clearly depict the existence of two stable and one unstable (saddle) solutions for some of exciting parameters under deterministic vibration. The basin of attraction of two stable solutions is different and dependent on the exciting frequency. From this analysis the range of the frequency which will result in a unique periodic response can be obtained and used in practical experiments. Furthermore the analytical responses determined by perturbation techniques can be used to detect the parameter region where the chaotic motion is avoided. On the other hand for FM-AFM, the relation between frequency shift and the system parameters can be extracted and used for investigation of the system nonlinear behavior. The nonlinear behavior of the oscillating tip can easily explain the observed shift of frequency as a function of tip sample distance. Also in this paper we have investigated the AM-AFM system response under a random excitation. Using two different methods we have obtained the statistical properties of the tip motion. The results show that we can use the mean square value of tip motion to image the sample when the excitation signal is random.

Bifurcations, chaos and adaptive backstepping sliding mode control of a power system with excitation limitation

Energy Technology Data Exchange (ETDEWEB)

Min, Fuhong, E-mail: minfuhong@njnu.edu.cn; Wang, Yaoda; Peng, Guangya; Wang, Enrong [School of Electrical and Automation Engineering, Nanjing Normal University, Jiangsu, 210042 (China)

2016-08-15

The bifurcation and Lyapunov exponent for a single-machine-infinite bus system with excitation model are carried out by varying the mechanical power, generator damping factor and the exciter gain, from which periodic motions, chaos and the divergence of system are observed respectively. From given parameters and different initial conditions, the coexisting motions are developed in power system. The dynamic behaviors in power system may switch freely between the coexisting motions, which will bring huge security menace to protection operation. Especially, the angle divergences due to the break of stable chaotic oscillation are found which causes the instability of power system. Finally, a new adaptive backstepping sliding mode controller is designed which aims to eliminate the angle divergences and make the power system run in stable orbits. Numerical simulations are illustrated to verify the effectivity of the proposed method.

Bifurcations, chaos and adaptive backstepping sliding mode control of a power system with excitation limitation

Directory of Open Access Journals (Sweden)

Fuhong Min

2016-08-01

Full Text Available The bifurcation and Lyapunov exponent for a single-machine-infinite bus system with excitation model are carried out by varying the mechanical power, generator damping factor and the exciter gain, from which periodic motions, chaos and the divergence of system are observed respectively. From given parameters and different initial conditions, the coexisting motions are developed in power system. The dynamic behaviors in power system may switch freely between the coexisting motions, which will bring huge security menace to protection operation. Especially, the angle divergences due to the break of stable chaotic oscillation are found which causes the instability of power system. Finally, a new adaptive backstepping sliding mode controller is designed which aims to eliminate the angle divergences and make the power system run in stable orbits. Numerical simulations are illustrated to verify the effectivity of the proposed method.

Dynamical polarizability of graphene irradiated by circularly polarized ac electric fields

DEFF Research Database (Denmark)

Busl, Maria; Platero, Gloria; Jauho, Antti-Pekka

2012-01-01

We examine the low-energy physics of graphene in the presence of a circularly polarized electric field in the terahertz regime. Specifically, we derive a general expression for the dynamical polarizability of graphene irradiated by an ac electric field. Several approximations are developed...... that allow one to develop a semianalytical theory for the weak-field regime. The ac field changes qualitatively the single- and many-electron excitations of graphene: Undoped samples may exhibit collective excitations (in contrast to the equilibrium situation), and the properties of the excitations in doped...

Development of spin-polarized transmission electron microscope

International Nuclear Information System (INIS)

Kuwahara, M; Saitoh, K; Tanaka, N; Takeda, Y; Ujihara, T; Asano, H; Nakanishi, T

2011-01-01

In order to study spin related phenomena in nano-size materials, spin-polarized electron source (PES) has been employed for the incident beam in transmission electron microscope (TEM). The PES has been designed and constructed with optimizing for spin-polarized TEM. The illuminating system of TEM is also designed to focus the spin-polarized electron beam emitted from a semiconductor photocathode with a negative electron affinity (NEA) surface. The beam energy is set to below 40 keV which is lower energy type as a TEM, because the spin interaction with condensed matters is very small corresponding with a Coulomb interaction. The polarized electron gun has realized in an extra high vacuum (XHV) condition and high field gradient of 4 MV/m on a surface of photocathode. Furthermore, it demonstrated that 40-keV polarized electron beam was operated with a sub-milli second pulse mode by using the backside excitation type photocathode. This high performance PES will make it possible to observe dynamically a magnetic field images with high contrast and highspeed temporal imaging in TEM.

Nonresonant Multiple-Pulse Control of Molecular Motions in Liquid

Directory of Open Access Journals (Sweden)

Nikiforov V.G.

2015-01-01

Full Text Available We propose the implementation of the multiple-pulse excitation for manipulation of the molecular contributions to the optically-heterodyne-detected optical-Kerr-effect. The key parameters controlling the specificity of the multiple-pulse excitation scenarios are the pulses durations, the delays between pulses, the relation between the pump pulses amplitudes and the pulses polarizations. We model the high-order optical responses and consider some principles of the scenarios construction. We show that it is possible to adjust the excitation scenario in such a way that the some responses can be removed from detected signal along with the enhancement of the interested response amplitude. The theoretical analysis and first experimental data reveal that the multiple-pulse excitation technique can be useful for the selective spectroscopy of the molecular vibrations and rotations in liquid.

Nuclear moments of inertia and wobbling motions in triaxial superdeformed nuclei

International Nuclear Information System (INIS)

Matsuzaki, Masayuki; Shimizu, Yoshifumi R.; Matsuyanagi, Kenichi

2004-01-01

The wobbling motion excited on triaxial superdeformed nuclei is studied in terms of the cranked shell model plus random phase approximation. First, by calculating at a low rotational frequency the γ dependence of the three moments of inertia associated with the wobbling motion, the mechanism of the appearance of the wobbling motion in positive-γ nuclei is clarified theoretically--the rotational alignment of the πi 13/2 quasiparticle(s) is the essential condition. This indicates that the wobbling motion is a collective motion that is sensitive to the single-particle alignment. Second, we prove that the observed unexpected rotational-frequency dependence of the wobbling frequency is an outcome of the rotational-frequency dependent dynamical moments of inertia

Progress in measurement and understanding of beam polarization in electron positron storage rings

International Nuclear Information System (INIS)

Barber, D.P.; Bremer, H.D.; Kewisch, J.; Lewin, H.C.; Limberg, T.; Mais, H.; Ripken, G.; Rossmanith, R.; Schmidt, R.

1983-07-01

A report is presented on the status of attempts to obtain and measure spin polarization in electron-positron storage rings. Experimental results are presented and their relationship to predictions of calculations discussed. Examples of methods for decoupling orbital and spin motion and thus improving polarization are discussed. (orig.)

Polarization and collision velocity dependence of associative ionization in cold Na (3p)-Na(3p) collisions

NARCIS (Netherlands)

Meijer, H.A.J.

1990-01-01

We studied the polarization dependence of the associative ionization (AI) process Na(3p) + Na(3p) → Na2+ at collision velocities between 100 and 700 m/s (5 and 200 K), using linearly and circularly polarized light for the excitation. We found that the polarization dependence varies strongly in the

Real-time identification of vehicle motion-modes using neural networks

Science.gov (United States)

Wang, Lifu; Zhang, Nong; Du, Haiping

2015-01-01

A four-wheel ground vehicle has three body-dominated motion-modes, that is, bounce, roll, and pitch motion-modes. Real-time identification of these motion-modes can make vehicle suspensions, in particular, active suspensions, target on the dominant motion-mode and apply appropriate control strategies to improve its performance with less power consumption. Recently, a motion-mode energy method (MEM) was developed to identify the vehicle body motion-modes. However, this method requires the measurement of full vehicle states and road inputs, which are not always available in practice. This paper proposes an alternative approach to identify vehicle primary motion-modes with acceptable accuracy by employing neural networks (NNs). The effectiveness of the trained NNs is verified on a 10-DOF full-car model under various types of excitation inputs. The results confirm that the proposed method is effective in determining vehicle primary motion-modes with comparable accuracy to the MEM method. Experimental data is further used to validate the proposed method.

Penetration of steady fluid motions into an outer stable layer excited by MHD thermal convection in rotating spherical shells

Science.gov (United States)

Takehiro, Shin-ichi; Sasaki, Youhei

2018-03-01

Penetration of steady magneto-hydrodynamic (MHD) disturbances into an upper strongly stratified stable layer excited by MHD thermal convection in rotating spherical shells is investigated. The theoretical model proposed by Takehiro (2015) is reexamined in the case of steady fluid motion below the bottom boundary. Steady disturbances penetrate into a density stratified MHD fluid existing in the semi-infinite region in the vertical direction. The axis of rotation of the system is tilted with respect to the vertical. The basic magnetic field is uniform and may be tilted with respect to the vertical and the rotation axis. Linear dispersion relation shows that the penetration distance with zero frequency depends on the amplitude of Alfvén wave speed. When Alfvén wave speed is small, viscous diffusion becomes dominant and penetration distance is similar to the horizontal scale of the disturbance at the lower boundary. In contrast, when Alfvén wave speed becomes larger, disturbance can penetrate deeper, and penetration distance becomes proportional to the Alfvén wave speed and inversely proportional to the geometric average of viscous and magnetic diffusion coefficients and to the total horizontal wavenumber. The analytic expression of penetration distance is in good agreement with the extent of penetration of mean zonal flow induced by finite amplitude convection in a rotating spherical shell with an upper stably stratified layer embedded in an axially uniform basic magnetic field. The theory expects that the stable layer suggested in the upper part of the outer core of the earth could be penetrated completely by mean zonal flows excited by thermal/compositional convection developing below the stable layer.

Nuclear spin polarization of targets

International Nuclear Information System (INIS)

Happer, W.

1990-01-01

Lasers can be used to produce milligrams to grams of noble gas nuclei with spin polarizations in excess of 50%. These quantities are sufficient to be very useful targets in nuclear physics experiments. Alkali-metal atoms are used to capture the angular momentum of circularly polarized laser photons, and the alkali-metal atoms transfer their angular momentum to noble gas atoms in binary or three-body collisions. Non-radiative collisions between the excited alkali atoms and molecular quenching gases are essential to avoid radiation trapping. The spin exchange can involve gas-phase van der Waals molecules, consisting of a noble gas atom and an alkali metal atom. Surface chemistry is also of great importance in determining the wall-induced relaxation rates of the noble gases

Motion characteristic of a free piston linear engine

Energy Technology Data Exchange (ETDEWEB)

Xiao, Jin; Li, Qingfeng; Huang, Zhen [Key Laboratory for Power Machinery and Engineering of Ministry of Education, Shanghai Jiao Tong University, Shanghai, 200240 (China)

2010-04-15

A mathematical model of a free piston linear engine is established. The motion characteristics as well as the natural frequency map of the free piston are established. Then, its motion characteristics are successfully explained from the oscillation point. The full simulation model is built up in Matlab/Simulink for a better understanding of its motion features. The results show that the free piston system is a forced vibration system with variable damping coefficient and stiffness. Its steady-state response of periodical excitation is convergent which means that the system is stable under the periodical combustion. Furthermore, it has some unique features which are different from those of traditional Internal Combustion (IC) engines. (author)

Nuclear magnetic resonance method and apparatus for reducing motion artifacts

International Nuclear Information System (INIS)

Bailes, D.R.

1988-01-01

A nuclear magnetic resonance apparatus for imaging a region of a body in which part of the region is moving with a motion such that its displacement with respect to time is a nonmonotonic function during a time period over which a plurality of NMR data signals, which together define an image, are collected. The apparatus is described comprising: excitation means arranged to excite nuclear magnetic spins preferentially in the region; encoding means arranged to encode the magnetic spins; data collection means arranged to collect data signals representative of encoded magnetic spins; display means responsive to collected data signals to display an image of the region; measuring means arranged to produce an output indicative of the displacement of the moving part of the region; and control means for controlling the encoding means during the time period in dependence on the output of the measuring means so that data signals collected during the time period are collected in an order dependent on the motion such that motion artifacts are reduced

The g-u interference oscillations observed in the emission cross sections and the optical polarizations in He+-He collisions

International Nuclear Information System (INIS)

Tani, M.; Hishikawa, A.; Okasaka, R.

1991-01-01

We have observed emission radiation from helium atoms excited in He + -He collisions by the direct and electron capture processes over the energy range 0.5-20 keV. The relative emission cross sections for transitions 2 1,3 P-3 1,3 S, 2 1,3 S-3 1,3 P and 2 1,3 P-2 1,3 D have been determined. Degrees of optical polarization have also been determined for the P- and D-state excitations. The emission cross section of the direct excitation and that of the electron capture excitation show oscillations against impact energy, which are in antiphase with each other. The polarization degrees for both processes are nearly the same magnitude and show weak oscillations in antiphase with each other. The oscillations of the cross section and those of the polarization degree are in phase in some cases and in antiphase in other cases. These oscillations are interpreted as due to the interference between the gerade and ungerade states of the helium quasimolecular ion. From the amplitude ratio and the phase correlation between the oscillations of the cross section and those of the polarization degree we find that the predominant g-u interference pair is Π g -Π u . (author)

Relevance of intracellular polarity to accuracy of eukaryotic chemotaxis

International Nuclear Information System (INIS)

Hiraiwa, Tetsuya; Nishikawa, Masatoshi; Shibata, Tatsuo; Nagamatsu, Akihiro; Akuzawa, Naohiro

2014-01-01

Eukaryotic chemotaxis is usually mediated by intracellular signals that tend to localize at the front or back of the cell. Such intracellular polarities frequently require no extracellular guidance cues, indicating that spontaneous polarization occurs in the signal network. Spontaneous polarization activity is considered relevant to the persistent motions in random cell migrations and chemotaxis. In this study, we propose a theoretical model that connects spontaneous intracellular polarity and motile ability in a chemoattractant solution. We demonstrate that the intracellular polarity can enhance the accuracy of chemotaxis. Chemotactic accuracy should also depend on chemoattractant concentration through the concentration-dependent correlation time in the polarity direction. Both the polarity correlation time and the chemotactic accuracy depend on the degree of responsiveness to the chemical gradient. We show that optimally accurate chemotaxis occurs at an intermediate responsiveness of intracellular polarity. Experimentally, we find that the persistence time of randomly migrating Dictyostelium cells depends on the chemoattractant concentration, as predicted by our theory. At the optimum responsiveness, this ameboid cell can enhance its chemotactic accuracy tenfold. (paper)

Experimental and analytical study on vibration control effects of eddy-current tuned mass dampers under seismic excitations

Science.gov (United States)

Lu, Zheng; Huang, Biao; Zhang, Qi; Lu, Xilin

2018-05-01

Eddy-current tuned mass dampers (EC-TMDs) are non-contacting passive control devices and are developed on the basis of conventional tuned mass dampers. They comprise a solid mass, a stiffness element, and a damping element, wherein the damping mechanism originates from eddy currents. By relative motion between a non-magnetic conductive metal and a permanent magnet in a dynamic system, a time-varying magnetic field is induced in the conductor, thereby generating eddy currents. The eddy currents induce a magnetic field with opposite polarity, causing repulsive forces, i.e., damping forces. This technology can overcome the drawbacks of conventional tuned mass dampers, such as limited service life, deterioration of mechanical properties, and undesired additional stiffness. The experimental and analytical study of this system installed on a multi-degree-of-freedom structure is presented in this paper. A series of shaking table tests were conducted on a five-story steel-frame model with/without an EC-TMD to evaluate the effectiveness and performance of the EC-TMD in suppressing the vibration of the model under seismic excitations. The experimental results show that the EC-TMD can effectively reduce the displacement response, acceleration response, interstory drift ratio, and maximum strain of the columns under different earthquake excitations. Moreover, an analytical method was proposed on the basis of electromagnetic and structural dynamic theories. A comparison between the test and simulation results shows that the simulation method can be used to estimate the response of structures with an EC-TMD under earthquake excitations with acceptable accuracy.

Relativistic Coulomb excitation of giant resonances in the hydrodynamic model

International Nuclear Information System (INIS)

Vasconcellos Gomes, Ana Cristina de.

1990-05-01

We investigate the Coulomb excitation of giant dipole resonances in relativistic heavy ion collisions using a macroscopic hydrodynamical model for the harmonic vibrations of the nuclear fluid. The motion is treated as a combination of the Goldhaber-Teller displacement mode and the Steinwedel-Jensen acoustic mode, and the restoring forces are calculated using the droplet model. This model is used as input to study the characteristics of multiple excitation of giant dipole resonances in nuclei. Possible signatures for the existence of such states are also discussed quantitatively. (author). 52 refs., 14 figs., 3 tabs

Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.

Science.gov (United States)

Santos, Fabiano da Silveira; Descalzo, Rodrigo Roceti; Gonçalves, Paulo Fernando Bruno; Benvenutti, Edilson Valmir; Rodembusch, Fabiano Severo

2012-08-21

Two azo compounds were obtained through the diazotization reaction of aminobenzazole derivatives and N,N-dimethylaniline using clay montmorillonite KSF as catalyst. The synthesized dyes were characterized using elemental analysis, Fourier transform infrared spectroscopy, and (13)C and (1)H NMR spectroscopy in solution. Their photophysical behavior was studied using UV-vis and steady-state fluorescence in solution. These dyes present intense absorption in the blue region. The spectral features of the azo compounds can be related to the pseudo-stilbene type as well as the E isomer of the dyes. Excitation at the absorption maxima does not produce emissive species in the excited state. However, excitation around 350 nm allowed dual emission of fluorescence, from both a locally excited (LE, short wavelength) and an intramolecular charge transfer (ICT, long wavelength) state, which was corroborated by a linear relation of the fluorescence maximum (ν(max)) versus the solvent polarity function (Δf) from the Lippert-Mataga correlation. Evidence of TICT in these dyes was discussed from the viscosity dependence of the fluorescence intensity in the ICT emission band. Theoretical calculations were also performed in order to study the geometry and charge distribution of the dyes in their ground and excited electronic states. Using DFT methods at the theoretical levels BLYP/Aug-cc-pVDZ, for geometry optimizations and frequency calculations, and B3LYP/6-311+G(2d), for single-point energy evaluations, the calculations revealed that the least energetic and most intense photon absorption leads to a very polar excited state that relaxes non-radioactively, which can be associated with photochemical isomerization.

Photodissociation dynamics of core-excited molecular oxygen

International Nuclear Information System (INIS)

Coutinho, L.H.; Homem, M.G.P.; Marinho, R.R.T.; Mocellin, A.; Naves de Brito, A.; Burmeister, F.

2004-01-01

Full text: The fragmentation of molecules after the excitation of a core orbital is of particular interest due to the localization of these orbitals and the possibility to observe dissociation in the same time scale as the electronic decay. This process, which occurs in a few femtoseconds and is known as ultrafast dissociation, has been observed for O 2 and the results will be presented. We used the PhotoElectron-PhotoIon COincidence (PEPICO) and PhotoElectron-PhotoIon-PhotoIon COincidence (PEPIPICO) spectroscopy technique to analyze the produced fragments in the 529 to 540 eV photon energy range. Usually Electron Spectroscopy (ES) is employed to establish whether this peculiar phenomenon occurs or not. Here we successfully put forward the use of partial ion yield (PIY) spectroscopy to investigate ultrafast dissociation. The experiment was performed at the Brazilian Synchrotron Light Laboratory (LNLS). The SGM beamline was equipped with an end-station composed by a time-of-flight mass spectrometer able to rotate with respect to the polarization of the exciting beam. The measurements were taken with the TOF axis performing an angle of 54.7 deg with respect to the polarization vector of the light. The data were corrected for non-unitary detection efficiency in the detectors

Amplitudes and state parameters from ion- and atom-atom excitation processes

International Nuclear Information System (INIS)

Andersen, T.; Horsdal-Pedersen, E.

1984-01-01

This chapter examines single collisions between two atomic species, one of which is initially in a 1 S state (there is only one initial spin channel). The collisions are characterized by a definite scattering plane and a definite orientation. Topics considered include an angular correlation between scattered particles and autoionization electrons or polarized photons emitted from states excited in atomic collisions (photon emission, electron emission, selectivity excited target atoms), experimental methods for obtaining information on the alignment and orientation parameters of atoms or ions excited in specific collisions, results of experiments and numerical calculations (quasi-oneelectron systems, He + -He collisions, other collision systems), and future aspects and possible applications of the polarizedphoton, scattered-particle coincidence techniques to atomic spectroscopy

Electronic excitations and their effect on the interionic forces in simulations of radiation damage in metals

International Nuclear Information System (INIS)

Race, C P; Mason, D R; Sutton, A P

2009-01-01

Using time-dependent tight-binding simulations of radiation damage cascades in a model metal we directly investigate the nature of the excitations of a system of quantum mechanical electrons in response to the motion of a set of classical ions. We furthermore investigate the effect of these excitations on the attractive electronic forces between the ions. We find that the electronic excitations are well described by a Fermi-Dirac distribution at some elevated temperature, even in the absence of the direct electron-electron interactions that would be required in order to thermalize a non-equilibrium distribution. We explain this result in terms of the spectrum of characteristic frequencies of the ionic motion. Decomposing the electronic force into four well-defined components within the basis of instantaneous electronic eigenstates, we find that the effect of accumulated excitations in weakening the interionic bonds is mostly (95%) accounted for by a thermal model for the electronic excitations. This result justifies the use of the simplifying assumption of a thermalized electron system in simulations of radiation damage with an electronic temperature dependence and in the development of temperature-dependent classical potentials.

Electronic excitations and their effect on the interionic forces in simulations of radiation damage in metals.

Science.gov (United States)

Race, C P; Mason, D R; Sutton, A P

2009-03-18

Using time-dependent tight-binding simulations of radiation damage cascades in a model metal we directly investigate the nature of the excitations of a system of quantum mechanical electrons in response to the motion of a set of classical ions. We furthermore investigate the effect of these excitations on the attractive electronic forces between the ions. We find that the electronic excitations are well described by a Fermi-Dirac distribution at some elevated temperature, even in the absence of the direct electron-electron interactions that would be required in order to thermalize a non-equilibrium distribution. We explain this result in terms of the spectrum of characteristic frequencies of the ionic motion. Decomposing the electronic force into four well-defined components within the basis of instantaneous electronic eigenstates, we find that the effect of accumulated excitations in weakening the interionic bonds is mostly (95%) accounted for by a thermal model for the electronic excitations. This result justifies the use of the simplifying assumption of a thermalized electron system in simulations of radiation damage with an electronic temperature dependence and in the development of temperature-dependent classical potentials.

Dynamical model of coherent circularly polarized optical pulse interactions with two-level quantum systems

International Nuclear Information System (INIS)

Slavcheva, G.; Hess, O.

2005-01-01

We propose and develop a method for theoretical description of circularly (elliptically) polarized optical pulse resonant coherent interactions with two-level atoms. The method is based on the time-evolution equations of a two-level quantum system in the presence of a time-dependent dipole perturbation for electric dipole transitions between states with total angular-momentum projection difference (ΔJ z =±1) excited by a circularly polarized electromagnetic field [Feynman et al., J. Appl. Phys. 28, 49 (1957)]. The adopted real-vector representation approach allows for coupling with the vectorial Maxwell's equations for the optical wave propagation and thus the resulting Maxwell pseudospin equations can be numerically solved in the time domain without any approximations. The model permits a more exact study of the ultrafast coherent pulse propagation effects taking into account the vector nature of the electromagnetic field and hence the polarization state of the optical excitation. We demonstrate self-induced transparency effects and formation of polarized solitons. The model represents a qualitative extension of the well-known optical Maxwell-Bloch equations valid for linearly polarized light and a tool for studying coherent quantum control mechanisms

PolarTREC: Successful Methods and Tools for Attaining Broad Educational Impacts with Interdisciplinary Polar Science

Science.gov (United States)

Timm, K. M.; Warburton, J.; Owens, R.; Warnick, W. K.

2008-12-01

topics. These highly relevant, adaptable, and accessible tools and resources are available to educators across the globe and have connected thousands of students and citizens to the excitement of polar science. PolarTREC provides a tested approach and a clear route for researcher participation in the education community, facilitating increased educator, student, and community understanding of science and the polar regions during times of interrelated global change. For more information, visit the PolarTREC website.

Magnetic elliptical polarization of Schumann resonances

International Nuclear Information System (INIS)

Sentman, D.D.

1987-01-01

Measurements of orthogonal, horizontal components of the magnetic field in the ELF range obtained during September 1985 show that the Schumann resonance eigenfrequencies determined separately for the north-south and east-west magnetic components differ by as much as 0.5 Hz, suggesting that the underlying magnetic signal is not linearly polarized at such times. The high degree of magnetic ellipticity found suggests that the side multiplets of the Schumann resonances corresponding to azimuthally inhomogeneous normal modes are strongly excited in the highly asymmetric earth-ionosphere cavity. The dominant sense of polarization over the measurement passband is found to be right-handed during local daylight hours, and to be left-handed during local nighttime hours. 16 references

Do vibrationally excited OH molecules affect middle and upper atmospheric chemistry?

Directory of Open Access Journals (Sweden)

T. von Clarmann

2010-10-01

Full Text Available Except for a few reactions involving electronically excited molecular or atomic oxygen or nitrogen, atmospheric chemistry modelling usually assumes that the temperature dependence of reaction rates is characterized by Arrhenius' law involving kinetic temperatures. It is known, however, that in the upper atmosphere the vibrational temperatures may exceed the kinetic temperatures by several hundreds of Kelvins. This excess energy has an impact on the reaction rates. We have used upper atmospheric OH populations and reaction rate coefficients for OH(v=0...9+O₃ and OH(v=0...9+O to estimate the effective (i.e. population weighted reaction rates for various atmospheric conditions. We have found that the effective rate coefficient for OH(v=0...9+O₃ can be larger by a factor of up to 1470 than that involving OH in its vibrational ground state only. At altitudes where vibrationally excited states of OH are highly populated, the OH reaction is a minor sink of O_x and O₃ compared to other reactions involving, e.g., atomic oxygen. Thus the impact of vibrationally excited OH on the ozone or O_x sink remains small. Among quiescent atmospheres under investigation, the largest while still small (less than 0.1% effect was found for the polar winter upper stratosphere and mesosphere. The contribution of the reaction of vibrationally excited OH with ozone to the OH sink is largest in the upper polar winter stratosphere (up to 4%, while its effect on the HO₂ source is larger in the lower thermosphere (up to 1.5% for polar winter and 2.5% for midlatitude night conditions. For OH(v=0...9+O the effective rate coefficients are lower by up to 11% than those involving OH in its vibrational ground state. The effects on the odd oxygen sink are negative and can reach −3% (midlatitudinal nighttime lowermost thermosphere, i.e. neglecting vibrational excitation overestimates the odd

Transitions and excitations in a superfluid stream passing small impurities

KAUST Repository

Pinsker, Florian

2014-05-08

We analyze asymptotically and numerically the motion around a single impurity and a network of impurities inserted in a two-dimensional superfluid. The criticality for the breakdown of superfluidity is shown to occur when it becomes energetically favorable to create a doublet—the limiting case between a vortex pair and a rarefaction pulse on the surface of the impurity. Depending on the characteristics of the potential representing the impurity, different excitation scenarios are shown to exist for a single impurity as well as for a lattice of impurities. Depending on the lattice characteristics it is shown that several regimes are possible: dissipationless flow, excitations emitted by the lattice boundary, excitations created in the bulk, and the formation of large-scale structures.

Transitions and excitations in a superfluid stream passing small impurities

KAUST Repository

Pinsker, Florian; Berloff, Natalia G.

2014-01-01

We analyze asymptotically and numerically the motion around a single impurity and a network of impurities inserted in a two-dimensional superfluid. The criticality for the breakdown of superfluidity is shown to occur when it becomes energetically favorable to create a doublet—the limiting case between a vortex pair and a rarefaction pulse on the surface of the impurity. Depending on the characteristics of the potential representing the impurity, different excitation scenarios are shown to exist for a single impurity as well as for a lattice of impurities. Depending on the lattice characteristics it is shown that several regimes are possible: dissipationless flow, excitations emitted by the lattice boundary, excitations created in the bulk, and the formation of large-scale structures.

Local Polar Fluctuations in Lead Halide Perovskite Crystals

Science.gov (United States)

Yaffe, Omer; Guo, Yinsheng; Tan, Liang Z.; Egger, David A.; Hull, Trevor; Stoumpos, Constantinos C.; Zheng, Fan; Heinz, Tony F.; Kronik, Leeor; Kanatzidis, Mercouri G.; Owen, Jonathan S.; Rappe, Andrew M.; Pimenta, Marcos A.; Brus, Louis E.

2017-03-01

Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low-frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in the cubic phase of both hybrid (CH3 NH3 PbBr3 ) and all-inorganic (CsPbBr3 ) lead-halide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar organic cation. MD simulations indicate that head-to-head Cs motion coupled to Br face expansion, occurring on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr3 .

Local Polar Fluctuations in Lead Halide Perovskite Crystals

Energy Technology Data Exchange (ETDEWEB)

Yaffe, Omer; Guo, Yinsheng; Tan, Liang Z.; Egger, David A.; Hull, Trevor; Stoumpos, Constantinos C.; Zheng, Fan; Heinz, Tony F.; Kronik, Leeor; Kanatzidis, Mercouri G.; Owen, Jonathan S.; Rappe, Andrew M.; Pimenta, Marcos A.; Brus, Louis E.

2017-03-01

Hybrid lead-halide perovskites have emerged as an excellent class of photovoltaic materials. Recent reports suggest that the organic molecular cation is responsible for local polar fluctuations that inhibit carrier recombination. We combine low-frequency Raman scattering with first-principles molecular dynamics (MD) to study the fundamental nature of these local polar fluctuations. Our observations of a strong central peak in the cubic phase of both hybrid (CH3NH3PbBr3) and all-inorganic (CsPbBr3) leadhalide perovskites show that anharmonic, local polar fluctuations are intrinsic to the general lead-halide perovskite structure, and not unique to the dipolar organic cation. MD simulations indicate that head-tohead Cs motion coupled to Br face expansion, occurring on a few hundred femtosecond time scale, drives the local polar fluctuations in CsPbBr3.

Motion Detection in Ultrasound Image-Sequences Using Tensor Voting

Science.gov (United States)

Inba, Masafumi; Yanagida, Hirotaka; Tamura, Yasutaka

2008-05-01

Motion detection in ultrasound image sequences using tensor voting is described. We have been developing an ultrasound imaging system adopting a combination of coded excitation and synthetic aperture focusing techniques. In our method, frame rate of the system at distance of 150 mm reaches 5000 frame/s. Sparse array and short duration coded ultrasound signals are used for high-speed data acquisition. However, many artifacts appear in the reconstructed image sequences because of the incompleteness of the transmitted code. To reduce the artifacts, we have examined the application of tensor voting to the imaging method which adopts both coded excitation and synthetic aperture techniques. In this study, the basis of applying tensor voting and the motion detection method to ultrasound images is derived. It was confirmed that velocity detection and feature enhancement are possible using tensor voting in the time and space of simulated ultrasound three-dimensional image sequences.

Angular Distribution and Linear Polarization of X-ray Radiation Resulting from Electron Impact Excitation of Highly Charged Ions in Debye Plasmas

Science.gov (United States)

Chen, Zhanbin

2018-05-01

Plasma-screening effects on the 1s _{1/2} → 2l (l = s , p ) and 1s _{1/2} → 3d _{3/2} electron-impact excitation of highly charged ions are investigated, together with their subsequent radiative decay. The analysis is performed based on the multi-configuration Dirac-Fock method and the fully relativistic distorted-wave method incorporating the Debye-Hückel potential. To explore the nature of the effects, calculations are carried out based on detailed analyses of the integrated total and magnetic sublevel cross sections, the alignment parameters, the linear polarizations, and the angular distribution of the X-ray photoemission, as well as on corresponding data calculated in various Debye lengths/environments, taking the 2p _{3/2}→ 1s _{1/2} and 3d _{3/2}→ 1s _{1/2} characteristic lines of H-like Fe^{25+} ion as an example. The present results are compared with experimental data and other theoretical predictions where available.

PolarTREC—A Model Program for Taking Polar Literacy into the Future

Science.gov (United States)

Warburton, J.; Timm, K.; Larson, A. M.

2009-12-01

on previous programs and successes, PolarTREC has developed a successful internet based program for teachers and researchers to interact, leveraging their diverse experiences and expertise for the creation of interdisciplinary educational tools including online journals and forums, real-time Internet seminars, lesson plans, classroom activities, audio, video, and other highly relevant and adaptable educational resources that address a broad range of scientific topics. These highly accessible methods and resources are available to educators and students of varying ages and abilities across the globe, and have connected thousands of students and citizens to the excitement of polar science. PolarTREC provides a tested approach and a clear route for varying levels of researcher participation in the education community, therefore facilitating the types of positive benefits and understanding that ensure increased educator, student, and community understanding of science and the polar regions during times of interrelated global change. For more information, email info@polartrec.com or call 907-474-1600.

Physiology of excitable membranes: proceedings of the 28th International Congress of Physiological Sciences, Budapest, 1980

National Research Council Canada - National Science Library

Salánki, J; Meves, H

1981-01-01

... - - - - - - - - - - - - - - - - - - - - - Regulatory Functions of the CNS. Principles of Motion and Organization Regulatory Functions of the CNS. Subsystems Physiology of Non-excitable Cells Physiology...

Plasmon-mediated circularly polarized luminescence of GaAs in a scanning tunneling microscope

Energy Technology Data Exchange (ETDEWEB)

Mühlenberend, Svenja; Gruyters, Markus; Berndt, Richard, E-mail: berndt@physik.uni-kiel.de [Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel (Germany)

2015-12-14

The electroluminescence from p-type GaAs(110) in a scanning tunneling microscope has been investigated at 6 K. Unexpectedly, high degrees of circular polarization have often been observed with ferromagnetic Ni tips and also with paramagnetic W and Ag tips. The data are interpreted in terms of two distinct excitation mechanisms. Electron injection generates intense luminescence with low polarization. Plasmon-mediated generation of electron-hole pairs leads to less intense emission, which, however, is highly polarized for many tips.

Polarized proton beam development at COSY with EDDA as a fast internal polarimeter

International Nuclear Information System (INIS)

Hinterberger, F.

2001-01-01

Polarized protons in the Cooler Synchrotron COSY encounter five imperfection and nine intrinsic depolarizing resonances during the acceleration from 300 to 3300 MeV/c. When crossing imperfection resonances vertical correction dipoles are excited in order to enhance the average vertical displacement and thereby the resonance strength to result in a complete spin flip without loss of polarization. When crossing intrinsic resonances a rapid vertical tune jump is applied to minimize polarization losses. In order to find the optimum machine parameters a novel and fast method was developed to measure the internal beam polarization as a function of the beam momentum in the vicinity of a depolarizing resonance as well as in the full acceleration ramp. Using very thin internal CH 2 - and/or C-fiber targets the polarization is deduced from the left-right asymmetry of fast scaler rates. To this end the EDDA detector is used. This detector consists of two cylindrical scintillation hodoscope layers covering about 87% of 4π for pp elastic scattering. The effective analyzing power of the fast method is obtained by a special calibration procedure using a 'slow but proper' EDDA-style measurement of the elastic pp scattering asymmetries. For this calibration precise analyzing power excitation functions measured by EDDA became available in time

Studies of the fluorescent excited state of impurities in ionic crystals

International Nuclear Information System (INIS)

Romestain, Robert

1972-01-01

The author of this research thesis first presents experimental methods used in this research: principles (recall on the optical spectrum of an impurity in a solid, use of fluorescence polarization) and techniques (sample preparation, liquid helium cryostat, application of a disturbance, optical detection). Then, he reports the study of the Mn ++ ion in a tetrahedron crystalline field, the study of the Jahn Teller effect on the excited state of the F + centre in CaO, and the study by double resonance of a specific excited state of this same centre in CaO

Motion of the Mantle in the Translational Modes of the Earth and Mercury

Science.gov (United States)

Grinfeld, Pavel; Wisdom, Jack

2005-01-01

Slichter modes refer to the translational motion of the inner core with respect to the outer core and the mantle. The polar Slichter mode is the motion of the inner core along the axis of rotation. Busse presented an analysis of the polar mode which yielded an expression for its period. Busse's analysis included the assumption that the mantle was stationary. This approximation is valid for planets with small inner cores, such as the Earth whose inner core is about 1/60 of the total planet mass. On the other hand, many believe that Mercury's core may be enormous. If so, the motion of the mantle should be expected to produce a significant effect. We present a formal framework for including the motion of the mantle in the analysis of the translational motion of the inner core. We analyze the effect of the motion of the mantle on the Slichter modes for a non-rotating planet with an inner core of arbitrary size. We omit the effects of viscosity in the outer core, magnetic effects, and solid tides. Our approach is perturbative and is based on a linearization of Euler's equations for the motion of the fluid and Newton's second law for the motion of the inner core. We find an analytical expression for the period of the Slichter mode. Our result agrees with Busse's in the limiting case of small inner core. We present the unexpected result that even for Mercury the motion of the mantle does not significantly change the period of oscillation.

2$^{+}$ anomaly and configurational isospin polarization of $^{136}$Te

CERN Multimedia

It is proposed to perform a Coulomb excitation experiment on beams of radioactive ions of $^{136}$Te delivered by HIE-ISOLDE impinging on a $^{58}$Ni target. Scattered particles will be detected by a DSSSD detector and $\\gamma$-rays will be detected by the MINIBALL array. The proposed Configurational Isospin Polarization (CIP) of the two lowest 2$^+$ states will be determined by measuring the E2 excitation yield distribution to them. The expected proton-dominated one-phonon character of the second excited 2$^+$ state of $^{136}$Te will be tested on the basis of absolute electromagnetic matrix elements from the observed Coulomb excitation cross sections. Complementary lifetime information on this predominant 2$^+_{1,ms}$ state will be extracted using the differential DSAM technique. The experiment will clarify to what extent CIP is responsible for the 2$^+$ anomaly in $^{136}$Te.

Applications of polarization speckle in skin cancer detection and monitoring

Science.gov (United States)

Lee, Tim K.; Tchvialeva, Lioudmila; Phillips, Jamie; Louie, Daniel C.; Zhao, Jianhua; Wang, Wei; Lui, Harvey; Kalia, Sunil

2018-01-01

Polarization speckle is a rapidly developed field. Unlike laser speckle, polarization speckle consists of stochastic interference patterns with spatially random polarizations, amplitudes and phases. We have been working in this exciting research field, developing techniques to generate polarization patterns from skin. We hypothesize that polarization speckle patterns could be used in biomedical applications, especially, for detecting and monitoring skin cancers, the most common neoplasmas for white populations around the world. This paper describes our effort in developing two polarization speckle devices. One of them captures the Stokes parameters So and S1 simultaneously, and another one captures all four Stokes parameters So, S1, S2, and S3 in one-shot, within milliseconds. Hence these two devices could be used in medical clinics and assessed skin conditions in-vivo. In order to validate our hypothesis, we conducted a series of three clinical studies. These are early pilot studies, and the results suggest that the devices have potential to detect and monitor skin cancers.

Analysis of piping system response to seismic excitations

International Nuclear Information System (INIS)

Wang, C.Y.

1987-01-01

This paper describes a numerical algorithm for analyzing piping system response to seismic excitations. The numerical model of the piping considers hoop, flexural, axial, and torsional modes of deformation. Hoop modes generated from internal hydrodynamic loading are superimposed on the bending and twisting modes by two extra degrees of freedom. A time-history analysis technique using the implicit temporal integration scheme is addressed. The time integrator uses a predictor-corrector successive iterative scheme which satisfies the equation of motion. Both geometrical and material nonlinearities are considered. Multiple support excitations, fluid effect, piping insulation, and material dampings can be included in the analysis. Two problems are presented to illustrate the method. The results are discussed in detail

Photophysical properties of 1-acetoxy-8-hydroxy-1,4,4a,9a-tetrahydroanthraquinone: Evidence for excited state proton transfer reaction

International Nuclear Information System (INIS)

Singh, Rupashree Balia; Mahanta, Subrata; Guchhait, Nikhil

2007-01-01

The photophysical properties of 1-acetoxy-8-hydroxy-1,4,4a,9a-tetrahydroanthraquinone (HTHQ) have been investigated by steady state and time resolved spectroscopy in combination with quantum chemical calculations. The effects of various parameters such as the nature of solvent and pH of the medium on the spectral properties confirm the existence of different neutral and ionic species in the ground and excited states. In the ground state, HTHQ exists as intramolecularly hydrogen bonded closed conformer in non-polar and polar aprotic solvents. Apart from the closed conformer, the intermolecular hydrogen bonded solvated species and the anion of HTHQ are present in hydroxylic solvents. The closed conformer shows excited state intramolecular proton transfer in all solvents and the solvent polarity independent red shifted emission indicates only keto-enol tautomerism. Evaluation of the potential energy surfaces by quantum chemical calculation using density functional theory point towards the possibility of proton transfer reaction in the first excited state but not in the ground state

Research of Short-range Missile Motion in Terms of Different Wind Loads

Directory of Open Access Journals (Sweden)

A. N. Klishin

2015-01-01

Full Text Available When modeling the aircraft motion it is advisable to choose a particular model of the Earth, depending both on the task and on the required accuracy of calculation. The article describes various models of the Earth, such as the flat Earth with a plane-parallel field of gravity, spherical and non-rotating Earth with a plane-parallel field of gravity, spherical and non-rotating Earth with a central gravitational field, spherical and non-rotating Earth, taking into account the polar flattening of the Earth, spherical Earth based compression and polar daily rotation. The article also considers the influence of these models on the motion of the selected aircraft.To date, there is technical equipment to provide highly accurate description of the Earthshape, gravitational field, etc. The improved accuracy of the Earth model description results in more correct description of the trajectory and motion parameters of a ballistic missile. However, for short ranges (10-20 km this accuracy is not essential, and, furthermore, it increases time of calculation. Therefore, there is a problem of choosing the optimal description of the Earth parameters.The motion in the model of the Earth, which takes into account a daily rotation of the planet and polar flattening, is discussed in more detail, and the geographical latitude impact on coordinates of the points of fall of a ballistic missile is analyzed on the basis of obtained graphs.The article individually considers a problem of the wind effect on the aircraft motion and defines dependences of the missile motion on the parameters of different wind loads, such as wind speed and height of its action.A mathematical model of the missile motion was built and numerically integrated, using the Runge-Kutta 4th order method, for implementation and subsequent analysis.Based on the analysis of the calculation results in the abovementioned models of the Earth, differences in impact of these models on the parameters of the

Circularly Polarized Microwave Antenna Element with Very Low Off-Axis Cross-Polarization

Science.gov (United States)

Greem. David; DuToit, Cornelis

2013-01-01

The goal of this work was to improve off-axis cross-polarization performance and ease of assembly of a circularly polarized microwave antenna element. To ease assembly, the initial design requirement of Hexweb support for the internal circuit part, as well as the radiating disks, was eliminated. There is a need for different plating techniques to improve soldering. It was also desirable to change the design to eliminate soldering as well as the need to use the Hexweb support. Thus, a technique was developed to build the feed without using solder, solving the lathing and soldering issue. Internal parts were strengthened by adding curvature to eliminate Hexweb support, and in the process, the new geometries of the internal parts opened the way for improving the off-axis cross-polarization performance as well. The radiating disks curvatures were increased for increased strength, but it was found that this also improved crosspolarization. Optimization of the curvatures leads to very low off-axis cross-polarization. The feed circuit was curved into a cylinder for improved strength, eliminating Hexweb support. An aperture coupling feed mechanism eliminated the need for feed pins to the disks, which would have required soldering. The aperture coupling technique also improves cross-polarization performance by effectively exciting the radiating disks very close to the antenna s central axis of symmetry. Because of the shape of the parts, it allowed for an all-aluminum design bolted together and assembled with no solder needed. The advantage of a solderless design is that the reliability is higher, with no single-point failure (solder), and no need for special plating techniques in order to solder the unit together. The shapes (curved or round) make for a more robust build without extra support materials, as well as improved offaxis cross-polarization.

Computation of the brightness of the variably-polarizing undulator

International Nuclear Information System (INIS)

Dattoli, G.; Torre, A.; Schettini, G.; Carpanese, M.

1999-02-01

Undulators, producing variably polarized radiation, generate magnetic fields which induce different types of electron motion (vertically, horizontally sinusoidal and helical). The properties of the emitted radiation reflect the complexity of the motion and cannot be described with the method based on the conventional Bessel functions expansion. It's shown that the problem can be overcome by exploiting a method which employs generalized forms of Bessel functions. The proposed technique provides an effective tool to analyze the properties of the emitted radiation [it

Acoustofluidics 4: Piezoelectricity and application in the excitation of acoustic fields for ultrasonic particle manipulation.

Science.gov (United States)

Dual, Jurg; Möller, Dirk

2012-02-07

Piezoelectric materials are widely used in the excitation of MHz frequency vibrations in devices for ultrasonic manipulation. An applied electrical voltage is transformed into mechanical stress, strain and displacement. Piezoelectric elements can be used in either a resonant or non-resonant manner. Depending on the desired motion the piezoelectric longitudinal, transverse or shear effects are exploited. Because of the coupling between electrical and mechanical quantities in the constitutive law the modelling of devices turns out to be quite complex. In this paper, the general equations that need to be used are delineated. For a one-dimensional actuator the underlying physics is described, including the consequences resulting for the characterization of devices. For a practical setup used in ultrasonic manipulation, finite element models are used to model the complete system, including piezoelectric excitation, solid motion and acoustic field. It is shown, how proper tailoring of transducer and electrodes allows selective excitation of desired modes.

Mitigation of ground motion effects in linear accelerators via feed-forward control

Directory of Open Access Journals (Sweden)

J. Pfingstner

2014-12-01

Full Text Available Ground motion is a severe problem for many particle accelerators, since it excites beam oscillations, which decrease the beam quality and create beam-beam offset (at colliders. Orbit feedback systems can only compensate ground motion effects at frequencies significantly smaller than the beam repetition rate. In linear colliders, where the repetition rate is low, additional counter measures have to be put in place. For this reason, a ground motion mitigation method based on feed-forward control is presented in this paper. It has several advantages compared to other techniques (stabilization systems and intratrain feedback systems such as cost reduction and potential performance improvement. An analytical model is presented that allows the derivation of hardware specification and performance estimates for a specific accelerator and ground motion model. At the Accelerator Test Facility (ATF2, ground motion sensors have been installed to verify the feasibility of important parts of the mitigation strategy. In experimental studies, it has been shown that beam excitations due to ground motion can be predicted from ground motion measurements on a pulse-to-pulse basis. Correlations of up to 80% between the estimated and measured orbit jitter have been observed. Additionally, an orbit jitter source was identified and has been removed, which halved the orbit jitter power at ATF2 and shows that the feed-forward scheme is also very useful for the detection of installation issues. We believe that the presented mitigation method has the potential to reduce costs and improve the performance of linear colliders and potentially other linear accelerators.

Ultra-broadband and high-efficiency polarization conversion metasurface with multiple plasmon resonance modes

International Nuclear Information System (INIS)

Dong Guo-Xiang; Xia Song; Li Wei; Zhang An-Xue; Xu Zhuo; Wei Xiao-Yong; Shi Hong-Yu

2016-01-01

In this paper, we present a novel metasurface design that achieves a high-efficiency ultra-broadband cross polarization conversion. The metasurface is composed of an array of unit resonators, each of which combines an H-shaped structure and two rectangular metallic patches. Different plasmon resonance modes are excited in unit resonators and allow the polarization states to be manipulated. The bandwidth of the cross polarization converter is 82% of the central frequency, covering the range from 15.7 GHz to 37.5 GHz. The conversion efficiency of the innovative new design is higher than 90%. At 14.43 GHz and 40.95 GHz, the linearly polarized incident wave is converted into a circularly polarized wave. (paper)

Developments in Polarization and Energy Control of APPLE-II Undulators at Diamond Light Source

Science.gov (United States)

Longhi, E. C.; Bencok, P.; Dobrynin, A.; Rial, E. C. M.; Rose, A.; Steadman, P.; Thompson, C.; Thomson, A.; Wang, H.

2013-03-01

A pair of 2m long APPLE-II type undulators have been built for the I10 BLADE beamline at Diamond Light Source. These 48mm period devices have gap as well as four moveable phase axes which provide the possibility to produce the full range of elliptical polarizations as well as linear polarization tilted through a full 180deg. The mechanical layout chosen has a 'master and slave' arrangement of the phase axes on the top and bottom. This arrangement allows the use of symmetries to provide operational ease for both changing energy using only the master phase while keeping fixed linear horizontal or circular polarization, as well as changing linear polarization angle while keeping fixed energy [1]. The design allows very fast motion of the master phase arrays, without sacrifice of accuracy, allowing the possibility of mechanical polarization switching at 1Hz for dichroism experiments. We present the mechanical design features of these devices, as well as the results of magnetic measurements and shimming from before installation. Finally, we present the results of characterization of these devices by the beamline, including polarimetry, which has been done on the various modes of motion to control energy and polarization. These modes of operation have been available to users since 2011.