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At least 1,009 records · Page 56Linked to original sources
PubMed2004

Secondary bifurcations of hexagonal patterns in a nonlinear optical system: alkali metal vapor in a single-mirror arrangement.

Secondary bifurcations of hexagonal patterns are analyzed in a model of a single-mirror arrangement with an alkali metal vapor as the nonlinear medium. A stability analysis of the hexagonal structures is performed numerically. Different instabilities are predicted in dependency on the wave number of the hexagons. Some of the instabilities take place at a finite wave number and result in the formation of structures with 12 spatial modes. These structures are compared with those observed experimentally.

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PubMed2005

Constants of motion in a minimum-B mirror magnetic field.

A complete description of the particle motion in a three-dimensional marginal minimum- B mirror field is obtained, including two new constants of motion. The energy and the two Clebsch coordinates of the gyrocenter motion are constants of motion, and the magnetic moment is an adiabatic invariant. The invariance of the gyrocenter Clebsch coordinates implies that each gyrocenter bounces back and forth on a single magnetic field line. Complete solutions of the Vlasov equation can be constructed in the equilibrium field. A small gyroradius expansion of the Clebsch coordinate invariants splits the distribution function into a gyroaveraged part and a new gyro-oscillating part that gives rise to perpendicular plasma current. Locally omnigenous Vlasov equilibria to the first order in the plasma beta can be constructed by including the diamagnetic drift. More than three time-independent invariants are required to obtain the general solution of the stationary Vlasov equation.

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PubMed2005

Analysis of a four-mirror-cavity enhanced Michelson interferometer.

We investigate the shot-noise-limited sensitivity of a four-mirror-cavity enhanced Michelson interferometer. The intention of this interferometer topology is the reduction of thermal lensing and the impact of the interferometers contrast although transmissive optics are used with high circulating powers. The analytical expressions describing the light fields and the frequency response are derived. Although the parameter space has 11 dimensions, a detailed analysis of the resonance feature gives boundary conditions allowing systematic parameter studies.

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PubMed2000

Quenching of giant hysteresis effects in La(1-z)Y(z)Hx switchable mirrors

The giant intrinsic hysteresis as a function of hydrogen concentration x in the optical and electrical properties of the archetypal switchable mirror YHx is eliminated by alloying Y with the chemically similar La. The La(1-z)Y(z)Hx films with z</=0.67 are essentially hysteresis-free. The origin of the large hysteresis of alloys with z>/=0.86 is the large uniaxial lattice expansion that accompanies their fcc to hexagonal phase transition in combination with lateral clamping.

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PubMed2000

Current mirror effect and correlated cooper-pair transport in coupled arrays of small Josephson junctions.

We have measured the transport properties of capacitively coupled one-dimensional arrays of small aluminum Josephson junctions. Under suitable biasing conditions, the samples act as current mirrors; the currents in the two arrays couple to each other and become equally large. The coupling is found both for currents flowing in the same direction and in opposite directions. We have also measured the time dependent fluctuations of the currents in the two arrays, and we find a strong correlation or anticorrelation of the fluctuations depending on the relative direction of the two currents.

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PubMed2001

Generalized scaling laws of the formation and effects of plasma-confining potentials for tandem-mirror operations in GAMMA 10.

The main operations from 1979 to 2000 in the GAMMA 10 tandem-mirror, characterized in terms of the high-potential mode having kV-order plasma-confining potentials and the hot-ion mode yielding fusion neutrons with 10-20 keV bulk-ion temperatures, are summarized and generalized as a result of scalings of the formation and the effects of the potentials. The wide validity of potential-formation physics from Cohen's theory and the validity of the generalized Pastukhov's theory for the effects of thermal-barrier potentials on electron confinement are verified and consolidated through electron-energy balance.

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PubMed2001

Light-induced metal-insulator transition in a switchable mirror.

Rare earth hydride films can be converted reversibly from metallic mirrors to insulating windows simply by changing the surrounding hydrogen gas pressure at room temperature. At low temperatures, in situ doping is not possible in this way as hydrogen cannot diffuse. However, our finding of persistent photoconductivity under ultraviolet illumination offers an attractive possibility to tune yttrium hydride through the T = 0 metal-insulator transition. Conductivity and Hall measurements are used to determine critical exponents. The unusually large value for the product of the static and dynamical critical exponents appears to signify the important role played by electron-electron interactions.

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PubMed2001

Coulomb energy differences in t = 1 mirror rotational bands in (50)Fe and (50)Cr.

Gamma rays from the N = Z-2 nucleus (50)Fe have been observed, establishing the rotational ground state band up to the state J(pi) = 11+ at 6.994 MeV excitation energy. The experimental Coulomb energy differences, obtained by comparison with the isobaric analog states in its mirror (50)Cr, confirm the qualitative interpretation of the backbending patterns in terms of successive alignments of proton and neutron pairs. A quantitative agreement with experiment has been achieved by exact shell model calculations, incorporating the differences in radii along the yrast bands, and properly renormalizing the Coulomb matrix elements in the pf model space.

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PubMed2002

0(+)(gs) --> 2(+)(1) excitations in the mirror nuclei 32Ar and 32Si.

We measured the strength of the 0(+)(gs)-->2(+)(1) excitations in the radioactive mirror nuclei 32Ar and 32Si using the techniques of intermediate-energy Coulomb excitation for 32Ar and inelastic proton scattering in inverse kinematics for 32Si. The 32Ar measurement, taken together with previously existing Coulomb excitation data for 32Si, yields the isoscalar and isovector multipole matrix elements for the 0(+)(1)-->2(+)(1) transition between T = 2 states in the A = 32 system. The proton scattering measurement for 32Si, when combined with the Coulomb excitation data for this nucleus, yields a ratio of neutron and proton matrix elements, M(n)/M(p), for 32Si.

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PubMed2002

Specular reflection of matter waves from a rough mirror.

We present a high resolution study of the specularity of the atomic reflection from an evanescent wave mirror using velocity selective Raman transitions. We observed a double structure in the velocity distribution after reflection: a peak consistent with specular reflection and a diffuse reflection pedestal whose contribution decreases rapidly with increasing detuning. The diffuse reflection is due to two distinct effects: spontaneous emission in the evanescent wave and roughness in the evanescent wave potential whose amplitude is smaller than the de Broglie wavelength of the reflected atoms.

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PubMed2002

Overcoming the diffraction limit in wave physics using a time-reversal mirror and a novel acoustic sink.

In recent years, time-reversal (TR) mirrors have been developed that create TR waves for ultrasonic transient fields propagating through complex media. A TR wave back propagates and refocuses exactly at its initial source. However, because of diffraction, even if the source is pointlike the wave refocuses on a spot size that cannot be smaller than half a wavelength. Here, by using a TR interpretation of this limit, we show that this latter limitation can be overcome if the source is replaced by its TR image. This new device acts as an acoustic sink that absorbs the TR wave. Here we report the first experimental result obtained with an acoustic sink where a focal spot size of less than 1/14th of one wavelength is recorded.

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PubMed2003

Mirror domain structures induced by interlayer magnetic wall coupling.

We have found that during giant magnetoresistance measurements in approximately 10 x 10 mm(2) NiFe/Cu/Co continuous film spin-valve structures, the resistance value suddenly drops to its absolute minimum during the NiFe reversal. The results reveal that the alignment of all magnetic domains in the NiFe film follow exactly that of corresponding domains in the Co film for an appropriate applied field strength. This phenomenon is caused by trapping of the NiFe domain walls through the magnetostatic interaction with the Co domain-wall stray fields. Consequently, the interlayer domain-wall coupling induces a mirror domain structure in the magnetic trilayer.

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PubMed2004

Unusual isospin-breaking and isospin-mixing effects in the A=35 mirror nuclei.

Excited states have been studied in 35Ar following the 16O(24Mg,1alpha1n)35Ar fusion-evaporation reaction at 60 MeV using the Ge-detector array GASP. A comparison with the mirror nucleus 35Cl shows two remarkable features: (i) A surprisingly large energy difference for the 13/2(-) states, in which the hitherto overlooked electromagnetic spin-orbit term is shown to play a major role, and (ii) a very different decay pattern for the 7/2(-) states, which provides direct evidence of isospin mixing.

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PubMed2004

Microstructured switchable mirror for polar molecules.

By miniaturizing electrode geometries high electric fields can be produced using modest voltages. A planar array of 20 microm wide gold electrodes, spaced 20 microm apart, is made on a sapphire substrate. A voltage difference of up to 350 V is applied to adjacent electrodes, generating an electric field that decreases exponentially with distance from the substrate. This microstructured array can be used as a mirror for polar molecules and can be rapidly switched on and off. This is demonstrated by retro-reflecting a beam of state-selected ammonia molecules with a forward velocity of about 30 m/s.

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PubMed2005

Stabilization of interchange modes in mirror plasmas by a nonlinear rf-plasma wave coupling process.

Experimental and theoretical studies are made of the consequences of a nonlinear coupling process between pump rf waves and interchange modes in mirror plasmas. It is demonstrated that the interchange-stable operation window exists depending on the applied rf power and gamma=omega(0)/Omega(i), where omega(0) (Omega(i)) is the angular frequency of the applied rf wave (ion cyclotron frequency). Results are shown that the nonlinear wave coupling process gives rise to the operation window near the resonance (gamma approximately equal to 1), which is elucidated by theoretical analyses combined with full rf wave simulations.

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PubMed2005

Zero-magnetic-field hall effect in broken-mirror-symmetry conductors under illumination.

A novel effect is predicted for conductors with a broken mirror symmetry [e.g., polar metals and asymmetrical quantum well (QW) structures]: if such a conductor is under the direct current J approximately E(d), the circular polarized infrared radiation should induce an additional transverse current JH approximately E(d)xc, where E(d) is the driving electric field and c is a vector directed either along the polar axis or perpendicular to a QW. The sign of the current JH can be reversed by switching the helicity of the light from right to left-handed. Thus the phenomenon is, in fact, something like the Hall effect in which light acts as an external magnetic field.

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PubMed2005

Evanescent-wave mirror for ultracold diatomic polar molecules.

We describe the interaction of an ultracold diatomic polar molecule with an evanescent-wave mirror. Several features of this system are explored, such as the coupling between internal rovibrational states of the molecule and the laser field. Numerical simulations show quantum reflection and state selection under attainable physical conditions. Such molecular optics components will facilitate the manipulation and trapping of ultracold molecules, and might serve in future applications in several fields, e.g., as devices to filter and select a state for ultracold chemistry, to measure extremely low temperatures of molecules, or to manipulate states for quantum information processing.

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PubMed2006

Neutron-mirror-neutron oscillations: how fast might they be?

We discuss the phenomenological implications of the neutron (n) oscillation into the mirror neutron (n'), a hypothetical particle exactly degenerate in mass with the neutron but sterile to normal matter. We show that the present experimental data allow a maximal n-n' oscillation in vacuum with a characteristic time tau much shorter than the neutron lifetime, in fact as small as 1 sec. This phenomenon may manifest in neutron disappearance and regeneration experiments perfectly accessible to present experimental capabilities and may also have interesting astrophysical consequences, in particular, for the propagation of ultra high energy cosmic rays.

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