Stable bonds and unstable bonds in Y(Pr)-123 system

The Pr content dependence of the bond lengths of Y–Cu, Y–O, O–O, Cu–O, Ba–Cu and Ba–O in PrBa₂Cu₃O_y are analyzed and discussed in detail. The different valence bonds can be divided into two groups: stable bonds and unstable bonds. Since the bond lengths and angles between every two ions among O2, Cu2 and O3 are very stable, we conclude that the three ions form an unchangeable triangle when the Pr doping changes. The triangle is called “fixed triangle”. This “fixed triangle” can slightly rotate around the Cu2 ions. It is just this rotation that leads to the unstable bonds. As the increase of the Pr content, the bond lengths between the two Cu(2)–O planes becomes larger and larger, the Cu(2)–O planes bend towards the Ba–O plane. The bonds lengths between the Cu(2)–O and Ba–O planes vary oppositely from those of Cu(2)–O, and become shorter and shorter. These changes connected with the superconductivity are discussed.     

Characteristic properties of the conical Mueller matrix

We present results of mathematical relations existing between the Mueller matrix obtained for an in-plane of incidence scattering geometry (plane Mueller matrix, PMM) and the Mueller matrix obtained for an out-the-plane of incidence scattering geometry (conical Mueller matrix, CMM), for light scattered from a rough surface. We obtain a similarity relation between the CMM and the PMM for one- (1-D) and for two-dimensional (2-D) surfaces. This similarity relation implies that the PMM and the CMM have the same determinant, trace and eigenvalues for 1-D and 2-D surfaces, respectively. We can say that measurements made in the conical geometry are “Similarity Equivalent” to those in the in-plane geometry for both kind of surfaces, respectively.     

Quantum interference rectifier

Electron transport in bent quantum wire in the presence of a magnetic field which is orthogonal to the system plane is considered. Possible constructions of “quantum interference switch” and “quantum interference rectifier” are suggested.     

Diffraction of laser-plasma-generated electron pulses

We report the observation of the Debye–Scherrer diffraction using electron pulses emitted from a fs-laser plasma. Titanium sapphire laser pulses with 1.6 mJ/45 fs at 1 kHz are focused on a moving steel tape at close to normal incidence. The laser plasma generated ejects a large number of electrons in the direction of polarization, with a continuous energy spectrum extending up to 100 keV. Selecting an energy range of these electrons and scattering them on a thin aluminium sample generates a “streaked” diffraction pattern with unique features.     

Detonability limits in thin annular channels

In this paper, detonability limits in two-dimensional annular channels are investigated. Since the channel heights are small in comparison to the tube diameter, curvature effects can be neglected and the annular channels can be considered to be essentially two-dimensional. Mixtures that are highly diluted with argon are used since previous investigations seem to indicate that detonations in such mixtures are “stable” in that cellular instabilities play minor roles on the propagation of the detonation. For stable detonations where the ZND structure is valid, boundary layer effects can be modeled as a flow divergence term in the conservation of mass equation following the pioneering work of Fay [J.A. Fay, Phys. Fluids 2(3) (1959) 283–289]. Expansion due to flow divergence in the reaction zone results in a velocity deficit. There exists a maximum deficit when an eigenvalue detonation velocity can no longer be found, which can be taken as the onset of the detonability limits. Experimentally, it was found that unlike “unstable” detonations, the detonability limits for “stable” detonations are well-defined. No unstable near-limit phenomena (e.g., galloping detonations) was observed. Good agreement is found between the theoretical predictions and the experimentally obtained velocity deficits and limits in the two channel heights of 2.2 and 6.9 mm for hydrogen–oxygen and acetylene–oxygen mixtures diluted with over 50% argon. It may be concluded that at least for these special mixtures where the detonation is “stable,” the failure mechanism is due to flow divergence caused by the negative displacement thickness of the boundary layer behind the leading shock front of the detonation wave.     

Vertical magneto-tunneling through a quantum dot and the density of states of small electronic systems

One-electron tunneling through a quantum dot with a strong magnetic field in the direction of the current is studied. The linear magneto-conductance is computed for a model parabolic dot with seven electrons in the intermediate states and for different values of the magnetic field. It is shown that the dot density of states at low excitation energies can be extracted from a precise measurement of the conductance at the upper edge of the Coulomb blockade diamond. We parametrized the density of states with a single “temperature” parameter (in the so called “constant temperature approximation”), and found that this parameter depends very weakly on the magnetic field.     

Structure of monolayer silica on Mo(1 1 2) investigated by rainbow scattering under axial surface channeling

The structure of a monolayer crystalline silica film grown on a Mo(1 1 2) substrate is investigated via grazing scattering of fast atoms. For scattering along low indexed directions in the surface plane (“axial surface channeling”) the corrugation of the interaction potential leads to an azimuthal out-of plane scattering with an intensity enhancement for the maximum deflection angle, the so called “rainbow”. From the comparison of the experimental angular distributions for scattered projectiles with classical trajectory simulations we obtain information on the arrangement of atoms in the topmost surface layer. Our work provides evidence for the structural model of a two-dimensional network for the silica film.     

Continuous and time-shared multiple optical tweezers for the study of single motor proteins

We present a comparison between continuous (CW) and time-shared (TS) multiple optical tweezers applied to the study of the interaction between a single motor protein (myosin) with its track (an actin filament). In the experimental assay, named “three-bead assay”, a single actin filament is stretched between two beads trapped in a CW or in a TS double trap. The actin filament is presented to a single myosin molecule lying on a third bead attached to the coverslide. The CW double trap is obtained by splitting a single laser source into two orthogonally polarized beams, while the TS one is obtained by rapidly scanning a single laser beam with acusto-optic modulators. When using the CW traps, position detection of the left or right bead is obtained by means of a single quadrant detector photodiode (QDP) placed in the back focal plane of the condenser and selected with a polarizer; when using the TS traps, the position of multiple traps with the same QDP can be collected independently using triggered and synchronized generation and acquisition. The two techniques are thoroughly analysed and compared, evidencing advantages and disadvantages of each one.     

Orientational dynamics of superfluid He: A “two-fluid” model. II. Orbital dynamics

We present a phenomenological theory of the homogeneous orbital dynamics of the class of “separable” anisotropic superfluid phases which includes the ABM state generally identified with ³He-A. The theory is developed by analogy with the spin dynamics described in the first paper of this series; the basic variables are the orientation of the Cooper-pair wavefunction (in the ABM phase, the l-vector) and a quantity K which we visualize as the “pseudo-angular momentum” of the Cooper pairs but which must be distinguished, in general, from the total orbital angular momentum of the system. In the ABM case l is the analog of d in the spin dynamics and K of the “superfluid spin” S_p. Important points of difference from the spin case which are taken into account include the fact that a rotation of l without a simultaneous rotation of the normal-component distribution strongly increases the energy of the system (“normal locking”), and that the equilibrium value of K is zero even for finite total angular momentum. The theory does not claim to handle correctly effects associated with any intrinsic angular momentum arising from particle-hole asymmetry, but it is shown that the magnitude of this quantity can be estimated directly from experimental data and is extremely small; also, the Landau damping does not emerge automatically from the theory, but can be put in in an ad hoc way. With these provisos the theory should be valid for all frequencies irrespective of the value of ωτ. (Δ = gap parameter, τ = quasi-particle relaxation time.) It disagrees with all existing phenomenological theories of comparable generality, although the disagreement with that of Volovik and Mineev is confined to the “gapless” region very close to T_c.The phenomenological equations of motion, which are similar in general form to those of the spin dynamics with damping, involve an “orbital susceptibility of the Cooper pairs” χ_orb(T). We give a possible microscopic definition of the variable K and use it to calculate χ_orb(T) for a general phase of the “separable” type. The theory is checked by inserting the resulting formula in the phenomenological equations for ωτ 1 and comparing with the results of a fully microscopic calculation based on the collisionless kinetic equation; precise agreement is obtained for both the ABM and the (real) polar phase, showing that the complex nature of the ABM phase and the associated “pair angular momentum” is largely irrelevant to its orbital dynamics. We note also that the phenomenological theory gives a good qualitative picture even when ω Δ(T), e.g., for the flapping mode near T_c. Our theory permits a simple and unified calculation of (1) the Cross-Anderson viscous torque in the overdamped regime, (2) the flapping-mode frequency near zero temperature, (3) orbital effects on the NMR, both at low temperatures and near T_c, (4) the orbit wave spectrum at zero temperature (this requires a generalization to inhomogeneous situations which is possible at T = 0 but probably not elsewhere). We also discuss the possibility of experiments of the Einstein-de Haas type. Generally speaking, our results for any one particular application can be also obtained from some alternative theory, but in the case of orbital and spin relaxation very close to T_c (within the “gapless” region) our predictions, while somewhat tentative and qualitative, appear to disagree with those of all existing theories. We discuss briefly how our approach could be extended to apply to more general phases.     

Polarized He spin-filters using MEOP for wide-angle polarization analysis

Polarized ³He spin-filters are currently employed on a wide range of neutron instruments at the ILL, primarily for diffraction, reflectometry and fundamental physics. A wide range of recent and ongoing improvements are enabling the implementation of this technique for wide-angle polarization analysis for inelastic measurements. These include

• Progress in metastability-exchange optical pumping (MEOP), resulting in on-beam polarization levels of up to 80%.

• 1st generation “Pastis-1” coils for rotating the neutron polarization at the sample position, allowing for “XYZ” polarization analysis.

• 2nd generation “Pastis-2” coils with no blind angles in the equatorial plane.

• Spin-filter cells with glued silicon windows, allowing for wide-angle “banana” cells with very low background scattering.

• Polarization-preserving capillaries for transferring polarized ³He gas into the cell without manual access.

The development of capillary transfer also allows for a completely new way of working with ³He spin-filters: connecting the cells on the instruments directly to the MEOP filling station several tens of meters away and allowing for quasi-continuous operation.     

Dynamical behavior of the phase transition of strained from atomistic simulations

Using an atomistic shell model we study the temperature dependence of the ferroelectric properties of BaTiO₃ under biaxial compressive strain applicable to growth on perovskites substrate. Molecular dynamics simulations show a “r→c→p” sequence of phase transitions when temperature is increased, and the absence of an “ac phase”. The first-order paraelectric-to-ferroelectric phase transition presents in bulk changes to a second-order one as a consequence of the in-plane constraint imposed by the mechanical boundary conditions. From the tetragonal ferroelectric c phase, the transition takes place in a finite range of temperature where the lattice parameter normal to the plane keeps approximately constant until T_c is reached. Analysis of the local polarization behavior reveals an order–disorder dynamics as the dominant mechanism of the transition.     

Noncommutative theories, the axial anomaly, Fujikawa's method and the Atiyah–Singer index

Fujikawa's method is employed to compute at first order in the noncommutative parameter the U(1)_A anomaly for noncommutative SU(N). We consider the most general Seiberg–Witten map which commutes with hermiticity and complex conjugation and a noncommutative matrix parameter, θ^μν, which is of “magnetic” type. Our results for SU(N) can be readily generalized to cover the case of general nonsemisimple gauge groups when the symmetric Seiberg–Witten map is used. Connection with the Atiyah–Singer index theorem is also made.     

A spin field effect transistor for low leakage current

In a spin field effect transistor, a magnetic field is inevitably present in the channel because of the ferromagnetic source and drain contacts. This field causes random unwanted spin precession when carriers interact with non-magnetic impurities. The randomized spins lead to a large leakage current when the transistor is in the “off”-state, resulting in significant standby power dissipation. We can counter this effect of the magnetic field by engineering the Dresselhaus spin–orbit interaction in the channel with a backgate. For realistic device parameters, a nearly perfect cancellation is possible, which should result in a low leakage current.     

The vectorial photoelectric effect on cesiated GaAs (110) and Si (111) surfaces

Polarization dependence of photoelectric emission at 45° incidence was investigated on cesiated Si (111) and GaAs (110) surfaces. Yield and energy distributions from surfaces covered with submonolayers of cesium did not depend on polarization of the light. Energy distributions and emitted current depend on the plane of polarization when more than a monolayer of cesium was deposited onto cooled samples. These phenomena can be explained in terms of radiation density calculated from Fresnel's equation and bulk optical properties of the semiconductor; no polarization dependence of the optical excitation need be invoked.     

Neutrinos and the Weak Interactions

We show that neutrinos and electrons share the same theoretical structure and satisfy parallel relations particularly of the Large Number kind. We then argue that the neutrino can be described as a “cold” electron in a sense that is detailed, and thereby the weak interactions are indeed a weak form of electromagnetism.     

Methods for evaluating the performance of emitters in plane parallel diodes

The curvature seen in Child's law plots of current-voltage characteristics measured using plane parallel diodes may be analysed in a number of ways to give information about the work function distribution of a cathode. This paper suggests a simple technique for characterising a cathode based on the assumption it has a “top-hat” work function distribution. The technique allows synthetic current/voltage characteristics to be generated which agree well with the practical characteristics from which the parameters of the work function distribution were derived. The parameters of the “top-hat” model may also be used to obtain an equivalent Gaussian work function distribution which gives almost identical synthetic characteristics and Schottky enhancement may be modelled in a rather empirical manner. Since either model gives good predictions, synthetic characteristics may be used to investigate other methods used to characterise cathodes. It is found that there is generally reasonable agreement which could be improved, for most practical work function distributions, by the choice of parameters slightly different from those normally used.     

Ultrasound-promoted a green protocol for the synthesis of 2,4-diarylthiazoles under ambient temperature in [bmim]BF4

A mild, efficient, facile and eco-friendly procedure for the synthesis of 2,4-diarylthiazoles from arylthioamides and α-bromoacetophenones in 1-n-butyl-3-methylimidazolium tetrafluoroborate as a “green” media under ultrasound irradiation at room temperature is described. It is interesting to mention that only one product was obtained when two different α-bromoacetophenones were reacted with 1,3-phenyl dithioamide as the substrate. Work-up is very simple and there is no need to purify the product. A recycling study confirmed that the ionic liquid can be reused multiple times without a significant loss in its activity.     

Modulated inflation

We have studied modulated inflation that generates curvature perturbation from light-field fluctuation. As discussed in previous works, even if the fluctuation of the inflaton itself does not generate the curvature perturbation, fluctuation of a light field may induce fluctuation for the end-line of inflation and this may lead to generation of cosmological perturbation “at the end of the inflation”. Our scenario is different from this kind of modulated scenario, as clearly explained in this Letter by using δN formalism. We also explain the crucial difference from the standard multi-field inflation model. We show concrete examples of the modulated inflation scenario in which large non-gaussianity can be generated. We also discuss the running of the non-gaussianity parameter.     

All-Fiber Optical Signal Inversion Using Stimulated Raman Scattering

We propose a method for all-optical signal inversion by means of stimulated Raman scattering (SRS). The idea is based on the transference of energy from the logic state #x201C;1#x201D; to the second stokes and making the logic state #x201C;0#x201D; into logic state #x201C;1#x201D; by receiving energy from the pump through SRS. According to the numerical simulation, a continuous wave pump source of LOW at 1453 nm and a few hundred meters of highly nonlinear fiber are required to invert an input signal at 1555 nm. The optical signal is inverted with high on-off contrast ratio.