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We model possible mechanical conformations and thermal dynamics of the recently synthesized graphene-based polymer nanocarpets for advanced optoelectronics applications, made by homogeneous valence attachment (functionalization) to one side of the graphene sheet of polyethylene chains or benzene rings. It is shown that on a flat substrate, the anisotropic quasi-two-dimensional nanocarpets always preserve a flat shape with the inner side bound to the substrate and with the attached polymer molecules at the outer side orthogonal to the plane of the graphene sheet. The flat shape of the nanocarpet bound to the substrate is resistant to thermal vibrations. The heat capacity of the nanocarpet increases monotonically with temperature in the equipartition limit. Most strong growth of heat capacity occurs for the graphene sheets with attached polyethylene chains at T ⩾ 450 K, when the disordering of the lattice of the attached polymer chains starts to occur from the edges of the nanocarpet.

The effect of the dynamic surface monolayer at the interface of a solid with superfluid helium on Kapitza thermal resistance is analyzed. A monolayer of impurity atoms adsorbed on a solid surface and weakly bound to the substrate is considered as a surface monolayer of this type. A resonance of phonons incident from the helium with oscillations in the two-dimensional system can cause a great increase in heat transfer through this kind of interface compared to an atomically clean boundary. Scalar and vector models of the interface are examined. New results from the macroscopic dynamics of an interface between two media are introduced in this review, with lattice anharmonicity (nonlinear effects) taken into account.

Destructive quantum interference between the waves propagating through laterally inhomogeneous layer can result in their total reflection, which in turn reduces energy flux carried by these waves. We consider the systems of Ge atoms, which fully or partly, in the chequer-wise order, fill a crystal plane in diamond-like Si lattice. We have revealed that a single type of the atomic defects, which are placed in identical positions in different unit cells in the defect crystal plane, can result in double transmission antiresonances of phonon wave packets. This new effect we relate with the complex structure of the diamond-like unit cell, which comprises two atoms in different positions and results in two distinct vibration resonances in two interfering phonon paths. We also consider the propagation of phonon wave packets in the superlatticies made of the defect planes, half-filled in the chequer-wise order with Ge atoms. We have revealed relatively broad phonon stop bands with center frequencies at the transm...

This study is devoted to experimentally achieving the phenomenon of periodic modulation of the acoustic-wave intensity, which is observed upon passage of an acoustic signal through a quasi-periodic structure and is the acoustic analog of the effect of Bloch oscillations (BO). Ultrasound at a frequency of 1 MHz is used, and a layered structure that consists of alternate plane-parallel glass and water layers serves as a super-lattice. In order to create an analog of the external electric field, the thickness of the water layers was changed inversely with respect to their ordinals. It is shown that the transmission spectrum of such a structure has the form of narrow equidistant peaks (an analog of the Wannier-Stark ladder), and the envelope of a transmitted signal undergoes periodic oscillations (analogous to BO). The experimental results are in good agreement with theoretical calculations performed by the transfer-matrix method.

Single-particle excitations in quasi-one dimensional ferromagnetic spin chains located in nonuniform magnetic fields with large gradients are examined. Spin waves are dynamically localized in a magnetic field with a constant gradient and a system of local levels with equidistant energies develops with a form similar to the Wannier-Zeeman “ladder.” This effect is similar to Bloch oscillations of an electron in a weak electric field. In a semi-infinite chain the spectrum of spin excitations is bounded below; with increasing energy a gradual transition from spin waves in a uniform magnetic field to states with Bloch-like oscillations occurs. An infinite spin chain in a magnetic field that is constant for x 0 is considered. Under these conditions a system of local Wannier-Zeeman states develops above the spin wave zone; their spectrum becomes equidistant at high energies. Possibilities for the experimental observation of Bloch oscillations of spin waves are discussed.

The reasons for the appearance of flexural rigidity of layers in strongly anisotropic layered crystals are investigated. Structures consisting of loosely bound monatomic layers (specifically, graphite) as well as formed loosely bound structural elements each consisting of several monolayers which are coupled much more strongly with one another (for example, in dichalcogenide transition metals) are examined. The effect of the flexural rigidity on the phonon spectra of these compounds—quasi-flexural bending of the dispersion curves of phonon modes polarized in a direction normal to the layers—and the particularities appearing in the phonon densities of states as a result of quasi-flexural vibrational branches crossing low-frequency optical modes are analyzed.

A scientific session of the Physical Sciences Division of the Russian Academy of Sciences (RAS) was held on 26 March 2008 at the conference hall of the P N Lebedev Physical Institute, RAS. The following reports were presented at the session: (1) Klimov V V (P N Lebedev Physical Institute, RAS, Moscow) "Nanoplasmonics"; (2) Istomin Ya N (P N Lebedev Physical Institute, RAS, Moscow) "Electron–positron plasma generation in the magnetospheres of neutron stars"; (3) Kosevich Yu A (N N Semenov Institute of Chemical Physics, RAS, Moscow) "Multichannel propagation and scattering of phonons and photons in low-dimension nanostructures". An abridged version of these reports is given below. • Nanoplasmonics, V V Klimov Physics-Uspekhi, 2008, Volume 51, Number 8, Pages 839-844 • Electron–positron plasma generation in the magnetospheres of neutron stars, Ya N Istomin Physics-Uspekhi, 2008, Volume 51, Number 8, Pages 844-848 • Multichannel propagation and scattering of phonons and photons in low-dimension nanostructures, Yu A Kosevich Physics-Uspekhi, 2008, Volume 51, Number 8, Pages 848-859

In this paper we develop a dynamical model of the propagating nonlinear localized excitations, supersonic kinks, in the cation layer in a silicate mica crystal. We start from purely electrostatic Coulomb interaction and add the Ziegler-Biersack-Littmark short-range repulsive potential and the periodic potential produced by other atoms of the lattice. The proposed approach allows the construction of supersonic kinks which can propagate in the lattice within a large range of energies and velocities. Due to the presence of the short-range repulsive component in the potential, the interparticle distances in the lattice kinks with high energy are limited by physically reasonable values. The introduction of the periodic lattice potential results in the important feature that the kinks propagate with the single velocity and single energy, which are independent on the excitation conditions. The unique average velocity of the supersonic kinks on the periodic substrate potential we relate with the kink amplitude of the relative particle displacements, which is determined by the interatomic distance corresponding to the minimum of the total, interparticle plus substrate, lattice potential. The found kinks are ultradiscrete and can be described with the "magic wave number" q=2\pi/3a, which was previously revealed in the nonlinear sinusoidal waves and supersonic kinks in the Fermi-Pasta-Ulam lattice. The extreme discreteness of the observed supersonic kinks, with basically two particles moving at the same time, allows the detailed interpretation of their double-kink structure, which is not possible for the multikinks without an account for the lattice discreteness. Analytical calculations of the displacement patterns and energies of the supersonic kinks are confirmed by numerical simulations. The computed energy of the found supersonic kinks in the considered realistic lattice potential is in a good agreement with the experimental evidence for the transport of localized energetic excitations in silicate mica crystals between the points of K40 recoil and subsequent sputtering., J.F.R.A., V.S.M., and L.M.G.R. acknowledge financial support from the projects FIS2008-04848, FIS2011-29731C02-02, and MTM2012-36740-C02-02 from Ministerio de Ciencia e Innovacion (MICINN). All authors acknowledge Prof. F. M. Russell for ongoing discussions.

The coherent coupling between electron Bloch and in-plane cyclotron oscillations in semiconductor superlatices in tilted electric and magnetic fields induces a unidirectional quasi-DC current in analogy to the DC Fiske effect observed when a superconductor Josephson junction or a superfluid weak link is coupled to an electromagnetic respectively an acoustic resonator. In all cases, the coupling opens an elastic rectifying transport channel. We explore the effect for the case of a superlattice both experimentally and theoretically, and specifically address the influence of the coupling on the frequency of the magnetoBloch oscillations.

We present our measurements and model for the reflectancre anisotropy of the (001) surface of polar cubic zinc-blende semiconductor in the far infrared. We observe that the relative reflectance difference of GaAs(001) in the far infrared can reach the value of twenty percents which is two orders of magnitude higher than the reflectance difference of the GaAs(001) in the near-ultraviolet - visible range. The most strong reflectance anisotropy was observed in the optical phonon Reststrahlbande and its vicinity. We relate the observed reflectance anisotropy with the anisotropy of the optical-phonon and plasma damping constants. Such anisotropy can be caused by anisotropic inhomogeneous broadening of the frequencies of the optical-phonon and plasma oscillations polarized respectively along the [110] and directions. This effect can be understood in terms of the lattice-deformation-induced changes of the optical-phonon force constants and electron-effective-mass tensor components. Anisotropic inhomogeneous strain of the lattice can in turn be induced by anisotropic microscopic short-range ordering of point defects (dopants) and dislocations in near-surface regions of noncentrosymmentric zinc-blende semiconductors. The observed giant reflectance anisotropy can be used as a sensitive tool for the far infrared characterization of zinc-blende semiconductors. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate transient coherent magneto-Bloch oscillations (MBO's) of electronic wave packet photo-excited in a biased semiconductor superlattice (SSL) in a crossed or tilted magnetic field, as well as temporal transition to nonlinear magnetotransport in the superlattice. The avoided crossing between the full-miniband MBO's and bottom-miniband cyclotron oscillations in SSL is described in general for tilted electric and magnetic fields. It is shown that the full-miniband MBO's in a biased SSL in a crossed magnetic field give rise to anomalous Hall velocity which is inverse to the electric field, depends in general on the excitation conditions and determines the shift of the MBO's frequency with respect to the frequency of Bloch oscillations without magnetic field. The electric-field-induced transition from the ordinary to anomalous Hall drift velocity determines the value of a peak stationary carrier velocity υ(p) and the corresponding fields. The general criterion for the value of the electric field at which the υ(p) is reached is found.

Spatial profiles of electrically excited surface waves on agarose gels were measured as a function of frequency and concentration of the agarose. Two surface waves were observed in the low-frequency region. One is a Rayleigh wave, which shows the elastic behavior up to a certain frequency and then gradually disappears with the increase in frequency. The other wave is also elastic; however, it has higher value of phase velocity than the Rayleigh wave and approaches the dispersion of the capillary wave in the high-frequency region. The surface response function analysis shows that the semi-infinite viscoelastic media support the propagation of the two elastic surface waves, but not the propagation of the elastic and pure capillary waves as was claimed previously. Moreover, the theoretical analysis reveals that the viscous losses effectively enhance the coexistence of the two elastic surface modes.

Resonance scattering of a transverse sound wave by a planar defect in an elastic isotropic medium is studied in a wide range of values of the ratio of the damping length and the size of the region of localization of longitudinal oscillations. The transition between two limiting cases is described. The character of the transition is demonstrated by typical plots of the dependence of the reflection and transmission coefficients on the parameter relating the wavelength of the incident wave and the strength of the defect. It is shown that renormalization of total reflection into conventional dissipative passage occurs for values of this parameter below a certain critical value.

This survey is devoted to studying some peculiar features of various surface and interface vibrational modes in strongly anisotropic and other nontraditional crystals. The group of the nontraditional crystals includes such anisotropic systems as layered and chain-type crystals, complex compounds of the ferroelastic and ferroelectric types in the vicinity of structural phase transitions and many compounds with weak interatomic bonds in some crystallographic directions or in certain planes. The majority of such materials can be considered as quasi-low-dimensional systems. It is shown that the presence of the weak interatomic bonds in the nontraditional crystals causes a considerable large effect of anharmonicity of the vibrations on properties of the longwavelength surface and interface modes. New types of deeply penetrating surface waves are analyzed in anisotropic crystals and crystals near structural phase transitions, and in nonlinear crystals. The contribution of capillary effects to the peculiarities of the surface and interface waves in the anisotropic crystals is estimated. The effect of the strong elastic anisotropy on the properties of the ordinary and generalized Rayleigh waves and the shear surface waves is described analitically. A possible connection of the geometry of the isofrequency surfaces (the inverse velocity surfaces) with the existence of the generalized surface waves is discussed. The longwave dynamics of twins in the matrix of layered crystals, such as high T c superconductors are also considered. In such systems, the dispersion relation for the interface elastic waves have the form of ω ~ √k , characteristic of the spectrum of two-dimensional plasmons.

We demonstrate the electric tuning of the acoustic field in acoustic microcavities (MCs) defined by a periodic arrangement of metal stripes within a surface acoustic delay line on LiNbO3 substrate. Interferometric measurements show the enhancement of the acoustic field distribution within a single MC, the presence of a “bonding” and “anti-bonding” modes for two strongly coupled MCs, as well as the positive dispersion of the “mini-bands” formed by five coupled MCs. The frequency and amplitude of the resonances can be controlled by the potential applied to the metal stripes.

In this contribution, we discuss the recent experimental demonstration of Wannier‐Stark ladders, Bloch Oscillations and Landau Zener tunneling in a solid by means of surface acoustic waves propagating through perturbed grating structures.

We present the experimental observation of Bloch oscillations, the Wannier-Stark ladder, and Landau-Zener tunneling of surface acoustic waves in perturbed grating structures on a solid substrate. A model providing a quantitative description of our experimental observations, including multiple Landau-Zener transitions of the anticrossed surface acoustic Wannier-Stark states, is developed. The use of a planar geometry for the realization of the Bloch oscillations and Landau-Zener tunneling allows a direct access to the elastic field distribution. The vertical surface displacement has been measured by interferometry.

A model is considered in which localized superconductivity (LS) is induced by a two-dimensional array of steps (twinning dislocations) at a non-coherent twin boundary in the bulk of a metallic crystal. It is proposed that the cores of the twinning dislocations are the sources of the local enhancement of the electron-phonon interaction parameter in superconductor. In the framework of the model the dependence of the LS critical temperature on the two-dimensional concentration of the steps and on the orientation angle of the twin boundary with respect to the crystalline plane of twinning is predicted.

The coupling due to the van der Waals and the dissipative thermal interactions of surface waves propagating along a thin vacuum gap between nonpiezoelectric crystals is investigated. The propagation of the Rayleigh and the shear horizontal surface waves in coupled massive crystals and the slow bending waves in coupled thin films is considered. It is shown that the van der Waals attractive forces cause a negative shift of the velocity and the existence of a terminal point k 0 for the propagation of the long-wavelength Rayleigh and bending waves, in which the frequency of the coupled waves goes to zero. The anomalous absorption of the grazing bulk shear acoustic waves scattered from the gap is predicted.

Low frequency collective oscillations in a superlattice consisting of alternating highly anisotropic layers are considered. This superstructure may be formed in the ferroelastic near the structural phase transition by alternation of twins. For the surface waves propagating along the layers, the conditions and the range of existence of those with the dispersion law ω ∼ k½, characteristic for two-dimensional plasmons, have been analyzed for a solid-state system with consideration for elastic anisotropy and retardation of acoustic waves. It is shown that such oscillations exist in a frequency range which becomes markedly wider near the ferroelastic phase transition and the “optimum” geometry of the phase matching for which there arise collective excitations of the type under consideration is found. For transverse and longitudinal waves propagating across the layers the existence is proved of low frequency acoustic branches separated by a wide gap from the nearest optical branches.

We have investigated the specific features of acoustic wave propagation in thin crystalline plates and rods near the continuous ferroelastic phase transition. It is shown that near such a transition in bounded ferroelastic the longitudinal acoustic phonons can become unstable (are softened)—unlike the behaviour of the bulk longitudinal phonons in unbounded ferroelastics. The influence of capillary parameters (the surface stress, the excess surface moduli and mass density) on the characteristics of the low-frequency Lamb waves is analyzed. It is emphasized that this influence considerably increases near the ferroelastic phase transitions. The thickness dependence of a ferroelastic phase transition temperature shift in bounded crystals (thin plates or rods) due to the surface stress is also evaluated.

The dispersion relation for the electromagnetic wave-guided oscillations of a twodimensional (2D-) electron layer periodic array in a transversal magnetic field is analysed. Oscillation frequencies much lower than the electron cyclotron frequency exist under certain conditions. Additionally, the perpendicular propagation to the layers is investigated. It is demonstrated that a strong magnetic field causes a frequency shift and splitting, which are in inverse relation to the external magnetic field and the period of the layered electron system.

The authors propose an acoustic method to measure directly the density of the normal component in thin films of superfluid helium. The effect of the helium film on the velocity and the penetration depth of Love and Gulyaev-Bleustein shear surface waves is analysed. The advantage of the method based on the application of shear surface waves is that the change in their velocity, as is shown, is proportional to the normal component density and the helium film thickness.

An exact solution has been constructed for the equations of nonlinear elasticity theory, describing monochromatic shear surface waves, supported by the interface between a uniaxial nonlinear crystal and a layer of a “linear” crystal of arbitrary thickness, and by the interface between a nonlinear crystal and another nonlinear crystal (both semi-infinite and in the form of a thin layer). We consider the propagation of surface waves in which the maximum of the amplitude is located at a finite depth under the boundary of the nonlinear self-focusing crystal. Shear surface waves not existing in linear theory are predicted at the interface between two semi-infinite crystals and at the interface betwwen a nonlinear crystal and an “accelerating” elastic layer. In particular, nonlinear shear surface waves with vanishingly small amplitude at the interface are described.

Terahertz-emission spectroscopy reveals two regimes of the Hall current of impulsively excited coherent charge-carrier wavepackets in a GaAs/AlGaAs superlattice as a function of the electric and magnetic bias fields.

Summary form only given. In the last decades, a number of macroscopic quantum effects in solids have been investigated. Among those are the Josephson effect in weakly coupled superconductors and Bloch oscillations in semiconductor superlattices (SLs). The key effect of both phenomena is the generation of an AC effect by the application of a DC electric field to the system. For Bloch oscillations (BO), the periodic motion is due to Bragg reflection of electrons in a periodic potential when a constant bias field is applied across the structure. Josephson effect and Bloch oscillations show interesting extensions when both DC and AC voltages are applied. The current across the junction of two superconductors shows resonances (the so-called Shapiro steps) which appear at voltages which are multiples of the photon energy of the AC field. Similar resonances for the incoherent (phase-independent) current in a semiconductor SL have been observed in a SL under THz illumination. We here observe a novel coherent Shapiro current in semiconductor superlattices.

We investigate the influence of scattering and coherent plasmon coupling on the temporal and spatial dynamics of Bloch-oscillating electrons in a semiconductor superlattice. We demonstrate that the dynamics are strongly influenced due to the scattering processes. For higher carrier densities, coupling to coherent plasmons leads to anharmonic Bloch oscillations since the static bias field is considerably changed by the oscillating carriers.

We predict an extreme sensitivity to the dissipative losses of the resonant interaction of bulk phonons with a 2D defect in a solid. We show that the total resonant reflection of the transverse phonon at the 2D defect, described earlier without an account for dissipation, occurs only in the limit of extremely weak dissipation and is changed into almost total transmission by relatively weak bulk absorption. Anomalous surface absorption of the transverse phonon, when one half of the incident acoustic energy is absorbed at the 2D defect, is predicted for the case of "intermediate" bulk dissipation., 11 preprint pages, no figures

It is known from the theory of waves in layered structures that a thin nonabsorbing layer on the free surface of a solid results only in a small change in the phase of a total reflection of bulk acoustic waves. The acoustic absorption in the layer leads to the variation (with the wave frequency) also of the reflection amplitude. When the layer posesses both the resonant and absorbing properties the phenomenon of anomalous absorption of bulk acoustic waves by a two-dimensional layer can take place. This phenomenon is characterized by an absence of the reflection and by an almost complete surface absorption of the incident wave. The origin of this effect is a strong enhancement of the resonant oscillations amplitude of a light and weakly bonded thin layer, which in the presence of the finite and relatively low absorption in the layer leads to an anomalously large ”absolute” value of acoustic losses of the incident bulk wave. The width of the resonant absorption curve is proportional to the ratio between the effective elastic impedance of a two-dimensional layer and the acoustic impedance of a solid. This effect can be experimentally revealed on two-dimensional layers of helium (or other noble gases), adsorbed on a solid (see, e.g., [1]), or on two-dimensional polymer or liquid-crystal Langmuir-Blodgett adsorbed films (see, e.g., [2]). When a weakly bonded resonant two-dimensional absorbing layer is placed at the interface between two different crystals the phenomenon of anomalous surface absorption can take place for the incident bulk wave in the conditions of a total reflection (in the absence of the transient layer). In this case the phenomenon is characterized by an almost complete absence of both reflected and transmitted bulk waves. All vibrational energy of the incident acoustic wave is absorbed at the interface, and then is reemitted in the adjacent media via the thermal phonons.

Low-frequency collective oscillations in a superlattice consisting of alternating highly anisotropic layers are considered. Such superstructure may be formed in the ferroelastic near the structural phase transition by alternation of twins. For the surface waves, propagating along the layers, the conditions and the range of existence of those with the dispersion law \ensuremath{\omega}\ensuremath{\sim}${\mathit{k}}^{1/2}$, characteristic for two-dimensional plasmons, have been analyzed for a solid-state system with consideration for elastic anisotropy and retardation of acoustic waves. Such excitations (``dyadons'') were used by Horovitz, Barsch, and Krumhansl [Phys. Rev. B 36, 8895 (1987)] in an attempt to explain the anomalies of low-temperature thermodynamic and kinetic characteristics of high-${\mathit{T}}_{\mathit{c}}$ superconductors. We have shown that the similarity of the densities of the matching phases and the retardation of elastic waves in the crystal narrow the range of existence of dyadons, but the high elastic anisotropy of the solid phases enlarges the range of existence of such excitations in solid-state systems. An example of possible crystalline geometry of the phase matching, for which there arise collective excitations of the type under consideration, is found. For transverse and longitudinal waves propagating across the layers, the existence is proved of low-frequency acoustic branches separated by a wide gap from the nearest optical branches.

The observation of Bloch oscillations in sound propagation through a multilayer of two different fluidlike components is predicted. In order to obtain the equivalent to the acoustic analog of a Wannier‐Stark ladder [E. E. Mendez et al., Phys. Rev. Lett. 60, 2426–2429 (1988)], a set of cavities with increasing thickness is employed. Bloch oscillations were theoretically predicted as time‐resolved oscillations in transmission in direct analogy to electronic Bloch oscillations in semiconductor superlattices [J. Feldmann et al., Phys. Rev. B 46, R7252–R7255 (1992)]. Finally, an experimental setup is proposed to observe the phenomenon by using arrays of cylindrical rods in air, which acoustically behaves as a fluidlike system with effective sound velocity and density [D. Torrent et al., Phys. Rev. Lett. 96, 204302 (2006)]. For the proposed system, Bloch oscillations and Zener tunneling are confirmed by using multiple scattering simulations. [Work supported by MEC of Spain.]

Macroscopic equations of adsorbed atom monolayer dynamics on a deformable crystal are derived. It is shown that a heavy decelerating adsorbed layer can induce two surface waves of the Rayleigh polarization. The higher-frequency one of them has the terminal point in the region of low wave numbers and changes into a pseudosurface longitudinal wave. In the case of a weakly bonded adsorbed monolayer the conditions for the appearance of weakly attenuating resonance modes are found. The situation is analysed for the case that the dispersion laws of the slow surface wave in the crystal with the adsorbed layer have the form ω∼k 1 2 typical for two-dimensional plasmons.

The spectrum of magnetoplasma oscillations of a two-dimensional electron layer in a transversal magnetic field is studied under the condition that the electron system is unbounded along the layer plane and screened in the perpendicular direction. It is shown that under certain conditions oscillation frequencies much lower than the electron cyclotron frequency exist. Also the electromagnetic wave-guided oscillations in the system are described. It is shown that a strong magnetic field causes a frequency shift and splitting, depending inversely on the external magnetic field and the transversal specific dimension.

Using the concept of capillary phenomena in the theory of elasticity the problem of elastic waves, localized near a plane defect of a crystal, is considered. The spectra, polarization and depth of penetration for the three types of localized elastic waves are found. The anomalous reflection of slipping sound waves from a plane defect is also considered and the relations between peculiarities of reflection coefficients with the spectra of localized waves are obtained. A possible instability of surface elastic waves is investigated.

The different mechanisms of resonant transport of phonons between two media in the presence of an impurity intermediate layer are described. Particular attention is focused on the resonance interaction of elastic waves with a two-dimensional defect on the contact boundary between two solids, on the multichannel interface phonon scattering, and on the experimentally observed nonmonotonic temperature dependence of the reduced heat flux. In the cases when there is a direct interaction between edge atoms of the matrix as non-nearest neighbors or when the impurities do not fill completely the 2D interface layer, an additional channel for the transmission of phonons through the interface opens. This additional transmission channel manifests itself as a transmission (or reflection or absorption) peak with an asymmetric line shape (the so-called Fano-like resonance for phonons due to interference between the two transmission channels). Some applications of the Fano-like interference phenomena in magnon heat condu...