D. Treves's research while affiliated with Weizmann Institute of Science and other places

Publications (88)

Article
The problem of a microstrip disk antenna excited by a probe at its center is studied using a moment-method approach for the evaluation of the surface current on the disk. The novelty of the work is a careful treatment of the singular effects of the probe and of the disk edge on the surface current on the disk. This is done by including in a proper...
Article
The radiation and losses in microstrip antennas with a corporate feed network are studied. A surface current approach is applied in which the electrical currents in the feed lines are modeled as in ideal transmission lines. The free-space radiation and the surface-wave excitation of typical segments in printed feed networks are studied. A four-elem...
Article
Full-text available
Design and measured results for two X-band conformal microstrip arrays are presented. The two 4*4 arrays are built on the surface of a cylinder of small radius. They differ by the orientation of the elements relative to the cylinder axis. The measured directivities and radiation patterns are in reasonable agreement with theoretical predictions.
Article
A feeding technique for double-sided printed dipoles enabling the realisation of flat arrays on foam-like substrates with bandwidths up to 25% is presented. An experimental comparison with thin single-layer microstrip arrays shows that the available gains are equal, while the bandwidths for the double-sided dipole are much larger. A modification of...
Article
Design and measured results for two X-band conformal microstrip arrays are presented. The two 4 × 4 arrays are built on the surface of a cylinder of small radius. They differ by the orientation of the elements relative to the cylinder axis. The measured directivities and radiation patterns are in reasonable agreement with theoretical predictions.
Article
Full-text available
Design and measured results of two printed dipole arrays conformed to a small radius cylinder are described. The two arrays differ by the orientation of the elements: one has an axial direction of elements and the other has a circumferential direction. The elements are printed on both sides of a thin and flexible substrate and then wrapped around a...
Conference Paper
This work extends a modular approach for the design of microstrip arrays to high gain (35 dB) printed antennas. A theoretical study of the gain limitation in single-layer microstrip antennas is compared to experimental results in a set of 16,64,256 and 1024 element arrays.
Article
An approach to the analysis of microstrip antennas which is applicable also to relatively thick substrates using the relevant Green's function is presented. The Green's function is derived and closed form expressions for various antenna characteristics which explicitly take into account the presence of the dielectric material are obtained in terms...
Article
Full-text available
An approach to the analysis of microstrip antennas on cylindrical bodies is presented. The printed radiator is replaced by as assumed surface current distribution, and the fields are solved taking into account the presence of the dielectric layer and the metallic cylinder. Calculation takes place in the Fourier domain. The far field, calculated asy...
Article
Full-text available
A radiometric method for measuring the efficiency of antennas with respect to a low-loss horn is presented. The letter includes a short explanation of the principle, a description of the measurement system and experimental results related to microstrip arrays.
Article
Full-text available
A method for the design of medium gain (15-25 dB) microstrip array antennas is described. A modular approach is utilized in which a given antenna is used as a building block for higher gain antennas. A series of X -band antennas were built in this way, and the results seem to validate the usefulness of the method.
Conference Paper
An automatic measurement technique for near field mapping of microstrip structures is described. Several field mapping examples indicate that this technique can serve as a diagnostic tool for microstrip antennas.
Article
Full-text available
A Michelson-type unequal path interferometer for measuring the effective thickness of dielectric slabs is presented. Due to unequal paths, this interferometer is frequency dependent so that frequency tuning of the source controls the phase difference between the two paths and serves as a phase shifter. FM modulation of the source enables determinat...
Article
The problem of transverse-mode matching between the lowest-loss mode of a confocal unstable resonator and a Gaussian beam, which is injected into the resonator through a coupling hole in its back mirror, is analyzed. It is found that in resonators having equivalent Fresnel number >0.5, there is a value of the coupling hole diameter for which a mode...
Article
Statistical properties of a He-Ne laser beam (0.63 microm) propagating through atmospheric folded paths of 1 and 12 km were investigated experimentally using direct and heterodyne detection. Measured scintillation histograms, power spectra, time autocorrelations, and phase fluctuations are reported. The turbulence parameters derived from the optica...
Article
An outdoor He-Ne laser transmitter/receiver is used to measure the optical properties of a turbulent atmosphere medium. The He-Ne transmitter/receiver is of a folded path configuration which uses a retroreflector placed away (500 meters) from the laser. This configuration is particularly convenient for rapid probing of several optical paths origina...
Article
Statistical properties of HeNe and CO2 laser beams retroreflected through a turbulent atmosphere were investigated experimentally for round paths of 1 km and 12 km. Both heterodyne and direct detection were used.
Article
Amplified spontaneous emission of laser media having a spherical or disk shape is numerically analyzed. Some properties are discussed and a comparison with linear systems is made. Analytical approximations, for the case of high pumping rates and high efficiency, are obtained. Energy level schemes of dye systems are used in the analysis and in the n...
Article
The performance of dye lasers with excited singlet-state absorption (ESA) at the pump and the lasing wavelengths is analyzed for short pulse pumped systems in the medium range of pumping intensities. Analytical and numerical solutions are presented for a wide range of the variable parameters such as ESA cross sections, the cavity reflectivity, and...
Article
A tunable, very narrow bandwidth, flashpumped dye laser is described. Publse energies up to 50 mJ at a bandwidth of less than 30 MHz, and with a divergence of 0.4 mrad, are obtained. Spectral narrowing and tuning is achieved by injection locking of the pulsed laser to the radiation, of a tunable cw dye laser. The cavity is designed for single longi...
Article
Bleaching experiments in some laser dyes under high power UV irradiation from a nitrogen laser are described. Very high bleaching quantum efficiencies, of the order of 10-3 molecules bleached/photon absorbed, and a dependence of this efficiency on intensity have been found. The diffusion coefficients for the dyes in ethyl alcohol were also measured...
Article
A pulsed dye laser system with a narrow-band signal injected into the cavity is considered. The injection starts prior to the excitation pulse. It is shown that during a transient period, injection locking can be achieved for a much wider range of parameters than under conventional CW conditions. The analysis is based on a set of coupled rate equat...
Article
The effects of absorption of pump radiation from the first excited singlet state on the fluorescence quantum yield are calculated by numerical solution of simple rate equations, and compared with experiments performed earlier for the dye 7-diethylamino-4-methyl-coumarin at N2-laser pumping. Analytical solutions for high and low pump intensities are...
Article
Transversely pumped dye-laser systems are investigated theoretically and experimentally. A set of coupled rate equations for the excited-state population densities and for the photon fluxes in both directions, at all wavelengths, is presented. Both the temporal and spatial dependence of these quantities are accounted for. The equations are solved n...
Article
Platinum‐cobalt thin films were prepared by rf sputtering with substrate biasing to contol composition. Contrary to what was expected from equilibrium bulk properties, films deposited at room temperature have the fcc structure, in‐plane magnetization, and low coercivity. At deposition temperatures above about 500 °C the coercivity increases and x‐r...
Article
An open resonator that consists of a spherical mirror and a reflection grating is described. The eigenmodes and eigenvalues are calculated numerically, utilizing the Fox and Li iterative method. By proper design of the grating, one may control the amount of energy coupled out through the grating's orders while the eigenmodes are almost unaffected.
Article
Dynamic measurements of velocity and temperature yield information on the temperature distribution and the thermal thickness of the evaporation front caused by focused laser irradiation on metals. The thermal thickness of the evaporation front is inversly proportional to the steady-state velocity of the front. Direct temperature values are obtained...
Article
Equilibrium bulk samples of Pt-Co near the 50-50 at.% composition are tetragonal below and fcc above 800°C. Alloys quenched from high temperatures retain the fcc phase at low temperatures. Films 400A˚ thick were prepared by rf sputtering with substrate biasing to control composition. Contrary to what was expected from equilibrium bulk properties, f...
Article
A technique for evaluating the optical anisotropy of fine-grain polycrystalline thin films is developed. This method is applied to MnBi with the low-temperature NiAs structure. It is estimated that the optical anisotropy is less than half the magneto-optic effect.
Article
The effect of birefringence and dichroism in materials for magneto‐optic memory applications is analyzed. The optical constants of MnAlGe and MnGaGe have been measured. The birefringence and dichroism are approximately equal and are an order of magnitude larger than the magneto‐optic effect. A statistical analysis of the effect of orientation and g...
Article
The morphology and crystallography of Co and Co(P) thin films (≪500 Å), produced by electroplating, were examined by electron microscopy and diffraction. It was found that the pH of the plating solution affects phase constitution and texture as it does in thicker films. Films deposited at low pH showed appreciable proportion of fcc grains, and the...
Article
The Faraday rotation of ErFeO3 as a function of temperature was measured from ambient down to the spin reorientation region (90 to 100°K) at a wavelength of 6070 Å. The intrinsic Faraday rotation increases gradually with decreasing temperature and then drops rapidly to zero in the spin reorientation region. It is concluded that the contribution of...
Article
The structure of the electromagnetic field near the focus of a stigmatic lens is investigated by use of the vectorial integral representation and the Fresnel formulas of refraction. The electric and magnetic vectors are calculated in the image space; from these, the energy densities and the Poynting vector are obtained. Numerical results, calculate...
Article
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Article
A method for the measurement and control of the velocity of moving objects using a single sideband interferometer (SSBI) is described. The method is applied to a Mössbauer spectrometer velocity transducer. The performance of the system operating between -1 and +1 cm/sec at constant velocity was measured. The long term mean velocity stability was 0....
Article
We present conclusive evidence that the magnetic-spin reorientation occurring in ErFeO3 at about 95°K proceeds by spin rotation.
Article
It has been demonstrated that longitudinal magnetooptic effect provides sufficiently large snr to make technique useful for reading stored information; however, many of advantages of optical memory system are sacrificed if laser optics cannot be used in record process as well; recently, temperature-sensitive cobalt film containing slight phosphorou...
Article
The historical development of Co-Fe-V permanent magnet alloys (vicalloys), their technological importance and scientific study, are reviewed. The basic, as yet unsolved, problem of the origin of their magnetic hardness is examined. Results of recent work employing Mössbauer spectroscopy and magnetic measurements at different temperatures, as well a...
Article
The magnetic susceptibility of YFeO3 has been measured in the temperature range 4.2-1000°K. The temperature dependence of the susceptibility is also derived theoretically using a Heisenberg Hamiltonian and applying the molecular-field approximation. In addition to nearest-neighbor isotropic exchange, antisymmetric exchange, and uniaxial anisotropy...
Article
Thin cobalt films, with low phosphorous content, electroplated on suitable substrates, at a pH of 6–6.5, have useful properties for thermomagnetic recording. They have a room-temperature coercivity, Hc(25°C) in excess of 200 Oe, Hc(25°C)∕Hc(150°C) in excess of 3, and good working margins.
Article
A method of recording digital information on a thin magnetic film is described. The change of magnetization in the film is accomplished by a coincidence of a high-power optical beam from a laser and a magnetic field. Films having coercive force ratios Hc(25°C)∕Hc(150°C) of at least 3 were used as the media. Information was recorded with a 1 W Argon...
Article
The magnetic moment of the 9.3-keV nuclear level of Kr83 was obtained by measuring the Zeeman splitting of the Mössbauer lines in an external magnetic field. Experiments with a Kr clathrate source and absorber in a longitudinal field and a ZnSe source with a solid Kr absorber in a transverse field yielded a magnetic moment of (-0.99+/-0.08)muN.
Article
The transient temperature distribution produced by a surface heat source with Gaussian distribution in one dimension and of infinite extent in the other is calculated. The heated medium is a thin metallic film on a thick substrate. The transverse temperature gradient in the thin film is neglected and it is assumed that all the heat is generated in...
Article
In the conventional magneto‐optic readout of digital information stored in a magnetic thin film, surface imperfections are a major source of noise. The readout method described here uses a low‐coercivity overlay film modulated by an external magnetic field, thus circumventing this noise source by detecting those light changes that are due only to t...
Article
In order to reduce the noise due to surface imperfections in a magneto‐optic readout system the following scheme was developed: the recording medium consists of a high‐coercivity storage film on top of which is deposited a low‐coercivity readout film. The leakage field of the bits stored in the storage film magnetizes the readout layer in a similar...
Article
Digital magnetic information is recorded on a rotating disc thin film by a conventional tape recorder head. The information is read out using the longitudinal magnetic Kerr effect, and a 1.5- MHz bandwidth electronic system. The use of spatial filtering and a differential scheme yields a ratio of peak-to-peak signal to rms noise of 32 dB, which is...
Article
The hyperfine interactions of the iron nuclei in the orthoferrites were studied between 85 and 770\ifmmode^\circ\else\textdegree\fi{}K using the M\"ossbauer effect. The temperature dependence of the sublattice magnetization ${$\sigma${}}_{s}(T)$ is compared with various statistical-mechanical theories. It obeys approximately a $\frac{1}{3}$ power l...
Article
The various noise sources in a high‐density magneto‐optic readout system are evaluated. It is shown that shot noise is not severe even at interrogation rates of 10<sup>7</sup> bit/sec and bit areas of 10<sup>-6</sup> cm<sup>2</sup>. Various techniques used to reduce the noise originating from surface imperfections are described and their effectiven...
Article
A vacuum thermostat for Mössbauer effect studies permitting temperature control from 85 to 870°K is described. Any temperature in this range can be maintained for long periods, utilizing an appropriate electronic temperature stabilizer. Temperature inhomogeneity over the sample is estimated to be less than 1°K. This thermostat can transmit radiatio...
Article
Alnico alloys were ground and separated by sedimentation. Mössbauer and fluorescence analysis techniques were used to study the separated phases. The main result is that alloys heat treated for optimum permanent magnet properties contain a paramagnetic phase, probably bcc, rich in nickel and copper, while quenched Alnico V does not contain such a p...
Article
Measurements of the temperature dependence of the magnetization in a weak ferromagnet YFeO3, along the ferromagnetic direction in the critical region , are reported. Analysis of the data gives the following results for the critical exponents: β = 0.55 ± 0.04, γ = 1.33 ± 0.04, γ″ = 0.7 ± 0.1,
Article
The temperature dependence of the internal field in orthoferrites at the iron nucleus was measured using the Mössbauer effect. It was found that, in the range 0.6 TN < T < 0.99 TN, the internal field varies approximately as the .ZusammenfassungLa dépendance du champ interne de la température dans le noyau de fer dans les orthoferrites est mesuré pa...
Article
Several explanations of the shift in the position of the centroid of the Mössbauer spectrum in metallic iron as the specimen is heated through the Curie temperature are considered.
Article
: The Neel temperature of the orthoferrites is calculated assuming a constant distance between Oxygen and Iron ions and that the superexchange integral varies as the cosine of the linkage angle. The calculated values fit well the measured Neel temperatures which cover a range of about 120K. (Author)
Article
A torque magnetometer GE type gaussmeter using weak ferromagnetic rotors is described. Such an instrument gives a reading essentially linear with fields up to 105 G. The actual torques are higher than those obtained with para‐ or diamagnetic rotors, even at 105 G. An experimental instrument was built, and found to yield a linear reading up to the h...
Article
The Curie point, lattice constants, sublattice magnetization, spontaneous magnetic moment, susceptibility, and the nonlinear susceptibility have been measured on the compounds RFeO<sub>3</sub> with R yttrium or a rare earth. The main conclusions from these measurements are: (1) The rare-earth ions contribution to the magnetic properties of these ma...
Article
Mossbauer spectra of 57Fe in ultrafine NiFe2O4 and CoFe2O4 powders were studied, as a function of crystallite size and temperature. The hyperfine field was found to collapse at a temperature, lower then the Curie points which decreased with particle size. This collapse of the hyperfine field is interpreted as motional narrowing due to the onset of...
Article
The coercive force Hc as a function of the angle between the easy axis of magnetization and the external field has been studied in orthoferrite single crystals using the vibrating sample technique. The experimental results are in good agreement with the Kondorsky 180° wall motion model which predicts the relation Hc(0)∕Hc(θ)=cosθ.
Article
An automatic recording constant velocity Mössbauer spectrometer for <sup>57</sup>Fe is described. The motor and the velocity sensor are integrated in a specially designed electromechanical unit. Feedback is used to make the velocity proportional to an input voltage. Recorded linewidths only 25% larger than the natural width are obtained.
Article
Two possible mechanisms for weak ferromagnetism, single-ion magnetocrystalline anisotropy and antisymmetric exchange, are examined on orthoferrites which contain a paramagnetic rare earth. The study was done by comparing the ferromagnetic components and the terms of the second-order susceptibility tensor that are obtained from torque measurements t...
Article
Curie temperatures of 14 different orthoferrites with the chemical formula RFeO3, (R = Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were measured by differential thermal analysis. Hyperfine interactions of the Fe57 nucleus in the same materials were determined from their Mo¨ssbauer spectra. The quadrupole splittings (except for Sm), isome...
Article
Use of symmetry considerations to study effects that reverse under time ; reversal and are therefore typical of ordered magnetic materials is explained. ; Effects of external parameters such as electric fields, magnetic fields, and ; strains are considered. The form of the interaction tensors related to these ; parameters can be determined from mag...
Article
Measurements of the magnetoelectric effect on Cr2O3 powders, after magnetoelectric annealing are described. The experimental results are compared with theoretically derived relations between the magnetoelectric effect in single crystals and powders. Reasonable agreement is found.
Article
The optical properties of magnetic materials are studied using symmetry considerations. It is found that in addition to birefringence, Faraday rotation, and optical activity there should exist another effect, namely gyrotropic birefringence. This birefringence is of opposite sign for magnetic domains related to each other by time reversal, and can,...
Article
Sensitive static torque measurements were carried out on single crystals of YFeO3 in order to determine if weak ferromagnetism in this material is caused by single ion magnetocrystalline anisotropy or by anisotropic exchange interaction.The following symmetry considerations show a priori which cubic and higher terms in the torque can be nonzero. Th...
Article
The anisotropy induced in gold-doped Permalloy by cold rolling and subsequent heat treatments has been investigated using a recording torque magnetometer. The material was cold rolled from 0.014 in. to 0.000125 in. and then heat treated for 2 hr in a dry hydrogen atmosphere. The torque curves obtained could be decomposed into a hard and soft compon...
Article
This paper describes a method to distinguish between two mechanisms that may cause weak ferromagnetism in the orthoferrites, i.e., antisymmetric exchange and single-ion magnetocrystalline anisotropy. The free energy of a magnetic crystal is expressed as a series in the applied field. The condition of invariance of the energy with respect to the mag...
Article
An improved magneto-optic Kerr instrument was used for observation of magnetic domains in iron whiskers undergoing a magnetization cycle with applied peak fields of 6000 oe, parallel to the axis of the whisker. It was found that a domain structure persisted near the tip of the whiskers even under the maximum applied field. The domain configuration...
Article
After considering the various factors that limit the performance of the Kerr technique in the observation of magnetic domains, it is concluded that the ellipticity caused by metallic reflection is of major importance. A detailed calculation of this effect is carried out, including the case of normal incidence. It is theoretically found that, for mi...
Article
An improved instrument utilizing the longitudinal Kerr magneto‐optic effect is used to observe the magnetic domain development in iron whiskers undergoing a magnetization cycle. It is found that domains persist at the tip of the whisker even under conditions for which the crystal is usually assumed to be saturated. Under applied fields of a few tho...
Article
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Article
The angular dependence of the maximum remanence parallel to the applied field, I<sub>p</sub> , and perpendicular to it, I<sub>t</sub> , when the specimen is rotated through an angle β about an axis perpendicular to the field direction, is considered theoretically. For a rather wide range of materials the relation I<sub>t</sub> = (dI<sub>p</sub>/dβ)...
Article
The possibility is examined that Brown's paradox results from the assumption that the shape of the crystal considered is ellipsoidal. It is argued that the large local demagnetizing fields developed near sharp corners of a uniformly magnetized crystal cause the appearance of closure domains, which serve as nuclei of reverse magnetization, thus lowe...
Article
The subdivision of a Bloch wall into a periodic structure of right- and left-hand walls observed by Williams and Goertz and by DeBlois and Graham is shown to be caused by the self-magnetostatic energy of the wall. The period of this structure is calculated by an approximate minimization of the energies involved. The results compare favorably with e...
Article
The coercive force of an infinite ferromagnetic cylinder is calculated as a function of the radius and of the inclination of the axis to the applied field. For this calculation it is assumed that only curling and rotation in unison take place ; and that whenever the curling is associated with a discontinuous jump, the magnetization is brought to th...
Article
It is already well known that the second harmonic magnetic transductor has instability regions. It has been found experimentally that in each region two modes of output current exist, differing only by the phase, which these currents have with respect to the exciting voltage. Under suitable parameters and excitation conditions, the transductor will...
Article
An improved model of a precision rotation viscometer with electrostatic restoring torque for the centipoise range is described. In this instrument torques from 0.1 to 500 dyne cm. are measured with an accuracy of 0.2%. Rates of shear range from 0.1 to 200 sec.−1.
Article
The field at which the spins of a previously saturated ideal ferromagnetic particle cease to be aligned is defined as the nucleation field. This field is calculated, using calculus of variation, for an infinite cylinder and a sphere, assuming three mechanisms of magnetization reversal: spin rotation in unison, magnetization curling, and magnetizati...

Citations

... A large is also needed for reducing required perpendicular coercivity, , [3], so as to keep thermal stability and a large output signal. Co-Pt materials were investigated for magneto-optical media [4] due to their large magnetic anisotropy. Vacuum evaporated Co Pt films deposited at an elevated temperature of 300 C exhibited a large magnetic anisotropy constant of about erg/cm [5]. ...
... The second phase transition near the magnetic phase transition is marked by some critical exponents b (related to the spontaneous magnetization), g (associated with the initial susceptibility) and d (related to the critical magnetization isotherm) [56e59]. The mathematical exponent definitions related to magnetization measurements can be described as [56,57]: ...
... First, we assumed that the amplitudes of the resonances Δμ j are constant with temperature. Second, we assumed a modified power law [46]: ...
... Inverse Fe 3þ spinel nature is clearly evidenced from the relative area data of two setuplets. Further nano-particle CoFe 2 O 4 shows superparamagnetic behavior with partial collapse of the hyperfine spectrum at temperatures below the Neel temperature [19]. MnFe 2 O 4 is partly inverse [20], therefore the degree of inversion of Co ferrite decreases with increasing the Mn content. ...
... As the thickness increased to 55 nm, the magnetic microstructures changed: a change in the contrast of two adjacent segment walls occurred as they appeared alternatively white and black, indicative of the presence of Bloch lines in the zigzag domain walls (digitally enhanced on the left side of the image for t = 55 nm in Figure 5) [63,64]. Shape irregularities were not present in the films with t = 55 nm. ...
... There is an extensive literature on the subject of the theory of line-of-sight propagation through the atmosphere (Andrews & Phillips, 1998; Andrews et al., 2000; Fante, 1975; Ishimaru, 1997; Strohbehn, 1978; Tatarskii, 1971). One of the most important works was developed by Tatarskii (Tatarskii, 1971). ...
... Note that the zigzag wall with chirality is distinct from the zigzag walls in thick films or bulk materials [1], e.g. garnet film [45], CoFeNiBSi metallic glass [46], silicon iron crystal [1,47], or iron whisker [1,48,49], where the aforementioned multidimensional domain wall structures are involved to minimize the system energies, however, without chirality [1]. The origin of the magnetic chirality in this study will be discussed later. ...
... 24 ). The extremely sharp magnetization switching at the coercive field is inconsistent with domain-wall dynamics 25 . It results from flipping all the spins by 180° (ref. ...
... In particular, amorphous films of the Co-Ni-P system have high magnetization, low coercive force, and low losses at ultrahigh frequencies [3]. Soft magnetic CoP films (in amorphous modification) have found application as materials for thermomagnetic magneto-optical memory [4] and can be used in microwave devices [5], while hard magnetic CoP films (in hexagonal modification) are considered as promising materials for micro / nano electromechanical systems (MEMS / NEMS) [6]. On the other hand, with using the chemical deposition method for the Co-P system by changing the technological conditions, it is relatively easy to make both magnetically soft and magnetically hard materials. ...
... Like most of the orthoferrites, SFO crystallizes in distorted orthorhombic perovskite structure with PbnmD h 2 16 space group at room temperature with four rare-earth ions and four Fe ions per unit cell [11]. The four Fe sites of SFO are crystallographically equivalent to the four rare earth sites of the material [12,13]. The SFO unit cell can be imagined as a corner sharing FeO 6 octahedron forming a three dimensional distorted perovskite type structure [14]. ...