Use of two-photon excitation for erasable-rewritable three-dimensional bit optical data storage in a photorefractive polymer

We report what is believed to be the first use of a photorefractive polymer in erasable-rewritable three-dimensional bit optical data storage under two-photon excitation. We successfully demonstrate writing, erasing, and rewriting of multilayered information in a photorefractive polymer consisting of 2,5-dimethyl-4-(p-nitrophenylazo)anisole, 2,4,7-trinitro-9-fluorenone, 9-ethylcarbazole, and poly(N-vinylcarbazole). A three-dimensional bit density of 5 Gbits/cm(3) is achieved by two-photon absorption under pulsed beam illumination at an infrared wavelength of 800 nm in the recording process. Complete erasing of the recording information is achieved by use of ultraviolet illumination.     

Recording of one-dimensional holograms in MnBi films

A new system of holographic recording on moving MnBi film is described. The data to be stored are recorded in a track of non-overlapping 1-d Fourier holograms. A cavity-dumped argon laser is used for writing. The feasibility of this new system has been demonstrated by writing and erasing tracks consisting of 20 μm by 2 μm holograms. A maximum bit density of 10⁷ bit/cm² and a writing data rate of 10⁸ bit/s should be attainable with such a system.     

Rotation of a Fine Particle with Circularly Polarized Anti-Parallel Collinear Laser Beams

We have succeeded in the operation of rotating a fine particle which was held without mechanical contact by circularly polarized laser beams with opposite propagation directions. A polystyrene latex particle 11.9 μm in diameter deformed in a disk-like shape was dispersed in water, and was trapped using the anti-parallel collinear laser beams which were set up so that they had the circular polarization rotating in the same direction. It was observed that the trapped particle rotated in the same direction as the rotation of the circular polarization of light. Inversion of the rotational direction of the circular polarization of light reversed the direction of the rotation of the particle. Although the rotational speed of a particle varied significantly from particle to particle, it was found to be proportional to the laser beam intensity. A typical value for the rotational speed per beam intensity was 2.1 Hz/W.     

Beam alignment with the axis of a rotation stage for laser fabrication of microcircular structures

An optical technique to align laser beam with the axis of a rotating stage is proposed for laser fabrication of circular microstructures. The laser beam is first aligned parallel to the rotation axis and subsequently adjusted to coincide with the axis. An optical arrangement consisting of two quadrant photodiodes for the x- and y-directions and a specially designed beam splitter is utilized for the alignment. Mathematical modeling of the alignment system is carried out to estimate alignment errors caused by misalignment of mirror surfaces in the beam path. It is shown that parallelness of the laser beam to the rotation axis is a key factor to reduce alignment errors. The proposed method was applied to a microstereolithography system and proved that the laser beam can be aligned within a distance of about 25 μm from the rotation axis.     

Bound Motion of Bodies and Paticles in the Rotating Systems

The Lagrange theory of particle motion in the noninertial systems is applied to the Foucault pendulum, isosceles triangle pendulum and the general triangle pendulum swinging on the rotating Earth. As an analogue, planet orbiting in the rotating galaxy is considered as the giant galactic gyroscope. The Lorentz equation and the Bargmann-Michel-Telegdi equations are generalized for the rotation system. The knowledge of these equations is inevitable for the construction of LHC where each orbital proton “feels” the Coriolis force caused by the rotation of the Earth.     

Diffusion anisotropy in a toroidal (ring) vortex in water

Diffusion of paint (ink) particles in a toroidal (ring) vortex in a density-homogeneous liquid (water) was experimentally studied. Particle diffusion anisotropy in rotating water of the vortex was detected. The effect consists in the fact that the particle diffusivity in the direction perpendicular to the rotation axis of the torus core is much lower than that in the direction parallel to the rotation axis.     

The effect of rotation on the steady state response of a spring-mass system under harmonic excitation

A two degree-of-freedom system, consisting of a point mass which is constrained to move in one plane, is considered. The motion is controlled by linear springs and viscous damping. A constant amplitude harmonic force is applied along one axis in the plane, which is rotating at a constant angular velocity about an axis perpendicular to the plane. Due to the rotation, oscillation takes place in the direction perpendicular to, as well as along, the axis of excitation.The amplitude and phase of the steady state vibrations are derived as a function of the excitation frequency and the rate of turn. For rates of turn very much less than the system natural frequencies, this theory covers the principles of vibratory rate sensors such as the tuning fork; however, the emphasis here is on the performance of the system when the angular velocity is of the same order as the natural frequencies of the system.     

The mechanics of particles inside a rotating cylindrical mass shell

It is shown that up to the second order in the gravitational constant the effect of a rotating mass shell on a particle moving near its axis is the same as that of a rotating coordinate system. Coriolis force and centrifugal force have, contrary to the case discussed by Thirring[1, 2], the value expected in a rotating reference frame.     

Information Geometry in Roegenian Economics

We characterise the geometry of the statistical Roegenian manifold that arises from the equilibrium distribution of an income of noninteracting identical economic actors. The main results for ideal income are included in three subsections: partition function in distribution, scalar curvature, and geodesics. Although this system displays no phase transition, its analysis provides an enlightening contrast with the results of Van der Waals Income in Roegenian Economics, where we shall examine the geometry of the economic Van der Waals income, which does exhibit a “monetary policy as liquidity—income” transition. Here we focus on three subsections: canonical partition function, economic limit, and information geometry of the economic Van der Waals manifold.     

Measurement of tilt of a diffuse object by double-exposure speckle photography using speckle fanning in a photorefractive BaTiO3 crystal

A technique has been proposed for the measurement of tilt of a diffuse object using speckle fanning in a photorefractive BaTiO₃ crystal. Free space geometry has been used for recording in which the axis of rotation of the object lies away in three-dimensional space. The method is based on recording of two exposures, one before- and another after the tilt, thus producing speckle correlation fringes due to overlapping of two speckle fans. We consider a generalized case of tilt, generating curved fringes with center shifted in the transverse direction. The axis of rotation lies perpendicular to the optical axis in three-dimensional space having the transverse and axial components of the shift in the center of rotation with respect to the diffuser plane. Fourier transform of the curved fringes produces correlation output. Measure of separation between the correlation peaks in transverse and axial directions provides information about the tilt angle, the direction of tilt, and the distance of rotation axis from the optical axis. Experimental results have been presented to validate the theoretical predictions.     

Measurement of the layer thickness on rotating substrates in molecular-beam epitaxy apparatus

A simple and effective method is developed for synchronous recording of an interference signal to measure the thickness of a layer grown on a rotating substrate in molecular_beam epitaxy apparatus. The separation of the information component of the signal from the noise induced by the rotation of a substrate (conditioning of the signal) increases the accuracy of recording the interference signal coming to a layer thickness calculation device and an automatic system of process management and, thus, increases the quality and reproducibility of film structures.     

Acoustic waves in a rotating ideal gas

The acoustic wave propagation in a rotating ideal gas with density stratification due to the rotation is considered. To describe the waves propagating normally to the rotation axis, an equation for a scalar quantity that is a function of density is proposed. The frequency dependences of the phase and group velocities of an acoustic-gyroscopic wave are presented. It is shown that the stratification of gas leads to an exponential amplitude decay for an acoustic wave generated near the rotation axis and has no effect on the inertial-gyroscopic wave.     

Bose-Einstein condensates with vortices in rotating traps

We investigate minimal energy solutions with vortices for an interacting Bose-Einstein condensate in a rotating trap. The atoms are strongly confined along the axis of rotation z, leading to an effective 2D situation in the x-y plane. We first use a simple numerical algorithm converging to local minima of energy. Inspired by the numerical results we present a variational ansatz in the regime where the interaction energy per particle is stronger than the quantum of vibration in the harmonic trap in the x-y plane, the so-called Thomas-Fermi regime. This ansatz allows an easy calculation of the energy of the vortices as function of the rotation frequency of the trap; it gives a physical understanding of the stabilisation of vortices by rotation of the trap and of the spatial arrangement of vortex cores. We also present analytical results concerning the possibility of detecting vortices by a time-of-flight measurement or by interference effects. In the final section we give numerical results for a 3D configuration. Received 16 December 1998 and Received in final form 18 March 1999     

Lagrangian acceleration of passive tracers in statistically steady rotating turbulence

The statistical properties of the Lagrangian acceleration vector of passive tracers in statistically steady rotating turbulence is studied by particle tracking velocimetry. Direct effects of the background rotation are the suppression of high-acceleration events parallel to the (vertical) rotation axis, the enhancement of high-acceleration events for the horizontal acceleration, and the strong amplification of the autocorrelation of the acceleration component perpendicular to both the rotation vector Ω and local velocity vector u. The autocorrelation of the acceleration component in the plane set up by Ω and u is only mildly enhanced.     

What Is Temperature? Modern Outlook on the Concept of Temperature

The meaning and evolution of the notion of “temperature” (which is a key concept for the condensed and gaseous matter theories) are addressed from different points of view. The concept of temperature has turned out to be much more fundamental than conventionally thought. In particular, the temperature may be introduced for systems built of a “small” number of particles and particles at rest. The Kelvin temperature scale may be introduced into quantum and relativistic physics due to the fact that the efficiency of the quantum and relativistic Carnot cycles coincides with that of the classical one. The relation of temperature with the metrics of the configurational space describing the behavior of systems built from non-interacting particles is demonstrated. The role of temperature in constituting inertia and gravity forces treated as entropy forces is addressed. The Landauer principle asserts that the temperature of a system is the only physical value defining the energy cost of the isothermal erasure of a single bit of information. The fundamental role of the temperature of the cosmic microwave background in modern cosmology is discussed. The range of problems and controversies related to the negative absolute temperature is treated.     

Rewritable polarization-encoded multilayer data storage in 2,5-dimethyl-4-(p-nitrophenylazo)anisole doped polymer

We report a rewritable polarization-encoded multilayer data storage method with a polymer film doped with the azo dye DMNPAA (2,5-dimethyl-4-(p-nitrophenylazo)anisole). It is found that under two-photon excitation by a linearly polarized femtosecond laser beam at wavelength 780 nm the optical axis of DMNPAA molecules can be oriented to the perpendicular direction of the beam via a trans-cis-trans isomerization process. As a result, multilayer polarization-encoded optical data storage is demonstrated by recording two letters of a bit spacing of 4 microm in the same region of a given layer. It is shown that erasing and rewriting a particular layer is possible.     

Mechanics of a particle near the center of a rotating ring

The equations of motion of a test particle moving near the center of a massive rotating ring are derived up to the post-post-Newtonian order of approximation, by using the metric tensor for many body system which is Minkowskian at spatial infinity. Logarithmic divergences due to self-interaction of the ring appear in the equations of motion. These divergences can be removed by the procedure which is similar to the renormalization method in particle physics. In the equations of motion there appears a force directing to the rotation axis and depending on the angular velocity of the ring. This force vanishes when the magnitude of the gravitational constant times the mass of the ring divided by the radius of the ring is about one tenth of the square of the velocity of light. Under this condition it is shown that the relative magnitude of the Coriolis force to the centrifugal force in the equations of motion agrees with the expected one from the equations of motion in a rotating reference frame.     

Geometrical statistics of the vorticity vector and the strain rate tensor in rotating turbulence

We report results on the geometrical statistics of the vorticity vector obtained from experiments in electromagnetically forced rotating turbulence. A range of rotation rates Ω is considered, from non-rotating to rapidly rotating turbulence with a maximum background rotation rate of Ω = 5 rad/s (with Rossby number much smaller than unity). Typically, the Taylor-scale Reynolds number in our experiments is around Re_λ ≈ 100. The measurement volume is located in the centre of the fluid container above the bottom boundary layer, where the turbulent flow can be considered locally statistically isotropic and horizontally homogeneous for the non-rotating case, see L.J.A. van Bokhoven, H.J.H. Clercx, G.J.F. van Heijst, and R.R. Trieling, Experiments on rapidly rotating turbulent flows, Phys. Fluids 21 (2009) 096601. Based on the full set of velocity derivatives, measured in a Lagrangian way by three-dimensional (3D) particle tracking velocimetry, we have been able to quantify statistically the effect of system rotation on several flow properties. For the range of rotation rates considered, the experimental results show how the turbulence evolves from almost isotropic 3D turbulence (Ω ? 0.2 rad/s) to quasi-two-dimensional turbulence (Ω ≈ 5.0 rad/s), and how this is reflected by several statistical quantities. In particular, we have studied the orientation of the vorticity vector with respect to the three eigenvectors of the local strain rate tensor and with respect to the vortex stretching vector. Additionally, we have quantified the role of system rotation on the self-amplification terms of the enstrophy and strain rate equations and the direct contribution of the background rotation on these evolution equations. The main effect of background rotation is the strong reduction of extreme events and related (strong) reduction of the skewness of PDFs of several quantities, for example, the intermediate eigenvalue of the strain rate tensor and the enstrophy self-amplification term.     

Study on the rewritability of bisazobenzene-containing films in optical storage based on two-photon process

In this paper, we use a two-photon technique to record data points on bisazobenzene-containing films. The recording data points are evidently polarization dependent. It is found that the recording data points can be erased by the linearly polarized light whose polarization direction is perpendicular to that of the recording beam and then, in the same region, new data can be rewritten after erasing. In addition, the recorded data can also be erased completely by the circularly polarized light. Compared with linearly polarized beam, the circularly polarized light is a better choice for erasure as no main orientation is regained after erasing rather than reorientation.     

样品转动方式对中子全息成像结果的影响

在中子全息成像实验中, 为避免透射中子干扰, 入射中子束方向与样品-探测器方向不能在一条直线上, 同时采用探测器移动结合样品转动或仅样品转动的方式, 避免探测系统的大范围移动. 因此在样品的转动过程中, 入射中子束和探测器相对于样品的位置同时发生改变, 内源全息项和内探测器全息项作为变量被记录在同一幅全息图中, 并在重建过程中相互干扰. 本文对基于中子三轴谱仪和四圆谱仪的三种不同转动方式进行了中子全息记录和重建模拟研究, 并讨论其修正方法. 结果表明, 各转动方式都可以通过适当的方法消除或减轻相关影响, 而其中基于三轴谱仪的纯样品转动方式可以使用两个探测器记录的方式, 避开入射中子束方向与样品-探测器方向不能在一条直线上的限制, 得到完整的全息图, 同时通过数据处理能基本消除相对转动造成的干扰, 达到理想的重建结果, 在条件允许的情况下应予优先采用.