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1.
Electrophoretic ratchets have been developed for both analytical and preparative electrophoresis. These ratchets use a new
type of pulsed field. The quality of the fractionations meets the usual standards for biochemistry-based electrophoresis.
The supporting medium is either an agarose gel or a capillary-contained polymer solution. The electrophoretic ratchets are
effective with a particle that has an electrophoretic mobility (μ=velocity/electrical field) that varies as the electrical
field varies. A ratchet developed for DNA molecules is effective because μ increases in magnitude as the electrical field
increases in magnitude. Ratchets developed for both DNA–protein complexes and spheres are effective because of the opposite
dependence of μ on the electrical field. Ratchet-based gel electrophoresis can be performed in a continuous, preparative mode.
Ratchet-based capillary electrophoresis provides a necessary component for cyclic capillary electrophoresis. Cyclic capillary
electrophoresis of DNA is a procedure for analyzing a DNA profile in several segments. These segments are separated by electrophoretic
enhancements of the DNA profile. Cyclic capillary electrophoresis is being developed for increasing both the length and the
accuracy of the analysis of a DNA-sequencing ladder.
Received: 16 October 2001 / Accepted: 14 January 2002 / Published online: 22 April 2002 相似文献
2.
Superconducting quantum interference devices (SQUIDs) are very well suited for experimental investigations of ratchet effects.
This is due to the periodicity of the Josephson coupling energy with respect to the phase difference δ of the superconducting
macroscopic wave function across a Josephson junction. We show first that, within the resistively and capacitively shunted
junction model, the equation of motion for δ is equivalent to the motion of a particle in the so-called tilted washboard potential,
and we derive the conditions which have to be satisfied to build a ratchet potential based on asymmetric dc SQUIDs. We then
present results from numerical simulations and experimental investigations of dc SQUID ratchets with critical-current asymmetry
under harmonic excitation (periodically rocking ratchets). We discuss the impact of important properties like damping or thermal
noise on the operation of SQUID ratchets in various regimes, such as adiabatically slow or fast nonadiabatic excitation.
Received: 22 November 2001 / Accepted: 14 January 2002 / Published online: 22 April 2002 相似文献
3.
I. Derényi 《Applied Physics A: Materials Science & Processing》2002,75(2):217-222
Although Brownian ratchets have been conceived to describe the operation of molecular motor proteins, their basic principles
are also applicable to a wide range of different physical systems. In this paper I line up two such possible applications
in condensed-matter physics. The first one is the removal of vortices from superconductors. Magnetic fields frequently penetrate
superconducting materials in the form of vortices, and once present, they dissipate energy and generate internal noise, limiting
the operation of numerous superconducting devices. We demonstrate theoretically that the application of an alternating current
to a superconductor patterned with an appropriate ratchet-like pinning potential induces an outward vortex motion. The second
application is based on the fact that the Schwoebel barrier induces an asymmetry in the lattice potential of nearly flat solid
surfaces. During epitaxial growth this asymmetry leads to a fast and unwanted increase in the surface roughness. We show,
however, that one can take advantage of the asymmetry by applying an alternating electric field parallel to the surface, which
induces a net electromigrational flow of the surface atoms from the peaks towards the wells, and thus results in a smoother
surface.
Received: 20 November 2001 / Accepted: 14 January 2002 / Published online: 22 April 2002 相似文献
4.
A detailed introduction to directed transport in Brownian motors occurring in spatially periodic systems far from equilibrium
is presented. We elucidate the prominent physical concepts and novel phenomena with a representative dissipative Brownian
motor dynamics. Its main ingredient is a thermal noise with time-dependent temperature modulations that drive the system out
of thermal equilibrium in a spatially asymmetric (ratchet-) potential. Yet, this asymmetric setup does not exhibit a concomitant
obvious bias into one or the other direction of motion. Symmetry conditions for the appearance (or not) of directed current,
its reversal upon variation of certain parameters, and various other generic features and applications are discussed. In addition,
we provide a systematic classification scheme for Brownian motor models and review historical landmark contributions to the
field.
Received: 9 November 2001 / Accepted: 14 January 2002 / Published online: 22 April 2002 相似文献
5.
A.B. Mundt A. Kreuter C. Russo C. Becher D. Leibfried J. Eschner F. Schmidt-Kaler R. Blatt 《Applied physics. B, Lasers and optics》2003,76(2):117-124
We demonstrate coherent coupling of the quadrupole S1/2D5/2 optical transition of a single trapped 40Ca+ ion to the standing wave field of a high-finesse cavity. The dependence of the coupling on temporal dynamics and spatial
variations of the intracavity field is investigated in detail. By precisely controlling the position of the ion in the cavity
standing wave field and by selectively exciting vibrational state-changing transitions the ion’s quantized vibration in the
trap is deterministically coupled to the cavity mode. We confirm coherent interaction of ion and cavity field by exciting
Rabi oscillations with short resonant laser pulses injected into the cavity, which is frequency-stabilized to the atomic transition.
Received: 23 August 2002 / Published online: 8 January 2003
RID="*"
ID="*"Corresponding author. E-mail: christoph.becher@uibk.ac.at
RID="**"
ID="**"Present address: Time and Frequency Division, National Institute of Standards and Technology, Boulder, CO 80305, USA 相似文献
6.
Y.G. Fokin T.V. Murzina O.A. Aktsipetrov S. Soria G. Marowsky 《Applied physics. B, Lasers and optics》2002,74(7-8):777-781
Ferroelectric properties of thin (1.5–4 μm planar cells of a ferroelectric liquid crystal (FLC) mixture are studied using
electro-optic measurements, second-harmonic generation (SHG) and SHG interferometry. A switching behaviour of the FLC cells
in external dc electric fields is observed. It is characterised by rotation of the polarisation plane of the transmitted light
and by changes in the SHG intensity, phase and anisotropy dependences, which are attributed to a collective motion of the
system as a ferroelectric uniform state with C2 symmetry.
Received: 16 October 2001 / Revised version: 18 March 2002 / Published online: 6 June 2002 相似文献
7.
J.M.R. Parrondo B.J. de Cisneros 《Applied Physics A: Materials Science & Processing》2002,75(2):179-191
We review the literature on the energetics of Brownian motors, distinguishing between forced ratchets, chemical motors – driven
out of equilibrium by differences of chemical potential, and thermal motors – driven by temperature differences. The discussion
is focused on the definition of efficiency and the compatibility between the models and the laws of thermodynamics.
Received: 13 November 2001 / Accepted: 10 January 2002 / Published online: 22 April 2002 相似文献
8.
Na,K-ATPase is a universal ion pump of the biological cell. Under physiological conditions, it uses the γ-phosphorus bond
energy of ATP during hydrolysis to pump 2 K+ inward and 3 Na+ outward; both being uphill transports. The experiment presented here demonstrates that the protein transporter can also use
electric energy to fuel its pump activity. A theory of electroconformational coupling (TEC) is described and an experiment
performed to verify several predictions of the model. Analysis based on the TEC model suggests that Na,K-ATPase is a Brownian
ratchet. The enzyme harvests energy from the applied field by means of the field-induced conformational oscillation or fluctuation.
However, high efficiency of energy transduction can only be achieved with an electric field of certain intensities, frequencies
and waveforms. This property of the enzyme allows us to define an electric signal and differentiate it from electric noise
on the basis of the analysis by the TEC model. Data show that electric noise alone does not induce pump activity. However,
an appropriate power level of noise imposed on a signal can enhance the pump efficiency. The effect of noise on the signal
transduction of Na,K-ATPase is reminiscent of the stochastic resonance phenomenon reported in other biological systems [3,
35]. The TEC model embodies many common features of enzymes and biological motors. It is potentially energy-efficient, much
more so than models based on the ion-rectification mechanism.
Received: 1 November 2001 / Accepted: 5 March 2002 / Published online: 22 April 2002 相似文献
9.
We report on the first layer growth of a Mn6+-doped material. Large-size BaSO4 substrates of 10×6×4 mm3 were grown from a LiCl solvent by the flux method. Flat surfaces of undoped BaSO4 were then achieved by use of liquid-phase epitaxy (LPE) from a CsCl–KCl–NaCl solvent. Finally, BaSO4:Mn6+ layers were grown by LPE with growth velocities of approximately 3 μm h-1, at temperatures of 550–508 °C. Absorption, luminescence, luminescence-excitation and luminescence-decay measurements confirmed
the incorporation of manganese solely in its hexavalent oxidation state. This material possesses potential as a near-infrared
tunable laser with a wavelength range larger than Ti:sapphire.
Received: 7 January 2002 / Revised version: 30 March 2002 / Published online: 8 August 2002 相似文献
10.
Measurements of the radial electric field profile in magnetically confined plasmas have yielded important new insights in
the physics of L-H transitions, edge biasing and/or the active control of Internal and Edge Transport Barriers. The radial
electric field is not an easy plasma parameter to diagnose. Techniques to measure the radial electric field in the plasma
core are the Heavy Ion Beam Probe and the Motional Stark Effect. An indirect method that is quite often applied is to derive
the electric field from measurements of the poloidal and toroidal rotation velocities via the radial ion force balance. This
paper will first briefly explain the need for detailed measurements of the radial electric field profile. Subsequently, the
various diagnostics to measure this parameter will be reviewed. The emphasis will be especially put on recent trends, rather
than on an exhaustive overview.
Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24,
2002.
Partner in the Trilateral Euregio Cluster 相似文献
11.
C. Fusco A. Fasolino T. Janssen 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):95-102
We study the dynamics of a dimer moving on a periodic one-dimensional substrate as a function of the initial kinetic energy
at zero temperature. The aim is to describe, in a simplified picture, the microscopic dynamics of diatomic molecules on periodic
surfaces, which is of importance for thin film formation and crystal growth. We find a complex behaviour, characterized by
a variety of dynamical regimes, namely oscillatory, “quasi-diffusive” (chaotic) and drift motion. Parametrically resonant
excitations of internal vibrations can be induced both by oscillatory and drift motion of the centre of mass. For weakly bound
dimers a chaotic regime is found for a whole range of velocities between two non-chaotic phases at low and high kinetic energy.
The chaotic features have been monitored by studying the Lyapunov exponents and the power spectra. Moreover, for a short-range
interaction, the dimer can dissociate due to the parametric excitation of the internal motion.
Received 8 July 2002 / Received in final form 15 November 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: fusco@sci.kun.nl. 相似文献
12.
P.L. Ramazza S. Ducci A. Zavatta M. Bellini F.T. Arecchi 《Applied physics. B, Lasers and optics》2002,75(1):53-58
We report an experimental study of the second harmonic generated in type I interaction by a Ti:Sa laser operating in the picosecond
regime at 786 nm in LBO crystals. A joint characterization of the dependence of conversion efficiency and spatial beam quality
on crystal length and degree of pump focusing is given. A simple heuristic formula, reproducing over a broad range of parameters
the predictions of classical Boyd–Kleinman theory, is derived and compared with the experimental results. The conditions for
the optimization of the generation process using an elliptically focused pump beam are quantitatively evaluated.
Received: 13 March 2002 / Revised version: 8 May 2002 / Published online: 12 July 2002 相似文献
13.
X. Zhu S. Lu H.L.W. Chan C.L. Choy K.H. Wong 《Applied Physics A: Materials Science & Processing》2003,76(2):225-229
Compositionally graded (Ba1-xSrx)TiO3 (BST) (x:0.0∼0.25) thin films were grown on Pt (111)/TiO2/SiO2/Si (100) substrates using layer-by-layer pulsed laser deposition in the temperature range 550–650 °C. Both downgraded (Ba/Sr
ratio varying from 100/0 at the bottom surface to 75/25 at the top surface) and upgraded (Ba/Sr ratio varying from 75/25 at
the bottom surface to 100/0 at the top surface) BST films were prepared. Their microstructures were systematically studied
by X-ray diffractometry and scanning electron microscopy. A grain morphology transition from large ‘rosettes’ (>0.30 μm) to
small compact grains (70–110 nm) was observed in the downgraded BST films as the deposition temperature was increased from
550 to 650 °C. No such grain morphology transition was detected in the upgraded BST films. Dielectric measurements with metal
electrodes revealed an enhanced dielectric behavior in the downgraded films. This enhancement is mainly attributed to the
large compressive stress field built up near the interface between the downgraded film and substrate. Furthermore, the BaTiO3 layer in the downgraded BST films not only serves as a bottom layer but also as an excellent seeding layer for enhancing
the crystallization of the subsequent film layers in the downgraded films.
Received: 10 December 2001 / Accepted: 12 March 2002 / Published online: 19 July 2002
RID="*"
ID="*"Corresponding author. Fax: 86-25/359-5535, E-mail: xhzhu@public1.ptt.js.cn 相似文献
14.
Classical study of the rovibrational dynamics of a polar diatomic molecule in static electric fields
We study the classical dynamics of a polar diatomic molecule in the presence of a strong static homogeneous electric field. Our full rovibrational investigation includes the interaction with the field due to the permanent electric dipole moment and the polarizability of the molecule. Using the LiCs molecule as a prototype, we explore the stability of the equilibrium points and their bifurcations as the field strength is increased. The phase space structure and its dependence on the energy and field strength are analyzed in detail. We demonstrate that depending on the field strength and on the energy, the phase space is characterized either by regular features or by small stochastic layers of chaotic motion. 相似文献
15.
M. Jelinek J. Lančok M. Pavelka P.A. Atanasov A. Macková F. Flory C. Garapon 《Applied Physics A: Materials Science & Processing》2002,74(4):481-485
Nd: KGd(WO4)2 thin films were deposited by KrF laser ablation on MgO, YAP, YAG and Si substrates at temperatures up to 800 °C. Film crystallinity,
morphology, stoichiometry (WDX, RBS and PIXE), excitation spectra, fluorescence, refractive index and waveguiding properties
were studied in connection with deposition conditions. The best films were crystalline and exhibited losses of approximately
5 dB cm-1 at a wavelength of 633 nm.
Received: 8 January 2001 / Accepted: 7 November 2001 / Published online: 11 February 2002 相似文献
16.
M. Danckwerts E. Savinova B. Pettinger K. Doblhofer 《Applied physics. B, Lasers and optics》2002,74(7-8):635-639
We combine in situ electrochemical second-harmonic generation (SHG) with voltammetry measurements using the hanging meniscus
configuration. This setup is used to investigate the interface between a Ag (111) electrode and an alkaline electrolyte. The
study offers a new in situ insight into the electrochemical processes at the Ag (111) electrode during OH adsorption and subsequent
oxidation. The behavior of SHG isotropic and anisotropic contributions as a function of potential is discussed and related
to the interfacial electric field. Comparison of the results with previous investigations of the Ag underpotential oxidation
in alkaline solutions shows that submonolayer oxidation is followed by bulk oxidation.
Received: 16 October 2001 / Revised version: 26 March 2002 / Published online: 6 June 2002 相似文献
17.
U. Schröter 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):297-310
Green's dyadic technique represents a powerful tool for calculations in electrodynamics, especially in modelling optical properties
of nanoscopic objects. The method does not only provide field distributions, but also maps of susceptibilities and densities
of states. Whereas the formalism is well established for dielectrics and electric fields, I present here a straight forward
extension to tensors of both electric and magnetic type as well as mixed ones and furthermore to the situation where objects
with dielectric and magnetic permeabilities are present together. As examples, characteristic field patterns are compared
for elementary dielectric and magnetic perturbations. Green's tensors calculated for a coral structure reveal that mixed susceptibilities
can exhibit other symmetries than pure electric or magnetic ones. Maps of all tensor components can thus give essential clues
to the interpretation of near-field images.
Received 15 December 2002 Published online 20 June 2003
RID="a"
ID="a"Files “maths.ps” and “tensors.ps” are only available in electronic form at http://www.edpsciences.org
RID="b"
ID="b"e-mail: Ursula.Schroeter@uni-konstanz.de 相似文献
18.
Electron ratchet effect in semiconductor devices and artificial materials with broken centrosymmetry
A.M. Song 《Applied Physics A: Materials Science & Processing》2002,75(2):229-235
Studies on nonlinear electron transport in nanometer-sized semiconductor devices with broken centrosymmetry are reviewed.
In these devices, an applied alternating (rocking) electric field induces a net flow of electrons in the direction perpendicular
to that of the applied field. Such an electron ratchet effect has been observed in a number of differently designed devices,
fabricated from two types of semiconductor material systems. The functionality is interpreted with an extended Büttiker–Landauer
formula. We show that the devices operate at both cryogenic and room temperatures and at frequencies up to at least 50 GHz.
Based on a similar microscopic mechanism, we have also constructed, to the best of our knowledge, the first artificial electronic
nanomaterial that operates at room temperature. The promising possibilities for practical applications, such as rectification,
microwave detection, second-harmonic generation, etc., are also discussed.
Received: 16 January 2002 / Accepted: 11 February 2002 / Published online: 22 April 2002 相似文献
19.
R. Dandoloff A. Saxena 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):265-267
For a spin-polarized electron gas on an elastic cylinder in an external axial magnetic field and an axial electric field we
find that the corresponding Euler-Lagrange equation is the double sine-Gordon (DSG) equation with an exact 2π-skyrmion solution.
The DSG skyrmion is stabilized, without Coulomb repulsion, by the curvature of the cylinder. It adopts a characteristic length
ξ which is smaller than the radius of the cylinder. For an elastic cylinder this mismatch of length scales causes a deformation
of the cylinder in the region of the skyrmion.
Received 23 October 2001 / Received in final form 8 March 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: rossen.dandoloff@ptm.u-cergy.fr 相似文献
20.
The complete set of self-consistent parameters of nominally undoped LiNbO3 crystals of congruent composition that describe the electro-optic, piezoelectric, elasto-optic, elastic, and dielectric response
has been determined by numerically evaluating available measurements. The parameters were determined at room temperature and
consist of the low-frequency clamped dielectric constants εS
ij, elastic stiffness constants at constant electric field CE
ijkl, piezoelectric stress coefficients eijk, elasto-optic constants at constant electric field pE
ijkl, and clamped electro-optic coefficients rS
ijk. It is shown that the complete set is required for calculating the effective electro-optic coefficients and dielectric constants
in photorefractive applications of LiNbO3.
Received: 4 January 2002 / Revised version: 1 February 2002 / Published online: 14 March 2002 相似文献