Oriented imaging of 3D subcellular structures in bacterial cells using optical tweezers

Using oscillating optical tweezers, we show that controlled alignment of rod-shaped bacterial cells allows imaging fluorescently labeled three-dimensional (3D) subcellular structures from different, optimized viewpoints. To illustrate our method, we analyze the Z ring of E. coli. We obtain that the radial width of the Z ring in unconstricted cells is about 120 nm. This result suggests that the Z ring consists of an extremely sparse network of FtsZ filaments.     

Mechanisms of organelle division and inheritance and their implications regarding the origin of eukaryotic cells

Mitochondria and plastids have their own DNAs and are regarded as descendants of endosymbiotic prokaryotes. Organellar DNAs are not naked in vivo but are associated with basic proteins to form DNA-protein complexes (called organelle nuclei). The concept of organelle nuclei provides a new approach to explain the origin, division, and inheritance of organelles. Organelles divide using organelle division rings (machineries) after organelle-nuclear division. Organelle division machineries are a chimera of the FtsZ (filamentous temperature sensitive Z) ring of bacterial origin and the eukaryotic mechanochemical dynamin ring. Thus, organelle division machineries contain a key to solve the origin of organelles (eukaryotes). The maternal inheritance of organelles developed during sexual reproduction and it is also probably intimately related to the origin of organelles. The aims of this review are to describe the strategies used to reveal the dynamics of organelle division machineries, and the significance of the division machineries and maternal inheritance in the origin and evolution of eukaryotes.     

Peculiarities of charged particle motion in an annular channel with electrified walls

The motion of charged particles in a straight hollow dielectric channel with electrified walls is considered in general form. It is shown that the motion of particles in the channel is periodic. In the first approximation, the potential of interaction of particles with the channel walls is harmonic. The relation between the period of oscillations of a particle in the channel and the physical parameters of the channel wall is derived. In a curvilinear channel (e.g., a ring), the resultant potential acquires a new term due to the centrifugal force. The particle in this case performs multiple contactless motion in the ring. At the same time, oscillations of particles in the ring take place. The motion in the ring is accompanied with emission of synchrotron and channeled radiation. If a thin (micrometer) target is introduced into the ring, high-intensity X rays and bremsstrahlung are observed. The directionality of radiation depends on the particle energy.     

Domain Wall Migration in 3-d in the Presence of Diffusing Impurities

A new three-dimensional simulation procedure was developed for domain wall (grain boundary, APB, magnetic, etc.) migration in the presence of diffusing impurities. The simulation is based upon a kinetic Monte Carlo algorithm and an extended Ising model, incorporating both conserved and non-conserved dynamics. The simulations show a dependence of the domain wall velocity on driving force which is very similar to that seen in 2-d and in qualitative agreement with experiment. That is, the presence of a low mobility regime at small driving force and an abrupt transition to a high mobility regime at larger forces, under some conditions, and a continuous, non-linear dependence of the velocity on the force in others. The main qualitative difference between the 2-d and 3-d simulation results is in how the domain wall roughness depends on driving force. The velocity-driving force relation is not consistent with classic continuum models, but may be described, in the high velocity regime, by a theory based upon a discrete version of these models.     

Domain Wall Migration in 3-d in the Presence of Diffusing Impurities

A new three-dimensional simulation procedure was developed for domain wall (grain boundary, APB, magnetic, etc.) migration in the presence of diffusing impurities. The simulation is based upon a kinetic Monte Carlo algorithm and an extended Ising model, incorporating both conserved and non-conserved dynamics. The simulations show a dependence of the domain wall velocity on driving force which is very similar to that seen in 2-d and in qualitative agreement with experiment. That is, the presence of a low mobility regime at small driving force and an abrupt transition to a high mobility regime at larger forces, under some conditions, and a continuous, non-linear dependence of the velocity on the force in others. The main qualitative difference between the 2-d and 3-d simulation results is in how the domain wall roughness depends on driving force. The velocity-driving force relation is not consistent with classic continuum models, but may be described, in the high velocity regime, by a theory based upon a discrete version of these models.     

Hydrodynamics of a rotating torus

The hydrodynamics of a torus is important on two counts: firstly, most stiff or semiflexible ring polymers, e.g. DNA miniplasmids are modeled as a torus and secondly, it has the simplest geometry which can describe self propelled organisms (particles). In the present work, the hydrodynamics of a torus rotating about its centerline is studied. Analytical expression for the velocity of a force free rotating torus is derived. It is found that a rotating torus translates with a velocity which is proportional to its internal velocity and to the square of the slenderness ratio, epsilon, similar to most low Reynolds number swimmers. The motion of a torus along a cylindrical track is studied numerically and it is observed that a force free torus changes its direction of motion (from a propelled state (weak wall effects) to a rolling state (strong wall effects)) as the diameter of the inner circular cylinder is increased. The rolling velocity is found to depend only on epsilon when the inner cylinder diameter approaches that of the torus.     

On the mechanoelectrical coupling in the cochlear outer hair cell

Outer hair cell electromotility, a manifestation of the interconnection between the mechanical and electrical processes occurring in outer hair cells, is believed to be an important contribution to the active cochlea. Two modes of mechanoelectrical coupling in the outer hair cell wall are studied: the potential shift caused by mechanical loading under the wall charge preservation conditions and the current (transferred charge) caused by mechanical loading under the voltage-clamp conditions. By using the previously reported elastic moduli of the wall and components of the active force, the potential shift under the charge preservation conditions is derived. This shift is expressed in terms of the wall strains and the active force derivatives with respect to the wall potential. The magnitudes of the potential shift corresponding to the conditions of cell inflation, axial stretch (compression), and the micropipet aspiration are estimated. In the last case, the distribution of the potential shift along the cell wall is also demonstrated. The potential shift can reach -20(-)-40 mV under the conditions of the micropipet aspiration or cell inflation. Such shift is much smaller under the condition of cell stretch (compression). The current and the charge transfer caused by the cell stretch under the voltage-clamp conditions is analyzed, and shows good agreement of predictions with experimental data.     

Outer hair cell active force generation in the cochlear environment

Outer hair cells are critical to the amplification and frequency selectivity of the mammalian ear acting via a fine mechanism called the cochlear amplifier, which is especially effective in the high-frequency region of the cochlea. How this mechanism works under physiological conditions and how these cells overcome the viscous (mechanical) and electrical (membrane) filtering has yet to be fully understood. Outer hair cells are electromotile, and they are strategically located in the cochlea to generate an active force amplifying basilar membrane vibration. To investigate the mechanism of this cell's active force production under physiological conditions, a model that takes into account the mechanical, electrical, and mechanoelectrical properties of the cell wall (membrane) and cochlear environment is proposed. It is shown that, despite the mechanical and electrical filtering, the cell is capable of generating a frequency-tuned force with a maximal value of about 40 pN. It is also found that the force per unit basilar membrane displacement stays essentially the same (40 pNnm) for the entire linear range of the basilar membrane responses, including sound pressure levels close to hearing threshold. Our findings can provide a better understanding of the outer hair cell's role in the cochlear amplifier.     

Electromagnetic force based on trapped mode of asymmetrical split ring

In this paper, a multi-layered structure based on coupled magnetic/electric resonators is presented. The multi-layered structure can generate a significant electromagnetic force in the terahertz band. The electromagnetic force is calculated by using Maxwell Stress Tensor. The asymmetrical split ring is utilized for field confinement and the multi-layered structure enhances the coupling in the dielectric layer and in the air gap. This leads to a high Q factor and large electromagnetic force. By taking the gravity and the area of the unit cell into consideration, we prove that this force is large enough (about three orders of magnitude higher than in the visible band) to manipulate the unit cell with a small incident power density (<50 nW/μm²).     

Analysis of axisymmetric shell structures under axisymmetric loading by the flexibility method

A method is developed for the static stress and deformation analysis of axisymmetric shells under axisymmetric loading by reduction of the shell to ring sections. In particular, the wall thickness of the shell may vary and the method is applicable to the analysis of shells with irregular meridional geometry. Explicit expressions for the influence coefficients for each ring element are derived. In the development of these expressions, exact evaluation of stresses in the circumferential direction of the ring is used. The distribution of stresses in the meridional direction of the ring element is assumed to be linear with each element. By using the derived influence coefficients, the unknown forces at the junctures of the ring elements are found by the standard flexibility method of indeterminate structural analysis. Subsequently, the displacements and internal stresses are determined. Example solutions for a flat circular plate under transverse loading and for a cylindrical shell under a boundary edge loading show excellent agreement with solutions found by solving the governing differential equations.     

Transport as a consequence of state-dependent diffusion

Overdamped particles subject to a drift in a force field with sinusoidal space dependence and also a sinusoidally modulated space-dependent diffusion, with the same period as the drift, experience a net driving force. The resulting current depends on the amplitude of the modulation of the diffusion and is a periodic function of the phase difference between the sinusoidal drift and the sinusoidal modulation of the diffusion. For small modulation amplitudes a particle subject to state-dependent noise behaves the same way as a particle subject to thermal noise but with a drift which, in addition to the sinusoidal term, contains a net force term [M. Büttiker,Z. Phys. B 68:161 (1987)]. A specific example of this behavior [N. G. van Kampen,IBM J. Res. Dev. 32:107 (1988); R. Landauer,J. Stat. Phys. 53:233 (1988).] is the motion of overdamped particles in a ring subject to a nonuniform temperature field. When the drift and the temperature, which are periodic with a period equal to the ring circumference, are not in phase a noise-induced circulating current results.This paper will appear in a forthcoming issue of theJournal of Statistical Physics.     

Motion of a red blood cell in interference field

The motion of a red blood cell suspended in blood plasma in a two-beam plane interference field was studied experimentally. A cw Argon Ion laser was used. A model is proposed to describe the observed motion. The model is based on a balance between the optical gradient force and the drag force, and yields the location of the cell as a function of time, starting from a stationary position at an arbitrary distance from a dark fringe until becoming trapped at the center of the closest bright fringe. It is suggested that the discrepancy between the predictions of the model and the observed motion is attributable to the influence of the wall close to which the cell flows.     

Stochastic elastohydrodynamics of a microcantilever oscillating near a wall

We consider the thermally driven motion of a microcantilever in a fluid environment near a wall, a configuration characteristic of the atomic force microscope. A theoretical model is presented which accounts for hydrodynamic interactions between the cantilever and wall over a wide range of frequencies and which exploits the fluctuation-dissipation theorem to capture the Brownian dynamics of the coupled fluid-cantilever system. Model predictions are tested against experimental thermal spectra for a cantilever in air and water. The model shows how, in a liquid environment, the effects of non-delta-correlated Brownian forcing appear in the power spectrum, particularly at low frequencies. The model also predicts accurately changes in the spectrum in liquid arising through hydrodynamic wall effects, which we show are strongly mediated by the angle at which the cantilever is tilted relative to the wall.     

Direct measurement of cell wall stress stiffening and turgor pressure in live bacterial cells

We study intact and bulging Escherichia coli cells using atomic force microscopy to separate the contributions of the cell wall and turgor pressure to the overall cell stiffness. We find strong evidence of power-law stress stiffening in the E. coli cell wall, with an exponent of 1.22±0.12, such that the wall is significantly stiffer in intact cells (E=23±8 MPa and 49±20 MPa in the axial and circumferential directions) than in unpressurized sacculi. These measurements also indicate that the turgor pressure in living cells E. coli is 29±3 kPa.     

New bosonization and conformal field theory over Z

New formulation of bosonization is given so that it is defined over the ring Z of integers. The charge zero sector of the new boson Fock space is the completion of the coordinate ring of the universal Witt scheme. By using new bosonization, conformal field theory of free fermions over Z is given.Dedicated to Professor M. Sato on his sixtieth birthdayPartially supported by Max-Planck-Institut für MathematikPartially supported by Max-Planck-Institut für Mathematik     

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.     

Study of CEPC performance with different collision energies and geometric layouts

The Circular Electron-Positron Collider(CEPC) is one of the largest projects planned for high energy physics in China.It would serve first as a Higgs factory and then upgrade to a hadron collider.In this paper we give the 50 km and 100 km design for both single ring and double ring schemes,including Z boson,W boson and Higgs boson,by using an optimized method.Also,we give the potential of CEPC running at the Z and W poles.We analyse the relationship of luminosity with circumference and filling factor,which gives a way to evaluate the choice of geometry,and compare the nominal performances of CEPC-SPPC,LHC and FCC.     

Intersoliton forces in the Wess–Zumino model

The spectrum of supersymmetric domain wall solitons of the Wess–Zumino model is known to be discontinuous across a curve (of marginal stability) in the moduli space of quartic superpotentials. Here we show how this phenomenon can be understood from the behaviour of the long-range inter-soliton force, which we compute by a method due to Manton.     

电子迥旋加热等离子体及热电子环特性的实验研究

在简单磁镜MM-2中,采用15GHZ大功率迴旋管进行了电子迴旋共振加热(ECRH)实验。结果表明,随充气压强的提高,预电离时间迅速变短。在高气压“C-模式”运行区,等离子体径向密度分布呈马鞍形。在迴旋管输出30kW功率的条件下,适于建立热电子环的气体压力窗为(0.4—1.2)×10^-5Torr。利用一个可移动Laugmuir探针配合反磁测量的简便方法,在中心场为2.95kG时,确定了电子环半径为7cm,环厚约4cm,环的轴向边界由z=±10cm一直延伸到z=±20cm。热电子温度为140—170keV,热电环平均β值为(4—5)％。观测到了由热电子环不稳定性引起的迸发式径向电子逃逸,并同时发生反磁信号跌落。