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1.
Using a contrast matching technique of small angle neutron scattering (SANS), we have investigated a phase separation to liquid-disordered
and liquid-ordered phases on ternary small unilamellar vesicles (SUVs) composed of deuterated-saturated, hydrogenated-unsaturated
phosphatidylcholine lipids and cholesterol, where the equilibrium size of these domains is constrained to less than 10nm by
the system size. Below a miscibility temperature, we observed characteristic scattering profiles with a maximum, indicating
the formation of nano-meter-sized domains on the SUVs. The observed profiles can be described by a multi-domain model rather
than a mono-domain model. The nano-meter-sized domain is agitated by thermal fluctuations and eventually ruptured, which may
result in the multi-domain state. The kinetically trapped nano-meter-sized domains grow to a mono-domain state by decreasing
temperature. Furthermore, between the miscibility and disorder-order transition temperature of saturated lipid, the integrated
SANS intensity increased slightly, indicating the formation of nano-meter-sized heterogeneity prior to the domain nucleation. 相似文献
2.
The role of the elastic properties of multicomponent lipid membranes during their phase separation has been studied. The phase
diagram of a three-component membrane, which consists of cholesterol and unsaturated lipids, has been derived. The calculation
has been performed using the theory of regular solutions, taking into account the contribution of the mechanical energy to
the parameters of pair interactions between the components. It has been shown that the difference in the spontaneous curvatures
of the components plays the major role in phase separation. The effective bending modulus has been calculated for the membrane
whose components have different bending rigidities. 相似文献
3.
Direct numerical simulation (DNS) of complex flows require solving the problem on parallel machines using high accuracy schemes. Compact schemes provide very high spectral resolution, while satisfying the physical dispersion relation numerically. However, as shown here, compact schemes also display bias in the direction of convection – often producing numerical instability near the inflow and severely damping the solution, always near the outflow. This does not allow its use for parallel computing using domain decomposition and solving the problem in parallel in different sub-domains. To avoid this, in all reported parallel computations with compact schemes the full domain is treated integrally, while using parallel Thomas algorithm (PTA) or parallel diagonal dominant (PDD) algorithm in different processors with resultant latencies and inefficiencies. For domain decomposition methods using compact scheme in each sub-domain independently, a new class of compact schemes is proposed and specific strategies are developed to remove remaining problems of parallel computing. This is calibrated here for parallel computing by solving one-dimensional wave equation by domain decomposition method. We also provide the error norm with respect to the wavelength of the propagated wave-packet. Next, the advantage of the new compact scheme, on a parallel framework, has been shown by solving three-dimensional unsteady Navier–Stokes equations for flow past a cone-cylinder configuration at a Mach number of 4.Additionally, a test case is conducted on the advection of a vortex for a subsonic case to provide an estimate for the error and parallel efficiency of the method using the proposed compact scheme in multiple processors. 相似文献
4.
This work demonstrates the feasibility of noninvasive studies of diffusion on a submicrometer length scale in aligned model lipid membranes using pulsed field gradient nuclear magnetic resonance with ultrahigh (up to 35 T/m) gradient strength. Application of such gradients allows the use of sufficiently small diffusion times under conditions of narrow-pulse approximation. As a result, monitoring anomalous or restricted diffusion in lipid membranes on a length scale in the range of 100 nm becomes possible. The ability to study diffusion in lipid membranes on this length scale is very important because it is comparable with the size of biologically relevant domains (i.e., rafts), which are believed to exist in biomembranes. 相似文献
5.
A. Ya. Khairullina T. V. Ol’shanskaya D. S. Filimonenko N. M. Kozlova Yu. M. Garmaza E. I. Slobozhanina 《Optics and Spectroscopy》2011,110(4):534-540
We studied changes in the surface of erythrocyte membranes exposed to the action of zinc sulfate in the concentration range
of 0.1–2.0 mM/l using methods of light scattering, spectrofluorimetry, and atomic force microscopy. Using the spectrofluorimetry
method, we revealed a dose-dependent increase in the fluorescence intensity of a fluorescamine probe incorporated into erythrocyte
membranes modified by zinc ions, which is indicative of an increase in the level of NH2 groups on the cell surface. Using atomic force microscopy, we revealed changes in the surface topography of erythrocyte membranes
exposed to the action of zinc sulfate in the concentration range of 0.1–2.0 mM/l. By performing a correlation analysis, we
revealed that the correlation length of the autocorrelation function of the erythrocyte surface irregularity profile directly
related to the fluorescence intensity of fluorescamine incorporated into erythrocyte membranes (r = 0.9, p < 0.05) modified by zinc ions. We showed that, in the zinc sulfate concentration range of 0.1–2.0 mM/l, zinc oxides form
in erythrocyte membranes, which is confirmed by the appearance of an absorption band at 330–340 nm and by an increase in the
light scattering. At more considerable concentrations, we identified absorption bands characteristic of zinc protein complexes
in erythrocyte membranes. A considerable decrease in the elongation of the scattering indicatrix of erythrocyte membranes
caused by luminescence correlates with the content of zinc proteins. Polarization measurements confirm the enhancement of
the aggregation of protein complexes observed by the atomic force microscopy method. The proposed complex approach can be
used in studies on the action of various abiotic factors on biological cells. 相似文献
6.
Transient circular pores can open in plasma membrane of cells due to mechanical stress, and failure to repair such pores lead to cell death. Similar pores in the form of defects also exist among smectic membranes, such as in myelin sheaths or mitochondrial membranes. The formation and growth of membrane defects are associated with diseases, for example multiple sclerosis. A deeper understanding of membrane pore dynamics can provide a more refined picture of membrane integrity-related disease development, and possibly also treatment options and strategies. Pore dynamics is also of great importance regarding healthcare applications such as drug delivery, gene or as recently been implied, cancer therapy. The dynamics of pores significantly differ in stacks which are confined in 2D compared to those in cells or vesicles. In this short review, we will summarize the dynamics of different types of pores that can be observed in biological membranes, which include circular transient, fusion and hemi-fusion pores. We will dedicate a section to floral and fractal pores which were discovered a few years ago and have highly peculiar characteristics. Finally, we will discuss the repair mechanisms of large area pores in conjunction with the current cell membrane repair hypotheses. 相似文献
7.
There is an increased interest in how lipids interact with each other, especially in the lateral separation of lipids into coexisting liquid phases as this is believed to be an attribute of raft formation in cell membranes. ToF-SIMS has shown itself to be an excellent tool for investigating cellular and model membrane systems and will be perhaps the most powerful one for investigating raft formation. Results from our laboratory show the capability of ToF-SIMS at identifying unequivocally the content of coexisting liquid lipid phases. Using supported lipid monolayers we find that the inclusion of dipalmitoylphosphatidylethanolamine (DPPE) to a homogeneous dipalmitoyl-phosphatidylcholine (DPPC)/cholesterol phase results in the formation of cholesterol-rich domains [A.G. Sostarecz, C.M. McQuaw, A.G. Ewing, N. Winograd, J. Am. Chem. Soc. 126 (2004) 13882]. Also, for DPPE/cholesterol systems a single homogeneous DPPE/cholesterol phase is formed at ∼50 mol% cholesterol, whereas DPPC/cholesterol systems form a single phase at 30 mol% cholesterol [C.M. McQuaw, A. Sostarecz, L. Zheng, A.G. Ewing, N. Winograd, Langmuir 21 (2005) 807]. Currently we are exploring the incorporation of sphingomyelin into phospholipid-cholesterol mixtures in an effort to gain a better understanding of its role in raft formation. 相似文献
8.
Warschawski DE Devaux PF 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,145(2):367-372
Polarization transfer is a key experiment for the detection of insensitive nuclei by NMR. Transfer in liquids is often achieved through J-coupling using the INEPT experiment, while in solids the dipolar coupling is used with cross polarization. Liquid crystals, including lipid membranes, are intermediate cases between solids and liquids. In the present article, we compare several transfer methods for lipid membranes spinning at the magic angle. It is shown that the most commonly used cross polarization technique is, in most cases, advantageously replaced by refocused INEPT or even by the NOE enhancement experiment, a method that is not normally used in that context. In principle, these enhancement techniques could be applied to other systems, including biological tissues and, more generally, soft matter systems that are neither solid nor liquid by NMR standards. 相似文献
9.
A novel scheme for image encryption of phase images is proposed, using fractional Hartley transform followed by Arnold transform and singular value decomposition in the frequency domain. Since the plaintext is a phase image, the mask used in the spatial domain is a random amplitude mask. The proposed scheme has been validated for grayscale images and is sensitive to the encryption parameters such as the order of the Arnold transform and the fractional orders of the Hartley transform. We have also evaluated the scheme's resistance to the well-known noise and occlusion attacks. 相似文献
10.
Adhesion between membranes is studied using a phenomenological model, where the inter-membrane distance is coupled to the
concentration of sticker molecules on the membranes. The model applies to both adhesion of two flexible membranes and to adhesion
of one flexible membrane onto a second membrane supported on a solid substrate. We mainly consider the case where the sticker
molecules form bridges and adhere directly to both membranes. The calculated mean-field phase diagrams show an upward shift
of the transition temperature indicating that the lateral phase separation in the membrane is enhanced due to the coupling effect. Hence the possibility of adhesion-induced lateral phase separation is predicted. For a particular
choice of the parameters, the model exhibits a tricritical behavior. We also discuss the non-monotonous shape of the inter-membrane
distance occurring when the lateral phase separation takes place. The inter-membrane distance relaxes to the bulk values with
two symmetric overshoots. Adhesion mediated by other types of stickers is also considered.
Received 12 January 2000 and Received in final form 15 May 2000 相似文献
11.
A fundamental attribute of raft formation in cell membranes is lateral separation of lipids into coexisting liquid phases. Using fluorescence microscopy, we observe spontaneous lateral separation in free-floating giant unilamellar vesicles. We record coexisting liquid domains over a range of composition and temperature significantly wider than previously reported. Furthermore, we establish correlations between miscibility in bilayers and in monolayers. For example, the same lipid mixtures that produce liquid domains in bilayer membranes produce two upper miscibility critical points in the phase diagrams of monolayers. 相似文献
12.
Adam Reichert Michael T. Heath Daniel J. Bodony 《Journal of computational physics》2012,231(16):5243-5265
Overlapping domain decomposition methods, otherwise known as overset grid or chimera methods, are useful for simplifying the discretization of partial differential equations in or around complex geometries. Though in wide use, such methods are prone to numerical instability unless numerical diffusion or some other form of regularization is used, especially for higher-order methods. To address this shortcoming, high-order, provably energy stable, overlapping domain decomposition methods are derived for hyperbolic initial boundary value problems. The overlap is treated by splitting the domain into pieces and using generalized summation-by-parts derivative operators and polynomial interpolation. New implicit and explicit operators are derived that do not require regularization for stability in the linear limit. Applications to linear and nonlinear problems in one and two dimensions are presented, where it is found the explicit operators are preferred to the implicit ones. 相似文献
13.
The dissipative dynamics of Gaussian squeezed states (GSS) and coherent superposition states (CSS) are analytically obtained and compared. Time scales for sustaining different quantum properties such as squeezing, negativity of the Wigner function or photon number distribution are calculated. Some of these characteristic times also depend on initial conditions. For example, in the particular case of squeezing, we find that while the squeezing of CSS is only visible for small enough values of the field intensity, in GSS it is independent of this quantity, which may be experimentally advantageous. The asymptotic dynamics however is quite similar as revealed by the time evolution of the fidelity between states of the two classes. 相似文献
14.
Determination of embedded layer properties using adaptive time-frequency domain analysis 总被引:2,自引:0,他引:2
A general model for determination of the complete set of acoustical and geometrical properties of an isotropic layer embedded between isotropic or anisotropic multilayered solids is developed. These properties include density, longitudinal and shear elastic moduli, layer thickness, and loss factors, simultaneously determined from two measurements, one at normal and one at oblique incidence. The inversion model is an extension of the method proposed by Lavrentyev and Rokhlin [J. Acoust. Soc. Am. 102, 3467 (1997)] which is applicable to thick substrates. In this new method, the inversion model mimics an experiment by using the same time-domain gating of the signal reflected from the embedded layer. This allows application of this method to layered solids when reflections from different layers overlap in the time domain. The sensitivity of the method, its stability against data scatter, and the effect of the oblique incident angle are evaluated. The effect of plane-wave approximation versus beam approximation in the inverse algorithm is discussed. Experimental results are given to demonstrate examples of adhesive layer property reconstruction. 相似文献
15.
Conventional oxazolidine spin-labelled lipids have the axial14N-hyperfine tensorz-axis directed along the long axis of the lipid chain. Investigation of lateral ordering of the lipids in membranes requires measurement of thex-y Zeeman anisotropy of the nonaxialg-tensor at high fields. Both the lateral and transverse ordering of the lipid chains in membranes of dimyristoyl phosphatidylcholine containing 40 mol% cholesterol in the liquid-ordered phase have been studied with 94 GHz electron paramagnetic resonance spectroscopy. This has been done by using probe amounts of phosphatidylcholine systematically spin-labelled at positionsn along the length of thesn- 2 chain [n-PCSL, 1-acyl-2-(n-(4,4-dimethyloxazolidine-N-oxyl) stearoyl)-sn-glycero-3-phosphocholine]. Nonaxial (gxx?gyy) anisotropy of the spin-labelled lipid chains is detected over a wide range of temperature throughout the liquid-ordered phase. The transverse profile of lateral ordering with position,n, of chain labelling follows the profile of the rigid steroid nucleus of cholesterol. It becomes progressively averaged towards the terminal methyl group of thesn- 2 chain, in the region of the flexible hydrocarbon chain of cholesterol. The nonaxial lipid ordering may be related to lipid domain formation in membranes containing cholesterol and saturated-chain lipids. 相似文献
16.
A study of voltage fluctuations in bilayer lipid membranes during electroporation and under current-clamp conditions is presented.
Qualitative considerations based on the electroporation theory are used in order to explain the phenomenon on long time scale.
Indeed, the current-clamp condition induces a feedback mechanism on the pore formation and therefore on the macroscopic conductance.
Voltage fluctuations can thus be recorded. These fluctuations are nonstationary long-living and have a flicker power spectrum
over nearly four decades of frequency between about 10-2 and 102Hz. The study of the fluctuations in the time domain has been performed by introducing an electrical model of the system formed
by the membrane and the circuit under current-clamp configuration. The analysis of the time series gives a characteristic
time of 100ms for the circuitry response to the fragments of electroporation signals with characteristic times faster than
100ms. During electroporation, the response to an external periodic stimulus in the frequency range 10-1-10Hz shows that the system behaves linearly, even if voltage fluctuations are present.
Received 1 June 1999 and Received in final form 1 October 1999 相似文献
17.
This paper presents a new non-overlapping domain decomposition method for the Helmholtz equation, whose effective convergence is quasi-optimal. These improved properties result from a combination of an appropriate choice of transmission conditions and a suitable approximation of the Dirichlet to Neumann operator. A convergence theorem of the algorithm is established and numerical results validating the new approach are presented in both two and three dimensions. 相似文献
18.
A simple model investigates the amplification of fluctuations on membranes constituted of two lipids having different lengths. Van der Waals and electrostatic interactions across the lipid bilayer result in a destabilization favoring thickness variations of the membrane. Close to spontaneous demixing of the two components, the additional gain in free energy due to thickness undulations shifts the stability boundary which promotes phase separation into domains. Interestingly, this effect can be induced by an applied electric field or membrane potential. In biological systems, the dynamic model presented here indicates that electric fields might be important for controlling phase separation and the formation of domains called rafts.Received: 26 March 2004, Published online: 15 July 2004PACS:
87.16.Dg Membranes, bilayers, and vesicles - 68.35.Rh Phase transitions and critical phenomena - 82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions) 相似文献
19.
A multiple-image encryption method is proposed that is based on row scanning compressive ghost imaging, (t, n) threshold secret sharing, and phase retrieval in the Fresnel domain. In the encryption process, after wavelet transform and Arnold transform of the target image, the ciphertext matrix can be first detected using a bucket detector. Based on a (t, n) threshold secret sharing algorithm, the measurement key used in the row scanning compressive ghost imaging can be decomposed and shared into two pairs of sub-keys, which are then reconstructed using two phase-only mask (POM) keys with fixed pixel values, placed in the input plane and transform plane 2 of the phase retrieval scheme, respectively; and the other POM key in the transform plane 1 can be generated and updated by the iterative encoding of each plaintext image. In each iteration, the target image acts as the input amplitude constraint in the input plane. During decryption, each plaintext image possessing all the correct keys can be successfully decrypted by measurement key regeneration, compression algorithm reconstruction, inverse wavelet transformation, and Fresnel transformation. Theoretical analysis and numerical simulations both verify the feasibility of the proposed method. 相似文献