Sharp Localization Research Articles

Simultaneous topography and recognition imaging: physical aspects and optimal imagingconditions

Simultaneous topography and recognition imaging (TREC) allows for the investigation ofreceptor distributions on natural biological surfaces under physiological conditions.Based on atomic force microscopy (AFM) in combination with a cantilever tipcarrying a ligand molecule, it enables us to sense topography and recognition ofreceptor molecules simultaneously with nanometre accuracy. In this study weintroduce optimized handling conditions and investigate the physical properties of thecantilever–tip–sample ensemble, which is essential for the interpretation of theexperimental data gained from this technique. In contrast to conventional AFMmethods, TREC is based on a more sophisticated feedback loop, which enablesus to discriminate topographical contributions from recognition events in theAFM cantilever motion. The features of this feedback loop were investigatedthrough a detailed analysis of the topography and recognition data obtained on amodel protein system. Single avidin molecules immobilized on a mica substratewere imaged with an AFM tip functionalized with a biotinylated IgG. A simpleprocedure for adjusting the optimal amplitude for TREC imaging is describedby exploiting the sharp localization of the TREC signal within a small range ofoscillation amplitudes. This procedure can also be used for proving the specificity ofthe detected receptor–ligand interactions. For understanding and eliminatingtopographical crosstalk in the recognition images we developed a simple theoretical model,which nicely explains its origin and its dependence on the excitation frequency.

Why photons cannot be sharply localized

Physicists have pondered over the problem of photon localization and the related problem of the photon wave function for almost 80 years now, beginning with the work of Landau and Peierls 1. An extensive review of the photon localization problem was recently presented by Keller 2. The problem of photon localization is closely related to the widely studied problem of the photon position operator. In this paper we introduce an operational definition of partial localization based on the measurements of correlation functions for electric or magnetic fields. For a want of better names, we shall use the terms electric localization and magnetic localization even though this might erroneously suggest the presence of some electric or magnetic devices that confine the photons. Since a sharp localization of photons according to our operational definition of localization is not possible, a photon position operator compatible with this definition does not exist. Earlier studies of the photon localization emphasized the mathematical aspects see, for example, 3‐5. In this paper we emphasize the physical properties of the electromagnetic field. In particular, we exhibit the role of the photon helicity and the symmetry between the electric and magnetic fields. We proceed in the footsteps of Glauber 6‐9 who was the first to recognize the significance of the space-dependent creation and annihilation operators. This approach was recently summarized and expanded in an extensive paper by Smith and Raymer 10. In our work we concentrate on the analysis of the photon localization in terms of the electric and magnetic field operators. We treat these fields after smearing over space-time regions as bona fide observables. We put emphasis on the field aspect that is complementary to the particle aspect. It might have a weaker connection with experiments usually based on photon counting as highlighted by Glauber, but it is more precise as was explained in detail by Bohr and Rosenfeld 11,12 The standard method of quantization of the free electromagnetic field based on the decomposition into monochromatic modes is not well suited for the discussion of localizability because the monochromatic mode functions are not localized. To overcome this problem we further developed an alternative method of quantization that does not require a mode decomposition. The essential mathematical tools in our analysis are the Riemann-Silberstein RS vector and the helicity operator. This formulation has some merits of its own, and it can also be used to study other general properties of

Analysis of non‐stationary electric signals using the S‐transform

PurposeThe purpose of this paper is to compare the accuracy of tracking the amplitude and frequency changes of non‐stationary electric signals.Design/methodology/approachShort‐time fourier transform (STFT) and S‐transform algorithms were applied to analyze non‐stationary signals originating from switching of capacitor banks in a power system.FindingsThe S‐transform showed possibilities of sharp localization of the basic component, and allowed improvement of tracking dynamism the transient components in comparison to STFT.Practical implicationsS‐transform is a better tool for the analysis of non‐stationary waveforms in power systems and its properties can be used for diagnostic and power quality applications.Originality/valueThe dynamic tracking of the changes in time and frequency of real‐like signals originating from a power system are investigated in this paper.

Existence and sharp localization in velocity of small-amplitude Boltzmann shocks

Using a weighted $H^s$-contraction mapping argument based on themacro-micro decomposition of Liu and Yu, we give an elementary proofof existence, with sharp rates of decay and distance from theChapman-Enskog approximation, of small-amplitude shock profiles ofthe Boltzmann equation with hard-sphere potential, recovering andslightly sharpening results obtained by Caflisch and Nicolaenkousing different techniques. A key technical point in both analysesis that the linearized collision operator $L$ is negative definiteon its range, not only in the standard square-root Maxwellianweighted norm for which it is self-adjoint, but also in norms withnearby weights. Exploring this issue further, we show that $L$ isnegative definite on its range in a much wider class of normsincluding norms with weights asymptotic nearly to a full Maxwellianrather than its square root. This yields sharp localization invelocity at near-Maxwellian rate, rather than the square-root rateobtained in previous analyses.

Compactification of Patterns by a Singular Convection or Stress

A wide variety of propagating disturbances in physical systems are described by equations whose solutions lack a sharp propagating front. We demonstrate that presence of particular nonlinearities may induce such fronts. To exemplify this idea, we study both dissipative u_{t}+ partial differential_{x}f(u)=u_{xx} and dispersive u_{t}+ partial differential_{x}f(u)+u_{xxx}=0 patterns, and show that a weakly singular convection f(u)=-u;{alpha}+u;{m}, 0<alpha<1<m, induces a sharp localization of fronts around the u=0 ground state. Notably, a sharp front also emerges in higher dimensional extensions: u_{t}+ partial differential_{x}[f(u)+nabla;{2}u]=0 or in wave phenomena of the Boussinesq type: Z_{tt}=nabla.[F_{*}(|nablaZ|)nablaZ]-nabla;{4}Z where F_{*}(sigma)=C;{2}sigma+f(sigma).

A Biologically Inspired Spiking Neural Network for Sound Source Lateralization

In this paper, a binaural sound source lateralization spiking neural network (NN) will be presented which is inspired by most recent neurophysiological studies on the role of certain nuclei in the superior olivary complex (SOC) and the inferior colliculus (IC). The binaural sound source lateralization neural network (BiSoLaNN) is a spiking NN based on neural mechanisms, utilizing complex neural models, and attempting to simulate certain parts of nuclei of the auditory system in detail. The BiSoLaNN utilizes both excitatory and inhibitory ipsilateral and contralateral influences arrayed in only one delay line originating in the contralateral side to achieve a sharp azimuthal localization. It will be shown that the proposed model can be used both for purposes of understanding the mechanisms of an NN of the auditory system and for sound source lateralization tasks in technical applications, e.g., its use with the Darmstadt robotic head (DRH).

Proper Perinuclear Localization of the TRIM-like Protein Myospryn Requires Its Binding Partner Desmin

Desmin, the muscle-specific intermediate filament protein, surrounds the Z disks and links the entire contractile apparatus to the sarcolemmal cytoskeleton, cytoplasmic organelles, and the nucleus. In an attempt to explore the molecular mechanisms of these associations, we performed a yeast two-hybrid screening of a cardiac cDNA library. We showed that the desmin amino-terminal domain (N-(1-103)) binds to a 413-kDa TRIM-like protein, myospryn, originally identified as the muscle-specific partner of dysbindin, a component of the biogenesis of lysosome-related organelles complex 1 (BLOC-1). Binding of desmin with myospryn was confirmed with glutathione S-transferase pulldown assays and coimmunoprecipitation experiments. Western blot analysis revealed that the complex immunoprecipitated by desmin antibodies, in addition to myospryn, contained the BLOC-1 components dysbindin and pallidin. Deletion analysis revealed that only the (N-(1-103)) fragment of desmin binds to myospryn carboxyl terminus and that this association takes place through the 24-amino acid-long carboxyl-terminal end of the SPRY domain of myospryn. Using an antibody against the COOH terminus of myospryn, we demonstrated that myospryn colocalizes with desmin at the periphery of the nucleus, in close proximity to the endoplasmic reticulum, of mouse neonatal cardiomyocytes. In adult heart muscle, the two proteins colocalize, predominantly at intercalated disks and costameres. We also showed that myospryn colocalizes with lysosomes. Using desmin null hearts, we determined that desmin is required for both the proper perinuclear localization of myospryn, as well as the proper positioning of lysosomes, thus suggesting a potential role of desmin intermediate filaments in lysosomes and lysosome-related organelle biogenesis and/or positioning.

Multitaper Time-Frequency Reassignment for Nonstationary Spectrum Estimation and Chirp Enhancement

A method is proposed for obtaining time-frequency distributions of chirp signals embedded in nonstationary noise, with the two-fold objective of a sharp localization for the chirp components and a reduced level of statistical fluctuations for the noise. The technique consists in combining time-frequency reassignment with multitapering, and two variations are proposed. The first one, primarily aimed at nonstationary spectrum estimation, is based on sums of estimates with different tapers, whereas the second one makes use of differences between the same estimates for the sake of chirp enhancement. The principle of the technique is outlined, its implementation based on Hermite functions is justified and discussed, and some examples are provided for supporting the efficiency of the approach, both qualitatively and quantitatively

Dynamics of films and droplets spreading on porous substrates

This paper numerically investigates spreading and sorption of films and droplets on an unsaturated porous substrate, a mechanism taking place in paper coating and ink jet printing. The dynamics of the fluid on the substrate surface are described by lubrication approximation. Fluid flow within the porous substrate, caused by the droplet penetrating into it, is treated with the Richards’ equation, which models unsaturated flow in porous media and describes fluid transport in the porous layer after complete absorption of the film or droplet. Numerical results for sorption of an axisymmetric droplet into a substrate of finite thickness show that a sharp localization of the penetrating fluid, as required for fine printing resolution, can be achieved by a steep capillary sorption curve. The interaction of the fluid with the impermeable bottom of the layer may drastically delay droplet absorption and thus require matching layer thickness and droplet volume to avoid limiting printing process speed.

Polycomb Complexes and the Propagation of the Methylation Mark at the Drosophila Ubx Gene

Polycomb group proteins are transcriptional repressors that control many developmental genes. The Polycomb group protein Enhancer of Zeste has been shown in vitro to methylate specifically lysine 27 and lysine 9 of histone H3 but the role of this modification in Polycomb silencing is unknown. We show that H3 trimethylated at lysine 27 is found on the entire Ubx gene silenced by Polycomb. However, Enhancer of Zeste and other Polycomb group proteins stay primarily localized at their response elements, which appear to be the least methylated parts of the silenced gene. Our results suggest that, contrary to the prevailing view, the Polycomb group proteins and methyltransferase complexes are recruited to the Polycomb response elements independently of histone methylation and then loop over to scan the entire region, methylating all accessible nucleosomes. We propose that the Polycomb chromodomain is required for the looping mechanism that spreads methylation over a broad domain, which in turn is required for the stability of the Polycomb group protein complex. Both the spread of methylation from the Polycomb response elements, and the silencing effect can be blocked by the gypsy insulator.

Junctional and extrajunctional acetylcholinesterase in skeletal muscle fibers

The asymmetric A 12 acetylcholinesterase (AChE) molecular form, consisting of three tetrameric catalytic oligomers and three non-catalytic subunits of collagen Q (ColQ), is the functional AChE form in the neuromuscular junction. Its extremely high concentration and sharp localization in the junction is mostly due to the binding of this AChE form to perlecan in the synaptic basal lamina. In the rat neuromuscular junctions, about two-thirds of AChE molecules appear to be bound by ionic interactions involving calcium and the rest is probably bound covalently. In immature rat muscles, the A 12 AChE forms are expressed also extrajunctionally. During the early post-natal period, this expression is completely suppressed in rat fast muscles, whereas it extends into adulthood in the slow soleus muscles because of the differences in the extrajunctional expression of ColQ between fast and slow muscles. The level of the A 12 molecular forms of AChE in the extrajunctional muscle regions is regulated by the motor nerve, probably via the pattern of muscle fibre activations triggered by the nerve. The pattern of muscle activations also regulates the extrajunctional expression of the catalytic subunits of AChE: phasic, infrequent, high frequency activations enhance expression, whereas prolonged tonic low-frequency activations tend to decrease it. Calcineurin signalling pathway seems to be involved.

Poroelastic damage rheology: Dilation, compaction, and failure of rocks

We present three‐dimensional numerical simulations for the behavior of porous rocks under loading based on the theoretical formulation recently developed by Y. Hamiel et al. This theoretical formulation combines the classic Biot poroelastic theory with a damage rheology model. The numerical simulations of triaxial compression tests reproduce the gradual transition from localized brittle failure to distributed cataclastic flow with increasing pressure at high‐porosity rocks. Under relatively low confining pressures (approximately lower than 100 MPa for Berea sandstone samples), porous rocks fail in a brittle mode with sharp localization of damage in a narrow deformation zone and dilatancy preceding the total failure. At these pressures the yield stress increases with confining pressure (positive slope for yield curve). In simulations with higher confining pressures, instead of dilatancy, the deformation zone has a reduced porosity due to compaction. The porosity reduction plays an essential role in strengthening the deformation zone, and therefore continuous loading of the sample leads to the progressive development of a wide deformation zone. Under relatively high confining pressures (approximately higher than 300 MPa for Berea sandstone samples), damage is nonlocalized, and the macroscopic deformation of the model corresponds to experimentally observed cataclastic flow. At these pressures the yield stress decreases with confining pressure (negative slope for yield curve). We found good agreement between the measured and calculated yield curve for Berea sandstone.

The mesoscopic chiral metal-insulator transition

Sharp localization transitions of chiral edge states in disordered quantum wires subject to a strong magnetic field are shown to be driven by crossovers from two-to one-dimensional localization of bulk states. As a result, the two-terminal conductance is found to exhibit discontinuous transitions at zero temperature between exactly integer plateau values and zero, reminiscent of first-order phase transitions. We discuss the corresponding phase diagram. The spin of the electrons is shown to result in a multitude of phases when the spin degeneracy is raised by the Zeeman energy. The width of conductance plateaus is found to depend sensitively on the spin flip rate 1/τs.

A sharp existence and localization theorem for a Neumann problem

We shall present a new version of a recently appeared theorem for the existence and localization of solutions of the Neumann problem associated to the equation $ -u^{\prime\prime} + u = \beta(t)g(u) $ , based on a general variational principle by Ricceri. Our study will be especially aimed to express a certain hypothesis regarding the function g in its sharpest form, and a ‘limit case’ is enquired by an approximation

Novel Mechanism of PTEN Regulation by Its Phosphatidylinositol 4,5-Bisphosphate Binding Motif Is Critical for Chemotaxis

In chemotaxing cells, localization of phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3) to the leading edge of the cell sets the direction and regulates the formation of pseudopods at the anterior. We show that the lipid phosphatase activity of PTEN mediates chemotaxis and that the sharp localization of PI(3,4,5)P3 requires localization of PTEN to the rear of the cell. Our data suggest that a phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) binding motif at the N terminus of PTEN serves the dual role of localizing the enzyme to the membrane and regulating its activity. Mutations in this motif enhance catalytic activity but render the enzyme inactive in vivo by preventing membrane association. The key role of this motif may explain the heretofore puzzling tumor-suppressing mutations occurring within the PI(4,5)P2 binding motif. On the other hand, the localization of PTEN does not depend on its phosphatase activity, the actin cytoskeleton, or the intracellular level of PI(3,4,5)P3, suggesting that events controlling localization are upstream of phosphoinositide signaling.

No benefit from microcrystalline silicon N layers in single junction amorphous silicon p-i-n solar cells

The use of phosphorous-doped microcrystalline silicon (μc-Si:H) as the n-type electrode in single junction hydrogenated amorphous silicon solar cells has been studied both experimentally and through computer modeling. The aim is to understand why, in spite of a considerable decrease in the activation energy of the n layer—from 0.2 eV in n-a-Si:H to 0.03 eV in n-μc-Si:H—the open-circuit voltage of solar cells fabricated using these two types of n layer remains almost unchanged. Experimental determination of the work function of n-μc-Si:H and n-a-Si:H by the “flatband heterojunction” technique, has revealed that n-μc-Si:H has a higher electron affinity. Thus, in spite of the fact that the difference in activation energy is 0.17 eV, the difference in built-in potential between the two types of cells reduces to about half. Moreover, modeling of the output characteristics of solar cells, having these two types of N layer, indicates a sharp localization of the field at the N/I interface for the cell with a μc-Si:H N layer. As a consequence, the field in the bulk of the intrinsic layer and, hence, the open-circuit voltage for the two types of cell, remain unchanged.

Chaos and exponentially localized eigenstates in smooth Hamiltonian systems

We present numerical evidence to show that the wave functions of smooth classically chaotic Hamiltonian systems scarred by certain simple periodic orbits are exponentially localized in the space of unperturbed basis states. The degree of localization, as measured by the information entropy, is shown to be correlated with the local phase-space structure around the scarring orbit. Sharp localization is observed when the orbit scarring the wave function undergoes a pitchfork bifurcation and loses stability.

Pump-probe anisotropies of Fenna-Matthews-Olson protein trimers from Chlorobium tepidum: a diagnostic for exciton localization?

Exciton calculations on symmetric and asymmetric Fenna-Matthews-Olson (FMO) trimers, combined with absorption difference anisotropy measurements on FMO trimers from the green bacterium Chlorobium tepidum, suggest that real samples exhibit sufficient diagonal energy disorder so that their laser-excited exciton states are noticeably localized. Our observed anisotropies are clearly inconsistent with 21-pigment exciton simulations based on a threefold-symmetric FMO protein. They are more consistent with a 7-pigment model that assumes that the laser-prepared states are localized within a subunit of the trimer. Differential diagonal energy shifts of 50 cm(-1) between symmetry-related pigments in different subunits are large enough to cause sharp localization in the stationary states; these shifts are commensurate with the approximately 95 cm(-1) inhomogeneous linewidth of the lowest exciton levels. Experimental anisotropies (and by implication steady-state linear and circular dichroism) likely arise from statistical averaging over states with widely contrasting values of these observables, in consequence of their sensitivity to diagonal energy disorder.

A variational formulation-based edge focussing algorithm

Many edge detection techniques exhibit scale-dependent distortion of edges. We develop two ideas, which may also be of independent interest, to produce sharp edge localization at all scales. The first is approximation of the functional associated with the variational formulation via epi-convergence, replacing the edge set with a function. We provide a fast algorithm for minimizing the approximate functional. The second is to scale parameters and data to focus the edges. The resulting edge detector is a singular perturbation of a coupled pair of partial differential equations, yielding an elegant structure, suitable for digital or analog parallel implementation on mesh-connected arrays.

Gravity wave characteristics in the middle atmosphere derived from the Empirical Mode Decomposition method

The recently developed Empirical Mode Decomposition (EMD) method is applied to analyzing gravity wave characteristics in the middle atmosphere. By establishing a close connection between the fundamental Intrinsic Mode Functions (IMFs) derived from the EMD method and WKB solutions of a dispersive‐dissipative wave equation, we show that the EMD method can provide useful insights into physical processes in the middle atmosphere where dispersive‐dissipative wave phenomena are dominant. A local power spectrum function P is introduced which provides a quantitative description of the spectrum at any particular location within a data series. The sharp localization of P in space and wavenumber leads to an identification of unphysical small scale oscillations by falling spheres embedded in the wind profiles above 60 km. Further analyses of the horizontal wind profiles derived from the Dynamics Adapted Network for the Atmosphere (DYANA) campaign suggest that for horizontal wind fluctuations with vertical wavenumber m≤3 km−1 (or vertical wavelength Lz≥2 km) the previously observed m−3 Fourier spectra could be produced by a linear wave packet whose characteristic vertical wavenumber decreases with altitude. For small vertical scale disturbances with m&gt;3 km−1 (Lz&lt;2 km) a near −3 slope in the marginal distribution exists locally in the middle atmosphere with a great degree of universality, suggesting that nonlinear energy cascade processes may dominate the spectral formation in this wavenumber range.