Point Interactions Research Articles

Polypyrimidine tract binding protein inhibits IgM pre-mRNA splicing by diverting U2 snRNA base-pairing away from the branch point

The mouse immunoglobulin (IgM) pre-mRNA contains a splicing inhibitor that bears multiple binding sites for the splicing repressor polypyrimidine tract binding protein (PTB). Here we show that the inhibitor directs assembly of an ATP-dependent complex that contains PTB and U1 and U2 small nuclear RNAs (snRNAs). Unexpectedly, although U2 snRNA is present in the inhibitor complex, it is not base-paired to the branch point. We present evidence that inhibitor-bound PTB contacts U2 snRNA to promote base-pairing to an adjacent branch point-like sequence within the inhibitor, thereby preventing the U2 snRNA-branch point interaction and resulting in splicing repression. Our studies reveal a novel mechanism by which PTB represses splicing.

Ultra High Voltage Electron Microscopy Study of {113}-Defect Generation in Si Nanowires

ABSTRACTResults are presented of a study of {113}-defect formation in Si nanowires with diameters ranging from 50 to 500 nm. The Si nanowires, used for the processing of tunnel-FET's, are etched into a moderately doped epitaxial Si layer on a heavily doped n-type Si substrate. {113}- defects are created in situ by 2 MeV e-irradiation at temperatures between room temperature and 375 °C in an ultra high voltage electron microscope. The observations are discussed in the frame of intrinsic point defect out-diffusion and interaction with dopant atoms.

On Two-Ridge Structure in Two-Particle Azimuthal Correlations in Proton-Lead Collisions at Large Hadron Collider Energy

Two-particle azimuthal correlations are studied in the framework of a multisource thermal model. Each source is assumed to produce many particles. Each particle pair measured in final state is considered to be produced at two emission points (subsources) in a single or two sources. The first emission point corresponds to the production of “trigger” particle and the second one corresponds to that of “associated” particle. There are oscillations and other interactions between the two emission points. In the rest frame of the “associated” particle's emission point, the oscillations and other interactions cause the momentum of the “trigger” particle to depart from the original value. The modelling results are in agreement with the experimental data of proton-lead (p-Pb) collisions atsNN= 5.02 TeV, one of the Large Hadron Collider energies, measured by the ALICE and ATLAS Collaborations.

The Cayley transform applied to non-interacting quantum transport

We extend the Landauer–Büttiker formalism in order to accommodate both unitary and self-adjoint operators which are not bounded from below. We also prove that the pure point and singular continuous subspaces of the decoupled Hamiltonian do not contribute to the steady current. One of the physical applications is a stationary charge current formula for a system with four pseudo-relativistic semi-infinite leads and with an inner sample which is described by a Schrödinger operator defined on a bounded interval with dissipative boundary conditions. Another application is a current formula for electrons described by a one dimensional Dirac operator; here the system consists of two semi-infinite leads coupled through a point interaction at zero.

The Infinite Square Well with a Point Interaction: A Discussion on the Different Parameterizations

The construction of Dirac delta type potentials has been achieved with the use of the theory of self adjoint extensions of non-self adjoint formally Hermitian (symmetric) operators. The application of this formalism to investigate the possible self adjoint extensions of the one dimensional kinematic operator $K=-d^2/dx^2$ on the infinite square well potential is quite illustrative and has been given elsewhere. This requires the definition and use of four independent real parameters, which relate the boundary values of the wave functions at the walls. By means of a different approach, that fixes matching conditions at the origin for the wave functions, it is possible to define a perturbation of the type $a\delta(x)+b\delta'(x)$, thus depending on two parameters, on the infinite square well. The objective of this paper is to investigate whether these two approaches are compatible in the sense that perturbations like $a\delta(x)+b\delta'(x)$ can be fixed and determined using the first approach.

CPphase from twisted Higgs vacuum expectation value in extra dimension

We propose a new mechanism for generating a CP phase via Higgs a vacuum expectation value originating from geometry of an extra dimension. A twisted boundary condition is the key to produce an extra-dimension coordinate-dependent vacuum expectation value, which contains a CP phase degree of freedom and can be a new source of a CP phase in higher-dimensional gauge theories. As an illustrative example, we apply our mechanism to a five-dimensional gauge theory with point interactions and show that our mechanism can dynamically produce a nontrivial CP-violating phase with electroweak symmetry breaking, even though the five-dimensional model does not include any CP-violating phases of Yukawa couplings in the five-dimensional Lagrangian because of a single generation of five-dimensional fermions. We apply our mechanism to a model with point interactions, which has no source of CP-violating phases in the couplings of the higher-dimensional action, and show that a nontrivial CP phase dynamically appears.

Gender difference in emotion regulation: a resting EEG study

Objective Frontal resting EEG asymmetry was used to evaluate the gender effect of emotion regulation. Methods The resting EEG was recorded in 30 healthy volunteers (19-26 years old) by the guide 40 amplifier, and off-line analysis on EEG data were conducted by scan4.3 software.The statistical analysis were performed using SPSS 17.0. Results In normal human, frontal resting EEG alpha power was statistically significant(F=4.918, P=0.035). Asymmetry and gender interaction group (F=0.668, P=0.421), electrode point and gender interaction group (F=0.283, P=0.756), electrode point and asymmetry interaction group (F=1.418, P=0.260), electrode point, asymmetry and gender interaction group (F=1.164, P=0.327) had no statistical significance(P>0.05). The comparison of male and female asymmetry degree of each electrode point (F4/F3 group t=0.465, F8/F7 group t=0.809, FP2/FP1 group t=1.542) had no statistical significance (P>0.05). Conclusion Normal human brain hemispheres exist asymmetry. The asymmetry does not exists gender effect. In non-task state, frontal resting EEG alpha power asymmetry can not be recognized as the indicator of emotion regulation ability. Key words: Emotion regulation; Resting EEG; Asymmetry; Gender

A comparison of reduced coordinate sets for describing protein structure

In all-atom molecular simulation studies of proteins, each atom in the protein is represented by a point mass and interactions are defined in terms of the atomic positions. In recent years, various simplified approaches have been proposed. These approaches aim to improve computational efficiency and to provide a better physical insight. The simplified models can differ widely in their description of the geometry and the interactions inside the protein. This study explores the most fundamental choice in the simplified protein models: the choice of a coordinate set defining the protein structure. A simplified model can use fewer point masses than the all-atom model and/or eliminate some of the internal coordinates of the molecule by setting them to an average or ideal value. We look at the implications of such choices for the overall protein structure. We find that care must be taken for angular coordinates, where even very small variations can lead to significant changes in the positions of far away atoms. In particular, we show that the φ/ψ torsion angles are not a sufficient coordinate set, whereas another coordinate set with two degrees of freedom per residue, virtual Cα backbone bond, and torsion angles performs satisfactorily.

Effects of Target Expansion on Selection Performance in Older Computer Users

Point and click interactions using a mouse are an integral part of computer use for current desktop systems. Compared with younger users though, older adults experience greater difficulties performing cursor positioning tasks, and this can present limitations to using a computer easily and effectively. Target expansion is a technique for improving pointing performance where the target grows dynamically as the cursor approaches. This has the advantage that targets conserve screen real estate in their unexpanded state, yet can still provide the benefits of a larger area to click on. This article presents two studies of target expansion with older and younger participants, involving multidirectional point-select tasks with a computer mouse. Study 1 compares static versus expanding targets, and Study 2 compares static targets with three alternative techniques for expansion. Results show that expansion can improve times by up to 14%, and reduce error rates by up to 50%. Additionally, expanding targets are beneficial even when the expansion happens late in the movement, that is, after the cursor has reached the expanded target area or even after it has reached the original target area. The participants’ subjective feedback on the target expansion are generally favorable, and this lends further support for the technique.

Unstable quantum oscillator with point interactions: Maverick resonances, antibound states and other surprises

Abstract In the search for solvable or quasi-solvable models for resonances, we consider a one-dimensional potential, which is a harmonic oscillator for x 0 , has a point potential at the origin of the form a δ ( x ) + b δ ′ ( x ) and no interaction for x > 0 . After a study of this model, we add a mass jump at the origin and study the effect of the combination of the mass jump and the point potential. We obtain the behavior of resonances, bound and antibound states in terms of given parameters. In spite of the simplicity of the model, it shows quite interesting and unexpected features.

Stochastic Search of Molecular Cluster Interaction Energy Surfaces with Coupled Cluster Quality Prediction. The Phenylacetylene Dimer.

We report a stochastic search methodology on the basis of dispersion-augmented density functional theory (DFT), aimed at finding low energy isomers of the phenylacetylene dimer as well as methane and benzene dimers. Stochastic search of the molecular cluster interaction energy surfaces was carried out with the computationally inexpensive dispersion-augmented, third-order self-consistent charge density functional tight-binding (DFTB3-D) method, and energetically low-lying molecular cluster geometries were identified, including several that had previously been optimized at the MP2/cc-pVTZ level of theory and had single point interaction energies evaluated at the coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) level of theory in the complete basis set limit (Maity, S. et al. Phys. Chem. Chem. Phys 2011, 13, 16706). In addition, the search procedure identifies several additional low-energy isomers that map a reaction path, rotating one monomer through a full 360° relative to the first. We found that binding energies from long-range corrected functional combined with the local response dispersion correction (LC-BOP+LRD) yields binding energies that are within 1 kJ mol(-1) of the CCSD(T)/CBS results for both π-stacked and CH···π structures. In contrast, other functionals and second-order Møller-Plesset perturbation methods favored one binding motif or the other and therefore are not ideal to describe a global potential energy surface.

Continuum Schrödinger Operators Associated With Aperiodic Subshifts

We study Schrödinger operators on the real line whose potentials are generated by an underlying ergodic subshift over a finite alphabet and a rule that replaces symbols by compactly supported potential pieces. We first develop the standard theory that shows that the spectrum and the spectral type are almost surely constant and that identifies the almost sure absolutely continuous spectrum with the essential closure of the set of energies with vanishing Lyapunov exponent. Using results of Damanik–Lenz and Klassert–Lenz–Stollmann, we also show that the spectrum is a Cantor set of zero Lebesgue measure if the subshift satisfies the Boshernitzan condition and the potentials are aperiodic and irreducible. We then study the case of the Fibonacci subshift in detail and prove results for the local Hausdorff dimension of the spectrum at a given energy in terms of the value of the associated Fricke–Vogt invariant. These results are elucidated for some simple choices of the local potential pieces, such as piecewise constant ones and local point interactions. In the latter special case, our results explain the occurrence of so-called pseudo bands, which have been pointed out in the physics literature.

Supersymmetric descendants of self-adjointly extended quantum mechanical Hamiltonians

We consider the descendants of self-adjointly extended Hamiltonians in supersymmetric quantum mechanics on a half-line, on an interval, and on a punctured line or interval. While there is a 4-parameter family of self-adjointly extended Hamiltonians on a punctured line, only a 3-parameter sub-family has supersymmetric descendants that are themselves self-adjoint. We also address the self-adjointness of an operator related to the supercharge, and point out that only a sub-class of its most general self-adjoint extensions is physical. Besides a general characterization of self-adjoint extensions and their supersymmetric descendants, we explicitly consider concrete examples, including a particle in a box with general boundary conditions, with and without an additional point interaction. We also discuss bulk-boundary resonances and their manifestation in the supersymmetric descendant.

Acute Consumption of Walnuts and Walnut Components Differentially Affect Postprandial Lipemia, Endothelial Function, Oxidative Stress, and Cholesterol Efflux in Humans with Mild Hypercholesterolemia

Walnut consumption improves cardiovascular disease risk; however, to our knowledge, the contribution of individual walnut components has not been assessed. This study evaluated the acute consumption of whole walnuts (85 g), separated nut skins (5.6 g), de-fatted nutmeat (34 g), and nut oil (51 g) on postprandial lipemia, endothelial function, and oxidative stress. Cholesterol efflux (ex vivo) was assessed in the whole walnut treatment only. A randomized, 4-period, crossover trial was conducted in healthy overweight and obese adults (n = 15) with moderate hypercholesterolemia. There was a treatment × time point interaction for triglycerides (P < 0.01) and increased postprandial concentrations were observed for the oil and whole walnut treatments (P < 0.01). Walnut skins decreased the reactive hyperemia index (RHI) compared with baseline (P = 0.02) such that a difference persisted between the skin and oil treatments (P = 0.01). The Framingham RHI was maintained with the oil treatment compared with the skins and whole nut (P < 0.05). There was a treatment effect for the ferric reducing antioxidant potential (FRAP) (P < 0.01), and mean FRAP was greater with the oil and skin treatments compared with the nutmeat (P < 0.01). Cholesterol efflux increased by 3.3% following whole walnut consumption in J774 cells cultured with postprandial serum compared with fasting baseline (P = 0.02). Walnut oil favorably affected endothelial function and whole walnuts increased cholesterol efflux. These 2 novel mechanisms may explain in part the cardiovascular benefits of walnuts.

On the many Dirichlet Laplacians on a non-convex polygon and their approximations by point interactions

By Birman and Skvortsov it is known that if Ω is a planar curvilinear polygon with n non-convex corners then the Laplace operator with domain H2(Ω)∩H01(Ω) is a closed symmetric operator with deficiency indices (n,n). Here we provide a Kreĭn-type resolvent formula for any self-adjoint extensions of such an operator, i.e. for the set of self-adjoint non-Friedrichs Dirichlet Laplacians on Ω, and show that any element in this set is the norm resolvent limit of a suitable sequence of Friedrichs–Dirichlet Laplacians with n point interactions.

Binding properties of the (2+1)-fermion system with zero-range interspecies interaction

We study analytically and numerically the binding properties, in particular the ground state, of the so-called $(2+1)$-fermion system, which is a three-dimensional system of two identical fermions interacting with a third particle of different species through a zero-range interaction. We model the system with a specific self-adjoint point interaction Hamiltonian recently constructed in the mathematical literature. First we characterize the internal symmetry of the bound states in the attractive case. Then we show that the system confines in a precise regime of masses and that its ground-state energy stays finite as the mass becomes close to the critical point of the collapse of the system.

Spherical Schrödinger operators with δ-type interactions

We investigate spectral properties of spherical Schrödinger operators (also known as Bessel operators) with δ-point interactions concentrated on a discrete set. We obtain necessary and sufficient conditions for these Hamiltonians to be self-adjoint, lower-semibounded and also we investigate their spectra. We also extend the classical Bargmann estimate to such Hamiltonians. In certain cases we express the number of negative eigenvalues explicitly by means of point interactions and the corresponding intensities. We apply our results to Schrödinger operators in \documentclass[12pt]{minimal}\begin{document}$L^2(\mathbb {R}^n)$\end{document}L2(Rn) with a singular interaction supported by an infinite family of concentric spheres.

Environmental drivers and spatial dependency in wildfire ignition patterns of northwestern Patagonia

Fire management requires an understanding of the spatial characteristics of fire ignition patterns and how anthropogenic and natural factors influence ignition patterns across space. In this study we take advantage of a recent fire ignition database (855 points) to conduct a comprehensive analysis of the spatial pattern of fire ignitions in the western area of Neuquén province (57,649 km2), Argentina, for the 1992–2008 period. The objectives of our study were to better understand the spatial pattern and the environmental drivers of the fire ignitions, with the ultimate aim of supporting fire management. We conducted our analyses on three different levels: statistical “habitat” modelling of fire ignition (natural, anthropogenic, and all causes) based on an information theoretic approach to test several competing hypotheses on environmental drivers (i.e. topographic, climatic, anthropogenic, land cover, and their combinations); spatial point pattern analysis to quantify additional spatial autocorrelation in the ignition patterns; and quantification of potential spatial associations between fires of different causes relative to towns using a novel implementation of the independence null model. Anthropogenic fire ignitions were best predicted by the most complex habitat model including all groups of variables, whereas natural ignitions were best predicted by topographic, climatic and land-cover variables. The spatial pattern of all ignitions showed considerable clustering at intermediate distances (<40 km) not captured by the probability of fire ignitions predicted by the habitat model. There was a strong (linear) and highly significant increase in the density of fire ignitions with decreasing distance to towns (<5 km), but fire ignitions of natural and anthropogenic causes were statistically independent. A two-dimensional habitat model that quantifies differences between ignition probabilities of natural and anthropogenic causes allows fire managers to delineate target areas for consideration of major preventive treatments, strategic placement of fuel treatments, and forecasting of fire ignition. The techniques presented here can be widely applied to situations where a spatial point pattern is jointly influenced by extrinsic environmental factors and intrinsic point interactions.

Spectral Theory of Semibounded Schrödinger Operators with δ′-Interactions

We study spectral properties of Hamiltonians $\rH_{X,\gB,q}$ with $\delta'$-point interactions on a discrete set $X={x_k}_{k=1}^\infty\subset\R_+$. %at the centers $x_n$ on the positive half line in terms of energy forms. Using the form approach, we establish analogs of some classical results on operators $\rH_q=-d^2/dx^2+q$ with locally integrable potentials $q\in L^1_{\loc}(\R_+)$. In particular, we establish analogues of the Glazman-Povzner-Wienholtz theorem, the Molchanov discreteness criterion, and the Birman theorem on stability of an essential spectrum. It turns out that in contrast to the case of Hamiltonians with $\delta$-interactions, spectral properties of operators $\rH_{X,\gB,q}$ are closely connected with those of $\rH_{X,q}^N=\oplus_{k}\rH_{q,k}^N$, where $\rH_{q,k}^N$ is the Neumann realization of $-d^2/dx^2+q$ in $L^2(x_{k-1},x_k)$.

The effect of rock decompaction on the interaction of movement zones in underground mining

An increased interest in scientific applications for underground mining, mainly to extend the productive life of open pit mines such as Chuquicamata in Chile, has motivated a growing effort to model experimental and theoretically phenomena found in these mines as well as the processes involved in their operation. There is a general consensus that contamination as a result of dilution, a critical problem found in the operation of underground mines, might be reduced by an adequate design of draw point grids and the appropriate handling of them. This requires understanding of the flow of rock fragments and the evolution of the movement zone created by the interaction of multiple draw points. In this paper, we present a theoretical study focused on determining the movement zone created by the interaction of two neighboring draw points operating in alternate mode that simulate those found in a sub-level caving mine. We employ a modified 2D kinematic model that includes a dilation front and assumes that rocks are restricted to move only along streamlines so that we may determine the modification of an isolated movement zone that results from the extraction of material from a neighboring draw point. The volume of extracted material required to initiate the interaction and the location where it occurs are predicted in terms of the material's previously extracted volume, diffusion coefficient, density variations, and extraction rate. The results show that the top surface of the previously isolated movement zone is modified in order to permit the surface to reach greater heights and displace its maximum position closer to the operating draw point. We also find that the regions outside of the operating draw point's isolated movement zone are affected by the interaction and this is confirmed by the deflection of tracer lines. This could have significant negative effects in underground mining operations because dilution, initially located out of range of an operating draw point, might be carried to either the neighboring draw points or the operating draw point's opening, consequently increasing pollution. The results presented can be extrapolated to 3D systems and generalized to other type of flows described by more complex models than a kinematic model.