Formation of superdense dark matter lumps at the radiation-dominated cosmological stage

We study the process of superdense dark matter clump (DMC) formation at the radiation-dominated stage of the Universe. High-magnitude density perturbations that lead to DMC formation can be peaks in the inflationary perturbation spectrum or closed loops of cosmic strings. A model with superdense DMCs provides new opportunities for annihilation of particles having small annihilation cross-sections. Superdense DMCs can be detected by their tidal effect on gravitational wave detectors.     

Multiscale Segmentation of Three-Dimensional MR Brain Images

Segmentation of MR brain images using intensity values is severely limited owing to field inhomogeneities, susceptibility artifacts and partial volume effects. Edge based segmentation methods suffer from spurious edges and gaps in boundaries. A multiscale method to MRI brain segmentation is presented which uses both edge and intensity information. First a multiscale representation of an image is created, which can be made edge dependent to favor intra-tissue diffusion over inter-tissue diffusion. Subsequently a multiscale linking model (the hyperstack) is used to group voxels into a number of objects based on intensity. It is shown that both an improvement in accuracy and a reduction in image post-processing can be achieved if edge dependent diffusion is used instead of linear diffusion. The combination of edge dependent diffusion and intensity based linking facilitates segmentation of grey matter, white matter and cerebrospinal fluid with minimal user interaction. To segment the total brain (white matter plus grey matter) morphological operations are applied to remove small bridges between the brain and cranium. If the total brain is segmented, grey matter, white matter and cerebrospinal fluid can be segmented by joining a small number of segments. Using a supervised segmentation technique and MRI simulations of a brain phantom for validation it is shown that the errors are in the order of or smaller than reported in literature.     

Rotating thin-shell wormhole from glued Kerr spacetimes

We construct a model of a rotating wormhole made by cutting and pasting two Kerr spacetimes. As a result, we obtain a rotating thin-shell wormhole with exotic matter at the throat. Two candidates for the exotic matter are considered: (i) a perfect fluid; (ii) an anisotropic fluid. We show that a perfect fluid is unable to support a rotating thin-shall wormhole. On the contrary, the anisotropic fluid with the negative energy density can be a source for such a geometry.     

Automatic multiple sclerosis lesion detection in brain MRI by FLAIR thresholding

Magnetic resonance imaging (MRI) is frequently used to detect and segment multiple sclerosis lesions due to the detailed and rich information provided. We present a modified expectation-maximisation algorithm to segment brain tissues (white matter, grey matter, and cerebro-spinal fluid) as well as a partial volume class containing fluid and grey matter. This algorithm provides an initial segmentation in which lesions are not separated from tissue, thus a second step is needed to find them. This second step involves the thresholding of the FLAIR image, followed by a regionwise refinement to discard false detections. To evaluate the proposal, we used a database with 45 cases comprising 1.5T imaging data from three different hospitals with different scanner machines and with a variable lesion load per case. The results for our database point out to a higher accuracy when compared to two of the best state-of-the-art approaches.     

Quantum information processing through a genuine five-qubit entangled state in cavity QED

The utility of a five-qubit entangled state for quantum teleportation, quantum state sharing and superdense coding is investigated. The state can be utilized for perfect teleportation and quantum state sharing of an arbitrary single- and two-qubit state. The capacity of superdense coding of the state reaches the “Holevo bound”, which means that five classical bits can be transmitted by sending three qubits. The preparation of the five-qubit state and detection of the multipartite states in cavity QED are discussed. The distinct advantage of the feasible cavity QED technology that we use is insensitive to the thermal field and the cavity decay.     

Scalar-isovector δ meson in the relativistic mean field theory and the structure of neutron stars with a quark core

In the framework of the relativistic mean field theory, we have considered the equation of state of superdense nuclear matter, taking into account an effective scalar-isovector δ meson field. The effect of the δ meson field on the characteristics of a Maxwell-type quark phase transition has been studied. The quark phase is described with the aid of the improved version of the MIT (Massachusetts Institute of Technology) bag model, in which interactions between the u, d, s quarks inside the bag are taken into account in the one-gluon exchange approximation. For different values of the bag parameter B, series of neutron star models with a quark core have been built. Stability problems for neutron stars with an infinitesimal quark core are discussed. An estimate is obtained for the amount of energy released in a catastrophic transformation of a critical neutron star to a star with a finite-size quark core. Talk given at the International Conference RUSGRAV-13, June 23–28, 2008, PFUR, Moscow.     

Quantum secure direct communication with optimal quantum superdense coding by using general four-qubit states

From the perspective of quantum circuit, a construction framework and a measurement framework of a general kind of four-qubit states are sketched, respectively. By utilizing the properties of this kind of states, a quantum secure direct communication (QSDC) protocol is put forward, which adopts the idea of optimal quantum superdense coding to achieve a maximal efficiency and high resources capacity. The security of the proposed protocol is discussed in detail and it is proved to be secure theoretically. Moreover, the sufficient and necessary condition of which multipartite states are suitable for optimal quantum superdense coding in quantum secure direct communication is figured out.     

Generating multi-photon W-like states for perfect quantum teleportation and superdense coding

An interesting aspect of multipartite entanglement is that for perfect teleportation and superdense coding, not the maximally entangled W states but a special class of non-maximally entangled W-like states are required. Therefore, efficient preparation of such W-like states is of great importance in quantum communications, which has not been studied as much as the preparation of W states. In this paper, we propose a simple optical scheme for efficient preparation of large-scale polarization-based entangled W-like states by fusing two W-like states or expanding a W-like state with an ancilla photon. Our scheme can also generate large-scale W states by fusing or expanding W or even W-like states. The cost analysis shows that in generating large-scale W states, the fusion mechanism achieves a higher efficiency with non-maximally entangled W-like states than maximally entangled W states. Our scheme can also start fusion or expansion with Bell states, and it is composed of a polarization-dependent beam splitter, two polarizing beam splitters and photon detectors. Requiring no ancilla photon or controlled gate to operate, our scheme can be realized with the current photonics technology and we believe it enable advances in quantum teleportation and superdense coding in multipartite settings.     

克服灰度不均匀性的脑MR图像分割模型

为了克服脑核磁共振图像中存在的灰度不均匀现象,提出一种有效的脑核磁共振图像分割模型.该模型利用多相位水平集方式来拟合图像的局部灰度,实现多种脑组织的同时分割,并提供光滑且准确的目标边界或曲面.在二维、三维的图像上的比较实验结果表明,该模型是有效的.     

The relativistic fluid ball as a stratified model of an astrophysical object

A relativistic fluid ball with an inhomogeneous static stratified matter configuration is considered. A model of an astrophysical object with this structure of matter is constructed.     

N-qubit quantum teleportation, information splitting and superdense coding through the composite GHZ–Bell channel

We introduce a general odd qubit entangled system composed of GHZ and Bell pairs and explicate its usefulness for quantum teleportation, information splitting and superdense coding. After demonstrating the superdense coding protocol on the five qubit system, we prove that ‘2N + 1’ classical bits can be sent by sending ‘N + 1’ quantum bits using this channel. It is found that the five-qubit system is also ideal for arbitrary one qubit and two qubit teleportation and quantum information splitting (QIS). For the single qubit QIS, three different protocols are feasible, whereas for the two qubit QIS, only one protocol exists. Protocols for the arbitrary N-qubit state teleportation and quantum information splitting are then illustrated.     

Rotating nonstationary cosmological models and astrophysical observations

A Bianchi type II cosmological model has been built with expansion and rotation. The sources of gravity in the model are a perfect fluid, pure radiation and a scalar field, where the perfect fluid describes rotating a phantom matter. This solution can be used for modeling both the first and the second inflationary stages of the Universe evolution with rotation. We discuss the possible manifestation of cosmological rotation in astrophysical observations.     

New features of a flat (4 + 1)-dimensional cosmological model with a perfect fluid in gauss-bonnet gravity

We study a flat multidimensional cosmological model in Gauss-Bonnet gravity in the presence of matter in the form of a perfect fluid. We find analytically new stationary regimes (these results are valid for an arbitrary number of spatial dimensions) and study their stability by means of numerical recipes in the (4 + 1)-dimensional case. In the vicinity of the stationary regime, we find numerically another nonsingular regime which appears to be periodical. Finally, we demonstrate that the presence of matter in the form of a perfect fluid lifts some constraints on the dynamics of the (4 + 1)-dimensional model which have been found earlier.     

Gluon matter plasma in the compact star core within a fluid QCD model

The structure of a compact star core filled with gluon matter plasma is investigated within the fluid-like QCD framework. The energy-momentum tensor, density and pressure relevant to gluonic plasma having the nature of a fluid bulk of gluon sea are derived within the model. It is shown that the model provides a new equation of state for the perfect fluid with only a single parameter of fluid distribution, ϕ(x). The results are applied to constructing the equation of state describing the gluonic plasma dominated compact star core. The equations of pressure and density distribution are solved analytically for a small compact star core radius. The phase transition of the plasma near the core surface is also discussed.     

Exact rotating and expanding cosmologies in Einstein-Cartan theory

In the framework of the Einstein-Cartan theory, nonstationary rotating cosmological models containing a nonminimally coupled scalar field with a potential and an anisotropic fluid are considered. Exact special solutions of the gravitational and scalar field equations are obtained for an arbitrary coupling constant. It is shown that the models are nonsingular and their evolution includes a transition from deceleration to an accelerated phase. At late stages, the models rapidly evolve to an isotropic state with critical matter density and a flat type of space.     

Modeling fibrin aggregation in blood flow with discrete-particles

Excessive clotting can cause bleeding over a vast capillary area. We study the mesoscopic dynamics of clotting by using the fluid particle model. We assume that the plasma consists of fluid particles containing fibrin monomers, while the red blood cells and capillary walls are modeled with elastic mesh of "solid" particles. The fluid particles interact with each other with a short-ranged, repulsive dissipative force. The particles containing fibrin monomers have a dual character. The polymerization of fibrin monomers into hydrated fibrins is modeled by the change of the interactions between fluid particles from repulsive to attractive forces. This process occurs with a probability being an increasing function of the local density. We study the blood flow in microscopic capillary vessels about 100 microm long and with diameters in order of 10 microm. We show that the model of polymerization reflects clearly the role played by fibrins in clotting. Due to the density fluctuations caused the by the high acceleration, the fibrin chains are produced within a very short time (0.5 ms). Fibrin aggregation modifies the rheological properties of blood, slows down the incipient flow, and entraps the red blood cells, thus forming dangerous clots.     

优化的PCNN自适应三维图像分割算法*

脉冲耦合神经网络(pulse coupled neural network,PCNN)对图像分割具有天然的优势,但是传统的PCNN模型参数难以确定,且算法耗时多。对多种PCNN模型进行研究改进,并利用统计学知识提出了一种精简高效的自适应三维分割算法。将其用于脑部磁共振成像(magnetic resonance imaging,MRI)图像的分割,把脑组织分成白质、灰质和脑脊液。与标准PCNN、传统的Otsu阈值方法、SPM8工具箱及专家手动分割结果的对比实验表明,该自适应算法具有精确性、高效性。     

Interaction of chiral fields of the dark sector with cold dark matter

We study models containing matter in the form of dust and the fields of a two-component nonlinear sigma model describing dark energy. We consider the background and perturbation equations for the suggested models and compare them with the ??CDM model.     

Genuine correlations of tripartite system

We define genuine total, classical and quantum correlations in tripartite systems. The genuine tripartite quantum discord can be interpreted as ‘quantum advantage’ in tripartite superdense coding. We find in a symmetrical tripartite state, for total correlation and classical correlation, the genuine tripartite correlations are no less than the pair-wise correlations. However, the genuine quantum tripartite correlation can be surpassed by the pair-wise quantum correlations. Analytical expressions for genuine tripartite correlations are obtained for pure states and rank-2 symmetrical states. The genuine correlations in both entangled and separable states are calculated.     

Simple schemes for quantum information processing with W-type entanglement

Simple schemes are proposed for implementing deterministic teleportation, superdense coding, and quantum information splitting with W-type entangled states. The physical realization of these schemes should be much simpler than previous ones due to the assistance of an auxiliary particle. We illustrate the ideas in cavity quantum electrodynamics. The important features of our schemes can also be demonstrated in other systems.