A non-reflecting wave equation through directional wave-field suppression and its finite difference implementation

The acoustic wave equation describes wave propagation directly from basic physical laws, even in heterogeneous acoustic media. When numerically simulating waves with the wave equation, contrasts in the medium parameters automatically generate all scattering effects. For some applications - such as propagation analysis or certain wave-equation based imaging techniques - it is desirable to suppress these reflections, as we are only interested in the transmitted wave-field. To achieve this, a modification to the constitutive relations is proposed, yielding an extra term that suppresses waves with reference to a preferred direction. The scale-factor $$\alpha$$ α of this extra term can either be interpreted as a penetration depth or as a typical decay time. This modified theory is implemented using a staggered-grid, time-domain finite difference scheme, where the acoustic Poynting-vector is used to estimate the local propagation direction of the wave-field. The method was successfully used to suppress reflections in media with bone tissue (medical ultrasound) and geophysical subsurface structures, while introducing only minor perturbations to the transmitted wave-field and a small increase in computation time.

Possible Observational Evidence for the Existence of a Parallel Universe

Many totally different kinds of astrophysical observations demonstrated that, in our universe, there exists a preferred direction. Specifically, from observations in a wide range of frequencies, the alignment of various preferred directions in different data sets was found. Moreover, the observed Cosmic Microwave Background (CMB) quadrupole, CMB octopole, radio and optical polarizations from distant sources also indicate the same preferred direction. While this hints at a gravitational pull from the “outside”, the observational data from the Plank satellite showed that the bulk flow velocity was relatively small: much smaller than was initially thought. In the present paper we propose a configuration where two three-dimensional universes (one of which is ours) are embedded in a four-dimensional space and rotate about their barycenter in such a way that the centrifugal force nearly (but not exactly) compensates their mutual gravitational pull. This would explain not only the existence of a preferred direction for each of the three-dimensional universes (the direction to the other universe), but also the fact that the bulk flow velocity, observed in our universe, is relatively small. We point out that this configuration could also explain the perplexing features of the Unidentified Aerial Phenomena (UAP), previously called Unidentified Flying Objects (UFOs), recorded by various detection systems—the features presented in the latest official report by the US Office of the Director of National Intelligence. Thus, the proposed configuration of the two rotating, parallel three-dimensional universes seems to explain both the variety of astrophysical observations and (perhaps) the observed features of the UAP.

Effect of Photoconductivity Precursor Volume on Structural, Physical, Electrical and Optical Properties of Thin Layers of Cadmium Oxide (CdO) Nanostructures Produced Using Spray Pyrolysis Technique

Thin layers of Cadmium Oxide (CdO) are produced over glassy substrate by spray pyrolysis technique with precursor volumes of 50, 75 and 100 (ml). FESEM images of samples show the formation of nanometric structures and structural characterization of them resulted from XRD spectroscopy indicate the formation of cubic polycrystalline structure in growing layers with preferred direction of (111). Evaluating the optical properties of samples show that optical band gap of layers is reduced from 3.6 to 3.4 (eV) by increasing the precursor volume and the optical absorption coefficient of samples is in UV region at about 105 (cm-1). Data analysis indicates that the produced sample in volume of 100 mL has the smallest penetration depth (smaller than 200 nm) in UV region. On the other hand, thin layers of Cadmium Oxide (CdO) with various volumes of Cadmium acetate solution (40, 50 and 70 ml) were deposited using spray pyrolysis technique over a glassy substrate. Samples were investigated using FESEM images, XRD and UV-Vis spectra as well as I-V characteristic. It was found that all samples were grew up with polycrystalline nanostructures along the preferred direction of (002). In addition, it was found that grew up sample in the volume of 50 (ml) are of optimum photoconductivity condition in visible range regarding optimum structural (largest crystallite size and lowest crystallite defect density) and optical (smallest band gap and highest light absorption) conditions.

Developing the Fringe Routing Protocol

<p>An ISP style network often has a particular traffic pattern not typically seen in other networks and which is a direct result of the ISP’s purpose, to connect internal clients with a high speed external link. Such a network is likely to consist of a backbone with the clients on one ‘side’ and one or more external links on the other. Most traffic on the network moves between an internal client and the external world via the backbone. But what about traffic between two clients of the ISP? Typical routing protocols will find the ‘best’ path between the two gateway routers at the edge of the client stub networks. As these routers connect the stubs to the ISP core, this route should be entirely within the ISP network. Ideally, from the ISP point of view, this traffic will go up to the backbone and down again but it is possible that it may find another route along a redundant backup path. Don Stokes of Knossos Networks has developed a protocol to sit on the client fringes of this ISP style of network. It is based on the distance vector algorithm and is intended to be subordinate to the existing interior gateway protocol running on the ISPs backbone. It manipulates the route cost calculation so that paths towards the backbone become very cheap and paths away from the backbone become expensive. This forces traffic in the preferred direction unless the backup path ‘shortcut’ is very attractive or the backbone link has disappeared. It is the analysis and development of the fringe routing protocol that forms the content of this ME thesis.</p>

Developing the Fringe Routing Protocol

<p>An ISP style network often has a particular traffic pattern not typically seen in other networks and which is a direct result of the ISP’s purpose, to connect internal clients with a high speed external link. Such a network is likely to consist of a backbone with the clients on one ‘side’ and one or more external links on the other. Most traffic on the network moves between an internal client and the external world via the backbone. But what about traffic between two clients of the ISP? Typical routing protocols will find the ‘best’ path between the two gateway routers at the edge of the client stub networks. As these routers connect the stubs to the ISP core, this route should be entirely within the ISP network. Ideally, from the ISP point of view, this traffic will go up to the backbone and down again but it is possible that it may find another route along a redundant backup path. Don Stokes of Knossos Networks has developed a protocol to sit on the client fringes of this ISP style of network. It is based on the distance vector algorithm and is intended to be subordinate to the existing interior gateway protocol running on the ISPs backbone. It manipulates the route cost calculation so that paths towards the backbone become very cheap and paths away from the backbone become expensive. This forces traffic in the preferred direction unless the backup path ‘shortcut’ is very attractive or the backbone link has disappeared. It is the analysis and development of the fringe routing protocol that forms the content of this ME thesis.</p>

Chirality-Helicity of Cumulenes: A Non-Scalar Charge Density Derived Perspective

We investigate the presence of helical character and chirality using a vector-based charge density perspective instead of energetic or structural measures. The vector-based perspective of the chemical bonding, constructed using the most preferred direction of charge density accumulation, finds the presence of induced symmetry-breaking for α,ω-disubstituted [4]cumulenes as the end groups are torsioned. The stress tensor trajectories Tσ(s) are used to provide the additional symmetry-breaking required to quantify the degree and nature of the chirality and helical character. We find an absence of chirality for [4]cumulene but a very significant degree of axiality as demonstrated by the purely axial form of the Tσ(s) indicating a lack of helical character. The S-1,5-dimethyl-[4]cumulene contains a very low degree of chiral character but significant axiality(helicity) resulting in a weakly helical morphology of the corresponding Tσ(s). The (-)S(-), (+)S(-) and (+)S(+) conformations of S-1,5-diamino-[4]cumulene contain very significant degrees of both chirality and helical character resulting in helical morphology of the corresponding Tσ(s). The chirality assignments are in agreement with the Cahn–Ingold–Prelog (CIP) classifications for the (-)S(-), (+)S(-) and (+)S(+) conformations of S-1,5-diamino-[4]cumulene. We discuss the consequences for the Tσ(s) in locating chiral character in these molecules in future experiment investigations.

Privacy Protection and Secondary Use of Health Data: Strategies and Methods

Health big data has already been the most important big data for its serious privacy disclosure concerns and huge potential value of secondary use. Measurements must be taken to balance and compromise both the two serious challenges. One holistic solution or strategy is regarded as the preferred direction, by which the risk of reidentification from records should be kept as low as possible and data be shared with the principle of minimum necessary. In this article, we present a comprehensive review about privacy protection of health data from four aspects: health data, related regulations, three strategies for data sharing, and three types of methods with progressive levels. Finally, we summarize this review and identify future research directions.

On the Direction of Time: From Reichenbach to Prigogine and Penrose

The question why natural processes tend to flow along a preferred direction has always been considered from within the perspective of the Second Law of Thermodynamics, especially its statistical formulation due to Maxwell and Boltzmann. In this article, we re-examine the subject from the perspective of a new historico-philosophical formulation based on the careful use of selected theoretical elements taken from three key modern thinkers: Hans Reichenbach, Ilya Prigogine, and Roger Penrose, who are seldom considered together in the literature. We emphasize in our analysis how the entropy concept was introduced in response to the desire to extend the applicability of the Second Law to the cosmos at large (Reichenbach and Penrose), and to examine whether intrinsic irreversibility is a fundamental universal characteristics of nature (Prigogine). While the three thinkers operate with vastly different technical proposals and belong to quite distinct intellectual backgrounds, some similarities are detected in their thinking. We philosophically examine these similarities but also bring into focus the uniqueness of each approach. Our purpose is not providing an exhaustive derivations of logical concepts identified in one thinker in terms of ideas found in the others. Instead, the main objective of this work is to stimulate historico-philosophical investigations and inquiries into the problem of the direction of time in nature by way of crossdisciplinary examinations of previous theories commonly treated in literature as disparate domains.

A theory of direction selectivity for macaque primary visual cortex

This paper offers a theory for the origin of direction selectivity (DS) in the macaque primary visual cortex, V1. DS is essential for the perception of motion and control of pursuit eye movements. In the macaque visual pathway, neurons with DS first appear in V1, in the Simple cell population of the Magnocellular input layer 4Cα. The lateral geniculate nucleus (LGN) cells that project to these cortical neurons, however, are not direction selective. We hypothesize that DS is initiated in feed-forward LGN input, in the summed responses of LGN cells afferent to a cortical cell, and it is achieved through the interplay of 1) different visual response dynamics of ON and OFF LGN cells and 2) the wiring of ON and OFF LGN neurons to cortex. We identify specific temporal differences in the ON/OFF pathways that, together with item 2, produce distinct response time courses in separated subregions; analysis and simulations confirm the efficacy of the mechanisms proposed. To constrain the theory, we present data on Simple cells in layer 4Cα in response to drifting gratings. About half of the cells were found to have high DS, and the DS was broadband in spatial and temporal frequency (SF and TF). The proposed theory includes a complete analysis of how stimulus features such as SF and TF interact with ON/OFF dynamics and LGN-to-cortex wiring to determine the preferred direction and magnitude of DS.