Biophysically motivated efficient estimation of the spatially isotropic R*2 component from a single gradient‐recalled echo measurement

Purpose To propose and validate an efficient method, based on a biophysically motivated signal model, for removing the orientation‐dependent part of R*2 using a single gradient‐recalled echo (GRE) measurement. Methods The proposed method utilized a temporal second‐order approximation of the hollow‐cylinder‐fiber model, in which the parameter describing the linear signal decay corresponded to the orientation‐independent part of R*2. The estimated parameters were compared to the classical, mono‐exponential decay model for R*2 in a sample of an ex vivo human optic chiasm (OC). The OC was measured at 16 distinct orientations relative to the external magnetic field using GRE at 7T. To show that the proposed signal model can remove the orientation dependence of R*2, it was compared to the established phenomenological method for separating R*2 into orientation‐dependent and ‐independent parts. Results Using the phenomenological method on the classical signal model, the well‐known separation of R*2 into orientation‐dependent and ‐independent parts was verified. For the proposed model, no significant orientation dependence in the linear signal decay parameter was observed. Conclusions Since the proposed second‐order model features orientation‐dependent and ‐independent components at distinct temporal orders, it can be used to remove the orientation dependence of R*2 using only a single GRE measurement

Kaon effective mass and energy from a novel chiral SU(3)-symmetric Lagrangian

A new chiral SU(3) Lagrangian is proposed to describe the properties of kaons and antikaons in the nuclear medium, the ground state of dense matter and the kaon-nuclear interactions consistently. The saturation properties of nuclear matter are reproduced as well as the results of the Dirac-Br\"{u}ckner theory. Our numerical results show that the kaon effective mass might be changed only moderately in the nuclear medium due to the highly non-linear density effects. After taking into account the coupling between the omega meson and the kaon, we obtain similar results for the effective kaon and antikaon energies as calculated in the one-boson-exchange model while in our model the parameters of the kaon-nuclear interactions are constrained by the SU(3) chiral symmetry.Comment: 13 pages, Latex, 3 PostScript figures included; replaced by the revised version, to appear in Phys. Rev.

DIAGNOSTIC REVIEW OF A BLACKOUT IN RHODES

U radu se daje tehnička analiza jednog incidenta koji se dogodio 21. ožujka 2007. godine u 00:50 sati u noći i doveo do dvosatnog potpunog raspada elektroenergetskog sustava na otoku Rodosu. Analiza događanja temelji se na registriranim operativnim podacima kao i nalazima na terenu. Izvršena je tehnička analiza smetnji kako bi se utvrdili vjerojatni uzroci i čimbenici koji su pridonijeli pojavi smetnji. S obzirom da se radi o izoliranom sustavu koji je osobito je osjetljiv na poremećaje, ispitane su uloge zaštite sustava kao i kolebanja proizvodnje vjetroelektrana tijekom incidenta. Izvučeni su zaključci od praktičnog značenja i dane su preporuke korektivnih mjera koje valja provesti kako bi se u budućnosti spriječile takve smetnje.A technical review of an incident on March 21, 2007 that began at 00:50 a.m. and led to a two-hour blackout of the island of Rhodes electric power system is presented with the complete sequence, including all the relevant registered operational data as well as the on-site field findings. A technical analysis of the disturbance was performed to determine the probable causes and factors that contributed to the duration of the disturbance. Since the system is an isolated one, it is particularly vulnerable to perturbations. The roles of system protection and wind power generation during the incident are examined. Conclusions of practical importance are drawn, including recommendations for corrective measures to be implemented for preventing disturbances of this kind from reoccurring in the future

Compact Stars - How Exotic Can They Be?

Strong interaction physics under extreme conditions of high temperature and/or density is of central interest in modern nuclear physics for experimentalists and theorists alike. In order to investigate such systems, model approaches that include hadrons and quarks in a unified approach, will be discussed. Special attention will be given to high-density matter as it occurs in neutron stars. Given the current observational limits for neutron star masses, the properties of hyperonic and hybrid stars will be determined. In this context especially the question of the extent, to which exotic particles like hyperons and quarks affect star masses, will be discussed.Comment: Contributon to conference "Nuclear Physics: Present and Future", held in Boppard (Germany), May 201

Nuclei, Superheavy Nuclei and Hypermatter in a chiral SU(3)-Modell

A model based on chiral SU(3)-symmetry in nonlinear realisation is used for the investigation of nuclei, superheavy nuclei, hypernuclei and multistrange nuclear objects (so called MEMOs). The model works very well in the case of nuclei and hypernuclei with one Lambda-particle and rules out MEMOs. Basic observables which are known for nuclei and hypernuclei are reproduced satisfactorily. The model predicts Z=120 and N=172, 184 and 198 as the next shell closures in the region of superheavy nuclei. The calculations have been performed in self-consistent relativistic mean field approximation assuming spherical symmetry. The parameters were adapted to known nuclei.Comment: 19 pages, 11 figure

Nuclei in a chiral SU(3) model

Nuclei can be described satisfactorily in a nonlinear chiral SU(3)-framework, even with standard potentials of the linear $\sigma$-model. The condensate value of the strange scalar meson is found to be important for the properties of nuclei even without adding hyperons. By neglecting terms which couple the strange to the nonstrange condensate one can reduce the model to a Walecka model structure embedded in SU(3). We discuss inherent problems with chiral SU(3) models regarding hyperon optical potentials.Comment: 25 pages, RevTe

Non-linear bigravity and cosmic acceleration

We explore the cosmological solutions of classes of non-linear bigravity theories. These theories are defined by effective four-dimensional Lagrangians describing the coupled dynamics of two metric tensors, and containing, in the linearized limit, both a massless graviton and an ultralight one. We focus on two paradigmatic cases: the case where the coupling between the two metrics is given by a Pauli-Fierz-type mass potential, and the case where this coupling derives from five-dimensional brane constructions. We find that cosmological evolutions in bigravity theories can be described in terms of the dynamics of two ``relativistic particles'', moving in a curved Lorenzian space, and connected by some type of nonlinear ``spring''. Classes of bigravity cosmological evolutions exhibit a ``locking'' mechanism under which the two metrics ultimately stabilize in a bi-de-Sitter configuration, with relative (constant) expansion rates. In the absence of matter, we find that a generic feature of bigravity cosmologies is to exhibit a period of cosmic acceleration. This leads us to propose bigravity as a source of a new type of dark energy (``tensor quintessence''), exhibiting specific anisotropic features. Bigravity could also have been the source of primordial inflation.Comment: 55 pages, 4 figures, references and comments added, final version published in Phys. Rev.

REST APIs: A large-scale analysis of compliance with principles and best practices

Quickly and dominantly, REST APIs have spread over the Web and percolated into modern software development practice, especially in the Mobile Internet where they conveniently enable offloading data and computations onto cloud services. We analyze more than 78GB of HTTP traffic collected by Italy’s biggest Mobile Internet provider over one full day and study how big the trend is in practice, how it changed the traffic that is generated by applications, and how REST APIs are implemented in practice. The analysis provides insight into the compliance of state-of-the-art APIs with theoretical Web engineering principles and guidelines, knowledge that affects how applications should be developed to be scalable and robust. The perspective is that of the Mobile Internet

Biophysically motivated efficient estimation of the spatially isotropic R∗2 component from a single gradient-recalled echo measurement

Purpose To propose and validate an efficient method, based on a biophysically motivated signal model, for removing the orientation‐dependent part of R∗2 using a single gradient‐recalled echo (GRE) measurement. Methods The proposed method utilized a temporal second‐order approximation of the hollow‐cylinder‐fiber model, in which the parameter describing the linear signal decay corresponded to the orientation‐independent part of R∗2. The estimated parameters were compared to the classical, mono‐exponential decay model for R∗2 in a sample of an ex vivo human optic chiasm (OC). The OC was measured at 16 distinct orientations relative to the external magnetic field using GRE at 7T. To show that the proposed signal model can remove the orientation dependence of R∗2, it was compared to the established phenomenological method for separating R∗2 into orientation‐dependent and ‐independent parts. Results Using the phenomenological method on the classical signal model, the well‐known separation of R∗2 into orientation‐dependent and ‐independent parts was verified. For the proposed model, no significant orientation dependence in the linear signal decay parameter was observed. Conclusions Since the proposed second‐order model features orientation‐dependent and ‐independent components at distinct temporal orders, it can be used to remove the orientation dependence of R∗2 using only a single GRE measurement