A 3+1 covariant suite of Numerical Relativity Evolution Systems

A suite of three evolution systems is presented in the framework of the 3+1 formalism. The first one is of second order in space derivatives and has the same causal structure of the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) system for a suitable choice of parameters. The second one is the standard first order version of the first one and has the same causal structure of the Bona-Masso system for a given parameter choice. The third one is obtained from the second one by reducing the space of variables in such a way that the only modes that propagate with zero characteristic speed are the trivial ones. This last system has the same structure of the ones recently presented by Kidder, Scheel and Teukolski: the correspondence between both sets of parameters is explicitly given. The fact that the suite started with a system in which all the dynamical variables behave as tensors (contrary to what happens with BSSN system) allows one to keep the same parametrization when passing from one system to the next in the suite. The direct relationship between each parameter and a particular characteristic speed, which is quite evident in the second and the third systems, is a direct consequence of the manifest 3+1 covariance of the approach

Internal stresses and breakup of rigid isostatic aggregates in homogeneous and isotropic turbulence

By characterising the hydrodynamic stresses generated by statistically homogeneous and isotropic turbulence in rigid aggregates, we estimate theoretically the rate of turbulent breakup of colloidal aggregates and the size distribution of the formed fragments. The adopted method combines Direct Numerical Simulation of the turbulent field with a Discrete Element Method based on Stokesian dynamics. In this way, not only the mechanics of the aggregate is modelled in detail, but the internal stresses are evaluated while the aggregate is moving in the turbulent flow. We examine doublets and cluster-cluster isostatic aggregates, where the failure of a single contact leads to the rupture of the aggregate and breakup occurs when the tensile force at a contact exceeds the cohesive strength of the bond. Due to the different role of the internal stresses, the functional relationship between breakup frequency and turbulence dissipation rate is very different in the two cases. In the limit of very small and very large values, the frequency of breakup scales exponentially with the turbulence dissipation rate for doublets, while it follows a power law for cluster-cluster aggregates. For the case of large isostatic aggregates it is confirmed that the proper scaling length for maximum stress and breakup is the radius of gyration. The cumulative fragment distribution function is nearly independent of the mean turbulence dissipation rate and can be approximated by the sum of a small erosive component and a term that is quadratic with respect to fragment size.Comment: 31 pages, 19 figure

Upper bounds on SUSY contributions to b to s transitions from B_s - B_sbar mixing

We study the constraints on supersymmetric contributions to b to s transitions from the recent allowed range and measurement of Bs-Bsbar mixing obtained by the D0 and CDF collaborations at the Tevatron. We compute the upper bounds on the relevant off-diagonal squark mass terms and compare them with the bounds coming from Delta F=1 decays. We find that the constraints on chirality-flipping mass insertions are unaffected. Conversely, the measurement of Bs-Bsbar mixing is effective in constraining chirality-conserving mass insertions, and it has striking effects in the case in which left- and right-handed insertions have similar size. Finally, we discuss the phase of the Bs-Bsbar mixing amplitude in the presence of SUSY contributions.Comment: 4 pages, 4 figures; v2: CDF measurement include

Physics at SuperB

Flavour will play a crucial role in understanding physics beyond the Standard Model. Progress in developing a future programme to investigate this central area of particle physics has recently passed a milestone, with the completion of the conceptual design report for SuperB, a very high luminosity, asymmetric e+e- collider. This article summarizes the important role of SuperB in understanding new physics in the LHC era.Comment: 4 pages, 2 figures. To appear in the proceedings of the International Europhysics Conference on High Energy Physics (EPS-HEP2007), Manchester, England, 19-25 July 200

Not all visual symmetry is equal: partially distinct neural bases for vertical and horizontal symmetry

Visual mirror symmetry plays an important role in visual perception in both human and animal vision; its importance is reflected in the fact that it can be extracted automatically during early stages of visual processing. However, how this extraction is implemented at the cortical level remains an open question. Given the importance of symmetry in visual perception, one possibility is that there is a network which extracts all types of symmetry irrespective of axis of orientation; alternatively, symmetry along different axes might be encoded by different brain regions, implying that that there is no single neural mechanism for symmetry processing. Here we used fMRI-guided transcranial magnetic stimulation (TMS) to compare the neural basis of the two main types of symmetry found in the natural world, vertical and horizontal symmetry. TMS was applied over either right Lateral Occipital Cortex (LO), right Occipital Face Area (OFA) or Vertex while participants were asked to detect symmetry in low-level dot configurations. Whereas detection of vertical symmetry was impaired by TMS over both LO and OFA, detection of horizontal symmetry was delayed by stimulation of LO only. Thus, different types of visual symmetry rely on partially distinct cortical networks

TMS over right OFA affects individuation of faces but not of exemplars of objects

In addition to its well-documented role in processing of faces, the occipital face area in the right hemisphere (rOFA) may also play a role in identifying specific individuals within a class of objects. Here we explored this issue by using fMRI-guided TMS. In a first experiment, participants had to judge whether two sequentially presented images of faces or objects represented exactly the same exemplar or two different exemplars of the same class, while receiving online TMS over either the rOFA, the right lateral occipital cortex (rLO) or the Vertex (control). We found that, relative to Vertex, stimulation of rOFA impaired individuation of faces only, with no effect on objects; in contrast, TMS over rLO reduced individuation of objects but not of faces. In a second control experiment participants judged whether a picture representing a fragment of a stimulus belonged or not to the subsequently presented image of a whole stimulus (part-whole matching task). Our results showed that rOFA stimulation selectively disrupted performance with faces, whereas performance with objects (but not with faces) was selectively affected by TMS over rLO. Overall, our findings suggest that rOFA does not contribute to discriminate between exemplars of non-face objects

Hyperbolicity of the Kidder-Scheel-Teukolsky formulation of Einstein's equations coupled to a modified Bona-Masso slicing condition

We show that the Kidder-Scheel-Teukolsky family of hyperbolic formulations of the 3+1 evolution equations of general relativity remains hyperbolic when coupled to a recently proposed modified version of the Bona-Masso slicing condition.Comment: 4 pages. Several changes. Main corrections are in eqs. 4.9 and 4.1

Gambaran Pengetahuan, Sikap, dan Praktik Perilaku Mahasiswa terhadap HIV/AIDS dan ODHA (Orang dengan HIV/AIDS)

Undergraduate students in adolescence and young adulthood period are sexually productive. It is crucial to discover their knowledge, attitude, and practice (KAP) towards HIV/AIDS since the highest HIV infection in Indonesia until 2016 is between those ages. The survey was conducted in Indonesia between November-December 2015. Data was collected using online structured KAP questionnaire to 350 undergraduate students (aged 18-23 years old) in Universitas Indonesia and analyzed with descriptive statistic. The KAP questionnaire used was adapted from Mulu, Abera, and Yinner (2014). Results shown that most participants answered correctly in knowledge items, but most of them still didn't know that HIV and AIDS are two different things, and they think that HIV can be infected through sharing foods, exchanging clothes and toilets with PLWH (People Living with HIV). Most participants have a positive attitude towards HIV/AIDS, but they have a negative attitude regarding on using condom while having sex as an affront to the couple, and disagreeing to live together with PLWH. Regarding on the practice, as much as 76 participants who have had sex ever had a risky sexual behavior but never had VCT (Voluntary Counseling & Testing), while the rest of participants who never had sex mostly have seen a condom but didn't feel comfortable to hold it. Knowledge towards HIV/AIDS was quite sufficient, the attitude was fair enough, but the practice for the participants who have had sex needed attention more. The results also might indicate stigma towards HIV/AIDS in Indonesia still exists because HIV is considered as an easily infected disease

Exploiting gauge and constraint freedom in hyperbolic formulations of Einstein's equations

We present new many-parameter families of strongly and symmetric hyperbolic formulations of Einstein's equations that include quite general algebraic and live gauge conditions for the lapse. The first system that we present has 30 variables and incorporates an algebraic relationship between the lapse and the determinant of the three metric that generalizes the densitized lapse prescription. The second system has 34 variables and uses a family of live gauges that generalizes the Bona-Masso slicing conditions. These systems have free parameters even after imposing hyperbolicity and are expected to be useful in 3D numerical evolutions. We discuss under what conditions there are no superluminal characteristic speeds

First order hyperbolic formalism for Numerical Relativity

The causal structure of Einstein's evolution equations is considered. We show that in general they can be written as a first order system of balance laws for any choice of slicing or shift. We also show how certain terms in the evolution equations, that can lead to numerical inaccuracies, can be eliminated by using the Hamiltonian constraint. Furthermore, we show that the entire system is hyperbolic when the time coordinate is chosen in an invariant algebraic way, and for any fixed choice of the shift. This is achieved by using the momentum constraints in such as way that no additional space or time derivatives of the equations need to be computed. The slicings that allow hyperbolicity in this formulation belong to a large class, including harmonic, maximal, and many others that have been commonly used in numerical relativity. We provide details of some of the advanced numerical methods that this formulation of the equations allows, and we also discuss certain advantages that a hyperbolic formulation provides when treating boundary conditions.Comment: To appear in Phys. Rev.