Fluid dynamics on ultrastatic spacetimes and dual black holes

We show that the classification of shearless and incompressible stationary fluid flows on ultrastatic manifolds is equivalent to classifying the isometries of the spatial sections. For a flow on R x S$^2$ this leaves only one possibility, since on the 2-sphere all Killing fields are conjugate to each other, and it is well-known that the gravity dual of such a (conformal) fluid is the spherical KNAdS$_4$ black hole. On the other hand, in R x H$^2$ the situation is more complicated, since the isometry group of H$^2$ admits elliptic, parabolic and hyperbolic elements. One might thus ask what the gravity duals of the flows corresponding to these three different cases are. Answering this question is one of the scopes of this paper. In particular we identify the black hole dual to a fluid that is purely translating on the hyperbolic plane. Although this lies within the Carter-Plebanski (CP) class, it has never been studied in the literature before, and represents thus in principle a new black hole solution in AdS$_4$. For a rigidly rotating fluid in R x H$^2$ (holographically dual to the hyperbolic KNAdS$_4$ solution), there is a certain radius where the velocity reaches the speed of light, and thus the fluid can cover only the region within this radius. Quite remarkably, it turns out that the boundary of the hyperbolic KNAdS$_4$ black hole is conformal to exactly that part of R x H$^2$ in which the fluid velocity does not exceed the speed of light. We extend these results to establish a precise mapping between possible flows on ultrastatic spacetimes (with constant curvature spatial sections) and the parameter space of the CP solution. Finally, we show that the alternative description of the hyperbolic KNAdS$_4$ black hole in terms of fluid mechanics on R x S$^2$ or on flat space is dynamical and consists of a contracting or expanding vortex.Comment: 43 pages, many figures. v2: Final version to appear in JHE

Experimental tests on slip factor in friction joints: Comparison between european and American standards

Friction joints are used in steel structures submitted to cyclic loading such as, for example, in steel and composite bridges, in overhead cranes, and in equipment subjected to fatigue. Slip-critical steel joints with preloaded bolts are characterized by high rigidity and good performance against fatigue and vibrational phenomena. The most important parameter for the calculation of the bolt number in a friction connection is the slip factor, depending on the treatment of the plane surfaces inside the joint package. The paper focuses on the slip factor values reported in European and North American Specifications, and in literature references. The differences in experimental methods of slip test and evaluation of them for the mentioned standards are discussed. The results from laboratory tests regarding the assessment of the slip factor related to only sandblasted and sandblasted and coated surfaces are reported. Experimental data are compared with other results from the literature review to find the most influent parameters that control the slip factor in friction joint and differences between the slip tests procedure

"She is Like a Sister to Me." Gender-Affirming Services and Relationships are Key to the Implementation of HIV Care Engagement Interventions with Transgender Women of Color.

We present findings from qualitative interviews (N = 67) with 36 staff and 31 participants of nine distinct individual and/or group level interventions to engage transgender women of color (TWOC) in HIV care in the U.S. We examine the commonalities amongst the intervention services (addressing unmet basic needs, facilitating engagement in HIV care, health system navigation, improving health literacy, emotional support), and the relationships formed during implementation of the interventions (between interventionists and participants, among participants in intervention groups, between participants and peers in the community). Interventionists, often TWOC themselves, who provided these services developed caring relationships, promoted personal empowerment, and became role models for participants and the community. Intervention groups engaged participants to reinforce the importance of health and HIV care and provided mutual support. Gender affirming services and caring relationships may be two key characteristics of interventions that address individual and structural-level barriers to engage TWOC in HIV care

Characteristics and Meteorological Environment of Terrestrial Gamma-ray Flashes

This thesis investigates the geographic and meteorological conditions in which Terrestrial Gamma-ray Flashes (TGFs) are produced. TGFs are submillisecond bursts of gamma radiation produced inside thunderclouds in association with lightning. The photons, which can reach energies of a few tens of MeV, travel upwards towards space and are then routinely detected by space-borne instruments such as CGRO, which discovered the phenomenon, RHESSI, Fermi, AGILE and ASIM. Because TGFs are associated with lightning, local climatology is thought to play an important role and has been investigated previously, but so far few distinctive characteristics of the parent thunderstorm have emerged. Lightning strikes associated with TGFs have been better described, but still not enough to pinpoint the exact moment of production of the TGF, or to be able to predict the production from the characteristics of the lightning and its environment. The papers in this thesis investigate the environment of production of TGFs both at a general and case-study level. The first two papers present the third TGF catalog of the AGILE mission. The catalog was developed by finding TGFs in the AGILE data on the basis of their association with lightning only and studying their characteristics to develop new selection criteria for the instrument. The resulting catalog contains almost 3000 events and is the most extensive one over tropical regions. The third paper examines a sample of TGFs from mid-latitudes (35° to 52° in both hemispheres), observed for the first time thanks to the high orbital inclination of the instrument. For each of the fourteen events we examine their characteristics, the associated lightning and the parent thunderstorm and we find that mid-latitude TGFs are produced by relative high-current lightning strokes inside compact and moderately intense storms.Doktorgradsavhandlin

Reproducibility and speed of landmarking process in cephalometric analysis using two input devices: mouse-driven cursor versus pen

To define if the new portable appliances, like smartphone, iPad, small laptop and tablet can be used in cephalometric tracing without dropping out the validity of any measurement. METHODS:We investigated and compared the reproducibility and the speed of landmarks identification process on lateral X-rays in two input devices: a mouse-driven cursor and a pen used as input means in mobile devices. One expert located 22 landmarks on 15 lateral X-rays in a repeated measure design two times, at time T1 and T2, after at least one month. The Intraclass Correlation coefficient was used to evaluate the reproducibility for each landmark tracing and the agreement between the value derived from both input devices. Also, the mean errors in measurements, the standard deviation and the Friedman Test significans (P < 0.05) between both input were statistically evaluated. RESULTS:All landmarks had a high agreement and the Friedman Test indicated statistically significant differences (P<0.05) for the identification of Na, Po, Pt, PNS, Ba, Pg, Gn, UIE, UIA, APOcc and PPOcc landmarks. CONCLUSIONS:Even if the mouse input give higher agreement for landmark tracing the differences are really minimal and they can be ignored in private practice. We suggest the adequacy of pen input in clinical setting

Moduli of sheaves, quiver moduli, and stability

The goal of this thesis is to provide a modern interpretation and an extension of the classical works of the 1970s and 1980s constructing moduli spaces of vector bundles and coherent sheaves on projective spaces by means of "linear data", that is spaces of matrices modulo a linear group action. These works culminated with the description by Dr\ue9zet and Le Potier of the moduli spaces of Gieseker-semistable sheaves on P2 as what are called today quiver moduli spaces. We show that this can be naturally understood and generalized using the language of derived categories and stability structures on them. In particular, we obtain analogous explicit constructions for moduli of sheaves on P1xP1, and we investigate these moduli spaces using the theory of quiver moduli