Measurement of identified charged hadron spectra with the ALICE experiment at the LHC

The ALICE experiment features multiple particle identification systems. The measurement of the identified charged hadron $p_{t}$ spectra in proton-proton collisions at $\sqrt{s}=900$ GeV will be discussed. In the central rapidity region ($|\eta|<0.9$) particle identification and tracking are performed using the Inner Tracking System (ITS), which is the closest detector to the beam axis, the Time Projection Chamber (TPC) and a dedicated time-of-flight system (TOF). Particles are mainly identified using the energy loss signal in the ITS and TPC. In addition, the information from TOF is used to identify hadrons at higher momenta. Finally, the kink topology of the weak decay of charged kaons provides an alternative method to extract the transverse momentum spectra of charged kaons. This combination allows to track and identify charged hadrons in the transverse momentum ($p_{t}$) range from 100 MeV/c up to 2.5 GeV/$c$. Mesons containing strange quarks (\kos, $\phi$) and both singly and doubly strange baryons (\lam, \lambar, and \xip + \xim) are identified by their decay topology inside the TPC detector. Results obtained with the various identification tools above described and a comparison with theoretical models and previously published data will be presented.Comment: 11 pages, 14 figures, contribution to conference proceedings of the 27th Winter Workshop on Nuclear Dynamic

Uncovering the physics of flapping flat plates with artificial evolution

We consider an experiment in which a rectangular flat plate is flapped with two degrees of freedom, and a genetic algorithm tunes its trajectory parameters so as to achieve maximum average lift force, thus evolving a population of trajectories all yielding optimal lift forces. We cluster the converged population by defining a dynamical formation number for a flapping flat plate, thus showing that optimal unsteady force generation is linked to the formation of a leading-edge vortex with maximum circulation. Force and digital particle image velocimetry measurements confirm this result

Opportunity Road: The Promise and Challenge of America's Forgotten Youth

There are millions of youth ages 16 to 24 who are out of school and out of work. They cost the nation billions of dollars every year and over their lifetimes in lost productivity and increased social services. They also represent an opportunity for the nation to tap the talents of millions of potential leaders and productive workers at a time when America's skills gap is significant. The central message of this report is that while these youth face significant life challenges, most start out with big dreams and remain confident or hopeful that they can achieve their goals; most accept responsibility for their futures; and most are looking to reconnect to school, work and service. They point the way to how they can effectively reconnect to education, productive work and civic life. On behalf of Civic Enterprises and the America's Promise Alliance, Peter D. Hart Research Associates undertook a national cross-section of opportunity youth in 23 diverse locations across the United States in August 2011 to learn about common elements in their personal histories and their lives today, and to explore opportunities to reconnect them to work and school. At the time of the survey, respondents were ages 16 to 24, neither enrolled in school nor planning to enroll in the coming year, were not working, and had not completed a college degree. In addition, they were not disabled such as to prevent long-term employment, were not incarcerated, and were not a stay-at-home parent with a working spouse. What the authors found was both heartbreaking and uplifting, frustrating and hopeful. Despite many growing up in trying circumstances of little economic means and weak family and social supports, the youth they surveyed were optimistic about their futures. More than half believed they would graduate college when they were growing up and their hopes remain high that they will achieve the American Dream with a strong family life of their own and a good job one day. For this reason, the authors believe they are truly "opportunity youth"--both for their belief in themselves that must be nurtured and for the opportunity they hold for America

Postponing Branching Decisions

Solution techniques for Constraint Satisfaction and Optimisation Problems often make use of backtrack search methods, exploiting variable and value ordering heuristics. In this paper, we propose and analyse a very simple method to apply in case the value ordering heuristic produces ties: postponing the branching decision. To this end, we group together values in a tie, branch on this sub-domain, and defer the decision among them to lower levels of the search tree. We show theoretically and experimentally that this simple modification can dramatically improve the efficiency of the search strategy. Although in practise similar methods may have been applied already, to our knowledge, no empirical or theoretical study has been proposed in the literature to identify when and to what extent this strategy should be used.Comment: 11 pages, 3 figure

Decomposition Based Search - A theoretical and experimental evaluation

In this paper we present and evaluate a search strategy called Decomposition Based Search (DBS) which is based on two steps: subproblem generation and subproblem solution. The generation of subproblems is done through value ranking and domain splitting. Subdomains are explored so as to generate, according to the heuristic chosen, promising subproblems first. We show that two well known search strategies, Limited Discrepancy Search (LDS) and Iterative Broadening (IB), can be seen as special cases of DBS. First we present a tuning of DBS that visits the same search nodes as IB, but avoids restarts. Then we compare both theoretically and computationally DBS and LDS using the same heuristic. We prove that DBS has a higher probability of being successful than LDS on a comparable number of nodes, under realistic assumptions. Experiments on a constraint satisfaction problem and an optimization problem show that DBS is indeed very effective if compared to LDS.Comment: 16 pages, 8 figures. LIA Technical Report LIA00203, University of Bologna, 200

Transverse momentum spectra of hadrons identified with the ALICE Inner Tracking System

The Inner Tracking System is the ALICE detector closest to the beam axis. It is composed of six layers of silicon detectors: two innermost layers of Silicon Pixel Detectors (SPD), two intermediate layers of Silicon Drift Detectors (SDD) and two outermost layers of Silicon Strip Detectors (SSD). The ITS can be used as a standalone tracker in order to recover tracks that are not reconstructed by the Time Projection Chamber (TPC) and to reconstruct low momentum particles with $p_{t}$ down to 100 MeV/c. Particle identification in the ITS is performed by measuring the energy loss signal in the SDD and SSD layers. The ITS allows to extend the charged particle identification capability in the ALICE central rapidity region at low $p_{t}$: it is possible to separate $\pi/K$ in the range 100 MeV/c $< p_{t} <$ 500 MeV/c and $K/p$ in the range 200 MeV/c $< p_{t} <$ 800 MeV/c. The identification of hadron in the ITS will be discussed in detail, different methods used to extract the $p_{t}$ spectra of $\pi, K$ and $p$ will also be described.Comment: 2 pages, 2 figures, submitted as contribution to PLHC2011 conference proceeding

Recommender systems and their ethical challenges

This article presents the first, systematic analysis of the ethical challenges posed by recommender systems through a literature review. The article identifies six areas of concern, and maps them onto a proposed taxonomy of different kinds of ethical impact. The analysis uncovers a gap in the literature: currently user-centred approaches do not consider the interests of a variety of other stakeholders—as opposed to just the receivers of a recommendation—in assessing the ethical impacts of a recommender system