Stability Selection of the Number of Clusters

Selecting the number of clusters is one of the greatest challenges in clustering analysis. In this thesis, we propose a variety of stability selection criteria based on cross validation for determining the number of clusters. Clustering stability measures the agreement of clusterings obtained by applying the same clustering algorithm on multiple independent and identically distributed samples. We propose to measure the clustering stability by the correlation between two clustering functions. These criteria are motivated by the concept of clustering instability proposed by Wang (2010), which is based on a form of clustering distance. In addition, the effectiveness and robustness of the proposed methods are numerically demonstrated on a variety of simulated and real world samples

Acute lower limb ischemia due to thrombo-embolic arterial occlusions in two previously healthy men with markedly elevated Lp(a)

Lipoprotein (a) (Lp(a)) is a well-documented risk factor for atherosclerotic cardiovascular disease. Its role in acute thrombo-embolic occlusions of peripheral arteries is not known. We describe two cases of multiple, acute, peripheral arterial occlusions in two previously healthy men with markedly elevated Lp(a). Both cases had unsatisfactory results after percutaneous and surgical revascularization procedures. Experience yielded in these two cases suggests that when an unfavorable outcome occurs in a peripheral artery disease patient in the absence of the regular risk factors, Lp(a) should be determined and its role investigated

Effective potential at finite temperature in a constant magnetic field I: Ring diagrams in a scalar theory

We study symmetry restoration at finite temperature in the theory of a charged scalar field interacting with a constant, external magnetic field. We compute the finite temperature effective potential including the contribution from ring diagrams. We show that in the weak field case, the presence of the field produces a stronger first order phase transition and that the temperature for the onset of the transition is lower, as compared to the case without magnetic field.Comment: Expanded comments, 4 figures added. Conclusions unchanged. Version to match published pape

Confronting the Material Convoy in Later Life

This is the peer reviewed version of the following article: Smith, G. V. and Ekerdt, D. J. (2011), Confronting the Material Convoy in Later Life*. Sociological Inquiry, 81: 377–391. doi:10.1111/j.1475-682X.2011.00378.x, which has been published in final form at http://doi.org/10.1111/j.1475-682X.2011.00378.x. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.We adapt a metaphor from life course studies to designate the whole of one’s possessions, across time, as a convoy of material support. This dynamic collection of things supports daily life and the self, but it can also present difficulty in later life. To alleviate the purported burdens of the material convoy, a discourse has arisen that urges elders and their family members to reduce the volume of possessions. An analysis of 11 such possession management texts shows authors addressing two distinct audiences about elders’ need to downsize: family members and elders themselves. Authors who speak to family members do so with an urgent, unsentimental tone that echoes mainstream clutter-control advice about disorderly, overfull households. In texts for elders, the standard critique about consumption and unruly lives is gentler, more sensitive to the meaning of things, and underplays the emotions of divestment. There is stress on the responsibility to spare the next generation and control one’s legacy. These latter texts seem to respect that downsizing in later life symbolizes a narrowing of the life world

On the dependence of galaxy morphologies on galaxy mergers

The distribution of galaxy morphological types is a key test for models of galaxy formation and evolution, providing strong constraints on the relative contribution of different physical processes responsible for the growth of the spheroidal components. In this paper, we make use of a suite of semi-analytic models to study the efficiency of galaxy mergers in disrupting galaxy discs and building galaxy bulges. In particular, we compare standard prescriptions usually adopted in semi-analytic models, with new prescriptions proposed by Kannan et al., based on results from high-resolution hydrodynamical simulations, and we show that these new implementations reduce the efficiency of bulge formation through mergers. In addition, we compare our model results with a variety of observational measurements of the fraction of spheroid-dominated galaxies as a function of stellar and halo mass, showing that the present uncertainties in the data represent an important limitation to our understanding of spheroid formation. Our results indicate that the main tension between theoretical models and observations does not stem from the survival of purely disc structures (i.e. bulgeless galaxies), rather from the distribution of galaxies of different morphological types, as a function of their stellar mass.Comment: MNRAS in press, 11 pages, 5 figure

An Investigation of Secondary Ion Yield Enhancement Using Bin2+ (n = 1, 3, 5) Primary Ions

We have investigated secondary ion yield enhancement using Bin2+ (n = 1, 3, 5) primary ions impacting phenylalanine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), cholesterol, Irganox 1010, and polymer films adsorbed on silicon and aluminum. Secondary ion yields are increased using Bi2+and Bi32+ primary ions for the molecular layers and polymers that can undergo allyl cation rearrangements. For Irganox 1010, the deprotonated molecular ion yields (m/z 1175; [M − H]−) are one to two times larger for Bi2+ and Bi32+ primary ions than for Bi+ and Bi3+ at the same primary ion velocities. In the positive ion mode, the largest fragment ion yield (m/z 899) is ∼1.5 times larger for Bi2+ ions than for Bi+. For Bi32+ the largest fragment ion yield is only ∼70% of the ion yield using Bi3+, but the secondary ion yields of the fragment ions at m/z 57 and 219 are enhanced. For polymers that can undergo allyl cation rearrangement reactions the secondary ion yield enhancements of the monomer ions range from 1.3 to 4.3. For Bi52+ primary ions, secondary ion yields were the same or slightly larger than for Bi5+ in the negative ion mass spectra for Irganox 1010, but lower in the positive ion mode. No secondary ion yield enhancements were measured on polymer samples for Bi52+. For all polymer films studied, secondary ion intensities from the oligomer regions are substantially decreased using Bin2+ (n = 1, 3, 5). We discuss differences in the ionization mechanisms for doubly and singly-charged Bi primary ion bombardment

Scaling laws of strategic behaviour and size heterogeneity in agent dynamics

The dynamics of many socioeconomic systems is determined by the decision making process of agents. The decision process depends on agent's characteristics, such as preferences, risk aversion, behavioral biases, etc.. In addition, in some systems the size of agents can be highly heterogeneous leading to very different impacts of agents on the system dynamics. The large size of some agents poses challenging problems to agents who want to control their impact, either by forcing the system in a given direction or by hiding their intentionality. Here we consider the financial market as a model system, and we study empirically how agents strategically adjust the properties of large orders in order to meet their preference and minimize their impact. We quantify this strategic behavior by detecting scaling relations of allometric nature between the variables characterizing the trading activity of different institutions. We observe power law distributions in the investment time horizon, in the number of transactions needed to execute a large order and in the traded value exchanged by large institutions and we show that heterogeneity of agents is a key ingredient for the emergence of some aggregate properties characterizing this complex system.Comment: 6 pages, 3 figure

Le Componenti della Soddisfazione delle Pubbliche Amministrazioni negli acquisti di beni e servizi: Un'Applicazione del Modello ECSI alla Realtà Consip

Obiettivo di questo lavoro è illustrare i risultati dell’indagine sulla customer satisfaction svolta dalla Consip S.p.a.. Per misurare la customer satisfaction è stato adottato il modello ECSI, dove la soddisfazione è intesa come un costrutto di natura multidimensionale non direttamente osservabile o misurabile e legato da relazioni di causalità con altri costrutti (immagine, attese, qualità percepita, valore percepito, fedeltà e reclami) anch’essi non direttamente osservabili, ma riconducibili a variabili osservate (manifeste). Lo studio delle relazioni complesse tra costrutti o variabili latenti viene effettuato per mezzo di un modello di causalità per il quale, definendo l’insieme di variabili manifeste (domande del questionario) e specificando le relazioni tra le variabili latenti (modello strutturale) e tra queste e le variabili manifeste (modello di misurazione), è possibile stimare e trattate le variabili latenti come se fossero manifeste

The Color-Magnitude Diagram of the Globular Cluster NGC 6362 and the Canonical Tilt of Horizontal Branches

In this paper we present new and accurate photometry for stars in the Galactic globular cluster NGC 6362. The color-magnitude diagram discloses two peculiarities in the distribution of stars: (1) a slightly tilted horizontal branch (HB) (Δ = 0.1 mag) and (2) a clump of stars near the red edge of the HB. We perform a detailed comparison with theoretical stellar models in both the HB and red giant branch (RGB) phases. It appears that in the moderately metal rich NGC 6362 the tilted HB can be explained as a natural product of canonical evolutionary theories, being a consequence of the minimum in the bolometric correction near 7500 K. We also investigate the effect of decreasing the efficiency of convective transport in stars climbing the RGB. Adopting Z = 0.002 and Y = 0.23, and performing a global fitting with the theoretical isochrones and zero-age HB, an age of 12 ± 1 Gyr is found, together with (m - M)V = 14.68 and E(B-V) = 0.08