The BHK Color Diagram: a New Tool to Study Young Stellar Populations

A new method to derive age differences between the various super star clusters observed in starburst galaxies using the two color diagram (B-H) vs (H-K) is presented. This method offers a quick and easy way to differentiate very young and intermediate age stellar populations even if data on extinction are unavailable. In this case, discrimination of regions younger and older than 4 Myr is feasible. With the availability of data on extinction, the time resolution can be improved significantly. The application of the method to the starbursting system Arp 299 is presented. The validity of the method is confirmed by comparing the equivalent width of the H-alpha line with the chronological map of the northern part of NGC 3690.Comment: 32 pages, 7 figures, 1 table, AJ accepte

Surface Brightness Gradients Produced by the Ring Waves of Star Formation

We compute surface brightness profiles of galactic disks for outwardly propagating waves of star formation with a view to investigate the stellar populations in ring galaxies. We consider two mechanisms which can create outwardly propagating star forming rings in a purely gaseous disk --- a self-induced wave and a density wave. We show that the surface brightness profiles produced by both scenarios of ring formation are similar and are strongly sensitive to the velocity of the wave. The results of our computations are compared with the observational quantities sensitive to the young and old stellar populations in the ring galaxies A0035-335 (the Cartwheel galaxy) and VIIZw466. The best fit to the observed radial H_alpha surface brightness distribution in the Cartwheel galaxy is obtained for a wave velocity of about 90 km/s. The red continuum brightness of the ring can be fully explained by the evolving stars present in the trailing part of the wave. However the red continuum brightness in regions internal to the ring indicates that the wave of star formation propagates in a pre-existing stellar disk in the Cartwheel. The H_alpha and K-band surface brightness profiles in VIIZw466 match the values expected from stellar populations produced by a wave of star formation propagating in a purely gaseous disk very well. We conclude that VIIZw466 is probably experiencing the first event of star formation in the disk.Comment: Uses aas2pp4.sty and epsfig.sty, 15 pages To appear in Astrophysical Journal, March 10, 199

Lower bounds for several online variants of bin packing

We consider several previously studied online variants of bin packing and prove new and improved lower bounds on the asymptotic competitive ratios for them. For that, we use a method of fully adaptive constructions. In particular, we improve the lower bound for the asymptotic competitive ratio of online square packing significantly, raising it from roughly 1.68 to above 1.75.Comment: WAOA 201

Subtle competition between ferromagnetic and antiferromagnetic order in a Mn(II) - free radical ferrimagnetic chain

The macroscopic magnetic characterization of the Mn(II) - nitronyl nitroxide free radical chain (Mn(hfac)2(R)-3MLNN) evidenced its transition from a 1-dimensional behavior of ferrimagnetic chains to a 3-dimensional ferromagnetic long range order below 3 K. Neutron diffraction experiments, performed on a single crystal around the transition temperature, led to a different conclusion : the magnetic Bragg reflections detected below 3 K correspond to a canted antiferromagnet where the magnetic moments are mainly oriented along the chain axis. Surprisingly in the context of other compounds in this family of magnets, the interchain coupling is antiferromagnetic. This state is shown to be very fragile since a ferromagnetic interchain arrangement is recovered in a weak magnetic field. This peculiar behavior might be explained by the competition between dipolar interaction, shown to be responsible for the antiferromagnetic long range order below 3 K, and exchange interaction, the balance between these interactions being driven by the strong intrachain spin correlations. More generally, this study underlines the need, in this kind of molecular compounds, to go beyond macroscopic magnetization measurements.Comment: 12 pages, 10 figures, submitted to Phys. Rev.

Radiation Hardness of Thin Low Gain Avalanche Detectors

Low Gain Avalanche Detectors (LGAD) are based on a n++-p+-p-p++ structure where an appropriate doping of the multiplication layer (p+) leads to high enough electric fields for impact ionization. Gain factors of few tens in charge significantly improve the resolution of timing measurements, particularly for thin detectors, where the timing performance was shown to be limited by Landau fluctuations. The main obstacle for their operation is the decrease of gain with irradiation, attributed to effective acceptor removal in the gain layer. Sets of thin sensors were produced by two different producers on different substrates, with different gain layer doping profiles and thicknesses (45, 50 and 80 um). Their performance in terms of gain/collected charge and leakage current was compared before and after irradiation with neutrons and pions up to the equivalent fluences of 5e15 cm-2. Transient Current Technique and charge collection measurements with LHC speed electronics were employed to characterize the detectors. The thin LGAD sensors were shown to perform much better than sensors of standard thickness (~300 um) and offer larger charge collection with respect to detectors without gain layer for fluences <2e15 cm-2. Larger initial gain prolongs the beneficial performance of LGADs. Pions were found to be more damaging than neutrons at the same equivalent fluence, while no significant difference was found between different producers. At very high fluences and bias voltages the gain appears due to deep acceptors in the bulk, hence also in thin standard detectors

On the Mixing of the Scalar Mesons f0(1370)f_0(1370), f0(1500)f_0(1500) and f0(1710)f_0(1710)

Based on a $3\times3$ mass matrix describing the mixing of the scalar states $f_0(1370)$, $f_0(1500)$ and $f_0(1710)$, the hadronic decays of the three states are investigated. Taking into account the two possible assumptions concerning the mass level order of the bare states $|N>=|u\bar{u}+d\bar{d}>/\sqrt{2}$, $|S>=|s\bar{s}>$ and $|G>=|gg>$ in the scalar sector, $M_G > M_S > M_N$ and $M_G > M_N > M_S$, we obtain the glueball-quarkonia content of the three states by solving the unlinear equations. Some predictions about the decays of the three states in two cases are presented, which can provide a stringent consistency check of the two assumptions.Comment: revtex 10 pages, 1 eps figur

Vector Bin Packing with Multiple-Choice

We consider a variant of bin packing called multiple-choice vector bin packing. In this problem we are given a set of items, where each item can be selected in one of several $D$-dimensional incarnations. We are also given $T$ bin types, each with its own cost and $D$-dimensional size. Our goal is to pack the items in a set of bins of minimum overall cost. The problem is motivated by scheduling in networks with guaranteed quality of service (QoS), but due to its general formulation it has many other applications as well. We present an approximation algorithm that is guaranteed to produce a solution whose cost is about $\ln D$ times the optimum. For the running time to be polynomial we require $D=O(1)$ and $T=O(\log n)$. This extends previous results for vector bin packing, in which each item has a single incarnation and there is only one bin type. To obtain our result we also present a PTAS for the multiple-choice version of multidimensional knapsack, where we are given only one bin and the goal is to pack a maximum weight set of (incarnations of) items in that bin

Building Bridges with Boats: Preserving Community History through Intra- and Inter-Institutional Collaboration

This chapter discusses Launching through the Surf: The Dory Fleet of Pacific City, a project which documents the historical and contemporary role of dory fishers in the life of the coastal village of Pacific City, Oregon, U.S. Linfield College’s Department of Theatre and Communication Arts, its Jereld R. Nicholson Library, the Pacific City Arts Association, the Pacific City Dorymen\u27s Association, and the Linfield Center for the Northwest joined forces to engage in a collaborative college and community venture to preserve this important facet of Oregon’s history. Using ethnography as a theoretical grounding and oral history as a method, the project utilized artifacts from the dory fleet to augment interview data, and faculty/student teams created a searchable digital archive available via open access. The chapter draws on the authors’ experiences to identify a philosophy of strategic collaboration. Topics include project development and management, assessment, and the role of serendipity. In an era of value-added services where libraries need to continue to prove their worth, partnering with internal and external entities to create content is one way for academic libraries to remain relevant to agencies that do not have direct connections to higher education. This project not only developed a positive “town and gown” relationship with a regional community, it also benefited partner organizations as they sought to fulfill their missions. The project also serves as a potential model for intra- and inter-agency collaboration for all types of libraries