A Catalogue of Optically Selected Cores

We present a new catalogue of 406 dense cores optically selected by using the STScI Digitized Sky Survey (DSS). In this catalogue 306 cores have neither an Embedded YSO (EYSO) nor a Pre-Main-Sequence (PMS) star, 94 cores have EYSOs (1 core has both an EYSO and a PMS star), and 6 cores have PMS star only. Our sample of dense cores in the catalogue is fairly complete within a category of northern Lynds class 5, 6 clouds, and southern Hartley et al. (1986)'s class A clouds, providing a database useful for the systematic study of dense cores. Most of the cores listed in the catalogue have diameters between $0.05 - 0.36$ pc with a mean of $\sim 0.24$ pc. The sizes ($\sim 0.33$ pc in the mean) of cores with EYSOs are found to be usually larger than the sizes ($\sim 0.22$ pc in the mean) of starless cores. The typical mean gas density of the cores is $\sim7\times 10^3 cm^{-3}$. Most of the cores are more likely elongated than spherical (mean aspect ratio: $\sim 2.4$). The ratio of the number of cores with EYSOs to the number of starless cores for our sample is about 0.3, suggesting that the typical lifetime of starless cores is $0.3-1.6$ Myr, about 3 times longer than the duration of the Class 0 and Class I phases. This lifetime is shorter than expected from models of ambipolar diffusion, by factors of 2-44.Comment: 22 pages, 8 figures, 3 tables, and to appear in ApJS. Harvard-Smithsonian Center for Astrophysic

Decoupling change from design

fied simplifying change as a critical criterion for mod-ularizing software. Successful designs are those in which a change can be accommodated by modifying a single module. There is a tacit assumption in most of the literature that once a change has been limited to a single module, the cost of making the change is essential y inconsequential. But modules have com-plexity of their own and are frequently large. Thus, making a change can be expensive, even if limited to a single module. We present a method of decomposing modules into smaller components for the purpose of supporting change. Although similar to the approach of modu-larizing programs described by Parnas, our approach is specific to decomposing modules. It is not intended to replace traditional high level modularization but rather to augment it with a second level of modulari-zation where the standard of information hiding can be relaxed. The goal of the method is to make mod-ules easier to change by decomposing them around smaller design decisions—ideally encoding only one design choice per submodule component, In this paper we show how submodule components can be used to address the issue of change. We also demonstrate how the ability to address change with submodule components is, to a large extent, indepen-dent of the design level modularization. Moreover, we show that, at least in some cases, by using submodule components the choice of high level modularization can itself be changed wit bout having to rewrite large amounts of code. Permission to make digital~ard wpy of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage, the copyright notice, the title of the publication and its date appear, and notice is given tha

Some security issues of wireless systems

Abstract. Wireless systems have found wide acceptance in many industries such as military and healthcare. These systems appear under a variety of architectures including fixed networks, cellular networks, and ad hoc networks. We survey some security problems, of interest to researchers, in wireless systems when used in these environments. Most studies of the security of these systems emphasize cryptographic aspects, we concentrate on other security aspects, such as operating systems, access control, web services, and location awareness.

Lean Six Sigma Fleet Management Model for the Optimization of Ore Transportation in Mechanized Underground Mines in Peru

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado.Mining activities around the world are undergoing constant change and modernization owing to technological and scientific advancements. Consequently, there are frequent proposals to streamline and enhance processes in mining operations. This study deals with ore transportation in mechanized mining units and aims to optimize fleet management using the Lean Six Sigma methodology to obtain a model in this specific process. The proposed method was implemented using a Lean Six Sigma instrument known as DMAIC (Define, Measure, Analyze, Improve, and Control). The case study was applied to an underground mine located in the Huancavelica region, Peru. The simulation showed that 24% of the time in the ore transport cycle is un-productive time and the improvement potential time represents 53% of the transportation process time