The young stellar population of NGC 4214 as observed with HST. II. Results

We present the results of a detailed UV-optical study of the nearby dwarf starburst galaxy NGC 4214 using multifilter HST/WFPC2+STIS photometry. The stellar extinction is found to be quite patchy, with some areas having values of E(4405-5495)< 0.1 mag and others, associated with star forming regions, much more heavily obscured, a result which is consistent with previous studies of the nebular extinction. We determined the ratio of blue-to-red supergiants and found it to be consistent with theoretical models for the metallicity of the SMC. The stellar IMF of the field in the range 20-100 solar masses is found to be steeper than Salpeter. A number of massive clusters and associations with ages between a few and 200 million years are detected and their properties are discussed.Comment: 49 pages, 12 figures, 6 table

Economic Geography and the Evolution of Networks

An evolutionary perspective on economic geography requires a dynamic understanding of change in networks. This paper explores theories of network evolution for their use in geography and develops the conceptual framework of geographical network trajectories. It specifically assesses how tie selection constitutes the evolutionary process of retention and variation in network structure and how geography affects these mechanisms. Finally, a typology of regional network formations is used to discuss opportunities for innovation in and across regions.evolution, network trajectory, evolutionary economic geography, social network analysis, innovation

Simulations in statistical physics and biology: some applications

One of the most active areas of physics in the last decades has been that of critical phenomena, and Monte Carlo simulations have played an important role as a guide for the validation and prediction of system properties close to the critical points. The kind of phase transitions occurring for the Betts lattice (lattice constructed removing 1/7 of the sites from the triangular lattice) have been studied before with the Potts model for the values q=3, ferromagnetic and antiferromagnetic regime. Here, we add up to this research line the ferromagnetic case for q=4 and 5. In the first case, the critical exponents are estimated for the second order transition, whereas for the latter case the histogram method is applied for the occurring first order transition. Additionally, Domany's Monte Carlo based clustering technique mainly used to group genes similar in their expression levels is reviewed. Finally, a control theory tool --an adaptive observer-- is applied to estimate the exponent parameter involved in the well-known Gompertz curve. By treating all these subjects our aim is to stress the importance of cooperation between distinct disciplines in addressing the complex problems arising in biology. Contents: Chapter 1 - Monte Carlo simulations in stat. physics; Chapter 2: MC simulations in biology; Chapter 3: Gompertz equationComment: 82 pages, 33 figures, 4 tables, somewhat reduced version of the M.Sc. thesis defended in Jan. 2006 at IPICyT, San Luis Potosi, Mx. (Supervisers: Drs. R. Lopez-Sandoval and H.C. Rosu). Last sections 3.3 and 3.4 can be found at http://lanl.arxiv.org/abs/physics/041108

Design and implementation of heart rate variability measures in the time domain

The following study was conducted to design and implement computer programs to derive five time domain and two frequency domain Heart Rate Variability (HRV) measures from 24 hour Holter monitor recordings and to generate activity plots that display the variation of three of the five time domain measures and two frequency domain measures over a period of 24 hours. Working with known pre and post experimental ECG data taken from a cyclical exercise program, standard parameters in both the time and frequency domains were derived using programs designed in Labview 7.0 engineering software package. Five parameters in the time domain namely SDNN, SDNN index, SDANN, rMSSD, pNN5O, and two in the frequency domain, namely the low and high frequency band areas. The designed programs were then tested on sample data files. Results of these tests were then validated by verifying them with results calculated on statistical tools available on Matlab and MS-Excel and also against standard ranges of values for the implemented measures. The calculated results were found to lie well within the standardized ranges obtained from literature. [2] A time domain analysis was then performed on a data set that consisted of 22 files of 24 hour Holter monitor recordings. These 22 files were part of a cyclical exercise study in which 11 healthy women with ages ranging from 32 to 58 participated as subjects. Eleven files were recorded prior to the cyclical exercise program and another 11 files were recorded upon completion of the program. Each recording contained the beat to beat intervals of a normal day in the subject\u27s life. The generated results were then tested for significance using standard t-tests and Analysis of Variance (ANOVA). In summary, no significant changes among pre and post experimental HRV measure values were revealed for parameters in the time and frequency domain. But the designed programs were found to reiterate a previously performed analyses in the frequency domain on the same data set, i.e., no significant changes. The implemented programs were then modified to plot 24 hour changes with pre-selected time and frequency domain parameters by dividing the 24 hour recording into 5 minute segments and generating the HRV measures from each interval. By performing such a calculation an array of HRV measures was formed. This array contained the HRV measure for each 5 minute interval over course of 24 hours. The array was then plotted using Labview 7.0 or Matlab and the peculiarities of the plots were then compared. Trends in change between the two domains that were studied were noted and suggestions made on how to derive a better understanding of the plots. The modified programs were designed with an objective to study the changes in the time domain parameters during a 24 hour period. Due to time constraints, the study of the time plot could not be completed, but the programs to generate 24 hour changes in 3 time domain and 2 frequency domain parameters and their corresponding plots were derived successfully. The programs now await to further testing and validation. Once all applications complete testing and validation, they will comprise a valuable toolbox for Heart Rate Variability Analysis

Economic-demographic interactions in long-run growth

Cliometrics confirms that Malthus’ model of the pre-industrial economy, in which increases in productivity raise population but higher population drives down wages, is a good description for much of demographic/economic history. A contributor to the Malthusian equilibrium was the Western European Marriage Pattern, the late age of female first marriage, which promised to retard the fall of living standards by restricting fertility. The demographic transition and the transition from Malthusian economies to modern economic growth attracted many Cliometric models surveyed here. A popular model component is that lower levels of mortality over many centuries increased the returns to, or preference for, human capital investment so that technical progress eventually accelerated. This initially boosted birth rates and population growth accelerated. Fertility decline was earliest and most striking in late eighteenth century France. By the 1830s the fall in French marital fertility is consistent with a response to the rising opportunity cost of children. The rest of Europe did not begin to follow until end of the nineteenth century. Interactions between the economy and migration have been modelled with Cliometric structures closely related to those of natural increase and the economy. Wages were driven up by emigration from Europe and reduced in the economies receiving immigrants

Modeling the life and death of competing languages from a physical and mathematical perspective

Recent contributions address the problem of language coexistence as that of two species competing to aggregate speakers, thus focusing on the dynamics of linguistic traits across populations. They draw inspiration from physics and biology and share some underlying ideas -- e. g. the search for minimal schemes to explain complex situations or the notion that languages are extant entities in a societal context and, accordingly, that objective, mathematical laws emerge driving the aforementioned dynamics. Different proposals pay attention to distinct aspects of such systems: Some of them emphasize the distribution of the population in geographical space, others research exhaustively the role of bilinguals in idealized situations (e. g. isolated populations), and yet others rely extremely on equations taken unchanged from physics or biology and whose parameters bear actual geometrical meaning. Despite the sources of these models -- so unrelated to linguistics -- sound results begin to surface that establish conditions and make testable predictions regarding language survival within populations of speakers, with a decisive role reserved to bilingualism. Here we review the most recent works and their interesting outcomes stressing their physical theoretical basis, and discuss the relevance and meaning of the abstract mathematical findings for real-life situations.Comment: 22 pages, 4 figures. Fifth chapter of the book Bilingualism and Minority Languages in Europe: Current trends and developments by F. Lauchlan, M. C. Parafita Couto, ed