The Decay of Debris Disks around Solar-Type Stars

We present a Spitzer MIPS study of the decay of debris disk excesses at 24 and 70 $\mu$m for 255 stars of types F4 - K2. We have used multiple tests, including consistency between chromospheric and X-ray activity and placement on the HR diagram, to assign accurate stellar ages. Within this spectral type range, at 24 $\mu$m, $13.6 \pm 2.8 \%$ of the stars younger than 5 Gyr have excesses at the 3$\sigma$ level or more, while none of the older stars do, confirming previous work. At 70 $\mu$m, $22.5 \pm 3.6\%$ of the younger stars have excesses at $\ge$ 3 $\sigma$ significance, while only $4.7^{+3.7}_{-2.2}$% of the older stars do. To characterize the far infrared behavior of debris disks more robustly, we double the sample by including stars from the DEBRIS and DUNES surveys. For the F4 - K4 stars in this combined sample, there is only a weak (statistically not significant) trend in the incidence of far infrared excess with spectral type (detected fractions of 21.9$^{+4.8}_{-4.3}\%$, late F; 16.5$^{+3.9}_{-3.3}\%$, G; and 16.9$^{+6.3}_{-5.0}\%$, early K). Taking this spectral type range together, there is a significant decline between 3 and 4.5 Gyr in the incidence of excesses with fractional luminosities just under $10^{-5}$. There is an indication that the timescale for decay of infrared excesses varies roughly inversely with the fractional luminosity. This behavior is consistent with theoretical expectations for passive evolution. However, more excesses are detected around the oldest stars than is expected from passive evolution, suggesting that there is late-phase dynamical activity around these stars.Comment: 46 pages. 7 figures. Accepted to Ap

The Dynamic Transition of Protein Hydration Water

Thin layers of water on biomolecular and other nanostructured surfaces can be supercooled to temperatures not accessible with bulk water. Chen et al. [PNAS 103, 9012 (2006)] suggested that anomalies near 220 K observed by quasi-elastic neutron scattering can be explained by a hidden critical point of bulk water. Based on more sensitive measurements of water on perdeuterated phycocyanin, using the new neutron backscattering spectrometer SPHERES, and an improved data analysis, we present results that show no sign of such a fragile-to-strong transition. The inflection of the elastic intensity at 220 K has a dynamic origin that is compatible with a calorimetric glass transition at 170 K. The temperature dependence of the relaxation times is highly sensitive to data evaluation; it can be brought into perfect agreement with the results of other techniques, without any anomaly.Comment: 4 pages, 3 figures. Phys. Rev. Lett. (in press

How social interactions matter when distance dies?

We consider an economic geography model with two inter-regional proximity structures, one due to trade linkages and the other due to social interactions. We investigate how the network structure of social interactions, or the social proximity structure, affects the timing of endogenous agglomeration and the spatial distribution of workers across regions. Endogenous agglomeration emerges when inter-regional trade and/or social interactions incur high transportation costs, and the uniform dispersion occurs when these costs become negligibly small (i.e., when distance dies). In many-region geography, the network structure of social proximity emerges as the determinant of the geographical distribution of workers when trade becomes freer. If social proximity is governed by geographical distance (as in ground transportation), a mono-centric concentration emerges. If geographically distant pairs of regions are “socially close” (due to, e.g., passenger transportation modes with strong distance economy such as regional airlines), then geographically multi-centric spatial distribution can be sustainable.info:eu-repo/semantics/publishedVersio

Effects of Temperature on the Toxicity to the Aquatic Biota of Waste Discharges - A Compilation of the Literature

An extensive compiliation and general evaluation of the literature is presented which describes the temperature interaction with toxicity. Recent literature is summarized and made accessible along with a few generalized relationships such that researchers may design studies in a manner that will increase the utility of their results. A detailed indexing system is employed which makes the information contained in the report accessible by author, toxicant, and text organism. Summary tables of the most pertinent literature are also presented for easy subject retrieval. It was concluded that very little uniformity in experimental design is found between experiments on temperature-toxicity relationships, and a generalized summary of the results presented in th eliterature is essentially impossible because of the inconsistencies in experimental designs. The utilization of standard bioassay procedures is highly recommened, and these procedures should be applied to experimental designs which allow the estimation of parameters related to the theoretical effects of temperature

Épidémiologie de l’Asthme et des Allergies dans les Pays de Langue Portugaise

The application of the same epidemiological methods in different countries allows important comparisons between different races and cultures. During the last decade, two large multi-centres epidemiological studies, the Portuguese Study of Allergic Diseases in Childhood (PAC study) and the International Study of Asthma and Allergies in Childhood (ISAAC study), were implemented in Portuguese speaking regions. The main objectives were to assess and compare allergic diseases prevalence. The authors stress out the significant differences observed in schoolchildren from the three continents, with different genetic and environmental background. It was found an increase trend in the prevalence of all allergic diseases, mainly rhinitis, in last decade. Rhinitis has been identified as an independent risk factor for asthma in Caucasian population

Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalogue

We present refined coordinates and proper motion data for the high proper motion (HPM) stars in the Luyten Half-Second (LHS) catalogue. The positional uncertainty in the original Luyten catalogue is typically >10" and is often >30". We have used the digital scans of the Palomar Observatory Sky Survey (POSS) I and POSS II plates to derive more accurate positions and proper motions of the objects. Out of the 4470 candidates in the LHS catalogue, 4323 objects were manually re-identified in the POSS I and POSS II scans. A small fraction of the stars were not found due to the lack of finder charts and digitized POSS II scans. The uncertainties in the revised positions are typically ~2", but can be as high as ~8" in a few cases; this is a large improvement over the original data. Cross-correlation with the Tycho-2 and Hipparcos catalogues yielded 819 candidates (with m_R < 12). For these brighter sources, the position and proper motion data have been replaced with the more accurate Tycho/Hipparcos data. In total, we have revised proper motion measurements and coordinates for 4040 stars and revised coordinates for 4330 stars, which are presented here.Comment: 108 pages. Accepted for Publication in ApJ Suppl. Some errors caused by the transcription errors in the original LHS catalogue have been corrected in this resubmission. The most current version of the catalogue is also available online at http://www.stsci.edu/~ksahu/lh

Breaking and sustaining bifurcations in SN-Invariant equidistant economy

This paper elucidates the bifurcation mechanism of an equidistant economy in spatial economics. To this end, we derive the rules of secondary and further bifurcations as a major theoretical contribution of this paper. Then we combine them with pre-existing results of direct bifurcation of the symmetric group SN [Elmhirst, 2004]. Particular attention is devoted to the existence of invariant solutions which retain their spatial distributions when the value of the bifurcation parameter changes. Invariant patterns of an equidistant economy under the replicator dynamics are obtained. The mechanism of bifurcations from these patterns is elucidated. The stability of bifurcating branches is analyzed to demonstrate that most of them are unstable immediately after bifurcation. Numerical analysis of spatial economic models confirms that almost all bifurcating branches are unstable. Direct bifurcating curves connect the curves of invariant solutions, thereby creating a mesh-like network, which appears as threads of warp and weft. The theoretical bifurcation mechanism and numerical examples of networks advanced herein might be of great assistance in the study of spatial economics.info:eu-repo/semantics/publishedVersio

Piezoresistor sensor fabrication by direct laser writing on hydrogenated amorphous silicon

In this paper we report on the 532 nm Nd:YAG laser-induced crystallization of 10 nm thick boron-doped hydrogenated amorphous silicon thin films deposited on flexible polyimide and on rigid oxidized silicon wafers by hot-wire chemical vapor deposition. The dark conductivity increased from ~10-7 -1cm-1, in the as-deposited films, to ~10 and 50 -1cm-1 after laser irradiation, on rigid and flexible substrates, respectively. Depending on type of substrate, laser power and fluence, a Raman crystalline fraction between 55 and 90% was measured in HWCVD films, which was higher than observed in rf-PECVD films (35 - 55%). Crystallite size remained small in all cases, in the range 6-8 nm. Due to a very high conductivity contrast (>7 orders of magnitude) between amorphous and crystallized regions, it was possible to define conductive paths in the a-Si:H matrix, by mounting the sample on a X-Y software-controlled movable stage under the laser beam, with no need for the usual lithography steps. The resistors scribed by direct laser writing had piezoresistive properties, with positive gauge factor ~1. The details of the laser interaction process with the Si film were revealed by scanning electron microscopy imaging.(undefined

Compact schemes in time with applications to partial differential equations

We propose a new class of fourth-and sixth-order schemes in time for parabolic and hyperbolic equations. The method follows the compact scheme methodology by elaborating implicit relations between the approximations of the function and its derivatives. We produce a series of A-stable methods with low dispersion and high accuracy. Several benchmarks for linear and non-linear Ordinary Differential Equations demonstrate the effectiveness of the method. Then a second set of numerical benchmarks for Partial Differential Equations such as convection-diffusion, Schrodinger equation, wave equation, Burgers, and Euler system give the numerical evidences of the superior advantage of the method with respect to the traditional Runge-Kutta or multistep methods.S. Clain and G.J. Machado acknowledge the financial support by Portuguese Funds through Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020. M.T. Malheiro acknowledges the financial support by Portuguese Funds through Foundation for Science and Technology (FCT) in the framework of the Projects UIDB/00013/2020 and UIDP/00013/2020 of CMAT-UM. S. Clain, G.J. Machado, and M.T. Malheiro acknowledge the fi-nancial support by FEDER - Fundo Europeu de Desenvolvimento Regional, through COMPETE 2020 - Programa Operacional Fatores de Competitividade, POCI-01-0145-FEDER-028118 and PTDC/MAT-APL/28118/2017

An a posteriori strategy for adaptive schemes in time for one-dimensional advection-diffusion transport equations

Stability condition is a more restrictive constraint that leads to unnecessary small-time steps with respect to the accuracy and results in computational time wastage. We propose a node by node adaptive time scheme to relax the stability constraint enabling a larger global time step for all the nodes. A nonlinear procedure for optimising both the schemes in time and space is proposed in view of increasing the numerical efficiency and reducing the computational time. The method is based on a four-parameter family of schemes we shall tune in function of the physical data (velocity, diffusion), the characteristic size in time and space, and the local regularly of the function leading to a nonlinear procedure. The a posteriori strategy we adopt consists in, given the solution at time t(n), computing a candidate solution with the highest accurate schemes in time and space for all the nodes. Then, for the nodes that present some instabilities, both the schemes in time and space are modified and adapted in order to preserve the stability with a large time step. The updated solution is computed with node-dependent schemes both in time and space. For the sake of simplicity, only convection-diffusion problems are addressed as a prototype with a two-parameters five-points finite difference method for the spatial discretisation together with an explicit time two-parameters four-stages Runge-Kutta method. We prove that we manage to obtain an optimal time-step algorithm that produces accurate numerical approximations exempt of non-physical oscillations.G.J. Machado and S. Clain acknowledge the financial support by FEDER -Fundo Europeu de Desenvolvimento Regional, through COMPETE 2020 -Programa Operacional Fatores de Competitividade, and the National Funds through FCT -Fundacao para a Ciencia e a Tecnologia, project no. UID/FIS/04650/2019.M.T. Malheiro acknowledge the financial support by Portuguese Funds through FCT (Fundacao para a Ciencia e a Tecnologia) within the Projects UIDB/00013/2020 and UIDP/00013/2020 of CMAT-UM.M.T. Malheiro, G.J. Machado, and S. Clain acknowledge the financial support by FEDER - Fundo Europeu de Desenvolvimento Regional, through COMPETE 2020 -Programa Operacional Fatores de Competitividade, and the National Funds through FCT -Fundacao para a Ciencia e a Tecnologia, project no. POCI-01-0145-FEDER-028118