Optimization of Powder Layer Density in Selective Laser Sintering

An important parameter for the overall quality of SLS parts is the density of powder layers before sintering. Previous studies have shownthatthe control of powder particle shape and size distribution can increase the density of non-packed powder beds. However, these studies concerned beds several orders of magnitude larger than the SLS layers. The purpose ofthis study. is to determine if,and to what extent, the density of thin powder layers can be ineteased. Experiments show that the density of thin layers increases from 53% to 63% when adding 30% fine powder to the coarse powder,/with a coarse-to-fine ratio of 1:10. Compared with the bulk experiments, this density improvement method is less efficient, because the particles do not arrange as efficiently, and the wall effects can become predominant.Mechanical Engineerin

Fred Gygax

https://arrow.tudublin.ie/scthebk/1008/thumbnail.jp

Evolution of group size in the dolphins and porpoises: interspecific consistency of intraspecific patterns

I investigated group size variability in dolphins and porpoises using intraspecific comparisons. Explanatory factors considered in the analysis were variables of the physical environment, the diet, and the life history of the species. Open habitat and small body size were viewed as increasing predation risk. This pattern was apparent in Risso's dolphins (Grampus griseus) and weakly apparent in bottlenose dolphins (Tursiops spp.). Group size was negatively correlated with body size in pilot whales (Globicephala spp.) and positively correlated with the openness of habitat in killer whales (Orcinus orca), striped dolphins (Stenella coeruleoalba), and common dolphins (Delphinus spp.). No such relationship was found for harbor and Dall's porpoises (Phocoena phocoena, P. dalli). Group size also seemed to vary depending on other physical measures of the habitat, which may indirectly reflect diet; group size showed U-shaped patterns if related to temperature. The predictive power of variables comprising detailed prey information on group size was variable. For example, pilot whales had smaller group sizes when they fed more on mesopelagic fish and less on mesopelagic cephalopods, and common dolphins had larger groups if they fed on varying types of fish. In most Delphinoidea species, group size could be described by the variables considered in this study. But each species showed its own pattern of correlations between group size and a specific set of explanatory variables. Thus, no general and consistent relation between group size and the other variables was found. It remains unknown whether these species-specific patterns result from a historical process or whether they are specialized adaptation

Gender representation in different languages and grammatical marking on pronouns: when beauticians, musicians, and mechanics remain men

Gygax, Gabriel, Sarrasin, Oakhill, and Garnham (2008) showed that readers form a mental representation of gender that is based on grammatical gender in French and German (i.e., masculine supposedly interpretable as a generic form) but is based on stereotypical information in English. In this study, a modification of their stimulus material was used to examine the additional potential influence of pronouns. Across the three languages, pronouns differ in their grammatical gender marking: The English they is gender neutral, the French ils is masculine, and the German sie, although interpretable as generic, is morphologically feminine. Including a later pronominal reference to a group of people introduced by a plural role name significantly altered the masculine role name’s grammatical influence only in German, suggesting that grammatical cues that match (as in French) do not have a cumulative impact on the gender representation, whereas grammatical cues that mismatch (as in German) do counteract one another. These effects indicate that subtle morphological relations between forms actually used in a sentence and other forms have an immediate impact on language processing, although information about the other forms is not necessary for comprehension and may, in some cases, be detrimental to it

A small helium liquifier which provides continuous cooling based on cycled isentropic expansion

This simple cryocooler provides a small reservoir of liquid helium at a stable temperature of 4.2K. It uses a novel adaptation of the Simon expansion cryocooler to provide continuous cooling. Operation is in a four stage cycle: (1) A closed vessel of helium under high pressure is cooled to 12K using a conventional Gifford-McMahon closed-cycle cryocooler. (2) The pressure is released adiabatically providing cooling to 4.2K. (3) Liquid helium is collected in a second, well insulated, vessel. (4) The first vessel is repressurized. The cycle time is 15-30 minutes. In this manner, a pool of liquid helium is continuously maintained in the second vessel, with a temperature stability of 0.03 degrees. The continuous cooling power available is 3mW. This design provides simplicity and reliability through the absence of any orifices or moving parts at cryogenic temperatures except for the conventional Gifford-McMahon cryocooler

High precision real-time location estimates in a real-life barn environment using a commercial ultra wideband chip

Structural changes lead to an increase in the number of dairy cows and dry sows kept per group. This has consequences in how easily a farmer can supervise his herd and may be detrimental to animal welfare, specifically regarding social relations, time budget and area of residence. An automated tracking system can support the farmer in his management activities and can provide the foundation for a scientific assessment of the welfare consequences of large groups. In this study, a relatively simple and inexpensive real time location system (RTLS) was developed with the aim of achieving precise localization of several tags (animals) in real time and in a real barn environment. The RTLS was based on the ultra-wideband (UWB) technology provided by DecaWave and was adapted for a time difference of arrival (TDoA) procedure to estimate the tags’ positions. The RTLS can handle up to a hundred tags simultaneously using a Pure ALOHA random access method at 1-second intervals. The localization of the tags was estimated in 2D on a given fixed height using a constrained Gauss-Newton algorithm to increase accuracy and stability. The performance of the overall system was evaluated in two different dairy barns. To determine the precision of the system, static and dynamic positions measured at withers height of a cow (1.5 m) and closer to the ground mimicking a lying cow were compared with a reference system (theodolite). The 2D deviations between the systems were used as a measure of precision. In addition, the scalability in respect to the number of tags and the size of the observed area was examined in situations with ten tags and the situation with 100 tags was simulated with a ten-fold increase in sampling rate. According to the field test, the system as developed can be used for the individual localization of animals. At withers height, most of the measured locations deviated less than 0.5 m from the localizations as measured by the theodolite. At lower heights, and closer to the corners of the observed area, some localization estimates were somewhat larger. This was also the case close to large metal barn infrastructure. The measured collision rate of 11% for 100 tags was low. In spite of its low price, the system as a whole is therefore promising and ready for a next step, which should include the observation of large groups of real animals on working farms

Observaciones sobre el orígen de la polis en Licia

A comienzos del siglo III a.C. encontramos en Licia poleis que, pese a presentar algunas particularidades en sus instituciones, son muy similares a la mayoría de poleis del resto de Asia Menor. A fin de estudiar su origen analizamos la evolución de los patrones de asentamiento entre época clásica y helenística, las relaciones entre las ciudades y la periferia rural, así como la situación política en el siglo IV a.e. en tiempos de la dominación persa. Algunos de los cambios que se observan en los patrones de asentamiento y el surgimiento de una población rural estrechamente vinculada a las ciudades, no parecen ser la causa, sino más bien la consecuencia del nacimiento de la polis, mientras que determinadas circunstancias políticas parecen haber tenido un peso especial en su formación. El lugar inusual que ocupan los perioikoi se explica por este particular origen de las poleis licias.At the beginning of the 3rd century B.C., the poleis in Lycia, although presenting some distinctive feautures in their institutions, are very similar to most of the poleis in Asia Minor. In order to study their origin, we analyze the evolution of the patterns of settlement between classical and Hellenistic times, the relationships between the cities and their rural peripheries, as well as the political situation under Persian domination in the 4th century B.e. Some of the changes in the patterns of settlement and the emergence of a rural population closely bound to the cities, do not seem to be the causes, but rather the consequences, of the rise of the poleis. Instead of these, certain political circumstances may have played a special role in their formation. The ambiguous status of the perioikoi might be explained, thus, by this particular origin of the Lycian poleis

Lourdeur de texte et féminisation

Dans notre étude, nous avons testé l’idée, avancée par l’Académie française (2002), que la féminisation du langage alourdissait le texte. Pour cela, nous avons fait lire à 40 étudiantes et étudiants cinq descriptions de différentes professions. Pour chacune de ces professions, quatre descriptions différentes ont été rédigées: une version avec la profession au masculin, une avec la profession au féminin et deux versions avec la profession sous formes épicènes. La vitesse de lecture des descriptions de professions sous une forme épicène ou féminine, même si celleci était plus lente à la première occurrence du nom de métier, retrouvait son rythme normal, ceci dès la deuxième occurrence, indiquant un effet d’habituation. Les résultats indiquent par ailleurs que la féminisation des noms de métiers ne joue pas de rôle quant à la valorisation ou la dévalorisation de ces métiers.In this paper, we tested the idea, raised by the Académie française (2002), that writing role names in both masculine and feminine forms would hinder reading. We presented 40 participants with different texts focused on several professions. The role names were written in one of four grammatical forms : masculine, feminine, or one of two epicène forms (i.e., mécanicien-ne-s or mécaniciens et mécaniciennes). Our study shows that although reading speed was slower on the first encounter of the role names when written in the epicène and feminine form, on the second and third encounter, the speed reached a normal reading speed, suggesting a rapid habituation effect. We also did not find any hint of devaluation of the role names due to the grammatical form of the role names