Modeling multiple time scales during glass formation with phase-field crystals

The dynamics of glass formation in monatomic and binary liquids are studied numerically using a microscopic field theory for the evolution of the time-averaged atomic number density. A stochastic framework combining phase field crystal free energies and dynamic density functional theory is shown to successfully describe several aspects of glass formation over multiple time scales. Agreement with mode coupling theory is demonstrated for underdamped liquids at moderate supercoolings, and a rapidly growing dynamic correlation length is found to be associated with fragile behavior.Comment: 4+ pages, 4 figures, to appear in Physical Review Letter

Anti-feminism in Recent Apocalyptic Film

As the second millennium winds down, apocalyptic themes inform many Hollywood plots. Several recent popular films and television shows depict epochal threats from space. This essay focuses on the films Independence Day, Armageddon, Deep Impact, Contact, and The Lion King and an episode from Futurama. Extremely popular-- Armageddon was the highest grossing film released in 1998--, these films and shows beg for attention. Strikingly, three of them give prominence to father-daughter relationships (in Armageddon, the oil driller hero dominates his coming of age daughter; in Deep Impact, the journalist hero, although estranged from her father, elects to join him on the beach as a fatal tidal wave sweeps the east coast; in Contact, the radio astronomer mourns her lost father and miraculously meets him again on a magical beach at the ends of the universe). What is all of this about? Clearly something vital is going on. This article examines what the social status and fate of these cinematic daughters say about contemporary gender politics, what this focus on father-daughter relationships reveals about the political unconscious. The article highlights the odd mix of initiative and passivity that characterizes the female protagonists of these films. It traces how these works link feminism with the threat from space, showing how these films suggest that the former causes the latter. This leads to a troubling conclusion, repugnant politically and ethically. According to the politics of these films, to avoid the apocalypse, women must be re-subordinated. The article employs theoretical approaches developed in Screening the Sacred: Religion, Myth, and Ideology in Popular American Film and advanced by scholars such as Douglas Kellner, Michael Ryan, and Janice Rushing

Parametric Analysis of the Selective Laser Sintering Process

Qualitative and quantitative analyses are required to develop Selective Laser Sintering into a viable Manufacturing process. A simplified mathematical model for sintering incorporating the heat tJ;ansfer equation. and the sintering rate equation, but using temperature independent thermal properties, is presented in this paper. A practical result is the calculation of sintering depthdeftned as the depth of powder where the void fraction is less than 0.1 as a function of control parameters, such as the laser power intensity, the laser scanning velocity, and the initial bedtemperature. We derive the general behavior of laser sintering. A comparison of model predictions with laser sinterlng tests is provided.Mechanical Engineerin

The First Larval Stage of Microprosthema semilaeve (von Martens, 1872) (Crustacea: Decapoda: Stenopodidea) Obtained in the Laboratory

The first larval stage of Microprosthema semilaeve (von Martens, 1872) is described from ovigerous females collected off Sombrero Key, Florida Keys, USA, and Guana Island, British Virgin Islands, Caribbean. The larvae are characterized by a broad, triangular telson bearing posterolateral spines and an “anomuran seta,” a first maxilliped that differs markedly from the very similar (to each other) second and third maxillipeds, and the presence of the first pereiopod as a swimming appendage upon hatching, as is apparently true of all stenopodidean first stage larvae. Characters of the larvae are compared to those described from the Indian Ocean by Raje and Ranade (1978) and mistakenly attributed to this same species, and to those of stenopodidean larvae described by Lebour (1941) from Bermuda plankton. Problems in identifying adult specimens of Microprosthema from the Caribbean are discussed

Color Variation in the Caribbean Crab Platypodiella spectabilis (Herbst, 1794) (Decapoda, Brachyura, Xanthidae)

The use of color in brachyuran crab systematics, and in particular the use of subtle color differences to suggest or differentiate cryptic or morphologically similar species, is now well documented (e.g., see Campbell and Mahon 1974 for species of Leptograpsus, Williams and Felder 1989 for species of Menippe, Zimmerman and Felder 1991 for species of Sesarma). Less clearly understood is why color patterns and intensities can sometimes vary appreciably within a species, even within narrowly restricted geographic regions. An appreciation of color patterns is critical to correctly identifying species for conservation and resource management purposes, yet often color patterns and ranges are unreported, causing confusion and sometimes misidentifications. Here we document a wide range of color patterns in a small Caribbean xanthid crab based on specimens collected in essentially the same habitat at the same time of year

Artificial Reef Matrix Structures (Arms): An Inexpensive and Effective Method for Collecting Coral Reef-Associated Invertebrates

Collecting reef-associated invertebrates usually involves disturbance of the reef area, often damaging the habitat and sometimes damaging live corals. We introduce a nondestructive, inexpensive, and effective method for collecting coral reef-associated invertebrates using approximations of small coral heads constructed of concrete, PVC pipes, nylon cleaning pads, and other materials easily obtainable in most tropical (coral-rich) countries. An example showing the effectiveness of the method is presented based on fieldwork in the eastern Caribbean

The Stomatopod Alachosquilla floridensis (Manning, 1962) (Crustacea, Stomatopoda, Nannosquillidae) Reported from Guana Island, British Virgin Islands, with Observations on Color

Although color pattern can vary among and within species of the Crustacea, it can also be a conservative feature that can be very helpful in field identifications. This is often the case in the Crustacea Decapoda, where sibling species can be detected by subtle differences in color (e.g., Williams and Felder 1989, Zimmerman and Felder 1991, Knowlton and Mills 1992). Stomatopods are among the most colorful crustaceans when living. Many species show a great deal of variability (Manning 1969, Camp 1973), and knowledge of this coloration is often key to their identification in the field and in the lab (Schotte and Manning 1993). As part of an ongoing survey of the marine invertebrate fauna of Guana Island, British Virgin Islands, we collected 2 large (45 mm and 48 mm TL) females, and one male specimen (30 mm TL) of the rarely reported stomatopod species Alachosquilla floridensis (Manning 1962). To our knowledge, the species has been reported previously in the literature only 4 times (see Schotte and Manning 1993). These reports are based on a total of 8 specimens. Previous distribution records for the species include Lake Worth Inlet, Florida; Virgin Gorda, US Virgin Islands; Isla Marguerita, Venezuela; Bahia, Brazil; and Saint Giles Island and London Bridge Rock, Tobago, West Indies (Manning 1969, Schotte and Manning 1993)

A 150-million-year-old crab larva and its implications for the early rise of brachyuran crabs

True crabs (Brachyura) are the most successful group of decapod crustaceans. This success is most likely coupled to their life history, including two specialised larval forms, zoea and megalopa. The group is comparably young, starting to diversify only about 100 million years ago (mya),with a dramatic increase in species richness beginning approximately 50 mya. Early evolution of crabs is still very incompletely known. Here, we report a fossil crab larva, 150 mya, documented with up-to-date imaging techniques. It is only the second find of any fossil crab larva, but the first complete one, the first megalopa, and the oldest one (other fossil ca. 110 mya). Despite its age, the new fossil possesses a very modern morphology, being indistinguishable from many extant crab larvae. Hence, modern morphologies must have been present significantly earlier than formerly anticipated. We briefly discuss the impact of this find on our understanding of early crab evolution

First Record and Habitat Notes for the Genus Lightiella (Crustacea, Cephalocarida, Hutchinsoniellidae) from the British Virgin Islands

The crustacean class Cephalocarida, as currently understood, is comprised of five genera and ten species (Hessler and Elofsson 1996, Hessler and Wakabara 2000). Although in some instances numerous specimens have been collected in a single locale (e.g., the nearly 120 specimens of Lightiella incisa Gooding, 1963 from Puerto Rico studied by Sanders and Hessler (1964), and the numerous specimens of Hutchinsoniella macracantha Sanders, 1955 now known from Buzzards Bay, Massachusetts, see Hessler and Sanders 1973:193), most reports are based on very few specimens. For example, the original description of the genus Hutchinsoniella Sanders, 1955 was based on only eight specimens from Long Island Sound, New York (Sanders 1955); the genus Sandersiella was originally described by Shiino (1965) on the basis of only one specimen from Japan; the genus Chiltoniella Knox and Fenwick, 1977 was based on two specimens from New Zealand (Knox and Fenwick 1977), and the genus Lightiella Jones, 1961 was based on seven specimens from San Francisco Bay (Jones 1961). Lightiella moniotae was described for a single individual from New Caledonia (Cals and Delamare-Deboutteville 1970); Sandersiella calmani for two specimens from Peru (Hessler and Sanders 1973); and Sandersiella bathyalis for two specimens from the deep ocean off southwest Africa (Hessler and Sanders 1973). The single eastern Caribbean record (Barbados) of a cephalocarid also was based on two specimens (Gooding 1963), although Gooding also discussed two specimens from Puerto Rico in that account. Cephalocarids are of such interest morphologically and phylogenetically, and are found so infrequently, that their presence anywhere is noteworthy. As part of an ongoing survey of the cryptic marine invertebrates of certain Caribbean islands, we obtained a single specimen of a cephalocarid from Guana Island, British Virgin Islands, that matches most closely the description by Gooding (1963) of L. incisa. The find is of interest not only because it is the first record for the far eastern Caribbean other than Gooding’s (1963) two type specimens from Barbados, but also because of the unusual habitat in which it was found