Thermal Conductivities of Unidirectional Materials

In this paper the composite thermal conductivities of unidirec tional composites are studied and expressions are obtained for pre dicting these conductivities in the directions along and normal to the filaments. In the direction along the filament an expression is presented based on the assumption that the filaments and matrix are connected in parallel. In the direction normal to the filaments composite thermal conductivity values are obtained first by utiliz ing the analogy between the response of a unidirectional composite to longitudinal shear loading and to transverse heat transfer; second by replacing the filament-matrix composite with an idealized ther mal model. The results of the shear loading analogy agree reason ably well with the results of the thermal model particularly at filament contents below about 60%. These results were also com pared to experimental data reported in the literature and good agreement was found between the data and those theoretical re sults that were derived for circular filaments arranged in a square packing array.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67863/2/10.1177_002199836700100206.pd

Rules for Computing Symmetry, Density and Stoichiometry in a Quasi-Unit-Cell Model of Quasicrystals

The quasi-unit cell picture describes the atomic structure of quasicrystals in terms of a single, repeating cluster which overlaps neighbors according to specific overlap rules. In this paper, we discuss the precise relationship between a general atomic decoration in the quasi-unit cell picture atomic decorations in the Penrose tiling and in related tiling pictures. Using these relations, we obtain a simple, practical method for determining the density, stoichiometry and symmetry of a quasicrystal based on the atomic decoration of the quasi-unit cell taking proper account of the sharing of atoms between clusters.Comment: 14 pages, 8 figure

On a Jansen leg with multiple gait patterns for reconfigurable walking platforms

Legged robots are able to move across irregular terrains and those based on 1-degree-of-freedom planar linkages can be energy efficient, but are often constrained by a limited range of gaits which can limit their locomotion capabilities considerably. This article reports the design of a novel reconfigurable Theo Jansen linkage that produces a wide variety of gait cycles, opening new possibilities for innovative applications. The suggested mechanism switches from a pin-jointed Grübler kinematic chain to a 5-degree-of-freedom mechanism with slider joints during the reconfiguration process. It is shown that such reconfigurable linkage significantly extend the capabilities of the original design, while maintaining its mechanical simplicity during normal operation, to not only produce different useful gait patterns but also to realize behaviors beyond locomotion. Experiments with an implemented prototype are presented, and their results validate the proposed approach

A straw drift chamber spectrometer for studies of rare kaon decays

We describe the design, construction, readout, tests, and performance of planar drift chambers, based on 5 mm diameter copperized Mylar and Kapton straws, used in an experimental search for rare kaon decays. The experiment took place in the high-intensity neutral beam at the Alternating Gradient Synchrotron of Brookhaven National Laboratory, using a neutral beam stop, two analyzing dipoles, and redundant particle identification to remove backgrounds

Sin Meets NuRD and Other Tails of Repression

Fuente, Carlos;Pericas, Enri

Locating the Youngest HII Regions in M82 with 7 mm Continuum Maps

We present 7mm Very Large Array continuum images of the starburst galaxy M82. On arcsecond scales, two-thirds of the 7mm continuum consists of free-free emission from HII regions. In the subarcsecond resolution map, we identify 14 compact sources, including 9 bright HII regions with N_Lyc > 10^51 sec^-1. Four of the HII regions have rising spectra, implying emission measures > 10^8 cm^-6 pc. Except for one compact source with peculiar features, all other compact radio sources are found in dust lanes and do not have optical or near-infrared continuum counterparts. Four regions of extended, high brightness (EM > 10^7 cm-6 pc) radio emission are found in our high resolution map, including some as large as ~2", or 30 pc, representing either associations of small HII regions, or sheetlike structures of denser gas. The good correlation between 7 mm emission and Spitzer IRAC 8 micron continuum-removed PAH feature suggests that PAH emission may track the recently formed OB stars. We find an excellent correlation between molecular gas and star formation, particularly dense gas traced by HCN, down to the ~ 45 pc scale in M82. We also find star formation efficiencies (SFEs) of 1-10% on the same scale, based on CO maps. The highest SFE are found in regions with the highest dense gas fractions.Comment: 18 pages, 10 figures. Accepted for publication in A

Coevolved mutations reveal distinct architectures for two core proteins in the bacterial flagellar motor

Switching of bacterial flagellar rotation is caused by large domain movements of the FliG protein triggered by binding of the signal protein CheY to FliM. FliG and FliM form adjacent multi-subunit arrays within the basal body C-ring. The movements alter the interaction of the FliG C-terminal (FliGC) "torque" helix with the stator complexes. Atomic models based on the Salmonella entrovar C-ring electron microscopy reconstruction have implications for switching, but lack consensus on the relative locations of the FliG armadillo (ARM) domains (amino-terminal (FliGN), middle (FliGM) and FliGC) as well as changes during chemotaxis. The generality of the Salmonella model is challenged by the variation in motor morphology and response between species. We studied coevolved residue mutations to determine the unifying elements of switch architecture. Residue interactions, measured by their coevolution, were formalized as a network, guided by structural data. Our measurements reveal a common design with dedicated switch and motor modules. The FliM middle domain (FliMM) has extensive connectivity most simply explained by conserved intra and inter-subunit contacts. In contrast, FliG has patchy, complex architecture. Conserved structural motifs form interacting nodes in the coevolution network that wire FliMM to the FliGC C-terminal, four-helix motor module (C3-6). FliG C3-6 coevolution is organized around the torque helix, differently from other ARM domains. The nodes form separated, surface-proximal patches that are targeted by deleterious mutations as in other allosteric systems. The dominant node is formed by the EHPQ motif at the FliMMFliGM contact interface and adjacent helix residues at a central location within FliGM. The node interacts with nodes in the N-terminal FliGc α-helix triad (ARM-C) and FliGN. ARM-C, separated from C3-6 by the MFVF motif, has poor intra-network connectivity consistent with its variable orientation revealed by structural data. ARM-C could be the convertor element that provides mechanistic and species diversity.JK was supported by Medical Research Council grant U117581331. SK was supported by seed funds from Lahore University of Managment Sciences (LUMS) and the Molecular Biology Consortium