The jamming transition and new percolation universality classes in particulate systems with attraction

We numerically study the jamming transition in particulate systems with attraction by investigating their mechanical response at zero temperature. We find three regimes of mechanical behavior separated by two critical transitions--connectivity and rigidity percolation. The transitions belong to different universality classes than their lattice counterparts, due to force balance constraints. We also find that these transitions are unchanged at low temperatures and resemble gelation transitions in experiments on colloidal and silica gels.Comment: 4 pages, 2 figures, 2 table

Morphometric Variation during Chick Development in Interior Double-crested Cormorants (\u3ci\u3ePhalacrocorax auritus\u3c/i\u3e)

In numerous avian species, egg size is correlated to female body condition, hatchling size and nestling growth. Recent demography studies of Interior Double-crested Cormorants (Phalacrocorax auritus) suggest a migratory divide across the Great Lakes; western populations winter in the Gulf of Mexico region of the southeastern United States (Alabama, Arkansas, Louisiana, and Mississippi) with extensive catfish (Ictalurus punctatus) aquaculture, and eastern populations winter in Florida, where catfish aquaculture is not pervasive. If Double-crested Cormorants have improved their overall body condition through catfish exploitation, then egg and chick sizes should also be affected. Three breeding areas in Ontario (east, central, and west) were selected for empirical measures of size variation. During the breeding seasons of 2006 and 2007, egg, naked young, fledgling, and adult morphometric data were collected. Eggs in eastern areas (volume = 465.8 ± 3.9 cm³) were on average larger than eggs in central (volume = 458.1 ± 3.5 cm³) and western (volume = 451.7 ± 3.5 cm³) areas. However, chicks in eastern areas (culmen = 54.9 ± 0.6 mm) were smaller than chicks in central (culmen = 57.6 ± 0.4 mm) and western (culmen = 59.3 ± 0.3 mm) areas, not only at hatching, but throughout development and fledging. A comprehensive Double-crested Cormorant morphometric gradient that may suggest a potential reproductive advantage for birds exploiting aquaculture facilities is presented

Morphometric Variation during Chick Development in Interior Double-crested Cormorants (\u3ci\u3ePhalacrocorax auritus\u3c/i\u3e)

In numerous avian species, egg size is correlated to female body condition, hatchling size and nestling growth. Recent demography studies of Interior Double-crested Cormorants (Phalacrocorax auritus) suggest a migratory divide across the Great Lakes; western populations winter in the Gulf of Mexico region of the southeastern United States (Alabama, Arkansas, Louisiana, and Mississippi) with extensive catfish (Ictalurus punctatus) aquaculture, and eastern populations winter in Florida, where catfish aquaculture is not pervasive. If Double-crested Cormorants have improved their overall body condition through catfish exploitation, then egg and chick sizes should also be affected. Three breeding areas in Ontario (east, central, and west) were selected for empirical measures of size variation. During the breeding seasons of 2006 and 2007, egg, naked young, fledgling, and adult morphometric data were collected. Eggs in eastern areas (volume = 465.8 ± 3.9 cm³) were on average larger than eggs in central (volume = 458.1 ± 3.5 cm³) and western (volume = 451.7 ± 3.5 cm³) areas. However, chicks in eastern areas (culmen = 54.9 ± 0.6 mm) were smaller than chicks in central (culmen = 57.6 ± 0.4 mm) and western (culmen = 59.3 ± 0.3 mm) areas, not only at hatching, but throughout development and fledging. A comprehensive Double-crested Cormorant morphometric gradient that may suggest a potential reproductive advantage for birds exploiting aquaculture facilities is presented

The connection between polymer collapse and the onset of jamming

Previous studies have shown that the interiors of proteins are densely packed, reaching packing fractions that are as large as those found for static packings of individual amino-acid-shaped particles. How can the interiors of proteins take on such high packing fractions given that amino acids are connected by peptide bonds and many amino acids are hydrophobic with attractive interactions? We investigate this question by comparing the structural and mechanical properties of collapsed attractive disk-shaped bead-spring polymers to those of three reference systems: static packings of repulsive disks, of attractive disks, and of repulsive disk-shaped bead-spring polymers. We show that attractive systems quenched to temperatures below the glass transition $T \ll T_g$ and static packings of both repulsive disks and bead-spring polymers possess similar interior packing fractions. Previous studies have shown that static packings of repulsive disks are isostatic at jamming onset, i.e. the number of contacts $N_c$ matches the number of degrees of freedom, which strongly influences their mechanical properties. We find that repulsive polymers are hypostatic at jamming onset, but effectively isostatic when including quartic modes. While attractive disk and polymer packings are hyperstatic, we identify a definition for interparticle contacts for which they can also be considered as effectively isostatic. As a result, we show that the mechanical properties (e.g. scaling of the potential energy with excess contact number and low-frequency contribution to the density of vibrational modes) of weakly attractive disk and polymer packings are similar to those of ${\it isostatic}$ repulsive disk and polymer packings. Our results demonstrate that static packings generated via attractive collapse or compression of repulsive particles possess similar structural and mechanical properties.Comment: 17 pages, 16 figures, 2 appendice

Dissociative electron attachment to the H2O molecule. II. Nuclear dynamics on coupled electronic surfaces within the local complex potential model

We report the results of a first-principles study of dissociative electron attachment to H2O. The cross sections are obtained from nuclear dynamics calculations carried out in full dimensionality within the local complex potential model by using the multi-configuration time-dependent Hartree method. The calculations employ our previously obtained global, complex-valued, potential-energy surfaces for the three (doublet B1, doublet A1, and doublet B2) electronic Feshbach resonances involved in this process. These three metastable states of H2O- undergo several degeneracies, and we incorporate both the Renner-Teller coupling between the B1 and A1 states as well as the conical intersection between the A1 and B2 states into our treatment. The nuclear dynamics are inherently multidimensional and involve branching between different final product arrangements as well as extensive excitation of the diatomic fragment. Our results successfully mirror the qualitative features of the major fragment channels observed, but are less successful in reproducing the available results for some of the minor channels. We comment on the applicability of the local complex potential model to such a complicated resonant system.Comment: Corrected version of Phys Rev A 75, 012711 (2007

Precision surveying using very long baseline interferometry

Radio interferometry measurements were used to measure the vector baselines between large microwave radio antennas. A 1.24 km baseline in Massachusetts between the 36 meter Haystack Observatory antenna and the 18 meter Westford antenna of Lincoln Laboratory was measured with 5 mm repeatability in 12 separate experiments. Preliminary results from measurements of the 3,928 km baseline between the Haystack antenna and the 40 meter antenna at the Owens Valley Radio Observatory in California are presented