1,840 research outputs found
Achieving a Strongly Temperature-Dependent Casimir Effect
We propose a method of achieving large temperature sensitivity in the Casimir
force that involves measuring the stable separation between dielectric objects
immersed in fluid. We study the Casimir force between slabs and spheres using
realistic material models, and find large > 2nm/K variations in their stable
separations (hundreds of nanometers) near room temperature. In addition, we
analyze the effects of Brownian motion on suspended objects, and show that the
average separation is also sensitive to changes in temperature . Finally, this
approach also leads to rich qualitative phenomena, such as irreversible
transitions, from suspension to stiction, as the temperature is varied
Designing evanescent optical interactions to control the expression of Casimir forces in optomechanical structures
We propose an optomechanical structure consisting of a photonic-crystal
(holey) membrane suspended above a layered silicon-on-insulator substrate in
which resonant bonding/antibonding optical forces created by externally
incident light from above enable all-optical control and actuation of stiction
effects induced by the Casimir force. In this way, one can control how the
Casimir force is expressed in the mechanical dynamics of the membrane, not by
changing the Casimir force directly but by optically modifying the geometry and
counteracting the mechanical spring constant to bring the system in or out of
regimes where Casimir physics dominate. The same optical response (reflection
spectrum) of the membrane to the incident light can be exploited to accurately
measure the effects of the Casimir force on the equilibrium separation of the
membrane
Neural crest contributions to the lamprey head
The neural crest is a vertebrate-specific cell population that contributes to the facial skeleton and other derivatives. We have performed focal DiI injection into the cranial neural tube of the developing lamprey in order to follow the migratory pathways of discrete groups of cells from origin to destination and to compare neural crest migratory pathways in a basal vertebrate to those of gnathostomes. The results show that the general pathways of cranial neural crest migration are conserved throughout the vertebrates, with cells migrating in streams analogous to the mandibular and hyoid streams. Caudal branchial neural crest cells migrate ventrally as a sheet of cells from the hindbrain and super-pharyngeal region of the neural tube and form a cylinder surrounding a core of mesoderm in each pharyngeal arch, similar to that seen in zebrafish and axolotl. In addition to these similarities, we also uncovered important differences. Migration into the presumptive caudal branchial arches of the lamprey involves both rostral and caudal movements of neural crest cells that have not been described in gnathostomes, suggesting that barriers that constrain rostrocaudal movement of cranial neural crest cells may have arisen after the agnathan/gnathostome split. Accordingly, neural crest cells from a single axial level contributed to multiple arches and there was extensive mixing between populations. There was no apparent filling of neural crest derivatives in a ventral-to-dorsal order, as has been observed in higher vertebrates, nor did we find evidence of a neural crest contribution to cranial sensory ganglia. These results suggest that migratory constraints and additional neural crest derivatives arose later in gnathostome evolution
Importance of SoxE in neural crest development and the evolution of the pharynx
The neural crest, a defining character of vertebrates, is of prime importance to their evolutionary origin. To understand neural crest evolution, we explored molecular mechanisms underlying craniofacial development in the basal jawless vertebrate, sea lamprey (Petromyzon marinus), focusing on the SoxE (Sox8, Sox9 and Sox10) gene family. In jawed vertebrates, these are important transcriptional regulators of the neural crest, and the loss of Sox9 causes abnormal craniofacial development. Here we report that two lamprey SoxE genes are expressed in migrating neural crest and crest-derived prechondrocytes in posterior branchial arches, whereas a third paralogue is expressed later in the perichondrium and mandibular arch. Morpholino knock-down of SoxE1 reveals that it is essential for posterior branchial arch development, although the mandibular arch is unaffected. The results show that chondrogenic function of SoxE regulators can be traced to the lamprey–gnathostome common ancestor and indicate that lamprey SoxE genes might have undergone independent duplication to have distinct functions in mandibular versus caudal branchial arches. This work sheds light on the homology of vertebrate branchial arches and supports their common origin at the base of vertebrates
Cosmic-ray Monte Carlo predictions for forward particle production in p-p, p-Pb, and Pb-Pb collisions at the LHC
We present and compare the predictions of various cosmic-ray Monte Carlo
models for the energy (dE/deta) and particle (dN/deta) flows in p-p, p-Pb and
Pb-Pb collisions at sqrt(s) = 14, 8.8, and 5.5 TeV respectively, in the range
covered by forward LHC detectors like CASTOR or TOTEM (5.2<|eta|<6.6) and ZDC
or LHCf (|eta|>8.1 for neutrals).Comment: 5 pages, 5 figs. Poster proceedings Quark-Matter'08, Jaipur. To
appear in Indian J. of Phy
Structural Information in Two-Dimensional Patterns: Entropy Convergence and Excess Entropy
We develop information-theoretic measures of spatial structure and pattern in
more than one dimension. As is well known, the entropy density of a
two-dimensional configuration can be efficiently and accurately estimated via a
converging sequence of conditional entropies. We show that the manner in which
these conditional entropies converge to their asymptotic value serves as a
measure of global correlation and structure for spatial systems in any
dimension. We compare and contrast entropy-convergence with mutual-information
and structure-factor techniques for quantifying and detecting spatial
structure.Comment: 11 pages, 5 figures,
http://www.santafe.edu/projects/CompMech/papers/2dnnn.htm
Re-evaluation of the Fijianolide/Laulimalide Chemotype Suggests an Alternate Mechanism of Action for C-15/C-20 Analogs.
Herein, we report on naturally derived microtubule stabilizers with activity against triple negative breast cancer (TNBC) cell lines, including paclitaxel, fijianolide B/laulimalide (3), fijianolide B di-acetate (4), and two new semisynthetic analogs of 3, which include fijianolide J (5) and fijianolide L (6). Similar to paclitaxel, compound 3 demonstrated classic microtubule stabilizing activity with potent (GI50 = 0.7–17 nM) antiproliferative efficacy among the five molecularly distinct TNBC cell lines. Alternatively, compounds 5 or 6, generated from oxidation of C-20 or C-15 and C-20 respectively, resulted in a unique profile with reduced potency (GI50 = 4–9 μM), but improved efficacy in some lines, suggesting a distinct mechanism of action. The C-15, C-20 di-acetate, and dioxo modifications on 4 and 6 resulted in compounds devoid of classic microtubule stabilizing activity in biochemical assays. While 4 also had no detectable effect on cellular microtubules, 6 promoted a reorganization of the cytoskeleton resulting in an accumulation of microtubules at the cell periphery. Compound 5, with a single C-20 oxo substitution, displayed a mixed phenotype, sharing properties of 3 and 6. These results demonstrate the importance of the C-15/C-20 chiral centers, which appear to be required for the potent microtubule stabilizing activity of this chemotype and that oxidation of these sites promotes unanticipated cytoskeletal alterations that are distinct from classic microtubule stabilization, likely through a distinct mechanism of action
Functional constraints on SoxE proteins in neural crest development: the importance of differential expression for evolution of protein activity
Depths and Thermal Habitat Used by Large versus Small Northern Pike in Three Minnesota Lakes
We monitored depths and temperatures used by large (>71‐cm) versus small Northern Pike Esox lucius in three north‐central Minnesota lakes with either acoustic telemetry or archival tags. Individual Northern Pike demonstrated flexibility in depths used within a season and between years. The fish had some tolerance for low levels of dissolved oxygen (<3 mg/L), but depth selection was generally constrained by low dissolved oxygen in summer and winter. The fish more fully exploited all available depths during winter and thermal turnover periods. During July and August, large Northern Pike tended to follow the thermocline into cooler water as upper water layers warmed. Selection ratios indicated that large Northern Pike preferred water temperatures of 16–21°C during August when temperatures up to 28°C were available. In two lakes providing dense overhead cover from water lilies in shallow water, small Northern Pike used warmer, shallower water compared with large fish during summer. In a third lake providing no such cover, small fish were more often in deeper, cooler water. For small Northern Pike, temperature seemed to be a secondary habitat consideration behind the presence of shallow vegetated cover. This study provided detailed temperature selection information that will be useful when considering temperature as an ecological resource for different sizes of Northern Pike.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141595/1/tafs1629.pd
Abstracts
Abstracts of papers about Giuseppe Verdi and his works, presented at joint meetings of the AIVS and Greater NY Chapter of the American Musicological Society, 1979-81 (Hepokoski, Lawton, Chusid, Hornick, Nádas, Tomlinson, Garrison, Powers), at the 1982 national meeting of the American Musicological Society (Harwood), and at an NEH-sponsored summer seminar at NYU in 1980 (Beams, Cole, Cordell, Davis, Fry, King, Mason, McCauley, Town)
- …