An optical model for the microwave properties of sea ice

The complex refractive index of sea ice is modeled and used to predict the microwave signatures of various sea ice types. Results are shown to correspond well with the observed values of the complex index inferred from dielectic constant and dielectric loss measurements performed in the field, and with observed microwave signatures of sea ice. The success of this modeling procedure vis a vis modeling of the dielectric properties of sea ice constituents used earlier by several others is explained. Multiple layer radiative transfer calculations are used to predict the microwave properties of first-year sea ice with and without snow, and multiyear sea ice

Rhode Island State Council on the Arts (1979-1992): Report 02

.csv file with the outcome data for predatory trials in the restraint experimen

Snap-jaw morphology is specialized for high-speed power amplification in the Dracula ant, \u3cem\u3eMystrium camillae\u3c/em\u3e

What is the limit of animal speed and what mechanisms produce the fastest movements? More than natural history trivia, the answer provides key insight into the form-function relationship of musculoskeletal movement and can determine the outcome of predator-prey interactions. The fastest known animal movements belong to arthropods, including trap-jaw ants, mantis shrimp and froghoppers, that have incorporated latches and springs into their appendage systems to overcome the limits of muscle power. In contrast to these examples of power amplification, where separate structures act as latch and spring to accelerate an appendage, some animals use a \u27snap-jaw\u27 mechanism that incorporates the latch and spring on the accelerating appendage itself. We examined the kinematics and functional morphology of the Dracula ant, Mystrium camillae, who use a snap-jaw mechanism to quickly slide their mandibles across each other similar to a finger snap. Kinematic analysis of high-speed video revealed that snap-jaw ant mandibles complete their strike in as little as 23 μsec and reach peak velocities of 90 m s-1, making them the fastest known animal appendage. Finite-element analysis demonstrated that snap-jaw mandibles were less stiff than biting non-power-amplified mandibles, consistent with their use as a flexible spring. These results extend our understanding of animal speed and demonstrate how small changes in morphology can result in dramatic differences in performance

The evolution and functional morphology of trap-jaw ants

Key innovations are traits that allow organisms to interact with their environment in novel ways and are thought to facilitate adaptive radiation. By providing access to previously untapped resources, key innovations allow organisms to move into new ecological niches and can promote morphological diversification and speciation. I am interested in the evolution of form and function of one particular morphological innovation in the diversification of “trap-jaw” ants: power-amplified mandibles used for prey capture, nest defense, and individual escape from predators. Insects are the most diverse and numerically abundant animal group on the planet. One feature that contributed to their evolutionary success was the diversification their mouthparts. From an ancestral mandibulate condition (still found in many extant taxa), insect mouthparts have diversified into many specialized forms such as the piercing-sucking mouthparts of true bugs and various parasites, the sponging mouthparts of flies, and the extendible proboscis of butterflies and moths. This diversity has allowed insects to occupy a variety of dietary niches, including predation, herbivory, liquid feeding, and parasitism. An understanding of the relationship between structure and function of insect mouthparts is, therefore, critical for understanding their ecological success. My dissertation consists of four chapters and investigates the evolution and functional morphology the highly specialized mouthparts of trap-jaw ants. In Chapter 1, I review the current literature on trap-jaw ant taxonomy, phylogenetics, and biomechanics. The trap-jaw morphology has independently evolved at least four times in the ant family Formicidae, and, in this chapter, I highlight the areas of convergence among the four trap-jaw ant lineages. The most well studied lineage of trap-jaw ants are found in the subfamily Ponerinae, and consist of the sister genera Anochetus and Odontomachus. In Chapter 2, I present my findings from the first comprehensive worldwide phylogeny for these two trap-jaw ant genera. Using molecular sequence from four nuclear and one mitochondrial gene, I establish a phylogenetic framework for approximately half of the currently described species. Specifically, I confirm that the two genera are monophyletic sister groups, and found support for seven monophyletic clades. These trap-jaw ants diversified approximately 30 million years ago predominately in Southeast Asia, with multiple dispersal events to Australasia, the Afrotropics, and South America. Size often determines the output of animal performance systems, and examples of these scaling relationships are common throughout nature. What is unclear is if scaling relationships in musculoskeletal systems are shared within and between species. To answer this question, I examined morphological and performance scaling relationships between different sized trap-jaw ants and within a polymorphic species. I found that among species of Anochetus and Odontomachus, there is a strong and significant negative relationship between speed and body size, with larger and having longer snap durations and lower peak speeds. Contrasting with interspecific scaling relationships, the speed of mandible strikes within the polymorphic species Odontomachus turneri did not show any relationship with body size. Instead the peak kinetic energy of mandibles within and among Odontomachus species scaled with body size, suggesting that there may be stabilizing selection acting on mandible speed, but that strike energy may be determined by body size constraints. In Chapter 4, I examine the biomechanics, morphology and kinematics of the trap-jaw ant, Myrmoteras barbouri. A member of the ant subfamily Formicinae, Myrmoteras trap-jaw ants have received relatively little attention compared to other trap-jaw ant lineages and the mechanism of their spring-loaded mandibles have previously been unstudied. Using high-speed videography, I measured mandible strikes that occur in less than 1 millisecond and peak speeds of 2.6 x 104 rad·s-1. These speeds are faster than can be explained by direct muscle contraction, and confirm that Myrmoteras jaws are spring-loaded. The spring that stores the potential energy required for the strikes is a modification of the occipital margin, which bends during mandible loading. Compared with other trap-jaw ants, Myrmoteras jaws reach similar peak velocities, but accelerate over a much longer period of time, which is likely a reflection of their unique mandible mechanism

Relaxed selection underlies genome erosion in socially parasitic ant species

Inquiline ants are highly specialized and obligate social parasites that infiltrate and exploit colonies of closely related species. They have evolved many times convergently, are often evolutionarily young lineages, and are almost invariably rare. Focusing on the leaf-cutting ant genus Acromyrmex, we compared genomes of three inquiline social parasites with their free-living, closely-related hosts. The social parasite genomes show distinct signatures of erosion compared to the host lineages, as a consequence of relaxed selective constraints on traits associated with cooperative ant colony life and of inquilines having very small effective population sizes. We find parallel gene losses, particularly in olfactory receptors, consistent with inquiline species having highly reduced social behavioral repertoires. Many of the genomic changes that we uncover resemble those observed in the genomes of obligate non-social parasites and intracellular endosymbionts that branched off into highly specialized, host-dependent niches

Radiative Muon Capture on Hydrogen and the Induced Pseudoscalar Coupling

The first measurement of the elementary process $\mu^- p \rightarrow \nu_{\mu} n \gamma$ is reported. A photon pair spectrometer was used to measure the partial branching ratio ($2.10 \pm 0.22) \times 10^{-8}$ for photons of k > 60 MeV. The value of the weak pseudoscalar coupling constant determined from the partial branching ratio is $g_p(q^{2}=-0.88m_{\mu}^2) = (9.8 \pm 0.7 \pm 0.3) \cdot g_a(0)$, where the first error is the quadrature sum of statistical and systematic uncertainties and the second error is due to the uncertainty in $\lambda_{op}$, the decay rate of the ortho to para $p \mu p$ molecule. This value of g_p is $\sim$1.5 times the prediction of PCAC and pion-pole dominance.Comment: 13 pages, RevTeX type, 3 figures (encapsulated postscript), submitted to Phys. Rev. Let

Transcriptional repressor ZEB2 promotes terminal differentiation of CD8⁺ effector and memory T cell populations during infection

ZEB2 is a multi-zinc-finger transcription factor known to play a significant role in early neurogenesis and in epithelial-mesenchymal transition-dependent tumor metastasis. Although the function of ZEB2 in T lymphocytes is unknown, activity of the closely related family member ZEB1 has been implicated in lymphocyte development. Here, we find that ZEB2 expression is up-regulated by activated T cells, specifically in the KLRG1(hi) effector CD8(+) T cell subset. Loss of ZEB2 expression results in a significant loss of antigen-specific CD8(+) T cells after primary and secondary infection with a severe impairment in the generation of the KLRG1(hi) effector memory cell population. We show that ZEB2, which can bind DNA at tandem, consensus E-box sites, regulates gene expression of several E-protein targets and may directly repress Il7r and Il2 in CD8(+) T cells responding to infection. Furthermore, we find that T-bet binds to highly conserved T-box sites in the Zeb2 gene and that T-bet and ZEB2 regulate similar gene expression programs in effector T cells, suggesting that T-bet acts upstream and through regulation of ZEB2. Collectively, we place ZEB2 in a larger transcriptional network that is responsible for the balance between terminal differentiation and formation of memory CD8(+) T cells

Population of a low-spin positive-parity band from high-spin intruder states in 177Au : The two-state mixing effect

The extremely neutron-deficient isotopes 177,179Au were studied by means of in-beam γ-ray spectroscopy. Specific tagging techniques, α-decay tagging in 177Au and isomer tagging in 179Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2d3/2 and 3s1/2 proton-hole configurations, from the 1i13/2 proton-intruder configuration was observed in 177Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state

Bacillus anthracis Lethal Toxin Disrupts TCR Signaling in CD1d-Restricted NKT Cells Leading to Functional Anergy

Exogenous CD1d-binding glycolipid (α-Galactosylceramide, α-GC) stimulates TCR signaling and activation of type-1 natural killer–like T (NKT) cells. Activated NKT cells play a central role in the regulation of adaptive and protective immune responses against pathogens and tumors. In the present study, we tested the effect of Bacillus anthracis lethal toxin (LT) on NKT cells both in vivo and in vitro. LT is a binary toxin known to suppress host immune responses during anthrax disease and intoxicates cells by protective antigen (PA)-mediated intracellular delivery of lethal factor (LF), a potent metalloprotease. We observed that NKT cells expressed anthrax toxin receptors (CMG-2 and TEM-8) and bound more PA than other immune cell types. A sub-lethal dose of LT administered in vivo in C57BL/6 mice decreased expression of the activation receptor NKG2D by NKT cells but not by NK cells. The in vivo administration of LT led to decreased TCR-induced cytokine secretion but did not affect TCR expression. Further analysis revealed LT-dependent inhibition of TCR-stimulated MAP kinase signaling in NKT cells attributable to LT cleavage of the MAP kinase kinase MEK-2. We propose that Bacillus anthracis–derived LT causes a novel form of functional anergy in NKT cells and therefore has potential for contributing to immune evasion by the pathogen

Single-particle and collective structures in Cr55 and V55

Excited states in V55 and Cr55 have been populated via pn and 2n evaporation channels, respectively, following the fusion of a Ca48 beam at 172 MeV with a Be9 target. Level schemes have been deduced for the two nuclides to excitation energies of 7467 (V55) and 12226 keV (Cr55), with spins of 27/2 + and 33/2+, respectively. Negative-parity states are compared with shell-model calculations using three different effective interactions in the full fp model space. Negative-parity levels of Cr55 are explained in terms of single-particle fp-shell configurations outside N=28 and N=32 cores. Positive-parity states in both isotopes show evidence for the involvement of neutron g9/2 configurations. In the case of Cr55, a quasirotational structure based on the 1/2+[440] Nilsson orbital is observed up to the terminating state. In V55, positive-parity states do not exhibit well-developed collective features, and the observation of octupole decays is an indication of their importance in transitions from neutron g 9/2 configurations to the fp shell. Experimental results are compared with the predictions of a traditional shell model, the projected shell model, and total-Routhian-surface calculations