Theoretical mass sensitivity of Love wave and layer guided acoustic plate mode sensors

A model for the mass sensitivity of Love wave and layer guided shear horizontal acoustic plate mode (SH–APM) sensors is developed by considering the propagation of shear horizontally polarized acoustic waves in a three layer system. A dispersion equation is derived for this three layer system and this is shown to contain the dispersion equation for the two layer system of the substrate and the guiding layer plus a term involving the third layer, which is regarded as a perturbing mass layer. This equation is valid for an arbitrary thickness perturbing mass layer. The perturbation, Δν, of the wave speed for the two-layer system by a thin third layer of density, ρp and thickness Δh is shown to be equal to the mass per unit area multiplied by a function dependent only on the properties of the substrate and the guiding layer, and the operating frequency of the sensor. The independence of the function from the properties of the third layer means that the mass sensitivity of the bare, two-layer, sensor operated about any thickness of the guiding layer can be deduced from the slope of the numerically or experimentally determined dispersion curve. Formulas are also derived for a Love wave on an infinite thickness substrate describing the change in mass sensitivity due to a change in frequency. The consequences of the various formulas for mass sensing applications are illustrated using numerical calculations with parameters describing a (rigid) poly(methylmethacrylate) wave-guiding layer on a finite thickness quartz substrate. These calculations demonstrate that a layer-guided SH–APM can have a mass sensitivity comparable to, or higher, than that of Love waves propagating on the same substrate. The increase in mass sensitivity of the layer guided SH–APMs over previously studied SH–APM sensors is of significance, particularly for liquid sensing applications. The relevance of the dispersion curve to experiments using higher frequencies or frequency hopping and to experiments using thick guiding layers is discussed

Optimized Synthesis, Structural Investigations, Ligand Tuning and Synthetic Evaluation of Silyloxy-Based Alkyne Metathesis Catalysts

Nitride- and alkylidyne complexes of molybdenum endowed with triarylsilanolate ligands are excellent (pre)catalysts for alkyne-metathesis reactions of all sorts, since they combine high activity with an outstanding tolerance toward polar and/or sensitive functional groups. Structural and reactivity data suggest that this promising application profile results from a favorable match between the characteristics of the high-valent molybdenum center and the electronic and steric features of the chosen Ar3SiO groups. This interplay ensures a well-balanced level of Lewis acidity at the central atom, which is critical for high activity. Moreover, the bulky silanolates, while disfavoring bimolecular decomposition of the operative alkylidyne unit, do not obstruct substrate binding. In addition, Ar3SiO groups have the advantage that they are more stable within the coordination sphere of a high-valent molybdenum center than tert-alkoxides, which commonly served as ancillary ligands in previous generations of alkyne metathesis catalysts. From a practical point of view it is important to note that complexes of the general type [(Ar3SiO)3MoΞX] (X = N, CR; R = aryl, alkyl, Ar = aryl) can be rendered air-stable with the aid of 1,10-phenanthroline, 2,2′-bipyridine or derivatives thereof. Although the resulting adducts are themselves catalytically inert, treatment with Lewis acidic additives such as ZnCl2 or MnCl2 removes the stabilizing N-donor ligand and gently releases the catalytically active template into the solution. This procedure gives excellent results in alkyne metathesis starting from air-stable and hence user-friendly precursor complexes. The thermal and hydrolytic stability of representative molybdenum alkylidyne and -nitride complexes of this series was investigated and the structure of several decomposition products elucidated

Incorporating expression data in metabolic modeling: a case study of lactate dehydrogenase

Integrating biological information from different sources to understand cellular processes is an important problem in systems biology. We use data from mRNA expression arrays and chemical kinetics to formulate a metabolic model relevant to K562 erythroleukemia cells. MAP kinase pathway activation alters the expression of metabolic enzymes in K562 cells. Our array data show changes in expression of lactate dehydrogenase (LDH) isoforms after treatment with phorbol 12-myristate 13-acetate (PMA), which activates MAP kinase signaling. We model the change in lactate production which occurs when the MAP kinase pathway is activated, using a non-equilibrium, chemical-kinetic model of homolactic fermentation. In particular, we examine the role of LDH isoforms, which catalyze the conversion of pyruvate to lactate. Changes in the isoform ratio are not the primary determinant of the production of lactate. Rather, the total concentration of LDH controls the lactate concentration.Comment: In press, Journal of Theoretical Biology. 27 pages, 9 figure

Results of UBV Photoelectric Observations of the Early-Type Eclipsing Binary System XZ Cep

Results of the three-colour photoelectric observation of the close binary system XZ Cep, obtained at the Abastumani Astrophysical observatory, are presented.Comment: 23 pages, 3 figures, 1 tebl

Networked buffering: a basic mechanism for distributed robustness in complex adaptive systems

A generic mechanism - networked buffering - is proposed for the generation of robust traits in complex systems. It requires two basic conditions to be satisfied: 1) agents are versatile enough to perform more than one single functional role within a system and 2) agents are degenerate, i.e. there exists partial overlap in the functional capabilities of agents. Given these prerequisites, degenerate systems can readily produce a distributed systemic response to local perturbations. Reciprocally, excess resources related to a single function can indirectly support multiple unrelated functions within a degenerate system. In models of genome:proteome mappings for which localized decision-making and modularity of genetic functions are assumed, we verify that such distributed compensatory effects cause enhanced robustness of system traits. The conditions needed for networked buffering to occur are neither demanding nor rare, supporting the conjecture that degeneracy may fundamentally underpin distributed robustness within several biotic and abiotic systems. For instance, networked buffering offers new insights into systems engineering and planning activities that occur under high uncertainty. It may also help explain recent developments in understanding the origins of resilience within complex ecosystems. \ud \u

Tudor domain containing 7 (Tdrd7) is essential for dynamic ribonucleoprotein (RNP) remodeling of chromatoid bodies during spermatogenesis

In the male germline in mammals, chromatoid bodies, a specialized assembly of cytoplasmic ribonucleoprotein (RNP), are structurally evident during meiosis and haploidgenesis, but their developmental origin and regulation remain elusive. The tudor domain containing proteins constitute a conserved class of chromatoid body components. We show that tudor domain containing 7 (Tdrd7), the deficiency of which causes male sterility and age-related cataract (as well as glaucoma), is essential for haploid spermatid development and defines, in concert with Tdrd6, key biogenesis processes of chromatoid bodies. Single and double knockouts of Tdrd7 and Tdrd6 demonstrated that these spermiogenic tudor genes orchestrate developmental programs for ordered remodeling of chromatoid bodies, including the initial establishment, subsequent RNP fusion with ubiquitous processing bodies/GW bodies and later structural maintenance. Tdrd7 suppresses LINE1 retrotransposons independently of piwi-interacting RNA (piRNA) biogenesis wherein Tdrd1 and Tdrd9 operate, indicating that distinct Tdrd pathways act against retrotransposons in the male germline. Tdrd6, in contrast, does not affect retrotransposons but functions at a later stage of spermiogenesis when chromatoid bodies exhibit aggresome-like properties. Our results delineate that chromatoid bodies assemble as an integrated compartment incorporating both germline and ubiquitous features as spermatogenesis proceeds and that the conserved tudor family genes act asmaster regulators of this unique RNP remodeling,which is genetically linked to the male germline integrity in mammals

Food-web structure in relation to environmental gradients and predator-prey ratios in tank-bromeliad ecosystems

Little is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators: prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests

Effects of intragastric infusion of inosine monophosphate and l-glutamate on vagal gastric afferent activity and subsequent autonomic reflexes

In this study we investigated the effects of intragastric infusion of palatable basic taste substances (umami, sweet, and salty) on the activity of the vagal gastric afferent nerve (VGA), the vagal celiac efferent nerve (VCE), and the splanchnic adrenal efferent nerve (SAE) in anesthetized rats. To test the three selected taste groups, rats were infused with inosine monophosphate (IMP) and l-glutamate (GLU) for umami, with glucose and sucrose for sweet, and with sodium chloride (NaCl) for salty. Infusions of IMP and GLU solutions significantly increased VGA activity and induced the autonomic reflex, which activated VCE and SAE; these reflexes were abolished after sectioning of the VGA. Infusions of glucose, sucrose and NaCl solutions, conversely, had no significant effects on VGA activity. These results suggest that umami substances in the stomach send information through the VGA to the brain and play a role in the reflex regulation of visceral functions

The transcriptional response of Caenorhabditis elegans to ivermectin exposure identifies novel genes involved in the response to reduced food intake

We have examined the transcriptional response of Caenorhabditis elegans following exposure to the anthelmintic drug ivermectin (IVM) using whole genome microarrays and real-time QPCR. Our original aim was to identify candidate molecules involved in IVM metabolism and/or excretion. For this reason the IVM tolerant strain, DA1316, was used to minimise transcriptomic changes related to the phenotype of drug exposure. However, unlike equivalent work with benzimidazole drugs, very few of the induced genes were members of xenobiotic metabolising enzyme families. Instead, the transcriptional response was dominated by genes associated with fat mobilization and fatty acid metabolism including catalase, esterase, and fatty acid CoA synthetase genes. This is consistent with the reduction in pharyngeal pumping, and consequential reduction in food intake, upon exposure of DA1316 worms to IVM. Genes with the highest fold change in response to IVM exposure, cyp-37B1, mtl-1 and scl-2, were comparably up-regulated in response to short–term food withdrawal (4 hr) independent of IVM exposure, and GFP reporter constructs confirm their expression in tissues associated with fat storage (intestine and hypodermis). These experiments have serendipitously identified novel genes involved in an early response of C. elegans to reduced food intake and may provide insight into similar processes in higher organisms