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Search Results: 1 - 10 of 118771 matches for " Spencer T. Behmer "
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Plant phloem sterol content: forms, putative functions, and implications for phloem-feeding insects
Spencer T. Behmer,Robert J. Grebenok
Frontiers in Plant Science , 2013, DOI: 10.3389/fpls.2013.00370
Abstract: All eukaryotes contain sterols, which serve as structural components in cell membranes, and as precursors for important hormones. Plant vegetative tissues are known to contain mixtures of sterols, but very little is known about the sterol composition of phloem. Plants are food for many animals, but plant-feeding arthropods (including phloem-feeding insets) are unique among animals in that they have lost the ability to synthesize sterols, and must therefore acquire these essential nutrients from their food, or via endosymbionts. Our paper starts by providing a very brief overview of variation in plant sterol content, and how different sterols can affect insect herbivores, including those specializing on phloem. We then describe an experiment, where we bulk collected phloem sap exudate from bean and tobacco, and analyzed its sterol content. This approach revealed two significant observations concerning phloem sterols. First, the phloem exudate from each plant was found to contain sterols in three different fractions – free sterols, sterols conjugated to lipids (acylated), and sterols conjugated to carbohydrates (glycosylated). Second, for both plants, cholesterol was identified as the dominant sterol in each phloem exudate fraction; the remaining sterols in each fraction were a mixture of common phytosterols. We discuss our phloem exudate sterol profiles in a plant physiology/biochemistry context, and how it relates to the nutritional physiology/ecology of phloem-feeding insects. We close by proposing important next steps that will advance our knowledge concerning plant phloem sterol biology, and how phloem-sterol content might affect phloem-feeding insects.
Seasonality Directs Contrasting Food Collection Behavior and Nutrient Regulation Strategies in Ants
Steven C. Cook,Micky D. Eubanks,Roger E. Gold,Spencer T. Behmer
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0025407
Abstract: Long-lived animals, including social insects, often display seasonal shifts in foraging behavior. Foraging is ultimately a nutrient consumption exercise, but the effect of seasonality per se on changes in foraging behavior, particularly as it relates to nutrient regulation, is poorly understood. Here, we show that field-collected fire ant colonies, returned to the laboratory and maintained under identical photoperiod, temperature, and humidity regimes, and presented with experimental foods that had different protein (p) to carbohydrate (c) ratios, practice summer- and fall-specific foraging behaviors with respect to protein-carbohydrate regulation. Summer colonies increased the amount of food collected as the p:c ratio of their food became increasingly imbalanced, but fall colonies collected similar amounts of food regardless of the p:c ratio of their food. Choice experiments revealed that feeding was non-random, and that both fall and summer ants preferred carbohydrate-biased food. However, ants rarely ate all the food they collected, and their cached or discarded food always contained little carbohydrate relative to protein. From a nutrient regulation strategy, ants consumed most of the carbohydrate they collected, but regulated protein consumption to a similar level, regardless of season. We suggest that varied seasonal food collection behaviors and nutrient regulation strategies may be an adaptation that allows long-lived animals to meet current and future nutrient demands when nutrient-rich foods are abundant (e.g. spring and summer), and to conserve energy and be metabolically more efficient when nutritionally balanced foods are less abundant.
A Dietary Test of Putative Deleterious Sterols for the Aphid Myzus persicae
Sophie Bouvaine, Marie-Line Faure, Robert J. Grebenok, Spencer T. Behmer, Angela E. Douglas
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0086256
Abstract: The aphid Myzus persicae displays high mortality on tobacco plants bearing a transgene which results in the accumulation of the ketosteroids cholestan-3-one and cholest-4-en-3-one in the phloem sap. To test whether the ketosteroids are the basis of the plant resistance to the aphids, M. persicae were reared on chemically-defined diets with different steroid contents at 0.1–10 μg ml?1. Relative to sterol-free diet and dietary supplements of the two ketosteroids and two phytosterols, dietary cholesterol significantly extended aphid lifespan and increased fecundity at one or more dietary concentrations tested. Median lifespan was 50% lower on the diet supplemented with cholest-4-en-3-one than on the cholesterol-supplemented diet. Aphid feeding rate did not vary significantly across the treatments, indicative of no anti-feedant effect of any sterol/steroid. Aphids reared on diets containing equal amounts of cholesterol and cholest-4-en-3-one showed fecundity equivalent to aphids on diets containing only cholesterol. Aphids were reared on diets that reproduced the relative steroid abundance in the phloem sap of the control and modified tobacco plants, and their performance on the two diet formulations was broadly equivalent. We conclude that, at the concentrations tested, plant ketosteroids support weaker aphid performance than cholesterol, but do not cause acute toxicity to the aphids. In plants, the ketosteroids may act synergistically with plant factors absent from artificial diets but are unlikely to be solely responsible for resistance of modified tobacco plants.
Transverse Singularities of Minimal Two-Valued Graphs in Arbitrary Codimension
Spencer T. Hughes
Mathematics , 2014,
Abstract: We prove some epsilon regularity results for n-dimensional minimal two-valued Lipschitz graphs. The main theorems imply uniqueness of tangent cones and regularity of the singular set in a neighbourhood of any point at which at least one tangent cone is equal to a pair of transversely intersecting multiplicity one n-dimensional planes, and in a neighbourhood of any point at which at which at least one tangent cone is equal to a union of four distinct multiplicity one n-dimensional half-planes that meet along an (n-1) - dimensional axis. The key ingredient is a new Excess Improvement Lemma obtained via a blow-up method (inspired by the work of L. Simon on the singularities of `multiplicity one' classes of minimal submanifolds) and which can be iterated unconditionally. We also show that any tangent cone to an n-dimensional minimal two-valued Lipschitz graph that is translation invariant along an (n-1) or (n-2)- dimensional subspace is indeed a cone of one of the two aforementioned forms, which yields a global decomposition result for the singular set
Spontaneous symmetry breaking of a hyperbolic sigma model in three dimensions
T. Spencer,M. R. Zirnbauer
Mathematics , 2004, DOI: 10.1007/s00220-004-1223-3
Abstract: Non-linear sigma models that arise from the supersymmetric approach to disordered electron systems contain a non-compact bosonic sector. We study the model with target space H^2, the two-hyperboloid with isometry group SU(1,1), and prove that in three dimensions moments of the fields are finite in the thermodynamic limit. Thus the non-compact symmetry SU(1,1) is spontaneously broken. The bound on moments is compatible with the presence of extended states.
On Entropy Bumps for Calderón-Zygmund Operators
Michael T. Lacey,Scott Spencer
Mathematics , 2015, DOI: 10.1515/conop-2015-0003
Abstract: We study two weight inequalities in the recent innovative language of `entropy' due to Treil-Volberg. The inequalities are extended to $ L ^{p}$, for $ 1< p \neq 2 < \infty $, with new short proofs. A result proved is as follows. Let $ \varepsilon $ be a monotonic increasing function on $ (1, \infty)$ which satisfy $ \int _{1} ^{\infty} \frac {dt} {\varepsilon (t) t} = 1$. Let $ \sigma $ and $ w$ be two weights on $ \mathbb R ^{d}$. If this supremum is finite, for a choice of $ 1< p < \infty $, $$ \sup _{Q} \biggl[ \frac {\sigma (Q)} {\lvert Q\rvert} \biggr]^{p-1} \frac {\int _{Q} M (\sigma \chi_{Q})} {\sigma (Q)} \cdot \frac {w (Q)} {\lvert Q\rvert}\biggl[ \frac {\int _{Q} M (w \chi_{Q})} {w (Q)}\biggr]^{p-1} < \infty, $$ then any Calder\'on-Zygmund operator $ T$ satisfies the bound $ \lVert T _{\sigma} f \rVert _{L ^{p} (w)} \lesssim \lVert f\rVert _{L ^{p} (\sigma)} $.
Air Plasma Spray for First Aid  [PDF]
Spencer Kuo
Open Journal of Emergency Medicine (OJEM) , 2016, DOI: 10.4236/ojem.2016.43010
Abstract: Hemorrhage during trauma occurred in emergency situations is a significant challenge. It may be life threatening if it is not treated swiftly. A new device which can effectively stop bleeding to save life of injured person, especially in battlefield situations and accidents, is presented. A plasma generator is designed to generate a low temperature air plasma spray for treating wounds. The spectral spike at 777.4 nm in the emission spectrum of the plasma plume and the spatial distribution of this emission line’s spectral intensity indicate that abundant atomic oxygen is generated and sprays out of the generator by about 25 mm. Atomic oxygen carried by the plasma spray can quickly activate the cascading of coagulation processes and works as dry disinfectant to advance healing. Tests on blood droplets reveal the strong dependence of blood clotting on the amount of atomic oxygen applied in the plasma treatment, which is maneuvered by increasing the plasma treatment time or decreasing the exposure distance; in both approaches, the degree of blood clotting increases. Treated smeared blood samples show that an increase of the erythrocyte concentration and a drastic decrease of the platelet count are also correlated to the increase of atomic oxygen dose applied in the plasma treatment. The results reveal the mechanisms of air plasma blood coagulation and wound healing. As animal models, pigs were used in the tests of stopping wound bleeding from a cross cut in the ham area, from a hole in an ear’s saphenous vein, and from cuts to arteries in an ear and in a real leg, all stopped swiftly. Moreover, both artery cuts were secure to remove tourniquet; downgrade of tourniquet necessary wound in under 2 minutes was demonstrated. The healing progress of cross cut wounds was observed. The healing time was shortened to about half. This battery power plasma spray can be carried to or placed at anywhere available for first aid applications. It stops bleeding swiftly to save life, and also downgrades tourniquet necessary wound to extend the golden period of saving the remaining part below tourniquet.
On Hemostasis of Cold Atmospheric Air Plasma  [PDF]
Spencer Kuo
Open Journal of Emergency Medicine (OJEM) , 2018, DOI: 10.4236/ojem.2018.64012
Abstract: The efficacy and mechanism of a cold atmospheric-pressure air plasma (CAAP), which carries abundant atomic oxygen (OI), on blood coagulation are studied. The tests on sodium citrate mixed blood-droplet samples show that 1) The heat delivered by the CAAP has no impact on the observed clot formation, 2) Plasma effluent activates platelets to promote coagulation state and cascade, and 3) The degree of clotting increases with the OI flux delivered by the CAAP. The full clotting time is shortened from about 25 minutes of the natural clotting time to about 16 s of the CAAP treatment time. The tests on smeared blood samples show that the reduction of the platelet count and the increase of RBC count are proportional to the applied OI flux. In vivo tests, using swine as nimal model, swift hemostasis of large and deep cut wounds on the back by the CAAP treatment was demonstrated. A cut artery was sealed completely with 25 s treatment. The pressure applied by a finger on the cut artery could be removed immediately after the treatment and there was no re-bleed. Based on the in vitro test results and the animal model trials, CAAP coagulation mechanism is presented.
The Refinement of Ipsilateral Eye Retinotopic Maps Is Increased by Removing the Dominant Contralateral Eye in Adult Mice
Spencer L. Smith,Joshua T. Trachtenberg
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0009925
Abstract: Shortly after eye opening, initially disorganized visual cortex circuitry is rapidly refined to form smooth retinotopic maps. This process asymptotes long before adulthood, but it is unknown whether further refinement is possible. Prior work from our lab has shown that the retinotopic map of the non-dominant ipsilateral eye develops faster when the dominant contralateral eye is removed. We examined whether input from the contralateral eye might also limit the ultimate refinement of the ipsilateral eye retinotopic map in adults. In addition, we examined whether the increased refinement involved the recruitment of adjacent cortical area.
Hemispheric biases and the control of visuospatial attention: an ERP study
Kevin M Spencer, Marie T Banich
BMC Neuroscience , 2005, DOI: 10.1186/1471-2202-6-51
Abstract: Consistent with our hypothesis, flanker interference effects were found on the N2c event-related brain potential and error rate for LH-biased individuals in the Attend-LVF condition. The error rate effect was correlated with the degree of hemispheric utilization bias for the LH-Bias group.We conclude that hemispheric utilization bias can enhance a hemisphere's contralateral attentional bias, at least for individuals with a LH utilization bias. Hemispheric utilization bias may play an important and largely unrecognized role in visuospatial attention.In this study we investigated the hypothesis that the control of spatial attention is influenced by hemispheric utilization bias, a characteristic bias of individuals to utilize one hemisphere more than the other for information processing [1]. Spatial selective attention is commonly thought to be mediated by a network in which attentional control systems based in prefrontal and posterior parietal areas modulate processing in perceptual areas [2,3]. Each of the cerebral hemispheres contains a set of mechanisms for attentional control and perceptual representation [4,5], which may be capable of operating independently in the intact brain [6]. These hemispheric attention systems appear to have mutually inhibitory biases that compete to direct attention to contralateral space, with the left hemisphere (LH) having a stronger and/or more focused intrinsic bias than the right hemisphere (RH) [7].Evidence for interhemispheric attentional competition comes from studies showing asymmetrical gradients in spatial attention in healthy individuals [8,9], split-brain patients [10-12], and neglect patients [13,14]. Also in neglect patients, disruption of the contralesional hemisphere by a subsequent stroke [15] or transcranial magnetic stimulation (TMS) [16] can cause recovery from neglect symptoms, consistent with the lesioned hemisphere being released from inhibition by the contralesional hemisphere. Furthermore, in healthy individual
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