13,575 research outputs found
Ultrasensitivity in phosphorylation-dephosphorylation cycles with little substrate
Cellular decision-making is driven by dynamic behaviours, such as the preparations for sunrise enabled by circadian rhythms and the choice of cell fates enabled by positive feedback. Such behaviours are often built upon ultrasensitive responses where a linear change in input generates a sigmoidal change in output. Phosphorylation-dephosphorylation cycles are one means to generate ultrasensitivity. Using bioinformatics, we show that in vivo levels of kinases and phosphatases frequently exceed the levels of their corresponding substrates in budding yeast. This result is in contrast to the conditions often required by zero-order ultrasensitivity, perhaps the most well known means for how such cycles become ultrasensitive. We therefore introduce a mechanism to generate ultrasensitivity when numbers of enzymes are higher than numbers of substrates. Our model combines distributive and non-distributive actions of the enzymes with two-stage binding and concerted allosteric transitions of the substrate. We use analytical and numerical methods to calculate the Hill number of the response. For a substrate with [Formula: see text] phosphosites, we find an upper bound of the Hill number of [Formula: see text], and so even systems with a single phosphosite can be ultrasensitive. Two-stage binding, where an enzyme must first bind to a binding site on the substrate before it can access the substrate's phosphosites, allows the enzymes to sequester the substrate. Such sequestration combined with competition for each phosphosite provides an intuitive explanation for the sigmoidal shifts in levels of phosphorylated substrate. Additionally, we find cases for which the response is not monotonic, but shows instead a peak at intermediate levels of input. Given its generality, we expect the mechanism described by our model to often underlay decision-making circuits in eukaryotic cells
The mid-infrared spectrum of the transiting exoplanet HD 209458b
We report the spectroscopic detection of mid-infrared emission from the
transiting exoplanet HD 209458b. Using archive data taken with the Spitzer/IRS
instrument, we have determined the spectrum of HD 209458b between 7.46 and
15.25 microns. We have used two independent methods to determine the planet
spectrum, one differential in wavelength and one absolute, and find the results
are in good agreement. Over much of this spectral range, the planet spectrum is
consistent with featureless thermal emission. Between 7.5 and 8.5 microns, we
find evidence for an unidentified spectral feature. If this spectral modulation
is due to absorption, it implies that the dayside vertical temperature profile
of the planetary atmosphere is not entirely isothermal. Using the IRS data, we
have determined the broad-band eclipse depth to be 0.00315 +/- 0.000315,
implying significant redistribution of heat from the dayside to the nightside.
This work required development of improved methods for Spitzer/IRS data
calibration that increase the achievable absolute calibration precision and
dynamic range for observations of bright point sources.Comment: 35 pages, 12 figures, revised version accepted by the Astrophysical
Journa
Contextual classification of multispectral image data
There are no author-identified significant results in this report
Transport and magnetic properties in YBaCo2O5.45: Focus on the high-temperature transition
The electronic transport properties and the magnetic susceptibility were
measured in detail in . Close to the so-called metal-insulator
transition, strong effects of resistance relaxation, a clear thermal hysteresis
and a sudden increase of the resistance noise are observed. This is likely due
to the first order character of the transition and to the underlying phases
coexistence. Despite these out of equilibrium features, a positive and linear
magneto-resistance is also observed, possibly linked to the heterogeneity of
the state. From a magnetic point of view, the paramagnetic to ordered magnetic
state transition is observed using non linear susceptibilty. This transition
shows the characteristics of a continuous transition, and time dependent
effects can be linked with the dynamics of magnetic domains in presence of
disorder. Thus, when focusing on the order of the transitions, the electronic
one and the magnetic one can not be directly associated.Comment: accepted for publication in PR
EFFECT OF SULPHUR DIOXIDE ON GROWTH, CHLOROPHYLL AND SULPHUR CONTENTS OF TOMATO (SOLANUM LYCOPERSICUM L.)
The direct toxic effect of atmospheric pollutant such as sulphur dioxide on plants has been well documented. It is essentially a potent phytotoxic gas and its toxicity to plant is manifested in typical chronic or acute foliar symptom injury. The mode and extent of damage caused by this pollutant to tomato has not been precisely and systematically studied. Under such circumstances, the present investigation was undertaken under simulating condition to find out the possible extent of adaptability of tomato in SO2 emission of our state. The effect of varying levels of sulphur dioxide (0.25, 0.5 and 1.0 ppm) fumigated for 1 hour, 2 hours and 3 hours under simulated conditions on tomato revealed that the important traits like leaf number, leaf area, fresh weight, dry weight and chlorophyll content in leaves were adversely affected, the latter treatment (SO2 1.0 ppm with 3 hours exposure) being more uninnocuous in this regards. However, no significant variation was seen amongst the treatments in respect of tissue fresh and dry weight when compared with that of control (ambient SO2). On the other hand, sulphur content in tissues increase progressively with increasing levels of SO2 and time of fumigation and the variation observed within treatments was significant to each other. It is suggested that the lowest concentration of SO2 (0.25 ppm) used in this study is more than sufficient to bring about a significant changes in most of the parameters studied
Phase-dependent spectra in a driven two-level atom
We propose a method to observe phase-dependent spectra in resonance
fluorescence, employing a two-level atom driven by a strong coherent field and
a weak, amplitude-fluctuating field. The spectra are similar to those which
occur in a squeezed vacuum, but avoid the problem of achieving squeezing over a
solid angle. The system shows other interesting features, such as
pronounced gain without population inversion.Comment: 4 pages and 4 figures. Submitted to Phys. Rev. Let
Evaluation of Two Assessment Techniques for Adaptation to Stress
Two conceptual nursing models, Roy's adaptation model and Erickson and Swain's adaptive potential assessment model are explained, and knowledge is identified within these two assessment techniques for adaptation to stress. The purpose is to identify common, noteworthy areas of nursing science as well as areas where further development in nursing knowledge is needed. A case study is used to compare and contrast these models. When assessing adaptation to stress, one simi larity between the approaches appears to be a propositional linkage that supports the influence of developmental level on basic need satisfaction. A divergent area between the two models identifies a need for further development in nursing knowledge regarding the adaptive potential sta tus. This includes information pertaining to what an individual can reasonably do or be expected to do when contending with stressors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68651/2/10.1177_089431848900200407.pd
Remote terminal system evaluation
An Earth Resources Data Processing System was developed to evaluate the system for training, technology transfer, and data processing. In addition to the five sites included in this project two other sites were connected to the system under separate agreements. The experience of these two sites is discussed. The results of the remote terminal project are documented in seven reports: one from each of the five project sites, Purdue University, and an overview report summarizing the other six reports
Optimal squeezing, pure states, and amplification of squeezing in resonance fluorescence
It is shown that 100% squeezed output can be produced in the resonance
fluorescence from a coherently driven two-level atom interacting with a
squeezed vacuum. This is only possible for squeezed input, and is
associated with a pure atomic state, i.e., a completely polarized state. The
quadrature for which optimal squeezing occurs depends on the squeezing phase
the Rabi frequency and the atomic detuning . Pure
states are described for arbitrary not just or as in
previous work. For small values of there may be a greater degree of
squeezing in the output field than the input - i.e., we have squeezing
amplification.Comment: 6 pages & 7 figures, Submitted to Phys. Rev.
Mechanical deformation of single-crystal ZnO
The deformation behavior of bulk ZnO single crystals is studied by a combination of spherical
nanoindentation and atomic force microscopy. Results show that ZnO exhibits plastic deformation
for relatively low loads (>~4–13 mN with an ~4.2 mm radius spherical indenter). Interestingly, the
elastic–plastic deformation transition threshold depends on the loading rate, with faster loading
resulting, on average, in larger threshold values. Multiple discontinuities (so called ‘‘pop-in’’ events)
in force–displacement curves are observed during indentation loading. No discontinuities are
observed on unloading. Slip is identified as the major mode of plastic deformation in ZnO, and
pop-in events are attributed to the initiation of slip. An analysis of partial load–unload data reveals
values of the hardness and Young’s modulus of 5.060.1 and 111.264.7 GPa, respectively, for a
plastic penetration depth of 300 nm. Physical processes determining deformation behavior of ZnO
are discussed
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