1,357 research outputs found
Programmable viscoelastic matrices from artificial proteins
Extracellular matrix compliance influences cellular adhesion and migration, proliferation and apoptosis,
and differentiation. Much of our current knowledge of the effects of substrate stiffness on cellular behavior is based on elastic substrates, in particular crossâlinked polyacrylamide hydrogels. Biological tissues, however, are viscoelastic and exhibit stress relaxation and energy dissipation on physiologically relevant timescales. While emerging evidence suggests that these physical properties also influence cellular behavior, materials in which viscoelasticity can be precisely engineered are currently lacking. Here, we describe programmable hydrogel matrices assembled from artificial recombinant proteins designed to be crossâlinked by covalent bonds involving cysteine residues, by association of helical domains as coiled coils, or by both mechanisms. Using these proteins, we construct chemical, physical, and chemicalâphysical hydrogel networks that deform elastically or viscoelastically depending on the type of crossâlinking (Dooling et al., Adv. Mater., 2016, 28, 4651â4657). In viscoelastic networks, the amount of stress relaxation is tuned by controlling the ratio of physical crossâlinking to chemical crosslinking, and the timescale for stress relaxation is tuned over five orders of magnitude by single point mutations to the coiledâcoil physical crossâlinking domain (Dooling and Tirrell, ACS Cent. Sci., 2016, 2,
812â819). The genetic engineering approach also allows biological activity to be encoded directly within
the protein sequence in the form of cellâadhesive domains and proteolytic cleavage sites. The capacity to program the viscoelasticity and biological activity of hydrogel matrices is anticipated to have applications in studying and engineering cellâmatrix interactions
Auditory brainstem responses in the Eastern Screech Owl: An estimate of auditory thresholds
The auditory brainstem response (ABR), a measure of neural synchrony, was used to estimate auditory sensitivity in the eastern screech owl (Megascops asio). The typical screech owl ABR waveform showed two to three prominent peaks occurring within 5 ms of stimulus onset. As sound pressure levels increased, the ABR peak amplitude increased and latency decreased. With an increasing stimulus presentation rate, ABR peak amplitude decreased and latency increased. Generally, changes in the ABR waveform to stimulus intensity and repetition rate are consistent with the pattern found in several avian families. The ABR audiogram shows that screech owls hear best between 1.5 and 6.4 kHz with the most acute sensitivity between 4â5.7 kHz. The shape of the average screech owl ABR audiogram is similar to the shape of the behaviorally measured audiogram of the barn owl, except at the highest frequencies. Our data also show differences in overall auditory sensitivity between the color morphs of screech owls
Higgs Boson Bounds in Three and Four Generation Scenarios
In light of recent experimental results, we present updated bounds on the
lightest Higgs boson mass in the Standard Model (SM) and in the Minimal
Supersymmetric extension of the Standard Model (MSSM). The vacuum stability
lower bound on the pure SM Higgs boson mass when the SM is taken to be valid up
to the Planck scale lies above the MSSM lightest Higgs boson mass upper bound
for a large amount of SUSY parameter space. If the lightest Higgs boson is
detected with a mass M_{H} < 134 GeV (150 GeV) for a top quark mass M_{top} =
172 GeV (179 GeV), it may indicate the existence of a fourth generation of
fermions. The region of inconsistency is removed and the MSSM is salvagable for
such values of M_{H} if one postulates the existence of a fourth generation of
leptons and quarks with isodoublet degenerate masses M_{L} and M_{Q} such that
60 GeV 170 GeV.Comment: 7 pages, 4 figures. To be published in Physical Review
CP Violation from Dimensional Reduction: Examples in 4+1 Dimensions
We provide simple examples of the generation of complex mass terms and hence
CP violation through dimensional reduction.Comment: 6 pages, typos corrected, 1 reference adde
Report of the Beyond the MSSM Subgroup for the Tevatron Run II SUSY/Higgs Workshop
There are many low-energy models of supersymmetry breaking parameters which
are motivated by theoretical and experimental considerations. Here, we discuss
some of the lesser-known theories of low-energy supersymmetry, and outline
their phenomenological consequences. In some cases, these theories have more
gauge symmetry or particle content than the Minimal Supersymmetric Standard
Model. In other cases, the parameters of the Lagrangian are unusual compared to
commonly accepted norms (e.g., Wino LSP, heavy gluino LSP, light gluino, etc.).
The phenomenology of supersymmetry varies greatly between the different models.
Correspondingly, particular aspects of the detectors assume greater or lesser
importance. Detection of supersymmetry and the determination of all parameters
may well depend upon having the widest possible view of supersymmetry
phenomenology.Comment: 78 pages, 49 figures, to appear in the Proceedings of the Tevatron
Run II SUSY/Higgs Workshop. Editor: J. F. Gunion; BTMSSM Convenors: M.
Chertok, H. Dreiner, G. Landsberg, J. F. Gunion, J.D. Well
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Dwarf mistletoe survey, Hebgen Lake Ranger District, Gallatin National Forest, Montana
Large areas of dwarf mistletoe-free, all-aged lodgepole pine have been identified in the West Yellowstone Basin. The option of uneven-aged management in these areas remains available to the District
The hidden sterile neutrino and the (2+2) sum rule
We discuss oscillations of atmospheric and solar neutrinos into sterile
neutrinos in the 2+2 scheme. A zeroth order sum rule requires equal
probabilities for oscillation into nu_s and nu_tau in the solar+atmospheric
data sample. Data does not favor this claim. Here we use scatter plots to
assess corrections of the zeroth order sum rule when (i) the 4 x 4 neutrino
mixing matrix assumes its full range of allowed values, and (ii) matter effects
are included. We also introduce a related "product rule". We find that the sum
rule is significantly relaxed, due to both the inclusion of the small mixing
angles (which provide a short-baseline contribution) and to matter effects. The
product rule is also dramatically altered. The observed relaxation of the sum
rule weakens the case against the 2+2 model and the sterile neutrino. To
invalidate the 2+2 model, a global fit to data with the small mixing angles
included seems to be required.Comment: 43 pages, 11 figures (same as v2, accidental replacement
Rephasing Invariants of CP and T Violation in the Four-Neutrino Mixing Models
We calculate the rephasing invariants of CP and T violation in a favorable
parametrization of the 4x4 lepton flavor mixing matrix. Their relations with
the CP- and T-violating asymmetries in neutrino oscillations are derived, and
the matter effects are briefly discussed.Comment: RevTex 9 pages. Slight changes. Phys. Rev. D (in press
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