252 research outputs found
Tropomyosin controls sarcomere-like contractions for rigidity sensing and suppressing growth on soft matrices
Cells test the rigidity of the extracellular matrix by applying forces to it through integrin adhesions. Recent measurements show that these forces are applied by local micrometre-scale contractions, but how contraction force is regulated by rigidity is unknown. Here we performed high temporal- and spatial-resolution tracking of contractile forces by plating cells on sub-micrometre elastomeric pillars. We found that actomyosin-based sarcomere-like contractile units (CUs) simultaneously moved opposing pillars in net steps of ∼2.5 nm, independent of rigidity. What correlated with rigidity was the number of steps taken to reach a force level that activated recruitment of α-actinin to the CUs. When we removed actomyosin restriction by depleting tropomyosin 2.1, we observed larger steps and higher forces that resulted in aberrant rigidity sensing and growth of non-transformed cells on soft matrices. Thus, we conclude that tropomyosin 2.1 acts as a suppressor of growth on soft matrices by supporting proper rigidity sensing
Universe from vacuum in loop-string cosmology
In this paper we study the description of the Universe based on the low
energy superstring theory modified by the Loop Quantum Gravity effects.This
approach was proposed by De Risi et al. in the Phys. Rev. D {\bf 76} (2007)
103531. We show that in the contrast with the string motivated pre-Big Bang
scenario, the cosmological realisation of the -duality transformation is not
necessary to avoid an initial singularity. In the model considered the universe
starts its evolution in the vacuum phase at time . In this phase
the scale factor , energy density and coupling of the
interactions . After this stage the universe evolves to the
non-singular hot Big Bang phase . Then the
standard classical universe emerges. During the whole evolution the scale
factor increases monotonically. We solve this model analytically. We also
propose and solve numerically the model with an additional dilaton potential in
which the universe starts the evolution from the asymptotically free vacuum
phase and then evolves non-singularly to the emerging dark energy
dominated phase with the saturated coupling constant .Comment: JHEP3 LaTeX class, 19 pages, 9 figures, v2: added some comments and
references, v3: new numerical result added, new figure
HMG1A and PPARG are differently expressed in the liver of fat and lean broilers
The expression of nine functional candidates for QT abdominal fat weight and relative abdominal fat content was investigated by real-time polymerase chain reaction (PCR) in the liver, adipose tissue, colon, muscle, pituitary gland and brain of broilers. The high mobility group AT-hook 1 (HMG1A) gene was up-regulated in liver with a ratio of means of 2.90 (P ≤ 0.01) in the «fatty» group (relative abdominal fat content 3.5 ± 0.18%, abdominal fat weight 35.4 ± 6.09 g) relative to the «lean» group (relative abdominal fat content 1.9 ± 0.56%, abdominal fat weight 19.2 ± 5.06 g). Expression of this gene was highly correlated with the relative abdominal fat content (0.70, P ≤ 0.01) and abdominal fat weight (0.70, P ≤ 0.01). The peroxisome proliferator-activated receptor gamma (PPARG) gene was also up-regulated in the liver with a ratio of means of 3.34 (P ≤ 0.01) in the «fatty» group relative to the «lean» group. Correlation of its expression was significant with both the relative abdominal fat content (0.55, P ≤ 0.05) and the abdominal fat weight (0.57, P ≤ 0.01). These data suggest that the HMG1A and PPARG genes were candidate genes for abdominal fat deposition in chickens. Searching of rSNPs in regulatory regions of the HMG1A and PPARG genes could provide a tool for gene-assisted selection
In-situ measurement of journal bearing lubricant viscosity by means of a novel ultrasonic measurement technique using matching layer
An ultrasonic viscometer was used to measure the circumferential viscosity variation in a journal bearing non-invasively. This sensing technique is based on the reflection of a shear wave at a solid-liquid boundary that depends on the viscosity of the liquid and the acoustic properties of the solid. Very little ultrasonic energy can propagate into the oil at a metal-oil interface because the acoustic mismatch is significant. Interleaving a matching layer between the metal and the lubricant enables accurate ultrasonic viscosity measurements [1] Schirru, M., Mills, R., Dwyer-Joyce, R., Smith, O., and Sutton, M. (2015). Viscosity Measurement in a Lubricant Film Using an Ultrasonically Resonating Matching Layer. Tribology Letters, 60(3) pp. 1–11.
[CrossRef], [Web of Science ®]
. This technique has been used to build a miniaturized ultrasonic viscometer that is accommodated inside a journal to obtain the circumferential viscosity profile. Four viscosity regions are identified due to the variations in the localized temperatures and loads. The results are compared with the isothermal solution of the Reynolds equations for hydrodynamic lubricated bearings. The ultrasonic viscometer locates the angle at which the maximum load occurs and the length of the loaded contact with good accuracy. Finally, the viscosity results are used to estimate the frictional power losses. It is shown that over 70% of the total losses in the journal bearing occur in the region where the load is maximum
Thermal conductivity of donor-doped GaN measured with 3ω and stationary methods
The thermal conductivity of three single crystal samples of n-type gallium nitride with electron densities of
4.0⋅10¹⁶, 2.6⋅10¹⁸, and 1.1⋅10²⁰ cm⁻³ has been determined in the temperature range 4–320 K. The measurements
were carried out within the ab plane using the stationary method. The thermal conductivity depends strongly on
the donor concentration. The analysis within the Callaway approach and the Debye model shows a significant influence
of phonon–electron scattering on the thermal conductivity of the samples. In addition, some preliminary
results obtained along the c axes of GaN layered samples are presented. The latter measurements have been carried
out using the 3ω method
Friction and wear phenomena of vegetable oil based lubricants with additives at severe sliding wear conditions
The tribological responses of palm oil and soybean oil, combined with two commercial antiwear
additives (zinc dialkyl dithiophosphate and boron compound), were investigated at a lubricant
temperature of 100 °C and under severe contact conditions in a reciprocating sliding contact. The
friction coefficient of palm oil with zinc dialkyl dithiophosphate was closest to the commercial
mineral engine oil, with a 2% difference. The soybean oil with zinc dialkyl dithiophosphate
produced a 57% improvement in wear resistance compared to its pure oil state. The existence of
boron nitride in vegetable oils was only responsive in reduction of wear rather than friction. The
response of commercial antiwear additives with vegetable oils showed a potential for the future
improvement in the performance of vegetable oils
Dark energy problem: from phantom theory to modified Gauss-Bonnet gravity
The solution of dark energy problem in the models without scalars is
presented. It is shown that late-time accelerating cosmology may be generated
by the ideal fluid with some implicit equation of state. The universe evolution
within modified Gauss-Bonnet gravity is considered. It is demonstrated that
such gravitational approach may predict the (quintessential, cosmological
constant or transient phantom) acceleration of the late-time universe with
natural transiton from deceleration to acceleration (or from non-phantom to
phantom era in the last case).Comment: LaTeX 8 pages, prepared for the Proceedings of QFEXT'05, minor
correctons, references adde
Variational Methods for Biomolecular Modeling
Structure, function and dynamics of many biomolecular systems can be
characterized by the energetic variational principle and the corresponding
systems of partial differential equations (PDEs). This principle allows us to
focus on the identification of essential energetic components, the optimal
parametrization of energies, and the efficient computational implementation of
energy variation or minimization. Given the fact that complex biomolecular
systems are structurally non-uniform and their interactions occur through
contact interfaces, their free energies are associated with various interfaces
as well, such as solute-solvent interface, molecular binding interface, lipid
domain interface, and membrane surfaces. This fact motivates the inclusion of
interface geometry, particular its curvatures, to the parametrization of free
energies. Applications of such interface geometry based energetic variational
principles are illustrated through three concrete topics: the multiscale
modeling of biomolecular electrostatics and solvation that includes the
curvature energy of the molecular surface, the formation of microdomains on
lipid membrane due to the geometric and molecular mechanics at the lipid
interface, and the mean curvature driven protein localization on membrane
surfaces. By further implicitly representing the interface using a phase field
function over the entire domain, one can simulate the dynamics of the interface
and the corresponding energy variation by evolving the phase field function,
achieving significant reduction of the number of degrees of freedom and
computational complexity. Strategies for improving the efficiency of
computational implementations and for extending applications to coarse-graining
or multiscale molecular simulations are outlined.Comment: 36 page
Engulfing tumors with synthetic extracellular matrices for cancer
available in PMC 2010 June 1.Local immunotherapies are under investigation for the treatment of unresectable tumors and sites of solid tumor resection to prevent local recurrence. Successful local therapy could also theoretically elicit systemic immune responses against cancer. Here we explored the delivery of therapeutic dendritic cells (DCs), cytokines, or other immunostimulatory factors to tumors via the use of ‘self-gelling’ hydrogels based on the polysaccharide alginate, injected peritumorally around established melanoma lesions. Peritumoral injection of alginate matrices loaded with DCs and/or an interleukin-15 superagonist (IL-15SA) around 14-day established ova-expressing B16F0 murine melanoma tumors promoted immune cell accumulation in the peritumoral matrix, and matrix infiltration correlated with tumor infiltration by leukocytes. Single injections of IL-15SA-carrying gels concentrated the cytokine in the tumor site ∼40-fold compared to systemic injection and enabled a majority of treated animals to suppress tumor growth for a week or more. Further, we found that single injections of alginate matrices loaded with IL-15SA and the Toll-like receptor ligand CpG or two injections of gels carrying IL-15SA alone could elicit comparable anti-tumor activity without the need for exogenous DCs. Thus, injectable alginate gels offer an attractive platform for local tumor immunotherapy, and facilitate combinatorial treatments designed to promote immune responses locally at a tumor site while limiting systemic exposure to potent immunomodulatory factors.United States. Defense Advanced Research Projects Agency ( (contract # W81XWH-04-C-0139)National Institutes of Health (U.S.) (NIH Grant EB007280)National Institutes of Health (U.S.) (NIH Grant U54-CA126515)National Institutes of Health (U.S.) (NIH Grant U54-CA112967)National Science Foundation (U.S.) (award 0348259
- …