119 research outputs found
Poisson's ratio in composite elastic media with rigid rods
We study the elastic response of composites of rods embedded in elastic
media. We calculate the micro-mechanical response functions, and bulk elastic
constants as functions of rod density. We find two fixed points for Poisson's
ratio with respect to the addition of rods in 3D composites: there is an
unstable fixed point for Poisson's ratio=1/2 (an incompressible system) and a
stable fixed point for Poisson's ratio=1/4 (a compressible system). We also
derive an approximate expression for the elastic constants for arbitrary rod
density that yields exact results for both low and high density. These results
may help to explain recent experiments [Physical Review Letters 102, 188303
(2009)] that reported compressibility for composites of microtubules in F-actin
networks.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Mechanics and force transmission in soft composites of rods in elastic gels
We report detailed theoretical investigations of the micro-mechanics and bulk
elastic properties of composites consisting of randomly distributed stiff
fibers embedded in an elastic matrix in two and three dimensions. Recent
experiments published in Physical Review Letters [102, 188303 (2009)] have
suggested that the inclusion of stiff microtubules in a softer, nearly
incompressible biopolymer matrix can lead to emergent compressibility. This can
be understood in terms of the enhancement of the compressibility of the
composite relative to its shear compliance as a result of the addition of stiff
rod-like inclusions. We show that the Poisson's ratio of such a composite
evolves with increasing rod density towards a particular value, or {\em fixed
point}, independent of the material properties of the matrix, so long as it has
a finite initial compressibility. This fixed point is in three
dimensions and in two dimensions. Our results suggest an important
role for stiff filaments such as microtubules and stress fibers in cell
mechanics. At the same time, our work has a wider elasticity context, with
potential applications to composite elastic media with a wide separation of
scales in stiffness of its constituents such as carbon nanotube-polymer
composites, which have been shown to have highly tunable mechanics.Comment: 10 pages, 8 figure
Statistical Isotropy violation of the CMB brightness fluctuations
Certain anomalies at large angular scales in the cosmic microwave background
measured by WMAP have been suggested as possible evidence of breakdown of
statistical isotropy(SI). Most CMB photons free-stream to the present from the
surface of last scattering. It is thus reasonable to expect statistical
isotropy violation in the CMB photon distribution observed now to have
originated from SI violation in the baryon-photon fluid at last scattering, in
addition to anisotropy of the primordial power spectrum studied earlier in
literature.
We consider the generalized anisotropic brightness distribution fluctuations,
(at conformal time ) in contrast to the
SI case where it is simply a function of and . The brightness fluctuations expanded in Bipolar Spherical Harmonic
(BipoSH) series, can then be written as where terms encode deviations from statistical isotropy. We
study the evolution of from
non-zero terms at last
scattering. Similar to the SI case, power at small spherical harmonic (SH)
multipoles of at the last
scattering, is transferred to at
larger SH multipoles. The structural similarity is more apparent in the
asymptotic expression for large values of the final SH multipoles. This
formalism allows an elegant identification of any SI violation observed today
to a possible origin in the SI violation present in the baryon-photon fluid
(eg., due to the presence of significant magnetic field).Comment: 14 pages, 4 figures, added illustrative example of SI violation in
baryon-photon fluid, matches version accepted for publication in Phys. Rev.
Synergistic Hepatoprotective Effect of Methanolic Extracts of Urtica Dioica LINN. Leaves and Silymarin CCL4 - Induced Hepatic Damage in HEPG2 Cells
In this current study, the methanolic leaves extract of Urtica dioica Linn. (UDLE-M) was tested for its hepatoprotective and antioxidant properties. The extract's hepatoprotective activity was assessed in HepG2 cell lines against CCl4-causedhepatic injury. Additionally, in order to assess the antioxidant activityof UDLE-M in vitro, the assessment of total antioxidant activity was looked at.The synergistic effect of UDLE-M + Silymarin was also investigated in HepG2 cell lines. The extract exhibited noteworthy antioxidant activity, matching that of common antioxidant chemicals such as BHA (Butylated hydroxyanisole) and α-tocopherol, according to the data. A notable hepatoprotective profile was also noted, with an enhanced level of % cell viability suggesting that the dose of 110 µg/mL would result in the highest hepatoprotection. A significant synergistic hepatoprotective effect had also been observed for UDLE-M + Silymarin
Mechanochemical synthesis of a new triptycene-based imine-linked covalent organic polymer for degradation of organic dye
In the present work, a novel triptycene-based imine-linked covalent organic polymer (TP-COP) was designed and synthesized via room-temperature, solvent-free mechanochemical grinding. The as-synthesized TP-COP material was fully characterized by Fourier transform infrared spectroscopy, solid-state NMR, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Brunauer-Emmett-Teller method, thermogravimetric analysis, diffuse reflectance spectroscopy (DRS), and electron paramagnetic resonance (EPR). The HRTEM image of TP-COP clearly indicates the presence of graphene-like layered morphology (exfoliated layers). The DRS study reveals that TP-COP exhibited a low optical band gap value of 2.49 eV, implying its semiconducting nature. Further, the EPR study confirmed the semiconducting behavior of TP-COP through the generation of free radicals. These findings suggest that TP-COP could be used as an efficient photocatayst for the degradation of organic dye (RhB) under solar irradiation. Moreover, TP-COP showed excellent reusability in degrading dye (RhB) without obvious performance decay
Buckling and force propagation along intracellular microtubules
Motivated by recent experiments showing the compressive buckling of microtubules in cells, we study theoretically the mechanical response of and force propagation along elastic filaments embedded in a non-linear elastic medium. We find that embedded microtubules buckle when their compressive load exceeds a critical value
Design and implementation of a noise temperature measurement system for the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX)
This paper describes the design, implementation, and verification of a
test-bed for determining the noise temperature of radio antennas operating
between 400-800MHz. The requirements for this test-bed were driven by the HIRAX
experiment, which uses antennas with embedded amplification, making system
noise characterization difficult in the laboratory. The test-bed consists of
two large cylindrical cavities, each containing radio-frequency (RF) absorber
held at different temperatures (300K and 77K), allowing a measurement of system
noise temperature through the well-known 'Y-factor' method. The apparatus has
been constructed at Yale, and over the course of the past year has undergone
detailed verification measurements. To date, three preliminary noise
temperature measurement sets have been conducted using the system, putting us
on track to make the first noise temperature measurements of the HIRAX feed and
perform the first analysis of feed repeatability.Comment: 19 pages, 12 figure
Mechanochemical synthesis of a new triptycene-based imine-linked covalent organic polymer for degradation of organic dye
In the present work, a novel triptycene-based imine-linked covalent organic polymer (TP-COP) was designed and synthesized via room-temperature, solvent-free mechanochemical grinding. The as-synthesized TP-COP material was fully characterized by Fourier transform infrared spectroscopy, solid-state NMR, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Brunauer-Emmett-Teller method, thermogravimetric analysis, diffuse reflectance spectroscopy (DRS), and electron paramagnetic resonance (EPR). The HRTEM image of TP-COP clearly indicates the presence of graphene-like layered morphology (exfoliated layers). The DRS study reveals that TP-COP exhibited a low optical band gap value of 2.49 eV, implying its semiconducting nature. Further, the EPR study confirmed the semiconducting behavior of TP-COP through the generation of free radicals. These findings suggest that TP-COP could be used as an efficient photocatayst for the degradation of organic dye (RhB) under solar irradiation. Moreover, TP-COP showed excellent reusability in degrading dye (RhB) without obvious performance decay
The 2019 and 2021 International Workshops on Alport Syndrome
In 1927 Arthur Cecil Alport, a South African physician, described a British family with an inherited form of kidney disease that affected males more severely than females and was sometimes associated with hearing loss. In 1961, the eponymous name Alport syndrome was adopted. In the late twentieth century three genes responsible for the disease were discovered: COL4A3, COL4A4, and COL4A5 encoding for the α3, α4, α5 polypeptide chains of type IV collagen, respectively. These chains assemble to form heterotrimers of type IV collagen in the glomerular basement membrane. Scientists, clinicians, patient representatives and their families, and pharma companies attended the 2019 International Workshop on Alport Syndrome, held in Siena, Italy, from October 22 to 26, and the 2021 online Workshop from November 30 to December 4. The main topics included: disease re-naming, acknowledging the need to identify an appropriate term able to reflect considerable clinical variability; a strategy for increasing the molecular diagnostic rate; genotype-phenotype correlation from monogenic to digenic forms; new therapeutics and new therapeutic approaches; and gene therapy using gene editing. The exceptional collaborative climate that was established in the magical medieval setting of Siena continued in the online workshop of 2021. Conditions were established for collaborations between leading experts in the sector, including patients and drug companies, with the aim of identifying a cure for Alport syndrome
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