2,487 research outputs found
Stress management in composite biopolymer networks
Living tissues show an extraordinary adaptiveness to strain, which is crucial
for their proper biological functioning. The physical origin of this mechanical
behaviour has been widely investigated using reconstituted networks of collagen
fibres, the principal load-bearing component of tissues. However, collagen
fibres in tissues are embedded in a soft hydrated polysaccharide matrix which
generates substantial internal stresses whose effect on tissue mechanics is
unknown. Here, by combining mechanical measurements and computer simulations,
we show that networks composed of collagen fibres and a hyaluronan matrix
exhibit synergistic mechanics characterized by an enhanced stiffness and
delayed strain-stiffening. We demonstrate that the polysaccharide matrix has a
dual effect on the composite response involving both internal stress and
elastic reinforcement. Our findings elucidate how tissues can tune their
strain-sensitivity over a wide range and provide a novel design principle for
synthetic materials with programmable mechanical properties
Radiocarbon measurements of Würm-interstadial samples from Jutland
Der Inhalt von radioaktivem Kohlenstoff in würminterstadialen Proben aus Brörup, Jütland, ist in den Datierungslaboratorien in Kopenhagen und Groningen gemessen worden. Die Proben waren durch verhältnismäßig große Mengen von infiltriertem, jüngeren Material verunreinigt; nach einer Extraktion von Humussäuren zeigte jedoch keine der Proben eine signifikante Aktivität. Dies läßt darauf schließen, daß das Interstadial von Brörup und die vorausgegangene kalte Periode älter als 50 000 Jahre v. Chr. sind. Wenn die Ansicht von Andersen (1957) richtig ist, daß in Brörup wirklich das Göttweiger Interstadial vorliegt, so würde daraus folgen, daß auch Altwürm und wenigstens der tiefere Teil des Göttweiger Interstadials älter als 50 000 Jahre v. Chr. sein müßten.researc
In Memoriam: Jean Luther Laffoon, 1922-1973
Jean L. Laffoon, Professor of Zoology and Entomology at Iowa State University, died January 19, 1973, in Ames, Iowa, after a brief illness.
Dr. Laffoon was born in Sioux City Iowa on August 19 1922. He graduated from Central High School, Sioux Citv, in 1939 and was awarded a B.S. degree in biology from Morningside College in 1942. In the fall of that year he entered the University of Michigan, Ann Arbor, but withdrew to volunteer for service in the United States Navy. Upon his discharge, three years later, he enrolled in the Graduate College at Iowa State University, where he earned an M.S. degree in 1948 and a Ph.D. degree in 1953, both in entomology
B polarization of the CMB from Faraday rotation
We study the effect of Faraday rotation due to a homogeneous magnetic field
on the polarization of the cosmic microwave background (CMB). Scalar
fluctuations give rise only to parity-even E-type polarization of the CMB.
However in the presence of a magnetic field, a non-vanishing parity-odd B-type
polarization component is produced through Faraday rotation. We derive the
exact solution for the E and B modes generated by scalar perturbations
including the Faraday rotation effect of a uniform magnetic field, and evaluate
their cross-correlations with temperature anisotropies. We compute the angular
autocorrelation function of the B-modes in the limit that the Faraday rotation
is small. We find that primordial magnetic fields of present strength around
G rotate E-modes into B-modes with amplitude comparable to those
due to the weak gravitational lensing effect at frequencies around
GHz. The strength of B-modes produced by Faraday rotation scales as
. We evaluate also the depolarizing effect of Faraday rotation upon
the cross correlation between temperature anisotropy and E-type polarization.Comment: 11 pages, 4 figures. Minor changes to match the published versio
Long Range Hops and the Pair Annihilation Reaction A+A->0: Renormalization Group and Simulation
A simple example of a non-equilibrium system for which fluctuations are
important is a system of particles which diffuse and may annihilate in pairs on
contact. The renormalization group can be used to calculate the time dependence
of the density of particles, and provides both an exact value for the exponent
governing the decay of particles and an epsilon-expansion for the amplitude of
this power law. When the diffusion is anomalous, as when the particles perform
Levy flights, the critical dimension depends continuously on the control
parameter for the Levy distribution. The epsilon-expansion can then become an
expansion in a small parameter. We present a renormalization group calculation
and compare these results with those of a simulation.Comment: As-published version; two significant errors fixed, two references
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Low-Cost and Readily Available Tissue Carriers for the Boston Keratoprosthesis: A Review of Possibilities
The Boston keratoprosthesis (B-KPro), currently the most commonly used artificial cornea worldwide, can provide rapid visual rehabilitation for eyes with severe corneal opacities not suitable for standard corneal transplantation. However, the B-KPro presently needs a corneal graft as a tissue carrier. Although corneal allograft tissue is readily available in the United States and other developed countries with established eye banks, the worldwide need vastly exceeds supply. Therefore, a simple, safe, and inexpensive alternative to corneal allografts is desirable for the developing world. We are currently exploring reasonable alternative options such as corneal autografts, xenografts, noncorneal autologous tissues, and laboratory-made tissue constructs, as well as modifications to corneal allografts, such as deep-freezing, glycerol-dehydration, gamma irradiation, and cross-linking. These alternative tissue carriers for the B-KPro are discussed with special regard to safety, practicality, and cost for the developing world
A Search for Small-Scale Clumpiness in Dense Cores of Molecular Clouds
We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high
signal-to-noise ratios toward distinct positions in three selected objects in
order to search for small-scale structure in molecular cloud cores associated
with regions of high-mass star formation. In some cases, ripples were detected
in the line profiles, which could be due to the presence of a large number of
unresolved small clumps in the telescope beam. The number of clumps for regions
with linear scales of ~0.2-0.5 pc is determined using an analytical model and
detailed calculations for a clumpy cloud model; this number varies in the
range: ~2 10^4-3 10^5, depending on the source. The clump densities range from
~3 10^5-10^6 cm^{-3}, and the sizes and volume filling factors of the clumps
are ~(1-3) 10^{-3} pc and ~0.03-0.12. The clumps are surrounded by inter-clump
gas with densities not lower than ~(2-7) 10^4 cm^{-3}. The internal thermal
energy of the gas in the model clumps is much higher than their gravitational
energy. Their mean lifetimes can depend on the inter-clump collisional rates,
and vary in the range ~10^4-10^5 yr. These structures are probably connected
with density fluctuations due to turbulence in high-mass star-forming regions.Comment: 23 pages including 4 figures and 4 table
Evaluation of early and late presentation of patients with ocular mucous membrane pemphigoid to two major tertiary referral hospitals in the United Kingdom
PURPOSE: Ocular mucous membrane pemphigoid (OcMMP) is a sight-threatening autoimmune disease in which referral to specialists units for further management is a common practise. This study aims to describe referral patterns, disease phenotype and management strategies in patients who present with either early or established disease to two large tertiary care hospitals in the United Kingdom.\ud
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PATIENTS AND METHODS: In all, 54 consecutive patients with a documented history of OcMMP were followed for 24 months. Two groups were defined: (i) early-onset disease (EOD:<3 years, n=26, 51 eyes) and (ii) established disease (EstD:>5 years, n=24, 48 eyes). Data were captured at first clinic visit, and at 12 and 24 months follow-up. Information regarding duration, activity and stage of disease, visual acuity (VA), therapeutic strategies and clinical outcome were analysed.\ud
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RESULTS: Patients with EOD were younger and had more severe conjunctival inflammation (76% of inflamed eyes) than the EstD group, who had poorer VA (26.7%=VA<3/60, P<0.01) and more advanced disease. Although 40% of patients were on existing immunosuppression, 48% required initiation or switch to more potent immunotherapy. In all, 28% (14) were referred back to the originating hospitals for continued care. Although inflammation had resolved in 78% (60/77) at 12 months, persistence of inflammation and progression did not differ between the two phenotypes. Importantly, 42% demonstrated disease progression in the absence of clinically detectable inflammation.\ud
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CONCLUSIONS: These data highlight that irrespective of OcMMP phenotype, initiation or escalation of potent immunosuppression is required at tertiary hospitals. Moreover, the conjunctival scarring progresses even when the eye remains clinically quiescent. Early referral to tertiary centres is recommended to optimise immunosuppression and limit long-term ocular damage.\ud
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