3,920 research outputs found
Method for finding metabolic properties based on the general growth law. Liver examples. A General framework for biological modeling
We propose a method for finding metabolic parameters of cells, organs and
whole organisms, which is based on the earlier discovered general growth law.
Based on the obtained results and analysis of available biological models, we
propose a general framework for modeling biological phenomena and discuss how
it can be used in Virtual Liver Network project. The foundational idea of the
study is that growth of cells, organs, systems and whole organisms, besides
biomolecular machinery, is influenced by biophysical mechanisms acting at
different scale levels. In particular, the general growth law uniquely defines
distribution of nutritional resources between maintenance needs and biomass
synthesis at each phase of growth and at each scale level. We exemplify the
approach considering metabolic properties of growing human and dog livers and
liver transplants. A procedure for verification of obtained results has been
introduced too. We found that two examined dogs have high metabolic rates
consuming about 0.62 and 1 gram of nutrients per cubic centimeter of liver per
day, and verified this using the proposed verification procedure. We also
evaluated consumption rate of nutrients in human livers, determining it to be
about 0.088 gram of nutrients per cubic centimeter of liver per day for males,
and about 0.098 for females. This noticeable difference can be explained by
evolutionary development, which required females to have greater liver
processing capacity to support pregnancy. We also found how much nutrients go
to biomass synthesis and maintenance at each phase of liver and liver
transplant growth. Obtained results demonstrate that the proposed approach can
be used for finding metabolic characteristics of cells, organs, and whole
organisms, which can further serve as important inputs for many applications in
biology (protein expression), biotechnology (synthesis of substances), and
medicine.Comment: 20 pages, 6 figures, 4 table
Lower Bounds of Quantum Search for Extreme Point
We show that Durr-Hoyer's quantum algorithm of searching for extreme point of
integer function can not be sped up for functions chosen randomly. Any other
algorithm acting in substantially shorter time gives incorrect
answer for the functions with the single point of maximum chosen randomly with
probability converging to 1. The lower bound as was
established for the quantum search for solution of equations where
is a Boolean function with such solutions chosen at random with probability
converging to 1.Comment: Some minor change
Equivalence is in the Eye of the Beholder
In a recent provocative paper, Lamport points out "the insubstantiality of
processes" by proving the equivalence of two different decompositions of the
same intuitive algorithm by means of temporal formulas. We point out that the
correct equivalence of algorithms is itself in the eye of the beholder. We
discuss a number of related issues and, in particular, whether algorithms can
be proved equivalent directly.Comment: See also the ASM web site at http://www.eecs.umich.edu/gasm
Beaming effect from increased-index photonic crystal waveguides
We study the beaming effect of light for the case of increased-index photonic
crystal (PhC) waveguides, formed through the omission of low-dielectric media
in the waveguide region. We employ the finite-difference time-domain numerical
method for characterizing the beaming effect and determining the mechanisms of
loss and the overall efficiency of the directional emission. We find that,
while this type of PhC waveguides is capable of producing a highly collimated
emission as was demonstrated experimentally, the inherent characteristics of
the structure result in a restrictively low efficiency in the coupling of light
into the collimated beam of light.Comment: 4 pages, 5 figures, submitted to Applied Physics
On the dependence of X-ray burst rate on accretion and spin rate
Nuclear burning and its dependence on the mass accretion rate are fundamental
ingredients for describing the complicated observational phenomenology of
neutron stars in binary systems. Motivated by high quality burst rate data
emerging from large statistical studies, we report general calculations
relating bursting rate to mass accretion rate and neutron star rotation
frequency. In this first work we neglect general relativistic effects and
accretion topology, though we discuss where their inclusion should play a role.
The relations we derive are suitable for different burning regimes and provide
a direct link between parameters predicted by theory and what is to be expected
in observations. We illustrate this for analytical relations of different
unstable burning regimes that operate on the surface of an accreting neutron
star. We also use the observed behaviour of burst rate to suggest new
constraints on burning parameters. We are able to provide an explanation for
the long standing problem of the observed decrease of burst rate with
increasing mass accretion that follows naturally from these calculations: when
accretion rate crosses a certain threshold, ignition moves away from its
initially preferential site and this can cause a net reduction of the burst
rate due to the effects of local conditions that set local differences in both
burst rate and stabilization criteria. We show under which conditions this can
happen even if locally the burst rate keeps increasing with accretion.Comment: Accepted for publication on Ap
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