1,298 research outputs found
Growth states of catalytic reaction networks exhibiting energy metabolism
All cells derive nutrition by absorbing some chemical and energy resources
from the environment; these resources are used by the cells to reproduce the
chemicals within them, which in turn leads to an increase in their volume. In
this study, we introduce a protocell model exhibiting catalytic reaction
dynamics, energy metabolism, and cell growth. Results of extensive simulations
of this model show the existence of four phases with regard to the rates of
both the influx of resources and the cell growth. These phases include an
active phase with high influx and high growth rates, an inefficient phase with
high influx but low growth rates, a quasi-static phase with low influx and low
growth rates, and a death phase with negative growth rate. A mean field model
well explains the transition among these phases as bifurcations. The
statistical distribution of the active phase is characterized by a power law
and that of the inefficient phase is characterized by a nearly equilibrium
distribution. We also discuss the relevance of the results of this study to
distinct states in the existing cells.Comment: 21 pages, 5 figure
Ureteroscopic biopsy of upper tract urothelial carcinoma and role of urinary biomarkers
Ureteroscopic biopsy is an integral part of diagnosis of urothelial carcinoma of the upper urinary tract. It can be a technical challenge, but diagnostic rates have improved remarkably with refinements in surgical technique and specimen processing. Cytology aids with diagnosis and other urinary biomarkers continue to evolve, which may help further stratify patients for treatment. The current literature on the ureteroscopic biopsy and role of urinary biomarkers is reviewed and summarized below
The effect of RO3201195 and a pyrazolyl ketone P38 MAPK inhibitor library on the proliferation of Werner syndrome cells
No description supplie
Overview of the Tevatron Collider Complex: Goals, Operations and Performance
For more than two decades the Tevatron proton-antiproton collider was the
centerpiece of the world's high energy physics program. The collider was
arguably one of the most complex research instruments ever to reach the
operation stage and is widely recognized for numerous physics discoveries and
for many technological breakthroughs. In this article we outline the historical
background that led to the construction of the Tevatron Collider, the strategy
applied to evolution of performance goals over the Tevatron's operational
history, and briefly describe operations of each accelerator in the chain and
achieved performance.Comment: Includes modifications suggested by reviewer
Retarding Sub- and Accelerating Super-Diffusion Governed by Distributed Order Fractional Diffusion Equations
We propose diffusion-like equations with time and space fractional
derivatives of the distributed order for the kinetic description of anomalous
diffusion and relaxation phenomena, whose diffusion exponent varies with time
and which, correspondingly, can not be viewed as self-affine random processes
possessing a unique Hurst exponent. We prove the positivity of the solutions of
the proposed equations and establish the relation to the Continuous Time Random
Walk theory. We show that the distributed order time fractional diffusion
equation describes the sub-diffusion random process which is subordinated to
the Wiener process and whose diffusion exponent diminishes in time (retarding
sub-diffusion) leading to superslow diffusion, for which the square
displacement grows logarithmically in time. We also demonstrate that the
distributed order space fractional diffusion equation describes super-diffusion
phenomena when the diffusion exponent grows in time (accelerating
super-diffusion).Comment: 11 pages, LaTe
The origin of large molecules in primordial autocatalytic reaction networks
Large molecules such as proteins and nucleic acids are crucial for life, yet
their primordial origin remains a major puzzle. The production of large
molecules, as we know it today, requires good catalysts, and the only good
catalysts we know that can accomplish this task consist of large molecules.
Thus the origin of large molecules is a chicken and egg problem in chemistry.
Here we present a mechanism, based on autocatalytic sets (ACSs), that is a
possible solution to this problem. We discuss a mathematical model describing
the population dynamics of molecules in a stylized but prebiotically plausible
chemistry. Large molecules can be produced in this chemistry by the coalescing
of smaller ones, with the smallest molecules, the `food set', being buffered.
Some of the reactions can be catalyzed by molecules within the chemistry with
varying catalytic strengths. Normally the concentrations of large molecules in
such a scenario are very small, diminishing exponentially with their size.
ACSs, if present in the catalytic network, can focus the resources of the
system into a sparse set of molecules. ACSs can produce a bistability in the
population dynamics and, in particular, steady states wherein the ACS molecules
dominate the population. However to reach these steady states from initial
conditions that contain only the food set typically requires very large
catalytic strengths, growing exponentially with the size of the catalyst
molecule. We present a solution to this problem by studying `nested ACSs', a
structure in which a small ACS is connected to a larger one and reinforces it.
We show that when the network contains a cascade of nested ACSs with the
catalytic strengths of molecules increasing gradually with their size (e.g., as
a power law), a sparse subset of molecules including some very large molecules
can come to dominate the system.Comment: 49 pages, 17 figures including supporting informatio
Interethnic bias in willingness to engage in casual sex versus committed relationships
Interethnic romantic relationships are widely seen as a strong indicator of a well-integrated society. However, racial bias may still be evidenced in the tendency to engage in casual sex versus committed relationships. Using a large, age-diverse sample of 3,453 White British participants, this study found a general preference for White partners over racial minority partners. Furthermore, in line with social structural theory, participants reported a relative preference for marriage (versus casual sex) with White partners, but a relative preference for casual sex (versus marriage) with racial minorities. This pattern was further modified by sex: men reported a general preference for casual sex (versus marriage) with all racial groups except White partners. Women, however, reported a general preference for marriage (versus casual sex) with all groups, but this preference was strongest for White partners. The pattern was not further modified by sexual orientation. Implications for contemporary interethnic romantic relationships are discussed
Mass coupling and ^3$He in a torsion pendulum
We present results of the and period shift, , for He
confined in a 98% nominal open aerogel on a torsion pendulum. The aerogel is
compressed uniaxially by 10% along a direction aligned to the torsion pendulum
axis and was grown within a 400 m tall pancake (after compression) similar
to an Andronikashvili geometry. The result is a high pendulum able to
resolve and mass coupling of the impurity-limited He over the
whole temperature range. After measuring the empty cell background, we filled
the cell above the critical point and observe a temperature dependent period
shift, , between 100 mK and 3 mK that is 2.9 of the period shift
(after filling) at 100 mK. The due to the He decreases by an order
of magnitude between 100 mK and 3 mK at a pressure of bar. We
compare the observable quantities to the corresponding calculated and
period shift for bulk He.Comment: 8 pages, 3 figure
The meaning of life in a developing universe
The evolution of life on Earth has produced an organism that is beginning to model and understand its own evolution and the possible future evolution of life in the universe. These models and associated evidence show that evolution on Earth has a trajectory. The scale over which living processes are organized cooperatively has increased progressively, as has its evolvability. Recent theoretical advances raise the possibility that this trajectory is itself part of a wider developmental process. According to these theories, the developmental process has been shaped by a larger evolutionary process that involves the reproduction of universes. This evolutionary process has tuned the key parameters of the universe to increase the likelihood that life will emerge and develop to produce outcomes that are successful in the larger process (e.g. a key outcome may be to produce life and intelligence that intentionally reproduces the universe and tunes the parameters of ‘offspring’ universes). Theory suggests that when life emerges on a planet, it moves along this trajectory of its own accord. However, at a particular point evolution will continue to advance only if organisms emerge that decide to advance the evolutionary process intentionally. The organisms must be prepared to make this commitment even though the ultimate nature and destination of the process is uncertain, and may forever remain unknown. Organisms that complete this transition to intentional evolution will drive the further development of life and intelligence in the universe. Humanity’s increasing understanding of the evolution of life in the universe is rapidly bringing it to the threshold of this major evolutionary transition
Infrared spectroscopy of phytochrome and model pigments
Fourier-transform infrared difference spectra between the red-absorbing and far-red-absorbing forms of oat phytochrome have been measured in H2O and 2H2O. The difference spectra are compared with infrared spectra of model compounds, i.e. the (5Z,10Z,15Z)- and (5Z,10Z,15E)-isomers of 2,3,7,8,12,13,17,18-octaethyl-bilindion (Et8-bilindion), 2,3-dihydro-2,3,7,8,12,13,17,18-octaethyl-bilindion (H2Et8-bilindion), and protonated H2Et8-bilindion in various solvents. The spectra of the model compounds show that only for the protonated forms can clear differences between the two isomers be detected. Since considerable differences are present between the spectra of Et8-bilindion and H2Et8-bilindion, it is concluded that only the latter compound can serve as a model system of phytochrome. The 2H2O effect on the difference spectrum of phytochrome supports the view that the chromophore in red-absorbing phytochrome is protonated and suggests, in addition, that it is also protonated in far-red-absorbing phytochrome. The spectra show that protonated carboxyl groups are influenced. The small amplitudes in the difference spectra exclude major changes of protein secondary structure
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