788 research outputs found
Open problems in artificial life
This article lists fourteen open problems in artificial life, each of which is a grand challenge requiring a major advance on a fundamental issue for its solution. Each problem is briefly explained, and, where deemed helpful, some promising paths to its solution are indicated
Non-normality and non-monotonic dynamics in complex reaction networks
Complex chemical reaction networks, which underlie many industrial and
biological processes, often exhibit non-monotonic changes in chemical species
concentrations, typically described using nonlinear models. Such non-monotonic
dynamics are in principle possible even in linear models if the matrices
defining the models are non-normal, as characterized by a necessarily
non-orthogonal set of eigenvectors. However, the extent to which non-normality
is responsible for non-monotonic behavior remains an open question. Here, using
a master equation to model the reaction dynamics, we derive a general condition
for observing non-monotonic dynamics of individual species, establishing that
non-normality promotes non-monotonicity but is not a requirement for it. In
contrast, we show that non-normality is a requirement for non-monotonic
dynamics to be observed in the R\'enyi entropy. Using hydrogen combustion as an
example application, we demonstrate that non-monotonic dynamics under
experimental conditions are supported by a linear chain of connected
components, in contrast with the dominance of a single giant component observed
in typical random reaction networks. The exact linearity of the master equation
enables development of rigorous theory and simulations for dynamical networks
of unprecedented size (approaching dynamical variables, even for a
network of only 20 reactions and involving less than 100 atoms). Our
conclusions are expected to hold for other combustion processes, and the
general theory we develop is applicable to all chemical reaction networks,
including biological ones.Comment: Software implementing our methods is available as a Github repository
at https://github.com/znicolaou/ratematrix and an animated version of Fig. 1
is available at
https://northwestern.box.com/s/otn3m2cov9gi3enht3r8jh5kjo9qnv6
SO(2,1) Covariant IIB Superalgebra
We propose a type IIB super-Poincare algebra with SO(2,1) covariant central
extension. Together with SO(2,1) and SO(9,1) generators, a SO(2,1) triplet
(momenta), a Majorana-spinor doublet (supercharges) and a Rarita-Schwinger
central charge generate a group, G. We consider a coset G/H where H=(SO(2) x
Lorentz), and the SL(2,R) 2-form doublet is obtained by the coset construction.
It is shown that U(1) connections, whose strengths are associated with 2-forms,
are recognized as coordinates of the enlarged space. We suggest that this is
the fundamental algebra governing the superstring theories which explains the
IIB SL(2,R) duality and geometrical origin of U(1) fields.Comment: 12 pages, Latex; <[email protected],
[email protected], [email protected]
X-ray harmonic comb from relativistic electron spikes
X-ray devices are far superior to optical ones for providing nanometre
spatial and attosecond temporal resolutions. Such resolution is indispensable
in biology, medicine, physics, material sciences, and their applications. A
bright ultrafast coherent X-ray source is highly desirable, for example, for
the diffractive imaging of individual large molecules, viruses, or cells. Here
we demonstrate experimentally a new compact X-ray source involving high-order
harmonics produced by a relativistic-irradiance femtosecond laser in a gas
target. In our first implementation using a 9 Terawatt laser, coherent soft
X-rays are emitted with a comb-like spectrum reaching the 'water window' range.
The generation mechanism is robust being based on phenomena inherent in
relativistic laser plasmas: self-focusing, nonlinear wave generation
accompanied by electron density singularities, and collective radiation by a
compact electric charge. The formation of singularities (electron density
spikes) is described by the elegant mathematical catastrophe theory, which
explains sudden changes in various complex systems, from physics to social
sciences. The new X-ray source has advantageous scalings, as the maximum
harmonic order is proportional to the cube of the laser amplitude enhanced by
relativistic self-focusing in plasma. This allows straightforward extension of
the coherent X-ray generation to the keV and tens of keV spectral regions. The
implemented X-ray source is remarkably easily accessible: the requirements for
the laser can be met in a university-scale laboratory, the gas jet is a
replenishable debris-free target, and the harmonics emanate directly from the
gas jet without additional devices. Our results open the way to a compact
coherent ultrashort brilliant X-ray source with single shot and high-repetition
rate capabilities, suitable for numerous applications and diagnostics in many
research fields
Development of the Virtual Earth\u27s Magnetosphere System (VEMS)
We have constructed a new research environment for geo-space science based on 3-D visualization tool and network database; Virtual Earth\u27s Magnetosphere System (VEMS). With an interactive research environment researchers can visually understand structures of the Earth\u27s magnetosphere using VEMS. On the VEMS, computer simulation results and observation data are simultaneously visualized, having a potential to data assimilation for geo-space studies in the future. Since the VEMS deals with time-dependent data, it also helps researchers to study dynamics of the Earth\u27s magnetosphere. We found that immersive data analyses are possible using the VEMS on a virtual reality system
The stability of the shell of D6-D2 branes in a supergravity solution
The stability of the shell of wrapped D6-branes on K3 is investigated from
the point of view of supergravity. We first construct an effective
energy-momentum tensor for the shell under the reasonable conditions and show
that supersymmetric solutions satisfy Israel's junction conditions at arbitrary
radius of the shell. Next we study the perturbation of the whole system
including the self-gravity of the shell. It is found that in spite of the
existence of wrapped D6-branes with negative tension, there is no eigenmode
whose frequencies of the shell and the fields are imaginary numbers, at any
radius of the shell. Furthermore, when the radius of the shell is less than the
enhan\c{c}on radius, resonances are produced, and this indicates a kind of
``instability'' of the system. This can even classically explain why the shell
is constructed at the enhan\c{c}on radius.Comment: 14 pages, 3 figures, corrected some calculation
Norcantharidin Induces Human Melanoma A375-S2 Cell Apoptosis through Mitochondrial and Caspase Pathways
Norcantharidin (NCTD) is the demethylated form of cantharidin, which is the active substance of mylabris. To examine the pathway of NCTD-induced A375-S2 cell death, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-dipheyltetrazolium bromide (MTT) assay, photomicroscopical observation, DNA agarose gel electrophoresis, caspase activity assay and Western blot analysis were carried out. A375-S2 cells treated with NCTD exhibited several typical characteristics of apoptosis. The inhibitory effect of NCTD on human melanoma, A375-S2 cells, was partially reversed by the inhibitors of pan-caspase, caspase-3 and caspase-9. The activities of caspase-3 and -9 were significantly increased after treatment with NCTD at different time. The expression of inhibitor of caspase-activated DNase was decreased in a time-dependent manner, simultaneously, the ratio of Bcl-2/Bax or Bcl-xL/Bax was decreased and the expression ratio of proteins could be reversed by caspase-3 inhibitor. The expression of cytochrome c in cytosol was increased after NCTD treatment and caspase-3 inhibitor had no significant effect on the up-regulation of cytochrom c. These results suggest that NCTD induced A375-S2 cell apoptosis and the activation of caspase and mitochondrial pathway were involved in the process of NCTD-induced A375-S2 cell apoptosis
Resonant particle production with non-minimally coupled scalar fields in preheating after inflation
We investigate a resonant particle production of a scalar field
coupled non-minimally to a spacetime curvature () as well as
to an inflaton field (). In the case of , effect assists -resonance in certain parameter regimes.
However, for , -resonance is not enhanced by
effect because of suppression effect as well as a back reaction effect.
If , the maximal fluctuation of produced -particle is
GeV for , which is larger than the minimally coupled case with .Comment: 33pages, 12figures. to appear in Physical Review
Factors considered by medical students when formulating their specialty preferences in Japan: findings from a qualitative study
<p>Abstract</p> <p>Background</p> <p>Little research addresses how medical students develop their choice of specialty training in Japan. The purpose of this research was to elucidate factors considered by Japanese medical students when formulating their specialty choice.</p> <p>Methods</p> <p>We conducted qualitative interviews with 25 Japanese medical students regarding factors influencing specialty preference and their views on roles of primary versus specialty care. We qualitatively analyzed the data to identify factors students consider when developing specialty preferences, to understand their views about primary and subspecialty care, and to construct models depicting the pathways to specialization.</p> <p>Results</p> <p>Students mention factors such as illness in self or close others, respect for family member in the profession, preclinical experiences in the curriculum such as labs and dissection, and aspects of patient care such as the clinical atmosphere, charismatic role models, and doctor-patient communication as influential on their specialty preferences. Participating students could generally distinguish between subspecialty care and primary care, but not primary care and family medicine. Our analysis yields a "Two Career" model depicting how medical graduates can first train for hospital-based specialty practice, and then switch to mixed primary/specialty care outpatient practice years later without any requirement for systematic training in principles of primary care practice.</p> <p>Conclusion</p> <p>Preclinical and clinical experiences as well as role models are reported by Japanese students as influential factors when formulating their specialty preferences. Student understanding of family medicine as a discipline is low in Japan. Students with ultimate aspirations to practice outpatient primary care medicine do not need to commit to systematic primary care training after graduation. The Two Career model of specialization leaves the door open for medical graduates to enter primary care practice at anytime regardless of post-graduate residency training choice.</p
Early effect of oral administration of omeprazole with mosapride as compared with those of omeprazole alone on the intragastric pH
<p>Abstract</p> <p>Background</p> <p>The ideal medication for acid-related diseases should have a rapid onset of action to promote hemostasis and cause efficient resolution of symptoms. The aim of our study was to comparatively investigate the inhibitory effect on gastric acid secretion of a single oral administration of omeprazole plus mosapride with that of omeprazole alone.</p> <p>Methods</p> <p>Ten Helicobacter pylori-negative male subjects participated in this randomized, two-way crossover study. Intragastric pH was monitored continuously for 6 hours after a single oral administration of omeprazole 20 mg or that of omeprazole 20 mg plus mosapride 5 mg (the omeprazole being administered one hour after the mosapride). Each administration was separated by a 7-days washout period.</p> <p>Results</p> <p>The average pH during the 6-hour period after administration of omeprazole 20 mg plus mosapride 5 mg was higher than that after administration of omeprazole 20 mg alone (median: 3.22 versus 4.21, respectively; <it>p </it>= 0.0247).</p> <p>Conclusions</p> <p>In H. pylori -negative healthy male subjects, an oral dose of omeprazole 20 mg plus mosapride 5 mg increased the intragastric pH more rapidly than omeprazole 20 mg alone.</p
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