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1.
A. J. MacDermott T. Fu G. O. Hyde R. Nakatsuka A. P. Coleman 《Origins of life and evolution of the biosphere》2009,39(5):407-437
The preceding paper described our coupled-perturbed Hartree-Fock (CPHF) and density functional theory (DFT) methods of computing
the parity-violating energy shift (PVES). This paper addresses the “conformation problem”—the difficulty determining which
hand of amino acids in solution is favoured by the weak force due to the difficulty determining the solution conformation.
We attempt to resolve this by using the methods of the preceding paper to compute the PVES of solution and gas-phase amino
acid structures determined by other groups from high level optimizations that include solvation. We conclude that the conformational hypersensitivity of the PVES still precludes a definite conclusion as to the sign of the PVES of L-alanine in solution, but that there is
no problem in the gas phase: the PVES of gas-phase L-alanine is decisively negative. We show that the PVES is very sensitive
to certain torsion angles, but is not hypersensitive to bondlengths or bond angles. In determining structures for PVES computations, there is therefore no need
for expensive full optimizations: one can just optimize the crucial torsion angles. We present new computations of gas-phase amino acids PVESs,
using partial optimizations with small basis sets, and the results agree well with those from higher level techniques. In
the following paper we apply these less costly techniques to larger amino acids. The “conformation problem” has led some to
dismiss the PVES as the source of life’s handedness, but we believe this is premature: we show here that amino acids are a
special case because their favoured conformations are almost achiral. 相似文献
2.
Fibrin, the structural scaffold of blood clots, spontaneously polymerizes through the formation of ‘A-a’ knob-hole bonds. When subjected to external force, the dissociation of this bond is accompanied by two to four abrupt changes in molecular dimension observable as rupture events in a force curve. Herein, the configuration, molecular extension, and kinetic parameters of each rupture event are examined. The increases in contour length indicate that the D region of fibrinogen can lengthen by ∼50% of the length of a fibrin monomer before rupture of the ‘A-a’ interaction. The dependence of the dissociation rate on applied force was obtained using probability distributions of rupture forces collected at different pull-off velocities. These distributions were fit using a model in which the effects of the shape of the binding potential are used to quantify the kinetic parameters of forced dissociation. We found that the weak initial rupture (i.e., event 1) was not well approximated by these models. The ruptured bonds comprising the strongest ruptures, events 2 and 3, had kinetic parameters similar to those commonly found for the mechanical unfolding of globular proteins. The bonds ruptured in event 4 were well described by these analyses, but were more loosely bound than the bonds in events 2 and 3. We propose that the first event represents the rupture of an unknown interaction parallel to the ‘A-a’ bond, events 2 and 3 represent unfolding of structures in the D region of fibrinogen, and event 4 is the rupture of the ‘A-a’ knob-hole bond weakened by prior structural unfolding. Comparison of the activation energy obtained via force spectroscopy measurements with the thermodynamic free energy of ‘A-a’ bond dissociation indicates that the ‘A-a’ bond may be more resistant to rupture by applied force than to rupture by thermal dissociation. 相似文献
3.
Luda Khait Chani J. Hodonsky Ravi K. Birla 《In vitro cellular & developmental biology. Animal》2009,45(10):592-601
Cardiac tissue-engineering research is focused on the development of functional three-dimensional (3D) heart muscle in vitro.
These models allow the detailed study of critical events in organogenesis, such as the establishment of cell–cell communication
and construction and modification of the extracellular matrix. We have previously described a model for 3D heart muscle, termed
cardioids, formed by the spontaneous delamination of a cohesive monolayer of primary cells in the absence of any synthetic scaffolding
material. In an earlier publication, we have shown that, upon electrical stimulation, cardioids generate a twitch force in the range of 200–300 μN, generate a specific force (twitch force normalized to total cross-sectional
area) of 2–4 kN/m2, and can be electrically paced at frequencies of up to 10 Hz without any notable fatigue. We have two objectives for the
current study: model development and model optimization. Our model development efforts are focused on providing additional
characterization of the cardioid model. In this study, we show for the first time that cardioids show a pattern of gene expression comparable to that of cells cultured in two dimensions on tissue culture plastic and normal
mammalian heart muscle. Compared with primary cardiac cells cultured on tissue culture plastic, the expression of α-myosin
heavy chain (MHC), β-MHC, SERCA2, and phospholamban was significantly higher in cardioids. Our second objective, model optimization,
is focused on evaluating the effect of several cell culture variables on cardioid formation and function. Specifically, we looked at the effect of plating density (1.0–4.0 × 106 cells per cardioid), concentration of two adhesion proteins (laminin at 0.2–2.0 μg/cm2 and fibronectin at 1–10 μg/cm2), myocyte purity (using preplating times of 15 and 60 min), and ascorbic acid stimulation (1–100 μl/ml). For our optimization
studies, we utilized twitch force in response to electrical stimulation as our endpoint metric. Based on these studies, we
found that cardioids formed with a plating density in the range 3–4 × 106 cells per cardioid generated the maximum twitch force, whereas increasing the surface adhesion protein (using either laminin or fibronectin)
and increasing the myocyte purity both resulted in a decrease in twitch force. In addition, increasing the ascorbic acid concentration
resulted in an increase in the baseline force of cardioids, which was recorded in the absence of electrical stimulation. Based on the model development studies, we have shown that
cardioids do indeed exhibit a gene expression pattern similar to normal mammalian heart muscle. This provides further validity
for the cardioid model. Based on the model optimization studies, we have identified specific cell culture regimes which support
cardioid formation and function. These results are specific to the cardioid model; however, they may be translated and applied to other tissue-engineering models. Collectively, the work described in
this study provides insight into the formation of functional 3D heart muscle and the effect of several cell culture variables
on tissue formation and function. 相似文献
4.
In recent years, it has been recognised that improvements to classic models of muscle mechanical behaviour are often necessary
for properly modelling co-ordinated multi-joint actions. In this respect, the purpose of the present study was to improve
on modelling stretch-induced force enhancement and shortening-induced force depression of muscle contraction. For this purpose,
two models were used: a modified Hill model and a model based loosely on mechano-chemistry of the cross-bridge cycle (exponential
decay model). The models were compared with a classic Hill model and experimental data. Parameter values were based, as much
as possible, on experimental findings in the literature, and tested with new experiments on the gastrocnemius of the rat.
Both models describe many features of slow-ramp movements well during short contractions (300–500 ms), but long-duration behaviour
is described only partly. The exponential decay model does not incorporate a force–velocity curve. Therefore, its good performance
indicates that the status of the classic force–velocity characteristic may have to be reconsidered. Like movement-induced
force depression and enhancement, it seems a particular manifestation of time-dependent force behaviour of muscle, rather
than a fundamental property of muscle (like the length–tension curve). It is argued that a combination of the exponential
decay model (or other models based on the mechano-chemistry of contraction) and structurally based models may be fruitful
in explaining this time-dependent contraction behaviour. Furthermore, not in the least because of its relative simplicity,
the exponential decay model may prove more suitable for modelling multi-joint movements than the Hill model.
Received: 19 March 1999 / Accepted in revised form: 9 June 2000 相似文献
5.
The well-known neural mass model described by Lopes da Silva et al. (1976) and Zetterberg et al. (1978) is fitted to actual
EEG data. This is achieved by reformulating the original set of integral equations as a continuous-discrete state space model.
The local linearization approach is then used to discretize the state equation and to construct a nonlinear Kalman filter.
On this basis, a maximum likelihood procedure is used for estimating the model parameters for several EEG recordings. The
analysis of the noise-free differential equations of the estimated models suggests that there are two different types of alpha
rhythms: those with a point attractor and others with a limit cycle attractor. These attractors are also found by means of
a nonlinear time series analysis of the EEG recordings. We conclude that the Hopf bifurcation described by Zetterberg et al.
(1978) is present in actual brain dynamics.
Received: 11 August 1997 / Accepted in revised form: 20 April 1999 相似文献
6.
Alexandra Maier Heinz Sklenar Herbert F. Kratky Alexander Renner Peter Schuster 《European biophysics journal : EBJ》1999,28(7):564-573
The protocol of conformational analysis applied here to ribonucleotide oligomers combines conformational search in the space
of torsion angles and energy minimization using the AMBER4.1 force field with a continuum treatment of electrostatic solute-solvent
interactions. RNA fragments with 5′-GGGCGNNAGCCU-3′ sequences commonly fold into hairpins with four-membered loops. The combinatorial
search for acceptable conformations using the MC-SYM program was restricted to loop nucleotides and yielded roughly 1500 structures
being compatible with a double-stranded stem. After energy minimization by the JUMNA program (without applying any experimental
constraints), these structures converged into an ensemble of 74 different conformers including 26 structures which contained
the sheared G-A base pair observed in experimental studies of GNRA tetraloops. Energetic analysis shows that inclusion of
solvent electrostatic effects is critically important for the selection of conformers that agree with experimentally determined
structures. The continuum model accounts for solvent polarization by means of the electrostatic reaction field. In the case
of GNRA loop sequences, the contributions of the reaction field shift relative stabilities towards conformations showing most
of the structural features derived from NMR studies. The agreement of computed conformations with the experimental structures
of GAAA, GCAA, and GAGA tetraloops suggests that the continuum treatment of the solvent represents a definitive improvement
over methods using simple damping models in electrostatic energy calculations. Application of the procedure described here
to the evaluation of the relative stabilities of conformers resulting from searching the conformational space of RNA structural
motifs provides some progress in (non-homology based) RNA 3D-structure prediction.
Received: 20 January 1999 / Revised version: 4 June 1999 / Accepted: 10 June 1999 相似文献
7.
The present model of the motoneuronal (MN) pool – muscle complex (MNPMC) is deterministic and designed for steady isometric
muscle activation. Time-dependent quantities are treated as time-averages. The character of the model is continuous in the
sense that the motor unit (MU) population is described by a continuous density function. In contrast to most already published
models, the wiring (synaptic weight) between the input fibers to the MNPMC and the MNs (about which no detailed data are known)
is deduced, whereas the input–force relation is given. As suggested by experimental data, this relation is assumed to be linear
during MU recruitment, but the model allows other, nonlinear relations. The input to the MN pool is defined as the number
of action potentials per second in all input fibers, and the excitatory postsynaptic potential (EPSP) conductance in MNs evoked
by the input is assumed to be proportional to the input. A single compartment model with a homogeneous membrane is used for
a MN. The MNs start firing after passing a constant voltage threshold. The synaptic current–frequency relation is described
by a linear function and the frequency–force transformation of a MU by an exponential function. The sum of the MU contraction
forces is the muscle force, and the activation of the MUs obeys the size principle. The model parameters were determined a
priori, i.e., the model was not used for their estimation. The analysis of the model reveals special features of the activation
curve which we define as the relation between the input normalized by the threshold input of the MN pool and the force normalized
by the maximal muscle force. This curve for any muscle turned out to be completely determined by the activation factor, the
slope of the linear part of the activation curve (during MU recruitment). This factor determines quantitatively the relation
between MU recruitment and rate modulation. This property of the model (the only known model with this property) allows a
quantification of the recruitment gain (Kernell and Hultborn 1990). The interest of the activation factor is illustrated using
two human muscles, namely the first dorsal interosseus muscle, a small muscle with a relatively small force at the end of
recruitment, and the medial gastrocnemius muscle, a strong muscle with a relatively large force at the end of recruitment.
It is concluded that the present model allows us to reproduce the main features of muscle activation in the steady state.
Its analytical character facilitates a deeper understanding of these features.
Received: 24 November 1997 / Accepted in revised form: 30 November 1998 相似文献
8.
C. Loring Brace 《Human Evolution》1993,8(3):151-166
The recent recommendation that it is preferable to recognize too many rather than too few species in the fossil record has
led to a growing proliferation of specific names. Single specimens are being referred to different species by different authors,
and new species are being proposed based on the juxtaposition of specimens from different sites and time levels representing
different anatomical parts. In part this may represent the continuity of the Medieval assertion that a multitude of species
is a better demonstration of the goodness of a divinely created world than a multitude of individuals in a single species.
This has apparently accompanied the resurgence of the Medieval faith that species relationship are best demonstrated by the
application of hierarchical Aristotelean logic. On the other hand, the suspicion remains that the vanity of the namer is frequently
involved in the creation of new nomina. In general, anthropologists do not exhibit the “wide experience” and consequent “sound
judgment” that Darwin recommended as necessary for those giving specific names. If the same criteria used to assign specific
fossil names were applied to modern Homo sapiens, the different regional human populations would have to be recognized as
specifically distinct. In opposition to the recommendation that we should recognize ever more specific names, there should
be a moratorium called and no new species names should be proposed at all. The continuation of patterns of trivial trait configurations
associated with the various inhabited regions of the world clearly indicates genetic continuity through time but, unless it
can be shown that there is no reproductive continuity between one region and another, these differences do not warrant taxonomic
recognition. Major adaptive changes such as significant increases in relative brain size do warrant formal named recognition. 相似文献
9.
Modelling the potential geographic distribution of invasive ant species in New Zealand 总被引:2,自引:0,他引:2
Darren F. Ward 《Biological invasions》2007,9(6):723-735
Despite their economic and environmental impacts, there have been relatively few attempts to model the distribution of invasive
ant species. In this study, the potential distribution of six invasive ant species in New Zealand are modelled using three
fundamentally different methods (BIOCLIM, DOMAIN, MAXENT). Species records were obtained from museum collections in New Zealand.
There was a significant relationship between the length of time an exotic species had been present in New Zealand and its
geographic range. This is the first time such a time lag has been described for exotic ant species, and shows there is a considerable
time lag in their spread. For example, it has taken many species several decades (40–60 years) to obtain a distribution of
17–25% of New Zealand regions. For all six species, BIOCLIM performed poorly compared to the other two modelling methods.
BIOCLIM had lower AUC scores and higher omission error, suggesting BIOCLIM models under-predicted the potential distribution
of each species. Omission error was significantly higher between models fitted with all 19 climate variables compared to those
models with fewer climate variables for BIOCLIM, but not DOMAIN or MAXENT. Widespread species had a greater commission error.
A number of regions in New Zealand are predicted to be climatically suitable for the six species modelled, particularly coastal
and lowland areas of both the North and South Islands. 相似文献
10.
Primary charge separation in Photosystem II 总被引:3,自引:3,他引:0
In this Minireview, we discuss a number of issues on the primary photosynthetic reactions of the green plant Photosystem II.
We discuss the origin of the 683 and 679 nm absorption bands of the PS II RC complex and suggest that these forms may reflect
the single-site spectrum with dominant contributions from the zero-phonon line and a pronounced ∼80 cm−1 phonon side band, respectively. The couplings between the six central RC chlorins are probably very similar and, therefore,
a `multimer' model arises in which there is no `special pair' and in which for each realization of the disorder the excitation
may be dynamically localized on basically any combination of neighbouring chlorins. The key features of our model for the
primary reactions in PS II include ultrafast (<500 fs) energy transfer processes within the multimer, `slow' (∼20 ps) energy
transfer processes from peripheral RC chlorophylls to the RC multimer, ultrafast charge separation (<500 fs) with a low yield
starting from the singlet-excited `accessory' chlorophyll of the active branch, cation transfer from this `accessory' chlorophyll
to a `special pair' chlorophyll and/or charge separation starting from this `special pair' chlorophyll (∼8 ps), and slow relaxation
(∼50 ps) of the radical pair by conformational changes of the protein. The charge separation in the PS II RC can probably
not be described as a simple trap-limited or diffusion-limited process, while for the PS II core and larger complexes the
transfer of the excitation energy to the PS II RC may be rate limiting.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
David Penny Marc P. Hoeppner Anthony M. Poole Daniel C. Jeffares 《Journal of molecular evolution》2009,69(5):527-540
We review the introns-first hypothesis a decade after it was first proposed. It is that exons emerged from non-coding regions
interspersed between RNA genes in an early RNA world, and is a subcomponent of a more general ‘RNA-continuity’ hypothesis.
The latter is that some RNA-based systems, especially in RNA processing, are ‘relics’ that can be traced back either to the
RNA world that preceded both DNA and encoded protein synthesis or to the later ribonucleoprotein (RNP) world (before DNA took
over the main coding role). RNA-continuity is based on independent evidence—in particular, the relative inefficiency of RNA
catalysis compared with protein catalysis—and leads to a wide range of predictions, ranging from the origin of the ribosome,
the spliceosome, small nucleolar RNAs, RNases P and MRP, and mRNA, and it is consistent with the wide involvement of RNA-processing
and regulation of RNA in modern eukaryotes. While there may still be cause to withhold judgement on intron origins, there
is strong evidence against introns being uncommon in the last eukaryotic common ancestor (LECA), and expanding only within
extant eukaryotic groups—the ‘very-late’ intron invasion model. Similarly, it is clear that there are selective forces on
numbers and positions of introns; their existence may not always be neutral. There is still a range of viable alternatives,
including introns first, early, and ‘latish’ (i.e. well established in LECA), and regardless of which is ultimately correct,
it pays to separate out various questions and to focus on testing the predictions of sub-theories. 相似文献
12.
We formulate a Dynamic Energy Budget (DEB) model for the growth and reproduction of individual organisms based on partitioning
of net production (i.e. energy acquisition rate minus maintenance rate) between growth and energy reserves. Reproduction uses
energy from reserves. The model describes both feeding and non-feeding stages, and hence is applicable to embryos (which neither
feed nor reproduce), juveniles (which feed but do not reproduce), and adults (which commonly both feed and reproduce). Embryonic
growth can have two forms depending on the assumptions for acquisition of energy from yolk. By default, when the energy acquisition
rate exceeds the maintenance rate, a fixed proportion of the resulting net production is spent on growth (increase in structural biomass), and the remaining portion is channelled to the reserves. Feeding organisms,
however, modulate their allocation of net production energy in response to their total energy content (energy in the reserves
plus energy bounded to structural biomass). In variable food environment an organism alternates between periods of growth,
no-growth, and balanced-growth. In the latter case the organism adopts an allocation strategy that keeps its total energy
constant. Under constant environmental conditions, the growth of a juvenile is always of von Bertalanffy type. Depending on
the values of model parameters there are two long-time possibilities for adults: (a) von Bertalanffy growth accompanied by
reproduction at a rate that approaches zero as the organism approaches asymptotic size, or (b) abrupt cessation of growth
at some finite time, following which, the rate of reproduction is constant. We illustrate the model's applicability in life
history theory by studying the optimum values of the energy allocation parameters for constant environment and for each of
the dynamic regimes described above.
Received: 11 May 1998 / Revised version: 18 February 2000 / Published online: 4 October 2000 相似文献
13.
Atomic force microscopy (AFM) indentation has become an important technique for quantifying the mechanical properties of live
cells at nanoscale. However, determination of cell elasticity modulus from the force–displacement curves measured in the AFM
indentations is not a trivial task. The present work shows that these force–displacement curves are affected by indenter-cell
adhesion force, while the use of an appropriate indentation model may provide information on the cell elasticity and the work
of adhesion of the cell membrane to the surface of the AFM probes. A recently proposed indentation model (Sirghi, Rossi in
Appl Phys Lett 89:243118, 2006), which accounts for the effect of the adhesion force in nanoscale indentation, is applied to the AFM indentation experiments
performed on live cells with pyramidal indenters. The model considers that the indentation force equilibrates the elastic
force of the cell cytoskeleton and the adhesion force of the cell membrane. It is assumed that the indenter-cell contact area
and the adhesion force decrease continuously during the unloading part of the indentation (peeling model). Force–displacement
curves measured in indentation experiments performed with silicon nitride AFM probes with pyramidal tips on live cells (mouse
fibroblast Balb/c3T3 clone A31-1-1) in physiological medium at 37°C agree well with the theoretical prediction and are used
to determine the cell elasticity modulus and indenter-cell work of adhesion.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
14.
John G. Frazier Harry L. Fierstine Sallie C. Beavers Federico Achaval Hiroyuki Suganuma Robert L. Pitman Yuichiro Yamaguchi Carlos Ma. Prigioni 《Environmental Biology of Fishes》1994,39(1):85-96
Synopsis Billfishes have long been known to impale a great variety of objects, but there are only two brief, obscure records of marine
turtles being speared. Details are presented on these two, as well as on two other confirmed records; data from two additional
unconfirmed records are also presented. In total, three species of marine turtles are known to have been impaled by three
species of billfishes; a fourth species of fish and a fourth species turtle are listed in an unconfirmed case. Records come
from the eastern and western Pacific as well as the eastern Atlantic. Of the four confirmed cases, the turtles survived in
two, and apparently died as an effect of the spearing in the other two. In three confirmed cases only the impaled rostrum
was encountered, and in one confirmed case the entire fish was found, with its rostrum piercing the turtle. There is no obvious
advantage — or clear disadvantage — involved in impaling turtles. It is argued that these attacks are accidental, and the
result of attempts made by the billfish to capture prey that are near the turtle. These spearings indicate that the chelonians
serve as shelters for prey animals on the high seas, and thus, are further evidence of the pelagic existence of marine turtles.
The impalings are evidence of a singular ecological role of the turtles — as live fish aggregation devices. 相似文献
15.
Robert Sugden 《Biology & philosophy》2011,26(5):717-736
The paper explores how, in economics and biology, theoretical models are used as explanatory devices. It focuses on a modelling
strategy by which, instead of starting with an unexplained regularity in the world, the modeller begins by creating a credible
model world. The model world exhibits a regularity, induced by a mechanism in that world. The modeller concludes that there
may be a part of the real world in which a similar regularity occurs and that, were that the case, the model would offer an explanation. Little concrete guidance is given about where such a regularity might be found. Three
modelling exercises in evolutionary game theory—one from economics and two from biology—are used as case studies. Two of these
(one from each discipline) exemplify ‘explanation in search of observation’. The third goes a step further, analysing a regularity
in a model world and treating it as informative about the real world, but without saying anything about real phenomena. The
paper argues that if the relation between the model and real worlds is understood in terms of similarity, and if modelling
is understood as an ongoing discovery process rather than as the demonstration of empirical truths, there can be value in
creating explanations before finding the regularities that are to be explained. 相似文献
16.
The attractive and spacing interaction between pairs of filaments via cross-linkers, e.g. myosin oligomers connecting actin
filaments, is modeled by global integral kernels for negative binding energies between two intersecting stiff and long rods
in a (projected) two-dimensional situation, for simplicity. Whereas maxima of the global energy functional represent intersection
angles of ‘minimal contact’ between the filaments, minima are approached for energy values tending to −∞, representing the
two degenerate states of parallel and anti-parallel filament alignment. Standard differential equations of negative gradient
flow for such energy functionals show convergence of solutions to one of these degenerate equilibria in finite time, thus
called ‘super-stable’ states. By considering energy variations under virtual rotation or translation of one filament with
respect to the other, integral kernels for the resulting local forces parallel and orthogonal to the filament are obtained.
For the special modeling situation that these variations only activate ‘spring forces’ in direction of the cross-links, explicit
formulas for total torque and translational forces are given and calculated for typical examples. Again, the two degenerate
alignment states are locally ‘super-stable’ equilibria of the assumed over-damped dynamics, but also other stable states of
orthogonal arrangement and different asymptotic behavior can occur. These phenomena become apparent if stochastic perturbations
of the local force kernels are implemented as additive Gaussian noise induced by the cross-link binding process with appropriate
scaling. Then global filament dynamics is described by a certain type of degenerate stochastic differential equations yielding
asymptotic stationary processes around the alignment states, which have generalized, namely bimodal Gaussian distributions.
Moreover, stochastic simulations reveal characteristic sliding behavior as it is observed for myosin-mediated interaction
between actin filaments. Finally, the forgoing explicit and asymptotic analysis as well as numerical simulations are extended
to the more realistic modeling situation with filaments of finite length.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
A permeant ion is known to create in the channel pore a local electrical field, the intensity of which exceeds the intensity
of an electrical field produced by the membrane potential. In our study, we consider a sodium channel model, in which the
effects of a permeant ion, an inactivating particle, and pharmacological agents on mobile charged groups of the channel are
semi-phenomenologically taken into account by using motion equations for a generalized structural variable. Stationary solutions
for the equation correspond to “open,” “closed,” and “inactivated” channel states. Because of this, the channel free energy
profile, as a function of the structural variable, has three local minima. The three energy values of these states depend
both on the electrical field applied externally and on the near-membrane concentrations of permeant ions and acting pharmacological
agents. Sodium channel activation and inactivation kinetics are considered resulting from relative changes of the free energy
typical of the above three states of the channel. The results we obtained in the course of channel activation and inactivation
modeling and their voltage dependence are qualitatively consistent with the commonly known experimental data. The proposed
model allows one to qualitatively predict the dependence of the sodium channel kinetic characteristics on the concentrations
of permeant ions and pharmacological agents. 相似文献
18.
On the reciprocal interaction between believing and feeling: an adaptive agent modelling perspective
An agent’s beliefs usually depend on informational or cognitive factors such as observation or received communication or reasoning,
but also affective factors may play a role. In this paper, by adopting neurological theories on the role of emotions and feelings,
an agent model is introduced incorporating the interaction between cognitive and affective factors in believing. The model
describes how the strength of a belief may not only depend on information obtained, but also on the emotional responses on
the belief. For feeling emotions a recursive body loop between preparations for emotional responses and feelings is assumed.
The model introduces a second feedback loop for the interaction between feeling and belief. The strength of a belief and of
the feeling both result from the converging dynamic pattern modelled by the combination of the two loops. For some specific
cases it is described, for example, how for certain personal characteristics an optimistic world view is generated in the
agent’s beliefs, or, for other characteristics, a pessimistic world view. Moreover, the paper shows how such affective effects
on beliefs can emerge and become stronger over time due to experiences obtained. It is shown how based on Hebbian learning
a connection from feeling to belief can develop. As these connections affect the strenghts of future beliefs, in this way
an effect of judgment ‘by experience built up in the past’ or ‘by gut feeling’ can be obtained. Some example simulation results
and a mathematical analysis of the equilibria are presented. 相似文献
19.
Henryk Chojnacki Janina Kuduk-Jaworska Iwona Jaroszewicz Jerzy J. Jański 《Journal of molecular modeling》2009,15(6):659-664
The behaviour of cisplatin in serum, and the drastic differences between the properties of this drug and its trans-isomer
were the main motivations for this work. In a search for model “thiol–platin(II)” interactions, the first steps of the following
reaction systems were evaluated: (1) cisplatin–thiomethanol; (2) transplatin–thiomethanol; (3) cisplatin–cysteine; and (4)
transplatin–cysteine. In each case, calculations for the associative mode of reactions were performed. The electronic structure
of these molecular systems was studied at the non-empirical all-electron level using density functional theory (DFT) within
the Huzinaga and WTBS basis sets including polarisation Gaussian functions and full geometry optimisation. B3LYP or EPBO density
functionals were applied throughout. The calculated molecular electrostatic potentials are presented graphically. Assuming
that electrostatic effects are dominant, cisplatin should interact more strongly with the sulfur atom of CH3S− and deprotonated CYS-S− than transplatin. This fact has been documented in the supermolecule model of the relevant interaction energies in both gas
phase as well as within the solvent polarisable continuum model. The opposite relationship was observed when we compared values
of energy differences between products and substrates for both isomers. The data obtained here could be applied to search
for correlation between the biological activity of platinum complexes and their properties as estimated by various physico-chemical
and in silico methodologies. 相似文献
20.
Blas M. Benito M. Montserrat Martínez-Ortega Luz M. Muñoz Juan Lorite Julio Peñas 《Biodiversity and Conservation》2009,18(9):2509-2520
The species distribution models (SDMs) are useful tools for investigating rare and endangered species as well as the environmental
variables affecting them. In this paper, we propose the application of SDMs to assess the extinction-risk of plant species
in relation to the spread of greenhouses in a Mediterranean landscape, where habitat depletion is one of the main causes of
biodiversity loss. For this purpose, presence records of the model species (Linaria nigricans, a endemic and threatened species) and the greenhouses, a dataset of environmental variables, and different only presence-based
modelling algorithms (Bioclim, Domain, GARP, MaxEnt and ENFA) were used to build SDMs for L. nigricans as well as for greenhouses. To evaluate the models a modified approach of the area-under-curve ROC was applied. Combining
the most accurate models, we generated an extinction-risk model of L. nigricans populations, which enabled us to assess the sustainability of the most threatened populations. Our results show that is possible
to model greenhouses spreading as a “biological invasion”. The procedure explained and used in this work is quite novel, and
offers an objective spatial criterion intended for the management of natural resources and for the conservation of the biodiversity
in areas threatened by habitat depletion processes as particular as greenhouses expansion. 相似文献