Magnetostructural relationships between the spin state of the Fe
III
ion, conformations of the ethylene bridges (-CH
2
-CH
2
-) in the five-membered chelates of the ligand, and Fe-N/O bonds were ...constructed due to an analysis of the literature data for 29 structures based on the
N,N
′-3,6-diazaoctane-1,8-diylbis(salicylidenaldiminato)iron(
iii
) Fe
III
(Sal
2
trien)
+
(H
2
Sal
2
trien is the hexadentate ((N
am
)
2
(N
im
)
2
O
2
) Schiffbase, condensation product of triethylenetetramine and salicylaldehyde). According to the analysis results for the dependences of the Fe-N bond lengths on the fraction of the high-spin state (γ
HS
,
S
= 5/2), the Fe-N
am
and Fe-N
im
bonds depend most strongly on the change in γ
HS
, since the donor N atoms are characterized by high σ-overlapping with the d-orbitals of the metal ion. The conformational switch of the ethylene bridges of the ligand occurs in the range 40% < γ
HS
< 85% at the relative elongations of the Fe-N
am
and Fe-N
im
bonds equal to 4.0–8.5% and 3.4–8.6%, respectively. Relationships were revealed between the γ
HS
values and ratios of high- and low-spin conformers of the complex cation in the unit cell. The scatter of bond length values was found in the polyhedron FeN
4
O
2
to 4% at γ
HS
= 0% and to 5% γ
HS
= 100%, which is caused by the effect of the crystalline environment of the complex cation. The determined features of the structural rearrangement of the hexadentate macrocyclic ligand of the Saltrien type can be used as a criterion for the estimation of γ
HS
and development of molecular design of Fe
III
compounds with controlled spin transition.
The spin state of the magnetic center for a spin-variable cation with nitrate Fe
III
(3-OMe-Sal
2
trien)NO
3
⋅H
2
O(
I
) and iodide Fe
III
(3-OMe-Sal
2
trien)I (
II
) anions is studied by Mössbauer ...spectroscopy on
57
Fe nuclei (3-OMe-Sal
2
trien is the condensation product of triethylenetetramine with 3-methoxy salicylaldehyde) in the temperature ranges of 5 to 305 and 85 to 296 K, respectively. It was shown that, for both complexes, only one low-spin (
S
= 1/2) doublet from iron(III) ions appears in the spectra, despite significant differences (up to ~10%) in the length of the iron(III)–ligand bonds in the N
4
O
2
coordination octahedron of the salt
II
compared with
I
, according to X-ray diffraction data at 293 K. The Debye temperatures were determined for both compounds, Θ = 157 and 153 K.
Morphogen gradients contribute to pattern formation by determining positional information in morphogenetic fields. Interpretation of positional information is thought to rely on direct, ...concentration-threshold-dependent mechanisms for establishing multiple differential domains of target gene expression. In Drosophila, maternal gradients establish the initial position of boundaries for zygotic gap gene expression, which in turn convey positional information to pair-rule and segment-polarity genes, the latter forming a segmental pre-pattern by the onset of gastrulation. Here we report, on the basis of quantitative gene expression data, substantial anterior shifts in the position of gap domains after their initial establishment. Using a data-driven mathematical modelling approach, we show that these shifts are based on a regulatory mechanism that relies on asymmetric gap-gap cross-repression and does not require the diffusion of gap proteins. Our analysis implies that the threshold-dependent interpretation of maternal morphogen concentration is not sufficient to determine shifting gap domain boundary positions, and suggests that establishing and interpreting positional information are not independent processes in the Drosophila blastoderm.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In the present work, a PLL with a lead-lag loop filter and a triangular phase detector characteristic is analysed. The exact value for the conservative lock-in range is obtained for the considered ...model. The solution is based on analytical integration of the considered model on the linear segments.
Genetic studies have revealed that segment determination in Drosophila melanogaster is based on hierarchical regulatory interactions among maternal coordinate and zygotic segmentation genes. The gap ...gene system constitutes the most upstream zygotic layer of this regulatory hierarchy, responsible for the initial interpretation of positional information encoded by maternal gradients. We present a detailed analysis of regulatory interactions involved in gap gene regulation based on gap gene circuits, which are mathematical gene network models used to infer regulatory interactions from quantitative gene expression data. Our models reproduce gap gene expression at high accuracy and temporal resolution. Regulatory interactions found in gap gene circuits provide consistent and sufficient mechanisms for gap gene expression, which largely agree with mechanisms previously inferred from qualitative studies of mutant gene expression patterns. Our models predict activation of Kr by Cad and clarify several other regulatory interactions. Our analysis suggests a central role for repressive feedback loops between complementary gap genes. We observe that repressive interactions among overlapping gap genes show anteroposterior asymmetry with posterior dominance. Finally, our models suggest a correlation between timing of gap domain boundary formation and regulatory contributions from the terminal maternal system.
Motivation: A new method is developed to query a relational database in natural language (NL). Results: The method, based on a semantic approach, interprets grammatical and lexical units of a natural ...language into concepts of subject domain, which are given in a conceptual scheme. The conceptual scheme is mapped formally onto the logical scheme. We applied the method to query the FlyEx database in natural language. FlyEx contains information on the expression of segmentation genes in Drosophila melanogaster. The method allows formulation of queries in various natural languages simultaneously, and is adaptive to changes in the knowledge domain and user’s views. It provides optimal transformation of queries from natural language to SQL, as well as visualization of information as a hyperscheme. The method does not require specification of all possible language constructions as well as a standard grammar accuracy in formulation of NL queries. Availability: http://urchin.spbcas.ru/NLP/NLP.html Contact: samson@spbcas.ru Keywords: natural language processing, relational databases, conceptual scheme, segmentation genes, D.melanogaster, query optimization. * To whom correspondence should be addressed.
Motivation: To create a spatiotemporal atlas of Drosophila segmentation gene expression at cellular resolution. Results: The expression of segmentation genes plays a crucial role in the establishment ...of the Drosophila body plan. Using the IBM DB2 Relational Database Management System we have designed and implemented the FlyEx database. FlyEx contains 2832 images of 14 segmentation gene expression patterns obtained from 954 embryos and 2 073 662 quantitative data records. The averaged data is available for most of segmentation genes at eight time points. FlyEx supports operations on images of gene expression patterns. The database can be used to examine the quality of data, analyze the dynamics of formation of segmentation gene expression domains, as well as estimate the variability of gene expression patterns. We also provide the capability to download data of interest. Availability: http://urchin.spbcas.ru/flyex, http://flyex.ams.sunysb.edu/flyex
In the present work, a second-order PLL with lead-lag loop filter and triangular phase detector characteristic is analysed. An exact value of the conservative lock-in range is obtained for the ...considered model. The solution is based on analytical integration of the considered model on the linear segments.
In the present paper the phase-locked loop (PLL), an electric circuit widely used in telecommunications and computer architectures is considered. A new modification of the PLL with tangential phase ...detector characteristic and active proportionally-integrating (PI) filter is introduced. Hold-in, pull-in and lock-in ranges for given circuit are studied rigorously. It is shown that lock-in range of the new PLL model is infinite, compared to the finite lock-in range of the classical PLL.
We perform elastic registration by an algorithm based on a pixelwise and regularized optimization criterion. We express the deformation field thanks to B-splines, which allows us to deal with a rich ...variety of deformations. The algorithm is able to handle soft landmark constraints, which is particularly useful when parts of the images contain very little information, or when it is unevenly distributed. We solve the problem by minimizing the distance between the target image and the warped source. We regularize this minimization problem by divergence and curl. We apply the proposed algorithm to the registration of the confocal scanning microscopy images of Drosophila embryos.PUBLICATION ABSTRACT
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