Search results for "Stability"
showing 10 items of 3085 documents
High-Spin → Low-Spin Relaxation in [Fe(bpp)2](CF3SO3)2 H2O after LIESST and Thermal Spin-State Trapping—Dynamics of Spin Transition Versus Dynamics o…
1996
The iron(II) complex [Fe(bpp)2]-(CF3SO3)2 H2O (bpp = 2,6-bis(pyrazolyl-3-yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T1/2 (where the fraction of HS species γHS = 0.5) are 147 K and ≈285 K in the cooling and heating directions, respectively. The compound shows the LIESST and reverse-LIESST effects at low temperatures. The relaxation of the metastable HS states generated by LIESST was observed quantitatively at temperatures between 77.5 and 85 K by Mossbauer spectroscopy. Metastable HS states can also be generated by rapid cooling of the sample. The relaxation of the metastable HS states formed by thermal …
Double-well thermodynamic potentials and spinodal curves: how real are they?
2007
The concept of double-well thermodynamic potentials, ubiquitous since the van der Waals description of the vapour-to-liquid transition and the Landau theory of phase transitions, is critically re-examined. Particular emphasis is put on the extent to which spinodal curves (separating ‘metastable’ from ‘unstable’ states) are meaningful. It is argued that in full thermodynamic equilibrium spinodals are well-defined when one either considers finite subsystems of an infinitely large system, or systems with all linear dimensions finite. Evidence is given that in a finite (cubic) d-dimensional box the spinodals correspond (in a fluid) to the rounded ‘droplet evaporation’ or ‘bubble condensation’ t…
Cooperative phenomena and light-induced bistability in iron(II) spin-crossover compounds
1999
In iron(II) spin-crossover compounds, the transition from the 1A1 low-spin state at low temperatures to the 5T2 high-spin state at elevated temperatures is accompanied by a large increase in metal-ligand bond lengths. The resulting elastic interactions may be pictured as an internal pressure which is proportional to the concentration of the low-spin species. Because pressure stabilises the low-spin state relative to the high-spin state this results in a positive feedback. Thermal transition curves in neat iron(II) spin-crossover compounds are thus invariable much steeper than in diluted mixed crystals, and the high-spin→low-spin relaxation following the light-induced population of the high-…
Nucleation and Collapse of the Superconducting Phase in Type-I Superconducting Films
2005
The phase transition between the intermediate and normal states in type-I superconducting films is investigated using magneto-optical imaging. Magnetic hysteresis with different transition fields for collapse and nucleation of superconducting domains is found. This is accompanied by topological hysteresis characterized by the collapse of circular domains and the appearance of lamellar domains. Magnetic hysteresis is shown to arise from supercooled and superheated states. Domain-shape instability resulting from long-range magnetic interaction accounts well for topological hysteresis. Connection with similar effects in systems with long-range magnetic interactions is emphasized.
Nonlinear analysis of phase-locked loop
2010
Abstract New method for the rigorous mathematical nonlinear analysis of PLL systems is suggested. This method allows to calculate the characteristics of phase detectors and carry out a rigorous mathematical analysis of transient process and stability of the system.
On the Gardner Problem for the Phase-Locked Loops
2019
This report shows the possibilities of solving the Gardner problem of determining the lock-in range for multidimensional phase-locked loops systems. The development of analogs of classical stability criteria for the cylindrical phase space made it possible to obtain analytical estimates of the lock-in range for third-order system.
NODAPA-OH and NODAPA-(NCS)n: Synthesis, 68Ga-radiolabelling and in vitro characterisation of novel versatile bifunctional chelators for molecular ima…
2008
This report concerns synthesis, (68)Ga-radiolabelling and stability data of 1,4,7-triazacyclononane-1,4-diacetic acid-7-p-isothio-cyanatophenyl-acetic acid (NODAPA-NCS), 1,4,7-triazacyclononane-1-acetic acid-4,7-di-p-isothiocyanatophenyl-acetic acid (NODAPA-(NCS)(2)) and 1,4,7-triazacyclononane-1,4-diacetic acid-7-p-hydroxyphenyl-acetic acid (NODAPA-OH), versatile bifunctional chelators with potential for molecular imaging. Protein binding and exemplified conjugation are also reported.
DNA-binding and in vitro cytotoxic activity of platinum(II) complexes of curcumin and caffeine
2019
Abstract Three Pt(II) complexes containing the natural ligands curcumin and caffeine, namely [Pt(curc)(PPh3)2]Cl (1), [PtCl(curc)(DMSO)] (2) (curc = deprotonated curcumin) and trans-[Pt(caffeine)Cl2(DMSO)] (3), were synthesized and fully characterized. The data obtained suggest that, for both 1 and 2, the anion of curcumin is coordinated to the platinum ion via the oxygen atoms of the β-diketonate moiety. Spectroscopic features reveal that in 2 and 3, a DMSO molecule is S-bonded to the metal centre. For 3, all data indicate a square-planar geometry formed by a 9-N bonded caffeine, two trans chloride anions and a DMSO. The three complexes undergo changes in solution upon incubation for 24 h;…
Activity and Thermal Stability of Cobalt(II)-Based Olefin Polymerization Catalysts Adorned with Sterically Hindered Dibenzocycloheptyl Groups.
2019
Five examples of unsymmetrical 2-(2,4-bis(dibenzocycloheptyl)-6-methylphenyl- imino)ethyl)-6-(1-(arylyimino)ethyl)pyridine derivatives (aryl = 2,6-Me2C6H3 in L1
Clathration of Five-Membered Aromatic Rings in the Bimetallic Spin Crossover Metal–Organic Framework [Fe(TPT)2/3{MI(CN)2}2]·G (MI = Ag, Au)
2014
Six clathrate compounds of the three-dimensional spin crossover metal−organic framework formulated [Fe(TPT)2/3{MI (CN)2}2]· nG, where TPT is 2,4,6-tris(4-pyridyl)-1,3,5-triazine, MI = Ag or Au and G represent the guest molecules furan, pyrrole and thiophene, were synthesized using slow diffusion techniques. The clathrate compounds were characterized by single-crystal X-ray diffraction at 120 and 300 K, thermogravimetric analysis and thermal dependence of the magnetic susceptibility. All compounds crystallize in the R3̅ m trigonal space group. The FeII defines a unique [FeN6] crystallographic site with the equatorial positions occupied by four dicyanometallate ligands while the axial positio…