19 research outputs found
Mackey-Glass type delay differential equations near the boundary of absolute stability
For equations with -nonlinearity which has negative Schwarzian derivative and
satisfies for , we prove convergence of all solutions to
zero when both and are less than some constant
(independent on ). This result gives additional insight to the
conjecture about the equivalence between local and global asymptotical
stabilities in the Mackey-Glass type delay differential equations.Comment: 16 pages, 1 figure, accepted for publication in the Journal of
Mathematical Analysis and Application
Yorke and Wright 3/2-stability theorems from a unified point of view
We consider a family of scalar delay differential equations ,
with a nonlinearity satisfying a negative feedback condition combined with
a boundedness condition. We present a global stability criterion for this
family, which in particular unifies the celebrated 3/2-conditions given for the
Yorke and the Wright type equations. We illustrate our results with some
applications.Comment: 10 pages, accepted for publication in the Expanded Volume of DCDS,
devoted to the fourth international conference on Dynamical Systems and
Differential Equations, held at UNC at Wilmington, May 2002. Minor changes
from the previous versio
Proton-conducting membrane with spatially heterogeneous structure based on polymer-silica nanocomposites
An original approach for the preparation of ternary proton-conducting membranes consisting of
high density polyethylene (PE), silicon dioxide, and phosphoric acid for the intermediate temperature (140-
180 oC) fuel cell is presented. The base of this method is a template synthesis of silica phase using
hyperbranched polyethoxysiloxane as a precursor by hydrolytic condensation reaction within the volume of
the nanoporous polymer matrix with pore’s diameter of about 10 nm obtained via the mechanism of
delocalized solvent-crazing. The received polymer-silica nanocomposites containing up to 40 wt.% of SiO2
were characterized by a structure of two interpenetrating networks, and silicon dioxide formed a rigid three-
dimensional framework. Loading of composites by phosphoric acid was carried out by their heating in an
environment of H3PO4 at 160 oC that was above the melting point of PE. In this case, the polyethylene melt
migrated from inner volume to surfaces of the composite while emerged pores were filled with acid. The
amount of introduced acid increased linearly with a growth of silica phase in the composite and maximum
content of H3PO4 equaled to 50 wt.%. The proton-conducting membranes obtained are characterized by
conductivity of 0.03 S/cm and the best performance of 0.4 V at current densities of 0.4 A/cm2 at 160 oC
ЛЮМИНЕСЦЕНТНОЕ ОПРЕДЕЛЕНИЕ МЕДИ, СЕРЕБРА, ЗОЛОТА И ПЛАТИНЫ С ИСПОЛЬЗОВАНИЕМ 2-МЕРКАПТО-5-БЕНЗИМИДАЗОЛСУЛЬФОКИСЛОТЫ, В ТОМ ЧИСЛЕ ЗАКРЕПЛЕННОЙ НА ПОВЕРХНОСТИ КРЕМНЕЗЕМА
Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.2-Mercapto-5-benzimidazolesulfonic acid (MBI), also noncovalently bound to a silica surface, is proposed as a reagent for the low-temperature luminescence determination of Cu(I), Ag(I), Au(I), and Pt(II). Luminescence excitation and luminescence spectra of metal complexes with MBI in solutions and on the adsorbent surface represent broad unstructured bands in the regions 250–400 and 450–700 nm, respectively. The developed procedures for the luminescence and sorption–luminescence determination of Cu, Ag, Au, and Pt with limits of detection at a level of 0.001–0.01 μg on 0.1 g of adsorbent are tested in the determination of metals in natural and industrial samples
Application of silica modified with polyhexamethylene guanidyne and 8-oxyquinolyne-5-sulfur acid for concentration and sorption-atomic emission determination of metals in natural waters
Рассмотрены особенности концентрирования ионов металлов кремнеземом, модифицированным полигексаметиленгуанидином и 8-оксихинолин-5-сульфокислотой (SiO2-ПГМГ-Oxin), и оксихинолинатов металлов кремнеземом, модифицированным полигексаметиленгуанидином (SiO2-ПГМГ). В статическом режиме количественное (более 99 %) извлечение Cu(II), Zn(II), Co(II), Ni(II), Cd(II), Fe(III) и Al(III) с помощью SiO2-ПГМГ-Oxin достигается из растворов с рН 4-7, Mn(II) - рН 5,5-7,0. При рН 5 в динамическом режиме достигается групповое концентрирование ионов металлов SiO2-ПГМГ-Oxin или их оксихинолинатов SiO2-ПГМГ. Сорбированные элементы десорбируют 1 М растворами HCl или HNO3 и определяют атомно-эмиссионным методом. Разработанная методика сорбционно-атомно-эмиссионного определения использована при определении содержания металлов в природных водах.Peculiarities of metal ions collection by silica, modified with polyhexamethylene guanidine and 8-oxyquinoline-5-sulfo-acid (SiO2-PHMG-Oxin), and metals' oxyquinolinates by silica, modified with polyhexamethylene guanidine (SiO2-PHMG), are considered. Quantitative (?99%) extraction of Cu(II), Zn(II), Co(II), Ni(II), Cd(II), Fe(III), Al(III) by SiO2-PHMG-Oxin from the solutions with pH 4-7, Mn(II) - рН 5,5-7,0 was observed at batch equilibrium conditions. Under pH 5 group collection of metal ions by SiO2-PHMG-Oxin or their oxyquinolinates by SiO2-PHMG was archived at flow-injection conditions. Sorbed elements were desorbed by 1M solutions of HCl or HNO3 and determined by atomic emission method. Developed technique of sorption-atomic-emission determination was used for determination of metals content in natural waters