17 research outputs found
Non-steady water percolation into granular beds
Przeprowadzono badania procesu przesi膮kania wody w warunkach nieustalonych przez warstwy ziarniste o r贸偶nej granulacji i r贸偶nej zawarto艣ci pocz膮tkowej wilgoci. Wykazano, 偶e proces ten mo偶e by膰 podzielony na dwa etapy. W czasie pierwszego z nich zachodzi saturacja warstwy porowatej, a przebieg tego zjawiska ma charakter liniowy. Zaproponowany opis matematyczny pozwalaj膮cy wyznaczy膰 pr臋dko艣膰 wsi膮kania w warstw臋 nieza-wieraj膮c膮 wilgoci. Przebieg drugiego etapu opisano za pomoc膮 zale偶no艣ci pot臋gowej wprowadzaj膮c poj臋cie wsp贸艂czynnika opor贸w przep艂ywu, korzystaj膮c przy tym z zasad opisuj膮cych przebieg zjawisk grawitacyjnego wyp艂ywu cieczy ze zbiornikaInvestigations concerning the non-steady water percolation into granular beds were performed. Two process stages were distinguished. In the first one rising saturation of the bed occurred and it can be described using linear equations. The applied procedure aHowed one to determine the percolation velocity in beds during a dry state. The second process stage was described using the approach typical for gravitational flow from a tank. A concept of flow resistance coefficient was introduced
Cyclic dipeptides as building units of nano- and microdevices : synthesis, properties, and structural studies
In this paper we report the influence
of stereochemistry on self-organization
in the solid state of cyclic dipeptides (CDP) employing two diastereomeric
samples cyclo颅(l-Tyr-l-Ala), cYA <b>1</b>,
and cyclo颅(l-Tyr-d-Ala), cY颅(D)颅A <b>2</b>, as
models. Both compounds were investigated by means of differential
scanning calorimetry (DSC), solid state NMR (SS NMR) spectroscopy,
scanning electron microscopy (SEM), powder X-ray diffraction (PXRD),
electronic circular dichroism (ECD) spectroscopy, and attenuated total
reflectance Fourier transform infrared spectroscopy (ATR鈥揊TIR).
It has been found that distinction in chirality of alanine residue
causes a significant difference in self-assembling and formation of
higher order structures. Sample <b>1</b> forms peptide nanotubes
(PNT) and nanowires (PNW), while for sample <b>2</b> only formation
of peptide microtubes (PMT) was observed. Crystal and molecular structures
for <b>1</b> and <b>2</b> were refined using PXRD due
to failure in attempts to grow crystals with quality suitable for
single crystal studies. Both compounds crystallize in the <i>P</i>2<sub>1</sub> space group and monoclinic system. The size
of the unit cell is highly similar; however small differences in alignment
of water molecules in the hydrophilic channels and geometry of diketopiperazine
rings were observed. Each technique confirmed high thermal stability
of PNT, PNW, and PMT under investigation. The water molecules can
be thermally removed from the lattice without destroying the subtle
crystal structures of nano- and microdevices. This reversible process
observed for sample <b>2</b> is a unique feature, rarely occurring
for the linear dipeptide devices