Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Phase Transition”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed2001

[Two-dimensional infrared correlation spectroscopy on dodecyloxy benzoic acid phase transition].

Thermal spectra of liquid crystal, dodecyloxy benzoic acid were collected over a temperature range of 26-150 degrees C by FTIR microspectroscopy. By taking investigations of temperature-induced changes in dodecyloxy benzoic acid by means of 2D infrared correlation spectroscopy, it was possible to clearly describe the molecular dynamic mechanism of dodecyloxy benzoic acid aggregates in the phase transitions. The analysis shows that p-dodecyloxy benzoic acid crystallized as multi-molecule aggregates through hydrogen bonds between the carboxylic groups, while the long polymethylene residues intermixed each other in solid state. Premelting phenomena in polymethylene residues were observed with temperature up to melting point. It seems that lots of oxy-benzoic acid part recrystallized to cycle dimer as supermolecular liquid crystal during alkyl chain melting in crystal-smectic phase transition. After temperature over 132 degrees C, oxy-benzoic acid part were melted to open dimer and separate molecule in liquid state.

Benzyl Compounds↗
PubMed2005

Distribution of current in nonequilibrium diffusive systems and phase transitions.

We consider diffusive lattice gases on a ring and analyze the stability of their density profiles conditionally to a current deviation. Depending on the current, one observes a phase transition between a regime where the density remains constant and another regime where the density becomes time dependent. Numerical data confirm this phase transition. This time dependent profile persists in the large drift limit and allows one to understand on physical grounds the results obtained earlier for the totally asymmetric exclusion process on a ring.

Journal Article↗
PubMed2006

Graphical analysis for gel morphology. III. Gel size and temperature effects on the volume phase transition of gels.

Just after poly(N-isopropylacrylamide) (PNIPA) gels are immersed into hot water over the critical temperature, they undergo a two- or three-step shrinking accompanied with the whitening. The size of gels and the destination temperature were changed and their effects on the shrinking process of PNIPA gels were studied. The following important knowledge in the volume phase transition process of PNIPA gels was obtained. The first is the fact that the fraction of first shrinking is determined by the shrinking rate in the first shrinking stage. The second is the fact that PNIPA gels are divided into small parts by the pinning of density fluctuation in the final stage of the first shrinking and that the shrinking process of each small part undergoes in the secondary shrinking stage. The volume phase transition process of PNIPA gels is briefly discussed from the viewpoint of the scaling theory.

Acrylic Resins↗
PubMed1991

How membrane chain-melting phase-transition temperature is affected by the lipid chain asymmetry and degree of unsaturation: an effective chain-length model.

Hydrocarbon effects on the lipid chain-melting phase-transition temperature are analyzed. The membrane fluidization temperature is shown to increase with the effective chain length, which is proportional to the thickness of the well-packed hydrocarbon region. The latter, as a rule, increases with the length of the longest ordered and aligned segment on each chain. This conclusion is independent of the cause for the reduced chain packing in membrane interior: chain unsaturation (which effectively decouples the two hydrocarbon segments disjoined by a double bond) or chain asymmetry (which causes the terminal hydrocarbon segments to lose close contact) both affect the bilayer chain-melting phase-transition temperature comparably on the effective chain-length scale. Thermodynamic consequences of the trans unsaturation are approximately 50% smaller than the effects of the double bonds in the cis conformation, owing to the smaller membrane perturbation by the former double bonds. A simple quantitative model is introduced for the analysis of the phospholipid chain-melting phase behavior. This new model permits quantitative predictions of the chain-melting transition temperature solely on the basis of the known lipid chemical composition. It also explains lipid sensitivity to the hydrocarbon type and attachment. The model agreement with the experimental data is usually better than to within 99% and thus comparable to experimental scatter, even when only a few or no adjustable parameters are used. The membrane fluidization temperature is calculated for a number of potentially interesting, also as yet unexplored, phospholipids, and the biological significance of the effective chain-length concept is discussed.

Hydrocarbons↗
PubMed1997

Cerebrosides alter the lyotropic and thermotropic phase transitions of DOPE:DOPC and DOPE:DOPC:sterol mixtures.

Freezing injury in rye and oat is a consequence of the formation of the inverted hexagonal (H(II)) phase in regions where the plasma membrane is brought into close proximity with cytoplasmic membranes during freeze-induced dehydration. Susceptibility to plasma membrane destabilization and H(II) phase formation during freezing is associated with alterations in plasma membrane lipid composition. This paper examines the influence of lipid composition and hydration on the propensity of lipid mixtures of DOPE:DOPC and DOPE:DOPC:sterols with added cerebrosides (CER) to form the H(II) phase during dehydration. The addition of CER to DOPE:DOPC:beta-sitosterol mixtures decreased the water content of the dispersions in a manner suggesting that most or all of the water in the dehydrated mixtures was associated with the phospholipids. The addition of CER significantly decreased the osmotic pressure at which the L(alpha) --> H(II) phase transition occurred from an osmotic pressure of 76.1 MPa for DOPE:DOPC (50:50) to 20 MPa in DOPE:DOPC:beta-sitosterol:CER (22.5:22.5:50:5) and 8 MPa in DOPE:DOPC:beta-sitosterol:CER (15:15:50:20). Experiments examining the effects of CER on the thermally-induced formation of the H(II) phase in fully hydrated mixtures and examining the influence of CER on the formation of the H(II) phase in DOPE:DOPC mixtures lacking beta-sitosterol suggested that CER facilitated the L(alpha) --> H(II) phase transition by effecting a decrease in bilayer hydration and by increased lateral packing pressures within the acyl domain of the bilayer. Taken in sum, these data indicate that the differential propensity of the rye and oat plasma membranes to undergo freeze-induced formation of the L(alpha) --> H(II) phase cannot be attributed to one lipid species. Rather, the propensity towards freeze-induced membrane destabilization is a consequence of the summation of physical characteristics of the membrane lipid components that included bilayer hydration, packing pressures within the hydrophobic domain of the membrane, the propensity of the lipid components to demix, and the relative proportions of the various lipid components.

Avena↗
PubMed2002

Kink pairs unbinding on domain walls and the sequence of phase transitions in fully frustrated XY models.

The unbinding of kink pairs on domain walls in the fully frustrated XY model (on square or triangular lattices) is shown to induce the vanishing of phase coupling across the walls. This forces the phase transition, associated with unbinding of vortex pairs, to take place at a lower temperature than the other phase transition, associated with proliferation of the Ising-type domain walls. The results are applicable for a description of superconducting junction arrays and wire networks in a perpendicular magnetic field, as well as of planar antiferromagnets with a triangular lattice.

Journal Article↗
PubMed1996

Temperature dependent intermediate structures during the main phase transition of dimyristoyl phosphatidylcholine vesicles a combined iodine laser-temperature jump and time resolved cryo-electron microscopy study.

The kinetics of the main phase transition of dimyristoylphosphatidyl choline (DMPC) unilamellar vesicles were investigated in the time range from microseconds to seconds. Iodine laser-temperature jump (ILTJ) experiments showed three discrete relaxation phenomena. Time resolved cryo-electron microscopy (CEM) was applied to produce images of intermediate states typical for the relaxation times of lipid vesicles in the micro- to millisecond time window. A careful measurement of the rate of temperature decrease observed during the production of vitrified lamellae of aqueous samples on a copper grid was performed. The best conditions resulted in average rates of cooling of 3 x 10(4) K/s. By comparing the images from CEM of DMPC vesicle samples vitrified above, at, and below the phase transition temperature a structural model was designed, which explains the temperature jump relaxation times in the micro- to millisecond time range by the formation and disappearance of coexisting clusters of crystalline, intermediate, and fluid lipid areas inside the DMPC bilayers.

Journal Article↗
PubMed2003

Interference of atomic levels and superfluid-Mott insulator phase transitions in a two-component Bose-Einstein condensate.

The superfluid-Mott insulator phase transition in a Bose-Einstein condensate of neutral atoms with doubly degenerate internal ground states in an optical lattice is theoretically investigated. The optical lattice is created by two counterpropagating linearly polarized laser beams with the angle theta between the polarization vectors (lin-angle-lin configuration). The phase diagram of the system and the critical values of the parameters are worked out. It is shown that the sign of the detuning plays an important role and that there is a strong suppression of the Mott transition in the case of blue detuning. Varying the laser intensity and/or the angle theta one can manipulate the Mott insulator to superfluid quantum phase transition as well as prepare the condensate in physically distinguishable "ferromagnetic" and "antiferromagnetic" superfluid states.

Journal Article↗
PubMedDate not supplied

Volume phase transition of bovine vitreous body in vitro and determination of its dynamics.

The phase equilibrium property and structural and dynamical properties of bovine vitreous body was studied by macroscopic observation of swelling behavior and dynamic light scattering under various conditions. It was found that the vitreous body collapses into a compact state isotropically or anisotropically depending on the external conditions. The vitreous body collapses while maintaining the shape when the pH (</= 4) and the concentration of calcium ions (</= 1 mol/L) are changed, whereas it collapses along the orbital axis in a mixed solvent of methanol and water. From observations of the dynamics of light scattered by the vitreous body, intensity autocorrelation functions that revealed two independent diffusion coefficients, D(fast) = 7.8 +/- 1.5 x 10 (- 8) cm(2)/s and D(slow) = 3.8 +/- 0.60 x 10 (-9) cm(2)/s, were obtained. The diffusion coefficients were found to be statistically independent of position within a focal depth range of 1-1.5 mm. Divergent behavior in the measured total scattered light intensities and diffusion coefficients was observed as the concentration of calcium ion approached the critical threshold, 1 mol/L. Namely, a slowing down of the dynamic modes accompanied by increased "static" scattered intensities was observed. The divergent behavior in the scattered light intensities and diffusion coefficients was reversible. This is indicative of the occurrence of a phase transition upon calcium ion concentration.

Animals↗
PubMed2006

Phase transition and critical dynamics in site-diluted Josephson-junction arrays.

Measurements of the IV characteristics of site-diluted Josephson-junction arrays have revealed intriguing effects of percolative disorder on the phase transition and the vortex dynamics in a two-dimensional XY system. Different from other types of phase transitions, the Kosterlitz-Thouless transition was eliminated with the introduction of percolative disorder far below the percolation threshold. Even after the Kosterlitz-Thouless order had been removed, the system remained superconducting at low temperatures by establishing a different type of order. Near the percolation threshold, evidence was found that, as a consequence of the underlying fractal structure, the critical dynamics of the phase degrees of freedom persisted down to zero temperature.

Journal Article↗
PubMed1985

Infrared spectroscopic study of the gel to liquid-crystal phase transition in live Acholeplasma laidlawii cells.

The temperature dependences of the infrared spectra of deuterium-labeled plasma membranes of live Acholeplasma laidlawii B cells and of the isolated plasma membranes demonstrate that the profiles of the gel to liquid-crystal phase transitions are very different. At temperatures within the range of the phase transition, the live mycoplasma is able to keep the "fluidity" of its plasma membrane at a much higher value than that of the isolated plasma membrane at the same temperature. The difference is particularly pronounced at and around the temperature of growth. Live Acholeplasma laidlawii, grown at 37 degrees C on a fatty acid depleted medium supplemented with myristic acid (C14:0), pentadecanoic acid (C15:0), or palmitic acid (C16:0), are highly "fluid"; i.e., at the temperature of growth, the fractional population of the liquid-crystalline phase is 95-100% at 37 degrees C, whereas in the case of the isolated plasma membranes the fractional population of the liquid-crystalline phase at 37 degrees C is only 58% (C14:0), 36% (C15:0), or 38% (C16:0).

Acholeplasma laidlawii↗
PubMed1984

Photon correlation spectroscopy as a probe of planar lipid bilayer phase transitions.

Photon correlation spectroscopy has been applied to study phase transitions of planar bilayer membranes. The membrane tension and one specific membrane viscosity are probed. Difficulties arising in the measurement of the temperature dependence of these properties are discussed and a servo-control system to overcome them is described. Typical data are presented for monoglyceride bilayers. Membranes incorporating cholesterol display effects below the lipid transition temperature which are interpreted in terms of separation within the membrane into cholesterol-rich fluid regions and regions of lipid in the gel phase. Some of the cholesterol-rich regions are apparently of macroscopic extent.

Cholesterol↗
PubMed2001

X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinites.

The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100-300 K. Using DSC measurements, a phase transition has been detected at 213 K. The space group of the low-temperature phase was determined to be P112(1) using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P2(1)3 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690 (8), b = 20.136 (2), c = 10.0329 (4) A, gamma = 90.01 (1) degrees ]. A precise analysis of the BeF(4) tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K(2)Mn(2)(BeF(4))(3) and also of a new type of low-temperature structure for langbeinite compounds.

Journal Article↗
PubMed1977

Cooperative unit size in the gel-liquid crystalline phase transition of dipalmitoyl phosphatidylcholine-water multilayers: an estimate from Raman spectroscopy.

The temperature dependence of the Raman spectral transitions assigned to the acyl chain C-C stretching modes of dipalmitoyl phosphatidylcholine was determined for the gel, phase transition and liquid crystalline states of the lipid multilayers. The van't Hoff enthalpy differences delta HVH between trans and gauche rotational isomers were obtained from the Raman spectral data for the temperature region characteristic of each bilayer state. An average size for the cooperative unit undergoing the chain melting process during the phase transition was estimated from the ratio of the appropriate van't Hoff enthalpy to an adjusted calorimetric enthalpy.

Binding Sites↗
PubMed1980

Lipid phase transition in planar bilayer membrane and its effect on carrier- and pore-mediated ion transport.

Using mixed-chain lipids, we have recorded cooling and heating curves of planar bilayer membranes while they passed the lipid phase transition range. With unmodified planar bilayers, spontaneous current fluctuations are observed near the lipid phase transition temperature (tc approximately 29 degrees C). This effect coincides with the expected and measured decrease in membrane capacitance. Carrier (valinomycin)-modified planar bilayers exhibit near tc an abrupt change from a high-conducting state above tc to the state of bare membrane conductance below tc. In contrast to this behavior, planar bilayers modified by pore-forming antibiotics (gramicidin A, alamethicin) do not show any peculiar effect at tc. However, at 22--23 degrees C a pronounced maximum in pore-induced conductance is seen. Whereas the gramicidin A pore abruptly stops stepwise fluctuations below approximately 16 degrees C, with alamethicin a few long-lasting pore and pore state fluctuations persist down to 10 degrees C. It is suggested that the carrier may freeze out into the membrane/water interface. The effects observed with pore-forming substances, on the other hand, are interpreted in terms of lateral phase separation into pure lipid and lipid/antibiotic domains.

Alamethicin↗
PubMed2005

Phase transition in a directed traffic flow network.

The generic feature of traffic in a network of flowing electronic data packets is a phase transition from a stationary free-flow phase to a continuously growing congested nonstationary phase. In the most simple network of directed oriented square lattice we have been able to observe all crucial features of such flow systems having nontrivial critical behavior near the critical point of transition. The network here is in the shape of a square lattice and data packets are randomly posted with a rate rho at one side of the lattice. Each packet executes a directed diffusive motion toward the opposite boundary where it is delivered. Packets accumulated at a particular node form a queue and a maximum of m such packets randomly jump out of this node at every time step to its neighbors on a first-in-first-out basis. The phase transition occurs at rho(c) = m. The distribution of travel times through the system is found to have a log-normal behavior and the power spectrum of the load time series shows 1/f-like noise similar to the scenario of Internet traffic.

Journal Article↗
PubMed1998

HiNF-D (CDP-cut/CDC2/cyclin A/pRB-complex) influences the timing of IRF-2-dependent cell cycle activation of human histone H4 gene transcription at the G1/S phase transition.

Cell cycle control of histone H4 gene transcription is mediated by the multipartite promoter domain H4-Site II, which supports transcriptional activation at the G1/S phase transition and modulates basal H4 gene transcription. Proliferation-specific transcription is determined by the integrated activities of three distinct promoter factors interacting with H4-Site II: the interferon regulatory factor IRF-2 (synonymous with HiNF-M), HiNF-D (a complex between the homeodomain protein CDP-cut and the cell cycle mediators CDC2, cyclin A and pRB), as well as HiNF-P/H4TF-2. However, the contribution of HiNF-D to the enhancement and/or suppression of H4 gene transcription at specific cell cycle stages remains to be established. We used a panel of synchronized HeLa S3 cell lines containing stably integrated H4 promoter/CAT reporter gene constructs with mutations in H4-Site II. The temporal regulation of CAT mRNA accumulation under the control of the H4 promoter was analyzed by RNase protection analysis. Our main finding is that mutation of the HiNF-D/CDP-cut binding site alters the timing of histone gene activation during the cell cycle. Furthermore, our data indicate that HiNF-P/H4TF-2 may functionally compensate for HiNF-M/IRF-2 at Site II to regulate histone H4 gene transcription in HeLa S3 cervical carcinoma cells during early S phase. We postulate that HiNF-D (CDP-cut/cyclin A/CDC2/pRB containing complex) promotes HiNF-M/IRF-2 (and/or HiNF-P/H4TF-2) dependent histone H4 gene activation at the G1/S phase transition and attenuates H4 gene transcription at later cell cycle stages. The mechanistic division in the gene regulatory functions of the three H4-Site II binding proteins may ensure that histone H4 gene expression is stringently coupled with the onset of S phase in response to growth factor/cytokine-induced cell cycle progression.

Base Sequence↗
PubMed1999

Renormalization group for renormalization-group equations toward the universality classification of infinite-order phase transitions.

We derive a renormalization group to calculate the nontrivial critical exponent of the divergent correlation length, thereby providing a universality classification of essential singularities in infinite-order phase transitions. This method thus resolves the vanishing scaling matrix problem. The exponent is obtained from the maximal eigenvalue of a scaling matrix in this renormalization group, as in the case of ordinary second-order phase transitions. We exhibit several nontrivial universality classes in infinite-order transitions different from the well known Berezinskiĭ-Kosterlitz-Thouless transition.

Journal Article↗