527 research outputs found
The Phase Behavior of Mixed Lipid Membranes in Presence of the Rippled Phase
We propose a model describing liquid-solid phase coexistence in mixed lipid
membranes by including explicitly the occurrence of a rippled phase. For a
single component membrane, we employ a previous model in which the membrane
thickness is used as an order parameter. As function of temperature, this model
properly accounts for the phase behavior of the three possible membrane phases:
solid, liquid and the rippled phase. Our primary aim is to explore extensions
of this model to binary lipid mixtures by considering the composition
dependence of important model parameters. The obtained phase diagrams show
various liquid, solid and rippled phase coexistence regions, and are in
quantitative agreement with the experimental ones for some specific lipid
mixtures.Comment: 8pages, 5figure
Viscoelasticity of two-layer-vesicles in solution
The dynamic shape relaxation of the two-layer-vesicle is calculated. In
additional to the undulation relaxation where the two bilayers move in the same
direction, the squeezing mode appears when the gap between the two bilayers is
small. At large gap, the inner vesicle relaxes much faster, whereas the slow
mode is mainly due to the outer layer relaxation. We have calculated the
viscoelasticity of the dilute two-layer-vesicle suspension. It is found that
for small gap, the applied shear drives the undulation mode strongly while the
slow squeezing mode is not much excited. In this limit the complex viscosity is
dominated by the fast mode contribution. On the other hand, the slow mode is
strongly driven by shear for larger gap. We have determined the crossover gap
which depends on the interaction between the two bilayers. For a series of
samples where the gap is changed systematically, it is possible to observe the
two amplitude switchings
A swollen phase observed between the liquid-crystalline phase and the interdigitated phase induced by pressure and/or adding ethanol in DPPC aqueous solution
A swollen phase, in which the mean repeat distance of lipid bilayers is
larger than the other phases, is found between the liquid-crystalline phase and
the interdigitated gel phase in DPPC aqueous solution. Temperature, pressure
and ethanol concentration dependences of the structure were investigated by
small-angle neutron scattering, and a bending rigidity of lipid bilayers was by
neutron spin echo. The nature of the swollen phase is similar to the anomalous
swelling reported previously. However, the temperature dependence of the mean
repeat distance and the bending rigidity of lipid bilayers are different. This
phase could be a precursor to the interdigitated gel phase induced by pressure
and/or adding ethanol.Comment: 7 pages, 6 figure
Determination of rain age via γ rays from accreted radon progeny
金沢大学自然計測応用研究センター自然計測研究部門The relative γ ray activities from P 214 b and B 214 i condensed from precipitation are used to determine its "age," the average time the accreted activity has been removed from secular equilibrium. A verifiable assumption that radon progeny on/in the surface/volume of droplets mostly remains in secular equilibrium until they begin their descent, enables estimates of their transit times to ground of typically a few tens of minutes. This agrees well with the time expected for the activity on the surface of droplets to reach the ground from heights of a few kilometers. The half lives of γ activities from B 214 i and P 214 b, 19.7 and 26.9 min, respectively, are on the same scale as transit time to ground and close enough to each other to measure ratios of activities from secular equilibrium (1.00) to transient equilibrium (3.88) within a few hundreds of minutes. The ratio of γ count rates is independent of knowledge of either initial activity or any systematic errors and thus limited only by the uncertainty from counting statistics, which from condensates of 5-30 l of rain viewed with 2π solid angle by a 50% efficient, high-resolution Ge detector is only a few percent. These ratios fit extremely well to known theoretical curves, which cannot only be used to date rain but can also be extrapolated backward to determine radon progeny activities in rain prior to its descent, knowledge of which may facilitate further studies using radon progeny as tracers. © 2008 American Institute of Physics
Mass transportation monitored by trace level radioactivity
金沢大学大学院自然科学研究科場所:金沢大学自然科学研究科図書館棟1階,講演会場:図書館棟1階 大会議室,ポスター会場:図書館棟1階12会議室,主催・共催:文部科学省21世紀COE「環日本海域の環境計測と長期・短期変動予測」, 大気環境学会, 金沢大学工学
Mass transportation monitored by trace level radioactivity
金沢大学大学院自然科学研究科場所:金沢大学自然科学研究科図書館棟1階,講演会場:図書館棟1階 大会議室,ポスター会場:図書館棟1階12会議室,主催・共催:文部科学省21世紀COE「環日本海域の環境計測と長期・短期変動予測」, 大気環境学会, 金沢大学工学
Ready ... Go: Amplitude of the fMRI Signal Encodes Expectation of Cue Arrival Time
What happens when the brain awaits a signal of uncertain arrival time, as when a sprinter waits for the starting pistol? And what happens just after the starting pistol fires? Using functional magnetic resonance imaging (fMRI), we have discovered a novel correlate of temporal expectations in several brain regions, most prominently in the supplementary motor area (SMA). Contrary to expectations, we found little fMRI activity during the waiting period; however, a large signal appears after the “go” signal, the amplitude of which reflects learned expectations about the distribution of possible waiting times. Specifically, the amplitude of the fMRI signal appears to encode a cumulative conditional probability, also known as the cumulative hazard function. The fMRI signal loses its dependence on waiting time in a “countdown” condition in which the arrival time of the go cue is known in advance, suggesting that the signal encodes temporal probabilities rather than simply elapsed time. The dependence of the signal on temporal expectation is present in “no-go” conditions, demonstrating that the effect is not a consequence of motor output. Finally, the encoding is not dependent on modality, operating in the same manner with auditory or visual signals. This finding extends our understanding of the relationship between temporal expectancy and measurable neural signals
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