608 research outputs found
Direct measurement of lateral transport in membranes by using time-resolved spatial photometry.
Spatially resolving light detectors allow, with proper calibration, quantitative analysis of the variations in two-dimensional intensity distributions over time. An ultrasensitive microfluorometer was assembled by using as a detector a microchannel plate-intensified video camera. The camera was interfaced with a software-based digital video analysis system to digitize, average, and process images and to directly control the timing of the experiments to minimize exposure of the specimen to light. The detector system has been characterized to allow its use as a photometer. A major application has been to perform fluorescence recovery after photobleaching measurements by using the camera in place of a photomultiplier tube (video-FRAP) with the goal of detecting possible anisotropic diffusion or convective flow. Analysis of the data on macromolecular diffusion in homogenous aqueous glycol solutions yielded diffusion constants in agreement with previous measurements. Results on lipid probe diffusion in dimyristoylphosphatidylcholine multibilayers indicated that at temperatures above the gel-to-liquid crystalline phase transition diffusion is isotropic, and analysis of video-FRAP data yielded diffusion coefficients consistent with those measured previously by using spot photobleaching. However, lipid probes in these multibilayers held just below the main phase transition temperature exhibited markedly anisotropic diffusive fluxes when the bleaching beam was positioned proximate to domain boundaries in the P beta' phase. Lipid probes and lectin receptor complexes diffused isotropically in fibroblast surface membranes with little evidence for diffusion channeled parallel to stress fibers. A second application was to trace the time evolution of cell surface reactions such as patching. The feasibility of following, on the optical scale, the growth of individual receptor clusters induced by the ligand wheat germ agglutinin was demonstrated
Squeezing superfluid from a stone: Coupling superfluidity and elasticity in a supersolid
In this work we start from the assumption that normal solid to supersolid
(NS-SS) phase transition is continuous, and develop a phenomenological Landau
theory of the transition in which superfluidity is coupled to the elasticity of
the crystalline He lattice. We find that the elasticity does not affect the
universal properties of the superfluid transition, so that in an unstressed
crystal the well-known -anomaly in the heat capacity of the superfluid
transition should also appear at the NS-SS transition. We also find that the
onset of supersolidity leads to anomalies in the elastic constants near the
transition; conversely, inhomogeneous strains in the lattice can induce local
variations of the superfluid transition temperature, leading to a broadened
transition.Comment: 4 page
Anomalies in Superfluids and a Chiral Electric Effect
We analyze the chiral transport terms in relativistic superfluid
hydrodynamics. In addition to the spontaneously broken symmetry current, we
consider an arbitrary number of unbroken symmetries and extend the results of
arXiv:1105.3733. We suggest an interpretation of some of the new transport
coefficients in terms of chiral and gravitational anomalies. In particular, we
show that with unbroken gauged charges in the system, one can observe a chiral
electric conductivity - a current in a perpendicular direction to the applied
electric field. We present a motivated proposal for the value of the associated
transport coefficient, linking it to the triangle anomaly. Along the way we
present new arguments regarding the interpretation of the anomalous transport
coefficients in normal fluids. We propose a natural generalization of the
chiral transport terms to the case of an arbitrary number of spontaneously
broken symmetry currents.Comment: 30 pages; v2: Onsager-relations argument corrected, references added;
v3: fixed missing line in eq. (38
Solution Equilibrium Studies of Anticancer Ruthenium(II)-η6-p-cymene Complexes of Pyridinecarboxylic Acids
Stoichiometry and stability of antitumor ruthenium(II)-η6-p-cymene complexes of picolinic acid and its 6-methyl and 6-carboxylic acid derivatives were determined by pH-potentiometry, 1H NMR spectroscopy and UV–Vis spectrophotometry in aqueous solution in the presence or absence of coordinating chloride ions. The picolinates form exclusively mono-ligand complexes in which they can coordinate via the bidentate (O,N) mode and a chloride or a water molecule is found at the third binding site of the ruthenium(II)-η6-p-cymene moiety depending on the conditions. [Ru(η6-p-cymene)(L)(H2O/Cl)] species are predominant at physiological pH in all studied cases. Hydrolysis of the aqua complex or the chlorido/hydroxido co-ligand exchange results in the formation of the mixed-hydroxido species [Ru(η6-p-cymene)(L)(OH)] in the basic pH range. There is no indication for the decomposition of the mono-ligand complexes during 24 h in the ruthenium(II)-η6-p-cymene-picolinic acid system between pH 3 and 11; however, a slight dissociation with a low reaction rate was found in the other two systems leading to the appearance of the dinuclear trihydroxido-bridged species [Ru2(η6-p-cymene)2(OH)3]+ and free ligands at pH > 10. The replacement of the chlorido by an aqua ligand in [Ru(η6-p-cymene)(L)Cl] was also monitored and equilibrium constants for the exchange process were determined
Hydrodynamics of Spatially Ordered Superfluids
We derive the hydrodynamic equations for the supersolid and superhexatic
phases of a neutral two-dimensional Bose fluid. We find, assuming that the
normal part of the fluid is clamped to an underlying substrate, that both
phases can sustain third-sound modes and that in the supersolid phase there are
additional modes due to the superfluid motion of point defects (vacancies and
interstitials).Comment: 24 pages of ReVTeX and 7 uuencoded figures. Submitted for publication
in Phys. Rev.
Structural instability of vortices in Bose-Einstein condensates
In this paper we study a gaseous Bose-Einstein condensate (BEC) and show
that: (i) A minimum value of the interaction is needed for the existence of
stable persistent currents. (ii) Vorticity is not a fundamental invariant of
the system, as there exists a conservative mechanism which can destroy a vortex
and change its sign. (iii) This mechanism is suppressed by strong interactions.Comment: 4 pages with 3 figures. Submitted to Phys. Rev. Let
Multi-threshold second-order phase transition
We present a theory of the multi-threshold second-order phase transition, and
experimentally demonstrate the multi-threshold second-order phase transition
phenomenon. With carefully selected parameters, in an external cavity diode
laser system, we observe second-order phase transition with multiple (three or
four) thresholds in the measured power-current-temperature three dimensional
phase diagram. Such controlled death and revival of second-order phase
transition sheds new insight into the nature of ubiquitous second-order phase
transition. Our theory and experiment show that the single threshold
second-order phase transition is only a special case of the more general
multi-threshold second-order phase transition, which is an even richer
phenomenon.Comment: 5 pages, 3 figure
What is Quantum? Unifying Its Micro-Physical and Structural Appearance
We can recognize two modes in which 'quantum appears' in macro domains: (i) a
'micro-physical appearance', where quantum laws are assumed to be universal and
they are transferred from the micro to the macro level if suitable 'quantum
coherence' conditions (e.g., very low temperatures) are realized, (ii) a
'structural appearance', where no hypothesis is made on the validity of quantum
laws at a micro level, while genuine quantum aspects are detected at a
structural-modeling level. In this paper, we inquire into the connections
between the two appearances. We put forward the explanatory hypothesis that,
'the appearance of quantum in both cases' is due to 'the existence of a
specific form of organisation, which has the capacity to cope with random
perturbations that would destroy this organisation when not coped with'. We
analyse how 'organisation of matter', 'organisation of life', and 'organisation
of culture', play this role each in their specific domain of application, point
out the importance of evolution in this respect, and put forward how our
analysis sheds new light on 'what quantum is'.Comment: 10 page
Superfluidity of Bose-Einstein Condensate in An Optical Lattice: Landau-Zener Tunneling and Dynamical Instability
Superflow of Bose-Einstein condensate in an optical lattice is represented by
a Bloch wave, a plane wave with periodic modulation of the amplitude. We review
the theoretical results on the interaction effects in the energy dispersion of
the Bloch waves and in the linear stability of such waves. For sufficiently
strong repulsion between the atoms, the lowest Bloch band develops a loop at
the edge of the Brillouin zone, with the dramatic consequence of a finite
probability of Landau-Zener tunneling even in the limit of a vanishing external
force. Superfluidity can exist in the central region of the Brillouin zone in
the presence of a repulsive interaction, beyond which Landau instability takes
place where the system can lower its energy by making transition into states
with smaller Bloch wavenumbers. In the outer part of the region of Landau
instability, the Bloch waves are also dynamically unstable in the sense that a
small initial deviation grows exponentially in time. In the inner region of
Landau instability, a Bloch wave is dynamically stable in the absence of
persistent external perturbations. Experimental implications of our findings
will be discussed.Comment: A new section on tight-binding approximation is added with a new
figur
Determination of the Michel Parameters rho, xi, and delta in tau-Lepton Decays with tau --> rho nu Tags
Using the ARGUS detector at the storage ring DORIS II, we have
measured the Michel parameters , , and for
decays in -pair events produced at
center of mass energies in the region of the resonances. Using
as spin analyzing tags, we find , , , , and . In addition, we report
the combined ARGUS results on , , and using this work
und previous measurements.Comment: 10 pages, well formatted postscript can be found at
http://pktw06.phy.tu-dresden.de/iktp/pub/desy97-194.p
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