Major Loss of the 28-kD Protein of Gap Junction in Proliferating Hepatocytes

There is a reduction in the 28-kD gap junction protein detectable by immunofluorescence in livers of partially hepatectomized rats and in cultured hepatocytes stimulated to proliferate. By the coordinate use of antibodies directed to the hepatic junction protein (HJP28) and the use of a monoclonal antibody that recognizes bromodeoxyuridine (BrdU) incorporated into DNA, we have been able to study the relationship between detectable gap junction protein and cell division. Hepatocytes that label with BrdU in the regenerating liver and in cell culture show a significant reduction of HJP28. Cells that do not synthesize DNA, on the other hand, show normal levels and distribution of immunoreactive gap junction protein. We postulate that the quantitative changes in gap junction expression might play an important role in the control of proliferation in the liver

Non-monotonic fluctuation spectra of membranes pinned or tethered discretely to a substrate

The thermal fluctuation spectrum of a fluid membrane coupled harmonically to a solid support by an array of tethers is calculated. For strong tethers, this spectrum exhibits non-monotonic, anisotropic behavior with a relative maximum at a wavelength about twice the tether distance. The root mean square displacement is evaluated to estimate typical membrane displacements. Possible applications cover pillar-supported or polymer-tethered membranes.Comment: 4 pages, 5 figure

Atomar aufgelöste Dynamik von korrelierten Quantensystemen

In this thesis ultra-fast phenomena are investigated with a scanning tunneling microscope (STM). The real space influence of atomic sized defects on ultra-fast dynamics in correlated systems is one of the great mysteries in experimental research of solid states and is investigated in this thesis using two different approaches. In the first part an artificially built few atom magnet is investigated whose dynamic prop-erties are slowed down by placing it on a decoupling layer. The dynamic properties have a direct impact on spin-dependent transport and lead to the appearance of negative dif-ferential resistance. The effects can be astonishingly well described by a rate equation model which allows a deep insight into the processes occurring. The dynamics investigated in the first part are in the microsecond to nanosecond regime, as much faster processes cannot be measured by a conventional STM. To break this barri-er, in the second part of the thesis the development of a new unconventional STM is pre-sented. By coupling picosecond free-space terahertz (THz) laser pulses into the tunnel junction and inducing ultra-fast voltage pulses this new instrument enables pump-probe experiments with femtosecond time resolution on the atomic scale. In the last part of the thesis the dynamics of the charge density wave (CDW) system 2H-NbSe2 are investigated with the new THz-STM. A complex dynamic response is thereby observed consisting of a 600 fs decay and oscillating features with THz frequencies. The data can be explained by the excitation of the electronic system by a strong screening cur-rent which leads to the launch of collective modes of the CDW system. Further spatial resolved measurements indicate a clear link of the dynamic response with atomic defects.In dieser Arbeit werden ultra-schnelle Phänomene mit einem Rastertunnelmikro-skop (STM) untersucht. Der lokale Einfluss von atomaren Defekten auf ultra-schnelle Phänomene in korrelierten Systemen ist eines der großen Mysterien der experimentellen Erforschung von Festkörpern. Diesem Thema wird sich in Rahmen dieser Arbeit aus zwei unterschiedlichen Richtungen angenähert. Im ersten Teil wird ein aus wenigen Atomen künstlich gebauter Magnet untersucht, des-sen dynamische Eigenschaften durch das Platzieren auf einer Entkopplungsschicht ver-langsamt wurden. Die dynamischen Eigenschaften haben einen direkten Einfluss auf die elektrischen Transport Eigenschaften und führen zu einem negativen differentiellen Wie-derstand. Die auftretenden Effekte können außergewöhnlich präzise mit einem Model basierend auf einer Raten-Gleichung beschrieben werden, das einen tiefen Einblick in die auftretenden Prozesse erlaubt. Während die dynamischen Prozesse des ersten Teils sich im Mikrosekunden bis in das Nanosekunden Regime abspielen, lassen sich schnellere Prozesse nicht mehr mit konven-tionellen STM messen. Um diese Barriere zu durchbrechen, wird im zweiten Teil die Ent-wicklung eines neuen unkonventionellen STM vorgestellt. Durch die Kopplung von Piko-sekunden Freiraum Terahertz Pulsen in den Tunnel Kontakt und dem induzieren von ultra-schnellen Spannungspulsen erlaubt das neue Instrument auf der atomaren Skala stroboskopische Messungen mit einer Zeitauflösung kleiner als Pikosekunden. Mit dem neuen Instrument wird im letzten Kapitel das Ladungsträgerdichtewellen-(CDW)-system 2H-NbSe2 untersucht. Dabei wird eine dynamische Antwort bestehend aus einem 600 fs Abklingen und Schwingung mit THz Frequenzen beobachtet. Die Mes-sungen können durch eine elektronische Anregung erklärt werden, die durch einen star-ken Schirmungsstrom hervorgerufen wird, und zur Anregung von kollektiven Moden der CDW führt. Die Verbindung zwischen der dynamischen Antwort und atomaren Defekten wird in weiteren räumlich aufgelösten Messungen deutlich gezeigt

Equilibration of Long Chain Polymer Melts in Computer Simulations

Several methods for preparing well equilibrated melts of long chains polymers are studied. We show that the standard method in which one starts with an ensemble of chains with the correct end-to-end distance arranged randomly in the simulation cell and introduces the excluded volume rapidly, leads to deformation on short length scales. This deformation is strongest for long chains and relaxes only after the chains have moved their own size. Two methods are shown to overcome this local deformation of the chains. One method is to first pre-pack the Gaussian chains, which reduces the density fluctuations in the system, followed by a gradual introduction of the excluded volume. The second method is a double-pivot algorithm in which new bonds are formed across a pair of chains, creating two new chains each substantially different from the original. We demonstrate the effectiveness of these methods for a linear bead spring polymer model with both zero and nonzero bending stiffness, however the methods are applicable to more complex architectures such as branched and star polymer.Comment: 12 pages, 9 figure