Quantum Phase Dynamics in an LC shunted Josephson Junction

We have studied both theoretically and experimentally how an LC series circuit connected in parallel to a Josephson junction influences the Josephson dynamics. The presence of the shell circuit introduces two energy scales, which in specific cases can strongly differ from the plasma frequency of the isolated junction. Josephson junctions were manufactured using Nb/Al-AlOx/Nb fabrication technology with various on-chip LC shunt circuits. Spectroscopic measurements in the quantum limit show an excellent agreement with theory taking into account the shunt inductance and capacitance in the Resistively and Capacitively Shunted Junction model. The results clearly show that the dynamics of the system are two-dimensional, resulting in two resonant modes of the system. These findings have important implications for the design and operation of Josephson junctions based quantum bits

Cholesterol-Induced Buckling in Physisorbed Polymer-Tethered Lipid Monolayers

The influence of cholesterol concentration on the formation of buckling structures is studied in a physisorbed polymer-tethered lipid monolayer system using epifluorescence microscopy (EPI) and atomic force microscopy (AFM). The monolayer system, built using the Langmuir-Blodgett (LB) technique, consists of 3 mol % poly(ethylene glycol) (PEG) lipopolymers and various concentrations of the phospholipid, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), and cholesterol (CHOL). In the absence of CHOL, AFM micrographs show only occasional buckling structures, which is caused by the presence of the lipopolymers in the monolayer. In contrast, a gradual increase of CHOL concentration in the range of 0–40 mol % leads to fascinating film stress relaxation phenomena in the form of enhanced membrane buckling. Buckling structures are moderately deficient in CHOL, but do not cause any notable phospholipid-lipopolymer phase separation. Our experiments demonstrate that membrane buckling in physisorbed polymer-tethered membranes can be controlled through CHOL-mediated adjustment of membrane elastic properties. They further show that CHOL may have a notable impact on molecular confinement in the presence of crowding agents, such as lipopolymers. Our results are significant, because they offer an intriguing prospective on the role of CHOL on the material properties in complex membrane architecture

Ligand Mediated Sequestering of Integrins in Raft-Mimicking Lipid Mixtures: The Role of Bilayer Asymmetry and Cholesterol Content

poster abstractLipid microdomains play an important functional role in plasma membranes. However, the small size and transient nature of lipid/membrane heterogeneities in the plasma membrane make characterization of microdomains and microdomain-related membrane processes quite challenging. To address this issue, we recently introduced a powerful model membrane system that allows the investigation of membrane protein sequestering and oligomerization in raft-mimicking lipid mixtures using combined confocal fluorescence spectroscopy, photon counting histogram (PCH), and epifluorescence microscopy. Our experiments on bilayer-spanning domains showed that αvβ3 and α5β1 integrins predominantly exist as monomers and sequester preferentially to the liquid-disordered (ld) phase in the absence of ligands. Notably, addition of vitronectin (αvβ3) and fibronectin (α5β1) caused substantial translocations of integrins into the liquid-ordered (lo) phase without altering receptor oligomerization state. Here we expand our previous studies and report on the sequestering and oligomerization state of αvβ3 and α5β1 in asymmetric bilayer compositions containing coexisting lo and ld phases located exclusively in the top leaflet of the bilayer (bottom leaflet shows only ld phase). Remarkably, in such a membrane environment, both integrins show a higher affinity for the top leaflet-restricted lo domains in the absence of their respective ligands. A slight change in the integrin sequestration was observed after addition of their respective ligands. We also present experimental findings, which show that cholesterol content has a substantial influence on integrin sequestering and oligomerization in raft-mimicking lipid mixtures. The described experimental results highlight the potential importance of membrane asymmetry and lipid composition in the sequestering of membrane proteins in biological membranes

Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by ²H NMR field-cycling relaxometry

We use ²H nuclear magnetic resonance to study the dynamics of deuterated water in a solution of linear poly (N-isopropyl acrylamide) (pNIPAM, 4 wt%) across its coil-to-globule transition at a lower critical solubility temperature (LCST) around 32°C. In agreement with previous studies, we find that the ²H spin-lattice (T₁) and, in particular, spin-spin (T₂) relaxation times abruptly decrease when heating through the LCST, indicating that the polymer collapse causes an emergence of a water fraction with strongly reduced mobility. To quantify the dynamics of this slow water fraction, we exploit the fact that ²H field-cycling relaxometry allows us to measure the spectral density of the water reorientation in a broad frequency range. We find that the slow water fraction is characterised by a broad logarithmic Gaussian distribution of correlation times (σ LG = 2.3), which is centred about τ LG ≈ 10⁻⁹ s near the LCST. Hence, the common assumption of a Debye spectral density does not apply. We argue that a minor water fraction, which is located inside the pNIPAM globules and shows dynamics governed by the disordered polymer matrix, accompanies a major water fraction with bulk-like dynamics above the LCST. The former fraction amounts to about 0.4 water molecules per NIPAM monomer. Several findings indicate fast exchange between these bound and free water fractions on the T₁ and T₂ time scales

Complete next-to-leading order gluino contributions to b--> s gamma and b--> s g

We present the first complete order alpha_s corrections to the Wilson coefficients (at the high scale) of the various versions of magnetic and chromomagnetic operators which are induced by a squark-gluino exchange. For this matching calculation, we work out the on-shell amplitudes b--> s gamma and b --> s g, both in the full and in the effective theory up to order alpha_s^2. The most difficult part of the calculation is the evaluation of the two-loop diagrams in the full theory; these can be split into two classes: a) diagrams with one gluino and a virtual gluon; b) diagrams with two gluinos or with one gluino and a four-squark vertex. Accordingly, the Wilson coefficients can be split into a part a) and a part b). While part b) of the Wilson coefficients is presented in this paper for the first time, part a) was given in (Bobeth et al.). We checked their results for the coefficients of the magnetic operators and found perfect agreement. Moreover, we work out the renormalization procedure in great detail. Our results for the complete next-to-leading order Wilson coefficients are fully analytic, but far too long to be printed. We therefore publish them in the form of a C++ program. They constitute a crucial building block for the phenomenological next-to-leading logarithmic analysis of the branching ratio Bbar --> X_s gamma in a supersymmetric model beyond minimal flavor violation.Comment: 38 pages, including c++ cod

Scientific Reports / The tactile window to consciousness is characterized by frequency-specific integration and segregation of the primary somatosensory cortex

We recently proposed that besides levels of local cortical excitability, also distinct pre-stimulus network states (windows to consciousness) determine whether a near-threshold stimulus will be consciously perceived. In the present magnetoencephalography study, we scrutinised these pre-stimulus network states with a focus on the primary somatosensory cortex. For this purpose participants performed a simple near-threshold tactile detection task. Confirming previous studies, we found reduced alpha and beta power in the somatosensory region contralateral to stimulation prior to correct stimulus detection as compared to undetected stimuli, and stronger event-related responses following successful stimulus detection. As expected, using graph theoretical measures, we also observed modulated pre-stimulus network level integration. Specifically, the right primary somatosensory cortex contralateral to stimulation showed an increased integration in the theta band, and additionally, a decreased integration in the beta band. Overall, these results underline the importance of network states for enabling conscious perception. Moreover, they indicate that also a reduction of irrelevant functional connections contributes to the window to consciousness by tuning pre-stimulus pathways of information flow.Julia Natascha Frey, Philipp Ruhnau, Sabine Leske, Markus Siegel, Christoph Braun, Nathan Weis