Search results for "FLUCTUATIONS"
showing 10 items of 167 documents
Thermal fluctuations and longitudinal relaxation of single-domain magnetic particles at elevated temperatures
2004
We present numerical and analytical results for the swiching times of magnetic nanoparticles with uniaxial anisotropy at elevated temperatures, including the vicinity of T_c. The consideration is based in the Landau-Lifshitz-Bloch equation that includes the relaxation of the magnetization magnitude M. The resulting switching times are shorter than those following from the naive Landau-Lifshitz equation due to (i) additional barrier lowering because of the reduction of M at the barrier and (ii) critical divergence of the damping parameters.
Evidence of quantum phase slip effect in titanium nanowires
2012
Electron transport properties of titanium nanowires were experimentally studied. Below the effective diameter $\lesssim$ 50 nm all samples demonstrated a pronounced broadening of the $R(T)$ dependencies, which cannot be accounted for thermal flcutuations. An extensive microscopic and elemental analysis indicates the absence of structural or/and geometrical imperfection capable to broaden the the $R(T)$ transition to such an extent. We associate the effect with quantum flucutuations of the order parameter.
Mechanical and Thermal Stability of Adhesive Membranes with Nonzero Bending Rigidity
2010
Membranes at a microscopic scale are affected by thermal fluctuations and self-adhesion due to van der Waals forces. Methods to prepare membranes of even molecular scale, e.g., graphene, have recently been developed, and the question of their mechanical and thermal stability is of crucial importance. To this end we modeled microscopic membranes with an attractive interaction and applied Langevin dynamics. Their behavior was also analyzed under external loading. Even though these membranes folded during isotropic compression as a result of energy minimization, the process at high confinement was similar to crumpling of macroscopic nonadhesive sheets. The main difference appeared when the com…
Silicon quantum point contact with aluminum gate
2000
Fabrication and electrical properties of silicon quantum point contacts are reported. The devices are fabricated on bonded silicon on insulator (SOI) wafers by combining CMOS process steps and e-beam lithography. Mobility of 9000 cm2 Vs−1 is measured for a 60 nm-thick SOI film at 10 K. Weak localization data is used to estimate the phase coherence length at 4.2 K The point contacts show step like behaviour in linear response conductance at 1.5 K. At 200 mK universal conductance fluctuations begin to dominate the conductance curve. The effective diameter of quantum point constrictions of the devices are estimated to be 30–40 nm. This estimate is based on TEM analysis of test structures and A…
Latent Heat of Spontaneous-Curvature-Induced Lamellar-to-Microemulsion Transitions
1995
Using differential scanning microcalorimetry we examine the latent heat of the temperature-induced structural transition from a lamellar to a microemulsion phase in a H2O/n-octane/C12E5 (n-dodecyl pentanethyleneglycol ether) system. The associated latent heat increases strongly with surfactant concentration yielding heat changes up to 1kB T per surfactant molecule. These large values are quantitatively described by an interfacial model which takes into account the temperature dependence of the spontaneous curvature. The model explains our data points without considering contributions to the free energy by thermal fluctuations, entropy of mixing, undulations of the lamellae and renormalizati…
Ages and stratigraphical architecture of late Miocene deposits in the Lorca Basin (Betics, SE Spain): New insights for the salinity crisis in margina…
2020
International audience; Unlike most Neogene basins of the Betic Cordillera where the Salinity Crisis is dated to the Messinian, a contradictory Tortonian dating was proposed for evaporites of the Lorca Basin. As a consequence, complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites. In order to integrate the Lorca Basin into the geological context of the western Mediterranean domain during the Late Miocene, new sedimentological and stratigraphical studies coupled with new dating were performed, which allow us to propose a Messinian age for both diatomite-bearing deposits and evaporites of the Lorca Basin. These new ages challeng…
Dielectric response of nanoscopic spherical colloids in alternating electric fields: a dissipative particle dynamics simulation.
2012
We study the response of single nanosized spherical colloids in electrolyte solution to an alternating electric field (AC field) by computer simulations. We use a coarse-grained mesoscopic simulation approach that accounts in full for hydrodynamic and electrostatic interactions as well as for thermal fluctuations. The solvent is modeled as a fluid of single Dissipative Particle Dynamics (DPD) beads, and the colloidal particle is modeled as a rigid body made of DPD beads. We compute the mobility and the polarizability of a single colloid and investigate systematically the effect of amplitude and frequency of the AC-fields. Even though the thickness of the Debye layer is not "thin" compared t…
Orientational dynamics of fluctuating dipolar particles assembled in a mesoscopic colloidal ribbon
2017
We combine experiments and theory to investigate the dynamics and orientational fluctuations of ferromagnetic microellipsoids that form a ribbonlike structure due to attractive dipolar forces. When assembled in the ribbon, the ellipsoids display orientational thermal fluctuations with an amplitude that can be controlled via application of an in-plane magnetic field. We use video microscopy to investigate the orientational dynamics in real time and space. Theoretical arguments are used to derive an analytical expression that describes how the distribution of the different angular configurations depends on the strength of the applied field. The experimental data are in good agreement with the…
Molecular dynamics simulation of sucrose- and trehalose-coated carboxy-myoglobin
2005
We performed a room temperature molecular dynamics (MD) simulation on a system containing 1 carboxy-myoglobin (MbCO) molecule in a sucrose–water matrix of identical composition (89% [sucrose/(sucrose + water)] w/w) as for a previous trehalose–water–MbCO simulation (Cottone et al., Biophys J 2001;80:931–938). Results show that, as for trehalose, the amplitude of protein atomic mean-square fluctuations, on the nanosecond timescale, is reduced with respect to aqueous solutions also in sucrose. A detailed comparison as a function of residue number evidences mobility differences along the protein backbone, which can be related to a different efficacy in bioprotection. Different heme pocket struc…
Mechanically interlocked calix[4]arene dimers display reversible bond breakage under force.
2009
The physics of nanoscopic systems is strongly governed by thermal fluctuations that produce significant deviations from the behaviour of large ensembles1,2. Stretching experiments of single molecules offer a unique way to study fundamental theories of statistical mechanics, as recently shown for the unzipping of RNA hairpins3. Here, we report a molecular design based on oligo calix[4]arene catenanes—calixarene dimers held together by 16 hydrogen bridges—in which loops within the molecules limit how far the calixarene nanocapsules can be separated. This mechanically locked structure tunes the energy landscape of dimers, thus permitting the reversible rupture and rejoining of the individual n…