Drop In Anisotropy Research Articles

Determining the structural origin of quantum behaviors in fluorescent proteins.

Under physiological conditions fluorescent proteins (FP) in close proximity unexpectedly exhibit photophysical effects that are consistent with excitonic coupling: (1) ultrafast drop in anisotropy, (2) Davydov splitting in its CD spectra and (3) multiple FPs behaving as a single quantum emitter in photon antibunching experiments. We hypothesize that the FP β-barrel structure protects its internal chromophore from environmental decoherence, and thus slows its dephasing time relative to its energy transfer rate. To test this idea, we follow two parallel lines of investigation, one empirical and one theoretical. Experimentally, we prepare a catalog of fluorescent protein constructs that exhibit different combinations of energy transfer phenomena, namely excitonic coupling, and homo-FRET, and we characterize these using the three techniques mentioned above. The current list of FPs consists of Venus, LanYFP, Cerulean, EGFP, Tomato, and Ametrine, all of which were engineered into tandem dimer constructs and their appropriate monomeric controls. The variety of structurally related FP constructs should allow us to parse the origin of excitonic coupling, whether in the specific local structure along the β-barrel or the chromophore. In parallel, we employ molecular dynamics simulations to predict how the environment (the protein shell and/or solvent) impacts the excitation of the internal chromophore. We do this by estimating the total spectral density for excitation energy correlation functions as well as the contributions of composite structures to that spectral density. By applying this analysis on the various FP tandem dimer constructs, we can compare to what extent environmental coupling is predictive of observed quantum behaviors, and thus elucidate the role of structure.

Zn and Zr co-doped M-type strontium hexaferrite: Synthesis, characterization and hyperthermia application

In the present study, hard ferromagnetic (M-type strontium hexaferrite) SrFe12O19 was co-doped by Zn and Zr for magnetic hyperthermia applications. As a result of the high concentration of single domain SrFe12O19 nanoparticles (suspended in the ferrofluid), they found a large hydrodynamic diameter, which caused a long-time Brownian relaxation under the AC magnetic field. On the other hand, increasing the Zn-Zr content (low concentration of SrFe12O19) led to a drop in anisotropy, which coincided with a short-time N´eel relaxation. All of the substituted samples with a multi-disperse state in ferrofluid exhibited an almost equal amount of the N´eel and Brownian effects. Consequently, the magnetic saturation (Ms) was considered as the dominant factor in the specific absorption rate (SAR) of the substituted samples. Transformation to the mono-disperse state was followed by the decrease of the Brownian relaxation time and hence the increase of the SAR. The interesting point in mono-disperse state was the heat generation of pure SrFe12O19 under the AC magnetic field as a result of the decrement of the Brownian relaxation time.

Ultrasonic velocity drops and anisotropy reduction in mica-schist analogues due to melting with implications for seismic imaging of continental crust

Melt generation in the continental crust is thought to significantly influence seismic bulk velocities and anisotropy, although existing laboratory data provide limited constraints on such seismic attributes. In this study we measured ultrasonic compressional wave speeds (Vp) and anisotropy during sample compaction, mica-breakdown and melt-generation in synthetic, foliated quartz–muscovite aggregates. Measurements were performed at peak conditions of 300 MPa hydrostatic confining pressure and 750 °C, over a six hour time period, for three separate samples where wave propagation directions were aligned at 0°, 45° and 90° with respect to the foliation plane. The experiments are initially marked by sample compaction and rapid reduction in porosity (from 25% to <2 vol%), with a corresponding increase in Vp. During initial stages of the experiment Vp ranges from 4.65 to 5.45 km/s, depending on the direction of the P wave propagation, resulting in up to ∼16% anisotropy, which originates mainly from the preferred orientation of muscovite and possible incipient melt lenses oriented parallel to foliation. As the experiment progresses the bulk Vp decreases gradually and Vp anisotropy drops from ∼16% to ∼2% after five hours into the experiment. The drop in anisotropy is caused by muscovite-breakdown and increasing amount of partial melting of the aggregate. The bulk velocities are considerably lower than predicted for a mixture of muscovite and β-quartz (stable at 300 MPa and 750 °C). Thermodynamic modeling indicates that mica breakdown and production of melt with ∼2 wt% dissolved water in the aggregate can explain the low Vp, even though β-quartz is stable; the modeled Vp is ∼4.75 km/s at 300 MPa and 750 °C. These ultrasonic attributes signify movement of the melt to fill vacant pores and coating grain boundaries, effectively connecting melt films and reducing seismic anisotropy. The results may apply to regions where crustal melting is on-going, in particular regions of elevated temperature that are only weakly deforming, with coupled anomalously low bulk velocities and seismic anisotropy.

Magnetic hardening of soft phase in nanocomposite permanent magnetic materials by exchange coupling

In this work, the issue of magentic hardening of soft phase in nanocomposite permanent magnetic materials has been investigated using one-and three-dimensional models. For the same microstructure, it is found that the coercivity is decreased and the low-field demagnetization curve keeps unchanged when the anisotropy constant of magnetic hard phase is decreased in anisotropic one-or three-dimensional samples. Therefore, the drop in anisotropy of magnetic hard phase will not lead to the increase of remanence and maximum energy product (BH)max. According to the simulation results of isotropic three-dimension samples, both the remanence and (BH)max will be obviously decreased by the drop in anisotropy. As a result, enhancing the anisotropy and/or enlarging the grain size of magnetic hard phase is one of the means to improve the hard magnetic properties of nanocomposite permanent magnetic materials.

The anisotropic seismic structure of the East European platform

We present models for the P and S velocity structure of the upper mantle beneath the East European platform including measurements of radial anisotropy. The models were obtained by full waveform inversion of 3‐component broadband seismograms from strike‐slip earthquakes located near the edge of the platform and recorded in Russia and Europe. We used direct and multiply reflected body wave arrivals (S, SS, P, PP) combined with fundamental mode Love and Rayleigh waves at source‐receiver distances between 15° and 50° to resolve mantle structure down to the 410 km discontinuity. The platform is underlain by a radially anisotropic mantle lid extending to a depth of 200 km with a largely isotropic mantle below. The model has a positive velocity gradient from 41 km to 100 km depth, and a relatively uniform velocity structure from 100 km to 200 km depth with high SH and PH velocities (4.77 km/s, 8.45 km/s). Shear anisotropy is uniform at 5% (βH &gt; βV) from 41 to 200 km depth, drops to 2% from 200 to 250 km and is isotropic below that. The average shear velocity from 100 to 250 km is also uniform at 4.65 km/s and the drop in anisotropy is matched by a drop in βH to 4.70 km/s combined with an increase in βV to 4.60 km/s. Below 250 km there is a positive velocity gradient in both P and S velocity down to 410 km. P anisotropy is not well resolved, but P structure mimics the SH velocity structure, suggesting that P is also anisotropic within the lid.