Sensitivity enhancement by exchange mediated magnetization transfer of the xenon biosensor signal

Hyperpolarized xenon associated with ligand derivatized cryptophane-A cages has been developed as a NMR based biosensor. To optimize the detection sensitivity we describe use of xenon exchange between the caged and bulk dissolved xenon as an effective signal amplifier. This approach, somewhat analogous to 'remote detection' described recently, uses the chemical exchange to repeatedly transfer spectroscopic information from caged to bulk xenon, effectively integrating the caged signal. After an optimized integration period, the signal is read out by observation of the bulk magnetization. The spectrum of the caged xenon is reconstructed through use of a variable evolution period before transfer and Fourier analysis of the bulk signal as a function of the evolution time.     

Dispersion measurements using time-of-flight remote detection MRI

Remote detection nuclear magnetic resonance and magnetic resonance imaging can be used to study fluid flow and dispersion in a porous medium from a purely Eulerian point of view (i.e., in a laboratory frame of reference). Information about fluid displacement is obtained on a macroscopic scale in a long-time regime, while local velocity distributions are averaged out. It is shown how these experiments can be described using the common flow propagator formalism and how experimental data can be analyzed to obtain effective porosity, flow velocity inside the porous medium, fluid dispersion and flow tracing of fluid.     

Drug-dendrimer supramolecular complexation studied from molecular dynamics simulations and NMR spectroscopy

Fully atomistic molecular dynamics (MD) simulations and NMR spectroscopy were employed to get insights about the molecular details of drug-dendrimer supramolecular association phenomena, using piroxicam (PRX) and the third generation poly(amido amine) (PAMAM-G3) dendrimer as model systems. Theoretical results concerning the complex stoichiometry suggest that PRX forms drug-dendrimer complexes of the type 24:1 at pH 7.0. This result was validated with the experimental quantities obtained from aqueous solubility profiles, which led to an empiric stoichiometry of 23:1 for the PRX:PAMAM-G3 system. The predicted binding mode between PRX and PAMAM-G3 accounts for the preferred encapsulation of the drug inside dendrimer cavities, which is mainly driven by van der Waals and hydrogen bonding interactions, and to a lesser extent, for the external association of the guest through electrostatic contacts with the positively charged amino groups of PAMAM periphery. The binding mode obtained from MD simulations was confirmed with 2D-NOESY experiments, which evidence the preferred internal complexation of PRX with PAMAM-G3. The predominance of internal encapsulation over external contacts in the PRX:PAMAM-G3 system differs from the general behaviour expected for acidic anionic guests, for which external electrostatic interactions with the positively charged PAMAM surface have been postulated as the most relevant factor for drug association.     

Thermal investigation on polymorphism in sodium saccharine

The thermal behavior of sodium saccharin polymorphic forms was investigated using thermogravimetry and differential scanning calorimetry, while structural changes during the dehydration processes were monitored by X-ray powder diffraction. In solid state, sodium saccharine may exhibit three forms: anhydrate, 2/3 hydrate (triclinic), and 15/8 hydrate (monoclinic) ones. In this investigation, it was established that monoclinic and triclinic forms compose an entantiotropically related polymorphs system. At 82 °C, the 15/8 hydrated monoclinic form is converted to 2/3 hydrated triclinic form, which showed to be the more thermodynamically stable form at room temperature. Spontaneous solidification leads to the formation of triclinic cell setting, and additionally, spontaneous hydration of the anhydrous form leads to formation of 2/3 hydrated triclinic form.     

NMR imaging of solid polymers: Strategies for chemical-shift selectivity

One reason that the solid-state imaging field is exciting is because of its potential to provide spatially resolved chemical information from deep inside a solid sample. To achieve this goal, methods are needed which exploit the many NMR parameters to generate image contrast. We describe two strategies for employing the chemical-shift anisotropy as a contrast mechanism in images of abundant nuclei in solid polymers. We illustrate these approaches with images which map spatial variations of molecular orientation in samples of polytetrafluoroethylene.     

Design and experimental validation of a nonlinear controller for underactuated surface vessels

Nonlinear Dynamics - This paper addresses the problem of trajectory tracking control of an underactuated surface vessel moving in a two-dimensional space in the presence of unknown disturbances. In...     

Magnetic nanotips: the realisation of an atomic-scale beam-splitter

We present the first realisation of ferromagnetic Fe nanotips. Studies of the field emitted beams of electrons and metallic ions above and under the Curie temperature T_c were made. We have observed a reversible splitting of the electron beams when the temperature crossed through T_c and multiple spot patterns for the emitted metallic ion beams. These phenomena were not observed with Fe microtips or non-magnetic nanotips and thus were correlated to a strong magnetic interaction at the atomic scale apex of the nanotips. The Fe nanotips constitute an atomic scale beam-splitter.     

An Edge Server Placement Method Based on Reinforcement Learning

In mobile edge computing systems, the edge server placement problem is mainly tackled as a multi-objective optimization problem and solved with mixed integer programming, heuristic or meta-heuristic algorithms, etc. These methods, however, have profound defect implications such as poor scalability, local optimal solutions, and parameter tuning difficulties. To overcome these defects, we propose a novel edge server placement algorithm based on deep q-network and reinforcement learning, dubbed DQN-ESPA, which can achieve optimal placements without relying on previous placement experience. In DQN-ESPA, the edge server placement problem is modeled as a Markov decision process, which is formalized with the state space, action space and reward function, and it is subsequently solved using a reinforcement learning algorithm. Experimental results using real datasets from Shanghai Telecom show that DQN-ESPA outperforms state-of-the-art algorithms such as simulated annealing placement algorithm (SAPA), Top-K placement algorithm (TKPA), K-Means placement algorithm (KMPA), and random placement algorithm (RPA). In particular, with a comprehensive consideration of access delay and workload balance, DQN-ESPA achieves up to 13.40% and 15.54% better placement performance for 100 and 300 edge servers respectively.     

Bright‐Dark Rogue Waves

During the last two decades, revealing mechanisms of origin waves with anomalous amplitude (rogue waves) have been in the focus of researchers from different fields ranging from oceanography to laser physics. Mode‐locked lasers, as a test bed system, provide a unique opportunity to collect more data on rogue waves in the form of random pulses (soliton rain) and to clarify the mechanisms of rogue‐wave emergence caused by soliton–soliton and soliton–dispersive wave interactions. Here, for the first time, for an Er‐doped mode‐locked laser, a new type of vector rogue waves is demonstrated experimentally and theoretically, which is driven by desynchronization of the orthogonal linear states of polarization, so leading to output power oscillations in the form of anomalous spikes‐dips (bright‐dark rogue waves). The results can pave the way to unlocking the universal nature of the origin of rogue waves and thus can be of interest to the broad scientific community.