Solid-state electron transport across azurin: from a temperature-independent to a temperature-activated mechanism

The temperature dependence of current-voltage values of electron transport through proteins integrated into a solid-state junction has been investigated. These measurements were performed from 80 up to 400 K [above the denaturation temperature of azurin (Az)] using Si/Az/Au junctions that we have described previously. The current across the ～3.5 nm thick Az junction was temperature-independent over the complete range. In marked contrast, for both Zn-substituted and apo-Az (i.e., Cu-depleted Az), thermally activated behavior was observed. These striking temperature-dependence differences are ascribed to the pivotal function of the Cu ion as a redox center in the solid-state electron transport process. Thus, while Cu enabled temperature-independent electron transport, upon its removal the polypeptide was capable only of supporting thermally activated transport.     

Diverging rabi oscillations in subwavelength photonic lattices

We show that Rabi oscillations between Bloch modes of an optical waveguide array with subwavelength periodicity diverge, both in frequency and in field amplitude, when the optical wavelength approaches a mathematical exceptional point at which the Bloch mode becomes self-orthogonal.     

Accelerating light beams along arbitrary convex trajectories

We demonstrate, theoretically and experimentally, nonbroadening optical beams propagating along any arbitrarily chosen convex trajectory in space. We present a general method to construct such beams, and demonstrate it by generating beams following polynomial and exponential trajectories. We find that all such beams, accelerating along any convex trajectory, display the same universal intensity cross section, irrespective of their acceleration. The universal features of these beams are explored using catastrophe theory.     

On Ideals of Minors of Matrices with Indeterminate Entries

This article studies ideals of minors of matrices whose entries are among the variables of a polynomial ring. The main result is a theorem which gives sufficient conditions for these to be prime.     

Shock mechanisms by ultrahigh laser accelerated plasma blocks in solid density targets for fusion

Ignition of nuclear fusion flames in solid state density fuel following Chu?s model of 1972 is evaluated using now available plasma blocks from ultrahigh acceleration with laser pulses of picosecond (ps) duration and power up to and beyond petawatt (PW). A new numerical approach is reported where genuine two-fluid hydrodynamics is used in order to study the shock mechanism of the generated fusion flame, its propagation velocities above 1000 km/s$1000\text{km}/\text{s}$, and fusion efficiencies for deuterium–tritium needing an energy flux of 10⁸ J/cm²${10}^8\text{J}/{\text{cm}}^2$. The results of the built-up of the shock process are reported showing a basic difference between the ps and nanosecond (ns) properties.     

Relaxation dispersion in MRI induced by fictitious magnetic fields

A new method entitled Relaxation Along a Fictitious Field (RAFF) was recently introduced for investigating relaxations in rotating frames of rank ≥ 2. RAFF generates a fictitious field (E) by applying frequency-swept pulses with sine and cosine amplitude and frequency modulation operating in a sub-adiabatic regime. In the present work, MRI contrast is created by varying the orientation of E, i.e. the angle ε between E and the z″ axis of the second rotating frame. When ε > 45°, the amplitude of the fictitious field E generated during RAFF is significantly larger than the RF field amplitude used for transmitting the sine/cosine pulses. Relaxation during RAFF was investigated using an invariant-trajectory approach and the Bloch-McConnell formalism. Dipole-dipole interactions between identical (like) spins and anisochronous exchange (e.g., exchange between spins with different chemical shifts) in the fast exchange regime were considered. Experimental verifications were performed in vivo in human and mouse brain. Theoretical and experimental results demonstrated that changes in ε induced a dispersion of the relaxation rate constants. The fastest relaxation was achieved at ε ≈ 56°, where the averaged contributions from transverse components during the pulse are maximal and the contribution from longitudinal components are minimal. RAFF relaxation dispersion was compared with the relaxation dispersion achieved with off-resonance spin lock T(?ρ) experiments. As compared with the off-resonance spin lock T(?ρ) method, a slower rotating frame relaxation rate was observed with RAFF, which under certain experimental conditions is desirable.     

Cellulose Nanocrystals (CNCs) Induced Crystallization of Polyvinyl Alcohol (PVA) Super Performing Nanocomposite Films

This study is aimed to explore the properties of cellulose nanocrystals (CNC)/polyvinyl alcohol (PVA) composite films with and without 1,2,3,4‐butane tetracarboxylic acid (BTCA), a nontoxic crosslinker. CNC and CNC‐PVA nanocomposite films are prepared using solution‐casting technique. Differential scanning calorimetry (DSC) analyses show that crosslinking increased the glass transition temperature but reduced the melting temperature and crystallinity. Furthermore, high CNC concentrations in the PVA matrix interfere with PVA crystallinity, whereas in specific ratio between CNC and PVA, two different crystalline structures are observed within the PVA matrix. Film surfaces and fracture topographies characterized using scanning electron microscope indicate that at certain CNC‐PVA ratios, micron‐sized needle‐like crystals have formed. These crystalline structures correlate with the remarkable improvement in mechanical properties of the CNC‐PVA nanocomposite films, that is, enhanced tensile strain and toughness to 570% and 202 MJ m^?3, respectively, as compared to pristine PVA. BTCA enhances the tensile strain, ultimate tensile stress, toughness, and modulus of CNC films compared to pristine CNC films. Water absorption of crosslinked CNC and CNC‐PVA nanocomposite films is significantly reduced, while film transparency is significantly improved as a function of PVA and crosslinker content. The presented results indicate that CNC‐PVA nanocomposite films may find applications in packaging, and though materials applications.     

Allowable Interval Sequences and Line Transversals in the Plane

Given a family F of n pairwise disjoint compact convex sets in the plane with non-empty interiors, let T(k) denote the property that every subfamily of F of size k has a line transversal, and T the property that the entire family has a line transversal. We illustrate the applicability of allowable interval sequences to problems involving line transversals in the plane by proving two new results and generalizing three old ones. Two of the old results are Klee??s assertion that if F is totally separated then T(3) implies T, and the following variation of Hadwiger??s Transversal Theorem proved by Wenger and (independently) Tverberg: If F is ordered and each four sets of F have some transversal which respects the order on F, then there is a transversal for all of F which respects this order. The third old result (a consequence of an observation made by Kramer) and the first of the new results (which partially settles a 2008 conjecture of Eckhoff) deal with fractional transversals and share the following general form: If F has property T(k) and meets certain other conditions, then there exists a transversal of some m sets in F, with k<m<n. The second new result establishes a link between transversal properties and separation properties of certain families of convex sets.     

Efficient Water Cleaning by Self-standing Carbon Nitride Films Derived from Supramolecular Hydrogels

The design of efficient self-standing hybrid systems for water purification that combines good adsorption properties with high photodegradation ability is highly challenging owing to the difficulty in simultaneously controlling the band structure and porosity of a semiconductor while maintaining its self-standing nature. Here, we report the synthesis of carbon-rich carbon nitride self-standing filters from supramolecular hydrogels composed of melamine and cyanobenzoic acid. The influence of the chemical structure on the properties of the hydrogels and the final films was studied by tuning parameters such as monomer nature, molar ratio, and pyrolysis temperature. Thanks to their ability to combine the adsorption and photodegradation of organic pollutants, the prepared self-standing films showed remarkable activity and stability in flow conditions (>95 % efficiency after 10 consecutive cycles). Additionally, the photocatalytic activity of the films was assessed in the powder form for the hydrogen evolution reaction and photocurrent generation in a photoelectrochemical cell. The reported work opens opportunities for the controlled synthesis of multifunctional filters for water purification and other energy-related and sustainable technologies.