Selective chemical oxidation and depolymerization of switchgrass [corrected] (Panicum virgatum L.) xylan with [corrected] oligosaccharide product analysis by mass spectrometry

Xylan is a barrier to enzymatic hydrolysis of plant cell walls. It is well accepted that the xylan layer needs to be removed to efficiently hydrolyze cellulose; consequently, pretreatment conditions are (in part) optimized for maximal xylan depolymerization or displacement. Xylan consists of a long chain of β-1,4-linked xylose units substituted with arabinose (typically α-1,3-linked in grasses) and glucuronic acid (α-1,2-linked). Xylan has been proposed to have a structural function in plants and therefore may play a role in determining biomass reactivity to pretreatment. It has been proposed that substitutions along xylan chains are not random and, based upon studies of pericarp xylan, are organized in domains that have specific structural functions. Analysis of intact xylan is problematic because of its chain length (> degree of polymerization (d.p.) 100) and heterogeneous side groups. Traditionally, enzymatic end-point products have been characterized due to the limited products generated. Analysis of resultant arabino-xylo-oligosaccharides by mass spectrometry is complicated by the isobaric pentose sugars that primarily compose xylan. In this report, the variation in pentose ring structures was exploited for selective oxidation of the arabinofuranose primary alcohols followed by acid depolymerization to provide oligosaccharides with modified arabinose branches intact. Switchgrass samples were analyzed by hydrophilic interaction chromatography (HILIC)-liquid chromatography (LC)-mass spectrometry/mass spectrometry (MSMS) and off-line nanospray MS to demonstrate the utility of this chemistry for determination of primary hydroxyl groups on oligosaccharide structures, with potential applications for determining the sequence of arabino-xylo-oligosaccharides present in plant cell wall material.     

Microstructure and Mössbauer studies on magnetostrictive Tb0.3Dy0.7Fe1.95 − x Nb x (x = 0, 0.025, 0.05 and 0.075)

³⁵Cl NQR measurements were carried out between 77 and 209 K for 3-chlorothiophene, which has a glass transition in a stable crystalline state. An NQR signal with full widths of about 100 kHz at half maximum was observed in this temperature range. The spin-lattice relaxation time T ₁ was measured at the peak frequencies. The activation energy Δε _a obtained from the results of the T ₁ measurements showed a good agreement with those estimated from calorimetric measurements.     

Clustered chimera states in delay-coupled oscillator systems

We investigate chimera states in a ring of identical phase oscillators coupled in a time-delayed and spatially nonlocal fashion. We find novel clustered chimera states that have spatially distributed phase coherence separated by incoherence with adjacent coherent regions in antiphase. The existence of such time-delay induced phase clustering is further supported through solutions of a generalized functional self-consistency equation of the mean field. Our results highlight an additional mechanism for cluster formation that may find wider practical applications.     

Beneficial effect of boron on the structural and magnetostrictive behavior of Fe77Ga23 alloy

Alloys of Fe₇₇Ga₂₃B_x (x=0, 0.025, 0.050, 0.075 and 0.1) were heat treated at 1000 °C/10 h and characterized for microstructural features and magnetostriction. The study indicates that the parent alloy consists of three phases viz. A2 as the major phase and L1₂ and DO₃ as minor phases. However, the volume fraction of L1₂ and DO₃ decreases with B addition and as a result magnetostriction improves. The decrease in volume fraction of these phases is attributed to B-segregation to the grain boundary, which seems to prevent the formation of these phases. The alloy with x=0.1, however, exhibits an additional Fe₂B phase and consequently its presence leads to the re-emergence of the DO₃ phase, affecting the magnetostriction.     

Covariant holographic entanglement negativity

We propose a covariant holographic conjecture for the entanglement negativity of bipartite mixed states in \((1+1)\)-dimensional conformal field theories dual to bulk non static \(AdS_{3}\) configurations. Application of our conjecture to \((1+1)\)-dimensional conformal field theories dual to bulk non extremal and extremal rotating BTZ black holes exactly reproduce the corresponding entanglement negativity obtained through the replica technique, in the large central charge limit. We briefly discuss the issue of the generalization of our conjecture to higher dimensions.     

Validation of numerical solvers for liquid metal flow in a complex geometry in the presence of a strong magnetic field

Following the magnetohydrodynamic (MHD) code validation and verification proposal by Smolentsev et al. (Fusion Eng Des 100:65–72, 2015), we perform code to code and code to experiment comparisons between two computational solvers, FLUIDYN and HIMAG, which are presently considered as two of the prospective CFD tools for fusion blanket applications. In such applications, an electrically conducting breeder/coolant circulates in the blanket ducts in the presence of a strong plasma-confining magnetic field at high Hartmann numbers, \(\textit{Ha}\) (\(\textit{Ha}^2\) is the ratio between electromagnetic and viscous forces) and high interaction parameters, \(\textit{N}\) (\(\textit{N}\) is the ratio of electromagnetic to inertial forces). The main objective of this paper is to provide the scientific and engineering community with common references to assist fusion researchers in the selection of adequate computational means to be used for blanket design and analysis. As an initial validation case, the two codes are applied to the classic problem of a laminar fully developed MHD flows in a rectangular duct. Both codes demonstrate a very good agreement with the analytical solution for \(\textit{Ha}\) up to 15, 000. To address the capabilities of the two codes to properly resolve complex geometry flows, we consider a case of three-dimensional developing MHD flow in a geometry comprising of a series of interconnected electrically conducting rectangular ducts. The computed electric potential distributions for two flows (Case A) \(\textit{Ha}=515\), \(\textit{N}=3.2\) and (Case B) \(\textit{Ha}=2059\), \(\textit{N}=63.8\) are in very good agreement with the experimental data, while the comparisons for the MHD pressure drop are still unsatisfactory. To better interpret the observed differences, the obtained numerical data are analyzed against earlier theoretical and experimental studies for flows that involve changes in the relative orientation between the flow and the magnetic field.     

Glycolytic Wave Patterns in a Simple Reaction-diffusion System with Inhomogeneous Influx: Dynamic Transitions

An inhomogeneous profile of chemostatted species generates a rich variety of patterns in glycolytic waves depicted in a Selkov reaction-diffusion framework here. A key role played by diffusion amplitude and symmetry in the chemostatted species profile in dictating the fate of local spatial dynamics involving periodic, quasiperiodic, and chaotic patterns and transitions among them are investigated systematically. More importantly, various dynamic transitions, including wave propagation direction changes, are illustrated in interesting situations. Besides numerical results, our analytical formulation of the amplitude equation connecting complex Ginzburg-Landau and Lambda-omega representation shed light on the phase dynamics of the system. This systematic study of the glycolytic reaction-diffusion wave is in line with previous experimental results in open spatial reactor and will provide a knowledge about the dynamics that shape and control biological information processing and related phenomena.