Influence of pressure on polyamide 66 shear viscosity: a case study towards polar polymers behavior

In the present work, we consider the dependence of the viscosity of polyamide 66 (PA66) as a function of both temperature and pressure. Measurements were carried out using a standard capillary rheometer to evaluate the effect of temperature and the corresponding shift factor of viscosity data. The pressure influence was accounted for by employing an at-line rheometer equipped with a counter-pressure cell, the so-called enhanced exit pressure method. Time-temperature-pressure superposition was applied to obtain the viscosity master curve. Interestingly, PA66 displays an unusual increase of the pressure coefficient as a function of temperature. On the contrary, previous studies on nonpolar liquids or polymers for which polar interactions are relatively weak indicated that the sensitivity to pressure, measured by the so-called Barus parameter, is a decreasing function of the temperature. Thus, we attribute the peculiar behavior of PA66 to the strong polar interactions which are present and which may dominate the viscosity at relatively low temperatures and would be less dominant at higher temperatures.     

A maximum entropy approach to the newsvendor problem with partial information

In this paper, we consider the newsvendor model under partial information, i.e., where the demand distribution D is partly unknown. We focus on the classical case where the retailer only knows the expectation and variance of D. The standard approach is then to determine the order quantity using conservative rules such as minimax regret or Scarf’s rule. We compute instead the most likely demand distribution in the sense of maximum entropy. We then compare the performance of the maximum entropy approach with minimax regret and Scarf’s rule on large samples of randomly drawn demand distributions. We show that the average performance of the maximum entropy approach is considerably better than either alternative, and more surprisingly, that it is in most cases a better hedge against bad results.     

Behavior of captive herring exposed to naval sonar transmissions (1.0-1.6 kHz) throughout a yearly cycle

Atlantic herring, Clupea harengus, is a hearing specialist, and several studies have demonstrated strong responses to man-made noise, for example, from an approaching vessel. To avoid negative impacts from naval sonar operations, a set of studies of reaction patters of herring to low-frequency (1.0-1.5 kHz) naval sonar signals has been undertaken. This paper presents herring reactions to sonar signals and other stimuli when kept in captivity under detailed acoustic and video monitoring. Throughout the experiment, spanning three seasons of a year, the fish did not react significantly to sonar signals from a passing frigate, at received root-mean-square sound-pressure level (SPL) up to 168 dB re 1 μPa. In contrast, the fish did exhibit a significant diving reaction when exposed to other sounds, with a much lower SPL, e.g., from a two-stroke engine. This shows that the experimental setup is sensitive to herring reactions when occurring. The lack of herring reaction to sonar signals is consistent with earlier in situ behavioral studies. The complexity of the behavioral reactions in captivity underline the need for better understanding of the causal relationship between stimuli and reaction patterns of fish.     

Finding and identifying optimal inventory levels for systems with common components

In this article, we consider the problem of finding the optimal inventory level for components in an assembly system where multiple products share common components in the presence of random demand. Previously, solution procedures that identify the optimal inventory levels for components in a component commonality problem have been considered for two product or one common component systems. We will here extend this to a three products system considering any number of common components. The inventory problem considered is modeled as a two stage stochastic recourse problem where the first stage is to set the inventory levels to maximize expected profit while the second stage is to allocate components to products after observing demand. Our main contribution, and the main focus of this paper, is the outline of a procedure that finds the gradient for the stochastic problem, such that an optimal solution can be identified and a gradient based search method can be used to find the optimal solution.     

Comparative Metabolomic Analysis of Four Fabaceae and Relationship to In Vitro Nematicidal Activity against Xiphinema index

The grapevine fanleaf virus (GFLV), responsible for fanleaf degeneration, is spread in vineyards by the soil nematode Xiphinema index. Nematicide molecules were used to limit the spread of the disease until they were banned due to negative environmental impacts. Therefore, there is a growing interest in alternative methods, including plant-derived products with antagonistic effects to X. index. In this work, we evaluated the nematicidal potential of the aerial parts and roots of four Fabaceae: sainfoin (Onobrychis viciifolia), birdsfoot trefoil (Lotus corniculatus), sweet clover (Melilotus albus), and red clover (Trifolium pratense), as well as that of sainfoin-based commercial pellets. For all tested plants, either aerial or root parts, or both of them, exhibited a nematicidal effect on X. index in vitro, pellets being as effective as freshly harvested plants. Comparative metabolomic analyses did not reveal molecules or molecule families specifically associated with antagonistic properties toward X. index, suggesting that the nematicidal effect is the result of a combination of different molecules rather than associated with a single compound. Finally, scanning electron microscope observations did not reveal the visible impact of O. viciifolia extract on X. index cuticle, suggesting that alteration of the cuticle may not be the primary cause of their nematicidal effect.     

Total Synthesis of the Four Stereoisomers of Cyclo(l-Trp-l-Arg) Raises Uncertainty of the Structures of the Natural Products and Invalidates Their Promising Antimicrobial Activities

New therapeutic options to combat the growing incidence of antimicrobial resistance are urgently needed. A 2015 publication reported the isolation and biological evaluation of two diketopiperazine natural products, cyclo(l-Trp-l-Arg) (CDP 2) and cyclo(d-Trp-d-Arg) (CDP 3), from an Achromobacter sp. bacterium, finding that the latter metabolite in particular exhibited strong antibacterial activity towards a range of wound-related microorganisms and could synergize the action of ampicillin. Intrigued by these biological activities and noting inconsistencies in the structural characterization of the natural products, we synthesized the four diastereomers of cyclo(Trp-Arg) and evaluated them for antimicrobial and antibiotic enhancement properties. The detailed comparison of spectroscopic data raises uncertainty regarding the structure of CDP 2 and disproves the structure of CDP 3. In our hands, none of the four stereoisomers of cyclo(Trp-Arg) exhibited detectable intrinsic antimicrobial properties towards a range of Gram-positive and Gram-negative bacteria or fungi nor could they potentiate the action of antibiotics. These discrepancies in biological properties, compared with the activities reported in the literature, reveal that these specific cyclic dipeptides do not represent viable templates for the development of new treatments for microbial infections.     

Recovery of Gallium-68 and Zinc from HNO3-Based Solution by Liquid–Liquid Extraction with Arylamino Phosphonates

The cyclotron production of gallium-68 via the ⁶⁸Zn(p,n)⁶⁸Ga nuclear reaction in liquid targets is gaining significant traction in clinics. This work describes (1) the synthesis of new arylamino phosphonates via the Kabachnik–Fields reaction, (2) their use for liquid–liquid extraction of ⁶⁸Ga from 1 M Zn(NO₃)₂/0.01 M HNO₃ in batch and continuous flow, and (3) the use of Raman spectroscopy as a process analytical technology (PAT) tool for in-line measurement of ⁶⁸Zn. The highest extraction efficiencies were obtained with the extractants functionalized with trifluoromethyl substituents and ethylene glycol ponytails, which were able to extract up to 90% of gallium-68 in batch and 80% in flow. Only ppm amounts of zinc were co-extracted. The extraction efficiency was a function of pKa and the aqueous solubility of the extractant and showed marked concentration, solvent, and temperature dependence. Raman spectroscopy was found to be a promising PAT tool for the continuous production of gallium-68.     

Pseudo‐Spectral Methods for the Laplace‐Beltrami Equation and the Hodge Decomposition on Surfaces of Genus One

The inversion of the Laplace‐Beltrami operator and the computation of the Hodge decomposition of a tangential vector field on smooth surfaces arise as computational tasks in many areas of science, from computer graphics to machine learning to computational physics. Here, we present a high‐order accurate pseudo‐spectral approach, applicable to closed surfaces of genus one in three‐dimensional space, with a view toward applications in plasma physics and fluid dynamics. © 2017 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 941–955, 2017