Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to examine the impact of hydrogen bonding on the reactive amine and hydroxyl groups of chitosan. Measurements ...were performed on powder and film samples hydrated under different conditions. To resolve the individual OH and NH bands that overlap in the region between 3000 and 3800 cm−1, the spectra were deconvoluted using a Gaussian curve fitting method. By analyzing the changes recorded for each Gaussian component along the dehydration process of the films at different pH values, a band assignment was proposed. This assignment was then used to analyze the ATR-FTIR spectra of the chitosan/montmorillonite composites. The changes induced by the presence of the clay were ascribed to particular mechanisms of interaction that involve the active sites of the clay and the amino or hydroxyl groups of chitosan. The comparison between the FTIR and the XRD data, evidenced that these mechanisms are intimately controlled by the type of nanostructures that are formed depending on the clay content.
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•FTIR- ATR spectra of chitosan under different environmental conditions were analyzed.•The OH and NH stretching vibrational modes were differentiate and identified.•The behavior of the OH and NH modes in chitosan/clay composites was investigated.•Correlation between nanostructures and mechanisms of interaction was evidenced.
In recent years, course-based undergraduate research experiences (CUREs) have been increasing in popularity as replacements for or adjuvants to the traditional laboratory experience. This approach ...shifts the focus from an exercise-based curriculum to an experiment-based curriculum and provides students with a more authentic and higher-impact scientific experience. Reported herein are the details of a CURE deployed in the organic chemistry II lab at a primarily undergraduate institution. In this instance, students are given nearly free rein regarding their group projects completed during the second semester. Quantitative assessment of the approach through student surveys is provided, though the statistical significance of the results is at best questionable. Qualitatively, one project has resulted in a paper in preparation and others are nearing this milestone, demonstrating the viability of the approach to expose students to doing publishable scientific research and the scientific process. Additionally, free responses to survey questions seem to suggest that the method is a success.
The suspension of in-person classes brought about by the COVID-19 pandemic necessitated adjustments to all manner of instruction. Laboratory instruction was particularly challenged since the primary ...response was to deliver content remotely, i.e., online. In an effort to reinforce laboratory topics and engage students, five click-through organic chemistry lab stories modeled after the Choose your Own Adventure book series were created. These “labventures” were (1) use of FT-IR; (2) identification by mixed melting point; (3) liquid–liquid extraction; (4) recrystallization; and (5) chemical reaction. To facilitate assessment, each story was deployed on the Learning Management System so the number of times students visit each page of the story could be counted. These assignments were generally well received by students and revealed varied levels of understanding of the laboratory material.
•Review into solutions to reduce degradation of ballasted railway tracks.•Innovative materials to be applied during track design.•Maintenance techniques to improve geometry and decelerate ballast ...degradation.•Summary of solutions and proposal of further research studies.
Ballasted railway tracks, despite their benefits, present some limitations and drawbacks, mainly associated with geometry degradation due to ballast settlement and particle breakage. Periodic maintenance interventions are thus required as well as renewal processes, which lead to the significant consumption of natural materials and energy whilst causing frequent interruptions to traffic. This is made more problematic when aggregates with appropriate characteristics for ballast are not available in the proximity of the construction/maintenance site, which is becoming increasingly common due to restrictive environmental guidelines. In this context, this paper presents a review of the effectiveness of the major conventional techniques/materials for track design and maintenance as well as innovative solutions that are being developed to reduce track degradation, whilst also analysing their main parameters to optimize track behaviour and durability, depending on its design and the required changes in its mechanical performance. The aim is to then provide a set of recommendations and guidelines for the use of such technologies to improve track response and durability as well as highlighting possible further research associated with both the development of innovative solutions and the improvement of conventional techniques.
Purpose
High altitude results in lower barometric pressure and hence partial pressure of O
2
decrease can lead to several molecular and cellular changes, such as generation of reactive oxygen species ...(ROS). Electron Paramagnetic Resonance technique was adopted in the field, to evaluate the effects of acute and sub-acute hypobaric hypoxia (HH) on ROS production by micro-invasive method. Biological biomarkers, indicators of oxidative stress, renal function and inflammation were investigated too.
Methods
Fourteen lowlander subjects (mean age 27.3 ± 5.9 years) were exposed to HH at 3269 m s.l. ROS production, related oxidative damage to cellular components, systemic inflammatory response and renal function were determined through blood and urine profile performed at 1st, 2nd, 4th, 7th, and 14th days during sojourn.
Results
Kinetics of changes during HH exposition showed out significant (range
p
< 0.05–0.0001) increases that at max corresponds to 38% for ROS production rate, 140% for protein carbonyl, 44% for lipid peroxidation, 42% for DNA damage, 200% for inflammatory cytokines and modifications in renal function (assessed by neopterin concentration: 48%). Conversely, antioxidant capacity significantly (
p
< 0.0001) decreased − 17% at max.
Conclusion
This 14 days in-field study describes changes of oxidative-stress biomarkers during HH exposure in lowlanders. The results show an overproduction of ROS and consequent oxidative damage to protein, lipids and DNA with a decrease in antioxidant capacity and the involvement of inflammatory status and a transient renal dysfunction. Exposure at high altitude induces a hypoxic condition during acute and sub-acute phases accompanied by molecular adaptation mechanism indicating acclimatization.
Context.Vortices in protoplanetary disks can capture solid particles and form planetary cores within shorter timescales than those involved in the standard core-accretion model. Aims.We investigate ...vortex generation in thin unmagnetized protoplanetary disks with an embedded giant planet with planet to star mass ratio 10-4 and 10-3. Methods.Two-dimensional hydrodynamical simulations of a protoplanetary disk with a planet are performed using two different numerical methods. The results of the non-linear simulations are compared with a time-resolved modal analysis of the azimuthally averaged surface density profiles using linear perturbation theory. Results.Finite-difference methods implemented in polar coordinates generate vortices moving along the gap created by Neptune-mass to Jupiter-mass planets. The modal analysis shows that unstable modes are generated with growth rate of order $0.3 \Omega_{{\rm K}}$ for azimuthal numbers $m=4,5,6$, where $\Omega_{{\rm K}}$ is the local Keplerian frequency. Shock-capturing Cartesian-grid codes do not generate very much vorticity around a giant planet in a standard protoplanetary disk. Modal calculations confirm that the obtained radial profiles of density are less susceptible to the growth of linear modes on timescales of several hundreds of orbital periods. Navier-Stokes viscosity of the order $\nu=10^{-5}$ (in units of $a^2 \Omega_{{\rm p}}$) is found to have a stabilizing effect and prevents the formation of vortices. This result holds at high resolution runs and using different types of boundary conditions. Conclusions.Giant protoplanets of Neptune-mass to Jupiter-mass can excite the Rossby wave instability and generate vortices in thin disks. The presence of vortices in protoplanetary disks has implications for planet formation, orbital migration, and angular momentum transport in disks.
We have analyzed a highly monochromatic (f = 1.67 mHz) and large‐amplitude Ultra Low Frequency (ULF) wave event observed at satellites and ground observatories on 23 June 2020 during super solar ...quiet geomagnetic conditions. The train wave was detected between 6:22 and 7:55 UT across a wide longitudinal range of ground stations from low to high latitudes. Using Deep Space Climate Observatory and THEMIS‐B spacecraft, which were in the interplanetary medium, we have identified the possible driver of such global ULF wave activity in the impact of a small pressure pulse accompanied by a discontinuity in the magnetic field. The prolonged duration (90 min) of the ULF waves as well as their latitude‐independent frequency and the small azimuthal wave number (m ∼ 0−2) can be explained in terms of a global magnetospheric waveguide mode. The amplitude and cross‐phase analysis of the wave activity at ground, together with the polarization pattern, suggest the waveguide mode coupling with field line resonance. Nevertheless, during the same time interval, indirect evidence exists of a rapid reconfiguration of the magnetotail in the form of Pi2 waves in the night‐side region. The analysis of energetic particle flux at ionospheric height (500 km) shows a direct connection between the ULF wave activity and particle precipitation.
Plain Language Summary
Ultra Low Frequency (ULF) waves illustrates the highly dynamical nature of the Earth's magnetosphere since they are directly connected with energy and mass transport. The event we analyzed occurred during a very low geomagnetic activity showing 10 min period (Pc5) waves between 6:22 and 7:55 UT across a wide longitudinal range of ground stations from low to high latitudes that lead to particle precipitation. The prolonged duration (90 min) of the ULF waves as well as their latitude‐independent frequency and the small azimuthal wave number can be explained in terms of a global magnetospheric waveguide mode. The latitude and local time polarization pattern of the Pc5 wave event, suggests the waveguide mode coupling with magnetospheric field line resonances. The satellite observations in the interplanetary medium suggest that small solar wind disturbances were able to trigger the dynamic of the system directly, with Pc5 waves in response to the impact of a small jump in dynamic pressure, and indirectly, together with a rotation of the interplanetary magnetic field, triggering magnetotail processes resulting in an additional higher frequency wave activity (Pi2). Such kind of studies need scrupulous attention when trying to identify the possible source of ULF wave activity.
Key Points
Global magnetospheric anomalous Ultra Low Frequency waves activity during super solar quiet conditions
Coupling between the waveguide mode and magnetospheric field line resonance
Signatures of particle precipitation at Low Earth Orbit orbit during Pc5 and Pi2 wave activity
Introduction: Extended spectrum β-lactamases (ESBL) and AmpC β-lactamases are increasing causes of resistance in many Gram-negative pathogens of common infections. This has led to a growing ...utilization of broad spectrum antibiotics, most predominately the carbapenem agents. As the prevalence of ESBL and AmpC-producing isolates and carbapenem resistance has increased, interest in effective alternatives for the management of these infections has also developed.
Areas covered: This article summarizes clinical literature evaluating the utility of carbapenem-sparing regimens for the treatment of ESBL and AmpC-producing Enterobacteriaceae, mainly β-lactam-β-lactamase inhibitor combinations and cefepime (FEP).
Expert opinion: Based on available data, the use of piperacillin-tazobactam (PTZ) and FEP in the treatment of ESBL-producing Enterobacteriaceae cannot be widely recommended. However, certain infections and patient characteristics may support for effective use of these alternative agents. In the treatment of infections caused by AmpC-producing Enterobacteriaceae, FEP has been shown to be a clinically useful carbapenem-sparing alternative. Carbapenems and FEP share many structurally similar characteristics in regards to susceptibility to AmpC β-lactamases, which further create confidence in the use FEP in these situations. Patient and infection specific characteristics should be used to employ FEP optimally.
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