14,882 research outputs found
Addressing the structural organization of silicone alternatives in formulations by molecular dynamics simulations and a novel equilibration protocol
The world of cosmetics is an always-evolving field with constant updates on its formulation components. The current reality asks for an ever-increasing need for natural and sustainable replacements for synthetic compounds in all fields of modern consumer products. However, the research and development stages of finding these alternatives can be an expensive, time-consuming, and often wasteful process that turns this task into a laborious procedure. This study introduces the development of a computational methodology that will aid the research of silicone alternatives, disclosing their structural performance in a formulation. Additionally, an equilibration protocol was developed to measure the distribution and densities of these silicone alternatives to determine how they behave in relation to their counterparts, using molecular dynamics simulations. Two systems were tested, A and B, where the former is composed of one ester (Dipentaerythrityl Hexa C5 Acid Ester) and the latter by an ester combined with an alkane (Triheptanoin and C13-Isoalkane); all three molecules are commercially available and widely used. Both systems were subjected to a 3-step thermal regulation strategy. The systems went through an initial simulation at 25 °C and at 70 °C, then a temperature switch took place (25 °C « 70 °C), then a shock to 200 °C, and finally a Simulated Annealing protocol reaching 250 °C. In the end, all systems converged towards micelle-like structures. These results come to further ascertain the position of computational chemistry and Molecular Dynamics Simulations as an important part of R&D processes in modern sciences and investigation.This research was developed with the support of computing facilities pro vided by the project: “Search-ON2: Revitalization of HPC infrastructure of UMinho” (NORTE-07- 0162-FEDER-000086), co-funded by the North Portugal Regional Operational Programme (ON.2— O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF).info:eu-repo/semantics/publishedVersio
Neutron scattering studies of heterogeneous catalysis
Understanding the structural dynamics/evolution of catalysts and the related surface chemistry is essential for establishing structure–catalysis relationships, where spectroscopic and scattering tools play a crucial role. Among many such tools, neutron scattering, though less-known, has a unique power for investigating catalytic phenomena. Since neutrons interact with the nuclei of matter, the neutron–nucleon interaction provides unique information on light elements (mainly hydrogen), neighboring elements, and isotopes, which are complementary to X-ray and photon-based techniques. Neutron vibrational spectroscopy has been the most utilized neutron scattering approach for heterogeneous catalysis research by providing chemical information on surface/bulk species (mostly H-containing) and reaction chemistry. Neutron diffraction and quasielastic neutron scattering can also supply important information on catalyst structures and dynamics of surface species. Other neutron approaches, such as small angle neutron scattering and neutron imaging, have been much less used but still give distinctive catalytic information. This review provides a comprehensive overview of recent advances in neutron scattering investigations of heterogeneous catalysis, focusing on surface adsorbates, reaction mechanisms, and catalyst structural changes revealed by neutron spectroscopy, diffraction, quasielastic neutron scattering, and other neutron techniques. Perspectives are also provided on the challenges and future opportunities in neutron scattering studies of heterogeneous catalysis
The impact of supernova feedback on the mass-metallicity relations
Metallicity is a fundamental physical property that strongly constrains
galaxy formation and evolution. The formation of stars in galaxies is
suppressed by the energy released from supernova explosions and can be enhanced
by metal production. In order to understand the impact of this supernova
feedback, we compare four different feedback methods, ejecting energy in
thermal, kinetic, stochastic and mechanical forms, into our self-consistent
cosmological chemodynamical simulations. To minimise other uncertainties, we
use the latest nucleosynthesis yields that can reproduce the observed elemental
abundances of stars in the Milky Way. For each method, we predict the evolution
of stellar and gas-phase metallicities as a function of galaxy mass, i.e., the
mass-metallicity relations. We then find that the mechanical feedback can give
the best match to a number of observations up to redshift , although
the predicted gas-phase metallicities seem to be higher than observed at . The feedback modelling can be further constrained by the metallicities in
distant galaxies with the James Web Space Telescope and those of a large sample
with ongoing and future spectroscopic surveys.Comment: Submitted to MNRAS, 14 pages, 13 figure
Edge Theories for Anyon Condensation Phase Transitions
The algebraic tools used to study topological phases of matter are not
clearly suited to studying processes in which the bulk energy gap closes, such
as phase transitions. We describe an elementary two edge thought experiment
which reveals the effect of an anyon condensation phase transition on the
robust edge properties of a sample, bypassing a limitation of the algebraic
description. In particular, the two edge construction allows some edge degrees
of freedom to be tracked through the transition, despite the bulk gap closing.
The two edge model demonstrates that bulk anyon condensation induces symmetry
breaking in the edge model. Further, the construction recovers the expected
result that the number of chiral current carrying modes at the edge cannot
change through anyon condensation. We illustrate the construction through
detailed analysis of anyon condensation transitions in an achiral phase, the
toric code, and in chiral phases, the Kitaev spin liquids.Comment: 25 pages, 9 figure
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Treatments for migraine and related disorders
Embodiments are directed to compositions and methods of treating migraine and related neurological disorders. In certain aspects, methods and compositions are for reducing cortical spreading depression and/or suppressing the neurochemical basis for chronic and acute migraine events, and provide methods and pharmaceutical compositions related to both acute and preventive therapies for migraine events and related headaches
Homeostasis in Immunity-Related Pupal Tissues of the Malaria Mosquito Anopheles gambiae and its regulation by the NF-kappaB-like Factor Rel2
Die Haut ist eine oft übersehene Komponente des angeborenen Immunsystems der Mücken. Die Haut der Mücke bildet eine physische Barriere, die die mikrobielle Homöostase aufrechterhält, das Eindringen von Toxinen wie Insektiziden verhindert und das Austrocknen verhindert. Die am meisten untersuchten Akteure des Immunsystems von Stechmücken sind das Fettgewebe und die Blutzellen, aber die Hauttalg-Fabriken, die Oenozyten, werden in Studien nur selten berücksichtigt.
Mückenpuppen haben aktiv funktionierende immunitätsbezogene Organe, einschließlich derjenigen, die Hautbarrieren produzieren. Ihre biologische Rolle in diesem Entwicklungsstadium ist kaum bekannt, aber der Übergang von der Puppen- zur Erwachsenenhaut und die Auffälligkeit der talgproduzierenden Zellen machen dieses Stadium zu einem vielversprechenden Entwicklungsstadium für die Untersuchung der Hautbildung.
Mit Hilfe der Transkriptomanalyse beschreiben wir die Rolle der Blutzellen bei der Entwicklung des chitinösen Teils der Insektenhaut, die Beteiligung des Fettkörpers an der Immunität und bestätigen die Rolle der talgproduzierenden Zellen im Lipidstoffwechsel. Darüber hinaus beschreiben wir talgsezernierende Zellen als einen bedeutenden Wirkungsort des NF-kappaB-ähnlichen IMD-Rel2-Pathway, in dem der Transkriptionsfaktor Rel2 die Retinoid-Homöostase reguliert. Schließlich bestätigen wir eine 100 Jahre alte Beobachtung, wonach sebumsezernierende Zellen der Stechmücke ihren Zellinhalt in einem Netzwerk von Vesikeln absondern. Wir beschreiben extrazelluläres Chromatin als Fracht in diesem Vesikelnetzwerk und sein antimikrobielles Potenzial.The skin is an often overlooked component of the mosquito's innate immune system. The mosquito skin provides a physical barrier that maintains microbial homeostasis, prevents the entry of toxins like insecticides, and avoids desiccation. The most studied players in the immune system of mosquitoes are the adipose tissue and blood cells, but studies rarely consider the skin sebum factories, oenocytes.
Mosquito pupae have actively functional immunity-related organs, including those producing skin barriers. Their biological roles at this developmental stage are poorly understood, but the pupae-to-adult metamorphic skin transition and the conspicuity of sebum-secreting cells make it a promising developmental stage to study skin formation.
We use transcriptomics to describe the role of blood cells in the development of the chitinous section of the insect skin, the involvement of the fat body in immunity, and confirm the lipid metabolism role of sebum-secreting cells. Furthermore, we describe sebum-secreting cells as a significant action site of the NF-kappaB-like IMD-Rel2 pathway where the transcription factor Rel2 regulates retinoid homeostasis. Finally, we confirm a 100-year-old observation of how mosquito sebum-secreting cells secrete their cellular contents in a network of vesicles. We describe extracellular chromatin as cargo inside this vesicle network and its antimicrobial potential
Designing carbon fibre-reinforced composites with improved structural retention on exposure to heat/fire
Carbon fibre-reinforced composites (CFRCs) are increasing in popularity due to their high
strength-to-weight ratio and resistance to corrosion. However, when exposed to temperatures
above 300°C, the polymer matrix within CFRCs decomposes and then starts burning, exposing
carbon fibres to the surroundings. The residual carbon fibres being electrically conductive, may
pose a hazard to the surrounding electronics. Moreover, at over 550°C the carbon fibres begin
to oxidise. This can lead to fibre defibrillation which also poses significant harm to human health
as broken fibres can be sharp enough to cut through human skin, and under 7µm these particles
are considered respirable where on inhalation they can causes damage to the trachea and lungs.
While considerable work has been carried out on assessing the effect of heat/fire on degradation
of the composite resin (matrix) and CFRCs themselves, there are limited studies on identifying
the damage to carbon fibres within CFRCs and the hazards posed by the exposed damaged
carbon fibres. This study examined the damage caused by high temperatures, radiant heat and
flames on carbon fibres and CFRCs, and the effects on their physical properties. A methodology
was developed to study and quantify the structural damage to carbon fibres and CFRCs after
exposure to a range of heat/fire conditions. These included thermogravimetric analysis (up to
900oC in nitrogen and air atmospheres), the tube furnace (450oC–900oC), cone calorimeter
(35kWm-2
to 75kWm-2
) and a propane burner (116kWm-2
) to simulate jet fuel fire conditions.
Residual fibres were removed from different parts of the CFRCs and the physical properties
were studied, such as fibre diameter reduction, change in electrical conductivity and decrease in
tensile strength. It was found that at heat fluxes ≥60kWm-2
oxidation of the carbon fibres
occurred. After 10min exposure to the propane flame, fibres in direct contact with the flame
showed signs of internal oxidation.The aim of this PhD project was to also improve the structural retention of CFRCs on exposure
to heat/fire so that the structural integrity is maintained and the carbon fibres are not exposed to
the environment. To address this, the following approaches were undertaken:
• Modification of the resin by adding flame retardants and nanoparticles in order to reduce the
flammability of CFRCs, improve the mechanical integrity of the char and its adherence to the fibre. Flame retardants included ammonium polyphosphate, resorcinol bis-(diphenyl
phosphate), 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide, and the nano-additives,
nano-clay, layered double hydroxide and carbon nano-tubes. Cone calorimeter testing at
75kWm-2 showed that the addition of 15wt% ammonium polyphosphate resulted in large char
formation and adherence to fibres in the underlying plies, which resulted in less oxidation to
these carbon fibres. The addition of layered double hydroxides and carbon nano-tubes on the
other hand caused pitting on fibres.
• Provide heat protection to carbon fibres within CFRCs by the inclusion of high performance
fibrous veils/woven fabrics of aramid, basalt, E-glass, polyphenylene sulphide and Kevlar.
The inclusion of the woven E-glass resulted in a notable reduction in the percentage of carbon
fibre oxidised. However, the volatiles produced during the decomposition of Kevlar and PPS
sensitised the carbon fibre to oxidation, causing it to occur more rapidly and at a lower
temperature.
• Using high temperature chemical coatings to individually coat carbon fibres prior to making
the CFRCs. Ceramic compounds (silica, alumina and zirconia), chosen as coating materials
because of their high thermal stability, were applied by different processes. The most
promising coatings included alumina and silica formed via sol-gel process and polysiloxane
deposited during plasma exposure. Tows coated in these chemicals underwent heat testing in
a tube furnace where those coated with alumina maintained the largest fibre diameters. While
polysiloxane coating provided oxidation protection up to 600°C, after which cracks in the
coating were observed. This was attributed to the mechanical mismatch of the polysiloxane
coating and the carbon fibre
A Sun-like star orbiting a boson star
The high-precision astrometric mission GAIA recently reported the remarkable
discovery of a Sun-like star closely orbiting a dark object, with a semi-major
axis and period of and days respectively. While the
plausible expectation for the central dark object is a black hole, the
evolutionary mechanism leading to the formation of such a two-body system is
highly challenging. Here, we challenge the scenario of a central black hole and
show that the observed orbital dynamics can be explained under fairly general
assumptions if the central dark object is a stable clump of bosonic particles
of spin-0, or spin-1, known as a boson star. We further explain how future
astrometric measurements of similar systems will provide an exciting
opportunity to probe the fundamental nature of compact objects and test compact
alternatives to black holes.Comment: 11 pages, 4 figures. Comments are very welcom
Effect of polydispersity in concentrated magnetorheological fluids
Magnetorheological fluids (MRF) are smart materials of increasing interest
due to their great versatility in mechanical and mechatronic systems. As main
rheological features, MRFs must present low viscosity in the absence of a
magnetic field (0.1 - 1.0 Pa.s) and high yield stress (50 - 100 kPa) when
magnetized, in order to optimize the magnetorheological effect. Such
properties, in turn, are directly influenced by the composition, volume
fraction, size, and size distribution (polydispersity) of the particles, the
latter being an important piece in the improvement of these main properties. In
this context, the present work aims to analyze, through experiments and
simulations, the influence of polydispersity on the maximum packing fraction,
on the yield stress under field (on-state), and on the plastic viscosity in the
absence of field (off-state) of concentrated MRF (phi = 48.5 vol.%). Three
blends of carbonyl iron powder in polyalphaolefin oil were prepared. These
blends have the same mode, but different polydispersity indexes, ranging from
0.46 to 1.44. Separate simulations show that the random close packing fraction
increases from about 68% to 80% as the polydispersity index increases over this
range. The on-state yield stress, in turn, is raised from 30 +/- 0.5 kPa to 42
+/- 2 kPa (B ~ 0.57 T) and the off-state plastic viscosity, is reduced from 4.8
Pa.s to 0.5 Pa.s. Widening the size distributions, as is well known in the
literature, increases packing efficiency and reduces the viscosity of
concentrated dispersions, but beyond that, it proved to be a viable way to
increase the magnetorheological effect of concentrated MRF. The Brouwers model,
which considers the void fraction in suspensions of particles with lognormal
distribution, was proposed as a possible hypothesis to explain the increase in
yield stress under magnetic field
Challenge and Research Trends of Solar Concentrators
Primary and secondary solar concentrators are of vital importance for advanced solar energy and solar laser researches. Some of the most recent developments in primary and secondary solar concentrators were firstly presented. A novel three-dimensional elliptical-shaped Fresnel lens analytical model was put forward to maximize the solar concentration ratio of Fresnel-lens-based solar concentrators. By combining a Fresnel lens with a modified parabolic mirror, significant improvement in solar laser efficiency was numerically calculated. A fixed fiber light guide system using concave outlet concentrators was proposed. The absence of a solar tracking structure highlights this research. By shaping a luminescent solar concentrators in the form of an elliptic array, its emission losses was drastically reduced. Simple conical secondary concentrator was effective for thermal applications. New progresses in solar-pumped lasers by NOVA University of Lisbon were presented. By adopting a rectangular fused silica light guide, 40 W maximum solar laser power was emitted from a single Ce:Nd:YAG rod. An aspheric fused silica secondary concentrator and a small diameter Ce:Nd:YAG rod were essential for attaining 4.5 % record solar-to-laser power conversion efficiency. A novel solar concentrator design for the efficient production of doughnut-shaped and top-hat solar laser beams were also reported. More importantly, a novel solar concentrator approach for the emission of 5 kW-class TEM00 mode solar laser beams from one megawatt solar furnace was put forward at the end of this book, revealing promising future for solar-pumped lasers
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