We investigate the Casimir effect, due to the confinement of a scalar field in a D-dimensional sphere, with Lorentz symmetry breaking. The Lorentz-violating part of the theory is described by an ...additional term λ ( u ⋅ ∂ ϕ ) 2 in the scalar field Lagrangian, where the parameter λ and the background vector u μ codify the breakdown of Lorentz symmetry. We compute, as a function of D > 2 , the Casimir stress by using Green's function techniques for two specific choices of the vector u μ . In the timelike case, uμ = ( 1 , 0 , … , 0 ) , the Casimir stress can be factorized as the product of the Lorentz invariant result times the factor ( 1 + λ ) − 1/2. For the radial spacelike case, uμ = ( 0 , 1 , 0 , … , 0 ) , we obtain an analytical expression for the Casimir stress which nevertheless does not admit a factorization in terms of the Lorentz invariant result. For the radial spacelike case we find that there exists a critical value λc = λc ( D ) at which the Casimir stress transits from a repulsive behavior to an attractive one for any D > 2. The physically relevant case D = 3 is analyzed in detail where the critical value λc|D=3 = 0.0025 was found. As in the Lorentz symmetric case, the force maintains the divergent behavior at positive even integer values of D.
•Review of classical static models for ambulance location problem.•Review of multi-period relocation problems.•Review of Dynamic relocation models.•Impact of dispatching decisions.
Over the past 10 ...years, a considerable amount of research has been devoted to the development of models to support decision making in the particular yet important context of Emergency Medical Services (EMS). More specifically, the need for advanced strategies to take into account the uncertainty and dynamism inherent to EMS, as well as the pertinence of socially oriented objectives, such as equity, and patient medical outcomes, have brought new and exciting challenges to the field. In this context, this paper summarizes and discusses modern modeling approaches to address problems related to ambulance fleet management, particularly those related to vehicle location and relocation, as well as dispatching decisions. Although it reviews early works on static ambulance location problems, this review concentrates on recent approaches to address tactical and operational decisions, and the interaction between these two types of decisions. Finally, it concludes on the current state of the art and identifies promising research avenues in the field.
The concept of a biorefinery that integrates processes and technologies for biomass conversion demands efficient utilization of all components. Hydrothermal processing is a potential clean technology ...to convert raw materials such as lignocellulosic materials and aquatic biomass into bioenergy and high added-value chemicals. In this technology, water at high temperatures and pressures is applied for hydrolysis, extraction and structural modification of materials. This review is focused on providing an updated overview on the fundamentals, modelling, separation and applications of the main components of lignocellulosic materials and conversion of aquatic biomass (macro- and micro- algae) into value-added products.
Passivation of interfacial defects serves as an effective means to realize highly efficient and stable perovskite solar cells (PSCs). However, most molecular modulators currently used to mitigate ...such defects form poorly conductive aggregates at the perovskite interface with the charge collection layer, impeding the extraction of photogenerated charge carriers. Here, a judiciously engineered passivator, 4‐tert‐butyl‐benzylammonium iodide (tBBAI), is introduced, whose bulky tert‐butyl groups prevent the unwanted aggregation by steric repulsion. It is found that simple surface treatment with tBBAI significantly accelerates the charge extraction from the perovskite into the spiro‐OMeTAD hole‐transporter, while retarding the nonradiative charge carrier recombination. This boosts the power conversion efficiency (PCE) of the PSC from ≈20% to 23.5% reducing the hysteresis to barely detectable levels. Importantly, the tBBAI treatment raises the fill factor from 0.75 to the very high value of 0.82, which concurs with a decrease in the ideality factor from 1.72 to 1.34, confirming the suppression of radiation‐less carrier recombination. The tert‐butyl group also provides a hydrophobic umbrella protecting the perovskite film from attack by ambient moisture. As a result, the PSCs show excellent operational stability retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking under continuous simulated solar irradiation.
A new passivator, 4‐tert‐butylbenzylammonium iodide (tBBAI), is introduced, which accelerates charge extraction while retarding nonradiative recombination, boosting the power conversion efficiency of perovskite solar cells (PSCs) from 20% to 23.5% and reducing the hysteresis to barely detectable levels. tBBAI‐passivated PSCs also show excellent stability, retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking.
Topological insulators (TIs) exhibit a quantized magnetoelectric response when time-reversal symmetry is broken on its surface. This unusual electromagnetic (EM) response is a unique macroscopic ...manifestation of the quantum Hall effect on the TI surface and it is described by a quantized Chern-Simons theory. In this paper, we construct the Green’s function (GF) describing the EM response of two topological media separated by a cylindrical interface. This GF, in the appropriate limits, describes the magnetoelectric effect of both (i) a cylindrical TI surrounded by a dielectric fluid and (ii) a TI with a cylindrical dielectric-filled cavity. We calculate the EM fields produced by a line charge and a line current near the TI surface and we show that, in addition to the standard image electromagnetic sources, charge and current densities of magnetic monopoles will also appear. We discuss some experimental setups which could be used to test these magnetic monopole fields.
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•Microwave heating pretreatment for lignocellulosic material.•Fundament of lignocellulosic material fractionation using microwave irradiation.•Energy consumption in microwave ...pretreatments and microwave reactors description.•Microwave heating as pretreatment in a biorefinery concept.
The development of a feasible biorefinery is in need of alternative technologies to improve lignocellulosic biomass conversion by the suitable use of energy. Microwave heating processing (MHP) is emerging as promising unconventional pretreatment of lignocellulosic materials (LCMs). MHP applied as pretreatment induces LCMs breakdown through the molecular collision caused by the dielectric polarization. Polar particles movement generates a quick heating consequently the temperatures and times of process are lower. In this way, MHP has positioned as green technology in comparison with other types of heating. Microwave technology represents an excellent option to obtain susceptible substrates to enzymatic saccharification and subsequently in the production of bioethanol and high-added compounds. However, it is still necessary to study the dielectric properties of materials, and conduct economic studies to achieve development in pilot and industrial scale. This work aims to provide an overview of recent progress and alternative configurations for combining the application of microwave technology on the pretreatment of LCMs in terms of biorefinery.
We report a new family of titanium–organic frameworks that enlarges the limited number of crystalline, porous materials available for this metal. They are chemically robust and can be prepared as ...single crystals at multi‐gram scale from multiple precursors. Their heterometallic structure enables engineering of their photoactivity by metal doping rather than by linker functionalization. Compared to other methodologies based on the post‐synthetic metallation of MOFs, our approach is well‐fitted for controlling the positioning of dopants at an atomic level to gain more precise control over the band‐gap and electronic properties of the porous solid. Changes in the band‐gap are also rationalized with computational modelling and experimentally confirmed by photocatalytic H2 production.
Metal doping in titanium MOFs: MUV‐10 are crystalline, porous titanium frameworks with excellent chemical stability in water. The presence of heterometallic clusters in the structure of the frameworks enables chemical engineering of the band‐gap by suitable doping with open shell metals rather than by linker functionalization. This observation is confirmed by computational modelling of the electronic structure of this family of solids.
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•Engineering aspects of hydrothermal pretreatment are presented.•Hydrothermal pretreatment stage plays an important role in the biorefinery concept.•Hydrothermal pretreatment and ...their effect on biomass structure.•Operation mode in batch and continuous of hydrothermal pretreatment are discuses.
Different pretreatments strategies have been developed over the years mainly to enhance enzymatic cellulose degradation. In the new biorefinery era, a more holistic view on pretreatment is required to secure optimal use of the whole biomass. Hydrothermal pretreatment technology is regarded as very promising for lignocellulose biomass fractionation biorefinery and to be implemented at the industrial scale for biorefineries of second generation and circular bioeconomy, since it does not require no chemical inputs other than liquid water or steam and heat. This review focuses on the fundamentals of hydrothermal pretreatment, structure changes of biomass during this pretreatment, multiproduct strategies in terms of biorefinery, reactor technology and engineering aspects from batch to continuous operation. The treatise includes a case study of hydrothermal biomass pretreatment at pilot plant scale and integrated process design.
Avocado (Persea americana Mill.) is a tropical and subtropical fruit that is native to Mexico and Central America; avocado is gaining increasing worldwide acceptance and has received extensive ...marketing and a wide distribution due to its relevant nutritional benefits for human health. Mexico harvests more than 30% of avocados worldwide, representing the main producer and exporter of avocado, which has become a crop of high interest and has great economic impact on Mexico.
In this paper, we describe relevant information on the production, composition and application of avocado, with an emphasis on its by-products, focusing on the proper use of waste and the possibility of monetizing waste for nutritional and environmental purposes. The entire avocado is rich in biocompounds (pulp, seed and peel) and has many health benefits, such as antimicrobial, antioxidant and anticancer activities, as well as dermatological uses and others. In this paper, we demonstrate the current panorama of production, exportation and uses of avocado in Mexico.
Several food grade ingredients can be obtained from avocado wastes, particularly premium-grade fats or extracts with a high functional power. Studies should continue to identify the profiles and phytochemicals available to the business sector, which can also be implemented to valorize the nutritional and functional potential of avocado seeds and peels.
•Avocado has worldwide acceptance, extensive marketing and relevant nutritional benefits.•Avocado by-products are viable sources of bioactive compounds with high functional power.•Avocado by-products are source of premium-grade fats or bioactive phytochemical extracts.•Avocado by-products have nutritional and functional properties.
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