Creation Of Hot Spots Research Articles

Hot spot generation, reactivity, and decay in mechanochemical reactors

In this work, a bottom-up modeling approach to describe the reactive conditions in mechanochemical reactors is presented. The approach is focused on the creation of hot spots as the mechanism of enhanced reaction. In this model, energy dissipated during a collision is converted to heat in the milling media, and the reaction proceeds thermochemically. The first step of the model, determining the energy dissipated during the collision, is done by treating the ball and powder bed as viscoelastic materials and using a Kelvin Voigt model. The energy dissipation profile from the collision model is imported into a COMSOL® simulation. The heat transfer through the powder bed, treated as a continuous medium, is calculated, providing the temperature, volume, and time needed to calculate reaction rates. The final result of the model is the extent of reaction over a single collision. To verify the approach, the mechanochemical decomposition of calcium carbonate is studied. The real-time CO2 production under varying milling frequencies is measured using an in-line mass spectrometer. The ball and mill velocities, as well as, collision frequencies is determined by analyzing high speed video of a transparent milling vessel. The model describes hot spots with temperatures exceeding 1000 K that persist for tens of milliseconds.

Bi-Ligand Modification of Nanoparticles: An Effective Tool for Surface-Enhanced Raman Spectrometry in Salinated Environments.

Elimination of massive aggregation of nanoparticles in the sample of high ionic strength is a prerequisite for the sensitive analysis through a surface-enhanced Raman spectrometry (SERS). We present a system of silver colloid modification composed of two thiolated modifiers (3-mercaptopropionic acid and thiolated polyethylene glycol) both creating a strong Ag-S bond. At their optimal molar ratio, the polymer acts as a steric barrier preventing direct nanoparticle–nanoparticle interaction, while the low-molecular organic acid creates areas accessible for the analyte molecules. Thus, this approach is an excellent tool for sustaining both the colloidal stability and SERS sensitivity. The functionality of the system was demonstrated on the SERS analysis of myoglobin from a saline solution. The favorable creation of hot spots was achieved by laser-induced sintering.

Hydrodeoxygenation Using Magnetic Induction: High-Temperature Heterogeneous Catalysis in Solution.

Magnetic heating has recently been demonstrated as an efficient way to perform catalytic reactions after deposition of the heating agent and the catalyst on a support. Here we show that in solution, and under mild conditions of mean temperature and pressure, it is possible to use magnetic heating to carry out transformations that are otherwise performed heterogeneously at high pressure and/or high temperature. As a proof of concept, we chose the hydrodeoxygenation of acetophenone derivatives and of biomass-derived molecules, namely furfural and hydroxymethylfurfural. These reactions are difficult, require heterogeneous catalysts and high pressures, and, to the best of our knowledge, have no precedent in standard solution. Here, hydrodeoxygenations are fully selective under mild conditions (3 bar H2 , moderate mean temperature of the solvent). The reason for this reactivity is the fast heating of the particles well above the boiling temperature of the solvent and the local creation of hot spots surrounded by a vapor layer, in which high temperature and pressure may be present. This technology may be practicable for many organic transformations.

Hydrodeoxygenation Using Magnetic Induction: High‐Temperature Heterogeneous Catalysis in Solution

AbstractMagnetic heating has recently been demonstrated as an efficient way to perform catalytic reactions after deposition of the heating agent and the catalyst on a support. Here we show that in solution, and under mild conditions of mean temperature and pressure, it is possible to use magnetic heating to carry out transformations that are otherwise performed heterogeneously at high pressure and/or high temperature. As a proof of concept, we chose the hydrodeoxygenation of acetophenone derivatives and of biomass‐derived molecules, namely furfural and hydroxymethylfurfural. These reactions are difficult, require heterogeneous catalysts and high pressures, and, to the best of our knowledge, have no precedent in standard solution. Here, hydrodeoxygenations are fully selective under mild conditions (3 bar H2, moderate mean temperature of the solvent). The reason for this reactivity is the fast heating of the particles well above the boiling temperature of the solvent and the local creation of hot spots surrounded by a vapor layer, in which high temperature and pressure may be present. This technology may be practicable for many organic transformations.

Damage on Escherichia coli and Staphylococcus aureus using white light photoactivation of Au and Ag nanoparticles

Bactericidal efficiency of Au and Ag nanoparticles (NPs) is reported with and without photoactivation by white light. Au and Ag NPs were synthesized with an average size of 14±1.2nm and of 4.6±0.5nm, respectively. The size distribution of the Ag colloid was relatively wide. Less than 4% of these NPs were largely decahedral, which, based on numerical calculations, determined the position of the optical band. In contrast, the Au colloid had a narrow optical band; a concentration of 1.3μg/ml was determined by theoretical and experimental spectra. Ag and Au NPs showed a superficial charge of −35mV and +57mV due to the presence of the citrate ions and cetyltrimethylammonium bromide on their surface, respectively. The effect of the NPs concentration on the viability of Escherichia coli and Staphylococcus aureus strains was investigated. It was found that Ag NPs were more effective against E. coli than Au NPs, whereas Au NPs were more effective against S. aureus than Ag NPs. The induced damage to the bacteria by the NPs was evaluated by AFM. The images show that the bacterial cell wall was changed in shape and in surface roughness, being more noticeable in S. aureus than in E. coli. The bactericidal activity of the photoactivated Ag NPs was almost doubled for both bacteria, whereas for the Au NPs, no bactericidal enhancement was observed for either strain. This can be explained by the high efficiency of Ag NPs to absorb white light and the consequent creation of hot spots that contribute to kill the bacteria.

Rapid detection of multiple organophosphorus pesticides (triazophos and parathion-methyl) residues in peach by SERS based on core-shell bimetallic Au@Ag NPs

ABSTRACTIn this study, a surface-enhanced Raman scattering (SERS) approach based on silver-coated gold nanoparticles (Au@Ag NPs) was established for rapid detection of multiple organophosphorus pesticides (triazophos and methyl-parathion) in peach fruit. The Raman enhancement of Au@Ag NPs for detecting organophosphorus pesticides was stronger than those of single Ag and Au NPs. It was revealed that core size of Au NPs was a critical parameter affecting the enhancement of Raman signals by joining two plasma resonance absorptions. The Au@Ag NPs with 26 nm Au core size and 6 nm Ag shell thickness showed significant Raman enhancement, especially by the creation of hot spots through NPs aggregation induced by connection between Au@Ag NPs and target molecules. The detection limits of triazophos and methyl-parathion in peach were 0.001 mg/kg. Good recovery (93.36 to 123.6 %) and high selectivity of the SERS activity allowed excellent precision for the detection of the triazophos and methyl-parathion in peach. Compared to earlier studies, the current approach was rapid, inexpensive and simple without lengthy sample pre-treatment. This study revealed that the proposed method could be employed for the analysis of trace contaminants such as triazophos and methyl-parathion in many food matrices.

ETAS: Energy and thermal‐aware dynamic virtual machine consolidation in cloud data center with proactive hotspot mitigation

SummaryData centers consume an enormous amount of energy to meet the ever‐increasing demand for cloud resources. Computing and Cooling are the two main subsystems that largely contribute to energy consumption in a data center. Dynamic Virtual Machine (VM) consolidation is a widely adopted technique to reduce the energy consumption of computing systems. However, aggressive consolidation leads to the creation of local hotspots that has adverse effects on energy consumption and reliability of the system. These issues can be addressed through efficient and thermal‐aware consolidation methods. We propose an Energy and Thermal‐Aware Scheduling (ETAS) algorithm that dynamically consolidates VMs to minimize the overall energy consumption while proactively preventing hotspots. ETAS is designed to address the trade‐off between time and the cost savings and it can be tuned based on the requirement. We perform extensive experiments by using the real‐world traces with precise power and thermal models. The experimental results and empirical studies demonstrate that ETAS outperforms other state‐of‐the‐art algorithms by reducing overall energy without any hotspot creation.

Fabrication of silver-coated gold nanoparticles to simultaneously detect multi-class insecticide residues in peach with SERS technique

Fast sampling and multicomponent detections are important in the analysis of pesticide residues detection. In this work, surface-enhanced Raman scattering (SERS) method based on silver-coated gold nanoparticles (Au@Ag NPs) was used to simultaneously detect multi-class pesticide residues such as thiacloprid (carbamate), profenofos (organophosphate) and oxamyl (neonicotinoid) in standard solution and peach fruit. The Au@Ag NPs with 26 nm Au core size and 6 nm Ag shell thickness exhibited significant Raman enhancement, especially by the creation of hot spots through NPs aggregation induced by the connection between Au@Ag NPs and target molecules. The findings demonstrated that the characteristic wavenumber of the pesticides (thiacloprid, profenofos, and oxamyl) could be precisely identified using the SERS method. Compared with earlier studies, the current approach was rapid, inexpensive and without lengthy sample pretreatment. Moreover, the results revealed that the limit of detection (LOD) was 0.1 mg/kg for thiacloprid obtained in the peach extract with determination coefficient (R2) of 0.986. Additionally, LOD for both profenofos and oxamyl was 0.01 mg/kg with a determination coefficient (R2) of 0.985 and 0.988, respectively. Good recovery percentage (78.6–162.0%) showed the high SERS activity with better accuracy for the detection of the thiacloprid, profenofos, and oxamyl in peach. The results of this study could offer a promising SERS platform for simultaneous detection of other contaminants such as thiacloprid, profenofos and oxamyl in multifaceted food matrices.

Frequency-Domain Proof of the Existence of Atomic-Scale SERS Hot-Spots.

The existence of sub-nanometer plasmonic hot-spots and their relevance in spectroscopy and microscopy applications remain elusive despite a few recent theoretical and experimental evidence supporting this possibility. In this Letter, we present new spectroscopic evidence suggesting that Angstrom-sized hot-spots exist on the surfaces of plasmon-excited nanostructures. Surface-enhanced Raman scattering (SERS) spectra of 4,4'-biphenyl dithiols placed in metallic junctions show simultaneously blinking Stokes and anti-Stokes spectra, some of which exhibit only one prominent vibrational peak. The activated vibrational modes were found to vary widely between junction sites. Such site-specific, single-peak spectra could be successfully modeled using single-molecule SERS induced by a hot-spot with a diameter no larger than 3.5 Å, located at the specific molecular sites. Furthermore, the model, which assumes the stochastic creation of hot-spots on locally flat metallic surfaces, consistently reproduces the intensity distributions and occurrence statistics of the blinking SERS peaks, further confirming that the sources of the hot-spots are located on the metallic surfaces. This result not only provides compelling evidence for the existence of Angstrom-sized hot-spots but also opens up the new possibilities for the vibrational and electronic control of single-molecule photochemistry and real-space visualization of molecular vibration modes.

2. Entropic closure for MRI-guided radiotherapy

Introduction The majority of patients affected by cancer are nowadays treated by radiotherapy, which consists in delivering a homogeneous dose with energetic particles. Magnetic Resonance Imaging (MRI)-guided radiotherapy shows precisely the tumor position in real time and allows to direct the photon beams to the tumor while sparing organs at risks. Our work consists in the validation of a new model developped to simulate the energy deposition of the particles used in radiotherapy (electrons, photons and protons) in the presence of strong magnetic field, within human tissues, and its adaptation to this new technology. Material and methods This model is based on a kinetic entropic closure of the linearized Boltzmann equation [1] , which describes the transport of energetic particles in the matter. This equation takes a lot of computation time to be solved due to the high number of variables. To simplify this, we replace fluences by angular moments, which allows getting rid of the angular variables and improve the calculation time. We obtain a set of angular moments equations, and we close this set using the Boltzmann’s principle of entropy maximization on the two first equations of the set. This model has an accuracy comparable to references Monte-Carlo (MC) codes [2] (Geant4, MCNPx, Penelope), and is less time-consuming than these ones. We added the Lorentz force into our code to study the influence of a magnetic field on the dose deposition, and compared it to the reference full MC code FLUKA. To further validate our model, we have carried out an experimental campaign in which we irradiated a composition of materials of different mass densities, with 6 and 18 MV photon beams of a Varian Clinac 21Ex accelerator, without and with the influence of a 0.87 T magnetic field of amplitude induced by a permanent magnet. Results We show a good agreement between our model and the FLUKA code ( Fig. 1 ). We highlight the effects that occur on the propagation of particles in the matter in presence of a magnetic field of a few Tesla. Indeed, it modifies the dose deposition by shifting the deposition of energy, leading to an increased diffusion depending on the orientation of the magnetic field. Moreover, it also leads to an increase or decrease of the dose deposited at the interfaces between materials depending on their difference between mass densities. The results of our experiments lead to the same conclusions. These effects have to be taken into account in order to prevent creation of hot spots or a spread of energy distribution in a human body, within computation times compatible with the clinical environment. Conclusion Our model is a good candidate for future Treatment Planning Systems since it allows a faster and efficient way to plan a viable treatment for a patient in presence of strong magnetic fields. A magnetic field modifies the profile of the dose deposition such as it has to be taken into account in calculations to prevent the dramatic changes which occur at interfaces between media of different density. This work takes place in the framework of POPRA (Programme Optique Physique et Radiotherapie en Aquitaine), which involves several laboratories around problematics on the topic of cancer treatment.

Subcellular Optical pH Nanoscale Sensor

AbstractCoated gold nanoparticles bearing a pH‐sensitive molecule serve as nanoscale optical sensors for non‐invasive pH quantification of their endocytosis through surface‐enhanced Raman scattering. Our sensor consists in colloidal gold spheres coated either with (polyethylene glycol) PEG molecules or a silica shell. They carry a sensor molecule that specifically recognize protons. The read out for monitoring changes in the pH is the Raman shift of the sensor molecule that is enhanced on the surface of the plasmonic spheres. Sensing was performed along the way of internalization from the extracellular site through different endo/lysosomal compartments where they are closely packed. The creation of hot spots favored by particle agglomeration inside cells was responsible for the enhancement of changes in signal intensity and was dependent on the surface chemistry. We establish a correlation between the physicochemical properties of the nanoscale sensor (shape, surface chemistry) and its ability to monitor the different pH along its cellular internalization. The PEGylated spheres can sensitively track the pH along their cellular internalization whereas the silica coated ones fail.

Towards Differentiated Rate Control for Congestion and Hotspot Avoidance in Implantable Wireless Body Area Networks

Implantable wireless body area networks (WBANs) are gaining considerable attention to the researchers due to their high potential in healthcare applications. However, one of the biggest challenges of WBANs is the heat produced by wireless implants because of the continuous sensing of physiological parameters that could cause thermal impairment to the human tissue. Again, an implantable WBAN can be equipped with heterogeneous nodes having diverse throughput, fidelity, and latency demands. Also, un-controlled traffic reporting rate could cause high contention as well as congestion in nodes, which are usually organized forming a many-to-one routing paradigm in a WBAN. The problem of congestion not only restrains in satisfying the desired QoS requirements of the diverse healthcare applications, but also increases the dissipated energy and the temperature of an implant biosensor. This paper proposes a novel rate control mechanism with the aim of providing a unified solution for both congestion and hotspot avoidance in an implantable WBAN. The proposed scheme also presents a scheduling rate allocation mechanism reflecting the relative priority of biosensors. The performance of the protocol is evaluated using simulations, which demonstrate that the proposed protocol maintains lower temperature rise as well as avoid the creation of hotspot(s). The results also indicate that the proposed protocol significantly improves the performance of healthcare applications in terms of throughput, reliability, latency, as well as energy consumption.

Superior Performance of Ablative Glass Coatings Containing Graphene Nanosheets

Glass compositions in the Y2O3–Al2O3–SiO2 (YAS) system are envisaged as promising coatings for high‐temperature protection, in particular for the thermal protection systems (TPS) looked for aerospace applications. Recently, thermally sprayed YAS hybrid coatings containing a small amount of graphene nanoplateletes (GNPs) showed enhanced performance as compared to the blank YAS coating, demonstrated by the occurrence of unusual electrical conductivity for these glasses and the development of better mechanical compliance, both phenomena associated with the presence of GNPs. Nevertheless, a crucial issue is to demonstrate if these kinds of coatings would also have superior behavior under ablation conditions, particularly regarding the mentioned TPS applications. This work goes far beyond, exploring the ablative behavior of new YAS/GNPs coatings flame sprayed over SiC substrates. These essential tests were carried out under laboratory conditions, reaching limit temperatures of 1350°C while blowing gas. Results evidence that hybrid coatings having just 1.05 vol% GNPs show enhanced ablation resistance, actually withstanding up to 30 thermal cycles (between 200°C and 1350°C) without apparent damage. This satisfactory performance is linked to the benefits of the GNP additions, and fundamentally to the higher emissivity and the directional thermal conduction characteristics of the hybrid coatings—produced by the formation of a GNP network with a preferential surface parallel arrangement—that preclude the creation of hot spots and also hinder heat propagation toward the substrate; accordingly, coating degradation is constrained to the uppermost layer of these coatings.

Flood control structures in tidal creeks associated with reduction in nursery potential for native fishes and creation of hotspots for invasive species

Habitat connectivity is important for maintaining biodiversity and ecosystem processes yet globally is highly restricted by anthropogenic actions. Anthropogenic barriers are common in aquatic ecosystems; however, the effects of small-scale barriers such as floodgates have received relatively little study. Here we assess fish communities in ten tributaries over the spring–summer season of the lower Fraser River (British Columbia, Canada), five with floodgates and five reference sites without barriers, located primarily in agricultural land use areas. While the Fraser River supports the largest salmon runs in Canada, the lower Fraser river–floodplain ecosystem has numerous dikes and floodgates to protect valuable agricultural and urban developments. Floodgate presence was associated with reduced dissolved oxygen concentrations, threefold greater abundance of invasive fish species, and decreased abundances of five native fish species, including two salmon species. These findings provide evidence that floodgates decrease suitable habitat for native fishes, and become hotspots for non-native species. Given climate change, sea-level rise, and aging flood protection infrastructure, there is an opportunity to incorporate biodiversity considerations into further development or restoration of this infrastructure.

FAMe-TM: Formal analysis methodology for task migration algorithms in Many-Core systems

Distributed Dynamic Thermal Management (dDTM) through task migrations across cores provides a very promising solution to cater for the heating issues in Many-Core architectures. However, the growing number of cores, the distributed nature of dDTM and the inherent sampling-based nature of traditional analysis techniques, like simulation and emulation, makes a complete and rigorous analysis of these task migration algorithms almost impossible. These limitations compromise the analysis integrity and in worst cases may lead to the deployment of an inefficient and inaccurate dDTM scheme on chip, which in turn can cause permanent defects in the chip due to excessive heating. Leveraging upon the exhaustive nature of model checking based verification, we propose to use a model checker to formally verify task migration algorithms. This work proposes an analysis methodology, i.e., Formal Analysis Methodology for Task Migrations (FAMe-TM), and identifies a generic set of properties for the formal verification of task-migration-based dDTM schemes. In particular, we propose an analysis flow using the scalable bounded model checker, nuXmv, to formally verify the suggested task migration properties, like tasks migrations, stalls, completion, creation of hot spots, time spent in migration and time to achieve stability. For illustration purposes, we apply FAMe-TM to two recently proposed task-migration-based dDTM schemes, i.e., Thermal Coupling Aware (TCA-TM) dDTM and Hot Spot Reduction (HR-TM) dDTM. • A formal analysis methodology, FAMe-TM, for task migration (TM) algorithms is given. • Distributed Dynamic Thermal Management (dDTM) schemes are analyzed using FAMe-TM. • A set of properties are proposed and formalized for comparing TM-based dDTM schemes. • An improved version of a dDTM scheme is proposed based on the findings using FAMe-TM.

Different approaches to modeling the LANSCE H⁻ ion source filament performance.

An overview of different approaches to modeling of hot tungsten filament performance in the Los Alamos Neutron Science Center (LANSCE) H(-) surface converter ion source is presented. The most critical components in this negative ion source are two specially shaped wire filaments heated up to the working temperature range of 2600 K-2700 K during normal beam production. In order to prevent catastrophic filament failures (creation of hot spots, wire breaking, excessive filament deflection towards source body, etc.) and to improve understanding of the material erosion processes, we have simulated the filament performance using three different models: a semi-empirical model, a thermal finite-element analysis model, and an analytical model. Results of all three models were compared with data taken during LANSCE beam production. The models were used to support the recent successful transition from the beam pulse repetition rate of 60 Hz-120 Hz.

Size and Persistence of Nitrous Oxide Hot-Spots in Grazed and Ungrazed Grassland

<p class="1Body">Nitrous oxide (N<sub>2</sub>O) emissions from agriculture contributed an estimated 60% of the global total in 2005. In the UK, grassland soils account for 30% of total emissions, 22% of which are estimated to come from urine and dung patches. These patches are possible sources of ‘hot-spots’ (area <em>ca.</em> 1 m<sup>2</sup>) of N<sub>2</sub>O fluxes. Spatial and temporal heterogeneity of N<sub>2</sub>O hot-spot fluxes were investigated in three grassland fields (grazed with dairy cows (DG), grazed with young stock (YG) or cut for silage (SC)) using gas sampling chambers surrounding historic hot-spots to establish their size. Fluxes from old dung and urine patches were measured, as well as freshly applied dung and urine to simulate the creation of hot-spots. Potential chemical and physical drivers were also measured. Large spatial variability of N<sub>2</sub>O fluxes was seen in all three grassland fields. Mean N<sub>2</sub>O fluxes for the historic hot-spots in the grazed fields (DG and YG) were significantly greater than (SC). The mean N<sub>2</sub>O fluxes in DG and YG (117.9 and 243.5 ng N m<sup>-2</sup> s<sup>-1</sup>) were 15 to 30% greater than for SC. Soil temperature (15 - 20 °C) was the most significant driver of N<sub>2</sub>O production with a 1°C rise in soil temperature increasing emissions under DG and YG. N<sub>2</sub>O fluxes were enhanced by the fresh dung but not by urine. However, in the urine treatment, the nutrient input increased the microbial respiration response for the CO<sub>2</sub> flux. Hot-spot N<sub>2</sub>O emissions from old urine and dung patches were persistent several months after application.</p>

Strategic Network Formation Game for Energy Consumption Balancing

Creation of hot-spots is unavoidable, in multihop wireless sensor networks using the least power (or shortest path) routing method. This happens due to the irregularity of underlying network structures. Since hot-spots lose their energy faster than other nodes, they might create network partitions. In this paper, first, we study constructing of energy balanced topologies in a multihop sensor network using only structural information of a network with any-to-any traffic pattern. We consider both forwarding load and transmission power in energy consumption of sensors. Then, we present a strategic network formation game model. We use pairwise stability concept instead of traditional Nash stability and discuss about its advantages over Nash model in our game. After analyzing the game properties, two global and local algorithms for constructing balanced networks are introduced. Our evaluations on sparse and dense uniform networks show that our local algorithm when nodes use their limited neighborhood information, effectively reduces energy consumption imbalance and maximum power consumption while keeping the total power consumption in an acceptable level.

Plasmon Modes and Hot Spots in Gold Nanostar–Satellite Clusters

Gold nanostars display strong electromagnetic field enhancement at their tips, and tip plasmon resonances can be tuned within the visible and near-infrared, which has been applied toward plasmonic molecular sensing. However, the sensitivity can be further increased by linking gold nanostars to other plasmonic nanoparticles and thereby inducing the creation of hot spots. We report the controlled formation of core–satellite assemblies comprising a central gold nanostar with gold spheres adsorbed to the tips via Raman active molecular linkers. Surface-enhanced Raman scattering (SERS) was recorded at the level of single gold nanostar–satellite clusters, and the experimental results were compared with detailed electromagnetic simulations.

Improve the surface-enhanced Raman scattering from rhodamine 6G adsorbed gold nanostars with vimineous branches

The surface-enhanced Raman scattering (SERS) activity of the gold nanostars with vimineous branches has been investigated by using rhodamine 6G (R6G) as the Raman active probe. The colloidal gold nanostars have two intense localized surface plasmon resonance (LSPR) peaks in the visible and infrared ranges, respectively. Besides the visible LSPR dependent local field effect induced Raman signal enhancement, the SERS ability also greatly depends on the infrared absorption from the plasmon resonance along the aligned branches. Whether increasing the peak intensity or wavelength of the infrared absorption leads to the efficient improvement of SERS. These correlations between plasmonic absorption and SERS indicate that the lightning rod effect and creation of hot spots have been enhanced with the length and number of gold branches.