Changes In Surface Pressure Research Articles

Dynamics of dual-pulse laser energy deposition in a supersonic flow

Dynamics of plasma generated by the dual-pulse laser in a supersonic flow was studied numerically. The mathematical model includes species, momentum, electronic, vibrational and translational energy equations for the multicomponent ionized air. The model examines temporal dynamics of the formed air plasma and how it affects the drag, pressure signature and vorticity generation in a supersonic flow around a wedge. We observed that nonequilibrium plasmas is more effective in the drag reduction compared with the simultaneous thermal energy addition. The maximum drag reduction of around 50% and the maximum drag coefficient reduction of 30% was attained through the dual-pulse laser energy deposition. Variation of the plasma spot orientation did not significantly influence the drag reduction. We suggested that the surface pressure changes were not controlled by the vorticity generation but occurred due to the density changes and the formation of the low-density plasma spot.

Numerical study of roundness effect on flow around a circular cylinder

Imperfectly round bridge stay cable cross section is speculated to be a key factor for wind-induced large-amplitude cable vibrations observed on site. A delayed detached eddy simulation implemented in Open source Field Operation and Manipulation is used to investigate the flow structure around and in the near-wake of an imperfectly round circular cylinder and the corresponding aerodynamic forces at a Reynolds number of 104 and an attack angle of 0° or 45°. With the increase in roundness imperfection, both monotonic and non-monotonic changes of the mean surface pressure and the wake velocity are found when the cylinder is normal to the flow. At an attack angle of 45° and when the roundness ratio is e/D = 4%, it is found that the geometric imperfection in the cross-sectional shape of the cylinder allows it to the retention of more axial flow in the proximity of the cylinder leeward surface due to a shorter recirculation length. The vortex formed by the intensified axial flow would interact with the conventional von Kármán vortex formation at a frequency a few times lower than that of the latter and lead to intermittently amplified transverse lift. This reveals that imperfect roundness in the cross section of a circular cylinder could be an excitation source of low frequency vibration. Thus, it provides evidence that this kind of geometric imperfection, which commonly exists in real stay cables, could contribute to the mechanisms that trigger large-amplitude or even divergent cable motion, such as dry inclined cable galloping on site.

Elastomer Characterization Method for Trapped Rubber Processing.

The increasing high-volume demand for polymer matrix composites (PMCs) brings into focus the need for autoclave alternative processing. Trapped rubber processing (TRP) of PMCs is a method capable of achieving high pressures during polymer matrix composite processing by utilizing thermally induced volume change of a nearly incompressible material inside a closed cavity mold. Recent advances in rubber materials and computational technology have made this processing technique more attractive. Elastomers can be doped with nanoparticles to increase thermal conductivity and this can be further tailored for local variations in thermal conductivity for TRP. In addition, recent advances in computer processing allow for simulation of coupled thermomechanical processes for full part modeling. This study presents a method of experimentally characterizing prospective rubber materials. The experiments are designed to characterize the dynamic in situ change in temperature, the dynamic change in volume, and the resulting real-time change in surface pressure. The material characterization is specifically designed to minimize the number and difficulty of experimental tests while fully capturing the rubber behavior for the TRP scenario. The experimental characterization was developed to provide the necessary data for accurate thermomechanical material models of nearly incompressible elastomeric polymers for use in TRP virtual design and optimization.

Influence of global sea‐surface temperature on ultra‐low‐frequency variability in Indian summer monsoon rainfall

AbstractA multidecadal or ultra‐low‐frequency mode of variability in Indian summer monsoon rainfall (ISMR) with a spectral peak at nearly 67 years is identified using a nonparametric approach, namely, singular spectrum analysis. Not only does this mode modulate the seasonal mean rainfall over India, but also frequent occurrences of excess or below normal rainfall over India are favored by the phases of this mode. We show that 80% of all droughts occur during the negative phase of this mode, compared with 60% of all floods during its positive phase. Although the existence of this mode was reported in many previous studies, proper understanding of its exact nature and driving mechanism, and how it relates to global sea‐surface temperature (SST), is still not clear. Here, we show that the 67‐year variability in ISMR is associated with a SST mode of similar periodicity, which primarily exhibits a hemispheric SST difference, with the strongest signals over the northern Pacific and Atlantic. The positive phase of this SST mode induces low surface pressure over the northern Arabian Sea. Changes in surface pressure over the northern Arabian Sea govern changes in ISMR. The bridge between the SST mode and central Asian circulation is possibly established through the North Pacific Oscillation. The positive phase of this mode enhances the meridional temperature gradient over India, which acts to strengthen the tropical easterly jet, and subsequently the low‐level westerly jet over India. These lead to a negative surface pressure anomaly over the Indian subcontinent and an associated anomalous cyclonic circulation. The environment thus created is conducive to increased seasonal mean monsoon rainfall over India. The phase of the SST mode is remarkably similar to, and leading by 2–3 years, that of the multidecadal mode in ISMR up to the 1990s. However, the relationship weakens after the early 1990s.

Comparison of Tanaka lipid mixture with natural surfactant Alveofact to study nanoparticle interactions on Langmuir film balance

Upon inhalation, nanoparticles enter the lungs where the pulmonary surfactant forms the first point of contact and plays a pivotal role for the subsequent absorption into the body. This can lead to interactions that alter the biophysical function of the surfactant monolayer. Therefore, a reliable prediction of the interaction is desired. In this study, we compared the behaviour of an artificial surfactant model with that of a natural surfactant upon exposure to chitosan nanoparticles. To simulate the physiology of the lungs, the surfactant monolayers were placed at an air/aqueous interface of a Langmuir film balance. Based on the data obtained from the experiments, the chitosan nanoparticles first integrated into the monolayer of the natural surfactant and then interact strongly with its compounds thereby moving out of the monolayer. The topographic changes in the monolayer were determined by atomic force microscopy analysis. Using this technique, the nanoparticle localisation on the monolayer could be studied. No visible interaction was observed with the artificial surfactant from surface pressure-time isotherms and atomic force microscopy analysis. Incomplete miscibility lead to instability of the artificial surfactant which left behind a DPPC rich monolayer after nanoparticle interaction. It was not stable enough to see a possible interaction (i.e. change in surface pressure) with the nanoparticles directly. These results should help understand the interactions of lipids among themselves and with the nanoparticles. Furthermore, it should help generate an efficient artificial surfactant model and to understand the underlying mechanisms of the nanoparticle interaction with the monolayer.

Biophysical studies on the antimicrobial activity of linearized esculentin 2EM

Linearized esculentin 2 EM (E2EM-lin) from the frog, Glandirana emeljanovi was highly active against Gram-positive bacteria (minimum lethal concentration ≤ 5.0 μM) and strongly α-helical in the presence of lipid mimics of their membranes (>55.0%). The N-terminal α-helical structure adopted by E2EM-lin showed the potential to form a membrane interactive, tilted peptide with an hydrophobicity gradient over residues 9 to 23. E2EM-lin inserted strongly into lipid mimics of membranes from Gram-positive bacteria (maximal surface pressure changes ≥5.5 mN m−1), inducing increased rigidity (Cs−1 ↑), thermodynamic instability (ΔGmix < 0 → ΔGmix > 0) and high levels of lysis (>50.0%). These effects appeared to be driven by the high anionic lipid content of membranes from Gram-positive bacteria; namely phosphatidylglycerol (PG) and cardiolipin (CL) species. The high levels of α-helicity (60.0%), interaction (maximal surface pressure change = 6.7 mN m−1) and lysis (66.0%) shown by E2EM-lin with PG species was a major driver in the ability of the peptide to lyse and kill Gram-positive bacteria. E2EM-lin also showed high levels of α-helicity (62.0%) with CL species but only low levels of interaction (maximal surface pressure change = 2.9 mN m−1) and lysis (21.0%) with the lipid. These combined data suggest that E2EM-lin has a specificity for killing Gram-positive bacteria that involves the formation of tilted structure and appears to be primarily driven by PG-mediated membranolysis. These structure/function relationships are used to help explain the pore forming process proposed to describe the membranolytic, antibacterial action of E2EM-lin.

New look for an old molecule – Solid/solid phase transition in cholesterol monolayers

Surface pressure (π) – molecular area (A) isotherms of cholesterol were precisely measured to get insight into the orientation of molecules in Langmuir monolayers, which allowed to obtain detailed information on their phase behaviour. This was possible from the detailed analysis of the interfacial compressibility modulus versus surface pressure (Cs−1- π) plots (obtained from the experimental surface pressure, π - area, A isotherms) and films thickness measurements (applying Brewster angle microscope, BAM) complemented with polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). At first glance, the isotherm for cholesterol is characterized by the major slope change of surface pressure versus area per molecule. However, a more detailed analysis showed the presence of a discontinuity and slope change both upon the compression and expansion of the monolayer. This discontinuity is more accurately reflected in the Cs−1- π plot as a pseudo-plateau visible at π values between approximately 5 and 10 mN/m. This plateau was found to be temperature-dependent. Also, film thickness versus area plot (th-A) exhibits a pseudo-plateau in this region of surface pressures, in which the monolayer thickness increased gradually from 1.15 nm to 1.5 nm. Interestingly, although cholesterol has been intensively investigated in Langmuir monolayers, the existence of such a plateau have been overlooked previously. By linking experimental thickness values with theoretical molecular conformations, we have identified the presence of this plateau to the solid-solid (S-S’) second-order transition. Using 2D analog of Clausius-Clapeyron equation, the thermodynamic functions (ΔH and ΔS) for this transition have been calculated. Based on monolayer experiments, the orientation of molecules in both solid phases was assumed to differ in the orientation of short alkyl chain attached to C17, which has additionally been confirmed with PM-IRRAS analysis.

The effects of stratospheric meridional circulation on surface pressure and tropospheric meridional circulation

Based on ERA-Interim and JRA-55 daily reanalysis datasets, connections among the variations in the Brewer–Dobson circulation (BDC) intensity, stratospheric air mass, surface pressure, and the tropospheric meridional circulation during the period from 1979 to 2015 are analyzed. The results show that the variations in the surface pressure, particularly at middle and high latitudes, have a close correlation with the variations in the stratospheric BDC intensity. When the upwelling at 450 K intensifies, the surface pressure increases in the high latitudes (poleward of 60°) and decreases in the adjacent mid-latitudes in both hemispheres. And these correlations are most significant during boreal winter in the Northern Hemisphere and during austral autumn in the Southern Hemisphere. It is found that the high latitude surface pressure changes follow the anomalous BDC by about 30 days. The increase in polar surface pressure associated with the stronger BDC is due to an increase in stratospheric air mass, while the decrease in mid-latitude surface pressure is related to a decrease in tropospheric air mass. These air mass changes are caused by the anomalous meridional transport of air mass by the residual mean circulation in the stratosphere and troposphere. In addition, we found a significant connection between the intensity of the BDC and the Ferrel cell, i.e., when the BDC strengthens (weakens), there is a weakened (strengthened) Ferrel cell with its position shifting equatorward (poleward).

Flow characteristics and dynamic responses of a parked straight‐bladed vertical axis wind turbine

AbstractWith the development of urbanization and the application of renewable energy, wind turbine is becoming an important approach for wind energy reservation and utilization. This study provides a numerical investigation on understanding the surface pressure distribution, flow characteristics and dynamic responses of a parked straight‐bladed vertical axis wind turbine (VAWT), which is helpful for its design. Together with the two‐way coupling method between simulation platforms such as STAR‐CCM+ and ABAQUS, the SST k‐ω turbulence model is used to obtain the surface pressure and surrounding flow of the VAWT, and the finite element method is used to obtain the dynamic responses of its structural components. The results show that the contours of the pressure distribution on the windward surface of the VAWT are similar even under a few different conditions, and the deformation of the VAWT can lead to changes in surface pressure; the turbulent flow characteristics and the wake effect become more obvious as the wind velocity increases; the blades and support arms of the VAWT need to be reinforced during the design, and the effect of the parked condition on the dynamic responses of the VAWT can be neglected. The two‐way coupling method as well as the numerical simulation results is expected to provide references for the design of VAWTs subjected to coming wind action.

Novel machine learning application for prediction of membrane insertion potential of cell-penetrating peptides.

Cell-penetrating peptides (CPPs) are often used as transporter systems to deliver various therapeutic agents into the cell. We developed a novel machine learning application which can quantitatively screen the insertion/interaction potential of various CPPs into three model phospholipid monolayers. An artificial neural network (ANN) was designed, trained, and ultimately tested on an external dataset using Langmuir experimental data for 13 CPPs (hydrophilic and amphiphilic) together with various features related to the insertion/interaction efficiency of CPPs. The trained ANN provided accurate predictions of the maximum change in surface pressure of CPPs when injected below three membrane models at pH 7.4. The accuracy of predictions was high for the dataset which was used to construct the model (r2 = 0.986) as well as for the external "prospective" dataset (r2 = 0.969). In conclusion, this study demonstrates the promising potential of ANNs for screening the insertion potential of CPPs into membrane models for efficient intracellular delivery of therapeutic agents.

Theory for Deriving Shallow Elasticity Structure From Colocated Seismic and Pressure Data

AbstractColocated seismic and pressure data are available at many seismic stations in the world. For frequencies approximately between 0.01 and 0.05 Hz, colocated data show evidence of strong coupling between the atmosphere and the solid Earth, especially when pressure is high. Coherence between vertical seismic data and pressure is often higher than 0.9. Such data provide information for shallow structure in the upper 50–100 m because they show how the Earth responds to surface pressure changes. We present the basic theory and an inversion scheme for shallow structure using surface observables η(f)=Sz/Sp where f is frequency and Sz and Sp are the power spectral densities of vertical seismic data and of surface pressure data. A vertically heterogeneous medium is assumed beneath a station where density, P wave velocity, and S wave velocity change with depth. We show that the integration of the minors for the equations of motion gives a fast algorithm to compute η(f). Using numerical differentiation, we derive depth sensitivity kernels for η(f) with which we invert η(f) for shallow structure, just like we invert phase velocity of surface waves for the Earth structure. Depth sensitivity kernels show that if we take density, bulk modulus, and rigidity as independent parameters, η(f) has no sensitivity to density structure, making it mainly a function of two elastic constants. We present examples of inversion based on this formulation.

Investigation of Drag Reduction Technologies for Light-Duty Vehicles Using Surface, Wake and Underbody Pressure Measurements to Complement Aerodynamic Drag Measurements.

Amulti-year, multi-vehicle study was conducted to quantify the aerodynamic drag changes associated with drag reduction technologies for light-duty vehicles. Various technologies were evaluated through fullscale testing in a large low-blockage closed-circuit wind tunnel equipped with a rolling road, wheel rollers, boundary-layer suction and a system to generate road-representative turbulent winds. The technologies investigated include active grille shutters, production and custom underbody treatments, air dams, wheel curtains, ride height control, side mirror removal and combinations of these.This paper focuses on mean surface-, wake-, and underbody-pressure measurements and their relation to aerodynamic drag. Surface pressures were measured at strategic locations on four sedans and two crossover SUVs. Wake total pressures were mapped using a rake of Pitot probes in two cross-flow planes at up to 0.4 vehicle lengths downstream of the same six vehicles in addition to a minivan and a pick-up truck. A smaller rake was used to map underbody total pressures in one cross-flow plane downstream of the rear axle for three of these vehicles.The results link drag reduction due to various technologies with specific changes in vehicle surface, rear underbody and wake pressures, and provide a database for numerical studies. In particular, the results suggest that existing or idealized prototype technologies such as active grille shutters, sealing the external grille and ride height control reduce drag by redirecting incoming flow from the engine bay or underbody region to smoother surfaces above and around the vehicle. This mechanism can enhance the reduction in wheel drag due to reduced wheel exposure at lowered ride height. Sealing the external grille was found to redirect the flow more efficiently than closing the grille shutters, and resulted in greater drag reduction. Underbody treatments were also found in some cases to redistribute the flow around the vehicle to reduce pressure drag in addition to underbody friction drag. The magnitude and spatial extent of the measured pressure changes due to the various technologies were often consistent with the amount of drag reduction.

Interfacial Activity of Phasin PhaF from Pseudomonas putida KT2440 at Hydrophobic-Hydrophilic Biointerfaces.

Phasins, the major proteins coating polyhydroxyalkanoate (PHA) granules, have been proposed as suitable biosurfactants for multiple applications because of their amphiphilic nature. In this work, we analyzed the interfacial activity of the amphiphilic α-helical phasin PhaF from Pseudomonas putida KT2440 at different hydrophobic-hydrophilic interfacial environments. The binding of PhaF to surfaces containing PHA or phospholipids, postulated as structural components of PHA granules, was confirmed in vitro using supported lipid bilayers and confocal microscopy, with polyhydroxyoctanoate- co-hexanoate P(HO- co-HHx) and Escherichia coli lipid extract as model systems. The surfactant-like capabilities of PhaF were determined by measuring changes in surface pressure in Langmuir devices. PhaF spontaneously adsorbed at the air-water interface, reducing the surface tension from 72 mN/m (water surface tension at 25 °C) to 50 mN/m. The differences in the adsorption of the protein in the presence of different phospholipid films showed a marked preference for phosphatidylglycerol species, such as 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphoglycerol. The PHA-binding domain of PhaF (BioF) conserved a similar surface activity to PhaF, suggesting that it is responsible for the surfactant properties of the whole protein. These new findings not only increase our knowledge about the role of phasins in the PHA machinery but also open new outlooks for the application of these proteins as biosurfactants.

Development of a Novel Intraoperative Neuromonitoring System Using a Surface Pressure Sensor to Detect Muscle Movement: A Rabbit Model Study.

ObjectivesFalse-negative or false-positive responses in intraoperative neuromonitoring (IONM) using electromyography (EMG) in thyroid surgery pose a challenge. Therefore, we developed a novel IONM system that uses a surface pressure sensor instead of EMG to detect muscle twitching. This study aimed to investigate the feasibility and safety of a new IONM system using a piezo-electric surface pressure sensor in an experimental animal model.MethodsWe developed the surface pressure sensor by modifying a commercial piezo-electric sensor. We evaluated the stimulus thresholds to detect muscle movement, as well as the amplitude and latency of the EMG and surface pressure sensor in six sciatic nerves of three rabbits, according to the stimulus intensity.ResultsThe surface pressure sensor detected the muscle movements in response to a 0.1 mA stimulation of all six sciatic nerves. There were no differences in the thresholds of stimulus intensity between the surface pressure sensor and EMG recordings to detect muscle movements.ConclusionIt is possible to measure the change in surface pressure by using a piezo-electric surface pressure sensor instead of EMG to detect muscle movement induced by nerve stimulation. The application of IONM using a piezo-electric surface pressure sensor during surgery is noninvasive, safe, and feasible. Measuring muscle twitching to identify the state of the nerves using the novel IONM system can be an alternative to recording of EMG responses.

Robust Design Optimization of Hydrodynamic Characteristics of Airfoil 791

In this paper, the influence of the continuous random variation of the flow velocity on hydrodynamic characteristics of airfoil 791 was discussed, and a robust design optimization method was proposed to reduce the influence of uncertain factors on the stability of hydrodynamic performance. Firstly, Bezier curve was used to parameterize the suction side of the airfoil, and its thickness was controlled by four points, which was then taken as the optimization variables. Secondly, the criterion of robustness was given, and then a robust mathematical model was established. Finally, two objective functions of robust optimization were gained on the basis of uncertainty analysis with surrogate model. Combined with multi-objective genetic algorithm, a robust optimal solution with better hydrodynamic characteristics was obtained. The results showed that compared with original case, the thickness near trailing edge altered more smoothly, the resistance and surface wave intensity were obviously decreased, and the maximum reduction of drag-lift ratio and wake unevenness were 6.89% and 25.04% respectively, which contributed to the improvement of wake quality. The change of surface pressure and resistance coefficients were also more stable under the variable inlet flow velocity conditions, and then the robustness was strengthened accordingly. In conclusion, the robust design optimization can obviously improve the hydrodynamic characteristics of the airfoil while reducing the sensitivity to uncertain factors, meanwhile, it can provide better stability during the operating process.

The effect of pH on the lytic activity of a synthetic mastoparan-like peptide in anionic model membranes

Peptide sequences containing acidic and basic residues could potentially have their net charges modulated by bulk pH with a possible influence on their lytic activity in lipid vesicles. The present study reports on a biophysical investigation of these modulatory effects on the synthetic mastoparan-like peptide L1A (IDGLKAIWKKVADLLKNT-NH2). At pH 10.0 L1A was 6 times more efficient in lysing large anionic (1-palmitoyl-oleoyl-sn-glycero-3-phosphocholine (POPC):1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG)/(8:2)) unilamellar vesicles (LUVs) than at pH 4.0. Despite the reduction of 60% in the L1A net charge in basic pH its affinity for this vesicle was almost insensitive to pH. On the other hand, L1A insertion into monolayers was dramatically influenced by subphase condition, showing that, in the neutral and basic subphases, the peptide induced surface pressure changes that surpassed the membrane lateral pressure, being able to destabilize a bilayer structure. In addition, in the basic subphase, visualization of the compression isotherms of co-spread 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC):POPG (8:2) + 4.8 mol% L1A showed that the peptide induced significant changes in solid lipid domains, indicating its capability in perturbing lipid-packing. An insight into L1A lytic activity was also obtained in giant unilamellar vesicles (GUVs) using phase contrast microscopy. The suppression of L1A lytic activity at acidic pH is in keeping with its lower insertion capability and ability to disturb the lipid monolayer. The lytic activity observed under neutral and basic conditions showed a quick and stochastic leakage following a lag-time. The permeability and the leakage-time averaged over at least 14 single GUVs were dependent on the bulk condition. At basic pH, permeability is higher and quicker than in a neutral medium in good accordance with the lipid-packing perturbation.

Drag and heat flux reduction induced by the pulsed counterflowing jet with different periods on a blunt body in supersonic flows

In the current study, three different kinds of pulsed jets with the period being 0.5 ms, 1.0 ms and 2.0 ms are established, and sinusoidal waveforms are used in all three pulsed jets. The pulsed counterflowing jets with the same amplitude but different periods on the nose of a blunt body in supersonic flows are investigated numerically, and an axisymmetric numerical simulation model of the counterflowing jet on the supersonic vehicle nose-tip is established. The obtained results show that the wall Stanton number and surface pressure change periodically with the pulsed jet, and the variations of the parameters show a strong hysteresis phenomenon. The hysteresis phenomenon becomes less significant as the period increases. At the same time, a better drag and heat flux reduction is obtained under larger period pulsed jet conditions. With the increase of the period of the pulsed jet, there is a significant decline in the maximum peak values of the wall Stanton number and surface pressure. Compared with the steady jet, the pulsed jet is more effective in heat flux reduction, but the drag reduction of the pulsed jet is less effective than the steady jet.

Interaction of green silver nanoparticles with model membranes: possible role in the antibacterial activity.

Silver nanoparticles (AgNPs) constitute a very promising approach for overcoming the emergence of antibiotic resistance bacteria. Although their mode of action could be related with membrane damage, the AgNPs-lipid membrane interaction is still unclear. In this sense, the present work investigated the interaction of model lipid membranes with AgNPs coated with different capping agents such as citrate (C-AgNPs) and phytomolecules (G-AgNPs) obtained via a green synthesis. The AgNPs-membrane interactions were evaluated studying i) the surface pressure changes on both zwitterionic (DMPC) and negatively charged (DMPC:DMPG) lipid monolayers, ii) the zeta potential and DLS of DMPC:DMPG liposomes and iii) Zeta potential on Escherichia coli membranes, incubated with this nanomaterials. The results showed that both negatively charged-AgNPs can interact with these lipid monolayers inducing an increase in the surface pressure but G-AgNPs presented a significantly higher affinity toward both monolayers in comparison with C-AgNPs. Zeta potential data confirmed again the interaction event showing that both DMPC:DMPG liposomes and E. coli bacteria became more negative with the addition of G-AgNPs. This increased net negative charge of the liposomes and E. coli allows to indicate an interfacial interaction where the green nanometal should keep adsorbed to the membrane via the insertion of aromatic/hydrophobic moieties of capping agents on the surface of AgNPs into the lipid bilayer. Summarizing, the AgNPs-membrane interaction should be an essential step in the antibacterial activity either because the membrane is the main target or by increasing the local concentration of silver from G-AgNPs accumulation which could cause the bactericidal effect.

Low‐Frequency Seismic Noise Characteristics From the Analysis of Co‐Located Seismic and Pressure Data

AbstractWe analyze the characteristics of seismic noise generated by surface pressure changes, using co‐located seismic and pressure data from the USArray Transportable Array for the entire year of 2014. We compare pressure and seismic signals at frequencies of 0.01 and 0.02 Hz and model their main characteristics. At these frequencies, vertical and horizontal seismic noise can be explained by the formulas SZ = A * Sp + NZ and SH = B * Sp + NH, where SZ and SH are the power spectral densities of vertical and horizontal ground velocities (sum of two horizontal components), Sp is the power spectral density of pressure, and NZ and NH are constant terms. We first determine A and B from the high pressure range (Sp &gt; 10 Pa2/Hz) in which NZ and NH are small. From A and B, we then determine the near‐surface rigidity and pressure wave speed. This rigidity is modified from true rigidity by a factor (λ + μ)/(λ + 2 μ); this factor is about 0.7 for typical crustal rocks but approaches 1 near the Earth's surface. To estimate true rigidity, empirical formulas that relate density and seismic velocities are needed. Once A and B are determined, NZ and NH are determined. NZ and rigidity of the subsurface determine a threshold pressure in vertical data. NH is generally small but at some stations it changes seasonally and creates separate branches in plots of pressure versus seismic velocity. This may explain why seismic‐noise reduction approaches using co‐located pressure data often fail to work for horizontal data but usually work well for vertical data.

Projections of Heat Waves Events in the Intra-Americas Region Using Multimodel Ensemble

Significant accelerated warming of the Sea Surface Temperature of 0.15°C per decade (1982–2012) was recently detected, which motivated the research for the present consequences and future projections on the heat index and heat waves in the intra-Americas region. Present records every six hours are retrieved from NCEP reanalysis (1948–2015) to calculate heat waves changes. Heat index intensification has been detected in the region since 1998 and driven by surface pressure changes, sinking air enhancement, and warm/weaker cold advection. This regional warmer atmosphere leads to heat waves intensification with changes in both frequency and maximum amplitude distribution. Future projections using a multimodel ensemble mean for five global circulation models were used to project heat waves in the future under two scenarios: RCP4.5 and RCP8.5. Massive heat waves events were projected at the end of the 21st century, particularly in the RCP8.5 scenario. Consequently, the regional climate change in the current time and in the future will require special attention to mitigate the more intense and frequent heat waves impacts on human health, countries’ economies, and energy demands in the IAR.