Decrease In Surface Pressure Research Articles

Simulation and experimental study on the aerodynamic characteristics of a high-speed elevator with three-sided arc fairings

To address the crucial issue of optimizing the design of fairings for drag and noise reduction, this study focuses on a high-speed elevator in operation as the research subject. The numerical and experimental analysis investigates the influence mechanism of a three-sided arc fairing on the surface pressure distribution, surrounding airflow velocity, and aerodynamic drag of elevator cars. The results indicate that the fairing is effective in reducing the high-pressure area on the top of the car. It also helps to prevent vibrations caused by early separation of the boundary layer and periodic vortex separation, and mitigates the impact of aerodynamic forces on the car when there is a sudden change in airflow direction. As the arc radius of the fairing increases, the airflow velocity between the car and the shaft decreases. This leads to a reduction in the tail vortex area at the bottom of the car, resulting in decreased aerodynamic drag. Among the four schemes, scheme D with the largest arc radius of the fairing demonstrates the best optimization performance. Compared to the case without fairing, the car surface pressure decreases by approximately 35%. The aerodynamic drag is reduced to 129.51 N, which corresponds to a 60.13% decrease. However, the fairing has little impact on the lateral lift. The airflow velocity variations in the numerical simulation and experimental tests exhibit the same trend. The average relative error is about 10%, verifying the effectiveness of the numerical calculation method.

AEROTHERMODYNAMICS OF COMBINED SPIKE AND COUNTERFLOW JET TECHNIQUE FOR REACTING HYPERSONIC FLOWS

Computational investigation is carried out to estimate the drag force and surface heating load for hypersonic reacting flows. An in-house viscous nonequilibrium finite volume-based reacting gas solver has been utilized. This solver is capable of investigating 11 chemical elementary reactions and temperature-dependent specific properties to reveal the effect of lower as well as higher freestream stagnation enthalpy conditions. Initially, the calorically perfect-gas and real-gas model-based simulations are carried out to understand the real-gas effects in the presence of a metallic spike. Computed surface pressure and heat flux are compared for the freestream stagnation enthalpy of 2 MJ/kg. The real-gas model predicts a 5% higher drag and 57.21 kW/m<sup>2</sup> higher peak heat flux compared to the perfect-gas model. However, lower enthalpy conditions predict almost the same drag force for any spike length. Further, a counterflowing jet is installed at the root of the spike, and flow field alterations are studied for this proposed integrated configuration. The root jet further pushes the conical shock in the upstream direction and provides an extra-large recirculation zone. Here, the possibility of drag and surface heat flux reduction is very much evident due to the decrease in surface pressure and presence of low-temperature jet gas in the vicinity of the object. Various freestream stagnation enthalpies, as well as the jet pressures, are considered to investigate the performance alterations by the combination technique. It is observed that the drag and surface heat load reduction efficiency of the combined configuration decreases with an increase in the freestream stagnation enthalpy. Moreover, it increases when increasing the root jet pressure for given enthalpy conditions. Hence, instead of attaching a long spike at the stagnation region of a blunt-shaped object, the use of a short spike and low-pressure root jet is recommended for a better reduction in drag and surface heat load.

N-terminal acetylation does not alter α-synuclein's interfacial properties

Alpha-synuclein (αS) is a membrane-binding protein found predominantly in neurons and erythrocytes. The protein remains unordered in aqueous solutions but folds into an α-helical structure when bound to membranes. Besides, it gets deposited as β-sheet rich aggregates in diseases known as synucleinopathies. The native αS has been reported to be acetylated at the N-terminus. Here, we compare the interfacial properties of the N-terminal acetylated αS (Ac-αS) with non-acetylated αS (NH2-αS) at the air-water interface. Both the protein forms are highly surface-active, with surface pressure reaching up to ~30 mN/m upon compression. The pressure-area isotherms obtained from the repeated compression-expansion cycles display large hysteresis suggesting self-assembly at higher surface pressures. The expansion isotherm is characterized by a rapid decrease in surface pressure followed by a slower transition phase starting around 15–17 mN/m. These data suggest that the compressed monolayer breaks into small clusters upon expansion, followed by these clusters' loosening. The circular dichroism spectroscopic analysis of the Blodgett-deposited films suggests the protein to be in largely α-helical conformation. The linear dichroism investigations suggest the protein to be anisotropically deposited. Blodgett deposition of the Langmuir films, therefore, is a rather simple method for preparing oriented monolayers of surface-active macromolecules.

Observational evidence of equatorial ionospheric response to severe cyclonic storms ‘AILA’ and ‘WARD’ observed over the North Indian Ocean

This work addresses the vertical atmosphere –ionosphere coupling through two cyclonic events AILA (23–26 May 2009) and ‘WARD’ (10–16 December 2009) observed over the North Indian Ocean. Combined ground Digisonde Tirunelveli (8.7oN, 77.8oE) observation, ECMWF reanalysis, and NOAA Outgoing Longwave Radiation data used to reveal the connection between atmosphere –ionosphere system. At the time of tropical cyclone, we observed a decrease in surface pressure and an increase of sustained oceanic winds. Thereby increases the tropical convection observed from the lowered OLR (Outgoing Longwave Radiation). The existence of Gravity wave oscillations of period ~4 h at the stratosphere and ionosphere regions indicate the propagation of low-frequency GWs (Gravity Waves) from the lower atmosphere. Weak eastward stratospheric winds observed at the time of onset of the cyclonic storm in both AILA and WARD events. The Ionospheric parameter foF2 and h’F2 show strong modulation at the time of cyclones AILA and WARD.

Atmospheric Circulation Response to Heat Flux Anomalies in a Two-Dimensional Baroclinic Model of the Atmosphere

The response of large-scale atmospheric circulation to the anomalous Barents and Kara sea ice-free surface heating, which has been observed over the past two decades, is considered. For this purpose, a simplified two-dimensional baroclinic atmospheric model obtained by averaging hydrothermodynamic equations over height is used, as well as its two-layer analogue with the effect of anomalous heating and, hence, of horizontal baroclinicity being concentrated within the surface-adjacent 1- to 2-km-thick atmospheric layer, which fits Arctic conditions more closely. Quasi-geostrophic approximations are derived for both models; for a single-layer model (in the adiabatic and inviscid approximation), the formulation is also given in terms of Nambu mechanics. Both models demonstrate the appearance of a center of increased surface air temperature over the area of anomalous heating; a slight decrease in surface pressure there; and, finally, anticyclonic circulation in the bulk of the atmosphere. The model results are shown to be extremely sensitive to the parameterization of the Ekman boundary layer.

\u2018Eastern African Paradox\u2019 rainfall decline due to shorter not less intense Long Rains

An observed decline in the Eastern African Long Rains from the 1980s to late 2000s appears contrary to the projected increase under future climate change. This “Eastern African climate paradox” confounds use of climate projections for adaptation planning across Eastern Africa. Here we show the decline corresponds to a later onset and earlier cessation of the long rains, with a similar seasonal maximum in area-averaged daily rainfall. Previous studies have explored the role of remote teleconnections, but those mechanisms do not sufficiently explain the decline or the newly identified change in seasonality. Using a large ensemble of observations, reanalyses and atmospheric simulations, we propose a regional mechanism that explains both the observed decline and the recent partial recovery. A decrease in surface pressure over Arabia and warmer north Arabian Sea is associated with enhanced southerlies and an earlier cessation of the long rains. This is supported by a similar signal in surface pressure in many atmosphere-only models giving lower May rainfall and an earlier cessation. Anomalously warm seas south of Eastern Africa delay the northward movement of the tropical rain-band, giving a later onset. These results are key in understanding the paradox. It is now a priority to establish the balance of mechanisms that have led to these trends, which are partially captured in atmosphere-only simulations.

Isolating the Observed Influence of Vegetation Variability on the Climate of La Plata River Basin

AbstractThis work aims to isolate and quantify the local and remote biogeophysical influences of slowly varying vegetation variability on the climate of La Plata basin (LPB) in the austral spring season (September–November) using observational records. Past studies have shown strong land–atmosphere coupling in LPB during this season. The analysis uses a 34-yr record (1981–2014) of the modified enhanced vegetation index (EVI2) from the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Vegetation Index and Phenology dataset and the third-generation normalized difference vegetation index (NDVI) from Global Inventory Modeling and Mapping Studies. The dominant patterns of vegetation index variability in space and time are assessed using empirical orthogonal function/principal component analysis over the LPB. The dominant mode in the austral spring is a vegetation dipole, with greening (browning) or positive (negative) vegetation index anomalies in the northeastern (southwestern) part of the basin. Using the stepwise generalized equilibrium feedback assessment (SGEFA), the effect of the vegetation variability on the atmosphere is then isolated. The dominant mode of LPB vegetation variability in austral spring is related to warmer temperatures in the southwest LPB and enhanced precipitation over the central and southern parts of the basin. A mechanism is proposed for the increase in latent heat flux and cooler temperatures in the northeastern LPB due to greening, and the increase in sensible heat flux, warmer temperatures, and decrease in surface pressure in southwestern LPB due to browning. The geostrophic response to this induced pressure gradient leads to anomalous northerly enhancement of moisture-laden winds, deeper penetration of moisture into LPB, and increased precipitation over the central and southern parts of the basin.

Urban impacts on the spatiotemporal pattern of short‐duration convective precipitation in a coastal city adjacent to a mountain range

AbstractThe present study examines urban impacts on short‐duration precipitation in an idealized coastal city adjacent to a mountain range using two‐dimensional idealized simulations performed with a modified version of the Weather Research and Forecasting (WRF) model. A unique aspect of this study is that an ensemble simulation approach with 243 members is used with sensitivity experiments to reduce uncertainty arising from nonlinearity in the precipitation simulation and to evaluate the statistical significance. Results of the experiments reveal that urbanization increases the precipitation leeward of the urban area and decreases it in the area further inland. These anomalies are statistically significant at the 99% level. Additional sensitivity experiments show that the urban influence on precipitation is slightly sensitive to the mountain height, urban scale and soil moisture, but not to the roughness length. Our analyses indicate that these precipitation changes arise because urbanization slows the sea‐breeze front, shifting the moisture convergence zone further inland. Additional analyses are done using the water‐budget equation and a linear theory on the diurnal variations of the planetary boundary layer. Results show that changes in the sea breezes and moisture transport arise from a decrease in surface pressure over the urban area associated with an increase in the surface sensible heat flux.

Similarity Among Atmospheric Thermal Stratifications Over Elevated Surfaces Under Radiative‐Convective Equilibrium

AbstractAn air column under radiative‐convective equilibrium is studied here to understand equilibrium climate over different surface elevations. Cloud‐resolving model (CRM) simulations show that atmospheric thermal stratifications exhibit similar structures when expressed in sigma coordinates over varying surface elevations under radiative‐convective equilibrium. A zero‐buoyancy plume model that reproduces CRM results is used to interpret related processes. As surface pressure decreases, decreased pressure on a certain σ level leads to decreases of moist adiabatic temperature lapse rate, which largely cancel the increases of moist adiabatic lapse rate by temperature decreases. Meanwhile, the invariance of convective entrainment/detrainment rates keeps the deviation of environmental temperature lapse rate from moist adiabat approximately invariant, result in similar thermal stratifications under varying surface pressures. A comparison of thermodynamic profiles over the Tibetan Plateau with those over plains in reanalysis confirms the similarity found in CRM simulations. This similarity provides a useful simplification for representing the effects of convection.

Effects of Cu(II) on the Formation and Orientation of an Arachidic Acid Langmuir-Blodgett Film.

The influence of the copper(II) ion on the formation, morphology, and organization of an arachidic acid monolayer was investigated using Langmuir-Blodgett (LB) monolayers, Π-A isotherms, and Brewster angle microscopy (BAM). Our findings indicate that a Cu2+-complexed LB film exhibits an order that depends on the subphase pH, analogous to other metal ions. Yazdanian , M. ; et al. Ionic Interactions of Fatty Acid Monolayers at the Air-Water Interface . Langmuir 1990 , 6 , 1093 - 1098 . Kurnaz , M. L. ; et al. Morphology of Microphase Separation in Arachidic Acid-Cadmium Arachidate Langmuir-Blodgett Multilayers . J. Phys. Chem. 1996 , 100 , 11113 - 11119 . The metal ion facilitates the formation of solid-phase films at surface pressures as low as 5 mN/m. The films exhibit a rigid, ordered phase, evidenced by the absence of a collapse point and an increase in surface pressure rather than the typical sharp decrease in surface pressure, indicative of film failure. Amphiphile ionic charge vs pH (i.e., the extent of arachidic acid protonation) plays a role in the observed absence of collapse and the ability of the films to maintain order and cohesion at high surface pressures (ca. 65 mN/m). Additionally, film thickness data suggest that the incorporation of Cu2+ ions induces a change in orientation of the aliphatic chains of the amphiphiles and that amphiphile solubility in the subphase may play a role in the observed film behavior at low surface areas and high pH.

Driving Coordination Polymer Monolayer Formation by Competitive Reactions at the Air/Water Interface.

We have developed a novel approach enabling us to follow and facilitate the formation of two-dimensional coordination polymer monolayers directly at the air/water interface without the need of complex instrumentation. The method is based on the use of a surface active ligand that, when spread at the air/water interface, progressively undergoes hydrolysis with consequent gradual decrease in surface pressure. Notably, if the aqueous subphase contains metal ions capable of coordinating the ligand, coordination competes with hydrolysis, resulting in a lower surface pressure decrease. As a consequence, the formation of the coordination polymer monolayer can be verified simply by surface pressure measurements. Competition between hydrolysis and coordination was investigated as a function of the main experimental parameters affecting the two reactions, enabling the formation of stable coordination polymer monolayers with controlled density. Finally, the formation of continuous rigid 2D layers was confirmed by compression isotherms and ex situ morphological characterization. This work will simplify the verification of coordination polymer monolayer formation; thus, it will boost the synthesis of novel and innovative 2D materials.

Structure of Polystyrenesulfonate/Surfactant Mixtures at Air-Water Interfaces and Their Role as Building Blocks for Macroscopic Foam.

Air/water interfaces were modified by oppositely charged poly(sodium 4-styrenesulfonate) (NaPSS) and hexadecyltrimethylammonium bromide (CTAB) polyelectrolyte/surfactant mixtures and were studied on a molecular level with vibrational sum-frequency generation (SFG), tensiometry, surface dilatational rheology and ellipsometry. In order to deduce structure property relations, our results on the interfacial molecular structure and lateral interactions of PSS–/CTA+ complexes were compared to the stability and structure of macroscopic foam as well as to bulk properties. For that, the CTAB concentration was fixed to 0.1 mM, while the NaPSS concentration was varied. At NaPSS monomer concentrations <0.1 mM, PSS–/CTA+ complexes start to replace free CTA+ surfactants at the interface and thus reduce the interfacial electric field in the process. This causes the O−H bands from interfacial H2O molecules in our SFG spectra to decrease substantially, which reach a local minimum in intensity close to equimolar concentrations. Once electrostatic repulsion is fully screened at the interface, hydrophobic PSS–/CTA+ complexes dominate and tend to aggregate at the interface and in the bulk solution. As a consequence, adsorbate layers with the highest film thickness, surface pressure, and dilatational elasticity are formed. These surface layers provide much higher stabilities and foamabilities of polyhedral macroscopic foams. Mixtures around this concentration show precipitation after a few days, while their surfaces to air are in a local equilibrium state. Concentrations >0.1 mM result in a significant decrease in surface pressure and a complete loss in foamability. However, SFG and surface dilatational rheology provide strong evidence for the existence of PSS–/CTA+ complexes at the interface. At polyelectrolyte concentrations >10 mM, air–water interfaces are dominated by an excess of free PSS– polyelectrolytes and small amounts of PSS–/CTA+ complexes which, however, provide higher foam stabilities compared to CTAB free foams. The foam structure undergoes a transition from wet to polyhedral foams during the collapse.

Binding of the Cationic Peptide (KL)4K to Lipid Monolayers at the Air-Water Interface: Effect of Lipid Headgroup Charge, Acyl Chain Length, and Acyl Chain Saturation.

The binding of the cationic peptide (KL)4K to monolayers of different anionic lipids was determined by adsorption experiments. The chemical structure of the anionic phospholipids was changed in different ways. First, the hydrophobic region of phosphatidylglycerols was altered by elongation of the acyl chain length. Second, an unsaturated chain was introduced. Third, lipids with negatively charged headgroups of different chemical structure were compared. (KL)4K itself shows no surface activity and does not bind to monolayers of zwitterionic lipids. Analysis of (KL)4K binding to anionic lipid monolayers reveals a competition between two binding processes: (i) incorporation of the peptide into the acyl chain region (surface pressure increase) and (ii) electrostatic interaction screening the negative charges with reduction of charge repulsion (surface pressure decrease due to monolayer condensation). The lipid acyl chain length and the chemical structure of the headgroup have minor effects on the binding properties. However, a strong dependence on the phase state of the monolayer was observed. In the liquid-expanded (LE) phase, the fluid monolayer provides enough space, so that peptide insertion due to hydrophobic interactions dominates. For monolayers in the liquid-condensed (LC) phase, peptide binding followed by monolayer condensation is the main effect.

Effects of salt concentration and spreading amounts on surface pressures of layers of latex particles grafted to polymer chains at interfaces between air and aqueous salt solutions

Polystyrene (PS) latex particles grafted to diacetone acrylamide chains were spread in layers at the air-aqueous interfaces of NaCl solutions. Their surface pressures were investigated as a function of the NaCl concentration in the water phase, at different initial surface concentrations of PS latex particles. At low initial surface concentrations of PS latex particles, the isotherms of the monolayers measured during compression-expansion cycles exhibited slightly a negative hysteresis, i.e. a decrease in surface pressure as the number of compression-expansion cycles increased, irrespective of the NaCl concentration. The isotherm obtained upon expansion was almost the same as the compression isotherm for three repeated compression-expansion cycles. On the other hand, at high initial concentrations of latex particles, in which the surface area per particle could reach much smaller values upon compression, the compression-expansion isotherms clearly showed a plateau region. In this region, PS latex particles were laterally close packed at the interface, irrespective of NaCl concentration as well as the number of cycles. The isotherm shape was strongly dependent on NaCl concentration; negative hysteresis was observed when NaCl concentrations were lower than 0.001 M and higher than 0.15 M, except for the plateau region in the expansion cycles. The isotherm recorded using a 0.025 M NaCl subphase exhibited negative hysteresis below the plateau region.

GsMTx4 Mutagenesis Reveals Dynamic Membrane Binding Properties that Confer Inhibition of Piezo1

GsMTx4 is a spider venom derived peptide selective for cationic mechanosensitive channels (MSCs). It has six lysine residues that have been proposed to affect membrane binding. We created six lysine to glutamate mutants and tested them against Piezo1 channels in outside-out patches and measured lipid binding using a variety of physicochemical assays. Most mutant peptides had lower efficacy (0-40%) compared to wild type (WT). Increased association rates for some of the mutants did not correlate with increased inhibition. And tryptophan fluorescence quenching and isothermal titration calorimetry showed that the free energy of binding to lipid vesicles was largely unaffected by the mutations, suggesting channel inhibition was not a simple function of peptide-lipid association strength. Fluorescence quenching assays showed that WT and mutant peptides bound near the lipid-water interface, but the mutants penetrated deeper than WT. Peptide association as a function of lipid tension was investigated in Langmuir monolayers. The peptides occupied a large fraction of the expanded monolayer area, but that fraction was reduced by peptide expulsion as the pressure approached the monolayer-bilayer equivalence pressure (indicated by a shallow slope of the pressure-area isotherms). Mutants with compromised efficacy had steeper slopes in this region suggesting tighter association. These data place GsMTx4 at the membrane surface where it is stabilized by the lysines, and occupying a small fraction of membrane area at normal tension. As surface pressure decreases and free volume increases during membrane stretching, available peptides penetrate deeper acting as outer monolayer “area reservoirs”, transferring tension to the inner monolayer.

Monolayer kinetic model of formation of β-cyclodextrin–β-carotene inclusion complex

The carotenoids are sensitive molecules and their chemical integrity must be preserved from pro-oxidant elements which could affect and decrease their physiological benefits. The encapsulation based on the inclusion of the carotenoids into cage molecules is a promising approach for preserving over time of the intrinsic properties of the carotenoids. It is well known that cyclic oligosaccharide β-cyclodextrin (CD) as a cage molecule possesses strong inclusion ability to β-carotene (C) and as a result of the hydrophobic interactions forms an inclusion complex.In the present paper a monolayer kinetic model was established with the notion to extract more information about the influence of the molecular structure and organization to the interfacial interactions between the interacting species as well as about the role of the specific areas, which are often underestimated in previously studied dispersed systems. We developed the monolayer kinetic model for the formation of the inclusion CD–C complex by applying an experimental approach for following the kinetics by means of measuring the decrease of the surface area (ΔA) versus time (t) at constant surface pressure (π) and the decrease of surface pressure (π) versus time (t) at constant surface area (A). We also visualized by AFM the state of the monolayers at the initial and end points of the kinetic process. The values for the degree (d) and constant (Ka) of the association were estimated and compared with those from the studies of dispersed systems.

Interannual variability of the onset of the South China Sea summer monsoon

ABSTRACTThis article investigates the year‐to‐year variability of the onset of the South China Sea summer monsoon (SCSSM) and the possible influences exerted by the surface temperature anomalies over land and sea. Early and late monsoon onsets are related to the temperature anomalies in different regions. It is found that an early onset follows negative sea surface temperature (SST) anomalies in the central tropical Pacific (CP) Ocean during the preceding winter and spring, corresponding to a CP La Niña. In contrast, a late onset is preceded by the negative surface air temperature anomalies over land in the central Asian continent. Negative SST anomalies in the central‐eastern equatorial Pacific Ocean and the associated warming in the western Pacific induce an anomalously enhanced Walker circulation. This anomalous Walker cell leads to an increase in convection, causing more latent heat release and a subsequent decrease of surface pressure. The anomalous Walker cell and the enhanced latent heat release weaken the Western North Pacific subtropical high and the Philippine Sea anticyclone, favouring a westerly flow from the Indian Ocean, resulting in an early SCSSM onset. On the other hand, negative land surface temperature anomalies cool the atmosphere over land, and locally modify the Hadley circulation, accompanied by the anomalous divergence in the low‐level atmosphere over the western equatorial Pacific. This divergence anomaly reduces the latent heat release and strengthens the anticyclone in the Philippine Sea, thus preventing the westward extension of the westerlies from the Indian Ocean and causing a late SCSSM onset.

Interaction of a Patterned Amphiphilic Polyphenylene Dendrimer with a Lipid Monolayer: Electrostatic Interactions Dominate

Dendrimeric macromolecules with defined shape and size are promising candidates for delivering drug or DNA molecules into cells. In this work we study the influence of an amphiphilic polyphenylene dendrimer on a model cell membrane consisting of a condensed 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid monolayer. A small surface pressure decrease is observed when the dendrimer solution is injected into the aqueous phase below the monolayer. X-ray reflectivity measurements show that the surface monolayer remains intact. The molecular-scale picture is obtained with sum-frequency generation spectroscopy. With this technique, we observe that the tails of the surfactant molecules become less ordered upon interaction with the amphiphilic polyphenylene dendrimer. In contrast, the water molecules below the DPPC layer become more ordered. Our observations suggest that electrostatic interactions between the negative charge of the dendrimer and the positively charged part of the DPPC headgroup keep the dendrimer located below the headgroup. No evidence of dendrimer insertion into the membrane has been observed. Apparently before entering the cell membrane the dendrimer can stick at the hydrophilic part of the lipids.

Effect of temperature on surface pressure–area isotherms and surface dilational moduli of poly(N-isopropyl acrylamide) monolayers spread at air–water interface

The surface pressure–area isotherms and surface dilational moduli of poly(N-isopropyl acrylamide) (PNIPAM) monolayers spread at an air–water interface were measured as a function of temperature from 5°C to 35°C. The isotherms of the PNIPAM monolayers measured by compression–expansion cycles clearly showed a negative hysteresis, i.e., a decrease in the surface pressure as the number of cycles increased, irrespective of temperature. An increase in temperature caused a decrease in surface pressure in the semidilute region and increase in the surface pressure in the collapse state below the lower critical solution temperature (LCST) of PNIPAM in water, ca. 32°C. The surface moduli in the semidilute region determined from the first loop of Lissajous orbits at fixed surface pressure and strain, slightly decreased with increasing temperature, indicating that the elastic forces for the entanglement of PNIPAM chains in the monolayers decreased with a decrease in the solvent power conditions of PNIPAM in water.

Using the reversible inhibition of gastric lipase by Orlistat for investigating simultaneously lipase adsorption and substrate hydrolysis at the lipid–water interface

The lipolysis reaction carried out by lipases at the water-lipid interface is a complex process including enzyme conformational changes, adsorption/desorption equilibrium and substrate hydrolysis. Mixed monomolecular films of the lipase inhibitor Orlistat and 1,2-dicaprin were used here to investigate the adsorption of dog gastric lipase (DGL) followed by the hydrolysis of 1,2-dicaprin. The combined study of these two essential catalysis steps was made possible thanks to the highest affinity of DGL for Orlistat than 1,2-dicaprin and the fact that the inhibition of DGL by Orlistat is reversible. Upon DGL binding to mixed 1,2-dicaprin/Orlistat monolayers, an increase in surface pressure reflecting lipase adsorption was first recorded. Limited amounts of Orlistat allowed to maintain DGL inactive on 1,2-dicaprin during a period of time that was sufficient to determine DGL adsorption and desorption rate constants. A decrease in surface pressure reflecting 1,2-dicaprin hydrolysis and product desorption was observed after the slow hydrolysis of the covalent DGL-Orlistat complex was complete. The rate of 1,2-dicaprin hydrolysis was recorded using the surface barostat technique. Based on a kinetic model describing the inhibition by Orlistat and the activity of DGL on a mixed 1,2-dicaprin/Orlistat monolayer spread at the air-water interface combined with surface pressure measurements, it was possible to monitor DGL adsorption at the lipid-water interface and substrate hydrolysis in the course of a single experiment. This allowed to assess the kcat/KM* ratio for DGL acting on 1,2-dicaprin monolayer, after showing that mixed monolayers containing a low fraction of Orlistat were similar to pure 1,2-dicaprin monolayers.