Low Surface Pressure Research Articles

Measurement report: In situ vertical profiles of below-cloud aerosol over the central Greenland Ice Sheet

Abstract. Surface radiative cooling in polar regions can generate persistent stability in the atmospheric boundary layer. Stable layers below clouds can decouple the cloud layer from the near-surface environment. Under these conditions, surface aerosol measurements are not necessarily representative of the near-cloud or intra-cloud aerosol populations. To better understand the variability in the vertical structure of aerosol properties over the central Greenland Ice Sheet, in situ measurements of aerosol particle size distributions up to cloud base were made at Summit Station in July and August 2023. These measurements identified distinct vertical aerosol layers between the surface- and cloud-base-associated thermodynamic decoupling layers. Such decoupling layers occur 49 % of the time during the summer in central Greenland, suggesting that surface aerosol measurements are insufficient for describing the cloud-relevant aerosol population half of the time. Experience during this first measurement season demonstrated the ability of a tethered-balloon platform to operate effectively under icing conditions and at low surface pressure (< 680 hPa). The results presented here illustrate the value of vertically resolved in situ measurements of aerosol properties in developing a nuanced understanding of the aerosol effects on cloud properties in polar regions.

Relations between cyclones and ozone changes in the Arctic using data from satellite instruments and the MOSAiC ship campaign

Abstract. Large-scale meteorological events (e.g. cyclones), referred to as synoptic events, strongly influence weather predictability but still cannot be fully characterised in the Arctic region because of the sparse coverage of measurements. Due to the fact that atmospheric dynamics in the lower stratosphere and troposphere influence the ozone field, one approach to analyse these events further is the use of space-borne measurements of ozone vertical distributions and total columns in addition to conventional parameters such as pressure or wind speed. In this study we investigate the link between cyclones and changes in stratospheric ozone by using a combination of unique measurements during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) ship expedition, ozone profile and total column observations by satellite instruments (OMPS-LP, TROPOMI), and ERA5 reanalysis data. The final goal of the study is to assess whether the satellite ozone data can be used to obtain information about cyclones and provide herewith an additional value in the assimilation by numerical weather prediction models. Three special cases during the MOSAiC expedition were selected and classified for the analysis. They are one “normal” cyclone, where a low surface pressure coincides with a minimum in tropopause height, and two “untypical” cyclones, where this is not observed. The influence of cyclone events on ozone in the upper-troposphere lower-stratosphere (UTLS) region was investigated, using the fact that both are correlated with tropopause height changes. The negative correlation between tropopause height from ERA5 and ozone columns was investigated in the Arctic region for the 3-month period from June to August 2020. This was done using total ozone columns and sub-columns from TROPOMI, OMPS-LP, and MOSAiC ozonesonde data. The greatest influence of tropopause height changes on ozone contour levels occurs at an altitude between 10 and 20 km. Moreover, the lowering of the 250 ppb ozonopause (at about 11 km altitude) below 9 km was used to detect cyclones using OMPS-LP ozone observations. The potential of this approach was demonstrated in two case studies where the boundaries of cyclones could be determined using ozone observations. The results of this study can help improve our understanding of the relationship between cyclones, tropopause height, and ozone in the Arctic and demonstrate the usability of satellite ozone data in addition to the conventional parameters for investigating cyclones in the Arctic.

The flow control mechanism of trailing-edge Gurney flap on a 50°-swept delta wing in forced pitching

The flow control effect of the trailing-edge Gurney flap (TG) on the dynamic lift characteristics for a 50°-swept delta wing during large-amplitude pitching oscillations at various reduced frequencies (k = 0.072, 0.144, 0.287, and 0.575) was investigated via force, particle image velocity, and dye visualization measurements in a water channel facility. Numerical simulations were carried out to further understand the flow control mechanism of the TG in low and high reduced frequency cases (k = 0.072 and 0.575). It was found that as the reduced frequency increases, the lift increments brought by the TG are magnified and abated during the upstroke and downstroke processes, respectively. The breakdown of the leading-edge vortex (LEV) on the upper surface of the wing is promoted by the TG during the early stage of the pitching cycle. The lift enhancement being benefited by the TG is mainly contributed by the recovery of lower surface pressure along the trailing edge due to the blockage effect of TG, which also stimulates the spanwise flow and strengthens the LEV upon the upper surface. The significant lift increment contribution of the upper surface during the upstroke process can be maintained to higher angle of attack as the reduced frequency increases.

Combining in-situ observation and interfacial rheology as a tool to investigate the possible mechanism for improved emulsifying performance of gliadin-based colloid particles

Interfacial deformation and interfacial rheology behaviour of prolamin particles are relevant factors affecting their emulsification performance but have not yet been paid considerable attention to. Based on the finding that CMC modification significantly improved the emulsifying property of gliadin colloid particles (GCPs), the present study combined in situ observation and interfacial rheology as a tool to investigate the effect of CMC on the structure characteristics, interfacial deformation and interfacial rheology behaviour of GCPs and their correlation with emulsifying performance. The results demonstrated that gliadin/CMC complex particles (GCCPs) presented looser core-shell structures than GCPs. The interfacial deformation of particles and the formation of smooth interfaces were observed for both GCPs and GCCPs, and GCCPs exhibited faster deformation behaviour, which should correlate to the looser structure. Although GCCPs showed lower surface pressure and viscoelasticity modulus, the existence of CMC promoted the initial adsorption of particles and accelerated the formation of viscoelastic interfacial films, which contributed to the improvement of emulsifying performance. In addition, CMC endowed the interfacial layers with moderate viscosity and fluidity to resist the destabilisation induced by oil droplet deformation. The present study should provide insights for intuitive understanding and fine regulation of the interfacial behaviour of protein particles.

Plasmonic Properties of Self-Assembled Gold Nanocrescents: Implications for Chemical Sensing.

A bottom-up approach, the Langmuir-Blodgett technique, is used for the preparation of composite thin films of gold nanoparticles and polymers: poly(styrene-b-2-vinylpyridine), poly-2-vinylpyridine, and polystyrene. The self-assembly of poly(styrene-b-2-vinylpyridine) at the air-water interface leads to the formation of surface micelles, which serve as a template for the organization of gold nanoparticles into ring assemblies. By using poly-2-vinylpyridine in conjunction with low surface pressure, the distance between nanostructures can be increased, allowing for optical characterization of single nanostructures. Once deposited on a solid substrate, the preorganized gold nanoparticles are subjected to further growth by the reduction of additional gold, leading to a variety of nanostructures which can be divided into two categories: nanocrescents and circular arrays of nanoparticles. The optical properties of individual structures are investigated by optical dark-field spectroscopy and numerical calculations. The plasmonic behavior of the nanostructures is elucidated through the correlation of optical properties with structural features and the identification of dominant plasmon modes. Being based on a self-assembly approach, the reported method allows for the formation of interesting plasmonic materials under ambient conditions, at a relatively large scale, and at low cost. These attributes, in addition to the resonances located in the near-infrared region of the spectrum, make nanocrescents candidates for biological and chemical sensing.

Molecular Templates on Surfaces by Exploiting Supramolecular Chemistry in Langmuir–Blodgett Monolayers

AbstractAttaining precise control over molecular arrangements is of paramount importance for numerous applications in nanotechnology, particularly in constructing molecular templates to accurately immobilize target materials on surfaces. A strategic combination of supramolecular and interfacial chemistry may serve to build a well‐organized molecular network, enabling the subsequent location of target molecules on specific positions of a surface. A supramolecular complex (compound 1) comprised of a melamine unit forming hydrogen bonds with dendritic arms terminated in a coumarin unit is utilized, which readily undergoes photodimerization. The research demonstrates the formation of well‐organized Langmuir films of compound 1 which can be transferred on substrates at low surface pressures adopting a lying‐flat orientation. Upon irradiation of the pristine films at 365 nm the coumarin units undergo photo‐cross linking, leading to the formation of a compact photo‐crosslinked film. Incubation of these photo‐crosslinked films in a solution containing 1‐hexanethiol results in the withdrawal of the melamine and the chemisorption of two thiol molecules per each melamine unit. The nanopores created by the removal of the melamine core are attributed to the disruption of hydrogen bonds in compound 1 by the thiols. This precisely defined molecular network holds significant promise as a template for orchestrating the arrangement of functional materials on surfaces.

Investigating the Role of the Low-Level Jet in Two Winters Severe Dust Rising in Southwest Iran

The dust storms with local and non-local dust sources mostly affect Khuzestan province in southwest (SW) Iran. In this study, the role of the low-level jet in the activation of the internal dust events in SW Iran during two severe dust cases was investigated. For this purpose, the fifth-generation ECMWF reanalysis for the global climate and weather (ERA5) data was used to identify the synoptic patterns and the low-level jet (LLJ) characteristics in the study area. Furthermore, the images of the moderate resolution imaging spectroradiometer (MODIS) sensor, the outputs of the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model, and a weather research and forecasting model coupled with chemistry (WRF-Chem) were used to investigate the propagation and transport of the dust particles. The results of the synoptic analysis in both dust cases show the simultaneous occurrence of the divergence zone associated with cyclonic curvature in the subtropical jet stream (STJ) at 300 hPa, causing convergence at 925 hPa, upward motion, and the development of low surface pressure in SW Iran. Examining the vertical wind profile shows the existence of the maximum horizontal wind speeds of 975 to 875 hPa, along with the positive and negative shear below and above it, respectively, which emphasizes the existence of the LLJ and its role in local dust emission. The results of the comparison between the satellite images, WRF-Chem, and HYSPLIT model outputs show the formation and transportation of dust particles from the inner regions of Khuzestan in SW Iran. The horizontal dust surface distribution, vertical raised dust mass, and kinetic energy transfers are well simulated by the WRF-Chem model when LLJ broke at 09:00 to 12:00 UTC. The most important finding of this research is that, for the first time, the role of low-level jet is investigated in the activation of internal dust events in SW Iran.

Effect of gurney flaps on a nonslender delta wing during large-amplitude and high-frequency dynamic pitching

The flow control effect of Gurney flaps on 50° swept delta wings during large-amplitude and high-frequency pitching were investigated both experimentally and numerically. Both force and velocity measurements were conducted and compared with the numerical simulation results. The lift hysteresis was found to be significantly affected by the Gurney flaps. It was found that the leading-edge Gurney flap (LG) acts to redistribute the vorticity over the suction surface of the wing during the upstroke process. The formation and development of the leading-edge vortex (LEV) on the suction surface was delayed by the LG, which was accompanied by enhancement of the lift at high angles of attack. The lower surface pressure can be altered with the flow velocity being slowed down by the trailing-edge Gurney flap (TG), which improves overall lift performance of the pitching wing at small to moderate angles of attack.

A novel wake flow control method for drag reduction of a high-speed train with vortex generators installing on streamlined tail nose

The head/tail of a high-speed train has been designed in a streamlined way to achieve good aerodynamic performance, which leads to the flow separation point moving close to the tail nose tip. Therefore, the conventional way with some add-ons, i.e., the passive flow control, to suppress the flow separation in advance is not a good choice for this train wake flow improvement. Also, with the increase of the train speed, it is urgent to study new methods for the aerodynamic drag reduction of the train. The wake of the high-speed train is characterized by a pair of counter-rotating vortices, contributing to low surface pressure on the streamlined tail and posing a risk to the train operation. Thus, lowering the intensity of counter-rotating vortices and enhancing the surface pressure become a significantly potential drag reduction method. In the current study, a novel wake flow control method, named the vortex intensity reduction theory (VIRT), for the drag reduction of a high-speed train with vortex generators installing on the streamlined tail nose, was proposed to generate a pair of vortices with opposite rotating directions, expecting to weaken the wake vortices and have a higher-pressure distribution on the tail, as compared to the base case. The results show that with the installation of vortex generators (VGs), the train wake flow intensity is suppressed, and the influence region is reduced, resulting in the better train wake flow structures, as compared to the train without VGs. The VGs have significant impact on the aerodynamic performance of the tail car, while this effect is not evidently observed on the head and middle cars. The VGs contribute to the surface pressure increase on the streamlined tail, resulting into a reduction of pressure difference between the head and tail cars. As a result, a reduction of 5.11% in the aerodynamic drag and a reduction of 14.93% in the aerodynamic lift of the tail car are obtained, while for a three-car grouping train model, the reductions are about 2.23% and 72.66%, respectively. Therefore, the VIRT based on VGs proposed in this paper can effectively reduce the aerodynamic force of the tail car and alleviate the intensity of wake flow of the high-speed train, which will provide a newly potential drag reduction method of the next generation high-speed train.

Surface Properties of Aqueous Dispersions of Bovine Serum Albumin Fibrils

The surface properties of aqueous dispersions of worm-like fibril aggregates of bovine serum albumin (BSA) differ from those of the adsorption layers of the native protein. The dispersions of BSA fibrils are characterized by slower changes of the surface tension and dynamic surface elasticity and also have different steady-state values of the surface properties. The fourfold compression of the adsorption layer of BSA fibrils leads to noticeably higher surface pressures than those of a compressed layer of the native protein, indicating the formation of a more rigid layer structure in the former case. The spreading of BSA fibrils onto a liquid surface from a concentrated dispersion reduces the effect of surface-active admixtures on the layer properties. The dependencies of the dynamic surface elasticity on surface pressure almost coincide for the spread layers of fibrils and the native protein in the range of low surface pressures, but only the spreading of the native protein can lead to surface pressures higher than 4 mN/m. This distinction is presumably caused by the formation of stable clusters of BSA fibrils at the interface and their slow propagation along the liquid surface.

Interfacial interactions in urease/stearic acid and urease/DOPC binary mixed systems at the air-water and the air-solid interfaces

In the present study, the protein-lipid interactions between water-soluble metalloenzyme urease (Urs) and insoluble stearic acid (SA) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were investigated at the air–water interface using the Langmuir-Blodgett (LB) technique. Surface pressure (π) - molecular area (A) isotherms were measured for the pure SA and pure DOPC monolayers in the presence of urease in the water subphase. From the (π – A) isotherms of the binary system, it was found that urease strongly interacts with SA and DOPC. The compressibility of the SA monolayer was reduced with the incorporation of urease; a similar trend was also found with DOPC. Moreover, an association of urease with lipid monolayers was found to be surface pressure (π) dependent. The presence of a little hump in the mixed isotherms of Urs-SA at low surface pressure supports this observation. However, the miscibility studies and the calculations of excess Gibb’s free energy indicate an attractive interaction between urease and SA molecules. The considerable morphological variations observed by atomic force microscopy (AFM) in urease-SA deposited films onto hydrophilic and hydrophobic Si(100) surfaces suggest that urease was strongly bound with the surrounding lipid SA on the hydrophilic surfaces but the urease molecules were rigorously denatured on the hydrophobic surfaces. The AFM analysis of Urs-DOPC mixed LB films at room temperature (RT) and elevated temperature suggests substantial denaturation of urease in a hydrophobic environment leading us to speculate the exposure of tryptophan moieties of the urease molecules to the hydrophobic air phase.

Cholesterol-Controlled Interaction of Ionic Liquids with Model Cellular Membranes.

While ionic liquids (ILs) are considered as prospective ingredients of new antimicrobial agents, it is important to understand the adverse effects of these molecules on human cells. Since cholesterol is the essential component of a human cell membrane, in the present study, the effect of an imidazolium-based IL has been investigated on the model membrane in the presence of cholesterol. The area per sphingomyelin lipid is found to reduce in the presence of the IL, which is quantified by the area-surface pressure isotherm of the lipid monolayer formed at the air-water interface. The effect is considerably diminished in the cholesterol-containing monolayer. Further, the IL is observed to decrease the rigidity of the cholesterol-free monolayer. Interestingly, the presence of cholesterol does not allow any change in this property of the layer at lower surface pressure. However, at a higher surface pressure, the IL increases the elasticity in the cholesterol-induced condensed phase of the lipid layer. The X-ray reflectivity measurement on a stack of cholesterol-free lipid bilayers proved the formation of IL-induced phase-separated domains in the matrix of a pure lipid phase. These domains are found to be formed by interdigitating the chains of the lipids, producing a thinner membrane. Such a phase is less intense in the cholesterol-containing membrane. All of these results indicate that the IL molecules may deform the cholesterol-free membrane of a bacterial cell, but the same may not be harmful to human beings as cholesterol could restrict the insertion in the cellular membrane of a human cell.

Spontaneous multilayer formation of an amphiphilic alkylammonium cation with a long hydrocarbon chain at an air-clay dispersion interface

Langmuir film formation behavior of a trimethylammonium cation with a long hydrocarbon chain (CH3(CH2)29N+(CH3)3, C30TMA+) was investigated. To weaken the hydrophobic interactions between the hydrocarbon chains, methanol was added to the subphases. A solution of C30TMA+·I– was spread at air-water and air-clay dispersion interfaces. The surface pressure-molecular area curves of the floating C30TMA+ films showed that the surface pressure at the collapse point decreased with increasing methanol concentration in water and in the dispersion, indicating the weakening of the hydrophobic interaction. For the floating films on clay dispersions, the molecular area at the collapse point decreased with increasing methanol concentration. The decrease in the molecular area indicates multilayer formation of C30TMA+ at the air-dispersion interface at a low surface pressure, which was confirmed by the atomic force microscope images and X-ray diffraction (XRD) patterns of the deposited films. The out-of-plane and in-plane XRD results of the multilayers showed not only layer-by-layer ordering, but also lateral ordering of the closely packed C30TMA+ cations in each layer.

Molecular Orientations of Myristic Acid Derivatives with Different Perfluoroalkyl Chain Lengths at the Air/Water Interface Evaluated by Heterodyne-Detected Sum Frequency Generation Spectroscopy

Surface-related properties of perfluoroalkyl compounds such as hydrophobicity and adhesion force can have a close relationship with the orientational order of the molecules at the surface. Myristic acid (MA) derivatives with perfluoroalkyl (Rf) groups have been known to form a well-ordered monolayer at the air/gold substrate interface. In this study, molecular orientations of the MA derivative monolayers at the air/water interface were investigated by heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy. We estimated the molecular orientation of MA derivative monolayers with a marker band observed at around 1370 cm–1. The Rf chain length and the surface pressure dependence of the molecular orientation of four MA derivatives were examined. The marker bands were observed except for the derivative with the shortest Rf chain at the higher surface pressure, whereas the marker bands were observed only for the two derivatives with relatively longer Rf chain lengths at the lower surface pressure. The observation indicates that the longer the Rf chain is and the higher the surface pressure is, MA derivatives tend to adopt a standing orientation closer to perpendicular to the interface.

Role of cholesterol in pulmonary surfactant at ambient and physiological temperatures.

Pulmonary surfactant is the mixture of lipids and proteins that lowers surface tension in the lungs. The material forms a thin film on the aqueous layer that lines the alveolar air-sacks. When compressed by the shrinking alveolar surface area during exhalation, the surfactant film achieves very low surface tensions. Our studies used monolayers of DPPC with variable amounts of cholesterol as a simple model of the alveolar film. A widely held supposition contends that, relative to the multilamellar vesicles secreted by the type II pneumocytes, the alveolar film is greatly enriched in DPPC. We have recently published that structural changes by which cholesterol causes faster collapse of DPPC monolayers and determined the structure of calf lung surfactant extract (CLSE) and DPPC/cholesterol mixed films with Xchol = 0.0-0.4. This work is an extension of this effort, but at physiological temperature of 37⁰C. Here, we compare the structure of CLSE and DPPC/cholesterol mixtures with varying Xchol at ambient and physiological temperatures. We have used grazing incidence X-ray off-specular scattering (GIXOS) and grazing incidence X-ray diffraction (GIXD) to obtain the detailed structural data of the interfacial films. GIXOS measurements showed that CLSE remains a single monolayer at surface pressures from 15mN/m to 45 mN/m, contrary to popular predictions that pulmonary surfactant must form a multilayer at low surface pressures. Both CLSE and DPPC/cholesterol films at 37C produced a single diffraction peak, indicating little change in the lattice-parameters of the ordered film. Predictably, with heating both CLSE and DPPC/cholesterol films showed the significant broadening of the GIXD peak and the dramatic decrease in its maximum scattered intensity, indicating a radical loss of the long range order among the hydrocarbon chains and the extensive conversion of ordered to disordered structures.

Identification of wake vortices using a simplified automobile model under parallel running and crosswind conditions

Previous studies have revealed that the change in aerodynamic drag on a test automobile under a parallel running condition is mainly because of the pressure effect, which is caused by the pressure field of the parallel running vehicle, and the effect of the change in wind direction caused by the parallel running vehicle. Apart from the drag change, which can be estimated by assuming a uniform crosswind, the change in wind direction has other effects. In this study, to clarify the other effects, the differences in the wake vortices associated with the change in drag between parallel running and uniform crosswind conditions were identified from the numerical simulation results. The surface pressure on the back excluding the pressure effect under the parallel running condition was lower on the opening side than that under the uniform crosswind condition. In addition, the wake vortices near the region of low surface pressure and their related vortices were focused. Visualizing the flows related to these vortices indicates that the non-uniformity of the flow along the upstream side and the strengthening of the entrainment at the rear end owing to the interference affect the change in the drag in the parallel running condition compared with the uniform crosswind condition. These results are useful for developing control methods to suppress the increase in drag in the parallel running condition.

A field study on the aerodynamics of freight trains with different stacking configurations

A full-scale 48-foot shipping container was instrumented with surface pressure taps and loaded onto a number of single- and double-stacked container freight trains. Surface pressure data enabled the container pressure drag coefficient to be evaluated for a range of different train loading configurations, container positions along the train, and atmospheric wind conditions. Field-based measurements show that for low and high crosswind conditions surface pressure distributions measured on the front face of the instrumented container are in good agreement with those reported in past studies. However, the magnitude of the pressure drag coefficient was found to be typically 50% lower for all loading cases analysed compared with previous seemingly analogous wind-tunnel and numerical investigations. For high crosswind conditions, the drag coefficient was found to increase and correlated well with the level of asymmetry observed in the measured pressure distributions. This was true for all cases regardless of the position along the length of the train. In the absence of direct information of the incident free-stream wind conditions, the level of asymmetry in the pressure distributions was found to provide a viable indirect method for assessing the impact that crosswinds have on the aerodynamic drag of freight trains.

Towards energy efficient autonomous exploration of Mars lava tube with a Martian coaxial quadrotor

Mapping and exploration of a Martian terrain with an aerial vehicle has become an emerging research direction, since the successful flight demonstration of the Mars helicopter Ingenuity. Although the autonomy and navigation capability of the state of the art Mars helicopter has proven to be efficient in an open environment, the next area of interest for exploration on Mars are caves or ancient lava tube like environments, especially towards the never-ending search of life on other planets. This article presents an autonomous exploration mission based on a modified frontier approach along with a risk aware planning and integrated collision avoidance scheme with a special focus on energy aspects of a custom designed Mars Coaxial Quadrotor (MCQ) in a Martian simulated lava tube. One of the biggest novelties of the article stems from addressing the exploration capability, while rapidly exploring in local areas and intelligently global re-positioning of the MCQ when reaching dead ends in order to efficiently use the battery based consumed energy, while increasing the volume of the exploration. The proposed novel algorithm for the Martian exploration is able to select the next way point of interest, such that the MCQ keeps its heading towards the local exploration direction where it will find maximum information about the surroundings. The proposed three layer cost based global re-position point selection assists in rapidly redirecting the MCQ to previously partially seen areas that could lead to more unexplored part of the lava tube. The Martian fully simulated mission presented in this article takes into consideration the fidelity of physics of Mars condition in terms of thin atmosphere, low surface pressure and low gravity of the planet, while proves the efficiency of the proposed scheme in exploring an area that is particularly challenging due to the subterranean-like environment. The proposed exploration-planning framework is also validated in simulation by comparing it against the graph based exploration planner. Intensive simulations with true Mars conditions are carried out in order to validate and benchmark our approach in a utmost realistic Mars lava tube exploration scenario using a Mars Coaxial Quadrotor.

Numerical Study on Aerodynamic Noise Reduction of Pantograph

A hybrid method incorporating the simulations of noise sources with delayed detached eddy simulation (DDES) and calculations of far-field noise with the Ffowcs Williams–Hawkings (FW-H) equation is used to study the suppression technique for the aerodynamic noise of a Faiveley CX-PG pantograph. Considering that China’s Fuxing bullet trains operate at 350 km/h, the inflow velocity of 350 km/h is applied in this paper. The noise radiated from the panhead area, middle area, and bottom area at an inflow velocity of 350 km/h is distinguished. The noise intensities at the standard observer show that the noise radiated from the panhead area is the strongest, and the sound pressure level spectrum value is larger than the other two in the range above 500 Hz. The influence of applying the wavy rods and modifying the contact strip shape on the aerodynamic noise is discussed in detail. By comparing the acoustic source distribution and the far-field noise intensity, it is found that applying the wavy rods can effectively reduce the panhead noise, especially around the peak frequency. Modifying the shape of the contact strip to a hexagon can suppress the vortex shedding, leading to a lower surface pressure level. Combining the strip modification and wavy rods, the total noise intensity can be diminished by about 3.0 dB.

DNA Penetration into a Lysozyme Layer at the Surface of Aqueous Solutions.

The interactions of DNA with lysozyme in the surface layer were studied by performing infrared reflection–absorption spectroscopy (IRRAS), ellipsometry, surface tensiometry, surface dilational rheology, and atomic force microscopy (AFM). A concentrated DNA solution was injected into an aqueous subphase underneath a spread lysozyme layer. While the optical properties of the surface layer changed fast after DNA injection, the dynamic dilational surface elasticity almost did not change, thereby indicating no continuous network formation of DNA/lysozyme complexes, unlike the case of DNA interactions with a monolayer of a cationic synthetic polyelectrolyte. A relatively fast increase in optical signals after a DNA injection under a lysozyme layer indicates that DNA penetration is controlled by diffusion. At low surface pressures, the AFM images show the formation of long strands in the surface layer. Increased surface compression does not lead to the formation of a network of DNA/lysozyme aggregates as in the case of a mixed layer of DNA and synthetic polyelectrolytes, but to the appearance of some folds and ridges in the layer. The formation of more disordered aggregates is presumably a consequence of weaker interactions of lysozyme with duplex DNA and the stabilization, at the same time, of loops of unpaired nucleotides at high local lysozyme concentrations in the surface layer.