Air Columns Research Articles

Concentration-dependent parsimonious releaser roles of gregarious male pheromone of the desert locust, Schistocerca gregaria

The responses of (i) groups of crowd-reared mature males of desert locust, Schistocerca gregaria to a choice of two columns of air, one permeated with different concentrations of phenylacetonitrile (PAN), the major component of gregarious-phase male-produced pheromone, and the other untreated, and (ii) individual crowd-reared mature males of the insect to varying concentration gradients of PAN, were studied in two different types of arena. In the choice assay, locusts preferred to be within PAN-permeated air column at low relative doses of the pheromone, but away from PAN at high relative doses. In the second assay, individual locusts were arrested close to PAN source at low PAN concentration gradients, but away from the source at high concentration gradients. The results are consistent with two reported releaser functions of the adult male-released pheromone that are dependent on different sensory thresholds: arrestment and cohesion at lower relative concentrations and male–male homosexual avoidance at higher relative concentrations.

Experimenting with woodwind instruments

Simple experiments involving musical instruments of the woodwind family can be used todemonstrate the basic physics of vibrating air columns in resonance tubes using nothingmore than straightforward measurements and data collection hardware and software. Moreinvolved experimentation with the same equipment can provide insight into the effects ofholes in the tubing and other factors that make simple tubes useful as musical instruments.

PHARYNGEAL DIMENSIONS IN HEALTHY MEN AND WOMEN

Epidemiological studies reveal a high male prevalence of obstructive sleep apnea syndrome. A possible explanation for this male predominance is the existence of anatomical differences in the upper airway between men and women. The upper airways of 10 male and 10 female healthy volunteers were prospectively evaluated by magnetic resonance imaging. Anatomical pharyngeal and column cross-sectional linear measurements were made in sagittal T1 and axial T1 and T2 weighted fast spin-echo images. Men had significantly greater mean sagittal pharyngeal structural dimensions compared to women for all structures with the exception of the craniocaudal length of the soft palate and the thickness of the submentonian fat. In contrast, cross-sectional linear dimensions were similar in men and women with the exception of the laterolateral tongue length, which was greater in men. All mean linear measurements of the pharyngeal air column were similar in men and women at all studied levels. Men and women present pharyngeal air columns with similar dimensions, but in women this column is surrounded by smaller structures, which might imply a smaller effort to keep its patency. Our data suggest the existence of an anatomical protective factor in women against the upper airway collapse.

Interactive program for computer-aided design of woodwind musical instruments

Current scientific knowledge on the acoustics of woodwind instruments allows accurate physical modeling of the sound generation mechanisms, and the acoustic interaction with the air column. These physical models can be incorporated into computer software, in order to evaluate not only the tuning, voicing, and other tonal characteristics of existing instrument designs, but also to estimate the potential effects of proposed modifications, and to anticipate the characteristics of new designs. This presentation describes the development of an interactive computer program for the acoustic design, evaluation, and auralization of woodwind musical instruments. The program displays a graphical user interface that allows convenient entry of air column data, including constant and variable cross-section segments, open and closed fingerholes, and air column terminations. It also implements different types of sound excitation mechanisms, which include jet-driven (flutelike) and single reed (clarinetlike) models. The program can produce input impedance and reflection function data for further acoustic analysis, and synthetic sounds that approximate the musical tones that can be expected form the actual instrument. The software has been validated by comparative analysis of calculated versus measured air columns, and simulated versus actual (recorded) flute tones.

Tropospheric dryness and clouds over tropical Indian Ocean

Dry layers in the free troposphere over Tropical Oceans have been studied for their role in convective activity and for their effects in the radiation budget. Previous studies concentrated, mostly, on the Western Pacific region because of the abundance of observations during the TOGA-COARE. This study aims to document the occurrence of dry layers over the Indian Ocean and to investigate the cloudiness observed, but poorly documented, during such events. One month (March 1999, during INDOEX) of combined Visible/Infrared and Microwave data from the TRMM radiometers had been processed to classify observations in terms of total precipitable water vapour (TPWV), cloud occurrence and type. Soundings (1978–2004) from the Seychelles station have been analysed to validate the capability, through the analysis of TPWV, to detect dry layers. The study area (40°E–80°E, 30°S–30°N) had been portioned into 2.5° × 2.5° boxes to investigate the spatial distribution of occurrence of dry events with associated cloudiness. South of the ITCZ cloudiness associated with low TPWV is due to low-level clouds: probably generated by shallow convection trapped by the trade inversion. North of the ITCZ cirrus are mostly observed during relatively dry events. Further analyses, concentrating on possible links between occurrence of cirrus and TPWV, suggest, in addition to the obvious mechanism (i.e. the higher the moisture, the higher the convective activity and as a consequence the higher the occurrence of cirrus), a second one that would be responsible of relatively high occurrence of cirrus for low TPWV. A case (14th–15th March 1999) is studied in detail with TRMM observations, sounding data and METEOSAT imagery. The observed cirrus, generated by convection, migrate over relatively dry air of extra-tropical origin. Cirrus extend as filaments for more than 1000 km in length and about 50 to 100 km in width, and they last for 2–3 days. A retrieval method is designed and applied to the data giving as cirrus top pressure approximately 250 hPa while the retrieved effective radius value is consistent with what expected, from literature, for dissipating cirrus at that pressure. The vertical structure of the atmosphere, observed during such event suggests the hypothesis that a combination of presented radiative and dynamical mechanisms could be responsible, through the supply of moisture from lower levels, of increasing the cirrus lifetime and, as a consequence, increasing the occurrence of cirrus over relatively dry air columns. A larger data set is investigated to confirm the results based on the March 1999 data set analysis. The average vertical structure of the atmosphere, during such events, as obtained from the Seychelles sounding data set (> 7000 soundings) analysis confirms the occurrence of the features observed in the study case. Similarly, the analysis of 105 days of TRMM orbits over the box containing the Seychelles station, confirms the statistical features that indicate a possible relationship between the occurrence of dry air and associated cirrus. However, possible interaction between dry layer and cirrus occurrence should be investigated in a detailed modelling framework (beyond the scope of this study) such as the one offered by the cloud resolving models.

Woodpile photonic crystals composed of air columns

Silicon-based woodpile photonic crystals (PhCs) composed of air columns have a large gap/midgap ratio exceeding 20% over a wide dimensional range of the cross section of the air column when the cross section is deformed to a rectangular shape extended normal to the stacking direction. Such a PhC structure can be formed using a simple technique based on 45° dry etching. Furthermore, introducing twin air columns with small cross sections instead of corresponding mother air columns yields a defect state at the region where the columns cross. Since the fabrication process is a planar-type Si wafer process, fabricated PhCs can be easily combined with conventional electronic circuits and optical elements, such as Si waveguides and switches.

Effects of bulk ice microphysics on the simulated monsoonal precipitation over east Asia

This study examines the effects of bulk ice microphysical processes on the simulation of monsoonal precipitation in summer over east Asia, centered over Korea. The mixed phase microphysics scheme of the WRF‐Single‐Moment‐MicroPhysics class 5 (WSM5) is implemented into the fifth‐generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5). The performance of the WSM5 scheme is compared to that of Reisner's mixed phase scheme, that is, the MM5‐Single‐moment‐Microphysics class 5 (MSM5). Together with looking at the impact of ice microphysics, the importance of the sedimentation of falling ice crystals on simulated rainfall events is investigated. The same sensitivity experiments are extended to a 2‐month‐long simulation of the east Asian summer monsoon. It was found that the new microphysics in the WSM5 scheme produces a more realistic vertical distribution of condensates. For a locally developed heavy rainfall event over Korea, the impact of revised ice microphysics is significant. The WSM5 scheme simulates more (less) precipitation in the south (north), compared with that of the MSM5 scheme, by stabilizing the air columns in the rainfall area, leading to a better agreement with the observed precipitation. By contrast, ice sedimentation becomes more important for those cases of heavy rainfall, associated with a mobile surface cyclone system, accomplished by suppressing large‐scale bias through a realistic ice cloud/radiation feedback. The sedimentation of cloud ice is found to be crucial to the successful simulation of monsoonal precipitation and large‐scale features within the east Asian summer monsoon.

An Energy-Balance Analysis of Deep Convective Self-Aggregation above Uniform SST

Abstract The spatial organization of deep moist convection in radiative–convective equilibrium over a constant sea surface temperature is studied. A 100-day simulation is performed with a three-dimensional cloud-resolving model over a (576 km)2 domain with no ambient rotation and no mean wind. The convection self-aggregates within 10 days into quasi-stationary mesoscale patches of dry, subsiding and moist, rainy air columns. The patches ultimately merge into a single intensely convecting moist patch surrounded by a broad region of very dry subsiding air. The self-aggregation is analyzed as an instability of a horizontally homogeneous convecting atmosphere driven by convection–water vapor–radiation feedbacks that systematically dry the drier air columns and moisten the moister air columns. Column-integrated heat, water, and moist static energy budgets over (72 km)2 horizontal blocks show that this instability is primarily initiated by the reduced radiative cooling of air columns in which there is extensive anvil cirrus, augmented by enhanced surface latent and sensible heat fluxes under convectively active regions due to storm-induced gustiness. Mesoscale circulations intensify the later stages of self-aggregation by fluxing moist static energy from the dry to the moist regions. A simple mathematical model of the initial phase of self-aggregation is proposed based on the simulations. In accordance with this model, the self-aggregation can be suppressed by horizontally homogenizing the radiative cooling or surface fluxes. Lower-tropospheric wind shear leads to slightly slower and less pronounced self-aggregation into bands aligned along the shear vector. Self-aggregation is sensitive to the ice microphysical parameterization, which affects the location and extent of cirrus clouds and their radiative forcing. Self-aggregation is also sensitive to ambient Coriolis parameter f, and can induce spontaneous tropical cyclogenesis for large f. Inclusion of an interactive mixed-layer ocean slows but does not prevent self-aggregation.

A unified digital waveguide (infra)structure for synthesizing wind instrument sounds

Virtual acoustic models provide researchers a means for testing and verifying their scientific understanding of physical systems. As well, they allow explorations in a world free from physical constraints. A digital waveguide structure is presented which implements a generalized air column, or resonator, model for wind instrument sound synthesis. This system has a physical inspiration and interpretation, a ‘‘blowed string,’’ but is an otherwise impossible reality. The structure produces harmonic resonant modes at integer multiples of a fundamental, with controls to vary harmonic content. It is useful for simulating both cylindrical and conical air columns of such instruments as clarinets, saxophones, flutes, oboes, and trumpets. Further, this structure robustly interconnects with several different non-linear ‘‘reed’’ models to produce a rich variety of wind instrument sounds. The result is a highly efficient computational algorithm that can be used to perform real-time sound synthesis on consumer-grade computers. [Work supported by the Canadian Foundation for Innovation.]

Electric Field Induced Instability and Pattern Formation in Thin Liquid Films

Electrostatic field induced instability, morphology, and patterning of a thin liquid film confined between two electrodes with an air gap are studied on the basis of nonlinear 3D simulations, both for spatially homogeneous and heterogeneous fields. In addition to the spinodal flow resulting from the variation of field because of local thickness changes, a heterogeneous imposed field also moves the liquid from the regions of low field to high field, thus allowing a more precise control of pattern. Hexagonal packing of liquid columns is observed for a spatially homogeneous electric field, which is in accord with the e-field experiments on thin polymer films (Schaffer et al. Nature 2000, 403, 874). For a large liquid volume fraction in the gap, varphi > or = 0.75, the coalescence of columns causes a phase inversion, leading to the formation of air columns or cylindrical holes trapped in the liquid matrix (air-in-liquid dispersion). Locally ordered aligned patterns are formed by imposing a spatial variation of the electrostatic field by using a topographically patterned electrode. For example, multiple rows/lines of liquid columns are formed near the edge of a step-like heterogeneity of the electrode and annular rings of ordered columns or concentric ripples are formed around a heterogeneous circular patch. Simulations predict that the electrode pattern is replicated in the film only when the pattern periodicity, L(p), exceeds the instability length scale on the basis of the minimum interelectrode separation distance, L(p) > or = lambda(m)-d(min). Thus, the formation of secondary structures can be suppressed by employing an electrode with deep grooves and stronger field gradients, which produces almost ideal templating. The number density of the electric field induced patterns can be altered by tuning the mean film thickness (or the volume fraction of liquid in the gap), periodicity and depth (amplitude) of the grooves on the top electrode, and the applied voltage. The implications are in electrostatic lithography, pattern replication in soft materials, and the design and interpretation of thin film experiments involving electric fields.

Biophysical Model of Intertidal Beach Crab Burrowing:Application and Significance

The biophysical principles and mechanisms involved in intertidal beach-crab burrowing have been studied. These answer some important and fundamental questions, such as how and what basic burrow patterns evolve in dynamic environmental conditions through a delicate balance struck between physical and biological (ethological) processes, and how does a burrow form faithfully record its environmental history in a sedimentary sequence? The study is primarily based on field and experimental data collected on the amphibious brachynuran crab family Ocypodidae (four species of Ocypodeand one species of Ilyoplax) from modern intertidal beach sectors on the Bay of Bengal coast, India. The model introduces a new concept of crab burrow cycle that includes three phases and involves three genetic categories of burrow forms—occupied, abandoned, and collapsed. The first phase (subaerial) begins with the excavation of simple (I or J types) occupied burrow populations and terminates with the development of plugged burrow apertures and sub-surface trapped air-column systems. Pressure equilibrium is reached between the burrow-base capillary water, air columns and sediment plugs. Formation of an air column is a mechanical means of supporting hollow burrow from collapse and creating an underwater quasi-terrestrial condition of living. The second phase (subaqueous) starts with tidal inundation and results in the final burrow architecture (Y, U, multibranched Y, and multiform U). The continued effects of external dynamic pressure fields on the plugs increases the internal air-column pressure causing pressure disequilibrium and lowering of capillary water levels unfavorable to the crabs for gill respiration. The burrower neutralizes the extra pressure to achieve previous pressure equilibrium and capillary water levels by excavating secondary branch(es) advantageously on the landward side of the main shaft and dumping the materials at the burrow-base. This mechanism, besides adding morphological complexities, ensures continued pressure equilibrium, the failure of which in any stage results in burrow collapse. The third phase (subaerial) creates a permanent pressure imbalance as the tidal water quickly recedes and protects the burrower inside as the air column bursts to set the crab free to start another burrow cycle afresh. The model has application potential in varied post-Jurassic coastal intertidal environmental settings occupied by quasiterrestrial crabs. It provides insight into various aspects of ichnology (taxonomy and recognition of ancient crab burrows; characterization and variability of the Psilonichnusichnofacies and intertidal ichnocoenoses; burrowing life habits of crabs and modalities of burrow preservation), environment (influence of bathymetry, tide and wave action, substrate properties, storm-induced episodic erosion and deposition on burrow architecture; environmental zonation of burrows; paleotidal range and marine transgression-regression events) and geomorphology (recognition of shoreline features). Being the first biophysical model of intertidal crab burrows, it contributes original data to the theoretical background of ichnology.

Calculating the Eigenfrequency of Rotating Acoustic Annulus Inside Labyrinth Seals of Turbomachines

This brief note describes a method for calculating the eigenfrequencies of a rotating acoustic air column inside labyrinth seals in turbomachinery. The method is applied to nonrotating air columns as well as to rotating air columns considering a body fixed and a spatial fixed coordinate system.

Solar Radiation Budget from the MRI Radiometers for Clear and Cloudy Air Columns within ARESE II

Abstract As an international collaborative research activity within the Japanese Cloud-Climate Study (JACCS) program, the authors participated in the second Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE II) using the Meteorological Research Institute (MRI) radiometers. This paper describes results of ARESE II, as well as specifications and calibration of the MRI radiometers. The solar radiation budget for 2 days of typical clear sky (27 February and 20 March 2000) and overcast sky (3 and 21 March 2000) has been analyzed using spatially collocated, total-band solar irradiances measured by the MRI pyranometers (Kipp & Zonen CM21). These were installed on a Twin Otter aircraft, and deployed at the ARM Southern Great Planes Central Facility site. On average, the clear-sky and overcast-sky air columns between the surface and the Twin Otter flight level of 7 km absorbed about 13% ± 2% and 20% ± 3%, respectively, of the total-band solar radiation incident on the column top. The measured solar radiation budgets agree well with those computed for models of clear and cloudy atmospheres. The present results indicate no evidence of anomalous solar absorption for either the clear- or cloudy-sky cases. It is suggested that about half of the observed absorption enhancement of 7% for the overcast-sky cases could be caused by the presence of larger water vapor, compared with the clear-sky cases, and that the other half could be caused by increased absorption within and above the rather low cloud layers.

35GHZ Patch Antenna Array Based on the Electromagnetic Band?Gap Structure

The electromagnetic band‐gap (EBG) structure, also called photonic band‐gap structure, consisted by triangular arrays of air columns on the dielectric structure is designed and studied by using the FDTD method. According to the simulated and measured results, the EBG structure effectively suppressing surface wave for TE and TM modes is designed. The optimized EBG structure is presented.The proposed EBG structure is applied to the four‐element microstrip patch array antenna. As results of simulation and measurements, the impedance bandwidth and the gain of proposed EBG patch array antenna are improved.

Experimental study of the gravity effect on the distribution of refrigerant flow in a multi-pass condenser

Gravity in multi-pass condensers affects the refrigerant flow rate distribution, owing to the gravitational pressure drop that occurs mainly in the U-bend tubes in fin and tube condensers with horizontal tubes. This effect was studied using an experimental approach. A condenser with two ‘nU’ circuits was selected, and the temperature variation of the refrigerant side was measured and compared along each circuit. The critical air velocity, which indicated the initiation of the gravity effect, was found for a given refrigerant flow rate. As the air velocity increased beyond the critical air velocity, the gravity effect (or mal-distribution of the refrigerant flow) developed further. Similarly, the critical refrigerant flow rate was also determined for a given air velocity. As the refrigerant flow rate decreased below the critical refrigerant flow rate, the gravity effect also developed further. The gravity-affected region was shown in the table with rows of air velocities and columns of refrigerant flow rates, and expressed using a single parameter for a given refrigerant flow circuit.

Female call preferences in tree-hole frogs: why are there so many unattractive males?

In tree-hole frogs, Metaphrynella sundana, the fundamental call frequency varies widely between males. In field playback experiments, females strongly preferred calls from the lower range of frequencies found in the population. There was no correlation, however, between male size and call frequency, as is normally the case for anurans, so large males were not necessarily more attractive to females. Presence or absence of upper harmonics in the call had no effect on female choice. Tree holes with shallow air columns were more often used by calling frogs, and were presumably more common, than deep holes. Since male M. sundana actively exploit the resonant properties of tree holes for mate attraction, and high frequencies match comparatively shallow holes, the benefits of attaining acoustic matching probably select for high-frequency calls. In addition, males with high-frequency calls may be heard from a greater distance in the vicinity of torrent streams. Since the level of such noise in the forest varies in time and space, different frequencies may prove optimal in different contexts, thereby preserving the observed variation within the population. Having an ‘unattractive’ high-frequency call should be potentially beneficial only when calling males do not congregate, a condition that our data suggest is fulfilled in this system.

Calculation of impulse responses with a cellular automata algorithm

The air columns in musical instruments usually have a predominant dimension and thus are very often modeled as 1D systems where uniparametric waves propagate. Different algorithms can be found in the literature to simulate this propagation. The more widely used are finite difference schemes and delay lines. A finite difference scheme (FD) is a numerical integration of a differential formulation (the wave equation), while delay lines (DL) use analytical exact solutions of the wave equation over finite lengths. A new and different approach is that of a cellular automaton (CA) scheme. The underlying philosophy is opposite those of FD and DL, as the starting point is not the wave equation. In a CA approach, the phenomenon to be studied is reduced to a few simple physical laws that are applied to a set of cells representing the physical system (in the present case, the propagation medium). In this paper, a CA will be proposed to obtain the impulse response of different bore geometries. The results will be compared to those obtained with other algorithms.

Fundamentals of sound with applications to speech and hearing

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Jet-based Photonic Crystals for Terahertz Technology – A Need for Higher Resolution

ABSTRACTTwo-dimensional hexagonal photonic crystals of air columns in a wax substrate were fabricated by jet-based methods. By modifying the structure of the photonic crystals (PC), electromagnetic waves can be controlled, enabling the design of novel devices for waveguides, filters, and couplers. The jet-based processing is a solid freeforming method that can fabricate complex 2D or 3D photonic structures quickly and easily as compared to micro-machining and lithographic methods. The resolution of our 3D Systems ThermoJet® solider object printer is 300 × 400 × 600 dpi (XYZ) with the layer thickness of 0.042 mm. The wax used is a thermopolymer build material, similar to production investment casting wax material. The periodicity of the lattice of our 2D PC structures was designed to form bandstop filters in the 0.1–0.3 THz range. Transmission spectra of the structures were measured with a Bruker IFS 66v FT-IR interferometer. Photonic band gaps were observed at 0.17 THz and 0.23 THz along the Γ-M direction for both the TM and TE polarized incident beam for the PC structures with lattice constant of 0.787 mm and 0.586 mm, respectively. The location and width of the bandgaps agree with theoretical calculation based on a block-iterative frequency-domain method for Maxwell's equations in a planewave basis. To the best of our knowledge, this is the first time a jet-based process has been used successfully to fabricate PC structures at these high frequencies. However, the ThermoJet® printer as well as other current available solid freeforming technologies lack the resolution to PC structures operating in the terahertz regime. To extend this technology to terahertz applications, such as terahertz lasers, waveguides, and imaging system, a 10-fold increase in machine resolution is required to produce finer structures. Engineering materials with lower electromagnetic absorption and higher dielectric constants at terahertz frequencies are also critical to developing THz photonic bandgap technology.

A simple model of the origin and transport of 222 Rn and 210 Pb in the atmosphere

This paper presents a simple model of the transport of the natural radionuclides 222Rn and 210Pb through the atmosphere in which it is assumed that the vertical distribution in a column of air moving horizontally over the earth's surface is largely controlled by turbulent diffusion. The inert gas 222Rn (half-life 3.82 days), a product of 226Ra decay in soils, enters the atmosphere by diffusion from land surfaces where it decays via various short-lived radionuclides to 210Pb and thence via 210Po and 210Bi to the stable isotope 206Pb. Individual 210Pb atoms in the atmosphere become readily attached to airborne particles and within the troposphere are removed both by wet and dry deposition. Although these processes are extremely complex and result in rapid fluctuations in concentrations and fluxes on short time-scales, the constancy of the mean annual 210Pb flux at particular sites suggests that the short-term fluctuations have little significance on these longer time-scales. The model is used to capture the main features of the global transport of 222Rn and 210Pb at northern mid-latitudes where, on annual time-scales, the transport of air is dominated by a global west-east circulation. Air columns travelling over a large ocean will have very low concentrations when they arrive at the western margin of a large land mass. 222Rn concentrations will then build up as the column moves over the land mass, declining again as the column passes over the eastern seaboard. The diffusion equation is solved to give a dynamic picture of the evolution of the 222Rn concentration versus altitude profile assuming a constant flux from the land surface, and zero flux from the oceans. Over the land surface the profile develops relatively quickly and, in the steady state, follows an exponential relation. These profiles represent a source term for the production 210Pb. Within the troposphere, the 210Pb transport equation also includes a sink term representing loss from the aerosol phase by incorporation in water droplets and rain. By fitting the theoretical profiles to measured data from continental USA and Eurasia, it is estimated that the mean 222Rn exhalation rate from northern land masses is 1570 Bq m - 2 y - 1 (0.87 atoms cm - 2 s - 1) and that the mean vertical diffusivity in the atmosphere is 2.7km2 d - 1 (3.1 x 105 cm2 s - 1). Further, the mean 210Pb residence time in the troposphere is estimated to be about 5 days. Results of the calculations show that over large continental land masses the 210Pb inventory is predominantly in the troposphere, but that as the air column moves out over the sea, the stratospheric inventory continues to increase over large distances and is an important factor controlling long-range transport. By mid-ocean it may contain 80% or more of the remaining inventory, and becomes the main source of 210Pb to the troposphere. Comparisons with the measured atmospheric fluxes across the USA and Eurasia are used to calculate the mean west-east global circulation velocity at mid latitudes, and intercontinental transport rates for 210Pb. The results suggest that as much as 40% of 210Pb fallout on the western seaboard of Europe is of North American origin, and that \(\sim \)30% of fallout on the western seaboard of the USA is of Eurasian origin.