Air Pressure Variations Research Articles

A coupled three-basin sea level model for the Baltic Sea

Sea level variations in the Baltic Sea on time-scales 2 days and longer are studied using a coupled three-basin quasi-stationary model. The three large sub-basins (Baltic proper, Bothnian Sea and Bothnian Bay) are coupled in series by two short and narrow straits. A third strait connects the Baltic proper with the Kattegat. Currents are forced through the connecting straits by the sea level difference. The mean sea levels in the sub-basins change due to freshwater supply and the water exchanges through the straits. Wind stress and horizontal variations of air pressure and density maintain sea-level slopes in the sub-basins. With the model, 85% of the total variance of the recorded sea levels can be explained. The unexplained variance is partitioned among different period bands, and for periods longer than 2 weeks 20% or less of the variance is unexplained. For shorter periods, 30–60% of the variance is unexplained. The relative importance of different forcings is also investigated. For periods longer than a few months the forcing provided by the sea level variations in the Kattegat is dominating but horizontal variations of air pressure and density also contribute. For short periods (2 days–2 weeks) the wind stress is most important, especially during winter. Estimated barotropic water transports between the subbasins are investigated, and it is found that major Baltic outflows have the same intensity and magnitude as major Baltic inflows.

Changes of the solid geocentre due to seasonal variations of ground water and air pressure: Zhou Xu-hua & Gao Bu-xi Institute of Geopesy and Geophysic, CAS, Wuhan 430077

Changes of the solid geocentre due to seasonal variations of ground water and air pressure: Zhou Xu-hua & Gao Bu-xi Institute of Geopesy and Geophysic, CAS, Wuhan 430077

Measuring sea ice draft and coverage with moored upward looking sonars

Presented is a method to derive ice draft and coverage from acoustic measurements made with moored Upward Looking Sonars (ULSs), sounding the sea surface remotely from below. The method was developed on the basis of two-year long time series obtained from four locations in the Weddell Sea. It takes into account the variations of sound speed and density that occur between the target and the instrument, the variations of the surface air pressure, and a possible bias of the mean ice draft within the ensonified window, which results from the combined effect of beam spreading and skewed ice distributions; ice and open water are differentiated by their specific echo amplitude signatures. The residual total error in the determined mean ice draft is estimated as 4 cm, compared to an initial error of almost 90 cm in the original uncorrected data. Suggestions for further instrumental improvements are made.

Mean sea‐level topography in the Baltic sea determined by oceanographic methods

The long‐term mean sea level in the Baltic Sea is investigated using the coupled three‐basin model constructed by Carlsson (1997). The model is forced by the observed sea level in the Kattegat, the freshwater supply, horizontal air pressure and density gradients, and the wind stress. Both the seasonal variations and the slope of the mean sea level are investigated and compared with the results of another oceanographic model (Lisitzin, 1962) and a geodetic model (Ekman & Mäkinen, 1996). In the geodetic model an unofficial height system, NH60, is used, and one part of the investigation is to find out whether this height system is useful for oceanographers. The estimated mean sea level difference between the northern and the southern parts of the Baltic Sea are: 17.1 cm (the present model), 26 cm (Lisitzin's model), and 18.3 cm (the geodetic model). It is concluded that the mean sea level difference between the northern and southern parts of the Baltic Sea is due mainly to horizontal variations of density and air pressure, and that the height system NH60 is suitable for oceanographie applications.

A novel design of solid state fermenter and its evaluation for cellulase production by Trichoderma viride SL-1

A novel design of a large scale solid state fermenter, designated as PPSSF--Periodic Pressure Solid State Fermenter-- was constructed. Due to the respiration created by periodical variations of air pressure, air was uptaken / expelled from the fermenting mass and heat moved from the fermenter easily. It is possible to operate the unit at different capacities simply by adding or removing the bins. The results of its evaluation for enzyme formation by Trichoderma viride SL-1 indicated that a 2-3 fold increased cellulase production can be obtained in this system.

A new conceptual model to compute the drying front in wheat

Small bins are used to conduct cooling and drying experiments on wheat, barley and peas. Seven conceptual models were tried. They consider different ways in which water may leave the grain. A new equation has been developed to take the hysteresis phenomenon into account. The loss of energy through the bin walls, the variation of air pressure in the bin and the grain respiration have been considered. All these concepts can be modelled with a single parameter to give a simple and accurate model which does not need a powerful computer.

History of the ear speculum. Images from the history of otorhinolaryngology, highlighted by instruments from the collection of the German Medical History Museum in Ingolstadt

BACKGROUND. Inspection of or interventions in the external ear canal and the nostrils pose similar technical problems. This is the reason why early instruments devised for otoscopy and rhinoscopy were based on an identical principle. They were shaped like a pair of tongs, comparable to nasal specula of today. A similar type of instrument had been developed earlier by barber surgeons for inspecting narrow wound cavities. TONG-SHAPED SPECULA. The first description and illustration of an aural and nasal speculum was provided by Guy de Chauliac in Montpellier, France in 1363. Sophisticated models were presented by Fabricius Hildanus in Germany in 1646 and J.J. Perret in Paris in 1772, who offered them in his illustrated catalogue of surgical instruments at fixed prices. W. Kramer (1836) in Berlin improved this tong-shaped instrument and devised the ear speculum named after him that was generally favored during the first half of the 19th century. Further variations of this type were presented by Lincke and Schmalz (1846) in Germany. FUNNEL-SHAPED SPECULA. Ignaz Gruber in Vienna in 1838 devised the first tunnel-shaped ear specula made of metal. They had a simple conical shape, were not divided into separate jaws, and could not be spread. Gruber himself did not publish his invention, but he demonstrated his ear specula to W. R. Wilde from Dublin, who had paid a visit to his office in Vienna. Wilde reported on this in 1844, and subsequently systematically refined Gruber's specula. A. v. Tröltsch from Würzburg (Germany) had seen these instruments at Wilde's office and it was Wilde himself and v. Tröltsch who helped this type of ear speculum to gain acceptance on an international scale. A different type of bottle-shaped ear speculum was first used by Schmalz (1846) and Erhard (1859) in Germany, but it was only developed into a commercially available instrument by Josef Gruber in Vienna in 1870. The ear specula most in use today were first presented by A. Hartmann in Berlin in 1881. SUPPLEMENTARY INVENTIONS. An important supplementary invention was the pneumatic ear speculum by E. Siegle in Stuttgart (Germany) in 1864. It permitted not only inspecting the tympanic membrane but also examining its compliance and response to variations in air pressure in the ear canal. The importance of this instrument was recognized at once and has remained undisputed to this day. J. Bruton, an English military surgeon, presented his otoscope in 1862. It was the first device to incorporate interchangeable ear specula, illumination by a perforated mirror, and a magnifying lens into one handy instrument. It is the precursor of the modern diagnostic sets comprised of a battery-handle, various specula, and accessories for otoscopy, rhinoscopy, and ophthalmoscopy which started to come into use in the late twenties of this century. This historical development of the ear specula is described and illustrated in detail.

Influence of air and fuel flows on gas turbine sprays at high pressures

A single-component phase-Doppler particle analyzer (PDPA) is used to measure local variations in dropsize distributions and drop velocities in the near-nozzle region of a practical, contraswirling, prefilming airblast atomizer. The technique of laser sheet imaging is used to obtain global patterns of the spray. Measurements are taken using air pressure drops across the atomizer of 5% and 10% and ambient air pressures of 1,6 and 12 bar. The liquid employed is aviation kerosine at flow rates of up to 75 g/s. The results show that the previously observed effect of an increase in ambient air pressure in widening the spray cone angle is not a pressure effect per se but is due to the increase in fuel flow rate that accompanies an increase in air pressure at constant air-fuel ratio (AFR). For any given air pressure, it is found that spray cone angle increases gradually and continously with increase in fuel flow rate. If the fuel flow rate is allowed to remain constant, the effect of an increase in air pressure is to reduce slightly the spray cone angle. In general, spray volume increases with fuel flow rate and/or reductions in air pressure. Variations in air pressure at a constant AFR, which corresponds to the normal practical situation, have little effect on either spray volume or the distribution of drop sizes in the spray.

Main characteristics of the long-term sea level variability in the Baltic sea

The horizontal variation of the sea level variability for periods between a few days and several years has been investigated using daily means of sea level records obtained along the coasts of Sweden in the period 1977–1987. Motions on these periods are forced, either “externally” by the varying sea level outside the mouth and the freshwater supply, or “internally” by varying air pressure, wind and density in the Baltic Sea. Free, natural oscillations (seiches) of the Baltic Sea are generally considered to have periods from two days and shorter, and may thus contribute some variance to the daily means of the sea level and by that to the studied motions. The externally and internally forced contributions to the sea level records in the Baltic Sea are separated using a model for the externally forced contribution. The externally forced sea level variations explain most of the variance for periods longer than one month, and between 50 and 80% of the total sea level variance in the Baltic Sea with maximum in the central parts (the Stockholm area). It is also found that for periods shorter than about one month the internally forced oscillations are kinematically similar to those occurring in the first natural seiche mode in a closed Baltic Sea, with maximal variability in the extreme north and south, and minimum in the Stockholm area. For longer periods, however, the internally forced oscillations are kinematically similar to those occurring in an open bay with increasing amplitudes from the mouth and inwards. The shift in the kinematics of the internally forced oscillations is explained by the limited transport capacity of the straits in the mouth for “high frequency” motion. DOI: 10.1034/j.1600-0870.1996.t01-4-00006.x

Helmholtz resonator in the induction system of a spark-ignition engine with production versus prototype manifolds

Following an earlier work [A. Selamet and J. M. Novak, J. Acoust. Soc. Am. 97, 3393 (1995)], the present study investigates the performance of a Helmholtz resonator installed in the induction system of a Ford 3.0 ℓ V6 Vulcan engine in a dynamometer test facility. Earlier findings with the production manifold are compared with the current results obtained with a modified prototype manifold in an attempt to determine the extent of multidimensional wave dynamics. The induction system is instrumented with fast-response piezoresistive transducers to capture the temporal and the spatial variation of air pressure. Measured insertion loss characteristics of the silencer are then discussed in comparison with the predictions from a nonlinear computational fluid dynamics approach in the time domain.

From Chandler wobble to free oscillations: comparison of cryogenic gravimeters and other instruments in a wide period range

The cryogenic gravimeter was developed to overcome the mechanical deficiencies of spring gravimeters. The stability of the instrument permits the study of long-term gravity variations for the first time. Short-term, especially periodical gravity variations have been well observed with spring gravimeters. This investigation tries to determine up to what level and frequency the various types of instrument have equivalent quality. Side-by-side runs of two cryogenic instruments, and comparisons with relative spring gravimeters and long-period seismometers, should help to answer this question. From the intercomparison of two cryogenic gravimeters in Bad Homburg, Germany (TT40 and TT60) and in Miami, USA (TT40 and UCSD SG B) one can see that, in general, the gravity signals coincide within several nanometres per second squared, but also intervals are noted where the differences are 10–30 nm s −2 over a timespan of 1–3 months. Usually, known instrumental problems are the cause for these discrepancies. Data analysis as well as comparisons with absolute gravity measurements in parallel demonstrate that the drift of the meters is monotonic and in general has exponential characteristics. This allows investigations in the long-period tide band as well as in the range of long-term gravity variations, e.g. the gravitational effects of polar motion, water table and air pressure variations. At the other end of the spectrum—in the period range from 15 min to 1 day—a side-by-side run of the cryogenic gravimeter SG-102 and the spring gravimeter LCR-ET-19 in the Black Forest Observatory in Schiltach, Germany, shows that the noise spectrum of the spring gravimeter is slightly lower than that of the cryogenic one. Analysis of the free oscillations of the Earth from several large earthquakes shows that this spring gravimeter and modern seismometers are at least of equal quality. Data sets recorded with cryogenic gravimeters open the possibility of investigating gravity variations in a wide frequency range. However, especially for investigations in the high-frequency band (1 c day −1 and above), one should also make use of well-maintained conventional spring gravimeters and possibly modern force-balance seismometers, which may have at least the same or better quality.

Levator Veli Palatini Muscle Activity in Relation to Intraoral Air Pressure Variation in Cleft Palate Subjects

Levator Veli Palatini Muscle Activity in Relation to Intraoral Air Pressure Variation in Cleft Palate Subjects

Levator Veli Palatini Muscle Activity in Relation to Intraoral Air Pressure Variation in Cleft Palate Subjects

A comparison of the ranges of levator veli palatini EMG activity for speech versus a nonspeech task for subjects with cleft palate was the focus of this study. EMG values are also compared with subjects without cleft palate obtained in a previous study. Hooked-wire electrodes were inserted into the levator muscle of five adult subjects with cleft palate exhibiting mild hypernasality. Intraoral air pressure was measured concurrently. A blowing task was used to determine the subject's operating range for the levator muscle. Both the nonspeech and speech tasks were designed to sample the widest possible ranges of levator EMG activity. It was found that the subjects with cleft palate used a relatively high activation level for the levator muscle during speech, in relation to their total activation range, compared with the subjects without cleft palate. Implications are discussed in relation to possible anatomic and physiologic differences for cleft palate subjects compared to normal.

Pressure equalised rainscreen joint modelling with the numerical model PERAM

A process is developed to forecast cladding joint air pressure variations which affect rainscreen joint weathertightness in buildings, without recourse to experimental testing. A numerical model, PERAM, is presented to solve equations governing the pressure response of air within the cavity of a rainscreened joint in a building cladding when subjected to an external sinusoidal air pressure variation. A measure of the pressure equalisation performance of the joint as a percentage (the PEP) can then be calculated from the model waveforms derived, as a determination of the degree of weathertightness of the joint system. The PEPs calculated by PERAM are shown to fit the experimental data by incorporating two physically well-defined floating parameters into PERAM. This suggests that the model can be applied at the design stage of detailing weathertight pressure equalised cladding systems.

Articulatory activity and aerodynamic variation during voiceless consonant production

The production of voiceless consonants is associated with changes in oral air pressure which reflect the time course and coordination of the requisite laryngeal and supralaryngeal articulations. The present experiments were conducted in order to characterize more precisely the relationships among glottal and supraglottal activities and the resulting aerodynamic changes in the vocal tract. In the first experiment, simultaneous recordings were made of glottal articulation (obtained via transillumination), two-dimensional lip and jaw movements, and air pressure variation during the production of voiceless labial consonants. In the second experiment, two-dimensional motion of the jaw and multiple points on the tongue were obtained along with air pressure during the production of voiceless lingual consonants. Analysis focused on the time-varying changes in the pressure waveform and the accompanying articulatory motion. The data suggest that the overall time course of pressure variation depends largely on the timing of the laryngeal devoicing gesture. However, details in the pressure waveforms showed a close correspondence to the time course of supraglottal articulations. Taken together, results suggest that laryngeal and supralaryngeal timing is highly constrained, and that different articulators contribute uniquely to producing pressure variations within the vocal tract. [Work supported by NIH.]

Levator Veli Palatini Muscle Activity in Relation to Intraoral Air Pressure Variation

The purpose of this investigation was to study the operating range of the levator veli palatini muscle for a nonspeech task (blowing) and to determine where in that range levator activity for speech lies. Ten adult subjects without speech or velopharyngeal abnormalities participated. Levator EMG activity for speech occurred in the lower region of the total range for blowing. In two subsequent experiments involving a subset of 4 subjects, it was found that overall effort may have had a small effect on levator activity apart from its role in velopharyngeal closure for aerodynamic purposes. The results of the main experiment are discussed in relation to the concept of threshold of fatigue as it may influence velopharyngeal control mechanisms.

Air Pulse Quantification of Supraglottic and Pharyngeal Sensation: A New Technique

There are no published studies evaluating the sensory capacity of the region innervated by the superior laryngeal nerve. A normal sensory capacity is important in this area, since hypesthesia or anesthesia of the pharynx and supraglottic larynx may result in dysphagia and aspiration. This often occurs after stroke or after ablative surgery of the pharynx and larynx. Evaluating the efficacy of restorative procedures for supraglottic and pharyngeal sensation is dependent on defining and quantifying the sensory deficit. We have developed a new, noninvasive method to measure sensation in the pharynx and supraglottic larynx. A puff of air--of precisely controlled duration and pressure--was delivered via a flexible telescope to the anterior wall of the pyriform sinus. Surface sensibility was determined according to the psychophysical method of limits by varying air pressure while holding puff duration constant. We conducted 204 trials in 20 healthy adults. The average sensory discrimination threshold was 2.09 +/- 0.15 mm Hg. An intraclass correlation revealed excellent consistency (R = .80). There was no statistically significant difference between the right and left sides. Brief air pulse stimulation is an easy, relatively safe, and reliable method of determining supraglottic and pharyngeal sensory discrimination thresholds.

Observations of the 18.6-year cycle of air pressure and a theoretical model to explain certain aspects of this signal

Evidence from barometric data in Japan, USSR, southern Europe, southern Africa, and South America shows that air pressure variations with period near 18.6-years can attain amplitudes as high as 0.9 mb, and are identified as induced by the luni-solar constituent tide M{sub n} (M for moon and n for nodal). Luni-solar waveforms commonly exhibit modulation effects due to the superposition of a longer period component with 180{degrees} changes in phase. Thus, the waveform amplitudes can be highly nonstationary. Pressure gradients at this period over subcontinental distances show that the amplitudes imply non equilibrium conditions. A theoretical coupling mechanism between E-W and N-S wind systems and the Coriolis force is envoked to explain the sub-continental extent and the, sometimes abrupt, amplitude changes of the pressure systems over small distances. 47 refs., 10 figs., 2 tabs.

Levator veli palatini muscle activity in relation to intranasal air pressure variation.

Continuous positive airway pressure (CPAP) therapy can be used to reduce hypernasality by elevating the air pressure in the nasal cavities during speech. The purpose of this study was to determine whether increased intranasal air pressure loads the major muscle of velopharyngeal closure, the levator veli palatini. Nine subjects, four with cleft palate and five without cleft palate, were studied. Electromyographic activity was measured from the levator veli palatini muscle with several levels of air pressure delivered to the nasal cavities using a commercially available CPAP instrument. It was found that levator veli palatini activity was significantly greater for the positive air pressure conditions than for the atmospheric pressure conditions for both subject groups. This indicates that the levator veli palatini muscle acts against the resistive load produced by the increased intranasal air pressure. The results support the use of CPAP therapy as a method of resistance exercise for strengthening velopharyngeal closure muscles.

The effect of systematic change in middle ear pressure on transitorily evoked otoacoustic emissions--a pressure chamber study

Otoacoustic emission power spectrum and amplitude are influenced by the middle ear transmission mechanism. In this study, the influence of progressive increase in atmospheric pressure on the frequency and amplitude of transiently evoked otoacoustic emissions (TEOAEs) was determined in normally hearing humans. For testing, subjects were seated in a pressure chamber. Transiently evoked otoacoustic emissions were tested in 20 ears of 20 subjects using of 80 microseconds unfiltered click and tone bursts duration at 0.5, 1, 2, 3, and 4 kHz presented at 40 dBnHL. Ambient air pressure was increased from 0 kPa up to 8 kPa in 2-kPa steps. In spite of large interindividual differences, the results demonstrate that the changes that occur in TEOAEs with variations in ambient air pressure are frequency specific. Amplitude and reproducibility of high-frequency TEOAEs are less influenced by middle ear pressure changes than are the amplitude and reproducibility of low- and middle-frequency TEOAEs. Results have implications for clinical and research applications of TEOAE measurements in that middle-ear and inner-ear effects on OAEs can be differentiated.