Characteristic Height Research Articles

Solar radiation‐induced changes in ionospheric height and the Schumann resonance waveguide on different timescales

This study draws together the available observations in the Schumann resonance frequency range to examine the general issue of sensitivity of ionospheric height variations to changes in ionizing radiation from the Sun on different timescales. Ionospheric height can be formally defined, and two characteristic heights are recognized in the Schumann resonance frequency range. In general, order of magnitude changes in radiation are needed to cause relative changes in ionospheric height as large as 10%, as is the case on both the diurnal and 11‐year timescales. Changes in EUV radiation are probably insufficiently strong to account for either the 27‐day or the 11‐year variation in ionospheric height. More ionization‐effective X radiation is needed, but much smaller height changes are expected on the solar rotation timescale because the variations in X radiation on this timescale are only tens of percent and not orders of magnitude. The annual variation in radiation from the Sun is only 7%, with an expected height variation less than 100 m, and this remains to be verified by observations. The general insensitivity of the Schumann resonance cavity to changes in ionizing radiation lends stability to the medium that is valuable toward quantifying absolute changes in the global lightning activity on various timescales within the cavity.

Reanalysis of Breaking Wave Statistics for Engineering Applications

A review is made on the statistical features of breaking waves in the nearshore waters. The bed slope effect in the breaker index formula by Goda (1973) is reduced in a newly revised formula. The breaker index of regular waves should be treated as a statistical variable with the coefficient of variation ranging from 5% to 14%. The significant wave height rarely exceeds 0.6 times the local water depth. The wave nonlinearity as expressed in the form of skewness and the ratios of one-third and one-tenth highest wave height to the energy-based significant wave height increases toward the middle of surf zone, but it is destroyed by wave breaking process and disappears near the shoreline. Changes of characteristic wave heights across the surf zone are also exhibited.

Mathematical Justification of a Shallow Water Model

The shallow water equations are widely used to model the flow of a thin layer of fluid submitted to gravity forces. They are usually formally derived from the full incompressible Navier-Stokes equations with free surface under the modeling hypothesis that the pressure is hydrostatic, the flow is laminar, gradually varied and the characteristic fluid height is small relative to the characteristics flow length. This paper deals with the mathematical justification of such asymptotic process assuming a non zero surface tension coefficient and some constraints on the data. We also discuss relation between lubrication models and shallow water systems with no surface tension coefficient necessity.

Characteristic Height Growth Pattern in Patients with Pseudohypoparathyroidism: Comparison between Type 1a and Type 1b.

Pseudohypoparathyroidism (PHP) is a metabolic disorder characterized by organ resistance to the action of parathyroid hormone. PHP type 1 is subclassified into two apparent disorders, type 1a (PHP1a) and type 1b (PHP1b). Patients with PHP1a show Albright hereditary osteodystrophy including short stature. Patients with PHP1b have no such skeletal defects, however, literature regarding the growth of PHP1b is not currently available. We evaluated growth charts of PHP patients, including four PHP1a patients and six PHP1b patients. Growth patterns were different between PHP type 1a and 1b. Adult height was abnormally low in all PHP1a patients. The growth pattern of PHP1a was characterized by mild growth impairment in the prepubertal period, a blunted growth spurt and premature cessation of the growth spurt. The adult height of male PHP1b was slightly lower than average. An early growth spurt was observed only in male patients with PHP1b and it may reduce the adult height of male patients with PHP1b. This warrants further investigation into the growth and pubertal development of PHP1b patients.

Roughness effects in turbulent pipe flow

Mean flow measurements are presented for fully developed turbulent pipe flow over a Reynolds number range of $57\,{\times}\,10^3$ to $21\,{\times}\,10^6$ where the flow exhibits hydraulically smooth, transitionally rough, and fully rough behaviours. The surface of the pipe was prepared with a honing tool, typical of many engineering applications, achieving a ratio of characteristic roughness height to pipe diameter of 1 : 17000. Results for the friction factor show that in the transitionally rough regime this surface follows a Nikuradse (1933)-type inflectional relationship rather than the monotonic Colebrook (1939) relationship used in the Moody diagram. This result supports previous suggestions that the Moody diagram in the transitional regime must be used with caution. Outer scaling of the mean velocity data shows excellent collapse and strong evidence for Townsend's outer layer similarity hypothesis for rough-walled flows. Finally, the pipe exhibited smooth behaviour for scaled roughness height $k_s^+ \,{\le}\, 3.5$, which supports the suggestion by Zagarola & Smits (1998) that their pipe was hydraulically smooth for $Re_D\,\,{\leq}\, 24\,{\times}\,10^6$.

Formation of GaAs nanowhisker arrays by magnetron sputtering deposition

The possibility is demonstrated of fabricating arrays of cone-shaped GaAs nanowhiskers with a surface number density of up to 109 cm-2, a characteristic height ranging from 300 to 10000 nm, and a transverse size of approximately 200 nm at the base and from 200 to 10 nm or smaller at the top. The characteristic height of GaAs nanowhiskers varies in direct proportion to the effective thickness of the deposited material layer and in inverse proportion to the transverse nanowhisker size at the top. The growth of GaAs nanowhiskers is studied as a function of the deposition rate, the temperature, and the crystallographic orientation of the substrate. From an analysis of the obtained dependences of the nanowhisker size on these parameters, it is concluded that GaAs nanowhiskers are formed through the diffusion mechanism.

Three-Dimensional Shear in Granular Flow

The evolution of granular shear flow is investigated as a function of height in a split-bottom Couette cell. Using particle tracking, magnetic-resonance imaging, and large-scale simulations, we find a transition in the nature of the shear as a characteristic height H* is exceeded. Below H* there is a central stationary core; above H* we observe the onset of additional axial shear associated with torsional failure. Radial and axial shear profiles are qualitatively different: the radial extent is wide and increases with height, while the axial width remains narrow and fixed.

三重県吉崎海岸の長期的海岸線変化

Long-term shoreline changes of the Yoshizaki coast located around a mouth of a tributary of the Suzuka River flowing into Ise Bay were investigated on the basis of the comparison of past geographical maps and aerial photographs. The characteristic height of beach changes was evaluated to be 4m from the bathymetric survey data. Longshore sand transport rate of 2×104m3/yr was obtained from the shoreline changes multiplied by this characteristic height of beach changes in the natural condition. In recent years, this longshore sand transport of the coast was totally exhausted and a long shoreline was separated into several pocket beaches.

FLOW-INDUCED FORCES ACTING ON A REVETMENT BLOCK WITH LARGE HEIGHT RELATIVE TO WATERDEPTH OF OPEN-CHANNEL FLOWS

The forces acting on a revetment block used for an element of roughness of the bed in open channel flows were measured by using a three components load cell. The ratio Hp/ ha of the water depth above the blokes Hp to the height of the revetment block ha was 2.1. Turbulent structures of the flow above the revetment blokes were also measured by using a Laser Doppler anemometer (LDA). The friction velocities near the boundary between the top part of blocks and flow were evaluated from the Reynolds stress measured by LDA . These values are nearly equal to the values evaluated from the energy gradient of flow, but less than the values estimated from the drag forces acting on a revetment block. The ratio ks/kc of the equivalent roughness ks for the block to the characteristic height kc of the block is about 1.6.

Electrical conduction in light-emitting organic polymer Schottky diodes

Schottky metal-polymer diodes, fabricated with a light-emitting polyvinylene polymer, have been studied for their electrical conduction characteristics. Radiative recombination localized at electron injection sites is seen. Device degradation at high drive voltages was observed, together with a self-passivation mechanism due to the formation of metal compounds at the periphery of electrical contacts. Reverse conduction characteristic and Schottky barrier height indicate a diffuse and extended depletion region in these devices.

Behaviour of torsional Alfven waves and field line resonance on rotating magnetars

Torsional Alfven waves are likely excited with bursts in rotating magnetars. These waves are probably propagated through corotating atmospheres toward a vacuum exterior. We have studied the physical effects of the azimuthal wavenumber and the characteristic height of the plasma medium on wave transmission. In this work, explicit calculations were carried out based on the three-layered cylindrical model. We found that the coupling strength between the internal shear and the external Alfven modes is drastically enhanced, when resonance occurs in the corotating plasma cavity. The spatial structure of the electromagnetic fields in the resonance cavity is also investigated when Alfven waves exhibit resonance.

Specific kinetic energy concept for regular waves

The global kinetic energy of regular waves is usually characterized through the characteristic parameters wave height and wave length without reference to its vertical distribution. In this paper a new methodology to evaluate the vertical energy distribution from the velocity components is presented. The methodology could also be an alternative for irregular wave fields, with several wave lengths, to which the traditional method in the evaluation of the energy per unit area or wave length is not applicable. The squared velocity components functions for each water level can be theoretical or determined from long enough measurements time series. The average of those functions at one specific depth level over the length of interest gives the mean horizontal and vertical specific kinetic energy at that level. The global kinetic energy corresponds to the total specific kinetic energy integration in depth.

Numerical simulation of three-dimensional flow and analysis of filling process in compression resin transfer moulding

In compression resin transfer moulding (CRTM), resin flows inside a mould filled with fibrous reinforcement as a result of resin injection and mould compression. This process facilitates the resin flow through the fibrous reinforcement particularly for high fiber content parts. This paper presents the numerical simulation of filling process of CRTM in full three-dimensional domain. A mathematical model of three-dimensional resin flow inside the CRTM mould is presented. An effective elastic modulus is introduced for multi-layer preforms connecting the mould closing speed to deformation rate of individual layers. Control volume/finite element method (CV/FEM) is used and the numerical algorithm developed to progress the flow front is based on a quasi-steady state approach, previously employed for resin transfer moulding (RTM), which is here modified for a deformable medium. Element characteristic height (ECH) and element characteristic surface area (ECSA) are introduced to take into account irregular elements in the simulation which are often observed in complex mould cavity. The numerical algorithm presented is coded and the resulting computer code is used to predict the necessary filling parameters such as flow progression, pressure distribution and mould clamping force. The validity of the numerical algorithm is verified by comparison with analytical solutions for simple moulds. Computer code developed is also used to analyse the CRTM process with different filling modes by providing various numerical examples. The results show the effectiveness of the numerical simulation in predicting the CRTM process.

Silicon columnar microstructures induced by an SF6/O2 plasma

An inductively coupled SF6/O2 plasma is used to form a columnar microstructure (CMS) on silicon samples cooled at very low temperature (∼ −100 °C). The formation of this CMS is studied as a function of bias voltage, temperature, RF power and gas pressure. The characteristic mean diameter and mean height of the microstructure are evaluated by image processing tools from SEM micrographs. A crystallographic effect is also observed at very low temperature, which induces a needle-shaped structure. A physical mechanism is proposed to explain the formation of this CMS.

Voltage-Height Spectroscopy in the Ex Situ Configuration of a Scanning Tunneling Microscope

Basic regularities of electrochemical processes in the gap of an ex situ scanning tunneling microscope in conditions of condensation of air moisture at the sample surface are considered on a qualitative level. A layer of condensed moisture is viewed as an electrolyte in a two-electrode cell. The depolarizers present in this layer may experience electrochemical conversions on the tip and in an area of the sample surface near the tip. As a result, the recorded “tunneling” current includes electrochemical constituents. Depending on the electrochemical processes in the gap, various dependences of the tip-sample distance on the current and applied voltage can be expected. For preliminary diagnostics of processes in the gap it is suggested to use voltage-height spectra, whose shape and characteristic heights are sensitive to the nature and location of redox active species. Experimental data for various films on conducting supports (quasi-two-dimensional adsorbed layers of hemin and peroxidase, electrodeposited nonstoichiometric tungsten oxides, doped tin dioxide, solid electrolyte with ionic conduction) are presented as an examples.

Dropsonde Observations in Low-Level Jets over the Northeastern Pacific Ocean from CALJET-1998 and PACJET-2001: Mean Vertical-Profile and Atmospheric-River Characteristics

Dropsonde observations are used to document the mean vertical profiles of kinematic and thermodynamic conditions in the pre-cold-frontal low-level-jet (LLJ) region of extratropical cyclones over the eastern Pacific Ocean. This is the region within storms that is responsible not only for the majority of heavy rainfall induced by orography when such storms strike the coast, but also for almost all meridional water vapor transport at midlatitudes. The data were collected from NOAA’s P-3 aircraft in 10 storms during the California Land-falling Jets Experiment (CALJET) of 1998 and in 7 storms during the Pacific Land-falling Jets Experiment (PACJET) of 2001. The mean position of the dropsondes was 500 km offshore, well upstream of orographic influences. The availability of data from two winters that were characterized by very different synoptic regimes and by differing phases of ENSO—that is, El Niño in 1998 and La Niña in 2001—allowed examination of interannual variability. The composite pre-cold-frontal profiles reveal a well-defined LLJ at 1.0-km altitude with a wind speed of 23.4 m s−1 and a wind direction of 216.7°, as well as vertical shear characteristic of warm advection. The composite thermodynamic conditions were also documented, with special attention given to moist static stability due to the nearly saturated conditions that were prevalent. Although the dry static stability indicated very stable conditions (4.5 K km−1), the moist static stability was approximately zero up to 2.8-km altitude. Although the composite winds, temperatures, and water vapor mixing ratios in 2001 differed markedly from 1998, the moist static stability remained near zero from the surface up to 2.8–3.0-km altitude for both seasons. Hence, orographic precipitation enhancement is favored in this sector of the storm, regardless of the phase of ENSO. The dropsonde data were also used to characterize the depth and strength of atmospheric rivers, which are responsible for most of the meridional water vapor transport at midlatitudes. The vertically integrated along-river water vapor fluxes averaged 525 × 105 kg s−1 (assuming a 100-km-wide swath), while the meridional and zonal components were 387 × 105 kg s−1 and 302 × 105 kg s−1, respectively. Although the composite meridional transport in 2001 was less than half that in 1998 (230 × 105 kg s−1 versus 497 × 105 kg s−1), the characteristic scale height of the meridional water vapor transport remained constant; that is, 75% of the transport occurred below 2.25-km altitude.

Observed electric fields associated with lightning initiation

In situ electric field (E) measurements and inferred lightning initiation locations of three cloud‐to‐ground flashes are used to identify a thunderstorm region in which the preflash E exceeded the threshold for runaway breakdown. The maximum measured E in the region was 186 kV m−1 at 5.77 km altitude, which for runaway electrons is equivalent to 370 kV m−1 at sea level; this E value is ∼130% of the estimated threshold for an avalanche of runaway electrons. In addition, the volume where E exceeded the runaway threshold was estimated to be 1–4 km3, with a vertical depth of about 1000 m. At least within part of this volume the characteristic scale height for exponential growth of runaway electrons was 100 m or less. Thus for these three flashes the electric field conditions necessary for runaway breakdown existed, and runaway breakdown could have initiated the flashes.

GaAs Nanowhisker Arrays Grown by Magnetron Sputter Deposition

Arrays of cone-shaped GaAs nanowhiskers (NWs) with a surface number density of up to 109 cm−2, a height ranging from 300 to 10000 nm, and a diameter of about 200 nm at the base and from 200 to 10 nm and below at the top have been obtained by means of magnetron sputtering. The characteristic NW height is proportional to the effective thickness of a deposited material layer and inversely proportional to the transverse whisker size at the top. An analysis of the NW parameters confirms the validity of the Dubrovskii-Sibirev diffusion mechanism of NW formation.

On thez-distribution of pulsars

The z-distribution of pulsars in the vicinity of the Sun is investigated using data from the ATNF pulsar catalogue and the recent model for the Galactic distribution of free electrons (NE2001). It is found that the z-distribution of pulsars with mJy kpc2 is exponential with a characteristic scale height of about 350 pc. Evidence of pulsar oscillations in the direction perpendicular to the Galactic plane is presented.

平行等深線海岸における航走波の変形

One of the important characteristics in the propagation of ship waves is to reduce the wave height with the increasing distance from the sailing line. In addition, the transformation due to wave shoaling and refraction must be considered in case that ship waves propagate on a sloping coast. In the present study, a method to estimate the maximum wave height has been proposed on the basis of results of numerical simulation for ship waves that are generated by a ferry sailing along the coast with straight, parallel depth contour lines. The proposed formula of the maximum wave height is the product of the relative shoaling coefficient, the relative refraction coefficient, the relative damping coefficient and the characteristic wave height defined at an appropriate distance from the sailing line. The coefficients are calculated by using the finite amplitude wave theory for shoaling and Snell's law for refraction. The damping coefficient is calculated so as to be proportional to -1/5th power of the distance from the sailing line. The maximum wave height estimated by the proposed method agrees well with the one by numerical simulations.