bluuebunny/crossref_metadata_2025_split huggingface dataset:
An enhanced model for the modulated reflectance spectra of vertical‐cavity surface‐emitting laser structures
Authors: Cripps S. A. , Hosea T. J. C. 
Published: February 2007

AbstractModulation spectroscopy has proved to be unique in being able to probe the vital active‐layer quantum well (QW) transitions in vertical‐cavity surface‐emitting lasers (VCSELs). We have been characterising an all‐AlGaAs‐based VCSEL structure designed to operate at high temperatures, using photo‐modulated reflectance (PR) as a function of temperature up to 180 °C. We previously developed an empirical model to fit VCSEL PR spectra when the features from the QW transitions and the Fabry–Perot cavity mode (CM) overlap and interact, and this fitting function has, so far, proved to be very successful. However, the present VCSEL has a particularly high finesse cavity and our established model is unable to fit the unusually detailed interacting CM/QW PR spectra. Here, we perform new reflectivity calculations for this VCSEL structure. These provide new insight into the Seraphin coefficients of the CM, and their inter‐relationship, when they lie near the QW transitions. This deepens our understanding of VCSEL PR lineshapes, yielding an enhanced model which we successfully fit to the temperature‐dependent PR spectra of the present VCSEL. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the deepness of contactless electroreflectance probing in semiconductor structures
Authors: Motyka M. , Kudrawiec R. , Misiewicz J. 
Published: February 2007

AbstractThe deepness of contactless electroreflectance (CER) probing (dCER) is investigated in this work. CER spectra have been measured for various semiconductor structures and compared with photoreflectance (PR) spectra. It has been shown that most of CER signal origins from the sample region which is very close to the sample surface. It has been found that the dCER is much smaller that the penetration depth of the probing beam (dλ ∼ 0.5–1 μm), dCER ! dλ. In addition, for samples containing a sheet of carriers (a two dimensional electron gas at an interface or a delta‐doped monolayer) the dCER is reduced to the distance from the sample surface to the carrier sheet (e.g. 20 nm). This phenomenon can be called as screening of electromodulation in CER technique. No screening of electromodulation mechanism is observed in PR technique. In addition, the deepness of PR probing (dPR) is much bigger than the dCER. It means that deeper parts of semiconductor structures (e.g. the buffer layer) can be probed in PR whereas these parts are usually not probed in CER. A different electromodulation mechanism in PR and CER techniques is the origin of various probing deepness for these two techniques. In the case of CER technique, the surface electric field is mainly modulated whereas both surface and interface electric fields can be effectively modulated in the PR technique. In the case of PR technique, the electron–hole pairs can be generated far to the sample surface and hence these carriers can modulate band bending at interfaces which are far to the sample surface, e.g. at the epilayer/buffer interface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mountain‐gap winds; a study of surface wind at Gibraltar
Authors: Scorer R. S. 
Published: February 2007

AbstractThe surface wind in the Straits of Gibraltar is determined by the interplay of its inclination to blow towards the end where surface pressure is lowest when the air is stable and its tendency to follow the upper wind if convection is active. The importance of cold pools of air lying below mountain‐top level is discussed and various kinds of wind reversal are described.
Some observations of air flow over the sea
Authors: Hay J. S. 
Published: February 2007

AbstractWind speeds were measured over the sea at five heights up to 8 m. Though the fetch was limited, the wind profiles obtained are considered representative of flow over the sea.The wind speed varies logarithmically with height when the temperature gradient is small. Assuming that laboratory laws of flow are applicable, values of the roughness parameter z0 are deduced. It is found that z0 increases from about 0·02 cm in a wind of 5 m/sec to 0·25 cm at 9 m/sec. The relationship between wind speed and z0 however is not unique for the state of the surface is determined by other factors beside wind speed. In inversion conditions the wind‐speed distribution departs from the logarithmic form a few metres above the surface. The results obtained are compared with those of some other workers.Bi‐directional vanes were used to obtain gustiness measurements at the site. While the vertical gustiness is found to be of similar magnitude to that over land surfaces of comparable roughness, the cross‐wind gustiness appears to be greater over the sea.
Further studies in world climate
Authors: Simpson George C. 
Published: February 2007

AbstractThe effects of changes in solar radiation on the climate of the earth are discussed with special reference to glacial phases in high latitudes and to pluvial periods which are common to the Earth as a whole. The relationship between the radiation and the glacial and pluvial phases is expressed in tabular form. Adopting the chronology of the glacial and pluvial phases during the Pleistocene Period, as published by K. P. Oakley, a curve of solar radiation is constructed using only the glacial phases; this proves to be a periodic curve with three complete oscillations between the begining of the Pleistocene Period and the present day. Using this radiation curve the periods of heavy and light precipitation are determined and compared with the pluvial periods. Three periods of heavy precipitation during the Pleistocene are indicated and a correlation of these with the observed pluvial periods in Africa is suggested.
The collision efficiency of small drops
Authors: Hocking L. M. 
Published: February 2007

AbstractThe forces on two moving spheres are found from the Stokes equations of motion, full allowance being made for the mutual interference of the flows round the spheres, and the relative trajectories when they are falling under gravity are calculated so that the collision efficiency E can be found. The values of E are determined for drops of radius up to 30 μ colliding with droplets of any smaller size. The results differ widely from those found by Pearcey and Hill (1957) and it is suggested that the reason for the discrepancy is that the motion of the spheres when they are close together is of great importance in determining E. The results also differ from those found by Schotland and Kaplin (1956). Their experiments did not model the ratio of the density of the spheres to that of the medium through which they are falling and since it is shown that this factor is of importance, their results are not considered applicable to water drops falling in air.
Observations from aircraft of temperatures and humidities near stratocumulus clouds
Authors: James D. G. 
Published: February 2007

AbstractObservations from aircraft of the Meteorological Research Flight flying near stratocumulus clouds showed steep inversions and hydrolapses directly above the tops of the clouds. Turbulence was encountered below and in the clouds and up to 300 ft above the cloud top. Above this level no turbulence was encountered. Analysis of the heat and water‐vapour budgets of the cloud and air below suggests that the cloud and the profiles of temperature and humidity can only be maintained if there is large‐scale subsidence. The effects of subsidence, outgoing radiation and turbulent transfer are all comparable.
Wind stress on a water surface: Measurements at low wind speeds with the aid of surface films
Authors: Vines R. G. 
Published: February 2007

AbstractA monolayer on a water surface is affected by the action of wind, and retracts until the wind drag is counter‐balanced by the opposing surface pressure gradient. This effect has been used to determine the shearing stress on water at low wind speeds. Estimates of the drag coefficient have been obtained.
The small‐ion concentration and space charge near the ground
Authors: Adkins C. J. 
Published: February 2007

AbstractA series of detailed measurements was made of the concentration of small ions near the ground. It was found that for values of the atmospheric potential gradient exceeding some ± 500 v m−1 the electrode effect in the small ions was readily observable, and that when rain fell in a large electric field, there took place a large production of ions of sign opposite to that of the field. The latter effect was examined in some laboratory experiments which showed that the release of charge in the form of ions was associated with splashing. The mechanism by which the ions were produced was found and a determination made of the dependence of the charge released by individual drops on the field, drop mass and drop speed at impact.To determine the importance of the charge released by splashing at the ground, another series of observations was made including the measurement of space charge. It was found that in fine weather the field was sometimes controlled by clouds of charge near the ground. In disturbed weather natural point discharge gave rise to considerable values of the space charge, and in comparison with these, the charges produced by the splashing of rain only became important during heavy rain.
Temperature fluctuations and trends over the earth
Authors: Callendar G. S. 
Published: February 2007

AbstractThe annual temperature deviations at over 400 meteorological stations are combined on a regional basis to give the integrated fluctuations over large areas and zones. These are shown in graphical form, and it is concluded that a solar or atmospheric dust hypothesis is necessary to explain the world‐wide fluctuations of a few years duration. An important change in the relationships of the zonal fluctuations has occurred since 1920. The overall temperature trends found from the data are considered in relation to the homogeneity of recording, and also to the evidence of glacial recession in different zones. It is concluded that the rising trend, shown by the instruments during recent decades, is significant from the Arctic to about 45°S lat., but quite small in most regions below 35°N. and not yet apparent in some. It is thought that the regional and zonal distribution of recent climatic trends is incompatible with the hypothesis of increased solar heating as the cause. On the other hand, the major features of this distribution are not incompatible with the hypothesis of increased carbon dioxide radiation, if the rate of atmospheric mixing between the hemispheres is a matter of decades rather than years.
The radiation balance of bare soil and vegetation
Authors: Monteith J. L. , Szeicz G. 
Published: February 2007

AbstractIncoming short‐wave radiation S, reflected short‐wave radiation α S and net radiation R were measured over bare soil and crops from 1957 to 1959, and net long‐wave radiation (L) was deduced from

For grass, α increased from 0·23 at solar elevation 60° to 0·28 at 20° with daily mean 0·26. For bare soil, the corresponding increase was from 0·16 to 0·19 with mean 0·17. In mid‐June, L for bare soil decreased from – 0·1 cal cm−2 min−1 during the night to – 0·4 cal cm−2 min−1 in the early afternoon. For long grass, in August, the corresponding change was from – 0·05 to – 0·22 cal cm−2 min−1. Under clear skies the incoming long‐wave component varied much less than the outgoing component, and net flux L was closely related to surface temperature.With a heating coefficient β = – dL/dR, the observed linear dependence of R on S in the absence of cloud may be expressed as

Where, formally, R = L0 when S = 0. For grass, sugar beet and potatoes, β lay between 0·15 and 0·22 with a variation which may depend on wind speed rather than on crop. The value for dry bare soil was higher (0·41) because there was greater surface heating.Measurements under clear skies and over grass at Cambridge and Kew agree well with Rothamsted values (β = 0·22, L0 = – 5·9 cal cm−2 hr−1). Over Nebraska prairie, β = 0·25, L0 = – 4·5 cal cm−2 hr−1 from selected observations during Projects Great Plains and Prairie grass.
Electrification produced by the rupture of large water drops in an electric field
Authors: Matthews J. H. , Mason B. J. 
Published: February 2007

AbstractThe deformation and break‐up of large freely‐falling water drops, of diameter greater than 15 mm, has been studied by high‐speed photography. In confirmation of observations by earlier workers, the drops become distorted and flattened and, if their velocity relative to the air exceeds a critical value, they blow up to form a large bag supported on a toroidal ring of liquid. Eventually the bag bursts to produce a fine spray of droplets and the toroid breaks up into several large drops. the critical conditions for break up and the rate of expansion of the bag are studied experimentally and the observations are compared with available theory. When the drops break in a vertical electric field, a charge of one sign is induced on the bag and a charge of opposite sign appears on the toroidal ring. Disintegration of the drop causes a separation of charge. the charges carried by the large fragments of drops breaking in fields of 30 V/cm, 300 V/cm and 1,500 V/cm have been measured by an induction method. In a downwardly‐directed field of 300 V/cm, such as may be provided by the primary charging mechanism of a thunderstorm, the fragments carry charges of order 1 e.s.u./g., i.e., two orders of magnitude greater than those measured by Simpson in the absence of a field, and may therefore contribute significantly to the formation of the subsidiary positive charge that sometimes appears in the bases of thunderclouds.
Rainfall and moon phase
Authors: O'mahony G. 
Published: February 2007

AbstractDaily rainfalls of an inch or more for 100 years at one station have been classified according to the phase of the moon with which they occurred. An apparent significant correlation between two 50‐year smoothed sub‐series is found to have been induced by the filtering process of taking running sums. When the effects of the ensuing serial dependence are eliminated, the results are not indicative of a significant overall relationship between the series of rainfalls and moon phase.In both sub‐series, a persistent trough in frequency count of heavy rainfalls about full moon has been investigated further by examining data from three additional stations in different rainfall regimes. The trough was evident in the data from each of the frequency counts of rainfalls near full moon. However, when each series was viewed in isolation, statistical tests revealed that the observed numbers of rainfall occurrences were not significantly different from the expectations based on the assumption that the series were random. The consistency of the trough rather than its amplitude suggested a weak non‐random influence might be present.An additional product of the statistical analysis of the single station data is an indication of the differing filtering effects of the smoothing process as the number of elements in the running sums is increased progressively from one to ten.
Critical layer instability in baroclinic flows
Authors: Bretherton F. P. 
Published: February 2007

AbstractIt is shown that for all inviscid, adiabatic, quasi‐geostrophic motions in a Boussinesq liquid or in a compressible atmosphere, subject to the usual boundary conditions, the integral over the fluid of the northward eddy flux of potential vorticity vanishes, provided a generalized interpretation of potential vorticity is adopted near rigid horizontal boundaries. For an infinitesimal disturbance in a normal mode to a general zonal flow, the presence of a critical layer within the fluid excludes the existence of stable modes, except in exceptional circumstances. A stable, or slowly growing mode, is associated with a down‐gradient flux of potential vorticity near the critical layer, which does not vanish as the growth rate tends to zero, and can only be balanced by the general growth in the disturbance.
Transvaal hailstones
Authors: Carte A. E. , Kidder R. E. 
Published: February 2007

AbstractCharacteristics of a large number of hailstones which have fallen in the Pretoria‐Johannesburg area in the past five years have been summarized under the following headings: size distributions, shapes, growth centres, layers and internal structures.Most hailstorms did not produce large hailstones. Only 4 per cent of over 5,000 hail reports were of stones exceeding 3 cm diameter. With increase in size of the largest hailstones, broader size spectra tended to occur and the modal size of hailstones reported as being most common increased. Spheroidal shapes were encountered more often than others in practically all size groups but their relative frequency diminished with size. A high proportion of the hailstones had opaque growth centres. An investigation of layering revealed that many hailstones have more changes of opacity than of crystal structure. Two, three and four crystal layers were often found in medium, large and extra‐large stones. A simple up‐and‐down trajectory can account for the structure of many stones. Slushy ice may form on large hailstones but it is not an essential growth stage.
Albedos of natural surfaces in Barbados
Authors: Chia Lin‐Sien 
Published: February 2007

AbstractIn Barbados, albedo values for bare soil surfaces varied according to colour, the moisture condition of the surface layer, the presence of limestone concretions and the roughness of the surface. The albedo of sugar cane increased with crop height until the leaves reached complete cover. The albedo of vegetation, but not bare soil, depended on the zenith angle of the sun. The albedo of vegetation and cane trash was larger under clear skies than under overcast. The estimated mean albedo of Barbados was 16·5 per cent.
The effects of winds on acoustic‐gravity waves from explosions in the atmosphere
Authors: Mackinnon R. F. 
Published: February 2007

AbstractPressure fluctuations due to an explosive point‐source in an atmosphere containing steady winds may be described in terms of a fundamental mode of long period followed by modes of the acoustic and gravity type, with relative amplitudes, group speeds and periods dependent upon winds. Far‐field ground‐pressure contributions of various modes are presented for a particular model atmosphere. Inverse dispersion and the Airy phase are found to be important features of the dispersion. A study is made of barograms in the light of new results obtained. Some previously unexplained features of barograms are seen to be attributable to winds.
Experimental and field studies of precipitation particles formed by the freezing of supercooled water
Authors: Brownscombe J. L. , Hallett J. 
Published: February 2007

AbstractDrops which freeze in isolation or by accretion on an ice particle are found to be single or polycrystalline depending on the drop supercooling and the particle temperature. Subsequent growth from the vapour depends on the number and orientation of these crystals. The airflow around the particle, characterized by the Reynolds Number, Re, is important in the initial accretion process. The particle falls steadily for small Re, but oscillates and eventually tumbles as Re approaches 500. The deformation of accreted drops depends both on the dendrite freezing velocity through the liquid compared with the impact velocity and on the drop impact kinetic energy compared with its surface energy. Viscous dissipation becomes important as the deformation, defined as the ratio of the base radius of the deformed drop to its height, exceeds 10. Deformations of about 10 have been measured for 40 μ radius supercooled drops impacting on an ice surface at 13.5 m sec−1. The heat economy of a freezing accreted drop is dominated by a collecting particle which is large compared with the drop, when complete freezing takes place from the contact area outwards. Symmetrical freezing, from top and bottom of the drop, only occurs for surface temperature approaching 0°C, or when the drop accretes on a narrow spike, when there is a possibility of drop shatter and separation of electric charge. Drops accreting on particles growing spongily may interact first with a liquid layer whose thickness may be of the same order as the drop size and produce splash droplets even at large supercoolings for critical values of layer thickness. Opacity is related to bubble size. Opaque ice forms when the particle is growing spongily or dry, with transparent ice forming when the growth is just wet. Just spongy growth at low temperatures is associated with small crystals and opaque ice.
A comparison between predictions of dimensional analysis for the constant‐flux layer and observations in unstable conditions
Authors: Swinbank W. C. 
Published: February 2007

AbstractA number of relationships are derived by dimensional arguments which connect the vertical fluxes of heat and horizontal momentum in the ‘constant‐flux’ layer with the other relevant variables. Observations, all made in unstable conditions, are used to test the correctness of the predicted relationships and to determine their functional form. In particular, it is found that δθ/δz = −1.42θu (gz2)−1 (z/L)0.56 and KH/KM = 2·7 (z/L)1/4.The analysis emphasises the intimate connection between the transfers of the two quantities.
The structure of rainbands within a mid‐latitude depression
Authors: Browning K. A. , Hardman M. E. , Harrold T. W. , Pardoe C. W. 
Published: February 2007

AbstractA case study is presented of a winter depression over the British Isles in which extensive banded structure was observed within precipitation ahead of the surface warm front. Measurements of the mesoscale airflow and precipitation structure of the rainbands were made using a variety of radar techniques together with multiple radiosonde and aircraft observations. The measurements were made over the sea to avoid the confusing effects of topography. The dominant rainbands were oriented parallel to the surface cold front and were typically 100 km wide. They moved with a velocity faster than the underlying warm front. For the most part the bands were characterized by clusters of weak small‐scale convective cells due to the release of potential instability produced where tongues of relatively dry air of low θw in the middle troposphere overran low‐level moist air undergoing slantwise ascent above the warm frontal zone. Although there was the usual large‐scale, and thermally‐direct, circulation associated with the active warm front, the air which ascended as small‐scale convection within the rainbands entered a region of weak cold frontal baroclinicity, whereupon it participated in a thermally direct circulation of its own. This led to each rainband having a rearward‐sloping anvil cloud canopy characterized by ascending air with colder drier air descending beneath. Precipitation falling from the canopy evaporated within the underlying drier air thereby probably intensifying the descending branch of the circulation. Very large ageostrophic winds were measured in association with these circulations.The important ingredient responsible for the convective nature of the rainbands appears to have been the incursion of tongues of relatively dry air of low θw in the middle troposphere above the moist warm‐sector air in a region where the resulting instability could be realized by large‐scale ascent. Although the potential instability was very weak in the present case, the origin of the rainbands appears to have been similar to that of pre‐frontal squall lines. The intensity of the convection within rainbands depends on the stability but the very existence of any precipitation in the first place depends on other dynamical factors leading to widespread ascent.