bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gamma Knife surgery for basal ganglia and thalamic arteriovenous malformations
Authors: Cheng Ching-Hsiao , Crowley R. Webster , Yen Chun-Po , Schlesinger David , Shaffrey Mark E. , Sheehan Jason P. 
Published: January 2012

Object
Gamma Knife surgery (GKS) has emerged as the treatment of choice for small- to medium-sized cerebral arteriovenous malformations (AVMs) in deep locations. The present study aims to investigate the outcomes of GKS for AVMs in the basal ganglia and thalamus.

Methods
Between 1989 and 2007, 85 patients with AVMs in the basal ganglia and 97 in the thalamus underwent GKS and were followed up for more than 2 years. The nidus volumes ranged from 0.1 to 29.4 cm3 (mean 3.4 cm3). The mean margin dose at the initial GKS was 21.3 Gy (range 10–28 Gy). Thirty-six patients underwent repeat GKS for residual AVMs at a median 4 years after initial GKS. The mean margin dose at repeat GKS was 21.1 Gy (range 7.5–27 Gy).

Results
Following a single GKS, total obliteration of the nidus was confirmed on angiograms in 91 patients (50%). In 12 patients (6.6%) a subtotal obliteration was achieved. No flow voids were observed on MR imaging in 14 patients (7.7%). Following single or repeat GKS, total obliteration was angiographically confirmed in 106 patients (58.2%) and subtotal obliteration in 8 patients (4.4%). No flow voids on MR imaging were observed in 18 patients (9.9%). The overall obliteration rates following one or multiple GKSs based on MR imaging or angiography was 68%. A small nidus volume, high margin dose, low number of isocenters, and no history of embolization were significantly associated with an increased rate of obliteration. Twenty-one patients experienced 25 episodes of hemorrhage in 850 risk-years following GKS, yielding an annual hemorrhage rate of 2.9%. Four patients died in this series: 2 due to complications of hemorrhage and 2 due to unrelated diseases. Permanent neurological deficits caused by radiation were noted in 9 patients (4.9%).

Conclusions
Gamma Knife surgery offers a reasonable chance of obliterating basal ganglia and thalamic AVMs and does so with a low risk of complications. It is an optimal treatment option in patients for whom the anticipated risk of microsurgery is too high.
A Case Study of an Easterly Jet Stream in the Tropics
Authors: Alaka M. A. 
Published: January 2012

An easterly current at 200 mb over the Southern Bahamas and Florida is identified as a jet stream which had originated in middle latitudes and had travelled along the eastern periphery of the dynamic anticyclone situated over the South Eastern United States. The properties of this current are studied and compared with those associated with middle latitudes jet streams. It is found that although this current is comparatively weak (core velocity about 70 kts), horizontal and vertical wind shears near its axis are comparable with those observed near the usually much stronger middle latitudes jet streams.
The mechanism responsible for the concentration of the kinetic energy in this narrow current is shown to be independent of any temperature contrast between two air masses in the lower and middle troposphere. The jet is further shown to be maintained by pressure heads and the continuous production and destruction of kinetic energy involved in its maintenance and motion occur as a result of accelerations in more or less laminar flow rather than by lateral or frictional stresses. Finally, the observed weather distribution is found to be influenced by the resonance and interference of the upper jet stream with waves in the lower easterlies.
The Strong Index Change Period from January 1 to January 7, 1956
Authors: Defant Fr. , Taba H. 
Published: January 2012

In continuation of a recent paper (Defant, Taba, 1957) a seven days period (January 1–7, 1956) has been investigated on a hemispheric scale. During this period strong world wide changes in the circulation type occurred. Such a circulation change from a meridional into a zonal type* has been studied for the first time by means of hemispheric tropopause maps and by using a special technique of dividing the total available material of atmospheric sound ings into three different groups as described in the previous paper. The following points summarize the results:
1. The hemispheric tropopause maps are most suitable for obtaining a clear picture of three dimensional structure of the atmosphere. The distribution of cold and warm air masses can easily be seen. Breaks in tropopause heights give an immediate impression of the location and the form of the two principal westwind maxima of the westerlies (polarfront jet and subtropical jet). The concentrations in the temperature field of the tropopause level are a further guide for the location of the main wind belts. This temperature field makes it possible to picture the meandering structure of the wind belts and shows the interaction of tropical and mid-latitude circulation. Clear distinction has to be made between subtropical and polar jet.
2. By the use of this method strong northward displacements of the tropical atmosphere have been shown. At the same time a strong meandering behaviour of the subtropical jet appears. These tropical impulses play a dominating role in producing pronounced changes in mid-latitude circulation and for the generation of large blocking anticyclones.
3. During the seven days period the character of soundings in the three selected groups (north of the polar jet, between the two jets and south of the subtropical jet) remained nearly unchanged.
4. Whenever the tropical atmosphere shifted northward stations inside deep troughs having a polar isothermal structure in the stratosphere showed a strong cooling in the higher stratosphere and at the end of the period even the polar stations showed the same feature. It is thought that this cooling is mainly due to advection from the tropical regions, but outgoing radiation and vertical motion may contribute.
5. A possible cyclic change and three dimensional interaction of the three different parts of the atmosphere is outlined at the end of the paper.
* meridional and zonal with respect to the form of polarfront jet.
Comparative Studies of 500 mb Barotropic Forecasts Based on Different Analyses
Authors: Berggren Roy 
Published: January 2012

Some barotropic 500 mb forecasts are compared in the following manners:
1 comparison of the differences between forecasts made from analyses with identical boundary regions but different inner parts
2 comparison of forecasts made from two independent analyses based on identical material, and
3 comparison between forecasts based on two analyses with identical inner region but different boundary regions.
The result of a computation of the standard deviation of the vorticity and the Jacobian J (η, φ) is given and discussed, the deviation being due entirely to the personal factor in upper air analysis.
Effects of the Solar Flares of 7 July 1958: Observed at Kiruna Geophysical Observatory, Sweden
Authors: Hultqvist Bengt , Aarons Jules , Ortner Johannes 
Published: January 2012

The very strong effects in the auroral zone of the solar flares of 7 July 1958 as observed at Kiruna Geophysical Observatory by means of magnetometers, an ionospheric sounder, a cosmic noise absorption receiver (riometer), oblique auroral reflection receivers, transpolar communications receivers, and cosmic ray telescopes are reported and discussed. Several remarkable features of the terrestrial disturbances were observed:

Extremely strong absorption became apparent a few hours after the solar flare. In spite of a linearly increasing absorption during the first seven hours after the flare no change in height or critical frequency of the F2 layer was noted during this period.
The SIDs reported by Pacific Observatories at the time of the flares were not observed at Kiruna although Kiruna was on the sunlit side of the earth.
A magnetic storm and a large decrease in the counting rate of the meson component of cosmic radiation appeared simultaneously 31 hours after the flare.
The maximum absorption at 27.6 Mc recorded during this period surmounted 20 decibels.
Measurements of the Air Concentration of Gross Fission Product Radioactivity during the IGY July 1957–December 1958
Authors: Lockhart, Jr. L. B. , Patterson, Jr. R. L. 
Published: January 2012

Measurements of the gross fission product radioactivity in the air at 21 sites along the 80th meridian 2nd 4 sites in the North Pacific area are reported for the period July 1957–December 1958. The activity levels at the various sites are related both to the stratospheric deposition of nuclear debris and to the direct introduction of radioactive material into the troposphere upwind of the collecting sites.
Radioactive debris injected into the troposphere at any particular site spreads rather rapidly throughout the same hemisphere but rarely crosses the equator in any quantity. An exception to this occurred during the Hardtack series in the Pacific when massive quantities of activity were transported to the Southern Hemisphere by winds in the upper troposphere.
It is again shown that periods of heavy rainfall, such as occur during the rainy season in Panama, cause a general decrease in the concentration of fission products in the air.
Measurements of the Vertical Distribution of Atmospheric Chloride Particles
Authors: Durbin W. G. , White G. D. 
Published: January 2012

An account is given of about 250 impactions made on ten flights to sample chloride particles. The particles are captured on small perspex slides coated with a gelatin-silver nitrate solution and become manifest as circular discs. The calibration of the method is described and the lower limit of detection is found to be about 10-13 gm. NaCl.
The results show that, in the main, chloride particles originate from the sea surface but there is a possibility that the land or the coast produce some in the range 10-11 to 10-13 g. Particle concentrations are found up to about 2,000 litre-1 and total chloride contents up to 230 μg m-3. The variations of these particle concentrations with height, wind speed, state of sea and the three-day history of the sampled air are discussed.
Data are also presented on the concentrations of dust particles which were inadvertently sampled simultaneously with the chloride particles.
Numerical Tests of a Method for Dynamic Analysis in Regions of Poor Data Coverage
Authors: Richardson Norman N. 
Published: January 2012

This paper describes a series of numerical experiments which were done to test a theoretical method for dynamic analysis in regions of poor data coverage. Theoretically, if vorticity were conserved, the exact vorticity field in such a region could be determined by Lagrangian advection of vorticity from areas of known data. The technique was applied to a field of rather dense data where a “hole” was created by withholding all observations within a given area.
The first experiments, assuming the atmosphere to be purely barotropic, resulted in a field within the hole that closely approached, after a reasonable time, the field obtained by a barotropic forecast using all the data. The remaining experiments, under simulated operational conditions, tested the effects of: 1) baroclinic processes, 2) size of hole, 3) frequency of observation, and 4) allowing a single strip of data across the hole. The results were much as predicted by the theory and reasonably accurate analyses were obtained.
Some numerical calculations of the vertical velocity field in hurricanes
Authors: Krishnamurti T. N. 
Published: January 2012

The commonly observed crescent-shaped geometry of the tangential wind field in hurricanes is imposed on the primitive equations of atmospheric motion, and solutions for the vertical velocity field are obtained. It is shown that the numerically computed vertical motion field exhibits a spiral form, very similar to what is observed in radar pictures in individual hurricanes.
Aircraft flight data from the National Hurricane Research Project are utilized to carry out the numerical calculations in several hurricanes over the Atlantic.
An attempt is made to obtain an analytic solution for the same complete system of equations for a generalized Rankine vortex with a prescribed crescent-shaped geometry. It is shown that the analytic solution has an interesting spiral form. This solution for the Rankine vortex is compared with the corresponding finite difference solution to estimate the errors in the finite difference solution.
Dynamic instability in barotropic flow
Authors: Haltiner G. J. , Song Lt. R. T. 
Published: January 2012

The dynamic stability of single-jet and double-jet zonal currents is investigated for several quasi-barotropic models by a finite difference method and by means of finite Fourier series.
The two methods give generally similar results, but some moderate differences occur when the mesh length is decreased or the number of Fourier components is increased. Also the stability characteristics of single-jet and double-jet profiles differ considerably.
The effect of wind on the propagation rate of acoustic-gravity waves
Authors: Clarke R. H. 
Published: January 2012

A method is described for deriving acoustic-gravity wave velocity in the presence of wind shear. It is used to calculate numerical weighting factors for a few special cases of two and three layer model atmospheres. These show that the wind velocity in a cold layer between two warm layers has a predominant positive influence on group velocity, and the wind at higher levels a negative influence, while phase velocity is quite differently affected.
The theory is illustrated by world-wide data relating to the Russian megaton explosion of 30 October 1961, and a study of global winds at the time. It was found possible to account for world-wide variations in wave propagation rate largely by a simple regression on the sine of the explosion longitude, which made possible estimates of effective wind over various ray path lengths. This was found, on the global scale, to be the mean of the wind in the 9-16 km layer, that is, approximately the mean wind in the “sound channel”. Negative weightings at higher levels predicted by the model appear to be incorrect, and due to its inadequacy. The data strongly suggest that the “level of effective mean wind” is approximately that of the tropopause in middle latitudes.
Finite difference approximations for the determination of dynamic instability
Authors: Haltiner G. J. 
Published: January 2012

Approximate forms of the vorticity and thermal equations are linearized and combined to yield a second-order partial differential equation for the amplitude of harmonic perturbations. Finite-difference approximations for the derivatives yield a homogeneous system of algebraic equations; and the condition that its determinants vanish for a non-trivial solution yields the “frequency” equation, which may be solved to give the phase velocities of the harmonic waves. Solutions are obtained for zonal currents in which the wind varies vertically and horizonally and for a variety of conditions with respect to grid distances, latitude and current width. Generally speaking, the computations showed that decreasing the latitude and shear and increasing the static stability were all destabilizing influences, not without some exceptions, however. In addition, very short waves were found to be stable; however, instability was found for very long waves, including a retrogressive unstable mode. Moreover, multiple unstable modes were found for many wavelengths.
Calculations based on actual observations of the jet stream in December show it to be dynamically unstable, both baroclinically and barotropically, with one mode of maximum instability at a wavelength of about 3000 to 4000 km and a secondary maximum at about 10,000 km.
Atmospheric stratification revealed by twilight scattering
Authors: Bigg E. K. 
Published: January 2012

The uses and limitations of the twilight method of detecting aerosol layers are discussed and an experimental modification capable of checking the reliability of the results is described. The data from several sequences of measurements are shown to give average distributions of stratospheric aerosols in good agreement with those determined by direct sampling.
The stratification revealed by the experiments is very variable. Simultaneous observations at different latitudes show that the aerosol distributions often have the same form over distances of 300 km, but that the degree of similarity decreases rapidly with increasing separations. There are preferred heights for layers showing intense scattering, which on the average, slope upwards towards the equator. Some features show a surprisingly high degree of persistence in time and some curious changes in apparent height.
Computations of the eddy heat and density transports across the Gulf Stream
Authors: Oort Abraham H. 
Published: January 2012

Data of the current velocity, temperature and density of the Gulf Stream, collected during 200 crossings of the current in cruises off Onslow Bay, Jacksonville (30° N) and Cape Hatteras, are used to compute the eddy fluxes of heat and density across the mean current. In each cruise an eddy transport of heat is observed, which is directed from the colder coastal water to the Sargasso Sea in the surface layers. The meanders in the stream appear to increase the thermal contrast across the so-called Gulf Stream front and thus violate the ordinary diffusion laws by not transporting heat from the warm to the cold source. The transport of density across the stream is, in general, towards the shore, reflecting mostly the influence of the temperature on the density.
WEBSTER (1961b) has shown in an earlier study that there is a surface flow of kinetic energy and momentum from the meanders to the mean flow of the Gulf Stream. Since the meanders of the scale considered in these studies appear to speed up the Gulf Stream and do not feed upon, but actually build up the thermal contrast near the surface, these eddies must be forced.
More measurements of the kind described in this paper, are needed to verify the observed abnormal heat and density fluxes in the Gulf Stream.
A direct method of stream-function computation
Authors: Endlich R. M. , Mancuso R. L. 
Published: January 2012

An iterative method is described that fits a stream function (Ψ) to wind observations. The technique was designed for use in tropical regions where errors in height data and other difficulties preclude use of the geostrophic or balance equations to obtain y; however, the technique is believed to be sufficiently general to have other applications. Since the calculations may be carried out rapidly by an electronic computer, the technique might serve as a replacement for the laborious streamline-isotach method of tropical analysis.
The equations basic to the computations are given. If the stream function is defined to have the units of height (i.e., meters), it is convenient to use observed heights as the initial-guess field. Several iterations are made until the computed values of Ψ stabilize within a pre-determined limit. Explicit calculations of vorticity and of boundary values of Ψ, as required in a stream function obtained by solution of a Poisson equation, are not needed. Analyses of computed values of Ψ in the Caribbean are compared with independent, subjective analyses of the same data, and show excellent agreement. Autocorrelations show that computed values of stream function were considerably more persistent than height data for the period studied.
On the Fields of Wind and Temperature over Japan and Adjacent Waters during Winter of 1950–1951
Authors: Mohri Keitaro 
Published: January 2012

First, a mean cross section along the meridian 140° E during three months (Dec. 1950–Feb. 1951) is discussed. The main characteristics are:

An extremely strong subtropical jet (75 m sec-1) situated at 33° N near 190 mb;
A semi-stationary sloping surface which divides almost barotropic warm tropical air in the south from more or less baroclinic temperate air situated in the north;
A slight indication of a polar-front jet situated near 230 mb at 41° N; the weak intensity of this jet depends upon the strong variability in position of the polar front.
Much warmer temperature in the upper troposphere to the south, and much colder temperature in the lower troposphere north of the subtropical jet, as compared with mean conditions at 76° E and 80° W.

The computed mean winds at 140° E are combined with the mean isotachs given by Yeh over China, at the 12-km level. Using the acceleration determined from the isotach pattern, the mean angle of cross-contour flow at 200 mb is determined to be about 8° (between longitudes 110° and 140° E), with a mean cross-contour component of 8 in sec–1 toward lower heights, in the center of the mean jet stream.
Second, daily meridional cross sections through Japan are presented for the period 8 to 15 December 1950. These show an extremely strong individual jet stream in which the observed maximum wind speed reached a velocity of more than 110 m sec–1, with near-zero absolute vorticity to the south. An associated nearly-isothermal layer underneath is much deeper (up to 4 and even 6 km) than in other parts of the globe. It is suggested that this unusual depth results from a combination of a stable layer associated with the semi-stationary subtropical jet, and the polar front, when the latter moves southward in east Asia. The behavior of the tropopause in the intermediate atmosphere south of the polar front during this series suggests subsidence of the tropopause and its transformation into the lower boundary of a deep stable layer which is transformed into some kind of front separating the real tropical air from a more temperate air moving in from the regions north of the Himalayas.
On the Structure of Some Cumulonimbus Clouds which Penetrated the High Tropical Troposphere
Authors: Malkus Joanne Starr , Ronne Claude 
Published: January 2012

Some extremely large oceanic trade-wind cumulonimbus clouds extending upwards of 40,000 ft into a region of strong winds and intense vertical shear have been studied by means of time-lapse photography. A simultaneous still picture of the clouds taken a known distance and direction away from the motion pictures permits triangulation upon the clouds and calculation of the vertical and horizontal motions of several of the individual towers. By means of a nearby radiosonde observation, it is established that the air forming the strongest of these towers must have risen from near cloud base with little or no dilution of its buoyancy by mixing with the clear-air surroundings.
The model of Malkus and Scorer (1955) concerning the erosion of cumulus towers is reviewed and tested upon these towers with satisfactory results. A minimum horizontal cloud dimension is apparently required for the production of undiluted towers. The horizontal motion of the clouds relative to the air is also estimated from the model and tested by the observations and the net upward transport of latent heat in water vapor is calculated approximately.