Trail Length Research Articles

Public response to differences between visually distinguishable forest stands in a recreation area

Studies of user-response to visual aspects of forests have generally been focused on single stands or on differences in preference within a sample of forest stands, and little attention has been paid to the effects of contrast and visual interaction between forest stands. Here we describe a pilot study on public response to the occurence of many vis-à-vis few visually different forest stands along two trails. A visually distinguishable forest stand is defined as an area of vegetation visually different in character from surrounding or adjacent vegetation. Two trails, each 2.5 km long, were laid out in a forest, one through eight visual forest stands and the other through three. After having walked each trail, 16 subjects made assessments of trail length, of time spent traversing it, and of the visual impression of the trail environment. They also assessed the suitability of the trail for the practise of typical open-air, recreational activities. The respondents made significantly more errors in assessing time and distance when judging the trail through few visual forest stands. The trail through many visual forest stands was considered to be decidedly more varied. The urge or willingness to engage in recreational activities was dependent on whether there were few or many visual stands. We have called the kind of visual variation we are dealing with the Forest Visual Oppurtunity Spectrum (FVOS), and it is our view that alternatives for the future planning and management of visual variation in a forest are derivable from documentation of the Forest Visual Oppurtunity Spectrum. At present we are attempting to establish criteria for the identification of visual vegetation stands in accordance with lay response.

Physical and Social Conditions Affecting Recreation Site Preferences

Recreation managers have focused much of their efforts on the analysis of relationships between perceived user satisfaction, participation levels, and the manipulation of supply features whereas other managers have been concerned with unwanted social interactions that take place at recreation facilities. This study focuses upon an analysis both of the environmental preferences of recreators and of the social conditions present at facilities which affect visitor satisfaction and use. Preferences for five attributes of trail areas within Chicago forest preserves were examined so that a predictive model for visitor satisfaction could be derived and used to evaluate alternative management strategies for trail design. The number of changes in views contributed more to visitor satisfaction than the type of trail surface, trail length, and the type of terrain on the trail. Proximity to residence was more important than the combination of all other physical characteristics. In addition, a positive correlation was found between the level of social interaction that one might experience and one's preference for a trail area. Neither one's choice of activity nor the characteristics of the person or persons encountered with regard to age, race, or behavior along the trail areas significantly affected concerns for social interactions or use of trail areas. However, differences did exist among the recreators with regard to the perceived effectiveness of alternative management strategies designed to mitigate social interactions. Last, the joint effects of recreators' preferences for environmental attributes and the effect of environmental management policies aimed at controlling social interaction were examined and shown to have interlocking and, sometimes, offsetting effects.

Behaviour of army antsEciton burchelli andE. hamatum (Hymenoptera, Formicidae) in the Belem region III. Raid activity

A study on the raiding behaviour ofE. burchelli (Westwood) andE. hamatum (Fabricius) was carried out in an Amazonian forest reserve at Instituto de Pesquisa e Experimentacao Agropecuarias do Norte (IPEAN), Belem, State of Para, Brazil. The data were collected during the years 1966 and 1968, on 5E. burchelli and 1E. hamatum colonies, with emphasis on the quantitative aspects (raid trail length, frequency and duration of raid activity, speed of workers on base column, booty types, and direction of raid trail). The average trail length was 75.4±3.3 m forE. burchelli, as calculated from 306 raid trails recorded during 24 nomadic phases; the figures forE. hamatum were 195±13.4 m, 54 and 5 respectively. A significant difference (0.01<P<0.05) was observed between the nomadic and statary phase, both forE. burchelli (308 records) andE. hamatum (72 records), with respect to raid trail length. The nomadic raids of both species are longer than those of the statary phase. The season of the year had a significant influence on raid trail length, but no relationship was found between raid trail length and the days of nomadic or statary phase. Data on worker speed on the raid trails, booty types and direction of the raid are also presented.

The Dislocation Movement in the Pre-Yield Region in White Tin Single Crystals by Using the Etch Hillock Technique

Single crystal plates of white tin were stretched in an etching solution to designated stresses below the macro yield stress using an Instron type tensile machine. The etching solution produced hillocks at the sites of dislocations and trails of hillocks along the loci of moved dislocations. Two types of dislocation movements could be distinguished by the shapes of hillock trails. The one corresponds to the movement of a dislocation which terminates at the surface, and the other, the movement of a dislocation which emerges by stressing from the interior. The movement of the former type takes place at stress levels ranging from about 30 g/mm2 to 50 g/mm2. The movement of the latter type occurs more frequently as the stress increases. The distribution of the trail length was found to depend on the dislocation density.

In-pile migration of fission product inclusions in mixed-oxide fuels

Migration velocities of fission-gas bubbles and solid fission-product inclusions in uranium-plutonium mixed oxide under irradiation have been obtained. Trails behind migrating second-phase particles are observed upon etching a polished metallographic section from an irradiated fuel pin. It was determined from the microstructure and the reactor power history that these trails were produced during one reactor power cycle of known duration. Particle velocity was computed from the observed trail length and the duration of the power cycle. Velocities varied between 1 and 10 Å/sec for particles with diameters between 1 and 10 μ. The temperature was between 1585 and 1850°C, and the average temperature gradient was [inverted lazy s]5400∘C/cm. In all cases, the particles moved in the direction of increasing temperature. The measured velocities for both bubbles and solid inclusions are shown to be in agreement with the calculated velocities based on a surface-diffusion mechanism with Qs*, the surface heat of transport, equal to 100 kcal/mole.

The fading of radio waves reflected obliquely from meteor trails

A study has been made of bursts of signal received at Cambridge over a distance of 500 km from the 53·25 Mc/s BBC television transmitter at Kirk o' Shotts. These signal bursts, believed to be due to reflections from meteor trails, were usually found to fade at a rate of several cycles per second. This fading is believed to be due to changes in the diffraction pattern formed on the ground by waves scattered from separate parts of a meteor trail. By observing the signal bursts on two aerials spaced 200 m apart deductions have been made about the size of the structure in the diffraction pattern and the way in which it changes with time. It is concluded that the scale of the diffraction pattern is determined by the total length of the meteor trail rather than by the size of the individual irregularities into which it breaks and the value found for the mean trail length is in good agreement with that found by other workers. The fading is found to be due to two causes, to random movements inside the trail and to rotation of the trail as a unit under the action of a wind shear. Values deduced for the r.m.s. random velocity and for the wind shear are again in agreement with those believed to exist in the E-region.

Meteor Height Distributions and the Fragmentation Hypothesis

This paper is concerned with a comparative study of the incidence of fragmentation amongst bright and faint meteors, as disclosed by photographic measurements of heights and light curves of brighter meteors (visual magnitudes &lt; +4), and by measured radioecho height distributions of faint meteors (visual magnitudes ~+6). The discussion is based on photometric and height data for sporadic and shower meteors obtained by Harvard and Canadian observers, and on radio-echo height distributions measured at J odrell Bank. Mean photographic light curves are shorter than predicted by evaporation theory, and there is a large residual scatter in the heights of maximum brightness after reduction to standard meteor velocity and brightness. Trail length is independent of reduced height, and also of velocity if this exceeds 25 km/sec; for slower meteors trail lengths shorten rapidly. The radio�echo height distribution as a function of trail length is calculated for a simple model which incorporates these features of the ablation process for brighter meteors. Comparison with radio height measurements indicates that meteors below the photographic threshold show a closer approach to the predictions of the evaporation theory than meteors bright enough to record photographically.

The theoretical length distribution of ionized meteor trails

The lengths of the columns of ionization formed by meteors are determined theoretically from the available theoretical and experimental information on 1. (1) the production and radio detection of meteoric ionization, 2. (2) the mass distribution of shower and sporadic meteors, and 3. (3) the distribution of sporadic meteor radiants. The primary factors controlling the length of an individual meteor trail are the mass of the meteoric particle and its angle of approach (radiant) into the upper atmosphere. The most likely (modal) value of trail length for meteors from the same radiant is found to be 12 sec ζ km for sporadic meteors, and approximately 17 sec ζ km for shower meteors, where ζ is the zenith angle of the radiant. The distribution of sporadic trail lengths is found to be relatively insensitive to the exact radiant distribution. For a representative radiant distribution, the most likely trail length for sporadic meteors is 15 km. When these trails are detected by a radar system, there is a selection process which favours the longer trails, so that the most likely length of the trails detected by a radar system employing a broad-beam antenna is about 25 km. This value compares well with a previous experimental determination of trail lengths. The theory indicates that the length distribution of detected trails is essentially independent of the sensitivity of the radar receiver and the power output of the radar transmitter.

The length of ionized meteor trails

The length of meteor ionization columns is defined as the maximum possible separation of points along the trail from which normal‐incidence radio reflections may be obtained, when a radio system of prescribed characteristics is used. A statistical method is employed to determine the relative frequency of trails of different lengths from simultaneous measurements made at two similar 23‐megacycle meteor detection stations 100 km apart. For sixth magnitude meteors, a mean trail length of 25 or 30 km is obtained.

The length of ionized meteor trails

By studying the rate of coincident detection of meteors at two widely separated locations, as a function of the differential time of first detection, it is possible to deduce the distribution in length of the meteoric ionization columns. A precise determination would require, in addition, that the velocity of the individual meteors used in the test be known. However, in the absence of such data, an approximate distribution of trail lengths whose mean value is probably representative of actual conditions, can still be deduced. For equipment generating about a kilowatt of continuous wave output, and capable of detecting meteors at a total rate of 450 meteors per hour, the mean trail length was found to be 25 or 30 km. Calculations based upon this value of trail length, and upon the use of a corrected rate of meteoric arrival, show that meteors up to the sixth magnitude were detected during the test. The method described provides a measure of trail length dependent upon the ability of the trail to reflect a signal at normal incidence. The accuracy of the determination of frequency of occurrence of trails of various lengths is independent of the rate of detection, but is proportional to the square root of the period of observation.