Showing papers by "University of Texas at Arlington published in 1988"

Electromagnetic scattering from a layer of finite length, randomly oriented, dielectric, circular cylinders over a rough interface with application to vegetation

Abstract: A scattering model for defoliated vegetation is developed by treating a layer of defoliated vegetation as a collection of randomly oriented dielectric cylinders of finite length over an irregular ground surface. Both polarized and depolarized backscattering are computed and their behavior versus the volume fraction, the incidence angle, the frequency, the angular distribution and the cylinder size are illustrated. It is found that both the angular distribution and the cylinder size have significant effects on the backscattered signal. The present theory is compared with measurements from defoliated vegetations.

Nursing interventions and patient outcomes: a meta-analysis of studies.

Abstract: The 84 subject-studies and 4,146 individual subjects in this meta-analysis were obtained from nurse-conducted experimental research over an 8-year period. The entire universe of accessible subject-studies that met criteria was included. Although both published and unpublished research were included to protect the study from publication bias, there was no statistically significant difference in findings. The mean effect size for the sample of comparisons from the 84 studies was .59. The associated U3 value of 72.2 and r of .28 indicate that patients who receive research-based nursing interventions can expect 28% better outcomes than 72% of the patients who receive standard nursing care.

Optimality conditions for maximizations of set-valued functions

Abstract: The maximization with respect to a cone of a set-valued function into possibly infinite dimensions is defined, and necessary and sufficient optimality conditions are established. In particular, an analogue of the Fritz John necessary optimality conditions is proved using a notion of derivative defined in terms of tangent cones.

A framework for interpreting recency effects in immediate serial recall.

Abstract: A descriptive framework is offered for the interpretation of recency effects in immediate serial recall. Basic to the framework is a distinction between two types of trace features: (1) modality dependent features, which represent the perceptual qualities of presentation, and (2) modality independent features, which result from the set of encoding operations known as the “inner voice.” Recency and modality effects emerge because certain types of modality-dependent (i.e., language based) features are typically not subject to postlist interfering events and are likely to be sampled as discriminative cues in recall. The framework is used to interpret problematic findings in the modality effect literature, such as the effects of visual presentation, lipreading, mouthing, and stimulus class on the recall of recency items.

Auger-electron emission resulting from the annihilation of core electrons with low-energy positrons.

Abstract: We report the first demonstration of positron-induced Auger-electron spectroscopy. A beam of low-energy (${10}^{1}$ eV) positrons was used to create core holes at the surface of Ni and Cu by matterantimatter annihilation. Estimates are developed for the probability of positrons annihilating with a $3p$ electron found to be as high as 3.7(7)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ in Ni. The implications of the extremely high signal to background are discussed and several important advantages of this process for surface analysis are suggested.

Annual Experimental Evaluation of the Effect of Invasion History on Community Structure

Abstract: Fifty-four communities were developed from repeated introductions of 28 phytoplankton species in three different orders of invasion at three different rates. Variation in species richness values in these communities was assignable to invasion order, invasion rate, and the timing between interspecific invasions. Invasion rate was most influential, explaining 21.8-78.8% of the variation on any given date; invasion order never explained >4.3%, and timing explained between 19.7 and 74.9%. All three facets of invasion had significant effects. One of the low-rate invasion categories developed a unique community structure that was dominated by Chlamydomonas. Communities in this category were invulnerable to the invasion of many species and as a result had low species richness values. The relative abundance patterns of species in categories having low or moderate in- vasion rates but identical invasion orders clustered more closely to each other than they did to their high invasion rate counterparts. In this sense, invasion order is more influential where immigration rates are relatively low (e.g., on islands) than it is where dispersal from outside sources is high (e.g., on continents). Because invasion history was controlled, the methodology used here provides inter- pretable data concerning the potential importance of chance historical events that occur during community assembly. The data indicate that idiosyncrasies in community structure often may be explained on the basis of the random invasion patterns of organisms to different habitats.

Ecological resistance to the invasion of a freshwater clam, Corbicula fluminea: fish predation effects

Abstract: Fish predation is shown to have a twenty nine fold effect on the abundance of the invasive freshwater clam, Corbicula fluminea, in a Texas reservoir. This predation has prevented the clam from establishing the high densities commonly reported for it elsewhere. The high magnitude of the fish effect is attributed to Corbicula being an invader to this reservoir and not being able to cope well with the mix of resident fish species. In the absence of fish, colonization of the reservoir by Corbicula is spatially patchy. When fish interact with these clams, they remove sufficient numbers of individuals from dense patches to create the appearance of a spatially uniform distribution.

Impact of system response time on state anxiety

Abstract: Recent research has shown that user satisfaction and productivity are affected by system response time. Our purpose is to provide the results of empirical research on system response time and its effect on state anxiety. Test subjects were classified as Type A or Type B personality in order to determine if personality type had any affect on the relationship between system response time and state anxiety. The results show that both Type A and Type B personalities exhibit a statistically significant increase in state anxiety during poor or variable system response times.

The Female Frontier: A Comparative View of Women on the Prairie and the Plains

Abstract: This book introduces the important concept of a female frontier a frontier "every bit as real and coherent, as, for example, the mining frontier." It gives us a new understanding of western women's shared experiences and of the full implications of their participation in America's westward movement. Riley has reconstructed women's roles and concerns from census data, legal proceedings, newspaper accounts, local histories, essays, sermons, novels, photographs, works of art, and in large part from their own words, as recorded in diaries, day books, journals, letters, memoirs, reminiscences, and interviews. These women include the barely literate and the educated, the young and the old, single and married, white and black, native-born and immigrant. What emerges is a new understanding of the shared experiences at home, in paid employment, and in community activities that constituted the female frontier."

Inference based on conditional speclfication

Abstract: The first bibliography in the area of inference based on conditional specification was published in 1977, A second bibliography is compiled, and a combined subject index is given.

The mnemonic value of perceptual identification.

Abstract: In four experiments, subjects were required to name words presented on a CRT screen. On generate trials, the words were presented quickly, at a point where roughly half could be identified correctly; on read trials, the items were presented for a full second, allowing for rapid and easy naming. A surprise recognition test for the presented items then revealed a substantial retention advantage for the briefly presented items, but no similar advantage was produced in recall. It is argued that under rapid viewing conditions subjects may fail to extract enough visual features to allow for immediate resolution, requiring the initiation of a kind of data-driven generation process. This latter process then produces a generation effect for the briefly presented items compared with the read items, but only on a retention test that shows sensitivity to data-driven processing. These results are discussed from the standpoint of current theoretical views on the generation effect.

Abuse in Intimate Relationships A Comparison of Married and Dating College Students

Abstract: This study compared the reported incidence among males and females of dominance-possessiveness, sexual pressure, and use of physical force by one's partner for a sample of 130 married college students and 130 college students in dating relationships. Possessiveness was common and similar in incidence for married and dating students. Sexual pressure was reported by more married students, with dating students who were sexually involved to the extent of having intercourse more like marrieds. Use of moderate physical force—pushing, slapping, or hitting with an object—was experienced more often by the dating students. Males were as likely as females to report the partner engaging in these behaviors, and this applied to both the married and dating students. About 11% of both married and dating students reported consequences such as requiring medical attention or calling the police, which suggest more severe physical abuse. Note that this is a study of ever occurring incidences and not of battering per se. The t...

Siderite formation in anoxic deep-sea sediments: A synergetic bacteria controlled process with improtant implications in paleomagnetism

Abstract: Recent work on magnetic properties of limestones has demonstrated that the mineral siderite can be very important in paleomagnetism, for two reasons. First, oxidation of siderite produces secondary (daughter) magnetic minerals (magnetite, maghemite, and hematite), either before, during, or after sampling. These daughter products can completely change the magnetic properties of limestone samples and if unrecognized may be one of the primary reasons why many paleomagnetic studies of limestones, especially Paleozoic limestones, are unsuccessful. Second, siderite in weakly magnetized rocks may indicate the potential for successful paleomagnetic results. Because the presence of siderite indicates that the primary magnetic carriers are still intact, appropriate demagnetization methods should yield successful results. We conclude that microenvironmental conditions in anoxic marine sediments may permit the formation of siderite from iron (II) produced during bacterial dissimilatory iron reduction.

Anion-exchange behavior of polypyrrole membranes.

Abstract: Les variations de conductivite observees sont dues au degre d'oxydation du polymere et a la morphologie du film

Short-term memory for Chinese characters and radicals.

Abstract: Short-term memory for Chinese radicals and characters, varying in orthographic complexity, frequency, and—for radicals—intercharacter frequency (the number of compound characters that contain the radical), was studied using an immediate free-recall task. When radicals or characters are relatively frequent, so that their pronunciations are well known by literate Chinese, they seem to be maintained in verbal form in short-term memory. For these stimuli, intercharacter frequency and complexity have relatively small influences on memory span. Stimuli low in frequency, with pronunciations that are not apt to be known, seem to be maintained in visual form in short-term memory. Memory span is much smaller for these stimuli and is influenced by both intercharacter frequency and complexity. Furthermore, short-term memory for relatively high-frequency characters is interfered with more by a verbal than by a visual intervening task, whereas the opposite is true for low-frequency characters.

Majorite fractionation recorded in the geochemistry of peridotites from South Africa

Abstract: The liquidus phase for ultrabasic rock compositions changes from olivine at low pressures to a pyroxene polymorph at high pressures1,2. In the range 13–25 GPa, the liquidus phase for a chondritic bulk Earth composition is majorite3,4, a pyroxene with the garnet crystal structure. For upper-mantle Iherzolite compositions, majorite is also the liquidus phase from ∼16–25 GPa5–7, and transforms to perovskite at similar or higher pressures7. As majorite has a density higher than peridotite magmas8,9, it could have fractionated during an early differentiation event in the Earth3. Here we argue that this process is recorded in the major-element geochemistry of peridotites from South Africa, and that it has resulted in a lower mantle enriched in silica.

Periodic boundary value problems for second order impulsive differential systems

Abstract: On etudie le probleme aux valeurs limites periodiques pour un systeme d'equations differentielles d'ordre 2 faiblement couplees avec impulsion

Magnetism in bcc and fcc manganese

Abstract: Density-functional theory is used to compute the ferromagnetic moment as a function of lattice constant for bcc and fcc Mn. For bcc Mn, a relatively small moment is found in the lattice-constant range 5.20lal6.025 a.u. and a large moment is found in the region ag5.90 a.u., with a discontinuous low-spin to high-spin transition occurring somewhere in the double-moment region 5.90lal6.025 a.u. For fcc Mn, the moment is found to be zero in the range 6.50lal\ensuremath{\sim}7.275 a.u. and large in the region ag\ensuremath{\sim}7.275 a.u., with a discontinuous zero-moment to high-moment transition occurring near a=7.275 a.u. Information obtained from magnetic susceptibility calculations is used to predict the magnetic order of the ground state in some of the lattice-constant ranges considered. The susceptibility calculations indicate that bcc Mn has a ferromagnetic ground state in the range 5.2lal5.4 a.u. and that fcc Mn has an antiferromagnetic ground state in the region ag6.8 a.u.

Widespread, lavalike silicic volcanic rocks of Trans-Pecos Texas

Abstract: Several silicic units of the Trans-Pecos volcanic field have outcrop and thin-section scale features of lava flows but areal extents and aspect ratios of ignimbrites. These voluminous rocks (up to hundreds of cubic kilometres per unit) are quartz trachytes to low-silica rhyolites (68% to 72%SiO 2 ). Lava flow features include flow banding and folding, elongated vesicles, and autobreccias and vitrophyres at the base and top of units. Pyroclastic flow features include sheetlike geometry, lateral extents up to 70 km, aspect ratios as low as 1:700, and areal extents up to 3000 km 2 . A few of these units are clearly rheomorphic ignimbrites, but others show no unambiguous evidence of a primary pyroclastic origin. Although no adequate explanation currently exists for the origin of the latter, we evaluate two end-member hypotheses: (1) they are ignimbrites in which extreme rheomorphism has obliterated primary internal features, and (2) they are highly viscous lavas with unusually high heat retention or effusion rates that allowed them to spread over great areas. Either origin requires a rock type and eruptive mechanism not commonly recognized.

The relationship between volcanic eruptions and climate change: Still a conundrum?

Abstract: What is the relationship between volcanic eruptions and climate change? More than 200 years after the connection was first proposed, it remains a thorny question. This article provides a brief historical overview of the problem and a review of the various data bases used in evaluating volcanic events and associated climatic change. We use the term “climate” to describe changes in the atmosphere over wide regions for periods of several months and longer. We use “weather” to describe shorter-term, variable atmospheric fluctuations experienced over more restricted areas. We appraise the present state of knowledge and highlight some pitfalls involved in using available information. Cautiously, we suggest future avenues for study, including the possibility of “volcanic winters,” or severe eruption-induced coolings.