Element banding and organic linings within chamber walls of two benthic foraminifera.

Trace and minor elements incorporated in foraminiferal shells are among the most used proxies for reconstructing past environmental conditions. A prominent issue concerning these proxies is that the inter-specimen variability in element composition is often considerably larger than the variability associated with the environmental conditions for which the proxy is used. Within a shell of an individual specimen the trace and minor elements are distributed in the form of bands of higher and lower concentrations. It has been hypothesized that differences in specimen-specific element banding patterns cause the inter-specimen and inter-species variability observed in average element composition, thereby reducing the reliability of proxies. To test this hypothesis, we compared spatial distributions of Mg, Na, Sr, K, S, P and N within chamber walls of two benthic foraminiferal species (Amphistegina lessonii and Ammonia tepida) with largely different average Mg content. For both species the selected specimens were grown at different temperatures and salinities to additionally assess how these parameters influence the element concentrations within the shell wall. Our results show that Mg, Na, Sr and K are co-located within shells, and occur in bands that coincide with organic linings but extend further into the calcite lamella. Changes in temperature or salinity modulate the element-banding pattern as a whole, with peak and trough heights co-varying rather than independently affected by these two environmental parameters. This means that independent changes in peak or trough height do not explain differences in average El/Ca between specimens. These results are used to evaluate and synthesize models of underlying mechanisms responsible for trace and minor element partitioning during calcification in foraminifera.

Coupling hydrocarbon degradation to anaerobic respiration and mineral diagenesis: theoretical constraints.

The diagenetic mineral assemblages in petroleum reservoirs control the formation fluid pH and pCO(2). Anaerobic biodegradation of petroleum is controlled by the transfer of electrons from reduced organic species to inorganic, redox sensitive, aqueous and mineral species in many cases through intermediates such as H(2) and CH(3)COO(-). The terminal electron accepting reactions induce the dissolution or precipitation of the same minerals that control the ambient pH and pCO(2) in petroleum reservoirs. In this study, we develop a model for anaerobic biodegradation of petroleum that couples the production of acetate and H(2) to 'late stage' diagenetic reactions. The model reveals that the principal terminal electron accepting process and electron donor control the type of diagenetic reaction, and that the petroleum biodegradation rate is controlled through thermodynamic restriction by the minimum DeltaG required to support a specific microbial metabolism, the fluid flux and the mineral assemblage. These relationships are illustrated by modeling coupled microbial diagenesis and biodegradation of the Gullfaks oil reservoir. The results indicate that the complete dissolution of albite by acids generated during oil biodegradation and the corresponding elevated pCO(2) seen in the Gullfaks field are best explained by methanogenic respiration coupled to hydrocarbon degradation and that the biodegradation rate is likely controlled by the pCH(4). Biodegradation of Gullfaks oil by a consortium that includes either Fe(3+)-reducing or -reducing bacteria cannot explain the observed diagenetic mineral assemblage or pCO(2). For octane, biodegradation, not water washing, was the principal agent for removal at fluid velocities <20 m Myr(-1).

Structure and rheology of organoclay suspensions.

We have characterized a montmorillonite-based organoclay dispersed in three different nonaqueous solvents using a combination of x-ray scattering, small-angle neutron scattering (SANS), and ultrasmall angle neutron scattering (USANS), together with rheological measurements. Consistent with these measurements, we present a structural model for the incompletely dispersed clay as consisting of randomly oriented tactoids made of partially overlapping clay sheets, with transverse dimensions of several microns. Intersheet correlation peaks are visible in x-ray scattering, and quantitatively fit by our model structure factor. SANS and USANS together show a power law of about -3 over a wide range of wave numbers below the intersheet correlation peak. Our model relates this power law to a power law distribution of the number of locally overlapping layers in a tactoid. The rheology data show that both storage and loss moduli, as well as yield stress, scale with a power law in volume fraction of about three. Equating the gel onset composition with the overlap of randomly oriented tactoids and taking into account the large transverse dimensions of the tactoids, we predict the gel point to be at or below 0.006 volume fraction organoclay. This is consistent with the rheology data.

Impurity mediated nucleation in hexadecane-in-water emulsions.

We report detailed nucleation studies on the liquid-to-solid transition of hexadecane using nearly monodisperse hexadecane-in-water emulsions. A careful consideration of the kinetics of isothermal and nonisothermal freezing shows deviations from predictions of classical nucleation theory, if one assumes that the emulsion droplet population is homogeneous. Similar deviations have been observed previously (3). As an explanation, we propose an argument based on the dynamic generation of droplet heterogeneity mediated by mobile impurities. This proposal is in good agreement with existing data.

Hypertension: cognitive and behavioral considerations.

This article reviews literature concerning functional changes resulting from elevated blood pressure, from reduction of blood pressure, and as a result of the medications used to treat high blood pressure. The research reviewed includes the areas of psychomotor speed, intelligence and cognitive processing, sensory and perceptual processes, and emotional and interpersonal behaviors. The conclusions reached are that the deficits noted to date in hypertensive individuals are not extreme nor are they specific. The greatest disadvantage, however, appears in the area of response speed.

Behavioural consequences of hypertension: effects of age and type of antihypertensive agent.

In order to investigate the effects on behaviour of hypertension, age, and the types of antihypertensive agents, we have conducted a retrospective analysis in 100 hypertensive patients receiving chronic treatment in our Hypertension Clinic. A group of 80 normotensive subjects, matched for age, were included in the study. Half of the hypertensive patients were under the age of 50 (young group) and half were over the age of 50 yrs (old group). The antihypertensive agents had not been administered according to any specific protocol, but represented the choice of the individual clinicians treating the patients in the clinic. All patients had received treatment for at least one year, and usually for two years. The behavioural tests performed were designed to measure sensory-perceptive ability, cognitive ability and psychomotor function and were those employed and described in our previous studies. The results achieved were varied, but indicated that older age was associated with an impairment in performance as was blood pressure. Test performances in the young hypertensives were similar to those achieved by older normotensives. These results were more prominent in cognitive and psychomotor functions than in the sensory-perceptive tests. The antihypertensive drugs used also affected these results; the worst behavioural performances tended to be in patients receiving the central nervous system agonists (methyl-dopa and clonidine) and better performances in patients receiving beta-blockers alone when compared with the other groups. Surprisingly, patients receiving diuretics showed poorer performance levels, but these were better in patients who received a beta-blocker in combination with their diuretic.(ABSTRACT TRUNCATED AT 250 WORDS)

Test-taking behaviors by hypertensive and normotensive individuals.

Systematic ratings were made on the Tulane Test-Behavior Scale of the global and integrated behaviors observable for hypertensive and normotensive subjects as they worked to complete a battery of neuropsychological tests--the degree of attention and effort displayed, for example, self-confidence and self-criticism. The results for 82 subjects (41 subject pairs matched for age, race, and education) revealed substantial and consistent differences between groups. Early, mild hypertensive subjects (unmedicated) displayed significantly less optimal behaviors than did normotensive controls. These may be best understood as subtle functional consequences of the abnormal physiological state imposed on the brain by a chronically elevated blood pressure, just as the functional disruptions of reduced kidney filtration fraction or minor abnormalities of the electrocardiogram appear early in the course of the disorder for other target organs. Certain testable implications of this hypothesis are discussed.

Group therapy with sexually abused adolescent girls.

Clinical guidelines are presented for conducting group therapy with sexually abused adolescent girls, based on a literature review and the authors' clinical experience. Common treatment themes, pragmatic issues related to setting up a group treatment program, and group process issues are discussed.

An objection to Owens' article on incest victims.

The use of Rorschach data for research purposes is growing and careful attention to accuracy needs to be maintained. A comment on a recent article's use of the lack of reflection responses to indicate poor self-esteem for incest victims is offered.

Effect of antihypertensive treatment on the behavioral consequences of elevated blood pressure.

It was shown in a prior study that mildly hypertensive patients performed significantly less effectively on several sensory-perceptual, cognitive, and psychomotor tests than did matched normotensive controls. To determine whether these deficits are attributable to elevated blood pressure per se, hypertensive and control subjects were recalled for reexamination 15 months after the original tests. Results indicated that those hypertensives in whom blood pressure had been lowered with antihypertensive drugs showed significant restoration of performance scores toward the levels of normotensive subjects. Hypertensives who had not received active treatment remained deficient as compared with controls. These results indicated that behavioral deficits in mild hypertension may be reversible consequences of the effects of elevated blood pressure on the central nervous system.

Behavioral consequences of mild hypertension.

Tests made of the sensory-perceptual, cognitive, and psychomotor abilities of untreated young patients with essential hypertension have revealed a pattern suggesting a slight functional impairment of the central nervous system. Reduced performance was most marked for those tasks requiring speed and psychomotor coordination, particularly when the behaviors observed were self-initiated. Lowered scores were more evident among female hypertensives; no differences in performance by race were noted. The deficits measured by these sensitive tests do not appear to be great enough to intrude on everyday activity nor to impair work ability. Changes that may result from blood-pressure-lowering therapies will require further study.

Incidental serial reaction time: normal and schizophrenic response to the onset and cessation of auditory signals.

This study tested the hypothesis that incidental serial reaction time (ISRT) latencies would be slower and more variable for schizophrenic than for normal Ss. It was predicted that the response of both groups to a manipulated stimulus dynamism would be proportionate, however,despite a difference in level of performance characterizing each sample. S responded to a series of 1000 Hz audiometric tones, signaling tone onset by pressure on a hand-switch, and offset by release. Thirty Ss without history of psychiatric disorder (16M, 14F) and 30 chronic schizophrenic patients (15M, 15F) were examined. All patients were drug-free and bore diagnoses of long standing. Signal tone length (1-3 sec) and interstimulus interval (1.5-15 sec) were varied randomly. Intensity levels were determined, in part, by reference to the individual threshold (T l, T j5 db) and partly by prior selection of fixed values to be used with all Ss (10 and 40 db). Mean ISRT response was significantly slowed for the schizophrenic group, and these latencies were markedly more variable. Increased signal intensity reduced the latency of ISRT, significantly, in each group. The stimulus dynamism induced change in ISRT was altogether similar for both groups, over a range of 15-65 db. No evidence for a diminished vigilance from the beginning to the end of the experimental sitting was found, for either sample.

Ethanol induced slowing of human reaction time and speed of voluntary movement.

This study tested the hypothesis that a CNS depressant (ethanol) would affect self-initiated psychomotor movement speed as much as the speed of an homologous movement made in response to an external stimulus. Four normal Ss (three male, one female, aged between 33-45 years) provided well-practiced measures of reaction time and a simple homologous traverse movement (a) in response to a signal from the E and (b) initiated at the S's own discretion. Performance by each S under ethanol conditions (B. A. L. .22%) was compared with his own baseline (pre- and postdrug) scores. Traverse originated by the S was consistently faster in the nondrug condition. Under peak-ethanol, both forms of traverse were slowed significantly in all Ss. Speed reductions were similar but consistently greater for self-initiated movement. A single S who repeated the experimental sequence under a minimally effective dosage (B. A. L. .08%) showed no important reduction in reactive movement speed, but was slowed significantly in self-initiated traverse measured concomitantly. The selective sensitivity of self-initiated movement to ethanol provides added evidence that a higher level of neural organization underlies control of human voluntary action.