Individual Threshold Values Research Articles

Pathophysiology of ventilator-associated lung injury

Mechanical ventilation is essential for the support of critically ill patients, but may aggravate lung damage, leading to ventilator-associated lung injury (VALI). VALI results from a succession of events beginning with mechanical alteration of lung parenchyma, because of disproportionate stress and strain. The resulting structural tension initiates a biological inflammatory cascade; however, tension can reach the limits of stress, triggering the destruction of structures. This article reviews and discusses the ongoing research into the mechanisms of VALI and their implications for the management of ventilated patients. Several experimental and clinical studies have been performed to evaluate the contribution of pathogenic mechanical forces to organ and cellular deformation and the implications for guiding ventilator management in patients at risk for VALI. VALI may be attenuated by reducing tidal volume, but the key variable in determining pulmonary overdistension is transpulmonary pressure. Other parameters associated with the induction of VALI include positive end-expiratory pressure, inspiratory airflow and time, and respiratory frequency. How ventilation strategy, specific mechanisms of mechanotransduction, and their individual threshold values impact on VALI remains to be elucidated. In addition, clinical studies are required to evaluate the usefulness of individualized ventilator strategies based on lung mechanics.

Thresholds, productivity, and context: an experimental study on determinants of distributive behaviour

In our questionnaire experiment we confronted students of economics, law and medicine with distributive situations in different contexts characterised by two features inspired by medical decision problems: First, individual threshold values indicate minimal amounts needed by potential recipients of the given resource to obtain positive benefits. Second, recipients differ with respect to their ability to benefit from the given quantity, which indicates the productivity of the resource. Allocations offered in the questionnaire are theoretically grounded. However, respondents were also able to make their own proposals. Well-known allocation rules, but also new procedures, were witnessed. Two multistage principles were most prominent: After distributing all minimal amounts, in a second step one aims for resource-equality while the other principle in the second step demands the maximisation of the sum of payoffs. Besides threshold values and productivity, the acceptance of different principles also depended on the field of study, the degree of scarcity of the resources and the sequential order of situations.

Genetic variance of tolerance and the toxicant threshold model

A statistical genetics method is presented for estimating the genetic variance (heritability) of tolerance to pollutants on the basis of a standard acute toxicity test conducted on several isofemale lines of cladoceran species. To analyze the genetic variance of tolerance in the case when the response is measured as a few discrete states (quantal endpoints), the authors attempted to apply the threshold character model in quantitative genetics to the threshold model separately developed in ecotoxicology. The integrated threshold model (toxicant threshold model) assumes that the response of a particular individual occurs at a threshold toxicant concentration and that the individual tolerance characterized by the individual's threshold value is determined by genetic and environmental factors. As a case study, the heritability of tolerance to p-nonylphenol in the cladoceran species Daphnia galeata was estimated by using the maximum likelihood method and nested analysis of variance (ANOVA). Broad-sense heritability was estimated to be 0.199 ± 0.112 by the maximum likelihood method and 0.184 ± 0.089 by ANOVA; both results implied that the species examined had the potential to acquire tolerance to this substance by evolutionary change.

Measuring Environmental Favorability for Tropical Cyclogenesis by Statistical Analysis of Threshold Parameters

Abstract As the climate changes, the ability to predict changes in the frequency of tropical cyclogenesis is becoming of increasing interest. A unique approach is proposed that utilizes threshold values in potential intensity, wind shear, vorticity, and normalized saturation deficit. Prior statistical methods generally involve creating an index or equation based on averages of important meteorological parameters for a given region. The new method assumes that threshold values exist for each important parameter for which cyclogenesis is unlikely to develop. This technique is distinct from previous approaches that seek to determine how each of these parameters interdependently favors cyclogenesis. To determine three of the individual threshold values (shear, potential intensity, and vorticity), an idealized climate is first established that represents the most advantageous but realistic (MABR) environment. An initial numerical simulation of tropical cyclone genesis in the MABR environment confirms that it is highly favorable for cyclogenesis. Subsequent numerical simulations vary each parameter individually until no tropical cyclone develops, thereby determining the three threshold values. The new method of point downscaling, whereby background meteorological features are represented by a single vertical profile, is used in the simulations to greatly simplify the approach. The remaining threshold parameter (normalized saturation deficit) is determined by analyzing the climatological record and choosing a value that is statistically observed to prevent cyclogenesis. Once each threshold value is determined, the fraction of time each is exceeded in the location of interest is computed from the reanalysis dataset. The product of each fraction for each of the relevant parameters then gives a statistical probability as to the likelihood of cyclogenesis. For predicting regional and monthly variations in frequency of genesis, this approach is shown to generally meet or exceed the predictive skills of earlier statistical attempts with some failure only during several off-season months. This method also provides a more intuitive rationale of the results.

Fair and Minimal Power Allocation in a Two-Hop Relay Network for QoS Support

In this paper, we consider a two-hop decode-and-forward relay network where relay nodes have heterogeneous channel conditions. We propose a new fair and minimal power allocation scheme where a relay node is selected to forward packets based on thresholds for channel conditions of relay nodes and the selected relay node uses an adaptive power control to meet a given data rate requirement. The individual threshold values of relay nodes are determined based on the following three criteria: i) the average amounts of power consumption at relay nodes are all equal, ii) given outage probability and data rate requirements are guaranteed to support quality of service (QoS), and iii) the average total power consumption at all relay nodes is minimized. To determine threshold values for relay nodes we first mathematically model the proposed scheme and derive the average power consumption of each relay node. We then formulate an optimization problem to determine the threshold values that satisfy the above-mentioned three criteria. To solve the optimization problem, we rigorously analyze the performance of the proposed scheme, and show that the threshold values can be uniquely determined. Numerical and simulation results are provided to demonstrate various properties and the benefits of the proposed scheme.

Steps toward subject-specific classification in ECG-based detection of sleep apnea

This study deals with ECG-based recognition of sleep apnea in epochs of 1 min duration using spectral- and correlation-based features extracted from the modulation of QRS amplitude, respiratory myogram interference and RR intervals. On a database comprising 140 simultaneous recordings of polysomnograms (PSGs) and 8-lead Holter-ECGs, it is shown that a single-parameter ROC threshold classification can achieve high detection rates up to 81.0% sensitivity and 85.6% specificity. Still, individual accuracy may be low, and the improvement employing feature combination by means of second order polynomial classifiers is only marginal. We speculate that individual differences, like co-morbidities, and even intra-individual confounding factors, like nocturnal changes in body position (BP), are major reasons for the difficulties to significantly raise the detection rate using multivariate techniques, which is evident in virtually all papers on that subject. Using the BP information in the PSG, we show a potential benefit for individualized single-feature classifiers by comparing the maximally achievable individual and global accuracy when either one optimal global threshold for the total dataset, individual threshold values for each subject or individual thresholds for each BP are applied. We developed an ECG-based BP segmentation algorithm and finally suggest a potential strategy to derive individually optimized subject-specific threshold values.

Optimal combinations of acute phase proteins for detecting infectious disease in pigs

The acute phase protein (APP) response is an early systemic sign of disease, detected as substantial changes in APP serum concentrations and most disease states involving inflammatory reactions give rise to APP responses. To obtain a detailed picture of the general utility of porcine APPs to detect any disease with an inflammatory component seven porcine APPs were analysed in serum sampled at regular intervals in six different experimental challenge groups of pigs, including three bacterial (Actinobacillus pleuropneumoniae, Streptococcus suis, Mycoplasma hyosynoviae), one parasitic (Toxoplasma gondii) and one viral (porcine respiratory and reproductive syndrome virus) infection and one aseptic inflammation. Immunochemical analyses of seven APPs, four positive (C-reactive protein (CRP), haptoglobin (Hp), pig major acute phase protein (pigMAP) and serum amyloid A (SAA)) and three negative (albumin, transthyretin, and apolipoprotein A1 (apoA1)) were performed in the more than 400 serum samples constituting the serum panel. This was followed by advanced statistical treatment of the data using a multi-step procedure which included defining cut-off values and calculating detection probabilities for single APPs and for APP combinations. Combinations of APPs allowed the detection of disease more sensitively than any individual APP and the best three-protein combinations were CRP, apoA1, pigMAP and CRP, apoA1, Hp, respectively, closely followed by the two-protein combinations CRP, pigMAP and apoA1, pigMAP, respectively. For the practical use of such combinations, methodology is described for establishing individual APP threshold values, above which, for any APP in the combination, ongoing infection/inflammation is indicated.

Detection Thresholds for 2‐Isopropyl‐3‐Methoxypyrazine in Concord and Niagara Grape Juice

2-isopropyl-3-methoxypyrazine (IPMP) is the compound responsible for the off-flavor known as ladybug taint, which occurs when Harmnonia axyridis beetles become incorporated with the grapes during juice processing. It is also an important grape-derived component of juice flavor in some varieties. The main objective of this study was to determine the orthonasal (ON) and retronasal (RN) detection thresholds for IPMP in juice. The ASTM E679 ascending forced choice method of limits was used to determine detection thresholds for 26 individuals in Concord and Niagara juices. Group best estimate thresholds (BETs) averaged 0.93 ng/L and were 50% and 21% higher in Concord than in Niagara juices for ON and RN evaluation, respectively. Group BETs for IPMP (ng/L) for Concord were ON: 1.11; RN: 1.02 and for Niagara were ON: 0.74; RN: 0.84. Variation in individual detection thresholds was observed, although familiarity with ladybug taint was not associated with individual threshold values. We conclude that humans are very sensitive to IPMP in juice, and that detection thresholds are more strongly influenced by grape variety than evaluation mode. These results may assist juice producers in establishing tolerance levels for IPMP in juice affected by ladybug taint or derived from grapes of suboptimal ripeness.

Effects of electromyographic and mechanomyographic biofeedback on upper trapezius muscle activity during standardized computer work

The purpose of this laboratory study was to investigate the effects of surface electromyography (EMG)- and mechanomyography (MMG)-based audio and visual biofeedback during computer work. Standardized computer work was performed for 3 min with/without time constraint and biofeedback in a randomized order. Biofeedback was given on the basis of an individual preset threshold value for the right trapezius EMG and MMG signal and a time factor (repetition of events above the threshold). The duration of muscle activity above the preset threshold, the right trapezius EMG and MMG root mean square (RMS) values as well as the work performance in terms of number of completed graph/mouse clicks/errors, the rating of perceived exertion (RPE) and the usefulness of the biofeedback were assessed. The duration of muscle activity above the threshold was significantly lower with MMG compared with EMG as source of biofeedback (p < 0.05). Biofeedback led to a significant decrease in the right trapezius EMG RMS, lower RPE and decreased number of errors and mouse clicks, but also decreased number of completed graphs (p < 0.05). Audio and visual biofeedbacks were as effective. MMG-based biofeedback is a potential reliable alternative to EMG in ergonomics. A lowering of the trapezius muscle activity may contribute to diminish the risk of work related musculoskeletal disorders development.

Mehrschicht-CT des Herzens: Schwellenwertgestützte 3D-Volumetrie zur Bestimmung der linksventrikulären Pumpfunktion im Vergleich zur Magnetresonanztomographie

Ziel: Ziel der Studie war es, die Möglichkeiten der Mehrschicht-CT (MSCT) zur Bestimmung der linksventrikulären Pumpfunktion des Herzens mithilfe einer schwellenwertgestützten 3D-Volumetrie im Vergleich zur MRT zu ermitteln. Zusätzlich sollte überprüft werden, inwieweit die Wahl der Schwellenwerte die Ergebnisse beeinflusst. Methode: Bei 7 Patienten wurden aus den Daten einer 4-Schicht-CT des Herzens (Volume Zoom, Fa. Siemens) Bilder sowohl in der endsystolischen als auch der enddiastolischen Herzphase berechnet. Auf der Grundlage dieser axialen Schnittbilder erfolgte eine SD-Volumetrie mit doppeltem Schwellenwert zur Bestimmung des endsystolischen (ESV) und des enddiastolischen Volumens (EDV). Hierbei wurde innerhalb einer vorher einzuzeichnenden „Region of Interest“ (ROI) die Grenze der linksventrikulären Herzhöhle zum umgebenden Myokard über den unteren Schwellenwert automatisch detektiert. Lediglich im Bereich des linksventrikulären Ausflusstraktes sowie im Bereich der Mitralklappe mussten interaktiv Korrekturen eingefügt werden. Bei für alle Berechnungen identischem oberem Schwellenwert, die zur Abgrenzung der Herzhöhle von Verkalkungen dienten, wurden verschiedene untere Schwellenwerte eingesetzt, um deren Einfluss auf die berechneten Volumina zu untersuchen. Neben vorher festgelegten Werten (100 HE, 150 HE, 200 HE, 250 HE) wurde für jede Bildserie zusätzlich ein optimierter unterer Schwellenwert in Abhängigkeit von der erreichten linksventrikulären Kontrastierung ermittelt. Dieser errechnete sich als Mittelwert aus der mittleren CT-Dichte im Myokard und der mittleren CT-Dichte in der Herzhöhle. Aus ESV und EDV wurde die Ejektionsfraktion (EF) berechnet. Ergebnisse: Die mittleren CT-Dichten in der linksventrikulären Herzhöhle zeigten interindividuelle Schwankungen bis zu 119 HE. Daraus resultierten optimierte untere Schwellenwerte zwischen 160 HE und 240 HE, die im Mittel bei etwa 200 HE lagen. Bei Verwendung der niedrigen festgelegten Schwellenwerte (100 HE, 150 HE) wurden ESV und EDV tendenziell überschätzt, beim hohen Schwellenwert (250 HE) tendenziell unterschätzt. Die besten Übereinstimmungen mit der MRT ergaben sich für das ESV und EDV bei Verwendung der jeweils optimierten unteren Schwellenwerte mit Korrelationen von 0,95 für das ESV und 0,93 für das EDV. Dabei wurde das ESV im Mittel um 3,7±14,9ml überschätzt, das EDV im Mittel um 2,9±26,8ml unterschätzt. Die daraus berechnete EF zeigte mit 0,83 eine gute Korrelation zur MRT, wobei hier die EF im Mittel um 3,6±9,4% unterschätzt wurde. Zusammenfassung: Die schwellenwertgestützte 3D-Volumetrie des Herzens ist ein einfaches, gutes und durch die weitgehende Automatisierung auch relativ untersucherunabhängiges Verfahren zur Bestimmung der LV-Funktion. Die Verwendung optimierter Schwellenwerte in Abhängigkeit von der jeweils erreichten linksventrikulären Kontrastierung ist dabei von entscheidender Bedeutung.

A comparison of day 3 fsh and estradiol levels using two assay systems

Determination of serum FSH and estradiol levels on day 3 of the menstrual cycle has been shown to have predicative value in determining the prognosis for success in women undergoing fertility therapy such as in vitro fertilization or superovulation plus intrauterine insemination. Most of the data generated to determine favorable and poor prognostic patients was generated by using radioimmunoassays (RIA), which are no longer widely used. A new generation of office-based rapid enzyme-linked immunoassays (EIA) has become available. To determine new threshold values that predict prognosis would require repeating the investigations by using the newer assays. This would be ideal, but is not practical. Therefore, we have compared the results of serum FSH and estradiol measurements by using a new EIA and compared these to values on the same serum sample run by using an established RIA. Day 3 FSH and estradiol levels were determined in 103 women presenting to the San Diego Fertility Center (SDFC). The blood was centrifuged and the serum divided into two samples and frozen. A sample from each woman was sent to UCLA for RIA and a sample was kept at SDFC for EIA. The RIA was run by using established criteria (Fertil Steril 1992;58:674) and the EIA by using an ACS-180 machine by Chiron Diagnostics. Seventy-four matched pairs of data were available for analysis. The results were compared using linear regression (Fig. 1). For FSH, Y = (1.23 ± 0.43) + (0.78 ± 0.03)X, r = 0.93, P<.0001, and for estradiol, Y = (−1.0 ± 3.23) + (0.83 ± 0.05)X, r = 0.89, P<.0001. These results allow the clinician the opportunity to estimate the threshold values for FSH and estradiol to aid in predicting the prognosis for success in infertility treatments when using data generated from the ACS-180. Individual threshold values must be determined by each practitioner.

Assessment of the toxicity of metals in soils amended with sewage sludge using a chemical speciation technique and a lux‐based biosensor

AbstractCurrently, regulations regarding the maximum permitted concentrations of metals in soils are based on measurements of the total concentration. However, a range of chemical and biological techniques are being developed to predict the bioavailable component of these pollutants. A lux‐based biosensor was tested in soil solutions extracted from two field experiments at Braunschweig, Germany, that had the same metal inputs, but differed in pH. The bioluminescence response was found to decline as the free Zn2+ increased, and both soils fitted the same relationship with soil solution metal concentrations. The EC25 and EC50 derived from this curve were 1.9 and 6.1 mg/L, respectively. In contrast, the response to total Zn concentrations in the bulk soil showed distinct curves for each soil, further highlighting the appropriateness of free Zn2+ as a toxicity indicator. Other metals were present in the soil, but were unlikely to be toxic, because the observed concentrations were less than their individual toxic threshold values in solution. Bioluminescence‐based biosensors were concluded to possibly offer an inexpensive and rapid technique to evaluate the bioavailability of metals in soil systems. The response of these biosensors can be related to soil solution speciation measurements, and this gives a common basis for expression of toxic thresholds in different soils.

ASSESSMENT OF THE TOXICITY OF METALS IN SOILS AMENDED WITH SEWAGE SLUDGE USING A CHEMICAL SPECIATION TECHNIQUE AND A lux-BASED BIOSENSOR

Currently, regulations regarding the maximum permitted concentrations of metals in soils are based on measurements of the total concentration. However, a range of chemical and biological techniques are being developed to predict the bioavailable component of these pollutants. A lux-based biosensor was tested in soil solutions extracted from two field experiments at Braunschweig, Germany, that had the same metal inputs, but differed in pH. The bioluminescence response was found to decline as the free Zn2+ increased, and both soils fitted the same relationship with soil solution metal concentrations. The EC25 and EC50 derived from this curve were 1.9 and 6.1 mg/L, respectively. In contrast, the response to total Zn concentrations in the bulk soil showed distinct curves for each soil, further highlighting the appropriateness of free Zn2+ as a toxicity indicator. Other metals were present in the soil, but were unlikely to be toxic, because the observed concentrations were less than their individual toxic threshold values in solution. Bioluminescence-based biosensors were concluded to possibly offer an inexpensive and rapid technique to evaluate the bioavailability of metals in soil systems. The response of these biosensors can be related to soil solution speciation measurements, and this gives a common basis for expression of toxic thresholds in different soils.

Method and apparatus for optically sensing the position and velocity of piano keys

An electronic keyboard musical instrument is provided having optical emitters and detectors both positioned beneath each of the instrument's keys, whereby optical energy is emitted upon the bottom reflective surface of the key and the reflected light is detected. The distance between the optoelectronic sensor and the bottom of the key is detected by the light detector which produces an analog output signal and, by measuring the time between a first and second threshold crossing, the key's velocity can be determined. The two thresholds are preferably chosen to measure a rising voltage as the key is depressed, and the threshold values are preferably chosen at 50% of key travel and 75% of key travel. By use of these thresholds, a relatively clean and useful waveform is available at both threshold crossings, particularly since the mechanical movement of the key has nearly reached its terminal velocity. Electronics in the keyboard instrument sequentially scan each of the output voltages produced by their corresponding light detectors so that a single microprocessor can measure all of the key position values. A single set of threshold voltages can be utilized for all of the keys of the keyboard instrument, if desired, or each of the keys can have its own individual threshold values depending upon the calibration values for its zero and span conditions. The time interval between threshold crossings can be determined, which in turn is used to determine the velocity of each key as it is being depressed. Once the velocity is known, the volume for that key's particular musical tone can be controlled by a sound engine, as well as its other characteristics, such as timbre, attack, and envelope.

Differential patterns of the number and proportion of blood leukocytes following endurance exercise of moderate, strenuous and severe conditions

A study was conducted to elucidate the acute effects of endurance exercise on white blood cells by setting three conditions of different intensity and duration; (a) an upper limit of aerobic exercise for health promotion and (b) superior limits within endurance exercise tolerance for untrained persons were prescribed separately for the same healthy untrained male student volunteers (n = 10) at intensities of 85% and 95% of the individual anaerobic threshold (AT) values for 1 h and 1.5 h, respectively, on a bicycle ergometer. In addition, (c) participants in a 100-km marathon race (n = 20) who continued running for 10-13 h were examined. Every condition caused significant leukocytosis due to predominant neutrophilia and, to a minor degree, a significant increase in monocyte number, the magnitude of which depended on the severity of endurance workload and persisted even 1 h after the termination of exercise. Simultaneously, microscopic evaluation of blood smears revealed the occurrence of an increased proportion of band neutrophils and a decreased proportion of hypersegmented neutrophils (shift to the left) following exercise in condition (b) but not in (a), suggesting that neutrophils are mobilized partly from the bone marrow reserve to the circulation. On the other hand, peripheral lymphopenia was observed after the termination of endurance exercise. These phenomena closely mimicked the known effects of exogenous glucocorticoid administration, suggesting an association with endogenous stress hormone (cortisol) secretion following strenuous exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of regional arrays in seismic verification research

Abstract This paper gives an account of the work related to the development of the NORESS concept of a regional array. The array design considerations and objectives are reviewed, and a description is given of the NORESS and ARCESS array facilities in Norway with their field installations, data transmission lines, and data-receiving center functions. The automatic signal detection processing of NORESS data applies multiple narrow-band frequency filters in parallel and forms array beams from selected subgeometries. The detection algorithm is based on computing the STA/LTA ratio for each beam individually, and a detection is declared whenever this ratio exceeds a given threshold. It is explained how the beam deployment and the individual threshold values can be tuned to ensure that the interesting phase arrivals are not missed, but at the same time how to avoid coda detections. For each detected signal, frequency-wavenumber analysis is invoked to determine arrival azimuth and apparent velocity. Currently, a broadband estimator is used, and it is demonstrated that the use of this algorithm increases the stability of the azimuth and apparent velocity estimates, relative to narrow-band methods. Local and regional events are automatically located on the basis of identification and association of P - and S -wave arrivals. The uncertainty in the arrival azimuth is the limiting factor in accurately determining single-array event locations, and it is shown that this uncertainty is as large as 10° to 15° for Pn phases from certain regions. In order to further investigate the potential of the NORESS concept, work was initiated toward installing a network of regional arrays in northern Europe. This involved the development of the ARCESS array in northern Norway and the installation of the FINESA array in Finland in cooperation with the University of Helsinki. Data from these three arrays have been used jointly in a location estimation scheme. It is shown that, for events in the Fennoscandian region of magnitude typically around 2.5 and for which at least one phase is detected by each array, location estimates can be obtained automatically that deviate from published network locations by only 16 km on the average. In the future, it is anticipated that additional arrays and single stations in northern Europe will contribute real-time data to NORSAR for analysis jointly with existing arrays. The first additional data to become available will be from the GERESS array, which will be established in the Federal Republic of Germany in 1990. Future perspectives also include the use of expert system technology in the data analysis, and the IMS system already in operation represents the initial attempt in this regard. A summary is given of problem areas where further work is needed in order to fully exploit the regional array concept.

The practice of zoning: How PRAs can be used as a decision-making tool in city and regional planning

Abstract In some cases large potentially hazardous industries have to deal with existing housing developments (too) close by or with future housing developments advancing the site perimeter. This will often result in tightening up existing regulations and the requirements of more stringent in-situ measures for that industry, while on the other hand no constraints are imposed on further urban developments of the surrounding municipalities. However risk can also be reduced by keeping the distance between the potential hazardous site and the public as large as possible (zoning). On the basis of calculated individual risk levels and threshold values for individual risk, zoning strategies can be developed. In several cases these zoning strategies have been used. Some examples are given.

Analysis of the volatile constituents of black chokeberry (Aronia melanocarpa Ell.)

AbstractThe volatile constituents of black chokeberry were analysed by gas chromatography and mass spectrometry. Concentrations of the 48 compounds identified were in general below their individual threshold values. The main compounds were benzaldehyde cyanohydrin, hydrocyanic acid and benzaldehyde. Among other benzene derivatives identified in the press juice were benzylalcohol, 2‐phenylethanol, phenylacetaldehyde, salicylaldehyde, acetophenone, 2′‐hydroxyacetophenone, 4′‐methoxyacetophenone, phenol, 2‐methoxyphenol and methyl benzoate.

Hydrodynamic factors controlling the distribution of heavy minerals (Bristol Channel)

Based on a knowledge of the Bristol Channel hydrography, the quantitative heavy mineral distribution, and the individual mineral threshold values, a model for equivalence/inequivalence values and heavy mineral enrichment is presented. Hydraulic inequivalence in the Channel is a result of (I) preferential mineral size from the source; this controls the mineral suite changes created by (2) differential entrainment of minerals by density and size. Differential mineral transport of heavy minerals depends upon the hydraulic conditions of unidirectional and oscillatory flow, separately and in combination, acting on a seabed of certain roughness. Such a model can be used to explain the development of heavy mineral enrichment found on the open (high energy) beaches and in the areas of local tidal current enhancement.

Effects of seizure and subseizure posttrial hippocampal stimulation on appetitive operant behavior in mice

Ninety-three BALB/c male mice were implanted bilaterally in the dorsal hippocampus. For each animal, the individual afterdischarge threshold intensity was determined for a 4-sec bilateral hippocampal stimulation train. Several days later, all animals underwent an initial 15 min session in a continuous reinforcement appetitive task (Skinner box). In Expt 1, all animals except a control group were stimulated 30 sec after the learning session either at half of the individual afterdischarge threshold value for 80 sec, or at the after-discharge threshold value for 4 or 80 sec. A 30-min second session took place 24 hr later. In the control group, an improvement of performance, the reminiscence effect, was found. In the subseizure stimulated group, the observed reminiscence effect was higher than that of the control group. Conversely, with the two durations of seizure stimulation, the reminiscence effect was erased. In Expt 2, the same learning paradigm was used, but the animals were stimulated at their individual afterdischarge threshold value at different times after the end of the first session (from 30 sec to 180 min). During the second session, 24 hr later, the impairment of the reminiscence effect for the different groups decreased as the learning-stimulation delay was increased. Thus, the effects of posttrial hippocampal stimulation on learning were studied. The duration of the long temporal amnesia gradient of seizure stimulation and of the shorter facilitatory gradient previously described at a half threshold value were discussed. The gradient duration in the first case could be related to the spread of afterdischarges from the hippocampus to other parts of the brain.