Showing papers by "University of Maryland, Baltimore County published in 1979"
TL;DR: In this article, the same authors reanalyze the same class of irreversible cyclic heat engines, treating the thermodynamic variables of the working fluid as dynamical variables, and obtain the optimal configuration of the engine when the performance goal is to maximize the average power output per cycle or, alternatively, maximize the efficiency of the engines.
Abstract: In a previous paper we analyzed a class of irreversible cyclic heat engines to find their optimal operating configuration for specific performance goals. In that paper the thermodynamic variables of the working fluid were not treated as dynamical variables, instead the dynamics was replaced by an integral constraint. In this paper we reanalyze the same class of heat engines treating the thermodynamic variables of the working fluid as dynamical variables, and we obtain the optimal configuration of the engine when the performance goal is to maximize the average power output per cycle or, alternatively, to maximize the efficiency of the engine. To carry through this program it is necessary to use mathematical techniques from optimal-control theory. Since this subject is unfamiliar to most physicists and chemists, we briefly introduce some of the central ideas of the theory.
289 citations
TL;DR: In this paper, the system of equations introduced by Lorenz to model turbulent convective flow is studied for Rayleigh numbers, which is somewhat smaller than the critical value required for sustained chaotic behavior.
Abstract: The system of equations introduced by Lorenz to model turbulent convective flow is studied here for Rayleigh numbersr somewhat smaller than the critical value required for sustained chaotic behavior. In this regime the system is found to exhibit transient chaotic behavior. Some statistical properties of this transient chaos are examined numerically. A mean decay time from chaos to steady flow is found and its dependence uponr is studied both numerically and (very close to the criticalr) analytically.
264 citations
TL;DR: The authors found that the police were most likely to use deadly force in the most unequal states, and that the amount of violent crimes and riots and the percentage change in population also predicted these lethal events.
Abstract: Conflict theorists assume that force or its threat is the fundamental element that holds unequal societies together. Because conflict theorists also hold that the state's monopoly of violence is controlled by those who benefit from inequality, it follows that the control agents of the state should be more likely to use extreme force when economic inequality is most pronounced. This hypothesis was tested with data on the number of killings committed by policemen in the American states. After controlling for six additional explanations, we found that the police were most likely to use deadly force in the most unequal states. The amount of violent crimes and riots and the percentage change in population also predicted these lethal events. But the major implication of our findings is that a hypothesis derived from confict theory does predict the amount of police-caused homicides.
147 citations
TL;DR: Both species responded to additional prey by significantly increasing the number of eggs produced per female, indicating that food was a limited resource for these species.
Abstract: A field experiment was performed to determine if food is a limited resource for adult females of two species of orb-weaving spiders, Mecynogea lemniscata and Metepeira labyrinthea. Spiders built webs after being added to open experimental units located in a mixed deciduous-pine forest in Maryland, USA. Each unit was a frame supporting dead branches of the type used by both species for anchoring webs. Spiders on half the units were exposed to natural prey densities only, while each spider on the other units was given laboratory-reared flies in order to increase prey availability above natural levels. Supplemental feeding continued for 2.5 months. At the end of the experiment all egg sacs were removed from the units.Providing additional prey did not increase the survival rate on the units (net effect of mortality, emigration and immigration). However, both species responded to additional prey by significantly increasing the number of eggs produced per female, indicating that food was a limited resource for these species. Median egg production per female increased from 34 to 62 for Mecynogea lemniscata and from 65 to 145 for Metepeira labyrinthea. Egg weight was not affected.Feeding rates and nearest neighbor distances were determined for spiders in non-experimental populations, which permitted evaluation of the experiment's naturalness. The effects of food supply upon the reproductive rates of the two species are discussed in relation to their numerical response and population dynamics.
129 citations
TL;DR: Although the Barnegat Inlet intertidal system appears to follow closely the patterns of community organization described for several other rocky interTidal coastlines, this organizational pattern is noteworthy because it is repeated here in a far more seasonal environment and with a new cast of interacting competitors and predators.
Abstract: Community organization was studied by experiment and observation from October 1972-October 1974 in the marine epifaunal assemblages at each end of Barnegat Inlet, New Jersey. The rock jetty at the wave-exposed eastern end of the inlet possesses an intertidal community with the following attributes: (1) a high intertidal zone dominated by the barnacle, Balanus balanoides, but also occupied by the blue mussel, Mytilus edulis, in rock crevices, (2) a mid and low intertidal zone with usually 85% cover) during summer and fall, and (3) almost no intertidal predators or herbivores. The predatory seastar, Asterias forbesi, is abundant subtidally. Controlled removal experiments indicate that in the mid and low intertidal underlying barnacles perish as a consequence of the establishmentof extensive secondary cover by Mytilus, probably because Mytilus outcompetes Balanus through suffocation or starvation. Mytilus transplants demonstrate that the mussels do not survive outside of crevices in the high intertidal, which thus may represent for Balanus a refuge from competition by Mytilus.The pilings on docks at the protected western end of Barnegat Inlet possess an intertidal epifaunal community with the following characteristics: (1) a high intertidal zone that includes Balanus balanoides, a second barnacle, Balanus eburneus, and an herbivorous gastropod, Littorina littorea, (2) a mid and low intertidal zone with usually >40% free space in the summer and fall and the remaining area covered by several abundant species with no extreme dominant, and (3) abundant predators, chiefly the oyster drill, Urosalpinx cinerea, the blue crab, Callinectes sapidus, and a mud crab, Neopanope texana sayi. Asterias forbesi, while abundant subtidally, is also occasionally present on intertidal surfaces. Controlled exclusion of predators by caging several replicate pilings at the western end of the inlet reveals that predation prevents monopolization of mid and low intertidal space by the apparent competitive dominant, Mytilus. Predation appears to be a direct cause of the relatively great temporal and spatial heterogeneity in the mid and low intertidal of these pilings.Thus, although the Barnegat Inlet intertidal system appears to follow closely the patterns of community organization described for several other rocky intertidal coastlines, this organizational pattern is noteworthy because it is repeated here in a far more seasonal environment and with a new cast of interacting competitors and predators. That crabs play an important role as predators is novel for North America, but only perhaps because all previous North American studies have ignored the rocky intertidal zones of quiet, estuarine waters where in Europe predatory crabs are known to be extremely significant.
117 citations
TL;DR: A growing body of evidence indicates that a variety of animals can sense the earth's magnetic field, and the possibility that the transducer of the magnetic sense is a microscopic ferromagnet of the sort observed in certain bacteria is examined theoretically.
100 citations
TL;DR: Findings indicate that visually directed hand extension and reaching skills progress from the ipsilateral to include the bilateral and later the contralateral domains.
Abstract: The development of the ability to extend the hand across the body midline to contact a visually presented object was examined in 48 normal, full-term, 9--20-week infants. One of the infant's arms was restrained while the behavior of the contralateral, unrestrained arm was observed. Results indicate that infants can first contact objects placed in front of the ipsilateral shoulder, then at the body midline, and later in front of the contralateral shoulder. Between 9 and 17 weeks, success at contacting objects at the midline progressed from 33% to 93%. During this interval, the success in contacting objects presented in front of the contralateral shoulder increased from 0% to 71%. By 18--20 weeks, all infants contacted objects in all three positions. These findings indicate that visually directed hand extension and reaching skills progress from the ipsilateral to include the bilateral and later the contralateral domains. The results are considered in regard to the development of bilateral coordination and complementarity.
88 citations
TL;DR: Colonization was rapid, and both total number of individuals and number of species colonizing the substrates had stopped increasing by the end of the experiment, suggesting that the drift is a major source of insect colonists.
Abstract: A field experiment was performed in a New Mexico (U.S.A.) stream to investigate the relation between size and diversity of substrate and numbers and diversity of colonizing insects. Baskets with either small gravel, large gravel, or a 1 : 1 mixture of the two sizes were placed in a riffle area and colonization was monitored for 19 days. Colonization was rapid, and both total number of individuals and number of species colonizing the substrates had stopped increasing by the end of the experiment. Fewer individuals colonized baskets downstream, suggesting that the drift is a major source of insect colonists. Small substrate supported more individuals and more species than the larger stones. Total number of individuals and the number of species on the mixed substrate were between numbers on small and large substrate. These results do not support previous generalizations on the relation between substrate size and complexity and the structure of invertebrate communities in streams. Results of the study are compared with the findings of recent experimental studies and it is suggested that earlier generalizations on the role of substrate size and complexity need to be reexamined.
81 citations
TL;DR: The results suggest that higher plant phostosynthetic preparations which retain the ability to reduce CO(2) also have a significant capacity to photoreduce O(2), and this process does not appear to supply significant amounts of ATP directly during steady-state CO( 2) fixation in strong light.
Abstract: The time course of light-induced O 2 exchange by isolated intact chloroplasts and cells from spinach was determined under various conditions using isotopically labeled O 2 and a mass spectrometer. In dark-adapted chloroplasts and cells supplemented with saturating amounts of bicarbonate, O 2 evolution began immediately upon illumination. However, this initial rate of O 2 evolution was counterbalanced by a simultaneous increase in the rate of O 2 uptake, so that little net O 2 was evolved or consumed during the first ∼ 1 minute of illumination. After this induction (lag) phase, the rate of O 2 evolution increased 3- to 4-fold while the rate of O 2 uptake diminished to a very low level. Inhibition of the Calvin cycle, e.g. with dl-glyceraldehyde or iodoacetamide, had negligible effects on the initial rate of O 2 evolution or O 2 uptake; both rates were sutained for several minutes, and about balanced so that no net O 2 was produced. Uncouplers had an effect similar to that observed with Calvin cycle inhibitors, except that rates of O 2 evolution and photoreduction were stimulated 40 to 50%. These results suggest that higher plant phostosynthetic preparations which retain the ability to reduce CO 2 also have a significant capacity to photoreduce O 2 . With near-saturating light and sufficient CO 2 , O 2 reduction appears to take place primarily via a direct interaction between O 2 and reduced electron transport carriers, and occurs principally when CO 2 -fixation reactions are suboptimal, e.g. during induction or in the presence of Calvin cycle inhibitors. The inherent maximum endogenous rate of O 2 reduction is approximately 25 to 50% of the maximum rate of noncyclic electron transport coupled to CO 2 fixation. Although the photoreduction of O 2 is coupled to ion transport and/or phosphorylation, this process does not appear to supply significant amounts of ATP directly during steady-state CO 2 fixation in strong light.
74 citations
TL;DR: The program appears to be a reasonable method of reducing and then maintaining daily caffeine intake at less harmful levels and was maintained during a 10-month follow-up, averaging a 67% reduction from baseline.
Abstract: Excessive coffee drinking can have deleterious effects because of the large amounts of caffeine that are ingested. Caffeine is thought to be addicting, and prolonged and excessive use can lead to caffeinism, a condition that has serious behavioral and physiological side effects. The present study developed and evaluated a treatment program to reduce excessive daily coffee drinking to moderate and presumably safer levels. Three habitual coffee drinkers received individualized changing criterion programs that systematically and gradually reduced their daily caffeine intake. The coffee drinkers were required to self-monitor and plot their daily intake of caffeine. They received monetary prizes for not exceeding the treatment phase criteria and forfeited a portion of their pretreatment deposit when they did. Their coffee drinking decreased from almost nine cups per day (over 1100 mg of caffeine) during baseline to less than three cups per day (less than 343 mg) at the end of treatment or a reduction of 69%. The treatment effect was maintained during a 10-month follow-up, averaging a 67% reduction from baseline. The program appears to be a reasonable method of reducing and then maintaining daily caffeine intake at less harmful levels.
60 citations
TL;DR: It is illustrated how network analysis can provide quantitative and qualitative data useful in therapeutic interventions and agency planning decisions.
Abstract: Despite a recent renewal of interest in natural community support networks and self-help groups, there currently exist no systematic therapeutic approaches for working with network systems. Over the past two decades advances in the field of social network analysis have laid the groundwork for its conversion to a clinical tool. This paper illustrates how network analysis can provide quantitative and qualitative data useful in therapeutic interventions and agency planning decisions.
TL;DR: Early Virginia was a nightmarish world of disease and death, perhaps uncurpassed in the annals of English colonization, yet Jamestown endured because the leaders of the Virginia Company misapprehended the nexus between the estuarine environment and water-borne, non-immunizing diseases.
TL;DR: The satiation plus oral hygiene punishment treatment program appears to be an immediate, effective, enduring, and humane method of treating the non-life-threatening rumination of retarded individuals.
Abstract: Food satiation and oral hygiene punishment were used to treat the non-lifethreatening rumination of two institutionalized profoundly retarded persons. Satiation consisted of allowing the clients to eat until a satiation criterion of food refusal was achieved or until two full meal portions were consumed. The oral hygiene procedure consisted of cleansing the clients' teeth and gums with Listerine for 2 minutes following each instance of rumination. In the formal study, three conditions—baseline, satiation, and satiation plus oral hygiene—were used following the lunch meal in a multiple-baseline across-subjects design. One client's rumination decreased from an average of 89.5% during baseline to 48.8% during the satiation condition and to 3% during satiation plus oral hygiene. The second client's rumination decreased from a baseline average of 49.9% to 7.9% during satiation and to 1.4% during satiation plus oral hygiene. Generalization probes taken following the breakfast and dinner meals showed a systematic decline in rumination as the various conditions were implemented following the lunch meal. In the 16-week follow-up, rumination was treated following all meals with oral hygiene, and satiation was used at one of the daily meals for 1 week on a rotating basis. Rumination remained at a near-zero level following all meals throughout the follow-up. Thereafter, a maintenance program was conducted by the ward staff. The satiation plus oral hygiene punishment treatment program appears to be an immediate, effective, enduring, and humane method of treating the non-life-threatening rumination of retarded individuals.
TL;DR: Typical drop-evoked, bilaterally symmetrical “wing-flapping” movements of a rate similar to that of the wings of intact control chicks were made by the wing-prostheses of the wingless chicks, indicating that postnatal practice and sensory and trophic influences from the wing are not necessary for the development of basic wing- flapping movements.
TL;DR: A model suggesting that tightly intertwined antiparallel clathrin dimers form the edges of the coat lattice is presented, supported by the observations that increasing Mg2+ (10 microM--10 mM) increases reassembly whereas chelation of M g2+ by (EGTA) inhibits reassembly.
Abstract: Disruption of the coat of coated vesicles is accompanied by the release of clathrin and other proteins in soluble form. The ability of solubilized coated vesicle proteins to reassemble into empty coats is influenced by Mg2+, Tris ion concentration, pH, and ionic strength. The proteins solubilized by 2 M urea spontaneously reassemble into empty coats following dialysis into isolation buffer (0.1 M MES--1 m M EGTA--1 mM MgCl2--0.02% NaN3, pH 6.8). Such reassembled coats have sedimentation properties similar to untreated coated vesicles. Clathrin is the predominant protein of reassembled coats; most of the other proteins present in native coated vesicles are absent. We have found that Mg2+ is important in the coat assembly reaction. At pH 8 in 0.01 M or 0.1 M Tris, coats dissociate; however, 10 mM MgCl2 prevents dissociation. If the coats are first dissociated at pH 8 and then the MgCl2 is raised to 10 mM, reassembly occurs. The results suggest that Mg2+ stabilizes the coat lattice and promotes reassembly. This hypothesis is supported by our observations that increasing Mg2+ (10 microM--10 mM) increases reassembly whereas chelation of Mg2+ by (EGTA) inhibits reassembly. Coats reassembled in low-Tris (0.01 M, pH 8) supernatants containing 10 mM MgCl2 do not sediment, but upon dialysis into isolation buffer (pH 6.8), these coats become sedimentable. Nonsedimentable coats are noted also either when partially purified clathrin (peak I from Sepharose CL4B columns) is dialyzed into low-ionic-strength buffer or when peaks I and II are dialyzed into isolation buffer. Such nonsedimentable coats may represent intermediates in the assembly reaction which have normal morphology but lack some of the physical properties of native coats. We present a model suggesting that tightly intertwined antiparallel clathrin dimers form the edges of the coat lattice.
TL;DR: In this paper, the set of states reachable at time T (with unconstrained controls) for an autonomous control problem with initial state 0 at t = 0 is defined.
TL;DR: In this article, three experiments employed procedures which allowed trust levels to be continuously monitored during ongoing two-party exchange and the level of trust was behaviorally defined by degree of "expansion" of the trust.
Abstract: Three experiments employed procedures which allowed trust levels to be continuously monitored during ongoing two-party exchange. Level of trust was behaviorally defined by degree of "expansion" of ...
TL;DR: The α and β isomers of spiro-3-oxiranyl-5α-androstan-17β-ol were tested as possible inhibitors of Δ5-3ketosteroid isomerase of Pseudomonas testosteroni as mentioned in this paper.
01 Jun 1979-Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology
TL;DR: The results are consistent with a model forLimax reproductive tract development in which the perception of long days by extraocular receptors results in the secretion of a “maturation hormone’ by the brain followed by the production of a separate “male-phase sex hormone” by the developing gonad.
Abstract: Physiological and endocrine mechanisms mediating long-day (LD 16∶8) triggered sexual maturation were studied in the terrestrial slug,Limax maximus. Our findings were: (1) Maturation was induced in immature slugs seeing only short days (LD 8∶16) after implantation of whole brains from maturing donors, but no development was found in sham-operated control slugs or in animals receiving implants of muscle from mature donors (Table 1). (2) Removal of the optic tentacles did not block maturation in LD 16∶8 or promote maturation in LD 8∶16 (Fig. 1). (3) Gonadectomy (castration) abolished penis development in 9 of 11 slugs exposed to LD 16∶8 for periods of up to 31 weeks (Table 2). The results are consistent with a model forLimax reproductive tract development in which the perception of long days by extraocular receptors results in the secretion of a “maturation hormone” by the brain followed by the production of a separate “male-phase sex hormone” by the developing gonad.
TL;DR: In the case of the bihelical polyribonucleotides the transition exhibits positive cooperativity and major differences from the deoxyribose polymers exist in the circular dichroism spectra, suggesting a different geometry for the complex species.
TL;DR: In this paper, the authors describe an approach to foster children's competency in question-asking by providing competence training in questioning to their teachers and find that children rarely ask questions in school, whereas teachers typically emit predominantly rote memory questions, at rates of 1-3 questions per minute.
Abstract: Cowen (1977) advocates that we select primary preventa‐tive interventions which either modify “impactful”; social systems and/or provide training in “pivotal”; competencies. He specifically notes that “the area of children's question‐asking behavior in class holds special interest because it can potentially wed the social systems and competence approaches … there is evidence linking curiosity behavior directly to good adjustment”; (p. 14). This paper describes an approach to foster children's competency in question‐asking by providing competence training in questioning to their teachers. Previous research had indicated that children rarely ask questions in school, whereas teachers typically emit predominantly rote memory questions, at rates of 1–3 questions per minute (see Gall, 1971, and Susskind, 1969).
TL;DR: Analysis of the Trp enzyme levels in B. subtilis harboring the constructed trp plasmids confirms the genetic constitution of the plasmid-specified complementing activity and specifies the corresponding enzyme activities.
Abstract: Plasmid pUB110 was previously used as a vector to clone fragments of deoxyribonucleic acid that complement the trpC2 mutation in Bacillus subtilis from endonuclease EcoRI digested B. licheniformis, B. pumilus, and B. subtilis cellular deoxyribonucleic acid. Each of several such trp plasmids was subsequently shown to contain a segment of the trp gene cluster on the basis of genetic complementing activity. In the present study, analysis of the Trp enzyme levels in B. subtilis harboring the constructed trp plasmids confirms the genetic constitution of the plasmids. Thus, plasmids that complement mutations in specific trp genes specify the corresponding enzyme activities. The levels of the plasmid-specified Trp enzymes in B. subtilis were generally above the repressed level of the chromosomally specified Trp enzymes and equal to or below the derepressed levels of the chromosomally specified Trp enzymes. Certain cloned trp segments contain a single HindIII-sensitive site. Insertion of HindIII-generated deoxyribonucleic acid fragments into these trp plasmids resulted in inactivation of trpC complementing activity, loss of the trpC-specified enzyme activity, and a 10-fold reduction in the specific activity of the plasmid-specified trpF product. The HindIII insertions had no detectable effect on the level of the trpD product, nor did the insertions detectably alter plasmid-specified complementing activity other than to abolish trpC complementation. Removal of the HindIII insertions was accompanied by recovery of trpC complementing activity and restoration of the trpC-and trpF-determined enzymes to the levels specified by the parent plasmids.
TL;DR: In this paper, the binding of the extra electron is considered as arising primarily from the large quadrupole field of the neutral molecule and the anion is predicted to be stable to both dissociation and autodetachment of an electron.
TL;DR: The results suggest that a significant component of postpacing inhibition in rabbit sinoatrial node is due to an electrogenic Na + pump and that pacemaker rate can be directly affected by alterations in pump activity.
TL;DR: In this article, the rotational correlation time of fluorescence conjugates of hemoglobin A, its isolated β-chain, and the apo-derivative of the β chain was investigated.
Abstract: Fluorescent conjugates of hemoglobin A, its isolated β-chain, and the apo-derivative of the β-chain have been prepared in which the β-93 sulfhydryl was conjugated with 1,5-AEDANS. Radiationless enery transfer to the heme group results in a major decrease in fluorescence intensity and decay time. Measurements of the time decay of fluorescence anisotropy, employing single-photon counting, indicate that the apparent rotational correlation time is, in each case, substantially reduced from the value expected for a rigid molecule of the same molecular weight. This observation raises the possibility that internal degrees of rotational freedom exist.
TL;DR: The results suggest that bound 125I-PV can only be displaced by unlabeled PV, and indicate that the 500,000 dalton species is a solubilized PV-receptor complex and that it is possible tosolubilize the PV- receptor in an active form.
Abstract: Phosvitin (PV), a subunit of a female-specific protein, vitellogenin, binds to oocyte membranes with a KD of 10−6 M. Binding reaches equilibrium within 30 min after incubation at 25°C. Bound 125I-PV dissociates from the membrane with a t1/2 of 13 h when incubated in buffer. However, when 125I-PV-labeled membranes are incubated in buffer containing 10−5 M unlabeled PV, 50% of the initially bound 125I-PV dissociates from the membrane within 10 min. These results support the conclusion that PV binds to a membrane-associated receptor.
Solubilization studies show that Triton X-100 solubilizes up to 45% of the total membrane-bound 125I-PV. Gel-exculsion chromatography of the solubilized material yields a 500,000 dalton 125I-PV-containing complex separated from free 125I-PV. The 500,000 dalton complex completely dissociates to yield free 125I-PV when incubated with excess unlabeled PV. However, when incubated with (1) no addition, (2) IgG, or (3) serum albumin, the extent of dissociation is significantly reduced and is consistent with that which would be predicted on the basis of the observed dissociation rate in the absence of unlabeled PV.
These results suggest that bound 125I-PV can only be displaced by unlabeled PV. These results also indicate that the 500,000 dalton species is a solubilized PV-receptor complex and that it is possible to solubilize the PV-receptor in an active form.