Showing papers by "University of Massachusetts Boston published in 1992"

Patterns of species diversity in the deep sea as a function of sediment particle size diversity

Abstract: UNDERSTANDING the processes that generate and maintain patterns of species diversity is a major focus of contemporary ecological and evolutionary research. In the deep sea, species diversity varies geographically and bathymetrically1–3, and may attain levels that rival tropical communities4. Many hypotheses have been proposed concerning the forces that shape patterns of species diversity in the deep sea5, but so far it has not been possible to relate these patterns to potential causes in a direct quantitative way. The nature of sediments should be important in structuring deep-sea communities because deposit feeders rely on the sediments for nutrition and comprise most of the organisms in the deep sea6. The composition of soft sediment communities is influenced by sediment particle size7,8. Shallow-water deposit feeders selectively ingest particular size fractions of the sediments9,10 and there are interspecific differences in particle size preference11–13. Partitioning of sediments with respect to size may be more likely in the deep sea if there is strong selection for macrophagy as a result of reduced food supply and digestive constraints imposed by feeding on deposits14; macrophagy would permit species to ingest selectively the more labile components of the sediments. If deposit feeders in the deep sea partition the sediments with respect to size, species diversity may in part be a function of sediment particle size diversity. Also, sediment particle size diversity may reflect habitat complexity because the organisms live on or within the sediments15–21. Here we show that species diversity is a significant positive function of sediment particle size diversity. The relationship seems to be scale-invariant, accounting for a similar proportion of the variance at inter-regional, regional and local scales. Bathymetric patterns of species diversity also appear to be largely attributable to changes in sediment characteristics with depth. These results suggest that sediment diversity has an important role in determining the number of species within a community and identify a direct environmental factor that potentially influences species diversity in the deep sea.

How unclear terms affect survey data

Abstract: Although writing clear questions is accepted as a gen- eral goal in surveys, procedures to ensure that each key term is consistently understood are not routine. Researchers who do not adequately test respondent understanding of questions must as- sume that ambiguity will not have a large or systematic effect on their results. Seven questions that were drawn from questions used in national health surveys were subjected to special pretest procedures and found to contain one or more poorly defined terms. When the questions were revised to clarify the definition of key terms, significantly different estimates resulted. The impli- cation is that unclear terms are likely to produce biased esti- mates. The results indicate that evaluation of survey questions to identify key terms that are not consistently understood and defining unclear terms are ways to reduce systematic error in survey measurement.

Variation in maternal care and individual differences in play, exploration, and grooming of juvenile Norway rat offspring.

Abstract: Individual differences in two different forms of maternal licking, time in nest and nursing, were measured during the first 2 weeks after birth. Two treatments were imposed to reduce maternal anogenital licking (AGL): peripheral zinc sulfate to interfere with reception of pup chemosignals, and dietary saline to reduce appetite for pup urine. Both treatments reduced AGL but did not affect other maternal licking. Zinc sulfate was more effective than saline during the first week, but was somewhat less selective as it also increased time in nest. Selected behavioral patterns were measured in male and female juveniles and related by multiple regression to the behavior of their mothers. Independent of the method of manipulation, maternal AGL was a significant predictor of play and open-field defecation males and of some forms of activity in the open field in both sexes. The relationships between other maternal variables and juvenile behavior were more modest. These data demonstrate that intervening in the sensory regulation of maternal behavior can produce predictable changes in stimulation provided by the dam, thereby providing a useful means for investigating the effects of protracted differences in early stimulation in otherwise normal developmental contexts. © 1992 Wiley & sons. Inc.

A key phase in the recruitment dynamics of coral reef fishes: post-settlement transition

Abstract: Recent studies of recruitment dynamics in demersal fishes have placed major emphasis on presettlement mortality, and little on events bridging late larval and early juvenile periods. Observations on 68 taxa of Caribbean coral reef fishes before and during settlement revealed the existence of a distinct post-settlement life phase called the transition juvenile, associated with the act of recruitment. Transition juveniles were found as solitary individuals, in conspecific groups, or in heterospecific groups. The groups were either uniform or heterogenous in appearance. The complexity of the transition phase and its apparently widespread occurrence in coral reef fishes suggests that important aspects of population structure may be determined between settlement and first appearance as a full-fledged juvenile.

Reinforcement learning and its application to control

Abstract: Learning control involves modifying a controller's behavior to improve its performance as measured by some predefined index of performance (IP). If control actions that improve performance as measured by the IP are known, supervised learning methods, or methods for learning from examples, can be used to train the controller. But when such control actions are not known a priori, appropriate control behavior has to be inferred from observations of the IP. One can distinguish between two classes of methods for training controllers under such circumstances. Indirect methods involve constructing a model of the problem's IP and using the model to obtain training information for the controller. On the other hand, direct, or model-free, methods obtain the requisite training information by observing the effects of perturbing the controlled process on the IP. Despite its reputation for inefficiency, we argue that for certain types of problems the latter approach, of which reinforcement learning is an example, can yield faster, more reliable learning. Using several control problems as examples, we illustrate how the complexity of model construction can often exceed that of solving the original control problem using direct reinforcement learning methods, making indirect methods relatively inefficient. These results indicate the importance of considering direct reinforcement learning methods as tools for learning to solve control problems. We also present several techniques for augmenting the power of reinforcement learning methods. These include (1) the use of local models to guide assigning credit to the components of a reinforcement learning system, (2) implementing a procedure from experimental psychology called "shaping" to improve the efficiency of learning, thereby making more complex problems amenable to solution, and (3) implementing a multi-level learning architecture designed for exploiting task decomposability by using previously-learned behaviors as primitives for learning more complex tasks.

Studies on the enzymes involved in puparial cuticle sclerotization in Drosophila melanogaster.

Abstract: The properties of cuticular enzymes involved in sclerotization of Drosophila melanogaster puparium were examined. The cuticle-bound phenoloxidase from the white puparium exhibited a pH optimum of 6.5 in phosphate buffer and oxidized a variety of catecholic substrates such as 4-methylcatechol, N-beta-alanyldopamine, dopa, dopamine, N-acetyldopamine, catechol, norepinephrine, 3,4-dihydroxyphenylglycol, 3,4-dihydroxybenzoic acid, and 3,4-dihydroxyphenylacetic acid. Phenoloxidase inhibitors such as potassium cyanide and sodium fluoride inhibited the enzyme activity drastically, but phenylthiourea showed marginal inhibition only. This result, coupled with the fact that syringaldazine served as the substrate for the insoluble enzyme, confirmed that cuticular phenoloxidase is of the "laccase" type. In addition, we also examined the mode of synthesis of the sclerotizing precursor, 1,2-dehydro-N-acetyldopamine. Our results indicate that this catecholamine derivative is biosynthesized from N-acetyldopamine through the intermediate formation of N-acetyldopamine quinone and N-acetyldopamine quinone methide as established for Sarcophaga bullata [Saul, S. and Sugumaran, M., F.E.B.S. Letters 251, 69-73 (1989)]. Accordingly, successful solubilization and fractionation of cuticular enzymes involved in the introduction of a double bond in the side chain of N-acetyldopamine indicated that they included o-diphenoloxidase, 4-alkyl-o-quinone:p-quinone methide isomerase, and N-acetyldopamine quinone methide:dehydro N-acetyldopamine isomerase and not any side chain desaturase.

Apposition in Contemporary English

Abstract: List of figures Preface 1. Apposition as a grammatical relation 2. The syntax of apposition 3. The semantics of apposition 4. The pragmatics of apposition 5. Apposition in the grammar of English Appendices Notes References Index.

Energy reserves and parity of nomadic and settled Turkana women.

Abstract: Members of the Turkana tribe include settled and nomadic peoples who reside in the southern part of Turkana District in the semiarid region of northwest Kenya. Nomadic Ngisonyoka Turkana keep livestock (camels, cattle, sheep, goats, donkeys), subsist principally on livestock products, and move camps frequently in search of forage for the livestock; settled Turkana cultivate foods along the principal rivers. Both nomadic and settled Turkana are subject to limited food resources on seasonal and long-term bases. Protein from meat, blood, and milk is sufficient in the diet, but food energy is limited, as are body fat reserves. Previous work has documented a decline in maternal adiposity with age in a large sample of the relatively lean nomadic women, and a negative association of fat stores with parity in a smaller sample of nomadic women. The problem of maternal depletion of fat energy reserves as a function of female reproductive history is explored in this study through anthropometry in a relatively large sample (N = 312) of nomadic and settled women. Both nomadic and settled women displayed some parity-related losses in fat stores. The relationship was stronger in the nomads, even after controlling for age. © 1992 Wiley-Liss, Inc.

Sequence of the gene encoding the mitochondrial capsule selenoprotein of mouse sperm: identification of three in-phase TGA selenocysteine codons.

Abstract: The mitochondrial selenoprotein is a major structural protein of the keratinous mitochondrial capsule in mammalian sperm, a structure that functions in shaping mitochondria into the helica...

Ethical-Clinical Tensions in Clinical Practice

Abstract: matically. More attention is being given to refining codes of ethics, analyzing conflicts of interest, probing tech nology's ramifications, understanding moral development, and exploring the theoretical underpinnings of social work ethics (Goldstein, 1984; Imre, 1982; Levy, 1976; Lowenberg& Dolgoff, 1982; Reamer, 1982; Rhodes, 1986; Siporin, 1983). This article examines ethical tensions that some clinicians

Acta, a framework for modeling and reasoning

Abstract: The ability of transactions to mask the effects of concurrency and failures makes them appropriate building blocks for emerging advanced applications such as design environments. Several extensions have been proposed to the transaction model adopted in traditional database systems in order to support the functional and performance requirements of these complex systems. Often, however, given a particular extended transaction model, its properties as well as its scope of applicability are unclear. To facilitate the formal description of transaction properties in an extended transaction model, we have developed ACTA, a comprehensive transaction framework. Specifically, using ACTA, one can specify and reason about the nature of interactions between extended transactions in a particular model. ACTA characterizes the semantics of interactions (1) in terms of different types of dependencies between transactions (e.g., commit dependency and abort dependency) and (2) in terms of transactions' effects on objects (their state and concurrency status, i.e., synchronization state). Through the former, one can specify relationships between significant (transaction management) events, such as begin, commit, abort, delegate, split, and join, pertaining to different transactions. Also, conditions under which such events can occur can be specified precisely. Transactions' effects on object's state and status are specified by associating a view and a conflict set with each transaction and by stating how these are affected when significant events occur. A view of a transaction specifies the state of objects visible to that transaction while the transaction's conflict set contains those operations with respect to which conflicts need be considered. The framework is capable of accommodating complex objects, as well as semantics-based multi-level concurrency control and recovery techniques. It has the potential to characterize transaction models that associate different semantics with the notions of visibility, consistency, recovery, and permanence. Its ability to capture the semantics of previously proposed transaction models is indicative of its generality. The reasoning capabilities of this framework have also been tested by using the framework to study the properties of new models derived either by combining existing transaction models or by extending existing transaction models using the ACTA formalism. In addition, ACTA can be used to show the correctness of a particular implementation of a transaction model by first formalizing the properties of the specific mechanisms used in the implementation and then showing that they will maintain the correctness properties of the model.

Social Work Challenges: The Boundaries of Ethics

Abstract: The author discusses the boundaries we draw around ethics in social work and how we distinguish ethical from nonethical concerns. The author purports that sometimes we restrict our ethical vision b...

Portrayal of Nurses in Advertisements in Medical and Nursing Journals

Abstract: This investigation examined the content of advertisements in medical and nursing journals to determine if the images of nurses reflect the roles nurses play in health care. The method used was content analysis. Thirty-five nursing journals and 48 medical journals yielded 313 different advertisements picturing nurses. Data were analyzed using descriptive statistics, chi-square, correlation coefficients, and interpreted for overall impressions of the portrayals. Nurses are portrayed as sex objects, ornaments and as handmaidens to physicians. The findings demonstrate a freezing of the image of nurses in the print media.

Nucleotide sequence of a mouse testis poly(A) binding protein cDNA.

Abstract: The vast majority of eukaryotic mRNAs possess a poly(A) tract at their 3' termini. Although the function of the poly(A) tail is controversial, most workers agree that it promotes mRNA translation and stability (reviewed in 1, 2). The effects of poly (A) on mRNA metabolism are thought to be mediated by a protein which binds preferentially to poly (A), the poly (A) binding protein (PABP) (reviewed in 1, 2). The sequences of PABP cDNAs from yeast (3,4), human (5), Xenopus (6) and Drosophila (7) indicate that PABPs have a conserved structure consisting of 4 repeated RNA binding domains near the amino terminus and a less conserved domain of unknown function at the carboxy terminus. The present study was undertaken to search for testis-specific PABP mRNAs in mice for two reasons. First, haploid spermatogenic cells are an unusual developing system because some translationally active mRNAs have shorter poly(A) tracts than translationally repressed mRNAs (8). Second, there are numerous testis-specific variants of mRNAs which are expressed in somatic cells (reviewed in 9). Two mouse testis cDNA libraries (10, 11) were screened with the 5' proximal EcoRI fragment of human liver PABP cDNA (5) isolating two groups of cDNAs with different sequences. One of these mouse testis PABP cDNAs encodes a 636 amino acid protein which is respectively 98.9% and 94% identical to human and Xenopus PABPs (5, 6) as shown in Figure 1, and 54.9% and 49.5% identical to Drosophila and yeast PABPs (3, 4, 7) (not shown). The slow rate of evolution of mammalian PABPs is noteworthy. Assuming that mice and humans diverged 80 million years ago, the rate of evolution of non-synonymous sites in the mouse and human PABP coding regions can be estimated as 0.035—0.061 substitutions/10 years depending on whether the gap between amino acids 210 and 211 in human is excluded or included (12). The rate of evolution of nonsynonymous sites in mouse and human PABP is the fifth slowest among 36 rodent and human proteins analyzed by Li and Grauer (13). Work is in progress comparing the function and expression of the two PABP mRNAs.

Nurse practitioners as prescribers: past research trends and future study needs.

Abstract: Nurse practitioners in many states still struggle to gain prescriptive authority, while those who have this authorization often face complex regulations governing their prescriptive privileges. Forward progress calls for NPs with prescriptive authority to participate in studies that provide policymakers with relevant data promoting regulatory reforms. This article reviews the literature on NP prescribing, presents a model of trends in NP-prescribing research, and alerts NPs to areas in need of further study.

Some methodological lessons for surveys of persons with AIDS.

Abstract: In the fall of 1989, we began a longitudinal survey study of persons with acquired immune deficiency syndrome (AIDS). The goals of the study were to identify ways in which the formal and informal services that patients receive affect their survival, quality of life, and costs of care.