Showing papers by "Memorial University of Newfoundland published in 1997"

A Compilation of New and Published Major and Trace Element Data for NIST SRM 610 and NIST SRM 612 Glass Reference Materials

Abstract: Microanalytical trace element techniques (such as ion probe or laser ablation ICP-MS) are hampered by a lack of well characterized, homogeneous standards. Two silicate glass reference materials produced by National Institute of Standards and Technology (NIST), NIST SRM 610 and NIST SRM 612, have been shown to be homogeneous and are spiked with up to sixty one trace elements at nominal concentrations of 500 μg g-1 and 50 μg g-1 respectively. These samples (supplied as 3 mm wafers) are equivalent to NIST SRM 611 and NIST SRM 613 respectively (which are supplied as 1 mm wafers) and are becoming more widely used as potential microanalytical reference materials. NIST however, only certifies up to eight elements in these glasses. Here we have compiled concentration data from approximately sixty published works for both glasses, and have produced new analyses from our laboratories. Compilations are presented for the matrix composition of these glasses and for fifty eight trace elements. The trace element data includes all available new and published data, and summaries present the overall average and standard deviation, the range, median, geometric mean and a preferred average (which excludes all data outside ± one standard deviation of the overall average). For the elements which have been certified, there is a good agreement between the compiled averages and the NIST data. This compilation is designed to provide useful new working values for these reference materials.

The Use of Constrained Cellular Automata for High-Resolution Modelling of Urban Land-Use Dynamics:

Abstract: A cellular automaton is specified to give a spatially detailed representation of the evolution of urban land-use patterns. Cell states represent land uses, and transition rules express the likelihood of a change from one state to another as a function both of existing land use in the 113-cell neighbourhood of the cell and of the inherent suitability of the cell for each possible use. The model is used to simulate the land-use pattern of Cincinnati, Ohio. The simulation results are realistic and sensitivity analysis shows that the predictions of the model are relatively accurate and reproducible, thus suggesting that cellular ast;automata-based models may be useful in a planning context.

Cellular Automata as the Basis of Integrated Dynamic Regional Modelling

Abstract: We present an integrated model of regional spatial dynamics consisting of a cellular automaton-based model of land use linked both to a geographic information system (GIS) and to standard nonspatia...

Closeness, strength, and satisfaction: Examining the nature of relationships between providers of financial services and their retail customers

Abstract: This article presents the results of the analysis of data collected in a telephone survey of retail customers of banks and other financial institutions. The objective of the research is to identify various dimensions of the customers' relationships with their principal financial institution and to ascertain the factors that contribute to the types of close relationships that are likely to lead to customer retention, referrals, and long-term profitability. A survey of 400 adult retail bank customers provided data for analysis. The results indicate that the factors that contribute most to the establishment of close, satisfying customer relationships are affective variables, rather than situational or behavioral variables. The results also point to the existence of quite different segments of the retail bank market as defined by the type of relationship the customer wishes to have with his or her main bank. © 1997 John Wiley & Sons, Inc.. Inc.

Uptake and Biotransformation of Trichloroethylene by Hybrid Poplars

Abstract: Poplar trees were found to be capable of taking up trichloroethylene (TCE) and degrading it to several known metabolic products: trichloroethanol, trichloroacetic acid, and dichloracetic acid. Poplars were also shown to transpire TCE in measurable amounts. To eliminate the possibility that the degradation we observed was produced solely by rhizosphere organisms, axenic poplar tumor cell cultures were tested; the cultures produced the same intermediate metabolic products. When dosed with [14C]TCE, cell cultures also produced low levels of radiolabeled carbon dioxide and a labeled insoluble residue. These results show that significant TCE uptake and biotransformation occurs in poplar, which demonstrates the potential for the use of poplars for in situ remediation of TCE.

Genetic tagging of humpback whales

Abstract: The ability to recognize individual animals has substantially increased our knowledge of the biology and behaviour of many taxa1. However, not all species lend themselves to this approach, either because of insufficient phenotypic variation or because tag attachment is not feasible. The use of genetic markers (‘tags’) represents a viable alternative to traditional methods of individual recognition, as they are permanent and exist in all individuals. We tested the use of genetic markers as the primary means of identifying individuals in a study of humpback whales in the North Atlantic Ocean. Analysis of six microsatellite loci2,3 among 3,060 skin samples collected throughout this ocean allowed the unequivocal identification of individuals. Analysis of 692 ‘recaptures’, identified by their genotype, revealed individual local and migratory movements of up to 10,000 km, limited exchange among summer feeding grounds, and mixing in winter breeding areas, and also allowed the first estimates of animal abundance based solely on genotypic data. Our study demonstrates that genetic tagging is not only feasible, but generates data (for example, on sex) that can be valuable when interpreting the results of tagging experiments.

Inorganic nutrient limitation of oceanic bacterioplankton

Abstract: Although it is commonly accepted that dissolved organic carbon (DOC) of algal origin limits bacterial growth in pelagic systems, there arc relatively few empirical studies documenting this effect. Depending on site and season, both organic and inorganic nutrients can limit the growth of freshwater bacteria. By contrast, inorganic nutrients have only recently been implicated as potentially growth-limiting for marine bacteria. At stations in the Gulf Stream, Sargasso, and Caribbean seas, we used a factorial experimental design to examine effects of inorganic (NH,, and PO,) and organic (glucose) nutrients on the uptake of thymidine and leucine and changes in bacterial abundance. Bacterial growth in seawater dilution cultures varied with station and treatment. Growth rates for the unamended controls (mean 2 SD = 0.11 +_ 0.02 d-l) were not significantly different among the stations or from the in situ rates. In the Caribbean Sea, additions of NH, and PO, resulted in a modest increase in growth rate (p = 0.20-0.35 d--l), whcrcas glucose, either alone or in combination with PO, and NH,, resulted in the largest increase (p = 0.500.55 d-l). By contrast, in the Gulf Stream and Sargasso Sea, the addition of glucose, either alone or in combination with NH,,, resulted in the smallest increase in growth rate (F = 0.2-0.4 d I), whereas the addition of PO.,, either alone or in combination with glucose and NH,, resulted in the largest increase (p = 0.55-0.60 d-l). Growth rates in the PO,,-amended seawalcr culture were 5-6-fold greater than the controls, suggesting that ambient concentrations of labile DOC were sufficient to sustain vigorous growth. We propose that PO, limitation or‘ bacterial growth may directly influence the accumulation of DOC in the surface layer and thus have a significant impact on carbon cycling in the sea. If bacterial growth were not constrained by inorganic nutrients, more DOC could be assimilated into bacterial biomass and subsequently transferred to protistan and metazoan grazers. At the third trophic step beyond bacteria, >90% of the DOC initially assimilated would be released as CO, and <5% would be transferred to mesozooplankton and hence converted into exportable biomass. Thus, when bacterial growth is P limited, the quantity of biogenic carbon (POC + DOC) exported to depth may be greater than would occur if DOC were first incorporated into bacterial biomass.

A direct torque controller for permanent magnet synchronous motor drives

Abstract: This paper describes an investigation of direct torque control (DTC) for permanent magnet synchronous motor (PMSM) drives. The analysis of PMSMs shows that the increase of electromagnetic torque is proportional to the increase of the angle between the stator and rotor flux linkages and therefore fast torque response can be obtained by increasing the rotating speed of the stator flux linkage as fast as possible. The implementation of DTC in PMSM drives is discussed and the switching table specific for an interior PMSM is derived. The proposed control is implemented on a prototype PMSM, which has a standard induction motor stator, and the experimental results show that the torque response is extremely fast. It is also demonstrated that the position sensor is not essential for the inner torque control loop of PMSM drives with DTC.

Guidelines for the diagnosis and management of migraine in clinical practice

Abstract: OBJECTIVE: To provide physicians and allied health care professionals with guidelines for the diagnosis and management of migraine in clinical practice. OPTIONS: The full range and quality of diagnostic and therapeutic methods available for the management of migraine. OUTCOMES: Improvement in the diagnosis and treatment of migraine, which will lead to a reduction in suffering, increased productivity and decreased economic burden. EVIDENCE AND VALUES: The creation of the guidelines followed a needs assessment by members of the Canadian Headache Society and included a statement of objectives; development of guidelines by multidisciplinary working groups using information from literature reviews and other resources; comparison of alternative clinical pathways and description of how published data were analysed; definition of the level of evidence for data in each case; evaluation and revision of the guidelines at a consensus conference held in Ottawa on Oct. 27-29, 1995; redrafting and insertion of tables showing key variables and data from various studies and tables of data with recommendations; and reassessment by all conference participants. BENEFITS, HARMS AND COSTS: Accuracy in diagnosis is a major factor in improving therapeutic effectiveness. Improvement in the precise diagnosis of migraine, coupled with a rational plan for the treatment of acute attacks and for prophylactic therapy, is likely to lead to substantial benefits in both human and economic terms. RECOMMENDATIONS: The diagnosis of migraine can be improved by using modified criteria of the International Headache Society as well as a semistructured patient interview technique. Appropriate treatment of symptoms should take into account the severity of the migraine attack, since most patients will have attacks of differing severity and can learn to use medication appropriate for each attack. When headaches are frequent or particularly severe, prophylactic therapy should be considered. Both the avoidance of migraine trigger factors and the application of nonpharmacological therapies play important roles in overall migraine management and will be addressed at a later date. VALIDATION: The guidelines are based on consensus of Canadian experts in neurology, emergency medicine, psychiatry, psychology, family medicine and pharmacology, and consumers. Previous guidelines did not exist. Field testing of the guidelines is in progress.

Gender and age differences in attitudes to dental pain and dental control

Abstract: In the literature, it is usual to find women and younger subjects reporting higher levels of dental anxiety than men and older subjects. Fear of pain was found to be the most important predictor of dental anxiety and issues of control were also related to such anxiety. Therefore, it was predicted that gender and age differences would be reflected in attitudes to pain and control. Subjects were randomly selected from the voters' list in metropolitan Toronto and mailed a questionnaire with a request for cooperation in a study of their thoughts, feelings, and behaviour regarding dental treatment. The questionnaire included demographic data, measures of dental anxiety and painful experiences as well as the Pain Anxiety Symptoms Scale and the Iowa Dental Control Index. The results supported the main predictions. In addition, attitudes to pain and control were found to be complex phenomena with characteristic gender differences.

Five-year follow-up of high-risk infants with family history of allergy who were exclusively breast-fed or fed partial whey hydrolysate, soy, and conventional cow's milk formulas.

Abstract: Background: Allergy is a common cause of illness. The effect of feeding different infant formulas on the incidence of atopic disease and food allergy was assessed in a prospective randomized double-blind study of high-risk infants with a family history of atopy. Methods: 216 high-risk infants whose mothers had elected not to breast-feed were randomized to receive exclusively a partial whey hydrolysate formula or a conventional cow's milk formula or a soy formula until 6 months of age. Seventy-two high risk infants breast-fed for ≥4 months were also studied. Results: Follow-up until 5 years of age showed a significant lowering in the cumulative incidence of atopic disease in the breast-fed (odds ratio 0.422 [0.200-0.891]) and the whey hydrolysate (odds ratio 0.322 [0.159-0.653) groups, compared with the conventional cow's milk group. Soy formula was not effective (odds ratio 0.759 [0.384-1.501]). The occurrence of both eczema and asthma was lowest in the breast-fed and whey hydrolysate groups and was comparable in the cow's milk and soy groups. Similar significant differences were noted in the 18-60 month period prevalence of eczema and asthma. Eczema was less severe in the whey hydrolysate group compared with the other groups. Double-blind placebo-controlled food challenges showed a lower prevalence of food allergy in the whey hydrolysate group compared with the other formula groups. Conclusions: Exclusive breast-feeding or feeding with a partial whey hydrolysate formula is associated with lower incidence of atopic disease and food allergy. This is a cost-effective approach to the prevention of allergic disease in children.

Centurial and decadal oceanographic influences on changes in northern gannet populations and diets in the north-west Atlantic: implications for climate change

Abstract: Millennial and centurial changes in oceanography influence the distributions and movement patterns of fish and invertebrates. These changes, in turn, determine the availability of food resources for higher trophic levels and, hence, aVect the distributions and abundances of marine birds. A century-long population trend of northern gannets (Sula bassana) is correlated with warming surface water conditions and increased mackerel (Scomber scombrus) availability. On a decadal scale, a major dietary change of breeding gannets from migratory warm-water pelagicfish and squids to cold-water fish is associated with cold-water perturbations in the north-west Atlantic during the 1990s. Cold-water influences appear to have inhibited migratory pelagic fish and squid from moving into the region in recent years, causing a major shift in pelagic food webs on the Newfoundland Shelf. Such findings imply that slight changes in oceanographic conditions, possibly associated with climate warming, could have large-scale and pervasive eVects on seabird distributions, feeding ecology, reproductive success, and populations. Such changes might be detected initially near the limits of seabird ranges and the margins of oceanographic regions. ? 1997 International Council for the Exploration of the Sea

Comparison of accuracy, precision, and sensitivity in elemental assays of fish otoliths using the electron microprobe, proton-induced X-ray emission, and laser ablation inductively coupled plasma mass spectrometry

Abstract: The elemental composition of fish otoliths is of considerable interest to those who wish to reconstruct temperature, migration, or environmental histories of individual fish based on assays of the ...

Perceived Level and Sources of Stress in University Professional Schools

Abstract: The purpose of this study was to investigate the perception of level and sources of stress in students of two baccalaureate nursing programs, to compare these groups in their perceived stress and to compare the nursing groups to those enrolled in other health-related disciplines: Medicine, Pharmacy and Social Work. The study was descriptive correlational in design. The sample consisted of 552 full-time university students enrolled in years 2, 3 and 4 of their programs in selected disciplines. Data were collected by means of a questionnaire consisting of three main instruments: the Beck-Srivastava Stress Inventory (BSSI), the General Health Questionnaire 30-item version (GHQ-30) and a demographic profile. Data were analyzed using the SPSSx Statistical Package and included analysis of variance, frequency distribution, measures of correlation, item analysis and factor analysis. The results revealed that baccalaureate nursing students, regardless of year in program or university of attendance, experienced higher levels of stress and higher levels of physiological and psychological symptoms than students in other health-related disciplines. Identified stressors among the disciplines are also reported in the article.

Antioxidant Activity of Green Tea and Its Catechins in a Fish Meat Model System

Abstract: The antioxidant activity of ground green tea (GGT) and commercial tea extracts, namely Polyphenon 25 (P-25), Polyphenon 30 (P-30), Polyphenon 60 (P-60), and Nikken Polyphenon 60 (NPP-60), as well as green tea extracts (GTE) prepared on laboratory scale and pure tea catechins, namely, (−)-epicatechin (EC), (−)- epigallocatechin (EGC), (−)-epicatechin gallate (ECG), and (−)-epigallocatechin gallate (EGCG), in a fish meat model system was evaluated. Results so obtained were compared with those of samples containing commonly used antioxidants such as α-tocopherol, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and tert-butylhydroquinone (TBHQ). The ground white muscle of mackerel (model system) was cooked at 75 °C and stored at 4 °C for 7 days. Progression of oxidation was monitored by measuring changes in the 2-thiobarbituric acid-reactive substances and selected and/or total volatile contents of samples. The samples treated with GGT leaves, tea extracts, and pure catechins showed excellent ...

Analysis of current controllers for voltage-source inverter

Abstract: Current-controlled pulsewidth modulated (PWM) inverters are widely used in high-performance AC drives because they give high dynamic responses in such systems. This paper presents a comparative study of several current controllers. Particular attention is paid to the hysteresis controller and the ramp-comparator controller, due to their simplicity and widespread use. An improved ramp comparator is proposed in which the current error signals are compared to three 120/spl deg/ phase-shifted triangular waveforms. This eliminates the zero voltage vector applied to the inverter and reduces the inherent amplitude and phase errors. Computer simulations are used to compare the performances. Fast Fourier transform technique is used to show the power spectrum of the current waveforms. Experimental results validate the simulated performances.

Choosing classes in conceptual modeling

Abstract: ion from Instances. A class can be defined only if there are instances in the relevant universe possessing all properties defining the class. Adherence to this principle supports the fundamental meaning of concept—a specification of the properties common to some instances. If no instances from the relevant universe share a specified set of properties, there is no “sameness” and no economy of representation. It would be cognitively wasteful to store such a set of properties as a concept, as it tells us nothing about the relevant universe. This principle is perhaps obvious for knowledge acquisition methods that build up abstract descriptions from a given set of objects. However, it is less obvious for methods based on inferring new categories from existing ones [5, 12], as these methods do not use instances to identify candidate classes. Moreover, abstraction from instances does not appear as an explicit requirement in object-oriented design and semantic data modeling. COMMUNICATIONS OF THE ACM June 1997/Vol. 40, No. 6 65 Maximal Abstraction. A relevant property possessed by all instances of a class should be included in the class definition. This principle supports both cognitive economy and inference. If certain properties shared by all instances are not part of the class (concept) definition, some similarities among the instances in the class are lost. Moreover, properties shared by all instances, but not included in the classification, cannot be inferred if an instance is identified as a member of the class. Abstraction from instances and maximal abstraction are requirements for a class to effectively express what the instances in a set have in common. We therefore propose that these principles be used as necessary requirements for a set of properties to be considered a class. We consider a set of properties a potential class in a relevant universe if and only if: • It has a nonempty extension (at some point in time); and • It contains all properties common to all instances in the extension. Note that although the set of properties forming a potential class is fixed, the properties possessed by an instance may change with time. As an instance acquires or loses properties, it might “move” in and out of a potential class. In other words, the population of a class might vary with time. It follows from the definition that two distinct potential classes cannot be defined by the same set of properties. In practice, if distinct names have been attached to identical sets of properties, these names are synonyms. Also, two distinct potential classes cannot have the same extension, that is, at every time, there is at least one instance in one class that is not included in the other. The implication of the second observation can be illustrated by an example. Consider a university department having a policy that only graduate students can serve as research assistants and that all of them must do so. Although “graduate student” and “research assistant” may reasonably be thought of as distinct classes, the fact that they must always have the same instances means they cannot constitute distinct potential classes. Even though different properties could be chosen to define graduate student and research assistant, the same instances must share these properties. Maintaining the two as distinct classes is redundant. Moreover, it might lead to misunderstandings, since for many purposes people think of “graduate student” and “research assistant” as different concepts. For instance, a user in the campus health center may reasonably distinguish graduate student and research assistant classes, believing instances of each carry different forms of health insurance. This example shows how examining class extensions can help avoid misconceptions arising from prior informal “conceptual baggage.” The analysis in this example required that the extension of the classes be known. In general, to prevent redundancy, we propose that classification strategies check whether different classes have identical extensions. This does not imply a need for complete enumeration of instances, which, in most cases, may be impractical. Instead, it may be possible to identify synonymous classes by some reasoning. For example, a student organization may use the concept “member.” If all students of a university are members of this organization and only students are members, the concept “member” can be identified as synonymous with “student” without examining the actual instances. Class Structures The potential class concept restricts the possible classes formed to model the relevant universe. Whether a given collection of properties is a potential class can be determined irrespective of the other classes being considered. However, in conceptual modeling we are interested in collections of classes (or concepts). We now turn to the implications of applying cognitive economy and inference to such collections. Inference relates to the ability to infer properties from class membership. Cognitive economy involves balancing the objective of maximizing information content with that of minimizing the number of stored concepts, by emphasizing the value of distinguishing between concepts whose instances possess “meaningful differences.” Thus, the full information about an instance is usually distributed among all classes to which it belongs. To eliminate loss of information and minimize redundancy, we propose two additional principles that apply to collections of classes: completeness, which requires that all properties from the relevant universe be used in a classification, and nonredundancy, which ensures there are no redundant classes. Completeness. Given a relevant universe of instances and properties, every property should be used in the definition of at least one class in the set of classes. If a property is part of the relevant universe, instances possessing it have “meaningful differences” 66 June 1997/Vol. 40, No. 6 COMMUNICATIONS OF THE ACM with respect to those that do not. By requiring all relevant properties to be part of the definition of some class, the principle of completeness supports the “maximum information” aspect of cognitive economy. The principle also supports inference, as it ensures every relevant property can be inferred by considering all classes to which the instance belongs. However, cognitive economy also requires “least cognitive effort,” leading to the next requirement. Nonredundancy. A class that is a subclass of several other classes should be defined by at least one property not in any of its superclasses. Suppose that, in violation of this requirement, a new class is defined by all the properties of some existing classes. Every instance of the new class is an instance of all of the original classes. If there are no additional properties, the new class adds no information about its instances. Therefore, the principle of nonredundancy supports the “minimize the number of classes” aspect of cognitive economy. We define class structure as a set of potential classes satisfying the principles of completeness and nonredundancy; that is: • Every property in the relevant universe appears in the definition of at least one class; and • No class is defined only in terms of the properties of a set of other classes. To have any practical consequence, it must be possible to construct a class structure for any given relevant universe. It can be proven by construction that for every relevant universe a class structure can be formed. Specialization of classes is widely used in both knowledge representation (where it is frequently called subsumption [2, 12]) and in object-oriented design and data modeling [11]. In our propertybased (intensional) view of classes, we defined specialization as forming one class from another class by adding properties. A direct consequence of the observation that distinct potential classes cannot have the same extension is that the instances of a subclass are a strict subset of those of every superclass and therefore are also instances of the latter. The second condition in the definition of class structure also implies that, in a class structure, a specialized class must have properties not possessed by any of its superclasses. To see the intuitive meaning of this, consider again the university example, except that now a research assistant may or may not be a student. If “research assistants who are students” is useful for modeling this domain, we contend there must be properties of this population in addition to those of students and of research assistants, such as a special tuition fee. From a cognitive perspective, without such properties there is no need to define a new class. Properties of Class Structures Class structures have a number of interesting and useful properties for conceptual modeling. First, there will generally be a “pluralism of views” supporting the cognitive principles. This is manifested by two observations: Multiplicity. More than one class structure may exist for a relevant universe having more than one property. Multiplicity implies that several views of a domain, each supporting cognitive economy and inference, can coexist. Inclusion. Every potential class can be included in some class structure. Inclusion ensures that every concept of interest can, in principle, be included in a model that supports cognitive principles. A second useful property of class structures is that they can be made fully descriptive of all instances in the relevant universe. A class structure is required to include all relevant properties. Yet it is possible for a given instance that not all its relevant properties are included in the classes to which it belongs. Also, it is possible for an instance in the relevant universe to be unclassified. In particular, when a class is removed from a class structure, some of its instances may no longer belong to any class. In terms of classification theory, these possibilities reflect

Design of low band gap polymers employing density functional theory—hybrid functionals ameliorate band gap problem

Abstract: Band gaps in solids and excitation energies in finite systems are underestimated significantly if estimated from differences between eigenvalues obtained within the local spin density approximation (LSDA). In this article we present results on 20 small- and medium-sized π-systems which show that HOMO–LUMO energy differences obtained with the B3LYP, B3P86, and B3PW91 functionals are in good agreement with vertical excitation energies from UV-absorption spectra. The improvement is a result of the use of the exact Hartree–Fock exchange with hybrid methods. Negative HOMO energies and negative LUMO energies do not provide good estimates for IPs and EAs. In contrast to Hartree–Fock theory, where IPs are approximated well and EAs are given poorly, DFT hybrid methods underestimate IPs and EAs by about the same amount. LSDA yields reasonable EAs but poor IPs. © 1997 John Wiley & Sons, Inc. J Comput Chem18: 1943–1953, 1997

Effects of the neurotrophins nerve growth factor, neurotrophin-3, and brain-derived neurotrophic factor (BDNF) on neurite growth from adult sensory neurons in compartmented cultures.

Abstract: We used compartmented cultures to study the regulation of adult sensory neurite growth by neurotrophins. We examined the effects of the neurotrophins nerve growth factor (NGF), neurotrophin-3 (NT3), and BDNF on distal neurite elongation from adult rat dorsal root ganglion (DRG) neurons. Neurons were plated in the center compartments of three-chambered dishes in the absence of neurotrophin, and neurite extension into the distal (side) compartments containing NGF, BDNF, or NT3 was quantitated. Initial proximal neurite growth did not require any of the neurotrophins, while subsequent elongation into distal compartments required NGF. After neurites had extended into NGF-containing distal compartments, removal of NGF by treatment with anti-NGF resulted in the cessation of growth with minimal neurite retraction. In contrast to the effects of NGF, no distal neurite elongation was observed into compartments with BDNF or NT3. To examine possible additive influences, neurite extension into compartments containing BDNF plus NGF or NT3 plus NGF was quantitated. There was no increased neurite extension into NGF plus NT3 compartments, while the combination of BDNF plus NGF resulted in an inhibition of neurite extension compared with NGF alone. We then investigated whether the regrowth of neurites that had originally grown into NGF subsequent to in vitro axotomy still required NGF. The results demonstrated that unlike adult sensory nerve regeneration in vivo, the in vitro regrowth did require NGF, and neither BDNF nor NT3 was able to substitute for NGF. Since the initial growth from neurons after dissociation (which is also a regenerative response) did not require NGF, it would appear that neuritic growth and regrowth of adult DRG neurons in vitro includes both NGF-independent and NGF-dependent components. The compartmented culture system provides a unique model to further study aspects of this differential regulation of neurite growth.

Propulsive performance from oscillating propulsors with spanwise flexibility

Abstract: The propulsive performance of oscillating foils with spanwise flexibility was studied using a time-domain panel method. The work was done to assess the effects of spanwise flexibility on the propulsive efficiency of these propulsors, especially those employed by relatively fast swimming marine animals. The method is valid for three-dimensional attached flows around the actual planforms found on these animals and was used in the study reported here to assess the performance of the flukes of an immature fin whale ( Balaenoptera physalus ). It is shown that passive spanwise flexibility reduces propulsive efficiency, but that propulsive efficiency of these planforms can be increased, over the value for an equivalent rigid foil, by careful control of the phase of the spanwise flexibility relative to other motion parameters.

Stimulation of corticotrophin-releasing hormone release by the obese (ob) gene product, leptin, from hypothalamic explants

Abstract: Recent data have suggested that adipocytes synthesize and secrete a 16 kDa peptide which acts centrally to regulate weight gain by suppressing appetite and activating the sympathetic nervous system. To exert such effects, it may function as an endogenous ligand in the CNS, since specific receptors (OB-R) have been recently reported to be widely distributed in the brain. We have speculated that this peptide, now known as leptin, may act centrally by stimulating the release of corticotrophin-releasing hormone (CRH), a recognized potent inhibitory modulator of appetite. We tested in vitro the effect of murine leptin on CRH secretion in the dose range of 0.1 pM-100 nM. The static rat hypothalamic incubation system used involved fresh hypothalamic explants maintained in EBSS with consecutive 20 min incubations, and estimation of CRH concentrations in the medium by a specific and sensitive radioimmunoassay. The effect of heat-denatured leptin at a dose of 1 nM and 10 nM, was also investigated. Any possible modulation of leptin effects by adrenergic pathways was then explored by coincubating hypothalami with leptin 10 nM and equimolar concentrations of the alpha 1-adrenergic antagonist prazosin or the beta-adrenergic antagonist propranolol. The active leptin, but not the heat-inactivated peptide, caused a dose-dependent stimulation of CRH release in vitro (p < 0.05- < 0.0001 vs control), with a plateau effect at a dose of 10 nM. The addition of either prazosin or propranolol was without effect on leptin-dependent CRH stimulation. These findings are consistent with the reported presence of leptin receptors in the rat brain, and suggest that leptin may act to regulate appetite at least in part by directly modulating the secretion of CRH from the hypothalamus. It would also appear that such effect occurs via a non-adrenergic mechanism.