bluuebunny/crossref_metadata_2025 huggingface dataset:
Attenuation and activation characteristics of steel and tungsten and the suitability of these materials for use in a fast neutron multileaf collimator
Authors: Maughan Richard L. , Yudelev Mark , Forman Jeffrey D. , Williams Samuel B. , Gries Donald , Fletcher Tristan M. , Chapman William , Blosser Emanuel J. , Horste Timothy
Published: June 2008

A computer controlled multileaf collimator (MLC) is being designed to replace the multirod collimator (MRC) at present used to shape the d(48.5)+Be neutron beam from the Harper Hospital superconducting cyclotron. The computer controlled MLC will improve efficiency and allow for the future development of intensity modulated radiation therapy with neutrons. The existing MRC uses tungsten rods, while the new MLC will use steel as the leaf material. In the current study the attenuation and activation characteristics of steel are compared with those of tungsten to ensure that (a) the attenuation achieved in the MLC is at least equivalent to that of the existing MRC, and (b) that the activation of the steel will not result in a significant change in the activation levels within the treatment room. The latter point is important since personnel exposure (particularly to the radiation therapy technologists) from induced radioactivity must be minimized. Measurement of the neutron beam attenuation in a broad beam geometry showed that a 30 cm thick steel leaf yielded 2.5% transmission. This compared favorably with the 4% transmission obtained with the existing MRC. Irradiation of steel and tungsten samples at different depths in a 30 cm steel block indicated that the activation of steel should be no worse than that of tungsten.
The water‐equivalence of phantom materials beta particles
Authors: Buckley Lesley A. , Thomadsen Bruce R. , DeWerd Larry A.
Published: June 2008

Intravascular brachytherapy requires that the dose be specified within millimeters of the source. High dose gradients near brachytherapy sources require that the source‐detector distance be accurately known for dosimetry purposes. Solid phantoms can be designed to accommodate these stringent requirements. This study reports dosimeter readings from sources measured in water, A150, polystyrene and in an epoxy‐based water‐equivalent plastic. Measurements showed that while A150 and the epoxy‐based plastic agreed well with water when the surface of the source contacted the detector housing, the relative response in the phantoms decreased with increasing depth in phantom, falling to ∼0.55 those of water at a depth of 5 mm. Readings in polystyrene were within 4% of those in water between 1 and 2 mm depth. However, while polystyrene followed water more closely than the other two materials, at greater depths the relative response in polystyrene to water varied from 0.65 to 1.34. When the density of the materials is accounted for, the relative response in A150 is nearly constant with increasing areal density. Furthermore, the response in A150 shows the closest agreement with that in water of any of the solid materials for higher areal densities. For values below 0.3 polystyrene shows the closest agreement with water.
Calculation of mean central dose in interstitial brachytherapy using Delaunay triangulation
Authors: Astrahan Melvin A. , Streeter Oscar E. , Jozsef Gabor
Published: June 2008

In 1997 the ICRU published Report 58 “Dose and Volume Specification for Reporting Interstitial Therapy” with the objective of addressing the problem of absorbed dose specification for reporting contemporary interstitial therapy. One of the concepts proposed in that report is “mean central dose.” The fundamental goal of the mean central dose (MCD) calculation is to obtain a single, readily reportable and intercomparable value which is representative of dose in regions of the implant “where the dose gradient approximates a plateau.” Delaunay triangulation (DT) is a method used in computational geometry to partition the space enclosed by the convex hull of a set of distinct points P into a set of nonoverlapping cells. In the three‐dimensional case, each point of P becomes a vertex of a tetrahedron and the result of the DT is a set of tetrahedra. All treatment planning for interstitial brachytherapy inherently requires that the location of the radioactive sources, or dwell positions in the case of HDR, be known or digitized. These source locations may be regarded as a set of points representing the implanted volume. Delaunay triangulation of the source locations creates a set of tetrahedra without manual intervention. The geometric centers of these tetrahedra define a new set of points which lie “in between” the radioactive sources and which are distributed uniformly over the volume of the implant. The arithmetic mean of the dose at these centers is a three dimensional analog of the two‐dimensional triangulation and inspection methods proposed for calculating MCD in ICRU 58. We demonstrate that DT can be successfully incorporated into a computerized treatment planning system and used to calculate the MCD.
A theoretical model for event statistics in microdosimetry. II: Nonuniform distribution of heavy ion tracks
Authors: Santa Cruz G. A. , Palmer M. R. , Matatagui E. , Zamenhof R. G.
Published: June 2008

A microdosimetry model, described in Part I, applies to the case of a convex site immersed in a uniform distribution of heavy particle tracks, and assumes no restrictions in site geometry or the kind of randomness. In Part II, this model is extended to include nonuniform distributions of particle tracks. This situation is relevant to the study of microdosimetry, for example, in boron neutron capture, in irradiation experiments using heavy ion particle beams, where the sources of particle tracks are external to the cell, or in irradiation from internally incorporated particle‐emitting radionuclides, such as environmental radon or occupational exposure to radioactive materials. The formalism developed permits the calculation of statistical properties, track length distributions, and microdosimetric spectra for convex sites where the “inner” and “outer” concentrations of sources may be different, or for tracks originating on the surface of a convex site. Expressions applicable to the case of surface‐distributed sources of tracks are presented that may represent situations such as boron compounds bound to the membrane of a cellular nucleus in boron neutron capture. A series of Monte Carlo calculations and analytical solutions, illustrating the case of spherical site geometry, are presented and compared. Finally, microdosimetric spectra and specific energy averages are calculated for alpha and lithium particles originating from thermal neutron capture in showing their dependence on localization (extra‐site, uniform, intra‐site, or surface‐distributed).
Variation of sensitometric curves of radiographic films in high energy photon beams
Authors: Danciu Claudia , Proimos Basil S. , Rosenwald Jean‐Claude , Mijnheer Ben J.
Published: June 2008

Film dosimetry is an important tool for the verification of irradiation techniques. The shape of the sensitometric curve depends on the type of film as well as on the irradiation and processing conditions. Existing data concerning the influence of irradiation geometry on the sensitometric curve are conflicting. In particular the variation of optical density, OD, with field size and depth in a phantom shows large differences in magnitude between various authors. This variation, as well as the effect of beam energy and film plane orientation on OD, was therefore investigated for two types of film, Kodak X‐Omat V and Agfa Structurix D2. Films were positioned in a solid phantom, either perpendicular or (almost) parallel to the beam axis, and irradiated to different dose levels using various photon beams (Co‐60, 6 MV, 15 MV, 18 MV, 45 MV). It was found that the sensitometric curves of the Kodak film derived at different depths are almost identical for the four x‐ray beams. For the Kodak film the differences in OD with depth are less than 2%, except for the Co‐60 beam, where the difference is about 4% at 10 cm depth for a 15 cm × 15 cm field. The slope of the sensitometric curve of the Agfa film is somewhat more dependent on photon beam energy, depth and field size. The sensitometric curves of both types of film are almost independent of the film plane orientation, except for shallow depths. For Co‐60 and for the same dose, the Kodak and Agfa films gave at dose maximum an OD lower by 4% and 6%, respectively, for the parallel compared to the perpendicular geometry. Good dosimetric results can be obtained if films from the same batch are irradiated with small to moderate field sizes (up to about 15 cm × 15 cm), at moderate depths (up to about 15 cm), using a single calibration curve, e.g., for a 10 cm × 10 cm field.
Experimental determination and verification of the parameters used in a proton pencil beam algorithm
Authors: Szymanowski H. , Mazal A. , Nauraye C. , Biensan S. , Ferrand R. , Murillo M. C. , Caneva S. , Gaboriaud G. , Rosenwald J. C.
Published: June 2008

We present an experimental procedure for the determination and the verification under practical conditions of physical and computational parameters used in our proton pencil beam algorithm. The calculation of the dose delivered by a single pencil beam relies on a measured spread‐out Bragg peak, and the description of its radial spread at depth features simple specific parameters accounting individually for the influence of the beam line as a whole, the beam energy modulation, the compensator, and the patient medium. For determining the experimental values of the physical parameters related to proton scattering, we utilized a simple relation between Gaussian radial spreads and the width of lateral penumbras. The contribution from the beam line has been extracted from lateral penumbra measurements in air: a linear variation with the distance collimator‐point has been observed. Analytically predicted radial spreads within the patient were in good agreement with experimental values in water under various reference conditions. Results indicated no significant influence of the beam energy modulation. Using measurements in presence of Plexiglas slabs, a simple assumption on the effective source of scattering due to the compensator has been stated, leading to accurate radial spread calculations. Dose measurements in presence of complexly shaped compensators have been used to assess the performances of the algorithm supplied with the adequate physical parameters. One of these compensators has also been used, together with a reference configuration, for investigating a set of computational parameters decreasing the calculation time while maintaining a high level of accuracy. Faster dose computations have been performed for algorithm evaluation in the presence of geometrical and patient compensators, and have shown good agreement with the measured dose distributions.
Modeling the output ratio in air for megavoltage photon beams
Authors: Zhu Timothy C. , Bjärngard Bengt E. , Xiao Ying , Yang C. J.
Published: June 2008

The output ratio in air, OR, for a high‐energy x‐ray beam describes how the incident central axis photon fluence varies with collimator setting. For field sizes larger than its variation is caused by the scatter of photons in structures in the accelerator head (primarily the flattening filter and the wedge, if one is used) and by the backscatter of radiation into the monitor ionization chamber. The objective of this study was to evaluate the use of an analytical function to parametrize OR for square collimator setting For open beams, these parameters can be attributed to explicit physical meanings within the systematical uncertainty of the model: accounts for backscatter into the monitor, is the maximum scatter‐to‐primary ratio for head‐scattered photons, and λ represents the effective width of the “source” of head‐scatter photons. is a constant that sets for This formula also fits OR for wedge beams and a Co‐60 unit, although the fitting parameters lose their physical interpretations. To calculate the output ratio for a rectangular field, an equivalent square can be used: where k is a constant. The study included a number of different accelerators and a cobalt‐60 unit. The fits for square fields agreed with measurements with a standard deviation (SD) of less than 0.5%. Using where and are the source‐to‐collimator distances and f is the source‐to‐detector distance, measurements and calculations agreed within a SD of 0.7% for rectangular fields. Sufficient data for the three parameters are presented to suggest constraints that can be used for quality assurance of the measured output ratio in air.
Evaluation of osteoporosis using conventional radiographic methods and dual energy x‐ray absorptiometry
Authors: Anburajan M.
Published: June 2008

In India, conventional radiographs play a major part in evaluating osteoporosis since advanced bone densitometers are expensive and not widely available. Our aim in this study was to investigate the usefulness of conventional radiographic methods, viz., clavicle and metacarpal radiogrammetry, quantitative vertebral morphometry, Singh's index, hip geometry compared to a sophisticated method, viz., DXA for studying osteoporosis in south Indian men (n=663) and women (n=741). This study provides data on BMD of the proximal femur in normal south Indian females. In women, aged above 65 years, BMD of femoral neck, trochanter, and Ward's triangle decreased by 0.90%, 0.84%, and 1.66% per annum, respectively. In 45 pre‐ and post‐menopausal women without fractures, total hip BMD correlated significantly (p<0.001) with Singh's index medial cortical thickness of the femoral shaft and neck combined cortical thickness (CCT) and %CCT of the clavicle each), and the second metacarpal and respectively). On comparing variables studied for osteoporotic women with corresponding values in the premenopausal group, the average difference in SD from the mean was greatest for clavicle radiogrammetry (−3.7 SD for %CCT of the clavicle). An empirical formula for predicting total hip BMD with good sensitivity was derived from a multiple linear regression equation involving three independent variables, viz., CCT, %CCT of the clavicle (measured from the chest radiograph) and the patient's age. This author's equation, with modified weightings, has 82% sensitivity and 94% specificity and a positive and negative predictive value of 88% and 91% respectively. A chest radiograph in combination with the formula would serve as a readily available, inexpensive tool for assessing post‐menopausal osteoporosis, especially in developing countries.
Computer‐aided diagnosis in chest radiography
Authors: van Ginneken Bram
Published: June 2008

Automating mass chest screening for tuberculosis (TB) requires segmentation and texture analysis in chest radiographs. Several rule‐based schemes, pixel classifiers, and active shape model techniques for segmenting lung fields in chest radiographs are described and compared. An improved version of the active shape model segmentation technique, originally developed by Cootes and Taylor from Manchester University, UK, is described that uses optimal local features to steer the segmentation process and outperforms the original method in segmentation tasks for several types of medical images: chest radiographs and slices from MRI brain data. In order to segment the posterior ribs in PA chest radiographs, a statistical model of the complete rib cage is constructed using principal components analysis and a method is described to fit this model to input images automatically. For texture analysis, an extension is proposed to the framework of locally orderless images, a multiscale description of local histograms recently proposed by Koenderink and Van Doorn from Utrecht University, The Netherlands. The segmentation and texture analysis techniques are combined into a single method that automatically detects textural abnormalities in chest radiographs and estimates the probability that an image contains abnormalities. The method was evaluated on two databases. On a 200 case database of clinical chest films with interstitial disease from the University of Chicago, excellent results are obtained (area under the ROC curve The results for a 600 case database from a TB screening program are encouraging (area under the ROC curve
Novelty and Uniqueness Patterns of Rare Members of the Soil Biosphere
Authors: Elshahed Mostafa S. , Youssef Noha H. , Spain Anne M. , Sheik Cody , Najar Fares Z. , Sukharnikov Leonid O. , Roe Bruce A. , Davis James P. , Schloss Patrick D. , Bailey Vanessa L. , Krumholz Lee R.
Published: July 2008

Soil bacterial communities typically exhibit a distribution pattern in which most bacterial species are present in low abundance. Due to the relatively small size of most culture-independent sequencing surveys, a detailed phylogenetic analysis of rare members of the community is lacking. To gain access to the rarely sampled soil biosphere, we analyzed a data set of 13,001 near-full-length 16S rRNA gene clones derived from an undisturbed tall grass prairie soil in central Oklahoma. Rare members of the soil bacterial community (empirically defined at two different abundance cutoffs) represented 18.1 to 37.1% of the total number of clones in the data set and were, on average, less similar to their closest relatives in public databases when compared to more abundant members of the community. Detailed phylogenetic analyses indicated that members of the soil rare biosphere either belonged to novel bacterial lineages (members of five novel bacterial phyla identified in the data set, as well as members of multiple novel lineages within previously described phyla or candidate phyla), to lineages that are prevalent in other environments but rarely encountered in soil, or were close relatives to more abundant taxa in the data set. While a fraction of the rare community was closely related to more abundant taxonomic groups in the data set, a significant portion of the rare biosphere represented evolutionarily distinct lineages at various taxonomic cutoffs. We reason that these novelty and uniqueness patterns provide clues regarding the origins and potential ecological roles of members of the soil's rare biosphere.
Roles of the Sortases of
Streptococcus pneumoniae
in Assembly of the RlrA Pilus
Authors: LeMieux Julianna , Woody Shauna , Camilli Andrew
Published: July 2008

Pili have been observed on the surface of several gram-positive bacteria, including
Streptococcus pneumoniae
. The
S. pneumoniae
strain TIGR4 pilus is composed of three structural subunit proteins encoded in the
rlrA
pathogenicity islet, RrgA, RrgB, and RrgC. RrgB comprises the pilus backbone, RrgA is observed at intervals along surface pili, while RrgC is found in a loosely defined relationship with RrgA. We investigated the incorporation of each subunit into pili and the reliance of such placement on each of the other subunits. Both accessory subunits RrgA and RrgC are present in similar quantities in pili of all sizes. However, neither protein is required for the polymerization of RrgB, suggesting a nonessential role for RrgA and RrgC in the initiation of pilus assembly. Additionally, the
rlrA
islet encodes three sortases, SrtC-1, SrtC-2, and SrtC-3 (formerly SrtB, SrtC, and SrtD), which are divergent in sequence from the housekeeping sortase, SrtA. We determined the contributions of these four sortases to pilus assembly and found that SrtA is dispensable for pilus assembly and localization to the cell wall. Instead, SrtC-1, SrtC-2, and SrtC-3 are responsible for pilus assembly and exhibit functional redundancy with respect to backbone assembly and cell wall localization. A level of specificity and coordination among the class C sortases was revealed by the finding that SrtC-1 and SrtC-3 are required for the incorporation of the accessory subunits and by showing a deleterious effect on pilus assembly upon alteration of the cell wall sorting signals of the accessory subunit proteins.
Control of Peripheral Light-Harvesting Complex Synthesis by a Bacteriophytochrome in the Aerobic Photosynthetic Bacterium
Bradyrhizobium
Strain BTAi1
Authors: Jaubert Marianne , Vuillet Laurie , Hannibal Laure , Adriano Jean-Marc , Fardoux Joël , Bouyer Pierre , Bonaldi Katia , Fleischman Darrell , Giraud Eric , Verméglio André
Published: July 2008

The recent sequence analysis of the photosynthetic and plant-symbiotic
Bradyrhizobium
sp. strain BTAi1 revealed the unexpected presence of a
pucBA
operon encoding the apoproteins of peripheral light-harvesting (LH) complexes. This
pucBA
operon is found close to a bacteriophytochrome gene (
BphP3

B
BTAi1

) and a two-component transcriptional regulator gene (TF
BTAi1
gene). In this study, we show that BphP3

B
BTAi1

acts as a bona fide bacteriophytochrome and controls, according to light conditions, the expression of the
pucBA
operon found in its vicinity. This light regulatory pathway is very similar to the one previously described for chromo-BphP4

Rp

in
Rhodopseudomonas palustris
and conducts the synthesis of a peripheral LH complex. This LH complex presents a single absorption band at low temperature, centered at 803 nm. Fluorescence emission analysis of intact cells indicates that this peripheral LH complex does not act as an efficient light antenna. One putative function of this LH complex could be to evacuate excess light energy in order to protect
Bradyrhizobium
strain BTAi1, an aerobic anoxygenic photosynthetic bacterium, against photooxidative damage during photosynthesis.
Self-assessed understanding as a tool for evaluating consent: reflections on a longitudinal study
Authors: Swartling U , Helgesson G
Published: June 2008

Based on extensive clinical questionnaire data, this paper explores the relation between research subjects’ self-assessed understanding and actual knowledge of a large-scale predictive screening study, and its implications for the proper handling of information and consent routines in longitudinal studies. The intitial data show that low self-assessed understanding among participants was correlated with limited knowledge, concern over participation and collected samples, less satisfaction with information, and feeling passive or negative towards the study. Among those reporting high understanding, a non-negligible number displayed a lack of knowledge regarding central aspects of the study. Regarding high assessed understanding, the multivariate analysis identified the main predictor variables to be knowledge, having a positive attitude towards participation and the study itself, being satisfied with information, having a stable psychosocial background and feeling calm regarding the handling of samples. These findings indicate that to evaluate participants' understanding through self-assessment may not be reliable method. Self-assessed understanding may rather be a good indicator of general attitudes than a tool for analysing content. The data also show that actual understanding varies considerably among participants, suggesting that more effort needs to be put into adjusting the information to the needs of different subgroups. It is argued that when doing this, researchers in longitudinal studies must be careful not to exhaust participants with excessive information that they do not want and that may cause them to drop out. The ethical relevance of obtaining repeated consents in longitudinal research is discussed.
The “four quadrants” approach to clinical ethics case analysis; an application and review: Table 1
Authors: Sokol D K
Published: June 2008

In 1982, Jonsen, Siegler and Winslade publishedClinical Ethics, in which they described the “four quadrants” approach, a new method of analysing clinical ethics cases. Although the book is now in its 6th edition, a literature search has revealed only one academic paper demonstrating the method at work. This paper is an attempt to start filling this gap. As a way of describing and testing the approach, I apply the four quadrants method to a detailed clinical ethics case. The analysis is interspersed with reflections on the method itself. It is hoped that this experiment will encourage ethicists and clinicians to devote more attention to this neglected approach.
Moral distress among Norwegian doctors
Authors: Førde R , Aasland O G
Published: June 2008

Background:

Medicine is full of value conflicts. Limited resources and legal regulations may place doctors in difficult ethical dilemmas and cause moral distress. Research on moral distress has so far been mainly studied in nurses.

Objective:

To describe whether Norwegian doctors experience stress related to ethical dilemmas and lack of resources, and to explore whether the doctors feel that they have good strategies for the resolution of ethical dilemmas.

Design:

Postal survey of a representative sample of 1497 Norwegian doctors in 2004, presenting statements about different ethical dilemmas, values and goals at their workplace.

Results:

The response rate was 67%. 57% admitted that it is difficult to criticise a colleague for professional misconduct and 51% for ethical misconduct. 51% described sometimes having to act against own conscience as distressing. 66% of the doctors experienced distress related to long waiting lists for treatment and to impaired patient care due to time constraints. 55% reported that time spent on administration and documentation is distressing. Female doctors experienced more stress that their male colleagues. 44% reported that their workplace lacked strategies for dealing with ethical dilemmas.

Conclusion:

Lack of resources creates moral dilemmas for physicians. Moral distress varies with specialty and gender. Lack of strategies to solve ethical dilemmas and low tolerance for conflict and critique from colleagues may obstruct important and necessary ethical dialogues and lead to suboptimal solutions of difficult ethical problems.
Pharmacist conscience clauses and access to oral contraceptives
Authors: Flynn D P
Published: June 2008

The introduction of conscience clauses after the 1973 US Supreme Court decision inRoe v. Wadeallowed physicians and nurses to opt out of medical procedures, particularly abortions, to which they were morally opposed. In recent years pharmacists have requested the same consideration with regard to dispensing some medicines. This paper examines the pharmacists’ role and their professional and moral obligations to patients in the light of recent refusals by pharmacists to dispense oral contraceptives. A review of John Rawls’s concepts of the “original position” and the “veil of ignorance”, along with consideration of the concept of compartmentalisation, are used to assess pharmacists’ requests and the moral and legal rights of patients to have their prescriptive needs met.
The ethics of non-heart-beating donation: how new technology can change the ethical landscape
Authors: Zeiler K , Furberg E , Tufveson G , Welin S
Published: June 2008

The global shortage of organs for transplantation and the development of new and better medical technologies for organ preservation have resulted in a renewed interest in non-heart-beating donation (NHBD). This article discusses ethical questions related to controlled and uncontrolled NHBD. It argues that certain preparative measures, such as giving anticoagulants, should be acceptable before patients are dead, but when they have passed a point where further curative treatment is futile, they are in the process of dying and they are unconscious. Furthermore, the article discusses consequences of technological developments based on improvement of a chest compression apparatus used today to make mechanical heart resuscitation. Such technological development can be used to transform cases of non-controlled NHBD to controlled NHBD. In our view, this is a step forward since the ethical difficulties related to controlled NHBD are easier to solve than those related to non-controlled NHBD. However, such technological developments also evoke other ethical questions.
The social psychology of amateur ethicists: blood product recall notification and the value of reflexivity
Authors: Wasserman J A , Dure L S
Published: June 2008

The purpose of this article is to highlight ways in which institutional policymakers tend to insufficiently conceptualise their role as ethics practitioners. We use the case of blood product recall notification as a means of raising questions about the way in which, as we have observed it, discourse for those who make institutional ethics policies is constrained by routine balancing of simplified principles to the exclusion of reflexive practices—those that turn ethics reasoning back on itself. The latter allows ethics practitioners with comparatively little formal training to take ownership of traditional parameters, which define their discussions and ultimately ought to make them more insightful when doing ethics. Thus, in the midst of calls for more training to increase the competency of ethics committees, we suggest that an additional problem of how these lay ethicists conceive of their roles also needs to be addressed.
Ethics review of research: in pursuit of proportionality
Authors: Edwards S J L , Omar R
Published: June 2008

The ethics review system of research is now well-established, at least in the developed world, although there are many differences in how countries view it and go about managing it. The UK specifically is now seeking to revise its system by speeding up the process of ethics approval but only for some studies. It is proposed that only those studies which pose “no material ethical issues” should be “fast-tracked”. However, it is unclear what this means, who should decide and what should be included in this category.

In this paper, we go some way towards answering these questions. While we are certain that the debate is only just beginning, we are equally certain that it will continue to run long after the system has been reformed. To stimulate this conversation and to inform a pilot project of the new system directly, we review two candidates to help give some substance to the notion of “material” ethical issues. Firstly, material could mean a certain type or degree of risk. Second, material could mean how physically invasive the research is. We conclude that there is still much work to be done on making the system of governing health and social care consistent and practicable.
Is genetic information relevantly different from other kinds of non-genetic information in the life insurance context?
Authors: Malpas P J
Published: June 2008

Within the medical, legal and bioethical literature, there has been an increasing concern that the information derived from genetic tests may be used to unfairly discriminate against individuals seeking various kinds of insurance; particularly health and life insurance. Consumer groups, the general public and those with genetic conditions have also expressed these concerns, specifically in the context of life insurance.

While it is true that all insurance companies may have an interest in the information obtained from genetic tests, life insurers potentially have a very strong incentive to (want to) use genetic information to rate applicants, as individuals generally purchase their own cover and may want to take out very large policies.

This paper critically focuses on genetic information in the context of life insurance. We consider whether genetic information differs in any relevant way from other kinds of non-genetic information required by and disclosed to life insurance companies by potential clients. We will argue that genetic information should not be treated any differently from other types of health information already collected from those wishing to purchase life insurance cover.
On Some Cossuridae and Maldanidae (Polychaeta) from Washington and British Columbia
Authors: Banse Karl
Published: June 2008

Cossura soyeri Laubier and Clymenella torquata (Leidy) are newly recorded for the Pacific Ocean. Praxillella praetermissa (Malmgren) is new to the northeast Pacific. Another species of Cossura (unidentifiable) and Maldanella harai (Izuka) are added to the fauna of Washington and British Columbia.Key words: Cossuridae, Maldanidae, new records, Northeast Pacific, Polychaetes
Environmental Control of Phytoplankton Patchiness
Authors: Therriault Jean-Claude , Platt Trevor
Published: June 2008

The relative importance of the various biological, chemical, and physical factors for the control of the phytoplankton patchiness in the environment has been studied for the near-surface waters of a small coastal embayment. It was found that during periods of low turbulent mixing (wind speed [Formula: see text]), the phytoplankton patchiness was induced by local differences (taxonomic or physiological) in its production efficiency which was linked to the dynamic fluctuation in the physicochemical characteristics of the medium. For periods of high winds [Formula: see text] it is indicated that the physical turbulent transport processes were responsible for damping out the spatial variations in the phytoplankton distribution.Key words: phytoplankton biomass, P/B ratio, spatial distribution, turbulence, wind stress
Effect of Sedimentation on Infaunal Invertebrate Populations of Cobequid Bay, Bay of Fundy
Authors: Turk Ted R. , Risk Michael J.
Published: June 2008

Construction of a tidal dam in the upper reaches of the Bay of Fundy is expected to result in deposition of sediment. We investigated the effect of sediment deposition on populations of three major benthic species of the upper reaches: Corophium volutator, Macoma balthica, and Mya arenaria. In fences and boxes that induced deposition on intertidal mudflats, accumulation of 1.0–3.5 cm of sediment at rates of 1.9–10.2 cm/mo caused Corophium density to decrease sharply, usually by an order of magnitude. Macoma density was generally unaffected. In fishing weirs, mud that accumulated at 1.5 cm/mo to a mean depth of 5.2 cm supported normal Corophium densities. The effect of sedimentation on Mya depends strongly on grain size: LD50 was 24 cm for coarse sand, 6 cm for fine sand, and 3 cm for mud. Mya is able to burrow upward in accumulating coarse sand. Even moderate rates and depths of sediment deposition, particularly of fine sediment, could have a major adverse effect on existing Corophium and Mya populations.Key words: Bay of Fundy, tidal power, sedimentation, grain size, water content, Corophium volutator, Macoma balthica, Mya arenaria
A Simple Growth Model for Salmonids in Hatcheries
Authors: Iwama George K. , Tautz Arthur F.
Published: June 2008

A simple growth model for salmonids in hatcheries was developed from several formulations presented in the literature. The model selected was Wt0.33 = W00.33 + (T/1000)t where Wt = weight at time t (g), W0 = initial weight, T = average temperature (°C), and t = time in days. The model was chosen from a number of possible formulations on the basis of its simplicity. Additional attributes are W0.33 is linear with time, the slope of the line W0.33 vs. time (termed growth slope) is linear with temperature (i.e. T/1000) over the temperature range commonly found in hatcheries that rear salmonids, and W0.33 is easily converted to length. Tests of the model on wild stock steelhead in British Columbia hatcheries provided good results under normal operating conditions of feeding, loading, etc. Applications of the model are also presented, including the development of a growth coefficient allowing comparisons of growth rate corrected for fish size and temperature effects.Key words: growth model, salmonids, fish culture
Optimum Size Limits for Trout Fisheries
Authors: Jensen A. L.
Published: June 2008

Application of conventional stock assessment methods to total catch of sport fisheries give neither optimum size limits nor optimum effort; as size limits decrease and effort increases total yield increases asymptotically. In this study total catch is separated into non-trophy and trophy catch; trophy catch has an optimum with respect to fishing effort. Increasing trophy catch decreases total catch, so to optimize the fishery a value is assigned to each category of catch. Optimum size limits for both conventional and slot limits are examined. A slot limit attempts to increase trophy catch without causing a substantial decrease in total catch. Fish are illegal until they reach some minimum size, then they are legal until they reach a certain size or age. They are then again illegal until they reach a trophy size. The results indicate recruitment age should be the smallest size acceptable to fishermen unless trophy fish have a very high value. With conventional size limits total catch decreases rapidly as age at entry increases and fishing effort decreases. Optimum slot limits are determined; slot limits produce a small increase in trophy catch and do not cause a large decrease in total catch.Key words: slot limits, trout fisheries, sport fisheries management, trophy catch
Biochemical Genetic Analysis of Population Differentiation in Greenland Halibut (Reinhardtius hippoglossoides) from the Northwest Atlantic, Gulf of St. Lawrence, and Bering Sea
Authors: Fairbairn Daphne J.
Published: June 2008

Greenland halibut (Reinhardtius hippoglossoides) from the Northwest Atlantic Ocean, the Gulf of St. Lawrence, and the Bering Sea were analyzed for allele and genotype frequencies at 16 electrophoretically detectable protein loci. Thirteen of these loci were monomorphic, with identical mobilities in all samples. One locus (MDH-1) was polymorphic only in the Bering Sea sample. Two loci, PGM and PHI-2, were polymorphic in all samples. An analysis of allele frequencies at these latter loci indicated that Greenland halibut from the Northwest Atlantic area form a single genetically homogeneous stock, but that those in the Gulf of St. Lawrence form a separate though not completely isolated stock. Greenland halibut from the Bering Sea differ greatly from these, and a genetic distance estimate based on all 16 loci suggested genetic divergence at the subspecific level between the two oceans.Key words: Greenland halibut, Reinhardtius hippoglossoides; biochemical genetic variation, electrophoresis, phosphoglucomutase, phosphohexose isomerase, genetic distance
Optimum Escapements in the Face of Alternative Recruitment Hypotheses
Authors: Walters Carl J.
Published: June 2008

Available data are often inadequate to discriminate among alternative models that make different predictions about the consequences of allowing escapements outside the range of recent historical experience. Dynamic programming is used to show that the optimum policy in such situations can involve active probing or experimentation with escapements. The optimum adaptive policy is usually difficult to compute, but generally may be closely approximated by a "Bayes equivalent" policy that is simpler to estimate but does not account explicitly for the value of information associated with allowing more extreme escapements. While there are various practical difficulties in estimating and implementing an optimum policy, it is concluded that regular probing experiments should be included in every fishery management plan.Key words: stock-recruitment, optimization, adaptive management, stochastic models
Adaptive Management of Stock–Recruitment Systems
Authors: Smith A. D. M. , Walters Carl J.
Published: June 2008

Management of escapements can be formulated as a problem in stochastic optimal control. Using the Ricker model as a reasonable representation of the average stock–recruit relationship, approximate optimal policies are found for cases where there is parameter uncertainty as well as environmental variation, by employing a "wide-sense adaptive dual control" algorithm. This algorithm accounts for the future information value of any escapement choice as well as the effect on immediate yield. The algorithm indicates that escapements should be deliberately varied to obtain better information for future management, provided that historical escapement levels have not been extremely variable. Such actively adaptive, or probing policies will become progressively more important in the future as managers learn how to control escapements more precisely and thus eliminate natural sources of informative variation.Key words: adaptive management, stock–recruitment, escapement
Effects of Measurement Errors on the Assessment of Stock–Recruitment Relationships
Authors: Walters Carl J. , Ludwig Donald
Published: June 2008

Errors in measuring spawning stocks can have a profound effect on the appearance of stock–recruitment relationships. Large errors make recruitments appear to be independent of spawning stocks. This effect promotes overexploitation rather than simply making the relationship noisier and harder to measure. Efforts to explain variation in recruitment through factors other than spawning stock may be deceptive as well. Much fisheries theory and practice are based on the assumption that recruitment is largely independent of spawning stock; that assumption is not credible except in cases where spawning stocks are known to have been measured accurately.Key words: stock, recruitment, statistics, overexploitation
Measurement Errors and Uncertainty in Parameter Estimates for Stock and Recruitment
Authors: Ludwig Donald , Walters Carl J.
Published: June 2008

A procedure is developed for estimating stock and recruitment parameters in the presence of measurement errors. It requires an independent assessment of the ratio of environmental and measurement error variances, and provides maximum likelihood estimates of the time series of errors as well as the average stock–recruit parameters. Measures of parameter uncertainty are also provided and are incorporated into an analysis of optimum spawning stocks. This analysis indicates that much higher, or at least more variable, spawning runs should be allowed in many Pacific salmon stocks. An immediate need in salmon management is to obtain estimates of the measurement error variance, so that recent historical data can be made more useful.Key words: statistics, stock recruitment, optimum spawning, uncertainty
Sex Reversal in Carp (Cyprinus carpio) by Oral Administration of Methyltestosterone
Authors: Nagy A. , Bercsényi M. , Csányi V.
Published: June 2008

Effects of oral administration of methyltestosterone on sex reversal from female to male in carp (Cyprinus carpio) was evaluated using all-female gynogenetic carp. Methyltestosterone supplemented in the diet at 100 μg/g for 36 d was tested at 20 and 25 °C and for varying times of initiation of treatment. The treatments induced partial and more complete sex reversal at 20 and 25 °C, respectively. At 20 °C hermaphrodites appeared frequently. At 25 °C, the most successful sex reversal occurred, particularly when methyltestosterone was administered starting 44 d and terminating 80 d after hatching.Key words: carp, all-female carp, sex reversal, gynogenesis, methyltestosterone, androgen treatment
Patterns of Nitrogen Excretion and Oxygen Consumption During Ontogenesis of Common Carp (Cyprinus carpio)
Authors: Kaushik Sadasivam J. , Dabrowski Konrad , Luquet Pierre
Published: June 2008

By monitoring nitrogen (ammonia and urea) excretion and oxygen consumption in a continuous manner during early development (from 18 to 350 degree days) of common carp, Cyprinus carpio, we noted high rates of ammonia-N excretion (> 100 and > 50 μgN∙h−1∙103 eggs−1) and of oxygen consumption (> 1 and > 2.5 mg∙h−1∙103 eggs−1) at hatching and at the onset of free-swimming stages, respectively. There was a diurnal rhythm in metabolic activity. The relative proportions of urea-N and ammonia-N varied during early development; the mean urea-N excretion rate amounted to 21.9 ± 8.7% of total nitrogen, and there was no significant difference between embryonic and postembryonic stages. Fasted free-swimming larvae exhibited increased metabolic activity just before the onset of massive mortality (> 75 μg N∙h−1∙103 eggs−1 and > 2 mg O2∙h−1∙103 eggs−1 of nitrogen excretion and oxygen consumption, respectively). Ammonia excretion rates increased with temperature, the Q10's being 2.36, 2.33, and 3.53 during embryonic, hatching, and free-swimming stages, respectively.Key words: carp, ontogenesis, nitrogen excretion, ammonia, urea, oxygen consumption, temperature, diurnal rhythm
Planktonic Ciliates: Their Distribution, Abundance, and Relationship to Microbial Resources in a Monomictic Lake
Authors: Pace Michael L.
Published: June 2008

The abundance, biomass, vertical distribution, and seasonal succession of planktonic ciliates were studied over a 13-mo period in a small monomictic lake. Measurements made concurrently of bacterial abundance (attached and free), chlorophyll a, and pheopigments were analyzed for correlations with the biomass of the major protozoan species and total protozoan biomass. Ciliate community structure varied primarily between periods of winter mixis and summer stratification. Oligotrich, tintinnid, and peritrich ciliates dominated the community during mixis (November to March). Vertical distributions tended to be uniform except for some species containing algal symbionts which occurred primarily in the photic zone. A more diverse community occurred during stratification. At this time species either tended to be restricted to the epilimnion or had sharply defined metalimnetic or hypolimnetic maxima. With the development of anoxia in the hypolimnion (June), bacterivorous scuticociliates reached high densities in the metalimnion and upper hypolimnion and dominated the community in terms of density and to a lesser extent biomass. Total protozoan (ciliates and the amoeba Difflugia) density varied over the annual cycle between 1 and 50 × 107∙m−2 (0.1 to 189 × 103∙L−1) while biomass as measured by volume varied between 6 and 60 mm3∙m−2 (61–610 mg dry wt∙m−2 and 1.57–1260 μm3∙L−1). Highest densities occurred from August through October when scuticociliates were abundant, but peak biomass occurred in November with a bloom of the large peritrich Rhabdostyla sp. Total ciliate biomass was correlated only with the concentration of pheopigments, but when the biomass due to Rhabdostyla was subtracted from the total, significant correlations were observed between protozoan biomass and chlorophyll a, pheopigments, attached bacteria, and free bacteria. Correlations between the biomass of specific ciliates and microbial parameters, as well as observations of their vertical and seasonal distributions, suggest that concentrations of appropriate food resources are important in determining the abundance of heterotrophic ciliates in the plankton.Key words: ciliates, plankton, protozoa, amoebae, lakes, monomictic, zooplankton, chlorophyll a, pheopigments, bacteria
Aspects of Larval American Lobster (Homarus americanus) Ecology in St. Georges Bay, Nova Scotia
Authors: Harding Gareth C. , Vass W. Peter , Drinkwter Ken F.
Published: June 2008

Lobster larvae first appeared in the neuston of St. Georges Bay, N.S., in 1978 on June 22 at a surface temperature of 12.5 °C. Abundances ranged from 0 to 243 × 103 larvae∙km−2 throughout the larval season with a seasonal average of 22.9 ± 37.9 × 103 larvae∙km−2 for the entire bay. Larval production in the bay equals the highest values reported in the literature for individual stations in nearby western Northumberland Strait. We derive the first survival estimate from larval stage 1 to recruits entering the fishery of 0.2–0.4%. On average 81.4, 14.1, and 4.5% of the larvae were caught within the upper 30-cm, 30- to 70-cm, and 70- to 110-cm levels beneath the sea surface, respectively. This daytime distribution of lobster larvae in the upper 110 cm is modified by cloud cover. The adult distribution in the bay and wind-driven surface drift are believed to be the two main causes of the observed large-scale horizontal patchiness. Lobster larvae have a significantly high probability of capture by our nets if patches of floating seaweed are encountered. A hypothesis is proposed that the observed small-scale patchiness of both larvae and weed is caused by Langmuir circulation.Key words: lobster larvae, Homarus americanus, ecology, Langmuir circulation, recruitment, survival, Nova Scotia